Recipe for single-pair-Weyl-points phonons carrying the same chiral charges

Recently, Wang et al. [Phys. Rev. B, 106, 195129 (2022)] challenged a widely held belief in the field of Weyl physics, demonstrating that single-pair-Weyl-points (SP-WPs) can exist in nonmagnetic spinless systems, contrary to previous assumptions that they could only exist in magnetic systems. Wang et al. observed that the SP-WPs with opposite and even chiral charges (i.e., |C| = 2 or 4) could also exist in nonmagnetic spinless systems. In this Letter, we present a novel finding in which SP-WPs have a partner, namely a charged nodal surface, in nonmagnetic spinless systems. In contrast to previous observations, we show that the SP-WPs can have uneven chiral charges (i.e., |C| = 1). We identify 6 (out of 230) space groups (SGs) that contain such SP-WPs by searching the encyclopedia of emergent particles in three-dimensional crystals. Our finds were confirmed through the phonon spectra of two specific materials Zr3O (with SG 182) and NaPH2NO3 (with SG 173). This discovery broadens the range of materials that can host SP-WPs and applies to other nonmagnetic spinless crystals

Genuine Dirac half-metal: A 2D d0-type ferromagnet Mg4N4

When the spin-orbit coupling (SOC) is absent, almost all the proposed half-metals with the twofold degenerate nodal points at the K (or K') in two-dimensional (2D) materials are misclassified as "Dirac half-metals" owing to the way graphene was utilized in the earliest studies. Actually, each band crossing point at K or K' is described by a 2D Weyl Hamiltonian with definite chirality; hence, it must be a Weyl point. To the best of our knowledge, there have been no reports of a genuine (i.e., fourfold degenerate) Dirac point half-metal in 2D yet. In this Letter, we proposed for the first time that the 2D d0-type ferromagnet Mg4N4 is a genuine Dirac half-metal with a fourfold degenerate Dirac point at the S high-symmetry point, intrinsic magnetism, high Curie temperature, 100% spin-polarization, robustness to the SOC and uniaxial and biaxial strains, and 100% spin-polarized edge states. The work can be seen as a starting point for future predictions of intrinsically magnetic materials with genuine Dirac points, which will aid the frontier of topo-spintronics researchers

Energy-efficient routing for mobile data collectors in wireless sensor networks with obstacles

This paper proposes an energy-efficient routing mechanism by introducing intentional mobility to wireless sensor networks (WSNs) with obstacles. In the sensing field, Mobile Data Collectors (MDCs) can freely move for collecting data from sensors. An MDC begins its periodical movement from the base station and finally returns and transports the data to the base station. In physical environments, the sensing field may contain various obstacles. A research challenge is how to find an obstacle-avoiding shortest tour for the MDC. Firstly, we obtain the same size grid cells by dividing the network region. Secondly, according to the line sweep technique, the spanning graph is easily constructed. The spanning graph composed of some grid cells usually includes the shortest search path for the MDC. Then, based on the spanning graph, we can construct a complete graph by Warshall-Floyd algorithm. Finally, we present a heuristic tour-planning algorithm on the basis of the complete graph. Through simulation, the validity of our method is verified. This paper contributes in providing an energy-efficient routing mechanism for the WSNs with obstacles

Energy-Efficient Scheduling for Mobile Sensors Using Connection Graphs in a Hybrid Wireless Sensor Network with Obstacles

This paper considers the scheduling problem of mobile sensors in a hybrid wireless sensor network (WSN) with obstacles. In a WSN, static sensors monitor the environment and report where events appear in the sensing field. Then, mobile sensors are dispatched to these event locations to perform in-depth analysis. The sensing field may contain obstacles of any shape and size. A big challenge is how to efficiently dispatch the mobile sensor to find an obstacle-avoiding shortest path. To remedy this issue, we propose an efficient scheduling mechanism based on connection graphs in this paper. Specifically, the region of network is divided into grid cells with the same size. Consequently, the search space of the shortest path is restricted to the connection graphs composed of some grid cells. Through simulation, we verify the effectiveness of our method. The paper contributes to developing an energy-efficient dispatch solution in the presence of obstacles

Quantized flocking control for second-order multiple agents with obstacle avoidance

A quantized flocking control for a group of second-order multiple agents with obstacle avoidance is proposed to address the problem of the exchange of information needed for quantification. With a reasonable assumption, a logarithmic or uniform quantizer is used for the exchange of relative position and velocity information between adjacent agents and the virtual leader, moving at a steady speed along a straight line, and a distributed flocking algorithm with obstacle avoidance capability is designed based on the quantitative information. The Lyapunov stability criterion of nonsmooth systems and the invariance principle are used to prove the stability of these systems. The simulations and experiments are presented to demonstrate the feasibility and effectiveness of the proposed approach

Coexistence of magnetic and phononic second-order topological phases in two-dimensional NiZrCl6

Second-order topological phases (SOTPs) in two-dimensional (2D) magnetic and phononic systems are rarely reported. In this Letter, using first-principles calculations, we propose that the NiZrCl6 monolayer with space group P312 (No. 149) is a 2D ferromagnetic material with rich SOTPs: (i) magnetic SOTPs can be found in the band structures of both spin channels in NiZrCl6. NiZrCl6 hosts topologically protected corner states that have a quantized fractional charge (e/3) and are spin-polarized and pinned at the corners of the sample in real space. The SOTP nature in the NiZrCl6 monolayer is resistant to the spin-orbit coupling effect. (ii) Phononic SOTPs can be found in the phonon curves of NiZrCl6. The corner vibrational modes appear inside the frequency gap around 7.98 THz of the NiZrCl6 monolayer, and the secondary topological index can verify the nontrivial phase. The proposed 2D NiZrCl6 material can be a starting point for exploring higher-order topological phases in 2D magnetic and phononic systems

Characterization and Removal Potential of Fluorine in Lignite from a Mine in Shaanxi Province, China: A Case Study

Fluorine appears in coal and is released into the atmosphere upon combustion, resulting in harmful impacts on the environment and life, which needs to be removed from coal before utilization. Coal can be processed by flotation and gravity separation to reduce its fluorine content. In this study, a lignite sample from a mine in Shaanxi Province, China, was characterized using the float–sink test, sieving test, X-ray diffraction (XRD), and polarized light microscopy. Mineralogical analysis indicated that the fluorine in coal is mainly contained in Muscovite and polylithionite, and partly in pyrite. The washability and floatability analyses were employed to evaluate the extent of fluorine removal from >0.5 and <0.5 mm size fractions of lignite, respectively. Compared to the raw sample that contained 347.74 μg/g fluorine content, the proposed combination of gravity-flotation separation process decreased the fluorine content to 90.14 μg/g, which meets the requisites of coal standards

Bioinspired Hemostatic Strategy via Pulse Ejections for Severe Bleeding Wounds

Efficient hemostasis during emergency trauma with massive bleeding remains a critical challenge in prehospital settings. Thus, multiple hemostatic strategies are critical for treating large bleeding wounds. In this study, inspired by bombardier beetles to eject toxic spray for defense, a shape-memory aerogel with an aligned microchannel structure was proposed, employing thrombin-carrying microparticles loaded as a built-in engine to generate pulse ejections for enhanced drug permeation. Bioinspired aerogels, after contact with blood, can rapidly expand inside the wound, offering robust physical barrier blocking, sealing the bleeding wound, and generating a spontaneous local chemical reaction causing an explosive-like generation of CO2 microbubbles, which provide propulsion thrust to accelerate burst ejection from arrays of microchannels for deeper and faster drug diffusion. The ejection behavior, drug release kinetics, and permeation capacity were evaluated using a theoretical model and experimentally demonstrated. This novel aerogel showed remarkable hemostatic performance in severely bleeding wounds in a swine model and demonstrated good degradability and biocompatibility, displaying great potential for clinical application in humans

Magnetic field-mediated Janus particles with sustained driving capability for severe bleeding control in perforating and inflected wounds

Severe bleeding in perforating and inflected wounds with forky cavities or fine voids encountered during prehospital treatments and surgical procedures is a complex challenge. Therefore, we present a novel hemostatic strategy based on magnetic field-mediated guidance. The biphasic Janus magnetic particle (MSS@Fe2O3-T) comprised aggregates of α-Fe2O3 nanoparticles (Fe2O3 NPs) as the motion actuator, negatively modified microporous starch (MSS) as the base hemostatic substrate, and thrombin as the loaded hemostatic drug. Before application, the particles were first wrapped using NaHCO3 and then doped with protonated tranexamic acid (TXA-NH3+), which ensured their high self-dispersibility in liquids. During application, the particles promptly self-diffused in blood by bubble propulsion and travelled to deep bleeding sites against reverse rushing blood flow under magnetic guidance. In vivo tests confirmed the superior hemostatic performance of the particles in perforating and inflected wounds (“V”-shaped femoral artery and “J”-shaped liver bleeding models). The present strategy, for the first time, extends the range of magnetically guided drug carriers to address the challenges in the hemorrhage control of perforating and inflected wounds