Phononic Stiefel-Whitney topology with corner vibrational modes in two-dimensional Xenes and ligand-functionalized derivatives

Two-dimensional (2D) Stiefel-Whitney (SW) insulator is a fragile topological state characterized by the second SW class in the presence of space-time inversion symmetry. So far, SWIs have been proposed in several electronic materials but seldom in phononic systems. Here we recognize that a large class of 2D buckled honeycomb crystals termed Xenes and their ligand-functionalized derivatives realize the nontrivial phononic SW topology. The phononic SWIs are identified by a nonzero second SW number $w_2=1$, associated with gaped edge states and robust topological corner modes. Despite the versatility of electronic topological properties in these materials, the nontrivial phononic SW topology is mainly attributed to the double band inversion between in-plane acoustic and out-of-plane optical bands with opposite parities due to the structural buckling of the honeycomb lattice. Our findings not only reveal an overlooked phononic topological property of 2D Xene-related materials, but also afford abundant readily synthesizable material candidates with simple phononic spectra for further experimental studies of phononic SW topology physics.Comment: Phys. Rev. B (in press

Liganded Xene as a Prototype of Two-Dimensional Stiefel-Whitney Insulators

Two-dimensional (2D) Stiefel-Whitney insulator (SWI), which is characterized by the second Stiefel-Whitney class, is a new class of topological phases with zero Berry curvature. As a novel topological state, it has been well studied in theory but seldom realized in realistic materials. Here we propose that a large class of liganded Xenes, i.e., hydrogenated and halogenated 2D group-IV honeycomb lattices, are 2D SWIs. The nontrivial topology of liganded Xenes is identified by the bulk topological invariant and the existence of protected corner states. Moreover, the large and tunable band gap (up to 3.5 eV) of liganded Xenes will facilitate the experimental characterization of the 2D SWI phase. Our findings not only provide abundant realistic material candidates that are experimentally feasible, but also draw more fundamental research interest towards the topological physics associated with Stiefel-Whitney class in the absence of Berry curvature.Comment: 6 pages 3figure

Hydrothermal Changes and Physicochemical Characteristics of Subtropical Subalpine Soils under Freezing and Thawing

The soil column samples were collected for indoor simulated freeze-thaw experiments to monitor the soil hydrothermal dynamics and measure the basic physicochemical properties to research the effects of freeze-thaw on the hydrothermal process of peat bog soil and its relationship with physicochemical properties. The results indicate that in the initial phase of freezing-thawing, soil water content decreases and soil temperature changes, respectively. Unfrozen water content in soil in the stable freezing period decreases sharply. Compared with the freezing period, the fluctuation of soil moisture rate during thawing is more moderate with the temperature change. Soil ammonium nitrogen content decreases with decreasing soil temperature and is significantly positively correlated with soil water content after freeze-thaw, while total phosphorus, fast-acting phosphorus, total nitrogen and nitrate have no significant correlation with soil temperature and soil moisture content after freeze-thaw

Hydrothermal Changes and Physicochemical Characteristics of Subtropical Subalpine Soils under Freezing and Thawing

The soil column samples were collected for indoor simulated freeze-thaw experiments to monitor the soil hydrothermal dynamics and measure the basic physicochemical properties to research the effects of freeze-thaw on the hydrothermal process of peat bog soil and its relationship with physicochemical properties. The results indicate that in the initial phase of freezing-thawing, soil water content decreases and soil temperature changes, respectively. Unfrozen water content in soil in the stable freezing period decreases sharply. Compared with the freezing period, the fluctuation of soil moisture rate during thawing is more moderate with the temperature change. Soil ammonium nitrogen content decreases with decreasing soil temperature and is significantly positively correlated with soil water content after freeze-thaw, while total phosphorus, fast-acting phosphorus, total nitrogen and nitrate have no significant correlation with soil temperature and soil moisture content after freeze-thaw

Economical energy allocation for the landward invasion of Spartina alterniflora in estuaries in the Yellow River Delta, east China

Smooth cordgrass (Spartina alterniflora) introduced to China in 1970 s for coastline stabilization threatening the habitat range of native Phragmites australis and even become more adaptive than P. australis. Thus, we used electronic universal testing machine and Van Soest method to compare the morphological and biomechanical responses of these two species to wave interference in the Yellow River Delta, east China. Our study showed that the morphological response of P. australis was more sensitive to waves with shorter individuals in wave zones but larger stem diameter and higher biomass than those in none-wave zones, while S. alterniflora did not exhibit such variations. In wave zones, S. alterniflora invaded P. australis’ habitat regardless higher stem-bending resistance of P. australis with excessive energy allocated in stem growth while decreasing reproduction and fitness. Compared with the none-wave zones, S. alterniflora allocated excessive energy in the stem to resist wind interference, and they are less fitted than P. australis. Thus, economic energy allocation to wave mechanical interference contributed to the successful invasion of S. alterniflora to landward in estuaries. S. alterniflora continued to expand landward in a semi-saline area but the community pattern may maintain the status quo for areas with low salinity and high wave interference

Application and Evaluation of the China Meteorological Assimilation Driving Datasets for the SWAT Model (CMADS) in Poorly Gauged Regions in Western China

The temporal and spatial differentiation of the underlying surface in East Asia is complex. Due to a lack of meteorological observation data, human cognition and understanding of the surface processes (runoff, snowmelt, soil moisture, water production, etc.) in the area have been greatly limited. With the Heihe River Basin, a poorly gauged region in the cold region of Western China, selected as the study area, three meteorological datasets are evaluated for their suitability to drive the Soil and Water Assessment Tool (SWAT): China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS), Climate Forecast System Reanalysis (CFSR), and Traditional Weather Station (TWS). Resultingly, (1) the runoff output of CMADS + SWAT mode is generally better than that of the other two modes (CFSR + SWAT and TWS + SWAT) and the monthly and daily Nash–Sutcliffe efficiency ranges of the CMADS + SWAT mode are 0.75–0.95 and 0.58–0.77, respectively; (2) the CMADS + SWAT and TWS + SWAT results were fairly similar to the actual data (especially for precipitation and evaporation), with the results produced by CMADS + SWAT lower than those produced by TWS + SWAT; (3) the CMADS + SWAT mode has a greater ability to reproduce water balance than the other two modes. Overestimation of CFSR precipitation results in greater error impact on the uncertainty output of the model, whereas the performances of CMADS and TWS are more similar. This study addresses the gap in the study of surface processes by CMADS users in Western China and provides an important scientific basis for analyzing poorly gauged regions in East Asia

Chronic fatigue syndrome patients have alterations in their oral microbiome composition and function.

Host-microbe interactions have been implicated in the pathogenesis of chronic fatigue syndrome (CFS), but whether the oral microbiome is altered in CFS patients is unknown. We explored alterations of the oral microbiome in Chinese Han CFS patients using 16S rRNA gene sequencing and alterations in the functional potential of the oral microbiome using PICRUSt. We found that Shannon and Simpson diversity indices were not different in CFS patients compared to healthy controls, but the overall oral microbiome composition was different (MANOVA, p < 0.01). CFS patients had a higher relative abundance of Fusobacteria compared with healthy controls. Further, the genera Leptotrichia, Prevotella, and Fusobacterium were enriched and Haemophilus, Veillonella, and Porphyromonas were depleted in CFS patients compared to healthy controls. Functional analysis from inferred metagenomes showed that bacterial genera altered in CFS patients were primarily associated with amino acid and energy metabolism. Our findings demonstrate that the oral microbiome in CFS patients is different from healthy controls, and these differences lead to shifts in functional pathways with implications for CFS pathogenesis. These findings increase our understanding of the relationship between the oral microbiota and CFS, which will advance our understanding of CFS pathogenesis and may contribute to future improvements in treatment and diagnosis

Fast mobility induced self-lubrication at metallic glass surface

The enhanced surface mobility in metallic glasses (MGs) has been a constant source of fascination due to its unique mechanical properties. We show experimentally that the mobile surface layer of MGs functions as a lubricating layer in friction experiments, which is evidenced by a reduction of a friction coefficient of 50% or less and suppression of dissipative stick-slip behavior with decreasing scratch depth down to nanoscale in the various MGs. The lubrication mechanism could be attributed to easier shearing of the mobile surface layer induced by homogeneous plastic flow. Importantly, the thickness of the self-lubricating layer is inversely proportional to glass transition temperature with a higher homologous temperature yielding a larger thickness. These results extend the fundamental understanding of the ubiquitous MG surface and present a path for the rational design of self-lubricating materials