Search

In this study, we investigated the effect of various O 2 concentrations, from 20% to 90%, in nitrogen–oxygen ( N 2 / O 2 ) mixtures on the characteristics of secondary streamers. As oxygen molecules have different molecular characteristics from nitrogen molecules in terms of ionisation threshold and electron attachment property, streamer discharges generated under various nitrogen–oxygen ratios may exhibit differing characteristics such as electron density, electric field, and radical formation. We focused on the changes in these parameters in secondary streamers using simulations. Simulations were first performed under the same conditions as those in previous experiments to compare the results of the ozone production, discharge current, and discharge emission characteristics. To compare the ozone production characteristics, simulated O radicals–the precursor of ozone–were used in the simulation for simplicity. This comparison showed that, although the absolute values of each parameter were different, the simulation exhibited a similar trend in the case of the experimentally obtained oxygen concentration dependence. After the validity of the simulation was verified to some extent via a comparison with the experiment, the results obtained from the simulation were analysed in detail. The results showed that, although the electric field strength in the secondary streamer did not change much as the oxygen concentration increased, the decrease rate of the electron density was greatly accelerated by the electron attachment reaction of oxygen. As a result, many of the electrons had already dissipate during the development of the primary streamer, and few electrons remained when the secondary streamer was formed. This effect suggests that the ratio of the amount of O radicals produced in the primary streamer to that produced in the secondary streamer changes as the oxygen concentration changes. [ABSTRACT FROM AUTHOR]

Normal-incidence irradiation by 100 MeV Ag ions is used to improve flux pinning in previously optimised commercial REBCO tapes from the American Superconductor Corporation. We observe distinct critical-current anisotropy enhancements below and above 40 K. Above 40 K a strong c -axis peak appears in the angular dependence of the critical current, as is usually expected upon the introduction of columnar defects. The critical current is enhanced significantly but only for a limited range of field angles. Close to the parallel-field direction there is no enhancement or even a reduction in critical current. Below 40 K, on the other hand, the enhancement is much broader with respect to field angle, creating an almost isotropic response at 20 K, 3 T. The absence of a prominent c -axis peak does not indicate a lack of pinning, since the absolute value of the critical current still increases by a factor of 2.8 compared to an unirradiated sample. Instead, we postulate that pre-existing point-like pinning centres act to mediate an interaction between the existing planar and newly-introduced columnar pins, broadening both contributions. The point-like pins become less effective with increasing temperature as the coherence length increases, leading to a reduction in this interaction and a separation of the individual peaks relating to planar and columnar pins. At 20 K, we achieve an enhancement in the angular-minimum critical current by a factor of 2.7, in a material that had already been process-optimised for low-temperature pinning. [ABSTRACT FROM AUTHOR]

Objective. While the accuracy of dose calculations in water with Acuros XB is well established, experimental validation of dose in bone is limited. Acuros XB reports both dose-to-medium and dose-to-water, and these values differ in bone, but there are no reports of measurements of validation in bone. This work compares Acuros XB calculations to measurements of absolute dose in aluminum (medium similar to bone). The validity of using selected relative dosimeters in aluminum is also investigated. Approach. A calorimeter with an aluminum core embedded in an aluminum phantom was selected as bone surrogate for the measurement of absolute dose. Matching the medium of the core to the medium of the phantom allowed eliminating the calculation of the conversion between media. The dose was measured at the fixed depth of 3.3 cm in aluminum (∼9 g·cm−2) with 6X, 10X, 6FFF and 10FFF photon beams from a TrueBeam Varian linac. In addition, experimental cross-calibration between water and aluminum was performed for an IBA CC13 ionization chamber, a PTW microDiamond and EBT3 Gafchromic film. Main results. Calculations with Acuros XB dose-to-medium in aluminum differed from the calorimetry data by −2.8% to −3.5%, depending on the beam. Use of dose-to-water would have resulted in about 39% discrepancy. The cross calibration coefficient between water and aluminum yielded values of about 0.87 for the CC13 chamber, 0.91 for the microDiamond, and 0.88 for the film, and independent of the beam within about ±1%. Significance. It was demonstrated the value of the dose-to-medium in aluminum (surrogate of bone) computed with Acuros XB is close to the value of the absolute dose measured with a calorimeter, and there is a significant discrepancy when dose-to-water is used instead. The use of an ionization chamber, a microDiamond and Gafchromic film in aluminum required a considerable correction from calibration in water. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs) are ideal candidates to explore the manifestation of spin-valley physics under external stimuli. In this study, we investigate the influence of strain on the spin and orbital angular momenta, effective g -factors, and Berry curvatures of several monolayer TMDCs (Mo and W based) using a full ab initio approach. At the K -valleys, we find a surprising decrease of the conduction band spin expectation value for compressive strain, consequently increasing the dipole strength of the dark exciton by more than one order of magnitude (for ∼ 1 % â€" 2 % strain variation). We also predict the behavior of direct excitons g -factors under strain: tensile (compressive) strain increases (decreases) the absolute value of g -factors. Strain variations of ∼1% modify the bright (A and B) excitons g -factors by ∼0.3 (0.2) for W (Mo) based compounds and the dark exciton g -factors by ∼0.5 (0.3) for W (Mo) compounds. Our predictions could be directly visualized in magneto-optical experiments in strained samples at low temperature. Additionally, our calculations strongly suggest that strain effects are one of the possible causes of g -factor fluctuations observed experimentally. By comparing the different TMDC compounds, we reveal the role of spinâ€"orbit coupling (SOC): the stronger the SOC, the more sensitive are the spin-valley features under applied strain. Consequently, monolayer WSe2 is a formidable candidate to explore the role of strain on the spin-valley physics. We complete our analysis by considering the side valleys, Î" and Q points, and by investigating the influence of strain in the Berry curvature. In the broader context of valley- and strain-tronics, our study provides fundamental microscopic insights into the role of strain in the spin-valley physics of TMDCs, which are relevant to interpret experimental data in monolayer TMDCs as well as TMDC-based van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

A novel modelling methodology has been developed for the creation of a realistic plasma gamma-ray source for Monte Carlo transport simulations in the tokamak JET. The methodology couples the TRANSP code for plasma transport calculations with the MCNP Monte Carlo particle transport code, thus connecting plasma physics with gamma-ray transport. This paper presents the validation of the developed source methodology by comparing calculated gamma-ray spectra with measurements performed at JET. The validation focuses on gamma-ray spectra measured by the tangential gamma-ray spectrometer during two JET three ion RF scenario discharges, performed in the JET 2019 deuterium experimental campaign. For validation the calculated plasma gamma-ray spectrum was combined with the neutron induced prompt gamma-ray background, originating in the vacuum vessel, and scaled to absolute values calculating the total number of plasma gamma-ray and neutron emitting reactions. The comparison between calculated and measured gamma-ray spectra shows good agreement with the shape of the calculated gamma-ray spectra matching that of measurements for both studied discharges. Moreover, the calculated absolute values of the gamma-ray spectra were of the same order of magnitude at the position of the gamma-ray detector located at the end of a long line-of-sight in a biological shield. The comparison has validated the developed plasma gamma-ray source methodology for MCNP photon transport calculations at JET. The validation provides a basis for the developed plasma gamma-ray source to be used as a support for the development of future tokamaks such as DEMO. [ABSTRACT FROM AUTHOR]

Vector vortex beams play an important role in tailoring tightly focused fields by creating an additional longitudinal component at the focal plane. Until now, mainly focusing properties of fundamental, higher order vector fields and negative indexed ellipse fields have been investigated. In this paper we numerically analyze tight focusing behaviour of ellipse fields embedding C-point singularities of index I C = ± 1 2 , I C = ± 1 , I C = ± 3 2 and I C = ± 2. We show that both the sign and absolute value of C-point index (I C ) of the ellipse fields play an important role in tailoring the focal intensity landscapes. For negative index C-points the intensity distribution of the longitudinal components show symmetries that correspond to the number of separatrices present in the polarization distribution. At the focal plane, both transverse and longitudinal components of the ellipse fields are found to be embedded with phase singularities. These ellipse fields can be useful in advanced microscopy for shaping the focus of light fields for various applications. [ABSTRACT FROM AUTHOR]

We utilize the ALMA-MaNGA QUEnch and STar formation (ALMaQUEST) survey to investigate the kpc-scale scaling relations, presented as the resolved star-forming MS (rSFMS: ΣSFR versus Σ*), the resolved Schmidt–Kennicutt relation (rSK: ΣSFR versus), and the resolved molecular gas MS (rMGMS: versus Σ*), for 11,478 star-forming and 1414 retired spaxels (oversampled by a factor of ∼20) located in 22 GV and 12 MS galaxies. For a given galaxy type (MS or GV), the retired spaxels are found to be offset from the sequences formed by the star-forming spaxels on the rSFMS, rSK, and rMGMS planes, toward lower absolute values of sSFR, SFE, and by ∼1.1, 0.6, and 0.5 dex. The scaling relations for GV galaxies are found to be distinct from that of the MS galaxies, even if the analyses are restricted to the star-forming spaxels only. It is found that, for star-forming spaxels, sSFR, SFE, and in GV galaxies are reduced by ∼0.36, 0.14, and 0.21 dex, respectively, compared to those in MS galaxies. Therefore, the suppressed sSFR/SFE/fgas in GV galaxies is associated with not only an increased proportion of retired regions in GV galaxies but also a depletion of these quantities in star-forming regions. Finally, the reduction of SFE and in GV galaxies relative to MS galaxies is seen in both bulge and disk regions (albeit with larger uncertainties), suggesting that, statistically, quenching in the GV population may persist from the inner to the outer regions. [ABSTRACT FROM AUTHOR]

We give new formulas for finding the complex (phased) scattering amplitude at fixed frequency and angles from absolute values of the scattering wave function at several points x 1, …, x m . In dimension d â©ľ 2, for m > 2, we significantly improve previous results in the following two respects. First, geometrical constraints on the points needed in previous results are significantly simplified. Essentially, the measurement points x j are assumed to be on a ray from the origin with fixed distance Ď„ = | x j +1 âˆ' x j |, and high order convergence (linearly related to m) is achieved as the points move to infinity with fixed Ď„. Second, our new asymptotic reconstruction formulas are significantly simpler than previous ones. In particular, we continue studies going back to Novikov (2015 Bull. Sci. Math. 139 923â€"936). [ABSTRACT FROM AUTHOR]

Based on the Parker Solar Probe mission, this paper presents the observations of two correlations in solar wind turbulence near the Sun for the first time, demonstrating the clear existence of the following two correlations. One is positive correlation between the proton temperature and turbulent magnetic energy density. The other is negative correlation between the spectral index and magnetic helicity. It is found that the former correlation has a maximum correlation coefficient (CC) at the wavenumber kρp ≃ 0.5 (ρp being the proton thermal gyroradius), and the latter correlation has a maximum absolute value of CC at kρp ≃ 1.8. In addition, investigations based on 11 yr of Wind observations reveal that the dimensionless wavenumbers (kρp) corresponding to the maximum (absolute) values of CC remain nearly the same for different data sets. These results tend to suggest that the two correlations enhanced near the proton gyroradius scale would be a common feature of solar wind turbulence. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet radiation from a high harmonic source has been used to measure the free-free attenuation coefficient and real refractive index of warm dense aluminium, with sample conditions of near solid density and temperature of 0.9 ± 0.23 eV. These were compared to results from the literature, where the measured attenuation coefficients showed some consistency with the modelling and existing data from a previous experiment. The absolute values of the attenuation coefficient were found to reside between the different sets of models for the warm dense matter (WDM) attenuation coefficient, and were found to be more in line with modelling and measurements of the cold opacity from the literature. Novel measurements of the real refractive index of WDM were also achieved—while ambiguity makes these measurements consistent with all the models, they prove useful as a proof-of-concept for future WDM studies. [ABSTRACT FROM AUTHOR]

This paper aims to develop self-sensing cement-based composites with high sensitivity through building a multiphasic and multiscale conductive network formed by hybrid super-fine stainless steel wires (SSWs) and carbon nanotubes (CNTs)/nano-TiO2 particles (NTs). Experimental results show that 0.15 vol% SSWs are already in the percolation threshold zone, and incorporating CNTs/NTs has a synergistic effect of decreasing the electrical resistivity and increasing the strain sensitivity of cement-based composites under cyclic/monotonic compressive loading. The hybrid modification effect is closely related to the dosage and conductivity of nano-fillers. The sensing mechanisms mainly include the change of capacitance, tunneling resistance between fillers and intrinsic resistivity of fillers. For cement-based composites with 0.3 vol% SSWs, the electrical resistivity and self-sensing properties are primarily dominated by the SSW network, and are barely affected by the addition of CNTs. However, the strain sensitivity corresponding to the maximum absolute value of fractional change in electrical resistivity under monotonic loading is increased by 62.8% and reaches up to 140 as NTs are added, resulting from the semiconductor and nano-core properties of NTs to form a barrier between overlapping SSW conductive networks. It can therefore be concluded that tailoring different conductive networks by incorporating hybrid multiscale and multicharacteristic fillers is an effective method of developing self-sensing cement-based composites with high sensitivity. [ABSTRACT FROM AUTHOR]

The emission in the near-ultraviolet Ca ii H and K lines is modulated by stellar magnetic activity. Although this emission, quantified via the S-index, has been serving as a prime proxy of stellar magnetic activity for several decades, many aspects of the complex relation between stellar magnetism and Ca ii H and K emission are still unclear. The amount of measured Ca ii H and K emission is suspected to be affected not only by the stellar intrinsic properties but also by the inclination angle of the stellar rotation axis. Until now, such an inclination effect on the S-index has remained largely unexplored. To fill this gap, we develop a physics-based model to calculate S-index, focusing on the Sun. Using the distributions of solar magnetic features derived from observations together with Ca ii H and K spectra synthesized in non-local thermodynamic equilibrium, we validate our model by successfully reconstructing the observed variations of the solar S-index over four activity cycles. Further, using the distribution of magnetic features over the visible solar disk obtained from surface flux transport simulations, we obtain S-index time series dating back to 1700 and investigate the effect of inclination on S-index variability on both the magnetic activity cycle and the rotational timescales. We find that when going from an equatorial to a pole-on view, the amplitude of S-index variations decreases weakly on the activity cycle timescale and strongly on the rotational timescale (by about 22% and 81%, respectively, for a cycle of intermediate strength). The absolute value of the S-index depends only weakly on the inclination. We provide analytical expressions that model such dependencies. [ABSTRACT FROM AUTHOR]

Taking the ultracold 85Rb–87Rb collision system as an example, we investigated the Feshbach resonances of nonzero partial waves above the threshold. The self-energy at the threshold, which represents the coupling strength between open and closed channels, is considered a critical parameter to quantitatively describe the properties of Feshbach resonances. The total elastic and inelastic cross sections are calculated as functions of the magnetic field B and collision energy Ecol, ranging from 0.1 to 600 μK. For a large absolute value of the self-energy at the threshold, the resonance decays rapidly with increasing collision energy, and narrow resonances of nonzero partial waves can be clearly resolved in the contour plot of the inelastic cross section versus the collision energy and magnetic field. It was found that the resonance tail appeared at the given magnetic field when the cross section decreased from the maximal value of the resonance peak to the minimum value, where a long resonance tail indicates an appreciable resonance in a relatively large region of collision energy. This relationship between the self-energy and the properties of Feshbach resonances still exists in the thermally averaged inelastic rate coefficient. The bound-state energies for nonzero partial waves split owing to the spin–spin interaction, which results in multiple nearly-overlapping resonances. Both the spin–spin and second-order spin–orbit effects are included. However, multiple nearly-overlapping resonances for nonzero partial waves are difficult to resolve in thermally averaged rate coefficients. [ABSTRACT FROM AUTHOR]

The unidirectional reflectionless (UR) light propagation is investigated in the waveguide coupled to gain and loss resonators by using a developed coupled mode-scattering matrix theory. The results show that there is almost no reflection in the case of the backward incidence, but total reflection in the case of the forward incidence under the condition of balancing gain and loss in the gain resonator for the proposed waveguide when the indirect coupling phase θ ranges from 0.8 rad to 2.3 rad and from 4 rad to 5.5 rad. Moreover, the coherent perfect absorption (CPA) can be observed at the same time. Especially, the UR light propagation appears when the absolute value of detuning δ is smaller than 1 × 1013 rad s−1. Based on the findings above, we propose a metal–insulator–metal non-parity-time symmetric plasmonic waveguide and obtain the UR plasmonic propagation and CPA. The theoretical results are in excellent agreement with the finite-difference time-domain simulations. These results will provide a new pathway for the realization of unidirectional propagation and absorption of light at the nanoscale. [ABSTRACT FROM AUTHOR]

In the present work, the microstructure evolution and macro-response of a ferromagnetic shape memory alloy under stimuli of magnetic fields with different frequency and coupled magnetic-mechanical loading are investigated via a real-space phase field simulation. It is found that the coercive field is reduced from 0.724 to 0.423 with the magnetic frequency f decrease from Hz to Hz, wherein the concomitant domain wall motion and magnetization rotation are captured as well. Moreover, simulation results demonstrate that, under the coupled magnetic-mechanical loading, the coercive field of the magnetic hysteresis loop could be reduced by applying a compressive strain perpendicular to the magnetic field direction. The domain evolution is mainly divided into three types during the coupled magnetic-mechanical loading, namely (a) domain wall motion with the magnetization rotation, (b) pure magnetization rotation, and (c) 180° domain coordinated domain switching. To better understand the domain evolution, we propose an index , with and indicating the absolute value of the averaged magnetization component and over the whole studied system, to characterize the magnetization change during the microstructure evolution. [ABSTRACT FROM AUTHOR]

Single molecule magnets (SMMs) with large magnetic anisotropy energy (MAE) have great potential applications in magnetic recording. Using the first-principles calculations, we investigate the MAE of 5d transition metal–porphyrin-based SMMs by using the PBE and PBE + U with different U values, respectively. The results indicate that W–P, Re–P, Os–P, and Ir–P possess the considerably large MAE among 5d TM–P SMMs. Furthermore, the MAE of 5d TM–P can be facilely manipulated by tensile strain. The reduction of the absolute value of MAE for Ir–P molecule caused by tensile strain makes it easier to implement the writing operation. The decreasing of the occupation number of minority-spin channels of Ir-dx2 – y2 orbital leads the MAE to decrease when the tensile strain increases. [ABSTRACT FROM AUTHOR]

The Ring of Fire (RoF) measurement concept to perform on-site experiments of aerodynamic drag for transiting objects is investigated with a study that identifies the main sources of uncertainty. The main contributors to the uncertainty of the drag measurement are examined for the case of a cyclist riding through the measurement domain. A sensitivity analysis is conducted that assesses how the estimated drag is affected by the choice of particle image velocimetry image processing parameters. The size of the cross-section considered in the control volume formulation is also investigated. It is found that the accuracy of the estimated drag depends on the procedure used to detect the edge of the momentum deficit region in the wake. Moreover imposing mass conservation yields the most accurate drag measurements. The drag estimation has little dependence upon the spatial resolution of the measurement as long as the interrogation window size stays within 5% to 25% of the equivalent diameter of the object cross section. Experiments are conducted in a sport-hall, where the aerodynamic drag estimates from the RoF are compared to a conventional torque power meter installed on the bicycle, and different rider's postures as well as equipment variations are considered. Although the discrepancy in the absolute value of drag can be as high as 20%, power metering and RoF agree within 4% on relative drag variations. [ABSTRACT FROM AUTHOR]

The interacting model describing the Rabi transition is essential in studying atom-photon interactions, where the kinetic energy term is often neglected for the convenience of analysis. We first study the approximation through the fidelity approach and verify its valid region in the parameter space of detuning and momentum. We find that as the radiation field's momentum and the absolute value of detuning decrease, the approximation becomes valid. We further discover that the omission of the kinetic energy term will overestimate the measuring accuracy of the Rabi frequency in some parameter regions and underestimate the precision in other regimes with Fisher information tools' help. Notably, a specific choice of the initial Gaussian state's variance in position space will improve the measuring accuracy when we take the kinetic energy term into account. We also study the realistic measurement of the Rabi frequency for cases with and without the kinetic energy. [ABSTRACT FROM AUTHOR]

Intrinsic, diffusion-driven toroidal (bootstrap) currents between −7 and 17 kA were measured in the optimised stellarator Wendelstein 7-X (W7-X) for several magnetic configurations at line-integrated plasma densities between 2 × 1019 and 1.6 × 1020 m−2 and heating powers between 0.5 and 6 MW. The sign of the bootstrap current changes with field reversal, and its magnitude decreases with the mirror term and the rotational transform of the magnetic configuration as well as the line-integrated plasma density, and increases with the heating power. Both the absolute values and the dependencies agree with neoclassical calculations within their respective uncertainties, confirming the neoclassical optimisation of W7-X for small bootstrap currents. [ABSTRACT FROM AUTHOR]

Objective: Auto-adaptive positive airway pressure (APAP) is an emerging therapeutic modality for obstructive sleep apnea (OSA) patients. However, their associated physiological effects have not been well-defined. Therefore, we aimed to investigate the impact of a 1 year APAP treatment on lung function and arterial stiffness parameters. Approach: This study enrolled male patients with newly diagnosed severe OSA who have undergone APAP treatment. A total of 35 patients completed a 1 year follow up. Blood pressure, arterial stiffness (PWV, cAIx, pAIx, cSBP), and lung function readings (FEV1, FVC, FEV1/FVC, PEF) were obtained basally and after 1, 3, 6, and 12 months of treatment. Main results: A gradual increase in FEV1 has been observed over the follow-up (2.92 ± 0.88 versus 3.07 ± 0.92 versus 3.18 ± 0.93 versus 3.28 ± 0.93 versus 3.41 ± 0.97 L), while PWV showed a gradual decrease over the follow-up (9.72 ± 1.64 versus 9.32 ± 1.73 versus 8.89 ± 1.65 versus 8.53 ± 1.61 versus 8.46 ± 1.60 m s−1), as measured by absolute values. Linear mixed effects model analysis revealed a statistically significantly higher FEV1 values (coefficient of 0.11, 0.20, and 0.33 for 3rd month, 6th month, and 12th month, respectively, P < 0.001) and lower PWV values (coefficient of −0.69, −0.63, and −0.34 for 3rd month, 6th month, and 12th month, respectively, P < 0.001), after the initiation of APAP treatment. Significance: We conclude that APAP treatment improves main lung function and arterial stiffness parameters in male patients with severe OSA over a 1 year follow-up. [ABSTRACT FROM AUTHOR]

This experimental study reveals intriguing thermoelectric effects and devices in epitaxial bismuthene, two-dimensional (2D) bismuth with thickness ⩽30 nm, on Si (111). Bismuthene exhibits interesting anisotropic Seebeck coefficients varying 2–5 times along different crystal orientations, implying the existence of a puckered atomic structure like black phosphorus. An absolute value of Seebeck coefficient up to 237 μV K−1 sets a record for elemental Bi ever measured to the best of our knowledge. Electrical conductivity of bismuthene can reach up to 4.6 × 104 S m−1, which is sensitive to thickness and magnetic field. Along with a desired low thermal conductivity ∼1.97 W m−1 K that is 20% of its bulk form, the first experimental zT value at room temperature for bismuthene was measured ∼10–2, which is much higher than many other VA Xenes and comparable to its bulk compounds. Above results suggest a mixed buckled and puckered Bi atomic structure for epitaxial 2D bismuth on Si (111). Our work paves the way to explore potential applications, such as heat flux sensor, energy converting devices and so on for bismuthene. [ABSTRACT FROM AUTHOR]

We discuss the influence of two factors on the deviations from the model of the magnetic field of a long straight wire. Firstly, we derive the magnetostatic analogue of McCullagh's formula for the case of the infinitely long straight conductor with an arbitrary cross-section. Using this equation on the basis of its practical significance, we find that the greatest deviations from the long straight wire model should be observed for a system of two parallel and infinitely long straight wires, equal in absolute value and direction currents. In this case the extremal direction of the magnetic field deviations respectively passes through these wires or is perpendicular to the plane passing through them. Our numerical estimations show that any infinitely long straight conductor with a cross-section having dihedral group symmetry can be considered with reasonable accuracy (the relative error in the determination of the magnetic flux density is less than 5%) as the infinite straight wire, if the distance to the observation point is approximately more than half order of magnitude larger than its maximum transverse size. We also analyse the effect of finite length of the carrying wire on the magnitudes of the magnetic field. We show that in this case, the smallest deviations from the infinite straight wire model should be observed for points belonging to the perpendicular plane passing through the midpoint of a wire. [ABSTRACT FROM AUTHOR]

This paper is dedicated to design a direct sampling method of inverse electromagnetic scattering problems, which uses multi-frequency sparse backscattering far field data for reconstructing the boundaries of perfectly conducting obstacles. We show that the smallest strip containing the unknown object can be approximately determined by the multi-frequency backscattering far field data at two opposite observation directions. The proof is based on the Kirchhoff approximation and Fourier transform. Such a strip is then reconstructed by an indicator, which is the absolute value of an integral of the product of the data and some properly chosen function over the frequency interval. With the increase of the number of the backscattering data, the location and shape of the underlying object can be reconstructed. Numerical examples are conducted to show the validity and robustness of the proposed sampling method, even with moderately sized frequencies. The numerical examples also show that the concave part of the underlying object can be well reconstructed, and the different connected components of the underlying object can be well separated. [ABSTRACT FROM AUTHOR]

As a typical solidification microstructure, anomalous eutectic is still not known of its growth mechanism. Mullis et al (2018, Acta Mater. 145:186) experimentally showed that the volume faction of anomalous eutectic was not consisted with the predictions by any model invoking partial remelting of primary solidified microstructure. In the present article, the anomalous eutectic microstructure of Ni–Sn alloy solidified from undercooled melts and laser remelting melt pool has been investigated through experiments and cellular automaton (CA) simulations. Computational and experimental results showed that the nucleated α-Ni particulates grew into globular, lamellar or 'tadpole' morphology. The 'tadpole' morphology, which has a globular 'head' and a lamellar 'tail', is an intermediate pattern between globular and lamellar morphologies, and would be seen as an evidence of the globular to lamellar transition (GLT). The occurrence of the GLT or not determines that the solidified microstructure is either anomalous eutectic or lamellar eutectic. CA simulations showed that the GLT was mainly influenced by the temperature gradient G and pulling velocity V. For positive G and V, representing the directional solidification at the bottom of melt pool, the GLT prefers to occur at high G and low V; for negative G and V, which refers to the solidification in undercooled melts, the GLT prefers to occur at low absolute value of G and V. The GLT was also experimentally observed under the above two circumstances. The GLT growth mechanism abstained from CA simulations well explains the experimental results. [ABSTRACT FROM AUTHOR]

Small perturbations and strong impurity exhaust capability associated with the small grassy ELMs render the grassy-ELM regime a suitable candidate for achieving steady-state H-mode operation with a radiative divertor, especially in a metal-wall device, such as the Experimental Advanced Superconducting Tokamak (EAST). As the degradation of pedestal performance with excessive divertor impurity seeding or accumulation tends to be accompanied with significantly increased radiation near the divertor X point, feedback control of the absolute extreme ultraviolet (AXUV) radiation near the X point has been employed to maintain the confinement property in EAST. However, the absolute value of the AXUV radiation at the outer target varies with plasma conditions as during the divertor detachment process. Thus, a new feedback-control scheme has been recently developed and applied to grassy-ELM H-mode plasmas in EAST to achieve stationary partial detachment while maintaining good global energy confinement with H98,y2 >1. In this scheme, electron temperatures (Tet) measured by divertor Langmuir probes are used to identify the onset of detachment, and then the plasma control system (PCS) switches to the feedback control of one channel of AXUV radiation near the X point, where a steep gradient in the radiation profile is present. The feedback is performed through pulse-width-modulated duty cycle of a piezo valve to seed impurities with mixed gas (50% Ne and 50% D2) from the outer target plate near the strike point in the upper tungsten monoblock divertor. Tet near the strike point is maintained in the range of 5–8 eV, and peak surface temperature on the outer target plate (TIR,peak) is suppressed and maintained at ∼180 °C, based on infrared camera measurements. The plasma stored energy maintains nearly constant over the entire feedback-control period. It thus offers a highly promising plasma control scenario suitable for long-pulse high-performance H-mode operation in EAST, which is potentially applicable to future steady-state fusion reactors as an integrated solution for the control of both ELM-induced transient and steady-state divertor heat loads while maintaining good core confinement. [ABSTRACT FROM AUTHOR]

We report an out-of-plane magnetic field induced large photoluminescence enhancement in WS2 flakes at 4 K, in contrast to the photoluminescence enhancement provided by an in-plane field in general. Two mechanisms for the enhancement are proposed. One is a larger overlap of the electron and hole caused by the magnetic field induced confinement. The other is that the energy difference between Λ and K valleys is reduced by magnetic field, and thus enhancing the corresponding indirect-transition trions. Meanwhile, the Landé g factor of the trion is measured to be −0.8, whose absolute value is much smaller than normal exciton, which is around |−4|. A model for the trion g factor is presented, confirming that the smaller absolute value of the Landé g factor is a behavior of this Λ–K trion. By extending the valley space, we believe this work provides a further understanding of the valleytronics in monolayer transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

We constructed a comprehensive model atom for Ne i –Ne ii using the most-up-to-date atomic data available and evaluated the nonlocal thermodynamic equilibrium (NLTE) line formation for Ne i and Ne ii in classical 1D models representing the atmospheres of B-type stars. We find that the large NLTE strengthening of the Ne i lines corresponding to the 2p53p–2p53s transition array occurs due to extremely small photoionization cross sections of the 2p53s levels that lead to strong overpopulation of these levels relative to their LTE populations. The deviations from LTE for most Ne ii lines are small and do not exceed 0.11 dex in absolute value. We analyzed 20 lines of Ne i and 13 lines of Ne ii for 24 B-type stars in the temperature range of 10,400 ≤ ≤ 33,400 K. For five stars, the NLTE leads to consistent abundances of Ne i and Ne ii , while the difference in LTE abundance can reach up to 0.50 dex. Using the experimental oscillator strengths recently measured by Piracha et al. leads to smaller line-by-line scatter for most of the investigated stars. The average neon abundance in 24 B-type stars in the solar neighborhood is 8.02 ± 0.05. This value may provide indirect constraints on the solar photospheric neon abundance. [ABSTRACT FROM AUTHOR]

In order to measure controllability of vertical instability in EAST, the calculation of model-based vertical growth rate, called rt-gamma, has been successfully carried out in real time. The numerical computing method is adapted from rigid plasma response model in TokSys, which is a widely-used analysis tool for tokamak devices in Matlab environment, but the code is rewritten by taking advantage of GPU parallel computing capability to accelerate the computation. The calculation of rt-gamma is validated by comparing it with the corresponding result generated by TokSys for totally 3508 cases. It is shown that the average absolute value of relative errors is about 0.85%. In addition, the calculation program of rt-gamma has been successfully applied during 2019 EAST campaign. The comparison with experimental results is discussed in this paper. The real-time calculation tool is well able to calculate model-based vertical growth rate, which is convenient for fast and continuous evaluations of EAST control system stability performances. [ABSTRACT FROM AUTHOR]

Gas density perturbations generated by an alternating-current dielectric-barrier-discharge plasma actuator (ac-DBDPA) are quantitatively visualised using the background-oriented schlieren (BOS) method. A method of setting the optimum boundary condition for solving the Poisson equation in the BOS method is studied, and an integration method for the boundary condition in the vicinity of the plasma where the density change is steep is proposed. The BOS method is applied in two cases with different voltage amplitudes, and the variation in the absolute value of the density is discussed with the discharge properties. The results show a decrease in density in the synthetic jet induced by the ac-DBDPA and a spatiotemporal variation indicating a step-wise gas-heating phenomenon due to plasma discharge. [ABSTRACT FROM AUTHOR]

Vibrational excitations of are investigated via the electron-impact excitation of the , , , , and states followed by radiative cascade to the vibrational bound and free (continuum) levels of the electronic ground state. The adiabatic-nuclei convergent close-coupling formalism is utilized to calculate cross sections from threshold to 500 eV. Results are in qualitative agreement with previous calculations, however absolute values differ significantly. [ABSTRACT FROM AUTHOR]

To reveal the correlation between the morphology of filaments and their writhe, we reconstruct the three-dimensional (3D) paths of the filament axes based on the data set of Atmospheric Imaging Assembly and Extreme Ultraviolet Imager on board the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory, respectively. Then, we calculate the writhe of the reconstructed filament axes with the polar writhe theory. All the cases obey that a projected forward (reverse) S-shaped filament possesses positive (negative) writhe. We conduct a further analysis by constructing theoretical 3D curves with non-centrosymmetric shape and only one maximum in height. It is demonstrated that (1) writhe depends on the relative height (the ratio of the height of the curve and the distance between its two footprints), the position of the highest point, and the position of the crossing point (the intersection of a projected axis curve and the line connecting two footprints); (2) for a filament with absolute value of the crossing angle less than π/3 and relative height less than 0.2, forward (reverse) S-shaped projection results in positive (negative) writhe; and (3) when the highest point and the crossing point are significantly separated, the sign of writhe can be conserved without changing the S shape orientation (forward or reverse) during the eruption. [ABSTRACT FROM AUTHOR]

Flexible electronics is expected to be one of the most active research areas in the next decade. In this study, a mechanically strong and flexible epoxy/GnP composite film was fabricated having a percolation threshold of electrical conductivity at 1.08 vol% GnPs and high thermal conductivity as 1.07 W m−1 K−1 at 10 vol% GnPs. The composite film shows high mechanical performance: Young's modulus and tensile strength were improved by 1344% and 66.7%, respectively, at 10 vol%. The film demonstrated high sensitivity to various mechanical loads: (i) it has gauge factors of 2 at strain range 0%–7% and 6 at range 7%–10%; (ii) it gives good electrical response with bending and twisting angles up to 180°; and (iii) it displays a good compressive load response up to 2 N where the absolute value of electrical resistance change increased by 71%. Furthermore, the film showed an excellent reliability up to 5.5 × 103 cycles with minor zero-point error. Above 20 °C, the film solely acts as a temperature sensor; upon cyclic temperature testing, the film demonstrated a stable resistive response in the range of 30–75 °C with a temperature sensitivity coefficient of 0.0063 °C−1. This flexible composite film has remarkable properties that enable it to be used as a full-fledged sensor for universal applications in aerospace, automotive and civil engineering. [ABSTRACT FROM AUTHOR]

We present the experiment observation of a giant topological Hall effect (THE) in a frustrated kagome bilayer magnet Fe3Sn2. The negative topologically Hall resistivity appears when the field is below 1.3 T and it increases with increasing temperature up to 300 K. Its maximum absolute value reaches ∼ 2.01 µΩ·cm at 300 K and 0.76 T. The origins of the observed giant THE can be attributed to the coexistence of the field-induced skyrmion state and the non-collinear spin configuration, possibly related to the magnetic frustration interaction in Fe3Sn2. [ABSTRACT FROM AUTHOR]

Absorption spectroscopy of gravitationally lensed quasars (GLQs) enables study of spatial variations in the interstellar and/or circumgalactic medium of foreground galaxies. We report observations of four GLQs, each with two images separated by 0.″8–3.″0, that show strong absorbers at redshifts 0.4 < zabs < 1.3 in their spectra, including some at the lens redshift with impact parameters 1.5–6.9 kpc. We measure H i Lyman lines along two sight lines each in five absorbers (10 sight lines in total) using Hubble Space Telescope Space Telescope Imaging Spectrograph, and metal lines using Magellan Echellette or Sloan Digital Sky Survey. Our data have doubled the lens galaxy sample with measurements of H i column densities (NH i ) and metal abundances along multiple sight lines. Our data, combined with the literature, show no strong correlation between absolute values of differences in NH i , NFe ii , or [Fe/H] and the sight line separations at the absorber redshifts for separations of 0–8 kpc. The estimated abundance gradients show a tentative anticorrelation with abundances at galaxy centers. Some lens galaxies show inverted gradients, possibly suggesting central dilution by mergers or infall of metal-poor gas. [Fe/H] measurements and masses estimated from GLQ astrometry suggest the lens galaxies lie below the total mass–metallicity relation for early-type galaxies as well as measurements for quasar-galaxy pairs and gravitationally lensed galaxies at comparable redshifts. This difference may arise in part from the dust depletion of Fe. Higher resolution measurements of H and metals (especially undepleted elements) for more GLQ absorbers and accurate lens redshifts are needed to confirm these trends. [ABSTRACT FROM AUTHOR]