Key factors affecting the compressive strength of foamed concrete

This contribution aims to highlight, from an experimental point of view, the key factors affecting the compressive strength of foamed concrete. An experimental campaign has been conducted on a broad group of cubic specimens made of foamed concrete under compression tests at 28 days. In addition to the obvious influence of the density on the achievement of the compressive strength, other factors have been studied. In particular, three different curing conditions, three foaming agents with either synthetic or protein nature, two different cement types, and three water/cement ratios have been included in this experimental investigation. As a result of this experimental campaign, it has been found that the not only the density, but also the foaming agent and the water/cement ratio play a major role in the strength achievement of the foamed concrete. It is also demonstrated that the combination of the foaming agent with a particular water/cement ratio is a crucial parameter affecting the compressive strength of this material

A numerical study of a binary Yukawa model in regimes characteristic of globular proteins in solutions

The main goal of this paper is to assess the limits of validity, in the regime of low concentration and strong Coulomb coupling (high molecular charges), for a simple perturbative approximation to the radial distribution functions (RDF), based upon a low-density expansion of the potential of mean force and proposed to describe protein-protein interactions in a recent Small-Angle-Scattering (SAS) experimental study. A highly simplified Yukawa (screened Coulomb) model of monomers and dimers of a charged globular protein ($\beta$-lactoglobulin) in solution is considered. We test the accuracy of the RDF approximation, as a necessary complementary part of the previous experimental investigation, by comparison with the fluid structure predicted by approximate integral equations and exact Monte Carlo (MC) simulations. In the MC calculations, an Ewald construction for Yukawa potentials has been used to take into account the long-range part of the interactions in the weakly screened cases. Our results confirm that the perturbative first-order approximation is valid for this system even at strong Coulomb coupling, provided that the screening is not too weak (i.e., for Debye length smaller than monomer radius). A comparison of the MC results with integral equation calculations shows that both the hypernetted-chain (HNC) and the Percus-Yevick (PY) closures have a satisfactory behavior under these regimes, with the HNC being superior throughout. The relevance of our findings for interpreting SAS results is also discussed.Comment: Physical Review E, in press (2005

Fermi-Walker gauge in 2+1 dimensional gravity.

It is shown that the Fermi-Walker gauge allows the general solution of determining the metric given the sources, in terms of simple quadratures. We treat the general stationary problem providing explicit solving formulas for the metric and explicit support conditions for the energy momentum tensor. The same type of solution is obtained for the time dependent problem with circular symmetry. In both cases the solutions are classified in terms of the invariants of the Wilson loops outside the sources. The Fermi-Walker gauge, due to its physical nature, allows to exploit the weak energy condition and in this connection it is proved that, both for open and closed universes with rotational invariance, the energy condition imply the total absence of closed time like curves. The extension of this theorem to the general stationary problem, in absence of rotational symmetry is considered. At present such extension is subject to some assumptions on the behavior of the determinant of the dreibein in this gauge. PACS number: 0420Comment: 28 pages, RevTex, no figure

Fiber-reinforced lightweight foamed concrete panels suitable for 3D printing applications

This contribution presents a set of experimental results on fiber-reinforced innovative lightweight panels (FRIL-panels) having thickness of 12mm. These panels are prepared with a peculiar foamed concrete that has a high viscosity and cohesion in the fresh state, which makes it particularly suitable for 3D printing applications. The FRIL-panels can be used for internal partitions, external infills, and suspended ceilings of buildings as more effective solutions than conventional plasterboard ones, with better thermal insulation and acoustic absorption properties due to the internal air-void microstructure. The aim of this work is to investigate the out-of-plane resistance of FRIL-panels, prepared with a density of 800kg/m3, under displacement-controlled three-point bending tests. In view of potential use in the precast industry, the FRIL-panels were placed into an accelerated concrete curing tank so as to speed up the overall production process. Modulus of rupture, ultimate deflection and collapse mode of FRIL-panels are critically analysed and discussed

Josephson current through a long quantum wire

The dc Josephson current through a long SNS junction receives contributions from both Andreev bound states localized in the normal region as well as from scattering states incoming from the superconducting leads. We show that in the limit of a long junction, this current, at low temperatures, can be expressed entirely in terms of properties of the Andreev bound states at the Fermi energy: the normal and Andreev reflection amplitudes at the left-hand and at the right-hand S-N interface. This has important implications for treating interactions in such systems.Comment: 25 pages, 5 figure

The Low Energy Tagger for the KLOE-2 experiment

The KLOE experiment at the upgraded DAFNE e+e- collider in Frascati (KLOE-2) is going to start a new data taking at the beginning of 2010 with its detector upgraded with a tagging system for the identification of gamma-gamma interactions. The tagging stations for low-energy e+e- will consist in two calorimeters The calorimeter used to detect low-energy e+e- will be placed between the beam-pipe outer support structure and the inner wall of the KLOE drift chamber. This calorimeter will be made of LYSO crystals readout by Silicon Photomultipliers, to achieve an energy resolution better than 8% at 200 MeV.Comment: 4 pages, 5 figures, in the proceedings of "Frontier detectors for frontier physics", isola d'Elba, Italy, May 200

Escaping the Phagocytic Oxidative Burst: The Role of SODB in the Survival of Pseudomonas aeruginosa Within Macrophages

Reactive oxygen species (ROS) are small oxygen-derived molecules that are used to control infections by phagocytic cells. In macrophages, the oxidative burst produced by the NOX2 NADPH-oxidase is essential to eradicate engulfed pathogens by both oxidative and non-oxidative killing. Indeed, while the superoxide anion (O2-) produced by NOX2, and the other ROS derived from its transformation, can directly target pathogens, ROS also contribute to activation of non-oxidative microbicidal effectors. The response of pathogens to the phagocytic oxidative burst includes the expression of different enzymes that target ROS to reduce their toxicity. Superoxide dismutases (SODs) are the primary scavengers of O2-, which is transformed into H2O2. In the Gram-negative Salmonella typhimurium, periplasmic SODCI has a major role in bacterial resistance to NOX-mediated oxidative stress. In Pseudomonas aeruginosa, the two periplasmic SODs, SODB, and SODM, appear to contribute to bacterial virulence in small-animal models. Furthermore, NOX2 oxidative stress is essential to restrict P. aeruginosa survival in macrophages early after infection. Here, we focused on the role of P. aeruginosa SODs in the counteracting of the lethal effects of the macrophage oxidative burst. Through this study of the survival of sod mutants in macrophages and the measurement of ROS in infected macrophages, we have identified a dual, antagonistic, role for SODB in P. aeruginosa survival. Indeed, the survival of the sodB mutants, but not of the sodM mutants, was greater than that of the wild-type (WT) bacteria early after infection, and sodB-infected macrophages showed higher levels of O2- and lower levels of H2O2. This suggests that SODB contributes to the production of lethal doses of H2O2 within the phagosome. However, later on following infection, the sodB mutants survived less that the WT bacteria, which highlights the pro-survival role of SODB. We have explained this defensive role through an investigation of the activation of autophagy, which was greater in the sodB-infected macrophages

The physics of spreading processes in multilayer networks

The study of networks plays a crucial role in investigating the structure, dynamics, and function of a wide variety of complex systems in myriad disciplines. Despite the success of traditional network analysis, standard networks provide a limited representation of complex systems, which often include different types of relationships (i.e., "multiplexity") among their constituent components and/or multiple interacting subsystems. Such structural complexity has a significant effect on both dynamics and function. Throwing away or aggregating available structural information can generate misleading results and be a major obstacle towards attempts to understand complex systems. The recent "multilayer" approach for modeling networked systems explicitly allows the incorporation of multiplexity and other features of realistic systems. On one hand, it allows one to couple different structural relationships by encoding them in a convenient mathematical object. On the other hand, it also allows one to couple different dynamical processes on top of such interconnected structures. The resulting framework plays a crucial role in helping achieve a thorough, accurate understanding of complex systems. The study of multilayer networks has also revealed new physical phenomena that remain hidden when using ordinary graphs, the traditional network representation. Here we survey progress towards attaining a deeper understanding of spreading processes on multilayer networks, and we highlight some of the physical phenomena related to spreading processes that emerge from multilayer structure.Comment: 25 pages, 4 figure

On the Asymptotic Dynamics of a Quantum System Composed by Heavy and Light Particles

We consider a non relativistic quantum system consisting of $K$ heavy and $N$ light particles in dimension three, where each heavy particle interacts with the light ones via a two-body potential $\alpha V$. No interaction is assumed among particles of the same kind. Choosing an initial state in a product form and assuming $\alpha$ sufficiently small we characterize the asymptotic dynamics of the system in the limit of small mass ratio, with an explicit control of the error. In the case K=1 the result is extended to arbitrary $\alpha$. The proof relies on a perturbative analysis and exploits a generalized version of the standard dispersive estimates for the Schr\"{o}dinger group. Exploiting the asymptotic formula, it is also outlined an application to the problem of the decoherence effect produced on a heavy particle by the interaction with the light ones.Comment: 38 page

A test of Local Realism with entangled kaon pairs and without inequalities

We propose the use of entangled pairs of neutral kaons, considered as a promising tool to close the well known loopholes affecting generic Bell's inequality tests, in a specific Hardy-type experiment. Hardy's contradiction without inequalities between Local Realism and Quantum Mechanics can be translated into a feasible experiment by requiring ideal detection efficiencies for only one of the observables to be alternatively measured. Neutral kaons are near to fulfil this requirement and therefore to close the efficiency loophole.Comment: 4 RevTeX page