4,771 research outputs found
Boundary driven waveguide arrays: Supratransmission and saddle-node bifurcation
In this report, we consider a semi-infinite discrete nonlinear Schr\"odinger
equation driven at one edge by a driving force. The equation models the
dynamics of coupled waveguide arrays. When the frequency of the forcing is in
the allowed-band of the system, there will be a linear transmission of energy
through the lattice. Yet, if the frequency is in the upper forbidden band, then
there is a critical driving amplitude for a nonlinear tunneling, which is
called supratransmission, of energy to occur. Here, we discuss mathematically
the mechanism and the source of the supratransmission. By analyzing the
existence and the stability of the rapidly decaying static discrete solitons of
the system, we show rigorously that two of the static solitons emerge and
disappear in a saddle-node bifurcation at a critical driving amplitude. One of
the emerging solitons is always stable in its existence region and the other is
always unstable. We argue that the critical amplitude for supratransmission is
then the same as the critical driving amplitude of the saddle-node bifurcation.
We consider as well the case of the forcing frequency in the lower forbidden
band. It is discussed briefly that there is no supratransmission because in
this case there is only one rapidly decaying static soliton that exists and is
stable for any driving amplitude.Comment: Some figures are removed due to file size limi
Real fermionic symmetry in type II supergravity
It is known that the transformations of fermionic T-duality, derived from the
worldsheet theory, generically transform real supergravity backgrounds to
complex supergravity backgrounds. We consider the low-energy target space
theory and show that the type II supergravity equations admit a symmetry that
transforms the Ramond-Ramond fields and the dilaton. The transformations given
by this symmetry involve Killing spinors and include the transformations of
Berkovits and Maldacena. However, we show that they also allow real
transformations.Comment: 30 pages; added comments and references. Corrected typo
Printable Nanoscopic Metamaterial Absorbers and Images with Diffraction-Limited Resolution
The fabrication of functional metamaterials with extreme feature resolution
finds a host of applications such as the broad area of surface/light
interaction. Non-planar features of such structures can significantly enhance
their performance and tunability, but their facile generation remains a
challenge. Here, we show that carefully designed out-of-plane nanopillars made
of metal-dielectric composites integrated in a metal-dielectric-nanocomposite
configuration, can absorb broadband light very effectively. We further
demonstrate that electrohydrodynamic printing in a rapid nanodripping mode, is
able to generate precise out-of-plane forests of such composite nanopillars
with deposition resolutions at the diffraction limit on flat and non-flat
substrates. The nanocomposite nature of the printed material allows the
fine-tuning of the overall visible light absorption from complete absorption to
complete reflection by simply tuning the pillar height. Almost perfect
absorption (~95%) over the entire visible spectrum is achieved by a nanopillar
forest covering only 6% of the printed area. Adjusting the height of individual
pillar groups by design, we demonstrate on-demand control of the gray scale of
a micrograph with a spatial resolution of 400 nm. These results constitute a
significant step forward in ultra-high resolution facile fabrication of
out-of-plane nanostructures, important to a broad palette of light design
applications. nanostructures, important to a broad palette of light design
applications
Дисфемизмы в арабском и русском языках и новые аспекты их формирования (на примере современных арабских СМИ)
This article considers dysphemism as a new linguistic phenomenon in the Arabic language, the development of ways of forming dysphemistic units and the effect of psychological, sociolinguistic, and social factors on this process. Our method is intellectual and we try forming dysphemistic units develop and new aspects appear in their formation. Results showed that dysphemisms are a poorly understood language phenomenon in ancient and modern Arabic footprints.Este artículo considera el disfemismo como un nuevo fenómeno lingüístico en el idioma árabe, el desarrollo de formas de formar unidades dishemísticas y el efecto de factores psicológicos, sociolingüísticos y sociales en este proceso. Nuestro método es intelectual e intentamos formar unidades disfemísticas para desarrollar y aparecen nuevos aspectos en su formación. Los resultados mostraron que los disfemismos son un fenómeno del lenguaje poco entendido en las huellas árabes antiguas y modernas.В этой статье дисфемизм рассматривается как новое языковое явление в арабском языке, разработка способов формирования дисфемистических единиц и влияние психологических, социолингвистических и социальных факторов на этот процесс. Наш метод интеллектуален, и мы стараемся формировать дисфемистические единицы, развиваться и в их формировании появляются новые аспекты. Результаты показали, что дисфемизмы являются плохо понятым языковым явлением в древних и современных арабских следах
Measuring intergranular force in granular media
A new method is proposed to measure intergranular forces in granular geomaterial from time-lapsehigh-resolution X-ray computed tomographyimaging using a grain trackingapproachand discrete element metho
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