2,244,555 research outputs found

    Debris cover and surface melt at a temperate maritime alpine glacier: Franz Josef Glacier, New Zealand

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    Melt rates on glaciers are strongly influenced by the presence of supraglacial debris, which can either enhance or reduce ablation relative to bare ice. Most recently, Franz Josef Glacier has entered into a phase of strong retreat and downwasting, with the increasing emergence of debris on the surface in the ablation zone. Previously at Franz Josef Glacier, melt has only been measured on bare ice. During February 2012, a network of 11 ablation stakes was drilled into locations of varying supraglacial debris thickness on the lower glacier. Mean ablation rates over 9 days varied over the range 1.2–10.1 cm d−1, and were closely related to debris thickness. Concomitant observations of air temperature allowed the application of a degree-day approach to the calculation of melt rates, with air temperature providing a strong indicator of melt. Degree-day factors (d f) varied over the range 1.1–8.1 mm d−1 °C−1 (mean of 4.4 mm d−1 °C−1), comparable with rates reported in other studies. Mapping of the current debris cover revealed 0.7 km2 of the 4.9 km2 ablation zone surface was debris-covered, with thicknesses ranging 1–50 cm. Based on measured debris thicknesses and d f, ablation on debris-covered areas of the glacier is reduced by a total of 41% which equates to a 6% reduction in melt overall across the entire ablation zone. This study highlights the usefulness of a short-term survey to gather representative ablation data, consistent with numerous overseas ablation studies on debris-covered glaciers

    An optimal subgradient algorithm for large-scale convex optimization in simple domains

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    This paper shows that the optimal subgradient algorithm, OSGA, proposed in \cite{NeuO} can be used for solving structured large-scale convex constrained optimization problems. Only first-order information is required, and the optimal complexity bounds for both smooth and nonsmooth problems are attained. More specifically, we consider two classes of problems: (i) a convex objective with a simple closed convex domain, where the orthogonal projection on this feasible domain is efficiently available; (ii) a convex objective with a simple convex functional constraint. If we equip OSGA with an appropriate prox-function, the OSGA subproblem can be solved either in a closed form or by a simple iterative scheme, which is especially important for large-scale problems. We report numerical results for some applications to show the efficiency of the proposed scheme. A software package implementing OSGA for above domains is available

    The Economic Impacts of GM Contamination Incidents on the Organic Sector

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    This paper examines the economic impact of GM co-existence on the global organic sector to date through GM contamination of organic food and crops. A total of 15 GM contamination incidents in the organic sector are identified, occurring either from cross-pollination from GM crops being grown in the area or due to contamination in the post-harvest supply chain. The financial losses incurred by organic farmers and food companies due to GM contamination are considerable, through lost markets, lost sales, lower prices, negative publicity, withdrawal of organic certification and product recalls. It is important that co-existence regimes address all of these impacts, with the GM sector being held accountabl

    Impact of glucuronide interferences on therapeutic drug monitoring of posaconazole by tandem mass spectrometry

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    Background: Posaconazole is a novel antifungal drug for oral application intended especially for therapy of invasive mycoses. Due to variable gastrointestinal absorption, adverse side effects, and suspected drug-drug interactions, therapeutic drug monitoring (TDM) of posaconazole is recommended. Method: A fast ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for quantification of posaconazole with a run-time <3 min was developed and compared to a LC-MS/MS method and HPLC method with fluorescence detection. Results: During evaluation of UPLC-MS/MS, two earlier eluting peaks were observed in the MRM trace of posaconazole. This was only seen in patient samples, but not in spiked calibrator samples. Comparison with LC-MS/MS disclosed a significant bias with higher concentrations measured by LC-MS/MS, while UPLC-MS/MS showed excellent agreement with the commercially available HPLC method. In the LC-MS/MS procedure, comparably wide and left side shifted peaks were noticed. This could be ascribed to in-source fragmentation of conjugate metabolites during electrospray ionisation. Precursor and product ion scans confirmed the assumption that the additional compounds are posaconazole glucuronides. Reducing the cone voltage led to disappearance of the glucuronide peaks. Slight modification of the LC-MS/MS method enabled separation of the main interference, leading to significantly reduced deviation. Conclusions: These results highlight the necessity to reliably eliminate interference from labile drug metabolites for correct TDM results, either by sufficient separation or selective MS conditions. The presented UPLC-MS/MS method provides a reliable and fast assay for TDM of posaconazole. Clin Chem Lab Med 2010; 48:1723-31