Background
The mixed dentition is an important transition period from primary teeth to permanent teeth. However, the caries prevalence of first permanent molar in mixed dentitions was about 30%, ...which almost represent the caries rate of permanent teeth in this period of time. Therefore, we assessed the oral bacterial profiles in young children (age 6–8) with mixed dentition with or without first molar caries for providing the research basis of caries etiology.
Methods
We collected samples of supragingival plaque and saliva from the children living in Guizhou, a rural isolated province in China. Then, we performed DNA extraction and purification followed by 454 pyrosequencing of the V1–V3 hypervariable regions of the 16S rRNA and compared our results with those of previous research.
Results
(i) We analyzed 48,320 unique sequences that represented 18 phyla, 29 classes, 44 orders, 74 families, 129 genera, 15,003 species‐level OUT in plaque and saliva samples; (ii) longitudinally, there was the “healthy core microbiome” between healthy deciduous dentition and early mixed dentition, for example, Neisseria, Porphyromonas, Selenomonas etc.; (iii) horizontally, there also existed the “healthy core microbiome” in early mixed dentition, for example, Neisseria, Streptococcus, Prevotella etc.; (iv) the dominant bacteria detected by Lefse in caries group including Actinomycetaceae, Streptobacillus (p < 0.05) and those in caries‐free group including Gammaproteobacteria, Pasteurellaceae, Aggregatibacter, Chloroflexi, (p < 0.05).
Conclusions
The oral cavity is a highly heterogeneous ecosystem with the “healthy core microbiome” in children, although microbial composition shifts along with aging. In addition, the abundance and diversity of microbiota vary between caries and caries‐free groups verify the ecological plaque hypothesis.
C 1s XPS spectra of various highly oriented pyrolytic graphite (HOPG) surfaces, untreated, as well as those treated by keV Ar+ beam bombardment and low-energy O2, N2, Ar, and H2O plasmas, have been ...systematically studied by comparing two XPS peak-fitting procedures. These procedures treat the spectrum as either (1) the overlap of several symmetric component peaks or (2) a single asymmetric peak. The results indicate that, in the case of HOPG, the asymmetry parameter defining the single peak is directly related to the extent of damage to the alternant hydrocarbon structure of the HOPG surface, as manifested by its correlation with the symmetric peak component due to the damaged HOPG structure.
The interaction between multiwalled carbon nanotubes (MWCNTs) and aqueous poly(diallyl dimethylammonium) chloride (PDDA) was studied by X-ray photoelectron (XPS) and photoacoustic Fourier transform ...infrared (PA-FTIR) spectroscopies. We have found that the mild sonication of MWCNTs in aqueous PDDA results in a significant improvement of CNT dispersibility and greatly enhances their adhesion to Au and Si substrates. The MWCNT−PDDA interaction is due to the presence of an unsaturated contaminant in the PDDA chain, as confirmed by both XPS and PA-FTIR, which enters into a π−π interaction with the CNTs. Electrostatic group repulsions of the coated CNTs then provide the dispersibility and adhesion.
The diffusion and coalescence of metal nanoparticles play important roles in many phenomena. Here, we offer a new integrated overview of the main factors that control the nanoparticle coalescence ...process. Three factors are considered in our description of the coalescence process: nanoparticle diffusion across the surface, their physical and thermodynamic properties, and the mechanism of coalescence. We demonstrate that the liquidlike properties of the surface layers of the nanoparticles play an essential role in this process. We present experimental evidence for our opinion, based on the high-resolution electron microscopic analysis of several different types of nanoparticles.
The magnesium effect on hydrogen-induced amorphization (HIA) of Sm2−xMgxNi4 compounds is investigated in this work. It is found that the HIA phenomenon occurs in the compounds with x = 0, 0.25 and ...0.5. The amorphous hydrides do not desorb hydrogen at 298 K. However, the pseudo-binary Sm1.25Mg0.75Ni4 compound can reversibly absorb and desorb hydrogen without the occurrence of HIA during hydrogen absorption and desorption cycles at 298 K. Hence, it is suggested that the critical RA/RB ratio for HIA of pseudo-binary AB2 compounds should shift to a slightly higher value than the empirical value 1.37 for the occurrence of HIA in binary AB2 compounds.
•HIA occurs in Sm2−xMgxNi4 compounds with x = 0, 0.25 and 0.5.•Sm1.25Mg0.75Ni4 reversibly absorbs and desorbs hydrogen without occurrence of HIA.•The critical RA/RB ratio for HIA of Sm2−xMgxNi4 is larger than 1.37.
A consistent daily bias correction procedure was applied at 4802 stations over high latitude regions (North of 45°N) to quantify the precipitation gauge measurement biases of wind‐induced undercatch, ...wetting losses, and trace amount of precipitation for the last 30 years. These corrections have increased the gauge‐measured monthly precipitation significantly by up to 22 mm for winter months, and slightly by about 5 mm during summer season. Relatively, the correction factors (CF) are small in summer (10%), and very large in winter (80–120%) because of the increased effect of wind on gauge undercatch of snowfall. The CFs also vary over space particularly in snowfall season. Significant CF differences were found across the USA/Canada borders mainly due to differences in catch efficiency between the national gauges. Bias corrections generally enhance monthly precipitation trends by 5–20%. These results point to a need to review our current understanding of the Arctic fresh water budget and its change.
This study investigates the leaching kinetics of gold-bearing pyrite in the potassium peroxydisulphate system and the potassium peroxydisulphate-ferrous sulphate combined system, using potassium ...peroxydisulphate as an oxidizing agent. Experimental results indicate that the pyrite leaching rate is roughly proportional to the potassium sulphate concentration. The pyrite leaching rate also increases with temperature, and is 48.19% faster at 70°C than at 30°C. Additionally, the pyrite leaching rate is inversely proportional to the particle size; the leaching rate of < 0.038 mm particles is 44.31% greater than that of 0.180–0.120 mm particles. At 70°C, the concentration of ferrous sulphate has no effect. However, at the more typical leaching temperature of 30°C, the addition of ferrous sulphate and hydrogen peroxide can increase the rate of leaching. Therefore, the kinetics of pyrite leaching in the potassium peroxydisulphate system at 70°C and in the potassium peroxydisulphate-ferrous sulphate combined system at normal temperatures were investigated in detail. Pyrite leaching kinetics follows the formula kt = 1 – 2/3x – (1 – x)2/3 where solid film diffusion is the limiting process. The effective activation energy of pyrite leaching in the temperature range 30–70°C was 65.30 kJ/mol. Pyrite had a regular crystal habit prior to leaching, but exhibited faviform holes after leaching. These results provide a basis for effective leaching of gold from gold-bearing pyrite ores using the advanced oxidative leaching system.
We have demonstrated halide effects in the rhodium-catalyzed asymmetric ring opening reaction of oxabicyclic alkenes. By employing halide and protic additives, the catalyst poisoning effect of ...aliphatic amines is reversed allowing the amount nucleophile to react in high yield and ee. Second, by simply changing the halide ligand on the rhodium catalyst from chloride to iodide, the reactivity and enantioselectivity of reactions employing an aromatic amine, malonate or carboxylate nucleophile are dramatically improved. Third, through the application of halide effects and more forcing reaction conditions, less reactive oxabicycle 2.2.1 substrates react to generate synthetically useful enantioenriched cyclohexenol products. Application of these new conditions to the more reactive oxabenzonorbornadiene permits the reaction to be run with very low catalyst loadings (0.01 mol %).
This study systematically analyzes long‐term (1936–1999) monthly discharge records for the major subbasins within the Lena River watershed in order to document significant streamflow hydrology ...changes induced by human activities (particularly reservoirs) and by natural variations/changes. The results show that the upper streams of the watershed, without much human impact, experience a runoff increase in winter, spring, and (particularly) summer seasons and a discharge decrease in fall season. These changes in seasonal streamflow characteristics indicate a hydrologic regime shift toward early snowmelt and higher summer streamflow perhaps due to regional climate warming and permafrost degradation in the southern parts of Siberia. The results also demonstrate that reservoir regulations have significantly altered the monthly discharge regime in the lower parts of Lena River basin. Because of a large dam in west Lena River, summer (high) flows at the outlet of the Vilui valley have been reduced by up to 55% and winter (low) flows have been increased by up to 30 times. These alterations, plus streamflow changes in the upper Lena regions, lead to strong upward trends (up to 90%) in monthly discharge at the basin outlet during the low‐flow months and weak increases (5–10%) in the high‐flow season. Monthly flow records at the basin outlet have been reconstructed by a regression method to reduce reservoir impacts. Trend analyses and comparisons between the observed and reconstructed monthly flows show that because of reservoir regulations, discharge records observed at the Lena basin outlet do not always represent natural changes and variations. They tend to underestimate the natural runoff trends in summer and overestimate the trends in both winter and fall seasons. Therefore the cold season discharge increase identified at the mouth of the Lena basin is not all naturally caused, but the combined effect of reservoir regulation and natural runoff changes in the unregulated upper subbasins. This study clearly illustrates the importance of human activities in regional and global environment changes and points to a need to examine human impacts in other large high‐latitude watersheds.
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