2,377 research outputs found
Spatial rogue waves in photorefractive SBN crystals
We report on the excitation of large-amplitude waves, with a probability of
around 1% of total peaks, on a photorefractive SBN crystal by using a simple
experimental setup at room temperature. We excite the system using a narrow
Gaussian beam and observe different dynamical regimes tailored by the value and
time rate of an applied voltage. We identify two main dynamical regimes: a
caustic one for energy spreading and a speckling one for peak emergence. Our
observations are well described by a two-dimensional Schr\"odinger model with
saturable local nonlinearity.Comment: 4 pages, 4 figure
Innovative instrumentation and methodology to characterize long distance heliostat beam quality in commercial solar power tower plants
The characterization of the whole solar field of a solar tower power plant is a time consuming labor that has to be performed to know the optical quality of each heliostat in the field. This allows to correct some deviations of each heliostat, leading to an improvement in its individual performance, and thus, improving the final performance of the whole field. The current methodology to characterize the optical quality of a heliostat is based on using a lambertian target, in which the solar beam is focused and its reflected radiation is captured using cameras. This leads to important measurement inaccuracies due to the non-uniformity of the lambertian target and the behavior of the camera. But the fact that the sun beam can overflow the size of the target, and its power density can be almost in the order of the ambient light, implies that a huge part of the heliostats in a plant cannot be well-characterized by these systems. These issues are even more important taking into account that plant size tends to grow even larger, increasing the distance of the furthest heliostats, and that small heliostats begin to be introduced in solar fields, whose reflected power is lower than that of common heliostats. Those issues will be overcome thanks to a new measurement system based on a non-tracking way to scan the sun spot, using an array of optoelectronic detectors which can be installed in new plants and even in plants that are now in operation
Increased HCO production in the outer disk around HD 163296
Three formaldehyde lines were observed (HCO 3--2, HCO
3--2, and HCO 3--2) in the protoplanetary disk
around the Herbig Ae star HD 163296 with ALMA at 0.5 arcsecond (60 AU) spatial
resolution. HCO 3--2 was readily detected via imaging, while
the weaker HCO 3--2 and HCO 3--2 lines
required matched filter analysis to detect. HCO is present throughout most
of the gaseous disk, extending out to 550 AU. An apparent 50 AU inner radius of
the HCO emission is likely caused by an optically thick dust continuum. The
HCO radial intensity profile shows a peak at 100 AU and a secondary bump at
around 300 AU, suggesting increased production in the outer disk. Different
parameterizations of the HCO abundance were compared to the observed
visibilities with minimization, using either a characteristic
temperature, a characteristic radius or a radial power law index to describe
the HCO chemistry. Similar models were applied to ALMA Science Verification
data of CO. In all modeling scenarios, fits to the HCO data show an
increased abundance in the outer disk. The overall best-fit HCO model shows
a factor of two enhancement beyond a radius of 27020 AU, with an inner
abundance of . The HCO emitting region has a lower
limit on the kinetic temperature of K. The CO modeling suggests
an order of magnitude depletion in the outer disk and an abundance of in the inner disk. The increase in HCO outer disk emission
could be a result of hydrogenation of CO ices on dust grains that are then
sublimated via thermal desorption or UV photodesorption, or more efficient
gas-phase production beyond about 300 AU if CO is photodisocciated in this
region
Synthesis, characterization of a new carbonylated zirconium metallocene using a dichloro-zirconocene derived from partially alkylated s-indacene
Indexación: ScieloThis work describes the synthesis and characterization of new organometallic species, an unprecedented mononuclear zirconium complex bearing a tetraalkylated s-indacene ligand, and secondly, its respective dicarbonyl complex obtained by reduction with Mg/HgCl2. Theoretical calculations of these two compounds were carried out to gain further understanding of these novel molecular systems.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000300014&lng=es&nrm=is
The g-factors of discrete levels in nanoparticles
Spin-orbit scattering suppresses Zeeman splitting of individual energy levels
in small metal particles. This suppression becomes significant when the
spin-orbit scattering rate \tau_{so}^{-1} is comparable with the quantum level
spacing \delta. The g-factor exhibits mesoscopic fluctuations; at small
\delta\tau_{so} it is distributed according to the Maxwell distribution. At
\delta\tau_{so}\to 0 the average g-factor levels off at a small value
g\sim(l/L)^{1/2} given by the ratio of the electron mean free path l to the
particle size L. On the contrary, in 2D quantum dots the g-factor is strongly
enhanced by spin-orbit coupling.Comment: 4 page
Compressible Sherrington-Kirkpatrick spin-glass model
We introduce a Sherrington-Kirkpatrick spin-glass model with the addition of
elastic degrees of freedom. The problem is formulated in terms of an effective
four-spin Hamiltonian in the pressure ensemble, which can be treated by the
replica method. In the replica-symmetric approximation, we analyze the
pressure-temperature phase diagram, and obtain expressions for the critical
boundaries between the disordered and the ordered (spin-glass and
ferromagnetic) phases. The second-order para-ferromagnetic border ends at a
tricritical point, beyond which the transition becomes discontinuous. We use
these results to make contact with the temperature-concentration phase diagrams
of mixtures of hydrogen-bonded crystals.Comment: 8 pages, 2 figures; added references, added conten
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