Helsinki University of Technology

About: Helsinki University of Technology is a based out in . It is known for research contribution in the topics: Artificial neural network & Finite element method. The organization has 8962 authors who have published 20136 publications receiving 723787 citations. The organization is also known as: TKK & Teknillinen korkeakoulu.

Activation of multiple cortical areas in response to somatosensory stimulation: combined magnetoencephalographic and functional magnetic resonance imaging.

Abstract: We combined information from functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) to assess which cortical areas and in which temporal order show macroscopic activation after right median nerve stimulation. Five healthy subjects were studied with the two imaging modalities, which both revealed significant activation in the contra- and ipsilateral primary somatosensory cortex (SI), the contra- and ipsilateral opercular areas, the walls of the contralateral postcentral sulcus (PoCS), and the contralateral supplementary motor area (SMA). In fMRI, two separate foci of activation in the opercular cortex were discerned, one posteriorly in the parietal operculum (PO), and one anteriorly near the insula or frontal operculum (anterior operculum, AO). The activation sites from fMRI were used to constrain the solution of the inverse problem of MEG, which allowed us to construct a model of the temporal sequence of activation of the different sites. According to this model, the mean onset latency for significant activation at the contralateral SI was 20 msec (range, 17-22 msec), followed by activation of PoCS at 23 msec (range, 21-25 msec). The contralateral PO was activated at 26 msec (range, 19-32 msec) and AO at 33 msec (range, 22-51 msec). The contralateral SMA became active at 36 msec (range, 24-48 msec). The ipsilateral SI, PO, and AO became activated at 54-67 msec. We conclude that fMRI provides a useful means to constrain the inverse problem of MEG, allowing the construction of spatiotemporal models of cortical activation, which may have significant implications for the understanding of cortical network functioning.

Meta‐materials with wideband negative permittivity and permeability

Abstract: Recently, electromagnetic materials with negative permittivity and permeability values (sometime called “media with negative refraction index”) have been given much attention in the literature. Negative values of the material parameters can be achieved in composite media near resonances, which implies very dispersive properties. The material parameters are complex numbers to account for dissipation, and the real parts can be negative only in narrow frequency bands. Here, we show that this limitation can be relaxed in composite materials with active inclusions. It is proven that, using small dipole and loop antennas loaded by certain simple electronic circuits as composite inclusions, the material behaves as an effective medium with real negative parameters in wide frequency bands. Similarly, thin sheets of negative materials can be simulated by strip or patch arrays loaded by active circuits. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 163–165, 2001.

Detection and Tracking of MIMO Propagation Path Parameters Using State-Space Approach

Abstract: This paper describes a novel approach for detection, estimation and tracking of multiple-input multiple-output (MIMO) radio propagation parameters from multidimensional channel sounding measurements. A realistic state-space model is developed for the purpose, and the extended Kalman filter (EKF) is applied in a particular computationally efficient form to track the geometrical double-directional propagation path parameters. The observation model utilizes the dense multipath component (DMC), describing the distributed scattering in the channel, as part of the underlying noise process. The DMC model assumes an exponential profile in delay, and allows for an arbitrary angular distribution. In addition, a novel dynamic state dimension estimator using statistical goodness-of-fit tests is introduced. The employed methods are supported by illustrative estimation examples from MIMO channel sounding measurements.