Nanostructured Metallo‐Dielectric Quasi‐Crystals: Towards Photonic‐Plasmonic Resonance Engineering

The first evidence of out‐of‐plane resonances in hybrid metallo‐dielectric quasi‐crystal (QC) nanostructures composed of metal‐backed aperiodically patterned low‐contrast dielectric layers is reported. Via experimental measurements and full‐wave numerical simulations, these resonant phenomena are characterized with specific reference to the Ammann‐Beenker (quasi‐ periodic, octagonal) tiling lattice geometry and the underlying physics is investigated. In particular, it is shown that, by comparison with standard periodic structures, a moderately richer spectrum of resonant modes may be excited, due to the easier achievement of phase‐matching conditions endowed by its denser Bragg spectrum. Such modes are characterized by a distinctive plasmonic or photonic behavior, discriminated by their field distribution and dependence on the metal film thickness. Moreover, the response is accurately predicted via computationally affordable periodic‐approximant‐based numerical modeling. The enhanced capability of QCs to control number, spectral position, and mode distribution of hybrid resonances may be exploited in a variety of possible applications. To assess this aspect, label‐free biosensing is studied via characterization of the surface sensitivity of the proposed structures with respect to local refractive index changes. Moreover, it is also shown that the resonance‐engineering capabilities of QC nanostructures may be effectively exploited in order to enhance the absorption efficiency of thin‐film solar cells.     

Novel Procedure for Lager Beer Clarification and Stabilization Using Sequential Enzymatic,Centrifugal, Regenerable PVPP and Crossflow Microfiltration Processing

In this work, the crossflow microfiltration (CFMF) performance of different lots of lager beer, produced in a pilot scale at the Italian Brewing Research Centre (CERB, Perugia, Italy), was assessed in a bench-top plant, equipped with a 0.8-μm ceramic tubular membrane module, under constant crossflow velocity of 6 m s^?1, transmembrane pressure difference of 3.74 bar, temperature of ~10 °C, and periodic CO₂ backflushing. By feeding different beer samples (i.e., as such, precentrifuged (C), or pretreated with a commercial enzyme preparation to degrade the original arabinoxylans and β-glucans and then centrifuged (EC) to minimize the fouling contribution of yeast cells, aggregates, and polysaccharides), it was possible to increase the average permeation flux (expressed as mean value?±?standard deviation) from 112?±?13 to 199?±?17 or 330?±?22 L m^?2 h^?1, respectively. Only when using the EC-pretreated beer specimens, the permeate turbidity at 20 °C approached the limiting one (<0.6 EBC unit) recommended by the European Brewery Convention standards. As expected, the permeate chill haze at 0 °C was generally higher than the above haze target. By submitting EC-pretreated beer seeded with 0.5 g L^?1 of regenerable polyvinylpolypyrrolidone (PVPP) to CFMF, it was possible to reduce the initial total polyphenol content by 30 % and permeate chill haze to 0.60?±?0.01 EBC unit, but the average permeation flux fell to 84?±?4 L m^?2 h^?1. By performing sequentially EC pretreatments, PVPP stabilization, cartridge filtration, and CFMF, it was possible not only to re-enhance the average permeation flux at about 230 L m^?2 h^?1 near to those achievable with DE filters, but also to obtain a chill haze-free permeate ready for aseptic packaging.     

Multifunctional cotton fabrics

Electrically conductive fabrics were produced by deposition of a thin film of doped polypyrrole on the surface of cotton fibres. In situ oxidative chemical polymerisation were carried out in aqueous solutions of pyrrole, oxidant and doping agents, at room temperature. Polypyrrole-coated fibres were characterized by Light Microscopy, SEM, EDX, FTIR and TGA. Moreover, fabric samples were also evaluated for moisture regain, electrical resistivity, heat generation and antibacterial activity. PPy alters the combustion process of cellulose fibres that maintain the fibrous shape after heating in air. Moreover, it seems that PPy is really an antibacterial agent, apart from the oxidant or dopant used. The results highlight potential applications as technical textiles with antistatic (low electrical resistance), heat generation, hygroscopy, antibacterial and high temperature resistance properties.     

Kinetic and fluid dynamics modeling of methane/hydrogen jet flames in diluted coflow

MILD combustion is a recent development in the combustion of hydrocarbon fuels which promises high efficiencies and low NO_x emissions. In this paper we analyze the mathematical and numerical modeling of a Jet in Hot Coflow (JHC) burner, which is designed to emulate a moderate and intense low oxygen dilution (MILD) combustion regime [1]. This paper initially discusses the effects of several modeling strategies on the prediction of the JHC flame structure using the CFD code FLUENT 6.3.26. Effects of various turbulence models and their boundary conditions have been studied. Moreover, the detailed kinetic mechanism adopted in the CFD simulations is successfully validated in the conditions of interest using recent literature data [2] on the effect of nitrogen dilution on the flame speeds of several CH₄/H₂/air lean mixtures. One of the aims of this paper is also to describe a methodology for computing pollutant formation in steady turbulent flows to verify its applicability to the MILD combustion regime. CFD results are post-processed for calculating the NO_x using a numerical tool called Kinetic Post Processor (KPP). The modeling results agree with the experimental results [1] and support the proposed approach as a useful tool for optimizing the design of new burners also in the MILD combustion regime.     

Effect of short carbon fibers and MWCNTs on microwave absorbing properties of polyester composites containing nickel-coated carbon fibers

Multiphase composite materials filled with multiwall carbon nanotubes (MWCNTs), short nickel-coated carbon fibers and millimeter-long carbon fibers with various weight fractions and compositions are developed and used for the design of wide-band thin radar-absorbing screens. The effective complex permittivity of several composite samples is measured in the frequency range from 8 GHz to 18 GHz. The obtained results show that the addition of the MWCNTs into the mixture allows tuning the EM properties of the composite filled with the short nickel-coated fibers. Numerical simulations are also performed in order to design new radar-absorbing shields. Single-layer and bi-layer thin dielectric Salisbury screens are designed to exhibit minimum reflection coefficient at 10 GHz and at 15 GHz, and maximum bandwidth at −10 dB. It results that the total thickness of the screen can be reduced below 2 mm by using a lossy sheet made with the composite filled with MWCNTs and nickel-coated carbon fibers, whereas the bandwidth at −10 dB can exceed 6 GHz in a bi-layer structure.     

Effects of different sealing conditions on the seal strength of polypropylene films coated with a bio‐based thin layer

This paper presents the results of an investigation through the design of experiment technique regarding the influence of temperature, dwell time and bar pressure on the heat seal strength of oriented polypropylene films coated with a gelatin‐based thin layer. This chemometric approach allowed achieving a thorough understanding of the effect of each independent factor on the two different responses (maximum force and strain energy) considered in this work as a measure of the strength necessary to break the bond across the sealed interface. Surprisingly, the factor affecting both responses the most was the bar pressure rather than the sealing temperature. Moreover, whereas the bar pressure negatively affected the seal strength of coated polypropylene films, the sealing temperature had a positive effect. Dwell time did not have any significant influence as a main factor, while influencing negatively the seal strength as an interaction term (i.e. time × pressure), together with the further interaction temperature × pressure. The mathematical models obtained for the two responses provided different results in terms of fitting capability (R²) and prediction ability (Q²). In particular, for the maximum force response, R² and Q² were equal to 0.571 and 0.405, respectively, whereas the model supporting the strain energy response gave R² = 0.932 and Q² = 0.937, highlighting that for quantifying the seal strength, the energy necessary to break a seal is a better measure than the maximum force. The highest seal strength values obtained during this work were of 0.6615 N and 19.6 N·mm for maximum force and strain energy, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Constriction Effects in Clear-Water Scour at Abutments

The erosion process at a bridge abutment may be affected by the flow constriction when the abutment occupies a significant part of the flume width. We devised a specific experimental campaign to investigate the effect of the obstruction ratio (i.e., the ratio between the abutment length and the channel width) on the erosion depth: we performed homogeneous series of clear-water scour experiments in each of which the obstruction ratio was the only parameter that varied. The experimental results are presented in light of a dimensionless framework. It was found that the effect of the obstruction ratio on the time development of local scour depth may not be large; nevertheless, significant effect can be observed, even for relatively small values of the parameter during the earliest phases. The latter are important, for example, for the step-by-step modeling of the erosion development under unsteady flow conditions. We propose a simple equation to quantify the scour enhancement due to the flow constriction in clear-water abutment scour.