496 research outputs found
Entropy and universality of Cardy-Verlinde formula in dark energy universe
We study the entropy of a FRW universe filled with dark energy (cosmological
constant, quintessence or phantom). For general or time-dependent equation of
state the entropy is expressed in terms of energy, Casimir energy,
and . The correspondent expression reminds one about 2d CFT entropy only for
conformal matter. At the same time, the cosmological Cardy-Verlinde formula
relating three typical FRW universe entropies remains to be universal for any
type of matter. The same conclusions hold in modified gravity which represents
gravitational alternative for dark energy and which contains terms growing at
low curvature. It is interesting that BHs in modified gravity are more entropic
than in Einstein gravity. Finally, some hydrodynamical examples testing new
shear viscosity bound, which is expected to be the consequence of the
holographic entropy bound, are presented for the early universe in the plasma
era and for the Kasner metric. It seems that the Kasner metric provides a
counterexample to the new shear viscosity bound.Comment: LaTeX file, 39 pages, references are adde
Universal procedure to cure future singularities of dark energy models
A systematic search for different viable models of the dark energy universe,
all of which give rise to finite-time, future singularities, is undertaken,
with the purpose to try to find a solution to this common problem. After some
work, a universal procedure to cure all future singularities is developed and
carefully tested with the help of explicit examples corresponding to each one
of the four different types of possible singularities, as classified in the
literature. The cases of a fluid with an equation of state which depends on
some parameter, of modified gravity non-minimally coupled to a matter
Lagrangian, of non-local gravity, and of isotropic turbulence in a dark fluid
universe theory are investigated in detail
Generalized Chaplygin gas model: Cosmological consequences and statefinder diagnosis
The generalized Chaplygin gas (GCG) model in spatially flat universe is
investigated. The cosmological consequences led by GCG model including the
evolution of EoS parameter, deceleration parameter and dimensionless Hubble
parameter are calculated. We show that the GCG model behaves as a general
quintessence model. The GCG model can also represent the pressureless CDM model
at the early time and cosmological constant model at the late time. The
dependency of transition from decelerated expansion to accelerated expansion on
the parameters of model is investigated. The statefinder parameters and
in this model are derived and the evolutionary trajectories in plane are
plotted. Finally, based on current observational data, we plot the evolutionary
trajectories in and planes for best fit values of the parameters of
GCG model. It has been shown that although, there are similarities between GCG
model and other forms of chaplygin gas in statefinder plane, but the distance
of this model from the CDM fixed point in diagram is shorter
compare with standard chaplygin gas model.Comment: 10 pages, 5 figures, accepted in Astrophys Space Sci. (2011
Unifying inflation with dark energy in modified F(R) Horava-Lifshitz gravity
We study FRW cosmology for a non-linear modified F(R) Horava-Lifshitz gravity
which has a viable convenient counterpart. A unified description of early-time
inflation and late-time acceleration is possible in this theory, but the
cosmological dynamic details are generically different from the ones of the
convenient viable F(R) model. Remarkably, for some specific choice of
parameters they do coincide. The emergence of finite-time future singularities
is investigated in detail. It is shown that these singularities can be cured by
adding an extra, higher-derivative term, which turns out to be qualitatively
different when compared with the corresponding one of the convenient F(R)
theory.Comment: LaTeX 12 pages, typos are correcte
Screening of cosmological constant for De Sitter Universe in non-local gravity, phantom-divide crossing and finite-time future singularities
We investigate de Sitter solutions in non-local gravity as well as in
non-local gravity with Lagrange constraint multiplier. We examine a condition
to avoid a ghost and discuss a screening scenario for a cosmological constant
in de Sitter solutions. Furthermore, we explicitly demonstrate that three types
of the finite-time future singularities can occur in non-local gravity and
explore their properties. In addition, we evaluate the effective equation of
state for the universe and show that the late-time accelerating universe may be
effectively the quintessence, cosmological constant or phantom-like phases. In
particular, it is found that there is a case in which a crossing of the phantom
divide from the non-phantom (quintessence) phase to the phantom one can be
realized when a finite-time future singularity occurs. Moreover, it is
demonstrated that the addition of an term can cure the finite-time future
singularities in non-local gravity. It is also suggested that in the framework
of non-local gravity, adding an term leads to possible unification of the
early-time inflation with the late-time cosmic acceleration.Comment: 42 pages, no figure, version accepted for publication in General
Relativity and Gravitatio
Tight-binding parameters for charge transfer along DNA
We systematically examine all the tight-binding parameters pertinent to
charge transfer along DNA. The molecular structure of the four DNA bases
(adenine, thymine, cytosine, and guanine) is investigated by using the linear
combination of atomic orbitals method with a recently introduced
parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are
discussed and then used for calculating the corresponding wavefunctions of the
two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO
and LUMO energies of the bases are in good agreement with available
experimental values. Our results are then used for estimating the complete set
of charge transfer parameters between neighboring bases and also between
successive base-pairs, considering all possible combinations between them, for
both electrons and holes. The calculated microscopic quantities can be used in
mesoscopic theoretical models of electron or hole transfer along the DNA double
helix, as they provide the necessary parameters for a tight-binding
phenomenological description based on the molecular overlap. We find that
usually the hopping parameters for holes are higher in magnitude compared to
the ones for electrons, which probably indicates that hole transport along DNA
is more favorable than electron transport. Our findings are also compared with
existing calculations from first principles.Comment: 15 pages, 3 figures, 7 table
Recent experimental results in sub- and near-barrier heavy ion fusion reactions
Recent advances obtained in the field of near and sub-barrier heavy-ion
fusion reactions are reviewed. Emphasis is given to the results obtained in the
last decade, and focus will be mainly on the experimental work performed
concerning the influence of transfer channels on fusion cross sections and the
hindrance phenomenon far below the barrier. Indeed, early data of sub-barrier
fusion taught us that cross sections may strongly depend on the low-energy
collective modes of the colliding nuclei, and, possibly, on couplings to
transfer channels. The coupled-channels (CC) model has been quite successful in
the interpretation of the experimental evidences. Fusion barrier distributions
often yield the fingerprint of the relevant coupled channels. Recent results
obtained by using radioactive beams are reported. At deep sub-barrier energies,
the slope of the excitation function in a semi-logarithmic plot keeps
increasing in many cases and standard CC calculations over-predict the cross
sections. This was named a hindrance phenomenon, and its physical origin is
still a matter of debate. Recent theoretical developments suggest that this
effect, at least partially, may be a consequence of the Pauli exclusion
principle. The hindrance may have far-reaching consequences in astrophysics
where fusion of light systems determines stellar evolution during the carbon
and oxygen burning stages, and yields important information for exotic
reactions that take place in the inner crust of accreting neutron stars.Comment: 40 pages, 63 figures, review paper accepted for EPJ
Sistema acuapónico con humedal subsuperficial para producción de carpa (Cyprinus carpio L.), fresa (Fragaria x ananassa (Duchesne ex Weston) y canola (Brassica napus L.)
Objective: a greenhouse pilot aquaponic system was installed, operated, and evaluated to produce carps-strawberry-canola.
Design / methodology / approach: the proposed aquaponics system was made of 4 modules: 1) module for the production of carp (Cyprinus Carpio comunis), 2) hydroponic module, deep flow type for the production of duckweed (Lemna minor L.) used to feed the carps, 3) hydroponic module for the strawberry production (Fragaria × ananassa), 4) hydroponic module with substrate (medium gravel) for the canola production (Brassica napus). The carps (Cyprinus carpio) had an average weight of 0.92 g at the beginning of the study (July 2018), the density was 500 carps/ 0.7 m3 of water. From September to December, a sample of 5% was taken to quantify their growth (length and weight) employing a Vernier, and a triple beam balance (OHAUS®). The carps were fed only with duckweed (Lemna minor L.). The carps were fed daily with 1.5% of duckweed as fresh matter concerning the average live weight of the 500 carps. Module 2 had an area of ??0.26 m2. The dry matter of duckweed was quantified using a PVC cylinder that had an area of ??0.010 m2, and then the fresh sample was weighed and dried at 105º C until constant weight. Module 3 (0.42 m2) had 23 plants in a vegetative state, the growth of 5 plants was evaluated by measuring the size of the root (cm), the height of the plant (cm), the length and width of the leaves (cm) and the foliar area (cm2). Module 4 had 0.42 m2, canola seed was sown at a density of 1.2 g/m2 that represented 185 seedlings. The growth of 9 plants was evaluated by measuring the same variables of strawberry plants.
Results: in module 1, an average weight per carp of 17.7 g was obtained, representing an average weight increase of 16.8 g in the period from September to December. Module 2 produced 12 kg of duckweed in a fresh basis with 5.6% of dry matter. duckweed production was maintained using the nutrients from the effluent of module 1. In module 3, it was observed that strawberry plants presented an increase of 2.5 g in the fresh weight, 1 cm in root size, 0.9 cm in plant height, 0.2 cm in leaf length, 0.2 cm in leaf width and 0.4 cm2 in the leaf area. In module 4, there was an increase of 8.1 g in plant height, 0.2 cm in the leaf length, 0.2 cm in the leaf width and 0.1 cm2 in the leaf area.
Limitations of the study/ implications: for the canola crop, only results of the vegetative growth were reported. For the carps, only three months were reported. However, there was evidence of the feasibility of the system.
Findings/ Conclusions: an aquaponic system was installed, operated, and evaluated to produce carps-strawberry-canola. The duckweed was the only source of dry matter for carps. The effluent from the carp module provided nutrients for strawberry growth, bearing fruits of the right color. Canola plants developed adequately, although they had a purple color on the leaves, indicating a possible phosphorus deficiency.Objetivo: se instaló, opero y evaluó un sistema acuapónico piloto bajo invernadero para la producción de carpa-fresa-canola utilizando lenteja de agua como única fuente de alimento.
Diseño/metodología/aproximación: el sistema acuapónico propuesto consistió en 4 módulos: 1) módulo para la producción de carpa (Cyprinus Carpio comunis), 2) módulo hidropónico tipo flujo profundo para la producción de lenteja de agua (Lemna minor L.) que se utilizó para alimentar a las carpas, 3) módulo hidropónico tipo raíz flotante para el cultivo de fresa (Fragaria × ananassa), 4) módulo hidropónico con sustrato (grava media) para el cultivo de canola (Brassica napus). En el módulo 1 se crio carpa (Cyprinus carpio) con peso promedio inicial de 0.92 g, a una densidad de 500 peces/0.7 m3 de agua en el mes de julio de 2018. De septiembre a diciembre del mismo año se tomó una muestra del 5% de la población para medir su crecimiento (longitud y peso) empleando un vernier de campo, y se obtuvo el peso (g) por carpa con una balanza granataria. Las carpas se alimentaron solamente con lenteja de agua (Lemna minor L.), se les ofreció 1.5% de peso fresco de Lemna con respecto al peso promedio de las 500 carpas. El módulo 2 tuvo un área de 0.26 m2, se cuantifico la producción de materia seca de la lenteja de agua mediante un cilindro de PVC con un área de 0.010 m2, la muestra fresca se pesó al momento del muestreo y posteriormente se secó a 105º C hasta peso constante. En el módulo 3 de 0.42 m2 se cultivaron 23 plantas de fresa en estado vegetativo, se monitoreó el crecimiento de 5 plantas mediante la medición del tamaño de la raíz (cm), la altura de la planta (cm), el largo y ancho de las hojas (cm) y el área foliar. El módulo 4 tuvo una superficie de 0.42 m2, se sembró semilla de canola a una densidad de 1.2 g/m2 que representó 185 plántulas. Se monitorio el crecimiento de 9 plantas y se evaluaron las mismas variables para las plantas de fresa.
Resultados: en el módulo 1 se obtuvo un peso promedio por carpa de 17.7 g representando un incremento de peso promedio de 16.8 g en el periodo de septiembre a diciembre. En el módulo 2 se produjo 12 kg de lenteja de agua fresca en un área de 0.26 m2 con 5.6% de materia seca. La producción de lenteja de agua se mantuvo utilizando los nutrientes del efluente del módulo 1. En el módulo 3 se observó que las plantas de fresa se adaptaron al sistema hidropónico tipo raíz flotante. En promedio se cuantifico un incremento de 2.5 g en el peso fresco de la planta, 1 cm en el tamaño de raíz, 0.9 cm en la altura de planta, 0.2 cm en el largo de hoja, 0.2 cm en el ancho de hoja y 0.4 cm2 en el área foliar. En el módulo 4 se cuantifico en promedio un incremento de 8.1 g en la altura de planta, 0.2 cm en el largo de hoja, 0.2 cm en el ancho hoja y 0.1 cm en el área foliar.
Limitaciones del estudio/implicaciones: se reportan resultados del crecimiento vegetativo para la canola, para las carpas solamente se reporta el crecimiento en tres meses, no obstante, se muestra evidencia de la factibilidad del sistema.
Hallazgos/conclusiones: se instaló, operó y evaluó un sistema acuapónico recirculante para la producción de carpa-fresa-canola. La lenteja de agua funcionó como la única fuente de alimento para el crecimiento de la carpa. El efluente del módulo carpa proporcionó nutrientes para el crecimiento de la fresa, dando frutos de buen color. Las plantas de canola se desarrollaron adecuadamente, aunque presentaron un color purpura en las hojas, lo que indicó una posible deficiencia de fosforo
Alirocumab Reduces Total Nonfatal Cardiovascular and Fatal Events : The ODYSSEY OUTCOMES Trial
The ODYSSEY OUTCOMES (Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment With Alirocumab) trial compared alirocumab with placebo, added to high-intensity or maximum-tolerated statin treatment, after acute coronary syndrome (ACS) in 18,924 patients. Alirocumab reduced the first occurrence of the primary composite endpoint and was associated with fewer all-cause deaths. This pre-specified analysis determined the extent to which alirocumab reduced total (first and subsequent) nonfatal cardiovascular events and all-cause deaths in ODYSSEY OUTCOMES. Hazard functions for total nonfatal cardiovascular events (myocardial infarction, stroke, ischemia-driven coronary revascularization, and hospitalization for unstable angina or heart failure) and death were jointly estimated, linked by a shared frailty accounting for patient risk heterogeneity and correlated within-patient nonfatal events. An association parameter also quantified the strength of the linkage between risk of nonfatal events and death. The model provides accurate relative estimates of nonfatal event risk if nonfatal events are associated with increased risk for death. With 3,064 first and 5,425 total events, 190 fewer first and 385 fewer total nonfatal cardiovascular events or deaths were observed with alirocumab compared with placebo. Alirocumab reduced total nonfatal cardiovascular events (hazard ratio: 0.87; 95% confidence interval: 0.82 to 0.93) and death (hazard ratio: 0.83; 95% confidence interval: 0.71 to 0.97) in the presence of a strong association between nonfatal and fatal event risk. In patients with ACS, the total number of nonfatal cardiovascular events and deaths prevented with alirocumab was twice the number of first events prevented. Consequently, total event reduction is a more comprehensive metric to capture the totality of alirocumab clinical efficacy after ACS
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Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity
Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements
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