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Search Results: 1 - 10 of 335222 matches for " S. Long "
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Ordered Rate Constitutive Theories for Non-Classical Thermoviscoelastic Fluids with Internal Rotation Rates  [PDF]
K. S. Surana, S. W. Long, J. N. Reddy
Applied Mathematics (AM) , 2018, DOI: 10.4236/am.2018.98063
Abstract:
The paper presents constitutive theories for non-classical thermoviscoelastic fluids with dissipation and memory using a thermodynamic framework based on entirety of velocity gradient tensor. Thus, the conservation and the balance laws used in this work incorporate symmetric as well as antisymmetric part of the velocity gradient tensor. The constitutive theories derived here hold in coand contra-variant bases as well as in Jaumann rates and are derived using convected time derivatives of Green’s and Almansi strain tensors as well as the Cauchy stress tensor and its convected time derivatives in appropriate bases. The constitutive theories are presented in the absence as well as in the presence of the balance of moment of moments as balance law. It is shown that the dissipation mechanism and the fading memory in such fluids are due to stress rates as well as moment rates and their conjugates. The material coefficients are derived for the general forms of the constitutive theories based on integrity. Simplified linear (or quasi-linear) forms of the constitutive theories are also presented. Maxwell, Oldroyd-B and Giesekus constitutive models for non-classical thermoviscoelastic fluids are derived and are compared with those derived based on classical continuum mechanics. Both, compressible and incompressible thermoviscoelastic fluids are considered.
Reforma educativa, reforma d'escola? Qüestions per al debat
Jordi Longàs Mayayo
Temps d'Educació , 1999,
Abstract:
What We Learn from Quantitative Ultraviolet Spectroscopy of Naked White D warfs in Cataclysmic Variables
Knox S. Long
Physics , 1999, DOI: 10.1016/S1387-6473(00)00025-7
Abstract: Using the Hopkins Ultraviolet Telescope and Hubble Space Telescope, observers have now obtained UV spectra with sufficient signal to noise and resolution to allow quantitative spectroscopic analyses of the WDs in several DNe. In the ``cleanest'' DNe, such as U Gem, the observations are allowing the basic physical parameters of the WD -- temperature, radius, gravity, rotation rate, and surface abundances -- to be established. A second component also exists in these systems, which may either be the disk or may be related to the WD itself. Here I summarize the current state of the observations and our understanding of the data, highlighting some of the uncertainties in the analyses as well the prospects for fundamentally advancing our understanding of DNe and WDs with future observations.
Rate Constitutive Theories of Orders n and 1n for Internal Polar Non-Classical Thermofluids without Memory  [PDF]
Karan S. Surana, Stephen W. Long, J. N. Reddy
Applied Mathematics (AM) , 2016, DOI: 10.4236/am.2016.716165
Abstract: In recent papers, Surana et al. presented internal polar non-classical Continuum theory in which velocity gradient tensor in its entirety was incorporated in the conservation and balance laws. Thus, this theory incorporated symmetric part of the velocity gradient tensor (as done in classical theories) as well as skew symmetric part representing varying internal rotation rates between material points which when resisted by deforming continua result in dissipation (and/or storage) of mechanical work. This physics referred as internal polar physics is neglected in classical continuum theories but can be quite significant for some materials. In another recent paper Surana et al. presented ordered rate constitutive theories for internal polar non-classical fluent continua without memory derived using deviatoric Cauchy stress tensor and conjugate strain rate tensors of up to orders n and Cauchy moment tensor and its conjugate symmetric part of the first convected derivative of the rotation gradient tensor. In this constitutive theory higher order convected derivatives of the symmetric part of the rotation gradient tensor are assumed not to contribute to dissipation. Secondly, the skew symmetric part of the velocity gradient tensor is used as rotation rates to determine rate of rotation gradient tensor. This is an approximation to true convected time derivatives of the rotation gradient tensor. The resulting constitutive theory: (1) is incomplete as it neglects the second and higher order convected time derivatives of the symmetric part of the rotation gradient tensor; (2) first convected derivative of the symmetric part of the rotation gradient tensor as used by Surana et al. is only approximate; (3) has inconsistent treatment of dissipation due to Cauchy moment tensor when compared with the dissipation mechanism due to deviatoric part of symmetric Cauchy stress tensor in which convected time derivatives of up to order n are considered in the theory. The purpose of this paper is to present ordered rate constitutive theories for deviatoric Cauchy strain tensor, moment tensor and heat vector for thermofluids without memory in which convected time derivatives of strain tensors up to order n are conjugate with the Cauchy stress tensor and the convected time derivatives of the symmetric part of the rotation gradient tensor up to orders 1n are conjugate with the moment tensor. Conservation and balance laws are used to determine the choice of dependent variables in the constitutive theories: Helmholtz free energy density Φ, entropy density η, Cauchy stress tensor,
MODES OF INTERANNUAL VARIABILITY OF OCEANIC EVAPORATION OBSERVED FROM GSSTF2
Chiu,Long S; Xing,Yukun;
Gayana (Concepción) , 2004, DOI: 10.4067/S0717-65382004000200021
Abstract: variations of the oceanic evaporation are examined using goddard satellite surface turbulence flux version 2 (gsstf2) data. an empirical orthogonal function (eof) analysis shows that the first non-seasonal eof, which explains 9.2% of the variance, is characterized by large changes in the subtropical oceanic dry regions, accompanied by small negative changes in the equatorial warm pool and the eastern equatorial pacific. the time series shows an increasing trend with decadal time scale that started around 1990. this pattern is interpreted as an enhancement of the hadley and walker circulation. the second eof, explaining 5.7% of the variance, is characterized by an equatorial east-west and a mid ocean north-south dipole in the pacific. the second pattern is similar to the first eof pattern of non-seasonal oceanic precipitation found in earlier studies, and is related to the el nino southern oscillation phenomena. it is correlated with a southern oscillation index at 0.74, which is significant at the 95% level. over the region 650s - 650n, oceanic evaporation, surface wind speed and air-sea humidity difference from gsstf2 shows increases of 17%, 6% and 11% over the period july 1988-december 2000. most of this linear trend is associated with a decadal variation of the atmospheric circulation and points to the need for quantifying interannual variations in long-term climate changes studies in the global hydrologic cycle
MODES OF INTERANNUAL VARIABILITY OF OCEANIC EVAPORATION OBSERVED FROM GSSTF2
Long S Chiu,Yukun Xing
Gayana (Concepción) , 2004,
Abstract: Variations of the oceanic evaporation are examined using Goddard Satellite Surface Turbulence Flux version 2 (GSSTF2) data. An Empirical Orthogonal Function (EOF) analysis shows that the first non-seasonal EOF, which explains 9.2% of the variance, is characterized by large changes in the subtropical oceanic dry regions, accompanied by small negative changes in the equatorial warm pool and the eastern equatorial Pacific. The time series shows an increasing trend with decadal time scale that started around 1990. This pattern is interpreted as an enhancement of the Hadley and Walker circulation. The second EOF, explaining 5.7% of the variance, is characterized by an equatorial east-west and a mid ocean north-south dipole in the Pacific. The second pattern is similar to the First EOF pattern of non-seasonal oceanic precipitation found in earlier studies, and is related to the El Nino Southern Oscillation phenomena. It is correlated with a Southern Oscillation Index at 0.74, which is significant at the 95% level. Over the region 65(0)S - 65(0)N, oceanic evaporation, surface wind speed and air-sea humidity difference from GSSTF2 shows increases of 17%, 6% and 11% over the period July 1988-December 2000. Most of this linear trend is associated with a decadal variation of the atmospheric circulation and points to the need for quantifying interannual variations in long-term climate changes studies in the global hydrologic cycle
Modeling the diverse fuv spectra of disk-dominated Cataclysmic variables
Knox S. Long,Christian Knigge
Revista mexicana de astronomía y astrofísica , 2004,
Abstract: Los espectros de FUSE y HST de novas enanas en explosiones y de variables semejantes a novas presentan un amplio rango de caracter sticas. En unos cuantos sistemas existen se~nales obvias de un viento r apido en la forma de los per les de OVI semejantes a P-Cygni y de otros iones en relativamente altos estados de ionizaci on. Pero estos casos son raros. Son m as comunes los sistemas con espectros FUV que presentan una compleja mezcla de l neas de alto y bajo estado de ionizaci on. Se describen intentos para reproducir los espectros utilizando el c odigo de Monte Carlo de transferencia radiativa, desarrollado para modelar vientos bic onicos en sistemas de disco.
Made-to measure galaxy models - I Methodology
R. J. Long,S. Mao
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.16438.x
Abstract: We re-derive the made-to-measure method of Syer and Tremaine 1996, for modelling stellar systems and individual galaxies, and demonstrate how extensions to the made-to-measure method may be implemented and used. We illustrate the enhanced made-to-measure method by determining the mass-to-light ratio of a galaxy modelled as a Plummer sphere. From the standard galactic observables of surface brightness and line-of-sight velocity dispersion together with the h_4 Gauss-Hermite coefficient of the line-of-sight velocity distribution, we successfully recover the true mass-to-light ratio of our toy galaxy. Using kinematic data from Kleyna et al 2002, we then estimate the mass-to-light ratio of the dwarf spheroidal galaxy Draco achieving a V-band value of 539 \pm 136 M_{\odot} / L_{\odot}. We describe the main aspects of creating a made-to-measure galaxy model and show how the key modelling parameters may be determined.
Modeling the Spectral Signatures of Accretion Disk Winds: A New Monte Carlo Approach
Knox S. Long,Christian Knigge
Physics , 2002, DOI: 10.1086/342879
Abstract: Bipolar outflows are present in many disk-accreting astrophysical systems. In disk-accreting cataclysmic variables (CVs), these outflows are responsible for most of the strong features in the ultraviolet spectra of these systems. However, there have been few attempts to model these features quantitatively. Here, we describe a new, hybrid Monte Carlo/Sobolev code, which allows us to synthesize the complete spectrum of a disk-dominated, mass-losing CV. The line profiles we calculate for C IV resemble those calculated by previous workers when an identical geometry is assumed. However, our synthetic spectra exhibit not only the well-known resonance lines of O VI, N V, Si IV and C IV, but, with an appropriate choice of mass-loss rate and wind geometry, also many lines originating from excited lower states. Many of these lines have already been seen in the far ultraviolet spectra of CVs obtained with HUT, FUSE, and HST. In order to illustrate the degree to which we are currently able to reproduce observed spectra, we finally present a preliminary fit to the Hopkins Ultraviolet Telescope spectrum of the dwarf nova Z Cam in outburst.
Modelling the Spectral Signatures of Accretion Disk Winds in Cataclysmic Variables
Knox S. Long,Christian Knigge
Physics , 2001,
Abstract: Bipolar outflows are known to be present in many disk-accreting astrophysical systems. In disk-dominated cataclysmic variables, these outflows are responsible for most of the features in UV and FUV spectra. However, there have been very few attempts to model the features that appear in the spectra of disk-accreting cataclysmic variables quantitatively. The modelling that has been attempted has been concentrated almost entirely on explaining the shape of C IV. Here we describe a new hybrid Monte Carlo/Sobolev code that allows a synthesis of the complete UV spectrum of a disk-dominated cataclysmic variable. A large range of azimuthally-symmetric wind geometries can be modelled. Changes in line shape in eclipsing systems can also be studied. Features in the synthesized spectra include not only well-known resonance lines of O VI, NV, Si IV, and C IV, but, with an appropriate choice of mass loss rate and wind geometry, many of the lines originating from excited lower states that are observed in HUT, FUSE, and ORFEUS spectra. The line profiles of C IV resemble those calculated by previous workers, when an identical geometry is assumed. We compare the synthesized spectra to HUT spectrum of Z Cam, showing that in this case a reasonably good ``fit'' to the spectrum can be obtained.
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