Free Layer Research Articles

MHD Free Convection Boundary Layer Flow on a Horizontal Circular Cylinder in a Williamson Hybrid Ferrofluid with Viscous Dissipation

The present research examined the flow of a horizontal circular cylinder immersed in a Williamson hybrid ferrofluid via free convection boundary layer flow. The fluid flow is modelled by means of governing partial differential equations that incorporate viscous dissipation and magnetohydrodynamic (MHD) effects. Prior to being converted into a more practical partial differential equation, these dimensional equations are reduced to a non-dimensional form by utilising appropriate dimensionless variables. The Keller-box approach is then used to solve these equations with fewer dependent variables numerically. Graphical representations are generated, and the impacts of different interested factors are analysed using MATLAB software. According to the results, the hybrid ferrofluid outperformed ferrofluid with the same particle volume fraction in terms of skin friction and convective heat transfer capabilities.

Instability of a vertical free convection boundary layer flow: Asymptotically from a perfectly flat one to a highly curved one

Instability of a vertical free convection boundary layer flow: Asymptotically from a perfectly flat one to a highly curved one

Research on Production Behavior of A Fractured Well in Gas Hydrate Reservoirs Considering Multilayer

Abstract Natural gas hydrates are internationally recognized as a new clean energy source with high prospects for commercial development. However, the vast majority of hydrates are hosted in oceanic clayey silty sediments, which are inefficient to exploit due to the extremely low effective permeability. In this paper, a novel development mode, that is, multilayer commingled production with a hydraulically fractured well, is proposed for the multilayered reservoir where hydrate and free gas coexist, to enhance productivity. Especially, the co-production behavior was numerically investigated, with the multilayered reservoir containing a hydrate-bearing layer, a three-phase layer, and a free gas layer located in the Shenhu Area as the geological background. The results indicated that the fracture provided flow channels for gas production in the multilayer, as well as greatly increasing the pressure drop spreading zone and changing the hydrate decomposition mode from around the wellbore to along the fracture surface. Compared with improving the fracture conductivity, increasing the fracture length is more effective for improving hydrate decomposition efficiency and co-production capacity. Specifically, when the fracture half-length was 30 m and the fracture conductivity was 100 D·cm, the cumulative gas production reached 949×104 m3 at 3600 days, which was 3.28 times that of the unfractured scenario. Additionally, fracturing the free gas layer hardly affects productivity as the free gas can be well-recovered by the wellbore. Overall, the proposed mode is promising for multilayered gas hydrate reservoirs, provides references for the co-production plan design, and contributes to the scale mining of hydrates.

Scaled-up production and recovery of lipopeptide biosurfactant and its application for washing petroleum-contaminated drill cuttings

A simple and efficient fermentation strategy using chitosan-immobilized Bacillus subtilis GY19 was developed for large-scale lipopeptide production from waste glycerol and palm oil. When a fed-batch fermentation approach was employed, excessive foaming was minimized, while lipopeptide production was greater than that of conventional batch fermentation. When a 700L stirred tank fermenter with a 400L working volume was used, a lipopeptide concentration and yield of 7.55g/L and 0.190g/g of substrate, respectively, were achieved. The pilot-scale recovery process involved sequential bacterial cell removal via centrifugation, elimination of impurities through acidification of the cell-free broth, and partial purification and concentration of the lipopeptides via ultrafiltration. A 5kDa stabilized cellulose-based membrane maintained a constant permeate flux and resulted in 67.2% lipopeptide recovery. The concentrated lipopeptide retentate contained 16.8g/L lipopeptides and a surface tension of 28.82 mN/m. A biobased washing agent for the treatment of petroleum-contaminated drill cuttings was later formulated with the retentate and various vegetable oil-based surfactants via the simplex−lattice mixture design methodology. The mixture of 1% retentate and 4% fatty alcohol ethoxylate 5EO presented the greatest removal efficiency of 83.2% for drill cuttings containing 15% (w/w) total petroleum hydrocarbons. The formulation also mobilized petroleum hydrocarbons into a distinct free oil layer, which would be easy to separate and subsequently recycle. These findings demonstrate the scalability of the lipopeptide production and recovery process, while the biobased washing agent offers an environmentally friendly approach for petroleum remediation.

Ultrahigh room and high − temperature mechanical properties of SiCf/SiC composites prepared by hybrid CVI and PIP methods: Effects of PIP temperature

Unidirectional (UD) SiCf/SiC composites were prepared using chemical vapor infiltration (CVI)-polymer infiltration and pyrolysis (PIP) hybrid procedure at different PIP temperatures of 1100 °C (1100PIP), 1300 °C (1300PIP), and 1500 °C (1500PIP). The effect of PIP temperature on the microstructure of each component was studied. Results showed that SiC fiber strength and interfacial shear strength (IFSS) were the main factors affecting the mechanical properties of the composite. At 1100 °C, the fiber was thermally stable and IFSS was high, due to which 1100PIP achieved ultrahigh mechanical performance with tensile strength of 901.0 ± 87.7 MPa, flexural strength of 2186.5 ± 192.5 MPa, and toughness of 80.6 ± 12.0 MPa·m1/2. At 1300 °C, IFSS decreased slightly, due to the crystallization of BN interphase. Hence, the mechanical performance of 1300PIP decreased slightly to 789.8 ± 42.9 MPa, 1935.9 ± 163.2 MPa, and 58.2 ± 4.0 MPa·m1/2, respectively. At 1500 °C, severe fiber ceramization and decrease in IFSS caused severe decline in mechanical performance to about half of that of 1100PIP. The crack could be deflected not only at the fiber/BN (F/B) interface, but also at the CVI SiC/PIP SiC (C/P) interface, due to the existence of free carbon layers at the C/P interface, which played an important role in improving the strength and toughness of the composite. 1300PIP also showed excellent strength at high − temperature. At 1350 °C and 1500 °C, its flexural strengths were as high as 1529.0 ± 73.0 MPa and 1223.1 ± 81.1 MPa, respectively. The thermal conductivity and thermal expansion coefficient were also tested. Their values were mainly affected by the grain size and thermal stabilities of the SiC fiber and PIP matrix.

Influence of back pressure adjustment of porous media on cavity flow noise control

Control of self-sustained oscillation and noise reduction poses a significant challenge. The present study employs Implicit Large Eddy Simulation at a Mach number of 0.85 to investigate the influence of a porous cavity floor on flow dynamics. By substituting the solid floor with porous media, the fundamental pressure–velocity relationship within the medium is established according to Darcy's law. Findings reveal marked suppression of wall pulsations, accompanied by a 10 dB decrease in sound pressure levels. The porous medium induces blowing and suction effects, effectively modulating large-scale re-circulation and mitigating shear layer instability, thereby approximating free mixing layer characteristics and suppressing cavity flow oscillations. At an optimized porosity for maximum noise reduction, altering back pressure at the cavity floor induces a transition in the local flow regime from suction-dominated to blowing-dominated state. Excessive reduction of back pressure promotes suction; conversely, increased pressure intensifies blowing, further attenuating feedback mechanisms and enhancing noise reduction. To explore noise reduction mechanisms, mode decomposition analyses demonstrate the efficacy of porous media in disrupting large-scale coherence structures within shear layer and redistributing energy from dominant modes to a broader frequency spectrum that engages smaller flow structures. This energy reallocation mechanism contributes to the mitigation of cavity flow noise and deepens insights into the role of porous media in flow modulation and noise control.

Fabrication of submicron CoFeB/MgO/CoFeB magnetic tunnel junction using a resistive mask HSQ/PMMA

The technology of manufacturing magnetic tunnel junctions based on CoFeB/MgO/CoFeB layers with characteristic lateral dimensions from 200 to 700 nm using a combination of HSQ/PMMA electronic resistors has been developed. To study the processes of magnetization reversal in the obtained samples, measurements of magnetoresistance curves were carried out. It is shown that, depending on the structure of the magnetically sensitive layer and the geometric parameters of the TMR contacts, elements with both vortex and quasi-homogeneous distribution of the magnetization of the free layer are realized. At the same time, in the latter, the width of the magnetization reversal front is from 2 to 6 Oe.

Numerical investigation and rapid prediction of the erosion rate of gate valve in gas-solid flow

Gate valves are essential control components in pneumatic conveying systems and often experience erosion on their sealing structures due to impacts from solid particles. The erosion leads to a degradation of the sealing effectiveness and, in severe cases, system malfunction. To address this issue, a numerical model based on computational fluid dynamics (CFD) is developed for the simplified two-dimensional gate valve. The two-way Euler-Lagrange method is utilized to investigate the characteristics of gas-solid two-phase flow and erosion rate. The simulation procedure is verified by comparing the simulation results with experimental data. Results show that the sealing surface separates the free shear layer above the cavity and a low-velocity zone is created on the sealing surface. The particles moving at the downstream bottom are the main particles that impact the sealing surface. The erosion results show that the maximum erosion rate occurs near the top of the sealing surface. And the low-velocity zone reduces the erosion rate within that region. Particle diameter, gas velocity, and valve opening have an important effect on erosion on the sealing surface. The erosion rate increases as the valve opening decreases. The value of the maximum erosion rate increases with particle diameter and gas velocity, and its position changes. Finally, based on the established numerical model, a prediction model for the sealing surface erosion rate is constructed using the surrogate model approach.

Oxidation behavior and oxidation kinetics of film cooling holes at different inclination angles of a Ni-based single-crystal blade

This paper examines the high-temperature oxidation behavior of Ni-based single-crystal turbine blade film cooling holes with varying inclination angles. Utilizing the theory of oxidation kinetics, the concept of an angle influence factor is introduced, and a novel oxidation kinetic equation is formulated. This allows for precise prediction of the oxide/γ′-free layer thickness in film cooling holes across different inclination angles throughout the oxidation process. It offers a new benchmark for future lifespan prediction models, significantly impacting the assessment of the operational life of air-cooled single crystal blades.

Complementary Polarizer SOT-MRAM for Low-Power and Robust On-Chip Memory Applications

Complementary polarized spin-transfer torque magnetic random-access memory (CPSTT-MRAM) has been proposed to address the sensing reliability issues caused by the single-ended sensing of STT-MRAM. However, it results in a three-fold increase in the free layer (FL) area compared to STT-MRAM, leading to a higher write current. Moreover, the read and write current paths in this memory are the same, thus preventing the optimization of each operation. To address these, in this study, we proposed a complementary polarized spin-orbit torque MRAM (CPSOT-MRAM), which tackles these issues through the SOT mechanism. This CPSOT-MRAM retains the advantages of CPSTT-MRAM while significantly alleviating the high write current requirement issue. Furthermore, the separation of the read and write current paths enables the optimization of each operation. Compared to CPSTT-MRAM, the proposed CPSOT-MRAM achieves a 4.0× and 2.8× improvement in write and read power, respectively, and a 20% reduction in layout area.

Stimulation Behavior of Fracture Networks in the Second Hydrate Trial Production Area of China Considering the Presence of Multiple Layers

The fracture network’s stimulation of China’s second hydrate trial production area was investigated. First, the stimulation potential of the fracture network and the influence of well arrangement on hydrate development were explored. Second, the fracture distributions’ influence on development behavior was investigated. Results showed that the fracture network could cause the trial production reservoir to reach the commercial production rate. The average CH4 production rate of unit horizontal well length using the depressurization method and depressurization combined with thermal stimulation (combined method) were 61.3 and 151.5 m3/d with the fracture network and 23.7 and 14.3 m3/d without the fracture network. In addition, without the fracture network, the development behavior of wells arranged in the mixed layer was better than that of wells arranged in the hydrate layer. However, with the fracture network, the result was reversed. With the depressurization method, the best production behavior was obtained by fracturing in the hydrate layer; however, for the combined method, the best production behavior was obtained by fracturing in the hydrate and mixed layer, while fracturing in the free gas layer was useless. This study provides a valuable reference for the hydrate development of China’s trial production reservoir.

A facilitated transport membrane composed of amine-containing ionic liquid confined in a GO/CNT network for highly efficient carbon capture

Carbon capture is a key approach to manage carbon dioxide (CO2) emissions and promote net removal of CO2 from the atmosphere. Post combustion flue gas emissions from power plants contribute a significant fraction of CO2 released into the atmosphere. Membrane-based separation strategies offer environmentally sustainable and economically viable solutions for efficient CO2 capture from power plants. Facilitated transport membranes, although showing strong capability for CO2 capture at low concentrations and under humid conditions, suffer from the loss of facilitators, such as amines, leading to decline in performance over long-term operation. Ionic liquids (ILs) are chemically and thermally stable and have low vapor pressure, which is ideal to prevent aforementioned losses. However, making a thin network for effective IL confinement is still a challenge. In this work, we developed a stable high performing IL based CO2 selective membrane that can operate at temperatures as high as 80 °C under humid conditions. An amino acid-based IL (containing facilitated carriers), 1-ethyl-3-methylimidazolium glycinate, [EMIM][GLY], was used as the separating agent. In order to selectively load and confine the IL in a thin selective layer, we designed and fabricated a network composed of stacked graphene oxide (GO) nanosheets intercalated by carbon nanotubes (CNT). While CNT acts as a nanowedge that helps in increasing the nanochannels to facilitate low-resistance gas transport, GO nanosheets act as anchoring sites due to presence of various functional groups resulting in electrostatic interaction between GO and cation of IL. Due to the aforementioned reason, distribution of GO in the network plays a critical role in forming a thin, uniform selective IL layer. The GO distribution was optimized by adjusting the pH of the coating solution; after optimizing IL coating, this results in a thin, defect free selective layer, providing a membrane with high CO2 permeance of ∼1600 GPU and CO2/N2 selectivity of 400, superior to most of the reported IL membranes. This network composed of GO/CNT network not only facilitates fabrication of a stable, ultrathin, high permeance and high selectivity supported IL membrane but also provides a platform for preparation of other IL-based membranes for desired separations.

Non‐Volatile Analog Control and Reconfiguration of a Vortex Nano‐Oscillator Frequency

AbstractMagnetic tunnel junctions are nanoscale devices that have recently attracted interest in the context of frequency multiplexed spintronic neural networks, due to their interesting dynamical properties, which are defined during the fabrication process, and depend on the material parameters and geometry. This work proposes an approach to extending the functionality of a standard magnetic tunnel junction (MTJ) by introducing an additional ferromagnet/antiferromagnet (FM/AFM) storage layer (SL) vertically integrated with the standard vortex MTJ stack into the nanopillar. The magnetostatic field created by this storage layer acts on the free layer and can be used to change its static and dynamic properties. To tune the magnitude and direction of this magnetostatic field, magnetic reconfiguration is carried out through a thermally assisted switching mechanism using a voltage pulse that heats the AFM layer in the SL above the Néel temperature in the presence of an external field. It is experimentally shown that using an MTJ based on a 600 nm diameter nanopillar with a vortex in the free layer, reconfiguration of the SL allows to continuously change the core precession frequency in the 15 MHz range, or ≈10% of the device frequency.

Multi-Level Synaptic Device Having Perpendicular Magnetic-Tunnel-Junction Spin-Valve Sensor Via Skyrmion Generated By Nano-Scale Current Emitter

Recently, with the expansion of deep learning-based artificial intelligence into various fields, high integration density and recognition accuracy are essentially necessary for neuromorphic devices. In particular, skyrmion-based artificial synaptic devices have been actively researched due to complete linearity, topological stability, and small nanoscale size. This device can emulate the synaptic plasticity (i.e., long-term potentiation (LTP) and long-term depression (LTD)) depending on the number of generated skyrmions. Magnetic skyrmions have been characterized by various methods such as perpendicular magnetic-tunnel-junction (p-MTJ) spin-valve structure, Hall bar measurements [3], and non-collinear magnetoresistance [4]: However, in the previous study using a p-MTJ spin-valve, they only measured the resistance of a single skyrmion and did not demonstrate synaptic behavior (i.e., multi-level characteristics) [5]. In addition, they essentially require an additional external magnetic field to generate skyrmions. Moreover, the reported device has low resistance margins, indicating it is extremely difficult to sense in bit-lines.In this study, for the first time, we introduced a novel multi-level synaptic device having a p-MTJ spin-valve sensor via skyrmion generated by a nano-scale current emitter. To generate skyrmion, we employed nano-scale oxygen vacancy filaments as a current emitter on the p-MTJ spin-valve sensor, and interface reducing W layer between the free layer and MgO layer, as shown in Fig.1(a). In addition, we performed a vibrating sample magnetometer (VSM) analysis to measure the PMA characteristics (i.e., squareness, saturation magnetization) of the SyAF layer and the free layer, as shown in Fig.1(b). Moreover, the generation of skyrmions depending on the thickness of the interface reducing W layer was investigated using VSM and magneto-optical Kerr effect (MOKE) analyses, as shown in Fig.1(c-f). Furthermore, MOKE analysis was conducted to analyze the mechanism of skyrmion generation in the synaptic device having the p-MTJ spin-valve sensor patterned by 5μm diameter, as shown in Fig. 1(g). Finally, we have directly observed the generation of skyrmions using a nano-scale current emitter and demonstrated synaptic plasticity via the skyrmion-based synaptic device having the p-MTJ spin-valve sensor into a 300 nm diameter cell. In our presentation, we will review in detail the synaptic behavior and generation mechanism of the skyrmions. Acknowledgements This work was supported by the Technology Innovation Program (or Industrial Strategic Technology Development Program-Public-private joint investment semiconductor R&D program(K-CHIPS) to foster high-quality human resources) ("RS-2023-00235634", Development of high speed/low power/high reliability 2-terminal field-free SOT-MRAM) funded By the Ministry of Trade, Industry & Energy(MOTIE, Korea)(1415187787) and Institute of Information & communications Technology Planning & Evaluation (IITP) under the artificial intelligence semiconductor support program to nurture the best talents (IITP-(2023)-RS-2023-00253914) grant funded by the Korea government(MSIT).

Growth of organized flow coherent motions within a single-stream shear layer: 4D-PTV measurements

This study investigates the evolution of a single-stream shear layer (SSSL) originating from a wall boundary layer past a backward-facing step. Utilizing a time-resolved 3D-Particle Tracking Velocimetry (4D-PTV) technique, we track the trajectories of fluorescent particles to gain insight into the flow characteristics of the SSSL. A compact water tunnel facility (Reτ=1240\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{Re}_\ au =1\\,240$$\\end{document}) is fabricated to obtain an SSSL with a perpendicular slow entrainment stream past the separation edge. A hybrid interpolation approach that combines ensemble binning and Gaussian weighting is implemented to derive minimally filtered mean and instantaneous lower- and higher-order flow field parameters. Spanwise-dominant coherent motion accompanied by finer flow scales is observed to grow due to flow entrainment through “nibbling” actions of small-scale vortices, “engulfing” by large-scale vortices, and vortex pairing events. Furthermore, the non-zero-speed stream edge grows relatively faster than the zero-speed stream edge, showing a strong asymmetry in mixing composition across a mixing layer. The SSSL reaches self-similarity at a streamwise distance of ≈55θ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\approx 55\\,\ heta _{0}$$\\end{document}, where θ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta _0$$\\end{document} is the initial momentum thickness from the separation edge, i.e., considerably shorter than reported in previous studies. A literature comparison of growth rate parameters raises intriguing questions regarding a potential inclusive growth scaling unifying the free shear layers. A turbulent kinetic energy (TKE) budget analysis reveals a negative production region immediately downstream of the separation edge attributed to a large positive streamwise gradient of streamwise velocity. In the self-similar region, the phase-averaged flow mapping demonstrates a larger concentration of turbulence production rate around the outer edges of spanwise vortices, specifically at the intersection of braids and vortices. Furthermore, a spatial separation exists in the regions of peak production and dissipation rates within the vortex core region favoring dissipation. The braids exhibit a larger concentration of turbulence diffusion rates, indicating their function as a conduit for exchanging turbulence between neighboring coherent motions.

Voltage-insensitive stochastic magnetic tunnel junctions with double free layers

Stochastic magnetic tunnel junction (s-MTJ) is a promising component of probabilistic bit (p-bit), which plays a pivotal role in probabilistic computers. For a standard cell structure of the p-bit, s-MTJ is desired to be insensitive to voltage across the junction over several hundred millivolts. In conventional s-MTJs with a reference layer having a fixed magnetization direction, however, the stochastic output significantly varies with the voltage due to spin-transfer torque (STT) acting on the stochastic free layer. In this work, we study a s-MTJ with a “double-free-layer” design theoretically proposed earlier, in which the fixed reference layer of the conventional structure is replaced by another stochastic free layer, effectively mitigating the influence of STT on the stochastic output. We show that the key device property characterized by the ratio of relaxation times between the high- and low-resistance states is one to two orders of magnitude less sensitive to bias voltage variations compared to conventional s-MTJs when the top and bottom free layers are designed to possess the same effective thickness. This work opens a pathway for reliable, nanosecond-operation, high-output, and scalable spintronics-based p-bits.

Effect of anti‐Agglomerants on carbon dioxide hydrate formation in oil–water systems

AbstractThe experiments in high‐pressure pipelines simulate the formation and fluid of hydrate under deep‐sea conditions, which has practical significance for the deep‐sea landfill of carbon dioxide (CO2) and the safe running of oil and gas pipelines. In this paper, pure water, white oil, CO2, and arquad 2C‐75 were used to study the formation and flow characteristics of CO2 hydrate in the oil–water system with the help of a loop device, and the growth morphology of hydrate was observed through the view‐window on the loop. The experimental results show that in the low water cut system without anti‐agglomerates, hydrate mainly forms on the surface of water droplets and the surface of the free water layer at the bottom of the loop. In the high water cut system, hydrate forms on the pipe wall in the form of hydrate film. Increasing water cuts can shorten the induction period of hydrate formation. Anti‐agglomerates in the oil–water system can inhibit the growth of hydrate film on the pipe wall effectively. Anti‐agglomerates can shorten the induction time of hydrate formation.

Effect of free liquid layer quantity on bacteria and protein adhesion to liquid infused polymers.

Liquid-infused polymers are recognized for their ability to repel foulants, making them promising for biomedical applications including catheter-associated urinary tract infections (CAUTIs). However, the impact of the quantity of free liquid layer covering the surface on protein and bacterial adhesion is not well understood. Here, we explore how the amount of free silicone liquid layer in infused silicone catheter materials influences the adhesion of bacteria and proteins relevant to CAUTIs. To alter the quantity of the free liquid layer, we either physically removed excess liquid from fully infused catheter materials or partially infused them. We then evaluated the impact on bacterial and host protein adhesion. Physical removal of the free liquid layer from the fully infused samples reduced the height of the liquid layer from 60 μm to below detection limits and silicone liquid loss into the environment by approximately 64% compared to controls, without significantly increasing the deposition of protein fibrinogen or the adhesion of the common uropathogen Enterococcus faecalis. Partially infused samples showed even greater reductions in liquid loss: samples infused to 70%-80% of their maximum capacity exhibited about an 85% decrease in liquid loss compared to fully infused controls. Notably, samples with more than 70% infusion did not show significant increases in fibrinogen or E. faecalis adhesion. These findings suggest that adjusting the levels of the free liquid layer in infused polymers can influence protein and bacterial adhesion on their surfaces. Moreover, removing the free liquid layer can effectively reduce liquid loss from these polymers while maintaining their functionality.

The role of adding carbon nanoparticles to free convective boundary layer viscoelastic fluid flow past a vertical porous cone surface: application in wastewater treatment

The role of adding carbon nanoparticles to free convective boundary layer viscoelastic fluid flow past a vertical porous cone surface: application in wastewater treatment

Low Hysteresis and High Stability in Tunneling Magnetoresistance Vortex Sensors With a Composite Free Layer

Low Hysteresis and High Stability in Tunneling Magnetoresistance Vortex Sensors With a Composite Free Layer