87,017 research outputs found
Domains and naĂŻve theories
Human cognition entails domainâspecific cognitive processes that influence memory, attention, categorization, problemâsolving, reasoning, and knowledge organization. This article examines domainâspecific causal theories, which are of particular interest for permitting an examination of how knowledge structures change over time. We first describe the properties of commonsense theories, and how commonsense theories differ from scientific theories, illustrating with children's classification of biological and nonbiological kinds. We next consider the implications of domainâspecificity for broader issues regarding cognitive development and conceptual change. We then examine the extent to which domainâspecific theories interact, and how people reconcile competing causal frameworks. Future directions for research include examining how different content domains interact, the nature of theory change, the role of context (including culture, language, and social interaction) in inducing different frameworks, and the neural bases for domainâspecific reasoning. WIREs Cogni Sci 2011 2 490â502 DOI: 10.1002/wcs.124 For further resources related to this article, please visit the WIREs websitePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87128/1/124_ftp.pd
Models of Neutrino Mass with a Low Cutoff Scale
In theories with a low quantum gravity scale, global symmetries are expected
to be violated, inducing excessive proton decay or large Majorana neutrino
masses. The simplest cure is to impose discrete gauge symmetries, which in turn
make neutrinos massless. We construct models that employ these gauge symmetries
while naturally generating small neutrino masses. Majorana (Dirac) neutrino
masses are generated through the breaking of a discrete (continuous) gauge
symmetry at low energies, e.g., 2 keV to 1 GeV. The Majorana case predicts
\Delta N_\nu \simeq 1 at BBN, neutrinoless double beta decay with scalar
emission, and modifications to the CMB anisotropies from domain walls in the
universe as well as providing a possible Dark Energy candidate. For the Dirac
case, despite the presence of a new light gauge boson, all laboratory,
astrophysical, and cosmological constraints can be avoided.Comment: 11 pages, 4 figure
Special complex manifolds
We introduce the notion of a special complex manifold: a complex manifold
(M,J) with a flat torsionfree connection \nabla such that (\nabla J) is
symmetric. A special symplectic manifold is then defined as a special complex
manifold together with a \nabla-parallel symplectic form \omega . This
generalises Freed's definition of (affine) special K\"ahler manifolds. We also
define projective versions of all these geometries. Our main result is an
extrinsic realisation of all simply connected (affine or projective) special
complex, symplectic and K\"ahler manifolds. We prove that the above three types
of special geometry are completely solvable, in the sense that they are locally
defined by free holomorphic data. In fact, any special complex manifold is
locally realised as the image of a holomorphic 1-form \alpha : C^n \to T^* C^n.
Such a realisation induces a canonical \nabla-parallel symplectic structure on
M and any special symplectic manifold is locally obtained this way. Special
K\"ahler manifolds are realised as complex Lagrangian submanifolds and
correspond to closed forms \alpha. Finally, we discuss the natural geometric
structures on the cotangent bundle of a special symplectic manifold, which
generalise the hyper-K\"ahler structure on the cotangent bundle of a special
K\"ahler manifold.Comment: 24 pages, latex, section 3 revised (v2), modified Abstract and
Introduction, version to appear in J. Geom. Phy
Hydrodynamic Spinodal Decomposition: Growth Kinetics and Scaling Functions
We examine the effects of hydrodynamics on the late stage kinetics in
spinodal decomposition. From computer simulations of a lattice Boltzmann scheme
we observe, for critical quenches, that single phase domains grow
asymptotically like , with in two dimensions
and in three dimensions, both in excellent agreement with
theoretical predictions.Comment: 12 pages, latex, Physical Review B Rapid Communication (in press
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