Isotropic State Research Articles

Hydromechanical behavior of unsaturated soils: Interpretation of compression curves in terms of effective stress

This state-of-the-art paper on the hydromechanical behavior of unsaturated soils focuses on the interpretation of the compression curves of unsaturated soils in terms of effective stress, with the goal of understanding the relative impacts of suction on the effective stress, net yield stress, effective yield stress and slope of the virgin compression line (VCL) during a monotonic increase in net stress. A database of compression curves was compiled for both high and low plasticity fine-grained soils under a wide range of suctions, isotropic or oedometric stress states, drainage conditions (constant suction or constant water content) and preparation techniques (impact compaction, static compaction, consolidation from slurry). Most of the compression curves plotted in terms of effective stress revealed a consistent hardening response with increasing suction and a slight suction dependency on the slope VCL. Interpretation of the compression curves in terms of effective stress led to load-collapse curves with a similar shape for a wide range of soils. Most soils evaluated had a greater rate of increase in effective yield stress with suction than the rate of increase in suction stress with suction, implying that these compacted soils may be susceptible to collapse upon wetting. Inconsistent trends were observed in some studies, which were attributed partially to natural variability but also experimental issues and limitations on the range of conditions investigated. Accordingly, recommendations are provided for future studies on the compression curves of unsaturated soils to ensure that results can be clearly interpreted in terms of effective stress.

Multiblock Thermoplastic Polyurethanes: In Situ Studies of Structural and Morphological Evolution under Strain.

The structural evolution of multiblock thermoplastic polyurethane ureas based on two polydiols, poly(1,4-butylene adipate (PBA) and poly-ε-caprolactone (PCL), as soft blocks and two diisocyanites, 2,4-toluylene diisocyanate (TDI) and 1,6-hexamethylene diisocyanate (HMDI), as hard blocks is monitored during in situ deformation by small- and wide-angle X-ray scattering. It was shown that the urethane environment determines the crystal structure of the soft block. Consequently, two populations of crystalline domains of polydiols are formed. Aromatic TDI forms rigid domains and imposes constrains on the crystallization of bounded polydiol. During stretching, the TDI–polydiol domains reveal limited elastic deformation without reorganization of the crystalline phase. The constrained lamellae of polydiol form an additional physical network that contributes to the elastic modulus and strength of the material. In contrast, polydiols connected to the linear semi-flexible HMDI have a higher crystallization rate and exhibit a more regular lamellar morphology. During deformation, the HMDI-PBA domains show a typical thermoplastic behavior with plastic flow and necking because of the high degree of crystallinity of PBA at room temperature. Materials with HMDI-PCL bonding exhibit elastic deformation due to the low degree of crystallinity of the PCL block in the isotropic state. At higher strain, hardening of the material is observed due to the stress-induced crystallization of PCL.

Detection Power of Separability Criteria Based on a Correlation Tensor: A Case Study

Detection power of separability criteria based on a correlation tensor is tested within a family of generalized isotropic states in [Formula: see text]. For [Formula: see text] all these criteria are weaker than the positive partial transposition (PPT) criterion. Interestingly, our analysis supports the recent conjecture that a criterion based on symmetrically informationally complete positive operator-valued measure (SIC-POVMs) is stronger than realignment criterion.

Generalized string-net models: A thorough exposition

We describe how to construct generalized string-net models, a class of exactly solvable lattice models that realize a large family of 2D topologically ordered phases of matter. The ground states of these models can be thought of as superpositions of different "string-net configurations", where each string-net configuration is a trivalent graph with labeled edges, drawn in the $xy$ plane. What makes this construction more general than the original string-net construction is that, unlike the original construction, tetrahedral reflection symmetry is not assumed, nor is it assumed that the ground state wave function $\Phi$ is "isotropic": i.e. in the generalized setup, two string-net configurations $X_1, X_2$ that can be continuously deformed into one another can have different ground state amplitudes, $\Phi(X_1) \neq \Phi(X_2)$. As a result, generalized string-net models can realize topological phases that are inaccessible to the original construction. In this paper, we provide a more detailed discussion of ground state wave functions, Hamiltonians, and minimal self-consistency conditions for generalized string-net models than what exists in the previous literature. We also show how to construct string operators that create anyon excitations in these models, and we show how to compute the braiding statistics of these excitations. Finally, we derive necessary and sufficient conditions for generalized string-net models to have isotropic ground state wave functions on the plane or the sphere -- a property that may be useful in some applications.

SYNERGISTIC MAGNETORHEOLOGICAL NR–NBR ELASTOMER BLEND WITH ELECTROLYTIC IRON PARTICLES

ABSTRACT This article presents the development of a new kind of magnetorheological elastomer blend made with natural rubber, acrylonitrile–butadiene rubber (NR-NBR), and electrolytic iron particles through solution mixing. The compressive stress and elastic modulus of the composites in the isotropic and anisotropic states of the filler were studied. A unique study of the filler distribution and filler orientation mechanism was proposed from the compressive properties and scanning electron microscopy. A strong improvement in the elastic modulus of the NR–NBR blend from isotropic to anisotropic change was achieved as compared with NR and NBR in single-rubber composites. The filler content in the anisotropic magnetorheological elastomers was optimized by measuring the field-dependent elastic modulus in the presence of an externally applied magnetic field. The blend rubber composites showed better sensitivity in the presence of a magnetic field than the NR and NBR composites did. The improvement might be due to the better filler orientation and strong adhesion of filler particles by the NR phase in the blend matrix. The new elastomer blends may have applications in active dampers, vibrational absorption, and automotive bushings.

Parametrized entanglement monotone

Entanglement concurrence has been widely used for featuring entanglement in quantum experiments. As an entanglement monotone it is related to specific quantum Tsallis entropy. Our goal in this paper is to propose a new parameterized bipartite entanglement monotone which is named as $q$-concurrence inspired by general Tsallis entropy. We derive an analytical lower bound for the $q$-concurrence of any bipartite quantum entanglement state by employing positive partial transposition criterion and realignment criterion, which shows an interesting relationship to the strong separability criteria. The new entanglement monotone is used to characterize bipartite isotropic states. Finally, we provide a computational method to estimate the $q$-concurrence for any entanglement by superposing two bipartite pure states. It shows that the superposition operations can at most increase one ebit for the $q$-concurrence in the case that the two states being superposed are bi-orthogonal or one-sided orthogonal. These results reveal a series of new phenomena about the entanglement, which may be interesting in quantum communication and quantum information processing.

Molecular packing analysis of the crystal smectic E phase of a benzothieno-benzothiophene derivative by a combined experimental / computational approach

ABSTRACT The molecule 2-decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene has gained a lot of attention since high charge carrier mobility was observed in thin film transistors. Its thermotropic liquid crystalline states may play an important role in the thin film formation since the smectic A and the crystal smectic E phase (SmE) are claimed to be pre-stages of the final bulk structure. To understand the phase diversity, structural characterisation of solution processed thin films is performed by X-ray diffraction in the complete temperature range up to the isotropic state at 240°C. The diffraction pattern of the SmE phase is analysed in detail. Peak broadening analysis reveals that the crystallographic order across the smectic layers is larger than the order along the smectic layers. A combined experimental and computational approach is used to determine the molecular packing within the SmE phase. It leads to a number of different packing motifs. A comparison of the calculated diffraction pattern with the experimental results reveals that nano-segregation is present within the SmE phase. Energy consideration clearly favours a herringbone arrangement of the aromatic units. The nano-segregation within the SmE phase with herringbone packing of the aromatic units is accompanied with interdigitation of side chains from neighbouringherringbone layers.

Broadcasting of NPT entanglement in two qutrit systems

It is known that beyond $2 \otimes 2$ and $2 \otimes 3$ dimensional quantum systems, Peres-Hordecki criterion is no longer sufficient as an entanglement detection criterion as there are entangled states with both positive and negative partial transpose (PPT and NPT). Further, it is also true that all PPT entangled states are bound entangled states. However, in the class of NPT states, there can exist bound entangled states as well as free entangled states. All free/useful/distillable entanglement is a part of the class of NPT entangled states. In this article, we ask the question that given an NPT entangled state in $3 \otimes3$ dimensional system as a resource, how much entanglement can we broadcast so that resource still remains NPT. We have chosen $3 \otimes 3$ system as a first step to understand broadcasting of NPT states in higher dimensional systems. In particular, we find out the range of broadcasting of NPT entanglement for Two parameter Class of States (TPCS) and Isotropic States (IS). Interestingly, as a derivative of this process we are also able to locate the existence of absolute PPT states (ABPPT) in $3 \otimes 3$ dimensional system. Here we implement the strategy of broadcasting through approximate cloning operations.

Spontaneous directional flow of active magnetic particles

We predict the emergence of large-scale polar order and spontaneous directional flows in a class of self-propelled autonomous particles that interact via passive repulsion between off-center sites. The coupling of active motion with the passive torque acting about the particle centers results in hybrid active-passive interactions responsible for a macroscopic phase transition from an isotropic state to a polar-aligned state in systems of particles with front interaction sites. We employ a continuum kinetic theory to explain that the emergence of long-ranged orientational order, which occurs in unbounded domains at finite densities, can be externally activated independently of the self-propulsion mechanism and drives a macroscopic particle flow in a direction selected by symmetry breaking.

Numerical Simulation on Mesoscale Mechanism of Seepage in Coal Fractures by Fluid-Sloid Coupling Method

Trying to reveal the mechanism of gas seepage in coal is of significance to both safe mining and methane exploitation. A series of FEM numerical models were built up and studied so as to explore the mesoscale mechanism of seepage in coal fractures. The proposed mesoscale FEM model is a cube with micron fractures along three orthogonal directions. The distribution of velocity and pressure under fluid-solid coupling was obtained, and furthermore, the seepage flow flux and an equivalent permeability of the whole model were calculated. The influences of fracture width, outlet velocity, and in situ stress level on seepage were investigated. The numerical results show that nonlinear Darcy seepage occurs during low velocity zone. The permeability is increased linearly with the increasing of facture width and outlet velocity. A certain change of lateral coefficient of in situ stress also affects seepage. The permeability is increased sharply once deviating the isotropic spherical stress state, but it is no longer changed obviously after the lateral coefficient has been increased or decreased more than 20%. The mesoscale seepage mechanism in coal fractures has been preliminarily revealed by considering fluid-solid coupling effect, and the key factors influencing fluid seepage in coal fractures were demonstrated. The proposed methods and results will be helpful to the further study of seepage behaviour in coal with more complex structures.

Charmonium transition in electromagnetic and rotational fields

We study charmonia in electromagnetic and rotational fields in the frame of a potential model. Different from the temperature field which is isotropic and leads to the well-known charmonium dissociation, the electromagnetic and rotational fields break down the radial symmetry, and the competition between strong interaction and electromagnetic and rotational interaction in the direction of Lorentz force makes the charmonia transit from an isotropic bound state of strong interaction with positive binding energy to an anisotropic bound state of electromagnetic and rotational interaction with negative binding energy. The transition seems possible to be realized in high energy nuclear collisions.

Development of an auto compensation system in cyclic triaxial apparatus for liquefaction analysis

When performing cyclic triaxial tests, the connection process between loading piston and specimen could have significant effect on the test results. Tensile pre-shearing effect occurs during saturation and consolidation stages in screw-based configurations and compressive pre-shearing stress is induced while making the connection between loading piston and specimen in vacuum-based configurations. In order to overcome these technical problems, a special auto compensation system was incorporated into an existing cyclic triaxial apparatus, allowing: (1) no physical contact between loading piston and specimen to achieve an isotropic consolidation state, (2) the later connection between these two components to be easily accomplished with almost insignificant disturbance on the specimen (maximum 100 N in axial force). To assess the performance of this auto compensation system, two experiments of same dense reference sand specimens were respectively conducted, and the results were found to be similar, showing the good repeatability. Moreover, as compared with screw-based configuration, the test specimen did not undergo an adverse tensile pre-shearing. As a result, the test specimen became more resistant to cyclic mobility. On the contrary, as compared with another vacuum-based configuration (without auto compensation) well-documented in the literature, the obtained result was less stable since the employment of auto compensation system ensured that there was no beneficial compressive pre-shearing during the connection stage. The results obtained in this study showed the good performance of the developed auto compensation system in the triaxial test apparatus for liquefaction analysis.

Activity-induced isotropic-polar transition in active liquid crystals

Active fluids are intrinsically out-of-equilibrium systems due to the internal energy injection of the active constituents. We show here that a transition from a motion-less isotropic state towards a flowing polar one can be possibly driven by the sole active injection through the action of polar-hydrodynamic interactions in absence of an ad hoc free energy which favors the development of an ordered phase. In particular, we propose an analytical argument and we perform lattice Boltzmann simulations where the appearance of large temporal fluctuations in the polar fraction of the system is observed at the transition point. We show that elastic absorption plays a relevant role in energy transfer dynamics, contrary to the case of the usual active gel theory where this term can be factually neglected.

A Thermodynamically Consistent Phase Field Model for Gas Transport in Saturated Bentonite Accounting for Initial Stress State

A thermodynamically consistent phase field model that accounts for initial stress state is proposed in this paper to simulate the gas migration process in saturated bentonite. The energy contribution due to the fracturing process is included in Coussy’s thermodynamic framework for unsaturated porous media. The possible effect of the interfaces between different phases on the driving force functional for phase field and the effective stress has been identified from the proposed thermodynamic framework. In addition, the initial stress state is innovatively accounted for in the phase field model by introducing a fictitious strain tensor that is calculated from its corresponding initial stress tensor. It is the sum of the fictitious strain tensor and the strain tensor due to elastic deformation that governs the evolution of the phase field. The simulated results showed that the effect of the swelling pressure (regarded as the initial effective stress for a high swelling clay) on the fracture initiation has been well described by the proposed method. Specifically, the effect of either isotropic or anisotropic stress state on the fracturing process can be well reflected by the phase field approach based on Rankine-type fracture criterion. In contrast, the phase field approach based on the Griffith fracture criterion is more appropriate for the isotropic stress state than the anisotropic stress state because of the Poisson’s effect. Moreover, the gas pressure required to trigger the fracturing process needs to exceed the sum of the porewater pressure and the initial stress. The effect of the boundary condition on the evolution of fluid pressure and total stress has been qualitatively captured. It is found that the boundary with higher stiffness leads to a higher gas pressure in the developed fracture and a higher water pressure and total stress in the surrounding porous matrix. In addition, some key experimental findings, such as the preferential gas flow, the build-up of porewater pressure, the almost fully saturated state and the localized consolidation, have been qualitatively captured by the developed phase field model.

DEM analysis on the stress wave response of spherical particle assemblies under triaxial compression

It is challenging to understand the stress wave response of cohesionless particle assemblies including compression and shear wave velocities (Vp and Vs) due to complicated particle-scale interactions particularly during a loading process. This contribution adopts the discrete element method to simulate triaxial compression experiments using spherical particles. Four samples are isotropically confined at various initial packing densities and then sheared monotonically up to the critical state. Small-amplitude wave propagation simulation is performed during shearing along the axis of loading. The results reveal that Vp is affected by the major principal stress and the coordination number contributing to the vertical direction rather than horizontal direction, while Vs is more influenced by the geometric mean stress and the mean coordination number. The wave velocity ratio (Vp/Vs) is well correlated with the fabric anisotropy, having a linear relationship. This enables prediction of microscopic change in fabric from macroscopic wave velocity values. Besides, a material-specific relationship between stress levels and wave velocities is found at the critical state with a unique fabric anisotropy, independent of initial packing. Vs in the isotropic state is found to be always larger that at the critical state under an equivalent stress level.

Tuning the Liquid Crystallinity of Cholesteryl-o-Carborane Dyads: Synthesis, Structure, Photoluminescence, and Mesomorphic Properties

A set of mesomorphic materials in which the o-carborane cluster is covalently bonded to a cholesteryl benzoate moiety (mesogen group) through a suitably designed linker is described. The olefin cross-metathesis between appropriately functionalized styrenyl-o-carborane derivatives and a terminal alkenyl cholesteryl benzoate mesogen (all type I terminal olefins) leads to the desired trans-regioisomer, which is the best-suited configuration to obtain mesomorphic properties in the final materials. The introduction of different substituents (R = H (M2), Me (M3), or Ph (M4)) to one of the carbon atoms of the o-carborane cluster (Ccluster) enables the tailoring of liquid crystalline properties. Compounds M2 and M3 show the chiral nematic (N*) phase, whereas M4 do not show liquid crystal behavior. Weaker intermolecular interactions in the solid M3 with respect to those in M2 may allow the liquid crystallinity in M3 to be expressed as enantiotropic behavior, whereas breaking the stronger intermolecular interaction in the solid state of M2 leads directly to the isotropic state, resulting in monotropic behavior. Remarkably, M3 also displays the blue phase, which was observed neither in the chiral nematic precursor nor in the styrenyl-cholesterol model (M5) without an o-carborane cluster, which suggests that the presence of the cluster plays a role in stabilizing this highly twisted chiral phase. In the carborane-containing mesogens (M2 and M3), the o-carborane cluster can be incorporated without destroying the helical organization of the mesophase.

Desynchronized liquid crystalline network actuators with deformation reversal capability

Liquid crystalline network (LCN) actuator normally deforms upon thermally or optically induced order-disorder phase transition, switching once between two shapes (shape 1 in LC phase and shape 2 in isotropic state) for each stimulation on/off cycle. Herein, we report an LCN actuator that deforms from shape 1 to shape 2 and then reverses the deformation direction to form shape 3 on heating or under light only, thus completing the shape switch twice for one stimulation on/off cycle. The deformation reversal capability is obtained with a monolithic LCN actuator whose two sides are made to start deforming at different temperatures and exerting different reversible strains, by means of asymmetrical crosslinking and/or asymmetrical stretching. This desynchronized actuation strategy offers possibilities in developing light-fueled LCN soft robots. In particular, the multi-stage bidirectional shape change enables multimodal, light-driven locomotion from the same LCN actuator by simply varying the light on/off times.

Plastic deformation of magnetically isotropic Cr single crystals compressed at 77 K

A series of compression tests at 77 K was carried out on chromium single crystals in magnetically isotropic state to investigate the slip activity during the first 2–4% of plastic strain. Macroscopic samples of 3 mm thickness were polished mechanically and electrolytically and their orientations determined before and after deformation by electron backscatter diffraction to assess the magnitudes and directions of crystal rotations. The crystals compressed in the direction close to [001] deformed primarily by slip on the most highly stressed (1‾01)[111] and (101)[1‾11] systems. Loading the crystals in the directions close to the [011]−[1‾11] edge of the stereographic triangle resulted in preferential twinning on 112111 systems. For loading in the center-triangle region, diffraction contrast imaging in TEM reveals the presence of [100] screw junctions between intersecting 1/2111 and 1/2[11¯1¯] screw dislocations. Using molecular statics simulations, we show that this junction does not break under the applied stress and moves together with the two dislocations on their common (01‾1) plane. In contrast to the prediction of the Schmid law, the slip morphology for center-triangle orientations is thus dominated by anomalous slip on the low-stressed (01‾1) plane.

Experimental Investigation and Modeling of Damage Accumulation of EN-AW 2024 Aluminum Alloy under Creep Condition at Elevated Temperature.

The paper is focused on creep-rupture tests of samples made of the 2024 alloy in the T3511 temper under uniaxial tensile stress conditions. The basic characteristics of the material at the temperatures of 100, 200 and 300 °C were determined, such as the Young’s modulus E, yield point σy, ultimate tensile strength σc and parameters K and n of the Ramberg–Osgood equation. Creep tests were performed for several different levels of nominal axial stress (load) at each temperature. It was observed that in the process of creep to failure at 200 and 300 °C, as the stress decreases, the creep time increases and, at the same time, the strain at rupture increases. However, such a regularity is maintained until a certain transition stress value σt is reached. Reducing the stress below this value results in a decreased value of the strain at rupture. A simple model of creep damage accumulation was proposed for the stress range above the transient value. In this model, the increase in the isotropic damage state variable was made dependent on the value of axial stress and the increase in plastic axial strain. Using the results of experimental creep-rupture tests and the failure condition, the parameters of the proposed model were determined. The surface of fractures obtained in the creep tests with the use of SEM technology was also analyzed.

Exploring the turbulent velocity gradients at different scales from the perspective of the strain-rate eigenframe

Abstract