| 1. |
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| 2. |
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| 3. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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A field investigation of the size, morphology and chemical composition of airborne particles in rail transport
- 2010
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Konferensbidrag (refereegranskat)abstract
- The health effects of inhalable airborne particles are well documented. In the European Union the European Council mandates that the level of airborne particles with a diameter smaller than 10 µm (PM10) must not exceed an annual average of 40 µg/m3. Examples of possible sources from rail transport are mechanical brakes, wheel rail contact, current collectors, ballast, sleepers and masonry structures. In this regard, a series of field tests have been conducted on a regular Swedish track using a regional train instrumented with: particle measurement devices, temperature sensors in brake pads and sensors to measure the magnitude of train speed and a GPS.Two sampling points for airborne particles were designated in the train under frame. One of the sampling points was near a pad to rotor disc brake contact and a second global sampling point was chosen under the frame, but not near a mechanical brake or the wheel-rail contact. The first one was highly influenced by brake pad wear debris and the other one was influenced by all of the brake pads, wheel and rail wear debris as well as re-suspension. In each sampling points, three tubes were linked to three particle measurement devices. Two sets of Ptrak, Dustrak and Grimm devices were used. The Ptrak 8525 was an optical particle measurement device which could measure particle diameter in the size interval of 20 nm up to 1 micrometer. The Dustrak was used to measure particle mass concentration. The Grimm 1.109 was an aerosol spectrometer which counted number of particles from 0.25 micrometer to 32 micrometer in 31 intervals. These two Grimm devices were equipped with Millipore filters in the devices outlets to capture particles for further studies on morphology and matter of particles.The total number and size distribution of the particles for these two sampling points were registered and evaluated in different situations such as activating and deactivating electrical brake or train curve negotiating.During braking, three peaks of 250 nm, 350 nm and 600 nm in diameter, with the 350 nm peak dominating were identified in the fine particle region. In the coarse particle region, a peak of around 3-6 µm in diameter was discovered. The brake pad temperature effects on particle size distribution were also investigated and the results showed that the peak around 250 nm increased. Furthermore, the activation of electrical braking significantly reduced the number of airborne particles.A SEM was used to capture the images from collected particles on filters. Furthermore, an ICP-Ms method was used to investigate the elemental contents of the particulates on the filter. In this case the main contribution belonged to Fe, Si, Al, Ca, Cu, Zn. The higher amount of some elements weights such as calcium, silicon, sodium and aluminum in the global sampling point filters revealed that ballast and concrete sleepers were the main sources for these particles although some of them originated from rail, wheel, brake disc and brake pad as well.
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| 4. |
- Abbasi, Saeed, et al.
(författare)
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A pin-on-disc study of the rate of airborne wear particle emissions from railway braking materials
- 2012
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Ingår i: Wear. - UK : Elsevier. - 0043-1648 .- 1873-2577. ; 284, s. 18-29
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Tidskriftsartikel (refereegranskat)abstract
- The current study investigates the characteristics of particles generated from the wear of braking materials, and provides an applicable index for measuring and comparing wear particle emissions. A pin-on-disc tribometer equipped with particle measurement instruments was used. The number concentration, size, morphology, and mass concentration of generated particles were investigated and reported for particles 10 nm-32 mu m in diameter. The particles were also collected on filters and investigated using EDS and SEM. The effects of wear mechanisms on particle morphology and changes in particle concentration are discussed. A new index, the airborne wear particle emission rate (AWPER), is suggested that could be used in legislation to control non-exhaust emissions from transport modes, particularly rail transport.
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| 5. |
- Abbasi, Saeed, et al.
(författare)
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A study of airborne wear particles generated from organic railway brake pads and brake discs
- 2011
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Ingår i: Wear. - UK : Elsevier. - 0043-1648 .- 1873-2577. ; 273:1, s. 93-99
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Tidskriftsartikel (refereegranskat)abstract
- Brake pads on wheel-mounted disc brakes are often used in rail transport due to their good thermal properties and robustness. During braking, both the disc and the pads are worn. This wear process generates particles that may become airborne and thus affect human health. The long term purpose of ‘Airborne particles in Rail transport’ project is to gain knowledge on the wear mechanisms in order to find means of controlling the number and size distribution of airborne particles. In this regard, a series of full-scale field tests and laboratory tests with a pin-on-disc machine have been conducted. The morphology and the matter of particles, along with their size distribution and concentration, have been studied. The validity of results from the pin-on-disc simulation has been verified by the field test results. Results show an ultra-fine peak for particles with a diameter size around 100 nm in diameter, a dominant fine peak for particles with a size of around 350 nm in diameter, and a coarse peak with a size of 3-7 μm in diameter. Materials such as iron, copper, aluminium, chromium, cobalt, antimony, and zinc have been detected in the nano-sized particles.
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| 6. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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A study of friction modifiers on airborne wear particles from wheel-rail contact
- 2012
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Konferensbidrag (refereegranskat)abstract
- Wheel-rail contact and its wear process are crucial issues in maintenance and operating of rolling stocks. During wheel-rail contact, materials in mating faces are worn off and some of them transferred to airborne particles. Eventhough the wear process in wheel-rail contact are well-known, few studies have been conducted on the airborne particles from wheel-rail contact.The purpose of this study is to investigate the effect of using different friction modifier on the amount of airbotne particles from wheel-rail contact in a laboratory simulation. In this regard, a series laboratory tests were used by using round head pin (R=25mm) and dead weight 40 N in a pin-on-disc machine. This set-up simulates a contact pressure around 750 MPa on the pin head.The amount of airborne particles and their characteristics were investigated in dry-contact, and non-dry contacts whereas a lubricant, Binol rail 510 and a friction modifier, tramsilence were used. According to the results, the effects of using Binol rail to reduce the amount of airborne particles were considerable.
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| 7. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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A field test study of airborne wear particles from a running regional train
- 2012
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Ingår i: IMechE, Part F: Journal of Rail and Rapid Transit. - UK : Sage Publications. - 0954-4097 .- 2041-3017. ; 226:1, s. 95-109
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Tidskriftsartikel (refereegranskat)abstract
- Inhalable airborne particles have inverse health affect. In railways, mechanical brakes, the wheel–rail contact, current collectors, ballast, sleepers, and masonry structures yield particulate matter. Field tests examined a Swedish track using a train instrumented with particle measurement devices, brake pad temperature sensors, and speed and brake sensors. The main objective of this field test was to study the characteristics of particles generated from disc brakes on a running train with an on-board measuring set-up.Two airborne particle sampling points were designated, one near a pad–rotor disc brake contact and a second under the frame, not near a mechanical brake or the wheel–rail contact; the numbers and size distributions of the particles detected were registered and evaluated under various conditions (e.g. activating/deactivating electrical brakes or negotiating curves). During braking, three speed/temperature-dependent particle peaks were identified in the fine region, representing particles 280 nm, 350 nm, and 600 nm in diameter. In the coarse region, a peak was discerned for particles 3–6 μm in diameter. Effects of brake pad temperature on particle size distribution were also investigated. Results indicate that the 280 nm peak increased with increasing temperature, and that electrical braking significantly reduced airborne particle numbers. FESEM images captured particles sizing down to 50 nm. The ICP-MS results indicated that Fe, Cu, Zn, Al, Ca, and Mg were the main elements constituting the particles.
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| 8. |
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| 9. |
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| 10. |
- Abbasi, Saeed
(författare)
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Characterisation of airborne particles from rail traffic
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the investigation of wear particles in rail transport started in late-1910s, the high mass concentration of these particles has raised worries among researchers concerned with air quality. However, effective action has yet to be taken because of lack of relevant knowledge. This thesis provides applicable information for the airborne wear particles in rail transport. Some aspects of their characteristics such as diameter size, mass concentration, number concentration, and morphology of particles were investigated in field tests and laboratory tests.The effects on particle characterisations from different operational conditions in the field tests, and applying different braking materials, conducting tests in different applied loads or sliding velocities in the laboratory tests were studied. The main advantage of conducting laboratory tests was to focus on studying particles from one source. The possibility of repetition, using high sensitive instruments and conducting tests at low costs are the other advantages of laboratory studies. Paper A describes how a pin-on-disc machine was used to reproduce similar real operational conditions during mechanical braking in a train. The results were validated by comparing the field tests results with the laboratory studies. The particles morphology and size distribution were also studied.Paper B presents a summary of field tests results. The effects of curve negotiating and applying braking in different real conditions were investigated with an on-board measurement.The element composition of the particles and their potential sources were also investigated outside of the particles morphologies.Paper C presents comprehensive results from laboratory studies on airborne particles from different braking materials. The differences in the particle characteristics in similar test conditions were attributable to different material compositions and dominant wear mechanisms. A new index was introduced in this paper and is suggested to be used as a qualitative factor with regard to the airborne wear particle emission rate.Paper D is a review of the recent studies of exhaust emission and non-exhaust emission from rail vehicles. A summary of results, measurements, adverse health effects, and proposed or applied solutions are reviewed in this paper.
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| 11. |
- Abbasi, Saeed, et al.
(författare)
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Experiences of measuring airborne wear particles from braking materials and the wheel - Rail contact
- 2012
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Ingår i: 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, CM 2012. - : Southwest Jiaotong University. ; , s. 608-609
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Konferensbidrag (refereegranskat)abstract
- During braking both of the discs and pads of disc brakes are worn. Since disc brakes are not sealed, some of the generated wear particles can become airborne. The same condition also holds for block brakes utilized in rail vehicles. Furthermore, the wheel-rail contact is also subjected to wear processes during braking as well as during normal running. This contact also contributes to generation of airborne particles. Several studies have found an association between adverse health effects and the concentration of particles in the atmosphere, so it is of interest to improve our knowledge of the airborne wear particles. The present work includes results from full scale testing of rail vehicles. Particle size distribution, morphology and elemental contents are presented and discussed. Due to high back ground concentration levels in field tests, dedicated laboratory test set ups on a reduced scale were designed and utilized for airborne particle studies with zero background level. Promising correlation between field test and the lab set up is identified. Different ways of using this test set up for evaluating how the composition of the airborne particles is classified with respect to their health effects are discussed. Furthermore, different ways of using the proposed method to rank and to quantify airborne particle emission factors are presented.
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| 12. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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Experiences of measuring airborne wear particles from braking materials and wheel-rail contact
- 2012
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Konferensbidrag (refereegranskat)abstract
- During braking both of the discs and pads of disc brakes are worn. Since disc brakes are not sealed, some of the generated wear particles can become airborne. Wheel-rail is also subjected to wear process during braking as well as normal running. They also contribute to generate airborne particles. Several studies have found an association between adverse health effects and the concentration of particles in the atmosphere, so it is of interest to improve our knowledge of the airborne wear particles generated by disc brakes.The present work includes results from full scale testing of rail vehicles. Particle size distribution, morphology and elemental contents are presented and discussed for different combinations of disc and pad materials. Due to high back ground concentration levels in field tests, dedicated laboratory test set ups on a reduced scale were designed and utilized for airborne particle studies with zero background level.Promising correlation between field test and the lab set up is identified. Different ways of using this test set up for evaluating how the composition of the airborne particles is classified with respect to their health effects are discussed. Furthermore, different ways of using the proposed method to rank and to quantify airborne particle emission factors are presented.
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| 13. |
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| 14. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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Particle emission from rail vehicles : A literature review
- 2012
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F. - Stirlingshire, UK : Sage Publications. ; 98
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Konferensbidrag (refereegranskat)abstract
- Emission of airborne particles is a side effect from rail transport. This work reviews recent research on particle emissions from rail vehicles. Both exhaust and non-exhaust particle emissions are characterized by size, morphology, composition, and size distribution. Current legislation, knowledge of adverse health effects, and available and proposed solutions for emission reductions are also treated. There has been much focus on exhaust emissions, but only a few limited studies have investigated non-exhaust particle emissions, which contain a significant amount of metallic materials. A new method for measuring the airborne wear particle emission rate (AWPER) is proposed as a first step to guide new legislations and to focus further research on non-exhaust airborne emission, i.e., research on the generation mechanisms for particle emissions and their adverse health effects.
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| 15. |
- Abbasi, Saeed, et al.
(författare)
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Particle emissions from rail traffic : a literature review
- 2013
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Ingår i: Critical reviews in environmental science and technology. - USA : Taylor & Francis. - 1064-3389 .- 1547-6537. ; 43:23, s. 2211-2244
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Forskningsöversikt (refereegranskat)abstract
- Particle emissions are a drawback of rail transport. This work is a comprehensive presentation of recent research into particle emissions from rail vehicles. Both exhaust and non-exhaust particle emissions are considered when examining particle characteristics such as PM10, and PM2.5 concentration levels, size, morphology, composition, as well as adverse health effects, current legislation, and available and proposed solutions for reducing such emissions. High concentration levels in enclosed rail traffic environments are reported and some toxic effects of the particles. We find that only a few limited studies have examined the adverse health effects of non-exhaust particle emissions and that no relevant legislation exists. Thus further research in this area is warranted.
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| 16. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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Pin-on-disc study of the effects of railway friction modifiers on airborne wear particles from wheel-rail contact
- 2013
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Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 60, s. 136-139
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of wheel–rail interaction is crucial to wheel and rail maintenance. In this interaction, some of theworn-off material is transformed into airborne particles. Although such wear is well understood, few studiestreat the particles generated. We investigated friction modifiers' effects on airborne particles characteristicsgenerated in wheel-rail contacts in laboratory conditions. Pin-on-disc machine testing with a round-head pinloaded by a dead weight load 40 N simulated maximum contact pressure over 550 MPa. Airborne particlecharacteristics were investigated in dry contacts and in ones lubricated with biodegradable rail grease andwater- and oil-based friction modifiers. The number of particles declined with the grease; the number ofultrafine particles increased with the water-based friction modifier, mainly due to water vaporization.
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| 17. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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Technical note: Experiences of studying airborne wear particles from road and rail transport
- 2013
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Ingår i: Aerosol and Air Quality Research. - : Taiwan Association for Aerosol Research. - 1680-8584 .- 2071-1409. ; 13:4, s. 1161-1169
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Tidskriftsartikel (refereegranskat)abstract
- Airborne particles and their adverse effects on air quality have been recognized by humans since ancient times. Current exhaust emission legislations increase the relative contribution of wear particles on the PM levels. Consequently, wearbased particle emissions from rail and road transport have raised concerns as ground transportation is developing quickly. Although scientific research on airborne wear-based particles started in 1909, there is almost no legislation that control the generation of wear-based particles. In addition, there is no accepted and approved standard measurement technique for monitoring and recording particle characteristics. The main objective of this study is to review recent experimental work in this field and to discuss their set-ups, the sampling methods, the results, and their limitations, and to propose measures for reducing these limitations.
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| 18. |
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| 19. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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Temperature and Thermoelastic Instability at Tread Braking Using Cast Iron Friction Material
- 2013
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 314:1–2, s. 171-180
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Tidskriftsartikel (refereegranskat)abstract
- Braking events in railway traffic often induce high frictional heating and thermoelastic instability (TEI) at the interfacing surfaces. In the present paper, two approaches are adopted to analyse the thermomechanical interaction in a pin-on-disc experimental study of railway braking materials. In a first part, the thermal problem is studied to find the heat partitioning between pin and disc motivated by the fact that wear mechanisms can be explained with a better understanding of the prevailing thermal conditions. The numerical model is calibrated using the experimental results. In a second part, the frictionally induced thermoelastic instabilities at the pin-disc contact are studied using a numerical method and comparing them with the phenomena observed in the experiments. The effects of temperature on material properties and on material wear are considered. It is found from the thermal analysis that the pin temperature and the heat flux to the pin increase with increasing disc temperatures up to a transition stage. This agrees with the behaviour found in the experiments. Furthermore, the thermoelastic analysis displays calculated pressure and the temperature distributions at the contact interface that are in agreement with the hot spot behaviour observed in the experiments.
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| 20. |
- Abbasi, Saeed, et al.
(författare)
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Temperature and thermoelastic instability of tread braking friction materials
- 2012
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Ingår i: Proceedings 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. ; , s. 606-607
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Konferensbidrag (refereegranskat)abstract
- Braking events in railway traffic often induce high frictional heating and thermoelastic instability (TEI) at the interfacing surfaces. In the present paper, two approaches are adopted to analyse the thermomechanical interaction in a pin-on-disc experimental study of railway braking materials. In a first part, the thermal problem is studied to find the heat partitioning between pin and disc motivated by the fact that wear mechanisms can be explained with a better understanding of the prevailing thermal conditions. The numerical model is calibrated using the experimental results. In a second part, the frictionally induced thermoelastic instabilities (TEI) at the pin-disc contact are studied using a numerical method and comparing them with the phenomena observed in the experiments. The effects of temperature on material properties and on material wear are considered. It is found from the thermal analysis that the pin temperature and the heat flux to the pin increase with increasing disc temperatures up to a transition stage. This agrees with the behaviour found in the experiments. Furthermore, the thermoelastic analysis displays calculated pressure and the temperature distributions at the contact interface that are in agreement with the hot spot behaviour observed in the experiments.
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| 21. |
- Abbasi, Saeed, 1973-
(författare)
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Towards elimination of airborne particles from rail traffic
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the investigation of wear particles from rail transport started in the late 1910s, the high mass concentrations of these particles have prompted concern among researchers interested in air quality. However, effective action has yet to be taken because relevant knowledge is still missing. This thesis provides knowledge of airborne wear particles originating from rail transport. Some aspects of their characteristic parameters, such as size, mass concentration, number concentration, and morphology, were investigated in the field and in laboratory tests. We also discuss means to mitigate non-exhaust emissions, as well as the advantages and disadvantages of various test set-ups in the seven appended journal papers:Paper A reviews recent studies of exhaust and non-exhaust emissions from rail vehicles. The results, measurements, adverse health effects, and proposed or applied solutions presented in this literature are summarized in this paper.Paper B summarizes the results of field tests we conducted. The effects of curve negotiation and braking under different real conditions were investigated in a field test in which on-board measurements were made. The elemental composition and morphology of the particles emitted and their potential sources were also investigated.Paper C describes how a pin-on-disc machine can be used to reproduce real operating conditions during mechanical train braking in a controlled laboratory setting. The results were validated by comparing the field test results with the results of laboratory studies.Paper D presents comprehensive results of laboratory studies of airborne particles from different braking materials. A new index is introduced in this paper, which can be used as a quantitative metric for assessing airborne wear particle emission rates.Paper E describes the effects of using various friction modifiers and lubricants on the characteristics of airborne particles from wheel–rail contact under lubricated and unlubricated conditions.Paper F reports work to simulate thermoelastic instability in the cast-iron braking material. We simulated the fluctuation of the flash temperature by considering the temperature dependency of the material properties and the transformation of the contact state due to thermomechanical phenomena and wear.Paper G reviews new full- and sub-scale measurements of non-exhaust emissions from ground transport. The advantages and disadvantages of on-board measurements, pin-on-disc tests, dynamometer tests, and test rig studies are discussed in this paper.
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| 22. |
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| 23. |
- Andersson, Martin
(författare)
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Churning losses and efficiency in gearboxes
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficient transmissions systems are key to producing competitive motor vehicles that have a smaller environmental impact. Gears are the main components in vehicle transmissions and although they are already highly efficient, there is still room for improvement. In this study, the focus falls on the lubricant used to create separating films between gears and todissipate heat. When driving, the gears churn this lubricant, giving rise to power losses that are related to the amount and properties of the lubricant. However, any attempt to reduce these losses must not compromise the required lubrication and heat dissipation. Paper A reports on the use of an FZG gear test rig to investigate power losses and heat generation for different gear immersion depths, surface roughness and coatings. The results show that lower gear roughness reduces gear mesh losses and heat generation. A polishing affect was obtained when a non-coated gear ran against a coated gear.The aim of the research reported in paper B was to increase the accuracy of efficiency testing. It investigated how and whether repeated disassembly and re-assembly of the same test equipment, as well as test performance and rig conditions, affect the measured torque loss in an FZG gear test rig. It was shown that the measured torque loss changes between one assembly and another. Repeatability between tests is crucial for accurate conclusions.The aim of the research reported in paper C was to study whether gear efficiency could be increased by a running-in procedure, which would reduce the need for a coolant. A back-to-back gear test rig was used to test two running-in loads. Higher gear mesh efficiency was seen when a higher running-in load was used.
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| 24. |
- Gaillard, Marie-José, 1953-, et al.
(författare)
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Holocene land-cover reconstructions for studies on land cover-climate feedbacks
- 2010
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 6, s. 483-499
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Tidskriftsartikel (refereegranskat)abstract
- The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past land-cover from pollen data, (3) to present a new project (LANDCLIM: LAND cover – CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past land-cover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The REVEALS model is demonstrated to provide better estimates of the regional vegetation/landcover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional- to continental-spatial scale throughout the Holocene. We present maps of REVEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs “grassland” and “agricultural land” at five time-windows from 6000 BP to recent time. The LANDCLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.
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| 25. |
- Harper, P., et al.
(författare)
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Evaluation of an ultrasonic method for measurement of oil film thickness in a hydraulic motor piston ring
- 2005
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Ingår i: Life Cycle Tribology. - : Elsevier. - 0444516875 ; , s. 305-312
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Bokkapitel (refereegranskat)abstract
- The efficiency of a hydraulic motor depends on the lubrication performance of the piston ring. If the film is too thin then wear occurs quickly, if it is too thick then oil is lost into the cylinder and efficiency is reduced. In this paper a technique for oil film measurement based on ultrasonic reflection is investigated. This has the potential to be used non-invasively on real components. An ultrasonic pulse will reflect from a thin film interposed between two solids. The proportion of the pulse that is reflected depends on the stiffness of the intermediate layer. If the acoustic properties of the film material are known, then the stiffness can readily be used to determine the film thickness. This principle has been employed for the piston ring lubrication case. A piston/cylinder test bench has been used to evaluate the ultrasonic method. A focusing piezo-electric transducer is mounted outside the cylinder and ultrasonic pulses reflected back from the inner bore. The variation of these pulses as the piston ring passes underneath is investigated and used to determine oil film thickness. Films in the range 0.7 to 1.3 μm were measured; the thickness did not depend strongly on either ring speed or sealed pressure. Several practical aspects were investigated such as, attenuation in the cylinder material, response time, and transducer resolution. Whilst this study demonstrated that film thickness measurement is feasible, there are a number of practical considerations that require further work, principally the focusing and coupling of the ultrasonic transducer and the response time.
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| 26. |
- Hovelius, Lennart, et al.
(författare)
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Non-operative treatment of primary anterior shoulder dislocation in patients forty years of age and younger : a prospective twenty-five-year follow-up
- 2008
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Ingår i: Journal of Bone and Joint Surgery. American volume. - : Journal of Bone and Joint Surgery. - 0021-9355 .- 1535-1386. ; 90:5, s. 945-952
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Tidskriftsartikel (refereegranskat)abstract
- Background: During 1978 and 1979, we initiated a prospective multicenter study to evaluate the results of nonoperative treatment of primary anterior shoulder dislocation. In the current report, we present the outcome after twenty-five years.Methods: Two hundred and fifty-five patients (257 shoulders) with an age of twelve to forty years who had a primary anterior shoulder dislocation were managed with immobilization (achieved by tying the arm to the torso with use of a bandage) or without immobilization. All 227 living patients (229 shoulders) completed the follow-up questionnaire, and 214 patients completed the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire.Results: Ninety-nine (43%) of 229 shoulders had not redislocated, and seventeen (7%) redislocated once. Thirty-three recurrent dislocations had become stable over time (14.4%), and eighteen were considered to be still recurrent (7.9%). Sixty-two shoulders (27%) had undergone surgery for the treatment of recurrent instability. Immobilization after the primary dislocation did not change the prognosis. Only two of twenty-four shoulders with a fracture of the greater tuberosity at the time of the primary dislocation redislocated (p < 0.001). When shoulders with a fracture of the greater tuberosity were excluded, forty-four (38%) of 115 shoulders in patients who had been twelve to twenty-five years of age at the time of the original dislocation and sixteen (18%) of ninety shoulders in patients who had been twenty-six to forty years of age had undergone surgical stabilization. At twenty-five years, fourteen (23%) of sixty-two shoulders that had undergone surgical stabilization were in patients who subsequently had a contralateral dislocation, compared with seven (7%) of ninety-nine shoulders in patients in whom the index dislocation had been classified as solitary (p = 0.01). Gender and athletic activity did not appear to affect the redislocation rate; however, women had worse DASH scores than men did (p = 0.006).Conclusions: After twenty-five years, half of the primary anterior shoulder dislocations that had been treated nonoperatively in patients with an age of twelve to twenty-five years had not recurred or had become stable over time.Level of Evidence: Prognostic Level I. See Instructions to Authors for a complete description of levels of evidence.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
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| 31. |
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| 32. |
- Olofsson, Sara, et al.
(författare)
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Chained Approach vs Contingent Valuation for Estimating the Value of Risk Reduction
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- To decide how much resources to spend on reducing mortality risk, governmental agencies in several countries turn to the value of a statistical life (VSL). VSL has been shown to vary depending on the size of the risk reduction, which indicates that WTP does not increase near-proportional in relation to risk reduction as suggested by standard economic theory. Chained approach (CA) is a stated preference method that was designed to deal with this problem. The objective of this study was to compare CA to the more traditional approach contingent valuation (CV). Data was collected from 500 individuals in the Swedish adult general population using two web-based questionnaires, whereof one based on CA and the other on the CV method. Despite the two different ways of deriving the estimates, the methods showed similar results. The CV result showed scale insensitivity with respect to the size of the risk reduction and disease duration and resulted in more zero and protest response. The CA result did also vary depending on the procedure used, but not when chaining on individual estimates. The CA result was also found to be more sensitive to disease duration and severity. This study provides support for the validity of studies of the WTP for a risk reduction. It also shows that CA is associated with encouraging features for the valuation of non-fatal road traffic accidents, but the result does not support the use of one method over the other.
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| 33. |
- OLOFSSON, SARA, et al.
(författare)
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Dread and Risk Elimination Premium for the Value of a Statistical Life
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The Value of a Statistical Life (VSL) is a widely used measure of the value of mortality risk reduction. Since VSL should reflect preferences and attitudes to risk, there are reasons to believe that it varies depending on the type of risk involved. It has been argued that cancer should be considered a “dread disease”, which supports the use of a “cancer premium”. The objective of this study is to elicit the existence and size of a cancer premium (for pancreatic cancer and multiple myeloma) in relation to road traffic accidents, sudden cardiac arrest and Amyotrophic Lateral Sclerosis (ALS). Data was collected from 500 individuals in the Swedish general population 50 -74 years old using a web-based questionnaire. Preferences were elicited using the Contingent Valuation method, and a split-sample design was applied to test for scale sensitivity. VSL differs significantly between contexts, being highest for ALS and lowest for road traffic accident. A premium (26-76 %) for cancer was found in relation to road traffic accidents, but not in relation to ALS and sudden cardiac arrest. The premium was higher for cancer with a shorter time from diagnosis to death. Eliminating risk was associated with a premium of around 17 %. Evidence of scale sensitivity was found when comparing WTP for all risks simultaneously. This study shows that there exist a dread premium and risk elimination premium. These factors should be considered when searching for an appropriate value for economic evaluation and health technology assessment.
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| 34. |
- Olofsson, Sara, et al.
(författare)
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Dread and Risk Elimination Premium for the Value of a Statistical Life
- 2019
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Ingår i: Risk Analysis. - : Blackwell Publishing. - 0272-4332 .- 1539-6924. ; 39:11, s. 2391-2407
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Tidskriftsartikel (refereegranskat)abstract
- The value of a statistical life (VSL) is a widely used measure for the value of mortality risk reduction. As VSL should reflect preferences and attitudes to risk, there are reasons to believe that it varies depending on the type of risk involved. It has been argued that cancer should be considered a "dread disease," which supports the use of a "cancer premium." The objective of this study is to investigate the existence of a cancer premium (for pancreatic cancer and multiple myeloma) in relation to road traffic accidents, sudden cardiac arrest, and amyotrophic lateral sclerosis (ALS). Data were collected from 500 individuals in the Swedish general population of 50-74-year olds using a web-based questionnaire. Preferences were elicited using the contingent valuation method, and a split-sample design was applied to test scale sensitivity. VSL differs significantly between contexts, being highest for ALS and lowest for road traffic accidents. A premium (92-113%) for cancer was found in relation to road traffic accidents. The premium was higher for cancer with a shorter time from diagnosis to death. A premium was also found for sudden cardiac arrest (73%) and ALS (118%) in relation to road traffic accidents. Eliminating risk was associated with a premium of around 20%. This study provides additional evidence that there exist a dread premium and risk elimination premium. These factors should be considered when searching for an appropriate value for economic evaluation and health technology assessment.
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| 35. |
- OLOFSSON, SARA, et al.
(författare)
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Measuring the End of Life Premium in Cancer using Individual ex ante Willingness to Pay
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- For the assessment of value of new therapies in healthcare, Health Technology Assessment (HTA) agencies often review the cost per Quality-Adjusted Life-Years (QALY) gained. Some HTAs accept a higher cost per QALY gained when treatment is aimed at prolonging survival for patients with a short expected remaining lifetime, a so called End-Of-Life (EoL) premium. The objective of this study is to elicit the existence and size of an EoL premium in cancer. Data was collected from 509 individuals in the Swedish general population 20-80 years old using a web-based questionnaire. Preferences were elicited using subjective risk estimation and the contingent valuation (CV) method. A split-sample design was applied to test for order bias. The value of a QALY at EoL in cancer was between €275,000 and €440,000, which is higher than the thresholds applied by HTAs. When expected remaining life expectancy was 6 months, the value of a QALY was 10-20 % higher compared to when remaining life expectancy was 24 months. Order of scenarios did not have a significant impact on the result and the result showed scale sensitivity. Thus this study supports an EoL premium in cancer when expected remaining lifetime is short.
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| 36. |
- Olofsson, Sara, et al.
(författare)
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Value of a QALY and VSI Estimated with the Chained Approach
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The value of a Quality-Adjusted Life-Year (QALY) and the Value of a Statistical Injury (VSI) are important measures within health economics and transport economics. Several studies have therefore estimated people’s WTP for these estimates, but most results show problems with scale insensitivity. The Chained Approach (CA) is a method developed to reduce this problem. The objective of this study was to estimate the value of a QALY and VSI in the context of non-fatal road traffic accidents using CA. Data was collected from a total of 800 individuals in the Swedish adult general population using two web-based questionnaires. The result showed evidence of scale sensitivity both within and between samples. The value of a QALY based on trimmed individual estimates where close to constant at €300,000 irrespective of the type and size of the QALY gain. The study shows promising results for using the original CA to estimate the value of a QALY and VSI. It also supports the use of a constant value of a QALY, but at a higher level than what is currently applied by HTA’s.
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| 37. |
- Olofsson, Ulf, et al.
(författare)
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The influence of snow on the tread braking performance of a train : A pin-on-disc simulation performed in a climate chamber
- 2016
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - : Sage Publications. - 0954-4097 .- 2041-3017. ; 230:6, s. 1521-1530
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Tidskriftsartikel (refereegranskat)abstract
- In trains with tread brakes, the coefficient of friction between the brake block and the railway wheel determines the stopping distance. The blocks have traditionally been manufactured from cast iron. Although these blocks have good braking capacity, their use is often restricted due to the squealing noise they emit. Tests of alternative composite block materials have been successful under summer conditions; however, in regions with snowy winters the use of such materials has been limited due to problems with braking capacity under snowy conditions. This research aims to develop a laboratory-scale test methodology for evaluating the braking capacity of tread brake materials under winter and snowy conditions. A pin-on-disc machine placed in a climate chamber was used for testing, and a block of standard cast iron was compared with blocks of standard composite materials. The results indicated that the blocks of standard composite materials generate a much smoother surface on the counter wheel and a significantly lower friction coefficient under snowy conditions. A second test series evaluated blocks of alternative composite materials, and a candidate material with low noise and a sufficiently high sliding friction coefficient was selected for further study. A third test series examining geometrical changes in the contact surface in terms of milled parallel tracks was performed; it revealed that the braking capacity under winter conditions can be increased by milling actions if the parallel tracks are properly oriented - in this case, at an angle of 45 degrees to the sliding direction.
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| 38. |
- Sellgren, Ulf, et al.
(författare)
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Application of a constitutive model for micro-slip in finite element analysis
- 1999
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - 0045-7825 .- 1879-2138. ; 170:1-2, s. 65-77
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Tidskriftsartikel (refereegranskat)abstract
- Micro-slip is a phenomenon that occurs between contacting surfaces when a frictional load, less than that necessary to produce macro-slip, is applied to the contacting surfaces. Micro-slip is an elastoplastic physical behavior that is important for fretting fatigue, control engineering, the damping and stiffness of connections and joints. A micro-slip friction lau, suitable for finite element (FE) analysis of systems of interacting bodies where micro-slip effects are of importance has been implemented in a commercial FE software. Physical arguments for a micro-slip friction law are presented. The friction law is based on asperity deformation and is capable of simulating oscillating movements. An important feature of the frictional model is that it decouples the parameters that are related to shape, material and surface topography, respectively. Two examples are chosen to illustrate the applicability of the model. Significant differences in friction force distribution between an elastic Coulomb friction law and the micro-slip friction law are detected on local level as well as on global level.
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| 39. |
- Sjödin, Ulf, et al.
(författare)
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Experimental study of wear interaction between piston ring and piston groove in a radial piston hydraulic motor
- 2004
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 257:12, s. 1281-1287
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Tidskriftsartikel (refereegranskat)abstract
- The wear interaction between piston ring and piston groove in a radial piston hydraulic motor was studied in regard to mass loss and changes in form and surface roughness. A specially developed test rig that simulates the tilting movements of pistons at the end of strokes was used in the test. The results show that wear on the piston ring groove can be up to 10 times greater than the wear on the piston ring. For both interacting surfaces, the dominant wear mechanism was mild wear. The results from a factorial design show that the form of the piston groove significantly influences the amount of wear.
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| 40. |
- Sjödin, Ulf, et al.
(författare)
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Initial sliding wear on piston rings in a radial piston hydraulic motor
- 2003
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 254:11, s. 1208-1215
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Tidskriftsartikel (refereegranskat)abstract
- The initial sliding wear of boundary lubricated piston rings used in a hydraulic motor is studied in terms of the changes in mass, form and surface toughness. The piston ring in a hydraulic motor makes an important contribution to high volumetric efficiency by properly sealing the cylinder bore and piston. The results show that the wear on the piston ring in this particular test rig takes place at the top of the asymmetric crowning at the outer surface contacting the cylinder bore. Initially, the roughness amplitude decreased rapidly, and had decreased by one-third after sliding 10 m. The dominant wear mechanism was mild wear. Abrasive wear also clearly influences the amount of wear.
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| 41. |
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| 42. |
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| 43. |
- Sosa, Mario, et al.
(författare)
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In situ running-in analysis of ground gears
- 2016
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 352-353, s. 122-129
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Tidskriftsartikel (refereegranskat)abstract
- The initial contact state between two interacting gears proves of interest due to empirical evidence indicating difference in life and efficiency in the long term due to the initial operation. Presented here is an analysis of the initial contact state of spur gears, made of case carburized 16MnCr5 steel, by the use of in situ surface measurements and friction measurements in a back-to-back test rig during the running-in cycles. Furthermore a method to estimate wear during running-in is proposed. Results show that the most significant changes in roughness and friction occurred during the first initial cycles at high load.
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| 44. |
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| 45. |
- Sosa, Mario, et al.
(författare)
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In situ surface characterization of running-in of involute gears
- 2015
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 340-341, s. 41-46
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Tidskriftsartikel (refereegranskat)abstract
- Gear life and operation are largely determined by the properties of the contacting surfaces, which inevitably change over the gear life. The initial topography transformation, a characteristic effect of running-in, is very important. This paper focuses on how the running-in of the surface topography can be characterized and what methodology can be used for this purpose. To characterize running-in, gears were run in an FZG back-to-back test rig and the changes in surface topography were measured in situ using a Form Talysurf Intra. This enables the same gear tooth surface to be measured with enough precision to follow its development through the different stages of running-in. Gear tooth surfaces as manufactured were measured on three occasions: in initial manufactured condition, after a standard running-in procedure, and after an efficiency test. Running-in was characterized both qualitatively by plotting roughness profiles and quantitatively by analyzing a selected set of roughness parameters. This paper demonstrates that: the asperity peaks were worn off in the initial running-in stage; roughness, waviness, and form can be separated using a carefully chosen polynomial fit and the Gaussian filter; surface topography can be examined initially, after running-in, and after operation in situ; and complete wear of the initial surface can be observed in specific circumstances.
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| 46. |
- Sosa, Mario, 1986-
(författare)
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Running-in of gears - surface and efficiency transformation
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With ever shorter development times and market demands on overall system performance such as efficiency, reliability and low maintenance, accurate predictive tools are necessary and gear drives prove to be no exception. All these characteristics have an impact on a process which has remained a riddle: running-in. Even though no consensus on a definition of this phenomena is readily available, this thesis examines efficiency, surface roughness and simulation through the optics of running-in.Geared transmissions are known for their formidable efficiency and their extreme reliability. However, with an ever increasing power density, the ability to accurately predict mesh losses becomes of utmost importance. The accurate quantification of bearing losses as well as efficiency of ground and superfinished gears under dip lubrication are examined with respect to running-in. Results show a considerable influence on the calculation of gear mesh losses originating from which bearing loss model is chosen. Furthermore, when a larger running-in load is used on ground gears, an increase in efficiency can be observed during working operation, while for superfinished no significant changes are found. These efficiency/frictional changes are also shown to occur in the initial cycles of the running-in phase.From a surface transformation point of view running-in is shown to be a reduction of asperity tips in case hardened ground gears, while in superfinished gears no changes were seen. These gear surface changes were measured with a novel method with a surface profilometer in-situ before, after running-in and after efficiency testing. Results also show that such changes in ground gear roughness profile occur during the very initial cycles.In order to predict running-in, a simulation method was developed. Such method utilizes a 2D surface integral method to simulate contact between rough surfaces, but requires the use of surface hardness and an accurate lower cutoff wavelength. This cutoff wavelength proved to play a pivotal role in determining an accurate contact pressure at the proper level of granularity, hence a well defined real contact area. The predicted and measured run-in surfaces are compared and are found to be in accordance with each other.
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| 47. |
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| 48. |
- Adamo, Karin, et al.
(författare)
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Risk for developing perianal abscess in type 1 and type 2 diabetes and the impact of poor glycemic control
- 2021
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Ingår i: International Journal of Colorectal Disease. - : Springer. - 0179-1958 .- 1432-1262. ; 36:5, s. 999-1005
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The primary aim of this study was to see whether perianal abscess rate differs between patients with type 1 and type 2 diabetes. A secondary aim was to determine whether poor glycemic control increases the risk for perianal abscess.Methods: Data from the Swedish National Diabetes Registry and the Swedish National Patient Registry between January 2008 and June 2015 were matched. The risk for anal abscess was evaluated in univariate and multivariate analyses with type of diabetes, HbA1c level, BMI, and various diabetes complications as independent factors.Results: Patients with type 1 diabetes had a lower rate of perianal abscess than patients with type 2 diabetes when adjusted for HbA1c, sex, and age (OR 0.65; 95% CI 0.57–0.73). The risk for perianal abscess increased with higher HbA1c. Incidence of perianal abscess was also elevated in diabetes patients with complications related to poor glycemic control such as ketoacidosis and coma (OR 2.63; 95% CI 2.06–3.35), gastroparesis, and polyneuropathy (OR 1.81; 95% CI 1.41–2.32).Conclusions: The prevalence of perianal abscess was higher among patients with type 2 diabetes than those with type 1, suggesting that metabolic derangement may be more important than autoimmune factors. Poor glycemic control was associated with higher risk for perianal abscess.
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| 49. |
- Alemani, Mattia, et al.
(författare)
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A study on emission of airborne wear particles from car brake friction pairs
- 2015
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Ingår i: SAE International Journal of Materials & Manufacturing. - : SAE International. - 1946-3979 .- 1946-3987. ; 9:1, s. 147-157
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Tidskriftsartikel (refereegranskat)abstract
- The emission of airborne wear particles from friction material / cast iron pairs used in car brakes was investigated, paying special attention to the influence of temperature. Five low-metallic materials and one non-asbestos organic material were tested using a pin-on-disc machine. The machine was placed in a sealed chamber to allow airborne particle collection. The concentration and size distribution of 0.0056 to 10 μm particles were obtained by a fast mobility particle sizer and an optical particle sizer. The temperature was measured by a thermocouple installed in the disc. The experiments show that as the temperature increases from 100 to 300 °C the emission of ultrafine particles intensifies while that of coarse particles decreases. There is a critical temperature at which the ultrafine particle emission rate rises stepwise by 4 to 6 orders of magnitude. For the friction pairs investigated, the critical temperature was found to be between 165 and 190 °C. Below the critical temperature, fine particles outnumber coarse and ultrafine particles, although coarse particles make up the bulk of the particulate matter mass. The friction pairs differ in the ultrafine particle emission rate by 1 to 2 orders of magnitude. Above the critical temperature, ultrafine particles constitute almost 100% of the total particle number and their relative mass contribution can exceed 50%. Analysis of the particle size distributions revealed peaks at 0.19-0.29, 0.9 and 1.7 μm. Above the critical temperature, one more peak appears in the ultrafine particle range at 0.011-0.034 μm.
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| 50. |
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