IoT & environmental analytical chemistry: Towards a profitable symbiosis

In a constantly evolving world, where the rising population and increased social awareness have led to a higher concern for the environment, research in this field (most notably in Environmental Analytical Chemistry) should take advantage of the great opportunities offered by new technologies such as Internet of Things (IoT) and Cloud-based services. Both of them are especially suitable when chemical sensors and related devices are used in the continuous in-line monitoring of environmental parameters. In this sense, it is very important to obtain spatially distributed information of these parameters as well as their temporal evolution.In this work, a friendly approach to IoT world for environmental applications is carried out. To get a global vision of these concepts, the starting point is their historical evolution. New trends are also identified along with associated challenges and potential threats. Furthermore, not only there will be (in the near future) a need to rely on distributed analytical sensors but also on even more complex, lab-based techniques that are connected to the IoT through appropriate mechanisms. A revision of the recent literature relating IoT with environmental issues has also been performed, the most relevant contributions being discussed. Finally, the need of a mutual cooperation between IoT and Environmental Analytical Chemistry is outlined and commented in detail. Ignoring the new capabilities offered by Cloud computing and IoT environments is no further an option. In this sense, the main contribution of this paper consists of highlighting the fact that the wiser course is to embrace these opportunities consciously for mutual profit.     

Effect of ultrasound on the structural and textural properties of copper-impregnated cerium-modified zirconium-pillared bentonite

In this study, the synthesis of zirconium-pillared bentonite modified with cerium was performed via two different methods by the application of conventional and ultrasonic treatments during the intercalation stage. To synthesise copper-impregnated pillared clays by wet impregnation, cerium-modified zirconium-pillared clays were used as supportive materials after being calcined at 300 °C. Ultrasonic treatment significantly decreased the required processing time compared with the conventional treatment of the synthesised pillared bentonites. Chemical analysis confirmed the incorporation of Zr⁴⁺, Ce⁴⁺ and Cu²⁺ species into the pillared bentonites. X-ray diffraction (XRD) patterns of zirconium- and cerium/zirconium-pillared bentonites prepared by conventional treatment show that one large d-spacing above 3.5 nm corresponds to the mesoporous delaminated part, and another small d-spacing above 1.7 nm is indicative of the microporous pillared part. Zirconium- and cerium/zirconium-pillared bentonites prepared via ultrasonic treatment exhibited similar results, with the same high d-spacing but with a second low-intensity d-spacing above 1.9 nm. The delaminated structures of the pillared bentonites synthesised by both methods were conserved after copper impregnation. Nitrogen-adsorption isotherm analysis showed that the textural characteristics of products synthesised by ultrasonic treatment were comparable to those of products synthesised by conventional treatment. Fourier-transform infrared spectroscopy (FTIR) analyses showed the presence of Brønsted- and Lewis-acid sites, and zirconium-pillared clays synthesised by conventional treatment exhibited increased numbers of Brønsted- and Lewis-acid sites after cerium addition and copper impregnation. However, the products synthesised by ultrasonic treatment exhibited an increased number of Brønsted- and Lewis-acid sites after cerium addition, but a decreased number of acid sites after copper impregnation.     

Synthesis and properties of silicon dioxide films prepared by pulsed laser deposition using ceramic SiO2 target

Silicon dioxide (SiO₂) thin films were deposited on BK7 substrates by pulsed laser deposition (PLD) method using ceramic SiO₂ targets (C-SiO₂-Ts), which was sintered by solid state sintering. The reason for using C-SiO₂-T instead of the silicon target is to reduce the oxygen-deficiency phenomenon in deposited SiO₂ thin films. The influence of substrate-temperatures, oxygen-pressures and oxygen-plasma-assistance on the properties of synthesized films was studied. X-ray diffraction, atomic force microscopy, ultraviolet–visible–near-infrared scanning spectrophotometry were used to characterize the crystallinity, morphology and optical properties of deposited films. Results show that the root-mean-square roughness of films increased with the increase of oxygen-pressure, substrate-temperature and with the employment of oxygen-plasma. The transmittance of films increased with the increase of oxygen-pressure and decreased with the increase of substrate-temperature and with the employment of oxygen-plasma. Stoichiometric SiO₂ thin film with high optical quality was synthesized at room-temperature and 20 Pa oxygen-pressure using C-SiO₂-T.     

An omnibus noise filter

A new noise filtering approach, based on flexible least squares (FLS) estimation of an unobserved component local level model, is introduced. The proposed FLS filter has been found to perform well in Monte Carlo analysis, independently of the persistence properties of the data and the size of the signal to noise ratio, ouperforming in general even the Wiener Kolmogorov filter, which, theoretically, is a minimum mean square estimator. Moreover, a key advantage of the proposed filter, relatively to available competitors, is that any persistence property of the data can be handled, without any pretesting, being computationally fast and not demanding, and easy to be implemented as well. This paper was partially written when the author was visiting the Department of Economics at Michigan State University. The author gratefully acknowledges funding from the Fulbright Commission and Michigan State University for hospitality. Many thanks to two anonymous referee and the associate editor for very constructive comments.     

Continuous dependence on the Soret coefficient for double diffusive convection in Darcy flow

In this paper, the Darcy model is used to describe the double diffusive flow of a fluid containing a solute. Continuous dependence of the solution on the Soret coefficient is established.     

Translational and localised ionic motion in materials with disordered structures

Ionic materials with disordered structures may be crystalline, glassy or polymeric. Broad-band spectra of their ionic conductivities are found to display surprisingly similar features. With the help of linear response theory, time-resolved information on the ion dynamics has been extracted from such spectra. It has thus become evident that three kinds of ionic motion may be distinguished, all of them being collective and cooperative. These are vibrations, strictly localised displacements, and hops along diffusion pathways.The translational motion along diffusion pathways is well described in terms of a model called the MIGRATION concept, the acronym standing for MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. The MIGRATION concept consists of a set of simple rules that are written in the form of rate equations. Model conductivity spectra can be derived from them.Strictly localised displacive movements may be performed by ions within voids provided by the structure. In our model, this situation requires a modification of one of the rate equations. As a result, we obtain the well-known features of the Nearly Constant Loss (NCL) behaviour.We present broad-band conductivity spectra of several ionic materials with disordered structures and discuss them in terms of our model treatment.     

The admissible parameter space for exponential smoothing models

We discuss the admissible parameter space for some state space models, including the models that underly exponential smoothing methods. We find that the usual parameter restrictions (requiring all smoothing parameters to lie between 0 and 1) do not always lead to stable models. We also find that all seasonal exponential smoothing methods are unstable as the underlying state space models are neither reachable nor observable. This instability does not affect the forecasts, but does corrupt the state estimates. The problem can be overcome with a simple normalizing procedure. Finally we show that the admissible parameter space of a seasonal exponential smoothing model is much larger than that for a basic structural model, leading to better forecasts from the exponential smoothing model when there is a rapidly changing seasonal pattern.     

A quasi-secant continuous model for the analysis of long-span cable-stayed bridges

In this paper a non-linear continuous model for the statical analysis of long-span cable-stayed bridges with fan scheme and H-shaped towers is proposed. This model is based on a quasi-secant large-displacement formulation of the stays-deck interaction and involves an Euler-Bernoulli/De Saint Venant model for the girder. An approximate closed-form solution of the statical problem, in which flexural and torsional terms are coupled, is obtained by means of a perturbative technique and according to the prevailing “truss-like” structural behavior. Results for some study-cases are compared with those relevant to both classical models and numerical solutions, proving effectiveness and applicability of the proposed model.     

Theory of electrically controlled exhibition of circular Bragg phenomenon by an obliquely excited structurally chiral material - Part 1: Axial dc electric field

The boundary-value problem of the reflection and transmission of a plane wave due to a slab of an electro-optic structurally chiral material (SCM) is formulated in terms of a 4×4 matrix ordinary differential equation. The SCM slab can be locally endowed with one of 20 classes of point group symmetry, and is subjected to a dc voltage across its thickness (i.e., parallel to the axis of non-homogeneity of the SCM). The enhancement (and, in some cases, the production) of the circular Bragg phenomenon (CBP) by the application of the dc voltage has either switching or circular-polarization-rejection applications in optics. The twin possibilities of thinner filters and electrical manipulation of the CBP, depending on the local crystallographic class as well as the constitutive parameters of the SCM, emerge.     

A new method of proving structural properties for certain class of stochastic dynamic control problems

This paper introduces the multimodularity concept to study structural properties for certain class of stochastic dynamic control problems through a new efficient approach. We demonstrate that this approach can substantially simplify the proofs of the main results of one recent article and provide an alternative method for two other models in the literature.