bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimization of the micromotion of trapped ions with artificial neural networks
Authors: Liu Yang , Lao Qi-feng , Lu Peng-fei , Rao Xin-xin , Wu Hao , Liu Teng , Wang Kun-xu , Wang Zhao , Li Ming-shen , Zhu Feng , Luo Le
Published: September 2021

Minimizing the micromotion of a trapped ion in a linear Paul trap is of great importance in maintaining long coherence time as well as implementing quantum logic gates with high fidelity, which is crucial for large-scale quantum computation with trapped ions. Here, by applying the RF (radio frequency)-photon correlation technique, we demonstrate that a machine learning method based on artificial neural networks can quickly search for optimal voltage settings of the electrodes to minimize the trapped ion's micromotion. This machine learning assisted RF-photon correlation technique can be straightforwardly applied to more complicated surface ion traps with many electrodes, where the manual minimization of the excess micromotion generated by stray electric fields would become extremely challenging for the larger number of electrodes with various voltage settings. Instead, the presented machine learning assisted method provides an effective and automatic way to address this need.
Cation-size mismatch as a predictive descriptor for structural distortion, configurational disorder, and valence-band splitting in II-IV-N2 semiconductors
Authors: Kute Malhar , Deng Zihao , Chae Sieun , Kioupakis Emmanouil
Published: September 2021

The II-IV-N2 class of heterovalent ternary nitrides has gained significant interest as alternatives to the III-nitrides for electronic and optoelectronic applications. In this study, we apply first-principles calculations based on density functional theory to systematically investigate the effects of structural distortions due to cation size mismatch on the configurational disorder of the cation sublattice and the valence band structure in this class of materials. We find that larger size mismatch between the group-II and the group-IV cations results in stronger lattice distortions from the ideal hexagonal ratio, which in turn inhibits the propensity of these materials toward octet-rule violating cation disorder. We also demonstrate that the formation energy of a single cation antisite pair, which is fast and simple to calculate, is a strong indicator of a material's propensity toward disorder. Furthermore, the breaking of in-plane symmetry leads to a splitting of the top three valence bands at Γ, which is also directly related to the magnitude of structural distortions. Our work demonstrates that the structural and functional properties of the II-IV-N2 materials can be finely tuned through controllable structural distortions that stem from the choice of cations.
The optimized interface characteristics of
β
-Ga2O3 Schottky barrier diode with low temperature annealing
Authors: Hong Yue-Hua , Zheng Xue-Feng , He Yun-Long , Zhang Fang , Zhang Xiang-Yu , Wang Xi-Chen , Li Jia-Ning , Wang Dang-Po , Lu Xiao-Li , Han Hong-Bo , Ma Xiao-Hua , Hao Yue
Published: September 2021

A low temperature controlled annealing technique was utilized to improve the performance of vertical β-gallium oxide (β-Ga2O3) Schottky barrier diodes (SBDs) in this work. The nickel is diffused into Ga2O3, and NiO was formed at the interface between the anode and semiconductor generating p–n junction after low temperature annealing. Simultaneously, the trap state density of interface Ni/Ga2O3 as well as the carbon bonded with oxygen on the surface was reduced, which was proved by the capacitance and conductance measurements and x-ray photoelectron spectroscopic analysis, respectively. Combined the decreased saturation current density by three orders of magnitude from 1.21 × 10−6 to 9.27 × 10−8 and 5.12 × 10−9 A/cm2 and larger breakdown voltage from 220 to 270 V owing to the optimized interface and the formation of NiO, a low temperature annealing technique makes certain effective improvement for vertical β-Ga2O3 SBDs via interface engineering.
Performance of reservoir discretizations in quantum transport simulations
Authors: Elenewski Justin E. , Wójtowicz Gabriela , Rams Marek M. , Zwolak Michael
Published: September 2021

Quantum transport simulations often use explicit, yet finite, electronic reservoirs. These should converge to the correct continuum limit, albeit with a trade-off between discretization and computational cost. Here, we study this interplay for extended reservoir simulations, where relaxation maintains a bias or temperature drop across the system. Our analysis begins in the non-interacting limit, where we parameterize different discretizations to compare them on an even footing. For many-body systems, we develop a method to estimate the relaxation that best approximates the continuum by controlling virtual transitions in Kramers turnover for the current. While some discretizations are more efficient for calculating currents, there is little benefit with regard to the overall state of the system. Any gains become marginal for many-body, tensor network simulations, where the relative performance of discretizations varies when sweeping other numerical controls. These results indicate that typical reservoir discretizations have little impact on numerical costs for certain computational tools. The choice of a relaxation parameter is nonetheless crucial, and the method we develop provides a reliable estimate of the optimal relaxation for finite reservoirs.
A numerical investigation of bubble dynamics in a ferrofluid by improved multicomponent multiphase pseudopotential lattice Boltzmann model coupled with magnetic field solver
Authors: Huang Yichen , Zhang Ying , Xu Meng , Lei Jie , Li Zhihao , Ye Wenlin
Published: September 2021

To simulate the dynamics of bubbles within a ferrofluid under the action of a uniform magnetic field, an improved multicomponent multiphase pseudopotential model with a multiple-relaxation-time collision operator coupled with the lattice Boltzmann model for solving magnetic field was constructed in the current study. By comparing with basic arithmetic examples and results of previous studies, it is well demonstrated that the coupled model proposed in this study has good reliability and accuracy in simulating the dynamics of bubbles in a ferrofluid under a uniform magnetic field. Then the proposed coupled model was used to study the dynamics characteristics of two asymmetrically arranged bubbles in a ferrofluid under the action of a horizontal uniform magnetic field. The results showed that the irregular nonlinear deformation, four representative bubble motion patterns, and the bubble oscillates along and perpendicular to the magnetic field direction were found in the dynamics of the bubbles. At different magnetic Bond numbers (Bom), the variation of distances parallel to the magnetic field (d) and distances perpendicular to the magnetic field (h) makes the nonlinear deformation effect, bubble motion mode, bubble oscillation amplitude, and bubble deformation throughout the process change accordingly. However, for each Bom number, different d and h at the same Bom number have almost no effect on the time of bubble oscillation and the deformation when the bubbles are stabilized after fusion.
Yield determinants, root distribution and soil water uptake in maize (Zea mays) hybrids differing in canopy senescence under post-silking drought
Authors: Antonietta M. , Maydup M. L. , Cano M. G. , Fanello D. D. , Acciaresi H. A. , Guiamet J. J.
Published: September 2021

Delayed canopy senescence or ‘stay-green’ (SG) trait in maize (Zea mays L.) could improve drought tolerance. Two field trials comparing four to six maize hybrids with different senescence rate were carried out at Buenos Aires, Argentina, varying water availability during the reproductive period. Green leaf area at maturity was related to kernel weight (r2 = 0.94***) but its relationship with yield was weaker (r2 = 0.51–53*) and post-silking dry matter remobilisation was negatively related with the SG trait (r2 = 0.84**). Two additional experiments were carried out in 63 L pots by withholding irrigation in half of the pots after silking. The SG hybrid achieved lower root biomass at silking, a shallower root distribution and larger root growth in the post-silking period. Under drought conditions, stomatal conductance was lower in the SG hybrid but photosynthetic electron transport rate was higher. Higher post-silking dry matter assimilation in the SG hybrid was compensated for by higher dry matter remobilisation in the non-SG. Higher kernel number per plant in the non-SG hybrid with no ability to compensate for by higher kernel weight in the SG, resulted in slightly higher yields in the non-SG under drought. A water conservation strategy associated with a shallower root system could be linked to the SG trait, promoting faster water depletion at upper soil levels and reduced stomatal conductance at the leaf level but with no conclusive yield advantage.
Short-term effects of rice straw biochar on hydraulic properties and aggregate stability of an Acrisol
Authors: Parker Nathaniel , Cornelis Wim M. , Frimpong Kwame Agyei , Danso Eric Oppong , Bessah Enoch , Arthur Emmanuel
Published: September 2021

Biochar application to a structurally poor tropical soil could potentially alter the soil’s aggregate strength and hydraulic properties. However, very few field studies have investigated the impact of biochar on the aggregate strength and hydraulic properties of tropical soils. A field experiment was therefore conducted to investigate the short-term effects of rice straw biochar on soil hydraulic properties and aggregate stability of an Acrisol in Ghana. The biochar was broadcast at rates of 10 t ha−1 and 20 t ha−1 as single applications that were incorporated into the top 20 cm of the soil using a spade and then the soil was levelled using a rake. Field saturated hydraulic conductivity and laboratory-measured soil water retention, aggregate stability and water-repellency were determined 10 months after the biochar application. Biochar increased aggregate stability against fast wetting by up to 33% compared to the control. This implies that biochar might improve the stability of aggregate of an Acrisol against slaking and erosivity of heavy rainfall. However, aggregate stability against slow wetting and mechanical breakdown after pre-wetting were unaffected by the biochar. Biochar did not affect field saturated hydraulic conductivity, water retention characteristics and water-repellency. Further field studies on weathered tropical soils with low native soil organic matter is recommended to elucidate the effect of repeated biochar addition on soil hydraulic and aggregate characteristics.
Relationship between earthworm abundance, ecological diversity and soil function in pastures
Authors: Schon N. L. , Fraser P. M. , Mackay A. D.
Published: September 2021

Earthworms contribute to a wide range of process that underpin soil function and ecosystem services and are an important component of a soil’s natural capital stocks. With increasing interest in soil health, it is important to better understand the type of earthworm community required to enhance soil functions. This is of particular interest in New Zealand where pasture systems are dominated by exotic earthworm species and low ecological diversity. Two separate mesocosm experiments were established to explore the interaction between earthworm abundance and ecological diversity as it influences soil functions. Experimental increases in earthworm abundance increased soil macroporosity and water infiltration, increased plant nitrogen (N) and plant growth. Although some benefits were observed at the lowest earthworm abundances, the greatest benefits were seen at the higher abundances. Earthworm ecological diversity is also critical to ensure soil functions are optimised. For example, the single species of Aporrectodea caliginosa alone was not able to improve water infiltration or pasture production. However, when this species was found in combination with Aporrectodea longa, there was positive influence on soil functions despite the abundance of A. longa itself not increasing. This study highlights the importance of including a measure of ecological diversity alongside a measure of abundance to assess soil biological health.
Comparing calibrated statistical and machine learning methods for wildland fire occurrence prediction: a case study of human-caused fires in Lac La Biche, Alberta, Canada
Authors: Phelps Nathan , Woolford Douglas G.
Published: September 2021

Wildland fire occurrence prediction (FOP) modelling supports fire management decisions, such as suppression resource pre-positioning and the routeing of detection patrols. Common empirical modelling methods for FOP include both model-based (statistical modelling) and algorithmic-based (machine learning) approaches. However, it was recently shown that many machine learning models in FOP literature are not suitable for fire management operations because of overprediction if not properly calibrated to output true probabilities. We present methods for properly calibrating statistical and machine learning models for fine-scale, spatially explicit daily FOP followed by a case-study comparison of human-caused FOP modelling in the Lac La Biche region of Alberta, Canada, using data from 1996 to 2016. Calibrated bagged classification trees, random forests, neural networks, logistic regression models and logistic generalised additive models (GAMs) are compared in order to assess the pros and cons of these approaches when properly calibrated. Results suggest that logistic GAMs can have similar performance to machine learning models for FOP. Hence, we advocate that the pros and cons of different modelling approaches should be discussed with fire management practitioners when determining which models to use operationally because statistical methods are commonly viewed as more interpretable than machine learning methods.
Robust wrinkled MoS
2
/N-C bifunctional electrocatalysts interfaced with single Fe atoms for wearable zinc-air batteries
Authors: Yan Yan , Liang Shuang , Wang Xiang , Zhang Mingyue , Hao Shu-Meng , Cui Xun , Li Zhiwei , Lin Zhiqun
Published: September 2021

Significance

Single-atom catalysis involves precise modulation of structures at the atomic level to markedly enhance catalytic activity. This work explores wrinkled MoS
2
@Fe-
N
-C core/shell nanospheres with atomic Fe-doped surface and interface (MoS
2
/Fe-
N
-C) as highly efficient bifunctional catalysts for both oxygen reduction and evolution reactions (ORR and OER), rivaling the ORR and OER activity of Pt/C and Ir/C, respectively. The robust performance can be attributed to the unique MoS
2
/Fe-
N
-C interface, at which the highly active Fe-N
4
moieties coupled with the grain boundary of MoS
2
simultaneously reduce the energy barriers of ORR and OER. Notably, the Fe-N-C shell protects the MoS
2
core from corrosion during the ORR and OER processes in the alkaline electrolyte, leading to a long-term stability for the as-constructed zinc-air batteries.
Looking at redefining sex(uality)
Authors: Urquízar José Iglesias
Published: September 2021

This article examines the dubbing of the 2014 American gay-themed series Looking and its treatment of sexual references into Castilian Spanish with a view to exploring the role of audiovisual translation in the discursive construction of homosexuality. While some scholars have decried a historical tendency in translation to attenuate or even suppress references in connection with non-normative sex, the dubbing of Looking, I claim, amplifies these references by way of two strategies: up-scaling and increased explicitness. Drawing upon Jeremy Munday’s (2012) concept of “evaluation” and on appraisal theory as expounded by Martin and White (2005), I aim at revealing the significance of the translator’s lexicogrammatical selections and how these may alter the semiotic import of the characters and, thus, of a certain portrayal of homosexuality. Additionally, such choices may be indicative of the translator’s own stance towards issues of sexuality. Though the strategies analyzed may appear to perpetuate commonplaces regarding gay sexual experience, they ultimately serve, I argue, as a device to generate a language that goes beyond diluted expressions of homosexuality.
Attitudinal stance towards the anti-extradition bill movement in China Daily and South China Morning Post
Authors: Cao Xiuling , Zhang Danqi , Luo Qianjun
Published: September 2021

Based on Appraisal Theory and critical discourse analysis, this corpus-assisted study examines how China Daily (CD) and South China Morning Post (SCMP) used appraisal resources to express their respective stances towards the anti-extradition bill movement. The results show that both newspapers employed negative resources of Judgement and the predication strategy to convey their stance, but SCMP seemed more refrained in the use of appraisal resources. CD openly stated that any illegal actions should be punished, and SCMP also criticised these actions. Besides, CD emphasized the consequences brought by violence and attributed the breakout of the protests to the opposition camp’s political intention for their own benefit, whereas SCMP highlighted Hong Kongers’ widespread opposition to the bill. These differences in language use and stance might be explained by the different press systems they respectively belong to and related to their respective historical and socio-political contexts.
Activated PI3Kδ signals compromise plasma cell survival via limiting autophagy and increasing ER stress
Authors: Al Qureshah Fahd , Sagadiev Sara , Thouvenel Christopher D. , Liu Shuozhi , Hua Zhaolin , Hou Baidong , Acharya Mridu , James Richard G. , Rawlings David J.
Published: September 2021

While phosphatidylinositide 3-kinase delta (PI3Kδ) plays a critical role in humoral immunity, the requirement for PI3Kδ signaling in plasma cells remains poorly understood. Here, we used a conditional mouse model of activated PI3Kδ syndrome (APDS), to interrogate the function of PI3Kδ in plasma cell biology. Mice expressing a PIK3CD gain-of-function mutation (aPIK3CD) in B cells generated increased numbers of memory B cells and mounted an enhanced secondary response but exhibited a rapid decay of antibody levels over time. Consistent with these findings, aPIK3CD expression markedly impaired plasma cell generation, and expression of aPIK3CD intrinsically in plasma cells was sufficient to diminish humoral responses. Mechanistically, aPIK3CD disrupted ER proteostasis and autophagy, which led to increased plasma cell death. Notably, this defect was driven primarily by elevated mTORC1 signaling and modulated by treatment with PI3Kδ-specific inhibitors. Our findings establish an essential role for PI3Kδ in plasma cell homeostasis and suggest that modulating PI3Kδ activity may be useful for promoting and/or thwarting specific immune responses.
A high-performance code for EPRL spin foam amplitudes
Authors: Gozzini Francesco
Published: September 2021

We presentsl2cfoam-next, a high-performance software library for computing Lorentzian EPRL spin foam amplitudes. The library improves on previous codes by many orders of magnitude in single-core performance, can be parallelized on a large number of CPUs and on the GPU, and can be used interactively. We describe the techniques used in the code and provide many usage examples. As first applications, we usesl2cfoam-nextto complete the numerical test of the Lorentzian single-vertex asymptotics and to confirm the presence of the ‘flatness problem’ of spin foam models in the BF and EPRL cases.
Minimizing magnetic fields of the low-noise MnZn ferrite magnetic shield for atomic magnetometer
Authors: Yang Ke , Lu Jixi , Wang Zixuan , Sun Bowen , Ma Yanning , Wang Yaoguo , Han Bangcheng
Published: September 2021

Several modern precision measurements require a low-noise magnetic shield composed of a MnZn ferrite shield and a multilayer µ-metal shield. However, the residual magnetic field and gradient reduce the performance of the low-noise magnetic shield. An appropriate demagnetization operation is crucial for obtaining a lower residual magnetic field and gradient. This study proposes an improved demagnetization scheme in which the toroidal coil and the solenoidal coil are employed simultaneously, while the ferrite and µ-metal shield layers are wound separately. This allows for a residual field below 0.6 nT and a gradient lower than 0.5 nT cm−1 to be obtained along all three axes within ±20 mm at the center, which is significantly lower than the results published in previous studies. The low-noise magnetic shield used in this study composed of a MnZn ferrite shield with an inner diameter of 112 mm, an outer diameter of 140 mm, and a height of 225 mm, and a five-layer µ-metal shield. This study considerably improves the performance of the low-noise magnetic shields. The proposed scheme can increase the sensitivity of the spin-exchange-relaxation-free atomic magnetometer by approximately 1 fT Hz-1/2. This study can help apply the low-noise magnetic shield in various fields more conveniently, such as low-field nuclear magnetic resonance detection, atomic gyroscope, and in cutting-edge physics research.
The status and future of direct nuclear reaction measurements for stellar burning
Authors: Aliotta M , Buompane R , Couder M , Couture A , deBoer R J , Formicola A , Gialanella L , Glorius J , Imbriani G , Junker M , Langer C , Lennarz A , Litvinov Yu A , Liu W-P , Lugaro M , Matei C , Meisel Z , Piersanti L , Reifarth R , Robertson D , Simon A , Straniero O , Tumino A , Wiescher M , Xu Y
Published: September 2021

The study of stellar burning began just over 100 years ago. Nonetheless, we do not yet have a detailed picture of the nucleosynthesis within stars and how nucleosynthesis impacts stellar structure and the remnants of stellar evolution. Achieving this understanding will require precise direct measurements of the nuclear reactions involved. This report summarizes the status of direct measurements for stellar burning, focusing on developments of the last couple of decades, and offering a prospectus of near-future developments.
Relation between spin current and spin torque in Rashba ferromagnets
Authors: Jiang Peng , Ma Zhongshui
Published: September 2021

We establish a brief relation between spin current and spin torque, including spin–orbit torque and spin transfer torque in 2D Rashba ferromagnets with nonuniform magnetic texture. Both electrically and thermally induced charge, heat, and spin current are investigated by the Luttinger’s mechanical method, and we derive the contributions of magnetization corresponding to the thermal spin current and the thermal spin torque. The novel transport currents are also found in this paper when the interplay between spin–orbit coupling and nonuniform magnetic texture is taken into account.
Molecular dynamics simulations of screw dislocation mobility in bcc Nb
Authors: Zotov Nikolay , Grabowski Blazej
Published: September 2021

The screw dislocation mobility in bcc Nb has been studied by molecular dynamics (MD) simulations at different strain rates and temperatures using an embedded-atom method (EAM) potential. Static properties of the screw dislocation, as determined with the EAM potential, are in agreement with previous density-functional-theory calculations. The elementary slip plane of the screw dislocation remains (110) for all studied strain rates (in the range 6.3 × 107–6.3 × 109 s−1) and temperatures (5 to 550 K). However, the consecutive cross-slip on different symmetry-equivalent (110) planes leads to an effective glide on (112) planes. It is demonstrated that the screw dislocation trajectories, velocities and waviness of the screw dislocation depend on the crystallographic indices, (110) or (112), of the maximum resolved shear stress plane. The waiting time for the start of the screw dislocation motion increases exponentially with decreasing strain rate, substantiating the necessity to apply in future accelerated MD techniques in order to compare with macroscopic stress-strain experiments.
Development of data-driven spd tight-binding models of Fe—parameterisation based on QSGW and DFT calculations including information about higher-order elastic constants
Authors: Barzdajn Bartosz , Garrett Alexander M , Whiting Thomas M , Race Christopher P
Published: September 2021

Quantum-mechanical (QM) simulations, thanks to their predictive power, can provide significant insights into the nature and dynamics of defects such as vacancies, dislocations and grain boundaries. These considerations are essential in the context of the development of reliable, inexpensive and environmentally friendly alloys. However, despite significant progress in computer performance, QM simulations of defects are still extremely time-consuming with ab-initio/non-parametric methods. The two-centre Slater–Koster (SK) tight-binding (TB) models can achieve significant computational efficiency and provide an interpretable picture of the electronic structure. In some cases, this makes TB a compelling alternative to models based on abstraction of the electronic structure, such as the embedded atom model. The biggest challenge in the implementation of the SK method is the estimation of the optimal and transferable parameters that are used to construct the Hamiltonian matrix. In this paper, we will present results of the development of a data-driven framework, following the classical approach of adjusting parameters in order to recreate properties that can be measured or estimated using ab-initio or non-parametric methods. Distinct features include incorporation of data from QSGW (quasi-particle self-consistent GW approximation) calculations, as well as consideration of higher-order elastic constants. Furthermore, we provide a description of the optimisation procedure, omitted in many publications, including the design stage. We also apply modern optimisation techniques that allow us to minimise constraints on the parameter space. In summary, this paper introduces some methodological improvements to the semi-empirical approach while addressing associated challenges and advantages.
Breakdown prediction of ion source at EAST-NBI using neural network
Authors: Wang Jinxin , Wang Na , Liu Zhimin , Zhao Yuanzhe , Xie Yahong , Xie Yuanlai
Published: September 2021

The designed neural networks are trained to appraise the risk of ion sources breakdown events in the neutral beam injector (NBI) experimental device using several offline diagnostic signals as inputs. A saliency analysis proves the reasonableness of the chosen inputs, some of which are helpful to improve the network performance. The experimental tests that were carried out refer to data collected from successfully-terminated and breakdown-terminated shots performed during three years of experimental advanced superconducting tokamak NBI experiments, from 2016 to 2019. Results show that it is very possible to develop a predictor base on neural network that intervenes well in advance to avoid ion sources breakdown or mitigate its effects during the beam extraction in the high-power and long-pulse mode.
Thermal confinement and transport in spherical tokamaks: a review
Authors: Kaye S M , Connor J W , Roach C M
Published: September 2021

In this paper, we review the thermal plasma confinement and transport properties observed and predicted in low aspect ratio tokamaks, or spherical tokamaks (STs), which can depart significantly from those observed at higher aspect ratio. In particular, thermal energy confinement scalings show a strong, near linear dependence of energy confinement time on toroidal magnetic field, while the dependence on plasma current is more modest, the opposite of what is seen at higher aspect ratio. STs have revealed a very strong improvement in normalized confinement with decreasing collisionality, much stronger than at higher aspect ratio, which bodes well for an ST-based fusion pilot plant should this trend continue at an even lower collisionality than has already been accessed. These differences arise because of fundamental differences in transport in STs due to the more extreme toroidicity (i.e. reduced region of bad curvature), and to the relatively larger

E
r

×
B

shearing rates, both of which can suppress electrostatic drift wave instabilities at both ion and electron gyroradius scales. In addition, electromagnetic effects are much stronger in STs because they operate at high β

T
. Gyrokinetic (GK) studies, coupled with low- and high-k turbulence measurements, have shed light on the underlying physics controlling transport. At lower β

T
, both ion- and electron-scale electrostatic drift turbulence may be responsible for transport. At higher βT
, microtearing, kinetic ballooning, and hybrid trapped electron/kinetic ballooning modes increasingly play a role, and they have a much stronger impact in the core of ST plasmas than at higher aspect ratio. Flow shear affects the balance between ion- and electron-scale modes. Non-linear GK simulations find regimes where the electron heat flux decreases with decreasing collisionality, consistent with the experimental global normalized confinement scaling. The ST is unique in that the relatively low toroidal magnetic field allows for localized measurements of electron-scale turbulence, and this coupled with turbulence measurements at ion-scales has facilitated detailed comparisons with GK simulations. These data have provided compelling evidence for the presence of ion temperature gradient and electron temperature gradient turbulence in some plasmas, and direct experimental support for the impact of experimental actuators like rotation shear, density gradient and magnetic shear on turbulence and transport.
On the use of CFD to obtain head loss coefficients in hydraulic systems and its application to liquid metal MHD flows in nuclear fusion reactor blankets
Authors: Suarez Daniel , Mas de les Valls Elisabet , Batet Lluis
Published: September 2021

When an incompressible fluid flows through a contraction in a conduit, the increase in the kinetic energy of the fluid is accompanied by a pressure drop. This pressure drop is not to be assimilated with head loss. If downstream the fluid encounters an expansion in the conduit, the energy conversion will take place in the opposite way. Therefore, when a geometrical singularity is analysed to assess its contribution to the pumping power requirements of the system, the whole mechanical energy transfer of the fluid in the singularity has to be taken into account, and not only the pressure variation. The first part of the present work establishes a method to obtain head loss coefficients in geometric singularities of hydrodynamic circuits using the results of computational fluid dynamics (CFD) calculations. These coefficients are of interest when modelling the whole system with a 1D system code, for instance. In the second part of the article, the method is applied to a more complex case, involving magnetohydrodynamic (MHD) phenomena. Thus, a prototypical channel singularity in a liquid metal circuit subject to a magnetic field is analysed. The layout is representative of a case that could be found in the liquid metal blankets to be used in nuclear fusion reactors. The influence of the MHD phenomena is studied and the differences with a purely hydrodynamic case are pointed out. The MHD analyses have been done in the Marconi High Performance Computing facility, using 48 cores, each case needing between one and two weeks to complete.
Phase transitions in virology
Authors: Solé Ricard , Sardanyés Josep , Elena Santiago F
Published: September 2021

Viruses have established relationships with almost every other living organism on Earth and at all levels of biological organization: from other viruses up to entire ecosystems. In most cases, they peacefully coexist with their hosts, but in most relevant cases, they parasitize them and induce diseases and pandemics, such as the AIDS and the most recent avian influenza and COVID-19 pandemic events, causing a huge impact on health, society, and economy. Viruses play an essential role in shaping the eco-evolutionary dynamics of their hosts, and have been also involved in some of the major evolutionary innovations either by working as vectors of genetic information or by being themselves coopted by the host into their genomes. Viruses can be studied at different levels of biological organization, from the molecular mechanisms of genome replication, gene expression and encapsidation, to global pandemics. All these levels are different and yet connected through the presence of threshold conditions allowing for the formation of a capsid, the loss of genetic information or epidemic spreading. These thresholds, as occurs with temperature separating phases in a liquid, define sharp qualitative types of behaviour. These phase transitions are very well known in physics. They have been studied by means of simple, but powerful models able to capture their essential properties, allowing us to better understand them. Can the physics of phase transitions be an inspiration for our understanding of viral dynamics at different scales? Here we review well-known mathematical models of transition phenomena in virology. We suggest that the advantages of abstract, simplified pictures used in physics are also the key to properly understanding the origins and evolution of complexity in viruses. By means of several examples, we explore this multilevel landscape and how minimal models provide deep insights into a diverse array of problems. The relevance of these transitions in connecting dynamical patterns across scales and their evolutionary and clinical implications are outlined.
Si tunnel junctions obtained by proximity rapid thermal diffusion for tandem photovoltaic cells
Authors: Li Xiao , Fave Alain , Lemiti Mustapha
Published: September 2021

Low-resistance c-Si Esaki tunnel junctions (TJ) can be applied in two-terminal Si-based tandem solar cells to electrically connect two sub-cells. Proximity rapid thermal diffusion (PRTD) is an economical and facile method to fabricate the Si tunnel junctions with a damage-free surface. The p++/n++ Si TJ on (111)-oriented c-Si wafer produced by combining PRTD and photovoltaic industrial techniques is reported in this work. The adjustment of the n++ emitter by a two-step rapid thermal annealing effectively facilitates the realization of the p++/n++ TJ. The peak current density of a tunnel diode based on this TJ is within the range 140–192 A cm−2 with a peak to valley current ratio of 1.9–3.2. Such a p++/n++ TJ is implemented in III–V nanowires (NWs) on Si tandem solar cells. Despite the defectuosity of the NWs array, we demonstrate that an increase of the open-circuit voltage is observed compared with the sole single-junction Si solar cell. This kind of TJ can also be integrated with other top cell materials such as perovskites and copper indium gallium selenide. Low-cost and high-efficiency c-Si based tandem solar cells might be produced with the application of Si TJs obtained by PRTD.
Monte Carlo evaluation of GaN THz Gunn diodes
Authors: Lee Wen Zhao , Ong Duu Sheng , Choo Kan Yeep , Yilmazoglu Oktay , Hartnagel Hans L
Published: September 2021

The performances of GaN-based Gunn diodes have been studied extensively for more than two decades, however, the diverging electron drift velocity characteristics employed in these studies merit a review of the potential of GaN Gunn diodes as THz sources. A self-consistent analytical-band Monte Carlo (MC) model capable of reproducing the electron drift velocity characteristics of GaN predicted theoretically by the first-principles full band MC model is used in this work to evaluate systematically the performance of GaN Gunn diodes in transit time mode. The optimal fundamental frequency of a sustainable current oscillation under a DC bias is determined as a function of the length of its transit region. The MC model predicts a GaN Gunn diode with a transit length of 500 nm capable of operating at frequencies up to 625 GHz with an estimated output power of 3.0 W. An MC model takes into account the effect of defects in order to replicate the much lower electron drift velocity characteristics derived from experimental work and predicts THz signal generation of 2.5 W at highest sustainable operating frequency of 326 GHz in a Gunn diode with a transit length of 700 nm.
Prediction of epidemics dynamics on networks with partial differential equations: A case study for COVID-19 in China*
Authors: Li Ru-Qi , Song Yu-Rong , Jiang Guo-Ping
Published: September 2021

Since December 2019, the COVID-19 epidemic has repeatedly hit countries around the world due to various factors such as trade, national policies and the natural environment. To closely monitor the emergence of new COVID-19 clusters and ensure high prediction accuracy, we develop a new prediction framework for studying the spread of epidemic on networks based on partial differential equations (PDEs), which captures epidemic diffusion along the edges of a network driven by population flow data. In this paper, we focus on the effect of the population movement on the spread of COVID-19 in several cities from different geographic regions in China for describing the transmission characteristics of COVID-19. Experiment results show that the PDE model obtains relatively good prediction results compared with several typical mathematical models. Furthermore, we study the effectiveness of intervention measures, such as traffic lockdowns and social distancing, which provides a new approach for quantifying the effectiveness of the government policies toward controlling COVID-19 via the adaptive parameters of the model. To our knowledge, this work is the first attempt to apply the PDE model on networks with Baidu Migration Data for COVID-19 prediction.
Synchronization in multilayer networks through different coupling mechanisms
Authors: Ling Xiang , Hua Bo , Guo Ning , Zhu Kong-Jin , Chen Jia-Jia , Wu Chao-Yun , Hao Qing-Yi
Published: September 2021

In recent years, most studies of complex networks have focused on a single network and ignored the interaction of multiple networks, much less the coupling mechanisms between multiplex networks. In this paper we investigate synchronization phenomena in multilayer networks with nonidentical topological structures based on three specific coupling mechanisms: assortative, disassortative, and anti-assortative couplings. We find rich and complex synchronous dynamic phenomena in coupled networks. We also study the behavior of effective frequencies for layers I and II to understand the underlying microscopic dynamics occurring under the three different coupling mechanisms. In particular, the coupling mechanisms proposed here have strong robustness and effectiveness and can produce abundant synchronization phenomena in coupled networks.
Radiation resistance property of barium gallo-germanate glass doped by Nb2O5
Authors: Liu Gui-Rong , Chen Xiao-Dong , Liu Hong-Gang , Wang Yan , Sun Min , Yan Na , Qian Qi , Yang Zhong-Min
Published: September 2021

Effects of Nb2O5 dopant on the radiation response of barium gallo-germanate (BGG) glass are studied mainly by electron paramagnetic resonance and absorption spectroscopy. Owing to the Nb5+↔Nb3+ interconversion in doped samples, formations of Ge-related non-bridging oxygen hole center and Ge-related electron center defects after γ-ray irradiation are inhibited. Thereby, Nb2O5 dopant can enhance radiation resistance of BGG glass, and 1.0% Nb2O5 concentration is the best.
Complex dynamic behaviors in hyperbolic-type memristor-based cellular neural network
Authors: Qi Ai-Xue , Zhu Bin-Da , Wang Guang-Yi
Published: September 2021

This paper presents a new hyperbolic-type memristor model, whose frequency-dependent pinched hysteresis loops and equivalent circuit are tested by numerical simulations and analog integrated operational amplifier circuits. Based on the hyperbolic-type memristor model, we design a cellular neural network (CNN) with 3-neurons, whose characteristics are analyzed by bifurcations, basins of attraction, complexity analysis, and circuit simulations. We find that the memristive CNN can exhibit some complex dynamic behaviors, including multi-equilibrium points, state-dependent bifurcations, various coexisting chaotic and periodic attractors, and offset of the positions of attractors. By calculating the complexity of the memristor-based CNN system through the spectral entropy (SE) analysis, it can be seen that the complexity curve is consistent with the Lyapunov exponent spectrum, i.e., when the system is in the chaotic state, its SE complexity is higher, while when the system is in the periodic state, its SE complexity is lower. Finally, the realizability and chaotic characteristics of the memristive CNN system are verified by an analog circuit simulation experiment.
Extrinsic equivalent circuit modeling of InP HEMTs based on full-wave electromagnetic simulation
Authors: Feng Shi-Yu , Su Yong-Bo , Ding Peng , Zhou Jing-Tao , Peng Song-Ang , Ding Wu-Chang , Jin Zhi
Published: September 2021

With the widespread utilization of indium-phosphide-based high-electron-mobility transistors (InP HEMTs) in the millimeter-wave (mmW) band, the distributed and high-frequency parasitic coupling behavior of the device is particularly prominent. We present an InP HEMT extrinsic parasitic equivalent circuit, in which the conductance between the device electrodes and a new gate–drain mutual inductance term L
mgd are taken into account for the high-frequency magnetic field coupling between device electrodes. Based on the suggested parasitic equivalent circuit, through HFSS and advanced design system (ADS) co-simulation, the equivalent circuit parameters are directly extracted in the multi-step system. The HFSS simulation prediction, measurement data, and modeled frequency response are compared with each other to verify the feasibility of the extraction method and the accuracy of the equivalent circuit. The proposed model demonstrates the distributed and radio-frequency behavior of the device and solves the problem that the equivalent circuit parameters of the conventional InP HEMTs device are limited by the device model and inaccurate at high frequencies when being extracted.
Erratum to “Floquet bands and photon-induced topological edge states of graphene nanoribbons”
Authors: Wang Weijie , Lü Xiaolong , Xie Hang
Published: September 2021

Figures 2(a) and 2(b) in the original paper [Chin. Phys. B
30 066701 (2021)] are replaced by the new ones.
Maximum entropy mobility spectrum analysis for the type-I Weyl semimetal TaAs
Authors: Li Wen-Chong , Zhao Ling-Xiao , Zhao Hai-Jun , Chen Gen-Fu , Shi Zhi-Xiang
Published: September 2021

Due to non-saturating magnetoresistance (MR) and the special compensation mechanism, the Weyl semimetal TaAs single crystal has attracted considerable attention in condensed matter physics. Herein, we use maximum entropy mobility spectrum analysis (MEMSA) to extract charge carrier information by fitting the experimentally measured longitudinal and transverse electric transport curves of TaAs. The carrier types and the number of bands are obtained without any hypothesis. Study of the temperature dependence shows details of carrier property evolution. Our quantitative results explain the non-saturated magnetoresistance and Hall sign change phenomena of TaAs.
Optimizing the establishment of bean and maize varieties in tropical environments
Authors: Andrade J A , Mateus M , Cadima J F , Abreu F G
Published: September 2021

The successful establishment of any crop is the initial indication of its productivity. Optimizing the establishment of a crop implies ensuring generalized, fast and concentrated emergence. This work studies optimal temperature ranges, under non-limiting water conditions, for both germination and emergence of two bean (Phaseolus vulgaris L.) varieties (catarina and ervilha) and two maize (Zea mays L.) varieties (matuba and sam3).

Experiments used a thermogradient plate. Petri dishes were used for germination experiments. Emergence experiments were performed in aluminium containers filled with packed portions of a sandy loam clay textured soil. Size, speed and spread of both germination and emergence were measured at different temperatures by Cu-CuNi thermocouples.

Thermal ranges with optimal counts of both germination and emergence [To1
sz, To2
sz] were identified using a flattened bell curve function. Speed was maximized for either germination or emergence over thermal ranges [To1
sp, To2
sp] defined using the plateau model to relate either germination or emergence rates with temperature. Ranges along which the spread of both germination and emergence are nearly minimized [To1
sd, To2
sd] were identified with the aid of even-degree polynomials. The intersection of all three thermal ranges gave rise to optimal temperature ranges [To1, To2] for germination (OTRG) of the four varieties in study and for emergence (OTRE) of three of them. In general, the lower thermal limit of OTRg was determined by speed (To1 = To1
sp) and the upper thermal limit by size (To2 = To2
sz). OTRe begins at To1
sp for ervilha and sam3 and at To1
sd for catarina and ends at To2
sz for catarina and at To2
sd for the others. The endpoints and length of both the OTRG and OTRE were also found to be crop-dependent. Thus, farmers can choose between crops and optimize their establishment. The identification of these parameters may also be useful in assessing weather forecasts and for warning systems and agro-climatic zoning. The influence of the substrate used in each experiment was also discussed.
Assessment of the potential environmental and ecological risks associated with traffic induced heavy metal contamination in country parks of Hong Kong
Authors: Ngai K W , Mak M W , Pun K L
Published: September 2021

Hong Kong is a densely populated area with a limited area, so most country parks are adjacent to busy traffic roads and town activities. The soil in country parks may be contaminated by heavy metals emitted by traffic activities. During the holidays, most people go to country parks to play. It is very important to assess the potential risks of residents, especially children. So far, data on pollution in Hong Kong’s country parks is very limited. The heavy metals arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), silver (Ag) and zinc (Zn) were collected in the Kam Shan (KS), Plover Cove (PC), Sai Kung West (SK) and Lion Rock (LR) country parks. The mean Zn concentration in KS Country Park was more than three times higher than the background concentration in Dutch soil standard, while Cu and Pb were more than 1.6 times higher. The average pollution index (PIave) of KS Country Parks was classified as high, and the potential ecological risk index (RI) was classified as moderate. Country parks should pay special attention to heavy metal pollution in order to continue further research and remedial measures.