Discrete Core Research Articles

Line vortices in a three-dimensional ordered Josephson medium at a small pinning parameter

The structure and energy of a line vortex whose axis is aligned with the symmetry axis of a finite-thickness slab indefinitely long in two directions is calculated by solving a set of linear finite-difference equations. Fluxoid quantization conditions in cells near the center of the vortex serve as boundary conditions. An exact solution is approached by iterations in phase stepwise discontinuities that cannot be considered small. A close similarity between the configuration under study and a periodic sequence (chain) of vortices makes it possible to allow for the effect of the domain boundary on the structure and energy of the vortex. It is shown that, at any width of the slab, one can find a pinning parameter value so small that the vortex cannot be viewed as solitary and contributions from other vortices should be taken into account in calculation. Proceeding in this way, one can find the structure and energy of the vortex however small the pinning parameter is. The total energy of the vortex is its intrinsic energy plus the sum of its energies of interaction with other members of the chain. In turn, the intrinsic energy is the sum of the energies of the small discrete core and quasi-continuous outer shell. It is demonstrated that the energy of the core is a linear function of the pinning parameter and is comparable to the energy of the shell.

Refined Analysis of Torsion and In-plane Shear of Honeycomb Sandwich Structures

Multiple-Pass Homogenization (MPH) technique is used to derive formulas for equivalent torsional and in-plane shear stiffness properties of sandwich plates with periodic core structures. In the first pass of the MPH, a discrete core structure is homogenized in a principal axis resulting in piecewise constant material properties, based on which the second pass can be analytically processed with respect to macroscopic torsion and in-plane shear modes. Two equivalent shear stiffness properties of periodic core structures, G* cxy and G* cxy, corresponding to torsion and in-plane shear, respectively, are conceptually and analytically distinguished from each other. By using the Saint-Venant’s semi-inverse method and periodic boundary conditions, analytical solutions of the equivalent shear stiffness are explicitly obtained in the form of Fourier series, which consist of a Voigt-type upper bound term and a correction term. Effects of thickness ratio and core transverse shear stiffness on the two equivalent shear stiffness properties are assessed and discussed. The approximation scheme proposed by this study improves modeling of sandwich structures as orthotropic plates, which is expected to be useful in the practical design and optimization of sandwich structures.

Structure of a Quantized Vortex near the BCS-BEC Crossover in an Atomic Fermi Gas

In order to clarify the structure of a singly quantized vortex in a superfluid fermion gas near the Feshbach resonance, we numerically solve the generalized Bogoliubov-de Gennes equation in the boson-fermion model. The superfluid gap, which contains contributions from both condensed fermion pairs and condensed bosons, is self-consistently determined, and the quasiparticle excitation levels bound in the vortex core are explicitly shown. We find that the boson condensate contributes to enhance the matter density depletion and the discreteness of localized quasiparticle spectrum inside the core. It is predicted that the matter density depletion and the discrete core levels are detectable in the vicinity of the BCS-Bose-Einstein condensation crossover point.

Forced Nonstationary Vibrations of a Sandwich Cylindrical Shell with Cross-Ribbed Core

The equations of nonaxisymmetric vibrations of sandwich cylindrical shells with discrete core under nonstationary loading are presented. The components of the elastic structure are analyzed using a refined Timoshenko theory of shells and rods. The numerical method used to solve the dynamic equations is based on the integro-interpolation method of constructing finite-difference schemes for equations with discontinuous coefficients. The dynamic problem for a sandwich cylindrical shell under distributed nonstationary loading is solved with regard for the discreteness of the core

Line Vortices in a Three-Dimensional Ordered Josephson Medium

Two equilibrium configurations of a line vortex in a three-dimensional ordered Josephson medium are considered: (i) the vortex core is at the center of a cell and (ii) the vortex core is on a contact. Infinite systems of equations describing these configurations are derived. In going to a finite system, the currents far away from the center are neglected. A new technique for solving the finite system of equations is suggested. It does not require smallness of phase discontinuities at all vortex cells and, therefore, can be applied for any values of pinning parameter I down to zero. The structures and energies of both equilibrium states for isolated line vortices are calculated for any I from the range considered. For I >0.3, a vortex can be thought of as fitting a square of 5×5 cells. For lower I, the vortex energy can be expressed as a sum of the energies of the small discrete core and the quasi-continuous outside. The core energy is comparable to the energy of the outside and is a major contributor to the vortex energy when I is not too small. For any I, the energy of the vortex centered on the contact is higher than the energy of the configuration centered at the center of the cell.

A systematic review of the incidence of schizophrenia: the distribution of rates and the influence of sex, urbanicity, migrant status and methodology.

BackgroundUnderstanding variations in the incidence of schizophrenia is a crucial step in unravelling the aetiology of this group of disorders. The aims of this review are to systematically identify studies related to the incidence of schizophrenia, to describe the key features of these studies, and to explore the distribution of rates derived from these studies.MethodsStudies with original data related to the incidence of schizophrenia (published 1965–2001) were identified via searching electronic databases, reviewing citations and writing to authors. These studies were divided into core studies, migrant studies, cohort studies and studies based on Other Special Groups. Between- and within-study filters were applied in order to identify discrete rates. Cumulative plots of these rates were made and these distributions were compared when the underlying rates were sorted according to sex, urbanicity, migrant status and various methodological features.ResultsWe identified 100 core studies, 24 migrant studies, 23 cohort studies and 14 studies based on Other Special Groups. These studies, which were drawn from 33 countries, generated a total of 1,458 rates. Based on discrete core data for persons (55 studies and 170 rates), the distribution of rates was asymmetric and had a median value (10%–90% quantile) of 15.2 (7.7–43.0) per 100,000. The distribution of rates was significantly higher in males compared to females; the male/female rate ratio median (10%–90% quantile) was 1.40 (0.9–2.4). Those studies conducted in urban versus mixed urban-rural catchment areas generated significantly higher rate distributions. The distribution of rates in migrants was significantly higher compared to native-born; the migrant/native-born rate ratio median (10%–90% quantile) was 4.6 (1.0–12.8). Apart from the finding that older studies reported higher rates, other study features were not associated with significantly different rate distributions (e.g. overall quality, methods related to case finding, diagnostic confirmation and criteria, the use of age-standardization and age range).ConclusionsThere is a wealth of data available on the incidence of schizophrenia. The width and skew of the rate distribution, and the significant impact of sex, urbanicity and migrant status on these distributions, indicate substantial variations in the incidence of schizophrenia.

Loss optimization of transverse Bragg resonance waveguides.

Coupled-mode theory was used to analyze guiding in a transverse Bragg resonance (TBR) waveguide structure composed of a GaAs substrate with air holes. This analysis predicts that propagation loss will be minimized for discrete widths of the waveguide core. Although the coupled-mode theory is normally applied to structures with small index perturbations, two-dimensional finite-difference time-domain simulations of the TBR waveguide show good quantitative agreement with the coupled-mode predictions, and these results corroborate the previously predicted existence of discrete core widths for low-loss propagation.

Vocalizations and movements suggest alternative mating tactics in male bearded seals

We combined observations of individual male bearded seal, Erignathus barbabus, behaviour at sea with acoustic localization techniques to investigate their reproductive strategies. Data on trill vocalizations and dive behaviour were collected over consecutive years during the seals' mating season in Svalbard, Norway. Males showed stereotypical dive and vocal displays, with clear individual variation. Acoustic localization provided at-sea locations for 17 males based on variation in trill parameters. Kernel home range analyses showed that 12 individuals displayed at set locations (95% kernels=0.27–1.93km2) and five other males displayed within considerably larger geographical areas (95% kernels=5.31–12.5km2). Males that used the set locations maintained single discrete core areas (50% kernels), while males with large areas moved between multiple core areas. Movement patterns of males suggest that those with small areas patrolled aquatic territories, while those that used larger areas appeared to ‘roam’. Territorial males showed little spatial overlap, while roaming males overlapped substantially with both territorial and other males' areas. Territorial males had significantly longer trills than roamers. We suggest that trill duration may be a useful indicator of male ‘quality’. Territorial male bearded seals may be ‘successful’ individuals while roaming males may be younger animals or males in poorer condition that are unable to maintain an aquatic territory. Our data on underwater vocalizations and movements of male bearded seals thus provide evidence for the use of alternative mating tactics in this species.Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Syntheses, Crystal Structure, and Nuclease Activity of Oxalato-Bridged Dicopper(II) Complexes with Planar N-Donor Heterocyclic Bases

Oxalato-bridged dicopper(II) complexes $[{CuL(H_2O)}_2(\mu - ox)]-(ClO_4)_2 (1-4)$, where L is a bidentate chelating heterocyclic base such as 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyridoquinoxaline (dpq, 3) and dipyridophenazine (dppz, 4), were prepared by treatment of copper(II) perchlorate hexahydrate with sodium oxalate and L in aqueous ethanol. Complex 3 has been structurally characterised. The coordination geometry of the copper centres is essentially square-pyramidal. The ${CuL(H_2O)}$ units are bridged by an oxalate moiety to form the discrete dimeric core. Magnetic studies in the 20-300 K temperature range show the presence of an antiferromagnetically coupled dicopper(II) unit, giving -2J values in the $346-384 cm^{-1}$ range. The redox-active complexes retain the dimeric core in solution, and two quasireversible $Cu^{II}/Cu^I$ couples are observed in the potential range from 0.2 to -0.4 V vs. SCE in a DMF/tris-HCl/0.1 M KCl buffer system (1:1, v/v, pH = 7.2) with a glassy carbon working electrode. The binding and cleavage of DNA by the complexes have been studied. The intercalating ability of the planar bases, determined from the decrease of the fluorescence intensity of ethidium bromide bound calf thymus DNA on addition of the complex, gave the order: 3 > 4 > 2 >> 1. The nuclease activity of the complexes with supercoiled pUC19 DNA in DMF/tris-HCl/NaCl buffer (pH = 7.2) in the presence of ascorbic acid follows the order: 3 > 2 >> 4 > 1. The dpq complex exhibits the most efficient DNA binding and cleavage activity. The dppz complex shows good binding ability but poor nuclease activity.

Pathway studies in the fragmentation of Ge(CH3)4 involving Ge(3d,3p,3s) and C(1s) inner-shell photoexcitation in the range 49.5–450 eV

The dissociative multiple photoionization of tetramethylgermane (Ge(CH3)4) in the valence, and in the Ge(3d,3p,3s) and C(1s) inner-shell regions has been studied by using time-of-flight mass spectrometry coupled to synchrotron radiation in the range 49.5–450eV. Total and individual photoion yields have been recorded as a function of the incident photon energy. Several discrete resonances over a structureless giant resonance are observed below the Ge(3p), Ge(3s) and C(1s) threshold regions. The structureless giant resonance corresponding to the Ge(3d) presumably arises from the continuum enhancement caused by the 3d→ϵf transition. Various monocations of H+, H2+, CHn+ (n=0–4), C2Hn+ (n=0–5), GeHn+, GeCHn+, GeC2Hn+, and GeC3Hn+ are detected in the whole energy range. Dissociation processes have also been investigated by photoelectron–photoion and photoion–photoion coincidence methods. The dominant dissociation channel is found to be CHn+–GeCHn+ in the whole energy examined. Specific energy dependence of dissociation processes is observed in the Ge(3p) and Ge(3s) regions. With the help of ab initio HF/6-311++G(2df,p) calculation, we roughly estimated the photoabsorption positions and symmetries for the discrete core hole states.

Dynamic Problems in the Theory of Sandwich Shells of Revolution with a Discrete Core under Nonstationary Loads

The equations of motion of sandwich shells of revolution with a discrete core are analyzed within the framework of the geometrically nonlinear theory of shells and plates. An efficient numerical algorithm is constructed to investigate nonstationary wave processes in elastic structures that are discrete-inhomogeneous across the thickness. Numerical examples are given

Quiescent double barrier regime in the DIII-D tokamak.

A new sustained high-performance regime, combining discrete edge and core transport barriers, has been discovered in the DIII-D tokamak. Edge localized modes (ELMs) are replaced by a steady oscillation that increases edge particle transport, thereby allowing particle control with no ELM-induced pulsed divertor heat load. The core barrier resembles those usually seen with a low (L) mode edge, without the degradation often associated with ELMs. The barriers are separated by a narrow region of high transport associated with a zero crossing in the E x B shearing rate.

Neolithic Dispersals from the Levantine Corridor: a Mediterranean Perspective

The earliest agro-pastoralists of the Near East are generally held to have emerged in a narrow Levantine Corridor. Agricultural life initially spread from this discrete core zone in the Early Pre-Pottery Neolithic B to adjacent inland regions, only reaching the Mediterranean coast of Syria by the Late Pre-Pottery Neolithic B. Recent discoveries on Cyprus, far to the west of the core zone, prompt re-configuration of several elements of this model. They also provide evidence for characteristics of a regional variant of the PPNB and, in a broader context, fresh data for an understanding of the triggers and mechanics of precocious neolithic dispersals.

On the discrete core of quadrilateral mesh refinement

We present a new approach to quadrilateral mesh refinement, which reduces the problem to its structural core. The resulting problem formulation belongs to a class of discrete problems, network-flow problems, which has been thoroughly investigated and is well understood. The network-flow model is flexible enough to allow the simultaneous incorporation of various aspects such as the control of angles and aspect ratios, local density control, and templates (meshing primitives) for the internal refinement of mesh elements. We show that many different variants of the general quadrilateral mesh-refinement problem are covered. In particular, we present a novel strategy, which provably finds a conformal refinement unless there is none. Copyright © 1999 John Wiley & Sons, Ltd.

Shining Soft X-rays on Magnetic Structures

The study of magnetic materials with x-rays is developing at a breathtaking pace. The methods used in these studies extend magneto-optics—the response of a material to optical excitation as a function of the relative orientation of magnetization and light polarization—to the x-ray regime. One of the key advantages of these techniques is that they are element specific, because the photon wavelength (or energy) in the x-ray regime can be tuned to match the excitation energy of a discrete core electronic level. Also, layer thicknesses of magnetic multilayers and lateral structures in novel magnetic devices that are presently being developed are comparable to soft x-ray wavelengths. Therefore, detailed insight into the magnetic properties of these technologically important magnetic structures can be obtained by use of soft x-rays. The soft x-ray regime is of importance because all technically relevant magnetic materials contain 3d transition metals, for which the 2p excitation that shows the highest sensitivity to the magnetic state lies between 500 and 1000 eV.

Macrocyclic Heterodinuclear Zn(II)Pb(II) Complexes: Synthesis, Structures, and Hydrolytic Function toward Tris(p-nitrophenyl) Phosphate.

A heterodinuclear Zn(II)Pb(II) complex ZnPb(L)(ClO(4))(2).2H(2)O (1) has been obtained where (L)(2)(-) is an unsymmetric macrocycle derived from the 2:1:1 condensation of 2,6-diformyl-4-methylphenol, ethylenediamine and diethylenetriamine and has the "salen"- and "saldien"-like metal-binding sites sharing the phenolic moiety. Its DMF adduct, ZnPb(L)(ClO(4))(2).MeOH.2DMF (1'), crystallizes in the triclinic space group P&onemacr; with a = 14.457(4) Å, b = 14.795(6) Å, c = 10.307(9) Å, alpha = 109.04(5) degrees, beta = 96.24(5) degrees, gamma = 102.56(3) degrees, V = 1995(2) Å(3), and Z = 2. The refinement converges with R = 0.058 and R(w) = 0.060 for 3532 reflections with |F(0)| > 3sigma(|F(0)|). It has a discrete heterodinuclear core with the Zn(II) in the "salen" site and the Pb(II) in the "saldien" site of the macrocycle (L)(2)(-). The Zn has a square-pyramidal geometry together with a methanol oxygen, and the Pb has a seven-coordinate geometry together with one DMF oxygen and one perchlorate oxygen. The complex 1 is converted into [ZnPb(L)(OH)ClO(4)]H(2)O (2) under a weak alkaline condition. Its anhydrous form, [ZnPb(L)(OH)]ClO(4) (2), crystallizes in the monoclinic space group C2/c with a = 25.835(4) Å, b = 13.190(6) Å, c = 16.553 Å, beta = 106.31(2) degrees, V = 5413(2) Å(3), and Z = 8. The refinement converges with R = 0.038 and R(w) = 0.029 for 3944 reflections with |F(0)| > 3sigma(|F(0)|). It has a dimer structure of a dinuclear {ZnPb(L)(OH)}(+) unit having the Zn(II) in the "salen" site and the Pb(II) in the "saldien" site of the macrocycle. The hydroxide is bound to the Zn(II) to afford a square-pyramidal geometry about the metal. The dimeric core [ZnPb(L)(OH)](2)(2+) is formed by the bridge of the hydroxide oxygen to the Pb of the adjacent molecule and vice versa. The geometry about the Pb in the dimer structure is a pentagonal pyramid showing a distortion to "umbrella-like" structure, with the bridging hydroxide oxygen at the apex. In a DMSO solution, an equilibrium exists between the dimeric and monomeric species: [{ZnPb(L)(OH)}(2)](2+) right harpoon over left harpoon 2[ZnPb(L)(OH)](+). On the basis of (31)P NMR and visible spectra, 2 is shown to hydrolyze tris(p-nitorophenyl) phosphate (TNP) into bis(p-nitrophenyl) phosphate (BNP) in DMSO. 1 also exhibits a low activity to hydrolyze TNP into BNP due to the equilibrium [ZnPb(L)(H(2)O)](2+) right harpoon over left harpoon [ZnPb(L)(OH)](+) + H(+). From the reaction mixture with 2, a BNP complex [ZnPb(L)(BNP)]ClO(4) (3) has been isolated. 3 crystallizes in the triclinic space group P&onemacr; with a = 13.494(9) Å, b = 13.88(1) Å, c = 12.765(8) Å, alpha = 94.71(6) degrees, beta = 97.02(6) degrees, gamma = 61.68(5) degrees, V = 2088(2) Å(3), Z = 2. The refinement converges with R = 0.044 and R(w) = 0.056 for 6070 reflections with |F(0)| > 3sigma(|F(0)|). The BNP(-) group bridges the pair of metal ions through its two oxygens, together with two phenolic oxygens of (L)(2)(-). On the basis of the above findings, a mechanistic scheme for the TNP hydrolysis by 2 is proposed; a TNP molecule is bound to the Pb center, and the hydroxide on the adjacent Zn ion attacks the phosphorus nucleus of TNP, leading to the formation of the BNP complex 3.

Prediction of Petrophysical Parameters Based on Digital Video Core Images

Summary Core-slab photography is a common way to document geological information from cores. Past practice has been to photograph core slabs with ordinary cameras that produce paper photographs. The presented method retrieves petrophysical properties from high-resolution digital video core images. The procedures described in this work are based on video images (standard RIO/B camera) of cores taken with a digital recording system. The system is able to record in both visible and UV light at different illumination angles, store images, compress/decompress images, and display one or several images as a continuous long core. The seamless core image is marked with depth scale and can be scrolled, scaled, and zoomed. Facilities for correlation with other related data, such as wireline logs, discrete core data, and microscopy images, are also included in the system. We used homogenous dry core plugs from three North Sea oil fields in this work. We recorded images of plug surface, together with conventional core-analysis data (i.e., porosity, gas permeability, average grain size, and mineralogy). The new method is based on processed digital images: light/shadow patterns are obtained by use of asymmetric, low-angle illumination in the green channel. Texture spectra of the rock material are obtained by dedicated image-analytical processing of these gray-scale images and by detecting textural features by use of a unique set of specially designed texture filters. We then calibrate these spectra with respect to measured petrophysical parameters by use of multivariate calibration [partial least squares (PLS)-regression]. Multivariate calibration is based on a set of representative training images, selected to span representative ranges of the intensive petrophysical parameters being modeled. On the basis of this calibration model, similar gray-level video images from new, unknown core sections (with geologically similar fades) are used to estimate properties of the core material by PLS-prediction. In this study it has been possible to model porosity, gas permeability, and average grain size (ORZ) of different formations with a relatively high accuracy and precision. PLS-modeling/-prediction is a strict empirical calibration procedure. The present method is critically dependent upon a thorough, geologically well-documented training data set. Results show that the method is capable of predicting a continuous log of these three petro-physical parameters based on core images calibrated against a set of routine laboratory core-analysis data taken at discrete intervals for a particular formation. The advantages of the new method are rapid and cost-efficient methods for prediction of petrophysical parameters, particularly from slim cores, and improved integration of geological records with wireline data. The method is proposed to be included in future routine laboratory core analysis studies because of its low cost and ability to predict values continuously along the core.

Inner-Shell Excitation Spectroscopy of closo-Carboranes

Oscillator strength spectra in the region of B 1s and C 1s excitation of three isomeric carborane cage compounds [closo-1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C2B10H12)] have been derived from inner-shell electron energy loss spectra (ISEELS) recorded under electric dipole-scattering conditions. Total ion yield spectra recorded at high resolution with synchrotron radiation are also reported. The spectral features are assigned on the basis of comparisons with spectral predictions derived from the results of ab initio and semiempirical (extended Hückel) molecular orbital calculations. The isomeric and core level variations in the discrete core excitations are related to changes in orbital symmetries as well as variations in electron localization in these isomers. The ionization efficiency in the region of the B 1s and C 1s edges is derived.

Ab initio and density functional calculations of core excitation spectra of CO, H2CO and F2CO

Abstract Calculations of the discrete core excitation spectra, including Rydberg transitions, are reported for CO, H2CO and F2CO employing ab initio and density functional approaches. The highly correlated QDPTCI approach compares well with experimental data and other accurate ab initio results. It appears that reliable values can be currently obtained for small molecules, although considerable uncertainty still affects intensity values, notably those experimentally derived. Comparison with the simpler 1h–1p CI approach indicates some deficiencies of the latter, attributed to the use of inadequate orbitals. The density functional approach proves generally reliable and can be profitably employed for the interpretation of experimental data in large systems, although presently limited to the case of nondegenerate core holes.

Vortex energies in the two-dimensional easy-plane ferromagnet

In the core region of a planar vortex in the two-dimensional Heisenberg model, the continuum approximation breaks down and a cut-off radius must be introduced as the lower limit of the energy integral. By expressing the total vortex energy as the sum of discrete core and continuum contributions it is possible to determine this cut-off radius as well as an accurate estimate of the vortex energy.