Chemical characterization of in vivo aged zinc phosphate dental cements

The chemical composition of zinc phosphate dental cements aged in vivo was studied. Twenty-seven samples aged 2 to 43 years were investigated using X-ray diffraction, infrared spectroscopy, ³¹P nuclear magnetic resonance spectroscopy, thermogravimetric analysis and differential scanning calorimetry. Evidence for the presence of zinc oxide, amorphous zinc phosphate, water of hydration and crystalline zinc phosphate tetrahydrate was found. The latter was identified as hopeite; it was present in 92% of the cements studied. No correlation with time concerning either the chemical structure of the components or their relative amounts was found. Zinc phosphate dental cements show very good chemical stability on long-term use.     

High-cycle fatigue monitoring in AgClxBr1-x fibres using absorption spectroscopy

The spectral transmittance of mixed silver-halide polycrystalline fibres was measured while they were undergoing repeated bending leading to mechanical fatigue. Microscopic mechanical defects were detected through their influence on the optical losses, without interfering with the deformation. Optical and mechanical lifetimes of the fibres were found to depend on the composition and to be larger for highly-mixed compositions. Scanning electron microscopy observations of fatigued fibres revealed a strong influence of the fibre composition on the fatigue damage. This dependence on the composition was explained using a theoretical model of solid-solution strengthening. This revised version was published online in November 2006 with corrections to the Cover Date.     

Thermal feedback control techniques for transistor-transistor logic triggered CO(2) laser used for irradiation of biological tissue utilizing infrared fiber-optic radiometry

A fiber-optic radiometer is used to monitor and control, in real time, the temperature of samples of biological tissue irradiated with a CO(2) laser. Several control algorithms are investigated and the optimal control mode is obtained. A silver halide infrared fiber is used both to deliver the CO(2) laser radiation needed to irradiate the target and to deliver the thermal radiation emitted from the target back to the radiometer. Such a system can be useful in medical applications of CO(2) lasers.     

Real and Ideal Institutional Frameworks for Managing the Common Arab-Israeli Water Resources

The Oslo A and B agreements of September 1993 and September 1995 were the beginning of a process aimed at a peaceful resolution of the Arab-Israeli conflict. The Israeli-Jordanian Treaty of 1994 addresses issues of water sharing between the two parties. In 1995, Israel and the Palestinians signed an Agreement on Water and Sewage as part of their Interim Agreement. In February 1996, Israel, Jordan, and the Palestinians agreed to a “Declaration of Principles for Joint Development of Water Resources.” The purpose of this paper is to compare the components of the two Agreements with an “ideal” institution for management of shared water resources. The “ideal” institution was formulated by 23 water experts who were interviewed on this issue. The main finding is that in most respects, expert opinions did not differ significantly from the Israeli-Jordanian Treaty of Peace and the Israeli-Palestinian Interim Agreement.     

Analyses of activity design in geometry in the light of student actions

Abstract

The goal of this study is to show that inquiry activities in a dynamic geometry environment, intentionally designed to confront students with contradictions and uncertainties, push them towards explanations that include deductive elements. Three different but dependent aspects of the activities are characterized and analysed: The epistemological, which includes all possible inquiry paths; the didactic, which involves only those paths that reflect the intention of the designer; and the cognitive, which accounts for actual student actions (conjectures and explanations) and their analyses. The research conclusions are based on the interplay among these three aspects. The analysis of students’ investigations and the analysis of their explanations fulfil, to a broad extent, the design goals.     

pH-metric study of the setting reaction of monocalcium phosphate monohydrate/calcium oxide-based cements

Hydraulic calcium phosphate cements (CPCs) that are used as osseous substitutes, set by an acid–base reaction between an acid calcium phosphate and a basic calcium salt (often a phosphate). In order to gain a better understanding of the setting of the monocalcium phosphate monohydrate–calcium oxide cement that we developed and in the aim to improve its mechanical properties, the setting reaction was studied by pH-metry. The two methods described in the literature were used. In the first, cement samples were prepared then crushed after different storage periods at 37 °C, 100% RH. The powder was then immersed in pure water with stirring and the pH was measured after equilibration. In the second technique, the starting materials were poured into water while stirring and the pH were followed over time. The two methods gave different results. The first procedure provided information concerning the pH of the surrounding liquid following the partial dissolution of the cement components, rather than any information about pH changes during setting. The second method is more appropriate to follow the pH variations during setting. In this second procedure, the effects of different parameters such as crushing time, stirring rate, liquid-to-powder (L/P) ratio and temperature were investigated. These parameters may impact substantially on the shape and position of the pH=f(t) curves. One or three pH jumps were observed during the setting depending on the composition of the liquid phase. The time at which these pH jumps occurred depended on the pH of the liquid phase, the concentration of the buffer, the crushing of starting materials, the L/P ratio and the temperature. Good linear correlations were obtained (i) between the time of the pH jumps and the L/P ratio and the temperature and (ii) between the time of the first pH jump and the compressive strength and the final setting time of the cements prepared with different liquid phases. It may be assumed in view of these correlations that the results obtained in dilute solution may be extrapolated to the conditions of cement sample preparation and that the mechanical properties of the cement are directly related to the phenomena that occur at the first pH jump which corresponds to precipitation of dicalcium phosphate dihydrate.     

Mid-infrared diffused planar waveguides made of silver halide chloro-bromide

We have developed waveguides for the mid-IR spectrum using silver halide crystals. Diffused planar waveguides constructed from silver chlorobromide (AgClBr) with different diffusion thicknesses were designed and characterized. The waveguides were based on our changing the refractive index of the guiding layer by a diffusion of Br- ions into crystalline AgCl substrates. The waveguides were analyzed and investigated with a 10.6-microm CO2 laser, and the optically measured thicknesses of the waveguides were found to vary between 65 and 600 microm. The propagation losses were in the range of 4-16 dB/cm, and the maximal entrance angle was 62 degrees. The output beam distribution was measured and was in good correlation with a numerical analysis simulation based on a ray-tracing model, by use of the eikonal equation.     

Overload, autonomy, and burnout as predictors of physicians' quality of care.

A model in which perceived overload and burnout mediated the relations of workload and autonomy with physicians' quality of care to their patients was examined. The study was based on data from 890 specialists representing six medical specialties. Including global burnout as well as its three first-order facets of physical fatigue, cognitive weariness, and emotional exhaustion improved the fit between the structural model and the data relative to an alternative model that included only global burnout. Workload (number of work hours) indirectly predicted quality of care through perceived overload. Additionally, the authors found that the paths from the first order factors of emotional exhaustion, physical fatigue, and cognitive weariness predicted quality of care negatively, positively, and nonsignificantly, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)