Browsing by master's degree program "Magisterprogrammet i materialforskning"
Now showing items 41-60 of 84
-
(2023)Tietokonetomografialla (TT) on ollut jo usean vuosikymmenen ajan tärkeä asema lääketieteellisenä kuvantamismenetelmänä, jolla pystytään tuottamaan tarkkoja leikekuvia kehon rakenteista. TT on historiansa aikana muuttunut ja kehittynyt menetelmänä teknologisten harppausten ansiosta. Kuvauksista on tullut nopeampia ja entistä tarkempia. Kaksoisenergiatietokonetomografia (KETT) on yksi TT-kuvantamisen kehitysaskel, jonka teoreettiset perusteet ovat olleet jo pitkään tiedossa, mutta joka on vasta viime vuosikymmenenä saanut enemmän sovelluskohteita. KETT lisää TT-kuvauksen materiaalierottelukykyä, mikä mahdollistaa tarkemman diagnostiikan ja vähentää jatkotutkimusten tarvetta. Laajempi KETT:n kliininen käyttö vaatii kuitenkin toimintatapojen muutosta ja pysyvän laadunvalvontaprotokollan muodostamista. Tämän maisterintutkielman tarkoituksena oli auttaa laadunvalvonnan kehittämistä HUS:n Diagnostiikkakeskuksessa kartoittamalla KETT-kuvausten toimintaa, kuvausparametrien vaikutusta tuloksiin ja laitekohtaisia eroja. Työhön kuuluvat mittaukset suunniteltiin ja toteutettiin yhdessä HUS:n Diagnostiikkakeskuksen Meilahden Tornisairaalan radiologian yksikön kanssa. Kuvauksissa käytettiin Siemens Healthineersin valmistamia SOMATOM Definition Flash - ja SOMATOM Force -laitteita sekä KETT-kuvantamiseen soveltuvaa testikappaletta. Mittauksissa tutkittiin testikappaleen pystysuuntaisen asettelun vaikutusta kuvauksista saataviin tuloksiin, materiaalien elektronitiheyden ja efektiivisen järjestysluvun määritystarkkuutta, varjoaineena käytetyn jodin pitoisuuden määritystarkkuutta ja kuvauksen annostason merkitystä. Työssä käytetyllä menetelmällä määritettiin testikappaleen materiaalien koostumuksellisia eroja. Tutkimuksen avulla voitiin havaita jodipitoisuuden määrittämisen olevan haasteellisempaa hyvin pienillä alueilla, mutta halkaisijaltaan 5 mm:n kokoisilla alueilla määritystarkkuus oli jo kohtalainen. Potilaan oikeanlaisen keskityksen ja kuvanlaadun havaittiin olevan erityisen tärkeää pehmytkudoksia kuvattaessa. Laitteiden välisten erojen todettiin olevan merkittävämpää eri laitemallien välillä kuin samanmallisten laitteiden välillä. Laadunvalvonnassa tulee ottaa huomioon laitteiden kalibraatio, jotta laitteiden välisiä eroja pystytään vähentämään. Jatkossa mittauksia tulee toteuttaa lisää mittausten välisen toistettavuuden varmistamiseksi.
-
(2023)Lentoaika-rekyylispektrometria (TOF-ERDA) on materiaalin tutkimusmenetelmä, minkä avulla kyetään selvittämään näytteen alkuainepitoisuudet syvyyden funktiona. Menetelmässä on huomattu esiintyvän systemaattista poikkeamaa teoriasta. Poikkeaman syy on toistaiseksi epäselvä. Tutkielmassa tutkittiin poikkeaman syytä sekä suuruutta. Tutkimiseen käytettiin Helsingin yliopiston kiihdytinlaboratorion 5 MV EPG-10-II-tandemkiihdyttimeen liitettyä TOF-ERDA-laitteistoa. Laitteistolla tutkittiin ilmiön esiintymistä eri hiukkasilla, eri energioilla ja eri näytteillä. Kokeiden tuloksia verrattiin teorian ehdottamiin tuloksiin. Suurimmat poikkeamat kokeiden ja teorian välillä esiintyi pienienergisillä ja keveillä ammusioneilla, kun tutkittiin raskasalkuaineista näytettä. Kokeissa käytettyjen hiukkasten sirontaa TOF-ERDA-laitteiston lentoaikaporteista selvitettiin simuloinneilla. Simulointityökaluna työssä käytettiin SRIM-ohjelmistoa. Simulointien pohjalta hiukkasille laskettiin korjauskertoimet. Korjauskertoimen suuruuden huomattiin olevan riippuvainen hiukkasen energiasta sekä järjestysluvusta. Korjauskertoimista luotiin malli, jonka avulla kyetään arvioimaan ja korjaamaan kokeissa tapahtuvaa sirontaa lentoaikaporteista. Myös varjostumisen vaikutusta tuloksiin tutkittiin. Varjostumista tutkittiin jo olemassa olevan Andersenin mallin avulla. Andersenin mallin mukaan varjostumisen vaikutus tuloksiin on hyvin vähäistä sekä ilmiötä pienentävää, ei ilmiötä selittävää. Huomioitavaa kuitenkin on mallin soveltumattomuus kyseisiin vuorovaikutuksiin, täten varjostumisen vaikutusta ilmiöön ei voida kokonaan poissulkea. Tutkielman tulokset valottavat TOF-ERDA:n systemaattisen poikkeaman syitä. Lentoaikaporttisironnan vaikutus tuloksiin on merkittävä, selittäen noin puolet ilmiöstä. Tulosten pohjalta luotu malli on voimassa vain kyseiselle TOF-ERDA-laitteistolle, sillä sironnan suuruus on riippuvainen lentoaikaporttien materiaalista, paksuuksista sekä laitteiston geometriasta. Kuitenkin mille tahansa TOF-ERDA-laitteistolle on mahdollista luoda vastaava malli, noudattamalla tämän tutkielman prosesseja. Jäljelle jäävän selittämättömän poikkeaman huomattiin olevan myös riippuvainen energiasta sekä järjestysluvuista. Tämä viittaisi jäljelle jäävän poikkeaman aiheutuvan mahdollisesta monikertasironnasta näytteessä, ja tai varjostumisesta, jota Andersenin malli ei kykene huomioimaan.
-
(2019)The spin-orbit-coupled insulator Sr 3 NiIrO 6 is a strongly correlated transition metal compound, where an interplay of geometric frustration and spin anisotropy gives rise to novel magnetic phases. Resonant inelastic x-ray scattering (RIXS) is a powerful probe of the low-lying quasi-particle excitations that underpin these emergent properties. In this work, we partition the active space into approximately non-interacting parts in order to introduce a tight-binding single-particle model Hamiltonian describing the distorted IrO6 octahedra in Sr3NiIrO6. We then use this model to calculate its RIXS spectrum at the Ir L3-edge in the sub-electronvolt range. The results of this calculation are compared with experiments performed at the European Synchrotron Radiation Facility, and with a multiplet crystal field model calculation. We find that this one electron model largely agrees with the full-multiplet model and describes the d-d excitations observed in experiment. The addition of an exchange field term explains the low-lying temperature-dependent magnetic feature, disambiguating the sign of the crystal-field term, and suggesting that the feature is well localized at low temperatures, and is best described as an orbitally- entangled local spin-flip excitation. However, the correspondence at room temperature diminishes, suggesting that dispersive description is necessary to model this regime. The drastic reduction in active space entailed by this model facilitates the creation of extended non-collinear Heisenberg-like models, which can be calculated at a lower computational cost than full multiplet extended models.
-
(2021)This thesis focuses on the initial measurements and development of a 1.5K target temperature cryostat to contain all quantum standards in the quantum metrological triangle. Currently, the cryostat can reach 4.2K end temperature with a cryocooler to liquefy helium for cooling experiments related to the quantum standards of SI-units which require 1.5K end temperature and the 1.5K cooling circuit is one of the research questions of the thesis for future development of the cryostat. Measurements included cooling cycles in a helium environment for liquefaction, as well as no load conditions. Results of the experimentation conclude that liquefaction was unsuccessful at this stage, but could be achieved with improved temperature control. The thesis is based on experimental work carried out in VTT technical research center of Finland, during the course of which the cryostat was progressively developed towards the future utility of combining experiments that realize the quantum standards of Ampere, voltage and resistance under a single low temperature experimental platform, the unified quantum standard cryostat.
-
(2021)Several nuclear power plants in the European Union are approaching the ends of their originally planned lifetimes. Extensions to the lifetimes are made to secure the supply of nuclear power in the coming decades. To ensure the safe long-term operation of a nuclear power plant, the neutron-induced embrittlement of the reactor pressure vessel (RPV) must be assessed periodically. The embrittlement of RPV steel alloys is determined by measuring the ductile-to-brittle transition temperature (DBTT) and upper-shelf energy (USE) of the material. Traditionally, a destructive Charpy impact test is used to determine the DBTT and USE. This thesis contributes to the NOMAD project. The goal of the NOMAD project is to develop a tool that uses nondestructively measured parameters to estimate the DBTT and USE of RPV steel alloys. The NOMAD Database combines data measured using six nondestructive methods with destructively measured DBTT and USE data. Several non-irradiated and irradiated samples made out of four different steel alloys have been measured. As nondestructively measured parameters do not directly describe material embrittlement, their relationship with the DBTT and USE needs to be determined. A machine learning regression algorithm can be used to build a model that describes the relationship. In this thesis, six models are built using six different algorithms, and their use is studied in predicting the DBTT and USE based on the nondestructively measured parameters in the NOMAD Database. The models estimate the embrittlement with sufficient accuracy. All models predict the DBTT and USE based on unseen input data with mean absolute errors of approximately 20 °C and 10 J, respectively. Two of the models can be used to evaluate the importance of the nondestructively measured parameters. In the future, machine learning algorithms could be used to build a tool that uses nondestructively measured parameters to estimate the neutron-induced embrittlement of RPVs on site.
-
(2021)Dendrite prevention can be achieved by manipulating the local chemical concentration gradient by ultrasound. An ultrasonic field, which generates acoustic streaming, can manipulate the ionic flux at the electrode surface by altering the local ion concentration gradient at said surface according to the streaming pattern. The pattern is determined by the ultrasonic field and the geometry of the sonication volume. The preventive action can be directed to an arbitrary point on the surface, or be swept across it to achieve a smoother electroplating. Dendritic growth is concentrated to areas of higher concentration gradient. This is because at the electrode surface both the electric and convective fluxes tend to zero. If the reduction of ions into their metallic form is fast enough, the metal layer growth rate is determined by the diffusive flux, which is determined by the ion concentration gradient and the diffusion constant of the ion in the electrolyte. In this study, tin was used as the transported ion instead of lithium for safety reasons. A custom-made battery mockup cell was constructed for the experiments. The anode was imaged with a usb microscope camera to determine the growth of the dendrites during the process. The electroplating current and piezo driving power were varied between 100 mA to 275 mA and 0 to 6.6 W, respectively. With piezo driving electrical power less than 10 W, it was possible to lower the maximum lengths of dendrites. Finite element method simulations were conducted to validate the hypothesis and experimental results. This ultrasonic method could be used to allow rechargeable, lightweight, high capacity lithium metal batteries. The piezos could be integrated into battery chargers.
-
(2020)Ultrasonic transducers convert electric energy into mechanical energy at ultrasonic frequencies. High-power ultrasound is widely used in the industry and in laboratories e.g. in cleaning, sonochemistry and welding solutions. To be effective in these cases, a piezoelectric transducer must deliver maximal power to the medium. Most of these systems rely on having the power delivery maximized during long driving sequences where stable performance is critical. Power ultrasonic transducers are typically narrowband, featuring high Q-value, that are finely tuned to a specific resonance frequency. The resonance frequency can vary during driving due to temperature, mechanical loading and nonlinear effects. When the transducers resonance frequency changes, drastic changes in its impedance (resonance to anti-resonance) can lead quickly to damage or failure of the driving electronics or the transducers themselves. In this work we developed a multi-channel high-power ultrasonic system with a software-based resonance frequency tracking and driving frequency control. The implementation features a feedback loop to maximize power delivery during long driving sequences in an ultrasonic cleaning vessel. The achieved total real power increased from 6.5 kW to almost 10 kW in peak with our feedback loop. The feedback loop also protected the electronics and transducers from breaking due to heating and varying impedance.
-
Mechanical Modeling of Multi-coil Transducers for Brain Stimulation in High Static Magnetic Fields (2023)Transcranial magnetic stimulation (TMS) is a non-invasive method for stimulating cortical neurons in the brain. Combining TMS with functional magnetic resonance imaging (fMRI) shows the effects of TMS through the changes in brain metabolism. This information is necessary for developing new applications of TMS and for improving the efficacy and safety of the existing treatments. The biggest setback in current TMS–fMRI technology arises from the mechanical forces formed on the transducer as the interplay of the magnetic fields from the MRI and the changing current in the coil, leading to breakage of the transducers and additional safety risks. The objective of this Thesis was to assess and compare the mechanical stresses on multi-locus TMS (mTMS) transducers inside a high-field fMRI bore using finite element modeling, and to build and test transducer options based on the simulation results. For a transducer design for rats, six different coil former materials and three mTMS coil combinations were simulated with two commonly used current waveforms. In addition, the effect of the transducer orientation relative to the magnetic field was modeled with a transducer designed for humans. Our results show that the current pulses ran through the coils produce shock waves on the coil formers, leading to regions of maximum stresses that depend on the time instant. The intensity and location of the maximum stresses depends on the current waveform and coil combination used. Based on the results, 30% glass-fiber filled polyamide was found to be the most durable material. This Thesis provides novel insights for more durable TMS coil designs.
-
(2023)Scanning probe microscopy (SPM), which includes atomic force microscopy (AFM), is an affordable and powerful tool for investigating surfaces. However, to ensure accuracy, a metrologically informed approach is required. In this thesis, a commercial Jupiter XR AFM was used for calibration experiments testing its reliability and accuracy. AFMs can further be improved by the use of active probes with added capabilities that allow for faster scanning speeds and other improvements. Efforts have been made to enable their broader use. At VTT MIKES, the commercial Jupiter XR AFM is being modified to use active probes capable of self-sensing and self-actuation. A simple AFM was first built as a test setup to better understand the probes and to split their integration into the Jupiter AFM into a step-by-step process where the mechanical, electronic, and software changes necessary could be separated into distinct parts. In this thesis, I describe experiments done to test the reliability of the commercial AFM, and the process of constructing and using the test setup AFM, after which I present some results obtained using them, and discuss the experiments and the integration process. Included is also an overview of metrology and some of the physics and other theory relevant to AFM, and a summary of the principles of AFM and its role in microscopy. This work is part of the MetExSPM project, which seeks to develop traceable high speed scanning probe microscopy, for example by achieving higher scanning speeds and larger scanning areas, while maintaining good resolution and metrologically traceable high accuracy. This will greatly increase the utility of SPMs, especially for industrial applications.
-
(2022)Imaging done with conventional microscopes is diffraction-limited, which sets a lower limit to the resolution. Features smaller than the resolution cannot be distinguished in images. This limit of the diffraction-limit can be overcome with different setups, such as with imaging through a dielectric microcylinder. With this setup it is possible to reach smaller resolution than with a diffraction-limited system, which is called super-resolution. Propagation of light can be modelled with various simulation methods, such as finite-difference time-domain and ray tracing methods. Finitedifference time-domain method simulates the light as waves which is useful for modelling the propagation of light accurately and take into account the interactions between different waves. Ray tracing method simulates the light as rays which requires approximations to the light’s behaviour. This means that some phenomena cannot be taken into account, which can affect the accuracy of the results. In this thesis the model for simulating super-resolution imaging with microcylinder is studied. The model utilizes the finite-difference timedomain method for modelling the near-field effects of the light propagating through the microcylinder and reflecting back from a sample. The reflected light is recorded on the simulation domain boundaries and a near-field-to-far-field transformation is performed to obtain the far-field corresponding to the recorded fields. The far-field is backward propagated to focus a virtual image of the sample, and the virtual image is then used in ray tracing simulation as a light source to focus it to a real image on a detector.
-
(2020)Acoustic levitation permits non-contacting particle manipulation. The position and orientation of the levitated particle can be controlled by altering the acoustic field. Existing acoustic levitators have employed a single frequency which limits the types of acoustic traps that can be created. The use of multiple frequencies makes it possible to control the forces acting on a particle independently in all directions. I predict theoretically the forces acting on particles placed in the acoustic fields created with multiple coexisting frequencies. I present two traps which demonstrate the benefits of multifrequency acoustic levitation. To realize the traps, I constructed a 450-channel phased array acoustic levitator with individual frequency, phase, and amplitude control for each channel.
-
(2022)Energy is an essential input for any non-spontaneous mechanism. In biological organisms, the process of producing energy currency, adenosine triphosphate, is called cellular respiration. It is made of three smaller steps, out of which the last one is oxidative phosphorylation that is responsible for the largest production of adenosine triphosphate molecules in the whole process. Oxidative phosphorylation is performed by the electron transport chain made of five protein complexes, named respiratory complex I-V. Complex I is the first and largest protein complex in the electron transport chain, and it is the least understood. Its primary function is to transfer electrons from nicotinamide adenine dinucleotide to ubiquinone, which is coupled to the pumping of four protons across the mitochondrial inner membrane. Although the overall reaction of complex I is understood, the intricate detail of the mechanism is still largely unknown. There is significance in the details because there are numerous point mutations, which have been strongly correlated with neurogenerative diseases, such as Leigh’s syndrome, and aging. Therefore, a more thorough understanding of its mechanism can give insight into potential target drug development. Complex I is made of 14 highly conserved subunits that can be found in most species that use the electron transport chain. They create an L-shape, where seven subunits are embedded in the inner membrane, the membrane domain, and the others are floating in the mitochondrial matrix, the peripheral arm. In mitochondrial complex I, however, there are in addition around 30 accessory subunits. It has been previously thought that the main mechanism is conducted by the 14 subunits that are found in all species. However, in the past couple of years, it has been shown that accessory subunits can play an important role in the mechanism of mitochondrial complex I. The work presented in this thesis uses a multiscale computational approach to study the effect of three mutations, F89A, Y43A and L42A, from an accessory subunit LYRM6 on the function of complex I. Previous experiments demonstrated that the mutations decreased the overall activity of complex I by 76-86 %. The LYRM6 subunit is located at the pivot of the membrane and periplasmic domains. The results of this study show that the point mutations have a long-range effect on the conformations of three loops from three conserved subunits in this region. The shift in the loop dynamics causes a drop in water occupancy. The observed water pathway is tested for the capability of proton transfer. The findings are demonstrated with the help of molecular dynamics and quantum mechanics/molecular mechanics simulations.
-
(2020)Omnidirectional microscopy (OM) is an emerging technology capable of enhancing the threedimensional (3D) microscopy widely applied in life sciences. In OM, precise position and orientation control are required for the sample. However, the current OM technology relies on destructive, mechanical methods to hold the samples, such as embedding samples in gel or attaching them to a needle to permit orientation control. A non-contacting alternative is the levitation of the sample. But, until now, the levitation methods have lacked orientation control. I enable omnidirectional access to the sample by introducing a method for acoustic levitation that provides precise orientation control. Such control around three axes of rotation permits imaging of the sample from any direction with a fixed camera and subsequent 3D shape reconstruction. The control of non-spherical particles is achieved using an asymmetric acoustic field created with a phase-controlled transducer array. The technology allows 3D imaging of delicate samples and their study in a time-lapse manner. I foresee that the described method is not only limited to microscopy and optical imaging, but is also compatible with automated sample handling, light-sheet microscopy, wall-less chemistry, and noncontacting tomography. I demonstrate the method by performing a surface reconstruction of three test samples and a biological sample. In addition, a simulation study and the levitation of test samples were used to characterize the levitation technique's performance. Both the shape reconstruction and orientation recovery were done by a computer vision based approach where the different images are stitched together. The results show the rotation stability and the wide angle range of the method.
-
(2022)This thesis examines the optical response of tuneable chiral plasmonic nanostructures in linear cross-polarization. Plasmonic gold-silver nanostructures composed of silver-coated gold nanorods, and dynamic DNA origami are investigated because of their optical properties of interest in the visible light wavelength region, and because of their controllable rotational asymmetry, which results in tuneable chirality in dimer structures. These plasmonic nanostructures present optical properties such as circular dichroism and optical rotatory dispersion. In this thesis we establish the relationship between perceived color, spectrometry, circular dichroism and optical rotatory dispersion of the samples, depending on the chiral geometry of the nanostructures within. The motivation is to predict perceived color from the chiral geometry of the nanostructures, which will enable visual detection for biosensing applications. Circular dichroism and optical rotatory dispersion give us detailed knowledge about the polarization state of a sample, but visible light detection and spectrometer measurements are more accessible and portable methods for characterizing the polarization state of a sample. We achieve color modulation from green to blue with the switching of chiral geometry, under cross-polarized white light. This has potential for biosensing applications, based on the perceived color change depending on the chiral geometry of the sample. The DNA origami structures react to the presence of an analyte by changing their chiral geometry. Possible applications in biosensing of analytes can be made more practical if the orientation of the DNA origami template can be determined from the perceived color or the transmission spectra, rather than from the less accessible circular dichroism or optical rotatory dispersion measurements.
-
(2021)Despite a vast body of knowledge that has already been accumulated on particle transport at both theoretical and experimental level, a simple method for estimating particle source impact on plasma density profile peaking has been lacking. Fable et al. presented a parameter for calculating the source strength (Sstr, the S parameter) in [1]. The parameter is derived from particle flux continuity equation, and after approximations takes as input parameters only the information on neutral beam injection (NBI) power, beam ions injection energy, effective core heat transport diffusivity and plasma density, radius, and volume together with a fitted coefficient from an ASDEX Upgrade experiment. The formula was applied to a database of 165 pulses in both high and low confinement mode, mostly with neutral beam heating, in JET, Joint European Torus, fusion experiment. The results appear reasonable considering the fitted parameter and the approximations in the formula. In addition to the S parameter values, also normalised density gradient dependence on neutral beam heating power and collisionality were investigated, to compare the results with those obtained at ASDEX Upgrade in [1]. Detailed studies of six gas puff modulation shots [2, 3, 4] at JET are used as reference. In [2] the source contribution for the H-mode shots was 50-60% and low confinement mode shots 10-20%. This is further validated in [3] and the high confinement mode shots are compared to similar shots DIII-D fusion experiment in [4], where the source impact on density peaking was negligible. Observed differences are attributed to different dominant turbulent environments. The average calculated level of S parameter values suggest mostly non-negligible source contribution to density peaking, and the values differ for high and low confinement mode plasmas, in line with [2, 3, 4]. However, the results imply that the coefficient 2000 is not constant across the database, and while a scalar correction to fit the coefficient to JET may be possible for low confinement mode plasmas, the high confinement mode plasmas require further research.
-
(2022)Ensuring adequate air quality is integral to healthy living. Since in modern societies the majority of time is spent indoors, understanding indoor air pollution and the means of air purification are of great importance. Adverse health effects are induced by volatile organic compounds (VOC) that originate from everyday activities and our surroundings. Photocatalysis is a radiation-activated chemical transformation that can be used to decompose organic pollutants into harmless constituents. However, existing air purification solutions employing photocatalysis often rely on UV light limiting the use of solar radiation. Titanium dioxide is a popular photocatalyst material, but it requires modification to its electronic properties to respond to visible light. An established approach is to introduce atoms of other dopant elements into the titania lattice. Atomic layer deposition (ALD) is a thin film deposition technique widely studied especially in metal and metal oxide research. Following from the principle of sequential saturation of the surface, control over the size and composition of the film may reach atomic level. Since the chemical configuration of a doped TiO2 film is of utmost importance to successful modification, ALD is an excellent tool to examine suitable photocatalytic TiO2 chemistries. Furthermore, thin solid films of catalytically active material would have a distinguished advantage for deployment in real-life settings over their powderous counterparts. The literature review of this thesis explores the semiconductor photocatalysis with an eye on its suitability to indoor air purification. The motivation is to give the reader a view on the air quality issue, the existing technological solutions and how a thin film photocatalyst could supplement the field. Titanium dioxide doping concepts are introduced to elucidate the rationale behind the experimental efforts. The experimental part describes a development project to deposit visible-light responding photocatalysts. Titanium dioxide thin films co-doped with nitrogen and zinc/fluorine were grown on steel plates. An in-house built reactor system was used to study acetaldehyde degradation under irradiation. Unfortunately, the reactor experienced a malfunction, rendering a large part of the results futile. Moreover, months of valuable time were lost in chasing a mirage of fallacious data. In the end an ALD grown photocatalyst responding to visible light could not be materialized.
-
(2021)Electroencephalography (EEG) is a non-invasive neurophysiological method for evaluating brain activity by measuring electrical potential at the scalp. The electrical potentials originate mainly from postsynaptic cortical currents created by neuronal activity. It is a valuable tool for both research and clinical practice. EEG can be used e.g. to diagnose epilepsy, focal brain disorders, brain death, and coma. Intermittent photic stimulation (IPS) is an important tool in clinical EEG. Healthcare professionals use it to induce epileptic activity in patients to help diagnose their conditions. In these tests, various IPS frequencies are used with eyes-closed, eyes-open, and eye-closure conditions. IPS test is listed in clinical practice guidelines in EEG globally, and it is mainly used to diagnose photosensitive epilepsy, i.e., to detect epilepsy-related abnormal sensitivity to flickering light. Magnetoencephalography (MEG) is a non-invasive neurophysiological method in which minute magnetic fields — produced by the same postsynaptic currents as in EEG — are measured with special superconductive sensors around the head. MEG is a valuable tool for research and clinical practice with increasing world-wide utilization. The main advantages of MEG over EEG are easier source modelling and higher resolution at cortical areas. IPS has not been introduced to MEG since the IPS stimulators used in EEG are not compatible with MEG. IPS in MEG could improve the analysis of IPS and provide better tools for diagnoses. Currently, data analysis of IPS is typically limited to healthcare professionals examining the visualization of the raw data while looking for induced epileptiform activites and lateralizing them. In this thesis, an MEG-compatible IPS stimulator is introduced and alternative ways of analyzing IPS data for both MEG and EEG are showcased. Although analysis methods were applied with decent signal-to-noise ratios, further research is needed—especially to compare responses between patients with epilepsy and healthy subjects.
-
(2022)Molecular hydrogen is considered as the primary alternative to replace fossil fuels for future energy supply. Hydrogen can be produced sustainably through electrocatalytic hydrogen evolution reaction which is a vital step in water electrolysis. So far, the efficiencies of electrochemical and photoelectrochemical water electrolysis systems are too low to satisfy the demands for hydrogen on a commercial scale. Plasmonic nanostructures containing a plasmonic and a catalytic component hold great promise for enhancing the performance of typical water electrolysis systems through plasmonic photocatalysis utilizing localized surface plasmon resonance excitation. Here, a novel plasmonic-catalytic u@AgPd nanorattle is synthesized, characterized, and investigated for plasmon-enhanced hydrogen evolution reaction to provide new insights into the design of light-assisted water electrolysis systems. The nanorattle exhibited significant improvements of performance towards hydrogen evolution reaction under 427 nm illumination, displaying a near 2-fold current increase and a decreased overpotential of 58 mV at a current density of 10 mAcm-2. The material is evidenced to plasmon-enhance the electrocatalytic performance through a combination of charge transfer and local heating mechanisms.
-
(2022)In this project, poly(2-methyl-2-oxazoline)-block-poly(2-n-butyl-2-oxazine)-block-poly(2-methyl-2- oxazoline) (PMeOx-b-PnBuOzi-b-PMeOx) and poly(2-methyl-2-oxazoline)-block-poly(2-n-propyl-2- oxazine) (PMeOx-b-PnPrOzi) with block lengths of 35-20-35 and 100-100, respectively, were synthesized. When dispersed in water these thermoresponsive polymers aggregate into micellar aggregates or form hydrogels. Polymers were characterized with 1H-NMR, GPC, and DLS. Age-related macular edema and diabetic macular edema are the most common reasons for blindness in industrialized countries. The triamcinolone acetonide, a corticosteroid used to treat both of these macular edemas, was loaded into the polymeric micelles or hydrogel of synthesized polymers using the thin film method. The loading efficiency for a triblock copolymer ((PMeOx35-b-PnBuOzi20- b-PMeOx35) polymeric micelles was 4 % at the polymer/drug ratio of 10/4 and for a hydrogel (PMeOx100-b-PnPrOzi100) it was 48 % with the same polymer/drug ratio. The properties of the PMeOx100-b-PnPrOzi100 hydrogel formulations with the drug were studied with rheological measurements, DSC, DLS, and GPC of formulations. The formulation showed storage modulus of 3 kPa and the gelation temperature at 16 °C. From the DSC two glass transition temperatures were obtained, Tg1 at around 12 °C and Tg2 at around 74 °C. The particle size distribution of the formulation obtained with DLS showed that there were assumingly micelles or vesicles with a hydrodynamic radius between 20 and 80 nm. The drug release from the hydrogel formulation was studied with the dialysis membrane method and all the drug was released within 24 hours. Both copolymers formed quite unstable formulations with the drug. The results from this study gives information how polyoxazoline- and polyoxazine-based materials can be used to encapsulate and release corticosteroids, such as triamcinolone acetonide. To increase the drug loading capacity and to stabilize formulations, some surfactants for the drug could be tested in the future.
-
(2022)In this master's thesis, polyzwitterionic copolymers were synthesized and analyzed with various methods. In the literature part, the theory behind the reactions and results is covered in order to explain the phenomena. In the literature part of the thesis, articles were used to describe the theory as extensively as possible. The theory elaborates on the most important topics considering the research part. The main topics are reversible addition-fragmentation polymerization (RAFT), polymerization-induced self-assembly (PISA), and polyzwitterions. In the reversible addition-fragmentation polymerization chapter the kinetics and possible monomers and RAFT agents are gone through also considering the pros and cons. Different disadvantages are dealt with as well when talking about RAFT polymerization. In the PISA chapter different possible morphologies and different types of PISA polymerizations are covered, concentrating still on RAFT polymerization. In this chapter also core blocks of PISA were discussed covering the core forming block used in the research, diacetone acrylamide. lastly, polyzwitterions were discussed explaining the theory, possible applications, polyelectrolyte complexes, and thermoresponsivity of polyzwitterions. Also, in this part polysulfobetaines were covered since it is the zwitterionic block in the copolymer synthesis. In the experimental part, PSBMA-PDAAM diblock copolymers were synthesized and studied with different methods. Different lengths of block copolymer were synthesized and they were studied with the most common characterization methods. Thermoresponsivity, morphology, and also the effect of the solids content of different block lengths were studied. Measurements turned out to be a success since many different morphologies were witnessed and the thermoresponsive behavior of this copolymer showed interesting results.
Now showing items 41-60 of 84