•Trees and shrubs show positive growth trends over the 20th century at the Pyrenean treeline.•Shrubs – more than trees - have benefited from climate change.•Tree and shrub species differ in their ...response to climate.•Rhododendron ferrugineum is increasingly negatively affected by decreasing snow cover.
Mountain ecosystems are particularly sensitive to climate change, which in part causes encroachment of woody plants at the treeline ecotone, with repercussions on treeline advance and ecosystem carbon balance. Yet, studies investigating the long-term trends in radial growth as well as year-to-year response of several tree and shrub species to climate change are scarce, especially in the Pyrenees where dendroecological studies are hitherto critically lacking. Here, we estimate and compare the long-term growth trends of two shrub (Rhododendron ferrugineum and Juniperus communis) and one tree (Pinus uncinata) species, and investigate their year-to-year growth response to changing climatic conditions and advancing snow melt-out timings. We used the Age-Class Isolation method (ACI) to derive growth trends from the ring width series of trees and shrubs. Climate-growth relationships were evaluated using fixed- and moving-window bootstrap correlation functions with the aim to determine the effects of changing climate and snowpack on shrub and tree growth. Overall, our results show that all species at our site, especially shrubs, have grown increasingly well over at least the last century, probably in response to increasing temperatures during the growing season and earlier snow melt-out dates. Nevertheless, the two shrub species differ quite strongly in their response to climate. Whereas the climate signal of J. communis has been relatively stable in recent decades despite the persistent and significant warming trend, R. ferrugineum shows a strong shift in climate sensitivity and is increasingly affected negatively by climate change. Altogether, our results address the different climate sensitivity of the two most common shrubs in the Pyrenees. They also contribute to a better understanding of vegetation dynamics in the Pyrenean treeline ecotone in the context of global change.
Come affrontare la valutazione neuropsicologica negli adulti? Quali domande porsi? Quali sono le insidie? Quali sono i suoi campi di applicazione? Se lo sviluppo degli strumenti psicometrici e del ...processo di valutazione neuropsicologica è cambiato assai poco negli ultimi dieci anni (a parte l’aggiornamento di alcuni strumenti), la loro applicazione è stata viceversa estesa a nuovi campi: psichiatria, guida dell’automobile, domicilio e così via. Lo scopo di questo articolo è di rivedere i principi della valutazione neuropsicologica in una duplice prospettiva: rispetto ai suoi campi di applicazione e scandendo ogni sfera cognitiva. Si pone così l’accento sul fatto che una valutazione non è un semplice successivo superamento di test ma un approccio scientifico supportato da precise ipotesi cliniche, adattate a ciascun paziente e a ciascun quadro valutativo, formulate alla luce delle conoscenze teoriche (sia sulle funzioni cognitive che sulle patologie), che lo psicologo deve padroneggiare e nel rispetto delle questioni etiche.
Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the ...observation of soft x-ray second harmonic generation near the carbon K edge (∼284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from the first atomic layer at the open surface. This technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.
Extreme ultraviolet and X-ray free-electron lasers (FELs) produce short-wavelength pulses with high intensity, ultrashort duration, well-defined polarization and transverse coherence, and have been ...utilized for many experiments previously possible only at long wavelengths: multiphoton ionization, pumping an atomic laser and four-wave mixing spectroscopy. However one important optical technique, coherent control, has not yet been demonstrated, because self-amplified spontaneous emission FELs have limited longitudinal coherence. Single-colour pulses from the FERMI seeded FEL are longitudinally coherent, and two-colour emission is predicted to be coherent. Here, we demonstrate the phase correlation of two colours, and manipulate it to control an experiment. Light of wavelengths 63.0 and 31.5 nm ionized neon, and we controlled the asymmetry of the photoelectron angular distribution by adjusting the phase, with a temporal resolution of 3 as. This opens the door to new short-wavelength coherent control experiments with ultrahigh time resolution and chemical sensitivity.
The FERMI free-electron lasers Allaria, E.; Badano, L.; Bassanese, S. ...
Journal of synchrotron radiation,
20/May , Letnik:
22, Številka:
3
Journal Article
Recenzirano
Odprti dostop
FERMI is a seeded free‐electron laser (FEL) facility located at the Elettra laboratory in Trieste, Italy, and is now in user operation with its first FEL line, FEL‐1, covering the wavelength range ...between 100 and 20 nm. The second FEL line, FEL‐2, a high‐gain harmonic generation double‐stage cascade covering the wavelength range 20–4 nm, has also completed commissioning and the first user call has been recently opened. An overview of the typical operating modes of the facility is presented.
Short wavelength free-electron lasers (FELs), providing pulses of ultrahigh photon intensity, have revolutionized spectroscopy on ionic targets. Their exceptional photon flux enables multiple photon ...absorptions within a single femtosecond pulse, which in turn allows for deep insights into the photoionization process itself as well as into evolving ionic states of a target. Here we employ ultraintense pulses from the FEL FERMI to spectroscopically investigate the sequential emission of electrons from gaseous, atomic argon in the neutral as well as the ionic ground state. A pronounced forward-backward symmetry breaking of the angularly resolved emission patterns with respect to the light propagation direction is experimentally observed and theoretically explained for the region of the Cooper minimum, where the asymmetry of electron emission is strongly enhanced. These findings aim to originate a better understanding of the fundamentals of photon momentum transfer in ionic matter.
Laser-heater systems are essential tools to control and optimize high-gain free-electron lasers (FELs) working in the x-ray wavelength range. Indeed, these systems induce a controllable increase of ...the energy spread of the electron bunch. The heating suppresses longitudinal microbunching instability which otherwise would limit the FEL performance. Here, we demonstrate that, through the action of the microbunching instability, a long-wavelength modulation of the electron beam induced by the laser heater at low energy can persist until the beam entrance into the undulators. This coherent longitudinal modulation is exploited to control the FEL spectral properties, in particular, multicolor extreme-ultraviolet FEL pulses can be generated through a frequency mixing of the modulations produced by the laser heater and the seed laser in the electron beam. We present an experimental demonstration of this novel configuration carried out at the FERMI FEL.
Single-photon laser-enabled Auger decay (spLEAD) is predicted theoretically B. Cooper and V. Averbukh, Phys. Rev. Lett. 111, 083004 (2013)PRLTAO0031-900710.1103/PhysRevLett.111.083004 and here we ...report its first experimental observation in neon. Using coherent, bichromatic free-electron laser pulses, we detect the process and coherently control the angular distribution of the emitted electrons by varying the phase difference between the two laser fields. Since spLEAD is highly sensitive to electron correlation, this is a promising method for probing both correlation and ultrafast hole migration in more complex systems.
The spectacular development of Laser-Plasma Accelerators (LPA) appears very promising for a free electron laser application. The handling of the inherent properties of those LPA beams already allowed ...controlled production of LPA-based spontaneous undulator radiation. Stepping further, we here unveil that the forthcoming LPA-based seeded FELs will present distinctive spatio-spectral distributions. Relying on numerical simulations and simple analytical models, we show how those interferometric patterns can be exploited to retrieve, in single-shot, the spectro-temporal content and source point properties of the FEL pulses.
Rhododendron ferrugineum L. is a widespread dwarf shrub species growing in high-elevation, alpine environments of the Western European Alps. For this reason, analysis of its growth rings offers ...unique opportunities to push current dendrochronological networks into extreme environments and way beyond the treeline. Given that different species of the same genus have been successfully used in tree-ring investigations, notably in the Himalayas where Rhododendron spp. has proven to be a reliable climate proxy, this study aims at (i) evaluating the dendroclimatological potential of R. ferrugineum and at (ii) determining the major limiting climate factor driving its growth. To this end, 154 cross-sections from 36 R. ferrugineum individuals have been sampled above local treelines and at elevations from 1800 to 2100masl on northwest-facing slopes of the Taillefer massif (French Alps). We illustrate a 195-year-long standard chronology based on growth-ring records from 24 R. ferrugineum individuals, and document that the series is well-replicated for almost one century (1920–2015) with an Expressed Population Signal (EPS) >0.85. Analyses using partial and moving 3-months correlation functions further highlight that growth of R. ferrugineum is governed by temperatures during the growing season (May–July), with increasingly higher air temperatures favoring wider rings, a phenomenon which is well known from dwarf shrubs growing in circum-arctic tundra ecosystems. Similarly, the negative effect of January–February precipitation on radial growth of R. ferrugineum, already observed in the Alps on juniper shrubs, is interpreted as a result of shortened growing seasons following snowy winters. We conclude that the strong and unequivocal signals recorded in the fairly long R. ferrugineum chronologies can indeed be used for climate–growth studies as well as for the reconstruction of climatic fluctuations in Alpine regions beyond the upper limits of present-day forests.
Display omitted
•Rhododendron ferrugineum allows the development of multi-decadal annually resolved ring-width chronologies.•The species allows the reconstruction of climate-growth associations for locations above treeline.•May–July temperatures are the key unifying growth-limiting factors at the study site.•R. ferrugineum integrates a winter signal in its rings, long-lasting snow cover has a detrimental effect on radial growth.
PDF
