287,675 research outputs found
Robust semicoherent searches for continuous gravitational waves with noise and signal models including hours to days long transients
The vulnerability to single-detector instrumental artifacts in standard
detection methods for long-duration quasimonochromatic gravitational waves from
nonaxisymmetric rotating neutron stars [continuous waves (CWs)] was addressed
in past work [D. Keitel et al., Phys. Rev. D 89, 064023 (2014).] by a Bayesian
approach. An explicit model of persistent single-detector disturbances led to a
generalized detection statistic with improved robustness against such
artifacts. Since many strong outliers in semicoherent searches of LIGO data are
caused by transient disturbances that last only a few hours, we extend the
noise model to cover such limited-duration disturbances, and demonstrate
increased robustness in realistic simulated data. Besides long-duration CWs,
neutron stars could also emit transient signals which, for a limited time, also
follow the CW signal model (tCWs). As a pragmatic alternative to specialized
transient searches, we demonstrate how to make standard semicoherent CW
searches more sensitive to transient signals. Considering tCWs in a single
segment of a semicoherent search, Bayesian model selection yields a new
detection statistic that does not add significant computational cost. On
simulated data, we find that it increases sensitivity towards tCWs, even of
varying durations, while not sacrificing sensitivity to classical CW signals,
and still being robust to transient or persistent single-detector instrumental
artifacts.Comment: 16 pages, 6 figures, REVTeX4.
Modeling the emergence of universality in color naming patterns
The empirical evidence that human color categorization exhibits some
universal patterns beyond superficial discrepancies across different cultures
is a major breakthrough in cognitive science. As observed in the World Color
Survey (WCS), indeed, any two groups of individuals develop quite different
categorization patterns, but some universal properties can be identified by a
statistical analysis over a large number of populations. Here, we reproduce the
WCS in a numerical model in which different populations develop independently
their own categorization systems by playing elementary language games. We find
that a simple perceptual constraint shared by all humans, namely the human Just
Noticeable Difference (JND), is sufficient to trigger the emergence of
universal patterns that unconstrained cultural interaction fails to produce. We
test the results of our experiment against real data by performing the same
statistical analysis proposed to quantify the universal tendencies shown in the
WCS [Kay P and Regier T. (2003) Proc. Natl. Acad. Sci. USA 100: 9085-9089], and
obtain an excellent quantitative agreement. This work confirms that synthetic
modeling has nowadays reached the maturity to contribute significantly to the
ongoing debate in cognitive science.Comment: Supplementery Information available here
http://www.pnas.org/content/107/6/2403/suppl/DCSupplementa
Fundamental principles in drawing inference from sequence analysis
Individual life courses are dynamic and can be represented as a sequence of states for some portion of their experiences. More generally, study of such sequences has been made in many fields around social science; for example, sociology, linguistics, psychology, and the conceptualisation of subjects progressing through a sequence of states is common. However, many models and sets of data allow only for the treatment of aggregates or transitions, rather than interpreting whole sequences. The temporal aspect of the analysis is fundamental to any inference about the evolution of the subjects but assumptions about time are not normally made explicit. Moreover, without a clear idea of what sequences look like, it is impossible to determine when something is not seen whether it was not actually there. Some principles are proposed which link the ideas of sequences, hypothesis, analytical framework, categorisation and representation; each one being underpinned by the consideration of time. To make inferences about sequences, one needs to: understand what these sequences represent; the hypothesis and assumptions that can be derived about sequences; identify the categories within the sequences; and data representation at each stage. These ideas are obvious in themselves but they are interlinked, imposing restrictions on each other and on the inferences which can be draw
Towards a More Well-Founded Cosmology
First, this paper broaches the definition of science and the epistemic yield
of tenets and approaches: phenomenological (descriptive only), well-founded
(solid first principles, conducive to deep understanding), provisional
(falsifiable if universal, verifiable if existential), and imaginary
(fictitious entities or processes, conducive to empirically unsupported
beliefs). The Big-Bang pardigm and the {\Lambda}CDM "concordance model" involve
such beliefs: the emanation of the universe out of a non-physical stage, cosmic
inflation (invented ad hoc), {\Lambda} (fictitious energy), and exotic dark
matter. They fail in the confidence check that is required in empirical
science. They also face a problem in delimiting what expands from what does
not. In the more well-founded cosmology that emerges, energy is conserved, the
universe is persistent (not transient) and the 'perfect cosmological principle'
holds. Waves and other perturbations that propagate at c (the escape velocity
from the universe) expand exponentially with distance. This dilatation results
from gravitation. The cosmic web of galaxies does not expand. Potential {\Phi}
varies as -H/(cz) instead of -1/r. Inertial forces arise from gravitational
interaction with the rest of the universe (not with space). They are increased
where the universe appears blueshifted and decreased more than proportionately
at very low accelerations. A cut-off acceleration a0 = 0.168 cH is deduced.
This explains the successful description of galaxy rotation curves by MoND. A
fully elaborated physical theory is still pending. The recycling of energy via
a cosmic ocean filled with photons (the CMB), neutrinos and gravitons, and
wider implications for science, are briefly discussed
The underlying social dynamics of paradigm shifts
We develop here a multi-agent model of the creation of knowledge (scientific progress or technological evolution) within a community of researchers devoted to such endeavors. In the proposed model, agents learn in a physical-technological landscape, and weight is attached to both individual search and social influence. We find that the combination of these two forces together with random experimentation can account for both i) marginal change, that is, periods of normal science or refinements on the performance of a given technology (and in which the community stays in the neighborhood of the current paradigm); and ii) radical change, which takes the form of scientific paradigm shifts (or discontinuities in the structure of performance of a technology) that is observed as a swift migration of the knowledge community towards the new and superior paradigm. The efficiency of the search process is heavily dependent on the weight that agents posit on social influence. The occurrence of a paradigm shift becomes more likely when each member of the community attaches a small but positive weight to the experience of his/her peers. For this parameter region, nevertheless, a conservative force is exerted by the representatives of the current paradigm. However, social influence is not strong enough to seriously hamper individual discovery, and can act so as to empower successful individual pioneers who have conquered the new and superior paradigm.Fil: Rodriguez Sickert, Carlos. Universidad del Desarrollo; ChileFil: Cosmelli, Diego. Pontificia Universidad Católica de Chile; ChileFil: Claro, Francisco. Pontificia Universidad Católica de Chile; ChileFil: Fuentes, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad San Sebastián; Chil
- …