Weak antilocalization and electron-electron interaction in coupled multiple-channel transport in a Bi2_2Se3_3 thin film

Electron transport properties of a topological insulator Bi$_2$Se$_3$ thin film are studied in Hall-bar geometry. The film with a thickness of 10 nm is grown by van der Waals epitaxy on fluorophlogopite mica and Hall-bar devices are fabricated from the as-grown film directly on the mica substrate. Weak antilocalization and electron-electron interaction effects are observed and analyzed at low temperatures. The phase-coherence length extracted from the measured weak antilocalization characteristics shows a strong power-law increase with decreasing temperature and the transport in the film is shown to occur via coupled multiple (topological surface and bulk states) channels. The conductivity of the film shows a logarithmically decrease with decreasing temperature and thus the electron-electron interaction plays a dominant role in quantum corrections to the conductivity of the film at low temperatures.Comment: 12 pages, 5 figure

Strong spin-orbit interaction and magnetotransport in semiconductor Bi2_2O2_2Se nanoplates

Semiconductor Bi$_2$O$_2$Se nanolayers of high crystal quality have been realized via epitaxial growth. These two-dimensional (2D) materials possess excellent electron transport properties with potential application in nanoelectronics. It is also strongly expected that the 2D Bi$_2$O$_2$Se nanolayers could be of an excellent material platform for developing spintronic and topological quantum devices, if the presence of strong spin-orbit interaction in the 2D materials can be experimentally demonstrated. Here, we report on experimental determination of the strength of spin-orbit interaction in Bi$_2$O$_2$Se nanoplates through magnetotransport measurements. The nanoplates are epitaxially grown by chemical vapor deposition and the magnetotransport measurements are performed at low temperatures. The measured magnetoconductance exhibits a crossover behavior from weak antilocalization to weak localization at low magnetic fields with increasing temperature or decreasing back gate voltage. We have analyzed this transition behavior of the magnetoconductance based on an interference theory which describes the quantum correction to the magnetoconductance of a 2D system in the presence of spin-orbit interaction. Dephasing length and spin relaxation length are extracted from the magnetoconductance measurements. Comparing to other semiconductor nanostructures, the extracted relatively short spin relaxation length of ~150 nm indicates the existence of strong spin-orbit interaction in Bi$_2$O$_2$Se nanolayers.Comment: 14 pages, 4 figures, and 5 pages of Supplementary Material

Universal conductance fluctuations and phase-coherent transport in a semiconductor Bi2_2O2_2Se nanoplate with strong spin-orbit interaction

We report on phase-coherent transport studies of a Bi$_2$O$_2$Se nanoplate and on observation of universal conductance fluctuations and spin-orbit interaction induced reduction in fluctuation amplitude in the nanoplate. Thin-layered Bi$_2$O$_2$Se nanoplates are grown by chemical vapor deposition (CVD) and transport measurements are made on a Hall-bar device fabricated from a CVD-grown nanoplate. The measurements show weak antilocalization at low magnetic fields at low temperatures, as a result of spin-orbit interaction, and a crossover toward weak localization with increasing temperature. Temperature dependences of characteristic transport lengths, such as spin relaxation length, phase coherence length, and mean free path, are extracted from the low-field measurement data. Universal conductance fluctuations are visible in the low-temperature magnetoconductance over a large range of magnetic fields and the phase coherence length extracted from the autocorrelation function is in consistence with the result obtained from the weak localization analysis. More importantly, we find a strong reduction in amplitude of the universal conductance fluctuations and show that the results agree with the analysis assuming strong spin-orbit interaction in the Bi$_2$O$_2$Se nanoplate.Comment: 11 pages, 4 figures, supplementary material

Spatial variability in soil pH and land use as the main influential factor in the red beds of the Nanxiong Basin, China

Soil pH is the main factor affecting soil nutrient availability and chemical substances in soil. It is of great significance to study the spatial variability of soil pH for the management of soil nutrients and the prediction of soil pollution. In order to explore the causes of spatial variability in soil pH in red-bed areas, the Nanxiong Basin in south China was selected as an example, and soil pH was measured in the topsoil by nested sampling (0–20 cm depth). The spatial variability characteristics of soil pH were analyzed by geostatistics and classical statistical methods, and the main factors influencing spatial variability in soil pH are discussed. The coefficient of variation in the red-bed areas of Nanxiong Basin was 17.18%, indicating moderate variability. Geostatistical analysis showed that the spherical model is the optimal theoretical model for explaining variability in soil pH, which is influenced by both structural and random factors. Analysis of the spatial distribution and pattern showed that soil pH is relatively high in the northeast and southwest, and is lower in the northwest. These results indicate that land use patterns and topographic factors are the main and secondary influencing factors, respectively

The Spatial Patterns of Red Beds and Danxia Landforms: Implication for the formation factors–China

This research examined the distribution features of red beds and 1,100 Danxia landform sites across China, while probing the relationship between these spatial patterns and geological elements. This study is based on geological and tectonic maps of China. ArcGIS software was used to process the adjacent index, then perform a spatial analysis of Danxia landforms and red beds, and a coupling analysis of Danxia landforms and red beds with tectonics. Based on a point pattern analysis of Danxia landforms, the adjacent index is 0.31, and the coefficient of variation verified by Thiessen polygon reaches 449%. These figures reflect the clustered distribution pattern of the Danxia landforms. Across the country, Danxia landforms are concentrated into three areas, namely, the Southeast China region, the Sichuan Basin region and the Qilian-Liupan region. The exposure of red beds covers 9.16 × 105 km2, which accounts for 9.5% of the total land area of China. With this research background, the geological elements of tectonics and their effects on the distribution, number, and spatial pattern of Danxia landforms and red beds were analyzed

Comparison of Water and Soil Conservation Effect of Trees, Shrubs and Grass in the Red Soil Area of Southern China

Assessing the effects of vegetation on water and soil conversation is the key basis for research and management of ecological restoration on water-eroded areas. In this study, the runoff depth, soil loss and corresponding precipitation of five plots planted respectively with Pueraria lobata, Lespedeza bicolor Turcz, Manglietia yuyuanensis Law, Paspalum natatu Fliigge, Paspalum wettsteinii Hackel and one control plot were observed monthly from 2003 to 2010 in Hetian town of Changting County, Fujian Province, a typical water-eroded area in southern China. Then the effects of different vegetation on water/soil conversation (RE/SE) were determined using the ratios of runoff depth/soil loss between vegetated plots to the control plot. Meanwhile, the effect of rainfall on the water and soil loss was also analyzed. The results showed that, both the water and soil conservation effects of Pueraria lobata and Manglietia yuyuanensis Law are better than Lespedeza bicolor Turcz and Paspalum natatu, while Paspalum wettsteinii Hackel are the worst. The differences of effects of water conservation are more significantly than those of soil conversation between five kinds of vegetations. The runoff depth is mainly affected by rainfall, the determination coefficients (R2) of linear regression models between rainfall and runoff depth of all planted plots are all greater than 0.9, whereas the determination coefficients of the linear regression models between rainfall and soil loss vary form 0.3 to 0.8 for different vegetated plots. These results provide a reference for vegetation reconstruction in the current and similar areas

Effects of high-temperature curing on hydration and microstructure of alkali-activated typical steel slag cementitious material

Hydration process, products, microstructure, and compressive strength of steel slag in alkaline environments at room and high temperature were investigated. Results show that high-temperature curing significantly promotes the early hydration, causing more products. The promoting effect of temperature becomes more apparent with higher activator content. The cumulative heat apparently increases by approximately twice at 6% alkali content. Increasing temperature has no effect on the types of products and hydration of inactive components. The products remain as Ca(OH)2 and C-(A)-S-H, but Ca/Si and Al/Si ratios significantly increase from 1.42 to 2.41 and from 0.14 to 0.21, respectively. High-temperature curing makes matrix denser, resulting in a substantial increase in the early strength. However, promoting effect on the strength diminishes over time. The growth rates of 28 d strength are only −1% and 4% at different alkali content. Moreover, alkali-activated steel slag material has great potential in the field of low-carbon cementitious materials

The pathogen Vibrio alginolyticus H1 and its antagonist Pseudoalteromonas piscicida H2 associated with the health status of cuttlefish Sepia pharaonis

The balance in bacterial community is very important for the maintenance of the health status in the hosts. During the occurrence of a pervasive skin ulcer disease in Sepia pharaonis, bacterial isolate H1 and its antagonist bacterial isolate H2 were simultaneously isolated from the healthy cuttlefish, but only bacterial isolate H1 was isolated from the diseased cuttlefish. In the present study, the genetic and biochemical analysis showed that isolate H1 was identified as Vibrio alginolyticus, and isolate H2 was identified as Pseudoalteromonas piscicida, respectively. The antibiotic susceptibility test using CLSI M45–2015 method showed that the antibiotic resistance of V. alginolyticus H1 and P. piscicida H2 was different, and V. alginolyticus H1 showed strongly resistance to ampicillin. LD50 was calculated based the infection using immerse infection experiment. The result showed that the LD50 for 7 d of V. alginolyticus H1 was 1.58 × 106 CFU/mL, while the no death was observed during the infection of P. piscicida H2. Since the virulence related factors were significantly influenced by host immunity, the virulence factors of pathogen V. alginolyticus H1 was assessed under the stressors of H2O2 and 2,2′-dipyridyl. The results showed that the pathogenicity of V. alginolyticus H1 was associated with the haemolytic activity and bacterial motility. Different components of the P. piscicida H2 were collected and were tested for the antagonistic activity. It was unexpected that no antagonistic substance was detected, while V. alginolyticus H1 showed obvious phobotaxis to P. piscicida H2. It could be concluded that V. alginolyticus H1 was a pathogen of S. pharaonis, and P. piscicida H2 was a potential antagonistic bacteria to inhibit V. alginolyticus H1 via chemotaxis instead of producing antagonistic substance

Downward Trends in Streamflow and Sediment Yield Associated with Soil and Water Conservation in the Tingjiang River Watershed, Southeast China

Soil erosion is one of the most serious environment problems in China. Soil and water conservation (SWC) measures play an important role in reducing streamflow and sediment yields. A nested watershed approach, together with the Mann–Kendall trend test, double mass curve, and path analysis were used to quantitatively explore hydrological effects of SWC measures in the Tingjiang River Watershed. Results showed the annual streamflow and sediment yields tended toward a remarkable downward trend since the implementation of SWC measures during 1982–2014, indicating that SWC measures produced significant hydrological effects. The contribution of precipitation to annual streamflow increased from 71% to 79% from the periods 1982–2000 to 2000–2014, indicating decreases in annual precipitation after 2003 and stronger impacts on streamflow than that of SWC measures. However, the contribution of SWC measures to sediment yields increased from 11% to 64% from 1982 to 2014 and gradually dominated contributions to the sediment yields in the watershed. An ecological threshold was established at which the proportion of the cumulative afforestation area due to SWC reaches 10% of the whole watershed, and the remarkable improvements of hydrological effects in the watershed can be observed. These findings could be used to evaluate performance of SWC measures in watersheds