831 research outputs found
On the Flux-Across-Surfaces Theorem
The quantum probability flux of a particle integrated over time and a distant
surface gives the probability for the particle crossing that surface at some
time. We prove the free Flux-Across-Surfaces Theorem, which was conjectured by
Combes, Newton and Shtokhamer, and which relates the integrated quantum flux to
the usual quantum mechanical formula for the cross section. The integrated
quantum flux is equal to the probability of outward crossings of surfaces by
Bohmian trajectories in the scattering regime.Comment: 13 pages, latex, 1 figure, very minor revisions, to appear in Letters
in Mathematical Physics, Vol. 38, Nr.
Scattering of massive Dirac fields on the Schwarzschild black hole spacetime
With a generally covariant equation of Dirac fields outside a black hole, we
develop a scattering theory for massive Dirac fields. The existence of modified
wave operators at infinity is shown by implementing a time-dependent
logarithmic phase shift from the free dynamics to offset a long-range mass
term. The phase shift we obtain is a matrix operator due to the existence of
both positive and negative energy wave components.Comment: LaTex, 17 page
Ionization of Atoms by Intense Laser Pulses
The process of ionization of a hydrogen atom by a short infrared laser pulse
is studied in the regime of very large pulse intensity, in the dipole
approximation. Let denote the integral of the electric field of the pulse
over time at the location of the atomic nucleus. It is shown that, in the limit
where , the ionization probability approaches unity and the
electron is ejected into a cone opening in the direction of and of
arbitrarily small opening angle. Asymptotics of various physical quantities in
is studied carefully. Our results are in qualitative agreement with
experimental data reported in \cite{1,2}.Comment: 27 pages, 1 figure
Negative workplace behaviour: temporal associations with cardiovascular outcomes and psychological health problems in Australian police
Negative workplace behaviour, such as workplace bullying, is emerging as an important work-related psychosocial hazard with the potential to contribute to employee ill health. We examined the risk of two major health issues (poor mental and cardiovascular health) associated with current and past exposure to negative behaviour in the workplace. Data from 251 police officers, who completed an anonymous mail survey at two time-points spaced 12 months apart, support the potential role of exposure to negative workplace behaviour in the development of physical disease and psychological illness. Specifically, we saw significant effects associated with past exposure to such behaviour on indicators of poor cardiovascular health, and a significant effect of current exposure on the indicator of mental health problems. Our findings reinforce the need to continue to study links between employee health and both negative workplace behaviour and more severe cases of bullying, particularly the mechanisms involved to strengthen theory in this area, and to protect against employee ill health (specifically cardiovascular outcomes and psychological problems) by preventing negative behaviour at work. Copyright (C) 2010 John Wiley & Sons, Ltd
Integrating psychosocial safety climate in the JD-R model: a study amongst Malaysian workers
ORIENTATION: Job characteristics are well accepted as sources of burnout and engagement amongst employees; psychosocial safety climate may precede work conditions. RESEARCH PURPOSE: We expanded the Job Demands and Resources (JD-R) model by proposing psychosocial safety climate (PSC) as a precursor to job demands and job resources. As PSC theoretically influences the working environment, the study hypothesized that PSC has an impact on performance via both health erosion (i.e. burnout) and motivational pathways (i.e. work engagement). MOTIVATION FOR THE STUDY: So far, integration of PSC in the JD-R model is only tested in a Western context (i.e. Australia). We tested the emerging construct of PSC in Malaysia, an Eastern developing country in the Asian region. RESEARCH DESIGN, APPROACH AND METHOD: A random population based sample was derived using household maps provided by Department of Statistics, Malaysia; 291 employees (response rate 50.52%) from the State of Selangor, Malaysia participated. Cross-sectional data were analysed using structural equation modelling. MAIN FINDINGS: We found that PSC was negatively related to job demands and positively related to job resources. Job demands, in turn, predicted burnout (i.e. exhaustion and cynicism), whereas job resources predicted engagement. Both burnout and engagement were associated with performance. Bootstrapping showed significant indirect effects of PSC on burnout via job demands, PSC on performance via burnout and PSC on performance via the resources-engagement pathway. PRACTICAL/MANAGERIAL IMPLICATIONS: Our findings are consistent with previous research that suggests that PSC should be a target to improve working conditions and in turn reduce burnout and improve engagement and productivity. CONTRIBUTION/VALUE-ADD: These findings suggest that JD-R theory may be expanded to include PSC as an antecedent and that the expanded JD-R model is largely valid in an Eastern, developing economy setting.Mohd A. Idris, Maureen F. Dollard and Anthony H. Winefiel
Scattering into Cones and Flux across Surfaces in Quantum Mechanics: a Pathwise Probabilistic Approach
We show how the scattering-into-cones and flux-across-surfaces theorems in
Quantum Mechanics have very intuitive pathwise probabilistic versions based on
some results by Carlen about large time behaviour of paths of Nelson
diffusions. The quantum mechanical results can be then recovered by taking
expectations in our pathwise statements.Comment: To appear in Journal of Mathematical Physic
Scattering theory for arbitrary potentials
The fundamental quantities of potential scattering theory are generalized to
accommodate long-range interactions. New definitions for the scattering
amplitude and wave operators valid for arbitrary interactions including
potentials with a Coulomb tail are presented. It is shown that for the Coulomb
potential the generalized amplitude gives the physical on-shell amplitude
without recourse to a renormalization procedure.Comment: To be published in Phys Rev
Tunneling times with covariant measurements
We consider the time delay of massive, non-relativistic, one-dimensional
particles due to a tunneling potential. In this setting the well-known Hartman
effect asserts that often the sub-ensemble of particles going through the
tunnel seems to cross the tunnel region instantaneously. An obstacle to the
utilization of this effect for getting faster signals is the exponential
damping by the tunnel, so there seems to be a trade-off between speedup and
intensity. In this paper we prove that this trade-off is never in favor of
faster signals: the probability for a signal to reach its destination before
some deadline is always reduced by the tunnel, for arbitrary incoming states,
arbitrary positive and compactly supported tunnel potentials, and arbitrary
detectors. More specifically, we show this for several different ways to define
``the same incoming state'' and ''the same detector'' when comparing the
settings with and without tunnel potential. The arrival time measurements are
expressed in the time-covariant approach, but we also allow the detection to be
a localization measurement at a later time.Comment: 12 pages, 2 figure
A powerful intervention: general practitioners' use of sickness certification in depression
<b>Background</b> Depression is frequently cited as the reason for sickness absence, and it is estimated that sickness certificates are issued in one third of consultations for depression. Previous research has considered GP views of sickness certification but not specifically in relation to depression. This study aimed to explore GPs views of sickness certification in relation to depression.<p></p>
<b>Methods</b> A purposive sample of GP practices across Scotland was selected to reflect variations in levels of incapacity claimants and antidepressant prescribing. Qualitative interviews were carried out between 2008 and 2009.<p></p>
<b>Results</b> A total of 30 GPs were interviewed. A number of common themes emerged including the perceived importance of GP advocacy on behalf of their patients, the tensions between stakeholders involved in the sickness certification system, the need to respond flexibly to patients who present with depression and the therapeutic nature of time away from work as well as the benefits of work. GPs reported that most patients with depression returned to work after a short period of absence and that it was often difficult to predict which patients would struggle to return to work.<p></p>
<b>Conclusions</b>
GPs reported that dealing with sickness certification and depression presents distinct challenges. Sickness certificates are often viewed as powerful interventions, the effectiveness of time away from work for those with depression should be subject to robust enquiry
Fermi-Walker gauge in 2+1 dimensional gravity.
It is shown that the Fermi-Walker gauge allows the general solution of
determining the metric given the sources, in terms of simple quadratures. We
treat the general stationary problem providing explicit solving formulas for
the metric and explicit support conditions for the energy momentum tensor. The
same type of solution is obtained for the time dependent problem with circular
symmetry. In both cases the solutions are classified in terms of the invariants
of the Wilson loops outside the sources. The Fermi-Walker gauge, due to its
physical nature, allows to exploit the weak energy condition and in this
connection it is proved that, both for open and closed universes with
rotational invariance, the energy condition imply the total absence of closed
time like curves. The extension of this theorem to the general stationary
problem, in absence of rotational symmetry is considered. At present such
extension is subject to some assumptions on the behavior of the determinant of
the dreibein in this gauge. PACS number: 0420Comment: 28 pages, RevTex, no figure
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