Theoretical investigation of atomic and electronic structures of Ga(2)O(3)(ZnO)(6)

Transparent conducting oxides (TCO) are widely used in technological applications ranging from photovoltaics to thin-film transparent field-effect transistors. In this work we report a first-principles investigation, based on density-functional theory, of the atomic and electronic properties of Ga(2)O(3)(ZnO)(6) (GZO(6)), which is a promising candidate to be used as host oxide for wide band gap TCO applications. We identify a low-energy configuration for the coherent distribution of the Ga and Zn atoms in the cation positions within the experimentally reported orthorhombic GZO(6) structure. Four Ga atoms are located in four-fold sites, while the remaining 12 Ga atoms in the unit cell form four shared Ga agglomerates (a motif of four atoms). The Zn atoms are distributed in the remaining cation sites with effective coordination numbers from 3.90 to 4.50. Furthermore, we identify the natural formation of twin-boundaries in GZO(6), which can explain the zigzag modulations observed experimentally by high-resolution transmission electron microscopy in GZO(n) (n=9). Due to the intrinsic twin-boundary formation, polarity inversion in the ZnO tetrahedrons is present which is facilitated by the formation of the Ga agglomerates. Our analysis shows that the formation of fourfold Ga sites and Ga agglomerates are stabilized by the electronic octet rule, while the distribution of Ga atoms and the formation of the twin-boundary help alleviate excess strain. Finally we identify that the electronic properties of GZO(6) are essentially determined by the electronic properties of ZnO, i.e., there are slight changes in the band gap and optical absorption properties.

The role of the Eph-ephrin signalling system in the regulation of developmental patterning

The Eph and ephrin system, consisting of fourteen Eph receptor tyrosine kinase proteins and nine ephrin membrane proteins in vertebrates, has been implicated in the regulation of many critical events during development. Binding of cell surface Eph and ephrin proteins results in bi-directional signals, which regulate the cytoskeletal, adhesive and motile properties of the interacting cells. Through these signals Eph and ephrin proteins are involved in early embryonic cell movements, which establish the germ layers, cell movements involved in formation of tissue boundaries and the pathfinding of axons. This review focuses on two vertebrate models, the zebrafish and mouse, in which experimental perturbation of Eph and/or ephrin expression in vivo have provided important insights into the role and functioning of the Eph/ephrin system.

Dynamiques de constitution de la communauté antiautoritaire au Québec, 2000-2010

Cette thèse par articles porte sur le processus de constitution de la communauté de mouvement social antiautoritaire au Québec, entre 2000 et 2010. Partant du constat de l’évolution de cet acteur politique d’inspiration anarchiste dans la province au cours de cette période, la thèse interroge les facteurs qui ont favorisé sa construction progressive autour de composantes diversifiées. Telles qu’elles se révèlent au grand jour vers la fin de la décennie, les composantes de cette communauté de mouvement social sont en effet hétérogènes au regard des enjeux qui retiennent leur attention, mais convergent néanmoins dans l’adoption de positions politiques, de stratégies d’action et de modes organisationnels caractéristiques de la perspective antiautoritaire contemporaine. Bien que l’environnement politique général dans lequel intervient la communauté antiautoritaire au Québec ait influencer son développement, la thèse démontre que les dynamiques internes à cette communauté sont celles qui ont assuré la pérennité de cet acteur politique en favorisant l’intégration de la diversité qui s’est exprimée en son sein au cours de la période étudiée. Le fait d’appréhender le mouvement antiautoritaire sous l’angle conceptuel de la communauté de mouvement social permet ainsi d’aborder le développement de cet acteur politique dans la continuité, au-delà des seuls moments publics d’interaction avec les autorités. Ce faisant, cette approche met également en lumière les facteurs endogènes qui ont contribué à son développement. Dans la lignée des travaux sur les mouvements sociaux qui proposent une perspective théorique synthétique liant la considération des aspects structurels et culturels dans l’analyse, l’étude du processus de constitution de la communauté antiautoritaire au Québec fait ressortir le rôle des dimensions organisationnelles et identitaires dans ce phénomène. Cette thèse par articles contribue à cette perspective théorique par l’application de l’approche mécanistique dans l’étude des mouvements sociaux. Celle-ci met en relief, d’une part, l’interaction de ces dimensions organisationnelles et identitaires dans la constitution de la communauté antiautoritaire et documente, d’autre part, les dynamiques qui leur sont inhérentes. Le passage graduel du mouvement antiautoritaire vers la configuration de communauté de mouvement social a ainsi été marqué, d’une part, par un processus de constitution organisationnelle qui a interagi avec le processus de démarcation identitaire en cours au sein du mouvement. D’autre part, la communauté antiautoritaire a pu se développer entre 2000 et 2010 grâce à un processus de conciliation identitaire réalisé par le travail identitaire des militants et des militantes. Ces processus ont favorisé la construction d’une identité collective fondée sur la lutte contre la pluralité des formes d’oppression, exprimée à la fois dans le discours et dans les pratiques des acteurs de la communauté antiautoritaire au Québec. La démonstration analytique proposée dans cette thèse repose sur une approche méthodologique de recherche-action participative combinant observation participante, analyse d’entretiens et étude de sources documentaires. L’interprétation empirique de la communauté antiautoritaire est basée sur un projet réalisé conjointement avec le Collectif de recherche sur l’autonomie collective (CRAC) de l’Université Concordia, à Montréal.

EphB1-mediated cell migration requires the phosphorylation of paxillin at Tyr-31/Tyr-118.

Interactions between Eph receptors and their membrane-bound ligands (ephrins) are of critical importance for key developmental processes such as boundary formation or vascular development. Their downstream signaling pathways are intricate and heterogeneous at several levels, the combined effect being a highly complex and flexible system. Here we demonstrate that activated EphB1 induces tyrosine phosphorylation of the focal adhesion protein paxillin at Tyr-31 and Tyr-118 and is recruited to paxillin-focal adhesion kinase (FAK) complexes. Pretreatment with the specific Src inhibitor PP2, or expression of dominant-negative, kinase-dead c-Src abrogates EphB1-induced tyrosine phosphorylation of paxillin. Cells transfected with the paxillin mutant Y31F/Y118F displayed a reduced migration in response to ephrin B2 stimulation. Furthermore, expression of an LD4 deletion mutant (paxillin DeltaLD4) significantly reduces EphB1-paxillin association, paxillin tyrosine phosphorylation, as well as EphB1-dependent cell migration. Finally, mutation of the Nck-binding site of EphB1 (Y594F) interrupts the interaction between Nck, paxillin, and EphB1. These data suggest a model in which ligand-activated EphB1 forms a signaling complex with Nck, paxillin, and focal adhesion kinase and induces tyrosine phosphorylation of paxillin in a c-Src-dependent manner to promote cell migration.

Subgrain boundaries and related microstructural features in EDML (Antarctica) deep ice core

Subgrain boundaries revealed as shallow sublimation grooves on ice sample surfaces are a direct and easily observable feature of intracrystalline deformation and recrystallization. Statistical data obtained from the EPICA Dronning Maud Land (EDML) deep ice core drilled in East Antarctica cannot detect a depth region of increased subgrain-boundary formation. Grain-boundary morphologies show a strong influence of internal strain energy on the microstructure at all depths. The data do not support the classical view of a change of dominating recrystallization regimes with depth. Three major types of subgrain boundaries, reflecting high mechanical anisotropy, are specified in combination with crystal-orientation analysis.

Geochemistry of Fe-Mn crusts at seamounts in the Northwest Pacific

Hydrogenetic ferromanganese crusts were dredged from four seamounts in the western Pacific, OSM7, OSM2, Lomilik, and Lemkein, aligned in a NW-SE direction parallel to Pacific Plate movement. The crusts consist of four well-defined layers with distinct textural and geochemical properties. The topmost layer 1 is relatively enriched in Mn, Co, Ni, and Mo compared to the underlying layer 2, which is relatively enriched in Al, Ti, K, and Rb and Cu, Zn, and excess Ba. Textural and geochemical properties of layer 2 suggest growth conditions under high biogenic and detrital flux. Such conditions are met in the equatorial Pacific (i.e., between the Intertropical Convergence Zone (ITCZ) and equatorial high-productivity zone). Layer 2 likely formed when each seamount was beneath the equatorial Pacific along its back track path. On the other hand, layer 1 probably started to grow after seamounts moved northwest from the ITCZ. This interpretation is consistent with the thickness of layer 1 across the four crusts, which increases to the northwest. Ages of the layer 1-layer 2 boundary in each crust, a potential proxy for northern margin of the ITCZ, also increase to the northwest at 17, 11, 8, and 5 Ma for OSM7, OSM2, Lomilik, and Lemkein, respectively. Assuming Pacific Plate motion of 0.3°/Myr, the seamounts were located at 12°N, 11°N, 9°N, and 8°N at the time of boundary formation. This result suggests that the north edge of the ITCZ has shifted south since the middle Miocene in the western Pacific, which agrees with information from the eastern Pacific.

Cloning and expression of the large zebrafish protocadherin gene, Fat

The cadherin superfamily members play an important role in mediating cell-cell contact and adhesion (Takeichi, M., 1991. Cadherin cell adhesion receptors as a morphogenetic regulator. Science 251, 1451-1455). A distinct subfamily, neither belonging to the classical or protocadherins includes Fat, the largest member of the cadherin super-family. Fat was originally identified in Drosophila. Subsequently, orthologues of Fat have been described in man (Dunne, J., Hanby, A. M., Poulsom, R., Jones, T. A., Sheer, D., Chin, W. G., Da, S. M., Zhao, Q., Beverley, P. C., Owen, M. J., 1995. Molecular cloning and tissue expression of FAT, the human homologue of the Drosophila fat gene that is located on chromosome 4q34-q35 and encodes a putative adhesion molecule. Genomics 30, 207-223), rat (Ponassi, M., Jacques, T. S., Ciani, L., ffrench, C. C., 1999. Expression of the rat homologue of the Drosophila fat tumour suppressor gene. Mech. Dev. 80, 207-212) and mouse (Cox, B., Hadjantonakis, A. K., Collins, J. E., Magee, A. I., 2000. Cloning and expression throughout mouse development of mfat 1, a homologue of the Drosophila tumour suppressor gene fat [In Process Citation]. Dev. Dyn. 217, 233-240). In Drosophila, Fat has been shown to play an important role in both planar cell polarity and cell boundary formation during development. In this study we describe the characterization of zebrafish Fat, the first non-mammalian, vertebrate Fat homologue to be identified. The Fat protein has 64% amino acid identity and 80% similarity to human FAT and an identical domain structure to other vertebrate Fat proteins. During embryogenesis fat mRNA is expressed in the developing brain, specialised epithelial surfaces the notochord, ears, eyes and digestive tract, a pattern similar but distinct to that found in mammals. (c) 2005 Elsevier B.V. All rights reserved.

The effect of channel geometry and wall boundary conditions on the formation of extrusion surface instabilities for LLDPE

It is believed that surface instabilities can occur during the extrusion of linear low density polyethylene due to high extensional stresses at the exit of the die. Local crack development can occur at a critical stress level when melt rupture is reached. This high extensional stress results from the rearrangement of the flow at the boundary transition between the wall exit and the free surface. The stress is highest at the extrudate surface and decreases into the bulk of the material. The location of the region where the critical level is reached can determine the amplitude of the extrudate surface distortion, This paper studies the effect of wall slip on the numerically simulated extensional stress level at the die exit and correlates this to the experimentally determined amplitude of the surface instability. The effect of die exit radius and die wall roughness on extrusion surface instabilities is also correlated to the exit stress level in the same way. Whereas full slip may completely suppress the surface instability, a reduction in the exit stress level and instability amplitude is also shown for a rounded die exit and a slight increase in instability is shown to result from a rough die wall. A surface instability map demonstrates how the shear rate for onset of extrusion surface instabilities can be predicted on the basis of melt strength measurements and simulated stress peaks at the exit of the die. (C) 2001 Elsevier Science B.V. All rights reserved.

Study on the K3Li2Nb5O15 formation during the production of (Na0.5K0.5)((1-x))LixNbO3 lead-free piezoceramics at the morphotropic phase boundary

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Void formation and grain boundary sliding in aluminum-magnesium solid solution alloys

"Materials Central, Contract no. AF 33(616)-5926. Project no. 7351."

Eddy formation and the boundary layer in fish locomotion

Cover title.

G-quadruplex Formation Enhances Splicing Efficiency Of Pax9 Intron 1.

G-quadruplexes are secondary structures present in DNA and RNA molecules, which are formed by stacking of G-quartets (i.e., interaction of four guanines (G-tracts) bounded by Hoogsteen hydrogen bonding). Human PAX9 intron 1 has a putative G-quadruplex-forming region located near exon 1, which is present in all known sequenced placental mammals. Using circular dichroism (CD) analysis and CD melting, we showed that these sequences are able to form highly stable quadruplex structures. Due to the proximity of the quadruplex structure to exon-intron boundary, we used a validated double-reporter splicing assay and qPCR to analyze its role on splicing efficiency. The human quadruplex was shown to have a key role on splicing efficiency of PAX9 intron 1, as a mutation that abolished quadruplex formation decreased dramatically the splicing efficiency of human PAX9 intron 1. The less stable, rat quadruplex had a less efficient splicing when compared to human sequences. Additionally, the treatment with 360A, a strong ligand that stabilizes quadruplex structures, further increased splicing efficiency of human PAX9 intron 1. Altogether, these results provide evidences that G-quadruplex structures are involved in splicing efficiency of PAX9 intron 1.

Eddy Formation in the Tropical Atlantic Induced by Abrupt Changes in the Meridional Overturning Circulation

The variability of the meridional overturning circulation (MOC) in the upper tropical Atlantic basin is investigated using a reduced-gravity model in a simplified domain. Four sets of idealized numerical experiments are performed: (i) switch-on of the MOC until a fixed value when a constant northward flow is applied along the western boundary; (ii) MOC with a variable flow; (iii) MOC in a quasi-steady flow; and (iv) shutdown of the MOC in the Northern Hemisphere. Results from experiments (i) show that eddies are generated at the equatorial region by shear instability and detached northward; eddies are responsible for an enhancement of the mean flow and the variability of the MOC. Results from experiments (ii) show a transitional behavior of the MOC related to the eddy generation in interannual-decadal time scales as the Reynolds number varies due to the variations in the MOC. In experiments (iii), a critical Reynolds number Re(c) around 30 is found, above which eddies are generated. Experiments (iv) demonstrate that even after the collapse of MOC in the Northern Hemisphere, eddies can still be generated and carry energy across the equator into the Northern Hemisphere; these eddies act to attenuate the impact of the MOC shutdown on short time scales. The results described here may be particularly pertinent to ocean general circulation models in which the Reynolds number lies close to the bifurcation point separating the laminar and turbulent regimes.

Scavenging of siliceous grain-boundary phase of 8-mol%-ytterbia-stabilized zirconia without additive

The grain-boundary conductivity (sigma (gb),) of 8-mol%-ytterbiastabilized zirconia increased markedly with heat treatment between 1000 degrees and 1300 degreesC with a slow heating rate (0.1 degreesC/min) before sintering. The extent of the sigma (gb) improvement was the same or larger than that via Al2O3 addition. The heat treatment did not affect the grain-interior conduction when sintered at 1600 degreesC, while Al2O3-derived scavenging significantly did, given the larger increment of total conductivity in the heat-treated sample. The formation of a silicon-containing phase in a discrete form was suggested as a possible route of scavenging the resistive phase from the correlation between average grain size and sigma (gb).