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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

Evaluation and implementation of neural brain activity detection methods for fMRI

Breitenmoser, Sabina January 2005 (has links)
Functional Magnetic Resonance Imaging (fMRI) is a neuroimaging technique used to study brain functionality to enhance our understanding of the brain. This technique is based on MRI, a painless, noninvasive image acquisition method without harmful radiation. Small local blood oxygenation changes which are reflected as small intensity changes in the MR images are utilized to locate the active brain areas. Radio frequency pulses and a strong static magnetic field are used to measure the correlation between the physical changes in the brain and the mental functioning during the performance of cognitive tasks. This master thesis presents approaches for the analysis of fMRI data. The constrained Canonical Correlation Analysis (CCA) which is able to exploit the spatio-temporal nature of an active area is presented and tested on real human fMRI data. The actual distribution of active brain voxels is not known in the case of real human data. To evaluate the performance of the diagnostic algorithms applied to real human data, a modified Receiver Operating Characteristics (modified ROC) which deals with this lack of knowledge is presented. The tests on real human data reveal the better detection efficiency with the constrained CCA algorithm. A second aim of this thesis was to implement the promising technique of constrained CCA into the software environment SPM. To implement the constrained CCA algorithms into the fMRI part of SPM2, a toolbox containing Matlab functions has been programmed for the further use by neurological scientists. The new SPM functionalities to exploit the spatial extent of the active regions with CCA are presented and tested.
142

Evaluation of Hardware Test Methods for VLSI Systems

Eriksson, Jens January 2005 (has links)
The increasing complexity and decreasing technology feature sizes of electronic designs has caused the challenge of testing to grow over the last decades. The purpose of this thesis was to evaluate different hardware test methods/approaches based on their applicability in a complex SoC design. Among the aspects that were investigated are test implementation effort, test efficiency and the performance penalties implicated by the test. This report starts out by presenting a general introduction to the basics of hardware testing. It then moves on to review available standards and methodologies. In the end one of the more interesting methods is investigated through a case study. The method that was chosen for the case study has been implemented on a DSP, and is rather new and not as prolific as many of the standards discussed in the report. This type of method appears to show promising results when compared to more traditional ones.
143

A comparison of circuit implementations from a security perspective

Sundström, Timmy January 2005 (has links)
In the late 90's research showed that all circuit implementations were susceptible to power analysis and that this analysis could be used to extract secret information. Further research to counteract this new threat by adding countermeasures or modifying the nderlaying algorithm only seemed to slow down the attack. There were no objective analysis of how different circuit implementations leak information and by what magnitude. This thesis will present such an objective comparison on five different logic styles. The comparison results are based on simulations performed on transistor level and show that it is possible to implement circuits in a more secure and easier way than what has been previously suggested.
144

Kontrollbox för häftare A6102 / Control box for stapler A6102

Brickarp, Erik, Josefsson, Oscar January 2007 (has links)
<p>This report describes the construction and development of a control box, which is a tool for testing and verifying a certain model of Rapid’s built in staplers (model A6102). Basically the function of the control box is to interpret any errors that may occur in the stapler and to make it possible to test fire the stapler.</p><p>The control box should be able to communicate with the stapler using a specialized communication protocol. The different data such as errors, firmware etc. from the stapler is presented in plain language on a display. Additional functions worth mentioning is the possibility to choose between several different firing modes and strengths of the stapler using two multiswitches.</p><p>Our ambition with the control box was to create a construction that was suitable to build in small series, provide a good documentation and to write a program that would be easy to modify in case someone would like to add new functions in the future. Since we focused on making the box as easy as possible to assemble we have not prioritised to find the cheapest possible solution using cheap components. Instead we have chosen multifunctional components that individually can do as much of the work as possible such as the display and the microprocessor.</p>
145

Stability of power systems with large amounts of distributed generation

Knazkins, Valerijs January 2004 (has links)
<p>This four-part dissertation is essentially concerned with some theoretical aspects of the stability studies of power systems with large penetration levels of distributed generation. In particular, in Parts I and II the main emphasis is placed upon the transient rotor angle and voltage stability. The remaining two parts are devoted to some system-theoretic and practical aspects of identification and modeling of aggregate power system loads, design of auxiliary robust control, and a general qualitative discussion on the impact that distributed generation has on the power systems. </p><p>One of the central themes of this dissertation is the development of analytical tools for studying the dynamic properties of power systems with asynchronous generators. It appears that the use of traditional tools for nonlinear system analysis is problematic, which diverted the focus of this thesis to new analytical tools such as, for example, the Extended Invariance Principle. In the framework of the Extended Invariance Principle, new extended Lyapunov functions are developed for the investigation of transient stability of power systems with both synchronous and asynchronous generators. In most voltage stability studies, one of the most common hypotheses is the deterministic nature of the power systems, which might be inadequate in power systems with large fractions of intrinsically intermittent generation, such as, for instance, wind farms. To explicitly account for the presence of intermittent (uncertain) generation and/or stochastic consumption, this thesis presents a new method for voltage stability analysis which makes an extensive use of interval arithmetics. </p><p>It is a commonly recognized fact that power system load modeling has a major impact on the dynamic behavior of the power system. To properly represent the loads in system analysis and simulations, adequate load models are needed. In many cases, one of the most reliable ways to obtain such models is to apply a system identification method. This dissertation presents new load identification methodologies which are based on the minimization of a certain prediction error. </p><p>In some cases, DG can provide ancillary services by operating in a load following mode. In such a case, it is important to ensure that the distributed generator is able to accurately follow the load variations in the presence of disturbances. To enhance the load following capabilities of a solid oxide fuel plant, this thesis suggests the use of robust control. This dissertation is concluded by a general discussion on the possible impacts that large amounts of DG might have on the operation, control, and stability of electric power systems.</p>
146

Characterization of electrical properties in 4H-SiC by imaging techniques

Österman, John January 2004 (has links)
<p>4H-SiC has physical properties supremely suited for a variety of high power, high frequency and high temperature electronic device applications. To fully take advantage of the material's potential, several problems remain to be solved. Two of the most important are (1) the characterization and understanding of crystallographic defects and their electrical impact on device performance, and (2) the introduction of acceptor dopants, their activation and control of the final distribution of charge carriers. Two main experimental methods have been employed in this thesis to analyze 4H-SiC material with respect to the issues (1) and (2): electron beam induced current (EBIC) and scanning spreading resistance microscopy (SSRM), respectively. </p><p>EBIC yields a map of electron-hole-pairs generated by the electron beam of a scanning electron microscope and collected in the depleted region around a junction. EBIC is conducted in two modes. In the first mode the EBIC contrast constitutes a map of minority carrier diffusion lengths. Results from these measurements are compared to white beam syncrotron x-ray topography and reveal a one-to-one correlation between lattice distortions and the electron diffusion length in n+p 4H-SiC diodes. In the second EBIC mode, the junction is highly reverse biased and local avalanche processes can be studied. By correlating these EBIC results with other techniques it is possible to separate defects detrimental to device performance from others more benign. </p><p>SSRM is a scanning probe microscopy technique that monitors carrier distributions in semiconductors. The method is for the first time successfully applied to 4H-SiC and compared to alternative carrier profiling techniques; spreading resistance profiling (SRP), scanning electron microscopy (SEM) and scanning capacitance microscopy (SCM). SCM successfully monitors the doping levels and junctions, but none of these techniques fulfill the requirements of detection resolution, dynamic range and reproducibility. The SSRM current shows on the other hand a nearly ideal behavior as a function of aluminum doping in epitaxially grown samples. However, the I-V dependence is highly non-linear and the extremely high currents measured indicate a broadening of the contact area and possibly an increased ionization due to sample heating. Finite element calculations are performed to further elucidate these effects. </p><p>SSRM is also applied to characterize Al implantations as a function of anneal time and temperature. The Al doping profiles are imaged on cleaved cross-sections and the measured SSRM current is integrated with respect to depth to obtain a value of the total activation. The evaluation of the annealing series shows a continuous increase of the activation even up to 1950 °C. Other demonstrated SSRM applications include local characterization of electrical field strength in passivating layers of Al2O3, and lateral diffusion and doping properties of implanted boron.</p>
147

Kontrollbox för häftare A6102 / Control box for stapler A6102

Brickarp, Erik, Josefsson, Oscar January 2007 (has links)
This report describes the construction and development of a control box, which is a tool for testing and verifying a certain model of Rapid’s built in staplers (model A6102). Basically the function of the control box is to interpret any errors that may occur in the stapler and to make it possible to test fire the stapler. The control box should be able to communicate with the stapler using a specialized communication protocol. The different data such as errors, firmware etc. from the stapler is presented in plain language on a display. Additional functions worth mentioning is the possibility to choose between several different firing modes and strengths of the stapler using two multiswitches. Our ambition with the control box was to create a construction that was suitable to build in small series, provide a good documentation and to write a program that would be easy to modify in case someone would like to add new functions in the future. Since we focused on making the box as easy as possible to assemble we have not prioritised to find the cheapest possible solution using cheap components. Instead we have chosen multifunctional components that individually can do as much of the work as possible such as the display and the microprocessor.
148

MODELLING OF THE POWER SYSTEM OF GOTLAND INPSS/E WITH FOCUS ON HVDC LIGHT

Brask, Martin January 2008 (has links)
The purpose with this project is to develop a model of the whole power system of Gotland in the power system simulation software PSS/E. A model of the whole power system of Gotland has earlier been used in the power system simulation software Simpow but now there is a need to develop a model in PSS/E. In the power system of Gotland there are several components that need to be modelled such as lines, loads, transformers, shunt impedances, synchronous machines, asynchronous machines, an HVDC Classic link and an HVDC Light link. These components are modelled in the Simpow model and needs to be converted to the PSS/E model. The aim is to develop a model in PSS/E that is as equal as possible to the model in Simpow. Especially the HVDC Light link at Gotland has been investigated in the project. A problem with converting data from Simpow to PSS/E is that the models of several components differ in Simpow and PSS/E. Lines and shunt impedances can be modelled in the same way but the models for loads, transformers, synchronous machines, asynchronous machines, the HVDC Classic link, and the HVDC Light link differ in Simpow and PSS/E. The models in Simpow are converted to the models in PSS/E in an as equal way as possible. The results in PSS/E are analyzed and compared with the Simpow model. In the project we have also made a test of fault simulations in time-domain simulations in PSS/E. The aim with this test is to verify the PSS/E calculations when a three-phase or a single-phase fault is applied. The reason for that is that PSS/E only calculates using positivesequence components and therefore only is able to calculate exact during circumstances of symmetrical loads and faults. The result shows that the calculations for both symmetrical and unsymmetrical faults in PSS/E are correct concerning the positive-sequence components. A drawback in PSS/E is, however, that we do not have any information concerning the negativeand zero-sequence  components, which results in that we cannot calculate the three phasequantities.
149

Analysis of Electro-Meachanical Actuator Systems in More Electric Aircraft Applications

Torabzadeh-Tari, Mohsen January 2005 (has links)
Conventional hydraulic actuators in aircraft are demanding regarding maintenance which implies high operation costs. In recent years the focus therefore has been set on electro-hydrostatic and electro-mechanical actuators. The aim of this work is to analyze and evaluate the possibility of introducing electro-mechanical actuators (EMAs) in more electric aircraft applications. The major goal is to optimize the weight of such actuator systems including the electro-machine (electric motor) gear mechanism and power converter, without loss of reliability. Other optimisation criteria on such solutions are low losses and good thermal properties. A quasi-static model approach of EMAs is used here in order to decrease the simulation time. It is possible because the low (mechanical) and high (electrical) frequency components are separated in the model, see [1]. The inverters and converters are described as fictive DC-DC transformers with corresponding efficiencies, see [2]. By introducing an object oriented approach the model is flexible and re-usable and can be used as a framework in the future build-up of models of entire MEA aircrafts, see [3]. Power density, cost and weight of the actuator systems are some of the important key factors for comparing purpose and as a platform for the dimensioning of the aircraft. The next issue becomes the scalability of the model and the key factors, because of the diversity of the actuators used in different parts of the MEA aircraft. Therefore the ambition is set to build up a database of different scalable actuator solutions which among others returns these key factors as output. / QC 20101222
150

Stöldskydd i Jordbruket / Theft prevention system for agriculture

Coops, Fabian, Adam, Grins January 2023 (has links)
This report examines and presents an effective way to alert the owner of a GPS device in case of theft in the agricultural sector. By implementing IR sensors that can be mounted under the object and monitor movements, the owner can receive a warning via SMS and email in case of a potential theft. The report also discusses any security risks associated with using LoRaWAN in IoT. The pre-study shows that grab and run is the most common theft method in agriculture. Signal jamming techniques are also a potential method, but there is no information specifically confirming their use in agriculture. The report presents an IoT solution with frequency hopping, encryption, and authentication that creates some security against interference. Tests in indoor environments have shown a working system, but more development and testing are needed to adapt the system to outdoor and agricultural environments where the components are farther apart. The report serves as a starting point for further development of a solution for practical use in the agricultural sector. / Denna rapport undersöker och presenterar ett effektivt sätt att larma ägaren till en GPS-enhet vid stöld i jordbrukssektorn. Genom att implementera IR-sensorer som kan monteras under objektet och övervaka rörelser, kan ägaren få en varning via SMS och e-post vid en potentiell stöld. Rapporten tar även upp eventuella säkerhetsrisker vid användning av LoRaWAN in om IoT. Förstudien visar att grab and run är den vanligaste stöldmetoden i jordbruket. Signalstörningstekniker är också en potentiell metod, men det finns ingen information som specifikt bekräftar användningen inom jordbruket. Rapporten presenterar en IoT-lösning med frekvenshoppning, kryptering och autentisering som skapar en viss säkerhet mot störningar. Tester i inomhusmiljö har visat på ett fungerande system, men det krävs mer utveckling och tester för att anpassa systemet till utomhusmiljöer och lantbruksmiljöer där komponenterna är längre ifrån varandra. Rapporten fungerar som en utgångspunkt för vidare utveckling av en lösning för praktisk användning i jordbrukssektorn.

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