Hexagonal Unit Research Articles

Imaging of Antiferroelectric Dark Modes in an Inverted Plasmonic Lattice.

Plasmonic lattice nanostructures are of technological interest because of their capacity to manipulate light below the diffraction limit. Here, we present a detailed study of dark and bright modes in the visible and near-infrared energy regime of an inverted plasmonic honeycomb lattice by a combination of Au+ focused ion beam lithography with nanometric resolution, optical and electron spectroscopy, and finite-difference time-domain simulations. The lattice consists of slits carved in a gold thin film, exhibiting hotspots and a set of bright and dark modes. We proposed that some of the dark modes detected by electron energy-loss spectroscopy are caused by antiferroelectric arrangements of the slit polarizations with two times the size of the hexagonal unit cell. The plasmonic resonances take place within the 0.5-2 eV energy range, indicating that they could be suitable for a synergistic coupling with excitons in two-dimensional transition metal dichalcogenides materials or for designing nanoscale sensing platforms based on near-field enhancement over a metallic surface.

Radar Infrared‐Compatible Camouflage Performance of High‐Entropy Alloy Coating Enhanced by Double‐Layer Hexagonal Metasurface

Recently, high‐entropy alloy (HEA) microwave‐absorbing materials have attracted extensive attention. Herein, a double‐layer structure consists of a low‐infrared emission metasurface and a FeCoNiMn0.5Si0.5Al0.5 HEA coating with enhanced microwave absorption performance is designed. The upper metasurface consisting of periodic hexagonal aluminum structural unit has excellent low‐infrared emission properties, while enabling selective transmission and absorption enhancement of radar waves. The emissivity of the low‐infrared emitting layer is lower than 0.2, and the metastructure on its surface affects more on the high‐frequency absorption performance. The bottom layer made of HEA coating with 1 mm hexagonal etching structure has an effective absorption bandwidth of 2.8 GHz, and its reflection loss (RL) can reach −42 dB. There is a certain fit relationship between the unit size of the periodic structure and the absorption performance of the underlying coating. For the coatings with high‐frequency RL peaks, a larger unit size of the periodic structure will lead to an obvious improvement on the absorption performance. A broad application prospect for multiband compatibility stealth is provided.

Geometric parameterization of unit cell configurations for reduced basis approximation

To facilitate rapid yet accurate multiscale homogenization, we formulate geometric mapping schemes that effectively handles the fiber radius changes of a unit cell to dispense with mesh regeneration. To further expedite unit cell analysis involving fiber radius variation, we integrate the formulated geometric transformations into reduced basis analysis using an empirical interpolation method. For demonstration, we examine the proposed geometric parameterization strategies with the linear elastic analyses of square and hexagonal unit cells under tension and shear loads, respectively. Overall, reduced basis analyses combined with the devised geometric mappings are found more efficient than the corresponding finite element analyses while producing insignificant errors.

Mechanical Behavior of Bamboo-Like Structures under Transversal Compressive Loading.

Inspired by many biological structures in nature, biomimetic structures demonstrate significantly better mechanical performance than traditional engineering structures. The exceptional mechanical properties of natural materials are attributed to the hierarchical architecture of their structure. Consequently, the implementation of biomimetic structures in the design of lightweight structures with tailored mechanical properties has been constantly increasing in many fields of science and engineering. The bamboo structure is of particular interest because it combines a light weight and excellent mechanical properties, often surpassing those of several engineering materials. The objective of this study was to evaluate the mechanical behavior of bamboo-inspired structures subjected to transversal compressive loading. Structures consisting of bamboo-like thin-walled hexagonal building blocks (unit cells) with different dimensions were fabricated by stereolithography 3D printing and their mechanical performance was evaluated by mechanical testing, high-speed camera video recordings, and finite element simulations. The results of the elastic modulus, yield strength, and strain energy density at fracture were interpreted in terms of characteristic dimensions of the unit cell structure. The failure process was elucidated in the light of images of the fractured structures and simulation strain maps. The results of this study demonstrate that ultralight bamboo-like structures with specific mechanical characteristics can be produced by optimizing the dimensions and number density of the hexagonal unit cell.

Structure of hexagonal ζ´-AlMnCo

The structure of ζ´-Al80Mn16Co4 was analyzed using single-crystal X-ray diffraction. The diffraction pattern indicated that the ζ´-AlMnCo phase has a hexagonal unit cell with a space group P63/m, a = 30.5173(5) Å, c = 12.4742(2) Å, and the a-axis is -times as large as that of the ζ-phases in the Al-Cr-Cu and Al-Cr-Ni systems. Mn atoms prefer icosahedral coordination similar to that of Cr in the ζ-phase, and the Co atoms are located in the interstitial area formed by the connection of the icosahedra. The icosahedral connection of the ζ´-phase is well characterized by the I3 cluster, a fragment of vertices sharing 3 icosahedra. The structural features of the superstructure are associated with the distribution of Co in the interstitial area.

Crystal structure changes of native and retrograded starches modified by high hydrostatic pressure: Physical dual modification

The effect of high hydrostatic pressure (HHP) on the structural changes of starches with different state of organization was investigated. Starch in native state (granular - NS) and in retrograded state (granular structure not present - RetS) were adjusted to 40% (w/v) of moisture and then treated at pressures of 300 and 600 MPa for 5 min at 10 °C. The structural changes of NS and RetS were significantly and differently affected by the HHP treatment. When the pressure increased, orthorhombic unit cell of NS showed an increase in crystal parameter of c-axis and a decrease of a- and b-axes. Crystallinity, crystallite size, short-range ordered structure (DO), organization of the double helix structures (DD), and enthalpy change (ΔH) gradually decreased. After treatment at 300 MPa, the granules get aggregated while keeping their granular structure, promoting a higher viscosity. At 600 MPa, leached material, aggregated granules, destroyed, and with collapsed “ellipsoid-shape” structure were observed, which contributes to decreasing the viscosity. In RetS, the dual physical modification achieved after pressurizing the hydrothermally treated starch, resulted in a significant increase in the crystal parameters (a, b, and c) of hexagonal unit cell. Furthermore, the crystallinity, crystallite size, DD, DO, ΔH, and viscosity were improved, while a gradual decrease of the amounts of cavities was observed. Crystal structure changes in RetS showed that the double helices of unit cell were stabilized by dual modification, while the unit cell was affected after pressurization of NS. This investigation is the first evidence of the application of HHP on RetS.

Bandgap properties and multi-objective optimization of double-cone pentamode metamaterials with curved side

Pentamode metamaterials (PM) have a promising application in noise reduction fields. In this paper, in order to improve the acoustic modulation capability of PMs, several novel curve PMs are proposed by replacing the straight sides of conventional PMs with curves. At first, the elliptic PMs (EPMs) with various unit cell arrangements (i.e., triangular, square, and hexagonal) are designed, respectively, and their bandgap properties are studied numerically in detail. The EPM with hexagonal unit cell arrangement (EPMH) presents better comprehensive bandgap properties in the EPMs. Subsequently, sinusoidal and power curves are introduced into the EPMH respectively to explore the influences of curve types on bandgap properties. The results show that the bandgap properties improvement of EPMH is higher in comparison with introducing other curves, and the reasons behind these improvements are carefully disclosed in combination with the spring-mass system. Finally, to further improve the bandgap properties of EPMH, a high accuracy Kriging model is constructed according to both the Latin hypercube design and double-point infilling. The Pareto optimal solution sets are determined using a non-dominated sorting genetic algorithm (NSGA-II), and the final compromise solution is gained by employing a fitness function. The bandwidths of phononic bandgap and single mode bandgap, and the total bandwidth of optimized EPMH are increased respectively by about 114.5, 4.3, and 7.7 times than those of the conventional straight side PMs. This investigation provides a fresh strategy for designing PMs with excellent bandgap properties.

Energy Absorption of 3D Printed ABS and TPU Multimaterial Honeycomb Structures.

Advances in multimaterial 3D printing are enabling the construction of advantageous engineering structures that benefit from material synergies. Cellular structures, such as honeycombs, provide high-energy absorption to weight ratios that could benefit from multimaterial strategies to improve the safety and performance of engineered systems. In this study, we investigate the energy absorption for honeycombs with square and hexagonal unit cells constructed from acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU). Honeycombs were fabricated and tested for out-of-plane and in-plane compression using ABS, TPU, and a combination of ABS with a central TPU band of tunable height. Out-of-plane energy absorption for square honeycombs increased from 2.2 kN·mm for TPU samples to 11.5 kN·mm for ABS samples and energy absorption of hexagonal honeycombs increased from 2.9 to 15.1 kN·mm as proportions of TPU/ABS were altered. In-plane loading demonstrated a sequential collapse of unit cell rows in square honeycombs with energy absorption of 0.1 to 2.6 kN·mm and a gradual failure of hexagonal honeycombs with energy absorption of 0.6 to 2.0 kN·mm. These results demonstrate how multimaterial combinations affect honeycomb compressive response by highlighting their benefits for controlled energy absorption and deformation for tunable performance in diverse engineering applications.

Strain Engineering of Sc2CBr2 MXene Monolayer by First Principle Approach

In this present work, using first-principle approach, we have simulated the structural, electronic, and optical properties of a Sc2CBr2 MXene monolayer. Here Sc2C MXene is functionalized with a Br atom. It has a hexagonal unit cell. The phonon dispersion curve ensures the kinetic stability of Sc2CBr2 monolayer structure. The generalized gradient approximation with projected augmented wave type pseudopotential is used to compute the electronic band structure, which indicates the semiconducting nature of monolayer with an indirect band gap of 0.71 eV. The bi-axial strain is applied on the monolayer and impact of tensile and compressive strain on above mentioned properties has been studied. The optical properties of the Sc2CBr2 monolayer confirm its applications in optoelectronic devices, especially UV absorbers, as the absorption peak and a minor absorption are found in the UV and visible regions respectively for the applied strain.

Application of geospatial and remote sensing data to support locust management

Negative impacts on agricultural activities by different locust species are well documented and have always been one of the major threats to food security and livelihoods, especially for local communities. Locust management and control have led to less frequent and intense plagues and outbreaks worldwide. However, political insecurity and armed conflicts affect locust management, and can as well as changing climate, and land use management contribute to new outbreaks. In the context of the increasing world population and higher demand for agricultural production, locust pests will remain of high concern. Geospatial and remote sensing data have become an important source of information for different applications within locust research and management. However, there is still a gap between available information and actual practical usage. In this study, we demonstrate the importance of geospatial and remote sensing data and how this information can be prepared for a straightforward application for stakeholders. For this purpose, we use the h3-hexagonal hierarchical geospatial indexing system to simplify and structure spatial information into standardized hexagon units. The presented concept provides decision makers and ground teams with a simplified information database that contains area-wide information over time and space and can be used without detailed geospatial knowledge and background. The concept is designed for the use case of Italian locust management in the Pavlodar region (Kazakhstan) and based on actual practices. It can be extrapolated to any other study area or species of interest. Our results underline the importance of actual land management on locust presence. Up-to-date land management information can be derived from time-series analyses of remote sensing data. Furthermore, essential meteorological data are used to generate locust-specific climatic characteristics within the h3-system. Within this system, areal prioritizing for locust management can be achieved based on the included spatial information and experience from ongoing practices.

Hydrogen Absorption Reactions of Hydrogen Storage Alloy LaNi5 under High Pressure.

Hydrogen can be stored in the interstitial sites of the lattices of intermetallic compounds. To date, intermetallic compound LaNi5 or related LaNi5-based alloys are known to be practical hydrogen storage materials owing to their higher volumetric hydrogen densities, making them a compact hydrogen storage method and allowing stable reversible hydrogen absorption and desorption reactions to take place at room temperature below 1.0 MPa. By contrast, gravimetric hydrogen density is required for key improvements (e.g., gravimetric hydrogen density of LaNi5: 1.38 mass%). Although hydrogen storage materials have typically been evaluated for their hydrogen storage properties below 10 MPa, reactions between hydrogen and materials can be facilitated above 1 GPa because the chemical potential of hydrogen dramatically increases at a higher pressure. This indicates that high-pressure experiments above 1 GPa could clarify the latent hydrogen absorption reactions below 10 MPa and potentially explore new hydride phases. In this study, we investigated the hydrogen absorption reaction of LaNi5 above 1 GPa at room temperature to understand their potential hydrogen storage capacities. The high-pressure experiments on LaNi5 with and without an internal hydrogen source (BH3NH3) were performed using a multi-anvil-type high-pressure apparatus, and the reactions were observed using in situ synchrotron radiation X-ray diffraction with an energy dispersive method. The results showed that 2.07 mass% hydrogen was absorbed by LaNi5 at 6 GPa. Considering the unit cell volume expansion, the estimated hydrogen storage capacity could be 1.5 times higher than that obtained from hydrogen absorption reaction below 1.0 MPa at 303 K. Thus, 33% of the available interstitial sites in LaNi5 remained unoccupied by hydrogen atoms under conventional conditions. Although the hydrogen-absorbed LaNi5Hx (x < 9) was maintained below 573 K at 10 GPa, LaNi5Hx began decomposing into NiH, and the formation of a new phase was observed at 873 K and 10 GPa. The new phase was indexed to a hexagonal or trigonal unit cell with a ≈ 4.44 Å and c ≈ 8.44 Å. Further, the newly-formed phase was speculated to be a new hydride phase because the Bragg peak positions and unit cell parameters were inconsistent with those reported for the La-Ni intermetallic compounds and La-Ni hydride phases.

Numerical investigation of magneto-thermal-convection impact on phase change phenomenon of Nano-PCM within a hexagonal shaped thermal energy storage

Latent heat storage is among the most effective thermal energy storage techniques. The heat can be stored or released in a phase change substance undergoing melting or solidification. The present research addresses the melting process of paraffin, a phase change material, enhanced with metallic alumina nanoparticles, inside a hexagonal heat storage unit in the presence of a uniform magnetic field is investigated. The melting process occurs during the thermal charge of the latent heat storage unit. The enthalpy-porosity method was employed to model the melting process. The influence of the Lorentz force strength and magnetic field inclination angle as well as the nanoparticle concentration on charging level was scrutinized. It was found that the Lorentz force can suppress the charging level of the thermal energy storage system, while the magnetic field inclination angle can be suitable to control the energy transport performance and melting motion within the thermal energy storage unit. Moreover, raising the nanoadditives concentration diminishes the melting process. Overall, the obtained results confirmed that altering the intensity or direction of the external magnetic field presents indeed a mean for controlling the flow and thermal behavior of nano-enhanced phase change materials. Imposing the Ha up to 500 increases 266% the dimensionless melting time compared to ignoring magnetic field (Ha = 0).

Nonlinear wave propagation analysis in architected materials with consideration of extension, shear and bending effects

The current paper deals with the wave dispersion characteristics of two-dimensional architected materials, considering both the linear and nonlinear regimes. We study the full non-linear coupling between the shear, extension, and bending deformation modes on the inner material deformation of the square, triangular, hexagonal, and re-entrant hexagonal unit cells. The dynamical analysis is done at high and low frequencies and for two different wave amplitudes. Based on the Linstedt–Poincare perturbation method, the non-linear correction to the dispersion diagram is evaluated. The relative contribution of each non-linear energy mode on the nonlinear wave dispersion attributes is quantified. The obtained results show that both the wavenumber and lattice design play an important role in the nonlinear wave corrections of the dispersion characteristics. The shear mode is shown to have the highest effect in the non-linear correction for all considered architected materials, compared to the flexural mode, which has the lowest energy contribution. The eigenwaves vectors are used to compare the deformation of hexagonal and re-entrant hexagonal unit cells at low and high frequencies over the entire Brillouin zone. Overall, the present work provides some guideline as to the proper selection of the inner design of architected materials prone to strong nonlinear dynamical effects.

Origami Tribo-Metamaterials with Mechanoelectrical Multistability

The emerging mechanical functional metamaterials reported with promising mechanoelectrical characteristics bring increasing attention to structurally functional materials. It is essential to deploy mechanical metamaterials in energy materials for effective triggering and controllable mechanoelectrical response. This study reports origami tribo-metamaterials (OTMs) that design triboelectric materials in the origami-enabled, tubular metamaterials. The octagonal, hexagonal, and conical origami units are deployed as the metamaterial substrates to trigger the triboelectric pairs for mechanoelectrical multistability. For the octagonal OTM configuration with the triboelectric pair of fluorinated ethylene propylene-paper, the peak open-circuit voltage, short-circuit current, and transferred charge are obtained as 206.4 V, 4.66 μA, and 0.38 μC, respectively, and the maximum instantaneous output power density is 0.96 μW/cm2 with the load resistance of 20 MΩ. The OTM takes advantage of the origami metamaterials to obtain the multistable force-displacement response as effective stimuli for the triboelectric materials, which leads to tunable mechanoelectrical performance for speed and weight sensing and energy harvesting. The proposed OTM not only offers a strategy to structurally design energy materials to achieve desirable mechanoelectrical response, but also provides a guideline for the applications of mechanical functional metamaterials in practice.

Elasticity-based locally-exact homogenization theory for three-phase composites considering the morphological effect of carbon fibers

Elasticity-based locally-exact homogenization theory (LEHT) is further extended in this paper to investigate the mechanical behaviors of three-phase composites with orthotropic interlayer as well as circumferentially orthotropic (CO) and radially orthotropic (RO) carbon fibers that are determined by their morphological basal plane. Taking advantage of the Fourier series representations for displacements of each phase, in-plane and out-of-plane exact solutions are obtained for orthotropic media through rigorous mathematical derivations and the internal eigenvalue functions are directly solved within rectangular and hexagonal representative unit cells (RUCs) subjected to axial normal, transverse loading and axial shear loading, respectively. The balanced variational principle is applied to enforce periodical boundary conditions which ensures rapid convergence of displacement fields. The solutions of LEHT are verified with far-field Eshelby problems with good agreement and the morphological effects of fiber are investigated by comparing CO/RO properties and equivalent transversely isotropic (TI) parameters obtained from replacement scheme. Homogenized elastic moduli of RUCs with orthotropic interlayer are predicted through homogenization constitutive relations and compared to special extension of the composite cylinders approach and numerical results based on the asymptotic expansion homogenization method to demonstrate excellent correlation. Finally, the effects of orthotropic interlayer have been demonstrated and local stress distributions are obtained from a “top-to-down” procedure, illustrating constituents’ interactions from microscope perspective and identifying the possible crack initiations/propagations within microstructures.

Enhanced photocatalytic performance of a stable type-II PtSe2/GaSe van der Waals heterostructure.

In this investigation, the structural, electronic, and optical properties of two-dimensional van der Waals heterostructure (vdwHS) PtSe2/GaSe with three different configurations have been studied using density functional theory with the generalized gradient approximation. All three optimized vdwHSs PtSe2/GaSe have positive phonon frequencies and hexagonal unit cells. The hybrid exchange-correlation functional has been employed to study the electronic properties of vdwHSs PtSe2/GaSe. The vdwHSs PtSe2/GaSe shows semiconducting behavior with indirect Type-II bandgaps, which have been confirmed by the charge density difference, electrostatic potential, work function, and band edge calculations. Additionally, from the band edge positions, the vdwHSs PtSe2/GaSe are analyzed for photocatalytic activities. The optical properties such as extinction coefficient, refractive index, reflectivity, energy loss spectrum, and absorption coefficient have been studied using norm-conserving pseudo-potentials. The vdwHSs PtSe2/GaSe exhibit consistent absorption from the visible to the ultraviolet region of the electromagnetic spectrum. From the obtained results, we conclude that vdwHSs PtSe2/GaSe could be utilized for H2 production through photocatalytic activity as well as for optoelectronic devices and their application.

The Dunkl-Williams constant related to the singer orthogonality and red isosceles orthogonality in Banach spaces

In this paper, we shall consider two new constants DWS(X) and DWI(X), which are the Dunkl-Williams constant related to the Singer orthogonality and theisosceles orthogonality, respectively. We discuss the relationships between DWS(X) and some geometric properties of Banach spaces, including uniform non-squareness, uniform convexity. Furthermore, an equivalent form of DWS(X) in the symmetric Minkowski planes is given and used to compute the value of DWS((R2, ???p)), 1 &lt; p &lt; ?, and we also give a characterization of the Radon plane with affine regular hexagonal unit sphere in terms of DWS(X). Finally, we establish some estimates for DWI(X) and show that DWI(X) does not necessarily coincide with DWS(X).

Experimental and theoretical study of β-As2Te3under hydrostatic pressure

Schematic view of the β-As2Te3polymorph (S. G.R3̄m) including the polyhedral units (AsTe6, TeAS6, and Te2 antiprism of β-As2Te3) of the hexagonal unit cell. Images of the experimental and theoretical techniques used are shown as well as the main results reported.

From angular to round: in depth interfacial analysis of binary phosphatidylethanolamine mixtures in the inverse hexagonal phase.

Packing stress in the lipidic inverse hexagonal HII phase arises from the necessity of the ideally cylinder-shaped micelles to fill out the hexagonally-shaped Wigner-Seitz unit cell. Thus, hydrocarbon chains stretch towards the corners and compress in the direction of the flat side of the hexagonal unit cell. Additionally, the lipid/water interface deviates from being perfectly circular. To study this packing frustration in greater detail, we have doped 1-palmitoyl-2-oleoyl-sn-phosphatidylethanolamine (POPE) with increasing molar concentrations of 1,2-palmitoyl-sn-phosphatidylethanolamine (DPPE: 0 to 15 mol%). Due to its effectively longer hydrophobic tails, DPPE tends to aggregate in the corner regions of the unit cell, and thus, increases the circularity of the lipid/water interface. From small angle X-ray diffraction (SAXD) we determined electron density maps. Using those, we analysed the size, shape and homogeneity of the lipid/water interface as well as that of the methyl trough region. At 6 and 9 mol% DPPE the nanotubular water core most closely resembles a circle; further to this, in comparison to its neighbouring concentrations, the 9 mol% DPPE sample has the smallest water core area and smallest number of lipids per circumference, best alleviating the packing stress. Finally, a three-water layer model was applied, discerning headgroup, perturbed and free water, demonstrating that the hexagonal phase is most stable in the direction of the flat faces (compression zones) and least stable towards the vertices of the unit cell (decompression zones).

PERFORMANCE ANALYSIS OF HEXAGONAL UNIT CELL STENT DESIGN AND SINGLE-LAYERED MANUFACTURABILITY WITH FDM

İlaç salınımlı stentlerden sonra geliştirilen biyobozunur polimer esaslı stentler için yapılan ön klinik çalışmalardan elde edilen sonuçlara göre polimer stentlerin kullanılabilirliği sorgulanmaktadır. Polimer stentlerde strat kalınlığının yüksek olması ve mekanik özelliklerin zayıflığı nedeniyle tasarım ve malzeme iyileştirmesine gidilerek yeni modellerin ortaya çıkarılması üzerine araştırmalara devam edilmektedir. Balonla genişleyen stentlerde oluşan uç açılması arter içerisinde intimal ve medial katmanlara zarar vermektedir. Bu zarar, erken dönemde neointimal hiperplazi ve restenoza sebep olmaktadır. Metalik stent geometrilerinden biri olan Palmaz-Schatz birim hücre modelinde balonla genişleme esnasında uç açılması ve kısalma oranı meydana gelmektedir. Bu çalışmada, Palmaz-Schatz stent geometrisinin genişlemesiyle oluşturduğu geometri dikkate alınarak PLLA malzemeden altıgen birim stent geometrisinde yeni tasarım gerçekleştirilmiştir. Sonlu elemanlar simülasyonuyla, ince strat kalınlığında tasarlanan altıgen stendin genişlemesinde oluşan uç açılması ve kısalma oranı belirlenmiştir. Ayrıca, stent genişlemesinde üç katmanlı arter ve kalsifik plak yapısında meydana gelen doku hasarı ölçülmüştür. Altıgen geometrideki stentte oluşan uç açılması ve kısalma oranı Palmaz-Schatz modeline göre azaltılmıştır. Bununla birlikte, PLA/PHA karışımı malzemeden eriyik yığma modelleme ile altıgen stent geometrisinin 3B plaka baskısı tek katmanlı olarak üretilmesi sonrası ısıtıcı bir tubular tabla üzerinde sarılarak stent formuna getirilmiştir