The Vaisala ceilometer CT25K is an eye-safe commercial lidar mainly used to report cloud base heights and vertical visibility for aviation safety purposes. Compared to ceilometers with biaxial optics, its single lens design provides a higher signal-to-noise ratio for lidar return signals from distances below about 600 m, thus increasing its abilities to examine the mixing layer. A CT25K ceilometer took part in the environmental research project VALIUM at the Lower Saxony State Agency for Ecology (NLÖ) in Hannover, Germany, investigating the air pollution in an urban surrounding with various sensors. Lidar return signals are reported every 15 s with a height resolution of 15 m. This paper covers two aspects of the interpretation of these signals. The aerosol backscatter of the atmosphere up to 30 m is compared to the PM10 concentration reported by an in situ sensor every 30 minutes, and the results are interpreted in respect of meteorological parameters such as humidity, temperature, wind, and global radiation. With relative humidity values below 62 % and no rain present the correlation between ceilometer backscatter and PM10 values is good enough to qualify standard ceilometers as instruments for a quantitative analysis of the atmospheric aerosol contents. Backscatter values up to 1000 m height are presented that allow an estimation of the convective boundary layer top in dry weather situations. The atmospheric boundary layer structures derived from ceilometer data are compared to those reported by a SODAR and a RASS that also took part in the VALIUM research project. Finally the backscatter data quality of a double lens ceilometer is compared to that of the single lens CT25K ceilometer to investigate to what extent these lidar systems are also able to report aerosol concentration.

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Precursor mRNA is complexed with proteins in the cell nucleus to form heterogeneous nuclear ribonucleoprotein (hnRNP), and these hnRNPs are found associated in vivo with small nuclear RNPs (snRNPs) for the processing of pre-mRNA. In order to better characterize the ATP-independent initial association of U1 snRNP with hnRNP, an important early event in assembly of the spliceosome complex, we have determined some of the components essential to an in vitro reassociation of U1 snRNP with hnRNP. U1 snRNP reassociated in vitro with 40S hnRNP particles from HeLa cells and, similar to the in vivo hnRNP/U1 snRNP association, the in vitro interaction was sensitive to high salt concentrations. U1 snRNP also associated with in vitro reconstituted hnRNP in which bacteriophage MS2 RNA, which lacks introns, was used as the RNA component. Purified snRNA alone would not associate with the MS2 RNA-reconstituted hnRNP, however, intact U1 snRNP did interact with protein-free MS2 RNA. This indicates that the U1 snRNP proteins are required for the hnRNP/U1 snRNP association, but hnRNP proteins are not. Thus, the initial, ATP-independent association of U1 snRNP with hnRNP seems to be mediated by U1 snRNP protein(s) associating with hnRNA without requiring a splice-site sequence. This complex may then be further stabilized by intron-specific interactions and hnRNP proteins, as well as by other snRNPs.