Fracture strength of class II slot cavities restored with polymerizable restorative materials

This study compared the fracture strength of Class II slot cavities restored with polymerizable restorative materials. Sixty, caries-free, posterior teeth were divided into five groups of 12 teeth. The Class II slot cavities were prepared. The teeth were restored with two packable composites (Filtek P60, Surefil), a microhybrid composite (Filtek Z250)and two ormocer (Definite, Admira). The restorations were then subjected to fracture resistance tests. The marginal ridges of the restorations were loaded at an angle of 13.5° to the long axis of the tooth in an Universal Testing Machine until failure. Analysis of mean forces indicated that, Filtek P60, Surefil and Filtek Z250 exhibited better performance than Definite and Admira. The tested resin composites differed in their mechanical properties. This study suggested that fracture behavior were highly influenced by the filler system. Overall, Filtek P60, Surefil, Filtek Z250, demonstrated good fracture resistance. Copyright © 2003 John Wiley & Sons, Ltd.     

Finding Robust Solutions Using Local Search

This paper investigates how a local search metaheuristic for continuous optimisation can be adapted so that it finds broad peaks, corresponding to robust solutions. This is relevant in problems in which uncertain or noisy data is present. When using a genetic or evolutionary algorithm, it is standard practice to perturb solutions once before evaluating them, using noise from a given distribution. This approach however, is not valid when using population-less techniques like local search and other heuristics that use local search. For those algorithms to find robust solutions, each solution needs to be perturbed and evaluated several times, and these evaluations need to be combined into a measure of robustness. In this paper, we examine how many of these evaluations are needed to reliably find a robust solution. We also examine the effect of the parameters of the noise distribution. Using a simple tabu search procedure, the proposed approach is tested on several functions found in the literature. This revised version was published online in August 2006 with corrections to the Cover Date.     

An anisotropic fibre-network model for mechano-sorptive creep in paper

In this paper a simplified network model for mechano-sorptive creep is presented, which is a further development of an earlier paper [Strömbro, J., Gudmundson, P., 2008. Mechano-sorptive creep under compressive loading – a micromechanical model. International Journal of Solids and Structures 45 (9), 2420–2450.]. It is assumed that the anisotropic hygroexpansion of the fibres leads to large stresses at the fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive effects in compression than in tension. Moisture dependent material parameters and anisotropy in the fibre distribution have been introduced. Theoretical predictions based on the model are compared to experimental results for an anisotropic paper both under tensile and compressive loading at varying moisture content and it is found that the important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined.     

Pulsed laser deposition of atomically flat La1-xSrxMnO3 thin films using a novel target geometry

A new ablation target geometry is presented that was used to produce thin films of La_1-xSr_xMnO₃ grown heteroepitaxially on SrTiO₃ by pulsed reactive crossed-beam laser ablation. The films were grown in order to perform angle-resolved photoelectron spectroscopy, which demands that the surface be atomically flat. In situ and ex situ analysis shows that this condition was met, even after depositing to a thickness of over 100 nm. PACS 61.10.-i; 61.18.Bn; 68.47.Gh; 71.27.+a; 81.15.Fg     

Study of ferroelectric switching by domain-wall induced light scattering

Measurements of 90°-scattering of weak laser light are used to investigate pulsed domain switching in ferroelectrics. The studies were performed on strontium-barium niobate (SBN) single crystals. A good agreement of the switching parameters estimated from the optical measurements with those obtained by means of conventional electrical methods proves the validity of the optical method for switching studies. Due to the limited scattering volume in all three spatial dimensions, the method facilitates local probing of the switching within the crystal bulk. In particular, local specialities of the domain density can be detected. Furthermore, the excellent time resolution inherent in optical probing techniques allows for a comprehensive study of the dynamics.     

Large-scale nonlocality in “doubly special relativity” with an energy-dependent speed of light

There are two major alternatives for violating the (usual) Lorentz invariance at large (Planckian) energies or momenta—either not all inertial frames (in the Planck regime) are equivalent (e.g., there is an effectively preferred frame) or the transformations from one frame to another are (nonlinearly) deformed (“doubly special relativity”). We demonstrate that the natural (and reasonable) assumption of an energy-dependent speed of light in the latter method goes along with violations of locality/separability (and even translational invariance) on macroscopic scales.     

Untersuchungen über Radium- und Bariumfällungen unter Anwendung von Thorium X als Indikator

Zusammenfassung Zunächst wird im Zusammenhang mit Messungen der Fällungsgeschwindigkeit von Thorium X in sulfathaltigen Lösungen eine Methode beschrieben, die es gestattet, während der Fällung, und zwar ohne Störung des Fällungsvorganges, diejenigen Mengen von Thorium X zu bestimmen, die sich jeweils zu bestimmten Zeitpunkten noch in Lösung befinden; dabei konnte der Gehalt an Th X mit Hilfe einer Emanationsmethode genau ermittelt werden.Die Versuchsergebnisse, die in Kurven wiedergegeben sind, lassen deutlich erkennen, daß die Fällung von Th X nicht momentan erfolgt, sondern eine gewisse Zeit beansprucht, die von der Konzentration der zugesetzten Sulfat- und Bariumchloridlösung sowie vom Zusatz anderer Fremdionen abhängig ist; es wird jedoch schließlich immer der gleiche Endzustand vollständiger Ausfällung erreicht, wenn mit äquivalenten Mengen gearbeitet wird.Die Annahme, daß die Fällung momentan erfolgt, daß aber das Fällungsprodukt sich im Laufe der Zeit von einem feinkristallinischen Zustand mit großer Emanierfähigkeit in einen grobkristallinen mit geringer Emanationsabgabe umwandelt, konnte durch besondere Experimente widerlegt werden.Schließlich wird noch eine Apparatur zur Messung des Thorongehalts angegeben, die auch für Untersuchungen des Thoriumgehalts von Quellwässern Anwendung finden kann.

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Summary A method has been worked out which makes it possible to determine the rate of precipitation of thorium X in solutions containing sulphate ion. The amount of thorium X is determined rapidly and accurately by the thorium emanation—thoron—evolved under fixed conditions. Determinations have been made every 5 minute during the time following precipitation, and the results are given graphically.They bring forward, very clearly, that the precipitation of thorium X requires a certain length of time, depending on the concentration of the sulphate and barium-chloride solutions used and on the presence of other ions. However, if equivalent quantities of barium- and sulphate ions are used, the same final result is always reached.It might have been supposed that the precipitation takes place instantaneously but that in course of time, the precipitate undergoes changes through recrystallisations and that the emanating power changes accordingly. That hypothesis, however, could be disproved by special experiments.At last an apparatus for measuring the thoron content is given which can also be applied for investigations of the thorium content of source waters.

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Résumé Les auteurs décrivent une méthode qui leur a permis de déterminer la vitesse de précipitation du thorium X en solutions contenant de l'ion sulfurique. Le thorium X est dosé par son émanation — le thoron — sous des conditions fixées, et les dosages peuvent se faire à intervalles régulières pendant le temps que demande la précipitation.Les résultats montrent que la précipitation du thorium X ne se fait point à l'instant, mais demande un certain temps, dépendant de la concentration des solutions de sulfate et de chlorure de baryum ajoutées et aussi de la présence d'ions étrangers.Les auteurs réfutent par leurs expériences la théorie que la précipitation se fait momentanément et que le précipité change peu à peu son état cristallin et par cela même, sa faculté de dégager l'émanation.Enfin les auteurs décrivent un appareil pour les dosages de thoron, qui pourra servir de même pour déterminer la teneur en thorium dans les eaux vives.