Thermal Effects Research Articles

Anisotropic behavior and thermal effects on concrete through evaluation of fracture parameters using three-point bending tests

Anisotropic behavior and thermal effects on concrete through evaluation of fracture parameters using three-point bending tests

Magnetic Properties, Spin-Vibration Couplings, and Temperature Effects in Phenalenyl and Triangulene.

We introduce a computational methodology for evaluating and analyzing spin-vibration couplings in molecular systems, enabling insights into the interplay between electronic spins and molecular vibrations. By mapping ab initio electronic structure calculations onto molecular spin Hamiltonians, our approach captures those vibrational interactions potentially driving spin relaxation process. Spin-vibration couplings, derived from Holstein and Peierls terms, highlight the pivotal role of vibrational mode symmetry in spin decoherence and efficient energy dissipation. Additionally, second-order couplings provide a framework to explore the temperature dependence of spin properties via the thermal population of higher vibrational levels. Applied to phenalenyl and [3]triangulene, the results indicate that direct spin transitions dominate over Orbach relaxation in both systems. Hyperfine interactions primarily dictate spin-vibration couplings and thermal effects in phenalenyl, whereas zero-field splitting contributions are dominant in [3]triangulene. These findings advance the understanding of spin relaxation mechanisms in organic molecular systems.

3D active-matrix multimodal sensor arrays for independent detection of pressure and temperature.

Pressure and temperature sensing simultaneously and independently is crucial for creating electronic skin that replicates complex sensory functions of human skin. Thin-film transistor (TFT) arrays with sensors have enabled cross-talk-free spatial sensing. However, the thermal dependence of charge transport in semiconductors has resulted in interference between thermal and pressure stimuli. We develop multimodal sensor arrays based on three-dimensional integration of an active matrix to detect temperature and pressure independently. Our approach includes a calibrated compensation to decouple temperature and pressure signals. An individual pixel device consists of a TFT-based pressure sensor layered above a TFT-based temperature sensor. The detected temperature is used to compensate for the thermal effect on TFT-based pressure sensors. We develop large-area sensor arrays to enable accurate detection of two-dimensional pressure and temperature, leveraging these technologies to demonstrate advanced robotic grippers. The grippers stably grasp and lift a cup regardless of temperature, proving their possibility in skin-like electronic applications.

3D modelling and simulation of thermal effects and dispersion of particles carrying infectious respiratory agents in a railway transport coach

Even though the COVID-19 pandemic now belongs to the long history of infectious diseases that have struck humanity, pathogenic biological agents continue to pose a recurring threat in private places, but also and mainly in places where the public congregates. In our recent research published in this journal in 2022 and 2023, we considered the illustrative example of a commuter train coach in which a symptomatic or asymptomatic passenger, assumed to be infected with a respiratory disease, sits among other travellers. The passenger emits liquid particles containing, for example, COVID-19 virions or any other pathogen. The size spectrum of particles varies depending on whether they are produced during breathing, speaking, coughing or sneezing. More specifically, droplets associated with breathing are in the range of 1–10 µm in aerodynamic diameter, while at the other end of the spectrum, drops associated with coughing can reach 100–1000 µm. In the first part of our research, we used Computational Fluid Dynamics (CFD) to model and simulate in 3D the transport and dispersion of particles from 1 µm to 1 mm in the turbulent flow generated by the ventilation of the railway coach. We used both the Eulerian approach and the Lagrangian approach and showed that the results were strictly similar and illustrated the very distinct aerodynamics, on one hand, of the aerosol of droplets suspended in the air and, on the other hand, of the drops falling or behaving like projectiles depending on their initial speed. In the second part of our research, we developed a model of filtration through a typical surgical mask and possible leaks around the mask if it is poorly adjusted. We resumed the twin experiment of the railway coach and compared the distribution of droplets depending on whether the passengers (including the infected one) wear masks or not and whether the masks are perfectly fitted or worn loosely. Our method made it possible to quantify the particles suspended in the air of the railway coach depending on whether the infected passenger wore their mask more or less well. In this third article, we specifically explore how thermal effects due to the presence of passengers influence the spatio-temporal distribution in the railway coach of aerosols produced by the breathing infected person. We demonstrate that the influence of thermal effects on aerodynamics is very significant and can be very favourable for air decontamination if the ventilation system is judiciously configured. Beyond its application to a commuter train, our work confirms the value of validated CFD tools for describing the airflow and dispersion of particles in complex spaces that do not always allow experimentation. The models that we have developed are applicable to any other semi-confined, ventilated public place, such as a classroom, a hospital room or a performance hall, and they enable the objective assessment of whether the occupation of these spaces could be critical with regard to infectious contamination and of how to limit this ubiquitous risk.

Thermal Enhanced Electrokinetic Bacterial Transport in Porous Media.

Soil bacterial communities are crucial to various ecosystem services, with significant implications for environmental processes and human health. Delivering functional bacterial strains to target locations enhances the preferred ecological features. However, the delivery process is often constrained by limited bacterial transport through low-permeability soil. Although electrokinetics breaks the bottleneck of bacterial transport in thin porous media, its efficiency remains limited. Here, we tested the hypothesis that thermal effects enhance electrokinetic transport by shifting the net force acting on the bacterium. We found that heating significantly increased electrokinetic transport by 2.75-fold at 1 V cm-1 through porous media. Thermal enhancement mechanisms were interpreted by the heating shift of net force integrating matrix attractive and electrokinetic forces and verified by the Quartz Crystal Microbalance with Dissipation Monitoring (QCMD) observed adhesion rigidity shift. Thermal-dependent parameters liquid viscosity and dielectric constant were the primary contributors to the net force shift. Their variations reduce the attractive force and augment the electrokinetic forces, resulting in lower adhesion rigidity and enhanced bacterial transport. A mechanism-based approach interlinking electric field strength, thermal effect, and collision efficiency was established to facilitate the application of thermally enhanced electrokinetic bacterial transport. These findings provide new prospects for improving bacterial transport, hence optimizing soil ecosystem functions.

Inverse-designed all-silicon nanowire array cavities

We designed silicon nanowire array cavities with high optical confinement (Γ) in the central nanowire and a high quality factor (Q) through an inverse design method that maximizes Γ×Q. Moreover, we fabricated an inversely designed cavity with inline input and output waveguides, which is a new configuration for such cavities. The experimental Q exceeded 50,000, which was consistent with a simulation. The cavity exhibited the thermal nonlinearity effect and optical bistability, which indicate that our cavity strongly confines the light in the nanowires.

Analysis of the Influence of Incorporating Different Thermal-Insulating Materials into the Sub-Ballast Layers

Adverse climatic conditions, particularly excessive water and frost, necessitate the design of thick protective sub-ballast layers when dealing with frost-susceptible subgrade surfaces, especially when using standard natural materials (crushed aggregate or gravel–sand). Given the current preference for conserving natural construction materials and promoting sustainable development in the dimensioning of sub-ballast layers, it is advisable to incorporate various thermal insulation, composite, or suitable recycled materials in their design. Therefore, the paper analyses the impact of incorporating different thermal insulation materials (including extruded polystyrene, Liapor, Liapor concrete, and composite foam concrete) into sub-ballast layers. As part of the experimental research, these modified sub-ballast layers were constructed on a real scale in the outdoor environment of the University of Žilina (UNIZA) campus. They were subsequently compared in terms of their thermal resistance to climatic loads. The research results demonstrate that extruded polystyrene provides the optimal thermal insulation effect in modified sub-ballast layers, which was subsequently used in the numerical modelling of railway track structure freezing under different climatic loads.

X-ray and optical analysis of the distant merging double cluster SPT-CLJ2228-5828, its gas bridge, and its shock front

Galaxy cluster mergers are excellent laboratories for studying a wide variety of different physical phenomena. An example of such a cluster system is the distant SPT-CLJ2228-5828 merger located at z≈ 0.77. Previous analyses via the thermal Sunyaev-Zeldovich effect and weak lensing (WL) data suggested that the system was potentially a dissociative cluster post-merger, similar to the Bullet cluster. In this work, we perform an X-ray and optical follow-up analysis of this rare system. We used new deep XMM-Newton data to study the hot gas in X-rays in great detail, spectroscopic Gemini data to precisely determine the redshift of the two mass concentrations, and new Hubble Space Telescope data to improve the total mass estimates of the two components. We find that SPT-CLJ2228-5828 constitutes a pre-merging double cluster system instead of a post-merger as previously thought. The merging process of the two clusters has started, with their gas on the outskirts colliding with a ∼ 22^ ∘ ∘ on the plane of the sky. Both clusters have a similar radius of R_ ∼ 700 kpc, with the two X-ray emission peaks separated by ≈ 1 Mpc (2.1^ We fully characterized the surface brightness, gas density, temperature, pressure, and entropy profiles of the two merging clusters for their undisturbed non-interacting side. The two systems have very similar X-ray properties, with a moderate cluster mass of tot ∼ (2.1-2.4) ⊙ according to X-ray mass proxies. Both clusters show good agreement with known X-ray scaling relations when their merging side is ignored. The WL mass estimate of the western cluster agrees well with the X-ray-based mass, whereas the eastern cluster is surprisingly only marginally detected from its WL signal. A gas bridge with ≈ 333 kpc length connecting the two merging halos is detected at a $5.8σ$ level. The baryon overdensity of the excess gas (not associated with the cluster gas) is δ_ b ∼ (75-320) across the length of the bridge, and its gas mass is M_ gas ∼ 1.4 ⊙ . The gas density and temperature jumps at ∼ 10^ cm^-3 and ∼ 5.5 keV, respectively, are also found across the gas bridge, revealing the existence of a weak shock front with a Mach number mathcal M ∼ 1.1. The gas pressure and entropy also increase at the position of the shock front. We estimate the age of the shock front to be lesssim 100 Myr and its kinetic energy ∼ 2.4 erg s^-1. SPT-CLJ2228-5828 is the first such high-z pre-merger with a gas bridge and a shock front, consisting of similarly sized clusters, to be studied in X-rays.

Conformal line defects at finite temperature

We study conformal field theories at finite temperature in the presence of a temporal conformal line defect, wrapping the thermal circle, akin to a Polyakov loop in gauge theories. Although several symmetries of the conformal group are broken, the model can still be highly constrained from its features at zero temperature. In this work we show that the defect and bulk one and two-point correlators can be written as functions of zero-temperature data and thermal one-point functions (defect and bulk). The defect one-point functions are new data and they are induced by thermal effects of the bulk. For this new set of data we derive novel sum rules and establish a bootstrap problem for the thermal defect one-point functions from the KMS condition. We also comment on the behaviour of operators with large scaling dimensions. Additionally, we relate the free energy and entropy density to the OPE data through the one-point function of the stress-energy tensor. Our formalism is validated through analytical computations in generalized free scalar field theory, and we present new predictions for the O(N)O(N) model with a magnetic impurity in the \varepsilonε-expansion and the large NN limit.

Thermal effects on the resistive superconducting transition in step-edge YBCO squid arrays

Thermal effects on the resistive superconducting transition in step-edge YBCO squid arrays

Finite Element Analysis of Stress Distribution in Cancellous Bone During Dental Implant Pilot Drilling

Background/Objectives: This study investigates stress distribution in cancellous bone during pilot drilling for dental implants using the Cowper–Symonds model. Understanding the biomechanical effects of drilling parameters on bone health is essential for optimizing implant stability and longevity. Methods: A finite element analysis (FEA) approach was employed to simulate the pilot drilling process in cancellous bone. A three-dimensional jawbone model was developed from CT scan data, processed using 3D Slicer, and refined with CAD tools. The drilling simulation incorporated a rigid pilot drill and flexible cancellous bone, utilizing explicit dynamic methods. Stress distribution was evaluated for drilling depths ranging from 6 mm to 16 mm, with mesh density and strain rate effects considered to ensure accuracy. Results: The results showed an increase in stress levels with drilling depth, with maximum stress recorded at 16 mm. Initial contact stress was 17.3 MPa, rising to 228.9 MPa at deeper penetration due to increased interaction between the drill and bone. Stress distribution patterns emphasized the critical role of drilling depth and design parameters in mitigating bone damage. Conclusions: This study highlights the importance of optimized drilling protocols and pilot drill design to reduce stress and preserve bone integrity. The findings provide valuable insights into improving implant procedures and demonstrate the utility of FEA as a robust tool for evaluating biomechanical impacts during implant placement. Future research should incorporate cortical bone and thermal effects for a comprehensive analysis.

A Review of Electroplastic Effect on Difficult‐to‐Machine Materials in Cutting Processing

Electroplastic effect refers to the role of pulsed current, material plasticity, and microstructural properties change, resulting in an increase in the plasticity of the material, the deformation resistance is reduced, and thus improves the processing performance of the phenomenon. This article summarizes the Joule thermal effect and a variety of nonthermal effects of the electrophysical effect mechanism, of which the nonthermal effects include pure electrophysical effect, magnetic field compression effect, and skin effect. The application of electroplastic‐assisted technology in cutting machining, such as turning, milling, drilling, and so on, and the potential application in other manufacturing processes are summarized. The limitations and shortcomings of the electroplastic‐assisted technology are analyzed, including the limitations of the required special equipment, machining platforms, and electric pulse parameters. The effects of different electric pulse parameters on the machinability of various types of difficult‐to‐machine metallic materials are summarized. The electric pulse parameters within a certain threshold range can promote the dynamic recrystallization of the workpiece, enhance the plastic deformation of the cutting zone, reduce the cutting force, improve the surface finish, and reduce tool wear. Finally, this article summarizes and looks forward to the electroplastic‐assisted cutting technology.

Thermal effects on the resistive superconducting transition in step-edge YBCO squid arrays

Abstract The effect of thermal fluctuations in Yttrium Barium Copper Oxide (YBCO) SQUID filters (SQIFs), containing arrays of 258, 2304, and 4080 SQUIDs, were investigated using the electrical resistivity and applied magnetic field up to 9 tesla. Our study reveals that the SQIFs experience a two-step superconductor transition. The transition at lower temperature is only present in the SQIF samples, not in the control sample without the SQFIs, and it is investigated here in terms of two primary dissipation mechanisms. The first dominates near the transition temperature and has the characteristics of thermally activated phase slippage (TAPS). At lower temperatures, the dominant characteristics are those of thermally-activated magnetic flux flow (TAFF). The mechanisms producing such behaviors contribute significantly to dissipation effects, resulting in an additional DC voltage that overlays the Josephson current, regardless of the quantity of SQUIDs in the SQIFs. These dissipation effects can have significant implications for technologies utilizing high-temperature superconductor SQIFs unless the operating temperature is lowered significantly below the superconducting transition temperature.

Finite Element Research of Cup Wheel Grinding Heat Based on Trochoid Scratch Model

Grinding is a highly precise machining process. However, excessive temperatures during grinding can result in adverse thermal effects on the machined material. In this study, cup wheel grinding was analyzed using a model that represents heat generation as a trochoid discrete heat source formed by the interactions between abrasive particles and the workpiece surface. With this approach, certain assumptions were made to facilitate analysis, including the modeling of abrasive grains as rigid point heat sources. Finite element simulations and experimental validations based on the trochoid model were conducted using COMSOL 6.2 software. These analyses evaluated the thermal behavior of cup wheel grinding under varying wheel speeds and feed rate ratios. The results revealed an asymmetrical distribution of the temperature field in cup wheel grinding. By examining both surface and subsurface temperature fields, this study provided a more comprehensive understanding of grinding heat. Furthermore, this investigation explored the influence of trochoid trajectories and process parameters on the temperature field, highlighting intersection and curvature thermal effects. These findings contribute valuable analytical methods and theoretical insights for controlling grinding heat in precision machining processes.

Temperature dynamics and mechanical properties analysis of carbon fiber epoxy composites radiated by nuclear explosion simulated light source

The impact of light radiation, a predominant energy release mechanism in nuclear explosions, on material properties is of critical importance. This investigation employed an artificial light source to replicate the effects of nuclear explosion radiation and utilized a physical information neural network (PINN) to examine the temperature evolution and corresponding changes in the mechanical properties of carbon fiber/epoxy composites (CFEC). A light source simulating nuclear explosion’s light radiation was built to irradiate the CFEC, then measure the reflection spectrum and temperature of samples. A heat conduction model was developed, and the temperature dynamics were obtained through the integration of PINN with experimental data. Post-irradiation testing indicated significant modifications to the sample properties, with the thermal and photochemical effects of the simulated radiation leading to a decrease in reflectance across multiple wavelengths. This resulted in different reductions in tensile strength (1.64%), compressive strength (17.35%), interlamellar shear strength (ILSS) (0.51%), and post-impact compressive strength (2.77%). The insights gained from this comprehensive analysis are essential for the rapid prediction of temperature changes and the formulation of robust light radiation protection strategies for equipment exposed to nuclear explosion environments.

Localized and Excimer Triplet Electronic States of Naphthalene Dimers: A Computational Study

We perform DFT calculations with different hybrid (ωB97X-D and M05-2X) and double hybrid (B2PLYP-D3 and ωB2PLYP) functionals to characterize the lowest energy triplet excited states of naphthalene monomer and dimers in different stacking arrangements and to simulate their absorption spectra. We show that both excimer and localized triplet minima exist. In the former, the spin density is delocalized over the two monomers, adopting a face-to-face arrangement with a short inter-molecular distance. In the latter, the spin density is localized on a single naphthalene molecule, and different minima or pseudo-minima are possible, the most stable one corresponding to a slipped parallel arrangement. According to B2PLYP-D3 calculations, excimer minima are the most stable, in line with the indications of ADC(2) studies. However, the relative stability of the minima is reverted when including thermal and vibrational effects. Excimer minima exhibit a very intense absorption spectrum, peaking above 500 nm. The computed absorption spectra of localized minima significantly depend on the stacking geometry and do not coincide with that of isolated naphthalene. Hybrid functionals provide very accurate vibronic absorption spectra for naphthalene monomer, both in the singlet and in the triplet state, but underestimate the stability of the excimer triplet.

Defect-mediated electron–phonon coupling in halide double perovskite

Optically active defects often play a crucial role in governing the light emission as well as the electronic properties of materials. Moreover, defect-mediated states in the midgap region can trap electrons, thus opening a path for the recombination of electrons and holes in lower energy states that may require phonons in the process. Considering this, we have probed electron–phonon interaction in halide perovskite systems with the introduction of defects and investigated the thermal effect on this interaction. Here, we report Raman spectroscopic study of the thermal evolution of electron–phonon coupling, which is tunable with the crystal growth conditions, in the halide perovskite systems Cs2AgInCl6 and Cs2NaInCl6. The signature of electron–phonon coupling is observed as a Fano anomaly in the lowest frequency phonon mode (51 cm−1), which evolves with temperature. In addition, we observe a broad band in the photoluminescence (PL) measurements for the defect-mediated systems, which is otherwise absent in defect-free halide perovskite. The simultaneous observation of the Fano anomaly in the Raman spectrum and the emergence of the PL band suggests the defect-mediated midgap states and the consequent existence of electron–phonon coupling in the double perovskite.

Numerical Investigation of the Coupling Effects of Pulsed H2 Jets and Nanosecond-Pulsed Actuation in Supersonic Crossflow

Numerical investigations were conducted to analyze the coupling effects of pulsed H2 jets and nanosecond-pulsed actuation (NS-SDBD) in a supersonic crossflow. The FVM was employed to solve the multi-component 2D URANS equations with the SST k-omega turbulence model, while H2-air combustion was described using a seven species–seven reactions chain reaction model, and the plasma thermal effect was represented by a phenomenological model. The backward-facing step flows with an inlet Mach number of 2.5 and a pulsed jet frequency of 10 kHz under different actuation conditions were simulated. The combustion enhancement mechanism under an actuation frequency of 20 kHz was analyzed. Research indicates that compression waves induced by NS-SDBD enhance H2-air mixing and facilitate temperature transport as the flow progresses. This progress is significantly associated with the flow structures generated by pulsed jets. Under this condition, the fuel utilization rate in the flow field increased by 61.2%, the total pressure recovery coefficient increased by 5.34%, and the outlet total temperature slightly increased even with a 50% reduction in fuel flow rate. Comparative analysis of different actuation cases demonstrates that evenly distributed actuation within the jet cycle yields better effects. The innovation of this study lies in proposing and exploring a potential method to address inadequate combustion under high-speed inflow conditions, which couples NS-SDBD with pulsed hydrogen jets.

Analysis of elastic stresses and thermal creep effect for a composite disk under the parabolic distribution of temperature using the Rayleigh-Ritz method with trigonometric Ritz functions

This research provides a detailed examination of the thermal creep effect on elastic stresses in a composite disk exposed to a parabolic temperature distribution. The disk, reinforced with steel fibers, is treated as a thermo-elastic composite material. The Rayleigh-Ritz method, a widely recognized numerical approach for solving boundary value problems, is utilized to derive analytical solutions for the radial and tangential stresses. This method employs the principle of minimum potential energy to approximate displacement fields using Trigonometric Ritz Functions, which are subsequently applied to calculate the stress components. The parabolic temperature distribution imparts a non-uniform thermal load across the disk, significantly affecting the stress distribution. The study explores how the thermal creep effect, intrinsic to the composite material, interacts with thermal variations, resulting in intricate stress patterns. By adjusting temperature parameters, the analysis demonstrates the sensitivity of stress components to thermal gradients. Comparative assessments are performed for various temperature profiles, identifying critical areas of stress concentration. The findings offer significant insights into the behavior of thermo-elastic composites under non-uniform thermal conditions, providing a robust analytical foundation for future research and engineering applications. This research emphasizes the necessity of considering both thermal creep effects and Trigonometric Ritz Functions in the design and analysis of composite structures subjected to varying temperature loads.

Impact and analysis of corrosion on elastic stress in a composite disk under parabolic temperature distribution using the Rayleigh-Ritz method with trigonometric Ritz functions

This study conducts an in-depth impact and analysis of corrosion on the elastic stresses within a composite disk exposed to a parabolic temperature distribution. The disk, reinforced with steel fibers, is modeled as a thermo-elastic composite material to evaluate its performance under thermal and corrosive conditions. The Rayleigh-Ritz method, a widely recognized numerical approach for solving boundary value problems, is utilized to derive analytical solutions for both radial and tangential stresses. This method applies the principle of minimum potential energy to approximate displacement fields through Trigonometric Ritz Functions, which are subsequently employed to calculate stress components. The parabolic temperature distribution imposes a non-uniform thermal load across the disk, significantly altering the stress distribution. The study explores how the inherent thermal properties of the composite material interact with temperature variations, resulting in intricate stress patterns. By systematically varying temperature parameters, the analysis uncovers the sensitivity of stress components to thermal gradients. Comparative evaluations are performed for different temperature profiles, identifying critical regions of stress concentration. The findings offer essential insights into the behavior of thermo-elastic composites under non-uniform thermal and corrosive conditions, establishing a robust analytical framework for future research and practical engineering applications. This research emphasizes the necessity of integrating both thermal effects and Trigonometric Ritz Functions in the design and analysis of composite structures exposed to varying temperature loads and corrosion.