Exergy analysis of a PWR core heat transfer

The exergetic analysis, a methodology of thermodynamics that quantifies of energy losses associated with irreversibility, allows to optimize the efficiencies of the various stages of a transformation process and thus its overall efficiency. In this contribution, a novel approach to the exergetic analysis is applied to the energy transformations taking place within the core of a nuclear reactor. To perform such analysis, reference was made to a pressurized light-water reactor (PWR), modeling the heat exchanges between the fuel assemblies and the coolant fluid in the core through the balance of incoming and outgoing mass and energy flows, incoming and outgoing the reactor. The results of the analysis are validated through a comparison with the actual reactor operating parameters. The main goals of the work –part of a wider ongoing research effort- are to develop the thermo-economic analysis of a PWR nuclear power plant (NPP) to assess the actual cost of the products obtainable downstream of the NPP (electric energy and thermal energy for industrial and civil users, very different products in terms of exergy contents), and to compare with the costs of similar products obtained from conventional thermal power plants

Polynomial ring representations of endomorphisms of exterior powers

A polynomial ring with rational coefficients is an irreducible representation of Lie algebras of endomorphisms of exterior powers of a infinite countable dimensional $\mathbb{Q}$-vector space. We give an explicit description of it, using suitable vertex operators on exterior algebras, which mimick those occurring in the bosonic vertex representation of the Lie algebra $gl_\infty$, due to Date--Jimbo--Kashiwara and Miwa (DJKM).Comment: few typos corrected, references updated, comments are very welcom

Current Density Equation in Turbulent Magnetized Plasmas

A turbulent extension of Ohm’s law, derived from the self-consistent action-angle transport theory, is presented. The equation describes the steady-state profile of the current density in axisymmetric magnetized plasmas in the presence of magnetic turbulence. The hyper-resistive, helicity-conserving contribution, usually derived in the framework of magneto-hydro-dynamics, is recovered, and the hyper-resistivity is defined. Additionally, the generalized Ohm’s law contains an anomalous resistivity term, and a term proportional to the current density derivative. For given thermodynamic profiles, the numerical solution of the equation shows that turbulent contributions, besides regularizing the current density profile in the central region, lead to an increase of the total plasma current. This “turbulent bootstrap” effect provides a possible explanation to discrepancies recently observed between experimental current profiles and neoclassical predictions

The tilted-coil concept for advanced tokamak devices

The implications of the adoption of a tokamak’s toroidal field coil characterized by tilting in the azimuthal direction are investigated. The major advantage introduced by tilted coils is that of a drastic reduction over most of the coil section of the electromagnetic forces. As a beneficial side-effect, the tilted coils generate a poloidal field, in addition to the toroidal field. The former advantage allows for a notable simplification of the machine layout, while the poloidal flux generated during the current rise, when used in conjunction with the conventional central solenoid, allows for discharges of much longer duration with respect to those obtainable in tokamaks with conventional (non-tilted legs) coils

The temporal patterns of disease severity and prevalence in schistosomiasis

Schistosomiasis is one of the most widespread public health problems in the world. In this work, we introduce an eco-epidemiological model for its transmission and dynamics with the purpose of explaining both intra-and inter-annual fluctuations of disease severity and prevalence. The model takes the form of a system of nonlinear differential equations that incorporate biological complexity associated with schistosome's life cycle, including a prepatent period in snails (i.e., the time between initial infection and onset of infectiousness). Nonlinear analysis is used to explore the parametric conditions that produce different temporal patterns (stationary, endemic, periodic, and chaotic). For the time-invariant model, we identify a transcritical and a Hopf bifurcation in the space of the human and snail infection parameters. The first corresponds to the occurrence of an endemic equilibrium, while the latter marks the transition to interannual periodic oscillations. We then investigate a more realistic time-varying model in which fertility of the intermediate host population is assumed to seasonally vary. We show that seasonality can give rise to a cascade of period-doubling bifurcations leading to chaos for larger, though realistic, values of the amplitude of the seasonal variation of fertility. (C) 2015 AIP Publishing LLC

Movement Strategies of Seed Predators as Determinants of Plant Recruitment Patterns

Plant recruitment in nature exhibits several distinctive patterns ranging from hump shaped to monotonically decreasing with distance from the seed source. We investigate the role of post-dispersal seed predation in shaping these patterns, introducing a new mechanistic model that explicitly accounts for the movement strategy used by seed eaters. The model consists of two partial differential equations describing the spatiotemporal dynamics of both seed and predator densities. The movement strategy is defined by how predators move in response to the different cues they can use to search for seeds. These cues may be seed density, seed intake, distance from the plant, density of conspecific foragers, or a mixture of these four.The model is able to reproduce all the basic plant recruitment pat-terns found in the field. We compare the results to those of the ideal free distribution (IFD) theory and show that hump-shaped plant recruitment patterns cannot be generated by IFD predators and, in general, by foragers that respond exclusively to seed density. These foragers can produce only non increasing patterns, the shapes of which are determined by the foragers’ navigation capacities. In contrast, hump-shaped patterns can be produced by distance-responsive predators or by foragers that use conspecifics as a cue for seed abundanc

Climate change: the potential impact on occupational exposure to pesticides

Objective. This study investigates the possible influence of global climate change (GCC) on exposure to plant protection products (PPP) in the workplace. Methods. The paper has evaluated the main potential relationships between GCC and occupational exposure to pesticides, by highlighting how global warming might affect their future use and by reviewing its possible consequence on workers’ exposure. Results. Global warming, influencing the spatial and temporal distribution and proliferation of weeds, the impact of already present insect pests and pathogens and the introduction of new infesting species, could cause a changed use of pesticides in terms of higher amounts, doses and types of products applied, so influencing the human exposure to them during agricultural activities. GCC, in particular heat waves, may also potentially have impact on workers’ susceptibility to pesticides absorption. Conclusions. Prevention policies of health in the workplace must be ready to address new risks from occupational exposure to pesticide, presumably different from current risks, since an increased use may be expected

EDITORIAL

Editoria

Spatially explicit effective reproduction numbers from incidence and mobility data

Current methods for near real-time estimation of effective reproduction numbers from surveillance data overlook mobility fluxes of infectors and susceptible individuals within a spatially connected network (the metapopulation). Exchanges of infections among different communities may thus be misrepresented unless explicitly measured and accounted for in the renewal equations. Here, we first derive the equations that include spatially explicit effective reproduction numbers, ℛk(t), in an arbitrary community k. These equations embed a suitable connection matrix blending mobility among connected communities and mobility-related containment measures. Then, we propose a tool to estimate, in a Bayesian framework involving particle filtering, the values of ℛk(t) maximizing a suitable likelihood function reproducing observed patterns of infections in space and time. We validate our tools against synthetic data and apply them to real COVID-19 epidemiological records in a severely affected and carefully monitored Italian region. Differences arising between connected and disconnected reproduction numbers (the latter being calculated with existing methods, to which our formulation reduces by setting mobility to zero) suggest that current standards may be improved in their estimation of disease transmission over time