A structural, spectroscopic and theoretical study of the triphenylphosphine chalcogenide complexes of tungsten carbonyl, [W(XPPh3)(CO)5], X=O, S, Se

The series [W(XPPh3)(CO)5], X=O, S, Se has been structurally determined by X-ray crystallography and fully characterised spectroscopically to provide data for comparing the bonding of the Ph3PX ligands to the metal. The P-X-W angles are 134.3°, 113.2° and 109.2°, respectively, for X=O, S, Se. The bonding has been analysed using EHMO calculations which suggest that lower P-X-W angles depend on the relative importance of σ-bonding, which in turn depends on the chalcogen in the order X=Se > S > O. The effect is enhanced by lower energies of the metal σ and π orbital energies

Protostellar Feedback Processes and the Mass of the First Stars

We review theoretical models of Population III.1 star formation, focusing on the protostellar feedback processes that are expected to terminate accretion and thus set the mass of these stars. We discuss how dark matter annihilation may modify this standard feedback scenario. Then, under the assumption that dark matter annihilation is unimportant, we predict the mass of stars forming in 12 cosmological minihalos produced in independent numerical simulations. This allows us to make a simple estimate of the Pop III.1 initial mass function and how it may evolve with redshift.Comment: 6 pages, Proceedings of 'The First Stars and Galaxies: Challenges for the Next Decade", Austin, TX, March 8-11, 201

Nesting ecology, chick survival, and juvenile dispersal of Ruffed Grouse (Bonasa umbellus) in the Appalachian Mountains

Ruffed Grouse (Bonasa umbellus) populations have been declining throughout the Appalachian Mountains for several decades. From 1996--2002, state natural resources agencies in the region initiated the Appalachian Cooperative Grouse Research Project (ACGRP) to investigate potential factors limiting Ruffed Grouse populations. At the onset, nest success, nest predation, and brood survival were identified as potential limiting factors, and numerous other aspects of grouse ecology (e.g., dispersal) in the Appalachians were poorly understood. Therefore, I designed my ACGRP project to examine (1) nest predation and factors that influence nest success, (2) cause-specific mortality and survival rates for chicks 2--4 days posthatch to 5 weeks posthatch, and (3) factors influencing dispersal distances, rates of movement, and risks during dispersal.;Using infrared video-surveillance systems during 2000--2001, I observed grouse nests (n = 15) in West Virginia, recording nest visitors, depredation events, and female behaviors. Incubation initiation date, clutch size, and hatching success did not differ by age (i.e., first-time breeders vs. adults). I observed 4 nest visitors during the egg-laying period, none of which removed or harmed any eggs. I observed 5 different species of nest visitor during incubation, 2 of which did not harm or remove any eggs. Nest predators included 2 raccoons (Procyon lotor), 1 black bear (Ursus americanus), and 1 long-tailed weasel (Mustela frenata). Females averaged 209 +/- 20 min on the nest per egg-laying event and I found no effect of female age, day in the nesting cycle, or age*day interaction on mean on-nest duration ratio, off-nest duration ratio, or number of egg-turnings per hour when females returned to lay an additional egg. I also found no effect of nest outcome, day in the nesting cycle, or outcome*day interaction on mean ratios females spent on or off their nests, or number of egg-turnings per hour during the egg-laying period. During incubation, I determined that on-nest ratios tended to increase through time regardless of age, off-nest ratios tended to decrease through time regardless of age, and nighttime egg turning events tended to increase through time. The number of daytime egg-turning events per hour differed between first-time breeders and adult grouse, indicating that nesting experience may influence daytime egg-turning behavior. I also found that both on-nest and off-nest duration ratios differed by day in the nesting cycle regardless of nest outcome; on-nest ratios tended to increase through time, whereas off-nest ratios tended to decrease through time. However, I did find that female Ruffed Grouse that lost their nest had higher on-nest ratios on the day of predation than all other days of incubation. In Ruffed Grouse, it appears likely that selection has led to incubation behaviors that favor high nest attentiveness and few foraging trips (i.e., reduced activity at the nest) to try and compensate for high levels of nest depredation. (Abstract shortened by UMI.)

Frog foams and natural protein surfactants

Foams and surfactants are relatively rare in biology because of their potential to harm cell membranes and other delicate tissues. However, in recent work we have identified and characterized a number of natural surfactant proteins found in the foam nests of tropical frogs and other unusual sources. These proteins, and their associated foams, are relatively stable and bio-compatible, but with intriguing molecular structures that reveal a new class of surfactant activity. Here we review the structures and functional mechanisms of some of these proteins as revealed by experiments involving a range of biophysical and biochemical techniques, with additional mechanistic support coming from more recent site-directed mutagenesis studies

Validating Semi-Analytic Models of High-Redshift Galaxy Formation using Radiation Hydrodynamical Simulations

We use a cosmological hydrodynamic simulation calculated with Enzo and the semi-analytic galaxy formation model (SAM) GAMMA to address the chemical evolution of dwarf galaxies in the early universe. The long-term goal of the project is to better understand the origin of metal-poor stars and the formation of dwarf galaxies and the Milky Way halo by cross-validating these theoretical approaches. We combine GAMMA with the merger tree of the most massive galaxy found in the hydrodynamic simulation and compare the star formation rate, the metallicity distribution function (MDF), and the age-metallicity relationship predicted by the two approaches. We found that the SAM can reproduce the global trends of the hydrodynamic simulation. However, there are degeneracies between the model parameters and more constraints (e.g., star formation efficiency, gas flows) need to be extracted from the simulation to isolate the correct semi-analytic solution. Stochastic processes such as bursty star formation histories and star formation triggered by supernova explosions cannot be reproduced by the current version of GAMMA. Non-uniform mixing in the galaxy's interstellar medium, coming primarily from self-enrichment by local supernovae, causes a broadening in the MDF that can be emulated in the SAM by convolving its predicted MDF with a Gaussian function having a standard deviation of ~0.2 dex. We found that the most massive galaxy in the simulation retains nearby 100% of its baryonic mass within its virial radius, which is in agreement with what is needed in GAMMA to reproduce the global trends of the simulation.Comment: 26 pages, 13 figures, 2 tables, submitted to ApJ (version 2

Aqueous solubilization of C60 fullerene by natural protein surfactants, latherin and ranaspumin-2

C60 fullerene is not soluble in water and dispersion usually requires organic solvents, sonication or vigorous mechanical mixing. However, we show here that mixing of pristine C60 in water with natural surfactant proteins latherin and ranaspumin-2 (Rsn-2) at low concentrations yields stable aqueous dispersions with spectroscopic properties similar to those previously obtained by more vigorous methods. Particle sizes are significantly smaller than those achieved by mechanical dispersion alone, and concentrations are compatible with clusters approximating 1:1 protein:C60 stoichiometry. These proteins can also be adsorbed onto more intractable carbon nanotubes. This promises to be a convenient way to interface a range of hydrophobic nanoparticles and related materials with biological macromolecules, with potential to exploit the versatility of recombinant protein engineering in the development of nano-bio interface devices. It also has potential consequences for toxicological aspects of these and similar nanoparticles