Browsing by Title

Sort by: Order: Results:

Now showing items 7303-7322 of 28481
  • Heiskanen, Tiina (1992)
    Tutkimuksen tarkoituksena oli selvittää hevosen nivelnesteen hyaluronihapon ja proteoglyknaanin konsentraatioiden vaihtelua eri artriittitiloissa korkean erotuskyvyn nestekromatografialla (HPLC). Hyaluronihappopitoisuuden muutokset heijastavat nivelen patofysiologista tilaa. Proteoglykaanipitoisuuksien nousun avulla voidaan mahdollisesti diagnosoida rustovauriot jo ennen muiden näkyvien muutosten havaitsemista. Nykyään ainoa menetelmä rustovaurion diagnosointiin on artroskopia. Nivelnesteet analysoitiin pakastuksen jälkeen HPLC-laitteella. Analysointi oli helppoa eikä muita edeltäviä näytteiden käsittelyjä tarvittu kuin sentrifugointi ja laimennus. Tämän puolesta laite sopisi mielestäni erittäin hyvin myös rutiinidiagnostiikkaan. Hyaluronihappopitoisuudet muodostivat samankaltaisen jakauman sekä kontrolli- että potilasnäytteissä. Tämän tutkimuksen mukaan hyaluronihappopitoisuuksien perusteella ei pystytä erottamaan akuutteja eikä kroonisia artriitteja kontrollinivelistä. Proteoglyknanipitoisuuksia ei määritetty sopivan standardiaineen puutteen takia. Tyydyttiin vain toteamaan pystytäänkö ko. laitteella detektoimaan pitoisuuden vaihtelut eri artriittitiloissa. Kaikissa infektiivisissä artriiteissa (5 kpl) todettiin proteoglykaania mutta myös muutamissa muissa artriiteissa sekä jopa kontrollinivelissä. Molempien yhdisteiden konsentraatiovaihteluiden arvostelua vaikeuttaa suuret yksilökohtaiset erot jopa terveiden nivelten välillä. Jatkuvaa perustutkimusta ko. yhdisteiden parissa tarvitaan, jotta menetelmästä saadaan kliinikkojakin hyödyntävä diagnoosimenetelmä.
  • Haapala, Johanna (Helsingin yliopisto, 2015)
    Nopeakasvuinen ja lyhytkuituinen hybridihaapa (Populus tremula L x P. tremuloides Michx) voi tulevaisuudessa osoittautua ekonomisesti merkittäväksi raaka-aineeksi materiaalitekniikan kehittyessä. Tautien sekä muiden mahdollisten viljelyä rajoittavien tekijöiden tarkka tutkiminen on haavan laajempaa käyttöä silmällä pitäen tärkeää. Tutkimuksen tarkoituksena oli selvittää 1) onko hybridihaapakloonien taudinkestävyydessä eroja Venturia tremulae -sienen aiheuttaman haavan mustaversotaudin suhteen, eli onko a) kloonien taudinkestävyydessä ja b) taudin aggressiivisuudessa eroja hybridihaapakloonien välillä, sekä 2) onko Neofabraea populi -sienen aiheuttaman kuoripoltteen aggressiivisuudessa eroja tutkittavien kloonien välillä. Aineisto on kerätty Metsäntutkimuslaitoksen Ruotsinkylän ja Suonenjoen koealoilta vuosina 2004 - 2006. Ruotsinkylässä tutkittiin yhteensä 12 kloonia, ja 1200 puuta, Suonenjoen koealalla oli 10 kloonia ja puita yhteensä 1000 kappaletta. Puista arvioitiin lehtilaikkujen peittävyys, infektoituneiden sivuversojen määrä sekä pääverson vaurioiden vakavuus. myös puiden kasvua seurattiin. Tulosten mukaan hybridihaapakloonit eroavat toisistaan mustaversotaudin kestävyyden osalta. Kun tautia esiintyi paljon, olivat erot merkittäviä. Ruotsinkylän aineiston mukaan kaksi kloonia olivat selkeästi muita kestävämpiä ja kasvuominaisuuksiltaan parempia. Suonenjoella tulokset olivat tasaisempia, mutta myös siellä kestävimmät kloonit kasvoivat parhaiten. Kuoripoltteen osalta puut jakautuvat kahteen ryhmään: niihin jotka pystyivät tarkastelujaksolla rajoittamaan sienen leviämistä ja niihin jotka eivät pystyneet. Kaikissa klooneissa oli taimia jotka pystyivät kontrolloimaan sienen leviämistä, mutta vain kahdessa kloonissa ei ollut yhtäkään taimea, joka olisi kärsinyt vakavista tuhoista. Tutkimuksen tuloksia voi käyttää hybridihaavan jalostukseen etsittäessä parasta viljelymateriaalia käytettäväksi Suomen oloihin. Kuoripoltteen osalta tutkimus antaa ainoastaan kuvan kloonien selviytymisen todennäköisyydestä infektion jälkeen, ja siksi kloonien kestävyyttä sienen taudinaiheuttamiskykyä kohtaan tulisi vielä tutkia.
  • Karesoja, Mikko (Helsingin yliopisto, 2015)
    In this study several inorganic-organic hybrids and multiresponsive hybrid polymers were prepared and characterised in detail. Especially the focus has been on stimuli responsive materials but also on nanocomposites based on modified montmorillonite clay. Furthermore thin SiO2-capillaries were modified for electrophoretic separations. In all cases different controlled radical polymerisation techniques have been used. The modification of montmorillonite clay was conducted by surface initiated atom transfer polymerisation. Clay was grafted with random copolymer of butyl acrylate and methyl methacrylate and the modified clay was further mixed with a matrix polymer with the same chemical composition to create nanocomposite films. The relation of the nanocomposite structure to its mechanical properties was in the main focus. The extent of exfoliation of the clay in the composite films clearly affected mechanical properties. Montmorillonite clay was also grafted with pH- and thermoresponsive poly(2-dimethylaminoethyl methacrylate). The thermoresponsive properties of the resulting hybrid materials were compared to similar homopolymer. The inner walls of thin silica capillaries were grafted with a cationic polymer, poly([2-(methacryloyl)oxyethyl]trimethylammonium chloride) (PMOTAC). These capillaries were further used in capillary electrophoresis to separate standard proteins, different β-blockers and low-density as well as high density lipoproteins. The separation of the analytes was not possible with bare SiO2-capillaries but with polymer coated capillaries good separation of the analytes was achieved. Hybrid materials based on mesoporous silica particles grafted with poly(N-vinylcaprolactam-b-polyethylene oxide) (PVCL-b-PEO) were synthesised. The challenging synthesis of these hybrids was performed as a combination of surface initiated atom transfer polymerisation and click reactions. Thermal behaviour and the colloidal stability of these hybrid particles were studied. The role of the PEO block in the colloidal stability of the particles was crucial. Finally, multiresponsive hybrid block copolymers based on N-vinylcaprolactam and 2-dimethylaminoethyl methacrylate was prepared. The thermal properties of these block copolymers can be tuned by varying the chain length of PVCL block. On the other hand the thermal behaviour of PDMAEMA block is highly dependent on the environmental conditions like pH and ionic strength.
  • Sillanpää, Ilkka (Helsingin yliopisto, 2008)
    In this dissertation we study the interaction between Saturn's moon Titan and the magnetospheric plasma and magnetic field. The method of research is a three-dimensional computer simulation model, that is used to simulate this interaction. The simulation model used is a hybrid model. Hybrid models enable individual tracking or tracing of ions and also take into account the particle motion in the propagation of the electromagnetic fields. The hybrid model has been developed at the Finnish Meteorological Institute. This thesis gives a general description of the effects that the solar wind has on Earth and other planets of our solar system. Planetary satellites can also have similar interactions with the solar wind but also with the plasma flows of planetary magnetospheres. Titan is clearly the largest among the satellites of Saturn and also the only known satellite with a dense atmosphere. It is the atmosphere that makes Titan's plasma interaction with the magnetosphere of Saturn so unique. Nevertheless, comparisons with the plasma interactions of other solar system bodies are valuable. Detecting charged plasma particles requires in situ measurements obtainable through scientific spacecraft. The Cassini mission has been one of the most remarkable international efforts in space science. Since 2004 the measurements and images obtained from instruments onboard the Cassini spacecraft have increased the scientific knowledge of Saturn as well as its satellites and magnetosphere in a way no one was probably able to predict. The current level of science on Titan is practically unthinkable without the Cassini mission. Many of the observations by Cassini instrument teams have influenced this research both the direct measurements of Titan as well as observations of its plasma environment. The theoretical principles of the hybrid modelling approach are presented in connection to the broader context of plasma simulations. The developed hybrid model is described in detail: e.g. the way the equations of the hybrid model are solved is shown explicitly. Several simulation techniques, such as the grid structure and various boundary conditions, are discussed in detail as well. The testing and monitoring of simulation runs is presented as an essential routine when running sophisticated and complex models. Several significant improvements of the model, that are in preparation, are also discussed. A main part of this dissertation are four scientific articles based on the results of the Titan model. The Titan model developed during the course of the Ph.D. research has been shown to be an important tool to understand Titan's plasma interaction. One reason for this is that the structures of the magnetic field around Titan are very much three-dimensional. The simulation results give a general picture of the magnetic fields in the vicinity of Titan. The magnetic fine structure of Titan's wake as seen in the simulations seems connected to Alfvén waves an important wave mode in space plasmas. The particle escape from Titan is also a major part of these studies. Our simulations show a bending or turning of Titan's ionotail that we have shown to be a direct result of the basic principles in plasma physics. Furthermore, the ion flux from the magnetosphere of Saturn into Titan's upper atmosphere has been studied. The modelled ion flux has asymmetries that would likely have a large impact in the heating in different parts of Titan's upper atmosphere.
  • Alho, Markku (2016)
    The localized, crustal magnetic fields on the Moon show complex interactions with the impinging solar wind. Understanding these interactions aid in characterizing the lunar plasma and dust environment, in developing advanced remote imaging techniques for airless bodies such as the Moon and Mercury, and in comprehending the basic plasma processes of plasma environments and phenomena on the Hall physics scale. In this work a lunar magnetic anomaly is modeled in the mesoscale of hundreds of kilometers with 100~nT surface field anomaly. A numerical hybrid plasma model is employed, in which ions are treated as fully kinetic macroparticles, with electrons providing a massless, charge-neutralizing fluid. The effects of electron currents in these environments are discussed, and results of the effect of the interplanetary magnetic field conditions on the minimagnetosphere are presented in three cases: Open, closed, nominal. Results for three different impinging solar wind velocities in the nominal case are presented. The results are compared with satellite observations and are found to reproduce observations of proton deceleration and reflection by anti-moonward electric field. The model is shown to reproduce observed ENA emission from the lunar surface, with predictions on solar wind-depentant features. Model development by the author is presented with regards to the convergence and stability of the numerical scheme, especially in terms of dealing with a fast whistler mode. Considerations on the validity of the results are presented, with the conclusion of reasonable confidence in the results, with suggested improvements to the model brought forwards.
  • Tuunainen, Juha (2004)
    This doctoral thesis focuses on the trajectory of an agricultural plant biotechnology research group and its transformation into a university start-up company under the auspices of a major Finnish university, the University of Helsinki. The data applied in this study consist of 79 interviews and an extensive body of documentary material including scientific publications, research plans and reports, and correspondences. The qualitative analysis of these materials was informed by conceptual resources drawn from several theoretical approaches that have addressed science and the university organization in terms of work and practice (e.g., cultural-historical activity theory, ethnomethodology and symbolic interactionism). On the grounds of the empirical results so achieved, several generalized sociological theories purporting a radical change of science and the university institution are discussed. The main body of the thesis is composed of four research articles, each analyzing a distinctive phase in the agricultural plant biotechnology group’s trajectory. The first article analyzes the construction of research objects in the laboratory and the transformation of experimental systems used at the early stages of the group’s research. The second paper relates to the social world perspective and investigates the complex organizational ecology of disciplines in the university department where the biotechnology group operated. The third paper makes use of the concept of boundary work and deals with the regulation of the emergent spin-off company at the university. Finally, the fourth article unites the empirical results and criticizes the Mode 2 knowledge production thesis and triple helix model of university-industry-government relations. Altogether, the thesis demonstrates the need to see science and universities as complex and contradictory entities whose development is shaped by multiple historical, political and cultural characteristics. It also substantiates the advantages that may be achieved when such developments are addressed in terms of the practice-oriented sociology of science vis-à-vis such generic models as Mode 2 knowledge production, the triple helix of university-industry-government relations, academic capitalism and the enterprise university.
  • Tuunainen, Juha (2004)
    Väitöskirjassa analysoidaan erään Helsingin yliopistossa toimineen, kasvibiotekniikkaa käyttäneen tutkimusryhmän kymmenvuotinen elinkaari ryhmän perustamisesta vuonna 1990 siihen saakka, kun se muuttui tutkimuslähtöiseksi spin-off –yritykseksi vuonna 2000. Tutkimusaineisto koostuu 79 haastattelusta ja laajasta dokumenttiaineistosta, johon kuuluu muun muassa tieteellisiä julkaisuja, tutkimussuunnitelmia ja –raportteja sekä kirjeenvaihtoa. Aineiston laadullisessa analyysissä hyödynnetään useita teoreettisia lähestymistapoja, jotka ovat tarkastelleet tiedettä ja yliopistoja työkäytäntöjen näkökulmasta (esim. kulttuuri-historiallinen toiminnan teoria, etnometodologia ja symbolinen interaktionismi). Näin saatujen tulosten perusteella kommentoidaan joitain sellaisia teorioita, joiden mukaan tiede ja yliopistot olisivat viime aikoina radikaalisti muuttuneet. Väitöskirjan pääosan muodostaa neljä kansainvälisissä lehdissä julkaistua artikkelia, joista kussakin eritellään jotakin tutkimusryhmän elinkaaren vaihetta. Ensimmäisessä artikkelissa tarkastellaan ryhmän laboratoriotyötä ja sitä, kuinka sen käyttämät kokeelliset järjestelmät muuttuivat 1990-luvun alkuvuosina. Toisessa artikkelissa hyödynnetään symboliseen interaktionismiin pohjaavaa sosiaalisten maailmojen näkökulmaa (social world perspective) tieteenalojen välisten konfliktien analysoimiseksi siinä yliopiston laitoksessa, jossa tutkittu ryhmä työskenteli. Kolmannessa artikkelissa tutkitaan sitä, kuinka raja tutkimusryhmän perustaman biotekniikkayrityksen ja yliopistotoiminnan välillä tuotettiin ja kuinka sitä ylläpidettiin 1990-luvun lopussa. Neljäs artikkeli puolestaan kokoaa tutkimuksen empiiriset tulokset yhteen ja kritisoi tältä pohjalta ns. tiedontuotannon mallia 2 (Mode 2 knowledge production) and teesiä yliopistojen, teollisuuden ja valtiovallan kolmoiskierteestä (triple helix). Väitöskirjan mukaan tiede ja yliopisto tulee nähdä monimutkaisina ja sisäisesti ristiriitaisina kokonaisuuksina, joiden kehitykseen vaikuttavat monet historialliset, poliittiset ja kulttuuriset tekijät. Lisäksi väitöskirja osoittaa sen, mitä etua tieteellisten ja organisatoristen käytäntöjen tutkimuksesta on verrattuna sellaisiin geneerisiin malleihin, kuten vaikkapa tiedontuotannon malli 2, yliopistojen, teollisuuden ja valtiovallan kolmoiskierre, akateeminen kapitalismi (academic capitalism) tai yritysyliopisto (enterpreneurial university).
  • Pellinen, Riikka (Helsingin yliopisto, 2001)
  • Lallo, Marko (Helsingin yliopisto, 2010)
    This research has been prompted by an interest in the atmospheric processes of hydrogen. The sources and sinks of hydrogen are important to know, particularly if hydrogen becomes more common as a replacement for fossil fuel in combustion. Hydrogen deposition velocities (vd) were estimated by applying chamber measurements, a radon tracer method and a two-dimensional model. These three approaches were compared with each other to discover the factors affecting the soil uptake rate. A static-closed chamber technique was introduced to determine the hydrogen deposition velocity values in an urban park in Helsinki, and at a rural site at Loppi. A three-day chamber campaign to carry out soil uptake estimation was held at a remote site at Pallas in 2007 and 2008. The atmospheric mixing ratio of molecular hydrogen has also been measured by a continuous method in Helsinki in 2007 - 2008 and at Pallas from 2006 onwards. The mean vd values measured in the chamber experiments in Helsinki and Loppi were between 0.0 and 0.7 mm s-1. The ranges of the results with the radon tracer method and the two-dimensional model were 0.13 - 0.93 mm s-1 and 0.12 - 0.61 mm s-1, respectively, in Helsinki. The vd values in the three-day campaign at Pallas were 0.06 - 0.52 mm s-1 (chamber) and 0.18 - 0.52 mm s-1 (radon tracer method and two-dimensional model). At Kumpula, the radon tracer method and the chamber measurements produced higher vd values than the two-dimensional model. The results of all three methods were close to each other between November and April, except for the chamber results from January to March, while the soil was frozen. The hydrogen deposition velocity values of all three methods were compared with one-week cumulative rain sums. Precipitation increases the soil moisture, which decreases the soil uptake rate. The measurements made in snow seasons showed that a thick snow layer also hindered gas diffusion, lowering the vd values. The H2 vd values were compared to the snow depth. A decaying exponential fit was obtained as a result. During a prolonged drought in summer 2006, soil moisture values were lower than in other summer months between 2005 and 2008. Such conditions were prevailing in summer 2006 when high chamber vd values were measured. The mixing ratio of molecular hydrogen has a seasonal variation. The lowest atmospheric mixing ratios were found in the late autumn when high deposition velocity values were still being measured. The carbon monoxide (CO) mixing ratio was also measured. Hydrogen and carbon monoxide are highly correlated in an urban environment, due to the emissions originating from traffic. After correction for the soil deposition of H2, the slope was 0.49±0.07 ppb (H2) / ppb (CO). Using the corrected hydrogen-to-carbon-monoxide ratio, the total hydrogen load emitted by Helsinki traffic in 2007 was 261 t (H2) a-1. Hydrogen, methane and carbon monoxide are connected with each other through the atmospheric methane oxidation process, in which formaldehyde is produced as an important intermediate. The photochemical degradation of formaldehyde produces hydrogen and carbon monoxide as end products. Examination of back-trajectories revealed long-range transportation of carbon monoxide and methane. The trajectories can be grouped by applying cluster and source analysis methods. Thus natural and anthropogenic emission sources can be separated by analyzing trajectory clusters.
  • Welsh, Shawna (Helsingfors universitet, 2013)
    The largest wetland drainage project in Michigan was initiated in 1912 near the town of Seney in the eastern Upper Peninsula. This project included the construction of a series of drainage ditches intended to prepare the land for agricultural use. The largest of these ditches was the 35 km-long Walsh Ditch. Much of the drained wetland affected by the Walsh Ditch is now managed by the U.S. Fish and Wildlife Service as part of Seney National Wildlife Refuge (Seney NWR). Starting in 2002, a series of earthen ditch plugs were installed along the length of the ditch found within Seney NWR (and adjacent to the Seney Wilderness Area) in an attempt to restore the hydrology and ecological integrity to the affected wetlands and streams. The plugs North of C-3 Pool were completed in 2002. The ditch plugs South of C-3 Pool were completed in 2005. This study explores the effect of the ditch plugs on the hydrology and vegetation structure in the adjacent landscape north of C-3 Pool at multiple scales. Plot level measurements of hydrology and vegetation, combined with an analysis of landcover change over the entire study area, indicate that some areas are converting from artificial upland communities created by wetland drainage to more natural wetland community types. Mortality of upland tree species and colonization by typical wetland species are good indications that these sites will continue to develop into wetland ecosystems over time. However, some areas have shown no response to the hydrologic restoration. This is expected, as areas of the landscape were upland (referred to as “pine islands” in the literature) before Walsh Ditch and should remain so as natural hydrology is restored to the area. Landcover change analysis showed a decrease in open water of 90.82 ha, a decrease of upland area of 67.88 ha and an increase in wetland area of 151.88 ha. The areas of change were concentrated around stream channels and in the area just east of Walsh Ditch. With time, it is possible that areas further removed from the ditch will show a shift towards more natural hydrology and vegetation composition, but for the areas furthest removed from the ditch this may require active management.
  • Salo, Jukka-Pekka K. (Helsingin yliopisto, 2003)