Anisotropic adaptivity for the finite element solutions of three-dimensional convection-dominated problems

Convection-dominated problems are typified by the presence of strongly directional features such as shock waves or boundary layers. Resolution of numerical solutions using an isotropic mesh can lead to unnecessary refinement in directions parallel to such features. This is particularly important in three dimensions where the grid size increases rapidly during conventional isotropic refinement procedures. In this work, we investigate the use of adaptive finite element methods using anisotropic mesh refinement strategies for convection-dominated problems. The strategies considered here aim to resolve directional features without excessive resolution in other directions, and hence achieve accurate solutions more efficiently. Two such strategies are described here: the first based on minimization of the least-squares residual; the second based on minimizing a finite element error estimate. These are incorporated into an hr-adaptive finite element method and tested on a simple model problem

A multilevel approach for obtaining locally optimal finite element meshes

In this paper we consider the adaptive finite element solution of a general class of variational problems using a combination of node insertion, node movement and edge swapping. The adaptive strategy that is proposed is based upon the construction of a hierarchy of locally optimal meshes starting with a coarse grid for which the location and connectivity of the nodes is optimized. This grid is then locally refined and the new mesh is optimized in the same manner. Results presented indicate that this approach is able to produce better meshes than those possible by more conventional adaptive strategies and in a relatively efficient manner

Effect of Additives on Mineral Trioxide Aggregate Setting Reaction Product Formation

Introduction Mineral trioxide aggregate (MTA) sets via hydration of calcium silicates to yield calcium silicate hydrates and calcium hydroxide (Ca[OH]2). However, a drawback of MTA is its long setting time. Therefore, many additives have been suggested to reduce the setting time. The effect those additives have on setting reaction product formation has been ignored. The objective was to examine the effect additives have on MTA\u27s setting time and setting reaction using differential scanning calorimetry (DSC). Methods MTA powder was prepared with distilled water (control), phosphate buffered saline, 5% calcium chloride (CaCl2), 3% sodium hypochlorite (NaOCl), or lidocaine in a 3:1 mixture and placed in crucibles for DSC evaluation. The setting exothermic reactions were evaluated at 37°C for 8 hours to determine the setting time. Separate samples were stored and evaluated using dynamic DSC scans (37°C→640°C at10°C/min) at 1 day, 1 week, 1 month, and 3 months (n = 9/group/time). Dynamic DSC quantifies the reaction product formed from the amount of heat required to decompose it. Thermographic peaks were integrated to determine enthalpy, which was analyzed with analysis of variance/Tukey test (α = 0.05). Results Isothermal DSC identified 2 main exothermal peaks occurring at 44 ± 12 and 343 ± 57 minutes for the control. Only the CaCl2 additive was an accelerant, which was observed by a greater exothermic peak at 101 ± 11 minutes, indicating a decreased setting time. The dynamic DSC scans produced an endothermic peak around 450°C–550°C attributed to Ca(OH)2 decomposition. The use of a few additives (NaOCl and lidocaine) resulted in significantly less Ca(OH)2 product formation. Conclusions DSC was used to discriminate calcium hydroxide formation in MTA mixed with various additives and showed NaOCl and lidocaine are detrimental to MTA reaction product formation, whereas CaCl2 accelerated the reaction

Baltic cod reproduction in the Gotland Basin: annual variability and possible causes

Baltic cod spawning takes place in the deep basins and reproduction success is mainly related to environmental conditions (salinity and oxygen regimes, i.e. the 'reproduction volume'). Due to the Baltic Sea heterogeneity, cod reproduction success in the Southem and Centrat Baltic spawning grounds can differ significantly. Recent oceanographic changes i.e. decrease of water exchange and stagnation, as weil as a strong reduction of spawning stock caused the diminishing of the reproduction potential of the Gotland spawning grounds. The Gotland spawning grounds belong to four main cod spawning sites in the Baltic and historical analyses revealed that abundant generations of Baltic cod were produced when successful cod reproduction took place also in the Gotland Basin. Analyses of revised reproduction volume estimates for the Gotland Basin taking into account the spatial structure of hydrology in the basin during stagnation and aeration periods reveals high seasonal and inter-annual variability. To describe changes of abundance and distribution of the spawning stock and the recruits in relation to hydrographic conditions, results from trawl surveys carried out in 1975-1998 in the Gotland Deep are analyzed. In this analysis, the reproduction volume is used as a proxy for the environmental conditions

Mineral Trioxide Aggregate Material Use in Endodontic Treatment: A Review of the Literature

Objective The purpose of this paper was to review the composition, properties, biocompatibility, and the clinical results involving the use of mineral trioxide aggregate (MTA) materials in endodontic treatment. Methods Electronic search of scientific papers from January 1990 to August 2006 was accomplished using PubMed and Scopus search engines (search terms: MTA, GMTA, WMTA, mineral AND trioxide AND aggregate). Results Selected exclusion criteria resulted in 156 citations from the scientific, peer-reviewed dental literature. MTA materials are derived from a Portland cement parent compound and have been demonstrated to be biocompatible endodontic repair materials, with its biocompatible nature strongly suggested by its ability to form hydroxyappatite when exposed to physiologic solutions. With some exceptions, MTA materials provide better microleakage protection than traditional endodontic repair materials using dye, fluid filtration, and bacterial penetration leakage models. In both animal and human studies, MTA materials have been shown to have excellent potential as pulp-capping and pulpotomy medicaments but studies with long-term follow-up are limited. Preliminary studies suggested a favorable MTA material use as apical and furcation restorative materials as well as medicaments for apexogenesis and apexification treatments; however, long-term clinical studies are needed in these areas. Conclusion MTA materials have been shown to have a biocompatible nature and have excellent potential in endodontic use. MTA materials are a refined Portland cement material and the substitution of Portland cement for MTA products is presently discouraged. Existing human studies involving MTA materials are very promising, however, insufficient randomized, double-blind clinical studies of sufficient duration exist involving MTA for all of its clinical indications. Further clinical studies are needed in these areas

A pilot study on occurrence of Yersinia enterocolitica and Yersinia pseudotuberculosis in Latvian pigs at slaughtering

The aim of the study was to detect the distribution of presumptive pathogenic Yersinia spec1es in pigs of Latvian origm. In total tonsils of 108 pigs were collected from 6 farms m two abattoirs situated in different parts of Latvia. Samples were investigated by using direct plating on the selective CIN media and cold enrichment technique for 2 weeks. All presumptive isolates were confirmed biochemically. During the direct plating only 58% of cultures of Y.enterocolitica and 4 Y. pseudotuberculosts were recovered. Y. enterocolitica was isolated from the pig tonsil samples orig1nated from all six farms The distribution of positive samples among different farms varied from 15 to 45%. Y. pseudotuberculosis was recovered from 3 out of 6 herds studied rangmg from 5 to 25% on each positive farm. The mean prevalence of Y.enterocolitica and Y. pseudotuberculosis in all six farms was 31% and 8% respectively Results of study indicate that none of the investigated herds was free of potentially pathogenic Yersinia. The presence of Yersinia species in pigs indicates that a possibility for contamination with bacteria occurs during the offal removal of and meat mspection of carcasses. Further investigations on pathogenic properties and slaughtenng techniques at the slaughterhouses involved in this study should be continued

Automated prototyping tool-kit (APT)

Automated prototyping tool-kit (APT) is an integrated set of software tools that generate source programs directly from real-time requirements. The APT system uses a fifth-generation prototyping language to model the communication structure, timing constraints, I/O control, and data buffering that comprise the requirements for an embedded software system. The language supports the specification of hard real-time systems with reusable components from domain specific component libraries. APT has been used successfully as a research tool in prototyping large war-fighter control systems (e.g. the command-and-control station, cruise missile flight control system, patriot missile defense systems) and demonstrated its capability to support the development of large complex embedded software. © 2002 Elsevier Science Inc. All rights reserved

Structure, Composition, and Mechanical Properties of Australian Orthodontic Wires

Objective: To investigate the surface morphology, structure, elemental composition, and key mechanical properties of various sizes and tempers of Australian wires. Materials and Methods: Three types of Australian wire were used: 0.016″ regular, 0.018″ regular+, and 0.018″ special+ (A.J. Wilcock, Whittlesea, Victoria, Australia). Each type of wire was subjected to scanning electron microscopy (SEM) analysis, x-ray energy dispersive spectroscopy (EDS) investigation, Vickers hardness testing, and tensile testing. The modulus of elasticity and ultimate tensile strength were determined. Hardness, modulus, and strength data were analyzed with one-way analysis of variance (ANOVA) and Tukey testing at the .05 level of significance. Results: All three types of Australian wire were found to possess considerably rough surfaces with striations, irregularities, and excessive porosity. All three wire types had high levels of carbon and a similar hardness, which ranged within 600 VHN (Vickers hardness number), and a similar modulus of elasticity (173 to 177 GPa). The 0.018″ special+ had a significantly lower tensile strength (1632 MPa) than the 0.016″ regular and the 0.018″ regular+ wire (2100 MPa). Conclusions: Australian wires did not show variation implied by the size or temper of the wires