Element Size Research Articles

Dual circularly polarized dual-band antenna combining transmitarray and reflectarray for K/Ka-band uplink and downlink satellite communication

This paper presents a dual-band antenna system utilizing transmitarray (TA) and reflectarray (RA) having dual-circularly polarized (CP) characteristics for K/Ka-band satellite communication. The antenna consists of the TA and RA surfaces operating at 19.5 GHz and 29.7 GHz respectively. The RA is designed on a single substrate layer with element size of 0.30 λ × 0.30 λ (λ corresponding to 30 GHz), whereas the TA is designed on two substrate layers with element size of 0.33 λ × 0.33 λ (λ corresponding to 20 GHz). The equivalent circuit model (ECM) of the TA and RA elements is extracted to validate the working of the proposed elements. A small window of the size of a patch antenna is cut in both the RA and TA surfaces to accommodate the coaxially-fed illuminating sources. The antenna shows the peak gain of 17 dBiC at 19.5 and 29.7 GHz. The 3 dB axial ratio bandwidths range from 19.3–19.6 GHz (1.55 % ) and 29.5–29.9 GHz (1.35 % ) in the two frequency bands. The antenna radiates two orthogonally polarized CP waves at two frequency bands which makes the antenna suitable for satellite communication applications.

Структурна анізотропія у виробах 3D-друку за технологією селективного лазерного плавлення

Using the Ti-6Al-4V alloy as an example, the influence of thermal conditions in 3D-printing on the anisotropy of its microstructure, phase composition, residual macrostresses, and mechanical properties during selective laser melting (SLM) is demonstrated. A fiber ytterbium laser with air cooling and a nominal power of 200 W, a laser beam diameter of ~45 µm, and a wavelength of 1070 ± 2 nm was employed, with a scanning speed of 500 mm/s, a layer thickness of 25 µm, and a hatch distance of 150 µm. It is shown that the synthesized microstructure consists of periodic scale-gradient layers with a banded structure, which results from the cyclic thermal history experienced by the SLM sample of Ti-6Al-4V, rather than from segregation or oxidation. The bands exhibit a Widmanstätten α-colony morphology with an average size of structural elements around (0.2–2) µm, while the nominal microstructure between the bands shows a basket-weave morphology. The gradient width of each band is determined by thermal effects, particularly the maximum heating temperature and cooling rate from this temperature, depending on the band’s position – whether in the lower, middle, or upper part of each layer and the distance of this layer from the substrate. The cooling rate of the deposited layer decreases as the number of added layers increases and is highest at the top plane of the SLM sample due to additional heat loss from convection and radiation, as well as the absence of remelting and thermal cycling experienced by the previous layers. As a result, the microstructure of the top plane is finer, and a greater probable amount of needle-like α'-martensite, a smaller OQR size, and a higher degree of deformation of the β-phase crystal lattice provide a higher microhardness value than in the lateral plane, despite the greater magnitude of tensile macrostresses. The obtained results convincingly demonstrate the feasibility of applying thermomechanical post-processing to ensure a homogeneous structure in SLM products.

Thresholds, Expectation Thresholds and Cloning

Let $p_\mathrm{c}$ and $q_\mathrm{c}$ be the threshold and the expectation threshold, respectively, of an increasing family $\mathcal{F}$ of subsets of a finite set $X$, and let $l$ be the size of a largest minimal element of $\mathcal{F}$. Recently, Park and Pham proved the Kahn–Kalai conjecture, which says that $p_\mathrm{c} \le K q_\mathrm{c} \log_2 l$ for some universal constant $K$. Here, we slightly strengthen their result by showing that $p_\mathrm{c} \le 1 - \mathrm{e}^{-K q_\mathrm{c} \log_2 l}$. The idea is to apply the Park-Pham Theorem to an appropriate "cloned" family $\mathcal{F}_k$, reducing the general case (of this and related results) to the case where the individual element probability $p$ is small.

Liner Damage Analysis for Hydrogen Storage Vessels Subjected to Local Compressive Loads Using the Submodeling Method

AbstractWhen a hydrogen storage vessel is subjected to a local impact load, damage may occur in the liner and result in hydrogen leakage and other catastrophic consequences. When predicting liner damage of a hydrogen storage vessel using the finite element method (FEM), although large element size is required to achieve a desired computational efficiency, it oftentimes causes inaccuracy in the damage model. To remedy this problem, in this study a novel approach which calculates the material damage based on the GISSMO (Generalized Incremental Stress State dependent damage Model) damage model and employs a submodeling strategy is proposed. According to this approach, the global model is discretized to large elements to increase the efficiency, while the submodel is meshed to much smaller elements to accurately reflect the material damage. Employing the established approach and material parameters calibrated from a large set of notched aluminum alloy 5083 specimens, the liner damage of a type III hydrogen storage vessel subjected to a local compressive load was simulated. This way, the study reveals how the characteristics of the stress and material damage interact with each other. In addition, the study also demonstrates that the proposed approach can be used as a viable means to evaluate the damage within hydrogen storage vessels.

Cytotoxicity and Antimicrobial Efficacy of Fe-, Co-, and Mn-Doped ZnO Nanoparticles.

Zinc oxide nanoparticles (ZnO NPs) are one of the most widely used nanoparticulate materials due to their antimicrobial properties. However, the current use of ZnO NPs is hindered by their potential cytotoxicity concerns, which are likely attributed to the generation of reactive oxygen species (ROS) and the dissolution of particles to ionic zinc. To reduce the cytotoxicity of ZnO NPs, transitional metals are introduced into ZnO lattices to modulate the ROS production and NP dissolution. However, the influence of the doping element, doping concentration, and particle size on the cytotoxicity and antimicrobial properties remains unexplored. This study presents a comprehensive investigation of a library of doped ZnO NPs to elucidate the relationship between their physicochemical properties, antimicrobial activity against Escherichia coli (E. coli), and cytotoxicity to mammalian cells. The library comprises 30 variants, incorporating three different dopant metals-iron, manganese, and cobalt-at concentrations of 0.25%, 1%, and 2%, and calcined at three temperatures (350 °C, 500 °C, and 600 °C), resulting in varied particle sizes. These ZnO NPs were prepared by low temperature co-precipitation followed by high-temperature calcination. Our results reveal that the choice of dopant elements significantly influences both antimicrobial efficacy and cytotoxicity, while dopant concentration and particle size have comparatively minor effects. High-throughput UV-visible spectroscopic analysis identified Mn- and Co-doped ZnO NPs as highly effective against E. coli under standard conditions. Compared with undoped ZnO particles, Mn- and Co-doping significantly increased the oxidative stress, and the Zn ion release from NPs was increased by Mn doping and reduced by Fe doping. The combined effects of these factors increased the cytotoxicity of Mn-doped ZnO particles. As a result, Co-doped ZnO particles, especially those with 2 wt.% doping, exhibited the most favourable balance between enhanced antibacterial activity and minimized cytotoxicity, making them promising candidates for antimicrobial applications.

Human-Scale Greenery in the Window View

In recent decades, the quality of life in cities has declined due to rapid growth. The global ecological crisis and climate change are leading to pollution and overheating of the environment, resulting in deteriorating health conditions and social segregation. The fact is that greenery in urban environments significantly improves people’s well-being, health, and satisfaction. The research presented in this paper was focused on the issue of greenery in residential neighborhoods, which has many positive effects in addition to the health benefits. The purpose of the article is to check whether greenery also has an artistic effect in addition to environmental benefits. In the research, the importance of greenery was highlighted by examining two residential neighborhoods in the urban environment of the city of Ljubljana, Slovenia. Elements of greenery were analyzed from the perspective of “human scale”, which refers to the size, texture, and arrangement of physical elements that correspond to human size and proportions. There were seven indicators highlighted that were used to verify the human scale: area connectivity, readability, and completeness of the ambience; transparency of tree canopies, and perception of artistic composition principles. The results show that the presence of greenery in residential neighborhoods is an important element of the human scale.

Evaluation Performance of Bloom Filter in Blockchain Network

A blockchain is a secret, scalability and decentralized p2p network in which all nodes follow similar protocols, preventing any single node from controlling the basic structure. In blockchain, Bloom filters are used to preserve the privacy of lightweight nodes. Bloom filter is a memory efficient randomized data structure to represent a set in order to support associate queries. Bloom filters offer a trade-off between (elements size in the network and bandwidth) and privacy metrics in untrusted environments. This paper proposes an analysis to evaluate the performance of Bloom filters. The evaluation results are based on the statistical distribution, standard deviation, entropy and y-deniability that are used by the attacker to analysis the leakage of the Bloom filter algorithm. Experimental results show that the degree of privacy in the network needs a large amount of elements and more bandwidth using the Bloom filter algorithm.

Structural-phase composition and mechanical properties of stainless steel – low carbon steel metal composite

The subject of the study is a metal composite obtained by electric arc surfacing in argon of corrosion–resistant steel on low-carbon steel. Powdered chromium-nickel steel was deposited with an increased content of silicon and molybdenum relative to the traditional composition. In this work, we studied the elemental and structural-phase compositions, as well as the mechanical properties of both components of the material and the composite as a whole in the initial state and after annealing at 680 °C for 3 h. The main part of the corrosion-resistant component is a two-phase auste­nitic-ferritic mixture with a ratio of 65 % HCC phase and 30 % BCC phase. The material has high microhardness (more than 4000 MPa). The highest microhardness (4550 MPa) is observed in a narrow strip of deposited metal with a width of 25 μm, where the phase composition is represented by martensite (BCC), and austenite is absent. The transition across the boundary into carbon steel is accompanied by a decrease in microhardness to 1225 MPa. Here, a decarbonized zone with a width of 180 μm was formed near the fusion line. The resulting non-equilibrium stress-strain state of the composite led to low strength, low plasticity and brittle fracture of the deposited layer during tensile testing. After annealing, microstructure of the corrosion-resistant component became more uniform in size of both austenitic and ferritic structural elements. As a result of these transformations, internal stresses decreased and microhardness decreased to 3100 MPa. At the same time, the width of the decarbonized zone in the base metal increased. All these changes led to the fact that, although the tensile stress of the annealed material increased by 8 %, and the deformation to rupture – by 27 %, however, nature of the fracture remained brittle and rupture still occurs along the deposited layer. This is determined by the austenitic-ferritic phase composition of the stainless component, which, in turn, is determined by chemical composition of the deposited material.

The Finite Element Method in Thermosetting Polymers' and FRPs' Supramolecular Structure and Thermomechanical Properties' Modeling.

The object of research is cured thermosetting epoxy polymer and FRP on the base of the same polymer matrix. The purpose of this research is to develop the finite element (FE) method in the modeling of cured thermosetting polymers and FRPs to predict their mechanical and thermal properties. The structural mathematical modeling with subsequent computer FE modeling was performed. The results of FE modeling were compared with the experimental data of cured polymer's and FRP's tensile strength and deformations under mechanical load at different temperatures. The design of the polymer's FE model was based on the tetrahedral supramolecular structure and then transformed into FRP's model by integrating glass fiber rods. Using the structural density as the structure model's parameter, the relative size and disposition of the finite elements were determined. The viscoelastic properties are set in the model by regulating the structural density and compressive/tensile properties of joints. The long-term plastic deformation and stress relaxation were determined as the result of the supramolecular structure's inner shearing with the decrease of its structural density. The FE models of the cured epoxy polymer and FRP were developed, making it possible to predict short-term and long-term deformations under load with high accuracy considering the temperature factor.

Damage and Failure Modeling of Composite Material Structures Using the Pam-Crash Code

Simulating composite material structures requires complex constitutive models, which normally require fine meshes to obtain an accurate prediction of their behavior. Pam-Crash software has been used for several years in the automotive industry and has been proved to be an efficient tool for simulating metallic structures, returning good correlations in a fast computational time. However, constitutive models for composite materials in Pam-Crash present some difficulties: some materials are not able to be suitably modeled and the predictive results depend on the mesh refinement. This work proposes a solution for predicting the progressive damage of composite materials in Pam-Crash, which scales the energy dissipated by the damage mechanisms and checks the viability of modeling the material behavior, taking into account the recommended size of finite elements in the automotive industry. The proposed solution is applied for the simulation of Open Hole specimens to evaluate the ultimate strength consistency. After this, it is applied for the simulation of Compact Tension specimens to check the consistency of crack propagation behavior. By considering the target size of the finite elements in the material card definition, the predictions demonstrate great improvement in the equivalence in results between different mesh refinements. Finally, the solution is applied to simulate impact tests on large structures. Good correlations with experimental data are obtained in fast computational times, making this methodology a candidate for application in composite-related automotive simulations.

Signature of viral fossils: a comparative genomics approach to understand the diversity of endogenous retroviruses in bats

Endogenous retroviruses (ERVs) are traces of past viral infections commonly found in vertebrate genomes. Many ERVs are tightly regulated by the host genomes and co-opted for various functions within the hosts. Bats are the only true volant mammals, with the smallest mammalian genomes and a high fraction of ERVs within the genomes. They are important hosts for various zoonotic viral pathogens and can effectively modulate their immune response to tolerate viral infections. Integrations of retroviruses have been implicated as one of the mechanisms by which bats have co-evolved strategies to combat viral infections. In this study, we investigated the diversity of ERVs in over 40 publicly available bat genomes to understand the distribution and the evolution of ERVs within bats. We observed all classes of ERVs within bat genomes including even the complex lenti retroviruses. Alpha and spuma retroviruses which are generally considered rare in mammals, were common within bats. We observed a positive correlation between bat genome size and length of ERV elements. Interestingly, nearly 30 % of the ERVs within bats are intact suggesting a recent origin or co-option by the host genome. Future studies focusing on comparative genomic and experimental data will be critical to understand the role of these ERVs in host genome evolution.

Relationship between void characteristics and re-liquefaction resistance: An image analysis study

To scrutinize the impact of void characteristics on re-liquefaction resistance, a series of constant-volume cyclic bi-axial tests was conducted on an assembly of plastic rods. The first and second liquefaction stages involved the application of isotropic compression at 100 kPa followed by constant-volume cyclic loading with the deviator stress set at 30 or 60 kPa. This study introduced an innovative image analysis method to quantify four void characteristics: anisotropy index (Ie) and average void element size (Ae) for the element-based analysis, and local anisotropy index (Ie,ij) and local void ratio (eij) for the grid-based analysis. The newly developed anisotropy index was seen to facilitate the assessment of the primary alignment and degree of anisotropy in void elements. The results confirmed that an increase in re-liquefaction resistance is evident in specimens with lower average eij, coefficient of variation (CV) of eij, and Ie, indicating denser, more homogeneous, and isotropic conditions. Nevertheless, specimens with a greater degree of anisotropy were found to be more susceptible to re-liquefaction. The development of strain in the early stages of cyclic loading was found to be predominantly influenced by the anisotropy index, underscoring the imperative need for an enhanced method that can predict liquefaction resistance, as well as re-liquefaction resistance, and incorporates the anisotropy index.

Large angle and high uniform diffractive laser beam splitter with divergent spherical wave illumination

Splitting angle, generally limited by the feature size of diffractive optical element (DOE), is one of the significant metrics of the diffractive laser beam splitter. In this study, we realize large angle and high uniform split beams by using a divergent spherical wave front incidence. For designing this diffractive beam splitter, the Gerchberg-Saxton (GS) optimization algorithm which is known as a widely used method in DOE design is modified. Meanwhile, a negative feedback method is proposed to further improve the uniformity in experiment to compensate the incident wavefront distortion. Finally, a phase-only spatial light modulator (SLM) was used to test the feasibility and adaptiveness of our design strategy. In the experiment, we achieved several kinds of beam splitters and the uniformities are all better than 3.0% which the uniformity is measured by the peak-to-valley (PV) ratio.

Diffusive-length-scale adjustable phase field fracture model for large/small structures

In phase field fracture (PFF) method, the sharp crack is approximated by a phase field crack zone whose size is characterized by a diffusive length scale. Recently, the diffusive length scale is usually regarded as a constant material parameter determined by the fracture toughness, material strength, and young's modulus. As a result, the application of the PFF method poses challenges when dealing with structures whose sizes are much too large or small compared to the constant diffusive length scale. In details, for a large-scale structure, a significant computational burden is inevitable due to the limitation imposed by the constant diffusive crack length scale on the element size (i.e. the element size is generally at least smaller than half of the diffusive crack length scale to achieve the sufficient precision for the phase field process zone). For a small-scale structure, the crack patterns tend to be unclear and unrealistic due to the excessively large diffusive crack zone. To address these limitations, we propose a novel PFF method to make the relation between the diffusive length scale and the material parameters adjustable via modifying the energetic degradation functions. It is found that with the increase of the diffusive crack length scale, a transition from quasi-brittleness to brittleness is observed in the constitutive relationship curves, which coincides with the classical size effect on structural strength. Further, the Bažant's size effect in classical fracture mechanics can be reproduced by the present PFF method through scaling the size of a geometrically similar structure, i.e. a large-scale structure exhibits toughness-dominated fracture while a small-scale structure behavior strength-dominated fracture. The present PFF method efficiently addresses the mismatch of diffusive length scales for various material constituents by examining phase field crack growth in particle-reinforced composite plates. By adjusting the diffusive crack length scale based on structure size, it avoids high computational costs from large structures and unrealistic crack patterns from small ones. Moreover, it outperforms traditional PFF methods using a constant diffusive length scale in handling composite materials.

Ecosystem of game animals is the economic and mathematical model for optimizing the size and structure of game animal populations in the ecosystem

Methodology of economic and mathematical modeling involves the formation of a system from subsystems and elements united by logical relationships. The size and structure of subsystems and elements can be optimized in the system for diff erent optimality criteria. According to this algorithm, mathematical models of ecosystems with diff erent content bases are formed. Biological subsystems and elements can serve as a basis for an ecosystem that is solved for economic optimality criteria, or economic indicators can act as relationships in the ecosystem. In this way, the content base of the mathematical model is represented by biological subsystems and elements, and the optimality criteria are formed on the basis of economic indicators. This process is refl ected in the economic and mathematical model of a specifi c ecosystem. An original economic and mathematical model (EMM) for optimizing the size and structure of game animal populations in a given ecosystem has been proposed in the paper. The presented EMM is based on optimizing the size and structure of populations of both predators and preys in hunting areas, taking into account the boundaries of their range. The EMM “Ecosystem of Game Animals” is based on the EMM “Predator-Prey” and has a block-diagonal structure, where the main blocks are the “Prey” and “Predator” blocks, and the feeding and habitat blocks of game animals act as connecting ones. The optimality criteria of the EMM “Ecosystem of Game Animals” can be expressed by objective functions that implement diff erent scenarios for the implementation of the model. The described model allows us to create a mathematical representation of the ecosystem and study the biological characteristics of game animal populations, which ultimately contributes to more rational resource management in the hunting areas of our country.

Modal analysis of concrete gravity dam incorporating pre-stress condition along with soil–structure interaction

Purpose The fundamental period of the structure plays an important role in the seismic analysis. This study aims to analyze the modal response of dam, the two-dimensional (2D) FEM model is developed by using ANSYS 2022 R1 software. Design/methodology/approach To examine the optimized mesh size to achieve grid independence, the variable element size has been considered, and its optimal value is calculated using the technique of response surface optimization. Further, the effect of damping ratios of 5%, 8% and 10% is also considered for the free vibration analysis of the dam structure. Findings The results show that the natural frequencies of the dam decrease with a reduction in stiffness of the whole structure. Further, the effect of pre-stress conditions is analyzed and the study has proved that the natural frequency increases after considering the pre-stress as initial condition during modal analysis. Further, it is found that the damping has a substantial effect on frequency for higher modes of vibrations. Research limitations/implications The study only focused on modal analysis of the gravity dam, and this study’s results can be used further to evaluate the dynamic behavior of the dam including hydrodynamic conditions. Originality/value The finite element tool is used to evaluate the modal response of gravity dam incorporating pre-stress and damping ratio along with soil–structure interaction. Moreover, to the best of the authors’ knowledge, no earlier study has been conducted to evaluate the effect of damping and pre-stress conditions on the stability and natural frequency of the system.

Relaxing strong compatibility at atomistic-continuum interface: Consistent linear coupling method

In this paper, we develop a brand-new coupling method called consistent linear coupling (CLC) with a view to resolving the difficulty of scaling down of the interface elements in the strong compatibility coupling (SCC), employed in the most accurate multiscale methods such as quasicontinuum. To this end, the CLC determines some conditions required to be satisfied to reproduce the SCC rigorously, regardless of the size of the interface elements. Therefore, it can produce a solution as accurate as the SCC with two additional features: significantly less computational cost and easier implementation. The CLC-based schemes are compared with well-known coupling methods including the SCC in terms of solving quasi-static 3D nanoscale contact and a 2D crystal under uniaxial tension. Numerical results demonstrate the superiority of the CLC with regard to the accuracy and computational efficiency.

Bayesian mesh optimization for graph neural networks to enhance engineering performance prediction

Abstract In engineering design, surrogate models are widely employed to reduce the computational costs of simulations by approximating design variables and geometric parameters from computer-aided design (CAD) models. However, traditional surrogate models often lose critical information when simplified to lower dimensions, and face challenges in handling the complexity of 3D shapes, especially in industrial datasets. To address these limitations, we propose a Bayesian graph neural network (GNN) framework that directly learns geometric features from CAD mesh representations for accurate engineering performance prediction. Our framework leverages Bayesian optimization (BO) to dynamically determine the optimal mesh element size, significantly improving model accuracy while balancing computational efficiency. This approach addresses the challenge of mesh quality by optimizing mesh resolution, ensuring that critical geometric features are preserved in 3D deep-learning-based surrogate models. Unlike existing models that rely on static or predefined mesh resolutions, our method adapts mesh size based on the task, making it highly flexible for a wide range of engineering applications. Experimental results demonstrate that mesh quality directly impacts prediction accuracy, and the proposed BO-EI GNN model outperforms state-of-the-art models such as 3D CNN, SubdivNet, GCN, and GNN in predicting mass, rim stiffness, and disk stiffness. Our method also significantly reduces the computational costs compared to traditional optimization techniques. The proposed framework shows promising potential for application in finite element analysis (FEA) and other mesh-based simulations, enhancing the utility of surrogate models across various engineering fields.

Predictive modeling for hat-stiffener delamination during low velocity impact

Barely visible impact damage poses a significant threat to composite structures, particularly prevalent in the aerospace industry. The occurrence of low velocity impact (LVI) events can lead to substantial deformations in composite structures, causing interlaminar delamination and diminishing their compression load carrying capacity. Beyond LVI-induced interlaminar delamination, it is crucial to investigate failures occurring between co-cured composite structures. This study focuses on hat-stiffened coupon structures, to investigate the delaminating phenomenon between the hat and skin components. The outcomes of experimental results inform the development of a finite element model, enabling to capture the structural response and delamination dynamics. The primary objective of the experiments is to understand the delamination process which occurs suddenly upon impact. LVI experiments are conducted to understand the structural behavior at varied impact locations. A mesh study establishes the relationship between cohesive parameters and element size in the model to enable computational efficiency by avoiding the need for a highly refined mesh. When the mesh is relatively coarse, the finite element model’s capability to resolve stresses at near singular locations is limited, however the computational time is lower. Therefore, the balance between computational efficiency on the one hand, and resolving gradients on the other, requires a fine balance in order to carry out a large number of design iterations efficiently. This research significantly contributes to advancing our understanding of delamination mechanisms at free edges in composite structures, offering valuable insights for computational modeling.

A combined approach for comprehensive explanation of defects' thermodynamics in highly non-stoichiometric oxides: Case of RBaCo2O6-δ family (R = La, Nd, Pr, Sm, Gd, Eu, Ho and Y)

The thermodynamics of defect formation in layered perovskite-like cobaltites RBaCo2O6-δ (R = La, Nd, Pr, Sm, Gd, Eu, Ho and Y) was investigated via two distinct methods – (I) processing experimental data on oxygen non-stoichiometry using a quasichemical model and (II) employing a combined approach within the framework of density functional theory (DFT) under general gradient (GGA) and quasiharmonic Debye (QHDA) approximations. The outcomes of the first-principles calculations exhibit a plausible agreement with the fitting results, thereby confirming the validity of the developed model. The study reveals that key thermodynamic parameters governing defect formation, such as the enthalpy and entropy of oxygen exchange, as well as the enthalpy of oxygen disordering over nonequivalent crystallographic positions, exhibit correlations with the size of the rare-earth element R. In contrast, the enthalpy of charge disproportionation is demonstrated to be independent of the nature of the R atom. In Addition, it is suggested that when R = Eu, partial reduction of the latter may be observed in the lattice of EuBaCo2O6-δ. The findings indicate that, at a first approximation, the parameters of defect formation in RBaCo2O6-δ remain relatively independent on temperature and oxygen non-stoichiometry δ. The employed combined approach has been demonstrated to be reliable for assessing the thermodynamic functions of defect formation at elevated temperatures.