| 1. |
- Alemani, Mattia
(författare)
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Particle emissions from car brakes : The influence of contact conditions on the pad-to-rotor interface
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to their adverse health effects emissions have been regulated for over three decades. Brake wear particulate matter is the most important non-exhaust source, however current knowledge is mainly limited to observational studies. This thesis aims to investigate relations between the brake system contact conditions and the related emissions on a model scale; validate the results on a component level; and understand to what extent they are significant on a full-scale.Paper A investigates the influence of nominal contact pressure on a model scale. Results show that higher pressure corresponds to higher emissionsPaper B investigates the influence of the nominal contact pressure, for different friction materials, on a model scale. A temperature threshold, responsible for a relevant emission increase, is identified.Paper C investigates particle characteristics and wear mechanisms for different nominal contact pressures, on a model scale. Results show an enhanced tribo-layer at higher pressure levels.Paper D investigates the influence of brake system conditions on emissions, on a model scale. Results show that frictional power is the most important parameter. A transition temperature independent of the contact condition is identified.Paper E investigates similarities occurring on a component scale and a model scale in terms of emissions. Results show a promising correlation, and the possibility of using a pin-on-disc tribometer for R&D activities.Paper F investigates analogies occurring on a component scale and a model scale, in terms of friction performance, fictional surface and chemical composition. Results show similar phenomena occurring for the two test stands.Paper G analyses real brake system working conditions in a urban environment defining, by means of an inertia dyno bench, the related emissions. Results reveal emission factors compliant to EURO6 and EURO2 regulations, in terms of number and mass, respectively.
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| 2. |
- Carlsson, Daniel, 1982-
(författare)
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Effects of cold and hand-arm vibration on the peripheral neurosensory and vascular system : an occupational perspective
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background In Swedish working life, exposure to cold and exposure to hand-arm vibration (HAV) are two common health hazards. Health effects of HAV in the neurosensory, vascular and musculoskeletal systems are collectively denoted hand-arm vibration syndrome (HAVS), and have been thoroughly studied. Effects of cold exposure in terms of effects on the peripheral neurosensory and vascular system are on the contrary limited, especially in an occupational setting. Effects of cold exposure or cold injury have not previously been assessed with quantitative sensory testing (QST). Commonly reported symptoms after exposure to HAV and after cold injuries, includes cold sensitivity and sensation of cold. Cold sensitivity can also occur without previous exposure to vibration or cold and may have a major impact on quality of life. Other possible risk factors for cold sensitivity need to be assessed. Sensation of cold hands could theoretically imply an early manifestation of damage to the neurosensory or vascular system, and therefore be of importance to enable early detection of vascular and neurosensory HAVS. The purpose of this thesis was to increase the knowledge about health effects from cold and HAV on the peripheral neurosensory and vascular system, with an occupational perspective. The aims were: first, to identify and evaluate health effects and sequelae in the peripheral neurosensory and vascular system due to cold injury and cold exposure; second, to investigate if sensation of cold hands is a predictor for future onset of Raynaud's phenomenon or paresthesia; and third, to identify possible risk factors associated with cold sensitivity.Methods A case series on 15 military conscripts with local cold injuries in the hands or feet, involving QST and symptom descriptions, was conducted to investigate the hypothesis that cold injuries can result in similar neurosensory and vascular impairments as in HAVS. To assess health effects of cold exposure, a cohort study on 54 military conscripts in cold winter military training, with cold exposure assessments, was conducted. Possible health effects were assessed after 14 months of military training, containing considerable cold exposure, by means of QST, Finger systolic blood pressure after local cooling (FSBP) and a questionnaire. To investigate if sensation of cold hands is a predictor for vascular or neurosensory HAVS we investigated a cohort of 178 employees at a manufacturing company where HAV was a common exposure. The cohort was followed during 21 years and both vibration exposure and health outcomes were assessed regularly. Questionnaire items were used to assess sensations of cold hands as well as signs of Raynaud’s phenomenon and paresthesia. To identify risk factors for cold sensitivity a case-control study was conducted involving 997iiiparticipants from the general population in northern Sweden. The study was cross-sectional and explored possible risk factors for cold sensitivity.Results Cold injuries and cold exposure were associated with reduced sensibility in QST and increase severity and prevalence of neurosensory and vascular symptoms. Our results did not show any impairment in peripheral blood flow due to cold exposure, detectable by FSBP. The risk of developing Raynaud's phenomenon was increased for workers previously reporting sensation of cold hands (OR 6.3, 95% CI 2.3-17.0). No increased risk for paresthesia in relation to a sensation of cold hands was observed. The identified risk factors for cold sensitivity were frostbite in the hands, rheumatic disease, nerve injury in upper extremities or neck, migraine and vascular disease. When analysing women and men separately, women’s risk factors were frostbite in the hands, rheumatic disease, migraine and cold exposure. Men’s risk factors were frostbite in the hands, vibration exposure and nerve injury in upper extremities or neck. BMI > 25 was a protective factor for both men and women.Conclusion Cold injury and cold exposure are associated with impairments in the neurosensory system, detectable by QST. Symptoms such as sensation of cold hands and white fingers indicate vascular involvement, even though no vascular impairments due to cold exposure could be detected by objective measurements. A sensation of cold hands is a risk factor for development of Raynaud´s phenomenon, but not for paresthesia. At the individual level, reporting cold hands does not appear to be useful information when considering the possibility of a future development of Raynaud’s phenomenon. Frostbite in the hands is a risk factor for cold sensitivity among both women and men. For women rheumatic disease, migraine and cold exposure are also independent risk factors, and for men, exposure to HAV. Being overweight is a protective factor for both women and men.
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| 3. |
- Nestorson, Jens, 1969-
(författare)
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Arthroplasty in Elbow Fracture Treatment
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Open reduction and internal fixation is the treatment of choice for distal humeral fractures. Stable fixation is required to allow early mobilisation and to reduce the risk of poor functional results. In an elderly patient with osteoporotic bone and with a comminuted intra-articular fracture stable internal fixation can be difficult to achieve. In these cases elbow arthroplasty is an option.An irreparable radial head fracture can be treated by excision or replacement. The indications for the respective procedure are unclear since reports include an array of different associated soft-tissue and bony injuries.The aim of this thesis was to evaluate the use, complication rates and functional outcome of elbow arthroplasty as primary treatment for complex distal humeral fractures and assess the usefulness of radial head replacement in Mason IV fracture dislocations.50 patients, aged 56-89 years were treated for a distal humeral fracture with primary hemi-arthroplasty using the Kudo© humeral component or the Latitude® prosthesis. The functional outcome was assessed retrospectively. The majority of the 50 patients treated with a primary hemi-arthroplasty for a distal humeral fracture had a good or excellent functional result and regained a functional arc of movement of at least 100 degrees at medium term follow-up. There were six patients suffering secondary surgery and two with persistent ulnar nerve symptoms. Wear of the olecranon fossa was seen, mainly in the eight patients treated with a non-anatomical implant (Kudo®). Functional results were comparable to total elbow arthroplasty and open reduction and internal fixation (ORIF) for distal humeral fractures. The use of implants that are more anatomical seemed to reduce the degree of olecranon wear but long-term results are lacking.The nationwide use of primary arthroplasty for a distal humeral fracture between 1999 and 2014 was examined using three different registers. The survival rates in relation to prosthetic desing, age and sex were investigated using Cox regression analysis and number of adverse events recorded.In total 405 patients were treated with primary arthroplasty for a distal humeral fracture. The mean age at surgery was 75 years and the mean observation time was 67 months. Eighteen patients had undergone revision surgery and another 26 patients suffered an adverse event, 24 of which required secondary surgery.Increasing age reduced the risk for revision and there was no significant difference in survival between total- and hemi arthroplasty. The cumulative survival rate at 5 years was 99% (CI 98-100) and at 10 years 90% (CI 85-96). Elbow arthroplasty as primary treatment for distal humeral fractures produced reliable results with regards to revision surgery and adverse events.18 patients, age 19-79 years, treated with radial head replacement, and 14 patients, age 29-70 years, treated with radial head resection, for a Mason IV fracture dislocation were retrospectively reviewed.There were no significant differences in functional outcome in patients treated with replacement or excision for a Mason IV fracture dislocation. The rate of secondary surgery was higher in patients treated with replacement and ulno-humeral osteoarthritis was more pronounced in patients treated with radial head excision but follow-up was longer in these patients. Functional results were not improved by using radial head arthroplasty for Mason IV fracture dislocation. Secondary osteoarthritis is a concern in patients treated with excision but did not affect functional outcome after a mean follow-up time of 108 months.
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| 4. |
- Riva, Gabriele, 1988-
(författare)
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A methodology to simulate automotive disc brake tribology and emissions
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Airborne particle emissions from road vehicles are one of the main issues affecting urban air quality. Vehicle disc brakes are one of the most important sources of non-exhaust emissions, which have recently been considered to be as important as exhaust emissions. In disc brakes, the pads are pushed against the rotating disc to slow down the vehicle. The contact surfaces of the disc and pads are worn, some of the debris becomes airborne and can be harmful to human health if inhaled. Particle emissions from disc brakes are influenced by a greater amount of contact phenomena at the sliding interfaces, e.g. friction, wear, contact temperature, contact pressure and surface topography. Due to the difficulty in accessing the pad-to-disc contact in the brake system during testing, it is hard to study contact phenomena. Moreover, experiments need the friction material and brake system to be produced at least in their prototype configuration. The aim of this thesis is to develop a methodology based on simulation to better understand contact phenomena and to evaluate the tribological and emission performance of friction material and brake systems in the early design phase.Different simulation approaches can be adopted, depending on what is to be evaluated. A macro-scale approach based on finite element analysis (FEA) can be used to evaluate wear, particle emission and the coefficient of friction (COF) of the entire brake system. A meso-scale approach based on cellular automaton (CA) simulation can be used to evaluate the local contact behaviour on the disc and pad surfaces, and the influence of the single components of the friction mixture. These two different-scale simulation approaches can be integrated to generate an overall multi-scale simulation procedure to investigate and predict the contact phenomena in brake systems.
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| 5. |
- Stjernbrandt, Albin, 1985-
(författare)
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Cold exposure and health : A study on neurological and vascular hand symptoms in northern Sweden
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Living in a cold climate is associated with several adverse health effects. The main purpose of this thesis was to describe cold exposure characteristics in northern Sweden, and investigate the associations between such exposure and the reporting of neurological and vascular hand symptoms. One common cold-related hand symptom is Raynaud’s phenomenon, defined as episodic attacks of acral pallor or cyanosis. There is evidence to suggest that cold exposure can act both as a causal factor and a trigger for such vasospastic symptoms. Other important associated factors include exposure to hand-arm vibration and the presence of rheumatic disease. A somewhat similar clinical entity, cold sensitivity, is defined as a collection of acquired symptoms, resulting in an abnormal aversion to cold, with pain, sensory alterations, stiffness, or color changes, which may occur after a traumatic injury. The condition is hypothesized to mainly originate from nerve injury. The effects of cold exposure on hand function, the occurrence of cold sensitivity in the general population, the link between cold exposure and cold sensitivity, as well as the interface between cold sensitivity and Raynaud’s phenomenon are not fully understood. Therefore, this thesis was also intended to expand the knowledge on Raynaud’s phenomenon and cold sensitivity.Methods: Postal surveys were sent to a sample of men and women between 18 and 70 years of age, living in Norrbotten, Västerbotten, Västernorrland, and Jämtland, drawn from the national Swedish population register. The first survey collected data on 12,627 subjects, and the results were used to describe cold exposure characteristics, and broadly investigate the statistical associations with different neurological and vascular hand symptoms (Paper I). A follow-up survey was sent to a subset of responders, to form nested case–control studies on cold sensitivity (N=1,230; Paper II) and Raynaud’s phenomenon (N=1,400; Paper III). Subjects with cold sensitivity (N=12) from Paper II were subsequently recruited to a laboratory study, to investigate the vascular and neurosensory function of the hands, by means of physical examination, laser speckle contrast analysis before and after cold stress testing, and thermal quantitative sensory testing (Paper IV). Finally, healthy controls (N=1,239) from the case–control studies were used as a reference population for the Cold intolerance symptom severity questionnaire, to establish a cut-off for abnormal cold sensitivity (Paper V).Results: In Paper I, cold exposure was commonly reported, both during work and leisure time. Exposure was most pronounced in alpine regions, generally higher among men than women, and decreased with age. Highly cold-exposed occupational groups were militaries; agricultural, forestry and fishery workers; and crafts and related trades workers (e.g. construction workers). The correlation between occupational and leisure-time cold climate exposure was low. Men reported more occupational exposure to hand-arm vibration than women, but the correlation between occupational cold and vibration exposure was low. A range of neurological and vascular hand symptoms were statistically associated with high cold exposure, such as decreased perception to touch, warmth, and cold, as well as Raynaud’s phenomenon. In Paper II, cold sensitivity was significantly associated with previous frostbite affecting the hands, rheumatic disease, upper extremity nerve injury, migraine, vascular disease, and high body mass index (inversely), in a multiple conditional logistic regression model. In Paper III, Raynaud’s phenomenon was significantly associated with previous frostbite affecting the hands, first degree heredity, and high body mass index (inversely), in a similar model. Previous upper extremity nerve injury was suggested as a separating trait between Raynaud’s phenomenon and cold sensitivity. In Paper IV, laser speckle contrast analysis indicated disturbances in microvascular regulation, while physical examination and thermal quantitative sensory testing mainly yielded normal results. In Paper V, the 95th percentile for the Cold intolerance symptom severity score was 49.5 for men, and 53.0 for women.Conclusions: Cold exposure in the working-age population of northern Sweden varied with age, gender, occupation, and place of residence. Cold exposure was related to the reporting of neurological and vascular hand symptoms in the population as a whole. There was a major overlap between reporting cold sensitivity and Raynaud’s phenomenon, and the conditions shared several associated factors. Previous upper extremity nerve injury was suggested to be a separating trait, supporting the neurosensory pathophysiological hypothesis for cold sensitivity. Cold sensitivity was not effectively assessed by physical examination or thermal quantitative sensory testing. However, laser speckle contrast analysis could prove a useful tool in further studies on cold sensitivity. A Cold intolerance symptom severity score above 50 could be considered to indicate abnormal cold sensitivity, and be used to guide further care.
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| 6. |
- Svedmark, Åsa, 1961-
(författare)
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Neck pain in women : effect of tailored treatment and impact of work environment
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Introduction: Musculoskeletal pain is a common problem in the working population. In Sweden, 40% of women and 30% of men report suffering from neck and shoulder pain weekly. The underlying cause for neck pain is often not known and the treatment is commonly guided by the individual’s symptoms. However, there is a lack of knowledge on how to receive the best effect based on the individual’s symptoms and functional limitations, and therefore this has been scarcely evaluated in research. Furthermore, the impact of work exposure and stress on long-term treatment for persons with neck pain is not clear.Aims: To develop (paper 1) and to evaluate a decision model for tailored treatment in women with neck pain (paper 2). Moreover, to determine if risk factors at work and stress influence intermediate and long-term treatment results (paper 3). Further, to investigate if changes in self-reported pain and disabilities are associated with changes of physical test outcomes of the neck and shoulder region after treatment (paper 4).Methods: In an RCT, 120 working women with non-specific neck pain were randomized to three different groups – tailored treatment (TT), non-tailored treatment (NTT) or treatment-as-usual (TAU) for an 11 weeks intervention with short-term, intermediate-term and long-term follow-ups. The TT group was guided by a decision model with cut-off levels to indicate impairments. The NTT group received two established treatment components randomly from those not indicated, and TAU group did not receive any treatment within the study. The RCT primary outcomes were self-reported neck pain and neck disability. A linear mixed model was used for analysing the effects. One week after the end of intervention work exposure and stress were assessed at a work-place visit and associations to treatment results were tested for, and mixed models were used to estimate longitudinal associations. Associations between self-reported neck problems and physical outcomes were estimated with univariate and multiple regressions analysis.Results: No differences between TT and NTT were revealed for neck pain and disability. In comparison to TAU, the TT and NTT groups both showed improvements at short-term follow-up, but not at intermediate and long-term follow-up. High stress level and low self-estimated control at work were associated with more pain and disability at the intermediate and long-term follow-ups. After intervention and at the intermediate-term follow-up, reduced neck pain, disability and frequency of symptoms were associated with increased peak speed of head rotation and cervical range of motion.Conclusion: Tailored treatment according to the decision model was not superior to the non-tailored treatment in women with non-specific neck pain. One explanation for this can be the weak relationships found between neck pain and disability and physical test outcomes. Further, perceived stress and psychosocial work exposure were associated with self-reported neck problems and should be taken into account to optimize the effects in neck pain rehabilitation.
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| 7. |
- Wahlström, Jens
(författare)
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A study of airborne wear particles from automotive disc brakes
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During braking, both the disc and pads in disc brakes are worn. Since disc brakes are not sealed,some of the wear particles generated can become airborne. Several studies have found anassociation 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 discbrakes. This thesis deals with experimental and computational methods focusing on airborne wearparticles from disc brakes. The eight appended papers discuss the possibility to both measure andnumerically determine the concentration and size distribution of airborne wear particles thatoriginate from the pad-to-disc contact. The objective is to increase the scientific knowledge ofairborne wear particles generated from disc brakes. Papers A, B and C describe tests of disc brake materials conducted in a modified pin-on-discmachine. The results show that the test set-up can be used to measure and rank disc brakematerials with respect to the concentration of airborne particles generated. Ultrafine (nanosized),fine and coarse airborne wear particles that contain metals such as iron, copper and tin werefound. Papers D and E describe a novel disc brake assembly test stand and tests of disc brake materialsconducted in it. The results show that the test set-up can be used to measure the concentrationand size distribution of airborne wear particles generated from disc brake materials. The resultsalso indicate an ability to rank different pad/disc combinations with respect to the concentrationof airborne wear particles. Furthermore, the results suggest that this test stand can be used tostudy rust layer removal from the disc and that airborne particles are generated even at low brakepressures, such as used to remove dirt from the disc. Paper F compares measurements made in passenger car field tests with measurements made in adisc brake assembly test stand and in a pin-on-disc machine. A promising correlation between thethree different test methods is found. Paper G presents and discusses a simulation methodology that numerically determines theconcentration and size distribution of airborne wear particles generated from the pad-to-disccontact in disc brakes by using general-purpose finite element software. Paper H discusses a cellular automaton model that describes the microscopic contact situationbetween the pad and disc in disc brakes. This model is used to numerically determine the amountof wear that leaves the contact. The results correlate qualitatively with experimental observationsfound in the literature.
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| 8. |
- Wahlström, Jens, 1972
(författare)
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Physical load, psychosocial and individual factors in visual display unit work
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of this thesis was to explore associations between physicalload, psychosocial and individual factors in visual display unit (VDU)work. Furthermore, the aim was to investigate whether perceived musculartension is a predictor of neck pain among VDU operators. The thesisis based upon five separate studies, two laboratory studies, two fieldstudies and one prospective cohort study.Several different methods were used to assess the physical load. Electromyography(EMG) was used to record muscle activity. Wrist postures andmovements were assessed by means of electrogoniometers. An instrumentedcomputer mouse was used to measure the forces applied to thecomputer mouse. Working technique was assessed with an observationprotocol. Perceived exertion, comfort, mental stress and perceivedmuscular tension were assessed with questionnaires.The results of this work are discussed in relation to a proposed model forVDU work and musculoskeletal symptoms. The first two studies (StudiesI and II) support an association between individual factors (workingtechnique and sex) and the physical load. In Study III we observed thatthe physical load increased as a result of mental stress and increasedproductivity. Besides an increase in muscle activity; increases in the forcesapplied to the computer mouse and increased repetitiveness of wristmovements were also observed. The results from the third study alsosupport an association between psychosocial factors and physical loadthrough increased physical demands. The fourth study (Study IV)supports an association between perceived muscular tension and physicalload and perceived muscular tension is hypothesized to be an early sign ofmusculoskeletal symptoms. In Study V an increased risk of developingneck pain was observed among subjects who perceived high musculartension, even when controlling for job strain, physical exposure and age.It is concluded that the physical load during VDU work is affected bypsychosocial and individual factors as well as physical demands. VDUusers who perceives muscular tension at least a few times per week appearto have an increased risk of developing neck pain.
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