Secondary Organic Aerosols from OH Oxidation of Cyclic Volatile Methyl Siloxanes as an Important Si Source in the Atmosphere

Cyclic volatile methyl siloxanes (cVMS) are active ingredients in widely used consumer products, which can volatilize into the atmosphere, thus attracting much attention due to their potential environmental risks. While in the atmosphere the cVMS undergo oxidation yielding both gaseous and particulate products. The aerosol yields and compositions from the OH oxidation of four cVMS (D3-D6) were determined under low and high-NOx conditions in an oxidation flow reactor. The aerosol yields progressively increased from D3 to D6, consistent with the volatilities and molecule weights of these cVMS. NOx can restrict the formation of SOA, leading to lower SOA yields under high-NOx conditions than under low-NOx conditions, with a yield decrease between 0.05–0.30 depending on the cVMS. Ammonium sulfate seeds exhibited minor impacts on SOA yields under low-NOx conditions, but significantly increased the SOA yields in the oxidation of D3-D5 at short photochemical ages under high-NOx conditions. The mass spectra of the SOA showed a dependence of its chemical compositions on OH exposure. At high exposures, equivalent to photochemical ages of > 6 days in the atmosphere, D4-D6 SOA mainly consisted of CxHy and CxHyOzSin under low-NOx conditions, whereas they primarily contained NmOz, CxHy, CxHyO1, CxHyO>1 and CxHyOzSin under high-NOx conditions. Using the yield data from the present study and reported cVMS annual production, a global cVMS-derived SOA source strength is estimated to be 0.16 Tg yr−1, distributed over major urban centers.

Aeciospore ejection in the rust pathogen Puccinia graminis is driven by moisture ingress

Fungi have evolved an array of spore discharge and dispersal processes. Here, we developed a theoretical model that explains the ejection mechanics of aeciospore liberation in the stem rust pathogen Puccinia graminis. Aeciospores are released from cluster cups formed on its Berberis host, spreading early-season inoculum into neighboring small-grain crops. Our model illustrates that during dew or rainfall, changes in aeciospore turgidity exerts substantial force on neighboring aeciospores in cluster cups whilst gaps between spores become perfused with water. This perfusion coats aeciospores with a lubrication film that facilitates expulsion, with single aeciospores reaching speeds of 0.053 to 0.754 m·s−1. We also used aeciospore source strength estimates to simulate the aeciospore dispersal gradient and incorporated this into a publicly available web interface. This aids farmers and legislators to assess current local risk of dispersal and facilitates development of sophisticated epidemiological models to potentially curtail stem rust epidemics originating on Berberis.

Evaluation of Dispersion of Lead-Bearing Mine Wastes in Kabwe District, Zambia

Dispersion of lead (Pb) in mine wastes was simulated for reproducing Pb contamination of soil in Kabwe District, Zambia. Local weather data of year 2019 were monitored in situ and used for the simulations. The plume model, weak puff model, and no puff model were adopted for calculation of Pb dispersion under different wind conditions. The results showed that Pb dispersion from the Kabwe mine was directly affected by wind directions and speeds in the dry season, although it was not appreciably affected in the rainy season. This may be because the source strength is lower in the rainy season due to higher water content of the surface. This indicates that Pb dispersion patterns depend on the season. In addition, the distribution of the amount of deposited Pb-bearing soils around the mine corresponded to the distribution of Pb contents in soils. These results suggest that Pb contamination in soils primarily results from dispersion of fine mine wastes.

3D Printed Brachytherapy Jig for Reference Air Kerma Rate Calibration

3D printing in modern radiotherapy provides creative autonomy which can be a valuable tool for use in brachytherapy source calibration. Radiotherapy centres may verify their brachytherapy source strength with a calibrated Farmer chamber. For this purpose, a jig was designed, 3D printed and commissioned for in-air source strength calibration. Measurements on four afterloaders with varied equipment and environments were completed. A full uncertainty budget was developed and measurements with the in-air jig were consistently within 3% of the certificate source strength. By creating a jig that is able to be customised to multiple catheter sizes and cylindrical chamber designs, centres can be provided with the option of independently checking their source strength with ease and for little cost.

TURKEY: THE REGIONAL ROLE IN THE GULF SYSTEM

Geographical environment any political system is a source strength or weakness that system, and then they represent either add or deduction from vocabulary power to the system, geographical environment different its elements of site area and topography affect directly or indirectly in formulation state its foreign policy, Consequently, it acts as one of the determinants of the strength of the state's external role. The geographical environment of the state determines the vital field for its external political movement, and determines - to a large extent - the threat directed to its security and its sources.

Aircraft Cabin Ventilation Theory

Ventilation on board of an aircraft is governed by the ventilation equation. In the steady state case, a concentration of any substance depends only on the source strength and the effective air flow rate for ventilation. Not all air for ventilation is effective and helps to lower concentration. Some air leaves the cabin without mixing and rinsing. This is expressed by the ventilation efficiency. The dynamics follows an exponential function and is expressed by a time constant that depends on the air change rate and the ventilation efficiency. The (theoretical) air change rate is the air flow rate divided by the volume of the room. With full mixing (i.e. ventilation efficiency of 1), the concentration is reduced to 36.8% after one air change.