bluuebunny/crossref_metadata_2025 huggingface dataset:
Control strategy of wind power smooth grid connection based on adaptive VMD and hybrid energy storage
Authors: Zhang Yu , Xiao Liexi , Zhou Hui , Zhao Guanhao
Published: April 2022

In nature, the variation of wind speed is characterized by randomness, fluctuation, and intermittence. In order to suppress the power fluctuation caused by wind speed changes in the process of wind turbine grid connection, a wind power smooth grid-connected control strategy based on the adaptive variational modal decomposition algorithm and the hybrid energy storage system is proposed. For the problem that the selection of variational modal decomposition parameters is subjective and experiential, which leads to the poor signal decomposition reduction degree, the sparrow search algorithm is proposed to optimize variational modal decomposition to realize the adaptive selection of key variational modal decomposition parameters k and α. First, the reference power of the hybrid energy storage system conforming to the grid-connected power fluctuation standard is obtained by the adaptive moving average algorithm. Then, adaptive variational modal decomposition of the reference power was performed to obtain a set of inherent modal functional components, and the low frequency and high frequency components of the modal components were allocated for lithium batteries and the supercapacitor, respectively. Finally, Matlab/Simulink was used to simulate and compare with the control strategy of low-pass filtering. The results show that the proposed algorithm realizes the selection of adaptive decomposition parameters of variational modal decomposition, solves the lag and frequency aliasing problems existing in power distribution of the low-pass filtering algorithm, and realizes the high reduction solution of reference power. The fluctuation of wind power connected to the grid is effectively suppressed.
Force and torque-free helical tail robot to study low Reynolds number micro-organism swimming
Authors: Das Asimanshu , Styslinger Matthew , Harris Daniel M. , Zenit Roberto
Published: April 2022

Helical propulsion is used by many micro-organisms to swim in viscous-dominated environments. Their swimming dynamics are relatively well understood, but a detailed study of the flow fields is still needed to understand wall effects and hydrodynamic interactions among swimmers. In this letter, we describe the development of an autonomous swimming robot with a helical tail that operates in the Stokes regime. The device uses a battery-based power system with a miniature motor that imposes a rotational speed on a helical tail. The speed, direction, and activation are controlled electronically using an infrared remote control. Since the robot is about 5 cm long, we use highly viscous fluids to match the Reynolds number, Re, to be less than 0.1. Measurements of swimming speeds are conducted for a range of helical wavelengths, λ, head geometries, and rotation rates, ω. We provide comparisons of the experimental measurements with analytical predictions derived from resistive force theory. This force and torque-free neutrally buoyant swimmer mimics the swimming strategy of bacteria more closely than previously used designs and offers a lot of potential for future applications.
A tighter generalization bound for reservoir computing
Authors: Han Xinyu , Zhao Yi , Small Michael
Published: April 2022

While reservoir computing (RC) has demonstrated astonishing performance in many practical scenarios, the understanding of its capability for generalization on previously unseen data is limited. To address this issue, we propose a novel generalization bound for RC based on the empirical Rademacher complexity under the probably approximately correct learning framework. Note that the generalization bound for the RC is derived in terms of the model hyperparameters. For this reason, it can explore the dependencies of the generalization bound for RC on its hyperparameters. Compared with the existing generalization bound, our generalization bound for RC is tighter, which is verified by numerical experiments. Furthermore, we study the generalization bound for the RC corresponding to different reservoir graphs, including directed acyclic graph (DAG) and Erdős–Re´nyi undirected random graph (ER graph). Specifically, the generalization bound for the RC whose reservoir graph is designated as a DAG can be refined by leveraging the structural property (i.e., the longest path length) of the DAG. Finally, both theoretical and experimental findings confirm that the generalization bound for the RC of a DAG is lower and less sensitive to the model hyperparameters than that for the RC of an ER graph.
Unusual divergence of magnetoacoustic beams
Authors: Perelomova A.
Published: April 2022

Two-dimensional magnetosonic beams directed along a line forming a constant angle θ with the equilibrium straight magnetic field are considered. Perturbations in a plasma are described by the system of ideal magnetohydrodynamic equations. The dynamics of perturbations in a beam are different in the cases of fast and slow modes, and it is determined by θ and equilibrium parameters of a plasma. In particular, a beam divergence may be unusual in the case of parallel propagation (θ = 0). Diffraction is more pronounced in the case of parallel propagation as compared to a flow without magnetic field, and less manifested in the case of perpendicular propagation. The beams propagating oblique to the magnetic field do not reveal diffraction. The dynamics of perturbations in a beam are analytically described in the cases of weak and strong nonlinearity compared to diffraction. Small magnitude perturbations at the axis of a beam in unusual cases propagate slower than that in the plane wave. Involving of thermal conduction leads to the coupling equations describing thermal self-action of a beam, which behaves differently in the ordinary and unusual cases. Self-focusing may occur in the presence of a magnetic field instead of conventional defocusing in gases.
Desynchronous learning in a physics-driven learning network
Authors: Wycoff J. F. , Dillavou S. , Stern M. , Liu A. J. , Durian D. J.
Published: April 2022

In a neuron network, synapses update individually using local information, allowing for entirely decentralized learning. In contrast, elements in an artificial neural network are typically updated simultaneously using a central processor. Here, we investigate the feasibility and effect of desynchronous learning in a recently introduced decentralized, physics-driven learning network. We show that desynchronizing the learning process does not degrade the performance for a variety of tasks in an idealized simulation. In experiment, desynchronization actually improves the performance by allowing the system to better explore the discretized state space of solutions. We draw an analogy between desynchronization and mini-batching in stochastic gradient descent and show that they have similar effects on the learning process. Desynchronizing the learning process establishes physics-driven learning networks as truly fully distributed learning machines, promoting better performance and scalability in deployment.
A study on the effect of temperature modulation on Darcy–Bénard convection using a local thermal non-equilibrium model
Authors: Bansal A. , Suthar Om P.
Published: April 2022

The criterion for the onset of Darcy–Bénard convection is analyzed when the fluid and porous medium are out of thermal equilibrium and the temperatures of the boundaries vary sinusoidally with time in either a synchronous or an asynchronous manner. A stability analysis of the linearized governing equations is performed by using the matrix differential operator theory. The shift in the critical Darcy–Rayleigh number is evaluated in terms of system parameters, and the effect of those on the shift is depicted graphically to realize the significant effect of temperature modulation on the onset, especially when the thermal non-equilibrium effects are prominent.
Hydrogen migration in triply charged acetylene
Authors: Yadav Jatin , Safvan C. P. , Bhatt Pragya , Kumari Pooja , Kumar Aditya , Rajput Jyoti
Published: April 2022

We report on the direct experimental evidence of hydrogen migration in triply charged acetylene. The roaming hydrogen atom in a triply charged molecular ion is counter intuitive. The three body breakup channel C2H23+→H++C++CH+ is studied using the technique of recoil ion momentum spectroscopy. The triply charged ion was generated in collisions of the neutral parent with a slow highly charged Xe9+ ion. Three different dissociation pathways have been identified and separated, namely, concerted breakup in an acetylene configuration, concerted breakup in a vinylidene configuration, and sequential breakup via a [C2H]2+ intermediate, and the branching ratio for all three pathways are determined.
Nanoscale friction of strained molybdenum disulfide induced by nanoblisters
Authors: Xu Mingyuan , Zhang Deliang , Wang Yin , Zhang Yuge , Li Qiang , Dong Mingdong
Published: April 2022

Nanoblisters have received substantial attention owing to their ability to controllably modulate physical properties of two-dimensional (2D) layered materials. Herein, we demonstrated that nanoblisters formed by molybdenum disulfide (MoS2) can produce in-plane strains via out-of-plane deformation. The in-plane strains can effectively modulate frictional behaviors of MoS2. Friction force microscopy results showed that the friction was significantly increased at the edge of MoS2 nanoblisters due to the “step edge effect.” In addition, the friction measured in the central area of the MoS2 nanoblisters was found increased as the height to radius aspect ratios of MoS2 nanoblisters increased. Our atomically resolved friction images revealed that the dynamic friction tuned via nanoblisters was originated from the changes in the movement state of the tip caused by the in-plane strains. This study clarified the feasibility of nanoblisters as a simple strain engineering strategy to modulate the friction properties of 2D materials.
Heat transfer and flow friction characteristics of dimple-type heat exchanger in axial piston pump
Authors: Wang Fengmin , Chen Lei , Liu Kuaile , Tang Hesheng , Ren Yan
Published: April 2022

The heat exchanger is widely applied to many axial piston machines, and its structure significantly affects the flow and heat transfer characteristics. The fluid flow and heat transfer characteristics of a dimple-type heat exchanger in the axial piston pump are numerically investigated. The variations of the Nusselt number, friction factor and heat transfer performance with the Reynolds number, and the dimple radius to depth are obtained. The results show that both the Nusselt number and the resistance coefficient of the spherical dimple channel are higher than those of the triangle dimple one. Thus, from the view of the heat transfer performance, the spherical dimple channel is better. Furthermore, the friction factor increases as the dimple radius to depth increases. With the increase in the dimple radius to depth ratio, the shear stress at the wall of the spherical dimpled channel gradually decreases and then reduces the wall friction resistance. Comparing with the triangle dimple channel, the friction factor in the spherical dimple channel is 0.044–0.022, which reduces about 9%. When the radius–depth ratio is set to 0.1, the effectiveness factor for the spherical dimpled channel has better performance.
Weed recognition using deep learning techniques on class-imbalanced imagery
Authors: Mahmudul Hasan A. S. M. , Sohel Ferdous , Diepeveen Dean , Laga Hamid , Jones Michael G. K.
Published: April 2022

Context Most weed species can adversely impact agricultural productivity by competing for nutrients required by high-value crops. Manual weeding is not practical for large cropping areas. Many studies have been undertaken to develop automatic weed management systems for agricultural crops. In this process, one of the major tasks is to recognise the weeds from images. However, weed recognition is a challenging task. It is because weed and crop plants can be similar in colour, texture and shape which can be exacerbated further by the imaging conditions, geographic or weather conditions when the images are recorded. Advanced machine learning techniques can be used to recognise weeds from imagery. Aims In this paper, we have investigated five state-of-the-art deep neural networks, namely VGG16, ResNet-50, Inception-V3, Inception-ResNet-v2 and MobileNetV2, and evaluated their performance for weed recognition. Methods We have used several experimental settings and multiple dataset combinations. In particular, we constructed a large weed-crop dataset by combining several smaller datasets, mitigating class imbalance by data augmentation, and using this dataset in benchmarking the deep neural networks. We investigated the use of transfer learning techniques by preserving the pre-trained weights for extracting the features and fine-tuning them using the images of crop and weed datasets. Key results We found that VGG16 performed better than others on small-scale datasets, while ResNet-50 performed better than other deep networks on the large combined dataset. Conclusions This research shows that data augmentation and fine tuning techniques improve the performance of deep learning models for classifying crop and weed images. Implications This research evaluates the performance of several deep learning models and offers directions for using the most appropriate models as well as highlights the need for a large scale benchmark weed dataset.
Improvement of resistance spot weldability of Al–Fe-alloy-coated HPF steel sheets
Authors: Yun Sang-Man , Gwon Hojun , Oh Jin-Keun , Kim Sung-Joon
Published: April 2022

The resistance spot weldability of Al–Fe-alloy-coated (AlFe-c) HPF steels manufactured by heat-treating Al–Si coated (AlSi-c) steel at 650°C for 10 h was investigated. Since AlFe-c steel had thick oxides in surface layer, the transition resistance was higher and weldability was poorer than the conventional AlSi-c steels. During spot welding of AlFe-c steels, expulsion occurred at low current, so the weld could not grow sufficiently. For this reason, AlFe-c steels had no weldable current range. To improve the weldability, pre-pulse current pattern was applied. By removing the oxides in the coating layer during the pre-pulse step, the resistance of the weld part was reduced, and the expulsion was delayed, so the weldable current range of AlFe-c steel was improved.
Blood flow restriction during self‐paced aerobic intervals reduces mechanical and cardiovascular demands without modifying neuromuscular fatigue
Authors: Smith Nathan D. W. , Girard Olivier , Scott Brendan R. , Peiffer Jeremiah J.
Published: April 2022

This study examined cardiovascular, perceptual and neuromuscular fatigue characteristics during and after cycling intervals with and without blood flow restriction (BFR). Fourteen endurance cyclists/triathletes completed four 4‐minute self‐paced aerobic cycling intervals at the highest sustainable intensity, with and without intermittent BFR (60% of arterial occlusion pressure). Rest interval durations were six, four and four minutes, respectively. Power output, cardiovascular demands and ratings of perceived exertion (RPE) were averaged over each interval. Knee extension torque and vastus lateralis electromyography responses following electrical stimulation of the femoral nerve were recorded pre‐exercise, post‐interval one (+1, 2 and 4‐minutes) and post‐interval four (+1, 2, 4, 6 and 8‐minutes). Power output during BFR intervals was lower than non‐BFR (233 ± 54 vs 282 ± 60 W, p < 0.001). Oxygen uptake and heart rate during BFR intervals were lower compared to non‐BFR (38.7 ± 4.5 vs 44.7 ± 6.44 mL kg−1 min−1, p < 0.001; 160 ± 14 vs 166 ± 10 bpm, p < 0.001), while RPE was not different between conditions. Compared to pre‐exercise, maximal voluntary contraction torque and peak twitch torque were reduced after the first interval with further reductions following the fourth interval (p < 0.001) independent of condition (p = 0.992). Voluntary activation (twitch interpolation) did not change between timepoints (p = 0.375). Overall, intermittent BFR reduced the mechanical and cardiovascular demands of self‐paced intervals without modifying RPE or knee‐extensor neuromuscular characteristics. Therefore, BFR reduced the cardiovascular demands while maintaining the muscular demands associated with self‐paced intervals. Self‐paced BFR intervals could be used to prevent cardiovascular and perceptual demands being the limiting factor of exercise intensity, thus allowing greater physiological muscular demands compared to intervals without BFR.

Highlights

The use of blood flow restriction (BFR) during self‐paced intervals (at the highest perceived sustainable intensity) causes a reduction in power output, pulmonary oxygen uptake and heart rate compared with non‐restricted self‐paced intervals.

Despite lower mechanical and physiological demands during BFR cycling, the magnitude and aetiology of neuromuscular fatigue were not different to intervals without BFR, indicating the internal muscular load during BFR was elevated and potentially equivalent compared to without BFR.

Self‐paced intervals could be a suitable model to prescribe aerobic BFR exercise as an adjunct training stimulus for endurance cyclists.
Comparing lab and field agility kinematics in young talented female football players: Implications for ACL injury prevention
Authors: Di Paolo Stefano , Nijmeijer Eline , Bragonzoni Laura , Dingshoff Evelien , Gokeler Alli , Benjaminse Anne
Published: April 2022

Modifiable (biomechanical and neuromuscular) anterior cruciate ligament (ACL) injury risk factors have been identified in laboratory settings. These risk factors were subsequently used in ACL injury prevention measures. Due to the lack of ecological validity, the use of on‐field data in the ACL injury risk screening is increasingly advocated. Though, the kinematic differences between laboratory and on‐field settings have never been investigated. The aim of the present study was to investigate the lower‐limb kinematics of female footballers during agility movements performed both in laboratory and football field environments. Twenty‐eight healthy young female talented football (soccer) players (14.9 ± 0.9 years) participated. Lower‐limb joint kinematics was collected through wearable inertial sensors (Xsens Link) in three conditions: (1) laboratory setting during unanticipated sidestep cutting at 40‐50°; on the football pitch (2) football‐specific exercises (F‐EX) and (3) football games (F‐GAME). A hierarchical two‐level random effect model in Statistical Parametric Mapping was used to compare joint kinematics among the conditions. Waveform consistency was investigated through Pearson's correlation coefficient and standardized z‐score vector. In‐lab kinematics differed from the on‐field ones, while the latter were similar in overall shape and peaks. Lower sagittal plane range of motion, greater ankle eversion, and pelvic rotation were found for on‐field kinematics (p < 0.044). The largest differences were found during landing and weight acceptance. The biomechanical differences between lab and field settings suggest the application of context‐related adaptations in female footballers and have implications in ACL injury prevention strategies.

Highlights

Talented youth female football players showed kinematical differences between the lab condition and the on‐field ones, thus adopting a context‐related motor strategy.

Lower sagittal plane range of motion, greater ankle eversion, and pelvic rotation were found on the field. Such differences pertain to the ACL injury mechanism and prevention strategies.

Preventative training should support the adoption of non‐linear motor learning to stimulate greater self‐organization and adaptability.

It is recommended to test football players in an ecological environment to improve subsequent primary ACL injury prevention programmes.
The HOPS tethering complex is required to maintain signaling endosome identity and TORC1 activity
Authors: Gao Jieqiong , Nicastro Raffaele , Péli-Gulli Marie-Pierre , Grziwa Sophie , Chen Zilei , Kurre Rainer , Piehler Jacob , De Virgilio Claudio , Fröhlich Florian , Ungermann Christian
Published: April 2022

The endomembrane system of eukaryotic cells is essential for cellular homeostasis during growth and proliferation. Previous work showed that a central regulator of growth, namely the target of rapamycin complex 1 (TORC1), binds both membranes of vacuoles and signaling endosomes (SEs) that are distinct from multivesicular bodies (MVBs). Interestingly, the endosomal TORC1, which binds membranes in part via the EGO complex, critically defines vacuole integrity. Here, we demonstrate that SEs form at a branch point of the biosynthetic and endocytic pathways toward the vacuole and depend on MVB biogenesis. Importantly, function of the HOPS tethering complex is essential to maintain the identity of SEs and proper endosomal and vacuolar TORC1 activities. In HOPS mutants, the EGO complex redistributed to the Golgi, which resulted in a partial mislocalization of TORC1. Our study uncovers that SE function requires a functional HOPS complex and MVBs, suggesting a tight link between trafficking and signaling along the endolysosomal pathway.
Establishing spatial control over TORC1 signaling
Authors: Schmidt Oliver , de Araujo Mariana E.G.
Published: April 2022

Target-of-rapamycin complex 1 resides on lysosomes/vacuoles and additionally on signaling endosomes. Gao et al. (2022. J. Cell Biol.https://doi.org/10.1083/jcb.202109084) set out to define the molecular identity of signaling endosomes, along with players required for the formation and maintenance of this endosomal subpopulation.
Monocytes transition to macrophages within the inflamed vasculature via monocyte CCR2 and endothelial TNFR2
Authors: Mysore Vijayashree , Tahir Suhail , Furuhashi Kazuhiro , Arora Jatin , Rosetti Florencia , Cullere Xavier , Yazbeck Pascal , Sekulic Miroslav , Lemieux Madeleine E. , Raychaudhuri Soumya , Horwitz Bruce H. , Mayadas Tanya N.
Published: April 2022

Monocytes undergo phenotypic and functional changes in response to inflammatory cues, but the molecular signals that drive different monocyte states remain largely undefined. We show that monocytes acquire macrophage markers upon glomerulonephritis and may be derived from CCR2+CX3CR1+ double-positive monocytes, which are preferentially recruited, dwell within glomerular capillaries, and acquire proinflammatory characteristics in the nephritic kidney. Mechanistically, the transition to immature macrophages begins within the vasculature and relies on CCR2 in circulating cells and TNFR2 in parenchymal cells, findings that are recapitulated in vitro with monocytes cocultured with TNF-TNFR2–activated endothelial cells generating CCR2 ligands. Single-cell RNA sequencing of cocultures defines a CCR2-dependent monocyte differentiation path associated with the acquisition of immune effector functions and generation of CCR2 ligands. Immature macrophages are detected in the urine of lupus nephritis patients, and their frequency correlates with clinical disease. In conclusion, CCR2-dependent functional specialization of monocytes into macrophages begins within the TNF-TNFR2–activated vasculature and may establish a CCR2-based autocrine, feed-forward loop that amplifies renal inflammation.
How to distinguish heat from work in irreversible processes?
Authors: Anacleto Joaquim
Published: April 2022

The theoretical foundations of the reservoir concept are presented and then applied to the discussion of two irreversible processes. As an alternative to what is stated in the literature, it is shown that heat and work can be clearly distinguished in irreversible processes, provided that the reservoir concept is considered. This discussion, which is expected to be both theoretically and instructively relevant, is intended primarily for graduate students and teachers, although it may also be of interest to undergraduate students with a solid background in thermodynamics. By covering specific examples of irreversible processes in which heat and work turn out to be controversial concepts, this article will also be useful in the introductory or upper-level undergraduate curriculum.
Renewable waste biomass-derived carbon materials for energy storage
Authors: Huang Yuancheng , Tang Zheng , Zhou Siyu , Wang Hong , Tang Yougen , Sun Dan , Wang Haiyan
Published: April 2022

It is crucial to develop high-performance electrode materials for the increasing energy demands of various energy storage systems. Biomass-derived carbons demonstrate great potential due to their rich structure, low cost, abundance in reserves, and excellent electrochemical performance. So far, various carbon structures ranging from highly disordered non-graphitic carbon to locally ordered graphite-like carbon have been achieved from different biomass. And they are employed as electrodes for different energy storage systems. However, to our best knowledge, there is no systematic review to show the latest progress in this area. Herein, we have systematically classified the waste biomass and discussed the microstructures of their derived carbons. In particular, as electrode materials, the effects of biomass-derived carbons’ structure, porosity, interlayer spacing, and heteroatomic doping on different energy storage devices are analyzed in detail. Furthermore, the challenges, as well as the corresponding solutions and developing trends to biomass-derived carbons, have been summarized.
Acoustic metamaterials with zero-index behaviors and sound attenuation
Authors: Wu Guanghua , Ke Yibo , Zhang Lin , Tao Meng
Published: April 2022

The Helmholtz resonator suffers from needing to be excessively large to manipulate low-frequency sound waves and supports only monopolar resonance. To solve these problems, combining the space-coiling concept and multiunit lumped coupling concept, a new metamaterial is proposed, that exhibits an extraordinary acoustic response related to multiple resonant patterns in the low-frequency regime. At the upper and lower edges of the bandgap, acoustic wavefront reshaping is achieved. Considering the shift of the modulation frequency and the mismatched impedance, an alternative and simple strategy is presented to achieve acoustic cloaking. Furthermore, by flexibly varying the distances between the metamaterial plates and inserted obstacles, acoustic cloaking independent of the boundary conditions of the inserted obstacles is achieved. Finally, based on the negative acoustic response of the structure, acoustic barriers capable of air ventilation and sound attenuation simultaneously are achieved and verified by experimental results.
First-order differential filtering spectrum division method and information fusion multi-scale network for fault diagnosis of bearings under different loads
Authors: Wang Junyuan , Han Fei , Li Yanfeng , Wang Zhijian , Du Wenhua
Published: April 2022

In recent years, data-driven intelligent diagnosis methods have been widely applied in the field of bearing fault diagnosis. However, these methods involve some expert experience and knowledge, and cannot accurately mine bearing fault characteristics under different loads. To solve this problem, this paper proposes a first-order differential filtering spectrum division (FDFSD) method and an information fusion multi-scale network (IFMSNet) to realize bearing fault diagnosis under different working conditions. First of all, the proposed spectrum division method based on the first-order differential filtering, the first-order differential processing of time domain signals, and the introduction of triangular filter, reclassify the spectrum features, highlight feature information, can accurately extract bearing fault features. Secondly, a new multi-scale network model of information fusion is constructed in this paper. Convolution kernels of different sizes are used to extract fault features of bearings of different scales, and information fusion is carried out to identify bearing working conditions and realize intelligent diagnosis of bearings under different loads. Finally, in order to verify the effectiveness and accuracy of the proposed method, it is verified on a variety of bearing experimental data sets. The results show that the average prediction accuracy of the proposed method is 99.11% and 97.74%, respectively. Compared with the proposed three single-scale network, K-nearest neighbor, Naive Bayes, support vector machine and random forest methods, the proposed method has more advantages in bearing intelligent diagnosis under different loads.
Tailoring the critical temperature of Ca/K-1144 superconductors: the effect of aliovalent substitution on tetragonality
Authors: Masi A , Duchenko A , Celentano G , Varsano F
Published: April 2022

Among the iron-based superconductors, the so-called 1144 family has, in recent years, attracted significant interest due to its stoichiometric nature, with materials robust towards chemical inhomogeneities and characterized by a well-defined critical temperature. The most studied 1144 compounds are characterized by the A1AE1Fe4As4 chemical composition, where A and AE constitute an appropriate combination of alkaline and alkaline-earth metals, respectively. The 1144 structure is in fact formed only when the A and AE elements respect specific requirements in terms of relative size and parent compound structure. The stoichiometric aspect, one of their strong points, has represented, however, up to today a restriction, limiting the conceptualization of 1144 structures to quaternary compounds. In this work, we demonstrate that to obtain the 1144 crystalline phase it may be sufficient to maintain a 1:1 ratio between ions of different size that intercalate the Fe-As planes, and that in selected conditions an opportunely tailored cation substitution is possible. Using a simple mechanochemically assisted synthesis route 1144 compounds where Ca is substituted by Na, K by Ba, and both simultaneously, are obtained. We demonstrate that the critical temperature of doped compounds is not simply related to the substitution amount or to the resulting Fe valence. We show that the superconducting transition is in fact linked to the structural distortion induced by the chemical composition variation: by tailoring the chemical composition we obtain doubly substituted samples—with substitution levels up to 20%—characterized by a tetragonality ratio c/a similar to the pristine compound and critical temperatures of approximately 34 K.
Manipulating photons in a way like an optical tweezer
Authors: Wu Jun-Fang , Chen Jia-Hui , Li Chao
Published: April 2022

Arbitrary control of photon flow is of fundamental significance in many applications of light. Here, we propose a new approach that can trap, store, and move the signal photons to arbitrary desired place, just like what optical tweezers do on micro particles. In addition, the trapped photons can also be released at a given direction. The mechanism is based on an ultrahigh-Q nanocavity formed by two dynamically-generated potential barriers in a photonic crystal (PC) waveguide. Different from the traditional fixed ultrahigh-Q nanocavities, this new-type cavity can be formed instantaneously at any moment and any position in a PC waveguide, and is completely movable while keeps ultrahigh Q factor simultaneously. These novel features make controlling the flow of light like an optical tweezer possible, and open up new opportunities for dynamic light–matter interactions and on-chip optical signal processing.
Scalarized black holes
in teleparallel gravity
Authors: Bahamonde Sebastian , Ducobu Ludovic , Pfeifer Christian
Published: April 2022

Black holes play a crucial role in the understanding of the gravitational interaction. Through the direct observation of the shadow of a black hole by the event horizon telescope and the detection of gravitational waves of merging black holes we now start to have direct access to their properties and behaviour, which means the properties and behaviour of gravity. This further raised the demand for models to compare with those observations.
In this respect, an important question regarding black holes properties is to know if they can support “hairs”. While this is famously forbidden in general relativity, in particular for scalar fields, by the so-called no-hair theorems, hairy black holes have been shown to exist in several class of scalar-tensor theories of gravity.
In this article we investigate the existence of scalarized black holes in scalar-torsion theories of gravity.
On one hand, we find exact solutions for certain choices of couplings between a scalar field and the torsion tensor of a teleparallel connection and certain scalar field potentials, and thus proof the existence of scalarized black holes in these theories.
On the other hand, we show that it is possible to establish no-scalar-hair theorems similar to what is known in general relativity for other choices of these functions.
Comparison of differential evolution, particle swarm optimization, quantum-behaved particle swarm optimization, and quantum evolutionary algorithm for preparation of quantum states
Authors: Cheng Xin , Lu Xiu-Juan , Liu Ya-Nan , Kuang Sen
Published: April 2022

Four intelligent optimization algorithms are compared by searching for control pulses to achieve the preparation of target quantum states for closed and open quantum systems, which include differential evolution (DE), particle swarm optimization (PSO), quantum-behaved particle swarm optimization (QPSO), and quantum evolutionary algorithm (QEA). We compare their control performance and point out their differences. By sampling and learning for uncertain quantum systems, the robustness of control pulses found by these four algorithms is also demonstrated and compared. The resulting research shows that the QPSO nearly outperforms the other three algorithms for all the performance criteria considered. This conclusion provides an important reference for solving complex quantum control problems by optimization algorithms and makes the QPSO be a powerful optimization tool.
Giant low-field cryogenic magnetocaloric effect in polycrystalline LiErF4 compound
Authors: Mo Zhaojun , Gong Jianjian , Xie Huicai , Zhang Lei , Fu Qi , Gao Xinqiang , Li Zhenxing , Shen Jun
Published: April 2022

Antiferromagnetic LiErF4 has attracted extensive attention due to its dipolar interaction domination and quantum fluctuations action. In the present work, the crystal structure, cryogenic magnetic properties, and magnetocaloric effect (MCE) of polycrystalline LiErF4 compound are investigated. Crystallographic study shows that the compound crystallizes in the tetragonal scheelite structure with I41/a space group. It exhibits an antiferromagnetic (AFM) phase transition around 0.4 K, accompanied by a giant cryogenic MCE. At 1.3 K, the maximum values of magnetic entropy changes are 24.3 J/kg⋅K, 33.1 J/kg⋅K, and 49.0 J/kg⋅K under the low magnetic field change of 0–0.6 T, 0–1 T, and 0–2 T, respectively. The giant MCE observed above Néel temperature T
N is probably due to the strong quantum fluctuations, which cause a large ratio of the unreleased magnetic entropy existing above the phase transition temperature. The outstanding low-field MCE below 2 K makes the LiErF4 compound an attractive candidate for the magnetic refrigeration at the ultra-low temperature.
Experimental observation of pseudogap in a modulation-doped Mott insulator: Sn/Si(111)-(

3×3

)R30°
Authors: Xiong Yan-Ling , Guan Jia-Qi , Wang Rui-Feng , Song Can-Li , Ma Xu-Cun , Xue Qi-Kun
Published: April 2022

Unusual quantum phenomena usually emerge upon doping Mott insulators. Using a molecular beam epitaxy system integrated with cryogenic scanning tunneling microscope, we investigate the electronic structure of a modulation-doped Mott insulator Sn/Si(111)-(

3

×

3

)R30°. In underdoped regions, we observe a universal pseudogap opening around the Fermi level, which changes little with the applied magnetic field and the occurrence of Sn vacancies. The pseudogap gets smeared out at elevated temperatures and alters in size with the spatial confinement of the Mott insulating phase. Our findings, along with the previously observed superconductivity at a higher doping level, are highly reminiscent of the electronic phase diagram in the doped copper oxide compounds.
Spatial correlation of irreversible displacement in oscillatory-sheared metallic glasses
Authors: Cui Shiheng , Liu Huashan , Peng Hailong
Published: April 2022

We report computer simulations on the oscillatory of CuZr metallic glasses at zero temperature with different shear amplitudes. In small system a homogenous shear deformation is found, while in large system an inhomogeneous shear deformation is found with a shear band formed. Concomitantly, spatial correlation of irreversible displacement exhibits an isotropic and exponential decay in the case of homogeneous deformation, whereas a mixed power-law and exponential decay in the case of anisotropic and inhomogeneous deformation. By projecting the azimuthal-dependent correlation function onto the spherical harmonics, we found a strong polar symmetry that accounts for the emerged shear band, and a weaker quadrupolar symmetry that accounts for the elastic filed generated by Eshelby inclusions. By this, we conclude that the anisotropy and decaying formula of the plastic correlation are dominated by the homogeneity or inhomogeneity for the deformation in the metallic glasses.
Effects of π-conjugation-substitution on ESIPT process for oxazoline-substituted hydroxyfluorenes
Authors: Wang Di , Zhou Qiao , Wei Qiang , Song Peng
Published: April 2022

Excited-state intramolecular proton transfer (ESIPT) molecules are broadly applied to UV absorbers, fluorescence sensing, and lighting materials. In previous work, the fluorescence colors of oxazoline-substituted hydroxyfluorenes and hydroxylated benzoxazole were diversified by adding the π-conjugation. There is intriguing that the mechanism of diversified fluorescence colors induced by ESIPT. Here, the density functional theory (DFT) and time-dependent DFT (TDDFT) are advised to identify the effects of π-conjugation on ESIPT and photophysical properties. The stabilized geometrical configurations, frontier molecular orbitals (FMOs) isosurfaces, and O–H stretching vibration frequency analysis demonstrate that PT processes are more active in S1 state. Constructing the minimum energy pathways of ESIPT processes, we find that the calculated peak of enol and keto fluorescence of naphthoxazole (NO–OH) is distinctly bathochromic-shift relative to the oxazoline-substituted hydroxyfluorenes (Oxa–OH) configuration when adding π-conjugation-substitution, and it means that π-conjugation-substitution can diversify the fluorescence color. We hope our studies can establish new channels to devise the ESIPT-based molecules.
Effect of pressure evolution on the formation enhancement in dual interacting vortex rings
Authors: Dong Jianing , Xiang Yang , Liu Hong , Qin Suyang
Published: April 2022

In the biological locomotion, the ambit pressure is of particular importance to use as a means of propulsion. The multiple vortex rings have been proved to generate additional thrust by interaction, but the mechanism of this thrust enhancement is still unknown. This study examines the effect of ambit pressure on formation enhancement in interacting dual vortex rings. The vortex rings, which have the same formation time, are successively generated in a piston-cylinder apparatus. The finite-time Lyapunov exponent (FTLE) visualizes the flow fields as an indication of Lagrangian coherent structures (LCSs), and the pressure field is calculated based on the digital particle image velocity (DPIV). We extract the back pressure of the rear vortex in dual vortices and the back pressure circulation Γ
b, which is defined as a form of overpressure circulation Γ
p. The Γ
b has a positive linear relationship with Γ
p. A critical interval distance

d

cr

*

in a range of 0.32–0.42 is found where Γ
b and Γ
p reach the maximum synchronously, leading to a full-interaction mode. Moreover, an over-interaction mode and an under-interaction mode are proposed when the dimensionless interval distance d* is smaller or larger than

d

cr

*

. To conclude, the high back pressure caused by vortex interaction can enhance the formation of vortex rings and lead to high thrust.
A modified heuristics-based model for simulating realistic pedestrian movement behavior
Authors: Wang Wei-Li , Li Hai-Cheng , Rong Jia-Yu , Fan Qin-Qin , Han Xin , Cong Bei-Hua
Published: April 2022

Pedestrian movement simulation models are used in various areas, such as building evacuation, transportation engineering, and safety management of large events. It also provides effective means to uncover underlying mechanisms of collective behaviors. In this work, a modified heuristics-based model is presented. In this model, the potential collisions in the moving process are explicitly considered. Meanwhile, a series of simulations is conducted in two typical scenarios to demonstrate the influence of critical parameters on model performance. It is found that when facing a wide obstacle in a corridor, the larger the visual radius, the earlier the pedestrian starts to make a detour. In addition, when a pedestrian observes a large crowd walking toward him, he chooses to make a detour and moves in the flow in a uniform direction. Furthermore, the model can reproduce the lane formation pedestrian flow phenomena in relatively high-density situations. With the increase of pedestrian visual radius and the weight of potential collision resistance, more stable pedestrian lanes and fewer moving-through-the-counterflow pedestrians can be observed. In terms of model validation, the density-speed relationship of simulation results accords well with that of the published empirical data. Our results demonstrate that the modified heuristics-based model can overcome the deficiency of the original model, and reproduce more realistic pedestrian movement behavior.
Simulations on edge localized modes mitigation with impurity seeding in the HL-2A tokamak
Authors: Zhu Yiren , Xiao Guoliang , Zou Xiaolan , Zhong Wulyu , Li Jiaxian , Li Zhengji , Xue Miao , Liang Anshu , Tong Ruihai , Yuan Boda , Zou Yunpeng , Zhang Yipo , Xu Min , HL-2A Team
Published: April 2022

Impurity seeding has been confirmed to be a potential way for edge localized modes (ELMs) to be mitigated in tokamaks. This paper mainly combines the integrated equilibria reconstruction framework and edge simulation codes such as BOUT++ to dive deeper into the mechanism of the ELM mitigation by impurity injection. On the one hand, impurity injection changes the pedestal pressure and current profiles that are closely related to ELM activities. The nonlinear simulation result shows that ELM size decreases by a factor of 2 to 4 when the current exceeds a threshold after impurity injection. On the other hand, the decrease of E
r shear is supposed to cause a larger ELM size for a less stabilized effect. However, ELMs are mitigated with smaller E
r shear as observed in the HL-2A experiment. This indicates that changes in the profiles of pressure gradient and hence the current density may play a more important role than E
r shear in this ELM mitigation process. In contrast to the high n modes destabilized by the pellet pacing, metallic impurity seeding leads to more unstable low n modes. The simulation results indicate that the combination of changes in pressure/current and E
r shear is a plausible explanation for the ELM mitigation by metallic impurity seeding.
Magnetic reconnection rate during sawtooth crashes in ASDEX Upgrade
Authors: Samoylov O. , Igochine V. , Yu Q. , Zohm H. , the ASDEX Upgrade Team
Published: April 2022

The radial velocity of the plasma core during the sawtooth crashes has been measured for the first time with electron cyclotron emission imaging diagnostic. The measurements have been compared with nonlinear two-fluid simulation. The comparison reveals good qualitative and quantitative agreement, which indicates that two-fluid effects (inertia and pressure gradient of electrons) are sufficient for the correct prediction of the experimental results. Contrarily, the crash time of the Kadomtsev model, which is based on a single-fluid picture of magnetic reconnection, disagrees with the experimental results.
GeMSE: a low-background facility for gamma-spectrometry at moderate rock overburden
Authors: Ramírez García D. , Baur D. , Grigat J. , Hofmann B.A. , Lindemann S. , Masson D. , Schumann M. , von Sivers M. , Toschi F.
Published: April 2022

The GeMSE (Germanium Material and meteorite Screening
Experiment) facility operates a low-background HPGe crystal in an
underground laboratory with a moderate rock overburden of
620 m.w.e. in Switzerland. It has been optimized for continuous
remote operation. A multi-layer passive shielding, a muon veto, and
a boil-off nitrogen purge line inside the measurement cavity
minimize the instrument's background rate, which decreased by 33%
to (164 ± 2) counts/day (100 – 2700 keV) after five years of
underground operation. This agrees with the prediction based on the
expected decay of short-lived isotopes. A fit to the known
background components, modeled via a precise simulation of the
detector, shows that the GeMSE background is now muon-dominated. We
also present updates towards a more accurate detection efficiency
calculation for the screened samples: the thickness of the crystal's
outer dead-layer is precisely determined and the efficiency can now
be easily calculated for any sample geometry. The advantage of this
feature is showcased via the determination of the 40K content
in the screening of a complex-shaped object: a banana.
R&D of ultra-fast 8 × 8 anodes MCP-PMT
Authors: Wu Q. , Cao Y. , Huang G. , Hua Z. , Jin M. , Jin Z. , Li D. , Li K. , Liu S. , Ma L. , Qian S. , Ren L. , Si S. , Sun J. , Wang X. , Wang Y. , Yan M. , Zhang H. , Zhu Y.
Published: April 2022

Cooperating with the North Night Vision Science & Technology
(Nanjing) Research Institute Co. Ltd, Institute of High Energy of
Physics in China is developing a 2-inch square shape 8 × 8
anodes micro-channel-plate photomultiplier tube (MCP-PMT) with a
time resolution of picosecond level. It has a
40 × 40 mm2 bi-alkali photocathode with a peak quantum
efficiency (QE) of about 22% around a wavelength of 410 nm. With
the chevron MCP stack, the MCP-PMT can reach a gain of over 106 
under a working voltage of 1500 V. The typical output waveform has
an amplitude of 64 mV and a rise time of 334 ps. Due to the
well-designed structure of the MCP-PMT, the transit time spread
(TTS) for the middle anode can reach 36 ps when working at single
photon mode. To evaluate the performance uniformity of the
8× 8 anodes MCP-PMT, ten anodes which constitutes the
smallest repetition unit of the anode array are chosen and
tested. The average transit time spread (TTS) for the 64 anodes is
44.1 ± 2.0 ps.