Modeling Carbon Chain Anions in L1527

The low-mass protostellar region L1527 is unusual because it contains observable abundances of unsaturated carbon-chain molecules including CnH radicals, H2Cn carbenes, cyanopolyynes, and the negative ions C4H- and C6H-, all of which are more associated with cold cores than with protostellar regions. Sakai et al. suggested that these molecules are formed in L1527 from the chemical precursor methane, which evaporates from the grains during the heat-up of the region. With the gas-phase osu.03.2008 network extended to include negative ions of the families Cn-, and CnH-, as well as the newly detected C3N-, we modeled the chemistry that occurs following methane evaporation at T~ 25-30 K. We are able to reproduce most of the observed molecular abundances in L1527 at a time of ~5000 yr. At later times, the overall abundance of anions become greater than that of electrons, which has an impact on many organic species and ions. The anion-to-neutral ratio in our calculation is in good agreement with observation for C6H- but exceeds the observed ratio by more than three orders of magnitude for C4H-. In order to explain this difference, further investigation is needed on the rate coefficients for electron attachment and other reactions regarding anions.Comment: 28 pages, 8 figures, ApJ accepte

Interstellar water chemistry: from laboratory to observations

Water is observed throughout the universe, from diffuse interstellar clouds to protoplanetary disks around young stars, and from comets in our own solar system and exoplanetary atmospheres to galaxies at high redshifts. This review summarizes the spectroscopy and excitation of water in interstellar space as well as the basic chemical processes that form and destroy water under interstellar conditions. Three major routes to water formation are identified: low temperature ion-molecule chemistry, high-temperature neutral-neutral chemistry and gas-ice chemistry. The rate coefficients of several important processes entering the networks are discussed in detail; several of them have been determined only in the last decade through laboratory experiments and theoretical calculations. Astronomical examples of each of the different chemical routes are presented using data from powerful new telescopes, in particular the Herschel Space Observatory. Basic chemical physics studies remain critically important to analyze astronomical data.Comment: Authors' manuscript 138 pages, 34 figures, 4 tables, published in a Thematic Issue "Astrochemistry" in Chemical Reviews (December 2013), volume 113, 9043-9085 following peer review by the American Chemical Society. The published paper is available as open access at http://pubs.acs.org/doi/abs/10.1021/cr400317

Induction of tetraploidy in zebrafish Danio rerio and Nile tilapia Oreochromis niloticus

The goals of this thesis were to: 1) induce tetraploidy in zebrafish; 2) characterize single-female spawning in Nile tilapia for egg collection; 3) design and construct hatching systems for tilapia eggs; 4) induce tetraploidy in Nile tilapia. Tetraploidy was induced in zebrafish Danio rerio, by applying a 41 C heat shock to eggs for 2 min at 11, 13, 15, 17, or 20 min after fertilization (AF). A trend of increasing percent tetraploid yield occurred the later the shocks were applied. Shocks applied at 11 min AF yielded 1% tetraploidy and shocks applied at 20 min AF yielded 10%. There were no significant differences (P = 0.20) in induction among treatments. This is the first report on induction of tetraploidy in zebrafish. Stocking of single-female Nile tilapia Oreochromis niloticus in ten 80-L aquaria yielded a reliable supply of eggs for polyploidy research conducted in this study. In one year, 72 spawns were recorded, yielding ~90,000 eggs. Peak spawning occurred in summer. The two egg hatching systems for artificial incubation of tilapia eggs proved to be effective, with 75% of control fish surviving to hatch. Methylene blue and ultraviolet sterilization reduced losses of eggs to disease and use of glass test tubes as hatching vessels allowed for constant rolling of the eggs and easy viewing and access. The systems occupied little space (\u3c 1 m2) and could accommodate up to 30 treatments of eggs. The use of egg baskets allowed for rapid and uniform heat shocking of multiple treatments of Nile tilapia eggs for polyploidy induction experiments. Tetraploidy and triploidy were induced by application of 42.8 ± 0.2 C heat shocks to eggs for 3 min at 22, 24, 26 and 28 min AF. Shocks applied at 24 min AF resulted in the highest tetraploid yield (10%) while shocks applied at 22 min AF resulted in the highest triploid yield (7%). This is the first study to report the simultaneous induction of tetraploidy and triploidy in Nile tilapia within treatments from a single spawn and raises questions about technical, maternal and genetic effects on synchrony of zygotic development in this species