Isotropic Pattern Research Articles

Protein Orientation and Polymer Phase Separation Induced by Poly(methyl methacrylate) Tacticity.

Stereochemistry may affect the physicochemical and biological properties of polymer films that are important for their applications, including substrates for the fabrication of protein microarrays. In this study, we investigated the effect of poly(methyl methacrylate) (PMMA) tacticity on the interaction of polymer thin films with proteins and on the phase separation process in blends with poly(tert-butyl methacrylate) (PtBMA). Thin films of isotactic, atactic, and syndiotactic PMMA were studied for topography, surface chemistry, and protein adsorption. Secondary ion mass spectrometry and contact angle measurements revealed a lower surface exposure of polar ester functional groups for iso-PMMA, resulting in the reduced adsorption of albumin and fibrinogen proteins. We also showed that changes in surface chemistry alter the orientation of proteins adsorbed on iso-PMMA through hydrophobic and electrostatic interactions. In addition, blends composed of PMMA and PtBMA, both of different tacticities, were investigated in terms of protein microarray fabrication. The two-dimensional domain structure was obtained by a phase separation process for at-PtBMA blends prepared on silicon substrates modified with amino-silane. Finally, for an isotropic and regular polymer pattern of iso-PMMA/at-PtBMA, the possibility of protein microarray formation on this blend was demonstrated, showing selective adsorption to PtBMA domains and perfect mirroring of the polymer patterns.

A sidelobe level control algorithm for wide-beam power gain pattern synthesis via array antenna

The paper tries to maximize the minimum power gain in a wide-beam mainlobe with a controllable peak sidelobe level (PSLL) by solving the power gain pattern synthesis (PGPS) problem. Since the PGPS problem is nonconvex, it cannot be solved effectively in polynomial time. In this paper, the nonconvex PGPS problem is simplified by converting it into two nonconvex subproblems. The first subproblem's solution space is divided into a finite set of smaller spaces in which the solution has a closed-form, resulting in the subproblem being pseudo-analytically solvable. The second subproblem's solution can be rapidly obtained with a bisection searching strategy. In such a way, the original problem can be solved effectively by iteratively solving these two subproblems. Another advantage of the proposed algorithm is that its convergence is theoretically guaranteed and the PSLL is strictly controllable. Numerical examples with both isotropic element pattern (IEP) array and active element pattern (AEP) array are simulated to validate the effectiveness and superiority of the proposed algorithm by comparing it with the existing algorithms.

Exploring the connection between AGN radiative feedback and massive black hole spin

We present a novel implementation for active galactic nucleus (AGN) feedback through ultrafast winds in the code GIZMO. Our feedback recipe accounts for the angular dependence of radiative feedback on black hole spin. We self-consistently evolve in time (i) the gas-accretion process from resolved scales to a smaller scale unresolved (subgrid) AGN disk, (ii) the evolution of the spin of the massive black hole (MBH), (iii) the injection of AGN-driven winds into the resolved scales, and (iv) the spin-induced anisotropy of the overall feedback process. We tested our implementation by following the propagation of the wind-driven outflow into an homogeneous medium, and here we present a comparison of the results against simple analytical models. We also considered an isolated galaxy setup, where the galaxy is thought to be formed from the collapse of a spinning gaseous halo, and there we studied the impact of the AGN feedback on the evolution of the MBH and of the host galaxy. We find that: (i) AGN feedback limits the gas inflow that powers the MBH, with a consequent weak impact on the host galaxy characterized by a suppression of star formation by about a factor of two in the nuclear (≲kpc) region; (ii) the impact of AGN feedback on the host galaxy and on MBH growth is primarily determined by the AGN luminosity rather than by its angular pattern set by the MBH spin (i.e., more luminous AGNs more efficiently suppress central star formation (SF), clearing wider central cavities and driving outflows with larger semiopening angles); (iii) the imprint of the angular pattern of AGN radiation emission is detected more clearly at high (i.e., Eddington) accretion rates. At such high rates, the more isotropic angular patterns, as occur for high spin values, sweep away gas in the nuclear region more easily, therefore causing a slower MBH mass and spin growths and a higher quenching of SF. We argue that the influence of spin-dependent anisotropy of AGN feedback on MBH and galaxy evolution is likely to be relevant in those scenarios characterized by high and prolonged MBH accretion episodes and by high AGN wind–galaxy coupling. Such conditions are more frequently met in galaxy mergers and/or high-redshift galaxies.

Diffusion dynamics of an overdamped active ellipsoidal Brownian particle in two dimensions

Shape asymmetry is the most abundant in nature and has attracted considerable interest in recent research. The phenomenon is widely recognized: a free ellipsoidal Brownian particle displays anisotropic diffusion during short time intervals, which subsequently transitions to an isotropic diffusion pattern over longer timescales. We have further expanded this concept to incorporate active ellipsoidal particles characterized by an initial self-propelled velocity. This paper provides analytical and simulation results of diffusion dynamics of an active ellipsoidal particle. The active ellipsoidal particle manifests three distinct regimes in its diffusion dynamics over time. In the transient regime, it displays diffusive behavior followed by a super-diffusive phase, and in the longer time duration, it transitions to purely diffusive dynamics. We investigated the diffusion dynamics of a free particle as well as a particle in a harmonic trap, and a particle subject to a constant field force. Moreover, we have studied the rotational diffusion dynamics and torque production resulting from an external constant force field. Furthermore, our investigation extends to the examination of the scaled average velocity of an ellipsoidal active particle, considering both a constant force field and a one-dimensional ratchet.

Design of a Compact Log Periodic Dipole Array Antenna for Broadband and High-Power Beam Synthesis Using Superposition

This paper investigates various array beam shapes for high-power electronic warfare applications using an actual broadband array antenna. For use in a limited mounting space, a compact printed log periodic dipole array (LPDA) operating over a wide bandwidth is designed. The LPDA is then extended to an 8 × 1 array, with active element patterns (AEPs) obtained through simulation and measurement. Beam synthesis is performed by the superposition of several array patterns, which involves adjusting the weight of each AEP. To derive a synthesized array beam shape that is similar to the guided mask, the Taylor window weighting method is applied to each array pattern. Finally, beam synthesis for the flat-top beam, cosecant-squared beam, and iso-flux beam is performed using Taylor window-weighted AEPs, and the results are compared with those of beam shapes using ideal isotropic patterns. The results demonstrate that various beam shapes can be achieved for high-power electronic warfare applications using the AEPs of an actual array antenna.

Research on Quasi-isotropic Radiation of Small Circular Arc Antenna

The radiation characteristics of circular arc antennas are studied by applying the method of moments (MoM) to solve the electric field integral equation (EFIE). Based on the triangular current distribution of small circular arc antennas, the analytical expression of radiation fields of circular arc antennas is derived. It is found that the circular arc antenna is equivalent to a superposition of an electric dipole and a magnetic dipole, resulting in near isotropic radiation pattern. Finally, both MoM and CST simulations show that the small arc antenna can realize the near isotropic radiation pattern.

Elasticity tunes mechanical stress localization around active topological defects.

Mechanical stresses are increasingly found to be associated with various biological functionalities. At the same time, topological defects are being identified across a diverse range of biological systems and are points of localized mechanical stress. It is therefore important to ask how mechanical stress localization around topological defects is controlled. Here, we use continuum simulations of nonequilibrium, fluctuating and active nematics to explore the patterns of stress localization, as well as their extent and intensity around topological defects. We find that by increasing the orientational elasticity of the material, the isotropic stress pattern around topological defects is changed substantially, from a stress dipole characterized by symmetric compression-tension regions around the core of the defect, to a localized stress monopole at the defect position. Moreover, we show that elastic anisotropy alters the extent and intensity of the stresses, and can result in the dominance of tension or compression around defects. Finally, including both nonequilibrium fluctuations and active stress generation, we find that the elastic constant tunes the relative effect of each, leading to the flipping of tension and compression regions around topological defects. This flipping of the tension-compression regions only by changing the elastic constant presents an interesting, simple, way of switching the dynamic behavior in active matter by changing a passive material property. We expect these findings to motivate further exploration tuning stresses in active biological materials by varying material properties of the constituent units.

Efficient three-dimensional (3D) human bone differentiation on quercetin-functionalized isotropic nano-architecture chitinous patterns of cockroach wings

Developing cost-effective, biocompatible scaffolds with nano-structured surface that truthfully replicate the physico-(bio)chemical and structural properties of bone tissue's extracellular matrix (ECM) is still challenging. In this regard, surface functionalization of natural scaffolds to enhance capability of mimicking 3D niches of the bone tissue has been suggested as a solution. In the current study, we aimed to investigate the potential of chitin-based cockroach wings (CW) as a natural scaffold for bone tissue engineering. To raise the osteogenic differentiation capacity of such a scaffold, a quercetin coating was also applied (hereafter this scaffold is referred as QCW). Moreover, the QCW scaffold exhibited effective antibacterial properties against gram-positive S. aureus bacteria. With respect to bone regeneration, the QCW scaffold optimally induced the differentiation of adipose-derived human mesenchymal stem cells (AD-hMSCs) into osteoblasts, as validated by mineralization assays, alkaline phosphatase (ALP) activity measurements, expression of pre-osteocyte marker genes, and immunocytochemical staining. Confirmation of the potent biocompatibility and physicochemical characteristics of the QCW scaffold through a series of in vitro and in vivo analysis revealed that surface modification had significant effect on multi-purpose features of obtained scaffold. Altogether, surface modification of QCW made it as an affordable bioinspired scaffold for bone tissue engineering.

Broken Inversion Symmetry in Van Der Waals Topological Ferromagnetic Metal Iron Germanium Telluride.

Inversion symmetry breaking is critical for many quantum effects and fundamental for spin-orbit torque, which is crucial for next-generation spintronics. Recently, a novel type of gigantic intrinsic spin-orbit torque is established in the topological van der Waals(vdW) magnet iron germanium telluride. However, it remains a puzzle because no clear evidence exists for interlayer inversion symmetry breaking. Here, the definitive evidence of broken inversion symmetry in iron germanium telluride directly measured by the second harmonic generation (SHG) technique is reported. The data show that the crystal symmetry reduces from centrosymmetric P63/mmc to noncentrosymmetric polar P3m1 space group, giving the threefold SHG pattern with dominant out-of-plane polarization. Additionally, the SHG response evolves from an isotropic pattern to a sharp threefold symmetry upon increasing Fe deficiency, mainly due to the transition from random defects to ordered Fe vacancies. Such SHG response is robust against temperature, ensuring unaltered crystalline symmetries above and below the ferromagnetic transition temperature. These findings add crucial new information to the understanding of this interesting vdW metal, iron germanium telluride: band topology, intrinsic spin-orbit torque, and topological vdW polar metal states.

Measurements of multijet event isotropies using optimal transport with the ATLAS detector

A measurement of novel event shapes quantifying the isotropy of collider events is performed in 140 fb−1 of proton-proton collisions with s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV centre-of-mass energy recorded with the ATLAS detector at CERN’s Large Hadron Collider. These event shapes are defined as the Wasserstein distance between collider events and isotropic reference geometries. This distance is evaluated by solving optimal transport problems, using the ‘Energy-Mover’s Distance’. Isotropic references with cylindrical and circular symmetries are studied, to probe the symmetries of interest at hadron colliders. The novel event-shape observables defined in this way are infrared- and collinear-safe, have improved dynamic range and have greater sensitivity to isotropic radiation patterns than other event shapes. The measured event-shape variables are corrected for detector effects, and presented in inclusive bins of jet multiplicity and the scalar sum of the two leading jets’ transverse momenta. The measured distributions are provided as inputs to future Monte Carlo tuning campaigns and other studies probing fundamental properties of QCD and the production of hadronic final states up to the TeV-scale.

Machine learning approach for the prediction of mixed lubrication parameters for different surface topographies of non-conformal rough contacts

PurposeThis study aims to use a machine learning (ML) model for the prediction of traction coefficient and asperity load ratio for different surface topographies of non-conformal rough contacts.Design/methodology/approachThe input data set for the ML model is generated using a mixed-lubrication model. Surface topography parameters (skewness, kurtosis and pattern ratio), rolling speed and hardness are used as input features in the multi-layer perceptron (MLP) model. The hyperparameter tuning and fivefold cross-validation are also performed to minimize the overfitting.FindingsFrom the results, it is shown that the MLP model shows excellent accuracy (R2 > 90%) on the test data set for making the prediction of mixed lubrication parameters. It is also observed that engineered rough surfaces with high negative skewness, low kurtosis and isotropic surface patterns exhibit a significant low traction coefficient. It is also concluded that the MLP model gives better accuracy in comparison to the random forest regression model based on the training and testing data sets.Originality/valueMixed lubrication parameters are predicted by developing a regression-based MLP model. The machine learning model is trained using several topography parameters, which are vital in the mixed-EHL regime because of the lack of regression-fit expressions in previous works. The accuracy of MLP with random forest models is also compared.

Maximum angular multiscale entropy: Characterization of the angular self-similarity patterns in two types of SAR images: Oil spills and low-wind conditions images

The characterization of irregular patterns in images has become a focal point in numerous studies due to its relevance in various applications. In particular, images depicting natural phenomena exhibit intricate patterns with unique irregularities, such as self-similarity and scaling. The classification of these phenomena based on their patterns has been an ongoing endeavor within the field of complex systems. However, existing techniques for characterizing these complex phenomena typically assume isotropic variability patterns, which is not always feasible. To address these limitations, this paper introduces a novel algorithm, called the maximum angular multiscale entropy (MAMSE), based on the multiscale entropy method. The MAMSE algorithm overcomes the challenges posed by anisotropic fractal properties and is tested on synthetic images featuring both isotropic irregularities and anisotropic fractal properties. The experimental results reveal a new concept of angular self-similarity enabled by MAMSE, which proves instrumental in effectively distinguishing between groups of oil spill and low-wind conditions images. Comparative analysis with the two-dimensional multiscalar entropy algorithm demonstrates the superior performance and efficiency of MAMSE, yielding better and faster results.

A numerical study on the impact of lubricant rheology and surface topography on heavily loaded non-conformal contacts

The increasing requirement of high-power density (power throughput/ weight) in modern day machines lead to thin film lubrication condition in various machine components (rolling element bearings, gears, cams, etc,) due to severe loading conditions. Surface roughness features and lubricant rheology plays a vital role in thin film lubrication, and significantly affects the lubrication performance and lifetime of machine components. The present work demonstrates surface topography and lubricant rheology effects on the traction coefficient for heavily loaded non-conformal contacts. The load-sharing concept considering elastic-plastic deformation of asperities, and Carreau shear-thinning rheological model is employed to describe the dry rough contacts and non-Newtonian behavior of lubricant. An influence of surface topography parameters such as roughness, skewness, kurtosis, and pattern ratio on the traction coefficient is discussed. From results, it is found that among different surface topographies, negatively skewed surfaces having isotropic surface pattern exhibit minimum traction coefficient. The load share function and the critical rolling speed are determined for various surface topographies which provides further insights into the surface topography effect on traction coefficient. The findings of present study are noteworthy as they provide a theoretical basis for an assessment of the lubrication performance of heavily loaded non-conformal contacts.

The Big Bang could be anisotropic. The case of Bianchi I model

We consider an evolution of anisotropic cosmological model on the example of the Bianchi type I homogeneous Universe. It is filled by the mixture of matter and dark energy with an arbitrary barotropic equation of state (EoS). The general solution for this case is found and analyzed. A complete list of possible future singularities for this model is given. Some new solution were obtained for a particular EoSs, e.g. for the Bianchi type I ΛCDM homogeneous model. It is shown that all special cases corresponding to different EoSs have common properties, provided that now or at another moment of time the Universe is expanding, and the density of the mixture is positive. Then the evolution always begins with an anisotropic ‘Big Bang’ which happened a finite time ago. After that the Universe is constantly expanding and in all cases, with rare exceptions, becomes more isotropic. A particularly strong isotropization is associated with the epoch of inflation. After its completion, the expansion of the Universe becomes almost isotropic, and this case cannot be distinguished from isotropic by astronomical observations. This fact allows us to consider an anisotropic cosmological model as a possible candidate for the description of the observed Universe despite the isotropic pattern of expansion.

Fabrication and analysis of micro carbon fiber filled nylon filament reinforced with Kevlar, Fiberglass, and HSHT Fiberglass using dual extrusion system

The optimal composition of Fiberglass, Kevlar, and high speed high temperature fiberglass (HSHT) in micro carbon fiber filled nylon polymer enhances properties like strength, wear resistance, and surface finish. Thus, the polymer composite fabricated by mixing Fiberglass, Kevlar, and HSHT in micro carbon fiber filled nylon filament designed to create strong, high-quality unrivalled parts will be extensively used in aerospace, automotive industry, and various engineering applications. In this work, continuous layers of Fiberglass, Kevlar, and HSHT have been reinforced in micro carbon fiber filled nylon filament to fabricate the composite at variable process parameters like fiberfill type, the thickness of the fiber layer, and the nature of the reinforcement. The tensile strength, wear strength, and surface roughness have been investigated for each test specimen using Universal Testing Machine, Pin on disc, and surfcom roughness tester as per American standards of testing (ASTM) ASTM D638 Type IV and ASTM G99 standard. Response surface methodology (RSM) has been implemented using a central composite design (CCD) approach for the modelling between input parameters and output responses. It is observed that fiber layer thickness of 1.071 mm, fiberglass and isotropic fill pattern provide the maximum tensile strength of 139 MPa, the minimum surface roughness of 3.087 µm, and wear rate of 0.4262 mm3/m. Further, the MOGA-ANN approach is used to optimize the multi response objectives. It is observed that 0.744 mm of fiber layer thickness, fiberglass reinforcement, and isotropic infill pattern provide the maximum tensile strength of 152.80 MPa and minimum surface roughness of 2.83 µm, 0.11709 mm3/m wear rate in MOGA-ANN. The balance and optimal response are accomplished in MOGA-ANN evolutionary hybrid algorithm, and the same has been validated experimentally. Data availability statementData used for this research paper is available upon request from the corresponding author. Data are provided in detail for all methods, results, and conclusions drawn throughout the paper.

Single-Feed Planar Multiband Quasi-Isotropic Antennas Through Collocating and Co-Design Approaches

This article presents single-feed planar multiband quasi-isotropic antennas through collocating and co-design approaches. The antenna element is a modified dipole with an inclined central part, whose effects are anticipated at the design stage. The concept is implemented on a dual-band quasi-isotropic antenna, fabricated, and verified experimentally with good correlation with simulations. The fabricated prototype covers the frequency bands of 815–1095 (280 MHz, 29.31%) and 1650–2090 MHz (440 MHz, 23.52%), with gain variations of 7.7 and 10.1 dB at 940 and 1800 MHz, respectively. The corresponding peak gains are near 1.7 and 1.2 dBi, with 90%–95% and 63%–93% efficiencies. The present design features are planar shape, single feed, wide impedance bandwidths, good isotropic patterns, and scalability to more isotropic bands. These options make the fabricated prototype suitable for most wireless applications, particularly for optimally collecting the ambient radio frequency (RF) power from any direction and frequency using a planar harvester.

Phase separation kinetics of binary mixture in the influence of bond disorder: sensitivity to quench temperature

ABSTRACT Morphologies in phase-separating systems can significantly influence final material properties. We present extensive Monte Carlo simulation results on segregation kinetics of critical binary mixture (-Ising system) with a fraction of bond disorder introduced regularly. The effect of various quench temperatures is studied on growth kinetics and scaling properties of evolved morphologies. The morphology changes from their usual bicontinuous isotropic patterns at zero disorder to short strips and lamellar patterns (anisotropy) with the increasing disorder at shallow quench depth. The domain evolution at lower disorder remains at a transient growth regime for deep quench; however, the lamellar pattern is observed at high disorder for the same quench depth. The scaling behavior changes significantly with quench depths at the higher fraction of disorder. Though, a tiny deviation is observed at lower disorder fractions for shallow quench depths. The length scale freezes () to finite size at the higher disorder asymptotically.

Numerical and Experimental Study of Elastohydrodynamic Grease Lubrication of Surfaces with Longitudinal and Transverse Pattern

The interaction of non-Newtonian grease with patterned surfaces was considered as a promising approach to find an effective method for reducing friction and wear in rolling contacts. Longitudinal and transverse patterns can retain the lubricant in the contact area and prevent it from escaping under high loads. In this paper, a model has been developed for grease elastohydrodynamic lubrication of surfaces with different patterns to estimate the lubrication parameters such as lubricant film thickness, pressure distribution, and viscous friction. Then several experimental tests are rolled out for different loads, velocities, and surface patterns. Because the friction model estimates only viscous friction, a correlation is recommended for considering the friction due to asperity interaction. This relation is based on average lubricant film thickness results which are calculated from the model. The calculated friction and experimental results have a good agreement. According to the experimental tests, transverse, longitudinal, and isotropic pattern had a lower friction coefficient, respectively. While the isotropic viscous friction coefficient estimated by the model is lower than others. Higher loads and lower velocities cause a higher friction coefficient in all surface patterns.

A Novel Miniaturized Isotropic Patch Antenna for X -Band Radar Applications Using Split Ring Resonators

A new circular patch antenna with a novel metamaterial structure that achieves high bandwidth and positive gain across the operating band. The proposed antenna was Designed by incorporating three split ring resonators into the patch and fabricating it with 15 ×10 ×1.6 mm3. The use of a metamaterial structure with negative permittivity and permeability reduced mutual coupling in a wideband antenna. The designed antenna shows the isotropic nature at 9.71 GHz in the operating band from 8.80 to 12.89 GHz for X band applications specifically for detecting objects using radars. The optimetrics technique analyzed impedance matching with a good return loss of -30 dB. In comparison to previous works, miniaturization achieved up to 81.94%. The efficiency of 95.6% and isotropic pattern were also achieved at 9.71 GHz using HFSS020R2.

A Miniaturized Arc Shaped Near Isotropic Self-Complementary Antenna for Spectrum Sensing Applications

This paper presents the design of an arc-shaped near-isotropic self-complementary antenna for spectrum sensing application. An arc-shaped dipole with horizontal and vertical arms is used to achieve a near isotropic radiation pattern. The radiation pattern improved by adjusting the horizontal and vertical arm lengths. Simulated and experimental results show that the proposed antenna has an impedance bandwidth of 146% (2.4-18.4 GHz) for VSWR ≤ 2 with a good radiation pattern. In order to quantify the antenna performance, antenna gain variation, bandwidth, efficiency, and size have been compared with previously reported designs. It is shown that the proposed arc-shaped antenna can achieve nearly isotropic radiation patterns with a maximum radiation efficiency of 92%. The isotropic performance of the antenna has been characterized by observing the radiation pattern and solid angle. The FR4 substrate is used as a dielectric with relative permittivity 4.4 and loss tangent of 0.02. (εr = 4.4, h = 1.6 mm) The simulated and measured results are in good comparison, and the proposed design is a suitable candidate for spectrum sensing.