Interplay between the glassy transition and granular superconductivity in organic materials

It is known that some (BEDT-TTF)2X layered organic superconductors undergo a glassy transition near 80 K. Our purpose is to exploit quenched disorder to get new insights on both the superconducting state (T < 12 K) and the glassy transition by studying the superconducting properties as functions of annealing time (ta) and temperature (Ta) around 80 K. The main results on the fully deuterated kappa-(BEDT-TTF)2Cu[N(CN)2]Br compound are: 1) The data can be described by a percolation cluster model. 2) At short time scales, the clusters grow with ta following a power law. 3) At large time scales the clusters grow toward a thermodynamic state following a stretched exponential law in (1 - exp(-(t/tau)beta)with beta varying from about 0.5 to 1 in our Ta range (65 - 110 K). 4) The relaxation time follows an Arrhenius law tau(T)=tau0exp(U/T) with U around 2660 K and 1/tau0 around 2x1013 s-1. 5) The asymptotic magnetization fits with a scaling law with Tg around 55K and n around 3.2. The results are consistent with a Ising spin-glass-like model.Comment: 17 pages; 4 figure

Boson gas in a periodic array of tubes

We report the thermodynamic properties of an ideal boson gas confined in an infinite periodic array of channels modeled by two, mutually perpendicular, Kronig-Penney delta-potentials. The particle's motion is hindered in the x-y directions, allowing tunneling of particles through the walls, while no confinement along the z direction is considered. It is shown that there exists a finite Bose- Einstein condensation (BEC) critical temperature Tc that decreases monotonically from the 3D ideal boson gas (IBG) value $T_{0}$ as the strength of confinement $P_{0}$ is increased while keeping the channel's cross section, $a_{x}a_{y}$ constant. In contrast, Tc is a non-monotonic function of the cross-section area for fixed $P_{0}$. In addition to the BEC cusp, the specific heat exhibits a set of maxima and minima. The minimum located at the highest temperature is a clear signal of the confinement effect which occurs when the boson wavelength is twice the cross-section side size. This confinement is amplified when the wall strength is increased until a dimensional crossover from 3D to 1D is produced. Some of these features in the specific heat obtained from this simple model can be related, qualitatively, to at least two different experimental situations: $^4$He adsorbed within the interstitial channels of a bundle of carbon nanotubes and superconductor-multistrand-wires Nb$_{3}$Sn.Comment: 9 pages, 10 figures, submitte

Linear-T scattering and pairing from antiferromagnetic fluctuations in the (TMTSF)_2X organic superconductors

An exhaustive investigation of metallic electronic transport and superconductivity of organic superconductors (TMTSF)_2PF_6 and (TMTSF)_2ClO_4 in the Pressure-Temperature phase diagram between T=0 and 20 K and a theoretical description based on the weak coupling renormalization group method are reported. The analysis of the data reveals a high temperature domain (T\approx 20 K) in which a regular T^2 electron-electron Umklapp scattering obeys a Kadowaki-Woods law and a low temperature regime (T< 8 K) where the resistivity is dominated by a linear-in temperature component. In both compounds a correlated behavior exists between the linear transport and the extra nuclear spin-lattice relaxation due to antiferromagnetic fluctuations. In addition, a tight connection is clearly established between linear transport and T_c. We propose a theoretical description of the anomalous resistivity based on a weak coupling renormalization group determination of electron-electron scattering rate. A linear resistivity is found and its origin lies in antiferromagnetic correlations sustained by Cooper pairing via constructive interference. The decay of the linear resistivity term under pressure is correlated with the strength of antiferromagnetic spin correlations and T_c, along with an unusual build-up of the Fermi liquid scattering. The results capture the key features of the low temperature electrical transport in the Bechgaard salts

Assessing forest availability for wood supply in Europe

14 Pág.The quantification of forests available for wood supply (FAWS) is essential for decision-making with regard to the maintenance and enhancement of forest resources and their contribution to the global carbon cycle. The provision of harmonized forest statistics is necessary for the development of forest associated policies and to support decision-making. Based on the National Forest Inventory (NFI) data from 13 European countries, we quantify and compare the areas and aboveground dry biomass (AGB) of FAWS and forest not available for wood supply (FNAWS) according to national and reference definitions by determining the restrictions and associated thresholds considered at country level to classify forests as FAWS or FNAWS. FAWS represent between 75 and 95 % of forest area and AGB for most of the countries in this study. Economic restrictions are the main factor limiting the availability of forests for wood supply, accounting for 67 % of the total FNAWS area and 56 % of the total FNAWS AGB, followed by environmental restrictions. Profitability, slope and accessibility as economic restrictions, and protected areas as environmental restrictions are the factors most frequently considered to distinguish between FAWS and FNAWS. With respect to the area of FNAWS associated with each type of restriction, an overlap among the restrictions of 13.7 % was identified. For most countries, the differences in the FNAWS areas and AGB estimates between national and reference definitions ranged from 0 to 5 %. These results highlight the applicability and reliability of a FAWS reference definition for most of the European countries studied, thereby facilitating a consistent approach to assess forests available for supply for the purpose of international reporting.This research was supported by the Specific contract n. 18 “Use of National Forest Inventories data to estimate area and above ground biomass in European forests not available for wood supply” in the context of the Framework contract for the provision of forest data and services supporting the European Forest Data Centre 2012/ S 78-127532 of 21/04/2012 of the Joint Research Centre of the European Commission; the EG-013-72 agreement of the Ministry of Agriculture, Fisheries and Food (MAPA) and the INIA belonging to the Spanish Ministry of Science and Innovation (MICINN); and the project No.APVV-15-0265 granted by the Slovak Research and Development Agency.Peer reviewe

An Animated Pedagogical Agent that Interacts Affectively with the Student

Abstract: This paper aims at the conception of an affective and animated pedagogical agent responsible for the interface of the environment with the student and for considering the affective aspects of the interaction with the student in a learning environment. The agent catches the student&apos;s affective state by hi

A Distributed Artificial Intelligence View for Complex Problem Solving - Three Case Studies in Computer Vision, Biomedical Imagery and Knowledge Acquisition

There has recently been considerable international interest in the use of Distributed Artificial Intelligence Techniques for Knowledge-based System Development. The use of Multi-Agent architectures has several advantages such as modularizing problem-solving knowledge, alleviating the complexity of developing knowledgebased systems by distributing knowledge amongst a group of cooperating agents, or facilitating the integration of heterogeneous knowledge schemes and reasoning mechanisms. However, a crucial question is to analyze how to work at the &quot;right&quot; level of knowledge when designing multi-agent architectures for complex problem solving. To achieve this, the nature of knowledge and distinct facets that knowledge can adopt are reviewed and analyzed which permits us to propose a coherent knowledge model. In the second part, a brief description of the MAPS programming environment will be given based on the knowledge model previously proposed. Then, three case studies are addressed whic..