Non-local permittivity from a quasi-static model for a class of wire media

A simple quasi-static model applicable to a wide class of wire media is developed that explains strong non-locality in the dielectric response of wire media in clear physical terms of effective inductance and capacitance per unit length of a wire. The model is checked against known solutions and found to be in excellent agreement with the results obtained by much more sophisticated analytical and numerical methods. Special attention is given to suppression of the spatial dispersion effects in wire media.Comment: 22 pagees, 4 figure

Effects of Spatial Dispersion on Reflection from Mushroom-type Artificial Impedance Surfaces

Several recent works have emphasized the role of spatial dispersion in wire media, and demonstrated that arrays of parallel metallic wires may behave very differently from a uniaxial local material with negative permittivity. Here, we investigate using local and non-local homogenization methods the effect of spatial dispersion on reflection from the mushroom structure introduced by Sievenpiper. The objective of the paper is to clarify the role of spatial dispersion in the mushroom structure and demonstrate that under some conditions it is suppressed. The metamaterial substrate, or metasurface, is modeled as a wire medium covered with an impedance surface. Surprisingly, it is found that in such configuration the effects of spatial dispersion may be nearly suppressed when the slab is electrically thin, and that the wire medium can be modeled very accurately using a local model. This result paves the way for the design of artificial surfaces that exploit the plasmonic-type response of the wire medium slab.Comment: submitted for publication, under revie

Separation of microplastics from water using superhydrophobic silane-coupling-agent-modified geopolymer foam

Microplastics are a topical environmental problem that requires urgent solutions. They are ubiquitously present in various wastewaters and are discharged into aquatic environments because of difficulties in their removal. In this study, a novel filtration medium, superhydrophobic geopolymer foam, was prepared and investigated for the separation of microplastics from water. The foam was prepared using metakaolin, sodium silicate, sodium hydroxide, hydrogen peroxide, and Triton X-100 surfactant as raw materials and superhydrophobized with a silane coupling agent, triethoxy(octyl)silane. The purpose of the superhydrophobization was to improve the attachment of hydrophobic microplastic particles to the foam surface via chemical interactions. The modified geopolymer foam exhibited a water contact angle of 152°, and the presence of octyl chains on its surface was confirmed using Fourier transform infrared and X-ray photoelectron spectroscopies. When applied as a filter, the modified foam separated 53-63-µm sized polyethylene microspheres with ∼99 % removal efficiency, and no change in its separation efficiency was observed for ∼200 bed volumes of treated water. A comparison with an unmodified foam filter confirmed that the removal mechanism was not based on physical separation at higher flow rates, because the performance of the unmodified foam began to degrade after treating ∼5 bed volumes of wastewater. The performance of the modified foam was also validated with laundry washing effluents (particle size of microplastics varied roughly within 2–2000 μm), achieving ∼84 % separation efficiency for ∼50 bed volumes of wastewater. This study provides proof of concept of using superhydrophobic geopolymers as efficient, easy-to-prepare, and potentially low-cost separation media for microplastics from water effluents

Systemic inflammatory responses following welding inhalation challenge test

Peer reviewe

Portmanteau tests for linearity of Stationary Time Series

This paper considers the problem of testing for linearity of stationary time series. Portmanteau tests are discussed which are based on generalized correlations of residuals from a linear model (that is, autocorrelations and cross-correlations of different powers of the residuals). The finite-sample properties of the tests are assessed by means of Monte Carlo experiments. The tests are applied to 100 time series of stock returns

Collaborative research: Accomplishments & potential

Although a substantial part of scientific research is collaborative and increasing globalization will probably lead to its increase, very few studies actually investigate the advantages, disadvantages, experiences and lessons learned from collaboration. In environmental epidemiology interdisciplinary collaboration is essential and the contrasting geographical patterns in exposure and disease make multi-location projects essential. This paper is based on a presentation given at the Annual Conference of the International Society for Environmental Epidemiology, Paris 2006, and is attempting to initiate a discussion on a framework for studying collaborative research. A review of the relevant literature showed that indeed collaborative research is rising, in some countries with impressive rates. However, there are substantial differences between countries in their outlook, need and respect for collaboration. In many situations collaborative publications receive more citations than those based on national authorship. The European Union is the most important host of collaborative research, mainly driven by the European Commission through the Framework Programmes. A critical assessment of the tools and trends of collaborative networks under FP6, showed that there was a need for a critical revision, which led to changes in FP7. In conclusion, it is useful to study the characteristics of collaborative research and set targets for the future. The added value for science and for the researchers involved may be assessed. The motivation for collaboration could be increased in the more developed countries. Particular ways to increase the efficiency and interaction in interdisciplinary and intercultural collaboration may be developed. We can work towards "the principles of collaborative research" in Environmental Epidemiology