Threshold behaviour of L x-ray excitation in Xe - Ag collisions

In the collision system Xe - Ag, the thresholds for excitation of quasimolecular L radiation and characteristic Ag L radiation have been found to lie at about 5 MeV and 1 MeV, respectively. These results are discussed on the basis of ab initio calculations of the screened interaction potential and the electron-correlation diagram.

Content aggregation on knowledge bases using graph clustering

Recently, research projects such as PADLR and SWAP have developed tools like Edutella or Bibster, which are targeted at establishing peer-to-peer knowledge management (P2PKM) systems. In such a system, it is necessary to obtain provide brief semantic descriptions of peers, so that routing algorithms or matchmaking processes can make decisions about which communities peers should belong to, or to which peers a given query should be forwarded. This paper proposes the use of graph clustering techniques on knowledge bases for that purpose. Using this clustering, we can show that our strategy requires up to 58% fewer queries than the baselines to yield full recall in a bibliographic P2PKM scenario.

Nuclear organisation and epigenetic regulation of gene expression in Dictyostelium discoideum

A series of vectors for the over-expression of tagged proteins in Dictyostelium were designed, constructed and tested. These vectors allow the addition of an N- or C-terminal tag (GFP, RFP, 3xFLAG, 3xHA, 6xMYC and TAP) with an optimized polylinker sequence and no additional amino acid residues at the N or C terminus. Different selectable markers (Blasticidin and gentamicin) are available as well as an extra chromosomal version; these allow copy number and thus expression level to be controlled, as well as allowing for more options with regard to complementation, co- and super-transformation. Finally, the vectors share standardized cloning sites, allowing a gene of interest to be easily transfered between the different versions of the vectors as experimental requirements evolve. The organisation and dynamics of the Dictyostelium nucleus during the cell cycle was investigated. The centromeric histone H3 (CenH3) variant serves to target the kinetochore to the centromeres and thus ensures correct chromosome segregation during mitosis and meiosis. A number of Dictyostelium histone H3-domain containing proteins as GFP-tagged fusions were expressed and it was found that one of them functions as CenH3 in this species. Like CenH3 from some other species, Dictyostelium CenH3 has an extended N-terminal domain with no similarity to any other known proteins. The targeting domain, comprising α-helix 2 and loop 1 of the histone fold is required for targeting CenH3 to centromeres. Compared to the targeting domain of other known and putative CenH3 species, Dictyostelium CenH3 has a shorter loop 1 region. The localisation of a variety of histone modifications and histone modifying enzymes was examined. Using fluorescence in situ hybridisation (FISH) and CenH3 chromatin-immunoprecipitation (ChIP) it was shown that the six telocentric centromeres contain all of the DIRS-1 and most of the DDT-A and skipper transposons. During interphase the centromeres remain attached to the centrosome resulting in a single CenH3 cluster which also contains the putative histone H3K9 methyltransferase SuvA, H3K9me3 and HP1 (heterochromatin protein 1). Except for the centromere cluster and a number of small foci at the nuclear periphery opposite the centromeres, the rest of the nucleus is largely devoid of transposons and heterochromatin associated histone modifications. At least some of the small foci correspond to the distal telomeres, suggesting that the chromosomes are organised in a Rabl-like manner. It was found that in contrast to metazoans, loading of CenH3 onto Dictyostelium centromeres occurs in late G2 phase. Transformation of Dictyostelium with vectors carrying the G418 resistance cassette typically results in the vector integrating into the genome in one or a few tandem arrays of approximately a hundred copies. In contrast, plasmids containing a Blasticidin resistance cassette integrate as single or a few copies. The behaviour of transgenes in the nucleus was examined by FISH, and it was found that low copy transgenes show apparently random distribution within the nucleus, while transgenes with more than approximately 10 copies cluster at or immediately adjacent to the centromeres in interphase cells regardless of the actual integration site along the chromosome. During mitosis the transgenes show centromere-like behaviour, and ChIP experiments show that transgenes contain the heterochromatin marker H3K9me2 and the centromeric histone variant H3v1. This clustering, and centromere-like behaviour was not observed on extrachromosomal transgenes, nor on a line where the transgene had integrated into the extrachromosomal rDNA palindrome. This suggests that it is the repetitive nature of the transgenes that causes the centromere-like behaviour. A Dictyostelium homolog of DET1, a protein largely restricted to multicellular eukaryotes where it has a role in developmental regulation was identified. As in other species Dictyostelium DET1 is nuclear localised. In ChIP experiments DET1 was found to bind the promoters of a number of developmentally regulated loci. In contrast to other species where it is an essential protein, loss of DET1 is not lethal in Dictyostelium, although viability is greatly reduced. Loss of DET1 results in delayed and abnormal development with enlarged aggregation territories. Mutant slugs displayed apparent cell type patterning with a bias towards pre-stalk cell types.

Attitudes and behaviour towards food attributes and organic food – a triangular methodological investigation of occasional organic consumers

Organic food is increasingly available in the conventional food retail, where organic products are offered alongside with various other types of products and compete mainly with conventional and the so-called conventional-plus products. The latter are conventional products displaying particular quality attributes on the product packaging, such as ‘no artificial additives’, or ‘from animal welfare husbandry’. Often, these quality attributes also apply to organic products. Occasional organic consumers might prefer such conventional-plus alternatives that are perceived to be ‘between’ organic and conventional products. The overall objective of this PhD thesis was to provide information about the segment of occasional organic consumers. In particular, the thesis focussed on consumer perceptions and attitudes towards the quality of, and preferences for, organic, conventional and conventional-plus products in two countries: Germany and Switzerland. To achieve these objectives, qualitative and quantitative consumer research was combined in order to explore occasional organic consumers’ perceptions and attitudes as well as to observe their preferences and buying behaviour regarding different types of food products: organic, conventional and conventional-plus products. The qualitative research showed that, depending on single criteria, organic production was both positively as well as negatively assessed by consumers. Consumer perception of organic food was found to be highly selective and primarily focussed on the final stage of the particular production process. A major problem is that consumers are still mostly unfamiliar with factors associated with organic production, have a lack of confidence, and often confuse organic with conventional products. Besides this, consumer expectations of organic products are different from the expectations of conventional products. The quantitative research revealed that attitudes strongly determine consumers’ preferences for organic, conventional and conventional-plus products. Consumer attitudes tended to differ more between organic and conventional choices rather than conventional-plus and conventional choices. Furthermore, occasional organic consumers are heterogeneous in their preferences. They can be grouped into two segments: the consumers in one segment were less price sensitive and preferred organic products. The consumers in the other segment were more price sensitive and rather preferred conventional-plus or conventional products. To conclude, given the selective and subjective nature of consumer perception and the strong focus of consumer perception on the final stage of the food production process, specific additional values of organic farming should be communicated in clear and catchy messages. At the same time, these messages should be particularly focussed on the final stage of organic food production. The communication of specific added values in relation with organic products to improve the perceived price-performance-ratio is important since conventional-plus products represent an interesting alternative particularly for price sensitive occasional organic consumers. Besides this, it is important to strengthen affirmative consumer attitudes towards organic production. Therefore, policy support should emphasise on long-term communication campaigns and education programmes to increase the consumer awareness and knowledge of organic food and farming. Since consumers expect that organic food is regionally or at least domestically produced while they less accept organic imports, policy support of domestic and regional producers is a crucial measure to fill the current gap between the increasing consumer demand of organic food and the stagnation of the domestic and regional organic food supply.

Exploratory and dust-bathing behaviour in laying hens kept in commercial aviaries and furnished cages

The aim of the present thesis was to identify management factors that affect the extent of exploratory behaviour (ground pecking, scratching) as well as quantitative and qualitative as-pects of dust-bathing behaviour in laying hens kept in commercial furnished cages (‘small group housing’) and aviaries. Based on the results, it should be considered which management measures can be recommended for farmers to enhance hen welfare. The feasibility of direct observations of dust-bathing behaviour as well as video observations of exploratory and dust-bathing behaviour was tested in two aviaries. The direct observations were judged to be unfeasible under the conditions encountered. For the analysis of the video recordings, different sampling intervals for instantaneous scan sampling, different extents of observation time, and intra- and inter-observer reliabilities were compared and the most ap-propriate observation scheme selected. Applying the selected scheme (observing the first 16 minutes of every hour distributed over two consecutive light days with a sample interval of two minutes), within the range of environmental conditions found in 22 aviaries, pecking, scratching and dust-bathing behaviour was performed on average 25, 2 and 7 % of the obser-vation time. Hen numbers in the litter were positively associated with stocking density and group size. More scratching was performed with increasing litter height as well as in humid litter. If no litter had been provided, thus substrate consisted of dust and faeces, a reduced proportion of dust-bathing was found. The same method was then used in 16 furnished cage systems. On average 12 % of the total hen number were found on the scratching mats. The hens spent 8 % of the observed time pecking at the mat, 4 % dust-bathing and 0.4 % scratch-ing. Higher proportions were found on the mats and more dust-bathing behaviour occurred, if substrate was provided. Also with increasing light intensity and stocking density more hens were observed on the mats. More pecking and scratching occurred in conditions of higher stocking density, probably due to social facilitation, and of increased mat area per hen. With increasing mat numbers per cage less pecking was observed. Wider mats led to increased dust-bathing behaviour. Finally, 129 dust-baths recorded in 17 aviaries were analysed in detail. On average they lasted 17 minutes, with the tossing phase taking 69 % of this time, including on average 2 vertical wing shakes and 3 scratches with one leg per minute tossing phase. Dust-bath duration de-creased with increasing litter height. Litter type influenced all recorded parameters: dust-bath duration was highest on straw and lowest on fine material and fine material mixed with straw, where on both also the proportion of the tossing phase was lowest. The number of vertical wing shakes during the dust-bath was highest on straw and lowest on fine material mixed with straw as against the frequency of vertical wing shaking that was lowest on straw and highest on fine material. If dust-bathing hens were disturbed twice or more, dust-bathing duration decreased. With increasing light intensity a decreased proportion of the tossing phase as well as a reduced number of vertical wing shakes were recorded. Possibly the light stimulated the hens to dust-bath more often with less tossing behaviour per performance. The observed variation of the dust-bathing parameters could reflect successful adaptation or frustration of the hens. The litter and light conditions on the investigated farms were predominantly restrictive in terms of stimulation of exploration and dust-bathing behaviour. Thus, it was only possible to analyse possible associations between these factors and exploration and dust-bathing behav-iour within the range found. Based on the results the following management recommendations can be given: To allow hens in furnished cages more normal activity, substrate availability should be improved and mat space and light intensity increased. With regard to aviaries as well litter availability should be improved. Litter height should not be too low. Disturbances during dust-bathing should be prevented, but no influencing factors could be identified.