25,046 research outputs found
Gauge fields in a string-cigar braneworld
In this work we investigate the properties of an Abelian gauge vector field
in a thin and in a smoothed string-like braneworld, the so-called string-cigar
model. This thick brane scenario satisfies the regularity conditions and it can
be regarded as an interior and exterior string-like solution. The source
undergoes a geometric Ricci flow which is connected to a variation of the bulk
cosmological constant. The Ricci flow changes the width and amplitude of the
massless mode at the brane core and recover the usual thin string-like behavior
at large distances. By numerical means we obtain the Kaluza-Klein (KK) spectrum
for both the thin brane and the string-cigar. It turns out that both models
exhibit a mass gap between the massless and the massive modes and between the
high and the low mass regimes. The KK modes are smooth near the brane and their
amplitude are enhanced by the string-cigar core. The analogue Schr\"odinger
potential is also tuned by the geometric flow.Comment: The discussion about the Kaluza-Klein spectrum of the gauge field was
improved. Numerical analysis was adapted to the conventional notation on
Kaluza-Klein number. Some graphics were modified for considering other
notation. Results unchanged. References added. Corrected typos. 17 pages. 6
figures. To match version to appears in Physics Letters
Análise de QTL 'S correlacionados à produção de leite em búfalos (Bubalus bubalis).
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Magnetic monopole and string excitations in a two-dimensional spin ice
We study the magnetic excitations of a square lattice spin-ice recently
produced in an artificial form, as an array of nanoscale magnets. Our analysis,
based upon the dipolar interaction between the nanomagnetic islands, correctly
reproduces the ground-state observed experimentally. In addition, we find
magnetic monopole-like excitations effectively interacting by means of the
usual Coulombic plus a linear confining potential, the latter being related to
a string-like excitation binding the monopoles pairs, what indicates that the
fractionalization of magnetic dipoles may not be so easy in two dimensions.
These findings contrast this material with the three-dimensional analogue,
where such monopoles experience only the Coulombic interaction. We discuss,
however, two entropic effects that affect the monopole interactions: firstly,
the string configurational entropy may loose the string tension and then, free
magnetic monopoles should also be found in lower dimensional spin ices;
secondly, in contrast to the string configurational entropy, an entropically
driven Coulomb force, which increases with temperature, has the opposite effect
of confining the magnetic defects.Comment: 8 pages. Accepted by Journal of Applied Physics (2009
Overview on lightweight multifunctional materials
Lightweight multifunctional materials represent an increasing field in materials science and engineering based on their technological applications in a wide variety of areas ranging from sensors and actuators, materials for structural and environmental applications, energy generation and storage, or biomedicine, among others. This chapter presents an overview on the main types, preparation techniques and applications of the most relevant lightweight multifunctional materials, as well as on relevant materials to be applied and/or implemented in lightweight structures.FCT (Fundação para a Ciência e Tecnologia) for financial support
under the framework of Strategic Funding grants UID/CTM/50025/2019,
UID/FIS/04650/2019; and supported by FEDER funds through the COMPETE 2020
Programme under the project number PTDC/FIS-MAC/28157/2017 and POCI-01-0145-
FEDER-007688. The authors also thank the FCT for financial support under grants
SFRH/BPD/112547/2015 (C.M.C.) and SFRH/BPD/110914/2015 (P. C.). Financial
support from the Basque Government under the ELKARTEK, HAZITEK and PIBA
(PIBA-2018-06
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