952 research outputs found
Autistic spectrum disorder symptoms in children and adolescents with attention-deficit/hyperactivity disorder: a meta-analytical review
BACKGROUND: Research identifies highly variable prevalence estimates for autism spectrum disorder (ASD) in children and adolescents with attention deficit hyperactivity disorder (ADHD), particularly between community and clinical samples, warranting quantitative meta-analyses to investigate the true prevalence of ASD in children and adolescents with ADHD. // METHODS: Studies were identified through a systematic literature search of PsycINFO, MEDLINE and Web of Science through January 2018. Twenty-two publications met inclusion criteria (total N = 61 985). Two random effects meta-analyses were conducted: (1) to identify the proportion of children and adolescents with ADHD that met criteria for ASD; and (2) to compare the severity of dimensionally-measured ASD symptomology in children and adolescents with and without ADHD. // RESULTS: The overall pooled effect for children and adolescents with ADHD who met threshold for ASD was 21%. There was no significant difference between community samples (19%) and clinical samples (24%) or between US studies v. those from other countries. Children and adolescents with ADHD had substantially more dimensionally-measured ASD traits compared with those who did not have ADHD (d = 1.23). // CONCLUSION: The findings provide further evidence that ADHD and ASD are associated in nature. Clinical and research implications are discussed
Geometrical aspects of integrable systems
We review some basic theorems on integrability of Hamiltonian systems, namely
the Liouville-Arnold theorem on complete integrability, the Nekhoroshev theorem
on partial integrability and the Mishchenko-Fomenko theorem on noncommutative
integrability, and for each of them we give a version suitable for the
noncompact case. We give a possible global version of the previous local
results, under certain topological hypotheses on the base space. It turns out
that locally affine structures arise naturally in this setting.Comment: It will appear on International Journal of Geometric Methods in
Modern Physics vol.5 n.3 (May 2008) issu
Chern-Simons Quantization of (2+1)-Anti-De Sitter Gravity on a Torus
Chern-Simons formulation of 2+1 dimensional Einstein gravity with a negative
cosmological constant is investigated when the spacetime has the topology . The physical phase space is shown to be a direct product of two
sub-phase spaces each of which is a non-Hausdorff manifold plus a set with
nonzero codimensions. Spacetime geometrical interpretation of each point in the
phase space is also given and we explain the 1 to 2 correspondence with the ADM
formalism from the geometrical viewpoint. In quantizing this theory, we
construct a "modified phase space" which is a cotangnt bundle on a torus. We
also provide a modular invariant inner product and investigate the relation to
the quantum theory which is directly related to the spinor representation of
the ADM formalism. (This paper is the revised version of a previous
paper(hep-th/9312151). The wrong discussion on the topology of the phase space
is corrected.)Comment: latex 28 page
Witten's 2+1 gravity on R x (Klein bottle)
Witten's formulation of 2+1 gravity is investigated on the nonorientable
three-manifold R x (Klein bottle). The gauge group is taken to consist of all
four components of the 2+1 Poincare group. We analyze in detail several
components of the classical solution space, and we show that from four of the
components one can recover nondegenerate spacetime metrics. In particular, from
one component we recover metrics for which the Klein bottles are spacelike. An
action principle is formulated for bundles satisfying a certain orientation
compatibility property, and the corresponding components of the classical
solution space are promoted into a phase space. Avenues towards quantization
are briefly discussed.Comment: 33 pages, REVTeX v3.0, 3 figures in a separate PostScript fil
Duality through the symplectic embedding formalism
In this work we show that we can obtain dual equivalent actions following the
symplectic formalism with the introduction of extra variables which enlarge the
phase space. We show that the results are equal as the one obtained with the
recently developed gauging iterative Noether dualization method (NDM). We
believe that, with the arbitrariness property of the zero mode, the symplectic
embedding method (SEM) is more profound since it can reveal a whole family of
dual equivalent actions. We illustrate the method demonstrating that the
gauge-invariance of the electromagnetic Maxwell Lagrangian broken by the
introduction of an explicit mass term and a topological term can be restored to
obtain the dual equivalent and gauge-invariant version of the theory.Comment: RevTeX4, 10 pages. To appear in Int. J. Mod. Phys.
Upper- and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs
Mantle plumes are thought to play a key role in transferring heat from the core\u2013mantle
boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging
on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate
hotspots, large igneous provinces and hence considerable dynamic topography. However, the
active role of mantle plumes on subducting slabs remains poorly understood. Here we show
that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern
Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau.
Our findings are based on comparisons between 3D anisotropic tomography images and 3D
petrological-thermo-mechanical models, which self-consistently explain several unique
features of the Fiji\u2013Tonga region. We identify four possible slip systems of bridgmanite in the
lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab
(VSH4VSV) with thermo-mechanical calculations
On the geometry of quantum indistinguishability
An algebraic approach to the study of quantum mechanics on configuration
spaces with a finite fundamental group is presented. It uses, in an essential
way, the Gelfand-Naimark and Serre-Swan equivalences and thus allows one to
represent geometric properties of such systems in algebraic terms. As an
application, the problem of quantum indistinguishability is reformulated in the
light of the proposed approach. Previous attempts aiming at a proof of the
spin-statistics theorem in non-relativistic quantum mechanics are explicitly
recast in the global language inherent to the presented techniques. This leads
to a critical discussion of single-valuedness of wave functions for systems of
indistinguishable particles. Potential applications of the methods presented in
this paper to problems related to quantization, geometric phases and phase
transitions in spin systems are proposed.Comment: 24 page
The Color of Childhood: The Role of the Child/Human Binary in the Production of Anti-Black Racism
The binary between the figure of the child and the fully human being is invoked with regularity in analyses of race, yet its centrality to the conception of race has never been fully explored. For most commentators, the figure of the child operates as a metaphoric or rhetorical trope, a non-essential strategic tool in the perpetuation of White supremacy. As I show in the following, the child/human binary does not present a contingent or merely rhetorical construction but, rather, a central feature of racialization. Where Black peoples are situated as objects of violence it is often precisely because Blackness has been identified with childhood and childhood is historically identified as the archetypal site of naturalized violence and servitude. I proceed by offering a historical account of how Black peoples came to inherit the subordination and dehumanization of European childhood and how White youth were subsequently spared through their partial categorization as adults
Coherent state quantization of a particle in de Sitter space
We present a coherent state quantization of the dynamics of a relativistic
test particle on a one-sheet hyperboloid embedded in a three-dimensional
Minkowski space. The group SO_0(1,2) is considered to be the symmetry group of
the system. Our procedure relies on the choice of coherent states of the motion
on a circle. The coherent state realization of the principal series
representation of SO_0(1,2) seems to be a new result.Comment: Journal of Physics A: Mathematical and General, vol. 37, in pres
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