Middle Frequency Region Research Articles

Observing the Effect of Architecture on Spiral and Bobbin Lithium Thionyl Chloride (Li/SOCl2) Batteries with Temperature-Dependent Electrochemical Impedance Spectroscopy (EIS)

Electrochemical Impedance Spectroscopy (EIS) has been utilized as an in situ, non-destructive diagnostic tool for the comprehensive electrochemical characterization of lithium thionyl chloride (Li/SOCl2) batteries. Li/SOCl2 batteries come in various geometries or architectures tailored for the application area and required specifications. In this study, detailed EIS studies of spiral and bobbin-type Li/SOCl2 batteries are performed at different temperatures to investigate the impedance response, calculate the activation energy of various processes, and observe the effect of geometry. An extensive comparison between the two geometries reveals that the processes can be differentiated by their time constants and capacitances. It was observed that the current collector impedance masks the high-frequency response of bobbin-type at elevated temperatures with similar Li redox processes in the middle-frequency region. Additionally, transmission line fit is performed on the bobbin type to investigate diffusion-related cathodic processes.

Age-related upregulation of dense core vesicles in the central inferior colliculus.

Presbycusis is one of the most prevalent disabilities in aged populations of industrialized countries. As we age less excitation reaches the central auditory system from the periphery. To compensate, the central auditory system [e.g., the inferior colliculus (IC)], downregulates GABAergic inhibition to maintain homeostatic balance. However, the continued downregulation of GABA in the IC causes a disruption in temporal precision related to presbycusis. Many studies of age-related changes to neurotransmission in the IC have therefore focused on GABAergic systems. However, we have discovered that dense core vesicles (DCVs) are significantly upregulated with age in the IC. DCVs can carry neuropeptides, co-transmitters, neurotrophic factors, and proteins destined for the presynaptic zone to participate in synaptogenesis. We used immuno transmission electron microscopy across four age groups (3-month; 19-month; 24-month; and 28-month) of Fisher Brown Norway rats to examine the ultrastructure of DCVs in the IC. Tissue was stained post-embedding for GABA immunoreactivity. DCVs were characterized by diameter and by the neurochemical profile (GABAergic/non-GABAergic) of their location (bouton, axon, soma, and dendrite). Our data was collected across the dorsolateral to ventromedial axis of the central IC. After quantification, we had three primary findings. First, the age-related increase of DCVs occurred most robustly in non-GABAergic dendrites in the middle and low frequency regions of the central IC during middle age. Second, the likelihood of a bouton having more than one DCV increased with age. Lastly, although there was an age-related loss of terminals throughout the IC, the proportion of terminals that contained at least one DCV did not decline. We interpret this finding to mean that terminals carrying proteins packaged in DCVs are spared with age. Several recent studies have demonstrated a role for neuropeptides in the IC in defining cell types and regulating inhibitory and excitatory neurotransmission. Given the age-related increase of DCVs in the IC, it will be critical that future studies determine whether (1) specific neuropeptides are altered with age in the IC and (2) if these neuropeptides contribute to the loss of inhibition and/or increase of excitability that occurs during presbycusis and tinnitus.

Hierarchical Porous Electrode Impedance Model Based on Diffusion Dynamics and the Electrode Morphology and Prediction of Electric Double-Layer Structures

The capacitance performance of a hierarchical porous carbon (HPC) electrode mainly depends on the dipole storage capacity and the rate of electric double-layer (EDL) reorganization. However, it is difficult to directly measure the effect of microscopic changes of pores and electrolytic characteristics on the internal ionic mechanism of the EDL. Therefore, a model is proposed to easily and accurately describe both the diffusion and EDL dynamics of the HPC electrode. In general, diffusion in the mesoporous channel can be characterized in the middle-frequency region (5–500 Hz) and in the micropore in the low-frequency region (0.05–5 Hz). What is more, we have proven that the diffusion layer thickness is inversely proportional to the electrolytic concentration and positively proportional to the mesoporous size, microporous depth, and surface roughness. In particular, the thicker diffusion layer makes it easier for ions diffusing into micropores and a better EDL recombination in mesoporous channels. However, the thinner diffusion layer means a better EDL recombination in micropores. The low-frequency region (0.01–0.05 Hz) characterized the compact layer dynamics, which shows the constant phase element behavior obviously. Moreover, the compact layer thickness is inversely proportional to the surface heterogeneity, thus determining the dipole storage capacity. The model offers a general framework for impedance analysis and EDL prediction of HPC.

Impedance-Based Characterization of Positive–Negative Sequence Separation and Its Effects on MMC-HVDC Stability

Impedance models of modular multilevel converter (MMC) are required to analyze the stability of the MMC high-voltage direct current (HVDC) system. In practical engineering, the positive–negative sequence separation algorithm is the basis of positive and negative sequence current control of MMC. Therefore, the influence of sequence separation on the impedance models and stability of MMC system needs to be further studied. This article develops complete impedance models of the MMC with consideration of all control loops and positive–negative sequence separation and comprehensively analyzes the impact of sequence separation on impedances and stability of the MMC-HVDC. It is found that the positive–negative sequence separation results in periodic fluctuations in the middle- and high-frequency regions of ac impedance and distinct fluctuations in the middle-frequency region of dc impedance. Meanwhile, the difference in the parameters of the positive and negative sequence current controllers will greatly aggravate the fluctuations of both ac and dc impedances and increase negative damping of the system. Moreover, the analysis reveals that the sequence separation is a key factor weakening the stability of the MMC-HVDC. Final, the correctness of the impedance models and the theoretical analysis are verified by the experimental results.

Dielectric dispersion impedance spectroscopy and polaron tunneling phenomenon in Au2O3 mixed PbO-B2O3-SeO2:Er2O3 glass ceramics

The glass ceramics of the composition PbO-B2O3-SeO2:Er2O3 (PBSE) doped with small concentrations of Au2O3 were synthesized. The results of detailed studies on various characterization techniques and also different spectroscopic investigations suggested that these glass ceramics are entrenched with Au2(SeO3)3 crystal phases and Au0 metallic particles (MPs). These studies further revealed increasing concentration of [SeO3]2- groups and Au0 metallic particles with the increase of Au2O3 content upto 0.075 mol%. Such [SeO3]2- groups are predicted to induce structural imperfections in the glass ceramic. Optical absorption (OA) and photoluminescence (PL) spectral studies also indicated increasing concentration of imperfections with increase of Au2O3 content. The dielectric viz, dielectric permittivity (ε′), electrical modulus (M), electrical impedance (Z) and a.c. conductivity (σac) spectra in the frequency (ω) region 4 Hz to 8 MHz and in the temperature (T) region 303–633 K of these glass ceramic samples were measured as functions of Au2O3 concentration. The dielectric permittivity (ε′) exhibited an increasing trend with Au2O3 concentration and it is ascribed to the increase in the magnitude of the space charge polarization (scp) due to the increase in the concentration of structural defects induced by [SeO3]2- units and Au0 metallic particles. The plots of electric modulus (M) with frequency and temperature exhibited dipolar relaxation phenomena. Such effects were analyzed further using Cole-Cole diagrams and the possible dipoles responsible for these effects were identified. A.C. conductivity (σac) exhibited increasing trend with the concentration of Au2O3 (up to 0.075 mol%) and such increase is attributed to the polaronic exchange between different structural groups of selenium oxide. The conduction mechanism is analyzed using polaronic tunneling effect in the middle frequency and high temperature regions, whereas in the lower temperature region QMT model seems to be applicable. Conclusions drawn from dielectric properties were found to be well in accordance with the results of spectroscopic properties.

Sodium/Lithium-Ion Transfer Reaction at the Interface between Low-Crystallized Carbon Nanosphere Electrodes and Organic Electrolytes.

Carbon nanosphere (CNS) electrodes are the candidate of sodium-ion battery (SIB) negative electrodes with small internal resistances due to their small particle sizes. Electrochemical properties of low-crystallized CNS electrodes in dilute and concentrated sodium bis(trifluoromethanesulfonyl) amide/ethylene carbonate + dimethyl carbonate (NaTFSA/EC + DMC) were first investigated. From the cyclic voltammograms, both lithium ion and sodium ion can reversibly insert into/from CNSs in all of the electrolytes used here. The cycling stability of CNSs in concentrated electrolytes was better than that in dilute electrolytes for the SIB system. The interfacial charge-transfer resistances at the interface between CNSs and organic electrolytes were evaluated using electrochemical impedance spectroscopy. In the Nyquist plots, the semicircles at the middle-frequency region were assigned to the parallel circuits of charge-transfer resistances and capacitances. The interfacial sodium-ion transfer resistances in concentrated organic electrolytes were much smaller than those in dilute electrolytes, and the rate capability of CNS electrodes in sodium salt-concentrated electrolytes might be better than in dilute electrolytes, suggesting that CNSs with concentrated electrolytes are the candidate of SIB negative electrode materials with high rate capability. The calculated activation energies of interfacial sodium-ion transfer were dependent on electrolyte compositions and similar to those of interfacial lithium-ion transfer.

Kinetic properties of sodium-ion transfer at the interface between graphitic materials and organic electrolyte solutions

Graphitic materials cannot be applied for the negative electrode of sodium-ion battery because the reversible capacities of graphite are anomalously small. To promote electrochemical sodium-ion intercalation into graphitic materials, the interfacial sodium-ion transfer reaction at the interface between graphitized carbon nanosphere (GCNS) electrode and organic electrolyte solutions was investigated. The interfacial lithium-ion transfer reaction was also evaluated for the comparison to the sodium-ion transfer. From the cyclic voltammograms, both lithium-ion and sodium-ion can reversibly intercalate into/from GCNS in all of the electrolytes used here. In the Nyquist plots, the semi-circles at the high frequency region derived from the Solid Electrolyte Interphase (SEI) resistance and the semi-circles at the middle frequency region owing to the charge-transfer resistance appeared. The activation energies of both lithium-ion and sodium-ion transfer resistances were measured. The values of activation energies of the interfacial lithium-ion transfer suggested that the interfacial lithium-ion transfer was influenced by the interaction between lithium-ion and solvents, anions or SEI. The activation energies of the interfacial sodium-ion transfer were larger than the expected values of interfacial sodium-ion transfer based on the week Lewis acidity of sodium-ion. In addition, the activation energies of interfacial sodium-ion transfer in dilute FEC-based electrolytes were smaller than those in concentrated electrolytes. The activation energies of the interfacial lithium/sodium-ion transfer of CNS-1100 in FEC-based electrolyte solutions were almost the same as those of CNS-2900, indicating that the mechanism of interfacial charge-transfer reaction seemed to be the same for highly graphitized materials and low-graphitized materials each other.Graphic abstract

Research on Prediction of Middle-frequency Ship Cabin Noise Based on Improved Statistical Energy Method

The ship vibration and noise calculation in middle-frequency region has always been a difficult point in engineering. The statistical energy method assumes that the coupling between structures is weakly coupled, which in turn limits its application in the calculation of ship’s middle frequency vibration and noise. In order to improve the vibration and noise calculation accuracy of statistical energy method in middle-frequency region, the equivalent coupling loss factors (ECLFs) between ship sub-structures were calculated based on the energy flow method (EFM), and the ECLFs were substituted into the statistics energy balance equation. The ship’s middle frequency cabin noise was calculated by the improved statistical energy method and compared with the measured values. The results show that the predicted values of the cabin noise are in good agreement with the measured values, which extends the application of the statistical energy method in the ship’s middle frequency cabin noise prediction.

Secure Image Authentication Using Watermarking and Blockchain

Image authentication is an important field that employs many different approaches and has several significant applications. In the proposed approach, we used a combination of two techniques to achieve authentication. Image watermarking is one of the techniques that has been used in many studies but the authentication field still needs to be studied. Blockchain technology is a relatively new technology that has significant research potential related to image authentication. The watermark is embedded into the third-level discrete wavelet transform (DWT) in the middle frequency regions to achieve security and imperceptibility goals. Peak signal-to-noise ratio PSNR, structural similarity matrix (SSIM), normalized correlation coefficient (NCC), and bit error rate (BER) are used to measure the performance of image watermarking. We used blockchain technology to avoid involving a trusted third party for authentication. Secure Hash Algorithm 256 (SHA-256) is applied on the watermark to save it into the blockchain. The watermark is encrypted using Advanced Encryption Standard (AES) and embedded into the image. The proposed method is tested on the USP SICI database and the MedPix medical image database. Ethereum blockchain is used to provide security, anonymity, and integrity of data with no third-party intervention. The proposed solution demonstrates enhanced security for image authentication compared with the state-of-the-art.

Development of Short Time Impedance Measurement Method for PEM Electrolysis Cell

Electrochemical impedance spectroscopy (EIS) is expected as a method to evaluate a polymer electrolyte membrane (PEM) water electrolysis cell. The internal state of electrolysis cell can be investigated by EIS without destruction. However, it may be difficult to measure stable impedance during electrolysis at high voltage since the large amount of oxygen is generated on the anode. Therefore, a short time impedance measurement is required. The purpose of this study is to develop short time impedance measurement method1,2) that can estimate the electrolyte membrane resistance R M and the charge transfer resistance R ct in a short time.A Japan Automobile Research Institute (JARI) standard cell with an electrode area of 25 cm2 was used as the test cell. The impedance measurement was performed in a frequency range from 100 mHz to 1 kHz and started from high frequency toward low frequency in the logarithmic scan.The Nyquist plot of impedance spectrum shows inductive behavior caused by wiring in the high frequency region and capacitive semicircle related to the anode in the middle frequency region. Under the condition of high current density, it was found that impedance spectrum was scattered in the low frequency range. The scattering originated from oxygen evolution at the anode when the measurement time is long. The measurement time was about 80 s to obtain an impedance spectrum, thus it is necessary to measure in a shorter time. Therefore, we obtained R ct in a short time by the two-point frequency method proposed by Haruyama et al.1,2) The equation (1) is used to calculate R ct. R ct = Re [Z] - R M + Im [Z]2/( Re [Z] - R M) (1)In the equation (1), R M is the electrolyte membrane resistance, which is the real component of the impedance at the high frequency. The real and imaginary parts of the impedance at the low frequency are represented by Re [Z] and Im [Z]. The measurement was performed by fixing the frequency at 1 kHz as a high frequency value and changing the low frequency value from 100 Hz to 10 mHz. R ct obtained from the measurement results by the two-point frequency method was compared with R ct obtained from the curve fitting of the impedance spectrum with the equivalent circuit. As a result, the relative error of the R ct calculated from the measurements at two frequencies 1 kHz and 10 Hz was -2.15% from the fitted result, and the measurement time was 5.33 s. From these results, it was found that the two-point frequency method was able to reduce the measurement time significantly compared to the normal EIS and to estimate R ct accurately. References 1) S. Haruyama, T. Tsuru, ASTM STP 727, ASTM Philadelphia, p.167 (1981).2) T. Tsuru, S. Haruyama, Boshoku Gijutsu, 33, p.579-582 (1984).

Sodium-Ion Transfer Reaction at the Interface between Carbon Nanosphere Electrodes and Electrolytes

Introduction Sodium-ion batteries (SIBs) are widely focused on as post lithium-ion batteries from the view of element strategy[1]. Hence, SIBs are attractive for large scale energy storage like electric vehicles. For the large scale energy storage, batteries with high rate capability are desired. Carbon nanosphere (CNS) covered with basal planes is expected as the candidate for carbon negative electrode material with high rate capability because CNS electrodes showed the high rate capability in LIBs owing to small particle sizes and short diffusion distances[2]. To enhance the rate capability of electrode materials, the internal resistances of electrodes should be investigated. In LIBs, the interfacial lithium-ion transfer at the interface between electrodes and electrolytes is one of the rate determining step[3]. However, the kinetic properties of interfacial sodium-ion transfer at the interface between carbon negative electrodes and electrolytes is unclear. In this study, the activation energies of interfacial sodium-ion transfer reaction at the interface between CNS electrodes and organic electrolyte solutions were evaluated. Experimental Electrochemical measurements were carried out using a three-electrode cell. Working electrode was CNS composite electrode. CNS treated at 1100°C and 2900°C were used and denoted as CNS-1100 and CNS-2900, respectively. Reference electrode was Ag/Ag+ electrode and counter electrode was natural graphite composite electrode. The electrolyte solutions were 0.9, 4 mol kg- 1 sodium bis(trifluoromethanesulfonyl)amide (NaTFSA)/ethylene carbonate (EC) + dimethyl carbonate (DMC) (1:1 by vol.) and 0.7 mol kg- 1 NaTFSA/fluoroethylene carbonate (FEC). Hereafter, all potentials are referred to as Fc/Fc+. Cyclic voltammetry (CV) was conducted between open circuit potential (OCV) and various potentials, and the scan rate was set at 0.1 mV s−1. Electrochemical impedance spectroscopy (EIS) was carried out with ac amplitude of 10 mV in a frequency range of 100 kHz − 10 mHz at temperatures ranging from 30°C to 10°C. Results Figure 1 shows the cyclic voltammograms of CNS-1100 composite electrodes in 0.9 mol kg- 1 NaTFSA/EC+DMC(1:1 by vol.). The irreversible currents were observed below −2 V and more than half of the irreversible currents disappeared from the 2nd cycle, indicating the formation of solid electrolyte interphase on CNS electrodes at the same manner of lithium ion-system. The redox peaks also appeared around −3 V, and were assigned to the peaks of reversible sodium-ion insertion into/from CNS-1100. Figure 2 shows the Nyquist plots of CNS-1100 composite electrode in 0.9 mol kg−1 NaTFSA/EC+DMC(1:1 by vol.). In the Nyquist plots, based on the potential dependence of the semi-circle, the semi-circle at the middle frequency region was assigned to the charge-transfer resistance. The same kinds of electrochemical behaviors were observed in the cases of other electrolytes and CNS-2900 electrodes.In the meeting, the activation energies of interfacial sodium-ion transfer will be reported. Acknowledgement This work was partially supported by ESICB, Kyoto University.

Colossal dielectric response and relaxation behavior in novel system of Zr4+ and Nb5+ co-substituted CaCu3Ti4O12 ceramics

In this work, we developed a novel system of isovalent Zr4+ and donor Nb5+ co-doped CaCu3Ti4O12 (CCTO) ceramics to enhance dielectric response. The influences of Zr4+ and Nb5+ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr4+ and Nb5+ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu3Ti3.8-xZrxNb0.2O12 (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr4+ and Nb5+ ions than that of single-doped with Zr4+ or Nb5+ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~105) at a frequency range of 102–105 Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr4+ and Nb5+ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus.

Detailed Consideration of Electrical and Dielectric Properties of Au/Ni/n-Si MS Structure in a Wide Frequency Range

In the presented study, the electrical and dielectric properties of Au/Ni/n–Si MS structure are examined in detail by performing frequency–dependent admittance spectroscopy technique over a wide frequency range (3 kHz–1 MHz). Dielectric constant, dielectric loss, dielectric loss tangent, real modulus, imaginary modulus, and electrical conductivity of the structures are calculated by evaluating the results obtained from admittance spectroscopy. The experimental data received in the wide frequency range is examined in three different frequency ranges as low (3–10 kHz), medium (20–100 kHz) and high (0.2–1 MHz) to a more detailed examination and a better understanding of electrical and dielectric properties. The dielectric loss tangent, real modulus and imaginary modulus values increase with increasing frequency, while dielectric constant and dielectric loss values decrease with increasing frequency. The electric modulus values increase with the increasing frequency is ascribed by the dipoles and the polarize electrons’ dielectric relaxation. In addition, despite the change of electrical conductivity values are constant in the low frequency and middle frequency regions, it decreases as the frequency increases in the high–frequency region. For all parameters, the frequency–dependent behavior of the structure is specifically studied at 2 V. It is concluded within the present study that Si–based MS structures created by integrating Au/Ni have the potential to be used especially in innovative and applicable electronic and optoelectronic devices such as rectifiers and switchers.

Effects of porous trailing edge on aerodynamic noise characteristics

The objective of this work is to investigate the effect of the porous trailing edge on the aeroacoustics performance of the NACA 65(12)-10 aerofoil. The motivation behind this study is to investigate the effect of the porous parameters to explore the noise control concepts. Experimental testing in an aeroacoustics open jet wind tunnel was performed at chord-based Reynolds numbers between 0.2 and 0.6 million, and effective angles of attack at ±1.7 degree, including at 0 degrees. The porous trailing edge at porosity 30% with different holes diameters and the length of these porous trailing edges are used in the acoustic experiments. The study reveals that the level of the reduction of the broadband noise becomes larger as the diameter of the holes decreases and the length of the porous trailing edge increases at lower Reynolds numbers. Bluntness-induced tone noise is produced at high Reynolds number. Meanwhile, the porous trailing edge can suppress the laminar instability noise at the middle and low frequency regions.

Interface control for high-performance all-solid-state Li thin-film batteries

We fabricated and evaluated four types of Li batteries, in this case a LTO/liquid electrolyte/Li battery, a LTO/LiPON/Li all-solid-state battery, and LTO/LiPON + liquid electrolyte/Li batteries with and without a separator to investigate and clarify the effects of each interface. Through the present research, it was found that a conventional polymer-based separator increases the impedance in the middle frequency region, resulting in an increase in the total cell resistance. After replacing the polymer-based separator with a thin-film solid electrolyte, the cycleability and capacity of the cell were comparable to those of a conventional Li-ion battery with a polymer separator. The all-solid-state Li thin-film battery without a liquid electrolyte exhibits the lowest capacity due to the large interfacial resistance between the Li metal and the LiPON solid electrolyte. However, we found that the insertion of an Al2O3 interlayer between the Li and LiPON improves the capacity.

Ceramic Panel for Sound Insulation Application

In order to reduce noise nowadays, many researcher find different way to solve this problem. One of the ways to reduce noise is by using a sound insulation. This research has been conducted in order to produce high density sound insulation panel made from ceramic. The fabrication of ceramic panel undergo several processes which are milling, mixing, forming, drying and sintering process. The ceramic panel of different types of forming were developed as square plate 110mm x 110 mm with a constant thickness of 5 mm. Type of forming were used for this particular study are slip casting and uniaxial press. The composition used were 100 % clay and 90% + 10 % clay cement. The transmission loss were determined by using acoustic insulation test. The apparatus consists of sound level meter, portable speaker and computer. The Sound Pressure Levels (SPL) were taken at 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz which based on 1 octave frequency bands. The analysis shown that the sample 90 % + 10 % clay cement casting has the higher transmission loss in the lower frequency region, the sample 90 % + 10 % clay cement uniaxial press has the higher transmission loss in the middle frequency region and lastly the sample 100 % clay uniaxial press has the higher transmission loss in higher frequency region. The sample also were tested using Charpy impact test in order to gain their impact energy and impact strength. The tests were according to ASTM-D256. Charpy impact test can determines the amount of energy absorbed by a material during fracture. The analysis shown that the impact energy of the ceramic panel have a small percentage different. It can be concluded that uniaxial press is better than the slip casting in forming ceramic insulation panel.

Characterization of the Effect of Electrolyte-to-Sulfur Ratio on the Lithium-Sulfur Cell Resistance Using Electrochemical Impedance Spectroscopy Method

Lithium-Sulfur (Li-S) batteries have gained significant attention in the last decade due to their high theoretical specific energy and non-toxic, naturally abundant and low-cost active material [1, 2]. In Li-S batteries, as a consequence of the complexity of the cathode kinetics, electrochemical performance is highly dependent on the cell design [1, 2]. Such as, electrolyte-to-sulfur (E/S) ratio in the cell is a critical design parameter determining the Li-S cell performance through the reaction and shuttle mechanisms in the cathode [1, 2]. Reducing the electrolyte amount in the cell is crucial for achieving high energy density Li-S batteries [1]. However, sulfur utilization and thus the discharge capacity of the Li-S cell are limited considerably at low E/S ratios. Consequently, identifying the impact of E/S ratio on the kinetic and transport resistances in a Li-S cell will be of significant interest. In this study, we present a characterization of the Li-S battery as a function of E/S ratio in the cell using the Electrochemical Impedance Spectroscopy (EIS) method. EIS, which is a powerful electroanalytical technique [3], is used here to determine the charge transfer and transport resistances in a Li-S cell. The impedance of Li-S cells with varying E/S ratios is measured at different depths of discharge (DOD) for the initial discharge. An equivalent electrical circuit is proposed accordingly and the physical and electrochemical processes occurring in the cell are related to the elements of the circuit. As a result, the impact of E/S ratio on the kinetic and transport mechanisms taking place in the cell during discharge is identified and discussed. Nyquist plots for the Li-S cells present two semicircles, one in the high-frequency and the other in the middle-frequency region, and a straight line in the low-frequency region (Figure 1). It is apparent in Figure 1a that the semicircle in the high-frequency region shrinks with increasing discharge depth while the one in the middle-frequency grows substantially. Furthermore, the impact of E/S ratio on the cell impedance is clear in Figure 1b; both semicircles get smaller with increasing E/S ratio in the cell. In order to link the E/S ratio to the kinetic and transport resistances in the cell, an equivalent electrical circuit is proposed. In the circuit, the resistances for the electrolyte, charge transfer (high-frequency semicircle), Li2S film (medium-frequency semicircle) and Warburg diffusion (low-frequency line) are all considered. It is concluded that all resistances within the cell increase significantly for an E/S ratio of 6 mL/g S especially during the initial and final stages of the discharge. This may be explained such that at low E/S ratios increasing polysulfide concentration increases the electrolyte resistance through the electrolyte viscosity, worsens the cathode kinetics through changing the reaction mechanisms [4] and enhances the Li2S film resistance by controlling the precipitation reactions. Figure 1. Nyquist plots in the frequency range of 10 mHz -100 kHz for the initial discharge of a Li-S cell (a) for different DODs at an E/S ratio of 19 mL/g S and (b) for different E/S ratios at ~50% DOD. Carbon-to-sulfur ratio is 1, S loading is ~1 mg/cm2 and discharge rate is C/10 for all results. Acknowledgment This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK), Grant No: 116M574.

A new implementation of electrochemical impedance spectroscopy (EIS) and other methods to monitor the progress of hydration of strontium monoaluminate (SrAl2O4) cement

Electrochemical impedance spectroscopy has been employed to monitor hydration of strontium monoaluminate (SrAl2O4) cement. Other supported techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, thermal analysis (DSC–TG–EGA) and microcalorimetry were also used. In the impedance spectrum at 102 day on a 0.5 water/cement ratio paste, a large double depressed low-frequency arc, a single depressed arc at middle-frequency region and a small part of a large depressed arc at high-frequency region were discriminated. It was due to the specific phase composition and crystal phase content in the fully hardened cement paste. Hence, the new electrochemical equivalent model R1(C1(R2W1))(C2(R3W2))(C3(R4W3))(C4(R5W4)) was implemented and fitted to the experimental results of the fully hydrated and hardened SrAH cement paste. Various hydration products including crystalline Sr3AH6, and amorphous phases SrAH7 and AH3-gel were formed at an early age of hydration. At final hydration process, the main reaction products detected are the ones most thermodynamically stable, i.e. crystalline Sr3AH6 and Al(OH)3. The heat evolution of SrAl2O4 cement under different temperatures (20 °C and 40 °C) was examined by isothermal calorimetry. The curing temperature was found to have a visible effect on cement hydration kinetics.

Influence of the substrate types on the molybdenum disulfide grown by thermal vapour sulfurization

Abstract The growth of molybdenum disulfide (MoS2) on different substrate types was demonstrated. MoS2(002) peak was found at ∼14°, however, single crystalline substrate with hexagonal lattice system shows the enhancement of peak intensity. Next, the single crystalline substrates result in highly compactness of MoS2 thin film. In contrast, nanoparticle feature surface morphology was grown by using the amorphous substrate. Multilayers of MoS2 was observed by using high-resolution transmission electron microscope. Several diffraction rings were detected which indicates the polycrystallinity quality of MoS2. Furthermore, the absorption features of MoS2 were found at ∼668 nm, ∼617 nm, and ∼447 nm. Resonant Raman features of MoS2 were determined. The lower, middle and higher frequency region reveals the structural defects, nanoparticle size or nanostructure topography and layer thickness estimation of MoS2, respectively.

The characteristics of semicircular canal injury frequency in vestibular neuritis patients

Objective:To evaluate the frequency characteristics of semicircular canal injury in patients with vestibular neuritis. Method:Fifty-three patients with vestibular neuritis were respectively evaluated by caloric test(CT)，head shaking test(HST),video head impulse test (vHIT),which reflects semicircular canal function in the low, middle, high frequency region. The asymmetric value of CT unilateral semicircular canal reaction (UW), head shaking nystagmus induced by HST, gain value of VHIT (VHIT-G) and presence or absence of saccade (VHIT-S) were used as observation indicators. The data were analyzed by SPSS 17.0 statistical software.The characteristics of the results of the three tests in patients with vestibular neuritis was analyzed and the functional status of the high, middle and low frequency regions of the semicircular canal was evaluated. Result:The positive rates of CT, HST, VHIT-G and VHIT-S in 53 patients with vestibular neuritis were 94.3%（50/53）,75.5%（40/53）,81.1%（43/53）,96.2%（51/53）,respectively. The positive rates of CT, HST, VHIT-G and VHIT-S were 92.9%（26/28）,89.3%（25/28）,92.9%（26/28）,96.4%（27/28）in 28 cases with disease course ≤ 7 days, and the positive rates in 25 patients with disease course >7 days were 96.0%（24/25）,60.0%（15/25）,68.0%（17/25）,96.0%（24/25）,respectively. Compared with the positive rate of each index, CT and VHIT-G (P=0.076), HST and VHIT-G (P=0.480) had no statistical significance. The difference between CT and HST (P=0.015), VHIT-G and VHIT-S(P=0.032) was statistically significant. The positive rates of CT, HST, VHIT-G and VHIT-saccade in patients with course of disease ≤7 days were compared, and there was no significant difference. In patients with disease course >7 days, except HST and VHIT-G, there were statistical differences in other indexes. The correlation test between VHIT-G and VHIT-S：r=-0.437, P=0.006. Conclusion:The vestibular injury in patients with vestibular neuritis showed in a manner of full frequency injury. The multi-frequency detection technique is helpful for the clinical diagnosis of vestibular neuritis, and also can reflect the compensation and recovery of vestibular function.