Topological and Entanglement Properties of Resonating Valence Bond wavefunctions

We examine in details the connections between topological and entanglement properties of short-range resonating valence bond (RVB) wave functions using Projected Entangled Pair States (PEPS) on kagome and square lattices on (quasi-)infinite cylinders with generalized boundary conditions (and perimeters with up to 20 lattice spacings). Making use of disconnected topological sectors in the space of dimer lattice coverings, we explicitly derive (orthogonal) "minimally entangled" PEPS RVB states. For the kagome lattice, we obtain, using the quantum Heisenberg antiferromagnet as a reference model, the finite size scaling of the energy separations between these states. In particular, we extract two separate (vanishing) energy scales corresponding (i) to insert a vison line between the two ends of the cylinder and (ii) to pull out and freeze a spin at either end. We also investigate the relations between bulk and boundary properties and show that, for a bipartition of the cylinder, the boundary Hamiltonian defined on the edge can be written as a product of a highly non-local projector with an emergent (local) su(2)-invariant one-dimensional (superfluid) t--J Hamiltonian, which arises due to the symmetry properties of the auxiliary spins at the edge. This multiplicative structure, a consequence of the disconnected topological sectors in the space of dimer lattice coverings, is characteristic of the topological nature of the states. For minimally entangled RVB states, it is shown that the entanglement spectrum, which reflects the properties of the edge modes, is a subset (half for kagome RVB) of the spectrum of the local Hamiltonian, providing e.g. a simple argument on the origin of the topological entanglement entropy S0=-ln 2 of Z2 spin liquids. We propose to use these features to probe topological phases in microscopic Hamiltonians and some results are compared to existing DMRG data.Comment: 15 pages, 19 figures. Large extension of the paper. Finite size scaling of the (topological) ground state energy splittings added (for the Kagome quantum antiferromagnet

Los secanos oleícolas del Bajo Aragón: ¿abocados al abandono?. Primeros resultados del análisis de la cadena de valor

La Denominación de Origen Protegida (DOP) Aceite del Bajo Aragón tiene registradas 22.000 ha, califica en torno a 5,5 millones de litros de aceite de media anual provenientes mayoritariamente de explotaciones tradicionales en secano, en un territorio aterrazado y distribuido entre 77 municipios de Zaragoza y Teruel. El objetivo del trabajo es analizar la rentabilidad del olivar y de las almazaras de la DOP estudiando las cadenas de valor del aceite a granel y envasado con y sin la marca de calidad de la DOP y en producción ecológica. Los primeros resultados muestran que en la mayoría de las explotaciones tradicionales, los ingresos que genera la venta del aceite coinciden con los costes de producción, reduciéndose la rentabilidad de esas explotaciones a la cuantía de las subvenciones que reciben de la PAC.Publishe

Preferencias inciertas y modelo Spike en la valoración del patrimonio natural

El ordenamiento jurídico en España contempla que toda afección al patrimonio natural deberá ser compensada por la pérdida que supone la desaparición de un elemento de los espacios o especies protegidos. En este trabajo se desarrolla una herramienta que permite llevar a cabo la valoración del daño asociado a las afecciones al m edio natural de manera sencilla. En primer lugar y aplicando el método de valoración contingente a una muestra de 1000 habitantes, se ha estimado el valor de existencia que tiene el conjunto de las especies y espacios protegidos de la com unidad autónoma de Aragón. Esta primera estimación se ha revisado considerando la existencia de valores nulos y preferencias inciertas ante bienes poco conocidos .Una vez considerados estos dos efectos, la disposición a pagar media se reduce de manera considerable (más del 50% ) apoyando recomendaciones previas de dividir por dos las estimaciones provenientes de formatos dicotómicos en valoración contingente.Under the Spanish conservation law, compensation is envisaged for the damage associated with all actions that reduce the quantity or quality of protected areas and species. This paper provides a tool to evaluate the monetary equivalent of this damage. First, we conduct a contingent valuation exercise to estimate the existence value related to protected areas and species in Aragon. This first estimate is then reconsidered including in first place the possibility of zero bids and also the possibility of uncertain preferences for non familiar goods. Considering these two effects, mean values are reduced dramatically (more than halved) giving support to previous recom mendations of dividing by two contingent valuation estimates from dichotom ous choice question formats.Publishe

Benchmarking the RDF(S) interoperability of ontology tools

The number of ontology tools, such as ontology editors and repositories, is constantly rising. Ideally, one could use them all seamlessly and thus benefit from all the functionalities they offer. As shown in previous EON workshops, interoperability among different development tools is not straightforward since ontology editors rely on specific internal knowledge models which are translated into common formats such as RDF(S). This paper addresses the urgent need for interoperability by providing an exhaustive set of RDF(S) benchmarks and demonstrating in an extensive field study the state-of-the-art of interoperability among six ontology tools. From the field study we have compiled a comprehensive set of best practices which may serve as guidelines. Tool developers benefit from having guidelines to design their import and export functionalities and a concrete set of benchmarks against which they can evaluate their import and export functionalities. Ontology engineers benefit from our work by having an overview to which extend interoperability is ensured for combinations of specific tools

Coupled Analysis of Thorium-based Fuels in the High-Performance Light Water Reactor Fuel Assembly

One of the six selected concepts to be part of Generation IV nuclear reactors is the Supercritical Light Water Cooled Reactor. The High-Performance Light Water Reactor (HPLWR) is the European version and it is a very promising design. In recent years, interest in the study of thorium-based fuel cycles has been renewed and its possibilities for current LWRs have been evaluated. The use of thorium-based fuels will be fundamental in the future sustainability of nuclear energy, since in addition to its abundance in nature, thorium has an important group of advantages. In this paper, performance of thorium-based fuels in the typical fuel assembly of the HPLWR reactor is evaluated, using a computational model based on CFD and Monte Carlo codes for the neutronic/thermal-hydraulic coupled analysis. The volumetric power density profiles, coolant temperature profiles, fuel temperature profiles and others are compared with those obtained for standard UO2 fuel. When the thorium-based fuels are used, the obtained infinite multiplication coefficients are smaller than the value obtained when UO2 is used, since the 232Th isotope has a lower contribution to the multiplicative properties of the medium than 238U. As a result, a difference of approximately 12 000 pcm was observed. The results verified that the HPLWR is a thermal reactor with a hard spectrum. There are no notable changes in the neutron spectrum if the mass fraction of thorium is slightly varied.  With coupled analysis, the potential benefits of the utilization of thorium-based fuels were verified. Moreover, a significant temperature decrease by 136 K on the center line of the fuel elements was observed. When the mass fraction of thorium increases in the oxides mixture, the weighted average temperature on the fuel elements decreases

Projected entangled pair states: fundamental analytical and numerical limitations

Matrix product states and projected entangled pair states (PEPS) are powerful analytical and numerical tools to assess quantum many-body systems in one and higher dimensions, respectively. While matrix product states are comprehensively understood, in PEPS fundamental questions, relevant analytically as well as numerically, remain open, such as how to encode symmetries in full generality, or how to stabilize numerical methods using canonical forms. Here, we show that these key problems, as well as a number of related questions, are algorithmically undecidable, that is, they cannot be fully resolved in a systematic way. Our work thereby exposes fundamental limitations to a full and unbiased understanding of quantum manybody systems using PEPS.Unión Europea. Horizonte 2020Ministerio de Economía y Competitividad (MINECO)Ministerio de Ciencia e Innovación (MICINN)Comunidad de MadridCentro de Excelencia Severo OchoaGeneralitat de CatalunyaDFG (German Research FoundationDepto. de Análisis Matemático y Matemática AplicadaFac. de Ciencias MatemáticasTRUEpu

Ballistic resistivity in aluminum nanocontacts

One of the major industrial challenges is to profit from some fascinating physical features present at the nanoscale. The production of dissipationless nanoswitches (or nanocontacts) is one of such attractive applications. Nevertheless, the lack of knowledge of the real efficiency of electronic ballistic/non dissipative transport limits future innovations. For multi-valent metallic nanosystems -where several transport channels per atom are involved- the only experimental technique available for statistical transport characterization is the conductance histogram. Unfortunately its interpretation is difficult because transport and mechanical properties are intrinsically interlaced. We perform a representative series of semiclassical molecular dynamics simulations of aluminum nanocontact breakages, coupled to full quantum conductance calculations, and put in evidence a linear relationship between the conductance and the contact minimum cross-section for the geometrically favored aluminum nanocontact configurations. Valid in a broad range of conductance values, such relation allows the definition of a transport parameter for nanomaterials, that represents the novel concept of ballistic resistivity

Lie symmetries and solitons in nonlinear systems with spatially inhomogeneous nonlinearities

Using Lie group theory and canonical transformations we construct explicit solutions of nonlinear Schrodinger equations with spatially inhomogeneous nonlinearities. We present the general theory, use it to show that localized nonlinearities can support bound states with an arbitrary number solitons and discuss other applications of interest to the field of nonlinear matter waves