Synthesis Of Large Arrays Research Articles

An efficient position optimization method based on improved genetic algorithm and machine learning for sparse array

Sparse array antennas are significant in communication and radar systems due to the advantages of high resolution, low complexity, and immunity to interference. In this letter, a novel array synthesis method based on an improved genetic algorithm (IGA) is proposed to optimize the antenna position in the sparse array. Different from the traditional generic methods with high computational complexity, a method combined with Gaussian process regression (GPR) prediction is proposed to optimize the antenna position with low computational complexity. The proposed method can minimize the peak sidelobe level (PSLL) during the beam scanning procedures. Moreover, the minimum antenna spacing constraint is also considered to ensure a physically achievable solution. Simulation results show that the proposed method can achieve a lower PSLL with fewer iterations and provide a global optimization solution for large array synthesis compared with existing methods. Furthermore, a prototype of the sparse array principle optimized by IGA is designed. Measurement results indicate that the optimized sparse array has good synthesis performance in high frequency.

An efficient synthesis method for large unequally spaced sparse linear arrays based on surrogate models of subarrays

The synthesis of large arrays with optimization of element locations including mutual coupling effects is always known as a computationally cost task. In this article, an efficient synthesis method for large unequally spaced sparse linear arrays in the presence of coupling effects based on artificial neural network (ANN) surrogate models of subarrays is presented. High-quality ANN surrogate models of arbitrary large linear arrays are built by grouping the surrogate models of subarrays together to tackle the “curse of dimensionality” of ANNs caused by the large number of array elements. The surrogate models of a complete group of subarrays with the given physical structures are built by several independent ANNs which are used to characterize the effects of mutual coupling on the active element patterns (AEPs) with variable element location distributions. After training, the surrogate models of subarrays can be called by an alternating convex optimization (ACO) method, so that arbitrary large arrays can be quickly synthesized including mutual coupling effects. Numerical experiments are conducted to determine the suitable parameters of subarray partition and build surrogate models of subarrays. The results of four examples for synthesizing unequally spaced linear arrays are demonstrated to validate the effectiveness of the proposed method.

Lithography-free, high-density MoTe2 nanoribbon arrays

Two-dimensional (2D) materials have shown a range of extraordinary properties including superconductivity, topological states and ferroelectricity. Among them, 2D arrays with emerging properties have drawn intense interest due to their great potentials in implementing high-density electric devices and advanced integrated circuits. The controllable synthesis of large arrays of 2D elements offers the key advance but remains unsolved. Here we report a one-step chemical vapor deposition (CVD) synthesis strategy for achieving single-crystalline MoTe2 nanoribbon arrays directly on normal SiO2/Si substrate, requiring neither the special stepped substrate nor the post-processing. The lithography-free synthesized ribbons are found to be well-aligned with a density ten times higher than that reported in MoS2. Further scanning transmission electron microscopy (STEM) and first-principles calculation results reveal a crystal-structure boosted solid–liquid-vapor (SLV) self-etching mechanism. Our findings provide a convenient synthesis strategy to achieve high-density nanoarrays that serve as platforms for integrated nanoscale electric devices.

Deterministic Array Configurations for Radiometric Sensitivity Optimization in Microwave Interferometric Radiometers

Radiometric sensitivity is crucially important for microwave interferometric radiometers. To pursue optimum performance of radiometric sensitivity, the minimum-degradation arrays (MDAs) or low-degradation arrays (LDAs) are usually employed. In this article, we propose a deterministic method for designing low-degradation linear arrays (LDLAs), which exploits the multiple-fold redundancy property of baseline coverage (i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$u$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$v$ </tex-math></inline-formula> coverage) of interferometric arrays and further devises analytical patterns for closed-form geometric construction. The proposed method can not only attain LDLAs with satisfactory radiometric sensitivity in significantly low computational complexity, given any number of sensor elements, but also has easy adoption on large array synthesis and configuration expansion scenarios. In addition, such analytically designed LDLAs also have the advantage of array robustness (or system reliability) in the sense of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$u$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$v$ </tex-math></inline-formula> coverage shrinking and “hole” occurrence (resulted from sensor failures). Numerical results are given to demonstrate the effectiveness of the proposed LDLA design method through comparison with stochastic algorithms based on heuristic search and combinatorial approaches uniting specific integer sequences, e.g., cyclic difference sets.

Design of Thioether Cyclic Peptide Scaffolds with Passive Permeability and Oral Exposure.

Advances in the design of permeable peptides and in the synthesis of large arrays of macrocyclic peptides with diverse amino acids have evolved on parallel but independent tracks. Less precedent combines their respective attributes, thereby limiting the potential to identify permeable peptide ligands for key targets. Herein, we present novel 6-, 7-, and 8-mer cyclic peptides (MW 774-1076 g·mol-1) with passive permeability and oral exposure that feature the amino acids and thioether ring-closing common to large array formats, including DNA- and RNA-templated synthesis. Each oral peptide herein, selected from virtual libraries of partially N-methylated peptides using in silico methods, reflects the subset consistent with low energy conformations, low desolvation penalties, and passive permeability. We envision that, by retaining the backbone N-methylation pattern and consequent bias toward permeability, one can generate large peptide arrays with sufficient side chain diversity to identify permeability-biased ligands to a variety of protein targets.

Combinatorial Design of Low-Degradation Linear Arrays in Interferometric Aperture Synthesis Radiometers

Radiometric sensitivity is a crucially important performance metric of interferometric aperture synthesis radiometers (IASRs). When synthesizing array geometries for optimum sensitivity performance, the minimum-degradation or low-degradation arrays (MDAs or LDAs) are employed to fulfill requirements of baseline coverage and redundancy distribution. This paper presents a study on combinatorial design of low-degradation linear arrays (LDLAs), based on a concept of multiple difference basis (MDB). Such a deterministic method can attain a satisfactory radiometric sensitivity performance in short computation time and can be easily applied in large array synthesis, compared with stochastic design methods (e.g., simulated annealing). Furthermore, the resultant LDLAs also have advantages of angular resolution and system reliability to element wreckage. Representative experiments are carried out to demonstrate the significance of the proposed MDB-based technique for designing LDLAs.

A dual circularly polarized slot‐fed horn array antenna with linear polarization‐tracking feature

An original architecture to generate two orthogonal circular polarizations with slotted waveguide arrays is presented in this communication. The proposed solution consists of two interleaved slotted ridge waveguide arrays sharing the same aperture and feeding a common polarizing layer represented by a dual circular polarization horn array. The radiating element realizing the linear-to-circular polarization conversion is made of a slot-fed compact septum polarizer flaring into a pyramidal horn. The horn-loaded slot model is extracted, thus allowing the synthesis of large arrays. A dual circular polarization slot-fed horn array antenna is designed for Ku-band operation. The two polarizations, when combined with proper phase relation, enable the tracking of two orthogonal linear polarizations. The antenna exhibits remarkable performance for both circular and linear polarization operating modes.

Template-assisted electrodeposition of Ni and Ni/Au nanowires on planar and curved substrates

We present a variant of the template-assisted electrodeposition method that enables the synthesis of large arrays of nanowires (NWs) on flat and curved substrates. This method uses ultra-thin (50 nm–10 μm) anodic aluminum oxide membranes as a template. We have developed a procedure that uses a two-polymer protective layer to transfer these templates onto almost any surface. We have applied this technique to the fabrication of large arrays of Ni and segmented composition Ni/Au NWs on silicon wafers, Cu tapes, and thin (0.2 mm) Cu wires. In all cases, a complete coverage with NWs is achieved. The magnetic properties of these samples show an accentuated in-plane anisotropy which is affected by the form of the substrate (flat or curve) and the length of the NWs. Unlike current lithography techniques, the fabrication method proposed here allows the integration of complex nanostructures into devices, which can be fabricated on unconventional surfaces.

Nanoherding: Plasma-Chemical Synthesis and Electric-Charge-Driven Self Organization of SiO2 Nanodots

We report on the chemical synthesis of the arrays of silicon oxide nanodots and their self-organization on the surface via physical processes triggered by surface charges. The method based on chemically active oxygen plasma leads to the rearrangement of nanostructures and eventually to the formation of groups of nanodots. This behavior is explained in terms of the effect of electric field on the kinetics of surface processes. The direct measurements of the electric charges on the surface demonstrate that the charge correlates with the density and arrangement of nanodots within the array. Extensive numerical simulations support the proposed mechanism and prove a critical role of the electric charges in the self-organization. This simple and environment-friendly self-guided process could be used in the chemical synthesis of large arrays of nanodots on semiconducting surfaces for a variety of applications in catalysis, energy conversion and storage, photochemistry, environmental and biosensing, and several others.

Helical peptide arrays for lead identification and interaction site mapping

Libraries composed of linear and cyclic peptides cannot fully represent the higher order structures of most antigenic sites. To map the binding site of ligands or antibodies, a larger part of the three-dimensional space should be sampled. Because parallel synthesis of large arrays of peptides on hydrogels is restricted to relatively small peptides, a simple and robust homodimeric helical system was chosen for antigen presentation. First, it was established in an heterodimeric system that the 26-mer peptide could be synthesized and that the helical coiled-coil peptides interact in the hydrogel in a predictable manner. Next, libraries of homodimeric coiled coils were synthesized into which the epitope was grafted. Using dedicated helical dimeric and trimeric coiled-coil libraries, the epitopes of two anti-HIV-1 gp41 monoclonal antibodies known to interact with helical structures were mapped at high resolution. These mappings precisely reflect existing X-ray data, and the arrays can be applied to lead identification, epitope mapping, and systematic analysis of amino acid contribution to coiled-coil systems.

Surface phenomena involved in the formation of Co nanoparticles on amorphous carbon and SiO2 deposited by magnetron sputtering

High-pressure DC magnetron sputtering was used for the deposition of cobalt on amorphous carbon (a-C) and SiO2. Deposition conditions, substrate surface morphology and annealing parameters are investigated in order to promote the synthesis of large arrays of nanoparticles, with regular size and shape. Uniformly distributed Co nanoparticles a few nanometers in size were formed under annealing at 700°C in H2. Particle nucleation and growth are discussed based on X-ray photoelectron spectroscopy, transmission and scanning electron microscopy and kinetic Monte Carlo modeling (KMC).

Synthesis of Large Monopulse Linear Arrays Through a Tree-Based Optimal Excitations Matching

In this letter, the synthesis of large arrays for monopulse tracking applications is addressed by means of a simple and effective subarraying technique. Towards this purpose, the synthesis problem is recast as the search of an optimal path in a noncomplete binary tree by exploiting some relationships between independently optimal sum and difference excitations. Because of a suitable reduction of the solution space and the implementation of a fast path-searching algorithm, the computational issues arising in dealing with large array aperture are properly addressed. Some numerical experiments are provided in order to assess the feasibility and the computational effectiveness of the tree-based approach.

A2255: The first detection of filamentary polarized emission in a radio halo

A deep radio observation of the A2255 cluster of galaxies has been carried out at 1.4 GHz with the Very Large Array synthesis telescope. Thanks to the excellent (u, v) coverage and sensitivity achieved by our observation, the low brightness diffuse extended sources in the cluster (radio halo and relic) have been imaged with unprecedented resolution and dynamic range. We find that the radio halo has filamentary structures that are strongly polarized. The fractional linear polarization reaches levels of 20–40% and the magnetic fields appear ordered on scales of ~400 kpc. This is the first successful attempt to detect polarized emission from a radio halo and provides strong evidence that in this cluster the magnetic field is ordered on large scales.

Synthesis of large arrays of aligned α-Fe 2O 3 nanowires

Aligned α-Fe 2O 3 nanowires over large areas were successfully synthesized by oxidation of pure iron. Most of the as-synthesized α-Fe 2O 3 nanowire arrays, grown vertically from the surface of the substrate, are perfect and single crystals with diameters of 20–40 nm and lengths of 2–5 μm. The high surface density of the nanowires (10 8–10 9cm −2) is considered to be responsible for the aligned growth. The size of the α-Fe 2O 3 nanowires may be tailored to required dimension by adjusting the flowing rate of the gases as well as the time and temperature of reaction. The aligned arrays of α-Fe 2O 3 nanowires reported here offered opportunities for both fundamental research and technological applications.

The development and application of a novel safety-catch linker for BOC-based assembly of libraries of cyclic peptides.

Cyclic peptides are appealing targets in the drug-discovery process. Unfortunately, there currently exist no robust solid-phase strategies that allow the synthesis of large arrays of discrete cyclic peptides. Existing strategies are complicated, when synthesizing large libraries, by the extensive workup that is required to extract the cyclic product from the deprotection/cleavage mixture. To overcome this, we have developed a new safety-catch linker. The safety-catch concept described here involves the use of a protected catechol derivative in which one of the hydroxyls is masked with a benzyl group during peptide synthesis, thus making the linker deactivated to aminolysis. This masked derivative of the linker allows BOC solid-phase peptide assembly of the linear precursor. Prior to cyclization, the linker is activated and the linear peptide deprotected using conditions commonly employed (TFMSA), resulting in deprotected peptide attached to the activated form of the linker. Scavengers and deprotection adducts are removed by simple washing and filtration. Upon neutralization of the N-terminal amine, cyclization with concomitant cleavage from the resin yields the cyclic peptide in DMF solution. Workup is simple solvent removal. To exemplify this strategy, several cyclic peptides were synthesized targeted toward the somatostatin and integrin receptors. From this initial study and to show the strength of this method, we were able to synthesize a cyclic-peptide library containing over 400 members. This linker technology provides a new solid-phase avenue to access large arrays of cyclic peptides.

Solid-Phase Synthesis of Large Tetrahydroisoquinolinone Arrays by Two Different Approaches

We have developed two new methods for the synthesis of large arrays of small organic molecules and employed them in the synthesis of tetrahydroisoquinolinones. The first method, using a combination of tea-bag synthesis and synthesis in microtiterplates with surface suction separation of solid and liquid phase, was ap- plied in the production of a library of 30,816 compounds for general screening. The second method, using tilted centrifugation, was employed for the rapid synthesis of an array of 768 compounds for lead explosion.

Synthesis of large arrays of well-aligned carbon nanotubes on glass

Free-standing aligned carbon nanotubes have previously been grown above 700 degreesC on mesoporous silica embedded with iron nanoparticles. Here, carbon nanotubes aligned over areas up to several square centimeters were grown on nickel-coated glass below 666 degreesC by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas was used as the carbon source and ammonia gas was used as a catalyst and dilution gas. Nanotubes with controllable diameters from 20 to 400 nanometers and lengths from 0. 1 to 50 micrometers were obtained. Using this method, large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication.