102,543 research outputs found
Inline self-diffraction dispersion-scan of over octave-spanning pulses in the single-cycle regime
We present an implementation of dispersion-scan based on self-diffraction (SD
d-scan) and apply it to the measurement of over octave-spanning sub-4-fs
pulses. The results are compared with second-harmonic generation (SHG) d-scan.
The efficiency of the SD process is derived theoretically and compared with the
spectral response retrieved by the d-scan algorithm. The new SD d-scan has a
robust inline setup and enables measuring pulses with over-octave spectra,
single-cycle durations and wavelength ranges beyond those of SHG crystals, such
as the ultraviolet and the deep-ultraviolet.Comment: 8 pages, 5 figure
High harmonic generation in crystals using Maximally Localized Wannier functions
In this work, the nonlinear optical response, and in particular, the high
harmonic generation of semiconductors is addressed by using the Wannier gauge.
One of the main problems in the time evolution of the Semiconductor Bloch
equations resides in the fact that the dipole couplings between different bands
can diverge and have a random phase along the reciprocal space and this leads
to numerical instability. To address this problem, we propose the use of the
Maximally Localized Wannier functions that provide a framework to map ab-initio
calculations to an effective tight-binding Hamiltonian with great accuracy. We
show that working in the Wannier gauge, the basis set in which the Bloch
functions are constructed directly from the Wannier functions, the dipole
couplings become smooth along the reciprocal space thus avoiding the problem of
random phases. High harmonic generation spectrum is computed for a 2D monolayer
of hBN as a numerical demonstration
Information entropy of classical versus explosive percolation
We study the Shannon entropy of the cluster size distribution in classical as
well as explosive percolation, in order to estimate the uncertainty in the
sizes of randomly chosen clusters. At the critical point the cluster size
distribution is a power-law, i.e. there are clusters of all sizes, so one
expects the information entropy to attain a maximum. As expected, our results
show that the entropy attains a maximum at this point for classical
percolation. Surprisingly, for explosive percolation the maximum entropy does
not match the critical point. Moreover, we show that it is possible determine
the critical point without using the conventional order parameter, just
analysing the entropy's derivatives.Comment: 6 pages, 6 figure
Autonomous thermal machine for amplification and control of energetic coherence
We present a model for an autonomous quantum thermal machine comprised of two
qubits capable of manipulating and even amplifying the local coherence in a
non-degenerate external system. The machine uses only thermal resources,
namely, contact with two heat baths at different temperatures, and the external
system has a non-zero initial amount of coherence. The method we propose allows
for an interconversion between energy, both work and heat, and coherence in an
autonomous configuration working in out-of-equilibrium conditions. This model
raises interesting questions about the role of fundamental limitations on
transformations involving coherence and opens up new possibilities in the
manipulation of coherence by autonomous thermal machines.Comment: v1: 5 + 3 pages, 2 figures. v2: Restructured version with several new
results and a new appendix, 11 + 14 pages, 4 + 3 figures. v3: Improved and
corrected version with new discussions, 8 + 8 pages, 4 + 3 figure
SLIC Based Digital Image Enlargement
Low resolution image enhancement is a classical computer vision problem.
Selecting the best method to reconstruct an image to a higher resolution with
the limited data available in the low-resolution image is quite a challenge. A
major drawback from the existing enlargement techniques is the introduction of
color bleeding while interpolating pixels over the edges that separate distinct
colors in an image. The color bleeding causes to accentuate the edges with new
colors as a result of blending multiple colors over adjacent regions. This
paper proposes a novel approach to mitigate the color bleeding by segmenting
the homogeneous color regions of the image using Simple Linear Iterative
Clustering (SLIC) and applying a higher order interpolation technique
separately on the isolated segments. The interpolation at the boundaries of
each of the isolated segments is handled by using a morphological operation.
The approach is evaluated by comparing against several frequently used image
enlargement methods such as bilinear and bicubic interpolation by means of Peak
Signal-to-Noise-Ratio (PSNR) value. The results obtained exhibit that the
proposed method outperforms the baseline methods by means of PSNR and also
mitigates the color bleeding at the edges which improves the overall
appearance.Comment: 6 page
Black Holes in AdS/BCFT and Fluid/Gravity Correspondence
A proposal to describe gravity duals of conformal theories with boundaries
(AdS/BCFT correspondence) was put forward by Takayanagi few years ago. However
interesting solutions describing field theories at finite temperature and
charge density are still lacking. In this paper we describe a class of theories
with boundary, which admit black hole type gravity solutions. The theories are
specified by stress-energy tensors that reside on the extensions of the
boundary to the bulk. From this perspective AdS/BCFT appears analogous to the
fluid/gravity correspondence. Among the class of the boundary extensions there
is a special (integrable) one, for which the stress-energy tensor is
fluid-like. We discuss features of that special solution as well as its
thermodynamic properties.Comment: 18 pages, 4 figures (7 pdf-files). Save and view with Adobe Reader if
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