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| 2. |
- Hao, X. J., et al.
(författare)
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Dendrimers as scaffolds for multifunctional reversible addition-fragmentation chain transfer agents : Syntheses and polymerization
- 2004
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Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 42:23, s. 5877-5890
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of novel first- and second-generation true dendritic reversible addition-fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3-benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z-group architecture based on 1,1,1-hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1.3 for PS) via bulk free-radical polymerization at 60 degreesC. The novel dendrimer-based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number-average molecular weight (M.) with the monomer-polymer conversion, yielding star polymers with molecular weights of up to M-n = 160,000 g mol(-1) for PBA (based on a linear PBA calibration) and up to M. = 70,000 g mol(-1) for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1-hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star-shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star-shaped polymeric materials.
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| 3. |
- Liwenga, Emma T., 1964-
(författare)
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Food insecurity and coping strategies in semiarid areas : the case of Mvumi in central Tanzania
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study examines how people in dryland areas cope with food insecurity and adversities over time. It draws from the experience of the Gogo people living in Mvumi in the semiarid zone of central Tanzania, an area with a long history of food shortages. The study specifically examines the potential for dryland resources to sustain livelihoods. The study looks at the historical perspective of the problem in order to explore factors influencing the food situation in the area. It specifically investigates the role of local knowledge as a factor for adapting to dryland conditions by exploiting seasonality and local diversity. A detailed account is made of the coping strategies among three identified wealth groups in the area. Apart from their wealth levels, households in these wealth categories differ in how they mobilise and deal with labour in various seasons. Households in the well-off group have greater ability in mobilising and using external labour as well as accumulating and managing food surplus. The households in the intermediate group are flexible in utilising their own labour by performing various farm and non-farm activities according to their seasonalities. The households in the poor category sell their own labour and perform various farm and non-farm activities regardless of the season. It is clear from the study that different wealth groups differ in their ability to develop immediate coping into more pro-active livelihood strategies. The study winds up by assessing the potentials of the prominent land resource utilisation strategies in terms of economic, social and environmental perspectives.
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- Ådahl, Emma, et al.
(författare)
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Can intraspecific brood parasitism be detected using egg morphology only?
- 2004
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Ingår i: Journal of Avian Biology. - : Wiley. - 0908-8857 .- 1600-048X. ; 35:4, s. 360-364
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Tidskriftsartikel (refereegranskat)abstract
- Intraspecific brood parasites lay their eggs in the nests of conspecifics. There are a number of methods for detecting intraspecific brood parasitism (IBP) in birds based on egg morphology. Here we test Eadie's (1989) method, which calculates the Euclidean distances between eggs in a given clutch in a three-dimensional space (weight, length and width). A parasitised clutch is predicted to contain an egg (or eggs) that is significantly different from the clutch's other eggs. Data from three species were analysed. Our captive zebra finch Taeniopygia guttata clutches did not include any instances of IBP, the wild jackdaw Corvus monedula data were unlikely to contain any, and for the goldeneye Bucephala clangula data set we had an observational estimate of IBP. We simulated IBP in the zebra finch, jackdaw and goldeneye data to test whether the method reliably detects an experimentally 'parasitised' clutch. We show that the distributions of the test statistics greatly overlap in 'parasitised' and unmodified clutches, and are dependent on the clutch size. We therefore conclude that the method can only be used with caution, after calibrating it for a given population.
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