| 271. |
- Lindström, Tom, et al.
(författare)
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Evolution of biobased and nanotechnology packaging - a review
- 2020
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 35:4, s. 491-515
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Forskningsöversikt (refereegranskat)abstract
- This review deals with the evolution of bio-based packaging and the emergence of various nanotechnologies for primary food packaging. The end-of life issues of packaging is discussed and particularly the environmental problems associated with microplastics in the marine environment, which serve as a vector for the assimilation of persistent organic pollutants in the oceans and are transported into the food chain via marine and wild life. The use of biodegradable polymers has been a primary route to alleviate these environmental problems, but for various reasons the market has not developed at a sufficient pace that would cope with the mentioned environmental issues. Currently, the biodegradable plastics only constitute a small fraction of the fossil-based plastic market. Fossil-based plastics are, however, indispensable for food safety and minimization of food waste, and are not only cheap, but has generally more suitable mechanical and barrier properties compared to biodegradable polymers. More recently, various nanotechnologies such as the use of nanoclays, nanocellulose, layer-by-layer technologies and polyelectrolyte complexes have emerged as viable technologies to make oxygen and water vapor barriers suitable for food packaging. These technological developments are highlighted as well as issues like biodegradation, recycling, legislation issues and safety and toxicity of these nanotechnologies.
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| 272. |
- Liu, Dongming, 1987-, et al.
(författare)
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Influence of Nanoparticle Surface Coating on Electrical Conductivity of LDPE/Al2O3 Nanocomposites for HVDC Cable Insulations
- 2017
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Ingår i: IEEE transactions on dielectrics and electrical insulation. - : IEEE. - 1070-9878 .- 1558-4135. ; 24:3, s. 1396-1404
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Tidskriftsartikel (refereegranskat)abstract
- LDPE/metal oxide nanocomposites are promising materials for future high-voltage DC cable insulation. This paper presents data on the influence of the structure of the nanoparticle coating on the electrical conductivity of LDPE/Al2O3 nanocomposites. Al2O3 nanoparticles, 50 nm in size, were coated with a series of silanes with terminal alkyl groups of different lengths (methyl, n-octyl and n-octadecyl groups). The density of the coatings in vacuum was between 200 and 515 kg m(-3,) indicating substantial porosity in the coating. The dispersion of the nanoparticles in the LDPE matrix was assessed based on statistics for the nearest-neighbor particle distance. The electrical conductivity of the nanocomposites was determined at both 40 and 60 degrees C. The results show that an appropriate surface coating on the nanoparticles allowed uniform particle dispersion up to a filler loading of 10 wt.%, with a maximum reduction in the electrical conductivity by a factor of 35. The composites based on the most porous octyl-coated nanoparticles showed the greatest reduction in electrical conductivity and the lowest temperature coefficient of electrical conductivity of the composites studied.
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| 273. |
- Liu, Rong, et al.
(författare)
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Chemoenzymatic preparation of (2S,3S)- and (2R,3R)-2,3-butanediols and their esters from mixtures of d,l- and meso-diols
- 2001
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Ingår i: Tetrahedron. - 0957-4166 .- 1362-511X. ; 12:5, s. 771-778
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Tidskriftsartikel (refereegranskat)abstract
- An efficient method of preparing the pure enantiomers of 2,3-butanediol front commercially available mixtures of the d,l- and meso-isomers was developed. It furnished (2S,3S)-2.3-butanediol with > 99% e.e. and a >9.5/0.5 diastereomeric ratio and (2R,3R)-2,3-butanediol in 95% e.e. and >9.5/<5 diastereomeric ratio.
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| 274. |
- Liu, Rong, et al.
(författare)
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Preparation of the four stereoisomers of 3-bromo-2-butanol or their acetates via lipase-catalysed resolutions of the racemates derived from dl- or meso-2,3-butanediol
- 2005
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Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 16:15, s. 2607-2611
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Tidskriftsartikel (refereegranskat)abstract
- The four stereoisomeric 3-bromo-2-butanols and/or their acetates were prepared via lipase-catalysed kinetic resolution by hydrolyses of the acetates of the (+/-)-syn- and (+/-)-anti-3-bromo-2-butanols, or via esterifications of the alc hols. The diastereomeric bromoacetates were obtained by syntheses from the dl- and meso-2,3-butanediols, respectively. On a preparative scale, the four stereoisomers, either as the free alcohols or as their acetates, were obtained in > 95% ee, and in 35-40% yield (based on the starting racemates).
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| 275. |
- Liu, Sirui, et al.
(författare)
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Design of Hygroscopic Bioplastic Products Stable in Varying Humidities
- 2023
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Ingår i: Macromolecular materials and engineering. - : Wiley. - 1438-7492 .- 1439-2054. ; 308:2
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Tidskriftsartikel (refereegranskat)abstract
- Hygroscopic biopolymers like proteins and polysaccharides suffer from humidity-dependent mechanical properties. Because humidity can vary significantly over the year, or even within a day, these polymers will not generally have stable properties during their lifetimes. On wheat gluten, a model highly hygroscopic biopolymer material, it is observed that larger/thicker samples can be significantly more mechanically stable than thinner samples. It is shown here that this is due to slow water diffusion, which, in turn, is due to the rigid polymer structure caused by the double-bond character of the peptide bond, the many bulky peptide side groups, and the hydrogen bond network. More than a year is required to reach complete moisture saturation (≈10 wt.%) in a 1 cm thick plate of glycerol-plasticized wheat gluten, whereas this process takes only one day for a 0.5 mm thick plate. The overall moisture uptake is also retarded by swelling-induced mechanical effects. Hence, hygroscopic biopolymers are better suited for larger/thicker products, where the moisture-induced changes in mechanical properties are smeared out over time, to the extent that the product remains sufficiently tough over climate changes, for example, throughout the course of a year.
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| 276. |
- Lundström, Nicole, et al.
(författare)
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Teachers’ Expectations of Learning Analytics from a Value-Based Perspective
- 2023
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Ingår i: Open Science in Engineering - Proceedings of the 20th International Conference on Remote Engineering and Virtual Instrumentation. - Cham : Springer Nature. ; , s. 811-822
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Konferensbidrag (refereegranskat)abstract
- Learning Analytics (LA) is an established field of research and practice. Yet, there is still scarce evidence of LA on improved learning and teaching. In this regard, researchers highlight a need to involve not only students but also teachers in the development of LA systems to ensure that LA is implemented effectively. Earlier research has pointed out several ethical issues that are important to consider when designing and using LA services. Ethics are interrelated with stakeholders’ values since the values represent things that are seen as important to individuals. These values are rarely considered when designing LA systems; it is problematic since it may influence the design and the implementation of effective LA solutions in a negative way. The aim of this study is therefore to explore which values teachers consider important in relation to LA systems to be used in higher education. The selected and adapted set of envisioning cards was used during an online workshop with 11 teachers. The results indicate that there are several critical values that are important for teachers in relation to LA systems, including variation, personalization, flexibility, insight, transparency, efficiency, and trust. By taking these values into consideration when designing LA systems, teachers’ needs can be better met in the setting of higher education.
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| 277. |
- Lundström, Ulla, et al.
(författare)
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Advances in understanding the podzolization process resulting from a multidisciplinary study of three coniferous forest soils in the Nordic Countries
- 2000
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 94:04-feb, s. 335-353
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Tidskriftsartikel (refereegranskat)abstract
- Geochemical, mineralogical, micromorphological, microbiological, hydrochemical and hpdrological joint investigations were performed at two coniferous podzolic sites in the north of Sweden and at one in the south of Finland. Mycorrhizal fungi were found to create numerous pens (3-10-mu m diameter) in many weatherable mineral grains in the eluvial (E) horizon. During the growing season, identified low molecular weight (LMW) organic acids such as citric, shikimic, oxalic and fumaric acids comprised 0.5-5% of the DOC and 0.5-15% of the total acidity in soil solutions. Between 20% and 40% of the dissolved Al was bound to the identified LMW organic acids. Mineral dissolution via complexing LMW acids, probably exuded in part by the mycorrhiza hyphae, is likely to be a major weathering process in podzols. We found no evidence for a decreasing C/metal ratio of the migrating organo-metal complexes that could explain the precipitation of secondary Fe and AL in the illuvial (B) horizon. Instead, microbial degradation of organic ligands resulting in the release of ionic,Al and Fe to the soil solution may he an important process facilitating the formation of solid Al-SI-OH and Fe-OH phases in the podzol B horizon. However, within the B horizon transport as proto-imogilite (PI) sols might be possible. In the B horizon, the extractable,Al and Fe was predominantly inorganic. The large specific surface area (SSA) removable by oxalate extraction, the high point of zero charge salt effect (PZSE), the low cation exchange capacity (CEC) and the high sulphate exchange capacity (SEC), painted to the presence of short-range ordered variable charge phases. Imogolite type material (ITM) was indeed identified in all B horizons by IR spectroscopy and crystalline imogolite was found in the deep B horizon of one profile. Mossbauer spectroscopy indicated that Fe in the form of ferrihydrite was formed by intergrowth with an Al-Si-OH phase. The high amounts of Fe and Al transported from the O to the E horizon indicate that there could be an upward transport of these elements before they are leached to the B horizon. We hypothesize that the LMW Al complexes an transported by hyphae to the mor (O) layer, partly released and subsequently complexed by high molecular weight (HMW) acids.
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| 278. |
- Löf, Carl-Gustav
(författare)
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Connection priority power control in cellular radio systems with multicast traffic
- 1998
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Ingår i: Universal Personal Communications, 1998. ICUPC '98. IEEE 1998 International Conference on. - : IEEE. - 0780351061 ; , s. 241-245
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Konferensbidrag (refereegranskat)abstract
- The number of applications where a subset of all receivers is addressed with the same information, so called multicasting, grow in most types of communication networks. In wireless personal communication systems, an effective integration of multicast services is required both from radio resource utilization and application point of view. We propose a combined centralized power control and connection removal algorithm for cellular radio systems with multicast services, utilizing physical multicasting. The aim is to obtain acceptable signal-to-interference-ratios (SIR) in all active communication links. The numerical results show that the power control method we propose outperforms a reference system using fixed transmitter power.
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| 279. |
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| 280. |
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