Wedge Domain Research Articles

Dynamic effects of aseismic ridge subduction: numerical modelling

The subduction of oceanic aseismic ridges, oceanic plateaus and seamount chains is a common process that takes place in a variety of tectonic settings and seems to coincide spatially and temporally with a gap of volcanic activity, shallow or even horizontal slab angles, enhanced seismic activity and various topographic features. In the present study we focus on these dynamic effects on the basis of 2D thermomechanical modelling incorporating effects of slab dehydration, mantle-wedge melting and surface topography development. In order to ascertain the impact of a moderate-size (200 × 18 km) aseismic ridge, 12 pairs of experiments (one for the case with a ridge, the other without) were carried out varying slab density and subducting- and overriding-plate velocities. By analysing pairs of experiments we conclude that subduction of a moderate-sized ridge does not typically result in strong slab flattening and related decrease of magmatic activity. This, in turn, suggests that, when slab flattening is indeed associated with the ridge subduction in nature, the slab itself should be in a nearly critical ( i.e ., transient from inclined to flat) state so that any local addition of positive buoyancy may strongly affect overall slab dynamics. Therefore, subducting ridges may serve as indicators of transient slab states in nature. Another important result from our study is the numerical quantification of strongly decreased magma production associated with flat slabs that may explain gaps in recent active volcanism at low-angle subduction margins. Lowering of magmatic rock production is caused by the absence of a hot mantle wedge above the flat slabs and does not directly depend on the mechanism responsible for the triggering of slab flattening. Finally we document several very distinct surface effects associated with the moderate-size ridge subduction such as local increase in elevation of overriding margin, enhancement of subduction erosion and landward trench displacement. Surface uplift may exceed the original ridge height due to additional uplift resulting from the overriding plate shortening. Topographic perturbations within the accretionary wedge domain are transient and have a tendency to relax after the ridge passes the trench. In contrast, the topographic high created in the continental portion of the overriding plate relaxes more slowly and may even be sustained for several millions of year after the ridge subduction.

Domain engineering in compositionally graded ferroelectric films for enhanced dielectric response and tunability

Functional materials with nonlinear dielectric response are ideally suited for telecommunications applications and threat detection in beam-steering and frequency tuning devices. Developing the theory of wedge domain in graded ferroelectrics, we present herein a quantitative model of domain evolution and dielectric response of compositionally graded ferroelectric multilayers. We show that the domain structure adapts itself to the applied electric field via domain modification. As the applied field rises, the domains are swept away layer by layer resulting in a strong nonlinear field dependence of the dielectric constant and tunability of the multilayers. There is approximately a fivefold improvement in the small-signal dielectric response and threefold enhancement in the dielectric tunability at 400 kV cm−1 in compositionally graded (001) BaxSr1−xTiO3 [BST x/(1−x)] compared to homogeneous BST layers on (001) SrTiO3 substrate. We also demonstrate that by controlling the relative thicknesses of the layers that make up the graded heterostructure, one could further enhance the dielectric response and tunability.

Domain structures in continuously graded ferroelectric films

Thermodynamic analysis of a graded ferroelectric epitaxial film demonstrates that in the equilibrium state the films subdivide into an alternation of polydomain bands consisting of wedge- or lens-shape domains and single-domain bands. Polarization under an external electrical field proceeds through an interband boundary movement due to the growth/shrinkage of the wedge domains. The domain structure and its evolution are determined by the distribution of the spontaneous polarization and dielectric constant. Through film grading, it is possible to design a controlled domain structure with desirable tunability. Graded films exhibit a sharp increase of the dielectric constant as electrical field approaches zero.

PTPN22 Deficiency Cooperates with the CD45 E613R Allele to Break Tolerance on a Non-Autoimmune Background

Pep and CD45 are tyrosine phosphatases whose targets include the Src-family kinases, critical mediators of Ag receptor signaling. A polymorphism in PTPN22, the gene that encodes the human Pep orthologue Lyp, confers susceptibility to multiple human autoimmune diseases in the context of complex genetic backgrounds. However, the functional significance of the R620W risk allele is not clear. We report that misexpression of wild-type or R620W Pep/Lyp in Jurkat cells, in the context of its binding partner Csk, unmasks the risk allele as a hypomorph. It has been shown previously that although Pep-deficient mice on the B6 background have hyperresponsive memory T cells, autoimmunity does not develop. Mice containing a point mutation in the CD45 juxtamembrane wedge domain (E613R) develop a B cell-driven, lupus-like disease on the mixed 129/B6 background, but not on the B6 background. We studied the ability of Pep deficiency to act as a genetic modifier of the CD45 E613R mutation on the nonautoimmune B6 background to understand how complex susceptibility loci might interact in autoimmunity. In this study we report that double mutant mice develop a lupus-like disease as well as lymphadenopathy, polyclonal lymphocyte activation, and accelerated memory T cell formation. Following Ag receptor stimulation, peripheral B cells in the double mutant mice phenocopy hyperresponsive CD45 E613R B cells, whereas peripheral T cells respond like Pep(-/-) T cells. These studies suggest that Pep(-/-) T cells in the context of a susceptible microenvironment can drive hyperresponsive CD45 E613R B cells to break tolerance.

A Payne-Weinberger eigenvalue estimate for wedge domains on spheres

A Faber-Krahn type argument gives a sharp lower estimate for the first Dirichlet eigenvalue for subdomains of wedge domains in spheres, generalizing the inequality for the plane, found by Payne and Weinberger. An application is an alternative proof to the finiteness of a Brownian motion capture-time estimate.

Domain evolution and polarization of continuously graded ferroelectric films

A thermodynamic analysis of graded ferroelectric films demonstrates that, in the equilibrium state, the films are subdivided into alternating single-domain and polydomain bands, the latter consisting of wedge-shape domains. Polarization under an external electrostatic field proceeds through inter-band boundary movements due to the growth or shrinkage of the wedge domains. It is shown how the domain structure and evolution are determined by the principal characteristics of the film: the distribution of the spontaneous polarization and dielectric constant. Graded films exhibit a sharp increase of polarization with the field for weak fields, with a drop of the dielectric constant when the field is increasing. A general approach to finding the dependence of the displacement and the wedge-domain shape on the field as well as analytical solutions for the fourth degree polynomial Landau–Ginzburg–Devonshire and parabolic potentials are presented.

Dirichlet-Neumann-impedance boundary value problems arising in rectangular wedge diffraction problems

Boundary value problems originated by the diffraction of an electromagnetic (or acoustic) wave by a rectangular wedge with faces of possible different kinds are analyzed in a Sobolev space framework. The boundary value problems satisfy the Helmholtz equation in the interior (Lipschitz) wedge domain, and are also subject to different combinations of boundary conditions on the faces of the wedge. Namely, the following types of boundary conditions will be under study: Dirichlet-Dirichlet, Neumann-Neumann, Neumann-Dirichlet, Impedance-Dirichlet, and Impedance-Neumann. Potential theory (combined with an appropriate use of extension operators) leads to the reduction of the boundary value problems to integral equations of Fredholm type. Thus, the consideration of single and double layer potentials together with certain reflection operators originate pseudo-differential operators which allow the proof of existence and uniqueness results for the boundary value problems initially posed. Furthermore, explicit solutions are given for all the problems under consideration, and regularity results are obtained for these solutions.

Saccharomyces cerevisiaeHop1 Protein Zinc Finger Motif Binds to the Holliday Junction and Distorts the DNA Structure: Implications for Holliday Junction Migration

Saccharomyces cerevisiae HOP1, which encodes a component of synaptonemal complex, plays an important role in crossing over between homologues. Hop1p contains a zinc finger motif, and substitution of a conserved Cys371 by Ser rendered the hop1 mutant allele defective in sporulation and meiosis. However, the molecular mechanism underlying the function of Hop1 zinc finger motif (ZnF) remains obscure. Here we show that wild-type Hop1 ZnF binds significantly better to the Holliday junction compared with other recombination intermediates. Consequently, the salt titration midpoint for dissociation of the Holliday junction-ZnF complex was higher than the complexes containing flush-ended linear or tailed duplex DNA. Although DNase I footprinting showed that Hop1 ZnF binds to each of the four arms of the junction, KMnO4 probing and 2-aminopurine fluorescence emission data disclosed that it distorts the DNA structure along a pair of symmetrical arms. Molecular modeling studies show that Hop1 ZnF forms a unique zinc-binding fold, reminiscent of the basic helix-loop-helix motif. In the presence of Zn2+, docking studies show that alpha helix 1, which is replete with basic amino acid residues, makes stabilizing contacts with the sugar-phosphate backbone. Structural comparison revealed a striking similarity between RecG wedge domain and Hop1 ZnF motif. We propose that Hop1 ZnF motif plays a key role in the physical monitoring of recombination intermediates and branch migration of the Holliday junction.

$H^\infty$-calculus for the sum of non-commuting operators

A recent result of Kalton and Weis is extended to the case of non-commuting operators, employing the commutator condition of Labbas and Terreni, or of Da Prato and Grisvard. Under appropriate assumptions it is shown that the sum of two non-commuting operators admits an H∞ -calculus. The main results are then applied to a parabolic problem on a wedge domain.

Reconstruction of Elliptic Voids in the Elastic Wedge: The Antiplane Problem

In this article we study the reconstruction of the geometry of elliptic voids located in the elastic wedge, in frames of an antiplane two-dimensional problem. The wedge domain is bounded by a pair of straight boundaries. The first boundary is horizontal, and the second one is inclined at some angle. We assume that a known point force is applied to the horizontal boundary surface of the wedge, whose other face is fixed or is free from load. It is also assumed that the defect is unknown and that we can measure the shape of the surface over a certain finite-length interval of the same side where the outer force is applied. Such measurements can in principle be performed experimentally, but for our numerical experiments we carried out them by solving the respective direct problem, with the use of boundary element method (BEM). Then it is shown that an explicit form of Green's function can be constructed when the interior angle of the wedge is an integer part of 180°. For these cases, we construct an algorithm to restore the position, the size, and the orientation of the elliptic void. Some numerical examples demonstrate the good stability of the proposed algorithm.

Protein-tyrosine Phosphatase (PTP) Wedge Domain Peptides: A NOVEL APPROACH FOR INHIBITION OF PTP FUNCTION AND AUGMENTATION OF PROTEIN-TYROSINE KINASE FUNCTION

Inhibition of protein-tyrosine phosphatases (PTPs) counterbalancing protein-tyrosine kinases (PTKs) offers a strategy for augmenting PTK actions. Conservation of PTP catalytic sites limits development of specific PTP inhibitors. A number of receptor PTPs, including the leukocyte common antigen-related (LAR) receptor and PTPmu, contain a wedge-shaped helix-loop-helix located near the first catalytic domain. Helix-loop-helix domains in other proteins demonstrate homophilic binding and inhibit function; therefore, we tested the hypothesis that LAR wedge domain peptides would exhibit homophilic binding, bind to LAR, and inhibit LAR function. Fluorescent beads coated with LAR or PTPmu wedge peptides demonstrated PTP-specific homophilic binding, and LAR wedge peptide-coated beads precipitated LAR protein. Administration of LAR wedge Tat peptide to PC12 cells resulted in increased proliferation, decreased cell death, increased neurite outgrowth, and augmented Trk PTK-mediated responses to nerve growth factor (NGF), a phenotype matching that found in PC12 cells with reduced LAR levels. PTPmu wedge Tat peptide had no effect on PC12 cells but blocked the PTPmu-dependent phenotype of neurite outgrowth of retinal ganglion neurons on a PTPmu substrate, whereas LAR wedge peptide had no effect. The survival- and neurite-promoting effect of the LAR wedge peptide was blocked by the Trk inhibitor K252a, and reciprocal co-immunoprecipitation demonstrated LAR/TrkA association. The addition of LAR wedge peptide inhibited LAR co-immunoprecipitation with TrkA, augmented NGF-induced activation of TrkA, ERK, and AKT, and in the absence of exogenous NGF, induced activation of TrkA, ERK, and AKT. PTP wedge domain peptides provide a unique PTP inhibition strategy and offer a novel approach for augmenting PTK function.

Diffraction by an elastic wedge with stress-free boundary: existence and uniqueness

Applying the spectral function techniques, developed by Croisille and Lebeau, we prove the existence of solutions to problems of plane and cylindrical waves diffraction by an elastic wedge with stress-free boundary conditions. We also formulate radiation conditions, under which the uniqueness holds. The latter implies absolute continuity of the spectrum of the Lamé operator in a wedge domain with stress-free boundary.

DNA Binding by the Substrate Specificity (Wedge) Domain of RecG Helicase Suggests a Role in Processivity

RecG differs from most helicases acting on branched DNA in that it is thought to catalyze unwinding via translocation of a monomer on dsDNA, with a wedge domain facilitating strand separation. Conserved phenylalanines in the wedge are shown to be critical for DNA binding. When detached from the helicase domains, the wedge bound a Holliday junction with high affinity but failed to bind a replication fork structure. Further stabilizing contacts are identified in full-length RecG, which may explain fork binding. Detached from the wedge, the helicase region unwound junctions but had extremely low substrate affinity, arguing against the "classical inchworm" mode of translocation. We propose that the processivity of RecG on branched DNA substrates is dependent on the ability of the wedge to establish strong binding at the branch point. This keeps the helicase motor in contact with the substrate, enabling it to drive dsDNA translocation with high efficiency.

The Bergman Kernels for the half-ball and for fractional wedge-shaped domains in Clifford Analysis

We compute the Bergman reproducing kernel for monogenic functions for half-ball, more general orthogonal ball sectors, and for fractional wedge domains. In the results we obtain the terms to be expected from analogy with complex analysis, viz in the first case the Bergman kernels for the half-space and the entire ball, and in the second the sum of rotated half-space Bergman kernels, but in both cases there also occur supplementary, purely hypercomplex correction terms. Finally, applying a periodisation argument we obtain closed and explicit formulas for the Bergman kernels of wedge shaped domains that are rectangularly bounded.

UHP GARNET ORTHOPYROXENITES (DABIE SHAN, CHINA) AS MONITORS OF PERCOLATION OF HYDROUS SI-RICH MELTS IN DEEP SUBDUCTION ENVIRONMENTS

UHP GARNET ORTHOPYROXENITES (DABIE SHAN, CHINA) AS MONITORS OF PERCOLATION OF HYDROUS SI-RICH MELTS IN DEEP SUBDUCTION ENVIRONMENTS

Lithium abundance and isotope systematics of forearc serpentinites, Conical Seamount, Mariana forearc: Insights into the mechanics of slab‐mantle exchange during subduction

Variable lithium contents and contrasting Li isotopic signatures are evident in the serpentininite muds and clasts extruded at Conical Seamount in the Mariana forearc. The muds have high Li contents compared to mantle values (3–7 ppm) and a mean δ7Li value of ∼+6‰. The clasts are generally lower in Li, and δ7Li varies from −6‰ to +10‰, with higher δ7Li correlating broadly to higher lithium contents. The diverse δ7Li in the serpentinite clasts suggests Li exchanges between mantle rocks and evolving slab‐derived fluids from different depths, producing a subarc mantle that is zoned in terms of Li abundances and δ7Li. Mariana forearc Li isotopic signatures reach values as high as those reported in Mariana arc lavas, but neither Mariana lavas nor lavas from other “mature” arcs show the variability observed in the serpentinites. Although elevated serpentinite Li contents indicate forearc releases of Li, large differences in δ7Li are not evident in the slab outputs at forearc versus arc depths in the Marianas, despite evidence for changes in other alkaline species (e.g., Ba, Sr, K). It is thus possible that the Li sampled by Mariana arc volcanoes is in large part Li which was released in the forearc and transported in the mantle via convection to arc depths, as has been proposed to explain B isotopic variations [Straub and Layne, 2002]. The uniform δ7Li signatures observed in “mature” volcanic arcs [Tomascak et al., 2002] are consistent with higher overall fluxes of slab fluids, which generate larger melting anomalies, including both modified and nonmodified mantle wedge domains. High or low δ7Li in lavas from anomalous arcs (e.g., Panama [Tomascak et al., 2000]) may indicate that the volumes of mantle sampled in these magmatic events are smaller and thus more likely to reflect the signatures of hydrated “plums” [e.g., Allègre and Turcotte, 1986; Phipps Morgan and Morgan, 1999] with extremely high or low δ7Li.

Role of décollement material with different rheological properties in the structure of the Aljibe thrust imbricate (Flysch Trough, Gibraltar Arc): an analogue modelling approach

The Miocene Aljibe thrust imbricate (Flysch Trough), in the external zone of the Gibraltar Arc, shows large changes in structural style towards the foreland. Rheological variation of the décollement rocks—Triassic evaporitic rocks and Mesozoic limestones—appears to be the main factor controlling the contrasts in structural style that characterise adjacent wedge domains. In order to test this hypothesis, we carried out analogue experiments involving three-dimensional variations of décollement material. A plate of viscous material was placed in the central part of the models, at the base of the sand multilayers. Different geometries of the viscous plate were used. Experimental results show a strong link between the rheological properties of the décollement material and the structure of the overlying thrust wedge. These results compare well with the internal geometry and vergence distribution in the Aljibe thrust imbricate. Indeed, the tectonic style of the wedge can be explained as a consequence of variations of rock type along the basal décollement.

On the use of the method of images to investigate nearshore dynamical processes

This note describes how the method of images may be used to determine the motion and evolution of two related kinds of phenomena within a wedge of inviscid fluid. The image field of a curved vortex within a wedge with vortex lines lying along sectors of circles around the apex of the wedge is that segment of a complete vortex ring which remains outside the wedge and of which the curved vortex forms a part. The image system can be used to describe the motion, interaction and stability of single or multiple vortices within the wedge. Axisymmetric jets form the image system for flow parallel to the edge of the wedge, akin to alongshore currents. Knowledge of the instability of jets provides information about the evolution of waves in the wedge domain. Existing results on the motion and instability of single or multiple co-axial ring vortices and of waves and instabilities in jets may be applied to describe the evolution of low Froude number eddies and waves in alongshore flow over a steadily shelving sea bed.

On the Joint Distribution of the First Hitting Time and the First Hitting Place to the Space-Time Wedge Domain of a Biharmonic Pseudo Process

We consider the equation \[ \frac{\partial u}{\partial t}(t,x)=-\Delta^{2}u(t,x) \] for the biharmonic operator $-\Delta^2$. We define the pseudo process corresponding to this equation as Nishioka's sense. We obtain the Laplace-Fourier transform of the joint distribution of the first hitting time $\tau(\omega)=\inf\{t>0:\omega(t)<\alpha t-a\}$ $(a>0, \alpha\in\mathbf{R})$ and the first hitting place $\omega(\tau)$, where each path $\omega(t)$ starts from 0 at $t=0$.

Barkhausen effect in stepped motion of a plane domain boundary in gadolinium molybdate

Barkhausen pulses generated in stepped motion of a single plane domain boundary (PDB) are investigated experimentally in single-crystalline wafers of the extrinsic ferroelastic ferroelectric gadolinium molybdate containing artificial pinning centers of the “field inhomogeneity” type near the edges of the sample. Two scenarios of the evolution of a PDB in interaction with “defects” are proposed on the basis of analyzing the shape of the pulses in a linearly increasing field: small changes of the pulse shape in a weak field and the generation of wedge domains in a strong field. The proposed mechanism of PDB motion due to the generation of steps near the edge of the sample and their longitudinal motion provides a means for explaining the experimentally observed linear field dependence of the PDB velocity and for determining the velocity of the steps.