Single Domain Model Research Articles

Numerical simulation of the flow around and through a hygroscopic porous circular cylinder

The flow around and through a hygroscopic porous circular cylinder was studied numerically in this paper. The cylinder is placed horizontally and exposed to a uniform flow of air. The effects of the important parameters, the hygroscopicity, the porosity, the Reynolds and Darcy numbers, on the flow are investigated in detail. A single-domain model is introduced to describe the flow around and through a porous circular cylinder with consideration of the adsorption effects. The flow is simulated by solving time-dependent Navier–Stokes equations in the homogenous fluid region and Darcy–Brinkman–Forchheimer extended model in the inner region. High order compact finite difference schemes are constructed for better simulation of this problem. Detailed numerical simulation results indicate that the effects of adsorption may have a significant effect on the flow behind the porous cylinder and suppress the occurrence of recirculating wake.

Finite-element simulation of myocardial electrical excitation

Based on a single-domain model of myocardial conduction, isotropic and anisotropic finite element models of the myocardium are developed allowing excitation wave propagation to be studied. The Aliev-Panfilov phenomenological equations were used as the relations between the transmembrane current and the transmembrane potential. Interaction of an additional source of initial excitation with an excitation wave that passed and the spread of the excitation wave are studied using heart tomograms. A numerical solution is obtained using a splitting algorithm that allows the nonlinear boundary-value problem to be reduced to a sequence of simpler problems: ordinary differential equations and linear boundary-value problems in partial derivatives.

비정질 리본의 ΔE 특성을 이용한 선형 자기센서에 관한 연구

<TEX>${\delta}$</TEX>E 효과는 재료의 영율(Young's modulus)이 자화 상태에 따라 변화하는 효과를 말한다. 본 연구에서는 두께 <TEX>$25{\mu}m$</TEX>, 길이 30 mm의 비정질 리본 2605SC를 폭 3 mm, 5 mm, 8.5 mm로 각각 에칭하여 외부 자기장 세기와 시편의 폭 변화에 따른 영율의 변화를 임피던스 공명 측정을 이용하여 측정하였다. 인가 자기장이 증가함에 따라 영율이 증가하는 것과, 시편의 폭이 넓을수록 시편에 인가되는 유효 자기장이 감소하여 영율이 감소하는 결과를 볼 수 있었고, 단원자 모델로 계산한 결과와 비교적 잘 일치하는 것을 확인하였으며, 외부 자기장 세기에 따라 변화하는 영율(<TEX>${\delta}$</TEX>E)의 선형적 변화 영역을 이용한 선형 자기센서 제작 가능성을 확인하였다. The width dependence of Delta E has been studied by impedance resonance method in Fe-rich amorphous ribbon of as received state. It can be explained by single domain model include effective magnetic field <TEX>$H_{eff}$</TEX> and demagnetization factor <TEX>$N_d$</TEX>. Wider width ribbon's effective is smaller than narrow it. Young's modulus also smaller than narrow width. These result well agreement in calculation. It has been also studied that linear magnetic field sensor using width dependence of Delta E under the field range 0 Oe~80 Oe. The sensitivity of the sensor was found to be 95 Hz/Oe.

Numerical Investigation of the High Temperature PEM Electrolyzer: Effect of Flow Channel Configurations

In this work, we aim to develop a mathematical and numerical framework for the HT-PEM electrolyzer that serves two main objectives: the first involves the study of the fundamental aspect of the HT-PEM electrolyzer and the associated transport and electrochemical processes. The second objective concerns with the development and integration of various flow channel design for high performance hydrogen production. Three different flow channel configurations, namely parallel, serpentine and multiple-serpentine were simulated and compared in term of hydrogen generation, parasitic load arising from pumping power and local temperature profiles. A single-domain model of a HT-PEM electrolyzer is implemented in the commercial CFD code ANSYS Fluent. The non-isothermal model considers conservation of mass, momentum, species, energy and charge (electronic and ionic). Good agreement between model prediction and experimental polarization curves is obtained within the experimental range. The established model is then extended to account for the effect of flow channel designs. The results suggest that multiple-serpentine channel design performs better in term of hydrogen production and uniformity of temperature with reasonable pressure drop.

Numerical Simulation of the Effect of the Size of Suspensions on the Solidification Process of Nanoparticle-Enhanced Phase Change Materials

Nanostructure-enhanced phase change materials (NePCM) have been widely studied in recent years due to their enhanced thermal conductivity and improved charge/discharge in thermal energy storage applications. In this study, the effect of the size of the nanoparticles on the morphology of the solid–liquid interface and the evolving concentration field during solidification is reported. Combining a one-fluid-mixture approach with the single-domain enthalpy-porosity model for phase change and assuming a linear dependence of the liquidus and solidus temperatures of the mushy zone on the local concentration of the nanoparticles subject to a constant value of the segregation coefficient, thermal-solutal convection as well as the Brownian and thermophoretic effects are taken into account. A square cavity containing a suspension of copper nanoparticles (diameter of 5 and 2 nm) in water was the model NePCM considered. Subject to a 5 °C temperature difference between the hot (top) and cold (bottom) sides and with an initial loading of the nanoparticles equal to 10 wt. % (1.22 vol. %), the colloid was solidified from the bottom. The solid–liquid interface for the case of NePCM with 5 nm particle size was almost planar throughout the solidification process. However, for the case of the NePCM with particle size of 2 nm, the solid–liquid interface evolved from a stable planar shape to an unstable dendritic structure. This transition was attributed to the constitutional supercooling effect, whereby the rejected particles that are pushed away from the interface into the liquid zone form regions of high concentration thus leading to a lower solidus temperature. Moreover, for the smaller particle size of 2 nm, the ensuing solutal convection at the liquid–solid interface due to the concentration gradient is affected by the increased Brownian diffusivity. Due to size-dependent rejection of nanoparticles, the frozen layer that resulted from a dendritic growth contains regions of depleted concentration. Despite the higher thermal conductivity of the colloids, the amount of frozen phase during a fixed time period diminished as the particle size decreased.

Single-domain shape anisotropy in near-macroscopic Ni80Fe20 thin-film rectangles

Shape anisotropy provides a simple mechanism to adjust the local bias field in patterned structures. It is well known that for ellipsoidal particles &amp;lt;1 μm in size, a quasi-single domain state can be realized with uniform anisotropy field. For larger patterned ferromagnetic thin-film elements, domain formation is thought to limit the effectiveness of shape anisotropy. In our work, we show that very soft lithographically patterned Ni80Fe20 films with control of induced magnetic anisotropy can exhibit shape anisotropy fields in agreement with single-domain models, for both hysteresis loop measurements at low field and ferromagnetic resonance measurements at high field. We show the superiority of the fluxmetric form over the magnetometric form of anisotropy estimate for thin films with control dimensions from 10 μm to 150 μm and in-plane aspect ratios above 10.

A Multidomain Engineering Change Propagation Model to Support Uncertainty Reduction and Risk Management in Design

Engineering change (EC) is a source of uncertainty. While the number of changes to a design can be optimized, their existence cannot be eliminated. Each change is accompanied by intended and unintended impacts both of which might propagate and cause further knock-on changes. Such change propagation causes uncertainty in design time, cost, and quality and thus needs to be predicted and controlled. Current engineering change propagation models map the product connectivity into a single-domain network and model change propagation as spread within this network. Those models miss out most dependencies from other domains and suffer from “hidden dependencies”. This paper proposes the function-behavior-structure (FBS) linkage model, a multidomain model which combines concepts of both the function-behavior-structure model from Gero and colleagues with the change prediction method (CPM) from Clarkson and colleagues. The FBS linkage model is represented in a network and a corresponding multidomain matrix of structural, behavioral, and functional elements and their links. Change propagation is described as spread in that network using principles of graph theory. The model is applied to a diesel engine. The results show that the FBS linkage model is promising and improves current methods in several ways: The model (1) accounts explicitly for all possible dependencies between product elements, (2) allows capturing and modeling of all relevant change requests, (3) improves the understanding of why and how changes propagate, (4) is scalable to different levels of decomposition, and (5) is flexible to present the results on different levels of abstraction. All these features of the FBS linkage model can help control and counteract change propagation and reduce uncertainty and risk in design.

Relationship Between Dual‐Domain Parameters and Practical Characterization Data

Dual-domain solute transport models produce significantly improved agreement to observations compared to single-domain (advection-dispersion) models when used in an a posteriori data fitting mode. However, the use of dual-domain models in a general predictive manner has been a difficult and persistent challenge, particularly at field-scale where characterization of permeability and flow is inherently limited. Numerical experiments were conducted in this study to better understand how single-rate mass transfer parameters vary with aquifer attributes and contaminant exposure. High-resolution reference simulations considered 30 different scenarios involving variations in permeability distribution, flow field, mass transfer timescale, and contaminant exposure time. Optimal dual-domain transport parameters were empirically determined by matching to breakthrough curves from the high-resolution simulations. Numerical results show that mobile porosity increases with lower permeability contrast/variance, smaller spatial correlation length, lower connectivity of high-permeability zones, and flow transverse to strata. A nonzero non-participating porosity improves empirical fitting, and becomes larger for flow aligned with strata, smaller diffusion coefficient, and larger spatial correlation length. The non-dimensional mass transfer coefficient or Damkohler number tends to be close to 1.0 and decrease with contaminant exposure time, in agreement with prior studies. The best empirical fit is generally achieved with a combination of macrodispersion and first-order mass transfer. Quantitative prediction of ensemble-average dual-domain parameters as a function of measurable aquifer attributes proved only marginally successful.

Two-Axis Magnetisation Analysis of Epitaxial Cobalt Films

Cobalt films were grown by molecular beam epitaxy on CaF2 buffer layers on silicon. Due to unique properties of CaF2/Si(100) interface, the surface of CaF2 has grooves along [110] direction. Cobalt grown on it has in-plane uniaxial magnetic anisotropy with easy axis along the grooves. The dependence of remanence magnetisation and coercivity on azimuth angle (between the grooves and field) follows single domain model in the range from 0 to 80 degrees. For hysteresis loops of both parallel and perpendicular components of magnetisation, quantitative agreement was achieved within the model of coherent rotation with certain distribution of anisotropy energy over regions of the sample. Between 80 degrees and 90 degrees, the film splits into multiple domains.

Growth and magnetism of low-temperature deposited Fe/Si(111) films as an intermediate layer for suppression of silicide formation

Low temperature (LT: 100 K) deposition of Fe on Si(111)7×7 surface effectively reduces Fe-silicide formation at the Fe/Si interface, as compared with conventional room temperature (RT) growth. The interface condition of 5–15 monolayers (ML) LT-Fe/Si(111) remains stable at least up to 350 K. Si segregation was observed after annealing at 400 K. LT-grown Fe films also reveal a relatively flat surface morphology with a roughness of 0.4–0.6 nm. Thus, LT-Fe films were suggested as an intermediate layer for the subsequent RT-growth of Fe. We use a single domain model of magnetic anisotropy to fit the magnetic coercivity evolution of n ML RT-Fe on 5 ML LT-Fe/Si(111). Accordingly, we deduce the surface and volume-contributed magnetic anisotropy for discussion.

Spin torque switching of perpendicular Ta∣CoFeB∣MgO-based magnetic tunnel junctions

Spin torque switching is investigated in perpendicular magnetic tunnel junctions using Ta∣CoFeB∣MgO free layers and a synthetic antiferromagnet reference layer. We show that the Ta∣CoFeB interface makes a key contribution to the perpendicular anisotropy. The quasistatic phase diagram for switching under applied field and voltage is reported. Low switching voltages, Vc 50 ns=290 mV are obtained, in the range required for spin torque magnetic random access memory. Switching down to 1 ns is reported, with a rise in switching speed from increased overdrive that is eight times greater than for comparable in-plane devices, consistent with expectations from a single-domain model.

Theory of giant magneto-impedance effect in amorphous ribbon with transverse bias magnetic field

Taking into account the amorphous alloy ribbon with the 180°magnetic domain walls and transverse bias magnetic field, and adopting multi-domain structure model, the theory of giant magneto-impedance (GMI) effect was found by minimizing the total free energy and by the solution of the Maxwell’s equations combining with Landau-Lifshitz equation. A new four-state method is proposed to calculate the average magnetic permeability of four states of the amorphous materials, which is used to replace the permeability obtained based on the single domain model. The method has an advantage in explaining the GMI effect over the theory established by single domain model.

Single and Dual-Domain Models to Evaluate the Effects of Preferential Flow Paths in Alluvial Sediments

Typical features of preferential flow paths were evidenced by numerical tests of convective transport of conservative solutes performed in three blocks of alluvial sediments at the scale of depositional elements. The numerical experiments are analysed with standard single-domain models (SDMs) and with dual-domain models (DDMs): the model parameters are identified by minimisation of the misfit between the “experimental” and the modelled cumulative breakthrough curves (BTCs) and between the “experimental” and the modelled temporal moments of the BTCs. The results for the SDMs show different behaviours for the three model blocks and for the different flow directions, in good agreement with their hydrostratigraphic characteristics. The results for the DDMs sometimes correspond to cases for which one of the two domains is dominant and its values of diffusivity and average velocity are close to those obtained for the SDM; in some cases the DDM performs much better than the SDM and correctly represents the effects of preferential flow paths. Finally the relevance of the DDM is analysed in the framework of multi-objective optimisation: a proper choice of the objective-functions yields Pareto sets whose geometries are different for single- and dual-domain media.

Cross-Domain Effects on Parse Selection for Precision Grammars

We examine the impact of domain on parse selection accuracy, in the context of precision HPSG parsing using the English Resource Grammar, using two training corpora and four test corpora and evaluating using exact tree matches as well as dependency F-scores. In addition to determining the relative impact of in- vs. cross-domain parse selection training on parser performance, we propose strategies to avoid cross-domain performance penalty when limited in-domain data is available. Our work supports previous research showing that in-domain training data significantly improves parse selection accuracy, and that it provides greater parser accuracy than an out-of-domain training corpus of the same size, but we verify experimentally that this holds for a handcrafted grammar, observing a 10---16% improvement in exact match and 5---6% improvement in dependency F-score by using a domain-matched training corpus. We also find it is possible to considerably improve parse selection accuracy through construction of even small-scale in-domain treebanks, and learning of parse selection models over in-domain and out-of-domain data. Naively adding an 11,000-token in-domain training corpus boosts dependency F-score by 2---3% over using solely out-of-domain data. We investigate more sophisticated strategies for combining data from these sources to train models: weighted linear interpolation between the single-domain models, and training a model from the combined data, optionally duplicating the smaller corpus to give it a higher weighting. The most successful strategy is training a monolithic model after duplicating the smaller corpus, which gives an improvement over a range of weightings, but we also show that the optimal value for these parameters can be estimated on a case-by-case basis using a cross-validation strategy. This domain-tuning strategy provides a further performance improvement of up to 2.3% for exact match and 0.9% for dependency F-score compared to the naive combination strategy using the same data.

Easy axis reorientation and magneto-crystalline anisotropic resistance of tensile strained (Ga,Mn)As films

We present a study of magnetic anisotropy by using magneto-transport and direct magnetization measurements on tensile strained (Ga,Mn)As films. The magnetic easy axis of the films is in-plane at low temperatures, while the easy axis flips to out-of-plane when temperature is raised or hole concentration is increased. This easy axis reorientation is explained qualitatively in a simple physical picture by Zener’s p–d model. In addition, the magneto-crystalline anisotropic resistance was also investigated experimentally and theoretically based on the single magnetic domain model. The dependence of sheet resistance on the angle between the magnetic field and [1 0 0] direction was measured. It is found that the magnetization vector M in the single-domain state deviates from the external magnetic field H direction at low magnetic field, while for high magnetic field, M continuously moves following the field direction, which leads to different resistivity function behaviors.

Thermally Activated Switching in Nanoscale Magnetic Tunnel Junctions

Magnetic tunnel junctions 90 to 300 nm wide and of aspect ratio ¿2 are studied using high-speed pulse fields with regard to the soft-layer magnetization reversal under thermal agitation. It is found that the larger cells, 200-300 nm wide, reverse through nonuniform magnetization states with the energy barriers to thermal activation an order of magnitude smaller than those expected for single-domain magnets. The single-domain limit is reached for the smallest cells, having elliptical soft layers approximately 90 nm wide and 150-200 nm long. The magnetization decay in the small cell limit is well described by the Stoner-Wohlfarth single-domain model and the Arrhenius activation law. The results demonstrate that the penalty due to the smaller magnetic volume is compensated by a larger relative energy barrier to activation as the junction size is reduced to ~ 90 nm. This determines the important length scale for geometric scaling of such technologies as magnetic random access memory.

Activation energy and switching behavior of two interacting identical magnetic particles

An analytical method to study the magnetization behavior of a system composed of two magnetic particles is presented, when the magnetic field is applied in-plane. The study is based on a single-domain model, assuming that the particles are two ellipsoids with both exchange and magnetostatic coupling. The model is used to study the synthetic antiferromagnetic structure and a pair of particles with only dipolar interaction for bond angles β=0 and π/2. When the magnetic field is applied along the easy axis a complete description for the system’s minima, activation energy, and possible switches is performed.

Fault type analysis along the San Andreas Fault zone: A numerical approach

Finite Element (FE) modeling under plane stress condition is used to analyze the fault type variation with depth along and around the San Andreas Fault (SAF) zone. In this simulation elastic rheology was used and was thought justifiable as the variation in depth from 0.5 km to 20 km was considered. Series of calculations were performed with the variation in domain properties. Three types of models were created based on simple geological map of California, namely, 1) single domain model considering whole California as one homogeneous domain, 2) three domains model including the North American plate, Pacific plate, and SAF zone as separate domains, and 3) Four domains model including the three above plus the Garlock Fault zone. Mohr-Coulomb failure criterion and Byerlee’s law were used for the calculation of failure state. All the models were driven by displacement boundary condition imposing the fixed North American plate and Pacific plate motion along N34°W vector up to the northern terminus of SAF and N50°E vector motion for the subducting the Gorda and Juan de Fuca plates. Our simulated results revealed that as the depth increased, the fault types were generally normal, and at shallow depth greater strike slip and some thrust faults were formed. It is concluded that SAF may be terminated as normal fault at depth although the surface expression is clearly strike slip.

Calculation of the magnetization oscillation frequency in a nanostructured synthetic ferrimagnet

Theoretical equations were derived for the resonance frequency of magnetization oscillation in a nanostructured synthetic ferrimagnet in the framework of a single domain model. The theoretical equations, which are applicable to various magnetization alignments including a spin flop, were then tested using a micromagnetic simulation in both the macrospin and microspin models. Excellent agreement was obtained between the results of the theoretical prediction and micromagnetic simulation in the macrospin model over the entire range of applied magnetic fields, confirming the validity of the theoretical equations derived in this study. The agreement between the results from the theoretical prediction and the micromagnetic simulation in the microspin model was not excellent, particularly in the acoustic mode, showing a substantial deviation from the ideal single domain behaviour. However, good agreement was obtained by decreasing the magnetization component in the thickness direction by 10% of that in the single domain state. This suggests that the magnetization deviates slightly from the single domain state as the magnetization moves out of the film plane during a magnetization oscillation.

Spin-transfer dynamics in spin valves with out-of-plane magnetized CoNi free layers

We have measured spin transfer-induced dynamics in magnetic nanocontact devices having a perpendicularly magnetized Co/Ni free layer and an in-plane magnetized CoFe fixed layer. The frequencies and powers of the excitations agree well with the predictions of the single-domain model and indicate that the excited dynamics correspond to precessional orbits with angles ranging from zero to 90 degrees as the applied current is increased at a fixed field. From measurements of the onset current as a function of applied field strength we estimate the magnitude of the spin torque asymmetry parameter lambda ~ 1.5. By combining these with spin torque ferromagnetic resonance measurements, we also estimate the spin wave radiation loss in these devices.