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Träfflista för sökning "L4X0:1402 1544 ;srt2:(1997-1999)"

Sökning: L4X0:1402 1544 > (1997-1999)

  • Resultat 51-60 av 128
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51.
  • Johansson, Ursula (författare)
  • Spectroscopic studies of kaolinite surfaces
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis, specific surface reactions on kaolinite have been investigated. The methods used are diffuse reflectance Fourier transform (DRIFT), FT-Raman and micro Raman spectroscopy. The deuterium exchange of the hydroxyl protons of kaolinite has been studied. Results show that long reaction time and increased temperature are needed for the deuteration to occur. A change in pH does not seem to influence the isotopic exchange. The adsorption of three silane coupling agents, starch and dextrin onto the kaolinite surface has been investigated. It is suggested that the adsorption occurs through hydrogen bonding. Studies of the hydroxyl vibrations of kaolinite in near-IR, mid-IR and Raman spectra were performed. Raman spectra were recorded at 298K and at 77K. Difference, combination and summation bands appear in near- and mid-IR spectra. Shifts of the hydroxyl bands, are observed in Raman spectra when kaolinite is cooled to 77K.
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52.
  • Jonsson, Ulf (författare)
  • Elastohydrodynamic lubrication and lubricant rheology in refrigeration compressors
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The introductory chapter gives a general description of the lubrication of rolling element bearings in refrigeration compressors and rheological properties of oil-refrigerant mixtures. The influence of refrigerants on the viscosity, pressure-viscosity coefficient and film forming ability in a EHD-contact is described. A method is described for measuring the viscosity of oil-refrigerant mixtures measured using optical interferometry film thickness. The effect of pressured natural gas on the viscosity of polyalkyleneglycols was measured ar pressures up to 10 MPa. Viscosity and pressure-viscosity coefficient was measured on different polyolesters mixed with refrigerant R- 134a. Optical film thickness measurements was used to compare film forming ability of polyolesters with different structure. Lubrication limits and wear of rolling element bearings operating in a refrigerant atmosphere was studied. A new method of supplying lubricants to refrigeration compressor using controlled superheat of the lubricant mixture is suggested.
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53.
  • Kahn, Md. Shafiquzzaman (författare)
  • Sound quality evaluation of heavy-duty engines in free field conditions
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Annoyance response to vehicle noise is commonly reported. The impact reduction measures must therefore be measured scientifically. A scientific system for describing and defining annoyance is therefore required. There is furthermore a need to reduce the annoying components of the sound of vehicles. The engine of a vehicle is one of the predominant sources of vehicle noise which cause annoyance. The sounds of engines heard outside of engines at idling, running and accelerating conditions have been reported to cause annoyance throughout the world. This study of sound quality focuses on noise heard outside vehicles, termed external vehicle noise, and which is outside the interior of the car, in free field conditions. The objectives of the study are a) the development of new descriptors and annoyance prediction models at idling and running conditions, b) comparison of several rating methods, c) testing of several recording and reproduction techniques, d) testing of the long-term repeatability of annoyance judgement obtained in tests, and e) comparison of the combustion process of various fuels in terms of annoyance. An annoyance prediction model for idling engine sound was developed using multivariate analysis on the basis of a new parameter which is termed "Ear Reasoning Range". Two further psychoacoustic descriptors, loudness and impulsiveness were also defined in the model. The sound spectrum which caused least annoyance was obtained by subjective adjustments to an idling engine sound. The quality of the sound was validated by subjective judgements, by test persons, and by objective measurements. An annoyance index for heavy-duty engine noise was developed on the basis of three psychoacoustic descriptors: loudness, sharpness, and harmonic ratio. The model was validated internally and externally and gave good predictions of annoyance judgement of 6-cylinder inline engine noise. Three rating techniques known as the method of paired comparisons, the method of equal-appearing intervals and the method of successive intervals were investigated with respect to annoyance judgements of engine noise in free field conditions. The method of successive intervals was shown to be useful for annoyance judgements of engine noise for a large number of samples. The annoyance response to engine sounds recorded by an artificial head did not differ significantly from that recorded by an orthostereophonic technique. The variance in annoyance response for headphone reproduction was higher than that for loundspeaker reproduction. It was found that both recording techniques gave similar predictions of annoyance. Subjects preferred loudspeaker reproduction to headphone reproduction. There was no significant difference in annoyance judgements between experienced and naive listeners. Annoyance judgements of engine noise were shown to be consistent when subjects were asked to judge the same stimuli on two occasions 10-20 days apart. A comparison of multivariate analysis and neural networks for modeling annoyance of engine noise in free field conditions was investigated. Partial Least Squares (PLS) regression and Neural Networks were used to develop the annoyance prediction models on the basis of loudness, sharpness and harmonic ratio (rumble noise). PLS regression and Neural Networks gave similar prediction of annoyance for engine noise but neural networks gave greater prediction accuracy than did PLS regression. Annoyance judgements of engine sounds in respect to six different fuels were investigated by forty subjects. The annoyance judgements were found to be consistent with the annoyance index based on loudness, sharpness and harmonic ratio. Engine sounds due to ethanol fuel with 9% beraid were rated as least annoying whereas engine sounds due to a mixture of diesel and ethanol fuels were rated as most annoying.
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54.
  • Kavian-Lanjani, Jaffar (författare)
  • Learning from miners' risk management : a case study from the Swedish mining industry
  • 1999
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This historical - empirical case study deals with miners' collective safety and risk management of an occupational lung disease (Silicosis) at Laisvall lead mine from 1943-1953. About 45 miners contracted the disease and the deaths of 25 are documented. The main information sources consisted of protocols from the Safety Committee meetings and interviews with retired workers. Highlighted is the role of workers in identification, definition and perception of lung diseases. Pre-existing worker traits and values such as: negligence, diligence, and self-discipline in the culture of the Swedish working class, shaped their encounters with a well-organised management. Furthermore, comparing Silicosis with analogous occupational diseases demonstrates a chronological generic pattern. This pattern is also found in many industrially developing countries, where known occupational diseases still claim the health of a large number of workers. Thus, the aim of the current research is to assess the role of human work principles in technological development when a new mining production technique is introduced in an industrialised country or in a industrially developing country.
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55.
  • Kemmlert, Kristina (författare)
  • On the identification and prevention of ergonomic risk factors : with special regard to reported occupational injuries of the musculo-skeletal system.
  • 1997
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • A checklist for the screening of ergonomic risks was designed, evaluated and applied at work place assessments. Training for measurements for the revised NIOSH lifting equation was described and the inter-observer reliability discussed. With a view to prevention and with an age perspective, 1 600 extual descriptions of slip trip and fall accidents were studied. Older people reported accidents of this kind more often than younger, but as regards contributing factors there were no considerable age differences in the studied material. Reports (n=195) on occupational musculo-skeletal injury from men and women with different occupations were collected consecutively, with he purpose to investigate the effect on ergonomic conditions by Labour Inspectorate intervention and to follow health and employment among injured. Fifteen Labour Inspectors investigated half of the reports by work place visits. The other half was kept for control. The inspectors were trained in ergononmics and performed the work place assessment by means of the mentioned checklist. All work places were later visited by ergonomists to evaluate possible improvements in ergonomic conditions. Due to turn-over and prolonged sick-leaves, evaluations were performed for only 92 of the injured. At 160 work places there were coworkers, who at the time of the injury report had performed similar tasks as the injured. Evaluations were performed also for these groups. As regards ergonomic improvements, there were no differences between the injured in study and control groups. For co-workers there was a significant positive association between delivered inspection notices and improved ergonomic conditions. The cost benefit of preventive measures was investigated by interviews with representatives at four companies. The ergonomic situation had caused repeated sick-leave periods, but only the report triggered the preventive measures. Expenses associated with the ergonomic improvements were accounted for and financial effects estimated. When costs were compared to gains, the improvements appeared to be highly profitable. Three years after the time of the reports a postal questionnaire on health, psychological well-being and employment was distributed to the injured. The response rate was high. There was a significantly higher prevalence of musculo-skeletal and psychological symptoms in the study group, compared to data from other populations. Activities in daily life were more restricted in the study group. After three years 109 people were in active employment. The association between reduced physical work load and active employment, and both individual and work related characteristics was analysed. The odds for improved ergonomic conditions were increased where the employer had given an informative injury description in the injury report. Prolonged sick-leaves had a significant negative association with active employment, whereas male sex and higher education had a positive association. Identification of ergonomic risk factors seemed to have a positive influence on the process of prevention.
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56.
  • Klug, Ottó (författare)
  • Phthalate adsorption on gamma-alumina: a spectroscopic study
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Adsorption of phthalic acid/phthalate has been investigated on anodically oxidized aluminium foils - used in wet electrolytic capacitors -, by different spectroscopic methods like UV, infrared, Raman and surface- enhanced Raman spectroscopy. In addition to the capacitor foils the adsorption was studied utilizing a high surface area, synthetic Y-aluminium oxide powder as a model material. The capacitor foils were first characterized comprising BET, SIMS, XRF and electron microscopic (SEM) measurements in order to determine the composition and structure of the oxide surface. Adsorption on the two different substrates has been compared and concluded to lead to the same type of surface complexes approving the applicability of the model material for further adsorption studies. In the adsorption experiments, the influence of time, pH and ionic media on the adsorbed amount, as well as on the structure of the surface complex has been studied. Based on the analyses of the different spectra the following conclusions can be drawn: The adsorption is a fast process driven by electrostatic forces. Complexation of the aromatic compound starts with either inner- or outer sphere co-ordination of the hydrogen phthalate ion. The ratio of the two types of complexes shows pH dependence which can be correlated to the different type of surface sites preferred at different pHs. Surface-enhanced Raman spectroscopy (SERS) was applied directly on the capacitor foils for detecting the adsorbed species. Besides of the analytical aspects of the method, a detailed investigation has been performed to explore of the mechanism of the SER effect in this particular experimental approach. It was concluded that SER spectra originate from a silver-phthalate complex rather than from the phthalate adsorbed on the oxide. The structure and orientation of the final SER species is discussed. Although the aluminium oxide surface of the capacitor foil is not involved in the SER complex, the roughness of the surface, and other properties of the substrate can have positive contribution to the enhancement.
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57.
  • Knutsson, Sven (författare)
  • Soil behavior at freezing and thawing
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Avhandlingens första del behandlar en teoretisk beräkningsmodell för tjällyftning samt studier av dess noggranhet i olika situationer. Tjällossningsförloppet analyseras och studeras genom noggranna mätningar av porvattentryckens fördelning i tid och rum. Porvattentrycksutvecklingen kopplas till läget av islinserna i jorden, som detekteras med hjälp av röntgenteknik. Avhandlingens andra del belyser hur frusen jord kan packas och vad deformationerna i sådan jord blir då den tinar. Beräkningar av kompressionen i samband med upptining jämförs med resultat från såväl laboratorieförsök som uppföljningar i fält. Strukturella förändringar i jorden till följd av frysning och tining belyses också.
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58.
  • Kuklane, Kalev (författare)
  • Footwear for cold environments : thermal properties, performance and testing
  • 1999
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Footwear with various insulation levels was evaluated. Some footwear was manufactured both with and without steel toe cap. Comparative studies between various methods (thermal foot model, human subjects, EN 344) were carried out. Data from subjects and foot model were used in evaluation of thermal properties of footwear. The data was tested in Lotens’ model for foot skin temperature prediction. Field studies were carried out for evaluation of footwear and feet conditions in real wear situation. Heavy winter boots had lowest insulation in toe zone and thin boots had heel zone as the coldest region. Even low sweat rates (3 g/h) can reduce footwear insulation considerably (9-19 %). At higher sweat rates (10 g/h) the reduction could be up to about 36 %. Combined effects of sweating, walking and wind could reduce insulation up to about 45 %. Reduction was bigger in warm winter boots. Minimal amount of moisture evaporates from winter footwear during use. Insulation reduction levelled off over longer period of use. The reduction can be calculated by simple equations. The thermal foot model gave similar insulation values as measured on human subjects in thermal comfort. The results from thermal foot model give more useful information on footwear than does the present standard method. The influence of steel toe cap could be related to the "after effect" that probably depends on the thermal inertia of steel toe cap. Recommendations for footwear choice and use are given.
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59.
  • Lampa, Conny (författare)
  • Laser welding : energy redistribution and weld geometry
  • 1997
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Over the past few years laser welding has developed into a process which has a wide range of application over a number of industries. Industrial growth in this area has been stimulated by improvements in production rates and quality but technologically the process is still not fully understood. This work aims to contribute to the understanding of deep penetration laser welding with emphasis on energy redistribution and weld geometry. The seven papers which make up the thesis investigate various aspects of the absorption and redistribution of energy during laser welding. Theoretical and experimental methods have been used to analyze the effects of process parameters on the geometry of the resultant welds. Considerable success has been achieved in matching theoretical predictions to actual results. This work has helped to clarify a number of features of the laser welding process including the following; 1. The effect of process parameters on the efficiency of laser welding. 2. The mechanisms of energy absorption which result in a weld. 3. The effect of an increased external pressure on the laser-material interaction. 4. The effect of thermocapillary flow and how it can be taken advantage of in industrial applications.
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60.
  • Land, Magnus (författare)
  • Weathering of till in northern Sweden and its implications for the geochemistry of soil water, groundwater and stream water
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Natural exogenic geochemical processes in northern Sweden have been studied. The thesis is focused on field weathering rates and variations in the chemical composition of water with time and space. Variations in weathering rates of silicate minerals are important for the global CO2 cycle, and thus also for climatic changes. Soil, soil water, groundwater, and stream water samples have been collected and analyzed. Complementary to the field studies, leaching experiments in the laboratory have also been performed. The results indicate that the release rates of SiO2, Al2O3, Fe2O3, K2O and Na2O due to weathering of till have decreased during the past 8700 years. The release rates of CaO and MgO appear to have increased. Chemical weathering of till is important for the chemical composition of soil water, groundwater and stream water in northern Sweden. Special emphasis is given to the mobility of heavy metals and rare earth elements during weathering.
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