Surface Topology Research Articles

Impact of Pressure on Metavalent Bonding in BiTe influencing Electronic Topological Transitions

BiTe, a member of the (Bi2)m(Bi2Te3)n homologous series, possesses natural van der Waals‐like heterostructure with a Bi2 bilayer sandwiched between the two [Te‐Bi‐Te‐Bi‐Te] quintuple layers. BiTe exhibits both the quantum states of weak topological and topological crystalline insulators, making it a dual topological insulator and a suitable candidate for spintronics, quantum computing and thermoelectrics. Herein, we demonstrate that the chemical bonding in BiTe is to be metavalent, which plays a significant role in the pressure dependent change in the topology of the electronic structure Fermi surface. The enhancement of the metavalent bonding character with pressure in BiTe is evidenced from first‐principles density functional theory (DFT) calculations. Due to the change in the Fermi surface topology, we have visualized electronic topological transitions (ETT) at 1 and 3 GPa through pressure dependent synchrotron X‐ray diffraction analysis and Raman spectroscopy. The correlation between the metavalent bonding and ETT offers insights into chemical bonding influenced transitions in quantum materials.

Impact of Pressure on Metavalent Bonding in BiTe influencing Electronic Topological Transitions.

BiTe, a member of the (Bi2)m(Bi2Te3)n homologous series, possesses natural van der Waals-like heterostructure with a Bi2 bilayer sandwiched between the two [Te-Bi-Te-Bi-Te] quintuple layers. BiTe exhibits both the quantum states of weak topological and topological crystalline insulators, making it a dual topological insulator and a suitable candidate for spintronics, quantum computing and thermoelectrics. Herein, we demonstrate that the chemical bonding in BiTe is to be metavalent, which plays a significant role in the pressure dependent change in the topology of the electronic structure Fermi surface. The enhancement of the metavalent bonding character with pressure in BiTe is evidenced from first-principles density functional theory (DFT) calculations. Due to the change in the Fermi surface topology, we have visualized electronic topological transitions (ETT) at 1 and 3 GPa through pressure dependent synchrotron X-ray diffraction analysis and Raman spectroscopy. The correlation between the metavalent bonding and ETT offers insights into chemical bonding influenced transitions in quantum materials.

A wideband coaxial-to-waveguide transition devised with topology optimization

Topology optimization is a powerful technique that utilizes the distribution of material properties along with surface topology as parameters to expand a specified performance. While primarily used as a foundational step in regenerative design for structural mechanics, the general TO framework is also applicable to many of the complex issues in electromagnetics such as frequency agile mode converters. This is considered a difficult parameter to optimize since RF components operate on resonance. TO is used on the coaxial-to-rectangular waveguide converter in the range X band. The radiative element chosen is a patch antenna with a ground stop. The original design is transformed into a binary material distribution matrix, where each cell is assigned a value of 0 or 1, while ensuring connectivity between the cells. Then the cell values are altered via a BPSO algorithm to optimize the width of the operating band, resulting in a complex structure that yields a bandwidth 38% larger than the control. The optimized patch structure is fabricated and its performance verified in the frequency range 8-12 GHz.

Rescuing ACE2-Deficiency-Mediated Nucleus Pulposus Senescence and Intervertebral Disc Degeneration by a Nanotopology-Enhanced RNAi System.

Nucleus pulposus cell (NPC) senescence contributes to intervertebral disc degeneration (IVDD). However, the underlying molecular mechanisms are not fully understood. In this study, it is demonstrated that angiotensin-converting enzyme 2 (ACE2) counteracted the aging of NPCs and IVDD at the cellular and physiological levels. The expression of ACE2 correlates negatively with the degree of NPC senescence and IVDD. Using both loss- and gain-of-function mouse models, it is revealed that ACE2 deficiency increased the senescence of NPCs and exacerbated injury- or instability-induced IVDD, whereas ACE2 overexpression counteracted these detrimental effects. Mechanistically, integrated analysis of single-cell and bulk transcriptomics shows that ACE2 deficiency results in the activation of TGFβ2/Smads signaling pathway and the transcription of Serpine1, ultimately triggering NPC senescence and IVDD. A nanomedical delivery system (virus-like nanovectors, VNs) composed of nanovectors with a virus-like surface topology and small interfering RNA targeting Serpine1 (VN-siSer) is developed. With nanotopology-enhanced transfection efficiency, RNA-interfering treatment by VN-siSer effectively alleviated NPC senescence and IVDD at both the cellular and animal levels. Overall, the data reveal the underlying mechanisms of ACE2 in NPC senescence and IVDD pathogenesis and propose a distinct paradigm of precise nanomedical senescence-blockade RNAi for IVDD treatment.

Survey of Inter‐Prediction Methods for Time‐Varying Mesh Compression

AbstractTime‐varying meshes (TVMs), that is mesh sequences with varying connectivity, are a greatly versatile representation of shapes evolving in time, as they allow a surface topology to change or details to appear or disappear at any time during the sequence. This, however, comes at the cost of large storage size. Since 2003, there have been attempts to compress such data efficiently. While the problem may seem trivial at first sight, considering the strong temporal coherence of shapes represented by the individual frames, it turns out that the varying connectivity and the absence of implicit correspondence information that stems from it makes it rather difficult to exploit the redundancies present in the data. Therefore, efficient and general TVM compression is still considered an open problem. We describe and categorize existing approaches while pointing out the current challenges in the field and hint at some related techniques that might be helpful in addressing them. We also provide an overview of the reported performance of the discussed methods and a list of datasets that are publicly available for experiments. Finally, we also discuss potential future trends in the field.

Optimization design of gearbox based on response surface optimization and topology optimization

Optimization design of gearbox based on response surface optimization and topology optimization

Спин-орбитальное взаимодействие в пятиорбитальной модели ферропниктидов

The effect of spin-orbit coupling on the band structure and Fermi surface in the five-orbital model for iron-based superconductors is studied. Since there are two iron ions in the unit cell and their orbitals indirectly coupled through as orbitals, we introduce the constants of the intra- and inter-ion spin-orbit coupling in the effective model to separate the effect of the corresponding contributions on the band structure. We show that the intra- and inter-ion parts of the spinorbit coupling lead to Fermi surface topology change – splitting of the four contours of the Fermi surface around the point M = (π, π).

Surface Structured Quadrilateral Mesh Generation Based on Topology Consistent‐Preserved Patch Segmentation

ABSTRACTSurface‐structured mesh generation is an important part of the Computational Fluid Dynamics (CFD) preprocessing stage. The traditional method cannot automatically divide the 3D surface topology in complex structures. Thus, we propose a surface‐structured quadrilateral mesh generation method based on topology‐consistent‐preserved patch segmentation. The core idea is to segment the complex 3D model into several simple parts according to mesh quality and map each part to the 2D parametric domain based on the conformal parameterization method. Then, we utilize pattern‐based topology partitioning to divide the parametric domain into multiple quadrilateral subdomains, facilitating the generation of 2D structured quadrilateral meshes. By using the inverse mapping algorithm based on barycentric weights, the generated 2D structured mesh is inversely mapped back to the 3D space. Finally, we splice each part accurately according to the structured mesh distribution. Experimental results show that our proposed method can generate higher‐quality structured quadrilateral meshes than previous methods without losing the mesh topology of the original model.

The Golden Ratio Family of Extremal Kerr-Newman Black Holes and Its Implications for the Cosmological Constant

This work explores the geometry of extremal Kerr-Newman black holes by analyzing their mass/energy relationships and the conditions ensuring black hole existence. Using differential geometry in E3, we examine the topology of the event horizon surface and identify two distinct families of extremal black holes, each defined by unique proportionalities between their core parameters: mass (m), charge (Q), angular momentum (L), and the irreducible mass (mir). In the first family, these parameters are proportionally related to the irreducible mass by irrational numbers, with a characteristic flat Gaussian curvature at the poles. In the second family, we uncover a more intriguing structure where m, Q, and L are connected to mir through coefficients involving the golden ratio −ϕ−. Within this family lies a unique black hole whose physical parameters converge on the golden ratio, including the irreducible mass and polar Gauss curvature. This black hole represents the highest symmetry achievable within the constraints of the Kerr-Newman metric. This remarkable symmetry invites further speculation about its implications, such as the potential determination of the dark energy density parameter ΩΛ for Kerr-Newman-de Sitter black holes. Additionally, we compute the maximum energy that can be extracted through reversible transformations. We have determined that the second, golden-ratio-linked family allows for a greater energy yield than the first.

SegCSR: Weakly-Supervised Cortical Surfaces Reconstruction from Brain Ribbon Segmentations.

Deep learning-based cortical surface reconstruction (CSR) methods heavily rely on pseudo ground truth (pGT) generated by conventional CSR pipelines as supervision, leading to dataset-specific challenges and lengthy training data preparation. We propose a new approach for reconstructing multiple cortical surfaces using weak supervision from brain MRI ribbon segmentations. Our approach initializes a midthickness surface and then deforms it inward and outward to form the inner (white matter) and outer (pial) cortical surfaces, respectively, by jointly learning diffeomorphic flows to align the surfaces with the boundaries of the cortical ribbon segmentation maps. Specifically, a boundary surface loss drives the initialization surface to the target inner and outer boundaries, and an inter-surface normal consistency loss regularizes the pial surface in challenging deep cortical sulci. Additional regularization terms are utilized to enforce surface smoothness and topology. Evaluated on two large-scale brain MRI datasets, our weakly-supervised method achieves comparable or superior CSR accuracy and regularity to existing supervised deep learning alternatives.

Ultrafast optical induction of magnetic order at a quantum critical point

Time-resolved ultrafast spectroscopy has emerged as a promising tool to dynamically induce and manipulate non-trivial electronic states of matter out-of-equilibrium. Here we theoretically investigate light pulse driven dynamics in a Kondo lattice system close to quantum criticality. Based on a time-dependent auxiliary fermion mean-field calculation we show that light can dehybridize the local Kondo screening and induce oscillating magnetic order out of a previously paramagnetic state. Depending on the laser pulse field amplitude and frequency the Kondo singlet can be completely deconfined, inducing a dynamic Lifshitz transition that changes the Fermi surface topology. These phenomena can be identified in harmonic generation and time-resolved angle-resolved photoemission spectroscopy spectra. Our results shed new light on non-equilibrium states in heavy fermion systems.

The effects of different pellet shapes on streamer dynamics in patterned dielectric barrier discharges

Abstract Dielectric barrier discharges (DBD) are frequently used for gas conversion for environmental protection by removing harmful components from gas streams and converting them into value added products. DBD operation is typically combined with catalysts placed on spherical dielectric beads in the plasma volume to enhance conversion rates and energy efficiency. However, the presence of such pellets blocks the gas flow and their random arrangement leads to unstable discharges. In this work, we use an advanced plasma source, the patterned DBD (p-DBD), where dielectric pellets are immersed into an electrode at fixed and controllable positions to enhance plasma stability and control. Based on experiments and simulations we study the effects of the pellet shape and the driving voltage on the spatio-temporally resolved dynamics of volume and surface streamers, that ultimately determine the generation of reactive species, plasma-catalyst coupling, and conversion rates/efficiencies via electron heating. The pellet shape is found to influence the streamer speed and the generation of energetic electrons. Via their effects on the effective capacitance of the pellet, shapes with a flatter plasma facing apex are polarized more strongly by approaching volume streamers. This results in a stronger local enhancement of the electric field at the apex, higher volume streamer speed, and more electron heating at this position. Depending on the surface topology maximum electron impact excitation of the background gas is observed at different locations along the pellet's surface. Changing the polarity of the rectangular driving voltage waveform provides control of the direction of positive/negative streamer propagation and selectivity towards anode or cathode directed streamer movement.

A Numerical Study of Topography and Roughness of Sloped Surfaces Using Process Simulation Data for Laser Powder Bed Fusion.

The simulation of additive manufacturing has become a prominent research area in the past decade. Process physics simulations are employed to replicate laser powder bed fusion (L-PBF) manufacturing processes, aiming to predict potential issues through simulated data. This study focuses on calculating surface roughness by utilizing 3D surface topology extracted from simulated data, as surface roughness significantly influences part quality. Accurately predicting surface roughness using a simulation remains a persistent challenge. To address this challenge, the L-PBF technique with two different cases (pre- and post-contouring) was simulated using two-step process physics simulations. The discrete element method was utilized to simulate powder spreading, followed by the Flow-3D melting simulation. Ten layers were simulated at three different linear energy density (LED) combinations for both cases, with samples positioned at a 30-degree angle to accommodate upskin and downskin effects. Furthermore, a three-dimensional representation of the melted region for each layer was generated using the thermal gradient output from the simulated data. All generated 3D layers were stacked and merged to consolidate a 3D representation of the overall sample. The surfaces (upskin, downskin, and side skins) were extracted from this merged sample. Subsequently, these surfaces were analyzed, and surface roughness (Sa values) was calculated using MATLAB. The obtained values were then compared with experimental results. The downskin surface roughness results from the simulation were found to be within the range of the experimental results. This alignment is attributed to the fact that the physics simulation primarily focuses on melt pool depth and width. These promising findings indicate the potential for accurately predicting surface roughness through simulation.

On the lift generation over a sphere using asymmetric roughness

This study investigates a novel phenomenon of lift generation around a sphere by pneumatically manipulating its surface topology with an asymmetric roughness distribution. A comprehensive series of systematic experiments were conducted for Reynolds numbers (Re=U∞d/ν, where U∞ is the free-stream velocity, d is the sphere diameter, and ν is the fluid kinematic viscosity) ranging from 6×104 to 1.3×105, and dimple depth ratios (k/d, where k is the dimple depth) from 0 to 1×10−2 using a smart morphable sphere. The findings show that an asymmetrically rough sphere can generate lift forces up to 80% of the drag, comparable to those produced by the Magnus effect. The dimple depth ratio affects both Re at which lift generation begins and the maximum lift coefficient (CL) achievable. The optimal k/d for maximum lift varies with Re: deeper dimples are needed at low Re, while shallower dimples are more effective at high Re. For a fixed Re, increasing k/d monotonically increases lift until a critical k/d is reached, beyond which lift decreases. Particle image velocimetry revealed that dimples delay flow separation on the rough side, while the smooth side remains unchanged, resulting in asymmetric boundary layer separation, leading to wake deflection and lift generation. Beyond the critical k/d, the flow separation location moved upstream, increasing the size of the rear wake, reducing wake deflection, and thus decreasing lift. This study is the first to report how manipulating surface topography can generate lift forces comparable to those produced by the Magnus effect, offering a new mechanism for aerodynamic control. These findings could have significant implications for the maneuvering capabilities of unmanned underwater vehicles, where fine control of lift is essential for agility.

Doping evolution of the normal state magnetic excitations in pressurized La3Ni2O7

Abstract The doping evolution behaviors of the normal state magnetic excitations
(MEs) of the pressurized nickelate La3Ni2O7 are theoretically studied in this paper. It
was found that the MEs of the parental compound have very strong dependence on the
vertical momentum qz. For small qz, the low energy MEs exhibit a square-like pattern
centered at (0, 0) which originates from the intrapocket particle-hole scatterings. With
the increasing of qz, this square pattern diminishes gradually, and the MEs turn to be
ruled by two new interpocket scattering modes with significantly larger intensity for
qz around π. Hence, we have established the exotic qz evolution of the normal state
MEs of the bilayer nickelates in the present study. Furthermore, we find that the main
features of the MEs are very robust against doping. They persist in the wide hole- or
electron-doping regime around the filling of n = 3.0. However, in the heavily electrondoped
regime, the behaviors of the MEs change qualitatively due to the occurrence of
a Lifshitz transition. With the absence of the hole γ pocket, for n = 4.0, there will
exist nearly perfect nesting between the electron α and the hole β pockets guaranteed
by the Luttinger theorem and the Fermi surface topology. As a result, a spin-densitywave
(SDW) phase was theoretically predicted to order around (π, π, π) near n = 4.0,
in contrast with the parental compound which orders at (π/2, π/2, π) under ambient
pressure. We expect that the doping-temperature phase diagram of the pressurized
La3Ni2O7 will be explored in the near future which is helpful to unravel the intricate
relation between the magnetic order and superconductivity.

Correlation between the structural, morphological, optical, nanomechanical, and tribological properties of ZnO films by USPT with their photocatalytic activities

The present work focused on studying the nanomechanical properties of ZnO thin films deposited on glass substrates using the ultrasonic spray pyrolysis technique. Structural and morphological properties are related to processing conditions, which affect mechanical, optical, and photocatalytic properties. To produce the ZnO films, three different molarities of spraying solution have been used which are 0.05 M; 0.075; and 0.10. The increase in the concentration of the spray solution led to an improvement in the crystal structure with the average crystallite size increasing from 28 nm to 35 nm. Morphological investigations revealed that the spherical nanoparticles with various size distributions. The rough surface topology emerged as a result of increasing solution molarity. Optical band gap values of the films decreased from 3.29 to 3.27 eV. Photocatalytic efficiency reached 93 % for ZnO film produced at higher solution molarity. Improved hardness values were determined for all films. Scratch tests showed better adhesion behavior for ZnO film at low solution molarity. Results indicate that solution molarity is an important parameter of the physical and photocatalytic properties of ZnO films as well as mechanical behaviors.

Surface engineering of paper via binary graphene inks for sustainable micro-supercapacitor with innovative architecture

Paper-based micro-supercapacitors (MSCs) are a vital on-chip micro-energy storage component for degradable and implantable electronics that are envisioned as the forerunner of sustainability revolutions. However, an easily-manipulated, macro-assembly proposal and innovative paper architecture to ameliorate the intrinsic topology surface and nonconducting feature remain challenging. In this work, a generalized surface assembly strategy is reported for controllably engineering a graphene-anchored monolithic network for the degradable metal-free paper MSCs. Devoid of insulating auxiliaries and multistep postprocessing (such as cryogenic assistance), the as-engineered paper electrodes essentially consist of unique conductive fiber layer featuring interconnected nanosheets and accumulated functionalized graphene layer based on micron-sized fibers, providing excellent flexibility and anti-aging properties. The multiscale capillary of cellulose fibers and effective space-charge of functionalized graphene ensure fast charge transport. Consequently, the resulting integrated paper MSCs deliver an impressive areal capacitance of 36.5 mF cm−2, high energy density of 3.25 μWh cm−2 and long-term cycling performance (66.4 % retention after 10 000 cycles), surpassing most previously reported paper-based MSCs. The new charge reservoir engineering on paper to fabricate sustainable energy storage system would open a novel available paradigm for the growing demand of portable and degradable electronics.

Resolving turbulence and drag over textured surfaces using texture-less simulations: the case of slip/no-slip textures

We study the effect of surface texture on an overlying turbulent flow for the case of textures made of an alternating slip/no-slip pattern, a common model for superhydrophobic surfaces, but also a particularly simple form of texture. For texture sizes $L^+ \gtrsim 25$ , we have previously reported that, even though the texture effectively imposes homogeneous slip boundary conditions on the overlying, background turbulence, this is not its sole effect. The effective conditions only produce an origin offset on the background turbulence, which remains otherwise smooth-wall-like. For actual textures, however, as their size increases from $L^+ \gtrsim 25$ the flow progressively departs from this smooth-wall-like regime, resulting in additional shear Reynolds stress and increased drag, in a non-homogeneous fashion that could not be reproduced by the effective boundary conditions. This paper focuses on the underlying physical mechanism of this phenomenon. We argue that it is caused by the nonlinear interaction of the texture-coherent flow, directly induced by the surface topology, and the background turbulence, as it acts directly on the latter and alters it. This does not occur at the boundary where effective conditions are imposed, but within the overlying flow itself, where the interaction acts as a forcing on the governing equations of the background turbulence, and takes the form of cross-advective terms between the latter and the texture-coherent flow. We show this by conducting simulations where we remove the texture and introduce additional, forcing terms in the Navier–Stokes equations, in addition to the equivalent homogeneous slip boundary conditions. The forcing terms capture the effect of the nonlinear interaction on the background turbulence without the need to resolve the surface texture. We show that, when the forcing terms are derived accounting for the amplitude modulation of the texture-coherent flow by the background turbulence, they quantitatively capture the changes in the flow up to texture sizes $L^+ \approx 70{-}100$ . This includes not just the roughness function but also the changes in the flow statistics and structure.

Impact energy absorption in 3D printed bio-inspired PLA structures

3D printing is an effective technique for designing and producing products with unique shapes that cannot be made using traditional methods. Polylactic acid (PLA) filaments, commonly used in 3D printing, are a promised material for fabricating composites and lightweight structures. This study investigates the fracture and damping properties of biodegradable PLA samples with a bio-inspired structure and different density under dynamical (ballistic) loading. PLA samples were fabricated using a 3D printer and a Fusion Deposition Modeling (FDM) method. A unique computer program for cellular samples with Schwartz-Diamond minimal surface topology was developed. The impact absorption energy under ballistic loading of PLA samples with Schwarz-Diamond surface structure was found to depend on their density and impact velocity. The internal structure of 3D-printed PLA cellular samples with a Schwarz-Diamond triply periodic minimal surface and the fracture mechanism of the cellular samples with different densities were demonstrated using scanning electron microscopy. It was found that the fracture mechanism changed from ductile to quasi-brittle with increasing sample density. This work provides a foundation for understanding the fabrication of plastic cellular products using 3D printing.

Mapping Li Concentration Gradients across Battery Cathodes

Lithium-ion batteries (LIBs) are playing an increasingly important role in enabling the transition to a low-carbon global economy, in electric vehicle and grid storage applications. Despite increasing LIB ubiquity, there remains gaps in our understanding of how to optimize further LIB electrode design and structure, and how to achieve such designs in practice and at scale without excessive trial-and-error experimentation. For example, thicker electrodes are desirable for improved volumetric capacity but particularly during rapid charging and discharging cycles, a significant through-electrode thickness Li ion concentration gradient in the electrolyte builds up. This leads to a spatially varying concentration overpotential that in turns leads to uneven utilization of the active material, resulting in diminished capacity and accelerated degradation. Although models of electrode dynamics can help qualitatively to understand concentration polarization effects as a function of electrode design, there are few practical experimental tools to visualize or resolve Li-ion concentration gradients in practice. For example, the widely-used energy dispersive X-ray spectroscopy (EDS) in a scanning electron microscopy cannot resolve elements with very low atomic number such as Li.In this presentation we describe the development of a methodology to visualize Li-ion concentration gradients across a range of electrodes based on secondary ion mass spectroscopy (SIMS). We combine SIMS with EDS to collect elemental maps of all principle LIB electrode elements in a single workflow, which is also extended to 3D by further combining with a plasma field ion microscope (P-FIB) capability. We apply the new methodology for LIB cathodes based on LiFePO4 (LFP) and LiMn2O4 (LMO) that are at different state of overall charge, achieved at a range charging rates. The electrodes also span a range of thicknesses from 100 to 700 µm. We show how the approach can operate over cross-sections large enough to encompass all the electrode thickness while maintaining sufficient spatial resolution to capture key features of the local Li concentration. While EDS elemental maps, with appropriate calibration, can be correlated to local element concentration with good accuracy, SIMS spectra and specifically the intensity of the 7Li+ peaks cannot be readily related to local Li concentration since the yield of 7Li+ ion relates to additional factors, such as the local atomic environment, surface topology and more. We describe how we inter-relate the EDS and SIMS maps for non-Li elements to account for some of these features, and show how these reveals the underlying Li distributions. We consider how these measurements of the Li concentration in the solid particles of the electrode relate to the local state of charge, and the conditions in the electrolyte when charge/discharge was halted and the sample was retrieved from the cell for examination. Fine-scale variations in local 7Li+ ion intensity are also revealed and explained in terms of local microstructural features such as particle size, any particle cracking, the growth of secondary electrolyte interphase, etc.