Comparing double-step and penalty-based semirecursive formulations for hydraulically actuated multibody systems in a monolithic approach

The simulation of mechanical systems often requires modeling of systems of other physical nature, such as hydraulics. In such systems, the numerical stiffness introduced by the hydraulics can become a significant aspect to consider in the modeling, as it can negatively effect to the computational efficiency. The hydraulic system can be described by using the lumped fluid theory. In this approach, a pressure can be integrated from a differential equation in which effective bulk modulus is divided by a volume size. This representation can lead to numerical stiffness as a consequence of which time integration of a hydraulically driven system becomes cumbersome. In this regard, the used multibody formulation plays an important role, as there are many different procedures for the constraint enforcement and different sets of coordinates to choose from. This paper introduces the double-step semirecursive approach and compares it with a penalty-based semirecursive approach in case of coupled multibody and hydraulic dynamics within the monolithic framework. To this end, hydraulically actuated four-bar and quick-return mechanisms are analyzed as case studies. The two approaches are compared in terms of the work cycle, energy balance, constraint violation, and numerical efficiency of the mechanisms. It is concluded that the penalty-based semirecursive approach has a number of advantages compared with the double-step semirecursive approach, which is in accordance with the literature.

     

On the reaction mechanism of L-lactate oxidase: quantitative structure-activity analysis of the reaction with para-substituted L-mandelates

The rate constants for reduction of the flavoenzyme, L-lactate oxidase, and a mutant (in which alanine 95 is replaced by glycine), by a series of para-substituted mandelates, in both the 2-1H- and 2-2H- forms, have been measured by rapid reaction spectrophotometry. In all cases, significant isotope effects (1H/2H = 3-7) on the rate constants of flavin reduction were found, indicating that flavin reduction is a direct measure of alpha-C-H bond breakage. The rate constants show only a small influence of the electronic characteristics of the substituents, but show a good correlation when combined with some substituent volume parameters. A surprisingly good correlation is found with the molecular mass of the substrate. The results are compatible with any mechanism in which there is little development of charge in the transition state. This could be a transfer of hydride to the flavin N(5) position or a synchronous mechanism in which the alpha-C-H is formally abstracted as a H+ while the resulting charge is simultaneously neutralized by another event.     

Effects of KW-3902, a selective and potent adenosine A1 receptor antagonist, on renal hemodynamics and urine formation in anesthetized dogs

Smyth line (SL) chickens develop a spontaneous, autoimmune, posthatch loss of pigment cells (vitiligo) in regenerating feather tissue. Smyth line vitiligo (SLV) is associated with lymphocyte infiltrations prior to and throughout the development of the disorder. It was the purpose of this study to determine the type, relative amounts, and proportions of pulp-infiltrating lymphocytes at various times throughout the growth of regenerating feathers. Feathers were plucked from 8-week-old chickens with and without SLV. Feather pulp cell suspensions were prepared when the regenerating feathers were 2, 3, 4, and 6 weeks of age. Cells were fluorescently labeled using a panel of mouse monoclonal antibodies specific for chicken lymphocytes. Both T and B cells infiltrated the feather pulp of chickens with SLV. T cell levels remained elevated throughout the 6 weeks of feather growth, while B cell levels steadily declined to control levels over the same time. The pulp-infiltrating cells were primarily T cells with an alphabeta T cell receptor expressing the Vbeta1 gene (TCR2+). The ratio between CD4+ and CD8+ cells was 1.42 and 0.75 in 2- and 6-week-old regenerating feathers from chickens with autoimmune SLV, respectively. In non-vitiliginous chickens this ratio was always near 1. These data suggest that TCR2+ T cells play an important role in SLV. CD4+ cells may play a recruiting/activating role, whereas CD8+ cells may have cytotoxic activity specifically directed against melanocytes. Additionally, this is the first report demonstrating the infiltration of B cells into the feather pulp of vitiliginous chickens. These B cells may directly/indirectly contribute to melanocyte destruction in SLV.     

On the cosimulation of multibody systems and hydraulic dynamics

Multibody System Dynamics - The simulation of mechanical devices using multibody system dynamics (MBS) algorithms frequently requires the consideration of their interaction with components of a...     

Microstructure and dielectric response of (Ba,Sr)TiO3 filler-dispersed resin composites

Resin-matrix composites dispersing low-loss dielectric ceramic filler have received a considerable interest for high-frequency application, because of their good shape flexibility and controllable dielectric properties. In this study, (Ba,Sr)TiO₃-type ceramic particles have been synthesized by KCl molten salt method to serve as filler particle for resin-matrix dielectric composite. Dielectric measurement confirmed that the composite fabricated by tape-casting demonstrated two times higher dielectric constant of 50.4 than the other composites fabricated by direct-casting using a metal mold. Pore-size distribution as well as ceramic filler content was strongly correlated with the formation of electrical flux in the composites to enhance dielectric constant.     

Profile of polyunsaturated fatty acids produced by Thraustochytrium sp. KK17-3

More than 300 strains of microorganisms producing polyunsaturated fatty acids (PUFA) were newly isolated from coastal seawater in the Seto Inland Sea and around Iriomote Island, Japan, by the baiting method. The profiles of PUFA from docosahexaenoic acid (DHA)-producing strains could be classified into four types. A strain, named KK17-3, was chosen for further study owing to its high DHA content (52.1% of total fatty acid) and wide range of PUFA (76.1%) including arachidonic, eicosapentaenoic, and docosapentaenoic acids as well as DHA. Glucose and tryptone were the optimal carbon and nitrogen sources, respectively, in a medium with salinity at 75% that of seawater. The PUFA contents in polar lipids (22.1% of total lipid), in which the DHA content was 39.3%, were higher than those in neutral lipids and glycolipids. Molecular phylogenetic analysis of 18S rRNA gene sequences showed KK17-3 to be a thraustochytrid. It also was observed to possess a life cycle composed of vegetative cells without successive bipartition, zoosporangium, and zoospore stage. Classification by the chemotaxonomic criterion based on PUFA compositions also supported this assignment.     

Effect of transurethral resection on serum free/total prostate-specific antigen levels in patients with benign prostatic hyperplasia

Endotoxin-induced early inflammatory reactions may inhibit the function and survival of isolated cells or cell aggregates after transplantation. By the chromogenic Limulus amebocyte lysate assay we found rather high but variable endotoxin concentrations in the chemicals used for islet isolation, i.e. collagenase and Ficoll. Liberase, a special collagenase preparation from Boehringer, was nearly endotoxin-free. Correlating to the endotoxin content, collagenase and Ficoll had the capacity to induce interleukin-1beta release from human peripheral blood mononuclear cells. Because collagenase and density gradient media are needed in most cell isolation procedures from solid organs, each lot of these chemicals should be tested for endotoxin contamination. In pancreatic islet transplantation, the use of endotoxin-free chemicals may diminish early local inflammatory reactions at the graft site and thereby reduce the number of islets needed for successful islet transplantation.     

Analysis of short fibres orientation in steel fibre-reinforced concrete (SFRC) by X-ray tomography

The mechanical properties of fibre composite materials are largely determined by the orientation of fibres within the matrix. Which orientation distribution short fibres follow in different parts of a structural element is still a subject for research and discussions in the scientific community. In this article, we present a modern and advanced method for measuring the orientation of short fibres in steel fibre-reinforced concrete (SFRC) by X-ray microtomography. With this method, a voxel image of the fibres is obtained directly in 3D, and the orientation of each individual fibre is calculated based on a skeletonized representation of this image. Scans of 12 SFRC samples, taken from the central height region of real-size floor slabs, reveal the fibres to be mostly horizontally oriented near the centre of a floor slab and more vertically oriented near the edge; here the alignment with the formwork dominates. The fibre orientation distributions are characterized by several orientation parameters as quantitative measures for the alignment. On the practical side, this method has the potential to be incorporated into the development and production process of SFRC structures to verify how the fibres contribute to capacity.