Coaxial Structure Research Articles

A High‐Performance Binary Ni–Co Hydroxide‐based Water Oxidation Electrode with Three‐Dimensional Coaxial Nanotube Array Structure

Developing nanostructured Ni and Co oxides with a small overpotential and fast kinetics of the oxygen evolution reaction (OER) have drawn considerable attention recently because their theoretically high efficiency, high abundance, low cost, and environmental benignity in comparison with precious metal oxides, such as RuO2 and IrO2. However, how to increase the specific activity area and improve their poor intrinsic conductivity is still challenging, which significantly limits the overall OER rate and largely prevent their utilization. Thus, developing effective OER electrocatalysts with abundant active sites and high electrical conductivity still remains urgent. In this work, a scrupulous design of OER electrode with a unique sandwich‐like coaxial structure of the three‐dimensional Ni@[Ni(2+/3+)Co2(OH)6–7]x nanotube arrays (3D NNCNTAs) is reported. A Ni nanotube array with open end is homogeneous coated with Ni and Co co‐hydroxide nanosheets ([Ni(2+/3+)Co2(OH)6–7]x) and is employed as multifunctional interlayer to provide a large surface area and fast electron transport and support the outermost [Ni(2+/3+)Co2(OH)6–7]x layer. The remarkable features of high surface area, enhanced electron transport, and synergistic effects have greatly assured excellent OER activity with a small overpotential of 0.46 V at the current density of 10 mA cm−2 and high stability.

Highly Flexible and Tough Concentric Triaxial Polystyrene Fibers

A combination of appropriate reinforcing material and morphology led to the highly tough, flexible, and strong polystyrene fibers by electrospinning. Concentric fiber morphology with reinforcing elastomeric thermoplastic polyurethane (TPU) sandwiched between the two layers of polystyrene made by a special nozzle (triaxial) showed toughness of >270 J g(-1) and 300% elongation without any cracks in comparison to toughness of <0.5 J g(-1) and elongation at break of <5% of polystyrene single fibers. The concentric triaxial morphology showed great advantage in comparison to the coaxial structure. Toughness and elongation at break were 1376 and 628% higher, respectively, for triaxial morphology in comparison to the coaxial fibers because of the better interface from the sandwich structure.

Temporally and spatially resolved characterization of microwave induced argon plasmas: Experiment and modeling

Experiments and modeling of the plasma-microwave interaction have been performed in a coaxial microwave plasma source at a field frequency of 2.45 GHz generating argon plasmas at pressures of 20 and 40 millibars and a ratio of flow rate to pressure of 0.125 sccm/Pa. The incident microwave power between 100 W and 300 W is supplied in a regime of a pulse-width modulation with cycle duration of 110 ms and a power-on time of 23 ms. The experiments are based on heterodyne reflectometry and microwave interferometry at 45.75 GHz. They provide the temporal behaviour of the complex reflection coefficient, the microwave power in the plasma, as well as the electron density in the afterglow zone of the discharge. The self-consistent spatially two-dimensional and time-dependent modeling complements the analysis of the plasma-microwave interaction delivering the plasma and electromagnetic field parameters. The consolidating experimental observations and model predictions allow further characterizing the plasma source. The generated plasma has a core occupying the region close to the end of the inner electrode, where maximum electron densities above 1020 m−3 and electron temperatures of about 1 eV are observed. Due to a longer outer electrode of the coaxial structure, the plasma region is extended and fills the volume comprised by the outer electrode. The electron density reaches values of the order of 1019 m−3. The heating of the gas occurs in its great part due to elastic collisions with the plasma electrons. However, the contribution of the convective heating is important especially in the extended plasma region, where the gas temperature reaches its maximum values up to approximately 1400 K. The temporally and spatially resolved modeling enables a thorough investigation of the plasma-microwave interaction which clearly shows that the power in-coupling occurs in the region of the highest electron density during the early stage of the discharge. In the steady state phase, however, the power in-coupling occurs close to the source walls where the electron density is significantly lower than on the discharge axis.

Topology Option of Bias Magnetic Field for Magnetostrictive Actuator

In the design of giant magnetostrictive material (GMM) actuator, the bias magnetic field is a vital part. For the use of GMM rod in the magnetostrictive actuator, there are two typical topology structures, in-line structure and coaxial structure. Although these structures have been used in the design of magnetostrictive actuator, little work has been done to compare the general features for concrete application conditions. In this paper, we use finite element analysis (FEA) as the main tool to analyze and compare these structures and come to a conclusion that, as to a diameter-limited actuator, when the length to diameter ratio of the rod is less than 5, coaxial actuator can provide more uniform magnetic field and less moving parts; when the length to diameter ratio of rod is 5, the field inhomogeneity is nearly equal, and coaxial actuator uses less moving parts and in-line actuator cost less permanent magnet (PM); when the length to diameter ratio of rod is more than 5, in-line actuator can provide more uniform magnetic field and use less PM.

Characterization of Heavy Metal Contaminated Wastewater Using a Coaxial Sensor and Electromagnetic Wave Reflection Technique

Industrial wastewater control is an important issue for protection of the environment. Liquid characterization using radio frequency signal is an interesting approach for selective detection of heavy metal contaminants in industrial wastewater. A simple sensor based on open-ended coaxial structure filled with the liquid under test is proposed. Liquid samples for the experiments are copper, zinc and nickel solutions with various concentrations of 1, 10, 100 and 1000 mg/liter each. From the measurement results using a vector network analyzer (VNA) in combination with the proposed sensor, the concentration of a specific contaminant can be determined by the magnitude of the measured reflection coefficient in a frequency range lower than 2 GHz. Applying a capacitive model of the sensor, complex permittivity of the liquid under test can be calculated from the measured reflection coefficient. Obvious relationship between the imaginary part of complex permittivity and the concentration of contaminant in a frequency range lower than 2 GHz was observed. The type of contaminants in the liquid samples can be identified by the position of the resonant peaks when the magnitude of reflection coefficient is plotted in the spectrum. The frequency range for contaminant’s identification lies between 2 and 3 GHz.

Observation and Control of Interfacial Defects in ZnO/ZnSe Coaxial Nanowires

Observation and Control of Interfacial Defects in ZnO/ZnSe Coaxial Nanowires W.A. Bhutto, Z.M. Wu∗, Y.Y. Cao, W.P. Wang and J.Y. Kang∗ Fujian Key Laboratory of Semiconductor Materials and Applications, Department of Physics, Xiamen University Xiamen 361005, P.R. China ZnO/ZnSe coaxial nanowires with di erent ZnO core diameters were synthesized by using a two-step chemical vapor deposition. The scanning electron microscopy images demonstrated that the coaxial nanowires with small ZnO core diameter had the smoother surface than that with large ZnO core diameter. A coherent ZnSe layer with wurtzite structure was observed in the nanowire interface between the ZnO core and the ZnSe shell by high resolution transmission electron microscopy. This coherent layer is bene cial to reduce the defect density and improve the crystal quality by suppressing the phase transition. It was found that the coherent thickness was signi cantly related to the ZnO core diameter. For the nanowire with large ZnO core, a thin critical thickness of 2 3 nm was obtained. As a result, a layer of zinc blende ZnSe appeared outside the nanowire, and a lot of defects existed in the interface between the ZnSe layers with di erent phase structures. For the nanowire with small ZnO core, however, the critical thickness increased and a coherent coaxial structure was observed with the same lattice spacing in the ZnO core and the ZnSe shell. To obtain defect-free coaxial nanowire, an optimal structure was also proposed by theoretical calculation.

A Ku-band coaxial relativistic transit-time oscillator with low guiding magnetic field

AbstractA novel coaxial relativistic transit-time oscillator with low guiding magnetic field is proposed and investigated to generate high power microwave at Ku-band. With the coaxial structure and a quasi body wave adopted as the operating mode, the device has a larger space-charge limiting current, higher power handling capacity, and lower guiding magnetic field. Moreover, for further improving the output power, a coaxial TM02mode resonant reflector is well designed. Main structure parameters of the device are optimized by particle in cell simulations. A typical simulation result is that, with a 358 keV, 7.25 kA beam guided by a magnetic field of about 0.7 T, an 810 MW microwave pulse at 14.25 GHz is generated, yielding a conversion efficiency of about 31%. The primary experiments are also carried out. At a low guiding magnetic field of 0.7 T, a microwave pulse with power of 400 MW, pulse duration of 30 ns, frequency of 14.3 GHz close to the simulation one, and efficiency of 15.4% is generated.

Microfluidic coaxial transmission line and phase shifter

ABSTRACTThis article presents a microfluidic coaxial transmission line assembly that is realized by weaving together stretchable metallic fibers composed of a liquid‐metal core inside an elastomeric shell. These fibers are woven around a core fiber to create a coaxial assembly. The resulting structure exhibits exceptional stretchability compared to conventional coaxial transmission lines. The mechanical properties of the supporting elastomer and the fluidic properties of the conductors ensure that the characteristic impedance of the transmission line is maintained while stretched. As a result, the system is well suited for applications requiring durable transmission lines and tunable phase shifters (or time‐delay lines). A prototype fluidic coaxial structure is characterized that consists of eutectic gallium indium (EGaIn) encased in an elastomeric poly‐styrene‐(ethylene‐co‐butylene)‐styrene (SEBS). © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1459–1462, 2014

Molecular orbital interpretation of the metal–metal multiple bonding in coaxial dibenzene dimetal compounds of iron, manganese, and chromium

Both coaxial and perpendicular singlet spin state structures are found for the dibenzene dimetal complexes (C6H6)2M2 (M = Fe, Mn, and Cr) using density functional theory. For (C6H6)2M2 (M = Fe, Mn), the coaxial structure is the lower energy structure, whereas for (C6H6)2Cr2 the perpendicular structure is the lower energy structure. These coaxial structures are predicted to have very short M–M distances of ~1.98 A for (C6H6)2Fe2, ~1.75 A for (C6H6)2Mn2, and ~1.68 A for (C6H6)2Cr2. Investigation into the frontier molecular orbitals suggests a formal 2π Fe=Fe double bond in (C6H6)2Fe2, a σ + 2π Mn≡Mn triple bond in (C6H6)2Mn2, and a σ + 2π + δ quadruple bond in (C6H6)2Cr2. This gives each metal atom in these coaxial (C6H6)2M2 (M = Fe, Mn, Cr) derivatives a 16-electron configuration suggesting an 8-orbital d 5 p 3 metal valence orbital manifold without the involvement of the s orbital. The coaxial (C6H6)2M2 (M = Fe, Mn) derivatives have ideal sixfold D 6h symmetry. However, distortion of coaxial (C6H6)2Cr2 from D 6h symmetry to D 2h symmetry is observed because of involvement of only one orbital from the {d(xy), d(x 2 − y 2)} set of δ symmetry of each chromium atom in the formal quadruple bond.

Synthesis and Photophysics of Coaxial Threaded Molecular Wires: Polyrotaxanes with Triarylamine Jackets

Conjugated polyrotaxanes jacketed with hole-transport groups have been synthesized from water-soluble polyrotaxanes consisting of a polyfluorene-alt-biphenylene (PFBP) conjugated polymer threaded through β-cyclodextrin macrocycles. The hydroxyl groups of the oligosaccharides were efficiently functionalized with triphenylamine (TPA) so that every polyrotaxane molecule carries a coat of about 200 TPA units, forming a supramolecular coaxial structure. This architecture was characterized using a range of techniques, including small-angle X-ray scattering. Absorption of light by the TPA units results in excitation energy transfer (EET) and photoinduced electron transfer (ET) to the inner conjugated polymer core. These energy- and charge-transfer processes were explored by steady-state and time-resolved fluorescence spectroscopy, femtosecond transient absorption spectroscopy, and molecular modeling. The time-resolved measurements yielded insights into the heterogeneity of the TPA coat: those TPA units which are...

A novel coaxial Ku-band transit radiation oscillator without external guiding magnetic field

A novel coaxial transit radiation oscillator without external guiding magnetic field is designed to generate high power microwave at Ku-band. By using a coaxial structure, the space-charge potential energy is suppressed significantly, that is good for enhancing efficient beam-wave interaction. In order to improve the transmission stability of the unmagnetized intense relativistic electron beam, a Pierce-like cathode is employed in the novel device. By contrast with conventional relativistic microwave generators, this kind of device has the advantages of high stability, non-guiding magnetic field, and high efficiency. Moreover, with the coaxial design, it is possible to improve the power-handing capacity by increasing the radial dimension of the Ku-band device. With a 550 keV and 7.5 kA electron beam, a 1.25 GW microwave pulse at 12.08 GHz has been obtained in the simulation. The power conversion efficiency is about 30%.

All‐epitaxial fabrication of a nanowire plasmon laser structure

AbstractAn all‐epitaxial approach was demonstrated to create coaxial plasmon laser structures composed of an aluminum plasmonic metal/SiNx dielectric/InGaN quantum well shell surrounding a p‐GaN nanowire core. Strong UV luminescence was observed from as‐grown vertically‐aligned arrays as well as horizontally‐aligned nanowires transferred to a transparent carrier wafer. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

동축 프로브 급전구조에 대한 FDTD 전원 모델들의 상호 관계에 관한 비교 연구

RF 및 마이크로파 대역에서 동축 프로브 급전구조에 대한 효율적인 유한 차분 시간 영역(FDTD: Finite-Difference Time-Domain) 해석을 위한 등가 전원 모델링 기법들의 상호 관계를 연구하였다. 기존에는 델타 갭(delta-gap) 또는 자기 프릴(magnetic-frill) 개념을 FDTD에 도입한 등가 전원 모델들이 여러 연구진에 의해서 개발되었다. 이러한 등가 전원 모델들의 FDTD 구현 방법과 모의 계산의 정확성은 서로 조금 다르다는 정도로만 잘 알려져 있었다. 본 논문에서는 준정적 근사(quasi-static approximation)하에서 동축-프로브 급전 구조에 대한 FDTD 등가 전원 모델들의 상호 관계를 제시하였다. FDTD 등가 전원 모델들의 적용방법에 따라 동축 급전된 원추형 모노폴 안테나의 시간영역과 주파수영역 응답을 수치계산하였다. 또한, FDTD 모의계산의 정확성과 효율성에 대한 비교 결과를 제시하였다. For an efficient finite-difference time-domain(FDTD) analysis of coaxial-probe feeding structures in radio frequency(RF) and microwave bands, an interrelation between equivalent source modeling techniques is investigated. In existing literature, equivalent source models with delta-gap or magnetic-frill concepts have been developed by many researchers. It is well known that FDTD implementation and computational accuracy of these source models are slightly different. In this paper, the interrelation between FDTD equivalent source models for coaxial feeding structures under the quasi-static approximation(QSA) is presented. As a function of FDTD equivalent source models, time-domain and frequency-domain responses of a coaxial-probe fed conical monopole antenna are calculated numerically. And comparison results of computational accuracy and efficiency are provided.

The effects of electrospinning parameters on coaxial Sn/C nanofibers: Morphology and lithium storage performance

For tin-based anode materials that suffer from poor cycling stability due to severe volume changes upon lithiation/delithiation processes, the morphology control method might provide a solution. Today, coaxial core-shell structure has attracted wide attention due to its ability to accommodate the volume changes of tin (core), which is well encapsulated in the carbon matrix (shell). Coaxial electrospinning is a simple and effective method to prepare this kind of material. In this work, tin was dispersed in the carbon core and then coated a carbon shell to form Sn@C/C nanofibers by coaxial electrospinning. Flow ratio and tin content were investigated as two main critical factors for controlling the core/shell structure, so as to improve the cycling preference of tin anodes. When tested as a lithium-ion battery anode, the material not only showed higher reversible specific capacity (626 mAh g−1) than pure carbon nanofibers, but also exhibited better cycling performance (50 cycles with 73% capacity retention), indicating that the volume change problem of tin anodes has been well resolved by this morphology control.

Dispersion characteristics of the coaxial interlaced disk-loaded waveguide slow-wave structure

The dispersion equation of the coaxial interlaced disk-loaded waveguide slow-wave structure is derived by the multi-conductor transmission line method. The simulation results by HFSS are in good agreement with the calculation results obtained from the dispersion equation. Influences of structure parameters on dispersion characteristics are discussed. It can be concluded that with the increase of inner conductor and the decrease of the period length, the bandwidth of the slow-wave structure becomes greater. The dispersion characteristics of the coaxial interlaced disk-loaded waveguide and those of the coaxial disk-loaded waveguide are compared. The results show that the coaxial interlaced disk-loaded structure can obtain a wide bandwidth and weak dispersion. This study will be a guide to the research of the coaxial interlaced disk-loaded waveguide slow wave structure used in the traveling-wave tube.

A non-uniform three-gap buncher cavity with suppression of transverse-electromagnetic mode leakage in the triaxial klystron amplifier

The triaxial klystron amplifier is an efficient high power relativistic klystron amplifier operating at high frequencies due to its coaxial structure with large radius. However, the coaxial structures result in coupling problems among the cavities as the TEM mode is not cut-off in the coaxial tube. Therefore, the suppression of the TEM mode leakage, especially the leakage from the buncher cavity to the input cavity, is crucial in the design of a triaxial klystron amplifier. In this paper, a non-uniform three-gap buncher cavity is proposed to suppress the TEM mode leakage. The cold cavity analysis shows that the non-uniform three-gap buncher cavity can significantly suppress the TEM mode generation compared to a uniform three-gap buncher cavity. Particle-in-cell simulation shows that the power leakage to the input cavity is less than 1.5‰ of the negative power in the buncher cavity and the buncher cavity can efficiently modulate an intense relativistic electron beam free of self-oscillations. A fundamental current modulation depth of 117% is achieved by employing the proposed non-uniform buncher cavity into an X-band triaxial amplifier, which results in the high efficiency generation of high power microwave.

A dual coaxial nanocable sulfur composite for high-rate lithium–sulfur batteries

Lithium-sulfur batteries have great potential for some high energy applications such as in electric vehicles and smart grids due to their high capacity, natural abundance, low cost and environmental friendliness. But they suffer from rapid capacity decay and poor rate capability. The problems are mainly related to the dissolution of the intermediate polysulfides in the electrolyte, and to the poor conductivity of sulfur and the discharge products. In this work, we propose a novel dual coaxial nanocable sulfur composite fabricated with multi-walled nanotubes (MWCNT), nitrogen-doped porous carbon (NPC) and polyethylene glycol (PEG), i.e. MWCNTs@S/NPC@PEG nanocable, as a cathode material for Li-S batteries. In such a coaxial structure, the middle N-doped carbon with hierarchical porous structure provides a nanosized capsule to contain and hold the sulfur particles; the inner MWCNTs and the outer PEG layer can further ensure the fast electronic transport and prevent the dissolution of the polysulfides into the electrolyte, respectively. The as-designed MWCNT@S/NPC@PEG composite shows good cycling stability and excellent rate capability. The capacity is retained at 527 mA h g(-1) at 1 C after 100 cycles, and 791 mA h g(-1) at 0.5 C and 551 mA h g(-1) at 2 C after 50 cycles. Especially, the high-rate capability is outstanding with 400 mA h g(-1) at 5 C.

In situ nitrogen-doped nanoporous carbon nanocables as an efficient metal-free catalyst for oxygen reduction reaction

A new N-doped carbon nanomaterial with nanoporous coaxial nanocable structure was designed for achieving the requirements of high nitrogen content, proper nitrogen bonding state, and sufficient electron and mass transportation for an oxygen reduction reaction (ORR) catalyst. The nanoporous sheaths provided more catalytic sites and allowed oxygen and reactants to easily access them for fast mass transfer, whereas carbon nanotube cores provided a three-dimensional conductive network and guaranteed fast electron transfer. As a result, the designed low-cost catalyst exhibited excellent electrocatalytic performance and is one of the most active metal-free ORR catalyst.

Quasi-solid-state, coaxial, fiber-shaped dye-sensitized solar cells

A quasi-solid-state, coaxial, fiber-shaped dye-sensitized solar cell is developed by wrapping transparent and conducting carbon nanotube sheets on a modified Ti wire. The use of eutectic melts and design of the coaxial structure enable effective contacts between the two electrodes and active layer with a good performance, including high thermal stability and flexibility.

Electrochemical flexible supercapacitor based on manganese dioxide-titanium nitride nanotube hybrid

The manganese dioxide-titanium nitride (MnO2-TiN) nanotube hybrid has been designed to improve its electroactivity and conductivity for a supercapacitor application. Titanium nitride (TiN) nanotube array was prepared by an anodization process of titanium in ethylene glycol (EG) solution containing ammonium fluoride, subsequent calcination process in an air atmosphere, and final nitridation process in an ammonia atmosphere. Electroactive MnO2 was then loaded into well-aligned TiN nanotubes to form MnO2-TiN nanotube hybrid with well-designed shell layer of MnO2 through a controlled cyclic voltammetry electrodeposition process, which was directly supported on ultra thin and supple titanium foil to establish a bendable electrode. The morphology and microstructure of MnO2-TiN nanotube hybrid were characterized by scanning electron microscopy and X-ray diffraction. The electrochemical capacitance was investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. The villiform MnO2 thin shell layer was fully covered on TiN nanotube walls to form a coaxial heterogeneous structure. Superior electrical conductivity and accessible nanochannels of TiN contributed to a high capacitance performance of MnO2. The specific capacitance of MnO2-TiN was determined to be 853.3Fg−1 (or 213.2mFcm−2) at a current density of 1.0Ag−1 (or 0.25mAcm−2). All-solid-state flexible supercapacitor was constructed using two symmetric film electrodes of MnO2-TiN nanotube hybrid and a polyvinyl alcohol gel electrolyte of KOH-KI-EG. The volume specific capacitance, energy and power density were determined to be 4.01Fcm−3, 1.81mWhcm−3 and 32.8mWcm−3 at a high potential window of 1.8V and a current density of 2.0mAcm−2. Such MnO2-TiN nanotube hybrid electrode material exhibited effective energy storage in flexible supercapacitor application.