Dynamics Of Relaxation Processes Research Articles

Shell analysis by different methods of dynamic relaxation

Shell analysis is a complex process. So far, many equations and theories have been proposed. With the increasing processing power of computers, numerical and approximate solutions were developed. The dynamic relaxation scheme is one of these methods. This procedure is an explicit technique for solving simultaneous equations. The fictitious mass and damping are added to the system of static structural equations in the dynamic relaxation technique to obtain a fictitious dynamic system. In this paper, 12 well-known dynamic relaxation processes were used for the linear analysis of shells. It is found that so far, the ability of many solutions of dynamic relaxation in the linear analysis of shells has not been shown. In each approach, the mass, damping and time step matrices are obtained based on the researchers’ work. Twelve samples are analysed. Most of these are examples of well-known benchmarks in non-linear analysis. The number of iterations and the analysis time gives the score of each technique. Then, the final rank of each method was obtained. Numerical solutions show that minimising the residual energy was the best process for linear shell analysis. Also, minimising the error of displacement, Zhang, Qiang and the power iteration methods behaved very similarly to each other.

Viscoelasticity-Controlled Relaxation in Wrinkling Surface for Multistage Time-Resolved Optical Information Encryption.

As counterfeit techniques continue to evolve, ensuring the security of conventional "static" encryption methods becomes increasingly challenging. Here, the viscoelasticity-controlled relaxation is introduced for the first time in a bilayer wrinkling system by regulating the density of hydrogen bond networks in polymer to construct a "dynamic" encryption material. The wrinkling surface can manipulate light during the dynamic relaxation process, exhibiting three stages with frosted glass, structural color, and mirror reflection. By regulating the viscoelasticity of skin layer through UV irradiation, the wavelength and the relaxation rate of the wrinkles can be controlled. As a result, dynamic wrinkling anti-counterfeiting patterns and time-resolved multistage information encryption are achieved. Crucially, the encryption material is developed as an anti-counterfeiting label for packing boxes in daily applications, allowing the encrypted information to be activated manually and identified by naked eyes, surpassing the existing time-resolved encryption materials in utilization potential. Besides, the dynamic hydrogen bond networks are extended to various dynamic interaction networks, demonstrating the versatility of the dynamic encryption strategy. This work not only provides an additional dimension for dynamic information encryption in daily practical use, but also offers theoretical guidance for the development of advanced optical anti-counterfeiting and smart display materials in the future.

Effect of the iron content on the thermal and dielectric relaxation process of sodium zinc-phosphate quaternary glassy systems

To explore the consequence of Na2O substitution by Fe2O3 on the physical, thermal and dielectric properties of zinc-phosphate-based glassy systems, a series of samples with chemical compositions of 25ZnO-40P2O5-(35-x)Na2O-xFe2O3 where, (x = 0.10, 0.15, 0.20, 0.25) have been prepared by melt quenching technique. The well-known Archimedes principle is deployed to measure the value of densities of the materials. DSC thermographs specify that the glass transition temperature (Tg) declines with the incorporation of Fe2O3 content. While thermal stability increases upon adding the Fe2O3 content. The dielectric constant (ε/) and dielectric loss (ε//) rise with an increase in temperature and fall as frequency rises sharply. The obtained relaxation time exhibits Arrhenius behaviour, and the dynamic conductivity relaxation process is not of the Debye type because the Kohlrausch stretching exponent (β) value is not equal to unity. According to the scaled electric modulus (complex) spectra, composition instead of temperature affects the dynamic conductivity relaxation mechanism.

Effects of Soliton Creation on Transient Transport through a Polymer Chain.

By using a nonadiabatic molecular dynamics method combined with the hierarchical equations of motion, we have investigated the nonequilibrium transient transport through a conjugated polymer chain. The polymer chain is described by the Su-Schrieffer-Heeger model, and its two ends are coupled with metal electrodes of different chemical potentials. In order to present the evolutions of the electronic injection and transport in the real-time domain, we have mainly discussed the dynamic relaxation processes of the excited states and transient transport currents. It is found that due to the existence of electron-phonon couplings in the conjugated polymers, creation of solitons not only affects the time of the system achieving the steady state but also leads to periodical oscillations of the steady-state transport currents with time in our simulations. Furthermore, with increasing applied bias voltage, the steady-state transport electronic current increases, which proved that the creation of the solitons can assist the electronic transport. These results have shown that the creation of the excited states is important in understanding the transport properties in organic nanostructures.

Effects of cooling rate on <i>β</i> relaxation process and stress relaxation of La-based amorphous alloys

The dynamic relaxation process and stress relaxation process are two important processes which can reflect the microstructures of materials, for they are closely related to the diffusions, the glass transition phenomena and the microstructural heterogeneities. It is of great significance to explore the relationship among them. In the current research, the <i>β</i>-relaxation characteristics and stress relaxation behaviors of bulk and ribbon samples obtained by different cooling rates are systematically investigated by taking the typical La-based amorphous alloys as model systems. The experimental results demonstrate that the cooling rate is an important parameter for controlling the energy state of the glass system, which further affects its physical and mechanical properties. Based on the dynamical mechanical spectra, the larger the cooling rate, the greater the low-temperature internal friction is and the smaller the beta relaxation activation energy according to Arrhenius calculations, and the greater the broadening of the beta relaxation behavior in the temperature spectra, suggesting that the higher cooling rate leads to greater atomic mobility and a high degree of heterogeneity in the microstructure. Thermodynamic analysis is conducted to study the slow process of thermal activation and the fast process driven by stress. At low temperature, the activation volume of the strip sample is larger than that of the bulk sample, and the activation volume values of the two samples are almost the same, as the cooling rate only affect the <i>β</i> relaxation stage, but exert little effect on the <i>α</i> relaxation, which is consistent with the conclusion that the stress relaxation behavior and <i>β</i> relaxation behavior are related to the structural non-uniformity of the amorphous alloy. The stress relaxation tests show that the characteristic time of deformation decreases at higher cooling rate, the normalized stress decay is larger, it is easier to deform under an applied force field, and the deformation unit is more likely to activate to accommodate structural deformation. The correlation between stress relaxation and <i>β</i> relaxation of amorphous alloy is further confirmed, and the proportion of liquid-like region is proportional to the relaxation mode spectrum, which also shows that <i>β</i> relaxation and stress relaxation are consistent. Finally, by calculating relaxation enthalpy <inline-formula><tex-math id="M1">\begin{document}$ \Delta {H}_{{\mathrm{r}}{\mathrm{e}}{\mathrm{l}}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231417_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231417_M1.png"/></alternatives></inline-formula>, the variation of microstructure heterogeneity with cooling rate is experimentally verified. The research sheds new light on further clarifying the relationship among <i>β</i> relaxation, deformation and microstructural heterogeneity of the amorphous alloy.

Tuning vibration-induced emission through macrocyclization and catenation.

In order to investigate the effect of macrocyclization and catenation on the regulation of vibration-induced emission (VIE), the typical VIE luminogen 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) was introduced into the skeleton of a macrocycle and corresponding [2]catenane to evaluate their dynamic relaxation processes. As investigated in detail by femtosecond transient absorption (TA) spectra, the resultant VIE systems revealed precisely tunable emissions upon changing the solvent viscosity, highlighting the key effect of the formation of [2]catenane. Notably, the introduction of an additional pillar[5]arene macrocycle featuring unique planar chirality endows the resultant chiral VIE-active [2]catenane with attractive circularly polarized luminescence in different states. This work not only develops a new strategy for the design of new luminescent systems with tunable vibration induced emission, but also provides a promising platform for the construction of smart chiral luminescent materials for practical applications.

Interface-type tunable oxygen ion dynamics for physical reservoir computing

Reservoir computing can more efficiently be used to solve time-dependent tasks than conventional feedforward network owing to various advantages, such as easy training and low hardware overhead. Physical reservoirs that contain intrinsic nonlinear dynamic processes could serve as next-generation dynamic computing systems. High-efficiency reservoir systems require nonlinear and dynamic responses to distinguish time-series input data. Herein, an interface-type dynamic transistor gated by an Hf0.5Zr0.5O2 (HZO) film was introduced to perform reservoir computing. The channel conductance of Mott material La0.67Sr0.33MnO3 (LSMO) can effectively be modulated by taking advantage of the unique coupled property of the polarization process and oxygen migration in hafnium-based ferroelectrics. The large positive value of the oxygen vacancy formation energy and negative value of the oxygen affinity energy resulted in the spontaneous migration of accumulated oxygen ions in the HZO films to the channel, leading to the dynamic relaxation process. The modulation of the channel conductance was found to be closely related to the current state, identified as the origin of the nonlinear response. In the time series recognition and prediction tasks, the proposed reservoir system showed an extremely low decision-making error. This work provides a promising pathway for exploiting dynamic ion systems for high-performance neural network devices.

Correlation between macroscopic and microscopic relaxation dynamics of water: Evidence for two liquid forms.

Water is vital for life, and without it, biomolecules and cells cannot maintain their structures and functions. The remarkable properties of water originate from its ability to form hydrogen-bonding networks and dynamics, which the connectivity constantly alters because of the orientation rotation of individual water molecules. Experimental investigation of the dynamics of water, however, has proven challenging due to the strong absorption of water at terahertz frequencies. In response, by employing a high-precision terahertz spectrometer, we have measured and characterized the terahertz dielectric response of water from supercooled liquid to near the boiling point to explore the motions. The response reveals dynamic relaxation processes corresponding to the collective orientation, single-molecule rotation, and structural rearrangements resulting from breaking and reforming hydrogen bonds in water. We have observed the direct relationship between the macroscopic and microscopic relaxation dynamics of water, and the results have provided evidence of two liquid forms in water with different transition temperatures and thermal activation energies. The results reported here thus provide an unprecedented opportunity to directly test microscopic computational models of water dynamics.

Effect of surface treatment on the dynamics of relaxation processes in confinement: ferroelectric liquid crystal in porous Anopore membrane

ABSTRACT Dielectric properties of a ferroelectric liquid crystal 2-methylbutyl 4-decyloxybenzylidene-4’-n-aminocinnamate (DOBAMBC) confined in untreated and treated porous Anopore membrane were investigated depending on the frequency and temperature. The confinement of a ferroelectric liquid crystal in an untreated Anopore membrane leads to the disappearance of the Goldstone mode. Moreover, despite the modification of the pore surface with various surfactants, no the Goldstone mode or other additional relaxation processes were observed. The relaxation rate of the molecular δ-process is slightly shifted for untreated and treated Anopore membrane in comparison to the bulk. Generally, the relaxation rate temperature dependence shows the Arrhenius-type course, while for lecithin-treated Anopore, it is similar to the Vogel–Fulcher–Tammann-type dependence. Dielectric spectra are dominated at low frequencies by conductivity and electrode polarization effects and are modified in geometric constraints.

The β relaxation process of La-based amorphous alloy: Effect of annealing and strain amplitude

The dynamic relaxation process of amorphous alloys is an important issue to understand the diffusion behavior, plastic deformation as well as glass transition phenomenon. In the current research, (La<sub>0.6</sub>Ce<sub>0.4</sub>)<sub>65</sub>Al<sub>10</sub>Co<sub>25</sub> amorphous alloy with a pronounced β relaxation process was selected as a model system to study the dynamic mechanical relaxation processes. Influence of driving frequency, physical aging and applied strain amplitude on the β relaxation of the La-based metallic glass was probed process using dynamic mechanical analysis. The experimental results demonstrated that the peak of the β relaxation process shifts to high temperature by increasing the driving frequency. Physical aging below the glass transition temperature induces a decrease of the intensity of the β relaxation process. The “defects” of amorphous alloy decreases during the physical aging process, which is ascribed to the glassy system shifts to more stable state induced by physical aging treatment. In parallel, the intensity of the β relaxation process of the amorphous alloy increases by increasing strain amplitude. The research sheds new light on further understanding the physical origin of β relaxation process of the amorphous alloy.

Effect of the physical aging on the secondary β relaxation process in a La-based metallic glass

Dynamic mechanical relaxation processes, i.e., main (α) relaxation and secondary (β) relaxation, are important issues to understand mechanical deformation, atomic diffusion as well as glass transition phenomenon of metallic glasses. In current work, La68Ni15Al15Cu2 metallic glass was selected as a protocol glass system. Mechanical relaxation processes were probed by dynamic mechanical analysis. The effects of annealing at different temperatures were analyzed by Kohlrausch–Williams–Watts (KWW)-type equation. The Kohlrausch exponent βKWW reflects the deviation from a single Debye relaxation, indicating the fact that dynamics in metallic glass are actually heterogeneous originating from the structural heterogeneity. The effects of thermal treatments were also discussed, which provides a potential solution to tune the relaxation behaviors in metallic glasses.

Evolution of the distribution of flow units of a metallic glass under cyclic loading

Dynamic mechanical relaxation processes (i.e., β relaxation and α relaxation) are closely connected with the mechanical and physical properties of metallic glasses. In the current work, the β relaxation of La60Ni15Al25 metallic glass was studied in sequential heating and cooling experiments by dynamic mechanical analysis. The values of the loss modulus peak were found to reach a relatively stable state during the progress of the heating-cooling cycles. The evolution of the flow unit distribution during thermal cycling was revealed by stress relaxation tests. The experimental results of stress relaxation were well described by a generalized Maxwell model, allowing the analysis of the underlying relaxation time and activation energy distributions. We also show here a suppressed relaxation behavior observed under repeated loading cycles, which is attributed to the annihilation of flow units and the modification of the relaxation time spectrum obtained in the framework of the generalized Maxwell model.

Enhanced optical, thermal and electrical properties of chlorinated natural rubber/zinc ferrite nanocomposites for flexible electrochemical devices

This work focused on optical, thermal stability and temperature-dependent electrical properties of chlorinated natural rubber (Cl-NR)/zinc ferrite (ZnFe2O4) nanocomposites. The insertion of ZnFe2O4 into Cl-NR showed a decrease in bandgap energy was revealed by UV spectroscopy. The thermal stability of rubber nanocomposites increased with an increase in the content of nanoparticles. The AC conductivity, dielectric constant and dielectric loss tangent of the nanocomposites were higher than the parent polymer and these properties increased with an increase in temperature and frequencies. The non-ohmic type of AC conductivity proves the dynamic relaxation process of typical semiconducting materials. The activation energy calculated from AC conductivity decreases with the temperature. The semi-circular arc obtained from Cole-Cole plot proved the temperature enhanced conductivity of the nanocomposites. The DC conductivity increased with the increase in content of nanoparticles and the changes in conductivity were correlated with different theoretical approaches such as Scarisbrick, Bueche and McCullough model. The experimental conductivity of nanocomposites was in good agreement with the McCullough model indicating the interfacial interaction developed in rubber nanocomposites. The enhanced optical properties, dielectric constant, thermal stability and electrical conductivity of Cl-NR/ZnFe2O4 systems enable the fabrication of highly-durable flexible electronic devices, actuators, super-capacitors and elastomeric pressure sensors.

A dynamic relaxation method with operator splitting and random-choice strategy for SPH

In this paper, we propose an efficient dynamic relaxation method for smoothed particle hydrodynamics (SPH) to address the time-consuming issue when dealing with achieving the equilibrium of a dynamic system. First, an artificial-viscosity-based damping term is added into the momentum equation to dissipate the velocity gradient without losing the momentum conservation of the system. Two operator splitting methods, which update velocities implicitly, are then developed to discretize the added damping term for relaxing the time-step limit. To further improve the computational efficiency, a random-choice strategy is also introduced into the dynamic relaxation process, by which the damping is imposed randomly rather than each time step. Furthermore, a splitting cell-linked list scheme is proposed by dividing the conventional cell-linked list into several blocks to avoid the thread conflict when shared-memory parallelization is applied to accelerate the computation. A number of benchmark tests show the fast and efficient feature of the present method for dynamic systems achieving their equilibrium.

Investigating Galactic binary cluster candidates with Gaia EDR3

ABSTRACT A number of stellar open cluster (OC) pairs in the Milky Way occupy similar positions in the phase space (coordinates, parallax, and proper motions) and therefore may constitute physically interacting systems. The characterization of such objects based on observational data is a fundamental step towards a proper understanding of their physical status and to investigate cluster pair formation in the Galaxy. In this work, we employed the Gaia EDR3 data to investigate a set of 16 OCs distributed as 7 stellar aggregates. We determined structural parameters and applied a decontamination technique that allowed us to obtain unambiguous lists of member stars. The studied OCs span Galactocentric distances and ages in the ranges of $7\lesssim \, R_\mathrm{ G}(\textrm {kpc})\lesssim 11$ and $7.3\le \textrm {log}\, t\le 9.2$. Eight OCs were found to constitute four gravitationally bound pairs (NGC 5617–Trumpler 22, Collinder 394–NGC 6716, Ruprecht 100–Ruprecht 101, and NGC 659–NGC 663, the latter being a dynamically unevolved binary) and other four clusters constitute two interacting, but gravitationally unbound, pairs (King 16–Berkeley 4 and NGC 2383–NGC 2384, the latter being a dissolving OC). Other four OCs (Dias 1, Pismis 19, Czernik 20, and NGC 1857) seem not associated with any stellar aggregates. Apparently, clusters within bound and dynamically evolved pairs tend to present ratios of half-light to tidal radius larger than single clusters located at similar RG, suggesting that mutual tidal interactions may possibly affect their structural parameters. Unbound or dynamically unevolved systems seem to present less noticeable signature of tidal forces on their structure. Moreover, the core radius seems more importantly correlated with the clusters’ internal dynamical relaxation process.

Dynamic relaxation characteristics and stress relaxation behavior of Pd-based<sub> </sub>metallic glass

As a potential functional and structural material, high-entropy metallic glasses have aroused tremendous research interest in condense matter physics and mechanics. The correlation between macroscopic mechanic properties and microstructure heterogeneity of high-entropy metallic glasses is one of the most important scientific issues in glassy solids. In the present research, Pd<sub>42.5</sub>Cu<sub>30</sub>Ni<sub>7.5</sub>P<sub>20</sub> metallic glass and Pd<sub>20</sub>Pt<sub>20</sub>Cu<sub>20</sub>Ni<sub>20</sub>P<sub>20</sub> high-entropy metallic glass are selected as the model alloys. Dynamic mechanical analysis (DMA) and stress relaxation are used to investigate the influences of temperature and physical aging on dynamic mechanical relaxation process and microstructure heterogeneity of the model alloys. The dynamic mechanical analysis results demonstrate that the Pd<sub>42.5</sub>Cu<sub>30</sub>Ni<sub>7.5</sub>P<sub>20</sub> metallic glass and Pd<sub>20</sub>Pt<sub>20</sub>Cu<sub>20</sub>Ni<sub>20</sub>P<sub>20</sub> high-entropy metallic glass both exhibit evident <i>β</i> relaxation process. In addition, the atomic mobility of model alloys is reduced in these processes, and the <i>β</i> relaxation shifts toward higher temperatures. In the stress relaxation process, the Gibbs free energy is reduced due to the high configurational entropy. This is the potential reason that high-entropy metallic glass possesses higher activation energy. In parallel, high-entropy metallic glass is more difficult to activate and needs to break through a higher energy barrier. With the increase of physical aging time, the flow unit in high-entropy metallic glass becomes smaller. This also benefits from the high-entropy effects that bring sluggish diffusion into high-entropy metallic glass. The change of activation volume under physical aging of high-entropy metallic glass is less sensitive to stress relaxation than that of metallic glass.

Effect of chemical strengthening residual stress on the flexural performance and fracture behavior of aluminosilicate glass

In this hybrid experimental, theoretical and numerical study the effect of chemical strengthening residual stress on the flexural strength and fracture behavior of aluminosilicate glass was investigated. Three-point bending tests were conducted on annealed and chemically strengthened glass specimens to obtain the flexural strength of both specimens and with the aid of high-speed cameras, the fracture and failure modes of these two kinds of specimens were analyzed and compared. A theoretical analysis based on the elastic fracture mechanics theory was employed to explain the strengthening effect of chemically strengthened glass. It is shown that the mechanical strength of chemically strengthened glass is highly related to the relation of the chemically strengthened layer depth and the surface flaw depth. Furthermore, this study provides an effective numerical approach to replicate the mechanical strength and failure modes for both annealed and chemically strengthened glass. The proposed finite element numerical method includes modeling techniques which consider the presence of pre-stress, random distributed surface flaws and the fracture onset in glass specimens. The residual stress pattern was defined exploiting the dynamic relaxation process for temperature-induced expansion of the elements before the loading process. Discrete distributed surface flaws were inserted in the model, the brittle fracture of glass was represented by the smeared crack method and the numerical results were compared to experimental data. It’s illustrated that the proposed method can be used to represent both the discrete fracture behavior and the chemically-strengthening effect of silicate glass.

Stochastic analysis of dynamic processes in the solar activity

Natural processes existing in complex objects of inanimate and living matter are of a stochastic and non-equilibrium nature. The main problem in the study of such systems is to determine the value of entropy as a quantitative measure of the uncertainty and systematicity of states of dynamical systems in different phase spaces. This paper presents a new method for analyzing active processes of solar dynamics using the theory of non-Markov random discrete processes (NMRDP). The NMRDP theory is based on the Zwanzig-Mori kinetic equations in a finite-difference discrete interpretation. This is consistent with the concept of non-equilibrium statistical condensed matter physics. Qualitative information about the set of behavioral patterns, relaxation processes, dynamic characteristics and internal properties of solar activity can be obtained using NMRDP modeling by the author’s methodological approach developed in this work. This approach is focused on the analysis of spectral frequency memory functions, dynamic orthogonal parameters, phase transformations, relaxation and kinetic processes and self-organization in complex physical systems. In this work, for modeling NMRDP, the author’s software package APSASA (automated program for solar activity stochastic analysis) was used, which also allows predicting the trend of solar activity for a limited period of time. Modeling NMRDP associated with active processes occurring on the Sun made it possible to build a mathematical model with whose help it is possible to study the regularities and randomness of stochastic processes, as well as to reveal the patterns arising from the recurrence and periodicity of solar activity.

Statistical mechanics of one-dimensional quantum droplets

We study the statistical mechanics and the dynamical relaxation process of modulationally unstable one-dimensional quantum droplets described by a modified Gross--Pitaevskii equation. To determine the classical partition function thereof, we leverage the semi-analytical transfer integral operator (TIO) technique. The latter predicts a distribution of the observed wave-function amplitudes and yields two-point correlation functions providing insights into the emergent dynamics involving quantum droplets. We compare the ensuing TIO results with the probability distributions obtained at large times of the modulationally unstable dynamics as well as with the equilibrium properties of a suitably constructed Langevin dynamics. We find that the instability leads to the spontaneous formation of quantum droplets featuring multiple collisions and which are found to coalesce at large evolution times. Our results from the distinct methodologies are in good agreement aside from the case of low temperatures in the special limit where the droplet widens. In this limit, the distribution acquires a pronounced bimodal character, exhibiting a deviation between the TIO solution and the Langevin dynamics.

Poly(l-lactic acid)/lithium ferrite composites: Electrical properties

Composites of lithium ferrite, LiFe5O8 (LFO) particles, dispersed in the biopolymer poly (l-lactic acid) (PLLA) were prepared by solvent casting in concentrations from 0 to 19.5 wt%, which were characterized by thermal analysis (TGA/DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and impedance spectroscopy (IS). As neat PLLA, all obtained composites are semi-crystalline, but the crystallinity decreasing with percentage LFO increase. Moreover, a good dispersion of LFO particles was found, with no interactions with the polymeric matrix. For the lower LFO content (3.5 wt%), dynamical relaxation processes were probed by IS, allowing to disclose subtle differences relative to the neat matrix. Above that concentration, the conductivity dominates and follows the percolation law above a quite low volume concentration of conductive particles (5.45%v/v). Therefore, depending on the LFO content different applications can be envisaged: energy storage for low concentrations and electromagnetic radiation shielding for concentrations above the percolation threshold.