Polar Clusters Research Articles

Self-Propelled Rods: Insights and Perspectives for Active Matter

A wide range of experimental systems including gliding, swarming and swimming bacteria, in vitro motility assays, and shaken granular media are commonly described as self-propelled rods. Large ensembles of those entities display a large variety of self-organized, collective phenomena, including the formation of moving polar clusters, polar and nematic dynamic bands, mobility-induced phase separation, topological defects, and mesoscale turbulence, among others. Here, we give a brief survey of experimental observations and review the theoretical description of self-propelled rods. Our focus is on the emergent pattern formation of ensembles of dry self-propelled rods governed by short-ranged, contact mediated interactions and their wet counterparts that are also subject to long-ranged hydrodynamic flows. Altogether, self-propelled rods provide an overarching theme covering many aspects of active matter containing well-explored limiting cases. Their collective behavior not only bridges the well-studied regimes of polar self-propelled particles and active nematics, and includes active phase separation, but also reveals a rich variety of new patterns.

Terahertz Probing Irreversible Phase Transitions Related to Polar Clusters in Bi0.5Na0.5TiO3‐Based Ferroelectric

AbstractElectric‐field‐induced phase transitions in Bi0.5Na0.5TiO3‐based relaxor ferroelectrics are essential to the control of their electrical properties and consequently in revolutionizing their dielectric and piezoelectric applications. However, fundamental understanding of these transitions is a long‐standing challenge due to their complex crystal structures. Given the structural inhomogeneity at the nanoscale or sub‐nanoscale in these materials, dielectric response characterization based on terahertz (THz) electromagnetic‐probe beam fields is intrinsically coordinated to lattice dynamics during DC‐biased poling cycles. The complex permittivity reveals the field‐induced phase transitions to be irreversible. This profoundly counters the claim of reversibility, the conventional support for which is based upon the peak that is manifest in each of four quadrants of the current–field curves. The mechanism of this irreversibility is solely attributed to polar clusters in the transformed lattices. These represent an extrinsic factor, which is quiescent in the THz spectral domain.

The origin of weak coupling between polar clusters in Ta2O5-doped 0.94Bi0.5Na0.5TiO3-0.06BaTiO3

Ta2O5-doped 0.94Bi0.5Na0.5 TiO3-0.06BaTiO3 [()(0.94BNT-0.06BT)-xTa ()] ceramics were prepared by a solid-state reaction technique. The single perovskite structure with space group R3c of the ceramics was identified by X-ray diffraction (XRD). Raman spectroscopy revealed the evolution of the local structure with Ta2O5 concentration. The temperature dependence of dielectric permittivity of the ceramics were deconvoluted by three Gaussian distribution functions which suggests that three dielectric anomalies exist in this system. The low-temperature dielectric anomaly exhibits a typical relaxor behavior with strong frequency dispersion (reentrant relaxor behavior). The activation energy derived from the V-F law is 0.298 eV, 0.338 eV, 0.412 eV and 0.449 eV, for , 0.005, 0.01 and 0.02, respectively. The mid-temperature and high-temperature anomalies are attributed to two structure phase transitions. The increase of the activation energies suggests that the coupling between polar clusters or polar nanoregions (PNRs) becomes weaker. The origin of the interaction between PNRs and phase transition behavior has been proposed according to the average structure, local structure and defect compensation mechanism of the system.

Air pollution hazard assessment using decision tree algorithms and bivariate probability cluster polar function: evaluating inter-correlation clusters of PM10 and other air pollutants

ABSTRACTThe automated classification of ambient air pollutants is an important task in air pollution hazard assessment and life quality research. In the current study, machine learning (ML) algorithms are used to identify the inter-correlation between dominant air pollution index (API) for PM10 percentile values and other major air pollutants in order to detect the vital pollutants’ clusters in ambient monitoring data around the study area. Two air quality stations, CA0016 and CA0054, were selected for this research due to their strategic locations. Non-linear RPart and Tree model of Decision Tree (DT) algorithm within the R programming environment were adopted for classification analysis. The pollutants’ respective significance to PM10 occurrence was evaluated using Random forest (RF) of DT algorithms and K means polar cluster function identified and grouped similar features, and also detected vital clusters in ambient monitoring data around the industrial areas. Results show increase in the number of clusters did not significantly alter results. PM10 generally shows a reduction in trend, especially in SW direction and an overall minimal reduction in the pollutants’ concentration in all directions is observed (less than 1). Fluctuations were observed in the behaviors of CO and NOx during the day while NOx displayed relative stability. Results also show that a direct and positive linear relationship exists between the PM10 (target pollutant) and CO, SO2, which suggests that these pollutants originate from the same sources. A semi-linear relationship is observed between the PM10 and others (O3 and NOx) while humidity shows a negative linearity with PM10. We conclude that most of the major pollutants show a positive trend toward the industrial areas in both stations while traffic emissions dominate this site (CA0016) for CO and NOx. Potential applications of nuggets of information derived from these results in reducing air pollution and ensuring sustainability within the city are also discussed. Results from this study are expected to provide valuable information to decision makers to implement viable strategies capable of mitigating air pollution effects.

Study of ferro- and anti-ferroelectric polar order in mesophases exhibited by bent-core mesogens

Ferroelectric nature in the NCybC phase and anti-ferroelectric nature in the SmC(I) and SmC(II) phases.

Performance Analysis of Internal Solitary Wave Detection and Identification Based on Compact Polarimetric SAR

This paper studies the application of compact polarimetric (CP) SAR in the detection and identification of ocean internal solitary waves (ISWs). First, based on full-polarimetric ALOS PALSAR images, we construct CP SAR images and extract 26 CP features. Then, the ISWS-sea surface differentiation capability for the different polarization features is analyzed by using the Jeffries and Euclidean distances. The results show that $\lambda _{1} $ , Entropy ( $H$ ), Lambda , the polarimetric total power ( Span ) and the Stokes parameters ( Stokesg 0, and $Stokesg_{3}$ ) improve the ISWs detection results. On this basis, a k-means clustering algorithm based on CP features is introduced, and the results show that the ISWs detection and identification performance of the algorithm are superior to that of the traditional Wishart polarization clustering algorithm, which suggests that CP SAR has good application prospects in the detection and identification of ocean ISWs.

Исследование механизмов изменения степени униполярности при термической обработке сильно легированных кристаллов LiNbO-=SUB=-3-=/SUB=-:ZnO

Phenomenological mechanisms of an increase in unipolarity degree at thermal treatment under short circuit conditions of strongly doped crystals are researched by comparison with thermal behavior of nominally pure LiNbO3 crystals of congruent composition. It has been shown that an increase in unipolarity degree, and correspondingly vanishing of domain structure in strongly doped LiNbO3:ZnО crystals starts by thermal decomposition of charged polar clusters. These clusters stabilize domain walls. The decomposition is accompanied by sharp jump-like injection of additional charge carriers (Li+ cations). Due to this, conductivity of LiNbO3:ZnО crystals is one order of magnitude higher at temperature above 800K than in nominally pure LiNbO3 crystals of congruent composition. The injection leads to decomposition of domain structure in LiNbO3:ZnО crystals in spite of LiNbO3 crystals of congruent composition.

Prenatal inflammation suppresses blood Th1 polarization and gene clusters related to cellular energy metabolism in preterm newborns.

Chorioamnionitis (CA, fetal membrane inflammation) predisposes to preterm birth and is associated with increased neonatal infection risk, but the separate effects of prematurity, CA, and postnatal adaptations on this risk are unclear. Using pigs as models for infants, we examined the systemic immune-metabolic status in cesarean-delivered preterm pigs, with and without CA induced by intra-amniotic (IA) LPS exposure. At birth, cord blood of preterm pigs showed neutropenia and low expressions of innate and adaptive immune genes, relative to term pigs. IA LPS induced CA and fetal systemic innate immune activation via complement and neutrophil-related pathways. These were mainly modulated via cellular regulations rather than granulopoiesis, as validated by the in vitro LPS stimulation of cord blood. After birth, IA LPS-exposed preterm pigs did not follow normal immune-metabolic ontogenies found in fetuses or newborns without prenatal insults, but showed consistently high levels of Treg, impaired Th1 polarization, and reduced expressions of multiple genes related to cellular oxidative phosphorylation and ribosomal activities. In conclusion, our results provide cellular and molecular evidence for CA-induced distinct neonatal immune-metabolic status with increased disease tolerance strategy, suggesting mechanisms for the clinical observation of elevated sepsis risks in immune-compromised preterm infants born with CA.

Effect of visual and auditory sensing cues on collective behavior in Vicsek models.

In the present study, we consider two independent sensing modes (auditory and visual) in Vicsek-like models and compare the emergent group-level behaviors in terms of polarization, cohesion, and cluster size. The auditory and visual modes differ in the determination of particle neighbors, which at the level of groups results in higher polarization, lower cohesion, and larger cluster size for the auditory mode relative to the visual. With the increase in average density of the particles, these differences are more pronounced. These differences are due to the fact that these sense modalities robustly generate distinct spatial distributions of the particles. We demonstrate the use of a data-driven approach, called transfer entropy, to distinguish the sensing modalities by considering only a pair of particle trajectories. Such an approach could be applicable to real-world systems, where it may be a challenge to measure the position and velocity of every particle within a swarm.

Domain‐scale imaging to dispel the clouds over the thermal depolarization of Bi0.5Na0.5TiO3‐based relaxor ferroelectrics

AbstractThermal depolarization temperature, Td, of ferroelectric oxides Bi0.5Na0.5TiO3 (BNT), where dielectric and piezoelectric signals exhibit remarkable changes, is providing rich research contents but is not well understood yet. Herein, on the domain‐scale, we give the direct and clear real‐space images of thermal depolarization process on BNT‐based complex oxides. As disclosed by the piezoresponse force microscopy (PFM), heating above Td breaks the poling‐induced large‐sized‐oriented domains into smaller sized polar clusters with different orientations, leading to the thermal depolarization phenomenon. Although the poling‐induced domain decays above Td, the broken domains exhibit a rather larger coherence length than that of the incipient labyrinth‐like nano‐domains. During the heating process, BNT possesses a structural transition from the long‐range‐correlated R3c (a−a−a− anti‐phase tilting) to the short‐range‐correlated P4bm (a0a0c+ in‐phase tilting) phase, which should be the fundamental driving force for the fluctuations of poling‐induced large‐sized‐oriented domains. We expect these results will further promote the understanding about the origin of Td in BNT‐based relaxor ferroelectrics, and provide an intuitive method for the characterization of the thermodynamic and kinetic process in this kind of materials.

Defect dynamics in clusters of self-propelled rods in circular confinement.

Rod-shaped active micro/nano-particles, such as bacterial and bipolar metallic micro/nano-motors, demonstrate novel collective phenomena far from the equilibrium state compared to passive particles. We apply a simulation approach --dissipative particle dynamics (DPD)-- to explore the collectively ordered states of self-propelled rods (SPRs). The SPRs are confined in a finite circular zone and repel each other when two rods touch each other. It is found that for a long enough rods system, the global vortex patterns, dynamic pattern oscillation between hedgehog pattern and vortex pattern, and hedgehog patterns are observed successively with increasing active force Fa. For the vortex pattern, the total interaction energy between the rods U is linear with active force Fa, i.e., U ∼ Fa . While the relation U ∼ Fa2 is obtained for the hedgehog structure. It is observed that a new hedgehog pattern with one defect core is created by two ejections of polar cluster in opposite directions from the original hedgehog pattern, and then merges into one through the diffusion of the two aggregates, i.e., the creation and annihilation of topological charges.

Ratiometric GPCR signaling enables directional sensing in yeast.

Accurate detection of extracellular chemical gradients is essential for many cellular behaviors. Gradient sensing is challenging for small cells, which can experience little difference in ligand concentrations on the up-gradient and down-gradient sides of the cell. Nevertheless, the tiny cells of the yeast Saccharomyces cerevisiae reliably decode gradients of extracellular pheromones to find their mates. By imaging the behavior of polarity factors and pheromone receptors, we quantified the accuracy of initial polarization during mating encounters. We found that cells bias the orientation of initial polarity up-gradient, even though they have unevenly distributed receptors. Uneven receptor density means that the gradient of ligand-bound receptors does not accurately reflect the external pheromone gradient. Nevertheless, yeast cells appear to avoid being misled by responding to the fraction of occupied receptors rather than simply the concentration of ligand-bound receptors. Such ratiometric sensing also serves to amplify the gradient of active G protein. However, this process is quite error-prone, and initial errors are corrected during a subsequent indecisive phase in which polarity clusters exhibit erratic mobile behavior.

Cluster-induced desorption investigated by means of molecular dynamics simulations-Microsolvation in clusters of polar and non-polar constituents.

The desorption of surface-adsorbed molecules induced by cluster-surface collisions of neutral molecular clusters, in particular, SO2 clusters, was investigated by means of molecular dynamics simulations. The desorption efficiency was found to be in general much higher for clusters of polar molecules when compared to nonpolar cluster constituents, for both nonpolar and polar adsorbates. In all cases, desorption is shown to proceed via dissolvation of the analyte in the cluster. In systems with nonpolar cluster constituents, the process is mainly driven by the increase in the entropy of the dissolved analyte in a larger cluster fragment. The latter process is enhanced by polar cluster constituents since the respective clusters show lower fragmentation at comparable kinetic energy and thus provide in average larger cluster fragments for the analytes to be dissolved in. In systems with clusters of polar constituents and polar adsorbates, the process is most efficient due to the additional energetic stabilization of the desorbed molecule in the solvation shell formed in the cluster fragment.

Elastic Anisotropy and Slowness Curves of BaTiO3 Single Crystals in the Paraelectric Phase Studied by Brillouin Spectroscopy

Elastic anisotropy and slowness curves of barium titanate (BaTiO3) single crystal in the paraelectric phase were investigated by using Brillouin spectroscopy. The directional dependence of sound velocities of the longitudinal and the transverse acoustic waves in the (001) plane showed a four-fold symmetry typical in the cubic phase. Especially, one of the two transverse modes exhibited a substantial softening along the directions. The sound velocity of this mode decreased significantly as temperature decreased toward the transition temperature, which corresponded to the elastic stiffness coefficient (C11 – C12)/2. This result suggests the tetragonal instability caused by the precursor polar clusters in the paraelectric phase of BaTiO3.

A Chiral and Polar Single-Molecule Magnet: Synthesis, Structure, and Tracking of Its Formation Using Mass Spectrometry.

The solvothermal reaction of cobalt(II) sulfate with S, S-1,2- bis(1-methyl-1 H-benzo[ d]imidazol-2-yl)ethane-1,2-diol, (H2L), neutralized with triethylamine (Et3N) in a mixture of methanol and water (2:1), resulted in triangular red crystals of [CoII7(L)3(SO4)3(OH)2(H2O)9]·4H2O·3CH3OH (Co7). It is formed of chiral and polar clusters crystallizing in the R3 space group. Co7 consists of apex-shared asymmetric dicubane units where all of the metals adopt an octahedral coordination and the three ligands wrap diagonally around the unit. One end of the cluster is bonded by six water molecules and the other end by three monodentate sulfates. The head-to-tail packing through extended H-bonds leads to polar chains. The ligand has lost two protons, adopts a cis-conformation, and is coordinated to five metals around the waist of the dicubane. Electrospray ionization mass spectrometry (ESI-MS) of solutions of the reaction as a function of time reveals the possible step-by-step assembly process of the cluster: the initial product [CoII(HL)(SO4)]2- combines with CoSO4, forming [CoII2(HL)(SO4)2]2-, and then, upon addition of Et3N, dimerizes through a [OH]- bridge to [CoII4(HL)2(OH)(CH3OH)2(SO4)3]- followed by capture of one Co2+ and one CoSO4 to form [CoII6(L)2(OH)(CH3O)(SO4)4]2- before eventually binding to CoL to form [CoII7(L)3(OH)2(SO4)4]2-. These results allow us to propose a possible process for the formation of Co7, which is a good example for chiral multidentate chelating ligand-controlled assembly of clusters. Magnetization measurements as a function of the temperature, field, and ac-frequency reveal ferromagnetic coupled moments and single-molecule magnetism (SMM).

Complete determination of elastic stiffness coefficients and local symmetry breaking in the paraelectric barium titanate

The temperature dependence of all independent elastic stiffness coefficients of cubic BaTiO3 was determined over a wide temperature range from 400 °C to the Curie point (Tc ∼ 131 °C) by using Brillouin light scattering spectroscopy. Among the two elastic eigen-modes corresponding to the two measured transverse acoustic waves, (C11-C12)/2 showed a large softening in the paraelectric phase, while the change in C44 was very small. This result caused the elastic anisotropy A, defined as 2C44/(C11-C12), to increase from ∼2.1 to ∼2.7 upon cooling toward the phase transition temperature. The large elastic anisotropy was attributed to the tetragonal instability and the associated anisotropic polarization fluctuations of precursor polar clusters formed by the correlated Ti motions. The elastic anisotropy was fitted by using the Curie-Weiss law resulting in a significant deviation in a certain temperature range between Tc and ∼Tc + 50 °C, similar to the dielectric permittivity.

Hemimethylation Patterns in Breast Cancer Cell Lines.

DNA methylation is an epigenetic event that involves adding a methyl group to the cytosine (C) site, especially the one that pairs with a guanine (G) site (ie, CG or CpG site), in a human genome. This event plays an important role in both cancerous and normal cell development. Previous studies often assume symmetric methylation on both DNA strands. However, asymmetric methylation, or hemimethylation (methylation that occurs only on 1 DNA strand), does exist and has been reported in several studies. Due to the limitation of previous DNA methylation sequencing technologies, researchers could only study hemimethylation on specific genes, but the overall genomic hemimethylation landscape remains relatively unexplored. With the development of advanced next-generation sequencing techniques, it is now possible to measure methylation levels on both forward and reverse strands at all CpG sites in an entire genome. Analyzing hemimethylation patterns may potentially reveal regions related to undergoing tumor growth. For our research, we first identify hemimethylated CpG sites in breast cancer cell lines using Wilcoxon signed rank tests. We then identify hemimethylation patterns by grouping consecutive hemimethylated CpG sites based on their methylation states, methylation “M” or unmethylation “U.” These patterns include regular (or consecutive) hemimethylation clusters (eg, “MMM” on one strand and “UUU” on another strand) and polarity (or reverse) clusters (eg, “MU” on one strand and “UM” on another strand). Our results reveal that most hemimethylation clusters are the polarity type, and hemimethylation does occur across the entire genome with notably higher numbers in the breast cancer cell lines. The lengths or sizes of most hemimethylation clusters are very short, often less than 50 base pairs. After mapping hemimethylation clusters and sites to corresponding genes, we study the functions of these genes and find that several of the highly hemimethylated genes may influence tumor growth or suppression. These genes may also indicate a progressing transition to a new tumor stage.

Tuning the self-organization of confined active particles by the steepness of the trap.

We consider the collective dynamics of self-propelling particles in two dimensions. They can align themselves according to the direction of propulsion of their neighbours, together with small rotational fluctuations. They also interact with each other via soft, isotropic, repulsive potentials. The particles are confined in a circular trap. The steepness of the trap is tuneable. The average packing fraction of the particles is low. When the trap is steep, particles flock along its boundary. They form a polar cluster that spreads over the boundary. The cluster is not spatially ordered. We show that when the steepness is decreased beyond a threshold value, the cluster becomes round and compact and eventually spatial order (hexagonal) emerges in addition to the pre-established polar order. We investigate the kinetics of such ordering. We find that while rotating around the centre of the trap along its circular boundary, the cluster needs to roll around its centre of mass to be spatially ordered. We have studied the stability of the order when the trap is suddenly switched off. We find that for the particles with velocity alignment interaction, the decay of the spatial order is much slower than the particles without the alignment interaction.

A highly proton-/vanadium-selective perfluorosulfonic acid membrane for vanadium redox flow batteries

The polar clusters of Nafion are blocked by the incorporation of the nanohybrid, which contributes to suppress vanadium ions crossover.

Ultrahigh energy storage and electrocaloric performance achieved in SrTiO3 amorphous thin films via polar cluster engineering

High energy storage density and a reversible electrocaloric effect are simultaneously achieved in Sr0.995(Na0.5Bi0.5)0.005(Ti0.99Mn0.01)O3 amorphous thin films via polar cluster engineering.