13,004 research outputs found
Removing zero Lyapunov exponents in volume-preserving flows
Baraviera and Bonatti proved that it is possible to perturb, in the c^1
topology, a volume-preserving and partial hyperbolic diffeomorphism in order to
obtain a non-zero sum of all the Lyapunov exponents in the central direction.
In this article we obtain the analogous result for volume-preserving flows.Comment: 10 page
Notes on the Two-brane Model with Variable Tension
Motivated by possible extensions of the braneworld models with two branes, we
investigate some consequences of a variable brane tension using the well
established results on consistency conditions. By a slight modification of the
usual stress-tensor used in order to derive the braneworld sum rules, we find
out some important constraints obeyed by time dependent brane tensions. In
particular it is shown that the tensions of two Randall-Sundrum like branes
obeying, at the same time, an Eotvos law, aggravate the fine tuning problem.
Also, it is shown that if the hidden brane tension obeys an Eotvos law, then
the visible brane has a mixed behavior allowing a bouncing-like period at early
times while it is dominated by an Eotvos law nowadays. To finalize, we discuss
some qualitative characteristics which may arise in the scope of dynamical
brane tensions, as anisotropic background and branons production.Comment: 7 pages, 1 figure, accepted for publication in Physical Review
Polyphenoloxidase activity of minimally processed "Jonagored" apples (Malus domestica)
The influence of three chemical dips using ascorbic acid (AA), citric acid (CA) and calcium chloride (CC) on the polyphenoloxidase (PPO) activity and on the total phenolic content of minimally processed (MP) apple (Malus domestica, cv. Jonagored) during cold storage was evaluated and a potential relationship with enzymatic browning was investigated. An ascorbic acid dip (42.6 mM) of 5 min duration was the most efficient chemical treatment in reducing the PPO activity of apple cubes. A 92% inhibition was achieved after 7 days of storage at 4C. All treatments were advantageous in comparison to the control in reducing color changes. Color changes, determined by absorbance at 420 nm (soluble pigments) and lightness (L) (insoluble pigments) of apple cubes treated with ascorbic acid were correlated with total phenolic content. No correlation was observed between PPO activity and tristimulus
color parameters, browning index or total phenolic content of AA-treated apple cubes
Shelf life of minimally processed apple (cv. Jonagored) determined by colour changes
Physical, chemical and sensory changes of cut apple (cv. Jonagored) stored in the dark at 4 °C were evaluated. Colour was found to be the critical parameter for this product. Apple cubes underwent severe surface browning primarily during the initial days of storage. The shelf-life of cut apple was therefore very limited, to three days maximum.
Sensory analyses and objective quality evaluations of cut apple were considered highly correlated in terms of colour and flavour, especially with respect to fructose and sucrose, showing that the selected sensory attributes were good indicators of overall fruit quality
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