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1. chinaXiv:202006.00230 [pdf]

Tree ring based drought variability in Northwest Tajikistan since 1895 AD

YANG Meilin; YU Yang; ZHANG Haiyan; WANG Qian; GAN Miao; YU Ruide
Subjects: Geosciences >> History of Geosciences

Determining the mechanisms controlling the changes of wet and dry conditions will improve our understanding of climate change over the past hundred years, which is of great significance to the study of climate and environmental changes in the arid regions of Central Asia. Forest trees are ecologically significant in the local environment, and therefore the tree ring analysis can provide a clear record of regional historical climate. This study analyzed the correlation between the tree ring width chronology of Juniperus turkestanica Komarov and the standardized precipitation evapotranspiration index (SPEI) in Northwest Tajikistan, based on 56 tree ring samples collected from Shahristan in the Pamir region. Climate data including precipitation, temperature and the SPEI were downloaded from the Climate Research Unit (CRU) TS 4.00. The COFECHA program was used for cross-dating, and the ARSTAN program was used to remove the growth trend of the tree itself and the influence of non-climatic factors on the growth of the trees. A significant correlation was found between the radial growth of J. turkestanica trees and the monthly mean SPEI of February–April. The monthly mean SPEI sequence of February–April during the period of 1895–2016 was reconstructed, and the reconstruction equation explained 42.5% of the variance. During the past 122 a (1895–2016), the study area has experienced three wetter periods (precipitation above average): 1901–1919, 1945–1983 and 1995–2010, and four drier periods (precipitation below average): 1895–1900, 1920–1944, 1984–1994 and 2011–2016. The spatial correlation analysis revealed that the monthly mean SPEI reconstruction sequence of February–April could be used to characterize the large-scale dry-wet variations in Northwest Tajikistan during the period of 1895–2016. This study could provide comparative data for validating the projections of climate models and scientific basis for managing water resources in Tajikistan in the context of climate change.

submitted time 2020-06-22 From cooperative journals:《Journal of Arid Land》 Hits182Downloads89 Comment 0

2. chinaXiv:201705.00074 [pdf]

Graphene oxide liquid crystals for reflective displays without polarizing optics

He, LQ [He, Liqun][ 1 ]; Ye, J [Ye, Jian][ 2 ]; Shuai, M [Shuai, Min][ 3 ]; Zhu, Z [Zhu, Zhuan][ 4 ]; Zhou, XF [Zhou, Xufeng][ 5 ]; Wang, YA [Wang, Yanan][ 4 ]; Li, Y [Li, Yang][ 4 ]; Su, ZH [Su, Zhihua][ 4 ]; Zhang, HY [Zhang, Haiyan][ 2 ]; Chen, Y [Chen, Ying][ 2 ]; Liu, ZP [Liu, Zhaoping][ 5 ]; Cheng, ZD [Cheng, Zhengdong][ 3 ]; Bao, JM [Bao, Jiming][ 4 ]
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The recent emergence of liquid crystals of atomically thin two- dimensional (2D) materials not only has allowed us to explore novel phenomena of macroscopically aligned 2D nanomaterials but also has provided a route toward their controlled assembly into three-dimensional functional macrostructures. Using flow- induced mechanical alignment, we prepared flakes of graphene oxide (GO) in different orientational orders and demonstrated that GO liquid crystals (LC) can be used as rewritable media for reflec- tive displays without polarizing optics. With a wire or stick as a pen, we can make the surface of GO LC reflective and bright, and we can then manually draw lines, curves, and any patterns with dark appearance. The contrast between bright and dark features is due to anisotropic optical responses of ordered GO flakes. Since optical anisotropy is an intrinsic property of 2D structures, our observations and demonstration represent one of many potential applications of macroscopically aligned 2D nanomaterials.

submitted time 2017-05-02 Hits515Downloads337 Comment 0

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