Coexistence Point Research Articles

Multiphase critical point type phase boundary induced superior magnetocaloric properties in ferromagnetic Tb1-xGdxCo2 alloys

In this work, we report an exotic combination of magnetic entropy change (ΔSM =4.56 Jkg-1K−1), refrigerant capacity (RC=190.6 J kg−1) and adiabatic temperature change (ΔTad=6.8 K) for varying magnetic fields (ΔH) from 0 to 5 T, with near-zero hysteresis loss at the critical point of multiphase coexistence of rhombohedral, cubic and tetragonal phases at x=0.9 in Tb1−xGdxCo2 alloys. Additionally, the ΔSM curves cover a broad temperature range of 42 K. Further analysis demonstrates that the excellent magnetocaloric performance observed at the multiphase coexistence point stems from the flattening free energy, which provides minimal energy barriers, enabling magnetic spins to switch between different crystal symmetries.

Numerical evidence for the existence of three different stable liquid water structures as indicated by local order parameter.

Structures of liquid water are controversial not only in supercooled polyamorphism but also in stable bulk liquids in the high temperature and pressure range. Several experimental studies in bulk liquid have assumed the existence of three different liquid water structures. If indeed the three liquid water structures are different, they should be clearly distinguished by some measure other than density that characterizes the difference in structural order. In this study, whether the three different bulk liquid water structures are real or not is numerically verified based on molecular simulations using a reliable water molecular model. Since these liquid water structures have been suggested to be related to three different crystal structures (i.e., ice Ih, III, and V), liquid structures are sampled from the vicinity of the ice Ih-liquid coexistence point, the ice III-V-liquid triple point, and the ice V-VI-liquid triple point, respectively. An attempt is made to introduce local order parameters (LOPs) as an indicator to distinguish these structures. A fast and exhaustive LOP search is performed by the molecular assembly structure learning package for Identifying order parameters. The selected LOP distinguishes the molecular structures of three different stable liquid waters with high accuracy, providing numerical evidence that these structural orders differ from each other. Furthermore, regions of the liquid water structures are drawn on a phase diagram using the LOP, demonstrating their consistency with experimental studies.

Design of shape memory alloys with low hysteresis via multiple phase coexistence

Shape memory alloys (SMAs) are the key components of actuators and sensors due to their shape memory effect and superelasticity. However, the thermal hysteresis associated with martensitic phase transformation limits their use in the long-duration precise control. We report a strategy that obtains SMAs with low hysteresis by constructing a composition-temperature pseudo phase diagram. This strategy is inspired by the physically parallel ferroelectric system where the hysteresis is minimized at the multiple phase coexistence point, due to the absence of energy barrier across different phases. Following this, an alloy in the phase diagram with a low hysteresis of about 5 K is synthesized. In contrast, those alloys compositionally different from the optimal one have large hysteresis. Microstructures characterization and diffraction analysis are employed to identify the multiple phase coexistence. The proposed strategy should be general and can shed light on the rational design of SMAs with low hysteresis.

E-consultation as existential media: Exploring doctor-patient 'digital thrownness' in Danish general practice.

In this article we use an existential media framework to explore the asynchronous, written and digital form of GP-patient communication that takes place through e-consultations in a Danish general practice context. This approach acknowledges e-consultation as more than a tool for information delivery and frames GP and patient not as skilful media users but as dependent co-existers: Both thrown into and trying to navigate the digital healthcare ecology. Through a thematic analysis of 38 semi-structured qualitative interviews with patients and GPs we carve out three themes unpacking the existential dimensions of e-consultation: 1. Patient and GP are placed in a Culture of non-stop connectivity and we show the ambivalences arising herein fostering both relief, reassurance and new insecurities. 2. Ethical challenges of responsible co-existence points to dilemmas of boundary setting and caring for self and co-exister in the digital encounter. 3. We-experiences illustrates the potential of e-consultation to signal GP presence, even when the GP is silent. We also discuss the existential ethics of care emerging from the contemporary digital healthcare ecology and call for empirically grounded studies of the existential dimensions tied to encounters in contemporary digital care infrastructures.

A new analytical study of prey–predator dynamical systems involving the effects of Hide-and-Escape and predation skill augmentation

The aim of this work is to provide a comprehensive analysis of the dynamics within an ecosystem characterized by interactions between prey and predators, through a combination of theoretical analysis and numerical simulation. The study investigates the impact of two pivotal effects: the “Hide-and-Escape” behavior exhibited by prey and the “Predation Skill Augmentation” strategy adopted by predators. Theoretical analysis identifies three equilibrium points, all of which show positive characteristics. Furthermore, local stability conditions are determined for each of these equilibrium points. The derivation of global stability conditions is also presented, and their validity and importance as local stability conditions for the coexistence point are demonstrated. In addition, Kolmogorov conditions for coexistence and extinction are verified, as well as local bifurcation analysis. For the validity of the results, a numerical simulation of the system using MATLAB is conducted.

Thermodynamic and transport properties of triangular-well fluids from molecular dynamics

Thermodynamic and transport properties of particles interacting via the triangular-well potential in the range of 1.4 ≤ λ ≤ 2.6 have been studied using perturbation theory and Molecular Dynamics simulations. We present thermodynamic properties such as vapour-liquid coexistence, vapour pressures, and density for different values of the attractive range potential. Good agreement is observed between the theoretical approach and computer simulations in a wide range of densities, temperatures, and pressures. Additionally, we show Molecular Dynamic simulation results of transport properties such as the self-diffusion coefficient as a function of both density and temperature. Finally, thermodynamic and transport properties of real fluids like oxygen, methane, hydrogen sulfide, and fluoromethane have been predicted using both approaches. Results of vapour-liquid coexistence, vapour pressures, and critical points were in excellent agreement with experimental data. The coupling of perturbation theory, Molecular Dynamics simulations, and the triangular-well pair potential offers a versatile and efficient method to explore various real fluid systems, which would include associating fluids, complex molecular liquids, and colloidal systems. This approach can advance our understanding of these systems using a simple approach and to contribute the development of more accurate and predictive models.

The Demographic-Wealth model for cliodynamics.

Cliodynamics is a still a relatively new research area with the purpose of investigating and modelling historical processes. One of its first important mathematical models was proposed by Turchin and called "Demographic-Fiscal Model" (DFM). This DFM was one of the first and is one of a few models that link population with state dynamics. In this work, we propose a possible alternative to the classical Turchin DFM, which contributes to further model development and comparison essential for the field of cliodynamics. Our "Demographic-Wealth Model" (DWM) aims to also model link between population and state dynamics but makes different modelling assumptions, particularly about the type of possible taxation. As an important contribution, we employ tools from nonlinear dynamics, e.g., existence theory for periodic orbits as well as analytical and numerical bifurcation analysis, to analyze the DWM. We believe that these tools can also be helpful for many other current and future models in cliodynamics. One particular focus of our analysis is the occurrence of Hopf bifurcations. Therefore, a detailed analysis is developed regarding equilibria and their possible bifurcations. Especially noticeable is the behavior of the so-called coexistence point. While changing different parameters, a variety of Hopf bifurcations occur. In addition, it is indicated, what role Hopf bifurcations may play in the interplay between population and state dynamics. There are critical values of different parameters that yield periodic behavior and limit cycles when exceeded, similar to the "paradox of enrichment" known in ecology. This means that the DWM provides one possible avenue setup to explain in a simple format the existence of secular cycles, which have been observed in historical data. In summary, our model aims to balance simplicity, linking to the underlying processes and the goal to represent secular cycles.

Phase diagram of a rigid rod system with attractive end groups

We present a molecular dynamics study into the thermotropic liquid crystalline phase behaviour of a coarse-grained model of a rigid bolaamphiphilic molecule. The model consists of 11 spherical beads held in a fixed linear arrangement, where the two opposing terminal beads are self-attracting, mimicking hydrophilic segments and the remaining internal beads, as well as cross-bead interactions, are softly repulsive, mimicking hydrophobic organic segments. The effect of the model’s end bead self-attraction strength on liquid crystalline phase behaviour is studied. Coexistence points between the smectic A, nematic and isotropic phases exhibited by the model are determined following a thermodynamic integration pathway, using equations of state constructed by multiple histogram reweighting of simulation data. Variants of Gibbs–Duhem integration are used to trace pressure–temperature coexistence curves. Under isobaric conditions, the effect of increasing the end-group self-attraction on the nematic–isotropic coexistence temperature is relatively small; however, the nematic phase stability is reduced at the expense of a significant increase in the smectic A–nematic coexistence temperature. Lower temperature simulations show the approximate smectic A–crystalline transition temperature to be only weakly dependent on the strength of the end-group self-attraction.

Attractive Solution of Binary Bose Mixtures: Liquid-Vapor Coexistence and Critical Point.

We study the thermodynamic behavior of attractive binary Bose mixtures using exact path-integral MonteCarlo methods. Our focus is on the regime of interspecies interactions where the ground state is in a self-bound liquid phase, stabilized by beyond mean-field effects. We calculate the isothermal curves in the pressure vs density plane for different values of the attraction strength and establish the extent of the coexistence region between liquid and vapor using the Maxwell construction. Notably, within the coexistence region, Bose-Einstein condensation occurs in a discontinuous way as the density jumps from the normal gas to the superfluid liquid phase. Furthermore, we determine the critical point where the line of first-order transition ends and investigate the behavior of the density discontinuity in its vicinity. We also point out that the density discontinuity at the transition could be observed in experiments of mixtures in traps.

Development of Fe2O3/YSZ ceramic plates for cryogenic operation of resistive-protected gaseous detectors

We present a ceramic material based on hematite (Fe2O3) and zirconia stabilized with yttria at 8% molar (YSZ), that exhibits stable electrical properties with transported charge and that can be tuned to the resistivities necessary to induce spark-quenching in gaseous detectors (ρ = 109-1012 Ω⋅cm), from room temperature down to the liquid-vapor coexistence point of nitrogen (77 K). It, thus, allows covering the operating temperatures of most immediate interest to gaseous instrumentation. The ceramics have been produced in a region of mass concentrations far from what has been usually explored in literature: optimal characteristics are achieved for Fe2O3 concentrations of 75%wt (LAr boiling temperature), 35%wt (LXe boiling temperature), and 100%wt (room temperature). The nine-orders-of-magnitude enhancement observed for the electrical conductivity of the mixed phases relative to that of pure Fe2O3 is startling, however it can be qualitatively understood based on existing literature. Plates of 4 cm × 4 cm have been manufactured and, prior to this work, operated in-detector at the LXe boiling point (165 K), demonstrating spark-free operation. Illustrative results obtained for the first time on a spark-protected amplification structure (RP-WELL) at around the LAr boiling point (90 K) are now presented, too.

Nonstandard Numerical Scheme for a Predator-Prey Model Involving Predator Cannibalism and Refuge

In this study, we implement a Nonstandard Finite Difference (NSFD) scheme for a predator-prey model involving cannibalism and refuge in predator. The scheme which is considered as a discrete dynamical system is analyzed. The performed analysis includes the determination of equilibrium point and its local stability. The system has four equilibrium points, namely the origin, the prey extinction point, the predator extinction point, and the coexistence point, which have exactly the same form and existence conditions as those in continuous system. The local stability of each first three equilibrium points is consistent with the one in continuous system. The stability of the coexistence point depends on the integration time step size. Nevertheless, the NSFD scheme allows us to choose the integration time step size for the solution to converge to a feasible point more flexible than the Euler and 4th order Runge-Kutta schemes. These are shown via numerical simulations.

Local Order Parameters Classifying Water Networks of Ice and Cyclopropane Clathrate Hydrates

Clathrate hydrates are crystalline solids with guest molecules in a hydrogen-bonding network of frozen water. Cyclopropane hydrate has a four-phase coexistence point of guest gas, ice, and two hydrates, suggesting ice–hydrate and hydrate–hydrate structural transitions, but little is known about the details. Microscopic approaches such as molecular simulations are expected as a means of elucidation, but these require reaction coordinates that are sensitive to structural changes (e.g., order parameters). Here, 1220 local order parameters (LOPs) and their combinations were used to classify cyclopropane hydrate and ice structures in the vicinity of the four-phase coexistence point. A total of 21 599 490 LOP combinations were automatically and systematically evaluated via supervised machine learning. The optimal (set of) LOP(s) distinguished between structure I and structure II cyclopropane hydrates and ice Ih with high accuracy and robustness.

Dynamical Behaviors of Four Dimensional Prey-Predator Model

In this paper, we study the dynamic behavior of a four-dimensional prey-predator suggested model of four species. The four species are two prey and two predator species, each of them grows logistically. The two prey live in diverse habitats and have the ability of group defense. In the mentioned model, one predator feeds on the two prey, the top predator feeds on other three species. The existents and, the boundedness of the positive solution, the existence and the local stability of all possible equilibrium points, of the model are investigated. The model has seven equilibrium points at most, four of them always exist and the others exist under certain conditions. Three equilibrium points are not stable while the others are locally asymptotically stable, under given conditions. For the coexistence point, a basin of attraction for it has been found. The steady-state bifurcation relative to the mortality rate of the predators in the neighborhood of three of the equilibrium points and the Hopf-bifurcation relative to the growth rate of the prey in the neighborhood of two of the equilibrium points has been found. Finally, two numerical example has been given to support the theoretical results.

Dynamics analysis of a predator–prey fractional-order model incorporating predator cannibalism and refuge

In this article, we consider a predator–prey interaction incorporating cannibalism, refuge, and memory effect. To involve the memory effect, we apply Caputo fractional-order derivative operator. We verify the non-negativity, existence, uniqueness, and boundedness of the model solution. We then analyze the local and global stability of the equilibrium points. We also investigate the existence of Hopf bifurcation. The model has four equilibrium points, i.e., the origin point, prey extinction point, predator extinction point, and coexistence point. The origin point is always unstable, while the other equilibrium points are conditionally locally asymptotically stable. The stability of the coexistence point depends on the order of the Caputo derivative, α. The prey extinction point, predator extinction point, and coexistence point are conditionally globally and asymptotically stable. There exists Hopf bifurcation of coexistence point with parameter α. The analytic results of stability properties and Hopf bifurcations are confirmed by numerical simulations.

Correlation between multi-factor phase diagrams and complex electrocaloric behaviors in PNZST antiferroelectric ceramic system

Ferroelectric (FE) phase transition with a large polarization change benefits to generate large electrocaloric (EC) effect for solid-sate and zero-carbon cooling application. However, most EC studies only focus on the single-physical factor associated phase transition. Herein, we initiated a comprehensive discussion on phase transition in Pb_0.99Nb_0.02[(Zr_0.6Sn_0.4)_1−<i>x</i>Ti_<i>x</i>]_0.98O₃ (PNZST100<i>x</i>) antiferroelectric (AFE) ceramic system under the joint action of multi-physical factors, including composition, temperature, and electric field. Due to low energy barrier and enhanced zero-field entropy, the multi-phase coexistence point (<i>x</i> = 0.12) in the composition–temperature phase diagram yields a large positive EC peak of maximum temperature change (Δ<i>T</i>_max) = 2.44 K (at 40 kV/cm). Moreover, the electric field–temperature phase diagrams for four representative ceramics provide a more explicit guidance for EC evolution behavior. Besides the positive EC peaks near various phase transition temperatures, giant positive EC effects are also brought out by the electric field-induced phase transition from tetragonal AFE (AFE_T) to low-temperature rhombohedral FE (FE_R), which is reflected by a positive-slope boundary in the electric field–temperature phase diagram, while significant negative EC responses are generated by the phase transition from AFE_T to high-temperature multi-cell cubic paraelectric (PE_MCC) with a negative-slope phase boundary. This work emphasizes the importance of phase diagram covering multi-physical factors for high-performance EC material design.

Diamond-like carbon coatings for cryogenic operation of particle detectors

Characterization of diamond-like carbon (DLC) coatings at cryogenic temperatures (down to 77 K) is presented, covering the electrical resistivity range of practical interest to gaseous and liquid particle instrumentation: 10−1−105 MΩ/□. The good behaviour observed in terms of linearity, surface uniformity and stability with time and transported charge add to other well-known characteristics like low chemical reactivity and tolerance to radiation. The observed temperature dependence and stability of electrical properties with transported charge is consistent with a conductivity mechanism based on 2-dimensional variable-range electron hopping, as expected for the surface conductivity of thin films made from amorphous carbon. First results from a resistive-protected WELL detector (‘RWELL’) built with DLC and operated close to the liquid–vapour coexistence point of argon (87.5 K at 1 bar) are presented.

Schooling behavior driven complexities in a fear-induced prey–predator system with harvesting under deterministic and stochastic environments

The well-being of humans is closely linked to the well-being of species in any ecosystem, but the relationship between humans and nature has changed over time as societies have become more industrialized. In order to ensure the future of our ecosystems, we need to protect our planet’s biodiversity. In this work, a prey–predator model with fear dropping prey’s birth as well as death rates and nonlinear harvesting, is investigated. In addition, we consider that the consumption rate of predators, i.e., the functional response, is dependent on schooling behavior of both species. We have investigated the local stability of the equilibrium points and different types of bifurcations, such as transcritical, saddle-node, Hopf and Bogdanov–Takens (BT). We find that consumption rate of predator, fear and harvesting effort give complex dynamics in the neighbourhood of BT-points. Harvesting effort has both stabilizing and destabilizing effects. There is bistability between coexistence and predator-free equilibrium points in the system. Further, we have studied the deterministic model in fluctuating environment. Simulation results of stochastic system includes time series solutions of one simulation run and corresponding phase portraits. Notably, several simulation runs are conducted to obtain time series solutions, histograms, and stationary distributions. Our findings exhibit that during stochastic processes, model species fluctuate around some average values of the deterministic steady-state for lower environmental disturbances. However, higher values of environmental disturbances lead the species to extinction.

Modeling the dynamics of Diamondback Moth infestations on cabbage biomass

The Diamondback Moth (Plutella xylostella) is a notorious agricultural pest that poses significant challenges to cabbage production. In this study, we formulated and analyzed the deterministic differential equations to capture the infestations dynamics of diamondback moth in a cabbages biomass, taking into account the use of environmentally friendly pesticides. To study its dynamics we computed the threshold number, ℛ∗, based on the pest-free equilibrium point. The results indicate that when ℛ∗≤1, the equilibrium point ξ1 is both locally and globally stable. Conversely, when ℛ∗>1, the coexistence point becomes globally asymptotically stable. The stability of the equilibrium points were both Locally and globally assessed using Ruth Hurwitz’s criteria for local stability and Lyapunov functions for global analysis. A comprehensive numerical analysis was conducted, confirming the substantial support for the analytical findings. Finally, this research suggests that in order to reduce the impact of the diamondback moth, it is necessary to decrease the threshold value smaller than a unity through the adoption of effective inter-cropping techniques and the use of environmentally friendly pesticides.

Dynamical Analysis of Ratio-dependent Predator-Prey Models with Prey Refuge and Optimal Harvesting on Both Populations

In this article, we discuss a dynamical analysis of ratio-dependent response predator-prey model with prey refuge and harvesting on both populations. Harvesting on predator and prey is used because both populations are assumed to have an economic value. In this model, it is also assumed that prey has an instinct to protect themselves from the threat of predators. The conducted dynamical analysis consists of determination of equilibria, existence conditions and their stability. Analytical results show that there are two equilibria: namely predator extinction point and the coexistence point which are exist and stable under certain condition. Furthermore, Pontryagin maximum principle is used to find optimal harvesting on predator and prey. Some numerical simulations are performed to illustrate the analytical result.

Magnetic structures of the iridium-based double perovskites Pr2NiIrO6 and Nd2NiIrO6 reinvestigated using neutron diffraction

The magnetic structures of the double perovskites ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$ have been reinvestigated using high-intensity neutron power diffraction and compared with previously published results by Kayser et al. [Acta Mater. 207, 116684 (2021)] and Ferreira et al. [Phys. Rev. Mat. 5, 064408 (2021)]. The strongly enhanced statistics of neutron diffraction data used in this paper help us to disentangle the complicated coexisting magnetic orderings of the three sublattices in ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$. A mainly ferrimagnetic ordering with additional antiferromagnetic components with propagation vector $k=0$ has been confirmed in both ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$ compounds below the magnetic orderings ${T}_{C}=110$ and 120 K, respectively. ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$ further undergoes a second magnetic transition from a ferrimagnet with $k=0$ to an antiferromagnetic state with $k=$ $(\frac{1}{2},$ $\frac{1}{2}, 0)$ below ${T}_{N}=15\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. A partial persistence of the $k=0$ type order leads, however, to a coexistence of both magnetic phases below ${T}_{N}$ not detected previously. The coexistence points to the energies of the magnetic ground states being very similar. Ordered magnetic moments of ${\mathrm{Ir}}^{4+}$ amounting at 1.5 K to $\ensuremath{\sim}0.6\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$ in ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and $0.4\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$ in ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$ are clearly detected and are compared with the expected value for the ${J}_{\mathrm{eff}}=$ $\frac{1}{2}$ model.