Plane Parallel (plane + parallel)

Distribution by Scientific Domains

Selected Abstracts

Analysis of the 2002 May earthquake sequence in the central Pyrenees, consequences for the evaluation of the seismic risk at Lourdes, France

Noalwenn Dubos
SUMMARY Three earthquakes of magnitudes 4.6, 4.3 and 3.7 occurred in 2002 May at two locations 20 km from the pilgrimage city of Lourdes in the French Pyrenees. They were well recorded by the permanent Pyrenean seismic networks, by a temporary local network, as well as by accelerometric stations. In order to understand their tectonic contexts, and to come to a better evaluation of the seismic risk at Lourdes, a detailed analysis of these events is performed. The first two events are located south of Lourdes in an area where only a few earthquakes have occurred up to now. Their focal solutions derived from first-motion polarities indicate reverse faulting, with a N110E strike consistent with the geological structures. 10 aftershocks were recorded and relocated with respect to the main events, benefiting from the waveform similarity of the various events. This analysis reveals that the two main events concern probably the same fault, the second rupture being in the prolongation of the first one, whereas the other small aftershocks are located on fault segments in the vicinity of the hypocentre of the second event. The third large event, located to the SE of Lourdes, involves a normal mechanism with a N120E plane parallel to the main geological structures. It occurred in a region of intense activity, including in particular an event of maximum macroseismic intensity IX in 1660. The first two events are at the boundary of a large quiet zone. In order to understand the related structural context, a new crustal tomographic model has been computed. It reveals that this quiet zone coincides with a block of high P -velocity. In contrast, the seismicity appears to be stronger at the northern and eastern boundaries of this block. The accelerometric data of the three main events recorded at Lourdes have been used to estimate the maximum peak ground accelerations in this city if a large event occurred, similar to those which damaged the city in the seventeenth and eighteenth centuries. Horizontal accelerations of 0.25 0.07 g are predicted in the frequency domain 1,5 Hz at the location of the Sanctuary for a magnitude 6 event occurring 10 km away from the city. Taking into account the error bars, these values could in some cases exceed those specified by the building codes in this region. [source]

Effects of Tooth Preparation Burs and Luting Cement Types on the Marginal Fit of Extracoronal Restorations

Mohamed F. Ayad BDS
Abstract Purpose: Although surface roughness of axial walls could contribute to precision of a cast restoration, it is unclear how the roughness of tooth preparation affects marginal fit of the restoration in clinical practice. The purpose of this study was to describe the morphologic features of dentin surfaces prepared by common rotary instruments of similar shapes and to determine their effects on the marginal fit for complete cast crowns. Materials and Methods: Ninety crowns were cast for standardized complete crown tooth preparations. Diamond, tungsten carbide finishing, and crosscut carbide burs of similar shape were used (N = 30). The crowns in each group were subdivided into three groups (n = 10) for use with different luting cements: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cement (Panavia 21). Marginal fit was measured with a light microscope in a plane parallel to the tooth surface before and after cementation between four pairs of index indentations placed at equal distances around the circumference of each specimen. Difference among groups was tested for statistical significance with analysis of variance (ANOVA) followed by Ryan-Einot-Gabriel-Welsch Multiple Range Test (,= 0.05). Results: Analysis of measurements disclosed a statistically significant difference for burs used to finish tooth preparations (p < 0.001); however, luting cement measurements were not significantly different (p= 0.152). Also, the interaction effect was not significantly different (p= 0.685). For zinc phosphate cement, the highest marginal discrepancy value (100 106 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (36 30 ,m) was for tooth preparations refined with finishing burs. For glass ionomer cement, the highest marginal discrepancy value (61 47 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (33 40 ,m) was for tooth preparations refined with finishing burs. For adhesive resin cement, the highest marginal discrepancy value (88 81 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (19 17 ,m) was for tooth preparations refined with finishing burs. Conclusions: Marginal fit of complete cast crowns is influenced by tooth preparation surface characteristics, regardless of the type of luting agent used for cementation. Tooth preparations refined with finishing burs may favor the placement of restorations with the smallest marginal discrepancies, regardless of the type of cement used. [source]

Use of a hexapod in diffraction measurements of substrate-supported crystals of organic semiconductors

Lin Yang
Thin films of organic semiconductor prepared on substrates generally contain crystals that have one common crystal plane parallel to the substrate but random in-plane orientations. In diffraction measurements of these structures, it is often required to anchor the X-ray beam on a fixed spot on the sample, such as an optically visible crystallite or island. Here, a hexapod is used in place of a traditional multi-circle diffractometer to perform area-detector-based diffraction measurements on an actual device that contains 6,13-bis(triisopropylsilyethynyl)-pentacene (TIPS-pentacene) crystals. The hexapod allows for sample rotations about any user-defined rotation center. Two types of complex sample motions have been programmed to characterize the structure of the TIPS-pentacene crystal: an in-plane powder average has been performed at a fixed grazing-incident angle to determine the lattice parameters of the crystal; then the in-plane component of the scattering vector was continuously rotated in transmission geometry to determine the local crystal orientation. [source]

Monitoring critical dimensions of bidimensional gratings by spectroscopic ellipsometry and Mueller polarimetry

M. Foldyna
Abstract In this work we characterized two bidimensional gratings consisting each of a square array of square holes etched in a photoresist layer deposited on silicon. Data were taken on both samples with a spectroscopic UV,VIS ellipsometer (SE) operated at 70 incidence and zero azimuth (with the incidence plane parallel to the lines of holes) and a VIS Mueller matrix polarimeter (MMP) at various incidence and azimuthal angles. The robustness of the parameters derived from the MMP data was evaluated from the stability of the values provided by regression the spectra taken at different angles. The optimal measurement geometries, featuring high sensitivity and low correlation of the fitting parameters, were determined theoretically, and validated experimentally with the sample featuring wider holes (500 500 nm), for which 45 incidence provided better results than the usual 70 value. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Expanding atmosphere models for SSS spectra of novae

D.R. van Rossum
Abstract Super Soft Source (SSS) spectra are powered by nuclear burning on the surface of a white dwarf. The released energy causes a radiatively-driven wind that leads to a radially extended atmosphere around the white dwarf. Significant blue shifts in photospheric absorption lines are found in the spectra of novae during their SSS phase, being an evidence of continued mass loss in this phase. We present spherically symmetric PHOENIX models that account for the expansion of the ejecta. A comparison to a plane parallel, hydrostatic atmosphere model demonstrates that the mass loss can have a significant impact on the model spectra. The dynamic model yields less pronounced absorption edges, and harder X-ray spectra are the result. Therefore, lower effective temperatures are needed to explain the observed spectra. Although both types of models are yet to be fine-tuned in order to accurately determine best fit parameters, the implications on the chemical abundances are going in opposite directions. With the expanding models the requirement for strong depletion of the crucial elements that cause these edges is now avoidable ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]