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- Hébert-Losier, Kim
(författare)
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An Investigation of the Influence of Knee Flexion Angle on the Activity of the Triceps Surae Muscles during the Heel-Raise Test
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: The heel-raise test (HRT) is used in clinical practice and research to assess the triceps suare (TS) muscles. The test involves repetitive unilateral heel-raises in upright stance. The test is administered with the knee straight for gastrocnemius medialis (GM) and lateralis (GL), and with the knee bent for soleus (SOL). The maximum number of heel-raises which can be performed is utilised as a clinical outcome measure and informs clinical decisions. The use of knee flexion (KF) to direct HRT assessment towards SOL or GAST currently relies on fundamental principles and has a limited evidence-base. Aims: The primary aim of this research was to investigate the influence of KF angle on SOL, GM, and GL activity and fatigue during the HRT. Secondary aims were to explore the total number of heel-raises completed, and the influence of age group on TS muscle activity and fatigue. Methods: Specific literature reviews were undertaken to contextualise the HRT within a comprehensive anatomical and biomechanical framework, and the experimental research involved a sequence of biomechanical studies. Seventeen subjects participated in a preliminary study that involved heel-raise testing to fatigue in two KF positions and generalised estimation equations were used to determine whether select KF angles were maintained. Forty-eight subjects, stratified by age and gender, participated in the main experimental study. Surface electromyography (EMG) activity of SOL, GM, and GL during maximum voluntary isometric contractions (MVIC) was collected in 0°KF, 45°KF, and 90°KF to inform EMG normalisation. Subjects then completed 10 unilateral heel-raises in 0°KF and 45°KF to investigate EMG amplitudes (% of MVIC) and heel-raises to fatigue for power spectrum analysis (median frequency and normalised slope). Mixed-effects models and stepwise regressions were used for the main analysis. Results: The preliminary study identified that select KF angles were reasonably well maintained during testing and subjects completed an average of 40 heel-raises in the two KF positions. The investigation of (EMG) muscle activity during MVIC developed a normalisation protocol specific to capturing SOL, GM, and GL peak activity. Data collected from heel-raises demonstrated higher SOL (p=.005) and lower GM (p<.001) and GL (p<.001) amplitudes in 45°KF rather than 0°KF; however, KF did not influence fatigue of the individual TS muscles. GM and GL fatigued at the same rate (p=.088), to the same extent (p=.385), and faster than SOL (p<.001) in both angles. GM (p=.008), but not GL (p=.118), fatigued more than SOL. Similar maximum numbers of heel-raises were performed in 0°KF (n=45) and 45°KF (n=48). Age did not influence any of the variables analysed. Conclusion: The research results question the common utilisation of KF to direct the HRT towards SOL or GAST assessment. Although influences of KF on EMG amplitudes were statistically significant, they may not be clinically meaningful. KF did not influence TS fatigue or the total number of heel-raises. While these findings do not imply the absence of clinical or rehabilitative benefits from HRT procedures in select KF positions, the evidence challenges the common perceptions and definitions that the test assesses SOL with the knee bent and GAST with the knee straight.
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| 2. |
- Kim, Jiyoung
(författare)
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External enablers and new venture creation : How characteristics of environmental changes and enabling mechanisms influence entrepreneurial responses
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Changes in the external environment—whether technological breakthroughs, natural environmental disasters, regulatory reforms, economic shifts, sociocultural movements, or demographic transitions—provide the essential enablement of entrepreneurial endeavors and outcomes. Despite extensive existing research on this topic, the predominant focus on a single type of change has hindered the attainment of broadly generalizable insights or advancements in theoretical and practical knowledge. This dissertation aims to foster a unified understanding of how environmental changes enable the creation of new ventures. To this end, it draws attention to the characteristics of changes and enablement shared across different nominal types of change.The notion of external enablers and the external enablement framework provide conceptual foundations for the four research articles included in this dissertation. The first article, a systematic literature review, demonstrates the potential for studying the characteristics of environmental changes and external enablement as a means of accumulating vastly broadened knowledge. The three remaining empirical articles delve into entrepreneurial responses to environmental changes. Experimental data evidence that variance in the characteristics of environmental changes and external enablement causes systematic differences in perceptions of entrepreneurial potential and intentions to create specific types of new ventures, i.e., family vs. non-family. This dissertation offers novel theoretical insights into the enabling impact of environmental changes on entrepreneurship. It also showcases different pathways for advancing generalizable knowledge that can be strategically applied.
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| 3. |
- Özeren, Hüsamettin Deniz
(författare)
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Plasticization of Biobased Polymers: A Combined Experimental and Simulation Approach
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The field of bio-based plastics has developed significantly in recent decades and there is an increasing demand for industries to shift from petrochemical to biobased polymers. Biobased polymers offer competitive properties, and in many cases have advantages in terms of cost. Thermoplastic starch is already commercially available, while wheat-gluten protein-based materials are considered to be promising candidates for commercial use.Biobased materials can, however, have several drawbacks that have to be handled. Starch-based materials are, in general, brittle due to the stiff glucose-based molecular chain and hydrogen bond network. This is the case also for proteins (due to the stiff peptide bond, bulky side groups and hydrogen bond network), like for example gluten. These issues can, however, be resolved with effective compatible plasticizers. But in order to be able to optimize the choice of the right plasticizer for a specific polymer, there is a need for an increased understanding of the plasticizer mechanisms. Besides, a methodology for prediction of the plasticizer amount needed, as well as to be able to rank possible plasticizer candidates, based on their effectiveness. As a part of the development of a methodology (based on the combination of experimental and molecular-dynamics simulations) for prediction of plasticization and to investigate and understand plasticizer mechanisms, the main material investigated was starch, but also wheat gluten, both plasticized with glycerol. The main plasticizer used to date for biobased polymer materials is glycerol, because of its effectiveness, stability and low cost. In addition, it is also a large byproduct of biodiesel production. A number of other plasticizer candidates were also studied for the starch system to see if the developed methodology could be used to rank plasticizers. Diols were tested in the starch system as plasticizers, but they had no or little plasticization effect. Nevertheless, they gave rise to unexpected structures and properties. Several techniques were used to determine the experimental properties of the bio-based films, including calorimetry, gravimetry, dynamic mechanical analysis, and tensile testing.The results (based on mechanical and thermal properties) showed that the methodology could be used to rank plasticizers in terms of their effectiveness. It was also possible to predict the amount of plasticizer needed for effective softening. With the help of the simulations, the emollient effect could be studied in detail and largely explained by hydrogen bonding effects. The methodology was also developed to be able to predict from simulation not only trends in mechanical properties but also absolute values in stiffness and strength at elongation rates corresponding to experimental measurements.
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