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Graphite nitrogen, pyridine nitrogen and pyrrole nitrogen are the main nitrogen types in nitrogen-doped graphene materials. In order to investigate the mechanism of the oxygen reduction activity of nitrogen-doped graphene, several models of nitrogen-doped graphene with different nitrogen contents and different nitrogen types are developed. The nitrogen content is varied from 1.3 at% to 7.8 at%, and the adsorption energy is calculated according to the established models, then the band gaps are analyzed through the optimization results, so as to compare the magnitude of the conductivity. Finally, the oxygen reduction activity of graphite nitrogen-doped graphene (GNG) is found to be better than pyridine nitrogen-doped graphene (PDNG) and pyrrole nitrogen-doped graphene (PLNG) when the nitrogen content is lower than 2.6 at%, and the oxygen reduction activity of PDNG is the best when the nitrogen content was higher than 2.6 at%.

Quantitative reconstruction of regional paleotemperature is the key to understanding temperature change and its driving mechanisms. In this study, 133 phytolith samples were collected as proxy indicators from lacustrine sediments of the Zhunzhahanjilin (ZZH) profile in the hinterland of the Badain Jaran Desert, China. The phytolith samples were then analyzed to quantitatively reconstruct the Holocene paleotemperature at the millennial scale. Based on accelerator mass spectrometry (AMS), 14C dates and an ordered clustering method were used to divide the phytoliths into five assemblage zones with environmental significance. The quantitative reconstruction results indicated that the paleotemperature in the Badain Jaran Desert was relatively high during the early Holocene (11,040–8,200 cal a BP), and the average paleotemperature was approximately 9.5°C. This may have led to increased melt water near the surrounding area and recharged the lakes in the Badain Jaran Desert, resulting in the expansion of the lakes during the early Holocene. The average paleotemperature during the middle Holocene (8,200–3,100 cal a BP) was approximately 7.9°C. This period was warm and the environment was humid, with extensive precipitation from summer monsoons and low evaporation leading to higher water levels in the lakes. The paleotemperature decreased during the late Holocene (3,100 cal a BP to the present), and lakes retreated or dried up because of the decreased summer monsoon rains. The Holocene paleotemperature in the Badain Jaran Desert may have been related to July insolation in the Northern Hemisphere and had a range of impacts on the hydrological cycle in this arid region.

Additional file 1: Table S1. The primers for genes used in real-time qPCR analysis.

Background Soil salinization is becoming an increasingly serious problem worldwide, resulting in cultivated land loss and desertification, as well as having a serious impact on agriculture and the economy. The indoleamine melatonin (N-acetyl-5-methoxytryptamine) has a wide array of biological roles in plants, including acting as an auxin analog and an antioxidant. Previous studies have shown that exogenous melatonin application alleviates the salt-induced growth inhibition in non-halophyte plants; however, to our knowledge, melatonin effects have not been examined on halophytes, and it is unclear whether melatonin provides similar protection to salt-exposed halophytic plants. Results We exposed the halophyte Limonium bicolor to salt stress (300 mM) and concomitantly treated the plants with 5 μM melatonin to examine the effect of melatonin on salt tolerance. Exogenous melatonin treatment promoted the growth of L. bicolor under salt stress, as reflected by increasing its fresh weight and leaf area. This increased growth was caused by an increase in net photosynthetic rate and water use efficiency. Treatment of salt-stressed L. bicolor seedlings with 5 μM melatonin also enhanced the activities of antioxidants (superoxide dismutase [SOD], peroxidase [POD], catalase [CAT], and ascorbate peroxidase [APX]), while significantly decreasing the contents of hydrogen peroxide (H2O2), superoxide anion (O2•−), and malondialdehyde (MDA). To screen for L. bicolor genes involved in the above physiological processes, high-throughput RNA sequencing was conducted. A gene ontology enrichment analysis indicated that genes related to photosynthesis, reactive oxygen species scavenging, the auxin-dependent signaling pathway and mitogen-activated protein kinase (MAPK) were highly expressed under melatonin treatment. These data indicated that melatonin improved photosynthesis, decreased reactive oxygen species (ROS) and activated MAPK-mediated antioxidant responses, triggering a downstream MAPK cascade that upregulated the expression of antioxidant-related genes. Thus, melatonin improves the salt tolerance of L. bicolor by increasing photosynthesis and improving cellular redox homeostasis under salt stress. Conclusions Our results showed that melatonin can upregulate the expression of genes related to photosynthesis, reactive oxygen species scavenging and mitogen-activated protein kinase (MAPK) of L. bicolor under salt stress, which can improve photosynthesis and antioxidant enzyme activities. Thus melatonin can promote the growth of the species and maintain the homeostasis of reactive oxygen species to alleviate salt stress.

The studies of surface dilational rheology are important to detent the nature of adsorption film and the properties of foam. In this paper, the adsorption and dilational rheological properties of branched cationic surfactant hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride (C16G(EO)3PC) at the air-water interface in the absence and presence of electrolyte (NaCl) were investigated by drop shape analysis. The results show that the surface adsorption layer of C16G(EO)3PC behaves elastic in nature with high value up to 90 mN/m, which indicates that the slow relaxation process plays a main role because of the re-arrangement of long branched alkyl chain. The addition of NaCl will enhance diffusion-exchange process and accelerate the formation of film and decreases dilational elasticity obviously. At low NaCl concentration, the in-film slow relaxation process dominates the nature of film, dilational viscosity decreases with an increase of oscillating frequency. By adding more NaCl, diffusion-exchange process plays the crucial role and dilational viscosity increase as a function of frequency. Moreover, viscosity at high NaCl concentration shows larger value under higher oscillating frequency, indicating the contributions of fast diffusion-exchange process. The elastic adsorption film becomes to be viscoelastic by adding electrolyte.

This study examined the bacterial and archaeal diversity from a worldwide range of wetlands soils and sediments using a meta-analysis approach. All available 16S rRNA gene sequences recovered from wetlands in public databases were retrieved. In November 2012, a total of 12677 bacterial and 1747 archaeal sequences were collected in GenBank. All the bacterial sequences were assigned into 6383 operational taxonomic units (OTUs 0.03), representing 31 known bacterial phyla, predominant with Proteobacteria (2791 OTUs), Bacteroidetes (868 OTUs), Acidobacteria (731 OTUs), Firmicutes (540 OTUs), and Actinobacteria (418 OTUs). The genus Flavobacterium (11.6% of bacterial sequences) was the dominate bacteria in wetlands, followed by Gp1, Nitrosospira, and Nitrosomonas. Archaeal sequences were assigned to 521 OTUs from phyla Euryarchaeota and Crenarchaeota. The dominating archaeal genera were Fervidicoccus and Methanosaeta. Rarefaction analysis indicated that approximately 40% of bacterial and 83% of archaeal diversity in wetland soils and sediments have been presented. Our results should be significant for well-understanding the microbial diversity involved in worldwide wetlands.

5 at%Yb3+:YNbO4 crystal is grown by Czochralski(CZ) method. Its transmission and emission spectra are measured. The absorption peaks are located at 933, 955, 974 and 1003 nm with their corresponding absorbtion cross section values 0.7310-20, 1.8510-20, 0.8610-20 and 0.4410-20 cm2; and the FWHM of 955 nm absorbtion peak is 17 nm. Its emission band centered at 1020 nm with the FWHM is 41 nm, which is over three times that of Yb3+:YAG crystal. The emission cross section values of 955, 974, 1005, 1021 and 1030 nm peaks are calculated to be 0.6910-20, 0.8610-20, 1.8110-20, 1.1110-20 and 0.5710-20 cm2, respectively, and the biggest one is comparable to that of Yb3+:YAG crystal. The laser parameters of 5 at% Yb3+:YNbO4 crystal are evaluated and the results suggest that it is a potential all-solid-state pumped laser crystal in tunable and ultrafast lasers field.

15at.%Yb3+:Gd2SiO5 crystal with a size of30 mm75 mm is grown by the Czochralski method, and its lattice parameters, atom coordinates and temperature factors are determined by the full-profile Rietveld refinement method. Its spectral parameters of oscillator strength, line strength, transition probability, energy lifetime and integral emission cross-section for Yb3+2F7/22F5/2 transition are calculated using the absorption spectraum. And the laser performance evaluation shows that this crystal is a potential laser crystal with relatively high threshold, and could be used as a medium of tunable or ultra-fast laser pumped by high-power laser diode.