The prediction and management of aquatic nitrogen pollution across Europe: an introduction to the Integrated Nitrogen in European Catchments project (INCA)

Excess nitrogen in soils, fresh water, estuarine and marine systems contributes to nutrient enrichment in key ecosystems throughout Europe, often leading to detrimental environmental impacts, such as soil acidification or the eutrophication of water bodies. The Integrated Nitrogenmodel for European Catchments (INCA) project aims to develop a generic version of the Integrated Nitrogen in Catchments (INCA) model to simulate the retention and transport of nitrogen within river systems, thereby providing a tool to aid the understanding of nitrogen dynamics and for river-basin management/policy-making. To facilitate the development of the model, 10 partners have tested the INCA model with data collected in study sites located in eight European countries as part of the INCA project. This paper summarises the key nitrogen issues within Europe, describes the main aims and methodology of the INCA project, and sets the project in the context of the current major research initiatives at a European level.</p> <p style='line-height: 20px;'><b>Keywords: </b>Europe, European Union, nitrogen, nitrate, ammonium, river basin management, modelling, water chemistry, acidification, eutrophication, Water Framework Directive, INCA

Gravitational Wave Propagation in Isotropic Cosmologies

We study the propagation of gravitational waves carrying arbitrary information through isotropic cosmologies. The waves are modelled as small perturbations of the background Robertson-Walker geometry. The perfect fluid matter distribution of the isotropic background is, in general, modified by small anisotropic stresses. For pure gravity waves, in which the perturbed Weyl tensor is radiative (i.e. type N in the Petrov classification), we construct explicit examples for which the presence of the anisotropic stress is shown to be essential and the histories of the wave-fronts in the background Robertson-Walker geometry are shear-free null hypersurfaces. The examples derived in this case are analogous to the Bateman waves of electromagnetic theory.Comment: 27 pages, accepted for publication in Phys.Rev.

Intramolecular vibronic dynamics in molecular solids: C60

Vibronic coupling in solid C60 has been investigated with a combination of resonant photoemission spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS). Excitation as a function of energy within the lowest unoccupied molecular orbital resonance yielded strong oscillations in intensity and dispersion in RPES, and a strong inelastic component in RIXS. Reconciling these two observations establishes that vibronic coupling in this core hole excitation leads to predominantly inelastic scattering and localization of the excited vibrations on the molecule on a femtosecond time scale. The coupling extends throughout the widths of the frontier valence bands.

Direct measurement of molecular stiffness and damping in confined water layers

We present {\em direct} and {\em linear} measurements of the normal stiffness and damping of a confined, few molecule thick water layer. The measurements were obtained by use of a small amplitude (0.36 $\textrm{\AA}$), off-resonance Atomic Force Microscopy (AFM) technique. We measured stiffness and damping oscillations revealing up to 7 layers separated by 2.56 $\pm$ 0.20 $\textrm{\AA}$. Relaxation times could also be calculated and were found to indicate a significant slow-down of the dynamics of the system as the confining separation was reduced. We found that the dynamics of the system is determined not only by the interfacial pressure, but more significantly by solvation effects which depend on the exact separation of tip and surface. Thus ` solidification\rq seems to not be merely a result of pressure and confinement, but depends strongly on how commensurate the confining cavity is with the molecule size. We were able to model the results by starting from the simple assumption that the relaxation time depends linearly on the film stiffness.Comment: 7 pages, 6 figures, will be submitted to PR

Observation and Modeling of the Solar Transition Region: II. Solutions of the Quasi-Static Loop Model

In the present work we undertake a study of the quasi-static loop model and the observational consequences of the various solutions found. We obtain the most general solutions consistent with certain initial conditions. Great care is exercised in choosing these conditions to be physically plausible (motivated by observations). We show that the assumptions of previous quasi-static loop models, such as the models of Rosner, Tucker and Vaiana (1978) and Veseckey, Antiochos and Underwood (1979), are not necessarily valid for small loops at transition region temperatures. We find three general classes of solutions for the quasi-static loop model, which we denote, radiation dominated loops, conduction dominated loops and classical loops. These solutions are then compared with observations. Departures from the classical scaling law of RTV are found for the solutions obtained. It is shown that loops of the type that we model here can make a significant contribution to lower transition region emission via thermal conduction from the upper transition region.Comment: 30 pages, 3 figures, Submitted to ApJ, Microsoft Word File 6.0/9

Phase Mixing of Alfvén Waves Near a 2D Magnetic Null Point

The propagation of linear Alfvén wave pulses in an inhomogeneous plasma near a 2D coronal null point is investigated. When a uniform plasma density is considered, it is seen that an initially planar Alfvén wavefront remains planar, despite the varying equilibrium Alfvén speed, and that all the wave collects at the separatrices. Thus, in the non-ideal case, these Alfvénic disturbances preferentially dissipate their energy at these locations. For a non-uniform equilibrium density, it is found that the Alfvén wavefront is significantly distorted away from the initially planar geometry, inviting the possibility of dissipation due to phase mixing. Despite this however, we conclude that for the Alfvén wave, current density accumulation and preferential heating still primarily occur at the separatrices, even when an extremely non-uniform density profile is considered

All-optical switching and strong coupling using tunable whispering-gallery-mode microresonators

We review our recent work on tunable, ultrahigh quality factor whispering-gallery-mode bottle microresonators and highlight their applications in nonlinear optics and in quantum optics experiments. Our resonators combine ultra-high quality factors of up to Q = 3.6 \times 10^8, a small mode volume, and near-lossless fiber coupling, with a simple and customizable mode structure enabling full tunability. We study, theoretically and experimentally, nonlinear all-optical switching via the Kerr effect when the resonator is operated in an add-drop configuration. This allows us to optically route a single-wavelength cw optical signal between two fiber ports with high efficiency. Finally, we report on progress towards strong coupling of single rubidium atoms to an ultra-high Q mode of an actively stabilized bottle microresonator.Comment: 20 pages, 24 figures. Accepted for publication in Applied Physics B. Changes according to referee suggestions: minor corrections to some figures and captions, clarification of some points in the text, added references, added new paragraph with results on atom-resonator interactio

The quest for the genuine visual mismatch negativity (vMMN): Event-related potential indications of deviance detection for low-level visual features

Research shows that the visual system monitors the environment for changes. For example, a left‐tilted bar, a deviant, that appears after several presentations of a right‐tilted bar, standards, elicits a classic visual mismatch negativity (vMMN): greater negativity for deviants than standards in event‐related potentials (ERPs) between 100 and 300 ms after onset of the deviant. The classic vMMN is contributed to by adaptation; it can be distinguished from the genuine vMMN that, through use of control conditions, compares standards and deviants that are equally adapted and physically identical. To determine whether the vMMN follows similar principles to the auditory mismatch negativity (MMN), in two experiments we searched for a genuine vMMN from simple, physiologically plausible stimuli that change in fundamental dimensions: orientation, contrast, phase, and spatial frequency. We carefully controlled for attention and eye movements. We found no evidence for the genuine vMMN, despite adequate statistical power. We conclude that either the genuine vMMN is a rather unstable phenomenon that depends on still‐to‐be‐identified experimental parameters, or it is confined to visual stimuli for which monitoring across time is more natural than monitoring over space, such as for high‐level features. We also observed an early deviant‐related positivity that we propose might reflect earlier predictive processing