Dynamics and control of the expansion of finite-size plasmas produced in ultraintense laser-matter interactions

The strong influence of the electron dynamics provides the possibility of controlling the expansion of laser-produced plasmas by appropriately shaping the laser pulse. A simple irradiation scheme is proposed to tailor the explosion of large deuterium clusters, inducing the formation of shock structures, capable of driving nuclear fusion reactions. Such a scenario has been thoroughly investigated, resorting to two- and three-dimensional particle-in-cell simulations. Furthermore, the intricate dynamics of ions and electrons during the collisionless expansion of spherical nanoplasmas has been analyzed in detail using a self-consistent ergodic-kinetic model. This study clarifies the transition from hydrodynamic-like to Coulomb-explosion regimes

All-optical trapping and acceleration of heavy particles

A scheme for fast, compact, and controllable acceleration of heavy particles in vacuum is proposed, in which two counterpropagating lasers with variable frequencies drive a beat-wave structure with variable phase velocity, thus allowing for trapping and acceleration of heavy particles, such as ions or muons. Fine control over the energy distribution and the total charge of the beam is obtained via tuning of the frequency variation. The acceleration scheme is described with a one-dimensional theory, providing the general conditions for trapping and scaling laws for the relevant features of the particle beam. Two-dimensional, electromagnetic particle-in-cell simulations confirm the validity and the robustness of the physical mechanism.Comment: 10 pages, 3 figures, to appear in New Journal of Physic

Physiological Responses to Drought Stress in Jatropha curcas Seedlings

Aims: The aim of the study was to investigate the physiological mechanisms of Jatropha curcas seedlings exposed to drought and the possible influence of seedling age. Study Design: A pot experiment was carried out using a completely randomized design with two seedling ages (2- and 3-month-old seedlings), two treatments per age (Watered: fully irrigated, and Unwatered: Not irrigated), six replicates (24 pots). Place and Duration of Study: The experiment was performed in a greenhouse facility located at the Experimental Station “Mauro Deidda” (Department of Agriculture of University of Sassari) at Ottava (Sassari, Italy) between June and September 2011. Methodology: To investigate the responses of 2- and 3-month-old J. curcas seedlings exposed to drought stress on 4th, 8th, 12th, 19th, and 26th day from treatment’s beginning, leaf and soil water content, biometric, gas exchange, and chlorophyll a fluorescence measurements were performed; on 26th day from treatment’s beginning, biometric destructive measurements were carried out. Results: Results support the hypothesis that J. curcas is appropriate to be cultivated in areas with limited water availability or prolonged periods of drought and highlight that mechanisms of drought response are highly influenced by seedling age. J. curcas seedlings maintained a good leaf water status by means of an effective stomatal closure, associated with a reduced aboveground growth and an increased root:shoot ratio. Under drought stress, 2-month seedlings showed a higher allocation of resources to roots compared to 3-month seedlings. Drought resulted in more detrimental effects on the photosynthetic response of 3-month seedlings, inducing the reduction of stomata conductance and the loss of photosystem II integrity. 2-month seedlings were instead able to activate mechanisms of drought tolerance through the activation of excess energy dissipation mechanisms. Conclusion: In the early stage of crop establishment, the transplanting of J. curcas 2-month seedlings proved to be more effective in order to avoid water stress related consequences

Patrimonio genetico delle pomacee in Sardegna: il pero: cenni storici e cultivar individuate

The cultivation of pomaceous varieties, especially the pear, has for many centuries been of great importance and widely diffused in Sardinia. This is confirmed by many historical documents, a brief riview of which is given in this paper. Also reviewed are the principal pomological and qualitative characteristics of pear cultivars, either of local origin or which were introduced in ancient times, and which can still be found on the island. For the most part they are cultivars either forgotten or on the way to becoming extinct, but which present special characteristics, both in form and taste, which justify plans being implemented for the recovery and exploitation. In fact, this idea appears to represent one of the approaches to the problem of limiting the importantion of fruit and vegetables into Sardinia: that of offering the consumer typical, high-quality produce with a «difference» with respect to italian national standards

Efficient calculation of van der Waals dispersion coefficients with time-dependent density functional theory in real time: application to polycyclic aromatic hydrocarbons

The van der Waals dispersion coefficients of a set of polycyclic aromatic hydrocarbons, ranging in size from the single-cycle benzene to circumovalene (C66H20), are calculated with a real-time propagation approach to time-dependent density functional theory (TDDFT). In the non-retarded regime, the Casimir-Polder integral is employed to obtain C6, once the dynamic polarizabilities have been computed at imaginary frequencies with TDDFT. On the other hand, the numerical coefficient that characterizes the fully retarded regime is obtained from the static polarizabilities. This ab initio strategy has favorable scaling with the size of the system - as demonstrated by the size of the reported molecules - and can be easily extended to obtain higher order van der Waals coefficients.Comment: submitted to J. Chem. Phy

Direct Acceleration of Ions With Variable-frequency Lasers

A method is proposed for producing monoergetic, high-quality ion beams in vacuum, via direct acceleration by the electromagnetic field of two counterpropagating, variable-frequency lasers: ions are trapped and accelerated by a beat-wave structure with variable phase velocity, allowing for fine control over the energy and the charge of the beam via tuning of the frequency variation. The physical mechanism is described with a one-dimensional theory, providing the general conditions for trapping and scaling laws for the relevant features of the ion beam. Two-dimensional, electromagnetic particle-in-cell simulations, in which hydrogen gas is considered as an ion source, confirm the validity and the robustness of the method.Comment: 15 pages, 6 figures, to appear in IEEE Transactions on Plasma Science, special issue Laser & Plasma Accelerator

Polycyclic aromatic hydrocarbons with SPICA

Thanks to high sensitivity and angular resolution and broad spectral coverage, SPICA will offer a unique opportunity to better characterize the nature of polycyclic aromatic hydrocarbons (PAHs) and very small grains (VSGs), to better use them as probes of astrophysical environments. The angular resolution will enable to probe the chemical frontiers in the evolution process from VSGs to neutral PAHs, to ionized PAHs and to "Grand-PAHs" in photodissotiation regions and HII regions, as a function of G$_0$/n (UV radiation field / density). High sensitivity will favor the detection of the far-IR skeletal emission bands of PAHs, which provide specific fingerprints and could lead to the identification of individual PAHs. This overall characterization will allow to use PAH and VSG populations as tracers of physical conditions in spatially resolved protoplanetary disks and nearby galaxies (using mid-IR instruments), and in high redshift galaxies (using the far-IR instrument), thanks to the broad spectral coverage SPICA provides. Based on our previous experience with ISO and Spitzer we discuss how these goals can be reached.Comment: To appear in Proc. Workshop "The Space Infrared Telescope for Cosmology & Astrophysics: Revealing the Origins of Planets and Galaxies". Eds. A.M. Heras, B. Swinyard, K. Isaak, and J.R. Goicoeche

The First Level Trigger of JEM-EUSO: Concept and tests

The trigger system of JEM-EUSO is designed to meet specific challenging requirements. These include managing a large number of pixels ( 3·10^5) and using a very fast, low power consuming, and radiation hard electronics. It must achieve a high signal-to-noise performance and flexibility and cope with the limited down-link transmission rate from the International Space Station (ISS) to Earth. The general overview of the First Level Trigger for cosmic ray detection is reviewed; tests that validate its performance are discussed