2,568 research outputs found
Gravitational wave generation in hybrid quintessential inflationary models
We investigate the generation of gravitational waves in the hybrid
quintessential inflationary model. The full gravitational-wave energy spectrum
is calculated using the method of continuous Bogoliubov coefficients. The
post-inflationary kination period, characteristic of quintessential
inflationary models, leaves a clear signature on the spectrum, namely, a peak
at high frequencies. The maximum of the peak is firmly located at the MHz-GHz
region of the spectrum and corresponds to . This
peak is substantially smaller than the one appearing in the gravitational-wave
energy spectrum of the original quintessential inflationary model, therefore
avoiding any conflict with the nucleosynthesis constraint on
\Omega_\Omega_{GW}.Comment: 10 pages, 11 figures, one reference adde
Gravitational wave generation in loop quantum cosmology
We calculate the full spectrum, as observed today, of the cosmological
gravitational waves generated within a model based on loop quantum cosmology.
It is assumed that the universe, after the transition to the classical regime,
undergoes a period of inflation driven by a scalar field with a chaotic-type
potential. Our analysis shows that, for certain conditions, loop quantum
effects leave a clear signature on the spectrum, namely, an over-production of
low-frequency gravitational waves. One of the aims of our work is to show that
loop quantum cosmology models can be tested and that, more generally,
pre-inflationary physical processes, contrary to what is usually assumed, leave
their imprint in those spectra and can also be tested.Comment: 7 pages, 8 figures, revtex
Nonzero orbital angular momentum superfluidity in ultracold Fermi gases
We analyze the evolution of superfluidity for nonzero orbital angular
momentum channels from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein
condensation (BEC) limit in three dimensions. First, we analyze the low energy
scattering properties of finite range interactions for all possible angular
momentum channels. Second, we discuss ground state () superfluid
properties including the order parameter, chemical potential, quasiparticle
excitation spectrum, momentum distribution, atomic compressibility, ground
state energy and low energy collective excitations. We show that a quantum
phase transition occurs for nonzero angular momentum pairing, unlike the s-wave
case where the BCS to BEC evolution is just a crossover. Third, we present a
gaussian fluctuation theory near the critical temperature (),
and we analyze the number of bound, scattering and unbound fermions as well as
the chemical potential. Finally, we derive the time-dependent Ginzburg-Landau
functional near , and compare the Ginzburg-Landau coherence length
with the zero temperature average Cooper pair size.Comment: 28 pages and 24 figure
Phase Fluctuations and Vortex Lattice Melting in Triplet Quasi-One-Dimensional Superconductors at High Magnetic Fields
Assuming that the order parameter corresponds to an equal spin triplet
pairing symmetry state, we calculate the effect of phase fluctuations in
quasi-one-dimensional superconductors at high magnetic fields applied along the
y (b') axis. We show that phase fluctuations can destroy the theoretically
predicted triplet reentrant superconducting state, and that they are
responsible for melting the magnetic field induced Josephson vortex lattice
above a magnetic field dependent melting temperature Tm.Comment: 4 pages (double column), 1 eps figur
Parametric Resonance and Cosmological Gravitational Waves
We investigate the production of gravitational waves due to quantum
fluctuations of the vacuum during the transition from the inflationary to the
radiation-dominated eras of the universe, assuming this transition to be
dominated by the phenomenon of parametric resonance. The energy spectrum of the
gravitational waves is calculated using the method of continuous Bogoliubov
coefficients, which avoids the problem of overproduction of gravitons at large
frequencies. We found, on the sole basis of the mechanism of quantum
fluctuations, that the resonance field leaves no explicit and distinctive
imprint on the gravitational-wave energy spectrum, apart an overall upward or
downward translation. Therefore, the main features in the spectrum are due to
the inflaton field, which leaves a characteristic imprint at frequencies of the
order of MHz/GHz.Comment: 8 pages, 7 figure
Coccolithophore fluxes in the open tropical North Atlantic: influence of thermocline depth, Amazon water, and Saharan dust
Coccolithophores are calcifying phytoplankton and major contributors to both the organic and inorganic oceanic carbon pumps. Their export fluxes, species composition, and seasonal patterns were determined in two sediment trap moorings (M4 at 12 degrees N, 49 degrees W and M2 at 14 degrees N, 37 degrees W) collecting settling particles synchronously from October 2012 to November 2013 at 1200 m of water depth in the open equatorial North Atlantic. The two trap locations showed a similar seasonal pattern in total coccolith export fluxes and a predominantly tropical coccolithophore settling assemblage. Species fluxes were dominated throughout the year by lower photic zone (LPZ) taxa (Florisphaera profunda, Gladiolithus flabellatus) but also included upper photic zone (UPZ) taxa (Umbellosphaera spp., Rhabdosphaera spp., Umbilicosphaera spp., Helicosphaera spp.). The LPZ flora was most abundant during fall 2012, whereas the UPZ flora was more important during summer. In spite of these similarities, the western part of the study area produced persistently higher fluxes, averaging 241 x 10(7) +/- 76 x 10(7) coccoliths m(-2) d(-1) at station M4 compared to only 66 x 10(7) +/- 31 x 10(7) coccoliths m(-2) d(-1) at station M2. Higher fluxes at M4 were mainly produced by the LPZ species, favoured by the westward deepening of the thermocline and nutricline. Still, most UPZ species also contributed to higher fluxes, reflecting enhanced productivity in the western equatorial North Atlantic. Such was the case of two marked flux peaks of the more opportunistic species Gephyrocapsa muellerae and Emiliania huxleyi in January and April 2013 at M4, indicating a fast response to the nutrient enrichment of the UPZ, probably by wind-forced mixing. Later, increased fluxes of G. oceanica and E. huxleyi in October-November 2013 coincided with the occurrence of Amazon-River-affected surface waters. Since the spring and fall events of 2013 were also accompanied by two dust flux peaks, we propose a scenario in which atmospheric dust also provided fertilizing nutrients to this area. Enhanced surface buoyancy associated with the river plume indicates that the Amazon acted not only as a nutrient source, but also as a surface density retainer for nutrients supplied from the atmosphere. Nevertheless, lower total coccolith fluxes during these events compared to the maxima recorded in November 2012 and July 2013 indicate that transient productivity by opportunistic species was less important than "background" tropical productivity in the equatorial North Atlantic. This study illustrates how two apparently similar sites in the tropical open ocean actually differ greatly in ecological and oceanographic terms. The results presented here provide valuable insights into the processes governing the ecological dynamics and the downward export of coccolithophores in the tropical North Atlantic.Netherlands Organization for Scientific Research (NWO) [822.01.008]; European Research Council (ERC) [311152]; University of Bremen; European Union [600411]info:eu-repo/semantics/publishedVersio
Gravitational waves in hybrid quintessential inflationary models
The generation of primordial gravitational waves is investigated within the hybrid quintessential inflationary model. Using the method of continuous Bogoliubov coefficients, we calculate the full gravitational-wave energy spectrum. The post-inflationary kination period, characteristic of quintessential inflationary models, leaves a clear signature on the spectrum, namely, a sharp rise of the gravitational-wave spectral energy density Omega(GW) at high frequencies. For appropriate values of the parameters of the model, Omega(GW) can be as high as 10(-12) in the MHz-GHz range of frequencies.Fundacao para a Ciencia e a Tecnologia, Portuga
Pragas quarentenárias que ameaçam a cultura da mangueira no Brasil.
Define-se como praga quarentenária todo organismo de natureza animal e/ou vegetal que, estando presente em outros países ou regiões, mesmo sob controle permanente, constitua ameaça à economia agrícola do país ou região importadora. Tais organismos são, geralmente, exóticos para esse país ou região e podem ser disseminados, entre outros meios, pelo trânsito de plantas, animais ou por frutos e sementes infestadas, isto é, podem ser transportados de um local para outro auxiliado pelo homem e seus meios de transporte e comércio. As pragas quarentenárias se agrupam nas seguintes categorias: A1- Pragas exóticas não presentes e A2- Pragas de importância econômica potencial, já presentes no país, porém apresentando disseminação localizada e submetidas a programa oficial de controle.bitstream/CPAF-AP-2009-09/14351/1/CTE87.pd
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