MODIS-Derived Spatiotemporal Changes of Major Lake Surface Areas in Arid Xinjiang, China, 2000–2014

Inland water bodies, which are critical freshwater resources for arid and semi-arid areas, are very sensitive to climate change and human disturbance. In this paper, we derived a time series of major lake surface areas across Xinjiang Uygur Autonomous Region (XUAR), China, based on an eight-day MODIS time series in 500 m resolution from 2000 to 2014. A classification approach based on water index and dynamic threshold selection was first developed to accommodate varied spectral features of water pixels at different temporal steps. The overall classification accuracy for a MODIS-derived water body is 97% compared to a water body derived using Landsat imagery. Then, monthly composites of water bodies were derived for the months of April, July, and September to identify seasonal patterns and inter-annual dynamics of 10 major lakes (\u3e100 km2) in XUAR. Our results indicate that the changing trends of surface area of major lakes varied across the region. The surface areas of the Ebinur and Bosten Lakes showed a significant shrinking trend. The Ulungur-Jili Lake remained relatively stable during the entire period. For mountain lakes, the Barkol Lake showed a decreasing trend in April and July, but the Sayram Lake showed a significant expanding trend in September. The four plateau lakes exhibited significant expanding trends in all three seasons except for Arkatag Lake in July. The shrinking of major lakes reflects severe anthropogenic impacts due to agricultural and industrial needs, in addition to the impact of climate change. The pattern of lake changes across the XUAR can provide insight into the impact of climate change and human activities on regional water resources in this arid and semi-arid region

Densification and Mechanical Properties of ZrN-Nb Composites

Densification of zirconium nitride (ZrN) ceramics was investigated by vacuum hot pressing at temperatures range from 1500℃to 2000℃with Nb as sintering additive. Densification was enhanced with Nb addition. ZrN with 5mol% Nb addition achieved a relative density of 98.5% at 1600℃.XRD and lattice parameter measurements indicated that there were structural differences between samples sintered in different temperatures. It was likely that due to the presence of point defects by changes in stoichiometry, the kinetics of mass transport enhanced. As a result, the relative density of the zirconium nitride (ZrN) ceramics have been improved, thus the fully densed ZrN ceramics can be prepared in a relative low temperature. The density, the room-temperature mechanical properties of ZrN ceramics are increased after the addition of Nb. Zirconium nitride (ZrN)doped with Nb sintered at 1600℃ are measured and obtained elasticity modulus of 238 GPa, flexural strength of 463.3 MPa, fracture toughness of 7.0 MPa·m1/2 and hardness of 10.7 GPa

Microstructure and Mechanical Properties of ZrC-TaC Ceramic Prepared by Hot Pressing Sintering

Zirconium carbide which is a kind of ultra high temperature ceramics has broad application prospects in the aerospace, nuclear technology, electronics and other fields. In order to improve the sintering properties and mechanical properties of ZrC ceramics, using ZrO2 powder and TaO2 powder as raw materials, TaC and ZrC solid solution powder were prepared by carbon thermal reduction, and the hot pressing sintering process was used to prepare ZrC-TaC ceramics. The effect of the sintering temperature on the solid solution behavior, densification behavior, tissue structure and mechanical properties was studied. The results show that the TaC in ZrC solid solubility is enhanced when the temperature is increased from 2000 ℃ to 2050 ℃.When TaC content is increased from 5% to 15%, the density of the composite, vickers hardness, fracture toughness and elastic modulus are decreased monotonously, and the bending strength has no apparent rule

ZnxCd1-xS/g-C3N4 nanocomposites: synthesis, characterization, and photocatalytic activity

In this work, we prepared ZnxCd1-xS/g-C3N4 nanocomposites with excellent catalytic effect by the simple chemical precipitation method. The ZnxCd1-xS/g-C3N4 composite with excellent effect of degrading methylene blue (MB) was prepared by adjusting the ratio of Zn to Cd. The Zn0.25Cd0.75S/g-C3N4 nanocomposites have the highest degradation efficiency, which can reach 92.25%. The specific surface area and visible light absorption range are increased by the synergistic effect of the combination of ZnxCd1-xS and g-C3N4. The ZnxCd1-xS/g-C3N4 nanocomposites prepared by this study with excellent photocatalytic properties provide a method for the preparation of new composite materials in the future.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Credible Navigation Algorithm for GNSS Attack Detection Using Auxiliary Sensor System

In order to effectively reduce the impact of Global Navigation Satellite System (GNSS) attacks while providing mobile terminals with credible navigation and positioning results, this paper proposes a credible navigation algorithm for GNSS attack detection using an auxiliary sensor system. Based on a credible Kalman filter and measurement information provided by the auxiliary sensor system on mobile terminals, the proposed algorithm can verify the credibility of the GNSS positioning result and determine whether it has suffered from a GNSS attack using the credible verification window and the credible verification threshold. According to the verification results, the algorithm can adaptively select an updated model for measurement correction and achieve a credible navigation result. The algorithm proposed in this paper has been verified on a self-developed mobile terminal, and the experimental results show that the algorithm can provide credible navigation and positioning services for mobile terminals in the context of GNSS attacks

Patterns and Potential Drivers of Dramatic Changes in Tibetan Lakes, 1972–2010

<div><p>Most glaciers in the Himalayas and the Tibetan Plateau are retreating, and glacier melt has been emphasized as the dominant driver for recent lake expansions on the Tibetan Plateau. By investigating detailed changes in lake extents and levels across the Tibetan Plateau from Landsat/ICESat data, we found a pattern of dramatic lake changes from 1970 to 2010 (especially after 2000) with a southwest-northeast transition from shrinking, to stable, to rapidly expanding. This pattern is in distinct contrast to the spatial characteristics of glacier retreat, suggesting limited influence of glacier melt on lake dynamics. The plateau-wide pattern of lake change is related to precipitation variation and consistent with the pattern of permafrost degradation induced by rising temperature. More than 79% of lakes we observed on the central-northern plateau (with continuous permafrost) are rapidly expanding, even without glacial contributions, while lakes fed by retreating glaciers in southern regions (with isolated permafrost) are relatively stable or shrinking. Our study shows the limited role of glacier melt and highlights the potentially important contribution of permafrost degradation in predicting future water availability in this region, where understanding these processes is of critical importance to drinking water, agriculture, and hydropower supply of densely populated areas in South and East Asia.</p></div

Climate variations on the Tibetan Plateau since the 1970s.

<p>a, Map showing the northward migration of 5-year annual average zero-temperature isolines (at 4500 m a.s.l). b, c, d, Variations in annual average temperature (b), precipitation (c), and evaporation (d) in five regions (A–E). e, Potential evapotranspiration trends before and after 1998 derived from meteorological stations within the Tibetan Plateau. The increasing or decreasing trends over time are represented by the correlation coefficient, R (R>0 indicates an increasing trend, and R<0 a decreasing trend).</p

TRMM-derived precipitation trends in 1998–2012 on the Tibetan Plateau and its surrounding regions.

<p>a, Spatial distribution of TRMM-derived precipitation trends. b, Comparison between lake-level and precipitation trends for the 94 lake basins listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111890#pone.0111890.s012" target="_blank">Table S1</a>. The increasing or decreasing trends over time are represented by the correlation coefficient, R. c, Numbers of lake basins with similar and opposite trends between lake-level and precipitation changes.</p

Relations between lake change and glacier/permafrost coverage in each lake’s drainage basin.

<p>a, Relations between lake-level change rate in 2003–2009 (m/a) and glacier coverage (%). b, Numbers of expanding, stable, and shrinking lakes in drainage basins with 0% glacier coverage. c, Relations between lake-level change rate in 2003–2009 (m/a) and permafrost coverage (%). d, Numbers of expanding, stable, and shrinking lakes in drainage basins with 100% permafrost coverage.</p