170,803 research outputs found
Visuospatial memory in dyslexia: evidence for strategic deficits.
Impairments in working memory are suggested to be one of the defining characteristics of dyslexia, and deficits in verbal recall are well documented. However, the situation regarding visuospatial memory is less clear. In a widely used measure, the Corsi blocks task, sequences of visuospatial locations can be recalled forwards, in the order presented (CF), or backwards, in reverse order (CB). Previous research has suggested that, while CF draws on spatial-sequential resources, CB may load executive and distinctly visual processes. While people with dyslexia typically show no deficit on CF, CB is rarely presented. We present three studies which indicate a consistent dyslexic deficit on CB that can be ameliorated by visual strategy instructions. Our data suggest that, without instruction, people with dyslexia are unable to adopt an effective CB strategy and this is consistent with a deficit in executive function. These results have implications for our understanding of visuospatial memory in dyslexia, and also in terms of the administration of the Corsi task to special populations
Thermodynamic properties of uranium dioxide: Electronic contributions to the specific heat
It has recently been proposed that the anomalous specific heat of uranium dioxide be ascribed to the effect of electronic defects rather than Frenkel disorder on the union sub-lattice. We here present calculations showing that the entropy contribution from electronic defects is large enough to make a major contribution to the specific heat whereas the contribution from Frenkel defects is much smaller
Impaired carotid viscoelastic properties in women with polycystic ovaries
Background-The purpose of this study was to assess the elastic properties of the carotid arteries in women with polycystic ovarian syndrome, asymptomatic women with polycystic ovaries. and healthy controls.Methods and Results-We recruited the following 60 subjects: 20 symptomatic women with polycystic ovaries attending the reproductive endocrinology clinics, 20 asymptomatic women with polycystic ovaries attending the family planning clinic, and 20 staff volunteers as healthy controls with normal ovaries on transvaginal scan. Compliance and stiffness index were assessed in the common and internal carotid arteries using duplex ultrasound equipped with an echo-locked arterial wall-tracking system. Compliance was significantly lower in the common carotid artery in symptomatic and asymptomatic women with polycystic ovaries than in the controls (10.7, 14.1, and 19.2%mm Hg-1 x 10(-2), respectively). The arterial stiffness index was correspondingly increased (12.3, 10.2, and 6.7, respectively). Similar results were obtained in the internal carotid artery for compliance (10.1. 11.0, and 16.9 %mm Hg-1 x 10(-2), respectively) and stiffness index (14.8, 16.2, and 8.7, respectively).Conclusions-The results of this study provide additional evidence of vascular dysfunction in women with polycystic ovaries and are compatible with the hypothesis that they are at increased risk from coronary artery disease and stroke
In situ nanocompression testing of irradiated copper.
Increasing demand for energy and reduction of carbon dioxide emissions has revived interest in nuclear energy. Designing materials for radiation environments necessitates a fundamental understanding of how radiation-induced defects alter mechanical properties. Ion beams create radiation damage efficiently without material activation, but their limited penetration depth requires small-scale testing. However, strength measurements of nanoscale irradiated specimens have not been previously performed. Here we show that yield strengths approaching macroscopic values are measured from irradiated ~400 nm-diameter copper specimens. Quantitative in situ nanocompression testing in a transmission electron microscope reveals that the strength of larger samples is controlled by dislocation-irradiation defect interactions, yielding size-independent strengths. Below ~400 nm, size-dependent strength results from dislocation source limitation. This transition length-scale should be universal, but depends on material and irradiation conditions. We conclude that for irradiated copper, and presumably related materials, nanoscale in situ testing can determine bulk-like yield strengths and simultaneously identify deformation mechanisms
On the absence of the usual weak-field limit, and the impossibility of embedding some known solutions for isolated masses in cosmologies with f(R) dark energy
This version deposited at arxiv 02-10-12 arXiv:1210.0730v1. Subsequently published in Physical Review D as Phys. Rev. D 87, 063517 (2013) http://link.aps.org/doi/10.1103/PhysRevD.87.063517. Copyright American Physical Society (APS).11 pages11 pages11 pages11 pagesThe problem of matching different regions of spacetime in order to construct inhomogeneous cosmological models is investigated in the context of Lagrangian theories of gravity constructed from general analytic functions f(R), and from non-analytic theories with f(R)=R^n. In all of the cases studied, we find that it is impossible to satisfy the required junction conditions without the large-scale behaviour reducing to that expected from Einstein's equations with a cosmological constant. For theories with analytic f(R) this suggests that the usual treatment of weak-field systems may not be compatible with late-time acceleration driven by anything other than a constant term of the form f(0), which acts like a cosmological constant. For theories with f(R)=R^n we find that no known spherically symmetric vacuum solutions can be matched to an expanding FLRW background. This includes the absence of any Einstein-Straus-like embeddings of the Schwarzschild exterior solution in FLRW spacetimes
Integrability of the Minimal Strain Equations for the Lapse and Shift in 3+1 Numerical Relativity
Brady, Creighton and Thorne have argued that, in numerical relativity
simulations of the inspiral of binary black holes, if one uses lapse and shift
functions satisfying the ``minimal strain equations'' (MSE), then the
coordinates might be kept co-rotating, the metric components would then evolve
on the very slow inspiral timescale, and the computational demands would thus
be far smaller than for more conventional slicing choices. In this paper, we
derive simple, testable criteria for the MSE to be strongly elliptic, thereby
guaranteeing the existence and uniqueness of the solution to the Dirichlet
boundary value problem. We show that these criteria are satisfied in a test-bed
metric for inspiraling binaries, and we argue that they should be satisfied
quite generally for inspiraling binaries. If the local existence and uniqueness
that we have proved holds globally, then, for appropriate boundary values, the
solution of the MSE exhibited by Brady et. al. (which tracks the inspiral and
keeps the metric evolving slowly) will be the unique solution and thus should
be reproduced by (sufficiently accurate and stable) numerical integrations.Comment: 6 pages; RevTeX; submitted to Phys. Rev. D15. Technical issue of the
uniqueness of the solution to the Dirichlet problem clarified. New subsection
on the nature of the boundary dat
Interactions of heavy-light mesons
The potential between static-light mesons forming a meson-meson or a
meson-antimeson system is calculated in quenched and unquenched SU(3) gauge
theory. We use the Sheikholeslami-Wohlert action and statistical estimators of
light quark propagators with maximal variance reduction. The dependence of the
potentials on the light quark spin and isospin and the effect of meson exchange
is investigated. Our main motivation is exploration of bound states of two
mesons and string breaking. The latter also involves the two-quark potential
and the correlation between two-quark and two-meson states.Comment: Contribution to LATTICE99 (QCD spectrum). 3 pages, 4 eps figure
Visibility Representations of Boxes in 2.5 Dimensions
We initiate the study of 2.5D box visibility representations (2.5D-BR) where
vertices are mapped to 3D boxes having the bottom face in the plane and
edges are unobstructed lines of sight parallel to the - or -axis. We
prove that: Every complete bipartite graph admits a 2.5D-BR; The
complete graph admits a 2.5D-BR if and only if ; Every
graph with pathwidth at most admits a 2.5D-BR, which can be computed in
linear time. We then turn our attention to 2.5D grid box representations
(2.5D-GBR) which are 2.5D-BRs such that the bottom face of every box is a unit
square at integer coordinates. We show that an -vertex graph that admits a
2.5D-GBR has at most edges and this bound is tight. Finally,
we prove that deciding whether a given graph admits a 2.5D-GBR with a given
footprint is NP-complete. The footprint of a 2.5D-BR is the set of
bottom faces of the boxes in .Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Systematic review of hospital readmissions in stroke patients
Background Previous evidence on factors and causes of readmissions associated with high-impact users of stroke is scanty. The aim of the study was to investigate common causes and pattern of short- and long-term readmissions stroke patients by conducting a systematic review of studies using hospital administrative data. Common risk factors associated with the change of readmission rate were also examined. Methods The literature search was conducted from 15th February to 15th March 2016 using various databases, such as Medline, Embase, and Web of Science. Results There were total of 24 studies (n=2,126,617) included in the review. Only 4 studies assessed causes of readmissions in stroke patients with the follow-up duration from 30 days to 5 years. Common causes of readmissions in majority of the studies were recurrent stroke, infections and cardiac conditions. Common patient-related risk factors associated with increased readmission rate were age and history of coronary heart disease, heart failure, renal disease, respiratory disease, peripheral arterial disease and diabetes. Among stroke-related factors, length of stay of index stroke admission was associated with increased readmission rate, followed by bowel incontinence, feeding tube and urinary catheter. Conclusion Although risk factors and common causes of readmission were identified, but none of the previous studies investigated causes and their sequence of readmissions among high-impact stroke users
- …