758 research outputs found
Factorization of Rational Curves in the Study Quadric and Revolute Linkages
Given a generic rational curve in the group of Euclidean displacements we
construct a linkage such that the constrained motion of one of the links is
exactly . Our construction is based on the factorization of polynomials over
dual quaternions. Low degree examples include the Bennett mechanisms and
contain new types of overconstrained 6R-chains as sub-mechanisms.Comment: Changed arxiv abstract, corrected some type
Competition as rational action : why young children cannot appreciate competitive games
Understanding rational actions requires perspective taking both with respect to means and with respect to objectives. This study addresses the question of whether the two kinds of perspective taking develop simultaneously or in sequence. It is argued that evidence from competitive behavior is best suited for settling this issue. A total of 71 kindergarten children between 3 and 5 years of age participated in a competitive game of dice and were tested on two traditional false belief stories as well as on several control tasks (verbal intelligence, inhibitory control, and working memory). The frequency of competitive poaching moves in the game correlated with correct predictions of mistaken actions in the false belief task. Hierarchical linear regression after controlling for age and control variables showed that false belief understanding significantly predicted the amount of poaching moves. The results speak for an interrelated development of the capacity for “instrumental” and “telic” perspective taking. They are discussed in the light of teleology as opposed to theory use and simulation
The practical other : teleology and its development
We argue for teleology as a description of the way in which we ordinarily understand others’ intentional actions. Teleology starts from the close resemblance between the reasoning involved in understanding others’ actions and one’s own practical reasoning involved in deciding what to do. We carve out teleology’s distinctive features more sharply by comparing it to its three main competitors: theory theory, simulation theory, and rationality theory. The plausibility of teleology as our way of understanding others is underlined by developmental data in its favour
IM Normae: The Death Spiral of a Cataclysmic Variable?
We present a study of the orbital light curves of the recurrent nova IM
Normae since its 2002 outburst. The broad "eclipses" recur with a 2.46 hour
period, which increases on a timescale of 1.28(16)x10^6 years. Under the
assumption of conservative mass-transfer, this suggests a rate near 10^-7
M_sol/year, and this agrees with the estimated /accretion/ rate of the
postnova, based on our estimate of luminosity. IM Nor appears to be a close
match to the famous recurrent nova T Pyxidis. Both stars appear to have very
high accretion rates, sufficient to drive the recurrent-nova events. Both have
quiescent light curves which suggest strong heating of the low-mass secondary,
and very wide orbital minima which suggest obscuration of a large "corona"
around the primary. And both have very rapid orbital period increases, as
expected from a short-period binary with high mass transfer from the low-mass
component. These two stars may represent a final stage of nova -- and
cataclysmic-variable -- evolution, in which irradiation-driven winds drive a
high rate of mass transfer, thereby evaporating the donor star in a paroxysm of
nova outbursts.Comment: PDF, 30 pages, 3 tables, 6 figures; accepted, in press, ApJ; more
info at http://cbastro.org
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Genome-wide association study identifies 30 loci associated with bipolar disorder.
Bipolar disorder is a highly heritable psychiatric disorder. We performed a genome-wide association study (GWAS) including 20,352 cases and 31,358 controls of European descent, with follow-up analysis of 822 variants with P < 1 × 10-4 in an additional 9,412 cases and 137,760 controls. Eight of the 19 variants that were genome-wide significant (P < 5 × 10-8) in the discovery GWAS were not genome-wide significant in the combined analysis, consistent with small effect sizes and limited power but also with genetic heterogeneity. In the combined analysis, 30 loci were genome-wide significant, including 20 newly identified loci. The significant loci contain genes encoding ion channels, neurotransmitter transporters and synaptic components. Pathway analysis revealed nine significantly enriched gene sets, including regulation of insulin secretion and endocannabinoid signaling. Bipolar I disorder is strongly genetically correlated with schizophrenia, driven by psychosis, whereas bipolar II disorder is more strongly correlated with major depressive disorder. These findings address key clinical questions and provide potential biological mechanisms for bipolar disorder
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