| 1. |
- Parwal, Arvind, et al.
(author)
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A Comparative Analysis of Linear and Nonlinear Control of Wave Energy Converter for a Force Control Application
- 2024
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In: International Marine Energy Journal. - Southampton, UK : International Marine Energy Journal. - 2631-5548.
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Journal article (peer-reviewed)abstract
- The aim of wave energy converters (WECs) is to harvest the energy from the ocean waves and convert into electricity. Optimizing the generator output is a vital point of research. A WEC behaves as a nonlinear system in real ocean waves and a control that approximates the behaviour of the system is required. In order to predict the behaviour of WEC, a controller is implemented with an aim to track the referenced trajectory for a force control application of the WEC. A neural model is implemented for the system identification and control of the nonlinear process with a neural nonlinear autoregressive moving average exogenous (NARMAX) model. The neural model updates the weights to reduce the error by using the Levenberg-Marquardt back-propagation algorithm for a single-input-single-output (SISO) nonlinear system. The performance of the system under the proposed scheme is compared to the same system under a PI-controller scheme, where the PI gains have been tuned accordingly, to verify the control capacity of the proposed controller. The results show a good tracking of dq (direct-quadrature) axes currents by regulating the stator currents, and hence a force control is achieved at different positions of the translator. The dynamic performance of the control is verified in a time domain analysis for the displacement of the translator.
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| 2. |
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| 3. |
- Röding, Fredrik, 1969-
(author)
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Injuries are not accidents! : an emergency-department population-based epidemiological study of injuries with special reference to trauma recidivism hip fractures and geriatric falls
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Injury is a major public health problem. In rich countries fall injures now kill more people than all other injury mechanisms together, because of global ageing and large-scale sustainable injury prevention programs for all other injury mechanisms but falls. Injuries from falls in the young are often trivial, but in old people falls may have devastating consequences.We used the Umeå Injury Database, 1993 – 2014, 220,014 injury events attended to by the emergency department: e.g., type of injury, localization, mechanism, activity and severity. Logistic regression was used to evaluate injury trends, Cox regression for associations between injury type, severity and recidivism.Fractures were responsible for 1⁄4 of all injuries and for 3⁄4 of trauma inpatient days. Fractures and contusions became more common with increasing age while sprains and wounds decreased with age. Injuries due to fall increased during the study period.Recurrent injuries accounted for some 40%, mostly in young men and in old women. Prior fractures and sprains were strongest predictors for recurrent serious injuries.The hip fracture incidence fell for the most important age/sex groups during the 22-year period, but the total number increased with 3,5%, due to an increasing elderly population. 40% of all hip fracture patients had sustained a previous injury. Multiple previous injuries also increase the risk of future hip fracture. No less than 12% hip fracture patients suffered a new one. With age, injury pattern changed, with more lower extremity fractures that also were more proximally located. Soft tissue injuries to the head/face also increased, also indicating that the ability to reduce and spread the impact of the kinetic energy is a key factor in geriatric trauma, in addition to tissue strengthThe most common, expensive and devastating injury mechanism, falls, are still outrageously neglected, especially concerning injury prevention, which has been so successful in reducing road traffic- and workplace-related deaths. Why? A common misconception is the primitive belief is that fall injuries are fated and therefore inevitable. There are also few economic and legal drivers to prevent falls, especially recurrent ones. Another reason is that GDPR has prohibited the injury database. Statistics on fall injuries are necessary for targeting preventive interventions. Without spying, no clue. On-line feedback of official statistics should be used to monitor the results. There are no technical, just legal hurdles. The Swedish parliament has since 1997 flagged a zero vision for road traffic injuries; in 2015 the government also launched a more modest goal for a 50% reduction of falls in the elderly. So far, nothing has happened...
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| 4. |
- Unneby, Anna, et al.
(author)
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Complications with focus on delirium during hospital stay related to femoral nerve block compared to conventional pain management among patients with hip fracture : A randomised controlled trial
- 2020
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In: Injury. - : Elsevier. - 0020-1383 .- 1879-0267. ; 51:7, s. 1634-1641
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Journal article (peer-reviewed)abstract
- Introduction: Patients with hip fracture often suffer complications leading to increased mortality and morbidity. Pain management are important, but opioids has many side effects. The aim of this study was to investigate whether Femoral Nerve Block (FNB) can reduce complications during hospital stay, with special focus on delirium compared to conventional pain management with opioids among patients with hip fracture, including those with dementia.Patients & Methods: In a randomized controlled trial involving patients >70 years with hip fracture (trochanteric and cervical), including those with dementia. Preoperatively, patients (n=236) were consecutively assigned to receive FNB and opioids if required (intervention group, n = 116) or conventional pain management using opioids if required (control group, n = 120). Delirium was set according to different assessments and DSM-IV-TR criteria. Other complications were set by a specialist in geriatric medicine and a trained research nurse according to a predefined protocol.Results: Most patients, 157 (66%), were women, mean age was 84 (+/- 6.7) years and 109 (46%) patients had dementia disorders. Forty-four patients (38.9%) developed delirium preoperatively in the intervention group compared to 59 (49.2%) patients in the control group (p=0.116). Common postoperative complications were pre- and postoperative delirium, nutritional problems, anaemia, constipation and urinary tract infection with no significant difference between the groups. In the subgroup analysis among patients with dementia, a large proportion developed delirium postoperative (96.3%) and they had a long duration of delirium during hospital stay (5.9 +/- 1.8), however no difference between the groups.Conclusion: Despite less preoperative pain and need of opioids, FNB did not reduce the incidence of complications. However, a preoperative FNB may result in less preoperative delirium, but this should be further investigated. As pain treatment, FNB is a good alternative with few documented adverse effects in order to reduce pain and opioids among patients with hip fracture.
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| 5. |
- Farhang, Mehdy, et al.
(author)
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The trend of radiological severity of hip fractures over a 30 years period : a cohort study
- 2019
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In: BMC Musculoskeletal Disorders. - : Springer Science and Business Media LLC. - 1471-2474. ; 20:1
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Journal article (peer-reviewed)abstract
- BACKGROUND: Despite advances in operative techniques and preoperative care, proximal femur fractures (PFF) still represent a great public health problem. Displacement and fracture stability have been assumed as important determinants of treatment modality and outcome in such fractures. Purpose of this study was to determine whether the radiological severity of PFF fractures has increased over time.METHODS: In a cohort study, the plain radiographs of all patients with PFF aged over 50 years who were admitted to Umeå University Hospital in 1981/82, 2002 and 2012 were recruited to examine the types of fractures.RESULTS: The ratio of undisplaced to displaced femoral neck (FN) fractures was 30 to 70% in 1981/82, 28 to 72% in 2002 and 25 to 75% in 2012. The ratio of stable to unstable intertrochanteric (IT) fractures was 64 to 36% in 1981/82, 68 to 32% in 2002 and 75 to 25% in 2012. The ratio of simple to comminute subtrochanteric fractures was 35 to 65% in 1981/82, 16 to 84% in 2002 and 12 to 88% in 2012. In both FN and IT fractures we found no statistical difference among these 3 study periods, p = 0.67 and p = 0.40. In subtrochanteric fractures we saw a tendency towards more comminute subtrochanteric fractures (1981/82 to 2012), p = 0.09.CONCLUSIONS: We found no significant increment in the radiological severity of FN and IT over a 30 years' period. However, there was tendency towards an increase in comminute subtrochanteric fractures.
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| 6. |
- Parwal, Arvind, et al.
(author)
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A comparative analysis of linear and nonlinear control of wave energy converter for a force control application
- 2019
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In: International Marine Energy Journal. - : European Wave and Tidal Energy Conference. - 2631-5548. ; 2:1, s. 39-50
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Journal article (peer-reviewed)abstract
- The aim of wave energy converters (WECs) is to harvest the energy from the ocean waves and convert into electricity. Optimizing the generator output is a vital point of research. A WEC behaves as a nonlinear system in real ocean waves and a control that approximates the behaviour of the system is required. In order to predict the behaviour of WEC, a controller is implemented with an aim to track the referenced trajectory for a force control application of the WEC. A neural model is implemented for the system identification and control of the nonlinear process with a neural nonlinear autoregressive moving average exogenous (NARMAX) model. The neural model updates the weights to reduce the error by using the Levenberg-Marquardt back-propagation algorithm for a single-input-single-output (SISO) nonlinear system. The performance of the system under the proposed scheme is compared to the same system under a PI-controller scheme, where the PI gains have been tuned accordingly, to verify the control capacity of the proposed controller. The results show a good tracking of dq (direct-quadrature) axes currents by regulating the stator currents, and hence a force control is achieved at different positions of the translator. The dynamic performance of the control is verified in a time domain analysis for the displacement of the translator.
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| 7. |
- Parwal, Arvind, et al.
(author)
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Grid integration and a power quality assessment of a wave-energy park
- 2019
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In: IET Smart Grid. - UK : Institution of Engineering and Technology (IET). - 2515-2947. ; 2:4, s. 625-634
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Journal article (peer-reviewed)abstract
- This study presents a step toward the grid connection of a wave-energy park through an electric power conversion system (EPCS) developed and installed for the wave-energy harvesting in Lysekil, Sweden. The EPCS comprises a rectifier, a DC bus, and an inverter followed by a harmonic filter (HF). The higher- and lower-order harmonics injected by the inverter in a power quality context are investigated. The lower-order voltage harmonics partially distort the voltage-source inverter output grid current. A phase-locked loop-based (PLL) grid-phase tracking is used to attenuate the lower-order harmonics by reflecting the grid harmonics in the inverter output. An expression for the grid-current harmonics as a function of the grid-voltage harmonics has been derived and implemented. A mathematical model is derived to obtain a transfer function for the PLL, and finally, proportional–integral gains are tuned for stable system operation. An HF for mitigating the higher-order harmonics has been implemented. The total harmonic distortion is evaluated experimentally, and the results fulfil the grid-code requirements at various frequencies and harmonic orders.
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| 8. |
- Aspenberg, Per, 1949-, et al.
(author)
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Artrosskolan : evidensen måste stärkas
- 2018
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In: Läkartidningen. - : Läkartidningen Förlag AB. - 0023-7205 .- 1652-7518. ; 115
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Journal article (pop. science, debate, etc.)
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| 9. |
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| 10. |
- Parwal, Arvind, et al.
(author)
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Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System
- 2018
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In: 2018 5th International Conference on Electric Power and Energy Conversion Systems, EPECS 2018. - 9781538664575
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Conference paper (peer-reviewed)abstract
- This paper provides an overview of electric power conversion system installed at the Lysekil research site, located at the west coast of Sweden. The electric power conversion system consists of rectifiers, rectifying the power from the wave energy converters, a DC-link and a grid-tied inverter. The paper focuses on the performance of the inverter and the filter and presents experimental results obtained during the grid integration.
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