5,108 research outputs found
Effect of high frequency ultrasounds on lycopene and total phenolic concentration, antioxidant properties and α-glucosidase inhibitory activity of tomato juice
Tomato juice was subjected to high frequency ultrasounds(378 and 583 kHz)at increasing energy densities (up to 250 MJ/m3). Results relevant to the treatments at high frequency providing an energy density of 250 MJ/m3 were compared with those obtained at 24 kHz delivering the same energy density. Lycopene and total phenolic concentration, as well as the α-glucosidase inhibitory activityof tomato juice, were not affected by ultrasound regardless the frequency and energy density. However, the antioxidant properties were negatively affected by high frequency ultrasounds
A Quantum Cosmological Model With Static and Dynamic Wormholes
Quantization is performed of a Friedmann-Robertson-Walker universe filled
with a conformally invariant scalar field and a perfect fluid with equation of
state . A well-known discrete set of static quantum wormholes is
shown to exist for radiation (), and a novel continuous set is
found for cosmic strings (), the latter states having throat
radii of any size. In both cases wave-packet solutions to the Wheeler-DeWitt
equation are obtained with all the properties of evolving quantum wormholes. In
the case of a radiation fluid, a detailed analysis of the quantum dynamics is
made in the context of the Bohm-de Broglie interpretation. It is shown that a
repulsive quantum force inversely proportional to the cube of the scale factor
prevents singularities in the quantum domain. For the states considered, there
are no particle horizons either.Comment: LaTex file, 13 pages. To appear in General Relativity and Gravitatio
Gravitational Collapse of Perfect Fluid in Self-Similar Higher Dimensional Space-Times
We investigate the occurrence and nature of naked singularities in the
gravitational collapse of an adiabatic perfect fluid in self-similar higher
dimensional space-times. It is shown that strong curvature naked singularities
could occur if the weak energy condition holds. Its implication for cosmic
censorship conjecture is discussed. Known results of analogous studies in four
dimensions can be recovered.Comment: 11 Pages, Latex, no figures, Accepted in Int. J. Mod. Phys.
Fast method for the determination of short-chain-length polyhydroxyalkanoates (scl-PHAs) in bacterial samples by In Vial-Thermolysis (IVT)
none8siA new method based on the GCâMS analysis of thermolysis products obtained by treating bacterial
samples at a high temperature (above 270 C) has been developed. This method, here named âIn-Vial-
Thermolysisâ (IVT), allowed for the simultaneous determination of short-chain-length polyhydrox-
yalkanoates (scl-PHA) content and composition. The method was applied to both single strains and
microbial mixed cultures (MMC) fed with different carbon sources.
The IVT procedure provided similar analytical performances compared to previous Py-GCâMS and Py-
GC-FID methods, suggesting a similar application for PHA quantitation in bacterial cells. Results from the
IVT procedure and the traditional methanolysis method were compared; the correlation between the
two datasets was
fit for the purpose, giving a R2 of 0.975. In search of further simplification, the rationale
of IVT was exploited for the development of a âfield methodâ based on the titration of thermolyzed
samples with sodium hydrogen carbonate to quantify PHA inside bacterial cells. The accuracy of the IVT
method was
fit for the purpose.
These results lead to the possibility for the on-line measurement of PHA productivity. Moreover, they
allow for the fast and inexpensive quantification/characterization of PHA for biotechnological process
control, as well as investigation over various bacterial communities and/or feeding strategies.mixedF. Abbondanzi; G. Biscaro; G. Carvalho; L. Favaro; P. Lemos; M. Paglione; C. SamorĂŹ; C. TorriF. Abbondanzi; G. Biscaro; G. Carvalho; L. Favaro; P. Lemos; M. Paglione; C. SamorĂŹ; C. Torr
Pair creation of higher dimensional black holes on a de Sitter background
We study in detail the quantum process in which a pair of black holes is
created in a higher D-dimensional de Sitter (dS) background. The energy to
materialize and accelerate the pair comes from the positive cosmological
constant. The instantons that describe the process are obtained from the
Tangherlini black hole solutions. Our pair creation rates reduce to the pair
creation rate for Reissner-Nordstrom-dS solutions when D=4. Pair creation of
black holes in the dS background becomes less suppressed when the dimension of
the spacetime increases. The dS space is the only background in which we can
discuss analytically the pair creation process of higher dimensional black
holes, since the C-metric and the Ernst solutions, that describe respectively a
pair accelerated by a string and by an electromagnetic field, are not know yet
in a higher dimensional spacetime.Comment: 10 pages; 1 figure included; RexTeX4. v2: References added. Published
version. v3: Typo in equation (46) fixe
Gravitational collapse to toroidal, cylindrical and planar black holes
Gravitational collapse of non-spherical symmetric matter leads inevitably to
non-static external spacetimes. It is shown here that gravitational collapse of
matter with toroidal topology in a toroidal anti-de Sitter background proceeds
to form a toroidal black hole. According to the analytical model presented, the
collapsing matter absorbs energy in the form of radiation (be it scalar,
neutrinos, electromagnetic, or gravitational) from the exterior spacetime. Upon
decompactification of one or two coordinates of the torus one gets collapsing
solutions of cylindrical or planar matter onto black strings or black
membranes, respectively. The results have implications on the hoop conjecture.Comment: 6 pages, Revtex, modifications in the title and in the interpretation
of some results, to appear in Physical Review
Derivation of an Abelian effective model for instanton chains in 3D Yang-Mills theory
In this work, we derive a recently proposed Abelian model to describe the
interaction of correlated monopoles, center vortices, and dual fields in three
dimensional SU(2) Yang-Mills theory. Following recent polymer techniques,
special care is taken to obtain the end-to-end probability for a single
interacting center vortex, which constitutes a key ingredient to represent the
ensemble integration.Comment: 18 pages, LaTe
Quantum cosmological perfect fluid models
Perfect fluid Friedmann-Robertson-Walker quantum cosmological models for an
arbitrary barotropic equation of state are constructed using
Schutz's variational formalism. In this approach the notion of time can be
recovered. By superposition of stationary states, finite-norm wave-packet
solutions to the Wheeler-DeWitt equation are found. The behaviour of the scale
factor is studied by applying the many-worlds and the ontological
interpretations of quantum mechanics. Singularity-free models are obtained for
.Comment: Latex file, 12 pages. New paragraphs in the Introduction and
Conclusion, and other minor corrections in the text and in some formulas.
Accepted for publication in General Relativity and Gravitatio
Dynamical Vacuum in Quantum Cosmology
By regarding the vacuum as a perfect fluid with equation of state p=-rho, de
Sitter's cosmological model is quantized. Our treatment differs from previous
ones in that it endows the vacuum with dynamical degrees of freedom. Instead of
being postulated from the start, the cosmological constant arises from the
degrees of freedom of the vacuum regarded as a dynamical entity, and a time
variable can be naturally introduced. Taking the scale factor as the sole
degree of freedom of the gravitational field, stationary and wave-packet
solutions to the Wheeler-DeWitt equation are found. It turns out that states of
the Universe with a definite value of the cosmological constant do not exist.
For the wave packets investigated, quantum effects are noticeable only for
small values of the scale factor, a classical regime being attained at
asymptotically large times.Comment: Latex, 19 pages, to appear in Gen. Rel. Gra
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