Reports on Progress in Physics | Year: 2013
Understanding the formation of the first stars is one of the frontier topics in modern astrophysics and cosmology. Their emergence signalled the end of the cosmic dark ages, a few hundred million years after the Big Bang, leading to a fundamental transformation of the early Universe through the production of ionizing photons and the initial enrichment with heavy chemical elements. We here review the state of our knowledge, separating the well understood elements of our emerging picture from those where more work is required. Primordial star formation is unique in that its initial conditions can be directly inferred from the Λ cold dark matter (ΛCDM) model of cosmological structure formation. Combined with gas cooling that is mediated via molecular hydrogen, one can robustly identify the regions of primordial star formation, the so-called minihalos, having total masses of ∼106 M ȯ and collapsing at redshifts z ≃ 20-30. Within this framework, a number of studies have defined a preliminary standard model, with the main result that the first stars were predominantly massive. This model has recently been modified to include a ubiquitous mode of fragmentation in the protostellar disks, such that the typical outcome of primordial star formation may be the formation of a binary or small multiple stellar system. We will also discuss extensions to this standard picture due to the presence of dynamically significant magnetic fields, of heating from self-annihalating WIMP dark matter, or cosmic rays. We conclude by discussing possible strategies to empirically test our theoretical models. Foremost among them are predictions for the upcoming James Webb space telescope (JWST), to be launched ∼2018, and for 'stellar archaeology', which probes the abundance pattern in the oldest, most-metal poor stars in our cosmic neighborhood, thereby constraining the nucleosynthesis inside the first supernovae. © 2013 IOP Publishing Ltd. Source
Johnson K.A.,Speedway |
Goody R.S.,Max Planck Institute of Molecular Physiology
Biochemistry | Year: 2011
Nearly 100 years ago Michaelis and Menten published their now classic paper [Michaelis, L., and Menten, M. L. (1913) Die Kinetik der Invertinwirkung. Biochem. Z. 49, 333-369] in which they showed that the rate of an enzyme-catalyzed reaction is proportional to the concentration of the enzyme-substrate complex predicted by the Michaelis-Menten equation. Because the original text was written in German yet is often quoted by English-speaking authors, we undertook a complete translation of the 1913 publication, which we provide as Supporting Information. Here we introduce the translation, describe the historical context of the work, and show a new analysis of the original data. In doing so, we uncovered several surprises that reveal an interesting glimpse into the early history of enzymology. In particular, our reanalysis of Michaelis and Mentens data using modern computational methods revealed an unanticipated rigor and precision in the original publication and uncovered a sophisticated, comprehensive analysis that has been overlooked in the century since their work was published. Michaelis and Menten not only analyzed initial velocity measurements but also fit their full time course data to the integrated form of the rate equations, including product inhibition, and derived a single global constant to represent all of their data. That constant was not the Michaelis constant, but rather V max/K m, the specificity constant times the enzyme concentration (k cat/K m ± E 0). © 2011 American Chemical Society. Source
Veterinary Clinics of North America - Exotic Animal Practice | Year: 2014
The domestic ferret (Mustela putorious furo) is a strict carnivore, also referred to as an obligate carnivore. Its dentition and gastrointestinal tract are adapted to a carnivorous diet. Its ancestor, the European polecat (Mustela putorius), feeds on birds and other small vertebrates. Domesticated ferrets have been fed mink feeds, cat foods, and now mostly subsist on commercial ferret diets formulated specifically to meet their needs. © 2014 Elsevier Inc. Source
Speedway | Date: 2014-04-11
The present invention is directed to a vehicle safety catch fence system, the system comprising: two or more posts; two or more longitudinal cables operatively coupled between the two or more posts; a transverse cable, wherein the transverse cable is operatively coupled to the two or more longitudinal cables; and two or more cable clamps, wherein the two or more cable clamps operatively couple the transverse cable to the two or more longitudinal cables.
Speedway | Date: 2014-06-24
An access gate and associated systems, apparatus, and methods are provided. The access gate provides access to cross a wall and may comprise at least one hinged wall portion configured to be moved between an open and a closed position. In the closed position, the hinged wall portion acts as a barrier between a first and a second side of the wall. In the open position, the hinged wall portion allows passage between the first and second sides of the wall. The access gate may comprise a crossing surface to allow passage between the first and second sides of the wall; and at least one hinged surface door configured to be moved between a closed and an open position. In the closed position, the surface door prevents access to the crossing surface and provides a walkable/drivable surface. In the open position, the surface door provides access to the crossing surface.