773 research outputs found
Current-carrying cosmic string loops 3D simulation: towards a reduction of the vorton excess problem
The dynamical evolution of superconducting cosmic string loops with specific
equations of state describing timelike and spacelike currents is studied
numerically. This analysis extends previous work in two directions: first it
shows results coming from a fully three dimensional simulation (as opposed to
the two dimensional case already studied), and it now includes fermionic as
well as bosonic currents. We confirm that in the case of bosonic currents,
shocks are formed in the magnetic regime and kinks in the electric regime. For
a loop endowed with a fermionic current with zero-mode carriers, we show that
only kinks form along the string worldsheet, therefore making these loops
slightly more stable against charge carrier radiation, the likely outcome of
either shocks or kinks. All these combined effects tend to reduce the number
density of stable loops and contribute to ease the vorton excess problem. As a
bonus, these effects also may provide new ways of producing high energy cosmic
rays.Comment: 11 pages, RevTeX 4 format, 8 figures, submitted to PR
Vegetative fragment production as a means of propagule dispersal for tropical seagrass meadows
Background and aims: Long distance dispersal (LDD) contributes to the replenishment and recovery of tropical seagrass habitats exposed to disturbance, such as cyclones and infrastructure development. However, our current knowledge regarding the physical attributes of seagrass fragments that influence LDD predominantly stems from temperate species and regions. The goal of this paper is to measure seagrass fragment density and viability in two tropical species, assessing various factors influencing their distribution.
Methods: We measured the density and viability of floating seagrass fragments for two tropical seagrass species (Zostera muelleri and Halodule uninervis) in two coastal seagrass meadows in the central Great Barrier Reef World Heritage Area, Australia. We assessed the effect of wind speed, wind direction, seagrass growing/senescent season, seagrass meadow density, meadow location and dugong foraging intensity on fragment density. We also measured seagrass fragment structure and fragment viability; i.e., potential to establish into a new plant.
Key results: We found that seagrass meadow density, season, wind direction and wind speed influenced total fragment density, while season and wind speed influenced the density of viable fragments. Dugong foraging intensity did not influence fragment density. Our results indicate that wave action from winds combined with high seagrass meadow density increases seagrass fragment creation, and that more fragments are produced during the growing than the senescent season. Seagrass fragments classified as viable for Z. muelleri and H. uninervis had significantly more shoots and leaves than non-viable fragments. We collected 0.63 (±0.08 SE) floating viable fragments 100 m−2 in the growing season, and 0.13 (±0.03 SE) viable fragments 100 m−2 in the senescent season. Over a third (38%) of all fragments collected were viable.
Conclusion: There is likely to be a large number of viable seagrass fragments available for long distance dispersal. This study's outputs can inform dispersal and connectivity models that are used to direct seagrass ecosystem management and conservation strategies
The Dirac Equation Is Separable On The Dyon Black Hole Metric
Using the tetrad formalism, we carry out the separation of variables for the
massive complex Dirac equation in the gravitational and electromagnetic field
of a four-parameter (mass, angular momentum, electric and magnetic charges)
black hole.Comment: 13 page
Slowly rotating charged black holes in anti-de Sitter third order Lovelock gravity
In this paper, we study slowly rotating black hole solutions in Lovelock
gravity (n=3). These exact slowly rotating black hole solutions are obtained in
uncharged and charged cases, respectively. Up to the linear order of the
rotating parameter a, the mass, Hawking temperature and entropy of the
uncharged black holes get no corrections from rotation. In charged case, we
compute magnetic dipole moment and gyromagnetic ratio of the black holes. It is
shown that the gyromagnetic ratio keeps invariant after introducing the
Gauss-Bonnet and third order Lovelock interactions.Comment: 14 pages, no figur
Ricci flat rotating black branes with a conformally invariant Maxwell source
We consider Einstein gravity coupled to an gauge field for which the
density is given by a power of the Maxwell Lagrangian. In -dimensions the
action of Maxwell field is shown to enjoy the conformal invariance if the power
is chosen as . We present a class of charge rotating solutions in
Einstein-conformally invariant Maxwell gravity in the presence of a
cosmological constant. These solutions may be interpreted as black brane
solutions with inner and outer event horizons or an extreme black brane
depending on the value of the mass parameter. Since we are considering power of
the Maxwell density, the black brane solutions exist only for dimensions which
are multiples of four. We compute conserved and thermodynamics quantities of
the black brane solutions and show that the expression of the electric field
does not depend on the dimension. Also, we obtain a Smarr-type formula and show
that these conserved and thermodynamic quantities of black branes satisfy the
first law of thermodynamics. Finally, we study the phase behavior of the
rotating black branes and show that there is no Hawking--Page phase transition
in spite of conformally invariant Maxwell field.Comment: 13 pages, one figur
Topological Charged Black Holes in High Dimensional Spacetimes and Their Formation from Gravitational Collapse of a Type II Fluid
Topological charged black holes coupled with a cosmological constant in
spacetimes are studied, where is an Einstein
space of the form . The global structure for
the four-dimensional spacetimes with is investigated systematically.
The most general solutions that represent a Type fluid in such a high
dimensional spacetime are found, and showed that topological charged black
holes can be formed from the gravitational collapse of such a fluid. When the
spacetime is (asymptotically) self-similar, the collapse always forms black
holes for , in contrast to the case , where it can form
either balck holes or naked singularities.Comment: 14 figures, to appear in Phys. Rev.
No spin-glass transition in the "mobile-bond" model
The recently introduced ``mobile-bond'' model for two-dimensional spin
glasses is studied. The model is characterized by an annealing temperature T_q.
On the basis of Monte Carlo simulations of small systems it has been claimed
that this model exhibits a non-trivial spin-glass transition at finite
temperature for small values of T_q.
Here the model is studied by means of exact ground-state calculations of
large systems up to N=256^2. The scaling of domain-wall energies is
investigated as a function of the system size. For small values T_q<0.95 the
system behaves like a (gauge-transformed) ferromagnet having a small fraction
of frustrated plaquettes. For T_q>=0.95 the system behaves like the standard
two-dimensional +-J spin-glass, i.e. it does NOT exhibit a phase transition at
T>0.Comment: 4 pages, 5 figures, RevTe
Carbono orgânico dissolvido e biodisponibilidade de N e P como indicadores de qualidade do solo
Nas últimas décadas, qualidade do solo tem se tornado um tópico importante na ciência do solo. Embora esforços consideráveis tenham sido dedicados com o intuito de definir "qualidade do solo", ainda não há um conceito amplamente aceito pela comunidade cientifica. A seleção de índices qualitativos para definir qualidade do solo é uma tarefa extremamente difícil, e diversas propriedades químicas, físicas e biológicas tem sido sugeridas como potenciais indicadores. A matéria orgânica do solo está associada com processos químicos, físicos e biológicos no solo, e, portanto, é considerada um dos melhores indicadores de qualidade do solo. O manejo do solo pode influenciar significativamente a dinâmica do carbono orgânico e o ciclo de N, P, e S. Entretanto, mudanças na concentração total da matéria organica em resposta ao manejo pode ser dificil de ser detectada devido à variabilidade natural do solo. Quando comparada com a matéria orgânica total do solo, a fração mais prontamente disponível, como o carbono orgânico dissolvido (COD), é mais sensível às mudanças no manejo do solo a curto e médio prazo e, portanto, pode ser utilizada como indicador fundamental de qualidade do solo ou das alterações das condições naturais. Embora a fração dissolvida represente apenas uma pequena porção da matéria orgânica total do solo, o COD é móvel no solo e constitui uma importante fonte de C para os microorganismos, podendo facilmente refletir os efeitos de diferentes sistemas de manejo. Inúmeros métodos são utilizados para caracterizar o COD, mas os processos que influenciam sua mineralização e a disponibilidade dos elementos associado com a matéria orgânica (N, P, e S) ainda não são completamente entendidos. Pesquisas futuras devem buscar entender os processos que governam a dinâmica de nutrientes e do COD e como os mesmos afetam a qualidade do solo.Soil quality has become an important issue in soil science. Considerable attempts have been made to define soil quality, but a general concept has not yet been accepted by the scientific community. The selection of quantitative indices for soil quality is extremely difficult, and a considerable number of chemical, physical, and biochemical properties have been suggested as potential indicators of soil quality. Because soil organic matter (SOM) can be associated with different soil chemical, physical and biological processes, it has been widely considered as one of the best soil quality indicator. Land use can significantly influence dynamics of organic carbon and N, P, and S cycle. However, changes in total soil organic carbon (SOC) contents in response to land use may be difficult to detect because of the natural soil variability. In the short to medium term, biological properties and readily decomposable fractions of SOC, such as dissolved organic carbon (DOC), are much more sensitive to soil management than is SOM as a whole, and can be used as a key indicator of soil natural functions. Despite the fact that labile C accounts for a small portion of the total organic matter in the soils, DOC is the most mobile and important C-source for microorganisms, and can easily reflect the effects of land use on soil quality. Although several methods are used to characterize DOC, the factors influencing mineralization and bioavailability of elements associated with organic matter (N, P, and S) remains unclear. Future research should focus on the processes that govern DOC and nutrient dynamics and how they affect soil quality
New Agegraphic Dark Energy in Gravity
In this paper we study cosmological application of new agegraphic dark energy
density in the gravity framework. We employ the new agegraphic model of
dark energy to obtain the equation of state for the new agegraphic energy
density in spatially flat universe. Our calculation show, taking , it is
possible to have crossing -1. This implies that one can
generate phantom-like equation of state from a new agegraphic dark energy model
in flat universe in the modified gravity cosmology framework. Also we develop a
reconstruction scheme for the modified gravity with action.Comment: 8 pages, no figur
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