Spinning Strings, Black Holes and Stable Closed Timelike Geodesics

The existence and stability under linear perturbation of closed timelike curves in the spacetime associated to Schwarzschild black hole pierced by a spinning string are studied. Due to the superposition of the black hole, we find that the spinning string spacetime is deformed in such a way to allow the existence of closed timelike geodesics.Comment: 5 pages, RevTex4, some corrections and new material adde

Geodesics around Weyl-Bach's Ring Solution

We explore some of the gravitational features of a uniform ring both in the Newtonian potential theory and in General Relativity. We use a spacetime associated to a Weyl static solution of the vacuum Einstein's equations with ring like singularity. The Newtonian motion for a test particle in the gravitational field of the ring is studied and compared with the corresponding geodesic motion in the given spacetime. We have found a relativistic peculiar attraction: free falling particle geodesics are lead to the inner rim but never hit the ring.Comment: 8 figures, 14 pages. LaTeX w/ subfigure, graphic

On the gravitational field of static and stationary axial symmetric bodies with multi-polar structure

We give a physical interpretation to the multi-polar Erez-Rozen-Quevedo solution of the Einstein Equations in terms of bars. We find that each multi-pole correspond to the Newtonian potential of a bar with linear density proportional to a Legendre Polynomial. We use this fact to find an integral representation of the $\gamma$ function. These integral representations are used in the context of the inverse scattering method to find solutions associated to one or more rotating bodies each one with their own multi-polar structure.Comment: To be published in Classical and Quantum Gravit

Domain Wall Spacetimes: Instability of Cosmological Event and Cauchy Horizons

The stability of cosmological event and Cauchy horizons of spacetimes associated with plane symmetric domain walls are studied. It is found that both horizons are not stable against perturbations of null fluids and massless scalar fields; they are turned into curvature singularities. These singularities are light-like and strong in the sense that both the tidal forces and distortions acting on test particles become unbounded when theses singularities are approached.Comment: Latex, 3 figures not included in the text but available upon reques

Stochastic contribution to the growth factor in the LCDM model

We study the effect of noise on the evolution of the growth factor of density perturbations in the context of the LCDM model. Stochasticity is introduced as a Wiener process amplified by an intensity parameter alpha. By comparing the evolution of deterministic and stochastic cases for different values of alpha we estimate the intensity level necessary to make noise relevant for cosmological tests based on large-scale structure data. Our results indicate that the presence of random forces underlying the fluid description can lead to significant deviations from the nonstochastic solution at late times for alpha>0.001.Comment: 6 pages, 1 figur

Circular Orbits in Einstein-Gauss-Bonnet Gravity

The stability under radial and vertical perturbations of circular orbits associated to particles orbiting a spherically symmetric center of attraction is study in the context of the n-dimensional: Newtonian theory of gravitation, Einstein's general relativity, and Einstein-Gauss-Bonnet theory of gravitation. The presence of a cosmological constant is also considered. We find that this constant as well as the Gauss-Bonnet coupling constant are crucial to have stability for $n>4$.Comment: 11 pages, 4 figs, RevTex, Phys. Rev. D, in pres

On the Solutions of the Lorentz-Dirac Equation

We discuss the unstable character of the solutions of the Lorentz-Dirac equation and stress the need of methods like order reduction to derive a physically acceptable equation of motion. The discussion is illustrated with the paradigmatic example of the non-relativistic harmonic oscillator with radiation reaction. We also illustrate removal of the noncasual pre-acceleration with the introduction of a small correction in the Lorentz-Dirac equation.Comment: 4 eps figs. to be published in GR

General-relativistic Model of Magnetically Driven Jet

The general scheme for the construction of the general-relativistic model of the magnetically driven jet is suggested. The method is based on the usage of the 3+1 MHD formalism. It is shown that the critical points of the flow and the explicit radial behavior of the physical variables may be derived through the jet ``profile function."Comment: 12 pages, LaTex, no figure

Superposition of Weyl solutions: The equilibrium forces

Solutions to the Einstein equation that represent the superposition of static isolated bodies with axially symmetry are presented. The equations nonlinearity yields singular structures (strut and membranes) to equilibrate the bodies. The force on the strut like singularities is computed for a variety of situations. The superposition of a ring and a particle is studied in some detailComment: 31 pages, 7 figures, psbox macro. Submitted to Classical and Quantum Gravit

Arthropods of the Limarí River basin (Coquimbo Region, Chile): taxonomic composition in agricultural ecosystems

The Limarí valley, located in the Coquimbo Region of Chile, is an important agricultural area that is immersed in the transverse valleys of the Norte Chico. In recent decades, the continuous expansion of agriculture towards dry land zones has favored the migration and establishment of potential pests, such as arthropods, that may affect crops or be zoonotic agents. Based on the limited knowledge we have about the arthropod group present in the Limarí basin, our objective is to describe the taxonomic composition of the assemblage of economically important arthropods inhabiting this basin of the semiarid region of Chile. After reviewing historical data, specimen collections, and the specialized literature, a total of 414 arthropod species were recorded. Of the total number of species recorded, 92.5% were insects, the most diverse taxon, with 11 orders. Arachnids, in turn, were represented only by Acari with 31 species. The most widely represented orders of insects were Coleoptera, Hemiptera, and Lepidoptera. Within Coleoptera the most species-rich families were, in decreasing order of importance, Curculionidae, Coccinellidae, Cerambycidae, Scarabaeidae, Chrysomelidae (Bruchinae), Ptinidae, and Bostrichidae; within Hemiptera these were Aphididae, Diaspididae, Coccidae, Pseudococcidae, Pentatomidae and Rhopalidae; and within Lepidoptera they were Noctuidae and Tortricidae. We hope this study serves as a starting point for identifying the most diverse arthropod groups and developing pest monitoring and control programs. Highlights: A large percentage of phytophagous species, mainly belonging to Acari, Lepidoptera, Hemiptera and Coleoptera, were registered in the Limarí basin. Some families of agricultural importance (Aleyrodidae, Aphididae, Coccidae, Diaspididae, Margarodidae, Pseudococcidae), were observed in large agricultural crops in the basin (e.g., vines, oranges, mandarins, lemon trees, avocado trees, walnuts, olive trees, vegetable crops). A smaller fraction corresponded to the group of predators and parasitoids, mainly represented by Coleoptera (Coccinellidae), Neuroptera (Chrysopidae) and Hymenoptera (Braconidae, Encyrtidae, Ichneumonidae, Platygastridae, Signiphoridae). The richness and spatial records of arthropods were mostly concentrated between the city of Ovalle and the estuary of Punitaqui - the areas with most intense agricultural activity in the Limarí basin.The Limarí valley, located in the Coquimbo Region of Chile, is an important agricultural area that is immersed in the transverse valleys of the Norte Chico. In recent decades, the continuous expansion of agriculture towards dry land zones has favored the migration and establishment of potential pests, such as arthropods, that may affect crops or be zoonotic agents. Based on the limited knowledge we have about the arthropod group present in the Limarí basin, our objective is to describe the taxonomic composition of the assemblage of economically important arthropods inhabiting this basin of the semiarid region of Chile. After reviewing historical data, specimen collections, and the specialized literature, a total of 414 arthropod species were recorded. Of the total number of species recorded, 92.5% were insects, the most diverse taxon, with 11 orders. Arachnids, in turn, were represented only by Acari with 31 species. The most widely represented orders of insects were Coleoptera, Hemiptera, and Lepidoptera. Within Coleoptera the most species-rich families were, in decreasing order of importance, Curculionidae, Coccinellidae, Cerambycidae, Scarabaeidae, Chrysomelidae (Bruchinae), Ptinidae, and Bostrichidae; within Hemiptera these were Aphididae, Diaspididae, Coccidae, Pseudococcidae, Pentatomidae and Rhopalidae; and within Lepidoptera they were Noctuidae and Tortricidae. We hope this study serves as a starting point for identifying the most diverse arthropod groups and developing pest monitoring and control programs. Highlights: A large percentage of phytophagous species, mainly belonging to Acari, Lepidoptera, Hemiptera and Coleoptera, were registered in the Limarí basin. Some families of agricultural importance (Aleyrodidae, Aphididae, Coccidae, Diaspididae, Margarodidae, Pseudococcidae), were observed in large agricultural crops in the basin (e.g., vines, oranges, mandarins, lemon trees, avocado trees, walnuts, olive trees, vegetable crops). A smaller fraction corresponded to the group of predators and parasitoids, mainly represented by Coleoptera (Coccinellidae), Neuroptera (Chrysopidae) and Hymenoptera (Braconidae, Encyrtidae, Ichneumonidae, Platygastridae, Signiphoridae). The richness and spatial records of arthropods were mostly concentrated between the city of Ovalle and the estuary of Punitaqui - the areas with most intense agricultural activity in the Limarí basin