黑龙江工程学院

High-pressure water environments formed during coal seam water injection can alter the physicochemical structure of coal, consequently influencing its susceptibility to low-temperature oxidation and spontaneous combustion. In this study, coal samples were immersed at 0.1, 3, 6, 9 and 12 MPa and analyzed using programmed-temperature oxidation, TG-DTG/DSC, low-temperature N2 adsorption, FTIR and ESR. The results show that the effect of water immersion pressure on coal spontaneous combustion propensity was non-monotonic. As pressure increased from 0.1 to 9 MPa, CO release and O2 consumption increased, while the crossing-point temperature decreased from 167.1 °C to 162.8 °C, indicating enhanced low-temperature oxidation activity. The 9 MPa sample showed the strongest thermal and structural responses, with the maximum main exothermic area, specific surface area and total pore volume of 1389.5 J/g, 22.41 m2/g and 0.03577 cm3/g, respectively. FTIR and ESR results further revealed that at 9 MPa, aliphatic hydrocarbons, oxygen-bearing functional groups, and the concentration of free radicals all peaked. Specifically, the radical density rose to 3.04 × 1017 spins·g−1. When pressure increased to 12 MPa, oxidation activity, heat release, pore development and microscopic active structures decreased relative to 9 MPa. These findings indicate that coal treated at 9 MPa showed the strongest oxidation activity under the present conditions and provide guidance for water-injection pressure optimization and coal fire risk assessment in deep mines.

The integration of renewable energy sources into power grids through voltage source converters reduces system inertia, severely endangering grid frequency stability. Existing research primarily focuses on frequency safety with limited consideration of economic aspects; additionally, it concentrates on grid following converters, leaving the frequency response of grid forming (GFM) converters underexplored. To tackle these issues, this paper proposes a transient frequency response strategy for GFM converters based on dynamic frequency reference (DFR) to achieve a trade-off between safety and economy, targeting minimal frequency regulation costs under the premise of ensuring frequency safety. Firstly, the design principle of the DFR strategy is introduced, which employs a critical threshold frequency curve for frequency control instead of the conventional rated frequency curve. Secondly, a detailed implementation of the DFR strategy is presented, including the threshold frequency and the safe frequency design method, as well as the dual mode operation scheme. Finally, the experimental and simulation results demonstrate the superiority and economic efficiency of the proposed DFR strategy.

This study focuses on the Permian strata and volcanic rocks in the Ondor Sum area, Inner Mongolia. By integrating zircon U–Pb geochronology, whole-rock geochemistry, and paleontological analysis, we constrain their formation age, provenance characteristics, and depositional environment, aiming to elucidate the Permian to Early Triassic tectonic evolution along the southern margin of the central Xing–Meng Orogenic Belt (XMOB). The meta–basalts of the Ondor Sum Group exhibit geochemical signatures consistent with an OIB source, including enrichment in LILEs (Rb, Ba, K, Sr), moderate enrichment in HFSEs (Nb, Ta, Zr), and the absence of a Nb–Ta negative anomaly. These features collectively indicate derivation from an enriched deep mantle source, possibly related to a mantle plume. The protolith was emplaced during the Late Permian. Detrital zircon data from sericite–bearing quartz schist within the group yield a maximum depositional age of 244 Ma. The lower part of the Amushan Formation yields a maximum depositional age of 411 Ma, while the upper part is dated at 252 Ma, indicating a substantial time gap between the two units. Combined with fossil assemblages and zircon provenance analysis, the unit is interpreted to have been deposited in a back–arc basin setting during the Late Carboniferous to Early Permian under a convergent plate regime. Integrating regional magmatic and sedimentary records, the Permian–Early Triassic tectonic evolution of the southern margin of the XMOB can be subdivided into three stages: (1) Early Permian (∼285 Ma), characterized by the development of typical calc-alkaline island arc volcanics and crustal thickening, marking the continued subduction of the Paleo-Asian Ocean (PAO); (2) Middle Permian (285–260 Ma), when slab break-off induced a shift in the magma source from juvenile arc crust to older basement, leading to peak crustal thickness and transition from subduction to collision; (3) Late Permian to Early Triassic (260–240 Ma), characterized by a post-collisional extensional regime evidenced by A–type granites, intraplate basalts, and crustal thinning. This extensional onset at 260 Ma marks the termination of collision, constraining final closure of the PAO to the Early Triassic. This study, by integrating previous research, reconstructs the spatiotemporal pattern of PAO closure and provides new constraints on the tectonic evolution of the XMOB.

Ultra-short pulses have seen rapid development and wide application in the nano-machining of viscoelastic structures. Consequentially, the transient thermo-mechanical responses at the micro/nano scale have gained utmost importance. At the microscale, the significance of size-dependent effect in elastic deformation and memory-dependent effect in the heat transfer process cannot be ignored. Many experimental and theoretical investigations suggest that, in practical analyses, thermal conductivity in materials should not be considered as a constant value. To compensate for such a deficiency, this work formulates a nonlocal thermoviscoelastic model with memory-dependent effect. This model integrates the fractional-order three-phase-lag (FTPL) heat conduction model and the nonlocal elasticity theory. The FTPL heat conduction model is based on the Caputo-Fabrizio (CF) definition of the fractional derivative, which does not have a singular kernel. In terms of application, the nonlinear electro-magneto-thermo-viscoelastic response of a polymer spherical nanoshell with variable thermal conductivity heated by a sinusoidal ultra-short pulse under the effect of a magnetic field is studied. Taking into account the variable thermal conductivity, the nonlinear governing equations are derived. The Laplace and Kirchhoff transformations are employed to derive and solve the governing equations that incorporate the fractional-order parameter, the nonlocal parameter and the variable thermal conductivity. The results show that the nonlinear thermoviscoelastic response of the polymer spherical microshell can be adjusted by the suitably modified parameters, which strongly depend on the size-dependent effect, memory-dependent effect and the variable thermal conductivity.

CONTEXT:In recent years, fluorescent probe molecular technology has received increasing attention. However, the mechanism by which fluorescent probe molecules detect ions still requires further study. This research explores the sensing mechanism of the 1,3,4-thiadiazole derivative 2-(5-(4-(diethylamino)phenyl)-1,3,4-thiadiazol-2-yl) phenol (L-E) as a highly selective fluorescent probe for Cu2+. The current theoretical calculations propose a detection mechanism that has not yet been observed experimentally. Analyses of structural parameters, interaction region indicators, infrared spectra, absorption and fluorescence spectra, electron distribution, and potential energy curves indicate that following the addition of Cu2+, the fluorescence quenching of L-E is due to twisted intramolecular charge transfer (TICT) rather than excited state intramolecular proton transfer (ESIPT). Cu replaces H to form the complex L-E-Cu, which inhibits the ESIPT process and facilitates the TICT process, leading to fluorescence quenching. This research elucidates novel mechanisms underlying metal ion detection and recognition, providing invaluable guidance for the development of advanced fluorescent probes. METHODS:The structures of the studied compounds in ground (S0) and excited (S1) states were optimized using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at the B3PW91/6-311G(d) level. All calculations were performed in the gas phase with singlet spin symmetry. Infrared spectra, absorption and fluorescence spectra, electron distribution analysis, and potential energy curves were all calculated using the same functional and basis set. Electron distribution and IRI analyses were performed using the Multiwfn program, and the results were visualized with Gnuplot and VMD software.