16,070 research outputs found
Turbidite record of frequency and source of large volume (>100 km3) Canary Island landslides in the last 1.5 Ma: Implications for landslide triggers and geohazards
No full textDuring the last two decades, numerous studies have focused on resolving the landslide histories of the Canary Islands. Issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate determination of event ages. However, submarine landslides often disaggregate and generate sediment gravity flows. Volcaniclastic turbidites sampled from Madeira Abyssal Plain piston cores represent a record of eight large-volume failures from the Western Canary Islands in the last 1.5 Ma. During this time, there is a mean recurrence rate of 200 ka, while the islands of El Hierro and Tenerife have individual landslide recurrences of 500 ka and 330 ka, respectively. Deposits from the 15 ka El Golfo landslide from El Hierro and 165 ka Icod landslide from Tenerife are examined. This study also identifies potential deposits associated with the Orotava (535 ka), Güímar (850 ka), and Rogues de García landslides (1.2 Ma) from Tenerife, El Julan (540 ka), and El Tiñor (1.05 Ma) landslides from El Hierro, and the Cumbre Nueva landslide (485 ka) from La Palma. Seven of eight landslides occurred during major deglaciations or subsequent interglacial periods, which represent 55% of the time. However, all of the studied landslides occur during or at the end of periods of protracted island volcanism, which generally represent 60% of the island histories. Although climate may precondition failures, it is suggested that volcanism presents a more viable preconditioning and trigger mechanism for Canary Island landslides
Fluvial Morphology as a Driver of Lead and Zinc Geochemical Dispersion at a Catchment Scale
No full textMetal-mining exploitation has caused ecosystem degradation worldwide. Legacy wastes are often concentrated around former mines where monitoring and research works are mostly focused. Geochemical and physical weathering can affect metal-enriched sediment locations and their capacity to release metals at a catchment scale. This study investigated how fluvial geomorphology and soil geochemistry drive zinc and lead dispersion along the Nant Cwmnewyddion (Wales, UK). Sediments from different locations were sampled for geochemical and mineralogical investigations (portable X-ray fluorescence, scanning electron microscope, X-ray diffraction, and electron microprobe analysis). The suspended sediment fluxes in the streamwater were estimated at different streamflows to quantify the metal dispersion. Topographical and slope analysis allowed us to link sediment erosion with the exposure of primary sulphide minerals in the headwater. Zinc and lead entered the streamwater as aqueous phases or as suspended sediments. Secondary sources were localised in depositional stream areas due to topographical obstruction and a decrease in stream gradient. Sediment zinc and lead concentrations were lower in depositional areas and associated with Fe-oxide or phyllosilicates. Streamwater zinc and lead fluxes highlighted their mobility under high-flow conditions. This multi-disciplinary approach stressed the impact of the headwater mining work on the downstream catchment and provided a low-cost strategy to target sediment sampling via geomorphological observations
Una interpretación de a-ka-na-jo ( a3-ka-na-jo)
No full textThe author studies the word a-ka-na-jo in the PY Cn 328 tablet and taking into account some factors she proposes αγναιος as the reading of this word.The author studies the word a-ka-na-jo in the PY Cn 328 tablet and taking into account some factors she proposes αγναιος as the reading of this word
Large Submarine Landslides on Continental Slopes: Geohazards, Methane Release, and Climate Change
No full textSubmarine landslides on open continental slopes can be prodigious in scale. They are an important process for global sediment fluxes, and can generate very damaging tsunamis. Submarine landslides are far harder to monitor directly than terrestrial landslides, and much greater uncertainty surrounds their preconditioning factors and triggers. Submarine slope failure often occurs on remarkably low (< 2°) gradients that are almost always stable on land, indicating that particularly high excess pore pressures must be involved. Earthquakes trigger some large submarine landslides, but not all major earthquakes cause widespread slope failure. The headwalls of many large submarine landslides appear to be located in water depths that are too deep for triggering by gas hydrate dissociation. The available evidence indicates that landslide occurrence is either weakly (or not) linked to changes in sea level or atmospheric methane abundance, or the available dates for open continental slope landslides are too imprecise to tell. Similarly, available evidence does not strongly support a view that landslides play an important role in methane emissions that cause climatic change. However, the largest and best-dated open continental slope landslide (the Storegga Slide) coincides with a major cooling event 8,200 years ago. This association suggests that caution may be needed when stating that there is no link between large open slope landslides and climate change
Environmental influences over the last 16 ka on compound-specific δ13C variations of leaf wax n-alkanes in the Hani peat deposit from northeast China
No full textCompound-specific carbon isotope ratios (δ13C) of leaf wax n-alkanes (C21-C33 odd carbon numbered n-alkanes) were measured in the Hani peat sequence from northeast China. These data were compared with lipid biomarker compositions to assess changes in local vegetation and paleoclimate for the last 16 ka The δ13C values of n-alkanes range between -36.6 and -30.7‰, showing that the compounds originate from C3 plants. Much larger variations (∼5.4‰) in the n-alkane δ13C values than those of atmospheric CO2 during the last 16 ka (< 0.5‰) indicate that the isotopic values were affected by environmental factors in addition to the postglacial δ13C variations in the atmospheric reservoir. The stratigraphic records of δ13C reveal decoupled fluctuations among the individual n-alkanes, particularly between 15.5 to 11.4 ka. Synchronous excursions in the δ13C offsets among individual n-alkanes (Δδ13C) and lipid biomarker paleoplant proxies (Paq, and C23/C31 and C27/C31) from 14.9 to 13.2 ka and 12.7 to 11.6 ka suggest that vegetational changes are the most likely causes for the decoupled δ13C variations. Parallel fluctuations of the δ13C values of terrestrial higher plant-derived C29 and C31 n-alkanes and the n-alkane average chain-length (ACL) from 11 to 6 ka indicate that the δ13C variations responded to net evaporation changes. Negative shifts in the n-alkane δ13C values coinciding with the ACL decreases at 10.5-9.3 ka and 8.1 ka indicate the short-term onset and fluctuations of the summer monsoon strength in eastern China during the early Holocene
NRF2 and chemoprevention: signaling, epigenetics and role in intestinal carcinogensis
No full textPrevention is better than cure. The carcinogenesis could take as long as 20 to 30 years to develop from initiated cells to malignant tumor, therefore providing us various opportunities to prevent the appearance of tumors with the use of chemopreventive compounds in the early stage. Chemoprevention becomes an increasing important concept and has led to the intense research about the mechanisms of actions of various chemopreventive compounds. They can be generally classified into blocking agents and suppressing agents. The chemopreventive compounds usually prevent or slow progression of cancer by maintaining a low oxidative stress and inflammatory environment in cells. This is brought about by the activation of Nrf2, the key protein being investigated in our lab. In this dissertation, I will be discussing the use of compounds as suppressing agents and blocking agents, how compounds activates Nrf2 signaling, how novel Nrf2 interaction partner IQGAP1 mediates Nrf2-Keap1 signaling axis, how expression level of Nrf2 could be regulated epigenetically, apart from the well-known post-translational control by Keap1-Ubiquitinase-Protesome axis and finally how loss of Nrf2 could enhance intestinal tumorigenesis in Apc(min/+) mice.Ph.D.Includes bibliographical referencesIncludes vitaby Ka Lung Cheun
Nearby fibroblasts' response to multiple acupuncture needle revolutions on fibroblast populated collagen gels
No full textAcupuncture is an ancient Chinese healing practice, and an alternative therapy for alleviating pain and chronic disorders. For over twenty years, research is trying to understand the mechanisms that lead to its therapeutic effect. Our laboratory investigates the cellular and molecular events in the connective tissue that occur by acupuncture needling. An in vitro assay was developed to evaluate some of the potential contributors to acupuncture’s effects using a cellular collagen gel as a loose connective tissue mimic. It was hypothesized besides immediate changes to cells under mechanical loading from an acupuncture needle, there were chemical factors released to nearby cells in acupuncture. This thesis investigates whether mechanically stimulating collagen gels with fibroblasts at different revolutions would release chemical factors to nearby fibroblasts where flow cytometry was used to observe cell proliferation as an indicator. Results reveal mechanically stimulating cellular collagen gels at different revolutions does not cause any changes in cell proliferation to nearby cells. However, dead stained mechanically stimulated cellular collagen gels showed cell death occurs around the acupuncture needle. It is possible there were no effects in cell proliferation because when a cellular collagen gel was needle manipulated, some chemical factors were released into the nearby cells. Then as needle manipulation increased, more chemical factors were released, but restricted by the larger amount of cell death around the needle from the increasing rotation.M.S.Includes bibliographical referencesby Ka Po Ch
Source apportionment of mine contamination across streamflows
No full textThis is the final version. Available from Elsevier via the DOI in this record.Data will be made available on request.Globally, metals released by mine waste represent a challenge for protecting water quality and ecosystems. Understanding metal dispersion in catchments is critical for developing efficient remediation strategies and reducing contamination from mining activities. Efforts to address the issue have been constrained by diffuse sources and variation of source contributions across streamflows. In the UK, metal source apportionment is typically addressed using monitoring strategies with low spatial resolution, which can underestimate the contribution of diffuse sources. In this proof-of-concept study, diffuse sources were accurately apportioned in a mining-impacted catchment in Mid-Wales (UK), using a hydrogeochemical approach with combined continuous tracer injections, gulp injections, and streambed sediment geochemistry. The continuous tracer injections identified a major Zn and Pb point source, diffuse sources due to mine waste tip runoff, and potential groundwater contributions. Variations in source contributions were estimated during high and low flow conditions, with Zn having similar sources and importance across streamflows and Pb being released mainly from overground tips during high flow conditions (22% Pb under low flow and 80% Pb under high flow). The distribution of metal-bearing sediment along the stream sheds light on metal release mechanisms across streamflow conditions. This hydrogeochemical approach for source apportionment, builds on common monitoring methods, and represents a substantial advance in accounting diffuse mine contamination sources, understanding potential metal release mechanisms, and designing remediation strategies.Liverpool John Moores Universit
Duan wei xia mu xie lei de xin xing he nei DNA fen zi xi tong biao ji zhi jian ding
No full textLeung Ka Chun.Thesis M.Phil. Chinese University of Hong Kong 2013.Includes bibliographical references (leaves 100-110).Abstracts also in Chinese.Title from PDF title page (viewed on 21, September, 2016).Leung Ka Chun
San zhong chao jian dai teng hu dui gao wen de sheng li fan ying ji zhuan lu ti yan jiu
No full textWong, Ka Wing Karen.Thesis M.Phil. Chinese University of Hong Kong 2014.Includes bibliographical references (leaves 143-157).Abstracts also in Chinese.Title from PDF title page (viewed on 30, November, 2016).Wong, Ka Wing Karen
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