TRIASSIC CARBONATE AND EVAPORITE SEDIMENTATION IN THE IONIAN ZONE (WESTERN GREECE): PALAEOGEOGRAPHIC AND PALAEOCLIMATIC IMPLICATION

The Triassic is considered a crucial interval because during that time huge areas in our planet suffered an intense, long lasting, period of aridity, which favored the formation of worldwide evaporitic bodies. During the Triassic, great volumes of evaporites were formed in the Ionian basin (Western Greece). On the surface chaotically textured gypsum, surrounded by dolomitic breccias of solution-collapse origin, appears. Sedimentological and diagenetical data proposed that these salt bodies were formed in an intertidal to supratidal environment. Although halite suggests precipitation under long-term arid conditions, clay film intercalations reveal intervals of short term humid conditions. During arid periods sabkhas prevailed and brines were of marine origin. Instead, during humid intervals brines were modified by meteoric water and stormy episodes could be responsible for the transportation of clay-sized material, from the low relief surrounding terrains, into the evaporative basin. Death and burial of cyanobactehal population during storm events could be responsible for the enrichment of clayey layers in carbonaceous material. The co-existence of halite and clays in the Ionian evaporitic sequence imposes a complicated climate, possibly periodically and seasonally controlled. The impact of the precession of the equinoxes plus the palaeogeographical position dominates the local climate. The insolation over the Triassic Ionian basin and nearby sea and land areas is a crucial factor. Climate responses to gradual insolation forcing with an ocean land atmosphere feedback mechanism. The desert / monsoonal dominated climatic model seems to be most proper for the explanation of the existing lithologigal record

Thermal treatment and environment effect on transient photoconductivity behavior of anatase TiO2 with dominant {0 0 1} facets

Nanosized anatase TiO2 powders with dominant {0 0 1} facets were prepared by solvothermal reaction of titanium isopropoxide in the presence of hydrofluoric acid as a capping agent. Two kinds of samples, as prepared and calcinated at 600 °C were fabricated and their UV-Visible and transient photoconductivity were investigated in vacuum and in air. The photoconductivity reaches high values and is sensitive on the environment. Thermal treatment improves the crystalline quality and enhances the amount of created excess charge carriers

Electrical conductivity studies of anatase TiO2 with dominant highly reactive {0 0 1} facets

Nanostructured powders of titanium dioxide anatase nanoplates with dominant highly reactive {0 0 1} facets were fabricated using a solvothermal method. Two kinds of samples, as prepared and calcinated at 600 °C, were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrical conductivity in vacuum and in air. The dependence of the conductivity versus the inverse of temperature in the temperature range 150-440 K indicated the contribution of at least two conduction mechanisms in vacuum. The electron transport was controlled by partially depleted of charge carriers grains and adiabatic small polaron conduction in the high temperature regime and by Mott variable-range hopping (VRH) at lower temperatures. The environment was found from the experimental results to influence significantly the electrical conductivity values and its temperature dependence. A decrease with temperature in air is observed in the ranges 290-370 and 285-330 K for the as prepared and the calcinated sample respectively. Potential barriers caused by partial depletion of carriers at grain boundaries control the electrical conductivity behavior in air at high temperatures and VRH in the lower temperature regime

Large N Field Theory and AdS Tachyons

In non-supersymmetric orbifolds of N =4 super Yang-Mills, conformal invariance is broken by the logarithmic running of double-trace operators -- a leading effect at large N. A tachyonic instability in AdS_5 has been proposed as the bulk dual of double-trace running. In this paper we make this correspondence more precise. By standard field theory methods, we show that the double-trace beta function is quadratic in the coupling, to all orders in planar perturbation theory. Tuning the double-trace coupling to its (complex) fixed point, we find conformal dimensions of the form 2 + i b, as formally expected for operators dual to bulk scalars that violate the stability bound. We also show that conformal invariance is broken in perturbation theory if and only if dynamical symmetry breaking occurs. Our analysis is applicable to a general large N field theory with vanishing single-trace beta functions.Comment: 26 pages, 6 figures. v3: small changes, version published on JHEP

Intersecting Flavor Branes

We consider an instance of the AdS/CFT duality where the bulk theory contains an open string tachyon, and study the instability from the viewpoint of the boundary field theory. We focus on the specific example of the AdS_5 X S^5 background with two probe D7 branes intersecting at general angles. For generic angles supersymmetry is completely broken and there is an open string tachyon between the branes. The field theory action for this system is obtained by coupling to N =4 super Yang-Mills two N =2 hyper multiplets in the fundamental representation of the SU(N) gauge group, but with different choices of embedding of the two N=2 subalgebras into N=4. On the field theory side we find a one-loop Coleman-Weinberg instability in the effective potential for the fundamental scalars. We identify a mesonic operator as the dual of the open string tachyon. By AdS/CFT, we predict the tachyon mass for small 't Hooft coupling (large bulk curvature) and confirm that it violates the AdS stability bound.Comment: 36 page

S-duality and 2d Topological QFT

We study the superconformal index for the class of N=2 4d superconformal field theories recently introduced by Gaiotto. These theories are defined by compactifying the (2,0) 6d theory on a Riemann surface with punctures. We interpret the index of the 4d theory associated to an n-punctured Riemann surface as the n-point correlation function of a 2d topological QFT living on the surface. Invariance of the index under generalized S-duality transformations (the mapping class group of the Riemann surface) translates into associativity of the operator algebra of the 2d TQFT. In the A_1 case, for which the 4d SCFTs have a Lagrangian realization, the structure constants and metric of the 2d TQFT can be calculated explicitly in terms of elliptic gamma functions. Associativity then holds thanks to a remarkable symmetry of an elliptic hypergeometric beta integral, proved very recently by van de Bult.Comment: 25 pages, 11 figure

Generating new dualities through the orbifold equivalence: a demonstration in ABJM and four-dimensional quivers

We show that the recently proposed large $N$ equivalence between ABJM theories with Chern-Simons terms of different rank and level, U(N_1)_{k_1}\times U(N_1)_{-k_1} and U(N_2)_{k_2}\times U(N_2)_{-k_2}, but the same value of N' =N_1 k_1=N_2 k_2, can be explained using planar equivalence in the mirror duals. The combination of S-dualities and orbifold equivalence can be applied to other cases as well, with very appealing results. As an example we show that two different quiver theories with k nodes can be easily shown to be Seiberg dual through the orbifold equivalence, but it requires order k^2 steps to give a proof when Seiberg duality is performed node by node.Comment: 18 pages, 7 figures, minor changes and references adde

Holographic and Wilsonian Renormalization Groups

We develop parallels between the holographic renormalization group in the bulk and the Wilsonian renormalization group in the dual field theory. Our philosophy differs from most previous work on the holographic RG; the most notable feature is the key role of multi-trace operators. We work out the forms of various single- and double-trace flows. The key question, `what cutoff on the field theory corresponds to a radial cutoff in the bulk?' is left unanswered, but by sharpening the analogy between the two sides we identify possible directions.Comment: 31 pages, 3 figures. v2: Minor clarifications. Added reference

Investigation into Photoconductivity in Single CNF/TiO2-Dye Core–Shell Nanowire Devices

A vertically aligned carbon nanofiber array coated with anatase TiO2 (CNF/TiO2) is an attractive possible replacement for the sintered TiO2 nanoparticle network in the original dye-sensitized solar cell (DSSC) design due to the potential for improved charge transport and reduced charge recombination. Although the reported efficiency of 1.1% in these modified DSSC’s is encouraging, the limiting factors must be identified before a higher efficiency can be obtained. This work employs a single nanowire approach to investigate the charge transport in individual CNF/TiO2 core–shell nanowires with adsorbed N719 dye molecules in dark and under illumination. The results shed light on the role of charge traps and dye adsorption on the (photo) conductivity of nanocrystalline TiO2 CNF’s as related to dye-sensitized solar cell performance