10,337 research outputs found
A variational formulation of analytical mechanics in an affine space
Variational formulations of statics and dynamics of mechanical systems
controlled by external forces are presented as examples of variational
principles.Comment: 17 pages, corrected typos, accepted for publication in Rep. Math.
Phy
On Poisson quasi-Nijenhuis Lie algebroids
We propose a definition of Poisson quasi-Nijenhuis Lie algebroids as a
natural generalization of Poisson quasi-Nijenhuis manifolds and show that any
such Lie algebroid has an associated quasi-Lie bialgebroid. Therefore, also an
associated Courant algebroid is obtained. We introduce the notion of a morphism
of quasi-Lie bialgebroids and of the induced Courant algebroids morphism and
provide some examples of Courant algebroid morphisms. Finally, we use paired
operators to deform doubles of Lie and quasi-Lie bialgebroids and find an
application to generalized complex geometry.Comment: 12 page
Influence of zinc on distiller’s yeast:cellular accumulation of zinc and impact on spirit congeners
Accumulation of zinc by a whisky distilling yeast strain of Saccharomyces cerevisiae was studied during fermentation of malt wort and synthetic defined medium. Zinc uptake by yeast cells was very rapid in malt wort, as zinc (0.32 μg/mL) was completely removed from the fermentation medium within one hour. The type of fermentable carbohydrate had an impact on the kinetics of zinc accumulation, with maltose most effective at enhancing metal uptake at zinc concentrations above 3.2 μg/mL. Enriching yeast cells with zinc by “preconditioning” impacted on the production of flavour congeners in the distillates produced from fermented cultures. Such distillates were characterized by an altered flavour and aroma profile. In particular, the production of some higher alcohols increased when yeast cells were preconditioned with zinc. This phenomenon is yeast strain related. Industrial fermentation processes, including brewing and distilling, may benefit from optimization of zinc bioavailability in yeast cultures resulting in more efficient fermentations and improved product quality
Entropic uncertainty relations for electromagnetic beams
The symplectic tomograms of 2D Hermite--Gauss beams are found and expressed
in terms of the Hermite polynomials squared. It is shown that measurements of
optical-field intensities may be used to determine the tomograms of
electromagnetic-radiation modes. Furthermore, entropic uncertainty relations
associated with these tomograms are found and applied to establish the
compatibility conditions of the the field profile properties with
Hermite--Gauss beam description. Numerical evaluations for some Hermite--Gauss
modes illustrating the corresponding entropic uncertainty relations are finally
given.Comment: Invited talk at the XV Central European Workshop on Quantum Optics
(Belgrade, Serbia, 30 May -- 3 June 2008), to appear in Physica Scripta
Zinc accumulation and utilisation by wine yeasts
The present study has focused on the accumulation of zinc by wine yeast strains of Saccharomyces cerevisiae during fermentation of both grape juice and chemically defined medium with different carbohydrates and at varying levels of zinc. The results have shown that zinc accumulation by wine yeast was very rapid with all zinc being removed from the medium by yeast cells within the first two hours. Zinc uptake was stimulated by the presence of sucrose. Zinc affected fermentation progress at defined levels, with optimal concentrations at 1.5–2.5 ppm, depending on yeast strain and zinc bioavailability. The bioavailability of metal ions in grape must and the roles of metals in wine yeast physiology are aspects poorly understood by enologists. In brewing, it has long been recognized that malt wort may be zinc deficient and brewers often carry out zinc supplementations to avoid sluggish and incomplete fermentations. In winemaking, zinc levels in grape musts may be compromised depending on the bioavailability of zinc ions in vineyard soils as well as treatments with fertilizers and fungicides during grape growing. As a consequence, sub-optimal zinc levels in grape musts may negatively influence the fermentative performance of yeasts. We believe that optimization of metal ion bioavailability will improve yeast fermentation performance in industrial processes and this study addresses some issues relating to zinc in enology
Variational approach to gravitational theories with two independent connections
A new variational approach for general relativity and modified theories of
gravity is presented. In addition to the metric tensor, two independent affine
connections enter the action as dynamical variables. In the matter action the
dependence upon one of the connections is left completely unspecified. When the
variation is applied to the Einstein-Hilbert action the Einstein field
equations are recovered. However when applied to and Scalar-Tensor
theories, it yields gravitational field equations which differ from their
equivalents obtained with a metric or Palatini variation and reduce to the
former ones only when no connections appear in the matter action.Comment: 11 pages, no figure
A formal approach to autonomic systems programming: the SCEL Language
The autonomic computing paradigm has been proposed to cope with size, complexity and dynamism of contemporary
software-intensive systems. The challenge for language designers is to devise appropriate abstractions
and linguistic primitives to deal with the large dimension of systems, and with their need to
adapt to the changes of the working environment and to the evolving requirements. We propose a set of
programming abstractions that permit to represent behaviors, knowledge and aggregations according to
specific policies, and to support programming context-awareness, self-awareness and adaptation. Based on
these abstractions, we define SCEL (Software Component Ensemble Language), a kernel language whose
solid semantic foundations lay also the basis for formal reasoning on autonomic systems behavior. To show
expressiveness and effectiveness of SCEL’s design, we present a Java implementation of the proposed abstractions
and show how it can be exploited for programming a robotics scenario that is used as a running
example for describing features and potentials of our approac
- …