Layer Phenomena Research Articles

Electro-osmosis of nematic liquid crystals under weak anchoring and second-order surface effects.

Advent of nematic liquid crystal flows has attracted renewed attention in view of microfluidic transport phenomena. Among various transport processes, electro-osmosis stands as one of the efficient flow actuation mechanisms through narrow confinements. In the present study, we explore the electrically actuated flow of an ordered nematic fluid with ionic inclusions, taking into account the influences from surface-induced elasticity and electrical double layer (EDL) phenomena. Toward this, we devise the coupled flow governing equations from fundamental free-energy analysis, considering the contributions from first- and second-order elastic, dielectric, flexoelectric, charged surface polarization, ionic and entropic energies. The present study focuses on the influence of surface charge and elasticity effects in the resulting linear electro-osmosis through a slit-type microchannel whose surfaces are chemically treated to display a homeotropic-type weak anchoring state. An optical periodic stripe configuration of the nematic director has been observed, especially for higher electric fields, wherein the Ericksen number for the dynamic study is restricted to the order of unity. Contrary to the isotropic electrolytes, the EDL potential in this case was found to be dependent on the external field strength. Through a systematic investigation, we brought out the fact that the wavelength of the oscillating patterns is dictated mainly by the external field, while the amplitude depends on most of the physical variables ranging from the anchoring strength and the flexoelectric coefficients to the surface charge density and electrical double layer thickness.

Variability of virtual layered phenomena in the mesosphere observed with medium frequency radars at 69°N

The MF-Saura radar positioned at polar latitudes is very sensitive to enhanced ionization caused by solar and geomagnetic activity. Differing from the intensities normally detected by partial reflections from the ionospheric D region during quiet conditions, distinct layers can be seen due to intense increase of electron number density at as low as 50 km altitude caused by particle precipitation. Effects of energetic particle precipitation on observations by medium frequency (MF) radars have been rarely reported so far, generally associated with solar proton events, which are rather scarce especially during solar minimum conditions. Here, we focus on events associated with precipitation of particles with lower energy (<10 MeV), which are seen by the MF radar with occurrence rates of as much as 40% at times. Such situations are studied for a period of continuous observations for one solar cycle and statistical results like diurnal and annual distributions are presented.

On supraconvergence phenomenon for second order centered finite differences on non-uniform grids

In the present study we consider an example of a boundary value problem for a simple second order ordinary differential equation, which may exhibit a boundary layer phenomenon depending on the value of a free parameter. To this equation we apply an adaptive numerical method on redistributed grids. We show that usual central finite differences, which are second order accurate on a uniform grid, can be substantially upgraded to the fourth order by a suitable choice of the underlying non-uniform grid. Moreover, we show also that some other choices of the nodes distributions lead to substantial degradation of the accuracy. This example is quite pedagogical and we use it only for illustrative purposes. It may serve as a guidance for more complex problems. • Construction of adaptive grids for BVPs is deeply analyzed. • It is shown that local mesh refinement does not necessarily lead to low numerical error. • The stability and convergence of the scheme on non-uniform grids are proved. • We demonstrate how a 2nd order finite difference scheme can become of the fourth order.

Analysis of the neutral layer offset of bimetal composite plate in the straightening process using boundary element subfield method

• The BESM is used to discuss the 3-D deformation in the straightening process. • There is a phenomenon of the neutral layer offset in the straightening process. • The changed law of the neutral layer is discussed by the BESM. • The neutral layer offset influence the precision of the straightening force. • The neutral layer offset must be considered in the straightening force model. In the classical straightening theory, it supposes that the geometric central layer and stress neutral layer are a coincidence. However, there is some offset in fact. This is one of the reasons why straightening force is inaccurate in the straightening process. In this paper, the boundary element subfield method is used to analyze the three-dimension elastic–plastic deformation of a bimetal composite plate in the straightening process. At first, the boundary integral equation of a bimetal composite plate is established by the boundary element subfield method. Then, through analyzing the deformation in the rolled piece straightening, it shows that the geometric central layer does not coincide with the neutral layer. The formula of the neutral layer offset is established and the change law is discussed. At the same time, the influence of the neutral layer offset on the precision of straightening force is researched. From the numerical analysis, it shows that the error of the straightening force reaches to 5% whether considering the neutral layer offset. This demonstrates that the neutral layer offset is one of the important factors to give the straightening force inaccurately. It is ought to consider the neutral layer offset when the model of straightening force is established.

Numerical Studies of Ventilation Effect on Methane Layering Behaviour in Underground Coal Mines

Layering of methane in underground coal mines owing to poor ventilation leads to methane explosion hazard. We study the methane layering phenomenon and the effect of ventilation on dispersion of methane in underground coal mines at air velocities varying from 0.5 to 4.0 m/s. Three-dimensional simulations using CFD code ANSYS Fluent 12.0 were performed assuming the flow to be unsteady, turbulent and incompressible. The study demonstrated that ventilation significantly affects the behaviour of methane layering and dispersion of methane in underground coal mines. The layering length decreased with increase in air velocity. At air velocity of 4.0 m/s, the methane layering length considerably reduced to a safer level of about 1 m. Moreover, the simulation results showed a good agreement with the experimental results.

Confinement effects on the rotational microflows of a viscoelastic fluid under electrical double layer phenomenon

The last decade has seen a rise in the use of microfluidics based portable diagnostic devices, especially on the rotational platform (lab on a compact disc). One of the intrinsic problems with such devices is that experimental measurement of the flow fields and flow rates is difficult, owing to high rotational speeds. Hence, there is a need to computationally explore the flow and mixing involved in such devices and identify the optimal parameters of operation with respect to bio-fluids, many of which exhibit viscoelastic behavior. We, therefore, study the startup electro-osmotic flow of a viscoelastic fluid in a rotatingrectangularmicrofluidic channel described by the Oldroyd-B model. The combination of the elastic and viscous nature of viscoelastic fluids brings out novel flow physics in a rotating rectangular microchannel, which we explore in detail. In particular, we show that the development of secondary flow in the channel due to the Coriolis forcing starts forming the vortex structures in the field aided by the lateral confinement of the channel, which may be of useful towards an enhancement in mixing in microfluidic devices.

Second-order uniformly convergent numerical method for singularly perturbed delay parabolic partial differential equations

ABSTRACTThis article proposes a second-order uniformly convergent numerical method for singularly perturbed delay parabolic convection-diffusion equation having a regular boundary layer. To handle this layer phenomenon, the problem is solved on a priori special mesh by using the implicit-Euler scheme for the discretization of the time derivative and the upwind scheme for the spatial derivatives which results almost first-order convergence, that is, . It is shown that, the implementation of Richardson extrapolation technique enhanced the order of convergence to . To support the theoretical results, numerical experiments are carried out by applying the proposed technique on two test examples.

The MetNet vehicle: a lander to deploy environmental stations for local and global investigations of Mars

Abstract. Investigations of global and related local phenomena on Mars such as atmospheric circulation patterns, boundary layer phenomena, water, dust and climatological cycles and investigations of the planetary interior would benefit from simultaneous, distributed in situ measurements. Practically, such an observation network would require low-mass landers, with a high packing density, so a large number of landers could be delivered to Mars with the minimum number of launchers.The Mars Network Lander (MetNet Lander; MNL), a small semi-hard lander/penetrator design with a payload mass fraction of approximately 17 %, has been developed, tested and prototyped. The MNL features an innovative Entry, Descent and Landing System (EDLS) that is based on inflatable structures. The EDLS is capable of decelerating the lander from interplanetary transfer trajectories down to a surface impact speed of 50–70 m s−1 with a deceleration of &lt; 500 g for &lt; 20 ms. The total mass of the prototype design is ≈ 24 kg, with ≈ 4 kg of mass available for the payload.The EDLS is designed to orient the penetrator for a vertical impact. As the payload bay will be embedded in the surface materials, the bay's temperature excursions will be much less than if it were fully exposed on the Martian surface, allowing a reduction in the amount of thermal insulation and savings on mass.The MNL is well suited for delivering meteorological and atmospheric instruments to the Martian surface. The payload concept also enables the use of other environmental instruments. The small size and low mass of a MNL makes it ideally suited for piggy-backing on larger spacecraft. MNLs are designed primarily for use as surface networks but could also be used as pathfinders for high-value landed missions.

Homogenization of elastic materials reinforced by rigid notched fibres

This paper deals with the homogenization of a composite material built with an elastic matrix periodically reinforced by elastic notched fibres. We assume that the Lamé constants in the fibres are highly contrasted with respect to those of the matrix. We derive a class of energy functionals involving additional degrees of freedom implying nonlocal description of localized geometrical discontinuities due to the fibre-notches, nonlocal effects associated with thin boundary layer phenomena, and nonlocal terms including macroscopic fields of extension or flexion.

Slip driven micro-pumping of binary system with a layer of non-conducting fluid under electrical double layer phenomenon

In this study, we report the consequences of the fluid/wall slippage on the micro-pumping of an immiscible binary system constituted by conducting (non-Newtonian) and non-conducting (Newtonian) fluid pair through a microchannel. We consider power-law model to represent the constitutive behaviour of the non-Newtonian fluid. We explore the effect of the combined influences of the applied pressure gradient and electrical forcing on micro-pumping by analytical calculations considering a flat interface between the fluids. We highlight the alteration in underlying dynamics, mainly attributable to the rheology driven modification in viscous resistance in the field as modulated by the interfacial slip and electrical double layer effect. Also, we establish a phenomenal amplification in micro-pumping effect, as realised through an enhanced volumetric flow rate though the channel under combined forcings environment. We believe that the inferences obtained from this analysis may improve the design of various bio-microfluidic devises/systems, which are often used for the transportation of binary layers including one non-Newtonain fluid in the system.

Pythiosis cutánea en equinos tratados con acetonida de triamcinolona. Parte 2. Descripción histológica e histoquímica

Objetivo. El objetivo del estudio fue realizar una descripción histológica e histoquímica del proceso de cicatrización de la pythiosis cutánea en equinos tratados con acetonida de triamcinolona. Materiales y métodos. Se Realizó un estudio de tipo descriptivo, no probabilístico en animales de conveniencia con pythiosis cutánea. Fueron utilizados 24 equinos con pythiosis, siendo aplicado 50 mg de acetonida de triamcinolona vía intramuscular a un grupo de 12 animales (GT) y en otro grupo no fue aplicado tratamiento (GC). Se realizaron biopsias de tejidos para evaluación histológica e histoquímica, en las coloraciones de hematoxilina eosina (H&amp;E), tricrómico de Gómori (TG), picrosirius red/polarization (PR/P) y plata metanamina de Grocott (GMS). Resultados. Se observó que en el GT el proceso inflamatorio fue disminuyendo progresivamente, evidenciado en la disminución de la capa fibrino leucocitaria, PMN y de los fenómenos de Splendore Hoepli, así como mayor angiogénesis, epiteliogénesis y aumento de la cantidad de fibroblastos y fibras colágenas generales, así mismo en el cambio progresivo de colágeno tipo III a colágeno tipo I al final del proceso, además de que la presencia de hifas intralesionales de Pythium insidiosum disminuyó a la segunda semana. Ninguno de los animales del GC presentó mejoría en las características histológicas e histoquímicas de la pythiosis y se mantuvieron iguales al primer día durante todo el estudio. Conclusiones. La acetonida de triamcinolona es una buena alternativa terapéutica en el tratamiento de las heridas granulomatosas por pythiosis en equinos con 100% de recuperación clínica y demostrada con las constataciones histológicas e histoquímicas.

Layering and rejuvenation inTsuga canadensis(Pinaceae) on Wachusett Mountain, Massachusetts

Abstract The phenomenon of layering in trees involves the production of adventitious roots by low-growing lateral branches and their subsequent reorientation from horizontal to vertical. This study provides the first documentation of layering in any natural populations of eastern hemlock, Tsuga canadensis. Twelve layered hemlock clumps, consisting of 5 to 20 layered branch stems originating from a parent tree, were observed on the upper slopes of Wachusett Mountain in central Massachusetts. Layered hemlocks ranged from 7 to 17 m tall, and several layered branches produced second-generation layers. Harsh growing conditions, slow hemlock growth, and the open habitat associated with small-statured hardwood species and exposed bedrock allowed the hemlocks to retain their lower branches for extended periods of time. Fallen limbs and debris associated with past disturbances pinned these branches to the ground and likely set the stage for layering. The production of physiologically rejuvenated hemlock ramets thr...

Numerical modeling of time-dependent bio-convective stagnation flow of a nanofluid in slip regime

Abstract A numerical investigation of unsteady stagnation point flow of bioconvective nanofluid due to an exponential deforming surface is made in this research. The effects of Brownian diffusion, thermophoresis, slip velocity and thermal jump are incorporated in the nanofluid model. By utilizing similarity transformations, the highly nonlinear partial differential equations governing present nano-bioconvective boundary layer phenomenon are reduced into ordinary differential system. The resultant expressions are solved for numerical solution by employing a well-known implicit finite difference approach termed as Keller-box method (KBM). The influence of involved parameters (unsteadiness, bioconvection Schmidt number, velocity slip, thermal jump, thermophoresis, Schmidt number, Brownian motion, bioconvection Peclet number) on the distributions of velocity, temperature, nanoparticle and motile microorganisms concentrations, the coefficient of local skin-friction, rate of heat transport, Sherwood number and local density motile microorganisms are exhibited through graphs and tables.

국내원전 배관계통 열성층 연구개발 현황

The thermal stratification phenomenon in the nuclear power plant can cause abnormal deformation of the piping, contact with the support, damage to the support system. Repetition of the thermal stratification phenomenon or variation of the thermal boundary layer can cause thermal fatigue. Thermal stratification phenomenon in nuclear power plants is still an ongoing issue and active research has been carried out. In this paper, the current situation in Korean nuclear power plants is described, followed by the status of research and the future problems on the thermal stratification phenomenon in Korea.

Electrochemical Impedance Spectroscopy response study of a commercial graphite-based negative electrode for Li-ion batteries as function of the cell state of charge and ageing

The successful development of electrified vehicles is a key factor in the transition to a more environmentally friendly transportation sector. Li-ion batteries, which are today’s choice to power electrified vehicles, have to fulfill more stringent requirements in terms of ageing and need advanced tools to study the interfaces evolution upon cycling. This work is thus focused on understanding the impedance behavior of a commercial graphite-based negative electrode, which is used in a Li-ion battery designed for such vehicles. 3-electrode pouch cells were assembled with such negative electrode, a LMO-layered oxide-based positive electrode, a Celgard® type separator soaked with a carbonate solvents-LiPF6 mixture electrolyte and a LTO-based electrode as reference. Electrochemical Impedance Spectroscopy measurements were performed at different cell states of charge and ageing times. The impedance of the graphite-based anode is analyzed for first time with de Levie’s equation for porous electrodes. The analysis is supported by designed SEI layer formation experiments with vinylene carbonate and vinylene ethyl carbonate additives. The high frequency domain of the interfacial kinetic loop reflects porosity effects and the graphite particles–composite matrix electric tranfer. The SEI layer and charge transfer phenomena are reflected in the medium and medium to low frequency domains respectively, and their impedance contributions depend on the Li content of the graphite particles. Upon ageing, the interfacial impedance of the graphite-based electrode should increase due to SEI layer growing. However, from 100% to 80% of battery capacity retention, the impedance decreases. Our analysis backed by post-mortem characterizations allows to assign this unexpected behavior to porosity rise and slight Mn-contamination of the SEI layer.

Relaxation limit in bipolar semiconductor hydrodynamic model with non-constant doping profile

The relaxation limit from bipolar semiconductor hydrodynamic (HD) model to drift–diffusion (DD) model is shown under the non-constant doping profile assumption for both stationary solutions and global-in-time solutions, which satisfy the general form of the Ohmic contact boundary condition. The initial layer phenomenon will be analyzed because the initial data is not necessarily in the momentum equilibrium. Due to the bipolar coupling structure, the analysis is hard and different from the previous literature on unipolar model or bipolar model with zero doping profile restriction. We first construct the non-constant uniform stationary solutions by the operator method for both HD and DD models in a unified procedure. Then we prove the global existence of DD model and uniform global existence of HD model by the elementary energy method but with some new developments. Based on the above existence results, we further calculate the convergence rates in relaxation limits.

PROSPECTS OF DISK PUMP FOR MECHANICAL CIRCULATORY SUPPORT IN CARDIAC SURGERY (REVIEW)

The need of circulatory support systems in the treatment of chronic heart failure is increasing constantly, as 20% of the patients on the waiting list die every year. Despite the great need for mechanical heart support systems, the use of available systems is limited by its expensiveness. In addition, there is no one system that is 100% responsible to all medical and technical requirements and that would be completely safe for patient. Therefore, further research in the field of circulatory support systems considering health and technical requirements is relevant. One of the new directions in the study are disc pumps of viscous friction for liquid transporting, based on the Tesla pump principle. The operation principle of such pumps is based on the phenomenon of the boundary layer which is formed on the disk rotating in a fluid. There are experimental studies of models with different variants of the rotor suspension, various forms and numbers of the disks, forms of the pump housing. However, none of the above samples was brought to clinical trials. Furthermore, despite the potential of that model there have been no pumps of similar type used so far in circulatory support systems. Published data provide a basis for further development and testing of the pump model and allow hoping for leveling a number of significant shortcomings of modern left ventricular bypass systems.

Effect of various surface conditions on nanochannel flows past permeable walls

In this paper, effects of surface conditions on the gas flow in nanochannels with permeable walls have been investigated by molecular dynamics simulations. The hydrodynamic characteristics of the gas flow in nanochannels, including the density distributions, slip length and boundary friction coefficient, have been significantly influenced by the molecular interactions between gas molecules and wall atoms. The density layering phenomena are observed at the fluid–wall interface under a strong fluid–wall interaction (FWI). Particularly, there is a peak of the gas density on the permeable surface where the gas density is increased and about 3 times larger than the bulk one under the strong FWI. It indicates a strong non-continuum density distribution on the permeable surface and the step down in density from nanopores to the bulk region. On the other hand, the nanoscale vortices are produced in the nanopores. Moreover, the mass flux of gas flow in nanopores is reduced, and the hydrodynamic boundary has been shifted above the permeable surface further under the weak FWI. Slip characteristics on the permeable surface under various conditions are explored. It has been found that the slip length on the permeable surface may vary as a logarithmic function with the molecular mean free path. Apparently, the skin friction on the permeable surface is affected by the velocity slip. These results are significant in the understanding of nanoscale hydrodynamics.

Comparing multi-scale cracking mechanisms in man-made composites and natural materials

Abstract Man-made composites, like reinforced and fiber-reinforced concrete elements, behave similarly to natural composite structures (e.g., brittle rocks lying on a ductile substratum). In both cases, the cracking phenomenon of brittle layers depends on the scale of observation and is ruled by the Golden Ratio. Thus, a unique size-effect relationship, herein called Golden Scaling Law (GSL), is introduced and used to predict the crack pattern of concrete and rock structures. In accordance with several experimental data, GSL permits to calculate the values of crack width and crack spacing when the geometry of crack patter is known at a lower scale. Moreover, GSL can be applied to large composite structures without knowing the material performances, but by testing prototypes of lower dimensions.

Influence of processing parameters on laser penetration depth and melting/re-melting densification during selective laser melting of aluminum alloy

A three-dimensional mesoscopic model, considering the powder-to-solid transition, motion of gas bubbles within molten pool and the effect of surface tension, has been established in order to investigate the evolution rule of pores and re-melting densification mechanism during selective laser melting of AlSi10Mg. The results indicated that re-melting phenomenon of previous fabricated layer induced by laser melting of current powder layer played a crucial role on the increase in densification rate. During the re-melting process, the trapped gas pores in previous layer rose up swiftly and came to the surface consequently, resulting in remarkably elevated densification in previous layer. The influences of laser scan speed on the single-track morphology, types of pores and laser penetration depth have also been studied. It showed that the maximum re-melting depth (31 µm) was attained, and meanwhile, pores left in preceding layer got eliminated completely due to the mass transfer within molten pool, when an appropriate laser scan speed (150 mm/s) was applied. In this case, reasonable laser energy per unit length and irradiation time tended to enhance the laser penetration depth for powder bed and decrease the porosity in as-fabricated layer. A series of experimental study were performed to verify the reliability of the above mesoscopic simulation, including the surface topography of single track and the types of pores. The redistribution of bubbles between the adjacent layers as well as the localized re-melting densification, which were observed from the longitudinal section of samples, was in good agreement with simulation results.