903 research outputs found
The Feasibility of Adopting an Evidence-Informed Tailored Exercise Program within Adult Day Services: The Enhance Mobility Program.
This article uses the RE-AIM framework to evaluate the feasibility of implementing Enhance Mobility (EM), a tailored, evidence-informed group exercise and walking program for older adults with dementia, into an adult day services center. Participant physical performance outcomes were measured at baseline and 8 months. Program staff were interviewed to understand implementation challenges. Participant outcomes did not change significantly, though gait speed improved from limited to community ambulation levels. Implementation challenges included space reallocation and adequate staffing. Adopting EM in adult day services is feasible, and has potential to reach older adults who could benefit from tailored exercise.Ye
Fermionic Linear Optics Revisited
We provide an alternative view of the efficient classical simulatibility of
fermionic linear optics in terms of Slater determinants. We investigate the
generic effects of two-mode measurements on the Slater number of fermionic
states. We argue that most such measurements are not capable (in conjunction
with fermion linear optics) of an efficient exact implementation of universal
quantum computation. Our arguments do not apply to the two-mode parity
measurement, for which exact quantum computation becomes possible, see
quant-ph/0401066.Comment: 16 pages, submitted to the special issue of Foundation of Physics in
honor of Asher Peres' 70th birthda
Electron transport in gated InGaAs and InAsP quantum well wires in selectively-grown InP ridge structures
The purpose of this work is to fabricate ribbon-like InGaAs and InAsP wires
embedded in InP ridge structures and investigate their transport properties.
The InP ridge structures that contain the wires are selectively grown by
chemical beam epitaxy (CBE) on pre-patterned InP substrates. To optimize the
growth and micro-fabrication processes for electronic transport, we explore the
Ohmic contact resistance, the electron density, and the mobility as a function
of the wire width using standard transport and Shubnikov-de Haas measurements.
At low temperatures the ridge structures reveal reproducible mesoscopic
conductance fluctuations. We also fabricate ridge structures with submicron
gate electrodes that exhibit non-leaky gating and good pinch-off
characteristics acceptable for device operation. Using such wrap gate
electrodes, we demonstrate that the wires can be split to form quantum dots
evidenced by Coulomb blockade oscillations in transport measurements.Comment: 5 pages, 4 figures, additional references and improved Fig. 4c,
MSS-14 conference, submitted to Physica
Spin splitting and precession in quantum dots with spin-orbit coupling: the role of spatial deformation
Extending a previous work on spin precession in GaAs/AlGaAs quantum dots with
spin-orbit coupling, we study the role of deformation in the external
confinement. Small elliptical deformations are enough to alter the precessional
characteristics at low magnetic fields. We obtain approximate expressions for
the modified factor including weak Rashba and Dresselhaus spin-orbit terms.
For more intense couplings numerical calculations are performed. We also study
the influence of the magnetic field orientation on the spin splitting and the
related anisotropy of the factor. Using realistic spin-orbit strengths our
model calculations can reproduce the experimental spin-splittings reported by
Hanson et al. (cond-mat/0303139) for a one-electron dot. For dots containing
more electrons, Coulomb interaction effects are estimated within the
local-spin-density approximation, showing that many features of the
non-iteracting system are qualitatively preserved.Comment: 7 pages, 7 figure
Emergence of Macro Spatial Structures in Dissipative Cellular Automata
This paper describes the peculiar behavior observed in a class of cellular automata that we have defined as dissipative, i.e., cellular automata that are open and makes it possible for the environment to influence their evolution. Peculiar in the dynamic evolution of this class of cellular automata is that stable macro-level spatial structures emerge from local interactions among cells, a behavior that does not emerge when the cellular automaton is closed, i.e., when the state of a cell is not influenced by the external world. Moreover, we observed that Dissipative Cellular Automata (DCA) exhibit a behavior very similar to that of dissipative structures, as macro-level spatial structures emerge as soon as the external perturbation exceeds a threshold value and it stays below the "turbulence" limit. Finally, we discuss possible relations of the performed experiments with the area of open distributed computing, and in particular of agent-based distributed computing
Proposal for the numerical solution of planar QCD
Using quenched reduction, we propose a method for the numerical calculation
of meson correlation functions in the planar limit of QCD. General features of
the approach are outlined, and an example is given in the context of
two-dimensional QCD.Comment: 31 pages, 10 figures, uses axodraw.sty, To appear in Physical Review
The Hamiltonian formulation of General Relativity: myths and reality
A conventional wisdom often perpetuated in the literature states that: (i) a
3+1 decomposition of space-time into space and time is synonymous with the
canonical treatment and this decomposition is essential for any Hamiltonian
formulation of General Relativity (GR); (ii) the canonical treatment
unavoidably breaks the symmetry between space and time in GR and the resulting
algebra of constraints is not the algebra of four-dimensional diffeomorphism;
(iii) according to some authors this algebra allows one to derive only spatial
diffeomorphism or, according to others, a specific field-dependent and
non-covariant four-dimensional diffeomorphism; (iv) the analyses of Dirac
[Proc. Roy. Soc. A 246 (1958) 333] and of ADM [Arnowitt, Deser and Misner, in
"Gravitation: An Introduction to Current Research" (1962) 227] of the canonical
structure of GR are equivalent. We provide some general reasons why these
statements should be questioned. Points (i-iii) have been shown to be incorrect
in [Kiriushcheva et al., Phys. Lett. A 372 (2008) 5101] and now we thoroughly
re-examine all steps of the Dirac Hamiltonian formulation of GR. We show that
points (i-iii) above cannot be attributed to the Dirac Hamiltonian formulation
of GR. We also demonstrate that ADM and Dirac formulations are related by a
transformation of phase-space variables from the metric to lapse
and shift functions and the three-metric , which is not canonical. This
proves that point (iv) is incorrect. Points (i-iii) are mere consequences of
using a non-canonical change of variables and are not an intrinsic property of
either the Hamilton-Dirac approach to constrained systems or Einstein's theory
itself.Comment: References are added and updated, Introduction is extended,
Subsection 3.5 is added, 83 pages; corresponds to the published versio
Strongly Hyperbolic Extensions of the ADM Hamiltonian
The ADM Hamiltonian formulation of general relativity with prescribed lapse
and shift is a weakly hyperbolic system of partial differential equations. In
general weakly hyperbolic systems are not mathematically well posed. For well
posedness, the theory should be reformulated so that the complete system,
evolution equations plus gauge conditions, is (at least) strongly hyperbolic.
Traditionally, reformulation has been carried out at the level of equations of
motion. This typically destroys the variational and Hamiltonian structures of
the theory. Here I show that one can extend the ADM formalism to (i)
incorporate the gauge conditions as dynamical equations and (ii) affect the
hyperbolicity of the complete system, all while maintaining a Hamiltonian
description. The extended ADM formulation is used to obtain a strongly
hyperbolic Hamiltonian description of Einstein's theory that is generally
covariant under spatial diffeomorphisms and time reparametrizations, and has
physical characteristics. The extended Hamiltonian formulation with 1+log
slicing and gamma--driver shift conditions is weakly hyperbolic.Comment: This version contains minor corrections and clarifications. The
format has been changed to conform with IOP styl
Planck 2015 results. XXVII. The Second Planck Catalogue of Sunyaev-Zeldovich Sources
We present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest all-sky catalogue of galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data-sets, and is the first SZ-selected cluster survey containing > confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that the Y5R500 estimates are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires. the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical and X-ray data-sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under- luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
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