1,067 research outputs found
Partial inner product spaces: Some categorical aspects
We make explicit in terms of categories a number of statements from the
theory of partial inner product spaces (PIP spaces) and operators on them.
In particular, we construct sheaves and cosheaves of operators on certain PIP
spaces of practical interest.Comment: 21 page
Effects of Supplemental Irrigation on Berseem Seed Crop in a Semi-Arid Mediterranean Environment
Berseem seed production in Mediterranean environments is strongly influenced by soil water availability, particularly during spring growth. A long-term study (11 years) in Sicily recorded seed yields of between 0 and 1600 kg/ha, for an annual rainfall range of 289 to 867 mm (Stringi et al., 2001). It was proposed that water irrigation during sensitive growth stages could increase and stabilize seed yield. This research investigated the response of berseem seed crop to low levels of irrigation applied at different growth stages
Filamentation in Kerr media from pulsed Bessel beams
In contrast with filamentation of ultrashort laser pulses with standard Gaussian beams in Kerr media, three different types of Bessel filaments are obtained in air or in water by focusing ultrashort laser pulses with an axicon. We thoroughly investigate the different regimes and show that the beam reshapes as a nonlinear Bessel beam which establishes a conical energy flux from the low intensity tails toward the high intensity peak. This flux efficiently sustains a high contrast long-distance propagation and easily generates a continuous plasma channel in air
Three dimensional imaging of short pulses
We exploit a slightly noncollinear second-harmonic cross-correlation scheme
to map the 3D space-time intensity distribution of an unknown complex-shaped
ultrashort optical pulse. We show the capability of the technique to
reconstruct both the amplitude and the phase of the field through the coherence
of the nonlinear interaction down to a resolution of 10 m in space and 200
fs in time. This implies that the concept of second-harmonic holography can be
employed down to the sub-ps time scale, and used to discuss the features of the
technique in terms of the reconstructed fields.Comment: 16 pages, 6 figure
Emergence of X-shaped spatiotemporal coherence in optical waves
Considering the problem of parametric nonlinear interaction, we report the experimental observation of electromagnetic waves characterized by an X-shaped spatiotemporal coherence; i.e., coherence is neither spatial nor temporal, but skewed along specific spatiotemporal trajectories. The application of the usual, purely spatial or temporal, measures of coherence would erroneously lead to the conclusion that the field is fully incoherent. Such hidden coherence has been identified owing to an innovative diagnostic technique based on simultaneous analysis of both the spatial and temporal spectra
X-shaped space-time coherence in optical parametric generation
We study the spatiotemporal coherence properties of superfluorescence radiation generated in optical parametric amplification of quantum noise. We show that the angular dispersion properties of the spatiotemporal spectra, measured in different phase-matching conditions, lead to a clear X-shaped structure of the mutual correlation function of the radiation. Within a statistical picture, we interpret the generated superfluorescence as a stochastic \u201cgas\u201d of quasistationary modes characterized by a skewed correlation in the spatiotemporal domain, with characteristics similar to linear and nonlinear X waves not describable within a separable approach in space and time
Light-filament dynamics and the spatiotemporal instability of the Townes profile
The origin of the spatiotemporal filament dynamics of ultrashort pulses in nonlinear media, including axial-conical emission coupling, temporal splitting, and X waves, is explained by the spatiotemporal instability
of spatially localized nonlinear modes. Our experiments support this interpretation
Surfactant-enhanced mobilization of hydrocarbons from soil: Comparison between anionic and nonionic surfactants in terms of remediation efficiency and residual phytotoxicity
The aim of the present study was to assess the effectiveness of two surfactants (Polysorbate 80 – Tween 80 and
Sodium Dodecyl Benzensulphonate – SDBS) for the remediation of hydrocarbon-contaminated soil. To study the
effectiveness of these surfactants, an experimental laboratory-scale apparatus was set up for the simulation of a
soil flushing intervention. Different surfactant concentrations and flushing flow rates were investigated. At the
end of the experiments, the removal efficiency was evaluated and phytotoxicity tests were performed by means
of germination index (GI). Results showed that the use of both surfactants allows to reach high removal efficiency
(~50% for Tween 80 and ~70% for SDBS) of hydrocarbons from soil and that either the surfactant concentration
and the contact time between surfactant and contaminant affected the extraction performance. GI results showed
different effects of the two surfactants on the phytotoxic features of the soil after treatment. Indeed, while the soil
treated with SDBS was found to be more phytotoxic, leading to a lowering of the GI (10.88 %), the soil samples
flushed with Tween 80 were characterized by higher values (146.61%). These results might be of interest in the
case of surfactant application in remediation interventions in soils intended for future agricultural activity
Forage Quality and Yield of Berseem Clover and Annual Ryegrass Grown in Pure and Mixed Stands in Relation to Different N Application Rates
Grass-legume mixtures offer several advantages over monocultures in forage-animal production systems (Haynes, 1980). In fact, in grass-legume mixtures forage yield and quality are generally higher compared to grass monocultures also due to more efficient soil N-utilisation (Ta & Faris, 1987); furthermore grasses often utilise some of the N fixed by legumes (Malhi et al., 2002). Legumes do not generally require the addition of N fertiliser due to symbiotically fixed N, but the yield of the grass component in a mixture may be further improved with N application. The objective of this study was to investigate forage yield and quality of berseem and annual ryegrass grown in pure stands, and in mixture, at different N fertiliser rates
Noise-seeded spatiotemporal modulation instability in normal dispersion
6In optical second-harmonic generation with normal dispersion, the virtually infinite bandwidth of the unbounded, hyperbolic, modulational instability leads to quenching of spatial multisoliton formation and to the occurrence of a catastrophic spatiotemporal breakup when an extended beam is left to interact with an extremely weak external noise with a coherence time much shorter than that of the pump.openD. Salerno; O. Jedrkiewicz; J. Trull; G. Valiulis; A. Picozzi; P. Di TrapaniSalerno, Domenico; Jedrkiewicz, Ottavia; J., Trull; G., Valiulis; A., Picozzi; DI TRAPANI, Paol
- …