Variation Of Order Parameter Research Articles

Depth-resolved X-ray residual stress analysis in PVD (Ti, Cr) N hard coatings

Abstract Physical vapour deposition (PVD) of thin hard coatings on TiN basis is usually performed at rather low temperatures (T D < 500 °C) far from thermal equilibrium, which leads to high intrinsic residual stresses in the growing film. In contrast to the extrinsic thermal residual stresses which can easily be estimated from the difference of the coefficients of thermal expansion between the substrate and the coating, a theoretical prediction of the intrinsic residual stresses is difficult, because their amount as well as their distribution within the film depend in a very complex way on the deposition kinetics. By the example of strongly fibre-textured PVD (Ti, Cr)N coatings which have been prepared under defined variation of the deposition parameters in order to adjust the residual stress distribution within the coatings, the paper compares different X-ray diffraction techniques with respect to their applicability for detecting residual stresses which are non-uniform over the coating thickness.

Symmetry-specific orientational order parameters for complex structures.

A comprehensive framework of characterizing complex self-assembled structures with a set of orientational order parameters is presented. It is especially relevant in the context of using anisotropic building blocks with various symmetries. Two classes of tensor order parameters are associated with polyhedral nematic and bond orientational order. For the latter, a variation of classical bond order parameters (BOPs) is introduced, which takes advantage of the symmetry of constituent particles and/or expected crystalline phases. These symmetrized BOPs can be averaged over an entire system or assigned locally to an individual bond. By combining that with the bond percolation procedure, one is able to identify coherent domains within a self-assembled structure. As a demonstration of the proposed framework, we apply it to a simulated hybrid system that combines isotropic and patchy particles with octahedral symmetry. Not only does the methodology allow one to identify individual crystalline domains but also it detects coherent clusters of a peculiar compact amorphous structure that is not space-filling and lacks any long-range order.

Controlling morphology in hybrid isotropic/patchy particle assemblies.

Brownian dynamics is used to study self-assembly in a hybrid system of isotropic particles (IPs), combined with anisotropic building blocks that represent special "designer particles." Those are modeled as spherical patchy particles (PPs) with binding only allowed between their patches and IPs. In this study, two types of PPs are considered: Octahedral PPs (Oh-PPs) and Square PPs (Sq-PPs), with octahedral and square arrangements of patches, respectively. The self-assembly is additionally facilitated by the simulated annealing procedure. The resultant structures are characterized by a combination of local correlations in cubatic ordering and a symmetry-specific variation of bond orientation order parameters (SymBOPs). By varying the PP/IP size ratio, we detected a sharp crossover between two distinct morphologies in both types of systems. High symmetry phases, NaCl crystal for Oh-PP and square lattice for Sq-PP, are observed for larger size ratios. For the smaller ones, the dominant morphologies are significantly different, e.g., Oh-PPs form a compact amorphous structure with predominantly face-to-face orientation of neighboring PPs. Unusually, for a morphology without a long-range order, it is still possible to identify well organized coherent clusters of this structure, thanks to the adoption of our SymBOP-based characterization.

Phenomenological theory in reentrant uranium-based superconductors

We develop a phenomenological theory for the family of uranium-based heavy fermion superconductors ($URhGe$, $UCoGe$, and $UTe_2$ ). The theory unifies the understanding of both superconductivity(SC) with a weak magnetic field and reentrant superconductivity(RSC) that appears at the first-order transition line with a high magnetic field. It is shown that the magnetizations along the easy and hard axis have opposite effects on superconductivity. The RSC is induced by the fluctuation parallel to the direction of the magnetic field. The theory makes specific predictions about the variation of triplet superconductivity order parameters $\vec{d}$ with applied external magnetic fields and the existence of a metastable state for the appearance of the RSC.

A generalized 2-DOF model for optimal design of MDOF structures controlled by Tuned Mass Damper Inerter (TMDI)

The paper illustrates a methodology to perform the optimal design of a Tuned Mass Damper Inerter (TMDI) equipped on a multi degree of freedom (MDOF) structure through a generalized model. The TMDI is considered in both configurations grounded and ungrounded. A generalized 2-DOF model is obtained: the primary oscillator, representing the original MDOF structure and the secondary oscillator, representing the control system. A Gaussian zero mean white noise random process is adopted for the excitation. The TMDI design is carried out adopting an energy objective function, maximized over the space of the design parameters which are: the mass and inertance ratios, the frequency ratio, the damping factor and a parameter that accounts for the TMDI location on the MDOF structure. Synthetic performance-based design maps of the TMDI parameters are carried out. It is shown that is possible to have different design configurations to achieve a target performance level. The maps furnish, as limit cases, the design of a Tuned Inerter Damper (TID) and a Tuned Mass Damper (TMD), when the mass or the inertance ratios are respectively assumed null. It is shown straightforwardly the regions of the design parameters where the inerter enhances the performances achievable by classical TMD. Furthermore, an analytical expression which links the optimal design variables necessary to obtain a desired target performance is proposed. Frequency response functions and modal parameters of certain 2-DOF models with optimally designed control system are reported and considerations on how the design parameters influence the system dynamics and the damping capabilities are highlighted. Comparisons of the TMDI optimally designed with cases of no control and same mass TMD are evidenced throughout the paper. Finally, the main responses of the primary structure and the TMDI are estimated in the space of variation of the design parameters in order to assess the effectiveness of the control system.

A theoretical study on chemical ordering of 38-atom trimetallic Pd–Ag–Pt nanoalloys

In this study, truncated octahedron (TO) structure is selected for further analysis and we focus on 38-atom Pd–Pt–Ag trimetallic nanoalloys. The best chemical ordering structures of PdnAg32 – nPt6 trimetallic nanoalloys are obtained at Gupta level. The structures with the lowest energy at Gupta level are then re-optimized by density functional theory (DFT) relaxations and DFT results confirm the Gupta level calculations with small shifts on bond lengths indicating TO structure is favorable for 38-atom of PdnAg32 – nPt6 trimetallic nanoalloys. The DFT excess energy analysis shows that Pd8Ag24Pt6 composition has the lowest excess energy value in common with excess energy analysis at Gupta level. In Pd8Ag24Pt6 composition, eight Pd atoms are central sites of 8 (111) hexagonal facets of TO, 24 Ag atoms locate on surface, and 6 Pt atoms locate at the core of the structure. It is also obtained that all of the compositions except Pd18Ag14Pt6 and Pd20Ag12Pt6 exhibit a octahedral Pt core. Besides, it is observed that there is a clear tendency for Ag atoms to segregate to the surface and also Pt atoms prefer to locate at core due to order parameter (R) variations.

Methylene blue removal by poly(acrylic acid)-grafted pineapple leaf fiber/polyester nonwoven fabric adsorbent and its comparison with removal by gamma or electron beam irradiation

This work aimed to synthesize poly(acrylic acid)-grafted pineapple leaf fiber/polyester nonwoven fabric (PPNWF-g-PAA) through radiation-induced graft polymerization. The synthesized PPNWF-g-PAAs were used as adsorbents for methylene blue (MB) adsorption in aqueous solution. The grafting was performed with a systematic variation of experimental parameters in order to produce PPNWF-g-PAA with a degree of grafting of at least 150%. Based on the results, the optimum experimental parameters were the following: irradiation with 2.0 MeV of energy, current of 12 mA, 30 kGy of absorbed dose, and grafting with 20% acrylic acid at 40 °C for 3 h. Results of the batch adsorption experiments revealed that PPNWF-g-PAA successfully adsorbed MB from aqueous solution with a contact time of about 3 h. The efficiency of MB adsorption was also compared with direct MB degradation through gamma or electron beam irradiation. Results of the irradiation experiments revealed that a minimum of 5 kGy was required in order to achieve complete removal of the MB molecules using direct irradiation which is lower than the absorbed dose requirement for the synthesis of PPNWF-g-PAA. However, the MB removal using the adsorbent does not generate degradation products unlike the MB removal using direct irradiation.

Energy Performance of a Kalina Cycle based CHP plant driven by low-enthalpy geothermal sources

The low-enthalpy geothermal sources can be efficiently exploited for heat and power cogeneration by using the KCS-34 Kalina cycle systems. The maximum power for given heat source temperature and cooling temperature is obtained for a certain value of the ammonia-water solution concentration and turbine exit pressure. The Cycle-Tempo simulation software is a very useful tool to investigate variation of some cycle parameters in order to obtain the maximum energy efficiency. In this paper the performance of a KCS-34 Kalina cycle based CHP plant is investigated to exploit a geothermal source with 120°C temperature present in North-West of Romania. It was found that by using the heat and power cogeneration the energy efficiency can be increased from 16.76% to 57.86% in winter and to 33.44% in summer.

Thermodynamic properties and phase diagrams of spin-1 quantum Ising systems with three-spin interactions

The spin-1 quantum Ising systems with three-spin interactions on two-dimensional triangular lattices are studied by mean-field method. The thermal variations of order parameters and phase diagrams are investigated in detail. The stable, metastable and unstable branches of the order parameters are obtained. According to the stable conditions at critical point, we find that the systems exhibit tricritical points. With crystal field and biquadratic interactions, the system has rich phase diagrams with single reentrant or double reentrant phase transitions for appropriate ranges of the both parameters.

Investigation into nonlinear phenomena for various railway vehicles in transition curves at velocities close to critical one

In this paper recent simulation results aimed at studying nonlinear phenomena that accompany motion of railway vehicle in transition curve at velocities around the vehicle critical velocity are presented by the authors. Such results concern six different objects representing railway vehicles. These are: three 2-axle railway bogies, two 2-axle railway cars, and 4-axle railway car. The paper attention is devoted to presenting as many different nonlinear behaviours of the studied objects as possible. This is done first of all to give an idea to the readers of great number of the nonlinear behaviour types that can appear for railway vehicles in transition curves at velocities lower and bigger than vehicle critical velocity. The differences arising from specificity of particular objects are highlighted while systematic variation of the system parameters in order to study influence of such variation on differences in the behaviour is less represented. The paper ends with the comprehensive comments by the authors to the results obtained.

Thermal elastohydrodynamic lubrication characteristics of double involute gears at the graded position of tooth waist

Abstract According to the meshing characteristics of double involute gears, a method for calculating its contact line length and equivalent curvature radius is proposed. Based on the EHL theory, established a thermal EHL calculation model for double involute gears at the graded position of tooth waist considering the characteristics of non-Newtonian fluid. The thermal EHL characteristics between the graded position of the tooth root and top are different. The variation of the tooth waist order parameters can influence the lubrication performance at the graded position of the tooth waist, and compared with the isothermal solutions, the influence of thermal effect on the EHL characteristics is unremarkable at this location.

Magnetic correlations in mixed valent layered La1.2Sr0.8CoO4

We present here investigations on a hole doped layered perovskite, La1.2Sr0.8CoO4. In these systems concentration of the holes in host matrix decides ratio of the Co2+/Co3+ and magnetic phase diagram. In addition, spin-state of the Co3+ ions has an important role in magnetic correlations. Magnetization measurements show the signature of some exotic phases like cluster glass or canonical spin-glass and ferromagnetic ordering (Tc ∼ 211 K). In addition, calculated temperature variation of order parameter by also including the spin-state variations of Co3+ manifests that the orbital magnetic moments are not quenched here and has an important role in overall magnetic moment at low temperatures.

Disorder correction to the Néel temperature of ruthenium-doped BaFe2As2 : Theoretical analysis

We analyze theoretically nuclear magnetic resonance data for the spin-density wave phase in the ruthenium-doped BaFe$_2$As$_2$. Since inhomogeneous distribution of Ru~atoms introduces disorder into the system, experimentally observable random spatial variations of the spin-density wave order parameter emerge. Using perturbation theory for the Landau functional, we estimate the disorder-induced correction to the N\'{e}el temperature for this material. Calculated correction is significantly smaller than the N\'{e}el temperature itself for all experimentally relevant doping levels. This implies that the N\'{e}el temperature is quite insensitive to the disorder created by the dopants.

Arduino based Agriculture Weather Monitoring and Security System using GPRSL

Smart farming is a way to do agriculture by precisely managing the inputs based on variation of field parameters in order to achieve optimized outputs at minimum disturbances to the environment. It is well known that climate is one of the most imperative field parameters that determine plant growth and its output. This is because each plant is susceptible to certain growing conditions such as air temperature, relative humidity, soil temperature, wind and light, etc. Therefore, it is vital for farmers to understand these climatic conditions of their farms. Many of the problems in managing farms to maximize productions while achieving environmental goals can be solved with appropriate information collected from the weather stations. Weather stations help to understand the interactive influence of climate and management factors on crop yield. The use of real-time weather monitoring system is one of the most effective ways to equip farmers with timely climatic information and knowledge for better crop management.

Decomposition of CH4 hydrate: effects of temperature and salt from molecular simulations

ABSTRACTWe report a molecular simulation study to investigate the decomposition of CH4 hydrate. The decomposition is revealed to be stepwise from the outer to inner layers. Upon decomposition, the number of 51262 cages drops faster than that of 512 cages. CH4 molecules are released, dissolved in water, then enter gas phase; meanwhile, CH4 bubbles may form particularly at a high temperature. Based on the variations of potential energy, order parameter, cage number and density profile of CH4 at different temperatures (300, 330, 345 and 360 K) and NaCl concentrations (0, 0.6 and 1.8 M), the effects of temperature and salt are comprehensively examined. With increasing temperature, the decomposition in pure water is accelerated, whereas two opposite effects are observed in NaCl solution. At 330 K, the decomposition is retarded at a higher NaCl concentration, as attributed to the reduced CH4 solubility in NaCl solution and the participation of ions in cage formation; at 360 K, however, the decomposition is accelerated when NaCl concentration increases due to bubble formation. This simulation study provides microscopic insights into hydrate decomposition, which might be useful towards the optimisation of operating conditions for CH4 production from CH4 hydrate.

Optical and X-ray studies of a four component cyano liquid crystal mixture: Comparison of properties with that of a similar mixture

Optical and X-ray studies have been conducted on a four component liquid crystal mixture (code name 2013) with cyano–end groups in all the four components and a lateral substitution of fluorine atom in one of them. The variations in the optical birefringence with temperature, have been investigated and the thermal dependence of polarisability anisotropy and orientational order parameter have been evaluated. X-ray studies have been conducted to determine the effective molecular characteristics such as apparent molecular length and inter molecular distance and their variations with temperature. From nature of molecular alignment as envisaged from X-ray photographs the order parameter variation with temperature has been determined and compared with macroscopic order parameter variation as determined from birefringence studies. The results have been compared with these obtained for another structurally similar four-component liquid crystal mixture (code name 2014) with isothiocyanato end group in place of cyano.

Macroscopic properties and their temperature dependence of the mesogen 4 cyano-4/-n-nonyl biphenyl as a function of temperature

ABSTRACTThe thermal dependence of optical and dielectric properties of one member namely 4 cyano-4/-n-nonyl biphenyl (code name 9CB) of the mesogenic homologous series of 4 cyano-4/-n-alkyl biphenyl (nCBs) is reported. The variation of orientational order parameter with temperature is determined and comparison made with theoretical Maier–Saupe values as well as the order parameter values of the other member of the series. The effect of temperature on the effective molecular dipole moment μ and the angle of inclination β of the dipole axis with the preferred direction are investigated.

Direct Measurements of Field-Dependent Ordering in a Low-Field Vortex Glass State

The variation of topological defect density and hexatic order parameter were measured over a range of micro-Tesla fields in a 2-D superconducting vortex glass. This was achieved through scanning SQUID microscopy of the vortex distribution in YBa2Cu3O7-δ thin films under field-cooled conditions. It was discovered that, although the defect density decreased for increasing magnetic fields, giving the impression of a more lattice-like vortex distribution, the hexatic order parameter also decreased, showing that the distribution was less orientationally ordered.

Monte Carlo simulations of dynamic phase transitions in ferromagnetic thin-films

By means of detailed Monte Carlo (MC) simulations, we have presented dynamic phase transition (DPT) properties of ferromagnetic thin-films. Thermal variations of surface, bulk and total dynamical order parameters (DOP) for a film and total order parameter for the films with different thicknesses have been examined. Opposite regimes of reduced exchange interaction (surface to bulk ratio values in R<Rc and R>Rc regimes where Rc is the critical value at which the critical temperature becomes independent of film thickness L) have also been taken into consideration. The average magnetizations with varying temperature of each layer are reversed in these two regimes. Based on the results, we have confirmed that the system represents a crossover behavior between ordinary and extraordinary transition in the presence of surface exchange enhancement.

Dynamic magnetic properties in the kinetic Ising ferromagnet on triangular lattice within the effective-field theory and using Glauber-type stochastic dynamics

Dynamic magnetic properties in the kinetic Ising ferromagnet on a triangular lattice are studied within the effective-field theory with correlations and using Glauber-type stochastic dynamics. In particular, we investigate the time variations of average order parameters and thermal behaviors of the dynamic total magnetizations and present the dynamic phase diagrams. The tricritical point, the triple point and zero critical end point as well as reentrant behaviors are found in the dynamic phase diagrams. We also study the dynamic hysteresis behaviors of the system. When the hysteresis behaviors of the system are examined, single hysteresis loop as well as S-shaped thin loops and elliptical shapes are observed for various values of the physical parameters. Results are compared with some other dynamic studies and quantitatively good agreement is found.