6,207 research outputs found
Nanomechanics of a Hydrogen Molecule Suspended between Two Equally Charged Tips
Geometric configuration and energy of a hydrogen molecule centered between
two point-shaped tips of equal charge are calculated with the variational
quantum Monte-Carlo (QMC) method without the restriction of the
Born-Oppenheimer (BO) approximation. Ground state nuclear distribution,
stability, and low vibrational excitation are investigated. Ground state
results predict significant deviations from the BO treatment that is based on a
potential energy surface (PES) obtained with the same QMC accuracy. The quantum
mechanical distribution of molecular axis direction and bond length at a
sub-nanometer level is fundamental for understanding nanomechanical dynamics
with embedded hydrogen. Because of the tips' arrangement, cylindrical symmetry
yields a uniform azimuthal distribution of the molecular axis vector relative
to the tip-tip axis. With approaching tips towards each other, the QMC sampling
shows an increasing loss of spherical symmetry with the molecular axis still
uniformly distributed over the azimuthal angle but peaked at the tip-tip
direction for negative tip charge while peaked at the equatorial plane for
positive charge. This directional behavior can be switched between both stable
configurations by changing the sign of the tip charge and by controlling the
tip-tip distance. This suggests an application in the field of molecular
machines.Comment: 20 pages, 10 figure
Application-layer Performance Analysis of PRIME in Smart Metering Networks
This paper assesses the performance of actual PRIME v1.3.6 and PRIME v1.4 systems when used for Smart Metering applications. The analysis is performed at the application level using the DLMS/COSEM stack. Hence, it considers performance indicators that are of practical interest for distribution system operators, such as the availability and the average time needed to read the energy load profile of all the meters.
To this end, two test networks with 112 smart meters have been deployed in the laboratory (to ensure the stability of the network). In one of them all the Service Nodes communicate directly with the Base Node, while there exist up to 5 switching levels in the other tested network.
First, the PRIME v1.3.6 system is evaluated, stressing the significant performance gain that can be obtained by implementing some MAC layer strategies, which are compatible with the specification but not specifically defined on it. Then,the improvement offered by the PRIME v1.4 system is assessed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
The complete theory of Maxwell and Proca fields
We present the most general ghost-free classical Lagrangian containing
first-order derivatives and describing interacting real Abelian spin-one fields
on Minkowski spacetime. We study both massive Proca and massless Maxwell fields
and allow for a non-linear realization of mass, in the form of derivative
self-interactions. Within this context, our construction notoriously extends
the existing literature, which is limited to the case of a single Proca field
and to multiple interacting Proca fields in the presence of a global rotational
symmetry. In the limit of a single Proca field, we reproduce the known healthy
interaction terms. We provide the necessary and sufficient conditions to ensure
ghost-freedom in any multi-field setup. We observe that, in general, the said
conditions are not satisfied by the rotationally symmetric multi-Proca
interactions suggested so far, which implies that they propagate ghosts. Our
theory admits a plethora of applications in a wide range of subjects. For
illustrative purposes, we provide concrete proposals in holographic condensed
matter and black hole physics.Comment: 6 pages. v2: References added. v3: Single Proca limit modified. v4:
Journal version. This work is dedicated to Mar\'{i}a Jos\'{e} D\'{i}ez
Segovian
En torno a la lógica de la inferencia
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Realismo selectivo: ¿un programa de investigación regresivo?
El realismo selectivo (RS) es la versión del realismo científico preponderante en nuestros días, y de hecho la única versión del realismo defendible después de las críticas de Laudan basadas en la llamada inducción pesimista. RS sostiene que (i) las predicciones observacionales novedosas (e.g. que la teoría no se ha diseñado con la intención de realizarlas) y exitosas de una teoría se deben a que aquella parte del contenido inobservable de la teoría que es responsable de la predicción exitosa es (aproximadamente) verdadero, y (ii) las teorías posteriores que la suceden retienen (aproximadamente) dicha parte del contenido teórico. RS es una tesis empírica, y por tanto debe ser verificada o falsada por la historia de la ciencia. En este trabajo repasaremos los principales versiones de RS y sus principales anomalías históricas.Universidad de Málaga. Campus de Excelencia Internacional Andalucia Tech
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