arXiv subjects

Jincheng Wang

Publications and source records attributed to Jincheng Wang.

At least 73 records · Page 4Linked to original sources

arXiv2023

Global energetics of solar powerful events on 6 September 2017

Solar flares and coronal mass ejections (CMEs) are thought to be the most powerful events on the Sun. They can release energy as high as 10^32 erg in tens of minutes,and could produce solar energetic particles (SEPs) in the interplanetary space. We explore global energy budgets of solar major eruptions on 6 September 2017, including the energy partition of a powerful solar flare, the energy budget of the accompanied CME and SEPs. In the wavelength range shortward of 222 nm, a major contribution of the flare radiated energy is in the soft X-ray (SXR) 0.1-7 nm domain. The flare energy radiated at wavelengths of Ly-alpha and middle ultraviolet is larger than that radiated in the extreme ultraviolet wavelength, but it is much less than that radiated in the SXR waveband. The total flare radiated energy could be comparable to the thermal and nonthermal energies. The energies carried by the major flare and its accompanied CME are roughly equal, and they are both powered by the magnetic free energy in the AR NOAA 12673. Moreover, the CME is efficient in accelerating SEPs, and that the prompt component (whether it comes from the solar flare or the CME) contributes only a negligible fraction.

astro-ph.SR↗

arXiv2023

Phase Field Model for Non-equilibrium Interface Conditions

This article presents a new phase-field formulation for non-equilibrium interface conditions in rapid phase transformations. With a particular way of defining concentration fields, the classical sharp and diffuse (thick) interface theories are unified into the present phase-field model. Each point inside the diffuse interface is comparable to the classical sharp interface model, governed by phase boundary migration and short-range atomic exchanges and connected by long-range diffusion. Their thermodynamic forces and fluxes are following the Onsager reciprocal relation and consistent with the classical irreversible thermodynamics. Furthermore, we establish the balance of driving forces and energy dissipations for both the diffuse interface and the single point inside it. The model is then validated by rapid solidification of Al-Cu alloys. With an effective mobility of considering non-equilibrium long-range diffusion, the model represents the main characteristics of non-equilibrium interface kinetics, i.e., solute trapping and solute drag. Especially, we reproduce the complete trapping at the high-velocity regime and provide a thermodynamic consistent description of the partial drag phenomena at the low-velocity region. Moreover, the dissipation analysis indicates that even the far-from-equilibrium diffuse interface is composed of numerous representative volume elements near the equilibrium, providing a new understanding of non-equilibrium interfaces.

cond-mat.mtrl-sci↗

arXiv2023

Thermodynamics of Non-equilibrium Diffuse-Interfaces in Mesoscale Phase Transformations

We present a new phase-field formulation for the non-equilibrium interface kinetics. The diffuse interface is considered an integral of numerous representative volume elements (RVEs), in which there is a two-phase mixture with two conserved and two non-conserved concentration fields. This particular way of separating concentration fields leads to two distinct dissipative processes besides the phase boundary migration, i.e., trans-sharp-interface diffusion between different phases within a single RVE and trans-diffuse-interface diffusion between different RVEs within a single phase. A two-part mechanism is proposed to balance the driving forces and energy dissipation for diffusionless and diffusional processes in RVEs. Moreover, the classical interface friction and solute drag can be recovered by integrating the diffuse interface. Compared with the sharp interface theory, the present diffuse interface can reproduce the atomic simulated partial-drag self-consistently in thermodynamics.

cond-mat.mtrl-sci↗

arXiv2022

Prediction of nonlinear interface dynamics in the unidirectional freezing of particle suspensions with rigid compacted layer

Water freezing in particle suspensions widely exists in nature. As a typical physical system of free boundary problem, the spatiotemporal evolution of the solid/liquid interface not only origins from phase transformation but also from permeation flow in front of ice. Physical models have been proposed in previous efforts to describe the interface dynamic behaviors in unidirectional freezing of particle suspensions. However, there are several physical parameters difficult to be determined in previous investigations dedicated to describing the spatiotemporal evolution in unidirectional freezing of particle suspensions. Here, based on the fundamental momentum theorem, we propose a consistent theoretical framework to address the unidirectional freezing process in the particle suspensions coupled with the effect of water permeation. An interface undercooling-dependent pushing force exerted on the compacted layer with a specific formula is derived based on the surface tension. Then a dynamic compacted layer is considered and analyzed. Numerical solutions of the nonlinear models reveal the dependence of system dynamics on some typical physical parameters, particle radius, initial particle concentration in the suspensions, freezing velocity and so on. The system dynamics are characterized by interface velocity, interface undercooling and interface recoil as functions of time. The models allow us to reconsider the formation mechanism of ice spears in freezing of particle suspensions in a simpler but novel way, with potential implications for both understanding and controlling not only ice formation in porous media but also crystallization processes in other complex systems.

cond-mat.mtrl-sci↗

arXiv2022

Cosmological Complexity from initial thermal state

The cosmological scalar perturbations should satisfy the thermal distribution at the beginning of inflation since the cosmic temperature is presumably very high. In this paper, we investigate, by the Fubini-study method, the effect of this thermal contribution, which is characterized by a parameter $κ_{0}$, on the evolution of the cosmological complexity $\mathcal{C}_{FS}$ . We find that when the thermal effect is considered, the Universe would ``decomplex" firstly with the cosmic expansion after the mode of the scalar perturbations exiting the horizon in the de Sitter (dS) phase and $\mathcal{C}_{FS}$ has a minimum about $π/4$. If $\mathcal{C}_{FS}$ can reach its minimum during the dS era, which requires a small $κ_0$ or a large e-folding number for a large $κ_0$, it will bounce back to increase, and after the Universe enters the radiation dominated (RD) phase from the dS one, $\mathcal{C}_{FS}$ will decrease, pass its minimum again, and then increase till the mode reenters the horizon. For the case of a large enough $κ_0$, $\mathcal{C}_{FS}$ decreases but does not reach its minimum during the dS era, and it begins to increase after the transition from the dS phase to the RD one. When the mode reenters the horizon during the RD era, the cosmological complexity will oscillate around about $κ_{0}$. These features are different from that of the initial zero-temperature case, i.e., the cosmological complexity increases during the dS phase and decreases in the RD era till the mode reenters the horizon. Our results therefore suggest that the thermal effect changes qualitatively the evolutionary behavior of the cosmological complexity.

gr-qc↗

arXiv2022

Pseudo-Phase Transitions of Ising and Baxter-Wu Models in Two-Dimensional Finite-Size Lattices

This article offers a detailed analysis of pseudo-phase transitions of Ising and Baxter-Wu models in two-dimensional finite-size lattices. We carry out Wang Landau sampling to obtain the density of states. Using microcanonical inflection point analysis with microcanonical entropy, we obtain the order of the psuedo-phase transitions in the models. The microcanonical analysis results of the second-order transition for the Ising model and the first-order transition for the Baxter-Wu model are consistent with the traditional canonical results. In addition, the third-order transitions are found in both models, implying the universality of higher-order phase transitions.

cond-mat.stat-mech↗

arXiv2022

Revisiting the transient coarsening kinetics: a new framework in the Lifshitz-Slyozov-Wagner space

Phase coarsening is a fundamental process of microstructure evolution in multiphase materials. A thorough understanding of its kinetics is of great significance for material processing and performance. Generally, coarsening can be divided into the transient stage and the steady stage. Compared with steady coarsening kinetics, the current understanding of transient coarsening is rather limited and contradictory. In the present work, a new framework in the dimensionless Lifshitz-Slyozov-Wagner space is developed to study transient coarsening kinetics co-controlled by interface migration/reaction and matrix diffusion, where the dynamic equation for individual particles is derived from the thermodynamic extremal principle.

cond-mat.mtrl-sci↗

arXiv2022

A formation mechanism for the large plumes in the prominence

To understand the formation mechanism of large plumes in solar prominences, we investigate the formation process of two such phenomena. We studied the dynamic and thermal properties of two large plumes using observations from New Vacuum Solar Telescope, the Solar Dynamic Observatory, and the Solar Terrestrial Relations Observatory-Ahead. We find that two large plumes observed with high-resolution data are quite different from previously studied small-scale plumes. They are born at the top of a prominence bubble with a large projected area of 10-20 Mm^2 . Before the occurrence of each large plume, the bubble expands and takes on a quasi-semicircular appearance. Meanwhile, the emission intensity of extreme-ultra-violet (EUV) bands increases in the bubble. A small-scale filament is found to erupt in the bubble during the second large plume. At the point at which the height of the bubble is comparable with half the width of the bubble, the bubble becomes unstable and generates the plumes. During the formation of plumes, two side edges of the top of the bubble, which are dominated by opposite Doppler signals, approach each other. The large plume then emerges and keeps rising up with a constant speed of about 13-15 km/s. These two large plumes have temperatures of 1.3 x 10^6 Kelvin and densities of 2.0 x 10^9 cm^-3, two orders hotter and one order less dense than the typical prominence. We also find that the bubble is a hot, low-density volume instead of a void region beneath the cold and dense prominence. Therefore, we conclude that these two large plumes are the result of the breakup of the prominence bubble triggered by an enhancement of thermal pressure; they separate from the bubble, most likely by magnetic reconnection.

astro-ph.SR↗

arXiv2022

In-situ comparison of interface instability of basal and edge planes during unidirectional growth of sea ice

The unique anisotropy of ice has endowed sea ice growth a peculiar and attractive subject from both fundamental and applied viewpoints. The distinct growth behaviors between edge and basal plane of ice are one of the central topics in ice growth. And the unidirectional freezing pattern stems from perturbations of both basal and edge planes. To date there is no direct comparison of unidirectional freezing behavior between basal and edge plane ice. Here, we in-situ investigate the planar instability as well as the unidirectional freezing pattern of basal and edge planes of ice by a design of parallel freezing samples with specified ice orientations in a NaCl solution as a modeled sea water. The planar instability is discussed via neutral stability curves with surface tension anisotropy for both basal and edge plane ice. For the first time, we realize the simultaneous observation of solid/liquid interfaces of basal and edge plane ice under the same set of freezing conditions. The results show that planar instability occurs faster for edge plane ice than basal plane ice. The time-lapse observations confirm a transient competitive interaction of perturbations between the basal and edge planes ice, which is explained by the anisotropic growth of perturbations in basal and edge planes of ice. These experimental results provide a link between morphology evolution of unidirectional grown sea ice and different ice orientations and are suggested to enrich our understanding of sea ice growth as well as crystallization pattern of other anisotropic materials.

cond-mat.mtrl-sci↗

arXiv2021

Yielding and jerky plasticity of tilt grain boundaries in high-temperature graphene

Graphene is well known for its extraordinary mechanical properties combining brittleness and ductility. While most mechanical studies of graphene focused on the strength and brittle fracture behavior, its ductility, plastic deformation, and the possible brittle-to-ductile transition, which are important for high-temperature mechanical performance and applications, still remain much less understood. Here the mechanical response and deformation dynamics of graphene grain boundaries are investigated through a phase field crystal modeling, showing the pivotal effects of temperature and local dislocation structure. Our results indicate that even at relatively high temperature (around 3350 K), the system is still governed by a brittle fracture and cracking dynamics as found in previous low-temperature experimental and atomistic studies. We also identify another type of failure dynamics with low-angle grain boundary disintegration. When temperature increases a transition to plastic deformation is predicted. The appearance of plastic flow at ultrahigh temperature, particularly the phenomenon of jerky plasticity, is attributed to the stick and climb-glide motion of dislocations around the grain boundary. The corresponding mechanism is intrinsic to two-dimensional systems, and governed by the competition between the driving force of accumulated local stress and the defect pinning effect, without the traditional pathways of dislocation generation needed in three-dimensional materials.

cond-mat.mtrl-sci↗

arXiv2021

Revealing curvature and stochastic effects on grain growth kinetics: A thermodynamic perspective from the extremal principle

In the theoretical development of normal grain growth, the roles of "drift" (curvature effect) and "diffusion" (stochastic effect) have been an open question for many years. By coupling contributions of microstructure entropy and grain topological interactions with thermodynamic extremal principle (TEP), this letter extends the existing thermodynamic framework of grain growth. It not only explains the curvature and stochastic effects by thermodynamics but provides a new mean-field model for grain growth. Through thermodynamic modification, this new model can yield a high accuracy representation of existing ultra-large phase-field simulated results.

cond-mat.mtrl-sci↗

arXiv2021

Naked emergence of an anti-Hale active region I. Overall evolution and magnetic properties

{In order to understand the emergence of the active region, we investigate the emerging process and magnetic properties of a naked anti-Hale active region during the period between August 24 to 25, 2018.} {Using the data from Helioseismic and Magnetic Imager on board the Soar Dynamic Observatory and the New Vacuum Solar Telescope, we calculated different evolving parameters (such as pole separation, tilt angle) and magnetic parameters (such as vertical electric current, force-free parameter, relative magnetic helicity) during the emergence of the active region. With these calculated parameters and some reasonable assumptions, we use two different methods to estimate the twist of the active region.} {The magnetic flux and pole separation continue increasing while the tilt angle exhibits a decreasing pattern during the emergence of the active region. The increase of the pole separation is mainly contributed as a result of the enhancement in the longitude direction. A power-law relationship between pole separation and total flux is found during the emergence of the active region. On the other hand, it is found that both the positive and negative electric currents increased equivalently and the average flux-weighted force-free parameter $\tilde α$ remains almost consistently positive, on the order of $\sim$ 10$^{-8}$ m$^{-1}$. The relative magnetic helicity is mainly contributed by the shear term, while the relative magnetic helicity injection flux of the shear term changes its sign at the latter stage of the emergence. The twist number of the whole active region remains on the order of 10$^{-1}$ turns during the emergence of the active region.} {We find that the magnetic flux tube with low twist also could emerge into the solar atmosphere.}

astro-ph.SR↗

arXiv2021

Tilting behavior of lamellar ice tip during unidirectional freezing of aqueous solutions

Freezing of ice has been largely reported from many aspects, especially its complex pattern formation. Ice grown from liquid phase is usually characteristic of lamellar morphology which plays a significant role in various domains. However, tilted growth of ice via transition from coplanar to non-coplanar growth in directional solidification has been paid little attention in previous studies and there is misleading explanation of the formation of tilted lamellar ice. Here, we in-situ investigated the variations of tilting behavior of lamellar ice tip under different conditions within a single ice crystal with manipulated orientation via unidirectional freezing of aqueous solutions. It is found that tilted growth of ice tips is sensitive to pulling velocity and solute type. These experimental results reveal intrinsic tilted growth behavior of lamellar ice and enrich our understanding in pattern formation of ice.

cond-mat.soft↗

arXiv2021

Crossover from lamellar to spongy ice morphologies within a single ice crystal during unidirectional freezing of an aqueous solution

Ice growth from liquid phase has been extensively investigated in various conditions, especially for ice freely grown in undercooled water and aqueous solutions. Although unidirectional ice growth plays a significant role in sea ice and freeze casting, the detailed pattern formation of unidirectionally grown ice in an aqueous solution remains elusive. For the first time, we in situ proved a crossover from lamellar to spongy ice morphologies of a single ice crystal via unidirectional freezing of an aqueous solution. The spongy ice morphology originates from the intersect of tilted lamellar ice and is observed in a single ice crystal, which is intrinsically different from the competitive growth of bi-crystal composed of two differently orientated grains in directional solidification. These results provide a complete physical picture of unidirectionally grown ice from aqueous solution and are believed to promote our understanding of various pattern of ice in many relevant domains where pattern formation of ice crystal is vital.

cond-mat.mtrl-sci↗

arXiv2020

The planar interface instability during freezing of a polymer solution: Diffusion-controlled or not?

Freezing of polymer solutions has been extensively investigated from many aspects, especially the complex pattern formation. The cell/dendrite micro-structures are believed to be in the type of diffusion-induced M-S instability. However, the presence of polymer as an impurity in water is significantly different from that of small ions. The quantitative transient investigation on directional freezing of polymer solutions remains lack due to some challenges. For the first time, we observed the planar instability behaviors during unidirectional freezing of a polymer solution together with a typical ionic solution with manipulated ice orientation, and their pattern formation of S/L interface morphology as a function of time in the transient planar instability process has been revealed and compared to each other. It is found with real-time observation that the polymer solution exhibits a global instability mode instead of a local instability mode that is common in ionic solution during planar instability. W-L model was applied to quantitatively address the variation of solute recoil of ionic/polymer solution. And it is found that the W-L model can only reproduce the solute recoil of ionic solution instead of polymer solution, which indicates the complex physics behind freezing of a polymer solution. The paper provides a spectacular contrast of directional freezing process between polymer solution and ionic solution and is believed to promote relevant investigations in terms of the theoretical approach to describing the freezing behavior of polymer solution.

cond-mat.soft↗

arXiv2020

In situ visualization of tip undercooling and lamellar microstructure evolution of sea ice with manipulated orientation

Sea ice growth with lamellar microstructure containing brine channels has been extensively investigated. However, the quantitative growth information of sea ice remains lack due to the uncontrolled crystalline orientation in previous investigations. For the first time, we in-situ observed the unidirectional growth of lamellar sea ice with well-manipulated ice crystal orientation and visualized tip undercooling of sea ice. A semi-empirical model was proposed to quantitatively address the variation of tip undercooling with growth velocity and salinity and compared with a very recent analytical model. With the real-time observation, interesting phenomena of doublon tip in cellular ice growth and growth direction shift of ice dendritic tip were discovered for the first time, which are attributed to the complex solutal diffusion and anisotropic interface kinetics in sea ice growth. The quantitative experiment provides a clear micro scenario of sea ice growth, and will promote relevant investigations of sea ice in terms of the theoretical approach to describing the diffusion field around faceted ice dendritic tip.

cond-mat.mtrl-sci↗

arXiv2020

Single ice crystal growth with controlled orientation during directional freezing

Ice growth has attracted great attention for its capability of fabricating hierarchically porous microstructure. However, the formation of tilted lamellar microstructure during freezing needs to be reconsidered due to the limited control of ice orientation with respect to thermal gradient during in-situ observations, which can greatly enrich our insight into architectural control of porous biomaterials. This paper provides an in-situ study of solid/liquid interface morphology evolution of directionally solidified single crystal ice with its C-axis (optical axis) perpendicular to directions of both thermal gradient and incident light in poly (vinyl alcohol, PVA) solutions. Misty morphology and V-shaped lamellar morphology were clearly observed in-situ for the first time. Quantitative characterizations on lamellar spacing, tilt angle and tip undercooling of lamellar ice platelets provide a clearer insight into the inherent ice growth habit in polymeric aqueous systems and are suggested exert significant impact on future design and optimization in porous biomaterials.

cond-mat.mtrl-sci↗

arXiv2020

A small-scale filament eruption inducing Moreton Wave, EUV Wave and Coronal Mass Ejection

With the launch of SDO, many EUV waves were observed during solar eruptions. However, the joint observations of Moreton and EUV waves are still relatively rare. We present an event that a small-scale filament eruption simultaneously results in a Moreton wave, an EUV wave and a Coronal Mass Ejection in active region NOAA 12740. Firstly, we find that some dark elongate lanes or filamentary structures in the photosphere existed under the small-scale filament and drifted downward, which manifests that the small-scale filament was emerging and lifting from subsurface. Secondly, combining the simultaneous observations in different Extreme UltraViolet (EUV) and H$α$ passbands, we study the kinematic characteristics of the Moreton and EUV waves. The comparable propagating velocities and the similar morphology of Moreton and different passbands EUV wavefronts were obtained. We deduce that Moreton and different passbands EUV waves were the perturbations in different temperature-associated layers induced by the coronal magneto-hydrodynamic shock wave. We also find the refracted, reflected and diffracted phenomena during the propagation of the EUV wave. By using power-law fittings, the kinematic characteristics of unaffected, refracted and diffracted waves were obtained. The extrapolation field derived by the potential field source surface (PFSS) model manifests that the existence of an interface of different magnetic system (magnetic separatrix) result in refraction, reflection and deviation of the EUV wave.

astro-ph.SR↗