The problem with which this investigation is concerned is that of determining the properties of three radicals defined on an arbitrary ring and determining when these radicals coincide. The three radicals discussed are the nil radical, the Jacobsson radical, and the Brown-McCoy radical.

Linear polarization can be used as a probe of the existence of atmospheric condensates in ultracool dwarfs. Models predict that the observed linear polarization increases with the degree of oblateness, which is inversely proportional to the surface gravity. We aimed to test the existence of optical linear polarization in a sample of bright young brown dwarfs, with spectral types between M6 and L2, observable from the Calar Alto Observatory, and cataloged previously as low gravity objects using spectroscopy. Linear polarimetric images were collected in I and R band using CAFOS at the 2.2-m telescope in Calar Alto Observatory (Spain). The flux ratio method was employed to determine the linear polarization degrees. With a confidence of 3 sigma, our data indicate that all targets have a linear polarimetry degree in average below 0.69 per cent in the I band, and below 1.0 per cent in the R band, at the time they were observed. We detected significant (i.e. P/sigma >= 3) linear polarization for the young M6 dwarf 2MASS J04221413+1530525 in the R band, with a degree of p* = 0.81 +/- 0.17 per cent.

We have followed up the three Y0 dwarfs WISEPA J041022.71+150248.5, WISEPA J173835.53+273258.9 and WISEPC J205628.90+145953.3 using the United Kingdom Infrared Telescope Wide Field Camera. We find parallaxes that are more consistent and accurate than previously published values. We estimate absolute magnitudes in photometric passbands from Y to W3 and find them to be consistent between the three Y0 dwarfs indicating that the inherent cosmic absolute magnitude spread of these objects is small. We examine the Mauna Kea Observatory system J magnitudes over the 4 yr time line and find small but significant monotonic variations. Finally, we estimate physical parameters from a comparison of spectra and parallax to equilibrium and non-equilibrium models finding values consistent with solar metallicity, an effective temperature of 450-475 K and log g of 4.0-4.5.

The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O I] 63 mu m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3-78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature-stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O I] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O I] 63 mu m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA-to establish if and how disk radii scale with stellar mass-should be pursued further.

No description available.

No description available.

In animals, reproductive behaviors serve to attract individuals together during the breeding season and to coordinate the behavioral and physiological states of individuals so that mating can successfully occur. In snakes, the various reproductive behaviors including courtship, mating, courtship inhibition, male combat and trailing are mediated primarily by pheromones. Pheromones are naturally produced chemical signals that influence the physiology or behavior of a conspecific when released by one individual into the environment. The research included in this study was designed to characterize the role pheromones play in the mediation of reproductive behaviors of the brown tree snake (Boiga irregularis) a rear-fanged, arboreal colubrid native to Australia, Papua-New Guinea and the Solomon Islands. Much attention has been paid to this species as it is an introduced pest species on the Pacific island of Guam where it has caused considerable economic and ecological damage. In order to create behavioral bioassays designed to experimentally determine the role pheromones play in the mediation of brown tree snake reproductive behavior, the complete repertoire of courtship, mating and male combat behaviors were described. Male brown tree snakes display combat and courtship behaviors similar to other colubrid species while female brown tree snakes take a very active role in courtship, displaying behaviors that both release and inhibit male courtship. These data represent the first description of any reproductive behaviors in this species and one of only a few studies examining the reproductive behaviors of a tropical species. A behavioral bioassay measuring the release of male courtship behavior was utilized to isolate and characterize the female sex pheromone of this species as a suite of non-polar, non-volatile skin lipid molecules. Using another bioassay, the pheromonal inhibition of male courtship behavior by a volatile pheromone originating from female cloacal secretions was characterized. Lastly, pheromone mediated mate attraction was examined by determining the abilities of male brown tree snakes to follow conspecific pheromone trails during the breeding season. Male brown tree snakes possess the ability to follow both male and female pheromone trails but did not, however, discriminate between male and female pheromones trails when given a choice. / Graduation date: 1999

Graduation date: 1997

The Feldmannia sp. virus is a large icosahedral virus that persistently infects marine brown alga Feldmannia sp.. So far, there is no information available about viral genome replication, gene structure and gene expression in this unique viral-host system. The purpose of this study was to characterize the general features of viral transcripts in the virus producing sporophyte plants. Northern analysis, using four cosmid clones that cover the entire viral genome, showed that there were six major transcripts and at least eighteen minor transcripts in the virus producing sporophyte plants. These transcripts are not evenly distributed in the viral genome. A 5.7 kb BamHI fragment-R was found to encode a 1.5 kb and a 0.9 kb major transcript, and those two major transcripts were chosen for detailed sequence analysis. The 1.5 kb transcript was identified as the putative major capsid protein (MCP) gene. The FsV MCP has significant similarity with the major capsid protein of Chlorella virus-PBCV-1 and with iridoviruses, fish lymphocystis disease virus, frog virus 3, and with African swine fever virus. / Graduation date: 1996

Graduation date: 1966