Cross sections

A detailed study of elastic scattering of electrons and positrons from a hydrogen sulphide (H 2 S) molecule is presented using the method of partial wave phase shift analysis with suitably chosen complex optical potentials. The important aspect of our present work is that we uniquely obtain static potential in an analytical form and use it along with exchange (only for electron), polarization and purely imaginary absorption potentials to define the complex optical potential. The static potential is evaluated by obtaining charge density from the H 2 S molecule using the molecular wavefunction represented through an accurate analytical form of the Gaussian orbitals. The primary aim of our study is to test our present approach, as applied to the electron and positron scattering from H 2 S. Therefore, the results for electron and positron impact differential, integral, momentum-transfer, absorption and total cross sections are obtained for the incident energies in the range of 10-500 eV. Comparisons of these different types of cross section results with the available measurements and other calculations show good agreement, which suggests the applicability of our present approach.

The objective of this study was to compare the quality of Guttaflow (Coltene/Whaledent, Langenau, Germany), Resilon/Epiphany (Jeneric/Pentron, Kusterdingen, Germany), and EndoREZ (Ultradent Products, Inc, South Jordan, UT) root canal fillings. Thirty single-rooted teeth were randomly assigned to three groups: Resilon/Epiphany, EndoREZ, and Guttaflow. After radiography of the root canal fillings, the roots were sectioned horizontally at the level of 2 mm and 4 mm from the apex. The area of voids and adaptation to canal walls and points were evaluated using light microscopy and calculated through a computer program. The radiographs showed no significant differences between the materials (p > 0.05, Mann-Whitney U test). Evaluation of cross-sections revealed sealer adaptation >99% to the root canals and >98% to the points. Resilon/Epiphany had significantly higher values at 98.8% (standard deviation [SD] = 3.9%) than EndoREZ at 98.7% (SD = 1.1%), and Guttaflow at 98.5 (SD = 2.1...

In the south-western Anti-Atlas of Morocco (Dra Plain), a continuous exposure of Lower Devonian sedimentary successions more than 400 km long provides an example of mixed siliciclastic-carbonate shelf sequences. The carbonates were deposited adjacent and down-dip to large lobes of storm-dominated deltaic complexes during sea-level lowstands, and subsequently transgressed over the 200 m thick prograding siliciclastic wedges during sea-level rise, depositing limestone units between 5 and 20 m thick. The deltaic lobes switched through time and caused alternating siliciclastic supply along the shoreline oblique–parallel transect. Condensed limestone successions formed in clastic sediment starved areas due to delta-complex abandonment.Down-gradient, in outer ramp environments, the direct juxtaposition of carbonate and siliciclastic lithofacies associations comprising rhythmic lime mudstones/marls and massive shelf sandstones, provides the opportunity for mutual interpretation of their mode of deposition and bathymetry. This lateral relationship suggests that significant amalgamation took place in falling stage systems tracts to produce laterally extensive shelf sandstone-sheets on the outer ramp.Two types of stacking patterns are observed in prograding siliciclastic wedges. A normal progradational shoreline pattern with well developed parasequence sets in the proximal ramp, and an abrupt-regressive succession in which the amalgamated shelf sandstones rest more or less directly on offshore siltstones in the distal ramp. In the latter case, the falling stage systems tract sandstones are overlain by a relatively thick cyclic alternation with brachiopod-rich storm-beds below a marked transgressive surface at the base of the capping transgressive limestones. The cyclic alternation is interpreted as lowstand systems tract deposits. Marked flooding surfaces on parasequence sets are Fe-enriched and contain abundant articulated brachiopods, indicating breaks in sedimentation and an overall deepening-upward facies from the underlying maximum regression and sequence boundary. These aggradational to retrogradational stacked lowstand systems tracts are thus rather ‘transgressive’, not regressive in character, as is commonly described in sequence stratigraphic ramp models.

The objective of this study is to investigate the effect of boundary element details of structural walls on their deformation capacities. Structural walls considered in this study have different sectional shapes and/or transverse reinforcement content at the boundaries of the walls (called boundary element details hereafter). Four full-scale wall specimens (3000mm (hw)×1500mm (lw)×200mm (T)) were fabricated and tested. Three specimens are rectangular in section and the other specimen has a barbell-shaped cross-section (a wall with boundary columns). The rectangular wall specimens are reinforced according to the common practice used for reinforced concrete residence buildings in Korea and Chile. In this study, the primary variable for these rectangular specimens is the content of transverse reinforcement to confine the boundary elements of a wall. The barbell-shaped specimen was designed in compliance with ACI 318-95. The response of the barbell-shaped specimen is compared with those of other rectangular specimens. The effective aspect ratio of the specimens is set to two in this study. Based on the experimental results, it is found that the deformation capacities of walls, which are represented by displacement ductility, drift ratio and energy dissipation capacities, are affected by the boundary element details. Copyright © 2002 John Wiley & Sons, Ltd.

A Monte Carlo model has been developed to study the degradation of <1000 eV electrons in an atmosphere of CO2, which is one of the most abundant species in Mars' and Venus' atmospheres. The e-CO2 cross sections are presented in an assembled set along with their analytical representations. Monte Carlo simulations are carried out at several energies to calculate the "yield spectra", which embodied all the information related to electron degradation process and can be used to calculate "yield" (or population) for any inelastic process. The numerical yield spectra have been fitted analytically resulting in an analytical yield spectra (AYS). We have calculated the mean energy per ion pair and efficiencies for various inelastic processes, including the double and dissociative double ionization of \car\ and negative ion formation. The energy distribution of the secondary electrons produced per incident electron is also presented at few incident energies. The mean energy per ion pair for CO2 is 37.5 (35.8) eV at 200 (1000) eV, compared to experimental value 32.7 eV at high energies. Ionization is the dominant loss process at energies above 50 eV with contribution of ~50%. Among the excitation processes, 13.6 eV and 12.4 eV states are the dominant loss processes consuming ~28% energy above 200 eV. Around and below ionization threshold, 13.6 eV, 12.4 eV, and 11.1 eV, followed by 8.6 eV and 9.3 eV excitation states are important loss processes, while below 10 eV vibrational excitation dominates.

Graviton absorption cross sections and emission rates for hydrogen are calculated by both semi-classical and field theoretic methods. We point out several mistakes in the literature concerning spontaneous emission of gravitons and related phenomena, some of which are due to a subtle issue concerning gauge invariance of the linearized interaction Hamiltonian.