Accretion through the inner hole of transitional disks: What happens to the dust?

We study the effect of radiation pressure on the dust in the inner rim of transitional disks with large inner holes. In particular, we evaluate whether radiation pressure can be responsible for keeping the inner holes dust-free, while allowing gas accretion to proceed. This has been proposed in a paper by Chiang and Murray-Clay (2007, Nature Physics 3, p. 604) who explain the formation of these holes as an inside-out evacuation due to X- ray-triggered accretion of the innermost layer of the disk rim outside of the hole. We show that radiation pressure is clearly incapable of stopping dust from flowing into the hole because of dust pile-up and optical depth effects, and also because of viscous mixing. Other mechanisms need to be found to explain the persistence of the opacity hole in the presence of accretion, and we speculate on possible solutions.Comment: 6 pages, 3 figures, Accepted for publication by Astronomy and Astrophysic

Diversidad de bacterias endofitas asociadas a cultivo de arroz en el departamento de Cordoba-Colombia. Estudio preliminar

Endophytic bacteria living within the plant without causing damage to them. Their presence has been linked to increased crop productivity because it produces growth hormones, pathogens or antagonists can fix nitrogen. This study examined the composition of communities of cultivable endophytic bacteria associated with different tissues of four commercial varieties of rice in the department of Cordoba. For isolation technique used tissue surface disinfection, the isolation was performed on R2A agar medium. The population density (CFU / g of tissue) was performed by counting of colonies on plate. The statistical significance between population density relative to tissues and variety was made using multivariate analysis and multiple range test (Tukey). The results show that there is a population density of endophytic bacteria associated with rice plants, the abundance is related to the tissue and the variety studied. This preliminary study initiates the knowledge of these bacterial communities and functionality that might be carrying in this plant species.Las bacterias endófitas viven en el interior de las plantas sin causar daño en ellas. Su presencia ha sido relacionada con un aumento en la productividad de los cultivos debido a que produce hormonas de crecimiento, antagonistas de patógenos o pueden fijar nitrógeno. En este trabajo se estudió la composición de comunidades de bacterias endófitas cultivables asociadas a diferentes tejidos de cuatro variedades comerciales de arroz del departamento de Córdoba. Para el aislamiento se utilizó técnica de desinfección superficial de tejidos, el aislamiento se llevó a cabo en medio de cultivo agar R2A. La densidad poblacional (UFC/g de tejido) se realizó por conteo de colonias en placa. Las significancias estadísticas entre densidad poblacional, con relación a tejidos y variedad, se hizo mediante análisis multifactorial y prueba múltiple de rango (Tukey). Los resultados muestran que existe una densidad poblacional de bacterias endófitas asociadas a plantas de arroz; la abundancia está relacionada con el tejido y la variedad estudiada. Este estudio preliminar da inicio al conocimiento de esas comunidades bacterianas y la funcionalidad que puedan estar ejerciendo en esta especie vegetal

Regresión logistica en la evaluación de la esporulación de micorrizas en pasto bothriochloa pertusa (l) a. Camus.

The purpose of this study was to obtain a logistic function or probability function to measure the chances of occurrence of the events sporulation of native arbuscular mycorrhizal-creater fungi associated with the grass Bothriochloa pertusa (L) A. Camus, located in four agro-ecological zones cattle farms, in the municipality of Corozal, Colombia, in response to the activity of certain soil chemical factors such as: pH, Organic Matter, Phosphorus, Potassium. Soil samples were collected in cattle farms planted with Colosoana grass. The isolation, the counting of soil spores / 100 g and the identification of fungi were carried out in the microbiology laboratory at the University of Sucre. The model created or probability function was used to measure the chances of occurrence of sporulation in response to the presence of certain chemical factors of soil. To obtain this logistic function, the importance of each of these risk factors was determined and their possible interactions. 48 cattle farms were sampled on four different agro-ecological zones, the amount of soil spores / 100, ranged from (900) from 2600 to 4000 (7300). 31 native morphotypes of arbuscular mycorrhizal-creating fungi were isolated, by distributing them in two types Glomus and Gigospora , being predominant the Glomus species. The logistic modeling process found that the factors that best explain the phenomenon of sporulation of mycorrhizal-creating fungi associated with Colosoana grass rhizospheres were pH and potassium.El objetivo del presente trabajo fue obtener una función logística o función de probabilidad que permitiera medir las posibilidades de ocurrencia del evento esporulación de hongos formadores de micorrizas arbusculares nativos, asociados al pasto Bothriochloa pertusa (L) A. Camus, localizas en fincas ganaderas de cuatro zonas agroecológicas, municipio de Corozal, Colombia, como respuesta a la actividad de ciertos factores químicos del suelo tales como: pH, Materia Orgánica, Fósforo, Potasio. Las muestras de suelo fueron colectadas en fincas ganaderas sembradas con pasto colosuana. El aislamiento, el conteo de esporas/ 100 g de suelo y la identificación de los hongos fue realizadas en el laboratorio de microbiología de la Universidad de Sucre. El modelo o función de probabilidad creada fue utilizado para medir las posibilidades de ocurrencia de la esporulación como respuesta a la presencia de ciertos factores químicos del suelo. Para obtener esta función logística se determinó la importancia de cada uno de estos factores de riesgo y sus posibles interacciones. Fueron muestreadas 48 fincas ganaderas distribuidas en cuatro zonas agroecológicas diferentes, la cantidad esporas/ 100 de suelo, oscilo entre (900) 2600 – 4000 (7300); se aislaron 31 morfotipos nativos de hongos formadores de micorrizas arbusculares distribuidos en dos géneros Glomus y Gigospora, predominando en su mayoría especies del género Glomus. El proceso de modelación logística encontró que los factores que mejor explican el fenómeno de la esporulación de hongos formadores de micorrizas asociados a rizosfera de pasto colosuana fueron el pH y el Potasio

Structural, mineralogical, and biochemical diversity in the lower part of the pearl layer of cultivated seawater pearls from Polynesia

A series of Polynesian pearls has been investigated with particular attention to the structural and compositional patterns of the early developmental stages of the pearl layer. These initial steps in pearl formation bear witness of the metabolic changes that have occurred during the pearl-sac formation. The resulting structurally and biochemically complex structures have been investigated using a variety of techniques that provide us with information concerning both mineral phases and the organic components. Results are discussed with respect to our understanding of the biomineralization mechanisms, as well as for the grafting process

Diversity of arbuscular mycorrhizal fungi (amf) in three agroecosystems with grass colosoana (Bothriochloa pertusa (L) A. Camus) in the department of Sucre

 El presente estudio evaluó la diversidad de hongos formadores de micorrizas arbusculares (HMA) asociadas a suelos de tres ecosistemas cultivados con pasto colosoana en tres localidades del departamento de Sucre, Colombia. Se recolectaron muestras de suelo, se aislaron esporas de HMA, se realizó conteo de espora y se identificaron morfotipos a nivel de especie y/o géneros. Se encontró que el género de HMA que más predomina en los suelos compactados y nativos de los tres municipios seleccionados es el género Glomus, seguido de otros géneros en menor proporción. En general los suelos que presentaron mayor riqueza de géneros de HMA fueron los del municipio de San Marcos, mientras que la menor riqueza se encontró en el municipio de Sincelejo.The present study evaluated the diversity of arbuscular mycorrhizal fungi (AMF) associated soils from three ecosystems grown with pasture colosoana in three localities of the Department of Sucre, Colombia. Soil samples were collected, AMF spores isolated, count of spore was made and morphotypes isolated were classification at the level of species or genera. We found that the genus of AMF over prevailing in native and compacted soils in the three selected municipalities is the genus Glomus, followed by other genera to a lesser extent. In general the soils that presented greater wealth of genres of HMA were those of the municipality of San Marcos, while the lowest richness was found in the municipality of Sincelejo

Bacterias endofitas: un nuevo campo de investigación para el desarrollo del sector agropecuario

The endophytic bacteria living within the tissues of the plants at least during part of their life cycle without causing any damage to the host, establish a symbiotic relationship where both benefit. The endophytic bacteria play a wide variety of roles as promoters of plant growth, biological control on a variety of pathogens, improve process efficiency of phytoremediation of toxic compound in the rhizosphere. These microorganisms are inexhaustible sources of over 20.000 biologically active compounds, which have a direct bearing on the performance and survival of host plants. The endophytic bacteria are reported to produce a number of metabolites such as antibiotics, secondary metabolites including some antitumor compounds and anti-inflammatory agents.Las bacterias endófitas habitan dentro de los tejidos de las plantas al menos durante una parte de su ciclo de vida sin causar daño alguno al hospedero, establecen asociación simbiótica y producen grandes beneficios para las plantas. Las bacterias endófitas cumplen una gran diversidad de funciones como promotoras de crecimiento vegetal, control biológico sobre una diversidad de fitopatógenos, mejoran la eficiencia de los procesos de fitoremediación de compuesto tóxicos en la rizósfera. Estos microorganismo son fuentes inagotable de más de 20.000 compuestos biológicamente activos, los cuales influyen de manera directa en el rendimiento y supervivencia de las plantas hospederas. Las bacterias endófitas son reportadas por producir un número de metabolitos como antibióticos, metabolitos secundarios incluyendo algunos compuestos antitumorales, agentes antiinflamatorios

Bacterias endófitas: una alternativa biologica para el control de burkholderia glumae en el cultivo del arroz en colombia.

Research common in microbial ecology have been directed toward the plantmicrobe interactions from the point of view of symbiotic and pathogenic. Endophytic bacteria reside in plant tissues mainly in intercellular, rarely in intracellular spaces and inside vascular tissues without causing symptoms of disease. The penetration in the plant can by stomates, wounds, areas of emergence by lateral roots, being that these bacteria can produce hydrolytic enzymes able to degrade the cell wall of vegetables. Recent molecular studies on endophytic diversity bacteria have revealed a large richness of species, endophytes promote plants growth and yield, suppress pathogens, may help to remove contaminants, solubilize phosphate and contribute assimilation biological nitrogen to plant.Las investigaciones más comunes en ecología microbiana, han sido orientadas a las interacciones microbio-planta desde el punto de vista simbiótico y de patogénico. Las bacterias endófitas colonizan el interior de los tejidos de las plantas, principalmente espacios intercelulares, raramente en espacios intracelulares y dentro de tejidos vasculares sin causar síntomas de enfermedad en la planta. La penetración en la planta puede ocurrir por estomas, heridas, áreas de emergencia de raíces laterales, siendo que estas bacterias pueden producir enzimas hidrolíticas capaces de degradar la pared celular de los vegetales. Estudios moleculares reciente sobre diversidad de bacterias endófitas han revelado una alta riqueza de filotipos, que promueven el crecimiento de las planta, suprimen fitopatógenos, ayudan a remover contaminantes, solubilizan fosfato y contribuyen a la asimilación biológica de nitrógeno

Relativistic Diskoseismology. I. Analytical Results for 'Gravity Modes'

We generalize previous calculations to a fully relativistic treatment of adiabatic oscillations which are trapped in the inner regions of accretion disks by non-Newtonian gravitational effects of a black hole. We employ the Kerr geometry within the scalar potential formalism of Ipser and Lindblom, neglecting the gravitational field of the disk. This approach treats perturbations of arbitrary stationary, axisymmetric, perfect fluid models. It is applied here to thin accretion disks. Approximate analytic eigenfunctions and eigenfrequencies are obtained for the most robust and observable class of modes, which corresponds roughly to the gravity (internal) oscillations of stars. The dependence of the oscillation frequencies on the mass and angular momentum of the black hole is exhibited. These trapped modes do not exist in Newtonian gravity, and thus provide a signature and probe of the strong-field structure of black holes. Our predictions are relevant to observations which could detect modulation of the X-ray luminosity from stellar mass black holes in our galaxy and the UV and optical luminosity from supermassive black holes in active galactic nuclei.Comment: 31 pages, 6 figures, uses style file aaspp4.sty, prepared with the AAS LATEX macros v4.0, significant revision of earlier submission to include modes with axial index m>

Generating photon-encoded W states in multiport waveguide-array systems

We propose a versatile approach for generating multipartite W states in predesigned on-chip multiport photonic lattices. It is shown that is possible to produce photon-encoded W states where exactly one photon is coherently shared among N optical modes by judiciously adjusting the coupling coefficients involved in one-dimensional arrays of evanescently coupled single-mode waveguides. Two-dimensional waveguide configurations are also investigated as possible avenues to produce W states with equal probability amplitudes and equal relative phases