Spatio-temporal EEG source localization using simulated annealing

The estimation of multiple dipole parameters in spatio-temporal source modeling (STSM) of electroencephalographic (EEG) data is a difficult nonlinear optimization problem due to multiple local minima in the cost function. A straightforward iterative optimization approach to such a problem is very susceptible to being trapped in a local minimum, thereby resulting in incorrect estimates of the dipole parameters. In this paper, we present and evaluate a more robust optimization approach based on the simulated annealing algorithm. The complexity of this approach for the STSM problem was reduced by separating the dipole parameters into linear (moment) and nonlinear (location) components. The effectiveness of the proposed method and its superiority over the traditional nonlinear simplex technique in escaping local minima were tested and demonstrated through computer simulations. The annealing algorithm and its implementation for multidipole estimation are also discussed. We found the simulated annealing approach to be 7-31% more effective than the simplex method at converging to the true global minimum for a number of different kinds of three-dipole problems simulated in this work. In addition, the computational cost of the proposed approach was only marginally higher than its simplex counterpart. The annealing method also yielded similar solutions irrespective of the initial guesses used. The proposed simulated annealing method is an attractive alternative to the simplex method that is currently more common in dipole estimation applications.     

EEG source localization: implementing the spatio-temporal decomposition approach

The results of longitudinal studies in geriatric medicine were reviewed by referring to relatively recent publications. "Longidufinal studies" comprised not only cohort studies but also prospective case-control studies in the broad sense. Poor self-rated health, weight loss hypoalbuminemia, inability to perform activities of daily living, low levels of physical activity, and cognitive dysfunction, all of which could be manifestations of chronic diseases, might shorten longevity. Cardiomegaly or left ventricular hypertrophy on ECG were again found to be important risk factors for cardiovascular disease in the aged, because of their relation to atherosclerosis. There is no evidence regarding the contribution of hyperlipidemia to the risk of cardiovascular disease in the aged, although insulin resistance can increase serum triglyceride levels and reduced level of high-density lipoprotein cholesterol even in the aged. Mortality due to stroke and heart disease have been decreasing in most developed countries, and several recent community-based studies have also shown decreases in the incidence of cerebral stroke. Large-scale case-control studies on the pharmacological treatment of hyperlipidemia have resulted in both primary and secondary prevention of coronary heart disease. However, information concerning the effects of treatment for hyperlipidemia on coronary heart disease in the aged is limited. Results of large-scale case-control studies indicate that pharmacological treatment of elderly hypertensive patients can reduce cardiovascular morbidity and mortality, and angiotensin-converting enzyme inhibitors have recently been shown ot be useful.     

Three-dimensional finite element modeling of gas metal-arc welding

The modeling of the gas metal-arc (GMA) welding process in three dimensions for moving heat sources has been attempted using the finite element method. The occurrence of finger penetration in the weldment resulting from a streaming type of metal transfer at high contents is explained by assuming that the heat content of transferring droplets is distributed in a certain volume of the workpiece below the arc. Volumetric distribution of the heat content of transferring droplets has been considered as an internal heat-generation term, and the differences between penetration characteristics in two cases of globular and streaming conditions of metal transfer have been analyzed. It is shown that weld penetration depends on the depth at which the droplets distribute their energy inside the workpieces. Temperature dependence of thermophysical properties,i.e., thermal conductivity and specific heat, has been included. Latent heat is incorporated by a direct iteration method. Heat losses from the plate caused by convection and radiation are also considered. The model is validated by predicting the weld-bead dimensions and comparing them with experimental data.     

Recursive MUSIC: a framework for EEG and MEG source localization

The multiple signal classification (MUSIC) algorithm can be used to locate multiple asynchronous dipolar sources from electroencephalography (EEG) and magnetoencephalography (MEG) data. The algorithm scans a single-dipole model through a three-dimensional (3-D) head volume and computes projections onto an estimated signal subspace. To locate the sources, the user must search the head volume for multiple local peaks in the projection metric. This task is time consuming and subjective. Here, we describe an extension of this approach which we refer to as recursive MUSIC (R-MUSIC). This new procedure automatically extracts the locations of the sources through a recursive use of subspace projections. The new method is also able to locate synchronous sources through the use of a spatio-temporal independent topographies (IT) model. This model defines a source as one or more nonrotating dipoles with a single time course. Within this framework, we are able to locate fixed, rotating, and synchronous dipoles. The recursive subspace projection procedure that we introduce here uses the metric of canonical or subspace correlations as a multidimensional form of correlation analysis between the model subspace and the data subspace. By recursively computing subspace correlations, we build up a model for the sources which account for a given set of data. We demonstrate here how R-MUSIC can easily extract multiple asynchronous dipolar sources that are difficult to find using the original MUSIC scan. We then demonstrate R-MUSIC applied to the more general IT model and show results for combinations of fixed, rotating, and synchronous dipoles.     

Artificial neural network and finite element modeling of nanoindentation tests

This study first presents two-dimensional (2-D) axisymmetric and three-dimensional (3-D) finite element (FE) models of nanoindentation tests. Calculated load-displacement curves from the FE models are compared with the load-displacement curves from nanoindentation measurements on annealed copper. Numerical parametric studies are also performed to examine the effect of indenter geometry and the material’s stress-strain behavior on the load-displacement response. The 2-D and 3-D FE load-displacement curves compare well with the measured results on annealed copper. The second aspect of this study introduces a new modeling approach for indentation tests using artificial neural networks (ANN). In this approach, ANN models are generated to approximate the FE load-displacement curves for a wide range of material and geometric parameters. The ability of the ANN models to predict the indentation response is examined against other FE results not used as part of the training data. These models are shown to accurately predict the load-displacement behavior of a nonlinear homogeneous material as well as one with a hard film, such as an oxide film, on a relatively soft substrate. It is shown that the monotonic indentation load-displacement response during loading contains ample information for the ANN model to extract material flow properties of the indented material.     

MEG and EEG topography of frontal midline theta rhythm and source localization

PURPOSE: We studied a case of corneal ulceration in utero from lower eyelid entropion. METHODS: A 3-week-old male infant was referred for examination of a left corneal ulcer that was present at birth and unresponsive to antibiotics. RESULTS: Examination disclosed a lower eyelid entropion that was treated surgically by a nonincisional method, leaving a central leukoma after re-epithelialization. CONCLUSION: Congenital lower eyelid entropion should be included in the differential diagnosis of congenital corneal opacities.     

Adaptive finite element modeling of long-term polyethylene wear in total hip arthroplasty

Adaptive remeshing capability was added to an existing sliding-distance-coupled finite element model of polyethylene wear in total hip arthroplasty. This augmentation allowed earlier postoperative wear simulation to be extended to the clinically more significant long-term regimen (as long as 20 years). Loads and femoral head excursions were taken from a physically validated gait analysis model of a patient with an instrumented total hip replacement. For otherwise identical 22, 28, and 32 mm components, the least volumetric wear but the most linear wear occurred for the 22 mm head. When the polyethylene thickness in a 22 mm component was reduced to the same as that in a 32 mm component, the volumetric wear rate for the 22 mm component was still much less than that for the larger component, indicating that sliding distance (head size), rather than polyethylene liner thickness, was primarily responsible for the difference in rates. A "28 mm" series, for which head sizes were varied across the range of currently accepted industrial tolerances, showed that although initial wear rates were greatest for the least congruent articulations, the long-term volumetric wear was nearly the same, regardless of initial clearance.     

Nonisothermal punch stretching: Measurements and finite element modeling simulations

In order to investigate the role of thermal effects in punch stretching, a simple nonisothermal forming operation was carried out and was simulated using finite element modeling (FEM). A heated hemispherical punch deformed a steel sheet which was fully clamped between room-temperature circular dies. Strains were measured at standard punch heights for comparison with FEM-simulated ones. The strain distributions were in reasonable agreement, and the qualitative changes in the distributions with punch temperature were predicted very well by the simulations. The form of the nonisothermal FEM formulation was verified by these agreements. Increased punch temperature improves formability by lowering the peak strain in the punch-sheet contact region. Nonisothermality can play a significant role in distributing strains throughout a deforming sheet under conditions similar to these. S. LATREILLE, formerly Granduate Student, The Ohio State Univerity     

Experimental investigation and finite element modeling of hemispherically stretched steel sheet

Hemispherical stretching experiments and corresponding finite element modeling (FEM) were performed on three aluminum-killed (AK) steels. Strain distributions measured from photogrids on the specimen surface were compared to those predicted by a three-dimensional (3-D), membrane, rigid-viscoplastic FEM program. The material model uses Hill's nonquadratic theory for normal anisotropy and Coulomb friction. The new anisotropy coefficient,M, and friction coefficient, μ, have opposite effects on the strain distribution. Balanced, biaxial simulations of highM materials required unrealistically high friction coefficients to produce agreement with measured strains. The discrepancies call into question the validity of Hill's nonquadratic yield surface and the method of measuringM. J.R. KNIBLOE, formerly Graduate Student, Department of Materials Science and Engineering, The Ohio State University     

宽厚板压力矫平压下模型理论建模与有限元分析

宽厚板压力矫平过程由于缺少精准可靠的压力矫平模型,工艺参数的设定主要依靠人工经验,制约了生产效率和产品质量的提升。针对实现全自动压力矫平关键瓶颈问题——压力矫平模型进行研究。采用弹塑性力学理论,结合压力矫平过程的特点,建立宽厚板压力矫平数学模型;在材料力学性能参数、初始平直度或曲率已知的情况下,自动计算出压平力、压头行程等参数;根据压力矫平模型计算出的数据,采用有限元方法模拟压力矫平过程,获得板材各节点位置和位移数据,计算出压力矫平后宽厚板的平直度。结果表明,各种工况下宽厚板的平直度小于2 mm/m,优于宽厚板的交货标准,证实了模型的可靠性。     

An efficient algorithm for computing multishell spherical volume conductor models in EEG dipole source localization

Computationally localizing electrical current sources of the electroencephalographic signal requires a volume conductor model which relates theoretical scalp potentials to the dipolar source located within the modeled brain. The commonly used multishell spherical model provides this source-potential relationship using a sum of infinite series whose computation is difficult. This paper provides a closed-form approximation to this sum based on an optimal fitting to the weights of the Legendre polynomials. The second-order (third-order) approximation algorithm, implemented by a provided C-routine, requires only 100 (140) floating point operations to compute a single scalp potential in response to an arbitrary current dipole located within a four-shell spherical volume conductor model. This cost of computation represents only 6.3% (8.9%) of that required by the direct method. The relative mean square error, measured by using 20,000 random dipoles distributed within the modeled brain, in only 0.29% (0.066%).     

基于Voronoi图的晶体塑性有限元多晶几何建模

通常用规则的六边形或四边形等来表示晶粒,不能够反映出晶界的不规则性,本文使用Voronoi方法在大型有限元软件ABAQUS中建立了多晶材料的几何模型,能够表达出晶粒的几何形状与晶界的不规则性;在此基础上提出了一种控制晶粒大小分布及织构的方法,通过调整参数能够建立具有不同晶粒尺寸分布及织构的模型.     

Biomechanical aspects of the insect wing: an analysis using the finite element method

Insect wings appear as highly functional and largely optimized mechanical constructions. A series of stabilizing constructional elements have been 'designed' to cope with loading during flight. One such element is the expenditure of material in constructing the wing, i.e. the vein system of the wing and its arrangement. It functions like a zig-zag folding framework which stiffens the wing against aerodynamic bending moments. To quantify the quality of material distribution, models of a dragonfly wing and of a fly wing were calculated using the finite element method (FEM).     

Finite element modeling simulation of in-plane forming limit diagrams of sheets containing finite defects

Finite element modeling (FEM) has been used to predict forming limit diagrams (FLDs) of thin sheets based on two-dimensional (2-D) finite thickness defects. The local growth of these defects is simulated until an arbitrary failure criterion is reached. Many aspects of this simulation re-produce the standard Marciniak-Kuczynski (M-K) results. For example, the plane strain intercept, FLD₀, is sensitive to the material work hardening,n, and the strain rate sensitivity,m, but is not affected by the normal anisotropy,r. The positive side of the FLD was characterized by a line of logarithmic slopeP. The value ofP decreases sharply asn andm increase. The effect ofr depends on the choice of yield function. The absolute location of the FLD, as given by the FLD₀, depends not only on the material properties, but also on the choice of failure criterion, defect geometry, and details of the simulative model (mesh size, number of defect dimensions,etc.). This is true of any measurement or simulation of the FLDs. Therefore, we propose that the FLD₀ be used as the single “fitting parameter” between modeling and experimental results: a more realistic approach based on what is actually measured in the FLD experiments. This method allows clarification of the role of material plasticity properties(e.g.,n, m, andr) vs fracture properties (contained in the FLD₀) in determining the shape of the FLDs.     

三维Boussinesq方程有限元格式的POD降维模型

针对帝国理工大学三维海洋模型(Boussinesq方程)的无结构有限元格式,用特征正交分解方法(POD)得到了降维模型.并且给出了POD降维模型的误差估计.最后,通过数值算例验证了POD方法的可行性和有效性.     

A finite element modeling analysis of flow and mass transfer through nonspherical bubbles in a copper converter

A mathematical model has been developed for the flow and mass-transfer processes associated with the nonspherical, deformed bubbles in a copper converter. The case of an isolated reacting bubble has been studied numerically by solving the pertinent transport equations with Galerkin finite element modeling (FEM) technique. The continuous change in bubble shape and size has been handled through an adaptive grid generation technique based upon a transfinite inter-polation scheme. Some of the results have shown a significant difference from the earlier analysis of spherical bubbles. The numerical predictions are well in accord with the existing theory and measurements.     

On finite element methods in metal working

In metal forming industries, many products are to be formed in large number and with highly accurate dimensions. To save energy and material it is necessary to understand the behaviour of material and to know the intermediate shapes of the formed parts and the mutual effects between tool and formed part during the forming process. The design of the tool and the manufacturing procedures are increasingly carried out by computer aided design and manufacturing (CAD/CAM). These procedures are normally based on numerical methods which take into account all physical conditions of the deformed material during the process. For this purpose, finite element methods (FEM) have been developed in the past in different ways. This paper highlights some of these methods which are particularly effective in simulating the forming processes.     

Dipole source localization of ictal epileptiform activity

Dipole source localization of ictal epileptiform activity recorded by scalp EEG was performed in patients prior to surgical treatment. The dipole tracing method combined with the scalp-skull-brain head model was used to locate epileptogenic foci. A digital EEG system was used for data collection. The accuracy of dipole source localization was evaluated by comparing the focus location with that obtained by chronic subdural electrocorticography. In a case of frontal lobe epilepsy with epileptogenic focus in the frontoparietal convexity, the results of dipole source localization agreed well with those obtained with chronic subdural electrocorticography. In a case of lateral temporal lobe epilepsy, the results of dipole source localization were consistent with those obtained with chronic subdural electrocorticography, but a small localization error was observed. The clinical usefulness of and suggestions for improving this method are discussed.