| 161. |
- Tu, Minghui, et al.
(författare)
-
Towards a two-part train traffic emissions factor model for airborne wear particles
- 2019
-
Ingår i: Transportation Research Part D. - : Elsevier Ltd. - 1361-9209 .- 1879-2340. ; 67, s. 67-76
-
Tidskriftsartikel (refereegranskat)abstract
- In 2017 a new railway tunnel containing two stations opened in Stockholm, Sweden. A series of field measurements were carried out on the platforms in this tunnel before and after it was opened for normal traffic. These measurements were used to investigate the contribution of airborne particle emissions from wear processes to total train emissions. This field data was used to develop a two-part train traffic emission factor model for PM10. The two parts are the accumulative effect term (relating to operating distance such as wheel-rail contact and overhead electric line sliding contact) and a brake effect term (relating to the number of braking operations such as brake disc and brake pad contact). The results show that operating a single trial train at a higher than normal frequency on an otherwise empty platform increases the platform particulate concentration until the concentration reaches a steady value. The model suggests that brake emissions account for about 50% of the total emissions measured in the tunnels.
|
|
| 162. |
- Uhlig, Jens, et al.
(författare)
-
Laser generated 300 keV electron beams from water
- 2011
-
Ingår i: Laser and Particle Beams. - 0263-0346. ; 29:4, s. 415-424
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract in Undetermined300 keV electron beams with energy peaked in the range 280–390 keV were generated by focusing a high contrast ratio but temporally double pulsed 800 nm ultrafast laser onto a flowing water jet under both helium atmosphere at ambient pressure and water aspirator vacuum conditions, using laser intensities in the range 1015–1018 Wcm−2. Their characteristics have been investigated as functions of inter-pulse delay, incidence geometry and laser pulse chirp. Shot-to-shot variation of the beams' equatorial and azimuthal distributions was also recorded in real time. Measurements of the emitted charge and energy have been performed. Secondary X-ray emission arising from impingement of the electron beams on the target chamber walls and other parts of the apparatus have been identified. Preliminary results after transition to a high repetition rate laser system have shown similar behavior. Approaches for improvements and applications are suggested.
|
|
| 163. |
- Varriale, Francesco, et al.
(författare)
-
A Brake System Coefficient of Friction Estimation Using 3D Friction Maps
- 2022
-
Ingår i: Lubricants. - : MDPI AG. - 2075-4442. ; 10:7
-
Tidskriftsartikel (refereegranskat)abstract
- The coefficient of friction (COF) is one of the core factors in the evaluation of brake system performance. It is challenging to predict the COF, since it is strongly influenced by several parameters such as contact pressure (p), slip rate (v) and temperature (T) that depend on the driving conditions. There is a need for better models to describe how the brake friction varies under different driving conditions. The purpose of this research is to study the possibility of using 3D friction pvTmaps to estimate the COF of a disc brake system under different driving conditions. The 3D friction pvT-maps are created by filtering results of material tests conducted in a mini-dyno inertia bench. The COF measured under different driving cycles in an inertia dyno bench with the full brake system are compared with the COF estimated by the friction maps coming from the reduced scale dyno bench to investigate the validity of the simulation approach. This study shows that mini dyno bench is suitable to obtain a tribological characterization of the friction pad–disc rotor contact pair and is able to replace the full inertia dyno bench to investigate the brake system performance.
|
|
| 164. |
- Varriale, Francesco, et al.
(författare)
-
A Mesoscopic Simulation Approach Based on Metal Fibre Characterization Data to Evaluate Brake Friction Performance
- 2022
-
Ingår i: Lubricants. - : MDPI AG. - 2075-4442. ; 10:3
-
Tidskriftsartikel (refereegranskat)abstract
- The coefficient of friction (COF) is an important parameter when evaluating brake system performance. It is complex to predict friction due to its dependence on parameters, such as sliding velocity, contact pressure, temperature, and friction material mixtures. The aim of this work is to evaluate the macroscopic COF of a disc brake system under specific braking conditions by a meso-scale approach, using a cellular automaton simulation where the friction material mixture is modelled starting from its basic components. The influence of the local components in contact is taken into account. Simulated COF values are in line with the experimental values.
|
|
| 165. |
- Varriale, Francesco, et al.
(författare)
-
On the impact of pad material ingredients on particulate wear emissions from disc brakes
- 2023
-
Ingår i: Results in Engineering. - 2590-1230. ; 19
-
Tidskriftsartikel (refereegranskat)abstract
- Besides friction and wear, airborne particle emission has become a central parameter when evaluating disc brake performance due to its potential adverse health effects as component of ambient air pollution. The pad friction material of brake system is composed of a mixture of ingredients grouped into four material categories: abrasives, reinforcing fibres, lubricants, and fillers. Some other ingredients which do not typically belong to aforementioned categories can be attributed to “fixed material”, such as aramid fibre, which is usually added into brake pad to harmonize the overall tribological properties. There is a gap of knowledge about how one ingredient from one category contributes to the emissions of particle number (PN) and mass (PM2.5, PM10). To investigate this, one ingredient from each category was chosen and produced as pins. As a reference, pins made of a commercial European brake friction material were also produced. The pins were tested using a pin-on-disc tribometer designed for airborne emission studies. Coefficient of friction, particle mass and number concentrations were measured during the tests. The results indicate that the abrasive and metal fibre have PN, PM2.5, and PM10 emission factors that are orders of magnitude higher than the lubricant and aramid fibre.
|
|
| 166. |
- Wahlström, Anna, et al.
(författare)
-
Specific binding of a beta cyclodextrin dimer to the amyloid beta peptide modulates the peptide aggregation process
- 2012
-
Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 51:21, s. 4280-4289
-
Tidskriftsartikel (refereegranskat)abstract
- Alzheimer's disease involves progressive neuronal loss. Linked to the disease is the amyloid beta (A beta) peptide, a 38-43-amino acid peptide found in extracellular amyloid plaques in the brain. Cyclodextrins are nontoxic, cone-shaped oligosaccharides with a hydrophilic exterior and a hydrophobic cavity making them suitable hosts for aromatic guest molecules in water. beta-Cyclodextrin consists of seven alpha-D-glucopyranoside units and has been shown to reduce the level of fibrillation and neurotoxicity of A beta. We have studied the interaction between A beta and a beta-cyclodextrin dimer, consisting of two beta-cyclodextrin monomers connected by a flexible linker. The beta-cyclodextrin monomer has been found to interact with A beta(1-40) at sites Y10, F19, and/or F20 with a dissociation constant (K-D) of 3.9 +/- 2.0 mM. Here H-1-N-15 and H-1-C-13 heteronuclear single-quantum correlation nuclear magnetic resonance (NMR) spectra show that in addition, the beta-cyclodextrin monomer and dimer bind to the histidines. NMR translational diffusion experiments reveal the increased affinity of the beta-cyclodextrin dimer (apparent K-D of 1.1 +/- .5 mM) for A beta(1-40) compared to that of the beta-cyclodextrin monomer. Kinetic aggregation experiments based on thioflavin T fluorescence indicate that the dimer at 0.05-5 mM decreases the lag time of A beta aggregation, while a concentration of 10 mM increases the lag time. The beta-cyclodextrin monomer at a high concentration decreases the lag time of the aggregation. We conclude that cyclodextrin monomers and dimers have specific, modulating effects on the A beta(1-40) aggregation process. Transmission electron microscopy shows that the regular fibrillar aggregates formed by A beta(1-40) alone are replaced by a major fraction of amorphous aggregates in the presence of the beta-cyclodextrin dimer.
|
|
| 167. |
|
|
| 168. |
- Wahlström, Jens, et al.
(författare)
-
A cellular automaton approach to numerically simulate the contact situation in disc brakes
- 2011
-
Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 42:3, s. 253-262
-
Tidskriftsartikel (refereegranskat)abstract
- Since brake wear is an important contributor to the concentration of airborne particles in urban atmospheres, it is important to increase our understanding of the origin of these particles. The contact situation between the pad and disc is complicated. Metal fibres in the pad (or other hard materials) form stable contact plateaus, which carry the main part of the load. A flow of wear particles in the boundary layer between the pad and disc partially stack up against these plateaus (and increase their area), and some will escape from the contact and become airborne. The purpose of this article is to investigate the possibility to numerically simulate the contact situation in the boundary layer between the pad and disc and the amount of wear that leaves the contact using a cellular automaton approach. To do so, the contact pressure, pad temperature and wear are determined in that order. Based on these results, the creation, growth and destruction of contact plateaus are simulated using a cellular automaton model. Finally, the amount of wear that leaves the contact is determined. The simulated behaviour of the contact situation correlates qualitatively with experimental observations found in the literature.
|
|
| 169. |
|
|
| 170. |
- Wahlström, Jens, 1979-
(författare)
-
A comparison of measured and simulated friction, wear, and particle emission of disc brakes
- 2015
-
Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 92, s. 503-511
-
Tidskriftsartikel (refereegranskat)abstract
- Airborne wear particles originating from disc brakes are among the main contributors to non-exhaust emissions. The macroscopic wear behaviour of disc brakes can be explained by the growth and destruction of mesoscopic contact plateaus. The pad wear and temperature has earlier been simulated using a cellular automaton mesoscopic approach. The present paper seeks to refine the simulation approach to include disc wear and temperature, and to investigate the validity of this approach by comparing simulated brake events with a dyno bench test. The comparison shows a promising qualitative correlation between the simulated and the experimental results.
|
|
