Polar Alignment Research Articles

Investigation of Polar Alignment Properties of Ferroelectric Nematic Liquid Crystals with Twist / Planar Alignment in Bulk

Investigation of Polar Alignment Properties of Ferroelectric Nematic Liquid Crystals with Twist / Planar Alignment in Bulk

Artificial patterns in spatially discrete models of cell migration and how to mitigate them

Several discrete models for diffusive motion are known to exhibit checkerboard artifacts, absent in their continuous analogues. We study the origins of the checkerboard artifact in the discrete heat equation and show that this artifact decays exponentially in time when following either of two strategies: considering the present state of each lattice site to determine its own future state (self-contributions), or using non-square lattice geometries. Afterwards, we examine the effects of these strategies on nonlinear models of biological cell migration with two kinds of cell-cell interactions: adhesive and polar velocity alignment. In the case of adhesive interaction, we show that growing modes related to pattern formation overshadow artifacts in the long run; nonetheless, artifacts can still be completely prevented following the same strategies as in the discrete heat equation. On the other hand, for polar velocity alignment we show that artifacts are not only strengthened, but also that new artifacts can arise in this model which were not observed in the previous models. We find that the lattice geometry strategy works well to alleviate artifacts. However, the self-contribution strategy must be applied more carefully: lattice sites should contribute to both their own density and velocity values, and their own velocity contribution should be high enough. With this work, we show that these two strategies are effective for preventing artifacts in spatial models based on the discrete continuity equation.

Vectorial active matter on the lattice: polar condensates and nematic filaments

We introduce a novel lattice-gas cellular automaton (LGCA) for compressible vectorial active matter with polar and nematic velocity alignment. Interactions are, by construction, zero-range. For polar alignment, we show the system undergoes a phase transition that promotes aggregation with strong resemblance to the classic zero-range process. We find that above a critical point, the states of a macroscopic fraction of the particles in the system coalesce into the same state, sharing the same position and momentum (polar condensate). For nematic alignment, the system also exhibits condensation, but there exist fundamental differences: a macroscopic fraction of the particles in the system collapses into a filament, where particles possess only two possible momenta. Furthermore, we derive hydrodynamic equations for the active LGCA model to understand the phase transitions and condensation that undergoes the system. We also show that generically the discrete lattice symmetries—e.g. of a square or hexagonal lattice—affect drastically the emergent large-scale properties of on-lattice active systems. The study puts in evidence that aligning active matter on the lattice displays new behavior, including phase transitions to states that share similarities to condensation models.

Nanoscale Hotspot-Induced Emitters in DNA Origami-Assisted Nanoantennas.

We report the observation of hotspot-induced emitters and photoluminescence enhancement of up to 42-fold from DNA origami-assisted plasmonic dimer nanoantennas upon excess polarized laser illumination. The presence of DNA and laser polarization alignment along the dimer axis are critical for the generation of bright emitters responsible for the observed PL increase. The emission spectrum reveals characteristic Raman peaks of amorphous carbon, suggesting the formation of carbon-based emitters in the nanoantenna due to the plasmonic hotspots at the longitudinal antenna resonance.

Polarization alignment in measurement-device-independent quantum key distribution with intrinsic events

Polarization alignment in measurement-device-independent quantum key distribution with intrinsic events

Polarization Alignment in Polycrystalline BiFeO3 Photoelectrodes for Tunable Band Bending.

Polarization in a semiconductor can modulate the band bending via the depolarization electric field (EdP), subsequently tuning the charge separation and transfer (CST) process in photoelectrodes. However, the random orientation of dipole moments in many polycrystalline semiconductor photoelectrodes leads to negligible polarization effect. How to effectively align the dipole moments in polycrystalline photoelectrodes into the same direction to maximize the polarization is still to be developed. Herein, we report that the dipole moments in a ferroelectric BiFeO3 photoelectrode can be controlled under external poling, resulting in a tunable CST efficiency. A negative bias of -40 voltage (V) poling to the photoelectrode leads to an over 110% increase of the CST efficiency, while poling at +40 V, the CST efficiency is reduced to only 41% of the original value. Furthermore, a nearly linear relationship between the external poling voltage and surface potential is discovered. The findings here provide an effective method in tuning the band bending and charge transfer of the emerging ferroelectricity driven solar energy conversion.

Enhancing piezoelectric response in (002)-Oriented TaxAl(1−x)N films by magnetron-sputtering composition-tunable AlTa alloys

Aluminum nitride (AlN) films suffer from poor piezoelectric response due to the local hexagonal symmetry of wurtzite crystal structure. The fundamental mechanism of improving piezoelectric response in Ta-doped AlN thin films has not been fully understood. Here, we report that composition-tunable AlTa alloys, instead of Al and Ta individual sputtering targets, can be employed to deposit (002)-oriented TaxAl(1-x)N films by magnetron-sputtering, where Ta-doping ratio is tunable by changing Al:Ta composition ratio of the AlTa alloys. Importantly, Ta-doping enhances spontaneous polarization to improve piezoelectricity significantly, as suggested by a threefold increase of the effective piezoelectric coefficients (d33,eff) upon doping 7 at.% Ta. A better alignment of spontaneous polarization for stronger piezoelectric response originates from the reduction in point defects and crystalline disorder in the reduced-symmetrical wurtzite structure by doping Ta in the TaxAl(1−x)N. This study provides significant insights in improving piezoelectric response in AlN for the development of high-performance film-bulk-acoustic-resonators.

AC Her: Evidence of the First Polar Circumbinary Planet

We examine the geometry of the post–asymptotic giant branch (AGB) star binary AC Her and its circumbinary disk. We show that the observations describe a binary orbit that is perpendicular to the disk with an angular momentum vector that is within 9° of the binary eccentricity vector, meaning that the disk is close to a stable polar alignment. The most likely explanation for the very large inner radius of the dust is a planet within the circumbinary disk. This is therefore both the first reported detection of a polar circumbinary disk around a post-AGB binary and the first evidence of a polar circumbinary planet. We consider the dynamical constraints on the circumbinary disk size and mass. The polar circumbinary disk feeds circumstellar disks with gas on orbits that are highly inclined with respect to the binary orbit plane. The resulting circumstellar disk inclination could be anywhere from coplanar to polar depending upon the competition between the mass accretion and binary torques.

Dynamic calculations of magnetic field and implications on spin polarization and spin alignment in heavy ion collisions

Dynamic calculations of magnetic field and implications on spin polarization and spin alignment in heavy ion collisions

Interface-Tuning of Ferroelectricity and Quadruple-Well State in CuInP2S6 via Ferroelectric Oxide.

Ferroelectric van der Waals CuInP2S6 possesses intriguing quadruple-well states and negative piezoelectricity. Its technological implementation has been impeded by the relatively low Curie temperature (bulk TC ∼ 42 °C) and the lack of precise domain control. Here we show that CuInP2S6 can be immune to the finite size effect and exhibits enhanced ferroelectricity, piezoelectricity, and polar alignment in the ultrathin limit when it is interfaced with ferroelectric oxide PbZr0.2Ti0.8O3 films. Piezoresponse force microscopy studies reveal that the polar domains in thin CuInP2S6 fully conform to those of the underlying PbZr0.2Ti0.8O3, where the piezoelectric coefficient changes sign and increases sharply with reducing thickness. High temperature in situ domain imaging points to a significantly enhanced TC of >200 °C for 13 nm CuInP2S6 on PbZr0.2Ti0.8O3. Density functional theory modeling and Monte Carlo simulations show that the enhanced polar alignment and TC can be attributed to interface-mediated structure distortion in CuInP2S6. Our study provides an effective material strategy to engineer the polar properties of CuInP2S6 for flexible nanoelectronic, optoelectronic, and mechanical applications.

Enhancement of piezophototronic hydrogen evolution reaction through the polarization of ferroelectric Bi4Ti3O12 microplates

In this study, we analyzed the properties of Bi4Ti3O12 microplates in the context of hydrogen evolution reaction. Piezoresponse force microscopy revealed a typical butterfly curve, indicating that as-synthesized Bi4Ti3O12 exhibits ferroelectric properties. Under ultrasonication, the amount of hydrogen produced by polarized (2000 V) Bi4Ti3O12 increased from 728 to 1349 μmol g−1, which was 1.85 times higher than that generated by unpolarized Bi4Ti3O12. The increase in hydrogen evolution rate may be attributed to the gradual alignment of polarization within the ferroelectric domains of Bi4Ti3O12. Moreover, with synergistic piezophototronic activity, the amount of hydrogen produced by Bi4Ti3O12 was further increased to 1478 μmol g−1, which was 200% higher than that generated by unpolarized Bi4Ti3O12. Theoretical calculations revealed that Bi4Ti3O12 microplates exhibit a high piezoelectric potential along the x-axis, which is consistent with the spontaneous polarization of the microplates. By applying an external polarization field, ferroelectric polarization was activated to effectively separate free charges and extend carrier lifetime (from 0.6 to 0.84 ns). The application of an external electric field to ferroelectric Bi4Ti3O12 appears to be a favorable strategy for enhancing its piezophototronic activity. Our findings may facilitate future studies in the fields of environmental science and renewable energy.

Spin density matrix for and its polarization alignment in * *Supported by the National Natural Science Foundation of China (12247121)

We investigate the spin density matrix of in the Cartesian coordinate system of baryon-antibaryon pairs produced in annihilation. Using the helicity formalism of Jacob and Wick, we derive the expression for the spin-3/2 density matrices. Our analysis is based on the angular distribution of the process in the BESIII experiment. By decomposing the polarization state of particles along different coordinate axes, we examine the polarization dependence of the cross-section. Our results demonstrate that particles exhibit varying degrees of tensor polarization along the x-, y-, and z-axes, as well as weak vector polarization and rank-3 tensor polarization along the y-axis. To the best of our knowledge, this is the first study to calculate the polarization dependence of the cross-section distributions for the annihilation process . Our theoretical predictions are in good agreement with the experimental measurements.

Circumbinary Accretion: From Binary Stars to Massive Binary Black Holes

We review recent works on the dynamics of circumbinary accretion, including time variability, angular momentum transfer between the disk and the binary, and the secular evolution of accreting binaries. These dynamics impact stellar binary formation/evolution, circumbinary planet formation/migration, and the evolution of (super)massive black hole binaries. We discuss the dynamics and evolution of inclined/warped circumbinary disks and connect with observations of protoplanetary disks. A special kind of circumbinary accretion involves binaries embedded in big disks, which may contribute to the mergers of stellar-mass black holes in AGN disks. Highlights include the following: ▪Circumbinary accretion is highly variable, being modulated at P b (the binary period) or ∼5P b, depending on the binary eccentricity e b and mass ratio q b.▪The inner region of the circumbinary disk can develop coherent eccentric structure, which may modulate the accretion and affect the physical processes (e.g., planet migration) taking place in the disk.▪Over long timescales, circumbinary accretion steers binaries toward equal masses, and it does not always lead to binary orbital decay. The secular orbital evolution depends on the binary parameters (e b and q b) and on the thermodynamic properties of the accreting gas.▪A misaligned disk around a low-eccentricity binary tends to evolve toward coplanarity due to viscous dissipation. But when e b is significant, the disk can evolve toward “polar alignment,” with the disk plane perpendicular to the binary plane.

A Polar Moving Base Alignment Based on Backtracking Scheme

In the polar region, the gravity vector and Earth’s rotation vector tend to be in the same direction, leading to a slower convergence speed and longer alignment time of the moving base alignment. When the alignment time is short, the alignment cannot converge, resulting in low azimuth accuracy. To address this issue, we propose a polar moving base alignment method based on a backtracking scheme. Notably, this work first derives a polar coarse alignment method with the inertial frame based on the transverse Earth model. On this basis, we designed a polar coarse alignment method based on a backtracking scheme and optimized the data storage scheme. Then, a backward navigation algorithm based on the transverse inertial navigation mechanical arrangement scheme was derived, and a polar fine alignment method based on a backtracking scheme was designed. Semi-physical simulation experiments showed that the alignment algorithm based on a backtracking scheme could converge in the 180 s with high alignment accuracy, which is 70% faster than the current polar moving base alignment method.

Online polarization error suppressed optical vector analyzer based on Bayesian optimization.

An optical vector analyzer (OVA) based on orthogonal polarization interrogation and polarization diversity detection is widely used to measure an optical device's loss, delay, or polarization-dependent features. Polarization misalignment is the OVA's primary error source. Conventional offline polarization alignment using a calibrator greatly reduces the measurement reliability and efficiency. In this Letter, we propose an online polarization error suppression method using Bayesian optimization. Our measurement results are verified by a commercial OVA instrument that uses the offline alignment method. The OVA featuring online error suppression will be widely used in the production of optical devices, not just in the laboratory.

Emergence of Spatial Scales and Macroscopic Tissue Dynamics in Active Epithelial Monolayers

Migrating cells in tissues are often known to exhibit collective swirling movements. In this paper, we develop an active vertex model with polarity dynamics based on contact inhibition of locomotion (CIL). We show that under this dynamics, the cells form steady-state vortices in velocity, polarity, and cell stress with length scales that depend on polarity alignment rate (ζ), self-motility (v0), and cell-cell bond tension (λ). When the ratio λ/v0 becomes larger, the tissue reaches a near jamming state because of the inability of the cells to exchange their neighbors, and the length scale associated with tissue kinematics increases. A deeper examination of this jammed state provides insights into the mechanism of sustained swirl formation under CIL rule that is governed by the feedback between cell polarities and deformations. To gain additional understanding of how active forcing governed by CIL dynamics leads to large-scale tissue dynamics, we systematically coarse-grain cell stress, polarity, and motility and show that the tissue remains polar even on larger length scales. Overall, we explore the origin of swirling patterns during collective cell migration and obtain a connection between cell-level dynamics and large-scale cellular flow patterns observed in epithelial monolayers.

Impact of Polarization on Distributed Optical Beamforming

In this letter, we propose the concept of distributed optical beamforming and its feasibility requirements. We quantify the importance of polarization beamforming among the beams for maximized beamforming. As a first step towards distributed polarization beamforming (DPolB), in this work we consider coplanar sources and receiver for beamforming and demonstrate the critical requirement of polarization alignment for maximized beamforming gain. We determine theoretically and verify via simulations the optimal polarization angle at the sources such that the electromagnetic waves interfere constructively at the receiver. Subsequently, we propose a novel method for automated polarization beamforming of multiple optical beams independent of source locations. Performance of the proposed DPolB is analytically captured in terms of average beamforming gain and verified using simulations. We also verify that the reduction in gain caused by slight deviation from coplanarity is not significant.

Dye-sensitized solar cell performance improvement by dye-solvent polarity and redox mediator potential alignment

Maximizing dye-adsorption onto semiconductor surface is critical to improve dye@ZnTiO3 n-type dye-sensitized solar cell (n-DSSC) performance. Polarity of solvent, used in loading merocyanine dye (MC-540) onto ZnTiO3 film electrode, is investigated here for the first time. With higher dye-adsorption energy (-37.1792 eV), the highly-polar water solvent yields an MC-540@ZnTiO3-based DSSC with higher cell performance, compared to organic solvents ethyl alcohol, acetone and diethyl ether, using iodide/iodine redox couple. This is evidenced by Time-Dependent Density-Functional Theory (TD-DFT). The least polar diethyl ether solvent shows a turbulent behavior at the MC-540@ZnTiO3 interface, with low absorbance (0.072 at 540 nm), and low adsorption energy −0.7952 eV (-18.3390 kcal/mol). The simulations are confirmed by experimental spectral results and photo-current density vs. potential (J-V) characteristics, where diethyl ether exhibits immeasurably low photo-current, let alone other technical difficulties due to high volatility. Among the various solvents, water exhibits highest short-circuit photocurrent density (0.075 mA/cm−2), open circuit potential (0.150 V), fill factor (0.363) and conversion efficiency (0.04%). Potential diagrams for the MC-540@ZnTiO3 interface in dark and under illumination are described. Simulation and experimental results combined dictate using the environmentally friendly highly polar water solvent over organic dyes in manufacturing MC-540@ZnTiO3-based DSSCs.

Precession and polar alignment of accretion discs in triple (or multiple) stellar systems

ABSTRACTWe investigate the mechanism of polar alignment for accretion discs in hierarchical systems (HSs) with more than two stars. In eccentric binary systems, low-mass discs that are sufficiently tilted to the binary orbit align in a polar configuration with respect to the binary plane by aligning their angular momentum to the binary eccentricity vector. In HSs, secular evolution of the orbital parameters makes the eccentricity vector of the system precess with time. This precession undermines the stability of the polar orbit for accretion discs hosted in HSs. We analytically show that the binary criteria for polar alignment derived in the literature are necessary but not sufficient conditions for polar alignment in HSs. Then, we derive an analytical criterion for polar alignment in HSs. In general, we find that discs orbiting the innermost level of an HS can go polar. Conversely, radially extended discs orbiting the outer levels of an HS cannot polarly align and evolve as orbiting around a circular binary. We confirm our findings through detailed numerical simulations. Also, our results are compatible with the observed distribution of disc–orbit mutual inclination. Finally, we compare the observed distribution of disc inclinations in the binary and in the HS populations. Binaries host mainly coplanar discs, while HSs show a wide range of disc inclinations. We suggest that the wider range of inclinations in HSs results from the secular oscillation of their orbital parameters (such as Kozai–Lidov oscillations), rather than from a different initial condition or evolution between HSs and binaries.

Grid-based simulations of polar circumbinary discs: polar alignment and vortex formation

ABSTRACT We describe the first grid-based simulations of the polar alignment of a circumbinary disc. We simulate the evolution of an inclined disc around an eccentric binary using the grid-based code athena++ . The use of a grid-based numerical code allows us to explore lower disc viscosities than have been examined in previous studies. We find that the disc aligns to a polar orientation when the α viscosity is high, while discs with lower viscosity nodally precess with little alignment over 1000 binary orbital periods. The time-scales for polar alignment and disc precession are compared as a function of disc viscosity, and are found to be in agreement with previous studies. At very low disc viscosities (e.g. α = 10−5), anticyclonic vortices are observed along the inner edge of the disc. These vortices can persist for thousands of binary orbits, creating azimuthally localized overdensities and multiple pairs of spiral arms. The vortex is formed at ∼3–4 times the binary semimajor axis, close to the inner edge of the disc, and orbits at roughly the local Keplerian speed. The presence of a vortex in the disc may play an important role in the evolution of circumbinary systems, such as driving episodic accretion and accelerating the formation of polar circumbinary planets.