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.

Temperature driven annealing of perforations in bicellar model membranes.

Abstract: Bicellar model membranes composed of 1,2-dimyristoylphosphatidylcholine (DMPC) and 1,2-dihexanoylphosphatidylcholine (DHPC), with a DMPC/DHPC molar ratio of 5, and doped with the negatively charged lipid 1,2-dimyristoylphosphatidylglycerol (DMPG), at DMPG/DMPC molar ratios of 0.02 or 0.1, were examined using small angle neutron scattering (SANS), 31P NMR, and 1H pulsed field gradient (PFG) diffusion NMR with the goal of understanding temperature effects on the DHPC-dependent perforations in these self-assembled membrane mimetics. Over the temperature range studied via SANS (300−330 K), these bicellar lipid mixtures exhibited a well-ordered lamellar phase. The interlamellar spacing d increased with increasing temperature, in direct contrast to the decrease in d observed upon increasing temperature with otherwise identical lipid mixtures lacking DHPC. 31P NMR measurements on magnetically aligned bicellar mixtures of identical composition indicated a progressive migration of DHPC from regions of high curvatu...

Rearrangement of human cell homologous chromosome domains in response to ionizing radiation.

Abstract: . Chromosomes are located within the interphase nucleus in regions called domains. Using fluorescence in situ hybridization with whole chromosome paints, a pair of homologous chromosomes can be visualized as two discrete domains and their relative spatial location determined. This study examines the effects of an ionizing radiation exposure on the relative spatial location of chromosome 7 and 21 domains in human skin fibroblasts and lung endothelial cells. The distance between homologous chromosome domains was assessed for each nucleus, before and after exposure to ionizing radiation, using conventional epifluorescence and confocal laser scanning microscopy. Results from conventional microscopy indicated that homologous chromosome domains were re-positioned closer to each other within interphase nuclei after exposure to radiation. Analysis of three-dimensional data obtained from confocal microscopy confirmed these results. In control cells, and in cells examined immediately after irradiation, 66.2...

First-forbidden β decay: Meson-exchange enhancement of the axial charge at A ∼16

Abstract: Calculations are presented for four relatively strong first-forbidden \ensuremath{\beta} decays in the region A=11--16 in order to study the very large mesonic-exchange-current enhancement of the rank-zero components. The ${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}$ capture on $^{16}\mathrm{O}$ is considered on the same footing. The wave functions utilized include up to 4\ensuremath{\Elzxh}\ensuremath{\omega} excitations. Two-body exchange-current matrix elements are calculated as well as one-body impulse-approximation matrix elements. The resultant enhancement factor that multiplies the impulse-approximation axial-charge matrix element is thereby determined by comparison to experiment to be ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{exp}}$=1.61\ifmmode\pm\else\textpm\fi{}0.03 from three ${\mathrm{\ensuremath{\beta}}}^{\mathrm{\ensuremath{-}}}$ decays and ${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}$ capture on $^{16}\mathrm{O}$, which is in excellent agreement with meson-exchange calculations in the soft-pion approximation.

Soft phonon columns on the edge of the Brillouin zone in the relaxor PbMg1/3Nb2/3O3

Abstract: which is similar to the onset temperature of the zone-center diffuse scattering, indicating a competition between ferroelectric and antiferroelectric distortions. We propose a model for the atomic displacements associated with these phonon modes that is based on a combination of structure factors and group theoretical analysis. This analysis suggests that the scattering is not from tilt modes rotational modes of oxygen octahedra, but from zone-boundary optic modes that are associated with the displacement of Pb 2+ and O 2� ions. Whereas similar columns of scattering have been reported in metallic and less commonly molecular systems, they are unusual in insulating materials, particularly in ferroelectrics; therefore, the physical origin of this inelastic feature in PMN is unknown. We speculate that the underlying disorder contributes to this unique anomaly.