Resuspension behavior of natural estuarine sediments

The resuspension behavior of natural estuarine sediments was studied using the VIMS Sea Carousel, a benthic annular flume. The bed shear stresses produced by the flume were measured by a hot-film sensor mounted flush on the bottom of a laboratory version of the Carousel under a clear-water and flat-bottom condition. Measurements showed a reasonably uniform bed shear stress across the channel and agreed with the relationship &\tau\sb{lcub}\rm b{rcub}=0.011\Omega\sp{lcub}1.69{rcub},& where &\Omega& = ring speed (rpm) and &\tau\sb{lcub}\rm b{rcub}& = spatially-averaged bed shear stress (N/m&\sp2&), predicted from a previous numerical study. Thus, the &\tau\sb{lcub}\rm b{rcub}& was used as a bed shear stress parameter for this study. Field resuspension experiments were conducted during each season for a full year at two sites in the lower Chesapeake Bay. All the field measurements indicated the existence of surficial fluff on top of the relatively well consolidated sediment beds. These sediment beds behaved like cohesive beds despite the sand dominance, and showed an exponentially decreasing resuspension rate with time for a constant &\tau\sb{lcub}\rm b{rcub}.& These characteristics reflect that the natural sediment beds at the study sites developed a depth-increasing erosion resistance profile. Measured critical bed shear stress, &\tau\sb{lcub}\rm cr{rcub},& was slightly larger at the Wolftrap site than at the Cherrystone site (0.13 &\sim& 0.15 vs. 0.1 &\sim& 0.12 N/m&\sp2&) because of the spatial variation of physical energy condition and biological activity. The temporal variation of sediment erodibility was observed at Cherrystone, but it was not apparent at Wolftrap. From all of the field measurements, a relationship (n = 32, r&\sp2& = 0.89) was found between initial resuspension rate (E&\sb{lcub}\rm o{rcub},& in kg/m&\sp2&/sec) and approximate excess bed shear stress (&\rm\tau\sb{lcub}b{rcub}&-&\rm\tau\sb{lcub}cr{rcub},& in N/m&\sp2&), E&\sb{lcub}\rm o{rcub}& = M(&\tau\sb{lcub}\rm b{rcub}&-&\tau\sb{lcub}\rm cr{rcub})\sp\eta,& where the constants M and &\eta& are 0.018 and 1.88, respectively. Laboratory resuspension tests using the bottom sediments collected at the field sites showed a noncohesive nature of sediment bed (e.g. ripple formation) and much smaller E&\sb{lcub}o{rcub}& (&1\sim2& orders of magnitude) than those measured in the field. These differences reflect the complex nature of sediment properties and constant biophysical reworking processes in the natural environments. The differences also indicate that the direct application of the laboratory results to predict the erodibility of natural sediment is not warranted

Parity-violating πNN\pi NN coupling constant from the flavor-conserving effective weak chiral Lagrangian

We investigate the parity-violating pion-nucleon-nucleon coupling constant $h^1_{\pi NN}$, based on the chiral quark-soliton model. We employ an effective weak Hamiltonian that takes into account the next-to-leading order corrections from QCD to the weak interactions at the quark level. Using the gradient expansion, we derive the leading-order effective weak chiral Lagrangian with the low-energy constants determined. The effective weak chiral Lagrangian is incorporated in the chiral quark-soliton model to calculate the parity-violating $\pi NN$ constant $h^1_{\pi NN}$. We obtain a value of about $10^{-7}$ at the leading order. The corrections from the next-to-leading order reduce the leading order result by about 20~\%.Comment: 12 page

Numerical Sensitivity Tests of Volatile Organic Compounds Emission to PM2.5 Formation during Heat Wave Period in 2018 in Two Southeast Korean Cities

A record-breaking severe heat wave was recorded in southeast Korea from 11 July to 15 August 2018, and the numerical sensitivity simulations of volatile organic compound (VOC) to secondarily generated particulate matter with diameter of less than 2.5 mu m (PM2.5) concentrations were studied in the Busan and Ulsan metropolitan areas in southeast Korea. A weather research and forecasting (WRF) model coupled with chemistry (WRF-Chem) was employed, and we carried out VOC emission sensitivity simulations to investigate variations in PM2.5 concentrations during the heat wave period that occurred from 11 July to 15 August 2018. In our study, when anthropogenic VOC emissions from the Comprehensive Regional Emissions Inventory for Atmospheric Transport Experiment-2015 (CREATE-2015) inventory were increased by approximately a factor of five in southeast Korea, a better agreement with observations of PM2.5 mass concentrations was simulated, implying an underestimation of anthropogenic VOC emissions over southeast Korea. The simulated secondary organic aerosol (SOA) fraction, in particular, showed greater dominance during high temperature periods such as 19-21 July, 2018, with the SOA fractions of 42.3% (in Busan) and 34.3% (in Ulsan) among a sub-total of seven inorganic and organic components. This is considerably higher than observed annual mean organic carbon (OC) fraction (28.4 +/- 4%) among seven components, indicating the enhancement of secondary organic aerosols induced by photochemical reactions during the heat wave period in both metropolitan areas. The PM2.5 to PM10 ratios were 0.69 and 0.74, on average, during the study period in the two cities. These were also significantly higher than the typical range in those cities, which was 0.5-0.6 in 2018. Our simulations implied that extremely high temperatures with no precipitation are significantly important to the secondary generation of PM2.5 with higher secondary organic aerosol fraction via photochemical reactions in southeastern Korean cities. Other possible relationships between anthropogenic VOC emissions and temperature during the heat wave episode are also discussed in this study