5,694 research outputs found
The flux of carbonyl sulfide and carbon disulfide between the atmosphere and a spruce forest
No full textTurbulent fluxes of carbonyl sulfide (COS) and carbon disulfide (CS2) were measured over a spruce forest in Central Germany using the relaxed eddy accumulation (REA) technique. A REA sampler was developed and validated using simultaneous measurements of CO2 fluxes by REA and by eddy correlation. REA measurements were conducted during six campaigns covering spring, summer, and fall between 1997 and 1999. Both uptake and emission of COS and CS2 by the forest were observed, with deposition occurring mainly during the sunlit period and emission mainly during the dark period. On the average, however, the forest acts as a sink for both gases. The average fluxes for COS and CS2 are -93 ± 11.7 pmol m-2 s-1 and -18 ± 7.6 pmol m-2 s-1, respectively. The fluxes of both gases appear to be correlated to photosynthetically active radiation and to the CO2 and \chem{H_2O} fluxes, supporting the idea that the air-vegetation exchange of both gases is controlled by stomata. An uptake ratio COS/CO2 of 10 ± 1.7 pmol m mol-1 has been derived from the regression line for the correlation between the COS and CO2 fluxes. This uptake ratio, if representative for the global terrestrial net primary production, would correspond to a sink of 2.3 ± 0.5 Tg COS yr-1
Carbonyl sulfide (COS) as a tracer for canopy photosynthesis, transpiration and stomatal conductance : potential and limitations
No full textThe theoretical basis for the link between the leaf exchange of carbonyl sulfide (COS), carbon dioxide (CO2) and water vapour (H2O) and the assumptions that need to be made in order to use COS as a tracer for canopy net photosynthesis, transpiration and stomatal conductance, are reviewed. The ratios of COS to CO2 and H2O deposition velocities used to this end are shown to vary with the ratio of the internal to ambient CO2 and H2O mole fractions and the relative limitations by boundary layer, stomatal and internal conductance for COS. It is suggested that these deposition velocity ratios exhibit considerable variability, a finding that challenges current parameterizations, which treat these as vegetation-specific constants. COS is shown to represent a better tracer for CO2 than H2O. Using COS as a tracer for stomatal conductance is hampered by our present poor understanding of the leaf internal conductance to COS. Estimating canopy level CO2 and H2O fluxes requires disentangling leaf COS exchange from other ecosystem sources/sinks of COS. We conclude that future priorities for COS research should be to improve the quantitative understanding of the variability in the ratios of COS to CO2 and H2O deposition velocities and the controlling factors, and to develop operational methods for disentangling ecosystem COS exchange into contributions by leaves and other sources/sinks. To this end, integrated studies, which concurrently quantify the ecosystem-scale CO2, H2O and COS exchange and the corresponding component fluxes, are urgently needed.
We investigate the potential of carbonyl sulfide (COS) for being used as a tracer for canopy net photosynthesis, transpiration and stomatal conductance by examining the theoretical basis of the link between leaf COS, carbon dioxide (CO2) and water vapour (H2O) exchange. Our analysis identifies several limitations that need to be overcome to this end, however at present we lack appropriate ecosystem-scale field measurements for assessing their practical significance. It however appears that COS represents a better tracer for CO2 than H2O. Concurrent measurements of ecosystem scale COS, CO2 and H2O exchange are advocated
A pedagogical proof for cos(sin x) > sin(cos x)
No full textA pedagogical proof for cos(sin x) > sin(cos x) is presented
Core Outcome Set-STAndardised Protocol Items: The COS-STAP Statement
No full textBackground: Several hundred core outcome set (COS) projects have been systematically identified to date which, if adopted, ensure that researchers measure and report those outcomes that are most likely to be relevant to users of their research. The uptake of a COS by COS users will depend in part on the transparency and robustness of the methods used in the COS development study, which would be increased by the use of a standardised protocol. This article describes the development of the COS-STAP (Core Outcome Set-STAndardised Protocol Items) Statement for the content of a COS development study protocol. Methods: The COS-STAP Statement was developed following the Enhancing the Quality and Transparency Of Health Research (EQUATOR) Network's methodological framework for guideline development. This included an initial item generation stage, a two-round Delphi survey involving more than 150 participants representing three stakeholder groups (COS developers, journal editors and patient and public involvement researchers interested in COS development), followed by a consensus meeting with eight voting participants. Results: The COS-STAP Statement consists of a checklist of 13 items considered essential documentation in a protocol, outlining the scope of the COS, stakeholder involvement, COS development plans and consensus processes. Conclusions: Journal editors and peer reviewers can use the guidance to assess the completeness of a COS development study protocol submitted for publication. By providing guidance for key content, the COS-STAP Statement will enhance the drafting of high-quality protocols and determine how the COS development study will be carried out
Facial design and synthesis of CoS x /Ni-Co LDH nanocages with rhombic dodecahedral structure for high-performance asymmetric supercapacitors
No full textIn this paper, two-component nanocages containing CoS x and nickel-cobalt layered double hydroxides (Ni-Co LDH) were facilely synthesized via a multistep transformation approach. The zeolitic imidazolate framework-67 (ZIF-67) nanocrystals were firstly synthesized, and then after partial sulfuration, the CoS x /Ni-Co LDH nanocages were achieved by adding nickel ions for etching and precipitation. The prepared CoS x /Ni-Co LDH nanocages consisted of the hollow rhombic dodecahedral morphology with many nanosheets arrays on the shell. When used as electrode materials for electrochemical capacitors, this CoS x /Ni-Co LDH nanocages deliver a specific capacitance of 1562 F g −1 at a current density of 1 A g −1 . In addition, an asymmetric supercapacitor assembled with CoS x /Ni-Co LDH as cathode and active carbon (AC) as anode shows a high energy density of 35.8 Wh kg −1 at a power density of 800 W kg −1 and has an excellent cycling performance with the retention rate of 94.56% after 10,000 cycles, suggesting their potential application in high-performance electrochemical capacitors. These exceptional electrochemical properties can be attributed to the unique structure and synergistic effects between the metal sulfide and the bimetallic hydroxide, which also indicate the potential application of CoS x /Ni-Co LDH nanocages in high-performance supercapacitors. © 201
Replacing the Monte Carlo Simulation with the COS Method for PFE (Potential Future Exposure) Calculations
No full textTo fulfil the need in the industry for fast and accurate PFE calculations in practice, a new, semi-analytical method of calculating the PFE metric for CCR has been developed, tested and analyzed in this thesis. Herewith we focus on the calculation of PFEs for liquid IR and FX portfolios involving up to three correlated risk-factors: a domestic and foreign short rate and the exchange rate of this currency pair. Both netting-set level and counterparty level PFEs are covered in our research. The short rates are modelled under the one-factor Hull-White (HW1F) model and for the exchange rate we assume they follow geometric Brownian motion. The key insight is that the cumulative distribution function (CDF) can be recovered semi-analytically using Fourier-cosine expansion, whereby the series coefficients are readily available from the characteristic function of the total exposure. The characteristic function in turn can be solved numerically via quadrature rules. Risk metrics, such as the potential future exposure (PFE), can be attained once the CDF is reconstructed using the Fourier series.Our theoretical error analysis predicts stable convergence of the COS method and observed exponential convergence of the COS method for both netting-set and counterparty level PFE calculations. For three artificial portfolios of different sizes, it was observed that the COS method is at least five times more accurate than the Monte Carlo (MC) simulation method but takes only one-tenth of the CPU time of the MC method. The advantage of the COS method becomes even more prominent when the number of derivatives in a portfolio increases. We conclude that the COS method is a much more efficient alternative for MC method for PFE calculations, at least for portfolios involving three risk factors.Our theoretical error analysis predicts stable convergence of the COS method and observed exponential convergence of the COS method for both netting-set and counterparty level PFE calculations. For three artificial portfolios of different sizes, it was observed that the COS method is at least five times more accurate than the Monte Carlo (MC) simulation method but takes only one-tenth of the CPU time of the MC method. The advantage of the COS method becomes even more prominent when the number of derivatives in a portfolio increases. We conclude that the COS method is a much more efficient alternative for MC method for PFE calculations, at least for portfolios involving three risk factors.We conducted theoretical analysis on the error convergence and observed exponential convergence of the COS method for both netting-set and counterparty level PFE calculations. For three artificial portfolios of different sizes, it was observed that the COS method is at least five times more accurate than the Monte Carlo (MC) simulation method but takes only one-tenth of the CPU time of the MC method. The advantage of the COS method becomes even more prominent when the number of derivatives in a portfolio increases. We conclude that the COS method is a much more efficient alternative for MC method for PFE calculations, at least for portfolios involving three risk factors.Applied Mathematic
Integrating cos^2 x and sin^2 x (MathsCasts)
No full textAn example of how double-angle formulae can be used to help with integrating sin^2 x and cos^2
Entwickelung von sin X und cos X in Reihen, welche nach wachsenden Potenzen von X fortschreiten
No full textvom Direktor GallenkampDie einfachsten Eigenschaften und Anwendungen der DeterminantenEntwickelung von sin X und cos X in Reihen, welche nach wachsenden Potenzen von X fortschreite
Interseção superfície obtida girando-se o gráfico de f(x)=2e^(-x/5) cos(2x)/Plano
No full textConhecimento em geometria analíticaA imagem mostra a interseção de uma superfície obtida girando-se o gráfico de
f(x)=2e^(-x/5) cos(2x) com um plano, onde a superfície obtida pelo gráfico de f(x)=2e^(-x/5) cos(2x) é representada pela função F(superfície verde)e o plano é representado pela função G(superfície vermelha). A imagem também mostra o domínio das funçõesComponente Curricular::Educação Superior::Ciências Exatas e da Terra::Matemátic
Interseção superfície obtida girando-se o gráfico de f(x)=2e^(-x/5) cos(2x)/Plano
No full textConhecimento em geometria analíticaA imagem mostra a interseção de uma superfície obtida girando-se o gráfico de
f(x)=2e^(-x/5) cos(2x) com um plano, onde a superfície obtida pelo gráfico de f(x)=2e^(-x/5) cos(2x) é representada pela função F(superfície verde)e o plano é representado pela função G(superfície vermelha). A imagem também mostra o domínio das funçõesComponente Curricular::Educação Superior::Ciências Exatas e da Terra::Matemátic
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