In source localization of electroencephalograpic (EEG) signals, as well as in targeted transcranial electric current stimulation (tES), a volume conductor model is required to describe the flow of ...electric currents in the head. Boundary element models (BEM) can be readily computed to represent major tissue compartments, but cannot encode detailed anatomical information within compartments. Finite element models (FEM) can capture more tissue types and intricate anatomical structures, but with the higher precision also comes the need for semi-automated segmentation, and a higher computational cost. In either case, adjusting to the individual human anatomy requires costly magnetic resonance imaging (MRI), and thus head modeling is often based on the anatomy of an ‘arbitrary’ individual (e.g. Colin27). Additionally, existing reference models for the human head often do not include the cerebro-spinal fluid (CSF), and their field of view excludes portions of the head and neck—two factors that demonstrably affect current-flow patterns. Here we present a highly detailed FEM, which we call ICBM-NY, or "New York Head". It is based on the ICBM152 anatomical template (a non-linear average of the MRI of 152 adult human brains) defined in MNI coordinates, for which we extended the field of view to the neck and performed a detailed segmentation of six tissue types (scalp, skull, CSF, gray matter, white matter, air cavities) at 0.5mm3 resolution. The model was solved for 231 electrode locations. To evaluate its performance, additional FEMs and BEMs were constructed for four individual subjects. Each of the four individual FEMs (regarded as the ‘ground truth’) is compared to its BEM counterpart, the ICBM-NY, a BEM of the ICBM anatomy, an ‘individualized’ BEM of the ICBM anatomy warped to the individual head surface, and FEMs of the other individuals. Performance is measured in terms of EEG source localization and tES targeting errors. Results show that the ICBM-NY outperforms FEMs of mismatched individual anatomies as well as the BEM of the ICBM anatomy according to both criteria. We therefore propose the New York Head as a new standard head model to be used in future EEG and tES studies whenever an individual MRI is not available. We release all model data online at neuralengr.com/nyhead/ to facilitate broad adoption.
•Individual head models for EEG source imaging and tCS stimulation are computationally expensive.•Instead, we propose a highly detailed standardized FEM model of the ICBM152 non-linear average head defined on MNI coordinates.•We approximate 4 individual heads and measure localization and targeting errors.•Our model compares favorably to individual and individualized models.•All data are made available.
Amidst the escalating demand for sustainable manufacturing practices aimed at mitigating global emissions and waste, industries are actively seeking novel forming solutions to address these pressing ...global challenges. Near Solidus Forming (NSF) processes emerge as a promising alternative to confront such issues, offering the capability to fabricate intricate components reliably while minimizing material waste and energy consumption. This promising manufacturing process is still in its developmental stages for industrial applications, necessitating further exploration and understanding of various factors such as friction, heat transfer, and others. From the literature review, a lack of friction data at these temperatures has been identified. Therefore, this study is dedicated to the advanced characterization of the friction coefficient for Near Solidus Forging (NSF) operations. With that aim, T-shape experimental tests of 42CrMo4 alloy steel have been conducted at high temperatures (up to 1360 °C). Additionally, a lack of consensus on the correct T-shape testing and inverse analysis procedure has been noted. Consequently, apart from the experimental work, an in-depth analysis of the friction coefficient identification procedure has been conducted. As a result, a new geometrical output index is proposed, highly sensitive to the friction coefficient and therefore more reliable compared to state-of-the-art indexes. Furthermore, the influence of the selected geometrical output index and the consideration of sample-to-sample transfer and holding times were studied. Results showed that the increase in workload to consider the sample-to-sample transfer and holding times is not worthwhile, as assuming the average values lead to significantly less work with little impact in the final results (<5 % of error). The study also concludes that a friction coefficient of 0.25, 0.45 and 0.6 has been identified at temperatures of 1250 °C, 1300 °C and 1360 °C, respectively. Additionally, the result of thermal camera showed good agreement with the thermocouple data. Overall, in this study a robust and reliable T-shape testing, and friction coefficient identification procedure is proposed and validated.
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•Near Solidus Forging (>1350 °C) friction conditions characterized by T-Shape•Friction coefficient starts at 0.25 for 1250 °C and reaches 0.6 at 1360 °C•Considering the averaged transfer and holding times resulted in an error below 5 %•The ear width geometrical parameter index is the optimal value to be considered•An optimum T-Shape friction identification procedure is stabilised and validated
The determination of accurate global and local modal information is a crucial step for any structural model updating process. Existing modal extraction methods can extract global modal properties ...with a good degree of accuracy; however, they have difficulties extracting accurate local information under transient excitations. This work presents a novel method, called Extended Empirical Wavelet Transformation (EEWT), in which local and global modal information can be accurately obtained under transient excitations. A new objective function is proposed in this work, where the local and global information resulting from EEWT can be used inside an optimization problem to solve for structures’ unknown parameters and boundary coefficients using a minimum number of measurement points. The proposed EEWT modal extraction and updating schemes were experimentally implemented in two problems: a simply supported beam and a scaled model of a highway bridge with unknown boundary conditions. The results showed the capability of the proposed approaches to identify structural material properties and boundary coefficients of both systems under transient excitations. Comparison between the proposed method and three other well-known modal extraction methods illustrated the effectiveness of EEWT and showed how the resulting optimum points can be affected by the inaccuracy of the extracted modal information.
Thermosonic flip chip (TSFC) bonding technology has become a developing area of chip packaging technology due to its advantages of low bonding temperature and bonding pressure. To explore the ...appropriate bonding parameters and to understand the relationship between each parameter and the stress/strain at the bonding interface. Bonding tests were carried out and then simulated orthogonal tests were conducted using the finite element model. The bonding test results show that: The initial position of the bumps does not affect the strength after bonding. But, an unreasonable selection of bonding pressure and ultrasonic parameters can lead to different degrees of cracks at the bonding interface after bonding and destroy the bonding strength. Simulation results show that: The order of influence of the three bonding parameters on von Mises stress/(shear stress) is: bonding pressure> ultrasonic amplitude>bonding temperature/(ultrasonic amplitude>bonding temperature>bonding pressure). Based on the simulation results, a multivariate nonlinear regression model between von Mises stress/shear stress and bonding parameters was constructed. Some recommendations for the selection of bonding parameters are given: 1 ) the bonding pressure was selected in the range of 9-11MPa, 2)the bonding temperature was chosen to be less than 200 °C and 3) the ultrasonic amplitude was 1.1μm(power about 22w). At the same time, the ultrasonic power can be increased by increasing the ultrasonic frequency to achieve better results in bonding. This study can provide some theoretical basis for the selection of bonding parameters for TSFC bonding.
Magnetorheological elastomers (MREs) are composite materials that consist of magnetically permeable particles in a nonmagnetic polymeric matrix. Under the influence of an external magnetic field, a ...reversible deformation change occurs in the mechanical properties of these materials. Due to their coupled magnetomechanical response, these materials have been found suitable for a range of applications including tunable vibration absorbers, sensors, and actuators. Notably, improvement of such devices are prerequisites to efficient energy conversion systems, hence the need to understand further the MRE technology. The Jiles-Atherton (JA) theory takes into consideration the magneto-coupling experienced by effective domains in a magnetic material. Algorithm based on the theory yields five model parameters; saturation magnetization (Ms), domain density (a), domain coupling (α), loss coefficient (k), and reversibility (c). Using JA theory, model parameters were calculated and linked to the physical attributes of Fe powder and isotropic MRE. The results show that the calculated Ms for the MRE is reasonably related to that of the Fe powder by a factor of the particle's volume fraction used in the MRE. Further, the calculated k, a, and α provided support for the reduced pinning factor, domain density, and increased domain coupling in the MRE due to the changes in the domain structure between the two materials. From the calculated JA parameters, finite-element modeling (FEM) of the MRE hysteresis loop was performed. The analysis showed that the modeled magnetic properties including coercivity, remanence, and coordinates of the hysteresis loop tip vary with geometric position.
Over the past four decades of developing superconducting machines, many topologies have been suggested. The most successful topology of high-power superconducting (HPS) machines is an air-cored ...radial flux synchronous machine. There are two possible topologies for this type of machine, rotational field, and stationary field. In this paper, the relative advantages and disadvantages of these topologies are compared in detail. Analytical study of these topologies shows that the inversed machine topology leads to more efficient high-temperature superconductor (HTS) wire utilization and hence more economical production. In order to confirm the result obtained by analytical calculations, 2-D finite element model (FEM) of the machine is utilized.
Magnetic field plays an essential role in negative ion-driven neutral beam injectors (NBIs), being necessary to counteract the inevitable interaction between electrons and negative ions, both to ...maximize the ion production and to minimize the electron extraction and acceleration. Magnetic field influences also the generation and confinement of the plasma from where the ions are extracted, and this is particularly significant for radio frequency (RF) inductively generated plasmas, such as the case of SPIDER. SPIDER is the full-scale prototype of the ITER NBI ion source, in operation since 2018. Its magnetic field configuration was modified in 2020 to solve issues related to plasma generation. The new configuration has significantly improved the performances, but some limitations and lack of symmetries emerge at high field. The present article describes the numerical and experimental assessment recently carried out in order to verify the actual distribution of the new magnetic field configuration inside the SPIDER ion source and accelerator, and to investigate on possible reasons of asymmetries.
Prestressed structures have been put into practice in construction since the beginning of this century, but the prestressed structure is concerned with the bearing capacity of anchorage ends. ...Applying steel reinforcement in anchorage zones can significantly improve the structure behavior and bearing capacity of post-tensioned anchorage zones. Proper reinforcing can relieve congestion and poses difficulty in pouring concrete. Based on materials test data, the nonlinear Finite Element Model (FEM) under local compression was established as part of this study. The nonlinear analysis of the load process was completed based on ABAQUS software. In addition, the model's accuracy was verified by comparing the FEM calculation results with experimental results.
Furthermore, the verified FEM was adapted for a parametric study to investigate the influence of various parameters on the bearing capacity, such as the spacing, shape, length of the bearing plate, and reinforcement spacing. The results demonstrate that enhancing steel reinforcement can withstand the forces and stresses and comprehensively improve the local bearing capacity of the specimens; with the decrease of reinforcement spacing, the bearing capacity of the specimen increases, indicating that the reinforcement can dissipate the high stresses among the member from the anchorage zone. The bearing capacity increases with the increase of the bearing plate length, meaning that the bearing plate has a significant influence on bearing the prestressing force in the anchorage zone. Meanwhile, the effect of the bearing plate shape was not obvious. The relationship between the local bearing capacity and the bearing plate length is linear, which indicates that the influence of the bearing plate length on the local pressure properties belongs to the structural layer.
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