5,373 research outputs found
Selection bias in the M_BH-sigma and M_BH-L correlations and its consequences
It is common to estimate black hole abundances by using a measured
correlation between black hole mass and another more easily measured observable
such as the velocity dispersion or luminosity of the surrounding bulge. The
correlation is used to transform the distribution of the observable into an
estimate of the distribution of black hole masses. However, different
observables provide different estimates: the Mbh-sigma relation predicts fewer
massive black holes than does the Mbh-L relation. This is because the sigma-L
relation in black hole samples currently available is inconsistent with that in
the SDSS sample, from which the distributions of L or sigma are based: the
black hole samples have smaller L for a given sigma or have larger sigma for a
given L. This is true whether L is estimated in the optical or in the NIR. If
this is a selection rather than physical effect, then the Mbh-sigma and Mbh-L
relations currently in the literature are also biased from their true values.
We provide a framework for describing the effect of this bias. We then combine
it with a model of the bias to make an estimate of the true intrinsic
relations. While we do not claim to have understood the source of the bias, our
simple model is able to reproduce the observed trends. If we have correctly
modeled the selection effect, then our analysis suggests that the bias in the
relation is likely to be small, whereas the relation is
biased towards predicting more massive black holes for a given luminosity. In
addition, it is likely that the Mbh-L relation is entirely a consequence of
more fundamental relations between Mbh and sigma, and between sigma and L. The
intrinsic relation we find suggests that at fixed luminosity, older galaxies
tend to host more massive black holes.Comment: 12 pages, 7 figures. Accepted by ApJ. We have added a figure showing
that a similar bias is also seen in the K-band. A new appendix describes the
BH samples as well as the fits used in the main tex
Predicting morphotropic phase boundary locations and transition temperatures in Pb- and Bi-based perovskite solid solutions from crystal chemical data and first-principles calculations
Using data obtained from first-principles calculations, we show that the
position of the morphotropic phase boundary (MPB) and transition temperature at
MPB in ferroelectric perovskite solutions can be predicted with quantitative
accuracy from the properties of the constituent cations. We find that the mole
fraction of PbTiO at MPB in Pb(BB)O-PbTiO,
BiBO-PbTiO and Bi(BB)O-PbTiO exhibits a linear
dependence on the ionic size (tolerance factor) and the ionic displacements of
the B-cations as found by density functional theory calculations. This
dependence is due to competition between the local repulsion and A-cation
displacement alignment interactions. Inclusion of first-principles displacement
data also allows accurate prediction of transiton temperatures at the MPB. The
obtained structure-property correlations are used to predict morphotropic phase
boundaries and transition temperatures in as yet unsynthesized solid solutions.Comment: Accepted for publication in J. Appl. Phy
Phase Transitions in a Dusty Plasma with Two Distinct Particle Sizes
In semiconductor manufacturing, contamination due to particulates
significantly decreases the yield and quality of device fabrication, therefore
increasing the cost of production. Dust particle clouds can be found in almost
all plasma processing environments including both plasma etching devices and in
plasma deposition processes. Dust particles suspended within such plasmas will
acquire an electric charge from collisions with free electrons in the plasma.
If the ratio of inter-particle potential energy to the average kinetic energy
is sufficient, the particles will form either a liquid structure with short
range ordering or a crystalline structure with long range ordering. Otherwise,
the dust particle system will remain in a gaseous state. Many experiments have
been conducted over the past decade on such colloidal plasmas to discover the
character of the systems formed, but more work is needed to fully understand
these structures. The preponderance of previous experiments used monodisperse
spheres to form complex plasma systems
Satellite-Derived Distributions, Inventories and Fluxes of Dissolved and Particulate Organic Matter Along the Northeastern U.S. Continental Margin
Estuaries and the coastal ocean experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine and estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements, optical properties and remote sensing to examine the distributions and inventories of organic carbon in the U.S. Middle Atlantic Bight and Gulf of Maine. Algorithms developed to retrieve colored DOM (CDOM), Dissolved (DOC) and Particulate Organic Carbon (POC) from NASA's MODIS-Aqua and SeaWiFS satellite sensors are applied to quantify the distributions and inventories of DOC and POC. Horizontal fluxes of DOC and POC from the continental margin to the open ocean are estimated from SeaWiFS and MODIS-Aqua distributions of DOC and POC and horizontal divergence fluxes obtained from the Northeastern North Atlantic ROMS model. SeaWiFS and MODIS imagery reveal the importance of estuarine outflow to the export of CDOM and DOC to the coastal ocean and a net community production of DOC on the shelf
A cascade of magnetic field induced spin transitions in LaCoO3
We present magnetization and magnetostriction studies of the insulating
perovskite LaCoO3 in magnetic fields approaching 100 T. In marked contrast with
expectations from single-ion models, the data reveal two distinct first-order
spin transitions and well-defined magnetization plateaux. The magnetization at
the higher plateau is only about half the saturation value expected for spin-1
Co3+ ions. These findings strongly suggest collective behavior induced by
strong interactions between different electronic -- and therefore spin --
configurations of Co3+ ions. We propose a model of these interactions that
predicts crystalline spin textures and a cascade of four magnetic phase
transitions at high fields, of which the first two account for the experimental
data.Comment: 5 pages + supplementary materials, 5 figure
The development and validation of a clinical prediction model to determine the probability of MODY in patients with young-onset diabetes
Aims/hypothesis Diagnosing MODY is difficult. To date,
selection for molecular genetic testing for MODY has used
discrete cut-offs of limited clinical characteristics with varying
sensitivity and specificity. We aimed to use multiple,
weighted, clinical criteria to determine an individual’s
probability of having MODY, as a crucial tool for rational
genetic testing.
Methods We developed prediction models using logistic
regression on data from 1,191 patients with MODY (n0594),
type 1 diabetes (n0278) and type 2 diabetes (n0319). Model
performance was assessed by receiver operating characteristic
(ROC) curves, cross-validation and validation in a further
350 patients.
Results The models defined an overall probability of
MODY using a weighted combination of the most discriminative
characteristics. For MODY, compared with type 1
diabetes, these were: lower HbA1c, parent with diabetes,
female sex and older age at diagnosis. MODY was discriminated
from type 2 diabetes by: lower BMI, younger age at
diagnosis, female sex, lower HbA1c, parent with diabetes,
and not being treated with oral hypoglycaemic agents or insulin.
Both models showed excellent discrimination (c-statistic0
0.95 and 0.98, respectively), low rates of cross-validated misclassification
(9.2% and 5.3%), and good performance on the
external test dataset (c-statistic00.95 and 0.94). Using
the optimal cut-offs, the probability models improved
the sensitivity (91% vs 72%) and specificity (94% vs 91%)
for identifying MODY compared with standard criteria of
diagnosis <25 years and an affected parent. The models are
now available online at www.diabetesgenes.org.
Conclusions/interpretation We have developed clinical prediction
models that calculate an individual’s probability of
having MODY. This allows an improved and more rational
approac
A Search for the Most Massive Galaxies. II. Structure, Environment and Formation
We study a sample of 43 early-type galaxies, selected from the SDSS because
they appeared to have velocity dispersion > 350 km/s. High-resolution
photometry in the SDSS i passband using HRC-ACS on board the HST shows that
just less than half of the sample is made up of superpositions of two or three
galaxies, so the reported velocity dispersion is incorrect. The other half of
the sample is made up of single objects with genuinely large velocity
dispersions. None of these objects has sigma larger than 426 +- 30 km/s. These
objects define rather different relations than the bulk of the early-type
galaxy population: for their luminosities, they are the smallest, most massive
and densest galaxies in the Universe. Although the slopes of the scaling
relations they define are rather different from those of the bulk of the
population, they lie approximately parallel to those of the bulk "at fixed
sigma". These objects appear to be of two distinct types: the less luminous
(M_r>-23) objects are rather flattened and extremely dense for their
luminosities -- their properties suggest some amount of rotational support and
merger histories with abnormally large amounts of gaseous dissipation. The more
luminous objects (M_r<-23) tend to be round and to lie in or at the centers of
clusters. Their properties are consistent with the hypothesis that they are
BCGs. Models in which BCGs form from predominantly radial mergers having little
angular momentum predict that they should be prolate. If viewed along the major
axis, such objects would appear to have abnormally large sigma for their sizes,
and to be abnormally round for their luminosities. This is true of the objects
in our sample once we account for the fact that the most luminous galaxies
(M_r<-23.5), and BCGs, become slightly less round with increasing luminosity.Comment: 21 pages, 19 figures, accepted for publication in MNRA
Dusty Plasma Correlation Function Experiment
Dust particles immersed within a plasma environment, such as those in
protostellar clouds, planetary rings or cometary environments, will acquire an
electric charge. If the ratio of the inter-particle potential energy to the
average kinetic energy is high enough the particles will form either a "liquid"
structure with short-range ordering or a crystalline structure with long range
ordering. Many experiments have been conducted over the past several years on
such colloidal plasmas to discover the nature of the crystals formed, but more
work is needed to fully understand these complex colloidal systems. Most
previous experiments have employed monodisperse spheres to form Coulomb
crystals. However, in nature (as well as in most plasma processing
environments) the distribution of particle sizes is more randomized and
disperse. This paper reports experiments which were carried out in a GEC rf
reference cell modified for use as a dusty plasma system, using varying sizes
of particles to determine the manner in which the correlation function depends
upon the overall dust grain size distribution. (The correlation function
determines the overall crystalline structure of the lattice.) Two dimensional
plasma crystals were formed of assorted glass spheres with specific size
distributions in an argon plasma. Using various optical techniques, the pair
correlation function was determined and compared to those calculated
numerically.Comment: 6 pages, Presented at COSPAR '0
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