Browsing by Subject "retention"

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  • Nguyen, Su Duy; Javanainen, Matti; Rissanen, Sami; Zhao, Hongxia; Huusko, Jenni; Kivelä, Annukka M.; Ylä-Herttuala, Seppo; Navab, Mohamad; Fogelman, Alan M.; Vattulainen, Ilpo; Kovanen, Petri T.; Öörni, Katariina (2015)
    Lipolytic modification of LDL particles by SMase generates LDL aggregates with a strong affinity for human arterial proteoglycans and may so enhance LDL retention in the arterial wall. Here, we evaluated the effects of apoA-I mimetic peptide 4F on structural and functional properties of the SMase-modified LDL particles. LDL particles with and without 4F were incubated with SMase, after which their aggregation, structure, and proteoglycan binding were analyzed. At a molar ratio of L-4F to apoB-100 of 2.5 to 20: 1, 4F dose-dependently inhibited SMase-induced LDL aggregation. At a molar ratio of 20: 1, SMase-induced aggregation was fully blocked. Binding of 4F to LDL particles inhibited SMase-induced hydrolysis of LDL by 10% and prevented SMase-induced LDL aggregation. In addition, the binding of the SMase-modifi ed LDL particles to human aortic proteoglycans was dose-dependently inhibited by pretreating LDL with 4F. The 4F stabilized apoB-100 conformation and inhibited SMase-induced conformational changes of apoB-100. Molecular dynamic simulations showed that upon binding to protein-free LDL surface, 4F locally alters membrane order and fluidity and induces structural changes to the lipid layer. Collectively, 4F stabilizes LDL particles by preventing the SMase-induced conformational changes in apoB-100 and so blocks SMase-induced LDL aggregation and the resulting increase in LDL retention.
  • Hollingsworth, A.; Lavrentiev, M. Yu; Watkins, R.; Davies, A. C.; Davies, S.; Smith, R.; Mason, D. R.; Baron-Wiechec, A.; Kollo, Z.; Hess, J.; Jepu, I.; Likonen, J.; Heinola, K.; Mizohata, K.; Meslin, E.; Barthe, M-F; Widdowson, A.; Grech, I. S.; Abraham, K.; Pender, E.; McShee, A.; Martynova, Y.; Freisinger, M.; De Backer, A. (2020)
    A new facility to study the interaction of hydrogen isotopes with nuclear fusion-relevant first wall materials, and their retention and release, has been produced. The new facility allows for implanting a range of gases into samples, including tritium. An accurate study of isotope effects, such as the isotopic exchange in damaged microstructure, has previously been difficult due to a background signal of light hydrogen. This new capability will allow virtually background free measurements using tritium and deuterium. The design and build of this facility are described and commissioning results are presented. Within the UKAEA-led tritium retention in controlled and evolving microstructure (TRiCEM) project, this facility is used for the comparative study of deuterium retention in self-ion irradiated Eurofer steel and Fe?Cr alloy. Self-ion bombardment with energies of 0.5 MeV is used to mimic the defects created by neutrons in fusion power plants and the created traps are then filled with deuterium in the new facility. Implanted samples are analysed using thermal desorption spectrometry (TDS), secondary ion mass spectrometry (SIMS), and transmission electron microscopy. Results on the total deuterium content as a function of time, TDS spectra and SIMS analysis are presented. A comparison of the results for Eurofer and Fe?Cr revealed several differences. While some of them may be due to experimental details like different time delays between exposure and analysis, others, such as deuterium retention as function of dose, might be genuine and require further studies.
  • Mikkonen, Kasperi (Helsingin yliopisto, 2019)
    Playing video games is a popular way to spend time and mobile gaming is one of the most growing entertainment industries in the world. Gaming is often associated with high level of motivation from the user as well as many negative and positive outcomes. Commitment towards games has invited countless of researches to examine what makes them so intriguing and motivating. This growing understanding gives developers more tools to design even better games and allows game-like features to be used in other contexts as well. This master’s thesis examines automatically gathered early log-data (n=100 000) from two free-to-play mobile games in order to create a model for retention. A model created using early log-data (first three days of play) creates opportunities to recognize potential players in an early phase and to evaluate early iterations of games that are in development. Furthermore, individual features are analyzed to study, what are the factors that influence coming back to the game at a later point (30 days after the installation of the game). The research questions in this thesis are: 1) Can commitment towards mobile games be modeled using early log-data? 2) How accurate predictions the created model can do? 3) What are the most important in-game features that predict retention? The model is created using a decision tree analysis, which was selected as a method due to its transparency and because it has been used before in earlier studies with similar designs. In both games, the rate of coming back to the game after 30 days of installation was 7.6%. A working model for retention was formulated which was able to predict coming back to the game with 33% accuracy. The most important in-game features that affect retention were the number of victories, the number of starts and the number of in-app-purchases during the three-day period after the game’s installation. Surprisingly, in-game rewards and achievements were the most insignificant features when predicting retention although they are often specifically designed to elevate user motivation. These results can influence design decisions made in game development by setting the focus on the factors that influence player commitment and behavior. Achievements and in-game rewards might feel too artificial and superficial compared to winning in game. If the system gives direct feedback of the effect of time and monetary sacrifice to the player’s performance, one might be able to reduce the number of players that decide to leave the game. The results also can be used to examine how game-like features are used in non-game systems where the goal is to tie together the high-level of motivation seen in games and socially impactful endeavors. Further studies of in-game behavior might also give new insights on game addiction and its negative effects on player well-being and business.
  • Stoycheva, Polina; Tiippana, Kaisa (2018)
    The brain's left hemisphere often displays advantages in processing verbal information, while the right hemisphere favours processing non-verbal information. In the haptic domain due to contra-lateral innervations, this functional lateralization is reflected in a hand advantage during certain functions. Findings regarding the hand-hemisphere advantage for haptic information remain contradictory, however. This study addressed these laterality effects and their interaction with memory retention times in the haptic modality. Participants performed haptic discrimination of letters, geometric shapes and nonsense shapes at memory retention times of 5, 15 and 30 s with the left and right hand separately, and we measured the discriminability index d '. The d ' values were significantly higher for letters and geometric shapes than for nonsense shapes. This might result from dual coding (naming + spatial) or/and from a low stimulus complexity. There was no stimulus-specific laterality effect. However, we found a time-dependent laterality effect, which revealed that the performance of the left hand-right hemisphere was sustained up to 15 s, while the performance of the right-hand-left hemisphere decreased progressively throughout all retention times. This suggests that haptic memory traces are more robust to decay when they are processed by the left hand-right hemisphere.
  • Ahlgren, Tommy; Jalkanen, Pasi; Mizohata, Kenichiro; Tuboltsev, Vladimir; Räisänen, Jyrki; Heinola, Kalle; Tikkanen, Pertti O. (2019)
    The radiological safety of the future thermonuclear fusion devices depends critically on the total tritium inventory in the plasma-facing components. The planned method to remove tritium from the ITER reactor tungsten divertor is to perform vacuum baking. We show that tritium removal from tungsten can be enhanced by the isotope exchange mechanism by doing the baking in H-2 atmosphere. The results show that the retained deuterium from 30 keV implantation can be expected to drop almost to zero after 24h annealing at 250 degrees C in H-2 atmosphere. Annealing in vacuum requires temperatures above 400 degrees C for close to zero retention.
  • Vuoriheimo, Tomi; Jalkanen, Pasi; Liski, Anna; Mizohata, Kenichiro; Ahlgren, Tommy; Heinola, Kalle; Räisänen, Jyrki (2020)
    Future fusion reactors use a D–T plasma mixture as fuel. A fraction of hydrogen species can escape the plasma confinement and hit the first wall. Hydrogen isotope exchange, a process in which trapped T atoms are replaced with lighter hydrogen isotopes D or H, is a potential method to minimize radioactive T retention in the wall materials. The present work extends our systematic research on isotope exchange by reversing the process, i.e. by implanting H ions into tungsten followed by subsequent annealing at different constant temperatures in D2 atmosphere. Elastic Recoil Detection Analysis was used to determine the H and D concentrations. The results show that the isotope exchange process takes place regardless of the mass of the active hydrogen isotope. This indicates that the isotope exchange is a statistical phenomenon in which the abundance of the neighboring hydrogen near the trapped hydrogen isotope defines the efficiency of the process.
  • Shekarchizadeh, Hajar; Ekhtiari, Hamed; Khami, Mohammad R.; Virtanen, Jorma I. (2012)
  • Korhonen, Vesa; Mattsson, Markus; Inkinen, Mikko; Toom, Auli (2019)
    In the description of the complex relationship between individual students and their education context, as well as understanding of questions related to progression, retention or dropouts in higher education, student engagement is considered the primary construct. In particular, the significance of the first year of higher education in terms of engagement is decisive. We aim at developing a multidimensional conceptualization of engagement and utilized network analysis. Data were collected as part of the annual Student Barometer survey in Finland during the 2012-2013 academic year, and we gathered a nationally representative sample (n = 2422) of first-year students in different disciplines at 13 Finnish universities. Network analysis confirmed the multidimensional process model of engagement and its six dimensions. The central dimensions of engagement are identity and sense of belonging, which develop in the interplay between individual and collective dimensions as a long-term process. Additional network analyses with covariates identified positive and negative factors that affect engagement. The study adds new perspectives to existing knowledge of engagement. It is important to understand the process-like nature of engagement and make visible factors affecting the process. Based on these findings, we provide novel practical recommendations for interventions for university students who struggle with engagement during their first year.