Integrals of Motion for Critical Dense Polymers and Symplectic Fermions

We consider critical dense polymers ${\cal L}(1,2)$. We obtain for this model the eigenvalues of the local integrals of motion of the underlying Conformal Field Theory by means of Thermodynamic Bethe Ansatz. We give a detailed description of the relation between this model and Symplectic Fermions including the indecomposable structure of the transfer matrix. Integrals of motion are defined directly on the lattice in terms of the Temperley Lieb Algebra and their eigenvalues are obtained and expressed as an infinite sum of the eigenvalues of the continuum integrals of motion. An elegant decomposition of the transfer matrix in terms of a finite number of lattice integrals of motion is obtained thus providing a reason for their introduction.Comment: 53 pages, version accepted for publishing on JSTA

The Baxter Q Operator of Critical Dense Polymers

We consider critical dense polymers ${\cal L}_{1,2}$, corresponding to a logarithmic conformal field theory with central charge $c=-2$. An elegant decomposition of the Baxter $Q$ operator is obtained in terms of a finite number of lattice integrals of motion. All local, non local and dual non local involutive charges are introduced directly on the lattice and their continuum limit is found to agree with the expressions predicted by conformal field theory. A highly non trivial operator $\Psi(\nu)$ is introduced on the lattice taking values in the Temperley Lieb Algebra. This $\Psi$ function provides a lattice discretization of the analogous function introduced by Bazhanov, Lukyanov and Zamolodchikov. It is also observed how the eigenvalues of the $Q$ operator reproduce the well known spectral determinant for the harmonic oscillator in the continuum scaling limit.Comment: improved version, accepted for publishing on JSTA

On the Integrable Structure of the Ising Model

Starting from the lattice $A_3$ realization of the Ising model defined on a strip with integrable boundary conditions, the exact spectrum (including excited states) of all the local integrals of motion is derived in the continuum limit by means of TBA techniques. It is also possible to follow the massive flow of this spectrum between the UV $c=1/2$ conformal fixed point and the massive IR theory. The UV expression of the eigenstates of such integrals of motion in terms of Virasoro modes is found to have only rational coefficients and their fermionic representation turns out to be simply related to the quantum numbers describing the spectrum.Comment: 18 pages, no figure

Depletion-interaction effects on the tunneling conductivity of nanorod suspensions

We study by simulation and theory how the addition of insulating spherical particles affects the conductivity of fluids of conducting rods, modeled by spherocylinders. The electrical connections are implemented as tunneling processes, leading to a more detailed and realistic description than a discontinuous percolation approach. We find that the spheres enhance the tunneling conductivity for a given concentration of rods and that the enhancement increases with rod concentration into the regime where the conducting network is well established. By reformulating the network of rods using a critical path analysis, we quantify the effect of depletion-induced attraction between the rods due to the spheres. Furthermore, we show that our conductivity data are quantitatively reproduced by an effective-medium approximation, which explicitly relates the system tunneling conductance to the structure of the rod-sphere fluid

Experimental and numerical evaluation of coring effects in reinforced concrete columns

The knowledge of in-situ material properties is the first step in the assessment process of existing structures and, where needed, in the design of the consequent strengthening interventions. In order to achieve this goal, destructive (DT; e.g., cores) and non-destructive (NDT; e.g., ultrasonic, rebound) test methods are generally adopted, either alone or combined. Although many literature papers and guidelines propose to minimize the number of cores in the estimation of the concrete strength in reinforced concrete structures, the European and Italian codes prescribe that the estimation of in-situ strength has to be mainly based on cores drilled from the structure (DT). In this framework, the paper reports results of an experimental program aimed at evaluating the effects of core tests on RC columns, as well as the effectiveness of the structural restoration of drilling holes. Specifically, three sets of column specimens have been considered: (i) drilled columns, (ii) drilled and subsequently restored columns, and (iii) reference not drilled (as-built) columns. Compression tests have been carried out on each column and the results have been compared with the prediction based on codes or other literature approaches. This helped to recognize the main phenomena affecting the column members behavior under axial loads. At the same time, the authors calibrated detailed finite element models based on the experimental results of the tests carried out on column specimens. An advanced Fem tool was used to set-up 3D models. Numerical simulations aimed at better understanding the failure mechanism, especially in the presence of the hole related to the core extraction. The role of longitudinal and transverse reinforcement has been evaluated, highlighting that concrete crushing in the areas around the hole causes the early buckling of rebars, leading to premature failure of drilled column specimens

The theatrical scenography and production systems

The transformation of a dramatic text into a spectacular text is a team work in which each professional develops his/her abilities to specify the representation. The set designer, the director and the producer participate together in the creative process. Scenographic production is a process, a set of operations that are unified under the concept of production where the following steps are distinguished: Concept-ProjectDesign, Materialization-Execution, Construction-Assembly and Circulation. This research analyzes the incidence of production systems in the realization of a scenography project. For this, the public, private and alternative production systems have been addressed. Once the research work is concluded, we demonstrate the importance of the productive systems fulfilling the programmed activities. Comparing the three production models, the asymmetry in the economic resources and the circulation possibilities, we can synthesize that the scenography is affected in all the productive levels. The effectiveness of the organization and planning, the dimension and the communication of productive / artistic teams affect the results.La transformación de un texto dramático a texto espectacular es un trabajo en equipo en el que cada profesional desarrolla sus capacidades para concretar la representación. En este proceso creativo participan el escenógrafo, el director y el productor. La producción escenográfica es un proceso de elaboración, un conjunto de operaciones que se unifican bajo el concepto de producción en el que se distinguen los siguientes pasos: Concepto-Proyecto-Diseño, Materialización-Ejecución, Construcción-Montaje y Circulación. La investigación analiza la incidencia de los sistemas de producción en la concreción de un proyecto de escenografía. Para esto, se han abordado los sistemas de producción público, privado y alternativo. Concluido el trabajo investigativo demostramos la importancia de los sistemas productivos cumpliendo las actividades programadas. Comparando los tres modelos de producción, la asimetría en los recursos económicos y las posibilidades de circulación, podemos sintetizar que la escenografía se encuentra afectada en todos los niveles productivos. La eficacia de la organización y planificación, la dimensión y la comunicación de equipos productivos/artísticos incide en los resultados

Tunneling conductivity in composites of attractive colloids

In conductor-insulator nanocomposites in which conducting fillers are dispersed in an insulating matrix the electrical connectedness is established by interparticle tunneling or hopping processes. These systems are intrinsically non-percolative and a coherent description of the functional dependence of the conductivity $\sigma$ on the filler properties, and in particular of the conductor-insulator transition, requires going beyond the usual continuum percolation approach by relaxing the constraint of a fixed connectivity distance. In this article we consider dispersions of conducting spherical particles which are connected to all others by tunneling conductances and which are subjected to an effective attractive square well potential. We show that the conductor-insulator transition at low contents $\phi$ of the conducting fillers does not determine the behavior of $\sigma$ at larger concentrations, in striking contrast to what is predicted by percolation theory. In particular, we find that at low $\phi$ the conductivity is governed almost entirely by the stickiness of the attraction, while at larger $\phi$ values $\sigma$ depends mainly on the depth of the potential well. As a consequence, by varying the range and depth of the potential while keeping the stickiness fixed, composites with similar conductor-insulator transitions may display conductivity variations of several orders of magnitude at intermediate and large $\phi$ values. By using a recently developed effective medium theory and the critical path approximation we explain this behavior in terms of dominant tunneling processes which involve interparticle distances spanning different regions of the square-well fluid structure as $\phi$ is varied. Our predictions could be tested in experiments by changing the potential profile with different depletants in polymer nanocomposites.Comment: 10 pages, 8 figure

Distribution and Community Characteristics of Staging Shorebirds on the Northern Coast of Alaska

Avian studies conducted in the 1970s on Alaska’s Arctic Coastal Plain (ACP) indicated that coastal littoral habitats are important to Arctic-breeding shorebirds for staging prior to fall migration. However, relatively little recent, broad-scale, or quantitative information exists on shorebird use of staging areas in this region. To locate possible shorebird concentration areas in the littoral zone of the ACP, we conducted aerial surveys from the southwest end of Kasegaluk Lagoon on the Chukchi Sea to Demarcation Point on the Beaufort Sea during the summers of 2005–07. These surveys identified persistent within- and between-year concentrations of staging shorebirds at Peard Bay, Point Barrow/Elson Lagoon, Cape Simpson, and Smith Bay to Cape Halkett. Among river deltas in the Beaufort Sea, the Sagavanirktok and Kongakut deltas had large concentrations of staging shorebirds. We also collected data on shorebird community characteristics, staging phenology, and habitat use in 2005 and 2006 by conducting land-based surveys at six camps: Kasegaluk Lagoon, Peard Bay, Point Barrow/Elson Lagoon, Colville Delta, Sagavanirktok Delta, and Okpilak Delta. The shorebird community was more even and diverse (evenness E and Shannon Weiner H’) along the Beaufort Sea compared to the Chukchi Sea and in 2005 versus 2006. Staging phenology varied by species and location and differed for several species from that reported in previous studies. Our results suggest the existence of three foraging habitat guilds among the shorebird species observed in this study: gravel beach, mudflat, and salt marsh/pond edge. A comparison to data collected in the mid-1970s suggests that these foraging associations are conserved through time. Results from this research will be useful to land managers for monitoring the effects of changing environmental conditions and human activity on shorebirds and their habitats in Arctic Alaska.Des études aviaires réalisées dans les années 1970 sur la plaine côtière de l’Arctique en Alaska ont permis de constater que les habitats du littoral côtier revêtent de l’importance pour les oiseaux de rivage nicheurs de l’Arctique en halte migratoire avant la migration d’automne. Cependant, relativement peu d’information récente, à grande échelle ou quantitative existe à propos de l’utilisation que font les oiseaux de rivage des haltes migratoires de cette région. Afin de localiser des zones de concentration possibles d’oiseaux de rivage dans la région littorale de la plaine côtière de l’Arctique, nous avons effectué des levés aériens du sud-ouest de la lagune Kasegaluk dans la mer des Tchouktches jusqu’à Demarcation Point dans la mer de Beaufort au cours des étés allant de 2005 à 2007. Ces levés ont permis de repérer des concentrations durables d’oiseaux de rivage en halte migratoire au cours d’une même année ainsi que d’une année à l’autre à la baie Peard, à pointe Barrow et à la lagune Elson, au cap Simpson de même que de la baie Smith jusqu’au cap Halkett. Parmi les deltas de rivières de la mer de Beaufort, les deltas Sagavanirktok et Kongakut comptaient de fortes concentrations d’oiseaux de rivage en halte migratoire. Nous avons également recueilli des données sur les caractéristiques des populations d’oiseaux de rivage, sur la phénologie des haltes migratoires de même que sur l’utilisation des habitats en 2005 et en 2006 au moyen de levés terrestres effectués à six camps, soit celui de la lagune Kasegaluk, de la baie Peard, de la pointe Barrow et de la lagune Elson, du delta Colville, du delta Sagavanirktok et du delta Okpilak. La population d’oiseaux de rivage était plus homogène et diverse (homogénéité E et Shannon Weiner H’) le long de la mer de Beaufort comparativement à la mer des Tchouktches, ainsi qu’en 2005 par rapport à 2006. La phénologie en halte migratoire variait selon les espèces et les emplacements, et différait pour plusieurs espèces de celles signalées dans le cadre d’études ultérieures. Nos résultats laissent croire à l’existence de trois guildes d’habitats de fourrage chez les espèces d’oiseaux de rivage observées dans cette étude : plage de gravier, vasière et marais salant ou bordure d’étang. La comparaison des données recueillies au milieu des années 1970 laisse entendre que ces associations de fourrage se sont conservées au fil du temps. Les résultats découlant de cette recherche seront utiles aux gestionnaires de terres dans le cadre de la surveillance des effets des conditions environnementales changeantes et de l’activité humaine sur les oiseaux de rivage et leurs habitats de l’Arctique alaskien

The effects of aging on neuropil structure in mouse somatosensory cortex-A 3D electron microscopy analysis of layer 1

This study has used dense reconstructions from serial EM images to compare the neuropil ultrastructure and connectivity of aged and adult mice. The analysis used models of axons, dendrites, and their synaptic connections, reconstructed from volumes of neuropil imaged in layer 1 of the somatosensory cortex. This shows the changes to neuropil structure that accompany a general loss of synapses in a well-defined brain region. The loss of excitatory synapses was balanced by an increase in their size such that the total amount of synaptic surface, per unit length of axon, and per unit volume of neuropil, stayed the same. There was also a greater reduction of inhibitory synapses than excitatory, particularly those found on dendritic spines, resulting in an increase in the excitatory/inhibitory balance. The close correlations, that exist in young and adult neurons, between spine volume, bouton volume, synaptic size, and docked vesicle numbers are all preserved during aging. These comparisons display features that indicate a reduced plasticity of cortical circuits, with fewer, more transient, connections, but nevertheless an enhancement of the remaining connectivity that compensates for a generalized synapse loss

Recent advances in the particle finite element method. Towards more complex fluid flow applications

One of the main drawbacks of the explicit integration using Eulerian formulations is the restricted stability of the solution with the time steps and with the spatial discretization. For the case of the Navier-Stokes equations, it is well known that the time step to be used in the solution is stable only for time step smaller than two critical values: the Courant- Friedrichs-Lewy (CFL) number and the Fourier number. The first one is concerning with the convective terms and the second one with the diffusive ones. Both numbers must be less than one to have stable algorithms. For convection dominant problems like high Reynolds number flows, the condition CFL<1 becomes crucial and limit the use of explicit method or outdistance it to be efficient. On the other hand, implicit solutions using Eulerian formulations is restricted in the time step size due to the lack of convergence of the convective non-linear terms. Both time integrations, explicit or implicit are, in most cases, limited to CFL no much larger than one. The possibility to perform parallel processing and the recent upcoming of new processors like GPU and GPGPU increase the possibilities of the explicit integration in time due to the facility to parallelize explicit methods having results with speedup closed to one. Although the incompressible condition cannot be solved explicitly, the solution of the momentum conservation equations with an explicit integration of the convective terms together with a parallel processing reduces considerably the computing time to solve the whole problem provided that a large time-step may be preserved independently to the discretization in space. Only to remember the new Particle Finite Element Method, called PFEM 2nd generation (PFEM-2) uses a Lagrangian formulation with an explicit time integrator without the CFL<1 restriction for the convective terms. This allows large timesteps, independent of the spatial discretization, having equal or better precision that an implicit integration. Moreover, PFEM-2 has two versions, one for moving mesh with permanent remeshing and one for fixed mesh [1]. In this lecture we will present some recent advances in the Particle Finite Element Method (PFEM) to solve the incompressible Navier- Stokes equations coupled with another fields like in multiphysics exploiting some nice features found in the fixed version. On the other hand we will also present the moving mesh version applied to multifluids using a parallel remeshing that makes this efficient in terms of cpu time. This updated proposal will be tested numerically and compared in terms of accuracy as in computing cpu time with other more standard Eulerian formulations