Discontinuous Phase Research Articles

Influence of Machining Parameter on Tool Life While Machining Hybrid Metal Matrix Composites

A metal matrix composite constitutes a continuous metallic matrix and a discontinuous phase known as reinforcement. The hybrid metal matrix composites (Hmmcs) have been used to manufacture drive shafts, disc brake rotors, brake drums, connecting rods pistons, engine block cylinder liners for automotive and rail vehicle applications. The Hmmcs castings of diameter 120 mm and length 300 mm were prepared through sand mould technique following stir casting methodology. The cast components further subjected to evaluation of physical properties and machining tests using two grades of coated inserts and PCD inserts. The experiments were carried out following ISO 3685 standards. The coating thickness of the TiN coated and TiAlN coated inserts were measured using Kalo testing method; the results of the test show that the interface of the substrate and coating was free from the porosity, and the coating thickness of TiN coating was 4.84 microns and TiAlN coating was measured 4.6 microns. The results of the experiments show that performance of the PCD insert was better than coated inserts at 0.1 mm/rev feed; however at 0.2 mm/revolution feed PCD insert failed by micro chipping of cutting edge while machining Hmmcs. When TiAlN coated inserts were used to machine Hmmcs the coated inserts failed by gradual wear and BUE formation.

Nonlinear q-voter model from the quenched perspective

We compare two versions of the nonlinear q-voter model: the original one, with annealed randomness, and the modified one, with quenched randomness. In the original model, each voter changes its opinion with a certain probability ϵ if the group of influence is not unanimous. In contrast, the modified version introduces two types of voters that act in a deterministic way in the case of disagreement in the influence group: the fraction ϵ of voters always change their current opinion, whereas the rest of them always maintain it. Although both concepts of randomness lead to the same average number of opinion changes in the system on the microscopic level, they cause qualitatively distinct results on the macroscopic level. We focus on the mean-field description of these models. Our approach relies on the stability analysis by the linearization technique developed within dynamical system theory. This approach allows us to derive complete, exact phase diagrams for both models. The results obtained in this paper indicate that quenched randomness promotes continuous phase transitions to a greater extent, whereas annealed randomness favors discontinuous ones. The quenched model also creates combinations of continuous and discontinuous phase transitions unobserved in the annealed model, in which the up–down symmetry may be spontaneously broken inside or outside the hysteresis loop. The analytical results are confirmed by Monte Carlo simulations carried out on a complete graph.

Hot-tearing susceptibilities of Al-4.5Cu nanocomposites fabricated by semi-solid stirring combined with ultrasonic cavitation

ABSTRACTSiC/Al-4.5Cu and SiO2/Al-4.5Cu nanocomposites were fabricated by semi-solid stirring combined with ultrasonic cavitation and their hot-tearing resistance during casting investigated. The hot-tearing susceptibilities of Al-4.5Cu alloy and its nanocomposites were studied using a constrained rod casting steel mould. The results showed that the extent of hot tearing in the Al-4.5Cu alloys is greatly reduced by the addition of 1 wt% SiC or 1 wt% SiO2 nanoparticles. Microstructural analysis suggested that SiC and SiO2 nanocomposites refined the θ-Al2Cu phases and α-Al dendrites and lead to discontinuous Al2Cu phases along the grain boundaries in the Al-4.5Cu alloys during solidification, which leads to an enhancement on the hot-tearing resistance of Al-4.5Cu to a considerable degree. Moreover, SiO2 nanoparticles have a remarkable effect on the microstructure refinement of the Al-4.5Cu alloys.

Influence of Capillary Number on the droplet Shape, Film Thickness, and Pressure Drop in a Liquid-Liquid Taylor Flow inside a Microcapillary

Numerical analysis of a two-dimensional, axisymmetric, incompressible, laminar liquid-liquid Taylor flow inside a vertical circular microchannel is carried out in the present study. The focus is laid on fluid flow characteristics in the slug flow regime. Although many researchers have performed numerical and experimental studies of two-phase flows in narrow channels, their efforts seem to have been fairly successful in explaining the underlying mechanisms of fluid flow phenomena, especially for slug flow regime. Here, an attempt has been made to explore the hydrodynamics of such flows. In the present study, dodecane and Pd5 have been used as the carrier phases and water is used as the discontinuous phase. The internal diameter of the circular microchannel is 1.5 mm with its wall being insulated. The flow and volume fraction equations are solved by the finite volume approach (FVM). The volume of fluid (VOF) method has been adopted for capturing the interface. The effect of Capillary number on film thickness and interfacial pressure drop is explained. The film thickness is found to increase with Capillary number and is also found to be in a close match with the models available in the literature. The pressure drop per unit length obtained from the CFD study is compared with a standard model available in the literature. The pressure drop across the unit cell is found to be following the phenomenological model. It is observed that the pressure drop at the interface has the highest contribution to the total pressure drop in contrast to the other pressure drops in the channel, with ~50-55% in dodecane-water and ~55-62% in Pd5-water systems. Besides, the distribution of the velocity, axial, and wall pressure fields inside the microcapillary are also discussed.

Influence of quenched disorder on discontinuous absorbing phase transition

Influence of quenched disorder on critical behavior of the deterministic conserved threshold transfer process (DCTTP) was investigated. DCTTP is a variant of the conserved threshold transfer process modified such that active-particle hopping is deterministic and has been reported to exhibit discontinuous phase transition (Lee and Lee 2009 Phys. Rev. E 80 011106) in all considered dimensions, i.e. one, two, and four dimensions. Two disorder types were considered. First, while particle hopping on ordered sites is deterministic, hopping on disordered sites is subject to be stochastic, i.e. active particles on disordered sites hop to randomly selected neighboring sites. Second, disorder is assumed to be random dilution of lattice sites, i.e. particles cannot occupy disordered sites. The order parameter was found to be continuous for disorder of stochastic hopping, i.e. the first-order transition was rounded to the second-order transition for any small amount of disorder, whereas the transition remained first order but the critical exponent associated with the power law decrease of active-site densities varied for considerable amount of lattice site dilution. These results are consistent with predictions established for equilibrium n-vector spin systems.

Thermomagnetic Behavior of a Ferrimagnet of High Spins: Monte Carlo Analysis

We investigate some critical phenomena of a Ising ferrimagnetic system on a square lattice with spins $Q=\pm 7/2, \pm 5/2, \pm 3/2$ , and ±1/2 in a $B$ sublattice and spins $S=\pm 5/2, \pm 3/2$ , and ±1/2 in a $A$ sublattice in presence of an $h'$ external magnetic field, such that $Q$ and $S$ are the nearest-neighbors ferrimagnetically coupled. Using Monte Carlo simulations, we calculate the finite-temperature phase diagrams of magnetization, specific heat, and magnetic susceptibility of the model. The system is defined by a Hamiltonian $(\mathcal {H})$ that contains ferromagnetic next-nearest-neighbors interactions between $S$ spins ( $J'_{2}$ ), as well as external magnetic field and anisotropy interactions at each point of lattice. For a defined range of parameters in $\mathcal {H}$ , the system exhibits discontinuities in their physical variables and spin compensation behaviors. In the planes $J'_{2}-k_{\mathrm{ B}}T'$ and $h'-k_{\mathrm{ B}}T'$ , we analyze the relationship between the critical, compensation, and discontinuous phase transition temperatures with the external magnetic field and the next-nearest-neighbors interaction between $S$ spins. We found that the existence of discontinuous phase transition depends on the strengths of $h'$ and $J'_{2}$ .

Universal and nonuniversal neural dynamics on small world connectomes: A finite-size scaling analysis.

Evidence of critical dynamics has been found recently in both experiments and models of large-scale brain dynamics. The understanding of the nature and features of such a critical regime is hampered by the relatively small size of the available connectome, which prevents, among other things, the determination of its associated universality class. To circumvent that, here we study a neural model defined on a class of small-world networks that share some topological features with the human connectome. We find that varying the topological parameters can give rise to a scale-invariant behavior either belonging to the mean-field percolation universality class or having nonuniversal critical exponents. In addition, we find certain regions of the topological parameter space where the system presents a discontinuous, i.e., noncritical, dynamical phase transition into a percolated state. Overall, these results shed light on the interplay of dynamical and topological roots of the complex brain dynamics.

Condensed matter physics, hybrid energy and entropy principles, and the hybrid first and second laws of thermodynamics

In this paper, we develop an energy-based, large-scale hybrid dynamical system model to present a generic framework for hybrid thermodynamics involving hybrid energy and entropy conservation and nonconservation principles. Specifically, using a hybrid compartmental dynamical system energy flow model we develop a hybrid state-space dynamical system formalism for addressing critical phenomena and discontinuous phase transitions in thermodynamics and provide hybrid extensions to the first and second laws of thermodynamics. In addition, using Lyapunov stability theory for impulsive differential equations, we show that our hybrid large-scale thermodynamic energy flow model has convergent trajectories to Lyapunov stable equilibria determined by the system initial subsystem energies. Moreover, we show that the steady-state distribution of the hybrid large-scale system energies is uniformly distributed over all of the subsystems, leading to system energy equipartitioning corresponding to a maximum entropy equilibrium state.

On the order of the phase transition in the spin-1 Baxter–Wu model

In this work we investigate the order of the phase transition of the spin-1 Baxter–Wu model. We used extensive entropic simulations to describe the behavior of quantities which reveal the order of the phase transition. We applied finite-size scaling laws for continuous and discontinuous phase transitions. Our results show that this system exhibits an indeterminacy regarding the order of the phase transition, i.e., the results are conclusive for both transitions, whether continuous or discontinuous. In such a scenario we carried out a study of the configurations in the region of the phase transition, which confirmed that the model seems to undergo a tetracritical transition, with the coexistence of a ferromagnetic and three ferrimagnetic configurations, suggesting that it may be a multicritical point, where the continuous and the discontinuous phase transitions may coexist reflecting different features of the system. We propose a new way of carrying out the entropic simulations where two densities of states are generated simultaneously, for the ferro- and the ferrimagnetic states. The behavior of the energy probability distribution, the inverse temperature, and the magnetizations for each state confirms the coexistence of the discontinuous and the continuous phase transitions.

Effects of setting temperatures in the parallel tempering Monte Carlo algorithm.

Parallel tempering Monte Carlo has proven to be an efficient method in optimization and sampling applications. Having an optimized temperature set enhances the efficiency of the algorithm through more-frequent replica visits to the temperature limits. The approaches for finding an optimal temperature set can be divided into two main categories. The methods of the first category distribute the replicas such that the swapping ratio between neighboring replicas is constant and independent of the temperature values. The second-category techniques including the feedback-optimized method, on the other hand, aim for a temperature distribution that has higher density at simulation bottlenecks, resulting in temperature-dependent replica-exchange probabilities. In this paper, we compare the performance of various temperature setting methods on both sparse and fully connected spin-glass problems as well as fully connected Wishart problems that have planted solutions. These include two classes of problems that have either continuous or discontinuous phase transitions in the order parameter. Our results demonstrate that there is no performance advantage for the methods that promote nonuniform swapping probabilities on spin-glass problems where the order parameter has a smooth transition between phases at the critical temperature. However, on Wishart problems that have a first-order phase transition at low temperatures, the feedback-optimized method exhibits a time-to-solution speedup of at least a factor of two over the other approaches.

Permeability jail for two-phase flow in tight sandstones: Formulation, application and sensitivity studies

Permeability jails in tight rocks correspond to saturation values where no phase is mobile. This can lead to severe impacts on hydrocarbon production. However, although this is a severe and significant problem, there is a limited understanding of the mechanisms behind the concept of a permeability jail, its dependence on pore size distributions, saturations and pressure. In a previous work, we describe a model to compute the flow resistance during two-phase flow in tight rocks. In this paper, we extend our work to propose a model for the permeability jail in tight rocks to calculate relative permeabilities during two-phase flow. The rock is assumed to be characterized by a bundle of capillary tubes with non-uniform radii where the fluids are present as discontinuous phases. The pore-scale flow resistance is calculated which takes into account the capillary pressure induced by the Jamin effect as well as the water and gas viscous forces. The model is validated by experimental data of gas-water relative permeability tests and Nuclear Magnetic Resonance (NMR) experiments on tight cores from the Sichuan Basin in Southwest China. According to the model, the pressure drop between the inlet and outlet sides of the core should be higher than the maximum capillary pressure to maintain flow during the experiments. We also observe that the relative permeability curves are pressure-sensitive. An increase in the pressure drop leads to a reduction of gas relative permeability and an increase of water relative permeability. However, the influence of this pressure drop is somewhat limited. Once trapped in a permeability jail, fluids generally cannot regain flow capability by changing the pressure drop over a small range of values. This necessitates a careful consideration of the factors contributing to the permeability jail in order to avoid loss of well productivity.

Micro-mechanism analysis of enhanced oil recovery for positive-negative drive

The positive and negative displacement field experiments have achieved good yield increase. The existing researches mainly focus on the microscopic mechanism site and reservoir non-homogeneity. At present, there is no relevant research on the change of crude oil state, quantitative statistical analysis and stimulation mechanism caused by positive and negative displacement in core scale.In this research, the core is subjected to positive and negative displacement and then imaged by quasi-real-time CT scan. The pore network model software is used to quantitatively analyze the oil-water distribution information at different moments in the core. Furthermore, the characteristics of reservoir pores, oil and water occurrence characteristics, positive and negative displacement increased mechanisms and seepage characteristics are clarified.From the study, it is observed that during the whole water flooding process, the volume fraction of the cluster flow gradually decreases. The cluster flow is continuously displaced or broken into other discontinuous phase flow states; multi-porous, columnar, droplet, membranous as a discontinuous phase. The volume percentage increases with the progress of the displacement process, and the increase of multi-porous flow is most obvious during the reverse drive process. The significant reduction of cluster flow during the anti-drive process is the main mechanism for anti-drive production.

Spin‐to‐Orbital Angular Momentum Conversion with Quasi‐Continuous Spatial Phase Response

AbstractVortex beams carrying orbital angular momentum have captivated great interest in the past few decades due to the inspiring application potential in both optical and microwave fields. More recently, assisted by Pancharatnam–Berry (PB) phase‐based meta‐atom, achieving spin–orbit‐converter becomes an encouraging topic. Commonly, however, spin–orbital‐converters are based on discontinuous phase distribution, which inevitably deteriorates their overall performance. To overcome this difficulty, here a paradigm of spin–orbital‐converter made of spirally arranged metastrip that can produce quasi‐continuously rotated phase profile with high‐efficiency is simulated and experimentally demonstrated in microwave regime. Using dispersion engineering, a meta‐atom capable of exciting spoof surface plasmon polaritons mode is designed to achieve PB phases. The metastrip consisting of a series of identical meta‐atoms is arranged along a proposed Archimedean spiral to obtain the rotated phase distribution of 4π. Near‐field performances reveal that the vortex electric distribution with topological charges of l = ± 2 can be generated. Significantly, this effort provides a strategy of achieving spin‐to‐orbital angular momentum conversion with phase continuity that may find applications in the fields of holography and communication systems.

Unification of multiple classes of explosive percolation

Percolation, characterizing the emergence of large-scale connectivity from a great number of isolated nodes, can generate continuous, multiple discontinuous and discontinuous phase transitions, which correspond to different physical processes, respectively. In this paper, we found a percolation model which unifies all the three types of phase transitions with a continuously tunable parameter α. When decreasing α from 1 to 0, the type of phase transition transfers from continuous to multiple discontinuous, and finally the percolation process exhibits a single discontinuity lacking a supercritical region. By carefully examining the evolving characteristic of the clusters, it is verified that the transition value of α is between 0.75 and 0.7 for the phase transition from continuous to multiple discontinuous, and the distinctly different behaviors of the relative variance of the order parameter at and confirm the result. On the other hand, the transition value of α is 0.5 at which the type of phase transition changes from multiple discontinuous to discontinuous. These results may be helpful in understanding the physical mechanisms behind various percolation transition processes.

Water-in-Water Emulsion as a New Approach to Produce Mesalamine-Loaded Xylan-Based Microparticles

The water-in-water emulsion method has been reported as a technique able to prepare microparticles without using harmful solvents. However, there are few reports showing the encapsulation of small molecules into microparticles produced within this technique. The probable reason relays on the rapid diffusion of these molecules from the discontinuous phase to the continuous phase. In the present study, xylan microparticles containing mesalamine were produced and the doubled crosslinking approach, used to promote higher encapsulation rates, was disclosed. To achieve this goal, a 23 full factorial design was carried out. The results revealed that all formulations presented spherical-shaped microparticles. However, at specific conditions, only few formulations reached up to 50% of drug loading. In addition, the new xylan-based microparticles formulation retained almost 40% of its drug content after 12 h of a dissolution assay likely due to the degree of crosslinking. Thus, the doubled crosslinking approach used was effective on the encapsulation of mesalamine and may pave the way to successfully produce other polysaccharide-based carriers for clinical use.

Discontinuous phase transition in chemotactic aggregation with density-dependent pressure.

Many small organisms such as bacteria can attract each other by depositing chemical attractants. At the same time, they exert repulsive force on each other when crowded, which can be modeled by effective pressure as an increasing function of the organisms' density. As the chemical attraction becomes strong compared to the effective pressure, the system will undergo a phase transition from homogeneous distribution to aggregation. In this work, we describe the interplay of organisms and chemicals on a two-dimensional disk with a set of partial differential equations of the Patlak-Keller-Segel type. By analyzing its Lyapunov functional, we show that the aggregation transition occurs discontinuously, forming an aggregate near the boundary of the disk. The result can be interpreted within a thermodynamic framework by identifying the Lyapunov functional with free energy.

Triethylphosphine as a molecular gear – phase transitions in ferrocenyl–acetylide–gold(I)

A sequence of two discontinuous phase transitions, occurring just above 125 K and 148 K, has been observed for a ferrocenyl–acetylide–gold(I) complex with triethylphosphine, structure (1), by means of a multi-temperature single-crystal X-ray diffraction technique. Three distinct phases have been identified. The high-temperature α and low-temperature γ phases share the same space group Pbca, whereas the intermediate β phase is in the Pb21a subgroup of Pbca. In all phases molecules of (1) form well defined double layers, with PEt3 groups interlocking in planes perpendicular to c. On the molecular level, both phase transitions involve almost uniquely a conformational change of triethylphosphine: a gear-like rotation around the P—Au axis and concerted flips of the ethyl moieties. The mechanism of these transitions may be imagined as initiated by a rotation of a single PEt3 group in a double layer (a single gear movement), followed by adjacent phosphines adjusting their conformations as a result of steric strain. The structural changes underlying phase transitions are sequential, occurring layer-wise, the γ→β transition involving approximately every other layer in the crystal lattice, the β→α yielding a total conformation change. The sequence of phase transitions results in a noticeable contraction of the crystal cell volume.

A Numerical Study of Initiation and Migration of Trapped Oil in Capillaries with Noncircular Cross Sections

To clarify the initiation and migration mechanisms of a discontinuous oil phase in pores, a numerical study was performed to interpret the starting phenomenon and flowing rules of oil trapped in capillaries that have noncircular cross sections. In this study, capillaries with three different cross sections were used to investigate the deformation law of oil and the pressure drop across these microchannels at different displacement velocities by computational fluid dynamics (CFD). The geometrical structure of the microchannels was precisely controlled, and the migration process of the oil, which is too small to be observed by direct experimentation, was assessed and quantitatively analyzed. By analyzing the shape of the trapped oil after reaching a steady state at different velocities, the nonstart and start conditions could be distinguished and the accuracy of the numerical method was verified by a comparison with an analytical method (the MS-P method). Two aspects of oil migration in noncircular microchannels were observed in combination with previous studies: there is a driving force on the cross section of the oil drop and a viscous force at the oil-water interface in the corners, and the more irregular the pore section is, the more easily the trapped oil will migrate. Additionally, the influence of the microchannel cross-sectional shape on the non-Darcy flow of a discontinuous oil phase was clarified. It can be concluded that the presence of the non-Darcy flow in pores arises because trapped oil, as a discontinuous phase, cannot be separated from the capillary wall without reaching critical velocity.

Cascading failures on interdependent networks with star dependent links

In this paper, we propose a cascading failure model with star interdependent links. To describe the model theoretically, a generalized percolation theory is developed. Through extensive numerical simulations and theoretical analyses, we study the phase transition of the system on artificial networks. On both ER-ER and SF-SF networks, the system exhibits a continuous (discontinuous) phase transition for small (large) fraction of service nodes. On ER-ER networks, the more service links of a service node, the system is more likely to exhibit a discontinuous phase transition. On SF-SF networks, the service links of a service node cannot alter the phase of the system. Our suggested theory agrees well with the numerical simulations.

Order-disorder transition in a two-dimensional associating lattice gas.

We study an associating lattice gas (ALG) using Monte Carlo simulation on the triangular lattice and semianalytical solutions on Husimi lattices. In this model, the molecules have an orientational degree of freedom and the interactions depend on the relative orientations of nearest-neighbor molecules, mimicking the formation of hydrogen bonds. We focus on the transition between the high-density liquid (HDL) phase and the isotropic phase in the limit of full occupancy, corresponding to chemical potential μ→∞, which has not yet been studied systematically. Simulations yield a continuous phase transition at τ_{c}=k_{B}T_{c}/γ=0.4763(1) (where -γ is the bond energy) between the low-temperature HDL phase, with a nonvanishing mean orientation of the molecules, and the high-temperature isotropic phase. Results for critical exponents and the Binder cumulant indicate that the transition belongs to the three-state Potts model universality class, even though the ALG Hamiltonian does not have the full permutation symmetry of the Potts model. In contrast with simulation, the Husimi lattice analyses furnish a discontinuous phase transition, characterized by a discontinuity of the nematic order parameter. The transition temperatures (τ_{c}=0.51403 and 0.51207 for trees built with triangles and hexagons, respectively) are slightly higher than that found via simulation. Since the Husimi lattice studies show that the ALG phase diagram features a discontinuous isotropic-HDL line for finite μ, three possible scenarios arise for the triangular lattice. The first is that in the limit μ→∞ the first-order line ends in a critical point; the second is a change in the nature of the transition at some finite chemical potential; the third is that the entire line is one of continuous phase transitions. Results from other ALG models and the fact that mean-field approximations show a discontinuous phase transition for the three-state Potts model (known to possess a continuous transition) lends some weight to the third alternative.