• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 242
  • 80
  • 1
  • 1
  • Tagged with
  • 324
  • 185
  • 91
  • 73
  • 72
  • 58
  • 49
  • 43
  • 41
  • 38
  • 26
  • 25
  • 23
  • 21
  • 21
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Minskad utbredning av apollofjäril, Parnassius apollo, i södra Stockholms län : En studie av möjliga faktorer utifrån artens habitatkrav

Reisner, Gunilla January 2011 (has links)
The Apollo butterfly, Parnassius apollo, is categorized as Near Threatened (NT) in IUCN Red List. Today in Sweden it is found only in strongly fragmentized populations. In the county of Stockholm, P. apollo exists exclusively in some islands of the archipelago and with one mainland population in Stora Vika. This study has the purpose of expanding the knowledge of the local conditions for the butterfly in the south parts of the county of Stockholm and thereby contributes to a sustainable land management that can preserve the Apollo butterfly. A comparative study was done between areas where the butterfly today have: a stable population (Stora Vika, Utö and Ålö), has disappeared (Muskö and Yxlö) or is strongly declining (north part of Ornö). The investigation was based on factors that was considered be contributing to the species decline. Factors that was investigated was the general distribution of host-plant S. telephium, overgrowth in rocky outcrops, presence of nectar plants close to host-plants and if a large proportion of forest in the surroundings of the investigation sites could have a isolating impact on sites. The study was based on 10 sites where the butterfly exist, 7 sites where it has disappeared and 3 sites where it has declined. No significant differences could be found for any factor. On the contrary, the general presence of host-plants at rocky outcrops seems to be the same in areas where the butterfly has disappeared as in areas where it exist today. However caterpillars were only found at sites with a wide distribution of host-plants and also at sites with a large proportion of forest in the surroundings. This was speaking against the hypothesis that a large proportion of forest could have an isolating effect on sites and therefore a negative impact on the adult butterfly preferences. The result creates new questions and the conclusion is that more knowledge of the local conditions is needed to ensure good practice in land management. Sites which are today hosted by the caterpillar should be identified, investigated and protected. Furthermore should the dispersal of nectar plants be investigated and it would be interesting to study the effects of limestone by analyzing and compare Cd concentrations in S. telephium from Muskö with plants from Stora Vika, Utö and Ålö.
102

Purification and surface modification of polymeric nanoparticles for medical applications

Hederström, Ida January 2008 (has links)
Polymeric nanoparticles are potential candidates as carriers for pharmaceutical agents. Development of such nanoparticles generally requires molecules immobilized on the particle surfaces to ensure biocompatibility and/or targeting abilities. Following particle preparation and surface modification, excess reagents must be removed. Ultracentrifugation, which is the most widely used purification technique as per today, is not feasible in industrial applications. In this diploma work, tangential flow filtration is studied as an alternative purification method which is better suited for implementation in a large-scale process. Comparison of ultracentrifugation and tangential flow filtration in diafiltration mode for purification of nanoparticles, indicate that they are comparable with respect to particle stability and the removal of the surfactant SDS from methacrylic anhydride nanoparticles. The purification efficiency of tangential flow filtration is superior to that of ultracentrifugation. Conductivity measurements of filtrates and supernatant liquids show that a stable conductivity value can be reached 6 times faster in filtration than in centrifugation with equipment and settings used. This conductivity arises from several types of molecules, and the contribution from surfactant molecules alone is not known. However, protein adsorption on the particles indicates successful removal of surfactant. Conductivity and tensiometry were evaluated as potential methods to quantify surfactant in solutions, but both proved unsatisfactory. Using bovine serum albumin as a model protein, the extent of immobilization to nanoparticles is evaluated at different pH. A maximum amount of 6,8 mg/m2 is immobilized, whereof an unknown part is covalently bound. This coverage is achieved at pH 4,0 and is probably partly due to low electrostatic repulsion between particle and protein. An estimation of 2,0 µmol covalently bound BSA per gram of nanoparticles corresponds to 5,3 mg/m2 and a surface coverage of 76%. Removal of excess reagents after surface modification is done with ultracentrifugation instead of filtration, as particle aggregates present after the immobilization reaction might foul the membrane.
103

Purification and surface modification of polymeric nanoparticles for medical applications

Hederström, Ida January 2008 (has links)
<p>Polymeric nanoparticles are potential candidates as carriers for pharmaceutical agents. Development of such nanoparticles generally requires molecules immobilized on the particle surfaces to ensure biocompatibility and/or targeting abilities. Following particle preparation and surface modification, excess reagents must be removed. Ultracentrifugation, which is the most widely used purification technique as per today, is not feasible in industrial applications. In this diploma work, tangential flow filtration is studied as an alternative purification method which is better suited for implementation in a large-scale process.</p><p>Comparison of ultracentrifugation and tangential flow filtration in diafiltration mode for purification of nanoparticles, indicate that they are comparable with respect to particle stability and the removal of the surfactant SDS from methacrylic anhydride nanoparticles. The purification efficiency of tangential flow filtration is superior to that of ultracentrifugation. Conductivity measurements of filtrates and supernatant liquids show that a stable conductivity value can be reached 6 times faster in filtration than in centrifugation with equipment and settings used. This conductivity arises from several types of molecules, and the contribution from surfactant molecules alone is not known. However, protein adsorption on the particles indicates successful removal of surfactant. Conductivity and tensiometry were evaluated as potential methods to quantify surfactant in solutions, but both proved unsatisfactory.</p><p>Using bovine serum albumin as a model protein, the extent of immobilization to nanoparticles is evaluated at different pH. A maximum amount of 6,8 mg/m2 is immobilized, whereof an unknown part is covalently bound. This coverage is achieved at pH 4,0 and is probably partly due to low electrostatic repulsion between particle and protein. An estimation of 2,0 µmol covalently bound BSA per gram of nanoparticles corresponds to 5,3 mg/m2 and a surface coverage of 76%. Removal of excess reagents after surface modification is done with ultracentrifugation instead of filtration, as particle aggregates present after the immobilization reaction might foul the membrane.</p>
104

Vegetation i förändring : – Hur har den återupptagna ängshävden påverkat kärlväxterna på Föllingsös slåtteräng?

Servin, Janni January 2015 (has links)
Föllingsö är odlingslandskapet som räddades undan från golfspelarnas klubbor och skyddades inom ramen för det Europiska nätverket Natura 2000. Slåtterängar är en viktig biotop då de hyser en hög biologisk mångfald och studien av Föllingsös slåtteräng i södra Östergötland omfattar en dels en återinventering av ängens kärlväxtarter dels en historisk kartanalys. Kartanalysen som omfattar tiden 1821-2013 visar att ängen inledningsvis brukats som äng och under en ca 50 år lång period nyttjats som betesmark innan ängsskötseln återupptogs 1993. En analys av 1821 års bonitetsgradering visar ett mönster som innebär att de ängsmarker med lägst bonitet är de som i störst utsträckning har undkommit rationalisering och omläggning till åkermark och därmed är de ängsmarker med längst kontinuitet. Inventeringen, i form av en täckningsgradsanalys, gjordes i syfte att undersöka om den återupptagna hävden har påverkat vegetationen. I kategorin ”betesgynnade” arter har en minskning skett. Orsakerna till detta tillskrivs förändringar i hävden då tramp och gödsling minskat avsevärt i och med övergången till slåtter. För att öka antalet slåttergynnade arter föreslås ett försök där ängen slåttras vid två tillfällen per år i stället för som nuvarande en.
105

Performance Indicator Analysis as a Basis for Process Optimization and Energy Efficiency in Municipal Wastewater Treatment Plants / Nyckeltalsanalys som underlag för processoptimering och energieffektivisering i kommunala avloppsvattenreningsverk

Wennerholm, Elin January 2014 (has links)
The aim of this Master Thesis was to calculate and visualize performance indicators for the secondary treatment step in municipal wastewater treatment plants. Performance indicators are a valuable tool to communicate process conditions and energy efficiency to both management teams and operators of the plant. Performance indicators should be as few as possible, clearly defined, easily measurable, verifiable and easy to understand. Performance indicators have been calculated based on data from existing wastewater treatment plants and qualified estimates when insufficient data was available. These performance indicators were then evaluated and narrowed down to a few key indicators, related to process performance and energy usage. Performance indicators for the secondary treatment step were calculated for four municipal wastewater treatment plants operating three different process configurations of the activated-sludge technology; Sternö wastewater treatment plant (Sweden) using a conventional activated-sludge technology, Ronneby wastewater treatment plant (Sweden) using a ring-shaped activated-sludge technology called oxidation ditch, Headingley wastewater treatment plant (Canada) and Kimmswick wastewater treatment plant (USA), both of which use sequencing batch reactor (SBR) activated-sludge technology. Literature reviews, interviews and process data formed the basis of the Master Thesis. The secondary treatment was studied in all the wastewater treatment plants. Performance indicators were calculated, to the extent it was possible, for this step in the treatment process. The results showed that all the wastewater treatments plants, studied in this master thesis, were well below regulatory requirements of effluent concentrations of organic matter and nutrients. This gap between legislated requirements and performance provides an opportunity for improving energy efficiency and maintaining discharge requirements. The removal of organic matter was consistently high at all wastewater treatment plants studied but the removal of nitrogen was slightly lower during the colder months. The results further showed that the discharge of nitrogen from wastewater treatment plants is the largest stress on the recipient. Data regarding the energy usage was almost nonexistent and energy for aeration was therefore calculated when possible since it is aeration that accounts for the largest fraction of energy usage in a wastewater treatment plant. Sternö wastewater-treatment plant proved to be more energy efficient than Rustorp wastewater treatment plant.
106

Kontinuerlig biologisk rening : En driftoptimering av pilotanläggningen för biologisk kväverening av lakvatten vid Löt avfallsanläggning / Continuous Biological Treatment : Optimisation of the operation of a test facility for biological nitrogen removal from leachate at Löt waste treatment site

Karlsson, Liselott January 2014 (has links)
Lakvatten innehåller ofta stora mängder föroreningar som kan vara skadliga för människor och miljön. På Löt avfallsanläggning som ägs och drivs av Söderhalls renhållningsverk AB (SÖRAB) finns en aktiv deponi för icke-farligt avfall (IFA-deponi) som ger upphov till ett lakvattenflöde med höga halter av ammoniumkväve. Om höga halter av kväve läcker ut i naturen kan det påverka biologiska processer negativt och orsaka problem som övergödning. Fram till 31/12 2014 står Löt avfallsanläggning under prövotid. Under prövotiden har SÖRAB fått ålagt att bland annat utvärdera den kemiska karaktären på samtliga vattenströmmar på anläggningen och optimera vattenreningen för de olika delströmmarna utifrån vattnets karaktär. Under prövotiden har SÖRAB tilldelats provisoriska utsläppsvillkor i form av riktvärden.  På grund av de höga halterna av kväve i lakvattnet från IFA-deponin har SÖRAB haft svårt att klara de provisoriska riktvärden som satts upp för utsläpp av kväve. För att undvika skadlig miljöpåverkan i recipienten dit vatten från anläggningen avleds har SÖRAB utvecklat och konstruerat en pilotanläggning för kontinuerlig biologisk rening (KBR-anläggning) där lakvattnet från IFA-deponin ska behandlas för att reducera utsläppen av kväve från avfallsanläggningen. I KBR-anläggningen utnyttjas de biologiska processerna nitrifikation och denitrifikation för att avskilja kväve från lakvattnet. Detta projekt syftar till att optimera driften av SÖRAB:s anläggning för kontinuerlig biologisk rening av näringsrikt lakvatten med avseende på avskiljning av kväve. I projektet undersöktes olika parametrars inverkan på avskiljningen av kväve. De parametrar som utvärderades var, uppehållstid i reningsstegen, vattentemperatur, fosforbehov samt behov av extern kolkälla. Resultaten visade att vid ett flöde på 420 m3/d genom KBR-anläggningen kunde fullständig nitrifikation och denitrifikation uppnås vid vattentemperaturer över 14 °C om en fosfatfosforhalt över cirka 1 mg/L upprätthölls i dessa reningssteg. Utöver detta krävdes en tillsats av kolkälla i denitrifikationssteget motsvarande en COD-tillsats på fyra gånger nitratkvävehalten i inkommande vatten till denitrifikationssteget. Med dessa parameterinställningar kunde närmare 100 % av det oorganiska kvävet i vattnet avskiljas i KBR-anläggningen, vilket motsvarade en reningseffekt på 66-85 % med avseende på avskiljning av totalkväve. I projektet gjordes även en jämförelse mellan KBR-teknik och andra tekniker för behandling av näringsrikt lakvatten. Jämförelsen visade att KBR-tekniken utgör ett mycket gott alternativ för avskiljning av kväve från näringsrika lakvatten med avseende på både reningseffekt och kostnad. Då reningseffekt och kostnad sammanvägdes var det enbart rening i konventionella avloppsreningsverk som kunde konkurrera med kontinuerlig biologisk rening i den form som användes i detta projekt. / Landfill leachate often contains contaminants that can be harmful if they are discharged into the environment without proper treatment. At SÖRAB’s (Söderhalls renhållningsverk AB) waste treatment site in Löt there is an active landfill for non-hazardous waste that generates leachate containing high levels of nitrogen in the form of ammonium. If large amounts of nutrients leak out into the environment it can have a negative impact on biological processes and cause problems such as eutrophication and acidification. The waste treatment site is until 31 December 2014 under a trial period where the owner company is obliged to, amongst other things, characterise the chemical composition in the runoff from the treatment areas and leachate from the landfill. The characterisation is done in order to find the best treatment methods for the different streams of water. Due to the high levels of nitrogen in the leachate from the landfill at Löt waste disposal plant the current regulations that are set up for the plant have been difficult to follow. To avoid negative environmental impact on the receiving waters and surrounding lands SÖRAB has constructed a pilot treatment plant for continuous biological treatment (KBR) where the nutrient rich leachate will be treated to reduce the total emissions of nitrogen from the waste disposal plant. The KBR-plant uses nitrification and denitrification to remove nitrogen from the leachate. This project is aimed at optimising SÖRAB’s plant for continuous biological treatment with respect to removal of nitrogen. An important part of the project was to examine the effect of different parameters on the removal of nitrogen in the KBR-plant.  The parameters examined and optimised were retention time in the treatment basins, water temperature, phosphorus demand, and the need of external carbon source. The results showed that for a operational flow of 420m3/d, complete nitrification and the denitrification could be achieved for temperatures above 14°C if the phosphate content was more than 1mg/L in the water. Furthermore, a need for an external carbon source in the denitrification basin was identified. It was found that the need of an external carbon source corresponded to a COD-addition of four times the content of nitrate in the incoming water. With these parameter settings almost 100% of the inorganic nitrogen in the water could be separated in the KBR-plant. The removal of total nitrogen was 66-85%. In the project a comparison was also done between the KBR treatment method and other available treatment methods for nitrogen removal from nutritious leachate. The comparison showed that the KBR treatment method is a very good alternative for removal of nitrogen with regard to treatment efficiency and costs. When both removal efficiency and costs were taken into account only traditional wastewater treatment plants could compete with the KBR treatment method used in this project.
107

Biological diversity in urban environments : positions, values, and estimation methods /

Gyllin, Mats, January 2004 (has links) (PDF)
Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2004. / Härtill 5 uppsatser.
108

Aspects in bioethics : theory and practice in a preventive screening for type 1 diabetes /

Gustafsson Stolt, Ulrica January 2002 (has links) (PDF)
Diss. (sammanfattning) Linköping : Univ., 2003. / Härtill 6 uppsatser.
109

Diversity, dispersal, and interactions among diving beetles and mosquitoes in Swedish wetlands /

Lundkvist, Elisabeth, January 2003 (has links) (PDF)
Diss. (sammanfattning) Linköping : Univ., 2003. / Härtill 5 uppsatser.
110

Projektet Livslinjen- världens längsta slåtteräng : En inventering med åtgärdsförslag för att gynna biologisk mångfald längs ett cykelstråk i en storstadskommun

Wedrén, Malin January 2015 (has links)
Den biologiska mångfalden har det senaste seklet utarmats i Sverige. Det beror till stor del på moderniseringen av jord- och skogsbruk som medfört drastiska habitatminskningar. En av de artrikaste biotoperna är den traditionellt hävdade slåtterängen. Projektet Livslinjen har initierats för att återskapa en sammanhängande slåtteräng genom en hel kommun. Den ska vara cykelbar med pedagogiska inslag för allmänheten och samtidigt fungera som en spridningskorridor för flora och fauna. Denna studie har inventerat örtskikt och övergripande struktur längs med tänkta sträcka. Utifrån de olika områdenas förutsättningar har åtgärder för restaurering och nyetablering föreslagits för att återskapa slåtterängslika miljöer samt generellt verka för en ökad biodiversitet. Merparten av det drygt 10 km långa stråket är präglad av kvävetillförsel och igenväxning. Några områden innehåller arter som indikerar slåtterängslika förhållanden. Äldre grova träd, sandiga marker, stenmurar och andra småbiotoper har noterats. Lämpliga skötselregimer måste implementeras på de flesta områdena. Ett estetiskt förhållningssätt bör finnas med i restaureringsprocessen speciellt i de urbana områdena. De ytor som huserar populationer av ängsvegetation måste fortsätta skötas med traditionella metoder för att kunna bevaras. Att starta med informationsförmedling till allmänheten i början av projektet är viktigt för att skapa förståelse. Uppföljning och nya inventeringar för att utvärdera effekterna av åtgärder tillråds. / Over the past century biodiversity has declined in Sweden as in all other western countries. Mainly due to modernization of agriculture and forestry which has resulted in drastic habitat losses for many species when rural areas have become less diverse and more fragmented. One of the most species-rich habitat is the traditional hay meadow. The Project Livslinjen (the “Lifeline”) has been initiated to re-create a coherent meadow trough a municipality. The public should be able to bike along it the whole way and it should also feature educational elements. At the same time, it should work as a wildlife corridor. In this study an inventory of forbes and the overall structure of the area is performed. This to identify potential actions to re-create meadow-like vegetation and generally increase biodiversity along the route. The study has found that the 10 km long route passes varied grounds with a city center in the middle. Most areas are influenced by nitrogen surplus and overgrowth. Though some areas hosts species that indicates meadow like conditions. Old large trees, sandy slopes, stonewalls and other microhabitats are noted as well. The initial stage of the restoration will focus on depleting nitrogen surpluses in the ground and selectively clear trees and shrubs. Appropriate management regimes must be implemented in most areas. An esthetics eye should be involved in the restoration process since it is recommended that biodiversity should not look untidy. Landscape variation should be a keyword in the process. Gradually, different parts of the route can start to be managed with traditional methods. Then active re-establishment of desirable species can commence. The areas which still house preserved meadow vegetation must continue to be managed accordingly. It is advised to commence with information to the public already at the start of the project to create understanding for what they see. Follow-ups and new inventories to evaluate the effects of measures is advised.

Page generated in 0.0744 seconds