Boundary Regime Research Articles

Unused Potential of the Far East Border Areas

The priority trend of the modern regional policy is searching for resources and opportunities of the regional self-development. In the border regions, these opportunities are determined by location, which has a huge potential associated with the possibilities of foreign economic cooperation. Despite the Federal authorities active policy to integrate the Far East into the Asia-Pacific region, as well as the expansion of regional autonomy within the framework of the policy of“new regionalism” in most cases, the development of border regions is traditionally considered from geopolitical points of view, and in this regard, economic and social efficiency is secondary. The object of this research is municipalities of the Amur region, which have a boundary with China. The paper assesses the differentiation of the border municipalities’ development. It is revealed that the core of foreign economic cooperation is the regional center, which concentrated the existing infrastructure. The hypothesis of this research is that the factors hindering the utilization of the contact areas potential are the insufficient level of infrastructure, non-compliance of border checkpoints with modern requirements, as well as the current boundary regime. The purpose of this research is to identify the perspective direction and a framework of the border areas potential development and using . As part of this research, the authors propose an algorithm for attracting private investors to the border infrastructure development using the public-private partnership.

On alpha-particle transport in inertial fusion

Analytical theory and models of inertial fusion implosion use parameterized microphysics models. In this paper, we consider the DT alpha-particle transport, and report new parameterizations of the range, heating efficacy, and energy partition using modern stopping-power theory. Our resulting heating efficacy is lower than previously published results, which reduces the temperature and pressure generated by a dynamic implosion hot-spot evolution model, and shifts the burning-plasma regime boundary slightly farther from current experimental results.

Friction-induced vibration in a two-mass damped system

A two degree of freedom mass-spring-damper model on a moving lubricated belt is considered in this paper. The motions of the two masses are coupled through spring and damper and each mass interacts with a moving lubricated belt. The friction model includes the boundary, mixed and hydrodynamic regimes of lubrication contact regimes. Friction coefficient is presented as a function of sliding velocity at each mass interface that includes a combination of linear, exponential and cubic functions to account for relatively large coefficient at low sliding speed, followed by Stribeck effect at low to moderate speed ranges and finally a full hydrodynamic lubrication regime. A set of dimensionless parameters is introduced and system's dynamic response behavior as well as stability are studied for various combination of parameters. The results show that the unstable system response can be quasiperiodic, or periodic in the form of limit cycles away from the origin when the sliding velocity is relatively small. Triple and double periodic behavior is observed in addition to other responses when mass suspended to the ground is larger than the second mass. All responses become asymptotically stable when dimensionless sliding velocity threshold is exceeded. Finally, for a qualitative analysis, the method of averaging is used to solve the nonlinear coupled equations of motion in order to find the amplitude and frequency of steady-state vibration. A comparison between the numerical results from direct time integration and analytical findings shows that approximate solution is acceptable.

Mechanisms of Calcium Leak from Cardiac Sarcoplasmic Reticulum Revealed by Statistical Mechanics

Heart muscle contraction is normally activated by a synchronized Ca release from sarcoplasmic reticulum (SR), a major intracellular Ca store. However, under abnormal conditions, Ca leaks from the SR, decreasing heart contraction amplitude and increasing risk of life-threatening arrhythmia. The mechanisms and regimes of SR operation generating the abnormal Ca leak remain unclear. Here, we employed both numerical and analytical modeling to get mechanistic insights into the emergent Ca leak phenomenon. Our numerical simulations using a detailed realistic model of the Ca release unit reveal sharp transitions resulting in Ca leak. The emergence of leak is closely mapped mathematically to the Ising model from statistical mechanics. The system steady-state behavior is determined by two aggregate parameters: the analogs of magnetic field (h) and the inverse temperature (β) in the Ising model, for which we have explicit formulas in terms of SR [Ca] and release channel opening and closing rates. The classification of leak regimes takes the shape of a phase β-h diagram, with the regime boundaries occurring at h = 0 and a critical value of β (β∗) that we estimate using a classical Ising model and mean field theory. Our theory predicts that a synchronized Ca leak will occur when h > 0 and β >β∗, and a disordered leak occurs when β <β∗ and h is not too negative. The disorder leak is distinguished from synchronized leak (in long-lasting sparks) by larger Peierls contour lengths, an output parameter reflecting degree of disorder. Thus, in addition to our detailed numerical model approach, we also offer an instantaneous computational tool using analytical formulas of the Ising model for respective ryanodine receptor parameters and SR Ca load that describe and classify phase transitions and leak emergence.

The effect of dilution on the diffusive-thermal instability of the rich premixed hydrogen deflagration

The study focuses on the dynamics of rich premixed diluted hydrogen-oxygen flames. The problem of unsteady flame propagation is treated numerically within a 1D framework with a detailed model for the chemical kinetics and mixture averaged molecular diffusion. The effect of mixture dilution on the onset of the diffusive-thermal pulsating instabilities of freely propagating flames is investigated by studying the characteristics of the pulsating instabilities e.g. critical pressure of the onset, period and amplitude of pulsations. The dilution with helium, nitrogen and argon shows quantitatively a similar effect on the flame instability: namely, the critical pressure for the onset of oscillations is essentially reduced, while the period of oscillations increases. It is also shown that the neutral stability boundary is affected to a leading order through the reduction of the adiabatic flame temperature rather than by modification of the species molecular diffusion. The observed reduction of the critical pressure for the onset of oscillations and the sensitivity of the stability boundary of a steady flame propagation regime to the thermo-chemical system parameters open new perspectives for additional experimental validation of mechanisms of chemical kinetics.

Self-similar solutions of kinetic-type equations: The boundary case

For a time dependent family of probability measures (ρt)t⩾0 we consider a kinetic-type evolution equation ∂ϕt∕∂t+ϕt=Q̂ϕt where Q̂ is a smoothing transform and ϕt is the Fourier–Stieltjes transform of ρt. Assuming that the initial measure ρ0 belongs to the domain of attraction of a stable law, we describe asymptotic properties of ρt, as t→∞. We consider the boundary regime when the standard normalization leads to a degenerate limit and find an appropriate scaling ensuring a non-degenerate self-similar limit. Our approach is based on a probabilistic representation of probability measures (ρt)t⩾0 that refines the corresponding construction proposed in Bassetti and Ladelli, (2012).

Photocarrier transport dynamics in lifetime and relaxation regimes of semiconductors

Understanding photogenerated carrier transport dynamics is important for optimizing the performance of various semiconductor optoelectronic devices, such as photocatalysts, solar cells, and radiation detectors. In this paper, the spatiotemporal evolution of photogenerated carriers after excitation is investigated both analytically and numerically, in order to reveal the origin of two contradictory photocarrier motion directions, i.e., separation and ambipolar transport in the semiconductors. An analytical solution of the separation distance between mean positions of photogenerated electrons and holes is derived, which shows that photocarriers will transport ambipolarly in the lifetime regime, where the carrier lifetime τ0 is larger than the dielectric relaxation time τd, and separate spontaneously in the relaxation regime, where τ0&amp;lt;τd. Numerical simulation verifies the analytical results and reveals rich dynamics of carrier transport near the boundary of two regimes. In the lifetime regime, the separation distance rises asymptotically to a polarization distance, while there is a transitional sub-region near the regime boundary where majority carriers go through a separating-ambipolar transformation dynamics. This phenomenon originates from two different components of the drift current. In the relaxation regime, majority carriers deplete because of a larger recombination rate in the minority carrier pulse region. Combining the analytical and numerical results, detailed photocarrier transport dynamics are obtained in the lifetime and relaxation regimes of semiconductors.

Slug flow hydrodynamics of immiscible fluids within a rectangular microchannel towards size-controllable fabrication of dextran-based cryogel beads

Cryogel beads are novel adsorbents with potential applications in biotechnology, environmental and tissue engineering. However, the controllable preparation of cryogel beads with expected small and uniform diameters is a challenging work. The micro-flow-focusing method combining with the cryo-polymerization has been suggested as a new approach for the fabrication of cryogel beads. In order to form the uniform droplet, the slug flow is generated in the microchannel, so the slug flow hydrodynamics are crucial and fundamental for this process. In the present work, the dextran-methacrylate (Dex-MA-PEGDA) solution and ethyl acetate containing surfactant of Span 80 were used as the aqueous phase and the water-immiscible, respectively. The fabrication of dextran-based cryogel beads and the slug flow hydrodynamics in a rectangular microchannel were investigated experimentally. The flow regime map was proposed and the typical regime boundaries were measured and correlated, and the formation mechanisms of slugs were also discussed. The regime boundaries were correlated by Weber number and Capillary number, i.e., Weo = 58.16Caw0.92 for the boundary between the annular and the slug flow, and Weo = 4.12Caw0.09 for the slug and the bubbly flow, respectively. Several crucial parameters of the droplets generated by the slug flow, i.e., the aqueous slug length, the aqueous slug velocity and the aqueous droplet size, were measured and correlated. The Dex-MA-PEGDA cryogel beads were prepared successfully under different conditions and their diameters were correlated to the sizes of the droplets. Eventually, the uniform size distributions and supermacroporous microstructures of dextran-based cryogel beads were demonstrated.

Penetration of boundary-driven flows into a rotating spherical thermally stratified fluid

Motivated by the dynamics within terrestrial bodies, we consider a rotating, strongly thermally stratified fluid within a spherical shell subject to a prescribed laterally inhomogeneous heat-flux condition at the outer boundary. Using a numerical model, we explore a broad range of three key dimensionless numbers: a thermal stratification parameter (the relative size of boundary temperature gradients to imposed vertical temperature gradients), $10^{-3}\leqslant S\leqslant 10^{4}$, a buoyancy parameter (the strength of applied boundary heat-flux anomalies), $10^{-2}\leqslant B\leqslant 10^{6}$, and the Ekman number (ratio of viscous to Coriolis forces), $10^{-6}\leqslant E\leqslant 10^{-4}$. We find both steady and time-dependent solutions and delineate the regime boundaries. We focus on steady-state solutions, for which a clear transition is found between a low $S$ regime, in which buoyancy dominates the dynamics, and a high $S$ regime, in which stratification dominates. For the low-$S$ regime, we find that the characteristic flow speed scales as $B^{2/3}$, whereas for high-$S$, the radial and horizontal velocities scale respectively as $u_{r}\sim S^{-1}$, $u_{h}\sim S^{-3/4}B^{1/4}$ and are confined within a thin layer of depth $(SB)^{-1/4}$ at the outer edge of the domain. For the Earth, if lower mantle heterogeneous structure is due principally to chemical anomalies, we estimate that the core is in the high-$S$ regime and steady flows arising from strong outer boundary thermal anomalies cannot penetrate the stable layer. However, if the mantle heterogeneities are due to thermal anomalies and the heat-flux variation is large, the core will be in a low-$S$ regime in which the stable layer is likely penetrated by boundary-driven flows.

Numerical Analysis on Boundary and Flow Regime of Magnetic Fluid in the Sealing Clearance With a Rotation Shaft

The magnetic fluid seal is one of the best known and widely used technical applications of magnetic fluid. However, the boundary and the flow regime with the rotation shaft cannot be observed by the experiment method. This paper presents a novel numerical simulation method to obtain the boundary and the velocity of the fluid in seals. The magnetic field of the seal is solved by the finite-element method, and the Navier–Stokes equations of the magnetic fluid based on the influence of magnetic force are solved by the finite-volume method. The two-phase flow is solved by the volume of fluid method. The seal capacities of the rectangle tooth and the trapezoid tooth with different rotation velocities are obtained. The result shows that the seal capacity decreases with the increase in the rotation velocity.

A new model for the bouncing regime boundary in binary droplet collisions

This work experimentally investigates binary collisions of identical droplets over a range of liquid viscosities, using 2%, 4%, and 8% of hydroxypropyl methylcellulose solutions in water. The collisions were captured by using a high-speed camera, and regime maps of collision outcomes were derived. The performance of existing models of the boundary of the bouncing regime was assessed and found to give poor predictions. This was attributed to assumptions and errors in the treatment of kinetic energy and the droplet shape factors used in these models. A new model was derived which addresses these issues: the definition of the kinetic energy that contributes to deformation was corrected; a new shape factor that accurately reflects the geometry of the droplet at maximum deformation was proposed, and, importantly, an empirical approach was implemented to account for the effect of the impact parameter on this shape factor. Moreover, the model includes an estimate of the viscous dissipation, which is calculated directly from the experimentally observed difference between the impact and the rebound kinetic energies and measurements of the post-collision droplet oscillations. The proposed model shows a striking improvement versus the existing models, reducing the mean absolute error by an order of magnitude.

A new kinetic theory model of granular flows that incorporates particle stiffness

Granular materials of practical interest in general have finite stiffness; therefore, the particle collision is a process that takes finite time to complete. Soft-sphere Discrete Element Method (DEM) simulations suggest that there are three regimes for granular shear flows: inertial regime (or rapid flow regime), elastic regime (or quasistatic regime), and the transition regime (or elastic-inertial regime). If we use tf to represent the mean free flight time for a particle between two consecutive collisions and tc to represent the binary collision duration, these regimes are implicitly related to the ratio tc/tf. Granular flows can be successfully predicted by the classical Kinetic Theory (KT) when they are in the inertial regime of low particle-particle collision frequencies and short time contacts (tc/tf ≈ 0). However, we find that KT becomes less accurate in the transition regime where the collision duration tc is no longer small compared with the collision interval tf (tc/tf &amp;gt; 0.05). To address this issue, we develop a soft-sphere KT (SSKT) model that takes particle stiffness k as an input parameter since tc/tf is mainly determined by k. This is achieved by proposing a modified expression for the collision frequency and introducing an elastic granular temperature Te. Compared with the classical KT that only considers the kinetic granular temperature Tk, a redefined total granular temperature (Tg = Tk + Te/3) that takes both kinetic fluctuation energy and elastic potential energy into consideration is used in the SSKT model. The model is developed for identical frictionless particles with the linear-spring-dashpot collision scheme; however, it can be extended to frictional systems as well after the modification of constitutive equations. We show that the proposed SSKT extends the applicability of the KT framework to the transition regime without losing significant accuracy. The rheological crossover has been explained physically, and the regime boundaries that separate the inertial regime and the elastic regime are quantitatively determined, showing good agreement with the previous regime map that was based on the DEM simulations. Our SSKT predictions also show that for unsteady flows such as homogeneous cooling, the particle stiffness could have a large impact on the granular flow behavior due to the energy transfer between Te and Tk.

Автоматизований розрахунок запасу статичної стійкості у перетині електроенергетичної системи

The approach adopted in the work involves focusing on the control of static stability of the UES on the criterion of existence of the regime, subject to weighing of certain sections. In practice, this means that on the trajectory of weighing it is necessary to find the mode which has the greatest power in the investigated section, for which the coefficient of the reserve of static stability at the active power in the intersection is calculated and normalized by the "Guideline" on the stability of the power systems. A modification of the program of calculating the stationary regime in a linearized formulation, which allows us to perform weighting at the angle of the vectors of electromotive forces (EMF), without the iterative approach to the boundary regime and to specify the stock of static stability at the intersection of the Electric Power System (EPS). The linearization of the EPS model is carried out by replacing the loads in the nodes of the conductivities, and the generating nodes — by constant electromotive forces, which are fixed on the reactive supports, the magnitude of which corresponds to the staticity of the voltage of the automatic regulators of excitation of the synchronous generators. Such a model is used in the programs for calculating the dynamic stability for the simulation of EPS at the time step of numerical integration of the differential equations of dynamics of the system. A block diagram of the algorithm for determining the maximum and unacceptable fluxes in controlled sections of the electric power system is proposed. A separate module for the automated calculation of the static stability reserve at the intersection of the EPS with a choice of certain weighting trajectories from the library was created. Trajectories weighing are prepared in a specially created editor, which provides a step-by-step change in the power of power stations and electrical loads in different parts of the mathematical model of the power system and the change of the angle of the EMF generators. Calculations were made to determine the boundary power at the cross sections of the UES of Ukraine for a scheme containing 614 nodes and 975 branches.

Tribology of natural Poly-Ether-Ether-Ketone (PEEK) under transmission oil lubrication

Abstract High performance polymeric materials such as poly-ether-ether-ketone (PEEK) are increasingly being used for challenging tribological applications in order to replace metal parts in vehicle engines and transmissions. The tribology of natural PEEK, under oil-lubricated conditions, was studied for different metal counterbody finishes. Two different finishing processes were selected for this study: turning and polishing. The test system used was a tri-pin on disc, with pins made of PEEK and counterbodies made of steel, and then dipped in ATF Dexron VI oil. The conclusion was that the wear rate generated by turning was about seven times as high as the wear rate generated by polishing. The friction coefficient displayed a direct correlation with the lubrication regime, and the level of counterbody roughness. On average, the friction coefficient on the hydrodynamic regime for polishing was more than 3 times lower than the friction coefficient in the boundary regime for turning.

Multiscale boundary frictional performance of diamond like carbon coatings

This paper investigates the frictional performance of a PECVD hydrogenated undoped DLC coating and the alternative super-finished gear steel surface pairs. A tribometer replicates the conditions found in the conjunction of a performance racing transmission spur gear pair. In mixed and boundary regimes of lubrication the DLC contact is shown to have lower friction despite having comparable surface topography when measured using optical interferometry. To determine the mechanisms responsible for improved friction of DLC coated tribo-pairs AFM is used. It is shown that the nanoscale surface topography of the investigated DLC coated pairs reduces the real asperity contact area formed at the same load carrying capacity. This highlights a contributing mechanism for improved friction with the DLC coating.

A novel triple-stage friction compensation for a feed system based on electromechanical characteristics

Friction compensation is an effective strategy to eliminate friction error and improve CNC tracking accuracy during reverse motion. However, most of the currently available methods can hardly precisely determine the boundaries of piecewise compensation or simultaneously deal with the command, control and mechanical subsystems of a feed drive. A novel triple-stage compensation method based on the electromechanical characteristics of feed drives is proposed in this paper. First, a simplified control model is derived that explains the transition from the pre-sliding to the sliding regime. Next, an analytical formulation is developed that predicts the boundary between pre-sliding and sliding regimes. Subsequently, a novel friction compensator is constructed with the reverse acceleration, velocity feedforward and proportional-proportional-integral controllers and an associated mechanical system. Based on the predicted regime boundaries, compensation pulses are established by a simple mathematical calculation for moving worktable from the dead zone quickly, speeding up to command velocity and pushing it to enter normal motion phase. The proposed method can be easily applied to the commercial CNC system for the online calculation of compensator parameters and adding external pulses to the speed loop. Experimental results show that the proposed method can effectively reduce friction errors by more than 70% under different working conditions.

Flow measurements in microporous media using micro-particle image velocimetry

An experimental study focused on the identification of the flow regimes and quantification of the velocity field at pore scale in microporous media is presented and discussed. Transparent porous media are fabricated by removing a pore forming agent in slightly sintered glass beads of size 50 μ m between two glass slides, leaving typical pores with a size of 500 μ m . Pressure-drop measurements and particle image velocimetry measurements are conducted simultaneously in order to evaluate the flow regimes and flow behaviors at pore size based Reynolds numbers from 0.1 to 140. Four different regimes, pre-Darcy, Darcy, Forchheimer, and turbulent, are found and presented. Spatial distribution and characteristics of the time-averaged velocity in all regimes and fluctuation intensity in transitional and turbulent regimes are investigated. Critical Reynolds numbers are identified using both velocity and pressure-drop measurements and the results agree very well, providing direct evidence underpinning the transition. The effects of porosity on these flow properties are also studied, and finally the flow regime boundaries are compared with the literature. These data provide an insight into the flow properties in microporous media with various porosities and an improved understanding that could be further utilized to enhance the flow and heat transfer performance of microporous media. It also demonstrates that velocity and pressure measurements used in combination can be an effective method for studying microporous media.

An experimental study on debris bed formation behavior at bottom-heated boiling condition

Motivated to further understand the effect of sodium boiling on the debris bed formation behavior that might be encountered during a core disruptive accident of sodium-cooled fast reactors, in this work a series of new experiments has been performed under the bottom-heated boiling condition. It is found that the four kinds of flow regimes (namely the particle-suspension regime, the pool-convection dominant regime, the transitional regime and the particle-inertia dominant regime), as observed from previous non-bubbling experiments, can be generally reproduced under current boiling condition, despite the existence of some local differences. Although a similar influence of particle properties (size, density and shape) on the regime transition is observable, the regime boundary is confirmed to be changed due to the steam bubbles generated from boiling. Even for the experimental cases without regime transition, the generated bubbling is verified to have an evident impact on the bed characteristic quantities during the debris bed formation process. As for the experimental parameter of water depth, different from previous non-boiling experiments, in this work for a given heating power, a non-monotonous effect is found to exist, due to the much diminished bubbling rate at rather higher water depths. To be comparable with previous experiments using gas-injection, based on energy conservation a quantity of effective bubbling rate is suggested. By using this quantity, the validity of gas-injection to simulate sodium boiling is justified, thereby providing us enhanced confidence for future studies over a much larger range of gas velocities.

On relating rheology and oral tribology to sensory properties in hydrogels

The aim of this study was to understand the relationship between rheological, tribological and sensory properties (n = 11 panellists) of hydrogels differing in hydrocolloid type, concentration and degree of inhomogeneity. Fracture properties of hydrogels containing different ratios of κ-carrageenan (κC) and/or locust bean gum (LBG), sodium alginate (NaA), 300/1000 μm calcium alginate beads (CaA) at 1–4 wt% concentration were determined. Viscosity and friction coefficients (μ) of the hydrogel-boli after simulated oral processing were characterized. Tribology measurements were conducted in a polydimethylsiloxane ball/disc set-up with pre-adsorbed artificial salivary film at 37 °C. ’Scaling’ with boli viscosity showed good agreement of observed data with the Stribeck master curve, however only in the mixed regime i.e. at intermediate values of the product of velocity and lubricant viscosity (Uη). Low μ values of gel boli in the boundary regime were largely driven by the formation of a viscous layer of bolus fragments between opposing surfaces. Fracture properties of hydrogels and boli viscosity were correlated with all chewing-related texture attributes i.e. ‘firm’, ‘elastic’, ‘chewy’ and ‘cohesive’ and inversely correlated with lubrication-related attributes ‘melting’ and ‘pasty’ (p<0.05). On the other hand, μ of the bolus filtrate at orally relevant speeds (50 mm/s) was inversely correlated with lubrication-related attributes ‘pasty’ and positively with ‘slippery’ (p<0.05). The lack of correlations with ‘smooth’ could be explained due to sample inhomogeneity and the absence of ‘ball-bearing’-ability of the gel beads. A combination of initial fracture properties, boli viscosity and tribology of bolus filtrates (mixed regime) impacted the lubrication-related attribute ‘salivating’ (p<0.05).

On autoignition mode under variable thermodynamic state of internal combustion engines

Autoignition modes under premixed combustion conditions are usually studied in constant-volume configurations. However, the autoignition events related to knocking combustion in spark-ignition engines do experience variable volumes in combustion chamber and ever-changing thermodynamic states caused by reciprocating piston motion and main flame front compression. Such combustion situations may lead to different autoignition modes from constant-volume scenarios. Using one-dimensional direct numerical simulations with detailed chemistry and transport of H2/air mixture, the autoignition modes during knocking combustion were studied under different engine combustion boundary conditions. It was the first to identify important influence of variable thermodynamic states on the development of autoignition modes through changing critical temperature gradients. Four autoignition modes—thermal explosion, supersonic deflagration, detonation, and subsonic deflagration—were observed, which, however, were quantitatively different from the constant-volume configurations in regime boundaries. Meanwhile, on comparison with intake temperature and equivalence ratio, intake pressure shows greater impact on detonation formation, characterized by a regime extension under high intake pressures. To classify the autoignition modes responsible for various knocking events with different intensities in a straightforward manner, a regime diagram was proposed based on the temperature gradients and the effective energy density used for universally quantifying various intake conditions. This diagram was found useful to determine the distributions of different autoignition modes (especially for detonation) and the potential approaches for achieving maximum thermal efficiency while suppressing engine knock. In addition, detonation mode was prevailing under high effective energy density conditions, and the underlying reasons were ascribed to the significant reduction of excitation time and pre-flame temperature increases by pressure wave.