University of Georgia

About: University of Georgia is a education organization based out in Athens, Georgia, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 41934 authors who have published 93622 publications receiving 3713212 citations. The organization is also known as: UGA & Franklin College.

The limiting effects of dust in brown dwarf model atmospheres

Abstract: We present opacity sampling model atmospheres, synthetic spectra, and colors for brown dwarfs and very low mass stars in the following two limiting cases of dust grain formation: (1) Inefficient gravitational settling (i.e., the dust is distributed according to the chemical equilibrium predictions) and (2) efficient gravitational settling (i.e., the dust forms and depletes refractory elements from the gas, but their opacity does not affect the thermal structure). The models include the formation of over 600 gas-phase species and 1000 liquids and crystals and the opacities of 30 different types of grains including corundum (Al2O3), the magnesium aluminum spinel MgAl2O4, iron, enstatite (MgSiO3), forsterite (Mg2SiO4), amorphous carbon, SiC, and a number of calcium silicates. The models extend from the beginning of the grain formation regime well into the condensation regime of water ice (Teff = 3000-100 K) and encompass the range of log g = 2.5-6.0 at solar metallicity. We find that silicate dust grains can form abundantly in the outer atmospheric layers of red and brown dwarfs with a spectral type later than M8. The greenhouse effects of dust opacities provide a natural explanation for the peculiarly red spectroscopic distribution of the latest M dwarfs and young brown dwarfs. The grainless (cond) models, on the other hand, correspond closely to methane brown dwarfs such as Gliese 229B. We also discover that the λλ5891, 5897 Na I D and λλ7687, 7701 K I resonance doublets play a critical role in T dwarfs, in which their red wings define the pseudocontinuum from the I to the Z bandpass.

The genome of woodland strawberry ( Fragaria vesca )

Abstract: The woodland strawberry, Fragaria vesca (2n = 2x = 14), is a versatile experimental plant system. This diminutive herbaceous perennial has a small genome (240 Mb), is amenable to genetic transformation and shares substantial sequence identity with the cultivated strawberry (Fragaria × ananassa) and other economically important rosaceous plants. Here we report the draft F. vesca genome, which was sequenced to ×39 coverage using second-generation technology, assembled de novo and then anchored to the genetic linkage map into seven pseudochromosomes. This diploid strawberry sequence lacks the large genome duplications seen in other rosids. Gene prediction modeling identified 34,809 genes, with most being supported by transcriptome mapping. Genes critical to valuable horticultural traits including flavor, nutritional value and flowering time were identified. Macrosyntenic relationships between Fragaria and Prunus predict a hypothetical ancestral Rosaceae genome that had nine chromosomes. New phylogenetic analysis of 154 protein-coding genes suggests that assignment of Populus to Malvidae, rather than Fabidae, is warranted.

Molecular Biology of the LysR Family of Transcriptional Regulators

Abstract: The LysR family is composed of > 50 similar-sized, autoregulatory transcriptional regulators (LTTRs) that apparently evolved from a distant ancestor into subfamilies found in diverse prokaryotic genera. In response to different coinducers, LTTRs activate divergent transcription of linked target genes or unlinked regulons encoding extremely diverse functions. Mutational studies and amino acid sequence similarities of LTTRs identify: (a) a DNA-binding domain employing a helix-turn-helix motif (residues 1-65), (b) domains involved in coinducer recognition and/or response (residues 100-173 and 196-206), (c) a domain required for both DNA binding and coinducer response (residues 227-253). DNA footprinting studies suggest that in the absence of coinducer many LTTRs bind to regulated promoters via a 15-bp dyadic sequence with a common structure and position (near -65). Coinducer causes additional interactions of LTTRs with sequences near the -35 RNA polymerase binding site and/or DNA bending that results in transcription activation.