WO3/Pt/PEG/SiO2 porous film for hydrogen sensing by the sol-gel method.

Tungsten oxide (W O 3) has been widely used in hydrogen sensing due to its stable chemical properties and high oxygen vacancy diffusion coefficient. However, the response of pure W O 3 to hydrogen is slow, and doping is an effective way to improve the hydrogen sensing performance of W O 3 materials. In this paper, W O 3/P t/P E G/S i O 2 porous film was prepared by the sol-gel method using tungsten powder, H 2 O 2 and C 2 H 5 O H as precursors, polyethylene glycol (PEG) as the pore-forming agent, and tetraethyl orthosilicate (TEOS) as the S i O 2 source material. The sensing properties of the W O 3 composite for hydrogen were characterized by a transmission optical fiber hydrogen sensing system made at home. The process parameters such as water bath time, aging time, W:PEG ratio, and W:TEOS ratio were optimized to improve the sensitivity and response time of the sensing film. The experimental results indicate that the sensitivity is 15.68%, the average response time is 45 s, and the repeatability is up to 98.74% in 16 consecutive tests. The linearity index R 2 is 0.9946 within the hydrogen concentration range of 5000 ppm to 50,000 ppm. The film responds only to H 2 when the concentration of interfering gases (C H 4, CO, C O 2) is 2000 ppm. The hydrogen sensing performance of the optimized film is significantly improved compared with that of the undoped film.

pH biosensors based on hydrogel optical fiber.

This paper presents a hydrogel optical fiber fluorescence pH sensor doped with 5(6)-carboxyfluorescein (5(6)-FAM). The hydrogel optical fiber was fabricated with 2-hydroxy-2-methylpropiophenone as a photoinitiator, with different concentrations of polyethylene glycol diacrylate (PEGDA) for the core and cladding. A pH-sensitive fluorescence indicator 5(6)-FAM was doped into the core of the fiber. The prepared hydrogel optical fiber pH sensor showed good response within the pH range of 5.0-9.0. The linear range of the pH sensor is 6.0 to 8.0, with R 2=0.9904; within this range, the sensor shows good repeatability and reversibility, and the resolution is 0.07 pH units. The pHs of pork tissues soaked in different pH buffers were detected by the hydrogel optical fiber pH sensor; the linearity is 0.9828 when the pork tissue pH is in the range of 6.0-7.5. Due to the good ion permeability and biocompatibility of the hydrogel, this hydrogel optical fiber pH sensor is expected to be used in biomedical applications.

Detection of internal humidity in a transformer via optical interferometry.

To detect the internal humidity of the transformer accurately and sensitively and eliminate the interference caused by electromagnetic fields, an interferometric measurement is proposed in this paper for the first time, to the best of our knowledge. The phase value distribution of the interferogram affected by humidity can be extracted quantitatively. The peak-to-peak value (P-P) of the phase image can reflect the humidity, according to theoretical analysis, and the main factors affecting the P-P are current and humidity. It has been tested by currents of 800 A, 1000 A, and 1200 A and different humidities. The paper reveals the relationship between humidity and P-P, proving that it is a reasonable application of real-time measurement of internal humidity in the transformer.

Nanosized Zn-In spinel-type sulfides loaded on facet-oriented CeO2 nanorods heterostructures as Z-scheme photocatalysts for efficient elemental mercury removal.

Developing of effective photocatalysts is of great significance for realizing photocatalytic environment purification. Herein, an interfacial bent bands and internal electric field modulated CeO2/ZnIn2S4 Z-scheme heterojunction for photocatalytic Hg0 oxidation. It is found that the charge transfer mechanism of Z-scheme was driven by the interfacial bent bands and internal electric field, which was confirmed by electrochemical measurements, electron spin paramagnetic resonance spectroscopy and density functional theory calculations. Moreover, the (110) dominant CeO2 nanorods partially converted Ce4+ to Ce3+ and formed oxygen vacancies, and as an electron mediator in Z-scheme systems to further facilitate charge transfer process and molecular oxygen activation. Under the strong synergistic effect between the large specific surface area, Z-scheme heterojunction and oxygen vacancies, the optimized photocatalyst exhibits 86.7% of photocatalytic removal efficiency. This work provides Z-scheme heterojunction photocatalyst design perspective for photocatalytic air purification.

First principles study on electronic properties and oxygen evolution mechanism of 2D bimetallic N-doped graphene.

Currently, the oxygen evolution reaction (OER) is constrained by complex four-electron transport, thus it is difficult to understand the catalytic mechanism. In this work, the electronic properties and catalytic performance of M1M2/NC (M = Mn, Fe, Co, Ni, Cu and Zn, random combination in pairs) is studied by density functional theory, the calculated results show that the overpotential of FeCu/NC is 0.88 V, which is used as the optimal catalyst to further study the OER reaction mechanism. Combined with the volcano map and the d-band center position, the low overpotential of FeCu/NC is because it has a more suitable position of d-band center -1.806 eV than other materials. Moreover, the calculation results show that the density of states (DOS) of iron-containing materials is stronger than that of other materials near the Fermi level, which can promote the catalytic reaction. In addition, O∗OH and O∗H, O∗H and O∗ linearly related theoretical equations are proposed, respectively. Furthermore, the analysis of the catalytic mechanism shows that the formation of the catalytic rate-determining step is affected by the movement of the d-band center, the distance of the transition state adsorption and the electric field.

Optimization of the phase generated carrier demodulation algorithm based on support vector regression.

The phase generated carrier (PGC) algorithm is often used in the demodulation of interference signals in optical fiber sensors for its high sensitivity, good linearity, and large dynamic range. However, the PGC demodulation method is often distorted by the amplitude of the interference signal and the depth of modulation. In this study, the support vector regression (SVR) method is used to compensate the distortion of the PGC demodulation schemes. Simulation results showed that the SVR algorithm can effectively reduce the nonlinear error of the PGC demodulation system. The fitting accuracy of the SVR algorithm is 97.5% and greater than 90% in noiseless and noise systems, which is better than the back propagation (BP) neural network algorithm. Also, the SVR-based algorithm can better restore the amplitude with smaller mean square error and good correlation. A vibration monitoring system has been built, and experiment results confirm that the performance of the SVR-based algorithm is better than direct PGC demodulation and BP algorithm with the mean square error of 0.0005 and relevance of 0.94.

Optical Interrogation of Single Levitated Droplets in a Linear Quadrupole Trap by Cavity Ring-Down Spectroscopy.

Optical trapping is a well-established technique to manipulate and levitate micro- and nanoscale particles and droplets. However, optical traps for single aerosol studies are most often limited to trapping spherical nonabsorbing droplets, and a universal optical trap for the stable confinement of particles regardless of their absorption strength and morphology is not established. Instead, new opportunities arise from levitating droplets using electrodynamic traps. Here, using a combined electrodynamic linear quadrupole trap and a cavity ring-down spectrometer, we demonstrate that it is possible to trap single droplets and simultaneously measure their extinction cross sections and elastic scattering phase functions over extended periods of time. To test the novel setup, we evaluated the evaporation of 1,2,6-hexanetriol under low-humidity conditions, and the evolution of aqueous (NH4)2SO4 and NaCl droplets experiencing changing environmental conditions. Our studies extended beyond spherical droplets and we measured particle extinction cross sections after the efflorescence (crystallization) of the inorganic salt particles. Comparison of measured cross sections for crystallized particles with light scattering model predictions (using Mie theory or the T-matrix/extended boundary-condition method (EBCM) implementations for random orientation, with either the spheroid or superellipsoid parameterizations) enables information on particle shape to be inferred. Specifically, we find that cross sections for dry (NH4)2SO4 particles are accounted for by Mie theory and, thus, particle shape is represented well by a sphere. Conversely, the cross sections for dry NaCl particles are only reconciled with light scattering models pertaining to nonspherical shapes. These results will have implications for accurate remote sensing retrievals of dry salt optical properties and for parameterizations implemented in radiative forcing calculations with changing humidity. Moreover, our new platform for precise and accurate measurement of optical properties of micron-scale and sub-micron particles has potential applications in a range of areas of atmospheric science, such as precise light scattering measurements for ice crystals and mineral dust. It represents a promising step toward accurate characterizations of optical properties for nonspherical and light-absorbing aerosols.

Identification and quantification of explosives in nanolitre solution volumes by Raman spectroscopy in suspended core optical fibers.

A novel approach for identifying explosive species is reported, using Raman spectroscopy in suspended core optical fibers. Numerical simulations are presented that predict the strength of the observed signal as a function of fiber geometry, with the calculated trends verified experimentally and used to optimize the sensors. This technique is used to identify hydrogen peroxide in water solutions at volumes less than 60 nL and to quantify microgram amounts of material using the solvent's Raman signature as an internal calibration standard. The same system, without further modifications, is also used to detect 1,4-dinitrobenzene, a model molecule for nitrobenzene-based explosives such as 2,4,6-trinitrotoluene (TNT).

Performance of an optical packet switch with fixed wavelength converter arrays under bursty traffic.

This paper focuses on the performance of a synchronous time-slotted optical packet switch. An optical packet switch with fixed wavelength converter arrays is proposed. The proposed node architecture uses shared fixed wavelength converter arrays and recirculation fiber delay lines to resolve optical packet collisions. To make full use of the fixed wavelength converter arrays and fiber delay lines, two control schemes are presented and studied. The packet loss probabilities of the proposed node architecture are evaluated in detail by simulation experiments.

Characterization of a dissolved oxygen sensor made of plastic optical fiber coated with ruthenium-incorporated solgel.

A dissolved oxygen sensor made of plastic optical fiber as the substrate and dichlorotris (1, 10-phenanthroline) ruthenium as a fluorescence indicator is studied. Oxygen quenching characteristics of both intensity and phase were measured; the obtained characteristics showed deviation from the linear relation described by the Stern-Volmer equation. A two-layer model is proposed to explain the deviation, and main parameters can be deduced with the model.