Multi-layers System Research Articles

Different correlations between spin Hall angle measured by the 2nd harmonic method and by the critical current density due to dimension effect in W/Ta multilayers

We obtain varying spin Hall angle (θSH, 2nd) values measured by the 2nd harmonic methods in W/Ta multilayers system with relatively low resistivity by doping Ta into mixed-phase W with both α and β phases (α-W, β-W). A remarkably increased value of θSH, 2nd is observed from 0.04 (W) to 0.47 (W1/Ta0.25), which is attributed to the formation of β-W3Ta. The influences of θSH, 2nd on the critical switching current density (Jc) were investigated by the spin Hall angle (θSH,Jc). It is found that the θSH,Jc has strong correlations with θSH, 2nd in large dimension samples, indicating the Jc can be lowered by the enhancement of θSH, 2nd. This correlation gradually disappears in smaller dimension samples, due to the pinning effect and domain wall (DW) surface tension, which are confirmed by microsimulations.

Prediction of Rutting in Flexible Pavements using Finite Element Method

In this research study three dimensional (3D) finite element analysis are performed on a flexible pavement section for different material properties, temperature and loading conditions. The main objective of this study is to predict the rut depth under different conditions of temperature, loadings and material properties. Three dimensional finite element model of flexible pavement is developed using ABAQUS to predict rut depth. The pavement system is assumed to be an elastic multi-layers system with each layer being isotropic, homogeneous with specified Resilient Modulus (Mr) and Poisson ratio (µ). With the exception of the bottom subgrade layer, each layer is extending to an unlimited horizontal extent and has a finite thickness. The pavement system analyze in this study for a cyclic load of 10000 cycles taken as 0.01sec per cycle. Standard Axle Load (ESAL) of 18 kips (80 kN) loading on an axle with a dual set of tires, the wheel spacing is 13.78 in (350 mm) with a tire contact pressure of 100 psi (0.69 MPa) is used. After performing a series of analysis the results showed that rut depth increases with increase in temperature and loading and decreases by using base stabilizer. Doi: 10.28991/cej-2021-03091727 Full Text: PDF

ReFOCUS+: Multi-Layers Real-Time Intelligent Route Guidance System With Congestion Detection and Avoidance

Due to random nature of traffic and unpredictability of human behaviors, one of challenging problems in transportation engineering is traffic congestion which has a direct impact on the economy and environment with the increase in traveling time, fuel consumption and emissions. One of approaches to reduce traffic congestions is the advance Route Guidance Systems (RGSs) which can propose alternative optimal routes for vehicles, which are in or will be entering congested roads or areas. Advanced RGSs, usually employ real-time and predicted traffic information of the roads to find the best possible route for vehicles in a way that total traffic congestions will be reduced. In this paper, The ReFOCUS+, a dynamic semi-distributed, multi-layer, and Fog-Cloud based advance route guidance system architecture has been introduced. The ReFOCUS+ architecture, employ Road Side Units (RSUs), to calculate different traffic-related factors such as current and predicted road congestions, area congestions, traveling time, etc. Then, the ReFOCUS+ uses traffic factors to proposes a novel method to detect congested roads in an area and, apply re-routing to vehicles to ease the traffic congestion within each area using a multi-metric fitness function, called Road Weight Measurement (RWM). To evaluate the performance of ReFOCUS+, a new open-source Python-based program has been developed which is able to connect to SUMO traffic simulator and control the simulation. The simulation results demonstrate that ReFOCUS+ outperforms existing solutions and improve traveling time, fuel consumption and gas emissions. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> The developed program and software in this paper available at https://www.github.com/hamednoori/ReFOCUS+

Controllable intrinsic Gilbert damping in Pt buffered [Co/Ni]n multilayers with enhanced perpendicular magnetic anisotropy

We systematically investigate the magnetization precession processes of post-prepared and after-annealing Pt buffered [Co/Ni]n multilayers with adjustable perpendicular magnetic anisotropy (PMA) by time-resolved magneto-optical Kerr effect. The PMA of the [Co/Ni]n multilayers could be modulated by changing the number of Co/Ni periods n, Pt thickness tPt and annealing temperature Ta, respectively. With a fixed tPt, both uniaxial magnetic anisotropy Ku and intrinsic damping constant α0 could be modulated by the variation of n. We observed that α0 is linearly proportional to Ku, since both of them originate from the spin–orbit coupling (SOC). For a fixed n, with the increase of tPt, Ku exhibits a non-monotonic change behavior, but α0 increases monotonously. It is found that α0 shows a nonlinear positve correlation to Ku. It suggests that the SOC is not the only factor affecting the damping process. Finally, for the specific sample, both α0 and Ku also display the different variation behaviors with increasing Ta. In this case, the changes in film microstructure caused by the annealing have different contributions to Ku and α0, resulting in a negative correlation between Ku and α0. The findings could be helpful to design the potential application of [Co/Ni]n multilayers system in STT-MRAM with high density, low power and high thermal stability.

Transmissivity testing of multilayer insulation at cryogenic temperatures

The problem of degraded emissivity of thin films at low temperatures has been a long observed phenomena. Previous efforts at measuring properties have suggested that transmission of energy through the films may play a key role in the thermal performance of multilayer insulation systems at low temperatures. Similarly, recent testing on tank applied systems has suggested a radiative degradation at low temperatures. Two different approaches were used to attempt to measure the transmission of energy through MLI at low temperatures. A laser based measurement system was set up to directly measure transmittance and a calorimetric based measurement system was used to measure relative emittance of a single layer between aluminum foil and double aluminized Mylar. Minimal transmission at long wavelengths were observed through standard MLI blanket materials at deposition thicknesses of even 35nm. Where transmission was measured, it was too low to effect the performance of a multilayers system. Similarly, the calorimeter showed similar increases of emissivity for both standard blanket materials and aluminum foils. Multiple different methodologies of measurement have all yielded the same result: that there is no transmission through standard MLI blanket materials at wavelengths associated with temperatures as low as 2K.

Inverse Model for the Solute Micro-Field Formation during Self-Propagating High Temperature Reaction

AbstractA new thermodynamic description for the self-propagating high temperature synthesis (SHS - reaction) is presented in the “inverse” version. This description is worked out for the diffusion barrier, thickness of which is at the limit, i.e. its value is infinitesimally small. The solution to the diffusion equation delivered in the description can be easily extended for the diffusion barrier of a greater thickness. The Ni/Al multi-layers system is treated as a virtual eutectic alloy solidifying with the rate equal to that involved by the self-propagating reaction. It is suggested to inverse the curves obtained for solidification in order to characterize the melting completed by the formation of the AlNi - intermetallic phase required in the self-propagating synthesis.

Electromagnetic Wave Absorber with Isotropic and Anisotropic Metamaterials

The absorption characteristics of the electromagnetic wave propagating through one dimensional system with the metamaterials are studied basing on the transfer matrix method. The relations between the absorptivity with the frequency of the incident wave and the thickness of the metamaterials are calculated. The results show that the absorptivity is about 100% near the resonant frequency of the isotropic metamaterials. This means that the metamaterials can be used as a narrow band absorber. The thickness of the metamaterials determines the width of the band. Furthermore the absorption characteristics of the multilayers system with the isotropic and anisotropic metamaterials are studied. The band width increases with the addition of the layer number. The absorption is dependent on the polarization direction of the incident electromagnetic wave for the anisotropic metamaterials. Thus the anisotropic metamaterials can be used to be the polarization tunable absorber. The layer number can also determine the frequency for the maximum absorption as for the multilayer system.

MHD Stability Analysis and Flow Controls of Liquid Metal Free Surface Film Flows as Fusion Reactor PFCs**supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2014GB125003 and 2013GB114002), National Natural Science Foundation of China (No. 11105044)

Numerical and experimental investigation results on the magnetohydrodynamics (MHD) film flows along flat and curved bottom surfaces are summarized in this study. A simplified modeling has been developed to study the liquid metal MHD film state, which has been validated by the existing experimental results. Numerical results on how the inlet velocity (V), the chute width (W) and the inlet film thickness (d0) affect the MHD film flow state are obtained. MHD stability analysis results are also provided in this study. The results show that strong magnetic fields make the stable V decrease several times compared to the case with no magnetic field, especially small radial magnetic fields (Bn) will have a significant impact on the MHD film flow state. Based on the above numerical and MHD stability analysis results flow control methods are proposed for flat and curved MHD film flows. For curved film flow we firstly proposed a new multi-layers MHD film flow system with a solid metal mesh to get the stable MHD film flows along the curved bottom surface. Experiments on flat and curved MHD film flows are also carried out and some firstly observed results are achieved.

Destruction Analysis of Broadside Multi-Cabin Protective Structure of Warship under Explosion Loading

Shock wave parameters of cabins for shipboard defensive structure are studied based on shock wave theory. The destroy of defensive structure can be estimated by impulse of shock wave. In the process of air shock wave propagating, isentropic suction wave is reflected from void cabin into defense structure. The solution of shock wave attenuation of void cabin can be reached by using isentropic line to replace the shock adiabatic of the reflected shock. It can be seen from the example that the multi-layers defense structure system of warship is very important to decrease the damage from explosive shock wave. The method can be used to predict the extent of damage of naval vessel.

Nanoindentation of nano-Al/Si3N4 multilayers with Vickers and Brinell indenters

Abstract The mechanical properties of ceramics films at the sub-micron, even nanometer length scale have attracted increased attention due to the high-speed development of microelectronic technology. In this work, nano-indentation hardness as a function of the different individual layer thickness has been measured and investigated in the sputtered Al/Si 3 N 4 multilayers with different indenters (Vickers and Brinell). For this ceramics/metal multilayers system, the hardness of the multilayers increases with decreasing individual layer thickness from 500 nm to 100 nm and from 50 nm to 10 nm, indicating a significant size effect. At the same time, changes in the deformation behavior may be controlled by different deformation mechanisms for submicron scale and nanometer scale.

Characterization of Taoura’s multilayers system by the geochemical tracers of carbonates and the evaporites (oriental extreme Algeria)

In the North-East Algeria, in the zone of diapirs, the previous hydrogeologic study of the region of Souk-Ahras Taoura had identified the multilayer aquifer system of Miocene sandstones and carbonates of lower and upper Cretaceous. The formations are generally dominated by carbonate intercalated with marl, highly fractured and folded (NE-SW), in parallel to the direction of the structures outcrops the Triassic diapiric. The thermal carbonated aquifer updates of the Neogene-quaternary of highly mineralized springs with low discharge (Hammam Tassa, Ain El Damssa); the fissural aquifer and the maastrichtian and campanian aquifers, widely exploited for the drinking water and the irrigation, contain an important potential in water. For a better understanding of the functioning of the aquifer system, it seemed necessary to characterize him by geochemical tracers of carbonates and evaporates. The geochemical data of waters of sources and main drillings showed, on one hand that thermal waters circulated rather profoundly by washing the Triassic evaporitic, and on the other hand which the fracturing in distension allowed waters to drain simultaneously aquifers. Thus, waters appearing to springs would be a mixture, in variable proportions, between the different types of water flowing in this hydrothermal karst system.

EVALUATION OF RUTTING DEPTH IN FLEXIBLE PAVEMENTS BY USING FINITE ELEMENT ANALYSIS AND LOCAL EMPIRICAL MODEL

The objective of this research is to predict rut depth in local flexible pavements. Predication model in pavement performance is the process that used to estimate the parameter values which related to pavement structure, environmental condition and traffic loading. The different local empirical models have been used to calculate permanent deformation which include environmental and traffic conditions. Finite element analysis through ANSYS computer software is used to analyze two dimensional linear elastic plane strain problem through (Plane 82) elements. Standard Axle Load (ESAL) of 18 kip (80 kN) loading on an axle with dual set of tires, the wheel spacing is 13.5 in (343 mm) with tire contact pressure of 87 psi (0.6 MPa) is used. The pavement system is assumed to be an elastic multi-layers system with each layer being isotropic, homogeneous with specified resilient modulus and Poisson ratio. Each layer is to extend to infinity in the horizontal direction and have a finite thickness except the bottom layer. The analysis of results show that, although, the stress level decrease 14% in the leveling course and 27% in the base course, the rut depth is increased by 12 and 28% in that layers respectively because the material properties is changed.

A 3D finite element model for free-surface flows

The present work deals with the validation of 3D finite element model for free-surface flows. The model uses the non-hydrostatic pressure and the eddy viscosities from the conventional linear turbulence model are modified to account for the secondary effects generated by strong channel curvature in the natural rivers with meandering open channels. The unsteady Reynolds-averaged Navier–Stokes equations are solved on the unstructured grid using the Raviart–Thomas finite element for the horizontal velocity components, and the common P 1 linear finite element in the vertical direction. To provide the accurate resolution at the bed and the free-surface, the governing equations are solved in the multi-layers system (the vertical plane of the domain is subdivided into fixed thickness layers). The up-to-date k– ε turbulence solver is implemented for computing eddy coefficients, the Eulerian–Lagrangian–Galerkin (ELG) temporal scheme is performed for enhancing numerical time integration to guarantee high degree of mass conservation while the CFL restriction is eliminated. The present paper reports on successful validation of the numerical model through available benchmark tests with increasing complexity, using the high quality and high spatial resolution three-dimensional data set collected from experiments.

Numerical simulation of land subsidence induced by groundwater overexploitation in Su-Xi-Chang area, China

Su-Xi-Chang area is one of the typical regions in China which suffers from severe land subsidence. Various field monitoring records were integrated to study the characteristics and mechanisms of land subsidence in this region. The development of the land subsidence in this region shows a tight spatial and temporal correlation with the groundwater pumping. Based on the analysis of the field data, it is found that the deformation patterns of the hydrogeologic units are greatly related to the hydrogeologic properties and groundwater level variations. Some have an elastic behavior, others may have an elastic–plastic rheology. Hence, a 3D finite element numerical model considering the rheological properties of the soil was developed to simulate the groundwater level and land subsidence. Both hydraulic conductivity and specific storage were expected to vary with the porosity during the process of consolidation. Multiscale finite element method (MsFEM) was applied to solve the model during the period from 1996 to 2004. After calibrating the model with the observed groundwater level and subsidence data, the parameters of the multi-layers system were estimated. The calibrated model outputs fit reasonably well with the observed data. Consequently the model can be applied to predict groundwater level and land subsidence in future pumping scenarios. The model predictive results show that land subsidence rate can be controlled and even rebound may occur after the implementation of the groundwater exploitation prohibition.

O2/N2 Plasma Etching of Acrylic in a Multi-layers Electrode RIE System

We investigated dry etching of acrylic (PMMA) in O2/N2 plasmas using a multi-layers electrode reactive ion etching (RIE) system. The multi-layers electrode RIE system had an electrode (or a chuck) consisted of 4 individual layers in a series. The diameter of the electrodes was 150 mm. The etch process parameters we studied were both applied RIE chuck power on the electrodes and % O2 composition in the N2/ O2 plasma mixtures. In details, the RIE chuck power was changed from 75 to 200 W.% O2 in the plasmas was varied from 0 to 100% at the fixed total gas flow rates of 20 sccm. The etch results of acrylic in the multi- layers electrode RIE system were characterized in terms of negatively induced dc bias on the electrode, etch rates and RMS surface roughness. Etch rate of acrylic was increased more than twice from about 0.2 µm/min to over 0.4 µm/min when RIE chuck power was changed from 75 to 200 W. 1 sigma uniformity of etch rate variation of acrylic on the 4 layers electrode was slightly increased from 2.3 to 3.2% when RIE chuck power was changed from 75 to 200 W at the fixed etch condition of 16 sccm O2/4 sccm N2 gas flow and 100 mTorr chamber pressure. Surface morphology was also investigated using both a surface profilometry and scanning electron microscopy (SEM). The RMS roughness of etched acrylic surface was strongly affected by % O2 composition in the O2/N2 plasmas. However, RIE chuck power changes hardly affected the roughness results in the range of 75-200 W. During etching experiment, Optical Emission Spectroscopy (OES) data was taken and we found both N2 peak (354.27 nm) and O2 peak (777.54 nm). The preliminarily overall results showed that the multi-layers electrode concept could be successfully utilized for high volume reactive ion etching of acrylic in the future.

Finite element modelling of free-surface flows with non-hydrostatic pressure andk-ɛ turbulence model

Validation of 3D finite element model for free-surface flow is conducted using a high quality and high spatial resolution data set. The commonly numerical models with the conventional hydrostatic pressure still remain the most widely used approach for the solution of practical engineering problems. However, when a 3D description of the velocity field is required, it is useful to resort to a more accurate model in which the hydrostatic assumption is removed. The present research finds its motivation in the increasing need for efficient management of geophysical flows such as estuaries (multiphase fluid flow) or natural rivers with the presence of short waves and/or strong bathymetry gradient, and/or strong channel curvature. A numerical solution is based on the unsteady Reynolds-averaged Navier-Stokes equations on the unstructured grid. The eddy viscosity is calculated from the efficient k-e turbulence model. The model uses implicit fractional step time stepping, and the characteristics method is used to compute the convection terms in the multi-layers system (suitable for the vertical stratified fluid flow), in which the vertical grid is located at predefined heights and the number of elements in the water column depends on water depth. The bottommost and topmost elements of variable height allow a faithful representation of the bed and the time-varying free-surface, respectively. The model is applied to the 3D open channel flows of various complexity