4,179 research outputs found
The quantum mechanical geometric phase of a particle in a resonant vibrating cavity
We study the general-setting quantum geometric phase acquired by a particle
in a vibrating cavity. Solving the two-level theory with the rotating-wave
approximation and the SU(2) method, we obtain analytic formulae that give
excellent descriptions of the geometric phase, energy, and wavefunction of the
resonating system. In particular, we observe a sudden -jump in the
geometric phase when the system is in resonance. We found similar behaviors in
the geometric phase of a spin-1/2 particle in a rotating magnetic field, for
which we developed a geometrical model to help visualize its evolution.Comment: 15pages,6figure
‘How I feel About My School’: The construction and validation of a measure of wellbeing at school for primary school children
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.There is a growing focus on child wellbeing and happiness in schools, but we lack self-report measures for very young children. Three samples (N = 2345) were combined to assess the psychometric properties of the How I Feel About My School (HIFAMS) questionnaire, which was designed for children aged 4-8 years. Test re-test reliability was moderate (intraclass correlation coefficient = 0.62). HIFAMS assessed a single concept and had moderate internal consistency (Cronbach’s alpha values from 0.62 to 0.67). There were low correlations between scores on the child-reported HIFAMS and parent- and teacher reports. Children at risk of exclusion had significantly lower HIFAMS scores than the community sample (mean difference = 2.4; 95% CI: 1.6 to 3.2; p < 0.001). Schools contributed only 4.5% of the variability in HIFAMS score; the remaining 95.5% reflecting pupil differences within schools. Girls’ scores were 0.37 units (95% CI: 0.16 to 0.57; p < 0.001) higher than boys, while year group and deprivation did not predict HIFAMS score. HIFAMS is a promising measure that demonstrates moderate reliability and discriminates between groups even among very young children
Rigorous Theory of Optical Trapping by an Optical Vortex Beam
We propose a rigorous theory for the optical trapping by optical vortices,
which is emerging as an important tool to trap mesoscopic particles. The common
perception is that the trapping is solely due to the gradient force, and may be
characterized by three real force constants. However, we show that the optical
vortex trap can exhibit complex force constants, implying that the trapping
must be stabilized by ambient damping. At different damping levels, particle
shows remarkably different dynamics, such as stable trapping, periodic and
aperiodic orbital motions
A consideration of the challenges involved in supervising international masters students
This paper explores the challenges facing supervisors of international postgraduate students at the dissertation stage of the masters programme. The central problems of time pressure, language difficulties, a lack of critical analysis and a prevalence of personal problems among international students are discussed. This paper makes recommendations for the improvement of language and critical thinking skills, and questions the future policy of language requirements at HE for international Masters students
A Method to Study Relaxation of Metastable Phases: Macroscopic Mean-Field Dynamics
We propose two different macroscopic dynamics to describe the decay of
metastable phases in many-particle systems with local interactions. These
dynamics depend on the macroscopic order parameter through the restricted
free energy and are designed to give the correct equilibrium
distribution for . The connection between macroscopic dynamics and the
underlying microscopic dynamic are considered in the context of a projection-
operator formalism. Application to the square-lattice nearest-neighbor Ising
ferromagnet gives good agreement with droplet theory and Monte Carlo
simulations of the underlying microscopic dynamic. This includes quantitative
agreement for the exponential dependence of the lifetime on the inverse of the
applied field , and the observation of distinct field regions in which the
derivative of the lifetime with respect to depends differently on . In
addition, at very low temperatures we observe oscillatory behavior of this
derivative with respect to , due to the discreteness of the lattice and in
agreement with rigorous results. Similarities and differences between this work
and earlier works on finite Ising models in the fixed-magnetization ensemble
are discussed.Comment: 44 pages RevTeX3, 11 uuencoded Postscript figs. in separate file
The SOS Pilot Study: a RCT of routine oxygen supplementation early after acute stroke—effect on recovery of neurological function at one week
Mild hypoxia is common after stroke and associated with poor long-term outcome. Oxygen supplementation could prevent hypoxia and improve recovery. A previous study of routine oxygen supplementation showed no significant benefit at 7 and 12 months. This pilot study reports the effects of routine oxygen supplementation for 72 hours on oxygen saturation and neurological outcomes at 1 week after a stroke
Numerical Confirmation of Late-time t^{1/2} Growth in Three-dimensional Phase Ordering
Results for the late-time regime of phase ordering in three dimensions are
reported, based on numerical integration of the time-dependent Ginzburg-Landau
equation with nonconserved order parameter at zero temperature. For very large
systems () at late times, the characteristic length grows
as a power law, , with the measured in agreement with the
theoretically expected result to within statistical errors. In this
time regime is found to be in excellent agreement with the analytical
result of Ohta, Jasnow, and Kawasaki [Phys. Rev. Lett. {\bf 49}, 1223 (1982)].
At early times, good agreement is found between the simulations and the
linearized theory with corrections due to the lattice anisotropy.Comment: Substantially revised and enlarged, submitted to PR
Non-state actors in hybrid global climate governance: justice, legitimacy, and effectiveness in a post-Paris era
In this article, we outline the multifaceted roles played by non-state actors within the United Nations Framework Convention on Climate Change and place this within the wider landscape of global climate governance. In doing so, we look at both the formation and aftermath of the 2015 Paris Agreement. We argue that the Paris Agreement cements an architecture of hybrid multilateralism that enables and constrains non-state actor participation in global climate governance. We flesh out the constitutive features of hybrid multilateralism, enumerate the multiple positions non-state actors may employ under these conditions, and contend that non-state actors will play an increasingly important role in the post-Paris era. To substantiate these claims, we assess these shifts and ask how non-state actors may affect the legitimacy, justice, and effectiveness of the Paris Agreement
Ohta-Jasnow-Kawasaki Approximation for Nonconserved Coarsening under Shear
We analytically study coarsening dynamics in a system with nonconserved
scalar order parameter, when a uniform time-independent shear flow is present.
We use an anisotropic version of the Ohta-Jasnow-Kawasaki approximation to
calculate the growth exponents in two and three dimensions: for d=3 the
exponents we find are the same as expected on the basis of simple scaling
arguments, that is 3/2 in the flow direction and 1/2 in all the other
directions, while for d=2 we find an unusual behavior, in that the domains
experience an unlimited narrowing for very large times and a nontrivial
dynamical scaling appears. In addition, we consider the case where an
oscillatory shear is applied to a two-dimensional system, finding in this case
a standard t^1/2 growth, modulated by periodic oscillations. We support our
two-dimensional results by means of numerical simulations and we propose to
test our predictions by experiments on twisted nematic liquid crystals.Comment: 25 RevTeX pages, 7 EPS figures. To be published in Phys. Rev.
Radiative falloff of a scalar field in a weakly curved spacetime without symmetries
We consider a massless scalar field propagating in a weakly curved spacetime
whose metric is a solution to the linearized Einstein field equations. The
spacetime is assumed to be stationary and asymptotically flat, but no other
symmetries are imposed -- the spacetime can rotate and deviate strongly from
spherical symmetry. We prove that the late-time behavior of the scalar field is
identical to what it would be in a spherically-symmetric spacetime: it decays
in time according to an inverse power-law, with a power determined by the
angular profile of the initial wave packet (Price falloff theorem). The field's
late-time dynamics is insensitive to the nonspherical aspects of the metric,
and it is governed entirely by the spacetime's total gravitational mass; other
multipole moments, and in particular the spacetime's total angular momentum, do
not enter in the description of the field's late-time behavior. This extended
formulation of Price's falloff theorem appears to be at odds with previous
studies of radiative decay in the spacetime of a Kerr black hole. We show,
however, that the contradiction is only apparent, and that it is largely an
artifact of the Boyer-Lindquist coordinates adopted in these studies.Comment: 17 pages, RevTeX
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