How to enhance crop production and nitrogen fluxes? A result-oriented scheme to evaluate best agri-environmental measures in Veneto Region, Italy

The cost-effectiveness of adopting agri-environmental measures (AEMs) in Europe, which combine agricultural productions with reduced N losses, is debated due to poorly targeted site-specific funding that is allocated regardless of local variability. An integrated DAYCENT model-GIS platform was developed combining pedo-climatic and agricultural systems information. The aim was to evaluate best strategies to improve N fluxes of agro-ecosystems within a perspective of sustainable intensification. Indicators of agronomic efficiency and environmental quality were considered. The results showed that agronomic benefits were observed with a continuous soil cover (conservation agriculture and cover crops), which enhanced nitrogen use efficiency (+17%) and crop yields (+34%), although in some cases these might be overestimated due to modelling limitations. An overall environmental improvement was found with continuous soil cover and long-term change from mineral to organic inputs (NLeach 45 Mg ha 121), which were effective in the sandy soils of western and eastern Veneto with low SOM, improving the soil-water balance and nutrients availability over time. Results suggest that AEM subsidies should be allocated at a site-specific level that includes pedo-climatic variability, following a result-oriented approach

Non-radial oscillation modes as a probe of density discontinuities in neutron stars

A phase transition occurring in the inner core of a neutron star could be associated to a density discontinuity that would affect the frequency spectrum of the non-radial oscillation modes in two ways. Firstly, it would produce a softening of the equation of state, leading to more compact equilibrium configurations and changing the frequency of the fundamental and pressure modes of the neutron star. Secondly, a new non-zero frequency g-- mode would appear, associated to each discontinuity. These discontinuity g--modes have typical frequencies larger than those of g--modes previously studied in the literature (thermal, core g-- modes, or g--modes due to chemical inhomogeneities in the outer layers), and smaller than that of the fundamental mode; therefore they should be distinguishable from the other modes of non radial oscillation. In this paper we investigate how high density discontinuities change the frequency spectrum of the non-radial oscillations, in the framework of the general relativistic theory of stellar perturbations. Our purpose is to understand whether a gravitational signal, emitted at the frequencies of the quasi normal modes, may give some clear information on the equation of state of the neutron star and, in particular, on the parameters that characterize the density discontinuity. We discuss some astrophysical processes that may be associated to the excitation of these modes, and estimate how much gravitational energy should the modes convey to produce a signal detectable by high frequency gravitational detectors.Comment: submitted to MNRA

Eccentric binary black-hole mergers: The transition from inspiral to plunge in general relativity

We study the transition from inspiral to plunge in general relativity by computing gravitational waveforms of non-spinning, equal-mass black-hole binaries. We consider three sequences of simulations, starting with a quasi-circular inspiral completing 1.5, 2.3 and 9.6 orbits, respectively, prior to coalescence of the holes. For each sequence, the binding energy of the system is kept constant and the orbital angular momentum is progressively reduced, producing orbits of increasing eccentricity and eventually a head-on collision. We analyze in detail the radiation of energy and angular momentum in gravitational waves, the contribution of different multipolar components and the final spin of the remnant. We find that the motion transitions from inspiral to plunge when the orbital angular momentum L=L_crit is about 0.8M^2. For L<L_crit the radiated energy drops very rapidly. Orbits with L of about L_crit produce our largest dimensionless Kerr parameter for the remnant, j=J/M^2=0.724. Generalizing a model recently proposed by Buonanno, Kidder and Lehner to eccentric binaries, we conjecture that (1) j=0.724 is the maximal Kerr parameter that can be obtained by any merger of non-spinning holes, and (2) no binary merger (even if the binary members are extremal Kerr black holes with spins aligned to the orbital angular momentum, and the inspiral is highly eccentric) can violate the cosmic censorship conjecture.Comment: Added sequence of long inspirals to the study. To match published versio

LISA observations of massive black hole mergers: event rates and issues in waveform modelling

The observability of gravitational waves from supermassive and intermediate-mass black holes by the forecoming Laser Interferometer Space Antenna (LISA), and the physics we can learn from the observations, will depend on two basic factors: the event rates for massive black hole mergers occurring in the LISA best sensitivity window, and our theoretical knowledge of the gravitational waveforms. We first provide a concise review of the literature on LISA event rates for massive black hole mergers, as predicted by different formation scenarios. Then we discuss what (in our view) are the most urgent issues to address in terms of waveform modelling. For massive black hole binary inspiral these include spin precession, eccentricity, the effect of high-order Post-Newtonian terms in the amplitude and phase, and an accurate prediction of the transition from inspiral to plunge. For black hole ringdown, numerical relativity will ultimately be required to determine the relative quasinormal mode excitation, and to reduce the dimensionality of the template space in matched filtering.Comment: 14 pages, 2 figures. Added section with conclusions and outlook. Matches version to appear in the proceedings of 10th Annual Gravitational Wave Data Analysis Workshop (GWDAW 10), Brownsville, Texas, 14-17 Dec 200

Two-dimensional elastic turbulence

We investigate the effect of polymer additives on a two-dimensional Kolmogorov flow at very low Reynolds numbers by direct numerical simulations of the Oldroyd-B viscoelastic model. We find that above the elastic instability threshold the flow develops the elastic turbulence regime recently observed in experiments. We observe that both the turbulent drag and the Lyapunov exponent increase with Weissenberg, indicating the presence of a disordered, turbulent-like mixing flow. The energy spectrum develops a power-law scaling range with an exponent close to the experimental and theoretical expectations

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Third post-Newtonian effective-one-body Hamiltonian in scalar-tensor and Einstein-scalar-Gauss-Bonnet gravity

We build an effective-one-body (EOB) Hamiltonian at third post-Newtonian(3PN) order in scalar-tensor (ST) and Einstein-scalar-Gauss-Bonnet (ESGB)theories of gravity. The latter is an extension of general relativity thatpredicts scalar hair for black holes. We start from the known two-bodyLagrangian at 3PN order, and use order-reduction methods to construct itsordinary Hamiltonian counterpart. We then reduce the conservative two-bodydynamics to the (non-geodesic) motion of a test particle in an effective metricby means of canonical transformations. The resulting EOB Hamiltonian is amodification of the general relativistic Hamiltonian, and already at 3PN order,it must account for nonlocal-in-time tail contributions. We include the latterbeyond circular orbits and up to sixth order in the binary's orbitaleccentricity. We finally calculate the orbital frequency at the innermoststable circular orbit (ISCO) of binary black holes in the shift-symmetric ESGBmodel. Our work extends F.L. Juli\'e and N. Deruelle [Phys. Rev. D95, 124054(2017)], and it is an essential step towards the accurate modeling ofgravitational waveforms beyond general relativity.<br

Quasinormal modes for the charged Vaidya metric

The scalar wave equation is considered in the background of a charged Vaidya metric in double null coordinates $(u,v)$ describing a non-stationary charged black hole with varying mass $m(v)$ and charge $q(v)$. The resulting time-dependent quasinormal modes are presented and analyzed. We show, in particular, that it is possible to identify some signatures in the quasinormal frequencies from the creation of a naked singularity.Comment: 4 pages. Prepared for the proceedings of the Spanish Relativity meeting (ERE2010), Granada, Spain, September 6-10, 201

The Plio-Quaternary uplift of the Apennine Chain: new data from the analysis of topography and river valleys in Central Italy

This study aimed at the reconstruction of magnitude and timing of uplift of a wide sector of the Central Apennines (Italy) by means of morphometric and morphostructural analyses. In the internal portion of the chain (where stratigraphic and geomorphological markers of past sea-level positions are lacking) the study was based on analysis of erosional landforms and river valleys. A large-scale topographic analysis was performed, processing 90-m and 230-m DEMs. The spatial distribution of several morphometric parameters, together with characteristic wavelengths of relief, allowed the distinction of three main regions affected by different cumulative surface uplift and tectonic/erosional fragmentation: a Peri-Tyrrhenian Belt; an Axial Belt; a Peri-Adriatic Belt. Particular attention was devoted to fluvial landforms, with analysis of longitudinal profiles and geometric pattern of the main stream-trunks and their relations with major structures. Major differences occur between the Tyrrhenian and Adriatic valley systems, the former being generally longitudinal and showing overall concave-upward longitudinal profiles, whereas the latter are generally transverse and possess less regular longitudinal profiles. Topographic features and river valleys architecture seem related to different styles and amounts of uplift in the three Belts. Within the study area, a narrower coast to coast transect (Gaeta-Vasto Transect, GVT) was investigated in detail, devoting particular attention to its axial sector, lying around the Apennines main divide (main divide area: MDA), and a possible scheme of the Quaternary surface uplift inside this transect was proposed. In the MDA, the main stages of landscape evolution and river network organization were reconstructed by analysis of paleosurfaces coupled with analysis of relic and present-day hydrographic network. This allowed recognition of a major phase of surface uplift (exceeding 1500 m in the Meta-Mainarde massif) occurred in response to thrusting during the Pliocene, whereas for the Quaternary uplift a minimum value around 400 m was estimated. Our study suggests that, during the Quaternary and in the GVT, the Peri-Tyrrhenian Belt suffered a subdued uplift operating over small wavelengths (10-15 km), while Axial and Peri- Adriatic Belts were subject to a stronger and long-wavelength (90 km) surface uplift, with maximum values (about 700 m) shifted NE of the Axial Belt and tapering to zero towards the Adriatic coast. The reconstructed pattern of uplift is coherent with the topographic properties of the three Belts and with the observed drainage features