Search

Tert-butyl functional groups can modulate the self-assembly behavior of organic molecules on surfaces. However, the precise construction of supramolecular architectures through their controlled thermal removal remains a challenge. Herein, we precisely controlled the removal amount of tert-butyl groups in tetraazaperopyrene derivatives by stepwise annealing on Ag(111). The evolution of 4tBu-TAPP supramolecular self-assembly from the grid-like structure composed of 3tBu-TAPP through the honeycomb network formed by 2tBu-TAPP to the one-dimensional chain co-assembled by tBu-TAPP and TAPP was successfully realized. This series of supramolecular nanostructures were directly visualized by high resolution scanning tunneling microscopy. Tip manipulation and density functional theory calculations show that the formation of honeycomb network structure can be attributed to the van der Waals interactions, N–Ag–N coordination bonds, and weak C–H⋯N hydrogen bonds. Further addition of two tert-butyl groups (6tBu-TAPP) leads to a completely different assembly evolution, due to the fact that the additional tert-butyl groups affect the molecular adsorption behavior and ultimately induce desorption. This work can possibly be exploited in constructing stable and long-range ordered nanostructures in surface-assisted systems, which can also promote the development of nanostructures in functional molecular devices. [ABSTRACT FROM AUTHOR]

Higher-order topological states, as emergent topological phases of matter, originating from condensed matter physics, have sparked a vibrant exploration of topological insulators. Their topologically protected multidimensional localized states are typically associated with nontrivial bulk band topology, and the significant impact of lattice geometry is unconsciously overlooked. Here, we construct coupled acoustic cavities on a two-dimensional honeycomb lattice to investigate the sensitivity of higher-order topological modes to the variations of edge contour. Fractional charge is utilized to accurately predict topological modes with distinct topological orders, in spite of the minimal bulk bandgaps inherent in the honeycomb lattice and bound states in the continuum. It is found that the presence and absence of the first-order and higher-order topological modes in the same topological phase are tightly linked to the sample boundaries, which can be demonstrated by both theoretical analysis and numerical calculation. Our study also discusses potential physical realization of geometry-dependent topological states across different platforms, providing inspiration for the prospective application of topological devices in acoustics. [ABSTRACT FROM AUTHOR]

Using the Full Potential Linear Augmented Plane Wave and the pseudo-potential method based on the Density Functional Theory, we investigate the physical properties of two-dimensional (2D) boron nitride, carbon nitride, and boron carbide as well as their ternary system boron carbon nitride (BCN). The structural and optoelectronic properties are determined and discussed in detail with available theoretical and experimental results. We show that the studied physical properties are influenced and tunable by atom concentration. A high concentration of nitrogen (> 50%) disturbs the honeycomb structure of binary and ternary alloys. Additionally, the optoelectronic properties are very sensitive to the amount of boron and nitrogen atoms. The zero bandgap is only conserved for B3C12N3 and B6C6N6 ternary systems. A large bandgap was observed for B9N9 (∼3.9 eV) and a moderate one for B6N12 and B3N15 (∼2 eV). The coexistence of boron, carbon, and nitrogen atoms with different concentrations has important optical properties as they can absorb light in all spectra. However, they have more active absorption in the ultraviolet than visible regions. It is more interesting to use ternary BCN than binary or pristine alloys with tunable optoelectric properties, by varying the nitrogen content in nanodevices. [ABSTRACT FROM AUTHOR]

In this study, we experimentally demonstrate a class of lightweight acoustic metamaterial barriers that block low-frequency sound. The acoustic metamaterial barrier is composed of a thin rubber membrane coated over a stiff honeycomb plate. Our findings, combined with high-fidelity finite element simulations, demonstrate that the sound insulation performance of the acoustic metamaterial surpasses the mass law in three distinct frequency ranges: (a) the stiffness law dominates insulation up to 140 Hz, (b) degeneracy and destructive superposition of high-order natural modes dominate within the frequency range of 300–500 Hz, and (c) destructive interference between high-order resonance and membrane resonance dominates in the frequency range of 800–1200 Hz. Notably, our study highlights the potential of high-order shear vibration of the periodic structure for the resonant bending waves of the honeycomb cell that coincide with the wavelengths of longitudinal sound waves in air, thereby offering new design guidelines for lightweight acoustic metamaterial barriers. This study reports for the first time the coincidence of high-order and membrane resonance modes within the honeycomb cell by employing an accurate finite element model and experimental validation. [ABSTRACT FROM AUTHOR]

The honeycomb's eponymous structure is omnipresent in our every day lives. We want to provide some inspiration to perform structural analyses of these structures and to draw comparisons between them. In the present study, we detect honeycomb patterns and related complex network structures on different length scales ranging from macroscopic objects down to the atomic scale of 2D materials. In 2D materials, a subset of the honeycomb structure—the kagome lattice—is very interesting due to unique material properties. For structure detection, we developed a program written in Python. The program is very adaptable and provides a graphical user interface to modify the detected network interactively. With the help of this program, we directly compare honeycomb structures with atomic network structures. Both honeycombs and 2D atom networks can show local deviations from their characteristic hexagonal pattern. The structural deviations at the macroscopic scale and at the atomic scale are very similar. We provide additional structural analyses of every day objects and encourage everyone to use our software that is freely accessible. [ABSTRACT FROM AUTHOR]

Icosahedral B12 serves as a fundamental building block for a variety of boron allotropes and plays a crucial role in enhancing the stability of fullerene-like boron nanoclusters. However, progress in the development of two-dimensional (2D) functional assemblies made from icosahedral B12 has been limited. In this context, we propose a 2D semiconducting boron allotrope (h-B12) using icosahedral B12 as a building block. This structure features a stable honeycomb lattice, with its unit cell comprising two mirror-symmetric icosahedral B12 clusters. The results of first-principles calculations indicate that the band structure exhibits Dirac cones and a relatively high group velocity, similar to graphene. Additionally, it is found to be a material with a negative Poisson's ratio and a relatively low Young's modulus. Finally, our calculations reveal that the zigzag nanoribbon constructed from h-B12 displays prominent edge states at both edges, indicating that this structure represents a potential topological electronic material. Our findings shed light on the design and construction of nano-electronic materials via cluster assembly. [ABSTRACT FROM AUTHOR]

Ferroelectric polarization induced by the magnetic field is one of the properties reported in honeycomb antiferromagnetic linear magnetoelectrics (LME) belonging to the A4M2O9P 3 ¯ c1 class of corundum compounds with A = Co, Fe, and Mn and M = Nb or Ta. Among them, Mn4Nb2O9 exhibits the highest TN of 108 K. We show that it can even be increased by substituting partly Mn by Fe. The study of Mn4−xFexNb2O9 allows one to reach a TN up to 126 K at x = 1.5. This beneficial effect, confirmed also for Fe substituted Mn4Ta2O9, is compared to substitutions by Co or by Zn, both cations inducing a TN decrease. The linear decrease in the unit cell volume with x in Mn4−xFexNb2O9 shows that the cation size effect only cannot be inferred to explain the TN(x) curve. Furthermore, the spin flop magnetic field of Mn4Nb2O9 decreases, thanks to the Fe for Mn substitution, a LME effect is evidenced at 10 K, ΔP(9T)10K = 11 μC/m2. These features, TN increase and LME properties, demonstrate the important role of substitutions to enhance the properties of such antiferrromagnets. [ABSTRACT FROM AUTHOR]

Ferroelectric polarization induced by the magnetic field is one of the properties reported in honeycomb antiferromagnetic linear magnetoelectrics (LME) belonging to the A4M2O9P 3 ¯ c1 class of corundum compounds with A = Co, Fe, and Mn and M = Nb or Ta. Among them, Mn4Nb2O9 exhibits the highest TN of 108 K. We show that it can even be increased by substituting partly Mn by Fe. The study of Mn4−xFexNb2O9 allows one to reach a TN up to 126 K at x = 1.5. This beneficial effect, confirmed also for Fe substituted Mn4Ta2O9, is compared to substitutions by Co or by Zn, both cations inducing a TN decrease. The linear decrease in the unit cell volume with x in Mn4−xFexNb2O9 shows that the cation size effect only cannot be inferred to explain the TN(x) curve. Furthermore, the spin flop magnetic field of Mn4Nb2O9 decreases, thanks to the Fe for Mn substitution, a LME effect is evidenced at 10 K, ΔP(9T)10K = 11 μC/m2. These features, TN increase and LME properties, demonstrate the important role of substitutions to enhance the properties of such antiferrromagnets. [ABSTRACT FROM AUTHOR]

A theoretical model has been developed to express the longitudinal and transverse piezoelectric effects in ferro/piezoelectrets. This model is an extension of the classic model based on layer-dielectric structures that focuses on the longitudinal piezoelectric effect. The improved model reveals that the relation between the longitudinal piezoelectric d33 coefficient and the transverse piezoelectric d31 coefficient is associated with Poisson's ratio μ13 (or μ31) and Young's moduli Y1 and Y3. The polarity of the two coefficients is opposite for materials with a positive Poisson's ratio as normally observed in conventional piezoelectric materials, and the same for materials with a negative Poisson's ratio, i.e., auxetic materials. The experimental results available in the literature and obtained from ferroelectret metamaterials with a honeycomb cross-sectional structure and two-dimensional (2D) symmetric structure, called 2D ferroelectret metamaterials, designed and prepared in this study reasonably agree with theoretical predictions. This study not only extends the scope of the metamaterials by inducing the concept of ferroelectret metamaterials but also provides a strategy for designing ferroelectrets with designable properties. [ABSTRACT FROM AUTHOR]

Based on the model of magnonic crystals (MCs) with honeycomb structure, we propose another model of two-dimensional MCs with honeycomb–kagome structure that is a periodic magnetic composite system composed of Fe, Co, or Py ferromagnetic cylindrical scatterers arranged in the EuO matrix as the honeycomb–kagome structure. The band structures of magnons in these systems are studied numerically by using the plane-wave expansion method. The results show that the Dirac points of magnons will be generated at the Brillouin region points if the scatterers are close-packed, that is to say, the edges of cylindrical scatterers are in contact with each other. The frequency of Dirac points can be indirectly adjusted by changing the radius ratio of close-packed cylinders. In addition, in the case of a large difference in the radius between the close-packed cylindrical scatterers, there will be a magnonic flat band in the band structure, which is a phenomenon of so-called compact localized states different from the impurity state in the crystal, and it is formed by the highly interference superposition of spin waves in the honeycomb–kagome structure. The research on the generation and modulation of magnonic Dirac points and flat bands not only expands the research content of condensed matter topological physics but also provides a promising platform for the application of artificial MCs in the fabrication of spin-wave topological devices. [ABSTRACT FROM AUTHOR]

We present a new setup for resonant inelastic hard x-ray scattering at the Bernina beamline of SwissFEL with energy, momentum, and temporal resolution. The compact R = 0.5 m Johann-type spectrometer can be equipped with up to three crystal analyzers and allows efficient collection of RIXS spectra. Optical pumping for time-resolved studies can be realized with a broad span of optical wavelengths. We demonstrate the performance of the setup at an overall ∼180 meV resolution in a study of ground-state and photoexcited (at 400 nm) honeycomb 5d iridate α-Li2IrO3. Steady-state RIXS spectra at the iridium L3-edge (11.214 keV) have been collected and are in very good agreement with data collected at synchrotrons. The time-resolved RIXS transients exhibit changes in the energy loss region <2 eV, whose features mostly result from the hopping nature of 5d electrons in the honeycomb lattice. These changes are ascribed to modulations of the Ir-to-Ir inter-site transition scattering efficiency, which we associate to a transient screening of the on-site Coulomb interaction. [ABSTRACT FROM AUTHOR]

Optical properties of two-dimensional bilayer silicon have been explored at midinfrared wavelengths using density functional theory. In this work, progressive atomic structural deformation and the resultant variations in the optical properties of the bilayer silicon films were investigated under external in-plane strain. A phase transformation of the atomic structure has been observed at an applied in-plane tensile strain of 5.17%, at which the atomic lattice is changed from a low buckled to a buckle-free honeycomb structure. Evaluations of the optical properties were carried out by taking into account the inter- and intraband transitions. An abrupt change in the optical refraction index was observed at the phase transition. In addition, the buckle-free honeycomb structure presents a strain-resistive absorption edge pinned at 1.14 μm wavelength. Exceeding a strain threshold of 12.26% results in the development of both direct- and indirect-energy bandgap openings. The direct bandgap induced interband optical transitions, resulting in absorption peaks at midinfrared wavelengths and a drastic increase in the refraction index. Moreover, by adjusting the strain, the optical absorptions can be tuned in a wide range of wavelength at midinfrared from 1.5 to 11.5 μm. [ABSTRACT FROM AUTHOR]

Ni4Nb2O9 displays magnetization reversal, a particular behavior in which magnetization opposes an applied magnetic field. Previous studies have shown that this is caused by the antiferromagnetic coupling of two different layers of ferromagnetic Ni cations. In this work, magnetization reversal is controlled by the substitution of Ni by non-magnetic Zn. Ni4−xZnxNb2O9 materials with x = 0.25, 0.50, and 0.75 maintain the orthorhombic Ni4Nb2O9-type structure but display counterintuitive changes in the magnetic properties including increases in low-temperature net magnetizations, remnant magnetizations, and compensation temperatures. Furthermore, the magnetization reversal is significantly enhanced for x = 0.50 while supressed for x = 0.75, underscoring the strong effects of Zn substitution. [ABSTRACT FROM AUTHOR]

Ni4Nb2O9 displays magnetization reversal, a particular behavior in which magnetization opposes an applied magnetic field. Previous studies have shown that this is caused by the antiferromagnetic coupling of two different layers of ferromagnetic Ni cations. In this work, magnetization reversal is controlled by the substitution of Ni by non-magnetic Zn. Ni4−xZnxNb2O9 materials with x = 0.25, 0.50, and 0.75 maintain the orthorhombic Ni4Nb2O9-type structure but display counterintuitive changes in the magnetic properties including increases in low-temperature net magnetizations, remnant magnetizations, and compensation temperatures. Furthermore, the magnetization reversal is significantly enhanced for x = 0.50 while supressed for x = 0.75, underscoring the strong effects of Zn substitution. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a dual-broadband dual-function polarization conversion metasurface, which can convert a linearly polarized (LP) incident electromagnetic wave into a cross-polarized LP wave and a circularly polarized wave, effectively, in different bands. The numerical simulations and experiments show that the metasurface can be used as a high-efficiency cross-polarization converter from 5.50 to 12.4 GHz, where the polarization conversion ratio is greater than 0.9 with a fractional bandwidth of 77.1%. Simultaneously, it can convert the LP incident wave into a right-handed circularly polarized wave from 13.50 to 19.75 GHz, where the axis ratio is lower than 3 dB and the fractional bandwidth is 37.4%. A honeycomb is used as a support layer instead of air gaps, which improves the efficiency of cross-polarization conversion and broadens the bandwidth of linear to circular conversion. To reveal the conversion mechanism of the proposed polarization converter, the surface current is analyzed. Finally, we fabricated and tested it, and the experimental results are in line with the simulation results. [ABSTRACT FROM AUTHOR]

Graphene on L 1 0 -FePd(001), which has been experimentally studied in recent years, is a heterogeneous interface with a significant lattice symmetry mismatch between the honeycomb structure of graphene and tetragonal alloy surface. In this work, we report on the density functional study of its atomic-scale configurations, electronic and magnetic properties, and adsorption mechanism, which have not been well understood in previous experimental studies. We propose various atomic-scale models, including simple nontwisted and low-strain twisted interfaces, and analyze their energetical stability by performing structural optimizations using the van der Waals interactions of both DFT-D2 and optB86b-vdW functionals. The binding energy of the most stable structure reached E B = − 0.22 eV/atom for DFT-D2 (E B = − 0.19 eV/atom for optB86b-vdW). The calculated FePd-graphene spacing distance was approximately 2 Å, which successfully reproduced the experimental value. We also find out characteristic behaviors: the modulation of π -bands, the suppression of the site-dependence of adsorption energy, and the rise of moiré-like corrugated buckling. In addition, our atomic structure is expected to help build low-cost computational models for investigating the physical properties of L 1 0 alloys/two-dimensional interfaces. [ABSTRACT FROM AUTHOR]

Truncated cluster models represent an effective way for simulating x-ray spectra of 2D materials. Here, we systematically assessed the influence of two key parameters, the cluster shape (honeycomb, rectangle, or parallelogram) and size, in x-ray photoelectron (XPS) and absorption (XAS) spectra simulations of three 2D materials at five K-edges (graphene, C 1s; C3N, C/N 1s; h-BN, B/N 1s) to pursue the accuracy limit of binding energy (BE) and spectral profile predictions. Several recent XPS experiments reported BEs with differences spanning 0.3, 1.5, 0.7, 0.3, and 0.3 eV, respectively. Our calculations favor the honeycomb model for stable accuracy and fast size convergence, and a honeycomb with ∼10 nm side length (120 atoms) is enough to predict accurate 1s BEs for all 2D sheets. Compared to all these experiments, predicted BEs show absolute deviations as follows: 0.4–0.7, 0.0–1.0, 0.4–1.1, 0.6–0.9, and 0.1–0.4 eV. A mean absolute deviation of 0.3 eV was achieved if we compare only to the closest experiment. We found that the sensitivity of computed BEs to different model shapes depends on systems: graphene, sensitive; C3N, weak; and h-BN, very weak. This can be attributed to their more or less delocalized π electrons in this series. For this reason, a larger cluster size is required for graphene than the other two to reproduce fine structures in XAS. The general profile of XAS shows weak dependence on model shape. Our calculations provide optimal parameters and accuracy estimations that are useful for x-ray spectral simulations of general graphene-like 2D materials. [ABSTRACT FROM AUTHOR]

We implement an all-optically reconfigurable triangular lattice of exciton–polariton condensates in a III–V semiconductor microcavity. For this, we utilize a spatial light modulator to structure an incident nonresonant excitation laser beam into a corresponding triangular lattice of Gaussian beams that are focused onto the cavity plane. The optical excitation pattern locally stimulates and blueshifts polaritons due to exciton interactions. At a critical pump power, polaritons condense into a macroscopically coherent Bloch state with sharp Bragg peaks. We reconstruct the full band structure of the system through energy tomography techniques as a function of lattice constant, allowing us to resolve polaritonic Bloch bands from the condensate emission. While for sufficiently large lattice constants, one observes the formation of triangular arrays of condensates, for small lattice constant and pump powers above condensation threshold, one observes the formation of honeycomb, instead of triangular, lattice of condensates, with clear evidence of condensation into the S-band. Our results underpin the quality of all-optically engineered polariton lattices to simulate condensed matter systems in the strong coupling regime. [ABSTRACT FROM AUTHOR]

We theoretically proposed a feasible way to design multi-topological states in one two-dimensional photonic crystal (PC). By sliding and rotating the meta-atoms of its unit cell, the topological phase of the PC can be continuously tuned, but without a closing of bandgap; it is similar to the Kekulé modulation in honeycomb lattices. We first show the existence of helical topological edge states in conventional topological insulator, which intersect together and form a Dirac cone in the two-dimensional synthetic space of the PC. Then, in full synthetic space, the PC behaves high-order topological insulator, and the corner state is then constructed in a heterostructure that consists of three different PCs. Furthermore, we demonstrate the photonic crystal with non-uniform modulation can behaves as a splitter and a rainbow trapper. Our proposal may provide interesting insight for designing of multiple topological states, which have potential in photonic on-chip devices. [ABSTRACT FROM AUTHOR]

Carbon honeycombs (CHs) are new carbon cellular structures, very promising in many respects, in particular, for high-capacity storage of various materials, especially in gaseous and liquid forms. In this study, we report a strong uptake of carbon dioxide kept inside carbon honeycomb matrices up to temperatures about three times higher as compared with CO2 desorption at ≈ 90 K from flat solid surfaces in vacuum where we conduct our high-energy electron diffraction experiments. Desorption of CO2 from CH matrices upon heating exhibits non-monotone behavior, which is ascribed to carbon dioxide release from CH channels of different sizes. It is shown that modeling of CO2 uptake, storage, and redistribution in the thin CH channels of certain types and orientations upon heating can explain experimental observations. [ABSTRACT FROM AUTHOR]

Half-valley semimetal (HVSM) and single-valley states are the hallmark of valleytronics in two-dimensional honeycomb lattice materials, but their quasi-one-dimensional analog that takes advantage of quantum manipulation has not yet been realized. We propose a double-helical ladder model described by a coupled double Su–Schrieffer–Heeger chain, wherein the interchain coupling controlled by magnetic flux induces time-reversal and particle-hole symmetry breaking and preserves only the chiral symmetry, which is classified into the AIII symmetry class. It realizes valley polarization, single-valley topological insulator, and HVSM as the topological quantum criticality (TQC), signaling well valley filter or valve effects. Furthermore, the TQC produces the largest inverse topological caloric effect accompanied by a T-linear relation of isothermal entropy change at ultra-low temperatures. Our findings not only open alternative perspectives for multifunctional quantum devices in valleytronics but also shed light on the thermodynamic characterization of TQC and promote the rapid development of topological quantum refrigeration technology. [ABSTRACT FROM AUTHOR]

In the Van der Waals material NiPS 3 , Ni atoms have spin S = 1 and realize a honeycomb lattice. Six sulfur atoms surround each Ni and split their d manifold into three filled and two unfilled bands. Aimed to determine the spin Hamiltonian of NiPS 3 , we study its exchange mechanisms using a two-band half-filled Hubbard model. Hopping between d-orbitals is mediated by p orbitals of sulfur and gives rise to bilinear and biquadratic spin couplings in the limit of strong electronic correlations. The microscopic model exposed a ferromagnetic biquadratic spin interaction K 1 , allowing the completion of a minimal J 1 − J 3 − K 1 spin Hamiltonian for NiPS 3 . In bulk, a ferromagnetic first nearest neighbor J 1 and a more significant antiferromagnetic third nearest neighbor spin coupling J 3 agreed with the literature, while in monolayer, J 1 is positive and very small in comparison. Using a variational scheme, we found that a zig–zag antiferromagnetic order is the ground state of bulk samples. The zig–zag pattern is adjacent to commensurate and incommensurate spin spirals, which could hint at the puzzling results reported in NiPS 3 monolayers. [ABSTRACT FROM AUTHOR]

This paper presents a method to generative design bionic bone structures wing ribs by simulating the formation process of soap bubble boundary. In this method, the position of the central control point is optimized by the genetic algorithm to simulate the moving process of the bubble, and the control point is simplified by the K-means classification method to improve the computational efficiency. The boundary formed by the extrusion of bubbles is filled with a bone-like grid structure to realize the optimal design of a bone-like rib structure. Compared with the traditional honeycomb sandwich structure, the bone-like rib structure can distribute the stress evenly throughout the structure, thus reducing the stress concentration and improving the bearing capacity of the structure. The method proposed in this paper provides a new idea for a multilevel structure design. [ABSTRACT FROM AUTHOR]

The study is focusing on the exploration of the magnetic properties of the frustrated decorated honeycomb lattices. The presence of geometrical frustration and C3 symmetry leads to an exotic ground state. Monte Carlo simulations and analytical calculations are used to analyze the system's behavior. The dependence of the magnetization on the external field of the Ising model exhibits a step-like behavior, while the magnetization of the classical Heisenberg model has no plateau in the isotropic case. An efficient Hamiltonian is proposed to describe the properties of this system on the unfrustrated hexagonal lattice within the framework of the chiral Potts model. Within a specific range of fields, the state of the effective Hamiltonian aligns with that of the original Hamiltonian. The ground state configurations and degeneracy of the system are explored, revealing fractured stripe patterns separated by spins with opposite orientations. These findings contribute to the knowledge of the properties of decorated lattices, offering valuable insights for potential experimental and practical applications. [ABSTRACT FROM AUTHOR]

We report the experimental observation of second-order corner states in a two-dimensional breathing honeycomb topolectrical circuit with sixfold rotational symmetry C 6 through voltage measurements. The topological corner states originate from the nontrivial bulk topology, which can be characterized by the topological invariant associated with the rotation eigenspectrum. We confirm two types of corner states, both originate from the C 6 symmetry, while one of them is specially pinned to zero admittance because of the emerging chiral symmetry protection. We then examine the robustness of zero modes in the presence of next-nearest-neighbor hopping terms that destroy chiral symmetry but still preserve C 6 symmetry. Our work provides a paradigm in circuit systems to study the exotic topological physics. [ABSTRACT FROM AUTHOR]

Lattice structures in additive manufacturing of 316L stainless steel have gained increasing attention due to their well-suited mechanical properties and lightweight characteristics. Infill structures such as honeycomb, lattice, and gyroid have shown promise in achieving desirable mechanical properties for various applications. However, the design process of these structures is complex and time-consuming. In this study, we propose a machine learning-based approach to optimize the design of honeycomb, lattice, and gyroid infill structures in 316L stainless steel fabricated using laser powder bed fusion (L-PBF) technology under different loading conditions. A dataset of simulated lattice structures with varying geometries, wall thickness, distance, and angle using a computational model that simulates the mechanical behavior of infill structures under different loading conditions was generated. The dataset was then used to train a machine learning model to predict the mechanical properties of infill structures based on their design parameters. Using the trained machine learning model, we then performed a design exploration to identify the optimal infill structure geometry for a given set of mechanical requirements and loading conditions. Finally, we fabricated the optimized infill structures using L-PBF technology and conducted a series of mechanical tests to validate their performance under different loading conditions. Overall, our study demonstrates the potential of machine learning-based approaches for efficient and effective designing of honeycomb, lattice, and gyroid infill structures in 316L stainless steel fabricated using L-PBF technology under different loading conditions. Furthermore, this approach can be used for dynamic loading studies of infill structures. [ABSTRACT FROM AUTHOR]

The broad application prospect of the honeycomb structure wave absorber in industrial and civil fields makes researchers focus on studying its wave absorbing mechanism so as to optimize its structural design and improve its wave absorbing performance. Distinguishing from the equivalent circuit thinking to study the honeycomb structured absorber, a kind of symmetry operation is adopted in this paper for the honeycomb structured absorber from the electromagnetic wave propagation point of view. The reflection loss is assumed to be the result of the loss of the incident electromagnetic wave in the absorbing body and the superposition of multiple refractions, and the symmetry operation can separate the specific physical process of the refracted wave involved in the superposition. The separated electromagnetic wave vector superposition is compared with the simulated and experimental values to verify the correctness of the conjecture. The separation results show that the absorption properties are determined by the internal loss and the phase change caused by the surface structure, which is of positive significance for the optimization and design of honeycomb absorbers. [ABSTRACT FROM AUTHOR]

A detailed high-pressure investigation is carried out on F e 4 N b 2 O 9 using angle resolved x-ray diffraction and Raman spectroscopy measurements. We find a structural transition from the ambient trigonal phase to a monoclinic phase above 8.8 GPa. The structural transition is assumed to be driven by a large distortion of Nb – O 6 octahedra as seen from x-ray diffraction analysis and a large pressure dependence of an Nb – O 6 octahedra breathing Raman mode. Anomalous behavior of Raman modes and an increase in the phonon lifetime at the phase transition pressure indicate a possible change in the magnetic property of the sample above 8.8 GPa. A decrease in the diffusive scattering rate of a low-frequency electronic contribution contradicts the results of a decrease in the intensity of a high-frequency electronic response and excludes the phenomenon of an insulator to metal transition. On the contrary, the enhancement of the intensity of the Raman modes up to about 8.8 GPa indicates a large change in ferroelectric polarization of the sample, indicating a possible pressure induced re-entrant multiferroic behavior in F e 4 N b 2 O 9 . [ABSTRACT FROM AUTHOR]

The investigation of synthetic jet vortex rings flowing through a honeycomb is measured by two-dimensional particle-image velocimetry. The vortex is established using free synthetic jets generated by a piston–cylinder apparatus upstream of the honeycomb. On that basis, turbulence is obtained at circulation Reynolds numbers of ReΓ = 3437, 5155, 6874, and 8592, and Reynolds numbers of the synthetic jets of Resj = 561, 841, 1121, and 1402. The effects of the diameter Reynolds number (ReM = 41–449) and the length-to-cell ratio of the honeycomb (Φ = 4.2–12.5) on the characterization of flow are discussed in detail. A combinatorial similarity parameter that can characterize the effect of passive control on flow fields using a honeycomb is proposed and validated. The combinatorial similarity parameter, ReM/Φ, is determined through dimensional analysis and according to the change in momentum flux loss; its predictive capability is verified quantitatively based on the change in loss of kinetic energy and vortex-ring circulation. The evolutions of phase-averaged vorticity fields and finite-time Lyapunov exponents fields are nearly consistent using the close combinatorial similarity parameters. Furthermore, as indicated by the results, ReM/Φ responds to the combined effect of the relative magnitude of flow inertial and viscous forces, and the shape resistance of the honeycomb geometry to the flow-field–honeycomb interactions. Understanding the characterization of a vortex ring flowing through honeycomb is important for the accuracy of the prediction of turbulence models and the selection of the honeycomb size. [ABSTRACT FROM AUTHOR]

A lightweight wideband honeycomb absorber is theoretically and experimentally investigated. The proposed absorber is constructed of aramid paper, which contains carbon fibers to absorb partially the incident electromagnetic wave. Graded silver paste circuits are also printed on aramid paper to improve the impedance matching properties and, thus, achieve wideband absorption performance. An absorber sample was fabricated and measured to verify the design strategies. The designed absorber has a fractional absorption bandwidth of 133% from 3.6–18 GHz, with a thickness of 0.19λL at the lowest frequency. The total weight of the absorber is 18.2 g, with a density of 28.4 kg/ m 3 . [ABSTRACT FROM AUTHOR]