| 41. |
- Afzal, Nadeem
(författare)
-
Complexity and Power Reduction in Digital Delta-Sigma Modulators
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A number of state-of-the-art low power consuming digital delta-sigma modulator (ΔΣ) architectures for digital-to-analog converters (DAC) are presented in this thesis. In an oversampling ΔΣ DAC, the primary job of the modulator is to reduce the word length of the digital control signal to the DAC and spectrally shape the resulting quantization noise. Among the ΔΣ topologies, error-feedback modulators (EFM) are well suited for so called digital to digital modulation.In order to meet the demands, various modifications to the conventional EFM architectures have been proposed. It is observed that if the internal and external digital signals of the EFM are not properly scaled then not only the design itself but also the signal processing blocks placed after it, may be over designed. In order to avoid the possible wastage of resources, a number of scaling criteria are derived. In this regard, the total number of signal levels of the EFM output is expressed in terms of the input scale, the order of modulation and the type of the loop filter.Further on, it is described that the architectural properties of a unit element-based DAC allow us to move some of the digital processing of the EFM to the analog domain with no additional hardware cost. In order to exploit the architectural properties, digital circuitry of an arbitrary-ordered EFM is split into two parts: one producing the modulated output and another producing the filtered quantization noise. The part producing the modulated output is removed after representing the EFM output with a set of encoded signals. For both the conventional and the proposed EFM architectures, the DAC structure remains unchanged. Thus, savings are obtained since the bits to be converted are not accumulated in the digital domain but instead fed directly to the DAC.A strategy to reduce the hardware of conventional EFMs has been devised recently that uses multiple cascaded EFM units. We applied the similar approach but used several cascaded modified EFM units. The compatibility issues among the units (since the output of each proposed EFM is represented by the set of encoded signals) are resolved by a number of architectural modifications. The digital processing is distributed among each unit by splitting the primary input bus. It is shown that instead of cascading the EFM units, it is enough to cascade their loop filters only. This leads not only to area reduction but also to the reduction of power consumption and critical path.All of the designs are subjected to rigorous analysis and are described mathematically. The estimates of area and power consumption are obtained after synthesizing the designs in a 65 nm standard cell library provided by the foundry.
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| 42. |
- Agnvall, Beatrix
(författare)
-
Early domestication? : Phenotypic alterations of Red Junglefowl selected for divergent fear of humans
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Domestication is the process through which animals adapt to conditions provided by humans. The domesticated phenotype differs from wild ancestors in a number of traits relating to physiology, morphology and behaviour. One of the most striking differences is the animals’ fear response towards humans, and reduced fear of humans is assumed to have been an early prerequisite for the success of domestication. The early alterations seen in the domesticated phenotype may be traits developed as a correlated selection response due to tameness rather than selected upon one by one.This thesis summarizes a project where Red Junglefowl were selected for divergent fear of humans during six generations. In every generation, fear response to human was assessed in a standardized test and, according to fear score, the animals were bred for either high fear of humans (H) or low fear of humans (L). The animals were, above that of the standardized selection test, behaviourally phenotyped in different tests in each generation mainly focusing on fear, exploration and social behaviour. In addition to behaviour, the animals were phenotyped for body weight, egg weight, metabolism, feed intake, plumage condition, blood plasma corticosterone and peripheral serotonin. After culling, vital organs and brains were harvested and weighed.In paper I, we demonstrated that the selection trait has a significant genetic heritability and is genetically correlated with other behavioural responses associated with fearfulness and exploration. In paper II, we concluded that animals from the L strain had better plumage condition, higher weight, laid larger eggs and also generated larger offspring. Furthermore, when tested in a social dominance test with a limited resource, they received less and performed more aggression regardless of whether the restricted source was edible or not. In paper III, we revealed that animals from the L strain had higher basal metabolic rate as chicks, gained more weight in relation to feed intake and were bolder in a Novel Object test. Furthermore, the L males had higher plasma levels of peripheral serotonin, but the corticosterone after a restraint stress test did not differ. In paper IV and V, we concluded the project by comparing brain and organ weights as well as behaviour of the parental generation (P0) with the fifth selected generation (S5). The absolute brain weight as well as the weight specific brain weight were larger in the animals selected on H than in the L-animals. The relative weight of telencephalon was significantly higher in H whereas relative weight of cerebellum was significantly lower. Heart, liver, spleen and testes were all relatively heavier in H animals than in L. Interestingly, the behaviours assessed in P0 and S5 seemed to be rather resilient to the selection with only small differences in S5.To summarize, the selection on divergent tameness in Red Junglefowl has affected several phenotypic traits associated with the domesticated phenotype. The results of this project indicate that tameness in Red Junglefowl could be an underlying factor driving trait modifications towards the domesticated phenotype.
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| 43. |
- Ahlberg, Jörgen, 1971-
(författare)
-
Model-based coding : extraction, coding, and evaluation of face model parameters
- 2002
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with model-based coding of human faces for low bitrate communication. The basicidea of model-based coding is that the appearance and motion of a human face are analysed. By thisanalysis, compact parameters allowing realistic visualization of a synthetic face are extracted. The parameterscan be transmitted at very low bitrates, potentially allowing video face-to-face communicationover narrow channels like GSM or PSTN. Recently, numerous web-based applications for animatedfaces have emerged as well.Although the idea is two decades old by now, there are still several technical problems to be solved,and some of them are treated in this thesis. With the advent of the MPEG-4 standard for face animationwhich provides a standardized way for storing and transmitting animation parameters, model-basedcoding and face animation have been increasingly popular research topics.The first topic treated here is th ecompression of face model parameters. We propose a new compressionscheme, showing that such parameters can be transmitted with reasonable quality at bitrates lowerthan 1 kbit/s.Then, techniques for analysis of images and image sequences containing a human face are treated. Forstatic face images, a method for the extraction of facial features is proposed. For image sequences, amethod for face tracking using the active appearance model search algorithmis proposed and foundto be useful in practical experiments. Methods for achieving real-time performance have been developed,and the robustness and accuracy are analysed.To set the analysis in the context of possible applications, different ways of video synthesis using theextracted parameters are discussed as well.Finally, we take a look at the synthesized face models. Comparing them to real video sequences, wetry to evaluate how well the synthetic face models can convey emotions. Standard data sets and performancemeasures are suggested.
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| 44. |
- Ahlner, Alexandra, 1984-
(författare)
-
Improved Methods for Characterization of Protein Dynamics by NMR spectroscopy and Studies of the EphB2 Kinase Domain
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proteins are essential for all known forms of life and in many lethal diseases protein failure is the cause of the disease. To understand proteins and the processes they are involved in, it is valuable to know their structures as well as their dynamics and interactions. The structures may not be directly inspected because proteins are too small to be visible in a light microscope, which is why indirect methods such as nuclear magnetic resonance (NMR) spectroscopy have to be utilized. This method provides atomic information about the protein and, in contrast to other methods with similar resolution, the measurements are performed in solution resulting in more physiological conditions, enabling analysis of dynamics. Important dynamical processes are the ones on the millisecond timeframe, which may contribute to interactions of proteins and their catalysis of chemical reactions, both of significant value for the function of the proteins.To better understand proteins, not only do we need to study them, but also develop the methods we are using. This thesis presents four papers about improved NMR techniques as well as a fifth where the kinase domain of ephrinB receptor 2 (EphB2) has been studied regarding the importance of millisecond dynamics and interactions for the activation process. The first paper presents the software COMPASS, which combines statistics and the calculation power of a computer with the flexibility and experience of the user to facilitate and speed up the process of assigning NMR signals to the atoms in the protein. The computer program PINT has been developed for easier and faster evaluation of NMR experiments, such as those that evaluate protein dynamics. It is especially helpful for NMR signals that are difficult to distinguish, so called overlapped peaks, and the soft- ware also converts the detected signals to the indirectly measured physical quantities, such as relaxation rate constants, principal for dynamics. Next are two new versions of the Carr-Purcell-Maiboom-Gill (CPMG) dispersion pulse sequences, designed to measure millisecond dynamics in a way so that the signals are more separated than in standard experiments, to reduce problems with overlaps. To speed up the collection time of the data set, a subset is collected and the entire data set is then reconstructed, by multi-dimensional decomposition co-processing. Described in the thesis is also a way to produce suitably labeled proteins, to detect millisecond dynamics at Cα positions in proteins, using the CPMG dispersion relaxation experiment at lower protein concentrations. Lastly, the kinase domain of EphB2 is shown to be more dynamic on the millisecond time scale as well as more prone to interact with itself in the active form than in the inactive one. This is important for the receptor function of the protein, when and how it mediates signals.To conclude, this work has extended the possibilities to study protein dynamics by NMR spectroscopy and contributed to increased understanding of the activation process of EphB2 and its signaling mechanism.
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| 45. |
- Ahlström, Christer, 1977-
(författare)
-
Nonlinear phonocardiographic Signal Processing
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work has been to develop signal analysis methods for a computerized cardiac auscultation system, the intelligent stethoscope. In particular, the work focuses on classification and interpretation of features derived from the phonocardiographic (PCG) signal by using advanced signal processing techniques.The PCG signal is traditionally analyzed and characterized by morphological properties in the time domain, by spectral properties in the frequency domain or by nonstationary properties in a joint time-frequency domain. The main contribution of this thesis has been to introduce nonlinear analysis techniques based on dynamical systems theory to extract more information from the PCG signal. Especially, Takens' delay embedding theorem has been used to reconstruct the underlying system's state space based on the measured PCG signal. This processing step provides a geometrical interpretation of the dynamics of the signal, whose structure can be utilized for both system characterization and classification as well as for signal processing tasks such as detection and prediction. In this thesis, the PCG signal's structure in state space has been exploited in several applications. Change detection based on recurrence time statistics was used in combination with nonlinear prediction to remove obscuring heart sounds from lung sound recordings in healthy test subjects. Sample entropy and mutual information were used to assess the severity of aortic stenosis (AS) as well as mitral insufficiency (MI) in dogs. A large number of, partly nonlinear, features was extracted and used for distinguishing innocent murmurs from murmurs caused by AS or MI in patients with probable valve disease. Finally, novel work related to very accurate localization of the first heart sound by means of ECG-gated ensemble averaging was conducted. In general, the presented nonlinear processing techniques have shown considerably improved results in comparison with other PCG based techniques.In modern health care, auscultation has found its main role in primary or in home health care, when deciding if special care and more extensive examinations are required. Making a decision based on auscultation is however difficult, why a simple tool able to screen and assess murmurs would be both time- and cost-saving while relieving many patients from needless anxiety. In the emerging field of telemedicine and home care, an intelligent stethoscope with decision support abilities would be of great value.
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| 46. |
- Ahlström, Petter, 1970-
(författare)
-
Strategier och styrsystem för seniorboendemarknaden
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Den demografiska utvecklingen i Sverige går mot en befolkningssammansättning med allt högre medelålder. Prognosen tyder på att nästan var fjärde svensk år 2025 kommer vara 65 år eller äldre. Många av dessa individer har en aktiv, frisk och relativt lång ålderdom framför sig. Studier har visat att morgondagens seniorer är en relativt välbeställd grupp med höga krav och stora förväntningar på ålderdomen och det framtida boendet. Allt detta innebär en utmaning för samhället där nödvändiga prioriteringar kan leda till att individen måste ta ett större ansvar och eget initiativ för boende och omvårdnadstjänster gentemot tidigare. I avhandlingen (”studien”) har seniorboendekonceptet med integrerade service-, vård- och omsorgstjänster studerats särskilt. Seniorboenden är ett marknadssegment med kraftig tillväxt under 2000-talet. Antalet seniorbostäder i Sverige har ökat från ca 10 000 år 2000 till ca 28 000 år 2007. Det som karaktäriserar konceptet är att boendet och de anslutande tjänsterna har anpassats och särskilt utformats för ett liv i åldrande.Studien rapporteras i form av en monografi bestående av två olika delstudier. Forskningsfrågan som varit vägledande för den första delstudien är ”Vad skapar en stark marknadsposition för en aktör på seniorbostadsmarknaden med integrerad service, vård och omsorg?”. Forskningsfrågan i den andra delstudien är ”Vilka produktionsstrategier och styrsystem går att identifiera hos några av de mest framgångsrika konceptbyggarna?”. Den andra delstudien utgår från den första delstudiens resultat. Forskningen, som har bedrivits som en explorativ fältstudie, har pågått under perioden 2002-2008. Mätinstrumentet har bestått av fasta intervjufrågor med öppna svarsalternativ. De underliggande intervjuerna har tillsammans med sekundärdata presenterats i ett antal fallbeskrivningar. I studien har ett antal framgångsrika, såväl svenska som nordamerikanska, aktörer medverkat. Den första delstudien har analyserats utifrån en föreställningsram som byggts upp kring begreppen omgivning, strategi, resurs, tjänstekoncept och konkurrenskraft. Resultaten har formulerats i ett antal strategiska vägval vilka sammanfattats i begreppen differentiering, fokus, integration, samverkan, kontroll, verksamhetsutveckling, kärnkompetens och resurser. Det har kunnat påvisas att framgångsrika aktörer följer den differentieringsstrategi om Porter (1980) definierat. Vidare har en affärsstrategisk typologi över aktörer på seniorboendemarknaden formulerats. Den första delstudiens slutsatser har formulerats i fyra strategiska idealtyper: förvaltare, konceptbyggare, entreprenörer och idealister.Utgångspunkten i den andra delstudien, som bl.a. hämtats i Nilssons och Rapps (2005) teoretiska ramverk, har varit idealtypen konceptbyggare. Med vissa kompletteringar har detta ramverk nyttjats och utvecklats för att beskriva och analysera orsakssambanden kring strategisk kongruens och integrerad styrning. Kompletteringar och justeringar har skett för att även omfatta strategier och styrsystem för bygg- och tjänsteproduktion. Föreställningsramen har, utifrån den erfarenhet som erhållits vid analysen av insamlad data, justerats. Justeringen har bestått i klassificeringsdimensionerna IT, organisationskultur och värdegrund. I studien, som bl.a. består av fallbeskrivning och analys av konceptbyggare, har framkommit att de konceptbyggare som nått framgång också har lyckats uppnå strategisk kongruens och integrerad styrning. Studien har bl.a. kunnat påvisa vad betydelsen av boendets fysiska planering innebär för möjligheten att bedriva tjänsteproduktion. Studien har bl.a. visat att nordamerikanska konceptbyggare har en hög grad av samstämmighet mellan strategi och styrsystem. Samstämmigheten kan sammanfattas i marknadskännedom, tydlig verksamhetsidé, branscherfarenhet, insikt om skalfördelar via klustring, organisatorisk småskalighet, känsla för värdeskapande, målinriktning, långtgående befogenheter och delegerat ansvar, värdestyrd verksamhet och en väl utvecklad organisationskultur. De nordamerikanska konceptbyggarna har definierat sina verksamheter som hotellverksamhet för seniorer vilket innebär att de boende blivit kunder och de äldre i allmänhet betraktas som en tillgång.
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| 47. |
- Ahmad, Azeem, 1984-
(författare)
-
Contributions to Improving Feedback and Trust in Automated Testing and Continuous Integration and Delivery
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An integrated release version (also known as a release candidate in software engineering) is produced by merging, building, and testing code on a regular basis as part of the Continuous Integration and Continuous Delivery (CI/CD) practices. Several benefits, including improved software quality and shorter release cycles, have been claimed for CI/CD. On the other hand, recent research has uncovered a plethora of problems and bad practices related to CI/CD adoption, necessitating some optimization. Some of the problems addressed in this work include the ability to respond to practitioners’ questions and obtain quick and trustworthy feedback in CI/CD. To be more specific, our effort concentrated on: 1) identifying the information needs of software practitioners engaged in CI/CD; 2) adopting test optimization approaches to obtain faster feedback that are realistic for use in CI/CD environments without introducing excessive technical requirements; 3) identifying perceived causes and automated root cause analysis of test flakiness, thereby providing developers with guidance on how to resolve test flakiness; and 4) identifying challenges in addressing information needs, providing faster and more trustworthy feedback. The findings of the research reported in this thesis are based on data from three single-case studies and three multiple-case studies. The research uses quantitative and qualitative data collected via interviews, site visits, and workshops. To perform our analyses, we used data from firms producing embedded software as well as open-source repositories. The following are major research and practical contributions. Information Needs: The initial contribution to research is a list of information needs in CI/CD. This list contains 27 frequently asked questions on continuous integration and continuous delivery by software practitioners. The identified information needs have been classified as related to testing, code & commit, confidence, bug, and artifacts. We investigated how companies deal with information needs, what tools they use to deal with them, and who is interested in them. We concluded that there is a discrepancy between the identified needs and the techniques employed to meet them. Since some information needs cannot be met by current tools, manual inspections are required, which adds time to the process. Information about code & commit, confidence level, and testing is the most frequently sought for and most important information. Evaluation of Diversity Based Techniques/Tool: The contribution is to conduct a detailed examination of diversity-based techniques using industry test cases to determine if there is a difference between diversity functions in selecting integrationlevel automated test. Additionally, how diversity-based testing compares to other optimization techniques used in industry in terms of fault detection rates, feature coverage, and execution time. This enables us to observe how coverage changes when we run fewer test cases. We concluded that some of the techniques can eliminate up to 85% of test cases (provided by the case company) while still covering all distinct features/requirements. The techniques are developed and made available as an open-source tool for further research and application. Test Flakiness Detection, Prediction & Automated Root Cause Analysis: We identified 19 factors that professionals perceive affect test flakiness. These perceived factors are divided into four categories: test code, system under test, CI/test infrastructure, and organizational. We concluded that some of the perceived factors of test flakiness in closed-source development are directly related to non-determinism, whereas other perceived factors concern different aspects e.g., lack of good properties of a test case (i.e., small, simple and robust), deviations from the established processes, etc. To see if the developers’ perceptions were in line with what they had labelled as flaky or not, we examined the test artifacts that were readily available. We verified that two of the identified perceived factors (i.e., test case size and simplicity) are indeed indicative of test flakiness. Furthermore, we proposed a light weight technique named trace-back coverage to detect flaky tests. Trace-back coverage was combined with other factors such as test smells indicating test flakiness, flakiness frequency and test case size to investigate the effect on revealing test flakiness. When all factors are taken into consideration, the precision of flaky test detection is increased from 57% (using single factor) to 86% (combination of different factors).
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| 48. |
- Ahmad, Shakeel, 1977-
(författare)
-
Stimuli Generation Techniques for On-Chip Mixed-Signal Test
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With increased complexity of the contemporary very large integrated circuits the need for onchip test addressing not only the digital but also analog and mixed-signal RF blocks has emerged. The standard production test has become more costly and the instrumentation is pushed to its limits by the leading edge integrated circuit technologies. Also the chip performance for high frequency operation and the area overhead appear a hindrance in terms of the test access points needed for the instrumentation-based test. To overcome these problems, test implemented on a chip can be used by sharing the available resources such as digital signal processing (DSP) and A/D, D/A converters to constitute a built-in-self-test. In this case, the DSP can serve both as a stimuli generator and response analyzer.Arbitrary test signals can be achieved using DSP. Specifically, the ΣΔ modulation technique implemented in software is useful to encode a single- or two-tone stimulus as a onebit sequence to generate a spectrally pure signal with a high dynamic range. The sequence can be stored in a cyclic memory on a chip and applied to the circuit under test using a buffer and a simple reconstruction filter. In this way ADC dynamic test for harmonic and intermodulation distortion is carried out in a simple setup. The FFT artifacts are avoided by careful frequency planning for low-pass and band-pass ΣΔ encoding technique. A noise shaping based on a combination of low- and band-pass ΣΔ modulation is also useful providing a high dynamic range for measurements at high frequencies that is a new approach. However, a possible asymmetry between rise and fall time due to CMOS process variations in the driving buffer results in nonlinear distortion and increased noise at low frequencies. A simple iterative predistortion technique is used to reduce the low frequency distortion components by making use of an on-chip DC calibrated ADC that is another contribution of the author.Some tests, however, like the two-tone RF test that targets linearity performance of a radio receiver, require test stimuli based on a dedicated hardware. For the measurement of the thirdor second-intercept point (IP3/IP2) a spectrally clean stimulus is essential. Specifically, the second- or third-order harmonic or intermodulation products of the stimulus generator should be avoided as they can obscure the test measurement. A challenge in this design is the phase noise performance and spurious tones of the oscillators, and also the distortion-free addition of the two tones. The mutual pulling effect can be minimized by layout isolation techniques.A new two-tone RF generator based on a specialized phase-locked loop (PLL) architecture is presented as a viable solution for IP3/IP2 on-chip test. The PLL provides control over the frequency spacing of two voltage controlled oscillators. For the two-tone stimulus a highly linear analog adder is designed to limit distortion which could obscure the IP3 test. A specialized feedback circuit in the PLL is proposed to overcome interference by the reference spurs. The circuit is designed using 65 nm CMOS process. By using a fine spectral resolution the observed noise floor can be reduced to enable the measurement of second- or third-order intermodulation product tones. This also reflects a tradeoff between the test time and the test performance. While the test time to collect the required number of samples can be of milliseconds the number of samples need not be excessive, since the measurements are carried out at the receiver baseband, where the required sampling frequency is relatively low.
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| 49. |
- Ahrén, Maria, 1979-
(författare)
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Metal Oxide Nanoparticles for Contrast Enhancement in Magnetic Resonance Imaging : Synthesis, Functionalization and Characterization
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis work focuses on the design and production of nanoparticle based contrast agents for signal enhancement in magnetic resonance imaging (MRI). Three different synthesis routes are explored, primarily to produce crystalline gadolinium oxide (Gd2O3) nanoparticles, and surface modification is done to obtain stable, dispersible, biocompatible probes inducing high proton relaxivities.In Paper I and II we utilized the polyol synthesis method and nanoparticle purification was performed with dialysis. Active surface functionalization was achieved by an innermost layer of 3-mercaptopropyl trimetoxy silanes (MPTS) and an outer layer of bifunctional PEG. Surface capping was shown to greatly affect the water proton relaxation to a degree which is strongly dependent on the purification time. PEGylation also induced stabilizing effects and the ability to provide the nanoparticles with luminescent properties was proven by linking the fluorescent dye Rhodamine to the bifunctional PEG.In Paper III the magnetic behavior of yttrium (Y) alloyed Gd2O3 nanoparticles was investigated as a function of Y concentration. This was done by performing magnetic measurements and by studying the signal line width in electron paramagnetic resonance spectroscopy for Gd2O3, Y2O3 and a series of (GdxY1-x)2O3 samples produced using the combustion synthesis. The results verified that the signal line width is dependent on the percent of yttrium dilution. This is considered as an indication of that yttrium dilution changes the electron spin relaxation time in Gd2O3.Paper IV and V present a novel precipitation synthesis method for Gd2O3 nanoparticles. Acetate molecular groups were found to coordinate the nanoparticle surface increasing the water dispersability. The Gd2O3 nanoparticles induce a twice as high relaxivity per gadolinium atom, as compared to the commercially available contrast agent Magnevist. Incorporation of luminescent europium (Eu3+) ions into the Gd2O3 nanoparticles in combination with surface modification with a fluorescent branched carboxyl terminated TEG, produced dual probes with tunable luminescence, maintained relaxivity and thus a bright contrast in MRI.In Paper VI, a new approach to accomplish a dual probe was investigated. Luminescent ZnO nanoparticles decorated with Gd ions bound in an organic matrix were evaluated for MR signal enhancement and ability to function as fluorescent probes. Interestingly, these nanoprobes did show an enhanced capability to both strengthen the MR signal and increase the fluorescent quantum yield, as compared to the pure oxides.In Paper VII we investigate sub 5 nm crystalline manganese based nanoparticles produced by the precipitation synthesis used for Gd2O3 nanoparticles. Manganese oxide was chosen as another candidate for MRI contrast enhancement as it is expected to have a straight forward surface coupling chemistry. Characterization of the crystal structure and chemical composition indicated nanoparticles with a MnO core and presence of manganese species of higher valences at the nanoparticle surface. The MnO nanomaterial showed a superparamagnetic behavior and less capability to increase the MR signal as compared to Gd2O3.Characterization of the nanoparticle crystal structure and size is, throughout the work, performed by means of transmission electron microscopy, X-ray diffraction and dynamic light scattering. The chemical composition is studied with X-ray photoelectron spectroscopy, infrared spectroscopy and near edge X-ray absorption fine structure spectroscopy and the fluorescence characteristics are evaluated with fluorescence spectroscopy. In addition, theoretical models and calculated IR spectroscopy and near edge X-ray absorption fine structure spectroscopy data have been used for evaluation of experimental results.To conclude, the aim of this work is the design, production and characterization of ultrasmall rare earth based nanoparticles for signal enhancement in biomedical imaging. Surface modification clearly increases the colloidal stability and biocompatibility of the nanoparticles. Compared to the agents in clinical use today, these nanoprobes have a higher capability to enhance the MR-signal, and they will in the near future be equipped with tags for specific targeting.
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| 50. |
- Ahsan, Naveed, 1974-
(författare)
-
Reconfigurable and Broadband Circuits for Flexible RF Front Ends
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Most of today’s microwave circuits are designed for specific function and special need. There is a growing trend to have flexible and reconfigurable circuits. Circuits that can be digitally programmed to achieve various functions based on specific needs. Realization of high frequency circuit blocks that can be dynamically reconfigured to achieve the desired performance seems to be challenging. However, with recent advances in many areas of technology these demands can now be met.Two concepts have been investigated in this thesis. The initial part presents the feasibility of a flexible and programmable circuit (PROMFA) that can be utilized for multifunctional systems operating at microwave frequencies. Design details and PROMFA implementation is presented. This concept is based on an array of generic cells, which consists of a matrix of analog building blocks that can be dynamically reconfigured. Either each matrix element can be programmed independently or several elements can be programmed collectively to achieve a specific function. The PROMFA circuit can therefore realize more complex functions, such as filters or oscillators. Realization of a flexible RF circuit based on generic cells is a new concept. In order to validate the idea, two test chips have been fabricated. The first chip implementation was carried out in a 0.2μm GaAs process, ED02AH from OMMICTM. The second chip was implemented in a standard 90nm CMOS process. Simulated and measured results are presented along with some key applications such as low noise amplifier, tunable band pass filter and a tunable oscillator.The later part of the thesis covers the design and implementation of broadband RF front-ends that can be utilized for multistandard terminals such as software defined radio (SDR). The concept of low gain, highly linear frontends has been presented. For proof of concept two test chips have been implemented in 90nm CMOS technology process. Simulated and measurement results are presented. These RF front-end implementations utilize wideband designs with active and passive mixer configurations.We have also investigated narrowband tunable LNAs. A dual band tunable LNA MMIC has been fabricated in 0.2μm GaAs process. A self tuning technique has been proposed for the optimization of this LNA.
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