966 resultados para CONCENTRATED COLLOIDAL DISPERSIONS


Relevância:

10.00% 10.00%

Publicador:

Resumo:

In remote-sensing studies, particles that are comparable to the wavelength exhibit characteristic features in electromagnetic scattering, especially in the degree of linear polarization. These features vary with the physical properties of the particles, such as shape, size, refractive index, and orientation. In the thesis, the direct problem of computing the unknown scattered quantities using the known properties of the particles and the incident radiation is solved at both optical and radar spectral regions in a unique way. The internal electromagnetic fields of wavelength-scale particles are analyzed by using both novel and established methods to show how the internal fields are related to the scattered fields in the far zone. This is achieved by using the tools and methods that were developed specifically to reveal the internal field structure of particles and to study the mechanisms that relate the structure to the scattering characteristics of those particles. It is shown that, for spherical particles, the internal field is a combination of a forward propagating wave with the apparent wavelength determined by the refractive index of the particle, and a standing wave pattern with the apparent wavelength the same as for the incident wave. Due to the surface curvature and dielectric nature of the particle, the incident wave front undergoes a phase shift, and the resulting internal wave is focused mostly at the forward part of the particle similar to an optical lens. This focusing is also seen for irregular particles. It is concluded that, for both spherical and nonspherical particles, the interference at the far field between the partial waves that originate from these concentrated areas in the particle interior, is responsible for the specific polarization features that are common for wavelength-scale particles, such as negative values and local extrema in the degree of linear polarization, asymmetry of the phase function, and enhancement of intensity near the backscattering direction. The papers presented in this thesis solve the direct problem for particles with both simple and irregular shapes to demonstrate that these interference mechanisms are common for all dielectric wavelength-scale particles. Furthermore, it is shown that these mechanisms can be applied to both regolith particles in the optical wavelengths and hydrometeors at microwave frequencies. An advantage from this kind of study is that it does not matter whether the observation is active (e.g., polarimetric radar) or passive (e.g., optical telescope). In both cases, the internal field is computed for two mutually perpendicular incident polarizations, so that the polarization characteristics can then be analyzed according to the relation between these fields and the scattered far field.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The use of buffer areas in forested catchments has been actively researched during the last 15 years; but until now, the research has mainly concentrated on the reduction of sediment and phosphorus loads, instead of nitrogen (N). The aim of this thesis was to examine the use of wetland buffer areas to reduce the nitrogen transport in forested catchments and to investigate the environmental impacts involved in their use. Besides the retention capacity, particular attention was paid to the main factors contributing to the N retention, the potential for increased N2O emissions after large N loading, the effects of peatland restoration for use as buffer areas on CH4 emissions, as well as the vegetation composition dynamics induced by the use of peatlands as buffer areas. To study the capacity of buffer areas to reduce N transport in forested catchments, we first used large artificial loadings of N, and then studied the capacity of buffer areas to reduce ammonium (NH4-N) export originating from ditch network maintenance areas in forested catchments. The potential for increased N2O emissions were studied using the closed chamber technique and a large artificial N loading at five buffer areas. Sampling for CH4 emissions and methane-cycling microbial populations were done on three restored buffer areas and on three buffers constructed on natural peatlands. Vegetation composition dynamics was studied at three buffer areas between 1996 and 2009. Wetland buffer areas were efficient in retaining inorganic N from inflow. The key factors contributing to the retention were the size and the length of the buffer, the hydrological loading and the rate of nutrient loading. Our results show that although the N2O emissions may increase temporarily to very high levels after a large N loading into the buffer area, the buffer areas in forested catchments should be viewed as insignificant sources of N2O. CH4 fluxes were substantially higher from buffers constructed on natural peatlands than from the restored buffer areas, probably because of the slow recovery of methanogens after restoration. The use of peatlands as buffer areas was followed by clear changes in plant species composition and the largest changes occurred in the upstream parts of the buffer areas and the wet lawn-level surfaces, where the contact between the vegetation and the through-flow waters was closer than for the downstream parts and dry hummock sites. The changes in the plant species composition may be an undesired phenomenon especially in the case of the mires representing endangered mire site types, and therefore the construction of new buffer areas should be primarily directed into drained peatland areas.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Hemispherical colloidal nanowells or microwells with hollow interiors are becoming increasingly important for the encapsulation of functional materials. There has been rapid progress to develop new methods to obtain such structures. In this work, we present emulsification approach to generate hemisphere and microcapsules of biocompatible organic polymer. The precise control over the size is exhibited by applying variable vortex effect. The hemispheres and microcapsules of a copolymer (BPVA-PVA) were characterized by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). These structures were used for loading of hydrophilic molecules and submicron colloidal particles to demonstrate their potential application. The introduction of hydrophobic groups on poly(vinyl alcohol) was crucial to obtain these structures.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The dominant discourses on the issue of asylum have placed it on a uniquely higher level of scrutiny as a politically very sensitive area for social research. Today, member states within the EU have implemented stricter policies to control new arrivals, whilst instituting statutory procedures to manage the existing asylum claims. In 2010, the number of applicants for asylum in Finland totalled 5988, out of which 1784 were given positive decisions. This thesis endeavour to highlight asylum seekers in the discourses about them by adding their voices to the discussions of them in contemporary Finland. Studies, which has concentrated on asylum seekers in Finland, uses the living conditions within asylum reception centres to assess the impacts of structural barriers on asylum seekers’ efforts to deal with the asylum process. By highlighting the impacts of the entire asylum process, which I believe starts from the country of origin; I focus on examining narratives of dealing with the experience of liminality whilst waiting for asylum, and then explore areas of possible participation within informal social networks for West African asylum seekers in Finland. The overall aim is to place the current research within the broader sociological discussion of ‘belonging’ for asylum seekers who are yet to be recognized as refugees, and who exist in a state of limbo. Methodologically, oral interviews, self-written autobiographical narratives, and ethnographic field work are qualitatively combined as data in this thesis for an empirical study of West African male asylum seekers in Finland. Narrative analysis is employed to analyze the data for this thesis. The ethnographic research data for the study began in May 2009 and ended in August of 2010. Altogether, ten interviews and four self-written narratives were collected as data. In total seven hours of audio recording were made, along eleven pages of hand-written autobiographical narratives. Field observation notes are employed in the study to provide contexts to the active interactional processes of interpretation throughout the analysis. Findings from the study suggest that within the experience of liminality, which surrounds the entire asylum process, participations within informal social networks are found to be important to the process of re-making place and the sense of belonging. My study shows that this is necessary to countering the experience of boredom, stress and social isolation, which permeate all aspects of life for West African asylum seekers, whilst they wait for asylum decisions in Finland.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

13 C resonances of carbonyl and methyl groups in amides are shifted down-field on interaction with alkali and alkaline earth metal salts. The magnitude of the shift depends on the ionic potential of the cation. Ions like Li+ bind to the amide carbonyl group both in neat amide solutions as well as in concentrated salt solutions in water.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Objectives. This study concentrated on the aspect of physical safety in the learning environment of primary and secondary schools in Helsinki. Taking a broad perspective, the study analysed the safety culture of Helsinki schools, ranked them with a point rating system, and thoroughly investigated reasons behind their differences. Safety culture in educa-tional institutions has not been studied previously although research related to safety culture in business is abundant and some studies have considered safety culture in the healthcare sector. The study focused on the attitudes and practices of teachers concerning safety. The main research question is as follows: "What factors related to safety culture distinguish schools with an exceptional safety culture from those weaker one?" Research methods. The study used a mixed-methods approach. It s quantitative part charted the safety attitudes, values and expertise of employees in selected schools. The study also analysed physical safety in selected schools through specific safety inspections. The 14 schools in the study were selected randomly, two from each district. Altogether 388 of 475 employees returned a Webropol questionnaire (N= 475, 81,68 %). The qualitative part of the study analysed the reasons behind perceived differences in school s safety cul-ture using theme interviews with school principals. Elements of a phenomenographic research approach were also used. Results and conclusions. According to the study the distinctive features of good safety cultures in the Helsinki schools included a well-developed understanding of safety hazards and the requirements of basic safety, good safety management practices, a developed understanding of the systematic nature of safety, an appreciation of safety evidenced through everyday practices and open and communal safety-related work. The study offers result-based safety culture improvements for teachers, those responsible for school safety, principals, educational administrators, teacher educators and authorities.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

In order to depict the mechanism of coalescence in fibrous bed coalescers, a model coalescer was fabricated. Both water/oil and oil/water dispersions were run through this model coalescer to check for coalescence on PTFE and glass surfaces. The equilibrium contact angle and the dynamic contact angle of the dispersed drops were measured on these surfaces in the presence of the continuous phase. Coalescence was monitored using a microscope. Based on these observations a mechanism of coalescence in the model coalescer is proposed. Different modes of coalescence are correlated to the equilibrium contact angle and the dynamic contact angle. Deposition of dirt on the coalescing surface is observed to result in change of wettability, leading to redispersion of the already coalesced dispersed phase into larger droplets.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The restricted three-body method is used to model the effect of the mean tidal field of a cluster of galaxies on the internal dynamics of a disk galaxy falling into the cluster for the first time. In the model adopted the galaxy experiences a tidal field that is compressive within the core of the cluster. The planar random velocities of all components in the disk increase after the galaxy passes through the core of the cluster. The low-velocity dispersion gas clouds experience a relatively larger increase in random velocity than the hotter stellar components. The increase in planar velocities results in a strong anisotropy between the planar and vertical velocity dispersions. It is argued that this will make the disk unstable to the 'fire-hose instability' which leads to bending modes in the disk and which will thicken the disk slightly. The mean tidal fields in rich clusters were probably stronger during the epoch of cluster formation and relaxation than they are in present-day relaxed clusters.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The aim of the thesis was to study the extent of spatial concentration of immigrant population in Helsinki and to analyse the impact of housing policy on ethnic residential segregation in 1992-2005. For the purpose of the study, immigrant population was defined based on the language spoken at home. The theory of residential segregation by Andersson and Molina formed the main theoretical framework for the study. According to Andersson and Molina ethnic residential segregation results from different dynamic intra-urban migration processes. Institutionally generated migration, i.e. migration patterns generated by various housing and immigrant policies and procedures, is one of the central factors in the development of ethnic segregation. The data of the study consisted of population and housing statistics and housing and immigrant policy documents of Helsinki municipality. Spatial concentration of immigrant population was studied both at district and building levels using GIS-methods and statistical methods. The housing policy of Helsinki municipality was analysed using a method created by Musterd et al. Musterd et al. categorise two types of policy approaches to residential segregation: spatial dispersion policy and compensating policy. The housing policy of Helsinki has a strong focus on social mixing and spatial dispersion of housing stock. Ethnic segregation is regarded as a threat. The importance of ethnic communities and networks is, however, acknowledged and small-scale concentration is therefore not considered harmful. Despite the spatial dispersion policy, the immigrant population is concentrated in the eastern, north-eastern and north-western suburbs of Helsinki. The spatial pattern of concentration was formed already at the beginning of the 1990's when immigration to Finland suddenly peaked. New immigrant groups were housed in the neighbourhoods where public housing was available at the time. Housing policy, namely the location of new residential areas and public housing blocks and the policies of public housing allocation were key factors influencing the residential patterns of immigrant population in the 1990's. The immigration and refugee policies of the state have also had an impact on the development. The concentration of immigrant population has continued in the same areas in the beginning of the 2000's. Dispersion to new areas has mainly taken place within the eastern and north-eastern parts of the city or in the adjacent areas. The migration patterns of native population and the reasonably rapid changes in the housing market have emerged as new factors generating and influencing the ethnic residential segregation in Helsinki in the 2000's. Due to social mixing and spatial dispersion policies, ethnic segregation in Helsinki has so far been fairly small-scale, concentrated in particular housing blocks. The number of residential buildings with a high share of immigrant population is very modest. However, the number of such buildings has doubled between 1996-2002. The concentration of immigrant population concerns mainly the public housing sector. The difference in the level of concentration between the public housing sector and privately owned housing companies is remarkable.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The aim of this thesis is to examine the skilled migrants’ satisfaction with the Helsinki Metropolitan Area. The examination is executed on three scales: housing, neighbourhoods and the city region. Specific focus is on the built environment and how it meets the needs of the migrants. The empirical data is formed of 25 semi-structured interviews with skilled migrants and additionally 5 expert interviews. Skilled and educated workforce is an increasingly important resource in the new economy, and cities are competing globally for talented workers. With aging population and a need to develop its innovational structure, the Helsinki Metropolitan Area needs migrant workforce. It has been stated that quality of place is a central factor for skilled migrants when choosing where to settle, and from this perspective their satisfaction with the region is significant. In housing, the skilled migrants found the price-quality ratio and the general sizes of apartments inadequate. The housing market is difficult for the migrants to approach, since they often do not speak Finnish and there are prejudices towards foreigners. The general quality of housing was rated well. On the neighbourhood level, the skilled migrants had settled in residential areas which are also preferred by the Finnish skilled workers. While the migrants showed suburban orientation in their settlement patterns, they were not concentrated in the suburban areas which host large shares of traditional immigrant groups. Migrants were usually satisfied with their neighbourhoods; however, part of the suburban dwellers were unsatisfied with the services and social life in their neighbourhoods. Considering the level of the city region, the most challenging feature for the skilled migrants was the social life. The migrants felt that the social environment is homogeneous and difficult to approach. The physical environment was generally rated well, the most appreciated features being public transportation, human scale of the Metropolitan Helsinki, cleanliness, and the urban nature. Urban culture and services were seen good for the city region’s size, but lacking in international comparison.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The aim of this thesis was to study the crops currently used for biofuel production from the following aspects: 1. what should be the average yield/ ha to reach an energy balance at least 0 or positive 2. what are the shares of the primary and secondary energy flows in agriculture, transport, processing and usage, and 3. overall effects of biofuel crop cultivation, transport, processing and usage. This thesis concentrated on oilseed rape biodiesel and wheat bioethanol in the European Union, comparing them with competing biofuels, such as corn and sugarcane-based ethanol, and the second generation biofuels. The study was executed by comparing Life Cycle Assessment-studies from the EU-region and by analyzing them thoroughly from the differences viewpoint. The variables were the following: energy ratio, hectare yield (l/ha), impact on greenhouse gas emissions (particularly CO2), energy consumption in crop growing and processing one hectare of a particular crop to biofuel, distribution of energy in processing and effects of the secondary energy flows, like e.g. wheat straw. Processing was found to be the most energy consuming part in the production of biofuels. So if the raw materials will remain the same, the development will happen in processing. First generation biodiesel requires esterification, which consumes approximately one third of the process energy. Around 75% of the energy consumed in manufacturing the first generation wheat-based ethanol is spent in steam and electricity generation. No breakthroughs are in sight in the agricultural sector to achieve significantly higher energy ratios. It was found out that even in ideal conditions the energy ratio of first generation wheat-based ethanol will remain slightly under 2. For oilseed rape-based biodiesel the energy ratios are better, and energy consumption per hectare is lower compared to wheat-based ethanol. But both of these are lower compared to e.g. sugarcane-based ethanol. Also the hectare yield of wheat-based ethanol is significantly lower. Biofuels are in a key position when considering the future of the world’s transport sector. Uncertainties concerning biofuels are, however, several, like the schedule of large scale introduction to consumer markets, technologies used, raw materials and their availability and - maybe the biggest - the real production capacity in relation to the fuel consumption. First generation biofuels have not been the expected answer to environmental problems. Comparisons made show that sugarcane-based ethanol is the most prominent first generation biofuel at the moment, both from energy and environment point of view. Also palmoil-based biodiesel looks promising, although it involves environmental concerns as well. From this point of view the biofuels in this study - wheat-based ethanol and oilseed rape-based biodiesel - are not very competitive options. On the other hand, crops currently used for fuel production in different countries are selected based on several factors, not only based on thier relative general superiority. It is challenging to make long-term forecasts for the biofuel sector, but it can be said that satisfying the world's current and near future traffic fuel consumption with biofuels can only be regarded impossible. This does not mean that biofuels shoud be rejected and their positive aspects ignored, but maybe this reality helps us to put them in perspective. To achieve true environmental benefits through the usage of biofuels there must first be a significant drop both in traffic volumes and overall fuel consumption. Second generation biofuels are coming, but serious questions about their availability and production capacities remain open. Therefore nothing can be taken for granted in this issue, expect the need for development.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Parkinson´s Disease (PD) is a neurodegenerative movement disorder resulting from loss of dopaminergic (DA) neurons in substantia nigra (SN). Possible causative treatment strategies for PD include neurotrophic factors, which protect and in some cases restore the function of dopaminergic neurons. Glial cell line-derived neurotrophic factor (GDNF) family of neurotrophic factors have been to date the most promising candidates for treatment of PD, demonstrating both neuroprotective and neurorestorative properties. We have investigated the role of GDNF in the rodent dopaminergic system and its possible crosstalk with other growth factors. We characterized the GDNF-induced gene expression changes by DNA microarray analysis in different neuronal systems, including in vitro cultured Neuro2A cells treated with GDNF, as well as midbrains from GDNF heterozygous (Hz) knockout mice. These microarray experiments, resulted in the identification of GDNF-induced genes, which were also confirmed by other methods. Further analysis of the dopaminergic system of GDNF Hz mice demonstrated about 40% reduction in GDNF levels, revealed increased intracellular dopamine concentrations and FosB/DeltaFosB expression in striatal areas. These animals did not show any significant changes in behavioural analysis of acute and repeated cocaine administration on locomotor activity, nor did they exhibit any changes in dopamine output following treatment with acute cocaine. We further analysed the significance of GDNF receptor RET signalling in dopaminergic system of MEN2B knock-in animals with constitutively active Ret. The MEN2B animals showed a robust increase in extracellular dopamine and its metabolite levels in striatum, increased tyrosine hydroxylase (TH) and dopamine transporter (DAT) protein levels by immunohistochemical staining and Western blotting, as well as increased Th mRNA levels in SN. MEN2B mice had increased number of DA neurons in SN by about 25% and they also exhibited increased sensitivity to the stimulatory effects of cocaine. We also developed a semi-throughput in vitro micro-island assay for the quantification of neuronal survival and TH levels by computer-assisted methodology from limited amounts of tissue. This assay can be applied for the initial screening for dopaminotrophic molecules, as well as chemical drug library screening. It is applicable to any neuronal system for the screening of neurotrophic molecules. Since our microarray experiments revealed possible GDNF-VEGF-C crosstalk we further concentrated on studying the neurotrophic effects of VEGF-C. We showed that VEGF-C acts as a neurotrophic molecule for the DA neurons both in vitro and in vivo, however without additive effect when used together with GDNF. The neuroprotective effect for VEGF-C in vivo in rat 6-OHDA model of PD was demonstrated. The possible signalling mechanisms of VEGF-C in the nervous system were investigated - infusion of VEGF-C to rat brain induced ERK activation, however no direct activation of RET signalling in vitro was found. VEGF-C treatment of rat striatum lead to up-regulation of VEGFR-1-3, indicating that VEGF-C can regulate the expression level of its own receptor. VEGF-C dopaminotrophic activity in vivo was further supported by increased vascular tissue in the neuroprotection experiments.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The lifestyles of people living in single-family housing areas on the outskirts of the Greater Helsinki Region (GHR) are different from those living in inner city area. The urban structure of the GHR is concentrated in the capital on the one hand, and spread out across the outskirts on the other. Socioeconomic spatial divisions are evident as well-paid and educated residents move to the inner city or the single-family house dominated suburban neighbourhoods depending on their housing preferences and life situations. The following thesis explores how these lifestyles have emerged through the housing choices and daily mobility of the residents living in the new single-family housing areas on the outskirts of the GHR and the inner city. The study shows that, when it comes to lifestyles, residents on the outskirts of the region have different housing preferences and daily mobility patterns when compared with their inner city counterparts. Based on five different case study areas my results show that these differences are related to residents values, preferences and attitudes towards the neighbourhood, on the one hand, and limited by urban structure on the other. This also confirms earlier theoretical analyses and findings from the GHR. Residents who moved to the outskirts of Greater Helsinki Region and the apartment buildings of the inner city were similar in the basic elements of their housing preferences: they sought a safe and peaceful neighbourhood close to the natural environment. However, where housing choices, daily mobility and activities vary different lifestyles develop in both the outskirts and the inner city. More specifically, lifestyles in the city apartment blocks were inherently urban. Liveliness and highest order facilities were appreciated and daily mobility patterns were supported by diverse modes of transportation for the purposes of work, shopping and leisure time. On the outskirts, by contrast, lifestyles were largely post-suburban and child-friendliness appreciated. Due to the heterachical urban structure, daily mobility was more car-dependent since work, shopping and free time activities of the residents are more spread around the region. The urban structure frames the daily mobility on the outskirts of the region, but this is not to say that short local trips replace longer regional ones. This comparative case study was carried out in the single-family housing areas of Sundsberg in Kirkkonummi, Landbo in Helsinki and Ylästö in Vantaa, as well as in the inner city apartment building areas of Punavuori and Katajanokka in Helsinki. The data is comprised of residential surveys, interviews, and statistics and GIS data sets that illustrate regional daily mobility, socio-economic structure and vis-à-vis housing stock.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Amorphous SiO2 thin films were prepared on glass and silicon substrates by cost effective sol-gel method. Tetra ethyl ortho silicate (TEOS) was used as the precursor material, ethanol as solvent and concentrated HCl as a catalyst. The films were characterized at different annealing temperatures. The optical transmittance was slightly increased with increase of annealing temperature. The refractive index was found to be 1.484 at 550 nm. The formation of SiO2 film was analyzed from FT-IR spectra. The MOS capacitors were designed using silicon (1 0 0) substrates. The current-voltage (I-V), capacitance-voltage (C-V) and dissipation-voltage (D-V) measurements were taken for all the annealed films deposited on Si (1 0 0). The variation of current density, resistivity and dielectric constant of SiO2 films with different annealing temperatures was investigated and discussed for its usage in applications like MOS capacitor. The results revealed the decrease of dielectric constant and increase of resistivity of SiO2 films with increasing annealing temperature. (C) 2010 Elsevier B.V. All rights reserved.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Influence of succinonitrile (SN) dynamics on ion transport in SN-lithium perchlorate (LiClO4) electrolytes is discussed here via dielectric relaxation spectroscopy. Dielectric relaxation spectroscopy (similar to 2 x 10(-3) Hz to 3 MHz) of SN and SN-LiClO4 was studied as a function of salt content (up to 7 mol % or 1 M) and temperature (-20 to +60 degrees C). Analyses of real and imaginary parts of permittivity convincingly reveal the influence Of trans gauche isomerism and solvent-salt association (solvation) effects on ion transport. The relaxation processes are highly dependent on the salt concentration and temperature. While pristine SN display only intrinsic dynamics (i.e., trans-gauche isomerism) which enhances with an increase in temperature, SN-LiClO4 electrolytes especially at high salt concentrations (similar to 0.04-1 M) show salt-induced relaxation processes. In the concentrated electrolytes, the intrinsic dynamics was observed to be a function of salt content, becoming faster with an increase in salt concentration. Deconvolution of the imaginary part of the permittivity spectra using Havriliak-Negami (HN) function show a relaxation process corresponding to the above phenomena. The permittivity data analyzed using HN and Kohlrausch-Williams-Watta (KWW) functions show non-Debye relaxation processes and enhancement in the trans phase (enhanced solvent dynamics) as a function of salt concentration and temperature.