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Search Results: 1 - 10 of 462343 matches for " A. Guenther "
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Corrigendum to "Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)" published in Atmos. Chem. Phys., 6, 3181–3210, 2006
A. Guenther
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2007,
Abstract: No abstract available.
Multidimensional perfect fluid cosmology with stable compactified internal dimensions
U. Guenther,A. Zhuk
Physics , 1998, DOI: 10.1088/0264-9381/15/7/017
Abstract: Multidimensional cosmological models in the presence of a bare cosmological constant and a perfect fluid are investigated under dimensional reduction to 4-dimensional effective models. Stable compactification of the internal spaces is achieved for a special class of perfect fluids. The external space behaves in accordance with the standard Friedmann model. Necessary restrictions on the parameters of the models are found to ensure dynamical behavior of the external (our) universe in agreement with observations.
A note on dynamical stabilization of internal spaces in multidimensional cosmology
U. Guenther,A. Zhuk
Physics , 2000, DOI: 10.1088/0264-9381/18/8/303
Abstract: The possibility of dynamical stabilization of an internal space is investigated for a multidimensional cosmological model with minimal coupled scalar field as inflaton. It is shown that a successful dynamical compactification crucially depends on the type of interaction between the geometrical modulus field and the inflaton and its decay products. In the considered model a stable compactification can be ensured via trapping of the modulus field by a minimum of the effective potential.
Gravitational excitons from extra dimensions
U. Guenther,A. Zhuk
Physics , 1997,
Abstract: We study inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold under dimensional reduction and show that small inhomogeneous excitations of the scale factors of the internal spaces near minima of effective potentials should be observable as massive scalar particles (gravitational excitons) in the external space-time.
Stable compactification and gravitational excitons from extra dimensions
U. Guenther,A. Zhuk
Physics , 1997,
Abstract: We study inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold under dimensional reduction. Stability due to different types of effective potentials is analyzed for specific configurations of internal spaces. Necessary restrictions on the parameters of the models are found and masses of gravitational excitons (small inhomogeneous excitations of the scale factors of the internal spaces near minima of effective potentials) are calculated.
Stabilization of internal spaces in multidimensional cosmology
U. Guenther,A. Zhuk
Physics , 2000, DOI: 10.1103/PhysRevD.61.124001
Abstract: Effective 4-dimensional theories are investigated which were obtained under dimensional reduction of multidimensional cosmological models with a minimal coupled scalar field as matter source. Conditions for the internal space stabilization are considered and the possibility for inflation in the external space is discussed. The electroweak as well as the Planck fundamental scale approaches are investigated and compared with each other. It is shown that there exists a rescaling for the effective cosmological constant as well as for gravitational exciton masses in the different approaches.
Gravitational Excitons as Dark Matter
U. Guenther,A. Zhuk
Physics , 2000, DOI: 10.1063/1.1363545
Abstract: In earlier work it was pointed out that for warped product spacetimes the conformal (geometrical moduli) excitations of the internal compactified factor spaces should be observable as massive scalar fields in the external spacetime. Here we show that these scalar fields (gravitational excitons) describe weakly interacting particles and can be considered as dark matter component. Masses of the gravexcitons are defined by the form of the effective potential of the theory and the stabilization scales of the internal space. This implies that different stabilization scales result in different types of DM. An essential role is played by the effective potential. On the one hand, its minima fix possible stabilization scales of the internal spaces; on the other hand, they provide possible values for the effective cosmological constant.
Gravitational excitons from extra dimensions
U. Guenther,A. Zhuk
Physics , 1997, DOI: 10.1103/PhysRevD.56.6391
Abstract: Inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold are investigated under dimensional reduction. In the Einstein conformal frame, small excitations of the scale factors of the internal spaces near minima of an effective potential have a form of massive scalar fields in the external space-time. Parameters of models which ensure minima of the effective potentials are obtained for particular cases and masses of gravitational excitons are estimated.
Observable effects from extra dimensions
U. Guenther,A. Zhuk
Physics , 1999,
Abstract: For any multidimensional theory with compactified internal spaces, conformal excitations of the internal space metric result in gravitational excitons in the external spacetime. These excitations contribute either to dark matter or to cross sections of usual particles.
Finding and Choosing among Multiple Optima  [PDF]
John Guenther, Herbert K. H. Lee, Genetha A. Gray
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.52031
Abstract:

Black box functions, such as computer experiments, often have multiple optima over the input space of the objective function. While traditional optimization routines focus on finding a single best optimum, we sometimes want to consider the relative merits of multiple optima. First we need a search algorithm that can identify multiple local optima. Then we consider that blindly choosing the global optimum may not always be best. In some cases, the global optimum may not be robust to small deviations in the inputs, which could lead to output values far from the optimum. In those cases, it would be better to choose a slightly less extreme optimum that allows for input deviation with small change in the output; such an optimum would be considered more robust. We use a Bayesian decision theoretic approach to develop a utility function for selecting among multiple optima.

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