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Search Results: 1 - 10 of 192907 matches for " Y. H. Mao "
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The Nature of the Diffuse Clumps and the X-ray Companion of Mrk 273
X. -Y. Xia,S. Mao,H. Wu
Physics , 1999, DOI: 10.1086/307828
Abstract: We present an optical spectrum for Mrk 273x, the X-ray source 1.3' to the northeast of Mrk 273. The new spectrum indicates that the object is at a much higher redshift (0.458) than the value (0.0376) previously reported. All the detected emission lines show properties of Seyfert 2 galaxies. Mrk 273x has one of the highest X-ray and radio luminosities L_x ~ 1.1 x 10^{44} erg/s, L_{1.37 GHz} ~ 2.0 x 10^{40} erg/s among Seyfert 2 galaxies, yet it has a low neutral hydrogen column density, N_H ~ 4.4 x 10^{20}/cm^2. These properties seem difficult to explain in the unified scheme of active galactic nuclei. The spectrum previously used to identify the redshift for Mrk 273x turns out to be for diffuse clumps in the northeast tail/plume about 20'' (~20 kpc in projected distance) from the nuclear region of Mrk 273. A new spectrum for this region was obtained; this spectrum is essentially the same as the previous one. These observations indicate that these clumps have the same redshift as Mrk 273 and are physically associated with the merger. The spectrum is dominated by strong emission from the [O III] doublet with Seyfert 2-like line ratios, which indicate that these northeast clumps are probably excited by the shock plus precursor mechanism during the merging process. This mechanism may be operating in other ultraluminous IRAS galaxies as well. (abridged)
Biomass burning contribution to black carbon in the Western United States Mountain Ranges
Y. H. Mao,Q. B. Li,L. Zhang,Y. Chen
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011, DOI: 10.5194/acp-11-11253-2011
Abstract: Forest fires are an important source to carbonaceous aerosols in the Western United States (WUS). We quantify the relative contribution of biomass burning to black carbon (BC) in the WUS mountain ranges by analyzing surface BC observations for 2006 from the Interagency Monitoring of PROtected Visual Environment (IMPROVE) network using the GEOS-Chem global chemical transport model. Observed surface BC concentrations show broad maxima during late June to early November. Enhanced potassium concentrations and potassium/sulfur ratios observed during the high-BC events indicate a dominant biomass burning influence during the peak fire season. Model surface BC reproduces the observed day-to day and synoptic variabilities in regions downwind of but near urban centers. Major discrepancies are found at elevated mountainous sites during the July-October fire season when simulated BC concentrations are biased low by a factor of two. We attribute these low biases largely to the underestimated (by more than a factor of two) and temporally misplaced biomass burning emissions of BC in the model. Additionally, we find that the biomass burning contribution to surface BC concentrations in the USA likely was underestimated in a previous study using GEOS-Chem (Park et al., 2003), because of the unusually low planetary boundary layer (PBL) heights in the GEOS-3 meteorological reanalysis data used to drive the model. PBL heights from GEOS-4 and GEOS-5 reanalysis data are comparable to those from the North American Regional Reanalysis (NARR). Model simulations show slightly improved agreements with the observations when driven by GEOS-5 reanalysis data, but model results are still biased low. The use of biomass burning emissions with diurnal cycle, synoptic variability, and plume injection has relatively small impact on the simulated surface BC concentrations in the WUS.
Control for Track of Swarm Systems
X. Mao,Y. Xu,J. Liu,H. Ma
Information Technology Journal , 2012,
Abstract: In this paper, we develop an algorithm for tracking the center of swarm systems to a desired trajectory by using the sliding-mode control method. The algorithm is robust with respect to system perturbations and external disturbance. Simulation further shows the effectiveness very well.
Carbonyl sulfide exchange in a temperate loblolly pine forest grown under ambient and elevated CO2
M. L. White,Y. Zhou,R. S. Russo,H. Mao
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: Vegetation, soil and ecosystem level carbonyl sulfide (COS) exchange was observed at Duke Forest, a temperate loblolly pine forest, grown under ambient (Ring 1, R1) and elevated (Ring 2, R2) carbon dioxide (CO2). During calm meteorological conditions, ambient COS mixing ratios at the top of the forest canopy followed a distinct diurnal pattern in both CO2 growth regimes, with maximum COS mixing ratios during the day (R1=380±4 pptv and R2=373±3 pptv, daytime mean ±standard error) and minimums at night (R1=340±6 pptv and R2=346±5 pptv, nighttime mean ±standard error) reflecting a significant nighttime sink. Nocturnal vegetative uptake ( 11 to 21 pmol m 2 s 1, negative values indicate uptake from the atmosphere) dominated nighttime net ecosystem COS flux estimates ( 10 to 30 pmol m 2 s 1) in both CO2 regimes. In comparison, soil uptake ( 0.8 to 1.7 pmol m 2 s 1) was a minor component of net ecosystem COS flux. In both CO2 regimes, loblolly pine trees exhibited substantial COS consumption overnight (50% of daytime rates) that was independent of CO2 assimilation. This suggests current estimates of the global vegetative COS sink, which assume that COS and CO2 are consumed simultaneously, may need to be reevaluated. Ambient COS mixing ratios, species specific diurnal patterns of stomatal conductance, temperature and canopy position were the major factors influencing the vegetative COS flux at the branch level. While variability in branch level vegetative COS consumption measurements in ambient and enhanced CO2 environments could not be attributed to CO2 enrichment effects, estimates of net ecosystem COS flux based on ambient canopy mixing ratio measurements suggest less nighttime uptake of COS in R2, the CO2 enriched environment.
Continental outflow from the US to the upper troposphere over the North Atlantic during the NASA INTEX-NA Airborne Campaign
S. Y. Kim,R. Talbot,H. Mao,D. Blake
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: A case of continental outflow from the United States (US) was examined using airborne measurements from NASA DC-8 flight 13 during the Intercontinental Chemical Transport Experiment – North America (INTEX-NA). Mixing ratios of methane (CH4) and carbon monoxide (CO) at 8–11 km altitude over the North Atlantic were elevated to 1843 ppbv and 134 ppbv respectively, while those of carbon dioxide (CO2) and carbonyl sulfide (COS) were reduced to 372.4 ppmv and 411 pptv respectively. In this region, urban and industrial influences were evidenced by elevated mixing ratios and good linear relationships between urban and industrial tracers compared to North Atlantic background air. Moreover, low mixing ratios and a good correlation between COS and CO2 showed a fingerprint of terrestrial uptake and minimal dilution during rapid transport over a 1–2 day time period. Analysis of synoptic conditions, backward trajectories, and photochemical aging estimates based on C3H8/C2H6 strongly suggested that elevated anthropogenic tracers in the upper troposphere of the flight region were the result of transport via convection and warm conveyor belt (WCB) uplifting of boundary layer air over the southeastern US. This mechanism is supported by the similar slope values of linear correlations between long-lived (months) anthropogenic tracers (e.g., C2Cl4 and CHCl3) from the flight region and the planetary boundary layer in the southeastern US. In addition, the aircraft measurements suggest that outflow from the US augmented the entire tropospheric column at mid-latitudes over the North Atlantic. Overall, the flight 13 data demonstrate a pervasive impact of US anthropogenic emissions on the troposphere over the North Atlantic.
Rapid convective outflow from the U.S. to the upper troposphere over the North Atlantic during the NASA INTEX-NA airborne campaign: flight 13 case study
S. Y. Kim,R. Talbot,H. Mao,D. Blake
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: A case study of convective outflow from the United States (U.S.) was examined using airborne measurements from NASA DC-8 flight 13 during the Intercontinental Chemical Transport Experiment – North America (INTEX-NA). Mixing ratios of methane (CH4) and carbon monoxide (CO) at 8–11 km altitude over the North Atlantic were elevated to 1843 ppbv and 134 ppbv respectively, while those of carbon dioxide (CO2) and carbonyl sulfide (COS) were reduced to 372.4 ppmv and 411 pptv respectively. In this region, urban and industrial influence was evidenced by elevated mixing ratios and good linear relationships between urban and industrial tracers compared to North Atlantic background air. Moreover, low mixing ratios and a good correlation between COS and CO2 showed a fingerprint of terrestrial uptake and minimal dilution during rapid transport over a 1–2 day time period. Analysis of synoptic conditions, backward trajectories, and photochemical aging estimates based on C3H8/C2H6 strongly suggested that elevated anthropogenic tracers in the upper troposphere of the flight region were the result of fast transport via convective uplifting of boundary layer air over the southeastern U.S. This mechanism is supported by the similar slopes values of linear correlations between long-lived (months) anthropogenic tracers (e.g., C2Cl4 and CHCl3) from the flight region and the planetary boundary layer in the southeastern U.S. In addition, the aircraft measurements suggest that outflow from the U.S. augmented the entire tropospheric column at mid-latitudes over the North Atlantic. Overall, the flight 13 data demonstrate a pervasive impact of U.S. anthropogenic emissions on the troposphere over the North Atlantic.
Multi-year (2004–2008) record of nonmethane hydrocarbons and halocarbons in New England: seasonal variations and regional sources
R. S. Russo,Y. Zhou,M. L. White,H. Mao
Atmospheric Chemistry and Physics Discussions , 2010,
Abstract: Multi-year time series records of C2-C6 alkanes, C2-C4 alkenes, ethyne, isoprene, C6-C8 aromatics, trichloroethene (C2HCl3), and tetrachloroethene (C2Cl4) from canister samples collected during January 2004–February 2008 at the University of New Hampshire (UNH) AIRMAP Observatory at Thompson Farm (TF) in Durham, NH are presented. The objectives of this work are to identify the sources of nonmethane hydrocarbons (NMHCs) and halocarbons observed at TF, characterize the seasonal and interannual variability in ambient mixing ratios and sources, and estimate regional emission rates of NMHCs. Analysis of correlations and comparisons with emission ratios indicated that a ubiquitous and persistent mix of emissions from several anthropogenic sources is observed throughout the entire year. The highest C2-C8 anthropogenic NMHC mixing ratios were observed in mid to late winter. Following the springtime minimums, the C3-C6 alkanes, C7-C8 aromatics, and C2HCl3 increased in early to mid summer, presumably reflecting enhanced evaporative emissions. Mixing ratios of C2Cl4 and C2HCl3 decreased by 0.7±0.2 and 0.3±0.05 pptv/year, respectively, which is indicative of reduced usage and emissions of these halogenated solvents. Emission rates of C3-C8 NMHCs were estimated to be 109 to 1010 molecules cm-2 s-1 in winter 2006. The emission rates extrapolated to the state of New Hampshire and New England were ~2–60 Mg/day and ~12–430 Mg/day, respectively. The 2002 and 2005 EPA National Emissions Inventory (NEI) emission rates of benzene, ethylbenzene, and xylenes for New Hampshire agreed within ±<5–20% of the emission rates estimated from the TF data, while toluene emissions were overestimated (20–35%) in both versions of the NEI.
Chemical transformations of Hg° during Arctic mercury depletion events sampled from the NASA DC-8
S. Y. Kim,R. Talbot,H. Mao,D. R. Blake
Atmospheric Chemistry and Physics Discussions , 2010, DOI: 10.5194/acpd-10-10077-2010
Abstract: Atmospheric Mercury Depletion Events (MDEs) in Arctic springtime were investigated utilizing a box model based on airborne measurements from the NASA DC-8 during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign. Measurements showed that MDEs occurred near the surface and always over the Arctic Ocean accompanied by concurrent ozone (O3) depletion, enhancement in Br2 mixing ratios, and decreases in ethyne and light weight alkanes. Backward trajectories indicated that most air masses inside the MDEs originated at low altitude over the ocean presumably generating a halogen-rich environment. We developed a box model which considered only gas phase reactions of mercury, halogen species, and O3 chemistry. We conducted a series of sensitivity simulations to determine the factors that are of most importance to MDE formation. The box model results suggested that continuous enhancement of Br2 mixing ratios, a high intensity of solar radiation, or a relatively high NOx regime expedited Hg° depletion. These environments generated high concentrations of Br radical, and thus the model results indicated that the Br radical was very important for Hg° depletion. Utilizing different rate constants for reaction of Hg° + Br produced times to reach Hg° depletion ranging from 22 to 32 h.
Corrigendum to "Carbonyl sulfide exchange in a temperate loblolly pine forest grown under ambient and elevated CO2" published in Atmos. Chem. Phys., 10, 547–561, 2010
M. L. White,Y. Zhou,R. S. Russo,H. Mao
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011, DOI: 10.5194/acp-11-12037-2011
Abstract: No abstract available.
Soil organic carbon storage changes in coastal wetlands of the modern Yellow River Delta from 2000 to 2009
J. Yu, Y. Wang, Y. Li, H. Dong, D. Zhou, G. Han, H. Wu, G. Wang, P. Mao,Y. Gao
Biogeosciences (BG) & Discussions (BGD) , 2012,
Abstract: Soil carbon sequestration plays an essential role in mitigating atmospheric CO2 increases and the subsequently global greenhouse effect. The storages and dynamics of soil organic carbon (SOC) of 0–30 cm soil depth in different landscape types including beaches, reservoir and pond, reed wetland, forest wetland, bush wetland, farmland, building land, bare land (severe saline land) and salt field in the modern Yellow River Delta (YRD) were studied based on the data of the regional survey and laboratory analysis. The landscape types were classified by the interpretation of remote sensing images of 2000 and 2009, which were calibrated by field survey results. The results revealed an increase of 10.59 km2 in the modem YRD area from 2000 to 2009. The SOC density varied ranging from 0.73 kg m 2 to 4.25 kg m 2 at depth of 0–30 cm. There were approx. 3.559 × 106 t and 3.545 × 106 t SOC stored in the YRD in 2000 and 2009, respectively. The SOC storages changed greatly in beaches, bush wetland, farm land and salt field which were affected dominantly by anthropogenic activities. The area of the YRD increased greatly within 10 years, however, the small increase of SOC storage in the region was observed due to landscape changes, indicating that the modern YRD was a potential carbon sink and anthropogenic activity was a key factor for SOC change.
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