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Elevers stress : En studie på grundskolans senare år om elevers upplevelser av stress och hur de tror att man kan reducera den / Students' stress : A research on students' experience of stress and how to reduce itMatsson, Annemarie, Albertsson, Kristian, Svensson, Linus January 2008 (has links)
Students’ experience of stress is generally considered to be an isolated problem, caused by school work. Students’ experience of stress at school can also be affected by exterior influences. This research aims to discover what factors Swedish students, age 13 – 16, experience as stressful. It also aims to describe how students believe this stress can be reduced. This project originated from a request from a secondary school. A questionnaire was used to map the different stress factors. Interviews enabled greater understanding of these factors and what students themselves believe can reduce the stress. The gathered material was interpreted in several steps by the use of ad hoc methods. The result shows that half of the students experience stress every week. The main causes are lack of time and demands. They lack “free time”, which enables the body to recover from the stress. The students desire management, including guidance from parents concerning prioritising and setting limits. The school should help the students to develop study techniques. The stress is caused by a feeling of not being able to live up to and deal with own and exterior demands. It can be reduced by planning (enabling “free time”), influence (co-operation), personal development (improvement of self-esteem and identity) and management (guidance, limitations, acceptance and development). / Elevers upplevda stress i skolan ses ofta som ett isolerat problem som framkallas och påverkas under skoltid. Upplevelser av stress i skolan kan även bero på andra faktorer som elever påverkas av utanför skoltid. Studien syftar till att kartlägga olika faktorer som elever i årskurs 7-9 upplever som stressande och hur de tror att stressen kan reduceras. Detta arbete har utgått från en frågeställning som framförts av en skola. En enkät användes för att kartlägga olika stressfaktorer. Intervjuer gav djupare förståelse för de olika stressfaktorerna och hur eleverna tror att den upplevda stressen kan reduceras. Det insamlade materialet tolkades i flera steg med ad hoc-metoder. Resultatet visar att hälften av eleverna känner sig stressade varje vecka. Elevernas största stressfaktorer är tidsbrist och krav. De saknar ”fri tid”, som ger kroppen återhämtning från stress. Eleverna efterlyser ledarskap, hjälp från föräldrar att prioritera och sätta gränser samt att skolan ska utveckla elevernas studietekniker. Stressen orsakas av en känsla att inte kunna leva upp till och hantera egna och omvärldens krav. Reducering av stressen kan ske genom planering (skapande av ”fri tid”), inflytande (samplanering), personlig utveckling (stärkt självkänsla och identitet) och ledarskap (ledning, gränssättning, acceptans och utveckling).
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Kinetics of anaerobic sulphate reduction in immobilised cell bioreactorsBaskaran, Vikrama Krishnan 08 November 2005
Many industrial activities discharge sulphate- and metal-containing wastewaters, including the manufacture of pulp and paper, mining and mineral processing, and petrochemical industries. Acid mine drainage (AMD) is an example of such sulphate- and metal-containing waste streams. Formation of AMD is generally the result of uncontrolled oxidation of the sulphide minerals present in the terrain in which the drainage flows with concomitant leaching of the metals. Acid mine drainage (AMD) and other sulphate- and metal-containing waste streams are amenable to active biological treatment. Anaerobic reduction of sulphate, reaction of produced sulphide with metal ions present in the waste stream, and biooxidation of excess sulphide are three main sub-processes involved in the active biotreatment of AMD. Anaerobic reduction of sulphate can be achieved in continuous stirred tank bioreactors with freely suspended cells or in immobilized cell bioreactors. The application of freely suspended cells in a continuous system dictates a high residence time to prevent cell wash-out, unless a biomass recycle stream is used. In an immobilized cell system biomass residence time becomes uncoupled from the hydraulic residence time, thus operation of bioreactor at shorter residence times becomes possible. In the present work, kinetics of anaerobic sulphate reduction was studied in continuous immobilized cell packed-bed bioreactors. Effects of carrier matrix, concentration of sulphate in the feed and sulphate volumetric loading rate on the performance of the bioreactor were investigated. The bioreactor performance, in terms of sulphate reduction rate, was dependent on the nature of the carrier matrix, specifically the total surface area which was provided by the matrix for the establishment of biofilm. Among the three tested carrier matrices, sand displayed the superior performance and the maximum volumetric reduction rate of 1.7 g/L-h was achieved at the shortest residence time of 0.5 h. This volumetric reduction rate was 40 and 8 folds faster than the volumetric reduction rates obtained with glass beads (0.04 g/L-h; residence time: 28.6 h) and foam BSP (0.2 g/L-h; residence time: 5.3 h), respectively. Further kinetic studies with sand as a carrier matrix indicated that the extent of volumetric reduction rate was dependent on the feed sulphate concentration and volumetric loading rate. At a constant feed sulphate concentration, increases in volumetric loading rate caused the volumetric reduction rate to pass through a maximum, while increases in feed sulphate concentrations from 1.0 g/L to 5.0 g/L led to lower volumetric reduction rates. The maximum volumetric reduction rates achieved in the bioreactors fed with initial sulphate concentration of 1.0, 2.5 and 5.0 g/L were 1.71, 0.82 and 0.68 g/L-h, respectively. The coupling of lactate utilization to sulphate reduction was observed in all experimental runs and the rates calculated based on the experimental data were in close agreement with calculated theoretical rates, using the stoichiometry of the reactions involved. The maximum volumetric reduction rates achieved in the immobilized cell bioreactors were significantly faster than those reported for freely suspended cells employed in the stirred tank bioreactors.
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Use of Drains for Passive Control of Flow Through a Permeable Reactive BarrierMcLean, Neil Ross 26 September 2007 (has links)
Abstract
Permeable reactive barrier technology is a cost effective means of treating near surface groundwater contaminant plumes. However, current reactive barrier technology lacks the capacity to manipulate flow rates and thus hydraulic retention time (HRT) within the barriers in order to maximize the effectiveness and longevity of the media. This study examines the effectiveness of tile drains as passive controls on the flow rate of ground-water through an existing wood particle media permeable reactive barrier treating agricultural nitrate. The use of upgradient and downgradient tile drains allowed HRT to be increased from 4.5 to 10 days in one trial and then to be decreased from 11.1 to 0.8 days in a second trial. Influent groundwater NO3-N concentrations of ~100 mg/L were attenuated to detection limit (0.02 mg/L) only 12% of the 4 m long barrier with HRTs of 4.5 to 10 days. During the second trial, HRT was decreased to 0.8 days and NO3-N penetrated to the downgradient edge of the PRB at 1.8 mg/L. The behaviour of SO4 in the PRB was also affected by flow rate. SO4 entered the PRB at 60 to 71 mg/L during the first trial. Under a HRT of 10 days it was depleted to detection limit after traveling through only 13% of the barrier. When HRT was decreased to 4.5 days, SO4 was able to penetrate the downgradient edge of the PRB at concentrations from 4 to 6 mg/L. With a 0.8 day HRT SO4 reduction was highly restricted as calculations showed 90% of available carbon in the PRB was being used to reduce NO3-N, compared to 7.5% being used for SO4 reduction at that time. In comparison, at the 10 day HRT, 61% of carbon being used for NO3-N reduction, 8.7% for SO4 reduction, 0.7 for dissolved oxygen and 29% was lost through DOC leaching. These calculations suggest that barrier efficiency can be greatly enhanced by manipulation of HRT through use of tile drains.
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Use of Drains for Passive Control of Flow Through a Permeable Reactive BarrierMcLean, Neil Ross 26 September 2007 (has links)
Abstract
Permeable reactive barrier technology is a cost effective means of treating near surface groundwater contaminant plumes. However, current reactive barrier technology lacks the capacity to manipulate flow rates and thus hydraulic retention time (HRT) within the barriers in order to maximize the effectiveness and longevity of the media. This study examines the effectiveness of tile drains as passive controls on the flow rate of ground-water through an existing wood particle media permeable reactive barrier treating agricultural nitrate. The use of upgradient and downgradient tile drains allowed HRT to be increased from 4.5 to 10 days in one trial and then to be decreased from 11.1 to 0.8 days in a second trial. Influent groundwater NO3-N concentrations of ~100 mg/L were attenuated to detection limit (0.02 mg/L) only 12% of the 4 m long barrier with HRTs of 4.5 to 10 days. During the second trial, HRT was decreased to 0.8 days and NO3-N penetrated to the downgradient edge of the PRB at 1.8 mg/L. The behaviour of SO4 in the PRB was also affected by flow rate. SO4 entered the PRB at 60 to 71 mg/L during the first trial. Under a HRT of 10 days it was depleted to detection limit after traveling through only 13% of the barrier. When HRT was decreased to 4.5 days, SO4 was able to penetrate the downgradient edge of the PRB at concentrations from 4 to 6 mg/L. With a 0.8 day HRT SO4 reduction was highly restricted as calculations showed 90% of available carbon in the PRB was being used to reduce NO3-N, compared to 7.5% being used for SO4 reduction at that time. In comparison, at the 10 day HRT, 61% of carbon being used for NO3-N reduction, 8.7% for SO4 reduction, 0.7 for dissolved oxygen and 29% was lost through DOC leaching. These calculations suggest that barrier efficiency can be greatly enhanced by manipulation of HRT through use of tile drains.
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Kinetics of anaerobic sulphate reduction in immobilised cell bioreactorsBaskaran, Vikrama Krishnan 08 November 2005 (has links)
Many industrial activities discharge sulphate- and metal-containing wastewaters, including the manufacture of pulp and paper, mining and mineral processing, and petrochemical industries. Acid mine drainage (AMD) is an example of such sulphate- and metal-containing waste streams. Formation of AMD is generally the result of uncontrolled oxidation of the sulphide minerals present in the terrain in which the drainage flows with concomitant leaching of the metals. Acid mine drainage (AMD) and other sulphate- and metal-containing waste streams are amenable to active biological treatment. Anaerobic reduction of sulphate, reaction of produced sulphide with metal ions present in the waste stream, and biooxidation of excess sulphide are three main sub-processes involved in the active biotreatment of AMD. Anaerobic reduction of sulphate can be achieved in continuous stirred tank bioreactors with freely suspended cells or in immobilized cell bioreactors. The application of freely suspended cells in a continuous system dictates a high residence time to prevent cell wash-out, unless a biomass recycle stream is used. In an immobilized cell system biomass residence time becomes uncoupled from the hydraulic residence time, thus operation of bioreactor at shorter residence times becomes possible. In the present work, kinetics of anaerobic sulphate reduction was studied in continuous immobilized cell packed-bed bioreactors. Effects of carrier matrix, concentration of sulphate in the feed and sulphate volumetric loading rate on the performance of the bioreactor were investigated. The bioreactor performance, in terms of sulphate reduction rate, was dependent on the nature of the carrier matrix, specifically the total surface area which was provided by the matrix for the establishment of biofilm. Among the three tested carrier matrices, sand displayed the superior performance and the maximum volumetric reduction rate of 1.7 g/L-h was achieved at the shortest residence time of 0.5 h. This volumetric reduction rate was 40 and 8 folds faster than the volumetric reduction rates obtained with glass beads (0.04 g/L-h; residence time: 28.6 h) and foam BSP (0.2 g/L-h; residence time: 5.3 h), respectively. Further kinetic studies with sand as a carrier matrix indicated that the extent of volumetric reduction rate was dependent on the feed sulphate concentration and volumetric loading rate. At a constant feed sulphate concentration, increases in volumetric loading rate caused the volumetric reduction rate to pass through a maximum, while increases in feed sulphate concentrations from 1.0 g/L to 5.0 g/L led to lower volumetric reduction rates. The maximum volumetric reduction rates achieved in the bioreactors fed with initial sulphate concentration of 1.0, 2.5 and 5.0 g/L were 1.71, 0.82 and 0.68 g/L-h, respectively. The coupling of lactate utilization to sulphate reduction was observed in all experimental runs and the rates calculated based on the experimental data were in close agreement with calculated theoretical rates, using the stoichiometry of the reactions involved. The maximum volumetric reduction rates achieved in the immobilized cell bioreactors were significantly faster than those reported for freely suspended cells employed in the stirred tank bioreactors.
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Application of enzymes for pre-treatment of wood chips for energy efficient thermomechanical pulpingMårtensson, Tomas January 2012 (has links)
Thermomechanical pulping (TMP) is a highly energy intensive process where most of the energy is used in therefining of chips to fibres. Various ways of reducing the energy consumption have earlier been studied, for examplechange of refiner pattern, addition of various chemicals, and also some biochemical implementation in the form of fungus and enzymes. This study includes pre-trials with the enzymes pectin lyase and pectin esterase,multipectinase, xylanase, and mannanase. The results are studied via a reducing sugar assay, an enzymatic assayusing spectrophotometry, and capillary zone electrophoresis. The study also includes results from a pilot scalerefining with multipectinase, xylanase, and mannanase, performed with a wing refiner at Helsinki University.Reductions of energy consumption in TMP by pre-treatment of Norwegian spruce chips are investigated and apotential reduction of energy consumption of 6 % is indicated.
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The function of magnesium compounds in an oxygen-alkali-carbohydrate system.Sinkey, John David 01 January 1973 (has links)
No description available.
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A study of the mechanism of alkali cellulose autoxidationMattor, John A. 01 January 1963 (has links)
No description available.
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Treatment of Wastewater Containing Sulfate by Vertical-Flow Constructed Wetlands.Chung, Chia-chi 22 July 2010 (has links)
The purpose of this study is to use vertical-flow constructed wetlands (VFCW) microcosm systems to investragte the removal efficiencies of sulfate. The system was located on the campus sewage treatment plant. nn National Sun Yat-sen University. In this study, two media, gravel and peat, were installed in four different systems. The two system with same media were separated into vegetated and non-vegetated (control) ones respectively. In the test runs, the operation methods included batch type filled with water, continuous flow and integrated vertical flow constructed wetland (IVCW) with continuous flow. In batch type test, it was run under an initial concentrations of SO42--S about 500 mg/L. The experimental results showed that the removal efficiencies were increased with increasing COD concentrations. Under the same conditions but with continuous flow operation, the removal efficiencies of SO42--S were lower than the batch type one, which 80% could be reached. The best system for operation was P1 (peat with vegetated), in which the removal effciency reached 90%. The experimental results also showed that the vegetated systems presented higher removal efficiencies of sulfate than the non-vegetated ones. In addition, this research were increased the concentrations of SO42--S and COD to about 1200 mg/L and 4000 mg/L respectively. The experimental results showed that the IVCW treatment system could achived greater efficiency than VFCW treatment system.
The experimental in depth research test run indicated that the anaerobic condition did not affect the removal efficiencies of ammonia by using batch type. However, nitrification was the main reaction of ammonia to nitrate in the continuous flow type systems. When ORP values were found below the -300 mV, the sulfate began to be drcreased. It was believed that if the anaerobic condition were well be established, while the organic carbon could be contented in this system, the sulfate reducing bacteria (SRB) might live, and then sulfate could be removed.
The effect of temperature on sulfate removal was generally established in this study. According to the experimental results, it was found that the activity of SRB motility was higher in higher temperature (35¢J) than that in lower temperature (25¢J).
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Research for polyethylene fibers Reinforced ConcreteChen, Yan-Shuo 24 May 2012 (has links)
In this study, Dyneema fiber can bear tension and not easy to react with the chemicals characteristics, to explore for the resistance to bending moment and compressive strength of concrete.
To compare with different rate of Dyneema fiber added at different ratio of AE water-reducing in the condition of concrete slump test and slump flow test. We planning in different water-cement ratio 0.48(non AE water-reducing)¡B0.4(add AE water-reducing), to test for its fresh properties and hardened properties, and discussion the effect by AE water-reducing and Dyneema fiber on the marine engineering.
According to this study, adding Dyneema fiber will make the slump and slump flow value dropped, and affecting the workability. Because of Dyneema fiber will tangle when add too much Dyneema fiber in concrete. So in mixing time, the Dyneema fiber and concrete will form clumps, in this study, we add the AE water-reducing to improve.
After we add AE water-reducing, the slump, slump flow, compressive strength, are increase, but we still had to pay attention to the ratio between Dyneema fiber and AE water-reducing, the strength of structure perhaps decrease if added too much Dyneema fiber or AE water-reducing.
This study can get the best positive effect when added 1.5% volume volume of Dyneema fiber.
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