| 1. |
- Apelfrojd, Senad, et al.
(author)
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A Back-to-Back 2L-3L Grid Integration of a Marine Current Energy Converter
- 2015
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In: Energies. - : MDPI AG. - 1996-1073. ; 8:2, s. 808-820
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Journal article (peer-reviewed)abstract
- The paper proposes a back-to-back 2L-3L grid connection topology for a marine current energy converter. A prototype marine current energy converter has been deployed by a research group at Uppsala University. The concept behind the prototype revolves around a fixed pitch vertical axis turbine directly connected to a permanent magnet synchronous generator (PMSG). The proposed grid connection system utilizes a well known and proven two level voltage source converter generator-side combined with a three-level cascaded H-bridge (CHB) multilevel converter grid-side. The multilevel converter brings benefits in terms of efficiency, power quality and DC-link utilization. The system is here presented for a single marine current energy converter but can easily be scaled up for clusters of marine current energy converters. Control schemes for both grid-side and generator-side voltage source converters are presented. The start-up, steady state and dynamic performance of the marine current energy converter are investigated and simulation results are presented in this paper.
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| 2. |
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| 3. |
- Ekström, Rickard, et al.
(author)
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Electrical damping of linear generators for wave energy converters : A review
- 2015
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In: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 42, s. 116-128
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Research review (peer-reviewed)abstract
- The electrical damping of point-absorber wave energy converters is crucial to optimize the power output. Many circuit topologies have been proposed, but the possible increase in power absorption must be weighed against parameters such as cost, reliability and control system complexity. In this paper, the known electrical damping circuits are categorized, described and compared. The hydrodynamic damping of the buoy is covered, and how a linear generator can be used as a power take-off unit to apply a damping force. A qualitative comparison of the circuits is presented in the end. A more complex and costly power electronics system may be viable for wave energy converters (WECs) of large-scale power rating. However, for farm operation with small-scale WECs, a simpler and passive damping may be more suitable.
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| 4. |
- Hellstrom, Per Anders Rickard, 1975-, et al.
(author)
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Evaluation of the IngVaL Pedobarography System for Monitoring of Walking Speed
- 2018
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In: Healthcare Informatics Research. - Seoul : Korean Society of Medical Informatics (KOSMI). - 2093-3681 .- 2093-369X. ; 24:2, s. 118-124
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Journal article (peer-reviewed)abstract
- ObjectivesWalking speed is an important component of movement and is a predictor of health in the elderly. Pedobarography, the study of forces acting between the plantar surface of the foot and a supporting surface, is an approach to estimating walking speed even when no global positioning system signal is available. The developed portable system, Identifying Velocity and Load (IngVaL), is a cost effective alternative to commercially available pedobarography systems because it only uses three force sensing resistors. In this study, the IngVaL system was evaluated. The three variables investigated in this study were the sensor durability, the proportion of analyzable steps, and the linearity between the system output and the walking speed.MethodsData was collected from 40 participants, each of whom performed five walks at five different self-paced walking speeds. The linearity between the walking speed and step frequency measured with R2 values was compared for the walking speed obtained ‘A’ only using amplitude data from the force sensors, ‘B’ that obtained only using the step frequency, and ‘C’ that obtained by combining amplitude data for each of the 40 test participants.ResultsImprovement of the wireless data transmission increased the percentage of analyzable steps from 83.1% measured with a prototype to 96.6% for IngVaL. The linearity comparison showed that the methods A, B, and C were accurate for 2, 15, and 23 participants, respectively.ConclusionsIncreased sensor durability and a higher percentage of analyzed steps indicates that IngVaL is an improvement over the prototype system. The combined strategy of amplitude and step frequency was confirmed as the most accurate method.
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| 5. |
- Hellstrom, Per Anders Rickard, 1975-, et al.
(author)
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Intelligent Wireless Body Area Network System for Human Motion Analysis
- 2015
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Conference paper (peer-reviewed)abstract
- Human motion analysis provides several important applications. Examples are fall risk assessment, sports biomechanics, physical activity monitoring and rehabilitation. This work in progress paper proposes an intelligent wireless body area network system for motion and gait symmetry analysis. A Bluetooth network with accelerometers, gyroscopes and in-shoe force sensing resistors gathers data and sends it to a web server after intelligent pre-processing and filtering. The system is flexible and adaptable for different use cases including combinations of gait analysis, gait symmetry and pressure measurements between foot and shoe.
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| 6. |
- Hellstrom, Per Anders Rickard, 1975-, et al.
(author)
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Walking Intensity Estimation with a Portable Pedobarography System
- 2016
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In: Studies in Health Technology and Informatics. - : IOS Press. ; , s. 27-32
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Conference paper (peer-reviewed)abstract
- The aim of this pilot study was to investigate the possibility to find a correlation between the output from a portable pedobarography system and the walking intensity expressed as walking speed. The system uses shoe insoles with force sensing resistors and wireless transmission of the data via Bluetooth. The force-time integral, at the toe-off phase of the step, for the force sensors in the forward part of the right foot was used to measure impulse data for 10 subjects performing walks in three different walking speeds. This data was then corrected by multiplication with the step frequency. This pilot study indicates that the portable pedobarography system output shows a linear relationship with the walking intensity expressed as walking speed on an individual level.
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| 7. |
- Hellstrom, Per Anders Rickard, 1975-, et al.
(author)
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Wearable Weight Estimation System
- 2015
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In: Procedia Computer Science, vol. 64. - : Elsevier BV. ; , s. 146-152
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Conference paper (peer-reviewed)abstract
- Heavy working conditions, as well as sedentary behaviour, are risk factors for health. There is a lack of wearable measurement systems for monitoring carried loads while walking. Pedobarography, the study of force fields acting between the plantar surface of the foot and a supporting surface, is supposed to be useable for estimating carried loads. Purpose. The aim of this paper is to present a novel method for selecting appropriate measurement samples for weight estimation of carried load during walk and a wearable system, based on pedobarography, consisting of commercial off the shelf components. The main idea is to choose samples when half of the total weight is on the forward sensors and the other half is on the heel sensor “equipoise” in one foot while the other foot not touches the ground. Methods. The system consists of insoles with force sensing resistors, data acquisition with IOIO-OTG and analysis in Excel. Each subject was weighed on an electronic floor scale. Three walks were performed on level ground. The first walk without any added load and then with two increases of carried load. Equipoise was defined as having half the weight distributed on the heel and the other half over the metatarsal pad. An equipoise value of 0.5 represents equilibrium regarding the weight distribution on one foot, with the other foot in the air. Samples were chosen in the equipoise region of 0.5±0.1 and then the average of the samples collected during one minute estimated the total weight. Results. The system can detect increases in carried loads but has a tendency to overestimate them. The estimated value was always larger with increased weight but the system was not always linear. The average overestimation error was 16.7 kg. Discussion. This study shows that this type of wearable system is usable for estimating carried load during walk after calibration of the system to the body weight force distribution on the sensors. There is still need for future development to obtain real-time analysis and direct feedback. A smaller and lighter measurement system is also desirable. Conclusion. This study shows that the novel method, equipoise, is usable for selecting appropriate measurement samples for weight estimation of carried load during walk. This study also shows that the wearable system, consisting of commercial off the shelf components, can be used for these measurements. However, there is a tendency to overestimate the loads.
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| 8. |
- Hellström, Per Anders Rickard, 1975-
(author)
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Wearable Pedobarography System for Monitoring of Walk Related Parameters
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Health care costs have increased over the last decades due to an ageing population. Therefore, research in personal health monitoring (PHM) has increased in response to this. PHM has advantages such as mobility (monitoring of health at work or at home), early detection of health problems enabling preventive health measures and a reduction of health care cost. Human motion analysis, using for example pedobarography (PBG), is an important subcategory of PHM. PBG is used to study the force fields acting between the plantar surface of the foot and a supporting surface. Gait and posture analysis, prosthetics evaluation and monitoring of recovery from injury or disease are examples of PBG applications. Portable PBG can be performed using force sensing resistors built into the insole inside the shoe. In accordance with this, the research aim for this thesis is to design, build and evaluate a wireless wearable measurement system based on PBG for monitoring of walk related parameters. Monitoring of carried weight and walking speed were chosen as the applications for validation of the system. Motivations for choosing these applications are that there is a lack of a wearable system for monitoring of weight while walking and a possible combination with accelerometers to improve the estimation of walking speed. Both walking speed and weight are important factors for estimating energy expenditure. A portable system, that estimates weight while walking, enables monitoring of heavy working conditions.The main research contributions include design of a PBG measurement system with a sensor implementation resulting in good sensor durability, several novel methods for weight estimation during walk and a novel method for analysing walking intensity and relating it to walking speed. The research results show that the new PBG system, in combination with the novel analysing methods, are suitable for use in wearable systems for monitoring of health related walk parameters.
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| 9. |
- Hellström, Per Anders Rickard, 1975-
(author)
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Wireless Wearable Measurement System Based on Pedobarography for Monitoring of Health
- 2016
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Licentiate thesis (other academic/artistic)abstract
- Health care costs have increased over the last decades due to an ageing population. Therefore, research in personal health monitoring (PHM) has increased in response to this. PHM has advantages such as mobility (monitoring of health at work or at home), early detection of health problems enabling preventive health measures and a reduction of health care cost. Human motion analysis, using for example inertial measurement units and pedobarography, is an important subcategory of PHM. Pedobarography (PBG) is the study of pressure fields acting between the plantar surface of the foot and a supporting surface. Gait and posture analysis, prosthetics evaluation and monitoring of recovery from injury or disease are examples of PBG applications. Portable PBG can be performed using force sensing resistors built into the insole inside the shoe.In accordance with this, the research goal for this licentiate thesis is to design, build and evaluate a wireless wearable measurement system based on pedobarography for monitoring of health. In order to fulfil the objectives of the research, literature studies were done and problems with existing in-shoe system solutions were identified. Thus, it was found that further opportunities existed for new designs of PBG systems which take these problems into account. Cross-sectional test case studies were used for validation. The research area is multidisciplinary and encompasses biomedical measurements, electronics and computer science.The main research contributions include design and implementation of a PBG measurement system consisting of commercial off the shelf components, a novel method for selecting measurement samples for weight estimation of carried load during walk, and a novel method for analysing walking intensity using force-time integrals at the toe-off phase of the step. The research results suggest that the new PBG system, in combination with the two novel analysing methods, are suitable for use in wearable systems for monitoring of health. Personal health measurements are done to help decision making related to health. Thus, the future work will strive towards designing different decision support systems.
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| 10. |
- Hofmann, Robin, et al.
(author)
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Oxygen therapy in suspected acute myocardial infarction
- 2017
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In: New England Journal of Medicine. - : MASSACHUSETTS MEDICAL SOC. - 0028-4793 .- 1533-4406. ; 377:13, s. 1240-1249
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Journal article (peer-reviewed)abstract
- BACKGROUND: The clinical effect of routine oxygen therapy in patients with suspected acute myocardial infarction who do not have hypoxemia at baseline is uncertain. METHODS: In this registry-based randomized clinical trial, we used nationwide Swedish registries for patient enrollment and data collection. Patients with suspected myocardial infarction and an oxygen saturation of 90% or higher were randomly assigned to receive either supplemental oxygen (6 liters per minute for 6 to 12 hours, delivered through an open face mask) or ambient air. RESULTS: A total of 6629 patients were enrolled. The median duration of oxygen therapy was 11.6 hours, and the median oxygen saturation at the end of the treatment period was 99% among patients assigned to oxygen and 97% among patients assigned to ambient air. Hypoxemia developed in 62 patients (1.9%) in the oxygen group, as compared with 254 patients (7.7%) in the ambient-air group. The median of the highest troponin level during hospitalization was 946.5 ng per liter in the oxygen group and 983.0 ng per liter in the ambient-air group. The primary end point of death from any cause within 1 year after randomization occurred in 5.0% of patients (166 of 3311) assigned to oxygen and in 5.1% of patients (168 of 3318) assigned to ambient air (hazard ratio, 0.97; 95% confidence interval [CI], 0.79 to 1.21; P=0.80). Rehospitalization with myocardial infarction within 1 year occurred in 126 patients (3.8%) assigned to oxygen and in 111 patients (3.3%) assigned to ambient air (hazard ratio, 1.13; 95% CI, 0.88 to 1.46; P=0.33). The results were consistent across all predefined subgroups. CONCLUSIONS: Routine use of supplemental oxygen in patients with suspected myocardial infarction who did not have hypoxemia was not found to reduce 1-year all-cause mortality. (Funded by the Swedish Heart–Lung Foundation and others; DETO2X-AMI ClinicalTrials.gov number, NCT01787110.)
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