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  • Vehkamäki, Marko (Helsingin yliopisto, 2007)
    Atomic layer deposition (ALD) is a method for thin film deposition which has been extensively studied for binary oxide thin film growth. Studies on multicomponent oxide growth by ALD remain relatively few owing to the increased number of factors that come into play when more than one metal is employed. More metal precursors are required, and the surface may change significantly during successive stages of the growth. Multicomponent oxide thin films can be prepared in a well-controlled way as long as the same principle that makes binary oxide ALD work so well is followed for each constituent element: in short, the film growth has to be self-limiting. ALD of various multicomponent oxides was studied. SrTiO3, BaTiO3, Ba(1-x)SrxTiO3 (BST), SrTa2O6, Bi4Ti3O12, BiTaO4 and SrBi2Ta2O9 (SBT) thin films were prepared, many of them for the first time by ALD. Chemistries of the binary oxides are shown to influence the processing of their multicomponent counterparts. The compatibility of precursor volatilities, thermal stabilities and reactivities is essential for multicomponent oxide ALD, but it should be noted that the main reactive species, the growing film itself, must also be compatible with self-limiting growth chemistry. In the cases of BaO and Bi2O3 the growth of the binary oxide was very difficult, but the presence of Ti or Ta in the growing film made self-limiting growth possible. The application of the deposited films as dielectric and ferroelectric materials was studied. Post-deposition annealing treatments in different atmospheres were used to achieve the desired crystalline phase or, more generally, to improve electrical properties. Electrode materials strongly influenced the leakage current densities in the prepared metal insulator metal (MIM) capacitors. Film permittivities above 100 and leakage current densities below 110-7 A/cm2 were achieved with several of the materials.
  • Hämäläinen, Jani (Helsingin yliopisto, 2013)
    Atomic layer deposition (ALD) is a chemical gas phase deposition method to grow thin films which are highly uniform and conformal over large and complex substrate areas. Film growth in ALD is precise, remarkably repeatable, and combined with unparalleled control of the film thickness. These inherent properties make ALD an attractive method to deposit thin films for advanced technological applications such as microelectronics and nanotechnology. One material group in ALD which has matured in ten years and proven to be of wide technological importance is noble metals. The purpose of this study was to investigate noble metal oxide film growth by ALD. The ALD of noble metal oxides has been very limited compared to the noble metal growth. Another aim was to examine noble metal film deposition at temperatures lower than required in the earlier ALD noble metal processes. In addition, the selection of noble metals that can be grown by ALD was expanded with osmium. The results of the study showed that oxides of iridium, rhodium, platinum, and palladium can be deposited from the common noble metal precursors using ozone as the reactant at temperatures below 200 °C. The development of ozone-based ALD noble metal oxide processes led further on to the low temperature deposition of noble metals by adding a reductive molecular hydrogen step after every oxidative ozone step. The noble metal deposition via noble metal oxide growth was achieved at lower temperatures than required with the common oxygen-based ALD noble metal processes. Film growth rates, resistivities, purities, and surface roughnesses resulting from the studied noble metal oxide and noble metal processes were reasonable. The processes showed some shortcomings but offer an alternative thermal ALD pathway to deposit noble metals and noble metal oxides compared to the oxygen-based ALD processes. Keywords: atomic layer deposition, ALD, noble metal oxide, noble metal, thin film, ozone
  • Aaltonen, Titta (Helsingin yliopisto, 2005)
  • Tolvanen, Antti (Helsingin yliopisto, 2010)
    Carbon nanotubes, seamless cylinders made from carbon atoms, have outstanding characteristics: inherent nano-size, record-high Young’s modulus, high thermal stability and chemical inertness. They also have extraordinary electronic properties: in addition to extremely high conductance, they can be both metals and semiconductors without any external doping, just due to minute changes in the arrangements of atoms. As traditional silicon-based devices are reaching the level of miniaturisation where leakage currents become a problem, these properties make nanotubes a promising material for applications in nanoelectronics. However, several obstacles must be overcome for the development of nanotube-based nanoelectronics. One of them is the ability to modify locally the electronic structure of carbon nanotubes and create reliable interconnects between nanotubes and metal contacts which likely can be used for integration of the nanotubes in macroscopic electronic devices. In this thesis, the possibility of using ion and electron irradiation as a tool to introduce defects in nanotubes in a controllable manner and to achieve these goals is explored. Defects are known to modify the electronic properties of carbon nanotubes. Some defects are always present in pristine nanotubes, and naturally are introduced during irradiation. Obviously, their density can be controlled by irradiation dose. Since different types of defects have very different effects on the conductivity, knowledge of their abundance as induced by ion irradiation is central for controlling the conductivity. In this thesis, the response of single walled carbon nanotubes to ion irradiation is studied. It is shown that, indeed, by energy selective irradiation the conductance can be controlled. Not only the conductivity, but the local electronic structure of single walled carbon nanotubes can be changed by the defects. The presented studies show a variety of changes in the electronic structures of semiconducting single walled nanotubes, varying from individual new states in the band gap to changes in the band gap width. The extensive simulation results for various types of defect make it possible to unequivocally identify defects in single walled carbon nanotubes by combining electronic structure calculations and scanning tunneling spectroscopy, offering a reference data for a wide scientific community of researchers studying nanotubes with surface probe microscopy methods. In electronics applications, carbon nanotubes have to be interconnected to the macroscopic world via metal contacts. Interactions between the nanotubes and metal particles are also essential for nanotube synthesis, as single walled nanotubes are always grown from metal catalyst particles. In this thesis, both growth and creation of nanotube-metal nanoparticle interconnects driven by electron irradiation is studied. Surface curvature and the size of metal nanoparticles is demonstrated to determine the local carbon solubility in these particles. As for nanotube-metal contacts, previous experiments have proved the possibility to create junctions between carbon nanotubes and metal nanoparticles under irradiation in a transmission electron microscope. In this thesis, the microscopic mechanism of junction formation is studied by atomistic simulations carried out at various levels of sophistication. It is shown that structural defects created by the electron beam and efficient reconstruction of the nanotube atomic network, inherently related to the nanometer size and quasi-one dimensional structure of nanotubes, are the driving force for junction formation. Thus, the results of this thesis not only address practical aspects of irradiation-mediated engineering of nanosystems, but also contribute to our understanding of the behaviour of point defects in low-dimensional nanoscale materials.
  • Åhlgren, Elina Harriet (2012)
    Graphene is the ultimately thin membrane composed of carbon atoms, for which future possibilities vary from desalinating sea water to fast electronics. When studying the properties of this material, molecular dynamics has proven to be a reliable way to simulate the effects of ion irradiation of graphene. As ion beam irradiation can be used to introduce defects into a membrane, it can also be used to add substitutional impurities and adatoms into the structure. In the first study introduced in this thesis, I presented results of doping graphene with boron and nitrogen. The most important message of this study was that doping of graphene with ion beam is possible and can be applied not only to bulk targets but also to a only one atomic layer thick sheet of carbon atoms. Another important result was that different defect types have characteristic energy ranges that differ from each other. Because of this, it is possible to control the defect types created during the irradiation by varying the ion energy. The optimum energy for creating a substitution for N ion is at about 50 eV (55%) and for B ion it is ca. 40% at about the same energy. Single vacancies are most probably created at an energy of about 125 eV for N (55%) and for B at ca. 180 eV (35%). For double vacancies, the maximum probabilities are roughly at 110 eV for N (16%) and at 70 eV for B (6%). The probabilities for adatoms are the highest at very small energies. A one atom thick graphene membrane is reportedly impermeable to standard gases. Hence, graphene's selectivity for gas molecules trying to pass through the membrane is determined only by the size of the defects and vacancies in the membrane. Gas separation using graphene membranes requires knowledge of the properties of defected graphene structures. In this thesis, I presented results of the accumulation of damage on graphene by ion irradiation using MD simulations. According to our results, graphene can withstand up to 35% vacancy concentrations without breakage of the material. Also, a simple model was introduced to predict the influence of the irradiation during the experiments. In addition to the specific results regarding ion irradiation manipulation of graphene, this work shows that MD is a valuable tool for material research, providing information on atomic scale rarely accessible for experimental research, e.g., during irradiation. Using realistic interatomic potentials MD provides a computational microscope helping to understand how materials behave at the atomic level.
  • Ullah, Mohammad Wali (Helsingin yliopisto, 2014)
    Gallium nitride (GaN) has emerged as one of the most important semiconductors in modern technology. GaN-based device technology was mainly pushed forward by invention of p-type doping and the successful fabrication of light emitting diodes (LEDs) and laser diodes (LDs). Intensive studies in the last 20 years on GaN have significantly advanced the understanding of the properties and have expanded the range of practical applications. Beside basic lighting, current applications of GaN include high-power and high temperature electronics, microwave, optoelectronic devices, and so on. The successful production of optical devices demands efficient tuning of charge carrier lifetime where defect engineering plays a vital role. During growth, varying the level of recombination centers is difficult, whereas ion irradiation can do this job efficiently on a final product. On the other hand, during doping, undesirable defects can also be produced and epitaxial GaN is known to have a highly defective structure. Thus, having both positive and negative aspects, it is very important to have a detailed understanding of irradiation-induced defects. To explain experimental findings, atomic level understanding is necessary, but it is not always possible to have an atomistic view of defect dynamics in experiments. Some damage build-up studies by single ions have been reported in the literature, but not many by molecular ions. In this thesis, the irradiation of GaN by single and molecular ions by the means of atomistic simulations was studied. Detailed analysis mainly of what kind of defects, their distribution, reason of defect formation and time evolution have been studied and compared with experiments. The irradiation response of both bulk and nano-structured GaN system were studied. For bulk studies, all projectiles were irradiated having the same energy per mass. The damage by molecular ions showed strong dynamic annealing. No non-linearity had been observed in the total number of point defects between single and molecular ions. On the other hand, molecular ions produce larger clusters of point defects than single ions. These large defect clusters can be one of the mechanisms of the experimentally observed faster carrier decay time for molecular projectiles. Defects were mostly concentrated at the surface and near surface regions, which is also evident from experiments. Comparison between a similar mass single ion and a molecular ion show that a single ion produced more defect clusters than molecular ions. This suggests that heavy ions are even more efficient than similar mass cluster ions to quench the carrier lifetime. Irradiation of a GaN nanowire (NW) reveals that a large surface to volume ratio promotes high density of surface defects. The experimentally observed yellow luminescence band is correlated with these defect induced surface states. Irradiation induced defects also expand the lattice parameters of the NW.
  • Lasa Esquisabel, Ane (Helsingin yliopisto, 2014)
    The world's energy demand and harmful green-house gas emissions are continuously increasing, while the fossil fuel reservoir may soon end. Currently, there is no clear alternative to the traditional energy production methods for a safe and clean future. Fusion could be part of the solution offering a green-house gas free, virtually endless, safe and large scale energy production. A major challenge for fusion is, however, to produce more energy than needed to achieve and maintain the fusion reaction. The most feasible fusion reaction is based on two hydrogen isotopes: deuterium and tritium, which fuse to produce a helium atom and a neutron. For these atoms to fuse, they must overcome the repulsive interaction between them, requiring extreme temperatures. Thus, the particles ionize forming gas plasma. On Earth, this condition can only be met by isolating the plasma from its environment, for instance, by using closed magnetic fields to form a torus-like shaped plasma, also known as tokamak. However, the plasma particles will interact with the reactor walls as their confinement is never perfect, the exhausted plasma must leave the reactor and impurities are introduced in the plasma boundary to control its characteristics. The plasma-wall interactions are especially intense at the divertor, where the plasma is designed to touch the wall. Understanding these processes is essential to develop safe, long-lasting materials and to avoid contaminating the plasma fuel. The main candidates as first wall materials in future fusion reactors are beryllium for the main wall, and tungsten and carbon for the divertor. Also, the materials may mix due to wall erosion, transport of the eroded particles and their deposition in a new location. Plasma-wall interactions can be studied in current experimental reactors or in linear plasma devices. However, this work is often insufficient to understand the underlying mechanisms. Further, the effects of plasma-wall interactions in materials develop in a wide range of time and length scales. Multi scale modelling is a tool that allows to overcome these challenges, improving the predictions for future fusion reactors. In this thesis, the plasma wall interactions taking place in a fusion reactors divertor have been studied by computational means. The interaction of pure and mixed divertor materials, with plasma and impurity particles were modelled. The work was mainly based on atomistic scale calculations, and a Kinetic Monte Carlo algorithm has also been developed to extend the results to macroscopic scales, enabling a direct comparison with experiments. First, deuterium irradiation of various W-C composites has been modelled, focusing on deuterium implantation, variations of the substrate composition and C erosion mechanisms. Carbon was preferentially eroded, varying the substrate's composition throughout the irradiation. The presence of carbon also affected the D implantation characteristics. As carbon became less likely to be an ITER first wall material, the present work focused on the tungsten-beryllium-deuterium system. The tungsten-beryllium mixing showed a strong dependence on irradiation energy and angle. Further, the presence of Be led to higher fuel implantation and W erosion was suppressed by mixed layer formation. The obtained yields were compared to Binary Collision Approximation results, in order to improve the description of the latter method. Furthermore, an unexpected and possibly harmful phenomenon has been addressed in this thesis: porous nano-morphology formation in tungsten by helium plasma exposure. First, the main characteristics and active mechanisms in the system were identified by atomistic simulations. Then, the porous morphology growth was modelled by implementing these processes in a Kinetic Monte Carlo code, resulting in rates that agreed with experimental findings. A morphology growth model was derived where the time dependence is driven by the evolution of the surface roughness, which is a stochastic process and thus evolves as the square root of time.
  • Parviainen, Stefan (Helsingin yliopisto, 2014)
    Modern society runs largely on electricity, and where there is electricity there are electric fields. As the boundaries of technology are pushed forward, stronger and stronger electric fields are either required, or appear due to unwanted effects. Examples of such applications, where very high electric fields are utilised include particle accelerators and atom probes. To further be able to improve on such techniques, it is necessary to gain a good understanding of the processes that are involved. Because it is often difficult, if not impossible, to observe these processes with high resolution in experiments, one needs to consider the use of atomistic simulations instead. This thesis provides an extension to classical molecular dynamics by describing an implementation where several electronic effects are considered when dealing with metal surfaces under high electric fields. These effects include the charging of surface atoms, field electron emission and the resulting resistive heating, as well as field evaporation of both neutral and charged atoms. In addition to the implementation details, the thesis also contains a brief background of the physics involved in these processes. Using the implementation, it is observed that a surface protrusion may grow on an initially flat surface in the presence of a near-surface void when a strong external electric field is applied. The growth is very rapid, resulting finally catastrophic breakage. This mechanism may explain the appearance of field emitters on otherwise pristine samples, and the instability of measured field emission currents. Simulations also reveal that high aspect ratio protrusions are subject to Rayleigh instability due to the temperature rise caused by field electron emission currents. As a result a large fraction of the protrusion can break off. The model also allows for the study of the trajectories of field evaporated ions from a surface, as they are accelerated in the electric field. From the simulations we see that even changes in the surface morphology on the atomic scale may result in aberrations in atom probe tomography experiments.
  • Leino, Aleksi (Helsingin yliopisto, 2015)
    Ions in the keV energy range are regularly used in the semiconductor industry for device fabrication. Irradiation with ions of higher energies can also induce favorable structural changes in the irradiated samples. Among these, irradiation effects of the so-called swift heavy ions (SHIs, heavy ions with specific energies in the 1 MeV / amu range) in electrically insulating materials are particularly interesting. Despite the wide range of existing applications (filters, printed circuit boards and geological dating) and application potential (fuel cells, cell mimicking membranes) of SHI irradiation, the mechanisms by which SHIs interact with insulators are still under debate. Modelling of SHIs is a very challenging task as, contrary to ions with lower energies, they mostly interact with electrons, inducing lots of electronic excitations. Incorporating the latter with atomistic dynamics is especially difficult in insulators, and the methods have not yet been fully established. SHIs can induce a cylindrical region of structural transformation known as an ion track. In crystalline silicon dioxide, a track consists of an amorphized region that is typically several microns long and has a radius of less than ten nanometers. Furthermore, it was recently found out that SHI irradiation can be used to induce a shape transformation in metal nanoclusters (NCs) that are embedded in amorphous silicon dioxide. Spherical NCs (radius 1-50 nm) elongate along the ion beam direction and are shaped into nanorods or prolate spheroids. The phenomenon can be exploited to produce large arrays of equally aligned nanoclusters within a solid substrate, which is difficult to achieve otherwise. In this thesis, ion track formation and the elongation of gold nanoclusters in silicon dioxide are studied using so called two-temperature molecular dynamics simulations. The structure of the tracks is studied and a mechanism is proposed for the nanoparticle elongation effect. The work presented here is a step towards the understanding of SHI related effects in a broader range of insulating materials for the SHI based applications.
  • Paloheimo, Marja Riitta (2000)
    Tutkielma käsittelee Suomen ensimmäisen ydinvoimalan hankintaprosessia poliittisena kysymyksenä. Atomiasiassa soudettiin ja huovattiin 1965-1969. Tutkielman tavoitteena on selvittää, miksi päätöksen tekeminen kesti niin kauan, mikä oli presidentti Urho Kekkosen rooli hankinnassa, liittyikö hankinta suomettumiseksi kutsuttuun ilmiöön sekä, mitkä tekijät lopulta ratkaisivat tilauksen. Imatran Voima Osakeyhtiö (IVO) käynnisti ensimmäisen tarjouskierroksen ydinvoimalan hankkimiseksi vuonna 1965. Samoihin aikoihin myös Suomen teollisuuden edustajat pohtivat omassa piirissään ydinvoiman rakentamismahdollisuuksia. Valtioneuvosto ei kuitenkaan hyväksynyt IVOn edullisimmaksi toteamaa vaihtoehtoa, saksalaista AEG:tä, vaan päätti jättää laitoksen tilaamatta saatujen tarjousten perusteella keväällä 1967. Jotta asiassa päästäisiin uudelleen liikkeelle, valtioneuvosto tilasi teollisuuden edustajista koostuneelta Suomen Atomiteollisuusryhmältä tutkimuksen, jossa selvitettiin teollisuuden mahdollisuuksia osallistua IVOn ydinvoimalan rakentamiseen. Vaikka asiaa ei julkisuudessa mainostettukaan, käytännössä tästä alkoi toinen tarjouskierros. Toisella kierroksella tilauksesta kilpailivat ruotsalainen Asea, englantilainen UKAEA sekä neuvostoliittolainen Technopromexport. Saksalainen vaihtoehto oli jäänyt pois. Tarjouskierroksen liikkeellelähtö oli epäselvä. Ei tiedetty, kuka asiaa johti tai missä oltiin menossa. Tarjoajat eivät kaihtanet keinoja kaupatessaan laitoksiaan, sillä jokaisella mukanaolijalla oli tarve saada tuotteensa myydyksi rajojensa ulkopuolelle referenssilaitokseksi. Suurin myyntitarve oli Neuvostoliitolla. Kesällä 1968 itänaapuri pudotti tarjouksensa hintaa lähes 30 prosenttia, kun se ensin oli saanut suomalaisilta muiden kilpailijoiden hintatiedot. Oltiin taas tilanteessa, jossa valtioneuvoston oli vihellettävä pelin poikki kauppapoliittisen selkkauksen välttämiseksi. Kolmannella kerralla laitoshankintaneuvottelut aloitettiin suoraan Neuvostoliiton kanssa ilman julkisuutta. Muilta tarjoajilta ei enää kysytty. Kesällä 1969 laitos päätettiin tilata Neuvostoliitosta. Tutkielmassa osoitetaan, että Suomi joutui kovan painostuksen kohteeksi asiassa, josta kenelläkään, ei Suomella sen enempää kuin muillakaan, ollut kokemusta. Selkeitä pelisääntöjä ei ollut. Tämä selittää osaltaan pitkään kestänyttä kaupanhierontaa. Presidentti Kekkonen, vaikka osallistui kauppaan välillä aktiivisestikin, ei lopulta tehnyt asiassa päätöstä yksin, kuten dosentti Hannu Rautkallio on esittänyt. Tutkielmassa osoitetaan, että suomalaiset rikkoivat räikeästi reilun pelin sääntöjä kertomalla yhdelle kilpailijalle muiden kilpailijoiden luottamuksella antamia tarjoustietoja. Silti suomettumisesta voidaan puhu kaupan osalta vain tietyiltä osin. Keskeisimpinä lähteinä tutkielmassa on käytetty laitoshankinnan käsittelyyn osallistuneiden ministereiden ja virkamiesten arkistoihin jättämiä muistioita ja kirjeenvaihtoa. Lisäksi lähteenä on käytetty tapahtumiin osallistuneiden muistelmia ja haastatteluita. Sanomalehtiä on käytetty julkisen kuvan ja joidenkin muistelmissa esiintyneiden ajoituksellisten ristiriitojen selvittämiseen. Vaikka poliittisista kuvioista on kirjoitettu lukuisia kirjoja ja artikkeleita, asiaa ei ole selvitetty aikaisemmin historian tutkimuksen keinoin.
  • Margaritis, Mihalitsa (2013)
    Koiran atooppinen dermatiitti (atopic dermatitis, AD) on yleinen ja pitkäaikainen kutiseva inflammatorinen ihosairaus. Sairautta ei voida parantaa, mutta oireita voidaan lievittää. Hoito on pitkäaikainen, usein jopa elinikäinen. Riittävän vasteen saavuttamiseksi joudutaan usein yhdistämään eri hoitoja. Hoitovaihtoehtojen valitsemiseen vaikuttavat hoidon tehokkuuden ja hinnan lisäksi hoidon turvallisuus. Glukokortikoidit tarjoavat tehokkaan ja uudempiin lääkkeisiin verrattuna taloudellisesti edullisen hoitovaihtoehdon. Glukokortikoidien käyttö aiheuttaa omistajissa kuitenkin pelkoa, sillä niiden pitkäaikaiskäytön turvallisuudesta ei ole tehty kattavia tutkimuksia. Kirjallisuuskatsauksen tavoitteena oli koota tärkeimmät koiran AD:n hoitovaihtoehdot, syventyä glukokortikoidien kliiniseen käyttöön ja selvittää, onko pitkäaikainen systeeminen anti-inflammatorinen glukokortikoidilääkitys turvallista. Koiran AD:n hoidossa ensisijaisesti pyritään välttämään oireita aiheuttavia allergeeneja. Tämä on käytännössä useimmiten vaikeaa tai mahdotonta. Tällöin on suositeltavaa kokeilla siedätyshoitoa, mikäli allergeenit on tunnistettu. Siedätyshoito ei kuitenkaan aina ole riittävä lievittämään oireita, jolloin hoitona voidaan käyttää akuuttia kutinaa ja inflammaatioreaktiota tehokkaasti vähentäviä glukokortikoideja tai kalsineuriini-inhibiittoreita. Antihistamiinit saattavat lisäksi osalla koirista lievittää oireita, mutta ne eivät tehoa akuuttiin kutinaan. Välttämättömillä rasvahapoilla ja ihoa kosteuttavilla tukihoidoilla pyritään parantamaan ihon eheyttä sekä vähentämään allergeenien ja hilseen määrää iholla. Koska AD:sta kärsivillä koirilla ihoinfektiot ovat tavallista yleisempiä, voi desifioivista topikaalisista puhdistusaineista, puhdistuspyyhkeistä tai shampoovalmisteista olla hyötyä. Tarvittaessa yleistyneissä tai syvissä ihoinfektioissa tulee hoitoon kombinoida systeeminen mikrobilääkitys. Liiallisella glukokortikoidien saannilla on lukuisia haittavaikutuksia, jotka on tunnettu jo kymmenien vuosien ajan. Sivuvaikutukset koirilla ovat moninaisia ja vaihtelevat lievistä vakaviin. Sivuvaikutusten riski kasvaa annoksen kasvaessa ja hoidon pitkittyessä sekä käytettäessä voimakkaampia valmisteita, mutta joitakin sivuvaikutuksia tavataan myös anti-inflammatorisella annoksella. Anti-inflammatoriseen glukokortikoidihoitoon keskittyviä kattavia turvallisuustutkimuksia on kuitenkin hyvin vähän ja tutkimustulokset ovat osittain ristiriitaisia. Lisäksi suurimmassa osassa tutkimuksia sivuvaikutuksia on tutkittu ihmisillä, joten tuloksia ei voida suoraan yleistää koiriin. Lopullisia johtopäätöksiä pitkäaikaisen anti-inflammatorisen glukokortikoidihoidon ja monien sivuvaikutusten välisistä yhteyksistä on vaikea tehdä. Täysin turvallisesta minimiannoksesta tai hoidon kestosta ei ole näyttöä, minkä vuoksi tulisi aina käyttää matalinta tehokasta annosta. Pitkäaikaisen anti-inflammatorisen glukokortikoidilääkityksen aiheuttamista vakavista haittavaikutuksista ei kuitenkaan vaikuta olevan selkeää näyttöä koirilla. Tutkimustulokset viittaavat siihen, ettei pitkäaikainen anti-inflammatorinen glukokortikoidihoito aiheuta dramaattisia sivuvaikutuksia ja että hoitoon liittyvä pelko saattaa olla liioiteltu.
  • Kauppinen, Jari (Helsingin yliopisto, 2000)
  • Lahelma, Antti (Suomen Muinaismuistoyhdistys r.y, 2008)
    Approximately 125 prehistoric rock paintings have been found in the modern territory of Finland. The paintings were done with red ochre and are almost without exception located on steep lakeshore cliffs associated with ancient water routes. Most of the sites are found in the central and eastern parts of the country, especially on the shores of Lakes Päijänne and Saimaa. Using shore displacement chronology, the art has been dated to ca. 5000 – 1500 BC. It was thus created mainly during the Stone Age and can be associated with the so-called ‘Comb Ware’ cultures of the Subneolithic period. The range of motifs is rather limited, consisting mainly of schematic depictions of stick-figure humans, elks, boats, handprints and geometric signs. Few paintings include any evidence of narrative scenes, making their interpretation a rather difficult task. In Finnish archaeological literature, the paintings have traditionally been associated with ’sympathetic’ hunting magic, or the belief that the ritual shooting of the painted animals would increase hunting luck. Some writers have also suggested totemistic and shamanistic readings of the art. This dissertation is a critical review of the interpretations offered of Finnish rock art and an exploration of the potentials of archaeological and ethnographic research in increasing our knowledge of its meaning. Methods used include ’formal’ approaches such as archaeological excavation, landscape analysis and the application of neuropsychological research to the study of rock art, as well as ethnographically ’informed’ approaches that make use of Saami and Baltic Finnish ethnohistorical sources in interpretation. In conclusion, it is argued that although North European hunter-gatherer rock art is often thought to lie beyond the reach of ‘informed’ knowledge, the exceptional continuity of prehistoric settlement in Finland validates the informed approach in the interpretation of Finnish rock paintings. The art can be confidently associated with shamanism of the kind still practiced by the Saami of Northern Fennoscandia in the historical period. Evidence of similar shamanistic practices, concepts and cosmology are also found in traditional Finnish-Karelian epic poetry. Previous readings of the art based on ‘hunting magic’ and totemism are rejected. Most of the paintings appear to depict experiences of falling into a trance, of shamanic metamorphosis and trance journeys, and of ‘spirit helper’ beings comparable to those employed by the Saami shaman (noaidi). As demonstrated by the results of an excavation at the rock painting of Valkeisaari, the painted cliffs themselves find a close parallel in the Saami cult of the 'sieidi', or sacred cliffs and boulders worshipped as expressing a supernatural power. Like the Saami, the prehistoric inhabitants of the Finnish Lake Region seem to have believed that certain cliffs were ’alive’ and inhabited by the spirit helpers of the shaman. The rock paintings can thus be associated with shamanic vision quests, and the making of ‘art’ with an effort to socialize the other members of the community, especially the ritual specialists, with trance visions. However, the paintings were not merely to be looked at. The red ochre handprints pressed on images of elks, as well as the fact that many paintings appear ’smeared’, indicate that they were also to be touched – perhaps in order to tap into the supernatural potency inherent in the cliff and in the paintings of spirit animals.
  • Myllymäki, Tuija (1992)
    Supistuessaan lihassolu käyttää energianlähteenä ATP:a, jonka konsentraatio lihaksessa siten laskee rasituksen aikana. Samalla kertyy ATP:n hajoamistuotteita lihakseen ja verenkiertoon. Tässä tutkimuksessa selvitettiin, mika näista hajoamistuotteista sopisi parhaiten rasituksen voimakkuuden mittaamiseen hevosella. Tutkimuksessa määritetään lämminveristen ravihevosten plasmasta ATP:n pilkkoutuessa syntyvien puriinien (hypoksantiini ja virtsahappo) sekä niiden lopullisen hajoamistuotteen allantoiinin konsentraatioita rasituksen aikana ja sen jälkeen. Lihassyykoostumuksen vaikutusta hypoksantiinin, virtsahapon ja allantoiinin konsentraatioihin tutkittiin vertailemalla suomenhevosia ja lämminverisiä kaskenaan. Tiedetään, että kylmäverisellä hevosella on enemmän hitaita aerobisesti energiansa muodostavia lihassoluja kuin lämminverisellä. Kontrolloidussa rasitustestissä juoksumatolla hypoksantiini- ja virtsahappokonsentraatiot eivät muuttuneet merkitsevästi. Kaikilla hevosilla korkeimmat konsentraatiot saavutettiin rasituksen lopettamisen jälkeen. Allantoiinikonsentraation nousu korreloi lineaarisesti sydänfrekvenssin nousuun ja oli merkittävästi korkeampi rasituksen jälkeen kuin leponäytteissä. Yksilöllinen vaihtelu ajassa, jossa korkein konsentraatio saavutettiin, oli pienempi allantoiinilla kuin hypoksantiinilla tai virtsahapolla. Ravikilpailujen jälkeen otetuissa näytteissä hypoksantiini-, virtsahappo- ja allantoiini- konsentraatiot olivat merkittävästi korkeampia lämminverisillä kuin suomenhevosilla. Rotujen väliset erot konsentraatioissa johtuvat todennäköisesti erilaisesta lihassyykoostumuksesta. Hypoksantiini- ja virtsahappokonsentraatio nousi osalla hevosista molemmilla roduilla vielä 30 minuuttia kilpailun jälkeen. Allantoiinikonsentraatio ei yhdellakään hevosella ollut 30 minuutin näytteessä korkeampi kuin 15 minuutin näytteessä. Sekä hypoksantiinilla, virtsahapolla seka mahdollisesti myös allantoiinilla rasituksen voimakkuus vaikutti konsentraatiohuipun esiintymisaikaan, joka piteni rasituksen koventuessa. Tulosten perusteella allantoiini sopii hypoksantiinia ja virtsahappoa paremmin rasituksen voimakkuuden ja ATP hävion osoittamiseen hevosella.
  • Pakarinen, Sami (Helsingin yliopisto, 2013)
    Dual chamber pacing can be employed to restore atrioventricular synchrony in patients with heart block; and chronotropic incompetence and sinus bradycardia in those with sinus node dysfunction (SND). The focus of this thesis is the feasibility and consequences of proper atrial sensing and pacing to atrioventricular (AV) synchrony in dual chamber pacing. With isolated AV block showed that single lead VDD pacing (single pass ventricular lead with a dual chamber electrode system) can be an alternative to standard dual chamber pacing systems. Adequate sinus-driven atrial rate and no history of paroxysmal atrial fibrillation or cardiac enlargement predict reasonably good long-term maintenance of the VDD pacing mode in elderly patients treated for heart block. Retrograde atrial waves can be discriminated from sinus waves in many patients by using a high sampling rate and algorithms for digital signal processing with data collected by a pacemaker (PM). This approach could enhance the capability of future devices to adapt their stimulation to the spontaneous heart rhythm and improve the collection of diagnostic information on arrhythmias. Atrial tachyarrhythmia (AT) sensing algorithms incorporated in a state-of-the art DDDR (dual lead atrioventricular pacing) pacemaker can accurately identify patients who develop ATs. However transient undersensing of continuous atrial fibrillation (AF) and failure to detect very short episodes ATs can occur frequently, despite the use of refined detection algorithms. With a fixed long AV delay in DDDR pacing as in this study, temporal disruption of AV synchrony and inappropriate mode switch (MS) due to repetitive non-reentrant ventriculo-atrial synchronous rhythm (RNRVAS) is relatively common with SND patients (in 25%) in the presence of retrograde VA conduction. An advanced atrio ventricular search hysteresis (AVSH) algorithm reduced incidence of unnecessary ventricular pacing in the majority of SND patients with both intact and impaired AV conduction and in patients with intermittent AV block, regardless of the lead positions in the right atrium and the ventricle. The avoidance of possible harmful right ventricular (RV) pacing with used state of art AVSH algorithm was not associated with unphysiological over-long AV delays. In conclusion, proper atrial detection and timing for atrioventricular pacing is also feasible in the long-term with contemporary clinical pacing. With appropriate programming, these devices may contribute to the avoidance of possible adverse consequences like congestive heart failure, atrial fibrillation and unwanted harmful symptoms. In future devices with digital signal processing the detection of atrial signals can be further improved.
  • Jurkko, Raija (Helsingin yliopisto, 2009)
    Atrial fibrillation (AF) is the most common tachyarrhythmia and is associated with substantial morbidity, increased mortality and cost. The treatment modalities of AF have increased, but results are still far from optimal. More individualized therapy may be beneficial. Aiming for this calls improved diagnostics. Aim of this study was to find non-invasive parameters obtained during sinus rhythm reflecting electrophysiological patterns related to propensity to AF and particularly to AF occurring without any associated heart disease, lone AF. Overall 240 subjects were enrolled, 136 patients with paroxysmal lone AF and 104 controls (mean age 45 years, 75% males). Signal measurements were performed by non-invasive magnetocardiography (MCG) and by invasive electroanatomic mapping (EAM). High-pass filtering techniques and a new method based on a surface gradient technique were adapted to analyze atrial MCG signal. The EAM was used to elucidate atrial activation in patients and as a reference for MCG. The results showed that MCG mapping is an accurate method to detect atrial electrophysiologic properties. In lone paroxysmal AF, duration of the atrial depolarization complex was marginally prolonged. The difference was more obvious in women and was also related to interatrial conduction patterns. In the focal type of AF (75%), the root mean square (RMS) amplitudes of the atrial signal were normal, but in AF without demonstrable triggers the late atrial RMS amplitudes were reduced. In addition, the atrial characteristics tended to remain similar even when examined several years after the first AF episodes. The intra-atrial recordings confirmed the occurrence of three distinct sites of electrical connection from right to left atrium (LA): the Bachmann bundle (BB), the margin of the fossa ovalis (FO), and the coronary sinus ostial area (CS). The propagation of atrial signal could also be evaluated non-invasively. Three MCG atrial wave types were identified, each of which represented a distinct interatrial activation pattern. In conclusion, in paroxysmal lone AF, active focal triggers are common, atrial depolarization is slightly prolonged, but with a normal amplitude, and the arrhythmia does not necessarily lead to electrical or mechanical dysfunction of the atria. In women the prolongation of atrial depolarization is more obvious. This may be related to gender differences in presentation of AF. A significant minority of patients with lone AF lack frequent focal triggers, and in them, the late atrial signal amplitude is reduced, possibly signifying a wider degenerative process in the LA. In lone AF, natural impulse propagation to LA during sinus rhythm goes through one or more of the principal pathways described. The BB is the most common route, but in one-third, the earliest LA activation occurs outside the BB. Susceptibility to paroxysmal lone AF is associated with propagation of the atrial signal via the margin of the FO or via multiple pathways. When conduction occurs via the BB, it is related with prolonged atrial activation. Thus, altered and alternative conduction pathways may contribute to pathogenesis of lone AF. There is growing evidence of variability in genesis of AF also within lone paroxysmal AF. Present study suggests that this variation may be reflected in cardiac signal pattern. Recognizing the distinct signal profiles may assist in understanding the pathogenesis of AF and identifying subgroups for patient-tailored therapy.