2,907 research outputs found
Can a falling tree make a noise in two forests at the same time?
It is a commonplace to claim that quantum mechanics supports the old idea
that a tree falling in a forest makes no sound unless there is a listener
present. In fact, this conclusion is far from obvious. Furthermore, if a
tunnelling particle is observed in the barrier region, it collapses to a state
in which it is no longer tunnelling. Does this imply that while tunnelling, the
particle can not have any physical effects? I argue that this is not the case,
and moreover, speculate that it may be possible for a particle to have effects
on two spacelike separate apparatuses simultaneously. I discuss the measurable
consequences of such a feat, and speculate about possible statistical tests
which could distinguish this view of quantum mechanics from a ``corpuscular''
one. Brief remarks are made about an experiment underway at Toronto to
investigate these issues.Comment: 9 pp, Latex, 3 figs, to appear in Proc. Obsc. Unr. Conf.; Fig 2
postscript repaired on 26.10.9
Quantum correlations versus Multisimultaneity: an experimental test
Multisimultaneity is a causal model of relativistic quantum physics which
assigns a real time ordering to any set of events, much in the spirit of the
pilot-wave picture. Contrary to standard quantum mechanics, it predicts a
disappearance of the correlations in a Bell-type experiment when both analysers
are in relative motion such that, each one in its own inertial reference frame,
is first to select the output of the photons. We tested this prediction using
acousto-optic modulators as moving beam-splitters and interferometers separated
by 55 m. We didn't observe any disappearance of the correlations, thus refuting
Multisimultaneity.Comment: 4 pages, 3 figures, RevTex 4 versio
Negative group delay for Dirac particles traveling through a potential well
The properties of group delay for Dirac particles traveling through a
potential well are investigated. A necessary condition is put forward for the
group delay to be negative. It is shown that this negative group delay is
closely related to its anomalous dependence on the width of the potential well.
In order to demonstrate the validity of stationary-phase approach, numerical
simulations are made for Gaussian-shaped temporal wave packets. A restriction
to the potential-well's width is obtained that is necessary for the wave packet
to remain distortionless in the travelling. Numerical comparison shows that the
relativistic group delay is larger than its corresponding non-relativistic one.Comment: 10 pages, 5 figure
Multibarrier tunneling
We study the tunneling through an arbitrary number of finite rectangular
opaque barriers and generalize earlier results by showing that the total
tunneling phase time depends neither on the barrier thickness nor on the
inter-barrier separation. We also predict two novel peculiar features of the
system considered, namely the independence of the transit time (for non
resonant tunneling) and the resonant frequency on the number of barriers
crossed, which can be directly tested in photonic experiments. A thorough
analysis of the role played by inter-barrier multiple reflections and a
physical interpretation of the results obtained is reported, showing that
multibarrier tunneling is a highly non-local phenomenon.Comment: RevTex, 7 pages, 1 eps figur
On a universal photonic tunnelling time
We consider photonic tunnelling through evanescent regions and obtain general
analytic expressions for the transit (phase) time (in the opaque barrier
limit) in order to study the recently proposed ``universality'' property
according to which is given by the reciprocal of the photon frequency.
We consider different physical phenomena (corresponding to performed
experiments) and show that such a property is only an approximation. In
particular we find that the ``correction'' factor is a constant term for total
internal reflection and quarter-wave photonic bandgap, while it is
frequency-dependent in the case of undersized waveguide and distributed Bragg
reflector. The comparison of our predictions with the experimental results
shows quite a good agreement with observations and reveals the range of
applicability of the approximated ``universality'' property.Comment: RevTeX, 8 pages, 4 figures, 1 table; subsection added with a new
experiment analyzed, some other minor change
Possibility of the tunneling time determination
We show that it is impossible to determine the time a tunneling particle
spends under the barrier. However, it is possible to determine the asymptotic
time, i.e., the time the particle spends in a large area including the barrier.
We propose a model of time measurements. The model provides a procedure for
calculation of the asymptotic tunneling and reflection times. The model also
demonstrates the impossibility of determination of the time the tunneling
particle spends under the barrier. Examples for delta-form and rectangular
barrier illustrate the obtained results.Comment: 8 figure
Tunneling Violates Special Relativity
Experiments with evanescent modes and tunneling particles have shown that i)
their signal velocity may be faster than light, ii) they are described by
virtual particles, iii) they are nonlocal and act at a distance, iv)
experimental tunneling data of phonons, photons, and electrons display a
universal scattering time at the tunneling barrier front, and v) the properties
of evanescent, i.e. tunneling modes is not compatible with the special theory
of relativity
Transverse Fresnel-Fizeau drag effects in strongly dispersive media
A light beam normally incident upon an uniformly moving dielectric medium is
in general subject to bendings due to a transverse Fresnel-Fizeau light drag
effect. In conventional dielectrics, the magnitude of this bending effect is
very small and hard to detect. Yet, it can be dramatically enhanced in strongly
dispersive media where slow group velocities in the m/s range have been
recently observed taking advantage of the electromagnetically induced
transparency (EIT) effect. In addition to the usual downstream drag that takes
place for positive group velocities, we predict a significant anomalous
upstream drag to occur for small and negative group velocities. Furthermore,
for sufficiently fast speeds of the medium, higher order dispersion terms are
found to play an important role and to be responsible for peculiar effects such
as light propagation along curved paths and the restoration of the spatial
coherence of an incident noisy beam. The physics underlying this new class of
slow-light effects is thoroughly discussed
Childhood adversity, mental ill-health and aggressive behavior in an African orphanage: Changes in response to trauma-focused therapy and the implementation of a new instructional system
<p>Abstract</p> <p>Background</p> <p>The number of orphans in Sub-Saharan Africa is constantly rising. While it is known that family or community care is preferable over institutional care of African orphans, little is known about the quality of care in orphanages and possibilities of improvement.</p> <p>Study 1</p> <p>Methods</p> <p>Exposure to traumatic stress, experiences of violence in the home, school and orphanage, as well as mental ill-health and aggression of 38 children (mean age of <it>M </it>= 8.64 years) living in an orphanage in rural Tanzania were assessed at two time points. The severity of post-traumatic stress disorder symptoms (PTSD), depressive symptoms, and internalizing and externalizing problems were used as indicators of mental ill-health.</p> <p>Results</p> <p>Violence experienced in the orphanage correlated more strongly with all indicators of mental ill-health than violence in the former home, school or neighborhood at time point 1. Additionally, violence experienced in the orphanage had a positive relationship with the aggressive behavior of the children at time point 2.</p> <p>Study 2</p> <p>Methods</p> <p>With the help of the pre-post assessment of Study 1, the implementation of a new instructional system and psychotherapeutic treatment (KIDNET) for trauma-related illness were evaluated.</p> <p>Results</p> <p>In response to both, a change in the instructional system and psychotherapeutic treatment of PTSD, a massive decline in experienced violence and in the severity of PTSD-symptoms was found, whereas depressive symptoms and internalizing and externalizing problems exhibited little change.</p> <p>Conclusions</p> <p>These studies show that violence, especially in the orphanage, can severely contribute to mental ill-health in orphans and that mental health can be improved by implementing a new instructional system and psychotherapeutic treatment in an orphanage. Moreover, the results indicate that the experience of violence in an orphanage also plays a crucial role in aggressive behavior of the orphans.</p
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