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Volumetric changes induced by soil moisture phase changes can lead to pore system redistribution in freezing and thawing soil, which in turn affects soil strength and stability. The prefreezing water content and the number of freeze–thaw cycles (FTCs) affecting key factors of soil pore changes, and they determine the volumetric change magnitude and frequency during ice–water phase transitions. This study aims to reveal the effect of the prefreezing water content and the number of freeze–thaw cycles on the pore size distribution (PSD) of black soil, meadow soil and chernozem, which account for the largest arable land area in Heilongjiang Province, China. In situ soil samples with different prefreezing water contents were subjected to 1, 2, 3, 5, 10, and 20 FTCs, and then nuclear magnetic resonance (NMR) was used to quantify the PSD. It was shown that the pore sizes of the three soil types spanned multiple orders of magnitude, ranging from 0.001 to 100 μm overall. The inflection point of the cumulative porosity curves of all three soils occurred near 0.1 μm. For black soil and chernozem with high prefreezing water contents, when the number of FTCs reached 10 or 20, the soil self-weight led to thaw settlement, which reduced the difference in the total porosity of the soils with varying moisture contents. The initial FTC exerts the most significant influence on the pore structure. The impact of the prefreezing water content on soil pore structure diminishes as the number of FTCs increases. The plant root residues rendered meadow soil less sensitive to water content differences after the first FTCs but also limited the development of macropores during the late freeze–thaw period. The prefreezing water content alters the distribution of soil moisture before freezing and has a greater influence on the pore distribution of frozen-thawed soils compared to the cumulative effect of multiple FTCs. [ABSTRACT FROM AUTHOR]

The soil freezing characteristic curve (SFCC) describes the relationship between the freezing point and unfrozen water content, which are two critical parameters in depicting the heat, solute, and water transport in frozen soil. In this paper, we propose a novel Generalized Clapeyron Equation (GCE)-based model, the GCE-Salt Model, to better capture the SFCC in frozen soil in the presence of solute. It keeps the matric potential Ψf in the GCE as its original meaning and incorporates the effect of solute potential in the equilibrium freezing temperature. The performance of our GCE-Salt Model was validated by both lab and field experimental data and compared with related models (Combined Model and GCE-Tan Model). The GCE-Salt Model performed exceptionally well in extremely saline soil and it performed well in both non-saline and saline soil. (1) Our GCE-Salt Model could capture the SFCC of non-saline soil equally as well as the Combined Model (NSE = 0.866); (2) our GCE-Salt Model performed similarly well as the Combined Model and a little better than the GCE-Tan Model for the slightly to highly saline soil (NSE ≥ 0.80 for three models); and (3) our GCE-Salt Model (NSE = 0.919) beat the Combined Model (NSE = 0.863) and the GCE-Tan Model (NSE = 0.62) in capturing the SFCC of extremely saline soil, mainly because the inherent expression of our GCE-Salt Model can more accurately capture the freezing point. Our findings highlight the effect of solute potential on the ice–water change and could improve the understanding of the effect of freezing and thawing on the thermal–hydrological processes, structure of saline soil, and landscape evolution in cold regions. [ABSTRACT FROM AUTHOR]

Generally, straw return can reduce soil freezing depth and inhibit soil evaporation in cold/dry agricultural regions. However, when crushed corn straw is returned with thoroughly mixed with the topsoil (0–20 cm), the influence on water and heat flux during soil freezing and thawing is still unclear. In this study, two years straw return experiments of total 9 treatments for 3 straw returns (1.6, 0.8 kg m−2, no return) and 3 autumn irrigation amounts (180, 135, 90 mm) were conducted in 27 lysmeters with bottomless. Spatial and temporal dynamics of water and heat within soil profiles were continuously observed for freezing and thawing period. The results showed that straw return inhibited the decrease and increase of soil temperature during the freeze-thaw period. Furthermore, straw return reduced the freezing rate and delayed the complete thawing date. Results showed that effect of straw return on soil temperature and water were affected obviously by irrigation amount. Finally, straw return can restrained soil evaporation after soil thawing completely, and the soil unfrozen water content and the total water content were higher for treatments with the straw return to topsoil. Our findings can enhance the understanding to soil temperature and water dynamics for freeze-thaw period. • Straw return delayed the freezing and thawing process, inhibited topsoil temperature fluctuation. • With increased autumn irrigation, the straw return cleanly reduced the soil freezing rate and depth. • Straw return increased the topsoil water content during the freeze-thaw period, especially after compete thawing. [ABSTRACT FROM AUTHOR]

This study proposed what we believe to be a novel method for fabricating superconducting nanowire single-photon detectors (SNSPDs) with high efficiency, polarization insensitivity, and ultrafast response. To achieve these properties in niobium nitride (NbN) SNSPDs, the periodic four-split rings (PFSR) were positioned above the nanowires. This design uses the localized surface plasmon resonance to enhance the electric field around nanowires. For an incident light with a wavelength of 1550 nm, the PFSR-SNSPD structure achieved a polarization extinction ratio of 1.0064 and absorptions of 88.94% and 88.37% under TE and TM polarizations, respectively. The nanowire length was reduced by 85% using a meandering nanowire arrangement with a fill factor of 0.074.

The stoichiometric characteristics of water-soluble ions (WSIs) in PM 2.5 , which can be used as an indicator socioeconomic development level, are mostly depending on the sources and formation mechanism of PM 2.5 . This work presents the stoichiometric characteristics and socioeconomic linkage of WSIs in PM 2.5 from a resource-dependent city. The relationship between NO 3 - /SO 4 2- and car parc indexes the contribution of mobile emission source. The equivalent ratio of WSIs suggested that aerosol particles were weak acidic due to the deficiency of cations in PM 2.5 , which was consistent with the average annual pH (6.27) of precipitation in Wuhai in 2015. NH 4 + neutralizes PM 2.5 acidity in clean and polluted days, while Ca 2+ and NH 4 + in dust storm days. Furthermore, the PCA analysis indicated the multi-sources pollution characteristics from Spring to Fall, which was related the small build-up area (only 62.30 km 2 ) and the close-set of various industrial enterprises in Wuhai. The ratios of NO 2 /SO 2 may not work effectively to identify the importance of mobile versus stationary pollution emission sources when the heavy emission from the secondary industry, especially the proportion of secondary industry higher than 65% and the ratios of NO 2 /SO 2 lower than 0.4. This work contributes to more effective control strategies for PM 2.5 in resource-dependent areas., (Copyright © 2020 Elsevier Inc. All rights reserved.)