A lumped bubble capacitance model controlled by matrix structure to describe layered biogenic gas bubble storage in shallow subtropical peat

Methane (CH4) accumulates in the gaseous phase in peat soils, being released to the atmosphere at rates higher than those for diffusion and plant‐mediated pathways. An understanding of the mechanisms regulating gas bubble storage in peat remains incomplete. We developed a layered capacitance model to compare the bubble storage ability of peat over different depths. A peat monolith (0.395 m × 0.243 m × 0.247 m) was collected from the U.S. Everglades and kept submerged for 102 days from a condition of minimum bubble storage to bubble saturation. Time‐lapse electromagnetic wave velocity and power spectrum data were used to estimate changes in both gas content and relative average dimensions of stored bubbles with depth. Bubble capacitance, defined as the increase in volumetric gas content (m3 m−3) divided by the corresponding pressure (Pa), ranges from 3.3 × 10−4 to 6.8 × 10−4 m3 m−3 Pa−1, with a maximum at 5.5 cm depth Bubbles in this hotspot were larger relative to those in deeper layers, while the decomposition degree of the upper layers was generally smaller than that of the lower layers. X‐ray computed tomography on peat sections identified a specific depth with a low void ratio, and likely regulating bubble storage. Our results suggest that bubble capacitance is related to (1) the difference in size between bubbles and peat pores, and (2) the void ratio. Our work suggests that changes in bubble size associated with variations in water level driven by climate change will modify bubble storage in peat soils

Phase transition and anomalous electronic behavior in layered dichalcogenide CuS (covellite) probed by NQR

Nuclear quadrupole resonance (NQR) on copper nuclei has been applied for studies of the electronic properties of quasi-two-dimensional low-temperature superconductor CuS (covellite) in the temperature region between 1.47 and 290 K. Two NQR signals corresponding to two non-equivalent sites of copper in the structure, Cu(1) and Cu(2), has been found. The temperature dependences of copper quadrupole frequencies, line-widths and spin-lattice relaxation rates, which so far had never been investigated so precisely for this material, altogether demonstrate the structural phase transition near 55 K, which accompanies transformations of electronic spectrum not typical for simple metals. The analysis of NQR results and their comparison with literature data show that the valence of copper ions at both sites is intermediate in character between monovalent and divalent states with the dominant of the former. It has been found that there is a strong hybridization of Cu(1) and Cu(2) conduction bands at low temperatures, indicating that the charge delocalization between these ions takes place even in 2D regime. Based on our data, the occurrence of energy gap, charge fluctuations and charge-density waves, as well as the nature of phase transition in CuS are discussed. It is concluded that some physical properties of CuS are similar to those of high-temperature superconductors (HTSC) in normal state.Comment: to be publishe

Правда коммунизма. 1959. № 002

Because of its electrically conducting properties combined with excellent thermal stability and transparency throughout the visible spectrum, tin oxide (SnO2) is extremely attractive as a transparent conducting material for applications in low-emission window coatings and solar cells, as well as in lithium-ion batteries and gas sensors. It is also an important catalyst and catalyst support for oxidation reactions. Here, we describe a novel nonaqueous sol-gel synthesis approach to produce tin oxide nanoparticles (NPs) with a low NP size dispersion. The success of this method lies in the nonhydrolytic pathway that involves the reaction between tin chloride and an oxygen donor, 1-hexanol, without the need for a surfactant or subsequent thermal treatment. This one-pot procedure is carried out at relatively low temperatures in the 160-260 °C range, compatible with coating processes on flexible plastic supports. The NP size distribution, shape, and dislocation density were studied by powder X-ray powder diffraction analyzed using the method of whole powder pattern modeling, as well as high-resolution transmission electron microscopy. The SnO2 NPs were determined to have particle sizes between 3.4 and 7.7 nm. The reaction products were characterized using liquid-state 13C and 1H nuclear magnetic resonance (NMR) that confirmed the formation of dihexyl ether and 1-chlorohexane. The NPs were studied by a combination of 13C, 1H, and 119Sn solid-state NMR as well as Fourier transform infrared (FTIR) and Raman spectroscopy. The 13C SSNMR, FTIR, and Raman data showed the presence of organic species derived from the 1-hexanol reactant remaining within the samples. The optical absorption, studied using UV-visible spectroscopy, indicated that the band gap (Eg) shifted systematically to lower energy with decreasing NP sizes. This unusual result could be due to mechanical strains present within the smallest NPs perhaps associated with the organic ligands decorating the NP surface. As the size increased, we observed a correlation with an increased density of screw dislocations present within the NPs that could indicate relaxation of the stress. We suggest that this could provide a useful method for band gap control within SnO2 NPs in the absence of chemical dopants