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  • Seppänen, Henri (Helsingin yliopisto, 2015)
    Tethers are key elements in the electric solar wind sail (E-sail). In this thesis I claim that E-sail tether manufacturing on km scale is possible. The E-sail is a space propulsion method for interplanetary missions. It uses long, thin and conductive, tethers to create thrust from the solar wind. Based on simulations a full scale E-sail using one hundred 20 km long tethers could create a continuous 1 N thrust. Compared to state of the art ion engines the proposed E-sail produces 10 100 times more specific impulse over the device lifetime. The E-sail is estimated to lower costs of interplanetary missions by reducing the payload mass needed to launch to orbit and by shortening the travel time. Manufacturing is an important technical challenge to the E-sail. A multifilament tether structure is needed to provide micrometeoroid tolerance to the tether. To address the challenge we combined an industrial ultrasonic wire bonder and a custom-built tether factory for tether production. A customized 3-wire bonding wedge enabled 4-wire multifilament tether manufacturing. The tether comprises 25 and 50 µm in diameter (Ø) aluminum wires that are ultrasonically welded together. The main result of this thesis is that we showed the feasibility of large-scale device manufacture by producing a continuous 1.04 km long multifilament tether comprising 90 704 wire-to-wire bonds. The measured bonding yield of the manufacture was 99.9%. Wire-to-wire bond pull strength was measured in a separate test on a 97 m long tether produced subsequent to the 1 km tether production. The maximum sustainable pull force of the tether bonds should exceed the estimated 50 mN centrifugal force of the spinning full scale E-sail. The measured average maximum sustainable pull force of 252 bonds along the 97 m test tether was (99 ± 8) mN with a minimum recorded value of 80 mN. This result shows that E-sail tether production on km scale is possible and thus supports the main claim of this thesis. Before this PhD project, no E-sail tether existed. The development of tether production and the results achieved brings the implementation of the most important E-sail component into the practical engineering realm and thus significantly advances the E-sail development. The produced 1 km tether was the most important objective of the ESAIL EU FP7 -framework project.
  • Ehn, Mikael (Helsingin yliopisto, 2010)
    It is widely accepted that the global climate is heating up due to human activities, such as burning of fossil fuels. Therefore we find ourselves forced to make decisions on what measures, if any, need to be taken to decrease our warming effect on the planet before any irrevocable damage occurs. Research is being conducted in a variety of fields to better understand all relevant processes governing Earth s climate, and to assess the relative roles of anthropogenic and biogenic emissions into the atmosphere. One of the least well quantified problems is the impact of small aerosol particles (both of anthropogenic and biogenic origin) on climate, through reflecting solar radiation and their ability to act as condensation nuclei for cloud droplets. In this thesis, the compounds driving the biogenic formation of new particles in the atmosphere have been examined through detailed measurements. As directly measuring the composition of these newly formed particles is extremely difficult, the approach was to indirectly study their different characteristics by measuring the hygroscopicity (water uptake) and volatility (evaporation) of particles between 10 and 50 nm. To study the first steps of the formation process in the sub-3 nm range, the nucleation of gaseous precursors to small clusters, the chemical composition of ambient naturally charged ions were measured. The ion measurements were performed with a newly developed mass spectrometer, which was first characterized in the laboratory before being deployed at a boreal forest measurement site. It was also successfully compared to similar, low-resolution instruments. The ambient measurements showed that sulfuric acid clusters dominate the negative ion spectrum during new particle formation events. Sulfuric acid/ammonia clusters were detected in ambient air for the first time in this work. Even though sulfuric acid is believed to be the most important gas phase precursor driving the initial cluster formation, measurements of the hygroscopicity and volatility of growing 10-50 nm particles in Hyytiälä showed an increasing role of organic vapors of a variety of oxidation levels. This work has provided additional insights into the compounds participating both in the initial formation and subsequent growth of atmospheric new aerosol particles. It will hopefully prove an important step in understanding atmospheric gas-to-particle conversion, which, by influencing cloud properties, can have important climate impacts. All available knowledge needs to be constantly updated, summarized, and brought to the attention of our decision-makers. Only by increasing our understanding of all the relevant processes can we build reliable models to predict the long-term effects of decisions made today.
  • Zhao, Kai (Helsingin yliopisto, 2015)
    Understanding urban human mobility is crucial for various mobile and network applications. This thesis addresses two key challenges presented by mobile applications, namely urban mobility modeling and its applications in Delay Tolerant Networks (DTNs). First, we model urban human mobility with transportation mode information. Our research is based on two real-life GPS datasets containing approximately 20 and 10 million GPS samples. Previous research has suggested that the trajectories in human mobility have statistically similar features as Lévy Walks. We attempt to explain the Lévy Walks behavior by decomposing them into different classes according to the different transportation modes, such as Walk/Run, Bike, Train/ Subway or Car/Taxi/Bus. We show that human mobility can be modelled as a mixture of different transportation modes, and that these single movement patterns can be approximated by a lognormal distribution rather than a power-law distribution. Then, we demonstrate that the mixture of the decomposed lognormal flight distributions associated with each modality is a power-law distribution, providing an explanation for the emergence of Lévy Walks patterns that characterize human mobility patterns. Second, we find that urban human mobility exhibits strong spatial and temporal patterns. We leverage such human mobility patterns to derive an optimal routing algorithm that minimizes the hop count while maximizing the number of needed nodes in DTNs. We propose a solution framework, called Ameba, for timely data delivery in DTNs. Simulation results with experimental traces indicate that Ameba achieves a comparable delivery ratio to a Flooding-based algorithm, but with much lower overhead. Third, we infer the functions of the sub-areas in three cities by analyzing urban mobility patterns. The analysis is based on three large taxi GPS datasets in Rome, San Francisco and Beijing containing 21, 11 and 17 million GPS points, respectively. We categorize the city regions into four categories, workplaces, entertainment places, residential places and other places. We show that the identification of these functional sub-areas can be utilized to increase the efficiency of urban DTN applications. The three topics pertaining to urban mobility examined in the thesis support the design and implementation of network applications for urban environments.
  • Amundsen, Lotta (Helsingin yliopisto, 2008)
    Determination of testosterone and related compounds in body fluids is of utmost importance in doping control and the diagnosis of many diseases. Capillary electromigration techniques are a relatively new approach for steroid research. Owing to their electrical neutrality, however, separation of steroids by capillary electromigration techniques requires the use of charged electrolyte additives that interact with the steroids either specifically or non-specifically. The analysis of testosterone and related steroids by non-specific micellar electrokinetic chromatography (MEKC) was investigated in this study. The partial filling (PF) technique was employed, being suitable for detection by both ultraviolet spectrophotometry (UV) and electrospray ionization mass spectrometry (ESI-MS). Efficient, quantitative PF-MEKC UV methods for steroid standards were developed through the use of optimized pseudostationary phases comprising surfactants and cyclodextrins. PF-MEKC UV proved to be a more sensitive, efficient and repeatable method for the steroids than PF-MEKC ESI-MS. It was discovered that in PF-MEKC analyses of electrically neutral steroids, ESI-MS interfacing sets significant limitations not only on the chemistry affecting the ionization and detection processes, but also on the separation. The new PF-MEKC UV method was successfully employed in the determination of testosterone in male urine samples after microscale immunoaffinity solid-phase extraction (IA-SPE). The IA-SPE method, relying on specific interactions between testosterone and a recombinant anti-testosterone Fab fragment, is the first such method described for testosterone. Finally, new data for interactions between steroids and human and bovine serum albumins were obtained through the use of affinity capillary electrophoresis. A new algorithm for the calculation of association constants between proteins and neutral ligands is introduced.
  • Hynninen, Anu (Helsingin yliopisto, 2011)
    The use of buffer areas in forested catchments has been actively researched during the last 15 years; but until now, the research has mainly concentrated on the reduction of sediment and phosphorus loads, instead of nitrogen (N). The aim of this thesis was to examine the use of wetland buffer areas to reduce the nitrogen transport in forested catchments and to investigate the environmental impacts involved in their use. Besides the retention capacity, particular attention was paid to the main factors contributing to the N retention, the potential for increased N2O emissions after large N loading, the effects of peatland restoration for use as buffer areas on CH4 emissions, as well as the vegetation composition dynamics induced by the use of peatlands as buffer areas. To study the capacity of buffer areas to reduce N transport in forested catchments, we first used large artificial loadings of N, and then studied the capacity of buffer areas to reduce ammonium (NH4-N) export originating from ditch network maintenance areas in forested catchments. The potential for increased N2O emissions were studied using the closed chamber technique and a large artificial N loading at five buffer areas. Sampling for CH4 emissions and methane-cycling microbial populations were done on three restored buffer areas and on three buffers constructed on natural peatlands. Vegetation composition dynamics was studied at three buffer areas between 1996 and 2009. Wetland buffer areas were efficient in retaining inorganic N from inflow. The key factors contributing to the retention were the size and the length of the buffer, the hydrological loading and the rate of nutrient loading. Our results show that although the N2O emissions may increase temporarily to very high levels after a large N loading into the buffer area, the buffer areas in forested catchments should be viewed as insignificant sources of N2O. CH4 fluxes were substantially higher from buffers constructed on natural peatlands than from the restored buffer areas, probably because of the slow recovery of methanogens after restoration. The use of peatlands as buffer areas was followed by clear changes in plant species composition and the largest changes occurred in the upstream parts of the buffer areas and the wet lawn-level surfaces, where the contact between the vegetation and the through-flow waters was closer than for the downstream parts and dry hummock sites. The changes in the plant species composition may be an undesired phenomenon especially in the case of the mires representing endangered mire site types, and therefore the construction of new buffer areas should be primarily directed into drained peatland areas.
  • Buzorius, Gintautas (Helsingin yliopisto, 2000)
  • Halme, Mia (Helsingin yliopisto, 2015)
    Toxic and incapacitating chemicals are ubiquitous in everyday life. Despite the prohibition of chemical weapons by the Chemical Weapons Convention (CWC), many toxic chemicals are still used: as legal riot control agents, in various processes and products of the chemical industry or as pesticides in agriculture. Validated analytical methods and knowledge of metabolism are therefore needed for the verification of possible intentional or unintentional exposures in carrying out occupational tasks or in civil incidents. The most reliable retrospective detection and confirmation of exposure to chemicals are achieved by analyzing unequivocal metabolites such as biomarkers, from biological samples, which have mainly been obtained from exposed persons, animals and experimental animal models. However, the use of animal testing for evaluating the safety and effects of chemicals that are known to be toxic or incapacitating raises ethical questions. Therefore, the use of an in vitro metabolism study approach to predict in vivo metabolite profiles, prior to obtaining more detailed knowledge in vivo could be a preferable strategy for evaluating the toxicology of these chemicals. Four toxic and incapacitating chemicals listed in the CWC or used for riot control were studied in this thesis, namely: sulfur mustard, capsaicinoids, chloropicrin and saxitoxin. The suitability of the conventional in vitro metabolism studies were assessed in this research. These assessments were achieved by using various mass spectrometric (MS) methods to screen and identify the formed metabolites. The validations of analyses methods for known biomarkers were carried out according to the current bioanalytical validation guidelines and identification criteria. The conventional in vitro metabolism studies used for sulfur mustard, capsaicinoids and chloropicrin, yielded new knowledge about the metabolic reactions and produced several novel metabolites by oxidative reactions and GSH conjugation. However, their clinical usefulness to serve as biomarkers of exposure in humans requires further studies. Quantitative fit for purpose analysis methods were optimized and validated for the following chemicals: saxitoxin, two b-lyase metabolites of sulfur mustard, and nitromethane as a metabolite of chloropicrin. All methods were found to be accurate and linear and fulfilled the general identification criteria.
  • Pettersson, Heidi (Helsingin yliopisto, 2004)
  • Salmi, Ari (Helsingin yliopisto, 2012)
    Globally, mechanical pulping consumes much energy (approximately 150 TWh of electric energy annually, approximately 27 Finnish nuclear reactors would be needed to produce this amount), and the paper consumption has been increasing despite the visions of a paper-free office. The research field has strived for energy efficiency for decades, and in recent years, innovations utilizing repetitive compressive loading have yielded significant energy savings. However, the fundamental physical reason for the energy efficiency of this technique is unknown it has been hypothesized that the compressive loading generates fatigue in the wood, resulting in an energy efficient process. In this thesis the physical question what is the significance of fatigue for mechanical pulping is broken down into five sub-questions: 1) can we model the repetitive compressive loading in a controlled manner (e.g. controllable frequency, amplitude of impacts and moisture content) and quantify the resulting decrease in stiffness (Paper I), i.e. the amount of fatigue? 2) What are the changes generated in the non-linear mechanical properties and where is the generated fatigue localized (Paper II)? 3) If the effects of fatigue in a well-controlled situation can be quantified, are the phenomena detected in the modelled process present in the actual industrial process (Paper III)? 4) What is the effect of fatigue on the energy consumption (Paper IV)? 5) How does the localization of the generated fatigue change in different wood geometries (radial and tangential, Paper V)? The proposed characterization techniques include (a) quantitative through-transmission ultrasonics for bulk wood (Paper I) and for depth profiling (Paper II, III and V). The latter allows determining stiffness tensor components in wood samples as a function of depth. (b) Micro-computed x-ray tomography which offers an image of the microstructure of the samples (Papers II, III and V); (c) An encapsulated split-Hopkinson device (ESHD, Paper II) combined with a high-speed photography system, enabling research of in situ mechanical phenomena occurring during fast compression; (d) thermoporosimetry, measuring changes in the nano-size pores in the wood cell walls induced by grinding (Paper III) and (e) quasi-static materials testing, measuring the changes in the tensile and compression behaviour in various wood directions both in the elastic and plastic regime (Paper IV). To answer the first sub-question, the EES grinding process was mimicked: a custom made device was used to generate cyclic unipolar compressional pulses at 500 Hz along the radial wood direction. These pulses were found to reduce the measured radial stiffness by up to 90%. A clear moisture dependence on the stiffness drop was discovered, lower moisture content yielding more fatigue. Above the fiber saturation point no change in the amount of fatigue as a function of moisture was discovered. Ultrasonic depth profiling results and X-ray tomography images answered the second and the fifth question: they revealed that the generated fatigue was concentrated to a layer near the sample surface in both radial and tangential wood geometries. This layer, 1-3 mm thick depending on the fatiguing parameters, comprised a zone with saturated fatigue and a transition zone extending from fatigued to intact wood. A theory based on elastic energy storage was formulated to explain this localization. ESHD experiments combined with the quasi-static tensile and compression tests revealed that at nanoscale, the fatigue is generated between the cellulose microfibrils and the surrounding lignin-hemicellulose matrix. To answer the third question, it was shown that the layer-like formation of fatigue is present in the actual industrial process, confirming a hypothesis originating from the 1960 s. After this, in order to answer the fourth question, experiments were done with a laboratory-scale grinder, which indicated that compared to non-fatigued samples the fatigued samples could be ground into similar quality pulp (Canadian Standard Freeness and fiber length) using less energy. This means that pre-fatiguing, revealed as a reduced radial stiffness, induced by repeated cyclic compression, reduces the energy consumption of the grinding process. This improvement was hypothesized to result from the previously detected, induced micro-scale damage into the cellulose lignin-hemicellulose matrix boundary, which makes it easier to liberate the fibers. The amount of energy used for pre-fatiguing was not included in the energy balance since we aimed to show whether pre-fatiguing wood reduces the energy consumption rather than to engineer an industrial process. The main conclusion is that inducing pre-fatigue can reduce the energy consumption of the wood grinding process. This could be done with a grinding surface comprising of two zones: a pre-fatiguing zone and a shearing zone.
  • Kangasharju, Jaakko (Helsingin yliopisto, 2008)
    In recent years, XML has been widely adopted as a universal format for structured data. A variety of XML-based systems have emerged, most prominently SOAP for Web services, XMPP for instant messaging, and RSS and Atom for content syndication. This popularity is helped by the excellent support for XML processing in many programming languages and by the variety of XML-based technologies for more complex needs of applications. Concurrently with this rise of XML, there has also been a qualitative expansion of the Internet's scope. Namely, mobile devices are becoming capable enough to be full-fledged members of various distributed systems. Such devices are battery-powered, their network connections are based on wireless technologies, and their processing capabilities are typically much lower than those of stationary computers. This dissertation presents work performed to try to reconcile these two developments. XML as a highly redundant text-based format is not obviously suitable for mobile devices that need to avoid extraneous processing and communication. Furthermore, the protocols and systems commonly used in XML messaging are often designed for fixed networks and may make assumptions that do not hold in wireless environments. This work identifies four areas of improvement in XML messaging systems: the programming interfaces to the system itself and to XML processing, the serialization format used for the messages, and the protocol used to transmit the messages. We show a complete system that improves the overall performance of XML messaging through consideration of these areas. The work is centered on actually implementing the proposals in a form usable on real mobile devices. The experimentation is performed on actual devices and real networks using the messaging system implemented as a part of this work. The experimentation is extensive and, due to using several different devices, also provides a glimpse of what the performance of these systems may look like in the future.
  • Ikonen, Teemu (Helsingin yliopisto, 2007)
    Scattering of X-rays and neutrons has been applied to the study of nanostructures with interesting biological functions. The systems studied were the protein calmodulin and its complexes, bacterial virus bacteriophage phi6, and the photosynthetic antenna complex from green sulfur bacteria, chlorosome. Information gathered using various structure determination methods has been combined to the low resolution information obtained from solution scattering. Conformational changes in calmodulin-ligand complex were studied by combining the directional information obtained from residual dipole couplings in nuclear magnetic resonance to the size information obtained from small-angle X-ray scattering from solution. The locations of non-structural protein components in a model of bacteriophage phi6, based mainly on electron microscopy, were determined by neutron scattering, deuterium labeling and contrast variation. New data are presented on the structure of the photosynthetic antenna complex of green sulfur bacteria and filamentous anoxygenic phototrophs, also known as the chlorosome. The X-ray scattering and electron cryomicroscopy results from this system are interpreted in the context of a new structural model detailed in the third paper of this dissertation. The model is found to be consistent with the results obtained from various chlorosome containing bacteria. The effect of carotenoid synthesis on the chlorosome structure and self-assembly are studied by carotenoid extraction, biosynthesis inhibition and genetic manipulation of the enzymes involved in carotenoid biosynthesis. Carotenoid composition and content are found to have a marked effect on the structural parameters and morphology of chlorosomes.
  • Fernandez Martinez, Manuel (Helsingin yliopisto, 2006)
    This thesis is a study of the x-ray scattering properties of tissues and tumours of the breast. Clinical radiography is based on the absorption of the x-rays when passing right through the human body and gives information about the densities of the tissues. Besides being absorbed, x-rays may change their direction within the tissues due to elastic scattering or even to refraction. The phenomenon of scattering is a nuisance to radiography in general, and to mammography in particular, because it reduces the quality of the images. However, scattered x-rays bear very useful information about the structure of the tissues at the supra-molecular level. Some pathologies, like breast cancer, produce alterations to the structures of the tissues, being especially evident in collagen-rich tissues. On the other hand, the change of direction due to refraction of the x-rays on the tissue boundaries can be mapped. The diffraction enhanced imaging (DEI) technique uses a perfect crystal to convert the angular deviations of the x-rays into intensity variations, which can be recorded as images. This technique is of especial interest in the cases were the densities of the tissues are very similar (like in mammography) and the absorption images do not offer enough contrast. This thesis explores the structural differences existing in healthy and pathological collagen in breast tissue samples by the small-angle x-ray scattering (SAXS) technique and compares these differences with the morphological information found in the DEI images and the histo-pathology of the same samples. Several breast tissue samples were studied by SAXS technique in the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Scattering patterns of the different tissues of the breast were acquired and compared with the histology of the samples. The scattering signals from adipose tissue (fat), connective tissue (collagen) and necrotic tissue were identified. Moreover, a clear distinction could be done between the scattering signals from healthy collagen and from collagen from an invasive tumour. Scattering from collagen is very characteristic. It includes several scattering peaks and scattering features that carry information about the size and the spacing of the collagen fibrils in the tissues. It was found that the collagen fibrils in invaded tumours were thinner and had a d-spacing length 0,7% longer that fibrils from healthy tumours. The scattering signals from the breast tissues were compared with the histology by building colour-coded maps across the samples. They were also imaged with the DEI technique. There was a total agreement between the scattering maps, the morphological features seen in the images and the information of the histo- pathological examination. The thesis demonstrates that the x-ray scattering signal can be used to characterize tissues and that it carries important information about the pathological state of the breast tissues, thus showing the potential of the SAXS technique as a possible diagnostic tool for breast cancer.
  • Dhalmann, Hanna (Helsingin yliopisto, 2011)
    Ethnic minorities residential patterns and integration are widely discussed issues in many European countries. They have also become topical in Finland due to an increase in foreign migration, especially in recent decades. This dissertation contributes to debates associated with attempts to explain ethnic minorities residential patterns by examining the role of cultural factors and ethnic preferences of the residential choices of Somali and Russian immigrants in Finland. The research is based on in-depth interviews with Somali (n=24) and Russian (n=26) immigrants living in the Helsinki metropolitan area. Housing officials and social workers (n=18) working in cities of Helsinki and Vantaa were also interviewed. The results of this study show that propinquity to one s own ethnic group is important to Somalis living in Finland. This is important for maintaining their traditional, communal life styles, but also as a safe haven against the racism which they experience on a regular basis. They have a preference for mixed neighbourhoods that contain both native Finnish residents and some ethnic minorities. For Russians the spatial propinquity to their country people is less significant at the neighbourhood level. However, this is not to indicate the insignificance of intra-ethnic networks or one s cultural background. Rather, the differences in ethnic preferences between Somalis and Russians predominantly reflect their varying levels of exposure to racial harassment and diverse meanings that they give to social relations with their neighbours. According to this study, the time spent in a host-country and interactions with other ethnic groups affect ethnic preferences. The importance of one s own ethnic community also varies in accordance with life situations. Therefore, ethnic minorities residential preferences and choices should not be viewed as static or something deriving from cultural background alone. Residential preferences and aspirations are constantly being reshaped vis-à-vis to immigrants experiences. Past and present experiences and the way that immigrants observe the host society and its functions are important for the interpretation of residential preferences and patterns.
  • Vilkama, Katja (Helsingin yliopisto, 2011)
    This thesis critically examines the patterns and processes of ethnic residential segregation in the Helsinki Metropolitan Area (HMA). These phenomena are examined in two main ways: a) between the native and immigrant populations and b) the extent to which different immigrant groups are sharing the same neighbourhoods. The main aim of the study is to test the extent to which the theoretical claims of the selective migration processes can explain the development of ethnic residential segregation in HMA. The data is mixed: it consists of neighbourhood-level statistics related to the migration, demography and housing stock. The selective migration flows are analysed within and between neighbourhood-types, defined on the basis of the percentages of foreign-language-speakers. For contextual purposes, the study also includes fifteen expert interviews who work within the housing sector. Firstly, the results show that, from the early 2000s the patterns of ethnic residential segregation have strengthened while the differences between neighbourhoods have grown. On a more general level the HMA can be divided into two main areas: some eastern and north-eastern neighbourhoods that have experienced the rise of immigrant concentrations and; the northern, north-western and southern parts of the HMA, where the number and percentages of immigrants have remained relatively low. However, within the eastern and north-eastern neighbourhoods there are also discernable internal differences that reflect the income levels of the inhabitants and the type of housing stock. The results also show that, the existing immigrant concentrations are ethnically and culturally mixed and thus qualitatively different from China town and Little-Italy enclaves of single groups of immigrants. Secondly, the results show that there are clear signs of the selective migration processes of the native and immigrant populations which have resulted in the discernable development of ethnic residential segregation. Migration flows of the native population have gravitated towards neighbourhoods, where the percentage of immigrants is below the HMA average. This has resulted in significant migration losses for neighbourhoods with established and developing concentrations of immigrants. Meanwhile, migration of immigrants has been drawn to neighbourhoods where their percentages are above the HMA average. However, the results also point to clear differences in the migration and spatial patterns of different immigrant groups. The spatial selectivity of migration is, thus, more prominent amongst the native population than when compared with immigrants. Overall, the results indicate that the reproduction of the selective migration flows of the native and immigrant populations will largely determine HMA s future development of ethnic residential segregation.
  • Sarparanta, Mirkka (Helsingin yliopisto, 2013)
    Poor biopharmaceutical properties such as low solubility and low permeability in the gastrointestinal (GI) tract plight many existing drugs and new chemical entities, presenting an impediment for efficient drug therapy. Incorporation of the drug to a delivery system based on a nanostructured material is increasingly investigated as a strategy to overcome these limitations and to achieve controlled and targeted delivery. Porous silicon (PSi) is a promising material for carrier-mediated drug delivery because of its biocompatibility, high chemical stability, and facile elimination from the body. Moreover, the physicochemical properties of PSi can be tailored by variation of the fabrication parameters and surface modifications to suit diverse payloads. Positron emission tomography (PET), a sensitive and quantitative method of molecular imaging, is a potent tool for drug delivery system development. Already at the preclinical stage PET can be employed for the investigation of drug delivery carrier biodistribution in vivo, thereby facilitating the selection of the most promising material candidates for further development and future drug delivery studies. In this dissertation, a direct nucleophilic radiolabeling method with a short-lived positron emitter fluorine-18 (18F) was developed for three different surface-modified PSi materials: thermally hydrocarbonized PSi (THCPSi), thermally carbonized PSi (TCPSi), and thermally oxidized PSi (TOPSi). Out of the investigated materials, nanosized [18F]THCPSi emerged as the one with the highest potential for imaging and drug delivery in terms radiolabeling yield, label stability, and biocompatibility in cell models in vitro, and was therefore forwarded to biodistribution studies in rats. After oral administration, [18F]THCPSi nanoparticles were shown to pass intact through the GI tract in 4 to 6 hours. Modification of [18F]THCPSi with a self-assembled layer of a fungal hydrophobin (HFBII) changed the hydrophilicity of the material bringing about bioadhesive properties that promoted gastric retention of the protein-coated nanoparticles. Intravenous delivery of [18F]THCPSi nanoparticles resulted in their rapid accumulation to the liver and spleen alluding to rapid immune recognition and removal of the particles from the bloodstream by macrophages of the mononuclear phagocyte system (MPS). HFBII-coating of the nanoparticles altered the adsorption of plasma proteins to the particle surface, which translated also to a change in the biodistribution pattern in vivo. In conclusion, the present work establishes 18F-radiolabeled particle tracers as useful means for the evaluation of new PSi-based drug delivery systems with PET.