Terms Of Polarization Research Articles

Completely Multipolar Model as a General Framework for Many-Body Interactions as Illustrated for Water.

We introduce a general framework for many-body force fields, the Completely Multipolar Model (CMM), that utilizes multipolar electrical moments modulated by exponential decay of electron density as a common functional form for all terms of an energy decomposition analysis of intermolecular interactions. With this common functional form, the CMM model establishes well-formulated damped tensors that reach the correct asymptotes at both long- and short-range while formally ensuring no short-range catastrophes. CMM describes the separable EDA terms of dispersion, exchange polarization, and Pauli repulsion with short-ranged anisotropy, polarization as intramolecular charge fluctuations and induced dipoles, while charge transfer describes explicit movement of charge between molecules, and naturally describes many-body charge transfer by coupling into the polarization equations. We also utilize a new one-body potential that accounts for intramolecular polarization by including an electric field-dependent correction to the Morse potential to ensure that CMM reproduces all physically relevant monomer properties including the dipole moment, molecular polarizability, and dipole and polarizability derivatives. The quality of CMM is illustrated through agreement of individual terms of the EDA and excellent extrapolation to energies and geometries of an extensive validation set of water cluster data.

The structure of water-ammonia mixtures from classical and abinitio molecular dynamics.

The structure of aqueous ammonia solutions is investigated through classical molecular dynamics (MD) and abinitio molecular dynamics (AIMD) simulations. We have preliminarily compared three well-known classical force fields for liquid water (SPC, SPC/E, and TIP4P) in order to identify the most accurate one in reproducing AIMD results obtained at the Generalized Gradient Approximation (GGA) and meta-GGA levels of theory. Liquid ammonia has been simulated by implementing an optimized force field recently developed by Chettiyankandy et al. [Fluid Phase Equilib. 511, 112507 (2020)]. Analysis of the radial distribution functions for different ammonia concentrations reveals that the three water force fields provide comparable estimates of the mixture structure, with the SPC/E performing slightly better. Although a fairly good agreement between MD and AIMD is observed for conditions close to the equimolarity, at lower ammonia concentrations, important discrepancies arise, with classical force fields underestimating the number and strength of H-bonds between water molecules and between water and ammonia moieties. Here, we prove that these drawbacks are rooted in a poor sampling of the configurational space spanned by the hydrogen atoms lying in the H-bonds of H2O⋯H2O and, more critically, H2O⋯NH3 neighbors due to the lack of polarization and charge transfer terms. This way, non-polarizable classical force fields underestimate the proton affinity of the nitrogen atom of ammonia in aqueous solutions, which plays a key role under realistic dilute ammonia conditions. Our results witness the need for developing more suited polarizable models that are able to take into account these effects properly.

Designing edge states from fractional polarization insulators

We theoretically investigated disconnected dispersive edge states in an anisotropic honeycomb lattice without chiral symmetry. When both mirror and chiral symmetries are present, this system is defined by a topological quantity known as fractional polarization (FP) term and exhibits a bulk band gap, classifying it as an FP insulator. While the FP insulator accommodates robust, flat topological edge states (TES), it also offers the potential to engineer these edge states by deliberately disrupting a critical symmetry that safeguards the underlying topology. These symmetry-breaking terms allow the edge states to become dispersive and generate differing configurations along the open boundaries. Furthermore, disconnected helical-like and chiral-like edge states analogous to TES seen in quantum spin and anomalous hall effect are achieved by the finite size effect, not possible from the symmetry-breaking terms alone. The demonstration of manipulating these edge states from a FP insulator can open up new avenues in constructing devices that utilize topological domain walls.

Analytical Model for the Molecular Ionization Energy in an External Electric Field.

A model for the molecular ionization energy in an applied electric field is presented on the basis of a perturbation expansion in the electric field. The leading term arises from the Frenkel approach, which is the same for all molecules normally used in the Poole-Frenkel model for conductivity in an electric field. For a set of test molecules, the quality of the results is comparable to that of previous results using constrained density functional theory. We conclude that the Frenkel term is dominant and sufficient at relatively low fields and that the dipole and polarizability terms, the leading terms dependent on the properties of the individual molecule, make a significant contribution only at high fields and for relatively large molecules. Because the presented model is analytical, quantum chemical calculations are avoided for a variety of electric field strengths and molecular orientations, and the model can therefore be applied directly in coarse-grained models for electronic processes in dielectric condensed phases.

Compensation of the multipolar polarizability shift in optical lattice clocks.

In neutral atom optical clocks, the higher-order atomic polarizability terms lead to the clock transition frequency shift that is motion-state dependent and nonlinear with the optical lattice depth. We propose to use an auxiliary optical lattice to compensate the influence of the E2-M1 differential polarizability or tune the associated coefficient to a favorable value. We show that by applying this method to Sr and Hg optical lattice clocks, the low or even sub-10-19 clock transition frequency uncertainty from the optical lattice becomes feasible. Finally, the proposed scheme is simple for experimental realization, is compatible with the use of an enhancement cavity, and can be implemented and tested in the existing setups.

Insects as radar targets: size, form, density and permittivity

ABSTRACT To make biologically useful interpretations of the echo signals from an entomological radar (a radar designed and operated to observe insects in flight), it is necessary to relate basic properties of insects (i.e. their mass, size, and form) to their radio-wave scattering characters – e.g. their radar cross-section (RCS) and its variation with aspect or beam polarization. Measurements of RCSs of live or freshly dead specimens in laboratory rigs have played an important role in establishing such relationships, but it is desirable to develop and validate methods employing numerical computation, using electromagnetic calculation software, as a more widely applicable and generalizable alternative. In such computations, the insect is represented by a model with specified size, form, and composition; composition appears as the complex relative permittivity, with both polarizability (real) and loss (imaginary) terms. As a preliminary to investigating how adequately different types of electromagnetic model perform, we have collected and analysed morphometric data on adult, flight-capable specimens of a wide range of insect species, including many known to be migratory and to fly at heights where they would be detectable by radar. Our analyses reveal that appropriate densities for prolate-spheroid models of flying insects are in the range 0.60–0.76 g cm−3, which is about half that measured for air-free samples of the solids and liquids from which insect bodies are formed. From this, appropriate permittivities for the material filling the model are found to be in the range 7–11 (real component) and 2.0–3.5 (imaginary); again, these are much lower than measured values for pure insect-body material. These results enable construction of simple electromagnetic models of insects in which both spatial dimensions and masses are accurate. Computation of model RCSs and their aspect and polarization variations, and comparison of these with laboratory measurements, will be the topic of a follow-up validation study.

Systematic improvement of empirical energy functions in the era of machine learning.

The impact of targeted replacement of individual terms in empirical force fields is quantitatively assessed for pure water, dichloromethane (CH Cl ), and solvated K and Cl ions. For the electrostatic interactions, point charges (PCs) and machine learning (ML)-based minimally distributed charges (MDCM) fitted to the molecular electrostatic potential are evaluated together with electrostatics based on the Coulomb integral. The impact of explicitly including second-order terms is investigated by adding a fragment molecular orbital (FMO)-derived polarization energy to an existing force field, in this case CHARMM. It is demonstrated that anisotropic electrostatics reduce the RMSE for water (by 1.4 kcal/mol), CH Cl (by 0.8 kcal/mol) and for solvated Cl clusters (by 0.4 kcal/mol). An additional polarization term can be neglected for CH Cl but further improves the models for pure water (by 1.0 kcal/mol) and hydrated Cl (by 0.4 kcal/mol), and is key for solvated K , reducing the RMSE by 2.3 kcal/mol. A 12-6 Lennard-Jones functional form performs satisfactorily with PC and MDCM electrostatics, but is not appropriate for descriptions that account for the electrostatic penetration energy. The importance of many-body contributions is assessed by comparing a strictly 2-body approach with self-consistent reference data. Two-body interactions suffice for CH Cl whereas water and solvated K and Cl ions require explicit many-body corrections. Finally, a many-body-corrected dimer potential energy surface exceeds the accuracy attained using a conventional empirical force field, potentially reaching that of an FMO calculation. The present work systematically quantifies which terms improve the performance of an existing force field and what reference data to use for parametrizing these terms in a tractable fashion for ML fitting of pure and heterogeneous systems.

General framework for ultrafast nonlinear photonics: unifying single and multi-envelope treatments [Invited

Numerical modeling of ultrashort pulse propagation is important for designing and understanding the underlying dynamical processes in devices that take advantage of highly nonlinear interactions in dispersion-engineered optical waveguides. Once the spectral bandwidth reaches an octave or more, multiple types of nonlinear polarization terms can drive individual optical frequencies. This issue is particularly prominent in χ(2) devices where all harmonics of the input pulse are generated and there can be extensive spectral overlap between them. Single-envelope approaches to pulse propagation have been developed to address these complexities; this has led to a significant mismatch between the strategies used to analyze moderate-bandwidth devices (usually involving multi-envelope models) and those used to analyze octave-spanning devices (usually involving models with one envelope per waveguide mode). Here we unify the different strategies by developing a common framework, applicable to any optical bandwidth, that allows for a side-by-side comparison between single- and multi-envelope models. We include both χ(2) and χ(3) interactions in these models, with emphasis on χ(2) interactions. We show a detailed example based on recent supercontinuum generation experiments in a thin-film LiNbO3 on sapphire quasi-phase-matching waveguide. Our simulations of this device show good agreement between single- and multi-envelope models in terms of the frequency comb properties of the electric field, even for multi-octave-spanning spectra. Building on this finding, we explore how the multi-envelope approach can be used to develop reduced models that help build physical insights about new ultrafast photonics devices enabled by modern dispersion-engineered waveguides, and discuss practical considerations for the choice of such models. More broadly, we give guidelines on the pros and cons of the different modeling strategies in the context of device design, numerical efficiency, and accuracy of the simulations.

Polarization characteristics and structural modifications of Cu nanoparticles under high electric fields

High electric fields affect the diffusion dynamics of atoms on a metal surface, causing biased surface diffusion that possibly leads to the growth of intensively field emitting protrusions and consequent vacuum breakdown (VBD). The scientific understanding of this process, as well as other fundamental VBD initiation mechanisms, is far from complete. Here we investigate the exact atomic behaviour of metal surfaces exposed to extremely high electric fields using density functional theory (DFT). Previous theories describe the field-surface dynamics in terms of the effective dipole moments and polarizability of surface atoms, disregarding higher-order (hyperpolarizability) terms. The validity of this approximation has been evaluated only for electric fields up to 3 GV/m, due to computational limitations of the plane-wave DFT basis used in previous works. In this work, we test the validity of this approximation for a much wider field range, relevant for VBD and field emission (FE), using Cu nanoparticles as our test structures. We find that although such high fields can change the entire structure of Cu nanoparticles, their energetics are described very precisely by the permanent dipole moment and polarizability terms. Thus, we show that neglecting the hyperpolarizability terms is valid even for field values that exceeds the range that is relevant for intense FE and VBD. This work lays a solid foundation for further developing atomic-level simulation models for electric field-induced surface diffusion on metal surfaces and its effects on protrusion growth and VBD initiation.

T helper cell responses to Opisthorchis viverrini infection associate with host susceptibility.

Opisthorchis viverrini infection is endemic in the lower Mekong subregion. The liver is an organ that worms are drawn to and cause damage. However, the immune-related susceptibility in the liver is poorly understood. In this study, we investigated T helper (Th) cell responses in the liver of BALB/c mice and golden Syrian hamsters during 2-28days post-infection (DPI). We found that Th cell responses were distinct between mice and hamsters in terms of dynamics and polarization. Mice exhibited the early induction of Th1, Th2, Th17, and regulatory T (Treg) cells responses after the presence of O. viverrini worms at 2 DPI. In hamsters, the late induction of Th1/Th17, downregulation of Th2/Treg responses and early elevation of suppressive cytokine interleukin (IL)-10 were found together with swift reduction of Th cell numbers. Interestingly, expressions of IL-4 (Th2 functional cytokine) and Foxp3 (Treg lineage) were completely different between mice and hamsters which elevated in mice but suppressed in hamsters. These results suggest that early induction and well-regulation are related to host resistance. In contrast, late induction of Th cell response might allow immature worms to develop in the host. Our findings provide a greater understanding in Th cell response-related susceptibility in O. viverrini infection which would be targeting immunity for the development of immune-based intervention such as vaccine.

A multi-stable deployable quadrifilar helix antenna with radiation reconfigurability for disaster-prone areas

In disaster-prone areas, damaged infrastructure requires impromptu communications leveraging lightweight and adaptive antennas. Accordingly, we introduce a bi-stable deployable quadrifilar helix antenna that passively reconfigures its radiation characteristics in terms of pattern and polarization. The proposed structure is composed of counter-rotating helical strips, connected by rotational joints to allow a simultaneous change in the helix height and radius. Each helical strip is composed of a fiber-reinforced composite material to achieve two stable deployed states that are self-locking. The reconfiguration between an almost omnidirectional pattern and a circularly polarized directive pattern enables the antenna to be suitable for both terrestrial and satellite communication within the L-band. More specifically, the presented design in infrastructure-less areas achieves satellite localization with directive circularly polarized waves and point-to-point terrestrial connectivity with an almost omnidirectional state. Hence, we present a portable, agile, and passively reconfigured antenna solution for low-infrastructure areas.

Optical red shift spectra in CuxGe32S68-x films for infrared and solar cell window applications

The physical characteristics of Cu-doped ternary glasses have been analyzed. The CuxGe32S68 − x (x = 0.0, 4.0, 7.0, 10.0 and 13.0 at.%) chalcogenide alloys have been manufactured by the conventional melt quenching method. The glass densities (ρ) increase with the Cu amounts, whereas the main atomic volume (Vm) decreases. Transmission and reflectance were measured in the wavelength range of 0.35–2.5 μm. The generated envelops (RM and Rm) of reflectance spectra were used to calculate the film thickness (t), the refractive index (n), and the extinction coefficient (k). With the increase in Cu contents from 0.0 to 13.0 at.%., the n values increased from 2.07 to 2.43, whereas the optical gap (Eg) decreased from 2.81 eV to 2.42 eV. The obtained results were explained in terms of electronic polarizability, plasma frequency, metallization parameter, and refraction losses, which have been calculated to understand the need for amorphous chalcogenide compositions that can be applied for optical device purposes. The effect of Cu content on the non-linear index of refraction (n2) and third-order susceptibility (χ (3)) has been studied. The value of n2 increased from 13.88 × 10−12 to 60.2 × 10−12 esu, whereas the value of χ (3) rose from 7.6 × 10−11 to 38.83 × 10−13 esu with the addition of denser and higher atomic radius elements Cu in the CGS system. Overall, the composition of Cu13Ge32S55 is suitable, as all-optical parameters show the maximum values that can be used for optical device purposes.

Effect of phosphate post-treatment on corrosion behavior of cerium-based conversion coated Mg-4.0Y-4.0Zn-0.5Zr-0.2Ca (wt.%) alloys

The present study aims to investigate the effect of cerium-based conversion coating and phosphate post-treatment on the corrosion behavior of Mg-4.0Y-4.0Zn-0.5Zr-0.2Ca (wt.%) alloy (WZ44) in chlorinated solution. In this regard, as-cast and forged WZ44 alloy was subjected to cerium salt bath treatment at ambient followed by NaH2PO4 solution at 85 °C. The morphological evolution and chemical composition of the composite coating were examined using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), two and three-dimensional surface topography, and X-ray photoelectron spectroscopy (XPS) reveal the formation of complex phase mixture of CeO2, Ce2O3, CePO4, Mg(OH)2, and unknown hydrated compounds. The as-prepared cerium conversion coating possesses nodular CeO2 precipitates with abundant mud-cracks features originating due to hydrogen evolution and film dehydration-induced tensile stress. However, phosphate treatment develops a relatively smoother and compact coating with minimum surface roughness and conversion of nodular CeO2 precipitates into CePO4, albeit with few fine cracks. The tape adhesion and scratch test disclose that coating delamination predominant in cerium conversion coated specimens was reduced drastically by phosphate treatment with ∼16–23 % improvement in scratch hardness. Corrosion in terms of mass loss and potentiodynamic polarization (PDP) highlights that phosphate treatment improves the corrosion rate by ∼25–65 % compared to blank. Electrochemical impedance spectroscopy (EIS) demonstrates that coating (Rcoat) and polarization resistance (RP) at the film-metal interface was substantially increased to ∼953 Ω cm2 and ∼729 Ω cm2 for phosphate-treated specimens with a progressive increase in semicircular capacitive loop diameter indicating surface passivation. Overall, a duplex coating strategy with cerium salt bath followed by phosphate treatment can essentially develop a compact double-layer that effectively minimizes severe corrosion of WZ44 alloy in a 0.1 M NaCl electrolyte.

Lewis and berry phases for a gravitational wave interacting with a quantum harmonic oscillator

In this work, we compute the Lewis and Berry phases for a gravitational wave interacting with a two dimensional quantum harmonic oscillator in the transverse-traceless gauge. We have considered a gravitational wave consisting of the plus polarization term only. Considering the cross polarization term to be absent makes the Hamiltonian separable in terms of the first and the second spatial coordinates. We then compute the Lewis phase by assuming a suitable form of the Lewis invariant considering only quadratic order contributions from both position and momentum variables. Next, we obtain two Lewis invariants corresponding to each separable part of the full Hamiltonian of the system. Using both Lewis invariants, one can obtain two Ermakov-Pinney equations, from which we finally obtain the corresponding Lewis phase. Then making an adiabatic approximation enables us to isolate the Berry phase for the full system. After this we obtain some explicit expressions of the Berry phase for a plane polarized gravitational wave with different choices of the harmonic oscillator frequency. Finally, we consider a gravitational wave with cross polarization only interacting with an isotropic two dimensional harmonic oscillator. For this we obtain the Lewis phase and the total Berry phase of the system, which is found to be dependent upon the cross polarization part of the gravitational wave.

Ionic doping engineered Ce2(Zr1−xBx)3(MoO4)9 (B[dbnd]Cd1/3Nb2/3, Cd1/3Ta2/3) ceramics: Structural, chemical bond, and microwave/terahertz dielectric performance

A series of Ce2(Zr1−xBx)3(MoO4)9 ceramics, where BCd1/3Nb2/3, Cd1/3Ta2/3 (abbreviated as CZ1−xNx, CZ1−xTx), were synthesized using the classical solid-state reaction method. This study focused on the intrinsic mechanisms affected by doping in terms of chemical bond parameters, polarizability, lattice parameters, and bond valence. X-ray diffraction (XRD) results showed that Cd/Nb and Cd/Ta were solidly dissolved into the matrix lattice, which crystallized in a pure trigonal structure (Space group of R-3c, No. 167). According to the Phillips-van Vechten-Levine (P–V-L) theory, the chemical bond features have been parameterized for exploring the relationships between crystal structure and property. Interestingly, the findings indicated that the dielectric parameters varied closely with the chemical bond features of Zr1–O4. Far-infrared reflectivity (FIR) spectrum and terahertz time-domain (THz-TD) were used to obtain information on lattice vibration. The results showed that the complex permittivity extrapolated from THz-TD was closer to the measured value (at microwave) than the former. The relaxation polarization mechanism may be a key intrinsic factor affecting dielectric loss. Additionally, the bond valence results showed a linear relationship between Zr1–O4 and τf. CZ1−xNx and CZ1−xTx exhibited Qf values that were 2.86 and 5.46 times greater than the matrix, respectively, with low permittivity (εr, roughly 10) suitable for high-frequency communication materials. Notably, CZ0.94T0.06 ceramic achieved excellent performance with Qf = 103,974 GHz, εr = 10.63, and τf = −17.68 ppm/°C at 725 °C.

Study of ferromagnetism, and thermoelectric behavior of double perovskites K2Z(Cl/Br)6 (Z = Ta, W, Re) for spintronic, and energy application

Spintronic is the developing technology which probes the properties of quantum devices with spin of electrons which reduce the size and enhance its speed. Therefore, here the role of 5d electrons and thermoelectric characteristics of double perovskites (DPs) K2ZCl/Br6 (Z = Ta, W, Re) elaborated comprehensively by density functional theory (DFT). The Heisenberg model spin polarization density (SP) has been applied to evaluate the Curie temperature (Tc) and spin polarization factor. The tolerance factor (tF) and formation energy (ΔH) have been calculated to confirm the stability of structures. Ferromagnetism has been discussed in terms of spin polarization, crystal field energy (ΔCF) and exchange energies (Δ(d), Δ(pd)). The double exchange mechanism, and exchange constants ensure the role of electrons spin in ferromagnetism instead of segregation of transition metal ions. The transferring of magnetic moments of transitions metals to nonmagnetic sites (K, Cl, Br) show the exchange of spin of electrons and integer values of total magnetic moment show 100 % spin polarization. Finally, the transport properties are studied in standings of electrical and thermal conductivities. The large value of Seebeck coefficient and power factor ensure the importance of studied DPs for thermoelectric generators.

Effect of Absorption and Polarization Potentials in The Distorted Wave Calculation of Positron Impact Excitation of Autoionizing State of Rubidium

This study focuses on the scattering of positrons and rubidium atoms. We utilized the distorted wave approach to compute the cross sections and alignment parameter from near excitation threshold up to 1500 eV. Our system employed Clementi and Roetti (1974) multi-zeta Roothan-Hatree-Fock wave. We employed a complex distortion potential comprising static, absorption, and polarization terms to calculate cross sections and the alignment parameter. Our results were compared with other available studies, and we found that including polarization and absorption potentials significantly affected the cross-sections and the alignment parameter, especially at low-impact energies. These two potentials enhanced the accuracy of both the cross-section and alignment parameter results.

Mechanical, and corrosive properties of AA7075 aluminium reinforced with rice husk ash particulates

The mechanical and corrosive properties of AA7075 alloy reinforced with rice husk ash (RHA) particles were studied. AA7075 matrix composite reinforced with varying percentage weight compositions of rice husk ash particles (5%, 10%, 15% and 20% wt) were prepared using stir casting technique. The mechanical, and corrosive properties of the new material were compared with that of the matrix alloy. The mechanical properties were also improved due to the automated stirring action employed during the casting process. AA7075-RHA composites had improved mechanical properties compared to the base matrix (AA7075). In terms of tensile strength there was an increase in this mechanical property with an increase in weight fraction of RHA particle (51% at 10% RHA), hardness (25.67% at 20% RHA), while for impact resistance, the reverse was the case as there was a 10.98% decrease in the resistance of the composite as the reinforcement fraction increased from 0%–20% RHA. The progressive decreases in the impact strength of the reinforced composite were probably due to agglomeration and non-homogeneity at higher reinforcements values. Corrosion experiments carried out showed improved properties in the reinforced composite compared to the unreinforced alloy, the corrosive properties improved with an increase in weight fraction of RHA in terms of weight loss (20.63% at 10% RHA), potentio-dynamic polarization (30.7% at 10% RHA) and open circuit potential (1.60% at 20%RH). The developed composite may be suitably applied in high-speed rotating shafts and automotive engineered brake parts.

Partially coherent twisted vector vortex beam enabling manipulation of high-dimensional classical entanglement.

In this paper, we present a novel form of a partially coherent beam characterized by classical entanglement in higher dimensions. We coin the term "twisted vector vortex (TVV) beam" to describe this phenomenon. Similar to multi-partite quantum entangled states in higher dimensions, the partially coherent twisted vector vortex beam possesses distinct properties such as non-uniform polarization, vortex phase, and twist phase. Through experiments, we offer empirical evidence for these three degrees-of-freedom in the light field. The results demonstrate that the state of the light is inseparable in terms of polarization and orbital angular momentum (OAM) modes. Additionally, the twist phase introduces an additional dimension in controlling the vector vortex beam. This research reveals the possibility of new controlling dimensions in classical entanglement through the chirality of coherence within partially coherent light. Consequently, this opens up new avenues for the utilization of partially coherent light in both classical and quantum domains.

Anisotropic Airy beams

Anisotropic Airy beams are presented as solutions to the parabolic wave equation. We obtain the cross polarization terms in the new beams using the elegant Mukunda–Simon–Sudarshan matrix substitution rule for transition from Helmholtz scalar wave optics to the Maxwell vector wave optics. Other properties such as the intensity distribution are also presented.