Suspension system performance optimization with discrete design variables

Suspension systems on commercial vehicles have become an important feature meeting the requirements from costumers and legislation. The performance of the suspension system is often limited by available catalogue components. Additionally the suspension performance is restricted by the travel speed which highly influences the ride comfort. In this article a suspension system for an articulated dump truck is optimized in sense of reducing elapsed time for two specified duty cycles without violating a certain comfort threshold level. The comfort threshold level is here defined as a whole-body vibration level calculated by ISO 2631-1. A three-dimensional multibody dynamics simulation model is applied to evaluate the suspension performance. A non-gradient optimization routine is used to find the best possible combination of continuous and discrete design variables including the optimum operational speed without violating a set of side constraints. The result shows that the comfort level converges to the comfort threshold level. Thus it is shown that the operational speed and hence the operator input influences the ride comfort level. Three catalogue components are identified by the optimization routine together with a set of continuous design variables and two operational speeds one for each load case. Thus the work demonstrates handling of human factors in optimization of a mechanical system with discrete and continuous design variables.     

Estimation of forming limit diagrams by the use of the finite element method and Monte Carlo simulation

A stochastic finite element-based approach for forming limit calculations of sheets is proposed and evaluated. Material inhomogeneities are represented by spatial thickness variations of the sheet which are modelled by the use of random fields. The effects of changing the smoothness, wavelengths, amplitude and anisotropy of the field realisations on the forming limit diagram are investigated. Further, the effects of the patch size and plastic anisotropy on the forming limit diagram are studied. The assumed thickness variations result in a quite wide scatter band, and changes of the characteristics of the thickness field result in changes of the shape and variance of the forming limit diagram.     

Potentiometric determination of the chloride ion activity in cement based materials

The chloride content at the reinforcement is one of the decisive factors for the initiation and propagation of localised corrosion in concrete structures. A monitoring technique for the chloride concentration which is accurate, non-destructive and continuous would thus be highly desirable. For this reason, the performance of ion selective electrodes (ISEs) was investigated both in alkaline solutions and embedded in mortar. The Ag/AgCl electrodes used in this work showed Nernstian behaviour with a slope of –59 ± 1 mV per decade and a detection limit for chloride ions below 10^?2 mol dm^?3 even at pH close to 14; the selectivity coefficient for hydroxide interference was estimated at \( k_{{{\text{Cl}}^{ - } ,{\text{OH}}^{ - } }}^{\text{pot}} \approx 4 \cdot 10^{ - 3} \). The Ag/AgCl membranes show good long-term stability over more than 6 months even in highly alkaline solutions as long as chloride ions are present; in the complete absence of chloride the measured potentials were affected by the pH of the solution. The sensors are, however, able to recover fast as soon as they come into contact with chloride. When using ISEs embedded in concrete, diffusion potentials between the reference electrode and the ISE, as arising e.g. from gradients in pH, significantly affect the potential measurement and present a most important error source for the application of direct potentiometry to concrete. To minimise such errors, the reference electrode has to be positioned as close to the ISE as possible.     

Synthesis and structural studies of “branched” 2-linked trisaccharides related to h-type 2 blood group determinants

A series of fucosylated trisaccharides l-Fuc-(1→2)-ß-d-Gal-(1→4)-ß-X-OMe (1-6, X = d-GlcNAc, d-Qui (6-deoxy-Glc), d-Xyl) related to H type 2 blood group determinant have been synthesized both as their α- and ß- L-Fuc anomers together with the component disaccharide starting compounds (7-11). The conformational properties of the trisaccharides together with their parent disaccharides have been investigated by NMR spectroscopy (proton and carbon chemical shifts and proton NOEs) in combination with computer modeling using the Monte Carlo approach and the HSEA force field using the GEGOP program with the main focus on the α-linked fucose series. The series of compounds allow for the investigation of interaction between the sugar units in the—in principle—linear structures, which in practice behave as branched trisaccharides. The interaction between the terminal fucose unit and the unit at the reducing end has been probed by substitution of the bulky CH₂OH group with CH₃ and H substituents, respectively. Compounds with severe steric interactions can be identified by the non-additivity of their carbon chemical shifts and subsequently confirmed by the detailed conformational assessment by NOEs and computer modeling. The most severe contacts arise in the GlcNAc and Qui trisaccharide series, whereas the Xyl-containing trisaccharide derivatives only exhibit weak steric interaction as probed by the NMR parameters.     

Pore solution composition and chloride binding capacity of silica-fume cement pastes

Samples of the capillary pore solution, associated with hardened cement pastes containing various proportions of silica-fume and sodium chloride, have been expressed at different stages of curing and analysed to determine concentrations of dissolved ions. The results indicate that partial replacement of Portland cement by increasing percentages of silica-fume causes a regular decrease in alkalinity of the pore solution and a reduction in the chloride-binding capacity of the material. Possible implications regarding the level of corrosion protection afforded to embedded steel are considered.

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Résumé On a préparé des échantillons de pates de ciment Portland mélangé dans diverses proportions de poids à de la poudre de silice (0–30%) avec une proportion constante d'eau, équivalente à 50% des poids combinés du ciment et de la poudre de silice. Dans certains cas, l'eau du mélange contenait du chlorure de sodium en quantités qui correspondaient à 0,4 ou 1% d'ions de chlorure, exprimés en pourcentages des poids combinés du ciment et de la poudre de silice. On a traité les pates dans des récipients scellés pendant des périodes allant jusqu'à 84 jours, puis on les a transférées dans une enceinte en acier spécial, dans laquelle la pression a été appliquée à des niveaux permettant d'exprimer en millimètres les solutions interstitielles capillaires et de les recueillir. On a effectué l'analyse par des méthodes de routine pour déterminer les concentrations dissoutes de Na⁺, K⁺, Ca²⁺, OH⁻, Cl⁻, SO ₄ ²⁻ . On a aussi évalué les quantités d'eau non évaporable dans des échantillons, afin de calculer les proportions du contenu total de chlorure dans les matériaux qui sont restés dissous. Les résultats ont indiqué que le remplacement partiel du ciment Portland par des pourcentages croissants de poudre de silice causait une diminution régulière de l'alcalinité des solutions interstitielles et une réduction de la capacité du matériau servant à lier le chlorure. On a attribué ce dernier effet à l'influence du pH de la solution sur la solubilité de 3CaO.Al₂O₃.CaCl₂.1OH₂O et on a démontré la validité de point de vue au moyen de l'analyse thermale. On a considéré la signification des résultats vis-à-vis du degré de protection de l'armature contre la corrosion et on a constaté qu'un certain nombre de questions demandait de nouvelles recherches.

     

Identification of Novel Fragments Binding to the PDZ1-2 Domain of PSD-95

Inhibition of PSD-95 has emerged as a promising strategy for the treatment of ischemic stroke, as shown with peptide-based compounds that target the PDZ domains of PSD-95. In contrast, developing potent and drug-like small molecules against the PSD-95 PDZ domains has so far been unsuccessful. Here, we explore the druggability of the PSD-95 PDZ1-2 domain and use fragment screening to investigate if this protein is prone to binding small molecules. We screened 2500 fragments by fluorescence polarization (FP) and validated the hits by surface plasmon resonance (SPR), including an inhibition counter-test, and found four promising fragments. Three ligand efficient fragments were shown by ¹H,¹⁵N HSQC NMR to bind in the small hydrophobic P⁰ pockets of PDZ1-2, and one of them underwent structure-activity relationship (SAR) studies. Overall, we demonstrate that fragment screening can successfully be applied to PDZ1-2 of PSD-95 and disclose novel fragments that can serve as starting points for optimization towards small-molecule PDZ domain inhibitors.     

Diffusion potentials as source of error in electrochemical measurements in concrete

Condition assessment or controlling systems for cathodic protection of reinforced concrete structures are usually based on potential measurements. In case of permanent monitoring systems, reference electrodes are embedded in the concrete, whereas for occasional investigations external reference electrodes are normally used and placed on the concrete surface. However, ionic concentration gradients between the inner solution of the reference electrode and the concrete pore solution give rise to liquid junction potentials. In addition, internal gradients in pH or chloride content, as well as permselective properties of the cement paste lead to membrane potentials. Although these phenomena are usually not considered to be significant, they might be underestimated in many cases and lead to misinterpretation of measurement results. This is especially important with regard to applications of potentiometric sensors such as chloride or pH sensors, where accurate potential readings are fundamental. This article presents the theoretical background and summarises available literature with regard to diffusion potentials in concrete. Liquid junction potentials between various solutions have been measured experimentally. Practical consequences and possible attempts to minimise measurement errors are discussed.     

Probabilistic considerations on the effect of specimen size on the critical chloride content in reinforced concrete

A probabilistic model was used to predict the critical chloride content (C_crit) for reinforcement corrosion as a function of specimen size. The specimen size is likely to be a reason for the large scatter of C_crit values as well as for the high threshold levels often observed in laboratory setups. Regarding test methods, it is discussed that the common combination of small specimens and low numbers of parallel samples results in poor reproducibility. If experimental data is to be used for service life modelling, the geometrical dimensions of the specimens on which C_crit was measured have to be taken into account.