489 research outputs found
Classical and quantum cosmology of Born-Infeld type models
We discuss Born-Infeld type fields (tachyon fields) in classical and quantum
cosmology. We first partly review and partly extend the discussion of the
classical solutions and focus in particular on the occurrence of singularities.
For quantization, we employ geometrodynamics. In the case of constant
potential, we discuss both Wheeler-DeWitt quantization and reduced
quantization. We are able to give various solutions and discuss their
asymptotics. For the case of general potential, we transform the Wheeler-DeWitt
equation to a form where it leads to a difference equation. Such a difference
equation was previously found in the quantization of black holes. We give
explicit results for the cases of constant potential and inverse squared
potential and point out special features possessed by solutions of the
difference equation.Comment: 14 pages, 8 figures, published versio
Infrared Spectroscopic Analysis of the Inorganic Deposits from Water in Domestic and Technical Heat Exchangers
Peer reviewedPublisher PD
Origin of the inflationary Universe
We give a consistent description of how the inflationary Universe emerges in
quantum cosmology. This involves two steps: Firstly, it is shown that a
sensible probability peak can be obtained from the cosmological wave function.
This is achieved by going beyond the tree level of the semiclassical expansion.
Secondly, due to decoherence interference terms between different semiclassical
branches are negligibly small. The results give constraints on the particle
content of a unified theory.Comment: LATEX, 6 pages, selected for honorable mention in the 1999 Essay
Competition of the Gravity Research Foundation. To appear in Mod. Phys. Lett.
A modified Ehlers model for the description of inelastic behavior of porous structures
This paper describes a modification of Ehlers' model for the inelastic
behavior of granular media. The modified model can be applied for describing
the inelastic behavior of porous media. The key feature is a subtle change of
the yield potential, which allows the correct orientation of the
triangular-shaped yield surface cross sections depending on the hydrostatic
stress state. The model is incorporated into a general framework for isotropic
plasticity. An elastic predictor/corrector algorithm is employed to solve the
constitutive equations. The necessary derivatives for a Newton update are also
given in detail. The model is calibrated using stress, and strain data obtained
from finite element simulations of a generic highly porous open-cell
Wheire-Phelan foam
Effective action and decoherence by fermions in quantum cosmology
We develop the formalism for the one-loop no-boundary state in a cosmological
model with fermions. We use it to calculate the reduced density matrix for an
inflaton field by tracing out the fermionic degrees of freedom, yielding both
the fermionic effective action and the standard decoherence factor. We show
that dimensional regularisation of ultraviolet divergences would lead to an
inconsistent density matrix. Suppression of these divergences to zero is
instead performed through a nonlocal Bogoliubov transformation of the fermionic
variables, which leads to a consistent density matrix. The resulting degree of
decoherence is less than in the case of bosonic fields.Comment: Latex, 26 page
Synergy of human spine in neutral posture
Musculoskeletal disorders -- Functional anatomy of the trunk -- Compendium of articles -- Hybrid kinematic method -- Effect of the geometry and load configuration -- Effect of muscles -- Pelvic rotation and muscles
Totalsynthese und biologische Evaluierung von Cyclomarin-Derivaten
In den spĂ€ten 1990er Jahren berichtete zum ersten Mal die Gruppe um Clardy ĂŒber die Isolierung und StrukturaufklĂ€rung einer kleinen Familie von peptischen Naturstoffen aus dem marinen Streptomyceten-Stamm CNB-982, den sogenannten Cyclomarine A-C. Diese weisen ein höchst ausgefallenes Wirkspektrum auf. So wirken sie einerseits antibiotisch, vor allem gegen resistente Mycobakterien und andererseits gegen Plasmodium falciparum, den Erreger von Malaria.
Diese Doktorarbeit beschreibt die Synthese neuer Cyclomarin-Analoga, mit denen durch Struktur-AktivitĂ€ts-Beziehungen ein tieferer Einblick in Bezug auf die biologischen AktivitĂ€ten gegenĂŒber Mycobacterium tuberculosis und Plasmodium falciparum ermöglicht wurde. In diesem Zusammenhang wurden bereits 16 der 21 synthetisierten Derivate auf ihre Wirkung untersucht. Durch schrittweise Variation und Vereinfachung der nicht-proteinogenen Amino-sĂ€uren des Cyclomarin-GrundgerĂŒstes gelang es so, zwei unterschiedliche potentielle Leit-strukturen fĂŒr beide Targets abzuleiten
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