Edge Of Sheet Research Articles

Vacancy-Activated B-Doping for Efficient 2e- Oxygen Reduction through Suppressing H2O2 Decomposition at High Overpotential.

The production of hydrogen peroxide (H2O2) through two-electron oxygen reduction reaction (2e- ORR) has emerged as a more environmentally friendly alternative to the traditional anthraquinone method. Although oxidized carbon catalysts have intensive developed due to their high selectivity and activity, the yield and conversion rate of H2O2 under high overpotential still limited. The produced H2O2 was rapidly consumed by the increased intensity of H2O2 reduction, which could ascribe to decomposition of peroxide radicals under high voltage in the carbon catalyst. To overcome this issue, a B doped carbon have been developed to catalyze 2e- ORR with high efficient through suppressing H2O2 decomposition at high potential. Thus, thermal reducing of oxygen containing groups (OCGs) on graphite could construct defects and vacancies, which in situ convert to B-Cx subunits on the edge of graphene sheets. The introduction of B-Cx effectively prevented the decomposition of the *O-O bond and provided suitable adsorption capacity for *OOH, achieving excellent selectivity for the 2e- ORR across a wide voltage range. Finally, a remarkable H2O2 yield of 7.91 mmol cm-2 h-1 was delivered at an industrial current density of 600 mA cm-2, which could provide "green" pathway for scale-upable synthesis H2O2.

Impact of material property variations and sensor positioning on the coating thickness determination of steel sheets using eddy current testing

Purpose This paper aims to investigate the reliable thickness, and more generally, the geometric and material parameter determination of thin electrically conductive and diamagnetic coatings on conductive and ferromagnetic substrates, e.g. steel, using eddy current testing (ECT). Design/methodology/approach The analytical model of an ECT coil arrangement known from the literature is analyzed to evaluate the numerical simulation performed by a Finite Element (FE) program. The latter is used to investigate the influence of the sheet edge on the measurement result. Finally, a measurement setup is presented and the unknown geometric and material parameters are estimated from measurement data of different sample sheets at different air gaps. Findings Generally, valid mesh rules are found for a very accurate FE analysis of eddy current problems with large air gaps. The influence of large air gaps on the parameter estimation is emphasized. Moreover, the formulated hypotheses can be widely confirmed by measurements. Research limitations/implications In this paper, electrical steel sheets coated with a conductive oven-cured ink are used. This sample configuration creates a discrete transition between the substrate and the coating as present in the analytical modeling approaches. Furthermore, the ferromagnetic substrate’s nonlinear B-H curve is not considered in the analytical model so far. Originality/value The analytical model is known from the literature. However, real practical measurements have not been carried out with the discussed setup. Furthermore, well-known literature on eddy current measurements usually only considers constant and very small air gaps.

What Is the "Other" Site in M-N-C?

Single metal atoms embedded in nitrogen-doped graphene (M-N-C) have emerged as a promising catalyst for a wide variety of reactions. In addition to the pyridinic site, there is another site responsible for the catalytic activity, but its structure is under debate. Here, we resolve its structure using first-principles calculations. Using Fe-N-C as a representative example, we systematically explore numerous possible structures and discover a new moiety with comparable energy to the pyridinic. This moiety features a hybrid coordination environment between pyridinic and porphyrinic and is located at the edge of graphene sheets or pores. We further calculate its X-ray absorption spectrum, catalytic thermodynamics for oxygen reduction reaction (ORR), and stability under ORR conditions, all of which support its existence. Lastly, we show that this site also exists in other M-N-C with different M elements. This study uncovers a new and important structure in M-N-C and paves a critical step toward site engineering for improved catalytic performance.

The Performance of PEFC with Marimo-like Carbon Considering Relative Humidity

1.IntroductionThe Pt catalyst supported on carbon black (Pt/CB) is widely used as a catalyst for the polymer electrolyte fuel cell (PEFC). As an alternative carbon support to the CB, which is a type of particulate carbon, we have used Marimo-like carbon (MC) which is a type of fibrous carbon. MC has a spherical structure comprised of carbon nanofilaments (CNFs) radially grown from an oxidized diamond core 1). The CNFs in the MC have a cup-stack primary structure of graphene sheets; thus, the sheet edge can effectively function as a supporting site for the Pt catalyst. There are voids of several hundred nanometers between the CNFs of the MC. These voids are expected to improve the diffusion of hydrogen gas and air and the removal of produced water. The diffusivity of hydrogen gas and air and the removal of produced water are different between the MC and CB due to their structural differences. These differences in mass diffusivity changed the state of water management and the PEFC performance. In this study, the performance of a PEFC with Pt/MC while considering the relative humidity (RH) of the hydrogen gas and air were investigated.2.ExperimentalThe catalyst supports were CB and MC. MC was synthesized by thermal chemical vapor deposition (CVD). For the synthesis, methane (CH4) gas was used as the carbon source of the CNFs and Ni supported diamond oxide (Ni/O-dia.) was used as a growth catalyst. The Ni/O-dia. was contacted with the CH4 gas in a reactor rotating at 5 rpm. The CH4 gas was supplied at the flow rate of 1000 CCM for 3 hours. During this time, the rotary reactor was heated to 550°C. Pt/MC was synthesized by reducing Pt ions in a suspension with MC. Pt/CB was prepared as a commercial Pt nanoparticle supported on the CB. Nafion was used as the ionomer in this study. The catalyst ink was prepared by adding a Nafion dispersion to the Pt/MC and Pt/CB. The ionomer/carbon (I/C) ratio was 0.1 and 0.7 for the MC and CB, respectively 3). The catalyst layer (CL) was prepared by spraying the catalyst ink onto a 50 mm × 50 mm PTFE sheet. The membrane electrode assembly (MEA) was fabricated by transferring CL to the Nafion membrane by hot pressing. The PEFC performance was evaluated at the cell temperature of 80.0°C. Hydrogen gas and air were saturated at this temperature using a humidifier. Humidified hydrogen gas was supplied to the anode and humidified air was supplied to the cathode. The relative humidity of the hydrogen gas and air was controlled by the humidifier temperature.3.Results and discussionThe structure of the MC was observed by a scanning electron microscope (SEM). SEM images of the MC showed numerous CNFs. Voids of several hundred nanometers were observed between the CNFs. The Pt supporting state of the Pt/MC was observed by a transmission electron microscope (TEM). TEM images of the Pt/MC showed Pt supported on the surface of the CNFs.The PEFC performances of the Pt/MC and the Pt/CB were compared. At a high current density, the PEFC performance of the Pt/MC was higher than that of the Pt/CB. The PEFC performance in the high current density region consumed a large amount of hydrogen gas and air. This result was due to the high hydrogen gas and air diffusivity and the high removal of produced water from the MC.The relative humidity of the air was controlled from 20 to 100% RH by supplying it to a humidifier at a temperature of 42.7 to 80.0°C. The humidification conditions of the air affected the PEFC performance of both the Pt/MC and the Pt/CB. Under the low humidification condition, the PEFC performance was reduced due to the decrease in proton conductivity of the Nafion membrane. Under the high humidification conditions, the PEFC performance decreased due to flooding. The change in the PEFC performance under these humidifying conditions was particularly high by the MC.1) N. Hirata, et.al., RSC Adv., 11, 39216-39222 (2021)2) M. Eguchi, et.al., Jpn. J. Appl. Phys., 52, 06GD06 (2013)3) M. Eguchi, et.al., polymers, 4, 1645-1656 (2012)

Using Theory to Understand the Origins of the High Activity of Earth-Abundant Transition Metal Oxide Electrocatalysts for the Hydrogen and Oxygen Evolution Reactions in Alkaline Media

A global hydrogen economy (GHE) was envisioned by Haldane in 1923 but has only recently captured wide attention. As the movement toward a GHE accelerates, the supply vs. demand of precious metals such as platinum and iridium will inevitably force their prices skyward. In order to ensure the future of the GHE, it is crucial to intensify the R&D of earth-abundant element-based electrocatalysts. We have recently focused on electrocatalysts for the oxygen evolution and hydrogen evolution reactions (OER, HER) based on Fe, Co, Ni and Mo-containing oxides.1-3 The use of density functional theory (DFT) calculations has enabled us to understand more deeply the origins of high catalytic activity.From OER experimental results, we have found that the activity is higher for Ni-Co oxides with lower structural order.1 This was explained by calculations indicating that the edges of NiOOH sheets are the active sites, at which the rate-determining step M-O + MOH  M-OOH-M is facilitated by the favorable geometry, in which the initial ) O—O distance is significantly shorter than that in the ideal structure (Fig. 1A). The presence of Co ("b" structure) further lowers the activation energy, to 0.15 eV. With the addition of Mo to NixCo1-xOOH, the rds M-O + M-O  M-O-O-M at the layer edges was found to become spontaneous, due to the electron-withdrawing effect of Mo.2 However, it was found that Mo slowly leached out of the structure during actual long-term operation. Ni-Fe oxide was found to be much more stable, and the corresponding DFT calculations showed that the activation energy for the M-O + M-OH  M-OOH-M step was lowered to 0.042 eV.3 In our work on the HER with Ni-Fe alloy/Ni-Fe oxide, we found experimentally that the activity was highest when the alloy was present in contact with a more crystalline form of the oxide.3 The DFT calculations showed that it is necessary to consider both the water dissociation step on the surface of the NixFe1-x(OH)2 sheets and the transfer of a proton to a metallic Ni-Fe alloy particle, on which two adsorbed hydrogens combine to produce H2 (Fig. 1B). This mechanism, which is similar to the bifunctional mechanism proposed by Markovic and coworkers for Pt/NiO,4 we have termed "reverse spillover."Thus, through the combination of experiment and theory, we are developing an understanding of how further increases in electrocatalytic activity for the OER and HER can be achieved with earth-abundant element-based materials.AcknowledgmentsThis work was partially based on results obtained from project JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan and a JSPS grant, KAKENHI (23H02059).References G. Shi, et al., ACS Catal., 12, 14209 (2022).G. Shi, et al., ACS Appl. Energy Mater., 6, 10742 (2023).G. Shi, et al., ACS Omega, 8, 13068 (2023).Z. Zeng, et al., Nature Energy, 2, 17070 (2017). Figure 1. (A) Reaction profile for the rate-determining step M-O + M-OH  M-O-OH-M on defective NixCo1-xOOH sheets with (a) only Ni and (b) Ni and Co in the active site (taken from Ref 1). (B) Reverse spillover reaction in which a proton is transferred from a water molecule at the surface of the Ni(OH)2 sheet to the Ni7Fe cluster that has a high coverage of H, from which H2 can subsequently desorb (taken from Ref. 3). Figure 1

Field emission from cylindrical graphene cathodes prepared by chemical vapor deposition and cold rolling

We report field emission (FE) properties of cold cathodes made by a scalable chemical vapor deposition synthesis of three-dimensional graphene (3DG) from a cast catalyst followed by cold rolling. This process leads to an increase in mechanical strength and electrical conductivity of the tested material. For a given distance between the tip of the cathode and the anode, it is found that the FE current from the edge of a single sheet of cold-rolled 3DG-based cathode can be increased by over one order of magnitude when rolling the 3DG sheet in the shape of a cylinder with several turns. A FE current in the order of 4.5 mA was measured from a 3 mm diameter cold-rolled 3DG cylinder with six turns at a bias of 2400 V for a separation of 0.5 mm between the tip of the cylindrical cathode and the anode. The FE data of all cold-rolled 3DG-based cathodes are well fitted by the expression proposed by Abbot, Henderson, Forbes, and Popov [Filippov et al., R. Soc. Open Sci. 9, 220748 (2022)], Im=CVmκexp(−B/Vm), where Im is the FE current, Vm is the bias applied between the cathode and anode, and B and C are fitting parameters. It is found that κ=1 and 3/2 for FE from the surface and edge of the cold-rolled based cathodes, respectively.

Prewetting induced underwater super oleophobic hydroxyethyl cellulose-SiO2-graphene microfiltration membranes for emulsion separation

Graphene (Gr)-based membranes with underwater superoleophobicity hold promise for separating oil droplets from oil-in-water emulsion. However, for the separation of small-sized emulsified oil droplets, how to achieve high-throughput is a major challenge. In order to optimize the microstructure of Gr-based membranes (transverse channels between Gr sheets and longitudinal pores along the edge of Gr sheets), we prepared a Gr microfiltration membrane modified by hydroxyethyl cellulose and silica (HEC-SiO2-Gr) by electrochemical exfoliation and thermal cross-linking, which exhibited excellent underwater superoleophobicity (150.0°). An electrochemical exfoliation process was employed to prepare water-dispersible Gr. Subsequently, the addition of SiO2 nanoparticles in the Gr-based membrane formed a continuous transverse channel of water permeation, which increased the water flux. The HEC was used to cross-link the Gr sheets and SiO2, which effectively prevented the Gr sheet movement and improved the mechanical properties. The membrane with stacked laminar flow microstructure showed high separation efficiency (97.9 %) in separating oil-in-water emulsions, and the flux of the membrane remained over 532.6 L·m−2·h−1 after 40 filtration cycles. The mechanical property reached 14.6 MPa, which was 1.2 times higher than that of the Gr membrane. The immersion tests of various organic solvents and corrosive solutions have fully proved the excellent stability and durability of the HEC-SiO2-Gr membrane. This work shows that the cross linking of the nanoparticles and polymers could effectively adjust the microstructure of the membrane, which provides a new viewpoint on the design Gr-based membranes for a variety of energy and environment-related applications.

Statistical Distributions of Plasma Density and Pressure in the Jovian Plasma Sheet

The Jovian plasma sheet is a key region of the Jovian magnetosphere populated by a mix of warm and hot plasma. It is the main channel for radial transport of mass and energy in the Jovian magnetosphere and provides a favorable environment for magnetic reconnection and wave–particle interactions although the understanding of its plasma properties is incomplete. This study combines observations from the Jovian Auroral Distributions Experiment and Juno Energetic Particle Detector Instrument on board the Juno spacecraft during its first 31 orbits to analyze the plasma properties of the Jovian plasma sheet from 20 R J to 100 R J. Our results indicate that the plasma number density decreases from 1 cm−3 at 20 R J to 0.005 cm−3 at 100 R J, while the plasma pressure decreases from 2 nPa at 20 R J to 0.02 nPa at 100 R J. The plasma pressure inside the plasma sheet is comparable to the magnetic pressure in the lobe region, suggesting a rough balance between the two. In the plasma sheet with r > 70 R J, the H+ density and pressure remain relatively constant, likely due to other plasma sources such as the solar wind. Additionally, we find that the pressure (density) ratios for heavy ions between the center and the edge of the plasma sheet are generally an order of magnitude, while that for H+ decreases with radial distance. These findings contribute to a more comprehensive understanding of the plasma properties of the Jovian plasma sheet.

Pore structure development of oxidized nuclear graphite

The oxidation-induced microstructure evolution of nuclear graphite (IG-110 and NBG-17) is studied. Graphite samples were oxidized in air at 500 °C. Complicated oxidation paths were observed on the ion-milled surface of oxidized graphite samples. The weight loss of graphite samples during oxidation is mainly attributed to the oxidation paths which are extended and broadened constantly. In contrast, the original gas-escape pores do not show obvious change in sizes during oxidation. The oxidation paths are characterized to be much thinner and more tortuous than the gas-escape pores, which should be taken into account in estimating the oxygen diffusivity in oxidized graphite. The edges of graphite sheets exposed in the oxidation paths could scatter the phonon and electrons strongly. Therefore, the thermal conductivity declines dramatically with oxidation time. At weight loss around 30 %, the thermal conductivity of the oxidized graphite decreased to ∼16.8 % of the corresponding original value.

Simultaneous exfoliation/fluorination for the preparation of fluorinated exfoliated graphite with high power densities in primary lithium batteries

Fluorinated carbons combining accordion-like morphology, high content of (C2F)n phase (43%), and residual non-fluorinated carbons were synthetized by two routes, i.e. fluorination of expanded graphite and simultaneous exfoliation/fluorination of expandable graphite. The latter allows the synthesis in a one-step process to be achieved. Accordion-like morphology allows the accommodation of LiF without detrimental accumulation onto the fluorocarbon sheet edges during the discharge in primary lithium battery. The faradic yield is then close to 100 % up to a discharge rate of 6C. Residual sp2 carbons (sub-fluorination) ensure the electron flux during the electrochemical process and enhance the power density (9828 W.Kg-1). High content of (C2F)n phase results in a flat galvanostatic discharge curve. The combination of those features results in a good compromise between energy and power densities, making fluorinated exfoliated graphite one of the best cathodes for primary lithium batteries.

Poly(dicarbon monofluoride) (C2F)n bridges the neutron reflectivity gap

Graphites covalently intercalated with fluorine to form (C2F)n structural type compounds shows a dramatic increase of the interlayer distance up to by a factor of almost 3 to reach ∼9 Å. Such graphite fluoride compounds containing only carbon and fluorine offer the rare opportunity to bridge the so-called gap in the reflectivity of neutron reflectors. Slow neutron reflectors are of great interest in designing neutron sources as well as in fundamental and applied science; they require synthesizing high thermal and chemical compound stability graphite fluorides. In this work, a new strategy is proposed for synthesizing (C2F)n compounds in a well-controlled method. Our results show that the outcome (C2F)n has a covalent character with only sp3 hybridized carbon atoms. Moreover, C–F bonds in the fluorocarbon sheets and CF2 groups on the sheet edges lead to the desired stability and hydrophobic character. A dedicated home-made neutron diffractometer was built for measurements of double-differential neutron cross sections of crystals with specific large interlayer distances found in (C2F)n compounds. We demonstrate that the synthesized fluorine intercalated graphites developed effectively cover the gap in the reflectivity for the new generation of neutron reflectors.

Experimental Study of the Cavitating Flow on an Independently Heated Venturi Nozzle

Abstract Despite the observation of change in the cavitation regime on a heated surface, the specific section of the wall surface that plays a more dominant role in this transition phenomenon remains unknown. This study experimentally investigated the effect of surface temperature of different regions on the cavitating flow in terms of the cavitation regime. The experiments were conducted using a convergent-divergent Venturi nozzle comprising two parts that could be heated independently. The Venturi nozzle could be fully or selectively heated at either the front, where the leading edge of the cavity sheet was located, or the rear, where the cavity sheet developed. The cavitation behavior under different heating conditions was investigated using high-speed visualization and fluctuating pressure measurements. Compared with the non-heated case, which exhibited a sheet-cloud cavitation regime, the cavitation regime on the completely heated Venturi nozzle exhibited transient cavitation. The same transition phenomenon was observed when only the front of the Venturi nozzle was heated. A liquid film was observed beneath the cavity sheet of transient cavitation when only the front portion was heated. In contrast, heating the rear part alone did not induce a change in the cavitation regime. Thus, it appeared that the transition of the cavitation regime on a heated surface was mainly influenced by the temperature increase at the leading edge of the cavity sheet.

Influence of Hole Preparation Technique on Stretch Flangeability of Aluminium Alloys

Application of aluminium alloys has increased for light-weighting the sheet metal parts in manufacturing of automobiles. Formability is important in sheet metal forming of aluminium alloys. In the assessment of formability of sheet metals, stretch flangeability or edge formability is an important aspect in application such as flanges or plunged rims. The stretch flangeability refers to the ability to avoid cracking during hole expansion and it is evaluated by performing the hole expansion test. Besides material properties, hole making process also influences the stretch flangeability of aluminium alloys. In this work, the stretch flangeability of two Al-Mg alloys has been investigated through hole expansion tests by using three different hole making techniques namely punching, water jet cutting and laser cutting. The stretch flangeability of aluminium alloys has been compared with that of a high strength steel (Dual phase steel of grade DP600) which is more commonly used steel for stretch flanging applications.

Edge Functionalization of Bulk γ-Graphyne Facilitates Mechanical Exfoliation and Modulates the Mode of Sheet Stacking.

We have successfully achieved selective and efficient functionalization of sheet edges in microcrystalline multilayer γ-graphyne through two methods: cross-coupling with residual bromide edge groups and copper-catalyzed azide-alkyne cycloaddition (CuAAC) with edge terminal alkyne groups. This modification significantly enhances the ease of mechanical exfoliation and dispersibility of the sheets of γ-graphyne. Specifically, C18-grafted γ-graphyne forms stable dispersions in compatible organic solvents, allowing for the imaging of atomically thin layers of γ-graphyne for the first time. Additionally, we have discovered that phenylacetylide edge groups alter the preferred stacking mode of γ-graphyne sheets. Few-layer flakes of Ph-edge γ-graphyne exhibit a preference for the R3m space group, contrasting with the aperiodic stacking of Br-edge γ-graphyne. These results open the door for scalable exfoliation of few-layer flakes of γ-graphyne with a high aspect ratio, enabling potential applications in carbon electronics.

Sustainable and cost-effective edge oxidized graphite/PEDOT:PSS nanocomposites with improved electrical conductivity

Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is a soft and conjugated polymer whose conductive properties can be properly tuned through doping with various additives or solvents, preserving its excellent processability. In this work PEDOT:PSS was combined with a cost-effective graphite derivative named Edge Oxidized Graphite (EOG) for developing a nanocomposite with improved electrical conductivity, with respect to the pristine PEDOT:PSS, through an easy and environmentally friendly doping process. Firstly, the EOG powders, produced by a green oxidation process of graphite, were deeply characterized through Fourier transform infrared (FT-IR), Thermogravimetric (TGA), and Wide-angle X-ray scattering (WAXD) analysis, showing that this nanofiller has oxygenated functional groups on the sheet edges. The quality and the stability of the EOG dispersions within PEDOT:PSS were investigated at different carbon-filler concentrations, up to high loading of 25 %wt/V of EOG through rheological analyses, demonstrating pseudo-plastic behavior and excellent long-term stability of the inks due to the absence of inhomogeneities and aggregates over time; in fact, the same inks were tested under the same rheological conditions after 21 days, showing the same viscosity trend for all EOG concentrations (%wt/V). Transmission electron microscopy (TEM) and (Scanning Electron microscopy) SEM investigation of spin-coated samples onto glass substrates were performed to morphologically evaluate the nanocomposites and estimate the average size of the sheets, particularly the mean length of 1.2 μm and an approximated thickness of 26 nm of the EOG sheets dispersed into the polymer matrix (PEDOT:PSS) was determined, while WAXD analysis allowed to identify the average layer number of the EOG sheets, obtaining thus, a direct measurement of the EOG sheets aspect ratio equal to 45. Finally, sheet resistance tests showed that the increasing concentration of EOG leads to a significant improvement in the electrical conductivity of the nanocomposites, from 1.1 S/cm for pristine PEDOT:PSS to 21.9 S/cm for nanocomposites with the highest EOG content (25 %wt/V). This work demonstrates the successful development of nanocomposite based on PEDOT:PSS doped with carbon-based filler synthesized through a green and cost-effective process, promoting their use in the production of bio/electrochemical sensors or optoelectronic devices.

Steel Sheet Deformation in Clinch-Riveting Joining Process

This paper presents the deformation of a joined sheet after the clinch riveting process. The DX51D steel sheet with zinc coating was used. The samples to be joined with clinch riveting technology had a thickness of 1 ± 0.05 mm and 1.5 ± 0.1 mm. The sheet deformation was measured before and after the joining process. The rivet was pressed in the sheets with the same dimension between the rivet axis and three sheet edges: 20, 30, and 40 mm. For fixed segments of the die, from the rivet side close to the rivet, the sheet deformation was greater than that of the area with movable segments. The movement of the die’s sliding element caused more sheet material to flow in the space between the fixed part of the die and movable segments. Hence, the sheet deformation in these places was smaller than for the die’s fixed element—the sheet material was less compressed. For sheet thickness values of 1.5 mm and a width value of 20 mm, the bulk of the sheet was observed. For a sheet width of 20 mm, it was observed that the deformation of the upper and lower sheets in the area of the rivet was greater than for sheet width values of 30 or 40 mm.

Undulatory Propulsion at Milliscale on Water Surface.

The oscillatory pitch motion at the leading edge of a millimeter-scale flexible sheet on the water surface can generate undulatory locomotion for swimming, similar to a honeybee vibrating its wings for propulsion. The influence of various parameters on such swimming strategy remains unexplored. This study uses magnetic milliswimmers to probe the propulsion mechanics and impact of different parameters. It is found that this undulatory propulsion is driven by capillary forces and added mass effects related to undulatory waves of the milliswimmers, along with radiation stress stemming from capillary waves at the interface. Modifying the parameters such as actuation frequency, pitch amplitude, bending stiffness, and hydrofoil length alters the body waveform, thus, affecting the propulsion speed and energy efficiency. Although undulatory motion is not a prerequisite for water surface propulsion, optimizing body stiffness to achieve a proper undulatory waveform is crucial for efficient swimming, balancing energy consumption, and speed. The study also reveals that the induced water flow is confined near the water surface, and the flow structures evolve with varying factors. These discoveries advance the understanding of undulatory water surface propulsion and have implications for the optimal design of small-scale swimming soft robots in the future.

Electrochemical Sensing of Vitamin C Using Graphene/Poly-Thionine Composite Film Modified Electrode

Background: Gastric irritation and kidney problems occur due to excess ascorbic acid content, whereas the lack of ascorbic acid in the human body leads to poor wound healing, muscle degeneration, and anemia. Objectives: Herein, we report the development of an electrochemical sensor for the detection of ascorbic acid using poly-thionine/ graphene (P-Th/Gr) modified glassy carbon electrode (GCE) in 0.1 M phosphate buffer solution (PBS) (pH 7.4). Electrostatically fused graphene affixed with poly-thionine was successfully illustrated for effective voltammetric sensing of ascorbic acid. Methodology: FE-SEM indicated the blended edge of a 2D graphene sheet with a deposited thin layer of polymer, which confirmed the formation of a poly-thionine/graphene composite. The cyclic voltammetry (CV) technique was utilized for the electrochemical assay of ascorbic acid (AsA, Vitamin C). Results: With the increased concentrations of AsA, the oxidation peak current of ascorbic acid increased at 0.0 V, and the overpotential showed a decrease compared to bare GCE. The effect of scan rate on cyclic voltammograms was recorded with 500 μM of ascorbic acid from 10 mV/s to 250 mV/s, which indicated that AsA oxidation is a diffusion-controlled process on poly-thionine/ graphene-modified electrode. Conclusion: It was concluded that a poly-thionine/graphene composite-based sensor could be useful for the determination of ascorbic acid in various biological samples.

Analysis of torsional buckling of a cylindrical sandwich shell with a magnetorheological fluid core layer

This study is an attempt to analyze the torsion buckling of a structure consisting of a cylindrical sandwich shell with two isotropic face sheets that surround a magnetorheological fluid (MRF) core layer. In this analysis, the simply supported boundary conditions were considered for the edges of the face sheets and the core layer. The components of displacement were calculated using the first-order shear deformation theory, and the governing equations were derived using Hamilton’s principle and were solved drawing upon the Galerkin method. The parameters of interest were magnetic field, buckling analysis, torsional buckling convergence, h/L ratio, ht/h ratio, and rt/L ratio. The equations obtained from MATLAB were verified using ABAQUS owing to the absence of any similar study in the existing literature. A good agreement was observed in terms of torsional buckling, indicating the robustness of the proposed structure. As smart sandwich structures are broadly used in robotics and aerospace, this structure can be a good choice thanks to its lightness (resulting from the thinness of the face sheets and hollowness) and strength and resistance (contributed by MRF core layer), which can be modified with the application of different magnetic fields.

Current Sheet Evolution in a Planar Inductive Pulsed Plasma Thruster

Abstract The evolution of the current sheet is fundamental to the understanding and operation of planar inductive pulsed plasma thrusters. Methods for experimentally determining the time-varying mutual inductance and plasma resistance associated with the current sheet are presented. From these, time-histories of the resistive heating in and electromagnetic acceleration of the sheet are found. Analysis of experimental data obtained from a compact, low discharge energy inductive pulsed plasma thruster shows that current sheet evolution is well described by three phases: ionization, formation, and acceleration. Evidence is provided for the plasma current and resistive heating becoming localized near the upstream edge of the current sheet as the sheet forms. The influence of initial propellant density and pre-ionization on the characteristics of the sheet are examined. Both higher propellant densities and increased pre-ionization are found to produce current sheets which exhibit greater magnetic impermeability. Higher densities cause the sheet to form closer to the coil face, improving coupling, while stronger pre-ionization leads to more rapid resistive heating, causing the sheet to form earlier in time.