10,243 research outputs found
Phase diagram and complexity of mode-locked lasers: from order to disorder
We investigate mode-locking processes in lasers displaying a variable degree
of structural randomness, from standard optical cavities to multiple-scattering
media. By employing methods mutuated from spin-glass theory, we analyze the
mean-field Hamiltonian and derive a phase-diagram in terms of the pumping rate
and the degree of disorder. Three phases are found: i) paramagnetic,
corresponding to a noisy continuous wave emission, ii) ferromagnetic, that
describes the standard passive mode-locking, and iii) the spin-glass in which
the phases of the electromagnetic field are frozen in a exponentially large
number of configurations. The way the mode-locking threshold is affected by the
amount of disorder is quantified. The results are also relevant for other
physical systems displaying a random Hamiltonian, like Bose-Einstein
condensates and nonlinear optical beams.Comment: 4 pages, 2 figure
Measurement of scaling laws for shock waves in thermal nonlocal media
We are able to detect the details of spatial optical collisionless
wave-breaking through the high aperture imaging of a beam suffering shock in a
fluorescent nonlinear nonlocal thermal medium. This allows us to directly
measure how nonlocality and nonlinearity affect the point of shock formation
and compare results with numerical simulations.Comment: 4 pages, 4 figure
Light diffusion and localization in 3D nonlinear disordered media
Using a 3D Finite-Difference Time-Domain parallel code, we report on the
linear and nonlinear propagation of light pulses in a disordered assembly of
scatterers, whose spatial distribution is generated by a Molecular Dynamics
code; refractive index dispersion is also taken into account. We calculate the
static and dynamical diffusion constant of light, while considering a pulsed
excitation. Our results are in quantitative agreement with reported
experiments, also furnishing evidence of a non-exponential decay of the
transmitted pulse in the linear regime and in the presence of localized modes.
By using an high power excitation, we numerically demonstrate the
``modulational instability random laser'': at high peak input powers energy is
transferred to localized states from the input pulse, via third-order
nonlinearity and optical parametric amplification, and this process is signed
by a power-dependent non-exponential time-decay of the transmitted pulse.Comment: 5 pages, 4 figures. Revised version with new figure 4 with localized
state
The Stellar Content of Obscured Galactic Giant HII Regions. VI: W51A
We present K-band spectra of newly born OB stars in the obscured Galactic
giant H II region W51A and ~ 0.8'' angular resolution images in the J, H and
K_S-bands. Four objects have been spectroscopically classified as O-type stars.
The mean spectroscopic parallax of the four stars gives a distance of 2.0 \pm
0.3 kpc (error in the mean), significantly smaller than the radio recombination
line kinematic value of 5.5 kpc or the values derived from maser propermotion
observations (6--8 kpc). The number of Lyman continuum photons from the
contribution of all massive stars (NLyc ~ 1.5 x 10^{50} s^{-1}) is in good
agreement with that inferred from radio recombination lines (NLyc = 1.3 x
10^{50} s^{-1}) after accounting for the smaller distance derived here.
We present analysis of archival high angular resolution images (NAOS CONICA
at VLT and T-ReCS at Gemini) of the compact region W51 IRS2. The K_S--band
images resolve the infrared source IRS~2 indicating that it is a very young
compact HII region. Sources IRS2E was resolved into compact cluster (within 660
AU of projected distance) of 3 objects, but one of them is just bright extended
emission. W51d1 and W51d2 were identified with compact clusters of 3 objects
(maybe 4 in the case of W51d1) each one. Although IRS~2E is the brightest
source in the K-band and at 12.6 \micron, it is not clearly associated with a
radio continuum source. Our spectrum of IRS~2E shows, similar to previous work,
strong emission in Br and HeI, as well as three forbidden emission
lines of FeIII and emission lines of molecular hydrogen (H_2) marking it as a
massive young stellar object.Comment: 31 pages and 9 figures, submitted to A
Semi-automatic spline fitting of planar curvilinear profiles in digital images using the Hough transform
We develop a novel method for the recognition of curvilinear profiles in digital images. The proposed method, semi-automatic for both closed and open planar profiles, essentially consists of a preprocessing step exploiting an edge detection algorithm, and a main step involving the Hough transform technique. In the preprocessing step, a Canny edge detection algorithm is applied in order to obtain a reduced point set describing the profile curve to be reconstructed. Also, to identify in the profile possible sharp points like cusps, we additionally use an algorithm to find the approximated tangent vector of every edge point. In the subsequent main step, we then use a piecewisely defined Hough transform to locally recognize from the point set a low-degree piecewise polynomial curve. The final outcome of the algorithm is thus a spline curve approximating the underlined profile image. The output curve consists of polynomial pieces connected G^1 continuously, except in correspondence of the identified cusps, where the order of continu- ity is only C^0 , as expected. To illustrate effectiveness and efficiency of the new profile detection technique we present several numerical results dealing with detection of open and closed profiles in images of dif- ferent type, i.e., medical and photographic image
Beyond B-splines: Exponential pseudo-splines and subdivision schemes reproducing exponential polynomials
The main goal of this paper is to present some generalizations of polynomial B-splines, which include exponential B-splines and the larger family of exponential pseudo-splines. We especially focus on their connections to subdivision schemes. In addition, we generalize a well-known result on the approximation order of exponential pseudo-splines, providing conditions to establish the approximation order of nonstationary subdivision schemes reproducing spaces of exponential polynomial function
Experimental evidence of replica symmetry breaking in random lasers
Spin-glass theory is one of the leading paradigms of complex physics and
describes condensed matter, neural networks and biological systems, ultracold
atoms, random photonics, and many other research fields. According to this
theory, identical systems under identical conditions may reach different states
and provide different values for observable quantities. This effect is known as
Replica Symmetry Breaking and is revealed by the shape of the probability
distribution function of an order parameter named the Parisi overlap. However,
a direct experimental evidence in any field of research is still missing. Here
we investigate pulse-to-pulse fluctuations in random lasers, we introduce and
measure the analogue of the Parisi overlap in independent experimental
realizations of the same disordered sample, and we find that the distribution
function yields evidence of a transition to a glassy light phase compatible
with a replica symmetry breaking.Comment: 10 pages, 5 figure
Trial by scanning electron microscopy (SEM) and semi-quantitative spectral analysis of restoration interface -dentin previously demineralized and restored with glass ionomer
El propósito del trabajo de investigación, fue desarrollar
un ensayo de complejidad aceptable para estudios
en el ámbito universitario, a fin de observar
el grado de penetrabilidad de la restauración con
ionómero vítreo de esmalte desmineralizado y a la
vez, constatar la presencia de metales y no metales
debidos a la restauración que pueden justificar
el poder remineralizante otorgado a los ionómeros
vítreos. Se utilizaron especímenes de terceros molares
retenidos sanos. Se sometieron a un protocolo de
desmineralización y posterior obturación con un ionómero
vítreo autocurable. Se los preparó para MEB
y posterior análisis semicuantitativo químico por espectroscopía
por dispersión de rayos X. Se observa
un enriquecimiento en masa de flúor en los canales
de dentina que incrementan la probabilidad de una
posterior remineralización en un elemento dentario
vivo.The purpose of the research was to develop a test
of acceptable complexity for studies in universities,
in order to observe the penetration degree of the
restoration with glass ionomer of demineralized
enamel and, simultaneously, verify the presence of
metals and non-metals due to restoration that can
justify the remineralizing power granted to glass
ionomers. Specimens of healthy third molars were
used and subjected to a demineralization protocol and
subsequent filling with a self-curable glass ionomer.
They were prepared for a SEM and subsequent semiquantitative
chemical analysis by X-ray scattering
spectroscopy. A massive enrichment of fluoride in
dentin channels is observed, which increases the
likelihood of further living tooth remineralization.Fil: Fasoli, L. C..
Universidad Nacional de Cuyo. Facultad de OdontologíaFil: Conti Viejo, María Noelia.
Universidad Nacional de Cuyo. Facultad de Odontologí
Condensation in disordered lasers: theory, 3D+1 simulations and experiments
The complex processes underlying the generation of a coherent-like emission
from the multiple-scattering of photons and wave-localization in the presence
of structural disorder are still mostly un-explored. Here we show that a single
nonlinear Schroedinger equation, playing the role of the Schawlow-Townes law
for standard lasers, quantitatively reproduces experimental results and
three-dimensional time-domain parallel simulations of a colloidal laser system.Comment: 4 pages, 5 figure
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