Gas-coaldust hybrid explosions represent one of the most severe hazards in underground coal mining. Their reaction mechanisms are far more complex than those of pure gas explosions, making them difficult to thoroughly investigate using conventional experiments or macroscopic simulations. In this study, the suppression characteristics and underlying mechanisms of a composite inhibitor on hybrid explosions in a pipeline network were investigated through a combination of experimental analysis and machine-learning potential simulations, with a focus on the physicochemical synergistic effects. The results demonstrate that a 1:1 composite of magnesium-aluminum layered double hydroxide (LDHs) and melamine polyphosphate (MPP), designated as LM1:1, at an addition ratio of 50 wt%, exhibits optimal suppression performance. This formulation reduces the peak explosion overpressure by more than 67.6%, the explosion severity index by more than 84.9%, the flame propagation speed by more than 89.4%, and the peak flame temperature by more than 85.3%, while maintaining a flame suppression ratio above 0.92. LM1:1 significantly inhibits the pyrolysis of coal dust, lowering the weight-loss rate to 65.22%, reducing the maximum mass-loss rate to 2.51%/min, and decreasing the total heat release by 75.23%. Moreover, the composite inhibitor effectively scavenges center dot OH radicals, thereby blocking key chain-branching reaction pathways (center dot CH3 + center dot OH -> center dot CH4O -> center dot CH3O -> center dot CH2O -> center dot CHO -> CO + center dot OH -> center dot CHO2 -> CO2 and center dot CHO + center dot OH -> center dot CH2O2 -> center dot CHO2 -> CO2). Consequently, the contribution of the primary CO formation route (center dot CHO -> CO + center dot H) decreases by 4.327%, and that of the main CO2 formation route (center dot CHO2 -> CO2 + center dot H) declines by 0.677%. The reduced center dot OH concentration also suppresses center dot CH3 generation, leading to a 0.578% decrease in the contribution of the reaction center dot OH + CH4 -> center dot CH3 + H2O. In addition, metal oxides formed during the suppression process firmly coat the coal dust surface, enhancing its thermal stability and mechanical strength, which further mitigates the explosibility. This study provides valuable insights for the development of high-efficiency explosion suppressants and the enhancement of safety in coal mining.
In contrast to the impressive dynamic current gain and cut-off frequency demonstrated by graphene field-effect transistors (GFETs), which compete with mature high-frequency (HF) technologies, GFETs still stay behind their HF counterparts in terms of power amplification and maximum oscillation frequency. This limitation is tipycally attributed to the absence of an energy bandgap, which leads to poor current saturation and hence high output conductance ( g_ds ), despite the exceptionally high carrier mobility attained in graphene and corresponding high transconductance ( g_m ). Indeed, the intrinsic voltage gain of GFETs ( A_v,i=g_m/g_ds ) is not competitive with that of conventional high-frequency technologies. As a consequence of this back-of-the-envelope reasoning, the study of the most relevant metrics of amplifiers at higher frequencies, i.e. the power gain, has been often disregarded. In this work, a comprehensive analysis of the physics-based small-signal parameters of GFETs reveals that strong current saturation and the resulting low g_ds are not mandatory for achieving reasonable power gain levels in the GHz range, demonstrating that A_v,i is not critical for HF performance evaluation. Specifically, we project a maximum stable gain exceeding 5 dB at 2.4 GHz in fabricated 1- μ m-long GFETs with A_v,i < 1 . This work provides a new perspective on performance improvement in GFET-based power gain amplifiers, showing that high carrier mobility and selecting the bias point with a focus on transconductance, as the most relevant figure of merit for amplifier operation, are crucial, while microwave stability must also be properly addressed.
This study investigates the influence of high rice husk ash (RHA) dosages (up to 40%) and particle sizes (5-100 mu m) on the permeability, hydration, and microstructural properties of ultrahigh-performance concrete (UHPC). Experimental assessments included water absorption, chloride migration coefficient, and electrical flux measurements, supported by microstructural characterization using mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Results demonstrated that fine RHA particles (<= 5 mu m) significantly enhance UHPC impermeability by reducing porosity, increasing gel pores, and promoting secondary hydration reactions. At 40% replacement, fine RHA achieved water absorption levels comparable to those of the control sample and reduced chloride migration by 17.2%, demonstrating its ability to maintain or improve performance at high dosages. In contrast, coarse RHA particles (>= 50 mu m) increased porosity by 45% and compromised durability, leading to higher chloride penetration. Furthermore, fine RHA improved hydration efficiency by consuming calcium hydroxide (CH) and generating additional calcium silicate hydrate (C & horbar; S & horbar; H) gel, whereas coarse particles exhibited lower pozzolanic activity and left unreacted residues, adversely affecting performance. The findings provide critical insights for optimizing RHA incorporation in UHPC, balancing performance, cost, and sustainability.
In Northeast China's degraded croplands, nitrate (NO3--N) leaching is the dominant pathway for fertilizer-nitrogen (N) loss, which presents an increasing threat to the quality of groundwater. Conservation tillage, defined as no-tillage (NT) and straw retention, is a widely adopted management strategy to maintain cropland fertility in the black soil (BS) regions. At present, however, the impact of shifting from conventional to conservation tillage on the vertical distribution and regulatory mechanisms of NO3--N derived from applied fertilizer-N (F-NO3) remains poorly understood. Based on a 12-year field experiment, we integrated N-15-tracing field monitoring with N-15-paired-labeling incubation to quantify the vertical migration of F-NO3 into deep soil profiles, and specify the dominant processes regulating N retention and supply. Across the tested BS croplands, total NO3--N production rates (4.06-6.58 mg N kg(-1) soil day(-1)) were faster than their consumption rates (0.36-0.92 mg N kg(-1) soil day(-1)), leading to a net accumulation of NO3--N, and implying a potential for leaching of NO3--N, from the perspective of substrate availability. The results of the field N-15 micro-plot experiment also indicated that, by maize maturity in the first growing season, an average of 7.5% of F-NO3 had migrated to the 80-100 cm soil layer. During the following two growing seasons, the maximum accumulation of F-NO3 had shifted downward to 140-160 cm and 180-220 cm, respectively. Such a pattern, particularly in light of the increased extreme precipitation in the studied regions, raises clear concerns about NO3--N leaching losses. Compared with conventional management, no-tillage with full-rate straw mulching decreased net rates of NO3--N production from 6.22 to 3.14 mg N kg(-1) soil day(-1). This reduction resulted from a decline in the gross oxidation of NH4+-N to NO3--N (from 6.39 to 3.70 mg N kg(-1) soil day(-1)) and an increase in DNRA (from 0.35 to 0.85 mg N kg(-1) soil day(-1)), which collectively delayed the downward transport of F-NO3. Conservation tillage also increased the gross rate of heterotrophic nitrification (from 0.19 to 0.36 mg N kg(-1) soil day(-1)) and its proportion relative to total nitrification (from 2.8% to 8.9%). Despite this shift, autotrophic nitrification remained the dominant process for NO3--N production in the tested BS croplands, likely due to a pH constraint on heterotrophic nitrification. With the increasingly widespread promotion of conservation tillage for soil fertility improvement, heterotrophic nitrification warrants greater attention, particularly in BS regions where pH < 6.5 and C/N contents are relatively high. Collectively, our findings provide a scientific basis for tailoring tillage practices to maintain sustainable agriculture in Northeast China.
Ceramic/metal composite armor faces limitations in lightweighting, environmental adaptability, and multi-impact resistance. This study proposes a bio-inspired gradient-structured modified polyurethane (PU)/ceramic composite armor. The PU matrix, modified via dynamic covalent disulfide (S-S) bonds, exhibits excellent self-healing (> 95
