610 research outputs found
Interference pattern in the collision of structures in the BEC dark matter model: comparison with fluids
In order to explore nonlinear effects on the distribution of matter during
collisions within the Bose-Einstein condensate (BEC) dark matter model driven
by the Schr\"odinger-Poisson system of equations, we study the head-on
collision of structures and focus on the interference pattern formation in the
density of matter during the collision process. We explore the possibility that
the collision of two structures of fluid matter modeled with an ideal gas
equation of state also forms interference patterns and found a negative result.
Given that a fluid is the most common flavor of dark matter models, we conclude
that one fingerprint of the BEC dark matter model is the pattern formation in
the density during a collision of structures.Comment: 7 pages, 22 eps figure
Accretion of phantom scalar field into a black hole
Using numerical methods we present the first full nonlinear study of phantom
scalar field accreted into a black hole. We study different initial
configurations and find that the accretion of the field into the black hole can
reduce its area down to 50 percent within time scales of the order of few
masses of the initial horizon. The analysis includes the cases where the total
energy of the space-time is positive or negative. The confirmation of this
effect in full nonlinear general relativity implies that the accretion of
exotic matter could be considered an evaporation process. We speculate that if
this sort of exotic matter has some cosmological significance, this black hole
area reduction process might have played a crucial role in black hole formation
and population.Comment: 5 revtex pages, 4 eps figures. Minor changes applie
I. Jet Formation and Evolution due to 3D Magnetic Reconnection
Using simulated data-driven three-dimensional resistive MHD simulations of the solar atmosphere, we show that magnetic reconnection can be responsible of the formation of jets with characteristic of Type II spicules. For this, we numerically model the photosphere-corona region using the C7 equilibrium atmosphere model. The initial magnetic configuration is a 3D potential magnetic field, extrapolated up to the solar corona region from a dynamic realistic simulation of solar photospheric magnetoconvection model which is mimicking quiet-Sun. In this case we consider a uniform and constant value of the magnetic resistivity of 12.56 Ω m. We have found that formation of the jets depends on the Lorentz force, which helps to accelerate the plasma upwards. Analyzing various properties of the jet dynamics, we found that the jet structure shows Doppler shift near to regions with high vorticity. The morphology, upward velocity, covering a range up to 100 km s−1, and life-time of the estructure, bigger than 100 s, are similar to those expected for Type II spicules
Sucrose effect on broomrape (Orobanche crenata) development on narbon bean (Vicia narbonensis L.)
The growth and development of broomrapes (Orobanche spp.) fully depends on the nutritional connection established between the parasitic plant and the root of the corresponding host plant. In thepresent study, narbon bean plants infected with Orobanche crenata were watered with different concentrations of sucrose (0.014, 0.044, 0.088 and 0.146 M) in order to evaluate its effect on the earlygrowth stages of the parasite. The germination of O. crenata seeds decreased with increasing sucrose concentrations and the number of infection attachments of crenata broomrapes decreased significantlywhen sucrose was present. A parallel experiment was conducted with identical sorbitol concentrations in order to determinate the role of the osmotic potential in the inhibition of the parasite growth. Ourresults showed that while low sucrose concentrations significantly reduced seed germination in O. crenata, similar concentrations of sorbitol have no significant effect thus indicating that the effect ofsucrose is not simply osmotic. Sucrose phytotoxicity was also studied by considering the dry weight of the host plants
Line-Strength Indices in Bright Spheroidals: Evidence for a Stellar Population Dichotomy between Spheroidal and Elliptical Galaxies
We present new measurements of central line-strength indices (namely Mg2,
, and Hbeta and gradients for a sample of 6 bright spheroidal galaxies
(Sph's) in the Virgo cluster. Comparison with similar measurements for
elliptical galaxies (E's), galactic globular clusters (GGC's), and stellar
population models yield the following results: (1) In contrast with bright E's,
bright Sph's are consistent with solar abundance [Mg/Fe] ratios; (2) Bright
Sph's exhibit metallicities ranging from values typical for metal-rich GGC's to
those for E's; (3) Although absolute mean ages are quite model dependent, we
find evidence that the stellar populations of some (if not all) Sph's look
significantly younger than GGC's; and (4) Mg2 gradients of bright Sph's are
significantly shallower than those of E galaxies. We conclude that the
dichotomy found in the structural properties of Sph and E galaxies is also
observed in their stellar populations. A tentative interpretation in terms of
differences in star formation histories is suggested.Comment: 14 pages, LaTeX file + 2 PostScript figures, aasms4.sty require
Instability of wormholes supported by a ghost scalar field. II. Nonlinear evolution
We analyze the nonlinear evolution of spherically symmetric wormhole
solutions coupled to a massless ghost scalar field using numerical methods. In
a previous article we have shown that static wormholes with these properties
are unstable with respect to linear perturbations. Here we show that depending
on the initial perturbation the wormholes either expand or decay to a
Schwarzschild black hole. We estimate the time scale of the expanding solutions
and the ones collapsing to a black hole and show that they are consistent in
the regime of small perturbations with those predicted from perturbation
theory. In the collapsing case, we also present a systematic study of the final
black hole horizon and discuss the possibility for a luminous signal to travel
from one universe to the other and back before the black hole forms. In the
expanding case, the wormholes seem to undergo an exponential expansion, at
least during the run time of our simulations.Comment: 16 pages, 15 figures, minor modifications, to appear in Classical and
Quantum Gravit
In situ generation of coronal Alfvén waves by jets
Within the framework of 3D resistive magnetohydrodynamic, we simulate the formation of a plasma jet with the morphology, upward velocity up to 130 km s−1, and time-scale formation between 60 and 90 s after beginning of simulation, similar to those expected for type II spicules. Initial results of this simulation were published in paper by, e.g. González-Avilés et al. (2018), and present paper is devoted to the analysis of transverse displacements and rotational-type motion of the jet. Our results suggest that 3D magnetic reconnection may be responsible for the formation of the jet in paper by González-Avilés et al. (2018). In this paper, by calculating times series of the velocity components vx and vy in different points near to the jet for various heights we find transverse oscillations in agreement with spicule observations. We also obtain a time-distance plot of the temperature in a cross-cut at the plane x = 0.1 Mm and find significant transverse displacements of the jet. By analysing temperature isosurfaces of 104 K with the distribution of vx, we find that if the line-of-sight (LOS) is approximately perpendicular to the jet axis then there is both motion towards and away from the observer across the width of the jet. This red–blue shift pattern of the jet is caused by rotational motion, initially clockwise and anti-clockwise afterwards, which could be interpreted as torsional motion and may generate torsional Alfvén waves in the corona region. From a nearly vertical perspective of the jet the LOS velocity component shows a central blue-shift region surrounded by red-shifted plasma
Instability of wormholes supported by a ghost scalar field. I. Linear stability analysis
We examine the linear stability of static, spherically symmetric wormhole
solutions of Einstein's field equations coupled to a massless ghost scalar
field. These solutions are parametrized by the areal radius of their throat and
the product of the masses at their asymptotically flat ends. We prove that all
these solutions are unstable with respect to linear fluctuations and possess
precisely one unstable, exponentially in time growing mode. The associated time
scale is shown to be of the order of the wormhole throat divided by the speed
of light. The nonlinear evolution is analyzed in a subsequent article.Comment: 12 pages, 1 figure, minor changes, to appear in Classical and Quantum
Gravit
Characterization of water uptake by organic coatings used for the corrosion protection of steel as determined from capacitance measurements
Water absorption by a coating on a metal is a major factor affecting its corrosion protection efficiency. It is usually determined from the increase of coating capacity with time, which is taken as a measure of the water volume ratio in the system. In this communication, the early stages of water uptake by three paint systems applied on galvanized steel have been investigated. The models proposed by Brasher and Kingsbury (BK), and the discrete (DM) and the continuous (CM) models proposed by Bellucci and Nicodemo, were employed to evaluate water absorption. It has been found that the amount of water adsorbed in the coating depended on both the nature and the thickness of the film, though different results were delivered by these methods, with convergence occurring only in the saturation stage. Next, water diffusion coefficients were determined, and they were observed to vary with the thickness of the polymer film regardless their actual composition. The time evolution of the diffusion coefficients could be adequately described using the DM model
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