| 1. |
- Ademuyiwa, Adesoji O., et al.
(författare)
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Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
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Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
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| 2. |
- Mauri, Massimiliano, 1987, et al.
(författare)
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Byproduct-free curing of a highly insulating polyethylene copolymer blend: An alternative to peroxide crosslinking
- 2018
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7534 .- 2050-7526. ; 6:42, s. 11292-11302
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Tidskriftsartikel (refereegranskat)abstract
- High-voltage direct-current (HVDC) cables are a critical component of tomorrow's power grids that seamlessly integrate renewable sources of energy. The most advanced power cable technology uses crosslinked polyethylene (XLPE) insulation, which is produced by peroxide crosslinking of low-density polyethylene (LDPE). Peroxide crosslinking gives rise to hazardous byproducts that compromise the initially excellent purity and cleanliness of LDPE, and hence increase the electrical conductivity of the insulation material. Therefore, a byproduct-free curing process, which maintains the processing advantages and high electrical resistivity of LDPE, is in high demand. Here, we demonstrate a viable alternative to peroxide crosslinking that fulfils these requirements. Click chemistry reactions between two polyethylene copolymers allow the design of a curing process that is additive-free and does not result in the release of any byproducts. The thermoplastic copolymer blend offers a broad processing window up to 140 °C, where compounding and shaping can be carried out without curing. At more elevated temperatures, epoxy and acrylic acid functional groups rapidly react without byproduct formation to form an infusible network. Strikingly, the crosslinked copolymer blend exhibits a very low direct-current (DC) electrical conductivity of 2 × 10-16 S cm-1 at a typical cable operating temperature of 70 °C, which is on par with values measured for both ultra-clean LDPE and commercial XLPE. Hence, the use of polyethylene copolymer blends opens up the possibility to replace peroxide crosslinking with click chemistry type reactions, which may considerably expand the versatility of the most common type of plastic used today.
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| 3. |
- Thomas, HS, et al.
(författare)
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- 2019
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swepub:Mat__t
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| 4. |
- Andersson, L. H. U., et al.
(författare)
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The effect of different structure parameters on the crosslinking behaviour and network performance of LDPE
- 2006
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 47:1, s. 200-210
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, we investigate the crosslinking behaviour of 6 ordinary low density polyethylenes, and the effect of relatively modest changes in the polyethylene structure on the properties of the resulting network. The observed variations in gel formation are mainly explained by differences in molecular weight, where both M̄n and M̄w affect the results. The presence of long chain branches (LCB) present on the polymer main chain is shown to have a significant effect on the network quality. The occurrence of LCB affects the ability in making effective entanglements, a behaviour which is largely dependent on the length of the branches. At high LCB frequencies, the long chain branches are relatively short and therefore more prone to disentangle. The frequency and the amount of LCB, together with the molecular weight, have a large impact on the coil size. The coil size is believed to be an important parameter for the crosslinking behaviour, as a large coil size facilitates interconnections between adjacent polymer coils. In addition, LCB increases the probability of creating intramolecular crosslinks. However, this study shows that a very high amount of LCB is needed in order to obtain any significant effect on the network quality originating from intramolecular crosslinks. © 2005 Elsevier Ltd. All rights reserved.
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| 5. |
- Berggren, Magnus, et al.
(författare)
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Controlling colour by voltage in polymer light emitting diodes
- 1995
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2185-2186
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Tidskriftsartikel (refereegranskat)abstract
- We report electroluminescence using different substituted polythiophenes as the emitting mterial. Different substituents cause different sterical interacion which force the thiophene rings out of planarity. This results in different bandgaps. Colours from blue to near infrared have been demonstrated in electroluminescent devices. We also demonstrate voltage controlled electroluminescence using mixtures of these polymers.
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| 6. |
- Berggren, Magnus, et al.
(författare)
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Green Electroluminescence in Poly-(3-cyclohexylthiophene) light-emitting diodes
- 1994
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag Berlin. - 0935-9648 .- 1521-4095. ; 6:6, s. 488-490
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Tidskriftsartikel (refereegranskat)abstract
- Electoluminescent devices based on polythiophene-system this films have been demonstrated that together span the entire visible range, steric hindrance being used to vary the bandgap between compunds. Poly-(3-cyclohexylthiophene), see Figures, exhibits green electoluminescence. Possible interpretations of this observation are proposed.
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| 7. |
- Berggren, Magnus, et al.
(författare)
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Thermal control of near‐infrared and visible electroluminescence in alkyl‐phenyl substituted polythiophenes
- 1994
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 65:12, s. 1489-1491
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Tidskriftsartikel (refereegranskat)abstract
- We report electroluminescence from a regioregular alkyl-phenyl substituted polythiophene. The polymer film exists in two forms, giving widely different optical absorption, as well as photoluminescence and electroluminescence spectra. In the low-bandgap form, we observe high emission intensity centered at 1.55 eV (800 nm), well into the infrared, while the high-bandgap form gives a maximum at 1.85 eV (670 nm). The conversion from the high-bandgap form to the low-bandgap form can be done by thermal treatment of the polymer light emitting diodes.
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| 8. |
- Dyreklev, Peter, et al.
(författare)
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Polarized electroluminescence from an oriented substituted polythiophene in a light emitting diode
- 1995
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag Berlin. - 0935-9648 .- 1521-4095. ; 7:1, s. 43-45
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Tidskriftsartikel (refereegranskat)abstract
- Polarized light sources based on stretch-oriented conjugated polymers are reported. The devices, based on poly 3(4-octylphenyl)-2,2′-bithiophene, show an external quantum efficiency of 0.1% and are produced using a very simple method which may be easily extended to other polymers. The fabrication of the devices is described and factors such as the emission and spectral differences parallel and prependicular to the stretching direction discussed.
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| 9. |
- Ekelund, Maria, 1977-
(författare)
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Long-term Performance of PVC and CSPE Cables used in Nuclear Power Plants : the Effect of Degradation and Plasticizer migration
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Enormous amounts of low voltage cables installed in a Swedish nuclear power plant are reaching their expected lifetimes. Since the cables are crucial to operational safety, it is of great importance that the actual condition of the installed cables is determined. In this study, cables based on poly(vinyl chloride) plasticized with di(2-ethylhexyl)phthalate (DEHP) were examined with respect to the degradation mechanisms responsible for the ageing of the insulation. This was achieved by studying samples that underwent accelerated ageing by different analytical methods, such as indenter modulus measurements, tensile testing, infrared spectroscopy, differential scanning calorimetry and liquid chromatography, to assess the condition of the cables. The results were unambiguous; the main deterioration mechanism differed for the jacket and the core insulation. The immediate increase in stiffness of the jacket insulation suggests that loss of plasticizer was the dominant cause for degradation. The core insulation on the other hand showed much smaller changes in the mechanical properties due to thermal ageing with an activation energy of the change in the indenter modulus matching that of the dehydrochlorination process. The electrical functionality during high-energy line break accident was correlated to the mechanical properties of the cable and this correlation was used to establish a lifetime criterion. The mechanical data showed Arrhenius temperature dependence with activation energies of 80 kJmol-1 and 100 kJmol-1 for the jacketing and 130 kJmol-1 for the core insulation. These activation energies were used to extrapolate the lifetimes to service temperatures (20 °C to 50 °C). Plasticizer migration was determined as the lifetime controlling mechanism at the service temperatures. Experimental data, obtained by extraction of DEHP followed by liquid chromatography, were analysed by numerical methods to gain a better understanding of the migration. The analysis showed that the transport of DEHP to the surrounding environment was diffusion controlled at temperatures between 120 °C and 150 °C, with an activation energy of 89 kJmol-1. At lower temperatures, HTML clipboard ≤100 °C, the loss of plasticizer was controlled by evaporation, with an activation energy of 99 kJmol-1. Under the latter conditions, the rate of plasticizer loss from the PVC cable was very similar to that from the pure plasticizer, suggesting that a film of plasticizer was formed on the PVC surface. The evaporation of DEHP showed a clear dependence on the rate of ventilation of the gas phase surrounding the cable. The ability to monitor the condition of the installed cables is dependent on good techniques for the remaining lifetime assessment. The condition monitoring technique, Line Resonance Analysis, was applied to chlorosulfonated polyethylene cables. A clear correlation between LIRA and indenter modulus data obtained and LIRA and tensile testing results was found. This is of interest since existing lifetime criteria used in the nuclear plants are based on these two testing techniques.
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| 10. |
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