Flat Interface Research Articles

Perturbative solution of a propagating interface in the phase field model

When a stable ordered phase and a metastable disordered phase are separated by a flat interface, the metastable state changes to the stable state through the propagation of the interface. For cases in which latent heat is generated, the interface displacement during some time interval is proportional to the square root of the time interval when the extent of supercooling is less than a certain value. We demonstrate this behavior by deriving a perturbative solution for a propagating interface in the phase field model. We calculate the leading-order contribution explicitly, and find that the interface temperature deviates from the equilibrium transition temperature in proportion to the interface velocity.

Lax–Wendroff type solver for two-phase system to restrain parasitic currents

In this paper, a Lax–Wendroff type solver is developed to solve the governing equations for two-phase flows. By incorporating the source term into the numerical flux and approximating the cell volume force by the interfacial forces, the proposed scheme is able to restrain parasitic currents in two-phase systems. Numerical results suggest that the magnitude of the parasitic currents is considerably reduced, and the stability is also improved. Particularly, for a one-dimensional flat interface and a two-dimensional (2D) stationary droplet, the velocity fields drop to machine zero even with a large density ratio (1:1000). It is also found that the viscosity plays an important role in the suppression of parasitic currents when the density ratio is large.

Fast Electromagnetic Waves on Metamaterial’s Boundary: Modeling of Gain

The paper presents the results of the study of properties of fast surface electromagnetic waves that propagate along the flat interface between the active metamaterial and air (or vacuum). The case of homogeneous and isotropic metamaterial is considered. The dispersion properties, the wave spatial attenuation, the phase and group velocities, as well as the spatial distribution of the electromagnetic field of the eigen TE and TM modes of such a waveguide structure are studied in the frequency range where the metamaterial has a simultaneously negative permittivity and permeability. It is shown that fast surface electromagnetic waves can exist in this waveguide structure and their properties are studied. It is shown that the phase speed of TM mode is several times higher than the speed of light in vacuum, while the phase speed of TE mode is slightly higher than the speed of light in vacuum. The TM mode is a direct wave in which the phase and group velocities have the same direction. It is obtained that the group velocity of the TM mode varies from zero to the about half of speed of light in vacuum, and reaches a minimum at a certain value of wave frequency, which depends on the characteristics of the metamaterial. It is shown that the penetration depth of the TM mode into the metamaterial is much smaller than into the vacuum. The TE mode is a backward wave with opposite directed phase and group velocities. The absolute value of the group velocity of the TE mode is about six times less than the speed of light in vacuum. In contrast to the TM mode the penetration depth of the TE mode into the metamaterial is much greater than in vacuum. The obtained properties of the fast surface electromagnetic waves can be used for modeling and design of modern generation and amplification devices containing metamaterials.

Mechanical degradation of magnetic pulse welded Al–Fe joint in neutral salt environment

The urgent need in lightweight of vehicle body promoted the application of multi materials with high specific strength, and this involves the reliable welding of dissimilar materials. In this study, AA5052 aluminum alloy and HC420LA steel were welded by magnetic pulse welding. The mechanical degradation of the dissimilar Al–Fe joint after different salt spray corrosion duration was investigated. The atomic force microscopy-scanning Kelvin probe force microscopy (AFM-SKPFM) and immersion tests were also performed. The fracture of the Al–Fe joint was observed by optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The ultimate shear strength of the Al–Fe joint only declines for 10% after three weeks' corrosion. Crevice corrosion is found in the overlapping region, and galvanic corrosion and stress corrosion occur in the weld region. The corrosion in the flat welding interface is mainly galvanic corrosion due to the high corrosion driving force, while the corrosion in the wave welding interface is mainly stress corrosion.

Identification of a PCSK9-LDLR disruptor peptide with in vivo function

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates plasma low-density lipoprotein cholesterol (LDL-C) levels by promoting hepatic LDL receptor (LDLR) degradation. Therapeutic antibodies that disrupt PCSK9-LDLR binding reduce LDL-C concentrations and cardiovascular disease risk. The epidermal growth factor precursor homology domain A (EGF-A) of the LDLR serves as a primary contact with PCSK9 via a flat interface, presenting a challenge for identifying small molecule PCSK9-LDLR disruptors. We employ an affinity-based screen of 1013invitro-translated macrocyclic peptides to identify high-affinity PCSK9 ligands that utilize a unique, induced-fit pocket and partially disrupt the PCSK9-LDLR interaction. Structure-based design led to molecules with enhanced function and pharmacokinetic properties (e.g., 13PCSK9i). In mice, 13PCSK9i reduces plasma cholesterol levels and increases hepatic LDLR density in a dose-dependent manner. 13PCSK9i functions by a unique, allosteric mechanism and is the smallest molecule identified to date with invivo PCSK9-LDLR disruptor function.

Can a liquid drop on a substrate be in equilibrium with saturated vapor?

It is well known that liquid and saturated vapor, separated by a flat interface in an unbounded space, are in equilibrium. One would similarly expect a liquid drop, sitting on a flat substrate, to be in equilibrium with the vapor surrounding it. Yet, it is not: as shown in this work, the drop evaporates. Mathematically, this conclusion is deduced using the diffuse-interface model, but it is also reformulated in terms of the maximum-entropy principle, suggesting model independence. Physically, evaporation of drops is due to the so-called Kelvin effect, which gives rise to a liquid-to-vapor mass flux if the boundary of the liquid phase is convex.

Superconducting Long-Range Proximity Effect through the Atomically Flat Interface of a Bi2Te3 Topological Insulator

We report on structural and electronic properties of superconducting nanohybrids made of Pb grown in the ultrahigh vacuum on the atomically clean surface of single crystals of topological Bi2Te3. In situ scanning tunneling microscopy and spectroscopy demonstrated that the resulting network is composed of Pb-nanoislands dispersed on the surface and linked together by an amorphous atomic layer of Pb, which wets Bi2Te3. As a result, the superconducting state of the system is characterized by a thickness-dependent superconducting gap of Pb-islands and by a very unusual position-independent proximity gap between them. Furthermore, the data analysis and DFT calculations demonstrate that the Pb-wetting layer leads to significant modifications of both topological and trivial electronic states of Bi2Te3, which are responsible for the observed long-range proximity effect.

A higher-order finite element method with unstructured anisotropic mesh adaption for two phase flows with surface tension

A novel finite element framework is proposed for the numerical simulation of two phase flows with surface tension. The Level-Set (LS) method with piece-wise quadratic (P2) interpolation for the liquid–gas interface is used in order to reach higher-order convergence rates in regions with smooth interface. A balanced-force implementation of the continuum surface force model is used to take into account the surface tension and to solve static problems as accurately as possible. Given that this requires a balance between the discretization used for the LS function, and that used for the pressure field, an equal-order P2/P2/P2 scheme is proposed for the Navier–Stokes and LS advection equations, which are strongly coupled with each other. This fully implicit formulation is stabilized using the residual-based variational multiscale framework. In order to improve the accuracy and obtain optimal convergence rates with a minimum number of elements, an anisotropic mesh adaption method is proposed where the unstructured mesh is kept as fine as possible close to the zero iso-value of the P2 LS function. Elements are automatically stretched in regions with flat interface in order to keep the complexity fixed during the simulation. The accuracy and efficiency of this approach are demonstrated for two and three dimensional simulations of a rising bubble.

Turbulent drag reduction over liquid-infused textured surfaces: effect of the interface dynamics

Direct numerical simulations of a turbulent channel with liquid infused surfaces made of longitudinal micro-ridges have been performed to study the effect of texture geometry and interface deformation. The flow conditions consider a viscosity ratio , several values of the micro-ridge pitch and two different Weber numbers, We = 0 and We = 50. The performance is analyzed in terms of drag reduction (DR) with respect to an equivalent smooth channel, and the results compared with those available for super-hydrophobic surfaces (SHS). It is found that, due to the relatively high viscosity of the liquid locked in the substrate, the drag reduction offered by LIS is substantially lower than the corresponding SHS. When reported in terms of the streamwise slip length normalized in wall units, the amount of DR obtained by LIS in the ideal case of flat interface collapses on the SHS data. The interface dynamics has a detrimental effect on the performance, that becomes particularly severe when the pitch increases. The degradation of DR is well parametrized by the log-law shift of the velocity profile, that is found to be proportional to the difference between the virtual origin of the mean flow and that experienced by the overlying turbulence.

Eliminating spurious currents in phase-field-theory-based lattice Boltzmann equation for two-phase flows

Spurious currents are frequently observed near an interface in the equilibrium multiphase flow system by lattice Boltzmann equation (LBE). These unphysical phenomena are the result of force imbalance of LBE at a discrete level. In this paper, we develop a well-balanced Cahn–Hilliard equation-based LBE for incompressible two-phase flows. The effects of small initial perturbation of order parameter or dynamic pressure and nonisotropic discretization of gradient in force term on eliminating the spurious currents are investigated systematically. Numerical simulations including flat interface and stationary droplet problems are carried out to show the capability of present LBE for eliminating the spurious currents and its accuracy. The results predicted by the present LBE are compared with those by mixed isotropic discretizations scheme (MIDS) frequently used in the LBE community. Numerical results show that the initial perturbation of order parameter or dynamic pressure and nonisotropic discretization of gradient term has no significant effect on eliminating the spurious currents by present LBE, while the MIDS is sensitive to them.

Analysis of natural frequency for imaging interface in liquid lens

Transmission beam can be modulated at the liquid–liquid interface inside an electrowetting liquid lens. The fluctuation characteristics of the interface has a decisive effect on the beam modulation. A closed cylinder in capillary constant scale is analyzed and the natural frequencies of a flat interface are obtained using capillary wave hydrodynamics. Results in modes 0 and 1 are in good agreement with previous experiments in the literature. The influences of the radius, the height ratio and the height-to-diameter ratio of a liquid lens on the interface eigenfrequencies are analyzed.

A taper-fit junction to improve long bone reconstruction: A parametric In Silico model

PurposeCritical size long bone defects represent a clinical challenge in orthopaedic surgery. Various grafting techniques have been developed through the years, but they all present several downsides. A key requirement of all grafting techniques is the achievement of a continuous interface between host bone and graft to enhance both biological processes and mechanical stability. This study used a parametric in silico model to quantify the biomechanical effect of the inaccuracies inherent to current osteotomy techniques, and to test a new concept of accurate taper-fit junction that may improve the biomechanical parameters of the reconstruction under load. MethodsA population-based in-silico 3D model of the reconstruction of a long bone defect was built to represent a defect of the femoral mid-diaphysis. To fix the reconstruction a titanium plate was placed on the lateral aspect of the reconstruction. The model was modified to (i) quantify the biomechanical consequences of actual inaccuracies in the realization of a flat host-graft interface, (ii) compare the contact behaviour and bone strains among different taper angles of the new design and the current host-graft flat interface, (iii) evaluate the robustness of the taper-fit design to inter-subject variability in bone geometry and defect length. ResultsThe influence of 2° single-plane misalignments of the host-graft interface is highly dependent on the misalignment orientation with respect to the metal plate. For some misalignment orientations, tangential micromotions of contact interfaces exceeded alert thresholds. When the angle of the taper-fit host-graft junction is changed from 10° to 30° and the results obtained are compared with the planar case, the overall stiffness is almost preserved, the bone strains are almost unchanged with safety factors higher than five, and full contact closure around the host-graft junction is achieved at 20°. Similarly, contact pressures decrease almost linearly with a 20% decrease at 30°. The host-graft micro motions are almost unchanged in both value and distribution up to 20° and never exceed the warning threshold of 50 μm. ConclusionsThe present in silico study developed quantitative biomechanical evidence that an osteotomy performed with attention to the perpendicularity of the cut planes is needed to reduce the risk of mismatch and possible complications of long bone reconstructions, and that a new concept of a taper-fit junction may improve the biomechanical environment of the interface between the graft and the host bone. The optimal taper-fit configuration is suggested to be around a 20° taper angle. These results will serve as an input to conduct exvivo experiments to further corroborate the proposed taper-fit junction concept and to refine its surgical implementation.

Theoretical analysis of Fresnel reflection and transmission in the presence of gain media

When a monochromatic electromagnetic plane-wave arrives at the flat interface between its transparent host (i.e., the incidence medium) and an amplifying (or gainy) second medium, the incident beam splits into a reflected wave and a transmitted wave. In general, there is a sign ambiguity in connection with the k-vector of the transmitted beam, which requires at the outset that one decide whether the transmitted beam should grow or decay as it recedes from the interface. The question has been posed and addressed most prominently in the context of incidence at large angles from a dielectric medium of high refractive index onto a gain medium of lower refractive index. Here, the relevant sign of the transmitted k-vector determines whether the evanescent-like waves within the gain medium exponentially grow or decay away from the interface. We examine this and related problems in a more general setting, where the incident beam is taken to be a finite-duration wavepacket whose footprint in the interfacial plane has a finite width. Cases of reflection from and transmission through a gainy slab of finite-thickness as well as those associated with a semi-infinite gain medium will be considered. The broadness of the spatiotemporal spectrum of our incident wavepacket demands that we develop a general strategy for deciding the signs of all the k-vectors that enter the gain medium. Such a strategy emerges from a consideration of the causality constraint that is naturally imposed on both the reflected and transmitted wavepackets.

Dynamic response mechanism of a rock-filling interfacial coupling body to blasting in it

The interfacial coupling structure between the backfill and ore rock body in the filling mining method will be continuously disturbed by the influence of mining and blasting. In the filling-rock interfacial coupling, it is easy to produce the behaviors of debonding and fissure expansion, which will bring potential safety hazards to underground production. Because the field experiment is time-consuming and laborious, and it is difficult to observe the impact effect and the rock crack propagation process when the explosive is detonated, the simulation method was adopted for research. In the simulation, reasonable simplification is particularly important. According to the actual situation of blasting hole layout, the three rows of blasting holes that were detonated at one time were simplified into a single-row blasting hole model and an edge blasting hole model. According to the research results in related literatures, the coupling surfaces of the filling bodies and the ore rocks were simplified into three kinds (a flat interface, wavy interface and serrated interface). The three different shapes of the interfaces correspond to the different roughnesses of the interfaces, respectively. By considering that the hole arrangement method used in stope blasting is vertical hole arrangement, the holes are parallel, and at the same time, in order to improve the calculation of the software efficiency, simplified the three-dimensional model of the stope into a two-dimensional plane model. After a series of simplifications, a physical model for the filling-rock interface coupling body was proposed, and the corresponding geometric analysis model was established by using the ANSYS/LS-DYNA software And different material parameters were assigned to the different parts of the model, and the blasting effect was analyzed by software calculation. The mechanical influence of the interface coupling body structure was obtained, and the response law of different interface roughness, the curing age of the filling body and the blasting method on the blasting shock was obtained, and the mechanism of the blasting dynamics was discussed. The research results can reveal mechanical behaviors such as debonding and crack propagation at the coupling of filling-rock interface, and clarify the influence of different factors on the law of blasting shock response and the mechanism of blasting dynamics, which has certain guiding significance for downhole safety production. The results show as follows. (1) The blasting impact has three mechanical effects in the interface coupling body: tension, pressure and shear. When the stress wave passes through the interface, the peak acceleration of the monitoring point at the interface will increase due to different degrees of refraction. After passing through the coupling interface, the stress wave energy decays rapidly. (2) The impact of different interface roughness on blasting action is different. The joint roughness coefficient (JRC) represents the roughness of the interface coupling body. With the increase of the JRC value, the interface stress tends to rise first and then decline, but the overall damage decreases. (3) As the curing time of the backfill increases, the fracture range at the coupling interface shrinks, and the interface damage gradually changes from tensile damage to shear damage. (4) The damage of different detonation modes to the interface coupling body is different, and the damage of simultaneous detonation to the coupling interface is weaker than that of hole-by-hole detonation.

Fixed-dimension renormalization group analysis of conserved surface roughening.

Conserved surface roughening represents a special case of interface dynamics where the total height of the interface is conserved. Recently, it was suggested [Caballero etal., Phys. Rev. Lett. 121, 020601 (2018)PRLTAO0031-900710.1103/PhysRevLett.121.020601] that the original continuum model known as the Conserved Kardar-Parisi-Zhang (CKPZ) equation is incomplete, as additional nonlinearity is not forbidden by any symmetry in d>1. In this work, we perform detailed field-theoretic renormalization group (RG) analysis of a general stochastic model describing conserved surface roughening. Systematic power counting reveals additional marginal interaction at the upper critical dimension, which appears also in the context of molecular beam epitaxy. Depending on the origin of the surface particle's mobility, the resulting model shows two different scaling regimes. If the particles move mainly due to the gravity, the leading dispersion law is ω∼k^{2}, and the mean-field approximation describing a flat interface is exact in any spatial dimension. On the other hand, if the particles move mainly due to the surface curvature, the interface becomes rough with the mean-field dispersion law ω∼k^{4}, and the corrections to scaling exponents must be taken into account. We show that the latter model consist of two subclasses of models that are decoupled in all orders of perturbation theory. Moreover, our RG analysis of the general model reveals that the universal scaling is described by a rougher interface than the CKPZ universality class. The universal exponents are derived within the one-loop approximation in both fixed d and ɛ-expansion schemes, and their relation is discussed. We point out all important details behind these two schemes, which are often overlooked in the literature, and their misinterpretation might lead to inconsistent results.

Non-Equilibrium Crystallization of Monotectic Zn-25%Bi Alloy under 600 g.

This study investigated the influence of supergravity on the segregation of components in the Zn–Bi monotectic system and consequently, the creation of an interface of the separation zone of both phases. The observation showed that near the separation boundary, in a very narrow area of the order of several hundred microns, all types of structures characteristic for the concentration range from 0 to 100% bismuth occurred. An additional effect of crystallization in high gravity is a high degree of structural order and an almost perfectly flat separation boundary. This is the case for both the zinc-rich zone and the bismuth-rich zone. Texture analysis revealed the existence of two privileged orientations in the zinc zone. Gravitational segregation also resulted in a strong rearrangement of the heavier bismuth to the outer end of the sample, leaving only very fine precipitates in the zinc region. For comparison, the results obtained for the crystallization under normal gravity are given. The effect of high orderliness of the structure was then absent. Despite segregation, a significant part of bismuth remained in the form of precipitates in the zinc matrix, and the separation border was shaped like a lens. The described method can be used for the production of massive bimaterials with a directed orientation of both components and a flat interface between them, such as thermo-generator elements or bimetallic electric cell parts, where the parameters (thickness) of the junction can be precisely defined at the manufacturing stage.

Liquid crystal thermography based study on melting dynamics and the effect of mushy zone constant in numerical modeling of melting of a phase change material

Melt front tracking is vital in a solid–liquid phase change process to understand the melting process and quantify the system’s liquid faction, sensible and latent energies. This study presents a method to track the solid–liquid interface during the melting of a phase change material using liquid crystal thermography. The melt front movement is captured simultaneously through temperature influenced color variation in Thermochromic Liquid Crystal (TLC) sheet and direct visualization. Experiments have been performed for the cases of (i) heating from the bottom and (ii) heating from the top. Further, three-dimensional numerical simulations have been performed to validate the mushy zone temperatures and understand the effect of the mushy zone constant in the mushy zone temperature and liquid fraction. The results show that the TLC easily captures the dynamic motion of the solid–liquid interface during melting. From numerical simulations, it is found that the mushy zone constant affects the numerical prediction of melting in the bottom heating case with the low and high mushy zone constants, respectively, over predicting and under predicting the mushy zone temperatures during melting. Additionally, in this case, it is seen that the Rayleigh–Benard convection creates a wavy interface and accelerates the melting rate of the PCM. In the case of heating from the top, the numerical prediction of melting is independent of the mushy zone constant. Besides, a flat interface is observed in this case due to the absence of convection in the PCM during melting. Additionally, in the case of heating from the top, the combination of the PCM’s low thermal conductivity and heat diffusion through conduction leads to the self insulation effect of the PCM during melting. The convection-driven melting of PCM maintains the heater temperature lower by up to 35%, reduces the melting thermal resistance up to 78%, and increases the average volumetric melting to 92% over the case of melting without convection in the PCM.

High strength impact welding of 7075 Al to a SiC-reinforced aluminum metal matrix composite

Vaporizing foil actuator welding (VFAW), an impact welding method, was used for the first time to produce high strength welds between SiC-reinforced 8009 aluminum metal matrix composite (MMC) (8009/SiC/11p) and 7075 aluminum alloy (AA7075). Microscopic characterization of the dissimilar impact weld revealed multiple heterogenous microstructural zones including an unbonded zone at the center, a flat interface, a wavy interface, and a trapped jet zone at the corner. SiC-depleted and SiC-rich bands were alternately distributed with consistent plastic flow patterns along the wavy interface. Microhardness tests prove that little or no heat or mechanically affected zones were formed in the dissimilar impact weld. Peel test yields a nugget pullout on the AA7075-T6 indicating high strength of the weld. VFAW process provides a solution to join the Al MMC with dissimilar metals in the applications of automotive and aerospace products.

Shear strength characteristics of interlocked EPS-block geofoam-sand interface

Translation of entire geofoam embankment at the bottom of geofoam block assemblage and bedding sand is a possible internal failure mode due to unbalanced hydrostatic forces. In addition, available shearing resistance along the bottom of geofoam block assemblage and bedding sand is an important design issue for internal seismic stability analysis. This study has focused on the methods to increase the interface shear resistance along the traditional flat surface geofoam block and bedding sand interface. In addition to traditional flat surface geofoam-sand interface, the effect of four different interlock configurations composed of geofoam blocks with one- and four-triangular and one- and four-square ledges were quantified by using direct shear tests. Two different densities (EPS19 and EPS29) and two different types of sand (Ottawa sand and Adapazari sand) were used. Therefore, the effects of geofoam stiffness, interface geometry, grain size and particle shape of the bedding sand on the interface stress-strain behavior was quantified. Manufacturing ledges along the traditional geofoam surface significantly improved the geofoam block-sand interface shear resistance. In addition, interrupting the failure plane with ledges changed the interface shear mechanism of the traditional flat surface geofoam block-bedding sand interface from purely frictional to frictional-cohesive behavior.

SUCTION FORCE ANALYSIS FOR DIGITAL LIGHT PROCESSING-BASED PROJECTION STEREOLITHOGRAPHY

Digital light processing (DLP)-based projection stereolithography is one of the most important photo-polymerization based additive manufacturing technologies that has distinctive advantages such as high-resolution and fast printing speed. But the excessive suction force in the liquid resin film limits the further improvement of printing speed. The existing researches mainly focus on the improvement of the transparent window of the resin tank and the technological process while the mechanism of suction force is poorly understood. In this work, a multi-physical model coupled with resin flow, free radical polymerization and phase transition is established. The evolution process of the resin liquid film is studied under the combined action of mass transfer, photopolymerization, curing deposition and oxygen polymerization inhibition by numerical simulation. It is found that the solid-liquid interface presents a stable non-uniform wave attenuation morphology and the liquid film thickness is small and fluctuates sharply at the boundary which is completely different from the assumption of flat interface in previous research. The effects of elevating velocity, oxygen concentration distribution and UV intensity on the interface morphology and suction force are discussed. The results indicate that increasing the equilibrium concentration of oxygen and decreasing the UV intensity can effectively reduce the suction force while significantly affect the printing precision. We propose that adjusting the distribution of UV intensity can improve the inhomogeneity of the interface morphology and is an effective measure to reduce the suction force and increase the printing speed. This research has important reference significance for the study of different types of photo-polymerization based additive manufacturing technologies.