Ageing of calcium silicate cements for endodontic use in simulated body fluids: a micro‐Raman study

To evaluate bioactivity properties, a calcium silicate experimental cement (wTC) and a phosphate‐doped wTC cement (wTC‐TCP) were aged for different times (1–180 days) at 37 °C in two simulated body fluids, i.e. Dulbecco's phosphate buffered saline (DPBS) and Hank's balanced salt solution (HBSS). The cements were analyzed by micro‐Raman spectroscopy to investigate the presence of calcium phosphate deposits and the composition changes as a function of the storage time (hydration of anhydrite/gypsum and formation of ettringite; hydration of belite/alite and formation of hydrated silicates). After 1 day of ageing in DPBS, the two cements already showed a different behavior: only the surface of wTC‐TCP cement showed the band at 965 cm⁻¹, suggesting the formation of a detectably thick calcium phosphate deposit. The trend of the I₉₆₅/I₉₉₀ Raman intensity ratio indicated the formation of a meanly thicker apatite deposit on the wTC‐TCP cement until 90 days. After 60 days of ageing in DPBS, the thickness of the apatite deposit on wTC and wTC‐TCP was about 200 and 500 µm, respectively, whereas at 180 days, the two cements did not appear significantly different (thickness of about 900 µm). The bioactivity of both cements in HBSS was less pronounced than in DPBS, according to the lower phosphate concentration of HBSS; at the same time, higher amounts of calcite were found on the surface of both cements. The wTC‐TCP cement showed a higher bioactivity in this medium also; after 180 days, the thickness of the apatite deposit on wTC and wTC‐TCP was < 50 µm and about 100 µm, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Revision of the model of a fibril with amorphous nodules for oriented soft-chain semicrystalline polymers

A critical analysis of literature data about calculations of small-angle x-ray scattering (SAXS) from a model of a fibril with amorphous nodules (FAN) is made. Changes in the SAXS patterns are reviewed for the effect of stretching the FAN. Possibilities of using the calculation results for interpretation of microdeformational behavior of oriented, flexible chain semicrystalline polymers are analyzed. Invoking the FAN model, a retrospective analysis of some literature data and also analysis of new experimental results obtained by SAXS and wide-angle x-ray scattering methods for oriented samples of cellulose triacetate, poly(vinylidene fluoride-co-hexafluoropropylene), and poly(vinyl alcohol) are carried out.     

Diffusion and Einstein relation for a massive particle in a one-dimensional free fas: Numerical evidence

A computer simulation is used to investigate the motion of a marked particle of massM in a free gas of particles with massm=1, for large times. Previous results seem to indicate a non-Wiener behavior for the rescaled trajectory whenMm. The results reported here, with better statistics, are compatible with the Wiener hypothesis. The Einstein relation between mobility and diffusion coefficient is also investigated. The results indicate that it holds both forM=m and forMm.     

Modification of a Theoretical Model for the Prediction of the Thermal Expansion Behavior of Particulate Composites: Application to Poly(vinyl chloride)/Talc Composites

The coefficients of thermal expansion (CTE) of poly(vinyl chloride) (PVC)/talc composites were tested and the experimental data showed that the CTE of PVC/talc composites were closely related to the talc particle size and its distribution; for a given talc volume fraction, the smaller the talc particle size, and the lower the CTE of the PVC/talc composites. The theoretical equations proposed by Sideridis and Papanicolaou and by Lombardo, which were based on a single, spherical particle size, were found to predict well the CTE of PVC/talc composites, but with the obtained interphase thicknesses were too large to be believed. In order to overcome the shortcomings of these equations, being without variation of filler particle size and its distribution, a modified model was proposed. It was found that the modified model can predict well the CTE of PVC/talc composites, with almost the same and more reliable interphase thicknesses for different talc particle sizes, confirming the correctness of the modified model to some extent.     

Correlation of grain boundary extra free volume with vacancy and solute segregation at grain boundaries: a case study for Al

Grain boundary extra free volume (GB EFV) can be considered as fundamental microstructural parameter for polycrystalline or nano-crystalline materials. Here, we present a systematic first principles study on a group of representative symmetric tilt grain boundaries of Al with various EFVs subjected to vacancy formation and Mg segregation. All grain boundaries were constructed using the coincident site lattice (CSL) and the structural unit (SU) models. It was found that the SU model is superior to the CSL in describing FCC-Al GBs, the same as we previously revealed for BCC-Fe. The predicted relation between GB misorientation angle and EFV, and the predicted EFV criteria for a stable GB, both agree with available experimental observations. Vacancy formation and Mg segregation show stronger preference to those GBs with high EFV values, due to the resultant high levels of atomic disorder. These findings not only provide a new, atomistic perspective on the significance of EFV, but also suggest a viable means of predicting GB properties based on direct experimental characterisation of GB EFVs.     

The stopped‐drop method: a novel setup for containment‐free and time‐resolved measurements

A novel setup for containment‐free time‐resolved experiments at a free‐hanging drop is reported. Within a dead‐time of 100 ms a drop of mixed reactant solutions is formed and the time evolution of a reaction can be followed from thereon by various techniques. As an example, a small‐angle X‐ray scattering study on the formation mechanism of EDTA‐stabilized CdS both at a synchrotron and a laboratory X‐ray source is presented here. While the evolution can be followed with one drop only at a synchrotron source, a stroboscopic mode with many drops is preferable for the laboratory source.     

syris: a flexible and efficient framework for X‐ray imaging experiments simulation

An open‐source framework for conducting a broad range of virtual X‐ray imaging experiments, syris, is presented. The simulated wavefield created by a source propagates through an arbitrary number of objects until it reaches a detector. The objects in the light path and the source are time‐dependent, which enables simulations of dynamic experiments, e.g. four‐dimensional time‐resolved tomography and laminography. The high‐level interface of syris is written in Python and its modularity makes the framework very flexible. The computationally demanding parts behind this interface are implemented in OpenCL, which enables fast calculations on modern graphics processing units. The combination of flexibility and speed opens new possibilities for studying novel imaging methods and systematic search of optimal combinations of measurement conditions and data processing parameters. This can help to increase the success rates and efficiency of valuable synchrotron beam time. To demonstrate the capabilities of the framework, various experiments have been simulated and compared with real data. To show the use case of measurement and data processing parameter optimization based on simulation, a virtual counterpart of a high‐speed radiography experiment was created and the simulated data were used to select a suitable motion estimation algorithm; one of its parameters was optimized in order to achieve the best motion estimation accuracy when applied on the real data. syris was also used to simulate tomographic data sets under various imaging conditions which impact the tomographic reconstruction accuracy, and it is shown how the accuracy may guide the selection of imaging conditions for particular use cases.