Search

In order to study the dynamic mechanical properties of hard coal and rock in northern Shaanxi Province, the basic dynamic and static tests of coal and rock specimens were carried out by using stress loading system and split Hopkinson pressure bar (SHPB) test device, and the failure mechanism was studied. The results show that under static load, most of the coal and rock specimens are damaged by single crack, while under dynamic load, the failure forms are relatively rich, such as splitting failure at low strain rate and crushing failure at high strain rate. The correlation between elastic modulus and strain rate of peak stress is significant, but the correlation between peak strain rate is weak. Under dynamic loading mode, the closure time of defects such as voids, cracks and particle spacing is too short due to the fast loading speed, which shows that the stress-strain curve is missing on the macro level.

Crack‐closure behaviour of rock materials is well‐known, while the three‐dimensional discrete element method (DEM) simulation of crack‐closure behaviour is still a challenge. Hence, a numerical method was proposed through the combination of notional surface method and flat‐joint model. The pre‐existing microcracks with finite width can be inserted into the three‐dimensional numerical sample through the present method. Since the two physical mechanisms, that is, closure of pre‐existing microcracks and fracture of flat‐joint bonds, are included in the simulations, various evolution trends of crack‐closure stage can be captured through the present method. Due to the high computational efficiency of flat‐joint model, the three‐dimensional DEM simulations of crack‐closure behaviour can be achieved. The results of parametric study show that the crack intensity determines the crack‐closure behaviour and the crack width significantly influences the evolution trend of crack‐closure stage. The simulated unconfined compressive strength (UCS) and tensile strength (TS) significantly decrease with the increase of crack intensity. The crack width significantly influences the deformation parameters, such as elastic modulus, Poisson's ratio and crack closure strain. A calibration procedure was proposed to ease the calibration of mechanical parameters and crack‐closure behaviour. Through the proposed numerical method and calibration procedure, the basic mechanical parameters and crack‐closure behaviour of sandstone were well matched. [ABSTRACT FROM AUTHOR]

From the perspective of the surgical scheduling problem in emergency, this paper considers the fatigue effect and the truncated learning effect caused by medical staffs' long-time work, regards the surgical scheduling problem as the hybrid flow-shop scheduling problem and proposes a three-stage surgical scheduling model which includes preoperative, intraoperative and postoperative. The improved grey wolf optimization is used to solve the emergency surgical scheduling model, and the effectiveness of the model and the algorithm are tested through simulation experiments. The results show that the improved grey wolf optimization algorithm can solve the emergency surgical scheduling model more effectively and get better scheduling results. [ABSTRACT FROM AUTHOR]

As one of the most promising Kitaev quantum-spin-liquid (QSL) candidates, α -RuCl3 has received a great deal of attention. However, its ground state exhibits a long-range zigzag magnetic order, which defies the QSL phase. Nevertheless, the magnetic order is fragile and can be completely suppressed by applying an external magnetic field. Here, we explore the evolution of magnetic excitations of α -RuCl3 under an in-plane magnetic field, by carrying out inelastic neutron scattering measurements on high-quality single crystals. Under zero field, there exist spin-wave excitations near the M point and a continuum near the Î" point, which are believed to be associated with the zigzag magnetic order and fractional excitations of the Kitaev QSL state, respectively. By increasing the magnetic field, the spin-wave excitations gradually give way to the continuous excitations. On the verge of the critical field ÎĽ 0 H c = 7.5 T, the former ones vanish and only the latter ones are left, indicating the emergence of a pure QSL state. By further increasing the field strength, the excitations near the Î" point become more intense. By following the gap evolution of the excitations near the Î" point, we are able to establish a phase diagram composed of three interesting phases, including a gapped zigzag order phase at low fields, possibly gapless QSL phase near ÎĽ 0 H c, and gapped partially polarized phase at high fields. These results demonstrate that an in-plane magnetic field can drive α -RuCl3 into a long-sought QSL state near the critical field. [ABSTRACT FROM AUTHOR]

Rock damage caused by its microcrack growth has a great influence on the deformation and strength properties of rock under compressive loading. Considering the interaction of wing cracks and the additional stress caused by rock bridge damage, a new calculation model for the mode-I stress intensity factor at wing crack tip was proposed in this study. The proposed calculation model for the stress intensity factor can not only accurately predict the cracking angle of wing crack, but can also simulate the whole range of variation of wing crack length from being extremely short to very long. Based on the modified stress intensity factor, a macro–micro damage model for rock materials was also established by combining the relationship between microcrack growth and macroscopic strain. The proposed damage model was verified with the results from the conventional triaxial compression test of sandstone sample. The results show that the proposed damage model can not only continuously simulate the stress-strain curves under different confining pressures, but also can better predict the peak strength. Furthermore, the sensitivities of initial crack size, crack friction coefficient, fracture toughness, initial damage and parameter m on the stress-strain relationship are discussed. The results can provide a theoretical reference for understanding the effect of microcrack growth on the progressive failure of rock under the compressive loading. [ABSTRACT FROM AUTHOR]

Ferromagnetic resonance (FMR) studies have been undertaken near 9.5 GHz on permalloy (Py) thin films. The giant magnetoresistance structures use antiferromagnetic NiO to achieve pinning of a magnetic layer. Magnetic anisotropies were observed for their resonances for fields perpendicular to and in the sample plane. Strong temperature dependencies of the isotropic shift may mean the presence of different spin pinning subsystems.

The terahertz (THz) vibrational spectroscopy of organic polycrystalline thin films is characterized, using a method of waveguide terahertz time domain spectroscopy (waveguide THz-TDS). X-ray diffraction has determined the orientation of the polycrystalline tetracyanoquinodimethane (TCNQ) films on the parallel plate waveguide (PPWG) surface.

Magnetic multilayer stacks incorporating several layers of graphene have been predicted to produce very high magnetoresistance and high conductivity, a combination of properties that would be useful in magnetic sensors and future spin-based data storage and processing technologies such as MRAM. To realize the theoretically modeled heterostructures and probe their properties, a clean, high-quality graphene-ferromagnet interface, such as one that results from CVD of graphene directly on ferromagnetic films, is required. However, past works using Ni and Co films for CVD of graphene employ the ferromagnetic film as a sacrificial layer to be dissolved after graphene growth and ignore changes to its morphology and magnetic properties. Here we investigated the effect of graphene CVD growth conditions on the properties of Co, Ni, Co 90 Fe 10 and Ni 80 Fe 20 ferromagnetic films. The magnetic films were grown by dc magnetron sputtering with different growth conditions onto c-Al 2 O 3 , Si/AlN and MgO substrates. The crystalline orientation, surface morphology/roughness and magnetic properties of the films were measured using X-ray diffraction, atomic force microscopy and vibrating sample magnetometry, respectively. Cobalt films grown at 500 °C were found to be hcp and heteroepitaxial on c-Al 2 O 3 . CoFe, Ni, and NiFe films on c-Al 2 O 3 were found to be fcc and to be (111) textured but with grains having in-plane rotation differing by 60°. The CoFe and NiFe films on c-Al 2 O 3 retained their small coercivity and high remanence while the pure Co and Ni films exhibited much smaller remanence after graphene growth, making them unsuitable for magnetic memory technologies. Films on Si/AlN were found to have the same rotational domains as those on sapphire c-Al 2 O 3 . The NiFe films on (111) MgO were found to be mostly single domain. [ABSTRACT FROM AUTHOR]

As one of the most promising Kitaev quantum-spin-liquid (QSL) candidates, α -RuCl3 has received a great deal of attention. However, its ground state exhibits a long-range zigzag magnetic order, which defies the QSL phase. Nevertheless, the magnetic order is fragile and can be completely suppressed by applying an external magnetic field. Here, we explore the evolution of magnetic excitations of α -RuCl3 under an in-plane magnetic field, by carrying out inelastic neutron scattering measurements on high-quality single crystals. Under zero field, there exist spin-wave excitations near the M point and a continuum near the Î" point, which are believed to be associated with the zigzag magnetic order and fractional excitations of the Kitaev QSL state, respectively. By increasing the magnetic field, the spin-wave excitations gradually give way to the continuous excitations. On the verge of the critical field ÎĽ 0 H c = 7.5 T, the former ones vanish and only the latter ones are left, indicating the emergence of a pure QSL state. By further increasing the field strength, the excitations near the Î" point become more intense. By following the gap evolution of the excitations near the Î" point, we are able to establish a phase diagram composed of three interesting phases, including a gapped zigzag order phase at low fields, possibly gapless QSL phase near ÎĽ 0 H c, and gapped partially polarized phase at high fields. These results demonstrate that an in-plane magnetic field can drive α -RuCl3 into a long-sought QSL state near the critical field. [ABSTRACT FROM AUTHOR]

Rutile RuO_{2} has been posited as a potential d-wave altermagnetism candidate, with a predicted significant spin splitting up to 1.4 eV. Despite accumulating theoretical predictions and transport measurements, direct spectroscopic observation of spin splitting has remained elusive. Here, we employ spin- and angle-resolved photoemission spectroscopy to investigate the band structures and spin polarization of thin-film and single-crystal RuO_{2}. Contrary to expectations of altermagnetism, our analysis indicates that RuO_{2}'s electronic structure aligns with those predicted under nonmagnetic conditions, exhibiting no evidence of the hypothesized spin splitting. Additionally, we observe significant in-plane spin polarization of the low-lying bulk bands, which is antisymmetric about the high-symmetry plane and contrary to the d-wave spin texture due to time-reversal symmetry breaking in altermagnetism. These findings definitively challenge the altermagnetic order previously proposed for rutile RuO_{2}, prompting a reevaluation of its magnetic properties.