| 1. |
- Almqvist, Torbjörn, et al.
(författare)
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A comparison between computational fluid dynamic and Reynolds approaches for simulating transient EHL line contacts
- 2004
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Ingår i: Tribology International. - 0301-679X .- 1879-2464. ; 37:1, s. 61-69
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Tidskriftsartikel (refereegranskat)abstract
- When simulating elastohydrodynamic lubrication (EHL), the Reynolds equation is the predominating partial differential equation for prediction of the fluid flow. Also very few attempts have been carried out using the full momentum and continuity equations separately. The aim of this investigation is to compare two different approaches for simulation of EHL line contacts where a single ridge travels through an EHL conjunction. One of the approaches is based on the Reynolds equation, addressing the coupling between the pressure and the film thickness. The solver uses the advantages of multilevel techniques to speed up the convergence rate. The other approach is based on commercial CFD software. The software uses the momentum and continuity equations in their basic form, enabling numerical simulations outside the contact regions, as well as in the thin film region to be carried out. The numerical experiments show that, under the running conditions chosen, only small deviations between the two approaches can be observed. The results are encouraging from several viewpoints: validation of the codes, the possibilities of further developments of the CFD approach and the justification of using a Reynolds approach under the running conditions chosen
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| 2. |
- Aberg, V., et al.
(författare)
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Synthesis and absolute configuration of methyl(-)-(3R)-8-(4-bromophenyl)-7-(naphthalen-1-yl-methyl)-5-oxo-2,3-dihydro-5H-thiazolo 3,2-a pyridine-3-carboxylate
- 2002
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Ingår i: Acta Crystallographica Section E. - : International Union of Crystallography (IUCr). - 1600-5368. ; 58, s. o812-o814
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Tidskriftsartikel (refereegranskat)abstract
- The title molecule, C26H20BrNO3S, contains a ring-fused 2-pyridinone framework substituted with a 4-bromo-phenyl-, a naphthalen-1-ylmethyl and a methoxycarbonyl substituent. The main goal of this work was to confirm the stereochemistry for the methoxycarbonyl substituent, which proved to be 3R. Moreover, the 4-bromophenyl substituent was shown to be rotated out of the plane of the 2-pyridinone ring, with a torsion angle of 61.2 (5)degrees. To allow the best packing arrangement, the naphthalen-1-ylmethyl substituent is positioned to mediate an intermolecular pi-pi interaction.
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| 3. |
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| 4. |
- Almqvist, Andreas
(författare)
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Rough surface elastohydrodynamic lubrication and contact mechanics
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the field of tribology, there are numerous theoretical models that may be described mathematically in the form of integro-differential systems of equations. Some of these systems of equations are sufficiently well posed to allow for numerical solutions to be carried out resulting in accurate predictions. This work has focused on the contact between rough surfaces with or without a separating lubricant film. The objective was to investigate how surface topography influences contact conditions. For this purpose two different numerical methods were developed and used. For the lubricated contact between rough surfaces the Reynolds equation were used as a basis. This equation is derived under the assumptions of thin fluid film and creeping flow. In highly loaded, lubricated, non- conformal contacts of surfaces after running-in, the load concentration no longer results in plastic deformations, however large elastic deformations will be apparent. It is the interaction between the hydrodynamic action of the lubricant and the elastic deformations of the surfaces that, in certain applications, enable the lubricant film to fully separate the surfaces. This is commonly referred to as full film elastohydrodynamic (EHD) lubrication. Typical machine elements that operates in the full film EHD lubrication (FL) regime include rolling element bearings, cams and gears. Unfortunately, a cost effective way of machining engineering surfaces seldom results in a surface topography that influence contact conditions in the same way as a surface after running-in. Such topographies may prevent the lubricant from fully separating the surfaces because of deteriorated hydrodynamic action. In this case the applied load is carried in part by the lubricant and in part by surface asperities and/or surface active lubricant additives. This could also be the case in lubricant starved contacts, which is a common situation in not only grease lubricated contacts but also in many liquid lubricated contacts, such as high speed operating rolling element bearings. The load sharing between the highly compressed lubricant and the surface and/or surface active lubricant additives is the reason why this lubrication regime is most commonly referred to as mixed EHD lubrication (ML). Machine elements that while running operate in the FL regime may experience a transition into the ML regime at stops or due to altered operating conditions. It is not possible to simulate direct contact between the surfaces using a numerical method based on Reynolds equation. A parameter study, of elementary surface features passing each other inside the EHD lubricated conjunction, was performed. The results obtained, even though no direct contact could be simulated, does indicate that a transition from the FL to the ML regime would occur for certain combinations of the varied parameters. At start-ups, the contact in a rolling element bearing could be both starved and drained from lubricant. In this case the hydrodynamic action becomes negligible in terms of load carrying capacity. The load is carried exclusively by surface asperities and/or surface active lubricant additives. This regime is referred to as boundary lubrication (BL). Operation conditions could also make both FL and ML impossible to achieve, for example, in the case in a low rpm operating rolling element bearing. The BL regime is in this work modeled as the unlubricated frictionless contact between rough surfaces, i.e., a dry contact approach. A variational principle was used in which the real area of contact and contact pressure distribution are those which minimize the total complementary energy. A linear elastic-perfectly plastic deformation model in which energy dissipation due to plastic deformation is accounted for was used. The dry contact method was applied to the contact between four different profiles and a plane. The variation in the real area of contact, the plasticity index and some surface roughness parameters due to applied load were investigated. The surface roughness parameters of the profiles differed significantly.
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| 5. |
- Almqvist, Andreas, et al.
(författare)
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The effect of two-sided roughness in rolling/sliding EHL line contacts
- 2004
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Ingår i: Transient processes in tribology. - Amstersam : Elsevier. - 0444517065
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Konferensbidrag (refereegranskat)abstract
- In most theoretical studies carried out to date on the effect of surface roughness in elastohydrodynamic lubrication (EHL) one surface is considered smooth and one as being rough. In real tribological contacts however, both surfaces normally have similar roughness heights. When modelling a rolling contact it is possible to simply sum the roughness of the two contact surfaces but in a sliding EHL contact, a continuously changing effective surface roughness occurs. The aim of this work was to investigate the influence of elementary surface features such as dents and ridges on the film thickness and pressure. This was done numerically using transient non-Newtonian simulations of an EHL line contact using a coupled smoother combined with a multilevel technique. Four different "overtaking" phenomena were investigated; ridge-ridge, dent-ridge, ridge-dent, and dent-dent. It was shown that the minimum film-thickness produced by a ridge is further reduced in a dent-ridge overtaking event. The squeeze effect seen in the ridge-ridge case resulted in large deformations and film-thickness heights comparable to the corresponding smooth case just before the overtaking event occurred. These local effects arising from simulating two-sided roughness were compared to simulations using a traditional "one-sided rough surface contacting a perfectly smooth surface.".
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| 6. |
- Larsson, Andreas, 1972-
(författare)
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Antiadhesive agents targeting uropathogenic Escherichia coli : Multivariate studies of protein-protein and protein-carbohydrate interactions
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes studies directed towards development of novel antiadhesive agents, with particular emphasis on compounds that prevent attachment of bacteria to a host-cell. Three different proteins involved in the assembly or function of adhesive pili in uropathogenic Escherichia coli have been targeted either by rational structure based design or statistical molecular methods. A library of substituted galabiose (Galα1-4Gal) derivatives was screened for binding to the E. coli adhesin PapG in an assay based on surface plasmon resonance, and for inhibition of Streptococcus suis adhesins PN and PO in a hemagglutination assay. The results were used to generate QSAR models which had good predictive powers and provided further insight in the structural requirements needed for high affinity binding. 2-pyridones and amino acid derivatives were modelled into the binding site of chaperones involved in pilus assembly in E. coli and a heuristic method, VALIDATE, was used for affinity prediction. The affinity of the compounds for the chaperones PapD and FimC were assessed in assays based on surface plasmon resonance and relaxation-edited NMR spectroscopy. Their ability to disrupt chaperone/subunit complexes was investigated in vitro through a FPLC assay and their capacity to inhibit pilus formation in vivo was determined via hemagglutination and confirmed with atomic force microscopy. Statistical molecular design was used to design a diverse peptide library targeting pili subunits, and an ELISA was developed to investigate the ability of the peptides to inhibit chaperone/subunit complexation. The resulting QSAR model provided extensive information regarding binding of the peptides to the subunits. Because the peptides were suggested to bind in an extended β-strand formation, β-strand mimetics consisting of oligomeric enaminones were designed. Finally, new methods to synthesize enaminone building blocks were developed using microwave assisted chemistry. The projects described have generated compounds that besides their value as leads for developing novel antibacterial agents, also constitute new chemical tools to study the mechanisms underlying bacterial virulence.
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| 7. |
- Pemberton, Nils, et al.
(författare)
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Microwave-assisted synthesis of highly substituted aminomethylated 2-pyridones
- 2004
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Ingår i: Journal of Organic Chemistry. - Easton, Pa. : American Chemical Society. - 0022-3263 .- 1520-6904. ; 69:23, s. 7830-7835
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Tidskriftsartikel (refereegranskat)abstract
- By employing microwave-assisted organic synthesis (MAOS) efficient conditions to introduce aminomethylene substituents in highly substituted bicyclic 2-pyridones have been established. Primary amino methylene substituents were introduced via a cyanodehalogenation followed by a borane dimethyl sulfide reduction of the afforded nitrile. In both of these transformations, microwave irradiation proved to be superior to traditional conditions and the primary amines were obtained in good overall yields (55-58% over three steps). To incorporate tertiary aminomethylene substituents in the 2-pyridone framework, a microwave-assisted Mannich reaction using preformed iminium salts proved to be effective. Thus highly substituted 2-pyridones were obtained in 48-93% yields.
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| 8. |
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