The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Marek Zreda - One of the best experts on this subject based on the ideXlab platform.
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the effect of atmospheric water vapor on neutron count in the cosmic Ray soil moisture observing system
Journal of Hydrometeorology, 2013Co-Authors: Rafael Rosolem, Marek Zreda, W J Shuttleworth, Xubin Zeng, Trenton E Franz, Shirley A KurcAbstract:The cosmic-Ray Method for measuring soil moisture, used in the Cosmic-Ray Soil Moisture Observing System (COSMOS), relies on the exceptional ability of hydrogen to moderate fast neutrons. Sources of hydrogen near the ground, other than soil moisture, affect the neutron measurement and therefore must be quantified. This study investigates the effect of atmospheric water vapor on the cosmic-Ray probe signal and evaluates the fast neutron response in realistic atmospheric conditions using the neutron transport code Monte Carlo N-Particle eXtended (MCNPX). The vertical height of influence of the sensor in the atmosphere varies between 412 and 265m in dry and wet atmospheres, respectively. Model results show that atmospheric water vapor near the surface affects the neutron intensity signal by up to 12%, corresponding to soil moisture differences on the order of 0.10m 3 m 23 . A simple correction is defined to identify the true signal associated with integrated soil moisture that rescales the measured neutron intensity to that which would have been observed in the atmospheric conditions prevailing on the day of sensor calibration. Use of this approach is investigated with in situ observations at two sites characterized by strong seasonality in water vapor where standard meteorological measurements are readily available.
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cosmos the cosmic Ray soil moisture observing system
Hydrology and Earth System Sciences, 2012Co-Authors: Marek Zreda, Darin Desilets, W J Shuttleworth, Xubin Zeng, C Zweck, Trenton E Franz, Rafael RosolemAbstract:The newly-developed cosmic-Ray Method for mea- suring area-average soil moisture at the hectometer horizon- tal scale is being implemented in the COsmic-Ray Soil Mois- ture Observing System (or the COSMOS). The stationary cosmic-Ray soil moisture probe measures the neutrons that are generated by cosmic Rays within air and soil and other materials, moderated by mainly hydrogen atoms located pri- marily in soil water, and emitted to the atmosphere where they mix instantaneously at a scale of hundreds of meters and whose density is inversely correlated with soil moisture. The COSMOS has already deployed more than 50 of the even- tual 500 cosmic-Ray probes, distributed mainly in the USA, each generating a time series of average soil moisture over its horizontal footprint, with similar networks coming into exis- tence around the world. This paper is written to serve a com- munity need to better understand this novel Method and the COSMOS project. We describe the cosmic-Ray soil moisture measurement Method, the instrument and its calibration, the design, data processing and dissemination used in the COS- MOS project, and give example time series of soil moisture obtained from COSMOS probes.
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measuring soil moisture content non invasively at intermediate spatial scale using cosmic Ray neutrons
Geophysical Research Letters, 2008Co-Authors: Marek Zreda, Darin Desilets, Ty P A Ferre, Russell L ScottAbstract:[3] We present a novel non-invasive technique that utilizes the dependence of the low-energy cosmic-Ray neutron intensity above the ground surface on the hydrogen content of soil. The cosmic-Ray Method is based on slowing down and thermalization of cosmic-Ray neutrons by hydrogen atoms present in soil. Soil moisture greatly affects the rate at which fast neutrons are moderated, controlling neutron concentration in soils and prescribing their emission into the air. Dry soils have low moderating power and are therefore highly emissive; wet soils are more moderating and therefore less emissive as highly moderated neutrons are more efficiently removed from the system. The change in soil neutron emission is sufficient to produce a clear signal in the neutron intensity above the surface. For soil moisture content varying from zero to 40% volumetrically, the corresponding decrease in cosmic-Ray neutron intensity above the surface is 60%, a hundredth of which can easily be measured using a neutron detector.
Rafael Rosolem - One of the best experts on this subject based on the ideXlab platform.
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the effect of atmospheric water vapor on neutron count in the cosmic Ray soil moisture observing system
Journal of Hydrometeorology, 2013Co-Authors: Rafael Rosolem, Marek Zreda, W J Shuttleworth, Xubin Zeng, Trenton E Franz, Shirley A KurcAbstract:The cosmic-Ray Method for measuring soil moisture, used in the Cosmic-Ray Soil Moisture Observing System (COSMOS), relies on the exceptional ability of hydrogen to moderate fast neutrons. Sources of hydrogen near the ground, other than soil moisture, affect the neutron measurement and therefore must be quantified. This study investigates the effect of atmospheric water vapor on the cosmic-Ray probe signal and evaluates the fast neutron response in realistic atmospheric conditions using the neutron transport code Monte Carlo N-Particle eXtended (MCNPX). The vertical height of influence of the sensor in the atmosphere varies between 412 and 265m in dry and wet atmospheres, respectively. Model results show that atmospheric water vapor near the surface affects the neutron intensity signal by up to 12%, corresponding to soil moisture differences on the order of 0.10m 3 m 23 . A simple correction is defined to identify the true signal associated with integrated soil moisture that rescales the measured neutron intensity to that which would have been observed in the atmospheric conditions prevailing on the day of sensor calibration. Use of this approach is investigated with in situ observations at two sites characterized by strong seasonality in water vapor where standard meteorological measurements are readily available.
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cosmos the cosmic Ray soil moisture observing system
Hydrology and Earth System Sciences, 2012Co-Authors: Marek Zreda, Darin Desilets, W J Shuttleworth, Xubin Zeng, C Zweck, Trenton E Franz, Rafael RosolemAbstract:The newly-developed cosmic-Ray Method for mea- suring area-average soil moisture at the hectometer horizon- tal scale is being implemented in the COsmic-Ray Soil Mois- ture Observing System (or the COSMOS). The stationary cosmic-Ray soil moisture probe measures the neutrons that are generated by cosmic Rays within air and soil and other materials, moderated by mainly hydrogen atoms located pri- marily in soil water, and emitted to the atmosphere where they mix instantaneously at a scale of hundreds of meters and whose density is inversely correlated with soil moisture. The COSMOS has already deployed more than 50 of the even- tual 500 cosmic-Ray probes, distributed mainly in the USA, each generating a time series of average soil moisture over its horizontal footprint, with similar networks coming into exis- tence around the world. This paper is written to serve a com- munity need to better understand this novel Method and the COSMOS project. We describe the cosmic-Ray soil moisture measurement Method, the instrument and its calibration, the design, data processing and dissemination used in the COS- MOS project, and give example time series of soil moisture obtained from COSMOS probes.
Charles Knessl - One of the best experts on this subject based on the ideXlab platform.
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asymptotics of barrier option pricing under the cev process
Applied Mathematical Finance, 2010Co-Authors: Charles KnesslAbstract:We apply a singular perturbation analysis to some option pricing models. To illustrate the technique we first consider the European put option under the standard Black-Scholes model, with or without barriers. Then we consider the same option under the constant elasticity of variance (CEV) assumption, which is also called the square root process. In the CEV model the variability effects in the evolution of the asset, on which the option is based, are proportional to the square root of the asset value. We also consider the CEV model with barriers, and this leads to a rich asymptotic structure. The analysis assumes that the variability is small and employs the Ray Method of geometrical optics and matched asymptotic expansions.
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asymptotics of american barrier option pricing
2008Co-Authors: Charles KnesslAbstract:We consider an American up-and-out put barrier option under the Black and Scholes model. This corresponds to a moving boundary problem for a PDE. We apply singular perturbation Methods to compute the moving boundary, as well as the full solution to the PDE. We analyze the problem in the limit of small ρ = 2r/σ2, where r is the interest rate and σ is the volatility, and employ the Ray Method of geometrical optics and matched asymptotic expansions.
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stirling number asymptotics from recursion equations using the Ray Method
Studies in Applied Mathematics, 1991Co-Authors: Joseph B. Keller, Charles KnesslAbstract:A technique for computing asymptotic expansions of combinatorial quantities from their recursion relations is presented. It is applied to the Stirling numbers of the first and second kinds, s(n,k) and S(n,k), for n>1 and three ranges of k:(i) k=O(1), (ii) n−k=O(1), (iii) k>1, 0
Methods such as the Ray Method and the Method of matched asymptotic expansions
Tamás Ungár - One of the best experts on this subject based on the ideXlab platform.
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characterization of nanocrystalline materials by x Ray line profile analysis
Journal of Materials Science, 2007Co-Authors: Tamás UngárAbstract:X-Ray line profile analysis is shown to be a powerful tool to characterize the microstructure of nanocrystalline materials in terms of grain and subgrain size, dislocation structure and dislocation densities and planar defects, especially stacking faults and twin boundaries. It is shown that the X-Ray Method can provide valuable complementary information about the microstructure, especially when combined with transmission electron microscopy and differential scanning calorimetry.
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an x Ray Method for the determination of stored energies in texture components of deformed metals application to cold worked ultra high purity iron
Acta Materialia, 2000Co-Authors: András Borbély, J.h. Driver, Tamás UngárAbstract:Abstract An X-Ray Method has been developed to evaluate the stored energy of cold work in different texture components of plastically deformed metals. The dislocation density and the outer cut-off radius of dislocations are obtained from Bragg peaks recorded from single texture components. The stored energy is approximated by the energy of dislocations, which is calculated according to the anisotropic theory of elasticity. As an example the Method is applied to the case of two major texture components developed in cold rolled ultra high purity (UHP) iron. The stored energy of the {111}〈112〉-γ fibre component of the 88% cold rolled UHP iron is about 3.6 times larger than that of the {001}〈110〉-α fibre component. The present results, of significantly higher accuracy than those of previous Methods, are in good agreement with data obtained from microhardness and recent calorimetric measurements.
John Lindeman - One of the best experts on this subject based on the ideXlab platform.
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fourier Ray modeling of transient trapped lee waves
Monthly Weather Review, 2006Co-Authors: Dave Broutman, Stephen D Eckermann, John LindemanAbstract:Abstract The Fourier-Ray Method involves Ray tracing in a Fourier-transform domain. The Ray solutions are then Fourier synthesized to produce a spatial solution. Here previous steady-state developments of the Fourier-Ray Method are extended to include a transient source of mountain waves. The Method is illustrated with an initial value problem in which the background flow is started abruptly from rest and then maintained at steady velocity. The resulting wave transience is modeled in a simple way. All Rays that radiate from the mountain, including the initial Rays, are assigned the full amplitude of the longtime steady-state solution. Time dependence comes in through the changing position of the initial Rays. This is sufficient to account for wave transience in a test case, as demonstrated by comparison with simulations from a mesoscale numerical model.
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fourier Ray modeling of short wavelength trapped lee waves observed in infrared satellite imagery near jan mayen
Monthly Weather Review, 2006Co-Authors: Stephen D Eckermann, Dave Broutman, John LindemanAbstract:Abstract A time-dependent generalization of a Fourier-Ray Method is presented and tested for fast numerical computation of high-resolution nonhydrostatic mountain-wave fields. The Method is used to model mountain waves from Jan Mayen on 25 January 2000, a period when wavelike cloud banding was observed long distances downstream of the island by the Advanced Very High Resolution Radiometer Version 3 (AVHRR-3). Surface weather patterns show intensifying surface geostrophic winds over the island at 1200 UTC caused by rapid eastward passage of a compact low pressure system. The 1200 UTC wind profiles over the island increase with height to a jet maximum of ∼60–70 m s−1, yielding Scorer parameters that indicate vertical trapping of any short wavelength mountain waves. Separate Fourier-Ray solutions were computed using high-resolution Jan Mayen orography and 1200 UTC vertical profiles of winds and temperatures over the island from a radiosonde sounding and an analysis system. The radiosonde-based simulations pr...
