Polar Order Research Articles

Density-Polarity Coupling in Confined Active Polar Films: Asters, Spirals, and Biphasic Orientational Phases.

Topological defects in active polar fluids can organize spontaneous flows and influence macroscopic density patterns. Both of them play an important role during animal development. Yet the influence of density on active flows is poorly understood. Motivated by experiments on cell monolayers confined to disks, we study the coupling between density and polar order for a compressible active polar fluid in the presence of a +1 topological defect. As in the experiments, we find a density-controlled spiral-to-aster transition. In addition, biphasic orientational phases emerge as a generic outcome of such coupling. Our results highlight the importance of density gradients as a potential mechanism for controlling flow and orientational patterns in biological systems.

Generation of high radial node vector vortex beams based on digital micromirror device

The modulation of amplitude, phase, and polarization to generate complex vector light fields with spatially variant polarization distribution has become a hot research topic in recent years. We propose a new method for generating high radial node vector vortex beams (VVB) based on a digital micromirror device (DMD). Firstly, we propose a multiplexed binary hologram with varying ellipticity, which can significantly optimize the vortex beam generated by DMD while the mode purity of the scalar vortex beam after optimization can reach 97.23%. Secondly, a novel interference experimental setup is proposed based on the Wollaston prism, which can realize arbitrary control of VVBs. Based on this, the high radial node VVBs with p=10 and high polarization order VVBs with polarization order up to 25 are generated experimentally. Finally, we reconstruct the State of Polarization (SoP) of the vector beam l=4,m=-4,p=4 based on the Stokes parameter S1,S2,S3, and the variation of vector quality factor (VQF) on the high-order Poincaré sphere (HOPS) is analyzed. Our technology provides a high-quality vector beam generation scheme with important applications in laser detection, optical communication, and optical micro-manipulation.

High-Temperature Ferroic Glassy States in SrTiO_{3}-Based Thin Films.

Disordered ferroics hold great promise for next-generation magnetoelectric devices because their lack of symmetry constraints implies negligible hysteresis with low energy costs. However, the transition temperature and the magnitude of polarization and magnetization are still too low to meet application requirements. Here, taking the prototype perovskite of SrTiO_{3} as an instance, we realize a coexisting spin and dipole reentrant glass states in SrTiO_{3} homoepitaxial films via manipulation of local symmetry. Room-temperature saturation magnetization and spontaneous polarization reach ∼ 10 emu/cm^{3} and ∼ 25 μC/cm^{2}, respectively, with high transition temperatures (101K and 236K for spin and dipole glass temperatures and 556K and 1100K for Curie temperatures, respectively). Our atomic-scale investigation points out an underlying mechanism, where the Ti/O-defective unit cells break the local translational and orbital symmetry to drive the formation of unusual slush states. This study advances our understanding of the nature of the intricate couplings of ferroic glasses. Our approach could be applied to numerous perovskite oxides for the simultaneous control of the local magnetic and polar orderings and for the exploration of the underlying physics.

Higher-order soliton solutions for the Sasa–Satsuma equation revisited via bar{partial } method

In optics, the Sasa–Satsuma equation can be used to model ultrashort optical pulses. In this paper higher-order soliton solutions for the Sasa–Satsuma equation with zero boundary condition at infinity are analyzed by bar{partial } method. The explicit determinant form of a soliton solution which corresponds to a single p_{l}-th order pole is given. Besides the interaction related to one simple pole and the other one double pole is considered.

Subsurface Flows Associated with Formation and Flaring Activity of Solar Active Regions

AbstractWe investigate the evolution of subsurface flows during the emergence and the active phase of sunspot regions using the time–distance helioseismology analysis of the full-disk Dopplergrams from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We present an analysis of emerging active regions of various types, including delta-type active regions and regions with the reverse polarity order (‘anti-Hale active regions’). The results reveal strong vortical and shearing flows during the emergence of magnetic flux, as well as the process of formation of large-scale converging flow patterns around developing active regions, predominantly in the top 6 Mm deep layers of the convection zone. Our analysis revealed a significant correlation between the flow divergence and helicity in the active regions with their flaring activity, indicating that measuring characteristics of subsurface flows can contribute to flare forecasting.

The European Union’s polar ambitions: regional geo-policies yet limited geo-strategic vision

ABSTRACTThe European Union influences the governance of the Arctic and the Antarctic, whose Global Spaces constitute a part of broader complex governance patchworks. This influence derives both from the EU’s role in global governance but also builds on some member states being Arctic states and Antarctic Treaty parties. The objective of this article is to propose an innovative conceptual approach – built on political geography and critical geopolitics – to better capture the EU’s presence and its visions for an EU-preferred shape of polar governance. We propose that the EU is an important participant to the process of ‘polar spatial ordering’ and has its own set of objectives, namely, to establish permanent EU-polar linkages and render itself a necessary element/participant of polar (geo)politics. These aims are supported or pursued via diverse geo-policies. However, the EU’s overarching visions – cross-sectoral geo-strategies – regarding its preferred shape of polar spaces remain underdeveloped.

Manipulating plasmonic vortex based on meta-atoms with four rectangular slits.

In this paper, four rectangular slits with the same size and regular rotation angle are regarded as the meta-atom, arranged on circular contours, to create plasmonic vortex lenses (PVLs) solely based on the geometric phase. These PVLs can achieve the same purpose of exciting surface plasmon polariton (SPP) vortices with arbitrary combinations of topological charge (TC) when illuminated by circularly polarized (CP) light with different handedness as the traditional PVLs. Furthermore, they can generate SPP vortices with different TCs and specific constant or varying electric-field intensities when excited by linearly polarized (LP) light, which marks the first instance of this phenomenon solely through geometric phase manipulation. The TC can be dynamically altered by controlling the polarization order of the incident vector beam. These PVLs not only possess advantages in terms of device miniaturization and the creation of a more uniform vortex field, as compared to PVLs based on the transmission phase, but also offer a more straightforward design process in comparison to traditional structures that rely solely on the geometric phase.

Antioxidant potential of leaf extracts from Zingiber officinale Roscoe and Curcuma longa L.

The rhizomes of the turmeric (Curcuma longa L.) and ginger (Zingiber officinale Roscoe) plant are commercialized for culinary and medicinal use, presenting antioxidant, anti-inflammatory and even antitumor activity. The leaves of these plants are considered post-harvest waste. The aim of this study was to evaluate the antioxidant potential of turmeric and ginger leaf extracts. After drying the leaves in an oven at 40ºC, cold extraction was performed by exhaustive maceration in methanol. The methanolic crude extract was partitioned in ascending order of polarity and the hexane, dichloromethane, ethyl acetate and hydromethanolic fractions were obtained. The antioxidant activity of the extracts and fractions was evaluated by the DPPH and ABTS methods and the results were expressed in μM of Trolox per g/extract. By the DPPH method, both in turmeric and ginger, the fraction that showed the highest antioxidant activity was ethyl acetate (752.18 and 393.32 μM Trolox/g, respectively). For ABTS, the highest antioxidant activity was in dichloromethane (935.54 and 704.31 μM Trolox/g, respectively), followed by ethyl acetate (393, 23 and 607.77 μM Trolox/g, respectively), indicating turmeric with higher antioxidant potential.

Artificial Visual Systems Fabricated with Ferroelectric van der Waals Heterostructure for In-Memory Computing Applications.

Rapid developments in artificial neural network techniques and retina-inspired artificial visual systems are required to realize the sensing, processing, and memorization of an optical signal in a single device. Herein, a ferroelectric field-effect transistor fabricated with CuInP2S6 and α-In2Se3 van der Waals heterostructures is proposed and demonstrated for the development of an artificial visual system. The dipole polarizations are coupled and bidirectionally locked inside the ferroelectric α-In2Se3 along the in-plane and out-of-plane directions and are controlled by the gate voltages. Furthermore, light-induced polarization can change the order of polarization of the dipoles inside α-In2Se3. We demonstrate that using the combined control of these electrical and optical signals, the device may function like a retina-inspired vision system. The device can operate across a wide wavelength range (405-850 nm) and detect very low incident light (0.03 mW/cm2). Color recognition, high paired-pulse facilitation (∼170%), and short- to long-term memory transitions through quick learning are observed using this device. Additionally, this device demonstrates different complex processing abilities, including pattern recognition, light adaptation, optical logic operation, and event learning. The proposed ferroelectric heterostructure-based artificial visual system can serve as an essential bridge for fulfilling the future requirements of all-in-one sensing and memory-processing devices.

Hybrid Dry and Wet Etching of LiNbO3 Domain-Wall Memory Devices with 90° Etching Angles and Excellent Electrical Properties.

Ferroelectric domain walls, agile nanoscale interfaces of polar order, can be selectively controlled by electric fields for their position, conformation, and function, which is ultimately the key to realizing novel low-energy memory and computing structures. LiNbO3 single-crystal domain wall memory has the advantages of high operational speed, high integration density, and virtually unlimited endurance cycles, appearing as a good solution for the next generation of highly miniaturized low-energy memories. However, the etching process poses significant challenges in the nanofabrication and high-density integration of LiNbO3 domain-wall memories. Here, we employed a hybrid etching technique to achieve smooth sidewalls with a 90° inclined angle, leading to a 24% reduction in the coercive field and a 2.5-fold increase in the linear domain wall current density with a retention time of more than 106 seconds and endurance of over 105 writing cycles. Combined with the results of X-ray diffraction patterns and X-ray photoelectric spectra, it is concluded that the excellent electrical performance is related to the formation of an oxygen-deficient LiNbO3-x layer on the sidewall surface during the wet chemical etching process, which is a conductive layer that reduces the thickness of the "dead" layer between the side electrodes and the LiNbO3 cell and rectifies the diode-like wall currents with an onset voltage reduced from 1.23 to 0.28 V. These results prove the high-density integration of ferroelectric domain-wall memories at the nanoscale and provide a new strategy applicable to the development of LiNbO3 photonic devices.

Many-body GW calculations with very large scale polarizable environments made affordable: A fully abinitio QM/QM approach.

We present a many-body GW formalism for quantum subsystems embedded in discrete polarizable environments containing up to several hundred thousand atoms described at a fully abinitio random phase approximation level. Our approach is based on a fragment approximation in the construction of the Green's function and independent-electron susceptibilities. Further, the environing fragments susceptibility matrices are reduced to a minimal but accurate representation preserving low order polarizability tensors through a constrained minimization scheme. This approach dramatically reduces the cost associated with inverting the Dyson equation for the screened Coulomb potential W, while preserving the description of short to long-range screening effects. The efficiency and accuracy of the present scheme is exemplified in the paradigmatic cases of fullerene bulk, surface, subsurface, and slabs with varying number of layers.

Bixa orellana ethyl acetate fraction and its isolated compound ellagic acid attenuate the progression of MIA-induced osteoarthritis in rat knees

Osteoarthritis (OA) is a pathology that is characterized by progressive erosion of articular cartilage. In this context, medicinal plants have become relevant tools regarding their potential role in the prevention and treatment of OA, being safe and effective. The aim of this work was investigate the therapeutic efficacy of the ethyl acetate fraction of Bixa orellana leaves (BoEA) and ellagic acid (ElAc) for the therapeutic treatment of OA induced by monosodium iodoacetate (MIA) in rats. The plant material was extracted via maceration with 70 % hydroalcoholic solvent (BoHE). The ethyl acetate (BoEA) fraction was by solvents in increasing order of polarity. The ElAc was identified and isolated in BoEA using high performance liquid chromatography (HPLC-DAD) and analytical curve. The OA was induced using MIA in the right knee at the knee joint. Doses of BoEA and ElAc were administered daily (every 24 h, orally) at concentrations of 50, 100 and 50 mg/kg, respectively, for 28 days after induced OA. We evaluated the animals through clinical and radiological examinations every 7 days and, on the 29th day, the animals were euthanized, the joints being removed for histopathological analysis and the serum for cytokine analysis. BoEA and ElAc compounds reduced inflammation and nociception in OA and were as effective as indomethacin in clinical parameters of joint discomfort and allodynia in rats, in addition to showing improvements in radiological and histopathological images, acting on the progress of cartilage deterioration, proving properties related to anti-inflammatory and analgesic processes, being important allies for new therapeutic interventions for the treatment of OA.

Three-dimensional implementation of multi-mode fractional-order elliptical perfect optical vortex arrays

Fractional-order vortex beams possess unique spin and orbital angular momentum structure, and have significant applications in various fields. Nevertheless, the construction and tuning of these beams require high-precision optical devices and systems that are challenging to implement. Here, we propose a simple and effective method for realizing multi-mode independent modulation of fractional-order vector elliptical perfect optical vortices. The linear modulation of the EPOV ring is demonstrated. By combining the mode extraction with optical pen, multi-mode independent modulation of fractional-order elliptical perfect optical vortex arrays are successfully constructed, including position, quantity, ellipticity, topological charge, and polarization order. The experimental results are highly consistent with the numerical simulation results. We also demonstrate the implementation process of constructing multiple fractional-order EPOV arrays in three-dimensional space. This work provides a simple and feasible solution for the control of complex structured light fields and is expected to play an important role in optical trapping, optical communication, optical imaging, and quantum optics.

Synthesis and Magnetic Properties of the Multiferroic [C(NH2)3]Cr(HCOO)3 Metal-Organic Framework: The Role of Spin-Orbit Coupling and Jahn-Teller Distortions.

We report for the first time the synthesis of [C(NH2)3]Cr(HCOO)3 stabilizing Cr2+ in formate perovskite, which adopts a polar structure and orders magnetically below 8 K. We discuss in detail the magnetic properties and their coupling to the crystal structure based on first-principles calculations, symmetry, and model Hamiltonian analysis. We establish a general model for the orbital magnetic moment of [C(NH2)3]M(HCOO)3 (M = Cr, Cu) based on perturbation theory, revealing the key role of the Jahn-Teller distortions. We also analyze their spin and orbital textures in k-space, which show unique characteristics.

GENERALISED AUTOMORPHIC SHEAVES AND THE PROPORTIONALITY PRINCIPLE OF HIRZEBRUCH-MUMFORD

AbstractWe axiomatise the algebraic properties of toroidal compactifications of (mixed) Shimura varieties and their automorphic vector bundles. A notion of generalised automorphic sheaf is proposed which includes sheaves of (meromorphic) sections of automorphic vector bundles with prescribed vanishing and pole orders along strata in the compactification, and their quotients. These include, for instance, sheaves of Jacobi forms and weakly holomorphic modular forms. Using this machinery, we give a short and purely algebraic proof of the proportionality theorem of Hirzebruch and Mumford.

Manipulation of plasmonic vortex fields using positive elliptically polarized beams

Several studies have investigated methods for the direct excitation of surface plasmon polariton (SPP) vortex fields by using scalar beams with linear and circular polarization. In this paper, we propose novel devices for generating SPP vortex fields by using positive elliptically polarized beams. These devices excited SPP vortices with a uniform electric field intensity distribution, that did not vary arbitrarily with changes in the incident beam amplitude ratio. Moreover, when the incident scalar beam was transformed into a vector beam with different amplitude ratios at every point in space, the topological charge of the SPP vortex field could be dynamically modulated by changing the polarization order and rotation direction of the incident vector beam. The fields generated by different structures after the superposition of SPP vortices had spatial intensity distributions that varied with changes in the incident beam amplitude ratio. These properties provide a new idea for realizing different spatial intensity distributions for a dynamic modulation SPP field.

Antidiabetic Activity of Apigenin (4, 5, 7 – Trihydroxy Flavone) from Leaves of Stachytarpheta jamaicensis (L) Vahl (Verbennaceae)

Background: Apigenin is a polyphenolic compound that belongs to the class of flavonoids and is considered highly therapeutic.
 Aim: To evaluate the antidiabetic activity of apigenin isolated from dichloromethane: methanol extract of leaves of Stachytarpheta jamiacensis (L) Vahl (Verbennaceae) in alloxan-induced diabetic rats.
 Methods: Cold maceration was used to extract the S. jamiacensis powdered leaves with dichloromethane: methanol (1:1). Hexane, dichloromethane, and aqueous methanol fractions of the extract were obtained through fractionation. To isolate the bioactive molecule, the dichloromethane fraction (DCMF) was then subjected to column chromatography and eluted with several solvent mixtures in ascending polarity order. With the aid of data from FTIR, UV, GC-MS, 1HNMR (400MHz), and 13CNMR (101MHz), the structure of the isolated compound was identified. The Phytochemical analysis of the isolate and acute toxicity study was done following standard procedures. The anti-diabetic potential of the isolate was assessed by determining fasting blood glucose levels on alloxan-induced rats at the dose of 25 and 50 mg/kg body weight.
 Results: The compound was identified as apigenin (4, 5, 7 – trihydroxy flavones) and showed significant (p<0.05) reduction of 79.56 and 81.74 % in fasting blood glucose levels at the dose of 25 and 50 mg/kg respectively when compared with the standard drug (glibenclamide 83.40 %). The isolate's phytochemical analysis revealed flavonoids and the LD50 test demonstrates that apigenin was not harmful.
 Conclusion: The findings show that the apigenin from Stachytarpheta jamaicensis (L) Vahl has potent anti-diabetic properties.

Justicia adhatoda L. vasicin and vasicinone as bioactive phytochemical compounds: Isolation, characterization, and computational studies

Justicia adhatoda L. has wide applications in traditional and modern medicine. Its major potency is due to the presence of two alkaloids viz. Vasicine and Vasicinone. In industry, the demand for both marker compounds as well as quality Justicia adhatoda L. material is very high. The isolation of bioactive phytochemical compounds for the development of an in-house phytochemical reference standard library to verify quality control is of prime demand for an analytical chemist. For these reasons, the objective of the present study was to isolate two members of the alkaloids Vasicine and Vasicinone marker compounds from Justicia adhatoda L. Extraction was carried out by using a cold percolation method in a successive manner by increasing the order of polarity of the solvents from petroleum-ether to ethanol. Isolation was achieved for the above said two maker compounds by using separation, purification though column chromatography on silica-gel using mobile phase chloroform, and ethanol. Characterization of the isolated compounds was carried out by UV–VIS, IR, 1H NMR, 13C NMR and mass spectroscopy techniques. The isolated and purified solid compounds were confirmed as Vasicine and Vasicinone by comparison and co-relating with observed spectroscopy data and literature data. The compounds had a good to high amount of yield (0.4 % to 0.63 %) with high purity (98–100 %) through HPL. Lastly, frontier molecular orbital analysis (HOMO and LUMO), and global descriptive parameters (such as chemical potential, electronegativity, hardness, softness, etc.) were analyzed using computational approaches. Results revealed a good correlation with experimental data except for a few alternations in 1H NMR data.

To Be or Not To Be Polar: The Ferroelectric and Antiferroelectric Nematic Phases.

We report two new series of compounds that show the ferroelectric nematic, NF, phase in which the terminal chain length is varied. The longer the terminal chain, the weaker the dipole-dipole interactions of the molecules are along the director and thus the lower the temperature at which the axially polar NF phase is formed. For homologues of intermediate chain lengths, between the non-polar and ferroelectric nematic phases, a wide temperature range nematic phase emerges with antiferroelectric character. The size of the antiparallel ferroelectric domains critically increases upon transition to the NF phase. In dielectric studies, both collective ("ferroelectric") and non-collective fluctuations are present, and the "ferroelectric" mode softens weakly at the N-NX phase transition because the polar order in this phase is weak. The transition to the NF phase is characterized by a much stronger lowering of the mode relaxation frequency and an increase in its strength, and a typical critical behavior is observed.

Strong electron-phonon coupling driven pseudogap modulation and density-wave fluctuations in a correlated polar metal

There is tremendous interest in employing collective excitations of the lattice, spin, charge, and orbitals to tune strongly correlated electronic phenomena. We report such an effect in a ruthenate, Ca3Ru2O7, where two phonons with strong electron-phonon coupling modulate the electronic pseudogap as well as mediate charge and spin density wave fluctuations. Combining temperature-dependent Raman spectroscopy with density functional theory reveals two phonons, B2P and B2M, that are strongly coupled to electrons and whose scattering intensities respectively dominate in the pseudogap versus the metallic phases. The B2P squeezes the octahedra along the out of plane c-axis, while the B2M elongates it, thus modulating the Ru 4d orbital splitting and the bandwidth of the in-plane electron hopping; Thus, B2P opens the pseudogap, while B2M closes it. Moreover, the B2 phonons mediate incoherent charge and spin density wave fluctuations, as evidenced by changes in the background electronic Raman scattering that exhibit unique symmetry signatures. The polar order breaks inversion symmetry, enabling infrared activity of these phonons, paving the way for coherent light-driven control of electronic transport.