bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of biotic interactions in invasion ecology: theories and hypotheses.
Authors: Hui Cang , Landi Pietro , Latombe Guillaume
Published: December 2020

Changes in biotic interactions in the native and invaded range can enable a non-native species to establish and spread in novel environments. Invasive non-native species can in turn generate impacts in recipient systems partly through the changes they impose on biotic interactions; these interactions can lead to altered ecosystem processes in the recipient systems. This chapter reviews models, theories and hypotheses on how invasion performance and impact of introduced species in recipient ecosystems can be conjectured according to biotic interactions between native and non-native species. It starts by exploring the nature of biotic interactions as ensembles of ecological and evolutionary games between individuals of both the same and different groups. This allows us to categorize biotic interactions as direct and indirect (i.e. those involving more than two species) that emerge from both coevolution and ecological fitting during community assembly and invasion. We then introduce conceptual models that can reveal the ecological and evolutionary dynamics between interacting non-native and resident species in ecological networks and communities. Moving from such theoretical grounding, we review 20 hypotheses that have been proposed in invasion ecology to explain the invasion performance of a single non-native species, and seven hypotheses relating to the creation and function of assemblages of non-native species within recipient ecosystems. We argue that, although biotic interactions are ubiquitous and quintessential to the assessment of invasion performance, they are nonetheless difficult to detect and measure due to strength dependency on sampling scales and population densities, as well as the non-equilibrium transient dynamics of ecological communities and networks. We therefore call for coordinated efforts in invasion science and beyond, to devise and review approaches that can rapidly map out the entire web of dynamic interactions in a recipient ecosystem.
Seed dispersal interactions promoting plant invasions.
Authors: Díaz Vélez M. Celeste , Ferreras Ana E. , Paiaro Valeria
Published: December 2020

Animal dispersers are essential for many non-native plants since they facilitate seed movement and might promote seed germination and seedling establishment, thereby increasing their chances of invasion. This chapter reviews the published literature on seed dispersal of non-native plant species by native and/or non-native animals. The following questions are addressed: (i) Are interactions between non-native plants and their animal dispersers evenly studied worldwide? (ii) Which are the distinctive traits (i.e. geographical origin, life form, dispersal strategy and propagule traits) of non-native plants that are dispersed by animals? (iii) Which are the most studied groups of dispersers of non-native plants around the world? (iv) Does the literature provide evidence for the Invasional Meltdown Hypothesis (non-native plant-non-native disperser facilitation)? (v) What is the role of animal dispersers at different stages of the non-native plant regeneration process? Our dataset of 204 articles indicates that geographical distribution of the studies was highly heterogeneous among continents, with the highest number coming from North America and the lowest from Asia and Central America. Most of the non-native plants involved in dispersal studies were woody species from Asia with fleshy fruits dispersed by endozoochory. More than the half of the animal dispersal agents noted were birds, followed by mammals, ants and reptiles. The dominance of bird-dispersal interactions over other animal groups was consistent across geographical regions. Although most of the studies involved only native dispersers, interactions among non-native species were detected, providing support for the existence of invasional meltdown processes. Of the total number of reviewed articles reporting seed removal, 74% evaluated seed dispersal, but only a few studies included seed germination (35.3%), seedling establishment (5.4%) or seed predation (23.5%). Finally, we discuss some research biases and directions for future studies in the area.
EICA 2.0: a general model of enemy release and defence in plant and animal invasions.
Authors: Honor Richard , Colautti Robert I.
Published: December 2020

Plants and animals have evolved a variety of strategies to limit the negative fitness consequences of natural enemies (i.e. herbivores, predators, parasites and pathogens). Demographic bottlenecks occurring during the invasion process reduce the number of co-introduced natural enemies, providing opportunities to study rapid evolution in environments with different or reduced enemy loads. Enemy release theory provides a set of hypotheses and predictions about the role of natural enemies in the proliferation of invasive species. This body of theory includes the Enemy Release Hypothesis (ERH) and the related Evolution of Increased Competitive Ability Hypothesis (EICA), but there is often confusion about these hypotheses and the data needed to test them. We introduce a simple, general model of enemy release to identify and clarify some of the key assumptions and predictions implicit in enemy release theory and its impacts on invasion. Although introduced populations likely benefit from a reduction in the direct fitness impacts of natural enemies in the early stages of invasion, an evolutionary shift in resource allocation from defence to growth and reproduction is much less likely and depends on a delicate balance between the fitness costs and benefits of defence and the fitness impacts of natural enemies in both the native and introduced ranges. Even when the abundance of natural enemies is lower in the introduced range, the majority of scenarios do not favour evolution of less defended genotypes that are more competitive or more fecund, contrary to predictions of EICA. Perhaps surprisingly, we find that the level of damage by natural enemies in field surveys is not generally a good parameter for testing enemy release theory. Instead, common garden experiments characterizing fitness reaction norms of multiple genotypes from the native and introduced range are crucial to estimate the historic rate of adaptive evolution or predict it into the future. Incorporating spatial autocorrelation and methods from population genetics can further improve our understanding of the role of enemy release and evolution in the proliferation of invasive species.
The role of pathogens in plant invasions.
Authors: Kendig Amy E. , Flory S. Luke , Goss Erica M. , Holt Robert D. , Clay Keith , Harmon Philip F. , Lane Brett R. , Adhikari Ashish , Wojan Christopher M.
Published: December 2020

Plant-pathogen interactions occur throughout the process of plant invasion: pathogens can acutely influence plant survival and reproduction, while the large densities and spatial distributions of invasive plant species can influence pathogen communities. However, interactions between invasive plants and pathogens are often overlooked during the early stages of invasion. As with introductions of invasive plants, the introduction of agricultural crops to new areas can also generate novel host-pathogen interactions. The close monitoring of agricultural plants and resulting insights can inform hypotheses for invasive plants where research on pathogen interactions is lacking. This chapter reviews the known and hypothesized effects of pathogens on the invasion process and the effects of plant invasion on pathogens and infectious disease dynamics throughout the process of invasion. Initially, pathogens may inhibit the transport of potentially invasive plants. After arrival in a new range, pathogens can facilitate or inhibit establishment success of introduced plants depending on their relative impacts on the introduced plants and resident species. As invasive plants spread, they may encounter novel pathogens and alter the abundance and geographic range of pathogens. Pathogens can mediate interactions between invasive plants and resident species and may influence the long-term impacts of invasive plants on ecosystems. As invasive plants shift the composition of pathogen communities, resident species could be subject to higher disease risk. We highlight gaps in invasion biology research by providing examples from the agricultural literature and propose topics that have received little attention from either field.
Direct and indirect effects of herbivores influencing plant invasions.
Authors: Kotanen Peter M.
Published: December 2020

Non-native plants rarely escape damage by herbivores. Instead, upon arrival in a new region, they begin to acquire new enemies, replacing those they have lost during their migration. These herbivores can include both natives to the new region and species that have themselves been accidentally or deliberately introduced from elsewhere, potentially including examples originating from the invader's original range. Shifts of new enemies from other hosts can occur over a range of timescales, depending in part on whether evolutionary change is required, but are likely to be faster for plants that are widespread and phylogenetically related to a herbivore's original host, and faster for generalist herbivores than for specialists. The occurrence of herbivores is not necessarily uniform across an invader's range; instead, they may be less diverse or abundant in host populations that are geographically or ecologically marginal, though existing evidence is mixed. Collectively, these new suites of herbivores can affect the growth and fitness of invaders, both directly by damaging them and indirectly by attacking their competitors. Studies comparing the demographic consequences of herbivory for successful vs unsuccessful invaders may help to clarify how often such impacts limit invasiveness. The view that an invader enters 'enemy-free' space is inaccurate; instead, persistence and spread of non-native plants often may be affected by the novel and changing assemblage of herbivores that they acquire within their new distribution.
Competition between native and non-native plants.
Authors: Wandrag Elizabeth M. , Catford Jane A.
Published: December 2020

The introduction of species to new locations leads to novel competitive interactions between resident native and newly-arriving non-native species. The nature of these competitive interactions can influence the suitability of the environment for the survival, reproduction and spread of non-native plant species, and the impact those species have on native plant communities. Indeed, the large literature on competition among plants reflects its importance in shaping the composition of plant communities, including the invasion success of non-native species. While competition and invasion theory have historically developed in parallel, the increasing recognition of the synergism between the two themes has led to new insights into how non-native plant species invade native plant communities, and the impacts they have on those plant communities. This chapter provides an entry point into the aspects of competition theory that can help explain the success, dominance and impacts of invasive species. It focuses on resource competition, which arises wherever the resources necessary for establishment, survival, reproduction and spread are in limited supply. It highlights key hypotheses developed in invasion biology that relate to ideas of competition, outlines biotic and abiotic factors that influence the strength of competition and species' relative competitive abilities, and describes when and how competition between non-native and native plant species can influence invasion outcomes. Understanding the processes that influence the strength of competition between non-native and native plant species is a necessary step towards understanding the causes and consequences of biological invasions.
Indirect biotic interactions of plant invasions with native plants and animals.
Authors: Allen Warwick J.
Published: December 2020

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

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.
SPRED1 deletion confers resistance to MAPK inhibition in melanoma
Authors: Ablain Julien , Liu Sixue , Moriceau Gatien , Lo Roger S. , Zon Leonard I.
Published: December 2020

Functional evaluation of genetic lesions can discover a role in cancer initiation and progression and help develop novel therapeutic strategies. We previously identified the negative MAPK regulator SPRED1 as a novel tumor suppressor in KIT-driven melanoma. Here, we show that SPRED1 is also frequently deleted in human melanoma driven by mutant BRAF. We found that SPRED1 inactivation in human melanoma cell lines and primary zebrafish melanoma conferred resistance to BRAFV600E inhibition in vitro and in vivo. Mechanistically, SPRED1 loss promoted melanoma cell proliferation under mutant BRAF inhibition by reactivating MAPK activity. Consistently, biallelic deletion of SPRED1 was observed in a patient whose melanoma acquired resistance to MAPK-targeted therapy. These studies combining work in human cells and in vivo modeling in zebrafish demonstrate a new mechanism of resistance to BRAFV600E inhibition in melanoma.
Structural basis of cytoplasmic NaV1.5 and NaV1.4 regulation
Authors: Nathan Sara , Gabelli Sandra B. , Yoder Jesse B. , Srinivasan Lakshmi , Aldrich Richard W. , Tomaselli Gordon F. , Ben-Johny Manu , Amzel L. Mario
Published: December 2020

Voltage-gated sodium channels (NaVs) are membrane proteins responsible for the rapid upstroke of the action potential in excitable cells. There are nine human voltage-sensitive NaV1 isoforms that, in addition to their sequence differences, differ in tissue distribution and specific function. This review focuses on isoforms NaV1.4 and NaV1.5, which are primarily expressed in skeletal and cardiac muscle cells, respectively. The determination of the structures of several eukaryotic NaVs by single-particle cryo-electron microscopy (cryo-EM) has brought new perspective to the study of the channels. Alignment of the cryo-EM structure of the transmembrane channel pore with x-ray crystallographic structures of the cytoplasmic domains illustrates the complementary nature of the techniques and highlights the intricate cellular mechanisms that modulate these channels. Here, we review structural insights into the cytoplasmic C-terminal regulation of NaV1.4 and NaV1.5 with special attention to Ca2+ sensing by calmodulin, implications for disease, and putative channel dimerization.
Entropy and the link action in the causal set path-sum
Authors: Mathur Abhishek , Singh Anup Anand , Surya Sumati
Published: December 2020

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

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

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

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

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

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

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

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

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

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

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.
Ultradilute self-bound quantum droplets in Bose–Bose mixtures at finite temperature*
Authors: Wang Jia , Liu Xia-Ji , Hu Hui
Published: December 2020

We theoretically investigate the finite-temperature structure and collective excitations of a self-bound ultradilute Bose droplet in a flat space realized in a binary Bose mixture with attractive inter-species interactions on the verge of mean-field collapse. As the droplet formation relies critically on the repulsive force provided by Lee–Huang–Yang quantum fluctuations, which can be easily compensated by thermal fluctuations, we find a significant temperature effect in the density distribution and collective excitation spectrum of the Bose droplet. A finite-temperature phase diagram as a function of the number of particles is determined. We show that the critical number of particles at the droplet-to-gas transition increases dramatically with increasing temperature. Towards the bulk threshold temperature for thermally destabilizing an infinitely large droplet, we find that the excitation-forbidden, self-evaporation region in the excitation spectrum, predicted earlier by Petrov using a zero-temperature theory, shrinks and eventually disappears. All the collective excitations, including both surface modes and compressional bulk modes, become softened at the droplet-to-gas transition. The predicted temperature effects of a self-bound Bose droplet in this work could be difficult to measure experimentally due to the lack of efficient thermometry at low temperatures. However, these effects may already present in the current cold-atom experiments.
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

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

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

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

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.
Description of transient processes in multiplying medium by the physical birth-and-death model
Authors: Bobkova M V , Korbut T N , Rudak Ed A
Published: December 2020

The work presents an approach to describe neutron and neutron-breeding medium interaction process based on the physical birth-and-death model. This model is an extended form of the basic birth-and-death model and operates with breeding medium parameters. Analytical solutions and physical interpretation of the processes within reactor can be obtained by such method. Recently, thermal reactor theory with an internal neutron source in the form of delayed neutrons on the basis of birth-and-death model within linear growth approximation was proposed. Particles radioactive decay properties and equation analysis for describing breeding medium parameters using point thermal reactor framework were also studied within the model using Poisson and binomial distribution formalism. Experimental data of three nuclear subcritical facilities were used in this work, KUCA (Japan), MASURCA (France) and GUINEVERE (Belgium). Reactivity and the average number of particles in the system were estimated in this work within physical model framework for three subcritical systems.
Novel Bio-compatible Tracers for Positron Emission Particle Tracking
Authors: Chang Yu-Fen , Balakin Boris V.
Published: December 2020

To study the flow of objects in opaque flow processes, the PEPT (positron emission particle tracking) technique may be utilized. The PEPT technique is based on the same principle of positron emission tomography (PET). Both techniques detect the characteristic back-to-back gamma pairs caused by positron-electron annihilation. PEPT allows tracking of β+ - activated objects (tracers) with high spatial (microns) and temporal resolutions (milliseconds). This makes the technique promising in a number of medical applications that require observation of fast transient phenomena e.g. heart and brain hemodynamics, the aerodynamics of respiratory tract etc. However, a majority of PEPT-tracers used nowadays are tailored for industrial applications and are based on solid particles of a micrometric size, which are hardly suitable for in-vivo tests. In this contribution, we propose new bio-compatible tracers. The tracers are based on frozen radioactive solutions rather than activated solids. We produced a number of millimetre-sized ice tracers dispersing the droplets of radioactive solution in oil at negative temperatures. In this preliminary study, we demonstrate how the tracers behave in a settling column and in an agitated vessel. The PEPT-tracks are presented together with a supplementary numerical analysis that was conducted in order to estimate the freezing time of the droplets.
Mathematical model of the distribution of the coolant flow rate in the group distribution header and its use to determine the flow rate in the RBMK reactor channel
Authors: Zagrebayev A M , Ramazanov R N
Published: December 2020

The paper proposes an elementary mathematical model of the distribution of coolant flows through water communications in the group distributing header (GDH) of a power unit with an RBMK reactor. This model used to determine the flow rate in the channel with a “forbidden” flow meter. An equation is given based on the mass balance of the coolant in the allocated volume. The results of the solution are used to construct an algorithm for determining the flow rate of the coolant in the channel. The results of the application of the technique on the measurement data from the power unit are presented. It is shown that the relative discrepancy with the measured value of the flow rate at a constant position of the flow control valve is on the order of several percent.
Computational analysis of experiments to determine the kinetic parameters at the ASTRA HTGR type critical facility
Authors: Kruglikov A E , Volkov Y N , Zizin M N , Boyarinov V F , Nevinitsa V A , Fomichenko P A
Published: December 2020

The zero power ASTRA critical facility is intended for experimental investigations of neutronic features of modular High Temperature Gas Cooled Reactors. The computational analysis of non-stationary experiments carried out at the ASTRA critical stand to determine the kinetic parameters is carried out using SHIPR diffusion program. To measure the kinetic parameters, the impulse Simmons-King method was used. The computational analysis were carried out for 4 different configurations of ASTRA critical stand. Since in case of nonstationary calculation by implementation of the spatial kinetics approximation, it is necessary to set the neutron group velocities the full-scale calculations of neutron spectra were carry oud using the MCU program in order to take into account the spectrum that is established in the full-scale reactor model. On the basis of a comparison of the experimental and calculated results, a conclusion was made about the applicability of the applied effective calculation models for neutronic calculations of HTGR-type reactors.
Homogenised group constants generation using Monte Carlo codes for diffusion calculation of pebble bed reactor
Authors: Kruglikov A E , Shchurovskaya M V , Volkov Yu N , Nevinitsa V A , Fomichenko P A , Zizin M N
Published: December 2020

This study is focused on the development of homogenization technique for the ASTRA pebble bed critical facility. The methods of generating homogenized few-group cross sections using continuous energy Monte Carlo codes MCU-PTR and Serpent 2.1.29 for full core diffusion calculation of pebble bed reactor were studied. 13-group cross sections were used in the SHIPR diffusion code to calculate the simplified cores of the ASTRA critical facility with HTGR-type fuel and a graphite reflector. Cross-verification of Serpent and MCU-PTR applied to HTGR system was carried out. Different homogenization schemes were tested for the SHIPR model and compared against Monte Carlo solutions. Diffusion coefficients for the fuel calculated using out-scatter approximation and cumulative migration method (CMM) were compared. It was shown that diffusion coefficients for fuel of pebble bed reactor calculated by CMM may reduce the difference between the diffusion and Monte Carlo simulation. The abilities of Serpent and MCU-PTR for modelling pebble bed reactors were compared.
Investigation of the power peaking factor Krin the fuel assembly during the maneuvering mode of the VVER-1000 reactor
Authors: Anisur Rahman SK , Uvakin M A
Published: December 2020

The aim of this thesis paper is to analysis the power peaking factors Krof the VVER-1000 reactor. Power peaking factor is important for the safety operation of the VVER-1000 power reactor. The maintenance of the core power distribution in a nuclear power plant is a precondition for the safety operation of a reactor. In this investigation used boron carbide. Boron carbide is a compound that contains boron and carbon, especially B4C; an extremely hard, non-metallic, black crystalline compound or solid solution. Only diamond is harder. In addition to its hardness property, boron carbide has the physical properties of corrosion resistance, heat strength, low specific gravity and high elastic modulus. It is used as an abrasive, neutron absorber for nuclear reactors, and as an alloying agent in composite structural materials. For this reason, when need to change the power of a reactor then the boron carbide (B4C) control insert the reactor core. In this step investigated the power picking factors and its deviation using the Boron carbide (B4C). Power peaking factors are connecting between the thermal-hydraulics and the nutronics of the nuclear power plant core. This power peaking factors was calculated by the comprehensive nutronics calculation program GETERA-93.