Earlier work in northeast Greenland has suggested a limited advance of the Greenland Ice Sheet during the Last Glacial Maximum (LGM). However, this concept has recently been challenged by marine ...geological studies, indicating grounded ice on the continental shelf at this time. New Be-10-ages from the Store Koldewey island, northeast Greenland, suggest that unscoured mountain plateaus at the outer coast were covered at least partly by cold-based ice during the LGM. It is, however, still inconclusive whether this ice was dynamically connected to the Greenland Ice Sheet or not. Regardless of the LGM ice sheet extent, the Be-10 results from Store Koldewey add to a growing body of evidence suggesting considerable antiquity of crystalline unscoured terrain near present and Pleistocene ice sheet margins.
Late Glacial ice advances in southeast Tibet Strasky, Stefan; Graf, Angela A.; Zhao, Zhizhong ...
Journal of Asian earth sciences,
03/2009, Letnik:
34, Številka:
3
Journal Article
Recenzirano
The sensitivity of Tibetan glacial systems to North Atlantic climate forcing is a major issue in palaeoclimatology. In this study, we present surface exposure ages of erratic boulders from a valley ...system in the Hengduan Mountains, southeastern Tibet, showing evidence of an ice advance during Heinrich event 1. Cosmogenic nuclide analyses (
10Be and
21Ne) revealed consistent exposure ages, indicating no major periods of burial or pre-exposure. Erosion-corrected (3
mm/ka)
10Be exposure ages range from 13.4 to 16.3
ka. This is in agreement with recalculated exposure ages from the same valley system by Tschudi, S., Schäfer, J.M., Zhao, Z., Wu, X., Ivy-Ochs, S., Kubik, P.W., Schlüchter, C., 2003. Glacial advances in Tibet during the Younger Dryas? Evidence from cosmogenic
10Be,
26Al, and
21Ne. Journal of Asian Earth Sciences 22, 301–306.. Thus this indicates that local glaciers advanced in the investigated area as a response to Heinrich event 1 cooling and that periglacial surface adjustments during the Younger Dryas overprinted the glacial morphology, leading to deceptively young exposure ages of certain erratic boulders.
All currently used scaling models for Terrestrial Cosmogenic Nuclide (TCN) production rates are based on neutron monitor surveys. Therefore, an assumption underlying all TCN studies is that ...production rates are directly proportional to secondary cosmic ray intensities for all cosmogenic nuclides. To test this crucial assumption, we measured cosmogenic (3)He and (2(1Ne in artificial quartz targets after one year of exposure at mountain altitudes in the Swiss Alps. The targets were inconel steel tubes containing 1 kg of artificial quartz sand (250-500 ?m), degassed for one week at 700 (o)C in vacuum prior to exposure. From August 2006 until August 2007, ten of these targets were exposed at five locations in Switzerland and Italy: Zurich (556 m), Davos (1560 m), Santis (2502 m), Jungfraujoch (3571 m), and Monte Rosa (4554 m). Additionally, a sixth set of two blank targets was kept in storage and effectively shielded from cosmic ray exposure. Cosmogenic noble gases were measured at room temperature and at 700 (o)C. Up to 9% of the cosmogenic (3)He was measured in the cold step, indicating that (3)He diffuses out of quartz at room temperature on short time scales. The remaining (3)He and all (2(1Ne were released at 700 (o)C, as shown by a repeat measurement at 800 (o)C for the Monte Rosa target, which yielded no additional cosmogenic helium and neon. As expected, the Monte Rosa target contained the highest cosmogenic nuclide content, with 1.56+/-0.07x10(6) atoms of excess (3)He and 4.5+/-1.2x10(5) atoms of excess (2(1Ne (all errors are 2s). The raw measurements were corrected for non-atmospheric blanks, shielding (roof+container wall), tritiogenic helium and solar modulation (normalised to the average neutron flux over the past five solar cycles). The (3)He/(2(1Ne production rate ratio of 6.8+/-0.9 indicates that cosmogenic (3)He production by the container walls is negligible. The main goal of the artificial target experiment was to determine the production rate attenuation length. Because all our targets had an identical design and were exposed under identical conditions, all systematic errors cancel out in the calculation of an attenuation length. Our best estimates for the (3)He and (2(1Ne attenuation lengths are 134.8+/-5.9 g /cm(2) and 135+/-25 g/cm(2), respectively, agreeing very well with currently used scaling models. We conclude that TCN production rates are indeed proportional to neutron monitor count rates, and that (3)He and (2(1Ne production rates follow the same altitudinal scaling relationships as the cosmogenic radionuclides. Finally, the measurements were scaled to sea level and high latitude using the empirical attenuation length, yielding weighted mean production rates of 107.6+/-6.6 at/g/yr for (3)He and 15.4+ /-2.1 at/g/yr for (2(1Ne. Despite the significant uncertainties associated with the corrections for shielding, solar modulation and especially the (3)He/(3)H branching ratio, these estimates are in good agreement with production rates derived from long-term exposure experiments at natural calibration sites and physics-based simulations.
All currently used scaling models for Terrestrial Cosmogenic Nuclide (TCN) production rates are based on neutron monitor surveys. Therefore, an assumption underlying all TCN studies is that ...production rates are directly proportional to secondary cosmic ray intensities for all cosmogenic nuclides. To test this crucial assumption, we measured cosmogenic super(3)He and super(2) super(1)Ne in artificial quartz targets after one year of exposure at mountain altitudes in the Swiss Alps. The targets were inconel steel tubes containing 1 kg of artificial quartz sand (250-500 approximately equal to m), degassed for one week at 700 super(o)C in vacuum prior to exposure. From August 2006 until August 2007, ten of these targets were exposed at five locations in Switzerland and Italy: Zurich (556 m), Davos (1560 m), Santis (2502 m), Jungfraujoch (3571 m), and Monte Rosa (4554 m). Additionally, a sixth set of two blank targets was kept in storage and effectively shielded from cosmic ray exposure. Cosmogenic noble gases were measured at room temperature and at 700 super(o)C. Up to 9% of the cosmogenic super(3)He was measured in the cold step, indicating that super(3)He diffuses out of quartz at room temperature on short time scales. The remaining super(3)He and all super(2) super(1)Ne were released at 700 super(o)C, as shown by a repeat measurement at 800 super(o)C for the Monte Rosa target, which yielded no additional cosmogenic helium and neon. As expected, the Monte Rosa target contained the highest cosmogenic nuclide content, with 1.56+/-0.07x10 super(6) atoms of excess super(3)He and 4.5+/-1.2x10 super(5) atoms of excess super(2) super(1)Ne (all errors are 2 sigma ). The raw measurements were corrected for non-atmospheric blanks, shielding (roof+container wall), tritiogenic helium and solar modulation (normalised to the average neutron flux over the past five solar cycles). The super(3)He/ super(2) super(1)Ne production rate ratio of 6.8+/-0.9 indicates that cosmogenic super(3)He production by the container walls is negligible. The main goal of the artificial target experiment was to determine the production rate attenuation length. Because all our targets had an identical design and were exposed under identical conditions, all systematic errors cancel out in the calculation of an attenuation length. Our best estimates for the super(3)He and super(2) super(1)Ne attenuation lengths are 134.8+/-5.9 g /cm super(2) and 135+/-25 g/cm super(2), respectively, agreeing very well with currently used scaling models. We conclude that TCN production rates are indeed proportional to neutron monitor count rates, and that super(3)He and super(2) super(1)Ne production rates follow the same altitudinal scaling relationships as the cosmogenic radionuclides. Finally, the measurements were scaled to sea level and high latitude using the empirical attenuation length, yielding weighted mean production rates of 107.6+/-6.6 at/g/yr for super(3)He and 15.4+ /-2.1 at/g/yr for super(2) super(1)Ne. Despite the significant uncertainties associated with the corrections for shielding, solar modulation and especially the super(3)He/ super(3)H branching ratio, these estimates are in good agreement with production rates derived from long-term exposure experiments at natural calibration sites and physics-based simulations.
Minto Island pedestrian bridge, Salem, Oregon, USA Strasky, Jiri; Necas, Radim; Kolacek, Jan
Structural concrete : journal of the FIB,
December 2021, 2021-12-00, 20211201, Letnik:
22, Številka:
6
Journal Article
•Layered Ti alloys prepared by SPS can be used for high-throughput testing.•Compression curves can be extracted from DIC data for each layer.•Acoustic emission can indicate the presence of ...twinning/stress-induced martensite.
Acoustic emission and digital image correlation (DIC) were used to determine mechanical properties of six biomedical alloys from a single compression deformation experiment. Layered sample of six Ti-(20–35)Nb-7Zr-0.2O alloys was prepared by spark plasma sintering. All six layers were deformed in compression at once. Advanced use of DIC allowed us to separate the deformation in each layer and determine the flow curve of each alloy. Simultaneous use of acoustic emission provides insight into active plastic deformation mechanisms. Nb content in the studied alloys significantly affects ductility of the material as well as shape of the compression flow curve suggesting different plastic deformation mechanisms in the studied alloys. Presented methods provide high-throughput determination of mechanical properties allowing efficient optimization of alloy composition.
Commercially pure (CP) gas-atomized titanium powder was processed by wet cryogenic milling in liquid argon and compacted by spark plasma sintering. The time-dependent sintering evolution at different ...temperatures was evaluated by using the master sintering curve (MSC) approach with the aim of achieving a material with maximum relative density and minimum grain size. Carrier-gas hot extraction (CGHE) confirmed a purity consistent with ASTM standard of Grade 4 CP Ti. Grain size and texture were determined by EBSD. An apparent activation energy of sintering of 115 kJ/mol was found based on the MSC approach. It is significantly lower than the activation energy of self-diffusion in Ti. This is attributed to an enhanced diffusion rate due to high concentration of defects in the powder after milling. The relative density was correlated with the resulting grain size and a general trade-off relationship between achieving high relative density and maintaining small grain size was found. The distribution of oxygen after milling and subsequent sintering at low temperatures is heterogeneous as determined by complementary XRD, CGHE and microhardness measurements. The distribution of oxygen becomes homogeneous with increasing sintering temperature. The microhardness of the material was shown to depend on residual porosity, the content and distribution of oxygen and also on texture. Processing parameters of milling and sintering were optimized to achieve fully dense, fine grained material with a low contamination by nitrogen and oxygen.
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