On the reactive uptake of gaseous compounds by organic-coated aqueous aerosols: theoretical analysis and application to the heterogeneous hydrolysis of N2O5

The presence of organic coatings on aerosols may have important consequences to the atmospheric chemistry, in particular to the N2O5 heterogeneous hydrolysis. This is demonstrated by recent experiments which show that the uptake of N2O5 by aqueous aerosols is slowed considerably when an organic coating consisting of monoterpene oxidation products is added on the particles. To treat the mechanisms behind the suppression, an extension of the resistor model, which has been widely applied in investigation of the heterogeneous uptake by aerosols, was derived. The extension accounts for dissolution, diffusion, and chemical reactions in a multilayered organic coating, and it provides a parametrization for the heterogeneous uptake by organic-coated aerosols that can be applied in large-scale models. Moreover, the framework was applied to interpret the findings regarding the decreased uptake of N2O5 by the organic-coated aerosols. Performed calculations suggested that the reaction rate constant of N2O5 in the coating is decreased by 3-5 orders of magnitude, in addition to which the product of the solubility of N2O5 and its diffusion coefficient in the coating is reduced more than an order of magnitude compared to the corresponding value for the aqueous phase. The results suggest also that the accommodation coefficient of N2O5 to such coatings is no more than a factor of 2 smaller than that to pure water surfaces. Finally, the relevance of the results to the atmospheric N2O5 heterogeneous hydrolysis is discussed and implications to planning further laboratory studies focusing on secondary organic aerosol formation are pointed out.     

Optimal control of ultrafast laser driven many-electron dynamics in a polyatomic molecule: N-methyl-6-quinolone

We report time-dependent configuration interaction singles calculations for the ultrafast laser driven many-electron dynamics in a polyatomic molecule, N-methyl-6-quinolone. We employ optimal control theory to achieve a nearly state-selective excitation from the S(0) to the S(1) state, on a time scale of a few ( approximately 6) femtoseconds. The optimal control scheme is shown to correct for effects opposing a state-selective transition, such as multiphoton transitions and other, nonlinear phenomena, which are induced by the ultrashort and intense laser fields. In contrast, simple two-level pi pulses are not effective in state-selective excitations when very short pulses are used. Also, the dependence of multiphoton and nonlinear effects on the number of states included in the dynamical simulations is investigated.     

Insights into the structure of the active site of the O2-tolerant membrane bound [NiFe] hydrogenase of R. eutropha H16 by molecular modelling

Structural models for the Ni-B state of the wild-type and C81S protein variant of the membrane-bound [NiFe] hydrogenase from Ralstonia eutropha H16 were derived by applying the homology model technique combined with molecular simulations and a hybrid quantum mechanical/molecular mechanical approach. The active site structure was assessed by comparing calculated and experimental IR spectra, confirming the view that the active site structure is very similar to those of anaerobic standard hydrogenases. In addition, the data suggest the presence of a water molecule in the second coordination sphere of the active centre.     

Fine-grained pitch processing of music and speech in congenital amusia

Congenital amusia is a lifelong disorder of music processing that has been ascribed to impaired pitch perception and memory. The present study tested a large group of amusics (n=17) and provided evidence that their pitch deficit affects pitch processing in speech to a lesser extent: Fine-grained pitch discrimination was better in spoken syllables than in acoustically matched tones. Unlike amusics, control participants performed fine-grained pitch discrimination better for musical material than for verbal material. These findings suggest that pitch extraction can be influenced by the nature of the material (music vs speech), and that amusics' pitch deficit is not restricted to musical material, but extends to segmented speech events.     

Artin's map in stable homology

Using a recent theorem of Galatius, we identify the map on stablehomology induced by Artin's injection of the braid group β_ninto the automorphism group of the free group Aut F_n.     

Fluorescence spectroscopy of potential electroluminescent materials: Substituent effects on DSB and segmented PPV derivatives

The absorption and fluorescence of substituted distyrylbenzene (DSB) derivatives and segmented poly(phenylene vinylene) (PPV) derivatives are characterized by long-wavelength absorption maxima and absorption coefficients of λ_a = 380–450 nm, ε = 20,000–60,000 M⁻¹ cm¹ and fluorescence maxima, quantum yields, and decay times of λ_r = 440–530 nm, Φ_f = 0.2–0.9, and Τ = 0.8–2.5 ns, respectively. Alkoxy substituents at the central phenylene ring of DSB groups increase the bathochromic shift in the spectra in comparison to DSB, without a significant decrease in the high DSB fluorescence quantum yield. Both phenyl and cyano substitutions at the vinylene bridge lead to a further bathochromic shift of the fluorescence and a decrease in the quantum yield to ca. 0.4. The DSB derivatives and the related segmented PPV derivatives show nearly the same absorption spectra, fluorescence spectra, and radiative rate constantsk _f= Φ_f/Τ, indicating the efficacy of the segmentation of the polymer chain. The radiative rate constants determined by the Φ_f and Τ values and by the Strickler/Berg formula are in reasonable agreement. This supports the possibility of interpreting the properties of the polymers in terms of their DSB units. The decrease in the emission anisotropy can be ascribed to multistep energy transfer processes between different oriented segments.