2,414 research outputs found
`Preliminary assays in Red Snapper Lutjanus synagris (Linnaeus, 1758) semen cryopreservation through the application of Dimethyl-Sulfoxide (DMSO) and 1,2 Propadiol Cryoprotectors with Santa Marta’s (Colombia) biological material [Poster abstract]
Inflationary spectra and partially decohered distributions
It is generally expected that decoherence processes will erase the quantum
properties of the inflationary primordial spectra. However, given the weakness
of gravitational interactions, one might end up with a distribution which is
only partially decohered. Below a certain critical change, we show that the
inflationary distribution retains quantum properties. We identify four of
these: a squeezed spread in some direction of phase space, non-vanishing
off-diagonal matrix elements, and two properties used in quantum optics called
non--representability and non-separability. The last two are necessary
conditions to violate Bell's inequalities. The critical value above which all
these properties are lost is associated to the `grain' of coherent states. The
corresponding value of the entropy is equal to half the maximal (thermal)
value. Moreover it coincides with the entropy of the effective distribution
obtained by neglecting the decaying modes. By considering backreaction effects,
we also provide an upper bound for this entropy at the onset of the adiabatic
era.Comment: 42 pages, 9 figures; 1 ref. adde
Tachyon warm inflationary universe models
Warm inflationary universe models in a tachyon field theory are studied.
General conditions required for these models to be realizable are derived and
discussed. We describe scalar perturbations (in the longitudinal gauge) and
tensor perturbations for these scenarios. We develop our models for a constant
dissipation parameter in one case and one dependent on in the
other case. We have been successful in describing such of inflationary universe
models. We use recent astronomical observations for constraining the parameters
appearing in our model. Also, our results are compared with their analogous
found in the cool inflationary case.Comment: 21 pages, Accepted by JCA
Shortcuts to adiabaticity in a time-dependent box
A method is proposed to drive an ultrafast non-adiabatic dynamics of an
ultracold gas trapped in a box potential. The resulting state is free from
spurious excitations associated with the breakdown of adiabaticity, and
preserves the quantum correlations of the initial state up to a scaling factor.
The process relies on the existence of an adiabatic invariant and the inversion
of the dynamical self-similar scaling law dictated by it. Its physical
implementation generally requires the use of an auxiliary expulsive potential
analogous to those used in soliton control. The method is extended to a broad
family of many-body systems. As illustrative examples we consider the ultrafast
expansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in
different dimensions, where the method exhibits an excellent robustness against
different regimes of interactions and the features of an experimentally
realizable box potential.Comment: 6 pp, 4 figures, typo in Eq. (6) fixe
Emission of intermediate mass fragments from hot Ba formed in low-energy Ni+Ni reaction
The complex fragments (or intermediate mass fragments) observed in the
low-energy Ni+NiBa reaction, are studied within
the dynamical cluster decay model for s-wave with the use of the
temperature-dependent liquid drop, Coulomb and proximity energies. The
important result is that, due to the temperature effects in liquid drop energy,
the explicit preference for -like fragments is washed out, though the
C (or the complementary Sn) decay is still predicted to be one
of the most probable -nucleus decay for this reaction. The production
rates for non- like intermediate mass fragments (IMFs) are now higher
and the light particle production is shown to accompany the IMFs at all
incident energies, without involving any statistical evaporation process in the
model. The comparisons between the experimental data and the (s-wave)
calculations for IMFs production cross sections are rather satisfactory and the
contributions from other -waves need to be added for a further
improvement of these comparisons and for calculations of the total kinetic
energies of fragments.Comment: 22 pages, 15 figure
A critical-density closed Universe in Brans-Dicke theory
In a Brans-Dicke (BD) cosmological model, the energy density associated with
some scalar field decreases as \displaystyle a^{{-2}(\frac{\omega_{o}+
{\frac12}%}{\omega_{o}+1})} with the scale factor of the Universe,
giving a matter with an Equation of state . In this model, the Universe
could be closed but still have a nonrelativistic-matter density corresponding
to its critical value, . Different cosmological expressions, such
as, luminosity distance, angular diameter, number count and ratio of the
redshift tickness-angular size, are determined in terms of the redshift for
this model.Comment: To appear in MNRAS, 7 pages, 5 eps figure
On time and the quantum-to-classical transition in Jordan-Brans-Dicke quantum gravity
Any quantum theory of gravity which treats the gravitational constant as a
dynamical variable has to address the issue of superpositions of states
corresponding to different eigenvalues. We show how the unobservability of such
superpositions can be explained through the interaction with other
gravitational degrees of freedom (decoherence). The formal framework is
canonically quantized Jordan-Brans-Dicke theory. We discuss the concepts of
intrinsic time and semiclassical time as well as the possibility of tunneling
into regions corresponding to a negative gravitational constant. We calculate
the reduced density matrix of the Jordan-Brans-Dicke field and show that the
off-diagonal elements can be sufficiently suppressed to be consistent with
experiments. The possible relevance of this mechanism for structure formation
in extended inflation is briefly discussed.Comment: 10 pages, Latex, ZU-TH 15/93, BUTP-93/1
Accelerated closed universes in scalar-tensor theories
We describe an accelerating universe model in the context of a scalar-tensor
theory. This model is intrinsically closed, and is filled with
quintessence-like scalar field components, in addition to the Cold Dark Matter
component. With a background geometry specified by the
Friedman-Robertson-Walker metric, we establish conditions under which this
closed cosmological model, described in a scalar-tensor theory, may look flat
in a genuine Jordan-Brans-Dicke theory. Both models become indistinguishable at
low enough redshift.Comment: 8 pages, 4 figures, in press (CQG
Extended Curvaton reheating in inflationary models
The curvaton reheating in a non-oscillatory inflationary universe model is
studied in a Jordan-Brans-Dicke theory. For different scenarios, the
temperature of reheating is computed. The result tells us that the reheating
temperature becomes practically independent of the Jordan-Brans-Dicke parameter
. This reheating temperature results to be quite different when compared
with that obtained from Einstein`s theory of gravity.Comment: Accepted by JCAP, 12 pages, 1 Figur
Causality and defect formation in the dynamics of an engineered quantum phase transition in a coupled binary Bose-Einstein condensate
Continuous phase transitions occur in a wide range of physical systems, and
provide a context for the study of non-equilibrium dynamics and the formation
of topological defects. The Kibble-Zurek (KZ) mechanism predicts the scaling of
the resulting density of defects as a function of the quench rate through a
critical point, and this can provide an estimate of the critical exponents of a
phase transition. In this work we extend our previous study of the
miscible-immiscible phase transition of a binary Bose-Einstein condensate (BEC)
composed of two hyperfine states in which the spin dynamics are confined to one
dimension [J. Sabbatini et al., Phys. Rev. Lett. 107, 230402 (2011)]. The
transition is engineered by controlling a Hamiltonian quench of the coupling
amplitude of the two hyperfine states, and results in the formation of a random
pattern of spatial domains. Using the numerical truncated Wigner phase space
method, we show that in a ring BEC the number of domains formed in the phase
transitions scales as predicted by the KZ theory. We also consider the same
experiment performed with a harmonically trapped BEC, and investigate how the
density inhomogeneity modifies the dynamics of the phase transition and the KZ
scaling law for the number of domains. We then make use of the symmetry between
inhomogeneous phase transitions in anisotropic systems, and an inhomogeneous
quench in a homogeneous system, to engineer coupling quenches that allow us to
quantify several aspects of inhomogeneous phase transitions. In particular, we
quantify the effect of causality in the propagation of the phase transition
front on the resulting formation of domain walls, and find indications that the
density of defects is determined during the impulse to adiabatic transition
after the crossing of the critical point.Comment: 23 pages, 10 figures. Minor corrections, typos, additional referenc
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