7,255 research outputs found
The ages and metallicities of galaxies in the local universe
We derive stellar metallicities, light-weighted ages and stellar masses for a
magnitude-limited sample of 175,128 galaxies drawn from the Sloan Digital Sky
Survey Data Release Two (SDSS DR2). We compute median-likelihood estimates of
these parameters using a large library of model spectra at medium-high
resolution, covering a comprehensive range of star formation histories. The
constraints we derive are set by the simultaneous fit of five spectral
absorption features, which are well reproduced by our population synthesis
models. By design, these constraints depend only weakly on the alpha/Fe element
abundance ratio. Our sample includes galaxies of all types spanning the full
range in star formation activity, from dormant early-type to actively
star-forming galaxies. We show that, in the mean, galaxies follow a sequence of
increasing stellar metallicity, age and stellar mass at increasing 4000AA-break
strength (D4000). For galaxies of intermediate mass, stronger Balmer absorption
at fixed D4000 is associated with higher metallicity and younger age. We
investigate how stellar metallicity and age depend on total galaxy stellar
mass. Low-mass galaxies are typically young and metal-poor, massive galaxies
old and metal-rich, with a rapid transition between these regimes over the
stellar mass range 3x10^9<M/Msun<3x10^10. Both high- and low-concentration
galaxies follow these relations, but there is a large dispersion in stellar
metallicity at fixed stellar mass, especially for low-concentration galaxies of
intermediate mass. Despite the large scatter, the relation between stellar
metallicity and stellar mass is similar to the correlation between gas-phase
oxygen abundance and stellar mass for star-forming galaxies. [abriged]Comment: 22 pages, 14 figures, accepted for publication on MNRAS, data
available at http://www.mpa-garching.mpg.de/SDSS
Differential coupling of G protein alpha subunits to seven-helix receptors expressed in Xenopus oocytes
Xenopus oocytes were used to examine the coupling of the serotonin 1c (5HT1c) and thyrotropin-releasing hormone (TRH) receptors to both endogenous and heterologously expressed G protein alpha subunits. Expression of either G protein-coupled receptor resulted in agonist- induced, Ca(2+)-activated Cl- currents that were measured using a two- electrode voltage clamp. 5HT-induced Cl- currents were reduced 80% by incubating the injected oocytes with pertussis toxin (PTX) and inhibited 50-65% by injection of antisense oligonucleotides to the PTX- sensitive Go alpha subunit. TRH-induced Cl- currents were reduced only 20% by PTX treatment but were inhibited 60% by injection of antisense oligonucleotides to the PTX-insensitive Gq alpha subunit. Injection of antisense oligonucleotides to a novel Xenopus phospholipase C-beta inhibited the 5HT1c (and Go)-induced Cl- current with little effect on the TRH (and Gq)-induced current. These results suggest that receptor- activated Go and Gq interact with different effectors, most likely different isoforms of phospholipase C-beta. Co-expression of each receptor with seven different mammalian G protein alpha subunit cRNAs (Goa, Gob, Gq, G11, Gs, Golf, and Gt) was also examined. Co-expression of either receptor with the first four of these G alpha subunits resulted in a maximum 4-6-fold increase in Cl- currents; the increase depended on the amount of G alpha subunit cRNA injected. This increase was blocked by PTX for G alpha oa and G alpha ob co-expression but not for G alpha q or G alpha 11 co-expression. Co-expression of either receptor with Gs, Golf, or Gt had no effect on Ca(2+)-activated Cl- currents; furthermore, co-expression with Gs or Golf also failed to reveal 5HT- or TRH-induced changes in adenylyl cyclase as assessed by activation of the cystic fibrosis transmembrane conductance regulator Cl- channel. These results indicate that in oocytes, the 5HT1c and TRH receptors do the following: 1) preferentially couple to PTX-sensitive (Go) and PTX-insensitive (Gq) G proteins and that these G proteins act on different effectors, 2) couple within the same cell type to several different heterologously expressed G protein alpha subunits to activate the oocyte's endogenous Cl- current, and 3) fail to couple to G protein alpha subunits that activate cAMP or phosphodiesterase
Global Phase Diagram of nu = 2 Quantum Hall Bilayers in Tilted Magnetic Field
We consider a bilayer quantum Hall system at total filling fraction nu=2 in
tilted magnetic field allowing for charge imbalance as well as tunneling
between the two layers. Using an "unrestricted Hartree Fock," previously
discussed by Burkov and MacDonald (Phys Rev B 66 115323 2002), we examine the
zero temperature global phase diagrams that would be accessed experimentally by
changing the in-plane field and the bias voltage between the layers while
keeping the tunneling between the two layers fixed. In accordance with previous
work, we find symmetric and ferromagnetic phases as well as a first order
transition between two canted phases with spontaneously broken U(1) symmetry.
We find that these two canted phases are topologically connected in the phase
diagram and, reminiscent of a first order liquid-gas transition, the first
order transition line between these two phases ends in a quantum critical
point. We develop a physical picture of these two phases and describe in detail
the physics of the transition
Роль маркетинга в сфере культуры
Сегодня все мы ощущаем завершение очередного этапа развития нашего общества, который выражается в многочисленных кризисах (политическом, экономическом, экологическом и т.д.), что в полной мере
отражает художественная культура
Single-photon emission associated with double electron capture in F9+ + C collisions
Radiative double electron capture (RDEC), the one-step process occurring in
ion-atom collisions, has been investigated for bare fluorine ions colliding
with carbon. RDEC is completed when two target electrons are captured to a
bound state of a projectile simultaneously with the emission of a single
photon. This work is a follow-up to our earlier measurement of RDEC for bare
oxygen projectiles, thus providing a recipient system free of electron-related
Coulomb fields in both cases and allowing for the comparison between the two
collision systems as well as with available theoretical studies. The most
significant mechanisms of x-ray emission that may contribute to the RDEC energy
region as background processes are also addressed.Comment: Submitted to Phys. Rev.
Proton conducting gel polymer electrolytes for supercapacitor applications
A non-aqueous, mechanically-stable, proton conducting gel polymer electrolyte has been prepared for Electrochemical Capacitor (supercapacitor) applications. It is based on 2-hydroxymethylmethacrylate monomer mixed with two different solvents (propylene carbonate and N,N-dimethylformamide). It was shown that the capacitive performance changes with the gel electrolyte composition. The proton conduction type mechanism affects ions mobility and transport into the porous carbon electrode. Addition of small amounts of DMF solvent leads to a change in the conduction mechanism from a vehicleto a Grotthuss-type, and capacitance of 90 F g-1 at 20 °C was achieved using a 15 wt. % DPhHPO4/P (HEMA)/30 wt. % DMF–70 wt. % PC gel composition. Electrochemical tests were done in a large temperature range (from -40 to 80 °C). The cell delivered a capacitance of 54 F g-1 at -40 °C, that is 60% of the value obtained at room temperature, and 90 F g-1 at 80 °C within voltage window of 1 V
Designed asymmetric coordination helicates with bis-β-diketonate ligands.
A new bis-(β-diketone) ligand featuring built-up structural asymmetry yields non-symmetric Fe(iii) and Ga(iii) dinuclear, triple-stranded helicates by design. Their structural properties have been studied, both in solid state and in solution, and compared with their corresponding symmetric analogues. The robustness observed shows the potential of this synthetic strategy to develop non-symmetric helicoidal motifs with specific functional groups
Informing aerial total counts with demographic models: population growth of Serengeti elephants not explained purely by demography
Conservation management is strongly shaped by the interpretation of population trends. In the Serengeti ecosystem, Tanzania, aerial total counts indicate a striking increase in elephant abundance compared to all previous censuses. We developed a simple age-structured population model to guide interpretation of this reported increase, focusing on three possible causes: (1) in situ population growth, (2) immigration from Kenya, and (3) differences in counting methodologies over time. No single cause, nor the combination of two causes, adequately explained the observed population growth. Under the assumptions of maximum in situ growth and detection bias of 12.7% in previous censuses, conservative estimates of immigration from Kenya were between 250 and 1,450 individuals. Our results highlight the value of considering demography when drawing conclusions about the causes of population trends. The issues we illustrate apply to other species that have undergone dramatic changes in abundance, as well as many elephant populations
Wing Defects in Drosophila xenicid Mutant Clones Are Caused by C-Terminal Deletion of Additional Sex Combs (Asx)
Background: The coordinated action of genes that control patterning, cell fate determination, cell size, and cell adhesion is required for proper wing formation in Drosophila. Defects in any of these basic processes can lead to wing aberrations, including blisters. The xenicid mutation was originally identified in a screen designed to uncover regulators of adhesion between wing surfaces [1]. Principal Findings: Here, we demonstrate that expression of the bPS integrin or the patterning protein Engrailed are not affected in developing wing imaginal discs in xenicid mutants. Instead, expression of the homeotic protein Ultrabithorax (Ubx) is strongly increased in xenicid mutant cells. Conclusion: Our results suggest that upregulation of Ubx transforms cells from a wing blade fate to a haltere fate, and that the presence of haltere cells within the wing blade is the primary defect leading to the adult wing phenotypes observed
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