Characteristic Relaxation Research Articles

Markers of low field NMR relaxation features of tissues

This work presents an approach to exploiting Nuclear Magnetic Resonance (NMR) relaxometry data (1H spin-lattice relaxation rates covering the frequency range from below 1 kHz to 10 MHz) for the purpose of differentiating between pathological and reference tissues. Characteristic quantities (markers) that can be obtained in a straightforward manner, not resorting to an advanced analysis of 1H spin-lattice relaxation data, have been identified and compared for pathological and reference colon tissues. Moreover, the relaxation data have been parametrised in terms of Lorentzian spectral densities and the possibility of using the obtained dipolar relaxation constants and correlation times as biomarkers to assess the state of tissues has been discussed. It has also been demonstrated that the relaxation data for the reference and the pathological tissues can be attributed to two groups (for each case). The studies are a step towards exploiting the potential of NMR relaxometry for characterisation of pathological changes in tissues.

Analysis of relaxation characteristics of multi-bolted connections under the transverse cyclic load

A modeling method under lateral cyclic loading is proposed for the complex multi-bolt connection loosening problem. Firstly, the thread stress surface is divided into n small sectors, and the self-relaxation mechanical model of multi-bolt connection is established considering the interaction between bolts. Secondly, the self-relaxation model is solved by MATLAB software and compared with Nassar model to verify the correctness of the model. Finally, considering the influence of different bolt number, hole clearance and connection spacing, the relaxation characteristics of multi-bolt connection are studied. The results show that during the loosening process, the bolt head undergoes a bending-sliding-bending cycle process, and the bolt tension shows a wave downward trend. When multiple bolts are connected, the number of loosening cycles decreases linearly with the increase of hole clearance. With the equidistant increase of bolt connection spacing, the number of bolt loosening cycles shows a decreasing trend. Compared with the number of bolts, the change of bolt hole clearance and connection spacing is more likely to affect bolt loosening.

Nonlinear dielectric response and conductivity characteristics of epoxy resin in high voltage AC electric field

Abstract High-voltage dielectric and AC conduction behaviors of epoxy resin (EP) insulation are beneficial for the design and application of solid-state power electronic devices. This study investigates the nonlinear dielectric response and AC conduction characteristics of EP. The dielectric relaxation characteristics, including permittivity and AC conductivity of the EP samples, were investigated using high-voltage dielectric spectroscopy and the ionic polarization model. The results demonstrate a nonlinear increase in the relative permittivity and AC conductivity concerning the AC electric field. The increase in AC conduction under a high-frequency electric field is attributed to the reduction in the threshold field for charge injection caused by elevated temperatures. Considering the dielectric response and carrier hopping, it is evident that the nonlinear dielectric response of EP primarily originates from the ionic process under high electric fields. Ionic polarization, in conjunction with ion-hopping conduction, enhances the dielectric loss at high frequencies and electric fields, thereby facilitating the nonlinear conversion of AC conduction. The equivalent free volume is likely to increase in high-frequency fields. This phenomenon leads to an increase in AC conduction and even dielectric breakdown. This study offers a pivotal theoretical framework for the design and application of high-frequency insulation.

Dielectric analysis of unpolymerized and photopolymerized NOA65 in a parallel-plate cell

The flourishing development of liquid crystal research in recent decades has highlighted the importance of polymer materials in enhancing liquid–crystal material and device properties, demonstrating tremendous potential in a wide range of industries. One of the polymer materials widely used in polymer-dispersed liquid crystal is Norland UV-curable optical adhesive (NOA65). This study focuses on the dielectric behavior of the optical adhesive in a parallel-plate cell. Given the broadness and asymmetry of the dielectric dispersion curve, the two-relaxation Havriliak–Negami model was employed to analyze the complex dielectric spectra of NOA65 before and after photocuring. Experimental results indicate that as temperature rises, the dielectric relaxation of NOA65 undergoes a blue shift, leading to an eventual overlap with pseudo-dielectric relaxation at a higher frequency. This brings about an increase in the obtained signal in the dielectric loss spectrum, implying that the observed feature of pseudo-dielectric relaxation is actually superposed or contributed by the intrinsic relaxation signal. Furthermore, as temperature continues to rise, the intrinsic dielectric loss signal of NOA65 becomes untraceable beyond the frequency span within which the pseudo-dielectric relaxation signal lies.

Dinuclear Dysprosium Compounds: The Importance of Rigid Bridges.

We report the synthesis, structures and magnetic behaviour of two isostructural dinuclear Dy3+ complexes where the metal ions of a previously reported monomeric building block are connected by a peroxide (O22-) or a pair of fluoride (2 x F-) bridges. The nature of the bridge determines the distance between the metal ion dipoles leading to a dipolar coupling in the peroxido bridged compound of only ca. 70% of that in the bis-fluorido bridged dimer. The sign of the overall coupling between the metals is antiferromagnetic for the peroxido bridged compound and ferromagnetic for the bis-fluorido bridged complex. This in turn influences the magnetisation dynamics. We compare the relaxation characteristics of the dimers with those of the previously reported monomeric building block. The relaxation dynamics for the bis-fluorido system are very fast. On the other hand, comparing the properties of the monomer, the peroxido bridged sample and the corresponding Y-doped sample show that the relaxation properties via a Raman process have very similar parameters. We show that a second dysprosium is important for either tuning or detuning the Single Molecule Magnet (SMM) properties of a system.

Optimized energy storage performances via high-entropy design in KNN-based relaxor ferroelectric ceramics

Dielectric capacitors play an irreplaceable role in complex and integrated electronic systems. However, attaining ultrahigh recoverable energy storage density (Wrec) alongside energy storage efficiency (η) poses a formidable challenge, impeding the advance towards the miniaturization and integration of cutting-edge energy storage devices. In this work, a high-entropy strategy with a viscous polymer process is adopted, bringing about ultrafine grains and polar nanoregions (PNRs) accompanied by enhanced electrical homogeneity and polarization relaxation characteristics. As a result, an ultrahigh Wrec ∼ 7.51 J/cm3 is achieved in a high-entropy KNN-based energy storage ceramic with a high η ∼ 88.4% at 750 kV/cm. Moreover, the ceramic capacitor exhibits a colossal power density reaching approximately 420 MW/cm3 and a discharge energy density of approximately 4.85 J/cm3 at 160 ℃. Impressively, it maintains low variation rates of less than 4% across a broad temperature range from 20 ℃ to 160 ℃. The new approach opens avenues for the design and development of superior dielectric materials used in next-generation high-power pulse devices.

Time-dependent relaxation dynamics of remanent strain in textured PMN–PZ–PT and PMN–PIN–PT piezoceramics

Crystallographically textured lead-based piezoceramics, particularly Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 (PMN–PZ–PT) and Pb(Mg1/3Nb2/3)O3–Pb(In1/2Nb1/2)O3–PbTiO3 (PMN–PIN–PT), play a pivotal role in electromechanical applications due to their enhanced field-induced strain responses. However, challenges in precision positioning arise from heightened remanent strain (Sr) caused by embedded templates in the textured grains, impacting strain cycle consistency due to increased time delay for Sr relaxation. This study investigates the time-dependent relaxation dynamics of Sr in textured PMN–PZ–PT and PMN–PIN–PT piezoceramics, focusing on experimentally determining relaxation time between cycles required for complete Sr relaxation. Our findings reveal that the relaxation time in textured piezoceramics is notably longer than that in their non-textured counterparts, primarily due to pinning of domain walls by embedded templates. This work provides insights into the strain relaxation characteristics of piezoceramics and underscores the importance of time delay in designing precision positioning systems for improved reliability.

Experimental study on the macroscopic and mesoscopic mechanical characteristics of deep damaged and fractured rock

Most of the rock surrounding deep roadways is in a fractured state; fractured rock has significant rheological properties, and the time-dependent mechanical properties of fractured rock affect excavation construction, support design, and long-term stability of deep roadways. Triaxial compression and mercury intrusion tests are conducted on the bearing characteristics of severely damaged and fractured rock samples, indicating the strength degradation properties of these samples. The evolution of the internal pore structure in damaged and fractured rock samples is analyzed in relation to changes in unloading points (pre-peak stage, peak point, and post-peak stage), leading to the establishment of a quantitative evaluation index for rock damage based on the porosity evolution. Short-term rheological testing is performed on rock samples with varying degrees of damage and fracture, demonstrating the evolution of creep and stress relaxation characteristics. The findings contribute to a deeper theoretical understanding of the post-peak mechanical properties of coal and rock masses, which hold significant theoretical implications and can inform research on long-term stability in underground engineering applications, such as deeply buried roadways, tunnels, and chambers.

Exploring the Impact of Ring Mobility on the Macroscopic Properties of Doubly Threaded Slide-Ring Gel Networks.

The integration of mechanically interlocked molecules (MIMs) into polymeric materials has led to the development of mechanically interlocked polymers (MIPs). One class of MIPs that have gained attention in recent years are slide-ring gels (SRGs), which are generally accessed by crosslinking rings on a main-chain polyrotaxane. The mobility of the interlocked crosslinking moieties along the polymer backbone imparts enhanced properties onto these networks. An alternative synthetic approach to SRGs is to use a doubly threaded ring as the crosslinking moiety, yielding doubly threaded slide-ring gel networks (dt-SRGs). In this study, a photo-curable ligand-containing thread was used to assemble a series of metal-templated pseudo[3]rotaxane crosslinkers that allow access to polymer networks that contain doubly threaded interlocked rings. The physicochemical and mechanical properties of these dt-SRGs with varying size of the ring crosslinking moieties were investigated and compared to an entangled gel (EG) prepared by polymerizing the metal complex of the photo-curable ligand-containing thread, and a corresponding covalent gel (CG). Relative to the EG and CG, the dt-SRGs exhibit enhanced swelling behavior, viscoelastic properties, and stress relaxation characteristics. In addition, the macroscopic properties of dt-SRGs could be altered by "locking" ring mobility in the structure through remetalation, highlighting the impact of the mobility of the crosslinks.

Exploring the Impact of Ring Mobility on the Macroscopic Properties of Doubly Threaded Slide‐Ring Gel Networks

AbstractThe integration of mechanically interlocked molecules (MIMs) into polymeric materials has led to the development of mechanically interlocked polymers (MIPs). One class of MIPs that have gained attention in recent years are slide‐ring gels (SRGs), which are generally accessed by crosslinking rings on a main‐chain polyrotaxane. The mobility of the interlocked crosslinking moieties along the polymer backbone imparts enhanced properties onto these networks. An alternative synthetic approach to SRGs is to use a doubly threaded ring as the crosslinking moiety, yielding doubly threaded slide‐ring gel networks (dt‐SRGs). In this study, a photo‐curable ligand‐containing thread was used to assemble a series of metal‐templated pseudo[3]rotaxane crosslinkers that allow access to polymer networks that contain doubly threaded interlocked rings. The physicochemical and mechanical properties of these dt‐SRGs with varying size of the ring crosslinking moieties were investigated and compared to an entangled gel (EG) prepared by polymerizing the metal complex of the photo‐curable ligand‐containing thread, and a corresponding covalent gel (CG). Relative to the EG and CG, the dt‐SRGs exhibit enhanced swelling behavior, viscoelastic properties, and stress relaxation characteristics. In addition, the macroscopic properties of dt‐SRGs could be altered by “locking” ring mobility in the structure through remetalation, highlighting the impact of the mobility of the crosslinks.

Simulation and experimental analysis of dynamic thermal rise relaxation characteristics for dry-type distribution transformer

Abstract The temperature distribution characteristics of dry-type distribution transformers reflect their overall performance and quality. Distribution transformer daily load changes dramatically, its temperature fluctuates within a certain range. However, most of the research results on transformer temperature rise focus on the steady-state temperature characteristics of transformers, and lack of research related to dynamic temperature rise characteristics. This paper carries out a multi-physics coupling simulation and experimental verification of the dynamic temperature rise relaxation characteristics. The simulation uses the “electromagnetic-flow-thermal” multi-physics coupling analysis method to simulate the steady-state temperature rise characteristics and dynamic temperature rise relaxation characteristics of windings under different load rates. Then, this paper also explores the correlation between the dynamic temperature rise relaxation characteristics and load rate at the typical positions of high-voltage windings and low-voltage windings. The results show that the temperature rise of the winding shows the law of increasing the saturation index function with the increase of the load application time at any load rate. A quantitative characterization model of dynamic temperature rise relaxation behavior at different positions of transformer windings is constructed. It is found that the steady-state temperature rise value of different parts of the winding increases regularly as a power function with the increase of load rate, while the constant value of dynamic temperature rise relaxation time in different parts of the winding decreases as a power function with the increase of load rate. The verification results of the quantitative characterization model of dynamic temperature rise relaxation behavior show that the maximum error of the measured and theoretical steady-state temperature rise value is only 1.56 K, and the maximum error of the constant value of dynamic temperature rise relaxation time is only 0.082 h. These findings provide valuable insights into the performance and quality of dry-type distribution transformers, and can help improve their design and operation for better efficiency and safety.

Data-Driven Cycle Life Prediction of Lithium Metal-Based Rechargeable Battery Based on Discharge/Charge Capacity and Relaxation Features.

Achieving precise estimates of battery cycle life is a formidable challenge due to the nonlinear nature of battery degradation. This study explores an approach using machine learning (ML) methods to predict the cycle life of lithium-metal-based rechargeable batteries with high mass loading LiNi0.8Mn0.1Co0.1O2 electrode, which exhibits more complicated and electrochemical profile during battery operating conditions than typically studied LiFePO₄/graphite based rechargeable batteries. Extracting diverse features from discharge, charge, and relaxation processes, the intricacies of cell behavior without relying on specific degradation mechanisms are navigated. The best-performing ML model, after feature selection, achieves an R2 of 0.89, showcasing the application of ML in accurately forecasting cycle life. Feature importance analysis unveils the logarithm of the minimum value of discharge capacity difference between 100 and 10 cycle (Log(|min(ΔDQ 100-10(V))|)) as the most important feature. Despite the inherent challenges, this model demonstrates a remarkable 6.6% test error on unseen data, underscoring its robustness and potential for transformative advancements in battery management systems. This study contributes to the successful application of ML in the realm of cycle life prediction for lithium-metal-based rechargeable batteries with practically high energy density design.

Stress relaxation assessment of high-temperature bolts under combined biaxial loads: Theory and simulation

Estimating bolt stress within high-temperature bolted connection systems is crucial for determining bolt preload and assessing bolt assembly integrity. This work proposes a theoretical model for estimating high-temperature bolt load under combined tension, bending, torque, and shear loads, considering the characteristics of bolt stress distribution and relaxation. To assess the model's accuracy, finite element analysis was employed to examine the impact of various creep parameters and load combinations on bolt stress relaxation. The results indicate that the introduction of bending moments, torque, and shear loads accelerates axial stress relaxation in bolts. Under a high-temperature load for 300,000 h, the stress relaxation predicted by the theoretical model aligns well with the results from finite element analysis.

Tension relaxation during the NOL ring winding process based on a novel tracking element method

The NOL ring is employed as a specimen to examine the properties of filament-wound composites, with its winding tension playing a pivotal role in determining the performance of the resultant wound products. Traditional methods used for modeling the winding process have several disadvantages, including inaccuracies in setting the tension and difficulties in controlling the thickness of the wound layers. To address these limitations, utilizing the response mechanism of the tracking element method, a precise three-dimensional (3D) winding finite element model of the NOL ring is constructed. Adopting a wireless film pressure testing system to dynamically measure interlayer pressures, improved the precision of our experimental results by decoupling factors affecting tension relaxation and focusing on the structural relaxation characteristics of winding tension in composite materials. Experimental results demonstrate that, using this model, the prediction error for the radial stress on the mandrel surface is only 6.03%, which is substantially lower than that of the conventional models (16.72%). In addition, the model is used to investigate the stress transfer mechanisms in the radial/circumferential directions of the winding layers on a macroscopic scale. Finally, it is demonstrated through examples that this model can also achieve equal residual tension through optimization, which is expected to improve the structural efficiency of wound products.

Performance Test of Artificial Defoliating Broccoli Conveyor Line and Analysis of Defoliating Broccoli Inflorescences

There is a close relationship between stem and leaf biological characteristics of mature broccoli plants and defoliation technology. Morphological parameters such as the spread degree and diameter of cauliflower stem and leaf and the connection performance of cauliflower stem and leaf were studied. These experiments are helpful to the research of defoliation devices and methods for large-scale manual transportation lines. In this paper, according to the damage forms that may be suffered in the separation process of mature broccoli stems and leaves, “sunny” broccoli varieties were selected. Firstly, the mechanical properties of mature broccoli stems were obtained through different loading methods such as stretching, compression, shearing and bending. Secondly, the stress relaxation characteristics of broccoli were analyzed by static compression of broccoli flower balls. Finally, the separation method of broccoli stems and leaves was simulated by ANSYS. The simulation results showed that shear fracture was more suitable for stem and leaf separation of broccoli than tensile fracture. Then, aiming at the separation of stems and leaves of broccoli, an artificial broccoli assembly line was proposed to ensure the efficiency of leaf removal through man–machine cooperation. The dynamic characteristics of the belt of broccoli leaf removal line were studied to ensure the efficient and stable operation of the conveyor system of broccoli artificial leaf removal line.

Long-term relaxation analysis of steel cables based on viscoelastic model

Steel cables, renowned for their lightweight and high-strength properties, stand as ubiquitous building materials in large-span structures. Serving as crucial load-bearing elements, cables endure sustained tension throughout the structure's lifecycle. To further investigate the long-term relaxation characteristics of steel cables and provide more theoretical basis for structural relaxation calculations, this paper introduces a long-term relaxation constitutive model for steel cables, formulated through theoretical derivation, experimental validation, and data fitting techniques to establish time-dependent constitutive relationships. By employing the Bingham and Kelvin viscoelastic models, a relaxation model for steel cables is presented and optimized accordingly. Experimental investigations involve long-term tests on steel cables with three different sizes and detailed fitting analysis on collected internal force relaxation data. The findings emphasize the indispensability of structural relaxation behavior and the significance of altering internal forces, particularly in large-span cable-strut structures. The developed numerical model enables accurate simulation and prediction of long-term time-dependent performance in such structures, serving as a springboard for future studies in this domain.

How to Distinguish Nonexponentiality and Nonlinearity in Isothermal Structural Relaxation of Glass-Forming Materials.

The nonexponentiality and nonlinearity are two essential features of the structural relaxation in any glass-forming material, which seem to be inextricably bound together by the material time. It is shown that the temperature down-jump and up-jump experiments of the same magnitude ΔT = T0 - T to the same temperature T provide a clue for their separation. The isothermal structural relaxation can be quantified using the stabilization period on the logarithmic time scale log(tm/t0). It is described as the sum of the nonexponentiality term 1.181/ß and the nonlinearity term (σ/2.303)ΔT for the temperature down-jump, and as their difference for the temperature up-jump. The material parameter σ = -(∂lnτ/∂Tf)i quantifies variation of the relaxation time with structural changes at the inflection point of the relaxation curve and is formulated for the most widely used phenomenological models. The asymmetry of approach to equilibrium after the temperature down-jump and up-jump was first described by Kovacs in 1963. A detailed analysis of this asymmetry is provided, and a simple method for the estimation of the parameters characterizing the nonexponentiality (ß) and nonlinearity (σ) is proposed. The applicability of this method is tested using previously reported isothermal experimental data as well as calculated data for aging of polymers and other glass-forming materials. This concept illuminates differences in structural relaxation kinetics in a simple and consistent way that can be useful in the design of novel materials and the evaluation of their physical aging treatment.

PNN-PST-PT ferroelectric ceramics with ultrahigh piezoelectricity and superior electromechanical performance for high quality piezo-sensors

A novel ferroelectric ceramic system, Pb(Ni1/3Nb2/3)O3–Pb(Sc1/2Ta1/2)O3–PbTiO3 (PNN-PST-PT), with ultrahigh piezoelectricity and super electromechanical performance is developed. The microstructure and crystal structure of PNN-PST-PT ceramics, along with their electrical properties, were examined regarding PNN content. The results indicated that the room-temperature dielectric constant was considerably enhanced with PNN content increasing and the values of Pr, Pmax, and Ec steadily declining. The optimal performance was achieved in the 0.4PNN-0.235PST-0.365 PT composition with a high piezoelectric coefficient (d33) of 1028 pC/N and an electromechanical coupling factor (kp) of 0.69. Strong piezoelectric response is attributed to the coexistence of R and T phases as well as the enhanced relaxation characteristics, which manifest as a specific polarization configuration resulting from the local structural distortion caused by the co-occupation of ions with different radii at the B-site. These suggest that PNN-PST-PT ceramics can be a desirable material for applications in high-quality piezosensors, actuators, etc.

Quantitative MRI post-processing algorithm and visualization research based on moisture status detection of winter jujube

Quantitative Magnetic Resonance Imaging (qMRI) offers precise measurements of the relaxation characteristics of microstructures, representing a cutting-edge method in non-destructive fruit analysis. This study aims to visualize information on changes in moisture status and distribution at the subcellular level of winter jujube. The 0.5 T nuclear magnetic imaging equipment was utilized to rapidly, non-invasively, and accurately capture the internal relaxation status of the sample with multiple-echo-imaging. By examining the signal and noise data, a simulated dataset was developed to tackle the optimization challenge of estimating parameters for the discrete relaxation model from the multiple-echo-imaging data, especially under conditions of low signal-to-noise ratio (SNR) and in the context of heteroscedastic noise. An optimal weighting factor and the T2NR truncation model have been identified to establish an effective experimental inversion strategy. Subsequently, multiple-echo-imaging can rapidly and stably yielded voxel-level maps under conditions of low signal-to-noise ratio. Utilizing this experimental approach, data from winter jujube was collected and analyzed, facilitating an exploration of water activity (T2 mapping) and associated water content (A2 mapping). Through analyzing winter jujube fruits across two maturity stages, this study elucidates the role of precise quantification and voxel-wise visualization in moisture status detection. The methodology presents an innovative approach for assessing internal moisture distribution in fruits.

Contribution of hall and ion slip effects with generalized mass and heat fluxes with entropy analysis on three-dimensional Prandtl model

A major challenging proffered study rely on the inquisitive optimization of entropy together with thermal as well as mass transportation towards the chemically reactive 3-D Prandtl liquid under consideration of applied magnetic field, variable thermal conductivity and also diffusivity, hall current together with ion slip features, viscous dissipation and heat generation. Moreover, in present research study, model such as Cattaneo Christov heat flux was implemented in order to explore the thermal relaxation characteristics. By employing correspondence transformations, the system of modeled equations modified into non-linear ODEs system. The Optimal Homotopy Analysis methodology (OHAM) was adopted to solve the proffered problem. The influential arising constraints demeanor within both velocities (horizontal as well as vertical), temperature and concentration profiles were discussed and also shown graphically. Moreover, outcomes of diverse parameters were also examined and presented graphically within the entropy formation rate and also Bejan number. The effects of implanted factors across the drag force, the rate of thermal as well as mass transportation are accessible in current study via tables and validate the obtained results. Both velocity profiles (horizontal as well as vertical) decreased for increment in Hartman number whilst opposite demeanor seen for other considered constraints. Temperature profile drops for Prandtl number and elastic constraints whereas enhanced for other influential considered parameters whilst concentration profile augmented with Prandtl number. Present problem novelty relies on the modeling of comprehensive system of equations which modified into nonlinear ODEs. In order to obtain the solution numerically, technique such as Optimal Homotopy was opted.