Potential Wave Research Articles

Lower‐Hybrid Wave Structures and Interactions With Electrons Observed in Magnetotail Reconnection Diffusion Regions

AbstractWe investigate waves close to the lower‐hybrid frequency in 12 magnetotail reconnection electron diffusion region (EDR) events with guide field levels of near‐zero to 30%. In about half of the events, the wave vector has a small component along the current sheet normal, consistent with known lower‐hybrid drift wave properties, but the perpendicular magnetic field fluctuations can be comparable or greater than the parallel component, a feature unique to the waves inside and adjacent to EDRs. Another new wave property is that the wave vector has a significant component along the current sheet normal in some events and completely along the normal for one event. In 1/4 of the events, the term has a significant contribution to the wave electric field, possibly a feature of lower‐hybrid waves more likely to exist in the diffusion region than further away from the X‐line. Electron temperature variations are correlated with the wave potential, due to wave electric field acceleration and crossings at the corrugated separatrix region with different amounts of mixing between reconnection inflowing and outflowing populations. The latter also leads to the anti‐correlation between parallel and perpendicular temperature components. Using four‐spacecraft measurements, the magnetic field line twisting is demonstrated by the correlated fluctuations in and . The lower‐hybrid wave in the EDR of weak guide field reconnection may be generated near separatrices and penetrate to the mid‐plane or locally generated, and the latter possibility is beyond the prediction of previous reconnection simulations.

A Full Investigation of Terahertz Wave Power Transmission in Plasma from Theoretical, Numerical, and Experimental Perspectives

Radio communication is a vital challenge during vehicle reentry into the Earth’s atmosphere in practice, because the plasma covering the aerospace vehicle can block the communication as the spacecraft reenters the atmosphere. To investigate the potential of the terahertz wave, the transfer function method is first applied to study the wave propagation behavior in plasma, validated by the numerical and the experimental results. The comparison of all three results shows a decent agreement, with the average absolute difference around 1.1 dB for the power loss between the theoretical and numerical results for 100 GHz and 220 GHz and around 0.8 dB for the power loss between the simulation and measurement for 100 GHz and 220 GHz, which shows the validity of the transfer function method and the great potential of the numerical model for future study. Moreover, the results shows the possibility of the application of the THz wave to deal with the blackout problem.

New lump interaction complexitons to the (2+1)-dimensional Korteweg-de Vries equation with electrostatic wave potential in plasmas

A soliton is a packet of self-reinforcing waves that maintains its structure when moving at a constant speed. Solitons are caused by the cancellation of the medium’s nonlinear and dispersive effects. In plasmas, the bilinear form of Hirota will be utilized to investigate the (2+1)-dimensional Korteweg-de Vries equation with electrostatic wave potential. Solutions for complexiton lump interaction have been developed. To throw further light on the physical qualities of the recorded data, certain 3-dimensional and contour plots are presented to illustrate the interaction elements of these solutions.

Calcined Co(II)-Chelated Polyazomethine as Cathode Catalyst of Anion Exchange Membrane Fuel Cells.

Polyazomethine (PAM) prepared from the polycondensation between p-phenylene diamine (PDA) and p-terephthalaldehyde (PTAl) via Schiff reaction can physically crosslink (complex) with Co ions. Co-complexed PAM (Co-PAM) in the form of gel is calcined to become a Co, N-co-doped carbonaceous matrix (Co-N-C), acting as cathode catalyst of an anion exchange membrane fuel cell (AEMFC). The obtained Co-N-C catalyst demonstrates a single-atom structure with active Co centers seen under the high-resolution transmission electron microscopy (HRTEM). The Co-N-C catalysts are also characterized by XRD, SEM, TEM, XPS, BET, and Raman spectroscopy. The Co-N-C catalysts demonstrate oxygen reduction reaction (ORR) activity in the KOH(aq) by expressing an onset potential of 1.19–1.37 V vs. RHE, a half wave potential of 0.70–0.92 V, a Tafel slope of 61–89 mV/dec., and number of exchange electrons of 2.48–3.79. Significant ORR peaks appear in the current–voltage (CV) polarization curves for the Co-N-C catalysts that experience two-stage calcination higher than 900 °C, followed by double acid leaching (CoNC-1000A-900A). The reduction current of CoNC-1000A-900A is comparable to that of commercial Pt-implanted carbon (Pt/C), and the max power density of the single cell using CoNC-1000A-900A as cathode catalyst reaches 275 mW cm−2.

Homocysteine and atrial fibrillation: novel evidences and insights.

Atrial fibrillation (AF) is one of the most prevalent rhythm disorders worldwide, with around 37.574 million cases around the globe (0.51 % global population). Different studies showed a high informative value of different biomarkers, including such related to the systemic inflammation, biomechanical stress and fibrosis. In this review article we aimed to study only the relation of homocysteine to the AF development. Homocysteine is a sulfur-containing amino acid, that is produced in the process of methionine metabolism. Which is a non-canonical amino acid, that is derived from the food proteins. From the scientific point of view there is a relation between hyperhomocysteinemia and myocardial fibrosis, but these mechanisms are complicated and not sufficiently studied. Homocysteine regulates activity of the ion channels through their redox state. Elevated homocysteine level can condition electrical remodeling of the cardiomyocytes through the increase of sodium current and change in the function of rapid sodium channels, increase of inwards potassium current and decrease in amount of rapid potassium channels. High homocysteine concentration also leads to the shortening of the action potential, loss of the rate adaptation of the action potential and persistent circulation of the re-entry waves. In a series of experimental studies on mice there was an association found between the homocysteine level and activity of vascular inflammation. Elevation of homocysteine level is an independent factor of the thromboembolic events and AF relapses. Population studies showed, that homocysteine is an independent risk factor for AF. So, homocysteine is an interesting target for up-stream therapy.

Scanning force sensing at micrometer distances from a conductive surface with nanospheres in an optical lattice.

The center-of-mass motion of optically trapped dielectric nanoparticles in a vacuum is extremely well decoupled from its environment, making a powerful tool for measurements of feeble subattonewton forces. We demonstrate a method to trap and maneuver nanoparticles in an optical standing wave potential formed by retroreflecting a laser beam from a metallic mirror surface. We can reliably position a ∼170nm diameter silica nanoparticle at distances of a few hundred nanometers to tens of micrometers from the surface of a gold-coated silicon mirror by transferring it from a single-beam tweezer trap into the standing wave potential. We can further measure forces experienced by the particle while scanning the two-dimensional space parallel to the mirror surface, and we find no significant excess force noise in the vicinity of the surface. This method may enable three-dimensional scanning force sensing near surfaces using optically trapped nanoparticles, promising for high-sensitivity scanning force microscopy, tests of the Casimir effect, and tests of the gravitational inverse square law at micrometer scales.

AlGaN/GaN Heterostructure Schottky Barrier Diodes with Graded Barrier Layer

The AlGaN/GaN Schottky barrier diodes (SBDs) working as high-power mixer and multiplier show great potential in millimeter wave (MMW) field owing to their high breakdown voltage. Nevertheless, its further application is severely limited by large reverse leakage current (Jr) since the two-dimensional electron gas (2DEG) channel is hard to be pinched off at low voltage. To address this limitation, a graded AlGaN/GaN heterostructure is introduced to extend the 2DEG channel into a quasi-three-dimensional electron slab. By comparing the fixed Al composition AlGaN/GaN SBD, Jr of the graded AlGaN/GaN SBD is significantly reduced due to the extension of channel carriers, confirming the effective Jr suppression effect of this structure. Furthermore, on this basis, a recessed anode structure is utilized to expect a smaller Jr. The results indicated that the graded AlGaN/GaN SBDs with air-bridge structure have achieved a pretty low Jr value (1.6 × 10−13 A at -15 V), and its cutoff frequency is as high as 60.6 GHz. It is expected that such SBDs with low Jr have significant advantages in future applications.

Joint Beam Training and Data Transmission Control for mmWave Delay-Sensitive Communications: A Parallel Reinforcement Learning Approach

Future communication networks call for new solutions to support their capacity and delay demands by leveraging potentials of the millimeter wave (mmWave) frequency band. However, the beam training procedure in mmWave systems incurs significant overhead as well as huge energy consumption. As such, deriving an adaptive control policy is beneficial to both delay-sensitive and energy-efficient data transmission over mmWave networks. To this end, we investigate the problem of joint beam training and data transmission control for mmWave delay-sensitive communications in this paper. Specifically, the considered problem is firstly formulated as a constrained Markov Decision Process (MDP), which aims to minimize the cumulative energy consumption over the whole considered period of time under delay constraint. By introducing a Lagrange multiplier, we transform the constrained MDP into an unconstrained one, which is then solved via a parallel-rollout-based reinforcement learning method in a data-driven manner. Our numerical results demonstrate that the optimized policy via parallel-rollout significantly outperforms other baseline policies in both energy consumption and delay performance.

Effects of Anatomical Variations of the Stomach on Body-Surface Gastric Mapping Investigated Using a Large Population-Based Multiscale Simulation Approach.

Body-surface gastric mapping (BSGM) measures the resultant body-surface potentials of gastric slow waves using an array of cutaneous electrodes. However, there is no established protocol to guide the placement of the mapping array and to account for the effects of biodiversity on the interpretation of BSGM data. This study aims to quantify the effect of anatomical variation of the stomach on body surface potentials. To this end, 93 subject specific models of the stomach and torso were developed, based on data obtained from the Cancer Imaging Archive. For each subject a set of points were created to model general anatomy the stomach and the torso, using a finite element mesh. A bidomain model was used to simulate the gastric slow waves in the antegrade wave (AW) direction and formation of colliding waves (CW). A forward modeling approach was employed to simulate body-surface potentials from the equivaelent dipoles. Simulated data were sampled from a 5 × 5 array of electrodes from the body-surface and compared between AW and CW cases. Anatomical parameters such as the Euclidean distance from the xiphoid process (8.6 ± 2.2 cm), orientation relative to the axial plane (195 ± 20.0°) were quantified. Electrophysiological simulations of AW and CW were both correlated to specific metrics derived from BSGM signals. In general, the maximum amplitude ( ∆ ϕ) and orientation ( θ) of the signals provided consistent separation of AW and CW. The findings of this study will aid gastric BSGM electrode array design and placement protocol in clinical practices.

Theory and simulations of field strengths in magnetosonic shock waves in finite beta plasmas

Field strengths in an oblique magnetosonic shock wave in a collisionless, finite beta plasma are studied with theory and simulations. With the use of the warm, two-fluid model, the maximum values of the magnetic field, the transverse electric field, and the electric potential in a shock wave are analytically obtained as functions of the shock speed. One-dimensional, electromagnetic particle simulations are then carried out to measure the field strengths in shock waves. The theory and the simulation results are found to be consistent.

Study on PtNWs/c Catalyst for Proton Exchange Membrane Fuel Cell

With the development of PEMFC, the process of commercial fuel cell is also accelerating. As one of the key points of fuel cell, catalyst is facing the problem of how to improve its performance and life. In order to improve the durability of fuel cell catalyst, this paper will study the preparation of Pt nanowire catalyst, so as to improve the electrochemical performance and durability of the catalyst. PtNWs were prepared by soft template method. By TEM, we can clearly see that PtNWs with uniform length were obtained by soft template method. Because of the special structure, the ORR performance of the catalyst was better. The test results showed that the hydrogen peroxide desorption from PtNWs was easier, and the half wave potential of LSV curve shifted forward, which indicated that the NWs catalyst performed better ORR performance. The linear structure of PtNWs is not easy to dissolve and lose compared with Pt particles, and the linear structure is more conducive to the transfer of materials and electrons at the reaction interface, so it can show better performance and life.

Waste cigarette butt-derived B, N doped bifunctional hierarchical mesoporous carbon for supercapacitor and oxygen reduction reaction

Utilization of hazardous waste into valuable materials is the prime need globally. Herein, discarded cigarette filters (a harmful waste/environmental hazard) were utilized to produce heteroatom (Nitrogen and Boron) doped hierarchical mesoporous carbon nanocomposite (NHMC and B-NHMC) via simple elegant hydrothermal route. The fabricated hierarchical mesoporous carbons (HMC), N-doped carbon (NHMC) and boron doped carbon (B-NHMC) composite exhibited high surface area about to 972, 1283 and 1869 m2 g−1 respectively with the mesoporosity (~ 13–16 nm). Scanning electron microscopy confirmed the hierarchical nature of the produced carbon. Elemental analysis (CHN) established the presence of C, H, N, B and O elements. Electrochemical studies showed remarkable super-capacitive behavior in 6 M KOH electrolyte. The specific capacitance of the fabricated electrode materials HMC, NHMC and B-NHMC was observed 309, 325 and 365 F g−1 respectively and was calculated through CV graphs at a potential of 2 mV s−1. Moreover, GCD showed an enhanced specific capacitance of 320, 355 and 373 F g−1 at a current density of 0.5 A g−1 for HMC, NHMC and B-NHMC sample electrodes. The capacitance retention graphs showed high retention of 91%, 93% and 95% after 5000 segments of charge discharge curves of HMC, NHMC and B-NHMC electrodes, which confirmed an excellent capacitance retention exhibited by the materials. An excellent electrocatalytic performance was exhibited by B-NHMC material for oxygen reduction reaction (ORR) with an onset and half wave potential of 0.975, 0.835 V respectively in O2 saturated 0.1 M KOH electrolyte, The value of Tafel slope of B-NHMC catalyst was examined 89.5 mV dec−1, which shows a close agreement with commercial Pt/C (20%) 87.7 mV dec−1, demonstrating good kinetic properties of B-NHMC catalyst, which is near about the commercial Pt/C (20%). The average number of electrons transferred during the ORR process is 3.96, which is found a close resemblance with the ideal four electrons ORR process. Thus, discarded cigarette filters can be smartly utilized as waste to manufacture heteroatom doped (N and B) hierarchical mesoporous carbon (NHMC/B-NHMC) composite at commercial scale to solve the municipality and environmental issue and to utilize in energy storage system and fuel cells.

On the Applicability of Single‐Spacecraft Interferometry Methods Using Electric Field Probes

AbstractWhen analyzing plasma waves, a key parameter to determine is the phase velocity. It enables us to, for example, compute wavelengths, wave potentials, and determine the energy of resonant particles. The phase velocity of a wave, observed by a single spacecraft equipped with electric field probes, can be determined using interferometry techniques. While several methods have been developed to do this, they have not been documented in detail. In this study, we use an analytical model to analyze and compare three interferometry methods applied on the probe geometry of the Magnetospheric Multiscale spacecraft. One method relies on measured probe potentials, whereas the other two use different E‐field measurements: one by reconstructing the E‐field between two probes and the spacecraft, the other by constructing four pairwise parallel E‐field components in the spacecraft spin‐plane. We find that the potential method is sensitive both to how planar the wave is, and to spacecraft potential changes due to the wave. The E‐field methods are less affected by the spacecraft potential, and while the reconstructed E‐field method is applicable in some cases, the second E‐field method is almost always preferable. We conclude that the potential based interferometry method is useful when spacecraft potential effects are negligible and the signals of the different probes are very well correlated. The method using two pairs of parallel E‐fields is practically always preferable to the reconstructed E‐field method and produces the correct velocity in the spin‐plane, but it requires knowledge of the propagation direction to provide the full velocity.

Electromagnetic Characterization of Breast Tissue Phantoms in D-Band Regime

The potential of higher band millimeter waves to characterize different types of breast tissues based on the dielectric contrast between normal and malignant tissues has been reported. Low–cost phantom samples of normal and malignant tissues have been prepared using naturally occurring components, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e.</i> , agar, water, olive oil, and pectin. A waveguide probe-based calibration technique was used to extract the complex permittivities of the two-component (water–agar) and three-component (water-oil–agar) phantoms. The two-component phantoms were used to study the change in the dielectric properties of phantom with change in agar concentration. Water, agar, and varying proportions of oil were used to develop three-component phantom mixtures to mimic the dielectric properties of fat, fibrous and malignant breast tissues. Finally, the reflection and transmission properties of tissue-mimicking phantoms were tested using the waveguide probe calibration-based measurement setup. The difference in the S parameters between the three types of phantoms demonstrates the potential utility of D band-based data acquisition setups for tumor margin assessment applications <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.</b>

The nitrogen-doped carbon supported ultra-small vanadium nitride nanoparticles as a highly efficient oxygen reduction electrocatalyst for the rechargeable Zn–air battery

• Vanadium-based polyoxometalate modified by [(C 8 H 17 ) 3 NCH 3 ] + has excellent dispersion. • The rapid calcination strategies can reduce the agglomerate of VN nanoparticles. • The size of VN nanoparticles is around 5–10 nm. • VN/NC has excellent ORR activity and stability in zinc–air batteries. The regulating active sites of vanadium nitride (VN)–based materials is an effective way to improve their oxygen reduction reaction (ORR) performance, which is expected to effectively solve the problem of sluggish kinetics in the cathode of Zn–air batteries. However, traditional synthesis methods cannot uniformly disperse VN, cause inadequate exposure to the active site, resulting in poor ORR performance. Herein, we successfully prepared a nitrogen–doped carbon supported ultra-small vanadium nitride nanoparticles (VN/NC) by organic group modification combined with rapid calcination strategies. The size of VN nanoparticles is around 5–10 nm. The smaller size can ultimately improve the ORR performance of VN/NC by exposing more active sites. Finally, the half–wave potential of the VN/NC is 0.813 V for ORR. More importantly, the Zn–air batteries assembled with the VN/NC catalyst as the air cathode shows a high power density (115 mW cm −2 ) and a large specific capacity (673 mAh g −1 ). It indicates that this approach can successfully synthesize ultra-small size VN nanoparticles, which is of great significance to the development of efficient air cathode materials for the Zn–air battery.

N-Doped Graphene-Coated Commercial Pt/C Catalysts toward High-Stability and Antipoisoning in Oxygen Reduction Reaction.

Stability and antipoisoning effects are the main challenges for the application of commercial Pt/C catalysts. Herein, we soaked and adsorbed polydopamine to coat Pt particles on commercial Pt/C and subsequently converted the coatings to few-layer N-doped graphene by calcination to produce Pt/C@NC. The coatings effectively block the direct contact of Pt nanoparticles and electrolyte, thus enhancing the catalyst stability by avoiding Ostwald ripening and suppressing the competitive adsorption of toxicants, contributing to the enhancement of the antipoisoning ability. More importantly, the coatings do not hurt the oxygen reduction reaction (ORR) activity of commercial Pt/C, which exhibits a half wave potential of 0.84 V in an acidic electrolyte. The spectroscopic and theoretical results confirmed that the coatings originate from a strong Pt bonding to pyridinic N of N-doped graphene and that the high ORR activity results from the coordinately unsaturated carbon atoms, as the real ORR active sites, to strongly capture electrons from Pt.

Acoustic Wave Propagation in a Borehole with a Gas Hydrate-Bearing Sediment

A knowledge of wave propagation in boreholes with gas hydrate-bearing sediments, a typical three-phase porous medium, is of great significance for better applications of acoustic logging information on the exploitation of gas hydrate. To study the wave propagation in such waveguides based on the Carcione–Leclaire three-phase theory, according to the equations of motion and constitutive relations, a staggered-grid finite-difference time-domain (FDTD) scheme and a real axis integration (RAI) algorithm in a two-dimensional (2D) cylindrical coordinate system are proposed. In the FDTD scheme, the partition method is used to solve the stiff problem, and the nonsplitting perfect matched layer (NPML) scheme is extended to solve the problem of the false reflection waves from the artificial boundaries of the computational region. In the RAI algorithm, combined with six boundary conditions, the displacement potentials of waves are studied to calculate the borehole acoustic wavefields. The effectiveness is verified by comparing the results of the two algorithms. On this basis, the acoustic logs within a gas hydrate-bearing sediment are investigated. In particular, the wave field in a borehole is analyzed and the amplitude of a Stoneley wave under different hydrate saturations is studied. The results indicate that the attenuation coefficient of the Stoneley wave increases with the increase of gas hydrate saturation. The acoustic responses in a borehole embedded in a horizontally stratified hydrate formation are also simulated by using the proposed FDTD scheme. The result shows that the amplitude of the Stoneley wave from the upper interface is smaller than that from the bottom interface.

Carbon nanotubes mediated chemical and biological decolorization of azo dye: Understanding the structure-activity relationship

Chemical structure of azo dyes molecules showed significant influence on their decolorization rate, while the structure-activity relationship between chemical structure and their reduction decolorization rate is not fully understand. In this study, we found that azo dye molecule with closer position for electron-withdrawing substituent to azo bond resulted in faster chemical and biotic reduction rate with or without presence of carbon nanotubes (CNTs), while electron-repulsive substituent closer to azo bond leading to slower azo dye chemical and biotic reduction rate no matter with or without presence of CNTs. Additionally, galvanic cell experiments implied that electron transfer process may play important roles for both chemical and biological reduction decolorization of azo dyes, and CV results indicated that the higher (azo bond breakage) reduction wave potential corresponding to a faster azo dye chemical decolorization reaction. Finally, the results of Lowest Unoccupied Molecular Orbital (LUMO) energy established that lower LUMO energy for azo dye corresponding to a faster chemical decolorization reaction. This study not only offer systematized relationships between structure property of azo dye and their decolorization rate, but also provide a universal and propagable reduction rules.

Fabrication and Integration of Functionalized N-rGO-Ni/Ag and N-rGO-Ni/Co Nanocomposites as Synergistic Oxygen Electrocatalysts in Fuel Cells.

Fabrication of composites by developing simple techniques can be an efficient way to modify the desire properties of the materials. This paper presents a detailed study on synthesis of low cost and efficient nitrogen doped reduced graphene oxide nickle-silver (N-rGO-Ni/Ag) and nickel-cobalt (N-rGO-Ni/Co) nanocomposites as electrocatalysts in fuel cell using one-pot blended reflux condensation route. An admirable correlation in the structures and properties of the synthesized nanocomposites was observed. The Oxygen Reduction Reaction (ORR) values for N-rGO-Ni/Ag and N-rGO-Ni/Co calculated from the onset potential, using Linear Sweep Voltammetry (LSV), were found to be 1.096 and 1.146. While the half wave potential were determined to be 1.046 and 1.106, respectively, N-rGO-Ni/Ag and N-rGO-Ni/Co. The Tafel and bi-functional (ORR/OER) values were calculated as 76 and 35 mV/decade and 1.23 and 1.12 V, respectively, for N-rGO-Ni/Ag and N-rGO-Ni/Co. The lower onset and half wave potential, low charge transfer resistance (Rct = 1.20 Ω/cm2) and internal solution resistance (Rs = 8.84 × 10−1 Ω/cm2), lower Tafel values (35 mV), satisfactory LSV measurements and mass activity (24.5 at 1.056 V for ORR and 54.9 at 1.056 for OER) demonstrate the remarkable electrocatalytic activity of N-rGO-Ni/Co for both ORR and OER. The chronamperometric stability for synthesized nanocomposites was found satisfactory up to 10 h.

Derivative-extremum analysis of current-potential curves showing electrochemical kinetics in the full reversibility range

Derivative-extremum analysis (DEA) of j-E curves is a newly proposed method of half wave potential (E1/2) and activation feature extraction from steady-state voltammetry. Here, the DEA is demonstrated to be valid in the full range of reversibility using numerical simulations with a derived universal electrode equation, providing a novel perspective of electrochemical kinetics in the reversibility domain. The results reveal that E1/2 is a better choice of the reference potential instead of equilibrium potential (Eeq) in electrode equations, especially since Eeq is meaningless in an irreversible case. The equations referenced with standard potential, E1/2 and Eeq, are summarized in three tables, and their applications in parameter determinations are specified. Finally, reversibility is proved to be a relative measure between kinetic slowness and mass transport of electroactive species, and the reversibility classifications are proposed according to the DEA feature in the reversibility domain. This work, based on the DEA principle, refines the electrode equation forms and generalizes their applicability in the full range of reversibility.