Strong Irreversibility Research Articles

Effective estimation of entropy production with lacking data

Observing stochastic trajectories with rare transitions between states, practically undetectable on time scales accessible to experiments, makes it impossible to directly quantify the entropy production and thus infer whether and how far systems are from equilibrium. To solve this issue for Markovian jump dynamics, we show a lower bound that outperforms any other estimation of entropy production (including Bayesian approaches) in regimes lacking data due to the strong irreversibility of state transitions. Moreover, in the limit of complete irreversibility, our effective version of the thermodynamic uncertainty relation sets a lower bound to entropy production that depends only on nondissipative aspects of the dynamics. Such an approach is also valuable when dealing with jump dynamics with a deterministic limit, such as irreversible chemical reactions.

Magnetic Hardening: Unveiling Magnetization Dynamics in Soft Magnetic Fe-Ni-B-Nb Thin Films at Cryogenic Temperatures.

Recent advancements in amorphous materials have opened new avenues for exploring unusual magnetic phenomena at the sub-nanometer scale. We investigate the phenomenon of low-temperature "magnetic hardening" in heterogeneous amorphous Fe-Ni-B-Nb thin films, revealing a complex interplay between microstructure and magnetism. Magnetization hysteresis measurements at cryogenic temperatures show a significant increase in coercivity (HC) below 25 K, challenging the conventional Random Anisotropy Model (RAM) in predicting magnetic responses at cryogenic temperatures. Heterogeneous films demonstrate a distinct behavior in field-cooled and zero-field-cooled temperature-dependent magnetizations at low temperatures, characterized by strong irreversibility. This suggests spin-glass-like features at low temperatures, which are attributed to exchange frustration in disordered interfacial regions. These regions hinder direct exchange coupling between magnetic entities, leading to magnetic hardening. This study enhances the understanding of how microstructural intricacies impact magnetic dynamics in heterogeneous amorphous thin films at cryogenic temperatures.

Enhanced heating efficiency for hollow Fe3O4 spherical submicron particles

We have investigated ac hysteresis loops of hollow Fe3O4 submicron particles with variable particle size of d = 100−696 nm by micromagnetic simulations to investigate the possible application to magnetic hyperthermia. For the hollow particle with the inner/outer diameter ratio of γ = 0.5, the hysteresis loss increases with increasing d and maximizes at d ∼ 300 nm, whereas the hysteresis loss generally increases with γ, but its behavior strongly depends on d. A specific absorption rate, calculated from the loop area at the field frequency of 500 kHz, attains 560 W/g for d = 296 nm and γ = 0.5, which is comparable to that for conventional superparamagnetic nanoparticles. This enhanced specific absorption ratio for the hollow particles can be explained by strong irreversibility between vortex states with different orientation of the vortex core, i.e. along the magnetic field and ⟨111⟩ easy axes.

ECG QT interval estimation with a transfer deep learning model

An experimental study of flows of the green non-motile Chlorella micro-alga in a plane micro-channel is presented. Depending on the value of the cell volume fraction, three distinct flow regimes are observed. For low values of the cell volume fraction a Newtonian flow regime characterised by a Poiseuille like flow field, absence of wall slip and hydrodynamic reversibility of the flow states is observed. For intermediate values of the cell volume fraction, the flow profiles are consistent with a Poiseuille flow of a shear thinning fluid in the presence of slip at the channel’s wall. For even larger cell volume fractions, a yield stress like behaviour manifested through the presence of a central solid plug is observed. Except for the Newtonian flow regime, a strong hydrodynamic irreversibility of the flow and wall slip are found. The calculation of the wall shear rate and wall stress based on the measured flow fields allows one to identify the mechanisms of wall slip observed in the shear thinning and yield stress regimes.

Non-equilibrium magnetic response in concentrated spin-glass Au0.89Fe0.11 alloy

We report a detailed study of dc magnetization and ac susceptibility performed on the zero field cooled (ZFC) and field cooled (FC) state of polycrystalline Au0.89Fe0.11 alloy. The temperature variation of ZFC and FC dc magnetization at low fields shows a distinct peak around Tf = 33 K, which indicates the cooperative freezing of the finite size spin clusters. A weak thermomagnetic irreversibility between ZFC and FC magnetization appears at a temperature Tir, which is slightly below Tf. Further down the temperature at Tsh<Tir, the ZFC and FC magnetization curves exhibit strong thermomagnetic irreversibility. The ac susceptibility recorded after cooling in presence of field shows significant dispersion below Tf, and also, the FC state of Au0.89Fe0.11 alloy exhibits a pronounced memory effect in the dc magnetization which clearly underline that the FC state is not an equilibrium state. In contrast to the general perception obtained through the mean-field theories of thermodynamic phase transition in spin-glass envisaging the FC state to be an equilibrium state, the present experimental results clearly indicate that the energy landscape of the FC state of Au0.89Fe0.11 alloy is a nontrivial one.

Room temperature ferromagnetism in oxygen-deficient gallium oxide films with cubic spinel structure

Oxygen-defective gallium oxide (Ga2O3-x with 0.4 < x < 0.7) thin films with cubic spinel structure were deposited on c-cut epi-polished sapphire wafers using thermal evaporation technique by keeping specific values of oxygen partial pressure in the evaporation chamber. The preparation method and post-treatment conditions induced distinct oxygen stoichiometries in the films which exhibit a ferromagnetic-like behavior at room temperature. Despite the measured saturation magnetization values do not exhibit a straightforward correlation to the oxygen stoichiometry of the films, the presence of oxygen vacancies and defects is presumably the origin of the unconventional magnetic behavior. Strong magnetic irreversibility exhibit by the magnetization measurements performed using field-cooling and zero-field-cooling protocols indicate the presence of disordered magnetic moment distributions which are likely non-collinear. Theoretical and experimental results available in the literature corroborate with the assumptions that oxygen vacancies and defects appear as the main reason for room-temperature ferromagnetism. All films exhibit soft magnetic behavior at room temperature, exhibiting remanent magnetizations between 7% and 20% of the saturation magnetization which saturated magnetic moments is estimated as 0.43 and 1.24 Bohr magneton per oxygen vacancy. The present results extend the functionalities of this interesting material, which is already investigated for applications in several technological areas, for possible uses in the areas of spintronics and emerging areas of the optospintronics.

Subgrid-scale models of isotropic turbulence need not produce energy backscatter

This investigation questions the importance of inverse interscale energy fluxes, the so-called energy backscatter, for the modelling of the energy cascade in large-eddy simulations (LES) of turbulent flows. The invariance of the filtered Navier–Stokes equations to divergence-preserving transformations of the subgrid-scale (SGS) stress tensor is exploited here to explore alternative representations of the local SGS energy fluxes. Numerical optimisation procedures are applied to the SGS stress tensor – obtained by filtering isotropic turbulence flow fields – to find alternative stresses that satisfy the filtered Navier–Stokes equations, but that produce negligible backscatter. These alternative SGS stresses show that backscatter represents not a flux of energy from the subgrid to the resolved scales, but conservative spatial fluxes, and that it need not be modelled to reproduce the local energetic exchange between the resolved and the subgrid scales in LES. From the perspective of statistical mechanics, it is argued that this is a consequence of the strong statistical irreversibility of inertial-range dynamics, which precludes inverse energy cascades even in a local sense. These findings show that the energy cascade is strongly unidirectional locally, and that it can be modelled as an irreversible sink of energy, justifying the extended use of purely dissipative SGS models in LES.

Traveling wave dynamics for Allen-Cahn equations with strong irreversibility

Constrained gradient flows are studied in fracture mechanics to describestrongly irreversible(orunidirectional) evolution of cracks. The present paper is devoted to a study on the long-time behavior of non-compact orbits of such constrained gradient flows. More precisely, traveling wave dynamics for a one-dimensional fully nonlinear Allen-Cahn type equation involving the positive-part function is considered. Main results of the paper consist of a construction of a one-parameter family ofdegeneratetraveling wave solutions (even identified when coinciding up to translation) and exponential stability of such traveling wave solutions with some basin of attraction, although they are unstable in a usual sense.

Fe-based superconducting transition temperature modeling by machine learning: A computer science method.

Searching for new high temperature superconductors has long been a key research issue. Fe-based superconductors attract researchers’ attention due to their high transition temperature, strong irreversibility field, and excellent crystallographic symmetry. By using doping methods and dopant levels, different types of new Fe-based superconductors are synthesized. The transition temperature is a key indicator to measure whether new superconductors are high temperature superconductors. However, the condition for measuring transition temperature are strict, and the measurement process is dangerous. There is a strong relationship between the lattice parameters and the transition temperature of Fe-based superconductors. To avoid the difficulties in measuring transition temperature, in this paper, we adopt a machine learning method to build a model based on the lattice parameters to predict the transition temperature of Fe-based superconductors. The model results are in accordance with available transition temperatures, showing 91.181% accuracy. Therefore, we can use the proposed model to predict unknown transition temperatures of Fe-based superconductors.

Electric, magnetic and microstructural features of the La2CoFeO6 lanthanide ferrocobaltite obtained by the modified Pechini route

In the search for new materials with applicable magnetic properties in spintronic devices, the aim of this work is to report the synthesis of the lanthanide ferrocobaltite La2CoFeO6 using the modified Pechini route; the experimental study of structural, morphological and magnetic properties, and the analysis of the electronic structure and bands are obtained in the framework of the Density Functional Theory. Rietveld refinement of experimental X-ray diffraction patterns revealed the crystallization of this oxide material in a perovskite-like monoclinic structure, space group [Formula: see text]21/[Formula: see text] (# 14). Scanning electron microscopy and atomic force microscopy images revealed that the surface morphology is essentially polycrystalline, with mean grain sizes between 177 and 188 nm. The dispersive X-ray spectroscopy suggests that the material obtained contains La, Fe, Co and O in the stoichiometric proportions expected by up to 98%. The magnetic susceptibility curves as a function of temperature indicated that the material is ordered ferromagnetically, showing strong irreversibility effects due to the disorder of the Fe and Co cations in the three crystallographic directions of the structure and to the strong distortions in the FeO6 and CoO6 octahedra. Magnetic hysteresis curves confirmed the ferromagnetic character of the material for all temperatures evaluated, up to room temperature. I–V response curves revealed a semiconductor-like behavior with a figure of merit exponent 1.53 of the varistor type. The ferromagnetic semiconductor behavior suggests the potential applicability of the material in spintronic technological devices.

Structural characterization and magnetic properties of single‐crystalline (La0.6Pr0.4)0.67Ca0.33MnO3 nanowires

AbstractHerein, structural and magnetic properties of single‐crystalline (La0.6Pr0.4)0.67Ca0.33MnO3 nanowires synthesized via a hydrothermal process are reported. The nanowires are crystallized in an orthorhombic structure (Pnma space group). Their lattice parameters follow the relationship a ≈ c ≈ b/√2 These nanowires exhibited a clean and smooth surface with diameters of 60‐120 nm and an average length of approximately 2.0 μm. High‐resolution transmission electron microscopy images confirmed the single‐crystalline nature of the nanowires growing along the [100] direction. The nanowires demonstrated magnetic hysteresis loops at low temperatures and a weak exchange bias (EB) effect. Paramagnetic (PM)–ferromagnetic (FM) phase transition occurred at a Curie temperature (TC) of 224 K, and strong irreversibility between zero‐field‐cooled (ZFC) and field‐cooled (FC) magnetization (MZFC and MFC, respectively) curves was observed at 273 K. The MZFC curve exhibited a significantly broad peak with a maximum at a freezing temperature (Tf) of 134 K. Relative difference between MFC and MZFC in the nanowires [(MFC − MZFC)/MFC] rapidly increased below Tf and reached approximately 50% below 35 K. The effective magnetic moment deduced from the Curie constant is larger than the theoretical value, indicating short‐range FM interactions in the nanowires. A positive PM TC (θp) implies dominant FM interactions in the nanowires, and θp &gt; TC observed herein indicates the existence of short‐range ordered states above TC.

High magnetic field properties in Ru2−xFexCrSi with antiferromagnetic and spin-glass states

We report experimental studies on ${\mathrm{Ru}}_{2\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{CrSi}$ focusing on properties related to antiferromagnetism in ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ and spin glass (SG) in ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$. By measuring the temperature dependence of magnetization $M(T)$, specific heat $C(T)$, electrical resistivity $\ensuremath{\rho}(T)$, and muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$), we observed that ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ exhibited an antiferromagnetic (AF) transition at a temperature ${T}_{N}$ of $\ensuremath{\sim}13$ K, and ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$ showed SG properties that could be interpreted as successive SG transitions, where the spin-freezing occurred at temperature ${T}_{g}$, and below that strong irreversibility in $M(T)$ and a gradual peak of $M(T)$ at ${T}^{*}\phantom{\rule{4pt}{0ex}}(&gt;{T}_{g})$ appeared. When the data for $0\ensuremath{\le}x\ensuremath{\le}0.1$ were compared, by substituting Fe the AF order was rapidly destroyed and it appeared to change to two anomalies at ${T}^{*}$ and ${T}_{g}$. With increasing $x$, there was a slight change in ${T}_{g}$ from ${T}_{N}$ for $x=0$; however, ${T}^{*}$ increased, suggesting that the AF and the SG states are closely related. Furthermore, the results of specific heat, resistivity, and magnetization in high fields were presented and compared. For ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ in specific heat under high magnetic fields up to 14 T, the peak shape around ${T}_{N}$ and the ${T}_{N}$ value were constant. The resistivity and magnetization in pulsed fields suggested that ${T}_{N}$ of ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ was constant up to over 50 T. These results demonstrated the unusual robustness of the AF transition to magnetic fields. In ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$, unusual hysteresis in magnetoresistance was observed in static and pulsed magnetic fields, although their appearances differed. These hystereses were considered a manifestation of the curious properties of the SG state with strong irreversibility.

Semiconducting Polymer Interfaces for Electrochemically Assisted Mercury Remediation.

Nanostructured polymer interfaces can play a key role in addressing urgent challenges in water purification and advanced separations. Conventional technologies for mercury remediation often necessitate large energetic inputs, produce significant secondary waste, or when electrochemical, lead to strong irreversibility. Here, we propose the reversible, electrochemical capture and release of mercury, by modulating interfacial mercury deposition through a sulfur-containing, semiconducting redox polymer. Electrodeposition/stripping of mercury was carried out with a nanostructured poly(3-hexylthiophene-2,5-diyl)-carbon nanotube composite electrode, coated on titanium (P3HT-CNT/Ti). During electrochemical release, mercury was reversibly stripped in a non-acid electrolyte with 12-fold higher release kinetics compared to nonfunctionalized electrodes. In situ optical microscopy confirmed the rapid, reversible nature of the electrodeposition/stripping process with P3HT-CNT/Ti, indicating the key role of redox processes in mediating the mercury phase transition. The polymer-functionalized system exhibited high mercury removal efficiencies (>97%) in real wastewater matrices while bringing the final mercury concentrations down to <2 μg L-1. Moreover, an energy consumption analysis highlighted a 3-fold increase in efficiency with P3HT-CNT/Ti compared to titanium. Our study demonstrates the effectiveness of semiconducting redox polymers for reversible mercury deposition and points to future applications in mediating electrochemical stripping for various environmental applications.

Spin-Glass Behavior in Spinel Compound ZnCoTiO4

In this paper, we report a spin-glass (SG) behavior by comprehensive magnetic measurements in spinel compound ZnCoTiO4. The temperature dependence of DC magnetization exhibits a strong irreversibility under zero field cooled and field cooled processes. At the same time, AC susceptibility measurement reveals that the peak position moves towards high temperature with increasing frequency. These results unanimously indicate that a magnetic frustration behavior has occurred in this system. In addition, the relevant parameters (T0 = 14.4 K, τ0 = 8.3165 × 10−11 s, zν = 4.53) are observed by the data of AC susceptibility measurement, suggesting a typical SG behavior. The magnetic relaxation behavior (MIRM vs. t) further manifests a SG behavior in ZnCoTiO4. Furthermore, the origin of SG behavior in ZnCoTiO4 may be contributed to atomic disorders or the competition between ferromagnetic (FM) and antiferromagnetic (AFM) interactions, or both.

Fundamental Insights from a Single‐Crystal Sodium Iridate Battery

AbstractElectrochemically driven chemical transformations play the key role in controlling storage of energy in chemical bonds and subsequent conversion to power electric vehicles and consumer electronics. The promise of coupling anionic oxygen redox with cationic redox to achieve a substantial increase in capacities has inspired research in a wide range of electrode materials. A key challenge is that these studies have focused on polycrystalline materials, where it is hard to perform precise structural determinations, especially related to the location of light atoms. Here a different approach is utilized and a highly ordered single crystal, Na2−xIrO3 is harnessed, to explore the role of defects and structural transformations in layered transition metal oxide materials on redox‐activity, capacity, reversibility, and stability. Within a combined experimental and theoretical framework, it is demonstrated that 1) it is possible to cycle Na2−xIrO3, offering proof of principle for single‐crystal based batteries 2) structural phase transitions coincide with Ir 4+/Ir 5+ redox couple with no evident contribution from anionic redox 3) strong irreversibility and capacity fade observed during cycling correlates with the Na + migration resulting in progressive growth of an electrochemically inert O3‐type NaIrO3 phase.

On “Strong Irreversibility” from Information Occupancy to Information Sharing and the Characteristics as “Semi-Public Goods”

On “Strong Irreversibility” from Information Occupancy to Information Sharing and the Characteristics as “Semi-Public Goods”

Appearance of glassy ferromagnetic behavior in [formula omitted] ([formula omitted]) thin films: A revised phase diagram

We report on results of electrical transport properties of Gd1-xCaxMnO3 (0⩽x⩽1) thin films fabricated on top of SrTiO3 substrates by pulsed laser deposition. The lowest studied doping level (x<0.1) was enough to trigger a transition from the antiferromagnetic state present in the parent compound (x = 0) to a ferrimagnetic state. Up to x = 0.3, the system exhibits a high temperature insulator paramagnetic state and a low temperature insulator ferrimagnetic one. At higher concentrations, the electrical and magnetical properties of the films differ drastically from the bulk form which shows a strong antiferromagnetic behavior. At mid Ca substitution (0.4⩽x⩽0.7), samples show a high temperature charge ordered state with ordering temperatures around room temperature and a low temperature glassy state which was not observed in their bulk counterparts. In contrast, high x samples show a high temperature conductive paramagnetic state and a low temperature insulator antiferromagnetic phase. More interestingly, sample x = 0.9 shows a distinct minimum in the resistivity versus temperature plots and a region of thermal hysteresis which indicate a first order transition. Magnetoresistance measurements display a strong irreversibility which we attributed to phase separation effect of a kinetically arrested ferromagnetic metallic phase and a stable antiferromagnetic insulator phase. Based on the above observations and previous magnetic results, we have reconstructed a phase diagram and characterized the properties of each phase.

Spin glass behavior in Zn0.8 -xNixCu0.2Fe2O4 (0 ≤ x ≤ 0.28) ferrites

The spin glass (SG) behavior of Ni substituted spinel ferrites having chemical formula Zn0.8-xNixCu0.2Fe2O4 (0 ≤ x ≤ 0.28) has been systematically investigated. By means of zero-field-cooling and field-cooling magnetizations, the strong irreversibility is distinct demonstrated. The measurement results demonstrate a typical SG behavior for 0 ≤ x ≤ 0.28. Antiferromagnetic (AFM) interaction is dominant in the competition between ferromagnetic (FM) and AFM interaction for x = 0. In addition, the freezing temperature of the SG state exhibits a decrease with increasing pressure since the SG state is inhibited. As the substitution of Ni for Zn increase, the interaction of FM gradually is equivalent to the AFM interaction and dominant, while the MS and TC increase which is due to the enhancement of the super-exchange interaction JAB.

Crystal Structure and Magnetic Properties of Cu-Substituted La0.90Ag0.10MnO3 Compounds

In the present work, a series of (La0.90Ag0.10)(Mn1 − yCuy)O3 compounds (y = 0–0.20) have been prepared by solid-state reaction route to study the influence of Cu substitution at Mn site of (La0.90Ag0.10)MnO3 compound on crystal structure and magnetic property. From the refinement of XRD patterns, it is found that no significant structural change has taken place by Cu substituion and all compounds are found to crystallize to rhombohedral structure ($$ R\overline{3}c $$ space group). However, it is observed that the Cu substitution into (La0.90Ag0.10)MnO3 compound has led to a drastic decrease of ferromagnetic (FM) transition temperature (TC), from 245.8 K for y = 0 to 174.3 K for y = 0.20 compound. The reduction of FM TC has been explained in terms of dilution of double exchange interaction across Mn3+-O2−-Mn4+ networks. The measurement of magnetization data under zero field cooling and field cooled warming conditions exhibits strong magnetic irreversibility, which is explained in terms of domain wall pinning. The hysteresis (M-H) curves measured for these compounds at 5 K indicate that the magnetization was found to saturate even at very low field and the value of saturation magnetization (MS) is found to decrease with increase in Cu doping and it is in correlation with theoretically estimated value of saturation magnetization. The measurement of Arrott plots (M2 versus H/M) for 10, 15, and 20% Cu-doped compounds indicates that these compounds exhibit second-order magnetic phase transition.

Macroalgal forests and sea urchin barrens: Structural complexity loss, fisheries exploitation and catastrophic regime shifts

In contrast to ecosystems that change smoothly and continuously in response to various stressors, some transitions between states with radically different properties can occur abruptly. An example are the sea urchin barrens and canopy algae (e.g. kelp beds) which represent alternative stable states. More precisely, the variation in grazing intensity in coastal rocky system may drive switches between one complex state into the barren state, the former dominated by erect algae and the latter by encrusting coralline algae and bare rock. Identifying the causes that drive a complex system towards a phase-shift becomes crucial for implementing strategies for the successful conservation and/or recovery of marine forests. Mathematical models that aim to assess effects of fisheries and sea urchins-seaweeds interaction may contribute to understand mechanisms driving transitions between alternative states. Fisheries exploitation has been considered the main driver of urchin population density transitions, with consequent effects on canopy algae distribution. The major novelty of the model here presented is the incorporation of habitat structural complexity, which explains the effect of algal biomass loss on coastal fish assemblages and the strong irreversibility of the system. We have found that as some critical parameters change macroalgae are more resilient and this may give rise to new scenarios, such as the emergence of new stationary states.