899 research outputs found
Negative phase velocity in nonlinear oscillatory systems --mechanism and parameter distributions
Waves propagating inwardly to the wave source are called antiwaves which have
negative phase velocity. In this paper the phenomenon of negative phase
velocity in oscillatory systems is studied on the basis of periodically paced
complex Ginzbug-Laundau equation (CGLE). We figure out a clear physical picture
on the negative phase velocity of these pacing induced waves. This picture
tells us that the competition between the frequency of the
pacing induced waves with the natural frequency of the oscillatory
medium is the key point responsible for the emergence of negative phase
velocity and the corresponding antiwaves. and
are the criterions for the waves with negative
phase velocity. This criterion is general for one and high dimensional CGLE and
for general oscillatory models. Our understanding of antiwaves predicts that no
antispirals and waves with negative phase velocity can be observed in excitable
media
Negative Refractive Index in Artificial Metamaterials
We discuss optical constants in artificial metamaterials showing negative
magnetic permeability and electric permittivity. Using effective field theory,
we calculate effective permeability of nanofabricated media composed of pairs
of identical gold nano-pillars with magnetic response in the visible spectrum.Comment: 16 pages, 4 figures, submitted to Optics Letter
A new class of photo-catalytic materials and a novel principle for efficient water splitting under infrared and visible light - MgB2 as unexpected example
Water splitting is unanimously recognized as environment friendly,
potentially low cost and renewable energy solution based on the future hydrogen
economy. Especially appealing is photo-catalytic water splitting whereby a
suitably chosen catalyst dramatically improves efficiency of the hydrogen
production driven by direct sunlight and allows it to happen even at zero
driving potential. Here, we suggest a new class of stable photo-catalysts and
the corresponding principle for catalytic water splitting in which infrared and
visible light play the main role in producing the photocurrent and hydrogen.
The new class of catalysts based on ionic binary metals with layered
graphite-like structures which effectively absorb visible and infrared light
facilitating the reaction of water splitting, suppress the inverse reaction of
ion recombination by separating ions due to internal electric fields existing
near alternating layers, provide the sites for ion trapping of both polarities,
and finally deliver the electrons and holes required to generate hydrogen and
oxygen gases. As an example, we demonstrate conversion efficiency of 27 percent
at bias voltage bias 0.5 V for magnesium di-boride working as a catalyst for
photo-induced water splitting. We discuss its advantages over some existing
materials and propose the underlying mechanism of photo-catalytic water
splitting by binary layered metals
Nanofabricated media with negative permeability at visible frequencies
We report a nanofabricated medium made of electromagnetically coupled pairs
of gold dots with geometry carefully designed at a 10-nm level. The medium
exhibits strong magnetic response at visible-light frequencies, including bands
with negative \mu. The magnetism arises due to the excitation of quadrupole
plasmon resonances. Our approach shows for the first time the feasibility of
magnetism at optical frequencies and paves a way towards magnetic and
left-handed components for visible optics.Comment: 16 pages, 4 figures. submitted to Nature on 1 April 200
Numerical Analysis of Stress-Strain State of Orthotropic Plates in the Form of Arbitrary Convex Quadrangle
A numerical and analytical approach to solving problems of the stress-strain state of quadrangular orthotropic
plates of complex shape has been proposed. Two-dimensional boundary value problem was solved using spline
collocation and discrete orthogonalization methods after applying the appropriate domain transform.
The influence of geometric shape of plate in different cases of boundary conditions on the displacement and
stress fields is considered according to the refined theory. The results were compared with available data from
other authors
Mechanics and Mathematical Modeling of Class III Treatment with Orthodontic Appliances with a Movable Ramp
Treatment of class III is a current problem in orthodontics that requires constant improvement of its methods, development of new or modifications of known methods and techniques. We have developed and studied the modification of removable functionally-directing orthodontic appliances for treatment of Class III, which consists of a plastic base, vestibular arc, retaining clasps, ramp, which is connected with the base by means of two torsion springs. Its usage ensures a prolonged contact of ramp with the teeth. We studied two types of club-shaped springs (torsion springs): one spring, which create an amortization effect during the action of the ramp, but do not change its inclination angle and second one – spring that seek to increase the angle of the ramp inclination due to the disclosure of its curl
An antisymmetric plasmon resonance in coupled gold nanoparticles as a sensitive tool for detection of local index of refraction
A nanofabricated regular array of coupled gold nano-pillars is employed to
detect local indices of refraction of different liquids using a shift of an
antisymmetric plasmon resonance peak observed in the reflection spectra. The
peak spectral position is found to be a unique function of the local refractive
index for a wide range of indices. We discuss possible applications of the
fabricated nanostructured arrays in bio and chemical sensors.Comment: 16 pages, 4 figure
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