Experimental Observations Research Articles

Post-fire behavior and residual resistances of S890 ultra-high strength steel circular hollow sections under combined compression and bending

This paper presents experimental and numerical investigations into the post-fire local buckling behavior and residual resistances of S890 ultra-high strength steel (UHSS) circular hollow section (CHS) under combined compression and bending. The physical testing was firstly conducted and encompassed heating, soaking and cooling of specimens, as well as post-fire tensile coupon tests, measurements of initial local geometric imperfections and eccentrically loaded stub column tests. Then, finite element models were developed and validated with reference to the experimental observations and then adopted for parametric analyses to derive additional numerical data, considering various cross-section dimensions and loading combinations. As a result of the lack of design provisions for ultra-high strength steel structures after exposure to elevated temperatures, the applicability of the relevant ambient temperature design interactive curves given in the current European, American and Australian standards to post-fire S890 UHSS CHS under combined compression and bending was assessed, with post-fire material properties used. The assessment results showed that all design standards exhibited conservative and scattered predictions of residual resistances for S890 UHSS CHS under combined compression and bending at ambient temperature and after exposure to elevated temperatures. The American specification provided more precise predictions of residual failure loads for non-compact and slender (Class 3 and 4) sections than the Eurocode and Australian standard, due to the accurate compression and bending endpoints. In comparison to the American and Australian specifications, the Eurocode resulted in more precise results in predicting residual failure loads of compact (Class 1 and 2) sections, owing to the accurate compression and bending endpoints as well as the nonlinear design interaction curve.

Theoretical Study of Infrared and Ultraviolet Spectroscopy in SiP Interstellar Molecules

Abstract Insufficient theoretical investigation is being conducted on the spectroscopic characteristics within the infrared wavelength range of SiP, an identified interstellar molecule. Using the ic-MRCI method, potential energy functions and dipole moment functions for the ground state (${X}^2\Pi $) and low excited states (${{\rm{A}}}^2{\Sigma }^ + $) of the SiP molecule were calculated. Based on experimental spectroscopy data, least squares fitting was used for the potential energy functions of the ${X}^2\Pi $ and ${{\rm{A}}}^2{\Sigma }^ + $ states. By combining these potential energy and dipole moment functions, the one-dimensional Schrödinger equation was solved to obtain the vibronic energy levels and Einstein A coefficients for the electronic states. Partition functions of the SiP molecule from 0.1 K to 3000 K and the radiative properties of ${X}^2\Pi \leftrightarrow {X}^2\Pi $ and ${X}^{\rm{2}}\Pi \leftrightarrow {{\rm{A}}}^2{\Sigma }^ + $ were derived. Infrared spectroscopy of the ${X}^2\Pi $ state and ultraviolet spectroscopy of the ${X}^{\rm{2}}\Pi \leftrightarrow {{\rm{A}}}^2{\Sigma }^ + $ transition at 100 K, a temperature crucial for astronomical research, were calculated. Results indicate that the spectral line intensity of the ${X}^{\rm{2}}\Pi \leftrightarrow {{\rm{A}}}^2{\Sigma }^ + $ transition is greater, making it more suitable for astronomical observation. The obtained computational results in this paper yield spectroscopic parameters for the characterization of the interstellar molecule SiP, furnishing theoretical underpinnings for subsequent experimental observations.

Lithium-Ion battery silicon Anodes: Surface engineering with novel additives for enhanced ion and electron transport

Silicon (Si) stands as a promising candidate for high-capacity anode materials in the next-generation lithium-ion batteries (LIBs) due to extremely high specific capacity. However, silicon application is hindered by its inherently poor electron and ion conductivities, as well as structural instability during the repeated charging/discharging. To address these challenges, a novel functional surface modification agent, diethylenetriaminepenta(methylenephosphonic) acid (DTPMP), was decorated on the surface of silicon particles for the first time. The experimental results demonstrate that the DTPMP effectively enhances the cohesion between nano Si particles. This study combines experimental observations with theoretical calculations to analyze the nucleophilic and electrophilic sites of DTPMP and carboxymethyl cellulose (CMC), elucidating the existence state of DTPMP on the nano Si surface. Furthermore, by examining the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), along with the electrostatic potential (ESP) of DTPMP and solvent molecules in conjunction with Li+, the impact of the phosphate group on the diffusion of Li+ and electrons at the nano Si surface was studied. The electron density difference (EDD) maps for DTPMP and CMC reveal that DTPMP exhibits a more pronounced response in the presence of an electric field, suggesting its enhanced role in facilitating Li+ diffusion. This research offers a novel perspective on enhancing the electrochemical performance of nano Si surfaces, paving the way for the development of advanced LIBs with improved energy storage capabilities.

Advancements in biomass conversion: Copper-catalyzed anaerobic dehydrogenation of 5-hydroxymethylfurfural to 2,5-diformylfuran

Developing cost-effective and inherently safe methods for accelerating the sustainable production of value-added chemicals from biomass presents a promising solution to the current energy crisis. This study introduces heterogeneous copper species anchored on a γ-Al2O3 catalyst (Cu/γ-Al2O3) with high dispersibility and small Cu particle size, synthesized via a straightforward incipient-wetness impregnation method. This method facilitates the selective anaerobic dehydrogenation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF) in the absence of any oxidant or hydrogen acceptor. An HMF conversion of 69.8 % and a DFF yield of 44.9 % were attained at 130 °C over a 12-h period. Extensive characterizations were conducted to elucidate the correlation between the catalyst’s structure and its dehydrogenation activity. The findings indicated that strong L-acid sites, elevated Cu dispersions, small Cu particle size and an increased number of Cu+ active sites were conducive to enhanced dehydrogenation reactivity. The Cu/γ-Al2O3 catalyst demonstrated superior catalytic efficiency and stability. A possible reaction mechanism is suggested, integrating DFT calculations with experimental observations. This research offers valuable insights into the selective conversion of HMF to DFF and encourages further exploration into the dehydrogenation of biomass alcohols into high-value chemicals under oxidant-free conditions.

Numerical modeling of seismic performance of shallow steel tunnel

Advanced numerical models can be used to complement experimental results and further elucidate their findings. This is particularly true when certain scaled model “adjustments” are incorporated in the testing scheme to reduce the testing cost or schedule. This study conducts comprehensive finite element modeling to simulate large-scale shaking table tests conducted by Kim et al. (2023) [1] to evaluate the seismic performance of steel tunnels. The numerical model was calibrated by comparing its predictions with the experimental observations in the initial tests. The calibrated model was then validated by comparing its predictions with the results obtained from other test models and subjected to different input ground motions. The validated model was employed to comprehensively investigate the effects of the testing scheme parameters including the input motion time scaling, tunnel burial depth, and soil relative density. It was found that reducing the time scale factor during the tests led to decreased seismic responses. It was also found that the presence of overburden soil on top of the tunnel resulted in higher seismic bending moment values, and that higher overburden height increased both lateral and vertical soil pressures on the tunnel side walls and top slab. In addition, lateral soil distortion and tunnel deformations were found to be directly correlated with the overburden soil height. Furthermore, in the absence of overburden soil, there was a significant amplification in horizontal soil acceleration. The results demonstrated that lower-density sand bed experienced greater acceleration amplification and larger displacement, and the tunnel experienced larger lateral soil pressure and higher racking. Additionally, the results revealed that subjecting the same soil bed to several shaking tests affected its stiffness, and hence affected the test observations in the subsequent tests. This should be considered when planning shaking table tests. Finally, the strain values and racking ratios obtained from the numerical simulations and the shaking tests were in agreement with the values obtained from the FHWA procedure.

Microscopic damage in eutectic SnPb alloy: First-principles calculations and experiments

This study aims to comprehensively elucidate the microscopic origins of damage in eutectic SnPb alloy through atomic-scale investigations, a crucial endeavor for enhancing the alloy’s properties and furthering the development of Pb-free solders. First-principles calculations based on density functional theory (DFT) were employed to examine the mechanical constants and defect formation energies of the Pb phase, the β-Sn phase, and potential Sn/Pb eutectic phases in the SnPb alloy. The Voigt-Reuss-Hill approximation was utilized to derive the mechanical parameters of the elastically stable structure in SnPb alloy, facilitating the prediction of its mechanical properties. The defect formation energy calculations revealed a higher difficulty in forming vacancy defects in the β-Sn phase compared to the Pb phase. This discrepancy can be attributed to the stronger interactions between Sn atoms, resulting in the formation of more stable Sn-Sn bonds, thereby impeding vacancy generation in the β-Sn phase. Furthermore, the Pb phase exhibited a tendency for Sn atoms to occupy octahedral interstitial sites, whereas in the β-Sn phase, Pb atoms tended to displace neighboring Sn atoms along the [110] orientation into adjacent interstitial sites and occupy their lattice positions. Experimental observations complemented these calculation findings, demonstrating significant Sn element presence, up to 27.22 at%, in the Pb-rich phase, with notable microvoid damage primarily concentrated within this region. This observation aligns with the conclusions drawn from first-principles calculations and unveils the microscopic origins of damage in eutectic SnPb alloys.

Experimental observation of cavity-free ice-free isochoric vitrification via combined pressure measurements and photon counting x-ray computed tomography

Isochoric (constant-volume or volumetrically confined) vitrification has shown potential as an alternative cryopreservation-by-vitrification technique, but the complex processes at play within the chamber are yet poorly characterized, and recent investigations have prompted significant debate around whether a truly isochoric vitrification process (in which the liquid remains completely confined by solid boundaries) is indeed feasible. Based on a recent thermomechanical simulation of a high-concentration Me2SO solution, Solanki and Rabin (Cryobiology, 2023, 111, 9–15.) argue that isochoric vitrification is not feasible, because differential thermal contraction of the solution and container will necessarily drive generation of a cavity, corrupting the rigid confinement of the liquid. Here, we provide direct experimental evidence to the contrary, demonstrating cavity-free isochoric vitrification of a ∼3.5 M vitrification solution by combined isochoric pressure measurement (IPM) and photon-counting x-ray computed tomography (PC-CT). We hypothesize that the absence of a cavity is due to the minimal thermal contraction of the solution, which we support with additional volumetric analysis of the PC-CT reconstructions. In total, this study provides experimental evidence both demonstrating the feasibility of isochoric vitrification and highlighting the potential of designing vitrification solutions that exhibit minimal thermal contraction.

Aharonov-Bohm effect in Generalized Electrodynamics

The Aharonov-Bohm (AB) effect is considered in the context of Generalized Electrodynamics (GE) by Podolsky and Bopp. GE is the only extension to Maxwell electrodynamics that is locally U(1)-gauge invariant, admits linear field equations and contains higher-order derivatives of the vector potential. GE admits both massless and massive modes for the photon. We recover the ordinary quantum phase shift of the AB effect, derived in the context of Maxwell electrodynamics, for the massless mode of the photon in GE. The massive mode induces a correction factor to the AB phase shift depending on the photon mass. We study both the magnetic AB effect and its electric counterpart. In principle, accurate experimental observations of AB the phase shift could be used to constrain GE photon mass.

The Reconstruction of Pt(001) Surface and the Shell-Like Reconstruction of the Vicinal Pt(001) Surfaces Revealed by Neural Network Potential.

In this work, a highly accurate neural network potential (NNP) is presented, named PtNNP, and the exploration of the reconstruction of the Pt(001) surface and its vicinal surfaces with it. Contrary to the most accepted understanding of the Pt(001) surface reconstruction, the study reveals that the main driving force behind Pt(001) quasi-hexagonal reconstruction is not the surface stress relaxation but the increased coordination number of the surface atoms resulting in stronger intralayer binding in the reconstructed surface layer. In agreement with experimental observations, the optimized supercell size of the reconstructed Pt(001) surface contains (5×20) unit cells. Surprisingly, the reconstruction of the vicinal Pt(001) surfaces leads to a smooth shell-like surface layer covering the whole surface and diminishing sharp step edges.

Theoretical study of infrared and ultraviolet spectroscopy in SiP interstellar molecules

ABSTRACT Insufficient theoretical investigation is being conducted on the spectroscopic characteristics within the infrared wavelength range of SiP, an identified interstellar molecule. Using the ic-MRCI method, potential energy functions and dipole moment functions for the ground state (${X^2}\Pi $) and low excited states (${{\rm{A}}^2}{\Sigma ^ + }$) of the SiP molecule were calculated. Based on experimental spectroscopy data, least squares fitting was used for the potential energy functions of the ${X^2}\Pi $ and ${{\rm{A}}^2}{\Sigma ^ + }$ states. By combining these potential energy and dipole moment functions, the one-dimensional Schrödinger equation was solved to obtain the vibronic energy levels and Einstein A coefficients for the electronic states. Partition functions of the SiP molecule from 0.1 to 3000 K and the radiative properties of ${X^2}\Pi \leftrightarrow {X^2}\Pi $ and ${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$ were derived. Infrared spectroscopy of the ${X^2}\Pi $ state and ultraviolet spectroscopy of the ${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$ transition at 100 K, a temperature crucial for astronomical research, were calculated. Results indicate that the spectral-line intensity of the ${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$ transition is greater, making it more suitable for astronomical observation. The obtained computational results in this paper yield spectroscopic parameters for the characterization of the interstellar molecule SiP, furnishing theoretical underpinnings for subsequent experimental observations.

Wigner molecular crystals from multielectron moiré artificial atoms.

Semiconductor moiré superlattices provide a versatile platform to engineer quantum solids composed of artificial atoms on moiré sites. Previous studies have mostly focused on the simplest correlated quantum solid-the Fermi-Hubbard model-in which intra-atom interactions are simplified to a single onsite repulsion energy U. Here we report the experimental observation of Wigner molecular crystals emerging from multielectron artificial atoms in twisted bilayer tungsten disulfide moiré superlattices. Using scanning tunneling microscopy, we demonstrate that Wigner molecules appear in multielectron artificial atoms when Coulomb interactions dominate. The array of Wigner molecules observed in a moiré superlattice comprises a crystalline phase of electrons: the Wigner molecular crystal, which is shown to be highly tunable through mechanical strain, moiré period, and carrier charge type.

Modeling the impact of neuromorphological alterations in Down syndrome on fast neural oscillations.

Cognitive disorders, including Down syndrome (DS), present significant morphological alterations in neuron architectural complexity. However, the relationship between neuromorphological alterations and impaired brain function is not fully understood. To address this gap, we propose a novel computational model that accounts for the observed cell deformations in DS. The model consists of a cross-sectional layer of the mouse motor cortex, composed of 3000 neurons. The network connectivity is obtained by accounting explicitly for two single-neuron morphological parameters: the mean dendritic tree radius and the spine density in excitatory pyramidal cells. We obtained these values by fitting reconstructed neuron data corresponding to three mouse models: wild-type (WT), transgenic (TgDyrk1A), and trisomic (Ts65Dn). Our findings reveal a dynamic interplay between pyramidal and fast-spiking interneurons leading to the emergence of gamma activity (∼40 Hz). In the DS models this gamma activity is diminished, corroborating experimental observations and validating our computational methodology. We further explore the impact of disrupted excitation-inhibition balance by mimicking the reduction recurrent inhibition present in DS. In this case, gamma power exhibits variable responses as a function of the external input to the network. Finally, we perform a numerical exploration of the morphological parameter space, unveiling the direct influence of each structural parameter on gamma frequency and power. Our research demonstrates a clear link between changes in morphology and the disruption of gamma oscillations in DS. This work underscores the potential of computational modeling to elucidate the relationship between neuron architecture and brain function, and ultimately improve our understanding of cognitive disorders.

Estimating the axial strain of circular short columns confined with CFRP under centric compressive static load using ANN and GRA techniques

This investigation introduces advanced predictive models for estimating axial strains in Carbon Fiber-Reinforced Polymer (CFRP) confined concrete cylinders, addressing critical aspects of structural integrity in seismic environments. By synthesizing insights from a substantial dataset comprising 708 experimental observations, we harness the power of Artificial Neural Networks (ANNs) and General Regression Analysis (GRA) to refine predictive accuracy and reliability. The enhanced models developed through this research demonstrate superior performance, evidenced by an impressive R-squared value of 0.85 and a Root Mean Square Error (RMSE) of 1.42, and significantly advance our understanding of the behavior of CFRP-confined structures under load. Detailed comparisons with existing predictive models reveal our approaches' superior capacity to mimic and forecast axial strain behaviors accurately, offering essential benefits for designing and reinforcing concrete structures in earthquake-prone areas. This investigation sets a new benchmark in the field through meticulous analysis and innovative modeling, providing a robust framework for future engineering applications and research.

Extending the Finite Area Method for enhanced simulation of deformable membranes and its application to extrusion blow moulding

This paper investigates the mechanics of the Extrusion Blow Moulding (EBM) process, focusing on the clamp and inflation phases. The simulation framework employed in this study has been developed using OpenFOAM ® and extends the available Finite Area Method with a vertex-centred approach. This cutting-edge developments integrated a corotational formulation with a quasi-static approximation. The computational code and algorithm are verified and validated through comparisons between analytical solutions, experimental measurements and simulation results, ensuring the accuracy and reliability of the proposed approach. The implemented code is verified by checking fundamental principles of hyperelastic materials behaviour, demonstrated through equibiaxial deformation of spherical balloons. The use of neo-Hookean and Mooney–Rivlin material models provides crucial insights into material responses under different inflation conditions. The studies begin employing a conceptual mould within the EBM process that allows examining the effects of mould clamping on parison deformation. Then the study extends to analysing a real bottle manufactured via EBM, employing Stereolithography (STL) digitization and thickness mapping to quantify the thickness distribution. The simulation results closely replicates experimental observations, capturing the inherent non-linearity of these process stages, including large deformations and displacements, hyperelasticity and parison-mould contacts. This interdisciplinary research enhances understanding of the EBM process phases and analogous processes, providing valuable insights for plastic manufacturing. It improves the design process for meeting specific requirements and offers guidelines to avoid potential failures. The findings underscore the importance of such studies in advancing sustainable and efficient plastic manufacturing practices, with applications ranging from inflatable structures to EBM processes.

Enhanced cation ordering, electron-spin-phonon interactions and Fano resonance in half-metallic Sr2FeMoO6 thin films

We report the presence of electron-spin-phonon interactions in half-metallic ferromagnetic Sr2FeMoO6 (SFMO) double perovskite thin films using temperature-dependent Raman spectroscopy. A series of SFMO thin films have been prepared on LaAlO3 (001) single-crystal substrate using the Pulsed Laser Deposition technique. These depositions have been made in different gas-conditions such as in vacuum, and under nitrogen and oxygen gas pressures. At room temperature, Raman spectra manifest a Fano feature which indicates the presence of electron-phonon coupling in the films. The electron-phonon coupling strength further changes with a change in deposition conditions. Magnetization results show that the SFMO film grown in vacuum has the highest saturation magnetization which suggests better cation ordering as compared to the other films. For enhanced understanding, Raman spectra were recorded at varied temperatures and the data were analyzed by theoretical model fittings. A parameter quantifying temperature-dependent anharmonic nature of phonons has been derived using Balkanski model fits. This parameter shows a drastic deviation in the vicinity of Curie temperatures, manifesting a spin-phonon coupling in SFMO films. We further show that the spin-phonon coupling strengthens with improved Fe–Mo ordering. Any experimental observation of spin-phonon coupling has not been reported for SFMO systems till date. The magnetization data corroborate well with these observations made by Raman measurements. Our results of Raman spectroscopy, magnetization and resistivity collectively suggest that the SFMO films exhibit electron-spin-phonon interactions, which are influenced by the cation ordering. We also devised out the method of relating the anharmonic nature of Raman modes with the degree of Fe–Mo ordering and spin-phonon coupling in double-perovskite materials.

How to catch a shear band and explain plasticity of metallic glasses with continuum mechanics

Capturing a shear band in a metallic glass during its propagation experimentally is very challenging. Shear bands are very narrow but extend rapidly over macroscopic distances, therefore, characterization of large areas at high magnification and high speed is required. Here we show how to control the shear bands in a pre-structured thin film metallic glass in order to directly measure local strains during initiation, propagation, or arrest events. Based on the experimental observations, a model describing the shear banding phenomenon purely within the frameworks of continuum mechanics is formulated. We claim that metallic glasses exhibit an elastic limit of about 5% which must be exceeded locally either at a stress concentrator to initiate a shear banding event, or at the tip of a shear band during its propagation. The model can successfully connect micro- and macroscopic plasticity of metallic glasses and suggests an alternative interpretation of controversial experimental observations.

Subtle dynamics of chaotic torsion pendulum: a detailed comparison between experiments and numerical simulations

Abstract We conduct a detailed experimental and numerical study on the subtle dynamics of chaotic torsion pendulum (CTP). We first present experimental observations reported by students, and then propose a revised model of CTP based on laws of mechanics and insights about the experiment to understand these observations. Parameters of the revised model are fit using experimental data. The revised model agrees well with experimental observations. The subtle dynamics hidden in these phenomena, from parameter sensibility to influences of bistability and noise, are thoroughly exhibited through this study, hoping to provide more insights to the nonlinear nature of CTP.

On the Origin of the Photoplethysmography Signal: Modeling of Volumetric and Aggregation Effects

This study aimed to examine the mechanisms of the photoplethysmography (PPG) signal formation using Monte Carlo simulations of light transport in biological tissues and experimental observations. Based on a three-layer skin model in backscattering geometry, we sequentially simulated volumetric blood changes and the aggregation/disaggregation of erythrocytes in the dermal layer and estimated their contribution to the registered PPG signal. The calculations were conducted for two wavelengths: 525 nm and 810 nm. For green light, absorption predominates over scattering in the formation of a PPG signal, whereas, for near-infrared light, scattering prevails over absorption. This theoretical result was verified using the Modified Beer–Lambert law and clinical in vivo PPG data of seven healthy subjects. Changes in the size of the scatterers during erythrocyte aggregation and disaggregation can significantly contribute to the PPG signal at near-infrared light. Thus, for the green waveband, the classical volumetric model can be considered dominant in the PPG signal formation. In contrast, for the near-infrared range, both volumetric and aggregation effects must be considered as being approximately equal.

Weak time-scale separation at the onset of oscillatory magnetoconvection in rapidly rotating fluids

Abstract Convective instabilities are one of the integral parts of the dynamics of flows driven by thermal buoyancy. Naturally, physical phenomena exhibit a wide disparity in the length and timescales of the field variables in numerical simulations and experimental observations. Such variations are not represented in the traditional normal mode stability analysis attempting to understand the onset of convection. This study attempts to incorporate different time constants for different perturbation variables in the linear stability analysis with the help of a Taylor series expansion. The infinite horizontal layer model is chosen for simplicity. Apart from the classical Rayleigh-B{'e}nard system, additional physical effects such as background rotation and magnetic field have been considered with plausible implications for geophysical flow applications. The time scale separation is implemented by considering a slight change in the frequency of temperature perturbation compared to that for other physical quantities. Both analytical and numerical methods have been utilised for the investigation. The threshold buoyancy force is reduced when the temperature perturbation has a smaller frequency than the frequencies of other variables. Besides that, the onset wavenumber and frequency of the oscillatory modes are modified due to weak scale separation from the onset characteristics of the reference case. In particular, enhanced frequency of temperature perturbations leads to smaller-scaled magnetically controlled convective rolls and larger-scaled viscously controlled instabilities at the onset. A robust dependence of the onset characteristics with the parameter quantifying the timescale separation is obtained. Additionally, two transitions in the convective onset modes with scale separation have been identified.

Ultrafast dynamics of exciton-polariton fluids at non-zero momenta

In this study, we have explored the ultrafast formation and decay dynamics of exciton-polariton fluids at non-zero momenta, non-resonantly excited by a small-spot femtosecond pump pulse in a ZnO microcavity. Using the femtosecond angle-resolved spectroscopic imaging technique, multidimensional dynamics in both the energy and momentum degrees of freedom have been obtained. Two distinct regions with different decay rate in the energy dimension and various decay-channels in the momentum dimension can be well-resolved. Theoretical simulations based on the generalized Gross–Pitaevskii equation can reach a qualitative agreement with the experimental observations, demonstrating the significance of the initial potential barrier induced by the pump pulse during the decay process. The finding of our study can provide additional insights into the fundamental understanding of exciton-polariton condensates, enabling further advancements for controlling the fluids and practical applications.