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1. chinaXiv:202005.00092 [pdf]

Land cover change and eco-environmental quality response of different geomorphic units on the Chinese Loess Plateau

SONG Yongyong; XUE Dongqian; DAI Lanhai; WANG Pengtao; HUANG Xiaogang; XIA Siyou
Subjects: Biology >> Botany >> Applied botany

Land cover in the Chinese Loess Plateau has undergone dramatic changes since the late 1980s. Revealing the trend in land cover change and eco-environmental quality response of different geomorphic units in this stage is a realistic requirement for promoting sustainable development of the Chinese Loess Plateau. Based on the data of geomorphic units and land cover in 1990, 2000, 2010 and 2018 of the Chinese Loess Plateau, we studied the trend of land cover change and eco-environmental quality response of different geomorphic units by using a significance index of land cover change, a proportion index of land cover change and an eco-environmental response model. The results indicated that from 1990 to 2018, the areas of forestland and construction land substantially increased, whereas those of cropland, grassland, wetland and unused land considerably decreased. Land cover change exhibited large geomorphic differences, and the main conversion of land cover was from cropland into other land types. Unstable trend of land cover change in the loess tablelands and sandy loess hills declined, whereas the unstable trends in the other geomorphic units enhanced. Eco-environmental quality varied among different geomorphic units. The expansion of construction land and degradation of forestland, grassland and wetland resulted in the deterioration of eco-environmental quality. The conversion of cropland and unused land into forestland and grassland, and the conversion of grassland into forestland were the main factors that drove the improvement of eco-environmental quality. The findings of this study may provide theoretical reference and support decision making for the optimization of land use structure and the improvement of eco-environmental quality on the Chinese Loess Plateau.

submitted time 2020-05-31 From cooperative journals:《Journal of Arid Land》 Hits7782Downloads490 Comment 0

2. chinaXiv:201807.00035 [pdf]

Rainfall patterns of Algerian steppes and the impacts on natural vegetation in the 20th century

BELALA, Fahima ; HIRCHE, Azziz ; MULLER, Serge D ; Mahmoud, TOURKI; SALAMANI, Mostefa ; GRANDI, Mohamed ; AIT HAMOUDA, Tahar ; Madjid, BOUGHANI
Subjects: Geosciences >> Hydrology

Since 1960, the steppe regions of North Africa have been subject to an increasing desertification, including the degradation of traditional pastures. The initially dominant species (Artemisia herba-alba, Lygeum spartum and Stipa tenacissima) declined and were progressively replaced by other species (Atractylis serratuloides and Salsola vermiculata) that are more tolerant to the new conditions. It is not clear whether these changes are due to anthropogenic reasons or climatic determinism. We have carried out a statistical analysis of the climate to detect putative rainfall changes during the 20th century in the Algerian steppes based on data from 9 meteorological stations, including 2 Saharan stations (El Oued and Touggourt), 3 pre-Saharan stations (Biskra, Laghouat and Ain Sefra) and 4 steppe stations (Djelfa, Saida, Méchéria and El-Bayadh) located in the arid high plains, which represent the bioclimate diversities of the region. Previous studies suggested that significant rainfall changes for the 20th century only had records in the south of the Oran region. Most of the studies, however, looked at restricted territories over limited periods, and did not integrate the rainiest period 2004–2014. Our work is designed to integrate all the longest time series of meteorological data available for the steppe regions of Algeria. Our results confirm the spatial rainfall distribution (significant rainfall changes only recorded in the southwestern region) evidenced by previous studies, and reveal a decreasing rainfall gradient from northeastern to southwestern Algeria. Moreover, the results reveal a trend of significant decrease of rainfall in the southern Oran region, marked by two drought periods in 1980–1985 and 1999–2003. However, with the exception of the southwestern region, rainfall overall has not declined since the beginning of the 20th century. While less marked in other regions, the drought appear to have affected all territories of the Algerian steppe. Consequently, our study implies that the climate was not a leading influence in the on-going degradation of the vegetation cover of steppe landscapes. Such a vegetation evolution thus appears to be have been determined more by human activities than by climate forcing.

submitted time 2018-07-05 From cooperative journals:《Journal of Arid Land》 Hits1575Downloads523 Comment 0

3. chinaXiv:201804.02345 [pdf]

CO2, CH4 and N2O flux changes in degraded grassland soil of Inner Mongolia, China

BAI, Yunxiao; LI, Xiaobing; WEN, Wanyu; MI, Xue; LI, Ruihua; HUANG, Qi; ZHANG, Meng
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The main purpose of this study was to explore the dynamic changes of greenhouse gas (GHG) from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China. Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO2, CH4 and N2O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO2, CH4 and N2O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO2, CH4 and N2O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO2 and N2O and the sink for CH4. Compared with CO2 fluxes, N2O and CH4 fluxes were relatively low. The exchange of CO2, N2O and CH4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO2 fluxes of –33.63–386.36 mg/(m?h), CH4 uptake fluxes of 0.113–0.023 mg/(m?h) and N2O fluxes of –1.68–19.90 ?g/(m?h). Grassland degradation significantly influenced CH4 uptake but had no significant influence on CO2 and N2O emissions. Soil moisture and temperature were positively correlated with CO2 emissions but had no significant effect on N2O fluxes. Soil moisture may be the primary driving factor for CH4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.

submitted time 2018-04-24 From cooperative journals:《Journal of Arid Land》 Hits1405Downloads547 Comment 0

4. chinaXiv:201712.00324 [pdf]

Determinants and rates of land degradation: Application of stationary time-series model to data from a semi-arid environment in Kenya

Mganga, Kevin; Nyariki, Dickson
Subjects: Geosciences >> History of Geosciences

The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years (1973–2007). The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed: (1) woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and (2) an increase in undesirable woody species, livestock population and cultivated area had a significant (P<0.05) negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.

submitted time 2017-12-18 From cooperative journals:《Journal of Arid Land》 Hits1127Downloads705 Comment 0

5. chinaXiv:201711.00129 [pdf]

A New Iodiplumbate-based Hybird Constructed from Asymmetric Viologen and Polyiodides: Structure, Properties and Photocatalytic Activity for the Degradation of Organic Dye

WANG Dao-Hua; LIN Xiao-Yan; WANG Yu-Kang; ZHANG Wen-Ting; SONG Kai-Yue; LIN Heng; LI Hao-Hong; CHEN Zhi-Rong
Subjects: Chemistry >> Physical Chemistry

A new iodiplumbate/organic hybrid constructed from asymmetric viologen and polyiodides, (PBPY-H2)2[PbI4(I3)2] (1, PBPY = N-(propionate)-4,4?-bipyridinium), has been synthesized via solvothermal reaction and structurally determined by X-ray diffraction method. Compound 1 crystallizes in monoclinic system, space group P21/c with Mr = 1936.72, a = 11.622(2), b = 14.839(3), c = 13.372(2) ?, β = 109.447(3)°, V = 2174.6(7) ?3, Z = 2, Dc = 2.958 g/cm3, F(000) = 1712, μ(MoKα) = 11.011 mm–1, the final R = 0.0389 and wR = 0.0854 for 3866 observed reflections with I > 2σ(I). [PbI4(I3)2]4- mononuclear cluster of 1 features a seldom example of coordinated I3- donors for the lead center. Intermolecular hydrogen bonds between [PbI4(I3)2]4- clusters and (PBPY-H)24+ dimmers contribute to the formation of a 2-D layer. Its absorption spectrum was investigated, and lower energy band gap of 1.42 eV was explained by DFT calculation. Interestingly, 1 exhibits photocatalytic activity for the degradation of rhodamine B.

submitted time 2017-11-05 From cooperative journals:《结构化学》 Hits2604Downloads1129 Comment 0

6. chinaXiv:201711.00141 [pdf]

Facile Synthesis of Uniform Zinc-blende ZnS Nanospheres with Excellent Photocatalytic Activity爐oward Methylene燘lue Degradation

PENG Si-Yan; YANG Liu-Sai; LV Ying-Ying; YU Le-Shu; HUANG Hai-Jin; WU Li-Dan
Subjects: Chemistry >> Physical Chemistry

Uniform and well-dispersed ZnS nanospheres have been successfully synthesized via a facile chemical route. The crystal structure, morphology, surface area燼nd爌hotocatalytic properties of the爏ample were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and ultraviolet-visible (UV-vis) spectrum. The results of characterizations indicate that the products are identified as mesoporous zinc-blende ZnS nanospheres with an average diameter of 200 nm, which are comprised of nanoparticles with the crystallite size of about 3.2 nm calculated by XRD. Very importantly, photocatalytic燿egradation爋f爉ethylene blue (MB)爏hows that the as-prepared ZnS nanospheres exhibit excellent photocatalytic activity with nearly 100% of MB decomposed after UV-light irradiation for 25 min. The excellent photocatalytic activity of ZnS nanospheres can be ascribed to the large specific surface area and hierarchical mesoporous structure.

submitted time 2017-11-05 From cooperative journals:《结构化学》 Hits924Downloads440 Comment 0

7. chinaXiv:201705.00572 [pdf]

Surface degradation process affected by heterogeneity in nano-titanium dioxide filled acrylic urethane coatings under accelerated UV exposure

Pang, YY [Pang, Yongyan][ 1,2 ]; Watson, SS [Watson, Stephanie S.][ 2 ]; Sung, LP [Sung, Li-Piin][ 2 ]
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The objective of this study was to investigate the effect of nanoparticle dispersion on surface morpho- logical changes and degradation process in polymeric coatings during exposure to ultraviolet (UV) ra- diation. Three types of nano-titanium dioxide (nano-TiO2) were selected and dispersed into acrylic urethane (AU) coating to generate degrees of nanoparticle dispersion states. Two accelerated exposure conditions: wet (30 C and 75% relative humidity (RH)) and dry (30 C and 0% RH), were selected. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used to monitor surface chemical degradation. Laser scanning confocal microscopy (LSCM) was used to characterize nanoparticle dispersion and surface/subsurface morphological changes in the AU coatings during UV exposure. For a given nanoparticle, similar surface morphological changes of the coatings indicated the similar degradation processes under the wet and dry conditions, but the degradation was faster under the wet condition. Surface morphological changes were closely related to the nanoparticle dispersion in three coatings, and the heterogeneity in nanoparticle dispersion significantly affects the degradation process and dominates the degradation patterns.

submitted time 2017-05-02 Hits476Downloads184 Comment 0

8. chinaXiv:201705.00478 [pdf]

Synthesis and investigation of imidazolium functionalized poly[arylene ether sulfone]s as anion exchange membranes for all-vanadium redox flow batteries

Lu, D [Lu, Di][ 1 ]; Wen, LL [Wen, Lele][ 1,2 ]; Nie, F [Nie, Feng][ 1 ]; Xue, LX [Xue, Lixin][ 1 ]
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

A serials of imidazolium functionalized poly(arylene ether sulfone) as anion exchange membranes (AEMs) for all-vanadium redox flow battery (VRB) application are synthesized successfully in this study. The AEMs obtained with different ionization levels, Im-PAES-0.5/0.7/1.1 (0.5/0.7/1.1 represents the different degrees of bromination, respectively) membranes are intensively characterized. Compared with commercial Nafion 117 membrane, the vanadium ion permeation values of AEMs are lower while their chemical stability in VO2+ are comparable. The ionic conductivities, vanadium ion permeability, stability of the membranes and their performance in VRB cells are greatly affected by ionic exchange capacity (IEC). In order to balance these important performance factors, the Im-PAES-0.7 membrane with a moderate IEC of 2.01 meq g 1 exhibits good stability, high ionic conductivity and low vanadium ion permeation, resulting in high voltage efficiencies (up to 87.5%), high coulombic efficiencies (up to 96.1%), as well as high energy efficiency. The VRB cell with the Im-PAES-0.7 membrane achieves comparable to or even slightly higher energy efficiency values (up to 81.7%) than those of Nafion 117 membranes (up to 78.9%) in the current density range of 60–120 mA cm 2. During 40 charge–discharge cycles at different current densities, the Im-PAES-0.7 anion exchange membrane exhibits a comparable short-term stability to Nafion 117 membrane.

submitted time 2017-05-02 Hits582Downloads238 Comment 0

9. chinaXiv:201705.00046 [pdf]

Evaluation of PHBHHx and PHBV/PLA fibers used as medical sutures

He, Y [He, Yu][ 1 ]; Hu, ZW [Hu, Zhiwei][ 2 ]; Ren, MD [Ren, Mengda][ 1 ]; Ding, CK [Ding, Changkun][ 3 ]; Chen, P [Chen, Peng][ 4 ]; Gu, Q [Gu, Qun][ 4 ]; Wu, Q [Wu, Qiong][ 1,5,6 ]
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Two types of fibers were prepared by using bio- based materials: a mono-filament made from poly(3- hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and a multi-filament made from poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) and polylactic acid (PLA) blend. The two fibers were evaluated for mechanical properties, biocompatibility and degradability for the potential appli- cation as medical sutures. The PHBHHx fiber showed remarkable biocompatibility by H.E. Stainning, with very little impact to the surrounding tissues. The degradation of the fiber was observed by SEM after implantation for 36 weeks, and the major degradation product was detected after 96 weeks. Consistently, the PHBHHx fiber main- tained more than half of the mechanical properties after 96 weeks. The other fiber was prepared by twisting PHBV/PLA blend strands to a bunch, and showed high biocom- patibility and relatively high degradability. The bunched structure loosed after 36 weeks of implantation. These low- cost and easily prepared fibers have great potential in medical applications, since they could avoid the formation of fibrous capsule, reduce the size of scar, and degrade into non-toxic and even beneficial products.

submitted time 2017-05-02 Hits851Downloads460 Comment 0

10. chinaXiv:201704.00068 [pdf]

Chlorobenzene vapor assistant annealing method for fabricating high quality perovskite films

He, Y; Hu, ZW; Ren, MD; Ding, CK; Chen, P; Gu, Q; Wu, Q

In this study, chlorobenzene (CB) vapor assistant annealing (VAA) method is employed to make high quality perovskite films and produce high efficiency CH3NH3PbI3-xClx perovskite solar cells. The perovskite films made by this method present several advanta

submitted time 2017-04-06 Hits473Downloads311 Comment 0

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