Glacial Lake in the Richardson and Rae River Basins, Northwest Territories

Systematic mapping of the surficial deposits in the Richardson River basin, south and west of Coppermine, District of Mackenzie, N.W.T. has yielded strong evidence for the former existence of a glacial lake. A sequence of glacial lakes occupied an extensive portion of the basins drained by the Richardson and Rae rivers. Water bodies were trapped in this large depression to the west of Coronation Gulf by easterly retreating glacier ice. Four lake phases are recognized, each controlled by progressively lower outlets at 330 m, 260 m, 235 m and 165 m a.s.l. It is proposed that the lake which finally drained in a postglacial sea be called Glacial Lake Richardson. The former presence of the glacial lake and the associated deltas and outlets are essential elements in reconstructing the déglaciation history of the area.La cartographie systématique des dépôts meubles du bassin de la rivière Richardson a permis de reconnaître l'existence d'au moins un lac glaciaire d'importance dans la région. Au cours de différentes phases, le lac glaciaire a occupé une partie ou une autre de la dépression topographique formée par les bassins des rivières Rae et Richardson, à l'ouest du golfe du Couronnement. Quatre phases distinctes ont été reconnues, chacune ayant été contrôlée par des exutoires à 330 m, 260 m, 235 m et 165 m a.n.m. On propose de nommer ce lac, qui s'est drainé dans la mer post-glaciaire, « Lac glaciaire Richardson ». L'identification des différentes phases du lac glaciaire a grandement facilité la détermination des modalités de la déglaciation dans la région du bassin de la rivière Richardson

The Eco - Geo - Clim model: explaining Madagascar’s endemism

No Abstrac

Anomalous Roughening of Viscous Fluid Fronts in Spontaneous Imbibition

We report experiments on spontaneous imbibition of a viscous fluid by a model porous medium in the absence of gravity. The average position of the interface satisfies Washburn's law. Scaling of the interface fluctuations provides a dynamic exponent z \simeq 3, indicative of global dynamics driven by capillary forces. The complete set of exponents clearly shows that interfaces are not self-affine, exhibiting distinct local and global scaling, both for time (b=0.64\pm 0.02, b* =0.33 \pm 0.03) and space (a=1.94 \pm 0.20, a_loc=0.94 \pm 0.10). These values are compatible with an intrinsic anomalous scaling scenario.Comment: 4 pages, 5 figure

Stable Photoinduced Separated Charge State in Viologen Halometallates: Some Key Parameters

With the aim to define key parameters causing the photochromic properties of (MV)[Bi2Cl8] and (MV)(4)[Bi6Cl26] (MV2+, methylviologen; 1,1-dimethyl-4,4-bipyridinium), the effects of substituting Bi by Sb, Cl by Br, or MV2+ by MOV2+ (1,1-dimethoxy-4,4-bipyridinium) or MeMOV2+ (1-methyl-1-methoxy-4,4-bipyridinium) on the photoinduced charge transfer properties of such viologen halometallates are explored. It appears that only salts containing chlorobismuthate anions undergo a color change upon UV irradiation and that the nature of viologen entities has a key role in the process. We also suggest that a key parameter for observing the stable photoinduced separated charge state in chlorobismuthate viologen hybrids is a high chloride/viologen ratio, rather than the size of the anionic oligomer, as observed in the previously reported unique series (MV)((2n+2)/2)[Bi2nCl8n+2]

3D Porous Architecture of Stacks of β-TCP Granules Compared with That of Trabecular Bone: A microCT, Vector Analysis, and Compression Study

The 3D arrangement of porous granular biomaterials usable to fill bone defects has received little study. Granular biomaterials occupy 3D space when packed together in a manner that creates a porosity suitable for the invasion of vascular and bone cells. Granules of beta-tricalcium phosphate (β-TCP) were prepared with either 12.5 or 25 g of β-TCP powder in the same volume of slurry. When the granules were placed in a test tube, this produced 3D stacks with a high (HP) or low porosity (LP), respectively. Stacks of granules mimic the filling of a bone defect by a surgeon. The aim of this study was to compare the porosity of stacks of β-TCP granules with that of cores of trabecular bone. Biomechanical compression tests were done on the granules stacks. Bone cylinders were prepared from calf tibia plateau, constituted high-density (HD) blocks. Low-density (LD) blocks were harvested from aged cadaver tibias. Microcomputed tomography was used on the β-TCP granule stacks and the trabecular bone cores to determine porosity and specific surface. A vector-projection algorithm was used to image porosity employing a frontal plane image, which was constructed line by line from all images of a microCT stack. Stacks of HP granules had porosity (75.3 ± 0.4%) and fractal lacunarity (0.043 ± 0.007) intermediate between that of HD (respectively 69.1 ± 6.4%, p < 0.05 and 0.087 ± 0.045, p < 0.05) and LD bones (respectively 88.8 ± 1.57% and 0.037 ± 0.014), but exhibited a higher surface density (5.56 ± 0.11 mm(2)/mm(3) vs. 2.06 ± 0.26 for LD, p < 0.05). LP granular arrangements created large pores coexisting with dense areas of material. Frontal plane analysis evidenced a more regular arrangement of β-TCP granules than bone trabecule. Stacks of HP granules represent a scaffold that resembles trabecular bone in its porous microarchitecture

Cell-selective modulation of the Drosophila neuromuscular system by a neuropeptide

Neuropeptides can modulate physiological properties of neurons in a cell-specific manner. The present work examines whether a neuropeptide can also modulate muscle tissue in a cell-specific manner, using identified muscle cells in third instar larvae of fruit flies. DPKQDFMRFa, a modulatory peptide in the fruit fly Drosophila melanogaster, has been shown to enhance transmitter release from motor neurons and to elicit contractions by a direct effect on muscle cells. We report that DPKQDFMRFa causes a nifedipine-sensitive drop in input resistance in some muscle cells (6 and 7) but not others (12 and 13). The peptide also increased the amplitude of nerve-evoked contractions and compound excitatory junctional potentials (EJPs) to a greater degree in muscle cells 6 and 7 than 12 and 13. Knocking down FMRFa receptor (FR) expression separately in nerve and muscle indicate that both presynaptic and postsynaptic FR expression contributed to the enhanced contractions, but EJP enhancement was due mainly to presynaptic expression. Muscle-ablation showed that DPKQDFMRFa induced contractions and enhanced nerve-evoked contractions more strongly in muscle cells 6 and 7 than cells 12 and 13. In situ hybridization indicated that FR expression was significantly greater in muscle cells 6 and 7 than 12 and 13. Taken together, these results indicate that DPKQDFMRFa can elicit cell-selective effects on muscle fibres. The ability of neuropeptides to work in a cell-selective manner on neurons and muscle cells may help explain why so many peptides are encoded in invertebrate and vertebrate genomes