Uniform Phases Research Articles

Domain Textures in the Fractional Quantum Hall Effect.

Impacts of domain textures on low-lying neutral excitations in the bulk of fractional quantum Hall effect (FQHE) systems are probed by resonant inelastic light scattering. We demonstrate that large domains of quantum fluids support long-wavelength neutral collective excitations with well-defined wave vector (momentum) dispersion that could be interpreted by theories for uniform phases. Access to dispersive low-lying neutral collective modes in large domains of FQHE fluids such as long wavelength magnetorotons at filling factor v=1/3 offer significant experimental access to strong electron correlation physics in the FQHE.

Effects of heat treatment on degradation, mechanical properties and cytocompatibility of Mg-1.5Zn-0.5Y-0.5Zr alloy

ABSTRACT Effects of solution treatment (T4), solution and ageing treatment (T6) on the degradation behaviours, mechanical properties and cytocompatibility of the extruded Mg-1.5Zn-0.5Y-0.5Zr alloy were studied in this work. Microstructural characterisation including SEM and TEM observation, degradation behaviours, tensile experiment and cytocompatibility tests was carried out. It showed that the alloy after 500°C × 2 h and 12 h ageing treatment exhibited the best degradation resistance with the degradation rate of 0.11 ± 0.01 mm/y in Hank’s solution. Moreover, the fine and uniform distributed second phases after 12 h ageing treatment could effectively improve the ultimate tensile strength (UTS) of the alloy. Due to the low degradation rate, the alloy after 500°C solution and 12 h ageing treatment also exhibited good cytocompatibility with cell viability value of more than 90%. In essence, 500°C × 2 h and 12 h ageing was the best heat treatment practice for Mg-1.5Zn-0.5Y-0.5Zr alloy.

Revisiting the Ocean’s Nonisostatic Response to 5-Day Atmospheric Loading: New Results Based on Global Bottom Pressure Records and Numerical Modeling

AbstractWe use bottom pressure records from 59 sites of the global tsunami warning system to examine the nonisostatic response of the World Ocean to surface air pressure forcing within the 4–6-day band. It is within this narrow “5-day” band that sea level fluctuations strongly depart from the isostatic inverted barometer response. Numerical simulations of the observed bottom pressures were conducted using a two-dimensional Princeton Ocean Model forced at the upper boundary by two versions of the air pressure loading: (i) an analytical version having the form of the westward propagating, 5-day Rossby–Haurwitz air pressure mode; and (ii) an observational version based on a 16-yr record of global-scale atmospheric reanalysis data with a spatial resolution of 2.5°. Simulations from the two models—consisting of barotropic standing waves of millibar amplitudes and near uniform phases in the Pacific, Atlantic, and Indian Oceans—are in close agreement and closely reproduce the observed bottom pressures. The marked similarity of the outputs from the two models and the ability of both models to accurately reproduce the seafloor pressure records indicate a pronounced dynamic response of the World Ocean to nonstationary air pressure fields resembling the theoretical Rossby–Haurwitz air pressure mode.

Permutation entropy-based improved uniform phase empirical mode decomposition for mechanical fault diagnosis

Uniform phase empirical mode decomposition (UPEMD) is an effective signal separation method, which is proposed to solve the mode mixing phenomenon of empirical mode decomposition (EMD) by adding uniform phase sinusoidal signal as masking signal. However, the decomposition effect of UPEMD depends on the selection of amplitude and phase number of masking signal. Besides, there are also some issues such as noise residue and incomplete decomposition that need to be solved. In this paper, a novel permutation entropy-based improved uniform phase empirical mode decomposition (PEUPEMD) method is proposed to address these problems. In PEUPEMD method, first of all, the sinusoidal signals with uniform phases are added to the raw signal as masking signals. Second, the superimposed signal is decomposed using EMD and the final intrinsic mode functions are obtained via an ensemble way. Third, the obtained IMFs with high-frequency are detected by permutation entropy algorithm. Finally, the residual signal containing low-frequency components is decomposed through EMD completely. Last, the simulated signal and tested data are applied to verify the feasibility of PEUPEMD via comparing it with EMD, UPEMD, CEEMDAN and ICEEMDAN methods. The results analysis indicated that PEUPEMD was superior to the comparative methods in decomposing accuracy and mode mixing suppression.

Reproductive strategy of spiny gurnard Lepidotrigla dieuzeidei Blanc and Hureau, 1973 from the south-eastern Adriatic Sea

This study provides the first data on the reproductive biology of the spiny gurnard Lepidotrigla dieuzeidei. A total of 1027 individuals were collected monthly from September 2011 to August 2012. The total length of the individuals in the sample ranged from 7.46 cm to 14.62 cm with a female to male ratio of 1 to 0.59. Positive allometric growth was observed for both females (b=3.07) and males (b=3.08). Variations of condition factor were similar in both sexes with mean values of 1.07 for females and 1.01 for males. The fish L. dieuzeidei had a long spawning period extending from November to July based on monthly values of gonadosomatic index. Histological analysis showed that this fish was multiple synchronous developments of ovaries with multiple spawning events. The ovaries were always represented with a group of primary oocytes and a diverse population of vitel-logenic oocytes, each specially recruited during the final stages of maturation in uniform or uneven phases. Batch fecundity was estimated gravimetrically using the hydrated oocyte method and was estimated to be around 558 to 10.230 oocytes per female. L. dieuzeidei is an important by-catch species and data from this study represent a valuable contribution to stock management.

FeNi3/NiFe-Mixed Metal Oxide Heterostructured Nanosheets for Catalytic Nitro-Amination

The two-dimensional heterostructured FeNi3/NiFe-mixed metal oxide porous nanocatalyst has been constructed through the coprecipitation-phase-transformation process, in which a large amount of interfaces and micropores caused by the topotactic transformation can expose abundant active sites, thus promoting catalytic activity. Simultaneously, by virtue of the strong interaction between metals and metal oxides derived from the in situ partial reduction, the uniform FeNi3 phases can be stably fixed on NiFe-MMO nanosheets. In such a designed FeNi3/NiFe-MMO nanocomposite, the synergistic effect between FeNi3 with excellent charge-transfer characteristics and the NiFe-MMO support with a selective adsorption of the −NO2 group in p-nitroaromatic compounds makes it have excellent catalytic performance of the nitro-amination reaction, especially for the amination of p-nitrophenol. The reaction rate constant k is as high as 0.08123 s–1, and there is no obvious performance degradation after 15 cycles of the reaction. This work provides a valid pathway for catalyzing the nitro-amination reaction.

Square-triangle tilings: an infinite playground for soft matter.

Regular square and triangle, two very simple geometrical figures, can be used to construct a fascinating variety of tilings which cover the 2D plane without any overlaps or holes. Such tilings are observed in many soft matter systems. Here we present a way to describe all possible globally uniform square-triangle phases using a three dimensional composition space. This approach takes into account both the overall composition and the orientations of the two kinds of tiles. The geometrical properties of special phases encountered in soft matter systems are described: the Archimedean Σ and H phases, the striped phases and the 12-fold maximally symmetric phases. We show how this very rich behavior with either periodic or aperiodic phases appears here as a consequence of the inherent incommensurability between the areas of the two tiles related by the ratio . Geometrical constraints on boundary lines and junction points between domains of different compositions are given, a situation likely to be encountered in experimental and numerical studies. Future developments are suggested like considering the effect on phase behavior of possible symmetry breaking.

A graphical calculus for integration over random diagonal unitary matrices

We provide a graphical calculus for computing averages of tensor network diagrams with respect to the distribution of random vectors containing independent uniform complex phases. Our method exploits the order structure of the partially ordered set of uniform block permutations. A similar calculus is developed for random vectors consisting of independent uniform signs, based on the combinatorics of the partially ordered set of even partitions. We employ our method to extend some of the results by Johnston and MacLean on the family of local diagonal unitary invariant matrices. Furthermore, our graphical approach applies just as well to the real (orthogonal) case, where we introduce the notion of triplewise complete positivity to study the condition for separability of the relevant bipartite matrices. Finally, we analyze the twirling of linear maps between matrix algebras by independent diagonal unitary matrices, showcasing another application of our method.

Orientational ordering in a fluid of hard kites: A density-functional-theory study.

Using density-functional theory we theoretically study the orientational properties of uniform phases of hard kites-two isosceles triangles joined by their common base. Two approximations are used: scaled particle theory and a new approach that better approximates third virial coefficients of two-dimensional hard particles. By varying some of their geometrical parameters, kites can be transformed into squares, rhombuses, triangles, and also very elongated particles, even reaching the hard-needle limit. Thus, a fluid of hard kites, depending on the particle shape, can stabilize isotropic, nematic, tetratic, and triatic phases. Different phase diagrams are calculated, including those of rhombuses, and kites with two of their equal interior angles fixed to 90^{∘},60^{∘}, and 75^{∘}. Kites with one of their unequal angles fixed to 72^{∘}, which have been recently studied via Monte Carlo simulations, are also considered. We find that rhombuses and kites with two equal right angles and not too large anisometry stabilize the tetratic phase but the latter stabilize it to a much higher degree. By contrast, kites with two equal interior angles fixed to 60^{∘} stabilize the triatic phase to some extent, although it is very sensitive to changes in particle geometry. Kites with the two equal interior angles fixed to 75^{∘} have a phase diagram with both tetratic and triatic phases, but we show the nonexistence of a particle shape for which both phases are stable at different densities. Finally, the success of the new theory in the description of orientational order in kites is shown by comparing with Monte Carlo simulations for the case where one of the unequal angles is fixed to 72^{∘}. These particles also present a phase diagram with stable tetratic and triatic phases.

Loading rate effect on the uniaxial compressive strength (UCS) behavior of cemented paste backfill (CPB)

Underground mined-out areas and tailings are the two major harmful consequences from metal mining industry. Cemented Paste Backfill (CPB) method, refilling the tailings back to the underground mined-out areas, has been widely used worldwide. Clear understanding on the uniaxial compressive strength (UCS) behavior of the CPB is very important for the stability analysis of the backfill structure and the parameters optimization of backfill plan. However, the UCS tests can be markedly affected by the testing loading rate. And few papers reported the effect of different loading rates on the UCS of CPB. In this study, the UCS behavior of 14-day cured CPB samples are investigated using five different loading rates: 0.1, 0.25, 0.5, 1, 2 mm/min. The digital image correlation (DIC) method and scanning electron microscope (SEM) analysis were also carried out to help clearly understand the different loading rates effect on the deformation behavior and failure surfaces. The findings show that, the increase of loading rate has a strengthening effect on the UCS. The correlation between the loading rates and the UCS is more in line with an exponential function when the loading rates are between 0.1 and 2 mm/min. During the loading process with different loading rates, the axial deformation characteristics of all the tested CPB samples can be divided into uniform and non-uniform phases. And the loading rates of 0.5 and 1 mm/min resulted the smallest standard deviation for both the axial displacement and the axial strain observed from the three preset monitoring points. As the loading rate increased, the Ca/Si parameter on the fracture surface of the samples also increased slightly. The findings of this research clearly demonstrated the behavior of UCS under different loading rates, and also provided a key research evidence in selecting appropriate loading rate in assessing USC of CPB sample for laboratory tests.

Columnar grains formation and mechanical properties improvement of Ti44Al alloy by cyclic directional heat treatment

Ti44Al alloys were conducted cyclic directional heat treatment (DHT) for 1, 4 and 6 cycles at 1750 K to obtain directional microstructure and research their microstructure evolution. Microstructure was observed and mechanical properties was tested. Results show that grains of all treated Ti44Al alloys grow up obviously, the width of grains increases and the number of grains decreases with increasing of cycles. More columnar grains are obtained and spacing of lamellar γ and α2 phases decreases to 0.60 μm approximately after cyclic DHT for 4 cycles. Refinement of lamellar phases is caused by increasing of nucleation sites for γ phases. And it is noted that the spacing of lamellar phases is homogenized after DHT, compared with that of as-cast Ti44Al alloy. In addition, there are about 80% columnar grains with small angles (less 60°) between their growth directions and orientation of lamellar phases after DHT. Micro-hardness of Ti44Al alloys increases firstly and then decreases with increasing of cycles. Micro-hardness value is the highest about 312.9 HV for Ti44Al alloy after 4 cycles of DHT, which increases by 28% compared with that of as-cast alloy (244.8 HV), due to thin and uniform lamellar phases. Compression strength of Ti44Al alloy also increases from 900 MPa to 1200 MPa after DHT, due to directional microstructure and jagged grain boundary.

Statics and dynamics of a finite two-dimensional colloidal system with competing attractive critical Casimir and repulsive magnetic dipole interactions.

We continue our theoretical study of a recently proposed two-dimensional colloidal system with attractive critical Casimir and repulsive magnetic dipole forces that can be tuned easily and independently from each other via the temperature and the strength of an external magnetic field, respectively [K. Marolt, M. Zimmermann, and R. Roth, Phys. Rev. E 100, 052602 (2019)2470-004510.1103/PhysRevE.100.052602]. Using this freedom, it is possible to construct a competing interaction potential that causes microphase separation featuring spatially inhomogeneous cluster, stripe, and bubble phases in the bulk, i.e., in an infinite system without an external potential. In the present work, we demonstrate by means of density functional theory that microphase separation can also occur in finite geometries. In a square cell with a side length of 20 or 30 colloid diameters, we observe the emergence of highly structured cluster and ring phases at intermediate bulk densities in addition to almost uniform fluid phases for lower and higher bulk densities. We then employ dynamic density functional theory to determine how the system reacts when the temperature and the magnetic field are altered over time, and we show how to induce a transition from the liquid to the cluster/ring phase and also from the cluster directly to the ring phase. We find that often a slowly varying and nontrivial path in parameter space is required to reach a stable state, whereas abrupt changes are prone to lead to metastable configurations.

Quantum Lifshitz points and fluctuation-induced first-order phase transitions in imbalanced Fermi mixtures

We perform a detailed analysis of the phase transition between the uniform superfluid and normal phases in spin- and mass-imbalanced Fermi mixtures. At mean-field level we demonstrate that at temperature $T\to 0$ the gradient term in the effective action can be tuned to zero for experimentally relevant sets of parameters, thus providing an avenue to realize a quantum Lifshitz point. We subsequently analyze damping processes affecting the order-parameter field across the phase transition. We show that, in the low energy limit, Landau damping occurs only in the symmetry-broken phase and affects exclusively the longitudinal component of the order-parameter field. It is however unavoidably present in the immediate vicinity of the phase transition at temperature $T=0$. We subsequently perform a renormalization-group analysis of the system in a situation, where, at mean-field level, the quantum phase transition is second order (and not multicritical). We find that, at $T$ sufficiently low, including the Landau damping term in a form derived from the microscopic action destabilizes the renormalization group flow towards the Wilson-Fisher fixed point. This signals a possible tendency to drive the transition weakly first-order by the coupling between the order-parameter fluctuations and fermionic excitations effectively captured by the Landau damping contribution to the order-parameter action.

Parameter Estimation of Fluctuating Two-Ray Model for Next Generation Mobile Communications

This paper focuses on the problem of parameter estimation for a Fluctuating Two-Ray (FTR) model in the context of wireless mobile communications. Precisely, the received signal is assumed to be the superposition of two dominant components (typically a direct plus a reflected path signal) in addition to diffusive secondary contributions. The signal components may be affected by random amplitude shadowing, statistically modeled by Nakagami- $m$ distribution, multiplied by unknown scaling factors with random uniform independent phases, whereas the diffusive component is assumed to follow the complex Gaussian distribution. Exploiting the method of moments, a $4\times 4$ nonlinear system is herein mathematically derived, which is very hard to be solved due to the strong nonlinearity. Therefore, a sequential procedure based on some prior information about the diffusive component power level is devised to solve it. The effectiveness of the proposed estimation technique is shown by evaluating the normalized root mean square errors as well as mean errors and standard deviations in several operating conditions of practical interest also considering the limit case of only one-ray in order to compare the proposed approach to simpler estimators, already presented in the literature. The results show the robustness of the new estimator even under a multipath model mismatch. Finally, the effectiveness of the proposed estimation procedure is confirmed through measured mmWave data.

Atomic self-organization emerging from tunable quadrature coupling

The recent experimental observation of dissipation-induced structural instability provides new opportunities for exploring the competition mechanism between stationary and nonstationary dynamics [Science 366, 1496 (2019)]. In that study, two orthogonal quadratures of cavity field are coupled to two different Zeeman states of a spinor Bose-Einstein condensate (BEC). Here we propose a novel scheme to couple two density-wave degrees of freedom of a BEC to two quadratures of the cavity field. Being drastically different from previous studies, the light-matter quadratures coupling in our model is endowed with a tunable coupling angle. Apart from the uniform and self-organized phases, we unravel a dynamically unstable state induced by the cavity dissipation. Interestingly, the dissipation defines a particular coupling angle, across which the instabilities disappear. Moreover, at this critical coupling angle, one of the two atomic density waves can be independently excited without affecting one another. It is also found that our system can be mapped into a reduced three-level model under the commonly used low-excitation-mode approximation. However, the effectiveness of this approximation is shown to be broken by the dissipation nature for some special system parameters, hinting that the low-excitation-mode approximation is insufficient in capturing some dissipation-sensitive physics. Our work enriches the quantum simulation toolbox in the cavity-quantum-electrodynamics system and broadens the frontiers of light-matter interaction.

Steady states of a driven dissipative dipolar XXZ chain

We study theoretically a driven dissipative one-dimensional XXZ spin-1/2 chain with dipole coupling and a tunable strength of the Ising and XY interaction. Within a mean-field approximation, we find a rich phase diagram with uniform, spin density wave, antiferromagnetic and oscillatory phases, as well as regions of phase bistability. We study the phase diagram of small quantum systems using exact diagonalisation, and compare the results to the mean-field theory. We find that while expectation values only capture the uniform phases of the mean-field theory, fluctuations about these expectation values give signatures of spatially non-uniform phases and bistabilities. We find these signatures for all ratios of the Ising to XY interaction, showing that they appear to be general features of spin-1/2 systems.

Pore pressure coefficient B for saturated geomaterials with compressible, isotropic and uniform solid and fluid phases

This paper derives an expression for pore pressure coefficient $$B$$ in terms of a geomaterial’s mesoscopic properties and jacketed and unjacketed macroscopic compressibilities. The mesoscopic properties include phase compressibilities and pressure distribution ratios. The pressure distribution ratios represent the geomaterial’s meso-heterogeneity, while the difference between the unjacketed bulk compressibility and the solid grain compressibility represents macroscopic effects, such as solid grain rearrangement. The difference in phase compressibilities is shown to be the principal determinant of $$B$$ , with the effects of meso-heterogeneity and macroscopic change relatively negligible. The unjacketed pore compressibility appears to be quite sensitive to the effects of both meso-heterogeneity and macroscopic change. Although $$B$$ can be derived reliably from a measured value of unjacketed pore compressibility, unjacketed pore compressibility derived from a measured value of $$B$$ is considered unreliable. The expression for $$B$$ includes five elastic coefficients. The necessary and sufficient condition for constant porosity in an unjacketed test is proposed. The published expressions for $$B$$ , the coefficient of fluid content and porosity change are recovered by introducing appropriate assumptions with regard to meso-heterogeneity and phase compressibilities.

Phase transitions in Ehrenfest urn model with interactions: Coexistence of uniform and nonuniform states.

A model based on the classic noninteracting Ehrenfest urn model with two urns is generalized to M urns with the introduction of interactions for particles within the same urn. As the inter-particle interaction strength is varied, phases of different levels of nonuniformity emerge and their stabilities are calculated analytically. In particular, coexistence of locally stable uniform and nonuniform phases connected by first-order transition occurs. The phase transition threshold and energy barrier can be derived exactly together with the phase diagram obtained analytically. These analytic results are further confirmed by Monte Carlo simulations.

Feasibility of grain refinement method for AZ91 alloy using commercial Al-SiC composite

SiC is well-known as an effective carbon inoculation material for grain refinement of Mg-Al-based alloys. In this study, grain refinement ability of stir-casted Al-SiC composite for Mg-Al-based alloy was investigated to confirm the feasibility of industrial application. Commercialized Al-20 vol.-% SiC composite ingot was used in AZ91 alloy as a grain refiner, and grain size of AZ91 alloy dramatically reduce from 650 to 74 µm and become uniform with 0.7 wt-% Al-SiC composite addition. And acicular type Al-Mn phase existed at the grain boundaries are changed to polygonal type and positioned inside grains after grain refinement. These morphological changes of small grain size and uniform second phases contributed to the excellent mechanical properties of AZ91 alloy.

Cluster-based Haldane phases, bound magnon crystals and quantum spin liquids of a mixed spin-1 and spin-1/2 Heisenberg octahedral chain

The mixed spin-1 and spin-1/2 Heisenberg octahedral chain with regularly alternating monomeric spin-1 sites and square-plaquette spin-1/2 sites is investigated using variational technique, localized-magnon approach, exact diagonalization (ED) and density-matrix renormalization group (DMRG) method. The investigated model has in a magnetic field an extraordinarily rich ground-state phase diagram, which includes the uniform and cluster-based Haldane phases, two ferrimagnetic phases of Lieb-Mattis type, two quantum spin liquids and two bound magnon crystals in addition to the fully polarized ferromagnetic phase. The lowest-energy eigenstates in a highly-frustrated parameter region belong to flat bands and hence, low-temperature thermodynamics above the bound magnon-crystal ground states can be satisfactorily described within the localized-magnon approach. The variational method provides an exact evidence for the magnon-crystal phase with a character of the monomer-tetramer ground state at zero field, while another magnon-crystal phase with a single bound magnon at each square plaquette is found in a high-field region. A diversity of quantum ground states gives rise to manifold zero-temperature magnetization curves, which may involve up to four wide intermediate plateaus at zero, one-sixth, one-third and two-thirds of the saturation magnetization, two quantum spin-liquid regions and two tiny plateaus at one-ninth and one-twelfth of the saturation magnetization corresponding to the fragmentized cluster-based Haldane phases.