310 research outputs found
TEDDY (The Task Force for Emotionally Disturbed and Potentially Delinquent Youth)
The Council on Correction of the National Council of Social Workers invited other Virginia organizations dealing with children to attend a meeting in December, 1969, to form a Task Force for Emotionally Disturbed and Potentially Delinquent Youth. Someone came up with the inspired acronym of TEDDY to avoid the long title while reminding people that this task force spoke for a group of children who need help
Nuclear Black Hole Formation in Clumpy Galaxies at High Redshift
Massive stellar clumps in high redshift galaxies interact and migrate to the
center to form a bulge and exponential disk in <1 Gyr. Here we consider the
fate of intermediate mass black holes (BHs) that might form by massive-star
coalescence in the dense young clusters of these disk clumps. We find that the
BHs move inward with the clumps and reach the inner few hundred parsecs in only
a few orbit times. There they could merge into a supermassive BH by dynamical
friction. The ratio of BH mass to stellar mass in the disk clumps is
approximately preserved in the final ratio of BH to bulge mass. Because this
ratio for individual clusters has been estimated to be ~10^{-3}, the observed
BH-to-bulge mass ratio results. We also obtain a relation between BH mass and
bulge velocity dispersion that is compatible with observations of present-day
galaxies.Comment: 10 pages, 3 figures, accepted by Ap
Drinking in the dark: shedding light on young peopleâs alcohol consumption experiences
This paper draws on 12 months of ethnographic research to explore the drinking experiences of young people, aged 15-24, living in the suburban case study locations of Chorlton and Wythenshawe, Manchester, UK. This paper moves beyond the contemporary geographical imaginary of alcohol consumption as a city-centre issue, to explore suburban indoor and outdoor drinking cultures. Through paying attention to atmospheres of darkness and lightness, I show how drinkscapes are active constituents of young peopleâs drinking occasions, rather than passive backdrops. More than this, I illustrate how young people transform dark and light drinkscapes, thereby shaping the drinking practices of themselves and others. Through looking at the interplay between the curating of an atmosphere, and the experience of that atmosphere when bodies, and practices are inserted into it, this paper offers a different take on the âdrinking at home is bad, drinking in public spaces is goodâ argument, with original policy suggestions
Resolving Gas Dynamics in the Circumnuclear Region of a Disk Galaxy in a Cosmological Simulation
Using a hydrodynamic adaptive mesh refinement code, we simulate the growth
and evolution of a galaxy, which could potentially host a supermassive black
hole, within a cosmological volume. Reaching a dynamical range in excess of 10
million, the simulation follows the evolution of the gas structure from
super-galactic scales all the way down to the outer edge of the accretion disk.
Here, we focus on global instabilities in the self-gravitating, cold,
turbulence-supported, molecular gas disk at the center of the model galaxy,
which provide a natural mechanism for angular momentum transport down to sub-pc
scales. The gas density profile follows a power-law scaling as r^-8/3,
consistent with an analytic description of turbulence in a quasi-stationary
circumnuclear disk. We analyze the properties of the disk which contribute to
the instabilities, and investigate the significance of instability for the
galaxy's evolution and the growth of a supermassive black hole at the center.Comment: 16 pages (includes appendix), submitted to ApJ. Figures here are at
low resolution; for higher resolution version, download
http://casa.colorado.edu/~levinerd/ms.pd
Toward precise constraints on growth of massive black holes
Growth of massive black holes (MBHs) in galactic centers comes mainly from
gas accretion during their QSO/AGN phases. In this paper we apply an extended
Soltan argument, connecting the local MBH mass function with the time-integral
of the QSO luminosity function, to the demography of MBHs and QSOs from recent
optical and X-ray surveys, and obtain robust constraints on the luminosity
evolution (or mass growth history) of individual QSOs (or MBHs). We find that
the luminosity evolution probably involves two phases: an initial exponentially
increasing phase set by the Eddington limit and a following phase in which the
luminosity declines with time as a power law (with a slope of -1.2--1.3) set by
a self-similar long-term evolution of disk accretion. Neither an evolution
involving only the increasing phase with a single Eddington ratio nor an
exponentially declining pattern in the second phase is likely. The period of a
QSO radiating at a luminosity higher than 10% of its peak value is about
(2-3)x10^8 yr, during which the MBH obtains ~80% of its mass. The
mass-to-energy conversion efficiency is , with the
latter error accounting for the maximum uncertainty due to Compton-thick AGNs.
The expected Eddington ratios in QSOs from the constrained luminosity evolution
cluster around a single value close to 0.5-1 for high-luminosity QSOs and
extend to a wide range of lower values for low-luminosity ones. The Eddington
ratios for high luminosity QSOs appear to conflict with those estimated from
observations (~0.25) by using some virial mass estimators for MBHs in QSOs
unless the estimators systematically over-estimate MBH masses by a factor of
2-4. We also infer the fraction of optically obscured QSOs ~60-80%. Further
applications of the luminosity evolution of individual QSOs are also discussed.Comment: 25 pages, 13 figures, ApJ in pres
Direct cosmological simulations of the growth of black holes and galaxies
We investigate the coupled formation and evolution of galaxies and their
embedded supermassive black holes using state-of-the-art hydrodynamic
simulations of cosmological structure formation. For the first time, we
self-consistently follow the dark matter dynamics, radiative gas cooling, star
formation, as well as black hole growth and associated feedback processes,
starting directly from initial conditions appropriate for the LambdaCDM
cosmology. Our modeling of the black hole physics is based on an approach we
have developed in simulations of isolated galaxy mergers. Here we examine: (i)
the predicted global history of black hole mass assembly (ii) the evolution of
the local black hole-host mass correlations and (iii) the conditions that allow
rapid growth of the first quasars, and the properties of their hosts and
descendants today. We find a total black hole mass density in good agreement
with observational estimates. The black hole accretion rate density peaks at
lower redshift and evolves more strongly at high redshift than the star
formation rate density, but the ratio of black hole to stellar mass densities
shows only a moderate evolution at low redshifts. We find strong correlations
between black hole masses and properties of the stellar systems, agreeing well
with the measured local M_BH-sigma and M_BH -M_* relationships, but also
suggesting (dependent on the mass range) a weak evolution with redshift in the
normalization and the slope. Our simulations also produce massive black holes
at high redshift, due to extended periods of exponential growth in regions that
collapse early and exhibit strong gas inflows. These first supermassive BH
systems however are not necessarily the most massive ones today, since they are
often overtaken in growth by quasars that form later. (abridged)Comment: 22 pages, 17 figures, submitted to Ap
Reciprocal regulation of PKA and rac signaling
Activated G protein-coupled receptors (GPCRs) and receptor tyrosine kinases relay extracellular signals through spatial and temporal controlled kinase and GTPase entities. These enzymes are coordinated by multifunctional scaffolding proteins for precise intracellular signal processing. The cAMP-dependent protein kinase A (PKA) is the prime example for compartmentalized signal transmission downstream of distinct GPCRs. A-kinase anchoring proteins tether PKA to specific intracellular sites to ensure precision and directionality of PKA phosphorylation events. Here, we show that the Rho-GTPase Rac contains A-kinase anchoring protein properties and forms a dynamic cellular protein complex with PKA. The formation of this transient core complex depends on binary interactions with PKA subunits, cAMP levels and cellular GTP-loading accounting for bidirectional consequences on PKA and Rac downstream signaling. We show that GTP-Rac stabilizes the inactive PKA holoenzyme. However, ÎČ-adrenergic receptor-mediated activation of GTP-Racâbound PKA routes signals to the Raf-Mek-Erk cascade, which is critically implicated in cell proliferation. We describe a further mechanism of how cAMP enhances nuclear Erk1/2 signaling: It emanates from transphosphorylation of p21-activated kinases in their evolutionary conserved kinase-activation loop through GTP-Rac compartmentalized PKA activities. Sole transphosphorylation of p21-activated kinases is not sufficient to activate Erk1/2. It requires complex formation of both kinases with GTP-Rac1 to unleash cAMP-PKAâboosted activation of Raf-Mek-Erk. Consequently GTP-Rac functions as a dual kinase-tuning scaffold that favors the PKA holoenzyme and contributes to potentiate Erk1/2 signaling. Our findings offer additional mechanistic insights how ÎČ-adrenergic receptor-controlled PKA activities enhance GTP-Racâmediated activation of nuclear Erk1/2 signaling
The mass assembly of galaxy groups and the evolution of the magnitude gap
We investigate the assembly of groups and clusters of galaxies using the
Millennium dark matter simulation and the associated gas simulations and
semi-analytic catalogues of galaxies. In particular, in order to find an
observable quantity that could be used to identify early-formed groups, we
study the development of the difference in magnitude between their brightest
galaxies to assess the use of magnitude gaps as possible indicators. We select
galaxy groups and clusters at redshift z=1 with dark matter halo mass M(R200) >
1E13/h Msun, and trace their properties until the present time (z=0). We
consider only the systems with X-ray luminosity L_X> 0.25E42/h^2 erg/s at z=0.
While it is true that a large magnitude gap between the two brightest galaxies
of a particular group often indicates that a large fraction of its mass was
assembled at an early epoch, it is not a necessary condition. More than 90% of
fossil groups defined on the basis of their magnitude gaps (at any epoch
between 0<z<1) cease to be fossils within 4 Gyr, mostly because other massive
galaxies are assembled within their cores, even though most of the mass in
their haloes might have been assembled at early times. We show that, compared
to the conventional definition of fossil galaxy groups based on the magnitude
gap Delta m(12)> 2 (in the R-band, within 0.5R200 of the centre of the group),
an alternative criterion Delta m(14)>2.5 (within the same radius) finds 50%
more early-formed systems, and those that on average retain their fossil phase
longer. However, the conventional criterion performs marginally better at
finding early-formed groups at the high-mass end of groups. Nevertheless, both
criteria fail to identify a majority of the early-formed systems.Comment: 16 pages, 11 figures, 2 tables. Accepted for publication in MNRA
Leptin-induced lipolysis opposes the tonic inhibition of endogenous adenosine in white adipocytes
The aim of the present study was to gain insight into the signaling pathway used
by leptin to stimulate lipolysis. The lipolytic rate of white adipocytes from
sex- and age-matched lean (+/+) and fa/fa rats was determined in the absence or
presence of leptin together with a number of agents acting at different levels of
the signaling cascade. Leptin did not modify FSK-, dbcAMP-, and IBMX-stimulated
lipolysis. Lipolysis can also be maximally stimulated by lowering media adenosine
levels with adenosine deaminase (ADA), i.e., in the ligand-free state. Although
ADA produced near maximal lipolysis in adipocytes of lean animals, only half of
the maximal lipolytic rate (50.9+/-3.2%) was achieved in fat cells from fa/fa
rats (P=0.0034). In adipocytes from lean animals preincubated with ADA, leptin
caused a concentration-related stimulation of lipolysis (P=0.0001). However,
leptin had no effect on the lipolytic activity of adipocytes in the ligand-free
state from fa/fa rats. The adenosine A1 receptor agonist CPA effectively
inhibited basal lipolysis in both lean and obese adipocytes (P=0.0001 and
P=0.0090, respectively). Leptin had no effect on the lipolytic rate of adipocytes
isolated from fa/fa rats and preincubated with CPA. When adipocytes were
incubated with the A1 receptor antagonist DPCPX, a significant increase in
glycerol release was observed in fa/fa fat cells (P=0.009), whereas cells
isolated from lean rats showed no differences to ADA-stimulated lipolysis. After
pretreatment with PTX, which inactivates receptor-mediated Gi function,
adipocytes of obese rats became as responsive to the stimulatory actions of ISO
as cells from lean rats (P=0.0090 vs. ISO in fa/fa rats; P=0.2416 vs. lean rats,
respectively). PTX treatment of lean cells, however, did not alter their response
to this lipolytic agent. It can be concluded that the lipolytic effect of leptin
is located at the adenylate cyclase/Gi proteins level and that leptin-induced
lipolysis opposes the tonic inhibition of endogenous adenosine in white
adipocytes
Detecting quasars at very high redshift with next generation X-ray telescopes
The next generation of X-ray telescopes have the potential to detect faint
quasars at very high redshift and probe the early growth of massive black holes
(BHs). We present modelling of the evolution of the optical and X-ray AGN
luminosity function at 2 < z < 6 based on a CDM merger-driven model for the
triggering of nuclear activity combined with a variety of fading laws. We
extrapolate the merger-driven models to z > 6 for a range of BH growth
scenarios. We predict significant numbers of sources at z ~ 6 with fluxes just
an order of magnitude below the current detection limits and thus detectable
with XEUS and Constellation-X, relatively independently of the fading law
chosen. The predicted number of sources at even higher redshift depends
sensitively on the early growth history of BHs. For passive evolution models in
which BHs grow constantly at their Eddington limit, detectable BHs may be rare
beyond z ~ 10 even with Generation-X. However, in the more probable scenario
that BH growth at z > 6 can be described by passive evolution with a small duty
cycle, or by our merger driven accretion model, then we predict that XEUS and
Generation-X will detect significant numbers of black holes out to z ~ 10 and
perhaps beyond.Comment: 18 pages, 11 Figures. Version accepted to MNRAS; extra data plotted,
XEUS and Con-X sensitivities corrected and predictions amended accordingl
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