911 research outputs found
Optically and Electrically Tunable Dirac Points and Zitterbewegung in Graphene-Based Photonic Superlattices
We demonstrate that graphene-based photonic superlattices provide a versatile
platform for electrical and all-optical control of photonic beams with
deep-subwavelength accuracy. Specifically, by inserting graphene sheets into
periodic metallo-dielectric structures one can design optical superlattices
that posses photonic Dirac points (DPs) at frequencies at which the spatial
average of the permittivity of the superlattice, ,
vanishes. Similar to the well-known zero- bandgaps, we show that these
zero- DPs are highly robust against structural disorder. We
also show that, by tuning the graphene permittivity via the optical Kerr effect
or electrical doping, one can induce a spectral variation of the DP exceeding
\SI{30}{\nano\meter}, at mid-IR and THz frequencies. The implications of this
wide tunability for the photonic Zitterbewegung effect in a vicinity of the DP
are explored too.Comment: 5 pages, 5 figures, to appear in Phys. Rev. B as a Rapid
Communicatio
Anderson Localization at the Subwavelength Scale and Loss Compensation for Surface-Plasmon Polaritons in Disordered Arrays of Metallic Nanowires
Using a random array of coupled metallic nanowires as a generic example of
disordered plasmonic systems, we demonstrate that the structural disorder
induces localization of light in these nanostructures at a deep-subwavelength
scale. The ab initio analysis is based on solving the complete set of 3D
Maxwell equations. We find that random variations of the radius of coupled
plasmonic nanowires are sufficient to induce the Anderson localization (AL) of
surface-plasmon polaritons (SPPs), the size of these trapped modes being
significantly smaller than the wavelength. Remarkably, the optical-gain
coefficient, needed to compensate losses in the plasmonic components of the
system, is much smaller than the loss coefficient of the metal, which is
obviously beneficial for the realization of the AL in plasmonic nanostructures.
The dynamics of excitation and propagation of the Anderson-localized SPPs are
addressed too.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
The impact of cultural dissonance and acculturation orientations on immigrant students' academic performance
Indexación: Scopus; Scielo; Redalyc.Prior research has documented meaningful differences between school
performance of immigrant and native students. Multicultural education has been
associated with academic failure of foreign students. e aim of this study was to examine
the impact of a set of psychosocial variables on the perceived academic achievement
of first generation immigrant adolescents from public secondary schools in Northern
Spain. Results showed that 46% of the variability in foreign students’ perceived academic
performance was explained by home-school cultural dissonance. We also explored the
impact of acculturation orientation to separation, perception of discrimination from
teachers, school adjustment, and psychological well-being in academic performance.
Any multicultural education context should take into account psychosocial adjustment,
given its influence on academic performance of all studentsSe han hallado diferencias significativas entre el rendimiento académico de
los inmigrantes y el de los estudiantes nativos. Sin embargo, hay una escasa evidencia
acerca de los aspectos psicosociales de este fenómeno. El objetivo de este estudio fue
examinar el impacto de un conjunto de variables psicosociales: disonancia cultural y
orientaciones de aculturación en el rendimiento académico percibido de adolescentes
inmigrantes de primera generación de centros de Educación Secundaria en el Norte
de España. Los resultados mostraron que alrededor del 46% de la variabilidad en el
rendimiento era explicada por la disonancia cultural entre escuela y hogar. Cualquier
contexto de educación multicultural ha de tomar en consideración el ajuste psicosocial,
dada su influencia en el rendimiento académico de los estudiantes.http://www.redalyc.org/jatsRepo/647/64753989003/index.htm
Controlled power flow capacitive divider for electric power tapping
Abstract: Capacitive divider systems for tapping electric power from high voltage transmission lines are known to exhibit certain detrimental problems of stability, sub-resonance harmonic oscillations, and ferroresonance when coupled with non-linear loads. On the other hand, they can improve reactive power flow, power factor and contribute to improved harmonic filtration of the larger power system. This paper, therefore, proposes a controlled power flow conditioner as an essential integral component of a capacitive divider system to control power transfer between the high voltage transmission line, capacitive divider system, and the load. The ultimate objective of this conditioner is to mitigate or minimize the attendant problems associated with coupling the system to the load, and optimize the derivable benefits to the larger network
Active power control for capacitive divider tapping method
Abstract: Capacitive divider systems for tapping electric power from high voltage transmission lines are known to exhibit certain detrimental problems of stability, sub-resonance harmonic oscillations, and ferroresonance when coupled with non-linear loads. On the other hand, they can improve reactive power flow, power factor and contribute to improved harmonic filtration of the larger power system. This paper, therefore, proposes a controlled power flow conditioner as an essential integral component of a capacitive divider system to control power transfer between the high voltage transmission line, capacitive divider system, and the load. The ultimate objective of this conditioner is to mitigate or minimize the attendant problems associated with coupling the system to the load, and optimize the derivable benefits to the larger network
Performance evaluation of a three-phase induction machine with auxilliary winding fed by a leading reactive current
Abstract In this paper the performance of three-phase induction machine equipped with a three-phase auxiliary winding which is only magnetically coupled to the stator main winding is evaluated. A capacitive load is connected in parallel to each phase of the auxiliary winding and serves to inject a leading reactive current into the machine. Steady state and dynamic performance of the machine are evaluated under various loading and compensative conditions. The experimental results show that it possible to obtain a comparatively good power factor with a fixed capacitive load for various loadings of the asynchronous machine
Surface modes in plasmonic Bragg fibers with negative average permittivity
We investigate surface modes in plasmonic Bragg fibers composed of
nanostructured coaxial cylindrical metal-dielectric multilayers. We demonstrate
that the existence of surface modes is determined by the sign of the spatially
averaged permittivity of the plasmonic Bragg fiber, \bar{% \varepsilon}.
Specifically, localized surface modes occur at the interface between the
cylindrical core with and the outermost uniform
dielectric medium, which is similar to the topologically protected plasmonic
surface modes at the interface between two different one-dimensional planar
metal-dielectric lattices with opposite signs of the averaged permittivity.
Moreover, when increasing the number of dielectric-metal rings, the propagation
constant of surface modes with different azimuthal mode numbers is approaching
that of surface plasmon polaritons formed at the corresponding planar
metal/dielectric interface. Robustness of such surface modes of plasmonic Bragg
fibers is demonstrated too.Comment: 10 pages, 5 figures, Optics Express, to be publishe
Icosahedral multi-component model sets
A quasiperiodic packing Q of interpenetrating copies of C, most of them only
partially occupied, can be defined in terms of the strip projection method for
any icosahedral cluster C. We show that in the case when the coordinates of the
vectors of C belong to the quadratic field Q[\sqrt{5}] the dimension of the
superspace can be reduced, namely, Q can be re-defined as a multi-component
model set by using a 6-dimensional superspace.Comment: 7 pages, LaTeX2e in IOP styl
- …