Ab initio simulations of accretion disks instability

We show that accretion disks, both in the subcritical and supercritical accretion rate regime, may exhibit significant amplitude luminosity oscillations. The luminosity time behavior has been obtained by performing a set of time-dependent 2D SPH simulations of accretion disks with different values of alpha and accretion rate. In this study, to avoid any influence of the initial disk configuration, we produced the disks injecting matter from an outer edge far from the central object. The period of oscillations is 2 - 50 s respectively for the two cases, and the variation amplitude of the disc luminosity is 10^38 - 10^39 erg/s. An explanation of this luminosity behavior is proposed in terms of limit cycle instability: the disk oscillates between a radiation pressure dominated configuration (with a high luminosity value) and a gas pressure dominated one (with a low luminosity value). The origin of this instability is the difference between the heat produced by viscosity and the energy emitted as radiation from the disk surface (the well-known thermal instability mechanism). We support this hypothesis showing that the limit cycle behavior produces a sequence of collapsing and refilling states of the innermost disk region.Comment: 11 pages, 15 Postscript figures, uses natbib.sty, accepted for publication in MNRA

Atmospheric ship emissions in ports: A review. Correlation with data of ship traffic

Ports represent a source of atmospheric pollutants that can contribute significantly to jeopardise air quality of port cities. NOx, SOx, PM and VOCs (Volatile Organic Compounds) are emitted by ships during manoeuvring in ports at arrival or departure and during hotelling when moored at wharves. Several methods exist to estimate emissions in function of ships' activity and engine parameters. However, there is still a significant uncertainty in these calculations. This is a severe limitation to develop effective plans of mitigation of air pollution in port cities. In this paper data of NOx and PM10 emitted in port and traffic of passenger and commercial ships have been reviewed and critically analysed. All vessels are lumped into three categories: cruise, passenger ships other than cruise and commercial ships. Emissions have been correlated with traffic data per year: passengers, hours at hotelling and manoeuvring, calls and tons of goods transported. The result is a summary of regression equations that can be used for the estimation of ship emissions in ports based on traffic data. The analysis does not consider emissions of all the ancillary activities that take place at land inside a port like: upload and download of goods, vehicular traffic, manipulation of containers and others. Keywords: Ship emissions, Ports, NOx, PM10, Traffic data, Regressio

Biomass Energy Resources: Feedstock Quality and Bioenergy Sustainability

The fossil fuel society is facing environmental, socio-economic, and geopolitical issues [...

The effect on air quality of lockdown directives to prevent the spread of SARS-CoV-2 pandemic in Campania Region-Italy: Indications for a sustainable development

Data on air quality collected by the regional network of fixed stations in the most urbanized areas of the Campania region in the south of Italy are examined. Two periods are considered: before and during the adoption of the main directives limiting human activities to fight the spread of SARS-CoV-2 infection. The first period is from 5 February to 5 March, and the second is from 13 March to 13 April. Meteorological conditions in the two periods were compared and significant differences were not observed. Therefore, the comparison of air quality data is feasible. During the second period, an intercontinental transport of particulate matter occurred. Data collected during this event (4 p.m. on 30 March to 4 p.m. on 31 March) were excluded from the analysis. The main reduction of pollutant concentration is observed for NO2 (-48% of the period average). PM10 shows a lower reduction (-17%). The PM2.5 average period concentration was quite constant, while the 98° percentile was reduced by -21%. Ozone shows, on the contrary, an increase in concentration due mainly to an increase in solar irradiation during the 2nd period, but also due to the decrease of NOx concentration. The reduction or the increase of pollutant concentration depends on the category of the station: background, industrial, residential, and traffic. In addition to air quality, the reduction of anthropogenic emissions is also studied. All the information available on the reduction of emissions from transport, industry, heating, and other main emissive sectors were collected. The results give useful insights for the development of air quality management policies that could be adopted when the sanitary emergency will end to guarantee the sustainable development of the Campania region

Sub-Planck phase-space structures and Heisenberg-limited measurements

We show how sub-Planck phase-space structures in the Wigner function can be used to achieve Heisenberg-limited sensitivity in weak force measurements. Nonclassical states of harmonic oscillators, consisting of superpositions of coherent states, are shown to be useful for the measurement of weak forces that cause translations or rotations in phase space, which is done by entangling the quantum oscillator with a two-level system. Implementations of this strategy in cavity QED and ion traps are described.Comment: 7 pages, 2 figure

Decays Z' -> \gamma\gamma\gamma{} and Z -> \gamma\gamma\gamma{} in the minimal 331 model

The possibility of a significant effect of exotic particles on the Z'->\gamma\gamma\gamma{} and Z->\gamma\gamma\gamma{} decays is investigated in the context of the minimal 331 model. This model, which is based in the SU_C(3)xSU_L(3)xU_X(1) gauge group, predicts the existence of many exotic charged particles that can significantly enhance the decay widths. It is found that the standard model prediction for the Z->\gamma\gamma\gamma{} decay remains essentially unchanged, as the new physics effects quickly decouples. On the other hand, it is found that the contributions of the new exotic quarks and gauge bosons predicted by this model lead to a branching fraction for the Z'->\gamma\gamma\gamma{} decay of about 10^(-6), which is about three orders of magnitude larger than that of the Z->\gamma\gamma\gamma{} decay.Comment: 20 pages and 20 figure