13,031 research outputs found
Cascaded Nondegenerate Four-Wave Mixing Technique for High-Power Single-Cycle Pulse Synthesis in the Visible and Ultraviolet Ranges
We present a new technique to synthesize high-power single-cycle pulses in
the visible and ultraviolet ranges by coherent superposition of a multiband
octave-spanning spectrum obtained by highly-nondegenerate cascaded four-wave
mixing of femtosecond pulses in bulk isotropic nonresonant media. The
generation of coherent spectra spanning over two octaves in bandwidth is
experimentally demonstrated using a thin fused silica slide. Full
characterization of the intervening multicolored fields using
frequency-resolved optical gating, where multiple cascaded orders have been
measured simultaneously for the first time, supports the possibility of direct
synthesis of near-single-cycle 2.2 fs visible-UV pulses without recurring to
complex amplitude or phase control, which should enable many applications in
science and technology.Comment: 13 pages, 4 figures. Submitted to Physical Review
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
On the Design of a Novel Joint Network-Channel Coding Scheme for the Multiple Access Relay Channel
This paper proposes a novel joint non-binary network-channel code for the
Time-Division Decode-and-Forward Multiple Access Relay Channel (TD-DF-MARC),
where the relay linearly combines -- over a non-binary finite field -- the
coded sequences from the source nodes. A method based on an EXIT chart analysis
is derived for selecting the best coefficients of the linear combination.
Moreover, it is shown that for different setups of the system, different
coefficients should be chosen in order to improve the performance. This
conclusion contrasts with previous works where a random selection was
considered. Monte Carlo simulations show that the proposed scheme outperforms,
in terms of its gap to the outage probabilities, the previously published joint
network-channel coding approaches. Besides, this gain is achieved by using very
short-length codewords, which makes the scheme particularly attractive for
low-latency applications.Comment: 28 pages, 9 figures; Submitted to IEEE Journal on Selected Areas in
Communications - Special Issue on Theories and Methods for Advanced Wireless
Relays, 201
Revisiting Complex Moments For 2D Shape Representation and Image Normalization
When comparing 2D shapes, a key issue is their normalization. Translation and
scale are easily taken care of by removing the mean and normalizing the energy.
However, defining and computing the orientation of a 2D shape is not so simple.
In fact, although for elongated shapes the principal axis can be used to define
one of two possible orientations, there is no such tool for general shapes. As
we show in the paper, previous approaches fail to compute the orientation of
even noiseless observations of simple shapes. We address this problem. In the
paper, we show how to uniquely define the orientation of an arbitrary 2D shape,
in terms of what we call its Principal Moments. We show that a small subset of
these moments suffice to represent the underlying 2D shape and propose a new
method to efficiently compute the shape orientation: Principal Moment Analysis.
Finally, we discuss how this method can further be applied to normalize
grey-level images. Besides the theoretical proof of correctness, we describe
experiments demonstrating robustness to noise and illustrating the method with
real images.Comment: 69 pages, 20 figure
Dispersion managed mode-locking dynamics in a Ti:Sapphire laser
We present what is to our knowledge the most complete 1-D numerical analysis
of the evolution and the propagation dynamics of an ultrashort laser pulse in a
Ti:Sapphire laser oscillator. This study confirms the dispersion managed model
of mode-locking, and emphasizes the role of the Kerr nonlinearity in generating
mode-locked spectra with a smooth and well-behaved spectral phase. A very good
agreement with preliminary experimental measurements is found.Comment: 11 pages, 4 figures, submitted to Optics Letter
Some experimental observations of crack-tip mechanics with displacement data
Estudio de la mecánica en el vértice de la grieta mediante datos de desplazamiento.In the past two decades, crack-tip mechanics has been increasingly studied with full-field
techniques. Within these techniques, Digital Image Correlation (DIC) has been most widely used due to its
many advantages, to extract important crack-tip information, including Stress Intensity Factor (SIF), Crack
Opening Displacement, J-integral, T-stress, closure level, plastic zone size, etc. However, little information is
given in the literature about the experimental setup that provides best estimations for the different parameters.
The current work aims at understanding how the experimental conditions used in DIC influence the crack-tip
information extracted experimentally. The influence of parameters such as magnification factor, size of the
images, position of the images with respect the crack-tip and size of the subset used in the correlation is studied.
The influence is studied in terms of SIF and T-stress by using Williams’ model. The concept of determination of
the K-dominance zone from experimental data has also explored. In this regard, cyclic loading on a fatigue
crack in a compact tension (CT) specimen, made of aluminium 2024-T351 alloy, has been applied and the
surface deformation ahead of the crack tip has been examined. The comparison between theoretical and
experimental values of KI showed that the effect of subset size on the measured KI is negligible compared to
the effect of size of the image.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech
Recommended from our members
Results for Channel Error Profiles for DECT
This letter presents the main statistical characterization
of the underlying error process obtained in the case of
the Digital European Cordless Telecommunications (DECT) radio
system. By simulation of the transmission link, error sequences
are generated for different channel parameters. Relevant statistics
are then computed for the purpose of efficient channel coding
design and evaluation
Soliton complexes in dissipative systems: vibrating, shaking and mixed soliton pairs
We show, numerically, that coupled soliton pairs in nonlinear dissipative systems modeled by the cubic-quintic complex Ginzburg-Landau equation can exist in various forms. They can be stationary, or they can pulsate periodically, quasiperiodically, or chaotically, as is the case for single solitons. In particular, we have found various types of vibrating and shaking soliton pairs. Each type is stable in the sense that a given bound state exists in the same form indefinitely. New solutions appear at special values of the equation parameters, thus bifurcating from stationary pairs. We also report the finding of mixed soliton pairs, formed by two different types of single solitons. We present regions of existence of the pair solutions and corresponding bifurcation diagrams
- …