1,625 research outputs found
Control of dissipation in superconducting films by magnetic stray fields
Hybrid superconducting/magnetic nanostructures on Si substrates have been
built with identical physical dimensions but different magnetic configurations.
By constructing arrays based on Co-dots with in-plane, out-of-plane, and vortex
state magnetic configurations, the stray fields are systematically tuned.
Dissipation in the mixed state of superconductors can be decreased (increased)
by several orders of magnitude by decreasing (increasing) the stray magnetic
fields. Furthermore, ordering of the stray fields over the entire array helps
to suppress dissipation and enhance commensurability effects increasing the
number of dissipation minima.Comment: 16 pages including 4 figures; accepted in Applied Physics Letter
Searching for the scale of homogeneity
We introduce a statistical quantity, known as the function, related to
the integral of the two--point correlation function. It gives us
straightforward information about the scale where clustering dominates and the
scale at which homogeneity is reached. We evaluate the correlation dimension,
, as the local slope of the log--log plot of the function. We apply
this statistic to several stochastic point fields, to three numerical
simulations describing the distribution of clusters and finally to real galaxy
redshift surveys. Four different galaxy catalogues have been analysed using
this technique: the Center for Astrophysics I, the Perseus--Pisces redshift
surveys (these two lying in our local neighbourhood), the Stromlo--APM and the
1.2 Jy {\it IRAS} redshift surveys (these two encompassing a larger volume). In
all cases, this cumulant quantity shows the fingerprint of the transition to
homogeneity. The reliability of the estimates is clearly demonstrated by the
results from controllable point sets, such as the segment Cox processes. In the
cluster distribution models, as well as in the real galaxy catalogues, we never
see long plateaus when plotting as a function of the scale, leaving no
hope for unbounded fractal distributions.Comment: 9 pages, 11 figures, MNRAS, in press; minor revision and added
reference
Effective penetration length and interstitial vortex pinning in superconducting films with regular arrays of defects
In order to compare magnetic and non-magnetic pinning we have nanostructured
two superconducting films with regular arrays of pinning centers: Cu
(non-magnetic) dots in one case, and Py (magnetic) dots in the other. For low
applied magnetic fields, when all the vortices are pinned in the artificial
inclusions, magnetic dots prove to be better pinning centers, as has been
generally accepted. Unexpectedly, when the magnetic field is increased and
interstitial vortices appear, the results are very different: we show how the
stray field generated by the magnetic dots can produce an effective reduction
of the penetration length. This results in strong consequences in the transport
properties, which, depending on the dot separation, can lead to an enhancement
or worsening of the transport characteristics. Therefore, the election of the
magnetic or non-magnetic character of the pinning sites for an effective
reduction of dissipation will depend on the range of the applied magnetic
field.Comment: 10 pages, 3 figure
Aggregation and Conformance in Differentiated Service Networks: A Case Study
The Differentiated Service (Diff-Serv) architecture [1] advocates a model based on different “granularity” at network edges and within the network. In particular, core routers are only required to act on a few aggregates that are meant to offer a pre-defined set of service levels. The use of aggregation raises a number of questions for end-to-end services, in particular when crossing domain boundaries where policing actions may be applied. This paper focuses on the impact of such policing actions in the context of individual and bulk services built on top of the Expedited Forwarding (EF) [7] per-hop-behavior (PHB). The findings of this investigation confirm and quantify the expected need for reshaping at network boundaries, and identify a number of somewhat unexpected behaviors. Recommendations are also made for when reshaping is not available
Superconducting/magnetic three state nanodevice for memory and reading applications
We present a simple nanodevice that can operate in two modes: i) three-state
memory and ii) reading device. The nanodevice is fabricated with an array of
ordered triangular-shaped nanomagnets embedded in a superconducting thin film.
The input signal is ac current and the output signal is dc voltage. Vortex
ratchet effect in combination with out of plane magnetic anisotropy of the
nanomagnets is the background physics which governs the nanodevice performance.Comment: 10 pages, 4 figure
The PENELOPE Physics Models and Transport Mechanics. Implementation into Geant4
[EN] A translation of the penelope physics subroutines to C++, designed as an extension of the Geant4 toolkit, is presented. The Fortran code system penelope performs Monte Carlo simulation of coupled electron-photon transport in arbitrary materials for a wide energy range, nominally from 50 eV up to 1 GeV. Penelope implements the most reliable interaction models that are currently available, limited only by the required generality of the code. In addition, the transport of electrons and positrons is simulated by means of an elaborate class II scheme in which hard interactions (involving deflection angles or energy transfers larger than pre-defined cutoffs) are simulated from the associated restricted differential cross sections. After a brief description of the interaction models adopted for photons and electrons/positrons, we describe the details of the class-II algorithm used for tracking electrons and positrons. The C++ classes are adapted to the specific code structure of Geant4. They provide a complete description of the interactions and transport mechanics of electrons/positrons and photons in arbitrary materials, which can be activated from the G4ProcessManager to produce simulation results equivalent to those from the original penelope programs. The combined code, named PenG4, benefits from the multi-threading capabilities and advanced geometry and statistical tools of Geant4.Financial support from the Spanish Ministerio de Ciencia, Innovacion y Universidades/Agencia Estatal de Investigacion/European Regional Development Fund, European Union, (projects nos. RTI2018-098117-B-C21 and RTI2018-098117-B-C22) is gratefully aknowledged. The work of VA was supported by the program Ayudas para la contratacion de personal investigador en formacion de caracter predoctoral, programa VALi+d under grant number ACIF/2018/148 from the Conselleria dEducacio of the Generalitat Valenciana and the Fondo Social Europeo (FSE). VG acknowledges partial support from FEDER/MCIyU-AEI under grant FPA2017-84543-P, by the Severo Ochoa Excellence Program under grant SEV-2014-0398 and by Generalitat Valenciana through the project PROMETEO/2019/087.Asai, M.; Cortés-Giraldo, MA.; Giménez-Alventosa, V.; Giménez Gómez, V.; Salvat, F. (2021). The PENELOPE Physics Models and Transport Mechanics. Implementation into Geant4. Frontiers in Physics. 9:1-20. https://doi.org/10.3389/fphy.2021.738735S120
Dispersion Relation Bounds for pi pi Scattering
Axiomatic principles such as analyticity, unitarity and crossing symmetry
constrain the second derivative of the pi pi scattering amplitudes in some
channels to be positive in a region of the Mandelstam plane. Since this region
lies in the domain of validity of chiral perturbation theory, we can use these
positivity conditions to bound linear combinations of \bar{l}_1 and \bar{l}_2.
We compare our predictions with those derived previously in the literature
using similar methods. We compute the one-loop pi pi scattering amplitude in
the linear sigma model (LSM) using the MS-bar scheme, a result hitherto absent
in the literature. The LSM values for \bar{l}_1 and \bar{l}_2 violate the
bounds for small values of m_sigma/m_pi. We show how this can occur, while
still being consistent with the axiomatic principles.Comment: 12 pages, 8 figures. Two references added, a few minor changes.
Published versio
The PENELOPE physics models and transport mechanics. Implementation into Geant4
A translation of the penelope physics subroutines to C++, designed as an extension of the Geant4 toolkit, is presented. The Fortran code system penelope performs Monte Carlo simulation of coupled electron-photon transport in arbitrary materials for a wide energy range, nominally from 50 eV up to 1 GeV. Penelope implements the most reliable interaction models that are currently available, limited only by the required generality of the code. In addition, the transport of electrons and positrons is simulated by means of an elaborate class II scheme in which hard interactions (involving deflection angles or energy transfers larger than pre-defined cutoffs) are simulated from the associated restricted differential cross sections. After a brief description of the interaction models adopted for photons and electrons/positrons, we describe the details of the class-II algorithm used for tracking electrons and positrons. The C++ classes are adapted to the specific code structure of Geant4. They provide a complete description of the interactions and transport mechanics of electrons/positrons and photons in arbitrary materials, which can be activated from the G4ProcessManager to produce simulation results equivalent to those from the original penelope programs. The combined code, named PenG4, benefits from the multi-threading capabilities and advanced geometry and statistical tools of Geant4
Adsorption Characteristics of Refrigerants for Thermochemical Energy Storage in Metal-Organic Frameworks
The adsorption of fluorocarbons has gained significant importance as its use
as refrigerants in energy storage applications. In this context, the adsorption
behavior of two low global warming potential refrigerants, R125 fluorocarbon
and its hydrocarbon analog, R170, within four nanoporous materials, namely
MIL-101, Cu-BTC, ZIF-8, and UiO-66 has been investigated. By analyzing the
validity of our models against experimental observations, we ensure the
reliability of our molecular simulations. Our analysis encompasses a range of
crucial parameters, including adsorption isotherms, enthalpy of adsorption, and
energy storage densities, all under varying operating conditions.We find
remarkable agreement between computed and observed adsorption isotherms for
R125 within MIL-101. However, to obtain similar success for the rest of the
adsorbents, we need to take into account a few considerations, such as the
presence of inaccessible cages in Cu-BTC, the flexibility of ZIF-8, or the
defects in UiO-66. Transitioning to energy storage properties, we investigated
various scenarios, including processes with varying adsorption and desorption
conditions. Our findings underscore the dominance of MIL-101 in terms of
storage densities, with R125 exhibiting superior affinity over R170. Complex
mechanisms governed by changes in pressure, temperature, and desorption
behavior make for complicated patterns, demanding a case-specific approach. In
summary, this study navigates the complex landscape of refrigerant adsorption
in diverse nanoporous materials. It highlights the significance of operating
conditions, model selection, and refrigerant and adsorbent choices for energy
storage applications
Un nuevo epígrafe latino de Pina de Montalgrao
La inscripción fue localizada en 1984 por G. Fenollosa. Se encontraba al pie de un bancal en un campo de cultivo abandonado, emplazado en el denominado Llano de la Masada de los Canónigos, un paraje en donde se advierten, alrededor de una pequeña loma, vestigios de un hábitat de época romana. En octubre de 1985 fue trasladada al Museo Provincial de Bellas Artes de Castelló, donde se conserva actualmente. Se trata de una losa de piedra caliza gris-azulada de forma rectangular, rota en su parte inferior a la altura de la ultima línea del texto, afectada en su mitad izquierda. El campo epigráfico viene enmarcado por un recuadro moldurado de unos 5 cm., desaparecido en la parte inferior. La superficie del campo aparece rebajada y alisada, en tanto que el resto de la cara frontal presenta un acabado más tosco, y las otras caras están, simplemente, desvastadas. El texto resulta de difcil lectura, a causa, tanto de una incisión poco profunda y en general a un acabado poco cuidado, como a un desgaste erosivo del campo epigráfico
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