A High-Gain Nonlinear Observer With Limited Gain Power

International audienceIn this note we deal with a new observer for nonlinear systems of dimension n in canonical observability form. We follow the standard high-gain paradigm, but instead of having an observer of dimension n with a gain that grows up to power n, we design an observer of dimension 2n − 2 with a gain that grows up only to power 2

Efficiency evaluation of food waste materials for the removal of metals and metalloids from complex multi-element solutions

Recent studies have shown the potential of food waste materials as low cost adsorbents for the removal of heavy metals and toxic elements from wastewater. However, the adsorption experiments have been performed in heterogeneous conditions, consequently it is difficult to compare the efficiency of the individual adsorbents. In this study, the adsorption capacities of 12 food waste materials were evaluated by comparing the adsorbents' efficiency for the removal of 23 elements from complex multi-element solutions, maintaining homogeneous experimental conditions. The examined materials resulted to be extremely efficient for the adsorption of many elements from synthetic multi-element solutions as well as from a heavy metal wastewater. The 12 adsorbent surfaces were analyzed by Fourier transform infrared spectroscopy and showed different types and amounts of functional groups, which demonstrated to act as adsorption active sites for various elements. By multivariate statistical computations of the obtained data, the 12 food waste materials were grouped in five clusters characterized by different elements' removal efficiency which resulted to be in correlation with the specific adsorbents' chemical structures. Banana peel, watermelon peel and grape waste resulted the least selective and the most efficient food waste materials for the removal of most of the elements

Ultrasonic metamaterials for use in water

This thesis describes several ways in which to manipulate ultrasound by means of Fabry-Perot resonant acoustic metamaterials (AMMs), Fresnel-type lenses and phononic crystals (PCs). These can be used to obtain properties such as sound focussing or sub-wavelength imaging in water, which are highly desirable characteristics in several applications such as biomedical imaging and flaw detection. The metamaterials and the other structures described in this thesis were mostly additively manufactured, with the further aim of validating the different layer-bylayer fabrication methods to build them. Experiments were conducted in a water tank and results were compared to numerical predictions obtained through Finite Element Modelling (FEM). Several tests on AMMs in the form of flat plates with periodic arrays of square holes were carried out. It was found that the use of tungsten to additively-manufacture patterned holey plates can lead to resonances in each channel, allowing sub-wavelength imaging below the conventional resolution limit. Periodic metamaterials are usually narrowband, but, in this work, irregularities due to additive manufacturing were seen to extend the bandwidth of usage, which can be useful in many applications. The concept of trapping air within a polymer shell for use in a metamaterial device will be described. Trapped air holey metamaterials were found to exhibit sub-wavelength imaging properties, leading to comparable performance with respect to metal metamaterials for a much lower fabrication cost. Moreover, the trapped-air concept was also applied to Fresnel-type lenses, leading to the possibility of focusing ultrasound in water using air volumes trapped within a polymeric shell. Additionally, additively-manufactured metallic two-dimensional PCs made of periodically arranged cylinders were investigated. These structures can block acoustic signals over a range of different frequencies, creating bandgaps. Other properties can arise from the periodicity of scatterers, such as negative refraction and sound focussing. Two properties of additively manufactured PCs, namely bandgaps and negative refraction, were compared to conventionally-manufactured ones to show similarities and differences. An additively manufactured crystal was then numerically simulated and tested to investigate its sound focusing properties. This led to the validation of selective laser melting as an additive manufacturing technique to fabricate PCs for use in water in the hundreds of kHz frequency range. It is expected that future advancements in additive-manufacturing resolution will stretch the present fabrication limits, making acoustic metamaterials even better candidates for applications in Nondestructive Testing, diagnostic medical ultrasound, and sensing

Influence of classroom acoustics on the vocal behavior of teacers

Erroneous vocal behavior of teachers and their changes in the voice production due to poor acoustics in classrooms can be investigated through recently developed voice-monitoring devices. These devices are portable analyzers that use a miniature contact-microphone glued to the jugular notch in order to sense the skin acceleration level due to the vibration of the vocal folds. They estimate the Sound Pressure Level (SPL) at a certain distance from the speaker's mouth provided that a preliminary calibration procedure is performed, the fundamental frequency and the time dose. Two different devices are compared in this work: the former is a commercial device, whose phonation sensor is a small accelerometer; the latter, recently developed by the authors, uses an electret condenser microphone to sense the skin acceleration level. SPL and fundamental frequency are estimated over fixed-length frames and the results that refer to a sample of 25 primary school teachers and a university professor are analyzed. The duration of the voice and pause periods is investigated in order to detect the peaks of occurrence and accumulation in different conditions of reverberation. A method for the detection and analysis of the emphatic speech is also propose

Duration of voicing and silence periods of continuous speech in different acoustic environments

This work deals with the duration of voicing and silence periods of continuous speech in rooms with very different reverberation times (RTs). Measurements were conducted using the Ambulatory Phonation Monitoring (APM) 3200 (Kaypentax) and Voice-Care devices (developed at the Politecnico di Torino, Italy), both of which have a contact microphone placed on the base of the neck to detect skin vibrations during phonation. Six university professors and 22 university students made short laboratory monologs in which they explained something that they knew well to a listener 6m away. Seven students also described a map with the intention of correctly explaining directions to a listener who drew the path on a blank chart. Longer speech samples were made by primary school teachers in classrooms. A tendency to increase the voicing periods as the RT increased was on average observed for the university professors, the school teachers, and the university students who described a map. These students also showed longer silence periods than the students who made short monologues. The recognized trends concerned voice professionals or subjects who were highly motivated to make themselves understood in a perturbed speaking situation. Nonparametric statistical tests, which were applied to detect the differences in distributions of voicing and silence periods, have basically supported the findings

Evaluation of the Efficiency of Arundo donax L. Leaves as Biomonitors for Atmospheric Element Concentrations in an Urban and Industrial Area of Central Italy

Washed and unwashed Arundo donax L. (A. donax) leaves were analyzed for elements, and results were compared with element concentrations detected in river water and particulate matter (PM) Samples were collected along a river in an urban and industrial hot spot of Central Italy, where element concentrations show relevant spatial gradients both in air and river water. The aim of this study is to identify the role of the two environmental matrices on leaves composition. Element concentrations of washed and unwashed leaves were compared to differentiate between the superficial deposition and the uptake into leaf tissues of elements. Water-soluble and -insoluble element concentrations were measured in PM10 samples collected on membrane filters by using innovative high spatial resolution samplers. The comparison among leaf and atmospheric concentrations of PM10 elements showed a similar trend for Ni, Mo, Cr, Ti, and Fe, which are reliable tracers of the PM10 contribution by steel plant and vehicular traffic. Soluble species appeared to be mainly bounded into leaf tissues, while insoluble species were deposited on their surface. On the other hand, element concentrations detected in washed A. donax leaves were poorly correlated with those measured in river water samples. The obtained results proved that A. donax leaves can be used as reliable biomonitors for the evaluation of the atmospheric concentrations of some PM10 elemental components

Bismuth exposure affects morpho-physiological performances and the ionomic profile in garden cress (Lepidium sativum L.) plants

Environmental pollution caused by heavy metals has long been considered a relevant threat to ecosystem survival and human health. The use of safer substitutes for the most toxic heavy metals in many industrial applications is discussed as a potential way to face this issue. In this regard, Bi has been proposed for replacing Pb in several production processes. However, few literature records reported on the effects of Bi on living organisms, particularly on plants. In this study, garden cress (Lepidium sativum L.) plants were exposed to different concentrations of Bi nitrate added to soil in growth chambers for 21 days. Results evidenced the toxic effect of Bi on shoot growth, regardless of the Bi nitrate concentration in the soil, paralleled by a similar reduction in the chlorophyll and carotenoid content, a decrease in the nitrogen balance index values, and an impairment of the photosynthetic machinery evaluated by chlorophyll fluorescence image analysis. The presence of Bi in the soil was shown to affect element accumulation in roots and translocation to shoots, with micronutrient content particularly reduced in the leaves of Bi-treated plants. A dose-dependent plant accumulation of Bi to metal concentration in the soil was observed, even if very low metal bioconcentration ability was highlighted. The reduced Bi translocation from roots to shoots in plants exposed to increasing Bi concentrations in the soil is discussed as a possible defense mechanism likely associated with the observed increase of anthocyan and flavonol contents and the activation of photoprotection mechanisms preventing higher damages to the photosynthetic apparatus

A low-cost portable vocal analyser for long-term monitoring and clinical investigation

A low-cost portable device has been developed at Politecnico di Torino to provide traceable measurements of vocal parameters during long-term monitoring as well as short ambulatory tests. The device, named Voice Care, is based on a contact microphone that is attached to the jugular notch of the subject under monitoring and on a wearable data acquisition unit that stores the raw samples of the signal generated by the vocal folds’ vibration. Post processing algorithms have been assessed to evaluate the vocal effort and the vocal load that voice professionals are subjected to during their daily activity, estimating the parameters sound pressure level, fundamental frequency and phonation time percentage. Other investigations are related to the length of voiced and unvoiced frames, whose distribution are dependent on the acoustic characteristics of the environment where the voice monitoring takes place. Another application of the Voice Care is related to short-term ambulatory tests, which allows the cooperation with physicians to make the device a reliable diagnostic tool. Processing algorithms have been extended to estimate other parameters, such as jitter, shimmer and voice quality indexes, that allow the phonatory status of the subject under monitoring to be evaluated. An experimental campaign has been performed involving thirty teachers in four primary schools who have been monitored for two to four days across one week of teaching. The effectiveness of the proposed device has been shown by the obtained results, which were in good agreement with the subjective impression and the classroom acoustics. Other specific tests have been performed in very different acoustic environments (anechoic, reverberant and semi- reverberant chambers) to highlight the device capability in evaluating the environment effects on the vocal production. Ambulatory tests for the optimization of the Voice Care as a diagnostic tool are planned to be carried out soon

A multi-analytical approach to studying the chemical composition of typical carbon sink samples

Peatlands in southern South America (Tierra del Fuego region, TdF) play a key role in the ecological dynamics of Patagonia. It is, therefore, necessary to increase our knowledge and awareness of their scientific and ecological value to ensure their conservation. This study aimed to assess the differences in the distribution and accumulation of elements in peat deposits and Sphagnum moss from the TdF. Chemical and morphological characterization of the samples was carried out using various analytical techniques, and total levels of 53 elements were determined. Furthermore, a chemometric differentiation based on the elemental content of peat and moss samples was performed. Some elements (Cs, Hf, K, Li, Mn, Na, Pb, Rb, Si, Sn, Ti and Zn) showed significantly higher contents in moss samples than in peat samples. In contrast, only Mo, S and Zr were significantly higher in peat samples than in moss samples. The results obtained highlight the ability of moss to accumulate elements and to act as a means to facilitate the entry of elements into peat samples. The valuable data obtained in this multi-methodological baseline survey can be used for more effective conservation of biodiversity and preservation of the ecosystem services of the TdF

Trapped air metamaterial concept for ultrasonic sub-wavelength imaging in water

Funding for this work was provided through the UK Engineering and Physical Sciences Research Council (EPSRC), Grant Numbers EP/N034163/1, EP/N034201/1 and EP/N034813/1.Acoustic metamaterials constructed from conventional base materials can exhibit exotic phenomena not commonly found in nature, achieved by combining geometrical and resonance effects. However, the use of polymer-based metamaterials that could operate in water is difficult, due to the low acoustic impedance mismatch between water and polymers. Here we introduce the concept of “trapped air” metamaterial, fabricated via vat photopolymerization, which makes ultrasonic sub-wavelength imaging in water using polymeric metamaterials highly effective. This concept is demonstrated for a holey-structured acoustic metamaterial in water at 200–300 kHz, via both finite element modelling and experimental measurements, but it can be extended to other types of metamaterials. The new approach, which outperforms the usual designs of these structures, indicates a way forward for exploiting additive-manufacturing for realising polymer-based acoustic metamaterials in water at ultrasonic frequencies.Publisher PDFPeer reviewe