Free Vibration Analysis of a Graphene-Reinforced Porous Composite Plate with Different Boundary Conditions.

Plates are commonly used in many engineering disciplines, including aerospace. With the continuous improvement in the capacity of high value-added airplanes, large transport aircrafts, and fighter planes that have high strength, high toughness, and corrosion resistance have gradually become the development direction of airplane plate structure production and research. The strength and stability of metal plate structures can be improved by adding reinforced materials. This paper studies graphene platelets (GPLs) reinforced with a free vibration porous composite plate. The porous plate is constructed with a multi-layer model in a metal matrix containing uniform or non-uniformly distributed open-cell internal pores. Considering the random and directional arrangement of graphene platelets in the matrix, the elastic modulus of graphene composites was estimated using the Halpin-Tsai micromechanical model, and the vibration frequencies of graphene composite were calculated using the differential quadrature method. The effects of the total number of layers, GPL distribution pattern, porosity coefficient, GPL weight fraction, and boundary conditions on the free vibration frequency of GPLs reinforced porous composite plates are studied, and the accuracy of the conclusions are verified by the finite element software.

[Pollution Characteristics of NH4+,NO3-,SO42- in PM2.5and Their Precursor Gases During 2015 in an Urban Area of Beijing].

Simultaneous measurements of precursor gases NH3,NO,NO2,SO2 and the main water-soluble ions in PM2.5 such as sulphate (SO42-),nitrate (NO3-) and ammonium (NH4+) (collectively called SNA)were carried out in the urban area of Beijing during 2015-01 to 2015-12,which obtained 325 groups of samples. PTFE membrane filters were used to collect particulate NH4+, NO3- and SO42-, followed by the online instruments to collect precursor gases. The pollution characteristics of the precursor gases and SNA were analyzed and their correlation was studied. The mean concentrations of NH3, NO, NO2, SO2, NH4+,NO3- and SO42- were 21.5, 17.7, 54.3, 14.2, 8.1, 13.5 and 12.7 µg·m-3 respectively during the period of monitoring, and SNA accounted for 43.4% of PM2.5. The concentrations of SO2,NOx and SNA declined compared to 2014. The concentrations of NO,NO2 and SO2 were highest in winter and lowest in summer. The concentration of NH3 was higher in summer and lower in autumn; The concentration and the percentage of NH4+ were stable during the four seasons,both the concentrations and the percentage of NO3- were lowest in summer. The concentrations of SO42- was highest in winter and the percentage was lowest in summer. The ratio of ([NO3-]+2[SO42-]) and NH4+ was 0.97 during the whole year, showing that anions mainly existed in the form of NO3- and SO42-. In summer, the ratio of[NO3-]+2[SO42-] and[NH4+] was slightly higher than 1.0, which was the reason why NO3- was bound to Ca2+, Mg2+ and Na+besides NH4+. With the increase of pollution, the mass concentration of precursor gases and SNA increased dramatically, among which NOx increased most rapidly, and SO2 decreased from severe pollution to serious pollution. The contribution rate of NH4+ was maintained at a relatively stable level. SO42- had a higher contribution when the pollution level was lower, whereas the concentration of NO3- was higher than others and contributed most to PM2.5 in heavy pollution. Heterogeneous transformation on the surface of particulate matter played a more important role in the formation of SO42- and NO3-. The correlations between NO3-, NO2 and NO,NH4+ and NH3,SO42- and SO2 were significant at the confidence level of 0.01. SO42- had negative correlation with SO2, and NO3- had positive correlation with NO2. Compared with NH3, the NH4+ concentration was more obviously affected by acid gases NO2, SO2.

[Comparison Test Between On-line Monitoring of Water-soluble Ions and Filter-based Manual Methods for PM2.5].

Concentrations of water-soluble ions were measured in Beijing during 2014 for comparison of URG online monitoring systems and filter-based manual methods. The differences of four main ions components in spring, summer, autumn and winter were compared. The total concentrations of eight ions measured by URG online were higher than those of filter-based manual method. There was no significant differences among the annual concentrations of Cl-,NO3-,Mg2+ and Ca2+ obtained by the two methods, while the concentrations of SO42-,NH4+,Na+,K+ from online were higher than those from filter. NO3-,SO42-,Cl- had good correlations in autumn and winter, and NH4+ only had better fitting performance in winter.

[Correlation, seasonal and temporal variation of water-soluble ions of PM2.5 in Beijing during 2012-2013].

A total of 486 daily PM2.5 samples were collected at a background site, 3 urban sites, 4 suburban sites and a boundary transfer site during August 2012-July 2013. Mass concentrations of 9 water-soluble ions were obtained. The average mass concentration of the 9 ions was 60.5 µg x m(-3), and the order of concentration of ions was NO3- > SO4(2-) > NH4(+)- > Cl- > Na+ > K+ > Ca2+ > F- > Mg2+; Secondary inorganic species NO3-, SO4(2-) and NH4+ were the major components of water-soluble ions in PM2.5, with a contribution of 88% to the total ions of PM2.5. NO3- was the most fluctuated anion during the sampling period. With the increase of pollution level, the accumulation of SNA was obvious, the components that contained nitrogen, NO3- and NH4+, occupied the dominant position in the formation of the secondary components. NO3- had a relatively higher contribution to the accumulation of heavy pollution.

[Characterization of Water-soluble Ions in PM2.5 of Beijing During 2014 APEC].

The mass concentration of PM2.5 associated with its online and off-line water-soluble ions were obtained during 2014- 10- 2014-11. Secondary inorganic species NO3⁻, SO4²â» and NH4⁺ were the major components of PM2.5 during different observation periods. The total concentration of NO3⁻, SO4²â» and NH4⁺ was (26.8 ± 22.5) µg · m⁻³, which contributed (41.7 ± 8.5)% to PM2.5. The concentration of NO3⁻ was higher than those of others and contributed most to PM2.5. The ions of NO3⁻, SO4²â» NH4⁺ and Cl⁻ all showed three different periods during 2014 Beijing APEC, besides the different meteorological condition, the cumulative effect caused by local emissions and regional pollution could also not be ignored. Although the characteristics of water-soluble ions was different during different observation periods, there was no obvious acidification of PM2.5 in Beijing at the end of autumn and beginning of winter.

Coordinated response of photosynthesis, carbon assimilation, and triacylglycerol accumulation to nitrogen starvation in the marine microalgae Isochrysis zhangjiangensis (Haptophyta).

The photosynthetic performance, carbon assimilation, and triacylglycerol accumulation of Isochrysis zhangjiangensis under nitrogen-deplete conditions were studied to understand the intrinsic correlations between them. The nitrogen-deplete period was divided into two stages based on the photosynthetic parameters. During the first stage, carbon assimilation was not reduced compared with that under favorable conditions. The marked increase in triacylglycerols and the variation in the fatty acid profile suggested that triacylglycerols were mainly derived from de novo synthesized acyl groups. In the second stage, the triacylglycerol content continued increasing while the carbohydrate content decreased from 44.0% to 26.3%. These results indicated that the intracellular conversion of carbohydrates to triacylglycerols occurred. Thus, we propose that sustainable carbon assimilation and incremental triacylglycerol production can be achieved by supplying appropriate amounts of nitrogen in medium to protect the photosynthetic process from severe damage using the photosynthetic parameters as indicators.