Critical Value Ec Research Articles

Friction Reduction by Laser Irradiation for a Friction System Using Bearing Steel and Aluminum Alloy in Engine Oil

Aluminum alloy sliding components are widely used in internal combustion engines. However, aluminum easily adheres to the countersurface, resulting in high friction. Hence, laser irradiation was used to oxidize the aluminum surface and promote tribofilm formation using molybdenum dithiocarbamate and zinc dialkyldithiophosphate (ZnDTP). This study investigated laser irradiation to reduce friction between steel balls and aluminum disks in fully formulated engine oil. Laser scanning was used to create 100-μm-pitch concentric circles on the disks. The friction behavior was classified into two modes: no friction reduction (mode-I, μ: 0.09–0.12) and friction reduction after the high-friction period (mode-II, μ: 0.06–0.09). Friction mode transition occurred when the laser energy density exceeded the critical value (Ec). Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy showed that, for mode-I, aluminum adhered to the ball, and no sulfur-containing tribofilm formed. For mode-II, the ZnDTP-derived phosphate film formed on the disk suppressed aluminum adhesion, and a sulfur-containing tribofilm formed on the ball. Micro-Vickers tests and X-ray diffraction showed that an amorphous/nanocrystalline structure formed in the unirradiated area owing to heat diffusion under high-energy-density laser irradiation (>Ec). Results suggest that metallographic structural change in the unirradiated area promotes ZnDTP reactions, causing the mode transition.

Dissecting the role of membrane defects with low-energy barrier on fouling development through A collision Attachment-Monte Carlo approach

Membrane defects with low energy-barrier characteristics are unavoidable in membrane fabrication. However, their influences on fouling have not been fully understood. This work systematically investigates the critical role of membrane defects on fouling development and characteristics by adopting a collision attachment-Monte Carlo approach. Simulations show that membrane defects influencing on fouling is highly governed by foulant-clean-membrane interaction (F-M) and foulant-fouled-membrane interaction (F–F). When F–F energy barrier (Ef) is above a critical value (Ec), the long-term stability of water flux is not affected by the presence of defects, thanks to high F–F repulsion preventing further particles deposition. At low Ef (<Ec) but high F-M energy barrier Em (≥Ec), there appears an extended metastable flux for defect-free membrane. Since the local defects serve as hotspots to accelerate fouling, increased coverage or lowered energy barrier of defects shortens or even vanishes metastable period. For both low Ef (<Ec) and Em (<Ec), severe fouling occurs at the beginning of filtration with/without defects as a result of the rapid fouling transition from F-M to F–F. Furthermore, membrane defects have less remarkable influences at higher initial flux where permeate drag plays a primary role. Our simulation provides important implications to membrane design and fouling mitigation.

Strings in irrelevant deformations of AdS3/CFT2

We generalize our recent analysis [1] of probe string dynamics to the case of general single-trace Toverline{T},Joverline{T} and Toverline{J} deformations. We show that in regions in coupling space where the bulk geometry is smooth, the classical trajectories of such strings are smooth and approach the linear dilaton boundary at either the far past or the far future. These trajectories give rise to quantum scattering states with arbitrarily high energies. When the bulk geometry has closed timelike curves (CTC’s), the trajectories are singular for energies above a critical value Ec. This singularity occurs in the region with CTC’s, and the value of Ec agrees with that read off from the dual boundary theory for all values of the couplings and charges.

Quantum dynamics in a cubic potential in the semi-classical limit: Smearing of the homoclinic bifurcation

We consider the dynamics of a particle inside the metastable well of a cubic potential. In the classical picture the particle can oscillate inside the well when its total energy is less than a critical value Ec at which point a homoclinic bifurcation occurs. The quantum particle is always supposed to tunnel out. We set up a semi classical dynamics (which cannot capture tunneling effects) of the quantum particle which can be analyzed in terms of fixed points and stabilities and thus yields quantitative results. We find that the quantum fluctuations smear out the homoclinic bifurcation and for energies greater than a new critical value, substantially less than Ec, the particle always escapes from the well. This implies that even for an initial wave packet centered at the minimum of the well, there is a critical value of the width for which the particle tunnels out even in this semi-classical limit.

Collapse of Landau levels in graphene under uniaxial strain

We examine the collapse of Landau levels in graphene under uniform uniaxial strain and in the presence of a pair of crossed homogeneous electric and magnetic fields. In particular, we obtain the Landau levels and examine their dependence on the strain . It is shown that the Landau levels collapse when the magnitude of the electric field E reaches a critical value Ec whose magnitude can be increased (decreased) by applying the strain in the zigzag (armchair) direction. We also examine the phenomena in the presence of crossed inhomogeneous fields.

Hysteretic phenomena in GFET: Comprehensive theory and experiment

We propose a comprehensive analytical theory for the description of versatile hysteretic phenomena in a graphene field effect transistor (GFET). Our theory account for the existence of the three most important rival factors, such as external dipoles on graphene free surface, localized states at the graphene-substrate interface, and the bound polarization charge coming from a ferroelectric substrate. In particular, we demonstrated that the absorbed dipole molecules (e.g., dissociated or highly polarized water molecules) can cause hysteretic form of carrier concentration as a function of gate voltage and corresponding dependence of graphene conductivity in GFET on the substrate of different types, including the most common SiO2 and ferroelectric ones. It was shown that the increase in the gate voltage sweeping rate leads to the complete vanishing of hysteresis for GFET on SiO2 substrate as well as for GFET on ferroelectric substrate for applied electric fields E less than the critical value Ec. For E &amp;gt; Ec, the cross-over from the anti-hysteresis to hysteresis take place. The carriers' trapping from the graphene channel by the interface states describes the “anti-hysteresis” in GFET on PZT substrate well enough. These results well correlate with the available experimental data up to the quantitative agreement. So, the obtained analytical results predict new and clarify existing effects in GFET. They describe quantitatively the physical principles of GFET operation and can become the first necessary step to transform the state-of-art from almost empirical to analytical level, because they can be directly applied to describe the basic characteristics of advanced non-volatile ultra-fast memory devices using GFET on versatile substrates.

Electrocoalescence behavior of two identical droplets with various droplet radii

In electric dehydration of crude oil, electrocoalescence of water droplets can be remarkably enhanced by increasing electric field strength, which promotes the settling separation of water droplets. However, non-coalescence of droplets occurs when the electric strength is higher than a critical value (Ec). Smaller daughter droplets will be ejected from the coalescing droplet in the process of the non-coalescence, which is undesirable for separation of droplets from crude oil. This work simulates the electrocoalescence of two identical droplets with dissolved KCl via molecular dynamics method. The results show that the value of Ec decreases with the increase of the droplet radius, this is because daughter droplets can be ejected more easily from the coalescing droplet with a larger radius due to stronger electric field force and smaller interfacial force. With the same initial centroid distances, the attractive energy between two larger droplets is stronger when an electric field is applied, and hence the two droplets migrate towards one another faster. However, the merging rate of the coalescing droplet is higher after two smaller droplets come into contact. In addition, it is also found that the daughter droplet with dissolved K+ is more easily ejected from the coalescing droplet during the non-coalescence, as compared to the daughter droplet with dissolved Cl−.

Electron interaction effects on the thermoelectric power of a quantum dot at T &gt; TK

In the absence of phonon thermal conductivity, we theoretically investigate the output power of an interacting quantum dot thermoelectric setup that is moderately coupled to two electronic reservoirs in the regime T ≫ T K . In the noninteracting case, the output power is maximized when the energy level of the dot is around a critical value e c . We find that when the energy level of the dot is lower than e c , Coulomb interaction can enhance the maximum thermoelectric power that can be achieved by tuning the bias and a wider operating region is also observed. However, when the energy level of the dot is higher than e c , Coulomb interaction suppresses the maximum power. Finally when the dot level is around e c , Coulomb interaction has minimal effects on the maximum power.

Maximum entropy states of quasi-geostrophic point vortices

The statistical equilibrium state of quasi-geostrophic point vortices is investigated theoretically, based on the maximum entropy theory. We search for the state of maximum Shannon entropy under the constraints of the vertical vorticity distribution P(z), the angular momentum I, and the energy of the vortex system E. Solutions of the mean field equation are obtained by the numerical procedure proposed by Turkington and Whittaker. The most probable state in an infinite fluid domain is axisymmetric, whose radial distribution depends both on the vertical vortex distribution P(z) and the total energy of the vortex system E. At a certain critical energy value Ec, the number of microscopic state of fixed angular momentum becomes largest (zero-inverse temperature state), where the radial distribution is Gaussian at any vertical height. When the energy is smaller (E Ec: negative temper...

Onset of space charge limited current for field emission from a single sharp tip

A protrusive model of the Child-Langmuir (CL) law is proposed for non-uniform electron field emission from a sharp tip of either Lorentzian or hyperboloid shape. The model is expressed as Jc = μ×J1D at large electric field higher than a critical value Ec, and J1D is the classical one-dimensional CL law. It is found that the enhancement μ over the 1D CL law depends only on the calculated field enhancement factor (β) of the emitter and is independent of the work function and gap spacing. In particular, μ increases with β and it converges to a constant at β≫ 1 for a very sharp tip with small emission area.

Primary and secondary tip coronae from splashing water drops in electric fields

An enquiry has been carried out into millimetre size water drops falling through vertical electric fields, at terminal and near terminal velocities, and impacting a water surface. A laboratory method was devised to electronically observe the splashing event, together with the onset, duration and magnitude of all ensuing coronae. The production of a secondary jet tip and the discovery of a previously unknown corona were originally recorded by Kinsey (1986) and are here described in detail. Emanating from the secondary jet tip, the corona is synonymous with the release and electrification of an airborne water drop and its nC range of charge transfer (being field/momentum dependant) offer low level luminosity to the dark adapted eye (mentioned by ur Rahman and Saunders, 1988).For terminal and near terminal velocity drops, the resulting water jets follow under-damped sinusoidal oscillation and, in fields above a critical value (Ec), their primary tips often support more than one corona, thus yielding charge to the aerosol and space charge below oceanic thunderstorms. Secondary tip, or jet drop, corona data show the phenomenon to occur in fields of 100Vcm−1 and maybe even lower. The role of such drops, in oceanic thunderstorm electrification, being subject to drop size, ambient field, updraft and wind shear speeds. Oscilloscopic and photographic evidence is presented in support of the discovered corona and oscillographs, photographs and data are taken from P. B. Kinsey Ph.D. thesis (1986).

MICROCANONICAL DETERMINATION OF THE ORDER PARAMETER CRITICAL EXPONENT

A highly efficient Monte Carlo method for the calculation of the density of states of classical spin systems is presented. As an application, we investigate the density of states ΩN(E, M) of two- and three-dimensional Ising models with N spins as a function of energy E and magnetization M. For a fixed energy lower than a critical value Ec,N the density of states exhibits two sharp maxima at M = ± Msp(E) which define the microcanonical spontaneous magnetization. An analysis of the form Msp(E) ∝ (Ec, ∞ - E)βε yields very good results for the critical exponent βε, thus demonstrating that critical exponents can be determined by analyzing directly the density of states of finite systems.

Nitrogen transformations during secondary coal pyrolysis

In electric dehydration of crude oil, electrocoalescence of water droplets can be remarkably enhanced by increasing electric field strength, which promotes the settling separation of water droplets. However, non-coalescence of droplets occurs when the electric strength is higher than a critical value (Ec). Smaller daughter droplets will be ejected from the coalescing droplet in the process of the non-coalescence, which is undesirable for separation of droplets from crude oil. This work simulates the electrocoalescence of two identical droplets with dissolved KCl via molecular dynamics method. The results show that the value of Ec decreases with the increase of the droplet radius, this is because daughter droplets can be ejected more easily from the coalescing droplet with a larger radius due to stronger electric field force and smaller interfacial force. With the same initial centroid distances, the attractive energy between two larger droplets is stronger when an electric field is applied, and hence the two droplets migrate towards one another faster. However, the merging rate of the coalescing droplet is higher after two smaller droplets come into contact. In addition, it is also found that the daughter droplet with dissolved K+ is more easily ejected from the coalescing droplet during the non-coalescence, as compared to the daughter droplet with dissolved Cl−.

Ising-Type and Other Transitions in One-Dimensional Coupled Map Lattices with Sign Symmetry

We consider a one-dimensional lattice of expanding antisymmetric maps [−1, 1]→[−1, 1] with nearest neighbor diffusive coupling. For such systems it is known that if the coupling parameter e is small there is unique stationary (in time) state, which is chaotic in space-time. A disputed question is whether such systems can exhibit Ising-type phase transitions as e grows beyond some critical value ec. We present results from computer experiments which give definite indication that such a transition takes place: the mean square magnetization appears to diverge as e approaches some critical value, with a critical exponent around 0.9. We also study other properties of the coupled map system.

Energy constrained sandpile models

We study two driven dynamical systems with conserved energy. The two automata contain the basic dynamical rules of the Bak, Tang, and Wiesenfeld sandpile model. In addition a global constraint on the energy contained in the lattice is imposed. In the limit of an infinitely slow driving of the system, the conserved energy E becomes the only parameter governing the dynamical behavior of the system. Both models show scale-free behavior at a critical value Ec of the fixed energy. The scaling with respect to the relevant scaling field points out that the developing of critical correlations is in a different universality class than self-organized critical sandpiles. Despite this difference, the activity (avalanche) probability distributions appear to coincide with the one of the standard self-organized critical sandpile. [S0031-9007(98)06024-4]

Steady-state behavior of dilute polymers in elongational flow. Dependence of the critical elongational rate on chain length, hydrodynamic interaction, and excluded volume

The steady-state properties of flexible polymer chains in solutions undergoing elongational flow have been studied using Brownian dynamics simulation. The coil–stretch transition is observed when the elongational rate, ε̇ exceeds a certain critical value ε̇c. In this work, we describe in detail the simulation procedure and how to extract polymer dimensions, solution viscosity, and birefringence from the trajectories. Preliminary simulations involving no hydrodynamic interaction (HI) are used to check the simulation procedures by comparing their results with theoretical predictions for such an (unphysical) case. Afterwards, simulations with fluctuating nonaveraged HI are carried out to provide results comparable with experiments. After simulations with and without intramolecular potential, we arrive at a most important conclusion: the chain length dependence of ε̇c is the same in theta conditions as in good solvent conditions. Combining ε̇c with other solution properties such as the longest relaxation time, the intrinsic viscosity, and the radius of gyration, dimensionless compound quantities can be formulated. From our simulation results, we obtain numerical values for such quantities, which include the HI effect, and which are therefore useful for analyzing experimental data.

Wave CISK of Equatorial Waves and the Vertical Distribution of Cumulus Heating

Abstract The dependence of Kelvin and Rossby wave CISK (conditional instability of the second kind) on the vertical distribution of cumulus heating is examined by expanding the vertical heating profile into its Fourier series with Fourier coefficients f1, f2, . . . , fN. In the standard analysis presented, N = 8 is used. The use of eight Fourier terms provides an adequate vertical resolution considering the current state of knowledge of the dependence of cumulus heating profiles on environmental conditions. The results of the analyses are illustrated in the stability diagrams in the parameter space of Fourier coefficients, showing regions of stability and instability. These results show that all Kelvin wave solutions are stable when the heating parameter e is smaller than a critical value ec, the precise value of which depends on how the Fourier coefficients, fn, decrease with n. For moderately large values of the heating parameter (say, for e ≥ 2), Kelvin wave solutions become unstable for sufficiently n...

A computational analysis of electrohydrodynamics of a leaky dielectric drop in an electric field

Axisymmetric steady flows driven by an electric field about a deformable fluid drop suspended in an immiscible fluid are studied within the framework of the leaky dielectric model. Deformations of the drop and the flow fields are determined by solving the nonlinear free-boundary problem composed of the Navier-Stokes system governing the flow field and Laplace's system governing the electric field. The solutions are obtained by using the Galerkin finite-element method with an elliptic mesh generation scheme. Under conditions of creeping flow and vanishingly small drop deformations, the results of finite-element computations recover the asymptotic results. When drop deformations become noticeable, the asymptotic results are often found to underestimate both the flow intensity and drop deformation. By tracking solution branches in parameter space with an arc-length continuation method, curves in parameter space of the drop deformation parameter D versus the square of the dimensionless field strength E usually exhibit a turning point when E reaches a critical value Ec. Along such a family of drop shapes, steady solutions do not exist for E > Ec. The nonlinear relationship revealed computationally between D and E2 appears to be capable of providing insight into discrepancies reported in the literature between experiments and predictions based on the asymptotic theory. In some special cases with fluid conductivities closely matched, however, drop deformations are found to grow with E2 indefinitely and no critical value Ec is encountered by the corresponding solution branches. For most cases with realistic values of physical properties, the overall electrohydrodynamic behaviour is relatively insensitive to effects of finite-Reynolds-number flow. However, under extreme conditions when fluids of very low viscosities are involved, computational results illustrate a remarkable shape turnaround phenomenon: a drop with oblate deformation at low field strength can evolve into a prolate-like drop shape as the field strength is increased.

Stable and unstable eigensolutions of laplace’s tidal equations for zonal wavenumber zero

Laplace's tidal equations are of great importance in various fields of geophysics. Here, the special case of zonal symmetry (zonal wavenumberm = 0) is investigated, where degenerate sets of eigensolutions appear. New results are presented for the inclusion of dissipative processes and the case of unstable conditions. In both instances the (nonzero) eigenfrequencies are complex. In the latter case, additional stable (i.e. real) eigenfrequencies appear in the numerical results for the absolute value of the Lambparametere being larger than a critical valueeC. Further, it is shown that any degeneracies are removed through the inclusion of dissipation. Moreover, asymptotic relations are derived employing the relation of Laplace's tidal equations form = 0 to the spheroidal differential equation. The implications of these findings to numerical techniques are demonstrated and results of computations are presented.

Electro-insertion of xeno-glycophorin into the red blood cell membrane

The electroporation technique, with field strengths slightly below the critical value Ec for electroporation of red blood cells (RBC), enables the insertion of xeno-proteins into the RBC membrane without damaging the cells. The electro-insertion has been used to insert biotinylated human glycophorin into human RBC membrane and human glycophorin into murine RBC membrane. Binding anti-human glycophorin antibody (10F7) to the murine RBC bearing human glycophorin indicates extracellular orientation of inserted glycophorin. Insertion of about 10 5 glycophorin molecule per cell has been estimated by whole cell ELISA.