Atomic Polarization Research Articles

An Inductively Coupled Plasma System for Investigating Spectropolarimetric Responses of Solar Plasmas to Anisotropic Fields

High precision measurements and accurate modeling of atomic polarization under three-dimensional radiation transfer are crucial to understand the structures of magnetized solar plasmas. To develop and validate spectropolarimetric measurements and analyses, we set up an inductively coupled plasma (ICP) generator designed especially for ∼1-eV plasmas interacting with radiation and weak magnetic fields. The device was put in front of the focal plane of the Horizontal Spectrograph of the Domeless Solar Telescope at Hida Observatory of Kyoto University. In helium discharges, the typical electron temperature, electron density, and helium column density of the ICP are comparable values to those of solar prominences, and the direct comparison of spectra shows almost the same opacity at He I 1083 nm. Magnetic and radiation fields were introduced to the ICP, and the system successfully reproduced reasonable spectropolarimetric signals as compared with those from the solar prominences.

Polar Nitride Perovskite LaWN3-δ with Orthorhombic Structure.

Nitride perovskite LaWN3 has been predicted to be a promising ferroelectric material with unique properties for diverse applications. However, due to the challenging sample preparation at ambient pressure, the crystal structure of this nitride remains unsolved, which results in many ambiguities in its properties. Here, the authors report a comprehensive study of LaWN3 based on high-quality samples synthesized by a high-pressure method, leading to a definitive resolution of its crystal structure involving nitrogen deficiency. Combined with theoretical calculations, these results show that LaWN3 adopts an orthorhombic Pna21 structure with a polar symmetry, possessing a unique atomic polarization along the c-axis. The associated atomic polar distortions in LaWN3 are driven by covalent hybridization of W: 5d and N: 2p orbitals, opening a direct bandgap that explains its semiconducting behaviors. The structural stability and electronic properties of this nitride are also revealed to be closely associated with its nitrogen deficiency. The success in unraveling the structural and electronic ambiguities of LaWN3 would provide important insights into the structures and properties of the family of nitride perovskites.

Symmetrized Drude Oscillator Force Fields Improve Numerical Performance of Polarizable Molecular Dynamics

Drude oscillator potentials are a popular and computationally efficient class of polarizable models that represent each polarizable atom as a positively charged Drude core harmonically bound to a negatively charged Drude shell. We show that existing force fields that place all non-Coulomb forces on the Drude core and none on the shell inadvertently couple the dipole to non-Coulombic forces. This introduces errors where interactions with neutral particles can erroneously induce atomic polarization, leading to spurious polarizations in the absence of an electric field, exacerbating violations of equipartition in the employed Carr-Parinello scheme. A suitable symmetrization of the interaction potential that correctly splits the force between the Drude core and shell can correct this shortcoming, improving the stability and numerical performance of Drude oscillator-based simulations. The symmetrization procedure is straightforward and only requires the rescaling of a few force field parameters.

Nearly Hamiltonian dynamics of laser systems

The Arecchi-Bonifacio (or Maxwell-Bloch) model is the benchmark for the description of active optical media. However, in the presence of a fast relaxation of the atomic polarization, its implementation is a challenging task even in the simple ring-laser configuration, due to the presence of multiple timescales. In this paper we show that the dynamics is nearly Hamiltonian over timescales much longer than those of the cavity losses. More precisely, we prove that it can be represented as a pseudo spatiotemporal pattern generated by a nonlinear wave equation equipped with a Toda potential. The existence of two constants of motion (identified as pseudo energies), thereby elucidates the reason why it is so hard to simplify the original model: the adiabatic elimination of the polarization must be accurate enough to describe the dynamics correctly over unexpectedly long timescales. Finally, since the nonlinear wave equation with Toda potential can be simulated on much longer times than the previous models, this opens up the route to the numerical (and theoretical) investigation of realistic setups.

Nonzero-Order Resonances in Single-Beam Spin-Exchange Relaxation-Free Magnetometers

Zero-field optically pumped magnetometers operating in the spin-exchange relaxation-free (SERF) regime have been extensively studied, and usually depend on zeroth-order parametric resonance to measure the magnetic field. However, the studies conducted on this topic lack thorough analyses and in-depth discussion of nonzero-order magnetic resonances in single-beam SERF magnetometers. In this paper, we analyzed the nonzero-order resonance, especially the first-order resonance, based on a single-beam SERF magnetometer, and discussed its various applications. A comprehensive theoretical analysis and experiments were conducted with respect to multiple functions, including nonzero finite magnetic field measurements, spin polarization measurement, and in situ coil constant calibration. The results showed that first-order resonance can be utilized for nonzerofinite magnetic field measurements, and the spin polarization of alkali-metal atoms can be determined by measuring the slowing-down factor using the resonance condition. Furthermore, acquiring the first-order resonance point at an equivalent zero pump light power through fitting offers an approach for quick and precise in situ coil constant calibration. This study contributes to the applications of SERF magnetometers in nonzero finite magnetic fields.

Bend-Induced Ferroelectric Domain Walls in α-In2Se3.

The low bending stiffness of atomic membranes from van der Waals ferroelectrics such as α-In2Se3 allow access to a regime of strong coupling between electrical polarization and mechanical deformation at extremely high strain gradients and nanoscale curvatures. Here, we investigate the atomic structure and polarization at bends in multilayer α-In2Se3 at high curvatures down to 0.3 nm utilizing atomic-resolution scanning transmission electron microscopy, density functional theory, and piezoelectric force microscopy. We find that bent α-In2Se3 produces two classes of structures: arcs, which form at bending angles below ∼33°, and kinks, which form above ∼33°. While arcs preserve the original polarization of the material, kinks contain ferroelectric domain walls that reverse the out-of-plane polarization. We show that these kinks stabilize ferroelectric domains that can be extremely small, down to 2 atoms or ∼4 Å wide at their narrowest point. Using DFT modeling and the theory of geometrically necessary disclinations, we derive conditions for the formation of kink-induced ferroelectric domain boundaries. Finally, we demonstrate direct control over the ferroelectric polarization using templated substrates to induce patterned micro- and nanoscale ferroelectric domains with alternating polarization. Our results describe the electromechanical coupling of α-In2Se3 at the highest limits of curvature and demonstrate a strategy for nanoscale ferroelectric domain patterning.

A microwave-enhanced method able to substitute traditional pyrometallurgy for the future of metals supply from spent lithium-ion batteries

This work presents a new and promising method to recover Li, Co, Mn, and Ni from spent LIBs, based on a hybrid heating mechanism, obtained by using microwave radiation. Due to the presence of graphite, the heating is induced by the interfacial polarization of carbon atoms. The hybrid heating is based on the synergistic combination of an external susceptor with a graphite crucible. The system allows reaching carbothermic reduction conditions of black mass originating from spent LIBs, with a treatment of only a few minutes considering an electromagnetic radiation power ⋜1000 W, without any other additives. This process reduces the required associated energy by more than 2 orders of magnitude in comparison to conventional thermal treatments.The thermal process is followed by leaching in water and l-malic acid, obtaining a recovery process resulting to be competitive with metals extraction from respective ores.

A Novel Measurement Method for Spin Polarization Three Axis Spatial Distribution in Spin-Exchange Relaxation Free Atomic Magnetometer

The measurement of atomic spin polarization distribution in spin-exchange relaxation free (SERF) magnetometer is an important topic for improving the sensitivity and consistency of multi-channel magnetic field measurement applications. A novel spin polarization spatial distribution measurement method is presented based on the transient response of the magnetometer after modulating the pumped light with a chopper. Polarization is obtained by a slow-down factor based on the fast spin-exchange interaction effects. Longitudinal and transverse polarization distributions are measured simultaneously without interrupting the operation of the SERF status. Under different oscillating magnetic fields, the spin polarization is measured at the cell centroid. Residual magnetic field inside the magnetometer is obtained from the linear relationship between the precession frequency and the oscillating magnetic field. The one-dimensional polarization distributions in the x, y, and z axes are measured using a digital micromirror device with a resolution of 0.25 cm. The measurement results conform to the Lambert-Bier absorption law and the Gaussian distribution law. Furthermore, 7 × 7 two-dimensional spatial distribution measurements of polarization on the xy and yz planes are performed. Nonuniformity of 1.04 in the xy plane and 1.82 in the yz plane in the built magnetometer. Compared with other measurement methods, the distribution measurement method proposed is independent of optical depth and suitable for low polarization and high polarization applications. Based on the results of the proposed measurement method of spin polarization spatial distribution, further compensation can improve the application consistency of multi-channel magnetic field measurements and improve the sensitivity of single-channel differential measurements.

Ground state and polarization of a hydrogenlike atom near a Weyl semimetal

In this paper we study the effects of a topological Weyl semimetal (WSM) upon the ground state and polarization of an hydrogen-like atom near its surface. The WSM is assumed to be in the equilibrium state and at the neutrality point, such that the interaction between the atomic charges and the material is fully described (in the non retarded regime) by axion electrodynamics, which is an experimentally observable signature of the anomalous Hall effect in the bulk of the WSM. The atom-WSM interaction provides additional contributions to the Casimir-Polder potential thus modifying the energy spectra and wave function, which now became distance dependent. Using variational methods, we solve the corresponding Schr\"{o}dinger equation for the atomic electron. The ground state and the polarization are analyzed as a function of the atom-surface distance, and we directly observe the effects of the nontrivial topology of the material by comparing our results with that of a topologically trivial sample. We also study the impact of the medium's permittivity by assuming a hydrogen atom in vacuum, and a donor impurity in the semiconductors gallium arsenide (GaAs) and gallium phosphide (GaP). We found that the topological interaction behaves as an effective-attractive charge so that the electronic cloud tends to be polarized to the interface of materials. Moreover, the loss of wave-function normalization is interpreted as a critical location from below which the bound state is broken.

Customizing the structure and chemical composition of ultralight carbon foams for superior microwave absorption performance

Developing biomass-derived three-dimensional porous carbon materials (porous carbon foam, PCF) has become a common strategy to obtain lightweight and efficient electromagnetic microwave-absorbing materials. Without the introduction of a template and subsequent activation process, several ultra-lightweight honeycomb PCF samples were successfully prepared from dried ballonflower/yamakurage (DB) by simple calcination. In addition, the calcination temperature plays a decisive role in regulating the pore size, composition and microwave absorption properties of PCF samples. Furthermore, it is worth noting that different cutting directions also influenced the hole size of the PCF sample and the microwave absorption performances. Under the combined effects of multiple reflections and scattering of PCF porous structure, dipole polarization of abundant heterogeneous atoms and good conductive loss of carbon material, the vertical cutting sample PCF-900V exhibits optimal microwave absorption performances with the minimal reflection loss (RLmin) value of −46.95 dB at 1.46 mm thickness and the effective absorption bandwidth (EAB) value of 5.52 GHz at 1.72 mm matching thickness respectively, indicating its great potential for application as a promising lightweight and efficient microwave absorbing material.

In situ simultaneous measurement of magnetic coil constants and nonorthogonal angles using atomic magnetometers

An in situ simultaneous measurement of magnetic coil constants and nonorthogonal angles method is proposed using the atomic magnetometer. Based on the transient response of the atomic spin polarization under the different magnetic fields, we establish the corresponding measurement model of magnetic coil constants and nonorthogonal angles through the relationship between the Larmor precession frequency and the external magnetic field. By this model, we experimentally obtained the coil constants of x , y, and z axes are, respectively, 9.04 ± 0.10, 8.94 ± 0.07, and 4.34 ± 0.02 nT / V in our system. The nonorthogonal angles are 89.04 deg between x axis and y axis, 88.60 deg between y axis and z axis, and 91.15 deg between z axis and x axis. This method can be used to simultaneously measure magnetic coil constants and nonorthogonal angles without relying on external instruments, which provides a basic guarantee for the accurate calculation sensitivity of spin-exchange-relaxation-free atomic magnetometers, especially for miniaturized atomic magnetometers.

Development of AMOEBA Polarizable Force Field for Rare-Earth La3+ Interaction with Bioinspired Ligands.

Rare-earth metals (REMs) are crucial for many important industries, such as power generation and storage, in addition to cancer treatment and medical imaging. One promising new REM refinement approach involves mimicking the highly selective and efficient binding of REMs observed in relatively recently discovered proteins. However, realizing any such bioinspired approach requires an understanding of the biological recognition mechanisms. Here, we developed a new classical polarizable force field based on the AMOEBA framework for modeling a lanthanum ion (La3+) interacting with water, acetate, and acetamide, which have been found to coordinate the ion in proteins. The parameters were derived by comparing to high-level ab initio quantum mechanical (QM) calculations that include relativistic effects. The AMOEBA model, with advanced atomic multipoles and electronic polarization, is successful in capturing both the QM distance-dependent La3+-ligand interaction energies and experimental hydration free energy. A new scheme for pairwise polarization damping (POLPAIR) was developed to describe the polarization energy in La3+ interactions with both charged and neutral ligands. Simulations of La3+ in water showed water coordination numbers and ion-water distances consistent with previous experimental and theoretical findings. Water residence time analysis revealed both fast and slow kinetics in water exchange around the ion. This new model will allow investigation of fully solvated lanthanum ion-protein systems using GPU-accelerated dynamics simulations to gain insights on binding selectivity, which may be applied to the design of synthetic analogues.

Synthesis, X-Ray Structure Analysis, Computational Investigations, and In Vitro Biological Evaluation of New Thiazole-Based Heterocycles as Possible Antimicrobial Agents

The thiazole ring is found in many pharmaceutical and natural products. In this article, the convenient synthesis of two new hybrid molecules carrying the thiazole nucleus linked to pyrazole or pyridine rings is described. The structure of the synthesized hybrids is confirmed by spectroscopic and X-ray analysis. Using Hirshfeld analysis, the molecular packing of thiazolyl-pyrazole hybrid 2 is controlled by many weak S…S, S…C, S…H, C…N, N…H, C…C, C…H and H…H non-covalent interactions. The percentage contributions of these contacts in the molecular packing are 1.6, 0.2, 22.1, 0.7, 7.9, 0.4, 27.5, and 39.6%, respectively. DFT calculations predicted the natural atomic charges, polarity, and frontier molecular orbitals and their derived reactivity parameters.

Transferability of the Electrostatic Parameters of the Polarizable Gaussian Multipole Model.

Accuracy and transferability are the two highly desirable properties of molecular mechanical force fields. Compared with the extensively used point-charge additive force fields that apply fixed atom-centered point partial charges to model electrostatic interactions, polarizable force fields are thought to have the advantage of modeling the atomic polarization effects. Previous works have demonstrated the accuracy of the recently developed polarizable Gaussian multipole (pGM) models. In this work, we assessed the transferability of the electrostatic parameters of the pGM models with (pGM-perm) and without (pGM-ind) atomic permanent dipoles in terms of reproducing the electrostatic potentials surrounding molecules/oligomers absent from electrostatic parameterizations. Encouragingly, both the pGM-perm and pGM-ind models show significantly improved transferability than the additive model in the tests (1) from water monomer to water oligomer clusters; (2) across different conformations of amino acid dipeptides and tetrapeptides; (3) from amino acid tetrapeptides to longer polypeptides; and (4) from nucleobase monomers to Watson-Crick base pair dimers and tetramers. Furthermore, we demonstrated that the double-conformation fittings using amino acid tetrapeptides in the αR and β conformations can result in good transferability not only across different tetrapeptide conformations but also from tetrapeptides to polypeptides with lengths ranging from 1 to 20 repetitive residues for both the pGM-ind and pGM-perm models. In addition, the observation that the pGM-ind model has significantly better accuracy and transferability than the point-charge additive model, even though they have an identical number of parameters, strongly suggest the importance of intramolecular polarization effects. In summary, this and previous works together show that the pGM models possess both accuracy and transferability, which are expected to serve as foundations for the development of next-generation polarizable force fields for modeling various polarization-sensitive biological systems and processes.

Rotational-electric principles of RNA/DNA and viability

<abstract> <p>Photographic investigations of rising bubbles in seawater revealed that each bubble may conduct a single or bi-spiraling motion, which resemble architecture of RNA or DNA respectively. The rotational motion results from acceleration of ionic hydrates, which are separated to anionic and cationic domains at the upper and bottom curvatures of the bubble. Afterwards, rotational motion undergoes further acceleration in the bubble upper vortex, followed by deceleration at the vortex tip. During that phase, the spiraling motion cause significant friction that result in polarization of electronegative atoms of H, C, N, O and P. These may be simultaneously arranged around a whirling cationic strands and form phosphate groups, ribose and nitrogen bases equipped with H<sub>2</sub> and H<sub>3</sub> rotors. It is hypothesized that such hydrogen rotors may operate as generators of electrons, which may be detached from valence shells of electropositive atoms. Then, electrons may flow via nitrogen bases and deoxyribose or ribose to phosphate groups. Next, the negatively charged edges of phosphate groups may attract cationic hydrates and energize their rotational motion in the grooves, then causing also its spiraling projection outward. That may be responsible for replication of nucleotides and its arrangement along the cationic flow into RNA or DNA polymers, in the same manner as originally produced by rising bubbles. Moreover, it points that hydrogen rotors may generate energy needed for viability as well as interact with all physical and chemical fields.</p> </abstract>

X-ray sensitive selenium-containing Ru complexes sensitize nasopharyngeal carcinoma cells for radio/chemotherapy.

Radiotherapy has been extensively applied to cancer therapy in clinical trials. However, radiation resistance and dose limitation generally hamper the efficacy of radiotherapy. There is an urgent need for radiosensitizers with high efficiency and safety to enhance the anti-tumor effect of radiotherapy. In this paper, a selenium-containing (Se) ruthenium (Ru) complex (RuSe) was designed as a radiosensitizer to synergistically augment the killing effect of radiotherapy on nasopharyngeal carcinoma cells. In this system, the heavy atomic effect of Ru enhances the photoelectron production triggered by X-rays, thus inducing a burst of reactive oxygen species (ROS). In addition, Se atoms with a strong polarization property were introduced into the ligand of the metal complex to enhance the tumor chemo/radiotherapy effect. Consequently, RuC with a weak atomic polarization effect, as a comparison for RuSe, was also rationally explored to elucidate the role of Se atoms on chemo/radiotherapy sensitization. Indeed, compared with RuC, RuSe at a sub-toxic dose was able to potentiate the lethality of radiotherapy after preconditioning with cancer cells, by inducing ROS over-production, decreasing the mitochondrial membrane potential, and arresting the cell cycle at the sub-G1 phase. Furthermore, upon radiation, RuSe was superior to RuC, by inducing apoptotic cell death by activating caspase-3, -8, and -9. In summary, this study not only demonstrates an effective and safe strategy for the application of RuSe complexes to the cancer-targeted chemo/radiotherapy of human cancers, but also sheds light on the potential mechanisms of such Se-containing drugs as efficient radiotherapy sensitizers.

Different Configurations of Radio-Frequency Atomic Magnetometers-A Comparative Study.

We comprehensively explore different optical configurations of a radio-frequency atomic magnetometer in the context of sensor miniaturisation. Similarities and differences in operation principles of the magnetometer arrangements are discussed. Through analysis of the radio-frequency and noise spectra, we demonstrate that all configurations provide the same level of atomic polarisation and signal-to-noise ratio, but the optimum performance is achieved for significantly different laser powers and frequencies. We conclude with possible strategies for system miniaturisation.

Origin and Acceleration of Insoluble Li2 S2 -Li2 S Reduction Catalysis in Ferromagnetic Atoms-based Lithium-Sulfur Battery Cathodes.

Accelerating insoluble Li2 S2 -Li2 S reduction catalysis to mitigate the shuttle effect has emerged as an innovative paradigm for high-efficient lithium-sulfur battery cathodes, such as single-atom catalysts by offering high-density active sites to realize in situ reaction with solid Li2 S2 . However, the profound origin of diverse single-atom species on solid-solid sulfur reduction catalysis and modulation principles remains ambiguous. Here we disclose the fundamental origin of Li2 S2 -Li2 S reduction catalysis in ferromagnetic elements-based single-atom materials to be from their spin density and magnetic moments. The experimental and theoretical studies disclose that the Fe-N4 -based cathodes exhibit the fastest deposition kinetics of Li2 S (226 mAh g-1 ) and the lowest thermodynamic energy barriers (0.56 eV). We believe that the accelerated Li2 S2 -Li2 S reduction catalysis enabled via spin polarization of ferromagnetic atoms provides practical opportunities towards long-life batteries.

Origin and Acceleration of Insoluble Li2S2−Li2S Reduction Catalysis in Ferromagnetic Atoms‐based Lithium‐Sulfur Battery Cathodes

AbstractAccelerating insoluble Li2S2−Li2S reduction catalysis to mitigate the shuttle effect has emerged as an innovative paradigm for high‐efficient lithium‐sulfur battery cathodes, such as single‐atom catalysts by offering high‐density active sites to realize in situ reaction with solid Li2S2. However, the profound origin of diverse single‐atom species on solid‐solid sulfur reduction catalysis and modulation principles remains ambiguous. Here we disclose the fundamental origin of Li2S2−Li2S reduction catalysis in ferromagnetic elements‐based single‐atom materials to be from their spin density and magnetic moments. The experimental and theoretical studies disclose that the Fe−N4‐based cathodes exhibit the fastest deposition kinetics of Li2S (226 mAh g−1) and the lowest thermodynamic energy barriers (0.56 eV). We believe that the accelerated Li2S2−Li2S reduction catalysis enabled via spin polarization of ferromagnetic atoms provides practical opportunities towards long‐life batteries.

High-resolution optical magnetic resonance imaging of electronic spin polarization in miniaturized atomic sensors

Miniaturized atomic sensors of magnetic field and inertia have great potential to be applied as geophysical instruments and in the detection of biomolecules. The distribution of the electronic spin polarization plays a key role as it defines the amount of noble gas that can achieve a state of hyperpolarization, which in turn determines the technique's accuracy and, consequently, its resolution. However, the current techniques for electronic spin polarization imaging are unsuited for the operating conditions of miniaturized atomic sensors besides only accomplishing submillimeter spatial resolution. In this study, optical magnetic resonance is applied to obtain electronic spin polarization images with a spatial resolution of 60 μm experimentally and 10 μm theoretically. This corresponds to an increase by one order of magnitude in resolution when compared to previous reports of electronic spin polarization imaging. By sweeping the RF frequency of the magnetic field while applying a magnetic field gradient of 0.22 μT/mm, it is possible to measure electronic spin polarization images for different average photon spins and pump beam positions. Spin polarization images present a high degree of correlation with pump beam images. Furthermore, this image method can be applied to suppressing the inhomogeneities in miniaturized cells, leading to a gain in signal-to-noise ratio. It also offers an opportunity to experimentally perform two-dimensional atomic polarization manipulation in the gas phase, optically transparent solids, and liquids.