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Search Results: 1 - 10 of 224538 matches for " R. Carr "
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The regional problem in Spain
R. Carr
BMGN : Low Countries Historical Review , 1979,
Abstract:
Listening in: Spontaneous Teacher Talk on Playscapes  [PDF]
H. Kloos, C. Maltbie, R. Brown, V. Carr
Creative Education (CE) , 2018, DOI: 10.4236/ce.2018.93030
Abstract: Nature-based playgroundsknown as playscapesoffer numerous opportunities for young children to learn about nature. In the current study, we focus on teacher talk on playscapes, namely to capture the spontaneous utterances teachers offer when engaging with young children during playscape visits. Two different playscapes were contrasted, both of which featured loose parts, native plants, and running water. The difference in playscape was whether it featured ecosystems: While the rural playscape had a natural forest and a wetland, the urban playscape had a man-made stream and a garden. Ten preschool teachers participated with their classrooms. They wore microphones during a series of field trips to playscapes. No specific training was provided, and teachers were told to interact with children as they naturally would. Teacher audio was transcribed and coded to capture science-relevant, science-neutral, science-diverting, and supervisory teacher talk. Findings were analyzed by playscape and number of visits. Results show a strong effect of?playscape type: Spontaneously occurring science-relevant utterances were about?twice as likely on the rural as the urban playscape, even by the same teacher. In contrast, the amount of supervisory utterances differed only by teacher, not playscape. Finally, science-diverting utterances were very rare, underscoring the opportunities for science learning that lie in playscapes. Our findings have important implications for how to design professional-development tool to support teachers in the delivery of early environmental education.
The 2011 International Year for People of African Descent (IYPAD): The paradox of colonized invisibility within the promise of mainstream visibility
Gina Thésée,Paul R. Carr
Decolonization : Indigeneity, Education & Society , 2012,
Abstract: The United Nations declared that 2011 be recognized as the “International Year for People of African Descent” (IYPAD). This year marks the tenth anniversary of the World Conference Against Racism (often referred to as the Durban Conference), in which a resolution was approved stating that slavery and the colonization that sustained it were crimes against humanity. The outcome for this International Year is disappointing, if not shocking, at several levels, in terms of mediatisation, appropriation, program content, educational connection, and, significantly, any tangible impact in relation to people of African descent (PAD). The IYPAD was largely ignored and trivialized at the local, regional and national levels in almost all of the countries concerned. Following the hegemonic leadership of the United States, a number of nations proceeded to convert this International Year, which sought to underscore and engage all peoples in debates, actions and measures that could formally acknowledge historic injustices in relation to people of African descent, into the paradox of willingly rendering the focus of the Year invisible. Within this context of banalization of the IYPAD, this study, within an anti-colonial perspective, seeks to examine the international dynamic and related motives that characterize the significance of this problematic. Our analysis has led to three central interpretations: i) Africa, and all related and inter-connected questions, remain on the periphery of the world’s politics, economics and international political economy; ii) the competition between nations for the recognition of human history remains a political and economic affair, and Africa and her descendants are not accorded a seat at the same table as the colonizing forces; and iii) the IYPAD declaration, ensconced in the yolk of an empathetic conscience by some and bad faith by others, can be seen as the residue of colonization, in which the degree of invisibility of people of African descent is still tethered to the heart-beat of colonizing nations and their proxy consorts, which are economically coerced and subjugated.
Reply to Comment on "Quantum Entangled Dark Solitons formed by Ultracold Atoms in Optical Lattices"
R. V. Mishmash,L. D. Carr
Physics , 2010, DOI: 10.1103/PhysRevLett.105.018904
Abstract: We reply to Jacek Dziarmaga, Piotr Deuar, and Krzysztof Sacha's comment, arXiv:1001.1045, supporting the authors' simulations but differentiating between near-mean-field and strongly quantum regimes. We clarify that we have three lines of evidence on decay of dark solitons and connect our work to Lieb's Type-II excitations and the true meaning of a quantum dark soliton.
Ultracold Atoms in 1D Optical Lattices: Mean Field, Quantum Field, Computation, and Soliton Formation
R. V. Mishmash,L. D. Carr
Physics , 2008, DOI: 10.1016/j.matcom.2009.08.025
Abstract: In this work, we highlight the correspondence between two descriptions of a system of ultracold bosons in a one-dimensional optical lattice potential: (1) the discrete nonlinear Schr\"{o}dinger equation, a discrete mean-field theory, and (2) the Bose-Hubbard Hamiltonian, a discrete quantum-field theory. The former is recovered from the latter in the limit of a product of local coherent states. Using a truncated form of these mean-field states as initial conditions, we build quantum analogs to the dark soliton solutions of the discrete nonlinear Schr\"{o}dinger equation and investigate their dynamical properties in the Bose-Hubbard Hamiltonian. We also discuss specifics of the numerical methods employed for both our mean-field and quantum calculations, where in the latter case we use the time-evolving block decimation algorithm due to Vidal.
Metastable Quantum Phase Transitions in a Periodic One-dimensional Bose Gas: Mean-Field and Bogoliubov Analyses
R. Kanamoto,L. D. Carr,M. Ueda
Physics , 2009, DOI: 10.1103/PhysRevA.79.063616
Abstract: We generalize the concept of quantum phase transitions, which is conventionally defined for a ground state and usually applied in the thermodynamic limit, to one for \emph{metastable states} in \emph{finite size systems}. In particular, we treat the one-dimensional Bose gas on a ring in the presence of both interactions and rotation. To support our study, we bring to bear mean-field theory, i.e., the nonlinear Schr\"odinger equation, and linear perturbation or Bogoliubov-de Gennes theory. Both methods give a consistent result in the weakly interacting regime: there exist \emph{two topologically distinct quantum phases}. The first is the typical picture of superfluidity in a Bose-Einstein condensate on a ring: average angular momentum is quantized and the superflow is uniform. The second is new: one or more dark solitons appear as stationary states, breaking the symmetry, the average angular momentum becomes a continuous quantity, and the phase of the condensate can be continuously wound and unwound.
Effect of Subphase Ca++ Ions on the Viscoelastic Properties of Langmuir Monolayers
R. S. Ghaskadvi,Sharon Carr,Michael Dennin
Physics , 1999, DOI: 10.1063/1.479648
Abstract: It is known that the presence of cations like Ca++ or Pb++ in the water subphase alters the pressure-area isotherms for fatty acid monolayers. The corresponding lattice constant changes have been studied using x-ray diffraction. Reflection-absorption spectroscopy has been used to probe the chemical composition of the film. We report on the first measurements of the time evolution of the shear viscosity of arachidic acid monolayers in the presence of Ca++ ions in the subphase. We find that the introduction of Ca++ ions to the water subphase results in an increase of the film's viscosity by at least three orders of magnitude. This increase occurs in three distinct stages. First, there is a rapid change in the viscosity of up to one order of magnitude. This is followed by two periods, with very different time constants, of a relatively slow increase in the viscosity over the next 10 or more hours. The corresponding time constants for this rise decrease as either the subphase pH or Ca++ concentration is increased.
Quantum Entangled Dark Solitons Formed by Ultracold Atoms in Optical Lattices
R. V. Mishmash,L. D. Carr
Physics , 2007, DOI: 10.1103/PhysRevLett.103.140403
Abstract: Inspired by experiments on Bose-Einstein condensates in optical lattices, we study the quantum evolution of dark soliton initial conditions in the context of the Bose-Hubbard Hamiltonian. An extensive set of quantum measures is utilized in our analysis, including von Neumann and generalized quantum entropies, quantum depletion, and the pair correlation function. We find that quantum effects cause the soliton to fill in. Moreover, soliton-soliton collisions become inelastic, in strong contrast to the predictions of mean-field theory. These features show that the lifetime and collision properties of dark solitons in optical lattices provide clear signals of quantum effects.
Metastable quantum phase transitions in a periodic one-dimensional Bose gas: II. Many-body theory
R. Kanamoto,L. D. Carr,M. Ueda
Physics , 2009, DOI: 10.1103/PhysRevA.81.049903
Abstract: We show that quantum solitons in the Lieb-Liniger Hamiltonian are precisely the yrast states. We identify such solutions clearly with Lieb's type II excitations from weak to strong interactions, clarifying a long-standing question of the physical meaning of this excitation branch. We demonstrate that the metastable quantum phase transition previously found in mean field analysis of the weakly-interacting Lieb-Liniger Hamiltonian [Phys. Rev. A {\bf 79}, 063616 (2009)] extends into the medium- to strongly-interacting regime of a periodic one-dimensional Bose gas. Our methods are exact diagonalization, finite-size Bethe ansatz, and the boson-fermion mapping in the Tonks-Girardeau limit.
Modeling a circular equatorial test-particle in a Kerr spacetime
r?me Carré,Edward K. Porter
Physics , 2012,
Abstract: Extreme Mass Ratio Inspirals (EMRIs) are one of the main gravitational wave (GW) sources for a future space detector, such as eLISA/NGO, and third generation ground-based detectors, like the Einstein Telescope. These systems present an interest both in astrophysics and fundamental physics. In order to make a high precision determination of their physical parameters, we need very accurate theoretical waveform models or templates. In the case of a circular equatorial orbit, the key stumbling block to the creation of these templates is the flux function of the GW. This function can be modeled either via very expensive numerical simulations, which then make the templates unusable for GW astronomy, or via some analytic approximation method such as a post-Newtonian approximation. This approximation is known to be asymptotically divergent and is only known up to 5.5PN order for the Schwarzschild case and to 4PN order for the Kerr case. A way to improve the convergence of the flux is to use re-summation methods. In this work we extend previous results using the Pad\'e and Chebyshev approximations, first by taking into account the absorption of the GWs by the central black hole which was neglected in previous studies, and secondly by using the information from the Schwarzschild and absorption terms to create a Kerr flux up to 5.5PN order. We found that these two additions both improve the convergence. We also demonstrate that the best re-summation method for improving the flux model is based on a flux function which we call the "inverted Chebyshev approximation".
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