Unified model for network dynamics exhibiting nonextensive statistics

We introduce a dynamical network model which unifies a number of network families which are individually known to exhibit $q$-exponential degree distributions. The present model dynamics incorporates static (non-growing) self-organizing networks, preferentially growing networks, and (preferentially) rewiring networks. Further, it exhibits a natural random graph limit. The proposed model generalizes network dynamics to rewiring and growth modes which depend on internal topology as well as on a metric imposed by the space they are embedded in. In all of the networks emerging from the presented model we find q-exponential degree distributions over a large parameter space. We comment on the parameter dependence of the corresponding entropic index q for the degree distributions, and on the behavior of the clustering coefficients and neighboring connectivity distributions.Comment: 11 pages 8 fig

Gas Geochemistry and Fractionation Processes in Florina Basin, Greece

Florina Basin is located in northern Greece, close to Mount Voras where the volcanic activity of Late Messinian age began. In the area, many CO2-rich gas emissions are present as a bubbling free-phase in groundwater (both springs and wells) and soil gases. Volcanism along with the geological and geodynamic regime of the basin, created the ideal conditions for CO2 accumulation in vertically stacked reservoirs. One of these, industrially exploited by the company Air Liquide Greece, produces 30,000 t/a of CO2. Results show that CO2 concentrations in the gases of Florina can arrive up to 99.8% and are mostly above 90%. Moreover, C-isotope composition (-2.1 to + 0.3 h vs. VPDB) indicates a mixed mantle-limestone origin for CO2, while He isotope composition (R/RA from 0.21 to 1.20) shows a prevailing crustal origin with an up to 15% mantle contribution. Helium and methane, with concentrations spanning over three orders of magnitude, show a positive correlation and a consequent high variability of He/CO2 and CH4/CO2 ratios. This variability can be attributed to the interaction of the uprising gases with groundwater that chemically fractionates them due to their different solubility. Based on the CO2, CH4 and He concentrations, gas samples collected in the basin can be divided in 3 groups: a) deep reservoir gases, b) enriched in less soluble gases and c) depleted in less soluble gases. The first group consists of gas samples collected at the Air Liquide extraction wells, which tap a 300m deep reservoir. This group can be considered as the least affected by fractionation processes due to interaction with groundwater. The gases of the second group due to their interaction with shallower unsaturated aquifers, become progressively enriched in less soluble gases (He and CH4). Finally, the third group represents residual gas phases after extensive degassing of the groundwater during its hydrological pathway

GROUNDWATER QUALITY ISSUES IN THE FLORINA AREA (N. GREECE)

The Florina basin developed in the Pelagonian Zone, the westernmost zone of the Internal Hellenides, in response to NE–SW extension in the Late Miocene and to a subsequent Pleistocene episode of NW–SE extension. Continuous sedimentation resulted in the accumulation of a 560 m thick succession of Late Miocene to Early Pleistocene lake sediments with intercalated lignites and alluvial deposits. The presence of intercalated volcanic ash beds of Pliocene age evidences volcanic activity related to the exstensional tectonics. Groundwaters in the central part of the Florina plain display high levels of dissolved gases, which often separate in a free gas phase. Their composition is dominated by carbon dioxide, which accounts for 85-99% of these gases. Apart from small amounts of atmospheric gases, minor components are CH4 (0.05-0.4%) and He (3-30 ppm). Carbon isotopic composition ranging from –1.6 to 0.3‰ (vs. VPDB) testifies for a deep (magmatic-hydrothermal) origin of CO2 and also He isotopic composition (0.24-0.55 R/Ra) reveals a small (3.5-8.4%) but significant mantle contribution. Furthermore the water composition of a deep well (Mesochori) shows important contribution from a hydrothermal component, displaying very high Li and B contents and a clear isotopic shift on a δD-δ18O diagram. Geothermometric estimates of the deep reservoir are in the range 150-180 °C. The uprise of mantle gases is related to the main tectonic structures, which probably allowed also magma intrusion episodes whose heat flow sustain the deep hydrothermal system. Because of the huge input of CO2, the shallow groundwaters of the studied area become acidic and consequently strongly aggressive with respect to the host rocks. At the sampling point many waters display pH values down to 5.5, being generally under the lower limit for drinking waters. Intense rock leaching results in metal release to the solution and enhanced metal fluxes in the aqueous system. As such, magmatic-hydrothermal CO2 input produces a “natural pollution” of the aquifer, where maximum admissible concentrations (MAC) fixed by European Union for drinking waters are exceeded at least for Ni, Mn and Fe in most of the analysed samples. Measured values reach respectively up to 30, 1700 and 55000 µg/l (MACs 20, 50 and 200 µg/l). This natural contamination combines with the pollution due to agricultural practices in the Florina plain, which is responsible for elevated nitrate contents (up to 90 mg/l) often exceeding maximum admissible concentration (50 mg/l). The interaction of natural and anthropogenic contamination of the shallow groundwater resources in the Florina area leads to serious water quality issues

Dilatonic interpolation between Reissner-Nordstrom and Bertotti-Robinson spacetimes with physical consequences

We give a general class of static, spherically symmetric, non-asymptotically flat and asymptotically non-(anti) de Sitter black hole solutions in Einstein-Maxwell-Dilaton (EMD) theory of gravity in 4-dimensions. In this general study we couple a magnetic Maxwell field with a general dilaton potential, while double Liouville-type potentials are coupled with the gravity. We show that the dilatonic parameters play the key role in switching between the Bertotti-Robinson and Reissner-Nordstr\"om spacetimes. We study the stability of such black holes under a linear radial perturbation, and in this sense we find exceptional cases that the EMD black holes are unstable. In continuation we give a detailed study of the spin-weighted harmonics in dilatonic Hawking radiation spectrum and compare our results with the previously known ones. Finally, we investigate the status of resulting naked singularities of our general solution when probed with quantum test particles.Comment: 27 pages, 4 figures, to appear in CQG

Preliminary results of systematic sampling of gas manifestations in geodynamically active areas of Greece

Greece is located on a convergent plate boundary comprising the subduction of the African Plate beneath the Eurasian, while the Arabian plate approaches the Eurasian in a northwestward motion. It is considered to be one of the most tectonically active regions of Earth with a complex geodynamic setting, deriving from a long and complicated geological history. Due to this specific geological background, conditions for the formation of many thermal springs are favoured. In the past years, almost all the already known sites of degassing (fumaroles, soil gases, mofettes, gas bubbling in cold and thermal waters) located in the Hellenic area were sampled at least one time. Collected samples were analysed for their chemical (He, Ne, Ar, O2, N2, H2, H2S, CO, CH4 and CO2) and isotopic composition (He, C and N). Some of these sites have been selected for systematic sampling. Four of them have records longer than 10 years with tens of samplings also considering some literature data. Two of the sites are located in active volcanic areas (Santorini and Nisyros) while the other two are close to actively spreading graben structures with intense seismic activity (Gulf of Korinth and Sperchios basin). Results allowed to define long term background values and also some interesting variation related to seismic or volcanic activity

A geochemical traverse along the “Sperchios Basin e Evoikos Gulf” graben (Central Greece): Origin and evolution of the emitted fluids

The studied area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence of a subduction slab at depth responsible for the recent (Quaternary) volcanic activity in the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). A high geothermal gradient is made evident by the presence of many thermal springs with temperatures from 19 to 82 C, that discharge along the normal faults bordering the graben. In the period 2004e2012, 58 gas and 69 water samples were collected and their chemical and isotopic analysis revealed a wide range of compositions. Two main groups of thermal waters can be distinguished on the basis of their chemical composition. The first, represented by dilute waters (E.C. <0.6 mS/cm) of the westernmost sites, is characterised by the presence of CH4-rich and mixed N2eCH4 gases. The second displays higher salinities (E.C. from 12 to 56 mS/cm) due to mixing with a modified marine component. Reservoir temperatures of 150e160 C were estimated with cationic geothermometers at the easternmost sites. Along the graben, from west to east, the gas composition changes from CH4- to CO2-dominated through mixed N2eCH4 and N2eCO2 compositions, while at the same time the He isotopic composi- tion goes from typical crustal values (<0.1 R/RA) up to 0.87 R/RA, showing in the easternmost sites a small (3e11%) but significant mantle input. The d13C values of the CO2-rich samples suggest a mixed origin (mantle and marine carbonates)

The fluids’ geochemistry along the "Sperchios Basin - Northern Evoikos Gulf" Graben, a geodynamically complex area of Central Greece

The study area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence at depth of a subduction slab responsible for the recent (Quaternary) volcanic activity in the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). Its high geothermal gradient is evidenced by the presence of many thermal springs with temperatures from 19 to 82 C, issuing along the normal faults bordering the graben. In the period 2004-2012 about 50 gas and water samples have been collected and their chemical and isotopic analysis revealed a wide range of compositions. Going from west to east the gas composition changes from CH4- to CO2-dominated passing through mixed N2- CH4 and N2-CO2 compositions, while at the same time the He isotopic composition goes from typical crustal values (0.05 R/Ra) up to 0.87 R/Ra (corrected for air contamination), showing in the easternmost sites a small but significant mantle input. Isotopic composition of CH4-C indicates a thermogenic origin for the CH4-rich samples and hydrothermal origin for the remaining samples. Positive 15N values indicate a contribution of crustal derived nitrogen for the N2-rich samples. The 13C values of most the CO2-enriched samples show a mixed origin (mantle and marine carbonates). Also the chemical composition of the waters shows differences along the graben and two main groups can be separated. The first, represented by dilute waters (E.C. < 600 S/cm), is found in the westernmost sites characterised by the presence of CH4-rich and mixed N2-CH4 gases. The remaining waters display higher salinities (E.C. from 12 to 56 mS/cm) due to the mixing with a modified marine component. Only the water composition of easternmost sites in the Giggenbach’s cation triangular graph plots in the field of the partially equilibrated waters giving estimated temperatures at depth of 150-160 C.PublishedVienna, Austria4.5. Studi sul degassamento naturale e sui gas petroliferiope

Origin and evolution of the fluids emitted along the “Sperchios Basin – Evoikos Gulf” Graben (Central Greece)

The study area is a 130 km long fast spreading graben in Central Greece bordered by active faults. Its complex geodynamical setting includes the presence at depth of a subduction slab responsible for the recent (Quaternary) volcanic activity in the area which possibly represents the northward continuation of the South Aegean active volcanic arc. To the area belongs also the western termination of the North-Anatolian fault a tectonic lineament of regional importance. The high geothermal gradient of the area is evidenced by the presence of many thermal springs with temperatures from 19 to 82 °C, issuing along the normal faults bordering the graben. In the period 2004-2012 more than 60 gas and water samples have been collected and their chemical and isotopic analysis revealed a wide range of compositions. Going from west to east the gas composition changes (Fig. 1) from CH4- to CO2-dominated passing through mixed N2-CH4 and N2-CO2 compositions, while at the same time the He isotopic composition goes from typical crustal values (0.02 R/Ra) up to 0.87 R/Ra (corrected for air contamination), showing in the easternmost sites a small but significant mantle input (up to ~ 10%). Isotopic composition of CH4-C indicates a thermogenic origin for the CH4-rich samples (δ13C from -50 to -37 ‰) and hydrothermal origin for the remaining samples (> -25‰). Positive δ15N values (around +2 ‰) indicate a contribution of crustal derived nitrogen for the N2-rich samples. The most pristine values of δ13C(CO2) refer to the most CO2-rich samples. These values (~ -3 ‰) point to a mixed mantle-marine carbonate source. Lower δ13C values (-10 ÷ -5 ‰) of the other sites can be explained by loss of CO2 due to dissolution processes. Also temperature and salinity of the waters shows differences along the graben increasing from west to east (Fig. 2). Two main groups can be separated on the basis of the total dissolved salts (TDS). The first, represented by dilute waters (TDS < 500 mg/l), is found in the westernmost sites characterised by the presence of CH4-rich and mixed N2-CH4 gases. The remaining waters display higher salinities (TDS from 9 to 35 g/l) due to the mixing with high salinity waters. The water composition can be explained by mixing of two end-members, one with low salinity of meteoric origin and the other with high salinity of marine origin. The mixing can be evidenced in Fig. 2. Low salinity waters show low chloride contents and their light water isotope composition overlaps the field of the cold groundwaters of the area confirming their meteoric origin. High salinity waters are aligned along the mixing line between the cold groundwaters and the seawater confirming the contribution of marine component. Most of the water compositions in the triangular graph of Giggenbach fall in the field of the non equilibrated waters being therefore unsuitable for geothermometric estimations. Only the easternmost sites (Gialtra, Ilion and Edipsos) falling the field of the partially equilibrated waters yield estimated temperatures in the range 150-170 °C. Silica geothermometers confirm these estimations. This study revealed that the complex geodynamic setting of the area is clearly reflected in the wide compositional range of the gases collected in the area that evidence contributions from different end-members (atmosphere, crust, mantle and hydrothermal systems). Water chemistry can be explained mainly from the mixing of a meteoric low-salinity end-member with a high-salinity marine end-member partially modified by hydrothermal water-rock interactions. The highest estimated temperatures in the hydrothermal reservoirs are in the range 150-170 °C

Contact symmetry of time-dependent Schr\"odinger equation for a two-particle system: symmetry classification of two-body central potentials

Symmetry classification of two-body central potentials in a two-particle Schr\"{o}dinger equation in terms of contact transformations of the equation has been investigated. Explicit calculation has shown that they are of the same four different classes as for the point transformations. Thus in this problem contact transformations are not essentially different from point transformations. We have also obtained the detailed algebraic structures of the corresponding Lie algebras and the functional bases of invariants for the transformation groups in all the four classes