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The common topic of this thesis is boundedness of integral and supremal operators between weighted function spaces. The first type of results are characterizations of boundedness of a convolution-type operator between general weighted Lorentz spaces. Weighted Young-type convolution inequalities are obtained and an optimality property of involved domain spaces is proved. Additional provided information includes an overview of basic properties of some new function spaces appearing in the proven inequalities. In the next part, product-based bilinear and multilinear Hardy-type operators are investigated. It is characterized when a bilinear Hardy operator inequality holds either for all nonnegative or all nonnegative and nonincreasing functions on the real semiaxis. The proof technique is based on a reduction of the bilinear problems to linear ones to which known weighted inequalities are applicable. Further objects of study are iterated supremal and integral Hardy operators, a basic Hardy operator with a kernel and applications of these to more complicated weighted problems and embeddings of generalized Lorentz spaces. Several open problems related to missing cases of parameters are solved, thus completing the theory of the involved fundamental Hardy-type operators. / Operators acting on function spaces are classical subjects of study in functional analysis. This thesis contributes to the research on this topic, focusing particularly on integral and supremal operators and weighted function spaces. Proving boundedness conditions of a convolution-type operator between weighted Lorentz spaces is the first type of a problem investigated here. The results have a form of weighted Young-type convolution inequalities, addressing also optimality properties of involved domain spaces. In addition to that, the outcome includes an overview of basic properties of some new function spaces appearing in the proven inequalities.  Product-based bilinear and multilinear Hardy-type operators are another matter of focus. It is characterized when a bilinear Hardy operator inequality holds either for all nonnegative or all nonnegative and nonincreasing functions on the real semiaxis. The proof technique is based on a reduction of the bilinear problems to linear ones to which known weighted inequalities are applicable.  The last part of the presented work concerns iterated supremal and integral Hardy operators, a basic Hardy operator with a kernel and applications of these to more complicated weighted problems and embeddings of generalized Lorentz spaces. Several open problems related to missing cases of parameters are solved, completing the theory of the involved fundamental Hardy-type operators. / <p>Artikel 9 publicerad i avhandlingen som manuskript med samma titel.</p>

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Published Article / The purpose of this paper is to investigate the consumer-related information tour operators in South African have access to. Data was obtained by means of a self-administered computer-aided questionnaire forwarded to 1 000 tour operators; it was viewed by 360 tour operators and a response rate of 42,45% was achieved. The results indicate that 68,4% are satisfied with their information systems while a concerning low 34,9% 'Agree' that their information systems do provide them with consumer-related information. Tour operators will not be in a position to satisfy the dynamic needs and wants of today's tourists, unless there is information system innovation.

We consider the inverse problem for the magnetic Schrödinger operator with the assumption that the magnetic potential is in Cλ and the electric potential is of the form p1 + div p2 with p1, p2 ∈ Cλ. We use semiclassical pseudodifferential operators on semiclassical Sobolev spaces and Bourgain type spaces. The Bourgain type spaces are defined using the symbol of the operator h2Δ + hμ ⋅ D. Our main result gives a procedure for recovering the curl of the magnetic field and the electric potential from the Dirichlet to Neumann map. Our results are in dimension three and higher.

The aim of this research was to compare the distribution channel relationships in two different tourism markets: the mature market of Britain and the evolving market in Poland, with a view to assessing likely courses of tourism development in Poland. Relationships in channels of distribution can be understood as all the interactions, processes and flows taking place between companies involved in exchange of products and services. The focus of the research was an investigation of channel relationships between travel agents and tour operators. The evolution of tourism channel relationships in Britain and Poland was investigated in three stages: initiation, implementation and review, following the Kale and McIntyre (1991) and Crotts et al. (1998) models. Analysis of existing literature established that historical, political and economic backgrounds, as well as demand and supply, impact in different ways upon the structure of such channels in each country. Following that recognition two phases of empirical research were conducted using a mixed methods approach. The exploratory phase was based on interviews with British and Polish travel agents and tour operators, and from this phase a set of propositions was developed regarding travel agents' and tour operators' attitudes towards channel relationships. These propositions were explored using data collected from a detailed questionnaire survey distributed to a sample of British and Polish tour operators and travel agents. The results from this quantitative research were qualitatively augmented by outcomes from indepth interviews. The key findings from the research were that the Polish distribution system resembled to some extent the old British tourism structure. It was, however, unable to directly follow the development route undertaken by British companies. The pattern of operation was different in both countries due to four factors. Firstly, the distortions in operations in Poland originated from the post-socialist business structure; secondly, the diversity of business in Poland was much greater than in Britain, whilst, thirdly, the level of vertical integration between companies and the level of the development of information technology was more extensive in Britain. Finally, although the relationship development process consisted of similar stages in both countries, the field investigations showed differences in partners' selection, monitoring and support. The Polish companies relied heavily on social bonding and social ties in the selection stage, while in Britain the transparency and higher stability in the market reduced the necessity of close social bonding between employees and companies. The overall conclusion from the research is that the Polish travel companies are likely to follow many aspects of the British route, though with some specifically Polish characteristics. The initial evaluation of channel partners and the evaluation of the relationship between agents and tour operators would be strengthened in Poland, if there were a strong, regulatory and advisory association in the Polish market such as ABTA in Britain. Further research is recommended in terms of the impact of information technology on channel relationships in tourism and the role of tourism associations in the organisation of the tourism market.