Browse Articles

Evaluation of arc quenching ability for SF6 replacements based on time-dependent Elenbaas–Heller and Boltzmann equations

Sulfur hexafluoride (SF6), a widely used arc quenching medium in the power industry, has been designated as a greenhouse gas, necessitating its reduction and replacement. Identifying eco-friendly alternatives to SF6 is a complex and expensive process, particularly since these alternatives often consist of gas mixtures that may function at varying pressures. In this work, we propose an efficient method for evaluating the arc quenching performance of gases or gas mixtures using the time-dependent Elenbaas–Heller and Boltzmann equations, which circumvents the computational costs associated with traditional 2D or 3D magnetohydrodynamic arc models. We segment the arc quenching process into four distinct stages: the thermal recovery stage, pre-dielectric recovery stage, post-dielectric recovery stage, and residual-gas cooling stage. To quantitatively assess arc quenching performance, we introduce two key parameters: recovery rate and recovery strength. The recovery rate is defined as the harmonic mean of thermal, pre-dielectric, and post-dielectric recovery rates. The recovery strength is characterized by the harmonic mean of the average recovery voltage, maximum critical electric field strength, and room-temperature dielectric strength. Our method is validated using several SF6 alternatives, including SF6 mixtures, C4F8, C4F7N, C5F10O, and their mixtures with CO2, N2, and O2. The results demonstrate that the coupling of the time-dependent Elenbaas–Heller and Boltzmann equations well describes the arc decaying process. Moreover, the proposed recovery rate and recovery strength metrics effectively quantify the arc quenching ability, enabling a systematic and efficient evaluation of various gas mixtures for arc interruption performance.

A networked station system for high-resolution wind nowcasting in air traffic operations: A data-augmented deep learning approach

This study introduces a high-resolution wind nowcasting model designed for aviation applications at Madeira International Airport, a location known for its complex wind patterns. By using data from a network of six meteorological stations and deep learning techniques, the produced model is capable of predicting wind speed and direction up to 30-minute ahead with 1-minute temporal resolution. The optimized architecture demonstrated robust predictive performance across all forecast horizons. For the most challenging task, the 30-minute ahead forecasts, the model achieved a wind speed Mean Absolute Error (MAE) of 0.78 m/s and a wind direction MAE of 33.06°. Furthermore, the use of Gaussian noise concatenation to both input and label training data yielded the most consistent results. A case study further validated the model’s efficacy, with MAE values below 0.43 m/s for wind speed and between 33.93° and 35.03° for wind direction across different forecast horizons. This approach shows that combining strategically deployed sensor networks with machine learning techniques offers improvements in wind nowcasting for airports in complex environments, possibly enhancing operational efficiency and safety.

Angle-resolved Raman scattering study of anisotropic two-dimensional tellurium nanoflakes

As an elemental crystal, anisotropic two-dimensional (2D) tellurium (Te) flakes have recently garnered significant attention due to their exceptional chemical stability, tunable bandgap, low thermal conductivity, and high carrier mobility. To further investigate the anisotropic properties of Te nanoflakes, a rapid and effective method of determining their crystal axes is essential. In this study, it is demonstrated that the intensity of the Raman-active mode in Te nanoflakes exhibits a laser-polarization-dependence, varying periodically with the polarization angle. The crystal axis in two-dimensional Te nanoflakes can be identified using angle-resolved polarized Raman spectroscopy. Specifically, the Raman intensity of the A1 mode is the highest when the incident light is polarized along the [12¯10] direction and the lowest when polarized along the [0001] direction. This identification of the crystal axis via Raman spectroscopy is further verified by transmission electron microscopy measurements. In addition, theoretical simulations reveal that anisotropic Raman scattering is closely associated with the interference effect in a multilayer stacking system, as well as anisotropic absorption and anisotropic electron–phonon coupling in Te nanoflakes. This discovery not only provides a rapid method for locating the crystal axes in Te nanoflakes but also offers new insights into the scattering phenomenon in anisotropic materials beyond Te nanoflakes.

Correction for Jury et al., Experimental coral reef communities transform yet persist under mitigated future ocean warming and acidification

Association of blood urea nitrogen with 28-day mortality in critically ill patients: A multi-center retrospective study based on the eICU collaborative research database

Objective Blood urea nitrogen (BUN) is a commonly used biomarker for assessing kidney function and neuroendocrine activity. Previous studies have indicated that elevated BUN levels are associated with increased mortality in various critically ill patient populations. The focus of this study was to investigate the relationship between BUN and 28-day mortality in intensive care patients. Methods This was a multi-centre retrospective cohort study that made use of data from the eICU Collaborative Research Database. The primary exposure variable was BUN, and the outcome was 28-day mortality. The following variables were included as covariates: age, gender, BMI, white blood cell count, creatinine, GCS score, APACHE IV score, and diabetes. The statistical analyses included univariate and multivariate logistic regression, as well as generalized additive modelling, which was employed to assess the non-linear relationship between BUN and mortality. Results A total of 63,757 elderly patients were included in the study, with a 28-day mortality of 6.5%. The univariate analysis indicated that elevated BUN quartiles were associated with an increased risk of mortality. The results of the multivariate analysis further confirmed the non-linear relationship between BUN and mortality. When BUN was less than 32 mg/dL, there was a significant positive association, with an adjusted odds ratio of 1.230 (95% CI: 1.154–1.311, p<0.0001) for every 10 mg/dL increase in BUN. However, when BUN was greater than or equal to 32 mg/dL, BUN level had no significant effect on mortality. Conclusion BUN showed a nonlinear, threshold correlation with 28-day mortality in critically ill patients. The higher the BUN, the greater the risk of death if the BUN is below the threshold.

Experimental discrimination of domain switching behaviors within interfacial and bulk layers in the LiNbO3 domain-wall memory

Multilevel resistance states with respect to the volume of the reversed domains in ferroelectric tunneling junctions and erasable conducting domain walls in an insulating ferroelectric matrix enable high-speed and energy-efficient ferroelectric synapses, memories, and transistors. According to the domain nucleation model, the operation speeds of these devices are assumedly limited by domain nucleation time while the subsequent domain growth time is neglected. Unfortunately, these two times cannot be separated from the experiment yet. Here, we observed independent switching behaviors of domain nucleation and growth at two discrete coercive fields for a mesa-like memory cell formed at the surface of a LiNbO3 single crystal. After the application of an in-plane electric field to two side electrodes, we observed the on currents upon antiparallel domain reversals via the creation of conducting domain walls between them. Once the applied electric field is removed, the domains within the interfacial layers between the two side electrodes and the cell are volatile and switch back into their initial orientations automatically, unlike the nonvolatile bulk domain encoding digital information. In consideration of volatile and nonvolatile natures of the two domains, we separately observed their switching behaviors from the measurements of frequency-dependent domain switching hysteresis loops after programing various write and read pulses. It is found that all coercive fields with the involvement of domain nucleation at the interfaces are always frequency-dependent, unlike domain forward growth within the bulk layer that is frequency-independent. This provides the direct evidence that the operation speed of the low-dimensional ferroelectric device is limited by the domain nucleation rate at the interface.

The role of health shocks after age 70 on housing and wealth profiles

We conduct a novel investigation into the effects of uncertain health shocks and medical costs on the life cycle consumption, housing, and saving decisions. Our model aids in understanding the role of health shocks and medical costs after age 70 in explaining the lack of wealth and housing decumulation during retirement. We utilize a comprehensive life-cycle model that includes housing, as well as shocks to house price, labor income, and health. Our model could be useful for policy evaluation and future studies concerning older adults. Our first contribution to the previous literature is modeling the whole adult life-cycle. This enables us to determine whether decisions in youth and middle age are influenced by anticipated health shocks in old age. Our second contribution is modeling housing explicitly with health shocks. Conclusions regarding the savings puzzle may be significantly influenced by the explicit modeling of housing. We develop a more realistic model by relaxing some of the assumptions made in previous studies. We find that health shocks motivate the household to accumulate higher wealth before retirement. Moreover, as health shocks become more severe, individuals reduce their consumption and decumulate less wealth in old age. Health shocks help explain the flat trends observed in the housing and wealth profiles of older adults. The possible health shocks after age 70 affect the decisions in young and middle ages only marginally. The wealth profile in middle and old age is affected by health shocks.

Prediction of neuronal functionality of asymmetric ferroelectric tunneling junction with coupled polarization and thermal dynamics

The performance of neuromorphic computing (NC) in executing data-intensive artificial intelligence tasks relies on hardware network structure and information processing behavior mimicking neural networks in the human brain. The functionalities of synapses and neurons, the key components in neural networks, have been widely pursued in memristor systems. Nevertheless, the realization of neuronal functionalities in a single memristor remains challenging. By theoretical modeling, here we propose asymmetric ferroelectric tunneling junction (AFTJ) as a potential platform to realize neuronal functionalities. The volatility, a necessary property for a memristor to implement a neuron device, is enhanced by the co-effect of polarization asymmetry and Joule heating. The simulated polarization reversal dynamics of the AFTJ memristor under trains of electric pulses reproduces the leaky integrate-and-fire functionality of spiking neurons. Interestingly, multiple spiking behaviors are found by modulating the pulse width and interval of trains of electric pulses, which has not yet been reported in ferroelectric neuron. The influences of several key factors on the neuronal functionalities of AFTJ are further discussed. Our study provides a novel design scheme for ferroelectric neuron devices and inspires further explorations of ferroelectric devices in neuromorphic computing.

Correction for Alboreggia et al., Targeted degradation of Pin1 by protein-destabilizing compounds

Wearable devices may aid the recognition of fluctuation-related pain in Parkinson’s disease—An exploratory, cross-sectional analysis of two prospective observational studies

Fluctuation-related pain (FRP) affects more than one third of people with Parkinson’s disease (PwP, PD) and has a harmful effect on health-related quality of life (HRQoL), but often remains under-reported by patients and neglected by clinicians. The National Institute for Health and Care Excellence (NICE) recommends The Parkinson KinetiGraphTM (the PKGTM) for remote monitoring of motor symptoms. We investigated potential links between the PKGTM-obtained parameters and clinical rating scores for FRP in PwP in an exploratory, cross-sectional analysis of two prospective studies: “The Non-motor International Longitudinal, Real-Life Study in PD—NILS” and “An observational-based registry of baseline PKG™ in PD—PKGReg”. 63 PwP (41.3% female; age: 64.24±9.88 years; disease duration, DD: 6.83±5.63 years; Hoehn and Yahr Stage, H&Y: 2 (1–4); Levodopa Equivalent Daily Dose 535 (0–3230) mg) were included. PwP with FRP (n = 23) had longer DD (8.88 (1.29–19.05) vs. 3.16 (0.34–28.92), p = 0.001), higher severity of motor symptoms (H&Y 3 (1–4) vs. 2 (1–4), p = 0.015; SCOPA Motor total score 21.35±10.19 vs. 13.65±8.99, p = 0.003), more dyskinesia (SCOPA Motor Item 18 ≥1 60.9% vs. 7.5%, p<0.001), and worse HRQoL (PDQ-8 Total Score 10.74±5.98 vs. 6.78±5.13, p = 0.007) then PwP without FRP (n = 40). In the multivariate logistic regression, after the adjustment for DD, H&Y and SCOPA-Motor total score, the presence of FRP was significantly associated with the PKGTM-derived Fluctuation-dyskinesia score (Exp (B) = 1.305, 95% CI for Exp (B) 1.012–1.683, p = 0.040) and the Bradykinesia score (Exp (B) = 0.917, 95% CI for Exp (B) 0.842–0.999, p = 0.048). The PKGTM system may potentially advance the way we screen for, assess, and treat FRP in clinical practice.

Coplanar nanoscale vacuum electron field emission triode with controllable gate distance

The typical nanoscale vacuum field emission triode with a controllable gate distance, created via focused ion beam etching and photolithography, is presented in this study. The field emission performance under coplanar gate control is distinguished from the gate distance (dg) in a low vacuum environment. It is, therefore, necessary to highlight a vital parameter dg defined by the nanogap between the center of the nanoscale channel and the edge of the coplanar gate, to methodically illustrate the working mechanism. For the case of a device with large dg, the F–N tunneling current was positively increased by up to one order of magnitude when high bias conditions on the anode and coplanar gate were applied. In contrast, the device with short dg displayed a negative drop in F–N tunneling current under the same measurement condition. As the gate bias increased continuously to a critical value, this device became cut off in this situation with an insignificant gate leakage current. This opposite trend of F–N emission current is eventually verified to have a relationship with dg and it is suggested to play a crucial role in the device. This work clarified the role of the coplanar gate when device operated in the F–N tunneling mechanism and conducted a thorough analysis of the charge transport mechanism related to dg. This work will aid coplanar nanoscale vacuum electron field emission device design in the future.

Maternal occupational exposures during early stages of pregnancy and adverse birth outcomes in the NINFEA birth-cohort

Objectives Maternal occupational exposures during early pregnancy can be detrimental to foetus health and have short- and long-term health effects on the child. This study examined their association with adverse birth outcomes. Methods The study included 3938 nulliparous women from the Italian NINFEA mother-child cohort. Their occupational exposures during the first trimester of pregnancy were assessed through prospectively collected questionnaire information and job-exposure matrices. Associations between maternal exposures and birthweight, preterm birth, and delivery by caesarean section were analysed by multivariable linear and logistic regression models. An exploratory factor analysis was carried out to explore co-exposure profiles in association with birth outcomes. Results Women exposed to passive smoking at work and those who reduced their working hours during pregnancy were found to have an increased likelihood of all analysed birth outcomes. Children of mothers performing a demanding work were less likely to be born preterm [OR 0.72 (95% CI 0.54 to 0.95)] and more likely to have a higher birthweight [β = 40.4 g (95% CI 7.5 to 73.4)]. Maternal exposures to heat and dust were associated with a lower birthweight [β = -160.1 g (95% CI -299.6 to -20.7)] and increased odds of caesarean section [OR 6.99 (95% CI 2.36 to 25.47)], respectively. Conclusions This study provides some evidence of the selection of healthy population into the workforce and of association between work-related passive smoking, heat and dust and adverse birth outcomes.

Compositional disordering: Nanoscale engineering of advanced crystalline scintillation materials

This article provides an overview of the latest results in the field of improving the properties of multiatomic inorganic oxide compounds for scintillators. A possibility to control the spatial distribution of nonequilibrium carriers in the ionization track by creating a compositional disorder in the crystalline matrix is in focus. Managing the disorder at the nanoscale level creates an opportunity for the efficient energy loss by carriers during thermalization, smaller spatial dispersion, and, consequently, more efficient binding into excitons and, further, an increase in the scintillation yield. The methods to produce multicationic crystalline scintillation materials have been discussed. The effectiveness of the approach is confirmed for both activated and self-activated scintillation materials.

Acoustic holograms for beam focusing in immersed anisotropic silicon

Ultrasonic inspection of anisotropic materials presents challenges due to directionally dependent wave propagation and beam distortion. Specifically, conventional spherically focused probes, which aim to converge the beam to a small cross section within the solid and increase inspection resolution, can yield spatially and temporally varying focal profiles in anisotropic media. This variability can make interpreting signals from defects within the samples more difficult. To address this challenge, acoustic holograms were designed to enhance ultrasonic beam focusing in silicon wafers. Lens geometries were inversely calculated using ray tracing in pursuit of conical focusing in the solid. Analytical modeling using the angular spectrum approach predicted higher amplitude and more circular focal cross sections for the custom lenses compared to the spherical lenses. The custom lenses, along with conventional spherical lens designs, were fabricated using stereolithographic 3D printing and tested on [3 1 1] and [1 3 5] silicon wafers with etched flat bottom holes. Experimental validation showed the custom lenses produced higher contrast defect signatures with smaller cross-sectional areas from sub-wavelength defects, suggesting improved defect sensitivity and anisotropy-dependent scattering. The results showcase the potential of customized acoustic holograms to enhance ultrasonic inspection of anisotropic materials. The presented design and modeling methods provide the framework for further optimization of acoustic lenses tailored to anisotropic media.

Novel high-<i>T</i>C piezo-/ferroelectric ceramics based on a medium-entropy morphotropic phase boundary design strategy

The medium- or high-entropy strategy has emerged as a new paradigm for designing high-performance piezoelectric ceramics. However, the effectiveness of this approach remains unclear to the development of high Curie temperature (TC) piezo-/ferroelectric materials with outstanding performance. To develop high-performance piezo-/ferroelectric materials suitable for high-temperature environments, in this work, we design a novel ceramic system based on a medium-entropy morphotropic phase boundary (ME-MPB) strategy. Piezo-/ferroelectric ceramics of the formula, Pb(Yb1/2Nb1/2)O3–Pb(In1/2Nb1/2)O3–PbTiO3, meeting the medium entropy criteria, were successfully synthesized using the conventional solid-state reaction method. The crystal structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the ceramics of the ME-MPB compositions were systematically investigated. X-ray diffraction and scanning electron microscopy analyses revealed that these ceramics possess a pure perovskite phase and dense microstructure. Notably, the prepared ceramics exhibited exceptional piezoelectric performance, with a high d33 up to 603 pC/N, a large strain of 0.20%, a high remanent polarization of 44.0 μC/cm2, and a high Curie temperature of 362 °C. This study demonstrates an effective design approach based on the ME-MPB strategy and points out a new pathway for developing high-performance materials for high-temperature applications as sensors, thereby expanding the research perspective on the design of medium-entropy piezo-/ferroelectric ceramics.

CO2 conversion products in α and γ modes of radio frequency capacitively coupled plasma

Radio Frequency Capacitively Coupled Plasma (RF-CCP) exhibits excellent spatial uniformity, high stability, and the capability to generate plasma over large areas, making it highly promising for applications in CO2 resource utilization in space environments. This study investigates the CO2 conversion products under two typical discharge modes (α and γ modes) of RF-CCP and their product selectivity under Martian nominal pressure. The results indicate that the optical emission spectra in both α and γ modes contain CO2+, O, and CO spectral bands/lines. The overall spectral line intensity is enhanced in the γ mode compared to the α mode, indicating a higher electron density and ionization degree in the γ mode. The key product, CO, is primarily generated through electron collisions with CO2, while O2 is produced via the dissociative recombination of electrons with CO2+. After the transition from α to γ mode, the content of CO2 decreases, but the concentrations of electrons and CO2+ increase significantly. This results in CO being the dominant product in the α mode, while in the γ mode, the overall abundance of products is higher and there is a greater selectivity for O2. Therefore, by controlling the discharge mode of RF-CCP, it is possible to achieve targeted regulation of the CO2 conversion products.

Optimizing time-of-flight secondary ion mass spectrometry depth profiles of semiconductor heterostructures

The continuous technological development of electronic devices and the introduction of new materials lead to ever greater demands on the fabrication of semiconductor heterostructures and their characterization. This work focuses on optimizing Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiles of semiconductor heterostructures aiming at a minimization of measurement-induced profile broadening. As a model system, a state-of-the-art Molecular Beam Epitaxy (MBE) grown multilayer homostructure consisting of natSi/28Si bilayers with only 2 nm in thickness is investigated while varying the most relevant sputter parameters. Atomic concentration-depth profiles are determined and an error function based description model is used to quantify layer thicknesses as well as profile broadening. The optimization process leads to an excellent resolution of the multilayer homostructure. The results of this optimization guide to a ToF-SIMS analysis of another MBE grown heterostructure consisting of a strained and highly purified 28Si layer sandwiched between two Si0.7Ge0.3 layers. The sandwiched 28Si layer represents a quantum well that has proven to be an excellent host for the implementation of electron-spin qubits.

Accurate machine learning of rate coefficients for state-to-state transitions in molecular collisions

We present an algorithm that combines quantum scattering calculations with probabilistic machine-learning models to predict quantum dynamics rate coefficients for a large number of state-to-state transitions in molecule–molecule collisions much faster than with direct solutions of the Schrödinger equation. By utilizing the predictive power of Gaussian process regression with kernels, optimized to make accurate predictions outside of the input parameter space, the present strategy reduces the computational cost by about 75%, with an accuracy within 5%. Our method uses temperature dependences of rate coefficients for transitions from the isolated states of initial rotational angular momentum j, determined via explicit calculations, to predict the temperature dependences of rate coefficients for other values of j. The approach, demonstrated here for rovibrational transitions of SiO due to thermal collisions with H2, uses different prediction models and is thus adaptive to various time and accuracy requirements. The procedure outlined in this work can be used to extend multiple inelastic molecular collision databases without exponentially large computational resources required for conventional rigorous quantum dynamics calculations.

A computational study on the effect of structural isomerism on the excited state lifetime and redox energetics of archetype iridium photoredox catalyst platforms [Ir(ppy)2(bpy)]+ and Ir(ppy)3

This study investigates the impact of structural isomerism on the excited state lifetime and redox energetics of heteroleptic [Ir(ppy)2(bpy)]+ and homoleptic Ir(ppy)3 photoredox catalysts using ground-state and time-dependent density functional theory methods. While the ground- and excited-state reduction potentials differ only slightly among the isomers of these complexes, our findings reveal significant variations in the radiative and non-radiative decay rates of the reactivity-controlling triplet 3MLCT states of these closely related species. The observed differences in radiative decay rates could be traced back to variations in the transition dipole moment, vertical energy gaps, and spin–orbit coupling of the isomers. In [Ir(ppy)2(bpy)]+, transition dipole moment differences play a significant role in controlling the relative lifetime of the triplet states, which we rationalized by a vectorial analysis of permanent dipole moments of the ground and excited states. Regarding the two isomers of Ir(ppy)3, changes in radiative decay rates were primarily attributed to variations in vertical energy gaps and intensity borrowing from other singlet-singlet transitions driven by spin–orbit coupling. Non-radiative decay variations were assessed in terms of differences in reorganization energies, adiabatic energy gap, and spin–orbit coupling. For both complexes, reorganization energies associated with low-energy molecular vibrations and metal–ligand bond length changes following the de-excitation process were major contributors. These insights provide a deeper understanding of how molecular design can be leveraged to optimize the performance of iridium-based photoredox catalysts, potentially guiding the development of more efficient catalytic systems for future applications.

Electronic spectroscopy and excited state mixing of OThF

Electronic spectra for OThF have been recorded using fluorescence excitation and two-photon resonantly enhanced ionization techniques. Multiple vibronic bands were observed in the 340–460 nm range. Dispersed fluorescence spectra provided ground state vibrational constants and evidence of extensive vibronic state mixing at higher excitation energies. Two-photon ionization measurements established the ionization energy for OThF of 6.283(5) eV. To guide the assignment of the OThF spectra, electronic structure calculations were carried out using relativistic equation-of-motion coupled-cluster singles and doubles methods. These calculations indicated that spin–orbit induced mixing of the 32A″ and 42A′ states was mediated by a seam of potential energy surface intersections.