Change In Order Parameter Research Articles

Energy Changing Paths for Li-Ion Batteries Under Nonequilibrium Process

It has been discovered that the electrodes of Li-ion batteries have abnormal phase transition phenomena during nonequilibrium process. As a two-phase-coexistence material, LiFePO4 (LFP) shows single phase during both high-rate lithiation and delithiation. Furthermore, a far from equilibrium state results in LFP particles with meta-stable amorphous structures and layered oxides exhibiting two-phase-coexistence during high rate delithiation. It is well known that a stable single-phase structure is an important characteristic for the electrodes with better high-rate performance, since the energy barriers of nucleation and growth for new phases are eliminated. Understanding the mechanisms of the abnormal phase transition during nonequilibrium process is therefore essential for designing the electrodes with fast (dis)charging. In this work, we model the free energy of electrodes with a series of order parameters based on nonequilibrium thermodynamics and continuum mechanics. Developed governing equations for the kinetics of the order parameters reveal the mechanism of the abnormal phase transitions for LFP and layered oxides under high rate (de)lithiation. The generation of dislocations is cross-coupled with the chemical reaction of Li-ion on the surface of electrode particles. Such coupling is the origin of materials choosing various energy changing paths under different (dis)charging conditions and resulting in various lattice parameters and structures. The dislocation density is the key parameter for the path selection since it alters dislocation-induced energy. In the simulations for LFP and layered oxides, the changes of order parameters agree with the abnormal phase transition observed in existing experimental studies. Our study indicates a potential strategy of introducing dislocations with surface engineering for optimizing the (dis)charging path of electrode materials to obtain stable single-phase characteristics and promote the kinetic capability.

Biorthogonal Dynamical Quantum Phase Transitions in Non-Hermitian Systems.

By utilizing biorthogonal bases, we develop a comprehensive framework for studying biorthogonal dynamical quantum phase transitions in non-Hermitian systems. With the help of the previously overlooked associated state, we define the automatically normalized biorthogonal Loschmidt echo. This approach is capable of handling arbitrary non-Hermitian systems with complex eigenvalues and naturally eliminates the negative value of Loschmidt rate obtained without the biorthogonal bases. Taking the non-Hermitian Su-Schrieffer-Heeger model as a concrete example, a 1/2 change of dynamical topological order parameter in biorthogonal bases is observed which is not shown in self-normal bases. Furthermore, we discover that the periodicity of biorthogonal dynamical quantum phase transitions depends on whether the two-level subsystem at the critical momentum oscillates or reaches a steady state.

Fluorite-pyrochlore-weberite phase transitions in a series of 20-component ultrahigh-entropy compositionally complex ceramics

A new series of 20-component fluorite-based compositionally complex oxides (20CCFBOxNb/Ta) with the general chemical formula (15RE1/15)2x+1(Ce1/3Zr1/3Hf1/3)3–3x(Nb1/2Ta1/2)xO8-δ (0 ≤ x ≤ 1, where 15RE1/15 = La1/15Pr1/15Nd1/15Sm1/15Eu1/15Gd1/15Tb1/15Dy1/15Y1/15Ho1/15Er1/15Tm1/15Yb1/15Lu1/15Sc1/15) are synthesized. Despite that the Gibbs phase rule allows for the existence of up to 20 phases at the thermodynamic equilibrium, 17 of the 20CCFBOxNb/Ta compositions synthesized in this study all possess single ultrahigh-entropy phases in fluorite, pyrochlore, or weberite structure, as shown by X-ray diffraction (XRD). Only < 1 vol% of secondary phases are observed in two compositions near the phase-transition points. With changing compositional variable x, this series of 20CCFBOxNb/Ta undergoes an abrupt fluorite-pyrochlore transition at x = ∼0.27 and an abrupt pyrochlore-weberite transition at x = ∼0.87. Careful characterization reveals abrupt changes of order parameters at both phase transitions. In addition, weberite short-range ordering can persist into the long-range pyrochlore phase, which leads to the lowest thermal conductivities.

Microscopic pathways of transition from low-density to high-density amorphous phase of water.

In recent years, much attention has been devoted to understanding the pathways of phase transition between two equilibrium condensed phases (such as liquids and solids). However, the microscopic pathways of transition involving non-equilibrium, non-diffusive amorphous (glassy) phases still remain poorly understood. In this work, we have employed computer simulations, persistence homology (a tool rooted in topological data analysis), and machine learning to probe the microscopic pathway of pressure-induced non-equilibrium transition between the low- and high-density amorphous (LDA and HDA, respectively) ice phases of the TIP4P/2005 and ST2 water models. Using persistence homology and machine learning, we introduced a new order parameter that unambiguously identifies the LDA- and HDA-like local environments. The LDA phase transitions continuously and collectively into the corresponding HDA phase via a pre-ordered intermediate phase during the isothermal compression. The local order parameter susceptibilities show a maximum near the transition pressure (P*)-suggesting maximum structural heterogeneities near P*. The HDA-like clusters are structurally ramified and spatially delocalized inside the LDA phase near the transition pressure. We also found manifestations of the first-order low-density to high-density liquid transition in the sharpness of the order parameter change during the LDA to HDA transition. We further investigated the (geometrical) structures and topologies of the LDA and HDA ices formed via different protocols and also studied the dependence of the (microscopic) pathway of phase transition on the protocol followed to prepare the initial LDA phase. Finally, the method adopted here to study the phase transition pathways is not restricted to the system under consideration and provides a robust way of probing phase transition pathways involving any two condensed phases at both equilibrium and out-of-equilibrium conditions.

Unveiling the effect of H2S concentration in CH4 hydrate formation and growth: A molecular dynamics study

We used molecular dynamics method to simulate the formation and growth of CH4 hydrates with different concentrations of H2S. At the large scale of simulation time, 10000 ns, it is unlikely to form hydrates at 10 MPa and 260 K if there are only CH4 and water; and if there was a small proportion of H2S in the gas, hydrates would easily form. When the molar concentration of H2S in the gas is 1 %, the formed hydrate is unstable and will eventually disintegrate, leaving the box in a two-phase state of gaseous and liquid. In contrast, at molar concentrations of 5 % or higher of H2S, hydrate formation is accelerated, and the hydrate will grow continuously. However, it is not structure I type as expected. These views are supported by the changes in F3 and F4 order parameters, numbers of different cage types, and the number of water molecules belonging to different states. Moreover, since the formation of hydrates is an energy reduction process, we can easily develop inhibitors targeted at hydrates in actual production and gas transportation. According to IGMH analysis, only van der Waals interactions occur between gas molecules inside the cages and the water cage.

Features of the formation of the rotationally ordered phases in perovskites

Based on the phenomenological theory, the conditions for the formation of a sequences of the rotationally ordered phase states observed in orthoaluminates, orthoferrites and several other ABX3 compounds with a perovskite structure have been studied. It was shown that the specificity of the phase state formation is due to the competition between two critical order parameters characterizing the in-phase and antiphase rotations of the octahedra. The condensation of one order parameter blocks the appearance of the other. The blocking can be overcome by the interaction of the competing order parameters with the displacements of the cation A. In this case, the degree of stretching of the A–X bonds is of great importance. The consequence of the removal of the blocking is the formation of the phase states described by two competing order parameters. The conditions under which a change in the critical order parameter occurs have discussed.

Structural transition of a nanodroplet under an alternating electric field: Understandings and predictions from a dynamic density functional theory

Alternating current (AC) electric field is an efficient means in controlling the nanostructure of a material but the mechanism is not so clear in many systems. We introduced a dynamic density functional theory (DDFT) to mimic the formation and evolution of a nanodroplet/nanocluster under an AC electric field. The prediction from DDFT is qualitatively consistent with real-world experiments and molecular simulations. The influence from the AC electric field is summarized into a diagram and the transition line can be fitted into an empirical function. It seems the crystallization mechanism is different at high and low temperatures, in which the AC electric field is a favorable and unfavorable condition for crystallization, respectively. The crystallization can be divided into two steps which corresponds to the change of order parameter and free energy, respectively. Additionally, different AC waves results in similar nanostructures and the pulse wave has the highest order parameter.

Biophysical investigations of antimicrobial peptide mimics for mechanistic studies.

With a relentless rise in the growth of antimicrobial resistance, much attention is being focused on Antimicrobial peptides (AMP) and the development of AMP mimicking agents to combat this nefarious issue. However lesser reports come up with adequate reasoning behind the driving force of the membrane perturbing nature. Here, we shall be discussing the two branches of AMP mimics, peptoids and small molecules. Further, we explore the mode of action behind the antimicrobial properties displayed by the library of peptoids and small molecule mimics. To address this big challenge of understanding how the membrane active compound behaves, each of the compounds were introduced to the liposomes, mimicking the bacterial model membranes, and their interactions was recorded using solid state nuclear magnetic resonance spectroscopy. We observe that each of the mimics interact with the liposome as the global shape of the vesicles gets deformed. Also we observed a definite interaction with the fatty acyl chain as changes in order parameters were observed with respect to that of pure lipids. To develop a thorough understanding of the pore forming abilities of these compounds, a fluorescent dye release studies was executed using both bacterial and mammalian model membranes. The calcein dye release test revealed that the small molecule mimics undergo a cooperative effect. For the peptoids investigated, the extent of release could be correlated with their antimicrobial activity as well as the toxicity data.

LOCALIZED PLASTICITY PATTERN AT THE PREFRACTURE STAGE: ORIGIN AND DEVELOPMENT

A pattern of macroscopic deformation bands with a characteristic size of ~10 mm was revealed experimentally in a uniaxially deformed sample at the prefracture stage prior to macroscopic necking. The bands moved at different velocities to the place of subsequent necking. The observed banding pattern in the deformed medium was described using two identified dynamic order parameters, which are the amplitudes of unstable plastic and elastic deformation modes. The change in the dynamic order parameters was described by a system of two coupled nonlinear parabolic equations. Analysis of solutions to the equations revealed the conditions for the formation and development of the found pattern at the prefracture stage.

Research on Tribo-Dynamic Characteristics of Double Involute Gears Based on Multiphysics Coupling

Abstract In order to accurately obtain the dynamic characteristics of double involute gears (DIGs), according to the characteristics of tooth profile engagement, a tribo-dynamic model of DIGs with multiphysics coupling characteristics is proposed by integrating the thermal elastohydrodynamic lubrication (TEHL) model, the temperature field analysis model and the dynamic model. The influence of different factors on its dynamic behaviors and the difference in dynamic characteristics between DIGs and common involute gears (CIGs) are comparatively analyzed. The results show that the thermal effect and tooth friction can intensify the dynamic response of the gear transmission. The variation of rotational velocity and torque has a significant impact on the dynamic behaviors of DIGs, the change of tooth waist order parameters have little effect on its dynamic characteristics, and the dynamic characteristics between DIGs and CIGs exist difference, but the difference is not obvious. Additionally, the theoretical model is verified through experiments.

Dynamical quantum phase transitions in spin- S U(1) quantum link models

Dynamical quantum phase transitions (DQPTs) are a powerful concept of probing far-from-equilibrium criticality in quantum many-body systems. With the strong ongoing experimental drive to quantum simulate lattice gauge theories, it becomes important to investigate DQPTs in these models in order to better understand their far-from-equilibrium properties. In this work, we use infinite matrix product state techniques to study DQPTs in spin-$S U(1)$ quantum link models. Although we are able to reproduce literature results directly connecting DQPTs to a sign change in the dynamical order parameter in the case of $S=1/2$ for quenches starting in a vacuum initial state, we find that for different quench protocols or different values of the link spin length $S&gt;1/2$ this direct connection is no longer present. In particular, we find that there is an abundance of different types of DQPTs not directly associated with any sign change of the order parameter. Our findings indicate that DQPTs are fundamentally different between the Wilson-Kogut-Susskind limit and its representation through the quantum link formalism.

Cascade of transitions in twisted and non-twisted graphene layers within the van Hove scenario

Motivated by measurements of compressibility and STM spectra in twisted bilayer graphene, we analyze the pattern of symmetry breaking for itinerant fermions near a van Hove singularity. Making use of an approximate SU(4) symmetry of the Landau functional, we show that the structure of the spin/isospin order parameter changes with increasing filling via a cascade of transitions. We compute the feedback from different spin/isospin orders on fermions and argue that each order splits the initially 4-fold degenerate van Hove peak in a particular fashion, consistent with the STM data and compressibility measurements, providing a unified interpretation of the cascade of transitions in twisted bilayer graphene. Our results follow from a generic analysis of an SU(4)-symmetric Landau functional and are valid beyond a specific underlying fermionic model. We argue that an analogous van Hove scenario explains the cascade of phase transitions in non-twisted Bernal bilayer and rhombohedral trilayer graphene.

Higher-order topological state induced by d -wave competing orders in high- Tc superconductor based heterostructures

We introduce a two-dimensional Chern insulator in proximity to a $d$-wave pseudogap state of the high-T$_c$ superconducting material as an effective platform to realize the higher order topological system. The proximity-induced $d$-density-wave (DDW) order in the Chern insulator layer serves as an effective mass. The edge states will be fully gapped by this DDW order. In the real space, the sign of the DDW order parameter changes at the system corners due to the $d$-wave factor, leading to the gapless corner states, indicating that this system may be in a higher order topological state. The higher order topology in this coupled system is confirmed based on the calculation of the edge polarization and the quadrupole moment. In the superconducting state where the superconducting order and the DDW order coexist, the Majorana corner states emerge.

Charged Small Molecule Binding to Membranes in MD Simulations Evaluated against NMR Experiments.

Interactions of charged molecules with biomembranes regulate many of their biological activities, but their binding affinities to lipid bilayers are difficult to measure experimentally and model theoretically. Classical molecular dynamics (MD) simulations have the potential to capture the complex interactions determining how charged biomolecules interact with membranes, but systematic overbinding of sodium and calcium cations in standard MD simulations raises the question of how accurately force fields capture the interactions between lipid membranes and charged biomolecules. Here, we evaluate the binding of positively charged small molecules, etidocaine, and tetraphenylphosphonium to a phosphatidylcholine (POPC) lipid bilayer using the changes in lipid head-group order parameters. We observed that these molecules behave oppositely to calcium and sodium ions when binding to membranes: (i) their binding affinities are not overestimated by standard force field parameters, (ii) implicit inclusion of electronic polarizability increases their binding affinity, and (iii) they penetrate into the hydrophobic membrane core. Our results can be explained by distinct binding mechanisms of charged small molecules with hydrophobic moieties and monoatomic ions. The binding of the former is driven by hydrophobic effects, while the latter has direct electrostatic interactions with lipids. In addition to elucidating how different kinds of charged biomolecules bind to membranes, we deliver tools for further development of MD simulation parameters and methodology.

Electrical modification of order parameters and director fluctuations in a dielectrically negative nematic doped with a positive additive

Electric effects of nematic liquid crystals (NLCs) have enabled the revolution of the display industry. Recently, the electro-optic switching of NLCs has been accelerated by applying electric fields in such a way that the field does not change the director orientation, but modifies the optical tensors of NLCs due to three effects: induced biaxial orientational order, enhanced uniaxial orientational order, and quenching of director fluctuations. Till now, these three effects have been explored only in NLCs with negative dielectric anisotropy. Here, we experimentally study the electrical modification of order parameters and director fluctuations in a dielectrically negative/positive composite NLC. The dielectrically positive dopant causes the following changes: (a) a faster nanosecond switching for optical responses attributed to the change of order parameters, (b) an increase of the biaxial order parameter, (c) a reduction of the uniaxial order parameter, and (d) a slight reduction in the field-induced birefringence change. This work provides a basis for further studies in nanosecond electro-optics.

Tracking Control of a Hyperchaotic Complex System and Its Fractional-Order Generalization

Hyperchaotic complex behaviors often occur in nature. Some chaotic behaviors are harmful, while others are beneficial. As for harmful behaviors, we hope to transform them into expected behaviors. For beneficial behaviors, we want to enhance their chaotic characteristics. Aiming at the harmful hyperchaotic complex system, a tracking controller was designed to produce the hyperchaotic complex system track common expectation system. We selected sine function, constant, and complex Lorenz chaotic system as target systems and verified the effectiveness by mathematical proof and simulation experiments. Aiming at the beneficial hyperchaotic complex phenomenon, this paper extended the hyperchaotic complex system to the fractional order because the fractional order has more complex dynamic characteristics. The influences order change and parameter change on the evolution process of the system were analyzed and observed by MATLAB simulation.

Light-Switching Surface Wettability of Chiral Liquid Crystal Networks by Dynamic Change in Nanoscale Topography.

Nano- and microscale morphology endows surfaces that play conspicuous roles in natural or artificial objects with unique functions. Surfaces with dynamic regulating features capable of switching the structures, patterns, and even dimensions of their surface profiles can control friction and wettability, thus having potential applications in antibacterial, haptics, and fluid dynamics. Here, a freestanding film with light-switchable surface based on cholesteric liquid crystal networks is presented to translate 2D flat plane into a 3D nanometer-scale topography. The wettability of the interface can be controlled by hiding or revealing the geometrical features of the surfaces with light. This reversible dynamic actuation is obtained through the order parameter change of the periodic cholesteric organization under a photoalignment procedure and lithography-free mode. Complex tailored structures can be used to encrypt tactile information and improve wettability by predesigning the orientation distribution of liquid crystal director. This rapid switching nanoprecision smart surface provides a novel platform for artificial skin, optics, and functional coatings.

Solid-State NMR and Impedance Spectroscopy Study of Spin Dynamics in Proton-Conducting Polymers: An Application of Anisotropic Relaxing Model.

The 1H–13C cross-polarization (CP) kinetics in poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) was studied under moderate (10 kHz) magic-angle spinning (MAS). To elucidate the role of adsorbed water in spin diffusion and proton conductivity, PMETAC was degassed under vacuum. The CP MAS results were processed by applying the anisotropic Naito and McDowell spin dynamics model, which includes the complete scheme of the rotating frame spin–lattice relaxation pathways. Some earlier studied proton-conducting and nonconducting polymers were added to the analysis in order to prove the capability of the used approach and to get more general conclusions. The spin-diffusion rate constant, which describes the damping of the coherences, was found to be strongly depending on the dipolar I–S coupling constant (DIS). The spin diffusion, associated with the incoherent thermal equilibration with the bath, was found to be most probably independent of DIS. It was deduced that the drying scarcely influences the spin-diffusion rates; however, it significantly (1 order of magnitude) reduces the rotating frame spin–lattice relaxation times. The drying causes the polymer hardening that reflects the changes of the local order parameters. The impedance spectroscopy was applied to study proton conductivity. The activation energies for dielectric relaxation and proton conductivity were determined, and the vehicle-type conductivity mechanism was accepted. The spin-diffusion processes occur on the microsecond scale and are one order faster than the dielectric relaxation. The possibility to determine the proton location in the H-bonded structures in powders using CP MAS technique is discussed.

On a Memristor-Based Hyperchaotic Circuit in the Context of Nonlocal and Nonsingular Kernel Fractional Operator

Memristor is a nonlinear and memory element that has a future of replacing resistors for nonlinear circuit computation. It exhibits complex properties such as chaos and hyperchaos. A five-dimensional memristor-based circuit in the context of a nonlocal and nonsingular fractional derivative is considered for analysis. The Banach fixed point theorem and contraction principle are utilized to verify the existence and uniqueness of the solution of the five-dimensional system. A numerical method developed by Toufik and Atangana is used to get approximate solutions of the system. Local stability analysis is examined using the Matignon fractional-order stability criteria, and it is shown that the trivial equilibrium point is unstable. The Lyapunov exponents for different fractional orders exposed that the nature of the five-dimensional fractional-order system is hyperchaotic. Bifurcation diagrams are obtained by varying the fractional order and two of the parameters in the model. It is shown using phase-space portraits and time-series orbit figures that the system is sensitive to derivative order change, parameter change, and small initial condition change. Master-slave synchronization of the hyperchaotic system was established, the error analysis was made, and the simulation results of the synchronized systems revealed a strong correlation among themselves.

Reprocessable Photodeformable Azobenzene Polymers.

Photodeformable azobenzene (azo) polymers are a class of smart polymers that can efficiently convert light energy into mechanical power, holding great promise in various photoactuating applications. They are typically of crosslinked polymer networks with highly oriented azo mesogens embedded inside. Upon exposure to the light of appropriate wavelength, they experience dramatic order parameter change following the configuration change of the azo units. This could result in the generation and accumulation of the gradient microscopic photomechanical force in the crosslinked polymer networks, thus leading to their macroscopic deformation. So far, a great number of photodeformable azo polymers have been developed, including some unoriented ones showing photodeformation based on different mechanisms. Among them, photodeformable azo polymers with dynamic crosslinking networks (and some uncrosslinked ones) have aroused particular interest recently because of their obvious advantages over those with stable chemical crosslinking structures such as high recyclability and reprocessability. In this paper, I provide a detailed overview of the recent progress in such reprocessable photodeformable polymers. In addition, some challenges and perspectives are also presented.