Plants in aquatic ecosystems: current trends and future directions

Aquatic plants fulfil a wide range of ecological roles, and make a substantial contribution to the structure, function and service provision of aquatic ecosystems. Given their well-documented importance in aquatic ecosystems, research into aquatic plants continues to blossom. The 14th International Symposium on Aquatic Plants, held in Edinburgh in September 2015, brought together 120 delegates from 28 countries and six continents. This special issue of Hydrobiologia includes a select number of papers on aspects of aquatic plants, covering a wide range of species, systems and issues. In this paper we present an overview of current trends and future directions in aquatic plant research in the early 21st century. Our understanding of aquatic plant biology, the range of scientific issues being addressed and the range of techniques available to researchers have all arguably never been greater; however, substantial challenges exist to the conservation and management of both aquatic plants and the ecosystems in which they are found. The range of countries and continents represented by conference delegates and authors of papers in the special issue illustrate the global relevance of aquatic plant research in the early 21st century but also the many challenges that this burgeoning scientific discipline must address

keV x-ray spectroscopy of plasmas produced by the intense picosecond irradiation of a gas of xenon clusters

Abstract. We have studied the characteristics of x-ray emission in the 12-16Å range from plasmas produced by the irradiation of a target of Xe clusters with picosecond laser pulses at intensities near 10 17 W cm −2 . These plasmas exhibit strong emission from Ni-like through to Mn-like Xe. We find that the strength and character of the x-ray spectra are very similar when either 1053 or 526 nm laser pulses are used to heat the clusters. Recently, a substantial amount of experimental The consequences of this high absorption by the clusters are quite striking. McPherson et al have observed strong emission from Xe clusters with wavelengths as short as 2.8Å [1]. They attributed the strong x-ray emission to the preferential ejection of inner-shell electrons in the cluster atoms by the coherent addition of oscillating electrons in the cluster, though this hypothesis has not been supported by the findings of other group

Generation of bright, extreme-ultraviolet harmonic radiation from a krypton fluoride laser

We present results of experiments studying the efficiency of high harmonic generation from a gas target using the TITANIA krypton fluoride laser at the Rutherford Appleton Laboratory. The variation of harmonic yield for the 7th to 13th harmonics (355-191 Å) is studied as a function of the backing pressure of a solenoid valve gas jet and of the axial position of the laser focus relative to the centre of the gas jet nozzle. Harmonic energies up to 1 μJ were produced in helium and neon targets from laser energies of approximately 200 mJ. This corresponds to absolute conversion efficiencies of up to 5 × 10-6

Feasibility study of high harmonic generation from short wavelength lasers interacting with solid targets

The generation of the third and fourth harmonics from the interaction of a 1 ps, ultraviolet (UV), krypton fluoride (KrF) laser with a solid surface is investigated. The conversion efficiency is seen to increase linearly with Iλ2, with a transition from specular harmonic emission to emission into 2π steradians occurring between 1015 and 1016 W cm-2 μm2. The diffuse emission is strongly dependent on the incidence angle of the laser, with the peak in emission at around 30° being consistent with measurements for resonance absorption. Finally, the conversion efficiencies are found to be in agreement with particle-in-cell (PIC) simulations including appropriate density scalelengths. © 1998 Elsevier Science B.V

Mapping the electronic structure of warm dense nickel via resonant inelastic x-ray scattering

The development of bright free-electron lasers (FEL) has revolutionised our ability to create and study matter in the high-energy-density (HED) regime. Current diagnostic techniques have been successful in yielding information on fundamental thermodynamic plasma properties, but provide only limited or indirect information on the detailed quantum structure of these systems, and on how it is affected by ionization dynamics. Here we show how the valence electronic structure of soliddensity nickel, heated to temperatures of around 10 of eV on femtosecond timescales, can be probed by single-shot resonant inelastic x-ray scattering (RIXS) at the Linac Coherent Light Source FEL. The RIXS spectrum provides a wealth of information on the HED system that goes well beyond what can be extracted from x-ray absorption or emission spectroscopy alone, and is particularly well-suited to time-resolved studies of electronic-structure dynamics

Probing the electronic structure of warm dense nickel via resonant inelastic x-ray scattering

The development of bright free-electron lasers (FEL) has revolutionized our ability to create and study matter in the high-energy-density (HED) regime. Current diagnostic techniques have been successful in yielding information on fundamental thermodynamic plasma properties, but provide only limited or indirect information on the detailed quantum structure of these systems, and on how it is affected by ionization dynamics. Here we show how the valence electronic structure of solid-density nickel, heated to temperatures of around 10 of eV on femtosecond timescales, can be probed by single-shot resonant inelastic x-ray scattering (RIXS) at the Linac Coherent Light Source FEL. The RIXS spectrum provides a wealth of information on the HED system that goes well beyond what can be extracted from x-ray absorption or emission spectroscopy alone, and is particularly well suited to time-resolved studies of electronic-structure dynamics

Detailed hydrodynamic and X-ray spectroscopic analysis of a laser-produced rapidly-expanding aluminium plasma

We present a detailed analysis of K-shell emission from laser-produced rapidly-expanding Al plasmas. This work forms part of a series of experiments performed at the Vulcan laser facility of the Rutherford Appleton Laboratory, UK. 1-D planar expansion was obtained by over-illuminating A1-microdot targets supported on CH plastic foils. The small size of the A1-plasma ensured high spatial and frequency resolution of the spectra, obtained with a single crystal spectrometer, two vertical dispersion variant double crystal spectrometers, and a vertical dispersion variant Johann Spectrometer. The hydrodynamic properties of the plasma were measured independently by spatially and temporally resolved Thomson scattering, utilizing a 4ω probe beam. This enabled sub- and super-critical densities to be probed relative to the 1ω heater beams. The deduced plasma hydrodynamic conditions are compared with those generated from the 1-D hydro-code Medusa, and the significant differences found in the electron temperature discussed. Synthetic spectra generated from the detailed term collisional radiative non-LTE atomic physics code Fly are compared with the experimental spectra for the measured hydrodynamic parameters, and for those taken from Medusa. Excellent agreement is only found for both the H- and He-like A1 series when careful account is taken of the temporal evolution of the electron temperature. © 2001 Published by Elsevier Science Ltd