Quasi-periodic solutions of completely resonant forced wave equations

We prove existence of quasi-periodic solutions with two frequencies of completely resonant, periodically forced nonlinear wave equations with periodic spatial boundary conditions. We consider both the cases the forcing frequency is: (Case A) a rational number and (Case B) an irrational number.Comment: 25 pages, 1 figur

Phase separation in quasi incompressible fluids: Cahn-Hilliard model in the Cattaneo-Maxwell framework

In this paper we propose a mathematical model of phase separation for a quasi-incompressible binary mixture where the spinodal decomposition is induced by an heat flux governed by the Cattaneo-Maxwell equation. As usual, the phase separation is considered in the framework of phase field modeling so that the transition is described by an additional field, the concentration c. The evolution of concentration is described by the Cahn-Hilliard equation and in our model is coupled with the Navier-Stokes equation. Since thermal effect are included, the whole set of evolution equations is set up for the velocity, the concentration, the temperature and the heat flux. The model is compatible with thermodynamics and a maximum theorem holds.Comment: Submitted to ZAM

Turbulence and coarsening in active and passive binary mixtures

Phase separation between two fluids in two-dimensions is investigated by means of Direct Numerical Simulations of coupled Navier-Stokes and Cahn-Hilliard equations. We study the phase ordering process in the presence of an external stirring acting on the velocity field. For both active and passive mixtures we find that, for a sufficiently strong stirring, coarsening is arrested in a stationary dynamical state characterized by a continuous rupture and formation of finite domains. Coarsening arrest is shown to be independent of the chaotic or regular nature of the flow.Comment: 4 pages, 5 figures; discussion on the dependence of the arrest scale on the shear rate has been added; figures have been modified accordingl

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

Ecosystem Services and Life Cycle Assessment of Perennial and Annual Cropping Systems

Corn cultivation has negative impacts to the environment, such as nitrate leaching, soil erosion, and nitrous oxide emissions. Perennial crops such as alfalfa (Medicago sativa L.) reduce annual disturbance of soil, which affects many biogeochemical cycles that are key to provide resilience and stability to cropping systems. Four three-year crop sequences were evaluated. 1) Corn-soybean-corn (CSC); 2) alfalfa-alfalfa-alfalfa (AAA); 3) Corn-spring planted alfalfa-alfalfa (CAA); and 4) Corn-intercropped/alfalfa-alfalfa-alfalfa (CAIAA). Modeling of C and N cycles were conducted with the Denitrification-Decomposition (DNDC) model and global warming potential (GWP) was estimated using life cycle assessment (LCA) methodology. The soil organic carbon (SOC) balance in Year 1 was greater for the CAIAA sequence since alfalfa in intercropping is not removed from the field the first year. In Year 2, CAAIC had the lowest SOC balance due to four harvests of alfalfa removed from the field in Year 2. In Year 3, SOC balances were positive for all sequences but greatest for AAA. This is because in the third-year alfalfa’s root mass increases sequestering carbon deep in the soil. The SOC for the sum of the three-years balance was greater for the CAIAC sequence. Nitrous oxide emissions and nitrate leaching for the three-year sequence were the highest for the CSC sequence and significantly lower for the three sequences containing alfalfa. The main driver of emissions was the nitrogen fertilization added to corn. The net GWP was negative for the CAA and CAIAA sequences, indicating these sequences sequestered carbon. The CAIC sequence had the lowest net GWP of -4509 kg of CO2 e./ha while the CSC sequence had 369 kg of CO2 e./ha