Computation of Electromagnetic Fields in Assemblages of Biological Cells Using a Modified Finite-Difference Time-Domain Scheme

When modeling objects that are small compared with the wavelength, e.g., biological cells at radio frequencies, the standard finite-difference time-domain (FDTD) method requires extremely small time-step sizes, which may lead to excessive computation times. The problem can be overcome by implementing a quasi-static approximate version of FDTD based on transferring the working frequency to a higher frequency and scaling back to the frequency of interest after the field has been computed. An approach to modeling and analysis of biological cells, incorporating a generic lumped-element membrane model, is presented here. Since the external medium of the biological cell is lossy material, a modified Berenger absorbing boundary condition is used to truncate the computation grid. Linear assemblages of cells are investigated and then Floquet periodic boundary conditions are imposed to imitate the effect of periodic replication of the assemblages. Thus, the analysis of a large structure of cells is made more computationally efficient than the modeling of the entire structure. The total fields of the simulated structures are shown to give reasonable and stable results at 900,1800, and 2450 MHz. This method will facilitate deeper investigation of the phenomena in the interaction between electromagnetic fields and biological systems

Computation of electromagnetic fields in assemblages of biological cells using a modified finite difference time domain scheme. Computational electromagnetic methods using quasi-static approximate version of FDTD, modified Berenger absorbing boundary and Floquet periodic boundary conditions to investigate the phenomena in the interaction between EM fields and biological systems.

yesThere is an increasing need for accurate models describing the electrical behaviour of individual biological cells exposed to electromagnetic fields. In this area of solving linear problem, the most frequently used technique for computing the EM field is the Finite-Difference Time-Domain (FDTD) method. When modelling objects that are small compared with the wavelength, for example biological cells at radio frequencies, the standard Finite-Difference Time-Domain (FDTD) method requires extremely small time-step sizes, which may lead to excessive computation times. The problem can be overcome by implementing a quasi-static approximate version of FDTD, based on transferring the working frequency to a higher frequency and scaling back to the frequency of interest after the field has been computed. An approach to modeling and analysis of biological cells, incorporating the Hodgkin and Huxley membrane model, is presented here. Since the external medium of the biological cell is lossy material, a modified Berenger absorbing boundary condition is used to truncate the computation grid. Linear assemblages of cells are investigated and then Floquet periodic boundary conditions are imposed to imitate the effect of periodic replication of the assemblages. Thus, the analysis of a large structure of cells is made more computationally efficient than the modeling of the entire structure. The total fields of the simulated structures are shown to give reasonable and stable results at 900MHz, 1800MHz and 2450MHz. This method will facilitate deeper investigation of the phenomena in the interaction between EM fields and biological systems. Moreover, the nonlinear response of biological cell exposed to a 0.9GHz signal was discussed on observing the second harmonic at 1.8GHz. In this, an electrical circuit model has been proposed to calibrate the performance of nonlinear RF energy conversion inside a high quality factor resonant cavity with known nonlinear device. Meanwhile, the first and second harmonic responses of the cavity due to the loading of the cavity with the lossy material will also be demonstrated. The results from proposed mathematical model, give good indication of the input power required to detect the weakly effects of the second harmonic signal prior to perform the measurement. Hence, this proposed mathematical model will assist to determine how sensitivity of the second harmonic signal can be detected by placing the required specific input power

Bio-electromagnetic model of deep brain stimulation

Functional stimulation is one of the most fascinating applications of bioelectromagnetism. It deals with the stimulation of excitable biological tissues by electromagnetic fields. One of its most impressive medical applications is the subthalamic nucleus deep brain stimulation (DBS). It consists in the insertion of an electrode into the deep brain, delivering electric pulses to treat Parkinson's disease and other movement disorders. But despite its wide use throughout the world for almost twenty years, the understanding of the mechanisms of action remains unclear. To help clinicians to better understand the mechanisms of DBS, its limitations and implications from an electrical point of view, electrical models of the head can be used to predict the electric potential distribution generated by the electric pulse. With the development of medical imaging techniques, the information on biological tissues that can be used to build these electrical models has never been so detailed. The diffusion tensor magnetic imaging (DT-MRI) is able to provide the orientation of the fibers within the cerebral tissues. Thus, the high inhomogeneity and anisotropy of the head can be modeled through anisotropic electrical conductivity tensors to set up realistic models of the patient's head. This thesis aims to provide to clinicians an accurate prediction of the potential distribution generated by the electric pulse. With this purpose, a finite element (FE) model is set up using electric conductivity values based on DT-MRI data. Special care has been taken to model more realistic boundary conditions than the ones commonly encountered in literature. A great effort has also been put to model the tissues surrounding the stimulation. The results show that these two aspects are impacting significantly the potential distribution. To predict the neural extent of the stimulation, electrical equivalent models of axons are combined with the obtained potentials. Volume of tissues activated (VTA) are thus obtained. Results show that the VTA are also impacted by the decision on how to model the boundary conditions. They show that the usual choice assumed in literature up to now leads to an overestimation of 30% of the VTA

Artistic Modulation of Consciousness by Bioelectromagnetic Stimulation

The thesis demonstrates why the application of bioelectromagnetic stimulation as a medium of artistic expression allows for the production of new and unprecedented realisations of integrative art. Furthermore, the modulation of consciousness in human beings relating with such realisations is argued to be the core of a new practice of research resulting from the technological confluence of Philosophy, Art and Science. The Brunelleschi Experiment is examined in order to establish the assumption that one of the fundamental characteristics of Art is to impact consciousness of those interacting with its forms. The aspects of disembodiment of the previously referred experiment, instrumental in provoking such impact, are argued to be consistent with those found in the philosophy and practice of Fernando Pessoa. The practice of the Portuguese philosopher is presented as proto-foundational grounds of the new research practice proposed. The recent findings of Olaf Blanke, specially the ones regarding the induction of out-of-body experiences by bioelectromagnetic stimulation are reassessed as previous technological foundations of the new artistic realisations proposed. The practice of art was an instrumental part of the research and is therefore described as a methodology to access consciousness and generate knowledge, a thinking process. Research was undertaken in the context of two projects: Sensitive Spheres and Collectron. Both projects are representations of the social implications of perceiving human beings as electromagnetic manifestations. In the context of these projects, Bioelectromagnetism is understood as the study of the intersections between biological entities and the electromagnetic spectrum. Each project represents a culture of interactions between biological beings, including their spiritual dimension, in which art plays a fundamental role in creating alternative forms of communication as well as in congregating and mediating consciousnesses at a collective level. In conclusion, Homo Conscientis, an audiovisual integrative experience applying bioelectromagnetics, is presented as the first manifestation of the new practice proposed. Both its technical aspects and the observations resulting from its application have been thoroughly described.Fundacao para a Ciencia e Tecnologia, Portuga

Experimental and computational investigation of heat transfer in a microwave-assisted flow system

Microwave technology is gaining popularity as a tool for chemical process intensification and an alternative to conventional heating. However, in flow systems non-uniform temperature profiles are commonly encountered and hence methods to characterise and improve them are required. In this work, we studied the effects of various operational parameters-microwave power, inlet flow rate, tube orientation and pressure-on the electric field and temperature profiles of water flowing in a PTFE tube (2.4 mm internal diameter), placed in a commercial single-mode microwave applicator. A finite element model was developed to estimate the longitudinal temperature profiles and the absorbed microwave power, while in situ temperature monitoring was performed by a fibre optic probe placed at multiple locations inside the tube. The water temperature inside the tube increased by increasing the microwave power input and temperature profiles stabilised beyond 20 W, while the percentage absorbed microwave power showed the inverse trend. When changing the tube orientation or decreasing the inlet flow rate, microwave absorption decreased significantly. When the pressure was increased to 2.3 bara, water temperature increased by ~ 20 o C. Results from this study provide valuable insights on achievable temperature profiles and energy efficiency of microwave-assisted flow synthesis systems.

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 343)

This bibliography lists 125 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during January, 1989. Subject coverage includes: aerospace medicine and psychology, life support systems and controlled environments, safety equipment, exobiology and extraterrestrial life, and flight crew behavior and performance

Funktionelle Bildgebung mittels swLORETA und Phasensynchronisierung

In order to overcome some of the limitations of the distributed inverse solution algorithms, a new algorithm named Standardized Weighted Low Resolution Tomography (swLORETA) was developed. The swLORETA algorithm incorporates a singular value decomposition (SVD) based lead field weighting to compensate the tendency of the linear inverse procedures in general, and sLORETA in particular, to reconstruct the sources close to the location of the sensors. It also contributes to decrease the sensitivity of the solution to the presence of noise. An extension of the swLORETA to the time-frequency domain was also developed by applying the Hilbert transform to the time series obtained with the swLORETA. Finally, the coherence and phase synchronization imaging methods were introduced to assess functional connectivity within the brain. The tomographic properties of swLORETA and sLORETA were compared using both simulated and real data. In the simulation studies, the reconstruction of single and multiple current dipoles was simulated varying their position and orientation across the source space and taking into account the presence of noise. The real data was obtained from healthy subjects who performed a classical spatial attention experiment. The tests performed demonstrated that the resulting algorithm is not only efficient but also accurate as demonstrated by the analysis of a spatial attention experiment.In dieser Arbeit wird ein neuer Algorithmus, Standardized Weighted Low Resolution Tomography (swLORETA) genannt, vorgestellt, der einige der Beschränkungen von verteilten Lösungen für eine Quellenlokalisation beseitigt. Der swLORETA-Algorithmus enthält eine Wichtung für das Leitungsfeld, das auf eine singular value decomposition (SVD) basiert. Damit wird die Tendenz der linearen Quellenlokalisation im Allgemeinen und von sLORETAim Besonderen, die Quellen zu nahe zu den Sensorpositionen zu lokalisieren, kompensiert. Die veränderte Wichtung trägt auch zu einer Abnahme der Rausch-Empfindlichkeit der Lösung bei. Eine Erweiterung von swLORETA in den Zeit-Frequenz-Bereich wurde entwickelt. Dies geschah durch Anwendung der Hilbert-Transformation auf Zeitreihen, die durch swLORETA erzeugt wurden. Schließlich wurden Bildgebungsmethoden für die Kohärenz und die Phasen-Synchronisation eingeführt, um die funktionalen Verbindungen im Gehirn zu untersuchen. Die tomographischen Eigenschaften von swLORETA und sLORETA wurden mit Hilfe simulierter und realer Daten verglichen. In den Simulations-Studien wurde die Rekonstruktion von einzelnen wie multiplen Dipolen bei Berücksichtigung von Rauschen simuliert, wobei sowohl die Position als auch die Orientierung variiert wurde. Die realen Daten wurden von gesunden Probanden aufgenommen, die ein klassisches räumliches Aufmerksamkeits-Experiment ausführten. Die Testergebnisse dieses Experiments zeigen, dass der Algorithmus nicht nur effizient arbeitet, sondern auch genaue Resultate zur Analyse derartiger Experimente liefert

A Simple Blass Matrix Design Strategy for Multibeam Arbitrary Linear Antenna Arrays

Multibeam antenna arrays are currently recognized as one of the enabling technologies for the next-generation communication standards. One of the key components of these systems is the beamforming network (BFN) that implements the array element excitations. This article addresses this issue by presenting a novel strategy to realize an analog feeding network, which allows an arbitrary linear array (LA) to radiate multiple arbitrary beams. In particular, an iterative procedure is conceived to design a Blass matrix using an identical directional coupler for all nodes, resulting in a very simple structure suitable for large-scale production. Two applications with arbitrary directions are illustrated as proofs-of-concept for the developed architecture: a dual-beam configuration with a null involving an aperiodic LA, and a four-beam configuration involving a periodic LA. For this second application, the effectiveness of the proposed solution is further verified by full-wave simulations and experimental measurements carried out on a fabricated prototype