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Advancing the Fundamentals in Molecular Beam Epitaxy of GaAs-based Nanowires
No full textIII-V yhdistepuolijohteita voidaan valmistaa suoraan piille nanolankojen muodossa, mikä puolestaan mahdollistaa fotoniikan ja mikroelektroniikan saumattoman integraation. Nanolankojen kasvatuksessa käytettävä itsekatalysoitu menetelmä, jossa kasvua tukeva katalyyttipisara koostuu samoista alkuaineista kuin nanolanka, on monimutkainen fysikaalinen prosessi. Se perustuu eri faasien, kaasun, nesteen ja kiinteän aineen keskinäisiin kemiallisiin potentiaaleihin ja aineiden supersaturaatioihin. Käytännön näkökulmasta näitä parametreja voidaan hallita molekyylisuihkuepitaksiakasvatuksen aikana muuttamalla III- ja V-ryhmän alkuaineiden vuosuhteita ja kasvatuslämpötilaa. Vaikka monet nanolankojen kasvatukseen liittyvät ilmiöt ovat jo hyvin tunnettuja, niiden kehitys käytännön sovelluksiin vaatii vielä tutkimusta kidelaadun, kapean kokojakauman, seostuksen sekä useiden alkuaineiden inkorporaation ymmärtämiseksi.
Tässä työssä pureudutaan näihin seikkoihin tutkimalla fysikaalisia ilmiöitä itsekatalysoitujen galliumarsenidipohjaisten nanolankojen molekyylisuihkuepitaksiassa. Nanolankojen kasvuprosessin ymmärryksen lisäksi työ tarjoaa konkreettisia menetelmiä nanolankojen toiminnallisuuden kasvattamiseksi kohti käytännön sovelluksia. Tässä työssä osoitetaan, että kehittämällämme menetelmällä kasvatettujen nanolankojen kidelaatu on erinomainen ja että sillä pystytään saavuttamaan Poissonin jakaumaa kapeampi kokojakauma. Tämä on ensimmäinen havainto nanolankajoukossa nähdystä atomikerrosten nukleaation ajallisesta antikorrelaatiosta. Puhtaan galliumarsenidin lisäksi työssä tutkitaan nanolankojen seostusta sähköä johtavaksi berylliumin ja telluurin avulla sekä vyöaukon kontrollointia antimonin avulla. Nämä yksityiskohtaiseen inkorporaatiomekanismien ymmärrykseen johtaneet tulokset ovat merkittäviä askeleita nanolankarakenteiden toiminnallisuuden lisäämiseksi käytännön sovelluksia varten. Eri alkuaineiden inkorporaation lisäksi työssä tutkittiin myös kasvatuksessa käytetyn arseenivuon molekyylityypin vaikutusta nanolankakasvuun. Molekyylityypin valinnan osoitettiin olevan käytännöllinen kasvatustyökalu, jolla voidaan säätää niin nanolankojen pituuden ja paksuuden suhdetta sekä kasvunopeutta kuin hallita eri alkuaineiden inkorporaatiomekanismeja.Semiconductor nanowires (NWs) allow epitaxial integration of III-V semiconductors directly on Si platform, offering an intriguing pathway towards integration of photonic and microelectronic functionalities. NW growth using internal metal catalyst, so called self-catalyzed growth, is a complicated physical process resulting from the interplay of the supersaturations and chemical potentials in vapor, liquid and solid phases of the elements present during the growth. Although many aspects of the epitaxy have been addressed during the recent years, advancing the NWs technology towards practical applications requires significant developments to guarantee high crystal purity, uniform size distributions, precise definition of doped heterostructures as well as improve ability to control the incorporation mechanisms of different elements. Accessing these properties requires detailed information on the physics controlling the NW growth and their relation to the technological control steps.
To this end, the thesis contributes to the development of NW technology by investigating the physical phenomena behind the self-catalyzed gallium arsenidebased NW growth but also by offering concrete pathways towards the desired NW functionality. The NW growth is investigated by molecular beam epitaxy growth on lithography-free templates. The templates provide a robust tool to focus on the NW growth mechanism while offering possibility to grow comparable samples. The crystal structure of these NWs is shown to be excellent. The first demonstration of sub-Poissonian length distribution is presented in this thesis providing evidence of the so-called nucleation antibunching in a large NW ensemble. Nucleation antibunching causes the nucleation events during NW growth be temporally anticorrelated. Furthermore, incorporation of Be and Te dopant atoms, and Sb as a ternary element have been studied; this is a significant step towards realization of practical structures yet marginally addressed before due to the early stage of development of the field overall. Details on the incorporation mechanisms of these elements into the NWs have been revealed for the first time. Moreover, the role of As species in the molecular beam epitaxy of NWs was clarified; the selection of As species was found to be a practical tool for NW grower to adjust the dimensions of NWs, but also select the primary incorporation mechanisms of elements
The Process of Building Inter-organizational Collaboration for Industrial Symbiosis : Two cases from Finland: ECO3 & Envitech
No full textThe present situation of environmental degradation and natural resource depletion encouraged researchers to find new ways of integrating sustainability in industrial activities. The concept of industrial symbiosis (IS) has the potential to fight these challenges by creating linkages among co-located industrial actors. In this system, the waste of one actor is considered a resource for another, and share common utilities for operations. The concept has been practically implemented in many countries to introduce resource-efficient operations. Therefore, this research aims to identify the collaboration process development toward the IS system while mapping the ecosystem actors and diverse driving or inhibiting factors.
To seek answers for the research questions, a qualitative multiple case study analysis on two nationally significant IS cases from Finland was conducted. The primary data sources for both of the case studies were direct interviews with the specified ecosystem actors. The interview data were transcribed, systematically grouped, and analyzed by following the research theme. The secondary data were multi-sourced from company webpages, thesis, reports, book chapter, and authenticity of some secondary data were double-checked during the inter-views. Data-driven thematic analysis was implemented to group the researched data on each case, with the identification of critical incidents during the IS evolution phases, followed by an ecosystem actor mapping through Kumu software and outlining the factors impacting the IS system. Lastly, a case comparison by defining dimensions under the researched themes was performed to define the distinctive pattern of both cases.
The key findings indicate that organization of the IS system can be categorized as a “publicly driven” or “company driven” model. Nevertheless, both models encompass the emergence, probation, and development & expansion phases of the IS evolution process with diverse activities organized by the ecosystem actors. A publicly driven IS model is mainly inaugurated by the local governments and the process advances as a planned symbiosis model. The company driven IS model mainly progresses through the spontaneous participation of local company actors based on their own need. The publicly driven IS model functions through a central operator while the individual company actors are the key decision taker of the company driven model without any centralized approach. The organization of activities in both cases is impacted by a similar set of driving or inhibiting factors like legislation, location, changes in people’s attitudes, and the main driving element is a human actor.
This study contributes to the existing knowledge of IS process development by looking into critical cases from processual dimensions. The investigator suggests that the successful evolution of an IS system will require active collaboration and co-operation from public organizations and private company actors. A co-operative mindset among all the stakeholders can be established by developing a shared vision and will require a platform company to centrally organize the IS system development. The company actors need to be more open, while a change in attitude and new legislation is highly required to encourage bio and circular economy businesses through IS
Improving the Visual Perception of Heavy Duty Manipulators in Challenging Scenarios
No full textRobotic vision is a subfield of computer vision intended to provide robots with the capability to visually perceive the surrounding environment. For example, a robotic manipulator leverages its visual perception system to gather visual data through cameras and other sensors, then uses that input to recognize different objects in order to safely perform an autonomous operation.
However, in many robotics applications, robots have to face a cluttered and dynamic scene, where classic computer vision algorithms show the limitation of tackling the environmental uncertainty. Such scene understanding requires a fusion of traditional and modern approaches involving classic computer vision, machine learning and deep learning methods.
This thesis examines visual perception challenges in remote handling and the mining industry. It begins with two research questions: Can the robustness of targetobject pose estimation be improved in challenging real-world, heavy-duty robotic scenarios? Can fast detection and localization for objects be obtained without prior known geometry in a scenario with piles of overlapping objects? Six publications cover the methods from algorithm design to system-level integration used to solve real-world problems.
In the ITER fusion reactor, the operator teleoperates a robotic manipulator to perform maintenance tasks amidst a high level of noise and erosion. The operator cannot fully rely on the virtual reality (VR) system, which may not reflect the current scene accurately, as physical conditions may have changed in the harsh environment. Meanwhile, every operation inside the reactor requires robust, millimeterlevel accuracy. This thesis analyzes research questions and presents a novel edgepoint iterative closest point (ICP) method as a solution for target-object detection, tracking and pose estimation. Using the knuckle of a divertor cassette as an example, the overall accuracy of the developed visual system meets ITER requirements, and the conducted experiments with the manipulator demonstrated the efficiency of the method.
Smartbooms2 is a project in the mining industry that requires a heavy manipulator with a hydraulic hammer to autonomously break rocks in a cluttered outdoor environment. Based on the output data of the three-dimensional (3D) sensors, several solutions are proposed. Examining a popular time-of-flight (TOF) sensor, this thesis explores state-of-the-art unsupervised machine learning methods and proposes a novel clustering method. Using an industrial stereo camera, this thesis proposes a novel 3D rock detection and localization pipeline. The results and system accuracy are detailed in published research papers
Trends of Physical Functioning, Morbidity and Disability-free Life Expectancy among the Oldest Old : Six Repeated Cross-sectional Surveys between 2001 and 2018 in the Vitality 90+ Study
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Knocking on Europe’s door : How narratives of fear, insecurity and nostalgia shape collective perceptions of immigration
No full textOptimizing adipogenic differentiation of adipose stem cells in two biocompatible hydrogels
No full textAdipose tissue serves as an important energy storage, but it also participates in several biological processes, including endocrine and paracrine regulation of energy metabolism and thermoregulation. Understanding these processes is vital for development of targeted therapeutics for diseases linked to them, such as diabetes and obesity. Moreover, regenerated adipose-like tissues are needed for soft tissue reconstruction in addition to in vitro models.
2D models fail to equate the features of native adipose tissue, which 3D models aim to mimic. Adipogenesis is the process during which stem cells differentiate into mature adipocytes. Aim of this study is to optimize adipogenic differentiation of adipose stem cells using two different hydrogels and varying cell densities. Hydrogels are polymer networks that have high water absorption capacity. Also, quantitative and qualitative analysis methods for adipogenic differentiation are optimized for 3D-cell culture.
In the study, adipogenic differentiation of human adipose-derived stem cells (hASCs) was tested in hydrazone crosslinked gellan gum/gelatin (1:1) hydrogel (gellan gum 40 mg/ml in αMEM and gelatin CDH 40 mg/ml in αMEM.) and in fibrin hydrogel (fibrinogen in DPBS 5 mg/ml and thrombin in EBM-2 2 iU/ml in a 1:1 mixture). The cells were seeded inside the hydrogel in a 48-well-plate format at densities of 0,5, 1,0, ja 2,0 x 106 cells/ml hydrogel and cultured in adipogenic differentiation medium (AM). Differentiation of hASCs was analyzed and quantified using AdipoRed staining and WST-1 cell proliferation assay after 14 or 21 days of culturing. 2D hASC culture with 1053 cells/cm2 was used as a differentiation control. Cell morphology and lipid droplet formation were observed during culture time.
In the study, we showed that the adipogenic differentiation of hASC is dependent on the cell number. Furthermore, quantification of lipid droplet formation, characteristic for differentiated adipocytes, can be performed in a hydrogel in 3D environment. Human adipose-derived stem cells differentiated in hydrogel and obtained features found in native, mature adipocytes, including intracellular lipid droplets and spherical shape. The simultaneous quantification of both lipid formation and cell viability can be performed in 3D hydrogel presented in this study