29,106 research outputs found
Release and Formation of Oxidation-Related Aldehydes during Wine Oxidation
Twenty-four Spanish wines were subjected to five consecutive cycles of air saturation at 25 °C. Free and bound forms of carbonyls were measured in the initial samples and after each saturation. Nonoxidized commercial wines contain important and sensory relevant amounts of oxidation-related carbonyls under the form of odorless bound forms. Models relating the contents in total aldehydes to the wine chemical composition suggest that fermentation can be a major origin for Strecker aldehydes: methional, phenylacetaldehyde, isobutyraldehyde, 2-methylbutanal, and isovaleraldehyde. Bound forms are further cleaved, releasing free aldehydes during the first steps of wine oxidation, as a consequence of equilibrium shifts caused by the depletion of SO2. At low levels of free SO2, de novo formation and aldehyde degradation are both observed. The relative importance of these phenomena depends on both the aldehyde and the wine. Models relating aldehyde formation rates to wine chemical composition suggest that amino acids are in most cases the most important precursors for de novo formation
Riccati-type equations, generalised WZNW equations, and multidimensional Toda systems
We associate to an arbitrary -gradation of the Lie algebra of a
Lie group a system of Riccati-type first order differential equations. The
particular cases under consideration are the ordinary Riccati and the matrix
Riccati equations. The multidimensional extension of these equations is given.
The generalisation of the associated Redheffer--Reid differential systems
appears in a natural way. The connection between the Toda systems and the
Riccati-type equations in lower and higher dimensions is established. Within
this context the integrability problem for those equations is studied. As an
illustration, some examples of the integrable multidimensional Riccati-type
equations related to the maximally nonabelian Toda systems are given.Comment: LaTeX2e, 18 page
Light scattering by a medium with a spatially modulated optical conductivity: the case of graphene
We describe light scattering from a graphene sheet having a modulated optical
conductivity. We show that such modulation enables the excitation of surface
plasmon-polaritons by an electromagnetic wave impinging at normal incidence.
The resulting surface plasmon-polaritons are responsible for a substantial
increase of electromagnetic radiation absorption by the graphene sheet. The
origin of the modulation can be due either to a periodic strain field or to
adatoms (or absorbed molecules) with a modulated adsorption profile.Comment: http://iopscience.iop.org/0953-8984/24/24/24530
Development of liquid xenon detectors for medical imaging
In the present paper, we report on our developments of liquid xenon detectors
for medical imaging, positron emission tomography and single photon imaging, in
particular. The results of the studies of several photon detectors
(photomultiplier tubes and large area avalanche photodiode) suitable for
detection of xenon scintillation are also briefly described.Comment: 13 pages, 5 figures, presented on the International Workshop on
Techniques and Applications of Xenon Detectors (Xenon01), ICRR, Univ. of
Tokyo, Kashiwa, Japan, December 3-4, 2001 (submitted to proceedings
Two-component mixture of charged particles confined in a channel: melting
The melting of a binary system of charged particles confined in a {\it
quasi}-one-dimensional parabolic channel is studied through Monte Carlo
simulations. At zero temperature the particles are ordered in parallel chains.
The melting is anisotropic and different melting temperatures are obtained
according to the spatial direction, and the different types of particles
present in the system. Melting is very different for the single-, two- and
four-chain configurations. A temperature induced structural phase transition is
found between two different four chain ordered states which is absent in the
mono-disperse system. In the mixed regime, where the two types of particles are
only slightly different, melting is almost isotropic and a thermally induced
homogeneous distribution of the distinct types of charges is observed.Comment: To appear in Journal of Physics: condensed matter ; (13 pages, 12
figures
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