873 research outputs found

    Static Cosmological Solutions of the Einstein-Yang-Mills-Higgs Equations

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    Numerical evidence is presented for the existence of a new family of static, globally regular `cosmological' solutions of the spherically symmetric Einstein-Yang-Mills-Higgs equations. These solutions are characterized by two natural numbers (m1m\geq 1, n0n\geq 0), the number of nodes of the Yang-Mills and Higgs field respectively. The corresponding spacetimes are static with spatially compact sections with 3-sphere topology.Comment: 7 pages, 5 figures, LaTe

    Two dimensional dynamical systems which admit Lie and Noether symmetries

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    We prove two theorems which relate the Lie point symmetries and the Noether symmetries of a dynamical system moving in a Riemannian space with the special projective group and the homothetic group of the space respectively. The theorems are applied to classify the two dimensional Newtonian dynamical systems, which admit a Lie point/Noether symmetry. Two cases are considered, the non-conservative and the conservative forces. The use of the results is demonstrated for the Kepler - Ermakov system, which in general is non-conservative and for potentials similar to the H\`enon Heiles potential. Finally it is shown that in a FRW background with no matter present, the only scalar cosmological model which is integrable is the one for which 3-space is flat and the potential function of the scalar field is exponential. It is important to note that in all applications the generators of the symmetry vectors are found by reading the appropriate entry in the relevant tables.Comment: 25 pages, 17 table

    Cosmological Analogues of the Bartnik--McKinnon Solutions

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    We present a numerical classification of the spherically symmetric, static solutions to the Einstein--Yang--Mills equations with cosmological constant Λ\Lambda. We find three qualitatively different classes of configurations, where the solutions in each class are characterized by the value of Λ\Lambda and the number of nodes, nn, of the Yang--Mills amplitude. For sufficiently small, positive values of the cosmological constant, \Lambda < \Llow(n), the solutions generalize the Bartnik--McKinnon solitons, which are now surrounded by a cosmological horizon and approach the deSitter geometry in the asymptotic region. For a discrete set of values Λreg(n)>Λcrit(n)\Lambda_{\rm reg}(n) > \Lambda_{\rm crit}(n), the solutions are topologically 33--spheres, the ground state (n=1)(n=1) being the Einstein Universe. In the intermediate region, that is for \Llow(n) < \Lambda < \Lhig(n), there exists a discrete family of global solutions with horizon and ``finite size''.Comment: 16 pages, LaTeX, 9 Postscript figures, uses epsf.st

    Paratransit: the need for a regulatory revolution in the light of institutional inertia

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    This chapter begins by defining what is traditionally meant by the term 'paratransit', before exploring why it has remained a relatively niche transport concern. Societal trends have shifted to a pattern of demand that is ill-suited to the system design for conventional public transport. Emerging IT applications offer the potential to introduce a new model of public transport appropriate to the travel needs of the 21st century. Paratransit modes are appealing because they could dynamically match the supply of a service with the level of demand required, unlike conventional models of public transport based on fading historical demand patterns. But the regulatory environment for the local passenger sector has been built incrementally over many years around the institutional frameworks for buses and taxis. Paratransit alternatives often do not fully fit under any of these categorisations with the result that they often do not have an institutional home and thus either upset the status quo (as with Uber currently) or else are still born. A redefinition of paratransit is proposed to facilitate a regulatory change to help address the institutional challenges of paratransit innovation

    Squeezed States of the Generalized Minimum Uncertainty State for the Caldirola-Kanai Hamiltonian

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    We show that the ground state of the well-known pseudo-stationary states for the Caldirola-Kanai Hamiltonian is a generalized minimum uncertainty state, which has the minimum allowed uncertainty ΔqΔp=σ0/2\Delta q \Delta p = \hbar \sigma_0/2, where σ0(1)\sigma_0 (\geq 1) is a constant depending on the damping factor and natural frequency. The most general symmetric Gaussian states are obtained as the one-parameter squeezed states of the pseudo-stationary ground state. It is further shown that the coherent states of the pseudo-stationary ground state constitute another class of the generalized minimum uncertainty states.Comment: RevTex4, 9 pages, no fingure; to be published in Journal of Physics

    Relationship between spatial proximity and travel-to-work distance : the effect of the compact city

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    In this paper, an assessment is made of the relationship between selected aspects of spatial proximity (density, diversity, minimum commuting distance, jobs-housing balance and job accessibility) and reported commuting distances in Flanders (Belgium). Results show that correlations may depend on the considered trip end. For example, a high residential density, a high degree of spatial diversity and a high level of job accessibility are all associated with a short commute by residents, while a high job density is associated with a long commute by employees. A jobs-housing balance close to one is associated with a short commute, both by residents and by employees. In general, it appears that the alleged sustainability benefits of the compact city model are still valid in a context of continuously expanding commuting trip lengths

    Musings and reflections on the meaning, context, and process of transformative learning

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    Abstract: After reviewing the literature on parental involvement, it is evident that there is a lack of scholarly information that speaks directly toward parents advocating for all children. This paper explores the common characteristics and motivations of mothers who are advocating for changes within the public school system

    Understanding consumer demand for new transport technologies and services, and implications for the future of mobility

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    The transport sector is witnessing unprecedented levels of disruption. Privately owned cars that operate on internal combustion engines have been the dominant modes of passenger transport for much of the last century. However, recent advances in transport technologies and services, such as the development of autonomous vehicles, the emergence of shared mobility services, and the commercialization of alternative fuel vehicle technologies, promise to revolutionise how humans travel. The implications are profound: some have predicted the end of private car dependent Western societies, others have portended greater suburbanization than has ever been observed before. If transport systems are to fulfil current and future needs of different subpopulations, and satisfy short and long-term societal objectives, it is imperative that we comprehend the many factors that shape individual behaviour. This chapter introduces the technologies and services most likely to disrupt prevailing practices in the transport sector. We review past studies that have examined current and future demand for these new technologies and services, and their likely short and long-term impacts on extant mobility patterns. We conclude with a summary of what these new technologies and services might mean for the future of mobility.Comment: 15 pages, 0 figures, book chapte
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