| 1. |
- Loy, Francesco, et al.
(författare)
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Morphological evidence that pentagastrin regulates secretion in the human parotid gland
- 2012
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Ingår i: Journal of Anatomy. - : Wiley. - 0021-8782 .- 1469-7580. ; 220, s. 447-453
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Tidskriftsartikel (refereegranskat)abstract
- Salivary secretion is principally regulated by autonomic nerves. However, recent evidence from in vivo animal experiments suggests that gastrointestinal peptide hormones can also influence saliva production. The aim of the present study was to define the secretagogue activity of the gastrin-analogue pentagastrin in human salivary glands. For this purpose, parotid tissues were exposed to pentagastrin in vitro. Morphological techniques were used to evaluate modifications to serous acinar cells associated with secretion. Using a variant of the osmium maceration method, high resolution scanning electron microscopy allowed assessment of the morphology of the cytoplasmic aspect of the plasmalemma to demonstrate secretory activity. To quantify responses to pentagastrin, we recorded morphometric data on microvilli, microbuds, and protrusions. Dose-dependent morphological changes were observed, whereas protein concentration increased in the incubate. The use of selective receptor antagonists showed pentagastrin to act principally via cholecystokinin-A receptors. The morphological responses observed following exposure to pentagastrin differed from those elicited following exposure to the pan-muscarinic agonist carbachol. This study provides the first demonstration of a direct secretory action of gastrointestinal peptides on salivary glands in humans. © 2012 The Authors. Journal of Anatomy © 2012 Anatomical Society.
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| 2. |
- Nicolas, Aude, et al.
(författare)
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Genome-wide Analyses Identify KIF5A as a Novel ALS Gene
- 2018
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Ingår i: Neuron. - : Cell Press. - 0896-6273 .- 1097-4199. ; 97:6, s. 1268-1283.e6
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Tidskriftsartikel (refereegranskat)abstract
- To identify novel genes associated with ALS, we undertook two lines of investigation. We carried out a genome-wide association study comparing 20,806 ALS cases and 59,804 controls. Independently, we performed a rare variant burden analysis comparing 1,138 index familial ALS cases and 19,494 controls. Through both approaches, we identified kinesin family member 5A (KIF5A) as a novel gene associated with ALS. Interestingly, mutations predominantly in the N-terminal motor domain of KIF5A are causative for two neurodegenerative diseases: hereditary spastic paraplegia (SPG10) and Charcot-Marie-Tooth type 2 (CMT2). In contrast, ALS-associated mutations are primarily located at the C-terminal cargo-binding tail domain and patients harboring loss-of-function mutations displayed an extended survival relative to typical ALS cases. Taken together, these results broaden the phenotype spectrum resulting from mutations in KIF5A and strengthen the role of cytoskeletal defects in the pathogenesis of ALS.
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| 3. |
- Riva, Gabriele, et al.
(författare)
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A CFD study of a pin-on-disc tribometer setup focusing on airborne particle sampling efficiency
- 2017
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Ingår i: ECOTRIB 2017.
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Konferensbidrag (refereegranskat)abstract
- One of the most important measures to evaluate air quality is the presence of particles. Pin-on-disc tribometers are used to study airborne wear particles originating from different sliding contacts in a controlled laboratory environment. One important aspect when measuring airborne particles is to ensure isokinetic sampling conditions. Another important aspect is that the concentration and the particles distribution entering the sampling probe are representative for the emissions generated. It is therefore important to have an estimation of the sampling efficiency of the test system. The aim of this paper is to investigate the particle sampling efficiency of a pin-on-disc tribometer setup. In addition, a modified sampling setup that allows isokinetic sampling is investigated. CFD simulations to investigate air and particle motion were performed for both the existing and the modified configuration. The results show that the velocity field at the outlet does not allow isokinetic sampling for the existing configuration. In the modified configuration a sampling pipe is used to make isokinetic sampling possible. A comparison between the two configurations show that the modified configuration increases the sampling efficiency with almost 40% for ultrafine particles and about 20% for fine and coarse particles. It remains to validate the CFD simulations with experiments.
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| 4. |
- Riva, Gabriele, et al.
(författare)
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A finite element analysis (FEA) approach to simulate the coefficient of friction of a brake system starting from material friction characterization
- 2021
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Ingår i: Friction. - : Springer Science and Business Media LLC. - 2223-7690 .- 2223-7704. ; 9:1, s. 191-200
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Tidskriftsartikel (refereegranskat)abstract
- The coefficient of friction (COF) is one of the most important parameters to evaluate the performance of a brake system. To design proper brake systems, it is important to know the COF when estimating the brake force and resulting torque. It is challenging to simulate the COF since friction in disc brakes is a complex phenomenon that depends on several parameters such as sliding velocity, contact pressure, materials, and temperatures, etc. There is a lack of studies found in the literature focusing on simulation of the COF for a full brake system based on tribometer material characterization. The aim of this work is therefore to investigate the possibility to use a finite element analysis (FEA) approach combined with a COF pv-map to compute the global COF of a disc brake system. The local COF is determined from a pv-map for each local sliding velocity and contact pressure determined by the FEA. Knowing the local COF, the braking force of the entire brake system and the global COF can be evaluated. Results obtained by the simulation are compared with dyno bench test of the same brake system to investigate the validity of the simulation approach. Results show that the simulation is perfectly in line with the experimental measurements in terms of in-stop COF development, but slightly higher with a positive offset for every braking.
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| 5. |
- 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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| 6. |
- Riva, Gabriele, et al.
(författare)
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A Multi-Scale Simulation Approach to Investigate Local Contact Temperatures for Commercial Cu-Full and Cu-Free Brake Pads
- 2019
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Ingår i: Lubricants. - Basel : MDPI. - 2075-4442. ; 7:9
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Tidskriftsartikel (refereegranskat)abstract
- Copper from vehicles disc brakes is one main contributor of the total copper found in the environment. Therefore, the U.S. Environmental Protection Agency (EPA) and the automotive industries started the Copper-Free Brake Initiative. The pad friction material is essentially composed of a binder, fillers, reinforcing fibres and frictional additives. Copper and brass fibres are the most commonly used fibres in brake pads. There is a need to understand how the contact temperature distribution will change if copper-based fibres are changed to steel fibres. The aim of this work is, therefore, to investigate how this change could influence the local contact temperatures. This is done by developing a multi-scale simulation approach which combines cellular automaton, finite element analysis (FEA) and computational fluid dynamics (CFD) approaches with outputs from inertia brake dyno bench tests of Cu-full and Cu-free pads. FEA and thermal-CFD are used to set the pressure and the temperature boundary conditions of the cellular automaton. The outputs of dyno tests are used to calibrate FEA and CFD simulations. The results of the study show lower peaks in contact temperature and a more uniform temperature distribution for the Cu-free pad friction material.
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| 7. |
- Riva, Gabriele, et al.
(författare)
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A NUMERICAL STUDY OF DISC BRAKES WEAR DEPENDENCE OF ROTOR SURFACE COATING
- 2018
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Konferensbidrag (refereegranskat)abstract
- Airborne emissions from disc brakes adversely affect the air quality in urban areas of EU. The emissions come from the wear of the pads and rotors in disc brakes. The wear of disc brakes depends on the contact situation between the pads and rotors. During braking, secondary contact plateaus are created on both the pads and rotors contact surfaces. Literature reports numerical studies of the creation of contact plateaus on the pad surface but no numerical studies known to the authors have taken into consideration the creation of contact plateaus on the rotor surface. Furthermore, experimental studies reported in the literature shows that secondary plateaus are created in the low-lands of the rotor contact surface and that this affects the wear performance. In particular, it has been reported that the creation of secondary plateaus on coated rotors have a relatively large affect the wear and emissions. The aim of this study is therefore to numerically investigate how the creation of contact plateaus on the rotor surface could affect the disc brake wear performance. This is done by expanding an existing simulation tool used for simulation of friction, wear and particle emission, which takes into account the creation of contact plateaus on the pad surface, to include creation of contact plateaus on the rotor surface. One rotor surface that corresponds to a cast iron rotor is compared with one rotor surface that corresponds to a coated rotor. The results are qualitatively in line with observations done in pin-on-disc tribometer tests. It remains to validate the numerical results with data obtained in experiments.
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| 8. |
- Riva, Gabriele, 1988-, et al.
(författare)
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An FEA approach to simulate disc brake wear and airborne particle emissions
- 2019
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 138, s. 90-98
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Tidskriftsartikel (refereegranskat)abstract
- Emissions from disc brake wear adversely affect the air quality in cities. Finite Element Analysis (FEA) approaches focussing on the macroscopic wear of pads and rotors can be found in the literature, but none of these take the wear and emission dependence of the local contact pressure and sliding speed into account. The aim of the present study is to further develop an FEA approach for simulation of macroscopic wear and airborne emission to include the dependences of local contact pressure and sliding speed by implementing wear and emission maps obtained by pin-on-disc tribometer tests. Results from a dyno bench test are compared with simulated results. The simulated rotor and pads wear, and airborne emissions are in line with the measured values.
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| 9. |
- Riva, Gabriele, et al.
(författare)
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Simulation of Contact Area and Pressure Dependence of Initial Surface Roughness for Cermet-Coated Discs Used in Disc Brakes
- 2019
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Ingår i: Tribology in Industry. - : Faculty of Engineering, University of Kragujevac. - 0354-8996 .- 2217-7965.
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Tidskriftsartikel (refereegranskat)abstract
- Friction, wear, and emission performance strongly depend on the contact pressure and area at the interface of the pad and disc. The contact situation at the pad-to-disc interface can be explained by the formation and destruction of mesoscopic sized contact plateaus on the pad surface. Experimental studies report that the initial surface roughness of cermet-coated discs strongly affects friction, wear and emission performance. This is explained by the formation of secondary plateaus on the disc surface. The aim of this work is to extend an existing cellular automaton approach to include the formation of secondary plateaus on the disc surface in order to explain experimental results reported in the literature. First, to investigate the validity of the novel simulation approach, a cermet-coated cast iron disc is tested against a low-met pad material with a pin-on-disc tribometer. The same conditions are used as input in a simulation. Then, the initial disc roughness influence on contact pressure and area of the same cermet-coated disc is compared with results reported in the literature. The topographies of the measured and simulated disc surfaces are qualitatively in line. An initial rougher disc surface results in a considerably lower contact area than does a smother surface.
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| 10. |
- Varriale, Francesco, et al.
(författare)
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A Brake System Coefficient of Friction Estimation Using 3D Friction Maps
- 2022
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Ingår i: Lubricants. - : MDPI AG. - 2075-4442. ; 10:7
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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.
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