Linear Scan Research Articles

Machine Learning Based Automatic Mode-Locking of a Dual-Wavelength Soliton Fiber Laser

Recent years have witnessed growing research interest in dual-wavelength mode-locked fiber lasers for their pivotal role in diverse applications and the exploration of nonlinear dynamics. Despite notable progress in their development, achieving reliable mode-locked dual-wavelength operation typically necessitates intricate manual adjustments of the cavity’s polarization components. In this article, we present the realization of automatic mode-locking in a dual-wavelength soliton fiber laser. To provide guidance for the algorithm design, we systematically investigated the impact of polarization configurations and initial states on the laser’s operation through numerical simulations and linear scan experiments. The results indicate that operational regimes can be finely adjusted around the wave plate position supporting the mode-locked dual-wavelength solution. Furthermore, the laser exhibits multiple stable states at the mode-locked dual-wavelength point, with critical dependence on the initial conditions. Accordingly, we developed a two-stage genetic algorithm that was demonstrated to be effective for realizing automatic dual-wavelength mode-locking. To further improve the performance of the algorithm, a feedforward neural network was trained and integrated into the algorithm, enabling accurate identification of the dual-wavelength states. This study provides valuable insights into understanding how polarization configurations and initial conditions impact the operational regimes of dual-wavelength mode-locked fiber lasers. The algorithm developed can be extended to optimize other systems with multiple stable states supported at the same parameter point.

Linear Scan Voltammetry of Two-Step Irreversible Electron Oxidation Enhanced by the Immobilization of an Intermediate (E E) on the Electrode Surface

Linear Scan Voltammetry of Two-Step Irreversible Electron Oxidation Enhanced by the Immobilization of an Intermediate (E E) on the Electrode Surface

Investigation of Pd Based Metal-Carbon As Bifunctional Electrocatalyst for OER and ORR

Developing oxygen reduction/ evolution reaction (ORR/OER) bifunctional electrocatalysts has great significance for promoting the sustainable energy conversion. Herein, Pd (5wt% only) based bimetallic catalyst adhered well on heteroatom doped conducting carbon substrate is designed and constructed. Rich defects, multiple active centers and strong synergistic effect with rapid ion/electron transport ability allow the electrocatalyst to exhibit superior performance (Li et al., 2019). Owing to its more active metal-Pd sites due to high surface area conducting carbon matrix an ultralow overpotential of 240 mV at 10 mA/cm2 for OER was obtained. It outperforms state of art RuO2 and Pt/C electrocatalyst. High half-wave potential (E1/2) of 0.821 V for ORR is comparable to commercial Pt/C (E1/2 =0.819 V) electrocatalysts was attained. The catalyst exhibits a prolonged stability in alkaline medium at 20 mA cm-2 for 24 h for OER and a small 20 mV shift in linear sweep voltammetry scan after accelerated durability test for 5000 cycles at 50mV/s for ORR. In-situ Raman analysis exhibits surface oxidation of electrocatalyst on OER in highly alkaline (1M KOH) conditions.Reference:Li, S., Hao, X., Abudula, A., & Guan, G. (2019). Nanostructured Co-based bifunctional electrocatalysts for energy conversion and storage: current status and perspectives. Journal of Materials Chemistry A, 7(32), 18674–18707. https://doi.org/10.1039/C9TA04949E

Electrochemical Stimulation of Monopolar Electrodes

Changes in the electrostatic potential within an aqueous acidic solution induced by the passage of current between the Au disk of a stationary Au|Au ring disk electrode and a distant counter electrode, Idisk made it possible to stimulate the reduction of selenite to elemental selenium at the concentric Au ring electrode polarized at Eringo just positive to its otherwise expected onset. This effect was ascribed to variations in the surface overpotential, and, thus, in the rates of selenite reduction along the ring, we define, hereafter, as a monopolar electrode. The stimulation efficiency could be accurately determined from a coulometric analysis of the peak for Se oxidation observed by subsequently scanning the ring linearly toward positive potentials to yield selenite. Shown in the figure below is a series of linear scan \\voltammograms, LSV, recorded at a scan rate of 50 mV/s for the ring polarized at Eringo in the range 0.39 - 0.45 V (see legend) following Nstim = 40 between Edisk = 0.75 and 1.00 V, where the black curve corresponds to the LSV recorded without any prior stimulation under otherwise identical conditions. As clearly indicated the stripping charge associated with the oxidation of elemental Se increases as the potential at which the ring is polarized is decreased. Excellent quantitative agreement was obtained between the current flowing through the ring, Iring , and Eringo as a fucntion of Idisk and theoretical simulations employing COMSOL using parameters extracted from independent measurements performed under otherwise identical experimental conditions. This novel tactic is expected to open new prospects for gaining insight into surfacediffusion and other interfacial dynamics phenomena.AcknowledgementsThis work was supported by the US NSF Award 1808592Literature Cited1) Han, Q.; Georgescu, N. S.; Gibbons, J.; Scherson, D. Electrochim. Acta 2019, 325, 134957 Figure 1

Intriguing properties of graphite/polysiloxane composite-based pencil electrodes

Pencil leads can be considered well-defined and cheap graphite electrodes for a wide range of electrochemistry applications. These electrodes display many intriguing properties; however, the origin of these properties is not clear. Using various analytical approaches applied to two different commercially available Tombow (TO) and Staedtler (ST) pencils we reveal a causal relationship between the unique properties of pencils and their graphite/polysiloxane composite. We explore the impact of chloroform etching on chemical composition changes, thermal stability and electrochemical parameters of pencils. Using a combination of X-ray photoelectron spectroscopy (XPS) and gas chromatography-mass spectrometry (GC-MS/MS) various polydimethylsiloxanes in composites are revealed. The polysiloxane species leave into the chloroform solvent during the etching resulting in a significant decrease of their content within the electrodes. Differential scanning calorimetry (DSC) data, corroborated by gravimetric measurements, provide additional proof of the presence of composite structures in ST and TO pencils, showing glass transition temperatures at around 76 °C and 81 °C. The main difference between the TO and ST electrodes is the content and composition of the polysiloxanes within the graphite matrix. ST composites have significantly higher polymer content (∼ 30 %) with traces of Na and S impurities compared to TO ones (∼ 14 %) free of contaminations. Furthermore, mainly cyclic nanostructures appear in chloroform extracts of ST composites whereas rather chain-like clusters are liberated out of the TO counterparts. Complementary electrochemical experiments using cyclic voltammetry (CV), impedance spectroscopy (EIS) and the less known elimination voltammetry with linear scan (EVLS) reflect the performance superiority of TO electrodes with much lower polysiloxane content and free of impurities. High conductivity, low capacitive current along with favoured charge carrier transfer all promise a wide range of technological applications for the TO pencil material.

Effect of different intraoral scanning strategies on the marginal and internal fit of CAD-CAM inlay restorations: An in vitro study

Whether the scanning strategy of intraoral scanners (IOSs) affects the accuracy of the digital recording for an indirect ceramic inlay restoration is unclear. Furthermore, which strategy would be optimal and most effective is uncertain. The purpose of this in vitro study was to evaluate the impact of 3 different scanning strategies using the Carestream CS 3700 IOS on the marginal and internal fit of a mesio-occluso-distal (MOD) ceramic inlay restoration. A typodont master model (ANA-4 VCER; Frasaco) was used with a standardized preprepared MOD inlay maxillary first molar typodont tooth (ANA-4 ZP16 CER99-008; Frasaco) (N=30). These inlay preparations were scanned with the CS 3700 IOS using 3 different scanning strategies: linear, wave, and S-figure scanning strategies. Each scan strategy group was scanned 10 times for all groups to obtain 30 standard tessellation language (STL) files. Thirty restorations were milled from lithium disilicate CAD blocks (IPS e.max; Ivoclar AG) and cemented into their typodont-prepared inlay cavities. A single examiner used a stereomicroscope to measure the marginal and internal gaps at the predetermined points. A 1-way ANOVA was used for the statistical analysis, followed by the Tukey post hoc test with Bonferroni adjustment. All tests were 2-tailed (α=.05). All scanning strategy groups demonstrated statistically significant differences for the marginal and internal fit of the inlay restorations (P<.001). Overall, the linear scanning strategy showed the lowest mean marginal and internal gap values (29.2 ±3.6µm and 39.0 ±6.4µm), followed by the wave scanning strategy, which had comparable mean marginal and internal gap values: 49.1 ±3.6µm and 48.2 ±6.0µm, respectively. The S-figure scan strategy had the highest mean marginal and internal gap values: 50.2 ±12.6µm and 71.3 ±7.7µm, respectively. Inlay restorations scanned by the linear scan strategy had the best marginal and internal fit when scanned with the CS 3700 IOS.

Oxygen reduction performance study of Fe/Ni doped PAAM/Agar double net hydrogel carbon materials

AbstractThe electrocatalytic performance plays a pivotal role in the widespread adoption of DMFCs. Hence, it is imperative to develop electrocatalysts with superior performance for oxygen reduction reactions. In this study, carbon materials doped with Fe and Ni were synthesized. The characterization results revealed that the morphology, pore size, pore capacity, and BET of the catalysts varied with different doping elements, thereby affecting their performance. Linear Scan Voltammetry demonstrated that the doped samples (Ni−NC, Fe−NC, Fe−Ni−NC) exhibited varying degrees of enhancement in ORR activity compared to the undoped NC samples containing only Fe and Ni. Among them, the Fe−Ni−NC catalyst showed remarkable methanol tolerance (67.3 %) and a lower Tafel slope (93.24 mV dec−1) in comparison to the Pt/C catalyst (47.9 %). Moreover, RRDE measurements indicated a 3.31 % H2O2 yield and n of 3.93 for Fe−Ni−NC. Additionally, in DMFC tests conducted at 20 and 50 °C, Fe−Ni−NC approached the performance of the Pt/C catalyst cathode.

Simple and Rapid Voltammetric Method Using a Gold Microwire Electrode to Measure Inorganic Arsenic in Holopelagic Sargassum (Fucales, Phaeophyceae)

The valorization of massive strandings of holopelagic Sargassum spp. is strongly limited by high levels of inorganic arsenic (Asi) that are potentially above the limit of current regulations. Monitoring Asi in algal biomass is currently achieved using standard chromatographic separation followed by spectroscopic detection. Here, we propose an alternative simpler procedure based on the extraction of Asi from the freeze-dried algal powder in deionized water and the electroanalytical detection of the diluted extract at a gold-microwire electrode. The protocol was optimized both in terms of extraction (powder/water ratio, extraction time, temperature) and electrolyte used for the voltammetric detection. Two electrolytes were tested: one composed of citric acid, sulfamic acid and KCl (pH 2.0) and another composed of an acetate buffer (pH 4.7) and NaCl. We demonstrate here that Asi determination is possible with the first electrolyte but it is necessary to deal with a relative unstable signal. Measurement of Asi was best achieved with the second electrolyte (acetate buffer and NaCl) with the following optimized electrochemical conditions: deposition potential of −1.2 V, deposition time of 30 seconds and linear scan voltammetry. Voltammetric results were then compared to a reference method (HPLC-ICP-MS) using different morphotypes of holopelagic Sargassum spp. (S. natans VIII, S. natans I and S. fluitans III), using commercial extracts of brown seaweeds and using a Hijiki certified reference material. Very good agreement was obtained between our novel method and HPLC-ICP-MS. Both methods show that inorganic arsenic is almost entirely present as As(V) in Sargassum spp. extracts.

High-accuracy roundness measurement of small cylindrical workpieces by a high-frequency filtering method

In this paper, a ruby ball stylus is employed as hardware filtering for high-frequency data in the stitching linear scan method for the roundness and diameter measurement of small cylinders (diameter less than 3 mm). The conventional rotary scan method is improper for measuring small cylinders due to the crucial alignment. Thus, the stitching linear scan method is proposed, with which the cross-sectional circle of small cylinders is divided into several arcs to be measured and stitched. Although small cylinders can be measured by this method, the final results of roundness and diameter are affected by the low-accuracy stitching due to the high-frequency data. To address this issue, a ruby ball stylus with a tip radius of 150 μm is used for eliminating the influence of high-frequency data which is obtained by a diamond stylus with a tip radius of 2 μm in the stitching linear scan method. Since the measuring force of the ruby ball stylus influences the measurement of the small cylinders very much, a series of new alignments are carried out. Two groups of experiments by ruby ball stylus and diamond stylus have been conducted under the same conditions respectively. Results show that the average matching coefficient of adjacent arc profiles is enhanced by 86% and the repeatability of the ruby ball stylus is better than the diamond stylus.

Revealing the surface modification effect on Li-ion insertion into Ni-rich NCM cathode material by cyclic voltammetry

This article presents a new approach to the determination of electrochemical parameters characterizing the degradation behavior of electrodes based on LiNi0.85Co0.10Mn0.05O2 (Ni-rich NCM) using the method of cyclic voltammetry with a linear scan of the electrode potential (CV). To establish the relationship between electrochemical, structural, and morphological characteristics, XRD, synchrotron XRD (SXRD) in the operando mode, and SEM were used. The results of the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) were used to verify the CV data. The features of the irreversible phase transition in NCM during the first cycle of extraction-insertion of lithium ions and its influence on the further behavior of the material during cycling were studied. It was found that the nature of the slope variation of capacity and coulomb efficiency dependences on the cycle number with an increase in the electrode potential scan rate is a criterion for the ratio of reversible and irreversible components of the electrode capacity degradation. Reversible electrode capacity degradation is due to the difference between the diffusion coefficients of lithium ions in the anodic and cathodic processes, irreversible degradation is due to the structural degradation of the material. For NCM samples with different particle surface conditions (with different composition of Cathode Electrolyte Interphase (CEI)) the values of Li+ ions diffusion coefficient (D) for each stage of the intercalation process were found in the range 4.5·10−14 – 1.2·10−13 cm2·s−1 for the anodic process, 1.7·10−14 – 5.6·10−14 cm2·s−1 for the cathodic process. It has been established that the reversible and irreversible degradation components of electrodes based on Ni-rich NCM in the potential range corresponding to the H2-H3/H3-H2 interphase transition correlate with each other. Therefore, the difference in D values in the anodic and cathodic processes, which correspond to the current peaks of the cyclic voltammogram in this region, is a criterion for the irreversible degradation of the material’s capacity: the greater the difference in the D values for these peaks, the higher the irreversible degradation of the material’s capacity.

Состояние сетчатки у пациентов, перенесших COVID-19 с поражением легких

Microvascular lesions are one of the main factors of lung and other organ damage in COVID-19. We hypothesized that patients with post-COVID lung dysfunction may also retain signs of systemic micro-vascular damage, in particular of the retina. Aim. To evaluate vascular and macular retinal area status in COVID-19 patients with pulmonary damage. Methods. 61 patient, average age 60.5 years, after in-patient COVID-19 treatment was examined. The volume of lung lesions according to high resolution computed tomography (HRCT) data ranged from 12 to 90 %. Decrease of diffusion capacity for carbon monoxide (DLCO) was observed in all patients after recovery: in 3 months in 18 patients (29.5 %) with severe COVID-19 DLCO was 58.4 % and in moderate COVID-19 – 73.2 % of the proper one. Optical coherence tomography (iVue-100, Optovue, USA) using Linear Scan and Nerve Fiber 3D Disc map was performed after 1 and 3 months. The control group included 20 patients comparable by sex, age, and comorbidity. Results. All patients showed typical signs of micro-circulatory disturbances in the posterior pole of the eye, increased caliber of arteries and first-order veins. In patients with severe COVID-19 an increase of arterial caliber by 22.5 μm and veins caliber by 35.04 μm, a decrease of retinal thickness in the macular region (by 8.78 μm in the fovea and by 6.6 μm in parafovea) compared to control group were revealed. After 6 months no significant dynamics of these parameters was revealed. Retinal changes in patients with moderate COVID-19 were similar but less pronounced. Conclusion.The revealed changes of retinal vessels and macular zone may indicate microcirculation disturbances and blood flow retardation in the posterior pole of the eye. The severity of the disturbances is comparable with the severity of the disease and the degree of DLCO reduction. Key words: COVID-19 with lung damage; retina; caliber of retinal vessels.

Evaluation of the Galvanostatic Charge Technique for the in Situ Characterization of Aged Meas in a PEMFC

Voltage-controlled in situ diagnostics like cyclic voltammetry (CV) are commonly used to characterize membrane electrode assemblies (MEAs) in single-cell proton exchange membrane fuel cells (PEMFCs) and to monitor MEA degradation over operating time. Their application, however, is more complex for characterizing individual cells in a PEMFC stack, depending on stack design and the capability of the fuel cell test station. Consequently, several studies have demonstrated a facile and easily adaptable alternative by using a galvanostatic (current-controlled) technique for diagnosing MEAs in a PEMFC stack, where all the cells are connected in series. It was demonstrated that a galvanostatic charge curve applied to a PEMFC stack permits the quantification of the electrochemical surface area (ECSA, m2/gPt) and the double layer capacitance (C dl, mFcm2 MEA ) of the cathode electrode as well as of the hydrogen crossover current (i H2,X, mA/cm2 MEA) and the electrical shorting resistance of the membrane (R short, mA/cm2 MEA) of each individual MEA in a stack.1, 3, 4 However, most of these studies only investigated healthy MEAs that represent their beginning-of-life (BoL) condition, and it is not clear whether the galvanostatic charge method can also yield quantitative measures for aged MEAs in a PEMFC stack, which may exhibit significant H2 permeation and shorting currents as well as very low electrode roughness factors (in units of cm2 Pt/cm2 MEA).In this study, we aim to investigate and understand the viability of the galvanostatic charge technique in the presence of substantial H2 permeation and shorting currents. For this, single cells with 50 cm2 MEAs exhibiting different characteristics are examined: 1) low i short, representing an MEA at BoL; 2) high i H2,X and i short, representing an MEA with a degraded membrane; and, 3) low electrode roughness factors (i.e., low ECSAs), representing, e.g., an MEA after a voltage-cycling AST (accelerated stress test). The MEAs were prepared by either ex situ or in situ methods. To quantify the ECSA, R short, and i H2,X, an anodic current (I) is supplied to the N2-filled cathode of the cell (using the H2-filled anode as counter and reference electrode), and the corresponding cell voltage profiles (V) within a defined time scale (t) are analyzed by equations 1 and 2:3 I⋅dt = Q Pt/H + C dl⋅dV + (i short + i H2,X)⋅dt equation 1 I = (Q Pt/H/dv+ C dl)⋅dV/dt + (i short + i H2,X) equation 2Here, Q Pt/H is the hydrogen desorption charge from Pt catalyst (i.e., from Pt-H → Pt + H++ e-) and C dl is the double-layer capacitance of the cathode electrode; further contributions are from i short and i H2,X. The results obtained from this galvanostatic analysis approach will be compared with those obtained from commonly used potentiodynamic methods (i.e., from CV and linear scan voltammetry (LSV)). An exemplary data set is shown in Figure 1. Additionally, the impact of operating conditions (e.g., cathode gas flow rate during the analysis) is systematically investigated. To conclude, we will propose an improved and general methodology for using a galvanostatic analysis approach for the diagnosis of MEAs in a PEMFC stack.Reference Y. Chatillon, C. Bonnet and F. Lapicque, Journal of Applied Electrochemistry, 43, 1017 (2013). K. Chen, Y. Hou, C. Jiang, X. Pan and D. Hao, International Journal of Hydrogen Energy, 46, 38469 (2021). P. Pei, H. Xu, X. Zeng, H. Zha and M. Song, Journal of Power Sources, 245, 175 (2014). I. Hartung, S. Kirsch, P. Zihrul, O. Müller and T. Von Unwerth, Journal of Power Sources, 307, 280 (2016). Figure 1

Adsorptive stripping voltammetric determination of carbofuran in food using novel type of modified carbon-based electrode with grafted layers of nickel

A voltammetric determination of carbofuran (CBF) was developed using a novel type of carbon-containing electrode (CCE) modified with carbon ink (CI) and a chromatographic sorbent (CS) based of chromaton (Ch), polyethylene glycol and nickel acetylacetonate with grafted layers of nickel (NiCS, stands for Ni modified CS) further denoted as CI/NiCS/CCE. The surface morphology of this modified electrode was investigated by scanning electron microscopy (SEM) and by electrochemical impedance spectroscopy (EIS). CBF which is not electrochemically oxidizable was first hydrolyzed in alkaline medium to give anodically active phenolic analogue CBFP. The electrochemical reactions of CBFP at CI/NiCS/CCE were studied in phosphate buffer (PB) by cyclic voltammetry (CV) and linear sweep adsorptive stripping voltammetry (LSAdSV) using linear scan voltammetry in the first derivative mode (LSVFD). Linear concentration dependences in the concentration ranges from 0.1 to 10 μM and from 10 to 100 μM were obtained by the LSAdSV with limit of detection (LOD) and limit of quantification (LOQ) 0.06 and 0.19 μM, respectively. The novel modified CI/NiCS/CCE showed good stability and selectivity and was successfully used to determine CBF in real samples of vegetables and fruits with LOD 0.01 mg kg−1.

Measurement Uncertainty Analysis of the Stitching Linear-Scan Method for the Measurable Dimension of Small Cylinders

A stitching linear scan method is proposed for roundness and diameter measurement of small cylindrical workpieces instead of the conventional rotary scan method due to the crucial alignments of eccentricity and inclination. To verify the reliability of the proposed method, by which the coordinates of the cross-sectional circle of a small cylinder is divided into several equal parts to be obtained and reconstructed, the diameter and roundness measurement uncertainties of the small cylinders with a diameter 1.5 mm are evaluated to be 0.047 μm and 0.095 μm, respectively, which can meet the uncertainty target of 0.1 μm. To investigate the measurable dimension by the proposed method, measurement uncertainty analysis of the small cylinders with various dimensions has been conducted according to the previous evaluation, since all the procedures are the same except for the uncertainty of X coordinates, which changes with the measured dimension’s change. The results show that the small cylinders with a diameter range from 0.01 mm to 50 mm can be measured by the proposed method when the position error θZ is reduced to the corresponding value. There is no measuring limitation set by the proposed model theoretically in the case of θX = θZ = 0.1°, while the machine has a measuring limitation.

Copper-nitrogen dual-doped activated carbon derived from alder wood as an electrocatalyst for oxygen reduction

In the present study, unmodified nitrogen-doped carbon material (N-doped C) and modified with copper nanoparticles (CuNPs) nitrogen-doped carbon material (Cu-N-doped C) have been synthesized using wood biomass as a carbon precursor, dicyandiamide as a nitrogen precursor, and anhydrous copper acetate as the precursor of Cu. The morphology, structure, and chemical composition of the obtained materials have been analyzed by performing nitrogen sorption experiments and described using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning-electron microscopy (SEM). The electrocatalytic performance of N-doped C and Cu-N-doped C materials has been evaluated for the electro-reduction of oxygen (ORR) in alkaline media using linear scan voltammetry (LSV) and the rotating disk and ring-disk electrode (RDE and RRDE) methods.It has been determined that the nitrogen-doped carbon material and that modified with CuNPs have been synthesized with graphene-like structures and especially high specific surface areas of 2631 m2 g−1 and 2243 m2 g−1, respectively. The onset potential (Eonset) and half-wave (E1/2) potential values are approximately 0.921 V and 0.828 V, respectively, for the N-doped carbon with the loading of 0.0889 mgcat cm−2 and 0.975 V and 0.843 V, respectively, for Cu–N-doped carbon (0.4044 mgcat cm−2), comparable with the commercial Pt/C catalyst.

Current electroanalytical approaches in the carbamates and dithiocarbamates determination.

Pesticides are a suitable tool for controlling plagues and disease vectors. However, their inappropriate use allows for contamination of the environment, soil, water, and foods. Carbamates and dithiocarbamates pesticides present accumulative effects in the human body resulting in hormonal, neurological and reproductive disorders, and some are still suspected or proven to give carcinogenic or mutagenic effects. This review provides a current electroanalytical approach in the carbamates and dithiocarbamates determination, showing the use of voltammetric techniques such as amperometry, cyclic and linear scan, differential pulse, and square wave voltammetry, indicating their advantages, disadvantages, and perspectives in electroanalytical detection of carbamates and dithiocarbamates in natural water and foods. Also are reported the different materials used in the preparation of working electrodes since their choice has an important impact on the success of the analytical applications, resulting in suitable sensitivity, selectivity, stability, and robustness.

Low Frequency GFRP Imaging with Variable Aperture TFM

Graphite or glass fiber reinforced polymer (GFRP) inspections are usually made with a zero-degree linear scan (L-scan) (1). Total focusing may not be applicable for some anisotropic materials, but in some cases, TFM may increase the ultrasound imaging quality. The imaging potential of 1D linear probes has been broadened by TFM by many aspects so there is an opportunity to apply the total focusing concepts to exotic composite assessment. The ultrasonic limitations associated with testing thicker sections of GFRP restrict inspections to lower frequency phased array probes. When a low frequency probe uses the L-Scan technique, the performance and sensitivity is negatively affected once compared to a typical phased array probe of a higher frequency due to the element size and pitch restrictions associated with low frequency probes. Therefore, new testing techniques should be found. The alternative imaging acquisition method presented here involves variable aperture receivers that improve the usual LScan characteristics. This study explicitly covers the differences over the L-scan type, the TFM image and its variable aperture TFM feature. In addition of the theory concepts, ultrasound metrics have been recorded on a real GFRP sample and using as reference reflector side drilled holes (SDH).

Self-supported polypyrrole flexible electrodes for electrochemical reduction of nitrite

The efficiency of an electrochemical oxidation/reduction process strongly depends on the working electrode's surface area to volume ratio. By making electrodes flexible and employing different configurations such as roll-to-roll membrane, the surface area to volume ratio can be enhanced, therefore improving the overall efficiency of electrochemical processes. Conductive polymers emerge as a new framework to enable alternative electrochemical water treatment cell configurations. Self-standing polypyrrole flexible electrodes were synthesized by electropolymerization and evaluated on the treatment of an oxyanion pollutant: nitrite. Mechanical characterization through stress-strain curves and bending tests demonstrated high electrode resilience that sustained over 1000 bending cycles without impacting mechanical integrity or electrocatalytic responses. The electrocatalytic response towards nitrite reduction was assessed under linear scan voltammetry (LSV) and removal performance evaluated under potentiostatic conditions reaching 79% abatement of initial concentrations of nitrite of 15 mg/L [NO2−-N]. Self-standing flexible electrodes appear as a novel framework to enable modular compact water treatment unit designs that maximize the electrode area/volume ratio and substitute expensive platinum group metal (PGMs) electrocatalysts.

Exploring nucleation modeling of the voltammetry of solid-to-solid-state redox processes with phase changes

An operational description of the linear potential scan voltammetry of solids experiencing a solid-state redox transformation with phase changes is described. The modeling is based on the application of nucleation equations of solid-state reaction kinetics to express the transferred charge/applied potential relationships. The flexible use of Prout-Tompkins and Avrami-Erofe’ev kinetics permits a satisfactory description of the voltammetry of solid-to-solid redox transformations with phase segregation. The model satisfactorily applies to reproduce linear potential scan curves recorded for graphite electrodes modified with several lead compounds in contact with aqueous electrolyte solutions.

A second-order and slice-specific linear shimming technique to improve spinal cord fMRI

PurposeTo develop a second-order and slice-specific linear shimming technique and investigate its efficiency in the mitigation of signal loss and distortions, and the increase of temporal signal-to-noise ratio (tSNR) within the spinal cord during functional Magnetic Resonance Imaging (fMRI) of the human cervical spinal cord. MethodsAll scans were performed on a General Electric Discovery MR750 3 T scanner, using a head, neck and spine coil and a neurovascular array. To improve B0 homogeneity, a field map was acquired, and second-order shims (SOS) were optimized over manually defined regions of interest (ROIs). Signal loss from dephasing by susceptibility-induced gradients was reduced by optimizing slice-specific x-, y- and z-shims to maximize signal within the spinal cord. Spectral-spatial excitation pulses were used in both the slice-specific linear shimming calibration scan and fMRI acquisitions. The shimming technique's efficiency was initially tested on eight healthy volunteers by comparing tSNR between images acquired with the manufacturer's standard linear shimming and with our SOS and xyz-shimming technique. Subsequently, using an increased spatial resolution as needed for fMRI of the spinal cord, tSNR measurements were performed on resting-state fMRI images from 14 healthy participants. ResultsSpinal fMRI images acquired with only the standard linear shimming suffered from severe signal loss below the C5 vertebral level. The developed shimming technique compensated for this loss especially at levels C6 and C7, while tSNR was significantly higher at all vertebral levels with SOS and xyz-shimming than without it. ConclusionA comprehensive shimming approach which includes the use of spectral-spatial excitation pulses along with both second-order and slice-specific linear shim optimization reduces regional signal loss and increases tSNR along the c-spine (C3-C7), improving the ability to record functional signals from the human spinal cord.