The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Thomas R. Knösche - One of the best experts on this subject based on the ideXlab platform.
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Processing of Syntactic Information Monitored by Brain Surface Current Density Mapping Based on MEG
Brain Topography, 1999Co-Authors: Thomas R. Knösche, B. Maeß, A.d. FriedericiAbstract:The cortical network subserving language processing is likely to exhibit a high spatial and temporal complexity. Studies using brain imaging methods, like fMRI or PET, succeeded in identifying a number of brain structures that seem to contribute to the processing of syntactic structures, while their dynamic interaction remains unclear due to the low temporal resolution of the methods. On the other hand, ERP studies have revealed a great deal of the temporal dimension of language processing without being able to provide more than very coarse information on the localisation of the underlying generators. MEG has a temporal resolution similar to EEG combined with a better spatial resolution. In this paper, Brain Surface Current Density (BSCD) mapping in a standard brain model was used to identify statistically significant differences between the activity of certain brain regions due to syntactically correct and incorrect auditory language input. The results show that the activity in the first 600 ms after violation onset is mainly concentrated in the temporal cortex and the adjacent frontal and parietal areas of both hemispheres. The statistical analysis reveals significantly different activity mainly in both frontal and temporal cortices. For longer latencies above 250 ms, the differential activity is more prominent in the right hemisphere. These findings confirm other recent results that suggest right hemisphere involvement in auditory language processing. One interpretation might be that right hemisphere regions play an important role in repair and re-analysis processes in order to free the specialised left hemisphere language areas for processing further input.
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Brain Surface Current Density mapping in pianists and non-pianists
2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1Co-Authors: Jens Haueisen, Thomas R. KnöscheAbstract:Brain Surface Current Density reconstructions are widely used to analyze magnetoencephalographic data arising from electrical activity in the human brain. Commonly, this mapping is performed in single subjects. We present a methodology to apply brain Surface Current Density mapping to group studies. The technique includes stepwise transformation of the magnetic sensors into a standard sensor system and linear scaling of individual heads in Talairach space. We demonstrate the usefulness of the technique with a comparison of the motor activation in pianists and non-pianists while listening to piano pieces.
Henk F. Arnoldus - One of the best experts on this subject based on the ideXlab platform.
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Integral equation formulation for reflection by a mirror
Journal of the Optical Society of America. A Optics image science and vision, 2008Co-Authors: Henk F. ArnoldusAbstract:When light is incident on a mirror, it induces a Current Density on its Surface. This Surface Current Density emits radiation, which is the observed reflected field. We consider a monochromatic incident field with an arbitrary spatial dependence, and we derive an integral equation for the Fourier-transformed Surface Current Density. This equation contains the incident electric field at the Surface as an inhomogeneous term. The incident field, emitted by a source Current Density in front of the mirror, is then represented by an angular spectrum, and this leads to a solution of the integral equation. From this result we derive a relation between the Surface Current Density and the Current Density of the source. It is shown with examples that this approach provides a simple method for obtaining the Surface Current Density. It is also shown that with the solution of the integral equation, an image source can be constructed for any Current source, and as illustration we construct the images of electric and magnetic dipoles and the mirror image of an electric quadrupole. By applying the general solution for the Surface Current Density, we derive an expression for the reflected field as an integral over the source Current distribution, and this may serve as an alternative to the method of images.
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Current Density in a perfect mirror.
Optics letters, 2008Co-Authors: Henk F. ArnoldusAbstract:Electromagnetic radiation incident upon a perfect mirror induces a Current Density on the Surface of the conducting material of the mirror. It is shown that this Surface Current Density can be expressed directly in terms of the source Current Density, which generates the incident field, without evaluating the electric and magnetic fields first.
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Reflection off a mirror
Journal of Modern Optics, 2007Co-Authors: Henk F. ArnoldusAbstract:Electromagnetic radiation incident upon a perfect conductor induces a Current Density at the Surface of the material. This Surface Current Density is the solution of an integral equation, and it is shown that for a flat Surface this equation has a very simple solution. The Current Density at a point of the Surface is determined by the incident magnetic field at the same point. The Surface Current Density generates an electromagnetic field, and the total radiation field is the sum of this field and the incident field. It is shown explicitly that inside the material the field of the Current Density cancels exactly the incident field. The reflected field can be expressed as an integral over the known Surface Current Density, and is therefore determined by the incident magnetic field at the Surface only. When the source of the incident field is known, the reflected field can be expressed in terms of a source function, which is determined by the Current Density of the source. It is shown that this approach lea...
A.d. Friederici - One of the best experts on this subject based on the ideXlab platform.
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Processing of Syntactic Information Monitored by Brain Surface Current Density Mapping Based on MEG
Brain Topography, 1999Co-Authors: Thomas R. Knösche, B. Maeß, A.d. FriedericiAbstract:The cortical network subserving language processing is likely to exhibit a high spatial and temporal complexity. Studies using brain imaging methods, like fMRI or PET, succeeded in identifying a number of brain structures that seem to contribute to the processing of syntactic structures, while their dynamic interaction remains unclear due to the low temporal resolution of the methods. On the other hand, ERP studies have revealed a great deal of the temporal dimension of language processing without being able to provide more than very coarse information on the localisation of the underlying generators. MEG has a temporal resolution similar to EEG combined with a better spatial resolution. In this paper, Brain Surface Current Density (BSCD) mapping in a standard brain model was used to identify statistically significant differences between the activity of certain brain regions due to syntactically correct and incorrect auditory language input. The results show that the activity in the first 600 ms after violation onset is mainly concentrated in the temporal cortex and the adjacent frontal and parietal areas of both hemispheres. The statistical analysis reveals significantly different activity mainly in both frontal and temporal cortices. For longer latencies above 250 ms, the differential activity is more prominent in the right hemisphere. These findings confirm other recent results that suggest right hemisphere involvement in auditory language processing. One interpretation might be that right hemisphere regions play an important role in repair and re-analysis processes in order to free the specialised left hemisphere language areas for processing further input.
Nikolaos K. Uzunoglu - One of the best experts on this subject based on the ideXlab platform.
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Scattering from a conductive rectangular plate covered by a thick dielectric layer and excited from a dipole source or a plane wave
IEEE Transactions on Antennas and Propagation, 1994Co-Authors: Dimitra I. Kaklamani, Nikolaos K. UzunogluAbstract:The scattering of electromagnetic radiation from a conductive rectangular plate of infinitesimal thickness covered by a dielectric parallelepiped of arbitrary size is analyzed. An integral equation formulation is employed in terms of the electric field inside the dielectric layer and the Surface Current Density on the conductive plate, and is solved approximately by using entire domain Galerkin technique. The electric field inside the dielectric layer is described in terms of a superposition of exponential waves while, in describing the Surface Current Density on the conductive plate, two types of entire domain basis functions are utilized: either Fourier-exponential series or Chebyshev series type finite-term expansions are employed alternatively. Numerical results are computed and presented for several scatterer sizes and excitation types. >
K.-f. Lee - One of the best experts on this subject based on the ideXlab platform.
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Input impedance of annular-ring microstrip antennas with a dielectric cover
IEEE Transactions on Antennas and Propagation, 1992Co-Authors: Z. Fan, K.-f. LeeAbstract:A theoretical and numerical analysis of the annular-ring microstrip antenna with a dielectric cover is performed. The problem is formulated in the Hankel transform domain, taking a coaxial feed into consideration. The integral equations for the Surface Current Density on the patch are derived. Galerkin's method is used to solve for the Surface Current Density, and a stationary formula for the input impedance is obtained. Numerical results showing the effects of a dielectric cover on the TM/sub 12/ mode of the annular ring are given. It is found that the dielectric cover reduces the resonant frequency, decreases the resonant resistance, and increases the impedance bandwidth. >
