Supermassive black holes as the regulators of star formation in central galaxies

We present a relationship between the black hole mass, stellar mass, and star formation rate of a diverse group of 91 galaxies with dynamically-measured black hole masses. For our sample of galaxies with a variety of morphologies and other galactic properties, we find that the specific star formation rate is a smoothly decreasing function of the ratio between black hole mass and stellar mass, or what we call the specific black hole mass. In order to explain this relation, we propose a physical framework where the gradual suppression of a galaxy's star formation activity results from the adjustment to an increase in specific black hole mass and, accordingly, an increase in the amount of heating. From this framework, it follows that at least some galaxies with intermediate specific black hole masses are in a steady state of partial quiescence with intermediate specific star formation rates, implying that both transitioning and steady-state galaxies live within this region known as the "green valley." With respect to galaxy formation models, our results present an important diagnostic with which to test various prescriptions of black hole feedback and its effects on star formation activity.Comment: 15 pages, 4 figures, 2 tables. Accepted for publication in The Astrophysical Journa

The endemic gastropod fauna of Lake Titicaca : correlation between molecular evolution and hydrographic history

Lake Titicaca, situated in the Altiplano high plateau, is the only ancient lake in South America. This 2- to 3-My-old (where My is million years) water body has had a complex history that included at least five major hydrological phases during the Pleistocene. It is generally assumed that these physical events helped shape the evolutionary history of the lake´s biota. Herein, we study an endemic species assemblage in Lake Titicaca, composed of members of the microgastropod genus Heleobia, to determine whether the lake has functioned as a reservoir of relic species or the site of local diversification, to evaluate congruence of the regional paleohydrology and the evolutionary history of this assemblage, and to assess whether the geographic distributions of endemic lineages are hierarchical. Our phylogenetic analyses indicate that the Titicaca/Altiplano Heleobia fauna (together with few extralimital taxa) forms a species flock. A molecular clock analysis suggests that the most recent common ancestor (MRCAs) of the Altiplano taxa evolved 0.53 (0.28–0.80) My ago and the MRCAs of the Altiplano taxa and their extralimital sister group 0.92 (0.46–1.52) My ago. The endemic species of Lake Titicaca are younger than the lake itself, implying primarily intralacustrine speciation. Moreover, the timing of evolutionary branching events and the ages of two precursors of Lake Titicaca, lakes Cabana and Ballivián, is congruent. Although Lake Titicaca appears to have been the principal site of speciation for the regional Heleobia fauna, the contemporary spatial patterns of endemism have been masked by immigration and/or emigration events of local riverine taxa, which we attribute to the unstable hydrographic history of the Altiplano. Thus, a hierarchical distribution of endemism is not evident, but instead there is a single genetic break between two regional clades. We also discuss our findings in relation to studies of other regional biota and suggest that salinity tolerance was the most likely limiting factor in the evolution of Altiplano species flocks

FISH ASSEMBLAGE STRUCTURE AND GROWTH IN THE LOWER MILK RIVER, MONTANA IN RELATION TO ENVIRONMENTAL CONDITIONS

With the major habitat alterations on the Missouri River in the 20th century, native fishes must rely more heavily on the larger, more natural, inflowing tributaries for spawning and rearing habitat. A two-year study was conducted to investigate the occurrence and abundance of fishes in the lower Milk River, Montana, which enters the Missouri River immediately below Fort Peck Dam. In sampling conducted from May to August in successive years (2002, 2003), the fish species assemblage included multiple species of special concern (blue sucker Cycleptus elongatus, paddlefish Polydon spathula, sauger Sander canadense) and multiple watch list species identified by the Montana Natural Heritage Program (burbot Lota lota, brassy minnow Hybognathus hankinsoni, plains minnow Hybognathus placitus). Relationships with environmental conditions and their interactions with temporal variables (month, year) were investigated for occurrence and total catch data. Models were generally similar for individual species with temperature and turbidity being the primary environmental conditions influencing fish occurrence and abundance. Age and growth analysis was conducted on channel catfish (Ictalurus punctatus), sauger, walleye (Sander vitreus), northern pike (Esox lucius) and shovelnose sturgeon (Scaphirhynchus platorynchus). Channel catfish, sauger, walleye and shovelnose sturgeon all grew slower and lived longer in the lower Milk River than populations at lower latitudes. In view of the lower Milk River’s role as spawning and rearing habitat for native fishes and its history of alterations from upriver dams and irrigation withdrawals, more attention should be given to maintaining or improving existing habitat conditions, including adequate instream flows and turbidity

Age Estimation of Burbot Using Pectoral Fin Rays, Branchiostegal Rays and Otoliths

Throughout much of its native distribution, burbot (Lota lota) is a species of conservation concern.  Understanding dynamic rate functions is critical for the effective management of sensitive burbot populations, which necessitates accurate and precise age estimates.  Managing sensitive burbot populations requires an accurate and precise non-lethal alternative.  In an effort to identify a non-lethal ageing structure, we compared the precision of age estimates obtained from otoliths, pectoral fin rays, dorsal fin rays and branchiostegal rays from 208 burbot collected from the Green River drainage, Wyoming.  Additionally, we compared the accuracy of age estimates from pectoral fin rays, dorsal fin rays and branchiostegal rays to those of otoliths.  Dorsal fin rays were immediately deemed a poor ageing structure and removed from further analysis.  Age-bias plots of consensus ages derived from branchiostegal rays and pectoral fin rays were appreciably different from those obtained from otoliths.  Exact agreement between readers and reader confidence was highest for otoliths and lowest for branchiostegal rays.  Age-bias plots indicated that age estimates obtained from branchiostegal rays and pectoral fin rays were substantially different from age estimates obtained from otoliths.  Our results indicate that otoliths provide the most precise age estimates for burbot

Uncertainty Analysis of Coaxial Thermocouple Calorimeters Used in Arc Jets

Recent introduction of Coaxial Thermocouple type calorimeters into the NASA Ames arc jet facilities has inspired an analysis of 2D conduction effects internal to this type of calorimeter. The 1D finite slab inverse analysis (which is typically used to deduce the heat transfer to the calorimeter) relies on the assumption that lateral conduction (i.e., 2D effects) is negligible. Most calorimeter bodies have a spherical nose, which in itself is a violation of the 1D finite slab analysis assumption. Secondly most calorimeters experience a variation in heating across the face of the body which is also a violation of the 1D finite slab analysis assumption. It turns out that these two effects tend to cancel each other to some extent. This paper shows the extent to which error exists in the analysis of the Coaxial Thermocouple type calorimeters, and also offers analysis strategies for reducing the errors

Closed Gap Slug Calorimeter for Plasma Stream Characterization

Slug calorimeters are used in sheer and stagnation mode to characterize heat flux levels for high enthalpy streams. The traditional design features a gap between slug and holder, which can be of concern in these convective heat flux environments. The challenge is to develop a calorimeter that closes the gap to gas flow, but largely maintains thermal insulation of the slug. The work presented herein introduces two new slug calorimeter designs featuring a closed gap. This is done using either aerogel as a filler or press fitting the slug with a disk. The designs were verified and compared to the baseline calorimeter design under radiative heat flux. Building on this, the calorimeters were exposed to convective heat flux in the arc-jet facilities. Results from the new designs and conclusions on the impact of the gap in convective heat flux will be shown

Polymerase-catalyzed synthesis of DNA from phosphoramidate conjugates of deoxynucleotides and amino acids

Some selected amino acids, in particular l-aspartic acid (l-Asp) and l-histidine (l-His), can function as leaving group during polymerase-catalyzed incorporation of deoxyadenosine monophosphate (dAMP) in DNA. Although l-Asp-dAMP and l-His-dAMP bind, most probably, in a different way in the active site of the enzyme, aspartic acid and histidine can be considered as mimics of the pyrophosphate moiety of deoxyadenosine triphosphate. l-Aspartic acid is more efficient than d-aspartic acid as leaving group. Such P-N conjugates of amino acids and deoxynucleotides provide a novel experimental ground for diversifying nucleic acid metabolism in the field of synthetic biology