5,317 research outputs found
The clock paradox in a static homogeneous gravitational field
The gedanken experiment of the clock paradox is solved exactly using the
general relativistic equations for a static homogeneous gravitational field. We
demonstrate that the general and special relativistic clock paradox solutions
are identical and in particular that they are identical for finite
acceleration. Practical expressions are obtained for proper time and coordinate
time by using the destination distance as the key observable parameter. This
solution provides a formal demonstration of the identity between the special
and general relativistic clock paradox with finite acceleration and where
proper time is assumed to be the same in both formalisms. By solving the
equations of motion for a freely falling clock in a static homogeneous field
elapsed times are calculated for realistic journeys to the stars.Comment: Revision: Posted with the caption included with the figure
The narrative potential of the British Birth Cohort Studies
This paper draws attention to the narrative potential of longitudinal studies such as the British Birth Cohort Studies (BBCS), and explores the possibility of creating narrative case histories and conducting narrative analysis based on information available from the studies. The BBCS have historically adopted a quantitative research design and used structured interviews and questionnaires to collect data from large samples of individuals born in specific years. However, the longitudinal nature of these studies means that they follow the same sample of individuals from birth through childhood into adult life, and this leads to the creation of data that can be understood as a quantitative auto/biography
Strain dependence of bonding and hybridization across the metal-insulator transition of VO2
Soft x-ray spectroscopy is used to investigate the strain dependence of the
metal-insulator transition of VO2. Changes in the strength of the V 3d - O 2p
hybridization are observed across the transition, and are linked to the
structural distortion. Furthermore, although the V-V dimerization is
well-described by dynamical mean-field theory, the V-O hybridization is found
to have an unexpectedly strong dependence on strain that is not predicted by
band theory, emphasizing the relevance of the O ion to the physics of VO2
Bremsstrahlung in Alpha-Decay
We present the first fully quantum mechanical calculation of photon radiation
accompanying charged particle decay from a barrier resonance. The soft-photon
limit agrees with the classical results, but differences appear at
next-to-leading-order. Under the conditions of alpha-decay of heavy nuclei, the
main contribution to the photon emission stems from Coulomb acceleration and
may be computed analytically. We find only a small contribution from the
tunneling wave function under the barrier.Comment: 12 pages, 2 Postscript figure
Photoemission evidence for crossover from Peierls-like to Mott-like transition in highly strained VO
We present a spectroscopic study that reveals that the metal-insulator
transition of strained VO thin films may be driven towards a purely
electronic transition, which does not rely on the Peierls dimerization, by the
application of mechanical strain. Comparison with a moderately strained system,
which does involve the lattice, demonstrates the crossover from Peierls- to
Mott-like transitions
Eulerian simulation of the fluid dynamics of helicopter brownout
A computational model is presented that can be used to simulate the development of the dust cloud
that can be entrained into the air when a helicopter is operated close to the ground in desert or dusty
conditions. The physics of this problem, and the associated pathological condition known as âbrownoutâ
where the pilot loses situational awareness as a result of his vision being occluded by dust suspended in the
flow around the helicopter, is acknowledged to be very complex. The approach advocated here involves
an approximation to the full dynamics of the coupled particulate-air system. Away from the ground, the
model assumes that the suspended particles remain in near equilibrium under the action of aerodynamic
forces. Close to the ground, this model is replaced by an algebraic sublayer model for the saltation and
entrainment process. The origin of the model in the statistical mechanics of a distribution of particles
governed by aerodynamic forces allows the validity of the method to be evaluated in context by comparing
the physical properties of the suspended particulates to the local properties of the flow field surrounding
the helicopter. The model applies in the Eulerian frame of reference of most conventional Computational
Fluid Dynamics codes and has been coupled with Brownâs Vorticity Transport Model. Verification of the
predictions of the coupled model against experimental data for particulate entrainment and transport in
the flow around a model rotor are encouraging. An application of the coupled model to analyzing the
differences in the geometry and extent of the dust clouds that are produced by single main rotor and
tandem-rotor configurations as they decelerate to land has shown that the location of the ground vortex
and the size of any regions of recirculatory flow, should they exist, play a primary role in governing the
extent of the dust cloud that is created by the helicopter
Disordered locality in loop quantum gravity states
We show that loop quantum gravity suffers from a potential problem with
non-locality, coming from a mismatch between micro-locality, as defined by the
combinatorial structures of their microscopic states, and macro-locality,
defined by the metric which emerges from the low energy limit. As a result, the
low energy limit may suffer from a disordered locality characterized by
identifications of far away points. We argue that if such defects in locality
are rare enough they will be difficult to detect.Comment: 11 pages, 4 figures, revision with extended discussion of result
Healthcare worker influenza immunization vaccinate or mask policy: Strategies for cost effective implementation and subsequent reductions in staff absenteeism due to illness
AbstractBackgroundA new policy requiring staff in clinical areas to vaccinate or wear a mask was implemented in British Columbia (BC) in the 2012/13 winter. This review assessed the impact of the policy on absenteeism in health care workers.MethodsA retrospective cohort study of full-time HCW that worked prior to and during the 2012/13 influenza season in a health authority in BC. The rate of absenteeism due to all cause illness was compared between vaccinated and unvaccinated staff controlling for behaviors outside influenza season.ResultsOf the 10079 HCW, 77% were vaccinated. By comparison to absenteeism rates in the pre-influenza season, unvaccinated staff in winter had twice the increase in absenteeism due to all-cause illness than vaccinated staff.ConclusionAfter controlling for baseline differences between those vaccinated and unvaccinated, influenza vaccination was associated with reduced absenteeism, saving the Health Authority substantial money. Having regular staff in attendance increases the quality of care
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