Lattice QCD calculation of ππ\pi\pi scattering length

We study s-wave pion-pion ($\pi\pi$) scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV. In the "Asqtad" improved staggered fermion formulation, we calculate the $\pi\pi$ four-point functions for isospin I=0 and 2 channels, and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results. Extrapolating to the physical pion mass gives the scattering lengths as $m_\pi a_0^{I=2} = -0.0416(2)$ and $m_\pi a_0^{I=0} = 0.186(2)$ for isospin I=2 and 0 channels, respectively. Our lattice simulation for $\pi\pi$ scattering length in the I=0 channel is an exploratory study, where we include the disconnected contribution, and our preliminary result is near to its experimental value. These simulations are performed with MILC 2+1 flavor gauge configurations at lattice spacing $a \approx 0.15$ fm.Comment: Remove some typo

Contributions of biomass/biofuel burning to organic aerosols and particulate matter in Tanzania, East Africa, based on analyses of ionic species, organic and elemental carbon, levoglucosan and mannosan

Atmospheric aerosol samples of PM_2.5 and PM₁₀ were collected at a rural site in Tanzania, East Africa, in 2011 during wet and dry seasons and were analysed for carbonaceous components, levoglucosan, mannosan and water-soluble inorganic ions. The contributions of biomass/biofuel burning to the organic carbon (OC) and particulate matter (PM) mass were estimated to be 46&ndash;52% and 87&ndash;13%, respectively. The mean mass concentrations of PM_2.5 and PM₁₀ were 28 ± 6 μg m⁻³ and 47 ± 8 μg m⁻³ in wet season, and 39 ± 10 μg m⁻³ and 61 ± 19 μg m⁻³ in dry season, respectively. Total carbon (TC) accounted for 16&ndash;19% of the PM_2.5 mass and 13&ndash;15% of the PM₁₀ mass. On average, 86 to 89% of TC in PM_2.5 and 87 to 90% of TC in PM₁₀ was OC, of which 67&ndash;72% and 63% was found to be water-soluble organic carbon (WSOC) in PM_2.5 and PM₁₀, respectively. We found that concentrations of levoglucosan and mannosan (specific organic tracers of pyrolysis of cellulose) well correlated with non-sea-salt potassium (nss-K⁺) (<i>r</i>² = 0.56&ndash;0.75), OC (<i>r</i>² = 0.75&ndash;0.96) and WSOC (<i>r</i>² = 0.52&ndash;0.78). The K⁺ / OC ratios varied from 0.06 to 0.36 in PM_2.5 and from 0.03 to 0.36 in PM₁₀ with slightly higher ratios in dry season. Mean percent ratios of levoglucosan and mannosan to OC were found to be 3&ndash;4% for PM_2.5 and PM₁₀ in both seasons. We found lower levoglucosan / K⁺ ratios and higher K⁺ / EC (elemental carbon) ratios in the biomass-burning aerosols from Tanzania than those reported from other regions. This feature is consistent with the high levels of potassium reported in the soils of Morogoro, Tanzania, suggesting an importance of direct emission of potassium by soil resuspension although K⁺ is present mostly in fine particles. It is also likely that biomass burning of vegetation of Tanzania emits high levels of potassium that may be enriched in plant tissues. The present study demonstrates that emissions from mixed biomass- and biofuel-burning activities largely influence the air quality in Tanzania

Seasonal variations of stable carbon isotopic composition and biogenic tracer compounds of water-soluble organic aerosols in a deciduous forest

To investigate the seasonal changes in biogenic water-soluble organic carbon (WSOC) aerosols in a boreal forest, aerosol samples were collected continuously in the canopy of a deciduous forest in northern Japan during 2009–2010. Stable carbon isotopic composition of WSOC (&amp;delta;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;WSOC&lt;/sub&gt;) in total suspended particulate matter (TSP) exhibited a distinct seasonal cycle, with lower values from June through September (−25.5&amp;plusmn;0.5 &amp;permil;). This cycle follows the net CO&lt;sub&gt;2&lt;/sub&gt; exchange between the forest ecosystem and the atmosphere, indicating that &amp;delta;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;WSOC&lt;/sub&gt; likely reflects the biological activity at the forest site. WSOC concentrations showed the highest values in early summer and autumn. Positive matrix factorization (PMF) analysis indicated that the factor in which biogenic secondary organic aerosols (BSOAs) dominated accounted for ~40 % of the highest concentrations of WSOC, where BSOAs mostly consisted of α-/β-pinene SOA. In addition, primary biological aerosol particles (PBAPs) made similar contributions (~57 %) to the WSOC near the forest floor in early summer. This finding indicates that the production of both primary and secondary WSOC aerosols is important during the growing season in a deciduous forest. The methanesulfonic acid (MSA) maximum was also found in early summer and had a distinct vertical gradient with larger concentrations near the forest floor. Together with the similar vertical gradients found for WSOC and &amp;delta;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;WSOC&lt;/sub&gt; as well as the α-/β-pinene SOA tracers, our results indicate that the forest floor, including ground vegetation and soil, acts as a significant source of WSOC in TSP within a forest canopy at the study site

Progressive Collapse Resistance of Precast Concrete Beam-Column Sub-assemblages with High-Performance Dry Connections

Due to its relatively lower integrity, precast concrete structures are considered to be more vulnerable to progressive collapse than cast-in-place concrete structures. However, to date, majority of existing studies on progressive collapse focused on cast-in-place concrete structures, little attentions were paid to precast concrete structures. Among existing precast concrete structures, unbonded post-tensioning precast concrete structure is one of innovation dry connection structural systems, which no casting at the connections on site. Its excellent seismic performance was recognized by many studies, while studies on its progressive collapse resistance were very few. To fill this knowledge gaps, in this paper, eight half-scaled unbonded post-tensioning precast concrete beam-column sub-assemblages with different connection configurations were tested through pushdown tests to investigate their capacities and resistance mechanisms to prevent progressive collapse. The test results demonstrated various behaviors of beam-column sub-assemblages with different connection types. It was found that, as the longitudinal reinforcements were discontinuous across the beam-column joint region in the beams, flexural action observed in the cast-in-place concrete frames was not mobilized for the specimens with purely unbonded post-tensioning connections. When the specimens installed top-seat angles at the beam-column interfaces, considerable flexural action capacity could be mobilized for load resistance. Moreover, it was found that the failure modes of the specimens are distinctly different to that of conventional reinforced concrete frames or precast concrete frames with cast-in-place joints. The characteristic of compressive arch action and tensile catenary action in tested specimens is quite different to that of conventional reinforced concrete frames

Impact of anthropogenic emission on air quality over a megacity – revealed from an intensive atmospheric campaign during the Chinese Spring Festival

The Chinese Spring Festival is one of the most important traditional festivals in China. The peak transport in the Spring Festival season (spring travel rush) provides a unique opportunity for investigating the impact of human activity on air quality in the Chinese megacities. Emission sources are varied and fluctuate greatly before, during and after the Festival. Increased vehicular emissions during the spring travel rush before the 2009 Festival resulted in high level pollutants of NOx (270 μg m−3), CO (2572 μg m−3), black carbon (BC) (8.5 μg m−3) and extremely low single scattering albedo of 0.76 in Shanghai, indicating strong, fresh combustion. Organics contributed most to PM2.5, followed by NO3−, NH4+, and SO42−. During the Chinese Lunar New Year\u27s Eve and Day, widespread usage of fireworks caused heavy pollution of extremely high aerosol concentration, scattering coefficient, SO2, and NOx. Due to the spring travel rush after the festival, anthropogenic emissions gradually climbed and mirrored corresponding increases in the aerosol components and gaseous pollutants. Secondary inorganic aerosol (SO42−, NO3−, and NH4+) accounted for a dominant fraction of 74% in PM2.5 due to an increase in human activity. There was a greater demand for energy as vast numbers of people using public transportation or driving their own vehicles returned home after the Festival. Factories and constructions sites were operating again. The potential source contribution function (PSCF) analysis illustrated the possible source areas for air pollutants of Shanghai. The effects of regional and long-range transport were both revealed. Five major sources, i.e. natural sources, vehicular emissions, burning of fireworks, industrial and metallurgical emissions, and coal burning were identified using the principle component analysis. The average visibility during the whole study period was less than 6 km. It had been estimated that 50% of the total light extinction was due to the high water vapor in the atmosphere. This study demonstrates that organic aerosol was the largest contributor to aerosol extinction at 47%, followed by sulfate ammonium, nitrate ammonium, and EC at 22%, 14%, and 12%, respectively. Our results indicated the dominant role of traffic-related aerosol species (i.e. organic aerosol, nitrate and EC) on the formation of air pollution, and suggested the importance of controlling vehicle numbers and emissions in mega-cities of China as its population and economy continue to grow

SU(3) Predictions of B→PPB\to PP Decays in the Standard Model

With SU(3) symmetry one only needs 13 hadronic parameters to describe $B\to PP$ decays in the Standard Model. When annihilation contributions are neglected, only 7 hadronic parameters are needed. These parameters can be determined from existing experimental data and some unmeasured branching ratios and CP asymmetries of the type $B\to PP$ can be predicted. In this talk we present SU(3) predictions of branching ratios and CP asymmetries for $B\to PP$ decays in the Standard Model.Comment: 4 pages, no figure. Talk present at the 5th International Conference on Hyperons, Charm and Beauty Hadrons, Vancouver, June 200

Non-uniform dispersion of toughening agents and its influence on the mechanical properties of polypropylene

To achieve excellent properties of polymer blends and composites, good dispersion and uniform distribution of second component or filler in the matrix are often required. However, more and more evidences reveal that uniform distribution is not always the best. To further prove this idea, in this work, we purposely designed and prepared different samples of isotactic polypropylene (iPP)/elastomer or iPP/β-nucleating agent with uniform and non-uniform distribution of the modifiers via stacking the blending sheets in different sequence. It was found that for a given amount of toughening agent, the impact strength of polymer blends with non-uniform distribution of elastomer or β-nucleating agent could be much higher than its uniformly dispersed counterpart, while the tensile strength and tensile modulus remain relatively constant. The instrumented impact test confirmed that among the samples with different layered structures, the absorbed energy during crack initiation differs little from each other. Whereas absorbed energy during crack propagation process shows the same trend as final impact strength, making it the controlling parameter during the impact process. When cracks are initiated at higher toughening agents content side, the relatively smooth fracture surfaces near the crack edge area proved that they absorb small energy and the adjacent inner part showed obviously plastic deformation, corresponding to higher energy absorption. Our work demonstrates again that design and control of the hierarchical structure of polymer articles is vital for high performance properties and non-uniform distribution of filler could be much better than the uniform distribution