2,195 research outputs found
Estimation and optimal designing under latent variable models for paired comparisons studies via a multiplicative algorithm
We consider:<BR/>
1. The problem of estimating the parameters of latent variable models such as the Bradley Terry or Thurstone Model by the method of maximum likelihood, given data from a paired comparisons experiment. The parameters of these models can be taken to be weights which are positive and sum to one;<BR/>
2. The problem of determining approximate locally optimal designs for good estimation of these parameters; i.e of determining optimal design weights which are also positive and sum to one
HST Observations of the Double-Peaked Emission Lines in the Seyfert Galaxy Markarian 78: Mass Outflows from a Single AGN
Previous ground based observations of the Seyfert 2 galaxy Mrk 78 revealed a
double set of emission lines, similar to those seen in several AGN from recent
surveys. Are the double lines due to two AGN with different radial velocities
in the same galaxy, or are they due to mass outflows from a single AGN?We
present a study of the outflowing ionized gas in the resolved narrow-line
region (NLR) of Mrk 78 using observations from Space Telescope Imaging
Spectrograph (STIS) and Faint Object Camera (FOC) aboard the Hubble Space
Telescope(HST) as part of an ongoing project to determine the kinematics and
geometries of active galactic nuclei (AGN) outflows. From the spectroscopic
information, we deter- mined the fundamental geometry of the outflow via our
kinematics modeling program by recreating radial velocities to fit those seen
in four different STIS slit positions. We determined that the double emission
lines seen in ground-based spectra are due to an asymmetric distribution of
outflowing gas in the NLR. By successfully fitting a model for a single AGN to
Mrk 78, we show that it is possible to explain double emission lines with
radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual
supermassive black holes.Comment: 22 pages, 7 figures (2 color), accepted for publication in The
Astrophysical Journa
Granger causality and transfer entropy are equivalent for Gaussian variables
Granger causality is a statistical notion of causal influence based on
prediction via vector autoregression. Developed originally in the field of
econometrics, it has since found application in a broader arena, particularly
in neuroscience. More recently transfer entropy, an information-theoretic
measure of time-directed information transfer between jointly dependent
processes, has gained traction in a similarly wide field. While it has been
recognized that the two concepts must be related, the exact relationship has
until now not been formally described. Here we show that for Gaussian
variables, Granger causality and transfer entropy are entirely equivalent, thus
bridging autoregressive and information-theoretic approaches to data-driven
causal inference.Comment: In review, Phys. Rev. Lett., Nov. 200
The Yang Lee Edge Singularity on Feynman Diagrams
We investigate the Yang-Lee edge singularity on non-planar random graphs,
which we consider as the Feynman Diagrams of various d=0 field theories, in
order to determine the value of the edge exponent.
We consider the hard dimer model on phi3 and phi4 random graphs to test the
universality of the exponent with respect to coordination number, and the Ising
model in an external field to test its temperature independence. The results
here for generic (``thin'') random graphs provide an interesting counterpoint
to the discussion by Staudacher of these models on planar random graphs.Comment: LaTeX, 6 pages + 3 figure
Multivariate Granger Causality and Generalized Variance
Granger causality analysis is a popular method for inference on directed
interactions in complex systems of many variables. A shortcoming of the
standard framework for Granger causality is that it only allows for examination
of interactions between single (univariate) variables within a system, perhaps
conditioned on other variables. However, interactions do not necessarily take
place between single variables, but may occur among groups, or "ensembles", of
variables. In this study we establish a principled framework for Granger
causality in the context of causal interactions among two or more multivariate
sets of variables. Building on Geweke's seminal 1982 work, we offer new
justifications for one particular form of multivariate Granger causality based
on the generalized variances of residual errors. Taken together, our results
support a comprehensive and theoretically consistent extension of Granger
causality to the multivariate case. Treated individually, they highlight
several specific advantages of the generalized variance measure, which we
illustrate using applications in neuroscience as an example. We further show
how the measure can be used to define "partial" Granger causality in the
multivariate context and we also motivate reformulations of "causal density"
and "Granger autonomy". Our results are directly applicable to experimental
data and promise to reveal new types of functional relations in complex
systems, neural and otherwise.Comment: added 1 reference, minor change to discussion, typos corrected; 28
pages, 3 figures, 1 table, LaTe
The Resolved Narrow Line Region in NGC4151
We present slitless spectra of the Narrow Line Region (NLR) in NGC4151 from
the Space Telescope Imaging Spectrograph (STIS) on HST, and investigate the
kinematics and physical conditions of the emission line clouds in this region.
Using medium resolution (~0.5 Angstrom) slitless spectra at two roll angles and
narrow band undispersed images, we have mapped the NLR velocity field from 1.2
kpc to within 13 pc (H_o=75 km/s/Mpc) of the nucleus. The inner biconical cloud
distribution exhibits recessional velocities relative to the nucleus to the NE
and approaching velocities to the SW of the nucleus. We find evidence for at
least two kinematic components in the NLR. One kinematic component is
characterized by Low Velocities and Low Velocity Dispersions (LVLVD clouds: |v|
< 400 km/s, and Delta_v < 130 km/s). This population extends through the NLR
and their observed kinematics may be gravitationally associated with the host
galaxy. Another component is characterized by High Velocities and High Velocity
Dispersions (HVHVD clouds: 400 130 km/s). This
set of clouds is located within 1.1 arcsec (~70pc) of the nucleus and has
radial velocities which are too high to be gravitational in origin, but show no
strong correlation between velocity or velocity dispersion and the position of
the radio knots. Outflow scenarios will be discussed as the driving mechanism
for these HVHVD clouds.Comment: 38 pages, 14 figures, accepted by ApJ. For higher resolution images
see http://www.pha.jhu.edu/~kaiser
The sharpest view on the high-mass star-forming region S255IR. Near-InfraRed Adaptive Optics Imaging on the Outbursting Source NIRS3
Massive stars have an impact on their surroundings from early in their
formation until the end of their lives. However, very little is known about
their formation. Episodic accretion may play a crucial role, but observations
of these events have only been reported towards a handful of massive
protostars. We aim to investigate the outburst event from the high-mass
star-forming region S255IR where recently the protostar NIRS3 underwent an
accretion outburst. We follow the evolution of this source both in photometry
and morphology of its surroundings. Methods: We perform near-infrared adaptive
optics observations on the S255IR central region using the Large Binocular
Telescope in the K broad-band and the H and Br
narrow-band filters with an angular resolution of \sim0\farcs06, close to the
diffraction limit. We discover a new near-infrared knot north-east from NIRS3
that we interpret as a jet knot that was ejected during the last accretion
outburst and observed in the radio regime as part of a follow-up after the
outburst. We measure a mean tangential velocity for this knot of
. We analyse the continuum-subtracted images
from H which traces jet shocked emission, and Br which traces
scattered light from a combination of accretion activity and UV radiation from
the central massive protostar. We observe a significant decrease in flux at the
location of NIRS3, with K=13.48\,mag being the absolute minimum in the historic
series. Our observations strongly suggest a scenario where the episodic
accretion is followed by an episodic ejection response in the near-infrared, as
it was seen in the earlier radio follow-up. The 30 years of
photometry suggests that NIRS3 might have undergone another outburst in the
late 1980s, being the first massive protostar with such evidence observed in
the near-infrared.Comment: Accepted for publication in Astronomy and Astrophysics. 10 pages, 8
figure
On The Nature of Low Luminosity Narrow Line AGN
There is clear observational evidence that some narrow line (type 2) AGN have
a hidden broad line region (BLR), and are thus intrinsically broad line (type
1) AGN. Does this AGN unification applies for all type 2 AGN? Indirect
arguments suggest that some "true" type 2 AGN, i.e. AGN having no obscured BLR
do exist, but it is not clear why the BLR is missing in these AGN. Here we
point out a possible natural explanation. The observed radius-luminosity
relation for the BLR implies an increasing line width with decreasing
luminosity for a given black hole mass (Mbh). In addition, there appears to be
an upper limit to the observed width of broad emission lines in AGN of Delta
v_max~25,000 km/s, which may reflect a physical limit above which the BLR may
not be able to survive. Thus, at a low enough luminosity the BLR radius shrinks
below the Delta v_max radius, leaving no region where the BLR can exist,
although the AGN may remain otherwise `normal'. The implied minimum bolometric
luminosity required to sustain a BLR with Delta v<25,000 km/s is
L_min~10^{41.8}(Mbh}/10^8M_sun)^2. All AGN with L<L_min are expected to be
`true' type 2 AGN, i.e. narrow line AGN without a hidden BLR. Predictions for
the true nature of low luminosity AGN in two samples of nearby galaxies are
provided. These can be used to test the above L_min conjecture, and the
predictions of other models for the size and origin of the BLR
Masculine femininities/feminine masculinities: power, identities and gender
This paper is basically about terminology. In it I discuss the terms 'masculinity' and 'femininity' and how they relate to being male and being female. My theme arises from an increasing difficulty that I am finding in understanding how individual identities relate to dominant constructions of masculinity and femininity. Christine Skelton and Becky Francis argue that we should not be afraid to name certain behaviours as masculine even when they are performed by girls. After a discussion of the problems of defining both 'masculinity' and 'femininity', and a consideration of the power relations between these terms, I go on to consider the concept of 'female masculinity' (Halberstam). I argue that this formulation is problematic, due to its dependence on a main term whose definition is unclear. Finally, I argue that we need to distinguish 'masculinity' and 'femininity' from 'masculinities' and 'femininities'
The black hole in IC 1459 from HST observations of the ionized gas disk
The peculiar elliptical galaxy IC 1459 (M_V = -21.19, D = 16.5 Mpc) has a
fast counterrotating stellar core, stellar shells and ripples, a blue nuclear
point source and strong radio core emission. We present results of a detailed
HST study of IC 1459, and in particular its central gas disk, aimed a
constraining the central mass distribution. We obtained WFPC2 narrow-band
imaging centered on the Halpha+[NII] emission lines to determine the flux
distribution of the gas emission at small radii, and we obtained FOS spectra at
six aperture positions along the major axis to sample the gas kinematics. We
construct different dynamical models for the Halpha+[NII] and Hbeta kinematics
that include a supermassive black hole, and in which the stellar mass
distribution is constrained by the observed surface brightness distribution and
ground-based stellar kinematics. All models are consistent with a black hole
mass in the range Mbh=1-4 x 10^8 Msun, and models without a black hole are
always ruled out at high confidence.Comment: 40 pages including 14 figures, Latex; submitted to A
- …