04. Väitöskirjat / Doctoral theses

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2-Dimensional Assembly of Cellulose-Based Materials
(2016) Niinivaara, Elina
School of Chemical Technology | Doctoral dissertation (article-based)
The objective of this thesis was to systematically investigate the two dimensional assembly of cellulose-based materials and the two dimensional response to various external stimuli. The motivation of studying such materials is the ever increasing trend in materials science to substitute synthetic polymers for greener materials. Studies such as the one presented here are essential to understand the fundamental behaviours and characteristics of bio-based polymers and to be able to utilize them in new functional materials. Trimethylsilyl cellulose (TMSC), cellulose triacetate (CTA), cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) were extensively studied by means of Langmuir-Schaefer deposition. The formation of nanostructures on the surface of solid substrates as a result of monolayer transfer from the air/water interface was investigated using substrates of varying total surface free energy. It was established that for TMSC, a decrease in substrate surface energy resulted in progressive dewetting of the transferred film, which eventually led to the formation of dendritic fractals. A similar pattern was not detected in the films of CTA, CAP and CAB however, it was found that the acetate and residual hydroxyl group content of the cellulose esters played a key role in the morphologies of the ultrathin films. The morphology of the cellulose derivative films could be tuned by regeneration, exposure to water or by altering film deposition surface pressure. The behaviour of the cellulose esters upon compression at the air/water interface was also thoroughly scrutinized by monitoring surface pressure-area Langmuir isotherms with a fast and slow compression. Results revealed the behavioural differences in monolayer assembly as a function of compression rate. The intricate relationship between cellulose-based materials and water was also studied using cellulose in its native form. The water vapour sorption behaviours of ultrathin films of cellulose nanocrystals (CNCs) and regenerated amorphous cellulose (from TMSC) along with films with a combination of both were studied using a quartz crystal microbalance with dissipation monitoring (QCM-D) and spectroscopic ellipsometry (SE). Quantitative analysis of the results showed that hydration of CNC networks occurs through the envelopment of the individual crystals by three monolayers of water. The water vapour response of the cellulose films became unexpectedly complex when CNCs were mixed with amorphous cellulose. Relative humidity studies showed that the crystalline/amorphous ratio of films containing both types of cellulose played a critical role in water vapour adsorption. Adsorption in films with a similar ratio to that prevalent in the woody plant cell wall (~50/50) was promoted by the addition of CNCs, whereas in predominantly amorphous films it was inhibited.
3D geovisualizations in human-centered quality assessments of urban and green spaces — from point clouds to nonabsolute spaces
(2022) Jaalama, Kaisa
School of Engineering | Doctoral dissertation (article-based)
Through technological advancement, vertical, three-dimensional (3D) geoinformation has been designated to fulfil the horizontal, two-dimensional data resources and viewpoint of the environment. However, 3D geovisualizations are still divergent and unstandardized. This also applies to our understanding of their impact on society—their ability to imitate their physical counterparts as a lived environment and places as a social entity. While a range of studies presents solutions and applications for 3D geovisualizations, fewer focus on their critical examination in human-centered urban and green space assessments in an interdisciplinary way. This dissertation contributed to filling this gap by presenting three case studies conducted with 3D geovisualizations. First, the role of 3D point cloud data acquisition was tested for objective-deductive urban green assessments with a green factor framework. Second, the applicability of 3D geovisualizations was tested for subjective-inductive assessments in terms of perceived affordances of an urban park deck, using in-situ-based interview data as a reference in the analysis of the virtual reality-based interview data. Third, the role of subjective place relations with perceived realism (i.e., sense of presence) and subjective place meanings (i.e., sense of place) in subjective-inductive assessments with 3D geovisualizations was demonstrated. Finally, a framework presenting distinct knowledge approaches with 3D geovisualizations was reconciled.The results show that design for data capture is an interplay of the respective framework, individual characteristics of the physical properties, measurement devices, and additional information sources available. Future frameworks for assessment tasks, such as green efficiency in cities, should be designed to include the possibilities of vertical strata and volume. Further, the results show that most of the dimensions of green space affordances were at least to some extent perceivable in a subjective-inductive assessment through 3D geovisualization. Compared to the in-situ interview data, challenges with 3D geovisualization were linked to the weaker perception of surroundings outside the park deck, lack of social clues, and deficits in visual detail and coherency. The results underline the perception-altering role of prior familiarity with the geovisualized place both for the sense of presence and sense of place. Visual realism and spatial presence can enforce the communicative effectiveness of 3D geovisualizations, but so can prior familiarity with the place. The results demonstrate that, apart from objective-deductive methods, urban and green space planning can benefit from subjective-inductive assessments with 3D geovisualizations. A central outcome is that 3D geovisualization possesses possibilities for distinct knowledge approaches that contribute to each other in a co-productive manner.
The 4th P - people - in urban development based on Public-Private-People Partnership
(2008) Majamaa, Wisa
Doctoral dissertation (article-based)
The topic and the scope of this dissertation is the inclusion of the end-users' perspective into Public-Private Partnership (PPP) based urban development processes. The examined and developed 4P-based urban development process is by its nature a strategic Public-Private-People Partnership (4P) of local government and public land owners (Public), developers and private land owners (Private), and end-users (People) for good living environment and separate customer relationships. The empirical study is based on communicative planning theory and on a theory of rational consumers. Also a residential choice and an innovation theory - where end-users are the primary stakeholders in the innovation process - are discussed in this study. The qualitative study includes two levels of PPP-based urban development process. A general level of urban development process in its early stages - planning and design - and a more detailed level - purchasing process of PPP-based real estate service delivery projects. The research methods used in this study are multiple case study and action research. The dissertation found that the inclusion of the end-users' perspective in the PPP-based, or, more likely, in the 4P-based urban development processes is both possible and rewarding. The results show that it is possible to identify and categorise the end-users' perspective in a more detailed level of PPP-based urban development process, i.e. in a real estate service delivery, and to transfer the knowledge to the general level of PPP-based urban development process. It is also argued that the developed 4P-based urban development process increases the participation of the potential end-users, and creates a new kind of end-user orientated knowledge for the process. Engaging the end-users in development processes opens previously unseen potential for including consumerist possibilities for cities and developers. In this context, the 4P-based urban development process has created possibilities for engaging new pro-active and positive participation methods and solutions, not only for the early stages of urban development process (planning and design), but also for construction, operation and management of local economic and social infrastructure. The more concrete practical value and implication of this dissertation is the developed framework to include end-users' perspective into purchasing process of 4P-based real estate service delivery projects.
Äänen tunto : elokuvaäänen kokemuksellisuudesta
(2014) Takala, Päivi
School of Arts, Design and Architecture | Doctoral dissertation (monograph)
This artistic study presents a deep approach to film sound. Arguing that traditional descriptions of the role of film sound such as enhancing emotional impact or revealing the unconscious fail to capture fully the heart of meaning-making in the film experience, the study proposes the term felt sense (tuntoisuus in Finnish) to describe a specific form of non-verbal understanding of the world. The role of sound in meaning-making has long challenged filmmakers. The study considers how sound has been dealt with in practice by filmmakers and review topical writings of select filmmakers and sound designers. The developed insights are then discussed in the context of three works: Coincidences; (documentary film), Inhale (documentary film), and The Most Beautiful Sound of Helsinki (sound-and-video installation). The theoretical part of the study sets forth the concepts of felt sense, meaning born in experiencing, and co-movement, all of which arise in early development. For example, repetitive movement and sound woven into the fabric of holistic meaning-making are central to the experience of the unborn infant. The practical discussion begins with an overview of writings and interviews of Walter Murch, Michel Chion, the Dardenne brothers and David Lynch about film sound. The concept of felt sense is considered in the production of the three artistic works both in understanding sound and as a basis for establishing working rules in the filmmaking process. The Most Beautiful Sound of Helsinki is examined as an artistic expression of the concept itself. The study concludes that a holistic treatment of sound could be used to broaden current filmmaking teaching that emphasizes verbal narrative structures and film as a visual art.
Abatement of industrial greenhouse gas emissions
(2021) Kajaste-Rudnitskaja, Raili
School of Chemical Engineering | Doctoral dissertation (article-based)
Reducing anthropogenic greenhouse gas (GHG) emissions is increasingly proposed as one of the key components in achieving global sustainable development goals. The GHG emissions are continuing to rise annually at a rate of 1.5%. The total GHG emissions reached a record high of 55GtCO2eq in 2018. The direct industry contribution accounts for 21% and indirect GHG emissionsfor 11% of the global electricity and heat production emissions in the sector. The key sectors dominating the generation of global industrial GHG emissions are the iron and steel, cement andchemical industries. The growing global demand, especially for cement and plastics, is increasing the GHG emissions from these sectors.The fundamental objective of this study was to explore the possibilities to manage GHG emissions in industrial production chains. The speciﬁc objective was to ﬁnd solutions for the reduction of GHG emissions in the production chains of cement, plastics and methanol. In addition, one aim was to highlight the possibilities of future bioreﬁneries to reduce GHG emissions by replacing fossil resources in the production of chemicals and fuels. In this dissertation the research approach and process was multidisciplinary including attributional life cycle assessment (LCA), the capital recovery factor (CRF) and regression analysis of contributors to further develop incomplete datasets of the GHG emissions from the global cement sector. The key results of this dissertation are: (1) the total emission reduction potential identiﬁed in the global cement and chemical industry amount to 1112 Mt/a, corresponding to 17% of the GHG emissions from these two sectors. For comparison, the GHG emissions from the whole European Union area in 2017 were 4483 Mt, excluding land use change and land use change forestry (LUCLUCF); (2) the emissions from the plastics production chain are responsible for 51% of the GHG emissions from the chemical industry. Improved resource efﬁciency and increased additional recycling would reduce the emissions by 673 Mt/a in the value chain of plastics; (3) despite the large volumes of available biomass resources, the fuels and chemicals produced from fossil resources will continue to dominate until the market pull and cost-efﬁciency of renewable replacements make them attractive enough to compete. Lignocellulosic biomass, residuals, organic waste and algae were assessed as more sustainable resources for bioreﬁneries than food and feed crops. Methanol production from biomass adjacent to a pulp and paper mill was evaluated to becommercially viable; (4) the production of methane and methanol will probably be the ﬁrst to beneﬁt from the emerging carbon capture and utilization technologies, and (5) this study proposed a method for the assessment of greenhouse gas emissions in production chains by introducing a climate impact management matrix together with a capital recovery factor. To conclude, many of the GHG mitigation measures identiﬁed in this study are readily available for implementation provided the ﬁnancial gains and political willingness lower the threshold to investment.
Absolute measurement methods for reflectance and fluorescence
(2009) Holopainen, Silja
Doctoral dissertation (article-based)
Reflectance and fluorescence are important properties when determining the colour and appearance of solid opaque material. They are also useful in several other industrial applications such as those in biochemical and medical industry and in remote sensing. In most industrial applications, the reflectance and / or fluorescence characteristics of samples are measured relative to a known reference standard. The uncertainty of the measurements is naturally dependent on the uncertainty of the reference standard and therefore it is vital to have high-accuracy calibration instruments capable of absolute measurements. In addition, the standards should be calibrated in the same measurement geometry as the application where they are used. Particularly, instruments capable of absolute fluorescence measurements commonly use a fixed measurement geometry and therefore there is a need for an instrument that does not have this limitation. In the thesis, goniometric measurement facilities for measuring reflectance and fluorescence characteristics of reference standards have been designed and developed. The significance of light scattering in goniometric diffuse reflectance measurements has been studied. The effect can cause errors of the order of 1 % in the measurements if it is not properly taken into account. Also, this effect may be at least partly responsible for the discrepancies reported earlier between goniometric and integrating-sphere-based diffuse reflectance measurements. The wavelength range of an existing gonioreflectometer for calibrating reflectance and radiance factors has been extended and an extensive bilateral comparison in the wavelength range 250 nm - 1650 nm is reported. Such extensive comparisons between goniometric instruments are very rare even though it is the only way to verify the reliability of the absolute scales in National Metrology Institutes. A goniofluorometer has been designed and developed for measuring bispectral luminescent radiance factors in various measurement geometries. Also, the theory and mathematics of a new method for measuring absolute fluorescence quantum yield based on goniometric measurements has been derived. One of the most significant results of this thesis is the discovery of non-Lambertian behaviour of fluorescence emission from solid amorphous material. In addition, it has been observed that the angular pattern of fluorescence emission is not very tightly linked to the angular pattern of reflectance. This is an important result since most commercial and research instruments are only capable of measurements in a fixed geometry and usually rely on the assumption of Lambertian emission of fluorescence.
Abstraktin aika - Epäesittävä suomalainen valokuvataide 1920-2020
(2021) Nissinen, Laura
School of Arts, Design and Architecture | Doctoral dissertation (monograph)
In recent years, no follower of photographic art can have avoided coming into contact with abstract photography. It seems to be everywhere, from the most expensive galleries to the smallest independent exhibition spaces. New makers emerge, and established artists who previously conﬁned themselves to representational art are now working on abstract works. Numerous photography magazines have covered it, dedicating entire issues to the theme. What is it all about? And what exactly is abstract photography? Then there is the question of whether combining photography and abstraction is even possible or meaningful? To answer these questions this research gathers together over 100 years of abstract photography and approaches photographers and artists about their practice through interviews. As concepts, photography and abstraction seem to be almost opposites. The concept of abstract is usually used speciﬁcally to refer to non-representational art and photographic medium is traditionally described as a medium of exact representation. Interpreting non-representational images is further complicated by the variety of deﬁnitions used. The thought patterns and manufacturing techniques involved in producing abstractions are manifold. However, what all the deﬁnitions have in common is that they refer to photography with unrecognisable or hard-to-recognise subjects.Other recurring themes in abstract photographic art include an investigative orientation, experimentalism, a focus on the working process, and commentary on technical reforms. Medium- related self-referentiality is key: the subjects of abstraction often include the history and characteristics of photography, and the materials of the medium. Throughout its existence, the main subject of photographic abstraction has been photography itself. Furthermore, abstract photographic art is pictorial, non-narrative, and non-verbal. However, this does not mean that abstract photographic art could not be political. Throughout its history, abstract photography has been used as a means to criticise the features and changes of the art world and society in large. Time after time, abstraction challenges the traditional forms of expression and methods of photography, and functions within this medium as a force promoting renewal and vitality. Abstraction reﬂects the historical changes in photography over the past century. It highlights the technical changes in photography, but also the relationship between photography and the issues surrounding it, such as science or other art. The history of abstraction reﬂects the essential questions in the ﬁeld of photography in each era. Finnish contemporary photographic abstraction returns to 19th-century scientiﬁc photography, 1920s avant-garde photograms, and studies of motion. With the emergence of new artists, however, each decade sees a change in content. What all abstractionists have in common is a desire to break the representational character of photography and to boldly study different aspects of photography. Makers of photographic abstractions are always required to consciously work against the norms of photography. Abstraction is bold thinking.
Accelerating the energy transition toward zero-emission district heating systems through policy codesign
(2024) Auvinen, Karoliina
School of Arts, Design and Architecture | Doctoral dissertation (article-based)
Achieving zero-emission energy systems is necessary for mitigating climate change. This requires replacing fossil fuels with energy-saving measures, low lifecycle-emission primary energy sources, energy storage, and smart control systems. A significant portion of fossil fuels is consumed in district heating systems in cold climate regions worldwide. The main research question in this thesis is: "How can the energy transition toward zero-emission district heating systems be accelerated with policy codesign?" My research intersects with literature on socio-technical transitions, energy system decarbonization, transition management, and codesign. My research was conducted in collaboration with four research groups in Finland. The research methods included a triangulation of qualitative and quantitative approaches, such as interviews, energy system modelling, and prototyping. In the context of transition management, we designed and developed a mid-range pathway creation toolset and a transition arena process, which we then experimented with high-level influencers. Furthermore, by engaging with investors and other key stakeholders, we investigated socio-technical barriers and formulated policy proposals aimed at decarbonizing district heating systems. Finally, we proposed a transition pathway model for Helsinki, incorporating heat auctions to promote third-party access to the local district heating network. Our research in Finland confirmed the presence of numerous barriers to energy system decarbonization. Our research experiments indicated that mid-range transition arena processes, along with other policy codesign events, have the potential to produce effective policy suggestions for accelerating zero-emission energy transitions. Achieving energy system transformation requires wide-range policy interventions. However, implementing these in formal policy decision-making processes is contested and challenging. Transitions produce uneven costs and benefits across society. Transforming energy systems requires destabilizing the existing regime, and incumbent actors often resist this change due to path dependency. In conclusion, I propose a transition management model to accelerate the zero-emission energy transition, aiming to achieve emission reductions within district heating systems that are in line with the Paris Climate Agreement's timeline. Transition management and codesign approaches need to evolve toward institutionalization in order to create societal impact, and they must develop further in order to handle the related tensions and conflicts. However, given the current paradigm and system complexities, achieving a rapid energy transition appears improbable.
Access Control and Machine Learning: Evasion and Defenses
(2019) Juuti, Mika
School of Science | Doctoral dissertation (article-based)
Machine learning (ML) and artificial intelligence (AI) systems have experienced significant proliferation during the recent years, for example in the new market of "machine learning as a service". ML is also increasingly being deployed in security-critical applications, such as access control systems. ML can be used to make security systems easier to use, or to defend against specific attacks, such as the "relay attack". Such ML applications are particularly sensitive to the recent development of "adversarial machine learning", where weaknesses in machine learning systems are exploited to undermine some security-critical property. For example, "evasion attacks" undermine a ML system's prediction integrity, while "model extraction attacks" undermine the system's confidentiality. It has become increasingly important to evaluate ML applications against such undesired behavior. The work described in this dissertation is divided into three parts. In the first part, I evaluate how security properties in so-called transparent authentication systems can be improved using machine learning, and describe how to evaluate security against strong adversaries. In the second part, I present state-of-the-art evasion and model extraction attacks against image classification systems. In the third part, I evaluate state-of-the-art hate speech classifiers against evasion attacks, and present a method of artificially creating credible fake restaurant reviews. Finally, I present general observations and conclusions about both transparent authentication, and the feasibility of using ML for purposes such as moderation.
Access Control in Distributed Systems using SPKI Authorisation Certificates
(2015) Kortesniemi, Yki
School of Electrical Engineering | Doctoral dissertation (article-based)
In distributed systems, the ability to effectively manage access to a large number of resources can be challenging. The situation becomes even more difficult, when there are limited computational resources or network availability to implement the access control solution. Examples are Internet of Things (IoT) applications, such as the many internet-connected devices at home. To make them easy to use, there has to exist a relatively simple way to manage the large number of devices and to, e.g., grant temporary access to some of them for a visiting friend. In this dissertation, I examine how the problem can be overcome with the Simple Public Key Infrastructure (SPKI), which expresses access rights as cryptographically signed authorisation certificates. I approach the issue from several angles. First, I develop a phase model to analyse the access control process / certificate life-cycle and use it to study SPKI and other certificate technologies for access control while pointing out areas requiring future work. Although SPKI has been studied for some 20 years, standardisation has not been completed. I identify three important missing parts of SPKI in utilising the certificates, as well as in managing and validating online conditions. I also expand the SPKI model to support usage quotas. I then design solutions for all these areas and analyse the resultant system for its applicability, scalability, security and usability. Of particular interest are system performance and privacy. My final focus area is certificate chain reduction, a proposed way to improve performance and privacy of SPKI. I study the approach in detail, identify the relevant design choices for the systems architect, and design a protocol for requesting reductions. For performance evaluation we implemented a prototype, which demonstrates that even modern embedded devices can reach transaction times of one second including all communication delays and using only a software implementation for cryptography. We also found that the transaction was over 40 % faster with chain reduction thus proving the promise of improved performance. Using such reductions does requires a reduction server, but calculations from our use case show that even with pessimistic assumptions, a single reduction server can support millions of users thus making scalability a manageable issue. Privacy-wise, SPKI is a good solution with support for anonymous identities - and chain reduction can further improve user privacy by hiding additional information. Finally, all my use cases demonstrate the same certificate chain structure, an hourglass-model, which I hypothesise is prevalent in many other systems, as well. It forms natural basis for reduction and provides for a consistent performance regardless of certificate chain length.
Access Denied: Patterns of Consumer Internet Information Search and the Effects of Internet Search Expertise
(2003) Ylikoski, Teemu
School of Business | Doctoral dissertation (monograph)
The Internet is said to improve the consumer’s position in relation to businesses. This is said to result from the improved accessibility of consumer information and, consequently, better decision-making. However, certain difficulties hinder the way to the improved situation. The Internet brings about completely new types of difficulty for consumers, as it is an entirely consumer-driven setting. The study argues that consumers’ Internet search patterns largely determine the information to which the consumer has access. The relevance of this information is vital – it is only used in a decision if it is perceived to match the consumer’s information needs. Access to relevant online information requires an ability to identify and choose appropriate search patterns. The focus is thus on the patterns of Internet search and Internet search expertise. Typologies are created based on differences among seekers of information (i.e. people) and paths to information in the searches. The first finding of the study suggests that in contrast to the previous classifications of seekers, on the Internet, a different approach to “search” and its dimensions is needed. Six Internet seeker typologies emerge based on their characteristic features: high knowledge seekers, navigators, low seekers, social seekers, offline ad seekers, and retail seekers. The composition of the clusters appears stable based on external validation. In previous studies, it is commonly assumed that the inherent properties of information sources distinguish among the search patterns. Results indicate that in online search, the way through which the consumer finds each of the sources is emphasized, rather than the source as such. The search paths in online search belong to heuristic or analytical modes. Specific coding is developed for analyzing the paths to the information. The second finding indicates that consumers’ Internet searches largely rely on heuristics, in other words, trial and error. This happens to the extent that heuristic search is more prominent than analytical search in consumer information acquisition. Although the diagnosticity (i.e. likelihood of finding sufficient information to terminate search) of heuristic search is rather low, it gives the consumer flexibility with different information types. This suggests an interesting conflict between consumers’ specific information needs and flexibility of low-specificity searches. The third finding is that locating information online requires capabilities of consumers. To embrace these, the study introduces the concept of “Internet search expertise”. Structural equation modeling is used to assess its effects. The results show that Internet search expertise increases the effectiveness of the search (gives greater diversity of information) but has negative effects on the efficiency of the search (increases effort). The results may be due to the motivational effects – consumers with Internet search expertise are also highly motivated to search online, to the extent that the relative productivity of the search starts to decrease. Comparisons of two conflicting theories on the relation of Internet search expertise and product class knowledge are performed. One interpretation suggests that Internet search expertise compensates for the lack of product class knowledge, as online information sources are accessible in a uniform fashion. The other suggests that the best results in search require “double expertise”, i.e. presence of both capabilities. The structural equation models support the first theory: Internet search expertise has a positive effect on the diversity of information found, while product class knowledge fails to achieve statistical significance. On the other hand, the results from classifying information seeker types appear to countervail these findings, as product class knowledge is clearly emphasized in certain groups.
Accessibility and enzymatic degradation of native and model cellulose substrates
(2011) Suchy, Miro
Kemian tekniikan korkeakoulu | Doctoral dissertation (article-based)
This thesis investigated two issues relevant to the bioconversion of lignocellulosic biomass. The first part relates to the accessibility of cellulose in wood, more specifically, the impact of initial drying on wood ultrastructure. The second part of this thesis pertains to the enzymatic hydrolysis of cellulose, including a characterization of a model film of amorphous cellulose and its subsequent utilization in a fundamental evaluation of the mechanism of cellulase action. In addition, the impact of cellulase treatment on the properties and the morphology of wood pulp fibers was evaluated. The impact of drying on the ultrastructure of fresh wood was studied by deuterium exchange coupled with FT-IR analysis. Initially, the experimental concept and its reliability were evaluated using fresh wood samples. The same experimental concept was then applied to study the impact of initial drying on wood pulps of different characteristics and composition. The objective was to correlate the trends in drying-induced alterations observed for wood and for pulps, bleached chemical pulp in particular. Drying-induced alterations of a native wood sample exhibited a remarkable similarity to those observed for wood pulp samples. The results suggest that the supramolecular rearrangements in the native wood matrix upon dehydration are qualitatively identical to the well-known changes occurring in pulp fibers after drying, although the changes are considerably different in quantity. Quantitative studies of cellulose degradation by cellulase enzymes were carried out using an amorphous cellulose model film with well-defined characteristics. First, the films were extensively characterized, particularly their crystalline nature and swelling behavior. The film swelled excessively in water, doubling its thickness, but returned to the original thickness upon water removal, while retaining its amorphous nature. This film was then used as a substrate in studying the action of monocomponent endoglucanase (EG) that acts on amorphous cellulose. The study was carried out using a quartz crystal microbalance with dissipation monitoring (QCMD). The main objectives were to study the impact of film thickness on the rate of hydrolysis and to directly quantify the extent of hydrolysis (decrease in thickness of films after hydrolysis). It was demonstrated that the amount of substrate available for hydrolysis did not have an impact on the rate of hydrolysis. The investigation also demonstrated impacts of various factors on the kinetic evaluation of the cellulase action. The investigation of the action of a commercial celobiohydrolase on wood pulp fibers showed that the treatment had no significant impact on the strength properties of the pulp. Changes of fiber morphology and of fracture type in the treated fibers during zero span evaluation,
Accessing multiversion data in database transactions
(2010) Haapasalo, Tuukka
Aalto-yliopiston teknillinen korkeakoulu | Doctoral dissertation (monograph)
Many important database applications need to access previous versions of the data set, thus requiring that the data are stored in a multiversion database and indexed with a multiversion index, such as the multiversion B+-tree (MVBT) of Becker et al. The MVBT is optimal, so that any version of the database can be accessed as efficiently as with a single-version B+-tree that is used to index only the data items of that version, but it cannot be used in a full-fledged database system because it follows a single-update model, and the update cannot be rolled back. We have redesigned the MVBT index so that a single multi-action updating transaction can operate on the index structure concurrently with multiple concurrent read-only transactions. Data items created by the transaction become part of the same version, and the transaction can roll back. We call this structure the transactional MVBT (TMVBT). The TMVBT index remains optimal even in the presence of logical key deletions. Even though deletions in a multiversion index must not physically delete the history of the data items, queries and range scans can become more efficient, if the leaf pages of the index structure are merged to retain optimality. For the general transactional setting with multiple updating transactions, we propose a multiversion database structure called the concurrent MVBT (CMVBT), which stores the updates of active transactions in a separate main-memory-resident versioned B+-tree index. A system maintenance transaction is periodically run to apply the updates of committed transactions into the TMVBT index. We show how multiple updating transactions can operate on the CMVBT index concurrently, and our recovery algorithm is based on the standard ARIES recovery algorithm. We prove that the TMVBT index is asymptotically optimal, and show that the performance of the CMVBT index in general transaction processing is on par with the performance of the time-split B+-tree (TSB-tree) of Lomet and Salzberg. The TSB-tree does not merge leaf pages and is therefore not optimal if logical data-item deletions are allowed. Our experiments show that the CMVBT outperforms the TSB-tree with range queries in the presence of deletions.
Accomplishing rural electrification for over a billion people: Approaches towards sustainable solutions
(2014) Rahman, Mizanur Md.
School of Engineering | Doctoral dissertation (article-based)
Access to electricity appears to be a prerequisite to materialize social, economic, and human development in the underprivileged rural areas. However, 1.1 billion rural people in the world, almost all of them living in developing countries, still do not have access to electricity. Although the rural electrification process poses more challenges than urban electrification, rural areas are blessed with abundant and relatively evenly distributed renewable energy resources. To facilitate electricity access to this huge population, it is essential to deal with the rural electrification task by considering its challenging features and the potential merits of renewable resources. The objective of this thesis is to present policy and techno-economic frameworks for sustainable and accelerated rural electrification for over a billion people in developing countries. This thesis considers grid expansion as the primary option for rural electrification, and renewable resource based off-grid options were considered as the alternative where grid expansion is not feasible. Grid-based rural electrification policies were examined by focusing on one case program (the Bangladesh rural electrification program) in light of challenges that are generic for developing countries. The assessment of the potentials and techno-economic viability of renewable resources were performed by utilizing analytical methodologies and well-established computer tools (HOMER and RETScreen). The evaluation of choices among rural electrification alternatives has been illustrated with the help of the Stochastic Multicriteria Acceptability Analysis (SMAA) tool. The evaluation methods and tools are illustrated by employing case data obtained mainly from Bangladesh. This thesis observed that some key policy elements influence the performance of a grid-based rural electrification program. These policy elements guide the rural electrification program towards success through addressing distinct rural electrification challenges. Agricultural residues have the potential to generate electricity to meet household-level demands in rural areas of many developing countries. Hybrid biogas and solar resources can serve both clean-cooking and electricity loads in rural households with achieving benefit (saving) more than the cost. The multicriteria decision support technique enables a rural electrification program to choose decision options from different alternatives based on sustainability criteria.
Accurate modelling of tissue properties in diffuse optical imaging of the human brain
(2009) Heiskala, Juha
Doctoral dissertation (article-based)
Diffuse optical imaging (DOI) is an emerging imaging modality for non-invasive functional medical imaging, using near infrared (NIR) or visible red light. The innovation is to derive functional information about living tissue from measurements of light that has passed through it. Optical imaging can be applied to imaging of tissues as diverse as the central nervous system, female breast, muscle, and joints of fingers. This thesis addresses the application of DOI to studying the human brain. In this thesis, the problems of modelling light propagation in the adult and infant human head, and reconstructing three-dimensional images of functional changes in the brain using optical measurements, are addressed. Difference imaging, where changes from baseline optical parameters rather than absolute parameter values are reconstructed, is considered. The goal was to develop methods for accurate modelling of light propagation and to clarify how specific aspects of the computational modelling affect the reconstruction of functional images from optical measurements of the human brain. Specifically, the significance of anisotropic light propagation in the white matter, and a priori knowledge of the anatomy and the optical properties of the head and brain are studied. Moreover, a generic probabilistic atlas model of the infant head to enhance image reconstruction is developed. Significance of anisotropic light propagation was found to be small in optical imaging of the adult brain. Although anisotropic light propagation may have a larger impact on the measured signal when infants are imaged, results suggest that image reconstruction can be performed without taking anisotropy into consideration. The use of a priori anatomical knowledge was found to significantly improve the accuracy and robustness of image reconstruction in difference imaging. The results suggest that for optimal reconstructions, individual MR imaging based anatomical data should be used when possible. For cases where individual anatomical data is not available, atlas models should be developed. An important consideration is how to obtain the baseline optical parameters of tissue classes in the anatomical model. Literature-derived parameters can be used as a starting point. For optimal results however, methods should be developed for estimating the baseline parameters from measured data.
Acoustic and optical investigations of superfluid 3He
(1993) Manninen, Antti
School of Science | Doctoral dissertation (article-based)
Acoustic Scattering for Spatial Audio Applications
(2022) Gonzalez, Raimundo
School of Science | Doctoral dissertation (article-based)
Modeling of sound propagation on the context of acoustic design and interactive applications have mainly focused on room acoustics as well as source and receiver modeling. In order to enrich the description and perceptual immersion of virtual sound-fields, modeling frameworks can also include the effects of scattering of bodies within the physical space. One of the main challenges in modeling the effects of scattering, is that its behaviour not only depends on the geometry of the scatterer but also the direction of arrival of the incident field. This thesis is a collection of five publications, the first two studies focus on the effects of near-field sources, and the last three studies involve the effects of scattering within spatial audio applications. The first publication explores the effects of near-field sources on High-order Ambisonics recording, processing and binaural reproduction. Results indicate that while near-field sources introduce low-frequency proximity gains in high-order microphones arrays, the regularization stages in Ambisonics recording prevents excessive gains. The second publication explores the directivity of near-field speech of 24 subjects and evaluates various repeatable speech reproduction alternatives. The third publication presents a scheme for encoding the acoustic scattering of arbitrary geometries into the spherical harmonic domain. After encoding, the scattering is represented as a multiple-input multiple-output matrix which describes the relation between the incoming and outgoing scattering modes of a geometry. This method allows for the standard transformations in the spherical harmonic domain (rotation, translation, scaling) and it is compatible with existing spatial audio frameworks such as Ambisonics and image-source methods. This method is validated using boundary element method simulations and indicates minimal synthesis error. The fourth publication presents a method to encode the space domain signals from a microphone array with arbitrary geometry and irregularly distributed sensors into Ambisonics. The algorithm relies on the array response and its enclosure's scattering properties to solve the direction of various active sources as well as the diffuse properties of the sound-field. Objective and subjective evaluations indicate that the proposed method outperforms traditional linear encoding. The fifth publication extends the method presented in the third publication by allowing sector-based encoding of acoustic scattering, optimal for geometries and surfaces which do not require entire spherical radiation. This last publication also presents a method to compress the data of the scattering matrix, allowing for more efficient memory storage. Methods proposed in the third and fifth publications can be used to introduce scattering geometries into interactive sound environments to produce more descriptive sound-fields while the fourth publication can be used to develop Ambisonic recording arrays on practical devices such as wearables and head-mounted displays.
ActionPool : a novel dynamic task scheduling method for service robots
(2010) Taipalus, Tapio
Aalto-yliopiston teknillinen korkeakoulu | Doctoral dissertation (monograph)
Service robots require the seamless utlisation of several technical disciplines. Most of the required technologies are sufficiently advanced to provide feasible solutions to be used in the designing of service robots. For instance, mechanical engineering, control theory, electronics and electrical engineering aspects of the design have all matured well. On the other hand, it is the perception and artificial intelligence that provide the means for modelling the environment and the knowledge which are lagging behind. The latter two disciples in their current state, greatly limit the complexity of the tasks which can be performed by service robots. In this thesis, an ActionPool method for representing task knowledge and executing multiple tasks simultaneously with service robots is presented. The method is based on a concept in which the actions that are ready for execution are placed into a pool and from those most suitable for the situation are selected one by one. The number of actions in a pool and the number of tasks are limited only by the available computational resources. The actions can belong to different tasks, and thus the action pool allows the robot's indivisible resource to be dynamically dealt out for various tasks requiring the resources. In the ActionPool method, the functional parts of the service robot are divided into resources and an action pool is assigned to each one of them. This way, numerous tasks can be executed simultaneously. The ActionPool method allows a natural way of dynamically adding and removing tasks to and from the robot's active execution. The action selection method can direct the perception processes to observe the relevant parts of the environment. The ActionPool method has been implemented on two different service robot platforms to verify the generic nature of the method. Several tasks have been executed successfully to validate the claims about the qualities of the method. Compared to previous approaches, this work provides a fresh execution- and contingency-centric vantage point to the well studied robot control problem.
Active and passive dielectric rod waveguide components for millimetre wavelengths
(2010) Pousi, Patrik
Aalto-yliopiston teknillinen korkeakoulu | Doctoral dissertation (monograph)
In this thesis, active and passive dielectric rod waveguide (DRW) components have been studied and developed for millimetre wavelengths. DRW antennas made of relatively high permittivity materials like silicon and sapphire are designed and simulated with HFSS (a commercial electromagnetic structure simulator based on Finite Element Method) at frequencies up to 325 GHz. A prototype antenna for D band (110-170 GHz) has been fabricated and measured. The location of the phase centre of an antenna is an important parameter in many applications, especially when the antenna is used as a feed for a reflector. This location of the phase centre for the DRW antenna has been studied with different methods from measurement results obtained with a planar scanner at W band. A high-permittivity DRW antenna is an interesting candidate for an antenna array element. According to W-band simulations and measurements the mutual coupling between the elements is relatively low even with the distance of ∼λ ⁄ 2 as the element spacing. This makes the DRW an appealing alternative as an element for densely packed arrays. However, mutual coupling studies for antenna arrays revealed a very strong coupling phenomenon when the distance between the elements is small. At some point the power is transferred completely from the excited waveguide to the neighbouring waveguide. This phenomenon is similar to cross-talk in optical fibres. In that regime cross-talk has been utilised in many applications, e.g. in directional couplers. In this thesis a frequency selective coupler based on that strong coupling has been developed. Frequency selectivity is based on the fact, that the waveguide length required for complete power transfer depends on the frequency. The length that is required for the power to transfer from one waveguide to the other and back is also called as the beat length. A prototype coupler has been simulated, manufactured and measured at W band. The results are very promising for this type of components made of DRWs for millimetre wavelengths. Different types of DRW junctions for power division have also been studied. Such junctions can be used also for monitoring the propagating power in a DRW. Junctions can be designed for both E and H planes depending on the application. Symmetric and asymmetric Y-type junctions have been designed and studied with simulations in both planes. Active components studied in this thesis include a travelling-wave amplifier based on GaAs/AlGaAs heterostructure and a DRW phase shifter designed for ferroelectric varactors fed through Au strips, both designed for W band. A DRW travelling-wave amplifier is based on the interaction between an electron drift and an electromagnetic wave travelling in a periodic structure. Electronic gain of 10 dB/cm at 150 V/cm has been measured at 70-80 GHz. The proposed novel prototype of millimetre-wave phase shifter includes a dielectric rod waveguide with a periodic printed array of electrically small dipoles loaded with ferroelectric varactors. Measurement results of a non-tunable phase shifter prototype show that optimally a phase shift of 60 deg/dB can be obtained at W band.
Active control of radial rotor vibrations : identification, feedback, feedforward, and repetitive control methods
(2007-05-04) Tammi, Kari
Doctoral dissertation (monograph)
Active vibration control methods for rotors were studied in order to develop solutions to enhance machines' dynamic behaviour, durability, and operating range. The aim of the thesis was to develop identification and control methods for active vibration control of a rotor. The identification method developed in the thesis improved run-time rotor identification by compensating rotation-related disturbances before the actual identification procedure. The control system design comprised an inner feedback loop and an outer loop for compensation for harmonic excitations due to mass unbalance and other rotation-related excitations. The feedback loop was shown to be essential in terms of providing favourable conditions for the other compensation algorithm in the outer loop. For the outer loop, three algorithms were tested: two feedforward control methods and a repetitive control method. The algorithms were validated and compared using an experimental set-up. Concerning the feedforward methods, the Convergent Control algorithm was found to be a more effective and simpler algorithm for the purpose than the adaptive FIR filter with the LMS algorithm. The adaptive gradient-based repetitive control, developed in this thesis, was found to have a poorer performance than the feedforward control methods, but to provide benefits for applications where excitation frequencies are not as predictable as in the current application.

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