A Labelled Analytic Theorem Proving Environment for Categorial Grammar

We present a system for the investigation of computational properties of categorial grammar parsing based on a labelled analytic tableaux theorem prover. This proof method allows us to take a modular approach, in which the basic grammar can be kept constant, while a range of categorial calculi can be captured by assigning different properties to the labelling algebra. The theorem proving strategy is particularly well suited to the treatment of categorial grammar, because it allows us to distribute the computational cost between the algorithm which deals with the grammatical types and the algebraic checker which constrains the derivation.Comment: 11 pages, LaTeX2e, uses examples.sty and a4wide.st

The Private Memory of Aggregate Shocks

We study constrained efficient aggregate risk sharing and its consequence for thebehavior of macro-aggregates in a dynamic Mirrlees’s (1971) setting. Privately observedidiosyncratic productivity shocks are assumed to be independent of i.i.d. publiclyobserved aggregate shocks. Yet, private allocations display memory with respectto past aggregate shocks, when idosyncratic shocks are also i.i.d.. Under a mild restrictionon the nature of optimal allocations the result extends to more persistentidiosyncratic shocks, for all but the limit at which idiosyncratic risk disappears, andthe model collapses to a pure heterogeneity repeated Mirrlees economy identical toWerning [2007]. When preferences are iso-elastic we show that an allocation is memorylessonly if it displays a strong form of separability with respect to aggregate shocks.Separability characterizes the pure heterogeneity limit as well as the general case withlog preferences. With less than full persistence and risk aversion different from unityboth memory and non-separability characterize optimal allocations. Exploiting thefact that non-separability is associated with state-varying labor wedges, we apply abusiness cycle accounting procedure (e.g. Chari et al. [2007]) to the aggregate datagenerated by the model. We show that, whenever risk aversion is great than one ourmodel produces efficient counter-cyclical labor wedges.

Scalar field self-force effects on orbits about a Schwarzschild black hole

For a particle of mass mu and scalar charge q, we compute the effects of the scalar field self-force upon circular orbits, upon slightly eccentric orbits and upon the innermost stable circular orbit of a Schwarzschild black hole of mass M. For circular orbits the self force is outward and causes the angular frequency at a given radius to decrease. For slightly eccentric orbits the self force decreases the rate of the precession of the orbit. The effect of the self force moves the radius of the innermost stable circular orbit inward by 0.122701 q^2/mu, and it increases the angular frequency of the ISCO by the fraction 0.0291657 q^2/mu M.Comment: 15 pages, 8 figure

Matter-wave 2D solitons in crossed linear and nonlinear optical lattices

It is demonstrated the existence of multidimensional matter-wave solitons in a crossed optical lattice (OL) with linear OL in the $x-$direction and nonlinear OL (NOL) in the $y-$direction, where the NOL can be generated by a periodic spatial modulation of the scattering length using an optically induced Feshbach resonance. In particular, we show that such crossed linear and nonlinear OL allows to stabilize two-dimensional (2D) solitons against decay or collapse for both attractive and repulsive interactions. The solutions for the soliton stability are investigated analytically, by using a multi-Gaussian variational approach (VA), with the Vakhitov-Kolokolov (VK) necessary criterion for stability; and numerically, by using the relaxation method and direct numerical time integrations of the Gross-Pitaevskii equation (GPE). Very good agreement of the results corresponding to both treatments is observed.Comment: 8 pages (two-column format), with 16 eps-files of 4 figure

Majority-vote on directed Small-World networks

On directed Small-World networks the Majority-vote model with noise is now studied through Monte Carlo simulations. In this model, the order-disorder phase transition of the order parameter is well defined in this system. We calculate the value of the critical noise parameter q_c for several values of rewiring probability p of the directed Small-World network. The critical exponentes beta/nu, gamma/nu and 1/nu were calculated for several values of p.Comment: 16 pages including 9 figures, for Int. J. Mod. Phys.

Biomimetic approaches to engineer bioactive glass-based nanosystems

Despite the remarkable osteoconductive properties attributed to bioactive glass since its discovery, it is still a brittle material. Therefore, its applications are limited by a proper engineering of the material’s structure, or by its combination with other materials, like polymers. In native mineralized tissues, the blend of organic with inorganic phases is frequently the key for the remarkable mechanical properties of this class of natural materials.The main goal of this work was to give a step further in producing in vitro materials able to mimic the structural and chemical environment necessary to bone growth. Micro and nanofabrication techniques were used to recapitulate the complex environment of mineralized tissues. Bioactive glass and chitosan were chosen as materials to be combined respectively as mineral and organic phase in order to mimic bone structure

Preparation and characterization of bioactive glass nanoparticles prepared by sol-gel for biomedical applications

Bioactive glass nanoparticles (BG-NPs), based on both ternary (SiO(2)-CaO-P(2)O(5)) and binary (SiO(2)-CaO) systems, were prepared via an optimized sol-gel method. The pH of preparation and the effect of heat treatment temperature were evaluated, as well as the effect of suppressing P in the bioactivity ability of the materials. The morphology and composition of the BG-NPs were studied using FTIR, XRD and SEM. The bioactive character of these materials was accessed invitro by analyzing the ability for apatite formation onto the surface after being immersed in simulated body fluid (SBF). XRD, EDX and SEM were used to confirm the bioactivity of the materials. The BG-NP effect on cell metabolic activity was assessed by seeding L929 cells with their leachables, proving the non-cytotoxicity of the materials. Finally the most bioactive BG-NPs developed (ternary system prepared at pH11.5 and treated at 700degreesC) were successfully combined with chitosan in the production of biomimetic nanocomposite osteoconductive membranes that could have the potential to be used in guided tissue regeneration.Fundação para a Ciência e a Tecnologia (FCT