Emulsions find a wide range of application in industry and daily life. In the pharmaceutical industry lipophilic active ingredients are often formulated in the disperse phase of oil-in-water emulsions. Milk, butter, and margarine are examples of emulsions in daily life. In the metal processing industry emulsions are used in the form of coolants. Emulsions can be produced with different systems. In the following, the process of high-pressure homogenization is briefly compared to other common mechanical emulsification systems. To facilitate the selection of an emulsification system, the influence of the most important parameters of the emulsion formulation on the resulting mean droplet diameter in the most prevalent continuous emulsification systems is outlined. Subsequently, the most common high-pressure homogenization systems are discussed in detail. On the basis of data from the literature and own experimental results the described high-pressure homogenization systems will be compared regarding their attainable mean droplet diameter. It shows that homogenizers with a relatively simple geometry like the patented ªcombined orifice valveº (Kombi-Blende) attain the smallest mean droplet diameters. The advantage of the ªcombined orifice valveº compared to other high-pressure homogenization systems is not more efficient droplet disruption but rather more efficient droplet stabilization against coalescence immediately after the droplet breakup. The greatest research potential concerning the development of new high-pressure homogenization systems is still to be seen in improvements of droplet stabilization, i.e., the reduction of coalescence.

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Emulsions now find a wide range of applications in industry and daily life. In the pharmaceutical industry lipophilic active ingredients as well as many nutritional products such as vitamins are often formulated in the dispersed phase of oil-in-water emulsions. Emulsions can be produced with different mechanical emulsification techniques. In the following review, the process of rotor-stator systems and disc systems are compared to other popular mechanical emulsification systems. On the basis of experimental results from the authors' laboratory, a discontinuous gear-rim dispersing system, discontinuous disc system, and a continuous high pressure system are compared with regard to their attainable mean droplet diameter and drop size distribution in an oil-in-water emulsion. It can be shown that dissolver discs with a very simple geometry attain very small mean droplet diameters and a very narrow droplet size distribution, comparable to the emulsions obtained with established rotorstator systems such as gear-rim dispersers.

Two-pion production reactions in proton-proton collisions have been studied using the PROMICE/WASA detector and an internal cluster gas-jet target at the CELSIUS storage ring in Uppsala. Three out of the four isospin-independent reaction channels have been measured at several energies in the intermediate and near threshold energy region. Important p a r t s o f the analysis include the identi cation of neutral pions from the invariant mass of the decay gammas, the identi cation of positive pions with the delayed pulse technique and the use of Monte Carlo simulations to understand the detector response. The total cross sections for the pp!pp + , the pp!pp 0 0 and the pp!pn + 0 reactions are presented at beam energies ranging from 650 to 775 MeV.The production mechanism for two-pion production near threshold seems to be dominated by resonance production. The contribution from the non-resonant terms alone can not reproduce the total cross sections. In most models, two-pion production is governed by the a n d the N resonances in either one or both of the participating nucleons. The N (1440)!N( ) T=0 S wave transition has been suggested as the dominating production mechanism for two-pion production in proton-proton collisions. However, the total cross sections presented in this thesis show that other production mechanisms also must give large contributions.

Exclusive measurements of the production of η-mesons in the pp → ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the η meson. However, evidence is also presented at the higher energy for the existence of an anisotropy in the angular distributions of the η-meson and also of the final proton-proton pair, probably to be associated with D-waves in this system interfering with the dominant S-wave term. The sign of the η angular anisotropy suggests that ρ-exchange is important for this reaction.