3,011 research outputs found
Information and communication in polygon theories
Generalized probabilistic theories (GPT) provide a framework in which one can
formulate physical theories that includes classical and quantum theories, but
also many other alternative theories. In order to compare different GPTs, we
advocate an approach in which one views a state in a GPT as a resource, and
quantifies the cost of interconverting between different such resources. We
illustrate this approach on polygon theories (Janotta et al. New J. Phys 13,
063024, 2011) that interpolate (as the number n of edges of the polygon
increases) between a classical trit (when n=3) and a real quantum bit (when
n=infinity). Our main results are that simulating the transmission of a single
n-gon state requires more than one qubit, or more than log(log(n)) bits, and
that n-gon states with n odd cannot be simulated by n'-gon states with n' even
(for all n,n'). These results are obtained by showing that the classical
capacity of a single n-gon state with n even is 1 bit, whereas it is larger
than 1 bit when n is odd; by showing that transmitting a single n-gon state
with n even violates information causality; and by showing studying the
communication complexity cost of the nondeterministic not equal function using
n-gon states.Comment: 18 page
Polarization enhancement in two- and three-component ferroelectric superlattices
Composition-dependent structural and polar properties of epitaxial
short-period CaTiO_3/SrTiO_3/BaTiO_3 superlattices grown on a SrTiO_3 substrate
are investigated with first-principles density-functional theory computational
techniques. Polarization enhancement with respect to bulk tetragonal BaTiO_3 is
found for two- and three-component superlattices with a BaTiO_3 concentration
of more than 30%. Individual BaTiO_3 layer thickness is identified as an
important factor governing the polarization improvement. In addition, the
degree of inversion-symmetry breaking in three-component superlattices can be
controlled by varying the thicknesses of the component layers. The flexibility
allowed within this large family of structures makes them highly suitable for
various applications in modern nano-electro-mechanical devices.Comment: The following article has been submitted to Applied Physics Letters.
After it is published, it will be found at http://apl.aip.org
Elasto-buoyant heavy spheres: a unique way to test non-linear elasticity
Extra-large deformations in ultra-soft elastic materials are ubiquitous, yet
systematic studies and methods to understand the mechanics of such huge strains
are lacking. Here we investigate this complex problem systematically with a
simple experiment: by introducing a heavy bead of radius in an
incompressible ultra-soft elastic medium. We find a scaling law for the
penetration depth () of the bead inside the softest gels as . While this result is inconsistent with an ideal neo-Hookean
model of elastic deformation, according to which the displacement fields must
diverge, it is vindicated by an original asymptotic analytic model developed in
this article. This model demonstrates that the observed relationship is
precisely at the demarcating boundary of what would be required for the field
variables to either diverge or converge. This correspondence between a unique
mathematical prediction and the experimental observation ushers in new insights
into the behavior of the deformations of strongly non-linear materials
Comment on "Demonstration of the Casimir Force in the 0.6 to 6 micrometer Range"
We comment on a recently published measurement of the Casimir force for
distances in the 0.6 to 6 micrometer range between two Au surfaces (Phys. Rev.
Lett. 78, 5(1997)) and the net discrepancy reported for the comparison with
theoretical predictions (Phys. Rev. Lett. 81, 5475 (1998)).Comment: 1 page, LaTeX, 2 encapsulated postscript figure
Network perspectives on epilepsy using EEG/MEG source connectivity
The evolution of EEG/MEG source connectivity is both, a promising, and controversial advance in the characterization of epileptic brain activity. In this narrative review we elucidate the potential of this technology to provide an intuitive view of the epileptic network at its origin, the different brain regions involved in the epilepsy, without the limitation of electrodes at the scalp level. Several studies have confirmed the added value of using source connectivity to localize the seizure onset zone and irritative zone or to quantify the propagation of epileptic activity over time. It has been shown in pilot studies that source connectivity has the potential to obtain prognostic correlates, to assist in the diagnosis of the epilepsy type even in the absence of visually noticeable epileptic activity in the EEG/MEG, and to predict treatment outcome. Nevertheless, prospective validation studies in large and heterogeneous patient cohorts are still lacking and are needed to bring these techniques into clinical use. Moreover, the methodological approach is challenging, with several poorly examined parameters that most likely impact the resulting network patterns. These fundamental challenges affect all potential applications of EEG/MEG source connectivity analysis, be it in a resting, spiking, or ictal state, and also its application to cognitive activation of the eloquent area in presurgical evaluation. However, such method can allow unique insights into physiological and pathological brain functions and have great potential in (clinical) neuroscience
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