Thermal/mechanical simulation and laboratory fatigue testing of an alternative yttria tetragonal zirconia polycrystal core-veneer all-ceramic layered crown design

This study evaluated the stress levels at the core layer and the veneer layer of zirconia crowns (comprising an alternative core design vs. a standard core design) under mechanical/thermal simulation, and subjected simulated models to laboratory mouth-motion fatigue. The dimensions of a mandibular first molar were imported into computer-aided design (CAD) software and a tooth preparation was modeled. A crown was designed using the space between the original tooth and the prepared tooth. The alternative core presented an additional lingual shoulder that lowered the veneer bulk of the cusps. Finite element analyses evaluated the residual maximum principal stresses fields at the core and veneer of both designs under loading and when cooled from 900 degrees C to 25 degrees C. Crowns were fabricated and mouth-motion fatigued, generating master Weibull curves and reliability data. Thermal modeling showed low residual stress fields throughout the bulk of the cusps for both groups. Mechanical simulation depicted a shift in stress levels to the core of the alternative design compared with the standard design. Significantly higher reliability was found for the alternative core. Regardless of the alternative configuration, thermal and mechanical computer simulations showed stress in the alternative core design comparable and higher to that of the standard configuration, respectively. Such a mechanical scenario probably led to the higher reliability of the alternative design under fatigue.

Effect of framework design on crown failure

This study evaluated the effect of core-design modification on the characteristic strength and failure modes of glass-infiltrated alumina (In-Ceram) (ICA) compared with porcelain fused to metal (PFM). Premolar crowns of a standard design (PFMs and ICAs) or with a modified framework design (PFMm and ICAm) were fabricated, cemented on dies, and loaded until failure. The crowns were loaded at 0.5 mm min(-1) using a 6.25 mm tungsten-carbide ball at the central fossa. Fracture load values were recorded and fracture analysis of representative samples were evaluated using scanning electron microscopy. Probability Weibull curves with two-sided 90% confidence limits were calculated for each group and a contour plot of the characteristic strength was obtained. Design modification showed an increase in the characteristic strength of the PFMm and ICAm groups, with PFM groups showing higher characteristic strength than ICA groups. The PFMm group showed the highest characteristic strength among all groups. Fracture modes of PFMs and of PFMm frequently reached the core interface at the lingual cusp, whereas ICA exhibited bulk fracture through the alumina core. Core-design modification significantly improved the characteristic strength for PFM and for ICA. The PFM groups demonstrated higher characteristic strength than both ICA groups combined.

Lattice-dome design using a knowledge-based system approach

In the design of lattice domes, design engineers need expertise in areas such as configuration processing, nonlinear analysis, and optimization. These are extensive numerical, iterative, and lime-consuming processes that are prone to error without an integrated design tool. This article presents the application of a knowledge-based system in solving lattice-dome design problems. An operational prototype knowledge-based system, LADOME, has been developed by employing the combined knowledge representation approach, which uses rules, procedural methods, and an object-oriented blackboard concept. The system's objective is to assist engineers in lattice-dome design by integrating all design tasks into a single computer-aided environment with implementation of the knowledge-based system approach. For system verification, results from design examples are presented.

Assessment of matrix metalloproteinase (MMP)-2, MMP-8, MMP-9, and their inhibitors, the tissue inhibitors of metalloproteinase (TIMP)-1 and TIMP-2 in obese children and adolescents

Objectives: To compare the circulating levels of matrix metalloproteinase (MMP)-8, pro-MMP-2, pro-MMP-9, and total MMP-9, their endogenous inhibitors, the tissue inhibitors of metalloproteinases (TIMP)-1 and TIMP-2, and the MMP-8/TIMP-1, MMP-9/TIMP-1, and MMP-2/TIMP-2 ratios in normotensive obese children and adolescents with those found in non obese children and adolescents. Design and methods: We studied 40 obese and 40 non obese (controls) children and adolescents in this cross-sectional study. MMP and TIMP concentrations were measured in plasma samples by gelatin zymography and ELISA. Results: Obese children and adolescents had higher circulating MMP-8 concentrations, lower plasma TIMP-1 concentrations, and higher MMP-8/TIMP-1 ratios than non obese controls (P < 0.05). We found no differences in pro-MMP-9 or total MMP-9 levels, or in MMP-9/TIMP-1 ratios between groups (P > 0.05). While we found no significant differences in pro-MMP-2 levels (P > 0.05) obese Subjects had higher TIMP-2 concentrations and lower pro-MMP-2/TIMP-2 ratios (P < 0.05) than non obese controls. Conclusions: In conclusion, we found evidence indicating higher net MMP-8 (but not MMP-9 and MMP-2) activity in childhood obesity. The increased MMP-8 levels found in obese children suggest a possibly relevant pathophysiological mechanism that may be involved in the increase of cardiovascular risk associated with childhood obesity. (c) 2009 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.

Influence of shaft design on the shaping ability of 3 nickel-titanium rotary systems by means of spiral computerized tomography

Objective. To evaluate the influence of shaft design on the shaping ability of 3 rotary nickel-titanium (NiTi) systems. Study design. Sixty curved mesial canals of mandibular molars were used. Specimens were scanned by spiral tomography before and after canal preparation using ProTaper, ProFile, and ProSystem GT rotary instruments. One-millimeter-thick slices were scanned from the apical end point to the pulp chamber. The cross-sectional images from the slices taken earlier and after canal preparation at the apical, coronal, and midroot levels were compared. Results. The mean working time was 137.22 +/- 5.15 s. Mean transportation, mean centering ratio, and percentage of area increase were 0.022 +/- 0.131 mm, 0.21 +/- 0.11, and 76.90 +/- 42.27%, respectively, with no statistical differences (P > .05). Conclusions. All instruments were able to shape curved mesial canals in mandibular molars to size 30 without significant errors. The differences in shaft designs seemed not to affect their shaping capabilities.

Considerations in the design of a mixed-method cluster evaluation of a community programme for 'at-risk' young people

This article discusses the design of a comprehensive evaluation of a community development programme for young people 'at-risk' of self-harming behaviour. It outlines considerations in the design of the evaluation and focuses on the complexities and difficulties associated with the evaluation of a community development programme. The challenge was to fulfil the needs of the funding body for a broad, outcome-focused evaluation while remaining close enough to the programme to accurately represent its activities and potential effects at a community level. Specifically, the strengths and limitations of a mixed-method evaluation plan are discussed with recommendations for future evaluation practice.

Earth pressure on cantilever walls at design retained heights

There are many methods for the analysis and design of embedded cantilever retaining walls. They involve various different simplifications of the pressure distribution to allow calculation of the limiting equilibrium retained height and the bending moment when the retained height is less than the limiting equilibrium value, i.e. the serviceability case. Recently, a new method for determining the serviceability earth pressure and bending moment has been proposed. This method makes an assumption defining the point of zero net pressure. This assumption implies that the passive pressure is not fully mobilised immediately below the excavation level. The finite element analyses presented in this paper examine the net pressure distribution on walls in which the retained height is less, than the limiting equilibrium value. The study shows that for all practical walls, the earth pressure distributions on the front and back of the wall are at their limit values, Kp and K-a respectively, when the lumped factor of safety F-r is less than or equal to2.0. A rectilinear net pressure distribution is proposed that is intuitively logical. It produces good predictions of the complete bending moment diagram for walls in the service configuration and the proposed method gives results that have excellent agreement with centrifuge model tests. The study shows that the method for determining the serviceability bending moment suggested by Padfield and Mair(1) in the CIRIA Report 104 gives excellent predictions of the maximum bending moment in practical cantilever walls. It provides the missing data that have been needed to verify and justify the CIRIA 104 method.

Design, modelling and analysis of a six component force balance for hypervelocity wind tunnel testing

A combination of modelling and analysis techniques was used to design a six component force balance. The balance was designed specifically for the measurement of impulsive aerodynamic forces and moments characteristic of hypervelocity shock tunnel testing using the stress wave force measurement technique. Aerodynamic modelling was used to estimate the magnitude and distribution of forces and finite element modelling to determine the mechanical response of proposed balance designs. Simulation of balance performance was based on aerodynamic loads and mechanical responses using convolution techniques. Deconvolution was then used to assess balance performance and to guide further design modifications leading to the final balance design. (C) 2001 Elsevier Science Ltd. All rights reserved.

Category-theoretic fibration as an abstraction mechanism in information systems

This paper examines the problem of establishing a formal relationship of abstraction and refinement between abstract enterprise models and the concrete information systems which implement them. It introduces and justifies a number of reasonableness requirements, which turn out to justify the use of category theoretic concepts, particularly fibrations, to precisely specify a semantics for enterprise models which enables them to be considered as abstractions of the conceptual models from which the implementing information systems are built. The category-theoretic concepts are developed towards the problem of testing whether a system satisfies the fibration axioms, and are applied to case studies to demonstrate their practicability.

Contrasting Epstein-Barr virus-specific cytotoxic T cell responses to HLA A2-restricted epitopes in humans and HLA transgenic mice: implications for vaccine design

This study investigates the hierarchy of cytotoxic T cell (CTL) responses to twelve HLA A2-restricted epitopes from the latent, lytic and structural proteins of Epstein–Barr virus (EBV) in acute infectious mononucleosis and in healthy seropositive donors and the relative immunogenecity of these epitopes in transgenic mice. Responses to the lytic epitope were uniformly strong in all healthy seropositive individuals and acute infectious mononucleosis donors while moderate or low responses were observed to the latent and structural epitopes, respectively in both groups studied. In contrast, when HLA A2/Kb transgenic mice were immunised with these peptide epitopes, CTL responses were observed to all epitopes with a maximal response to the epitopes within the structural proteins and low to moderate responses to the latent epitopes. This hierarchy of CTL responses in mice was also reflected in an MHC stabilisation analysis. These contrasting CTL responses in humans following natural infection compared to the immunogenicity of these epitopes and their ability to stabilise MHC may need to be considered when designing an EBV vaccine.

Discovery and structure of a potent and highly specific blockerof insect calcium channels

We have isolated a novel family of insect-selective neurotoxins that appear to be the most potent blockers of insect voltage-gated calcium channels reported to date. These toxins display exceptional phylogenetic specificity, with at least a 10,000-fold preference for insect versus vertebrate calcium channels. The structure of one of the toxins reveals a highly structured, disulfide-rich core and a structurally disordered C-terminal extension that is essential for channel blocking activity. Weak structural/functional homology with omega -agatoxin-IVA/B, the prototypic inhibitor of vertebrate P-type calcium channels, suggests that these two toxin families might share a similar mechanism of action despite their vastly different phylogenetic specificities.

The cystine knot motif in toxins and implications for drug design

The cystine knot structural motif is present in peptides and proteins from a variety of species, including fungi, plants, marine molluscs. insects and spiders. It comprises an embedded ring formed by two disulfide bonds and their connecting backbone segments which is threaded by a third disulfide bond. It is invariably associated with nearby beta-sheet structure and appears to be a highly efficient motif for structure stabilization. Because of this stability it makes an ideal framework for molecular engineering applications. In this review we summarize the main structural features of the cystine knot motif, focussing on toxin molecules containing either the inhibitor cystine knot or the cyclic cystine knot. Peptides containing these motifs are 26-48 residues long and include ion channel blockers, haemolytic agents, as well as molecules having antiviral and antibacterial activities. The stability of peptide toxins containing the cystine knot motif, their range of bioactivities and their unique structural scaffold can be harnessed for molecular engineering applications and in drug design. Applications of cystine knot molecules for the treatment of pain. and their potential use in antiviral and antibacterial applications are described. (C) 2000 Elsevier Science Ltd. All rights reserved.

Toxicity and uptake mechanism of cylindrospermopsin and lophyrotomin in primary rat hepatocytes

The toxicities and uptake mechanisms of two hepatotoxins, namely cylindrospermopsin and lophyrotomin, were investigated on primary rat hepatocytes by using microcystin-LIZ (a well-known hepatotoxin produced by cyanobacteria) as a comparison. Isolated rat hepatocytes were incubated with different concentrations of hepatotoxins for 0, 24, 48 and 72 h. The cell viability was assayed by the tetrazolium-based (MTT) assay. Microcystin-LR, cylindrospermopsin and lophyrotomin all exhibited toxic effects on the primary rat hepatocytes with 72-h LC50 of 8, 40 and 560 ng/ml, respectively. The involvement of the bile acid transport system in the hepatotoxin-induced toxicities was tested in the presence of two bile acids, cholate and taurocholate. Results showed that the bile acid transport system was responsible for the uptake, and facilitated the subsequent toxicities of lophyrotomin on hepatocytes. This occurred to a much lesser extent with cylindrospermopsin. With its smaller molecular weight, passive diffusion might be one of the possible mechanisms for cylindrospermopsin uptake into hepatocytes. This was supported by incubating a permanent cell line, KB (devoid of bile acid transport system), with cylindrospermopsin which showed cytotoxic effects. No inhibition of protein phosphatase 2A by cylindrospermopsin or lophyrotomin was found. This indicated that other toxic mechanisms besides protein phosphatase inhibition were producing the toxicities of cylindrospermopsin and lophyrotomin, and that they were unlikely to be potential tumor promoters. (C) 2001 Elsevier Science Ltd. All rights reserved.