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  • 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 (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 (2014)
    Kemia tieteenalana on suuressa roolissa kestävämmän tulevaisuuden tekijänä ja globaalien ongelmien ratkaisijana. Kestävää kehitystä ja eettiseen vastuullisuuteen kasvattamista painotetaan opetussuunnitelmien perusteissa, kansallisissa ja kansainvälisissä opetusalan strategioissa, kemian opetuksen tutkimuskirjallisuudessa ja Suomen kemianteollisuudessa. Tarvitaan lisää ympäristötietoisia kemistejä, kemian opettajia ja oppilaita – tulevia kansalaisia lukuisten koko maapalloa koskettavien ympäristöhaasteiden ratkaisemiseen. Lisensiaattitutkielman päätavoitteena oli kehittää kestävään kehitykseen liittyvää tutkimuksellista kemian opetusta, joka vahvistaa oppilaiden ympäristötietoisuutta sekä positiivista kemiakuvaa. Kestävä kehitys kemian opetuksessa liittyy yhteiskuntaperustaisiin kemian aiheisiin, esimerkiksi elinkaariajatteluun ja vihreään kemiaan. Kehittämistutkimuksen teoreettisessa ongelma-analyysissä tarkasteltiin tutkimuksen näkökulmasta keskeisiä lähestymistapoja: kestävää kehitystä ja kemiaa, vihreää kemiaa, elinkaarianalyysiä ja -ajattelua, ympäristötietoisuutta, yhteiskuntaperustaisuutta ja tutkimuksellista opiskelua. Empiirisessä kehittämisosassa etsittiin vastauksia seuraaviin tutkimuskysymyksiin: 1) Minkälaista on kestävää kehitystä edistävä elinkaariajattelun tutkimuksellinen kemian opetus? 2) Miten yhteisöllisesti kehitetty kehittämistuotos elinkaariaiheen kemian opetukseen vaikuttaa oppilaiden ympäristötietoisuuteen ja kemiakuvaan? Tutkimus toteutettiin kemian opettajien täydennyskoulutusten yhteydessä, joissa aiheina olivat tutkielmassa käsitellyt asiat: kestävä kehitys, vihreä kemia, erilaisten tuotteiden elinkaaret, ympäristötietoisuus, yhteiskuntaperustaisuus ja tutkimuksellinen opiskelu. Täydennyskoulutuksissa luotiin yhteisöllisesti elinkaariaiheisia tutkimuksellisia kemian opetusmalleja. Kemian tieto kytkettiin tuotteen tai materiaalin elinkaareen. Tutkimuksen kohteena olivat kemian opettajien opetusmallit, niistä yhteisöllisesti kehitetty kehittämistuotos ja sen avulla opiskelevien yläkoulun oppilaiden kokemukset. Yhteisölliseen kehittämisprosessiin osallistuivat 21 kemian opettajaa ja aineistoa analysoineet kaksi tutkijaa vuosina 2010–2012. Opetusmallien kehittäminen pohjautui teoreettiseen ongelma-analyysiin. Tutkimuksessa yhteisöllisesti kehitetyn opetusmallin vaikuttavuustarkasteluun osallistui 105 peruskoulun yhdeksäsluokkalaista. Tutkimusmenetelminä kehittämistutkimuksessa käytettiin tekstimuotoisen aineiston ja puolistrukturoitujen haastattelujen sisällönanalyysiä sekä kvantitatiivisia kyselyitä. Kehittämistutkimuksen empiirisen kehittämisosan tuloksena saatiin: 1) kestävän kehityksen opetukseen uusia elinkaariaiheisia tutkimuksellisia kemian opetusmalleja ja niistä yhteisöllisesti kehitetty kehittämistuotos, ja 2) tietoa elinkaariaiheisen tutkimuksellisen kemian opetuksen vaikutuksista oppilaiden ympäristötietoisuuteen ja kemiakuvaan. Tutkimustulosten luotettavuutta tarkasteltiin tutkija- ja menetelmätriangulaatiolla. Opettajat toteuttivat kestävää kehitystä edistävää elinkaariajattelun tutkimuksellista kemian opetusta usealla eri tavalla. He kehittivät yhteensä 20 uutta opetusmallia. Opettajien eniten käyttämä lähestymistapa oli pienryhmissä toteutettava avoin projektityö. Siinä oppilaat saivat tutkia itse valitsemansa tuotteen elinkaarta. Tästä lähestymistavasta kehitettiin yhteisöllisesti kehittämistuotos elinkaariajattelun kemian opetukseen. Osa opettajista valitsi tutkimuskohteen oppilaille valmiiksi, jolloin tutkimustehtävät liittyivät raaka-aineisiin, kulutustavaroihin, ruoka-aineisiin tai veteen. Opetusmenetelminä opetusmalleissa käytettiin pienryhmissä tapahtuvaa kysymysten tekoa, tiedon etsintää ja arviointia, tulosten muodostamista ja esittämistä, laboratoriokokeita, videoita, opintovierailuita, väittelyä, uusien tuotteiden suunnittelua, draamaa ja oppimispäiväkirjoja. Kehittämistuotoksena saatu elinkaariaiheinen tutkimuksellinen projektityö lisäsi oppilaiden yhteiskunnallista ja ympäristötietoista pohdintaa. Oppilaat korostivat erityisesti luonnonsuojelun ja kierrätyksen merkitystä. Enemmistö oppilaista uskoi vastaavien projektien vaikuttavan positiivisesti nuorten ympäristötietoisuuteen. Projektityö vaikutti positiivisesti oppilaiden kemiakuvaan. He huomasivat, että kemiassa oppii arkeen ja yhteiskuntaan liittyviä hyödyllisiä asioita. Oppilaat arvostivat uudenlaista kemian opiskelutapaa, joka oli itsenäinen ja sosiaalinen. Lisensiaattitutkielmassa esitetty opetusmalli elinkaariajattelun tutkimukselliseen kemian opetukseen on uudenlainen esimerkki tutkimuksellisesta työtavasta, joka tukee monipuolisia opiskelu- ja kansalaistaitoja, motivoi oppilasta kemian opiskeluun sekä ohjaa häntä pohtimaan kestävää kehitystä. Elinkaariaiheinen tutkimuksellinen kemian opetus sopii perusopetukseen, mutta sitä voi soveltaa myös kaikille kouluasteille. Tämän lisensiaattitutkielman teoreettisen ongelma- analyysin havaintoja ja empiirisen kehittämisosan tutkimustuloksia voidaan käyttää kemian opetuksen suunnittelussa ja kemian opettajien koulutuksessa kestävän kehityksen aiheisiin liittyen.
  • 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.
  • 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.
  • 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.
  • Kemppainen, Mikko (Helsingin yliopisto, 2010)
    Tools known as maximal functions are frequently used in harmonic analysis when studying local behaviour of functions. Typically they measure the suprema of local averages of non-negative functions. It is essential that the size (more precisely, the L^p-norm) of the maximal function is comparable to the size of the original function. When dealing with families of operators between Banach spaces we are often forced to replace the uniform bound with the larger R-bound. Hence such a replacement is also needed in the maximal function for functions taking values in spaces of operators. More specifically, the suprema of norms of local averages (i.e. their uniform bound in the operator norm) has to be replaced by their R-bound. This procedure gives us the Rademacher maximal function, which was introduced by Hytönen, McIntosh and Portal in order to prove a certain vector-valued Carleson's embedding theorem. They noticed that the sizes of an operator-valued function and its Rademacher maximal function are comparable for many common range spaces, but not for all. Certain requirements on the type and cotype of the spaces involved are necessary for this comparability, henceforth referred to as the “RMF-property”. It was shown, that other objects and parameters appearing in the definition, such as the domain of functions and the exponent p of the norm, make no difference to this. After a short introduction to randomized norms and geometry in Banach spaces we study the Rademacher maximal function on Euclidean spaces. The requirements on the type and cotype are considered, providing examples of spaces without RMF. L^p-spaces are shown to have RMF not only for p greater or equal to 2 (when it is trivial) but also for 1 < p < 2. A dyadic version of Carleson's embedding theorem is proven for scalar- and operator-valued functions. As the analysis with dyadic cubes can be generalized to filtrations on sigma-finite measure spaces, we consider the Rademacher maximal function in this case as well. It turns out that the RMF-property is independent of the filtration and the underlying measure space and that it is enough to consider very simple ones known as Haar filtrations. Scalar- and operator-valued analogues of Carleson's embedding theorem are also provided. With the RMF-property proven independent of the underlying measure space, we can use probabilistic notions and formulate it for martingales. Following a similar result for UMD-spaces, a weak type inequality is shown to be (necessary and) sufficient for the RMF-property. The RMF-property is also studied using concave functions giving yet another proof of its independence from various parameters.
  • 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.
  • Veilahti, Antti (Helsingin yliopisto, 2008)
    Many problems in analysis have been solved using the theory of Hodge structures. P. Deligne started to treat these structures in a categorical way. Following him, we introduce the categories of mixed real and complex Hodge structures. Category of mixed Hodge structures over the field of real or complex numbers is a rigid abelian tensor category, and in fact, a neutral Tannakian category. Therefore it is equivalent to the category of representations of an affine group scheme. The direct sums of pure Hodge structures of different weights over real or complex numbers can be realized as a representation of the torus group, whose complex points is the Cartesian product of two punctured complex planes. Mixed Hodge structures turn out to consist of information of a direct sum of pure Hodge structures of different weights and a nilpotent automorphism. Therefore mixed Hodge structures correspond to the representations of certain semidirect product of a nilpotent group and the torus group acting on it.
  • Kuusisto, Minna (Helsingin yliopisto, 2007)
    Aim of this study is to investigate composition of the crust in Finland using seismic wide-angle velocity models and laboratory measurements on P- and S-wave velocities of different rock types. The velocities adopted from wide-angle velocity models were compared with laboratory velocities of different rock types corrected for the crustal PT conditions in the study area. The wide-angle velocity models indicate that the P-wave velocity does not only increase step-wise at boundaries of major crustal layers, but there is also gradual increase of velocity within the layers. On the other hand, the laboratory measurements of velocities indicate that no single rock type is able to provide the gradual downward increasing trends. Thus, there must be gradual vertical changes in rock composition. The downward increase of velocities indicates that the composition of the crust becomes gradually more mafic with increasing depth. Even though single rock types cannot simulate the wide-angle model velocities, it can be done with a mixture of rock types. There are a large number of rock type mixtures giving the correct P-wave velocities. Therefore, the inverse solution of rock types and their proportions from velocities is a non-unique problem if only P-wave velocities is available. Amount of the possible rock type mixtures can be limitted using S-wave velocities, reflection seismic results and other geological and geophysical results of the study area. Crustal model FINMIX-2 is presented in this study and it suggest that the crustal velocity profiles can be simulated with rock type mixtures, where the upper crust consists of felsic gneisses and granitic-granodioritic rocks with a minor contribution of quartzite, amphibolite and diabase. In the middle crust the amphibolite proportion increases. The lower crust consists of tonalitic gneiss, mafic garnet granulite, hornblendite, pyroxenite and minor mafic eclogite. This composition model is in agreement with deep crustal kimberlite-hosted xenolith data in eastern Finland and reflectivity of the FIRE (Finnish Reflection Experiment). According to FINMIX-2 model the Moho is deeper and the crustal composition is a more mafic than an average global continental model would suggest. Composition models of southern Finland are quite similar than FINMIX-2 model. However, there are minor differencies between the models, which indicates areal differences of composition. Models of northern Finland shows that the crustal thickness is smaller than southern Finland and composition of the upper crust is different. Density profiles calculated from the lithological models suggest that there is practically no density contrast at Moho in areas of the high-velocity lower crust. This implies that crustal thickness in the central Fennoscandian Shield may have been controlled by the densities of the lower crustal and upper mantle rocks.
  • 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.
  • Laitila, Jussi (Helsingin yliopisto, 2004)
  • Erästö, Panu (Helsingin yliopisto, 2001)
  • Lindén, Greger (Helsingin yliopisto, 1993)