1,762 research outputs found
Mental state estimation for brain-computer interfaces
Mental state estimation is potentially useful for the development of asynchronous brain-computer interfaces. In this study, four mental states have been identified and decoded from the electrocorticograms (ECoGs) of six epileptic patients, engaged in a memory reach task. A novel signal analysis technique has been applied to high-dimensional, statistically sparse ECoGs recorded by a large number of electrodes. The strength of the proposed technique lies in its ability to jointly extract spatial and temporal patterns, responsible for encoding mental state differences. As such, the technique offers a systematic way of analyzing the spatiotemporal aspects of brain information processing and may be applicable to a wide range of spatiotemporal neurophysiological signals
Nonequilibrium dressing in a cavity with a movable reflecting mirror
We consider a movable mirror coupled to a one-dimensional massless scalar
field in a cavity. Both the field and the mirror's mechanical degrees of
freedom are described quantum-mechanically, and they can interact each other
via the radiation pressure operator. We investigate the dynamical evolution of
mirror and field starting from a nonequilibrium initial state, and their local
interaction which brings the system to a stationary configuration for long
times. This allows us to study the time-dependent dressing process of the
movable mirror interacting with the field, and its dynamics leading to a local
equilibrium dressed configuration. Also, in order to explore the effect of the
radiation pressure on both sides of the movable mirror, we generalize the
effective field-mirror Hamiltonian and previous results to the case of two
cavities sharing the same mobile boundary. This leads us to address, in the
appropriate limit, the dynamical dressing problem of a single mobile wall,
bounded by a harmonic potential, in the vacuum space.Comment: 10 pages, 4 figure
Tuning the collective decay of two entangled emitters by means of a nearby surface
We consider the radiative properties of a system of two identical correlated
atoms interacting with the electromagnetic field in its vacuum state in the
presence of a generic dielectric environment. We suppose that the two emitters
are prepared in a symmetric or antisymmetric superposition of one ground state
and one excited state and we evaluate the transition rate to the collective
ground state, showing distinctive cooperative radiative features. Using a
macroscopic quantum electrodynamics approach to describe the electromagnetic
field, we first obtain an analytical expression for the decay rate of the two
entangled two-level atoms in terms of the Green's tensor of the generic
external environment. We then investigate the emission process when both atoms
are in free space and subsequently when a perfectly reflecting mirror is
present, showing how the boundary affects the physical features of the
superradiant and subradiant emission by the two coupled emitters. The
possibility to control and tailor radiative processes is also discussed.Comment: 11 pages, 8 figure
Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect
We discuss different physical effects related to the uniform acceleration of
atoms in vacuum, in the framework of quantum electrodynamics. We first
investigate the van der Waals/Casimir-Polder dispersion and resonance
interactions between two uniformly accelerated atoms in vacuum. We show that
the atomic acceleration significantly affects the van der Waals force, yielding
a different scaling of the interaction with the interatomic distance and an
explicit time dependence of the interaction energy. We argue how these results
could allow for an indirect detection of the Unruh effect through dispersion
interactions between atoms. We then consider the resonance interaction between
two accelerated atoms, prepared in a correlated Bell-type state, and
interacting with the electromagnetic field in the vacuum state, separating
vacuum fluctuations and radiation reaction contributions, both in the
free-space and in the presence of a perfectly reflecting plate. We show that
nonthermal effects of acceleration manifest in the resonance interaction,
yielding a change of the distance dependence of the resonance interaction
energy. This suggests that the equivalence between temperature and acceleration
does not apply to all radiative properties of accelerated atoms. To further
explore this aspect, we evaluate the resonance interaction between two atoms in
non inertial motion in the coaccelerated (Rindler) frame and show that in this
case the assumption of an Unruh temperature for the field is not required for a
complete equivalence of locally inertial and coaccelerated points of views.Comment: 8 pages, Proceedings of the Eighth International Workshop DICE 2016
Spacetime - Matter - Quantum Mechanic
Effect of boundaries on vacuum field fluctuations and radiation-mediated interactions between atoms
In this paper we discuss and review several aspects of the effect of boundary
conditions and structured environments on dispersion and resonance interactions
involving atoms or molecules, as well as on vacuum field fluctuations. We first
consider the case of a perfect mirror, which is free to move around an
equilibrium position and whose mechanical degrees of freedom are treated
quantum mechanically. We investigate how the quantum fluctuations of the
mirror's position affect vacuum field fluctuations for both a one-dimensional
scalar and electromagnetic field, showing that the effect is particularly
significant in the proximity of the moving mirror. This result can be also
relevant for possible gravitational effects, since the field energy density
couples to gravity. We stress that this interaction-induced modification of the
vacuum field fluctuations can be probed through the Casimir-Polder interaction
with a polarizable body, thus allowing to detect the effect of the mirror's
quantum position fluctuations. We then consider the effect of an environment
such as an isotropic photonic crystal or a metallic waveguide, on the resonance
interaction between two entangled identical atoms, one excited and the other in
the ground state. We discuss the strong dependence of the resonance interaction
with the relative position of the atomic transition frequency with the gap of
the photonic crystal in the former case, and with the cut-off frequency of
waveguide in the latter.Comment: 8 pages, 2 figures, Proceedings of the Eighth International Workshop
DICE 2016 Spacetime - Matter - Quantum Mechanic
Gender in the Construction Industry: Literature Review and Comparative Survey of Men’s and Women’s Perceptions in UK Construction Consultancies
For more than two decades, construction industry leaders have made attempts to attract more women into professional roles to ease skills shortages and diversify the workforce. However, the number of women working in the industry has not improved significantly. This paper reviews previous literature on gender diversity in the construction industry and disseminates findings from a survey that investigated whether there are significant differences in self-perception between men and women in construction consultancies operating in the United Kingdom (UK). The survey questionnaire was completed by 60 men and 57 women. Analysis of the results confirmed that women tend to follow “zig-zag” career development paths and that “global self-worth” of women over the age of 40 is the lowest among all ages. However, little variation was found on initiatives to improve retention of women in construction consultancies. The results reveal that both men and women regarded improved flexible working-arrangements, transparent promotion criteria, return-to-work training, and outreach programs to schools the most crucial initiatives to retain women. This reinforces the call for organizations to introduce innovative strategic plans to change the masculine culture of the construction profession and modernize working practice away from the existing rather outdated traditional structure
Field fluctuations near a conducting plate and Casimir-Polder forces in the presence of boundary conditions
We consider vacuum fluctuations of the quantum electromagnetic field in the
presence of an infinite and perfectly conducting plate. We evaluate how the
change of vacuum fluctuations due to the plate modifies the Casimir-Polder
potential between two atoms placed near the plate. We use two different methods
to evaluate the Casimir-Polder potential in the presence of the plate. They
also give new insights on the role of boundary conditions in the Casimir-Polder
interatomic potential, as well as indications for possible generalizations to
more complicated boundary conditions.Comment: 10 page
Testing the gamma-ray burst variability/peak luminosity correlation on a Swift homogeneous sample
We test the gamma-ray burst correlation between temporal variability and peak
luminosity of the -ray profile on a homogeneous sample of 36 Swift/BAT
GRBs with firm redshift determination. This is the first time that this
correlation can be tested on a homogeneous data sample. The correlation is
confirmed, as long as the 6 GRBs with low luminosity (<5x10^{50} erg s^{-1} in
the rest-frame 100-1000 keV energy band) are ignored. We confirm that the
considerable scatter of the correlation already known is not due to the
combination of data from different instruments with different energy bands, but
it is intrinsic to the correlation itself. Thanks to the unprecedented
sensitivity of Swift/BAT, the variability/peak luminosity correlation is tested
on low-luminosity GRBs. Our results show that these GRBs are definite outliers.Comment: Accepted for Publication in MNRAS. 10 pages, 5 figures, 3 table
Field observables near a fluctuating boundary
We review several aspects related to the confinement of a massless scalar field in a cavity with a movable conducting wall of finite mass, free to move around its equilibrium position to which it is bound by a harmonic potential, and whose mechanical degrees of freedom are described quantum mechanically. This system, for small displacements of the movable wall from its equilibrium position, can be described by an e↵ective interaction Hamiltonian between the field and the mirror, quadratic in the field operators and linear in the mirror operators. In the interacting, i.e. dressed, ground state, we first consider local field observables such as the field energy density: we evaluate changes of the field energy density in the cavity with the movable wall with respect to the case of a fixed wall, and corrections to the usual Casimir forces between the two walls. We then investigate the case of two one-dimensional cavities separated by a movable wall of finite mass, with two massless scalar fields defined in the two cavities. We show that in this case correlations between the squared fields in the two cavities exist, mediated by the movable wall, at variance with the fixed-wall case
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