2,315 research outputs found
Coexistence of Quantum Theory and Special Relativity in signaling scenarios
The coexistence between Quantum Mechanics and Special Relativity is usually
formulated in terms of the no-signaling condition. Several authors have even
suggested that this condition should be included between the basic postulates
of Quantum Theory. However, there are several scenarios where signaling is, in
principle, possible: based on previous results and the analysis of the relation
between unitarity and signaling we present an example of a two-particle
interferometric arrangement for which the dynamics is, in principle, compatible
with superluminal transmission of information. This type of non-locality is not
in the line of Bell's theorem, but closer in spirit to the one-particle
acausality studied by Hegerfeldt and others. We analyze in this paper the
meaning of this non-locality and how to preserve the coexistence of the two
fundamental theories in this signaling scenario.Comment: See also the comment by G C Hegerfeldt in the online version of the
journal, including more reference
Self-sustained spatiotemporal oscillations induced by membrane-bulk coupling
We propose a novel mechanism leading to spatiotemporal oscillations in
extended systems that does not rely on local bulk instabilities. Instead,
oscillations arise from the interaction of two subsystems of different spatial
dimensionality. Specifically, we show that coupling a passive diffusive bulk of
dimension d with an excitable membrane of dimension d-1 produces a
self-sustained oscillatory behavior. An analytical explanation of the
phenomenon is provided for d=1. Moreover, in-phase and anti-phase
synchronization of oscillations are found numerically in one and two
dimensions. This novel dynamic instability could be used by biological systems
such as cells, where the dynamics on the cellular membrane is necessarily
different from that of the cytoplasmic bulk.Comment: Accepted for publication in Physical Review Letter
First Principles Studies on 3-Dimentional Strong Topological Insulators: Bi2Te3, Bi2Se3 and Sb2Te3
Bi2Se3, Bi2Te3 and Sb2Te3 compounds are recently predicted to be
3-dimentional (3D) strong topological insulators. In this paper, based on
ab-initio calculations, we study in detail the topological nature and the
surface states of this family compounds. The penetration depth and the
spin-resolved Fermi surfaces of the surface states will be analyzed. We will
also present an procedure, from which highly accurate effective Hamiltonian can
be constructed, based on projected atomic Wannier functions (which keep the
symmetries of the systems). Such Hamiltonian can be used to study the
semi-infinite systems or slab type supercells efficiently. Finally, we discuss
the 3D topological phase transition in Sb2(Te1-xSex)3 alloy system.Comment: 8 pages,17 figure
Diet of three large pelagic fishes associated with drifting fish aggregating devices (DFADs) in the western equatorial Indian Ocean
Dieta de tres peces pelágicos de gran tamaño asociados a agregaciones de peces bajo objetos flotantes (DFADs) en el Océano Índico ecuatorial occidental
Los objetos flotantes congregan distintas especies de peces en aguas tropicales marinas. Se capturaron tres especies depredadoras: atún de aleta amarilla (Thunnus albacares), petos (Acanthocybium solandri) y llampugas (Coryphaena hippurus) en agregaciones bajo objetos flotantes en el Océano Índico occidental, para caracterizar su dieta y determinar si se alimentan de organismos asociados a las DFADs. Los atunes de aleta amarilla no se alimentaron de presas asociadas a objetos flotantes, mientras los petos y llampugas sí explotaron los recursos agregados a estos objetos flotantes, aunque predominantemente se alimentaron de otros organismos no asociados a ellos. En atunes de aleta amarilla y en llampugas asociados a FADs se observó una predación oportunista en la superficie de agrupaciones de crustáceos estomatópodos pero no así en los petos.
Palabras clave: Dispositivos agregadores de peces, Atún de aleta amarilla, Llampuga, Peto, Contenidos estomacales, Dieta.Several species of fish, aggregate around DFADs in marine tropical waters. We captured three predatory species: yellow fin tuna (Thunnus albacares), wahoo (Acanthocybium solandri) and dolphinfish (Coryphaena hippurus) from aggregations under DFADs in the Western Indian Ocean to characterize their diet and determine whether they fed on other DFAD associated organisms. Yellowfin tuna did not feed on DFAD–associated prey, while wahoo and dolphinfish did exploit resources aggregated by the DFADs, though they predominantly fed on other non–associated organisms. Opportunistic feeding on surface swarming stomatopod crustaceans was observed in yellowfin tuna and dolphinfish associated with FADs, but was not observed in wahoo.
Key words: FAD, Yellowfin tuna, Dolphinfish, Wahoo, Stomach contents, Diet.Dieta de tres peces pelágicos de gran tamaño asociados a agregaciones de peces bajo objetos flotantes (DFADs) en el Océano Índico ecuatorial occidental
Los objetos flotantes congregan distintas especies de peces en aguas tropicales marinas. Se capturaron tres especies depredadoras: atún de aleta amarilla (Thunnus albacares), petos (Acanthocybium solandri) y llampugas (Coryphaena hippurus) en agregaciones bajo objetos flotantes en el Océano Índico occidental, para caracterizar su dieta y determinar si se alimentan de organismos asociados a las DFADs. Los atunes de aleta amarilla no se alimentaron de presas asociadas a objetos flotantes, mientras los petos y llampugas sí explotaron los recursos agregados a estos objetos flotantes, aunque predominantemente se alimentaron de otros organismos no asociados a ellos. En atunes de aleta amarilla y en llampugas asociados a FADs se observó una predación oportunista en la superficie de agrupaciones de crustáceos estomatópodos pero no así en los petos.
Palabras clave: Dispositivos agregadores de peces, Atún de aleta amarilla, Llampuga, Peto, Contenidos estomacales, Dieta
From subdiffusion to superdiffusion of particles on solid surfaces
We present a numerical and partially analytical study of classical particles
obeying a Langevin equation that describes diffusion on a surface modeled by a
two dimensional potential. The potential may be either periodic or random.
Depending on the potential and the damping, we observe superdiffusion,
large-step diffusion, diffusion, and subdiffusion. Superdiffusive behavior is
associated with low damping and is in most cases transient, albeit often long.
Subdiffusive behavior is associated with highly damped particles in random
potentials. In some cases subdiffusive behavior persists over our entire
simulation and may be characterized as metastable. In any case, we stress that
this rich variety of behaviors emerges naturally from an ordinary Langevin
equation for a system described by ordinary canonical Maxwell-Boltzmann
statistics
Speeding chemical reactions by focusing
We present numerical results for a chemical reaction of colloidal particles which are transported by
a laminar fluid and are focused by periodic obstacles in such a way that the two components are well
mixed and consequently the chemical reaction is speeded up. The roles of the various system param-
eters (diffusion coefficients, reaction rate, and obstacles sizes) are studied. We show that focusing
speeds up the reaction from the diffusion limited rate, ~t-1/2 to very close to the perfect mixing rate,
~t1/2~t-1Postprint (published version
Hole Pairs in the Two-Dimensional Hubbard Model
The interactions between holes in the Hubbard model, in the low density,
intermediate to strong coupling limit, are investigated. Dressed spin polarons
in neighboring sites have an increased kinetic energy and an enhanced hopping
rate. Both effects are of the order of the hopping integral and lead to an
effective attraction at intermediate couplings. Our results are derived by
systematically improving mean field calculations. The method can also be used
to derive known properties of isolated spin polarons.Comment: 4 page
Diffusion on a solid surface: Anomalous is normal
We present a numerical study of classical particles diffusing on a solid
surface. The particles' motion is modeled by an underdamped Langevin equation
with ordinary thermal noise. The particle-surface interaction is described by a
periodic or a random two dimensional potential. The model leads to a rich
variety of different transport regimes, some of which correspond to anomalous
diffusion such as has recently been observed in experiments and Monte Carlo
simulations. We show that this anomalous behavior is controlled by the friction
coefficient, and stress that it emerges naturally in a system described by
ordinary canonical Maxwell-Boltzmann statistics
Class of self-limiting growth models in the presence of nonlinear diffusion
The source term in a reaction-diffusion system, in general, does not involve
explicit time dependence. A class of self-limiting growth models dealing with
animal and tumor growth and bacterial population in a culture, on the other
hand are described by kinetics with explicit functions of time. We analyze a
reaction-diffusion system to study the propagation of spatial front for these
models.Comment: RevTex, 13 pages, 5 figures. To appear in Physical Review
- …