Anisotropic State Research Articles

Uniaxial and Biaxial Response of Anisotropic Polypropylene

AbstractThe response of uniaxial and biaxial anisotropic polypropylene is discussed. A 3D elasto‐viscoplastic constitutive model is developed to account for material anisotropy. The famous Hill’s anisotropic yield criterion is combined with the Eyring relation and implemented in a finite element framework to model the response of the polymer during uniaxial loading. An associated viscoplastic flow rule that describes the magnitude and the direction of the viscoplastic flow is incorporated in the model to simulate complex loading conditions. The model quantitatively captures the yield stresses for uniaxial deformation at a given anisotropic state and material orientation. In addition, the results of simulations demonstrate that the constitutive relations qualitatively describe the material deformation during biaxial loading for both isotropic and anisotropic cases.

Detailed electron impact fine-structure excitation cross-sections of Kr+ and linear polarization of its subsequently emitted photons

An extensive calculation for electron impact excitation cross-sections of Kr+ ion is performed using relativistic distorted wave theory. The transitions considered are from the ground state i.e. 4s24p5 (J=3/2) to the 4s24p5 (J = 1/2), 4s4p6 (J=1/2) levels and fine structure levels of 4s24p45s, 4s24p45p, 4s24p46s, 4s24p46p, 4s24p44d and 4s24p45d excited states. The transition matrix is evaluated using the relativistic multi-configuration Dirac-Fock bound state wave functions of the initial and final states of Kr+ ion obtained from the GRASP2K program. The 4s24p5, 4s4p6, 4s24p45s, 4s24p45p, 4s24p46s, 4s24p46p, 4s24p44d and 4s24p45d configuration state functions are used to calculate the required wave functions. The incident and scattered projectile electron continuum wave functions are calculated numerically by solving the Dirac equations using static potential of the target ion. Oscillator strengths and transition probabilities are calculated and reported for the dipole allowed transitions, making these available to check the accuracy of the bound state wave functions for future comparison purposes. The detailed excitation cross-sections and their corresponding excitation rate coefficients are reported for considered 116 fine-structure excitation transitions from the ground state 4s24p5 (J=3/2). Further, analytic fittings of the obtained cross-sections with respect to incident electron energy are also performed for all the transitions considered in the present work so that these can be directly used in any plasma model for diagnostics purposes. In addition, using the obtained magnetic sub-level cross-sections, the degree of linear polarization of the photon emissions from the decay of electron impact excited anisotropic states of Kr+ ion through the dipole allowed transitions is calculated and reported.

Endohedral metallofullerene single molecule magnets

Nanoscale magnetic materials have been attracting enormous interests during the past few decades due to the rapid development of high-density magnetic storage devices. A breakthrough in nanomagnetism is the discovery of single molecule magnets (SMMs), which exhibit slow relaxation and quantum tunneling of the magnetization resulted from a molecular-based blocking anisotropy, and thus have potential applications in high-density data storage, molecular spintronics and quantum computing. Since the report of Mn12-complex as the first SMM by Sessoli et al. in 1993, a large number of SMMs based on organometallic coordination compounds have been synthesized. Compared to the traditional bulk magnets, the magnetic properties of SMMs are determined by their instrinsic spin structures resulting in slow magnetic relaxation. SMM is characterized by a bi-stable magnetic ground state and a certain spin-reversal barrier ( U eff). Additionally, hysteresis loops can be observed below the blocking temperature ( T B). Therefore, SMMs with excellent magnetic properties always have high T B and U eff. U eff depends strongly on spin ground state ( S ) and magneto-crystalline anisotropy ( D ), and can be expressed with the formula U eff =| D|S 2. For transition metal-based SMMs, their low magneto-crystalline anisotropies ( D ) result in relative low U eff. In recent years, lanthanide based SMMs have been studied intensively and become the most promising high-performance SMMs, owning to their strong single ion anisotropy. Encapsulating metal atoms or metallic clusters into fullerene cages generate a special class of fullerenes, the so-called endohedral metallofullerenes (EMFs), for which the encapsulation of metal atoms endow EMFs more fascinating properties compared to empty fullerenes. For instance, EMFs are paramagnetic when the entrapped metal ions have unpaired electrons. Furthermore, EMFs were able to show excellent SMM properties when the encapsulated clusters induce appropriate ligand-fields. EMFs with lanthanide open up a new avenue in the field of SMMs in 2012 when single molecule magnetism was proved for the metal nitride clusterfullerene (NCF) DySc2N@ I h-C80. Fullerene cages are stable in air and thus they can protect the magnetic ions from ambient conditions, and the negatively charged nonmetallic atom(s) within the cluster and the negatively charged carbon atoms of fullerene cages provide magnetic anisotropy which is necessary for single molecule magnetism. Moreover, the molecular structures of EMFs can be modulated by varying the encapsulated metal ions, metal cluster and cage isomer; hence the research on EMF-SMMs has been developed rapidly since 2012. Up to now, metal nitride clusterfullerenes (NCFs), metal carbide clusterfullerenes (CCFs), metal oxide clusterfullerenes (OCFs), metal sulfide clusterfullerenes (SCFs), metal cyanide clusterfullerenes (CYCFs) and dimetallofullerenes (di-EMFs) have been confirmed as SMMs. In this paper, we present an exhaustive review on all kinds of EMF-SMMs reported to date including their 1D, 2D and 3D assemblies. We mainly discuss the influences of the types and the numbers of the encapsulated metal ions and non-metal atoms on the magnetic properties of EMF-SMMs. Finally, the prospects and challenges of EMF-SMMs are also discussed.

Magnetic properties of the Fe-24%Cr-15%Co-3%Mo-1.5%Ti hard magnetic alloy in anisotropic and isotropic states

The magnetic properties of the Fe-24%Cr-15%Co-3%Mo-1.5%Ti (in wt. %) hard magnetic alloy in anisotropic and isotropic states after various heat treatments were studied. The alloy was prepared by the methods of powder metallurgy. The relative density was 98 %. The coefficient of thermal expansion of the alloy during heating and cooling was 17, 4*10 6 K−1 and 19, 0 *10− 6 K1 in the temperature range of 100 °C - 1300 °C. The kinetics of o-phase formation caused by an isothermal annealing at T = 750 ºC was investigated by means of the hardness measurements. The best magnetic properties of the alloy in anisotropic state were obtained after thermomagnetic treatment with cooling rate 200 ºC/h as Br = 1.22 T, Hc = 42.2 kAm-1 and (BH)max = 31.2 kJm- 3 and on the alloy in isotropic state with cooling rate 40 ºC/h.

On the highly swirling flow through a confined bluff-body

We address highly swirling, confined-bluff-body-flow evolving through a burner; particularly, contributions of the swirling motion to a central-recirculation-zone (CRZ) downstream the injector. Previous studies suggest that flame stability reduces in combustors lacking this zone; careful consideration of the CRZ is thus desirable. We use Reynolds-Averaged-Navier–Stokes (RANS) and Large-Eddy-Simulation (LES) to simulate the flow, and the influence of the swirl device was included in defining the inflow conditions for LES simulations. We use mean velocity profiles and turbulence statistics to test results. There is qualitative agreement between computed and reported experimental data, and we document quantitative differences obtained with the RANS models. LES velocity field results are mostly within 3% of the experimental data, better than the latest reported LES data, reinforcing the suitability of our approach. We took advantage of the quality of the LES mesh, which solves 95.6% of the resolved-turbulence-energy, to present the vorticity structures showing the precessing vortex motion on the CRZ boundaries. Anisotropic states of the Reynolds-stress were characterized with the aid of an anisotropy invariant map, a novelty for this type of burner; the turbulence states considerably vary inside the burner, behaving isotropically in the center of the CRZ, whereas axisymmetric turbulence is predominant in the other areas of the CRZ. The results reinforce the importance of applying appropriate turbulence models and inflow conditions for simulations involving confined-bluff-body-flows in order to capture the main flow fields and structures in the CRZ.

Holographic spontaneous anisotropy

We construct a family of holographic duals to anisotropic states in a strongly coupled gauge theory. On the field theory side the anisotropy is generated by giving a vacuum expectation value to a dimension three operator. We obtain our gravity duals by considering the geometry corresponding to the intersection of D3- and D5- branes along 2+1 dimensions. Our backgrounds are supersymmetric and solve the fully backreacted equations of motion of ten-dimensional supergravity with smeared D5-brane sources. In all cases the geometry flows to AdS5× \U0001d54a5 in the UV, signaling an isotropic UV fixed point of the dual field theory. In the IR, depending on the parameters of the solution, we find two possible behaviors: an isotropic fixed point or a geometry with anisotropic Lifshitz-like scaling symmetry. We study several properties of the solutions, including the entanglement entropy of strips. We show that any natural extension of existing c-functions will display non-monotonic behavior, conforming with the presence of new degrees of freedom only at intermediate regions between the boundary and the origin of the holographic dual.

Photoinduced anisotropic edge states and signatures of nonequilibrium spin polarization in silicene nanoribbons

Most topological phase transitions are accompanied by the emergence of surface/edge states with spin dependence. Usually, the quantized Hall conductivity cannot characterize the anisotropic transports and spin dependence of topological states. Here, we study the intricate topological phase transition and the anisotropic behavior of edge states in silicene nanoribbon submitted to an electric field or/and a light irradiation. It is interesting to find that a circularly polarized light can induce a type-II quantum anomaly Hall phase, which is manifested as the high Chern number and the strong anisotropic edge states. Besides the measurement of the quantized Hall conductivity, we further propose to probe these topological phase transitions and the anisotropy of edge states by measuring the current-induced nonequilibrium spin polarization. It is found that the spin polarization exhibits more signatures about the behavior of surface/edge states, beyond the quantized Hall conductivity, especially for spin-dependent transports with different velocities.

Anisotropy of the transport properties of NdFeAs(O,F) thin films grown on vicinal substrates

NdFeAs(O,F) thin films with different fluorine contents were grown on 5° or 10° vicinal cut MgO and CaF2 single crystalline substrates by molecular beam epitaxy. Structural characterisations from reflection high-energy electron diffraction and x-ray diffraction confirmed the epitaxial growth of NdFeAs(O,F). The resistivities of the ab-plane and along the c-axis (ρab and ρc) were derived from the resistivity measurements in the longitudinal and transversal directions. The c-axis resistivity was always higher than ρab, resulting from the anisotropic electronic structure. The resistivity anisotropy at 300 K was almost constant in the range of 50 ≤ γρ ≤ 90 irrespective of the fluorine content. On the other hand, at 56 K showed a strong fluorine dependence: was over 200 for the films with optimum fluorine contents (superconducting transition temperature Tc around 50 K), whereas γρ was around 70 for the films in the under-doped regime (Tc between 35 and 45 K). The mass anisotropy ( and are the effective masses along the c-axis and on the ab-plane) close to Tc derived from the anisotropic Ginzburg-Landau approach using the angular-dependency of ρab was in the range from 2–5. On the assumption , those values are small compared to the normal state anisotropy.

Single Photon vs Two Photon Excitation of Silver Nanocluster

Silver nanodots, nanoparticles and nanoclusters have been of immense interest to researchers for some time now. A lot has been published in this field from synthesis to optical properties of various types of silver nanoclusters. In this work we explore the impact of polarized excitation on modulatability and fluorescence enhancement of silver (Ag) nanocluster. Ag nanoclusters as previously reported are enhancible and modulatable, however, for pathological application purposes emission in NIR even IR is desirable, so that the fluorescence signal detection over the auto-fluorescence background signal in vivo mode becomes easier. In a preliminary work we have seen a rise in anisotropic values beyond the maximum steady state anisotropy of 0.4 when the sample is excited using two colored laser light. Though there are numerous multi-photon study results available in literature, this is first of its kind where we use two polarized excitations to sequentially probe the excitable dark state of the cluster and the emission is then analyzed to obtain a value of steady state anisotropy along with changes observed in signal enhancement owing to modulation of the secondary excitation source. Ag nanocluster samples encapsulated by 10- or 12-mer ss-DNA capable of producing red to NIR light upon excitation at shorter wavelengths were prepared in-house.

Hybrid Color Glass Condensate and hydrodynamic description of the Relativistic Heavy Ion Collider small system scan

Multi-particle correlation observables in the Relativistic Heavy Ion Collider small system scan are computed in a framework that contains both initial state momentum anisotropies from the Color Glass Condensate effective theory and final state hydrodynamic evolution. The initial state is computed using the IP-Glasma model and coupled to viscous relativistic hydrodynamic simulations, which are followed by microscopic hadronic transport. All parameters of the calculation were previously constrained using experimental data on Au+Au collisions at the same center of mass energy. We find that the qualitative features of the experimental data, such as the system and centrality dependence of the charged hadron momentum anisotropy, can only be reproduced when final state interactions are present. On the other hand, we also demonstrate that the details of the initial state are crucially important for the quantitative description of observables in the studied small systems, as neglecting the initial transverse flow profile or the initial shear stress tensor, which contain information on the momentum anisotropy from the Color Glass Condensate, has dramatic effects on the produced final state anisotropy. We further show that the initial state momentum anisotropy is correlated with the observed elliptic flow in all small systems, with the effect increasing with decreasing multiplicity. We identify the precise measurement of v2 in d+Au and Au+Au collisions at RHIC energy at the same multiplicity as a means to reveal effects of the initial state momentum anisotropy.

Experimental investigation of ASR-affected concrete – The influence of uniaxial loading on the evolution of mechanical properties, expansion and damage indices

The alkali silica reaction (ASR) in concrete causes internal localized swelling and micro cracking, which result in expansion and correlated deterioration of the concrete material. The stress state of the concrete is known to affect expansion due to ASR, with an anisotropic stress state giving rise to anisotropic expansion. Similarly, the orientation and extent of micro cracking have a directional effect on the concrete mechanical behaviour. This research studied the effect of sustained uniaxial compressive stress on the evolution of the mechanical behaviour of concrete in compression. Concrete cubes of 230 mm side length were uniaxially restrained and stored in accelerated conditions, with cores drilled in two directions for mechanical tests: a cyclic test in compression, i.e. a stiffness damage test (SDT) and a complete stress-strain test. A clear directional dependency of the mechanical characteristics was found. Furthermore, the results indicate that reduction in modulus of elasticity is well correlated with the expansion in the test direction. On the other hand, the damage indices obtained from the SDT merely relate to the expansion, which puts in question the SDT’s ability to predict ASR expansion in stressed concrete and therefore in concrete structures.

Numerical modeling of plastic deformation and failure around a wellbore in compaction and dilation modes

SummaryIn many wellbore stability analyses, the ability to forecast both the occurrence and extent of plastic deformation and failure hinges upon a fundamental understanding of deformation mode and failure mechanism in the reservoir rock. This study focuses on analyzing plastic zones, localized deformations, and failures around a borehole drilled overbalanced or underbalanced through a highly porous rock formation. Based on several laboratory experiments, porous rocks are prone to deform under both shear‐induced dilation and shear‐enhanced compaction mechanisms depending on the stress state. The shapes of the deformation and failure patterns around the borehole are shown, depending on the initial stress state and the local stress paths. The inquiry of the local stress paths in the near‐wellbore zone facilitates the understanding of the reasons for different types of failure mechanisms, including the mixed‐mode and the plastic deformation structures. The modification of the 2D plane strain condition by imitating third stress in the numerical scheme helps us bring the stress paths closer to the real state of loading conditions. Our modeling reveals that the transition from isotropic to anisotropic stress state is accompanied by an increase in the deviatoric part of effective shear tensor that leads to the development of inelastic deformation, degradation, and subsequent rock failure. Particular interest is devoted to the modeling of strain localization especially in compaction mode around a wellbore and computing the amount of stress concentration at the tips of dog‐eared breakouts. Stress concentration can result in a change in irreversible deformation mode from dilatancy to compaction, elucidating the formation of the shear‐enhanced compaction phenomenon at the failure tips in the direction of the minimum horizontal stress.

A hypoplastic model for granular soils incorporating anisotropic critical state theory

SummaryIt is well known that soil is inherently anisotropic and its mechanical behavior is significantly influenced by its fabric anisotropy. Hypoplasticity is increasingly being accepted in the constitutive modeling for soils, in which many salient features, such as nonlinear stress‐strain relations, dilatancy, and critical state failure, can be described by a single tensorial equation. However, within the framework of hypoplasticity, modeling fabric anisotropy remains challenging, as the fabric and its evolution are often vaguely assumed without a sound basis. This paper presents a hypoplastic constitutive model for granular soils based on the newly developed anisotropic critical state theory, in which the conditions of fabric anisotropy are concurrently satisfied along with the traditional conditions at the critical state. A deviatoric fabric tensor is introduced into the Gudehus‐Bauer hypoplastic model, and a scalar‐valued anisotropic state variable signifying the interplay between the fabric and the stress state is used to characterize its impact on the dilatancy and strength of the soils. In addition, fabric evolution during shearing can explicitly be addressed. Modifications have also been undertaken to improve the performance of the undrained response of the model. The anisotropic hypoplastic model can simulate experimental tests for sand under various combinations of principle stress direction, intermediate principal stress (or mode of shearing), soil densities, and confining pressures, and the associated drastic effect of different principal stress orientations in reference to the material axes of anisotropy can be well captured.

Experimental consequences of Bogoliubov Fermi surfaces

Superconductors involving electrons with internal degrees of freedom beyond spin can have internally anisotropic pairing states that are impossible in single-band superconductors. As a case in point, in even-parity multiband superconductors that break time-reversal symmetry, nodes of the superconducting gap are generically inflated into two-dimensional Bogoliubov Fermi surfaces. The detection and characterization of these quasiparticle Fermi surfaces requires the understanding of their experimental consequences. In this paper, we derive the low-energy density of states for a broad range of possible nodal structures. Based on this, we calculate the low-temperature form of observables that are commonly employed for the characterization of nodal superconductors, i.e., the single-particle tunneling rate, the electronic specific heat and Sommerfeld coefficient, the thermal conductivity, the magnetic penetration depth, and the NMR spin-lattice relaxation rate, in the clean limit. We also address the question whether the topological invariant of the Bogoliubov Fermi surfaces is associated with topologically protected surface states, with negative results. This work is meant to serve as a guide for experimental searches for Bogoliubov Fermi surfaces in time-reversal-symmetry-breaking superconductors.

Pyridine-d5 as a 2H NMR probe for investigation of macrostructure and pore shapes in a layered Sn(iv) phosphonate-phosphate material.

Isotropic and anisotropic motions and molecular states of pyridine-d5, adsorbed on the surface within the pores of a layered Sn(iv) phosphonate-phosphate material (1) have been characterized thermodynamically and kinetically by solid-state NMR. The data obtained provide formulation of macrostructure and shapes of pores in 1.

Structural characterization and magnetic property studies of a mixed-valence {CoIIICo} complex with a μ4-oxo tetrahedral {Co} motif.

We have synthesized and structurally characterized a new mixed valence pentanuclear Co complex, bearing a rare μ4-O-tetrahedral CoII4 unit, by employing a pyridine-like Schiff base ligand. We have performed DC magnetic susceptibility and magnetization measurements over polycrystalline samples and chemical quantum computations in order to understand the exchange interaction pattern within Co(ii) sites and ground state magnetic anisotropy. This new complex shows an overall antiferromagnetic exchange interaction whose strength strongly depends on the local symmetry of Co(ii) sites. Also, local ion magnetic anisotropy reveals a strongly axial behaviour with the lowest Kramers doublet (KD) at each Co(ii) ion sufficiently isolated from excited states at low temperatures. Two Co(ii) sites show tetrahedral symmetry and the spin only formalism including axial zero-field splitting (ZFS) term properly described them; on the other hand, the other two Co(ii) sites have distorted octahedral and square base pyramidal coordination spheres, and a strong orbital contribution leads to a failure of the spin only formalism. A model of four Seff = 1/2 exchange interacting sites is necessary in order to account for low temperature magnetization behaviour. In view of the strongly anisotropic KD states, the exchange interactions are forced to be modelled as anisotropic ones. Overall, experimental data and quantum chemical computations are in good agreement, supporting the proposed model for magnetic behaviour.

Experimental evidence of a new class of massless fermions.

The discovery of graphene with its massless fermions established a new branch of nanomaterials in which linear bands can be realized. It has been predicted that beside Dirac fermions revealing isotropic character and observed in a number of two-dimensional materials, another class of massless fermions can also be found: strongly anisotropic fortune teller-like states which form planes instead of cones in the electronic structure. Here, we demonstrate that such distinct electronic structures exist and can be found in a surface layer of silicon.

Systematic spectroscopic investigation of structural changes and corona formation of bovine serum albumin over magneto-fluorescent nanoparticles.

Magneto-fluorescent nanoparticles have attracted great attention because of their dual nature as multimodal imaging probes in various biomedical applications. Particulary, it is desirable to understand how these nanoparticles interact with human serum proteins before they are used in biological systems. In this work, the physiological interactions between magneto-fluorescent nanoparticles (MFNPs) and bovine serum albumin (BSA) were systematically investigated. The present observations identified that the collision of MFNPs and BSA caused fluorescence quenching of BSA. Steady state fluorescence, lifetime and anisotropy measurements in the presence of MFNPs supported dynamic quenching of the BSA emission. Furthermore, in the presence of MFNPs, the conformation changes in the BSA structure indicate merely the secondary structural changes. The findings demonstrated that random interactions and hydrophobic forces play a major role in the dynamic quenching. Further, subsequent coating of BSA over MFNPs result in protein corona formation, as is evident through spectroscopic measurements. In light of the present work, MFNPs could serve a purpose in magnetic separation and optical detection of serum proteins from blood plasma in real-time disease diagnosis.

Physics-constrained local convexity data-driven modeling of anisotropic nonlinear elastic solids

Abstract As characterization and modeling of complex materials by phenomenological models remains challenging, data-driven computing that performs physical simulations directly from material data has attracted considerable attention. Data-driven computing is a general computational mechanics framework that consists of a physical solver and a material solver, based on which data-driven solutions are obtained through minimization procedures. This work develops a new material solver built upon the local convexity-preserving reconstruction scheme by He and Chen (2020) A physics-constrained data-driven approach based on locally convex reconstruction for noisy database. Computer Methods in Applied Mechanics and Engineering 363, 112791 to model anisotropic nonlinear elastic solids. In this approach, a two-level local data search algorithm for material anisotropy is introduced into the material solver in online data-driven computing. A material anisotropic state characterizing the underlying material orientation is used for the manifold learning projection in the material solver. The performance of the proposed data-driven framework with noiseless and noisy material data is validated by solving two benchmark problems with synthetic material data. The data-driven solutions are compared with the constitutive model-based reference solutions to demonstrate the effectiveness of the proposed methods.

The influence of stress state, density and moisture on the dynamic properties of soil cement samples created by the method of deep soil mixing

The transformation of the properties of the bases by the method of deep soil mixing allows the construction of buildings and structures on sites with soft soils. As a rule, adverse geological conditions are accompanied by the presence of dynamic effects on the designed buildings. The objective of this research is to forecast changes in the mechanical properties of the base under dynamic loads. The object of study is the propagation velocity of elastic shear waves, since these parameters significantly affect the calculations of deformations and stability of earthquake-resistant industrial and civil buildings and structures, as well as objects of energy and transport construction. The paper contains a review of similar studies, on the basis of which the conclusions obtained during the experiments are further generalized. Based on the analysis of the results of laboratory tests performed by the authors of this work, by the method of low-amplitude torsion vibrations in a resonant column in the anisotropic triaxial compression mode, the influence of the density of soil cement samples, humidity, and additional load on the propagation velocity of elastic transverse waves is estimated. The paper provides a description of the essence of the research method, a review of the equipment on which special laboratory tests were performed. The tests were carried out on samples of unbroken soil cement taken from the base of a nuclear power plant (NPP) under construction. Dried samples of soil cement were investigated, and tests were carried out at full water saturation and at a given humidity. The anisotropic stress state of soil cement samples during triaxial tests in a resonance column was due to the features of the base of the designed NPP. Studies have shown that the most significant factor affecting the shear wave velocity is the additional vertical load. It is noted that with increasing density, the velocity of the shear waves decreases. Humidity is directly related to the density of soil cement and the amount of water in the pores, so the assessment of its effect on the dynamic properties of soil cement is similar to the effect of changes in density.