Browsing by master's degree program "Materiaalitutkimuksen maisteriohjelma"
Now showing items 21-34 of 34
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(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.
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(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.
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(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.
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(2021)The sub-λ/2 focusing, also known as super resolution, is widely studied in optics, but only few practical realizations are done in acoustics. In this contribution, I show a novel way to produce sub- λ/2 focusing in the acoustic realm. I used an oil-filled cylinder immersed in liquid to focus an incident plane wave into a line focus. Three different immersion liquids were tested: water, olive oil, and pure ethanol. In addition to the practical experiment, we conducted a series of finite element simulations, by courtesy of Joni Mäkinen, to compare to the experimental results.
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(2019)Particle Induced X-ray Emission (PIXE) was originally introduced as an ion-beam analytical technique in Lund in the 1970s and has since then been part of the available techniques in many laboratories around the world. The external beam PIXE set-up is used in probing the annual tree rings. The goal is to see the effects of volcanic eruption activities from the perspectives of tree plants here in Finland. In the theory part, I tried to include the description of how volcanoes are formed and created with a bit of volcanic activity history, the growth metabolism mechanism in tree plants and characteristics x-ray productions. The two tree sample used for this experiment were gotten from two different regions of Finland. The first tree is a Pine tree from Parikkala(a small place near Savolinna) in the south-eastern part of Finland and the second tree is a Spruce tree from Pielavesi (place near Kuopio) in the central part of Finland. These samples were carefully prepared for ionisation. The collected spectra data were analysed in a software called PyMCA. PyMCA has been developed by the Software Group of the European Synchrotron Radiation Facility (ESRF). PyMCA is a ready to use and in many aspects state-of-the-art, set of applications implementing most of the needs of X-ray fluorescence data analysis. PyMCA is use to interpret X-ray fluorescence spectra from a diverse array of samples
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(2021)Chiral assemblies of metal nanoparticles absorb and/or scatter left and right handed circularly polarized light with different intensities usually from the visible light spectral region. This difference in the absorption called circular dichroism (CD) and closely related anisotropy factor (g-factor), which is the CD spectrum normalized with the overall absorption, describe the optical activity of the chiral assemblies. The aim of this thesis was to study and optimize the different structural parameters affecting the g-factor of a chiral gold nanorod (AuNR) dimer to reach the highest possible value. The structure consisted of two AuNRs bound together with a DNA origami in a crossed fingers conformation. The properties studied were silver as a coating material of the AuNRs, the dimensions of the AuNRs, angle between the long axes of the AuNRs and the interparticle distance. The dimensions comparison was studied with different sized AuNRs, the angle was controlled by changing the DNA strands working as a bridge between the two bundles in the DNA origami and the distance between the AuNRs was controlled by the length of the thiol treated DNA strands used for the AuNR binding to the origami. The experiments showed that the best g-factor was achieved with 33×74 nm sized AuNRs with an angle of approximately 55° and an interparticle distance of 24nm. Optimized assembly made a notable increase in the g-factor from 0.05 to 0.12. This is a highest g-factor recorded in a AuNR dimer structure up to date and thus the assembly could be of great use in the chiral sensing field in the future.
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(2021)Maa-aineksessa fosfori on sitoutunut alkuaineisiin, joista rauta on merkittävässä osassa. Fosfori voi vapautua vedessä tai pohja-aineksessa liuenneeseen muotoon aiheuttaen rehevöitymistä. Fosforin vapautumiseen vesistössä vaikuttavat maa-aineksen koostumus, veden ominaisuudet ja hiilen saatavuus. Raudan pitoisuudet ja esiintymismuodot selittävät osittain vesistöjen välisiä eroja rehevöitymisessä. Röntgenabsorptiospektroskopialla voidaan tutkia alkuaineen atomien hapetustilaa, koordinaatiolukua, koordinaatiokemiaa ja atomien välisiä etäisyyksiä. Menetelmässä mitataan absorptiokerrointa energian funktiona. Näytteiden analysoinnissa käytetään yleensä vertailukohtana hyvin tunnettuja referenssien spektrejä. Tulokset ovat luotettavimmat, kun referenssien spektrit ovat mitattu samoilla asetuksilla yhdessä näytteiden kanssa. Tässä työssä on tutkittu yhtätoista (11) eri maa-ainesta röntgenabsorptiospektroskopialla raudan K-reunan lähiympäristössä. Maa-aineksista tutkittiin; 1. käsittelemätön, 2. oksalaattiuutettu, 3. poltettu sekä 4. oksalaattiuutettu ja poltettu versio. Oksalaattiuuton ja polton tarkoituksena oli selventää maa-ainesten välillä olevia eroja. Uuttaminen tarkoittaa oksalaattiuuttoa, jossa maa-aineksesta poistuu heikosti kiteistä rautaa. Polttaminen tarkoittaa näytteen kuumentamista 700 asteeseen, jolloin maa-aineksen rautaoksidit hapettuvat ja kiteytyvät. Näytteet, 44 kpl, mitattiin kolmeen kertaan. Eri maa-aineksien ja niiden eri käsittelyiden välillä havaittiin eroja absorptioreunan energiassa, joka on yhteydessä raudan hapetustilaan. Polttaminen teki absorptiospektreistä keskenään lähes samanlaisia ja tasoitti käsittelemättömissä näytteissä olleita eroja. Oksalaattiuuttamisella ei havaittu olevan vastaavaa vaikutusta. Näytteiden rautamineraalien spektripainoista voidaan päätellä näytteiden mineraalikoostumuksia. Jotta raudan merkitystä fosforin kierrossa voidaan tarkentaa, tarvitaan lisää tutkimusta.
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(2020)Polysiloxanes are silicon-based polymers consisting of R2SiO repeating units. They are commonly used in many commercial applications, for example, as adhesives, additives, or waterproof coatings. This thesis concentrates on polysiloxanes used as optically clear adhesives, which are needed in display applications to, for instance, bond cover lenses to touch panel sensors. This kind of a material needs to have a high refractive index to match glass or plastic, and it has to be transparent and thermally stable. In addition, it must resist degradation and yellowing from UV exposure and humidity. Anionic ring-opening polymerization was used to synthesize optically transparent polysiloxanes with varying side-groups. These polymers exhibited high refractive index values, which were adjusted by changing the amount of phenyl group -containing monomers or with chain terminating agents. End-functionalization reactions were performed for the synthesized polymers to introduce methacrylate groups to the chain ends, which could later be used in crosslinking trials involving a photoinitiator. The results present an effective synthetic route for the ring-opening polymerization for transparent, high refractive index poly(dimethylsiloxane-co-diphenylsiloxane) and poly(methylphenylsiloxane) that could be used as adhesives after selective chain end functionalization and crosslinking reactions. The properties of the synthesized polysiloxanes were characterized with several different methods, such as size exclusion chromatography, rheology, and NMR spectroscopy. End functionalization reactions were performed for some of the synthesized polymers. These were then further characterized to verify the suitability of the reaction.
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(2021)The plasma-facing materials of future fusion reactors are exposed to high doses of radiation. The characterization of the radiation damage is an essential part in the study of fusion relevant materi- als. Electron microscopy is one of the most important tools used for characterization of radiation damage, as it provides direct observations of the microstructure of materials. However, the char- acterization of defects from electron microscope images remains difficult. Simulated images can be used to bridge the gap between experimental results and models. In this thesis, scanning transmission electron microscope (STEM) images of radiation damage were simulated. Molecular dynamics simulations were employed in order to create defects in tungsten. STEM images were simulated based on the created systems using the multislice method. A data- base of images of h001i dislocation loops and defects produced from collision cascade simulations was generated. The simulated images provide insight into the observed contrast of the defect structures. Differences in the image contrast between vacancy and interstitial h001i dislocation loops were reported. In addition to this, the results were compared against experimental images and used in identification of a dislocation loop. The simulated images demonstrate that it is feasible to simulate STEM images of radiation damage produced from collision cascade simulations.
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(2020)In this thesis, synthesis and solution properties of the polyampholyte poly(acrylic acid)-b-poly[(vinylbenzyl)trimethylammonium chloride], PAA-PVBTMA-Cl, were investigated in aqueous solutions. First, the diblock copolymer was synthesized via RAFT polymerization where poly(acrylic acid), PAA was used as a chain transfer agent (CTA). In addition, the homopolymer poly[(vinylbenzyl)trimethylammonium chloride], PVBTMA-Cl, was synthesized via RAFT polymerization to compare the solution properties with the block copolymer. Molar masses of the polymers were determined using several methods such as NMR, UV-Vis spectroscopy and SEC. The experimental molar masses were close to theoretical values and block ratio in diblock copolymer from NMR was 30% of AA and 70% of VBTMA-Cl. Furthermore, the solution properties of the polyampholyte were studied under external stimuli such as pH and temperature. UCST type of behaviour was observed for aqueous PAA-PVBTMA-Cl solutions when the hydrophobic trifluoromethanesulfonate (OTf) anion was introduced. In addition, self-assembly of the diblock copolymer was confirmed by zeta potential measurements in different pH conditions. The expected reverse of the micelle structure with changing pH was not observed. However, aqueous PAA-PVBTMA-Cl showed UCST behaviour and micellization induced by the hydrophobic counterion.
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(2020)In this thesis, thermoresponsive poly(N-acryloyl glycinamide-co-methacrylic acid) (P(NAGA-co-MAA)) microgels were synthesized via surfactant stabilized free radical precipitation polymerization. Also, PNAGA microgel was synthesized as reference. The upper critical solution temperature (UCST) behavior of the microgels was tuned by changing the molar ratio of the monomers in the copolymer. The phase transition behavior of the formed microgel particles were characterized with NMR spectroscopy, microcalorimetry, turbidimetry and light scattering. It was observed that both PNAGA and P(NAGA-co-MAA) microgels display UCST type temperature response. However, in neutral pH, the phase transition of the copolymer gels was prevented due to the deprotonated acid groups of MAA. Hence, all the measurements were made in pH 3, below the pKa of MAA. The phase transition became sharper when the amount of MAA repeating units was increased in the copolymer. Also, the phase transition temperature of the copolymer gels increased when the amount of MAA was increased. In addition to phase transition behavior studies, the reactivity ratios of the monomers were studied during polymerization to analyze the structure of the forming copolymer gels. It was concluded that, as the both monomers had similar reactivity rates, statistical random copolymer gels are formed.
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(2021)Pipe fouling is a challenging problem in many industrial applications. Established cleaning techniques require that the production is aborted during the cleaning phase. These techniques are unable to focus cleaning power, even though fouling often is localized to certain areas inside the pipeline. This study introduces an effective method to clean fouling inside complex structures. We use finite-element modelling (FEM) -based time-reversed signals to focus ultrasound power onto a predetermined pipe residing inside a Plexiglas container. We compare the cleaning effect obtained by this method with the cleaning obtained with standard ultrasound cleaning when using the same input electric power and cleaning time. Our results indicate that the proposed time-reversal based technique removes more fouling compared to when using the standard technique. Moreover, we demonstrate ability to relocate the focus including changing the target from one pipe to another one inside the container.
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(2020)Two different bio transfer standards (BTS), composed of fatty acid bilayers, NanoRuler and NanoStar were developed. NanoRuler consists of a nanometer scale staircase with eight steps that are 5 nm tall each and NanoStar is designed to have topological structure with sharp edge and three height planes 5 nm elevated with respect to each other. With NanoRuler nanometer vertical calibration from 5 nm to 40 nm is possible and NanoStar allows the evaluation of the instrument transfer function (ITF). Due to the soft nature of the standards, the topographical stability was researched. Thus, an investigation of the topographical stability of three NanoRulers and one NanoStar across 24 months was done by measuring the surface topography with a custom-built Scanning White Light Interferometer (SWLI). The BTS were measured over 100 times during the experiments and were stored in laboratory conditions. The step heights of the structures were calculated with a histogram method and the surface roughness of the samples was evaluated using the Sq parameter. The step height analysis method was compared to the standard method (ISO 5436-1) where applicable and no notable differences were found. In both roughness and step height data no linear or non-linear trends were found, and the step heights compared well with the literature values. For NanoRuler the step heights were 4.9 nm, 10.1 nm, 15.1 nm, 20.1 nm, 25 nm, 30.1 nm, 35.1 nm and 40.2 nm and the respective stabilities were 0.3 nm, 0.3 nm, 0.6 nm, 0.9 nm, 1.3 nm, 1.6 nm, 2.1 nm, and 2.5 nm. For NanoStar the step heights were -5.1 nm and 5.2 nm with stabilities 0.3 nm and 0.4 nm respectively. The NanoRuler had a surface roughness stability of 0.02 nm whereas NanoStar had a roughness stability of 0.01 nm. After 24 months both BTS types preserved their topographical structure and no issues with surface topographical stability were observed.
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(2019)Rehevöityminen on yksi merkittävimmistä vesistöjen ekologista tilaa heikentävistä tekijöistä. Järvivesissä fosfori on useimmiten levien kasvua rajoittava tekijä, jolloin fosforin määrän kasvu vastaanottavassa vesistössä lisää kasvillisuuden perustuotantoa ja kiihdyttää näin ollen vesistön rehevöitymistä. Fosforia päätyy vesistöihin valumavesien mukana liuenneessa muodossa ja eroosion ansiosta hiukkasmaisessa muodossa sitoutuneena esimerkiksi erodoituneessa maa-aineksessa oleviin raudan oksideihin. Erodoitunut maa-aines laskeutuu vesistöjen pohjalle, päätyy osaksi pohjasedimenttiä ja lopulta kohtaa hapettomat olosuhteet. Pohjasedimentteihin varastoituneet ravinteet voivat hapettomissa olosuhteissa vapautua takaisin vesistön tuottavaan kerrokseen ja näin ollen kiihdyttää rehevöitymistä. Hiukkasmaisen fosforin vapautuminen liuenneeseen, leville käyttökelpoiseen muotoon tunnetaan huonosti, joten erodoituneen maa-aineksen mukana kulkeutuvan fosforin merkitys vesistöjen rehevöitymisessä ei ole täysin selvä. Tässä työssä tutkitaan maa-aineksen matkaa pelloilta järvien pohjasedimentteihin käyttäen raudan K-reunan röntgenabsorptiospektroskopiaa lähireuna-alueella. Keskipisteessä on raudan kemiallisen tilan muutos siirryttäessä hapellisista olosuhteista hapettomiin olosuhteisiin sekä mahdollisesti järvien sedimenteissä muodostuva raudan fosfaattimineraali vivianiitti, jolla voi olla merkittävä rooli fosforin pidättämisessä sedimenttiin. Lisäksi tutustutaan röntgenabsorptiospektroskopian teoriaan sekä tutkimuksessa käytettävän spektrometrin toimintaan. Erilaisten maa-ainesten päätymistä järvien sedimentteihin simuloitiin valmistamalla järviveden ja maa-ainesten seoksia, joista osaan lisättiin myös orgaanista hiiltä. Seoksista valmistettiin näytteet röntgenabsorptiomittauksia varten vuorokauden aerobisen sekä neljän kuukauden anaerobisen inkuboinnin jälkeen. Mittaustuloksista havaitaan selvästi raudan pelkistyminen anaerobisissa olosuhteissa, ja että pelkistymistä edesauttaa orgaanisen hiilen läsnäolo. Vertailemalla järvivesi-maanäytteiden spektrejä mitattuun vivianiittimineraalista valmistetun näytteen spektriin, havaitaan että raudan pelkistyminen anaerobisessa ympäristössä suosii Fe(II)-mineraalien muodostumista. Mitattuja spektrejä verrattiin vivianiitin spektriin ja vertailun perusteella vivianiittia muodostui neljän kuukauden anaerobisen inkuboinnin aikana hiilettömissä näytteissä 12 - 22 % ja hiilellisissä näytteissä 31 - 50 % verrattuna hapelliseen alkutilanteeseen. Prosenttiluvut ovat todennäköisesti yliarvioita vivianiitin muodostumiselle, mutta tuloksista voidaan kuitenkin päätellä, että raudan voimakkaampi pelkistyminen edesauttaa vivianiitin tai muiden Fe(II)-mineraalien muodostumista ja että vivianiitin muodostumisella saattaa olla vaikutus fosforin pidättämisessä sedimenttiin.
Now showing items 21-34 of 34