Dimensional Anisotropy Research Articles

The role of drift on the diurnal anisotropy and on temporal changes in the energy spectra of the 11-year variation for galactic cosmic rays

Neutron monitor and interplanetary magnetic field data have been used to study features of the role of drift effect in the temporal changes of the diurnal anisotropy and of the energy spectrum of the 11-year variation of galactic cosmic rays. In order to strictly separate the sectors of the interplanetary magnetic field and its influence on the anisotropy of galactic cosmic rays four solar minima periods (1965, 1976, 1987 and 1997) have been considered. An attempt to separate drift effects in the diurnal anisotropy of galactic cosmic rays, first, due to the gradient and curvature of the regular interplanetary magnetic field, and second, due to the heliospheric neutral sheet has been made. The global survey methods has been used to calculate the components of the three dimensional diurnal anisotropy of galactic cosmic rays based on neutron monitors data. It is shown that there are significant differences between the diurnal anisotropy of galactic cosmic rays found in the reliably established various sectors (duration of each sectors is ≥ 4 days) of the interplanetary magnetic field. The interplanetary magnetic field sector structure effect in the diurnal anisotropy of galactic cosmic rays is assumed to be connected to the heliospheric neutral sheet drift, while 22-year variation of the diurnal anisotropy of galactic cosmic rays is assumed to be connected to drift due to the gradient and curvature of the regular interplanetary magnetic field for different qa > 0 and qA<0 solar magnetic cycles. It is shown that the role of drift in the temporal changes of the energy spectrum of the 11-year variation of GCR is insignificant in both of the qA > 0 and the qA<0 solar magnetic cycles. The temporal changes of the exponent index of the 11-year variation of GCR generally is connected with the various character of the diffusion in interplanetary space for minima and maxima epochs of solar activity.

Interplay between the vortex phase coherence and extended disorder defects in the vortex-liquid regime of thin films and superlattices of 123 superconductors

a-axis oriented (CuO_2 planes perpendicular to the substrate) films and superlattices grown on cubic substrates show a structure with 90° microdomains. The microdomains are grains with a 90° rotation of the c axis. In the vortex liquid region, this microstructure induces a change from the usual three-dimensional (3D) behavior of the anisotropy toward a 2D behavior, in a temperature range above the usual crossover from 2D to 3D. Moreover, when the thickness of the superconducting part of the multilayers becomes smaller (or of the same order as) than the microdomain size the 3D dimensional anisotropy behavior is recovered.

磁石・磁性材料の化学 Ｉ Ｓｒ‐フェライトの収縮異方性と組み合わせ焼結接合への応用

For the purpose of producing ferrite part with a complicated shape which has different alignment of the ferrite crystallites, the feasibility of combined sinter joining method was studied. Disk was compacted under magnetic field of 915kA⋅m-1 and ring compacted under non-magnetic field, respectively. The two compacts was assembled into a unit and then sintered at 1150°C.The oriented ferrite compacted under the magnetic field has dimensional anisotropy owing to sintering shrinkage. The anisotropic shrinkage, which will be capable of affecting the joining behavior, was investigated with respect to the effects of powder particle size, powder lubricant, compacting lubricant and compacting pressure before applying the magnetic field. It was found that the sintering shrinkage and degree of ferrite alignment in forming using a dry-type lubricant are largely affected by the compacting pressure before applying the magnetic field, even if the compacting pressure was several MPa or so, and that the alignment of the anisotropic compacts were similar to that of the compact consolidated under non-magnetic field. Effect of the magnetic field on joint strength of the sinter joined compact was also investigated.

Development of a Reynolds stress closure for modeling of homogeneous MHD turbulence

A Reynolds stress closure is developed for homogeneous shear-free turbulence subjected to a strong magnetic field at low magnetic Reynolds numbers. A scalar dimensionality anisotropy parameter is introduced to carry information about the distribution of energy in spectral space. This information is vital in modeling MHD turbulence, as it determines both magnitude and anisotropy of the Joule dissipation tensor. The Joule dissipation tensor is modeled by a tensor function, which is bilinear in the Reynolds stress anisotropy and the unit direction vector of the magnetic field. The tensor function coefficients are second-order in the scalar dimensionality parameter. A phenomenological transport equation for the dimensionality parameter is proposed. The model is closed using the pressure–strain model of Sarkar, Speziale and Gatski and a magnetic destruction term in the standard dissipation equation. The purely magnetic linear problem contains no undetermined constants, while the complete model contains two constants. Model predictions for the case of decaying turbulence show very good agreement with direct numerical simulations.

Microstructure Development in Al2O3‐Platelet‐Reinforced Ce‐ZrO2/Al2O3 Composites

Composites containing Ce‐ZrO2, Al2O3, and aligned Al2O3 platelets were produced by centrifugal consolidation and pressureless sintering, followed by heat treatments at 1600°C for varied duration. Constituents in the consolidated microstructures were either uniformly distributed throughout or segregated into gradient layers, depending critically on platelet content. Quantitative image analysis was used to examine microstructure development with heat treatment. Changes in the volume fraction, dimensional anisotropy, and gradient of pores and platelets, as well as changes in the phase gradient, were quantified. Microstructure development was strongly dependent on the initial microstructure design attained from suspension processing.

New approaches to the study of polyaniline

Freestanding films of polyaniline (PANI) base were fabricated from N,N′-dimethyl propylene urea (DMPU) solution by both casting and spin coating procedures with subsequent drawing. A new near infrared wave guide coupling technique was used to determine the three dimensional refractive indices and symmetry axis direction of the anisotropic films. Quantitative infrared dichroism measurements were made on the same films. A direct correlation was predicted and observed between the measured birefringence and the infrared dichroic function of the PANI absorption bands studied. The three dimensional molecular anisotropy developed by the different fabrication and deformation procedures were compared and found to differ.

Dimensional crossover and confinement-induced optical anisotropy in GaAs T-shaped quantum wires.

On a series of GaAs T-shaped quantum wires (T-QWR's) fabricated by the cleaved-edge-overgrowth method, the spatially resolved polarization-dependent photoluminescence is studied systematically. The dimensional crossover between one and two dimensions has been demonstrated in terms of the characteristic energy of the lateral confinement and the confinement-induced optical anisotropy in T-QWR's. The Bloch functions of holes in T-QWR's and the confinement potential for holes affected by the Coulomb interaction with electrons have been clarified.

Requirements for finite element model generation from CAD data—An approach using numerical conformal mapping

A critical problem facing the mechanical design community is that of bridging the gap between mechanical CAD data (typically boundary rep trimmed NURB surfaces) and finite element models. A number of papers have discussed this issue and identified it as a critical technology for developing future mechanical design methodologies [Crabb, In Implementation Road Map for Design and Manufacturing, D. H. Brown Sponsored Conference, Ann Arbor, MI (1994)]. While a variety of procedures for finite element model generation from CAD data have been proposed and commercialized, the resulting models have, in general, received much resistance from the professional analyst community. A set of criteria by which the quality of a proposed finite element model generation procedure can be evaluated analytically using elementary control theory is discussed. Additional observations of mesh behavior based on the dimensional anisotropy of general geometric components are presented. Finally a criterion for qualitatively evaluating optimal edge orientations for many of the classical element families is discussed. It is suggested that a combination of these approaches provides an opportunity to semi-quantitatively rank order proposed finite element model generation procedures. A finite element model generation procedure based on numerical conformal mapping is then proposed. It is demonstrated that this procedure ranks very highly when evaluated against the previous criteria. Further, a technical proof of concept implementation demonstrates that numerical conformal mapping appears to be suitable for application to a wide variety of boundary rep solid models.

Texture and Microstructure Development in Al2O3-Platelet Reinforced Ce-ZrO2/Al2O3 Laminates Produced by Centrifugal Consolidation

A dispersed, low-solids-fraction suspension containing Ce-ZrO2, fine Al2O3 and 5 vol% Al2O3-platelets was segregated using centrifugal consolidation to produce functionally gradient laminates (FGLs). Platelet alignment facilitated efficient packing of highly anisometric platelets to high densities. The complexity and anisotropy of the microstructure warrants a quantitative analysis of the microstructural evolution prior to any property evaluation. Quantitative image analysis was used to examine changes in the volume fraction, dimensional anisotropy, and gradient of pores and platelets with sintering time. In all cases, special attention was given to the effects of texture during microstructural evolution. Platelet alignment enhanced densification via anisotropic shrinkage, overcoming constraint that otherwise inhibits densification in platelet-containing materials. Also, platelet alignment and microstructural design were used to initiate and control anisotropic grain growth. Platelet growth (at the expense of smaller particles of the same phase) during annealing promoted further phase segregation and produced higher platelet content composites consisting of larger platelets, without having to consolidate high contents of large platelets.

Magnetic resonance axonography of the rat spinal cord.

In spite of dramatic advancement in biomedical imaging technologies, non-invasive visualization of anatomic detail of the spinal cord has remained a major challenge. Here, a novel color-coded contrast method for magnetic resonance imaging (MRI) which provides superb resolution of the spinal cord in live animals, comparable to that of histological preparations, is described. The method, referred to here as three dimensional anisotropy (3DAC) contrast MRI, displays cross-sectional images in the full visible color spectrum, encoding directional information regarding intravoxel anisotropic water motion in space. Since neuronal fibers, especially axons, possess significantly higher intravoxel anisotropic water motion compared with other elements in the nervous system, 3DAC is highly sensitive to axonal direction and density. Axonography of the spinal cord of rats obtained using this technique showed anatomic detail at a resolution hitherto unobtainable in live animals.

A New Variety of Natural Graphite Powder: Elaboration and Properties

Abstract An original process was performed to obtain pulverulent graphite powder by grinding an exfoliated graphite—organic solvent mixture. This method leads to particles characterized by a large dimensional anisotropy. The sizes of the flakes are: an average diameter of about ten micrometers and a thickness below 0.1 micrometer. Scanning electron microscopy confirms this morphology; transmission electron microscopy indicates that most of the flakes are single crystals. Specific area is superior to 20 m2/g with a surface homogeneity identical to that of the parent exfoliated graphite. The planeity of the particles allows them to lay on a surface with a mosaic spread less than 15°. This new material has been called G.M.P. “Graphite Micronique Plat” (Flat Micronic Graphite)

Study of Crossover Behaviour in Layered Antiferrormagnets

AbstractThe dimensional crossover from 3D to quasi‐2D character in magnetic properties of layered antiferromagnets such as La2CuO4 (2‐1‐4) is studied. The theoretical framework is based on an anisotropic Heisenberg model. Random phase approximation (RPA) is used to obtain a self‐consistent expression for the magnetization. It is shown that under specific approximations on this theory, free‐spin‐wave (FSW) results can be obtained. With the help of this self‐consistent theory it is shown that the crossover occurs as the value of dimensional anisotropy parameter (Jc/Jab) changes from about 10−3. Numerical results for the sublattice magnetization are obtained depicting this crossover and compared with free‐spin‐wave results. The results obtained from this self‐consistent calculations are in excellent agreement with the experimental results obtained for 2‐1‐4 materials.

Dimensional crossover and anisotropy effects in the magnetization of Fe(110)/Ag(111) superlattices

Recent experimental data, showing a dimensional crossover of the T-dependent magnetization in MBE-grown Fe(110)/Ag(111) superlattices with different Ag spacer thickness, are theoretically reanalyzed, using a Heisenberg model of localized spins with intraplane and interplane exchange interactions and including easy-plane and easy-axis surface anisotropies. The latter ones are shown to play an important role in the stabilization of the long range order, more evident for large thickness of the Ag spacer. The spin-wave dispersion curves and the magnetization are calculated in the framework of a Green’s function method and the correct asymptotic forms for the temperature dependence of the spin deviation in the quasi-2D regime (T ln T) and in the 3D one (T3/2) are obtained.

Spinning characteristics of mesophase pitches derived from naphthalene and methylnaphthalene with HF/BF 3

Transverse shape, texture, and the degree of preferred orientation along the fiber axis in mesophase pitch fibers were studied by varying spinning temperature and spinning nozzle to clarify the influences of the structure of mesophase pitch. The mesophase pitch derived from methylnaphthalene (mNP) showed much larger Lc(002) and smaller d 002 than that from naphthalene (NP), indicating larger and better ordered stacking of the aromatic planes in the former pitch, although their softening points, melt viscosities, spinning temperatures, and molecular weight distributions were much the same. MNP provided a higher degree of preferred orientation in the round shaped fiber, which led to an open wedge in the radial texture in a particular spinning temperature range, and larger width/ thickness ( W T ) ratio of tape spun through the slit-shaped spinning nozzle. Addition of NP to mNP in their melt states decreased Lc(002), lowering the degree of orientation and decreasing W T ratio according to the added amount. Such structural factors of fiber and tape are related to the stacking of aromatic molecules in the mesophase pitches. The higher stacking may emphasize the dimensional anisotropy of molecular assembly, influencing the viscoelastic flow of the mesophase pitch in the spinning nozzle. Larger anisotropy may also contribute to the better alignment of molecular assembly along the spinning nozzle wall.

The Effect of Polymers on Ceramic Suspension Rheology and Green Component Properties

AbstractCeramic suspensions were formulated based on an alumina/plasticized-polymer system. The total polymer volume in suspension was held constant, while the relative amount of high-to-low molecular weight polyvinyl butyral (PVB) in suspension was varied. Experiments were performed to elucidate the effects of polymer molecular weight and distribution on the rheological properties of these casting suspensions as well as on the green microstructure of tape-cast components. The polymer properties affected not only the suspension viscosity at a given shear rate as expected, but also the shear thinning behavior of each suspension. Tapes (thickness ≈ 250 μm) were cast from these suspensions and their properties were evaluated. Pore volume, a measure of the packing efficiency, was found to depend strongly on the polymer molecular weight and distribution. In addition, preliminary lamination studies revealed that dimensional stability and anisotropy were also affected by the relative amount of high-to-low molecular weight PVB. A direct correlation was shown to exist between the shear thinning behavior of these suspensions and the resulting dimensional anisotropy exhibited by the tapes cast from each of them. These results demonstrate that polymeric aids influence not only the suspension rheology, but the green component microstructure as well, and, hence, are an integral aspect of ceramic processing.

Modèle d'anisotropie de susceptibilité magnétique induite par orientation préférentielle de forme de marqueurs paramagnétiques anisotropes dans une roche déformée

Many rocks contain minerals with a significant paramagnetic anisotropy at room temperature. Quantitative relationships between preferred dimensional orientation (O.P.F.) and anisotropy of magnetic susceptibility (A.S.M.) constitute the bases of magnetic methods of structural analysis. These relationships are derived from strain response models, assuming that (1) a polymineralic rock is made of distinct groups of minerals dispersed in a non-magnetic deforming viscous matrix and (2) these groups are mechanically and magnetically independent. Accordingly, the partial magnetic contribution of each mineral may be deduced knowing the theoretical behaviour of one population of markers of that mineral. The bulk magnetic behaviour of the rock is obtained by weighting the contribution of each population by its volumic proportion in the rock. The mechanical behaviour of the rock is assumed to be described by Fernandez's O.P.F. model. Because of the magnetic properties of minerals and the magnetic and mechanical independence of each population, the bulk magnetic fabric may be described by the Relative Magnetic Susceptibility Tensor [S ij ]. We consider firstly the case of markers for which K 1 =K 2 ¬=K 3 (cylindrical symmetry). For isovolumic axial flattening or constriction on rocks containing one single family of magnetic markers a very simple analytical solution is derived showing that the tensor [S ij ] is related to the strain intensity and to two parameters: the first parameter (k) is a function of the shape of the markers; the second (r) is a function of the intrinsic magnetic anisotropy of the markers. The eigenvectors of [S ij ] coincide with the principal axes of the strain. It is expected that knowing the magnetic properties of the minerals constituting a rock experimental measurements of [S ij ] may be used to estimate the finite strain (λ 3 ). The «power law» derived by Rathore is not verified by our model. Rathore's model gives only approximate result

The Mechanisms by Which Splitting Occurs Along Sheared Edges and in Charpy Specimens of a 12% Chromium Steel

A study was made of the delamination or splitting behaviour in transverse Charpy specimens and along the sheared edges of 12-mm plate specimens of a low carbon titanium-stabilized 12% chromium steel (designated 3CR12).It was found that planar-oriented splits, parallel to the rolling plane, which occur during transverse impact tests and shearing, result in a decrease in the impact shelf energy as well as in the ductile-to-brittle transition temperature. The degree of planar splitting is controlled mainly by the degree of mechanical anisotropy, which is related to the dimensional anisotropy of the grain structure. It is shown that splitting cannot be attributed to microstructural features alone; it is governed by different mechanisms that depend upon both the microstructure and the stress distribution at the crack tip. Splitting at sheared edges, which are subject to intense shear deformation, are nucleated by planar-oriented inclusions. Splitting in Charpy specimens was found to occur by transgranular cleavage, as well as by decohesion of ferrite-ferrite and ferrite-martensite grain boundaries, and was not related to the presence of inclusions in the microstructure. The excellent transverse toughness of 3CR12 steel is due to its fine-grained microstructure and the fact that splitting precedes transverse fracturing.Although a relatively high through-thickness tensile ductility was obtained for 12-mm 3CR12 plate, It is concluded that 12-mm 3CR12 plate could be susceptible to lamellar tearing in highly restrained welded joints.

The Mechanisms by Which Splitting Occurs Along Sheared Edges and in Charpy Specimens of a 12% Chromium Steel

A study was made of the delamination or splitting behaviour in transverse Charpy specimens and along the sheared edges of 12-mm plate specimens of a low carbon titanium-stabilized 12% chromium steel (designated 3CR12).It was found that planar-oriented splits, parallel to the rolling plane, which occur during transverse impact tests and shearing, result in a decrease in the impact shelf energy as well as in the ductile-to-brittle transition temperature. The degree of planar splitting is controlled mainly by the degree of mechanical anisotropy, which is related to the dimensional anisotropy of the grain structure. It is shown that splitting cannot be attributed to microstructural features alone; it is governed by different mechanisms that depend upon both the microstructure and the stress distribution at the crack tip. Splitting at sheared edges, which are subject to intense shear deformation, are nucleated by planar-oriented inclusions. Splitting in Charpy specimens was found to occur by transgranular cleavage, as well as by decohesion of ferrite-ferrite and ferrite-martensite grain boundaries, and was not related to the presence of inclusions in the microstructure. The excellent transverse toughness of 3CR12 steel is due to its fine-grained microstructure and the fact that splitting precedes transverse fracturing.Although a relatively high through-thickness tensile ductility was obtained for 12-mm 3CR12 plate, It is concluded that 12-mm 3CR12 plate could be susceptible to lamellar tearing in highly restrained welded joints.

The effect of hydrostatic pressure on the Fermi surfaces of rubidium and cesium

The anisotropy and absolute values of the pressure coefficients for the Fermi surfaces of rubidium and cesium in the 25-bar pressure range at 1 K have been measured. In both cases the area pressure coefficient anisotropy is considerably greater than the dimensional anisotropy, about 4.7 times in Rb and 5.6 times in Cs. The mean values, at 2.133±0.005×10−2 kbar−1 for Rb and 2.874±0.01×10−2 kbar−1 for Cs, are in fair agreement with those derived from ultrasonic measurements of the bulk modulus, but are several percent lower than the corresponding piston-displacement figures.

Escherichia coli lac repressor is elongated with its operator DNA binding domains located at both ends

From small-angle X-ray scattering experiments on solutions of Escherichia coli lac repressor and repressor tryptic core, we conclude that the domains of repressor that bind to operator DNA lie at the ends of an elongated molecule. The addition of the inducer, isopropyl-β- d-thiogalactoside, to either repressor or core does not produce a measurable structural change, since the radius of gyration of repressor is 40.3 ± 1.9 Å without and 42.2 ± 1.7 Å with isopropyl-β- d-thiogalactoside; the core radius of gyration is 35.4 ± 1.1 Å without ligand and 36.3 ± 1.1 Å with isopropyl-β- d-thiogalactoside. In the context of data from single crystals of repressor and core, the measured radii of gyration are shown to be consistent with a core (or repressor) molecule of dimensional anisotropy 1: (1.5 to 2.0): (3.0 to 4.0). The 5 Å difference in radius of gyration between native and core repressor is interpreted to mean that the amino terminal 59 residues (headpieces) lie at the ends of an elongated repressor molecule. This structure implies that the repressor may have DNA binding sites, consisting of two adjacent headpieces, on each end of the molecule and this binds to the DNA with its long axis perpendicular to the DNA.