Metastable Conditions Research Articles

Zirconia as a biomaterial for dental use

Due to the biocompatibility and mechanical properties that are more than satisfying, zirconia has been successfully used in recent years as a preferred dental biomaterial. Zirconia is a polymorphic material that occurs in three temperature-dependant forms that are: monoclinic (room temperature to 1170 C), tetragonal (1170 C–2370 C) and cubic (2370 C – up to melting point)1. However, when stabilizing oxides such as magnesia, ceria, yttria and calcium are added to zirconia, the tetragonal phase is retained in a metastable condition at room temperature, enabling a phenomenon called transformation toughening to occur. Y-TZP Ceramics have a unique characteristic of „Stress Induced Transformation” that gives them superior mechanical properties compared with other ceramics. Scientific studies suggest that zirconium dioxide does not relieve allergens and other non-compatible substances in the mouth. In addition, it is excellently tolerated by soft tissues. Successfully used for more than 20 years in medicine-surgery and orthopedics, and now has already entered the dental medicine. Zirconia cores are generally covered with ceramic because of the opaque color of the zirconia. The incrustation of zirconia with ceramic is giving the restoration a more natural and aesthetic look but there are registered incidences of chipping. This is why the more translucent zirconia (full-contour-without ceramic incrustation ) restorations are used nowadays.

Improvement of surface properties of an Al–Sn–Cu plain bearing alloy produced by rapid solidification

Al–Sn based alloys are widely used as plain bearings in several engineering applications, particularly in internal combustion engines. The microstructures of these alloys are composed by two main phases, α-Al and β-Sn. The latter provides the low friction coefficient required for bearing applications. The new combustion engines and hybrid systems impose harder working conditions to plain bearings, thus the bearing materials need to be stronger with improved friction properties. The conventional Al20Sn1Cu (wt.%) alloy produced at different cooling rates by means of different casting processes such as Belt Casting, Twin Roller and Single Roller Melt Spinning techniques was studied. The effects of the cooling rate and of the Mn addition on the microstructure and properties were studied. The samples produced by the melt-spinning technique with cooling rates higher than ∼5 × 105 K/s conducts the alloy to a solidification pathway in a metastable condition through a miscibility gap. A microstructure characterized by an homogeneous small rounded β-Sn particles distributed in a refined α-Al grain size matrix is obtained. Samples produced with cooling rate higher than ∼1.4 × 106 K/s show an anisotropic microstructure of a <100> α-Al crystallographic texture in a columnar microstructure. The melt-spun samples with an isotropic microstructure reach a Vickers hardness 86% higher and an improved wetting property than the alloy produced by the traditional Belt-Casting technique. However the melt-spun samples with crystallographic texture showed a downfall in the properties. The addition of Mn leads to a more homogeneous and refined microstructure independently of the casting technique used.

Surface tension of seawater at low temperatures including supercooled region down to – 25 °C

The experimental apparatus used for the measurement of surface tension of supercooled water using a capillary rise technique [Hrubý et al. J. Phys. Chem. Lett 5 (2014) 425 and Vinš et al. J. Phys. Chem. B 119 (2015) 5567] was modified for the measurements with seawater. New data for the surface tension of IAPSO seawater standard were collected for a salinity range from 10 g/kg to 38 g/kg and at temperatures from 30 °C down to −25 °C. The reported measurements are relative to the surface tension of pure water at the reference temperature of 15 °C. The combined standard uncertainty of the relative surface tension is better than 0.30%. The new data do not indicate any anomaly in the temperature trend of the surface tension of low-temperature and supercooled seawater down to temperature of −25 °C. The data agree with other literature data measured at stable conditions above 0 °C. Recent correlation by Nayar et al. [J. Phys. Chem. Ref. Data 43 (2014) 043103], considered as a potential standard for the surface tension of seawater, shows a very good agreement with the new data both in the stable region and under the metastable supercooled conditions. The differences between the correlation and the experimental data are entirely within the experimental uncertainty. Consequently, the recommended range of validity of the correlation by Nayar et al. can be extended into the supercooled region down to −25 °C for salinity up to 38 g/kg. In addition, an alternative correlation for the surface tension of seawater compatible with the recent correlation by Pátek et al. [J. Chem. Eng. Data 61 (2016) 928] for pure water is introduced. The new correlation has the same form as that by Nayar et al., however with slightly modified coefficients. Both correlations for seawater provide comparable results over the temperature and salinity ranges of the available experimental data.

A novel CFD approach for the computation of R744 flashing nozzles in compressible and metastable conditions

The present paper describes a novel CFD approach for the flashing of CO2 through nozzles and ejectors. The novelty of the method is represented by the possibility of defining both the liquid and vapor phases as compressible materials. The properties of each phase are obtained via look-up tables calibrated against standard fluid libraries and are valid in the whole domain of interest, including the supercritical, subcritical and metastable regions.The model has been implemented within a commercial CFD solver and is completely general, i.e., it can be applied to any type of compressible multiphase flow. In the present study, the proposed approach has been validated against an experimental test-case available in literature.

Comparative Study on Solid-State and Metastable Liquid-State Aging for SAC305/Cu Joints

In order to study the influence of the physical state of solder on the interfacial reaction of dip-soldered Sn–3.0Ag–0.5Cu/Cu system, two kinds of experiments were designed, including: (1) solid-state aging between the solder and Cu substrate; (2) liquid-state aging between the metastable supercooled liquid-state solder and Cu substrate. The aging times were 30, 60, 120 and 180 min, respectively, and the aging temperature was 8 °C lower than the melting point of the Sn–3.0Ag–0.5Cu (SAC305) alloy (217 °C). The experimental data revealed that the physical state of the solder obviously affected the formation of the intermetallic compound (IMC), and resulted in the difference in the diffusion of atoms on the interface between the SAC305 solder and Cu substrate. The IMC interface after aging for 30 min presents unique characteristics compared with that of the sample after dip soldering. The IMC interface of solid-state aged SAC305/Cu couple is relatively planar, while the IMC interface under metastable supercooled liquid-state aging conditions presents scallop-like shape.

Negative Pressure Regimes in Ionic Liquids: Structure and Interactions in Stretched Liquids as Probed by NMR

Condensed matter - solids or liquids, but not gases - might be deeply, homogeneously stretched to absolute negative pressures (metastable regimes of isotropic tension). For instance, we were able to stretch macroscopically-sized liquid solutions down to p ~ - 35 MPa,[1] a value which still constitutes a world record for large volume liquid samples. Up to now, the absolute record for neat liquids is hold for liquid water in microscopic porous crevices of natural rocks, p ~ -140 MPa. There are several strategies to force a liquid entering into negative pressure regimes. The most common one is the Berthelot method.[2] Negative pressures can be either directly measured - via a highly elaborated Bourdon-Berthelot combination methodology[3,4] or safely, though approximately, estimated through the liquid’s isochoric thermal-pressure coefficient, g v = a p/k T. In this work, a broad pallete of macroscopically sized samples of ionic liquids was used, in which tensions of about -100 MPa were obtained before cavitation would occur. This value constitutes a new record for large samples. The underlying success for achieving such great absolute negative pressures in ionic liquids as compared to other liquids seems to be the best combination of (i) their negligible vapour pressure and (ii) their generally high viscosity. Good adhesion (wettability) to the container’s walls (in this case Pyrex glass) is a paramount, minimum requirement. For the first time, NMR studies have been performed on ionic liquids under homogeneous tension. Due to potential hazard issues related to the protection/safety of the NMR instrumentation, negative pressures beyond the value of – 20 MPa were avoided. Upon entering into these metastable regimes of negative pressure, it was possible to observe a sharp increase in the ions self-diffusion coefficients as compared to the equilibrium saturated liquid conditions at the same temperatures. MD simulations have been performed to gain insights into the ILs structure and interactions under these deep metastable conditions.

Remote spectral–compositional analysis of basalt mineralogy at Hansteen‐Billy, Moon

AbstractThe Hansteen‐Billy region of the Moon lying toward the southwest edge of Oceanus Procellarum is characterized by emplacement of three different aged basaltic units viz. INm, Im, and Em. The present study primarily utilizes high‐resolution Chandrayaan‐I, Moon Mineralogy Mapper (M3) data clipped at ~2.5 μm for mineral analysis of these units. The spectra of all the three regions show two prominent absorption bands. Spectral analysis characterizes the earliest INm basalts as low‐Ca pyroxenes with large band area ratios (BAR) and nearly similar B‐I and B‐II strength. The Em and Im basalts are Ca and high‐Ca pyroxenes, respectively, with relatively less BAR values and more B‐II/B‐I strength. The relative content of their spectra after olivine correction appears to be dominated by pyroxene. The obtained results have been used for estimation of the compositional characteristics of pyroxenes from laboratory‐based calibration equations. The pyroxene composition for INm basalts indicates their pigeonitic affinity, whereas the Im and Em basalts is close to augite. The estimated temperature of crystallization suggests that basalts in this region evolved at higher temperature and are preserved in a metastable condition due to quick cooling. Furthermore, the area is characterized by increase in concentration of both the Fe and Ti with age as assessed from Clementine mineral map. The obtained results have been discussed in relation with source of the magma.

A hybrid kinetic-thermodynamic Monte Carlo model for simulation of homogeneous burst nucleation

Abstract We develop in this paper a hybrid kinetic Monte Carlo and continuous thermodynamically based model for the simulation of homogeneous nucleation under burst regime when a long incubation time is followed by rapid nucleation of stable nuclei. In this model we assume that the kinetics of particle nucleation and disaggregation is governed by a Smoluchowski equation while the size of a stable nuclei is taken from the thermodynamic theory of nucleation with varying supersaturation under metastable conditions. We show that the Smoluchowski equations without the metastable conditions cannot describe the regime of burst nucleation showing the following general feature: the longer the incubation time, the slower the nucleation rate even if a multiple disaggregation is assumed. In contrast, a combined hybrid Monte Carlo and metastable thermodynamic model suggested is able to predict a long incubation time followed by rapid nucleation regime. A series of numerical simulations presented supports this conclusion.

Effect of annealing treatments on CeO2 grown on TiN and Si substrates by atomic layer deposition.

In this work, we investigate the effect of thermal treatment on CeO2 films fabricated by using atomic layer deposition (ALD) on titanium nitride (TiN) or on silicon (Si) substrates. In particular, we report on the structural, chemical and morphological properties of 25 nm thick ceria oxide with particular attention to the interface with the substrate. The annealing treatments have been performed in situ during the acquisition of X-Ray diffraction patterns to monitor the structural changes in the film. We find that ceria film is thermally stable up to annealing temperatures of 900 °C required for the complete crystallization. When ceria is deposited on TiN, the temperature has to be limited to 600 °C due to the thermal instability of the underlying TiN substrate with a broadening of the interface, while there are no changes detected inside the CeO2 films. As-deposited CeO2 films show a cubic fluorite polycrystalline structure with texturing. Further, after annealing at 900 °C an increase of grain dimensions and an enhanced preferential (200) orientation are evidenced. These findings are a strong indication that the texturing is an intrinsic property of the system more than a metastable condition due to the ALD deposition process. This result is interpreted in the light of the contributions of different energy components (surface energy and elastic modulus) which act dependently on the substrate properties, such as its nature and structure.

Accounting for the Effect of Noncondensing Gases on Interphasic Heat and Mass Transfer in the Two-Fluid Model Used in the KORSAR Code

A model is presented of the interphasic heat and mass transfer in the presence of noncondensable gases for the KORSAR/GP design code. This code was developed by FGUP NITI and the special design bureau OKB Gidropress. It was certified by Rostekhnadzor in 2009 for numerical substantiation of the safety of reactor installations with VVER reactors. The model is based on the assumption that there are three types of interphasic heat and mass transfer of the vapor component: vapor condensation or evaporation on the interphase under any thermodynamic conditions of the phases, pool boiling of the liquid superheated above the saturation temperature at the total pressure, and spontaneous condensation in the volume of gas phase supercooled below the saturation temperature at the vapor partial pressure. Condensation and evaporation on the interphase continuously occur in a two-phase flow and control the time response of the interphase heat and mass transfer. Boiling and spontaneous condensation take place only at the metastable condition of the phases and run at a quite high speed. The procedure used for calculating condensation and evaporation on the interphase accounts for the combined diffusion and thermal resistance of mass transfer in all regimes of the two-phase flow. The proposed approach accounts for, in a natural manner, a decrease in the rate of steam condensation (or generation) in the presence of noncondensing components in the gas phase due to a decrease (or increase) in the interphase temperature relative to the saturation temperature at the vapor partial pressure. The model of the interphase heat transfer also accounts for the processes of dissolution or release of noncondensing components in or from the liquid. The gas concentration at the interphase and on the saturation curve is calculated by the Henry law. The mass transfer coefficient in gas dissolution is based on the heat and mass transfer analogy. Results are presented of the verification of the interphase heat and mass transfer used in the KORSAR/GP code based on the data on film condensation of steam-air flows in vertical pipes. The proposed model was also tested by solving a problem of nitrogen release from a supersaturated water solution.

Atomic ordering and coercive force of nanocrystalline Fe-Co alloy films

In single crystal films of the Fe0,5Co0,5 alloys grown by the method of vacuum condensation, a metastable condition may be received that is similar to the completely disordering condition. Approximately during ten days after the condensation in the film at the room temperature the short range and then long range atomic ordering is developed. Simultaneously the changes of magnetic anisotropy, electroresistance and coercive force of the films were investigated. This investigations show that the appearance of the shot range atomic ordering increases the electroresistance of films and the long range atomic ordering reduces it. The dependence of coercive force from time to time at room temperature atomic ordering films Fe0,5Co0,5 alloys, and Fe0,75Co0,25. Found that the biggest change Hc (double) is observed in single-crystal films when changing mechanism of magnetization reverse. Most is a consequence of the changes to the crystallographic anisotropy.

There is need in new generation smart grid for the space and ground energy systems

The aim of the article is to considerate the opportunities of synchronization of the space and ground systems that generate and transfer energy on the basis of new generation smart grid using. The authors substantiate the necessity of new intellectual monitoring services that assess the processes took place in "generation-transportation-distribution-consumption" space and ground systems. This is made in order to improve the dynamic indicators of the energy system and to avoid the emergencies. The authors also give a prognosis of the dynamic indicators of the electric power super-system in analyzing metastable conditions in different energy modes.

The repassivation response from single cycle anodic polarization: The case study of a sensitized Al-Mg alloy

The repassivation behaviour of artificially aged 5083-H111 Al-Mg alloy in near neutral NaCl solutions was investigated by means of single cycle anodic polarization. Artificial aging was carried out at 150 °C during different times up to 360 h. The characterization of the microstructure and composition by XRD, SEM/EDS and metallographic analyses pointed out most favoured grain-boundary β(Al3Mg2) phase precipitation for 168 h of isothermal treatment time. Nitric acid mass loss test (NAMLT) and microhardness measurements indicated the highest degree of sensitization (DoS) and developed strength for 168 h as well. For all the aging conditions, the potential drop at high currents during the reverse scan of the cyclic polarization was detected at the pit transition potential Eptp with similar but higher values than the corrosion potential of β phase (Ecorr ≈ −900 mV vs SCE). The associated current density iptp and the steepness of the potential drop increase as the amount and contiguity of β phase precipitates along grain boundaries. The onset and sustenance of metastable conditions that limit the simultaneous repassivation of all the corroded surfaces are driven by the anodic dissolution of β(Al3Mg2). Metastable processes that limit the hydration of metal ions while producing high local hydrogen concentration are more likely to involve the formation/decomposition of reactive hydride intermediates. Eptp corresponds to the mixed electrode potential at which both metal dissolution and hydrogen evolution occur beyond some distance into the cavity, while iptp evaluates the catalytic activity of the corroding surfaces. The effective anodic charge transfer coefficient αeff determined from the steepness of the potential drop estimates the contribution of Cl− electromigration in response to local electrodissolution processes.

Nonlinear dynamics, seismic activity and aerospace sounding systems

Processes and phenomena are under consideration, which can be realized from the viewpoint of nonlinear dynamics and are typical for geosystems. Attention is focused on the main features and new possibilities given by the ideas and approaches of nonlinear dynamics for solving applied problems of geophysics. Premises for physical interpretation of spontaneous electromagnetic and seismoacoustic emission as a product of temporally uninterrupted transitional dynamic processes related to interaction of different subsystems of geo-medium as its metastable conditions and succession of such conditions are analyzed. An attempt has been undertaken to analyze lithosphere-atmosphere-ionosphere relations, methods of multiparametric aerospace monitoring of short-term precursors of strong seismic events. Its possibilities and limits are considered and the necessity of integrating passive monitoring systems based on the study of medium-generated emission signals spectra with active ones, oriented to system receptivity control. Baselessness of attempts to give reliable and accurate short-term forecast without studying physics of producing destruction sources and development of deformation process within the Earth’s crust during the final stage in a regime with intensification has been noticed.

Constraints representing a meta-stable régime facilitate exploration during practice and transfer of learning in a complex multi-articular task

Previous investigations have shown that inducing meta-stability in behavior can be achieved by overlapping affordances through constraint manipulation, allowing cooperative and competitive tendencies to functionally coexist. The purpose of this paper was to test a number of conditions applying these design principles on performance during skills practice and transfer. Of additional interest, was whether the existing skill level interacted with the environmental properties of the experimental tasks (varying indoor climbing routes). Two skill groups practised on three routes per session over four separate sessions. At the end of the final session, climbers undertook a transfer test. Routes, matched for difficulty, were manipulated in terms of hand-hold design. Route-1 and Route-2 were designed with holds with a single graspable edge, aligned entirely parallel or perpendicular to the ground plane respectively. Route-3 had at each hold, two graspable edges (one parallel and one perpendicular to the ground plane). Behavioral exploration at the hip and hands were largest under the metastable condition (Route-3). Skill level also interacted with route properties during practice and influenced transfer. Data suggest meta-stability induces exploratory behaviors. Less skilled individuals explore both hand and hip levels, whereas, more experienced climbers explore at the hip level.

Spontaneous emission activity of lithosphere and seismoelectromagnetic phenomena

New ideas and approaches to describing spontaneous emission of lithosphere are being discussed — seismic, seismoacoustic and electromagnetic based on analysis of non-stationary processes and metastable conditions in active geomedium. It is accentuated that these emissions are not only a dynamic but also spatial-temporal chaos in distributed energy-saturated geo-systems. Attention is concentrated on a diffusion-relaxation component of lithospheric noise interpreted as a reflection of non-linear dynamics of non-equilibrium geomedium, a result of interaction and concordance between mechanisms of its self-organization, which determine the trends of evolutionary processes development and effects of dynamic relaxation, which reflect the role of fluctuation-dissipative factors. Essential role of criticality fronts in the processes of their generation is being noted, in particular, of percolation-diffusion ones and of related transitional processes in non-stationary geomedium, which are called transitional dispersion. It is considerable that spontaneous emissions as ordered spatial-temporal structures, which are determined by the properties of the geo-system, might be interpreted in terms of self-excited oscillations of relaxation type and, in particular, auto-structures.

The importance of supersaturation on determining the solid-liquid equilibrium temperature of waxy oils

Crystallization is a process where an ordered solid structure is formed from a disordered phase. This event is divided in two main stages, namely nucleation and crystals growth. As paraffin nucleation is a stochastic process, a supercooling is needed to initiate the process. In other words, the beginning of crystal precipitation does not coincide with the highest thermodynamic solid-liquid equilibrium temperature. Therefore, during the cooling it is required that the fluid reaches a certain temperature below saturation, i.e., a metastable state, to initiate the crystal nucleation process. The difference between the saturation temperature and the crystallization temperature is called degree of supercooling. As this metastable condition may exist during not only the crystallization but also the dissolution of crystals, this work proposes a procedure to determine consistently the highest solid-liquid thermodynamic equilibrium temperature by using the results of rheometer and DSC experiments. It can be anticipated that the proposed protocol states that the highest solid-liquid thermodynamic equilibrium temperature is considered to approach the dissolution temperature when the material is heated at a very low heating rate.

Polyphenic trait promotes liver cancer in a model of epigenetic instability in mice.

Hepatocellular carcinoma (HCC) represents the fifth‐most common form of cancer worldwide and carries a high mortality rate attributed to lack of effective treatment. Males are 8 times more likely to develop HCC than females, an effect largely driven by sex hormones, albeit through still poorly understood mechanisms. We previously identified TRIM28 (tripartite protein 28), a scaffold protein capable of recruiting a number of chromatin modifiers, as a crucial mediator of sexual dimorphism in the liver. Trim28hep–/– mice display sex‐specific transcriptional deregulation of a wide range of bile and steroid metabolism genes and development of liver adenomas in males. We now demonstrate that obesity and aging precipitate alterations of TRIM28‐dependent transcriptional dynamics, leading to a metabolic infection state responsible for highly penetrant male‐restricted hepatic carcinogenesis. Molecular analyses implicate aberrant androgen receptor stimulation, biliary acid disturbances, and altered responses to gut microbiota in the pathogenesis of Trim28hep–/–‐associated HCC. Correspondingly, androgen deprivation markedly attenuates the frequency and severity of tumors, and raising animals under axenic conditions completely abrogates their abnormal phenotype, even upon high‐fat diet challenge. Conclusion: This work underpins how discrete polyphenic traits in epigenetically metastable conditions can contribute to a cancer‐prone state and more broadly provides new evidence linking hormonal imbalances, metabolic disturbances, gut microbiota, and cancer. (Hepatology 2017;66:235–251).

Building Skill in Videogames: A Play of Bodies, Controllers and Game-Guides

In his now-seminal book, Pilgrim in the Microworld (1983), David Sudnow details his process of learning to play the game Breakout on the Atari 2600. Sudnow develops an account of his graduation from a novice (having never played a videogame prior, and middle-aged at time of writing) to being able to fluidly perform the various configurative processes involved in an acclimated Breakout player’s repertoire.

Visualization of Electrochemical Reactions in Battery Materials with X-ray Microscopy and Mapping

Unlocking the full performance capabilities of battery materials will require a thorough understanding of the underlying electrochemical mechanisms at a variety of length scales. A broad arsenal of X-ray microscopy and mapping techniques is now available to probe these processes down to the nanoscale. The tunable nature of X-ray sources allows for the extraction of chemical states through spectromicroscopy. The addition of phase contrast imaging can retrieve the complex-valued refraction of the material, giving an even more nuanced chemical picture. Tomography and coherent Bragg diffraction imaging provide a reconstructed three-dimensional volume of the specimen, as well as internal strain information from the latter. Many recent insights into battery materials have been achieved through the creative use of these, and similar, methods. Experiments performed while the battery is being actively cycled reveal behavior that differs significantly from what is observed at equilibrium and metastable conditions. ...