Low-frequency Processes Research Articles

Characterization of A-site doped PrBaCo2O5+δ perovskites as cathode materials for IT-SOFCs

Creating highly efficient and durable cathodes persists as a formidable task in the realm of intermediate temperature solid oxide fuel cells (IT-SOFCs). Hence, we present a double perovskite oxide, Pr0.6Sr0.4BaCo2O5+δ (PS0.4BC), and its electrocatalytic activity is thoroughly investigated. The XRD test is carried out and a notable transformation in the phase structure is observed upon the introduction of Sr2+ ions into the PBC matrix. That is, the phase structure of the material changes from double perovskite structure to single perovskite structure. Through the TG and TEC test that the introduction of Sr2+ ions into the lattice can create additional sites for oxygen vacancy formation and reduce TEC values. Further verify that Sr doping can enhance the concentration of oxygen vacancies of the material. The PS0.4BC cathode material exhibits remarkably low polarization resistance, achieving an impressive value of 0.027 Ω cm2 at an operating temperature of 800 °C. Oxygen partial pressure test shows that as the oxygen partial pressure decreases, there is a notable increase in impedance, particularly evident in the low frequency region of the Nyquist plots. This indicates that the oxygen content has obvious effects on the low-frequency processes. When the oxygen partial pressure exceeds 0.05 atm, the oxygen adsorption-dissociation and diffusion process is the rate-limiting step in the ORR. However, when the oxygen partial pressure is less than 0.05 atm, the formation of lattice oxygen through the combination of oxygen ions and oxygen vacancies processes is the rate-limiting step. Compared PBC cathode material, the more pronounced changes in the high frequency arc of the PS0.4BC cathode at the same oxygen content. It shows that Sr doping significantly changes the high frequency process. After doping, the oxygen vacancy concentration increases, which facilitates the occurrence of the charge transfer process at high frequency.

Inherent Temporal Metamaterials with Unique Time-Varying Stiffness and Damping.

Time-varying metamaterials offer new degrees of freedom for wave manipulation and enable applications unattainable with conventional materials. In these metamaterials, the pattern of temporal inhomogeneity is crucial for effective wave control. However, existing studies have only demonstrated abrupt changes in properties within a limited range or time modulation following simple patterns. This study presents the design, construction, and characterization of a novel temporal elastic metamaterial with complex time-varying constitutive parameters induced by self-reconfigurable virtual resonators (VRs). These VRs, achieved by simulating the resonating behavior of mechanical resonators in digital space, function as virtualized meta-atoms. The autonomously time-varying VRs cause significant temporal variations in both the stiffness and loss factor of the metamaterial. By programming the time-domain behavior of the VRs, the metamaterial's constitutive parameters can be modulated according to desired periodic or aperiodic patterns. The proposed time-varying metamaterial has demonstrated capabilities in shaping the amplitudes and frequency spectra of waves in the time domain. This work not only facilitates the development of materials with sophisticated time-varying properties but also opens new avenues for low-frequency signal processing in future communication systems.

Multiscale interaction underlying 2022 concurrent extreme precipitation in Pakistan and heatwave in Yangtze River Valley

Unprecedentedly extreme precipitation occurred in Pakistan (PAK), and mega heat waves persisted along the Yangtze River Valley (YRV) from July to August 2022. Using the advanced multiscale window transform-based canonical transfer attribution framework, we quantitatively delineated intra-scale and inter-scale interactions leading to record-breaking spatially concurrent extremes in 2022 and comprehensively revealed differences in dynamic processes affecting extreme events in July and August. The basic flow scale window lost the available potential energy (APE), and through APE canonical transfers to the intraseasonal-scale and synoptic-scale windows, the inter-scale dynamic processes and barotropic instability of the basic flow scale preserved the concurrent extreme in July. In August, the eruptive synoptic-scale kinetic energy convergence provided dynamic conditions for the sinking motion of the YRV and its advection to PAK from the Indian Ocean. Consequently, the interaction between high- and low-frequency processes drove atmospheric circulation in summer, but the high-frequency process in August played a vital role in extreme events. Additionally, the heat source in the tropical western-central Pacific is considered one of the key drivers for localized repetitive bursts of energy. This study emphasizes both the interactions between multiple scales of atmospheric dynamics and reveals the driving mechanisms behind the impacts of warming on extreme events, linking the external forcing issue with the free problem of atmospheric internal instability.

UWLPIPE: Ultra-wide Bandwidth Low-frequency Pulsar Data Processing Pipeline

For real-time processing of ultra-wide bandwidth low-frequency pulsar baseband data, we designed and implemented an ultra-wide bandwidth low-frequency pulsar data processing pipeline (UWLPIPE) based on the shared ringbuffer and GPU parallel technology. UWLPIPE runs on the GPU cluster and can simultaneously receive multiple 128 MHz dual-polarization VDIF data packets preprocessed by the front-end FPGA. After aligning the dual-polarization data, multiple 128M subband data are packaged into PSRDADA baseband data or multi-channel coherent dispersion filterbank data, and multiple subband filterbank data can be spliced into wideband data after time alignment. We used the Nanshan 26 m radio telescope with the L-band receiver at 964 ∼ 1732 MHz to observe multiple pulsars. Finally, we processed the data using DSPSR software, and the results showed that each subband could correctly fold out the pulse profile, and the wideband pulse profile accumulated by multiple subbands could be correctly aligned.

Exploring temperature effects on raw polysaccharide in semi-diluted solution using complex conductivity: Correlation analysis of activation energies

The evolution of the complex conductivity of raw polysaccharides extracted from Cystoseira myriophyloides algae exhibited significant temperature dependence in an aqueous solution. An analysis of the complex conductivity versus frequency was conducted using an appropriate electrical circuit based on our theoretical approach. This facilitated the generation of analytical functions representing the relaxation processes occurring at different temperatures. Subsequently, extrapolation and deconvolution procedures were employed to further investigate and identify all relaxation processes and their origins. These approaches revealed the presence of three relaxation processes. The first relaxation, observed at low frequency, is attributed to interfacial polarization between the electrode and the solution. The second and third relaxations, observed at medium and high frequencies, are attributed to bulk relaxation processes. Then, subtracting the low-frequency process clarified the bulk relaxation processes. Both relaxations are described by the Cole-Cole relaxation, which effectively models the well-known Maxwell-Wagner-Sillars (MWS) phenomenon typically observed in polyelectrolyte solutions. This relaxation is typically caused by interfacial polarization between molecular chains and counterions in the sample. Both relaxations were found to be thermally activated. The temperature dependence of useful parameters extracted from each relaxation, such as relaxation time (τσ) and conductivity (σdc) and (σ∞), followed Arrhenius law behavior. Furthermore, activation energy values for each relaxation process were determined, establishing a linear correlation between activation energy values related to relaxation time (τσ) and both conductivities (σdc) and (σ∞). These results confirm the origin of bulk relaxations and demonstrate a strong link between relaxation and conduction mechanisms.

Effect of Low-Frequency High-Power Ultrasound Processing on the Volatile Compounds and Aroma Profile of Cashew Apple Juice

Effect of Low-Frequency High-Power Ultrasound Processing on the Volatile Compounds and Aroma Profile of Cashew Apple Juice

Effect of low-frequency ultrasound-assisted acid extraction on gel properties and structural characterization of sheep's hoof gelatin

In this study, we investigated the effects of various low-frequency ultrasound-assisted extraction processes, including ultrasound-assisted acid-soaked water bath extraction (UAW), ultrasound-assisted water bath extraction after acid soaking (AUW), acid-soaked water bath extraction followed by ultrasonics (AWU), and acid-soaked water bath extraction without ultrasound (CON), on the structural properties, thermal stability, gel properties, and microstructure of sheep's hoof gelatin. The results revealed that the primary components of sheep's hoof gelatin consisted of α1-chain, α2-chain (100–135 kDa), and β-chain. In addition, it was observed that among the three sonication groups, sheep's hoof gelatin extracted in the AUW group exhibited the highest yield (27.16 ± 0.41 %), the best gel strength (378.55 ± 7.34 g), and higher viscosity at the same shear rate. The gelling temperature (25.38 ± 0.45 °C) and melting temperature (32.28 ± 0.52 °C) of sheep's hoof gelatin in the AUW group were significantly higher than those in the other groups (p > 0.05). Moreover, our experiments revealed that the sequence of low-frequency ultrasonic pretreatment processes was a crucial factor influencing the gel properties and structural characteristics of sheep's hoof gelatin. Specifically, the acid treatment followed by the ultrasound-assisted approach in the AUW group yielded high-quality and high-yield sheep's hoof gelatin.

Exploring the impact of solvent additives on dielectric properties in polymer photovoltaics: A deconvolution and in-depth study of electrical modulus, complex conductivity, and impedance responses

Impedance and dielectric spectroscopy is a well-known technique for characterizing interfaces, especially donor/receiver interfaces in bulk heterojunction (BHJ) solar cells. This technique was employed to investigate the interface of poly (4,8-bis-alkyloxybenzo(1,2-b:4,5-b0) dithio-phene-2,6-diyl-alt- (alkyl thieno (3,4-b) thiophene-2-carboxylate)-2,6-diyl) (PBDTTT-C): PC70BM in bulk heterojunction with DIO as additive. For this reason, a simulation was carried out to generate the complex impedance, modulus, and complex conductivity data based on the electrical parameters extracted from the equivalent circuit. Therefore, a new approach based on the coupling of complex functions such as impedance, modulus, and conductivity has been proposed. In addition, an extrapolation and deconvolution approaches are used to highlight the relaxation processes, the BHJ layer process, the two electrical contacts of the interfaces between PEDOT: PSS/PBDTTT-C: PC70BM and PBDTTT-C: PC70BM/Ca process, and the electrode polarization process. In the next step, the remove the low-frequency process enhances the visibility of other processes, particularly observable in the evolution of the electrical modulus and the conduction parameters associated with each process. In the complex functions, there was a good correlation between all parameters derived from both processes. The characteristics of the conduction processes, such as conductivity values at low and high frequencies and ionic strength were then extracted. All these parameters were evaluated and discussed as a function of the thickness of the active layer. Finally, we demonstrate that the electrical modulus and complex conductivity can be perfect tools to characterize the donor/acceptor interfaces.

Anomaly Detection of Permanent Magnet Synchronous Motor Based on Improved DWT-CNN Multi-Current Fusion.

The Permanent Magnet Synchronous Motor (PMSM) is the power source maintaining the stable and efficient operation of various pieces of equipment; hence, its reliability is crucial to the safety of public equipment. Convolutional Neural Network (CNN) models face challenges in extracting features from PMSM current data. A new Discrete Wavelet Transform Convolutional Neural Networks (DW-CNN) feature with fusion weight updating Long Short-Term Memory (LSTM) anomaly detection is proposed in this paper. This approach combines Discrete Wavelet Transform (DWT) with high and low-frequency separation processing and LSTM. The anomaly detection method adopts DWT and CNN by separating high and low-frequency processing. Moreover, this method combines the hybrid attention mechanism to extract the multi-current signal features and detects anomalies based on weight updating the LSTM network. Experiments on the motor bearing real fault dataset and the PMSM stator fault dataset prove the method's strong capability in fusing current features and detecting anomalies.

Improved Approach for ab Initio Calculations of Rate Coefficients for Secondary Reactions in Acrylate Free-Radical Polymerization.

Secondary reactions in radical polymerization pose a challenge when creating kinetic models for predicting polymer structures. Despite the high impact of these reactions in the polymer structure, their effects are difficult to isolate and measure to produce kinetic data. To this end, we used solvation-corrected M06-2X/6-311+G(d,p) ab initio calculations to predict a complete and consistent data set of intrinsic rate coefficients of the secondary reactions in acrylate radical polymerization, including backbiting, β-scission, radical migration, macromonomer propagation, mid-chain radical propagation, chain transfer to monomer and chain transfer to polymer. Two new approaches towards computationally predicting rate coefficients for secondary reactions are proposed: (i) explicit accounting for all possible enantiomers for reactions involving optically active centers; (ii) imposing reduced flexibility if the reaction center is in the middle of the polymer chain. The accuracy and reliability of the ab initio predictions were benchmarked against experimental data via kinetic Monte Carlo simulations under three sufficiently different experimental conditions: a high-frequency modulated polymerization process in the transient regime, a low-frequency modulated process in the sliding regime at both low and high temperatures and a degradation process in the absence of free monomers. The complete and consistent ab initio data set compiled in this work predicts a good agreement when benchmarked via kMC simulations against experimental data, which is a technique never used before for computational chemistry. The simulation results show that these two newly proposed approaches are promising for bridging the gap between experimental and computational chemistry methods in polymer reaction engineering.

RHEOLOGICAL AND COLLOID-STRUCTURAL BEHAVIOUR OF HIGH-VISCOSITY CRUDE OIL AND EMULSION AFTER WAVE ACTION

One of the main problems in oil production is the formation of stable oil-water emulsions that cause corrosion of pipelines, malfunction of pumping equipment, and poisoning of catalysts at refineries. The features of the viscosity-temperature behaviour of high-viscosity resinous crude oil from the Russkoye field (Yamal-Nenets autonomous district) and its 30 wt% emulsion after exposure to electromagnetic and low-frequency acoustic fields are investigated. Electromagnetic treatment of crude oil leads to a decrease in the phase transition temperature and the yield strength coefficient. Low-frequency acoustic processing of the emulsion is accompanied by a decrease in the effective viscosity and the yield strength coefficient. After a complex wave action, the viscosity-temperature characteristics of crude oil continue to fall, and the stability of the formed emulsions decreases due to the intense coalescence of water-phase droplets. It is shown that the amount of released asphaltenes in oil-containing systems decreases after wave treatment. On the contrary, after a complex impact, their content in crude oil increases, while in the emulsion it continues to decrease. This is likely to occur due to the release of hydrocarbons occluded in the asphaltene structure into the liquid oil phase.

Gadolinium Doped Ceria as Nickel–Free Fuel Electrode in High Temperature CO2‐Electrolysis

AbstractIn this work, the performance, electrochemical processes, and stability of GDC (Ce0.8Gd0.2O1.9) fuel electrode containing single cells (GDC/8YSZ/GDC/LSCF) were examined in CO2 electrolysis conditions. The current density and area specific resistance is determined for different operation conditions. The examined cells showed a higher performance compared to state‐of‐the‐art Ni−YSZ fuel electrode (Ni‐YSZ/8YSZ/GDC/LSCF) based single cells with a similar production route. Furthermore, the cells were examined by means of electrochemical impedance spectroscopy (EIS) and the recorded data were evaluated by the distribution of relaxation times (DRT) analysis. An equivalent circuit model (ECM) consisting of four time constants and a Gerischer impedance (LR−RQ1−RQ2−G−RQ4−RQ5) was established to gain further insight into the individual processes in the cells. For instance, the low–frequency process P5 referring to RQ5 is the rate‐determining step in CO2 electrolysis and is assigned to a surface reaction including the charge transfer and possibly the gas diffusion in the GDC fuel electrode. A long–term stability test was performed in CO2 electrolysis conditions at 900 °C with a constant current load of −0.5 A ⋅ cm−2 for up to 1200 h. A degradation rate of 62 mV ⋅ kh−1 was observed. By EIS analysis, a similar contribution of the ohmic and polarization resistances to the degradation was determined. The low–frequency process P5 and thus the surface reaction including the charge transfer in the GDC fuel electrode is contributing most to the increase in polarization resistance. After the long–term stability test, scanning electron microscopy (SEM) analysis was carried out and a coarsening of GDC particles in the fuel electrode was observed.

The biogas upgrading from landfill leachate pretreated with low-frequency ultrasonic: anaerobic digestion performances and energy balance

The efficient biogas production from landfill leachate (LL) is one of hot topics in anaerobic digestion systems. Higher bioavailability of LL can be achieved by application a feasible and promising pretreatment technologies in order to utilize as a substrate for anaerobic reactors. Here, the enhanced bioavailabity of LL using the low-frequency ultrasonic process and energy balance in anaerobic digestion process was estimated within incubation period of 24 days. The optimal performance of low-frequency ultrasonic for LL biodegradability index: sCOD and TVFA were estimated under influencing parameters: ultrasonic density (UD) (0.02–0.14 W/mL) and Ultrasonic time (UT) (0–12 min). Moreover, the effects of low-frequency ultrasonic pretreatment process on biogas production in batch mode anaerobic reactors operated at 37 ± 1 °C were surveyed for daily and cumulative methane production, operational performance and energy balance. An increased sCOD (820 mg/L) and TVFA (659 mg/L) were observed under optimum codition: UD (0.1 W/mL) and UT (10 min). The highest methane production (430 mL) was found in reactor 4, where %15 volume ratio of LL pretreated with low frequency ultrasonic were feed in. Energy balance assessment indicated that output energy for anaerobic reactors assissted with ultrasonic in range of + 6.99 and + 7.98 kJ/g VS removed. Therefore, incorporation the low-frequency ultrasonic and digestion process revealed a promising and economic technique to improve biomethane potential and energy balance from LL.

Investigating Enzyme-Based Electrode Processes Using Electrochemical Impedance Spectroscopy and Distribution of Relaxation Time Analysis

Enzymatic fuel cells (EFCs) are an emerging class of electrochemical devices that have the potential to harness renewable energy sources by converting the chemical energy of an organic substrate into electrical energy. Enzymes are responsible in an EFC for highly selective and efficient electrode processes under typically mild ambient conditions, such as the oxidation reaction at the anode and the reduction reaction at the cathode 1. In addition to more conventional techniques, electrochemical impedance spectroscopy (EIS) can be employed to characterize such systems. Electrochemical behavior of enzymatic electrodes, such as enzyme reaction kinetics, substrate mass transport, and electrode stability, can be studied by measuring the system's impedance over a wide frequency range and then performing a precise post-process analysis based on the distribution of relaxation time (DRT). DRT analysis is rarely used to interpret EIS spectra within the EFCs research field, despite the fact that it is widely acknowledged as relevant for properly understanding the EIS potential to improve power density in fuel cells 2,3. Glucose oxidase (GOx) and bilirubin oxidase (BOD) were immobilized on multi-walled carbon nanotubes (MWCNTs) to catalyze the bioelectrocatalytic oxidation of glucose at the anode and the bioelectrocatalytic reduction of oxygen at the cathode, respectively. This study presents a promising approach for the investigation of enzyme-based anodic and cathodic processes by measuring them with EIS and then interpreting the results with DRT analysis, as depicted in Figure 1. By varying different operating parameters, such as the enzymatic loading on the electrode surface or electrolyte conditions, this method can be used to identify three primary relaxation processes occurring at both electrodes. At the interface between the electrolyte and the electrode, it is possible to conclude that high-frequency processes are accountable for ionic conduction, intermediate-frequency processes are accountable for charge transfer, and low-frequency processes are accountable for oxygen surface exchange and diffusion.This method provides access to preliminary fundamental information about enzymatic bioelectrode processes, which can be used to optimize biofuel cell construction and compositions and increase their power output. Figure 1. Schematic representation of the characterization method used to characterize a GOx-CNT-modified anode consisting of EIS measurements and subsequent DRT analysis. Concentration of glucose 175 mM in 0.1 M HEPES Buffer, pH 7; EIS parameters: 20 mV sinusoidal excitation, 0.1 Hz-100 kHz. References K. Herkendell, A. Stemmer and R. Tel-Vered, Nano Res., 12(4), 767–775 (2019). H. Wang, X. Long, Y. Sun, D. Wang, Z. Wang, H. Meng, C. Jiang, W. Dong and N. Lu, Frontiers in microbiology, 13, 973501 (2022). F. Ciucci, Current Opinion in Electrochemistry, 13, 132–139 (2019). Figure 1

Dual contrast attention-guided multi-frequency fusion for multi-contrast MRI super-resolution

Objective. Multi-contrast magnetic resonance (MR) imaging super-resolution (SR) reconstruction is an effective solution for acquiring high-resolution MR images. It utilizes anatomical information from auxiliary contrast images to improve the quality of the target contrast images. However, existing studies have simply explored the relationships between auxiliary contrast and target contrast images but did not fully consider different anatomical information contained in multi-contrast images, resulting in texture details and artifacts unrelated to the target contrast images. Approach. To address these issues, we propose a dual contrast attention-guided multi-frequency fusion (DCAMF) network to reconstruct SR MR images from low-resolution MR images, which adaptively captures relevant anatomical information and processes the texture details and low-frequency information from multi-contrast images in parallel. Specifically, after the feature extraction, a feature selection module based on a dual contrast attention mechanism is proposed to focus on the texture details of the auxiliary contrast images and the low-frequency features of the target contrast images. Then, based on the characteristics of the selected features, a high- and low-frequency fusion decoder is constructed to fuse these features. In addition, a texture-enhancing module is embedded in the high-frequency fusion decoder, to highlight and refine the texture details of the auxiliary contrast and target contrast images. Finally, the high- and low-frequency fusion process is constrained by integrating a deeply-supervised mechanism into the DCAMF network. Main results. The experimental results show that the DCAMF outperforms other state-of-the-art methods. The peak signal-to-noise ratio and structural similarity of DCAMF are 39.02 dB and 0.9771 on the IXI dataset and 37.59 dB and 0.9770 on the BraTS2018 dataset, respectively. The image recovery is further validated in segmentation tasks. Significance. Our proposed SR model can enhance the quality of MR images. The results of the SR study provide a reliable basis for clinical diagnosis and subsequent image-guided treatment.

A Novel Method for Fatigue Damage Assessment in Bimodal Processes Considering High- and Low-Frequency Reduction Effects

Due to inherent nonlinearities within floating systems and the second-order wave forces affecting them, the dynamic responses of floating systems manifest as bimodal Gaussian processes. Consequently, the classical spectral fatigue assessment method grounded in the Rayleigh distribution cannot be applied. This paper introduces the double frequency coupled (DFC) method as a spectral fatigue assessment approach, providing an accurate estimation of fatigue damage originating from bimodal Gaussian processes. Within the DFC method, the bimodal Gaussian process is partitioned into two components: low-frequency (LF) and high-frequency (HF) processes. A Gaussian distribution is employed to describe the probability distribution function (PDF) of the amplitude reduction induced by the interaction between LF and HF processes. The PDF of small-cycle fatigue can be computed by convoluting the PDF of HF amplitudes and the reduction amplitude between LF and HF. Similarly, the PDF of large-cycle fatigue can be determined through convolution, which involves the PDF of LF amplitudes and small-cycle fatigue. The overall fatigue damage arising from the bimodal Gaussian process is obtained by directly summing the contributions of small-cycle and large-cycle fatigue. Numerical investigations of the DFC method’s effectiveness are presented through a series of parametric studies, demonstrating its robustness, efficiency, and accuracy within engineering expectations. Furthermore, the DFC method is found to be applicable to both single-slope and two-slope S-N curves.

Temperature-dependent hydration behavior of aqueous lysine: an approach towards protein binding through dielectric spectroscopy

Present work reports interaction between water and amino acid lysine for understanding the physicochemical properties that will be useful in the structure formation of protein. The dielectric relaxation of aqueous lysine was systematically investigated over a temperature range spanning from 298.15 K to 278.15 K, encompassing frequencies ranging from 10 MHz to 30 GHz, and across a concentration range of 0.152 M to 0.610 M. Within this study, aqueous lysine revealed the presence of two distinct relaxation modes. The low-frequency relaxation process (l-process) is primarily associated with the relaxation of lysine molecules, whereas the high-frequency relaxation process (h-process) is attributed to water molecules interacting with lysine. Several key dielectric parameters, including static dielectric constant (εj), relaxation time (τj), dipole moment (μj), correlation factor (gj), and the number of water molecules rotationally bonded by solute molecules (Zib), were meticulously determined. These parameters were interpreted in terms of molecular interactions, hydrogen bonding, hydrophobicity, and Lys-Lys binding. Additionally, various thermodynamic parameters such as molar enthalpy (ΔHj), molar entropy (ΔSj), and molar free energy (ΔFj) were calculated to provide further insights into the system’s characteristics and behavior. Communicated by Ramaswamy H. Sarma

Thermodynamic hydration behaviour of glycine below room conditions using time domain reflectometry

The present work reports the concentration-dependent hydrophobicity of glycine below room temperature. The dynamics of aqueous glycine have been studied by means of dielectric relaxation spectroscopy using Time Domain Reflectometry (TDR) technique in the frequency region of 10 MHz–30 GHz. Complex permittivity spectra are obtained using TDR that allowed evaluation of the static dielectric constant (ε0) and average relaxation time (τ). As dielectric relaxation spectroscopy provides information on the average relaxation time (τ) related to the mechanism of hydrogen bond (HB) formation and breaking, therefore the concentration-temperature dependence of τ was used to evaluate and study hydration behaviour through dielectric parameters such as dipole moment (μ), correlation factor (g), and the dynamics of irrationally bound water molecules (Zib). Aqueous glycine relaxes in two different relaxation modes in the broad microwave frequency region from MHz to GHz. The low-frequency relaxation process (l-process) observed is associated with glycine relaxation, while the detected peak in the high-frequency relaxation process (h-process) is attributed to water associated with glycine. We have attempted a concentration-temperature-dependent hydrogen bonding mechanism in both relaxation processes, and the results were corroborated with thermodynamical parameters such as molar entropy of activation (∆Sj), molar enthalpy of activation (∆Hj), and molar free energy of activation (∆Fj).

Low-frequency incremental permeability for the evaluation of deep carburization treatments: Theoretical understanding

Precise evaluation of deep carburization treatments is essential to prevent degradation of high-performance mechanical components. A nondestructive magnetic method called low-frequency incremental permeability testing appears to be particularly suitable for this purpose. This method consists of slowly magnetizing the specimen to be controlled and then superimposing a relatively low-frequency eddy current testing process on the specimen (<2 kHz). The sensor’s coil impedance is monitored along with the magnetization cycle. When plotted versus the magnetic excitation, the impedance produced butterfly-shaped curves that were dependent on the carburization depth. Operating at low frequency increases the scanned layer thickness up to the untreated inner part of the specimen and induces characteristic variations in the butterfly-shaped curves. A model to solve for the indirect relationship between the magnetic properties and the carburization treatment properties is presented in this manuscript. This model combines the Dodd and Deeds analytical expression for a flat sensor coil above a two-layer conductor with Jiles-Atherton theory for consideration of the hysteresis. The magnetic and electromagnetic responses are well considered, providing accurate reconstructions of experimental data. The model predictions reveal magnetic indicators that are highly correlated with the carburization depth and provide optimal conditions for nondestructive testing observation.

Electrochemical Impedance Spectroscopy of Amorphous TiO2 Protected Photocathodes Under Hydrogen Evolution Conditions

Despite widespread use of electrochemical impedance spectroscopy (EIS) to study multi-layer photoelectrochemical (PEC) cells, the appropriate equivalent circuits describing these devices under hydrogen evolution conditions are not commonly investigated.1 This creates ambiguity with respect to the pathways of charge recombination and ionic movement within layers of the device during operation, therefore limiting rational development of future PEC devices. In this study, amorphous TiO2 (a-TiO2) protected silicon photocathodes have been investigated using EIS to show that these devices behave according to the Maxwell circuit during hydrogen evolution, which occurs when the semiconductor is in depletion. Therefore, there are two simultaneous processes occurring in parallel and on different timescales. While the high frequency component is the result of the depletion region in the semiconductor, the low frequency component of this circuit is found to originate from the a-TiO2 itself, implying a capacitive charging process of this protective overlayer during PEC cell operation. Studies to isolate the physical mechanism of capacitive charging in the a-TiO2 from a range of possibilities such as proton intercalation and vacancy migration have been carried out. This result is important for the development of future PEC devices using emerging semiconductors which heavily rely on the a-TiO2 overlayer in acidic electrolytes, such as Cu2O and Sb2Se3, where this low frequency process has previously been observed.1 Using the Maxwell circuit for a-TiO2 protected photocathodes under hydrogen evolution conditions, one can independently determine properties of the semiconductor, such as the depletion capacitance and doping density, and the protective overlayer in these PEC devices under hydrogen evolution conditions. With this baseline, EIS can continue to aid the development of PEC cells as additional overlayers are developed and tested for further performance improvements. Yang, W. et al. Operando Analysis of Semiconductor Junctions in Multi-Layered Photocathodes for Solar Water Splitting by Impedance Spectroscopy. Adv. Energy Mater. 11, 2003569 (2021). Figure 1