Chalk River Laboratories

About: Chalk River Laboratories is a based out in . It is known for research contribution in the topics: Neutron diffraction & Neutron scattering. The organization has 2297 authors who have published 2700 publications receiving 73287 citations.

Supporting the Learning of Recursive Problem Solving

Abstract: This research is about the problem solving activities of novice programmers as they learn to create recursive LISP programs. Their problem solving not only includes the issue of mental models, but also how to use these mental models in conjunction with other problem solving techniques. In fact, at various stages of their learning, learners seem to use different packages of problem solving methods. Each of these packages we call a mental method. In this article, we discuss the PETAL learning environment which assists learners in the use of three of these mental methods: the syntactic method, the analytic method and the analysis/synthesis method. PETAL externalizes each mental method through its own customized interface, called a programming environment tool #opPET#cp. Such externalization helps learners internalize concepts, and organize relevant knowledge and generally leads to improved learning. The PETAL System itself is presented. Next we discuss a study where one group of students used PETAL ...

Third structure determination by powder diffractometry round robin (SDPDRR-3)

Abstract: The results from a third structure determination by powder diffractometry (SDPD) round robin are discussed. From the 175 potential participants having downloaded the powder data, nine sent a total of 12 solutions (8 and 4 for samples 1 and 2, respectively, a tetrahydrated calcium tartrate and a lanthanum tungstate). Participants used seven different computer programs for structure solution (ESPOIR, EXPO, FOX, PSSP, SHELXS, SUPERFLIP, and TOPAS), applying Patterson, direct methods, direct space methods, and charge flipping approach. It is concluded that solving a structure from powder data remains a challenge, at least one order of magnitude more difficult than solving a problem with similar complexity from single-crystal data. Nevertheless, a few more steps in the direction of increasing the SDPD rate of success were accomplished since the two previous round robins: this time, not only the computer program developers were successful but also some users. No result was obtained from crystal structure prediction experts.

pH Effect on Sulfur-Induced Passivity Degradation of Alloy 800 in Simulated Crevice Chemistries

Abstract: The effects of pH on sulfur-induced passivity degradation of Alloy 800 in simulated crevice chemistries were evaluated using electrochemical impedance spectroscopy (EIS), secondary ion mass spectroscopy (SIMS), and Mott-Schottky analysis methods. Experimental results reveal that the detrimental effect of impurities containing sulfur at the reduced or intermediate oxidation level (Sx) on the passivity of Alloy 800 depends significantly on the solution pH. In neutral crevice (NC) chemistry containing chloride ions, the Sx obstructs the healing process during repassivation, retards the dehydration reaction and also incorporates H, ‐OH and S into the passive film. However, the detrimental effect of S x is insignificant in an alkaline crevice (AKC) solution due to a change in surface adsorption and surface charge. Impurities containing sulfur at the reduced or intermediate oxidation level would cause Alloy 800 to lose its passivity and become active in an acidic crevice (AC) chemistry. Experimental evidence also indicates that the solution pH alters the semiconductor type of the surface film —from n-type in NC solution to p-type in AKC solution. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any

Correlations between charge ordering and local magnetic fields in overdoped YBa 2 Cu 3 O 6 + x

Abstract: Zero-field muon spin-relaxation $(\mathrm{ZF}\ensuremath{-}\ensuremath{\mu}\mathrm{SR})$ measurements were undertaken on under- and overdoped samples of superconducting ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ to determine the origin of the weak static magnetism recently reported in this system. The temperature dependence of the muon spin-relaxation rate in overdoped crystals displays an unusual behavior in the superconducting state. A comparison to the results of NQR and lattice structure experiments on highly doped samples provides compelling evidence for strong coupling of charge, spin, and structural inhomogeneities.