Synthesis Of Arrays Research Articles

Synthesis and photoelectrochemical properties of tungsten oxide arrays with a snowflake-like hierarchical structure

In this study, we successfully fabricated well-aligned WO3 snowflake-like hierarchical arrays (SHAs) with (020) facet perpendicular to FTO substrate. The fabricated samples were characterized by XRD, SEM, and UV–vis. The SHA photoanode exhibited an impressive photocurrent density of 2.43 mA·cm−2 at 1.23 V vs RHE, which is 1.76 times higher than the sandwich-like structures (SSs). This improved performance can be attributed to the special SHAs and the preferred orientation, which would effectively promote the separation and transfer of carriers.

Urea-assisted synthesis of nickel sulfide arrays with enriching high-valence W species to boost Ni3+ active sites for water oxidation

Introduction of high-valence transition metal in nickel sulfides is an effective strategy to boost Ni3+ active sites, resulting in excellent OER performance. However, it is a challenge to enhance the amount of high-valence transition metal for ensuring Ni3+-rich specie in nickel sulfides. In this work, one-pot urea-assisted synthesis method was applied to fabricate Ni3+-rich W,V co-modified nickel sulfide nanohorn arrays grown on nickel foam (W, V-NiS@NF-UR1) as OER electrocatalyst in alkaline media. Urea can not only improve the crystallinity of electrocatalysts but also regulate their composition, which is favorable for the formation of the high content of W6+ species in the electrocatalyst, consequently increasing the Ni3+ active sites and enhancing the electrocatalytic OER performance. As a result, a small overpotential of 214 mV is required for a current density of 10 mA cm−2 by the as-prepared W, V-NiS@NF-UR1 electrocatalyst and a small Tafel slope of 69 mV dec−1 is observed in 1 M KOH. Meanwhile, the introduction of V species is also beneficial to keeping the high-valence W6+ in the electrocatalyst during the sulfurization process. For comparison, the counterpart electrocatalysts were also investigated systematically without urea.

Synthesis of Linear Sparse Array Using DNN-Based Machine-Learning Method

In this paper, a deep neural network (DNN)-based machine learning (ML) approach is presented to synthesize linear sparse arrays (LSAs). Due to the powerful fitting capability of neural networks, a DNN framework is established to map the relation between the desired array pattern and LSA geometry. In this manner, the array synthesis is accomplished by training a proper DNN that can generate the desired LSA geometry. To obtain better training, the density tapering (DT) technique is introduced to the training process as the prior domain knowledge to specify the varying boundaries of each element in the LSA. Consequently, an efficient DT-assisted DNN (D-DNN) synthesis method is developed. The proposed D-DNN method has the ability to simultaneously optimize the element positions and excitations, and directly constrain the inter-element spacings. Furthermore, by introducing the active element pattern (AEP) technique, the presented method can synthesize both ideal arrays and arrays with mutual coupling. Numerical results of a wide variety of synthesis scenarios are presented to demonstrate the validity, efficiency, and flexibility of the proposed method.

Synthesis of Large Ultrawideband Sparse Planar Arrays by Utilizing a Cooperative Coevolutionary Iterative Fourier Transform

This letter introduces a cooperative coevolutionary iterative Fourier transform (CCIFT) technique to extend the conventional IFT to large ultra-wideband (UWB) sparse planar array synthesis. In the proposed CCIFT, a dense initial element position grid such as a spacing of half a wavelength at the highest frequency is adopted to avoid the presence of grating lobes at high frequency band, and a probability-assisted element selection mechanism is presented to guarantee the obtained array layout to meet a preset minimum spacing constraint, enabling the placement of physical UWB antenna elements. In addition, a cooperative coevolutionary strategy is presented to avoid prematurity by establishing the information interaction between different excitation distributions from multiple parallel IFT procedures. Two examples are conducted and results show that the CCIFT can achieve a considerably lower peak sidelobe level (PSL) than some state-of-art algorithms within an acceptable CPU time, which demonstrates its effectiveness and superiority.

Preparation and Performance Study of ZnO Nanorod Array with Anti-Ultraviolet and Superhydrophobic Surface

A two-step low-temperature hydrothermal method was used to construct an aluminum-nickel compound network structure on the substrate surface, followed by a secondary hydrothermal synthesis of ZnO nanorod array. After low surface energy material modification, a superhydrophobic and superoleophobic surface was obtained. The aluminum-nickel compound network structure plays a key guiding role in the growth of ZnO nanorod arrays. The uniformly shaped and densely arranged ZnO nanorod arrays have high roughness and exhibit excellent hydrophobic properties after modification. The surface of the ZnO nanorod array is improved in terms of UV resistance due to the size effect. The effects of hydrothermal reaction temperature, hydrothermal reaction time, hydrothermal reaction pH value, and Zn[Formula: see text] concentration on the surface structure, morphology, and properties of the ZnO nanorod array were also studied.

Analytical beampattern synthesis for symmetric nonuniform linear array based on superposition principle

AbstractIn this letter, an analytical method for the beampattern synthesis of symmetric nonuniform array is proposed. This method consists of two steps. In the first step, it acquires a real symmetric excitation by the convex optimization method to attain a pencil beam. In the second step, it superposes the pencil beams pointing in different directions to synthesize the prescribed beampattern. Numerical results are provided to verify the effectiveness of the proposed method.

Multi-pattern synthesis in fourth-dimensional antenna arrays using BGM-based quasi-Newton memetic optimization method

Abstract The advancement in wireless communication is fueling the growth of innovative antenna array designs toward cost-effective and performance-oriented solutions. This paper proposed unconventional methods to design antenna arrays for multi-pattern synthesis without using attenuators or phase shifters. A low-cost alternative is proposed with “Time-modulation”-based antenna array capable of electronic scanning and beam steering. Here, “Time” is utilized as a fourth-dimensional (4D) array parameter, and that is why “Time-modulated” arrays are also called as 4D antenna arrays. The idea is to control the high-speed switch attached with each antenna periodically to produce desirable current and phase tapering. This article expanded the “Time-modulation” concept to synthesize multiple radiation patterns like monopulse patterns, scanned beam patterns, shaped beam patterns, and cosecant-squared beam patterns for multifunctional radar systems. Suitable time schemes are developed to generate the narrowband sum–difference patterns useful for monopulse radars. Simultaneous scanned beam patterns are also proposed for narrowband communication. Furthermore, to address the wideband applications, shaped flat-top beam patterns and cosecant-squared beam patterns are also proposed. In this regard, 20- and 16-element “Time-modulated” linear array antennas are developed, and the parameters of the arrays are controlled by suitably designed objective functions with quasi-Newton method (QNM)-based memetic optimization method. For this purpose, first a well-known genetic algorithm is adopted to search the potential trust regions in the exploration stage and QNM is used for fine-tuning. Furthermore, the Broyden’s good method-based direction-updating equation is used with QNM to improve the performance.

A Multiform Optimization Framework for Constrained Multiobjective Optimization.

Constrained multiobjective optimization problems (CMOPs) pose great difficulties to the existing multiobjective evolutionary algorithms (MOEAs), in terms of constraint handling and the tradeoffs between diversity and convergence. The constraints divide the search space into feasible and infeasible regions. A key to solving CMOPs is how to effectively utilize the information of both feasible and infeasible solutions during the optimization process. In this article, we propose a multiform optimization framework to solve a CMOP task together with an auxiliary CMOP task in a multitask setting. The proposed framework is designed to conduct a search in different sizes of feasible space that is derived from the original CMOP task. The derived feasible space is easier to search and can provide a useful inductive bias to the search process of the original CMOP task, by leveraging the transferable knowledge shared between them, thereby helping the search to toward the Pareto optimal solutions from both the infeasible and feasible regions of the search space. The proposed framework is instantiated in three kinds of MOEAs: 1) dominance-based; 2) decomposition-based; and 3) indicator-based algorithms. Experiments on four sets of benchmark test problems demonstrate the superiority of the proposed method over four representative constraint-handling techniques. In addition, the comparison against five state-of-the-art-constrained MOEAs demonstrates that the proposed approach outperforms these contender algorithms. Finally, the proposed method is successfully applied to solve a real-world antenna array synthesis problem.

Synthesis of linear thinned array based on improved binary brain storm optimization

In this paper, an improved binary brain storm optimization (ImBBSO) method is presented for pattern synthesis of linear thinned array. To avoid local convergence and obtain the global optimum, on the basic of original binary brain storm optimization (BBSO) algorithm, the designed method mainly modifies three aspects, containing the clustering centers selection, the forced bit transposition mechanism and the survival of population. The interactions of these three operations drive optimization variables to move toward a better direction. During optimization process, the formulated cost function balances the relationship among the number of active elements, the peak sidelobe level and the half power beam width, which are eventually in the best balance state after completing iterations. Besides, the subarray partition strategy is also integrated into the proposed optimization framework with slight amendments, which can be applied to many engineering fields with space restrictions. Finally, several numerical examples demonstrate the effectiveness and applicability of the proposed method compared with other existing results of state-of-the-art methods, whether in benchmarking functions or linear array application.

Morphologically controlled synthesis of MnCo2O4 arrays on ACF as binder-free electrode for asymmetric supercapacitor

MnCo2O4 with a unique spinel structure has great potential as advanced electrode materials for supercapacitors. In this work, MnCo2O4 nano-arrays with controllable morphologies were pleasingly deposited on the surface of ACF by a simple hydrothermal route followed by an annealing process. The MnCo2O4@ACF binder-free electrode with nanowire morphology exhibited the most excellent electrochemical performance: specific capacitance of 1.58 mAh·cm−2 at 1 mA.cm−2 and 89.13% capacity retention after 1000 cycles at 5 A.g−1. Asymmetric supercapacitor devices were assembled to further investigate the performance of the composite electrodes. A high energy density of 47.83 Wh.kg−1 was obtained at 1.0 A.g−1 with a power density of 2623.45 W.kg−1. In the light of the above results, active layers with controllable morphology and fabrication of binder-free composite electrode systems may provide feasible design ideas for advanced electrode materials of high-performance supercapacitors.

An effective approach for hydrothermal synthesis of ZnO nanorod arrays activated under UV/Vis light: Different supporting ligands for hydrothermal precursor solutions

In this study, an effective approach is proposed for the controlled production of ZnO nanorod arrays that can be used in degradation of wastewater pollutants. Hydrothermal precursor solutions prepared using HMTA-different supporting ligands having different lengths and ends, which have not been tried before, allowed to control the type, size, and alignment of ZnO nanorods. Their physical properties were investigated by using X-ray diffraction patterns, Raman, FTIR and photoluminescence spectroscopies, UV/Vis Spectrophotometer, atomic force microscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Photoactivity tests were performed using methylene blue under UV/visible light and the reusability of ZnO nanorod arrays with the best properties was checked. The approach of using different supporting ligands led to different effects on the physical and photocatalytic properties. ZnO nanorod arrays gained the ZnO films, which became photoactive with UV light, the ability to benefit from visible light as well. Especially ZnO-HMTA-HMDA nanorod arrays will shed light on researchers as an effective strategy for the development of new functional nanomaterials having high photodegradation efficiency and fast kinetic.

Slotted-Waveguide Antenna Array Development by Means of Complementarity оf CST Microwave Studio and Compass 3D Programs

The main steps of the methodology for complex slotted-waveguide antenna arrays development using the complementary application of the COMPASS 3D design program and electromagnetic modeling CST Microwave Studio are considered. The presentation of the technique steps is carried out on the example of a structurally complex slotted-waveguide antenna array of the Ka-band with dimensions (117 mm ´ 30 mm) and two-dimensional array of 64 (2 ´ 8 ´ 4) slotted emitters. To facilitate the synthesis of the design parameters of such grids, it is proposed to use a three-stage process: 1) design of slotted antenna emitting modules with adjustment to a given operation frequency range; 2) development of harmonized multichannel power divider for them; 3) combining the antenna modules and the branched power divider into an effective antenna array with additional adjustment of their coordination parameters. According to this sequence, in the illustrated example, on the first step, the antenna emitter module with four slits is designed in the CST Microwave Studio program. Afterwards, on the second stage, a complex multi-channel waveguide power divider was designed. It is first drawn in COMPASS 3D and then imported and analysed in CST Microwave Studio. On the final third stage, the entire slotted-waveguide antenna array was assembled and simulated in CST Microwave Studio. At the same time, the obtained radiation pattern of the antenna array, the functions of electromagnetic field distribution in the waveguide path and other electromagnetic characteristics corresponded to the required ones. Equally, there was a slight shift in the standing wave ratio (SWR) of the operating frequency matching, as well as some deterioration in the SWR. This is explained by the fact that the links between the models of antenna emitters and the waveguide power distributor were carried out 'in ideal ports'. Meanwhile, the real values of the input resistances in these planes of the assembled structure are somewhat different from the ideal ones. Therefore, to complete the process of structural synthesis of the antenna-slot array, two approaches should be used: 1) it is better to complete design parameter optimization according to the criterion of improving the harmonization, if required to shift the operating frequency, 2) to reduce the SWR value, it is better to improve the coordination of the antenna array at its input by adjusting the matching device.

Silver ion beam formation and implantation on nano-pyramidal template for isolated nano-dot formation

We report the development of silver (Ag) ion-beam by Electron Cyclotron Resonance (ECR) plasma sputtering and synthesis of Ag nano-dot arrays by implantation of the Ag+ ions on a pre-fabricated silicon nano-template. Ag atoms are mixed with the argon plasma by sputtering a biased silver plate placed inside the ECR chamber. The extracted and mass-separated Ag+ ions are transported to a UHV target chamber for implantation. The variation of the flux of Ag+ ion beam is studied by changing the various parameters, such as applied bias voltage of Ag plate, microwave power, argon gas pressure and specifically, the position of silver plate from the ECR plasma center. It is observed that the sputtering rate of Ag and thereby the final Ag beam current strongly depends on the applied bias and position of the plate. The dependence of microwave power and gas pressure on beam intensity is also investigated and explained in terms of ionization and mean free path of the ionized atoms. Finally, 6 keV Ag+ ions are implanted on pre-patterned nano-pyramidal templates to form an array of Ag nano dots on a large area, by exploiting the geometrical shape of the templates and the directionality of the ion beam.

Synthesis of ZnO Nanoflower Arrays on a Protrusion Sapphire Substrate and Application of Al-Decorated ZnO Nanoflower Matrix in Gas Sensors

In this study, we utilized a sapphire substrate with a matrix protrusion structure as a template. We employed a ZnO gel as a precursor and deposited it onto the substrate using the spin coating method. After undergoing six cycles of deposition and baking, a ZnO seed layer with a thickness of 170 nm was formed. Subsequently, we used a hydrothermal method to grow ZnO nanorods (NRs) on the aforementioned ZnO seed layer for different durations. ZnO NRs exhibited a uniform outward growth rate in various directions, resulting in a hexagonal and floral morphology when observed from above. This morphology was particularly evident in ZnO NRs synthesized for 30 and 45 min. Due to the protrusion structure of ZnO seed layer, the resulting ZnO nanorods (NRs) displayed a floral and matrix morphology on the protrusion ZnO seed layer. To further enhance their properties, we utilized Al nanomaterial to decorate the ZnO nanoflower matrix (NFM) using a deposition method. Subsequently, we fabricated devices using both undecorated and Al-decorated ZnO NFMs and deposited an upper electrode using an interdigital mask. We then compared the gas-sensing performance of these two types of sensors towards CO and H2 gases. The research findings indicate that sensors based on Al-decorated ZnO NFM exhibit superior gas-sensing properties compared to undecorated ZnO NFM for both CO and H2 gases. These Al-decorated sensors demonstrate faster response times and higher response rates during the sensing processes.

Optimal Amplitude–Density Synthesis of Linear Aperiodic Arrays

New deterministic procedures for the design of linear aperiodic arrays are described which permit exploiting, in a combined way, both the positions and the excitation amplitudes of the array elements obtaining a pattern which optimally fits, in terms of a weighted L2 norm, the pattern of a reference linear continuous aperture. A first numerical procedure is based on alternating optimization of positions and amplitudes by means of closed-form convex projectors. Sufficient conditions for the solution to be optimal are established. A second numerical procedure is based on a domino-like sequential determination of the unknowns which can be iterated to convergence. Additionally, analytical asymptotic expressions for the optimal inter-element spacing and amplitude are derived by means of variational techniques. The optimal asymptotic inter-element spacing is demonstrated to be proportional to the reference tapering to the power (-2/3) while the optimal asymptotic array amplitude is proportional to the reference tapering to the power (1/3). For aperiodic arrays with equiamplitude excitation it is proved that the optimal inter-element spacing is proportional to the reference tapering to the power (-1). Based on these asymptotic dependencies, closed-form analytical solutions are obtained for amplitudes and positions of the elements. Several numerical results confirm the effectiveness and accuracy of the new procedures.

Synthesis of Near-Field Arrays Based on Electromagnetic Inner Products

Near-field antennas have been successfully adopted in several wireless applications. To exploit the high reconfigurability of array antennas, multiple synthesis techniques for arrays operating in the near-field region have been proposed. Building upon previous works on eigenmode expansions of the radiated fields, two synthesis methods for the excitations of near-field arrays based on the definition of an inner product on the electromagnetic fields are investigated: the "maximum norm" and "minimum error field norm" methods. The "maximum norm" method computes the array excitations that maximize either the active power flow through a target surface or the electric/magnetic energy stored in an assigned volume, depending on the adopted inner product. The performance of the maximum active power flow method is compared with the one of the simpler conjugate phase method. Furthermore, the limit solution achieved when the target surface reaches the far-field region is compared against the "maximum Beam Collection Efficiency" method. The "minimum error field norm" method allows to synthesize a given target field. As an example, the latter method is used to find the optimal excitation of a Plane Wave Generator with a spherical quiet zone. The effectiveness and performance of the discussed synthesis methods are validated through numerical simulations.

Regioselective access to polycyclic N-heterocycles via homogeneous copper-catalyzed cascade cyclization of allenynes

Polycyclic N-heterocycles are important structural motifs commonly found in bioactive compounds, however, their selective construction via the cyclization of allenynes remains challenging yet highly desirable. Here we show a homogeneous copper-catalyzed hetero Diels−Alder (HDA) reaction of allenynes with cis-diazenes (PTAD, 4-phenyl-1,2,4-triazoline-3,5-dione), allowing the practical and efficient synthesis of a diverse array of valuable polycyclic N-heterocycles. A temperature-controlled and stereocontrolled chemoselectivity of the reaction was observed, leading to the chemodivergent synthesis of tetracyclic pyrrolidines, pentacyclic triazepanes and tricyclic pyrrolidines. Compared with related Au-catalyzed cyclization of allenynes, this copper catalysis achieves cyclization of allenynes terminating in C–N bond formation via the HDA reaction.

Cis-Selective Acyclic Diene Metathesis Polymerization of α,ω-Dienes.

The cis/trans stereochemistry of repeating alkenes in polymers provides a powerful handle to modulate the thermal and mechanical properties of these soft materials, but synthetic methods to precisely dictate this parameter remain scarce. We report herein a cis-selective acyclic diene metathesis (ADMET) polymerization of readily available α,ω-diene monomers with high functional group tolerance. Identification of a highly stereoselective cyclometalated Ru catalyst allowed the synthesis of a broad array of polymers with cis contents up to 99%. This platform was leveraged to study the impact of the cis geometry on the thermal and mechanical properties of polyalkenamers, including an ABA triblock copolymer synthesized via extension of a cis-rich telechelic polyoctenamer with d,l-lactide. These results suggest that cis-selective ADMET affords an efficient strategy to tune the properties of a variety of polymers.

Teaching quality evaluation-based differential evolution and its application on synthesis of linear sparse arrays

Teaching quality evaluation-based differential evolution and its application on synthesis of linear sparse arrays

An efficient, selective, and solventless approach to carbamates in DBU-derived ionic liquids: Experimental and theoretical investigations

Herein, we report the synthesis of a diverse array of DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene) based monocationic and dicationic ionic liquids with different inorganic and organic anions. All the synthesized ILs have been characterized by recording their 1H and 13C NMR spectra. The synthesized ILs have been utilized as catalysts in the carbamation of amines with dimethyl carbonate. A detailed study has been conducted to illuminate the possible mechanistic establishment by probing the role of catalysts played by the DBU and DBU-derived ionic liquids in the carbamation process. The attachment of the butyl group to the nitrogen of the DBU unit reversed the selectivity, which has been well established with the help of spectral techniques and theoretical (DFT) studies. The DBU-derived ionic liquids facilitated the N-methoxycarbonylation of amines over N-alkylation. Among all, the best carbamate yields were obtained in the presence of [BuDBU]Ala IL under optimized reaction conditions. The IL catalyst was efficiently reused five times without any significant catalytic loss. The current carbamation protocol possesses advantages like ease of setup, eco-friendly, catalytic reusability, and selectivity.