Dynamic relaxation is an intrinsic and universal feature of glasses and enables fluctuation and dissipation to occur, which induces plentiful behaviour, maintains equilibrium, and achieves evolution ...in glass systems. Relaxation covers a broad time, frequency, and temperature ranges and determines the functions, behaviour, properties and applications of glassy system. Investigations of dynamic relaxation are significant for understanding the nature of glasses, liquids, and the critical issues of glass formation and transition, dynamic and structural heterogeneities, flow behaviour and flow units, various crossover temperatures, deformations, aging and rejuvenation, stability, crystallization, and the mechanical and physical properties of glasses. Metallic glasses (MGs) with unique microstructure and mechanical and functional properties, offer a simple but effective system for study of relaxation and related issues in glass science. In this review, a panoramic view of the state of the art of various aspects of dynamic relaxation in metallic glassy system, as well as a comparison with other glassy systems, is presented. The features and mechanisms of each known relaxation mode including primary α-relaxation, slow and fast 7 -relaxations, nearly constant loss, and boson peak, as well as their coupling in MGs, are reviewed and summarized. Emphasis is presented to the microstructural origin of these dynamic relaxation modes and their connection with the dynamic and structural heterogeneities in MGs. The factors which determine and affect the relaxation modes and behaviour in low-dimensional MGs are also introduced. It is shown that the relaxation in MGs is connected with their structural characteristics, heterogeneity, formation, glass transition, flow behaviour, physical and mechanical properties, crystallization, stability, and the localized atomic diffusion. The roles and the importance of dynamic relaxation in understanding many crucial issues in glassy physics are demonstrated. The correlations between dynamic relaxation and various properties of MGs are established and summarized. With this review on dynamic relaxation in metallic glasses, relaxation in MG can provide an effective perspective for understanding nearly all issues in metallic glasses. It is demonstrated that the relationship of relaxation to various properties, similar to the relationship of structure–property of crystalline materials, can be applied to control and design of new glassy materials with multiple functionalities, superior mechanical performance, and other extraordinary physical and chemical properties. Finally, the key unsolved questions regarding dynamic relaxation in metallic glasses are listed, and several emerging research directions in this still-evolving field are highlighted for future investigations.
Biophysical modeling of macroscopic diffusion-weighted MRI signal in terms of microscopic cellular parameters holds the promise of quantifying the integrity of white matter. Unfortunately, even ...fairly simple multi-compartment models of proton diffusion in the white matter do not provide a unique, biophysically plausible solution. Here we report a nontrivial diffusion MRI signal dependence on echo time (TE) in human white matter in vivo. We demonstrate that such TE dependence originates from compartment-specific T2 values and that it is a promising “orthogonal measure” able to break the degeneracy in parameter estimation, and to yield important relaxation metrics robustly. We thereby enable the precise estimation of the intra- and extra-axonal water T2 relaxation times, which is precluded by a limited signal-to-noise ratio when using multi-echo relaxometry alone.
•Empirical evidence for different compartmental T2 values.•TE dependency of diffusion MRI signals biases the interpretation of diffusion parameters.•Including compartmental diffusivities in the biophysical models improves T2 relaxometry.•Including compartmental T2's in the biophysical models improve diffusion modeling.•Compartmental T2's may become valuable parameters for WM microstructure.
Patients with Coronavirus Disease 2019(COVID-19) will experience high levels of anxiety and low sleep quality due to isolation treatment. Some sleep-improving drugs may inhibit the respiratory system ...and worsen the condition. Prolonged bedside instruction may increase the risk of medical infections.
To investigate the effect of progressive muscle relaxation on anxiety and sleep quality of COVID-19.
In this randomized controlled clinical trial, a total of 51 patients who entered the isolation ward were included in the study and randomly divided into experimental and control groups. The experimental group used progressive muscle relaxation (PMR) technology for 30 min per day for 5 consecutive days. During this period, the control group received only routine care and treatment. Before and after the intervention, the Spielberger State-Trait Anxiety Scale (STAI) and Sleep State Self-Rating Scale (SRSS) were used to measure and record patient anxiety and sleep quality. Finally, data analysis was performed using SPSS 25.0 software.
The average anxiety score (STAI) before intervention was not statistically significant (P = 0.730), and the average anxiety score after intervention was statistically significant (P < 0.001). The average sleep quality score (SRSS) of the two groups before intervention was not statistically significant (P = 0.838), and it was statistically significant after intervention (P < 0.001).
Progressive muscle relaxation as an auxiliary method can reduce anxiety and improve sleep quality in patients with COVID-19.
•In patients with COVID-19, all confirmed patients need to be treated in isolation due to strong infectivity. According to clinical observation, anxiety and sleep disturbances increased significantly after isolation treatment. Some sleep-promoting drugs may have respiratory depression, and the new coronary virus mainly affects lung tissue, and the use of drugs may increase respiratory depression. Therefore, we use asymptotic muscle relaxation training to alleviate the anxiety and improve sleep quality of patients with COVID-19. This training can be performed remotely and multiple times after one training session, without directly facing the patient, reducing doctor-patient contact and reducing medical infection risk. Currently, COVID-19 has a large number of cases in South Korea, Japan, Iran, and Italy. I hope our clinical research will be helpful to our country's clinical treatment and the above countries.
Underground openings can experience time-dependent deformations and stress changes. Studying time-dependent rock behaviour is commonly done with static load (creep) tests in the laboratory which ...typically exhibit three distinct stages of behaviour. In this study relaxation tests were conducted to examine if three stages also exist under constant strain boundary conditions and to understand how the relaxation behaviour changes as the driving stress to strength ratio is increased. Tests were conducted on two types of limestone. At different load levels similar stress-time responses were measured indicating three distinct stages of stress relaxation. The first stage of stress relaxation (RI) where the stress relaxes with a decreasing rate is followed by the second stage (RII) in which the stress decrease approaches a constant rate and in the third stage (RIII) no further stress relaxation takes place. In the first stage 55% to 95% of the total stress relaxation takes place. The test results are compared with literature data to understand the influence of the stiffness on the magnitude and time to reach the maximum stress relaxation. Relaxation tests could be used to derive numerical model inputs to describe the time-dependent behaviour in a manner similar to static load tests.
•We give insight into the time-dependent behaviour of rock materials and the importance of performing laboratory testing.•The paper focuses on stress relaxation of brittle rocks, the time-dependent response under constant (controlled) strain.•We show that three distinct stages during stress relaxation take place.•A data set of stress relaxation test results is presented to estimate and predict the relaxation of different rock types.
•Effect of cyclic weak disturbance on stress relaxation is studied.•The influence of confining pressure on cyclic weak disturbance relaxation is considered.•A impact factor of weak disturbance is ...defined.
Cyclic weak disturbance caused by blasting, drilling, earthquake and transport is an important factor to deep rock projects failure. In order to study the influence of cyclic weak disturbance on the stress relaxation of rock under different confining pressures, a step loading stress cyclic weak disturbance relaxation test was carried out on marble, and an impact factor of weak disturbance was defined. The test results showed that the rock peak strength was the smallest under cyclic weak disturbance relaxation; before the peak stress was reached, the relaxation magnitude of weak disturbance increased with the increase of the initial stress level; and it continuously increased with the decrease of the initial stress level after the peak stress. The stress relaxation rate nonlinearly decreased with axial strain levels; by contrast, the initial stress relaxation rate was proportional to the strain level. As the strain increased, the weak disturbance effect presented a nonlinear growth characteristic of first decreasing and then increasing.
The anisotropy of brain white matter microstructure manifests itself in orientational-dependence of various MRI contrasts, and can result in significant quantification biases if ignored. ...Understanding the origins of this orientation-dependence could enhance the interpretation of MRI signal changes in development, ageing and disease and ultimately improve clinical diagnosis. Using a novel experimental setup, this work studies the contributions of the intra- and extra-axonal water to the orientation-dependence of one of the most clinically-studied parameters, apparent transverse relaxation T2. Specifically, a tiltable receive coil is interfaced with an ultra-strong gradient MRI scanner to acquire multidimensional MRI data with an unprecedented range of acquisition parameters. Using this setup, compartmental T2 can be disentangled based on differences in diffusional-anisotropy, and its orientation-dependence further elucidated by re-orienting the head with respect to the main magnetic field B→0. A dependence of (compartmental) T2 on the fibre orientation w.r.t. B→0 was observed, and further quantified using characteristic representations for susceptibility- and magic angle effects. Across white matter, anisotropy effects were dominated by the extra-axonal water signal, while the intra-axonal water signal decay varied less with fibre-orientation. Moreover, the results suggest that the stronger extra-axonal T2 orientation-dependence is dominated by magnetic susceptibility effects (presumably from the myelin sheath) while the weaker intra-axonal T2 orientation-dependence may be driven by a combination of microstructural effects. Even though the current design of the tiltable coil only offers a modest range of angles, the results demonstrate an overall effect of tilt and serve as a proof-of-concept motivating further hardware development to facilitate experiments that explore orientational anisotropy. These observations have the potential to lead to white matter microstructural models with increased compartmental sensitivity to disease, and can have direct consequences for longitudinal and group-wise T2- and diffusion-MRI data analysis, where the effect of head-orientation in the scanner is commonly ignored.
GdxNi20Al80−x (x = 50, 60, 65, 70 at%) metallic glasses (MGs) with prominent β-relaxation were developed, which provide a new model system for studying some controversial issues concerning ...β-relaxation. The relaxation behavior and thermal stability of GdxNi20Al80−x MGs were probed by dynamic mechanical relaxation, static stress relaxation, and differential scanning calorimetry. In view of the temperature and frequency dependence of the dynamic mechanical relaxation spectrum, we investigated the β-relaxation and α-relaxation separation phenomena of Gd50Ni20Al30 and Gd60Ni20Al20 MGs. With increasing Gd/Al ratio, the activation energy of the β-relaxation decreased, which was conducive to the flow units and prominent β-relaxation. The Gd70Ni20Al10 alloy had the most significant β-relaxation phenomenon, although some nanocrystalline Gd3Ni phase was distributed in the amorphous matrix. The Gd50Ni20Al30 glass had a crystallization activation energy of 476 kJ/mol, corresponding to the highest thermal stability. At a constant strain, the static stress relaxation process of the Gd70Ni20Al10 alloy was analyzed over a wide time window and temperature range. A decoupling phenomenon of the relaxation into a two-step process occurred in the Gd70Ni20Al10 alloy, namely, a fast relaxation process and a slow relaxation process, at different time scales. Analysis of the relaxation dynamics and time scales of the relaxation confirmed that the fast relaxation process differed from the β-relaxation process. This study elucidates the β-relaxation behavior and stress relaxation decoupling phenomenon in Gd-Ni-Al MGs and should, therefore, help clarify the mechanical relaxation behavior and intrinsic characteristics of MGs in future work.
•GdxNi20Al80−x metallic glasses (MGs) with prominent β-relaxation were developed.•Mechanical relaxation processes were probed by DMA and static stress relaxation.•Gd-Ni-Al MGs have higher Tβ, Tα and thermal stability than La-based MGs.•A stress relaxation decoupling phenomenon occurred in the Gd70Ni20Al10 alloy.
Existing two-frequency reconstructive methods can only capture primary (single) molecular relaxation processes in excitable gases. In this paper, we present a reconstructive method based on the novel ...decomposition of frequency-dependent acoustic relaxation spectra to capture the entire molecular multimode relaxation process. This decomposition of acoustic relaxation spectra is developed from the frequency-dependent effective specific heat, indicating that a multi-relaxation process is the sum of the interior single-relaxation processes. Based on this decomposition, we can reconstruct the entire multi-relaxation process by capturing the relaxation times and relaxation strengths of N interior single-relaxation processes, using the measurements of acoustic absorption and sound speed at 2N frequencies. Experimental data for the gas mixtures CO2-N2 and CO2-O2 validate our decomposition and reconstruction approach.
In this paper, a thermomechanical constitutive model was developed for the time-dependent behaviors of the glass transition of amorphous networks. The model used multiple discrete relaxation ...processes to describe the distribution of relaxation times for stress relaxation, structural relaxation, and stress-activated viscous flow. A non-equilibrium thermodynamic framework based on the fictive temperature was introduced to demonstrate the thermodynamic consistency of the constitutive theory. Experimental and theoretical methods were developed to determine the parameters describing the distribution of stress and structural relaxation times and the dependence of the relaxation times on temperature, structure, and driving stress. The model was applied to study the effects of deformation temperatures and physical aging on the shape-memory behavior of amorphous networks. The model was able to reproduce important features of the partially constrained recovery response observed in experiments. Specifically, the model demonstrated a strain-recovery overshoot for cases programmed below Tg and subjected to a constant mechanical load. This phenomenon was not observed for materials programmed above Tg. Physical aging, in which the material was annealed for an extended period of time below Tg, shifted the activation of strain recovery to higher temperatures and increased significantly the initial recovery rate. For fixed-strain recovery, the model showed a larger overshoot in the stress response for cases programmed below Tg, which was consistent with previous experimental observations. Altogether, this work demonstrates how an understanding of the time-dependent behaviors of the glass transition can be used to tailor the temperature and deformation history of the shape-memory programming process to achieve more complex shape recovery pathways, faster recovery responses, and larger activation stresses.
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