Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Signal Attenuation Curve for Different Surface Detector Arrays  [PDF]
J. Vicha,P. Travnicek,D. Nosek,J. Ebr
Physics , 2014, DOI: 10.1142/9789814603164_0025
Abstract: Modern cosmic ray experiments consisting of large array of particle detectors measure the signals of electromagnetic or muon components or their combination. The correction for an amount of atmosphere passed is applied to the surface detector signal before its conversion to the shower energy. Either Monte Carlo based approach assuming certain composition of primaries or indirect estimation using real data and assuming isotropy of arrival directions can be used. Toy surface arrays of different sensitivities to electromagnetic and muon components are assumed in MC simulations to study effects imposed on attenuation curves for varying composition or possible high energy anisotropy. The possible sensitivity of the attenuation curve to the mass composition is also tested for different array types focusing on a future apparatus that can separate muon and electromagnetic component signals.
On Bayesian Curve Fitting Via Auxiliary Variables  [PDF]
Y. Fan,J. -L Dortet-Bernadet,S. A. Sisson
Statistics , 2009,
Abstract: In this article we revisit the auxiliary variable method introduced in Smith and kohn (1996) for the fitting of P-th order spline regression models with an unknown number of knot points. We introduce modifications which allow the location of knot points to be random, and we further consider an extension of the method to handle models with non-Gaussian errors. We provide a new algorithm for the MCMC sampling of such models. Simulated data examples are used to compare the performance of our method with existing ones. Finally, we make a connection with some change-point problems, and show how they can be re-parameterised to the variable selection setting.
Determination of intersecting curve between two surfaces of revolution with parallel axes by use of auxiliary planes and auxiliary spheres  [PDF]
Obradovi? Ratko
Facta Universitatis Series : Architecture and Civil Engineering , 2002, DOI: 10.2298/fuace0204267o
Abstract: In this paper the space intersecting curve between two surfaces of revolution with parallel axes of surfaces have been determined. Two mathematical models for determination of intersecting curve between two surfaces of revolution have been formed: auxiliary planes have been used in the first mathematical model and auxiliary spheres have been used in the second model (Obradovi 2000). In the first case each auxiliary plane intersected with each surface of revolution on circle and two points of intersecting curve are obtained as intersecting points between these two circles. In the second case centres of two locks of auxiliary spheres are put on axes of surfaces of revolution (centre of first lock is on axis of the first surface of revolution and centre of second lock is on axis of the second surface of revolution) on saine z coordinate (when axes of surfaces of revolution are parallel with z axis of coordinate system). First lock sphere intersects the first surface of revolution on w1 parallels and second lock corresponding sphere intersects the second surface of revolution on w2 circles. It is possible to find a relationship that for selected radius of the first lock sphere can determine the radius of second lock sphere and real points of intersecting curve have been determined by use of these two spheres. The points of intersecting curve between two surfaces of revolution are obtained by intersection between w1 circles from the first surface with w2 circles from the second surface (Obradovi 2000).
On the methods to determine signal attenuation curve for different surface arrays  [PDF]
J. Vicha,P. Travnicek,D. Nosek,J. Ebr
Physics , 2013,
Abstract: Large surface arrays of current cosmic ray experiments measure the signals of electromagnetic or muonic components or their combination. The correction to the zenith angle (the attenuation curve) has to be taken into account before the signal is converted to the shower energy. Either Monte Carlo simulations or indirect estimation using collected data (Constant Intensity Cut method) can be used. However, the assumptions of composition or isotropy used for the determination of the attenuation curve can still influence the final physics results such as the energy spectrum, or modify anisotropy searches and composition analysis. Using simplified Toy Monte Carlo with an output from CORSIKA simulations we try to find several examples of what kind of effects can be caused by the methods of inferring the attenuation curve. Surface arrays of different sensitivities to electromagnetic and muonic components were considered.
Soil water thermodynamic to unify water retention curve by pressure plates and tensiometer  [PDF]
Erik Braudeau,Gaghik Hovhannissian,Amjad T. Assi,Rabi H. Mohtar
Frontiers in Earth Science , 2014, DOI: 10.3389/feart.2014.00030
Abstract: The pressure plate method is a standard method for measuring the pF curves, also called soil water retention curves, in a large soil moisture range from saturation to a dry state corresponding to an applied pressure of near 1500 kPa. However, the pressure plate can only provide discrete water retention curves represented by a dozen measured points. In contrast, the measurement of the soil water retention curves by tensiometer is direct and continuous, but limited to the range of the tensiometer reading: from saturation to near 70–80 kPa. The two methods stem from two very different concepts of measurement and the compatibility of both methods has never been demonstrated. The recently established thermodynamic formulation of the pedostructure water retention curve, will allow the compatibility of the two curves to be studied, both theoretically and experimentally. This constitutes the object of the present article. We found that the pressure plate method provides accurate measurement points of the pedostructure water retention curve h(W), conceptually the same as that accurately measured by the tensiometer. However, contrarily to what is usually thought, h is not equal to the applied air pressure on the sample, but rather, is proportional to its logarithm, in agreement with the thermodynamic theory developed in the article. The pF curve and soil water retention curve, as well as their methods of measurement are unified in a same physical theory. It is the theory of the soil medium organization (pedostructure) and its interaction with water. We show also how the hydrostructural parameters of the theoretical curve equation can be estimated from any measured curve, whatever the method of measurement. An application example using published pF curves is given.
Radiative transfer in disc galaxies II - The influence of scattering and geometry on the attenuation curve  [PDF]
Maarten Baes,Herwig Dejonghe
Physics , 2001, DOI: 10.1046/j.1365-8711.2001.04626.x
Abstract: We investigate the influence of scattering and geometry on the attenuation curve in disc galaxies. We investigate both qualitatively and quantitatively which errors are made by either neglecting or approximating scattering, and which uncertainties are introduced due to a simplification of the star-dust geometry. We find that the magnitude of these errors depends on the inclination of the galaxy, and in particular that for face-on galaxies, the errors due to an improper treatment of scattering dominate those due to an imprecise star-dust geometry. Therefore we argue that in all methods which aim at determining the opacity of disc galaxies, scattering should be taken into account in a proper way.
On Bayesian quantile regression curve fitting via auxiliary variables  [PDF]
J. -L. Dortet-Bernadet,Y. Fan
Statistics , 2012,
Abstract: Quantile regression has received increased attention in the statistics community in recent years. This article adapts an auxiliary variable method, commonly used in Bayesian variable selection for mean regression models, to the fitting of quantile regression curves. We focus on the fitting of regression splines, with unknown number and location of knots. We provide an efficient algorithm with Metropolis-Hastings updates whose tuning is fully automated. The method is tested on simulated and real examples and its extension to additive models is described. Finally we propose a simple postprocessing procedure to deal with the problem of the crossing of multiple separately estimated quantile curves.
Chemical migration during soil water retention curve evaluation
Pires, Luiz F.;Villanueva, Felipe C.A.;Dias, Nivea M.P.;Bacchi, Osny O. Santos;Reichardt, Klaus;
Anais da Academia Brasileira de Ciências , 2011, DOI: 10.1590/S0001-37652011005000032
Abstract: wetting and drying (w-d) cycles can induce important elemental migrations in soils. the main purpose of this work was to study the possible existence of soil chemical elemental migrations in samples submitted to repeated w-d cycles during evaluations of soil water retention curve (swrc). the experimental measurements were carried out by atomic absorption spectrometry (aas) for ca2+, mg2+ and k+ on samples of three different brazilian tropical soils (geric ferralsol, eutric nitosol and rhodic ferralsol). results demonstrate an increase in the electrical conductivity of the water extracted from the samples and significant losses of ca2+, mg2+ and k+ during the applications of up to nine w-d cycles. it was also observed differences in swrc for all soils when samples submitted to the application of several w-d cycles were compared with samples not submitted to it. these differences occurred at the region of both structural and textural pores. a possible explanation for these results could be the soil chemical migration during the sequences of w-d cycles, which can affect the soil structure development.
The MOSDEF Survey: Measurements of Balmer Decrements and the Dust Attenuation Curve at Redshifts z~1.4-2.6  [PDF]
Naveen A. Reddy,Mariska Kriek,Alice E. Shapley,William R. Freeman,Brian Siana,Alison L. Coil,Bahram Mobasher,Sedona H. Price,Ryan L. Sanders,Irene Shivaei
Physics , 2015,
Abstract: We present results on the dust attenuation curve of z~2 galaxies using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey. Our sample consists of 224 star-forming galaxies with nebular spectroscopic redshifts in the range z= 1.36-2.59 and high S/N measurements of, or upper limits on, the H-alpha and H-beta emission lines obtained with Keck/MOSFIRE. We construct composite SEDs of galaxies in bins of specific SFR and Balmer optical depth in order to directly constrain the dust attenuation curve from the UV through near-IR for typical star-forming galaxies at high redshift. Our results imply an attenuation curve that is very similar to the SMC extinction curve at wavelengths redward of 2500 Angstroms. At shorter wavelengths, the shape of the curve is identical to that of the Calzetti relation, but with a lower normalization (R_V). Hence, the new attenuation curve results in SFRs that are ~20% lower, and log stellar masses that are 0.16 dex lower, than those obtained with the Calzetti attenuation curve. Moreover, we find that the difference in the reddening---and the total attenuation---of the ionized gas and stellar continuum correlates strongly with SFR, such that for dust-corrected SFRs larger than 20 Msun/yr assuming a Chabrier IMF, the nebular emission lines suffer an increasing degree of obscuration relative to the continuum. A simple model that can account for these trends is one in which the UV through optical stellar continuum is dominated by a population of less reddened stars, while the nebular line and bolometric luminosities become increasingly dominated by dustier stellar populations for galaxies with large SFRs, as a result of the increased dust enrichment that accompanies such galaxies. Consequently, UV- and SED-based SFRs may underestimate the total SFR at even modest levels of ~20 Msun/yr. [Abridged]
Attenuation characteristics of laser beam in water

Liu Juan,Bai Jian-Hui,Ni Kai,Jing Hong-Mei,He Xing-Dao,Liu Da-He,

物理学报 , 2008,
Abstract: Through different sample lengths the attenuation coefficient of laser beam with different pulse energy was measured experimentally in water. And the effect of stimulated Brillouin scattering on the attenuation characteristics of water was studied. It was found that the attenuation coefficient is dependent on the pulse energy and the line width of the laser, but not a constant, as usually assumed to be. Theoretical analysis is also given.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.