bluuebunny/crossref_metadata_2025_split huggingface dataset:
Indirect biotic interactions of plant invasions with native plants and animals.
Authors: Allen Warwick J. 
Published: December 2020

Abstract

Invasive plants often occur at high densities and tend to be highly generalist in their interactions with herbivores, pathogens, mycorrhiza, endophytes and pollinators. These characteristics mean that invasive plants should frequently participate in diverse indirect biotic interactions with the surrounding community, mediated by their direct interaction partners (e.g. antagonists and mutualists). Indirect interactions play an important role in many ecological processes, yet we still lack a systematic understanding of the circumstances under which they influence the success and impacts of invasive species. In this chapter, I first describe several of the indirect interaction pathways that are commonly encountered in invasion biology and review their contribution to the impacts of plant invasions on co-occurring species. The literature review revealed that there are now many case studies describing various indirect impacts of invasive plants. However, identical interaction motifs (e.g. plant-enemy-plant, plant-mutualist-plant) can bring about several possible outcomes, depending upon each species' provenance, relative abundances and interaction strengths, abiotic resource availability, spatial and temporal scale and the influence of other species. Moreover, knowledge gaps identified include a lack of studies of indirect facilitation outside of plant-pollinator systems, limited consideration of indirect invader impacts on other non-native species, and the scarcity of generalizable results to date. Second, I integrate the literature with some trending research areas in invasion biology (interaction networks, biogeography, invasion dynamics) and identify some potential future research directions. Finally, I discuss how knowledge about indirect biotic interactions could be incorporated into the management of invasive plants.
Restoration of pollination interactions in communities invaded by non-native plants.
Authors: Kaiser-Bunbury Christopher N. , Simmons Benno I. 
Published: December 2020

Abstract

Invasive plant species degrade and homogenize ecosystems worldwide, thereby altering ecosystem processes and function. To mitigate and reverse the impact of invasive plants on pollination, a key ecosystem function, conservation scientists and practitioners restore ecological communities and study the impact of such management interventions on plant-pollinator communities. Here, we describe opportunities and challenges associated with restoring pollination interactions as part of a holistic ecosystem-based restoration approach. We introduce a few general concepts in restoration ecology, and outline best planning and evaluation practices of restoring pollination interactions on the community level. Planning involves the selection of suitable plant species to support diverse pollinator communities, which includes considerations of the benefits and disadvantages of using native vs exotic, and bridge and framework plant species for restoration. We emphasize the central role of scientific- and community-level approaches for the planning phase of pollination restoration. For evaluation purposes, we argue that appropriate network indicators have the advantage of detecting changes in species behaviour with consequences for ecosystem processes and functions before these changes show up in altered species communities. Suitable network metrics may include interaction diversity and evenness, and network measures that describe the distribution of species, such as network and species-level specialization, modularity and motifs. Finally, we discuss the usefulness of the network approach in evaluating the benefits of restoration interventions for pollination interactions, and propose that applied network ecologists take a central role in transferring theory into practice.
Entropy and the link action in the causal set path-sum
Authors: Mathur Abhishek , Singh Anup Anand , Surya Sumati 
Published: December 2020

Abstract
In causal set theory the gravitational path integral is replaced by a path-sum over a sample space Ω
n
of n-element causal sets. The contribution from non-manifold-like orders dominates Ω
n
for large n and therefore must be tamed by a suitable action in the low energy limit of the theory. We extend the work of Loomis and Carlip on the contribution of sub-dominant bilayer orders to the causal set path-sum and show that the ‘link action’ suppresses the dominant Kleitman–Rothschild orders for the same range of parameters.
Comment on ‘Video analysis-based estimation of bearing friction factors’
Authors: Hinrichsen Peter F 
Published: December 2020

Abstract
A simple technique for studying wheel bearing friction is to turn the wheel into a pendulum by adding a mass m at radius l and study the damping of the oscillatory motion. However, due to the reversal of the frictional torque each half oscillation the motion has to be analysed in terms of a piecewise function, and combinations, of frictional plus viscous damping should be included in the analysis.
Vertex-type thermal correction to the one-photon transition rates
Authors: Solovyev D , Zalialiutdinov T , Anikin A 
Published: December 2020

Abstract
Thermal corrections to the one-photon spontaneous and induced transition probabilities for hydrogen and hydrogen-like ions are evaluated. The found thermal corrections are given by the vertex Feynman graph, where the vertex represents the thermal interaction between the bound electron and the nucleus. All derivations of thermal corrections to bound–bound transitions for an atom exposed to blackbody radiation are made in a fully relativistic approach within the framework of the adiabatic S-matrix formalism. It is found that the vertex-type radiative corrections to the transition rates can be at the level of a few percent to corresponding spontaneous rates for highly excited states in the hydrogen atom. A comprehensive analysis of the vertex-type thermal corrections for hydrogen-like atomic systems is presented.
A robust, high-flux source of laser-cooled ytterbium atoms
Authors: Wodey E , Rengelink R J , Meiners C , Rasel E M , Schlippert D 
Published: December 2020

Abstract
We present a high-flux source of cold ytterbium atoms that is robust, lightweight and low-maintenance. Our apparatus delivers 1 × 109 atoms s−1 into a 3D magneto-optical trap without requiring water cooling or high current power supplies. We achieve this by employing a Zeeman slower and a 2D magneto-optical trap fully based on permanent magnets in Halbach configurations. This strategy minimizes mechanical complexity, stray magnetic fields, and heat production while requiring little to no maintenance, making it applicable to both embedded systems that seek to minimize electrical power consumption, and large scale experiments to reduce the complexity of their subsystems.
Fluorescent dynamics of CsPbBr3 nanocrystals in polar solvents: a potential sensor for polarity
Authors: Zhao Aiqing , Sheng Yuhang , Liu Cihui , Yuan Songyan , Shan Xiaoli , Di Yunsong , Gan Zhixing 
Published: December 2020

Abstract
During synthesis, device processes, and applications of perovskite nanocrystals (NCs), there are usually inevitable interactions between perovskite NCs and polar solvents. To elaborately control the properties of perovskite NCs, investigating the effects of solvent polarity on perovskite NCs is thus highly important. Herein, fluorescent variations induced by different solvents into CsPbBr3 NCs solution are systematically studied. In this report, it is found that when CsPbBr3 NCs are treated with polar solvents, the fluorescence intensity decreases with a general redshift of fluorescence peak position. Moreover, the fluorescence quenching and peak position shift amplitude monotonously increase with the solvent polarity. Absorption spectra and fluorescent lifetime suggest that, with addition of polar solvents, the surface of NCs are destroyed and defect states are generated, leading to the fluorescent variations. Besides, dielectric constant of the solvent also increases with polarity, which may weaken the quantum confinement effect and decrease the exciton binding energy. We find the fluorescence may slightly blue shift if the emission of free carrier is strong enough with certain solvents, such as dimethylsulfoxide (DMSO). We also find the fluorescence intensity generally deceases to a stable state in 2 min, indicating quick interactions between CsPbBr3 NCs and solvents. However, water continuously quenches the fluorescence of CsPbBr3 NCs up to 72 h due to the poor miscibility between water and n-hexane. This work not only provides a comprehensive understanding on the fluorescent dynamics of CsPbBr3 NCs in polar solvents but also affords a potential fluorescent indicator for solvent polarity.
Enhanced density in a stabilized high-current plasma beam
Authors: Zheng X J , Gou F J , Zhang Y P , Wang H X , Wallace A C , Wang H B , Huang Z H , Ji X Q , Ye Z B , Liang S Y , Zhang J Z , Wu N , Feng Y T , Deng B Q 
Published: December 2020

Abstract
Externally generated, axial magnetic fields used to confine high-current plasma beams in compact linear devices are usually 0.5 Tesla or less and can be insufficient to suppress plasma instabilities. Such an issue is addressed in this study by closely winding the current-carrying cable around a small chamber attached to the end of a linear device. The magnetic field generated inside the small chamber during the high-current pulse reached 0.8 Tesla at the peak current of 10.83 kA. Formation of a steady plasma beam through a mixture of argon, hydrogen and helium was photographed by a high-speed camera at the instant of the peak current. The beam width profile starts from over 24.8 mm at the upstream location and becomes thinner with distance down-stream. At the location of laser-interferometer measurement, at the right-most viewing window on the test chamber, the beam width was estimated as 7.4 mm and plasma density was evaluated to be 1.0 × 1022 m−3, an increase of two orders of magnitude compared to a previous study. A simple relationship was derived for the plasma density as a function of beam width. Based on examination of the metal target at the far end, the final beam width was estimated as 50 µm, with the plasma density evaluated to be 4.31 × 1022 m−3, with a calculated ion energy of 4.35 keV, consistent with x-ray spectrum measurements.
Atmospheric pressure dual RF–LF frequency discharge: transition from
α
to
α
–
γ
-mode
Authors: Magnan Romain , Hagelaar Gerjan , Chaker Mohamed , Massines Françoise 
Published: December 2020

Abstract
This paper investigates the transition from α to α–γ-mode of a dual frequency (5 MHz/50 kHz) dielectric barrier discharge (DBD) at atmospheric pressure. The study is based on both experiments and modeling of a plane/plane DBD in a Penning mixture (Ar–NH3). The discharge is in the α-RF mode with three different voltage amplitudes (250, 300 and 350 V) and biased by a low-frequency (LF) voltage with an amplitude varying from 0 to 1300 V. At a given threshold of LF voltage amplitude (of about 400 V for a 2 mm gap and 133 ppm of NH3), a transition from α to α–γ-mode occurs. It is characterized by a drastic increase of both the argon and NH emissions. Increasing the NH3 concentration leads to a decrease of the LF voltage amplitude required to reach the α–γ-mode (experiment). The transition from α to α–γ-mode is initiated when the ionization in the sheath increases and the α–γ-mode is established when this ionization becomes higher than the self-sustainment criterion (1/γ). The transition from α to α–γ-mode results in an increase of the particle densities and a stabilization of the gas voltage independently of the LF voltage amplitude. Without secondary electron emission there is no transition. In the model, increasing the secondary emission coefficient from 0.05 to 0.15 leads to a decrease of the LF voltage amplitude required to switch from α to α–γ-mode from 700 to 550 V.
Electric field dependence of SF6 nonlinear discharge characteristics: N-curve estimations
Authors: Wu Zhicheng , Lin Binqi , Fan Xing , Zhang Qiaogen , Li Licheng 
Published: December 2020

Abstract
The N-curve of SF6 describes the relationship between the AC breakdown voltage in an extremely inhomogeneous electric field and pressurized SF6 gas. It is directly dependent on the electric field distribution, which is determined by the gas gap, curvature radius, and background electric field. An increase in gap distance, a decrease in curvature radius, and relatively weak background electric field are all conducive to corona stabilization. The electrode curvature radius is the determining factor in the positive glow corona (PGC) discharge quenching pressure. The breakdown voltage dominated by the streamer mechanism can be estimated accurately by calculating the electric field based on the Deutsch assumption and combining it with the SF6 static field breakdown criterion. The proposed method is applicable to the estimation of N-curves in gaps with varying field distributions. The work presented in this paper may support further quantitative research on the discharge mechanism of strongly electronegative gas dielectrics.
Dynamical current correlations in Cooper pair splitters based on proximized quantum dots
Authors: Michałek Grzegorz , Bułka Bogdan R 
Published: December 2020

Abstract
Entanglement of electrons is studied by means of current–current correlations in two Cooper pair splitter devices: with one and two proximized quantum dots (1QD and 2QD), in presence of intra- and inter-dot Coulomb interactions, and weakly coupled with metallic electrodes. The 1QD system, where Cooper pairs can be transmitted to the same or split to different normal electrodes, is contrasted with the 2QD device, where double occupancy of a single quantum dot is forbidden and transport is only through an inter-dot singlet due to non-local crossed Andreev reflection processes deep in the superconducting energy gap. Separating the current correlation function into components for partial currents of electrons and holes through various Andreev bound states, one can see bunching and antibunching of split particles: inter-level components between electron and hole currents flowing to different electrodes are positive, while intra-level electron–electron or hole–hole components are negative, respectively. Spectral decomposition of the frequency-dependent current cross-correlation is performed to get better insight into mechanisms of entanglement and dynamics of split Cooper pairs, and to extract various charge fluctuation processes with different relaxation times, related to electron and hole currents flowing through the Andreev bound states. Only low frequency polarization fluctuations are seen in the current cross-correlations, while various negative and positive high frequency (charge fluctuations) components compensate each other in the symmetric system.
Quantum scarring in a spin-boson system: fundamental families of periodic orbits
Authors: Pilatowsky-Cameo Saúl , Villaseñor David , Bastarrachea-Magnani Miguel A , Lerma-Hernández Sergio , Santos Lea F , Hirsch Jorge G 
Published: December 2020

Abstract
As the name indicates, a periodic orbit is a solution for a dynamical system that repeats itself in time. In the regular regime, periodic orbits are stable, while in the chaotic regime, they become unstable. The presence of unstable periodic orbits is directly associated with the phenomenon of quantum scarring, which restricts the degree of delocalization of the eigenstates and leads to revivals in the dynamics. Here, we study the Dicke model in the superradiant phase and identify two sets of fundamental periodic orbits. This experimentally realizable atom–photon model is regular at low energies and chaotic at high energies. We study the effects of the periodic orbits in the structure of the eigenstates in both regular and chaotic regimes and obtain their quantized energies. We also introduce a measure to quantify how much scarred an eigenstate gets by each family of periodic orbits and compare the dynamics of initial coherent states close and away from those orbits.
Numerical investigation of a new ICRF heating scenario in D-T plasma on CFETR
Authors: Song Chengyi , Yin Lan , Yang Cheng , Gong Xueyu , Zheng Pingwei , Huang Qianhong , Xia Yanbo , Chen You 
Published: December 2020

Abstract
For a fusion device, plasma pre-heating is required before the self-sustaining burning-state reactions of deuterium (D) and tritium (T) commence. Plasma heating with waves in the ion-cyclotron range of frequencies (ICRF) is effective in tokamaks. A new three-ion ICRF heating scheme for plasmas in the Chinese Fusion Engineering Test Reactor (CFETR) that require an increase in the bulk ion temperature via heating the lithium impurities in the D–T plasmas, was studied numerically. Our simulations show that the radio-frequency wave power is strongly absorbed by very few 7Li ions with concentrations of 0.01%–0.2% in a suitable mixture of D–T plasmas, the enhanced minority ion heating is related to that the 7Li fundamental resonance layer is very close to the two mode conversion layers. In adjusting the mixtures over a wide range of composition, an oscillatory behaviour in the 7Li absorption efficiency arises because of interference. Moreover, from estimates of the 7Li ion tail energy, most of the tail energy of the minority ions is found to be transferred to background ions via collisions. Compared with the routine (3He)-D–T scheme, the ICRF power is absorbed more effectively by the 7Li ions in the (7Li)-D–T heating scenario, and after the Fokker–Planck equations were solved, a large fraction of bulk ion heating was evident in the (7Li)-D–T heating scenario. The new three-ion scenario may therefore be an attractive proposition for bulk ion heating during the activated phase of the reactor.
Development of megawatt radiofrequency ion source for the neutral beam injector on HL-2A tokamak
Authors: Lei G.J. , Yan L.W. , Liu D.P. , Zhang X.M. , Zhao M. , Geng S.F. , Li M. , Zhang Y.X. , Bi Z.H. , Bu Y.N. , Xie W.M. , Zou G.Q. , Huang L.P. , Zhou B.W. , Fan H.Y. , Ma X.Z. , Yu Q. , Lu Bo , Shi Z.B. , Zhou C.P. , Xu M. , Duan X.R. 
Published: December 2020

Abstract
A radiofrequency (RF) ion source with a megawatt power extraction, thunder I, has been developed for the neutral beam injector (NBI) on HL-2A tokamak. A full solid-state RF generator with output power of 80 kW and frequency of 2 MHz was built by an RF combiner using 8 modules of solid-state RF generator with power of P
RF = 10 kW. The line electric efficiency of whole RF generator reaches 92% and its voltage standing wave ratio (VSWR) is 1.01, thus no water-cooling system is supplied. A quartz vessel with the inner diameter of 250 mm is directly adopted for resisting atmospheric pressure, which can dramatically simplify source structure. Nowadays, the extracted beam parameters of RF hydrogen ion source are 32 kV/20 A/0.1 s on a test bed, while the design parameters are 50 kV/20 A/3 s. The beam density profile measured by the infrared imaging technique at 1.3 m downstream from the grounded grid obeys a Gaussian distribution, and the corresponding half width of 1/e power decay at the matched condition is about 80 mm. Plasma homogeneity is over 90% at low RF power. The beam divergence angle meets the requirement of NBI system on HL-2A tokamak. The extractable current density increases almost linearly with the RF power. It reaches 2400 A m−2 at P
RF = 32 kW. The ion density in front of plasma grid is about 1 × 1018 m−3, corresponding to an ionized fraction of about 1% at the gas pressure of 0.5 Pa. Single hydrogen ion fraction reaches 79% at the beam current of 12.4 A. Some improvements have been considered for optimizing ion source performance on next experimental campaign. One smaller auxiliary RF discharge chamber equipped with a gas feed path, driven by 13.56 MHz/3.5 kW generator, is connected to main discharge chamber driven by 2 MHz/40 kW generator. By this dual-driven configuration, the innovative RF plasma source with high-pressure density gradient solves the initial ignition problem of powerful RF ion source even if the gas pressure below 0.1 Pa. In addition, the RF negative hydrogen ion source of 200 kV/20 A/3600 s is also developed at SWIP for the China fusion engineering test reactor.
Edge-coherent oscillation providing nearly continuous transport during edge-localized mode mitigation by n = 1 resonant magnetic perturbation in HL-2A
Authors: Sun T.F. , Liu Y. , Ji X.Q. , Liu Y.Q. , Ke R. , Gao J.M. , Wu N. , Deng W. , Xu M. , Duan X.R. 
Published: December 2020

Abstract
An edge-coherent oscillation (ECO) with a bursting feature was observed in the steep-gradient pedestal region of H-mode plasmas in the HL-2A tokamak, where the type-I edge-localized modes (ELMs) were mitigated by application of n = 1 (n is the toroidal mode number) resonant magnetic perturbation (RMP). Utilizing a newly developed beam emission spectroscopy (BES) system, it was found that the ECO with a frequency of about 2 kHz is located at the edge pedestal region, and is excited by three-wave interaction of turbulence enhanced by the RMP field through the change of electron density gradient in the pedestal region because of the pump-out effect. The oscillation drives a significant outflow of particles as directly measured by probes, thus providing a channel for nearly continuous extra particle transport across the pedestal during ELM mitigation by RMP.
The influence of precipitates upon the thermal conductivity of nitride fuel
Authors: Zadorozhnyi A V , Ozrin V D 
Published: December 2020

Abstract
In the article presented are the results modeling the behavior of mixed uranium-plutonium nitride fuel with an admixture of oxygen and carbon during irradiation in fast reactor. It was shown that accumulation of fission products and formation of secondary phases lead to formation of heterogeneous multicomponent solid solution including, in particular, metal, telluride, oxide, intermetal and sesquialteral nitride secondary phases. Influence of the secondary phases formed during irradiation on the effective thermal conductivity of the fuel is assessed in the framework of a generalized theory by Odelevskii developed for heterogeneous systems with isolated inclusions. It was found that in the irradiated nitride fuel, the main correction of the thermal conductivity is related to formation of the U2N3 phase. As it is shown, that with increase of fuel burnup and growth of secondary condensed phases, the effective thermal conductivity decreases up to about 3% for burnup of 5.5%.
Internationalization of nuclear education and training with the use of nuclear infrastructure and simulation tools
Authors: Varseev E 
Published: December 2020

Abstract
Internationalization the training programmes with inclusion of web-based training modules and students’ mobility access to the research facilities within the international initiative is a proposed mechanism to bring nuclear education to the new level in terms of attractiveness and quality. The paper discusses proposed nuclear-educating forums which could be international training courses, which are the complex of training modules containing practical exercises and theoretical training in both online format and traditional face-to-face sessions. Among foreign countries demostrating interest in Russian reactor facilities, there is a demand for training courses on the use of software to justify the safety and technical parameters of nuclear power plants based on different design: from classic VVER to advanced SMR technologies At the Rosatom Tech, the new format of regional courses are held on an annual basis within the framework of the technical cooperation project of Rosatom State Corporation and the IAEA on infrastructure development and safety assessment of VVER-type pressurized water reactors with the active use of Russian computational tools.