Measurement and modeling of cloud condensation nuclei in continental air

Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. Knowledge of the spatial and temporal distribution of CCN in the atmosphere is essential to understand and describe the effects of aerosols in meteorological models. In this study, CCN properties were measured in polluted and pristine air of different continental regions, and the results were parameterized for efficient prediction of CCN concentrations.The continuous-flow CCN counter used for size-resolved measurements of CCN efficiency spectra (activation curves) was calibrated with ammonium sulfate and sodium chloride aerosols for a wide range of water vapor supersaturations (S=0.068% to 1.27%). A comprehensive uncertainty analysis showed that the instrument calibration depends strongly on the applied particle generation techniques, Köhler model calculations, and water activity parameterizations (relative deviations in S up to 25%). Laboratory experiments and a comparison with other CCN instruments confirmed the high accuracy and precision of the calibration and measurement procedures developed and applied in this study.The mean CCN number concentrations (NCCN,S) observed in polluted mega-city air and biomass burning smoke (Beijing and Pearl River Delta, China) ranged from 1000 cm−3 at S=0.068% to 16 000 cm−3 at S=1.27%, which is about two orders of magnitude higher than in pristine air at remote continental sites (Swiss Alps, Amazonian rainforest). Effective average hygroscopicity parameters, κ, describing the influence of chemical composition on the CCN activity of aerosol particles were derived from the measurement data. They varied in the range of 0.3±0.2, were size-dependent, and could be parameterized as a function of organic and inorganic aerosol mass fraction. At low S (≤0.27%), substantial portions of externally mixed CCN-inactive particles with much lower hygroscopicity were observed in polluted air (fresh soot particles with κ≈0.01). Thus, the aerosol particle mixing state needs to be known for highly accurate predictions of NCCN,S. Nevertheless, the observed CCN number concentrations could be efficiently approximated using measured aerosol particle number size distributions and a simple κ-Köhler model with a single proxy for the effective average particle hygroscopicity. The relative deviations between observations and model predictions were on average less than 20% when a constant average value of κ=0.3 was used in conjunction with variable size distribution data. With a constant average size distribution, however, the deviations increased up to 100% and more. The measurement and model results demonstrate that the aerosol particle number and size are the major predictors for the variability of the CCN concentration in continental boundary layer air, followed by particle composition and hygroscopicity as relatively minor modulators. Depending on the required and applicable level of detail, the measurement results and parameterizations presented in this study can be directly implemented in detailed process models as well as in large-scale atmospheric and climate models for efficient description of the CCN activity of atmospheric aerosols.

Chemical composition measurements of cloud condensation nuclei and ice nuclei by aerosol mass spectrometry

In this study the Aerodyne Aerosol Mass Spectrometer (AMS) was used during three laboratory measurement campaigns, FROST1, FROST2 and ACI-03. The FROST campaigns took place at the Leipzig Aerosol Cloud Interaction Simulator (LACIS) at the IfT in Leipzig and the ACI-03 campaign was conducted at the AIDA facility at the Karlsruhe Institute of Technology (KIT). In all three campaigns, the effect of coatings on mineral dust ice nuclei (IN) was investigated. During the FROST campaigns, Arizona Test Dust (ATD) particles of 200, 300 and 400 nm diameter were coated with thin coatings (< 7 nm) of sulphuric acid. At these very thin coatings, the AMS was operated close to its detection limits. Up to now it was not possible to accurately determine AMS detection limits during regular measurements. Therefore, the mathematical tools to analyse the detection limits of the AMS have been improved in this work. It is now possible to calculate detection limits of the AMS under operating conditions, without losing precious time by sampling through a particle filter. The instrument was characterised in more detail to enable correct quantification of the sulphate loadings on the ATD particle surfaces. Correction factors for the instrument inlet transmission, the collection efficiency, and the relative ionisation efficiency have been determined. With these corrections it was possible to quantify the sulphate mass per particle on the ATD after the condensation of sulphuric acid on its surface. The AMS results have been combined with the ice nucleus counter results. This revealed that the IN-efficiency of ATD is reduced when it is coated with sulphuric acid. The reason for this reduction is a chemical reaction of sulphuric acid with the particle's surface. These reactions are increasingly taking place when the aerosol is humidified or heated after the coating with sulphuric acid. A detailed analysis of the solubility and the evaporation temperature of the surface reaction products revealed that most likely aluminium sulphate is produced in these reactions.

PREMATURE CONDENSATION OF SPERMATOGENIC CELL CHROMOSOMES

The technique of premature chromosome condensation (PCC) has been used primarily to study interphase chromosomes of somatic cells. In this study, mitotic cells were fused to cells from the mouse testes to examine the chromosomes of germ cells. The testes contain various types of cells, both germinal and nongerminal. In these initial studies, four types of PCC morphologies were observed. Chromosome morphology of the PCC and labeling experiments demonstrated the mouse cell origin of various PCC. Attempts were next made to determine the cell types producing the PCC. Spermatogonia, diplotene spermatocytes, secondary spermatocytes and round spermatids are proposed to be the origin of the PCC morphologies. Some PCC could be banded by G and C banding techniques and the mouse chromosomes identified.^ Studies were subsequently undertaken to evaluate this technique as a method of evaluating damage to germ cells. Testicular cells from irradiated mice were fused to mitotic cells and the PCC examined. Both round spermatids and secondary spermatocytes exhibited chromosome damage in the form of chromatid breaks. A linear correlation was found between the dose of irradiation and the number of breaks per cell. This technique may develop into a useful method for evaluating the clastogenic effect of agents on the germ cells. ^

Dynamics of dissipative Bose-Einstein condensation

We resolve the real-time dynamics of a purely dissipative s=1/2 quantum spin or, equivalently, hard-core boson model on a hypercubic d-dimensional lattice. The considered quantum dissipative process drives the system to a totally symmetric macroscopic superposition in each of the S3 sectors. Different characteristic time scales are identified for the dynamics and we determine their finite-size scaling. We introduce the concept of cumulative entanglement distribution to quantify multiparticle entanglement and show that the considered protocol serves as an efficient method to prepare a macroscopically entangled Bose-Einstein condensate.

Continuous condensation particle (CP) observations from 1984 through 2009 at Neumayer Station, Antacrtica

Continuous condensation particle (CP) observations were conducted from 1984 through 2009 at Neumayer Station under stringent contamination control. During this period, the CP concentration (median 258 1/cm**3) showed no significant long term trend but exhibited a pronounced seasonality characterized by a stepwise increase starting in September and reaching its annual maximum of around 10**3/cm**3 in March. Minimum values below 10**2/cm**3 were observed during June/July. Dedicated time series analyses in the time and frequency domain revealed no significant correlations between inter-annual CP concentration variations and atmospheric circulation indices like Southern Annular Mode (SAM) or Southern Ocean Index (SOI). The impact of the Pinatubo volcanic eruption and strong El Niño events did not affect CP concentrations. From thermodenuder experiments we deduced that the portion of volatile (at 125 °C) and semi-volatile (at 250 °C) particles which could be both associated with biogenic sulfur aerosol, was maximum during austral summer, while during winter non-volatile sea salt particles dominated. During September through April we could frequently observe enhanced concentrations of ultrafine particles within the nucleation mode (between 3 nm and 7 nm particle diameter), preferentially in the afternoon.

Condensation in ducts

Phase changing flows are being considered for thermal management in space platforms. The resulting flow patterns are very complicated and extremely sensitive to gravity action. Concerning fluid flow in ducts, the available evidence indicates that although the pressure loss does not depend too much on the fluid flow pattern,the heat transfer (and resulting phase change) does. A simple exercise to illustrate this point is presented in this paper. It deals with condensing flow in straight circular cross-sectional ducts. Two extreme configurations are considered here, one corresponds to a stratified flow and the other to an annular flow. Both types of flow patterns have been extensively considered in the past and from this point of view almost nothing is new in the paper, but past results look conflictive and this could be due to the limitations and computational intricacies of the models used. Thus the problem has been reformulated from the onset and the results are presented as the evolution of the vapor quality (vapor to total mass flow rate) along the duct, in typical cases. The results presented here indicate that within the validity of the present models and the assumed ranges of mass flow rate, duct diameter, thermal conditions and fluid characteristics,the length of the ducts required to achieve complete condensation under zero gravity are an order of magnitude larger than in horizontal tubes under normal terrestrial conditions.

Phosphorylation of histone H3 at serine 10 is correlated with chromosome condensation during mitosis and meiosis in Tetrahymena

H3 phosphorylation has been correlated with mitosis temporally in mammalian cells and spatially in ciliated protozoa. In logarithmically growing Tetrahymena thermophila cells, for example, H3 phosphorylation can be detected in germline micronuclei that divide mitotically but not in somatic macronuclei that divide amitotically. Here, we demonstrate that micronuclear H3 phosphorylation occurs at a single site (Ser-10) in the amino-terminal domain of histone H3, the same site phosphorylated during mitosis in mammalian cells. Using an antibody specific for Ser-10 phosphorylated H3, we show that, in Tetrahymena, this modification is correlated with mitotic and meiotic divisions of micronuclei in a fashion that closely coincides with chromosome condensation. Our data suggest that H3 phosphorylation at Ser-10 is a highly conserved event among eukaryotes and is likely involved in both mitotic and meiotic chromosome condensation.

Resistance to DNA fragmentation and chromatin condensation in mice lacking the DNA fragmentation factor 45

The DNA fragmentation factor 45 (DFF45) is a subunit of a heterodimeric nuclease complex critical for the induction of DNA fragmentation in vitro. To understand the in vivo role of DFF45 in programmed cell death, we generated DFF45 mutant mice. DNA fragmentation activity is completely abolished in cell extracts from DFF45 mutant tissues. In response to apoptotic stimuli, splenocytes, thymocytes, and granulocytes from DFF45 mutant mice are resistant to DNA fragmentation, and splenocytes and thymocytes are also resistant to chromatin condensation. Nevertheless, development of the immune system in the DFF45 mutant mice is normal. These results demonstrate that DFF45 is critical for the induction of DNA fragmentation and chromatin condensation in vivo, but is not required for normal immune system development.

The Role of Topoisomerase II in Meiotic Chromosome Condensation and Segregation in Schizosaccharomyces pombe

Topoisomerase II is able to break and rejoin double-strand DNA. It controls the topological state and forms and resolves knots and catenanes. Not much is known about the relation between the chromosome segregation and condensation defects as found in yeast top2 mutants and the role of topoisomerase II in meiosis. We studied meiosis in a heat-sensitive top2 mutant of Schizosaccharomyces pombe. Topoisomerase II is not required until shortly before meiosis I. The enzyme is necessary for condensation shortly before the first meiotic division but not for early meiotic prophase condensation. DNA replication, prophase morphology, and dynamics of the linear elements are normal in the top2 mutant. The top2 cells are not able to perform meiosis I. Arrested cells have four spindle pole bodies and two spindles but only one nucleus, suggesting that the arrest is nonregulatory. Finally, we show that the arrest is partly solved in a top2 rec7 double mutant, indicating that topoisomerase II functions in the segregation of recombined chromosomes. We suggest that the inability to decatenate the replicated DNA is the primary defect in top2. This leads to a loss of chromatin condensation shortly before meiosis I, failure of sister chromatid separation, and a nonregulatory arrest.

Molecular mechanism for silencing virally transduced genes involves histone deacetylation and chromatin condensation

Virally transduced genes are often silenced after integration into the host genome. Chromatin immunoprecipitation and nuclease sensitivity experiments now demonstrate that silencing of the transgene is characterized by deacetylation of histone H4 lysines and chromatin condensation. Trichostatin A treatment results in dramatic reactivation of gene expression that is preceded by histone acetylation and chromatin decondensation. Analysis of individual histone H4 lysines demonstrate that chromatin domain opening is coincident with rapid acetylation of histone H4 K5, K12, and K16 and that maintenance of the open domain is correlated with acetylation of histone H4 K8. Removal of trichostatin A results in rapid deacetylation of histone H4 K8, chromatin condensation, and transcription silencing. The results suggest that deacetylation of histone H4 lysines and coincident chromatin condensation are critically involved in the silencing of virally transduced genes.

The reversible condensation and expansion of the rotavirus genome

Understanding the structural organization of the genome is particularly relevant in segmented double-stranded RNA viruses, which exhibit endogenous transcription activity. These viruses are molecular machines capable of repeated cycles of transcription within the intact capsid. Rotavirus, a major cause of infantile gastroenteritis, is a prototypical segmented double-stranded RNA virus. From our three-dimensional structural analyses of rotavirus examined under various chemical conditions using electron cryomicroscopy, we show here that the viral genome exhibits a remarkable conformational flexibility by reversibly changing its packaging density. In the presence of ammonium ions at high pH, the genome condenses to a radius of ≈180 Å from ≈220 Å. Upon returning to physiological conditions, the genome re-expands and fully maintains its transcriptional properties. These studies provide further insights into the genome organization and suggest that the observed isometric and concentric nature of the condensation is due to strong interactions between the genome core and the transcription enzymes anchored to the capsid inner surface. The ability of the genome to condense beyond what is normally observed in the native virus indicates that the negative charges on the RNA in the native state may be only partially neutralized. Partial neutralization may be required to maintain appropriate interstrand spacing for templates to move around the enzyme complexes during transcription. Genome condensation was not observed either with increased cation concentrations at normal pH or at high pH without ammonium ions. This finding indicates that the observed genome condensation is a synergistic effect of hydroxyl and ammonium ions involving disruption of protein–RNA interactions that perhaps facilitate further charge neutralization and consequent reduction in the interstrand spacing.