3,762 research outputs found
Preliminary Results on Contents of Resveratrol in Wine of Organic and Conventional Vineyards
Phytoalexins are compounds synthesised by plants in response to various stresses. In grapevines, these compounds belong to the stilbene family. Several studies have shown that resveratrol is usually triggered by infection of berries by Botrytis cinerea. In organic viticulture, grapevines are usually more stressed by attempted or successful infections of various pathogens than in conventionally grown grapevines. Furthermore, crop protection agents such as acidified clays or copper may trigger defence reactions of the plants. The aim of this study was to verify if differences between organically and conventionally produced wines exist. The preliminary results will be used as a starting point for further research of quality aspects of organic grape-vine production
Prospects for a Nuclear Optical Frequency Standard based on Thorium-229
The 7.6-eV-isomer of Thorium-229 offers the opportunity to perform high
resolution laser spectroscopy of a nuclear transition. We give a brief review
of the investigations of this isomer. The nuclear resonance connecting ground
state and isomer may be used as the reference of an optical clock of very high
accuracy using trapped and laser-cooled thorium ions, or in a compact
solid-state optical frequency standard of high stability.Comment: 5 pages, 1 figure; Proceedings of the 7th Symposium on Frequency
Standards and Metrology, 5-11 October 2008; reference added for section
Folding and cytoplasm viscoelasticity contribute jointly to chromosome dynamics
The chromosome is a key player of cell physiology, and its dynamics provides
valuable information about its physical organization. In both prokaryotes and
eukaryotes, the short-time motion of chromosomal loci has been described as a
Rouse model in a simple or viscoelastic medium. However, little emphasis has
been put on the role played by the folded organization of chromosomes on the
local dynamics. Clearly, stress-propagation, and thus dynamics, must be
affected by such organization, but a theory allowing to extract such
information from data, e.g.\ of two-point correlations, is lacking. Here, we
describe a theoretical framework able to answer this general polymer dynamics
question, and we provide a general scaling analysis of the stress-propagation
time between two loci at a given arclength distance along the chromosomal
coordinate. The results suggest a precise way to detect folding information
from the dynamical coupling of chromosome segments. Additionally, we realize
this framework in a specific theoretical model of a polymer with variable-range
interactions in a viscoelastic medium characterized by a tunable scaling
exponent, where we derive analytical estimates of the correlation functions.Comment: 14 pages including supplementary material
Narrow-escape times for diffusion in microdomains with a particle-surface affinity: Mean-field results
We analyze the mean time t_{app} that a randomly moving particle spends in a
bounded domain (sphere) before it escapes through a small window in the
domain's boundary. A particle is assumed to diffuse freely in the bulk until it
approaches the surface of the domain where it becomes weakly adsorbed, and then
wanders diffusively along the boundary for a random time until it desorbs back
to the bulk, and etc. Using a mean-field approximation, we define t_{app}
analytically as a function of the bulk and surface diffusion coefficients, the
mean time it spends in the bulk between two consecutive arrivals to the surface
and the mean time it wanders on the surface within a single round of the
surface diffusion.Comment: 8 pages, 1 figure, submitted to JC
Necklace-Cloverleaf Transition in Associating RNA-like Diblock Copolymers
We consider a diblock copolymer, whose links are capable
of forming local reversible bonds with each other. We assume that the resulting
structure of the bonds is RNA--like, i.e. topologically isomorphic to a tree.
We show that, depending on the relative strengths of A--A, A--B and B--B
contacts, such a polymer can be in one of two different states. Namely, if a
self--association is preferable (i.e., A--A and B--B bonds are comparatively
stronger than A--B contacts) then the polymer forms a typical randomly branched
cloverleaf structure. On the contrary, if alternating association is preferable
(i.e. A--B bonds are stronger than A--A and B--B contacts) then the polymer
tends to form a generally linear necklace structure (with, probably, some rear
side branches and loops, which do not influence the overall characteristics of
the chain). The transition between cloverleaf and necklace states is studied in
details and it is shown that it is a 2nd order phase transition.Comment: 17 pages, 9 figure
Lamplighter model of a random copolymer adsorption on a line
We present a model of an AB-diblock random copolymer sequential
self-packaging with local quenched interactions on a one-dimensional infinite
sticky substrate. It is assumed that the A-A and B-B contacts are favorable,
while A-B are not. The position of a newly added monomer is selected in view of
the local contact energy minimization. The model demonstrates a
self-organization behavior with the nontrivial dependence of the total energy,
(the number of unfavorable contacts), on the number of chain monomers, :
for quenched random equally probable distribution of A- and
B-monomers along the chain. The model is treated by mapping it onto the
"lamplighter" random walk and the diffusion-controlled chemical reaction of
type with the subdiffusive motion of reagents.Comment: 8 pages, 5 figure
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