7,451 research outputs found

    Caregivers' experiences with the new family‐centred paediatric physiotherapy programme COPCA : a qualitative study

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    Caregivers' experiences during early intervention of their infant with special needs have consequences for their participation in the intervention. Hence, it is vital to understand caregivers' view. This study explored caregivers' experiences with the family-centred early intervention programme "COPing with and CAring for infants with special needs" (COPCA)

    Variational Approach to Gaussian Approximate Coherent States: Quantum Mechanics and Minisuperspace Field Theory

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    This paper has a dual purpose. One aim is to study the evolution of coherent states in ordinary quantum mechanics. This is done by means of a Hamiltonian approach to the evolution of the parameters that define the state. The stability of the solutions is studied. The second aim is to apply these techniques to the study of the stability of minisuperspace solutions in field theory. For a λφ4\lambda \varphi^4 theory we show, both by means of perturbation theory and rigorously by means of theorems of the K.A.M. type, that the homogeneous minisuperspace sector is indeed stable for positive values of the parameters that define the field theory.Comment: 26 pages, Plain TeX, no figure

    Sharp Metal-Insulator Transition in a Random Solid

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    We have measured zero temperature metallic conductivities above and below Mott's minimum value σ_(MIN) in bulk crystals of P doped Si. Studies of lattice heating, electronic heating and macroscopic inhomogeneities support the finding that conductivities below σ_(MIN) increase by over 10 as the P density is increased by 1%, and that over a wider density range the data can be fit t o a scaling form with a characteristic length that tends to diverge with the same exponent (ν = 0.55±0.10) in the metal and insulator

    Critical Behavior of the Conductivity of Si:P at the Metal-Insulator Transition under Uniaxial Stress

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    We report new measurements of the electrical conductivity sigma of the canonical three-dimensional metal-insulator system Si:P under uniaxial stress S. The zero-temperature extrapolation of sigma(S,T -> 0) ~\S - S_c\^mu shows an unprecidentedly sharp onset of finite conductivity at S_c with an exponent mu = 1. The value of mu differs significantly from that of earlier stress-tuning results. Our data show dynamical sigma(S,T) scaling on both metallic and insulating sides, viz. sigma(S,T) = sigma_c(T) F(\S - S_cT^y) where sigma_c(T) is the conductivity at the critical stress S_c. We find y = 1/znu = 0.34 where nu is the correlation-length exponent and z the dynamic critical exponent.Comment: 5 pages, 4 figure

    High Resolution Study of Magnetic Ordering at Absolute Zero

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    High fidelity pressure measurements in the zero temperature limit provide a unique opportunity to study the behavior of strongly interacting, itinerant electrons with coupled spin and charge degrees of freedom. Approaching the exactitude that has become the hallmark of experiments on classical critical phenomena, we characterize the quantum critical behavior of the model, elemental antiferromagnet chromium, lightly doped with vanadium. We resolve the sharp doubling of the Hall coefficient at the quantum critical point and trace the dominating effects of quantum fluctuations up to surprisingly high temperatures.Comment: 5 pages, 4 figure

    Conductivity Cusp in a Disordered Metal

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    A tendency toward a cusp at zero temperature in the electrical conductivity of Si crystals doped with P is observed. It is found that, within the metallic state, decreasing P concentration enhances the cusp and then rapidly changes its sign as a pseudogap opens. Such a cusp has been predicted for a disordered metal in which Coulomb interactions dominate the scattering

    Inference with interference between units in an fMRI experiment of motor inhibition

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    An experimental unit is an opportunity to randomly apply or withhold a treatment. There is interference between units if the application of the treatment to one unit may also affect other units. In cognitive neuroscience, a common form of experiment presents a sequence of stimuli or requests for cognitive activity at random to each experimental subject and measures biological aspects of brain activity that follow these requests. Each subject is then many experimental units, and interference between units within an experimental subject is likely, in part because the stimuli follow one another quickly and in part because human subjects learn or become experienced or primed or bored as the experiment proceeds. We use a recent fMRI experiment concerned with the inhibition of motor activity to illustrate and further develop recently proposed methodology for inference in the presence of interference. A simulation evaluates the power of competing procedures.Comment: Published by Journal of the American Statistical Association at http://www.tandfonline.com/doi/full/10.1080/01621459.2012.655954 . R package cin (Causal Inference for Neuroscience) implementing the proposed method is freely available on CRAN at https://CRAN.R-project.org/package=ci

    The magnetoresistance of homogeneous and heterogeneous silver-rich silver selenide

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    The magnetoresistance (MR) effect of the low-temperature phase of silver selenide (-Ag2 + Se) is measured as a function of composition. Very small composition variations in the order of = 10–6 are achieved by coulometric titration and can be performed simultaneously during the MR measurement. A homogeneous Ag2 + Se shows an ordinary magnetoresistance (OMR) effect, which can be well described by the two-band model. For silver selenide with a heterogenous silver excess, we found quite a different MR behavior. Up to a minor silver excess of 1×10–4 10–2) shows again an OMR effect
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