Polarity Time Research Articles

Room-temperature unidirectional routing of valley excitons of monolayer WSe2 via plasmonic near-field interference in symmetric nano-slits.

Due to the short valley polarization time, it is hardly to separate opposite valley pseudospin of transition metal dichalcogenides (TMDs) for their practical applications in valleytronics. Coupling TMDs to unidirectional surface plasmon polariton (SPP) can overcome this obstacle. However, it is required to break the symmetry to induce the asymmetric coupling between valley exciton dipole and SPP to route valley exciton in previously proposed strategies. Herein, by utilizing a new mechanism that near-field interference can create directional SPP in symmetric nanostructures, we realize directional routing of valley exciton emission of monolayer WSe2 at room temperature with a symmetric nano-slits array. The near-field interference enabled directional SPP in our device not only render the exciton diffusion length increase from 0.9 to 3.0 μm, but also lead to a valley exciton separation length of 0.7 μm with degree of valley polarization up to 22 %. This valley excitons separation is attributed to the non-flat WSe2 in the nano-slits region, which makes the exciton dipoles present in-plane and out-of-plane simultaneously. Our work provides a convenient and promising strategy towards room temperature on-chip integrated valleytronic devices.

Probing the variations in the timing of the Sun’s polar magnetic field reversals through observations and surface flux transport simulations

ABSTRACT The polar field reversal is a crucial process in the cyclic evolution of the large-scale magnetic field of the Sun. Various important characteristics of a solar cycle, such as its duration and strength, and also the cycle predictability, are determined by the polar field reversal time. While the regular measurements of solar magnetic field have been accumulated for more than half a century, there is no consensus in the heliophysics community concerning the interpretation of the Sun’s polar field measurements and especially the determination of polar field reversal time. There exists a severe problem of non-reproducibility in the reported results even from studies of the same observational data set, and this causes an obstacle to make more accurate forecasts of solar cycle. Here, we analyze the solar magnetograms from four instruments for the last four cycles, to provide a more correct interpretation of the polar field observations and to find more accurate time of the reversals. We show the absence of triple (multiple) reversals in Cycles 21–24, significant variations in the time interval between reversals in the hemispheres and in the time interval between a reversal and a cycle beginning. In order to understand the origin of the reversal time variation, we perform Surface Flux Transport (SFT) simulations and find out that the presence of the ‘anomalous’ bipolar magnetic regions (BMRs) in different phases of a cycle can cause cycle-to-cycle variations of the reversal time within the similar range found in observations.

Electron spin dynamics in multi-energy level systems under the excitation of circular polarization modulated continuous-wave laser

Time-resolved photoluminescence spectroscopy under the excitation of circular polarization modulated continuous-wave laser can quantitatively extract the electron spin polarization degrees and electron spin relaxation time, providing an important tool to detect electron spin dynamics. We theoretically analyze the electron spin dynamics in four-, six- and eight-energy level systems under the excitation of circular polarization modulated continuous-wave laser by solving the rate equations of electron population. The relationship between the time-resolved photoluminescence spectra and the spin information of the spin system is provided. The electron spin polarization degrees of the ground and excited states, the establishment time of the steady-state spin polarization and the electron spin relaxation time can be directly derived from the time-resolved photoluminescence spectra. And the theoretical model is verified experimentally by the measurement of electron spin dynamics in Ce3+: YAG crystal.

Formulation and testing of a high-tin borosilicate nuclear waste glass for in-can melting

Borosilicate waste glasses were successfully developed to immobilize two high-level waste raffinate streams via an in-can melter process with an Inconel 601 canister at 1050 °C. Measured viscosity and crystallinity thermal profiles were within the targeted processing constraints for the in-can melter process. Measured chemical durability of the glass by ASTM C1285–21 (Method A), ranged from normalized loss of boron, NL(B) = 1.44 – 2.65 g·m−2, and NL(B) decreased with increased waste loading, accompanied by increased SnO2 crystallinity. Measured corrosion of the in-can melter canister by a glass melt showed that Inconel 601 performed well at 1100 °C for up to 500 hr. Resistance polarization measurements versus time revealed that Inconel 601 corrosion rates in (and by) glass melts decreased from an initial rate of 63 mm·y−1 down to 10.2 mm·y−1 after 137 h with increased duration, which was attributed to formation of an oxide passivation layer (mainly Cr2O3) at the alloy-glass interface.

Modelling and correcting the impact of RF pulses for continuous monitoring of hyperpolarized NMR.

Monitoring the build-up or decay of hyperpolarization in nuclear magnetic resonance requires radio-frequency (RF) pulses to generate observable nuclear magnetization. However, the pulses also lead to a depletion of the polarization and, thus, alter the spin dynamics. To simulate the effects of RF pulses on the polarization build-up and decay, we propose a first-order rate-equation model describing the dynamics of the hyperpolarization process through a single source and a relaxation term. The model offers a direct interpretation of the measured steady-state polarization and build-up time constant. Furthermore, the rate-equation model is used to study three different methods to correct the errors introduced by RF pulses: (i)a correction ( denoting the RF pulse flip angle), which is only applicable to decays; (ii)an analytical model introduced previously in the literature; and (iii)an iterative correction approach proposed here. The three correction methods are compared using simulated data for a range of RF flip angles and RF repetition times. The correction methods are also tested on experimental data obtained with dynamic nuclear polarization (DNP) using 4-oxo-TEMPO in H glassy matrices. It is demonstrated that the analytical and iterative corrections allow us to obtain accurate build-up times and steady-state polarizations (enhancements) for RF flip angles of up to 25 during the polarization build-up process within % error when compared to data acquired with small RF flip angles ( ). For polarization decay experiments, corrections are shown to be accurate for RF flip angles of up to 12. In conclusion, the proposed iterative correction allows us to compensate for the impact of RF pulses offering an accurate estimation of polarization levels, build-up and decay time constants in hyperpolarization experiments.

Mediatized Public Sphere and Journalism in Times of Algorithms, Polarization and Crisis of Democracy in Brazil

Mediatized Public Sphere and Journalism in Times of Algorithms, Polarization and Crisis of Democracy in Brazil

Dynamic nuclear polarization by two-pulse phase modulation.

The coherent transfer of electron spin polarization to nuclei by means of a microwave pulse sequence is a promising new approach to enhancing the sensitivity of solid-state nuclear magnetic resonance (NMR). The development of pulse sequences for dynamic nuclear polarization (DNP) of bulk nuclei is far from complete, as is the understanding of what makes a good DNP sequence. In this context, we introduce a new sequence, termed Two-Pulse Phase Modulation (TPPM) DNP. We provide a general theoretical description for electron-proton polarization transfer by periodic DNP pulse sequences and find it in excellent agreement with numerical simulations. In experiments at 1.2T, TPPM DNP generates a higher gain in sensitivity than existing sequences XiX (X-inverse-X) and TOP (Time-Optimized Pulsed) DNP but does so at relatively high nutation frequencies. In contrast, we find that the XiX sequence performs very well at nutation frequencies as low as 7MHz. A combination of theoretical analysis and experimental investigation makes clear that fast electron-proton polarization transfer, due to a well-preserved dipolar coupling in the effective Hamiltonian, correlates with a short build-up time of the dynamic nuclear polarization of the bulk. Experiments further show that the performances of XiX and TOP DNP are affected differently by the concentration of the polarizing agent. These results constitute important reference points for the development of new and better DNP sequences.

Influence of Stratosphere Polar Vortex Variability on the Mesosphere, Thermosphere, and Ionosphere

AbstractThe Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) is used to investigate the influence of stratosphere polar vortex variability on the mesosphere, thermosphere, and ionosphere during Northern Hemisphere winter. Based on 40 simulated Northern Hemisphere winters, the mesosphere and lower thermosphere (MLT) residual circulation is found to depend on whether the stratosphere polar vortex is strong or weak. In particular, during weak stratosphere polar vortex time periods, the MLT circulation anomalies are characterized by clockwise and anti‐clockwise flow in the Northern and Southern Hemispheres, respectively. Opposite, though weaker, anomalies are found to occur during time periods when the stratosphere polar vortex is strong. The MLT circulation anomalies influence the composition of the lower thermosphere, leading to ±5% changes in the thermosphere column integrated atomic oxygen to molecular nitrogen ratio (ΣO/N2). Large differences between strong and weak stratosphere polar vortex events are also found to occur in the semidiurnal migrating tide (SW2) in the MLT, which leads to ±15%–20% differences in the SW2 component of the ionosphere total electron content (TEC) at low latitudes. The WACCM‐X simulation results indicate that variability in the stratosphere polar vortex can explain ∼30% and ∼18% of the quiet time variability in thermosphere ΣO/N2 and the SW2 component of TEC during Northern Hemisphere winter, respectively.

The biological activity features and mineral element analyses of some Inula L. species exhibit natural spread in Mugla (Turkiye)

Medicinal and aromatic plants (MAPs) are rich in nutrients and alternative therapies. Some MAPs become industrial crops that are grown around the world for their nutritional and medicinal properties. The aim of this study was to assess the relationship between mineral nutrient content and antioxidant properties of Inula viscosa (I. viscosa) and Inula graveolens (I. graveolens) species found in the Köyceiz region of Muğla province. In this study, the antioxidant activity values of the extracts obtained were found to be the highest in methanol and acetone extracts of Inula viscosa. In contrast, the lowest in hexane extracts of Inula graveolens species. It was determined that the methanolic extract of I. viscosa had the highest 137.1 (µg PE /mg) a and the hexane extract of I. graveolens L. had the lowest 22.40 (µg PE /mg) total phenolic content. On the other hand, the mineral content of the species (macro (%): N, P, K, Ca, Mg, and micro (ppm): Fe, Mn, Zn, Cu, B) were also taken into consideration. As a result, it was observed by the analysis that there was a significant interaction between the antioxidant activity values of the species and their mineral nutrition. The antioxidant activities of plants are influenced by a variety of factors. The plant's activity is influenced by a number of variables, including the time of harvest (flowering, seed formation, etc.), extraction technique, solvent polarity, fresh or dry plant material, mineral nutrient content, and method. It is thought to broaden perceptions of these plants beyond their nutritional value by putting the antioxidant effects of the plant on a scientific basis. In this study, Inula graveolens L. and Inula viscosa L. demonstrated the potential of plant extracts as a readily available source of natural antioxidants, potential food additives, pharmaceuticals, and pharmaceutics.

Slab tear and rotation imaged with core-refracted shear wave anisotropy

We investigate the complex flow field around the Vrancea slab in Romania, a steeply sinking seismogenic lithospheric block that experienced lateral tear-off and possible rotation. The Vrancea slab is located beneath the South-East Carpathians and generates frequent seismicity despite its remote location from active collisional boundaries. We analyse core-refracted shear wave (SKS) splitting recorded by permanent broadband seismic stations from the Romanian Seismic Network for periods up to 10 years, and compare our results with seismic tomography of the upper mantle. We identify several stations with large backazimuthal variations of SKS fast axis polarization and delay times both in the slab hinge zone, the back-arc and the circum-slab region, indicating complex mantle deformation patterns. To investigate the effect of a two-level rotated slab we invert SKS waveforms using cross-convolutional misfit combined with a neighbourhood search algorithm to model two layers of anisotropy. In the shallow mantle, anisotropy aligns with the upper slab strike and reorients along the strike of the lower slab at depths below the hinge zone. In the back-arc trench-perpendicular anisotropy switches to trench-parallel, due to the recent retreat and roll-back of the slab. Our results have important implications for understanding SKS interference from subducted slab fragments and provide evidence of the recent retreat, break-off and rotation of two Vrancea slab levels sinking into the upper mantle.

Ideology, knowledge, and the assessment of science policy agencies

Abstract In the USA, politics often dominates the conversation surrounding science and related technologies. We also live in times of high political polarization, leading to political debate over scientific discoveries and subsequent policy implications. Given these dynamics, there is much to be learned about the politicization of science, individuals’ policy views, and the public’s relationship with the communication and interpretation of scientific findings. Agencies are often responsible for facilitating scientific research and framing its policy relevance for decision makers and the public. This paper uses data from a large national public opinion survey to investigate citizen attitudes about government science agencies. We theorize that disparities between objective and self-assessed scientific knowledge coupled with ideological cues help frame citizen evaluations of agencies. We find that individuals’ political ideologies and disparities between knowledge types shape citizen assessments of energy-related scientific agencies. These findings have important implications for our understanding of public acceptance of the work of government science agencies.

Investigation on ethylene glycol and glycerol mixture concentration dependent optical, dielectric, electrical, rheological, and thermophysical properties of EG+Gly/ZnO semiconductor nanofluids

Wide energy bandgap metal oxide nanomaterials containing semiconductor nanofluids (SNFs) are technologically established as advanced multifunctional materials for progress in high performance soft condensed devices. Therefore, to strengthen this field of materials, the present study reports in detail the optical, dielectric, electrical, rheological, and thermophysical properties of the SNFs based on ethylene glycol (EG) and glycerol (Gly) mixture of an entire concentration range (Gly volume fractions; 0.00, 0.25, 0.50, 0.75, and 1.00) with a fixed amount of zinc oxide (ZnO) semiconductor nanomaterial (0.05 wt%). These green-formulated EG + Gly/ZnO SNF materials showed a longer stability of the suspended nanoparticles in the highly viscous hydrogen bonded base fluid and exhibited an increase in absorbance with the decrease wavelength of visible range photons and the ZnO electronic transition at about 3.2 eV energy of ultraviolet radiations. Dielectric measurements over the 20 Hz–1 MHz range of these SNFs, at 298.15 K, explained a dominant contribution of the electrode and interfacial polarization processes at low frequencies and the molecular dipole polarization of static permittivity about 40 at the higher frequencies. Electrode polarization and conductivity relaxation times enhanced exponentially when the Gly concentration increased in the EG + Gly base fluid which governs the electrical conductivity decrement from 0.79 to 0.04 μS/cm for these SNFs. The rheological study explained the Newtonian characteristics of EG + Gly/ZnO nanofluids with their base fluid mixture concentration controllable dynamic viscosity in the wide range of 17–702 mPa s, at 298.15 K. The density, refractive index, ultrasound velocity, prominent acoustic parameters, and thermal conductivity are determined and discussed to explore the solid-liquid interaction and interfaces formed in these innovative SNF materials.

Dinosaur and tree-line invasion of southeastern Australia during Cretaceous greenhouse spikes

The paleosol record of the Early Cretaceous Wonthaggi and Eumeralla formations of Victoria reveals a suite of non-calcareous Histosols and Ultisols, as well as stump casts, indicative of humid temperate ecosystems. At some stratigraphic levels, frigid temperatures are indicated by clastic dykes (ice wedges), load casts of mud (periglacial convolutions), and coal-mantled stone rolls (aapamires). The largest tree stumps and thickest paleosols correspond to known Early Cretaceous greenhouse spikes, as revealed by stomatal index of fossil ginkgo leaves, by black shales of oceanic anoxic events, and both marine and non-marine carbon isotopic anomalies. Temperature and CO2 spikes coincide with appearance of broadleaf deciduous forests, including Ginkgo australis, with dinosaurs, monotremes, placentals, early birds and angiosperms. In contrast, permafrost paleosols represent fern-lycopsid tundra and coniferous taiga vegetation. Early Cretaceous CO2 greenhouse spikes allowed southward migration of tree lines and polar biomes several times during the Cretaceous, which was not continuously a hothouse period. The same greenhouse spikes are recorded by maximal marine transgressions in the Great Artesian Basin of Queensland, and the frigid intervals by dropped pebbles and glendonites in South Australia, New South Wales and Arctic regions.

Assessment of the Power Equipment State by Measuring Dielectric Absorption Currents

The need to operate electrical devices the design capabilities of which have been exhausted almost completely under the conditions of more stringent reliability requirements gives rise to increased attention to the development and research of methods for diagnosing the power equipment state. This problem acquires not only a scientific interest, but also practical significance, which follows, in particular, from the mass-scale use of power transformers for operating voltages above 35 kV. One of promising development lines is the method of constructing dielectric absorption spectra, which is based on using the capabilities of isothermal depolarization current measurements. In this case, the information that accumulates as a result of the insulation system’s dielectric medium polarization as a certain number of loosely coupled charges displaced from their locations is adequate (equivalent) to the information obtained as a result of depolarization when measuring the return voltage (RV) value. Owing to the above-mentioned adequacy, it is possible to use the quantity tI(t) as a parameter for monitoring the state of the power equipment insulation system. The spectrum construction algorithm presented in the article is similar to the algorithm for constructing the RV spectrum, but is produced in the course of computer-aided processing of measurement results using the time windows that specify the insulation gap polarization time interval. As a result, it becomes possible not only to produce the dielectric absorption spectrum, but also to calculate the values of the main parameters characterizing the gap state.

Properties of PSN-PZT piezoelectric ceramic powder prepared by fast solid-phase reaction method

Piezoelectric smart materials have been developed from piezoelectric ceramics in various fields, and thus piezoelectric ceramics play a vital role in new materials. However, the complex process involved in the preparation of piezoelectric ceramic powder is expensive, making it difficult to achieve large-scale production. Therefore, in this study, we propose a fast solid-phase method for preparing a piezoelectric ceramic powder (PSN-PZT). The method optimises two procedures in the conventional solid-phase method, saving 43.9% and 34.7% in power cost and time, respectively, and saving 34.8% in total cost. Optimisation of the process did not significantly reduce the piezoelectric and ferroelectric properties of PSN-PZT. The optimal polarisation conditions were a polarisation temperature of 40 ℃, a polarisation time of 25 min, and a polarisation voltage of 3.5 kV. Under these conditions, the piezoelectric constant (d33), dielectric constant εr, and depolarisation rate at 7 days were 895 pC/N, 4340, and 0.34%, respectively. In this paper, the preparation process of the piezoelectric ceramic powder used in the preparation process of piezoelectric composites is optimized, and the preparation of piezoelectric ceramics by the fast solid-phase method provides technical support for the mass production of piezoelectric composites.

ДИЭЛЕКТРИЧЕСКИЕ СВОЙСТВА КЕРАМИК НИОБАТА ТИТАНАТА НАТРИЯ КАЛИЯ

The paper considers the preparation of potassium sodium niobate ceramics doped with titanium in an amount of 5 mol. %. The structure and dielectric properties were investigated in the temperature range 30–650 °C. It is shown that acceptor doping leads to a decrease in the grain size. Violation of stoichiometry in the anionic sublattice contributes to a decrease in the relaxation time of thermal ionic polarization compared to the case of nonstoichiometry in the cationic sublattice.

Misperceptions and Minipublics: Does Endorsement of Expert Information by a Minipublic Influence Misperceptions in the Wider Public?

ABSTRACT As misperceptions undermine the factual basis for public debate, they pose a serious challenge to expert knowledge and the democratic legitimacy of public policy informed by expert evidence. In this paper, we theorize that in times of politicization and polarization of expertise, endorsement of expert information by a minipublic can serve to legitimize expert correction and render it more persuasive in the eyes of individuals. In developing our theoretical argument, we focus on the effect of a minipublic on individuals in the wider public – those who did not participate in such institutions. To test our theoretical predictions, we designed, pre-registered and fielded two experiments in the US (N = 2168) and one experiment in Ireland (N = 1125), during two different waves of COVID-19. The results show that minipublic endorsement significantly increases the uptake of expert information among (nonparticipating) citizens. Furthermore, when an expert correction explicitly asserts a scientific consensus, it is as effective as the minipublic endorsement. The findings have implications for the research on misperceptions, expertise and deliberative institutions.

Research on assessment method for main insulation state of converter transformer based on time‐frequency domain dielectric response

AbstractThe converter transformer is an essential part of the DC transmission system. Compared with the traditional oil‐impregnated AC transformer, the main insulation of the converter transformer bears more complex electric field aging stress during long‐term operation. The influence of the proportion of AC components in the AC/DC composite electric field on insulation aging is still unclear. Therefore, a combined aging test platform of composite electric field and thermal was built in the laboratory, and accelerated aging tests of oil‐paper insulation under different AC/DC ratios were carried out. Through the time‐frequency domain dielectric response characteristics of oil‐paper insulation, the quantitative relationship between the time‐frequency domain dielectric response characteristic parameters and AC proportional coefficient in different aging stages was obtained. The results show that the influence of the AC component on the aging of the oil‐impregnated pressboard is more prominent. The maximum relaxation polarization time and the maximum exponential coefficient of polarization–depolarization current (PDC) can effectively characterize the aging of oil‐paper insulation. Meanwhile, to accurately assess the insulation state of the converter transformer, this paper established the equivalent dielectric relaxation model for the main insulation structure. A quantitative assessment method for moisture content and aging of oil‐paper insulation based on time‐frequency domain dielectric response was proposed. The influence of transformer oil conductivity, test temperature, and main insulation structure was eliminated. The effectiveness of this method was verified by comparative tests, the maximum error for DP is 20, and the maximum error for moisture content is 0.15%. The research results of this paper can provide theoretical support for on‐site assessment of converter transformer insulation status.

Effects of optical and radar satellite observations within Google Earth Engine on soil organic carbon prediction models in Spain

The modeling and mapping of soil organic carbon (SOC) has advanced through the rapid growth of Earth observation data (e.g., Sentinel) collection and the advent of appropriate tools such as the Google Earth Engine (GEE). However, the effects of differing optical and radar sensors on SOC prediction models remain uncertain. This research aims to investigate the effects of different optical and radar sensors (Sentinel-1/2/3 and ALOS-2) on SOC prediction models based on long-term satellite observations on the GEE platform. We also evaluate the relative impact of four synthetic aperture radar (SAR) acquisition configurations (polarization mode, band frequency, orbital direction and time window) on SOC mapping with multiband SAR data from Spain. Twelve experiments involving different satellite data configurations, combined with 4027 soil samples, were used for building SOC random forest regression models. The results show that the synthesis mode and choice of satellite images, as well as the SAR acquisition configurations, influenced the model accuracy to varying degrees. Models based on SAR data involving cross-polarization, multiple time periods and “ASCENDING” orbits outperformed those involving copolarization, a single time period and “DESCENDING” orbits. Moreover, combining information from different orbital directions and polarization modes improved the soil prediction models. Among the SOC models based on long-term satellite observations, the Sentinel-3-based models (R2 = 0.40) performed the best, while the ALOS-2-based model performed the worst. In addition, the predictive performance of MSI/Sentinel-2 (R2 = 0.35) was comparable with that of SAR/Sentinel-1 (R2 = 0.35); however, the combination (R2 = 0.39) of the two improved the model performance. All the predicted maps involving Sentinel satellites had similar spatial patterns that were higher in northwest Spain and lower in the south. Overall, this study provides insights into the effects of different optical and radar sensors and radar system parameters on soil prediction models and improves our understanding of the potential of Sentinels in developing soil carbon mapping.

Self-Sustained Constant Anodic Dissolution Rate on Iron Electrode Under a Magnetic Field

The evolution of the wavy surface of an iron electrode with anodic polarization time in a sulfuric acid solution under a 0.4 T magnetic field is quantified by 3D tomographic depth profile measurements. The electrode surface after anodic dissolution under a magnetic field is irregular and the 3D profile changes with the anodic polarization time. The anodic dissolution rate is specific to the geometrical location on the electrode, which is, in general, insensitive to the polarization time as well as the surface irregularity.