Carbon dioxide concentration in Mediterranean greenhouses : how much lost production?

In the absence of artificial supply of carbon dioxide in the greenhouse environment, the CO2 absorbed in the process of photosynthesis must ultimately come from the external ambient through the ventilation openings. This requires that the CO2 concentration within the house must be lower than the external concentration, as there would be no flow inwards otherwise. Since potential assimilation (that is, the assimilation level that can be attained when no other factor is limiting) is heavily dependent on carbon dioxide concentration, this implies that assimilation is reduced, whatever the light level or crop status. The ventilation of the greenhouse implies a trade-off between ensuring inflow of carbon dioxide and maintaining an adequate temperature within the house, particularly during sunny, chilly days. We apply a simple model, on which the Dutch ¿philosophy¿ of CO2 fertilisation is based, for estimating the potential production loss, through data measured in commercial greenhouses in Almeria and Sicily. Thereafter we discuss the management options for a grower to limit losses. In particular we analyse costs, potential benefits and consequences of bringing in more carbon dioxide either through increased ventilation, at the cost of lowering temperature, or through artificial supply. We find out that, whereas the reduction in production caused by depletion is comparable to the reduction resulting from the lower temperature caused by ventilation to avoid depletion, compensating the effect of depletion is much cheaper than making up the loss by heating

Attosecond pulse shaping around a Cooper minimum

High harmonic generation (HHG) is used to measure the spectral phase of the recombination dipole matrix element (RDM) in argon over a broad frequency range that includes the 3p Cooper minimum (CM). The measured RDM phase agrees well with predictions based on the scattering phases and amplitudes of the interfering s- and d-channel contributions to the complementary photoionization process. The reconstructed attosecond bursts that underlie the HHG process show that the derivative of the RDM spectral phase, the group delay, does not have a straight-forward interpretation as an emission time, in contrast to the usual attochirp group delay. Instead, the rapid RDM phase variation caused by the CM reshapes the attosecond bursts.Comment: 5 pages, 5 figure

A comprehensive approach to establish the impact of worksites air emissions

Worksite activities are time-limited events associated with continuous releases of airborne pollutants, such as carbon monoxide, particulate matter, and NOx, and they impact potentially vast areas. The side-effects on the environment can be severe, and they are subject of literature studies, with the final aim of proposing solutions that may improve the management of air emissions. No general assessment method or approach is yet available to estimate their effects on the environment and workers’ health. In this work, a general procedure that can be potentially applied to every type of worksite is proposed (i.e., construction sites, upgrading of chemical plants, road sites, etc..). The approach involves a detailed assessment of emissions and their expected pollutant concentrations. A dedicated mathematical model has been defined to assess pollutant emissions over time, consistent with all the different phases of foreseen activities. Emissions are defined on base of the GANTT descriptions of the activities and air pollutant dispersion is simulated with a dedicated model. Finally, the obtained results are evaluated against air quality thresholds as defined by laws and conditioning the human health risks for workers and citizens potentially exposed to pollutants

Inelastic scattering of broadband electron wave packets driven by an intense mid-infrared laser field

Intense, 100 fs laser pulses at 3.2 and 3.6 um are used to generate, by multi-photon ionization, broadband wave packets with up to 400 eV of kinetic energy and charge states up to Xe+6. The multiple ionization pathways are well described by a white electron wave packet and field-free inelastic cross sections, averaged over the intensity-dependent energy distribution for (e,ne) electron impact ionization. The analysis also suggests a contribution from a 4d core excitation in xenon

Attosecond Synchronization of High-Order Harmonics from Midinfrared Drivers

The group delay dispersion, also known as the attochirp, of high-order harmonics generated in gases has been identified as the main intrinsic limitation to the duration of Fourier-synthesized attosecond pulses. Theory implies that the attochirp, which is inversely proportional to the laser wavelength, can be decreased at longer wavelength. Here we report the first measurement of the wavelength dependence of the attochirp using an all-optical, in situ method [N. Dudovich et al., Nature Phys. 2, 781 (2006)]. We show that a 2 μm driving wavelength reduces the attochirp with respect to 0.8 μm at comparable intensities