Browsing by Title
Now showing items 3928-3947 of 4026
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(2021)Maxwell’s equations are a set of equations which describe how electromagnetic fields behave in a medium or in a vacuum. This means that they can be studied from the perspective of partial differential equations as different kinds of initial value problems and boundary value problems. Because often in physically relevant situations the media are not regular or there can be irregular sources such as point sources, it’s not always meaningful to study Maxwell’s equations with the intention of finding a direct solution to the problem. Instead in these cases it’s useful to study them from the perspective of weak solutions, making the problem easier to study. This thesis studies Maxwell’s equations from the perspective of weak solutions. To help understand later chapters, the thesis first introduces theory related to Hilbert spaces, weak derivates and Sobolev spaces. Understanding curl, divergence, gradient and their properties is important for understanding the topic because the thesis utilises several different Sobolev spaces which satisfy different kinds of geometrical conditions. After going through the background theory, the thesis introduces Maxwell’s equations in section 2.3. Maxwell’s equations are described in both differential form and timeharmonic differential forms as both are used in the thesis. Static problems related to Maxwell’s equations are studied in Chapter 3. In static problems the charge and current densities are stationary in time. If the electric field and magnetic field are assumed to have finite energy, it follows that the studied problem has a unique solution. The thesis demonstrates conditions on what kind of form the electric and magnetic fields must have to satisfy the conditions of the problem. In particular it’s noted that the electromagnetic field decomposes into two parts, out of which only one arises from the electric and magnetic potential. Maxwell’s equations are also studied with the methods from spectral theory in Chapter 4. First the thesis introduces and defines a few concepts from spectral theory such as spectrums, resolvent sets and eigenvalues. After this, the thesis studies non-static problems related to Maxwell’s equations by utilising their time-harmonic forms. In time-harmonic forms the Maxwell’s equations do not depend on time but instead on frequencies, effectively simplifying the problem by eliminating the time dependency. It turns out that the natural frequencies which solve the spectral problem we study belong to the spectrum of Maxwell’s operator iA . Because the spectrum is proved to be discrete, the set of eigensolutions is also discrete. This gives the solution to the problem as the natural frequency solving the problem has a corresponding eigenvector with finite energy. However, this method does not give an efficient way of finding the explicit form of the solution.
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(2019)Climate change is globally considered as one of the biggest threats to the economy and development. Agriculture is the sector that faces the heaviest consequences and agriculture is also the primary livelihood for 2.5 billion people. Especially vulnerable are those who rely on rain-fed agriculture and for them adequate information on weather and climate is essential, enabling the adaptation to climatic changes. Weather and climate information services (WCIS) which are the entity from the generation to the dissemination and utilization of the information, plays a significant role for farmers especially in the developing countries. Adequate information is accessible and accurate, also in terms of time and location, and is communicated in a way that enables using the information in practice. The connection between agricultural production and WCIS has been more acknowledged and most of the African countries are able to provide monthly and seasonal forecasts, agrometeorological forecasts and extreme weather event warnings. However, still many areas suffer from lack of information systems which would help farmers to plan their agricultural activities and to adopt better farming practices. This study focuses on the adequacy of WCIS through farmer’s experiences in the Taita Hills, Kenya. Using semi-structured interviews, it identifies ICT- and human-based sources, content, and utilization of the information and how the information is shared through social networks. Additionally, it acknowledges the role of traditional knowledge to forecast weather through indicators in the environment. Local subsistence farmers, who are the key informants of this study, have experienced the impacts of climate change mainly as delayed rain seasons and decreased rainfall as well as increased temperatures. Important weather information for the farmers, in terms of agriculture, is dominantly the information about the onset and volume of rainfall that is used to schedule farming practices to achieve successful yield. The results of the study indicate that ICT-based information sources, such as daily forecasts from the radio, do not offer useful information for the farmers due to high uncertainty. The main sources of weather and climate information are human-based sources such as chiefs’ barazas and agricultural extension officers which offer seasonal forecasts and guidance on suitable crop types and other agricultural counselling. The information is shared in a communicative way which enables a dialog between the source and the farmer. In addition to seasonal forecasts, farmers rely heavily on traditional knowledge and regard it as reliable since it is observed through own senses and has a long local history through generations. Social networks in general, including barazas and extension officers but also, for example, neighbours and farmer groups, play an essential role in sharing information. Farmers both receive and share information through several forums. However, there are still farmers that are excluded from any WCIS related social networks and hence lack capacity to adapt to climatic changes. There is still a need to develop extension services to reach everybody in need and to generate more locally accurate forecasts which require local weather data gathering. Also, there is great potential in ICT as an information dissemination tool to a large audience.
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(2015)The World Wide Web has emerged as a powerful tool and an entity that has formed a major part of everyday human life. Since web technology has become vital to humans, it is emerging as a platform where web applications mean more than they have ever meant. This demands for the user experience to be pleasurable and fast. But the disruptions in flow in traditional web applications stop the user from getting the desired experience. Initially web browsers were developed for displaying static pages linked together and user navigated to retrieve information from a server. This phenomenon is also known as multipage paradigm. It took more than two decades to evolve from a mere information-displaying entity to an application execution platform. The Ubiquitous nature of the web changed the trends, and complex web applications started emerging. These applications on user actions reload the entire web page from the server. Client and server communicate using synchronous communication mode. User action on the client triggers a call to the server and blocks the input/output until the server responds. Even after the advancement of web technologies, the web applications multipage paradigm remains the same and so do the problems of disruption in the user experience and application workflow. This thesis analyzes the design and development of modern web applications aimed at providing new single page paradigm and asynchronous communication between the client and the server to solve problems found in the multipage web application paradigm. This thesis also discusses the tools and technologies used in building single page web applications. The new single page paradigm introduces some challenges that are also considered in this thesis. Furthermore, the thesis covers that how the new paradigm can be used to develop applications on fragmented devices. Finally, the thesis describes the implementation of an example application aimed at producing a single page paradigm.
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(2020)Location tracking has been quite an important tool in our daily life. The outdoor location tracking can easily be supported by GPS. However, the technology of tracking smart device users indoor position is not at the same maturity level as outdoor tracking. AR technology could enable the tracking on users indoor location by scanning the AR marker with their smart devices. However, due to several limitations (capacity, error tolerance, etc.) AR markers are not widely adopted. Therefore, not serving as a good candidate to be a tracking marker. This paper carries out a research question whether QR code can replace the AR marker as the tracking marker to detect smart devices’ user indoor position. The paper has discussed the research question by researching the background of the QR code and AR technology. According to the research, QR code should be a suitable choice to implement as a tracking marker. Comparing to the AR marker, QR code has a better capacity, higher error tolerance, and widely adopted. Moreover, a web application has also been implemented as an experiment to support the research question. It utilized QR code as a tracking marker for AR technology which built a 3D model on the QR code. Hence, the position of the user can be estimated from the 3D model. This paper discusses the experiment result by comparing a pre-fixed target user’s position and real experiment position with three different QR code samples. The limitation of the experiment and improvement ideas have also been discussed in this paper. According to the experiment, the research question has being answered that a combination of QR code and AR technology could deliver a satisfying indoor location result in a smart device user.
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(2018)Welcome, in this thesis, some of the higher ranked, popular web content management software (CMS), namely Drupal, WordPress, Joomla and Plone, are compared by usability, from a developer’s perspective, and by performance of the resultant site build with these CMSs, to find out, among other topics, about their potential to build websites to different needs. This thesis tries to discover if a CMS exists, in this selected group, that is a clear choice above the others in both usability and performance. A substantial portion of source material for this research comes from measurements, and small demo systems built and used, in addition to any literature sources used and experience garnered from career as a web developer. In this thesis, we provide an overview of these four selected CMS; their characteristics, statistics and how they measure up to each other. And so doing, expand upon the still narrow research done in this field.
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(Helsingin yliopistoUniversity of HelsinkiHelsingfors universitet, 2001)
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(2019)Tässä tutkielmassa vertaillaan vertaillaan keskenään web-sovellusten käyttöliittymien automaattitestauksen menetelmiä. Tutkielmassa selvitetään mitä erityistä webohjelmistojen testaamisessa on, ja miten niitä on mahdollista testata. Tutkielmassa vertaillaan myös muutamia testiautomaation tekniikoita ja niitä hyödyntäviä ohjelmointikirjastoja ja työkaluja. Cypress on Javascript-pohjainen testiautomaatio kehys web-ohjelmistojen testaamiseen. Selenium Webdriver on Wedriver protokollaa hyödyntävä selainautomaatiokirjasto, jota käytetään mm. selainohjelmistojen testaamiseen. Sikuli on automaatiokirjasto, joka perustuu kuvantunnistukseen. Näitä kirjastoja ja niiden soveltamia tekniikoita vertaillaan keskenään niiden webohjelmistojen testaamiseen soveltuvuuden, testien kehityksen ja suorituksen tehokkuuden sekä alusta- ja selaintuen näkökulmista.
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(2020)Tässä tutkielmassa ohjelmiston vaiheittaisella käyttöönotolla tarkoitetaan sitä, että ohjelmiston käyttäjille annetaan vaiheittain pääsy tuotantoon vietyyn ohjelmistoon. Otettaessa ohjelmistoa vaiheittain käyttöön annetaan tuotantoon vietyyn ohjelmistoon aluksi pääsy esimerkiksi vain tietylle osajoukolle ohjelmiston käyttäjistä. Tämän jälkeen kasvatetaan vaiheittain käyttäjien pääsyä ohjelmistoon. Vaiheittainen käyttöönotto päättyy, kun kaikille ohjelmiston käyttäjille on annettu pääsy ohjelmistoon. Tässä tutkielmassa kehitettiin menetelmä web-ohjelmiston uuden version vaiheittaiselle käyttöönotolle ympäristöön, jossa vaatimuksena on palvelun käytön katkottomuus. Tutkielman tutkimuskysymyksenä on, miten web-ohjelmiston vaiheittainen käyttöönotto voidaan toteuttaa käytännössä. Tutkielma toteutettiin ohjelmistopalveluita tarjoavalle kohdeyritykselle, joka toimii yritykseltä-yritykselle-toimialalla. Tutkimusmenetelmänä tutkielmassa käytettiin design science -tutkimusmenetelmää. Tutkielman aikana kehitettiin AphoDeploy-sovellus, jonka avulla vaiheittainen käyttöönotto voitiin automatisoida Kubernetes-klusterissa. Kubernetes-klusteriin asennettiin palveluverkkoratkaisu, jonka tarjoamien välityspalvelinten avulla Kubernetes-klusterissa tehtiin ajonaikaista liikenteenohjausta. AphoDeploy-sovelluksen avulla toteutettiin uuden ohjelmistoversion vaiheittainen käyttöönotto muuttamalla palveluverkkoratkaisun ja Kubernetes-klusterin konfiguraatioita automatisoidusti. Vaiheittaisen käyttöönoton menetelmän toimintaa tutkittiin muun muassa automatisoiduilla testitapauksilla, joiden avulla selvitettiin, toteuttaako menetelmä vaiheittaiselle käyttöönotolle asetetut vaatimukset. Vaatimukset jaoteltiin teknisiin vaatimuksiin, vaiheittaisen käyttöönoton vaatimuksiin ja vaiheittaisen käyttöönoton päättymisen vaatimuksiin. Vaiheittaisen käyttöönoton menetelmän arvioinnin perusteella voitiin todeta, että kahdeksasta vaiheittaiselle käyttöönotolle asetetusta vaatimuksesta seitsemän vaatimusta täyttyi kokonaan ja yksi vaatimus täyttyi osittain. Tutkielmassa löydettiin tapa toteuttaa web-ohjelmiston vaiheittainen käyttöönotto käytännössä AphoDeploy-sovelluksen avulla. Näin ollen tutkielmassa löydettiin vastaus tutkielman tutkimuskysymykseen. Tutkielman aikana kehitetyn menetelmän avulla luotiin lisäksi pohjaa työkaluinfrastruktuurille, joka voisi tulevaisuudessa tukea kohdeyrityksessä esimerkiksi tuotannossa tehtävää kokeilua. Vaiheittaisen käyttöönoton menetelmän arvioinnin perusteella AphoDeploy-sovelluksesta löydettiin tulevaisuutta varten myös mahdollisia jatkokehityskohteita. ACM Computing Classification System (CCS): - Software and its engineering -> Software organization and properties -> Contextual software domains -> Software infrastructure -> Middleware - General and reference -> Cross-computing tools and techniques -> Experimentation
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(2013)Web-palvelut ovat tekniikkana suosittu tapa toteuttaa yritysten sisäiset ja ulkoiset liiketoimintaprosessit sähköisenä palveluna. Koostamisen avulla olemassa olevista web-palveluista voidaan rakentaa uusia monipuolisempia palveluja. Tässä työssä tutkitaan, minkälainen transaktionaalisuuden taso koosteisessa web-palvelussa voidaan saavuttaa käytettävissä olevilla teknologioilla. Tämä tehdään vertailemalla web-palveluiden transaktionaalisia ominaisuuksia tietokantateoriasta tuttuihin transaktion ACID-ominaisuuksiin, sarjallistuvuusteoriaan, sekä transaktiomalleihin. Työssä tutkitaan myös sitä, tarvitaanko web-palveluiden transaktionaalisessa koostamisessa ylipäätään tietokantojen teoriasta tuttuja käsitteitä ja malleja. Tutkimuksessa syvennytään niihin web-palveluiden koostamisessa käytettäviin menetelmiin ja protokolliin, jotka tarjoavat transaktionaalisia piirteitä liiketoimintaprosessien toteuttamiseksi. Nämä ovat web-arkkitehtuuripinon WS-AtomicTransaction- ja WS-BusinessActivity -protokollat. Tulosten analysoinnissa on käytetty apuna erään matkatoimiston web-palvelua. Web-palveluiden välisten transaktioiden ACID-ominaisuudet käytiin läpi kahden web-palvelun käyttötapauksen kautta. Tuloksista selvisi, että web-palveluiden välisissä transaktioissa toteutuu ainoastaan transaktion ACID-atomisuus. Samalla selvitettiin, miten tämä saavutettu transaktionaalisuuden taso käytännössä vaikuttaa web-palveluiden väliseen toimintaan. Tutkielman tuloksien vaikutuksia web-palveluiden väliseen kanssakäyntiin arvioitiin sekä palvelun toteuttajan, että loppukäyttäjän näkökulmasta. Tuloksien perusteella kävi ilmi, että vakavien ongelmien välttämiseksi toteuttajan on tunnettava sovelluksen ongelmakenttä erityisen hyvin ja ymmärrettävä se, miten koosteisen web-palvelun transaktionaalisuuden taso vaikuttaa kyseisessä ympäristössä palvelun toimintaan. Tutkielman lopussa esitellään tämän tutkielman tuloksena syntynyt eksklusiivinen malli, jonka avulla koosteeseen osallistuvien web-palveluiden välisissä transaktioissa voidaan saavuttaa globaali ACID-eristyvyys. Mallia soveltamalla web-palvelut voivat etsiä eksklusiivista kauppaa käyviä web-palveluja SOA-arkkitehtuurimallin mukaisesti UDDI-rekisteristä, ja suorittaa näiden kanssa häiriöttämästi sarjallistuvia transaktioita. ACM Computing Classification System (CCS): - Information systems~Web services - Information systems~Database transaction processing
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(2023)Security of web communication is crucial. When accessing an online bank, for example, one of the key issues is that the user can be assured they are communicating with the bank as they intended to. This assurance is achieved with the public key infrastructure for the Web, Web PKI. Its purpose is to manage digital certificates on the Web. Certificates are used to prove one’s identity with the help of public-key cryptography. Certificate authorities and software vendors that operate certificate root stores have key roles in the Web PKI. The first issue certificates and the latter choose which CAs are trusted. The Web PKI has multiple challenges and it is a highly researched topic. Numerous countermeasures and enhancements to the Web PKI have been developed over the years. This thesis investigates challenges in the Web PKI and proposed countermeasures, some of which are based on blockchain technology. Of the non-blockchain-based solutions, we introduce Certificate Transparency, CAA and DANE. Of the blockchain-based solutions, CertLedger, IKP and a solution for decentralising ACME protocol are described. We find that the challenges are mainly related to certificate authorities, revocation and root stores. From the numerous solutions, Certificate Transparency and CAA are utilised in the Web PKI. Shortening the validity period of certificates can resolve some of the challenges. Blockchain-based solutions are numerous but none has yet seen wide deployment.
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(2015)Web Real Time Communication (WebRTC) is a project that aims to enable plug-in free, real time communications across multiple web-browsers. With WebRTC enabled web-browsers, users can make direct browser to browser audio calls, video calls or transfer arbitrary data. In a simple network with no Network Address Translation (NAT), firewalls or HTTP-proxies, WebRTC applications work well without any problems. But in the real world, the networks are complex and clients are usually behind NAT, firewalls and (or) HTTP proxies. Introduction of such network middle boxes creates problems for WebRTC media flow, leading to a failure in WebRTC call establishment. WebRTC uses Interactive Connectivity Establishment (ICE) framework to work around the problems posed by these middle boxes. ICE uses a combination of Session Traversal Utilities for NAT (STUN) and Traversal Using Relays around NAT (TURN) depending on the network configuration and tries to give the WebRTC media the best possible chance to traverse these middle boxes. A TURN server is required to relay the WebRTC media between peers when STUN methods fail. In this work, we evaluate the different network configurations in which WebRTC peers can be present and how the WebRTC connectivity problem can be solved using the ICE framework, when peers are present in such network configurations. We also evaluate the TURN server for its computational, memory and bandwidth requirements for relaying different types of WebRTC calls.
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(2022)With increasing amounts of software services provided to users and the more demanding requirements needed from them, monitoring of services is becoming increasingly important. Web service monitoring is the process of confirming system functionality by studying its various attributes, such as availability, reliability, and performance. Monitoring the services helps the software developers, maintainers and owners as they allow for increased reliability, robustness and possibly performance analysis. This thesis focuses on web service monitoring and the tools that it is done with. Specific goals are to learn about the different categories that monitoring services can take and to showcase a custom web service monitoring tool and its further development. The subject is important to the case company LogiNets, which has specific monitoring requirements that need to be fulfilled. These goals were achieved by researching literature on different types of monitoring tools for a literature review and then doing a case study of monitoring tool development. The case study was done about adding a new functionality to LogiNets’s indoor web service monitoring tool called Agent. The literature review was successful in identifying different categories of monitoring tools both by their location relative to the monitored service as well as by the quality of service requirements they fulfill. The review did not, however, discover significant research about existing commercial monitoring tools, and thus provided little help in the case study. The case study was more successful, with the new functionality added and similar extensions planned for the future.
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(2021)The Streamr Network is a decentralized publish-subscribe system. This thesis experimentally compares WebSocket and WebRTC as transport protocols in the system’s d-regular random graph type unstructured stream overlays. The thesis explores common designs for publish-subscribe and decentralized P2P systems. Underlying network protocols including NAT traversal are explored to understand how the WebSocket and WebRTC protocols function. The requirements set for the Streamr Network and how its design and implementations fulfill them are discussed. The design and implementations are validated with the use simulations, emulations and AWS deployed real-world experiments. The performance metrics measured from the real-world experiments are compared to related work. As the implementations using the two protocols are separate incompatible versions, the differences between them was taken into account during analysis of the experiments. Although the WebSocket versions overlay construction is known to be inefficient and vulnerable to churn, it is found to be unintentionally topology aware. This caused the WebSocket stream overlays to perform better in terms of latency. The WebRTC stream overlays were found to be more predictable and more optimized for small payloads as estimates for message propagation delays had a MEPA of 1.24% compared to WebSocket’s 3.98%. Moreover, the WebRTC version enables P2P connections between hosts behind NATs. As the WebRTC version’s overlay construction is more accurate, reliable, scalable, and churn tolerant, it can be used to create intentionally topology aware stream overlays to fully take over the results of the WebSocket implementation.
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(2013)Ketterässä ohjelmistokehityksessä laadunhallinnan perustana ovat laadukkaat ohjelmistokehityskäytännöt sekä automaattinen testaus. Automaattinen testaus on ennen kaikkea kohdistunut yksikkötestaukseen, jolla pyritään varmistamaan ohjelmiston sisäistä laatua. Toiminnallinen testaus ja hyväksymistestaus ovat myös automatisoitavissa, mutta niiden automatisointia ovat hidastaneet kustannukset sekä testien vaatima ylläpito. Toiminnallisen testauksen automatisointiin on kehitetty työkaluja sekä menetelmiä, joiden avulla voidaan kustannustehokkaasti toteuttaa automatisoituja toiminnallisia testitapauksia. Jatkuva integraatio on yleensä automaattisen yksikkötestauksen pohjana ketterässä kehityksessä ja osana jatkuvaa integraatiota on myös mahdollista automatisoida toiminnallinen testaus. Automaattisen toiminnallisen testauksen kustannuksiin voidaan vaikuttaa valituilla testauskehyksillä, testitapausten suunnittelulla sekä toteuttamalla testitapauksia hyväksi todettujen käytäntöjen mukaan. Toiminnallinen testaus perustuu toiminnallisiin vaatimuksiin, joten käyttötapaukset ja käyttäjätarinat ketterässä kehityksessä sekä niiden hyväksymiskriteerit auttavat testitapausten suunnittelussa ja toteutuksessa. Testitapaukset ovat helposti toteutettavissa nauhoita-ja-toista -menetelmällä ja refaktoroimalla testitapauksista selkeämpiä. Esimerkiksi sivuobjekti -suunnittelumallin mukaisilla testitapauksilla voidaan pienentää testauksen ylläpidon kustannuksia. Testauskehyksiä on tarjolla automaattisen testauksen eri menetelmiin, jolloin automaattinen toiminnallinen onnistuu myös erilaisissa kehitysympäristöissä. ACM Computing Classification System (CCS): Software and its engineering → Software verification; Agile software development; Software testing and debugging; Documentation;
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(2020)Web-sovellusten tietoturva on jokaiselle internetin käyttäjälle tärkeä asia. Yksittäiseen sivustoon tai web-palveluun tapahtuvasta tietomurrosta voi seurata palvelun käyttäjille paljon harmia, joka olisi usein ollut estettävissä. Pienellä vaivalla toteutettavissa olevalla automaattisella tietoturvaskannauksella pystytään havaitsemaan suuri osa web-sovellusten haavoittuvuuksista. Tässä työssä tutkitaan automaattisen tietoturvaskannauksen liittämistä sovelluksen kehitysprosessiin. Lisäämällä tietoturvaskannaus osaksi kehitettävien sovelluksien jatkuvaa koontiajoa pyritään parantamaan sovellusten tietoturvaa havaitsemalla uudet haavoittuvuudet heti niiden synnyttyä. Automaattisen tietoturvaskannauksen käyttämisellä osana regressiotestausta pyritään myös vähentämään käsin tehtävän testauksen määrää, sekä parantamaan sovelluksen tietoturvaa kehitysprosessin jokaisessa vaiheessa. Tämän työn tavoitteena on tuottaa yksinkertainen ja tehokas GitLab CI -koontiajoon liitettävä tietoturvaskannauksen tekevä komponentti, joka on helppo lisätä myös tuleviin sovellusprojekteihin. Komponentti hyödyntää Arachni- ja ZAP-nimisiä avoimen lähdekoodin skannausohjelmistoja. Työssä selvitetään samalla, kuinka helppoa tämä tietoturvatarkistuksen tekevä komponentti on pystyttää ja miten pienellä vaivalla sen uudelleenkäyttö muissa sovellusprojekteissa onnistuu. Lisäksi tutkitaan, kuinka tehokkaasti toteutettu järjestelmä löytää haavoittuvuuksia sovelluksista.
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(2008)The Weddell Sea on the Antarctic coast is one of the most important areas of deep-water formation in the oceans. The processes that result in deep-water formation depend on the sea area's oceanic transport mechanisms and on the climatological conditions. The primary purpose of this master’s thesis is to calculate the prevailing current conditions and to estimate changes in the water-mass properties in the Weddell Sea. This was performed by using hydrographic data collected during the SWEDARP 88/89 expedition. The first part of the thesis includes a literature study on the oceanographic conditions in the Weddell Sea. The study describes the conditions that regulate the Weddell Sea's circulation field and characteristic oceanographic processes. Transport calculations were performed by applying geostrophic methodology to data from the station network in the southwestern Weddell Sea. First, the baroclinic flow field was determined with the assumption that the cyclonic circulation of the Weddell Sea flows in a clockwise direction through each transect of the gyre. The barotropic component of the current field was then calculated using an inverse method which balances the transports through the measurement transects by meeting given criteria. These were that the transport of salt and mass is equal through each measurement transect. The total volume transport in the Weddell gyre was calculated to be about 19 Sverdrup (1 Sv = 10^6 m^3/s), which is about 60% of the transport estimated in the literature. The formation of Weddell Sea Bottom Water (WSBW) was estimated to 1.4 Sv. The primary result of the study was the amount of heat released from the water column to the atmosphere within the measurement area. The heat loss was calculated to 12 TW (terawatt). The unique SWEDARP 88/89 stations measured in the Filchner depression on the continental shelf would deserve further analysis and would enrich the studies of the global deep-water circulation.
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(2022)Aluminium nitride is a piezoelectric material commonly used in piezoelectric microelectromechanical systems (MEMS) in the form of thin films deposited by sputtering. AlN-based devices are found in wireless electronics in the form of acoustic filters, but they also have prospective applications in a wide variety of sensor systems. To enhance the piezoelectric properties of AlN, some of the Al can be replaced with scandium, which is required for next-generation devices. However, addition of Sc makes both the deposition and patterning of the film more difficult. This work focuses on patterning of AlN and Sc0.2Al0.8N thin films with wet etching. Both materials are etched anisotropically, which in theory enables etching the materials with little deviation from the mask dimensions. However, in practise, undercutting at the mask edges occurs easily making the structures narrower compared to the etch mask. This work investigates and compares the mechanisms and etch rates of AlN and Sc0.2Al0.8N. Tetramethyl ammonium hydroxide was mostly used for etching, but also H3PO4 and H2SO4 were tested. Addition of 20 atom-% Sc lowered the etch rate of the material and resulted in more undercutting. The causes behind mask undercutting were examined by using 11 differently deposited etch masks, and the undercutting was minimized by optimizing the mask deposition, using thermal annealing, and optimizing the etching temperature. Finally, the work identifies and discusses the relevant factors in depositing and patterning the AlN, ScxAl1-xN and mask films.
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(2018)The field of superhydrophobicity i.e. extreme water-repellency is a fast growing one ever since artificial ways of manufacturing such surfaces have been developed. Superhydrophobic surfaces have several potential applications including surfaces that are self-cleaning, corrosion and stain resistant, anti-fogging and anti-fouling. For the use of superhydrophobic surfaces in applications there is a need for a precise characterization of their wetting properties. However, conventional methods for characterization have several drawbacks when applied to superhydrophobic surfaces. This has resulted in a need to develop new method for characterizing wetting properties of superhydrophobic surfaces. This thesis presents one auspicious method for wetting characterization of ultra water-repellent surfaces along with the theory the method is based on. In the method a magnetic water droplet is forced to oscillate on the superhydrophobic surface. The friction affecting droplet during oscillations is proportional to the wetting degree of surface. Furthermore, using a moving droplet allows the investigation of dynamic wetting properties of superhydrophobic surfaces.
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(Helsingin yliopistoUniversity of HelsinkiHelsingfors universitet, 2008)The possible presence of periodicity in the terrestrial impact crater data has been discussed in several papers since 1984. The authenticity of this detected periodicity data is controversial. It is possible, however, that real periodicity is present and could be detected from more accurate and complete data. In our study we created simulated different probability distributions for terrestrial impact crater record, that covered completely aperiodic and periodic impact cratering scenarios, as well as two specific combinations of these two cases, with four different impact crater age uncertainties. From these distributions we then generated simulated time series of impact craters with different numbers of craters and tested if the periodicity in the distribution could be detected using the Rayleigh method. Our analysis shows that if only one third of the terrestrial impact craters are caused by periodic cratering events, the detection of a real period in the data is very difficult and probably could not be detected even if better impact crater data became available. If two thirds of the craters are caused by periodic impacts, detection is possible, but would require substantially better data than which is currently available. We conclude that the periodicities reported so far in the impact crater data are not caused by real physical phenomena.
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(2020)Kymmenottelu on yleisurheilulaji, joka koostu kymmenestä yksilölajista, jotka suoritetaan sa-massa järjestyksessä kahden vuorokauden aikana. Kymmenen lajin tulokset pisteytetään viralli-sen pistetaulukon mukaan ja lopputulos on näiden lajien yhteenlaskettu pistemäärä. Tutkielman tavoitteena on tutkia, mikä tekee huippuluokan kymmenottelijaa. Lisäksi tarkastellaan miten henkilökohtaiset kehityskäyrät vertautuvat lajeittain. Aineistona käytetään vuonna 1970-2019 yli 8 500 pisteen kymmenottelijoiden kaudenparhai-den ottelusarjassa tehtyjen tuloksien tietoja. Ottelijaprofiilin muutoksia tutkitaan neljässä tasos-sa. Erikseen tarkastellaan ottelijan henkilökohtainen kehitys lajeittain ja näiden mahdollisia ero-ja. Teoriaosassa käsitellään Lairdin ja Waren lineaarinen sekamalli (LME malli) sekä siihen liittyvä rajoitettu suuremman uskottavuuden menetelmää (REML). Tutkielman tuloksien valossa vaikuttaa siltä, että kymmenottelussa pikajuoksulajit ovat tär-keimmässä roolissa. Varsinkin lähtökohtaisesti heikoille 400 metrin juoksijoille kehitys on suu-ri. Kymmenottelijan profiilissa on havaittavissa, että tietyt lähtökohtaisesti heikot lajit pysyvät suhteellisen heikkona verrattuna muihin.
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