Coordinates Of Critical Point Research Articles

Analytic solution of pull-out failure on bond-slip relationship between deformed rebar and ultra-high-performance concrete

Numerous studies have explored the bond performance between deformed rebar and ultra-high-performance concrete (UHPC), yet an analytical solution to the bond-slip relationship remains elusive. This study presents an analytical solution of pull-out failure for the staged bond-slip constitutive relationship between rebar and UHPC, taking into account the meso-scale bond properties of fibers. The critical point coordinates for different stages are determined by the analytical solution. Utilizing the elastic mechanic solution of thick-walled cylinder under uniform internal pressure, the fictitious crack model, and the fiber-matrix discrete model, analytical solutions and simplified formulas for bond stress and slip at the critical points are provided respectively. The simplified formulas for predicting bond characteristics are proposed. The bond-slip test data are composed of 107 groups from 15 literatures, and the predictions of different formulas are compared. The average ratios of the theoretical ultimate bond stress and peak slip to the test results are 0.995 and 1.033, with a standard deviation of 0.179 and 0.231, and the error is generally within 20%. Compared with the bond-slip relationship, it is more reasonable that the ascending and descending sections are exponential. Moreover, the parameters in the bond-slip relationship can be calculated by the theoretical predictions of bond characteristics at each critical point.

Application of thermodynamics at different scales to describe the behaviour of fast reacting binary mixtures in vapour-liquid equilibrium

The use of reactive working fluids in thermodynamic cycles is currently being considered as an alternative to inert working fluids, because of the preliminarily attested higher energy-efficiency potential. The current needs to simulate their use in thermodynamic cycles, which may operate in liquid, vapour or vapour-liquid state, are an accurate real-fluid equation of state and ideal gas thermochemical properties of each molecule constituting the mixture, to calculate the equilibrium constant. To this end, the appeal to a multi-scale theoretical methodology is paramount and its definition represents the objective of the present work. This methodology is applied and validated on the system N2O4 ⇌ 2NO2. Firstly, the equations solved for simultaneous two-phase and reaction equilibrium are presented. Secondly, ideal gas thermochemical properties of N2O4 and NO2 are computed at atomic scale by quantum mechanics simulations. Then, to apply the selected cubic equation of state, pure-component properties of the species forming the reactive mixture (critical point coordinates and acentric factor) are required as input. However, these properties are not measurable, since NO2 and N2O4 do not exist in nature as pure components. To get around this difficulty, the methodology relies on molecular Monte Carlo simulations of the pure N2O4 and NO2, as well as on the reactive N2O4 ⇌ 2NO2, enabling the determination of those missing pure-component properties and thus the calculation, on a macroscopic scale, of the reactive mixture properties. Finally, the comparison of calculated mixture properties with available experimental data leads to validate the accuracy of the proposed methodology.

Adaptive approach formation using machine vision technology to determine the parameters of enrichment products deposition

In this paper, an adaptive approach has been developed for automatic initialization of the thickening curve using machine vision technology, which makes it possible to determine with high accuracy the material parameters necessary for the design of thickening and clarification apparatuses. Software has been developed that made it possible to search for the coordinates of the condensation critical point in automatic mode. Studies on two samples of materials (tailings of apatite-containing ores and gold-bearing concentrate) were carried out and made it possible to statistically prove the reproducibility of the results obtained using the parametric criteria of Fisher and Bartlett. It has been established that the deposition curves are approximated with high accuracy by the Weibull model, which, together with the piecewise linear approximation, makes it possible to formalize the method for determining the critical point coordinates. The empirical coefficients of the Weibull model for two samples are found, and the final liquefaction and settling rates of the studied materials are determined.

A Thermodynamic Model for Carbon Dioxide Storage in Underground Salt Caverns

In the context of green energy and decarbonization, carbon dioxide storage in underground facilities, such as salt caverns, is one promising technical solution that has aroused attention. However, the thermodynamic behavior of CO2 and the geomechanical response of salt cavities have not been studied comprehensively. In this study, we proposed a thermomechanical model that integrated a salt cavity and wellbore and implemented a series of simulations for carbon dioxide storage in a salt cavern. The model was verified by gas capacity calculations using field testing data. The thermodynamic behaviors of CO2 were determined and compared to methane. The results showed that the critical point coordinates of carbon dioxide were within the storage operation conditions, a phase transition could occur, and the thermodynamic properties around the critical point varied dramatically. For a short CO2 withdrawal operation, the salt cavity remained stable, while the near-wellbore area (NWA) was prone to fracture due to tensile stress concentration. Thus, we concluded that the proposed thermomechanical coupling numerical simulation method provided a comprehensive and quantitative tool for the feasibility analysis of CO2 storage in underground salt caverns.

Balance control in unstable sitting in individuals with an acute episode of low back pain

BackgroundLow back pain (LBP) is associated with altered postural control, mostly observed at later stages in the LBP trajectory. It is unclear whether postural control differs in the acute phase of LBP. Research questionIs postural control different in the acute phase of LBP (<2 weeks) and do differences depend on pain intensity, psychological features and/or availability of vision to control posture? MethodsCross-sectional study design. An unstable sitting paradigm (to reduce the contribution of the legs) assessed postural control of participants with acute LBP (n = 133) and pain-free controls (n = 74). Centre of pressure (CoP) reflected seat movements. Participants balanced with eyes closed, open, or with visual feedback of the anteroposterior CoP position. Balance performance was expressed by CoP displacement and velocity, and stabilogram diffusion analysis. Generalised estimating equations (GEEs) including body mass index, sex, and safety bar touch, tested differences between groups and between balance conditions. Separate GEEs were used to model performance measures and bar touch (yes/no) including pain intensity, disability and psychological features. ResultsCoP displacement and critical point coordinates (time and distance where CoP diffusion rate or spread slows) were larger in LBP than pain-free controls independent of balance condition. Long-term diffusion rate was greater in LBP than controls with eyes closed. CoP velocity measures (RMS, short term diffusion rate) were not different between groups. Pain intensity and psychological features were not linearly related to balance performance in participants with acute LBP. Higher pain catastrophizing was associated with touching the safety bar. SignificancePostural control differs in acute LBP than pain-free controls. Findings might be explained by altered sensory processing, lesser ability to reweight proprioceptive information and/or less accurate trunk muscle control. Although not linearly related to pain-intensity or psychological features in the acute stage, reduced balance performance could potentially have impact on LBP recovery.

Особенности фазовых переходов в висмутсодержащих упругонапряженных гетеросистемах AlGaInSbBi-InSb

In this paper the features of phase transformations in elastically stressed Al–Ga–In–Sb–Bi heterosystems and its subsystems In–Sb–Bi and Al–In–Bi are discussed. Isotherms for the aforesaid heterosystems and its subsystems are researched at temperatures from 653 to 923 K. The critical temperatures and critical point coordinates of spinodal decomposition of AlGaInSbBi solid solution are determined with regard to the coherent deformation energy. The elastic stresses effect on the thermodynamic behavior of the AlGaInSbBi–InSb heterosystem is investigated.

Second-Order Differential Accelerators Based on the Geometry of Equilibrium for Thermodynamic Calculations. Part I. Pure Fluids

This work presents an automatic and robust methodology for calculating phase equilibria with any equation of state (EOS). Its major advantage is applicability to the recent sophisticated thermodynamic approaches that exhibit multiple roots and which can challenge other methods. The proposed approach is based on the second-order geometrical approximation and the critical points as initial estimations. Its applications are illustrated by calculating phase equilibria in pure compounds by PC-SAFT, SAFT-VR, and the Johnson–Zollweg–Gubbins EOS along with the IAPWS formulation for water. The preliminary implementation to mixtures is discussed as well. Because this methodology requires determination of critical point coordinates, the relevant simple correlation and the Wolfram Mathematica code are provided.

A method to estimate statistical errors of properties derived from charge-density modelling.

Estimating uncertainties of property values derived from a charge-density model is not straightforward. A methodology, based on calculation of sample standard deviations (SSD) of properties using randomly deviating charge-density models, is proposed with the MoPro software. The parameter shifts applied in the deviating models are generated in order to respect the variance-covariance matrix issued from the least-squares refinement. This `SSD methodology' procedure can be applied to estimate uncertainties of any property related to a charge-density model obtained by least-squares fitting. This includes topological properties such as critical point coordinates, electron density, Laplacian and ellipticity at critical points and charges integrated over atomic basins. Errors on electrostatic potentials and interaction energies are also available now through this procedure. The method is exemplified with the charge density of compound (E)-5-phenylpent-1-enylboronic acid, refined at 0.45 Å resolution. The procedure is implemented in the freely available MoPro program dedicated to charge-density refinement and modelling.

The Detection Algorithm Development of Cutting Quality Defects of Paper Cutter Based on Regional Identification

This paper has a brief introduction to a algorithm that can automatically identify the defective cutting region when automatic paper cutter does quality analysis. The algorithm analyzed the characteristics of processed shear mark image,detected defects,found a critical point of defective part ,then a unique regional recognition algorithm was developed based on the basis of the general processing algorithm. The algorithms can pinpoint the region that cutting defects exist according to the coordinates of critical point accurately, improve the efficiency of quality analysis, and also has stated that image processing is available in the regional recognition of automatic paper cutter.

Calculation of critical point coordinates of ternary miscibility gap from experimental tie-lines

Demixing phenomena in liquid ternary systems are widely used in chemical engineering processes. When a critical point is observed, the composition of this invariant point of major interest is experimentally difficult to determine. A simple calculation method for the critical point is proposed using the experimental tie-lines. The computing treatment is based on the application of the barycentric weighting of the binodal points in order to extend the rectilinear diameter method and the exploitation of the modulus of the experimental tie-lines. A systematic study was carried out on a large set of ternary systems taken from DECHEMA and NIST. The results are compared with those available in literature or calculated by standard methods using binary interaction parameters. Very good agreements are obtained when the experimental tie-lines are located close to the critical point.The method can be extended to wide miscibility gaps by using a polynomial deviation instead of the rectilinear diameter line. A typical case is detailed (2-butanone+2-butanol+water at various temperatures). The results lead to (i) the point by point calculation of the entire binodal curve and (ii) the thermal evolution of the critical point and the possible disappearance of the critical point when temperature increases.

Studying equilibrium thermophysical properties of simple liquids based on a four-parameter oscillating interaction potentia

The equilibrium thermodynamic properties of a system with a four-parameter oscillating interaction potential which can be reduced to an oscillating potential with a single varying parameter is studied in the context of the statistical approach. The appearance of a phase transition of the first kind in the system is established. The relations between the geometric characteristics of potential with coordinates of critical points are obtained. The temperature dependences of some thermophysical properties on the phase equilibrium line and in the supercritical region are found. Thermodynamic parameters that depend on temperature and density are represented as functions of a constituting parameter connected with the interaction potential. The results of calculations are compared with the measurement data.

Non-classical gas dynamics of vapour mixtures

AbstractThe non-classical gas dynamics of binary mixtures of organic fluids in the vapour phase is investigated for the first time. A predictive thermodynamic model is used to compute the relevant mixture properties, including its critical point coordinates and the local value of the fundamental derivative of gas dynamics $\Gamma $. The considered model is the improved Peng–Robinson Stryjek–Vera cubic equation of state, complemented by the Wong–Sandler mixing rules. A finite thermodynamic region is found where the nonlinearity parameter $\Gamma $ is negative and therefore non-classical gas dynamics phenomena are admissible. A non-monotone dependence of $\Gamma $ on the mixture composition is observed in the case of binary mixtures of siloxane and perfluorocarbon fluids, with the minimum value of $\Gamma $ in the mixture being always larger than that of its more complex component. The observed dependence indicates that non-ideal mixing has a strong influence on the gas dynamics behaviour, either classical or non-classical, of the mixture. Numerical experiments of the supersonic expansion of a mixture flow around a sharp corner show the transition from the classical configuration, exhibiting an isentropic rarefaction fan centred at the expansion corner, to non-classical ones, including mixed expansion waves and rarefaction shock waves, if the mixture composition is changed.

The calculation of vapor-liquid coexistence curve of Morse fluid: Application to iron

The vapor-liquid coexistence curve of Morse fluid was calculated within the integral equations approach. The critical point coordinates were estimated. The parameters of Morse potential, fitted for elastic constants in solid phase, were used here to apply the results of present calculations to the determination of iron binodal. The properties of copper and sodium were considered in an analogous way. The calculations of pair correlation functions and isobars at liquid phase have shown that only for sodium these potential parameters allow one to obtain agreement with the measurements data. For iron another parameters are necessary to get this agreement in liquid phase. However, they give rise to very low critical temperature and pressure with respect to the estimates of other authors. Consequently, one can suppose that Morse potential is possibly inapplicable to the calculation of high temperature properties of non-alkali metals in disordered phases.

Transferable Force Field for Alcohols and Polyalcohols

A new force field has been developed for alcohol and polyalcohol molecules. Based on the anisotropic united-atom force field AUA4 developed for hydrocarbons, it only introduces one new anisotropic united atom corresponding to the hydroxyl group OH. In the case of polyalcohols and complex molecules, the calculation of the intramolecular electrostatic energy is revisited. These interactions are calculated between charges belonging to the different local dipoles of the molecule, one dipole being defined as a group of consecutive charges globally neutral. This new method allows avoiding the use of empirical scaling parameters commonly introduced to calculate 1-4 electrostatic interactions. The transferability of the proposed potential is demonstrated through the simulation of a wide variety of alcohol families: primary alcohols (methanol, ethanol, propan-1-ol, hexan-1-ol, octan-1-ol), secondary alcohols (propan-2-ol), tertiary alcohols (2-methylpropan-2-ol), phenol, and diols (1,2-ethanediol, 1,3-propanediol, 1,5-pentanediol). Monte Carlo simulations carried out in the Gibbs ensemble lead to a good agreement between calculated and experimental data for the thermodynamic properties along the liquid/vapor saturation curve, for the critical point coordinates and for the liquid structure at room temperature. Additional simulations were performed on the methanol + n-butane system showing the capability of the proposed potential to reproduce the azeotropic behavior of such mixtures with a good agreement.

Liquid-liquid equilibrium in the-n-heptane-n-perfluorohexane system

The shape of the liquid-liquid coexistence curve in the C7H16-C6F14 system in the molar concentration-temperature coordinates close to the critical solution point was studied by narrow-beam gamma-raying of two-phase samples. The molar volumes of the coexisting liquid phases and critical point coordinates (critical temperature Tc = 316.266 ± 0.03 K and critical concentration xc = 39.0 ± 0.4 mol % C6F14) were determined. The critical index β of the coexistence curve was found to be 0.322 ± 0.005. The diameter of the coexistence curve did not obey the classic “rectilinear diameter rule.”

The First Observation of the Tricritical Point in Ferroelectrics

The existence of Curie critical point (tricritical point in more recent terminology) was predicted by Landau in 1935. In 1945 Ginzburg created the phenomenological theory, of ferroelectricity based on Landau theory of the second order phase transitions. Ginzburg supposed, that ferroelectric phase transition of the first order in BaTiO 3 takes place in vicinity of the critical Curie point. This correct supposition could not be confirmed experimentally at this time and accordingly the Curie critical point coordinates could not be obtained because corresponding critical pressure for BaTiO 3 is more than 20 kbar. The first experimental observation of the critical (tricritical) point and estimation of its coordinates was performed in the ferroelectric SbSI crystals in 1967 and published next year. Later on, the tricritical point was found almost in the all ferroelectrics. This paper summarizes the results of experimental investigation of tricritical point in SbSI.

The Widom line of supercooled water

Water can be supercooled to temperatures as low as−92 °C, the experimental crystal homogeneous nucleation temperatureTH at 2 kbar. Within the supercooled liquid phase its response functions show an anomalousincrease consistent with the presence of a liquid–liquid critical point located in a regioninaccessible to experiments on bulk water. Recent experiments on the dynamics ofconfined water show that a possible way to understand the properties of wateris to investigate the supercooled phase diagram in the vicinity of the Widomline (locus of maximum correlation length) that emanates from the hypothesizedliquid–liquid critical point. Here we explore the Widom line for a Hamiltonianmodel of water using an analytic approach, and discuss the plausibility of thehypothesized liquid–liquid critical point, as well as its possible consequences, on the basisof the assumptions of the model. The present analysis allows us (i) to find ananalytic expression for the spinodal line of the high-density liquid phase, withrespect to the low-density liquid phase, showing that this line becomes flat in theP–T phase diagram in the physical limit of a large number of available orientationsfor the hydrogen bonds, as recently seen in simulations and experiments (Xu et al 2005 Proc. Natl Acad. Sci. 102 16558); (ii) to find an estimate of the values forthe hypothesized liquid–liquid critical point coordinates that compare very wellwith Monte Carlo results; and (iii) to show how the Widom line can be locatedby studying the derivative of the probability of forming hydrogen bonds withlocal tetrahedral orientation which can be calculated analytically within thisapproach.

A new translational platform for evaluating aging or pathology-related postural disorders

ConclusionsDynamic posturography using a translational platform and new parameters for quantifying postural reactions to linear displacements were suitable for differentiating between aging and pathological effects in upright postural control. These tools should be used on a wider scale in the near future for both routine tests and rehabilitation purposes, including the prevention of falls in elderly people.ObjectiveTo demonstrate that dynamic posturography using a translational platform and new parameters for quantifying postural reactions to linear displacements constitute a more suitable way of discriminating age and/or pathology-induced postural effects.Material and methodsThree groups of young healthy, elderly healthy and elderly unstable patients were tested on a translational platform using ramp (0.03, 0.07 and 0.1 m/s) and sinusoidal (0.25 and 0.5 Hz) stimulations. Their dynamic performances were compared to their postural evaluation on a static platform using classical stabilometric parameters (surface, length, etc.) and stabilogram–diffusion analysis (critical point coordinates and short-term diffusion coefficient).ResultsThe translational platform, the new parameters elaborated for quantifying postural reactions (energy and time for postural stabilization, phase and gain of the postural response) and the visual condition under which the subjects were tested (eyes open versus eyes closed) discriminated all groups better than the classical methods.

On some tуре оf transition from order tо chaos in thе system of coupled maps with period doubling

The critical behavior аt the onset оf chaos in thе system оf coupled invertible 2D-maps is investigated. It is shown that the type оf critical behavior which was found in the system of coupled noninvertible 1D-maps exists also in the system of coupled invertible 2D-maps, but only for the special type of coupling. For this system we obtained the coordinates of critical point and demonstrated scaling in the parameter plane near this point.

The effects of visual input on postural control of the lumbar spine in unstable sitting

Postural control of the lumbar spine in unstable sitting was quantified through the analysis of the center of pressure (CoP) movement recorded by a force plate situated underneath a seat that incorporated a hemisphere. Thirteen healthy subjects were tested under conditions of increasing seat instability and elimination of visual input. The purpose of this study was to determine the relative effects of visual input and support surface instability on open and closed loop postural control mechanisms in sitting and to determine the association between traditional summary statistics and random walk analysis of CoP movement. The effects of the seat instability level and visual input on the CoP movement parameters were tested with a two-factor, repeated measures ANOVA ( p<0.01). In all summary statistics CoP movement parameters increased significantly due to the seat instability level and lack of visual input. The random walk analysis identified two regions, short- and long-term, which has been postulated to represent open and closed loop control mechanism, respectively. While short-term scaling exponents were independent from visual input, CoP displacement in the short-term region was significantly increased in the eyes closed condition. Summary statistic of CoP total path length per second correlated highly with critical point coordinates and short-term diffusion coefficients. The CoP movement in the long-term region was consistent with a closed loop control mechanisms. The findings of visual influence on what is assumed as an open-loop control mechanism does not, at face value, support the hypothesis that two separate mechanisms are working to achieve postural control.