13,899 research outputs found
Optical amplification enhancement in photonic crystals
Improving and controlling the efficiency of a gain medium is one of the most
challenging problems of laser research. By measuring the gain length in an opal
based photonic crystal doped with laser dye, we demonstrate that optical
amplification is more than twenty-fold enhanced along the Gamma-K symmetry
directions of the face centered cubic photonic crystal. These results are
theoretically explained by directional variations of the density of states,
providing a quantitative connection between density of the states and light
amplification
Non-Linear Affine Embedding of the Dirac Field from the Multiplicity-Free SL(4,R) Unirreps
The correspondence between the linear multiplicity-free unirreps of SL(4, R)
studied by Ne'eman and {\~{S}}ija{\~{c}}ki and the non-linear realizations of
the affine group is worked out. The results obtained clarify the inclusion of
spinorial fields in a non-linear affine gauge theory of gravitation.Comment: 13 pages, plain TeX, macros include
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Towards a global model of the martian atmosphere
In an effort to continuously improve the capabilities of the Martian atmospheric predictions at LMD, the GCM has been extended into thermospheric heights thus creating the first model to self-consistently couple the lower and upper
regions of the Martian atmosphere. The behaviour of
the Martian thermosphere is strongly influenced by
lower atmospheric processes and has complex dynamics.
Such a fully coupled model will certainly aid in the preparation of future missions and on the analysis of future high altitude data, as well as serve as a base for the simulation of ionospheric processes, escape, etc
Specific heat and magnetic measurements in Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3 samples
We studied the magnetization as a function of temperature and magnetic field
in the compounds Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3. It allowed
us to identify the ferromagnetic, antiferromagnetic and charge ordering phases
in each case. The intrinsic magnetic moments of Nd3+ and Ho3+ ions experienced
a short range order at low temperatures. We also did specific heat measurements
with applied magnetic fields between 0 and 9 T and temperatures between 2 and
300 K in all three samples. Close to the charge ordering and ferromagnetic
transition temperatures the specific heat curves showed peaks superposed to the
characteristic response of the lattice oscillations. Below 10 K the specific
heat measurements evidenced a Schottky-like anomaly for all samples. However,
we could not successfully fit the curves to either a two level nor a
distribution of two-level Schottky anomaly. Our results indicated that the peak
temperature of the Schottky anomaly was higher in the compounds with narrower
conduction band.Comment: submitted to PR
Segon rahonament que tingueren Don Pascasio y Patatorta [Texto impreso] : abentse tornat à encontrar una vesprada en la alameda, y no podentse negar Patatorta al argument, comensà Don Pascasio de este modo
Hay un ejemplar encuadernado con: Romans, y coloqui nou, pera divertir el humor y desterrar la melancolia, yà que no tenim dinès ... (NP849.91/3085
Smooth Approximation of Lipschitz functions on Riemannian manifolds
We show that for every Lipschitz function defined on a separable
Riemannian manifold (possibly of infinite dimension), for every continuous
, and for every positive number , there exists
a smooth Lipschitz function such that
for every and
. Consequently, every separable
Riemannian manifold is uniformly bumpable. We also present some applications of
this result, such as a general version for separable Riemannian manifolds of
Deville-Godefroy-Zizler's smooth variational principle.Comment: 10 page
Morphological Study of Granular-Granular Impact Craters through Time-of-Flight Cameras: from Concept to Automation in Python
Laboratory made granular-granular impact craters have been used as model
analogues of planetary impact craters. These kind of craters have been observed
and studied using profilometry techniques that allow to retrieve important
morphologic features from the impacted surface. In this work, we propose to use
a Time-of-Flight camera (Microsoft Kinect One) for the acquisition of depth
data. We show comparisons between the typically used technique and the analysis
derived from the Time-of-Flight data. We also release craterslab, a Python
library developed to automate most of the tasks from the process of studying
impact craters produced by granular projectiles hitting on the surface of
granular targets. The library is able to acquire, identify, and measure
morphological features of impacted surfaces through the reconstruction of 3D
topographic maps. Our results show that using a Time-of-Flight camera and
automating the data processing with a software library for the systematic study
of impact craters can produce very accurate results while reducing the time
spent on different stages of the process
Spontaneous Symmetry Breakdown in non-relativistic Quantum Mechanics
The advantages and disadvantages of some pedagogical non-relativistic
quantum-mechanical models, used to illustrate spontaneous symmetry breakdown,
are discussed. A simple quantum-mechanical toy model (a spinor on the line,
subject to a magnetostatic interaction) is presented, that exhibits the
spontaneous breakdown of an internal symmetry.Comment: 19 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1111.1213. Equations (30) and (31) have been corrected. Other minor
correction
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