Search Results (14)

Using a single sensor as a virtual electronic nose, we demonstrate the possibility of obtaining good results with underperforming sensors that, at first glance, would be discarded. For this aim, we characterized chemical gas sensors with low repeatability and random drift towards both dangerous and innocuous volatile organic compounds (VOCs) under different levels of relative humidity. Our results show classification accuracies higher than 90% when differentiating harmful from harmless VOCs and coefficients of determination, R², higher than 80% when determining their concentration in the parts per billion to parts per million range. Full article

We present a method to monitor methane at atmospheric concentrations with errors in the order of tens of parts per billion. We use machine learning techniques and periodic calibrations with reference equipment to quantify methane from the readings of an electronic nose. The results obtained demonstrate versatile and robust solution that outputs adequate concentrations in a variety of different cases studied, including indoor and outdoor environments with emissions arising from natural or anthropogenic sources. Our strategy opens the path to a wide-spread use of low-cost sensor system networks for greenhouse gas monitoring. Full article

Nowadays, extensive livestock farming faces substantial threats in the Mediterranean region, provoking a setback dynamic in the sector. In 2016, the Fire Flocks (FF) project was conceived and implemented as a regional strategy to revert this situation and revalue the sector in Catalonia, in the NE of the Iberian Peninsula. FF promotes forest management through extensive livestock farming, and more specifically silvopastoralism, to reduce vegetation load and wildfire risk. The initiative also works on fire risk awareness with the aim of promoting extensive livestock products through FF label and valorization strategies. Five years after its initial implementation, the project managers detected several weaknesses and potential improvements directly affecting the economic and environmental performance of the participating farms. It was therefore considered necessary to conduct targeted qualitative interviews with the farmers participating in the project in order to gather their opinions on the project’s functioning and further steps. To this end, 17 farmers were interviewed with the aid of a qualitative questionnaire. The farmers stated that although FF is not providing them with any direct financial benefits, it does present an opportunity to belong to a group of farmers working on wildfire prevention, thereby lending them a voice as a group, and reaching more social visibility. The qualitative analyses elucidate key elements to be promoted in FF, such as redesign of the operational structure, expansion to a regional scale and action lines to facilitate grazing activity. Full article

Although many chemical gas sensors report high sensitivity towards volatile organic compounds (VOCs), finding selective gas sensing technologies that can classify different VOCs is an ongoing and highly important challenge. By exploiting the synergy between virtual electronic noses and machine learning techniques, we demonstrate the possibility of efficiently discriminating, classifying, and quantifying short-chain oxygenated VOCs in the parts-per-billion concentration range. Several experimental results show a reproducible correlation between the predicted and measured values. A 10-fold cross-validated quadratic support vector machine classifier reports a validation accuracy of 91% for the different gases and concentrations studied. Additionally, a 10-fold cross-validated partial least square regression quantifier can predict their concentrations with coefficients of determination, R², up to 0.99. Our methodology and analysis provide an alternative approach to overcoming the issue of gas sensors’ selectivity, and have the potential to be applied across various areas of science and engineering where it is important to measure gases with high accuracy. Full article

We provide a review on the state-of-the-art of gravitational waves induced by primordial fluctuations, so-called induced gravitational waves. We present the intuitive physics behind induced gravitational waves and we revisit and unify the general analytical formulation. We then present general formulas in a compact form, ready to be applied. This review places emphasis on the open possibility that the primordial universe experienced a different expansion history than the often assumed radiation dominated cosmology. We hope that anyone interested in the topic will become aware of current advances in the cosmology of induced gravitational waves, as well as becoming familiar with the calculations behind. Full article

Active research in nanostructured materials aims to explore new paths for improving electronic device characteristics. In the field of gas sensors, those based on metal oxide single nanowires exhibit excellent sensitivity and can operate at extremely low power consumption, making them a highly promising candidate for a novel generation of portable devices. The mix of two different metal oxides on the same nanowire can further broaden the response of this kind of gas sensor, thus widening the range of detectable gases, without compromising the properties related to the active region miniaturization. In this paper, a first study on the synthesis, characterization and gas sensing performance of (Ga_xIn_1-x)₂O₃ nanowires (NWs) is reported. Carbothermal metal-assisted chemical vapor deposition was carried out with different mixtures of Ga₂O₃, In₂O₃ and graphite powders. Structural characterization of the NWs revealed that they have a crystalline structure close to that of In₂O₃ nanowires, with a small amount of Ga incorporation, which highly depends on the mass ratio between the two precursors. Dedicated gas nanosensors based on single NWs were fabricated and tested for both ethanol and nitrogen dioxide, demonstrating an improved performance compared to similar devices based on pure In₂O₃ or Ga₂O₃ NWs. Full article

Gas sensitive iridium-gated field effect transistors based on silicon carbide were used to study the response towards formaldehyde, ammonia, carbon monoxide and nitrogen dioxide at concentrations ranging from parts per million to parts per billion diluted in dry synthetic air and under 50% of relative humidity. The sensor performance was studied using temperature cycled operation mode from 270 to 390 °C to investigate the capability of these devices to discriminate between the studied gases under different background conditions via pattern recognition algorithms. Full article

A new method for the site-selective synthesis of nanowires has been developed to enable the material growth with specific morphology and different compositions on one single chip. Based on a modification of the chemical vapor deposition method, the growth of nanowires on top of micromembranes can be easily tuned and represents a simple and adjustable fabrication process for the direct integration of different nanowire-based resistive multifunctional devices. This proof-of-concept is exemplified by the deposition of SnO₂, WO₃ and Ge nanowires on the membranes of one single chip and their gas sensing responses towards different concentrations of CO, NO₂ and humidity diluted in synthetic air are evaluated. The principal component analysis of the collected data allows gas identification and, thus, the system is suitable for environmental monitoring. Full article

Chemoresitive gas sensors based on multiple nanowires (M-NWs) randomly grown and electrically inter-connected on the top of interdigitated electrodes (IDEs) and arrays of single nanowires connected between faced nanoelectrodes (A-S-NWs) are developed in this work. These systems, consisting of gas sensitive tungsten oxide nanowires (NWs), are tested to NO₂, and their performance regarding the response magnitude, sensitivity and response rate are evaluated here. Full article

In this work, the fabrication of a SPR (Surface Plasmon Resonance)-grating coupler using Laser Interference Lithography (LIL) has been investigated, giving rise to large area diffraction gratings on a 100 nm-thick gold film. The period of the diffraction grating is Λ = 500 nm. The SPR sensor has been tested towards several liquids showing a maximum sensitivity of S = 390 nm/RIU. Full article

In this work the growth and characterisation of (Ga, In)₂O₃ NWs inside a CVD furnace using different mixtures of Ga₂O₃ and In₂O₃ is reported. The NWs have been characterised by SEM, XRD and TEM, proving their cubic crystalline nature similar to In₂O₃ and the degree of incorporation of Ga in this lattice. Furthermore, gas nanosensors based on single NWs have been fabricated and measured, demonstrating the sensing properties of the synthesized material. Full article

Here we present the gas sensing characterization of single-nanowire sensor array systems based on either non-functionalized or Pt-functionalized single tungsten oxide nanowires towards various concentrations of nitrogen dioxide and ethanol. The sensor systems demonstrate stable and reproducible responses to the tested analytes, showing consistency with previous systems based on multiple-nanowire based films and validating the fabrication process of these devices. Full article

Gallium oxide nanowires (NWs) were synthetized using a vapor-liquid-solid route via carbothermal reduction. These NWs were characterized using XRD, SEM and TEM as well as photoluminescence spectroscopy, confirming their crystalline nature. Gas sensors, based on individual NWs, deposited on suspended microhotplates, were tested towards several gases of interest at different temperatures. The sensing towards relative humidity provided the best results, with responses up to 20% at room temperature (~25 °C). Full article