Tetrahedralization of a Hexahedral Mesh

Two important classes of three-dimensional elements in computational meshes are hexahedra and tetrahedra. While several efficient methods exist that convert a hexahedral element to a tetrahedral elements, the existing algorithm for tetrahedralization of a hexahedral complex is the marching tetrahedron algorithm which limits pre-selection of face divisions. We generalize a procedure for tetrahedralizing triangular prisms to tetrahedralizing cubes, and combine it with certain heuristics to design an algorithm that can triangulate any hexahedra.Comment: The previous version had an error in the proof of Observation 2.1, which has since been rectified in this version. Formatting and title change

Beta Blockers in Mental Retardation and Developmental Disorders

β-Adrenergic blockers appear to be effective in the management of verbal aggression, physical aggression, or self-injurious behavior associated with mental retardation and other developmental disorders. However, methodological limitations of the available studies make it difficult to judge the value of these treatments. Optimal doses for treating patients with mental retardation or developmental disorders appear lower than described in the general psychiatric literature, so low doses of β-blockers may be preferred in such patients with abnormal brain development. Children and adolescents with mental retardation or developmental disorders appear to respond to particularly low doses (e.g., below propranolol 150 mg daily). Propranolol is recommended for central blockade, and nadolol is recommended for peripheral blockade. Most β receptors in the brain (except cerebellum) seem to be β1 (cardiac type), but it is not clear that central blockade is required for psychotropic effects. Interim suggestions for empirical trials are offered, and rating scales and other measurement approaches are discussed. Since evidence supporting the efficacy of β-blockers in mental retardation or developmental disorders in children and adolescents is not definitive, the clinician is advised to consider designing an empirical trial for each patient, utilizing pre- and postmedication measures, when conventional treatments have been unsuccessful

Geometrothermodynamics of black holes

The thermodynamics of black holes is reformulated within the context of the recently developed formalism of geometrothermodynamics. This reformulation is shown to be invariant with respect to Legendre transformations, and to allow several equivalent representations. Legendre invariance allows us to explain a series of contradictory results known in the literature from the use of Weinhold's and Ruppeiner's thermodynamic metrics for black holes. For the Reissner-Nordstr\"om black hole the geometry of the space of equilibrium states is curved, showing a non trivial thermodynamic interaction, and the curvature contains information about critical points and phase transitions. On the contrary, for the Kerr black hole the geometry is flat and does not explain its phase transition structure.Comment: Revised version, to be published in Gen.Rel.Grav.(Mashhoon's Festschrift

Methylphenidate Treatment in Children with Borderline IQ and Mental Retardation: Analysis of Three Aggregated Studies

Objective: To determine response of low-IQ children with attention deficit hyperactivity disorder (ADHD) symptoms to methylphenidate (MPH). Methods: An aggregated analysis was conducted in 90 children with low IQ who received the same dose regimen of MPH in three independent, placebo-controlled studies. Active drug and placebo were given from 2 to 4 weeks each. Outcome measures included teacher and parent ratings on standardized behavior scales (mean n = 84), performance on computer-controlled cognitive-motor tests (n = 62), and measures of cardiovascular response (n = 85). Results: Both teachers and parents rated the children consistently as being improved on subscales assessing attention, overactivity, and conduct problems. Some 44% of the subjects showed at least a 30% reduction compared with placebo on teacher ratings. MPH improved accuracy on several cognitive tests, response speed was increased on some, and seat activity declined for one of three tests; heart rate was mildly increased (3.9 beats/minute) with MPH. Analyses of IQ and mental age as moderator variables suggested that lower functional level (especially lower IQ) may be associated with a less favorable response to MPH. Conclusions: Children with low IQ and ADHD clearly respond to MPH, but their rate of beneficial response appears to be well under that of normal-IQ children and more varied. Different attentional mechanisms may moderate response to psychostimulants

Direct numerical simulations of ripples in an oscillatory flow

Sea ripples are small-scale bedforms which originate from the interaction of an oscillatory flow with an erodible sand bed. The phenomenon of sea ripple formation is investigated by means of direct numerical simulation in which the sediment bed is represented by a large number of fully-resolved spherical grains (i.e, the flow around each individual particle is accounted for). Two sets of parameter values (differing in the amplitude and frequency of fluid oscillations, among other quantities) are adopted which are motivated by laboratory experiments on the formation of laminar rolling-grain ripples. The knowledge on the origin of ripples is presently enriched by insights and by providing fluid- and sediment-related quantities that are difficult to obtain in the laboratory (e.g. particle forces, statistics of particle motion, bed shear stress). In particular, detailed analysis of flow and sediment bed evolution has confirmed that ripple wavelength is determined by the action of steady recirculating cells which tend to accumulate sediment grains into ripple crests. The ripple amplitude is observed to grow exponentially consistent with established linear stability analysis theories. Particles at the bed surface exhibit two kinds of motion depending on their position with respect to the recirculating cells: particles at ripple crests are significantly faster and show larger excursions than those lying on ripple troughs. In analogy with segregation phenomenon of polydisperse sediments the non-uniform distribution of the velocity field promotes the formation of ripples. The wider the gap between the excursion of fast and slow particles, the the larger the resulting growth rate of ripples. Finally, it is revealed that, in the absence of turbulence, the sediment flow rate is driven by both the bed shear stress and the wave-induced pressure gradient, the dominance of each depending on the phase of the oscillation period. In phases of maximum bed shear stress, the sediment flow rate correlates more with the Shields number while the pressure gradient tends to drive sediment bed motion during phases of minimum bed shear stress

Development of the Guernsey Community Participation and Leisure Assessment – Revised (GCPLA-R).

A sufficiently psychometrically robust measure of community and leisure participation of adults with intellectual disabilities was not in existence, despite research identifying this as an important outcome and a key contributor to quality of life. The current study aimed to update the Guernsey Community Participation and Leisure Assessment (GCPLA). Adults with intellectual disabilities, carers and experts were consulted in creating a revised pool of 46 items. These were then tested and data from 326 adults with intellectual disabilities were analysed for their component structure and psychometric properties. Principal Component analysis discovered a stable set of components describing seven different clusters. This revised measure (the GCPLA-R) was demonstrated to have satisfactory reliability, and scores were related to challenging behaviour and adaptive behaviour in theoretically consistent ways and were correlated with scores on comparable measures