4,593 research outputs found
Using Perturbative Least Action to Recover Cosmological Initial Conditions
We introduce a new method for generating initial conditions consistent with
highly nonlinear observations of density and velocity fields. Using a variant
of the Least Action method, called Perturbative Least Action (PLA), we show
that it is possible to generate several different sets of initial conditions,
each of which will satisfy a set of highly nonlinear observational constraints
at the present day. We then discuss a code written to test and apply this
method and present the results of several simulations.Comment: 24 pages, 6 postscript figures. Accepted for publication in
Astrophysical Journa
User Intent Prediction in Information-seeking Conversations
Conversational assistants are being progressively adopted by the general
population. However, they are not capable of handling complicated
information-seeking tasks that involve multiple turns of information exchange.
Due to the limited communication bandwidth in conversational search, it is
important for conversational assistants to accurately detect and predict user
intent in information-seeking conversations. In this paper, we investigate two
aspects of user intent prediction in an information-seeking setting. First, we
extract features based on the content, structural, and sentiment
characteristics of a given utterance, and use classic machine learning methods
to perform user intent prediction. We then conduct an in-depth feature
importance analysis to identify key features in this prediction task. We find
that structural features contribute most to the prediction performance. Given
this finding, we construct neural classifiers to incorporate context
information and achieve better performance without feature engineering. Our
findings can provide insights into the important factors and effective methods
of user intent prediction in information-seeking conversations.Comment: Accepted to CHIIR 201
The redshift-space two-point correlation functions of galaxies and groups in the Nearby Optical Galaxy sample
We use the two-point correlation function in redshift space, , to
study the clustering of the galaxies and groups of the Nearby Optical Galaxy
(NOG) sample, which is a nearly all-sky, complete, magnitude-limited sample of
7000 bright and nearby optical galaxies. The correlation function of
galaxies is well described by a power law, , with
slope and Mpc (on scales Mpc), in agreement with previous results of several redshift surveys of
optical galaxies. We confirm the existence of morphological segregation between
early- and late-type galaxies and, in particular, we find a gradual decreasing
of the strength of clustering from the S0 galaxies to the late-type spirals, on
intermediate scales. Furthermore, luminous galaxies turn out to be more
clustered than dim galaxies. The luminosity segregation, which is significant
for both early- and late-type objects, starts to become appreciable only for
galaxies brighter than () and is
independent on scale. The NOG group correlation functions are characterized by
-values ranging from Mpc (for groups with at least three
members) to Mpc (for groups with at least five members). The
degree of group clustering depends on the physical properties of groups.
Specifically, groups with greater velocity dispersions, sizes and masses tend
to be more clustered than those with lower values of these quantities.Comment: Astrophysical Journal, in press, 72 pages, 16 eps figure
Constraints on the Neutrino Mass from SZ Surveys
Statistical measures of galaxy clusters are sensitive to neutrino masses in
the sub-eV range. We explore the possibility of using cluster number counts
from the ongoing PLANCK/SZ and future cosmic-variance-limited surveys to
constrain neutrino masses from CMB data alone. The precision with which the
total neutrino mass can be determined from SZ number counts is limited mostly
by uncertainties in the cluster mass function and intracluster gas evolution;
these are explicitly accounted for in our analysis. We find that projected
results from the PLANCK/SZ survey can be used to determine the total neutrino
mass with a (1\sigma) uncertainty of 0.06 eV, assuming it is in the range
0.1-0.3 eV, and the survey detection limit is set at the 5\sigma significance
level. Our results constitute a significant improvement on the limits expected
from PLANCK/CMB lensing measurements, 0.15 eV. Based on expected results from
future cosmic-variance-limited (CVL) SZ survey we predict a 1\sigma uncertainty
of 0.04 eV, a level comparable to that expected when CMB lensing extraction is
carried out with the same experiment. A few percent uncertainty in the mass
function parameters could result in up to a factor \sim 2-3 degradation of our
PLANCK and CVL forecasts. Our analysis shows that cluster number counts provide
a viable complementary cosmological probe to CMB lensing constraints on the
total neutrino mass.Comment: Replaced with a revised version to match the MNRAS accepted version.
arXiv admin note: text overlap with arXiv:1009.411
The Reference Image Database to Evaluate Response to Therapy in Lung Cancer (RIDER) Project: A Resource for the Development of ChangeâAnalysis Software
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110105/1/cptclpt2008161.pd
Cosmic Shear Statistics and Cosmology
We report a measurement of cosmic shear correlations using an effective area
of 6.5 sq. deg. of the VIRMOS deep imaging survey in progress at the
Canada-France-Hawaii Telescope. We measured various shear correlation
functions, the aperture mass statistic and the top-hat smoothed variance of the
shear with a detection significance exceeding 12 sigma for each of them. We
present results on angular scales from 3 arc-seconds to half a degree. The
consistency of different statistical measures is demonstrated and confirms the
lensing origin of the signal through tests that rely on the scalar nature of
the gravitational potential. For Cold Dark Matter models we find at the 95% confidence level. The
measurement over almost three decades of scale allows to discuss the effect of
the shape of the power spectrum on the cosmological parameter estimation. The
degeneracy on sigma_8-Omega_0 can be broken if priors on the shape of the
linear power spectrum (that can be parameterized by Gamma) are assumed. For
instance, with Gamma=0.21 and at the 95% confidence level, we obtain
0.60.65 and
Omega_0<0.4 for flat (Lambda-CDM) models. From the tangential/radial modes
decomposition we can set an upper limit on the intrinsic shape alignment, which
was recently suggested as a possible contribution to the lensing signal. Within
the error bars, there is no detection of intrinsic shape alignment for scales
larger than 1'.Comment: 13 pages, submitted to A&
Early Dark Energy at High Redshifts: Status and Perspectives
Early dark energy models, for which the contribution to the dark energy
density at high redshifts is not negligible, influence the growth of cosmic
structures and could leave observable signatures that are different from the
standard cosmological constant cold dark matter (CDM) model. In this
paper, we present updated constraints on early dark energy using geometrical
and dynamical probes. From WMAP five-year data, baryon acoustic oscillations
and type Ia supernovae luminosity distances, we obtain an upper limit of the
dark energy density at the last scattering surface (lss), (95% C.L.). When we include higher redshift
observational probes, such as measurements of the linear growth factors,
Gamma-Ray Bursts (GRBs) and Lyman- forest (\lya), this limit improves
significantly and becomes (95%
C.L.). Furthermore, we find that future measurements, based on the
Alcock-Paczy\'nski test using the 21cm neutral hydrogen line, on GRBs and on
the \lya forest, could constrain the behavior of the dark energy component and
distinguish at a high confidence level between early dark energy models and
pure CDM. In this case, the constraints on the amount of early dark
energy at the last scattering surface improve by a factor ten, when compared to
present constraints. We also discuss the impact on the parameter , the
growth rate index, which describes the growth of structures in standard and in
modified gravity models.Comment: 11 pages, 9 figures and 4 table
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