bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined effect of cavitation and multi-scale texture on the bearing properties of seawater-lubricated friction pair
Authors: Wang Zhiqiang , Dai Zhangxiang , Wu Shaofeng , Zhang Ben , Cao Jiangtao , Ye Rihong
Published: August 2023

To explore the tribological properties of a seawater-lubricated friction pair, the influence of cavitation and multi-scale texture on the load-carrying capacity is investigated under seawater lubrication conditions. In this paper, a numerical simulation method is proposed to reveal the influence mechanism of cavitation on the load-carrying capacity, and the simulation results are verified by experiments. The results show that cavitation, wedge action, and the vortex flow effect are the main mechanisms responsible for affecting the load-carrying capacity. Cavitation is not always advantageous for the load-carrying capacity. The results indicate that cavitation enhances the load-carrying capacity when the velocity is between 5 and 10 m/s. However, the cavitation effect shows a negative effect with a velocity exceeding 10 m/s. In three different scales of surface textures, the load-carrying capacity of the millimeter-scale texture is the highest, followed by the cross-scale texture and the micrometer-scale texture. The load-carrying capacity of the millimeter-scale texture is almost 10 times that of the micrometer-scale texture. Furthermore, regardless of the texture scale, a texture with a high depth-to-diameter ratio (H = 1) always exhibits a higher load-carrying capacity at low speeds (V < 10 m/s).
Validation of THz absorption spectroscopy by a comparison with ps-TALIF measurements of atomic oxygen densities
Authors: Wubs J. R. , Invernizzi L. , Gazeli K. , Macherius U. , Lü X. , Schrottke L. , Lombardi G. , Weltmann K.-D. , van Helden J. H.
Published: August 2023

Terahertz (THz) absorption spectroscopy has recently been developed as a diagnostic technique for measuring absolute ground-state atomic oxygen densities in plasmas. To demonstrate the validity of this approach, we present in this Letter a benchmark against a more established method. Atomic oxygen densities were measured with THz absorption spectroscopy and compared to those obtained from picosecond (ps) two-photon absorption laser induced fluorescence (TALIF) measurements on the same capacitively coupled radio frequency oxygen discharge. Similar changes in the atomic oxygen density were observed with both diagnostics when varying the applied power (20–100 W) and the gas pressure (0.7–1.3 mbar). Quantitatively, the results are in good agreement as well, especially when considering the total margin of error of the two diagnostics. For example, for a gas pressure of 1.3 mbar and an applied power of 30 W, atomic oxygen densities measured with THz absorption spectroscopy and TALIF were (7.0 ± 1.7)×1014 cm−3 and (5.3 ± 3.2)×1014 cm−3, respectively. This shows that THz absorption spectroscopy is an accurate technique that can be reliably used for real-world applications to determine atomic oxygen densities in plasmas.
Decomposition of skin-friction and wall heat flux of temporal transition in compressible channel flows with direct numerical and constrained large-eddy simulations
Authors: Chen Sanmu , Lee HsuChew , Xu Dehao , Wan Minping , Chen Shiyi
Published: August 2023

The twofold integral-based decompositions of skin-friction and wall heat flux coefficients are implemented in compressible temporal transitional channel flows with direct numerical simulation and constrained large eddy simulation (CLES) to explore (i) the generations of the skin-friction and wall heat flux coefficients and their overshoot during the transition and (ii) why CLES under-predicts the overshoot phenomenon. The Reynolds shear stress, the mean velocity gradient with respect to time, and the mean velocity convection are dominating terms during the transition process of skin friction coefficient Cf, and the effect of the mean velocity convection becomes stronger as the Mach number (Ma) increases. For the wall heat flux coefficient Bq, the turbulent heat transfer, the mean energy gradients in time, and the viscous stress are significant contributors. The effects of molecular heat transfer and the mean convection on transition are increasingly important to Bq as Ma increases. The overshoot of Cf and Bq at Ma = 1.5 is mainly caused by the significant changes of mean velocity profiles and mean energy profiles with respect to time respectively. At Ma = 3.0, the overshoot of Cf is due to the significant change of mean velocity profiles in time and the mean velocity convection, while the overshoot of Bq is due to the mean energy changes in time and mean energy convection. It is found that the underestimation of the overshoots of Cf and Bq in CLES is primarily caused by the variances of the mean velocity gradient and mean energy gradient, respectively.
Efficient Co/Pt THz spintronic emitter with tunable polarization
Authors: Buryakov A. M. , Gorbatova A. V. , Avdeev P. Y. , Lebedeva E. D. , Brekhov K. A. , Ovchinnikov A. V. , Gusev N. S. , Karashtin E. A. , Sapozhnikov M. V. , Mishina E. D. , Tiercelin N. , Preobrazhensky V. L.
Published: August 2023

We report on the design of a spintronic emitter based on the Pt(3 nm)/Co(3 nm) structure, which enables the control over terahertz radiation polarization. Utilizing the field-induced magnetization rotation that takes place at low magnetic fields of up to 250 Oe at room temperature, we have achieved the full range of terahertz polarization rotation from 0° to 360°. This rotation became possible due to the uniaxial magnetic anisotropy induced in the plane of the cobalt film during its fabrication. We evaluated the efficiency of the Co/Pt structure in generating terahertz radiation and found that the terahertz pulse energy flux reaches ∼160 nJ/cm2 at an excitation flux of 4 mJ/cm2.
Large amplification of the sensitivity of symmetric-response magnetic tunnel junctions with a high gain flux concentrator
Authors: Manceau Samuel , Brun Thomas , Fischer Johanna , Ducruet Clarisse , Sabon Philippe , Cavoit Claude , Jannet Guillaume , Pinçon Jean-Louis , Prejbeanu Ioan Lucian , Kretzschmar Matthieu , Baraduc Claire
Published: August 2023

Miniaturized, ultra-sensitive and easily integrable magnetometers are needed for many applications like space exploration or medical survey. In this study, we combine innovative magnetic tunnel junctions having a symmetric resistance-field (R–H) response with a high gain flux concentrator. In our junctions, the magnetization of the free layer (FL) is stabilized in an anti-parallel configuration with respect to that of the reference layer. This configuration is achieved by using a soft exchange pinning of the FL. We precisely adjust the exchange field value with a dusting layer of ruthenium used to weakly decouple the magnetization of the FL from the local moments of the antiferromagnet. In order to improve the junction's sensitivity, we study the influence of the exchange field value and of the shape anisotropy on the even-function R–H response. In particular, we compare circular junctions with elliptic or rectangular junctions of various aspect ratios and orientations. We find that the sensitivity of the junctions increases when reducing the soft-pinning exchange field and by using junctions with an elongated shape in the direction of the applied field. Finally, we were able to further increase the sensitivity by a factor 440 due to a flux concentrator placed around the junction by electrochemical deposition of NiFe. Its design is optimized (elongated shape, 5–7 μm thickness and 10 μm air-gap) in order to obtain this very high gain. The complete sensor system composed of these magnetic tunnel junctions and the flux concentrator allows to reach sensitivities larger than 1000%/mT.
Experimental and numerical investigation of cylinder rising in co-current turbulent air pipe flow: Application in pneumatic ice drilling
Authors: Cao Pinlu , Cao Jine , Cao Hongyu , Wang Mengke , Wen Chengda , Yao Shanshan
Published: August 2023

Air-reverse-circulation drilling into ice sheets is a promising clean technology for fast and safe ice sample recovery in the polar regions. However, a few studies in the literature explore an ice cylinder's rising from rest in tubing filled by co-current air flow. This study builds an experimental setup as well as uses the computational fluid dynamics (CFD) method to characterize the process of ice cylinder rising from being seated at bottom. Variations of the drag coefficient when a cylinder starts to rise and the critical velocity, i.e., the minimum air injection velocity to raise a cylinder, are investigated with the experiments and simulations. Reynolds number is found to have a marginal effect on the drag coefficient and critical velocity while ice-cylinder-pipe geometry can influence the two factors. Wall effect resulting from the existence of pipe lateral wall can enhance the drag coefficient and accordingly, reduce critical velocity. Decreasing the clearance between cylinder and pipe or increasing cylinder length is observed to strengthen the wall effect, but enlarging the cylinder diameter surprisingly weakens the wall effect. A mathematical correlation is developed to quantify the interplay between cylinder-pipe geometry and critical velocity by using parameters like sphericities and diameter ratio. When a cylinder continues to rise off bottom, its drag coefficient would first increase quickly and then decrease gradually to a value where terminal velocity is achieved.
Description of electron mobilities in epitaxial lanthanum-doped barium stannate films: Influences of LO phonons, threading dislocation, and ionized donor defects
Authors: Thongnum Anusit
Published: August 2023

Lanthanum-doped barium stannate (La-doped BaSnO3 or LBSO) has attracted the attention of researchers and engineers because of its wide range of potential applications in electronic and optoelectronic devices. This is due to a combination of its exceptional room temperature (RT) mobility of 320 cm2 V−1 s−1 and high visible range transparency. However, epitaxial LBSO films made using strategic deposition techniques such as molecular beam epitaxy, pulsed laser deposition, and magnetron sputtering show comparatively low RT mobilities, between 24 and 183 cm2 V−1 s−1, and an accurate description of these RT mobilities is still sought. Herein, we provide the underlying scattering mechanisms related to longitudinal optical (LO) phonons, threading dislocation, and ionized donor defects to elucidate the RT mobilities in LBSO epitaxial films. It was found that the total mobility estimated using Matthiessen's rule provided strong quantitative agreement with experimental results. The large polaron mobility based on LO phonon scattering dominated the whole spectrum of electron concentrations in this system. It was an upper bound mobility, i.e., the mobility limit attained at 320 cm2 V−1 s−1. The calculated mobility associated with LO phonon and threading dislocation scatterings adequately verified the experimental results between 150 and 183 cm2 V−1 s−1. The predicted results for all three scattering types were predominant in experimental data at less than 150 cm2 V−1 s−1. These investigations deepen our understanding of mechanisms governing the charge transport scattering in epitaxial LBSO films and pave the way for the development of novel semiconductor thin films for use in electronic and optoelectronic devices.
Two-dimensional anisotropic monolayers NbOX2 (X = Cl, Br, I): Promising candidates for photocatalytic water splitting with high solar-to-hydrogen efficiency
Authors: Pan Lu , Wan Yu-Lu , Wang Zhao-Qi , Geng Hua-Yun , Chen Xiang-Rong
Published: August 2023

Motivated by the recent experimental synthesis of two-dimensional (2D) NbOI2 which possesses a moderate bandgap and outstanding absorption of sunlight, using the first-principles calculations, we conduct a thorough study of the geometric configuration, electronic structures, and photocatalytic properties for NbOX2 (X = Cl, Br, I) monolayers. These NbOX2 monolayers have been demonstrated to be dynamically, thermally, and mechanically stable. The significant anisotropic mechanical properties of NbOX2 monolayers are reflected by the calculated Young's modulus and Poisson's ratio. Our results indicate that these NbOX2 materials unfold semiconductor characters with indirect bandgaps of 1.886, 1.909, and 1.813 eV, respectively. Among these monolayers, it is found that the NbOBr2 system exhibits a favorable photocatalytic activity in an acidic condition (pH = 0), and the NbOI2 monolayer can act as a potential photocatalyst for spontaneous photocatalytic water splitting under a neutral environment (pH = 7). Furthermore, the response of bandgap and band edge positions of NbOX2 monolayers to the exerting in-plane strain (–6% to 6%) are investigated. These NbOX2 monolayers also show strong light absorption from the visible to ultraviolet region and anisotropic high carrier transport. Particularly, the high solar-to-hydrogen efficiency of the NbOCl2 (1% tensile strain), NbOBr2, and NbOI2 monolayers are predicted to be 14.11% (pH = 0), 16.34% (pH = 0), and 17.05% (pH = 7), respectively. Therefore, we expect the NbOX2 monolayers to be promising candidates for highly efficient photocatalytic water splitting.
The dynamic behavior of a self-propelled droplet on a conical fiber: A lattice Boltzmann study
Authors: Zhang Jinggang , Shen Hao , Cui Haihang , Chen Li , Chen Liguo
Published: August 2023

In this paper, the dynamic behavior of a self-propelled droplet along a conical fiber is simulated by using an improved lattice Boltzmann color-gradient method. This method is developed on the basis of our recently developed density ratio model [Zhang et al., Int. Commun. Heat Mass Transfer, 137, 106284 (2022).], but a wetting boundary condition is added to account for the moving contact line on an arbitrary solid surface. First, this method is validated against the analytical droplet shapes and contact angles for droplets surrounded by matrix fluids of different densities on flat and spherical surfaces, and the spontaneous transport of a droplet on a conical fiber. This method is then adopted to systematically study the effects of the Bond number (Bo), surface wettability (θ), cone hemi-angle (α), and droplet volume on the droplet dynamic behavior. In each case, the results show that the droplet climbing velocity first increases and then decreases, and a velocity fluctuation is observed, which is due to that the apparent receding and advancing contact angles do not simultaneously reach the equilibrium contact angle. As droplet volume increases, the equilibrium droplet height monotonically increases. As Bo or θ increases, the droplet climbing height and the wetting area both decrease. We also found that the equilibrium climbing height first increases and then decreases with α, and its maximum is reached around α=2.5°.
Optimization of diamond sensor for trace detection of SARS-CoV-2 N-protein using Au nanoparticles
Authors: Zhang Qianwen , Wu Huaxiong , Du Yuxiang , Zhang Minghui , Xu Bangqiang , Chen Genqiang , He Shi , Zhang Dan , Li Qi , Wang Hong-Xing
Published: August 2023

In this study, Au nanoparticles were introduced to functionalize hydrogen-terminated diamond (H-diamond) to optimize surface modification and improve the performance of diamond sensor for trace detection of SARS-CoV-2 N-protein. The Au nanoparticles were obtained by an electron beam evaporation system and annealing. Atom force microscope and scanning electron microscope were utilized to characterize the structure, morphology, and distribution of fabricated Au nanoparticles. The concentration of SARS-CoV-2 N-protein was determined by the investigation of transfer characteristics of a diamond solution gate field effect transistor. Sensitivity of this sensor was obtained as 27.43 mV/lg (N-protein concentration), which was higher than a regular H-diamond sensor. In addition, it had a wider linear detection range of 10−15–10−5 mg/ml and a lower limit of detection of 10−15 mg/ml. Accordingly, the detection performance of diamond sensor has been greatly improved due to the functionalization of Au nanoparticles.
Decomposing cryptocurrency high-frequency price dynamics into recurring and noisy components
Authors: Wątorek Marcin , Skupień Maria , Kwapień Jarosław , Drożdż Stanisław
Published: August 2023

This paper investigates the temporal patterns of activity in the cryptocurrency market with a focus on Bitcoin, Ethereum, Dogecoin, and WINkLink from January 2020 to December 2022. Market activity measures—logarithmic returns, volume, and transaction number, sampled every 10 s, were divided into intraday and intraweek periods and then further decomposed into recurring and noise components via correlation matrix formalism. The key findings include the distinctive market behavior from traditional stock markets due to the nonexistence of trade opening and closing. This was manifested in three enhanced-activity phases aligning with Asian, European, and U.S. trading sessions. An intriguing pattern of activity surge in 15-min intervals, particularly at full hours, was also noticed, implying the potential role of algorithmic trading. Most notably, recurring bursts of activity in bitcoin and ether were identified to coincide with the release times of significant U.S. macroeconomic reports, such as Nonfarm payrolls, Consumer Price Index data, and Federal Reserve statements. The most correlated daily patterns of activity occurred in 2022, possibly reflecting the documented correlations with U.S. stock indices in the same period. Factors that are external to the inner market dynamics are found to be responsible for the repeatable components of the market dynamics, while the internal factors appear to be substantially random, which manifests itself in a good agreement between the empirical eigenvalue distributions in their bulk and the random-matrix theory predictions expressed by the Marchenko–Pastur distribution. The findings reported support the growing integration of cryptocurrencies into the global financial markets.
A convenient switch design for high time resolution and energy resolution in ion velocity imaging
Authors: Yu Tongpo , Yang Xinlang , Gao Zhi , Shan Baokun , Xu Lei , Zhou Xiaoguo , Liu Shilin
Published: August 2023

Time-sliced velocity map imaging (VMI) has extensively been applied in photodissociation dynamics studies, thanks to its unique advantages, such as high energy resolution and no requirement of inverse Abel or Hankel transformations. However, its time resolution is generally insufficient for distinguishing adjacent m/z ions with a certain kinetic energy due to the overlapping of time-of-flight distributions. Herein, we have made a novel and convenient switch design for the common ion optics in three-dimensional (3D) VMI. By simply introducing two additional resistors out of the vacuum chamber, the strength ratio of the extraction and acceleration fields is easily changed from 3D VMI to two-dimensional (2D) VMI under optimized conditions, as well as a significant extension of free drift length, leading to a higher time resolution while maintaining the high energy resolution. As a result, 2D and 3D VMI can be quickly switched without breaking the vacuum and replacing the electrostatic plates.
Injection and Escape: A new model on the thrust generated by a thin pitching plate
Authors: De Arnab Kumar , Sarkar Sandip
Published: August 2023

We have proposed a physical model to describe the underlying physics behind the drag or thrust produced by a pitching panel in a uniform stream. Over the clockwise and counterclockwise pitching motions, the model categorizes Injection and Escape kinematic phases. The former estimates the total fluid volume gathered at the trailing edge, and the latter amount to the fluid volume fenced by the plate reaching the trailing edge. To verify our proposed model, we have performed three-dimensional simulations using an immersed boundary-based numerical code for the flow past a thin pitching plate at a Reynolds number of Re = 1000 for the aspect range of 0.54≤AR≤16 at maximum pitching angle of θmax=5°,15° with pitching frequency St=0.5,1. Our model reveals that the plate generates a net thrust in a pitching cycle when Injection dominates Escape and conversely for the drag cases.
Barriers to optimal management of syphilis in pregnancy and congenital syphilis in south-east Queensland: a qualitative investigation
Authors: Fowler James A. , Warzywoda Sarah , Nourse Clare , Wu Mandy , Britton Sumudu , Rowling Diane , Griffin Paul , Lazarou Mattea , Hamilton Zoe , Dean Judith A.
Published: August 2023

Background Australia, like many high-income countries, is experiencing a resurgence of infectious syphilis in pregnancy and congenital syphilis. Evaluations of public health notifications and clinical records suggest that healthcare systems may not be providing optimal care to women and their neonates. This study aims to explore the barriers to optimal management of syphilis in pregnancy and congenital syphilis to identify key areas for improvement. Methods Between 2021 and 2022, 34 healthcare workers (HCW) practicing in south-east Queensland (SEQ) Australia were recruited to complete semi-structured interviews regarding their perceptions towards management of syphilis in pregnancy and congenital syphilis. Interviews were analysed thematically. Results Thematic analysis identified four themes related to the management of syphilis in pregnancy. These included poor communication between disciplines, services, and teams from delivery through to management and post-delivery, lack of formal internal and external referral pathways, unclear and often complex maternal and congenital syphilis management procedures, and limited HCW knowledge of infectious syphilis in pregnancy and congenital syphilis. Conclusion As congenital syphilis numbers continue to rise in SEQ, it is imperative that healthcare systems and HCWs identify and address gaps in the provision of health care.
Dryland sensitivity to climate change and variability using nonlinear dynamics
Authors: Sasaki Takehiro , Collins Scott L. , Rudgers Jennifer A. , Batdelger Gantsetseg , Baasandai Erdenetsetseg , Kinugasa Toshihiko
Published: August 2023

Primary productivity response to climatic drivers varies temporally, indicating state-dependent interactions between climate and productivity. Previous studies primarily employed equation-based approaches to clarify this relationship, ignoring the state-dependent nature of ecological dynamics. Here, using 40 y of climate and productivity data from 48 grassland sites across Mongolia, we applied an equation-free, nonlinear time-series analysis to reveal sensitivity patterns of productivity to climate change and variability and clarify underlying mechanisms. We showed that productivity responded positively to annual precipitation in mesic regions but negatively in arid regions, with the opposite pattern observed for annual mean temperature. Furthermore, productivity responded negatively to decreasing annual aridity that integrated precipitation and temperature across Mongolia. Productivity responded negatively to interannual variability in precipitation and aridity in mesic regions but positively in arid regions. Overall, interannual temperature variability enhanced productivity. These response patterns are largely unrecognized; however, two mechanisms are inferable. First, time-delayed climate effects modify annual productivity responses to annual climate conditions. Notably, our results suggest that the sensitivity of annual productivity to increasing annual precipitation and decreasing annual aridity can even be negative when the negative time-delayed effects of annual precipitation and aridity on productivity prevail across time. Second, the proportion of plant species resistant to water and temperature stresses at a site determines the sensitivity of productivity to climate variability. Thus, we highlight the importance of nonlinear, state-dependent sensitivity of productivity to climate change and variability, accurately forecasting potential biosphere feedback to the climate system.
The strong metal–support interactions induced electrocatalytic three-electron oxygen reduction to hydroxyl radicals for water treatment
Authors: Xie Liangbo , Wang Pengfei , Zheng Wenwen , Zhan Sihui , Xia Yuguo , Liu Yuepeng , Yang Wenjing , Li Yi
Published: August 2023

As a promising environmental remediation technology, the electro-Fenton (EF) process is mainly limited by the two rate-limiting steps, which are H
2
O
2
generation and activation. The electrocatalytic three-electron oxygen reduction reaction (3e
−
ORR) can directly activate oxygen to hydroxyl radicals (•OH), which is expected to break through the rate-limiting steps of the EF process. However, limited success has been achieved in the design of 3e
−
ORR electrocatalysts. Herein, we propose Cu/CoSe
2
/C with the strong metal–support interactions to enhance the 3e
−
ORR process, exhibiting remarkable reactivity and stability for •OH generation. Both experiment and DFT calculation results reveal that CoSe
2
is conducive to the generation of H
2
O
2
. Meanwhile, the metallic Cu can enhance the adsorption strength of *H
2
O
2
intermediates and thus promotes the one-electron reduction to •OH. The Cu/CoSe
2
/C catalyst exhibits the electron-transfer number close to 3.0 during the ORR process, and exhibits the outstanding •OH generation performance, achieving a higher apparent rate constant (6.0 times faster) toward ciprofloxacin compared with its analogy without the SMSI effect. Our work represents that the SMSI effect endows Cu/CoSe
2
/C high activity and selectivity for •OH generation, providing a unique perspective for the design of a high-efficiency 3e
−
ORR catalyst.
Physics-supervised deep learning–based optimization (PSDLO) with accuracy and efficiency
Authors: Li Xiaowen , Chang Lige , Cao Yajun , Lu Junqiang , Lu Xiaoli , Jiang Hanqing
Published: August 2023

Identifying efficient and accurate optimization algorithms is a long-desired goal for the scientific community. At present, a combination of evolutionary and deep-learning methods is widely used for optimization. In this paper, we demonstrate three cases involving different physics and conclude that no matter how accurate a deep-learning model is for a single, specific problem, a simple combination of evolutionary and deep-learning methods cannot achieve the desired optimization because of the intrinsic nature of the evolutionary method. We begin by using a physics-supervised deep-learning optimization algorithm (PSDLO) to supervise the results from the deep-learning model. We then intervene in the evolutionary process to eventually achieve simultaneous accuracy and efficiency. PSDLO is successfully demonstrated using both sufficient and insufficient datasets. PSDLO offers a perspective for solving optimization problems and can tackle complex science and engineering problems having many features. This approach to optimization algorithms holds tremendous potential for application in real-world engineering domains.
A methanotrophic bacterium to enable methane removal for climate mitigation
Authors: He Lian , Groom Joseph D. , Wilson Erin H. , Fernandez Janette , Konopka Michael C. , Beck David A. C. , Lidstrom Mary E.
Published: August 2023

The rapid increase of the potent greenhouse gas methane in the atmosphere creates great urgency to develop and deploy technologies for methane mitigation. One approach to removing methane is to use bacteria for which methane is their carbon and energy source (methanotrophs). Such bacteria naturally convert methane to CO
2
and biomass, a value-added product and a cobenefit of methane removal. Typically, methanotrophs grow best at around 5,000 to 10,000 ppm methane, but methane in the atmosphere is 1.9 ppm. Air above emission sites such as landfills, anaerobic digestor effluents, rice paddy effluents, and oil and gas wells contains elevated methane in the 500 ppm range. If such sites are targeted for methane removal, technology harnessing aerobic methanotroph metabolism has the potential to become economically and environmentally viable. The first step in developing such methane removal technology is to identify methanotrophs with enhanced ability to grow and consume methane at 500 ppm and lower. We report here that some existing methanotrophic strains grow well at 500 ppm methane, and one of them,
Methylotuvimicrobium buryatense
5GB1C, consumes such low methane at enhanced rates compared to previously published values. Analyses of bioreactor-based performance and RNAseq-based transcriptomics suggest that this ability to utilize low methane is based at least in part on extremely low non-growth-associated maintenance energy and on high methane specific affinity. This bacterium is a candidate to develop technology for methane removal at emission sites. If appropriately scaled, such technology has the potential to slow global warming by 2050.
Convolutional neural networks for the classification of glitches in gravitational-wave data streams
Authors: Fernandes Tiago , Vieira Samuel , Onofre Antonio , Calderón Bustillo Juan , Torres-Forné Alejandro , Font José A
Published: August 2023

We investigate the use of convolutional neural networks (including the modern ConvNeXt network family) to classify transient noise signals (i.e. glitches) and gravitational waves (GWs) in data from the Advanced LIGO detectors. First, we use models with a supervised learning approach, both trained from scratch using the Gravity Spy dataset and employing transfer learning by fine-tuning pre-trained models in this dataset. Second, we also explore a self-supervised approach, pre-training models with automatically generated pseudo-labels. Our findings are very close to existing results for the same dataset, reaching values for the F1 score of 97.18% (94.15%) for the best supervised (self-supervised) model. We further test the models using actual GW signals from LIGO-Virgo’s O3 run. Although trained using data from previous runs (O1 and O2), the models show good performance, in particular when using transfer learning. We find that transfer learning improves the scores without the need for any training on real signals apart from the less than 50 chirp examples from hardware injections present in the Gravity Spy dataset. This motivates the use of transfer learning not only for glitch classification but also for signal classification.
Quasinormal modes from Penrose limits
Authors: Fransen Kwinten
Published: August 2023

We use Penrose limits to approximate quasinormal modes (QNMs) with large real frequencies. The Penrose limit associates a plane wave to a region of spacetime near a null geodesic. This plane wave can be argued to geometrically realize the geometrical optics approximation. Therefore, when applied to the bound null orbits around black holes, the Penrose limit can be used to study QNMs. For instance, this Penrose limit point of view makes manifest the symmetry that emerges in the geometrical optics approximation of QNMs in terms of isometries of the resulting plane wave spacetime. We apply the procedure to warpedAdS3, Schwarzschild black holes and Kerr black holes. In the former we show explicitly how the symmetry algebra contracts to that of the limiting plane wave while in the latter we find the expected agreement with numerically computed QNMs for large (real) frequencies.
Semiclassical dynamics of Hawking radiation
Authors: Lowe David A , Thorlacius Lárus
Published: August 2023

We consider gravity in 3+1 spacetime dimensions coupled to N scalar matter fields in a semiclassical limit where

N
→
∞

. The dynamical evolution of a black hole including the back-reaction of the Hawking radiation on the metric is formulated as an initial-value problem. The quantum stress-energy tensor is evaluated using a point-splitting regularization along spacelike geodesics. To account for the quantum entanglement of the matter fields, they are treated as a set of bilocal collective fields defined on spacelike hypersurfaces. The resulting semiclassical field equations include terms up to fourth order in derivatives that can be treated in a perturbative

ℏ

expansion. The formulation we arrive at should be amenable to numerical simulation of time-dependent semiclassical spacetime.
Bouncing Universe in loop quantum gravity: full theory calculation
Authors: Kisielowski Marcin
Published: August 2023

In loop quantum gravity mathematically rigorous models of full quantum gravity were proposed. In this paper we will study a cosmological sector of one of the models describing quantum gravity with positive cosmological constant coupled to massless scalar field. In our previous research we introduced a method to reduce the model to homogeneous-isotropic sector at the quantum level. In this paper we propose a method to restrict our homogeneous-isotropic model to the spatially flat sector. After this restriction the number of degrees of freedom gets substantially reduced. This allows us to make numerical and analytical calculations. Remarkably, the resulting model shares some structural similarities with the loop quantum cosmological models and therefore sheds some new light on the relation between loop quantum gravity and loop quantum cosmology. According to our model the evolution of the Universe is periodic. The quantum gravity effects resolve the Big Bang singularity leading to a Big Bounce and cause the Universe to contract after a classical expansion phase.
Cryogenic mechanical loss of amorphous germania and titania-doped germania thin films
Authors: Khadka S , Markosyan A , Prasai K , Dana A , Yang L , Tait S C , Martin I W , Menoni C S , Fejer M M , Bassiri R
Published: August 2023

The mechanical loss of amorphous thin films of germania (GeO2) and titania-doped germania (Ti:GeO2) deposited by ion-beam sputtering onto silicon double-paddle oscillators was studied from 10 K to 290 K. Undoped germania was found to show a wide cryogenic mechanical loss peak centered at

∼

60

 K with

ϕ
=
3.1
×

10

−
3

, which decreases to

1.1
×

10

−
3

as Ti-concentration increases to 44%. In addition to decreasing the height of this low-temperature peak, Ti-doping increases its width, and shifts its position toward lower temperatures. Annealing reduces the room temperature mechanical loss of Ti:GeO2 and increases its cryogenic mechanical loss, which is consistent with trends observed in most amorphous oxides.
Are the oscillations found in magnetized collisional electronegative warm plasma artifact during plasma-surface interaction?
Authors: Dhawan Rajat , Malik Hitendra K
Published: August 2023

The formation of the sheath and its characteristics are investigated in an electronegative plasma under the impact of an oblique and constant magnetic field. Specifically, the role of the magnetic field and initial conditions of positive ion velocity on the sheath characteristics are uncovered by adopting the Sagdeev potential approach for the determination of the modified Bohm’s criterion. At the sheath edge, the upper and lower components of the positive ion velocity perpendicular to the probe/wall are determined and examined in greater detail. The sheath structure is found to be modified considerably by the initial conditions. If the magnetic field is strong near the sheath edge, then the profile of the positive ion density shows a pulse-like structure for the case when we neglect the x-component (parallel to the wall) of positive ion velocity at the sheath edge. This pulse-like structure disappears when all the components of the positive ion velocity at the sheath edge are included, i.e. the ions are considered to move in any direction but towards the probe. The occurrence or disappearance of pulse-like structures or oscillations completely depend upon the initial conditions. Since in real situations the ions are expected to move in any direction (carrying all their velocity components) and are not aligned only in the direction perpendicular to the wall, these oscillations are artifact in nature. The sheath thickness is observed to be reduced with increasing magnetic field strength and its inclination. In order to better understand the phenomenon, isothermal and adiabatic cases are also discussed.
All-dielectric metasurface refractive index sensor with high figure of merit based on quasi-bound states in the continuum
Authors: Yin Xiangyu , Wang Qi , Yang Ning , Yan Xin , Wang Lei
Published: August 2023

All-Dielectric metasurfaces are widely used in the field of sense due to their small size, freedom of design, and low radiation loss. However, the optical sensor still has the problem of wide full width at half maximum (FWHM), which leads to a low figure of merit (FOM). In order to solve this problem, an all-dielectric metasurface based on quasi-bound states in the continuum (q-BIC) was proposed for refractive index sensing. The sensor structure consisted of a prism/metasurface/analyte, where the metasurface was composed of periodically arranged subwavelength asymmetric silicon gratings. The asymmetry of the structure led to the coupling of the tangential and radiative field components in the superficial layer at the resonance position, which formed a q-BIC resonance peak with a narrow FWHM in the reflection spectrum. We explained the causes of the q-BIC resonance peak generation by finite element analysis, and analyzed the factors affecting the FWHM, and also simulated the machining errors. The results showed that by reducing the asymmetry of the sensor, it could have a high FOM, with a FOM of 1.35 × 107 RIU−1. In addition, simulated machining errors within ±5 nm showed that small machining errors did not lead to the disappearance of q-BIC, which proved that the sensor had good robustness. These findings had provided ideas for the accurate detection of trace substances.
Atomistic simulation of brittle-to-ductile transition in silicon carbide embedded with nano-sized helium bubbles
Authors: Pan Chenglong , Zhang Limin , Jiang Weilin , Wang Rongshan , Chen Liang , Wang Tieshan
Published: August 2023

The tensile response of cubic silicon carbide (SiC) bulk containing cavities (voids and He bubbles) has been investigated using molecular dynamic simulations. The formation of cavities in SiC leads to a significant degradation in the mechanical properties of SiC with more influence on material fracture than initial elastic deformation. The brittle-to-ductile transition occurs in cavity-embedded SiC as the pressure in He bubbles increases. This is associated with the deformation mechanism that bond breaking at a low He bubble pressure transfers to extensive dislocation activities at a higher He bubble pressure. The cavities can effectively concentrate stress around them in the direction perpendicular to the tension, which leads to preferred cracking in the region with a higher tensile stress. The failure mechanism as revealed by this study improves understanding of property degradation in SiC that may be useful for applications of SiC in advanced nuclear energy systems.
Out-of-plane polarization modulated band alignments in β-In2X3/α-In2X3 (X = S and Se) vdW heterostructures
Authors: Xiong Rui , Xiao Fengpeng , Wen Jiansen , Xiong Hao , Jiang Linqin , Qiu Yu , Wen Cuilian , Wu Bo , Sa Baisheng
Published: August 2023

The construction of two-dimensional (2D) van der Waals (vdW) heterostructures is an effective strategy to overcome the intrinsic disadvantages of individual 2D materials. Herein, by employing first-principles calculations, the electronic structures and potential applications in the photovoltaic field of the β-In2X3/α-In2X3 (X = S and Se) vdW heterostructures have been systematically unraveled. Interestingly, the band alignments of β-In2S3/α-In2S3, β-In2Se3/α-In2Se3, and β-In2Se3/α-In2S3 heterostructures can be transformed from type-I to type-II by switching the polarization direction of α-In2X3 layers. It is highlighted that the light-harvesting ability of the β-In2X3/α-In2X3 vdW heterostructures is significantly higher than the corresponding monolayers in nearly the entire visible light region. Interestingly, type-II β-In2S3/α-In2Se3↓ heterostructure can achieve the power conversion efficiency of 17.9%, where the α-In2Se3 layer acts as a donor and the β-In2S3 layer displays as the acceptor. The present research not only provides an in-depth understanding that the out-of-plane polarization of α-In2X3 monolayers can efficiently modulate the band edge alignment of the β-In2X3/α-In2X3 vdW heterostructures, but also paves the way for the application of these heterostructures in the field of photovoltaics and optoelectronics.
The development of a novel apparatus to measure the emissivity of high-roughness materials at 82 K
Authors: Dewasi Avijit , Gangradey Ranjana , Mukherjee Samiran Shanti , Gupta Vishal , Dutta Rohan , Desai Abhinav B , Mishra Jyoti S , Panchal Paresh , Nayak Pratik A , Agravat Hemang S
Published: August 2023

The emissivity of a material changes with temperature. The knowledge of emissivity plays an important role in the estimation of radiation heat load in cryogenic systems. As the emissivity values of different materials at cryogenic temperatures are scarcely available in the literature, room-temperature emissivity values have been extensively used to estimate the radiation heat load in cryogenic systems. This may lead to a significant deviation between the predicted and actual radiation properties at cryogenic temperatures. Therefore, in the present work, an apparatus is developed based on a calorimetric technique for measuring the emissivity of an opaque material around 82 K. The novelties of the apparatus are its compact size, ease of sample handling, shorter time required to reach thermal equilibrium and, most importantly, capacity to measure the emissivity of a sample of high roughness. To understand the effectiveness of low and high emissivity-coated heat radiators for the system, a theoretical and an experimental approach has been followed. It is found that the high-emissivity heat radiator leads to a significant reduction in the time required to reach thermal equilibrium compared to a low-emissivity heat radiator. To verify and validate this setup, the emissivities of Aeroglaze Z306 (high emissivity) and Cu (low emissivity) are measured and compared with the values reported in the literature. Finally, this work has been extended to measure emissivity at cryogenic temperature for the first time for PU1, SG121FD and indigenously developed novel materials, such as black paints, adhesive and activated charcoals of different granule sizes.
An improved single-stage convolutional neural network for rail transit obstacle detection
Authors: Qin Yuliang , He Deqiang , Sun Haimeng , Liu Qi , Li Xianwang , Ren Chonghui
Published: August 2023

Obstacles that intrude into the rail area can lead to serious rail accidents, so obstacle detection technology is an essential guarantee for the safe operation of fully automatic trains. To meet the high-performance requirements of onboard obstacle detection, an efficient feature-aware convolutional neural network (EFA-Net) is proposed in this paper. The multi-scale aware feature pyramid network (MA-FPN) is designed as feature fusion network to extract multi-scale context information. In the detection head, the dynamic awareness block is used to refine the features. A joint representation branch and the generalized focal loss function are introduced to optimize the training effect. The experiments are based on the dataset of real-world rail transit environment. The results show that EFA-Net can achieve a detection accuracy of 90.4% mAP at a detection speed of 20.4 frames per second, and the lightweight design significantly reduces the computational complexity of the proposed model. Compared with other classical detectors, EFA-Net has the best comprehensive performance.
Reconstructing echoes completely submerged in background noise by a stacked denoising autoencoder method for low-power EMAT testing
Authors: Zhou Jinjie , Yu Dianrui , Li Xiang , Zheng Yang , Liu Yao
Published: August 2023

Low-power electromagnetic-acoustic transducer (EMAT) is crucially important for safety-critical equipment in industry, especially for potential explosives and inflammable petrochemical equipment and facilities. When the excitation power is very low, the corresponding echoes are overwhelmed in noise and related measurement would be inaccurate. To solve this problem, this paper presents a new echo reconstruction method based on a deep stacked denoising autoencoder (DSDAE) for nondestructive evaluation. First, the uses of reference signals and new data structure are to improve the training efficiency. A hybrid method based on variational mode decomposition and wavelet transform is used to obtain clean reference signals as inputs of the deep network. Then, the modified network structure and loss function aim to improve the ability of feature extraction and reconstruct clean echoes from low-power EMAT signals. To validate the effectiveness of the proposed method, the experiments of self-excitation and receiving A-scan inspections of stepped specimens with different thicknesses are conducted at some excitation voltages, as low as 25 V. The results indicate that the proposed DSDAE shows better and more stable denoising performance than some popular processing methods for different specimens and excitation voltages. It greatly improves the signal-to-noise ratio of the reconstructed signal to 20 dB. When applying to thickness measurement of specimens, its relative error is lower than 0.3%, which provides a practical and accurate tool for low-power EMAT testing.
Adaptive iterative optimization method for spectral calibration based on deep learning
Authors: Qu Dingran , Song Jun , Lin Yandan
Published: August 2023

The miniature fiber optic spectrometer is smaller, cheaper and has a wide range of applications. However, the measurement error is larger. In order to solve this problem, the adaptive iterative optimization method for spectral calibration is proposed. In this study, a trinity neural network model is built based on spectral wavelength segmentation to improve the calibration degree. Based on the ‘pseudo-label’, a self-optimization method for spectral calibration is proposed to reduce the amount of data required. This study optimizes the measurement accuracy without changing the structure of the spectrometer. And the self-optimization of calibration model in practical application is realized. After experiment, the calibration degree of the calibration model can reach 75.72%. After a self-optimization, it can be increased to 87.45%. The calibration time of 401 spectral values (380 nm–780 nm) is less than 0.01 s. The results show that the operator can use this method to calibrate spectral data without having optical knowledge. This method has low cost, high calibration speed, good reliability and application value.
Nano-Ni/Co-PBA as high-performance cathode material for aqueous sodium-ion batteries
Authors: Zeng Yunshu , Wang Yuyuan , Huang Zhen , Luo Hongyu , Tang Han , Dong Shijie , Luo Ping
Published: August 2023

Prussian blue analogues (PBAs) are reliable and promising cathode materials for aqueous sodium-ion batteries (ASIBs) owing to their open three-dimensional frameworks, outstanding stability, and low production costs. However, PBAs containing only a single type of transition-metal ion often have limited charge-storage capacities in aqueous systems. This study reports the first example of K0.11Ni0.39Co0.79[Fe(CN)6]·2.04H2O nanoparticles (Ni/Co-PBA) being used as a high-capacity cathode material for ASIBs. Owing to multi-electron redox reactions involving Co and Fe ions, Ni/Co-PBA has an initial capacity of 65 mAh g−1 and a capacity retention rate of 80% after 1000 cycles at 1.0 A g−1, indicating its outstanding cycle performance and capacity retention. Ex-situ x-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and the galvanostatic intermittent titration technique were used to analyze the redox mechanisms and kinetics of Ni/Co-PBA. Ni/Co-PBA-based ASIBs are among the most promising energy-storage technologies for large-scale fixed energy-storage systems because of their outstanding electrochemical performance, low costs, and high efficiency.