| 1. |
- Austrin, Lars
(author)
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On magnetic amplifiers in aircraft applications
- 2007
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Licentiate thesis (other academic/artistic)abstract
- In the process of designing an electric power supply system for an aircraft, parameters like low weight and low losses are important. Reliability, robustness and low cost are other important factors. In the Saab Gripen aircraft, the design of the primary power supply of the electric flight control system was updated by exchanging a switching transistor regulator to a magnetic amplifier (magamp). By introducing a magamp design, weight was saved and a more reliable power supply system at a lower cost was achieved. In this particular case, with the power supply of the electric flight control system in the Saab Gripen fighter, advantage could be taken of a specific permanent magnet generator (PM-generator). The frequency of the generator offered the perfect conditions for a magamp controller. A key parameter in designing magnetic amplifiers (magamps) is low losses. New amorphous alloys offer new possibilities of the technique in designing magnetic amplifiers, because of their extremely low losses. The core losses are evaluated by studying the equations and diagrams specifying the power losses. The core losses are evaluated and compared with the copper losses in the process of optimizing low weight and low losses. For this an engineering tool is developed and demonstrated. Evaluations of the hysteresis characteristics for the magnetic alloys, as well as modeling and simulation of the core losses, are presented in this work. The modeling of the core losses includes hysteresis losses, eddy current losses and excess losses as well as copper losses. The losses are studied dynamically during realistic operational conditions. The model can be used for any generic analysis of hysteresis in magnetic circuits. Applications of magnetic amplifiers in aircrafts have been demonstrated to be a feasible alternative
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| 2. |
- Holmer, Hampus, et al.
(author)
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The global met need for emergency obstetric care: a systematic review.
- 2015
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In: BJOG: An International Journal of Obstetrics & Gynaecology. - : Wiley. - 1471-0528 .- 1470-0328. ; 122:2, s. 183-189
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Research review (peer-reviewed)abstract
- Of the 287 000 maternal deaths every year, 99% happen in low- and middle-income countries. The vast majority could be averted with timely access to appropriate emergency obstetric care (EmOC). The proportion of women with complications of pregnancy or childbirth who actually receive treatment is reported as 'Met need for EmOC'.
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| 3. |
- Holmer, Hampus, et al.
(author)
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The rate and perioperative mortality of caesarean section in Sierra Leone
- 2019
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In: BMJ Global Health. - : BMJ. - 2059-7908. ; 4:5
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Journal article (peer-reviewed)abstract
- Introduction Sierra Leone has the world's highest maternal mortality, partly due to low access to caesarean section. Limited data are available to guide improvement. In this study, we aimed to analyse the rate and mortality of caesarean sections in the country. Methods We conducted a retrospective study of all caesarean sections and all reported in-facility maternal deaths in Sierra Leone in 2016. All facilities performing caesarean sections were visited. Data on in-facility maternal deaths were retrieved from the Maternal Death Surveillance and Response database. Caesarean section mortality was defined as in-facility perioperative mortality. Results In 2016, there were 7357 caesarean sections in Sierra Leone. This yields a population rate of 2.9% of all live births, a 35% increase from 2012, with district rates ranging from 0.4% to 5.2%. The most common indications for surgery were obstructed labour (42%), hypertensive disorders (25%) and haemorrhage (22%). Ninety-nine deaths occurred during or after caesarean section, and the in-facility perioperative caesarean section mortality rate was 1.5% (median 0.7%, IQR 0-2.2). Haemorrhage was the leading cause of death (73%), and of those who died during or after surgery, 80% had general anaesthesia, 75% received blood transfusion and 22% had a uterine rupture diagnosed. Conclusions The caesarean section rate has increased rapidly in Sierra Leone, but the distribution remains uneven. Caesarean section mortality is high, but there is wide variation. More access to caesarean sections for maternal and neonatal complications is needed in underserved areas, and expansion should be coupled with efforts to limit late presentation, to offer assisted vaginal delivery when indicated and to ensure optimal perioperative care.
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| 4. |
- Hou, Yining, 1984-, et al.
(author)
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Impact on voltage rise of PV generation in future swedish urban areas with high PV penetration
- 2014
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In: ENERGYCON 2014 - IEEE International Energy Conference. - : IEEE Computer Society. - 9781479924493 ; , s. 904-911
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Conference paper (peer-reviewed)abstract
- There have been a large amount of statements from different countries, claiming that the integration of photovoltaic generation in the distribution grids can eventually impact the power quality and pose challenges for the distribution system operator. In Sweden, the level of penetration of small scale distributed generation is still low and no such problems have been observed. This study is conducted to investigate the voltage levels in an urban distribution grid when the level of photovoltaic generation is increased. The study is done by modeling the Swedish urban area by PSCAD. The aspects of the model include network design of a real distribution grid, everyday load, photovoltaic generation based on real data, photovoltaic penetrations at different levels and considers the current regulations in Sweden. The results indicate that there are no problems with overvoltages even with a high penetration of photovoltaic generation. Instead the risk of over-current through the installed cables seems to be a greater limitation. The loading of the distribution transformers is decreased due to the mix of commercial and domestic loads in the local grid.
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| 5. |
- Ijumba, Petrida, 1951-
(author)
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Intervention for improved newborn feeding and survival where HIV is common : Perceptions and effects of a community-based package for maternal and newborn care in a South African township
- 2014
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Doctoral thesis (other academic/artistic)abstract
- South Africa recently changed infant feeding policy within Prevention of Mother to Child Transmission (PMTCT) of HIV from free formula to recommendation of breastfeeding for all. The country is evaluating the role of Community Health Workers (CHWs) in supporting mothers and newborns.The aim of this thesis is to explore perceptions of household members on the value given to and the social forces behind formula feeding in light of the recent policy change, and to assess the effect of a community-based package of maternal and newborn care delivered by CHWs on HIV-free survival and exclusive and appropriate infant feeding up to 12 weeks of age.Studies were conducted in a high HIV prevalence township. Focus group discussions were performed (grandmothers, fathers and teenage mothers) and in-depth interviews with HIV-positive and HIV-negative mothers. Perceptions of household members on the formula policy change were explored and the value household members place on formula feeding and circumstances that drive it. In a cluster-randomized trial (15 intervention, 15 control clusters) CHWs provided two antenatal and five post-natal home visits to support and promote PMTCT activities.There were misunderstandings by community members on the free formula policy change. Mothers transferred the motherhood role to their mothers while partners provided inadequate financial support, leading to risky mixed feeding. Teenage mothers rarely breastfed their infants due to perceived constraints including embarrassment, sagging breasts and loss of freedom and boyfriends.At 12 weeks of age the intervention had doubled exclusive breastfeeding (EBF) (28% vs. 14%) and slightly increased infant weight and length. No difference was seen between study arms in HIV-free survival. The effect on EBF at12 weeks did not differ with maternal education or wealth levels, but was higher among HIV-negative mothers. Focusing on teenage mothers breastfeeding challenges, involvement of grandmothers and fathers in infant feeding decision-making, improving communication strategies on policy change and breastfeeding to the community and health workers and CHWs home visits supporting PMTCT activities are important for infant feeding and child health.
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| 6. |
- Magnusson, Jesper, 1984-, et al.
(author)
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On the Use of Metal Oxide Varistors as a Snubber Circuit in Solid-State Breakers
- 2013
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In: 2013 4th IEEE/PES Innovative Smart Grid Technologies Europe, ISGT Europe 2013. - : IEEE. - 9781479929849 ; , s. 6695454-
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Conference paper (peer-reviewed)abstract
- When solid-state switches are used in DC-breaker topologies, the turn-off operation can cause transient over-voltages that might harm the semiconductor itself. The over-voltage is caused by the combination of the very rapid current decrease of a solid-state switch and an undesired stray inductance in the parallel MOV-branch. The authors have proposed a possible solution where a smaller MOV is connected close to the solid-state switch to limit the over-voltage. This way, the over-voltage protection can be separated from the energy absorption task of the MOV. A small scale test set-up has been used to show that the peak voltage across the breaker is fully determined by the inner MOV. It is also shown that the performance can be increased by changing the U-I-characteristics of the outer MOV by adding several components in parallel.
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| 7. |
- Ohlson, Mats, et al.
(author)
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Tandtekniska arbeten : en vägledning till reglerna om medicintekniska produkter
- 2011
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Reports (other academic/artistic)abstract
- Läkemedelsverket genomför i egenskap av tillsynsmyndighet regelbundet inspektioner av tandtekniska laboratorier. Verket har också med expertstöd av Socialstyrelsen genomfört en omfattande granskning av kronersättningar tillverkade både av laboratorier i Sverige och utanför EU/EES. Vi har kunnat konstatera att det föreligger brister, som kan ha betydelse för patientsäkerheten. Bristerna omfattar både kunskap om och efterlevnad av det medicintekniska regelverket. Innebörden av laboratoriets ansvar som tillverkare och vad det medför är också dåligt känd bland tandtekniker och tandläkare. Det medicintekniska regelverket riktar sig till alla tillverkare av medicintekniska produkter och är alltså inte specifikt skrivet för tandtekniska arbeten. Det kan vara en viktig anledning till att regelverket upplevs som svårt att överföra till det tandtekniska området. Detta har framförts både från tandtekniker och från tandläkare. Avsikten med denna vägledning är att ”översätta” regelverket till den odontologiska verkligheten, klargöra ansvarsförhållanden och därigenom öka patientsäkerheten. Vägledningen riktar sig både till den tandtekniska verksamheten i egenskap av till-verkare av specialanpassade produkter och till tandläkare som beställare och ansvariga för den färdiga tandtekniska produkt, som lämnas ut till patient. Vägledningen är inte rättsligt bindande utan är en tolkning av det medicintekniska regelverket och är att se som ett stöd för den tandtekniska verksamheten men också för tandläkarna i egenskap av beställare av tandtekniska arbeten. De lagar, förordningar och föreskrifter som nämns i vägledningen är däremot bindande.
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| 8. |
- Stavroulaki, Ioanna, 1976, et al.
(author)
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Methodology and results of an international observational study on pedestrian movement tracking anonymised Wi-Fi signals from mobile phones
- 2018
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Conference paper (other academic/artistic)abstract
- This paper presents the methodology and results of an international observational study on pedestrian movement, using innovative high-end technology of tracking anonymised Wi-Fi signals from mobile phones. The pedestrian survey was conducted during three weeks in October 2017 in 60 neighbourhoods across three cities in Europe - London, Amsterdam, Stockholm. The survey was led by Chalmers University in cooperation with Bumbee Labs consultancy firm. More than 300 streets of different network centrality profiles were monitored, ranging from small alleys to high streets, in neighbourhoods which differed in density type,from suburban villa areas of low density to central high-density areas with primarily closed building blocks.The aim is to quantify the separate and combined effects of spatial form, particularly built density and street centrality, on pedestrian movement. The collected data record how many people passed each street per hour, but also their average speed and exact paths through the area; revealing both flow patterns and intensities, and the microstructure of individual paths. The paper, first, presents the methodology and technology of collecting and processing anonymised pedestrian data through mobile phone Wi-Fi tracking and the results of the study. Then, results are tested against spatial variables and types to discuss how movement is influenced by street centrality, density and other attractors. Finally, the paper discusses the possible utilisations of pedestrian data in urban analysis and design, not least in a time when big data become increasingly accessible and when the boost of pedestrian mobility in cities is a central planning objective.
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