4 research outputs found
Quantum Fluctuations, Decoherence of the Mean Field, and Structure Formation in the Early Universe
We examine from first principles one of the basic assumptions of modern
quantum theories of structure formation in the early universe, i.e., the
conditions upon which fluctuations of a quantum field may transmute into
classical stochastic perturbations, which grew into galaxies. Our earlier works
have discussed the quantum origin of noise in stochastic inflation and quantum
fluctuations as measured by particle creation in semiclassical gravity. Here we
focus on decoherence and the relation of quantum and classical fluctuations.
Instead of using the rather ad hoc splitting of a quantum field into long and
short wavelength parts, the latter providing the noise which decoheres the
former, we treat a nonlinear theory and examine the decoherence of a quantum
mean field by its own quantum fluctuations, or that of other fields it
interacts with. This is an example of `dynamical decoherence' where an
effective open quantum system decoheres through its own dynamics. The model we
use to discuss fluctuation generation has the inflation field coupled to the
graviton field. We show that when the quantum to classical transition is
properly treated, with due consideration of the relation of decoherence, noise,
fluctuation and dissipation, the amplitude of density contrast predicted falls
in the acceptable range without requiring a fine tuning of the coupling
constant of the inflation field (). The conventional treatment which
requires an unnaturally small stems from a basic
flaw in naively identifying classical perturbations with quantum fluctuations.Comment: 35 pages, latex, 0 figure
Antimicrobial activity and bioactive compounds of portuguese wild edible mushrooms methanolic extracts
The antimicrobial properties of phenolic extracts of Portuguese wild edible mushroom species (Lactarius deliciosus,
Sarcodon imbricatus and Tricholoma portentosum)
against pathogens were investigated. The minimal inhibitory
concentrations (MICs) were evaluated for the entire mushroom,
the cap and the stipe, separately; the portion of the
mushroom used proved to be influenced in the results obtained,
which are directly correlated with the content of total
phenols and flavonoids in the extracts. The growth of Grampositive
bacteria (Bacillus cereus, B. subtilis,) was well inhibited
by these mushrooms, while Escherichia coli (Gramnegative
bacteria) was resistant. The study on the antifungal
effect of these mushrooms revealed that Candida albicans
and Cryptococcus neoformans were differently inhibited for
the mushrooms used