16,082 research outputs found
Nongauge bright soliton of the nonlinear Schrodinger (NLS) equation and a family of generalized NLS equations
We present an approach to the bright soliton solution of the NLS equation
from the standpoint of introducing a constant potential term in the equation.
We discuss a `nongauge' bright soliton for which both the envelope and the
phase depend only on the traveling variable. We also construct a family of
generalized NLS equations with solitonic sech^p solutions in the traveling
variable and find an exact equivalence with other nonlinear equations, such as
the Korteveg-de Vries and Benjamin-Bona-Mahony equations when p=2Comment: ~4 pages, 3 figures, 16 references, published versio
EuCo2P2: A Model Molecular-Field Helical Heisenberg Antiferromagnet
The metallic compound EuCo2P2 with the body-centered tetragonal ThCr2Si2
structure containing Eu spins 7/2 was previously shown from single-crystal
neutron diffraction measurements to exhibit a helical antiferromagnetic (AFM)
structure below TN = 66.5 K with the helix axis along the c axis and with the
ordered moments aligned within the ab-plane. Here we report crystallography,
electrical resistivity, heat capacity, magnetization and magnetic
susceptibility measurements on single crystals of this compound. We demonstrate
that EuCo2P2 is a model molecular-field helical Heisenberg antiferromagnet from
comparisons of the anisotropic magnetic susceptibility chi, high-field
magnetization and magnetic heat capacity of EuCo2P2 single crystals at
temperature T < TN with the predictions of our recent formulation of molecular
field theory. Values of the Heisenberg exchange interactions between the Eu
spins are derived from the data. The low-T magnetic heat capacity ~ T^3 arising
from spin-wave excitations with no anisotropy gap is calculated and found to be
comparable to the lattice heat capacity. The density of states at the Fermi
energy of EuCo2P2 and the related compound BaCo2P2 are found from the heat
capacity data to be large, 10 and 16 states/eV per formula unit for EuCo2P2 and
BaCo2P2, respectively. These values are enhanced by a factor of ~2.5 above
those found from DFT electronic structure calculations for the two compounds.
The calculations also find ferromagnetic Eu-Eu exchange interactions within the
ab-plane and AFM interactions between nearest- and next-nearest planes, in
agreement with the MFT analysis of chi{ab}(T < TN).Comment: 20 pages, 17 figures, 3 tables, 46 references. This is an extended
replacement of arXiv:1512.02958 with an additional coautho
GONG p-mode frequency changes with solar activity
We present a correlation analysis of GONG p-mode frequencies with nine solar
activity indices for the period 1995 August to 1997 August. This study includes
spherical harmonic degree in the range 2 to 150 and the frequency range of
1500-3500 \mu Hz. Using three statistical tests, the measured mean frequency
shifts show strong to good correlation with activity indices. A decrease of
0.06 \mu Hz in frequency, during the descending phase of solar cycle 22 and an
increase of 0.04 \mu Hz in the ascending phase of solar cycle 23 is observed.
These results provide the first evidence for change in p-mode frequencies
around the declining phase of solar cycle 22 and beginning of new cycle 23.
This analysis further confirms that the temporal behaviour of the solar
frequency shifts closely follow the phase of the solar activity cycle.Comment: 14 pages, 3 figures. To appear in Ap.
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Analysis of capillary-like structures formed by endothelial cells in a novel organotypic assay developed from heart tissue
In this work, we present an algorithm to perform automatic segmentation, feature extraction and dosage classification of images derived from a novel organotypic angiogenesis assay developed to assess the effects of ionising radiation in the mouse heart. The images presented very different conditions of illumination and conditions of density and shapes of cells. The algorithm consists of a pipeline of several steps, which were validated against hand-segmented images. The algorithm provided satisfactory results, as all images were correctly dose-classified. The cells exposed to the lowest radiation dose were observed to have the greatest relative feature variability
The Rotation Of The Deep Solar Layers
From the analysis of low-order GOLF+MDI sectoral modes and LOWL data (l > 3),
we derive the solar radial rotation profile assuming no latitudinal dependance
in the solar core. These low-order acoustic modes contain the most
statistically significant information about rotation of the deepest solar
layers and should be least influenced by internal variability associated with
the solar dynamo. After correction of the sectoral splittings for their
contamination by the rotation of the higher latitudes, we obtain a flat
rotation profile down to 0.2 solar radius.Comment: accepted in ApJ Letters 5 pages, 2 figure
Is This a Joke? Detecting Humor in Spanish Tweets
While humor has been historically studied from a psychological, cognitive and
linguistic standpoint, its study from a computational perspective is an area
yet to be explored in Computational Linguistics. There exist some previous
works, but a characterization of humor that allows its automatic recognition
and generation is far from being specified. In this work we build a
crowdsourced corpus of labeled tweets, annotated according to its humor value,
letting the annotators subjectively decide which are humorous. A humor
classifier for Spanish tweets is assembled based on supervised learning,
reaching a precision of 84% and a recall of 69%.Comment: Preprint version, without referra
A note on Verhulst's logistic equation and related logistic maps
We consider the Verhulst logistic equation and a couple of forms of the
corresponding logistic maps. For the case of the logistic equation we show that
using the general Riccati solution only changes the initial conditions of the
equation. Next, we consider two forms of corresponding logistic maps reporting
the following results. For the map x_{n+1} = rx_n(1 - x_n) we propose a new way
to write the solution for r = -2 which allows better precision of the iterative
terms, while for the map x_{n+1}-x_n = rx_n(1 - x_{n+1}) we show that it
behaves identically to the logistic equation from the standpoint of the general
Riccati solution, which is also provided herein for any value of the parameter
r.Comment: 6 pages, 3 figures, 7 references with title
Evidence of unconventional low-frequency dynamics in the normal phase of Ba(Fe1-xRhx)2As2 iron-based supercondutors
This work presents 75As NMR spin echo decay rate (1/T2) measurements in
Ba(Fe1-xRhx)2As2 superconductors, for 0.041 < x < 0.094. It is shown that 1/T2
increases upon cooling, in the normal phase, suggesting the onset of an
unconventional very low-frequency activated dynamic. The correlation times of
the fluctuations and their energy barriers are derived. The motion is favored
at large Rh content, while it is hindered by the application of a magnetic
field perpendicular to the FeAs layers. The same dynamic is observed in the
spin-lattice relaxation rate, in a quantitatively consistent manner. These
results are discussed in the light of nematic fluctuations involving domain
wall motion. The analogies with the behaviour observed in the cuprates are also
outlined
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