Conductive Research Articles

Monolayer Interfacial Assembly toward Two‐Dimensional Mesoporous Heterostructure for Boosting Wave Absorption

AbstractMicrowave absorption materials play a key role in various fields, including military stealth, human safety protection, and so on. Construction of 2D mesoporous heterostructures is an attractive approach to enhance wave‐absorbing ability, while it is still a great challenge. Herein, 2D mesoporous carbon‐MXene‐carbon heterostructures (MCMCH) with channels parallel to surface are successfully prepared via a monolayer interfacial assembly strategy. Through the precise adjustment and polymerization, cylindrical micelles orderly monolayered assemble on both surfaces of 2D MXene nanosheets, resulting in 2D switch‐like polydopamine‐MXene‐polydopamine nanosheets, and 2D MCMCH are finally generated by further calcination. Due to the excellent dielectric polarization relaxation and conductive loss, MCMCH achieves the strongest reflection loss of −54.2 dB at a thickness of only 1.5 mm. The presence of mesochannels not only introduces air with a low permittivity for optimal impedance matching, but also further extends the attenuation path of the incident electromagnetic wave. The maximum radar cross‐section reduction of 26.9 dB m2 is achieved for the MCMCH compared to the perfect electric conductor. This work provides a reference for surface engineering based on 2D mesoporous heterostructures to enhance the microwave absorption performance.

Title: Optimizing Recruitment Practices for the Quality Assurance Department of Daewoo Bus Service

Transportation sector taking a central place inside the national economic growth cannot be overemphasized. The transportation sector of Pakistan is sophisticated and diverse, but still its development is kind of at its premature stage. Several people ride daily on public and private transport to come to their final destination either within the city or outside city's border. Use of roads by people has been largest in Pakistan among many transport modes. Subsequently when it comes to buses, the current ones make no claim to be in a good condition and are not air- conditioned. The individuals are suffering as a result of bad busses, conductors and passengers who show hatred that end up frustrating the directions even more by overloading and delaying the buses and non-availability of transport. The country of Pakistan has over170million inhabitants, but the state of transportation in general is not a good one. Nevertheless, one cannot say that the situation is much better compared to last year, i.e. before the crisis came. The Daewoo bus still remain the only travel option specially during the times of economic crisis when other transportation modes such as airplanes and trains are expensive beyond people's budget. Even though Daehost service enjoys monopolistic conditions in the market, the given theoretical concept ‘Marketing Mix’ and its implementation are crucial. According to the findings provided, the marketers should take on all the marketing mix concepts issue fully and practice reliably in order to add value to the service, which in turn increases the company's market share.

Application of aluminum nanoparticles in reagents for oil viscosity reduction

The problem of extracting hard-to-recover reserves, which belong to the category of heavy and highly bound oil, is one of the most pressing oil industries. Many mining companies actively use physical and chemical methods to solve this problem. The use of nanotechnology in physical and chemical methods for increasing oil production is a relatively new area. Nanoparticles easily enter the regime, their size allows them to spread more easily in porous media without reducing permeability. The main goal of the research was to reduce oil viscosity and achieve increased production. In order to increase oil recovery, the proposed method for reducing oil viscosity in reservoir conditions based on treating the bottomhole zone of production wells with a solution of caustic soda and nanoparticles affects the dimension of 40-60 nm (concentrations of 1, 0.1 and 0.01 %). The nanoparticles were obtained using an electrical conductor method and studied by transmission electron microscopy. Determination of surface tension using a DSA30 device (Kruss, Germany) using the pendant drop (PD) method. The samples for testing were oil samples, visible wells No. 222761 Binagadi-North, No. 220051 Fatmai area and No. 221937 Kirmaki area, trading company "Binagadi Oil". Based on experimental data, it was found that the proposed composition reduces the viscosity of oil by several times in all three experimental samples, nanoparticles have a positive effect on reducing viscosity, the greatest effect was noted with 0.01% nanoparticles, this composition can be used to increase the production of high-viscosity oils. Keywords: nanotechnology; metal nanoparticles; enhanced oil recovery; reduce oil viscosity.

Study of the Influence of Electromagnetic Fields on the Corrosion of District Heating Pipelines

One of the primary indicators influencing the dependability of the district heating system system is the corrosion of the pipeline surface. This article presents the findings of measurements and tests conducted on the example of the heat supply system in our country. The effects of electromagnetic fields on the surface corrosion of heat pipelines located in the area intersecting with high voltage lines and along overhead power lines are discussed. In the contemporary era, ecological concerns, including those about electromagnetic ecology, have emerged as a significant area of focus within science, technology, and socioeconomics. The study of the impact of energy pollution factors has led to the development of electromagnetic safety norms and standards. However, there is a lack of unified norms and standards for electromagnetic ecological assessment at the current stage. The measurements indicate that the electric field strength is 0.38-32.33 V/m, while the magnetic field strength is 0.07-11.56 A/m. The voltage of the electric field is directly proportional to the voltage of the conductor. At the measurement point near the overhead power line (at a height of 1 m above the heat transmission line), the maximum voltage was 32.33 V/m. However, since the voltage of the magnetic field is directly proportional to the current running through the electric conductor, the current flowing through the conductor on the output of the extension generator had the highest value, resulting in the maximum magnetic field voltage of 11.56 A/m, which indicates that the measurement is accurate.

Copper catastrophic oxidation: Theory and mechanisms

Copper and its alloys with transition metals (as good conductors of electricity and heat) are extensively used in electrical industry, electronics, and cooling systems and can be the subject of surface degradation by oxidation. In certain circumstances, surface degradation of copper occurs catastrophically. Predicting catastrophic oxidation kinetics and developing protective technology require understanding the mass transfer mechanisms in the solid/liquid/gas composite scale formed on the copper surface during catastrophic degradation. However, these mechanisms are not clear enough. The role of capillary forces in the mass transport process in the composite scale with a high density of solid/liquid and liquid/gas interfaces has not been established. Here, we show the significant contribution of both electrochemical and solutocapillary forces to mass transfer and suggest the mechanisms, involving selective transport of ions, gas bubbles, and liquid, and their relationships with the microstructure of the composite scale. The bubble nucleation is discussed.

FUNCTIONS OF PROTECTION DEVICES IN THE FIRE SAFETY SYSTEM OF ELECTRICAL INSTALLATIONS

In this article, the goal of the research was achieved regarding the definition of regulatory requirements for fire safety of protection devices in 0.4 kV electrical wiring. This article describes the main functions of protection devices that affect the fire safety of electrical installations, identifies the possibilities of strengthening the functions of protection devices, and substantiates the approach to the formation of further research for the introduction of new functions of protection devices. The article describes the study of the development of automation of processes and the saturation of electronic and electrical equipment in industry and everyday life. Because of this, there is a high degree of increase in the risk of the emergency mode of operation of electrical conductors and the occurrence of burning and fire, which may lead to a rise in the number of accidents in the future. Analysis of Ukrainian and foreign publications shows that the direction of development of power supply systems is infrastructure: p2p market for households, electric car charging networks, demand response services, and the possibility of participation in frequency support in the network and operation in the virtual power plant mode. This will lead to a further increase in requirements for reliability, safety, and protection of power supply, in particular, an increase in the functions of protection devices. The development of digitalization, security, and cloud technologies is marked by constant growth and innovation that are aimed at increasing the efficiency and reliability of the protection of electrical networks. This article also describes some modern trends in surge protection devices as a component of low-voltage network protection devices in the fire safety system of electrical installations. Devices for the protection of low-voltage networks play an important role in ensuring the fire safety of electrical installations. Correct selection, installation, and regular maintenance of these devices significantly reduce fire risks and contribute to the facility's overall safety. Due to the rapid development of the complexity of electrical consumers and requirements for their protection, it is necessary to conduct further research on the introduction of new functions of protection devices to increase their reliability, accuracy, and safety.

Integrated Modeling and Target Classification Based on mmWave SAR and CNN Approach.

This study presents a numerical modeling approach that utilizes millimeter-wave (mm-Wave) Frequency-Modulated Continuous-Wave (FMCW) radar to reconstruct and classify five weapon types: grenades, knives, guns, iron rods, and wrenches. A dataset of 1000 images of these weapons was collected from various online sources and subsequently used to generate 3605 samples in the MATLAB (R2022b) environment for creating reflectivity-added images. Background reflectivity was considered to range from 0 to 0.3 (with 0 being a perfect absorber), while object reflectivity was set between 0.8 and 1 (with 1 representing a perfect electric conductor). These images were employed to reconstruct high-resolution weapon profiles using a monostatic two-dimensional (2D) Synthetic Aperture Radar (SAR) imaging technique. Subsequently, the reconstructed images were classified using a Convolutional Neural Network (CNN) algorithm in a Python (3.10.14) environment. The CNN architecture consists of 10 layers, including multiple convolutional, pooling, and fully connected layers, designed to effectively extract features and perform classification. The CNN model achieved high accuracy, with precision and recall values exceeding 98% across most categories, demonstrating the robustness and reliability of the model. This approach shows considerable promise for enhancing security screening technologies across a range of applications.

Softening, Conformable, and Stretchable Conductors for Implantable Bioelectronics Interfaces

AbstractNeural implantable devices serve as electronic interfaces facilitating communication between the body and external electronic systems. These bioelectronic systems ideally possess stable electrical conductivity, flexibility, and stretchability to accommodate dynamic movements within the body. However, achieving both high electrical conductivity and mechanical compatibility remains a challenge. Effective electrical conductors tend to be rigid and stiff, leading to a substantial mechanical mismatch with bodily tissues. On the other hand, highly stretchable polymers, while mechanically compatible, often suffer from limited compatibility with lithography techniques and reduced electrical stability. Therefore, there exists a pressing need to develop electromechanically stable neural interfaces that enable precise communication with biological tissues. In this study, a polymer that is softening, flexible, conformal, and compatible with lithography to microfabricate perforated thin‐film architectures is utilized. These architectures offer stretchability and improved mechanical compatibility. Three distinct geometries are evaluated both mechanically and electrically under in vitro conditions that simulate physiological environments. Notably, the Peano structure demonstrates minimal changes in resistance, varying less than 1.5× even when subjected to ≈150% strain. Furthermore, devices exhibit a maximum mechanical elongation before fracture, reaching 220%. Finally, the application of multi‐electrode spinal cord leads employing titanium nitride for neural stimulation in rat models is demonstrated.

Power Transmission Technology Using Wireless Network

In this paper, we have presented the concept of wireless transmission i.e. power transmission without using any type of the electrical conductor and/or wires. We have presented an idea that is discussed here about how electrical energy can be transmitted as microwaves so that to reduce the transmission, allocation and other types of losses. Such technique is known as Microwave Power Transmission (MPT). We have also presented and correlated several aspects with the currently available Power transmission systems to the related history of wireless power transmission systems and also the related developmental changes. The basic design, merits and demerits, applications of Wireless Power Transmission are also discussed . The paper describes the various types of WPT technologies; Inductive Coupling, Magnetic Resonance and Radio Frequency (RF) technology. It also discusses the advantages and shortfalls of each type. An extensive survey of past works was discussed. Results from the research findings showed that distance and conversion efficiency were limiting factors in implementing wireless transfer technology

Online High Frequency Impedance Identification Method of Inverter-Fed Electrical Machines for Stator Health Monitoring

In electric powertrain traction applications, the adopted trend to improve the performance and efficiency of electromechanical power conversion systems is to increase supply voltages and inverter switching frequencies. As a result, electrical machine conductors are subjected to ever-increasing electrical stresses, leading to premature insulation degradation and eventual short-circuits. Winding condition monitoring is crucial to prevent such critical failures. Based on the scientific literature, several methods can be used for early identification of aging. A first solution is to monitor partial discharges. This method requires the use of a specific measurement device and an undisturbed test environment. A second solution is to monitor the inter-turn winding capacitance, which is directly related to the condition of the insulation and can cause a change in the stator impedance behavior. Several approaches can be used to estimate or characterize this impedance behavior. They must be performed on a machine at standstill, which limits their application. In this paper, a new characterization method is proposed to monitor the high-frequency stator impedance evolution of voltage source inverter-fed machines. This method can be applied at any time without removing the machine from its operating environment. The range and accuracy of the proposed frequency characterization depend in particular on the supply voltage level and the bandwidth of the measurement probes. The effects of parameters such as temperature, switching frequency, and DC voltage amplitude on the impedance characteristic were also studied and will be presented. Tests carried out on an automotive traction machine have shown that the first two series and parallel resonances of the high-frequency impedance can be accurately identified using the proposed technique. Therefore, by monitoring these resonances, it is possible to predict the aging rate of the conductor.

In-situ Construction of Petal-liked porous Co coating layers for electromagnetic wave absorption materials with rich interface-polarization

With the rapid advancements in 5G and communication technology, electromagnetic wave (EMW) absorption materials play a crucial role in reducing interference, enhancing the efficiency and stability of communication equipment, and minimizing maintenance requirements. However, the challenge remains in effectively utilizing cost-effective raw materials with simple synthesis conditions to achieve highly consistent product quality and superior EWM absorption performance. This study employs carbon nanofibers (CNFs) derived from polyacrylonitrile (PAN) as substrates and utilizes electrodeposition technology to create a composite material that exhibits both magnetic and dielectric properties. The results show that the petal-like porous Co composite CNFs (Co/CNFs) demonstrates excellent impedance matching and significant EMW absorption capabilities, which can be attributed to synergistic microstructural effects and multiple loss mechanisms. At a filling ratio of 20 wt% and a thickness of 1.8 mm, the Co/CNFs achieves a minimum reflection loss of −45 dB, extending the effective absorption bandwidth to 4.6 GHz. Performance assessment through power loss density (PLD) and radar cross-section (RCS) simulations evaluates the material’s capabilities, confirming the enhanced performance of Co/CNFs compared to the perfect electrical conductor (PEC). This efficient preparation method holds substantial potential for practical applications and serves as a comprehensive guide for achieving a balance between high performance, efficiency, and cost-advantages.

Fast-Charging Li4Ti5O12 Anode Driven By Light

The development of fast-charging lithium-ion batteries (LIBs) is crucial for achieving significant market adoption of electric vehicles (EVs). The successful achievement of fast-charging LIBs depends on efficient charge transfer and the diffusivity of lithium ions. The photo-assisted battery system exhibits promising fast-charging properties. Previous research has shown that direct exposure to white light can induce a more oxidized center in a spinel LiMn2O4 (LMO) cathode, accelerating its charging rate.[ 1] Recently, our group found that illumination with red light on an operating LMO cathode induces an Mn d-d electron excitation, simultaneously shrinks the Mn-Mn lattice, and facilitates faster delithiation of the LMO cathode.[ 2] Consequently, the charging time of the battery decreases. This encourages us to consider whether the photon energy from a specific wavelength of light can also enhance the lithiation process on the anode side. Spinel Li4Ti5O12 (LTO) is a promising material for faster-charging anodes due to its small volume charge and high-rate capability in lithium intercalation. However, the system displays slow lithium diffusivity due to poor bulk ionic conductivity. To examine the photon effect of light on these anodes, we demonstrate the photo-accelerated fast-charging (lithiation process) mechanism with an LTO spinel anode.The thin film LTO's energy band gap (Eg), approximately 3.4 eV, was determined through intense UV-visible (UV-Vis) absorption spectrum analysis, assessed in a transmission mode employing Tauc’s Law. This indicates that an LED light with photon energy around 3.4 eV might trigger rapid charging by exciting electron transfer to the T-t2g band. To explore the impact of light on the fast-charging behavior of the LTO electrode, current was measured while applying a constant voltage of 1.2 V. During the 20-minute chronoamperometry experiment, utilizing the 3.4 eV UV LED to illuminate the cell resulted in a progressive increase in current. This current increase peaked at approximately 200s, leading to a maximum average capacity increase of 13 mA h g-1. This suggests that UV illumination accelerates the lithiation process compared to the dark state, particularly favoring the early lithiation stage. Subsequently, a red LED emitting 2 eV photon energy was used to illuminate the same cell, resulting in no discernible change in current levels compared to the dark state. Electrochemical impedance spectroscopy (EIS) further revealed a significant reduction in charge transfer resistance of the window cell when illuminated with UV light compared to both the dark state and red illumination. This alteration in electrode reaction kinetics at the interface suggests a distinct influence of different light wavelengths on the charging process.In addition to assessing charge transfer at the electrode interface, galvanostatic intermittent titration technique (GITT) analysis was conducted at a 2 C rate to further elucidate diffusion within the LTO electrode. The GITT curves reveal that the diffusion of Li+ ions was approximately 1.3 times faster when the cell was illuminated by UV light compared to dark conditions. Consequently, we deduce that photo-accelerated fast charging can also occur during the lithiation process (reduction reaction) of anode materials, driven by optical forces.To delve into the underlying mechanisms, we conducted first-principles density functional theory (DFT) calculations. The outcomes revealed that the generation of additional electrons in LTO results in a reduction in the bandgap and shifts the Fermi level above the conduction band minimum, effectively transforming LTO into an active conductor of electricity. These calculations indicate that UV light illumination has the capability to surmount the bandgap of LTO, generating electron-hole pairs and thereby facilitating charge transfer and lithium-ion diffusion.In conclusion, our study showcased that UV light illumination on the LTO anode can lead to a faster charging speed of approximately 17% compared to dark conditions. We posit that the observed phenomenon of photo-accelerated fast charging in LTO is linked to the formation of electron-hole pairs in intrinsically wide-bandgap insulators or semiconducting materials. This discovery holds considerable implications for the advancement of fast charging technologies for lithium-ion batteries, potentially mitigating range anxiety concerns and facilitating the widespread adoption of electric vehicles.Acknowledgments: This work was supported by funding from Royal Dutch Shell plc. Argonne National Laboratory operates under contract no. DE-AC02-06CH11357 with the U.S. Department of Energy Office of Science. We gratefully acknowledge use of the Bebop or Swing or Blues cluster in the Laboratory Computing Resource Center at Argonne National Laboratory and supported by the U.S. Department of Energy Office of Science.Reference[1] A. Lee et al., Nat. Commun., 10, 4946 (2019).[2] J. Lipton et al., Cell Reports Physical Science, 3, 101051 (2022).

Cavity-modulated visualization of dual magnetic coupling behavior for multifunctional Co/DMAOP composites

The demand of microwave-absorbing materials for the marine environment requires the multifunctional characteristic, including microwave absorption, corrosion protection, and antimicrobial. However, achieving these properties without compromising on the microwave-absorbing performance remains a significant challenge. Here, we present a self-sacrificial template strategy to synthesize Co-metal–organic framework (MOF)-74 nanorods, achieving synergistic anticorrosion and antibacterial effects by the introduction of dimethyl octadecyl (3-trimethoxysilylpropyl) ammonium chloride (DMAOP). Our findings show that by adjusting the cavity shape, internal and exterior double-coupling behaviors may occur simultaneously, greatly increasing the synthetic composites’ capacity for magnetic loss. As a result, the Co/DMAOP-120 with 100.00 % cavity structure has an ideal reflection loss (RL) value of up to − 68.05 dB and an effective absorption bandwidth (EAB) of 4.88 GHz at a thickness of 3 mm. This material also shows significant corrosion resistance and a bacterial inhibition rate against Staphylococcus aureus (S. aureus) of 93.89 %. The maximum radar scattering cross section (RCS) of Co/DMAOP-120 under far-field conditions is significantly reduced compared to that of a perfect electrical conductor (PEC), further validating the highly efficient wave-absorbing capability of Co/DMAOP-120 in real-world environments. The new magnetic loss mechanism offers fresh recommendations for designing the microstructure of materials that waves in absorb several ways.

High-Frequency Modeling and Analysis of Single-Layer NiZn Ferrite Inductors for EMI Filtering in Power Electronics Applications

In the high-frequency (HF) region, specifically within the 150 kHz to 30 MHz range for conducting electromagnetic interference (EMI) modeling, NiZn inductors exhibit enhanced efficiency due to their low core losses and stable permeability. Consequently, the accurate modeling of NiZn ferrite toroidal inductors is essential, given their widespread applications in the HF domain, with the aim of addressing existing knowledge gaps. Previous inductor models often relied on the perfect electric conductor (PEC) assumption, which simplifies the analysis but does not fully represent the electromagnetic behavior of the cores to which the PEC assumption cannot be applied. This study investigates the actual electromagnetic behavior of NiZn cores, treating them as dielectrics, which diverges from the traditional PEC-based models. Furthermore, this research fully considers the actual geometry of the inductors, proposing a comprehensive and precise analytical model for NiZn ferrite toroidal inductors. The impact of various winding methods on core capacitance is also explored. The paper provides a detailed explanation of the physical significance underlying the proposed model. A comparative analysis of both modeling methods is presented, and the efficacy of the suggested approach is validated through simulations and experimental results in several distinct scenarios.

Flexible CoNiZn@Ti3CNTx MXene@carbon fabrics with hierarchical structure for efficient electromagnetic wave absorption

The widespread application of 5G technology has significantly exacerbated concerns regarding electromagnetic radiation. However, the rigidity and lack of flexibility of traditional electromagnetic wave (EMW) absorption materials make them ill-suited for protecting humans and certain specialized, complex shapes of equipment. Therefore, there is an increasing urgency to develop flexible EMW absorbing fabrics to effectively mitigate electromagnetic pollution. In this study, hierarchical structure CoNiZn@Ti3CNTx MXene@carbon fabrics (CoNiZn@Ti3CNTx@CF) were constructed from nano-flower structure CoNiZn-MOF, Ti3CNTx MXene and fabrics by self-assembly, in-situ growth and pyrolysis. The carbon fabric acts as a skeleton to form a 3D interconnected conductive network, in which loaded nano-flower structure CoNiZn@Ti3CNTx MXene (CoNiZn@Ti3CNTx@C) composites exists excellent dielectric loss and magnetic loss, so that EMW enters the fabric and optimizes the impedance matching, increasing the multiple reflection and scattering of EMW, thereby effectively attenuating EMW. The minimum reflection loss (RLmin) of CoNiZn@Ti3CNTx@CF reaches -44.51 dB at 14.88 GHz with filling ratio of 15 % and thickness of 1.50 mm and the effective absorption bandwidth (EAB) of CoNiZn@Ti3CNTx@CF reaches 4.32 GHz (13.04–17.36 GHz) at 1.55 mm. The EAB of CoNiZn@Ti3CNTx@CF is expanded to 14.56 GHz (3.44–18.00 GHz) through thickness adjustment (1–5.50 mm), covering most of the S, C, X, and Ku bands. The radar cross-section (RCS) value of CoNiZn@Ti3CNTx@CF is 17.3 dB m2 lower than the perfect electrical conductor (PEC), which effectively reduces the probability of the target being detected by the radar detector. This work provides ideas for design and development of flexible EMW absorbing materials.

Discovery of Electromagnetic Surface Waves at the Interface between Perfect Electric Conductor and Perfect Magnetic Conductor Parallel-Plate Waveguides.

We propose new electromagnetic surface waves at the interface formed by connecting perfect electric conductor (PEC) and perfect magnetic conductor (PMC) parallel plate waveguides containing materials with positive permittivities and permeabilities. This challenges the conventional understanding that surface waves require materials with negative permittivity or permeability. Theoretical mode analysis and numerical simulations have confirmed the existence of surface waves at the PEC-PMC interface. Additionally, a simulated prism coupling experiment validated the excitation of the surface watpdel 1ve at the PEC-PMC interface. The resonant response of the localized surface waves on the enclosed PEC-PMC surface of a cylinder also closely resembles that of a Drude cylinder. Our finding broadens the understanding of the conditions for generating electromagnetic surface waves and deepens our comprehension of electromagnetic phenomena.

The Effect of the Wall Thickness of the Material Loaded Cavity On the RCS Reduction

In this paper, the effect of a parallel plate waveguide's wall thickness on radar cross-section reduction (RCS) is rigorously analyzed for H-polarization by using the Wiener-Hopf Technique, when the waveguide region is loaded with dielectric material and terminated with a perfect electric conductor (PEC) plate. Transfer matrices are incorporated into the analysis to account for the effect of different material layers through continuity relations. The Fourier transforms of the diffracted field and the boundary conditions yield a modified scalar Wiener-Hopf equation of the second kind (MWHE-2). The classical procedure to solve the MWHE-2 is applied and the approximate expression of the diffracted far field is obtained. Numerical results are given by comparing with the results available in the literature for the case of the wall thickness of the cavity not being considered.

Invented models – relating students’ constructions of computational models to their learning gains

ABSTRACT Does inventing representations in open-ended computational environments contradict the goal of acquiring canonical scientific knowledge? We analyze the computational models of electric conductors that N = 35 eight-grade students built with a NetLogo-based microworld. Students used the microworld to sketch structures that represent models of electric conductors and then observed the resulting electric current. We use data from classroom discourse, computer log files and questionnaires, to identify different ways through which students used the platform, and how their engagement in construction, explains the variance in their learning gains. We found differences in the number and types of models that students constructed in the microworld: while most students built the models that were intended by the instructors, some added unconventional doodling models, that deviated from the intended structures. We found that students who built more models made larger gains in conceptual knowledge about electric current. However, we also found that students who constructed more unconventional models, produced lower learning gains on items that assessed the particle-level mechanism of electrons in conductors.

Enhanced high-rate performance and cyclic stability of LiNi0.8Co0.1Mn0.1O2 through LiAlO2 and polyaniline double-layer coating

LiNi0.8Co0.1Mn0.1O2 (NCM811) is widely utilized in electric vehicle batteries due to its high capacity and low cost, but its poor high-rate performance and cyclic stability restrict its applications. In this study, the NCM811 was surface coated both with ionic conductor LiAlO2 and electrical conductor polyaniline to simultaneously improve its high-rate performance and cyclic stability. Results show that the coated NCM811 has excellent capacity retention rate, namely 93.6% (25 ℃) and 83.9% (50 ℃) at 10C after 100 cycles. These results demonstrate that prepared double-layer coating is effective way to improve high-rate performance of Ni-rich cathode materials.

A Hybrid Mechanism Metasurface Based on Absorption and Phase Cancellation for Ultra‐Wideband RCS Reduction

AbstractThis paper proposes a hybrid mechanism based on phase cancellation and absorption to design a metasurface with ultra‐wideband 10 dB radar cross‐section (RCS) reduction from 6 to 64.7 GHz (171%). At high frequencies of 15–64.7 GHz, 10 dB RCS reduction is achieved by a phase cancellation mechanism, which is realized by arranging a perfect electric conductor (PEC) to form an arrayed structure with varying heights. At low frequencies of 6–15 GHz, 10 dB RCS reduction is achieved by the absorption mechanism, which is realized by designing a rotationally symmetric dual‐pattern absorber. The coupled mode theory (CMT) is used to explain the absorption mechanism. Additionally, it is found that a 180° phase difference is obtained by two different patterns to enhance RCS reduction in the high‐frequency band of 28–35 GHz. Finally, the phase cancellation and absorption mechanisms are combined to achieve an ultra‐wideband 10 dB RCS reduction from 6 to 64.7 GHz, which is realized by integrating the absorber into the arrayed structure to form the ultra‐wideband RCS reduction metasurface. The designed metasurface has a compact size (subwavelength), and a thin profile with 0.105λL.