Isotropic State Research Articles

Anisotropic magnetorheological elastomers with carbonyl iron particles in natural rubber and acrylonitrile butadiene rubber: A comparative study

This work examines magneto-rheological elastomers (MREs) based on isotropic and anisotropic distribution of carbonyl iron particles (CIP) in natural rubber (NR) and acrylonitrile butadiene rubber (NBR). Measurements of the compressive mechanical properties were done to determine the isotropic and anisotropic properties of the MREs. Scanning electron microscopy (SEM) and optical microscopy were employed to study the CIP filler mixing behavior in the rubber matrix and orientation of particles in an anisotropic state. CIP-NBR composites show higher ultimate compressive stress in both isotropic and anisotropic states than NR-based composites. NBR-based composites show positive increases in both the elastic modulus and compressive stress at higher deformation when changing from isotropic to anisotropic, whereas NR-based composites show a positive increase in the elastic modulus and a decrease in the compressive stress. Elastic modulus measurements of anisotropic composites under a magnetic field suggest that NBR composites have much better field-dependent magnetic properties than NR composites. Anti-stress-relaxation measurements indicate that NBR composites have better magnetic effect than NR composites. The better performance of NBR-based anisotropic composites in field-dependent and independent behaviors might be due to better filler distribution, a greater number of chain-like filler structures, and less aggregation of the chain-like filler strands. The MREs based on NBR could be more useful than NR for wide range of magneto rheological applications.

Effects of anisotropic misfit strains on equilibrium phases and domain structures in (111)-oriented ferroelectric PbTiO3 films

Advances in high-index-oriented ferroelectric films offer the exciting possibility of utilizing strain engineering to tune the desired properties related to the nanostructures. Previous studies often considered ferroelectric films grown on cubic substrates (isotropic strain), while the effects of anisotropic strains introduced by orthorhombic substrates are still not well understood. In our recent work, we grew (111)-oriented PbTiO3 (PTO) films on orthorhombic GdScO3 substrates and studied the domain structure evolution with film thickness. However, the theoretical understanding is lacking. In this work, the physical mechanism of the formation and evolution of domain structures was clearly revealed from the viewpoint of energy competition. Moreover, through the stereographic projection (SP) analysis of polarization vectors, a wide variety of ferroelectric phases for (111)-oriented PTO films under anisotropic strains were identified, and the misfit strain-misfit strain domain stability diagram was then constructed at room temperature. It was indicated that anisotropic misfit strains not only lead to the separation of ferroelectric domain variants that could co-exist under isotropic strain states for tetragonal-like d and monoclinic ma phases, but also stabilize the monoclinic mb phase. Their representative domain morphologies with separated domain variants under different anisotropic strains were analyzed in detail. These results provide guidance for interpreting and understanding more experimental data as well as the designing of (111)-oriented epitaxial ferroelectrics under anisotropic strains.

Phase equilibrium and dielectric relaxation in mixture of 5CB with dilute dimethyl phthalate: effect of coupling between orientation and composition fluctuations on molecular dynamics in isotropic one-phase state.

Phase equilibrium and dielectric relaxation were examined for mixtures of liquid-crystalline (LC)-forming 4-cyano-4'-pentylbiphenyl (5CB) with dilute dimethyl phthalate (DMP). The mixtures were in an isotropic one-phase state at high temperatures T but were separated into nematic and isotropic phases at low T < TIN (isotropic-to-nematic transition temperature), and the isotropic phase disappeared and a nematic one-phase state was realized on a further decrease of T below another transition temperature . These TIN and data (phase diagram) were described considerably well by a simple model of free energy contributed from a Flory-Huggins type mixing entropy (no enthalpic contribution) and a Landau-de Gennes type nematic interaction. This success of the model, not expected for ordinary (not LC-forming) components exhibiting enthalpically-driven phase separation, suggested that the phase separation in the DMP/5CB mixtures was triggered by the nematic transition of 5CB (possibly governed by the packing entropy) and thus the orientation fluctuation of 5CB molecules was coupled with the composition fluctuation. This coupling was expected to affect the dielectric relaxation detecting the rotational dynamics of 5CB molecules, the major component in the mixtures. This expectation was examined for a representative mixture having the DMP content of wDMP = 3.1 wt% and TIN ≅ 27.0 °C. In a high-T asymptote (T > TIN + 10 °C), the dielectric relaxation of this mixture was close to that of pure 5CB, which suggested no significant effect of the above coupling on 5CB dynamics in the mixture at such high T. Nevertheless, in a significantly wide range of T between TIN and TIN + 10 °C, the dielectric relaxation time τε of the isotropic one-phase mixture increased on cooling much more significantly compared to τε in that high-T asymptote. The kinematic viscosity ν of the mixture exhibited a qualitatively similar increase in the same range of T, but this increase was weaker than that of τε. This difference between the dielectric τε and the rheological ν was attributed to coupling of the orientation and the composition fluctuations mentioned above. Namely, the composition fluctuation enhances the orientation fluctuation in the mixture thereby providing τε (reflecting the orientation fluctuation) with an extra increase. Pure 5CB exhibited similar increases of τε and ν (stronger for the former) but only in a close vicinity of (within 2-3 °C), because the orientation fluctuation in pure 5CB is coupled with the density fluctuation, not with the composition fluctuation being absent in the pure 5CB system. This behavior of pure 5CB in turn suggests an importance of the coupling of orientation and composition fluctuations in the mixture.

Analytical and DEM studies of thermal stress in granular materials

The ability to predict thermal-induced stresses in granular materials is of practical importance across a range of disciplines ranging from process engineering to geotechnical engineering. This study presents an analytical formula to predict thermal-induced stress increments in mono-disperse granular materials subject to an initial isotropic stress state. A complementary series of DEM simulations were carried out to explore the applicability of the proposed analytical formula. The comparative analysis showed that the proposed expression can accurately predict stress changes in packings where there are negligible particle displacements as a consequence of the thermal loading (e.g. regular packings and medium/dense random packings); however large errors were observed in loose samples with a random packing.

Nonlinear cosmogony of the spiral galaxy bulges

Abstract In this paper, we develop an early idea of one of the authors (Nuritdinov 1992a,b), who was the first to propose the mechanism of instability of the warp perturbation mode on the background of a nonstationary disk. For this aim, we have studied a model of a nonlinearly non-stationary self-gravitating disk with an anisotropic velocity diagram. The model has a composite nature, or rather, it is a superposition of isotropic and anisotropic states of the disk. In the general case, it is obtained a nonstationary analogue of the dispersion equation of this composite model. We have also investigated the behavior of the domed perturbation mode, the instability of which leads to the formation of a classical bulge in the central region of the disk. In addition, we considered the critical diagrams of the dependence of the virial ratio on the rotation rate of the system for various values of the superposition parameter and the corresponding diagrams for the increments of instability.

Об изотропных точках в примесных кристаллах K-=SUB=-2-=/SUB=-SO-=SUB=-4-=/SUB=-

The temperature, spectral and pressure dependences of the birefringence Δni of potassium sulfate crystals doped with 1.7% of copper have been studied. The introduction of the impurity is found to change the absolute value of Δni and lead to an increase in the temperature dependence of Δnі(Т). It is shown that the isotropic points appear in the doped crystal of potassium sulfate, and are shifted, compared with a pure crystal, towards low temperatures by 5 K and 11 K, respectively. It was established, that uniaxial stresses change the magnitude of the Δni absolute values, as well as the region of existence of the isotropic state. Generalized temperature-spectral-baric diagrams of the isotropic state of doped potassium sulfate crystal are constructed, making it possible to use them as a crystal-optical sensor.

Composition-dependent phase transformation in side-chain liquid crystalline copolymers with mesogenic groups at different substituent positions.

Copolymerization is an effective approach to tailor the thermal and structural properties of liquid crystalline polymer materials, which is essential for various applications. In this work, two series of polynorbornene copolymers, A-r-B and A-r-C, with the biphenyl mesogenic side group at different substituent positions were synthesized via ring-opening metathesis polymerization in various compositions. The corresponding homopolymers A and C are liquid crystalline polymers, exhibiting an oblique columnar structure (Colob/p2) and lamellar structure, respectively, while homopolymer B is amorphous. The composition-dependent phase behaviors of copolymers were systematically studied with the combination of SAXS, GISAXS, AFM, DSC and POM techniques. With increasing molar content of A (xA), the self-organzied structure of copolymer A-r-B follows the sequence from amorphous to lamellar, undulated lamellar, and Colob/p2 structures, and that of A-r-C follows the sequence of lamellar, undulated lamellar, and Colob/p2 structures. Then, copolymers with undulated lamellar or Colob/p2 structures tend to enter lamellar phase first at higher temperature and then change to the isotropic state during heating. The composition-induced transition from lamellar to supramolecular columnar organization is somewhat reminiscent of block copolymers and other soft matter systems that can form ordered structures. Furthermore, the subsitituent number and position of rigid mesogenic units in the side chain can further modify the morphologies of self-organized phases.

Quantization and Isotropic Submanifolds

We introduce the notion of an isotropic quantum state associated with a Bohr–Sommerfeld manifold in the context of Berezin–Toeplitz quantization of general prequantized symplectic manifolds, and we study its semiclassical properties using the off-diagonal expansion of the Bergman kernel. We then show how these results extend to the case of noncompact orbifolds and give an application to relative Poincaré series in the theory of automorphic forms.

Fluid dynamics far-from-equilibrium: a concrete example

In this contribution we propose a more general derivation of relativistic fluid dynamics from kinetic theory, in which the fluid is assumed to be close to an isotropic non-equilibrium state instead of an equilibrium one. We demonstrate that, for a classical gas of massless particles, it is possible to obtain a hydrodynamic theory described by equations of motion that are identical to those commonly solved in heavy ion collisions. The only difference appears in the form of the transport coefficients that enter the equations of motion. We then calculate these transport coefficients for a few choices of isotropic distribution functions and discuss their sensitivity to the underlying non-equilibrium state.

Magnetically Controllable Isotropic/Anisotropic Slippery Surface for Flexible Droplet Manipulation.

Controllable wetting surfaces play a significant role in numerous applications such as smart liquid manipulation, lab-on-a-chip, drug delivery, liquid robot, and so on. A novel type of magnetically controllable isotropic/anisotropic slippery surface was prepared by femtosecond laser ablation. The slippery liquid-infused porous surface (SLIPS) can be switched between an isotropic smooth state and an anisotropic groove state by the magnetic field. The relationship between the sliding property of the SLIPS and the magnetic flux density, water droplet volume, microgroove width, and microgroove height are systematically studied. Passively flexible movement on the isotropic SLIPS and actively directional movement on the anisotropic SLIPS of water droplets were realized. This work provides a fresh understanding of the controllable isotropic/anisotropic SLIPS and reveals great potential in versatile applications which are related to magnetically controllable smart liquid manipulation.

Structural Controls on Alteration Stages at the Chuquicamata Copper-Molybdenum Deposit, Northern Chile

AbstractAll existing bench and tunnel vein and fault structural data with identified mineral infill, acquired in Chuquicamata, were georeferenced, digitized, and, according to their mineralogy, assigned to one or more of the major alteration events developed between 35 and 31 Ma. Veins and faults were separated into two main stages: (1) the late magmatic and potassic stage that comprises the background potassic and the propylitic alteration and (2) the hydrothermal stage composed by early (intense potassic), main (principal and late sericite; hydrothermal stages H1 through H4), and late (advanced argillic alteration) hydrothermal events. The spatial distribution of the propylitic to late-hydrothermal events that plotted within the major fault framework indicate these had either permeable or impermeable (±barrier) behavior through time. The area of the deposit was divided into 600 square grids measuring 100 × 100 m, and a stress orientation analysis was carried out for every propylitic to late-hydrothermal alteration event. The analysis indicates that the local principal horizontal stress (σH) trajectories are nonlinear and noncoaxial through the successive alteration events, differing from the previous and following stages, and in the majority of cases do not coincide with the approximate east-northeast orientation of the inferred tectonic far-field stress orientation. The differences between the stress trajectories, away from the far-field stress orientation throughout the evolution of the system, are considered to be principally related to the dynamic variations experienced by the stress components, such as thermal-magmatic stresses linked to temperature fluctuations due to cooling or heating by progressive igneous/hydrothermal activity and/or elastic, overburden-related stresses associated with reaccommodations developed during uplift and erosion. The estimated stresses resulting after erosional unroofing and decreasing temperature indicate that the maximum horizontal stress varied as the system evolved from the commonly accepted depth of emplacement of ~6 km. During the late magmatic, background potassic, and intense potassic stages, the calculated differential stress was contractional, decreasing to an isotropic state at the contraction-extension stress reversal that hosted the main hydrothermal H1 through H3 events, to finally become extensional at the shallow late-hydrothermal event. The most significant mineralization occurred at the time of stress reversal, coincidental with the sericite and quartz-sericite events (H1-H4), associated with hydrothermal fluid accumulation, overpressuring, and multiple-orientated hydraulic fracture development.The Chuquicamata study suggests that the local stress control involved in the emplacement of porphyry copper systems is fundamentally related to variable and progressive heat energy release, associated with igneous and hydrothermal activity, and to the elastic stresses derived from uplift and unloading, rather than to a constant far-field tectonic stress. The continuous local stress fluctuations led to bulk stress readjustments and cyclical stress-fluid interactions for local fault reactivation, damage zone modification, brecciation, permeability creation/destruction, and fluid focusing, as well as the discharge of hydrothermal fluids throughout the evolution of the system.

Information-theoretic aspects of Werner states

In a seminal study of quantum states with Einstein–Podolsky–Rosen correlations (entanglement) admitting a hidden-variable model (Werner, 1989), Werner introduced the dichotomy of entanglement/separability and devised a family of highly symmetric states, now termed the Werner states, some of which exhibit entanglement but no Bell nonlocality. It turns out that the Werner states have a rich structure of correlations and constitute a paradigm which has played an innovative role in both theoretical and experimental explorations of quantum information. Given the theoretical significance and wide applications of the Werner states, here we first give a concise review of information contents of the Werner states, and then present an information-theoretic characterization of them in terms of the Wigner–Yanase skew information: The Werner states are identified as the states with the minimum quantum uncertainty with respect to a natural family of observables (i.e., the generators of the diagonal unitary group). For this purpose, we introduce a measure of quantum uncertainty which is of independent interest in studying asymmetry, coherence, and uncertainty, and reveal its fundamental properties. We further identify the Bell triplet states as the opposite states of the Werner states in the sense that they have the maximal amount of quantum uncertainty. Analogously, we provide a similar characterization of the isotropic states as the minimum quantum uncertainty states with respect to a closely related family of operators.

Spin Symmetry Breaking: Superparamagnetic and Spin Glass-Like Behavior Observed in Rod-Like Liquid Crystalline Organic Compounds Contacting Nitroxide Radical Spins

Liquid crystalline (LC) organic radicals were expected to show a novel non-linear magnetic response to external magnetic and electric fields due to their coherent collective molecular motion. We have found that a series of chiral and achiral all-organic LC radicals having one or two five-membered cyclic nitroxide radical (PROXYL) units in the core position and, thereby, with a negative dielectric anisotropy exhibit spin glass (SG)-like superparamagnetic features, such as a magnetic hysteresis (referred to as ‘positive magneto-LC effect’), and thermal and impurity effects during a heating and cooling cycle in weak magnetic fields. Furthermore, for the first time, a nonlinear magneto-electric (ME) effect has been detected with respect to one of the LC radicals showing a ferroelectric (chiral Smectic C) phase. The mechanism of the positive magneto-LC effect is proposed and discussed by comparison of our experimental results with the well-known magnetic properties of SG materials and on the basis of the experimental results of a nonlinear ME effect. A recent theoretical study by means of molecular dynamic simulation and density functional theory calculations suggesting the high possibility of conservation of the memory of spin-spin interactions between magnetic moments owing to the ceaseless molecular contacts in the LC and isotropic states is briefly mentioned as well.

Evolution of shear wave velocity during triaxial compression

Accurate design of geotechnical structures requires precise estimation of the shear wave velocity (Vs) and the small-strain shear modulus. However, the interpretation of Vs data measured in deformed/sheared soil has not been extensively considered. This study used a triaxial apparatus equipped with planar piezoelectric transducers to monitor the evolution of Vs during triaxial compression of cohesionless soils. Recognizing that the grain shape and surface characteristics affect the overall mechanical response of granular materials, various natural sands and glass bead samples were considered. Discrete element method (DEM) simulations using spherical particles were carried out to compute particle-scale responses that cannot be measured in the laboratory. The experimental results revealed that the Vs values for samples with different initial densities tend to approach one another and have similar values (merge) at large axial strains. This merging occurs at a lower strain level for spherical particles in comparison with non-spherical particles. The linear Vs-void ratio relationship, which is often developed and used for homogeneous and isotropic stress states, is no longer applicable during shearing. It is the mean coordination number that dictates the evolution of Vs during triaxial compression. Furthermore, the axial strain at which the peak Vs is achieved is found to be comparable to the axial strain at which specimen dilation takes place.

Practical Considerations in Alternate Fracturing with Shift/Fracture/Close Operation: Learnings from Geomechanical Modeling and Downhole Diagnostics

SummaryAlternate or out-of-sequence fracturing (OOSF) has been field tested in western Siberia in 2014 and in western Canada in 2017, 2018, and 2019, with operational success and positive well-production performance. It is conducted by fracturing Stage 1 (at the toe) and then fracturing Stage 3 (toward the heel), followed by tripping back to place Stage 2 (center fracture) between Stages 1 and 3 (outside fractures). During placing the center fracture, OOSF can exploit the reduced stress anisotropy to effectively activate the planes of weakness (natural fractures, fissures, faults, and joints) to potentially create failure surfaces with different breakdown angles in virtually all directions. This can potentially lead to branch fractures that can connect the hydraulic fractures to stress-relief fractures that are created while placing the outside fractures, ultimately generating a complex fracture network and enhancing fracture connectivity.Despite prior works on fracture modeling (calibrated by field tests) and geomechanical modeling, a comparative analysis of wellbore-breakdown character and hydraulic-fracture orientation during OOSF is still lacking. Thus, in this study, the solutions to 3D Kirsch equations are provided for both low and high stress anisotropies to analyze the differences in breakdown gradient, failure angle, and fracture orientation under various geomechanical and treatment-design conditions. The consideration is given to an intact rock from an isotropic stress state to high-stress-anisotropy conditions. The results are analyzed in the context of the downhole-measured pressures and temperatures.The results indicate that the reduced stress anisotropy during OOSF leads to favorable treating conditions: With a net fracture-extension pressure greater than the reduced stress anisotropy, fracture complexity can be created by allowing the fracture to grow with different failure angles. Also, a well can be drilled and fractured at any inclination or azimuth with favorable breakdown gradients of 45 to 85% of the overburden gradient. The reduced stress anisotropy can also trigger some challenges. The near-well stress-concentration effects can become more pronounced, promoting longitudinal fracture creation. For treatments with tortuosity greater than the stress anisotropy, longitudinal fractures can be created instead of transverse fractures because the tortuosity is transmitted to the wellbore body and not into the fractures. In this case, to initiate transverse fractures, either the wellbore must intersect the pre-existing transverse notches or the near-well pore-fluid pressure must exceed the axial stress and rock strength (before the hoop stress reaches the tensile failure point). In addition, the fracture might lose directional control and follow any path of weakness. Hence, the rock-fabric effects become more dominant under a low-stress-anisotropy regime, which means that with no pre-existing transverse natural fractures or notches, a longitudinal fracture can be generated at the bottom and top of an intact horizontal wellbore.This is the first attempt in identifying the circumstances that should be avoided for optimizing OOSF through geomechanical modeling and the analysis of the downhole-measured pressures and temperatures to reveal the differences in breakdown character using the Kirsch equations under various geomechanical and treatment conditions during the low-stress-anisotropy regime.

Transient optical symmetry breaking for ultrafast broadband dichroism in plasmonic metasurfaces

Ultrafast nanophotonics is an emerging research field aimed at the development of nanodevices capable of light modulation with unprecedented speed. A promising approach exploits the optical nonlinearity of nanostructured materials (either metallic or dielectric) to modulate their effective permittivity via interaction with intense ultrashort laser pulses. While the ultrafast temporal dynamics of such nanostructures following photoexcitation has been studied in depth, sub-ps transient spatial inhomogeneities taking place at the nanoscale have been so far almost ignored. Here we theoretically predict and experimentally demonstrate that the inhomogeneous space-time distribution of photogenerated hot carriers induces a transient symmetry breaking in a plasmonic metasurface made of highly symmetric metaatoms. The process is fully reversible, and results in a broadband transient dichroic optical response with a recovery of the initial isotropic state in less than 1 picosecond, overcoming the speed bottleneck caused by slower relaxation processes, such as electron-phonon and phonon-phonon scattering. Our results pave the way to the development of ultrafast dichroic devices, capable of Tera bit/s modulation of light polarization.

Semi-classical Limit of Quantum Free Energy Minimizers for the Gravitational Hartree Equation

For the gravitational Vlasov-Poisson equation, Guo and Rein constructed a class of classical isotropic states as minimizers of free energies (or energy-Casimir functionals) under mass constraints. For the quantum counterpart, that is, the gravitational Hartree equation, isotropic states are constructed as free energy minimizers by Aki, Dolbeault and Sparber. In this paper, we are concerned with the correspondence between quantum and classical isotropic states. Precisely, we prove that as the Planck constant $\hbar$ goes to zero, free energy minimizers for the Hartree equation converge to those for the Vlasov-Poisson equation in terms of potential functions as well as via the Husimi transform and the T\"oplitz quantization.

Geometry of skew information-based quantum coherence

We study the skew information-based coherence of quantum states and derive explicit formulas for Werner states and isotropic states in a set of autotensors of mutually unbiased bases (MUBs). We also give surfaces of skew information-based coherence for Bell-diagonal states and a special class of X states in both computational basis and in MUBs. Moreover, we depict the surfaces of the skew information-based coherence for Bell-diagonal states under various types of local nondissipative quantum channels. The results show similar as well as different features compared with relative entropy of coherence and l1 norm of coherence.

Anisotropic and extreme magnetoresistance in the magnetic semimetal candidate erbium monobismuthide

Rare-earth monopnictides display rich physical behaviors, featuring most notably spin and orbital orders in their ground state. Here, we grow ErBi single crystal and study its magnetic, thermal and electrical properties. An analysis of the magnetic entropy and magnetization indicates that the weak magnetic anisotropy in ErBi possibly derives from the mixing effect, namely the anisotropic ground state of Er3+ (4f11) mingles with the isotropic excited state through exchange interaction. At low temperature, an extremely large magnetoresistance (~104%) with a parabolic magnetic-field dependence is observed, which can be ascribed to the nearly perfect electron-hole compensation and ultrahigh carrier mobility. When the magnetic field is rotated in the ab (ac) plane and the current flows in the b axis, the angular magnetoresistance in ErBi shows a twofold (fourfold) symmetry. Similar case has been observed in LaBi where the anisotropic Fermi surface dominates the low-temperature transport. Our theoretical calculation suggests that near the Fermi level ErBi shares similarity with LaBi in the electronic band structures. These findings indicate that the angular magnetoresistance of ErBi could be mainly determined by its anisotropic Fermi surface topology. Besides, contributions from several other possibilities, including the spin-dependent scattering, spin-orbit scattering, and demagnetization correlation to the angular magnetoresistance of ErBi are also discussed.

Temperature-dependent chirality of cholesteric liquid crystal for terahertz waves.

Recently, the terahertz (THz) chiral field control opens a new window to THz devices and their applications. In this Letter, the active manipulation for THz chiral states based on the cholesteric liquid crystal (CLC) has been demonstrated by THz time domain cross-polarization spectroscopy. The results show that the CLC has strong THz optical activity and circular dichroism (CD) effect, and the strongest THz CD of 22 dB and a polarization rotation angle of 88.4° occur around the phase transition temperature TS-N=250K. Rising to a room temperature of 300 K, the CLC turns from a chiral state to an isotropic state for THz waves with the phase transition processes of CLC molecules. Therefore, this CLC device can be performed as a thermally active THz circular polarizer, which brings potential applications in THz polarization imaging, broadband communication, and spectroscopy.