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Size distributions and particle number concentrations of atmospheric aerosols in the size (diameter) range from 15 nm to 10 μm were measured on board of a research ship during three cruises in China adjacent seas. The total parti...
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Size distributions and particle number concentrations of atmospheric aerosols in the size (diameter) range from 15 nm to 10 μm were measured on board of a research ship during three cruises in China adjacent seas. The total particle number concentrations were in average around 4000 cm~(-3) in Yellow Sea, 2000 cm~(-3) in East China Sea and 1000 cm~(-3) in South China Sea. The observed size distributions were fitted with two or three log-normal modes and the data were classified according to time, regions and calculated air mass back-trajectories. The size distribution spectra of air masses of polluted continental origin as their back-trajectories showed were characterized by single mode with total number concentrations between 1000 and 10000 cm~(-3). The size distributions in marine air masses showed dual mode characteristics, one maximum at 40-60 nm and the other at 160-190 nm with total number concentrations below 1000cm~(-3). This type of dual mode was more pronounced at longer residence time of the air masses over the ocean. The burst of ultra-fine (UF) particles and the consequent growth processes were observed twice in Yellow Sea and possible reasons leading to these events are discussed. The particle growth rate (GR) was 3.4 ±0.9 and 3.5 ± 1.6 nm h~(-1), respectively (95% confidence interval), indicating that the UF particles can grow to cloud condensation nuclei (CCN) within the next 1-2 days.
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Using the quasi-classical trajectory (QCT) method, this paper has explored the product rotational polarization for the reaction O(3P) + HCl → OH + Cl on the 3A″ potential energy surface constructed by Ramachandran B et al. (Rama...
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Using the quasi-classical trajectory (QCT) method, this paper has explored the product rotational polarization for the reaction O(3P) + HCl → OH + Cl on the 3A″ potential energy surface constructed by Ramachandran B et al. (Ramachandran B et al., J. Chem. Phys.119: 9590, 2003). The distributions of product polarization P(θr),P(φr) and the generalized polarization-dependent differential cross-sections (2π/σ)(dσ00/dσt) and (2π/σ)(dσ22+/dωt) have been calculated. The results indicate that the vibrational excitation of HCl has a considerable influence on the distribution of the k-j′ correlation and the k-k′-j′ correlation.
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During the CAREBEIJING campaign in 2006, imaging differential optical absorption spectroscopy (I-DOAS) measurements were made from 08:00 to 16:00 on September 9 and 10 over Beijing, China. Detailed images of the near-surface NO_2 ...
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During the CAREBEIJING campaign in 2006, imaging differential optical absorption spectroscopy (I-DOAS) measurements were made from 08:00 to 16:00 on September 9 and 10 over Beijing, China. Detailed images of the near-surface NO_2 differential slant column density (DSCD) distribution over Beijing were obtained. Images with less than a 30-min temporal resolution showed both horizontal and vertical variations in NO_2 distributions. For DSCD to mixing ratio conversion, path length along the lines of I-DOAS lines of sight was estimated using the light-extinction coefficient and Angstrom exponent data obtained by a transmissometer and a sunphotometer, respectively. Mixing ratios measured by an in-situ NO_2 analyzer were compared with those estimated by the I-DOAS instrument. The obtained temporal and spatial variations in NO_2 distributions measured by I-DOAS for the two days are interpreted with consideration of the locations of the major NO_X sources and local wind conditions. I-DOAS measurements have been applied in this study for estimating NO_2 distribution over an urban area with multiple and distributed emission sources. Results are obtained for estimated temporal and spatial NO_2 distributions over the urban atmosphere; demonstrating the capability of the I-DOAS technique. We discuss in this paper the use of I-DOAS measurements to estimate the NO_2 distribution over an urban area with multiple distributed emission sources.
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As the need for novel antibiotic classes to combat bacterial drug resistance increases, the paucity of leads resulting from target-based antibacterial screening of pharmaceutical compound libraries is of major concern. One explana...
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As the need for novel antibiotic classes to combat bacterial drug resistance increases, the paucity of leads resulting from target-based antibacterial screening of pharmaceutical compound libraries is of major concern. One explanation for this lack of success is that antibacterial screening efforts have not leveraged the eukary-otic bias resulting from more extensive chemistry efforts targeting eukaryotic gene families such as G protein-coupled receptors and protein kinases. Consistent with a focus on antibacterial target space resembling these eukaryotic targets, we used whole-cell screening to identify a series of antibacterial pyridopyrimidines derived from a protein kinase inhibitor pharmacophore. In bacteria, the pyridopyrimidines target the ATP-binding site of biotin carboxylase (BC), which catalyzes the first enzymatic step of fatty acid biosynthesis. These inhibitors are effective in vitro and in vivo against fastidious Gram-negative pathogens including Haemophi-lus influenzae. Although the BC active site has architectural similarity to those of eukaryotic protein kinases, inhibitor binding to the BC ATP-binding site is distinct from the protein kinase-binding mode, such that the inhibitors are selective for bacterial BC. In summary, we have discovered a promising class of potent antibacterials with a previously undescribed mechanism of action. In consideration of the eukaryotic bias of pharmaceutical libraries, our findings also suggest that pursuit of a novel inhibitor leads for antibacterial targets with active-site structural similarity to known human targets will likely be more fruitful than the traditional focus on unique bacterial target space, particularly when structure-based and computational methodologies are applied to ensure bacterial selectivity.
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The enantiomeric signatures of organochlorine pesticides were measured in air masses from Okinawa, Japan and three remote locations in the Pacific Northwestern United States: Cheeka Peak Observatory (CPO), a marine boundary layer ...
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The enantiomeric signatures of organochlorine pesticides were measured in air masses from Okinawa, Japan and three remote locations in the Pacific Northwestern United States: Cheeka Peak Observatory (CPO), a marine boundary layer site on the Olympic Peninsula of Washington at 500 m above sea level (m.a.s.l); Mary's Peak Observatory (MPO), a site at 1250 m.a.s.l in Oregon's Coast range; and Mt. Bachelor Observatory (MBO), a site at 2763 m.a.s.l in Oregon's Cascade range. The enantiomeric signatures of composite soil samples, collected from China, South Korea, and the western U.S. were also measured. The data from chiral analysis was expressed as the enantiomeric fraction, defined as (+) enantiomer/(sum of the (+) and (-) enantiomers), where a racemic composition has EF = 0.5. Racemic a-hexachlorocyclohexane (a-HCH) was measured in Asian air masses at Okinawa and in Chinese and South Korean soils. Nonracemic α-HCH (EF = 0.528 ± 0.0048) was measured in regional air masses at CPO, and may reflect volatilization from the Pacific Ocean and regional soils. However, during trans-Pacific transport events at CPO, the a-HCH EFs were significantly more racemic (EF = 0.513 ± 0.0003, p < 0.001). Racemic a-HCH was consistently measured at MPO and MBO in trans-Pacific air masses that had spent considerable time in the free troposphere. The a-HCH EFs in CPO, MPO, and MBO air masses were negatively correlated (p = 0.0017) with the amount of time the air mass spent above the boundary layer, along the 10-day back air mass trajectory, prior to being sampled. This suggests that, on the West coast of the U.S., the α-HCH in the free troposphere is racemic. Racemic signatures of cis- and frans-chlordane were measured
in air masses at all four air sampling sites, suggesting that Asian and U.S. urban areas continue to be sources of chlordane that has not yet been biotransformed.
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Molecular mechanisms that initiate meiosis have been studied in fungi and mammals, but little is known about the mechanisms directing the meiosis transition in other organisms. To elucidate meiosis initiation in plants, we charact...
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Molecular mechanisms that initiate meiosis have been studied in fungi and mammals, but little is known about the mechanisms directing the meiosis transition in other organisms. To elucidate meiosis initiation in plants, we characterized and cloned the ameiotic1 (am1) gene, which affects the transition to meiosis and progression through the early stages of meiotic prophase in maize. We demonstrate that all meiotic processes require ami, including expression of meiosis-specific genes, establishment of the meiotic chromosome structure, meiosis-specific telomere behavior, meiotic recombination, pairing, synapsis, and installation of the meiosis-specific cytoskeleton. As a result, in most am1 mutants premeiotic cells enter mitosis instead of meiosis. Unlike the genes involved in initiating meiosis in yeast and mouse, am1 also has a second downstream function, whereby it regulates the transition through a novel leptotene-zygotene checkpoint, a key step in early meiotic prophase. The am1 gene encodes a plant-specific protein with an unknown biochemical function. The AM1 protein is diffuse in the nucleus during the initiation of meiosis and then binds to chromatin in early meiotic prophase I when it regulates the leptotene-zygotene progression.
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A kinetic study on the reactions of the OH radical and ozone with acetylacetone (AcAc) has been performed in a 1080 L quartz glass reaction chamber using in situ FTIR spectroscopy analysis. Temperature dependent rate coefficients ...
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A kinetic study on the reactions of the OH radical and ozone with acetylacetone (AcAc) has been performed in a 1080 L quartz glass reaction chamber using in situ FTIR spectroscopy analysis. Temperature dependent rate coefficients for the reaction of AcAc with the OH radical were determined over the temperature range 285-31 OK using the relative kinetic method. The following Arrhenius expression was derived: k = 3.35 × 10~(-12) exp((983 ± 130)/T) cm~3 molecule~(-1) s~(-1), where the indicated error is the two least-squares deviation. A rate coefficient (in units of cm~3 molecule~(-1) s~(-1)) of (1.03 ± 0.31) × 10~(-18) has been obtained at (298 ± 3) K for the reaction of ozone with AcAc. A product investigation on the gas-phase reaction of OH radical with AcAc was conducted in a 405 L borosilicate glass chamber using in situ FIR spectroscopy to monitor reactants and products. Methylglyoxal, acetic acid, peroxy acetic nitrate (PAN) were positively identified as products with molar yields of (20.8 ± 4.5)%, (16.9 ± 3.4)%, and (2.0 ± 0.5)%, respectively. From the residual infrared spectrum the main products are attributed to 2,3,4-pentantrione (CH_3-CO-CO-CO-CH_3) and its hydrated analogue pentan-2,3-dione-4-diol (CH_3-CO-CO-C(OH)_2-CH_3). Based on the observed products, a simplified mechanism for the reaction of the OH radical with AcAc is proposed.
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