2,671 research outputs found
Thermal Excitation of Broadband and Long-range Surface Waves on SiO 2 Submicron Films
We detect thermally excited surfaces waves on a submicron SiO 2 layer,
including Zenneck and guided modes in addition to Surface Phonon Polaritons.
The measurements show the existence of these hybrid thermal-electromagnetic
waves from near-(2.7 m) to far-(11.2 m) infrared. Their propagation
distances reach values on the order of the millimeter, several orders of
magnitude larger than on semi-infinite systems. These two features, spectral
broadness and long range propagation, make these waves good candidates for
near-field applications both in optics and thermics due to their dual nature.Comment: Applied Physics Letters, American Institute of Physics, 201
Dynamics for a 2-vertex Quantum Gravity Model
We use the recently introduced U(N) framework for loop quantum gravity to
study the dynamics of spin network states on the simplest class of graphs: two
vertices linked with an arbitrary number N of edges. Such graphs represent two
regions, in and out, separated by a boundary surface. We study the algebraic
structure of the Hilbert space of spin networks from the U(N) perspective. In
particular, we describe the algebra of operators acting on that space and
discuss their relation to the standard holonomy operator of loop quantum
gravity. Furthermore, we show that it is possible to make the restriction to
the isotropic/homogeneous sector of the model by imposing the invariance under
a global U(N) symmetry. We then propose a U(N) invariant Hamiltonian operator
and study the induced dynamics. Finally, we explore the analogies between this
model and loop quantum cosmology and sketch some possible generalizations of
it.Comment: 28 pages, v2: typos correcte
Ab Initio Molecular Dynamics on the Electronic Boltzmann Equilibrium Distribution
We prove that for a combined system of classical and quantum particles, it is
possible to write a dynamics for the classical particles that incorporates in a
natural way the Boltzmann equilibrium population for the quantum subsystem. In
addition, these molecular dynamics do not need to assume that the electrons
immediately follow the nuclear motion (in contrast to any adiabatic approach),
and do not present problems in the presence of crossing points between
different potential energy surfaces (conical intersections or spin-crossings).
A practical application of this molecular dynamics to study the effect of
temperature in molecular systems presenting (nearly) degenerate states - such
as the avoided crossing in the ring-closure process of ozone - is presented.Comment: published in New J. Phy
Seed dormancy responses to temperature relate to Nothofagus species distribution and determine temporal patterns of germination across altitudes in Patagonia
507-520. Seeds integrate environmental cues that modulate their dormancy and germination. Although many mechanisms have been identified in laboratory experiments, their contribution to germination dynamics in existing communities and their involvement in defining species habitats remain elusive. . By coupling mathematical models with ecological data we investigated the contribution of seed temperature responses to the dynamics of germination of three Nothofagus species that are sharply distributed across different altitudes in the Patagonian Andes. . Seed responsiveness to temperature of the three Nothofagus species was linked to the thermal characteristics of their preferred ecological niche. In their natural distribution range, there was overlap in the timing of germination of the species, which was restricted to mid - spring. By contrast, outside their species distribution range, germination was temporally uncoupled with altitude. This phenomenon was described mathematically by the interplay between interspecific differences in seed population thermal parameters and the range in soil thermic environments across different altitudes. . The observed interspecific variations in seed responsiveness to temperature and its environmental regulation, constitute a major determinant of the dynamics of Nothofagus germination across elevations. This phenomenon likely contributes to the maintenance of patterns of species abundance across altitude by placing germinated seeds in a favorable environment for plant growth
Revisiting the Simplicity Constraints and Coherent Intertwiners
In the context of loop quantum gravity and spinfoam models, the simplicity
constraints are essential in that they allow to write general relativity as a
constrained topological BF theory. In this work, we apply the recently
developed U(N) framework for SU(2) intertwiners to the issue of imposing the
simplicity constraints to spin network states. More particularly, we focus on
solving them on individual intertwiners in the 4d Euclidean theory. We review
the standard way of solving the simplicity constraints using coherent
intertwiners and we explain how these fit within the U(N) framework. Then we
show how these constraints can be written as a closed u(N) algebra and we
propose a set of U(N) coherent states that solves all the simplicity
constraints weakly for an arbitrary Immirzi parameter.Comment: 28 page
Development methodology to share vehicles optimizing the variability of the mileage
A simulation is a tool used to visualize the behaviors of a system, which will later help make decisions regarding how to handle the variables involved in the system, as well as the specific changes that have to be made. This study shows a case of vehicle allocation for different people within a company, evaluating methodologies, vehicle rotation to reduce the variance of the mileage and eliminating penalties with rental agencies for exceeding the permitted mileage. The paper shows a literature review of allocation models and similar studies, and later displays a detailed description of the problem, the variables that was used, the composition of the simulation and the optimization model that were generated, the results of the simulation, and finally, the findings of the research
- …