Quasi-uniform Distribution Research Articles

Impact of Electrode Distance in a Quasi-Uniform Model Electrode System on Lightning Impulse Breakdown Voltage in Various Insulating Liquids

This study presents findings on the influence of gap length distance on the lightning impulse breakdown voltage of three dielectric liquids of different chemical origins. The liquids were tested in a model electrode system with a quasi-uniform electric field distribution and a pressboard plate placed on the grounded electrode. The experimental studies were supported using calculations and simulations to show the individual relationships between the lightning impulse breakdown voltage and gap distance, which represent the so-called volume effect of the most stressed liquid. The results of the experiment, which involved four considered gap distances of 2, 4, 6, and 8 mm, show that a dynamic increase in lightning impulse breakdown voltage with an increase in gap distance is associated with mineral oil and bio-based hydrocarbons. However, similar trends were not observed for synthetic ester. Calculations that allowed us to assess the impact of gap length distance on lightning impulse breakdown voltage support the observations from the experimental studies. The curves obtained in this field can be considered in the process of designing insulating systems for transformers.

Nano-indentation deformation behavior of heavy ion irradiated reduced activation ferritic/martensitic (RAFM) steels

The Nano-indentation deformation behavior of the heavy ion irradiated RAFMs is investigated in the present work. Specimens of the CLF-1 steel were irradiated with 123.4 MeV 20Ne ion at both -50 °C and 400 °C, respectively, to achieve a mean displacement damage level of 0.15 dpa. A quasi-uniform distribution of the displacement damage was produced in the specimens by utilizing an energy degrader at the irradiation chamber. The results of nano-indentation experiments indicate that during the loading stage, the irradiated materials exhibit a lower strain rate, but during the holding stage after reaching the maximum load, the irradiated materials show a higher strain rate than the un-irradiated material. Transmission electron microscopy observation showed that the low-temperature irradiation produced a high density of irradiation-induced dislocation loops, which impeded the glide of dislocation lines during the loading stage. However, as the load increases gradually to the holding stage, the dislocation lines can overcome the pinning by the dislocation loops. The strain that did not occur due to the pinned effect of the dislocation loops in the loading stage was released during the holding stage, resulting in a higher strain rate in the irradiated specimen during the holding stage. Based on the Peierls mechanism, a quantitative relationship between the number density of the irradiation-induced dislocation loops and the strain rate during the holding stage was established. The calculated results agree well with the experimentally obtained strain rate during the holding stage.

Boron carbon nitride nanosheets via induction plasma: Insights on synthesis, characterization, and control of band gap

Band gap-controlled two-dimensional boron carbon nitride nanosheets (BCNNS) were synthesized via a scalable one-step thermal plasma-based process near atmospheric pressure. Monotonic change in the band gap of BCNNS from 2.4 to 4.1 eV was achieved through manipulating the carbon loading during the nanosheet formation from ammonia borane and methane. Electron microscopy images showed 2D structures with sizes of 100–200 nm and 1.1–3.7 nm in sheet thickness (3–10 atomic layers). The sheets displayed non-uniformity in layer stacking and dislocation-type defects indicating the inclusion of BN in the C framework. Quasi-uniform distribution of the B/N/C was shown through energy dispersive X-ray spectroscopy. The presence of these elements as well as the sp2 hybridization of the bonding were confirmed using electron energy loss spectroscopy. Fourier Transform infrared spectroscopy showed the presence of B–N/BN, C–N/CN, and C–B/CB groups, and Raman spectroscopy showed progressive graphitization across the BCNNS samples as the BN content is decreased. The optical band gap of various samples is estimated using the Tauc method and found to increase as the carbon content decreased.

Wideband and Miniaturized Phase-Corrected Empty Substrate-Integrated H-Plane Horn Antenna for 5G Millimeter Waves

This paper introduces a substrate integrated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -plane horn antenna with phase-corrected structures. The quadratic curves etched on the horn aperture improve the impedance matching and the gain performance. The quasi-uniform phase distribution is achieved by the phase-corrected structure which consists of the quadratic curves and metallized via-holes embedded symmetrically on the top and bottom layers. To integrate with other planar circuits and test the proposed antenna, the transition from microstrip line to empty substrate-integrated wave guide (ESIW) is used. Compared with the optimum horn, the proposed antenna realizes a 60% reduction of the longitudinal length. A wide impedance bandwidth of 22% for |S11|<– 10dB which covers the n257, n258, and n261 5G frequency bands (24.25–29.5 GHz) is verified by a fabricated prototype. Moreover, the stable realized gain varying from 9.3 to 11 dBi is obtained during the operating bandwidth.

Microstructural and high-temperature dielectric, piezoelectric and complex impedance spectroscopic properties of K0.5Bi0.5TiO3 modified NBT-BT lead-free ferroelectric ceramics

Solid solutions (1-x-y)(Na0.5Bi0.5)TiO3-xBaTiO3-y(K0.5 Bi0.5)TiO3 with (x (mol.%) = 0, 7 and 100); y(mol.%) = 0, 20 and 100) compositions have been prepared by a conventional solid-state reaction method, and their structure, dielectric properties and depolarization temperature have been examined. At room temperature, X-ray diffraction (XRD) patterns reveal that the crystalline structure of the ceramics was perovskite. The morphotropic phase boundary (MPB) of the ternary system lying between rhombohedral (R3c) and tetragonal (P4mm) phases is in the range of (x (mol.%) = 7 and y (mol.%) = 20). The Raman-active modes for 0.73NBT-0.07BT-0.20KBT were separated and identified under the framework of group theory. SEM micrographs illustrate the quasi-uniform distribution of the grains, which are compact. The dielectric properties of the ceramics were studied in the frequency range of 1 kHz–100 kHz from ambient temperature to 600 °C. Dielectric measurements indicate that all ceramics show a diffuse phase transition near the temperature (Tm) for diffusivity of the order of 1.4–1.7 and a shift of (Tm) towards high temperatures. The resistance and capacitance of the various contributors (grain and grain boundary) in our samples are also discussed using a brick-layer model. Excellent piezoelectric properties for d33 = 146 pCN−1 and electromechanical coupling factors kp = 29.4% were observed at morphotropic phase boundary (MPB), which was assumed to be associated with the coexistence of rhombohedral and tetragonal phases and accurate grain size. This work establishes a new approach for improving lead-free piezoelectric ceramics based on 0.73NBT-0.07BT-0.20KBT.

Guided-wave manipulation in SIW H-plane horn antenna by combining phase correction and holographic-based leakage

A hybrid technique is proposed to manipulate the field distribution in a substrate integrated waveguide (SIW) H-plane horn to enhance its radiation characteristics. The technique comprises two cascaded steps to govern the guided waves in the structure. The first step is to correct the phase of fields and form a quasi-uniform distribution in the flare section so that the gain increases and side-lobe-level (SLL) decreases. This is obtained by loading the structure with a novel modulated metal-via lens. Field expansion on the radiating aperture of the SIW H-plane horn generates backward surface waves on both broad walls which increases the backlobe. In the second step, these backward surface waves are recycled and directed forward with the aid of holography theory. This is achieved by adding a couple of dielectric slabs with holographic-based patterns of metallic strips on both broad walls. With this step, the backlobe is reduced and the endfire gain is further increased. Using the proposed technique, the structure is designed and fabricated to operate at f=30 GHz which simultaneously improves the measured values of gain to 11.65 dBi, H-plane SLL to -,17.94 dB, and front-to-back ratio to 17.02 dB.

Unravelling the sex-specific diversity and functions of adrenal gland macrophages.

SummaryDespite the ubiquitous function of macrophages across the body, the diversity, origin, and function of adrenal gland macrophages remain largely unknown. We define the heterogeneity of adrenal gland immune cells using single-cell RNA sequencing and use genetic models to explore the developmental mechanisms yielding macrophage diversity. We define populations of monocyte-derived and embryonically seeded adrenal gland macrophages and identify a female-specific subset with low major histocompatibility complex (MHC) class II expression. In adulthood, monocyte recruitment dominates adrenal gland macrophage maintenance in female mice. Adrenal gland macrophage sub-tissular distribution follows a sex-dimorphic pattern, with MHC class IIlow macrophages located at the cortico-medullary junction. Macrophage sex dimorphism depends on the presence of the cortical X-zone. Adrenal gland macrophage depletion results in altered tissue homeostasis, modulated lipid metabolism, and decreased local aldosterone production during stress exposure. Overall, these data reveal the heterogeneity of adrenal gland macrophages and point toward sex-restricted distribution and functions of these cells.

Mathematical modelling of active chlorine based UV/Electro-Fenton-like process: Elucidation of reactor engineering implications to guide scaling-up

Electrochemically-driven processes are emerging as competitive solution for environmental remediation. When considering scaling of processes accurate engineering modeling can aid on process engineering design for real application. This work defines step stones on electrochemical reactor engineering understanding and sets guidelines for UV/Electro-Fenton-like process modelling to ease scale-up to pilot plant. The UV/Electro-Fenton-like process considers the use of a flow-by cell with parallel plate electrodes to electrogenerated in situ active chlorine species. The turbulent convection-diffusion equation was solved for mass transport simulations considering for the first time a simplified kinetic model in recirculation mode of operation to remove a model contaminant. Tertiary current distribution was solved to simulate the electrochemical production of HClO. The theoretical analysis evidences a quasi-uniform current distribution in the working electrode, a continuous consumption of chloride, and sustained production of HClO for effective treatment at larger scale system level. Comparisons between numerical and experimental results evidence high predictability of the designed model that can be effectively translated for other electrochemically-driven processes.

Numerical study to control the filler distribution in fibrous media during the particle-filled resin transfer molding process

A numerical model is developed for analyzing the filtration of suspension through fibrous media, during the particle-filled resin transfer molding process. The modeling approach is based on a coupling between flow and filtration models, and it is validated by comparison to various experimental results. The effect of process parameters on the distribution of the concentration and retention of particles within the preform was studied. Four parameters were considered: (i) the injection velocity, (ii) the injection pressure, (iii) the initial filler concentration, and (iv) the overflow time and the lost suspension. The obtained results reveal that the particle distribution and retention depend strongly on the initial concentration and the injection pressure, but very weakly on the injection velocity. A comparison between the distributions of the concentration and retention obtained was established with the two injection modes (imposed velocity and imposed pressure). A quasi-uniform distribution is obtained with the injection at imposed pressure, while a significant non-homogeneity in the distribution is observed in the case of injection at imposed velocity. In the latter case, a marked improvement in the distribution of the concentration and the retention of the particles is obtained by modifying the injection strategy. This operation consists of continuing the suspension injection after filling the mold and evacuating the suspension overflow through the vent. It was found that a small volume of lost suspension is enough to significantly improve particle distribution.

Recursive Algorithm to Verify Quasi-Uniform Entropy Vectors and its Applications

It is of central interest in information theory to determine whether a given vector in the entropy space is an almost entropic vector. This problem can be answered if all the information inequalities are known, but this is an extremely challenging problem. On the other hand, we can establish that a given vector is an entropy vector if we can show the existence of distribution such that the corresponding entropy vector is the same as the given vector. However, there is no known algorithm to solve this problem. Only for the simplest case of binary entropy vectors, an algorithm is known to solve this problem. In this paper, we present a recursive algorithm to determine whether a given vector is a quasi-uniform entropy vector and, if it is, to return a consistent quasi-uniform distribution. We also present two applications of the recursive procedure: (i) to generate all quasi-uniform distributions motivated by the problem of finding the smallest quasi-uniform distribution such that its entropy vector violates the well known Ingleton inequality and (ii) to obtain an entropy vector (not necessarily quasi-uniform) near to a target vector in the entropy space for random variables with given alphabet size.

Generating Bessel-Gaussian Beams with Controlled Axial Intensity Distribution

This paper investigated the diffraction of a Gaussian laser beam on a binary mask and a refractive axicon. The principles of the formation of a zero-order Bessel beam with sharp drops of the axial field intensity edges were discussed. A laser optical system based on an axicon for the formation of a Bessel beam with quasi-uniform distribution of axial field intensity was proposed. In the laser optical system, the influence of the axicon apex did not affect the output beam. The results of theoretical and experimental studies are presented. It is expected that the research results will have practical application in optical tweezers, imaging systems, as well as laser technologies using high-power radiation.

FRACTOGRAPHY OF IRRADIATED STEEL 0.12C18Cr10NiTi IN A BN-350 REACTOR AFTER MECHANICAL TESTS AT TEMPERATURES OF 350 AND 450 °C

The results are presented of a fractographic study of the fracture surface of samples of irradiated steel 0.12C18Cr10NiTi after tensile tests at temperatures of 24, 350, 450 °C. Samples for research were cut from the face of duct of spent fuel assemblies of fast neutron reactor BN-350. On the basis of a multilevel approach of physical mesomechanics, an attempt is made to explain the decrease in the ductility of steel with an increase in the temperature of mechanical tests. Based on the analysis results, it was concluded that a decrease in the ductility of steel with an increase in the test temperature may be due to quasi-uniform stress distribution in the area of localization of deformations, which was facilitated by the local increase in the porosity of the material caused by the accommodative processes of the rotary type.

On a universal solution to the transport-of-intensity equation.

The transport-of-intensity equation (TIE) is one of the most well-known approaches for phase retrieval and quantitative phase imaging. It directly recovers the quantitative phase distribution of an optical field by through-focus intensity measurements in a non-interferometric, deterministic manner. Nevertheless, the accuracy and validity of state-of-the-art TIE solvers depend on restrictive pre-knowledge or assumptions, including appropriate boundary conditions, a well-defined closed region, and quasi-uniform in-focus intensity distribution, which, however, cannot be strictly satisfied simultaneously under practical experimental conditions. In this Letter, we propose a universal solution to TIE with the advantages of high accuracy, convergence guarantee, applicability to arbitrarily shaped regions, and simplified implementation and computation. With the "maximum intensity assumption," we first simplify TIE as a standard Poisson equation to get an initial guess of the solution. Then the initial solution is further refined iteratively by solving the same Poisson equation, and thus the instability associated with the division by zero/small intensity values and large intensity variations can be effectively bypassed. Simulations and experiments with arbitrary phase, arbitrary aperture shapes, and nonuniform intensity distributions verify the effectiveness and universality of the proposed method.

Wireless Power Transfer System With High Misalignment Tolerance for Bio-Medical Implants

A hybrid array resonator structure for Wireless Power Transfer (WPT) is presented. The proposed structure exploits an array of four identical coils surrounded by a larger coil to generate uniform magnetic field. As a result, a nearly constant and high efficiency is achieved over a large misalignment region. The quasi-uniform magnetic field distribution of the proposed structure is analytically derived. For demonstration, one prototype operating at 40 MHz is designed for implantable medical devices (IMDs). According to experimental results, the developed WPT system exhibits an efficiency of 53% when the receiver and the transmitter are aligned, while the efficiency is 44% when they operate with a lateral misalignment of 10 mm. As per a conventional WPT system using a single spiral resonator as transmitter and receiver, the efficiency is 47.2% in aligned condition, while, it is 30.5% for a 10 mm lateral misalignment. The reported results demonstrate that the proposed design approach provides a high misalignment tolerance. This represents an attractive future for applications, such as the recharge of embedded devices, where the alignment between the transmitter and the receiver is difficult to guarantee.

Self-Navigated Three-Dimensional Ultrashort Echo Time Technique for Motion-Corrected Skull MRI.

Ultrashort echo time (UTE) MRI is capable of detecting signals from protons with very short T2 relaxation times, and thus has potential for skull-selective imaging as a radiation-free alternative to computed tomography. However, relatively long scan times make the technique vulnerable to artifacts from involuntary subject motion. Here, we developed a self-navigated, three-dimensional (3D) UTE pulse sequence, which builds on dual-RF, dual-echo UTE imaging, and a retrospective motion correction scheme for motion-resistant skull MRI. Full echo signals in the second readout serve as a self-navigator that yields a time-course of center of mass, allowing for adaptive determination of motion states. Furthermore, golden-means based k-space trajectory was employed to achieve a quasi-uniform distribution of sampling views on a spherical k-space surface for any subset of the entire data collected, thereby allowing reconstruction of low-resolution images pertaining to each motion state for subsequent estimation of rigid-motion parameters. Finally, the extracted trajectory of the head was used to make the whole k-space datasets motion-consistent, leading to motion-corrected, high-resolution images. Additionally, we posit that hardware-related k-space trajectory errors, if uncorrected, result in obscured bone contrast. Thus, a calibration scan was performed once to measure k-space encoding locations, subsequently used during image reconstruction of actual imaging data. In vivo studies were performed to evaluate the effectiveness of the proposed correction schemes in combination with approaches to accelerated bone-selective imaging. Results illustrating effective removal of motion artifacts and clear depiction of skull bone voxels suggest that the proposed method is robust to intermittent head motions during scanning.

Metasurface for Near-Field Wireless Power Transfer With Reduced Electric Field Leakage

Wireless power transfer is a breakthrough technology which can be used in all aspects of humans daily life. Here, a bi-layer metasurface as a transmitter for near-field wireless power transfer is proposed and studied. The novelty and advantage of the proposed metasurface is the spatial separation of the electric and magnetic near fields. Magnetic fields responsible for power transfer are sufficiently high on top of the metasurface whereas the electric fields are almost completely confined between two layers of the metasurface. These unique properties have been obtained due to the special metasurface design based on two orthogonal layers of resonant wires immersed in high-permittivity background. The theoretical and experimental study reveal the quasi-uniform magnetic field distribution over the metasurface dimensions of 40×40 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> that makes it suitable for wireless power transfer via resonant magnetic coupling to one or several receivers placed above it. Compared with a conventional planar spiral coil solution, the specific absorption rate of the proposed metasurface is reduced by 47 times, which enables to greatly increase the allowable transferred power without violating the safety regulation and reducing the efficiency.

Malaria-Infected Red Blood Cell Analysis through Optical and Biochemical Parameters Using the Transport of Intensity Equation and the Microscope's Optical Properties.

The accuracy, reliability, speed and cost of the methods used for malaria diagnosis are key to the diseases’ treatment and eventual eradication. However, improvement in any one of these requirements can lead to deterioration of the rest due to their interdependence. We propose an optical method that provides fast detection of malaria-infected red blood cells (RBCs) at a lower cost. The method is based on the combination of deconvolution, topography and three-dimensional (3D) refractive index reconstruction of the malaria-infected RBCs by use of the transport of intensity equation. Using our method, healthy RBCs were identified by their biconcave shape, quasi-uniform spatial distribution of their refractive indices and quasi-uniform concentration of hemoglobin. The values of these optical and biochemical parameters were found to be in agreement with the values reported in the literature. Results for the malaria-infected RBCs were significantly different from those of the healthy RBCs. The topography of the cells and their optical and biochemical parameters enabled identification of their stages of infection. This work introduces a significant method of analyzing malaria-infected RBCs at a lower cost and without the use of fluorescent labels for the parasites.

Two-Dimensional Near-Field Focusing Folded Reversely Fed Leaky-Wave Antenna Array With High Radiation Efficiency

This paper presents a 2-D near-field focusing (NFF) substrate-integrated-waveguide (SIW) leaky-wave antenna (LWA) array with high radiation efficiency. In most of the existing 2-D NFF antenna arrays, the required quadratic phase and balanced amplitude distribution are achieved by the use of the transverse topology with a complex feeding network or the simple radial topology with high polarization loss. Here, a folded reversely fed LWA with transverse polarization is proposed to achieve natural balanced radiation with a sample series-fed network. Meanwhile, the width of the single linear LWA is complementary with the reversely fed topology. In this case, the SIW with a stepped width is applied to achieve a quasi-uniform slot distribution and to avoid the spurious radiation. Then, all reversely fed linear LWAs are connected by the meander-line structure, which can simplify the feeding network and enhance the radiation efficiency. The limitation of the NFF LWA in radiation efficiency is broken. The 2-D focusing principle and the design process of the proposed antenna are presented in this paper. As an example, a 2-D focusing SIW LWA array operated at 35 GHz with an 80% radiation efficiency is fabricated and measured.

Morphology, Ordering, Stability, and Electronic Structure of Carbon‐Doped Hexagonal Boron Nitride

Theoretical studies of morphology, stability, and electronic structure of monolayer hexagonal CBN alloys with rich content of h‐BN and carbon concentration not exceeding 50% are presented. The studies are based on the bond order type of the valence force field to account for the interactions between atomic constituents and Monte Carlo method with Metropolis algorithm to establish equilibrium distribution of atoms over the lattice. It is found that the phase separation into graphene and h‐BN domains occurs in the majority of growth conditions. Only in N‐rich growth conditions, it is possible to obtain a quasi uniform distribution of carbon atoms over the boron sublattice. It is been predicted that the energy gap in stoichiometric Cx(BN)1−x alloys exhibits extremely strong bowing.

High kt2 Exceeding 6.4% Through Metal Frames in Aluminum Nitride 2-D Mode Resonators.

This work describes a new method to enhance the electromechanical coupling coefficient ( kt2 ) of 2-D mode resonators (2DMRs). This approach exploits the multimodal excitation of different Lamb waves to achieve a quasi-uniform vertical displacement distribution in the electrode regions of 2DMRs. To do so, the 2DMRs reported in this work rely on the use of metal frame structures placed at the edges of each metal strip forming the electrode gratings. To demonstrate the effectiveness of this new technique in enhancing kt2 , we report the design and simulated performance through the finite-element methods of a 2.5-GHz 2DMR using metal frames. Our analysis proves that this device can simultaneously exhibit high kt2 in excess of 6.4% and wide lithographic frequency tunability in excess of 10%, thus approaching the reported performance of aluminum nitride (AlN) film bulk acoustic resonators (FBARs) operating within the same frequency range.