Theoretical Approach of Bubble Entrapment Through Interconnected Pores: Supplying Principle

Fiber-reinforced composite materials are often composed of fibers collected in bundles that are stitched together. During the impregnation of a fibrous preform by a liquid resin, the multiscale porous medium leads to an heterogenous flow front, and therefore bubbles may be created and entrapped. Indeed, for a wetting system, capillary pressure is higher inside bundle, due to the microspace between fibers, than outside the bundles that represent the macrospace, thus, inducing an overflow between both pore scales. Motivated by the prediction of bubble formation during fiber fabric infiltration for composite materials, we attempt to determine the bubble rate in imbibition through a simple model network with two connected capillaries, called ??Pore Doublet Model?? (PDM). Our system is composed of two parts: a first part, continuously interconnected, in which the suppling mass to the microchannel from the macrochannel occurs, and a second part connected only by nodes. To quantify the leading flow front, a theoretical model based on the supplying principle and arranged Washburn equation is proposed. This approach has been conducted for wetting liquids, Newtonian flows, incompressible fluids and pores, no inertial and gravitational forces and no dynamic contact angle. The geometrical variability (channel radius and length) and the different configuration of connections (continuous and discrete) influence the entrapped bubble rate, leading to either microbubble in the microchannel or macrobubble in the macrochannel. The outcomes can contribute to the knowledge of void formation especially during the filling of fibrous preforms and may extend the previous works on the PDM in general.     

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In order to improve the computational accuracy of fusion reactor deep penetration shielding problems with complex streaming gaps, MC-SN coupling method is developed. Based on the Theta Weighted differencing scheme, the Directional Theta Weighted and Exponential Directional Weighted differencing schemes, which have adaptive features, are introduced. Biased quadrature sets are also constructed on base of Legendre-Chebyshev sets and angular refinement technique to deal with shielding calculation problems of strong fusion neutron penetration and anisotropic scattering. Through the comparative analysis with MCNP simulation results, it can be found that these methods can effectively improve the accuracy for some deep penetration shielding calculation in fusion reactors.     

Charm Hadrons in Dense Matter

The properties of the D and D _s charmed mesons in normal nuclear matter density are studied within a coupled channel approach using a t-channel vector-meson exchange mechanism as driving force. The in-medium scattering amplitudes are obtained by solving the Lippmann?CSchwinger equation including Pauli blocking effects and medium self-energies in a self-consistent way.     

New Properties of 9-Point Finite Difference Solution of the Laplace Equation

Two new properties of the 9-point finite difference solution of the Laplace equation are obtained, when the boundary functions are given from C ^5,1. It is shown that the maximum error is of order O (h⁶ (|ln h| + 1)){O\,\left(h^6\,(|{\rm ln}\,h| + 1)\right)}, and this order cannot be obtained for the class of boundary functions from C ^5,λ, 0 < λ < 1. These properties of the 9-point solution can be used to justify different versions of domain decomposition, composite grids, and combined methods.     

A social approach for target localization: simulation and implementation in the marXbot robot

Foraging is a common benchmark problem in collective robotics in which a robot (the forager) explores a given environment while collecting items for further deposition at specific locations. A typical real-world application of foraging is garbage collection where robots collect garbage for further disposal in pre-defined locations. This work proposes a method to cooperatively perform the task of finding such locations: instead of using local or global localization strategies relying on pre-installed infrastructure, the proposed approach takes advantage of the knowledge gathered by a population about the localization of the targets. In our approach, robots communicate in an intrinsic way the estimation about how near they are from a target; these estimations are used by neighbour robots for estimating their proximity, and for guiding the navigation of the whole population when looking for these specific areas. We performed several tests in a simulator, and we validated our approach on a population of real robots. For the validation tests we used a mobile robot called marXbot. In both cases (i.e., simulation and implementation on real robots), we found that the proposed approach efficiently guides the robots towards the pre-specified targets while allowing the modulation of their speed.     

Good Deals and compatible modification of risk and pricing rule: a regulatory treatment

This work studies Good Deals in a scenario in which a firm uses decision-making tools based on a coherent risk measure, and in which the market prices are determined with a sub-linear pricing rule. The most important observation of this work is that the existence of a Good Deal is equivalent to the incompatibility between the pricing rule and the risk measure. In this paper, we look into this situation from a regulatory point of view to rule out Good Deals with the purpose of stabilizing financial markets. We propose some practical ways of modifying a risk measure so a regulator can set appropriate levels of capital requirements for a financial institution.     

Introduction to the special issue Stochastic Financial Economics, Volume 1

Outlined here are the research papers published in Volume 1 of the special issue Stochastic Financial Economics, each considering investor behavior in financial markets.     

M?ssbauer study of carbon coated iron magnetic nanoparticles produced by simultaneous reduction/pyrolysis

Magnetic iron nanoparticles immersed in a carbon matrix were produced by a combined process of controlled dispersion of Fe^3?+? ions in sucrose, thermal decomposition with simultaneous reduction of iron cores and the formation of the porous carbonaceous matrix. The materials were prepared with iron contents of 1, 4 and 8 in %wt in sucrose and heated at 400, 600 and 800°. The samples were analyzed by XRD, Mössbauer spectroscopy, magnetization measurements, TG, SEM and TEM. The materials prepared at 400° are composed essentially of Fe₃O₄ particles and carbon, while treatments at higher temperatures, e.g. 600 and 800° produced as main phases Fe⁰ and Fe₃C. The Mössbauer spectra of samples heated at 400° showed two sextets characteristic of a magnetite phase and other contributions compatible with Fe^3?+? and Fe^2?+? phases in a carbonaceous matrix. Samples treated at temperatures above 600° showed the presence of metallic iron with concentrations between 16?C43%. The samples heated at 800° produced higher amounts of Fe₃C (between 20% and 58%). SEM showed for the iron 8% sample treated at 600?C800°C particle sizes smaller than 50 nm. Due to the presence of Fe⁰ particles in the carbonaceous porous matrix the materials have great potential for application as magnetic adsorbents.     

A4 Compton polarimetry

For the A4 parity violation experiment at MAMI we have installed a Compton laser polarimeter in our beam line. We have now operated this polarimeter at different beam energies of 315, 855, and 1508 MeV. A short overview of our detectors for scattered photons and electrons is given, together with a discussion of the extraction of Compton asymmetries using tagged photon spectra.