Guarding the walls of an art gallery

P so that each point of P is seen by at least one guard. We introduce and explore the edge-covering problem; the guards are required to observe the edges of P; metaphorically the paintings on the walls of the art gallery, and not necessarily every interior point. We compare minimum edge and interior covers for a given polygon and analyze the bounds and complexity for the edge-covering problem. We also introduce and analyze a restricted edge covering problem, where full visibility of each edge from at least one guard is required. For this problem we present an algorithm that computes a set of regions where a minimum set of guards must be located. The algorithm can also deal with the external visibility of a set of polygons.     

Characterization of acrylic resins and fluoroelastomer blends as potential materials in stone protection

Films of blends of Paraloid® B72 (copolymer of ethyl methacrylate and methyl acrylate) and Tecnoflon NM® (copolymer of vinylidene fluoride and hexafluoropropene) with different compositions were investigated by means of FT‐IR spectroscopy and FT‐IR microspectroscopy before and after UV and thermal treatments. Preliminary results of DSC measurements are also reported. Paraloid B72 has been extensively applied as a protective agent for stone since the 1950s. More recently considerable research has also been carried out on the application of fluorinated polymers in the field of stone conservation, eg the fluoroelastomer Tecnoflon®. A high content of Tecnoflon with respect to Paraloid increases the stability of the blends when they are submitted to UV radiation and thermal treatments. A THF solution of a blend of this kind was successfully applied to a marble surface of the Saint Maria Cathedral in Lucca, Tuscany, Italy. The changes in the properties of such mixtures with different compositions can offer new possibilities in developing suitable protective materials. © 2000 Society of Chemical Industry     

Novel Glass Fiber‐Reinforced Composites Having a UV and Peroxy Curable Fluoropolymer Matrix

Novel glass fiber‐reinforced composites were prepared from E‐glass fibers and perfluoropolyether (PFPE), polyurethane acrylate, and methacrylate resins. The PFPE resins were synthesized by a two‐step process and formulated with reactive acrylic diluents obtaining two compositions with different viscosity and fluorine content. These formulations were photocrosslinked by UV‐A radiation and characterized by tensile and dynamic‐mechanical properties as well as by impact resistance. The two UV cured fluoropolymer compositions are high modulus (> 1 GPa), polyphasic materials characterized by a fracture toughness higher than conventional polymer matrices, like epoxies and unsaturated polyesters. Unidirectional laminate composites were also prepared by hand lay‐up and crosslinked both photochemically and thermally. Mechanical characterization of glass fiber‐reinforced composites was carried out by tensile tests and shear adhesion measurements, showing a good fluoropolymer‐glass adhesion strength (ca. 9 MPa). Surface characterization of composites by static contact angle measurements allowed the calculation of the total surface tension γ_s according to Wu's harmonic mean approximation. Surface tension is very low (< 20 mN/m) suggesting a preferential stratification of PFPE segments at the material‐air interface.

     

Comparison between different conditions of the chemical polymerization of polyaniline on top of PET films

Composites produced during the in situ chemical polymerization of aniline on top of a poly(ethylene terephthalate) (PET) film, in different conditions, were studied by open‐circuit potential (Voc), ultraviolet‐visible, and infrared spectroscopy, electrical conductivity measurements, scanning electron microscopy, and atomic force microscopy. The polymerization monitoring by Voc showed a maximum associated with the intermediate pernigraniline oxidation state and a final formation of polyaniline (PANI) in the doped emeraldine salt (ES) form. Furthermore, high electrical conductivity values were obtained for the PANI–ES coating prepared under selected conditions. A globular formation was observed for the doped PANI–ES coating with globules of sizes of the same order and same shape of the PET, demonstrating the influence of the substrate on the coating morphology. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1220–1229, 2001     

Progress on Electrospun Composite Fibers Incorporating Bioactive Glass: An Overview

Electrospinning is a promising approach for the development of fibrous tissue engineering (TE) scaffolds suitable for hard and soft tissues. Apart from physicomechanical properties, electrospun fibers are required to incorporate bioactive cues to control cellular functions, including facilitating biomineralization and osteogenic differentiation in case of bone TE, as well as vascularization, to support successful tissue regeneration. In recent years, bioactive glass (BG) addition to electrospun biopolymer fibers has shown promising results in enhancing the properties of fibers, including the improvement of biological performance. In this article, a comprehensive overview of BG-containing electrospun polymer composite fibers is presented, identifying the parameters that affect the mechanical properties as well as the biological response in vivo and in vitro. Subsequently, the effects of BG addition on the properties of the scaffolds are discussed. Recent developments in the fields of bone regeneration, wound healing, and drug delivery using BG-containing electrospun fibrous scaffolds are described in detail. Essential aspects related to BG-polymer composite fibers for translational research in TE are highlighted for future research in this field.     

Fabrication of functional zirconia surfaces using a two-beam interference setup employing a picosecond laser system with 532-nm wavelength: Morphology,microstructure, and wettability

The aim of this work was to evaluate the feasibility of the fabrication of microtextures in zirconia using the direct laser interference patterning (DLIP) technique. A green ultra-short pulsed laser (532 nm, 10 ps) with a two-beam interference setup was used to produce line-like structures with a spatial period of 3 µm. For a fixed set of fluence and pulse-to-pulse overlap values (6.2 J/cm², 81%), periodic structures were successfully created for different hatch distances. The average depth of the features ranged from 0.37 µm for a hatch distance of 14.4 µm up to 0.84 µm for a hatch distance of 12.4 µm. However, a further decrease in hatch distance did not result in an increase in depth since the region of the ridges is also ablated. Scanning electron microscopy analysis showed pores formation on the laser grooves, but no sign of micro-cracking could be observed. Wettability tests showed an increase in hydrophobicity after DLIP. These results bring exciting perspectives on the fabrication of micro-textures with DLIP on zirconia surface.     

Fractal characteristics of the middle reach of the Paraná River floodplain during extreme hydrological events

The hydrological events that occur on floodplains are largely defined by precipitation and runoff inputs interacting with their geomorphological characteristics. In the middle Paraná River (MPR), hydrological events have traditionally been studied using water level time series and topographic charts or satellite images of certain floodplain sectors, using the same scale throughout the study area. Different zones of the floodplain were integrated using fractal dimension (FD) to better understand hydrological processes. FD is a useful tool used to characterize the geomorphological complexity of river networks in watersheds. The box-counting method was applied in the MPR floodplain. The result showed that as water levels increase, FD decreases, thereby indicating the direct relation with the hydrological attributes of the floodplain (e.g., duration, magnitude, recurrence of the flood event, and connectivity). This relation constitutes the basis of a new approach of the analysis of hydrological events and their effect on the MPR floodplain. This research provides fundamental information obtained from two hydrological stages and different spatial scales which may complement the method designed to accurately understand the hydrogeomorphological processes that operate on the Paraná River floodplain. It provides a simple parameter that can be used to evaluate the role that each floodplain section plays in attenuating the hydrograph recorded at each gauge analyzed along the river. This information will be useful in the implementation of management policies directed to the mitigation of future hydrological threats generated by alterations in the hydrological regime due to hydroclimatic variations or watershed alterations. The results further strengthen the basis for integrated sustainable planning of the main channel of the Paraná River, its floodplain, and the resources provided by this ecosystem.     

Bio-electrochemical production of hydrogen and electricity from organic waste: preliminary assessment

Clean Technologies and Environmental Policy - This study investigated the performance of a novel integrated bio-electrochemical system for synergistic hydrogen production from a process combining a...