558 research outputs found
Building population models for large-scale neural recordings: opportunities and pitfalls
Modern recording technologies now enable simultaneous recording from large
numbers of neurons. This has driven the development of new statistical models
for analyzing and interpreting neural population activity. Here we provide a
broad overview of recent developments in this area. We compare and contrast
different approaches, highlight strengths and limitations, and discuss
biological and mechanistic insights that these methods provide
Metastatic model of HPV+ oropharyngeal squamous cell carcinoma demonstrates heterogeneity in tumor metastasis
Human papillomavirus induced (HPV+) cancer incidence is rapidly rising, comprising 60–80% of oropharyngeal squamous cell carcinomas (OPSCCs); while rare, recurrent/metastatic disease accounts for nearly all related deaths. An in vivo pre-clinical model for these invasive cancers is necessary for testing new therapies. We characterize an immune competent recurrent/metastatic HPV+ murine model of OPSSC which consists of four lung metastatic (MLM) cell lines isolated from an animal with HPV+ OPSCC that failed cisplatin/radiation treatment. These individual metastatic clonal cell lines were tested to verify their origin (parental transgene expression and define their physiological properties: proliferation, metastatic potential, heterogeneity and sensitivity/resistance to cisplatin and radiation. All MLMs retain expression of parental HPV16 E6 and E7 and degrade P53 yet are heterogeneous from one another and from the parental cell line as defined by Illumina expression microarray. Consistent with this, reverse phase protein array defines differences in protein expression/activation between MLMs as well as the parental line. While in vitro growth rates of MLMs are slower than the parental line, in vivo growth of MLM clones is greatly enhanced. Moreover, in vivo resistance to standard therapies is dramatically increased in 3 of the 4 MLMs. Lymphatic and/or lung metastasis occurs 100% of the time in one MLM line. This recurrent/metastatic model of HPV+ OPSCC retains the characteristics evident in refractory human disease (heterogeneity, resistance to therapy, metastasis in lymph nodes/lungs) thus serving as an ideal translational system to test novel therapeutics. Moreover, this system may provide insights into the molecular mechanisms of metastasis
History of Hydrogen Reionization in the Cold Dark Matter Model
We calculate the reionization history in Cold Dark Matter (CDM) models. The
epoch of the end of reionization and the Thomson scattering optical depth to
the cosmic microwave background depend on the power spectrum amplitude on small
scales and on the ionizing photon emissivity per unit mass in collapsed halos.
We calibrate the emissivity to reproduce the measured ionizing background
intensity at z=4. Models in which all CDM halos have either a constant
emissivity or a constant energy emitted per Hubble time, per unit mass, predict
that reionization ends near z~6 and the optical depth is in the range 0.05 <
tau_e < 0.09, consistent with WMAP results at the 1 to 2 sigma level. If the
optical depth is as high as 0.17 (as suggested by WMAP), halos of velocity
dispersion ~ 3-30 km/s at z>15 must have ionizing emissivities per unit mass
larger by a factor >~ 50 compared to the more massive halos that produce the
ionizing emissivity at z=4. This factor increases to 100 if the CDM power
spectrum amplitude is required to agree with the Croft et al. (2002)
measurement from the Lyman alpha forest. If tau_e >~ 0.17 were confirmed, a
higher ionizing emissivity at z>15 compared to z=4 might arise from an enhanced
star formation rate or quasar abundance per unit mass and an increased escape
fraction for ionizing photons; the end of reionization could have been delayed
to z~6 because of the suppression of gas accretion and star formation in
low-mass halos as the medium was reionized.Comment: 19 pages, 4 figues, submitted to Ap
The Mass of the Central Black Hole in the Seyfert Galaxy NGC 4151
In order to improve the reverberation-mapping based estimate of the mass of
the central supermassive black hole in the Seyfert 1 galaxy NGC 4151, we have
reanalyzed archival ultraviolet monitoring spectra from two campaigns
undertaken with the International Ultraviolet Explorer. We measure
emission-line time delays for four lines, C IV 1549, He II 1640, C III] 1909,
and Mg II 2798, from both campaigns. We combine these measurements with the
dispersion of the variable part of each respective emission line to obtain the
mass of the central object. Despite the problematic nature of some of the data,
we are able to measure a mass of 41.1 (+/- 7.3) million solar masses, although
this, like all reverberation-based masses, is probably systematically uncertain
by a factor of 3-4.Comment: 25 pages, 5 figures. Accepted for publication in The Astrophysical
Journa
Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
We present improved black hole masses for 35 active galactic nuclei (AGNs)
based on a complete and consistent reanalysis of broad emission-line
reverberation-mapping data. From objects with multiple line measurements, we
find that the highest precision measure of the virial product is obtained by
using the cross-correlation function centroid (as opposed to the
cross-correlation function peak) for the time delay and the line dispersion (as
opposed to full width half maximum) for the line width and by measuring the
line width in the variable part of the spectrum. Accurate line-width
measurement depends critically on avoiding contaminating features, in
particular the narrow components of the emission lines. We find that the
precision (or random component of the error) of reverberation-based black hole
mass measurements is typically around 30%, comparable to the precision attained
in measurement of black hole masses in quiescent galaxies by gas or stellar
dynamical methods. Based on results presented in a companion paper by Onken et
al., we provide a zero-point calibration for the reverberation-based black hole
mass scale by using the relationship between black hole mass and host-galaxy
bulge velocity dispersion. The scatter around this relationship implies that
the typical systematic uncertainties in reverberation-based black hole masses
are smaller than a factor of three. We present a preliminary version of a
mass-luminosity relationship that is much better defined than any previous
attempt. Scatter about the mass-luminosity relationship for these AGNs appears
to be real and could be correlated with either Eddington ratio or object
inclination.Comment: 61 pages, including 8 Tables and 16 Figures. Accepted for publication
in The Astrophysical Journa
X-Ray Properties of Narrow-Line Seyfert 1 Galaxies with Very Small Broad-Line Widths
Narrow-line Seyfert\,1 galaxies (NLS1s) with very small broad-line widths
(say, FWHM(\hb) \la 1200\,\kms) represent the extreme type of Seyfert\,1
galaxies that have small black hole masses (\mbh) and/or high Eddington ratios
(\redd). Here we study the X-ray properties of a homogeneously and optically
selected sample of 13 such objects, termed as very narrow line Seyfert\,1
galaxies (VNLS1s), using archival \xmm\ data. It is found that the Fe K
emission line is at most weak in these objects. A soft X-ray excess is
ubiquitous, with the thermal temperatures falling within a strict range of
0.1--0.2\,keV. Our result highlights the puzzling independence of the thermal
temperature by extending the relations to even smaller FWHM(\hb), i.e., smaller
\mbh\ ( \msun) and/or higher \redd. The excess emission can be
modeled by a range of viable models, though the disk reflection and
Comptonization models generally give somewhat better fits over the smeared
absorption and the -free models. At the Eddington ratios around unity and
above, the X-ray spectral slopes in the 2--10\,keV band are systematically
flatter than the Risaliti et al.'s predictions of the relationship with \redd\
suggested previously. Short timescale (1--2 hours) X-ray variability is common,
which, together with the variability amplitude computed for some of the
objects, are supportive of the scenario that NLS1s are indeed AGN with
relatively small \mbh.Comment: 11 figures and 4 table. Accepted for publication in the Astrophysical
Journa
Formation of a galaxy with a central black hole in the Lemaitre-Tolman model
We construct two models of the formation a galaxy with a central black hole,
starting from a small initial fluctuation at recombination. This is an
application of previously developed methods to find a Lemaitre-Tolman model
that evolves from a given initial density or velocity profile to a given final
density profile. We show that the black hole itself could be either a collapsed
object, or a non-vacuum generalisation of a full Schwarzschild-Kruskal-Szekeres
wormhole. Particular attention is paid to the black hole's apparent and event
horizons.Comment: REVTeX, 22 pages including 11 figures (25 figure files). Replacement
has minor changes in response to the referee, and editorial corrections. To
appear in PR
Supermassive Black Holes in Active Galactic Nuclei. II. Calibration of the M-sigma Relationship for AGNs
We calibrate reverberation-based black hole masses in active galactic nuclei
(AGNs) by using the correlation between black hole mass, M, and bulge/spheroid
stellar velocity dispersion, sigma. We use new measurements of sigma for 6 AGNs
and published velocity dispersions for 10 others, in conjunction with improved
reverberation mapping results, to determine the scaling factor required to
bring reverberation-based black hole masses into agreement with the quiescent
galaxy M-sigma relationship. The scatter in the AGN black hole masses is found
to be less than a factor of 3. The current observational uncertainties preclude
use of the scaling factor to discriminate between broad-line region models.Comment: 16 pages, including 3 figures. Accepted for publication in Ap
- …