Unveiling the thermal and magnetic map of neutron star surfaces though their X-ray emission: method and light-curve analysis

Recent Chandra and XMM–Newton observations of a number of X-ray 'dim' pulsating neutron stars have revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is relatively large (pulsed fractions in the range ∼12–35 per cent), the pulse shape is often non-sinusoidal, and the hard X-ray colour appears to be anticorrelated in phase with the total emission. Moreover, the prototype of this class, RX J0720.4−3125, has been found to undergo rather sensible changes in both its spectral and timing properties over a time-scale of a few years. All these new findings seem difficult to reconcile with the standard picture of a cooling neutron star endowed with a purely dipolar magnetic field, at least if surface emission is produced in an atmosphere on top of the crust. In this paper we explore how a dipolar+quadrupolar star-centred field influences the properties of the observed light curves. The phase-resolved spectrum has been evaluated accounting for both radiative transfer in a magnetized atmosphere and general relativistic ray-bending. We computed over 78 000 light curves, varying the quadrupolar components and the viewing geometry. A comparison of the data with our model indicates that higher-order multipoles are required to reproduce the observations.     

Late glacial and Holocene Ostracoda from the Melilla cold-water coral mound field

The ostracod assemblages from sediment core TTR17-401G recovered from the Melilla cold-water coral mound field in the eastern Alboran Sea spanning the last 13 ka are analysed quantitatively, taxonomically and palaeoecologically. The core can be subdivided in three distinct assemblages linked to environmental shifts during the Younger Dryas and the Bølling–Allerød interstadial. A total of 9 ostracod species is recorded, Paracypris polita is dominant throughout the core. Common accessory taxa Cytherella robusta, Echinocythereis vidua and Macromckenziea ligustica characterize the well-oxygenated ostracod assemblage 2 affected by the Younger Dryas. Favourable growth conditions for ostracods during the latter are indicated by large-sized Krithe praetexta specimens.     

Distribution of benthic foraminiferal assemblages in the transitional environment of the Djerba lagoon (Tunisia)

The eastern edge of the Djerba Island represents an important tourist pole. However, studies describing the environmental processes affecting this Island are scarce. Although never studied before, the peculiar Djerba lagoon is well known by the local population and by tourists. In July 2014, surface sediment and seawater samples were collected in this lagoon to measure grain size, organic matter content and living foraminiferal assemblages to describe environmental conditions. Seawater samples were also collected and the concentration of 17 chemical elements were measured by ICP-OES. The results show that a salinity gradient along the studied transect clearly impacts seagrass distribution, creating different environmental conditions inside the Djerba lagoon. Biotic and abiotic parameters reflect a transitional environment from hypersaline to normal marine conditions. Living benthic foraminifera show an adaptation to changing conditions within the different parts of the lagoon. In particular, the presence of Ammonia spp. and Haynesina depressula correlates with hypersaline waters, whilst Brizalina striatula characterizes the parts of the lagoon colonized by seagrass. Epifaunal species, such as Rosalina vilardeboana and Amphistegina spp. colonize hard substrata present at the transition between the lagoon and the open sea.     

Using topographical attributes to evaluate gully erosion proneness (susceptibility) in two mediterranean basins: advantages and limitations

Empirical multivariate predictive models represent an important tool to estimate gully erosion susceptibility. Topography, lithology, climate, land use and vegetation cover are commonly used as input for these approaches. In this paper, two multivariate predictive models were generated for two gully erosion processes in San Giorgio basin (Italy) and Mula River basin (Spain) using only topographical attributes as independent variables. Initially, nine models (five for San Giorgio and four for Mula) with pixel sizes ranging from 2 to 50 m were generated, and validation statistics were calculated to estimate the optimal pixel size. The best models were selected based on model performance using the area under the receiver operating characteristic (AUC) curve and the generalized cross-validation. The best pixel size was 4 m in the San Giorgio basin and 20 m in the Mula basin. The finest resolution was not necessarily the best; rather, the relationship between digital elevation model resolution and size of the landform was important. The two selected models showed an excellent performance with AUC values of 0.859 and 0.826 for San Giorgio and Mula, respectively. The Topographic Wetness Index and the general curvature were identified as key topographical attributes in San Giorgio and Mula basins, respectively. Both attributes were related to the processes observed in the field and described in the literature. Finally, maps of gully erosion susceptibility were produced for each basin. These maps showed that 22 and 20 % of San Giorgio and Mula basins, respectively, present favourable conditions for the development of gullies.     

On the Effect of a Low-level Jet on Atmospheric Pollutant Dispersion: A Case Study Over a Coastal Complex Domain,Employing High-Resolution Modelling

Boundary-Layer Meteorology - A low-level-jet (LLJ) event that occurred over a coastal area in complex terrain is analyzed to investigate its effect on the dispersion of potential air pollutants...     

Discharge variability in Romania using Palmer indices and a simple atmospheric index of large-scale circulation

ABSTRACT

The aim of this study is to analyse the seasonal characteristics of four Palmer indices calculated on the basis of data from 27 meteorological stations in Romania, and the impact of these indices on river discharges in the period 1931–1998. Our research also tests the influence of large-scale atmospheric circulation on these indices and on discharge. For each season, developments in the empirical orthogonal functions (EOF) and multivariate EOF (MEOF) are achieved. The MEOF representation highlights the overall characteristics of the four Palmer indices. It maximizes specific information for each season compared with individual information of each Palmer index. We then identify geographical areas with homogeneous distribution, taking into account both the discharge distribution and the rotated EOF components of each Palmer index. Finally, we analysed the impact of large-scale atmospheric circulation on hydro-climatic events in Romania by means of the Greenland-Balkan Oscillation Index (GBOI), which is shown to have a greater influence on southeastern Europe than the North Atlantic Oscillation Index (NAOI).     

A new hydrostratigraphic model of Venice area (Italy)

Two environmental problems affect the Venice area: subsidence, which has been increasing due to the intensive water abstraction after the Second World War, and contamination of the soil and shallow aquifers. In order to address these problems, which are decisive factors in the entire Venetian ecosystem, the aquifer structure must be known in detail. The lithologic data are abundant and of good quality up to a depth of 50 m, whereas boreholes beyond this depth are much rarer and more dispersed, making their associated lithological data unreliable. This work, which uses the available data together with fast and low cost passive seismic measurements, provides an improved understanding of the deeper hydrogeologic domain. For this purpose, a MATLAB package (Modalstrata) has been developed to improve the correlation of the stratigraphic succession for each selected homogeneous sub-area and applied to obtain a new, upgraded hydrostratigraphic model. The horizontal to vertical spectral ratio passive seismic surveys have confirmed the lateral correlations among the sample areas at least for the two main aquifer horizons. Analysis and comparisons of several previous studies performed on the data related to the only drilling continuous coring 951 m deep in the Tronchetto Island (Venice), have allowed a satisfactory validation of the proposed hydrogeological model.     

Use of recession-curve analysis for estimation of karstification degree and its application in assessing overflow/underflow conditions in closely spaced karstic springs

In the southern part of the Slovensky Kras Mountains, located on the Hungarian–Slovakian border, a transboundary karstic aquifer Dolny vrch/Alsóhegy underlies the structure and discharges groundwater flow to 15 major karst springs around its margin. Hydrograph recession curves from nine-gauged springs on the Slovak part of the aquifer were analysed, and for each individual spring, depletion hydrograph equations were classified into different categories based on recessional parameters quantitatively describing individual groundwater flow sub–regimes. Discharge depletion was used to create recessional equations, and these were linked to karstification degree, a qualitative scale ranging from 1 to 10. A new application of hydrograph separation was based on examining and combining pairs of springs that likely fit into the category of overflow/underflow springs for a single groundwater reservoir. Recession-curve analysis performed on coupled discharges of two pairs of neighbouring springs was conducted to examine their possible linkage as a single groundwater reservoir, with an overflow outlet and underflow outlet. In the process of discharge coupling, discharges of the springs, hypothesized to be branches of the same source and observed at the same time were simply added together. By analyzing the resulting new time series, a new classification of sub-regimes could be generated. Surprisingly, new facts were revealed about the overflow/underflow springs, which primarily were not recognized previously as being connected components of a single groundwater reservoir. Summations of combined overflow/underflow discharge volumes of a single spring reservoir led to discovery of apparent presence of turbulent flow sub-regimes on the coupled recession curve. Presence of possible overflow/underflow springs of a single groundwater basin should be considered during hydrograph analyses if the springs have attributes that suggest they may be part of a combined flow system. Treating these springs as separate entities as a result can produce significant misinterpretation of drainage parameters. Furthermore, identification of overflow branches facilitates the generation of new research ideas for further speleological investigations nearby, and for assessing the system in a more effective manner.     

Spatially distributed rainfall thresholds for the initiation of shallow landslides

The evaluation of the combined influence of rainfall patterns (in terms of mean intensity and duration) and the geomorphological and mechanical characteristics of hillslopes on their stability conditions is a major goal in the assessment of the shallow landslide triggering processes. Geographic Information Systems (GIS) represent an important tool to develop models that combine hydrological and geomechanical analyses for the evaluation of slope stability, as they allow to combine information concerning rainfall characteristics with topographic and mechanical properties of the slopes over wide areas. In this paper, a GIS-based code is developed to determine physically based intensity/duration rainfall thresholds at the local scale. Given the rainfall duration and the local geometric, hydrological and mechanical characteristics of the slopes, the code evaluates the spatial distribution of the minimum rainfall intensity that triggers shallow landslides and debris flows over a given area. The key feature of the code is the capability of evaluating the time t _p required to reach the peak pore pressure head on the failure surface and computing the corresponding critical intensity/duration thresholds based on post-event peak pore pressures. The reliability of the model is tested using a set of one-dimensional analyses, comparing the physically based thresholds obtained for three different slopes with some empirical rainfall thresholds. In a log–log scale, the thresholds provided by the model decrease linearly with increased rainfall duration and they are bracketed by the empirical thresholds considered. Finally, an example of application to a study area of the Umbria region in central Italy is presented, describing the capability of the model of providing site-specific thresholds for different rainfall scenarios.     

Anodic Oxidation as Green Alternative for Removing Diethyl Phthalate from Wastewater Using Pb/PbO2 and Ti/SnO2 Anodes

The electrochemical oxidation (EO) of diethyl phthalate (DEP) in aqueous solution was studied at Pb/PbO₂ and Ti/SnO₂ anode materials under galvanostatic‐experimental conditions. Results obtained clearly demonstrated that the anode plays a significant role for the optimization of the oxidation process, deciding the mechanisms and by‐products formed. DEP and by‐products of oxidation were also analyzed during various stages of the electrolysis reaction by HPLC and GC/MS techniques. Before the analysis by GC/MS technique, the samples were treated by solid phase microextraction (SPME) in order to concentrate the compounds from the reaction solution and identify all electrolysis intermediates. Current efficiencies (instantaneous current efficiency; ICE and total current efficiency; TCE) achieved during EO experiments were dependent on anode used and current density (20–40 mA cm^?2) at 40°C. The results obtained demonstrated that the environmental electrochemical methods can be a feasible alternative for the wastewater treatment containing hazardous phthalates.