1,184 research outputs found
Data Integration by combining big data and survey sample data for finite population inference
The statistical challenges in using big data for making valid statistical
inference in the finite population have been well documented in literature.
These challenges are due primarily to statistical bias arising from
under-coverage in the big data source to represent the population of interest
and measurement errors in the variables available in the data set. By
stratifying the population into a big data stratum and a missing data stratum,
we can estimate the missing data stratum by using a fully responding
probability sample, and hence the population as a whole by using a data
integration estimator. By expressing the data integration estimator as a
regression estimator, we can handle measurement errors in the variables in big
data and also in the probability sample. We also propose a fully nonparametric
classification method for identifying the overlapping units and develop a
bias-corrected data integration estimator under misclassification errors.
Finally, we develop a two-step regression data integration estimator to deal
with measurement errors in the probability sample. An advantage of the approach
advocated in this paper is that we do not have to make unrealistic
missing-at-random assumptions for the methods to work. The proposed method is
applied to the real data example using 2015-16 Australian Agricultural Census
data
Bounded Search Tree Algorithms for Parameterized Cograph Deletion: Efficient Branching Rules by Exploiting Structures of Special Graph Classes
Many fixed-parameter tractable algorithms using a bounded search tree have
been repeatedly improved, often by describing a larger number of branching
rules involving an increasingly complex case analysis. We introduce a novel and
general search strategy that branches on the forbidden subgraphs of a graph
class relaxation. By using the class of -sparse graphs as the relaxed
graph class, we obtain efficient bounded search tree algorithms for several
parameterized deletion problems. We give the first non-trivial bounded search
tree algorithms for the cograph edge-deletion problem and the trivially perfect
edge-deletion problems. For the cograph vertex deletion problem, a refined
analysis of the runtime of our simple bounded search algorithm gives a faster
exponential factor than those algorithms designed with the help of complicated
case distinctions and non-trivial running time analysis [21] and computer-aided
branching rules [11].Comment: 23 pages. Accepted in Discrete Mathematics, Algorithms and
Applications (DMAA
The prediction of preference for unfamiliar urban places
Preferences for unfamiliar urban environments were studied as a function of urban categories, viewing time, and four predictor variables: complexity, coherence, identifiability, and mystery. A nonmetric factor analysis of the preference ratings for the longest viewing-time condition yielded five dimensions: Contemporary Life, Alley/Factory, Urban Nature, Unusual Architecture, and Older Buildings. The five categories differed significantly in preference, with Urban Nature by far the most preferred and Alley/Factory distinctly disliked. The combination of low coherence and high complexity characterizes the least liked Alley/Factory category, while the role of mystery in the urban setting is highlighted by the most preferred Urban Nature category. The results point to various ways in which the urban environment could be more responsive to people's preferences.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43513/1/11111_2005_Article_BF01359051.pd
Diffraction Symmetry in Crystalline, Close-Packed C60
We have grown crystals of the carbon structure C60 by sublimation. In contrast to solution-grown crystals, the sublimed crystals have long range order with no evidence of solvent inclusions. Sublimed C60 forms three dimensional, faceted crystals with a close-packed, face-centered cubic unit cell. We have refined a crystal structure using the "soccer ball" model of the C60 molecule. The results indicate that the C60 molecule has the expected spherical shape, however the data are not sufficiently accurate to unambiguously determine atomic positions
Social determinants of content selection in the age of (mis)information
Despite the enthusiastic rhetoric about the so called \emph{collective
intelligence}, conspiracy theories -- e.g. global warming induced by chemtrails
or the link between vaccines and autism -- find on the Web a natural medium for
their dissemination. Users preferentially consume information according to
their system of beliefs and the strife within users of opposite narratives may
result in heated debates. In this work we provide a genuine example of
information consumption from a sample of 1.2 million of Facebook Italian users.
We show by means of a thorough quantitative analysis that information
supporting different worldviews -- i.e. scientific and conspiracist news -- are
consumed in a comparable way by their respective users. Moreover, we measure
the effect of the exposure to 4709 evidently false information (satirical
version of conspiracy theses) and to 4502 debunking memes (information aiming
at contrasting unsubstantiated rumors) of the most polarized users of
conspiracy claims. We find that either contrasting or teasing consumers of
conspiracy narratives increases their probability to interact again with
unsubstantiated rumors.Comment: misinformation, collective narratives, crowd dynamics, information
spreadin
Measuring proper motions of isolated neutron stars with Chandra
The excellent spatial resolution of the Chandra observatory offers the
unprecedented possibility to measure proper motions at X-ray wavelength with
relatively high accuracy using as reference the background of extragalactic or
remote galactic X-ray sources. We took advantage of this capability to
constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray
bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and
lacking an optical counterpart. In this paper, we present results from a
preliminary analysis from which we derive 2 sigma upper limits of 76 mas/yr and
138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022
respectively. We use these values together with those of other ROSAT discovered
INSs to constrain the origin, distance and evolutionary status of this
particular group of objects. We find that the tangential velocities of radio
quiet ROSAT neutron stars are probably consistent with those of 'normal'
pulsars. Their distribution on the sky and, for those having accurate proper
motion vectors, their possible birth places, all point to a local population,
probably created in the part of the Gould Belt nearest to the earth.Comment: 8 pages, 3 figures, to appear in Astrophysics and Space Science, in
the proceedings of "Isolated Neutron Stars: from the Interior to the
Surface", edited by D. Page, R. Turolla and S. Zan
The Effective Field Theory of Inflation
We study the effective field theory of inflation, i.e. the most general
theory describing the fluctuations around a quasi de Sitter background, in the
case of single field models. The scalar mode can be eaten by the metric by
going to unitary gauge. In this gauge, the most general theory is built with
the lowest dimension operators invariant under spatial diffeomorphisms, like
g^{00} and K_{mu nu}, the extrinsic curvature of constant time surfaces. This
approach allows us to characterize all the possible high energy corrections to
simple slow-roll inflation, whose sizes are constrained by experiments. Also,
it describes in a common language all single field models, including those with
a small speed of sound and Ghost Inflation, and it makes explicit the
implications of having a quasi de Sitter background. The non-linear realization
of time diffeomorphisms forces correlation among different observables, like a
reduced speed of sound and an enhanced level of non-Gaussianity.Comment: 26 pages. v2: minor corrections, JHEP published versio
- …