Gas sensing technology is widely applied in various fields, including environmental monitoring, industrial process control, medical diagnostics, safety warnings, and more. As a detection element, the quartz tuning fork (QTF) offers advantages such as high-quality factor (Q-factor), strong noise immunity, compact size, and low cost. Notably, its resonant characteristics significantly enhance system signal strength. Two spectroscopic techniques based on QTF detection, Quartz-enhanced photoacoustic spectroscopy (QEPAS) and light-induced thermoelastic spectroscopy (LITES), are currently research hotspots in the field of spectral sensing. This paper provides a comprehensive and detailed review and highlights pivotal innovations in these two QTF-based spectroscopic techniques. For QEPAS, these encompass high-power excitation methods, novel excitation sources, advanced QTF detection elements, and acoustic wave amplification strategies. Regarding LITES, the researches on optical cavity-enhanced approaches, modified QTF improvement mechanisms, integration with heterodyne demodulation technique, and combination with QEPAS were analyzed. These advances have enabled quartz-enhanced laser spectroscopy to achieve detection limits ranging from parts-per-billion (ppb) to parts-per-trillion (ppt) levels for trace gases such as methane (CH₄), acetylene (C₂H₂), carbon monoxide (CO), and so on. Additionally, prospects for future technological developments are also discussed in the concluding section. QEPAS and LITES, collectively called quartz-enhanced laser spectroscopy technology, may bring a paradigm shift in gas sensing for applications.
Using the formalism of species and twisted objects, we introduce two structures of cointeracting bialgebras on hypergraphs, induced by two notions of induced sub-hypergraphs. We study the associated unique morphisms of cointeracting bialgebras from hypergraphs to the polynomial algebra in one indeterminate: in the first case, this gives the chromatic polynomial of a graph attached to the considered hypergraph. In the second case, we obtained Helgason's notion of chromatic polynomial of a hypergraph. We obtain Hopf-algebraic proves of results about the values of this chromatic polynomial in -1 or about its coefficients, with the help of the action of a monoid of characters. This allows to give multiplicity-free formulas for the antipodes of these objects, using various notions of acyclic orientations of hypergraphs. Mixing the two notions of induced sub-hypergraphs, we obtain a third Hopf algebra, firstly described by Aguiar and Ardila. We obtain negative results on the existence of a second coproduct making it a cointeracting bialgebra. Anyway, it is still possible to obtain a polynomial invariant from this structure, which is the chomatic polynomial described by Aval, Kharagbossian and Tanasa. We nally study Iovanov and Jaiung's Hopf algebra of multi-complexes, making it a cointeracting bialgebra which has for quotient one of the preceding cointeracting bialgebras of hypergraphs.
In the context of chemical and process industries, the ability to accurately assess system reliability and identify potential failure modes is fundamental to ensuring safety and preventing losses. Fault Tree Analysis (FTA) is a widely adopted method for modelling failure logic and estimating risk. Traditional FTA uses AND and OR gates to construct coherent fault trees, where system failure is attributed exclusively to the failure of components. However, this approach can be insufficient for complex process systems, where both component failure and component operation may contribute to hazardous events. To address this limitation, non-coherent fault trees (NC-FTs) extend classical FTA by incorporating NOT gates, enabling analysts to model scenarios where the presence or absence of a function leads to system-level failures. While effective, NC-FTs can lead to exponentially larger trees and increased computational complexity, limiting their practical use in large-scale industrial systems. This study proposes a novel approach, the semi-coherent fault tree methodology, which serves as a bridge between coherent and non-coherent models. By identifying key events that contradict the desired system behaviour and modelling their inverses, this method significantly simplifies the fault tree structure without compromising analytical rigor. The methodology is applied to the cooling system of a fixed-bed adiabatic catalytic reactor, a critical subsystem in preventing thermal runaway, a major hazard in chemical plants, often responsible for severe accidents and economic loss. The reactor's loop configuration presents inherently non-coherent behaviour, making it an ideal test case. Results show that the traditional approach requires modelling 54 basic events, while the proposed method reduces this to 21, substantially improving analysis efficiency and interpretability. This semi-coherent FTA approach enhances the ability to model, analyse, and prevent complex failure scenarios in process industries, offering a valuable tool for advancing risk assessment, system reliability, and loss prevention practices.
Bismuth sesquioxide attracts considerable attention due to the numerous stable and metastable phases it exhibits in nature, as well as the diverse range of properties it displays. Despite their high potential for numerous applications, surprisingly few investigations have been carried out on nanocomposites where the stability range of particular crystallographic phases has been significantly extended in the form of nanocrystallites embedded in a residual amorphous matrix. Quite recently, nanocrystallites of delta-like Bi2O3 phase were observed at room temperature, confined in Bi2O3-Al2O3-SiO2 glassy matrix. In this work, we performed 27Al and 29Si solid-state NMR, HT-XRD, and TEM with EDS/EELS microanalysis experiments to clarify the role of Al and Si additives, which had been barely understood. These systematic investigations provided evidence that neither Al nor Si additives are incorporated into the delta-like Bi2O3 phase. Instead, their local environments remain similar to those in pristine glass. Therefore, we postulate that it is the size and strain effects that provide the delta-like phase stabilisation in the nanocomposite glass-ceramics studied in this work, making it a fascinating phenomenon for further studies.
In this work, a single-port surface acoustic wave (SAW) resonator with a Co40Fe40B20/SiO2/(X+90 degrees) ST-cut quartz multilayer structure is investigated as a magnetic field sensor. The Love wave resonator design is aimed at achieving a high magnetic field sensitivity, together with a temperature compensation. Two versions of sensitive layers are studied: Co40Fe40B20 (100 nm) and Co40Fe40B20(100 nm)/ SiO2(3 nm)/Co40Fe40B20(100 nm). For the latter, the 3-nm-thick SiO2 layer is inserted between two 100-nmthick amorphous Co40Fe40B20 layers, with the objective of controlling the magnetic properties of the magnetoelastic layer. A quartz crystal is selected as the piezoelectric substrate and a 375-nm-thick SiO2 layer is used as insulating medium. This thickness is chosen to achieve insensitivity to temperature variations of the Love wave velocity at 433 MHz industrial, scientific, and medical (ISM) band, when no magnetic field is applied. Optimized structures are fabricated and characterized, demonstrating a good agreement between experimental results and the simulation. The structure exhibits high magnetic field sensitivity of -6900 ppm/mT (corresponding to 3 Hz/nT) along the hard axis with the 200 nm total thickness of Co40Fe40B20 bi-layer. A substantial 26-fold increase in magnetic field sensitivity is achieved compared to that of the 100-nm-thick Co40Fe40B20.
