290 research outputs found
Infinite Order Differential Operators in Spaces of Entire Functions
We study infinite order differential operators acting in the spaces of
exponential type entire functions. We derive conditions under which such
operators preserve the set of Laguerre entire functions which consists of the
polynomials possessing real nonpositive zeros only and of their uniform limits
on compact subsets of the complex plane. We obtain integral representations of
some particular cases of these operators and apply these results to obtain
explicit solutions to some Cauchy problems for diffusion equations with
nonconstant drift term
Relaxation Time of Quantized Toral Maps
We introduce the notion of the relaxation time for noisy quantum maps on the
2d-dimensional torus - a generalization of previously studied dissipation time.
We show that relaxation time is sensitive to the chaotic behavior of the
corresponding classical system if one simultaneously considers the
semiclassical limit ( -> 0) together with the limit of small noise
strength (\ep -> 0).
Focusing on quantized smooth Anosov maps, we exhibit a semiclassical regime
\hbar^{-1}\ep\hbar$ << 1,
quantum and classical relaxation times behave very differently. In the special
case of ergodic toral symplectomorphisms (generalized ``Arnold's cat'' maps),
we obtain the exact asymptotics of the quantum relaxation time and precise the
regime of correspondence between quantum and classical relaxations.Comment: LaTeX, 27 pages, former term dissipation time replaced by relaxation
time, new introduction and reference
Protons accelerated in the target normal sheath acceleration regime by a femtosecond laser
Advanced targets based on thin films of graphene oxide covered by metallic layers have been irradiated at high laser intensity (∼1019 W/cm2) with 40 fs laser pulses to investigate the forward ion acceleration in the target normal sheath acceleration regime. A time-of-flight technique was employed with silicon-carbide detectors and ion collectors as fast on-line plasma diagnostics. At the optimized conditions of the laser focus position with respect to the target surface was measured the maximum proton energy using Au metallic films. A maximum proton energy of 2.85 MeV was measured using the Au metallization of 200 nm. The presence of graphene oxide facilitates the electron crossing of the foil minimizing the electron scattering and increasing the electric field driving the ion acceleration. The effect of plasma electron density control using the graphene oxide is presented and discussed
Study of shock waves generation, hot electron production and role of parametric instabilities in an intensity regime relevant for the shock ignition
We present experimental results at intensities relevant to Shock Ignition
obtained at the sub-ns Prague Asterix Laser System in 2012 . We studied shock waves
produced by laser-matter interaction in presence of a pre-plasma. We used a first beam at
1ω (1315 nm) at 7 × 10 13 W/cm 2 to create a pre-plasma on the front side of the target and
a second at 3ω (438 nm) at ∼ 10 16 W/cm 2 to create the shock wave. Multilayer targets
composed of 25 (or 40 μm) of plastic (doped with Cl), 5 μm of Cu (for Kα diagnostics)
and 20 μm of Al for shock measurement were used. We used X-ray spectroscopy of Cl
to evaluate the plasma temperature, Kα imaging and spectroscopy to evaluate spatial and
spectral properties of the fast electrons and a streak camera for shock breakout measurements.
Parametric instabilities (Stimulated Raman Scattering, Stimulated Brillouin Scattering and
Two Plasmon Decay) were studied by collecting the back scattered light and analysing its
spectrum. Back scattered energy was measured with calorimeters. To evaluate the maximum
pressure reached in our experiment we performed hydro simulations with CHIC and DUED
codes. The maximum shock pressure generated in our experiment at the front side of the
target during laser-interaction is 90 Mbar. The conversion efficiency into hot electrons was
estimated to be of the order of ∼ 0.1% and their mean energy in the order ∼50 keV.
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributio
Angular distributions of ions emitted from laser plasma produced at various irradiation angles and laser intensities
AbstractAngular distributions of currents and velocities (energies) of ions produced at various target irradiation angles and laser intensities ranged from 1010 W/cm2 to 1017 W/cm2 were analyzed. It was confirmed that for low laser intensities the ion current distributions are always peaked along the target normal. However, at laser intensities comparable to or higher than 1014 W/cm2, the preferred direction of ion emission strongly depends on the irradiation geometry (laser focus setting, the irradiation angle), and can be off the target normal. This is very likely caused by the non-linear interaction of the laser beam with produced plasma, in particular, by the action of ponderomotive forces and the laser beam self-focusing
Factors influencing parameters of laser ion sources
Various applications demand various kinds of ions. Charge state, energy and the amount of laser produced ions depend, primary, on the wavelength, the energy, the pulse duration, and the focusing ability of the laser used. Angle of the target irradiation, angle of the ion extraction (recording), and mainly the focus setting may significantly influence especially the portion of ions with the highest charge states. The participation of non-linear processes on the generation of ions with extremely high parameters is demonstrated. The observed effects support the idea of a longitudinal structure of the self-focused laser beam with a space period of ∼200 µm
Correction to: GloPL,a Global Data Base on Pollen Limitation of Plant Reproduction (Scientific Data, (2018), 5, (180249), 10.1038/sdata.2018.249)
J. H. Burns was omitted in error from the author list of the original version of this Data Descriptor. This omission has now been corrected in both the HTML and PDF versions
Interações Planta-polinizador Em Vegetação De Altitude Na Mata Atlântica
Tropical high-altitude vegetation is unique due to susceptibility to severe weather conditions in relation to lower formations, and by the peculiarity of its flora with many relictual components. Studies on plant-pollinator interactions in high-altitude rocky outcrops and forests of the Atlantic Forest are scarce, but compilation of information allows us to identify some patterns: low frequency of visits, high floral longevity and generalized pollination system. In tropical mountain ecosystems, the degree of generalization of pollination systems in functional (pollinator groups) and ecological (number of species) terms tends to be high, mainly due to the over-representation of certain plant taxa (e.g., Asteraceae in rocky outcrops and Fabaceae, Myrtaceae, Rubiaceae and Sapindaceae in montane forests). Generalized pollination systems and autogamy may be advantageous for tropical high-altitude plants due to the more severe weather conditions (e.g., low temperature), which decrease abundance and limit the activity of pollinators, resulting in lower visitation frequency. Nevertheless, some well represented groups in forests, such as orchids and plants pollinated by hummingbirds and bats, exemplify cases of higher functional specialization, as well as plants with poricidal anthers pollinated by bees in the high-altitude grasslands. However, in rocky outcrops, for some functional groups of pollinators (e.g., hummingbirds, bats, beetles and hawkmoths), the availability of resources does not allow the maintenance of all species throughout the year, favoring possible local or altitudinal migrations. Thus, rocky outcrops and high-altitude forests constitute a unit in the sense of sustaining the pollinator community. Indeed rocky outcrops and high-altitude forests share an evolutionary history at the regional scale since they passed through similar events of expansion and retraction in response to climate changes in the Quaternary. This could explain the complementarity between the two types of vegetation in the use of floral resources by pollinators. Besides the associations identified here, the ecology and evolution of plant-pollinator interactions in high-altitude vegetation of the Atlantic Forest remain poorly understood, making urgent the development of an integrative research program, as well as projects on issues related to climate change and biodiversity conservation. © 2016, Universidade Federal do Rio de Janeiro (UFRJ). All rights reserved.20272
The influence of an intense laser beam interaction with preformed plasma on the characteristics of emitted ion streams
AbstractIntense laser-beam interactions with preformed plasma, preceding the laser-target interactions, significantly influence both the ion and X-ray generation. It is due to the laser pulse (its total length, the shape of the front edge, its background, the contrast, the radial homogeneity) as well as plasma (density, temperature) properties. Generation of the super fast (FF) ion groups is connected with a presence of non-linear processes. Saturated maximum of the charge states (independently on the laser intensity) is ascribed to the constant limit radius of the self-focused laser beam. Its longitudinal structure is considered as a possible explanation for the course of some experimental dependencies obtained
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