Metastable Stage Research Articles

Effect of dynamic contact angle behavior on droplet topological structure and film thickness evolutions in droplet mode

The droplet mode falling film evaporation was an area of intense research due to its thin liquid film and large interfacial area. A two-dimensional mathematical model based on the dynamic contact angle (DCA) model was developed to quantitatively analyze the effect of DCA behavior on droplet topological structure and film thickness evolutions of droplet mode in falling-film evaporation. Due to the movement of the three-phase contact line (vc) considered in the DCA model, the fact that the calculated DCA was significantly greater than the static contact angle (SCA) resulted in the phenomena of the liquid ring and droplet pulsation captured by the DCA model. The observed fluctuations of the DCA and vc might be attributed to the break-up of the liquid neck. For the impact stage, the peaks of the transient film thickness calculated by the DCA model were thicker than those by the SCA model and their differences increased with the increasing circumferential angle. For the metastable stage, the average film thickness predicted by the DCA model was thicker than that by the SCA model due to the captured droplet pulsation and calculated shorter metastable state by the DCA model.

Этапы подготовки к прерывистому скольжению на предварительно вырезанных разломах в лабораторных моделях и проверка этапов в природе

This study is focused on analog modeling of the stick-slip process along an existing large fault in an elastic-viscoplastic model subjected to loading at a constant strain rate. Based on our model results and data from (Ma et al., 2012, 2014), we distinguish stable, meta-stable, and meta-instable stages of the stick-slip process (the latter includes the early and late sub-stages). Our experiments show that the fault is periodically reactivated by segmentation. We analysed this mechanism from one fault reactivation to another, and identified regressive and progressive trends of segmentation. The regressive segmentation takes place during the stable and meta-stable stages of the stick-slip process. Under regressive segmentation the number of active segments and their lengths are reduced. The progressive segmentation is initiated at the early meta-instable sub-stage of the stick-slip process. Its activity is desplayed by an increase in the number of active segments to a certain critical density, while their pattern becomes more chaotic. In the late sub-stage, number of segments decreases as they rapidly grow and join with each other to form larger active segments, up to full reactivation of the entire fault. For comparison with the model results, we interpret rock deformation monitoring records before the Bystroe earthquake. Our analysis confirms specific features of the anomalous rock deformation that are similar to the strain features observed along the model fault during the meta-instable stage. There are evidence to suggest that meta-instability of a fault is a potential candidate to short-term precursor of earthquakes.

Topological Ordering of Memory Glass on Extended Length Scales.

Identifying ordering in non-crystalline solids has been a focus of natural science since the publication of Zachariasen's random network theory in 1932, but it still remains as a great challenge of the century. Literature shows that the hierarchical structures, from the short-range order of first-shell polyhedra to the long-range order of translational periodicity, may survive after amorphization. Here, in a piece of AlPO4, or berlinite, we combine X-ray diffraction and stochastic free-energy surface simulations to study its phase transition and structural ordering under pressure. From reversible single crystals to amorphous transitions, we now present an unambiguous view of the topological ordering in the amorphous phase, consisting of a swarm of Carpenter low-symmetry phases with the same topological linkage, trapped in a metastable intermediate stage. We propose that the remaining topological ordering is the origin of the switchable "memory glass" effect. Such topological ordering may hide in many amorphous materials through disordered short atomic displacements.

Structural investigations on Ge2Sb2Te5 thin films using polarised Raman studies

Ge-Sb-Te (GST) based materials are the main source of ingredient for Phase change memory (PCM) applications. This ternary compound has the capacity to shift faster between crystalline as well as amorphous state when a suitable electrical or optical pulse is applied on it. Its crystalline phase has two states viz. face centered cubic (FCC) which is actually the metastable state and hexagonal phase which is primarily more stable state as compared to the FCC state. However, only FCC phase is suitable for PCM applications, but this study emphasizes the study of stable hexagonal phase also. The need to understand the stable hexagonal phase arises to further understand the useful metastable FCC stage. In this work, local anatomical studies have been carried out using X-ray diffraction technique (XRD) along with Raman spectroscopy that includes polarization studies on Ge2Sb2Te5 thin films in amorphous, FCC and hexagonal states. This work provides information about the symmetry of vibrational states using inelastic Raman scattering studies in polarization mode having vertical and horizontal geometries showing different Raman scattering intensities corresponding to parallel (VV-vertical vertical) and perpendicular (VH-vertical horizontal) scattering configurations. It is expected that interpretations from these studies will be helpful to understand the molecular structure and orientation of various flawed structural states such as coordination and orientation defects.

Sintering mechanism of Ag nanoparticle-nanoflake: a molecular dynamics simulation

This paper studied the behaviors of sintering between Ag nanoparticle (NP) and nanoflake (NF) in the same size by molecular dynamics simulation. Before the sintering simulation, the melting simulation of NF was carried out to calculate the melting points of NFs and investigate the thermostability of NF. The Lindemann index and potential energy showed that the melting points of NF were significantly size-dependent. During the heating process, the sharp corner of NF transformed to the round corner and could bend spontaneously lower than melting points. In sintering simulation, the sintering process of NF-NP showed a metastable stage before equilibrium. Under low sintering temperature (500 K), the degree of plasticity sintering mechanism of NF-NP was more prominent, which generated more defects, such as amorphous atoms, dislocations, and stacking faults, than NP-NP. The sintered products of NF-NP also presented a better neck size and shrinkage than NP-NP in the same size. A new sintering behavior was observed: NF was bent toward the NP during the sintering. The bending curvature of NF increased as the thickness or the length/width decreased. For the NF with the ratio of length/width to thickness of 5:1, bending could further significantly facilitate neck growth. At 700 K, the plasticity mechanism dominated both the sintering processes of NF-NP and NP-NP. And NF-NP showed a larger diffusivity than NP-NP. At last, we investigated the effects of crystal misorientation, and found that a tilted grain boundary generated in the neck. The NF had the trend of rotation to decrease the crystal misorientation.

Metastable order protected by destructive many-body interference

The phenomenon of metastability can shape dynamical processes on all temporal and spatial scales. Here, we induce metastable dynamics by pumping ultracold bosonic atoms from the lowest band of an optical lattice to an excitation band, via a sudden quench of the unit cell. The subsequent relaxation process to the lowest band displays a sequence of stages, which include a metastable stage, during which the atom loss from the excitation band is strongly suppressed. Using classical-field simulations and analytical arguments, we provide an explanation for this experimental observation, in which we show that the transient condensed state of the atoms in the excitation band is a dark state with regard to collisional decay and tunneling to a low-energy orbital. Therefore the metastable state is stabilized by destructive interference due to the chiral phase pattern of the condensed state. Our experimental and theoretical study provides a detailed understanding of the different stages of a paradigmatic example of many-body relaxation dynamics.

In-situ monitoring of pitting corrosion of Q235 carbon steel by electrochemical noise: Wavelet and recurrence quantification analysis

Abstract Pitting corrosion of Q235 carbon steel in 0.25 M NaHCO3 with different concentrations of chloride ions was in-situ monitored by electrochemical noise (EN) technique, and the EN signals were analyzed by transient shape analysis, wavelet analysis and recurrence quantification analysis (RQA). Four typical electrochemical current noise (ECN) transients corresponding to different pitting stages including passivation, random metastable pitting, transition stage and stable pitting stage were observed. It was found that the RQA parameters, recurrence rate (R) and determinism (D), show the ability to separate the four ECN transients, while wavelet parameter show poor ability to distinguish the ECN transients arising from random metastable pitting and transition stage. Furthermore, the ratio of D and R (η) was proposed to monitor the pitting corrosion. The average value of η for the passivation and random metastable pitting is 1.88 and 1.63, and it gradually increases to around 6 during the transition stage and early stable pitting stage, the value slightly decreased to 4.16 at the late stable pitting stage. The detailed relationship between the EN characteristic parameters and dynamic process of pitting corrosion is discussed.

Entire crystallization process of Lennard-Jones liquids: A large-scale molecular dynamics study.

By using a graphics processing unit-accelerated parallel algorithm on a compute unified device architecture platform, we perform large-scale molecular dynamics simulations in a Lennard-Jones system to observe the entire crystallization process, including metastable stage, critical nuclei formation, and the stage of crystal growth. Although the intermediated precursors that play a role in determining the polymorphs are predominantly bcc ordered, the polymorph selection is rather different at different stages. The precursors that have a relatively high orientational order will be on average in a denser region than uniform liquids, but microscopically the crystal nucleation happens without a density change. The average density of nuclei first increases significantly, and then almost keeps independent on the crystallite size after the growing post-critical nucleus becomes large enough. With such a large enough system, the crystal growth rate is able to be calculated directly by doing a linear fit to the temporal evolution of growing crystallite size. The obtained value of the growth rate indicates that the actual crystal growth in the Lennard-Jones system where the crystal-liquid interface has several kinds of structures is possibly driven by both collision-controlled and diffusion-controlled mechanisms.

Nondestructive high-throughput screening of nanopore geometry in porous membranes by imbibition

A fluid dynamic model for imbibition into closed-end, axisymmetric pores having diameters that change as a function of the pore depth is presented. Despite the fact that liquid invasion into nonbranched closed-end pores is characterized by a wealth of different transient and/or metastable nonequilibrium stages related to precursor film formation, we show that a simple hydraulic model accounting for geometry- and air compression-induced deviations from classical Lucas-Washburn dynamics precisely describes the imbibition dynamics except at the late stage. The model was validated by laser interferometry experiments with submillisecond temporal resolution. Imbibition of three simple liquids (isopropanol, ethanol, and hexane) into self-ordered anodic alumina membranes containing arrays of parallel closed-end nanopores characterized by slight conicity was studied. The model provides an improved description of nanoscale fluid dynamics and allows geometric characterization of nanoporous membranes by their imbibition kinetics accounting for the back pressure of the compressed gas. Thus, a precise calibration of porous membranes with simple liquids becomes possible, and changes in the mean pore diameter as a function of the pore depth can be assessed.

Perspective on “Metastable Pitting of Stainless Steel,” G.S. Frankel, L. Stockert, F. Hunkeler, H. Boehni,Corrosion43, 7 (1987): p. 429-436

Abstract:Metastable pitting is a phenomenon that many passive metals exhibit in aggressive solutions at low potentials. Furthermore, it is accepted that stable pits experience a metastable stage pr...

A 3D in vitro model to explore the inter-conversion between epithelial and mesenchymal states during EMT and its reversion.

Epithelial-to-mesenchymal transitions (EMT) are strongly implicated in cancer dissemination. Intermediate states, arising from inter-conversion between epithelial (E) and mesenchymal (M) states, are characterized by phenotypic heterogeneity combining E and M features and increased plasticity. Hybrid EMT states are highly relevant in metastatic contexts, but have been largely neglected, partially due to the lack of physiologically-relevant 3D platforms to study them. Here we propose a new in vitro model, combining mammary E cells with a bioengineered 3D matrix, to explore phenotypic and functional properties of cells in transition between E and M states. Optimized alginate-based 3D matrices provided adequate 3D microenvironments, where normal epithelial morphogenesis was recapitulated, with formation of acini-like structures, similar to those found in native mammary tissue. TGFβ1-driven EMT in 3D could be successfully promoted, generating M-like cells. TGFβ1 removal resulted in phenotypic switching to an intermediate state (RE cells), a hybrid cell population expressing both E and M markers at gene/protein levels. RE cells exhibited increased proliferative/clonogenic activity, as compared to M cells, being able to form large colonies containing cells with front-back polarity, suggesting a more aggressive phenotype. Our 3D model provides a powerful tool to investigate the role of the microenvironment on metastable EMT stages.

X-Ray Diffraction Application for the Study of the Fine Structure of Carbon Fibers

The fine structure of carbon fibers, obtained according to specific preparation techniques, has been studied. It has been shown that the fiber material is heterogeneous, its component composition is determined by thermomechanical treatment conditions and addition of boron; also it depends on the angle φ of coherent scattering domain orientation relative to the thread axis. The mean coherent scattering domain sizes increase in transition to the components corresponding to smaller d002 values. Increase in temperature and duration of heat treatment, as well as the presence of a boron-containing additive, ensures formation of the components corresponding to smaller interplanar spacing d002 values in the carbon material. The observed influence of temperature and duration of heat treatment, as well as the angle of coherent scattering domain orientation relative to the thread axis, upon the component composition makes it possible to assume that the process of carbon fiber material transformation into a state of greater stability presumably develops through a number of metastable stages.

Mesoscopic study of micellar inversion pathways of the thermoresponsive PMEMA–PSBMA copolymer via applied stimulus intensity

In this work, two micellar inversion pathways of a thermoresponsive material were explored through dissipative particle dynamics simulations. The simulation results have demonstrated that poly(2-(N-morpholino)ethyl methacrylate)–poly(sulfobetaine methacrylate) (PMEMA–PSBMA) copolymer has tuneable critical solution temperatures (LCST and UCST) and can develop two different micellar states with a well-defined core–corona structure. All transitory and metastable stages on each micellar inversion pathway are controlled by the combination of the critical solution temperatures of each polymeric segment and by the applied stimulus intensity. The first structural inversion pathway (continuous thermal heating) involves three transitory stages (micellar dissociation, stabilization of free unimer chains and formation of inverse micelles), and the second micellar inversion pathway (abrupt thermal heating) implies two simultaneous transitory stages (immersion and ascent of polymeric segments). Each structural inversion pathway is described and analysed in detail in this document.

Identification of micellar stability zones and structural inversion process of thermoresponsive polymeric micelles by dissipative particle dynamics simulations

ABSTRACTThe stimuli-sensitive polymeric micelles have huge applications to industrial and technological level, know their behaviour under the influence of a pure stimulus, such as the temperature is an important aspect to control and amplify its application field. In this paper, we investigate the micellar stability zones together with the structural inversion process of thermoresponsive polymeric micelles formed by a diblock copolymer (poly(N-isopropylacrylamide-b-3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]ammoniopropane sulphonate (PNIPA-b-PSPP)) in an aqueous environment employing dissipative particle dynamics simulations. Our outcomes show that the PNIPA-b-PSPP copolymer has the ability to form thermodynamically stable micelles with different core-shell structure (PSPP-core/PNIPA-shell and PNIPA-core/PSPP-shell) depending on the direction of the applied stimulus (low or high temperature), the duality of this micellar behaviour is controlled by temperature effect and by the double hydrophilic character that exhibit the PNIPA and PSPP polymeric segments. Four micellar stability zones and one zone where only exist free unimer chains were detected during the thermal scan. The micellar inversion process is triggered by purely temperature effect, is totally reversible and involves three main stages: (1) micellar dissociation, (2) stabilisation of free unimer chains and (3) formation of inverse micelles, all transitory and metastable stages of micellar inversion process are described and analysed in this paper.

Cultural evolution as a nonstationary stochastic process

We present an individual based model of cultural evolution, where interacting agents are coded by binary strings standing for strategies for action, blueprints for products or attitudes and beliefs. The model is patterned on an established model of biological evolution, the Tangled Nature Model (TNM), where a “tangle” of interactions between agents determines their reproductive success. In addition, our agents also have the ability to copy part of each other's strategy, a feature inspired by the Axelrod model of cultural diversity. Unlike the latter, but similarly to the TNM, the model dynamics goes through a series of metastable stages of increasing length, each characterized by mutually enforcing cultural patterns. These patterns are abruptly replaced by other patterns characteristic of the next metastable period. We analyze the time dependence of the population and diversity in the system, show how different cultures are formed and merge, and how their survival probability lacks, in the model, a finite average life‐time. Finally, we use historical data on the number of car manufacturers after the introduction of the automobile to the market, to argue that our model can qualitatively reproduce the flurry of cultural activity which follows a disruptive innovation. © 2015 Wiley Periodicals, Inc. Complexity 21: 214–223, 2016

Intercalation Compounds from LiH and Graphite: Relative Stability of Metastable Stages and Thermodynamic Stability of Dilute Stage Id

The intercalation of lithium into graphite was studied at temperatures between 400 and 550 °C by heating mixtures of LiH and graphite powders with molar ratios 4:1, 1:1, and 1:6 under dynamic vacuum for periods between 1 and 72 h. These conditions probe the formation and thermal stability of metastable staged Li–graphite intercalation compounds (Li-GICs) close to the competing formation of the thermodynamically stable carbide Li2C2. Li-GICs of stages I (LiC6, Aα), IIa (Li0.5C6, AαA), IIb (Li∼0.33C6, AαABβB), III (Li∼0.22C6, AαAB), IV (Li∼0.167C6), and dilute stage lithium Id have been identified and characterized by powder X-ray diffraction and Raman spectroscopy. The rate and extent of intercalation (i.e., the achieved stage of Li-GIC) depends on LiH activity and temperature. Stage I was only observed for temperatures above 500 °C. At 400 °C, the highest intercalation corresponded to stage IIb, which was obtained after 2 and 24 h for 4:1 and 1:1 reaction mixtures, respectively. Lower-staged Li-GICs attained at temperatures below 500 °C deintercalate upon prolonged dwelling with the exception of stage IIa, which can be maintained for very long periods (several days) in the presence of LiH. At temperatures above 500 °C, the kinetically controlled formation of Li-GICs is followed by Li2C2 carbide formation. It is shown that the Li-GIC Id coexists with Li2C2 at temperatures up to 800 °C and that the Li content of Id (solubility of Li in graphite) increases between 550 and 800 °C. Consequently, Id with a temperature-dependent homogeneity range should be added as a stable phase in the Li–C phase diagram. A sketch of a revised Li–C phase diagram is provided.

The TCR ligand-inducible expression of CD73 marks γδ lineage commitment and a metastable intermediate in effector specification

Numerous studies indicate that γδ T cell receptor (γδTCR) expression alone does not reliably mark commitment of early thymic progenitors to the γδ fate. This raises the possibility that the γδTCR is unable to intrinsically specify fate and instead requires additional environmental factors, including TCR-ligand engagement. We use single cell progenitor assays to reveal that ligand acts instructionally to direct adoption of the γδ fate. Moreover, we identify CD73 as a TCR ligand-induced cell surface protein that distinguishes γδTCR-expressing CD4(-)CD8(-) progenitors that have committed to the γδ fate from those that have not yet done so. Indeed, unlike CD73(-) γδTCR(+) progenitors, which largely adopt the αβ fate upon separation from the intrathymic selecting environment, those that express CD73 remain CD4(-)CD8(-) and committed to the γδ fate. CD73 is expressed by >90% of peripheral γδ cells, suggesting this is a common occurrence during development. Moreover, CD73 induction appears to mark a metastable intermediate stage before acquisition of effector function, suggesting that γδ lineage and effector fate are specified sequentially. These findings have important implications for the role of ligand in γδ lineage commitment and its relationship to the specification of effector fate.

Metastability in Supersaturated Solution and Transition towards Chirality in the Crystallization of NaClO3

This way or that: Analysis of the chiral composition of the crystal mixture obtained from samples of boiling solutions of NaClO3 (see picture) indicates that symmetry breaking towards homochiral compositions may begin in the metastable stage preceding crystallization, that is, at the level of subcritical clusters.

Involvement of p38α in the mitotic progression of p53-/- tetraploid cells

The tumor suppressor protein p53 plays a major role in preserving genomic stability. p53 suppresses a pathway leading from normal diploidy to neoplastic aneuploidy (via an intermediate metastable stage of tetraploidy) at two levels: first by preventing the generation/survival of tetraploid cells, and second by repressing their aberrant multipolar division. Here, we report the characterization of p53-/- tetraploid cells, which - at difference with both their p53-/- diploid and their p53+/+ tetraploid counterparts - manifest a marked hyperphosporylation of the mitogen-activated protein kinase MAPK14 (best known as p38α) that is particularly strong during mitosis. In p53-/- tetraploid cells, phosphorylated p38α accumulated at centrosomes during the metaphase and at midbodies during the telophase. Selective knockdown or pharmacological inhibition of p38α had a dramatic effect on p53-/- (but not p53+/+) tetraploids, causing the activation of the spindle assembly checkpoint, an arrest during the metaphase, a major increase in abnormal bipolar and monopolar mitoses, as well as an increment in the generation of multinuclear cells. We conclude that the mitotic progression of p53-/- (but not p53+/+) tetraploids heavily relies on p38α, revealing a novel function for this protein in the context of aneuploidizing cell divisions.

Structure and phase stability of hydrogenated first-stage alkali- and alkaline-earth metal–graphite intercalation compounds

We report the hydrogenation temperature and pressure dependence of hydrogen absorption capacity in CaC 6. In addition, the structure and phase stability of hydrogenated CaC 6, LiC 6 and KC 8 has been investigated using X-ray diffraction and Raman spectroscopy. It is found that the hydrogen chemisorption in both CaC 6 and LiC 6 leads to either metastable or higher stage intermediate compounds but eventually leaves completely deintercalated graphite by forming stable metal hydrides. In contrast hydrogenation of KC 8 generates a restaged ternary hydride compound. The phase stability of hydrogenated compounds is discussed in the text based on the observed experimental results and correlated to the thermodynamic and kinetic aspects of intercalated metal.