Phase Transition Point Research Articles

Water phase transition and signal nulling in 3D dual-echo adiabatic inversion-recovery UTE (IR-UTE) imaging of myelin.

The semisolid myelin sheath has very fast transverse relaxation and is invisible to conventional MRI sequences. UTE sequences can detect signal from myelin. The major challenge is the concurrent detection of various water components. The inversion recovery (IR)-based UTE (IR-UTE) sequence employs an adiabatic inversion pulse to invert and suppress water magnetizations. TI plays a key role in water suppression, with negative water magnetizations (negative phase) before the null point and positive water magnetizations (positive phase) after the null point. A series of dual-echo IR-UTE images were acquired with different TIs to detect water phase transition. The effects of TR in phase transition and water suppression were also investigated using a relatively long TR of 500 ms and a short TR of 106 ms. The water phase transition in dual-echo IR-UTE imaging of myelin was investigated in five ex vivo and five in vivo human brains. An apparent phase transition was observed in the second echo at the water signal null point, where the myelin signal was selectively detected by the UTE data acquisition at the optimal TI. The water phase transition point varied significantly across the brain when the long TR of 500 ms was used, whereas the convergence of TIs was observed when the short TR of 106 ms was used. The results suggest that the IR-UTE sequence with a short TR allows uniform inversion and nulling of water magnetizations, thereby providing volumetric imaging of myelin.

Novel first-order phase transition and critical points in SU(3) Yang-Mills theory with spatial compactification

We investigate the thermodynamics and phase structure of SU(3) Yang-Mills theory on T2×R2 in Euclidean spacetime in an effective-model approach. The model incorporates two Polyakov loops along two compactified directions as dynamical variables, and is constructed to reproduce thermodynamics on T2×R2 measured on the lattice. The model analysis indicates the existence of a novel first-order phase transition on T2×R2 in the deconfined phase, which terminates at critical points that should belong to the two-dimensional Z2 universality class. We argue that the interplay of the Polyakov loops induced by their cross-term in the Polyakov-loop potential is responsible for the manifestation of the first-order transition. Published by the American Physical Society 2024

Quantum steering ellipsoids and quantum obesity in critical systems

Abstract Quantum obesity (QO) is a novel function introduced to quantify quantum correlations that go beyond traditional measures like entanglement, while also functioning as an entanglement witness. One of the key strengths of QO lies in its analyticity for arbitrary states of bipartite systems, making it a more accessible and versatile tool compared to other measures of quantum correlations, such as quantum discord. In this work, we highlight the importance of QO as a fundamental quantity for identifying signatures of quantum phase transitions, which are critical changes in the ground state of quantum systems driven by quantum fluctuations. We introduce a mechanism based on local filtering operations designed to enhance the critical behavior of QO near phase transition points, providing a deeper understanding of these phenomena. Furthermore, we present a theorem that characterizes how QO transforms under local quantum operations and classical communications (LOCC), which broadens its applicability to a wider range of quantum systems. This opens new avenues for exploring quantum criticality and other novel quantum phenomena by leveraging the analytically computable, pairwise QO, thus offering both theoretical insights and practical applications in quantum information science.

CFTD from TQFTD+1 via Holographic Tensor Network, and Precision Discretization of CFT2

We show that the path integral of conformal field theories in D dimensions (CFTD) can be constructed by solving for eigenstates of a renormalization group (RG) operator following from the Turaev-Viro formulation of a topological field theory (topological quantum field theory) (TQFT) in D+1 dimensions (TQFTD+1), explicitly realizing the holographic sandwich relation between a symmetric theory and a TQFT. Generically, exact eigenstates corresponding to symmetric TQFTD follow from Frobenius algebra in TQFTD+1. For D=2, we construct eigenstates that produce 2D rational CFT path integrals exactly, which curiously connect a continuous-field theoretic path integral with the Turaev-Viro state sum. We also devise and illustrate numerical methods for D=2, 3 to search for CFTD as phase transition points between symmetric TQFTD. Finally, since the RG operator is in fact an exact analytic holographic tensor network, we compute “bulk-boundary” correlators and compare them with the AdS/CFT dictionary at D=2. Promisingly, they are numerically compatible given our accuracy, although further works will be needed to explore the precise connection to the AdS/CFT correspondence. Published by the American Physical Society 2024

Experimental investigation on temperature distribution characteristics inside the condensing tube of the R134a two-phase natural circulation loop

Temperature distribution of two-phase flow inside the condensing tube can effectively reflect the heat transfer characteristic of the fluid, playing a pivotal role in the study of heat transfer in two-phase flow systems. In this study, we use the stainless steel capillary sealed distributed fiber Bragg grating (S-DFBGs) to measure and characterize the temperature distribution of R134a fluid inside the condensing tube under steady-state (pump-driven two-phase circulation) and unsteady-state (type I and II density wave instabilities in two-phase natural circulation loop) conditions, and the frequency and time domain characteristics of the fluid temperature distribution inside the tube has been investigated in detail. Through frequency-domain analysis, the temperature spectrum inside the condensing tube can indentify two types of the instability together with flowrate and pressure. Through time-domain analysis, temperature distribution inside the condenser can dermine the phase transition point, hence the condensation length. Moreover, two types of the instability exhibit different temperature fluctuation characteristics, providing reliable and effective information for further research on two phase natural circulation instability mechanisms.

Corrected thermodynamics and stability of magnetic charged AdS black holes surrounded by quintessence

In this study, we explore the corrected thermodynamics of non-linear magnetic charged anti-de Sitter (AdS) black holes surrounded by quintessence, incorporating thermal fluctuations and deriving the corrected thermodynamic potentials. We analyze the effects of corrections due to thermal fluctuations on various thermodynamic potentials, including enthalpy, Helmholtz free energy, and Gibbs free energy. Our results show significant impacts on smaller black holes, with first-order corrections destabilizing them, while second-order corrections enhance stability with increasing parameter values. The specific heat analysis further elucidates the stability criteria, indicating that the large black holes ensure stability against phase transitions. However, the thermal fluctuations do not affect the physical limitation points as well as the second-order phase transition points of the black hole. Our findings highlight the intricate role of thermal fluctuations in black hole thermodynamics and their influence on stability, providing deeper insights into the behaviour of black holes under corrected thermodynamic conditions.

Effect of Fe-doping on magnetic structures and “spin-lattice-charge” strong correlation properties in Mn3Sn1-xFexC compounds

The influences of Fe-doping on the magnetic structure, correlated lattice variation, and electronic transport of the antiperovskite compounds Mn3Sn1-xFexC have been reported for the first time. The results indicate that Fe-doping is effective in altering the magnetic behaviors in the Mn3Sn1-xFexC compounds. The magnetic phase transition point (TC) initially shifts to lower temperatures at low Fe-doping concentrations and then increases to higher temperatures at higher Fe-doping levels. This change is accompanied by the development of macroscopic ferromagnetism in the compound, which is essentially due to the emergence of a new canted ferrimagnetic phase named MCF, revealed by neutron powder diffraction (NPD). By virtue of the Fe-doping effect on the magnetism, the regulation of the negative thermal expansion (NTE) behavior and the abrupt change of resistivity in Mn3SnC are also realized. Based on these results, a magnetic phase diagram for the Mn3Sn1-xFexC series is established. This work not only provides a method for effective regulation of magnetic ordering but also strengthens our understanding of strongly correlated physical properties.

Simulation of Dynamic Characteristics of Supercritical Boiler Based on Coupling Model of Combustion and Hydrodynamics

To accommodate the integration of renewable energy, coal-fired power plants must take on the task of peak regulation, making the low-load operation of boilers increasingly routine. Under low-load conditions, the phase transition point (PTP) of the working fluid fluctuates, leading to potential flow instability, which can compromise boiler safety. In this paper, a one-dimensional coupled dynamic model of the combustion and hydrodynamics of a supercritical boiler is developed on the Modelica/Dymola 2022 platform. The spatial distribution of key thermal parameters in the furnace and the PTP position in the water-cooled wall (WCW) are analyzed in a 660 MW supercritical boiler when parameters on the combustion side change under full-load and low-load conditions. The dynamic response characteristics of the temperature, mass flow rate, and the PTP position are investigated. The results show that the over-fire air (OFA) ratio significantly influences the flue gas temperature distribution. A lower OFA ratio increases the flue gas temperature in the burner zone but reduces it at the furnace exit. The lower OFA ratio leads to a higher fluid temperature and shortens the length of the evaporation section. The temperature difference in the WCW outlet fluid between the 20% and 60% OFA ratios is 11.7 °C under BMCR conditions and 7.4 °C under 50% THA conditions. Under the BMCR and 50% THA conditions, a 5% increase in the coal caloric value raises the flue gas outlet temperature by 32.7 °C and 35.4 °C and the fluid outlet temperature by 6.5 °C and 9.9 °C, respectively. An increase in the coal calorific value reduces the length of the evaporation section. The changes in the length of the evaporation section are −2.95 m, 2.95 m, −2.62 m, and 0.54 m when the coal feeding rate, feedwater flow rate, feedwater temperature, and air supply rate are increased by 5%, respectively.

Detecting phase transitions based on siamese neural network

Machine learning has been widely applied in physics research. Although unsupervised learning can extract the critical points of phase transitions, the percolation model remains a challenge. Unsupervised learning using the raw configurations of the percolation model fails to capture the critical points. To capture the configuration characteristics of the percolation model, this paper proposes using the maximum cluster as input to the neural network. It is well understood that the order parameter of the percolation model is not simply the particle density, but rather the probability that a given site or bond belongs to the percolating cluster. Additionally, we introduce the use of a Siamese Neural Network (SNN) to detect percolation phase transitions. Unlike unsupervised dimensionality reduction methods or supervised binary classification outputs, the SNN produces a scalar output referred to as similarity. By combining the maximum cluster and the SNN, we not only successfully extract the critical value of the percolation model, but also calculate the correlation exponent via data collapse. We believe that the SNN has great potential in handling phase transition classification problems and can serve as a reference for studying other phase transition systems.

Anomalous Directed Percolation on a Dynamic Network Using Rydberg Facilitation.

The facilitation of Rydberg excitations in a gas of atoms provides an ideal model system to study epidemic evolution on (dynamic) networks and self-organization of complex systems to the critical point of a nonequilibrium phase transition. Using MonteCarlo simulations and a machine learning algorithm we show that the universality class of this phase transition can be tuned but is robust against decay inherent to the self-organization process. The classes include directed percolation (DP), the most common class in short-range spreading models, and mean-field (MF) behavior, but also different types of anomalous directed percolation (ADP), characterized by rare long-range excitation processes. In a frozen gas, ground state atoms that can facilitate each other form a static network, for which we predict DP universality. With atomic motion the network becomes dynamic by long-range (Lévy-flight type) excitations. This leads to continuously varying critical exponents, varying smoothly between DP and MF values, corresponding to the ADP universality class. These findings also explain the recently observed critical exponent of Rydberg facilitation in an ultracold gas experiment [Helmrich etal., Nature (London) 577, 481 (2020)NATUAS0028-083610.1038/s41586-019-1908-6], which was in between DP and MF values.

Molecular simulations of increased thermal energy storage in metal–organic heat carriers with R1234ze(E)/R32 mixtures combined with IRMOF-1

Metal-organic heat carrier (MOHC) nanofluids offer a promising solution to enhance the efficiency of Organic Rankine Cycle systems. In this study, we developed a computational model to assess the thermal energy storage capacity of MOHC nanofluids using a base fluid mixture of R1234ze(E) and R32 refrigerants. Through Grand Canonical Monte Carlo and molecular dynamics simulations, we examined the adsorption characteristics, desorption heat, and thermodynamic properties of MOHCs. Our findings reveal that R32 molecules are preferentially adsorbed in IRMOF-1 compared to R1234ze(E), with adsorption selectivity of R32 over R1234ze(E) increasing under higher adsorption pressures. When the temperature during the endothermic process surpasses the phase transition point of the base fluid, the latent heat of phase transition can be fully exploited to enhance energy storage. Moreover, the inclusion of IRMOF-1 nanoparticles significantly improves the energy storage properties of both R32 and R1234ze(E), as well as their mixtures. The energy storage enhancement provided by IRMOF-1 is particularly pronounced under high working pressures and low temperature differences. These insights offer valuable guidance for selecting appropriate base fluids in MOHC systems, thereby optimizing the utilization of low-grade energy sources.

Electrically charged black holes in [formula omitted]-Euler–Heisenberg theory

Drawing on the concept of the non-linear dynamics of electromagnetic fields in vacuum in terms of the Euler–Heisenberg system, a static and spherically symmetric black hole solution is derived by coupling the Euler–Heisenberg term and F(R) gravity. In applying the curvature singularity tools, the black hole solution induces a singular behaviour at the centre r=0 while exhibiting a regular shape at high distances. Using the heat capacity (CQ) and the Helmholtz free energy (F), we analyse the thermodynamic stability locally and globally. Furthermore, an investigation is conducted using class tools of Geometrothermodynamics (GTs) features such as Weinhold, Ruppeiner, Hendi–Panahiyan–Eslam–Momennia (HPEM), and Quevedo to identify phase transition points associated with heat capacity, including both physical boundary points (root of the heat capacity) and second critical phase transition points (divergent points of the heat capacity). We have even examined the relevant sparsity of Hawking radiation, showing how the black hole solution behaves as a black body at specific limits. Overall, this study enhances our knowledge of the mergers of a class of non-linear dynamics of electromagnetic fields in a vacuum within F(R) gravity by modelling black hole solutions.

Phase transitions in quantum many-body scars

We propose a type of phase transition in quantum many-body systems that occurs in highly excited quantum many-body scar states while most of the spectrum is largely unaffected. Such scar-state phase transitions can be realized by embedding a matrix product state, known to undergo a phase transition, as a scar state into the thermal spectrum of a parent Hamiltonian. We find numerically that the mechanism for the scar-state phase transition involves the formation or presence of low-entropy states at energies similar to the scar state in the vicinity of the phase transition point. Published by the American Physical Society 2024

From Geometry of Hamiltonian Dynamics to Topology of Phase Transitions: A Review.

In this review work, we outline a conceptual path that, starting from the numerical investigation of the transition between weak chaos and strong chaos in Hamiltonian systems with many degrees of freedom, comes to highlight how, at the basis of equilibrium phase transitions, there must be major changes in the topology of submanifolds of the phase space of Hamiltonian systems that describe systems that exhibit phase transitions. In fact, the numerical investigation of Hamiltonian flows of a large number of degrees of freedom that undergo a thermodynamic phase transition has revealed peculiar dynamical signatures detected through the energy dependence of the largest Lyapunov exponent, that is, of the degree of chaoticity of the dynamics at the phase transition point. The geometrization of Hamiltonian flows in terms of geodesic flows on suitably defined Riemannian manifolds, used to explain the origin of deterministic chaos, combined with the investigation of the dynamical counterpart of phase transitions unveils peculiar geometrical changes of the mechanical manifolds in correspondence to the peculiar dynamical changes at the phase transition point. Then, it turns out that these peculiar geometrical changes are the effect of deeper topological changes of the configuration space hypersurfaces ∑v=VN-1(v) as well as of the manifolds {Mv=VN-1((-∞,v])}v∈R bounded by the ∑v. In other words, denoting by vc the critical value of the average potential energy density at which the phase transition takes place, the members of the family {∑v}v<vc are not diffeomorphic to those of the family {∑v}v>vc; additionally, the members of the family {Mv}v>vc are not diffeomorphic to those of {Mv}v>vc. The topological theory of the deep origin of phase transitions allows a unifying framework to tackle phase transitions that may or may not be due to a symmetry-breaking phenomenon (that is, with or without an order parameter) and to finite/small N systems.

Indicators of quantum phase transitions in the one-dimensional J1-J2 Heisenberg model: Global quantum discord and multipartite nonlocality analysis

We here investigate the ground state phase transitions of the one-dimensional J1-J2 Heisenberg model. The phase transition is characterized by analyzing the quantum discord, global quantum discord (GQD), bipartite nonlocality, and multipartite nonlocality of the ground state. Our findings reveal that these correlations serve as effective indicators of the phase transition point at J2/J1=0.5. Specifically, quantum discord and bipartite nonlocality display more pronounced critical behavior in small-sized systems. Conversely, for large-scale systems, GQD and multipartite nonlocality offer a more practical and reliable method for detecting many-body driven phase transitions. Additionally, several linear relationships among these correlations are identified.

Effect of Trace Rare Earth Element Cerium (Ce) on Microstructure and Mechanical Properties of High Strength Marine Engineering Steel

In this paper, FH460 special steel with rare earth element cerium (Ce) was selected, and the control group without Ce was set up. By changing the content of Ce, the microstructure, phase transition point, and mechanical properties of the test steel were observed to study the effect of trace rare earth element Ce on the microstructure and mechanical properties of high-strength marine engineering steel. The morphology and energy spectrum of inclusions in three kinds of test steels were observed by SEM, and the morphological changes in inclusions in FH460 high-strength marine engineering steel after adding Ce were investigated. The fracture morphology and energy spectrum analysis were carried out by combining the tensile test at room temperature and the gradient low temperature impact toughness test, and the effect of trace Ce on the mechanical properties of the test steel was comprehensively analyzed. The results show that the addition of Ce changes the phase transformation temperature of Ac1 and Ac3, and refines the original microstructure of the test steel. SEM observation showed that the addition of Ce changed the long strip MnS and polygonal irregular Al2O3 inclusions into ellipsoids, which reduced the size of inclusions. The gradient low temperature impact test shows that with the decrease in temperature, the fracture dimple depth of the three test sheets of steel decreases, and the Ce-containing test steel forms a deep dimple centered on rare earth inclusions, which hinders the crack propagation and significantly improves the low temperature impact toughness of the test steel.

On the Polymorphism of Cu2V2O7: Synthesis and Crystal Structure of δ-Cu2V2O7, a New Polymorph

Single crystals of the new modification of copper pyrovanadate, δ-Cu2V2O7, were prepared using the chemical vapor transport reaction method. The crystal structure (monoclinic, P21/n, a = 5.0679(3), b = 11.4222(7), c = 9.4462(6) Å, β = 97.100(6)°, V = 542.61(6) Å3, Z = 4) was solved by direct methods and refined to R1 = 0.029 for 1818 independent observed reflections. The crystal structure contains two Cu sites: the Cu1 site in [4 + 2]-octahedral coordination and the Cu2 site in [4 + 1]-tetragonal pyramidal coordination. There are two V5+ sites, both tetrahedrally coordinated by O atoms. Two adjacent V1O4 and V2O4 tetrahedra share the O4 atom to form a V2O7 dimer. The crystal structure of δ-Cu2V2O7 can be described as based upon layers of V2O7 dimers of tetrahedra parallel to the (001) plane and interlined by chains of the edge-sharing Cu1O6 and Cu2O5 polyhedra running parallel to the a axis and arranged in the layers parallel to the (001) plane. The crystal chemical analysis of the three other known Cu2V2O7 polymorphs indicates that, by analogy with δ-Cu2V2O7, they are based upon layers of V2O7 groups interlinked by layers consisting of chains of CuOn coordination polyhedra (n = 5, 6). The crystal structures of the Cu2V2O7 polymorphs can be classified according to the mutual relations between the Cu-O chains, on the one hand, and the V2O7 groups, on the other hand. The analysis of the literature data and physical density values suggests that, at ambient pressure, α- and β-Cu2V2O7 are the low- and high-temperature polymorphs, respectively, with the phase transition point at 706–710 °C. The β-phase (ziesite) may form metastably under temperatures below 560 °C and, under heating, transform into the stable α-phase (blossite) at 605 °C. The δ- and γ-polymorphs have the highest densities and most probably are the high-pressure phases. The structural complexity relations among the polymorphs correspond to the sequence α = β &lt; γ &lt; δ; i.e., the δ phase described herein possesses the highest complexity, which supports the hypothesis about its stability under high-pressure conditions.

Research on the Phase Behavior of Multi-Component Thermal-Fluid-Heavy Oil Systems

Multi-component thermal luid technology optimizes development effects and has a strong adaptability, providing a new choice for the efficient development of heavy oil reservoirs. However, due to the significant differences between the phase behavior of multi-component thermal-fluid-heavy oil systems and conventional systems, and the lack of targeted and large-scale research, key issues such as the phase behavior of these systems are unclear. This research studies the phase behavior and influencing factors of emulsions and foamy oil in a multi-component thermal-fluid-heavy oil system through high-temperature and high-pressure PVT experiments, revealing the characteristics of the system’s special phase behavior. In the heavy oil emulsion system, the water content directly affects changes in the system’s phase state. The higher the temperature, the larger the phase transition point, and the two are positively correlated. As the stirring speed increases, the phase transition point first increases and then decreases. The amount of dissolved gas is negatively correlated with the size of the phase transition point, and dissolution can form foamy oil. In the heavy oil–foamy oil system, the dissolution capacity of CO2 is greater than that of multi-component gases, which is greater than that of N2. A high water content and high temperature are not conducive to the dissolution of multi-component gases. While an increase in stirring speed is beneficial for the dissolution of gases, there are limitations to its enhancement ability. Therefore, the development of multi-component thermal fluids should avoid the phase transition point of emulsions and promote the dissolution of multi-component gases.

Vulnerability of AND/OR logic networks under cascading failures

Cascading failures in AND/OR logic networks present a critical challenge in domains such as digital circuits and communication systems where reliability and resilience are paramount. This work investigates the vulnerability of AND/OR logic networks under cascading failures by examining the propagation mechanisms, failure modes, and robustness of such systems. In detail, we propose a hybrid fault propagation model based on the basic principles of AND/OR logic operations. Then, by utilizing both analytical and simulation approaches, we explore how initial localized disruptions can escalate through interconnected logical elements and lead to widespread system failures. Notably, it is shown that a Sigmoid function can be developed to quantify the vulnerability of the complex logic network. Moreover, the phase transition of the failures against the logic parameters is depicted and it is illustrated that the phase transition point is independent of the AND links. This study contributes to the understanding of cascading dynamics in logical networks and could facilitate design of feasible strategies for mitigating these vulnerabilities and recovering from substantial failures.

Giant Photocaloric Effects across a Vast Temperature Range in Ferroelectric Perovskites.

Solid-state cooling presents an energy-efficient and environmentally friendly alternative to traditional refrigeration technologies that rely on thermodynamic cycles involving greenhouse gases. However, conventional caloric effects face several challenges that impede their practical application in refrigeration devices. First, operational temperature conditions must align closely with zero-field phase-transition points; otherwise, the required driving fields become excessively large. However, phase transitions occur infrequently near room temperature. Additionally, caloric effects typically exhibit strong temperature dependence and are sizable only within relatively narrow temperature ranges. In this Letter, we employ first-principles simulation methods to demonstrate that light-driven phase transitions in polar oxide perovskites have the potential to overcome such limitations. Specifically, for the prototypical ferroelectric KNbO_{3} we illustrate the existence of giant "photocaloric" effects induced by light absorption (ΔS_{PC}∼100 J K^{-1} kg^{-1} and ΔT_{PC}∼10 K) across a vast temperature range of several hundred Kelvin, encompassing room temperature. These findings are expected to be generalizable to other materials exhibiting similar polar behavior.