bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental study of reaction properties of aluminum/polytetrafluoroethylene powder under laser ablation
Authors: Ding Tong , Guo Wencan , Cao Wei , Pei Hongbo , Zheng Xianxu , Liu Cangli
Published: August 2021

Metal particle size and environment will affect the reaction properties of aluminized polytetrafluoroethylene (Al/PTFE) reactive material. This study experimentally investigated the reaction properties of Al/PTFE with different Al particle sizes through time-resolved self-emitting imaging and emission spectroscopy under nanosecond laser ablation in air and an inert argon environment. The results show that the laser ablation causes a continuous combustion characteristic and a long energy release time in Al/PTFE. Furthermore, the reaction properties of Al/PTFE are closely related to the particle size of Al powder. The emission intensities and durations increase as Al particle size decreases, but it no longer conforms to this rule when Al particle size decreases to nanometers. This inconsistency may be due to the oxidation of Al powder and agglomeration of nano-Al powder. The experiments in different gas environments proved that the reactivity of Al/PTFE in the inert gas environment is not as good as that in air because of the lack of the oxidation reaction between Al and oxygen from the air.
Experimental study on self-excited thermoacoustic instabilities and intermittent switching of azimuthal and longitudinal modes in an annular combustor
Authors: Fang Yuanqi , Yang Yao , Hu Keqi , Wang Gaofeng , Li Jingxuan , Zheng Yao
Published: August 2021

For annular combustors, the interactions between different modal structures (longitudinal, azimuthal spinning, standing, and slanted) remain a challenge in ongoing studies of thermoacoustic instabilities. The present work develops an annular combustor named TurboCombo, similar to the multiple-injector annular combustor named MICCA, but with a convergent turbine section connected to the combustor outlet. A Helmholtz solver provides a proper estimate of the modal frequencies and reveals the spatial structures for both two rigs. The experimental results present the consistencies of frequency domains between the acoustic pressure signals and the hydroxyl (OH*) radicals emission signal. The high-speed flame images are processed by the dynamic mode decomposition method, statistically showing longitudinal, azimuthal spinning, or standing nature in different cases. The stability maps of the two combustors show slight differences under atmospheric conditions. In the TurboCombo rig, there are two types of interaction behaviors between the 1/4 wave longitudinal mode of the chamber and the 1st order azimuthal mode of the plenum. Unlike the prevalent “dual-mode coexistence” characteristics, an interesting behavior of “intermittent switching” is revealed, which manifests as conspicuous two-way jumps between the two modes with different frequencies. Such intermittent switching occurs randomly between two stable limit cycles in a long-time observation without any external excitation, but is driven by the turbulence-induced stochastic process. Moreover, there still exist some weak azimuthal oscillations while the longitudinal mode is dominated. The standing or spinning bias of the azimuthal mode also features intermittent transition, corresponding to the occasions dominated by longitudinal mode or azimuthal mode, respectively.
Effect of swirl ratio on charge convection, temperature stratification, and combustion in gasoline compression ignition engine
Authors: Jena Ashutosh , Singh Harsimran , Agarwal Avinash Kumar
Published: August 2021

Various low-temperature combustion strategies (namely, homogeneous charge compression ignition, reactivity controlled compression ignition, and partially premixed charge compression ignition) have shown the potential to comply with upcoming and prevailing stringent emissions legislations. Low octane gasoline has emerged as an ideal fuel candidate for premixed charge combustion under diesel-like conditions in gasoline compression ignition (GCI) engines. GCI is an excellent technology to rectify future global energy demand imbalance, because it aims to replace diesel (which is in short supply) with low octane fractions/naphtha (which is in surplus supply) in compression ignition engines. However, this novel combustion concept requires modifications in the conventional design of diesel engines. The combustion chamber shape and in-cylinder flows play a crucial role in charge distribution and temperature stratification. Therefore, understanding the combined effect of combustion chamber geometry and in-cylinder flows is essential for future engine designs. GCI combustion engine simulations for varying swirl ratios (SRs) were performed in CONVERGE CFD software to understand the effect of in-cylinder air motion on the mixture stratification and combustion. A 1/7th sector geometry for a conventional re-entry piston bowl was modeled and then simulated. Two different mechanisms were used for model validation. The results indicated that the large-scale flow structures govern the fuel distribution in the combustion chamber. The charge convection because of increased swirl has a substantial effect on the combustion characteristics of the engine. A distinguished ignition kernel was observed for all test cases. An interfacial region with counter-rotating vortices formed a lean mixture zone, hindering flame propagation and combustion. A lower SR, shallow depth piston, and modifications to avoid flame quenching in the squish zone need to be further investigated to optimize the engine performance.
Two positrons can form a chemical bond in (PsH)2
Authors: Bressanini Dario
Published: August 2021

We show that two positrons can form a chemical bond between two otherwise repelling ions, similar to what happens to two hydrogen atoms forming a hydrogen molecule. Two positronium hydride atoms (PsH) can form the stable species (PsH)2 when the two coupled positrons have opposite spins, while they form an antibonding state if they have the same spin. This is completely analogous to the landmark description by Heitler and London [Z. Phys. 44, 455 (1927)] on the formation of a chemical bond in the hydrogen molecule coupling two electrons with opposite spins. This is the first time two positrons are shown to behave like two electrons in ordinary matter, enlarging the definition of what is a chemical bond dating back to Lewis [J. Am. Chem. Soc. 38, 762 (1916)]. We suggest a few experimental routes to form and detect such a peculiar molecule.
Variations of flight patterns for falling flexible plates
Authors: Lau Edwin M. , Huang Wei-Xi
Published: August 2021

The natural passive flight of a falling leaf is a captivating fluid–solid interaction problem. To resolve their perplexing trajectories, falling leaves have been traditionally modeled as rigid plates. However, the falling of such flat bodies are accompanied by some deformation, which plays an important role in their flight dynamics. This study simulates the flight patterns of freely falling flexible plates in a two-dimensional viscous fluid using direct numerical simulations. Plates of different bending rigidity are analyzed. Results show that flexibility alters the flight state of a falling plate. The changes in flight states with respect to bending stiffness are mapped. This is in addition to the flight states established within ranges of moment of inertia and Reynolds numbers. The coupling effect between the plate deformation and its generated wake is analyzed via flow field and surface pressure relationships. The analysis reveals that the predominate effects are the recirculation of wakes and surface pressure distribution. From those effects, the plates have generated unique flight patterns that have not been previously observed for rigid plates, such as periodic “chaotic” flights and interesting twirling motions.
Respiratory droplets interception in fibrous porous media
Authors: Maggiolo Dario , Sasic Srdjan
Published: August 2021

We investigate, by means of pore-scale lattice Boltzmann simulations, the mechanisms of interception of respiratory droplets within fibrous porous media composing face masks. We simulate the dynamics, coalescence, and collection of droplets of the size comparable with the fiber and pore size in typical fluid-dynamic conditions that represent common expiratory events. We discern the fibrous microstructure into three categories of pores: small, large, and medium-sized pores, where we find that within the latter, the incoming droplets tend to be more likely intercepted. The size of the medium-sized pores relative to the fiber size is placed between the droplet-to-fiber size ratio and a porosity-dependent microstructural parameter Lϵ*=ϵ/(1−ϵ), with ϵ being the porosity. In larger pores, droplets collection is instead inhibited by the small pore-throat-to-fiber size ratio that characterizes the pore perimeter, limiting their access. The efficiency of the fibrous media in intercepting droplets without compromising breathability, for a given droplet-to-fiber size ratio, can be estimated by knowing the parameter Lϵ*. We propose a simple model that predicts the average penetration of droplets into the fibrous media, showing a sublinear growth with Lϵ*. Permeability is shown also to scale well with Lϵ* but following a superlinear growth, which indicates the possibility of increasing the medium permeability at a little cost in terms of interception efficiency for high values of porosity. As a general design guideline, the results also suggest that a fibrous layer thickness relative to the fiber size should exceed the value Lϵ* in order to ensure effective droplets filtration.
Mean-field models of populations of quadratic integrate-and-fire neurons with noise on the basis of the circular cumulant approach
Authors: Goldobin Denis S.
Published: August 2021

We develop a circular cumulant representation for the recurrent network of quadratic integrate-and-fire neurons subject to noise. The synaptic coupling is global or macroscopically equivalent to it. We assume a Lorentzian distribution of the parameter controlling whether the isolated individual neuron is periodically spiking or excitable. For the infinite chain of circular cumulant equations, a hierarchy of smallness is identified; on the basis of it, we truncate the chain and suggest several two-cumulant neural mass models. These models allow one to go beyond the Ott–Antonsen Ansatz and describe the effect of noise on hysteretic transitions between macroscopic regimes of a population with inhibitory coupling. The accuracy of two-cumulant models is analyzed in detail.
Ab initio study of the O3–N2 complex: Potential energy surface and rovibrational states
Authors: Kalugina Yulia N. , Egorov Oleg , van der Avoird Ad
Published: August 2021

The formation and destruction of O3 within the Chapman cycle occurs as a result of inelastic collisions with a third body. Since N2 is the most abundant atmospheric molecule, it can be considered as the most typical candidate when modeling energy-transfer dynamics. We report a new ab initio potential energy surface (PES) of the O3–N2 van der Waals complex. The interaction energies were calculated using the explicitly correlated single- and double-excitation coupled cluster method with a perturbative treatment of triple excitations [CCSD(T)-F12a] with the augmented correlation-consistent triple-zeta aug-cc-pVTZ basis set. The five-dimensional PES was analytically represented by an expansion in spherical harmonics up to eighth order inclusive. Along with the global minimum of the complex (De = 348.88 cm−1), with N2 being perpendicular to the O3 plane, six stable configurations were found with a smaller binding energy. This PES was employed to calculate the bound states of the O3–N2 complex with both ortho- and para-N2 for total angular momentum J = 0 and 1, as well as dipole transition probabilities. The nature of the bound states of the O3–oN2 and O3–pN2 species is discussed based on their rovibrational wave functions.
On-demand cold plasma activation of acetyl donors for bacteria and virus decontamination
Authors: Szili Endre J. , Ghimire Bhagirath , Patenall Bethany Lee , Rohaim Mohammed , Mistry Dharmit , Fellows Adrian , Munir Muhammad , Jenkins A. Toby A. , Short Robert D.
Published: August 2021

Antibiotics are commonly used as the first line of defense in the treatment of infectious diseases. However, the rise of antimicrobial resistance (AMR) is rendering many antibiotics less effective. Consequently, effective non-antibiotic antimicrobial strategies are urgently needed to combat AMR. This paper presents a strategy utilizing cold plasma for the “on-demand” activation of acetyl donor molecules. The process generates an aqueous-based antimicrobial formulation comprising a rich mixture of highly oxidizing molecules: peracetic acid, hydrogen peroxide, and other reactive oxygen and nitrogen species. The synergistic potent oxidative action between these molecules is shown to be highly effective at eradicating common wound pathogenic bacteria (Pseudomonas aeruginosa and Staphylococcus aureus) and at inactivating a virus (SARS-CoV-2).
Evaluating the representation of Australian East Coast Lows in a regional climate model ensemble
Authors: Luca Alejandro Di , Evans Jason P. , Pepler Acacia S. , Alexander Lisa V. , Argüeso Daniel
Published: August 2021

Due to their large influence on both severe weather and water security along the east coast of Australia, it is increasingly important to understand how East Coast Lows (ECLs) may change over coming decades. Changes in ECLs may occur for a number of reasons including changes in the general atmospheric circulation (e.g. poleward shift of storm tracks) and/or changes in local conditions (e.g. changes in sea surface temperatures). Numerical climate models are the best available tool for studying these changes however, in order to assess future projections, climate model simulations need to be evaluated on how well they represent the historical climatology of ECLs. In this paper, we evaluate the performance of a 15-member ensemble of regional climate model (RCM) simulations to reproduce the climatology of cyclones obtained using three high-resolution reanalysis datasets (ERA-Interim, NASA-MERRA and JRA55). The performance of the RCM ensemble is also compared to results obtained from the global datasets that are used to drive the RCM ensemble (four general circulation model simulations and a low resolution reanalysis), to identify whether they offer additional value beyond the driving data. An existing cyclone detection and tracking algorithm is applied to derive a number of ECL characteristics and assess results at a variety of spatial scales. The RCM ensemble offers substantial improvement on the coarse-resolution driving data for most ECL characteristics, with results typically falling within the range of observational uncertainty, instilling confidence for studies of future projections. The study clearly highlights the need to use an ensemble of simulations to obtain reliable projections and a range of possible future changes.
Statistical testing of dynamically downscaled rainfall data for the Upper Hunter region, New South Wales, Australia
Authors: Manage Nadeeka Parana , Lockart Natalie , Willgoose Garry , Kuczera George , Kiem Anthony S. , Chowdhury AFM Kamal , Zhang Lanying , Twomey Callum
Published: August 2021

This study tests the statistical properties of downscaled climate data, concentrating on the rainfall which is required for hydrology predictions used in water supply reservoir simulations. The datasets used in this study have been produced by the New South Wales (NSW) / Australian Capital Territory (ACT) Regional Climate Modelling (NARCliM) project which provides a dynamically downscaled climate dataset for southeast Australia at 10 km resolution. In this paper, we present an evaluation of the downscaled NARCliM National Centers for Environmental Prediction (NCEP) / National Center for Atmospheric Research (NCAR) reanalysis simulations. The validation has been performed in the Goulburn River catchment in the Upper Hunter region of New South Wales, Australia. The analysis compared time series of the downscaled NARCliM rain-fall data with ground based measurements for selected Bureau of Meteorology rainfall stations and 5 km gridded data from the Australian Water Availability Project (AWAP). The initial testing of the rainfall was focused on autocorrelations as persistence is an important factor in hydrological and water availability analysis. Additionally, a cross-correlation analysis was performed at daily, fort-nightly, monthly and annually averaged time resolutions. The spatial variability of these statistics were calculated and plotted at the catchment scale. The auto-correlation analysis shows that the seasonal cycle in the NARCliM data is stronger than the seasonal cycle present in the ground based measurements and AWAP data. The cross-correlation analysis also shows a poor agreement between NARCliM data, and AWAP and ground based measurements. The spatial variability plots show a possible link between these discrepancies and orography at the catchment scale.
A seasonal climatology of the Melbourne 1965-1975 ozonesonde record
Authors: Lehmann Paul
Published: August 2021

A seasonal climatology of the 1965-1975 Melbourne ozonesonde ozone profile record is presented, spanning a period when minimal stratospheric ozone chemical depletion existed and prior to adequate satellite ozone profiling. Results are presented as monthly isentropic weighted means of ozone mixing ratio and partial pressure, with associated uncertainties, plotted against potential temperature and altitude. Corrections for pump inefficiency and referencing to the current ozonesonde type are included. The general seasonal and altitudinal features of the results are consistent with our current understanding of ozone variations in the southern mid-latitudes. These results are of value to atmospheric chemical and climate change models.
Large seasonal and diurnal anthropogenic heat flux across four Australian cities
Authors: Chapman S. , Watson J.E.M. , McAlpine C.A.
Published: August 2021

Anthropogenic heat release is a key component of the urban heat island. However, it is often excluded from studies of the urban heat island because reliable estimates are not available. This omission is important because anthropogenic heat can contribute up to 4ºC to the urban heat island, and increases heat stress to urban residents. The exclusion of anthropogenic heat means the urban heat island effect on temperatures may be under-estimated. Here we estimate anthropogenic heat for four Australian capital cities (Brisbane, Sydney, Melbourne and Adelaide) to inform the management of the urban heat island in a changing climate. Anthropogenic heat release was calculated using 2011 population census data and an inventory of hourly traffic volume, building electricity and gas use. Melbourne had the highest annual daily average anthropogenic heat emissions, which reached 376 W/m2in the city centre during the daytime, while Brisbane’s emissions were 261 W/m2 and Sydney’s were 256W/m2. Adelaide had the lowest emissions, with a daily average of 39 W/m2 in the city centre. Emissions varied within and among the four cities and decreased rapidly with distance from the city centre, to 2 at 20 km from the city in Brisbane, and 15 km in Adelaide. The highest emissions were found in the city centres during working hours. The peak emissions reached in the centre of Melbourne are similar to the peak emissions in London and Tokyo, where anthropogenic heat is a large component of the urban heat island. This indicates that anthropogenic heat could be an important contributor to the urban heat island in Australian capital cities, and needs to be considered in climate adaptation studies. This is an important problem because climate change, combined with an ageing population and urban growth, could double the deaths from heatwaves in Australian cities over the next 40 years.
The distribution of daily rainfall in Australia and simulated future changes
Authors: Watterson Ian G. , Rafter Tony
Published: August 2021

This study extends recent projections of monthly and daily precipitation over Australia by analysing the full frequency distribution of daily rain amounts and making projections of the new statistics wet-day fraction and top percentile of rain. Simulations from an ensemble of 33 CMIP5 models are used, together with six simulations from the downscaling model CCAM, with the data analysed on the model grids. Consistent with its higher resolution (0.5°), CCAM provides a more skilful simulation for the extreme grid point rainfall than most CMIP5 models. CCAM compares well with AWAP gridded data for wet-day fraction, while there is a wide range of CMIP5 results. In the future climate of 2080–2099 under the RCP8.5 scenario, changes in mean rainfall of both signs occur within the CMIP5 ensemble for most regions and seasons, although mean winter rainfall in southern Australia declines 5 to 30 per cent in most models and in CCAM. CCAM simulates increases in summer, and also more wet days, in contrast to CMIP5. Aside from the north in winter, the changes from CMIP5 become increasingly positive, on stepping from mean to top percentile to twenty-year extreme rainfall, a contrast of typically 25 per cent. There is much less contrast between these statistics from CCAM. The distributions of rain amounts shed light on these different projections. Averaged over Australia and four seasons, CCAM produces a broader distribution than the CMIP5 ensemble mean. However much of the future increase is in the 2 to 8 mm daily range, whereas CMIP5 distributions tend to shift towards amounts in the range 30 mm to 200 mm. Further assessment of such distributions in both these and newer versions of CCAM, ACCESS and other GCMs is recommended.
Ion correlations drive charge overscreening and heterogeneous nucleation at solid–aqueous electrolyte interfaces
Authors: Lee Sang Soo , Koishi Ayumi , Bourg Ian C. , Fenter Paul
Published: August 2021

Significance

Ion distributions at charged solid–water interfaces, referred to as the electrical double layer (EDL), are poorly understood at high ion concentrations, in part due to the lack of molecular-scale descriptions of the interactions between adsorbed hydrated ions. Here, direct visualization of the salinity-dependent evolution of EDL structure reveals molecular origins of nonclassical transformation of the EDL, in which charge overscreening and heterogeneous nucleation are driven by ion–ion correlations at the interfaces. This manifestation of the atomistic basis of nonclassical behaviors provides a much-needed understanding of the impact of ion cooperativity at charged interfaces for the development of predictive models for element transport in natural environments and advanced technologies for material growth and synthesis in saline environments.
Novel synthesis approach for “stubborn” metals and metal oxides
Authors: Nunn William , Manjeshwar Anusha Kamath , Yue Jin , Rajapitamahuni Anil , Truttmann Tristan K. , Jalan Bharat
Published: August 2021

Significance

Atomically precise complex oxides containing “stubborn” elements, such as ruthenium, iridium, and platinum, hold tremendous promise as designer quantum materials for exploring novel electronic, magnetic, superconducting, and topological phases owing to their strong spin–orbit interaction. This study shows a method to synthesize such materials by eliminating the major synthesis bottleneck of low vapor pressure and difficulty in oxidation. This study serves as a “proof-of-concept” allowing us to 1) grow Pt, RuO
2
, and SrRuO
3
thin films by supplying Pt and Ru precursors at 65 to 100 °C in a low-temperature effusion cell, as opposed to the several thousand degrees Celsius needed using electron beam evaporators; 2) reveal bulk-like room-temperature resistivity; and 3) ultimately provide pathways to creating atomically precise quantum structures.
A
Gata3
enhancer necessary for ILC2 development and function
Authors: Kasal Darshan N. , Liang Zhitao , Hollinger Maile K. , O’Leary Crystal Y. , Lisicka Wioletta , Sperling Anne I. , Bendelac Albert
Published: August 2021

Significance

Group 2 innate lymphoid cells (ILC2s) and adaptive CD4
+
T helper type 2 (Th2) cells express a common effector program orchestrated by the “master” transcription factor GATA3 that is acquired through development or differentiation, respectively. To elucidate the regulatory mechanisms controlling the acquisition of this shared program, we used a combination of chromatin accessibility data and CRISPR/Cas9-mediated deletion, which revealed a
Gata3
enhancer necessary for ILC2 development and function. Notably, this enhancer was largely dispensable for Th2 cell differentiation. Thus, ILC2s and Th2 cells display different requirements for the induction of a common type 2 helper effector program.
Evidence that toxin resistance in poison birds and frogs is not rooted in sodium channel mutations and may rely on “toxin sponge” proteins
Authors: Abderemane-Ali Fayal , Rossen Nathan D. , Kobiela Megan E. , Craig Robert A. , Garrison Catherine E. , Chen Zhou , Colleran Claire M. , O’Connell Lauren A. , Du Bois J. , Dumbacher John P. , Minor Daniel L.
Published: August 2021

Many poisonous organisms carry small-molecule toxins that alter voltage-gated sodium channel (NaV) function. Among these, batrachotoxin (BTX) from Pitohui poison birds and Phyllobates poison frogs stands out because of its lethality and unusual effects on NaV function. How these toxin-bearing organisms avoid autointoxication remains poorly understood. In poison frogs, a NaV DIVS6 pore-forming helix N-to-T mutation has been proposed as the BTX resistance mechanism. Here, we show that this variant is absent from Pitohui and poison frog NaVs, incurs a strong cost compromising channel function, and fails to produce BTX-resistant channels in poison frog NaVs. We also show that captivity-raised poison frogs are resistant to two NaV-directed toxins, BTX and saxitoxin (STX), even though they bear NaVs sensitive to both. Moreover, we demonstrate that the amphibian STX “toxin sponge” protein saxiphilin is able to protect and rescue NaVs from block by STX. Taken together, our data contradict the hypothesis that BTX autoresistance is rooted in the DIVS6 N→T mutation, challenge the idea that ion channel mutations are a primary driver of toxin resistance, and suggest the possibility that toxin sequestration mechanisms may be key for protecting poisonous species from the action of small-molecule toxins.
Self-Bound Quantum Droplet with Internal Stripe Structure in One-Dimensional Spin-Orbit-Coupled Bose Gas
Authors: Xiong Yuncheng , Yin Lan
Published: August 2021

We study the quantum-droplet state in a three-dimensional (3D) Bose gas in the presence of 1D spin-orbit coupling and Raman coupling, especially the stripe phase with density modulation, by numerically computing the ground state energy including the mean-field energy and Lee–Huang–Yang correction. In this droplet state, the stripe can exist in a wider range of Raman coupling, compared with the BEC-gas state. More intriguingly, both spin-orbit coupling and Raman coupling strengths can be used to tune the droplet density.
Supervised Machine Learning Topological States of One-Dimensional Non-Hermitian Systems
Authors: Cheng Zhuo , Yu Zhenhua
Published: August 2021

We apply supervised machine learning to study the topological states of one-dimensional non-Hermitian systems. Unlike Hermitian systems, the winding number of such non-Hermitian systems can take half integers. We focus on a non-Hermitian model, an extension of the Su–Schrieffer–Heeger model. The non-Hermitian model maintains the chiral symmetry. We find that trained neuron networks can reproduce the topological phase diagram of our model with high accuracy. This successful reproduction goes beyond the parameter space used in the training process. Through analyzing the intermediate output of the networks, we attribute the success of the networks to their mastery of computation of the winding number. Our work may motivate further investigation on the machine learning of non-Hermitian systems.
Polarity Reversal of Terahertz Electric Field from Heavily p-Doped Silicon Surfaces
Authors: Wu Hai-Zhong , Guo Quan , Tu Yan-Yun , Lyu Zhi-Hui , Wang Xiao-Wei , Li Yong-Qiang , Zhou Zhao-Yan , Zhang Dong-Wen , Zhao Zeng-Xiu , Yuan Jian-Min
Published: August 2021

Above-band-gap optical excitation of electron-hole pairs screens the doping-induced surface electric field and generates terahertz (THz) pulses via free-carrier transport. THz emission from a heavily doped silicon surface is much weaker than that of lightly doped samples. A polarity reversal of the THz electric field is observed in heavily doped p-type silicon, indicating that the doping related and carrier induced surface electric fields oppose each other. By comparing the penetration depth of the excitation laser with the thickness of the depletion layer for the doped silicon, it is shown that competition between diffusion and drift current causes the polarity reversal.
Improvement of Cyclic Stability of Na0.67Mn0.8Ni0.1Co0.1O2 via Suppressing Lattice Variation
Authors: Ren Zhongmin , Wang Muqin , Chen Shuaishuai , Ding Lei , Li Hua , Liu Jian , Zheng Jieyun , Liu Zhihong , Wang Deyu , Wang Mingkui
Published: August 2021

Strategies to prolong operational life are highly pursued to strengthen the advantage of cost-effectiveness on sodium-ion batteries (SIBs). We demonstrate the crucial influence of particles – internal mechanical strains on durability of cathode, which does not attract enough attentions from the community. Among the investigated samples, 2% Ti-modified-Na0.67Ni0.1Co0.1Mn0.8O2 suppresses the c-axis lattice variation by 38%, attains the reversible capacity 86% higher after 200 cycles, and still keeps intact morphology. This approach indicates that the mechanical properties could tailor cyclic stability of cathode, which is particular important to further improve competitiveness for SIBs.
Thermal Stability of High Power 26650-Type Cylindrical Na-Ion Batteries
Authors: Zhou Quan , Li Yuqi , Tang Fei , Li Kaixuan , Rong Xiaohui , Lu Yaxiang , Chen Liquan , Hu Yong-Sheng
Published: August 2021

As a new electrochemical power system, safety (especially thermal safety) of Na-ion batteries (NIBs) is the key towards large-scale industrialization and market application. Thus, research on the thermal stability of NIBs is helpful to evaluate the safety properties and to provide effective strategies to prevent the occurrence of battery safety failure. Thermal stability of the high-power 26650 cylindrical NIBs using Cu-based layered oxide cathode and hard carbon anode is studied. The high power NIBs can achieve fast charge and discharge at 5–10 C rate and maintain 80% capacity after 4729 cycles at 2 C/2C rate, where the unit C denotes a measure of the rate at which a battery is charge-discharged relative to its maximum capacity. The results of accelerating rate calorimeter and differential scanning calorimetry (ARC-DSC) test results show that NIBs have a higher initial decomposition temperature (≥110 °C) and a lower maximum thermal runaway temperature (≤350 °C) than those of Li-ion batteries (LIBs), exhibiting a favorable thermal stability. It should be noted that the heat generation of cathode accounts for a large proportion of the total heat generation while the thermal stability of the anode determines the initial thermal runaway temperature, which is similar to LIBs. Finally, the whole temperature characteristics of the NIBs in the range of –60 °C–1000 °C are summarized, which provide guidance for the safety design and applications of NIBs.
Dual Topological Features of Weyl Semimetallic Phases in Tetradymite BiSbTe3
Authors: Zhou Z. Z. , Liu H. J. , Wang G. Y. , Wang R. , Zhou X. Y.
Published: August 2021

Based on first-principles calculations and symmetry arguments, we reveal that the non-centrosymmetric ternary tetradymite BiSbTe3 possesses exotic dual topological features of Weyl semimetallic phases with Z
2 index (1:000). The results show that the helical Dirac-type surface states protected by the time-reversal symmetry are present in the vicinity of the Brillouin zone center, which is consistent with the experimental report. Furthermore, we show that four pairs of Weyl points reside exactly at the Fermi level, which are guaranteed to be located on high-symmetry planes due to mirror symmetries. The helical surface states and the projected Weyl nodes are well separated in the momentum space, facilitating their observations in experiments. This work not only uncovers a unique quantum phenomenon with dual topological features in the tetradymite family but also paves a fascinating avenue for exploring the coexistence of multi-topological states with wide applications.
S-Wave Superconductivity in Kagome Metal CsV3Sb5 Revealed by 121/123Sb NQR and 51V NMR Measurements
Authors: Mu Chao , Yin Qiangwei , Tu Zhijun , Gong Chunsheng , Lei Hechang , Li Zheng , Luo Jianlin
Published: August 2021

We report 121/123Sb nuclear quadrupole resonance (NQR) and 51V nuclear magnetic resonance (NMR) measurements on kagome metal CsV3Sb5 with T
c = 2.5 K. Both 51V NMR spectra and 121/123Sb NQR spectra split after a charge density wave (CDW) transition, which demonstrates a commensurate CDW state. The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first-order phase transition. At low temperature, electric-field-gradient fluctuations diminish and magnetic fluctuations become dominant. Superconductivity emerges in the charge order state. Knight shift decreases and 1/T
1
T shows a Hebel–Slichter coherence peak just below T
c, indicating that CsV3Sb5 is an s-wave superconductor.
Strong Coupled Magnetic and Electric Ordering in Monolayer of Metal Thio(seleno)phosphates
Authors: Hua Chenqiang , Bai Hua , Zheng Yi , Xu Zhu-An , Yang Shengyuan A. , Lu Yunhao , Wei Su-Huai
Published: August 2021

The coupling between electric ordering and magnetic ordering in two-dimensional (2D) materials is important for both fundamental research of 2D multiferroics and future development of magnetism-based information storage and operation. Here, we introduce a scheme for realizing a magnetic phase transition through the transition of electric ordering. We take CuMoP2S6 monolayer as an example, which is a member of the large 2D transition-metal chalcogen-phosphates family. Based on first-principles calculations, we find that it is a multiferroic with unprecedented characters, namely, it exhibits two different phases: an antiferroelectric-antiferromagnetic phase and a ferroelectric-ferromagnetic phase, in which the electric and magnetic orderings are strongly coupled. Importantly, the electric polarization is out-of-plane, so the magnetism can be readily switched by using the gate electric field. Our finding reveals a series of 2D multiferroics with special magnetoelectric coupling, which hold great promise for experimental realization and practical applications.
Complexity and the Big Bang
Authors: Nicolai Hermann
Published: August 2021

After a brief review of current scenarios for the resolution and/or avoidance of the Big Bang, an alternative hypothesis is put forward implying an infinite increase in complexity towards the initial singularity. This may result in an effective non-calculability which would present an obstruction to actually reaching the beginning of time. This proposal is motivated by the appearance of certain infinite-dimensional duality symmetries of indefinite Kac–Moody type in attempts to unify gravity with the fundamental matter interactions, and deeply rooted in properties of Einstein’s theory.
Frustrated tunneling dynamics in ultrashort laser pulses
Authors: Olofsson Edvin , Carlström Stefanos , Dahlström Jan Marcus
Published: August 2021

We study a model for frustrated tunneling ionization using ultrashort laser pulses. The model is based on the strong field approximation and it employs the saddle point approximation to predict quasiclassical trajectories that are captured on Rydberg states. We present a classification of the saddle-point solutions and explore their behavior as functions of angular momentum of the final state, as well as the carrier-envelope phase (CEP) of the laser pulse. We compare the final state population computed by the model to results obtained by numerical propagation of the time-dependent Schrödinger equation (TDSE) for the hydrogen atom. While we find qualitative agreement in the CEP dependence of the populations in principal quantum numbers, n, the populations to individual angular momentum channels, ℓ, are found to be inconsistent between model and TDSE. Thus, our results show that improvements of the quasiclassical trajectories are in order for a quantitative model of frustrated tunneling ionization.
Cosmological particle production: a review
Authors: Ford L H
Published: August 2021

This article will review quantum particle creation in expanding universes. The emphasis will be on the basic physical principles and on selected applications to cosmological models. The needed formalism of quantum field theory in curved spacetime will be summarized, and applied to the example of scalar particle creation in a spatially flat Universe. Estimates for the creation rate will be given and applied to inflationary cosmology models. Analog models which illustrate the same physical principles and may be experimentally realizable are also discussed.
Modulation of Weyl semimetal state in half-Heusler GdPtBi enabled by hydrostatic pressure
Authors: Zhang Junli , Jin Lei , Chen Jie , Zhang Chenhui , Li Peng , Yuan Ye , Wen Yan , Zhang Qiang , Zhang Xiaoming , Liu Enke , Wang Wenhong , Zhang Xixiang
Published: August 2021

The excitation of Weyl semimetals obeys the relativistic Weyl equation and attracted significant research attention due to its unique electronic state. In this paper, we present an emerging approach for modulating the electron state of half-Heusler GdPtBi by hydrostatic pressure. Through measurements of the temperature-dependent resistivity and magnetoresistance (MR), a phase transition from a Weyl semimetal to a semiconductor state was identified at about 2.0 GPa upon increasing the hydrostatic pressure. Electron transport in semiconductive GdPtBi is found to be well describable by Mott variable-range-hopping. The simulated electronic structures under different hydrostatic pressures further indicate that changes in the electronic states of atoms in the primary unit cell result in a phase transition in GdPtBi. This work presents an effective strategy for modulating the electronic state by tuning the lattice constant.
Long-term intracortical microelectrode array performance in a human: a 5 year retrospective analysis
Authors: Colachis Samuel C , Dunlap Collin F , Annetta Nicholas V , Tamrakar Sanjay M , Bockbrader Marcia A , Friedenberg David A
Published: August 2021

Objective. Brain-computer interfaces (BCIs) that record neural activity using intracortical microelectrode arrays (MEAs) have shown promise for mitigating disability associated with neurological injuries and disorders. While the chronic performance and failure modes of MEAs have been well studied and systematically described in non-human primates, there is far less reported about long-term MEA performance in humans. Our group has collected one of the largest neural recording datasets from a Utah MEA in a human subject, spanning over 5 years (2014–2019). Here we present both long-term signal quality and BCI performance as well as highlight several acute signal disruption events observed during the clinical study. Approach. Long-term Utah array performance was evaluated by analyzing neural signal metric trends and decoding accuracy for tasks regularly performed across 448 clinical recording sessions. For acute signal disruptions, we identify or hypothesize the root cause of the disruption, show how the disruption manifests in the collected data, and discuss potential identification and mitigation strategies for the disruption. Main results. Neural signal quality metrics deteriorated rapidly within the first year, followed by a slower decline through the remainder of the study. Nevertheless, BCI performance remained high 5 years after implantation, which is encouraging for the translational potential of this technology as an assistive device. We also present examples of unanticipated signal disruptions during chronic MEA use, which are critical to detect as BCI technology progresses toward home usage. Significance. Our work fills a gap in knowledge around long-term MEA performance in humans, providing longevity and efficacy data points to help characterize the performance of implantable neural sensors in a human population. The trial was registered on ClinicalTrials.gov (Identifier NCT01997125) and conformed to institutional requirements for the conduct of human subjects research.
The Impact of Nuclear Physics Uncertainties on Galactic Chemical Evolution Predictions
Authors: Côté Benoit , Denissenkov Pavel , Herwig Falk , Fryer Chris L. , Belczynski Krzysztof , Vassh Nicole , Mumpower Matthew R. , Lippuner Jonas , Pignatari Marco , Ruiter Ashley J.
Published: August 2021

Modeling the evolution of the elements in the Milky Way is a multidisciplinary and challenging task. In addition to simulating the ∽ 13 billion years evolution of our Galaxy, chemical evolution simulations must keep track of the elements synthesized and ejected from every astrophysical site of interest (e.g., supernova, compact binary merger). The elemental abundances of such ejecta, which are a fundamental input for chemical evolution codes, are usually taken from theoretical nucleosynthesis calculations performed by the nuclear astrophysics community. Therefore, almost all chemical evolution predictions rely on the nuclear physics behind those calculations. In this proceedings article, we highlight the impact of nuclear physics uncertainties on galactic chemical evolution predictions. We demonstrate that nuclear physics and galactic evolution uncertainties both have a significant impact on interpreting the origin of neutron-capture elements in our Solar System. Those results serve as a motivation to create and maintain collaborations between the fields of nuclear astrophysics and galaxy evolution.
Exploring the relative importance of socio-ecological factors to ecosystem services clusters: a support to spatially targeted management
Authors: Li Jiangyue , Zhang Chi , Chen Xi
Published: August 2021

Identifying the relative importance of different socio-ecological drivers that affect the ecosystem services (ESs) clusters provides a potential opportunity for spatially targeted policy design. Taking Central Asia (CA) as a case study, the spatiotemporal distribution of seven ESs was evaluated at the state level, and then a principal component analysis and k-means clustering were applied to explore the ES clusters. Based on Spearman’s correlation coefficients, the trade-offs and synergies relationship between ESs were analyzed at the different ES clusters scales. A redundancy analysis (RDA) was used to determine the relative contribution of socio-ecological factors affecting the distribution of ES clusters. The ES quantification revealed the spatial consistency and separation among different types of ESs. Similarities and differences of the trade-offs and synergies among ESs existed in five ES clusters (i.e. ‘ESC1: agricultural cluster’, ‘ESC2: carbon cluster’, ‘ESC3: sand fixation cluster’, ‘ESC4: habitat cluster’ and ‘ESC5: Soil and water cluster’). Pairwise water yield, soil retention, carbon storage and net primary production had good synergetic relationships in ESC1, ESC2, ESC4 and ESC5; sand fixation displayed negative correlations with other ESs in all ESCs; and the trade-offs relationships existed between food production and habitat quality in ESC1, ESC2 and ESC5. The RDA demonstrated that the explanatory power of the ecological variables (e.g. climate and vegetation) to the spatial distribution of ES clusters was much higher than that of the socio-economic variables (e.g. population and GDP). An important information/recommendation provided by this study is that ES clusters should be treated as the basic ecological management unit in CA, and different management strategies should be designed in accordance to the major interactions among the ESs in each ES cluster.
The fate of the Caspian Sea under projected climate change and water extraction during the 21st century
Authors: Koriche Sifan A , Singarayer Joy S , Cloke Hannah L
Published: August 2021

The Caspian Sea (CS) delivers considerable ecosystem services to millions of people. It experienced water level variations of 3 m during the 20th century alone. Robust scenarios of future CS level are vital to inform environmental risk management and water-use planning. In this study we investigated the water budget variation in the CS drainage basin and its potential impact on CS level during the 21st century using projected climate from selected climate change scenarios of shared socioeconomic pathways (SSPs) and representative concentration pathways (RCPs), and explored the impact of human extractions. We show that the size of the CS prescribed in climate models determines the modelled water budgets for both historical and future projections. Most future projections show drying over the 21st century. The moisture deficits are more pronounced for extreme radiative forcing scenarios (RCP8.5/SSP585) and for models where a larger CS is prescribed. By 2100, up to 8 (10) m decrease in CS level is found using RCP4.5 (RCP8.5) models, and up to 20 (30) m for SSP245 (SSP585) scenario models. Water extraction rates are as important as climate in controlling future CS level, with potentially up to 7 m further decline, leading to desiccation of the shallow northern CS. This will have wide-ranging implications for the livelihoods of the surrounding communities; increasing vulnerability to freshwater scarcity, transforming ecosystems, as well as impacting the climate system. Caution should be exercised when using individual models to inform policy as projected CS level is so variable between models. We identify that many climate models either ignore, or do not properly prescribe, CS area. No future climate projections include any changes in CS surface area, even when the catchment is projected to be considerably drier. Coupling between atmosphere and lakes within climate models would be a significant advance to capture crucial two-way feedbacks.
Analytical measurements of contact resistivity in two-dimensional WSe2 field-effect transistors
Authors: Moon Inyong , Choi Min Sup , Lee Sungwon , Nipane Ankur , Hone James , Yoo Won Jong
Published: August 2021

It becomes clear that, in two-dimensional (2D) materials-based devices, sheet resistances underneath electrodes change due to a metallic contact, leading to substantial errors in determining a transfer length. Thus, the extraction of transfer length and corresponding contact resistivity must be revisited to assess the performance of 2D devices. In this study, we present the three different approaches of determining the contact resistivity in 2D WSe2 field effect transistors for the first time by theoretical analysis using the resistive network model as well as electrical measurements using the contact-end resistance and transfer length methods, based on the followings: (a) contact resistance multiplied by transfer length (

R

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L

Tk

), (b) integrated contact resistance (

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L

R

(
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)

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d
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), and (c) contact resistance raised to a constant power

R

cf

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). These different extraction methods give rise to almost identical transfer length and contact resistivity, validating our model and its accuracy from the results obtained by using various contact metals and plasma doping conditions. This work serves as a foundation for future research on the determination of physical parameters responsible for the carrier transport at the metallic contact interface in 2D semiconductor devices.