Abstract
In order to further improve accuracy and stability of detection of combustion coal fallout propensity of cigarettes, author of the paper adopted computational fluid dynamics (CFD) technology ...for a three-dimensional numerical simulation of exhaust system of detection instrument, aiming to study characteristics of flow field near cigarettes. Moreover, a simulation model of eight-channel exhaust enclosure was established, obtaining vector diagram for flow velocity of flow field, velocity contour diagram, and pressure distribution cloud diagram. According to findings, flow field of eight channels is evenly distributed, with slow flow velocity around the instrument but furious inside channels. The wind velocity of cigarette monitoring channel is stable at about 200mm/s specified as per standard. However, there is significant change in pressure and flow velocity at the corners of channels, causing local turbulence. In experiments, average wind velocity of 8 monitoring channels was measured, and simulation results were compared with experiment data. Eventually, a conclusion is drawn that simulation result at cigarette monitoring channels changes consistently with the experimental data, with small errors as a whole. Therefore, the designed exhaust system complies with regulations on wind velocity stipulated by YC/T558-2018 Cigarettes—Determination of Combustion Coal Fallout Propensity of Burning Cigarettes. In a word, this paper is hoped to provide technical support for analogue simulation of exhaust system of cigarette detection instrument, and improve detection accuracy.
Magnetic Weyl semimetalsWeyl semimetals (WSMs)—materials that host exotic quasiparticles called Weyl fermions—must break either spatial inversion or time-reversal symmetry. A number of WSMs that ...break inversion symmetry have been identified, but showing unambiguously that a material is a time-reversal-breaking WSM is tricky. Three groups now provide spectroscopic evidence for this latter state in magnetic materials (see the Perspective by da Silva Neto). Belopolski et al. probed the material Co2MnGa using angle-resolved photoemission spectroscopy, revealing exotic drumhead surface states. Using the same technique, Liu et al. studied the material Co3Sn2S2, which was complemented by the scanning tunneling spectroscopy measurements of Morali et al. These magnetic WSM states provide an ideal setting for exotic transport effects.Science, this issue p. 1278, p. 1282, p. 1286; see also p. 1248Bulk–surface correspondence in Weyl semimetals ensures the formation of topological “Fermi arc” surface bands whose existence is guaranteed by bulk Weyl nodes. By investigating three distinct surface terminations of the ferromagnetic semimetal Co3Sn2S2, we verify spectroscopically its classification as a time-reversal symmetry-broken Weyl semimetal. We show that the distinct surface potentials imposed by three different terminations modify the Fermi-arc contour and Weyl node connectivity. On the tin (Sn) surface, we identify intra–Brillouin zone Weyl node connectivity of Fermi arcs, whereas on cobalt (Co) termination, the connectivity is across adjacent Brillouin zones. On the sulfur (S) surface, Fermi arcs overlap with nontopological bulk and surface states. We thus resolve both topologically protected and nonprotected electronic properties of a Weyl semimetal.
Magnetic Weyl semimetals with broken time-reversal symmetry are expected to generate strong intrinsic anomalous Hall effects, due to their large Berry curvature. Here, we report a magnetic Weyl ...semimetal candidate, Co
Sn
S
, with a quasi-two-dimensional crystal structure consisting of stacked Kagomé lattices. This lattice provides an excellent platform for hosting exotic topological quantum states. We observe a negative magnetoresistance that is consistent with the chiral anomaly expected from the presence of Weyl nodes close to the Fermi level. The anomalous Hall conductivity is robust against both increased temperature and charge conductivity, which corroborates the intrinsic Berry-curvature mechanism in momentum space. Owing to the low carrier density in this material and the significantly enhanced Berry curvature from its band structure, the anomalous Hall conductivity and the anomalous Hall angle simultaneously reach 1130 Ω
cm
and 20%, respectively, an order of magnitude larger than typical magnetic systems. Combining the Kagomé-lattice structure and the out-of-plane ferromagnetic order of Co
Sn
S
, we expect that this material is an excellent candidate for observation of the quantum anomalous Hall state in the two-dimensional limit.
COVID-19 has created long-lasting yet unprecedented challenges worldwide. In addition to scientific efforts, political efforts and public administration are also crucial to contain the disease. ...Therefore, understanding how multi-level governance systems respond to this public health crisis is vital to combat COVID-19. This study focuses on China and applies social network analysis to illustrate interactive governance between and within levels and functions of government, confirming and extending the existing Type I and Type II definition of multi-level governance theory. We characterize four interaction patterns—vertical, inter-functional, intra-functional, and hybrid—with the dominant pattern differing across governmental functions and evolving as the pandemic progressed. Empirical results reveal that financial departments of different levels of government interact through the vertical pattern. At the same time, intra-functional interaction also exists in provincial financial departments. The supervision departments typically adopt the inter-functional pattern at all levels. At the cross-level and cross-function aspects, the hybrid interaction pattern prevails in the medical function and plays a fair part in the security, welfare, and economic function. This study is one of the first to summarize the interaction patterns in a multi-level setting, providing practical implications for which pattern should be applied to which governmental levels/functions under what pandemic condition.
This work designed a simple, sensitive, and low‐cost immunosensor for the detection of protein marker by using a carbon sphere/gold nanoparticle (CNS/AuNP) composite as an electrochemical label. The ...nanoscale carbon spheres, prepared with a hydrothermal method by using glucose as raw material, were used to load AuNPs for labeling antibody by electrostatic interaction, which provided a feasible pathway for electron transfer due to the remarkable conductivity. The disposable immunosensor was constructed by coating a polyethylene glycol (PEG) film on a screen‐printed carbon‐working electrode and then immobilizing capture antibody on the film. With a sandwich‐type immunoassay format, the analyte and then the CNS/AuNP‐labeled antibody were successively bound to the immunosensor. The bound AuNPs were finally electro‐oxidized in 0.1 M HCl to produce AuCl4− for differential pulse voltammetric (DPV) detection. The high‐loading capability of AuNPs on CNS for the sandwich‐type immunorecognition led to obvious signal amplification. By using human immunoglobulin G (IgG) as model target, the DPV signal of AuNPs after electro‐oxidized at optimal potential of +1.40 V for 40 s showed a wide linear dependence on the logarithm of target concentration ranging from 10 pg mL−1 to 10 ng mL−1. The detection limit was around 9 pg mL−1. The immunosensor showed excellent analytical performance with cost effectivity, good fabrication reproducibility, and acceptable precision and accuracy, providing significant potential application in clinical analysis.
A convenient and low‐cost immunosensor was designed by using a polyethylene‐glycol‐film‐modified screen‐printed carbon electrode combined with a self‐synthesized carbon sphere/gold nanoparticle composite as an electrochemical label for signal amplification (see scheme). This efficient method provides a potential application for clinical detection of protein markers.
The vital role of electrocatalysts in determining the efficiency of renewable energy conversion inspired the uncovering of the relation between the catalytic efficiency and electronic structure, in ...which the volcano-type plot based on adsorption energies and d-band model has achieved great success. At the same time, catalysts with nontrivial topological electronic structures have received considerable attention because of their robust topological surface states and high-mobility electrons, which favor the electrons transfer processes in the heterogeneous catalysis reactions. Under the guidance of this theory, excellent catalysts were reported among topological materials. Inspired by the current development of catalyst and topological materials, we tried to extract a pure intrinsic physical parameter, projected Berry phase (PBP), that only depends on the bulk electronic structure. Applying this parameter to the well-known nonmagnetic transition-metal electrocatalysts, we found a linear relationship between PBP and catalytic efficiency of hydrogen evolution reaction (HER) after considering the symmetry constraint. This can be used as a descriptor for the prediction and designing of promising catalysts for HER, which is realized experimentally in Pt7Cu nanostructures. This work illustrates the importance of the pure bulk band structure effect on electrochemical activities and implies an effective way to understand the mechanism of HER catalysts.
Sodium (Na) metal batteries (SMBs) using Na anode are potential “beyond lithium” electrochemical technology for future energy storage applications. However, uncontrollable Na dendrite growth has ...plagued the application of SMBs. Understanding Na deposition mechanisms, particularly the early stage of Na deposition kinetics, is critical to enable the SMBs. In this context, we conducted
in situ
observations of the early stage of electrochemical Na deposition. We revealed an important electrochemical Ostwald ripening (EOR) phenomenon which dictated the early stage of Na deposition. Namely, small Na nanocrystals were nucleated randomly, which then grew. During growth, smaller Na nanocrystals were contained by bigger ones via EOR. We observed two types of EOR with one involving only electrochemical reaction driven by electrochemical potential difference between bigger and smaller nanocrystals; while the other being dominated by mass transport governed by surface energy minimization. The results provide new understanding to the Na deposition mechanism, which may be useful for the development of SMB for energy storage applications.
Topological magnets comprising 2D magnetic layers with Curie temperatures (TC) exceeding room temperature are key for dissipationless quantum transport devices. However, the identification of a ...material with 2D ferromagnetic planes that exhibits an out‐of‐plane‐magnetization remains a challenge. This study reports a ferromagnetic, topological, nodal‐line, and semimetal MnAlGe composed of square‐net Mn layers that are separated by nonmagnetic Al–Ge spacers. The 2D ferromagnetic Mn layers exhibit an out‐of‐plane magnetization below TC ≈ 503 K. Density functional calculations demonstrate that 2D arrays of Mn atoms control the electrical, magnetic, and therefore topological properties in MnAlGe. The unique 2D distribution of the Berry curvature resembles the 2D Fermi surface of the bands that form the topological nodal line near the Fermi energy. A large anomalous Hall conductivity of ≈700 S cm–1 is obtained at 2 K and related to this nodal‐line‐induced 2D Berry curvature distribution. The high transition temperature, large anisotropic out‐of‐plane magnetism, and natural heterostructure‐type atomic arrangements consisting of magnetic Mn and nonmagnetic Al/Ge elements render nodal‐line MnAlGe one of the few, unique, and layered topological ferromagnets that have ever been observed.
A layered topological nodal‐line magnet MnAlGe is reported. The material exhibits a large anomalous Hall conductivity driven by the unique 2D Berry curvature distribution. The search for new layered topological magnets and exploration of magnetism and topological properties are enabled by this work.
Abstract
Spin Hall effect (SHE) has its special position in spintronics. To gain new insight into SHE and to identify materials with substantial spin Hall conductivity (SHC), we performed ...high-precision high-throughput ab initio calculations of the intrinsic SHC for over 20,000 nonmagnetic crystals. The calculations revealed a strong relationship between the magnitude of the SHC and the crystalline symmetry, where a large SHC is typically associated with mirror symmetry-protected nodal line band structures. This database includes 11 materials with an SHC comparable to or even larger than that of Pt. Materials with different types of spin currents were additionally identified. Furthermore, we found that different types of spin current can be obtained by rotating applied electrical fields. This improves our understanding and is expected to facilitate the design of new types of spin-orbitronic devices.
Since spin currents can be generated, detected, and manipulated via the spin Hall effect (SHE), the design of strong SHE materials has become a focus in the field of spintronics. Because of the ...recent experimental progress also the spin Nernst effect (SNE), the thermoelectrical counterpart of the SHE, has attracted much interest. Empirically strong SHEs and SNEs are associated with d-band compounds, such as transition metals and their alloys-the largest spin Hall conductivity (SHC) in a p-band material is ∼450ℏ/eΩcm−1 for a Bi-Sb alloy, which is only about a fifth of platinum. This raises the question whether either the SHE and SNE are naturally suppressed in p-bands compounds, or favourable p-band systems were just not identified yet. Here we consider the p-band semimetal InBi, and predict it has a record SHC σxyz≈1100ℏ/eΩcm−1 which is due to the presence of nodal lines in its band structure. Also the spin-Nernst conductivity αzxy≈1.2(ℏ/e)(A/m⋅K) is very large, but our analysis shows its origin is different as the maximum appears in a different tensor element compared to that in SHC. This insight gained on InBi provides guiding principles to obtain a strong SHE and SNE in p-band materials and establishes a more comprehensive understanding of the relationship between the SHE and SNE.
PDF
