Role Of Anisotropy Research Articles

In situ bending of layered compounds: The role of anisotropy in Ti2AlC microcantilevers

The paper concentrates on in situ bending tests and analysis of the failure of materials exhibiting strong anisotropy. As a typical example, Ti2AlC microcantilevers (MCs) were scrutinized. The anisotropic flexural strength of Ti2AlC MCs was measured, and the strength of the strong orientation was found to be two and half times as high as that of the weak orientation. The transition of fracture strength and mechanisms could be evaluated. Our findings have generic implications for future study on the fracture behavior of layered materials. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The role of anisotropy in holographic modified gravity

In this paper, we study a cosmological implication of holographic dark energy in modified gravity. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in a nonisotropic universe. The purpose of this work is to develop a reconstruction scheme for the modified gravity with f(R) action using the holographic energy density. Hence one can generate a phantom-like equation of state from a holographic dark energy model in a nonisotropic universe in the modified gravity cosmology framework.

Lewis' law revisited: the role of anisotropy in size–topology correlations

Since F T Lewis' pioneering work in the 1920s, a linear correlation between the average in-plane area of domains in a two-dimensional (2D) cellular structure and the number of neighbors of the domains has been empirically proposed, with many supporting and dissenting findings in the ensuing decades. Revisiting Lewis' original experiment, we take a larger set of more detailed data on the cells in the epidermal layer of Cucumis, and analyze the data in the light of recent results on size–topology correlations. We find that the correlation between the number-of-neighbor distribution (topology) and the area distribution is altered over that of many other 2D cellular systems (such as foams or disc packings), and that the systematic deviation can be explained by the anisotropic shape of the Cucumis cells. We develop a novel theory of size–topology correlation taking into account the characteristic aspect ratio of the cells within the framework of a granocentric model, and show that both Lewis' and our experimental data is consistent with the theory. In contrast to the granocentric model for isotropic domains, the new theory results in an approximately linear correlation consistent with Lewis' law. These statistical effects can be understood from the increased number of configurations available to a plane-filling domain system with non-isotropic elements, for the first time providing a firm explanation of why Lewis' law is valid in some systems and fails in others.

Role of anisotropy in dipolar bosons in triple-well potentials

Mesoscopic samples of polarized dipolar atoms confined in three spatially separated traps conform an extended Bose-Hubbard Hamiltonian in which different quantum phases appear depending on the competition between tunneling, on-site and long range inter-site dipole-dipole interactions. Here, by choosing an appropriate configuration of triple-wells, we analyze the role played by the anisotropic character inherent to the dipolar interaction in the phase diagram of the system. We further characterize the different phases as well as their boundaries by means of their entanglement properties.

Role of anisotropy in the expansion-free plane gravitational collapse

In this paper, we study the instability range of the collapsing fluid bounded by the plane geometry. For this purpose, the expansion-free dynamical equations in Newtonian and post-Newtonian regimes are obtained through perturbation scheme. We investigate the role of pressure anisotropy and energy density inhomogeneity in the instability ranges of expansion-free fluid. It is concluded that the instability regions for the plane geometry turns out to be large than the spherical case.

Energy landscape and dynamics of an HP lattice model of proteins —The role of anisotropy

We present the results of exact numerical studies of the energy landscape and the dynamics of a 12-monomer chain comprised of two types of amino acids called the HP model. We benchmark our findings against the corresponding results of previous studies of a Go model, which encodes the native state conformation. We also show how the energy landscape gets modified dramatically and improves the folding properties on incorporating the inherent anisotropy of a chain, albeit in a simplified manner.

Modification of interface anisotropy and its effect on microstructural evolution during ostwald ripening

We performed an experiment to study the role of anisotropy in interfacial energy during the coarsening of a complex oxide CaCu3Ti4O12 (CCTO) material system. When we altered the interface anisotropy, we observed that evolution and sizes of spherical grains completely altered to facetted cubes. When interface became anisotropic, crystal growth appears to occur by the surface attachment/detachment, the motion of ledges, and the nucleation of new layers. Our observations showed that new layers grew by screw dislocation mechanism. This suggests that nucleation limited coarsening is occurring by the development of a transient bimodal grain size distribution consisting of large growing grains with step. In presence of PbO we always observed the development of shaped nucleus which grew larger. Sometimes very complex shaped crystals grew as a metastable shape. These shapes became uniform as the growth progressed and size of grains became larger. This process produces smaller grains that act as a source of material for the growing less defective larger grains.

Role of Anisotropy in Tissue Engineering

Tissue engineering is a highly interdisciplinary field that requires the integrated expertise of clinicians, cell biologists, engineers and material scientists, to make progress in the development and deployment of biological substitutes that restore, maintain, or improve tissue function. The purpose is to provide the opportunities for tissue regeneration and organ replacement. Key advances in biological materials especially in the area of stem cells; growth and differentiation factors generate realistic opportunities to create tissues in the laboratory using an engineered extracellular matrix or scaffold and biologically active molecules. The scaffold acts as an artificial extracellular matrix and it needs to mimic the chemical composition and physical architecture of natural extracellular matrix to facilitate cell adhesion, proliferation, differentiation and new tissue formation. In this contribution we review the role of the scaffold system in promoting cell adhesion, proliferation and differentiation with respect to the anisotropic nature of the scaffold system. We address both the anisotropy which may exist at a microscopic or mesoscopic scale, for example the shape of pores as well as the molecular level interactions which may arise in a scaffold containing a molecular organization with a preferred orientation which may have been induced during the processing procedures used to prepare the scaffold. Of course some approaches to the preparation of scaffolds systems are inherently anisotropic, for example the wide-spread utilization of meshes prepared by electrospinning. In other words although the overall scaffold is isotropic, the basic elements in terms of an electrospun fibre is highly anisotropic in terms of its external form and possibly in terms of its internal structure. By reviewing the possible advantages of the inclusion of anisotropic elements in the scaffold we add to the knowledge base which allows scaffolds design to be optimised for specific tissue growth.

Role of Anisotropy in Electrodynamically Induced Colloidal Aggregates

We investigate the assembly of spherical and anisotropic colloidal particles with the shape of peanuts when subjected to an external alternating electric field. By varying the strength and frequency of the applied field, we observe that both types of particles form clusters at low frequencies due to attractive electrohydrodynamic interactions or disperse into a liquidlike phase at high frequencies due to repulsive dipolar interactions. We characterize the observed structures via pair correlation functions and radius of gyration, and observe a clear difference in the ordering process between the isotropic and anisotropic colloids. Further on, we interpret the cluster formation kinetics in terms of dynamic scaling theory, and observe a faster aggregation of the anisotropic colloids with respect to the isotropic ones.

Role of anisotropy in the Förster energy transfer from a semiconductor quantum well to an organic crystalline overlayer

We consider the non-radiative resonant energy transfer from a two-dimensional Wannier exciton (donor) to a Frenkel exciton of a molecular crystal overlayer (acceptor). We characterize the effect of the optical anisotropy of the organic subsystem on this process. Using realistic values of material parameters, we show that it is possible to change the transfer rate within typically a factor of two depending on the orientation of the crystalline overlayer. The resonant matching of donor and acceptor energies is also partly tunable via the organic crystal orientation.

Helium diffusion in rutile and titanite, and consideration of the origin and implications of diffusional anisotropy

Diffusion of helium has been characterized in natural sphene (titanite) and synthetic rutile. Polished slabs of sphene and rutile were implanted with 100 keV 3He at a dose of 5 × 10 15 3He/cm 2 and annealed in 1-atm furnaces. 3He distributions following experiments were measured with nuclear reaction analysis using the reaction 3He(d,p) 4He. For diffusion in rutile we obtain the following Arrhenius relations: D ‖ a = 2 . 26 × 1 0 − 1 0 exp ( − 126 ± 11 kJ mol − 1 / RT ) m 2 sec − 1 . D ‖ c = 1 . 75 × 1 0 − 8 exp ( − 12 0 ± 7 kJ mol − 1 / RT ) m 2 sec − 1 . Although activation energies for diffusion parallel to the c- and a-axes are comparable, there is marked diffusional anisotropy, with diffusion parallel to the c-axis about 2 orders of magnitude faster than transport parallel to the a-axis. These diffusivities bracket the values determined for He diffusion in rutile in bulk release experiments ( Stockli et al., 2005, 2007; Wolfe, 2009), although the role of anisotropy could not be directly evaluated in those measurements. In titanite, the following Arrhenius relation was obtained over the temperature range 252–550 °C for diffusion parallel to the a-axis: D = 2 . 14 × 1 0 − 6 exp ( − 148 ± 8 kJ mol − 1 / RT ) m 2 sec − 1 . In contrast to rutile and zircon ( Cherniak et al., 2009), titanite shows little evidence of anisotropy, as diffusivities parallel to the a- and c-axes are similar, and diffusivities for titanites from two different localities are similar. He diffusion coefficients obtained in this study are similar to those measured through bulk release of He by step heating ( Shuster et al., 2003). Over the investigated temperature range, diffusion of He in titanite is similar to that of He diffusion in rutile parallel to the c-axis, but much faster than diffusion parallel to the a-axis. Since the diffusion of He in rutile exhibits such pronounced anisotropy, we model diffusional loss of He with a recently developed finite-element code ( Watson et al., 2010) created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients. We present example applications to evaluate helium losses from rutile grains as a function of grain size and length to diameter ratios. In efforts to better understand the occurrence of pronounced anisotropy for He diffusion in some crystals (e.g., rutile, zircon) but not in others (e.g., apatite, titanite), we consider the density and distribution of interstitial apertures in the crystal structure that might permit He migration. These determinations, an extension of the concept of ionic porosity, are consistent with observations of relative diffusivities and the existence or absence of significant anisotropy for the minerals rutile, zircon, apatite and titanite.

The possible role of anisotropy in kinetic electronic excitation of solids by particle bombardment

The kinetic excitation of a solid surface by impact of energetic particles is investigated by means of internal electron emission across a buried metal–insulator–metal (MIM) tunnel junction. By bombarding the top metal surface of such a device with keV noble gas ions, internal emission yields were determined as a function of projectile impact energy and angle of incidence with respect to the surface normal. In order to understand the observed impact angle dependence, we apply a modified formalism originally published to describe external electron emission. As a result, we find that the measured data can be explained by assuming the spatial distribution of excited electrons propagating towards the buried oxide interface to be strongly influenced by the projectile impact angle. A simple ballistic model assuming excited electrons generated by direct collisions with the projectile to preferably propagate along the direction of the original projectile motion, while electrons excited by scattering from moving recoils propagate isotropically, appears to describe the observed experimental data quite well.

Spin depolarization and spin exchange in cold collisions involving 3He: role of anisotropy

Mechanisms of spin depolarization, spin relaxation and spin exchange in cold atom-atom, atom-molecule collisions are discussed. The formation of weakly-bound van der Waals molecules in buffer-gas cooled magnetic traps, intermediated by anisotropic hyperfine interaction is considered.

Role of anisotropy and interactions in magnetic nanoparticle systems

Magnetic nanoparticle systems are characterized by several competing effects like anisotropy, an inherent disorder, the long range dipolar and the short range exchange interactions due to clustering effects. The sensitivity of the observed static and dynamical properties of these systems like the blocking temperature, the hysteresis and the susceptibility, to the methods of preparation, annealing and the resulting morphology is a manifestation of this. However, given the complexity of the system, it is often difficult to isolate the effects which might be dominant in a particular sample, which has a direct bearing on the desired applications. In this paper we report the effects of anisotropy, interactions and particle concentration on the temperature dependent remanence and coercivity through a numerical simulation on an array of single domain magnetic particles which incorporates all the above mentioned factors. Our results show that it is possible to distinguish between purely anisotropic systems and interacting systems with these measurements. In confirmation of our simulation results we also present the experimental results on the remanence and coercivity of nanomagnetic nickel ferrite composites.

Diffusion of helium in zircon and apatite

Diffusion of helium has been characterized in natural zircon and apatite. Polished slabs of zircon and apatite, oriented either normal or parallel to c were implanted with 100 keV 3He at a dose of 5 × 10 15 3 He/cm 2. Diffusion experiments on implanted zircon and apatite were run in Pt capsules in 1-atm furnaces. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p) 4He. For diffusion in zircon we obtain the following Arrhenius relations: D ⊥ c = 2.3 × 10 − 7 exp ( − 146 ± 11 kJ mol − 1 / R T ) m 2 s − 1 . D ∥ c = 1.7 × 10 − 5 exp ( − 148 ± 17 kJ mol − 1 / R T ) m 2 s − 1 . Although activation energies for diffusion normal and parallel to c are comparable, there is marked diffusional anisotropy, with diffusion parallel to c nearly 2 orders of magnitude faster than transport normal to c. These diffusivities bracket the range of values determined for He diffusion in zircon in bulk-release experiments, although the role of anisotropy could not be directly evaluated in those measurements. In apatite, the following Arrhenius relation was obtained over the temperature range of 148–449 °C for diffusion normal to c: D = 2.10 × 10 − 6 exp ( − 117 ± 6 kJ mol − 1 / R T ) m 2 s − 1 . In contrast to zircon, apatite shows little evidence of anisotropy. He diffusivities obtained in this study fall about an order of magnitude lower than diffusivities measured through bulk release of He through step-heating, and within an order of magnitude of determinations where ion implantation was used to introduce helium and He distributions measured with elastic recoil detection. Since the diffusion of He in zircon exhibits such pronounced anisotropy, helium diffusional loss and closure cannot be modeled with simple spherical geometries and the assumption of isotropic diffusion. A finite-element code (CYLMOD) has recently been created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients. We present some applications of the code in evaluating helium lost from zircon grains as a function of grain size and length to diameter ratios, and consider the effects of “shape anisotropy”, where diffusion is isotropic (as in the case of apatite) but shapes of crystal grains or fragments may depart significantly from spherical geometry.

Influence of Landscape Elements in Riparian Buffers on the Conservation of Semiaquatic Amphibians

Studies on riparian buffers have usually focused on the amount of land needed as habitat for the terrestrial life stages of semiaquatic species. Nevertheless, the landscape surrounding wetlands is also important for other key processes, such as dispersal and the dynamics of metapopulations. Multiple elements that influence these processes should therefore be considered in the delineation of buffers. We analyzed landscape elements (forest cover, density of roads, and hydrographic network) in concentric buffers to evaluate the scale at which they influence stream amphibians in 77 distinct landscapes. To evaluate whether our results could be generalized to other contexts, we determined whether they were consistent across the study areas. Amphibians required buffers of 100-400 m of suitable terrestrial habitat, but interspecific differences in the amount of habitat were large. The presence of amphibians was related to roads and the hydrographic network at larger spatial scales (300-1500 m), which suggests that wider buffers are needed with these elements. This pattern probably arose because these elements influence dispersal and metapopulation persistence, processes that occur at large spatial scales. Furthermore, in some cases, analyses performed on different sets of landscapes provided different results, which suggests caution should be used when conservation recommendations are applied to disparate areas. Establishment of riparian buffers should not be focused only on riparian habitat, but should take a landscape perspective because semiaquatic species use multiple elements for different functions. This approach can be complex because different landscape elements require different spatial extents. Nevertheless, a shift of attention toward the management of different elements at multiple spatial scales is necessary for the long-term persistence of populations.

The role of anisotropy in the response of the titanium alloy Ti–6Al–4V to shock loading

Manganin stress gauges in lateral orientation have been used to monitor the shock response of Ti–6Al–4V when loaded either parallel to or radial to the long axis of the original bar stock studied in this investigation. Materials characterization has shown that the c-axis of the hexagonal unit cell is preferentially orientated radially to the axis of the bar. Shear strengths measured along the long axis of the bar were found to be in agreement with previous data in the literature, while strength in the radial direction was found to be significantly lower. It was also noted that the lateral stress, when measured in the radial direction, displayed a pronounced drop in the lateral stress after reaching the peak shock stress unlike the longitudinal orientation. This decrease is indicative of an increase in shear strength behind the shock front. In both instances, it is postulated that extensive deformation twinning during the early stages of deformation in the shock and thereafter c+a slip and dislocation tangling builds up over a longer time period, resulting in the higher degree of hardening noted.

Picosecond dynamics of gas-phase dimers in liquid carbon dioxide

An inelastic neutron scattering and molecular dynamics simulation study of the interaction properties of liquid CO 2 is reported. By means of an interaction-based interpretation of neutron scattering and simulation results for the dynamic structure factor we also show that ( CO 2 ) 2 equilibrium dimers characteristic of the gas phase are present in dense liquid carbon dioxide and predominantly contribute to the observed picosecond dynamics. Such a memory of the gas-phase structures was not observed in liquid methane. The role of anisotropy and strength of interactions on these important differences is discussed.

Tailoring of magnetocaloric response in nanostructured materials: Role of anisotropy

The magnetocaloric response of an ensemble of oriented uniaxial magnetic objects, perpendicularly magnetized to their easy axes, for temperatures close to the blocking temperature is calculated with the aim of demonstrating that the control of the sample's microstructure makes up an effective way to tailor its magnetocaloric response. Coexisting positive and negative magnetocaloric effect (MCE) is found for a model material with a single magnetic phase transition. Both MCE regimes are controlled by the magnitude of the applied magnetic field. As a proof of concept, experimental results for arrays of self-assembled ferromagnetic nanowires embedded into highly ordered nanoporous anodic alumina templates are shown, suggesting the validity of the numerical calculations.

DYNAMICAL SYMMETRY WITH GENERAL INITIAL AREA RADIUS IN QUASI-SPHERICAL GRAVITATIONAL COLLAPSE, AND ANISOTROPY AND INHOMOGENEITY OF SPACE–TIME

This paper deals with the role of anisotropy and inhomogeneity of space–time in quasi-spherical gravitational collapse. The effect of the initial area radius has been studied in characterizing the final state of collapse. Both dust and fluid with anisotropic pressure are considered as the collapsing matter. The results are presented in the form of propositions.