Domain Rotation Research Articles

Chaos over order: mapping 3D rotation of triaxial asteroids and minor planets

ABSTRACT Celestial bodies approximated with rigid triaxial ellipsoids in a two-body system can rotate chaotically due to the time-varying gravitational torque from the central mass. At small orbital eccentricity values, rotation is short-term orderly and predictable within the commensurate spin–orbit resonances, while at eccentricity approaching unity, chaos completely takes over. Here, we present the full three-dimensional rotational equations of motion around all three principal axes for triaxial minor planets and two independent methods of numerical solution based on Euler rotations and quaternion algebra. The domains of chaotic rotation are numerically investigated over the entire range of eccentricity with a combination of trial integrations of Euler’s equations of motion and the GALI(k) (Generalized Alignment Index) method. We quantify the dependence of the order–chaos boundaries on shape by changing a prolateness parameter, and find that the main 1:1 spin–orbit resonance disappears for specific moderately prolate shapes already at eccentricities as low as 0.3. The island of short-term stability around the main 1:1 resonance shrinks with increasing eccentricity at a fixed low degree of prolateness and completely vanishes at approximately 0.8. This island is also encroached by chaos on longer time-scales, indicating longer Lyapunov exponents. Trajectories in the close vicinity of the 3:2 spin–orbit resonance become chaotic at smaller eccentricities, but separated enclaves of orderly rotation emerge at eccentricities as high as 0.8. Initial perturbations of rotational velocity in latitude away from the exact equilibrium result in a spectrum of free libration, nutation, and polar wander, which is not well matched by the linearized analysis omitting the inertial terms.

High-Mobility Metastable Rock-Salt Type (Sn,Ca)Se Thin Film Stabilized by Direct Epitaxial Growth on a YSZ (111) Single-Crystal Substrate.

Metastable cubic (Sn1-xPbx)Se with x ≥ 0.5 is expected to be a high mobility semiconductor due to its Dirac-like electronic state, but it has an excessively high carrier concentration of ∼1019 cm-3 and is not suitable for semiconductor device applications such as thin film transistors and solar cells. Further, thin films of (Sn1-xPbx)Se require a complicated synthesis process because of the high vapor pressure of Pb. We herein report the direct growth of metastable cubic (Sn1-xCax)Se films alloyed with CaSe, which has a wider bandgap and lower vapor pressure than PbSe. The cubic (Sn1-xCax)Se epitaxial films with x = 0.4-0.8 are stabilized on YSZ (111) single crystalline substrates by pulsed laser deposition. (Sn1-xCax)Se has a direct-transition-type bandgap, and the bandgap energy can be varied from 1.4 eV (x = 0.4) to 2.0 eV (x = 0.8) by changing x. These films with x = 0.4-0.6 show p-type conduction with low hole carrier concentrations of ∼1017 cm-3. Hall mobility analysis suggests that the hole transport would be dominated by 180° rotational domain structures, which is specific to (111) oriented epitaxial films. However, it, in turn, clarifies that the in-grain carrier mobility in the (Sn0.6Ca0.4)Se film is as high as 322 cm2/(Vs), which is much higher than those in thermodynamically stable layered SnSe and other Sn-based layered semiconductor films at room temperature. Therefore, the present results prove the potential of high mobility (Sn1-xCax)Se films for semiconductor device applications via a simple thin-film deposition process.

Epitaxial growth of β-Ga2O3 on SrTiO3 (001) and SrTiO3-buffered Si (001) substrates by plasma-assisted molecular beam epitaxy

Thin Ga2O3 films were deposited by plasma-assisted molecular beam epitaxy on SrTiO3 (001) and SrTiO3-buffered Si (001) substrates. Examination using reflection-high-energy electron diffraction, x-ray diffraction, and transmission electron microscopy shows a consistent picture of (100)- and (1¯12)-oriented β-Ga2O3 grains. The structural alignments are β-Ga2O3[010] || STO ⟨110⟩ and β-Ga2O3 [021] || STO ⟨100⟩, respectively, each with four in-plane rotational domain variants. Successful integration of epitaxial β-Ga2O3 with Si could enable major opportunities for monolithically integrated Ga2O3 technology by serving as a high-quality seed layer for further epitaxial growth.

Close oxygen coupled low-pressure chemical vapor deposition growth of high quality [formula omitted] on sapphire

We report on the close oxygen coupled low-pressure chemical vapor deposition (COC-LPCVD) hetero-epitaxial growth of atomically smooth (−201) oriented β−Ga2O3 on c-plane sapphire. Utilizing a dedicated line within the main tube, O2 could be delivered to the substrate surface which enables effective control of growth regime. Under optimized conditions (Ga-rich and near stoichiometric feed rate), step flow growth was obtained with X-ray rocking curve full-width at half maximum of 0.09° and 0.20° at a growth rate of 0.49 μm/h and 3.42 μm/h, respectively. On the other hand, oxygen-rich growth at high growth rates produced in-plane rotational domains. In addition, the alignment of single crystal (−201) β−Ga2O3 with respect to the sapphire offcut direction was revealed such that [-20-1] β−Ga2O3 is along [11–20] (offcut direction) sapphire. This study demonstrates the potential of the versatile COC-LPCVD system on the thin film growth of high quality β−Ga2O3.

Scalable Moir\xe9 Lattice with Oriented TMD Monolayers

Moiré lattice in artificially stacked monolayers of two-dimensional (2D) materials effectively modulates the electronic structures of materials, which is widely highlighted. Formation of the electronic Moiré superlattice promises the prospect of uniformity among different moiré cells across the lattice, enabling a new platform for novel properties, such as unconventional superconductivity, and scalable quantum emitters. Recently, epitaxial growth of the monolayer transition metal dichalcogenide (TMD) is achieved on the sapphire substrate by chemical vapor deposition (CVD) to realize scalable growth of highly-oriented monolayers. However, fabrication of the scalable Moiré lattice remains challenging due to the lack of essential manipulation of the well-aligned monolayers for clean interface quality and precise twisting angle control. Here, scalable and highly-oriented monolayers of TMD are realized on the sapphire substrates by using the customized CVD process. Controlled growth of the epitaxial monolayers is achieved by promoting the rotation of the nuclei-like domains in the initial growth stage, enabling aligned domains for further grain growth in the steady-state stage. A full coverage and distribution of the highly-oriented domains are verified by second-harmonic generation (SHG) microscopy. By developing the method for clean monolayer manipulation, hetero-stacked bilayer (epi-WS2/epi-MoS2) is fabricated with the specific angular alignment of the two major oriented monolayers at the edge direction of 0°/ ± 60°. On account of the optimization for scalable Moiré lattice with a high-quality interface, the observation of interlayer exciton at low temperature illustrates the feasibility of scalable Moiré superlattice based on the oriented monolayers.

Expected signature of stopped Brownian motion on d-dimensional C2,α-domains has finite radius of convergence everywhere: 2 ≤ d ≤ 8

A fundamental question in rough path theory is whether the expected signature of a geometric rough path completely determines the law of signature. One sufficient condition is that the expected signature has infinite radius of convergence, which is satisfied by various stochastic processes on a fixed time interval, including the Brownian motion. In contrast, for the Brownian motion stopped upon the first exit time from a bounded domain Ω, it is only known that the radius of convergence for the expected signature on sufficiently regular Ω is strictly positive everywhere, and that the radius of convergence is finite at some point when Ω is the 2-dimensional unit disc ([2]).In this paper, we prove that on any bounded C2,α-domain Ω⊂Rd with 2≤d≤8, the expected signature of the stopped Brownian motion has finite radius of convergence everywhere. A key ingredient of our proof is the introduction of a “domain-averaging hyperbolic development” (see Definition 4.1), which allows us to symmetrize the PDE system for the hyperbolic development of expected signature by averaging over rotated domains.

Suppression of Rotational Domains of CuI Employing Sodium Halide Buffer Layers.

The occurrence of rotational domains is a well-known issue for copper iodide (CuI) that naturally occurs for growth on popular substrates like sapphire. However, this has detrimental effects on the thin film quality like increasing surface roughness or deteriorated transport characteristics due to grain boundary scattering. Utilizing pulsed laser deposition and the in situ growth of sodium chloride (NaCl) and sodium bromide (NaBr) template layers, studies were performed on their potential on suppressing the formation of rotational domains of CuI on c-plane sapphire and SrF2(111) substrates. Corresponding samples were investigated concerning their epitaxial properties and further characterized regarding (volume) crystalline, morphological, and electrical properties. Particularly for NaBr template layers, fully single-crystalline growth of CuI thin films was obtained and resulted in significantly reduced surface roughness of the CuI layer.

Systematic Investigation of Growth and Properties of Ga2O3 Films on C-Plane Sapphire Substrates Prepared by Plasma-Assisted Molecular Beam Epitaxy

We investigated the growth and properties of Ga2O3 films on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). Growth parameters generally affect the structure and properties of films. In growing Ga2O3 films on sapphire substrates by PAMBE, source flux and growth temperature are main key factors and effects of those on growth behaviors, surface morphology, crystallinity, structural quality, and optical properties have been investigated by systematic experimental design using various characterization methods including reflection high energy electron diffraction, atomic force microscope, X-ray diffraction, transmission electron microscopy etc. The source flux strongly affected growth rate of Ga2O3 films by PAMBE, and the growth temperature strongly affected surface morphology and structural properties. The orientation relationship was determined to be β-Ga2O3 //Al2O3(0001) and β-Ga2O3[010]//Al2O3[]. However, the β-Ga2O3 films were not single crystalline but showed six-fold in-plane symmetry with six rotational domain structures. The detailed rotational domain structures were investigated by transmission electron diffraction analysis. The smooth surface with the RMS value of 0.95 nm can be obtained at growth temperature of 800 °C. All the grown β-Ga2O3 films are highly transparent and the optical bandgaps were 4.79–4.89 eV.

Multipolar spherical and cylindrical vortices

Multipolar spherical solutions to the three-dimensional steady vorticity equation are provided. These solutions are based on the separation of radial and angular contributions in terms of the spherical Bessel functions and vector spherical harmonics, respectively. In this set of multipolar vortex solutions, the Hicks–Moffatt swirling vortex is categorized as a vortex of degree ${\ell }=1$ and therefore as a vortex dipole. This swirling vortex is the three-dimensional dipole in spherical geometry equivalent to the two-dimensional Lamb–Chaplygin dipole in polar geometry. The three-dimensional dipole solution admits two linearly superposable solutions. The first one is a Trkalian flow and the second one is a cylindrical solid-body rotation with swirl. The higher ${\ell }>1$ multipolar vortices found are either vanishing-helicity vortices or Trkalian flow vortices. The multipolar Trkalian flows admit two circular polarizations given by the sign of the wavenumber $k$ . It is also found that piecewise vortex solutions, consisting of interior rotational and exterior potential flow domains, satisfying velocity continuity conditions at the vortex boundary, are possible in the general multipolar Trkalian spherical vortex. A particular polarized dipole solution in three-dimensional cylindrical geometry, consisting as well in the superposition of a Trkalian flow and a rigid motion, is also analysed. This swirling vortex may be interpreted as the three-dimensional dipole in cylindrical geometry equivalent to the two-dimensional Lamb–Chaplygin dipole in polar geometry.

Epitaxial Ferrimagnetic Mn4N Thin Films on GaN by Molecular Beam Epitaxy

Direct epitaxial integration of magnetic layers with wide bandgap nitride semiconductors will enable spin-controlled transport and photonic phenomena, seeding ideas for functional spintronic devices. Using plasma-assisted molecular beam epitaxy (MBE) in a previously unexplored window, significantly improved ferrimagnetic Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N layers are successfully grown on GaN with ~1 nm surface roughness. Distinct from earlier reports, the Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N layers grown on GaN are found to be [001] oriented with 12-fold in-plane symmetry in the diffraction pattern. This unique epitaxial registry originates from three equivalent rotational domains. The ferrimagnetic magnetotransport properties of low growth temperature Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N layers on GaN are comparable to those reported on cubic substrates such as MgO. However, a sign-flip of the Hall resistance is discovered for Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N layers grown above 300 °C.

Structure of Strained Low‐Dimensional Sb by In Situ Surface X‐Ray Diffraction

Antimony ultrathin films in tensile strain are grown on InAs(111)B substrates and studied in situ using surface X‐ray diffraction. The detailed atomic structures of two highly crystalline Sb(0001) films are derived, with thicknesses of 19 and 4 bilayers. Features considered in structural modeling include interfacial intermixing, surface roughness, individual layer relaxations, and rotational twin domains (RTDs). The four‐bilayer film shows significant structural relaxation in every layer, while both films include RTDs. The results are discussed in relation to the topological properties of low‐dimensional Sb.

Atomic-scale polar vortices in Na0.5Bi0.5TiO3 grains

Ferroelectric materials have great potential applications in non-volatile ferroelectric random access memories because of the singularity of one-dimensional topological defects. In this paper, we have found for the first time the atomic-level dipole rotations of vortex structures in crystalline materials. By the aberration-corrected high resolution scanning transmission electron microscopy (STEM), the atomic-scale multiple rotation domains and polar vortices in Na0.5Bi0.5TiO3 (NBT) grains have been clearly observed in lead-free perovskite NBT. Meanwhile, nanobeam electron diffraction experiments provided the strong evidences of the coexistence of tetragonal, orthorhombic and rhombohedra phases at room temperature. These polar vortices are constructed by the competition of these atomic-scale polar domains, which are originated from the multiphase coexistence of NBT and can be well confirmed by our theoretical calculations. These observations have put forward new implications for the creation of vortex topologies in crystalline materials without sophisticated thin-film technologies, and it can also help to understand the complicated polar mechanism in lead-free perovskite ferroelectric materials.

Fabrication, structural and magnetic behavior of novel one-dimensional Fe2MnGa nanostructures

Well aligned Fe2MnGa nanowires (NWs) have been synthesized through low cost and versatile electrochemical deposition technique with constant stirring during the growth process in anodic aluminum oxide (AAO) templates. The average diameter is 50 nm and the lengths up to a few micrometers have been confirmed through morphological analysis. The NWs are found to be in body centered cubic structure with (220) preferred orientation. The magnetic behavior has been investigated at room temperature (RT) as well as at low temperatures. The dominant shape anisotropy compelled the preferable magnetization axis to be in axial direction of NWs. Angular dependence of coercivity shows coherent rotation of magnetic domain on reversal of external magnetic field due to the stronger interwire couplings. At lower temperatures, superparamagnetic contributions from very small nanoparticles in blocking state significantly improved saturation magnetization (Ms) from 0.101 to 0.205 emu and coercivity from 1354 to 1632 Oe. A mixed behavior of exchange bias has been manifested by the NWs at lower temperatures owing to the rearrangement of atoms between the interface of antiferromagnetic and ferromagnetic grains. This causes significant disturbance for pining effect resulting fluctuating exchange bias phenomenon.

Null-Pol Response Pattern in Polarimetric Rotation Domain: Characterization and Application

Man-made targets with various orientations usually exhibit scattering diversity which makes polarimetric radar target recognition difficult. The recently developed polarimetric rotation domain techniques provide solutions to understand and utilize target scattering diversity. Meanwhile, the Null-Pol theory is the important component of target optimal polarization in radar polarimetry. This work first extends the Null-Pol theory into the polarimetric rotation domain and discloses the different scattering responses from canonical man-made structures. In this vein, the Null-Pol response pattern interpretation tool is established and a set of Null-Pol features are extracted and characterized. Then, a man-made structure identification approach is proposed based on selected features derived from the Null-Pol response pattern. Comparison studies are carried out with simulated datasets of canonical structures considering polarimetric measurement errors, simulated, and measured data of unmanned aerial vehicles (UAVs). Compared with the Cameron decomposition, the proposed method achieves more accurate and stable performance.

Man-Made Target Structure Recognition With Polarimetric Correlation Pattern and Roll-Invariant Feature Coding

Man-made target recognition is of great significance for many applications within microwave remote sensing. The scattering diversity of various man-made target structures makes radar target identification a difficult task. This work aims at mitigating this issue by mining and utilization of man-made target scattering diversity in polarimetric rotation domain with the interpretation tool of polarimetric correlation pattern. The optimal polarimetric roll-invariant feature set is collected from polarimetric correlation pattern. Then, a polarimetric roll-invariant feature coding scheme is developed for man-made target structure recognition. Moreover, polarimetric radar measurement errors in terms of channel coupling and imbalance are also considered. Experimental studies with electromagnetic computation datasets including canonical structures and an unmanned aerial vehicle (UAV) target and real spaceborne polarimetric synthetic aperture radar (PolSAR) data of a ship target are carried out. Compared with the Cameron decomposition, the proposed method exhibits better recognition performance and stronger robustness, especially for oriented man-made structures.

Three-Dimension Polarimetric Correlation Pattern Interpretation Tool and its Application

Polarimetric radar can acquire complete polarization information and is widely used in many applications. However, target orientation relative to the radar line of sight usually exhibits significant influences on the scattering mechanisms. Recently, such target scattering diversity has been successfully characterized and utilized with the polarimetric rotation domain interpretation techniques. In radar polarimetry, target scattering responses are affected by both polarization orientation angle and polarization ellipticity angle. In this vein, this work aims at exploring and utilizing the complete target scattering diversity by extending polarimetric rotation domain techniques to the polarization ellipticity angle dimension. The main idea is to develop a three-dimension polarimetric correlation pattern (3-D PCP) interpretation tool, which can visualize and exhibit targets’ polarimetric rotation domain properties in terms of both the polarimetric orientation and ellipticity angles. Then, a set of global, local, and mutual polarimetric features are proposed to characterize the responses of a 3-D PCP interpretation tool. Especially, the curvatures in differential geometry are first introduced to describe the properties of the 3-D surface. The performance of these new polarimetric features is investigated with spaceborne polarimetric synthetic aperture radar (PolSAR) data. Experimental results demonstrate the advantage of the proposed 3-D PCP features in enhancing the target clutter ratio (TCR), especially for the weak ship area. Based on this, a non-local superpixel-level contrast measure (NSLCM) method for ship detection is proposed. Pure sea samples can be determined adaptively for salient map construction. Comparison results demonstrate better detection performance for both the inshore dense ship area and weak ship area.

Investigations of pressure field along a channel of a pressure wave supercharger

The aim of the paper is a numerical investigation of the evolution of the pressure field along the wave rotor channels of a pressure wave ICE supercharger. In the present literature, most of the studies are considering the fluids as incompressible and inviscid in a 2D field. The present study is using the compressible and viscous terms in the unsteady Lattice Boltzmann method for fluid in a 3D field. The geometry was drawn in CAD software using measurements made on a real model of the CX-93 pressure wave supercharger. The simulation was conducted using a code for native unsteady LBM approach to reproduce data such as pressures, temperature and mass flows, which are usually hard to be measured in a real pressure wave supercharger. The computational domain was modelled as a moving rotational domain with adaptive refinement. Results such as velocity, pressure and temperature field in the rotor channels were obtained for exhaust gas inlet pressure of 0.292 MPa and 721 K temperature at different rotational speeds. The air inlet state considered was: 0,096 MPa and 313 K. The simulated values obtained are similar to the reported experimental results found in the literature showing a good concordance with the model.

Numerical investigation of a pressure wave supercharger

The paper aims at a numerical investigation of the evolution of velocity, pressure and temperature field along the wave rotor channels for a pressure wave supercharger. Since in literature most of the studies are made considering the working fluid as incompressible and inviscid in a 2D field, the present study is using the compressible and viscous terms in unsteady Navier-Stokes equations for fluid in 3D field. The geometry was drawn in CAD software using measurements made on a real model of the CX-93 pressure wave supercharger. The simulation was conducted using a CFD code for unsteady 3D k-e, k-co model approach to reproduce data such as pressures, temperature and mass flows which are usually measured in real engine pressure wave supercharging. The computational domain for uRANS was modeled as a moving rotational domain with adaptive meshing. Results such as velocity, pressure and temperature field in the rotor channels were obtained for exhaust gas inlet pressure of 0.28 MPa and 1465 K temperature at different rotational speeds. The air inlet state considered was: 0,098 MPa and 293 K. Supercharging by means of a pressure wave supercharger, in order to improve the performance of an internal combustion engine, appears to be a promising solution since the exhaust gas generates a benefice boost of intake air with significant advantages when compared to the conventional turbocharging. The numerical modelling of the complex phenomena occurring within the narrow channels might be a useful tool for improving the pressure exchange between the working fluids, either by modifying the input parameters or by optimizing the geometry of the rotor, ports or pockets.

Nanoheterogeneity response in large-magnetostriction Fe-Ga alloys: An in-situ magnetic small-angle neutron scattering study

The underlying mechanism of large magnetostriction in Fe-Ga alloys is obviously beyond the conventional domain rotation and twin boundary motion, but has been attributed to the nanoscale magnetic heterogeneities. However, the nanoheterogeneity response as well as the interaction with matrix during magnetization process is still an open question. Through in-situ magnetic small-angle neutron scattering (SANS) study on a Fe81Ga19 alloy, the present work clearly reveals that the reorientation of nanodomains relevant to face-centered-tetragonal L60 nanoprecipitates occurs at relatively lower fields than that of the magnetic domains. These nanoheterogeneities show a larger magnetic correlation length than their size, ensuring the exchange coupling between nanoprecipitates and matrix as well as the flipping of their magnetizations. This process contributes to the low-field-triggered large magnetostriction, unlike that induced by non-180° domain switches in the homogeneous magnetostrictive materials (such as Terfenol-D). Further study reveals that the correlation length can be effectively tuned by simple heat-treatment, which in turn significantly enhances the magnetostriction without enlarging the triggering field. Consequently, this work contributes to uncover the physical mechanism of the large heterogeneous magnetostriction besides the typical magnetic domain theory, and may also provide a general guideline for achieving tunable magnetostriction in heterogeneous ferromagnets.

The roles of Sn4+ in affecting performance of Potassium Sodium Niobate ceramics

In the KNN ceramics system, the contradictory relationship between piezoelectricity and phase transition temperature has received extensive attention from researchers. Herein, by studying the doping mechanism of Sn4+ in 0.957(K0.48Na0.52)NbO3-0.003BiCoO3-0.04(Bi0.5K0.5)Zr1-xSnxO3 (KNN-BC-BKZ1-xSx), the coexistent of excellent piezoelectricity and ideal Curie temperature is realized in KNN ceramics. The addition of Sn4+ keeps R-O-T coexistence system in KNN-BC-BKZ1-xSx ceramics, thereby maintaining the low energy barrier of domain rotation. Further investigation has shown that the substitution of Sn4+ can promote grain growth and increase the density of ceramics. In addition, the optimal comprehensive properties (d33 = 391 pC/N, kp = 0.518, TC = 332 °C, d33* = 512 pm/V) are simultaneously obtained at x = 0.15. Particularly, due to growth of grain size, excellent temperature stability is obtained within a broad temperature range. The discovery of Sn4+ doping is useful to the development of KNN-based materials with both piezoelectric electrical properties and Curie temperature as it provides a new idea for enhancing performances of ceramics.