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Laser-induced plasma deviates from LTE faster with the increase of radius r and slower with the increase of delay time Td in a higher-pressure environment.

This review aims to summarize existing approaches and their progress on the interpretation of gas-sensing mechanisms in semiconductor materials.

Semiconductor gas sensors are important candidates with small size, low power consumption, and low cost characteristics for gas sensing in the internet of things, but the nonlinear response, unstable baseline, and the variability of the responses towards temperature and humidity fluctuation harm its performance. Here, we proposed a new technique called virtual alternating current (AC) measurements to enable semiconductor gas sensors to achieve high linear response (R2 > 0.99), stable baseline, and easily calibrated temperature and humidity fluctuation. The most outstanding advantage of our technique is to achieve excellent performance simply by measuring resistance. The universality and feasibility of our technique were verified by a range of commercial and homemade sensing elements and a range of analyte. We also successfully generalized our technique to non-Debye relaxation systems, which further expands the scope of semiconductor gas sensor types available in our technique. We believe that our technique will enable gas sensing nodes built with semiconductor gas sensors in the internet of things to achieve markedly superior performance.

We present here exact solutions to the equations of geophysical fluid dynamics that depict inviscid flows moving in the azimuthal direction on a circular path, around the globe, and which admit a velocity profile below the surface and along it. These features render this model suitable for the description of the Antarctic circumpolar current (ACC). The governing equations we work with–taken to be the Euler equations written in spherical coordinates–also incorporate forcing terms which are generally regarded as means that ensure the general balance of the ACC. Our approach allows for a variable density (depending on the depth and latitude) of discontinuous type which divides the water domain into two layers. Thus, the discontinuity gives rise to an interface. The velocity in both layers and the pressure in the lower layer are determined explicitly, while the pressure in the upper layer depends on the free surface and the interface. Functional analytical techniques render (uniquely) the surface and interface-defining functions in an implicit way. We conclude our discussion by deriving relations between the monotonicity of the surface pressure and the monotonicity of the surface distortion that concur with the physical expectations. A regularity result concerning the interface is also derived.

In this paper, we study steady two-dimensional periodic equatorial water waves of small amplitude which propagate over a flat bed and with a specified fixed mean-depth. In particular, we focus on irrotational flows and develop an equivalent formulation using flow force functions. The analysis is based on the local bifurcation theory due to Crandall-Rabinowitz.

We consider three-dimensional geophysical flows with centripetal forces and at arbitrary latitude, with constant vorticity beneath a wave train and above a flat bed. We consider the f-plane approximation as well as the β-plane approximation. For the f-plane approximation, we determine all possible flow solutions that exhibit constant vorticity vector. For the β-plane approximation, we show that the flow is necessarily irrotational and the free surface is necessarily flat if it exhibits a constant vorticity. Our results reveal some essential differences from those results in the literature, due to the presence of centripetal forces. Moreover, for the case exhibiting the surface tension, we prove that there are no flows exhibiting constant vorticity.

A difficult issue restricting the development of gas sensors is multicomponent recognition. Herein, a gas-sensing (GS) microchip loaded with three gas-sensitive materials was fabricated via a micromachining technique. Then, a portable gas detection system was built to collect the signals of the chip under various decomposition products of sulfur hexafluoride (SF6). Through a stacked denoising autoencoder (SDAE), a total of five high-level features could be extracted from the original signals. Combined with machine learning algorithms, the accurate classification of 47 simulants was realized, and 5-fold cross-validation proved the reliability. To investigate the generalization ability, 30 sets of examinations for testing unknown gases were performed. The results indicated that SDAE-based models exhibit better generalization performance than PCA-based models, regardless of the magnitude of noise. In addition, hypothesis testing was introduced to check the significant differences of various models, and the bagging-based back propagation neural network with SDAE exhibits superior performance at 95% confidence.

In this paper, we consider three-dimensional equatorial flows with constant vorticity beneath a wave train and above a flat bed in the β-plane approximation with centripetal forces. As a striking upshot, we show that the equatorial flow is necessarily irrotational and the free surface is necessarily flat if it exhibits a constant vorticity, owing to the presence of centripetal forces. For the case exhibiting the surface tension, we prove that there are no equatorial flows exhibiting a constant vorticity.

In this paper, we adopted the first-principles calculations to investigate the sensing properties of the GeP monolayer to four SF6 decomposition gas molecules (H2S, SO2, SO2F2 and SOF2). By discussing the calculated adsorption energy, charge transfer, work function variation combined with charge density difference and electron localization function analysis, we find that GeP monolayer exhibits favorable adsorption strength to SO2 molecule with the most intense charge interaction. And SO2 adsorption can remarkably change the density of states (DOS) of GeP monolayer. Furthermore, we also study the adsorption performance of SO2 molecule on GeP monolayer under applied biaxial strain and external electric field. And the results demonstrate that applying negative electric field can significantly enhance the sensitivity of GeP monolayer to SO2. Therefore, GeP monolayer is a potential candidate for highly sensitive and selective tunable SF6 decomposition gas sensor for on-line diagnostics of power equipment.

In this paper, we apply the bifurcation theory to study the steady two-dimensional periodic equatorial water waves for the f-plane approximation. We consider the waves with vorticity which propagate with a specified fixed depth between the thermocline and the upper boundary of the centre layer. Moreover, we present a functional J and its first variation corresponds to the exact equations in the transformed variables. Using the second variation of J , we prove a formal stability result for the bifurcation inducing the laminar solution.

Tellurene has a phosphorene-like puckered configuration and exhibits great air stability. This characteristic makes it highly sensitive to some gases, and therefore, it has a huge potential in gas sensing applications. In this paper, the sensing performance of tellurene-based gas sensors toward SF6 decomposition products, including H2S, SO2, SO2F2, and SOF2, was systematically investigated. Three types of tellurene-based gas sensors were fabricated: single tellurene flake with ohmic contact (RCTF sensor), single tellurene flake with nonohmic contact (DCTF sensor), and drop-cast tellurene flakes with heat function (HTF sensor). The RCTF sensor exhibited good sensitivity and selectivity toward hydrogen sulfide but slow recovery speed like most two-dimensional materials. The DCTF sensor exhibited a significant improvement in sensitivity, selectivity, and recovery speed compared with the RCTF sensor. Finally, the HTF sensor demonstrated the fastest recovery speed of all tellurene-based sensors. This work showed that the nonohmic contact and heat pulse are easy and efficient methods to enhance the performance of tellurene-based gas sensors toward hydrogen sulfide, which supports the application potential of tellurene in gas sensors.

In previous studies, the selection of optimal gas-sensing materials for detecting target gases mainly relied on their response value, but other indices, such as the recovery capability of materials...

We present a variational formulation for steady periodic water waves in two-layer flows by showing that critical points of a natural energy functional are solutions to the governing equations derived from first principles. We also compute the second variation of the functional.

The field of chemical (gas) sensing has witnessed an unprecedented increase in device sensitivity with single molecule detection now becoming a reality. In contrast to this, the ability to distinguish or discriminate between gas species has lagged behind. This is problematic and results in a high rate of false alarms. Here, we demonstrate a short period sinusoidal thermal modulation strategy to quantitatively and rapidly identify two industrially relevant gases (hydrogen sulfide (H2S) and sulfur dioxide (SO2)) by using a single semiconducting metal oxide sensor device. By applying sinusoidal heating voltages with a fixed short period, we were able to simultaneously obtain distinct patterns of dynamic responses. These characteristic patterns were adopted to build and validate a gas recognition library. Our approach does not rely on large-scale sensor arrays and complex algorithms and is amenable for real-time and low-power gas monitoring.

The aim of this paper is to study one class of nonlinear differential equations, which model the Antarctic circumpolar current. We prove the existence results for such equations related to the geophysical relevant boundary conditions. First, based on the weighted eigenvalues and the theory of topological degree, we study the semilinear case. Secondly, the existence results for the sublinear and superlinear cases are proved by fixed point theorems.

A difficult issue restricting the development of gas sensors is multicomponent recognition. Herein, a gas-sensing (GS) microchip loaded with three gas-sensitive materials was fabricated via a micromachining technique. Then, a portable gas detection system was built to collect the signals of the chip under various decomposition products of sulfur hexafluoride (SF

In previous studies, the selection of optimal gas-sensing materials for detecting target gases mainly relied on their response value, but other indices, such as the recovery capability of materials, have usually been overlooked. Here, we propose a new method for evaluating sensor effectiveness that includes a broader range of performance indices. In this study, four gas sensors based on metal-oxide semiconductors (WO

Of concern are steady two-dimensional periodic geophysical water waves of small amplitude near the equator. The analysis presented here is based on the bifurcation theory due to Crandall-Rabinowitz. Dispersion relations for various choices of the vorticity distribution, including constant, affine, and some nonlinear vorticities are obtained.

We present an exact solution to the nonlinear governing equations in the \begin{document}$ \beta $\end{document} -plane approximation for geophysical waves propagating at arbitrary latitude on a zonal current. Such an exact solution is explicit in the Lagrangian framework and represents three-dimensional, nonlinear oceanic wave-current interactions. Based on the short-wavelength instability approach, we prove criteria for the hydrodynamical instability of such waves.

Chemiresistive sensor devices using two-dimensional (2D) materials have been extensively studied. However, so far no single material has all the desirable attributes. For example, graphene and MXenes lack a band gap, transition metal dichalcogenides (such as MoS2) lack high sensitivity, while phosphorene exhibits poor air-stability. Here we report that tellurene, a new emergent single-element 2D material, excels as a sensor for NO2 detection. Devices based on tellurene exhibit a detection limit of ∼25 ppb, large detection range (from 25 ppb to 5 ppm), baseline noise as low as ∼0.5%, and excellent “selectivity” to NO2 even in the presence of cross-contaminants such as CO, SO2, H2S, acetone and ethanol. Density functional theory calculations indicate that large adsorption energy and intense charge redistribution are the reasons for the high sensitivity and selectivity of tellurene for NO2 detection. Further, we find that “heat-pulsing” enables fast sensor response and recovery time, without damaging the tellurene sheets. Most importantly, tellurene exhibits outstanding air-stability, making it a promising candidate for next-generation chemical sensors.

Metal oxide semiconductors (MOSs) are widely used gas-sensing materials because of their large response values and fast response speed. However, high operating temperature hinders the development of MOS-based gas sensors. To detect SF6 decomposition components (including H2S, SO2, SOF2, and SO2F2), here, we have synthesized cerium oxide nanoparticles (CeO2 NPs) via a facile hydrothermal routine, followed by functionalization with Au, Ag, and Pd noble metals to improve sensor performance. Our developed CeO2-based sensor exhibited high response to target gases at a low working temperature. After doping various metals into the CeO2 NPs, we acquired distinct patterns of dynamic responses for SF6 decomposition components. Au functionalization could maximize the enhancements of sensor responses to H2S (976%), SO2 (153%), and SOF2 (151%) at 100 °C, and a Pd-modified CeO2-based sensor exhibited optimal response to SO2F2 at a relatively high temperature of 250 °C. In addition, high response values, short response–recovery times, good repeatability, and low detection limits were also obtained from CeO2-based sensors. Our results verified that doping different noble metals into CeO2 NPs should be a promising strategy to design high-performance gas sensors for SF6 decomposition component detection. Keywords: Gas sensor, CeO2, Noble metal functionalization, SF6 decomposition components