bluuebunny/crossref_metadata_2025_split huggingface dataset:
The appearance of non trivial torsion for some Ricci dependent theories in the Palatini formalism
Authors: Osorio Juliana , Santillán Osvaldo P 
Published: November 2021

Abstract
As is known from studies of gravity models in the Palatini formalism, there exist two inequivalent definitions of the generalized Ricci tensor in terms of the generalized curvature namely,

R

~

μ
ν

=

R

μ
ρ
ν

ρ

and

R

ν

μ

=

g

α
β

R

α
ν
β

μ

. A deep formal investigation of theories with Lagrangians of the form

L
=
L

(

R

~

(

μ
ν

)

)

was initiated in Alfonso et al (2017 Class. Quantum Grav.

34 235003). In that work, the authors leave the connection free, and find out that the torsion only appears as a projective mode. This agrees with the widely employed condition of vanishing torsion in these theories as a simple gauge choice. In the present work the complementary scenario is studied namely, the one described by a Lagrangian that depends on the other possible Ricci tensor L = L(R
(μν)). The torsion is completely characterized in terms of the metric and the connection, and a rather detailed description of the equations of motion is presented. It is shown that these theories are non trivial even for 1 + 1 space time dimensions, and admit non zero torsion even in this apparently simple case. It is suggested that to impose zero torsion by force may result into an incompatible system. In other words, the presence of torsion may be beneficial for insuring that the equations of motion are well posed. The results of the present paper do not contradict the ones of Alfonso et al (2017 Class. Quantum Grav.

34 235003), as the underlying theories are inequivalent.
A new look at the Bondi–Sachs energy–momentum*
Authors: Frauendiener Jörg , Stevens Chris 
Published: November 2021

Abstract
How does one compute the Bondi mass on an arbitrary cut of null infinity

I

when it is not presented in a Bondi system? What then is the correct definition of the mass aspect? How does one normalise an asymptotic translation computed on a cut which is not equipped with the unit-sphere metric? These are questions which need to be answered if one wants to calculate the Bondi–Sachs energy–momentum for a space-time which has been determined numerically. Under such conditions there is not much control over the presentation of

I

so that most of the available formulations of the Bondi energy–momentum simply do not apply. The purpose of this article is to provide the necessary background for a manifestly conformally invariant and gauge independent formulation of the Bondi energy–momentum. To this end we introduce a conformally invariant version of the GHP formalism to rephrase all the well-known formulae. This leads us to natural definitions for the space of asymptotic translations with its Lorentzian metric, for the Bondi news and the mass-aspect. A major role in these developments is played by the ‘co-curvature’, a naturally appearing quantity closely related to the Gauß curvature on a cut of

I

.
BMS3 mechanics and the black hole interior
Authors: Geiller Marc , Livine Etera R , Sartini Francesco 
Published: November 2021

Abstract
The spacetime in the interior of a black hole can be described by an homogeneous line element, for which the Einstein–Hilbert action reduces to a one-dimensional mechanical model. We have shown in Geiller et al (2021 SciPost Phys.
10 022) that this model exhibits a symmetry under the (2 + 1)-dimensional Poincaré group. Here we extend the Poincaré transformations to the infinite-dimensional BMS3 group. Although the black hole model is not invariant under those extended transformations, we can write it as a geometric action for BMS3, where the configuration space variables are elements of the algebra

b
m
s

3

and the equations of motion transform as coadjoint vectors. The BMS3 symmetry breaks down to its Poincaré subgroup, which arises as the stabilizer of the vacuum orbit. This symmetry breaking is analogous to what happens with the Schwarzian action in AdS2 JT gravity, although in the present case there is no direct interpretation in terms of boundary symmetries. This observation, together with the fact that other lower-dimensional gravitational models (such as the BTZ black hole) possess the same broken BMS3 symmetries, provides yet another illustration of the ubiquitous role played by this group.
Design, fabrication, and testing of microelectromechanical system spark gap switch based on streamer theory
Authors: Zhao Yuecen , Lou Wenzhong , Feng Hengzhen , He Bo 
Published: November 2021

Abstract
In order to realize that the fuze micro system has both high security and miniaturization characteristics, the spark gap research of Micro-Electro-Mechanical System safety system is carried out. So that to solve the safe and reliable function of the spark gap switch under the low power supply voltage (35 V) of the fuze micro system, the gas gap size and electrode radius are shown to significantly affect the gas breakdown voltage using streamer theory. Based on these results, a spark gap switch with triggering electrodes is designed. The triggering electrode gap is 2 μm and the main electrode gap is 10 μm. A spark gap switch test circuit is designed based on the RLC circuit. Through finite element simulation, it is verified that the gas breakdown voltage increases nonlinearly with increasing gap size. Pre-breakdown spark gap switches were fabricated based on the surface silicon process and tested. The test results show that the conduction voltage values of the triggering electrode and the main electrode are basically consistent with the simulation and calculation results. The breakdown voltage of the main electrode can be greatly reduced by applying a certain voltage to the triggering electrode, realize the reliable function in the micro fuze system.
Relativistic and QED corrections for the ground state lithiumlike ionization energies
Authors: Earwood William P , Davis Steven R 
Published: November 2021

Abstract
The ground state ionization energies of Z ⩽ 10 lithiumlike ions are calculated using fully correlated Gaussian wavefunctions. Leading-order relativistic corrections are evaluated, while QED corrections are established with small uncertainties by directly calculating the Araki–Sucher energy and expanding the three-electron Bethe logarithm in 1/Z. The non-relativistic α6 level shifts have also been calculated, and we have used these energies to recommend ionization energies, which include estimates of the influence of the relativistic portion of the α6 energy. The results emphasize the importance of the direct computation of the complete α6 correction, but also the need for new, higher accuracy experimental ionization limits.
MIL-88B (Fe) driven Fe/Fe3C encapsulated in high-crystalline carbon for high-efficient microwave absorption and electromagnetic interference shielding
Authors: Yang Xianfeng , Zhou You , Xing Hongna , Wang Hongpeng , Feng Wei , Feng Juan , Zhu Xiuhong , Shi Zhenhua , Zong Yan , Li Xinghua , Zheng Xinliang 
Published: November 2021

Abstract
Dual-functional magnetic/dielectric Fe/Fe3C@C composites were fabricated by pyrolysis of MIL-88B (Fe) in an Ar atmosphere, which was used for microwave absorption and electromagnetic interference (EMI) shielding. The Fe/Fe3C nanocrystals were completely encapsulated in crystalline carbon, which can improve oxidation resistance capacity. Owing to remarkable impedance matching and strong attenuation constants, the Fe/Fe3C@C composites show an optimal reflection loss (RL) value of −56.4 dB at 14.0 GHz and a broad effective absorption bandwidth (RL ⩽ −10 dB) of 4.8 GHz when the filling ratio and absorber thickness are only 20 wt% and 1.9 mm, respectively. Resulting from the high conductivity of crystalline carbon, magnetic loss of Fe/Fe3C, and core–shell structure, the Fe/Fe3C@C composites also show remarkable EMI shielding properties at the X band, which are enhanced by increasing the filling ratio of the Fe/Fe3C@C composites. When the filling ratio is 50 wt%, the EMI shielding efficiency can reach 35 dB. This work suggests that magnetic/dielectric Fe/Fe3C@C is a good candidate in microwave absorption and EMI shielding.
Characteristics of pulsed nanosecond discharge excited by compact solid-state pulse forming line at atmospheric pressure air
Authors: Li Jie , Liu Yi , Li Xi , Dong Pan , Liu Feixiang , Xie Yutong , Xia Liansheng , Long Jidong , Zhang Linwen 
Published: November 2021

Abstract
Non-equilibrium plasma is a promising technology for the generation of ozone and removal of exhausted fuel gases. However, applications of non-equilibrium plasma are restricted by energy utilization efficiency in many industry fields. Discharge excited by nanosecond pulsed power is regarded as one of the most efficient methods. In this study, a compact five stages stacked Blumlein pulse forming line and photoconductive semiconductor switches-based power source was introduced to generate pulsed plasma. This compact source could achieve over 50 kV with 10.1 ns pulse width and 4.8 ns pulse rising time. Coaxial cylindrical reactor was employed to generate a pulsed streamer discharge driven by the nanosecond pulsed source in atmospheric pressure air. Electrical parameters of the streamer discharge have been obtained in this study, the instantaneous power dissipation exceeds 8 MW and the average energy consumption of each pulse exceeds 56 mJ. Experiments of high speed photography have been conducted to observe the evolution process. It can be found that streamer heads start from the central wire electrode and then head to the grounded cylinder electrode in all radial direction of the coaxial electrode. Triple wire-to-cylinder electrodes discharge shows that all the three coaxial discharges develop synchronously and symmetrically, which shows that is capable of generating large volume non-equilibrium diffusive streamer discharge plasma.
Narrowband terahertz metasurface circular polarization beam splitter with large spectral tunability based on lattice-induced chirality
Authors: Luo Xiaoqing , Dong Xiaoxiang , Xu Xinlong , Hu Fangrong , Li Guangyuan 
Published: November 2021

Abstract
We propose a terahertz metasurface with chirality induced by surface lattice resonance to create a narrowband circular polarization beam splitter (PBS) with large spectral tunability in both transmission and reflection modes. Results show that strong circular dichroism effects can be observed in two spectrally narrow bands, and thus a dual-band circular PBS can be achieved. We show that surface lattice resonance induces much narrower and stronger circular dichroism effects than localized resonance, resulting in higher polarization extinction ratios, higher quality factors, and more circular polarization states. The narrowband operation frequency of lattice-induced PBS with extinction ratio larger than 10 dB can be tuned over a large spectral range, from 1.6 THz to 2.3 THz, by varying the incidence angle. We expect the proposed strong, narrowband, and spectrally tunable circular PBS will find applications in polarization-dependent systems including imaging, spectroscopy, sensing and telecommunication in the terahertz regime.
A review on recent advances and challenges of ionic wind produced by corona discharges with practical applications
Authors: Qu Jingguo , Zeng Minjun , Zhang Dewei , Yang Dakai , Wu Xiongwei , Ren Qinlong , Zhang Jianfei 
Published: November 2021

AbstractIonic wind, an induced phenomenon during corona discharge, possessing the features of silent operation and no moving parts, has a wide range of applications. Ionic wind generation is accompanied by complex physical processes, involving gas ionization, ion recombination, flow, and various chemical reactions, as well as mutual couplings between some of them. Therefore, understanding the corona discharge process and ionic wind generation is crucial for researchers and engineers to better utilize this phenomenon in practical applications. In this review, the principles of corona discharge and its induced ionic wind are presented. Subsequently, ionic wind generators are discussed according to their applications, and the corresponding advances based on experimental studies and numerical simulations are also reviewed. Moreover, the challenges of transitioning the ionic wind technology from laboratory studies to practical applications are discussed. These challenges include the excessively high onset voltage of the corona, ozone emission, and influence of environmental conditions. Furthermore, the mechanisms of these barriers and several effective approaches for mitigating them are provided. Finally, some future research prospects and the conclusions are presented.
Multi-wavelength achromatic bifocal metalenses with controllable polarization-dependent functions for switchable focusing intensity
Authors: Chen Long , Shao Zhenglong , Liu Jia , Tang Dongliang 
Published: November 2021

Abstract
In this paper, a bifocal metalens is designed through simultaneously controlling two polarization-dependent functions, which can respectively focus x-polarized and y-polarized light into different positions, and the relative intensity between two foci can be continuously tuned through a simple rotation of the incident linear polarization angle. The proposed metalenses are composed of rectangle nanopillars with spatially varying widths and lengths, which provide distinct propagating phases under two orthogonal polarizations. Therefore, there exists a degree of freedom to achieve two polarization-dependent focusing functions. More importantly, these nanopillars possess excellent dispersion engineering, and provide an effective method for the realization of achromatic bifocal metalenses. After powerful optimizations, two achromatic bifocal metalenses are constructed and further demonstrated numerically. The x-polarized and y-polarized components are focused into different positions under different working wavelengths. Simulated results agree well with our designs. The approach here is expected to find optical applications in micro-manipulation, optical communication and multicolor display.
Reconstructive dosimetry and radiation dose evaluation of workers and public due to a Brazilian radiological accident in industrial radiography
Authors: Lima Camila Moreira Araujo de , Almeida Silva Tadeu Augusto de , Hunt John Graham , Da Silva Francisco Cesar Augusto 
Published: November 2021

Abstract
Radiological accidents occur mainly in the practices recognized as high risk and which are classified by the International Atomic Energy Agency (IAEA) as Categories 1 and 2: radiotherapy, industrial irradiators and industrial radiography. In Brazil, five important cases in industrial gamma radiography occurred from 1985 to 2018, involving seven radiation workers and 19 members of the public. The accidents caused localized radiation lesions on the hands and fingers. One of these accidents is the focus of this paper. In this accident, a 3.28 TBq 192Ir radioactive source was left unshielded for 9 h in a non-destructive testing (NDT) company parking lot, and many radiation workers, employees and public, including teachers of a primary school were exposed. The radioactive source was also directly handled by a security worker for about 1.5 min causing severe radiation injuries in the hand and fingers. This paper presents radiation dose estimates for all accidentally exposed individuals. Four scenarios were considered, and three internationally recognised and updated reconstructive dosimetry techniques were used, named, Brazilian visual Monte Carlo Dose Calculation (VMC), virtual environment for radiological and nuclear accidents simulation (AVSAR) and RADPRO Calculator®. The main radiation doses estimated by VMC were the absorbed dose of 34 Gy for the security worker’s finger and his effective dose of 91 mSv; effective doses from 43 to 160 mSv for radiation workers and NDT employees; and effective doses of 9 mSv for teachers in the schoolyard.
Comparative DFT dual gas adsorption model of ZnO and Ag/ZnO with experimental applications as gas detection at ppb level
Authors: Kumar Utkarsh , Huang Shih-Ming , Deng Zu-Yin , Yang Cheng-Xin , Haung Wen-Min , Wu Chiu-Hsien 
Published: November 2021

Abstract
By experimental and density functional theory calculations, the toxic gases (O3 and NO2) sensing capability and mechanism of ZnO NRs and Ag/ZnO NRs have been comparatively studied in this work. Ag NPs arrays were employed for the growth of ZnO NRs. The experimental results show that when ZnO NRs are grown on Ag NPs, the response and adsorption rate towards the gases change significantly. The TDOS plot shows that the HOMO-LUMO gap changes after interaction with different oxidizing gases, and the peak intensity also decreases confirming the electron are transferred from ZnO to NO2 and O3. The response to gases decreases and the adsorption reaction rate increases in Ag/ZnO NRs, as calculated by the Eyring-Polanyi equation, which is very similar to our experimental data. We also find that the absorption coefficient is different for O3 and NO2. Finally, experimental response and theoretical results were compared and found to be in good agreement.
Understanding machine learning classifier decisions in automated radiotherapy quality assurance
Authors: Chen Yunsheng , Aleman Dionne M , Purdie Thomas G , McIntosh Chris 
Published: November 2021

AbstractThe complexity of generating radiotherapy treatments demands a rigorous quality assurance (QA) process to ensure patient safety and to avoid clinically significant errors. Machine learning classifiers have been explored to augment the scope and efficiency of the traditional radiotherapy treatment planning QA process. However, one important gap in relying on classifiers for QA of radiotherapy treatment plans is the lack of understanding behind a specific classifier prediction. We develop explanation methods to understand the decisions of two automated QA classifiers: (1) a region of interest (ROI) segmentation/labeling classifier, and (2) a treatment plan acceptance classifier. For each classifier, a local interpretable model-agnostic explanation (LIME) framework and a novel adaption of team-based Shapley values framework are constructed. We test these methods in datasets for two radiotherapy treatment sites (prostate and breast), and demonstrate the importance of evaluating QA classifiers using interpretable machine learning approaches. We additionally develop a notion of explanation consistency to assess classifier performance. Our explanation method allows for easy visualization and human expert assessment of classifier decisions in radiotherapy QA. Notably, we find that our team-based Shapley approach is more consistent than LIME. The ability to explain and validate automated decision-making is critical in medical treatments. This analysis allows us to conclude that both QA classifiers are moderately trustworthy and can be used to confirm expert decisions, though the current QA classifiers should not be viewed as a replacement for the human QA process.
A Geant4 Fano test for novel very high energy electron beams
Authors: McManus M , Romano F , Royle G , Palmans H , Subiel A 
Published: November 2021

Abstract

Objective. The boundary crossing algorithm available in Geant4 10.07-p01 general purpose Monte Carlo code has been investigated for a 12 and 200 MeV electron source by the application of a Fano cavity test. Approach. Fano conditions were enforced through all simulations whilst varying individual charged particle transport parameters which control particle step size, ionisation and single scattering. Main Results. At 12 MeV, Geant4 was found to return excellent dose consistency within 0.1% even with the default parameter configurations. The 200 MeV case, however, showed significant consistency issues when default physics parameters were employed with deviations from unity of more than 6%. The effect of the inclusion of nuclear interactions was also investigated for the 200 MeV beam and was found to return good consistency for a number of parameter configurations. Significance. The Fano test is a necessary investigation to ensure the consistency of charged particle transport available in Geant4 before detailed detector simulations can be conducted.
Radially-dependent ignition process of a pulsed capacitively coupled RF argon plasma over 300 mm-diameter electrodes: multi-fold experimental diagnostics
Authors: Su Zi-Xuan , Shi De-Hua , Liu Yong-Xin , Zhao Kai , Gao Fei , Wang You-Nian 
Published: November 2021

Abstract
A synergistic combination of multi-diagnostic methods are proposed to investigate temporal evolution of electrical and plasma parameters at various radial positions over 300 mm-diameter electrodes during the pre-ignition, ignition, and post-ignition phases of a pulsed capacitively coupled radio-frequency (RF) argon discharge. The electron density, n
e, and the optical emission intensity (OEI) of argon at 750.4 nm at different radial positions are measured time-resolved by using a hairpin probe and an optical probe, respectively. A B-dot probe is employed to determine the waveforms of the azimuthal magnetic field at different radii, from which the waveforms of the axial current density at corresponding radial positions are derived based on Ampere’s law. Then, the time evolution of the power density at various radii can be calculated, provided that the voltage drop between the electrodes is independent of radius. Meanwhile, the time-dependent total power deposited into the reactor is calculated with the voltage and the current waveforms measured by a voltage and a current probe at the power feeding point. It was found that during pre-ignition phase, the OEI and n
e cannot be measurable due to extremely low power deposition when the system exhibits pure capacitive impedance. During the ignition phase, the OEI, the power density, and the current density exhibit the most significant increase at the electrode center, while the time evolution of n
e measured by the hairpin probe seems to exhibit a relatively weak radial dependence during this phase. In particular, at r ⩽ 8 cm, the OEI at every radius was observed to change with time in the same manner as the power density during the ignition phase, because the RF power is absorbed primarily by electrons, which dissipate their energy via inelastic collisions. Shortly, the profile of n
e becomes edge-high during the post-ignition phase and remains thereafter until the end of the pulse-on period. Methodologically, the synergistic diagnostics lay the foundation for extensive studies on spatiotemporal evolution of plasma ignition process under broader conditions, e.g. electronegative gas, lower working gas pressure and very high driving frequency, widely used by practical etching process.