Single Domain Model Research Articles

Bond Graph Method for the Dynamic Similarity Analysis of Complex Electromechanical System

The existing similitude methods can only be applied to the dynamic similarity analysis of elements (or components) with single-energy domain,and there are many difficulties when they are utilized to study the dynamic similarity of complex electromechanical system with multi-energy domains. To solve this problem,the prerequisite condition for the similarity of bond graph of system is explored and the dynamic similarity conditions for the elements of bond graph are derived on the basis of bond graph which is an effective tool for modeling of system with multi-energy domains. The system modal similarity is analyzed and studied according to the mode analysis theory based on bond graph. The similarity relations of major modal parameters such as frequency and vibration mode are established. Thus,the bond graph method for dynamic similarity analysis of complex electromechanical system is presented. The similarity requirements for the system can be easily derived without the physical equations,and the dynamic model test of system with multi-energy domains can be achieved by a simple single-domain model system when the new method proposed is utilized in the dynamic similarity analysis,which provides new methods and ideas for the research on dynamic similarity of complex electromechanical system. The example provided shows that the similarity conditions can be derived efficiently and conveniently when the method is utilized to instruct the dynamic similarity design and model test of complex electromechanical system.

Finite separation method: an efficient boundary element crack modeling technique

In computational fracture mechanics, great benefits are obtained from the reduced modeling dimension order and the accurate integral formulation of the boundary element method (BEM). However, the direct representation of co-planar surfaces (i.e., cracks) causes a degeneration of the standard displacement BEM formulation which can only be circumvented with special modeling techniques. Aiming to simplify the generalized application of the BEM to fracture mechanics problems, this paper presents a two-dimensional crack modeling approach. The method uses the direct BEM displacement formulation within a single-domain model to efficiently and precisely calculate any mixed mode crack tip stress intensity factor. Details of the application of the method are presented, while its accuracy and reliability are demonstrated through numerous comparisons with benchmark results.

Magnetic properties of single crystalline Co nanowire arrays with different diameters and orientations

Single crystalline Co nanowire arrays with different diameters and orientations were grown within porous anodic alumina membranes by a pulsed electrodeposition technique and the magnetic properties of the nanowire were systematically studied. It was found that the magnetization behavior of the Co nanowire arrays is anisotropic and their magnetic properties can be effectively modulated through tuning either the diameter or the orientation of the nanowires. The magnetic properties of the Co nanowires were discussed qualitatively by using the classical magnetization theory and single domain model.

Temperature effects in exchange-biased planar hall sensors for bioapplications

The temperature dependence of exchange biased planar Hall effect sensors is investigated between T = −10 and 70 °C. It is shown that a single domain model describes the system well and that the temperature coefficient of the low-field sensitivity at T = 25 °C is 0.32%/°C. A procedure for temperature correction by use of a reference sensor is demonstrated. Consequences for magnetic biosensing are exemplified with calculations on M-280 Dynabeads ®.

Analysis of Heat Transport in a Proton Exchange Membrane (PEM) Fuel Cell

In this study a two-phases, single-domain and non-isothermal model of a Proton Exchange Membrane (PEM) fuel cell has been studied to investigate thermal management effects on fuel cell performance. A set of governing equations, conservation of mass, momentum, species, energy and charge for gas diffusion layers, catalyst layers and the membrane regions are considered. These equations are solved numerically in a single domain, using finite-volume-based computational fluid dynamics technique. Also the effects of four critical parameters that are thermal conductivity of gas diffusion layer, relative humidity, operating temperature and current density on the PEM fuel cell performance is investigated. In low operating temperatures the resistance within the membrane increases and this could cause rapid decrease in potential. High operating temperature would also reduce transport losses and it would lead to increase in electrochemical reaction rate. This could virtually result in decreasing the cell potential due to an increasing water vapor partial pressure and the membrane water dehydration. Another significant result is that the temperature distribution in GDL is almost linear but within membrane is highly non-linear. However at low current density the temperature across all regions of the cell dose not change significantly. The cell potential increases with relative humidity and improved hydration which reduces ohmic losses. Also the temperature within the cell is much higher with reduced GDL thermal conductivities. The numerical model which is developed is validated with published experimental data and the results are in good agreement.

An Assembly Model for Simulation of Large‐Scale Ground Water Flow and Transport

When managing large-scale ground water contamination problems, it is often necessary to model flow and transport using finely discretized domains--for instance (1) to simulate flow and transport near a contamination source area or in the area where a remediation technology is being implemented; (2) to account for small-scale heterogeneities; (3) to represent ground water-surface water interactions; or (4) some combination of these scenarios. A model with a large domain and fine-grid resolution will need extensive computing resources. In this work, a domain decomposition-based assembly model implemented in a parallel computing environment is developed, which will allow efficient simulation of large-scale ground water flow and transport problems using domain-wide grid refinement. The method employs common ground water flow (MODFLOW) and transport (RT3D) simulators, enabling the solution of almost all commonly encountered ground water flow and transport problems. The basic approach partitions a large model domain into any number of subdomains. Parallel processors are used to solve the model equations within each subdomain. Schwarz iteration is applied to match the flow solution at the subdomain boundaries. For the transport model, an extended numerical array is implemented to permit the exchange of dispersive and advective flux information across subdomain boundaries. The model is verified using a conventional single-domain model. Model simulations demonstrate that the proposed model operated in a parallel computing environment can result in considerable savings in computer run times (between 50% and 80%) compared with conventional modeling approaches and may be used to simulate grid discretizations that were formerly intractable.

Predicting protein function from domain content

Computational assignment of protein function may be the single most vital application of bioinformatics in the post-genome era. These assignments are made based on various protein features, where one is the presence of identifiable domains. The relationship between protein domain content and function is important to investigate, to understand how domain combinations encode complex functions. Two different models are presented on how protein domain combinations yield specific functions: one rule-based and one probabilistic. We demonstrate how these are useful for Gene Ontology annotation transfer. The first is an intuitive generalization of the Pfam2GO mapping, and detects cases of strict functional implications of sets of domains. The second uses a probabilistic model to represent the relationship between domain content and annotation terms, and was found to be better suited for incomplete training sets. We implemented these models as predictors of Gene Ontology functional annotation terms. Both predictors were more accurate than conventional best BLAST-hit annotation transfer and more sensitive than a single-domain model on a large-scale dataset. We present a number of cases where combinations of Pfam-A protein domains predict functional terms that do not follow from the individual domains. Scripts and documentation are available for download at http://sonnhammer.sbc.su.se/multipfam2go_source_docs.tar

Size dependence of intrinsic spin transfer switching current density in elliptical spin valves

We studied current-induced magnetization reversal in elliptical spin valves with CoFeB free layers. The data obtained from high-speed pulsed switching experiments showed that the intrinsic switching current densities were size dependent and 50%–100% higher than predicted by a single-domain model. Micromagnetic simulations reveal a complex behavior of magnetization switching in which end-mode oscillations are important, and indicate that the switching current density depends on the device dimensions. Experimental values for the intrinsic switching current density agree with those predicted by micromagnetic simulations.

Interface between turbulent flows above and within rough porous walls

This paper explores the concept of a macroscopic boundary between turbulent flows above and within rough permeable walls. The macroscopic boundary and the associated conditions for macroscopic flow variables have been thoroughly investigated for laminar, but not for turbulent flows. The literature on laminar flows follows two main conceptual models of the boundary: sharp boundary with step changes in macroscopic variables and gradual boundary with smooth changes of variables. The former approach is usually associated with the two-domain simulation models and the latter one with the single-domain models. This paper presents the derivation of the step conditions for velocity and shear stress at the macroscopic boundary between turbulent boundary layer and turbulent porous media flows. The physical meaning of the main terms in the shear stress condition is discussed in order to clarify the relationship between two-domain and single-domain simulation models.

Local domain structure of exchange-coupled NiFe∕CoO nanowire probed by nonlocal spin valve measurement

We investigate the local magnetization process in a 100-nm-wide Permalloy/CoO exchange-coupled wire by means of nonlocal spin valve measurements for a structure with lateral geometry. The domain structure in the exchange-coupled wire is found to change with the direction of the exchange bias. When the exchange bias is parallel to the easy axis of the Permalloy wire, the magnetization-reversal process can be expressed by the single domain model. However, when the exchange bias is perpendicular to the easy axis, the magnetization reversal is accompanied by domain nucleation and annihilation processes even in the lateral dimension of 100nm. The reason for the dependence of the domain structure on the direction of the exchange bias is discussed.

Toggle switching of weakly coupled synthetic antiferromagnet for high-density magnetoresistive random access memory

The toggle-switching behavior for circular and elliptic cylinder shaped memory cells of weakly coupled synthetic antiferromagnet with a diameter and thickness (ferromagnetic layer) ranging from 200 to 400 and from 2.5to5.0nm, respectively, has been studied by micromagnetic simulation. The critical fields for a circular cylinder are much larger than those predicted by a single domain model. This is due to the formation of edge domains resulting in a so-called S state. The elliptic cylinder with an aspect ratio of >1.2 is found to be necessary to prevent the increase of the start field by the edge domains.

Exchange-biased planar Hall effect sensor optimized for biosensor applications

This article presents experimental investigations of exchange-biased Permalloy planar Hall effect sensor crosses with a fixed active area of w×w=40×40μm2 and Permalloy thicknesses of t=20, 30, and 50nm. It is shown that a single domain model describes the system well and that the thicker film will have a higher signal as well as a lower noise. It is estimated that the signal-to-noise ratio for bead detection increases by a factor 2.1 when t is increased from 20to50nm and hence a higher t is beneficial for biosensor applications. This is exemplified with calculations on M-280 Dynabeads®.

Micromagnetic simulation of critical fields of rectangular and elliptical cells for the toggle‐mode magnetic random access memory

AbstractA micromagnetic simulation is carried out to examine the effects of the shape of exchange‐coupled trilayer cells on the magnetization switching behavior, in an effort to reduce the switching field in the toggle‐mode magnetic random access memory. Two different shapes of rectangular and elliptical cells are considered. The switching behavior of the elliptical cells shows a qualitative agreement with the single domain model for 3D ellipsoids. However, the magnetization‐flop field differs significantly, except for the small aspect ratio and the thickness asymmetry of the two magnetic layers. For the rectangular cells, the switching behavior differs significantly, particularly at a small aspect ratio, due to very strong demagnetizing fields, causing to form end domains. As the aspect ratio increases, the magnetization‐flop field increases while the saturation field decreases. This opposite dependence of the two critical fields on the aspect ratio results in the decrease in the write window margin with increasing aspect ratio. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theory for toggle magnetic random access memory: The asymmetric case

A single domain model is used to analyze the magnetic switching of two coupled magnetic layers, relevant for toggle magnetic random access memory, for the nonideal case where the layers are not identical. In general, we show that discontinuous transitions occur across the critical switching curve and continuous transitions occur around cusps in the critical switching curve. We illustrate this with examples of thickness imbalance, anisotropy mismatch, and Néel coupling and derive the corresponding switching behavior. Features in the direct-write switching can be used to experimentally distinguish between these various sources of asymmetry.

Three-Dimensional Simulation of Liquid Water Distribution in a PEMFC with Experimentally Measured Capillary Functions

Modeling of liquid water distribution in polymer electrolyte membrane fuel cells (PEMFCs) is challenged by uncertainties in characterizing the two-phase transport properties of the porous transport layer (PTL) and the catalyst layer (CL). Capillary pressure, representing both pore structures and wetting features of the porous media, is a key factor in controlling liquid water transport and distribution in the porous electrode of PEMFCs. By incorporating experimentally measured capillary pressure functions, a single-domain, three-dimensional, and two-phase transport model was developed to predict liquid water saturation in the PTL and CL of a PEMFC with long straight channels, where the two-phase flow complications were minimized at practical stoichiometry. In the cathode CL, the liquid water saturation was found to be higher under the channel than that under the ribs at high current densities. In the cathode PTL, however, the liquid water saturation level was observed to be lower under the channel than that under the ribs. At high current densities, the average water saturation levels are insensitive to current density and fall in the range of 0.4–0.5 in the CL and 0.2–0.3 in the PTL. Finally, the effects of liquid water on oxygen transport and cell performance were investigated.

An empirical study of AI-based multiple domain models for selecting attributes that drive company wealth

This paper explores what attributes drive company wealth creation in the Miscellaneous Industrials sector of the Australian Stock Market. We examine traditional and artificial intelligent (AI) feature selection techniques, to select attributes that drive company wealth and observe if a multiple domain model outperforms single domain models with regards to predicting company wealth. Using a large number of calculated attributes, our empirical findings suggest that a multiple domain model was most effective. We find that Market Capitalisation, Debt Asset Ratio, ROI and Beta Value attributes are the main contributors to following the directional change in the shareholder value. This was using a J4.8 and GRNN multiple domain model.

Thickness dependence of parallel and perpendicular anisotropic resistivity in Ta/NiFe/IrMn/Ta multilayer studied by anisotropic magnetoresistance and planar Hall effect

Ferromagnetic layer thickness dependence of anisotropic magnetoresistivities in Ta∕NiFe(t)∕IrMn (10 nm)∕Ta has been investigated for t=3, 4, 5, 7, 8, 10, 12, 15, and 20 nm by the method of anisotropic magnetoresistance and planar Hall effect. Our results revealed that the parallel and perpendicular resistivity components performed a varying function with increment in NiFe thickness. Both the resistivities at first were observed to increase when the NiFe thickness increases from 3 to 10 nm; then for the NiFe thicknesses from 10 to 20 nm, the resistivities of NiFe layer decrease as the NiFe thickness increases. However, the anisotropic resistivity change, which is the difference between parallel and perpendicular resistivities, was observed to increase for the whole range of thicknesses when the NiFe thickness increases. The measured quantities were found to be in good agreement with the theoretically estimated parameters using single domain model; thus these behaviors are well explained based on the modern electron theory transition metals.

Analysis for toggling magnetic random access memories with low writing field using four ferromagnetic layers for free layer stack

We calculate writing characteristics of two kinds of low-current magnetic random access memory (MRAM) devices using a single domain model. A four-layer synthetic antiferromagnet (SAF) has four antiferromagnetically coupled ferromagnetic (FM) layers, and a two-SM-layer-FC SAF has a two-FM-layer SAF with ferromagnetically coupled (FC) two soft magnetic (SM) layers. The threshold field of these free layers can be calculated analytically. The spin flop field of four-FM-layer SAF film is independent of the strength of antiferromagnetic coupling (AFC) between inner films. The saturation field increases with increasing the AFC strength. The spin flop field of the two-SM-layer-FC SAF film decreases, and the saturation field increases with decreasing ferromagnetic coupling strength. However, activation energy analysis demonstrates that both types of films exhibit a decrease in activation energy near the spin flop field. Considering the activation energy decrease during the toggling write sequence and a sufficient writing margin, MRAM with four ferromagnetic layers decreases writing current by 40%.

Materials and devices for reduced switching field toggle magnetic random access memory

Toggle magnetic random access memory (MRAM) has been proposed to solve the problems of small switching margins and half-select activated errors found in Stoner-Wohlfarth MRAM. However, it is widely acknowledged that the switching fields required for toggle MRAM are substantially larger than those needed for Stoner-Wohlfarth MRAM. Previously published reports on toggle switching use large toggle start fields around 75Oe. Here we examine, both experimentally and with a single-domain model, how both the toggle start and end fields vary with free layer intrinsic anisotropy, thickness, width, aspect ratio, and interlayer exchange coupling. By optimizing these parameters, we obtain 400nm width devices with toggle start fields below 30Oe.

Inhomogeneous Spin Reorientation Transition (SRT) in Giant Magnetostrictive TbCo$_2$/FeCo Multilayers

Inhomogeneous magnetization states occurring when inducing the spin reorientation transition (SRT) in uniaxial giant magnetostrictive thin films are studied in detail. Theoretical background of SRT in the layers is given and the limitations of the single domain model are explained. The results of the magneto-optical measurements are then given and discussed. We showed that the behavior of devices using the SRT can be explained by the creation of magnetic domains, if the applied magnetic field is perfectly aligned with the hard axis. Magneto-optic evidence of the hyper sensitivity near the SRT is also given