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Search Results: 1 - 10 of 119 matches for " CRENSHAW KIMBERLé "
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Documento para o encontro de especialistas em aspectos da discrimina??o racial relativos ao gênero
Revista Estudos Feministas , 2002, DOI: 10.1590/S0104-026X2002000100011
Abstract: neither the gender aspects of racial discrimination nor the racial aspects of gender discrimination are fully comprehended within human rights discourses. building on the growing recognition that race and gender discrimination are not mutually exclusive phenomena, this background paper forwards a provisional framework to identify various forms of subordination that can be said to reflect the interactive effects of race and gender discrimination. it suggests a provisional protocol to be followed to better identify the occasions in which such interactive discrimination may have occurred, and posits further that the responsibility to address the causes and consequences of such discrimination be shared widely among all human rights institutions.
Documento para o encontro de especialistas em aspectos da discrimina o racial relativos ao gênero
Revista Estudos Feministas , 2002,
Abstract: Tanto os aspectos de gênero da discrimina o racial quanto os aspectos raciais da discrimina o de gênero n o s o totalmente apreendidos pelos discursos dos direitos humanos. O presente documento, baseado no crescente reconhecimento de que as discrimina es de ra a e de gênero n o s o fen menos mutuamente excludentes, prop e um modelo provisório para a identifica o das várias formas de subordina o que refletem os efeitos interativos das discrimina es de ra a e de gênero. Este documento também sugere um protocolo provisório a ser seguido, a fim de melhor identificar as situa es em que tal discrimina o interativa possa ter ocorrido e, além disso, defende que a responsabilidade de lidar com as causas e as conseqüências dessa discrimina o deva ser amplamente compartilhada entre todas as institui es de direitos humanos.
Comparison of Quantum and Classical Local-field Effects on Two-Level Atoms in a Dielectric
Michael E. Crenshaw
Physics , 2008, DOI: 10.1103/PhysRevA.78.053827
Abstract: The macroscopic quantum theory of the electromagnetic field in a dielectric medium interacting with a dense collection of embedded two-level atoms fails to reproduce a result that is obtained from an application of the classical Lorentz local-field condition. Specifically, macroscopic quantum electrodynamics predicts that the Lorentz redshift of the resonance frequency of the atoms will be enhanced by a factor of the refractive index n of the host medium. However, an enhancement factor of (n*n+2)/3 is derived using the Bloembergen procedure in which the classical Lorentz local-field condition is applied to the optical Bloch equations. Both derivations are short and uncomplicated and are based on well-established physical theories, yet lead to contradictory results. Microscopic quantum electrodynamics confirms the classical local-field-based results. Then the application of macroscopic quantum electrodynamic theory to embedded atoms is proved false by a specific example in which both the correspondence principle and microscopic theory of quantum electrodynamics are violated.
Quantum Theory of Electrodynamics in Linear Media Subject to Boundary Conditions
Michael E. Crenshaw
Physics , 2009,
Abstract: We show that the material dependencies of macroscopically quantized fields in linear media are not consistent with the classical electromagnetic boundary conditions. We then phenomenologically construct macroscopic quantized fields that satisfy quantum--classical correspondence with the result indicating that the canonical momentum in a linear medium is modified as a consequence of the reduced speed of light. We re-derive D'Alembert's principle and Lagrange's equations for an arbitrarily large region of space in which light signals travel slower than in the vacuum and show that the resulting modifications to Lagrangian dynamics, including the canonical momenta, repair the violation of the correspondence principle for macroscopically quantized fields.
Electrodynamics in a Filled Minkowski Spacetime with Application to Classical Continuum Electrodynamics
Michael E. Crenshaw
Physics , 2008,
Abstract: Minkowski spacetime is a convenient setting for the study of the relativistic dynamics of particles and fields in the vacuum. In order to study events that occur in a dielectric or other linear medium, we adopt the familiar continuum assumption of a linear, isotropic, homogeneous, transparent medium of refractive index n filling all space and seek the principle of relativity that applies in the filled spacetime. Applying the Einstein postulates with c/n as the speed of light, we show how the effective signal velocity results in a scaling of the proper time by the refractive index and examine the consequences for D'Alembert's principle, the Lagrange equations, and the canonical momentum field. The principles of dynamics in the filled spacetime are then applied to the electromagnetic Lagrangian and we derive equations of motion that are invariant with respect to a material Lorentz transformation. The new representation of the dynamics of macroscopic fields is shown to be consistent with the equal-time commutation relation for quantized macroscopic fields, quantum--classical correspondence, the principle of superposition, and electromagnetic boundary conditions.
Electromagnetic momentum and the energy-momentum tensor in a linear medium with magnetic and dielectric properties
Michael E. Crenshaw
Physics , 2013, DOI: 10.1063/1.4869746
Abstract: In a continuum setting, the energy-momentum tensor embodies the relations between conservation of energy, conservation of linear momentum, and conservation of angular momentum. The well-defined total energy and the well-defined total momentum in a thermodynamically closed system with complete equations of motion are used to construct the total energy-momentum tensor for a stationary simple linear material with both magnetic and dielectric properties illuminated by a quasimonochromatic pulse of light through a gradient-index antireflection coating. The perplexing issues surrounding the Abraham and Minkowski momentums are bypassed by working entirely with conservation principles, the total energy, and the total momentum. We derive electromagnetic continuity equations and equations of motion for the macroscopic fields based on the material four-divergence of the traceless, symmetric total energy-momentum tensor. We identify contradictions between the macroscopic Maxwell equations and the continuum form of the conservation principles. We resolve the contradictions, which are the actual fundamental issues underlying the Abraham-Minkowski controversy, by constructing a unified version of continuum electrodynamics that is based on establishing consistency between the three-dimensional Maxwell equations for macroscopic fields, the electromagnetic continuity equations, the four-divergence of the total energy-momentum tensor, and a four-dimensional tensor formulation of electrodynamics for macroscopic fields in a simple linear medium.
Continuum Electrodynamics of a Piecewise-Homogeneous Linear Medium
Michael E. Crenshaw
Physics , 2015,
Abstract: The energy--momentum tensor and the tensor continuity equation serve as the conservation laws of energy, linear momentum, and angular momentum for a continuous flow. Previously, we derived equations of motion for macroscopic electromagnetic fields in a homogeneous linear dielectric medium that is draped with a gradient-index antireflection coating (J. Math Phys. 55, 042901 (2014) ). These results are consistent with the electromagnetic tensor continuity equation in the limit that reflections and the accompanying surface forces are negligible thereby satisfying the condition of an unimpeded flow in a thermodynamically closed system. Here, we take the next step and derive equations of motion for the macroscopic fields in the limiting case of a piecewise-homogeneous simple linear dielectric medium. The presence of radiation surface forces on the interface between two different homogeneous linear materials means that the energy--momentum formalism must be modified to treat separate homogeneous media in which the fields are connected by boundary conditions at the interfaces. We demonstrate the explicit separation of the total momentum into a field component and a material motion component, we derive the radiation pressure that transfers momentum from the field to the material, we derive the electromagnetic continuity equations for a piecewise homogeneous dielectric, and we provide a lucid reinterpretation of the Jones and Richards experiment.
Application of axiomatic formal theory to the Abraham--Minkowski controversy
Michael E. Crenshaw
Physics , 2015,
Abstract: The Abraham--Minkowski controversy refers to a long-standing inability to adequately address certain issues involving the momentum of an electromagnetic field in a linear dielectric medium. We treat continuum electrodynamics as an axiomatic formal theory based on the macroscopic Maxwell equations applied to a thermodynamically closed system consisting of an antireflection coated block of a linear dielectric material situated in free-space that is illuminated by a quasimonochromatic field. We demonstrate that the Minkowski-based formulation of the continuity of energy and momentum is a valid theorem of the formal theory of Maxwellian continuum electrodynamics that is proven false by conservation laws. We show that another valid theorem of continuum electrodynamics is contradicted by special relativity. Our options are that the axioms of the formal theory, the macroscopic Maxwell equations, are proven false by conservation laws and relativity or that conservation and relativity are proven false by continuum electrodynamics. Electrodynamics, conservation, and relativity are fundamental principles of physics that are intrinsic to the vacuum in which the speed of light is c. Here we show that the current theories of these physical principles are inconsistent in a region of space in which c/n is the speed of light. The contradictions are resolved by a reformulation of these physical principles in a flat non-Minkowski material spacetime in which the timelike coordinate corresponds to ct/n. Applying Lagrangian field theory, we derive relativistically correct equations of motion for the macroscopic electric and magnetic fields in a simple dielectric medium. We derive a resolution of the Abraham--Minkowski controversy in which a traceless symmetric total energy--momentum tensor is a component of the tensor energy--momentum continuity theorem of a new formal theory of continuum electrodynamics.
The Theory of Electrodynamics in a Linear Dielectric
Michael E. Crenshaw
Physics , 2013,
Abstract: We adopt the continuum limit of a linear, isotropic, homogeneous, transparent, dispersion-negligible dielectric of refractive index $n$ and examine the consequences of the effective speed of light in a stationary dielectric, $c/n$, for D'Alembert's principle and the Lagrange equations. The principles of dynamics in the dielectric-filled space are then applied to the electromagnetic Lagrangian and we derive equations of motion for the macroscopic fields. A direct derivation of the total energy--momentum tensor from the field strength tensor for the electromagnetic field in a dielectric is used to demonstrate the utility of the new theory by resolving the century-old Abraham--Minkowski electromagnetic momentum controversy in a way that preserves the principles of conservation of energy, conservation of linear momentum, and conservation of angular momentum.
Decomposition of the Total Electromagnetic Momentum in a Linear Dielectric into Field and Matter Components
Michael E. Crenshaw
Physics , 2013, DOI: 10.1016/j.aop.2013.07.005
Abstract: The long-standing resolution of the Abraham--Minkowski electromagnetic momentum controversy is predicated on a decomposition of the total momentum of a closed continuum electrodynamic system into separate field and matter components. Using a microscopic model of a simple linear dielectric, we derive Lagrangian equations of motion for the electric dipoles and show that the dielectric can be treated as a collection of stationary simple harmonic oscillators that are driven by the electric field and produce a polarization field in response. The macroscopic energy and momentum are defined in terms of the electric, magnetic, and polarization fields that travel through the dielectric together as a pulse of electromagnetic radiation. We conclude that both the macroscopic energy and the macroscopic momentum are entirely electromagnetic in nature for a simple linear dielectric in the absence of significant reflections.
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