432 research outputs found
Alternative approach to computing transport coefficients: application to conductivity and Hall coefficient of hydrogenated amorphous silicon
We introduce a theoretical framework for computing transport coefficients for
complex materials. As a first example, we resolve long-standing inconsistencies
between experiment and theory pertaining to the conductivity and Hall mobility
for amorphous silicon and show that the Hall sign anomaly is a consequence of
localized states. Next, we compute the AC conductivity of amorphous
polyanaline. The formalism is applicable to complex materials involving defects
and band-tail states originating from static topological disorder and extended
states. The method may be readily integrated with current \textit{ab initio}
methods.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Building surface damage recognition based on synthetic data
To detect surface damage to buildings, it is necessary to involve workers who are at risk of industrial injuries when inspecting hard-to-reach areas of industrialpremises. Attraction of special means, such as aerial platforms, safety systems, etc. increase the financial costs with this approach. The use of unmanned aerial vehicles, coupled withneural network algorithms, can simplify this procedure. Due tothe inaccessibility, the problem of obtaining training data forneural networks arises, which can be solved by synthesizingthem in a virtual environment
Optical properties of small polarons from dynamical mean-field theory
The optical properties of polarons are studied in the framework of the
Holstein model by applying the dynamical mean-field theory. This approach
allows to enlighten important quantitative and qualitative deviations from the
limiting treatments of small polaron theory, that should be considered when
interpreting experimental data. In the antiadiabatic regime, accounting on the
same footing for a finite phonon frequency and a finite electron bandwidth
allows to address the evolution of the optical absorption away from the
well-understood molecular limit. It is shown that the width of the multiphonon
peaks in the optical spectra depends on the temperature and on the frequency in
a way that contradicts the commonly accepted results, most notably in the
strong coupling case. In the adiabatic regime, on the other hand, the present
method allows to identify a wide range of parameters of experimental interest,
where the electron bandwidth is comparable or larger than the broadening of the
Franck-Condon line, leading to a strong modification of both the position and
the shape of the polaronic absorption. An analytical expression is derived in
the limit of vanishing broadening, which improves over the existing formulas
and whose validity extends to any finite-dimensional lattice. In the same
adiabatic regime, at intermediate values of the interaction strength, the
optical absorption exhibits a characteristic reentrant behavior, with the
emergence of sharp features upon increasing the temperature -- polaron
interband transitions -- which are peculiar of the polaron crossover, and for
which analytical expressions are provided.Comment: 16 pages, 6 figure
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
Stochastic Green's function approach to disordered systems
Based on distributions of local Green's functions we present a stochastic
approach to disordered systems. Specifically we address Anderson localisation
and cluster effects in binary alloys. Taking Anderson localisation of Holstein
polarons as an example we discuss how this stochastic approach can be used for
the investigation of interacting disordered systems.Comment: 12 pages, 7 figures, conference proceedings: Progress in
Nonequilibrium Green's Functions III, 22-26 August 2005, University of Kiel,
German
Optical models of the molecular atmosphere
The use of optical and laser methods for performing atmospheric investigations has stimulated the development of the optical models of the atmosphere. The principles of constructing the optical models of molecular atmosphere for radiation with different spectral composition (wideband, narrowband, and monochromatic) are considered in the case of linear and nonlinear absorptions. The example of the development of a system which provides for the modeling of the processes of optical-wave energy transfer in the atmosphere is presented. Its physical foundations, structure, programming software, and functioning were considered
Neural network analysis of hyperspectral images of soil
The article approaches to the classification of high-resolution hyperspectral images in the problem of classification of soil species is proposed. A spectral-spatial convolutional neural network with compensation for lighting variations is used as a classifier. The effectiveness of the proposed approach in the problem of classification of hyperspectral images of soils obtained by a scanning hyperspectral camera is shown. The essence of the developed method is to use binary classification together with multiclass, thereby improving the result of the latter
- …