7 resultados para Snowball sampling

em Helda - Digital Repository of University of Helsinki


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The aim of this research was to explore how issues of power manifest themselves in bringing up children at home. The starting point for the study was a phenomenon centered, power focused, and theoretically orientated view which also included an empirical part as well. The most common aim of the research was to find out and theoretize of power which is suitable for bringing up children at home. Power was defined and researched on the basis of existing power theories, mostly those presented in anglo-american research on power. For closer investigation I chose the most common categorizations and theories of power, namely, the nature of power, the four dimensions of power, and forms of power. The empirical part of the research consisted of 22 thematic interviews with mothers, fathers and 14 – 16-year-old teenagers from 11 different families. The interviewees were found through snowball sampling. The questions for the interviews were based on power theories. The result of the research was that the most common categorizations and theories of power were useful but not satisfactory in the study of power in bringing up children at home. The nature of authority in bringing up children at home appears to have same characteristics as the categorization of authority put forward by Weber but in addition it included extra categories called moral authority and ontological-existential authority. Theoretically the most challenging problem concerns the conflict between modern and postmodern views of power. None of them alone is able to describe power in bringing up children at home. The best solution appeared to be to add an assumption about the inner relation to the modern power view and an assumption about the Popperian three worlds to the postmodern view of power. The relationship between the parent and the child is necessary the inner power relation where the relation itself modifies the parties’ identities. In that case positive and productive elements are also included in the power relationship. Parents use many forms of power in bringing up children at home. Manipulative and violent forms of power are not justifiable but other forms of power and their open exercise is sometimes necessary. The important criteria to use in order to determine the most suitable forms of power and the most appropriate ways of exercising that power is to see how they improve the development of the identity and internalization of values of the child. An ethically justified exercise of power in bringing up children at home is based on a dialogical, pedagogical relationship between the parent and the child, focuses on the relationship between the parent and the child, orientates itself further than present, aspires to promote the good of the child, and comes true in a caring atmosphere.

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This is a qualitative and multimethodological comparative study, which consists of two main parts: examining the development of new media and analysing and comparing the new media strategies of the three companies studied (Alma Media, Sanoma and the Finnish Broadcasting Company Yleisradio). The study includes the first large-scale review in Finnish of the development of new media, paying attention to the birth of the Internet as well as to mobile media, web TV and any other element of new media. It also concentrates on the function of electronic distribution channels before the age of the Internet, e.g. cable text and videotext. Answers about how the three traditional Finnish media houses began spreading their content to the Internet and wireless applications in 1994–2004 are also given. In researching the new media strategies the study pays special attention to the attitudes that the three media companies adopted towards the Internet and other forms of new media in their strategies during the years in question. By analysing and comparing, e.g., the companies’ strategies and their investments, the study ascertains whether the companies had a joint functional model in adopting new media or acted totally on their own without taking too much notice of the media field overall. The study makes extensive use of previously published material. The researcher has also interviewed almost twenty people who were involved in getting the companies’ new media functions under way. The methods for the interviews were dialogue and snowball sampling. The researcher has created a classification in which he divides the business strategies into four different categories: active strategy, careful strategy, permissive strategy, and passive strategy. In comparing and analysing the companies the researcher has used the classification devised by Allan Afuah & Christopher L. Tucci. The seven element classification consists of dominant managerial logic, competency trap, fear of cannibalisation and loss of revenue, channel conflict, political power, co-opetitor power and emotional attachment. In analysing the company strategies the researcher has also noted the classifications of convergence made by Everette E. Dennis and Graham Murdock as well as the aspects formulated by Sylvia Chan-Olmsted and Louisa Ha concerning the success of the companies in adopting the Internet into their functions. Based on all these classifications and by further developing them the researcher analyses and compares the success of the new media strategies of the three Finnish companies. The outcome of the study is a conclusion as to what kind of strategies the companies have carried out their new media functions and how they have succeeded in it.

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This thesis examines the feasibility of a forest inventory method based on two-phase sampling in estimating forest attributes at the stand or substand levels for forest management purposes. The method is based on multi-source forest inventory combining auxiliary data consisting of remote sensing imagery or other geographic information and field measurements. Auxiliary data are utilized as first-phase data for covering all inventory units. Various methods were examined for improving the accuracy of the forest estimates. Pre-processing of auxiliary data in the form of correcting the spectral properties of aerial imagery was examined (I), as was the selection of aerial image features for estimating forest attributes (II). Various spatial units were compared for extracting image features in a remote sensing aided forest inventory utilizing very high resolution imagery (III). A number of data sources were combined and different weighting procedures were tested in estimating forest attributes (IV, V). Correction of the spectral properties of aerial images proved to be a straightforward and advantageous method for improving the correlation between the image features and the measured forest attributes. Testing different image features that can be extracted from aerial photographs (and other very high resolution images) showed that the images contain a wealth of relevant information that can be extracted only by utilizing the spatial organization of the image pixel values. Furthermore, careful selection of image features for the inventory task generally gives better results than inputting all extractable features to the estimation procedure. When the spatial units for extracting very high resolution image features were examined, an approach based on image segmentation generally showed advantages compared with a traditional sample plot-based approach. Combining several data sources resulted in more accurate estimates than any of the individual data sources alone. The best combined estimate can be derived by weighting the estimates produced by the individual data sources by the inverse values of their mean square errors. Despite the fact that the plot-level estimation accuracy in two-phase sampling inventory can be improved in many ways, the accuracy of forest estimates based mainly on single-view satellite and aerial imagery is a relatively poor basis for making stand-level management decisions.

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Emissions of coal combustion fly ash through real scale ElectroStatic Precipitators (ESP) were studied in different coal combustion and operation conditions. Sub-micron fly-ash aerosol emission from a power plant boiler and the ESP were determined and consequently the aerosol penetration, as based on electrical mobility measurements, thus giving thereby an indication for an estimate on the size and the maximum extent that the small particles can escape. The experimentals indicate a maximum penetration of 4% to 20 % of the small particles, as counted on number basis instead of the normally used mass basis, while simultaneously the ESP is operating at a nearly 100% collection efficiency on mass basis. Although the size range as such seems to appear independent of the coal, of the boiler or even of the device used for the emission control, the maximum penetration level on the number basis depends on the ESP operating parameters. The measured emissions were stable during stable boiler operation for a fired coal, and the emissions seemed each to be different indicating that the sub-micron size distribution of the fly-ash could be used as a specific characteristics for recognition, for instance for authenticity, provided with an indication of known stable operation. Consequently, the results on the emissions suggest an optimum particle size range for environmental monitoring in respect to the probability of finding traces from the samples. The current work embodies also an authentication system for aerosol samples for post-inspection from any macroscopic sample piece. The system can comprise newly introduced new devices, for mutually independent use, or, for use in a combination with each other, as arranged in order to promote the sampling operation length and/or the tag selection diversity. The tag for the samples can be based on naturally occurring measures and/or added measures of authenticity in a suitable combination. The method involves not only military related applications but those in civil industries as well. Alternatively to the samples, the system can be applied to ink for note printing or other monetary valued papers, but also in a filter manufacturing for marking fibrous filters.

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The Earth s climate is a highly dynamic and complex system in which atmospheric aerosols have been increasingly recognized to play a key role. Aerosol particles affect the climate through a multitude of processes, directly by absorbing and reflecting radiation and indirectly by changing the properties of clouds. Because of the complexity, quantification of the effects of aerosols continues to be a highly uncertain science. Better understanding of the effects of aerosols requires more information on aerosol chemistry. Before the determination of aerosol chemical composition by the various available analytical techniques, aerosol particles must be reliably sampled and prepared. Indeed, sampling is one of the most challenging steps in aerosol studies, since all available sampling techniques harbor drawbacks. In this study, novel methodologies were developed for sampling and determination of the chemical composition of atmospheric aerosols. In the particle-into-liquid sampler (PILS), aerosol particles grow in saturated water vapor with further impaction and dissolution in liquid water. Once in water, the aerosol sample can then be transported and analyzed by various off-line or on-line techniques. In this study, PILS was modified and the sampling procedure was optimized to obtain less altered aerosol samples with good time resolution. A combination of denuders with different coatings was tested to adsorb gas phase compounds before PILS. Mixtures of water with alcohols were introduced to increase the solubility of aerosols. Minimum sampling time required was determined by collecting samples off-line every hour and proceeding with liquid-liquid extraction (LLE) and analysis by gas chromatography-mass spectrometry (GC-MS). The laboriousness of LLE followed by GC-MS analysis next prompted an evaluation of solid-phase extraction (SPE) for the extraction of aldehydes and acids in aerosol samples. These two compound groups are thought to be key for aerosol growth. Octadecylsilica, hydrophilic-lipophilic balance (HLB), and mixed phase anion exchange (MAX) were tested as extraction materials. MAX proved to be efficient for acids, but no tested material offered sufficient adsorption for aldehydes. Thus, PILS samples were extracted only with MAX to guarantee good results for organic acids determined by liquid chromatography-mass spectrometry (HPLC-MS). On-line coupling of SPE with HPLC-MS is relatively easy, and here on-line coupling of PILS with HPLC-MS through the SPE trap produced some interesting data on relevant acids in atmospheric aerosol samples. A completely different approach to aerosol sampling, namely, differential mobility analyzer (DMA)-assisted filter sampling, was employed in this study to provide information about the size dependent chemical composition of aerosols and understanding of the processes driving aerosol growth from nano-size clusters to climatically relevant particles (>40 nm). The DMA was set to sample particles with diameters of 50, 40, and 30 nm and aerosols were collected on teflon or quartz fiber filters. To clarify the gas-phase contribution, zero gas-phase samples were collected by switching off the DMA every other 15 minutes. Gas-phase compounds were adsorbed equally well on both types of filter, and were found to contribute significantly to the total compound mass. Gas-phase adsorption is especially significant during the collection of nanometer-size aerosols and needs always to be taken into account. Other aims of this study were to determine the oxidation products of β-caryophyllene (the major sesquiterpene in boreal forest) in aerosol particles. Since reference compounds are needed for verification of the accuracy of analytical measurements, three oxidation products of β-caryophyllene were synthesized: β-caryophyllene aldehyde, β-nocaryophyllene aldehyde, and β-caryophyllinic acid. All three were identified for the first time in ambient aerosol samples, at relatively high concentrations, and their contribution to the aerosol mass (and probably growth) was concluded to be significant. Methodological and instrumental developments presented in this work enable fuller understanding of the processes behind biogenic aerosol formation and provide new tools for more precise determination of biosphere-atmosphere interactions.

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Tiivistelmä: Havaintotiheyden vaikutus valumavesien laatuarvioihin