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  • Public defence: 2017-08-25 09:00 Campus US, Linköping
    Latorre, Malcolm
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    The Physical Axon: Modeling, Simulation and Electrode Evaluation2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Electrodes are used in medicine for detection of biological signals and for stimulating tissue, e.g. in deep brain stimulation (DBS). For both applications, an understanding of the functioning of the electrode, and its interface and interaction with the target tissue involved is necessary. To date, there is no standardized method for medical electrode evaluation that allows transferability of acquired data. In this thesis, a physical axon (Paxon) potential generator was developed as a device to facilitate standardized comparisons of different electrodes. The Paxon generates repeatable, tuneable and physiological-like action potentials from a peripheral nerve. It consists of a testbed comprising 40 software controlled 20 μm gold wires embedded in resin, each wire mimicking a node of Ranvier. ECG surface Ag-AgCl electrodes were systematically tested with the Paxon. The results showed small variations in orientation (rotation) and position (relative to axon position) which directly impact the acquired signal. Other electrode types including DBS electrodes can also be evaluated with the Paxon.

    A theoretical comparison of a single cable neuronal model with an alternative established double cable neuron model was completed. The output with regards to DBS was implemented to comparing the models. These models were configured to investigate electrode stimulation activity, and in turn to assess the activation distance by DBS for changes in axon diameter (1.5-10 μm), pulse shape (rectangular biphasic and rectangular, triangular and sinus monophasic) and drive strength (1-5 V or mA). As both models present similar activation distances, sensitivity to input shape and computational time, the neuron model selection for DBS could be based on model complexity and axon diameter flexibility. An application of the in-house neuron model for multiple DBS lead designs, in a patient-specific simulation study, was completed. Assessments based on the electric field along multiple sample planes of axons support previous findings that a fixed electric field isolevel is sufficient for assessments of tissue activation distances for a predefined axon diameter and pulse width in DBS.

    List of papers
    1. A Physical Action Potential Generator: Design, Implementation and Evaluation
    Open this publication in new window or tab >>A Physical Action Potential Generator: Design, Implementation and Evaluation
    2015 (English)In: Frontiers in Neuroscience, ISSN 1662-4548, E-ISSN 1662-453X, Vol. 9, 1-11 p., 371Article in journal (Refereed) Published
    Abstract [en]

    The objective was to develop a physical action potential generator (Paxon) with the ability to generate a stable, repeatable, programmable, and physiological-like action potential. The Paxon has an equivalent of 40 nodes of Ranvier that were mimicked using resin embedded gold wires (Ø = 20 μm). These nodes were software controlled and the action potentials were initiated by a start trigger. Clinically used Ag-AgCl electrodes were coupled to the Paxon for functional testing. The Paxon’s action potential parameters were tunable using a second order mathematical equation to generate physiologically relevant output, which was accomplished by varying the number of nodes involved (1 to 40 in incremental steps of 1) and the node drive potential (0 to 2.8V in 0.7 mV steps), while keeping a fixed inter-nodal timing and test electrode configuration. A system noise floor of 0.07 ± 0.01 μV was calculated over 50 runs. A differential test electrode recorded a peak positive amplitude of 1.5 ± 0.05 mV (gain of 40x) at time 196.4 ± 0.06 ms, including a post trigger delay. The Paxon’s programmable action potential like signal has the possibility to be used as a validation test platform for medical surface electrodes and their attached systems.

    Place, publisher, year, edition, pages
    Frontiers Research Foundation, 2015
    Keyword
    Action potential, biomedical electrode, electronic nerve model, nodes of Ranvier, ulnar nerve
    National Category
    Medical Engineering
    Identifiers
    urn:nbn:se:liu:diva-121086 (URN)10.3389/fnins.2015.00371 (DOI)
    Note

    Funding agencies| Linköping University; the Swedish Research Council (Grant No. 621-2013-6078)

    At the time for thesis presentation publication was in status: Manuscript

    Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2017-06-19Bibliographically approved
    2. Describing Measurement Behaviour of a Surface Ag-AgCl Electrode Using the Paxon Test Platform
    Open this publication in new window or tab >>Describing Measurement Behaviour of a Surface Ag-AgCl Electrode Using the Paxon Test Platform
    2016 (English)In: XIV MEDITERRANEAN CONFERENCE ON MEDICAL AND BIOLOGICAL ENGINEERING AND COMPUTING 2016, SPRINGER , 2016, Vol. 57, 442-445 p.Conference paper (Refereed)
    Abstract [en]

    A better understanding of bioelectrodes can be acquired with extended testing, which will lead to better methodology and data quality. Today electrodes are evaluated for intraelectrode differences and performance with a traditional gain-phase method, while using the physical axon action potential generator (Paxon) test platform offers extended test possibilities. The direct gain-phase measurements are useful to extract the transfer function of the electrode, as well as some other base parameters. The Paxon test platform is a complementary method that tests electrodes under conditions that are more realistic, mimicking real measurement situations in comparison to the gain-phase method. The Paxon also allows tests to be performed beyond what the gain-phase methods can measure, for example electrode rotation, which would uncover variations in the symmetry of the electrode. When tested, the symmetry properties of the electrode, where the electrodes are rotated in steps of 90 degrees, resulted in a peak to peak variation in detected amplitude of 5.3 +/- 8.9 mV. Therefore, the Paxon appears to be a feasible test platform for characterizing electrodes beyond the gain-phase tests in a semiautomatic manner.

    Place, publisher, year, edition, pages
    SPRINGER, 2016
    Series
    IFMBE Proceedings, ISSN 1680-0737
    Keyword
    Electrode testing; Characterization; Coupling Parameters; Stability test; Axon potential
    National Category
    Medical Equipment Engineering
    Identifiers
    urn:nbn:se:liu:diva-129510 (URN)10.1007/978-3-319-32703-7_86 (DOI)000376283000086 ()978-3-319-32703-7 (ISBN)978-3-319-32701-3 (ISBN)
    Conference
    14th Mediterranean Conference on Medical and Biological Engineering and Computing (MEDICON)
    Available from: 2016-06-20 Created: 2016-06-20 Last updated: 2017-06-19Bibliographically approved
    3. Investigation into Deep Brain Stimulation Lead Designs: A Patient-Specific Simulation Study
    Open this publication in new window or tab >>Investigation into Deep Brain Stimulation Lead Designs: A Patient-Specific Simulation Study
    Show others...
    2016 (English)In: Brain Sciences, ISSN 2076-3425, E-ISSN 2076-3425, Vol. 6, no 3, 1-16 p.Article in journal (Refereed) Published
    Abstract [en]

    New deep brain stimulation (DBS) electrode designs offer operation in voltage and current mode and capability to steer the electric field (EF). The aim of the study was to compare the EF distributions of four DBS leads at equivalent amplitudes (3 V and 3.4 mA). Finite element method (FEM) simulations (n = 38) around cylindrical contacts (leads 3389, 6148) or equivalent contact configurations (leads 6180, SureStim1) were performed using homogeneous and patient-specific (heterogeneous) brain tissue models. Steering effects of 6180 and SureStim1 were compared with symmetric stimulation fields. To make relative comparisons between simulations, an EF isolevel of 0.2 V/mm was chosen based on neuron model simulations (n = 832) applied before EF visualization and comparisons. The simulations show that the EF distribution is largely influenced by the heterogeneity of the tissue, and the operating mode. Equivalent contact configurations result in similar EF distributions. In steering configurations, larger EF volumes were achieved in current mode using equivalent amplitudes. The methodology was demonstrated in a patient-specific simulation around the zona incerta and a “virtual” ventral intermediate nucleus target. In conclusion, lead design differences are enhanced when using patient-specific tissue models and current stimulation mode.

    Place, publisher, year, edition, pages
    MDPI, 2016
    Keyword
    deep brain stimulation (DBS), steering, patient-specific, electric field, finite element method, neuron model, brain model, zona incerta (ZI), electrode design
    National Category
    Medical Engineering
    Identifiers
    urn:nbn:se:liu:diva-131863 (URN)10.3390/brainsci6030039 (DOI)27618109 (PubMedID)
    Available from: 2016-10-11 Created: 2016-10-11 Last updated: 2017-06-19Bibliographically approved
  • Public defence: 2017-08-31 10:15 C3, C-huset, Linköping
    Munjulury, Raghu Chaitanya
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Knowledge-Based Integrated Aircraft Design: An Applied Approach from Design to Concept Demonstration2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The design and development of new aircraft are becoming increasingly expensive and timeconsuming. To assist the design process in reducing the development cost, time, and late design changes, the conceptual design needs enhancement using new tools and methods. Integration of several disciplines in the conceptual design as one entity enables to keep the design process intact at every step and obtain a high understanding of the aircraft concepts at early stages.

    This thesis presents a Knowledge-Based Engineering (KBE) approach and integration of several disciplines in a holistic approach for use in aircraft conceptual design. KBE allows the reuse of obtained aircrafts’ data, information, and knowledge to gain more awareness and a better understanding of the concept under consideration at early stages of design. For this purpose, Knowledge-Based (KB) methodologies are investigated for enhanced geometrical representation and enable variable fidelity tools and Multidisciplinary Design Optimization (MDO). The geometry parameterization techniques are qualitative approaches that produce quantitative results in terms of both robustness and flexibility of the design parameterization. The information/parameters from all tools/disciplines and the design intent of the generated concepts are saved and shared via a central database.

    The integrated framework facilitates multi-fidelity analysis, combining low-fidelity models with high-fidelity models for a quick estimation, enabling a rapid analysis and enhancing the time for a MDO process. The geometry is further propagated to other disciplines [Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA)] for analysis. This is possible with an automated streamlined process (for CFD, FEM, system simulation) to analyze and increase knowledge early in the design process. Several processes were studied to streamline the geometry for CFD. Two working practices, one for parametric geometry and another for KB geometry are presented for automatic mesh generation.

    It is observed that analytical methods provide quicker weight estimation of the design and when coupled with KBE provide a better understanding. Integration of 1-D and 3-D models offers the best of both models: faster simulation, and superior geometrical representation. To validate both the framework and concepts generated from the tools, they are implemented in academia in several courses at Linköping University and in industry

    List of papers
    1. A knowledge-based integrated aircraft conceptual design framework
    Open this publication in new window or tab >>A knowledge-based integrated aircraft conceptual design framework
    2016 (English)In: CEAS Aeronautical Journal, ISSN 1869-5582, 1869-5590, Vol. 7, no 1, 95-105 p.Article in journal (Refereed) Published
    Abstract [en]

    "The conceptual design is the early stage of aircraft design process where results are needed fast, both analytically and visually so that the design can be analyzed and eventually improved in the initial phases. Although there is no necessity for a CAD model from the very beginning of the design process, it can be an added advantage to have the model to get the impression and appearance. Furthermore, this means that a seamless transition into preliminary design is achieved since the CAD model can guardedly be made more detailed. For this purpose, knowledge-based aircraft conceptual design applications Tango (Matlab) and RAPID (CATIA) are being developed at Linköping University. Based on a parametric data definition in XML, this approach allows for a full 3D CAD integration. The one-database approach, also explored by many research organizations, enables the flexible and efficient integration of the different multidisciplinary processes during the whole conceptual design phase. This paper describes the knowledge-based design automated methodology of RAPID, data processing between RAPID and Tango and its application in the courses ‘‘Aircraft conceptual design’’ and ‘‘Aircraft project course’’ at Linköping University. A multifaceted user interface is developed to assist the whole design process."

    Place, publisher, year, edition, pages
    Springer, 2016
    Keyword
    Aircraft conceptual design, Knowledge based, XML database
    National Category
    Aerospace Engineering
    Identifiers
    urn:nbn:se:liu:diva-126689 (URN)10.1007/s13272-015-0174-z (DOI)
    Projects
    NFFP5/NFFP6
    Available from: 2016-04-01 Created: 2016-04-01 Last updated: 2017-05-30
    2. Knowledge-based design for future combat aircraft concepts
    Open this publication in new window or tab >>Knowledge-based design for future combat aircraft concepts
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    2014 (English)Conference paper (Refereed)
    Abstract [en]

    A new fighter aircraft will most likely be acollaborative project. In this study conceptualknowledge-based design is demonstrated, usingmodels of comparable fidelity for sizing, geometrydesign, aerodynamic analysis and system simulationfor aircraft conceptual design. A newgeneration fighter is likely to involve advancedcontrol concept where an assessment of feasibilitythrough simulation is needed already atthe conceptual stage. This co-design leads to adeeper understanding of the trade-offs involved.In this paper a study for a future combat aircraftis made. Conceptual knowledge-based design isdemonstrated by optimizing for a design mission,including a super-cruise segment.

    Place, publisher, year, edition, pages
    St. Peterberg: , 2014
    Keyword
    Conceptual design, Aircraft design, Engine design, Knowledge-based
    National Category
    Aerospace Engineering
    Identifiers
    urn:nbn:se:liu:diva-114902 (URN)
    Conference
    29th Congress of the International Council of the Aeronautical Sciences, St. Petersburg, Russia
    Projects
    NFFP5/NFFP6
    Available from: 2015-03-05 Created: 2015-03-05 Last updated: 2017-05-30Bibliographically approved
    3. Knowledge-based future combat aircraft optimization
    Open this publication in new window or tab >>Knowledge-based future combat aircraft optimization
    2016 (English)In: 30th Congress of the International Council of the AeronauticalSciences (ICAS 2016), Bonn: International Council of Aeronautical Sciences (ICAS) , 2016, Vol. 1, 273-280 p.Conference paper (Refereed)
    Abstract [en]

    Future combat aircraft inherently conceal all the components internally essentially for stealth reasons. The geometry is optimized for subsonic and supersonic flight area distribution and the components and payload to be fitted inside the aircraft. The basic requirements to accomplish are fuel consumption, mission profile, and military performance. Analytical methods comprise of a quick aerodynamic and structural optimization. The result obtained is then compared with multi-fidelity aero-structural analysis

    Place, publisher, year, edition, pages
    Bonn: International Council of Aeronautical Sciences (ICAS), 2016
    Keyword
    Knowledge Based, Combat aircraft, Conceptual Design, Optimization
    National Category
    Aerospace Engineering Vehicle Engineering Applied Mechanics Energy Engineering
    Identifiers
    urn:nbn:se:liu:diva-137644 (URN)978-1-5108-3455-2 (ISBN)
    Conference
    30th Congress of the International Council of the Aeronautical Sciences, Daejeon, South Korea, 25-30 September 2016.
    Projects
    NFFP5/NFFP6
    Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-06-02Bibliographically approved
    4. A comprehensive computational multidisciplinary design optimization approach for a tidal power plant turbine
    Open this publication in new window or tab >>A comprehensive computational multidisciplinary design optimization approach for a tidal power plant turbine
    Show others...
    2017 (English)In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 9, no 3, 1-13 p., 1687814017695174Article in journal (Refereed) Published
    Abstract [en]

    Multidisciplinary design optimization has become a powerful technique to facilitate continuous improvement of complex and multidisciplinary products. Parametric modeling is an essential part with tremendous impact on the flexibility and robustness of multidisciplinary design optimization. This article investigates the effect of relational and non-relational parameterization techniques on the robustness and flexibility of the conceptual design of a multidisciplinary product. Bench marking between relational and non-relational parameterization and their effect on flexibility and robustness indicate that the relational parameterization is an efficient method in the multidisciplinary design optimization process. The inherent properties of the method contribute to an efficient parametric modeling with improved communication between different disciplines. This enhances the performance of the multidisciplinary design optimization process and allows a more flexible and robust design. The considered disciplines are computer-aided design, computational fluid dynamics, finite element analysis, and dynamic simulation. A high-fidelity geometry created in a computer-aided design environment is computer-aided design centric approach and later used in computational fluid dynamics, finite element analysis for a better understanding of the product as it leads to precise outcomes. The proposed approach is implemented for the conceptual design of a novel product, a tidal power plant developed by Minesto AB using a multidisciplinary design optimization process.

    Place, publisher, year, edition, pages
    London: Sage Publications, 2017
    Keyword
    Parametric modeling, conceptual design, computer-aided design, computational fluid dynamics, finite element analysis, dynamic simulation, multidisciplinary design optimization
    National Category
    Aerospace Engineering Production Engineering, Human Work Science and Ergonomics Interaction Technologies
    Identifiers
    urn:nbn:se:liu:diva-137645 (URN)10.1177/1687814017695174 (DOI)000400394500001 ()2-s2.0-85018345706 (ScopusID)
    Projects
    NFFP5/NFFP6
    Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-06-14Bibliographically approved
  • Public defence: 2017-09-06 13:15 Ada Lovelace, hus B, Linköping
    Bendtsen, Marcus
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Gated Bayesian Networks2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Bayesian networks have grown to become a dominant type of model within the domain of probabilistic graphical models. Not only do they empower users with a graphical means for describing the relationships among random variables, but they also allow for (potentially) fewer parameters to estimate, and enable more efficient inference. The random variables and the relationships among them decide the structure of the directed acyclic graph that represents the Bayesian network. It is the stasis over time of these two components that we question in this thesis.

    By introducing a new type of probabilistic graphical model, which we call gated Bayesian networks, we allow for the variables that we include in our model, and the relationships among them, to change overtime. We introduce algorithms that can learn gated Bayesian networks that use different variables at different times, required due to the process which we are modelling going through distinct phases. We evaluate the efficacy of these algorithms within the domain of algorithmic trading, showing how the learnt gated Bayesian networks can improve upon a passive approach to trading. We also introduce algorithms that detect changes in the relationships among the random variables, allowing us to create a model that consists of several Bayesian networks, thereby revealing changes and the structure by which these changes occur. The resulting models can be used to detect the currently most appropriate Bayesian network, and we show their use in real-world examples from both the domain of sports analytics and finance.