Geometric Effects Research Articles

Geometrical uncertainties effects on the dynamics and effectiveness of a multi-stable vibratory energy harvester

Geometrical uncertainties effects on the dynamics and effectiveness of a multi-stable vibratory energy harvester

Numerical analysis of the geometrical modifications effects on the tensile strength of bonded single-lap joints

Nowadays, bonded joints have increasingly become the most used joining process in many industrial fields and even in civil engineering due to their simple geometry and structural efficiency and especially with the development of structural adhesives. Several solutions have been proposed in order to improve the mechanical strength of bonded joints by taking into consideration modifications to the adhesive edges and adherends to attenuate as much as possible the high stress concentration at the level of the adhesive. In this study, a 3D numerical model was developed in Abaqus to evaluate the influence of geometric changes in the adherends’ and adhesive edges on the mechanical strength of a single-lap joint under uniaxial tensile stress. Two modified geometric configurations of the bonded joint were proposed, taking into account on the one hand the presence of an adhesive fillet as the first modification and on the other hand, a removal of material at the level of the free edges of the adherends (adherends notching) as the second modification. The objective is to analyze the impact of these geometric modifications on the reduction of stress concentration in the adhesive and to explore how this new joint design can contribute to improve the strength of bonded joints. The results clearly show that a geometric modification at the level of the two free edges of the two substrates improves the strength of the joint and reduces the high stress concentrations in the adhesive. The joint strength is greatly improved if these modifications are optimized in relation to the overlap length and especially in relation to the thickness of the adherends and the adhesive. Adherend notching or applying an adhesive fillet resulted in a considerable reduction in peel stresses.

Insights into the Activity and Stability of Dual-Site Single Atom Catalysts for Oxygen Reduction Reaction Using a 2D Phthalocyanine-MOF

Hydrogen fuel cells have been considered as an effective strategy to shift fossil-fuel based economy to hydrogen economy. The performance of the fuel cells is often limited by the slow kinetics of the cathodic oxygen reduction reaction (ORR). Metal-organic frameworks (MOFs) based on 2D Phthalocyanine offer dual-site single atom catalyst (SAC) where M1 site typically amine coordinated node and M2 site is the phthalocyanine center (M1/M2 = Co, Cu, Ni). Here we conduct both computational studies and experimental measurements to elucidate the site selectivity and activity of two- and four-electron ORR process for pure (contains same element on both sites) and mixed (different M1 and M2) MOF system, and their overall stability. Using density functional theory (DFT), we find that regardless of site, Cobalt (Co) element shows better four-electron ORR activity than other elements in the mixed MOF system. Our integrated crystal orbital Hamilton population (ICOHP) calculations indicate that for pure MOF system, M1(d)-4N(2p) bonds are stronger than M2(d)-4N(2p), which raises d-band center of M2 sites closer to Fermi level, hence improves its activity towards four-electron ORR process. For mixed systems, M2 sites activity largely depends on the geometrical effects caused by M1 site elements. Our activity calculations reveal that Co (as M2) in the Ni-Co mixed MOF systems predicts lowest overpotential for ORR among all studied MOF system. Our dissolution mechanism and stability calculations show that Cu (as M1) causes stress/strain within the mixed MOF system denoting least stable among all studied during ORR process. In experiment, we found Co-based MOF, particularly Ni-Co demonstrates the highest kinetic activity and Cu is the least stable element, showing excellent agreement with computational studies. We hope this study will help in understanding the insight into the rational design of highly active and stable MOF for electrochemical processes. This research was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Catalysis Science Program to the SUNCAT Center for Interface Science and Catalysis.

Breaking through the State-of-the-Art Frontier in Oxygen Electrocatalysis: Geometry Adaptive Catalysts (GACs)

The grand challenge in oxygen electrocatalysis lies in overcoming scaling relations. The theoretical activity volcano positions the ideal catalyst at the apex. However, the OH–OOH scaling relation determines a linear path on the volcano surface that limits the activity. The current state-of-the-art (SOTA) in modeling confirms this scaling relation, at the same time it hinders the experimental development of novel oxygen reduction reaction (ORR) catalysts, impeding progress in sustainable energy solutions. To address this challenge, we propose to use the geometry effect and introduce the concept of Geometry Adaptive Catalysts (GACs).[1]The geometry effect, based on preliminary research, involves changing catalytic activity by adjusting the adsorption energy of intermediates through the control of catalyst geometry. Our goal is to break through the SOTA frontier for ORR by synthesizing GACs and supporting our efforts with theoretical and computational modeling of the geometric effect. In this work we aimed to utilize the geometry effect by synthesizing GACs with various controlled structures, including specific intersite distances, and variable curvature. This enables precise control of catalyst geometry, allowing manipulation of catalytic activity and overcoming scaling relations. Key geometric parameters, namely inter-site distance, curvature, and specific stabilizations of ORR intermediates, are explored to test our hypothesis: Controlling catalyst geometry adjusts the ORR mechanism and adsorption energies of intermediates, enabling the switching, pushing, and even bypassing of scaling relations.This approach holds promise for substantial improvements in environmental sustainability and human life quality, with broad applicability to various electrocatalytic reactions beyond ORR.

Examining Shape Dependence on Small Mild Steel Specimens during Heating Processes.

With regard to the heating technology of small test specimens (D < 1 inch, i.e., 25.4 mm), only a limited amount of data and literature are available for making adequate technological decisions. Heating time of small geometric shapes is influenced by the technological parameters of the furnace, the temperature, the disposition technique in the furnace and the geometric characteristics of the workpiece. How to shorten heating time to achieve a suitable material structure is a vital question, while considerable energy is saved at the same time. Among the geometric characteristics, shape dependence is one of the important aspects that must be taken into account in terms of heating technology. Shape dependence is usually taken into account with empirically produced correction factors, which can result in significant oversizing of heating time, energy-wasting technology and material structure of insufficient fineness. In the course of our work, we investigated and compared the shape dependence of cylindrical and prismatic specimens with the same surface-to-volume ratios, which were combined with surface heat transfer analyses and geometric effect tests to formulate new approximate equations for determining heating time. As a result, we could mathematically derive a relationship between heating time, size and shape of the active surfaces, the correlation of which can shorten heating time by 20%. In addition, a shape factor (1.125) between cylinder and prismatic-shaped specimens was determined, which can be used with the new equation to calculate heating time for similar specimens. At last, a relationship is developed between the amount of heat that can be stored in the body during heat equalization and the complexity of the shape, which can be characterized through ratios depending on heating times and active surfaces in the function of total surface/volume ratio. Based on this relationship it can be determined more precisely when heat equalization occurs; therefore, shorter heating time can be achieved. In conclusion, with the help of this new method, optimal heating time for structural steel components, in the case of small cross-section and weight, can be determined.

Lanthanide-Induced Ligand Effect to Regulate the Electronic Structure of Platinum-Lanthanide Nanoalloys for Efficient Methanol Oxidation.

The ligand effect in alloy catalysts is one of the decisive parameters of the catalytic performance. However, the strong interrelation between the ligand effect and the geometric effect of the active atom and its neighbors as well as the systematic alteration of the microenvironment of the active site makes the active mechanism unclear. Herein, Pt3Tm, Pt3Yb, and Pt3Lu with a cubic crystal system (Pm-3m) were selected. With the difference of Pt-Pt interatomic distance within 0.02 Å, we minimize the geometric effect to realize the disentanglement of the system. Through precise characterization, due to the low electronegativity of Ln (Ln = Tm, Yb, and Lu) and the ligand effect in the alloy, the electronic structure of Pt is continuously optimized, which improves the electrochemical methanol oxidation reaction (MOR) performance. The Ln electronegativity has a linear relationship with the MOR performance, and Pt3Yb/C achieves a high mass activity of up to 11.61 A mgPt-1, which is the highest value reported so far in Pt-based electrocatalysts. The results obtained in this study provide fundamental insights into the mechanism of ligand effects on the enhancement of electrochemical activity in rare-earth nanoalloys.

Unraveling the effect and difference of S or Si atoms modified Pd-based catalysts in tuning catalytic performance of C2H2 semi-hydrogenation

Modifying the spatial scale of active site has been proven a good strategy for enhancing catalytic performance. In this study, the Pd-based catalysts with different spatial scale of active site were constructed via the modification of non-metallic S or Si atoms over Pd, Cu alloyed Pd SACs, PdAg surface alloy and PdM (M=Au, Ag) IMCs catalysts, then, C2H2 semi-hydrogenation catalytic performance was identified based on DFT calculations. The findings indicate that the catalytic performance of C2H2 semi-hydrogenation is greatly influenced by the spatial extent of active site and the electronic effect modified by the S or Si atoms. Geometric effect caused by S or Si atoms reduces the spatial scale of active site over S/Pd-2 × 2, Si/Pd-3 × 3, S/Pd6Ag, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1, thereby preventing green oil generation. Electronic effect caused by S or Si atoms leads to far away from the Fermi level of d-band center over S/Pd-2 × 2, Si/Pd-3 × 3, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1 to improve C2H4 production activity and selectivity. Seven catalysts S/Pd-2 × 2, Si/Pd-3 × 3, PdCu-2 × 2, S/Pd6Ag, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1 are screened out to present high selectivity and activity of C2H4 production, and effectively prevent green oil generation. This study provides valuable structural insights for designing high-performance catalysts by the modification of non-metallic atom in C2H2 semi-hydrogenation.

Evident structural anisotropies arising from near-zero particle asphericity in granular spherocylinder packings.

With magnetic resonance imaging experiments, we study packings of granular spherocylinders with merely 2% asphericity. Evident structural anisotropies across all length scales are identified. Most interestingly, the global nematic order decreases with increasing packing fraction, while the local contact anisotropy shows an opposing trend. We attribute this counterintuitive phenomenon to a competition between gravity-driven ordering aided by frictional contacts and a geometric frustration effect at the marginally jammed state. It is also surprising to notice that such slight particle asphericity can trigger non-negligible correlations between contact-level and mesoscale structures, manifested in drastically different nonaffine structural rearrangements upon compaction from that of granular spheres. These observations can help improve statistical mechanical models for the orientational order transformation of nonspherical granular particle packings, which involves complex interplays between particle shape, frictional contacts, and external force field.

Design and simulation of a microfluidics-based artificial glomerular ultrafiltration unit to reduce cell-induced fouling.

The microfluidic-based Glomerulus-on-Chips (GoC) are mostly cell based, that is, 3D cell culture techniques are used to culture glomerular cells in order to mimic glomerular ultrafiltration. These chips require high maintenance to keep cell viability intact. There have been some approaches to build non-cell-based GoCs but many of these approaches have the drawback of membrane fouling. This article presents a structural design and simulation study of a dialysate free microfluidic channel for replicating the function of the human glomerular filtration barrier. The key advancement of the current work is addressing the fouling issue by combining a pre-filter to eliminate cellular components and performing filtration on the blood plasma. The Laminar Flow Mixture Model in COMSOL Multiphysics 5.6 has been utilized to simulate the behavior of blood flow in the microchannels. The geometrical effect of microchannels on the separation of the filtrate was investigated. The velocity at the inlet of the microchannel and pore size of the filtration membrane are varied to see the change in outflow and filtration fraction. The efficiency of the device is calculated in terms of the filtration fraction (FF%) formed. Simulation results show that the filtrate obtained is ~20% of the plasma flow rate in the channel, which resembles the glomerular filtration fraction. Given that it is not dependent on the functionality of grown cells, the proposed device is anticipated to have a longer lifespan due to its non-cell-based design. The device's cost can be reduced by avoiding cell cultivation inside of it. It can be integrated as a glomerular functional unit with other units of kidney model to build a fully developed artificial kidney.

Mechanical Effect Produced by Photo‐Switchable Reactions: Insights from Molecular Simulations

AbstractLight‐responsive shape‐changing polymers are photonastic materials: they can convert light into mechanical energy through macroscopic transformations. Indeed, photochromic molecules embedded in these polymer films present light‐induced structural modifications that can trigger a significant macroscopic deformation. In this theoretical study based on molecular dynamics simulations, analysis tools ranging from atomic to supramolecular scales are developed to investigate this photonastic phenomenon. To this purpose, a model system built upon an azobenzene photochrome embedded in different environments (tetrahydrofuran, cis‐1,4‐polybutadiene and hydroxyl‐terminated polybutadiene) is considered. First, the impact of the environment on the photochrome properties is discussed through the analysis of the structural properties, ultra‐violet visible (UV–vis) absorption spectra and dynamical properties of the photoswitch. Then, the impact of the presence of the photochrome on the polymer is studied. At the atomic scale, the radial distribution functions show some differences between the cis and trans isomers due to geometrical effects. At the molecular scale, the analysis of the size and shape of the polymer chains reveals that the photochrome has no impact on the chain properties. Finally, at the macroscopic scale, the cohesive energy density shows that the polymer is stabilized by the presence of photochrome molecules.

Facets of Correlated Non‐Markovian Channels

AbstractThe domain of correlated non‐Markovian channels are investigated, exploring the potential memory arising from the correlated action of channels and the inherent memory due to non‐Markovian dynamics. The impact of channel correlations is studied using different non‐Markovianity indicators and measures. In addition, the dynamical aspects of correlated non‐Markovian channels, including entanglement dynamics as well as changes in the volume of accessible states, are explored. The analysis is presented for both unital and non‐unital correlated channels. A new correlated channel constructed with modified Ornstein–Uhlenbeck noise (OUN) is also presented and explored. Further, the geometrical effects of the non‐Markovianity of the correlated non‐Markovian channels are discussed with a study of change in the volume of the accessible states. The link between the correlation factor and error correction success probability is highlighted.

Fracture modeling of curved composite shell structures using augmented finite element method

This paper presents an augmented finite element method for the fracture modeling of curved composite shell structures considering geometric nonlinear effects. We first derive the composite shell AFEM (CS-AFEM) formulation using a dynamic implicit algorithm, which enhances the numerical convergence when dealing with unstable crack propagations. Besides, the cohesive zone model featuring with shell kinematics is incorporated into the CS-AFEM to describe the quasi-brittle fracture behaviors of composite laminates. Furthermore, a coordinate transformation scheme is proposed to describe both the local material orientation and the crack evolving path in the curved shell structures. Finally, several benchmark examples are numerically investigated, and the capability of the proposed method in modeling the arbitrary evolving cracks in curved composite shell structures has been thoroughly demonstrated.

Tri-site Synergistic Cu(I)/Cu(II)─N Single-Atom Catalysts for Additive-Free CO2 Conversion.

As the highly stable and abundant carbon source in nature, the activation and conversion of CO2 into high-value chemicals is highly desirable yet challenging. The development of Cu(I)/Cu(II)─N tri-site synergistic single-atom catalysts (TS-SACs) with remarkable CO2 activation and conversion performance is presented, eliminating the need for external additives in cascade reactions. Under mild conditions (40°C, atmospheric CO2), the catalyst achieves high yields (up to 99%) of valuable 2-oxazolidinones from CO2 and propargylamine. Notably, the catalyst demonstrates easy recovery, short reaction times, and excellent tolerance toward various functional groups. Supported by operando techniques and density functional theory calculations, it is elucidated that the spatially proximal Cu(I)/Cu(II)─N sites facilitate the coupling of multiple chemical transformations. This surpasses the performance of supported isolated Cu(I) or Cu(II) catalysts and traditional organic base-assisted cascade processes. These Cu(I)/Cu(II)─N tri-site synergistic atom active sites not only enable the co-activation of CO2 at the Cu(II)─N pair and alkyne at the Cu(I) site but also induce a di-metal locking geometric effect that accelerates the ring closure of cyclic carbamate intermediates. The work overcomes the limitations of single metal sites and paves the way for designing multisite catalysts for CO2 activation, especially for consecutive activation, tandem, or cascade reactions.

Confinement and synergy effects of supported-confined bimetal catalysts with superior stability and catalytic activity

Bimetallic nanocrystals have attracted considerable attention because of their complicated systems, which are far superior to those of their individual constituents. A TiO2-confined PtMnP bimetallic catalyst (PtMnP@TiO2) was prepared using an ultrasonic-assisted coincident strategy, which demonstrated exceptional catalytic activity in the universal hydrogen evolution reaction (HER). Owing to the bimetallic synergistic effect and TiO2 confinement, PtMnP@TiOx showed ultrasmall metal nanoparticles (NPs), a higher active Pt0 content, adequate activation at the porous surface, and abundant acid sites. Simulations were performed to visualize the strain properties of Mn and Pt during the bending process and demonstrate the high activity of Pt. The Pt-Mn bimetallic catalysts were enriched with Pt NPs, convoyed by electron transfer from Mn to Pt. Briefly, PtMnP@TiO2 showed robust evolution reaction activities (an overpotential of 220 mV at a current density of 10 mA cm−2 and a Tafel slope of 186 mV dec−1) and the ability to contrast stated catalysts without ultrasonication-plasma. This protocol revealed that the geometrical and electronic effects of Pt and P surrounding the Mn species in PtMnP@TiO2 were crucial for increasing the catalytic activity (99%) and durability (over 20 cycles), which were far superior to those of other reported catalysts.

Simulation on fabricating graphene-coated nickel powders through micromechanical exfoliation

Fabricating graphene-coated metal powders have become a crucial method for preparing advanced composites, yet the encapsulation mechanism and mechanical behavior remain unclear. In this work, the mechanical behavior of exfoliation, encapsulation as well as the uniform dispersion of graphene nanoplatelets (GNPs) was elucidated for the first time through molecular dynamics simulation based on a two-step three-dimensional (3D) vibration milling for fabricating graphene-coated nickel powders. The critical collision velocity for separating GNPs layer by layer was obtained and the geometric effects of bulk graphite on graphene exfoliation were analyzed. Compared to cuboid graphite, collisions between nickel powders and spherical graphite were prone to the exfoliation of few-layer graphene. A comprehensive experimental study was conducted to investigate the effects of geometry on the exfoliation of graphene. These results suggest that the cuboid graphite is prone to obtaining graphite sheets rather than few-layer graphene, leading to the formation of GSs/Ni composite powders. While the GNPs coated nickel powders are obtained after the two-step 3D vibration milling via spherical graphite. This study provides a comprehensive understanding of the preparation of graphene-coated nickel powders via micromechanical exfoliation.

Unveiling Atomic-Scaled Local Chemical Order of High-Entropy Intermetallic Catalyst for Alkyl-Substitution-Dependent Alkyne Semihydrogenation.

High-entropy intermetallic (HEI) nanocrystals, composed of multiple elements with an ordered structure, are of immense interest in heterogeneous catalysis due to their unique geometric and electronic structures and the cocktail effect. Despite tremendous efforts dedicated to regulating the metal composition and structures with advanced synthetic methodologies to improve the performance, the surface structure, and local chemical order of HEI and their correlation with activity at the atomic level remain obscure yet challenging. Herein, by determining the three-dimensional (3D) atomic structure of quinary PdFeCoNiCu (PdM) HEI using atomic-resolution electron tomography, we reveal that the local chemical order of HEI regulates the surface electronic structures, which further mediates the alkyl-substitution-dependent alkyne semihydrogenation. The 3D structures of HEI PdM nanocrystals feature an ordered (intermetallic) core enclosed by a disordered (solid-solution) shell rather than an ordered surface. The lattice mismatch between the core and shell results in apparent near-surface distortion. The chemical order of the intermetallic core increases with annealing temperature, driving the electron redistribution between Pd and M at the surface, but the surface geometrical (chemically disordered) configurations and compositions are essentially unchanged. We investigate the catalytic performance of HEI PdM with different local chemical orders toward semihydrogenation across a broad range of alkynes, finding that the electron density of surface Pd and the hindrance effect of alkyl substitutions on alkynes are two key factors regulating selective semihydrogenation. We anticipate that these findings on surface atomic structure will clarify the controversy regarding the geometric and/or electronic effects of HEI catalysts and inspire future studies on tuning local chemical order and surface engineering toward enhanced catalysts.

Dark energy as a geometrical effect in geodetic brane gravity

Within the framework of the modified geodetic brane gravity, conformed by the Regge–Teitelboim model and enhanced with a linear term in the extrinsic curvature of the brane, the possibility that under an FRW geometry this theory emulates the so-called dark energy is discussed. The cosmological behavior of this model displays a self-(non-self)-accelerated expansion of this universe which is caused by a combination of usual matter and gravitational geometric effects controlled by a [Formula: see text] parameter that accompanies the correction K term. Indeed, the self-accelerated branch, provided by the trace K model raises the question of whether the extrinsic curvature correction terms might be suitable for dark energy candidates. We discuss the analytical expression obtained for [Formula: see text] in addition to the main cosmological parameters such as the state parameter [Formula: see text] and the deceleration parameter q. Moreover, when we call for the contribution of dark radiation-like energy to be switched off, [Formula: see text], we find the same acceleration behavior, as well as the same dark energy content provided by the DGP theory. The relationship of our findings to the analysis for [Formula: see text] performed by Davidson and Gurwich within the unified brane cosmology is briefly discussed.

Acid corrosion inhibition of mild steel by 8-hydroxyquinoline derivatives: organic synthesis, characterization, chemical, electrochemical investigation and theoretical calculations

In this study, two 8-hydroxyquinoline derivatives, HAPAQ and EAPAQ, were first synthesized, and their molecular structures were confirmed by 1H and 13C NMR. The effects of HAPAQ and EAPAQ on corrosion processes were investigated using weight loss, electrochemical, and theoretical methods. Overall, the data unmistakably demonstrate that the inhibition performance (η %) increases with an increase as HAPAQ and EAPAQ concentrations rise, peaking at 96.08% (HAPAQ) and 94.37% (EAPAQ) at the optimal concentration (10−3 M) for PPD technology. The two 8-hydroxyquinoline derivatives exhibit inhibitory behavior, as seen by the polarization curve impedance tests; however, they demonstrate that adsorption promotes protective action on metal surfaces, creating a geometric blocking effect and a protective coating that impedes metal breakdown. HAPAQ and EAPAQ's inhibitory efficacy may be reduced by the rising temperature. Furthermore, it adheres to Langmuir’s single-layer adsorption isotherm, and the physisorption and chemisorption mechanisms are linked to the corresponding value of the adsorption energy (ΔG ads). Additionally, the MS scanning electron microscope (SEM) has been studied and discussed. The possibility of complex organization between the inhibitor molecules, 8-hydroxyquinoline derivatives (HAPAQ and HAPAQ), and the Fe2+ ions generated during the oxidation process was established by examining the test solutions using UV–visible spectroscopy. Consequently, it is evident from DFT simulations that the surface recovery is dependent on the local reactivity descriptors. The theoretical outcomes derived from DFT are aligned with the findings of the experimental studies.

Geometric topological effect on non-relativistic solution under pseudoharmonic and extended double ring-shaped potentials

Geometric topological effect on non-relativistic solution under pseudoharmonic and extended double ring-shaped potentials

Unprecedented Strength Enhancement Observed in Interpenetrating Phase Composites of Aperiodic Lattice Metamaterials

AbstractSimultaneous high strength and high toughness are highly sought‐after in lattice metamaterials, but these properties are typically mutually exclusive. To overcome this challenge, the development of interpenetrating phase composite (IPC), which incorporates a net matrix infill into the lattice, has shown great potential in overcoming these constraints and is thus of continuous practical interest. In this work, a novel aperiodic monotile truss lattice and polymer IPC that exhibit unprecedented enhancement in both strength and toughness are reported. Specifically, the aperiodic unit cell is inspired by Einstein's monotile, a single space‐filling shape where the cell orientation never repeats. The IPCs are achieved through 3D‐printed Ti‐6Al‐4V truss lattices and epoxy infiltration. The highest gain in compressive strength reveals an impressive 246.61% increase, significantly exceeding the “1 + 1 &gt; 2” idealization typically associated with strength in IPC metamaterials. Furthermore, a high specific energy absorption of 46.2 J g−1 demonstrates superior toughness. The underlying mechanisms, including damage sequences, two‐phase interactions, and geometric effects between truss and epoxy, are fully elucidated. Overall, this work reports unprecedented enhancement in IPC's properties and demonstrates the potential of utilizing idealized structures to achieve an optimal combination of strength and toughness in mechanical metamaterials.