Wedge Structures Research Articles

Magnetization study of interlayer exchange in semiconductor EuS–PbS ferromagnetic wedge multilayers

Interlayer coupling was experimentally studied in semiconductor EuS–PbS ferromagnetic superlattice wedge structures grown on KCl (0 0 1) substrates with the wedges covering the semiconductor nonmagnetic PbS spacer layer thickness from 0.3 to 6 nm. Structural parameters of the wedges were examined by X-ray diffraction analysis of EuS–PbS superlattice period. Measurements of magnetic hysteresis loops of EuS–PbS structures were performed by both SQUID (for small terminal parts of the wedge) and MOKE (magneto-optical analysis along the wedge) magnetometry. A strong decrease of magnetic remanence and an increase of saturation field observed for EuS–PbS structures with the PbS spacer thickness decreasing below about 1.5 nm is discussed in terms of the influence of antiferromagnetic interlayer coupling.

Composite-wedge pseudomorphs in Flanders, Belgium

Large-scale polygonal crop marks underlain by sand-filled wedge structures cover extensive surfaces on the West Flanders plateau (Flanders, Belgium). Wedge structures (∼1.0 m wide, up to ≥1.6 m deep) observed at several sites are interpreted as composite-wedge pseudomorphs, formed by thermal contraction cracking in a permafrost environment. The composite infilling points to former relatively dry conditions on the plateaus. Superimposed wedge structures may indicate discrete growth stages. The structures probably formed during the Pleniglacial (comprising Marine Isotope Stages 2–4), although an older age is not excluded. The widespread occurrence of composite-wedge pseudomorphs on the plateaus conflicts with the literature suggesting that ice-wedge pseudomorphs are dominant in Flanders. As a consequence, palaeoenvironmental reconstructions may have been biased towards environmental conditions suitable for ice-wedge formation. Ice wedges probably formed mainly in depressions, whereas composite wedges may have been common on the plateaus. Copyright © 2006 John Wiley & Sons, Ltd.

Syncollisional delamination and tectonic wedge development in convergent orogens

Delamination of the lower crust and lithospheric mantle has occurred in several convergent orogens, most notably the Alps and Pyrenees. Some workers suggest that the process is mechanically similar to tectonic wedging and triangle‐zone development, and dependent on the pattern of mechanical layering. A search of over 35 orogens that have been explored by geophysical techniques showed that no correlation exists between crustal composition and delamination. Delamination of passive subducting plate margins is more common than that of tectonically and/or volcanically active overriding margins. Estimates show that the lithospheric mantle of cool passive margins may contain greater net negatively buoyant mass than warmer active margins. The top of the lower lithospheric layer containing the greatest net negatively buoyant mass is aligned with a weak zone near the Moho. Passive margin lithosphere thus has a greater tendency to delaminate during a collisional event than active margin lithosphere. For delamination to initiate above the Moho, the lower crust must be subducted or depressed to allow for exposure to eclogite grade conditions. Transformation of the mafic lower crust to mafic eclogite also creates a likely delamination horizon above a lower lithospheric layer containing net negatively buoyant mass aligned with a weak zone in the lithosphere. In contrast to the stratigraphic delamination that is key to the development of small‐scale wedge structures, syncollisional delamination is likely to occur in response to an increase in the lateral tectonic stress on a weak horizon already stressed by net negatively buoyant mass in the lower lithosphere.

Intra- and Intermolecular Interactions between Intracellular Domains of Receptor Protein-tyrosine Phosphatases

The presence of two protein-tyrosine phosphatase (PTP) domains is a striking feature in most transmembrane receptor PTPs (RPTPs). The generally inactive membrane-distal PTP domains (RPTP-D2s) bind and are proposed to regulate the membrane-proximal PTP domains (RPTP-D1s). We set out to characterize the interactions between RPTP-D1s and RPTP-D2s in vivo by co-immunoprecipitation of hemagglutinin-tagged fusion proteins encoding the transmembrane domain and RPTP-D1 and myc-tagged RPTP-D2. Seven RPTPs from four different subfamilies were used: RPTPalpha, RPTPepsilon, LAR, RPTPvarsigma, RPTPdelta, CD45, and RPTP(mu). We found that RPTP-D2s bound to RPTPs with different affinities. The presence of intrinsic RPTP-D2 altered the binding specificity toward other RPTP-D2s positively or negatively, depending on the identity of the RPTPs. Furthermore, the C terminus of RPTP-D2s and the "wedge" in RPTP-D1s played a central role in binding specificity. Finally, full-length RPTPalpha and LAR heterodimerized in an oxidative stress-dependent manner. Like RPTPalpha-D2, the LAR-D2 conformation was affected by oxidative stress, suggesting a common regulatory mechanism for RPTP complex formation. Taken together, interactions between RPTP-D1s and RPTP-D2s are a common but specific mechanism that is likely to be regulated. The RPTP-D2s and the wedge structures are crucial determinants of binding specificity, thus regulating cross-talk between RPTPs.

Sequence conservation in the chagasin family suggests a common trend in cysteine proteinase binding by unrelated protein inhibitors.

The recently described inhibitor of cysteine proteinases from Trypanosoma cruzi, chagasin, was found to have close homologs in several eukaryotes, bacteria and archaea, the first protein inhibitors of cysteine proteases in prokaryotes. These previously uncharacterized 110-130 residue-long proteins share a well-conserved sequence motif that corresponds to two adjacent beta-strands and the short loop connecting them. Chagasin-like proteins also have other conserved, mostly aromatic, residues, and share the same predicted secondary structure. These proteins adopt an all-beta fold with eight predicted beta-strands of the immunoglobulin type. The phylogenetic distribution of the chagasins generally correlates with the presence of papain-like cysteine proteases. Previous studies have uncovered similar trends in cysteine proteinase binding by two unrelated inhibitors, stefin and p41, that belong to the cystatin and thyroglobulin families, respectively. A hypothetical model of chagasin-cruzipain interaction suggests that chagasin may dock to the cruzipain active site in a similar manner with the conserved NPTTG motif of chagasin forming a loop that is similar to the wedge structures formed at the active sites of papain and cathepsin L by stefin and p41.

Laser-induced precession in canted-spin ferromagnets

The laser-induced precession of the magnetization vector is studied for Cu(1 1 1)/Ni/Cu wedge structures using the time-resolved magneto-optical Kerr effect. A comparison with Landau–Lifshitz–Gilbert simulations is presented. Thus we obtain a quantitative estimate of the anisotropy parameters and an unambiguous verification of the canted-spin arrangement.

Quaternary geology and assessment of aggregate resources of Korea for the national industrial resources exploration and development

Abstract Demand for aggregates in Korea, fueled by construction, has increased rapidly in recent years. Quaternary aggregate resources are associated with Holocene alluvial deposits and shallow marine sands, and with fluvial sequences developed during the Late Quaternary. Soil wedge structures developed in palaeosols on river terraces indicate that periglacial conditions prevailed during oxygen isotope stages 2 and 4. Along the margins of the Yellow Sea, sea level fluctuations involved a drop to −120 m a.s.l. during the LGM ca. 15,000 yr BP, resulting in the formation of three seismosequences, the uppermost sequence of which contains aggregate sediments. Repetitive episodes of sedimentation along the major river valleys have resulted in the production of fluvial aggregates, preferred by construction engineers. Intensive exploitation of these resources, however, has forced Korea to turn to other Quaternary deposits for aggregate.

Growth and magnetic oscillatory exchange coupling of Mn/Fe [formula omitted] and Fe/Mn/Fe [formula omitted

The magnetic ordering and the interlayer exchange coupling in Mn and Fe/Mn wedge structures grown epitaxially on Fe(0 0 1) whisker substrates were investigated using scanning electron microscopy with polarization analysis (SEMPA). In bare Mn/Fe(0 0 1) samples, the magnetization of the top Mn layer is collinear with the Fe magnetization, and oscillates between ferromagnetic and antiferromagnetic alignment as the Mn thickness increases. The period of the oscillation is two layers of Mn, consistent with the growth of an antiferromagnetic Mn wedge. The bare Mn behaves very much like antiferromagnetic Cr, however the magnetic coupling in the Fe/Mn/Fe(0 0 1) sandwich structures is very different. For Mn thicknesses greater than four layers, the coupling between the top Fe layer and the Fe whisker substrate is not collinear. Between 4 to 8 layers of Mn, the direction of the top Fe in-plane magnetization lies at an angle of 60–80° relative to the magnetization of the Fe substrate. Beginning at the 9th Mn layer, the direction of the coupling oscillates, with a two-layer period, between 90°− φ and 90°+ φ, where φ is sample dependent. Values of φ between 10 and 30° were observed.

Conformal mapping and field singularities in perfectly conducting wedge and rotational symmetry structures

Exponential function models already introduced in the literature for singular fields near perfectly conducting wedges are derived from conformal mapping. The performances of a numerical two-step procedure based on conformal mapping and finite-difference calculations are then discussed for axisymmetric geometries, in particular, for cone tips and for cone tips terminating with small spheres. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 191–195, 2000.

Conformal mapping and field singularities in perfectly conducting wedge and rotational symmetry structures

Exponential function models already introduced in the literature for singular fields near perfectly conducting wedges are derived from conformal mapping. The performances of a numerical two-step procedure based on conformal mapping and finite-difference calculations are then discussed for axisymmetric geometries, in particular, for cone tips and for cone tips terminating with small spheres. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 191–195, 2000.

Anisotropy in Fe layers imestigated by ferromagnetic resonance

Ferromagnetic resonance (FMR) is performed together with superconducting quantum interference device and Faraday magnetometry to investigate the magnetic anisotropy of epitaxial bcc Fe(001) films on Ag(001) and Cr(001) The Fe/Ag(001) and Fe/Cr(001) layers as well as corresponding wedge structures were grown by molecular-beam epitaxy. On these samples the following investigations were done. Firstly the temperature dependence of the surface anisotropy of the Fe/Ag system was determined. To achieve high precise values of the surface anisotropy a locally resolved FMR technique was applied to an Fe wedge film coated in Ag layers. Secondly the influence of strong deformation of the Fe layer on the magnetic properties was investigated by high-dose Fe-ion implantation in thermally immiscible Fe/Ag(001) layer structures. FMR measurements have shown a pronounced tetragonal symmetry of the anisotropy, which can be precisely controlled by implantation conditions. Thirdly in Fe/Cr single-crystal layers the magnetic parameters of the Fe films show an anomalous temperature behaviour for a distinct Cr thickness range that can be related to the spin-flip transition. The transition temperature decreases continuously with decreasing Cr thickness, ceasing in a suppression of the spin flip for Cr thicknesses below 60 A, Below the transition temperature an increase in the dynamic contribution to the FMR linewidth occurs which depends on the Cr thickness. The temperature variation in the dynamic line broadening is explained by a band theoretical description which agrees qualitatively with the temperature variation in the magnetic Fe moment.

Symmetry breaking at magnetic surfaces and interfaces

Examples are presented of how symmetry breaking enters into consideration of the physical properties of magnetic surfaces and ultrathin films. The role of magnetic anisotropy is discussed with a view to understanding: (i) the existence of two-dimensional magnetic long-ranged order at finite temperature; (ii) magnetization scaling behavior at the Curie transition; (iii) the two-dimensional spin reorientation transition; and (iv) step-induced magnetic behavior. Experimental examples cited include ultrathin magnetic Fe and Co overlayer and wedge structures grown onto single crystal substrates that are either flat or curved to produce vicinal surfaces with a continuous gradient in the step density. Also included is an example of an atomically flat manganite intergrowth that appears as a stacking fault in a bulk single crystal of a naturally layered structure.

Oblique incidence MOKE in ultrathin Au/Co wedges

Magneto-optic Kerr effect (MOKE) spectra on ultrathin Au/Co wedge structures with perpendicular magnetic anisotropy are investigated in a wide range of angles of incidence. Experimental results are well explained by the electromagnetic wave theory for stratified media. This agreement is consistent with a good definition of layer thicknesses on an atomic scale and sharp Au–Co inter-faces. Analytical expressions for MOKE at oblique incidence, in sandwiches and bilayers, are presented.

The Global Geoscience Transect from Altay, China to the Philippine Sea and Taiwan

The geoscience transect from Altay to Taiwan has a total length of ∼4,334 km. The transect begins along the northwestern border of China and ends in the Philippine Sea basin to the east of Taiwan. Systematic seismic soundings, magnetotelluric soundings, and heat-flow, gravity, aeromagnetic, and geological studies were conducted along the transect. The main tectonic features that are suggested by geological and geophysical data collected along the transect can be understood in the context of the tectonic history of the craton. The tectonic evolution of China can be divided into three stages— (1) development of continental crust during the Archean era with separate cratonic blocks (the West China and the East Asia cratons) that subsequently were juxtaposed to form the Old China craton; (2) remobilization and breakup of the continental land mass during the Paleozoic period, forming the Northern and the Southern China plates; and (3) development of three tectonic domains (the eastern extensional domain, the Qinghai-Tibet compressional domain, and the relatively stable tectonic domain between them) of continental China during the Mesozoic to Cenozoic period, subject to the effects of Pacific and Indian plate motions. The convergence between cratonic blocks in China resulted in wedge structures. The deformation of lithosphere began with the mantle lithosphere, followed by the crust. Where cratonic lithosphere was compressed, such as in the West China craton, the mantle lithosphere folded and the crust was imbricated along thrusts forming major nappe structures along zones of weakness. Where a relatively weak accreting lithosphere, such as Tibet, was compressed, the mantle lithosphere shortened and thickened, with decoupling between the crust and the mantle lithosphere. Where cratonic lithosphere was extended, such as in the East Asian craton, tectonic thinning resulted in formation of a rhombochasm basin or rift. The inhomogeneity of mantle material has exerted an important effect on surface structure, with the stable region at the surface frequently coinciding with mantle structure. The boundaries of mantle features coincide with zones of mineralization that contain deposits with economic potential.

Rigorous solutions of acoustic wave diffraction by penetrable wedges

A well-known problem of acoustic wave propagation in two fluid wedges with different densities and wave speeds is addressed by a recently developed approach to more general problems of wave propagation in bi-material solid wedges. The obtained solutions are valid for arbitrary frequencies and the approach is also extendable to wedge structures in which one or both wedges support propagation of shear waves.

Structural insight into the south Ryukyu margin: effects of the subducting Gagua Ridge

This study presents three multi-channel deep seismic reflection profiles located in the south Ryukyu margin between 122°30′E and 123°30′E, where a N-S-trending oceanic ridge, the Gagua Ridge, is entering the subduction zone, for the purpose of examining the effects of ridge subduction on structures of the forearc region. Structural features which correspond to different stages of the oblique ridge subduction are observed. East of 123°E, a short-lived sequence of indentation, tunneling, then resumption of frontal accretion occurred in the accretionary wedge (the Yaeyama Ridge) as the subducted portion of the Gagua Ridge swept the overriding Ryukyu margin from below along the northwesterly convergent direction. Under the forearc basin, the subducted portion of the Gagua Ridge is uplifting the arc basement to form the Nanao Basement Rise which separates the sedimentary strata of the Nanao and East Nanao forearc basins. Results from this study suggest that the oblique subduction of the Gagua Ridge has not only affected accretionary wedge structures but also the arc basement of the south Ryukyu margin.

Analysis of the diffraction coefficients of corrugated surfaces with the use of a numerical GTD method

In this article the numerical method for extracting diffraction coefficients of wedge structures is extended to calculate diffraction coefficients of wedges with the corrugated surfaces for which no closed-form expressions exist. Extensive numerical results are given, and they may be useful in design and engineering applications. We also provide some assessment of the diffraction coefficients of artificially soft surfaces derived more recently. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 297–303, 1997

Magnetic quantum well states in ultrathin film and wedge structures

Magnetic quantum-well (QW) states are probed with angle- and spin-resolved photoemission to address critical issues pertaining to the origin of the giant magnetoresistance (GMR) optimization and oscillatory coupling of magnetic multilayers. Two epitaxial systems are highlighted: Cu/Co(wedge)/Cu(100) and Cr/Fe(100)-whisker. The confinement of Cu sp-QW states by a Co barrier requires a characteristic Co thickness of 2.2/spl plusmn/0.6 /spl Aring/, which is consistent with the interfacial Co thickness reported to optimize the GMR of Permalloy-Cu structures. The controversial k-space origin of the 18-/spl Aring/ long period oscillation in Fe/Cr multilayers is identified by the vector that spans the d-derived lens feature of the Cr Fermi surface , based on the emergence of QW states with 17/spl plusmn/2 /spl Aring/ periodicity in this region.

Geometrical optics exact solutions for two classes of dielectric wedge structures

Two classes of dielectric wedges with a common edge are considered. For a certain direction of incidence and polarization of the primary plane wave, conditions are given under which total transmission occurs at all interfaces, i.e., the edge does not scatter and geometrical optics is the exact solution to the boundary value problem.

Frontal Wedge Structures in the Flathead Creek Area, Northeast British Columbia: ABSTRACT

Frontal Wedge Structures in the Flathead Creek Area, Northeast British Columbia: ABSTRACT