Gaseous pollutants in Beijing urban area during the heating period 2007–2008: variability, sources, meteorological, and chemical impacts

Gaseous pollutants, NO<sub>y</sub>/NO<sub>x</sub>, SO<sub>2</sub>, CO, and O<sub>3</sub>, were measured at an urban site in Beijing from 17 November 2007 to 15 March 2008. The average concentrations (with ± 1σ) of NO, NO<sub>2</sub>, NO<sub>x</sub>, NO<sub>y</sub>, CO, SO<sub>2</sub>, and O<sub>3</sub> were 29.0 ± 2.7 ppb, 33.7 ± 1.4 ppb, 62.7 ± 4.0 ppb, 72.8 ± 4.5 ppb, 1.99 ± 0.13 ppm, 31.9 ± 2.0 ppb, and 11.9 ± 0.8 ppb, respectively, with hourly maxima of 200.7 ppb, 113.5 ppb, 303.9 ppb, 323.2 ppb, 15.06 ppm, 147.3 ppb, and 69.7 ppb, respectively. The concentrations of the pollutants show "saw-toothed" patterns, which are attributable mainly to changes in wind direction and speed. The frequency distributions of the hourly mean concentrations of NO<sub>y</sub>, SO<sub>2</sub>, CO, and O<sub>3</sub> can all be decomposed in the two Lorentz curves, with their peak concentrations representing background levels under different conditions. During the observation period, the average ratio NO<sub>x</sub>/NO<sub>y</sub> was 0.86 ± 0.10, suggesting that the gaseous pollutants in Beijing in winter are mainly from local emissions. Data of O<sub>3</sub>, NO<sub>z</sub>, and NO<sub>x</sub>/NO<sub>y</sub> indicate that photochemistry can take place in Beijing even in the cold winter period. Based on the measurements of O<sub>3</sub>, NO<sub>x</sub>, and NO<sub>y</sub>, ozone production efficiency (OPE) is estimated to be in the range of 0–8.9 (ppb ppb<sup>−1</sup>) with the mean(± 1σ) and median values being 1.1(± 1.6) and 0.5 (ppb ppb<sup>−1</sup>), respectively, for the winter 2007–2008 in Beijing. This low OPE would cause a photochemical O<sub>3</sub> source of 5 ppb day<sup>−1</sup>, which is small but significant for surface O<sub>3</sub> in winter in Beijing. Downward transport of O<sub>3</sub>-rich air from the free troposphere is the more important factor for the enhancement of the O<sub>3</sub> level in the surface layer, while high NO level for the destruction of O<sub>3</sub>. The concentrations of SO<sub>2</sub>, CO, and NO<sub>x</sub> are strongly correlated among each other, indicating that they are emitted by some common sources. Multiple linear regression analysis is applied to the concentrations of NO<sub>y</sub>, SO<sub>2</sub>, and CO and empirical equations are obtained for the NO<sub>y</sub> concentration. Based the equations, the relative contributions from mobile and point sources to NO<sub>y</sub> is estimated to be 66 ± 30 % and 40 ± 16 %, respectively, suggesting that even in the heating period, mobile sources in Beijing contribute more to NO<sub>y</sub> than point sources

Coverage analysis of heterogeneous cellular networks in urban areas

© 2016 IEEE. In this article, a network model incorporating both line-of-sight (LOS) and non-line-of-sight (NLOS) transmissions is proposed to investigate impacts of blockages in urban areas on heterogeneous network coverage performance. Results show that co-existence of NLOS and LOS transmissions has a significant impact on network performance. We find in urban areas, that deploying more BSs in different tiers is better than merely deploying all BSs in the same tier in terms of coverage probability

Effects of Capping on the (Ga,Mn)As Magnetic Depth Profile

Annealing can increase the Curie temperature and net magnetization in uncapped (Ga,Mn)As films, effects that are suppressed when the films are capped with GaAs. Previous polarized neutron reflectometry (PNR) studies of uncapped (Ga,Mn)As revealed a pronounced magnetization gradient that was reduced after annealing. We have extended this study to (Ga,Mn)As capped with GaAs. We observe no increase in Curie temperature or net magnetization upon annealing. Furthermore, PNR measurements indicate that annealing produces minimal differences in the depth-dependent magnetization, as both as-grown and annealed films feature a significant magnetization gradient. These results suggest that the GaAs cap inhibits redistribution of interstitial Mn impurities during annealing.Comment: 12 pages, 3 figures, submitted to Applied Physics Letter

New Insights into Traffic Dynamics: A Weighted Probabilistic Cellular Automaton Model

From the macroscopic viewpoint for describing the acceleration behavior of drivers, this letter presents a weighted probabilistic cellular automaton model (the WP model, for short) by introducing a kind of random acceleration probabilistic distribution function. The fundamental diagrams, the spatio-temporal pattern are analyzed in detail. It is shown that the presented model leads to the results consistent with the empirical data rather well, nonlinear velocity-density relationship exists in lower density region, and a new kind of traffic phenomenon called neo-synchronized flow is resulted. Furthermore, we give the criterion for distinguishing the high-speed and low-speed neo-synchronized flows and clarify the mechanism of this kind of traffic phenomena. In addition, the result that the time evolution of distribution of headways is displayed as a normal distribution further validates the reasonability of the neo-synchronized flow. These findings suggest that the diversity and randomicity of drivers and vehicles has indeed remarkable effect on traffic dynamics.Comment: 12 pages, 5 figures, submitted to Europhysics Letter

Effect of Dietary Methionine on Taurine Distribution and Non-specific Immune Responses in Juvenile Blunt Snout Bream, Megalobrama amblycephala at A Constant Dietary Cystine Level

A 9-week feeding trial was conducted to investigate taurine distribution by supplementation of methionine in juvenile Megalobrama amblycephala at a constant dietary cystine level. Six semi-purified diets were formulated to contain graded dietary methionine levels from 0.39-1.54% in about 0.25% increments. At the end of feeding trial, plasma methionine content significantly increased with increasing dietary methionine level from 0.39 to 1.0% (P < 0.05) and thereafter reached a plateau. The taurine content of muscle, intestine, liver, and eye in the fish fed dietary methionine level ranged from 1.24-1.54% and was significantly higher than that of the control group (P < 0.05). Taurine content of the brain in fish fed 1.54% methionine diet was higher than the fish fed 0.39% (P < 0.05). Cysteine sulfinic acid decarboxylase content significantly increased with increasing dietary methionine level from 0.39-0.85% (P < 0.05) and thereafter stayed at a similar level. Supplementation with methionine significantly increased (P < 0.05) plasma total protein (TP) content, complement 3 (C3) content and superoxide dismutase (SOD) activity (0.85% methionine diet groups), aspartate transaminase (AST) activity (1.24% methionine diet groups) and albumin content (1.0% methionine diet groups). Supplemented groups had significantly decreased plasma urea content (0.85% methionine diet groups) (P < 0.05). In conclusion, these results indicate that crystalline methionine can be utilized efficiently, juvenile blunt snout bream were able to convert methionine to taurine directly, and appropriate dietary methionine supplementation improves non-specific immune responses in blunt snout bream

Temporal and spatial distribution pattern of Bullacta exarata in a tidal flat at south shore of Hangzhou Bay, China

The distribution pattern of Bullacta exarata was studied in different seasons of 2004 at south shore of Hangzhou Bay, China. We found that the distribution pattern of B. exarata was aggregated in each season by Taylor's power regression and Iwao's plot regresses methods (P < 0.001). Based on two-way ANOVA analysis, the results indicated that the densities were significantly affected by the factors of season (P < 0.001), distance to the dyked dam (P < 0.001) and the interaction between them (P < 0.001). The densities distribution followed with the distance gradient was significantly different in each season with one-way ANOVA analysis. The results of Pearson correlation coefficients analysis on data of density indicated that in the warmer seasons (spring and summer) the highest densities occurred at 150 m to the dyked dam, while in the cooler seasons peak in densities were at 250 m to the dyked dam (autumn and winter). In the study area, seasonal variation of B. exarata densities should be the response of the species to the environmental change, especially the food resource