Faculty of Science


Recent Submissions

  • Christopher, Solomon (2020)
    The study of how transmissible an infectious pathogen is and what its main routes of transmission are is key towards management and control of its spread. Some infections which begin with zoonotic or common-source transmission may additionally exhibit potential for direct person-to-person transmission. Methods to discern multiple transmission routes from observed outbreak datasets are thus essential. Features such as partial observation of the outbreak can make such inferences more challenging. This thesis presents a stochastic modelling framework to infer person-to-person transmission using data observed from a completed outbreak in a population of households. The model is specified hierarchically for the processes of transmission and observation. The transmission model specifies the process of acquiring infection from either the environment or infectious household members. This model is governed by two parameters, one for each source of transmission. While in continuous time they are characterised by transmission hazards, in discrete time they are characterised by escape probabilities. The observation model specifies the process of observation of outbreak based on symptom times and serological test results. The observation design is extended to address an ongoing outbreak with censored observation as well as to case-ascertained sampling where households are sampled based on index cases. The model and observation settings are motivated by the typical data from Hepatitis A virus (HAV) outbreaks. Partial observation of the infectious process is due to unobserved infection times, presence of asymptomatic infections and not-fully- sensitive serological test results. Individual-level latent variables are introduced in order to account for partial observation of the process. A data augmented Markov chain Monte Carlo (DA-MCMC) algorithm to estimate the transmission parameters by simultaneously sampling the latent variables is developed. A model comparison using deviance-information criteria (DIC) is formulated to test the presence of direct transmission, which is the primary aim in this thesis. In calculating DIC, the required computations utilise the DA-MCMC algorithm developed for the estimation procedures. \\ The inference methods are tested using simulated outbreak data based on a set of scenarios defined by varying the following: presence of direct transmission, sensitivity and specificity for observation of symptoms, values of the transmission parameters and household size distribution. Simulations are also used for understanding patterns in the distribution of household final sizes by varying the values of the transmission parameters. From the results using simulated outbreaks, DIC6 consistently indicates towards the correct model in almost all simulation scenarios and is robust across all the presented simulation scenarios. Also, the posterior estimates of the transmission parameters using DA- MCMC are fairly consistent with the values used in the simulation. The procedures presented in this thesis are for SEIR epidemic models wherein the latent period is shorter than the incubation period along with presence of asymptomatic infections. These procedures can be directly adapted to infections with similar or simpler natural history. The modelling framework is flexible and can be further extended to include components for vaccination and pathogen genetic sequence data.
  • Elo, Outi (2019)
    The scope of this thesis was to investigate the uptake of the actinide neptunium-237 (237Np) by solid phases of relevance for the disposal of spent nuclear fuel (SNF) in deep, granitic underground repositories. Investigations were performed with the mineral phases corundum (α-Al2O3) and montmorillonite ((Na)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O) as well as with bentonite colloids and crushed Kuru gray granite, which are constituents of the Engineered Barrier System (EBS), and the host-rock, respectively. The uptake of neptunium in the pentavalent oxidation state (NpO2+) by these solid phases was investigated by batch sorption experiments, which provided information about the quantity of neptunium(V) removal from solution as a function of pH, neptunium concentration, and mineral concentration. By repeated exchange of the background electrolyte it was possible to obtain information about the desorption of neptunium(V) from the mineral surfaces, and to gain an insight into the potential re-mobilization of the actinide under flowing-water conditions. As batch sorption and desorption experiments do not provide information about the exact chemical species of neptunium on the mineral surface, the macroscopic sorption experiments were complemented by spectroscopic investigations using Attenuated Fourier Transform Infra-red (ATR FT-IR) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopies. This enabled the extraction of the complex structure and speciation of neptunium on the solid surfaces including bond lengths, neighboring atoms, coordination numbers and the type of surface complex formed on the solid phases, i.e. outer- vs. inner-sphere bound neptunium. Most of the investigations were performed under stagnant conditions, however, due to the role of potential stable and mobile colloids in the subsurface environment and their role as carriers and mobilizers of colloid-borne neptunium with flowing groundwater, additional granite column experiments were conducted in the absence and presence of bentonite colloids. Here, the migration of neptunium through the column was investigated as a function of time, and the role of colloids was evaluated from the obtained breakthrough curves. Under the chosen experimental conditions, colloids were found to have a negligible influence on the neptunium(V) breakthrough behavior, where most of the neptunium(V) was found to migrate through the column without adsorption onto the granitic column material.
  • Jenu, Saana (2019)
    Röntgenkuvaus on tärkeä diagnostinen menetelmä, jonka tuottaman sädeannoksen optimointi on oleellista terveyshaittojen ehkäisemiseksi. Monte Carlo -simulointia ei ole vielä käytetty laajasti röntgenkuvauksen optimointiin, mutta se on potentiaalinen menetelmä. Tämä työ on ensimmäinen askel HUS-Kuvantamisen ja Helsingin yliopiston käyttöön tarkoitetun Monte Carlo -annossimulaattorin kehittämisessä. Simulaattori toteutettiin Geant4-työkalulla, ja se perustui Geant4:n DICOM-ohjelmaan. Ohjelmaa kehitettiin edelleen, ja se testattiin yksittäisellä tietokoneella ja tietokoneklusterilla. Kehityksellä pyrittiin helpottamaan simulaattorin käyttöä ja mahdollistamaan suurten kuvapakkojen käyttö. Olennaisena osana työtä oli myös simulaattorin käytön dokumentointi sekä Monte Carlo -menetelmän kuvaaminen. Työkalu lukee DICOM-muodossa olevat kuvat, minkä perusteella se muodostaa vokseleista koostuvan fantomin. Fantomin vokselit on luokiteltu eri materiaaleiksi HU-lukujen mukaan, jolloin hiukkasten kulkuratoja fantomissa voidaan laskea. Vokselit toimivat myös detektoreina, joihin absorboitunut energia tallennetaan. Simulaattorin jatkokehityksen ja Monte Carlo -menetelmän kuvaamisen lisäksi simulaattoria testattiin keinotekoisilla ja tietokonetomografialaitteen tuottamilla DICOM-kuvilla. Sillä tehtiin kaksi testisimulointia, joissa arvioitiin intensiteettiä vedessä ja absorboitunutta annosta polymetyylimetakrylaatissa eri syvyyksillä. Tuloksia verrattiin teoreettisen intensiteetin vaimenemiseen ja MOSFET-antureilla mitattuun absorboituneeseen annokseen. Toinen simulaatio toistettiin kaupallisella ImpactMC-simulaattorilla. Kahden simuloinnin tulokset poikkesivat referenssidatasta maksimissaan 5 % ja 17 %. Tarkempien tuloksien saamiseksi seuraavissa mittauksissa olisi hyvä käyttää herkempiä annosmittareita kuin nyt käytetyt MOSFET-anturit. Menetelmä, jonka avulla navigoidaan fantomin vokseleissa, on merkittävä sekä tulosten tarkkuuden että simulointinopeuden suhteen. Potentiaalisin menetelmä toimi kuitenkin huonosti klusterilla. Fantomin luomiseen tietokonetomografiakuvista saattaa vaikuttaa kuvien artefakta. Simulaattori vaatii vielä kehittämistä: jatkossa työkalun toimintavarmuutta ja laskentanopeutta klusterilla voidaan parantaa, ja työkaluun on mahdollista rakentaa geometriat eri röntgenmodaliteeteille.
  • Hägele, Miriam (2018)
    Insurance supervision demands that the ruin probability of an insurance company does not exceed a certain level. To compute these ruin probabilities, insurance companies model inter alia the cumulative payout process as a multivariate random walk, where the different components represent different lines of insurance. In particular, in non-life insurance, those random walks can have heavy-tailed increments. Companies are interested in the asymptotic behaviour of multivariate random walks because it provides useful information, such as probability bounds, for ruin probabilities. This licentiate thesis presents different viewpoints on large deviations of such multivariate random walks with subexponentially distributed increments. After introducing the concept of subexponentiality and its main properties, we derive the asymptotic behaviour of a random walk with generalized Weibull distributed increments. This generalized Weibull distribution belongs to the class of stretched exponential distributions, which are heavy-tailed distributions but have finite moments of all orders. Then, we extend subexponentiality to a multivariate setting. Therefore, we define a one-dimensional distribution as the probability that the random vector belongs to a shifted increasing set. Furthermore, we study the asymptotic behaviour of large deviation probabilities of the sum of subexponentially distributed random vectors. We generalize the result for random vectors with independent components to a binomial model and give sufficient conditions for the principle of a single big jump to hold in each component. Finally, we examine the ruin probabilities for multivariate random walks with subexponentially distributed increments. Here, we study a model with discrete time and compute the asymptotic behaviour of the ruin probability.
  • Canarecci, Giovanni (University of Helsinki, 2018)
    The purpose of this study is to analyse two related topics: the Rumin cohomology and the H-orientability in the Heisenberg group H^n. In the first three chapters we carefully describe the Rumin cohomology with particular emphasis at the second order differential operator D, giving examples in the cases n=1 and n=2. We also show the commutation between all Rumin differential operators and the pullback by a contact map and, more generally, describe pushforward and pullback explicitly in different situations. Differential forms can be used to define the notion of orientability; indeed in the fourth chapter we define the H-orientability for H-regular surfaces and we prove that H-orientability implies standard orientability, while the opposite is not always true. Finally we show that, up to one point, a Möbius strip in H^1 is a H-regular surface and we use this fact to prove that there exist H-regular non-H-orientable surfaces, at least in the case n=1. This opens the possibility for an analysis of Heisenberg currents mod 2.
  • Nuottokari, Jaakko (Helsingin yliopisto, 2017)
    Meteorological information and services supporting the various operations of air transport enable a safe, efficient and cost-effective operating environment for airspace users, air navigation service providers and air traffic management. The continuing pursuit towards an improved quality of observation, forecasting and decision support services is driven by an increasingly weather-sensitive society and growing impacts of hazardous weather events. This thesis provides an overview of the field of aeronautical meteorological research by introducing the organisations involved, global and regional strategies, impacts of weather on air transport, current state of the art in meteorological research and decision support systems serving air transport needs with a view of where the field should evolve next. This thesis is an attempt to highlight key findings and point the reader towards the direction of further research on the given topics. Research supporting air transport operations with the optimal use of weather information is a specialized field where advances are led by the needs of various airspace users. Research institutions for example in the United States have contributed greatly due to the severe weather impacts experienced by the National Airspace System (NAS), the ability of the Federal Aviation Administration (FAA) and the National Oceanic and Atmospheric Administration (NOAA) to direct long-term funding to solve specific aviation-related research questions. The creation and maintenance of long-lived teams of scientists and engineers working together to produce end-to-end solutions that meet the needs of the aviation industry is the key to improving meteorological information to aviation users while university research is typically shorter duration and typical does not result in operational systems. From a global perspective, research is yet to be organised in a way that would contribute to solving aviation issues beyond single research projects and/or programmes. There is a lot more the scientific community could do to develop tailored information to decision support systems used by the aviation sector, but it would require systematic investments and the establishment of research groups focusing on the applied science questions and technology transfer. This thesis provides an overview of recommended decision support system development topics with an outline of potential milestones.
  • Karppinen, Sini (University of Helsinki, 2016)
    The theory of transformations groups is the theory of symmetries of a set. Formally, a symmetry of a set is a bijective map from the set to itself. If the set has some kind of mathematical structure, then we are naturally interested in those symmetries which preserve the given structure. For example, the symmetries of a topological space are homeomorphisms. When the transformations of a set form a group, we call the group a transformation group and the set a G-set. We also say that the group G acts on the set X. The study of these groups will reveal a lot about the set itself. In this thesis we are interested in topological transformation groups i.e. the transformation groups of topological spaces.We will, in particular, study the case where the topological space X is completely regular and where the transformation group G is a Lie group. The theory of Lie groups is vast and they have a well-understood structure. Our main goal is to present and prove the so-called slice theorem which is one of the most important results in the theory of transformation groups. A slice in a G-space X characterizes the action of G locally in an invariant neighbourhood of an orbit of X. The slice theorem i.e. the fact that there exists a slice at every point in a G-space X was first proved in the case where G is a compact Lie group. This was done in the 1950s by Gleason, Koszul, Montgomery and Yang and in full generality by Mostow. In order to prove the existence of slices in the case of non-compact Lie groups, the way that G acts needs to somehow be restricted. It turns out that proper action is the right way to do this. The existence of slices for proper actions of noncompact Lie groups was firsst proved by Palais in 1961. Abels and Lütkepohl presented a different kind of proof in 1977. We will present these two proofs in detail and compare them. We will present the machinery needed for the two proofs. The first four chapters are dedicated to the general theory of topological transformation groups, Lie groups and their representations and infinite-dimensional manifolds. Chapter five is dedicated to proper actions. Then in chapter six the two different proofs for the existence of slices for proper actions of non-compact Lie groups arepresented. After the detailed presentations of the proofs, we will compare them in a more general level. We will also present some applications of the slice theorem and consider possible ways to generalize the slice theorem for non-Lie groups.
  • Tiala, Heidi (Helsingin yliopisto, 2017)
    The starting point for the work was to develop a method for covalent binding of phospholipids on fused silica capillaries for capillary electrochromatography (CEC). The method consists of three steps. First, the silanol groups in the fused silica capillary were aminopropylsilylated with 3-(aminopropyl)-triethoxy silane (APTES). Secondly, the product of aminopropylsilylation was allowed to react with glutaraldehyde giving an imidoaldehyde, which further reacted with the primary amino group of phospholipids. The stability of the coating was verified by measuring the electroosmotic flow (EOF) mobility after aminopropylsilylation with APTES and liposome coating. The highest stability of the EOF was obtained using coatings made of liposomes comprising 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS). The EOF remained stable even after injection of a large number of analytes. The tested phospholipids were selected to mimic biological membranes. In the coating procedure the following phospholipids were used: POPC, 1,2-didodecanoyl-sn-glycero-3-phosphate (DLPA), 1,2-didodecanoyl-sn-glycero-3-phosphoethanolamine (DLPE), and POPS. Primary amino groups were needed for stable covalent binding of liposomes to the fused silica capillary wall. The phospholipids POPC and POPS contained primary amino groups. The highest stability of the covalent binding was achieved using liposome dispersions of 3 mM POPC/POPS 80/20 mol-% but the retention factors for aldosterone, testosterone, and progesterone were higher using a 2 mM POPC/POPS 80/20 mol-% dispersion. The thickness of the liposome layers was measured with quartz crystal microbalance (QCM). The mass of the adsorbed liposomes was higher for the 2 mM POPC/POPS 80/20 mol-% dispersion than for the 3 mM POPC/POPS 80/20 mol-% dispersion, which explained the higher retention factors for the analytes studied. The developed coating method was used to the separation of model steroids by on-line open-tubular CEC mass spectrometry (OT-CEC-MS). The steroids, which are poorly visible or non-visible by UV-detection, could be separated and detected by on-line OT-CEC-MS. Six different type of steroids were separated and detected by this method. There was no ion suppression in the MS due to lipid leakage. The effect of reducing the formed Schiff’s base with sodium borohydride and the impact of liposome composition on the stability of the coating were investigated. NaBH4 treatment did not improve the stability of the EOF, but rather decreased it. The effect of NaBH4 reduction on 40/40/20 mol % POPC/POPS/cholesterol-coated capillaries was also investigated, and the results were similar to those obtained with the 80/20 mol % POPC/POPS-coated capillaries: the stability of the coating was better without NaBH4 treatment. The effect of cholesterol in the phospholipid coating was studied and the results show that cholesterol can well be included in phospholipid coatings covalently attached to silica. 2 mM 40/40/20 mol% POPC/POPS/cholesterol showed greater stability than 2 mM 80/20 mol% POPC/POPS. However, much higher retention factors of aldosterone, testosterone, and progesterone were obtained with 2 mM 80/20 mol % POPC/POPS liposome coatings than with 2 mM 40/40/20 mol% POPC/POPS/cholesterol coatings. This may be due to the fact that cholesterol is likely to increase the rigidity of lipid membranes. Also the stability and robustness of the capillary column was tested by individual injections of a large amount of analytes into the capillary: almost 400 injections were made into the 40/40/20 mol% POPC/POPS/cholesterol coated capillary (different type of drugs). The EOF was stable for over 200 injections.
  • Gilmore, Clifford (Helsingin yliopisto, 2014)
    Linear dynamics is a rapidly evolving area of operator theory, however the only results related to the dynamics of the commutator operators have hitherto been on the characterisation of the hypercyclicity of the left and right multiplication operators. This text introduces the requisite background theory of hypercyclicity before surveying the hypercyclicity of the left and right multiplication operators. It expands on this to prove sufficient conditions for the hypercyclicity of the two-sided multiplication operator. Conditions are established under which the general class of elementary operators are never hypercyclic on Banach algebras and notably it is shown that elementary operators are never hypercyclic on the space of bounded linear operators of the Argyros-Haydon Banach space. In the first main result of this text, large classes of operators for which the induced commutator operators are never hypercyclic on separable Banach ideals are identified. In particular it is proven that commutator operators induced by compact and Riesz operators are never hypercyclic on the ideal of compact operators and that commutator operators are also never hypercyclic on the ideal of compact operators of the Argyros-Haydon Banach space. In the Hilbert space setting it is demonstrated that commutator operators induced by hyponormal operators are never hypercyclic on the ideal of Hilbert-Schmidt operators. In the second main result, nonzero scalar multiples of the backward shift operator on the Hilbert space H is identified as a strong candidate to induce a hypercyclic commutator operator on the separable ideal of compact operators on the separable Hilbert space H. However it is proven that it cannot have a dense orbit and hence is never hypercyclic. This study indicates that the commutator operator typically behaves in a non-hypercyclic fashion and that if they exist, instances of hypercyclic commutator operators are rare.
  • Luisto, Rami (Helsingin yliopisto, 2014)
    The work focuses on the basic properties of BLD-mappings between geometric manifolds. We are especially interested in the limit properties of sequences of BLD-mappings and the regularity properties of the branch sets of BLD-mappings induced by these limit properties. The main result of the thesis shows via topological-metric tools that the locally uniform limit of L-BLD-mappings is an L-BLD-mapping.
  • Tuomisto, Maiju (Helsingin yliopisto, 2015)
    Interest in studying chemistry has decreased among lower secondary school students in Finland. Learning chemistry is challenging: one must move between the macro, sub-micro and symbolic levels of chemistry knowledge and construct models of abstract concepts that cannot be seen. The periodic table is one of these complicated yet useful models. How can we motivate students to learn the periodic table and to use the related skills? Adolescents like to play during their free time. In research literature, educational games are mentioned as one motivational teaching method that improves learning results. The main objectives of this research project were 1) To develop a framework for designing and evaluating chemistry-related educational games to support both learning and teaching at the lower secondary level ; and 2) To develop games for chemistry education to support the learning of the periodic table and the use of related skills. Three different design research projects are included in this licentiate thesis. The theoretical framework for these projects consisted of the theory of design research, the theory of educational games and the theory of the periodic table as a teaching model. Problem analyses conducted as part of the design research projects broadened the theory framework to also cover misconceptions about the contents of the periodic table and quality criteria for educational games. In design challenge 1, a design and evaluation framework for chemistry-related educational card and board games on the lower secondary level was developed. Based on an integrative literature review, the features of high-quality digital and non-digital games were uncovered. The design result was further developed based on these features and the new Finnish National Curriculum Framework 2014. The inter-rater agreement of the developed framework was tested with two educational card games. The calculated Cohen s kappa values (κ = 0.718 and κ = 0.756) indicate that the framework is concordant and working well. In design challenges 2 and 3, two novel card games for teaching the periodic table were developed. These games were called Jaksollisuusdomino (Periodic Table Dominoes) and Kerää kolmikko (Collect the Triad). The games were tested on chemistry teachers. Based on the results, the games were developed further and subjected to the novel design and evaluation framework developed in design challenge 1. The games were found to be of good quality, but some improvements should be made at least in the categories of pre- and post-game evaluation and connection to the macroscopic level. As results of this research, three design solutions were developed. The created design and evaluation framework for educational games works both as a descriptive theory and a prescriptive model for teachers and game developers. Both of the developed card games work as prescriptive models for teachers. All three of the design solutions may also be adapted to other teaching and learning purposes. Keywords: board game, card game, chemistry, design research, education, educational game, elements, evaluation, games, learning game, lower-secondary level, periodic table, teaching method
  • Astuti, Davide Nicola (Helsingin yliopisto, 2014)
    The provision of wireless access to voice and data services experienced an impressive growth of importance during the last 20 years. Most of the Internet applications employ the TCP/IP protocol suite to deliver their services. TCP has been developed to operate in a terrestrial network environment. However, with the rapid rise in wireless communication in recent years, it has become important to adapt TCP to heterogeneous environments that include both wireline networks and Wireless Wide-Area Networks (W-WANs), such as satellite and terrestrial wireless networks, in order to optimize performance. The specific link characteristics of wireless and satellite links, in particular high latencies and frequent frame losses due to bit-corruption, affect performance of transport protocols. TCP suffers because of low bandwidth, long connection set-up times, high latency and error rate, inefficient use of air link capacity. Most of next generation satellite systems utilizes Bandwidth-on-Demand (BoD) mechanisms to efficiently share radio resources among a large number of users. BoD mechanisms often causes additional link delay, which has a detrimental effect on TCP performance. In this thesis, we propose a new TCP/IP-friendly link level protocol, namely Satellite Link Aware Communication Protocol (SLACP) which incorporates a novel error-recovery mechanism aimed at drastically reduce the residual Packet Error Rate (PER) as seen by higher layers without producing significant extra delay. The protocol has been validated with experimental evaluations conducted in a Digital Video Broadcasting-Return Channel System (DVB-RCS) satellite environment, where the BoD technique Demand Assignment Multiple Access (DAMA) is employed to regulate the access to the satellite channel. Cross-layer interactions between link layer and transport layer as well as the impact of BoD mechanisms on TCP dynamics are investigated. Furthermore, experiments using a selected set of state-of-the-art TCP enhancements in conjunction with our TCP/IP-friendly link-level protocol have been carried out. The proposed mechanisms and improvements of the link and transport layer would be relevant for many wireless WAN systems.
  • Kangas, Kaisa (University of Helsinki, 2014)
    We study quasiminimal classes, i.e. abstract elementary classes (AECs) that arise from a quasiminimal pregeometry structure. For these classes, we develop an independence notion, and in particular, a theory of independence in $M^{eq}$. We then generalize Hrushovski's Group Configuration Theorem to our setting. In an attempt to generalize Zariski geometries to the context of quasiminimal classes, we give the axiomatization for Zariski-like structures, and as an application of our group configuration theorem, show that groups can be found in them assuming that the pregeometry obtained from the bounded closure operator is non-trivial. Finally, we study the cover of the multiplicative group of an algebraically closed field and show that it provides an example of a Zariski-like structure.
  • Juntunen, Marianne (University of Helsinki, 2014)
    Chemistry plays an important role in making the future more sustainable and solving the global issues. The curricula, national and international educational strategies, research literature and Finnish chemical industry are all focusing on sustainable development. We need more environmentally literate chemists, chemistry teachers and students – future citizens, who solve the several environmental challenges that face the whole world. The main aim of this study was to design novel methods for teaching sustainable development in chemistry, using inquiry methods, to foster students’ environmental literacy and positive attitudes towards chemistry. Sustainable development is linked to chemistry education through socio-scientific issues, e.g. life-cycle thinking and green chemistry. The theoretical problem-analysis of the design study investigated the approaches, which are of key importance for the study: sustainable development, green chemistry, the life-cycles of different products, environmental literacy, socio- scientific education, and inquiry-based learning. The empirical design phase answered the research questions: 1) What kind of inquiry-based life-cycle thinking promotes sustainable development in chemistry education? 2) How collaboratively developed design solution on life-cycle teaching affects students’ environmental literacy and chemistry attitudes? The research was conducted in chemistry teachers’ in-service training, where the topics were related to the study: sustainable development and chemistry, green chemistry, life-cycle analysis and thinking, environmental literacy, socio- scientific issues, and inquiry-based learning. There, novel methods for teaching inquiry-based life-cycle thinking in chemistry education were developed collaboratively. Chemistry knowledge was connected to the life-cycle of a product or material. The study focused on chemistry teachers’ teaching concepts, the collaboratively developed design solution of those and the upper-secondary school students’ perceptions. The collaborative design involved 21 chemistry teachers and two researchers, who analysed the research data during the years 2010–2012. The goals of the in-service training were planned according to the problem-analysis. The study involved 105 9th grade students. The design research methods included the content analysis of the texts, semi-structured interviews, and quantitative surveys. As the outcome of the empirical design phase, two types of knowledge was generated: 1) novel chemistry teaching concepts for sustainability education using life-cycle thinking and inquiry-based learning methods, and a collaboratively developed design solution, and 2) knowledge about the effects of combining life-cycle thinking and inquiry-based learning on students’ environmental literacy and chemistry attitudes. The validity of the results was examined by researcher and method triangulation. To teach sustainable development, the teachers combined inquiry methods and life-cycle thinking in chemistry in several different ways. They developed 20 novel teaching concepts. The most used concept was an open project work in small groups. In this, the students independently chose a product the life-cycle of which they wanted to investigate. This approach was collaboratively developed into a design solution to teach life-cycle thinking in chemistry. Some of the teachers chose the research focus for their students. There, the investigation tasks included raw materials, consumer products, food or water. The teaching methods in the concepts included making questions, searching and analysing information, forming and presenting results, laboratory experiments, videos, study visits, debate, designing new products, drama, and learning diaries. The design solution, which combined life-cycle thinking and inquiry, increased the students’ societal and environmental ideas. They emphasized the importance of environmental protection and recycling. Most students thought that these types of projects could positively affect the youths’ environmental literacy. The project work positively affected the students’ attitudes towards chemistry. They noticed that one could learn important things about chemistry that are related to the society and everyday life. The students valued the new learning setting, which was independent and social. The method to teach inquiry-based life-cycle thinking in chemistry in this study is a novel example of an inquiry-based approach, which supports versatile studying and citizenship skills, motivates the student to study chemistry and guides the student to take sustainable development into account. The inquiry-based life-cycle thinking is suitable for primary and secondary education, but it can also be applied to other educational levels. The remarks of the theoretical problem- analysis and the results of the empirical design phase can be used for planning chemistry education and chemistry teachers’ education related to the issues of sustainable development.
  • Tuovinen, Riikka (Helsingin yliopisto, 2012)
    Kuuluisa, edelleen avoin, invariantin aliavaruuden ongelma kysyy onko jokaisella rajoitetulla lineaarisella operaattorilla (separoituvassa, ääretönulotteisessa) Hilbertin avaruudessa olemassa ei-triviaalia invarianttia aliavaruutta. Erään lähestymistavan kyseisen ongelman ratkaisuun tarjoavat niin sanotut universaalit operaattorit. Nimittäin, positiivinen vastaus invariantin aliavaruuden ongelmaan on yhtäpitävää sen kanssa, että jonkin universaalin operaattorin kaikki minimaaliset invariantit aliavaruudet ovat yksiulotteisia. Nordgren et al. löysivät artikkelissaan Invertible composition operators on H^p (J. Funct. Anal. 73, 1987, 324--344) klassisessa Hardyn avaruudessa H^2 erään konkreettisen universaalin operaattorin, joka on hyperbolisen kompositio-operaattorin ja sen pistespektriin kuuluvalla luvulla kerrotun identiteettioperaattorin erotus. Näin invariantin aliavaruuden ongelma voitaisiin ratkaista selvittämällä hyperbolisen kompositio-operaattorin invarianttien aliavaruuksien muodostama hila Hardyn avaruudessa H^2 tarpeeksi hyvin. Lisensiaatintutkielmani on yksityiskohtainen selvitys edellä mainitun hyperbolisen kompositio-operaattorin avulla muodostetun operaattorin universaalisuudesta. Tähän tarvitaan laajaa matemaattista koneistoa liittyen mm. sisäfunktioihin (mukaan lukien yksikkökiekon Möbius-kuvaukset ja Blaschken tulot), interpoloiviin jonoihin, spektraali- ja operaattoriteoriaan sekä Rieszin kantoihin.
  • Ojala, Heikki (Helsingin yliopisto, 2011)
    A single molecule is enough to initiate a biological function. Therefore methods to study single biomolecules are important. By measuring one biomolecule at a time it is possible to reveal the differences from molecule to molecule. Moreover, with these methods one can measure short-lived non-equilibrium states of the molecules. An optical tweezers instrument for single molecule experiments was modified to permit constant force experiments. The resulting force-clamp control was then used to measure enzymatic activity of the molecular motor lambda exonuclease at different temperatures. The force-clamp experiments were performed in a dumbbell geometry where two polystyrene spheres are connected by a DNA molecule. A single continuous wave laser source created the dual trap optical tweezers with one stationary and one steerable trap. Acousto-optic deflectors steered the trap according to a digital feedback control from a field programmable gate array. Using the feedback control, at 1.3±0.3 pN force, the lambda exonuclease reaction rate was measured to be 23±16 nt/s at 25±1°C and 54±15 nt/s at 37±1°C. The most important achievement in this thesis was the detected increase in the reaction rate of lambda exonuclease due to the increased temperature. Thus, the real-time force- clamp control opens up new possibilities to study the molecular machinery that generates forces and movements in living organisms.
  • Rosberg, Eira (Helsingin yliopisto, 2012)
    This study examined the field of Finnish Environmental Impact Assessment procedures from years 2000-2008 in Finland. In addition two case studies of critical cases revealed insights into projects and their context. The theoretical background of the research included Popper s philosophy of three worlds: knowledge can be absolute, relative and symbolic. In addition the theory of values and process thinking was utilized. One of the most important findings was that Finnish Environmental Impact Assessment procedures display large regional variation. This variation was obvious in the amount and types of projects in different regions. Furthermore, the duration of procedures as well as the types of competent authorities statements showed regional variation. Variation in the competent authorities opinions indicates that the quality of procedures in Finland also had regional variation. The study also found the EIA process is inconsistent and has regional variation. The knowledge of some key EIA personnel expanded during the procedure, yet for some there can be a conflict in their environmental values. Some practices inhibited learning, which prevented deliberative planning practice and caused a quality risk to planning. Variation in the EIA process complicates the process predictability and can harm trust creation in the temporary project network which causes another quality risk to urban and regional planning. Environmental Impact Assessment procedure is a steering method for society. But it has not developed from a ´toolbox´ level to a systemic level to promote sustainable development in a region. The effects of environmental impact assessments on decision-making, such as land-use planning, environmental permits, the responsible developer s plans and municipal decision-making are guiding, at best. But worse, it can almost paralyze the decision-making process. The weak link between EIA in projects and other processes of urban and regional planning complicates the way in which procedures operate. To conclude, it is important to understand how EIA can better respond to its demands. Rather than following strict protocols, one should focus on the ultimate purpose of the procedure and how the procedure and its results may systemically advance sustainable development in the region. By applying similar protocols one can enhance sustainable development in other regional planning processes in our project-intensive society. Strengthening process and quality thinking does not mean that the procedure should be a mechanistic tool or a strict recipe for implementation. In urban and regional planning one needs communicative and methodical participation and context sensitivity. It is possible to strengthen the quality of planning in a changing context and in project networks, which are of limited duration and temporary organization.
  • Lindén, Greger (Helsingin yliopisto, 1993)
  • Daniel, Laila (Helsingin yliopisto, 2008)
    With the proliferation of wireless and mobile devices equipped with multiple radio interfaces to connect to the Internet, vertical handoff involving different wireless access technologies will enable users to get the best of connectivity and service quality during the lifetime of a TCP connection. A vertical handoff may introduce an abrupt, significant change in the access link characteristics and as a result the end-to-end path characteristics such as the bandwidth and the round-trip time (RTT) of a TCP connection may change considerably. TCP may take several RTTs to adapt to these changes in path characteristics and during this interval there may be packet losses and / or inefficient utilization of the available bandwidth. In this thesis we study the behaviour and performance of TCP in the presence of a vertical handoff. We identify the different handoff scenarios that adversely affect TCP performance. We propose several enhancements to the TCP sender algorithm that are specific to the different handoff scenarios to adapt TCP better to a vertical handoff. Our algorithms are conservative in nature and make use of cross-layer information obtained from the lower layers regarding the characteristics of the access links involved in a handoff. We evaluate the proposed algorithms by extensive simulation of the various handoff scenarios involving access links with a wide range of bandwidth and delay. We show that the proposed algorithms are effective in improving the TCP behaviour in various handoff scenarios and do not adversely affect the performance of TCP in the absence of cross-layer information.
  • Kangasharju, Jaakko (Helsingin yliopisto, 2006)
    In recent years, XML has been accepted as the format of messages for several applications. Prominent examples include SOAP for Web services, XMPP for instant messaging, and RSS and Atom for content syndication. This XML usage is understandable, as the format itself is a well-accepted standard for structured data, and it has excellent support for many popular programming languages, so inventing an application-specific format no longer seems worth the effort. Simultaneously with this XML's rise to prominence there has been an upsurge in the number and capabilities of various mobile devices. These devices are connected through various wireless technologies to larger networks, and a goal of current research is to integrate them seamlessly into these networks. These two developments seem to be at odds with each other. XML as a fully text-based format takes up more processing power and network bandwidth than binary formats would, whereas the battery-powered nature of mobile devices dictates that energy, both in processing and transmitting, be utilized efficiently. This thesis presents the work we have performed to reconcile these two worlds. We present a message transfer service that we have developed to address what we have identified as the three key issues: XML processing at the application level, a more efficient XML serialization format, and the protocol used to transfer messages. Our presentation includes both a high-level architectural view of the whole message transfer service, as well as detailed descriptions of the three new components. These components consist of an API, and an associated data model, for XML processing designed for messaging applications, a binary serialization format for the data model of the API, and a message transfer protocol providing two-way messaging capability with support for client mobility. We also present relevant performance measurements for the service and its components. As a result of this work, we do not consider XML to be inherently incompatible with mobile devices. As the fixed networking world moves toward XML for interoperable data representation, so should the wireless world also do to provide a better-integrated networking infrastructure. However, the problems that XML adoption has touch all of the higher layers of application programming, so instead of concentrating simply on the serialization format we conclude that improvements need to be made in an integrated fashion in all of these layers.

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