Quasi-spherical ice in convective clouds

Homogeneous freezing of supercooled droplets occurs in convective systems in low and midlatitudes. This droplet-freezing process leads to the formation of a large amount of small ice particles, so-called frozen droplets, that are transported to the upper parts of anvil outflows, where they can influence the cloud radiative properties. However, the detailed microphysics and, thus, the scattering properties of these small ice particles are highly uncertain. Here, the link between the microphysical and optical properties of frozen droplets is investigated in cloud chamber experiments, where the frozen droplets were formed, grown, and sublimated under controlled conditions. It was found that frozen droplets developed a high degree of small-scale complexity after their initial formation and subsequent growth. During sublimation, the small-scale complexity disappeared, releasing a smooth and near-spherical ice particle. Angular light scattering and depolarization measurements confirmed that these sublimating frozen droplets scattered light similar to spherical particles: that is, they had angular light-scattering properties similar to water droplets. The knowledge gained from this laboratory study was applied to two case studies of aircraft measurements in midlatitude and tropical convective systems. The in situ aircraft measurements confirmed that the microphysics of frozen droplets is dependent on the humidity conditions they are exposed to (growth or sublimation). The existence of optically spherical frozen droplets can be important for the radiative properties of detraining convective outflows.Peer reviewe

Teaching mathematics with multimedia-based representations-what about teachers' competencies?

International audienceMultimedia-based representations play a major role in mathematics and mathematics education. Consequently, they are important with regard to teaching purposes, as they are supposed to be useful to represent mathematical structures and processes in different ways. Within the presented project we developed an instrument by using video-vignettes in order to assess the competencies of mathematics teachers for multimedia use in mathematics lessons. For coping with complexity we reduced the instrument's focus on two facets: cognitive load and mutual supplement of multimedia representations. As the work is still in progress, we here focus on the project's theoretical background as well as on the development of the assessment instrument based on video-vignettes

Untersuchung der spontanen Spaltung von "2"5"2Cf am Darmstadt-Heidelberger-Kristallkugel-Spektrometer

SIGLETIB Hannover: DR 6452 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Asymmetric expression of the BMP antagonists chordin and gremlin in the sea anemone Nematostella vectensis: Implications for the evolution of axial patterning

The evolutionary origin of the anterior-posterior and the dorsoventral body axes of Bilateria is a long-standing question. It is unclear how the main body axis of Cnidaria, the sister group to the Bilateria, is related to the two body axes of Bilateria. The conserved antagonism between two secreted factors, BMP2/4 (Dpp in Drosophila) and its antagonist Chordin (Short gastrulation in Drosophila) is a crucial component in the establishment of the dorsoventral body axis of Bilateria and could therefore provide important insight into the evolutionary origin of bilaterian axes. Here, we cloned and characterized two BMP ligands, dpp and GDF5-like as well as two secreted antagonists, chordin and gremlin, from the basal cnidarian Nematostella vectensis. Injection experiments in zebrafish show that the ventralizing activity of NvDpp mRNA is counteracted by NvGremlin and NvChordin, suggesting that Gremlin and Chordin proteins can function as endogenous antagonists of NvDpp. Expression analysis during embryonic and larval development of Nematostella reveals asymmetric expression of all four genes along both the oral-aboral body axis and along an axis perpendicular to this one, the directive axis. Unexpectedly, NvDpp and NvChordin show complex and overlapping expression on the same side of the embryo, whereas NvGDF5-like and NvGremlin are both expressed on the opposite side. Yet, the two pairs of ligands and antagonists only partially overlap, suggesting complex gradients of BMP activity along the directive axis but also along the oral-aboral axis. We conclude that a molecular interaction between BMP-like molecules and their secreted antagonists was already employed in the common ancestor of Cnidaria and Bilateria to create axial asymmetries, but that there is no simple relationship between the oral-aboral body axis of Nematostella and one particular body axis of Bilateria

ACRIDICON–CHUVA Campaign: Studying Tropical Deep Convective Clouds and Precipitation over Amazonia Using the New German Research Aircraft HALO

Between 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period of Green Ocean Amazon 2014/15 (GoAmazon2014/5). In this paper we focus on the airborne data measured on HALO, which was equipped with about 30 in situ and remote sensing instruments for meteorological, trace gas, aerosol, cloud, precipitation, and spectral solar radiation measurements

Dataset: A High-resolution Mosaic of the Neutral Hydrogen in the M81 Triplet

This dataset shows the distribution of neutral hydrogen in and around the M81 galaxy triplet (M81, M82, NGC 3077) and consists of a 3° × 3°, 105-pointing, high-resolution neutral hydrogen (H I) mosaic obtained with the Very Large Array C and D arrays

The pivotal role of astrocytes in an in vitro stroke model of the blood-brain barrier

Stabilization of the blood-brain barrier during and after stroke can lead to less adverse outcome. For elucidation of underlying mechanisms and development of novel therapeutic strategies validated in vitro disease models of the blood-brain barrier could be very helpful. To mimic in vitro stroke conditions we have established a blood-brain barrier in vitro model based on mouse cell line cerebEND and applied oxygen/glucose deprivation (OGD). The role of astrocytes in this disease model was investigated by using cell line C6. Transwell studies pointed out that addition of astrocytes during OGD increased the barrier damage significantly in comparison to the endothelial monoculture shown by changes of transendothelial electrical resistance as well as fluorescein permeability data. Analysis on mRNA and protein levels by qPCR, western blotting and immunofluorescence microscopy of tight junction molecules claudin-3,-5,-12, occludin and ZO-1 revealed that their regulation and localisation is associated with the functional barrier breakdown. Furthermore, soluble factors of astrocytes, OGD and their combination were able to induce changes of functionality and expression of ABC-transporters Abcb1a (P-gp), Abcg2 (bcrp), and Abcc4 (mrp4). Moreover, the expression of proteases (matrixmetalloproteinases MMP-2, MMP-3, MMP-9, and t-PA) as well as of their endogenous inhibitors (TIMP-1, TIMP-3, PAI-1) was altered by astrocyte factors and OGD which resulted in significant changes of total MMP and t-PA activity. Morphological rearrangements induced by OGD and treatment with astrocyte factors were confirmed at a nanometer scale using atomic force microscopy. In conclusion, astrocytes play a major role in blood-brain barrier breakdown during OGD in vitro