Bulgarian Academy of Sciences

About: Bulgarian Academy of Sciences is a government organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Coupling constant & Catalysis. The organization has 17989 authors who have published 36276 publications receiving 642820 citations. The organization is also known as: Bulgarian Academy of Sciences，簡稱：BAS & Balgarska Akademiya na Naukite.

Number size distributions and seasonality of submicron particles in europe 2008–2009

Abstract: Two years of harmonized aerosol number size distribution data from 24 European field monitoring sites have been analysed. The results give a comprehensive overview of the European near surface aerosol particle number concentrations and number size distributions between 30 and 500 nm of dry particle diameter. Spatial and temporal distribution of aerosols in the particle sizes most important for climate applications are presented. We also analyse the annual, weekly and diurnal cycles of the aerosol number concentrations, provide log-normal fitting parameters for median number size distributions, and give guidance notes for data users. Emphasis is placed on the usability of results within the aerosol modelling community. We also show that the aerosol number concentrations of Aitken and accumulation mode particles (with 100 nm dry diameter as a cut-off between modes) are related, although there is significant variation in the ratios of the modal number concentrations. Different aerosol and station types are distinguished from this data and this methodology has potential for further categorization of stations aerosol number size distribution types. The European submicron aerosol was divided into characteristic types: Central European aerosol, characterized by single mode median size distributions, unimodal number concentration histograms and low variability in CCN-sized aerosol number concentrations; Nordic aerosol with low number concentrations, although showing pronounced seasonal variation of especially Aitken mode particles; Mountain sites (altitude over 1000 m a.s.l.) with a strong seasonal cycle in aerosol number concentrations, high variability, and very low median number concentrations. Southern and Western European regions had fewer stations, which decreases the regional representativeness of these results. Aerosol number concentrations over the Britain and Ireland had very high variance and there are indications of mixed air masses from several source regions; the Mediterranean aerosol exhibit high seasonality, and a strong accumulation mode in the summer. The highest concentrations were observed at the JRC station in Northern Italy with high accumulation mode number concentrations in the winter. The aerosol number concentrations at the Arctic station Zeppelin in Ny-Alesund in Svalbard have also a strong seasonal cycle, with higher concentrations of accumulation mode particles in winter, and dominating summer Aitken mode indicating more recently formed particles. Observed particles did not show any statistically significant regional work-week or weekday related variation in number concentrations studied. Analysis products are made for open-access to the research community, available in a freely accessible internet site. The results give to the modelling community a reliable, easy-to-use and freely available comparison dataset of aerosol size distributions. © Author(s) 2011.

Distortion-dependent Raman spectra and mode mixing in R MnO 3 perovskites ( R = La , Pr , Nd , Sm , Eu , Gd , Tb , Dy , Ho , Y )

Abstract: The polarized Raman spectra of orthorhombic $R{\mathrm{MnO}}_{3}$ series $(R=\mathrm{La},\mathrm{Pr},\mathrm{Nd},\mathrm{Sm},\mathrm{Eu},\mathrm{Gd},\mathrm{Tb},\mathrm{Dy},\mathrm{Ho},\mathrm{Y})$ were studied at room temperature. The variation of phonon frequencies with $R$ ionic radius ${r}_{R}$ as a whole confirms the commonly accepted Raman line assignments with two noticeable exceptions: (1) with decreasing ${r}_{R}$ the stretching ${A}_{g}(1)$ and bending ${A}_{g}(3)$ modes strongly mix for $R=\mathrm{Sm}$ to Tb, while for further decrease or ${r}_{R}$ $(R=\mathrm{Dy},\mathrm{Ho},\mathrm{Y})$ the ${A}_{g}(3)$ mode is observed at higher frequency than ${A}_{g}(1)$ mode; (2) similar distortion-dependent mode mixing takes place for the rotational ${A}_{g}(2)$ and $\mathrm{O}1(x)$ $[{A}_{g}(7)]$ modes. The mode mixing is particularly strong for the $R{\mathrm{MnO}}_{3}$ compounds with ${r}_{R}$ values close to the transition from $A$ type to incommensurate sinusoidal antiferromagnetic ordering at low temperatures. The frequency of rotational ${A}_{g}(2)$ and ${A}_{g}(4)$ modes scales to the angles of ${\mathrm{MnO}}_{6}$ $[101]$ and $[010]$ rotations, respectively, and could be used as a measure of their value.