The Experts below are selected from a list of 31854 Experts worldwide ranked by ideXlab platform
Johan Jakob Mohr - One of the best experts on this subject based on the ideXlab platform.
-
combining sar interferometry and the Equation of Continuity to estimate the three dimensional glacier surface velocity vector
Journal of Glaciology, 1999Co-Authors: Niels Reeh, Soren Norvang Madsen, Johan Jakob MohrAbstract:Until now, an assumption of surface-parallel glacier flow has been used to express the vertical velocity component in terms of the horizontal velocity vector, permitting all three velocity components to be determined from synthetic aperture radar interferometry. We discuss this assumption, which neglects the influence of the local mass balance and a possible contribution to the vertical velocity arising if the glacier is not in steady state. We find that the mass-balance contribution to the vertical surface velocity is not always negligible as compared to the surface-slope contribution. Moreover, the vertical velocity contribution arising if the ice sheet is not in steady state can be significant. We apply the principle of mass conservation to derive an Equation relating the vertical surface velocity to the horizontal velocity vector. This Equation, valid for both steady-state and non-steady-state conditions, depends on the ice-thickness distribution. Replacing the surface-parallel-flow assumption with a correct relationship between the surface velocity components requires knowledge of additional quantities such as surface mass balance or ice thickness.
Suresh G. Advani - One of the best experts on this subject based on the ideXlab platform.
-
a model for unsaturated flow in woven fiber preforms during mold filling in resin transfer molding
Journal of Composite Materials, 1998Co-Authors: Krishna M. Pillai, Suresh G. AdvaniAbstract:In this paper, the unsaturated flow encountered in the woven or stitched fiber mats used in RTM is studied for the case of constant rate injection into a 1-D mold. Such fiber mats are characterized as a dual scale porous medium and a two-layer model, based on the difference in the length scales of the intra-tow and inter-tow spaces, is proposed. The mass balance is derived from first principles for an idealized representation of such type of porous media and incorporation of a sink term in the macroscopic Equation of Continuity is established. First a simple sink function, the constant sink, is studied and the downwardly drooping profile of the injection pressure, reported in previous experiments, is shown to be a natural consequence of the absorption of resin by the tows. Next an On/off type constant sink function is proposed; critical parameters of unsaturated flows such as pore volume ratio and sink strength are introduced. Then the two-layer model with rectangular cross section is extended to two othe...
-
Numerical simulation of unsaturated flow in Woven fiber preforms during the resin transfer molding process
Polymer Composites, 1998Co-Authors: Krishna M. Pillai, Suresh G. AdvaniAbstract:In this paper, the unsaturated flow encountered in the woven or stitched fiber mats used in RTM is simulated using an adaptation of the Finite Element Method/Control Volume (FEM/CV) technique. The movement of resin through such fiber mats is modeled as flow through dual scale porous media and the mass balance in such media creates a sink term in the Equation of Continuity of the macroscopic flows. Combining this Equation with Darcy's law leads to a non-homogeneous nonlinear elliptic partial differential Equation for pressure that is solved iteratively. First the simulation is used to study simple flows encountered during the characterization of preforms, such as the constant injection pressure 1-D flow and the constant flow rate radial injection flow. Previously observed experimental results of relatively flatter pressure histories for the latter type of flows in wove fiber mats are replicated, both numerically and analytically, by the pressure Equation with the sink term. A quantity called pore volume ratio is shown to play an important role in such flows. Finally, the unsaturated flow in a typical RTM mold, packed with woven fiber mats, is simulated numerically, and inlet pressures, fill times, and mat saturation are studied.
Chengshi Liu - One of the best experts on this subject based on the ideXlab platform.
-
description of spin transport and precession in spin orbit coupling systems and general Equation of Continuity
Physical Review B, 2007Co-Authors: Huatong Yang, Chengshi LiuAbstract:By generalizing the usual current density to a matrix with respect to spin variables, a general Equation of Continuity satisfied by the density matrix and current density matrix has been derived. This Equation holds in arbitrary spin-orbit coupling systems as long as its Hamiltonian can be expressed in terms of a power series in momentum. Thereby, the expressions of the current density matrix and a torque density matrix are obtained. The current density matrix completely describes both the usual current and spin current as well, while the torque density matrix describes the spin precession caused by a total effective magnetic field, which may include a realistic and an effective one due to the spin-orbit coupling. In contrast to the conventional definition of spin current, this expression contains an additional term if the Hamiltonian includes nonlinear spin-orbit couplings. Moreover, if the degree of the full Hamiltonian $\ensuremath{\ge}3$, then the particle current must also be modified in order to satisfy the local conservation law of number.
Niels Reeh - One of the best experts on this subject based on the ideXlab platform.
-
combining sar interferometry and the Equation of Continuity to estimate the three dimensional glacier surface velocity vector
Journal of Glaciology, 1999Co-Authors: Niels Reeh, Soren Norvang Madsen, Johan Jakob MohrAbstract:Until now, an assumption of surface-parallel glacier flow has been used to express the vertical velocity component in terms of the horizontal velocity vector, permitting all three velocity components to be determined from synthetic aperture radar interferometry. We discuss this assumption, which neglects the influence of the local mass balance and a possible contribution to the vertical velocity arising if the glacier is not in steady state. We find that the mass-balance contribution to the vertical surface velocity is not always negligible as compared to the surface-slope contribution. Moreover, the vertical velocity contribution arising if the ice sheet is not in steady state can be significant. We apply the principle of mass conservation to derive an Equation relating the vertical surface velocity to the horizontal velocity vector. This Equation, valid for both steady-state and non-steady-state conditions, depends on the ice-thickness distribution. Replacing the surface-parallel-flow assumption with a correct relationship between the surface velocity components requires knowledge of additional quantities such as surface mass balance or ice thickness.
Krishna M. Pillai - One of the best experts on this subject based on the ideXlab platform.
-
a model for unsaturated flow in woven fiber preforms during mold filling in resin transfer molding
Journal of Composite Materials, 1998Co-Authors: Krishna M. Pillai, Suresh G. AdvaniAbstract:In this paper, the unsaturated flow encountered in the woven or stitched fiber mats used in RTM is studied for the case of constant rate injection into a 1-D mold. Such fiber mats are characterized as a dual scale porous medium and a two-layer model, based on the difference in the length scales of the intra-tow and inter-tow spaces, is proposed. The mass balance is derived from first principles for an idealized representation of such type of porous media and incorporation of a sink term in the macroscopic Equation of Continuity is established. First a simple sink function, the constant sink, is studied and the downwardly drooping profile of the injection pressure, reported in previous experiments, is shown to be a natural consequence of the absorption of resin by the tows. Next an On/off type constant sink function is proposed; critical parameters of unsaturated flows such as pore volume ratio and sink strength are introduced. Then the two-layer model with rectangular cross section is extended to two othe...
-
Numerical simulation of unsaturated flow in Woven fiber preforms during the resin transfer molding process
Polymer Composites, 1998Co-Authors: Krishna M. Pillai, Suresh G. AdvaniAbstract:In this paper, the unsaturated flow encountered in the woven or stitched fiber mats used in RTM is simulated using an adaptation of the Finite Element Method/Control Volume (FEM/CV) technique. The movement of resin through such fiber mats is modeled as flow through dual scale porous media and the mass balance in such media creates a sink term in the Equation of Continuity of the macroscopic flows. Combining this Equation with Darcy's law leads to a non-homogeneous nonlinear elliptic partial differential Equation for pressure that is solved iteratively. First the simulation is used to study simple flows encountered during the characterization of preforms, such as the constant injection pressure 1-D flow and the constant flow rate radial injection flow. Previously observed experimental results of relatively flatter pressure histories for the latter type of flows in wove fiber mats are replicated, both numerically and analytically, by the pressure Equation with the sink term. A quantity called pore volume ratio is shown to play an important role in such flows. Finally, the unsaturated flow in a typical RTM mold, packed with woven fiber mats, is simulated numerically, and inlet pressures, fill times, and mat saturation are studied.