Chiral topological metals with multiple types of quasiparticle fermions and large spin Hall effect in the SrGePt family materials

We present a prediction of chiral topological metals with several classes of unconventional quasiparticle fermions in a family of SrGePt-type materials in terms of first-principles calculations. In these materials, fourfold spin-3/2 Rarita-Schwinger-Weyl (RSW) fermion, sixfold excitation, and Weyl fermions coexist around the Fermi level as spin-orbit coupling is considered, and the Chern number for the first two kinds of fermions is the maximal value four. We found that large Fermi arcs from spin-3/2 RSW fermion emerge on the (010)-surface, spanning the whole surface Brillouin zone. Moreover, there exist Fermi arcs originating from Weyl points, which further overlap with trivial bulk bands. In addition, we revealed that the large spin Hall conductivity can be obtained, which attributed to the remarkable spin Berry curvature around the degenerate nodes and band-splitting induced by spin-orbit coupling. Our findings indicate that the SrGePt family of compounds provide an excellent platform for studying on topological electronic states and the intrinsic spin Hall effect.Comment: 10 pages and 7 figures in the main tex

A Modeling and Experiment Framework for the Emergency Management in AHC Transmission

Emergency management is crucial to finding effective ways to minimize or even eliminate the damage of emergent events, but there still exists no quantified method to study the events by computation. Statistical algorithms, such as susceptible-infected-recovered (SIR) models on epidemic transmission, ignore many details, thus always influencing the spread of emergent events. In this paper, we first propose an agent-based modeling and experiment framework to model the real world with the emergent events. The model of the real world is called artificial society, which is composed of agent model, agent activity model, and environment model, and it employs finite state automata (FSA) as its modeling paradigm. An artificial campus, on which a series of experiments are done to analyze the key factors of the acute hemorrhagic conjunctivitis (AHC) transmission, is then constructed to illustrate how our method works on the emergency management. Intervention measures and optional configurations (such as the isolation period) of them for the emergency management are also given through the evaluations in these experiments

Magnetic eight-fold nodal-point and nodal-network fermions in MnB2

Realizing topological semimetal states with novel emergent fermions in magnetic materials is a focus of current research. Based on first-principle calculations and symmetry analysis, we reveal interesting magnetic emergent fermions in an existing material MnB2. In the temperature range from 157 K to 760 K, MnB2 is a collinear antiferromagnet. We find the coexistence of eightfold nodal points and nodal net close to the Fermi level, which are protected by the spin group in the absence of spin-orbit coupling. Depending on the Neel vector orientation, consideration of spin-orbit coupling will either open small gaps at these nodal features, or transform them into magnetic linear and quadratic Dirac points and nodal rings. Below 157 K, MnB2 acquires weak ferromagnetism due to spin tilting. We predict that this transition is accompanied by a drastic change in anomalous Hall response, from zero above 157 K to 200 $\Omega\cdot \text{cm}^{-1}$ below 157 K.Comment: 5 figures and 7 page

Third-order charge transport in a magnetic topological semimetal

Magnetic topological materials and their physical signatures are a focus of current research. Here, by first-principles calculations and symmetry analysis, we reveal topological semimetal states in an existing antiferromagnet ThMn2Si2. Depending on the N\'eel vector orientation, the topological band crossings near the Fermi level form either a double-nodal loop or two pairs of Dirac points,which are all fourfold degenerate and robust under spin-orbit coupling. These topological features produce large Berry connection polarizability, which leads to enhanced nonlinear transport effects. Particularly, we evaluate the third order current response, which dominates the transverse charge current. We show that the nonlinear response can be much more sensitive to topological phase transitions than linear response, which offers a powerful tool for characterizing magnetic topological semimetals.Comment: 5 pages, 5 figure

Investigation of the Hot Stamping-in-Die Quenching Composite Forming Process of 5083 Aluminum Alloy Skin

Aluminum alloy has been used as the skin material for rail vehicles and automobiles to meet the requirements of environmental protection. The hot stamping-in-die quenching composite forming (HFQ) process is a promising technology to compensate for the poor formability of the aluminum alloy sheet at room temperature. In this paper, the high-temperature mechanical properties of 5083 aluminum alloy under various temperature (200 °C, 300 °C, 400 °C, 450 °C) and strain rate conditions (0.01 s−1, 0.10 s−1, 1.00 s−1) were investigated by uniaxial tensile tests. The finite element software of PAM-STAMP was employed to simulate the forming process of high-speed train skin. The effects of forming method and process parameters on the minimum thickness and springback of the skin were analyzed using the Response Surface Methodology (RSM). After parameter optimization, the forming experiment verified the simulation results and the test part met the quality requirements: the thickness above 3.84 mm and the springback within 1.1 mm. Mechanical properties of the sheet before and after HFQ were examined by uniaxial tensile tests at room temperature. It can be inferred from the comparison that the yield strength of the Al5083 sheet increases, but the elongation decreases from the HFQ process

Quantitative Research on the Effect of Natural Aging on the Mechanical Properties and Bake Hardening Properties of AA6014 Alloy within Six Months

This article is dedicated to quantitatively and systematically revealing the changes of mechanical properties and bake hardening properties of AA6014 alloy during six-month natural aging in detail. Three directions (0, 45, and 90° relative to the rolling direction) of the aluminum alloy sheets and 16 time points within six months were selected to conduct experiments. The change trend of six mechanical properties (0.2% offset yield strength, ultimate tensile strength, plastic extension at maximum force, elongation after fracture, and strain hardening exponent) were obtained by a large number of micro-hardness measurements and tensile tests. The results show that elongations along the three directions are basically the same and do not drop significantly with the progress of natural aging but fluctuate within a certain range. The trends of the n value during natural aging before and after bake hardening are opposite and bake hardening leads to ~0.07 decrease of the n value. The PLC phenomenon disappears after 90 days of natural aging, and the yield strengths along the three directions also stabilize; thus, it can be inferred that the cluster changes tend to stabilize after 90 days natural aging. The large and systematic dataset are clearly and intuitively presented, which can not only be used to provide data reference for industrial production of automobile manufacturers but also be used to reveal the microscopic mechanism of the natural aging process

Low Resistance Hot-Spot Diagnosis and Suppression of Photovoltaic Module Based on I-U Characteristic Analysis

In the hot-spot fault of photovoltaic modules, there is a low resistance hot-spot fault caused by crystal defects, such as internal crack and PN junction failure. When the faulty area is partially shaded, it will produce severe temperature rise, accelerate the aging of battery unit, and even cause fire, which will affect the safe operation of the photovoltaic system. In this paper, the low resistance hot-spot fault endangering the safe operation of photovoltaic modules is taken as the research object; the shunt effect of equivalent low resistance caused by crystal defects under local shadow occlusion is explained by using the reverse characteristic of PN junctions of battery units, and its failure mechanism is analyzed. The three working states of the power generation system and the formation conditions of hot-spots in the process of power generation are analyzed in detail. By building a simulation model, the heating power distribution characteristics of hot-spots under different external local shadow occlusions are simulated, and finally, the fault characteristics and the fault diagnosis criterion of low resistance hot-spots are obtained. A control algorithm for low resistance hot-spot diagnosis and suppression based on I-U characteristic analysis is designed, and verified by simulation and experiment. The experimental results show that the control algorithm proposed in this paper can use the I-U characteristics of photovoltaic modules to determine whether there is a low resistance hot-spot fault, and carry out real-time control according to the judgment results. If it is judged that a low resistance hot-spot module is partially shaded, actively fixing the working point of the system near the safe voltage will protect the safety of the photovoltaic module. Otherwise, performing global MPPT will ensure the maximum power output of the system

Low Resistance Hot-Spot Diagnosis and Suppression of Photovoltaic Module Based on I-U Characteristic Analysis

In the hot-spot fault of photovoltaic modules, there is a low resistance hot-spot fault caused by crystal defects, such as internal crack and PN junction failure. When the faulty area is partially shaded, it will produce severe temperature rise, accelerate the aging of battery unit, and even cause fire, which will affect the safe operation of the photovoltaic system. In this paper, the low resistance hot-spot fault endangering the safe operation of photovoltaic modules is taken as the research object; the shunt effect of equivalent low resistance caused by crystal defects under local shadow occlusion is explained by using the reverse characteristic of PN junctions of battery units, and its failure mechanism is analyzed. The three working states of the power generation system and the formation conditions of hot-spots in the process of power generation are analyzed in detail. By building a simulation model, the heating power distribution characteristics of hot-spots under different external local shadow occlusions are simulated, and finally, the fault characteristics and the fault diagnosis criterion of low resistance hot-spots are obtained. A control algorithm for low resistance hot-spot diagnosis and suppression based on I-U characteristic analysis is designed, and verified by simulation and experiment. The experimental results show that the control algorithm proposed in this paper can use the I-U characteristics of photovoltaic modules to determine whether there is a low resistance hot-spot fault, and carry out real-time control according to the judgment results. If it is judged that a low resistance hot-spot module is partially shaded, actively fixing the working point of the system near the safe voltage will protect the safety of the photovoltaic module. Otherwise, performing global MPPT will ensure the maximum power output of the system