Bielefeld University

About: Bielefeld University is a education organization based out in Bielefeld, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Population & Quantum chromodynamics. The organization has 10123 authors who have published 26576 publications receiving 728250 citations. The organization is also known as: University of Bielefeld & UNIVERSITAET BIELEFELD.

Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water

Abstract: . We present a novel kinetic multi-layer model for gas-particle interactions in aerosols and clouds (KM-GAP) that treats explicitly all steps of mass transport and chemical reaction of semi-volatile species partitioning between gas phase, particle surface and particle bulk. KM-GAP is based on the PRA model framework (Poschl-Rudich-Ammann, 2007), and it includes gas phase diffusion, reversible adsorption, surface reactions, bulk diffusion and reaction, as well as condensation, evaporation and heat transfer. The size change of atmospheric particles and the temporal evolution and spatial profile of the concentration of individual chemical species can be modeled along with gas uptake and accommodation coefficients. Depending on the complexity of the investigated system and the computational constraints, unlimited numbers of semi-volatile species, chemical reactions, and physical processes can be treated, and the model shall help to bridge gaps in the understanding and quantification of multiphase chemistry and microphysics in atmospheric aerosols and clouds. In this study we demonstrate how KM-GAP can be used to analyze, interpret and design experimental investigations of changes in particle size and chemical composition in response to condensation, evaporation, and chemical reaction. For the condensational growth of water droplets, our kinetic model results provide a direct link between laboratory observations and molecular dynamic simulations, confirming that the accommodation coefficient of water at ~270 K is close to unity (Winkler et al., 2006). Literature data on the evaporation of dioctyl phthalate as a function of particle size and time can be reproduced, and the model results suggest that changes in the experimental conditions like aerosol particle concentration and chamber geometry may influence the evaporation kinetics and can be optimized for efficient probing of specific physical effects and parameters. With regard to oxidative aging of organic aerosol particles, we illustrate how the formation and evaporation of volatile reaction products like nonanal can cause a decrease in the size of oleic acid particles exposed to ozone.

Predictions for $p+$Pb Collisions at sqrt s_NN = 5 TeV

Abstract: Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p+Pb collisions at $\sqrt{s_{_{\it NN}}} = 5\, {\rm TeV}$ are compiled and compared. When test run data are available, they are compared to the model predictions.

Broadly tunable vacuum-ultraviolet/extreme-ultraviolet radiation generated by resonant third-order frequency conversion in krypton

Abstract: Resonant third-order sum- and difference-frequency conversion (ωuv = 2ωR ± ωT) of pulsed-dye-laser radiation is investigated in the rare gas, Kr. The frequency ωR(λR = 216.6 nm) is resonant with the Kr two-photon transition 4p–5p[5/2, 2]. On tuning ωT in the range λT = 219–364 nm, the sum frequency generates light in the extreme ultraviolet (XUV) (λxuv = 72.5–83.5 nm). In agreement with theoretical predictions, the conversion efficiency η is almost constant within this spectral range. At input powers PR = 14 kW and PT = 400 kW, the pulse power of the XUV exceeded Pxuv = 20 W. However, absorptions in the Kr gas reduced the power of the detected XUV light to about 5 W (effective efficiency, η = 1.2 × 10−5). With laser light at λT = 272–737 nm, the difference frequency generates continuously tunable radiation in the vacuum ultraviolet (VUV) (λvuv = 127–180 nm). In this range, the conversion efficiency increases with wavelength by more than 1 order of magnitude. At λvuv = 135 nm, for example, input powers PR = 0.2 MW and PT = 1.2 MW generate VUV light with Pvuv = 250 W (n = 1.8 × 10−4). At λvuv = 175 nm, a lower input (PR = 80 kW, PT = 560 kW) produced VUV light pulses of Pvuv = 1.8 kW (η = 2.8 × 10−3). This spectral variation of η is in agreement with the calculated wavelength dependence of the nonlinear susceptibility and of the gas pressure required for optimum VUV output.