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Browsing by master's degree program "Magisterprogrammet i materialforskning"

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  • Mäntysaari, Matti (2021)
    This thesis describes the data and data analysis concerning Compton scattering experiments to obtain the Compton profiles of metallic sodium (Na) as a function of temperature. The temperatures used in the experiment were 6 K and 300 K. The purpose of the work was to visualize the effect of temperature in the electron momentum density in a free electron gas. The effects of temperature were expected to be manifested through changes to the Fermi momentum according to the free-electron theory, but also more subtle changes could have been possible owing to possible deviations from the free electron theory. The measurements were done at the European Synchrotron Radiation Facility (Grenoble, France) beamline ID20. The data was analyzed with a help of a program written with Matlab, and it converted the measured Compton spectra from photon energy space to electron momentum space, while applying self-absorption corrections to the data, subtracting background, and normalizing the data using trapezoidal numerical integral to yield final Compton profiles. Results were obtained as valence Compton profiles and their differences between 300 K and 6 K, and compared with the prediction from free-electron gas theory. The Compton profiles followed the predictions of the free-electron gas theory well, although the theoretical profiles had a higher amplitude than the measured profiles. This is a commonly found phenomenon in Compton spectroscopy and assigned to originate from electron-electron correlations. The effect of the temperature in the Compton profiles is in good agreement with the free-electron theory.
  • Ahmadzai, Shabana (2023)
    Industrial ultrasonic cleaning plays a crucial role in optimizing processes and production in various industrial equipment by eliminating the need for harmful chemicals and minimizing production downtime. While previous research has focused on optimizing ultrasonic cleaning for larger and complex geometries, by controlling acoustic pressure fields and cavitation, the potential contribution of online cleaning using elastic vibrations of the equipment wall remains insufficiently explored. To bridge this gap, this study employs a combination of simulation techniques and laboratory experiments to investigate the significance of elastic guided waves and evaluate the influence of different pulsed driving waveform properties on cleaning efficacy. Specifically, the study focuses on the delivery of ultrasonic energy along the pipe wall. While confirming the effective delivery of ultrasonic energy across the length of pipes, the mechanisms underlying scale removal are still open to interpretation. Notably, specific flexural wave modes of a fluid-filled pipe, e.g. F_FFP (n,1) mode family, are identified as potential carriers of the cleaning effect. The research highlights the significance of high momentary power and total effective power in achieving efficient cleaning. The presence of liquid introduces complexities such as mode conversions and the possibility of cavitation. Further investigations are recommended to explore the individual roles of normal and tangential vibration components at the wall-scale interface. The study emphasizes the need for comprehensive analysis to optimize ultrasonic cleaning processes for larger and complex geometries, determine effective parameters for particle detachment, and enhance overall cleaning efficiency.
  • Zaka, Ayesha (2021)
    X-ray absorption spectroscopy(XAS) measures the absorption response of the system as a function of incident X-ray photon energy. XAS can be a great tool for material characterization due to its ability to reveal characteristic information specific to chemical state of element by using the core level electrons as a probe for empty electronic states just above the Fermi level of the material (XANES) or for the neighboring atoms (EXAFS). For years, the highly brilliant synchrotron light sources remained the center of attention for these XAS experiments, but the increasing competition for available beamtime at these facilities led to an increased interest in laboratory scale X-ray spectroscopy instruments. However, the energy resolution of laboratory scale instruments still remains sometimes limited as compared to their synchrotron counterparts. When operating at low Bragg angles, the finite source size can greatly reduce the energy resolution by introducing the effects of dispersion in the beam focus at the detector. One method to overcome this loss in resolution can be to use a position sensitive detector and use the 'pixel compensation correction' method in the post-processing of the experimental data. The main focus of this study was to improve the energy resolution of a wavelength dispersive laboratory-scale X-ray absorption spectrometer installed at the University of Helsinki Center for X-ray Spectroscopy. The project focuses on the case of Fe K-absorption edge at 7.112 keV energy and a Bragg angle of 71.74 degrees when using Silicon (5 3 1) monochromator crystal. Our results showed that the data that had been corrected using this method showed sharper spectral features with reduced effects of broadening. Moreover, contribution of other geometrical factors to the energy resolution of this laboratory X-ray spectrometer were also estimated using ray-tracing simulation and an expected improvement in resolution due to pixel compensation correction was calculated. The same technique can be extended to other X-ray absorption edges where a combination of a large deviation of Bragg angle from 90 degrees and a large source size contributes a dominant factor to the energy resolution of the instrument.
  • Spönla, Elisa (2020)
    The aim of the thesis was to study enzymatic treatment as a way to modify paper grade pulp to be a suitable raw material for the future textile industry. Wood as a raw material is an environmentally friendly option for textile production but its sustainable exploitation is not easy. Currently, ionic liquids are assumed to enable a safe and sustainable process for the production of wood-based regenerated fibres. These processes commonly use dissolving pulp as their raw material but replacing dissolving pulp with a paper grade kraft pulp would decrease environmental impact and production expenses. In this work, molar mass distribution of softwood paper grade kraft pulp was selectively modified using enzymes. Enzymes were utilized instead of acids because of their favourable abilities to selectively modify targeted polymers and to increase fibre porosity. Enzymatic modifications of softwood kraft pulp were performed to decrease degree of polymerization of cellulose and lower the quantity of hemicellulose. Hydrolysis of cellulose was catalysed with endo-1,4-β-glucanase (endoglucanase) and hemicellulose was degraded using endo-1,4-β-mannanase and endo-1,4-β-xylanase. The treatments were carried out both at high (20%) and low (3%) pulp consistency to examine the synergistic effect of enzymatic and mechanical action arising in the high consistency treatment. Additionally, influence of different enzyme combinations on the pulp properties was studied. The modified pulp samples were characterized by determining intrinsic viscosity, molar mass distribution, yield loss, and its composition. The fibres were imaged with light microscopy. The degree of polymerization of the pulp cellulose was successfully decreased with a relatively small endoglucanase dose. The amount of hemicellulose was reduced by removing 11% of the total galactoglucomannan and 40% of the total arabinoglucuronoxylan. The high consistency treatments decreased intrinsic viscosity 1.9 times more on average than the low consistency treatments. The high consistency treatments were effective with low enzyme doses, easy to control, and reliably repeated. Therefore, enzymatic pulp treatment at high consistency seems to be a compatible way to modify paper grade kraft pulp to suitable raw material for textile production. Further studies related to pulp dissolution in ionic liquids, fibre spinning, and fibre regeneration should be concluded to confirm applicability of the modified fibres.
  • Bäckroos, Sami (2021)
    High pressure inside e.g. blood vessels or other biological cavities is a major risk factor for many preventable diseases. Most of the measuring methods require physical contact or other kinds of projected forces. Both variants can be unpleasant for the patient and additionally physical contact might warrant for either continuous disinfecting or single-use probes, depending on the measurement method and the target body part. We have been experimenting with handheld non-contacting pressure measuring devices based on acoustic waves. These excite mechanical waves, whose velocity varies with pressure, on the surface of a biological cavity. The tried excitation methods are nearly unnoticeable for the patient, allowing for more pleasant and waste free measurements. Using the data from the latest clinical trial, a new analysis algorithm was devised to improve the accuracy of the pressure estimates. Instead of the time-of-flight (TOF) of the main mechanical wave (MMW), the new algorithm estimates the pressure using the MMW and a previously unseen feature, improving the R^2 from 0.60 to 0.72.
  • Hyvönen, Jere (2021)
    High-intensity and -amplitude focused ultrasound has been used to induce cavitation for decades. Well known applications are medical (lithotripsy and histotripsy) and industrial ones (particle cleaning, erosion, sonochemistry). These applications often use low frequencies (0.1-5 MHz), which limits the spatial precision of the actuation, and the chaotic nature of inertial cavitation is rarely monitored or compensated for, constituting a source of uncertainty. We demonstrate the use of high-frequency (12 MHz) high-intensity (ISPTA=90 W/cm2 ) focused-ultrasound- induced cavitation to locally remove solid material (pits with a diameter of 20 µm to 200 µm) for non- contact sampling. We demonstrate breaking cohesion (aluminium) and adhesion (thin film on a substrate, i.e. marker ink on microscope glass). The eroded surfaces were analyzed with a scanning acoustic microscope (SAM). We present the assembly and the characterization of a focused ultrasound transducer and show quantification of the effect of different sonication parameters (amplitude, cycle count, burst count, defocus) on the size and shape of the resulting erosion pits. The quantitative precision of this method is achieved by systematic calibration measurements, linking the resulting erosion to acoustic parameters to ensure repeatability (sufficient probability of cavitation), and inertial cavitation monitoring of the focal echoes. We discuss the usability of this method for localized non-contact sampling.
  • Tommiska, Oskari (2021)
    Työssäni tutkin mahdollisuutta käyttää akustista ajankääntömenetelmää (time-reversal) teollisen ultraäänipuhdistimen puhdistustehon kohdentamiseen. Akustisella ajankääntömenetelmällä pystytään kohdistamaan painekenttä takaisin alkuperäiseen pisteeseen, tallentamalla ko. pisteestä lähetetyt painesignaalit akustisilla antureilla (etusuunta) ja lähettämällä ne takaisin ajassa käännettyinä (takasuunta). Tässä työssä tutkitun kohdentamismenetelmän perusteena toimii elementtimenetelmällä toteutettu simulaatiomalli, jossa sekä ultraäänipuhdistin, että puhdistettava järjestelmä oli mallinnettu tarkasti. Simulaatiomallin avulla voitiin puhdistettavasta alueesta valita mielivaltainen piste johon halutaan kohdentaa puhdistustehoa. Simuloidun etusuuntaisen ajon tuloksena tuotetut signaalit tuotiin ulos mallista ja takasuuntainen ajo suoritettiin kokeellisessa ympäristössä käyttäen simuloituja signaaleja. Työssä esitetään vertailu simuloidun ja kokeellisen ajankääntömenetelmään perustuvan kohdentamisen tuloksista ja osoitetaan, että simuloiduilla signaaleilla on mahdollista kohdentaa akustista tehoa ennalta valittuun mielivaltaiseen pisteeseen. Lisäksi työssä esitetään analyysi anturien määrän vaikutuksesta kohdentamiskykyyn, tarkastellaan ultraäänipuhdistimen avaruudellista kohdentamiskykyä sekä vahvistetaan simulaatioissa tehdyn lineaarisen oletuksen paikkansapitävyys.
  • Mäkinen, Joni (2022)
    Nonlinear acoustic and electric effects for the purposes of fluid and fluid-fluid interface manipulation find many applications in the literature. Some examples include: electrospinning, electrospraying, ultrasonic sonoreactors, acoustic drop sampling and microfluidic particle manipulation via acoustic streaming. Ultrasound-enhanced electrospinning (USES) is one application in which both an acoustic and an electric field deform the surface of an aqueous polymer solution in order to achieve electrospinning of nanofibers. In this thesis, the nonlinear physics involved in USES are reviewed and applied to a finite element method based model of the system. This work builds on my previous publication on acoustic fountain formation and subsequent electrostatic deformation of a liquid-air interface in USES by also considering the effects of acoustic streaming. Results for acoustic streaming near a liquid-air interface in a case where the acoustic field is also focused around the interface are studied with simulations and compared against experiments. The results display an intricate balance of the shape and strength of the acoustic streaming field as the liquid-air interface simultaneously deforms. This even leads to situations where the streaming field could completely change direction. Finally, simulation predictions for acoustic streaming, fountain formation and electrostatic deformation of liquid-air interface in the USES set-up in its standard configuration are given. This simulation predicts a very weak acoustic streaming field and a smaller contribution from the electric field, compared to the acoustic field, on the interface forces. This implies that in the simulated configuration, the electric field serves more as force to pull the acoustic fountain a bit more in order for the acoustic field to find its new balance and exert an even stronger force than it was able to by itself. The simulation also indicates that for the robust and reproducible operation of USES, and possibly for the resulting nanofibers, one needs to have precise control of the process parameters, acoustic field and surface level, due to the complex nature of the fountain formation.
  • Paajanen, Santeri (2022)
    NMDA receptors are ionotropic glutamate receptors (iGluRs), tetrameric proteins, mediating synaptic transmission in the brain and the whole nervous system. Together with another type of iGluRs, AMPA receptors, they are considered essential for neuronal plasticity and memory. Understanding their dynamics and different kinetics is vital for studying various neurological diseases. The relatively slow dynamics, where the time scales of related processes range up to hundreds of milliseconds, make studying them with Molecular Dynamics (MD) simulations challenging. We developed the Functional Sampling Tool (FST), a novel method for enhancing the sampling of a function of interest. Compared to existing enhanced sampling schemes it strikes a balance between generality and simplicity, minimising the need of user input, while allowing for maximal customisability. Using FST, we studied two processes of the NMDA receptor. By keeping all four ligands bound we simulated a desensitisation pathway, and by removing all four we simulated an inactivation pathway. The tool sampled both, giving a good distribution between open and closed states. The tool also allowed us to change the function in the middle of sampling. With the new function we were able to produce more data, focusing on a certain value range.
  • Lipsunen, Werner (2023)
    This thesis examines the implementation of general purpose graphics processing unit (GPGPU) acceleration to a non-equilibrium Green’s function (NEGF) equation solver in the context of a computational photoelectrochemical (PEC) cell model. The goal is to find out whether GPGPU acceleration of the NEGF equation solver is a viable option. The current model does not yet have electron-photon scattering, but from the results it is possible to assess the viability of GPGPU acceleration in the case of a complete PEC cell model. The viability of GPGPU acceleration was studied by comparing the performance difference of two graphics processing unit (GPU) solutions against a multi core central processing unit (CPU) solution. The difference between the two GPU solutions was in the used floating-point precision. The GPU solutions would use LU factorization to solve the NEGF equations, and the CPU solution a banded solver (Gauss tridiagonal) provided by Scipy Python package. The performance comparison was done on multiple different GPU and CPU hardware. The electrical transport properties of the PEC cell were modeled by a self-consistent process in which the NEGF and Poisson equations were solved iteratively. The PEC cell was described as a semiconductor device connected with a metal and electrolyte contacts. The device was assumed to be a simple one dimensional tight-binding atom chain made of GaAs, where the transverse modes in the y–z plane are treated with a logarithmic function. The computational model did lack electron-photon scattering, which would be implemented in the future. From the benchmark results, it can be concluded that the GPGPU acceleration via LU factorization is not a viable option in the current code or in the complete model with electron-photon scattering and the assumed approximations. The parallel multi-core CPU code generally outperformed the GPU codes. The key weakness of the GPU code was the usage of LU factorization. Despite of this, there could be an opportunity for GPGPU acceleration if a more complex lattice structure and more exact scattering terms would be used. Also, a GPU accelerated tridiagonal solver could be a possible solution.
  • Heczko, Vilma (2021)
    Plasmonic catalysis utilises light energy to drive chemical reactions. Compared to conventional catalytic processes, which are run by high temperatures and pressures, light-driven processes can lower energy consumption and increase selectivity. Conventional plasmonic nanoparticles (Ag, Au) are relatively scarce and expensive, and therefore the use of materials with earth-abundant elements in plasmonic catalysis is widely pursued. Despite their good optical properties, plasmonic nanoparticles are often unsuitable catalysts. Hybrid catalysts, structures consisting of a light-harvesting plasmonic part and a catalytical centre of different material, have emerged as an opportunity to address these challenges and obtain desired properties. This thesis consists of two parts: In the first part, properties of plasmonic materials are described, and previous studies of hybrid catalysts with earth-abundant plasmonic materials are reviewed. Experimental work on plasmonic-catalytic nanohybrids, with TiN as the plasmonic part and Pd as the catalytic entity, is described in the second part. In this context, a Pd/TiN (Pd nanoparticles supported into TiN) catalyst was synthesised, characterised and applied to test catalytical reactions. Contrary to the hypothesis, light-induced rate enhancement was not observed in our current catalytical studies. These results call for further optimisation of synthesis and reaction conditions to prepare an earth-abundant, light-active catalyst.
  • Huttunen, Heli (2023)
    Eye plaque radiotherapy is a treatment method of ocular tumors: A sealed radiation source is temporarily placed on the surface of the eye in day surgery. Compared to externally delivered conventional radiation treatments, more precisely targeted brachytherapy allows a higher dose in the target tissue while keeping the dose to healthy tissue relatively low. In Finland, all eye plaque treatments are centralised in Helsinki and brachytherapy of the eye is performed annually on approximately 70 patients. Patient specific anatomy takes into account determination of specific location and shape of the tumor in respect of radio-biologically critical structures of the eye. Until now, this has not been systematically modeled in dose calculation of eye plaque brachytherapy at HUS. The new version of Plaque Simulator, a 3D treatment simulation and modeling package for I-125, Pd-103, Ir-192 and Ru-106 plaque therapy of ocular tumors, enables importation and digitisation of patient imaging data (fundus imaging, CT and MRI) which consequently allows for systematically accurate estimation of dose distribution not only in the tumor but also in surrounding healthy tissues. The aim of this Master’s thesis is to prepare the new version of Plaque Simulator simulation and modeling package for clinical use in patient dose calculation at HUS. A comparison is done between the dose calculation method of the old and the new version of Plaque Simulator, and the dose calculation parameters as well as the plaque modeling parameters are reviewed. The function of the image-based dose calculation method is also tested with an anonymised patient treated for a tumor of a more peculiar shape. The absorbed dose to water on the central axis of the radiation source is measured experimentally for two individual I-125-seed along with Ru-106-CCB-, I-125-CCB-, and two I-125-COB-plaques. Experimental results are compared with the results obtained from Plaque Simulator. Individual I-125-seed is used to calibrate the detector at a distance of 10 mm, yielding to a calibration factor of 0.808. The use of the gold parameter in the dose calculation is justified, and a dosimetry modifier of Plaque Simulator is found to be 1.226 for I-125-plaques. Ru-106-plaque measurements are not calibrated, making them only relative. However, an excellent correspondence is observed between Ru-106-plaque dose calculations in Plaque Simulator and the manufacturer’s certificate. The measurements are normalized to the manufacturer’s certificate with a normalisation factor of 1.117.
  • Kurki, Lauri (2021)
    Atomic force microscopy (AFM) is a widely utilized characterization method capable of capturing atomic level detail in individual organic molecules. However, an AFM image contains relatively little information about the deeper atoms in a molecule and thus interpretation of AFM images of non-planar molecules offers significant challenges for human experts. An end-to-end solution starting from an AFM imaging system ending in an automated image interpreter would be a valuable asset for all research utilizing AFM. Machine learning has become a ubiquitous tool in all areas of science. Artificial neural networks (ANNs), a specific machine learning tool, have also arisen as a popular method many fields including medical imaging, self-driving cars and facial recognition systems. In recent years, progress towards interpreting AFM images from more complicated samples has been made utilizing ANNs. In this thesis, we aim to predict sample structures from AFM images by modeling the molecule as a graph and using a generative model to build the molecular structure atom-by-atom and bond-by-bond. The generative model uses two types of ANNs, a convolutional attention mechanism to process the AFM images and a graph neural network to process the generated molecule. The model is trained and tested using simulated AFM images. The results of the thesis show that the model has the capability to learn even slight details from complicated AFM images, especially when the model only adds a single atom to the molecule. However, there are challenges to overcome in the generative model for it to become a part of a fully capable end-to-end AFM process.
  • Kistol, Joanna (2024)
    Monoenergetic neutron reference fields are used in neutron metrology for the calibration of different neutron detectors, including dose rate meters. The International Standardization Organization ISO has composed guidelines and requirements for the production of narrow energy spread neutron fields using a particle accelerator. The objective of this Thesis was to investigate a target material that could be used to produce a monoenergetic neutron field by irradiating it with protons. A broader energy distribution was deemed satisfactory in regard to the initial phase of the station’s development, as significant modifications to the beamline would be necessary to acquire more precise beam current values and to achieve proton energies closer to the reaction threshold energy. The target material was chosen to be lithium fluoride (LiF) based on a literature review and Monte Carlo simulations. The simulations were executed with the proton energy of 2.5 MeV, which is close to the threshold energy of the 7Li(p, n)7Be reaction, and with the fixed energy 10 MeV of the IBA cyclotron used to conduct the experiment. The simulations were executed with the MCNP6 code, and the results were compared to those obtained from equivalent Geant4 simulations. The simulations suggested two wide peaks around 3 MeV and 0.6 MeV at the proton energy of 10 MeV. The irradiation experiment included two phases, one of which entailed the use of a shadow cone to estimate the number of scattered neutrons in the neutron yield. The maximum neutron fluence of (2.62 ± 0.78)∙109 s-1 was measured at the pop-up probe current of (8.3 ± 0.8) µA. Gamma spectrometry was utilized after the experiment to further evaluate the number of 7Li(p,n)7Be reactions taken place in the target by calculating the number of 7Be nuclei in the LiF plate. Altogether, lithium fluoride exhibits promising characteristics as a target material for accelerator-based monoenergetic neutron production, although its application demands further considerations regarding for instance, the decrement of the proton energy and the aiming and measurement of the proton beam. These results contribute to the future development of a neutron irradiation station at the University of Helsinki.
  • Heikkilä, Jesse (2022)
    Nanoformation of an active pharmaceutical ingredient (API) in controlled expansion of supercritical solution (CESS®) was studied in situ with a schlieren imaging technique in wide range of pre-expansion and expansion conditions, involving pressures up to 1000 bars. The optical methods allowed measurements on solvent state in the first micro and milliseconds of the expansion. Quantitative values on jet shape and solvent thermodynamic state were obtained for different nozzle configurations. These values, combined with mathematical modelling, enabled tracking the nanoparticle formation along the flow. We also report on the importance of solvent phase behavior demonstrated by three fundamentally different expansion schemes: supercritical (SC) to liquid/gas, SC to gas/liquid, and SC to SC. Scanning electron microscope images of the nanosized API are presented. This shows that one can have controlled particle formation by altering the thermodynamic conditions at the nozzle and changing the expansion path. The results guide the in-house process optimization and offer insight into the physics of supercritical fluid processing.
  • Kauppala, Juuso (2021)
    The rapidly increasing global energy demand has led to the necessity of finding sustainable alternatives for energy production. Fusion power is seen as a promising candidate for efficient and environmentally friendly energy production. One of the main challenges in the development of fusion power plants is finding suitable materials for the plasma-facing components in the fusion reactor. The plasma-facing components must endure extreme environments with high heat fluxes and exposure to highly energetic ions and neutral particles. So far the most promising materials for the plasma-facing components are tungsten (W) and tungsten-based alloys. A promising class of materials for the plasma-facing components is high-entropy alloys. Many high-entropy alloys have been shown to exhibit high resistance to radiation and other wanted properties for many industrial and high-energy applications. In materials research, both experimental and computational methods can be used to study the materials’ properties and characteristics. Computational methods can be either quantum mechanical calculations, that produce accurate results while being computationally extremely heavy, or more efficient atomistic simulations such as classical molecular dynamics simulations. In molecular dynamics simulations, interatomic potentials are used to describe the interactions between particles and are often analytical functions that can be fitted to the properties of the material. Instead of fixed functional forms, interatomic potentials based on machine learning methods have also been developed. One such framework is the Gaussian approximation potential, which uses Gaussian process regression to estimate the energies of the simulation system. In this thesis, the current state of fusion reactor development and the research of high-entropy alloys is presented and an overview of the interatomic potentials is given. Gaussian approximation potentials for WMoTa concentrated alloys are developed using different number of sparse training points. A detailed description of the training database is given and the potentials are validated. The developed potentials are shown to give physically reasonable results in terms of certain bulk and surface properties and could be used in atomistic simulations.
  • Hägg, Veera (2023)
    Nanodiscs are a synthetic model system for studying the behavior of cell membranes. They are used in experimental biological research to understand structural and functional properties of membrane proteins. Their utility is chiefly due to their water solubility and a relative native lipid environment for membrane proteins compared to other synthetic membrane systems. Though membrane proteins are frequently solubilized and stabilized in a nanodisc environment, the physical conditions that they are exposed to in a nanodisc have not been studied in detail. Additionally, the dynamic behavior of transmembrane proteins in a nanodisc environment has not been characterized with respect to a more typical planar bilayer environment. The results presented in this thesis formulate an answer to these open questions through atomistic molecular dynamics simulations and machine learning methods. Nanodiscs and bilayer systems with identical lipid compositions are systematically studied, and separately, both types of systems with adenosine receptor A2AR to understand the differences between the model systems. The membrane environment in the two systems is characterized by two well understood physical properties: the order parameter, and the diffusion of lipids in the membrane. The results not only affirm previous studies of nanodiscs but also provide novel insights into the membrane environment of the nanodisc systems. Finally, with the help of machine learning methods, the dynamical behaviour of the protein is shown to be significantly altered in the nanodisc system when compared to a planar bilayer environment. Specifically, it is shown that the activation behavior of A2AR is dependent on model system used to reconstitute the protein.
  • Keränen, Laura (2021)
    Tutkielman kirjallisuusosassa tarkastellaan johtavien metalli-, oksidi- ja nitridikalvojen kasvattamista epitaksiaalisesti strontiumtitanaatille. Epitaksiaalisia kalvoja on kasvatettu fysikaalisilla kasvatusmenetelmillä, kuten laserpulssikasvatuksella, elektronisuihkuhöyrystyksellä ja sputteroimalla, sekä kemiallisilla kasvatusmenetelmillä, kuten atomikerroskasvatuksella, sooli-geeli-menetelmällä sekä metalliorgaanisella kemiallisella kaasufaasikasvatuksella. Useiden tekijöiden, kuten substraattien lämpötilan ja esikäsittelyn todettiin vaikuttavan kalvojen orientaatioon. Kokeellisessa osassa iridium- ja platinaohutkalvoja kasvatettiin (100)-orientoiduille strontiumtitanaattisubstraateille atomikerroskasvatuksella. Iridiumkalvojen lähtöaineina käytettiin iridiumasetyyliasetonaattia sekä happea tai otsonia ja vetyä. Platinakalvojen lähtöaineina käytettiin platina-asetyyliasetonaattia, otsonia ja vetyä tai metyylisyklopentadienyylitrimetyyliplatinaa ja happea. Kalvojen rakennetta ja tekstuuria tutkittiin θ-2θ- ja in plane -röntgendiffraktiolla. Osaa iridiumkalvojen poikkileikkauksista tutkittiin myös läpäisyelektronimikroskopialla. Iridiumkalvojen todettiin olevan vahvasti (100)-orientoituneita, mutta monikiteisiä. Platinan (h00)-piikkejä ei kyetty erottamaan substraatin (h00)-piikeistä, mutta vahvojen (111)-piikkien perusteella kalvot eivät olleet epitaksiaalisia. Kalvojen kuumentaminen lisäsi (111)-orientaatiota molemmissa metalleissa.
  • Alenius, Saara (2023)
    Kartiokeilatietokonetomografia eli KKTT on tyypillisimmin käytetty kuvausmodaliteetti kuvantaohjatussa sädehoidossa ja sitä käytetään pääasiassa potilaan asemointiin ja sädehoidon kohdistamiseen. KKTT-kuvantaminen perustuu röntgensäteilyyn ja sen käytön haittapuolena potilas saa ylimääräistä säteilyannosta sekä hoidettavalle alueelle että sitä ympäröiville terveille kudoksille. Eturauhassyöpä on miesten yleisin syöpätyyppi Suomessa ja paikallista eturauhassyöpää voidaan hoitaa esimerkiksi sädehoidolla. Ionisoivan säteilyn käyttö lisää terveiden kudosten syöpäriskiä ja siksi KKTT-kuvantamisen aiheuttaman säteilyannoksen määritys ja optimointi on tärkeää. Tämän työn tarkoituksena on selvittää yhdeksässä suomalaisessa sairaalassa käytettäviä KKTT-kuvantamisen kuvausparametreja ja kuvauskäytäntöjä sekä laskennallisesti määrittää kuvantamisen aiheuttamia potilasannoksia ja optimoinnin vaikutuksia. Laskenta tehdään käyttäen Monte Carlo menetelmään perustuvaa ImpactMC-ohjelmaa, ICRP:n vokselitestikappaletta ja suomalaisten sairaaloiden käyttämiä kuvantamisen parametreja. Tulosten esittämiseen käytetään riskielinten kokonais- ja elinannoksia, isodoosipiirroksia xy- ja xz-tasoissa, riskielinten annostilavuushistogrammeja sekä annosprofiileja xy- ja xz-tasoissa. Tässä työssä lasketut riskielinten elinannokset ovat yhdellä kuvauskerralla noin mGy:n luokkaa ja kokonaissäteilyannokset riippuvat vahvasti kuvausfraktioiden määrästä. Symmetrisen keilan geometriassa säteilyannokset ovat pienempiä kuin epäsymmetrisen keilan geometriassa. Kuvantamisessa käytettävä kuvausalueen pituus, kuvausputken aloituskulma ja kuvausputken kiertosuunta vaikuttavat symmetrisessä geometriassa myös eri riskielimien saamaan säteilyannokseen ja säteilyn jakautumiseen xz-tasossa. Tuloksista havaitaan, että sekä symmetrisen että epäsymmetrisen keilan tapauksissa kuvausparametrien optimointi esimerkiksi putkivirtaa laskemalla pienentää eturauhasen, peräsuolen, reisiluun punaista luuydintä sisältävän osan ja virtsarakon saamaa elinannosta. Kuvausparametrien optimointi pienentää annostasoja myös kaikissa muissa lasketuissa tapauksissa kuten isodoosipiirroksissa ja annosprofiileissa.
  • Tikkanen, Emmi (2020)
    Röntgenabsorptiospektroskopia (X-ray absorption spectroscopy, XAS) kuvaa röntgensäteilyn absorboitumistodennäköisyyttä tutkittavaan materiaaliin röntgenfotonien energian funktiona. XAS-spektroskopiaa hyödynnetään monilla tieteenaloilla kuten fysiikassa, materiaalitutkimuksessa, kemiassa ja biologiassa. Menetelmällä saadaan yksityiskohtaista tietoa valitun alkuaineen ympäristöstä ja materiaalin rakenteesta atomitasolla. Kun röntgenfotonin energia vastaa tutkittavan atomin sidosenergiaa, absorptio kasvaa jyrkästi. Tämän nousun eli absorptioreunan paikkaa ei ole yksiselitteisesti määritelty, vaan kirjallisuudessa esiintyy yhä toisistaan poikkeavia menetelmiä absorptioreunan paikan määritykseen XAS-spektristä. Tutkielmassa hyödynnetään XANES-spektroskopiaa (X-ray Absorption Near Edge Structure), joka kuvaa absorptioreunan läheistä aluetta XAS-spektrissä, ja keskitytään koboltin K-kuoren XANES-spektroskopiaan. Työssä tutkitaan absorptioreunan paikan eri määritysmenetelmiä kobolttioksidien CoO, Co2O3, Co3O4 ja LiCoO2 XANES-spektreistä. Käytetyt reunan määritysmenetelmät ovat 1) absorptioreunan puolivälikorkeutta vastaavan energian etsiminen, 2) keskiarvon laskeminen niistä energioista, joilla reunan korkeus saavuttaa 20% ja 80% maksimiabsorptiosta, 3) reunan ensimmäisen käännepisteen etsiminen ja 4) reunan jyrkimmän käännepisteen etsiminen. Tutkielman kirjallisuuskatsauksessa käsitellään röntgenabsorptiospektroskopiaa keskittyen XANES-spektroskopiaan. Kirjallisuuskatsauksessa esitellään eri menetelmiä absorptioreunan määritykseen. Kokeellisessa osiossa mitataan kobolttioksidien spektrit ja verrataan eri menetelmillä määritettyjä absorptioreunojen paikkoja tunnettuihin hapetustiloihin ja pyritään etsimään lineaarista riippuvuutta reunan paikan ja hapetustilan välille. Pienin epätarkkuus, noin 10%, suoran sovituksessa saatiin hapetustilojen ja jyrkimmän käännepisteen menetelmällä määritettyjen reunan paikkojen välille. Tällä menetelmällä sovitussuoran kulmakerroin oli myös suurin, joten voidaan todeta tämän menetelmän herkkyyden olevan suurin. Toisaalta kulmakerroin poikkeaa myös selvästi muilla menetelmillä määritetyistä kulmakertoimista.