Showing papers by "University of Bremen published in 1998"

Singlet Oxygen Quantum Yields of Different Photosensitizers in Polar Solvents and Micellar Solutions

Abstract: The singlet oxygen luminescence method and the photochemical methods using 1,3-diphenylisobenzofuran (DPBF) or bilirubin ditaurate (BDT) as chemical quenchers were employed to determine the single oxygen quantum yields (ΦΔ) of different phthalocyanines and tris(2,2″-bipyridyl)ruthenium(II) dichloride in dimethylformamide (DMF) or aqueous micellar solution of 0.1 M CTAC (cetyltrimethylammonium chloride). Additionally, a perylenetetracarboxylic acid diimide derivative was examined in DMF. In a series of tetrasulfonated phthalocyanines (PTS) the following order was found: ZnPTS > GaPTS > AlPTS ≈ H2PTS > CoPTS. In general, the singlet oxygen quantum yields are higher in DMF than in 0.1 M CTAC/H2O. The results obtained with the photochemical systems are comparable with those obtained by the photophysical method. The photochemical DPBF method results in absolute values of ΦΔ. However, in micellar solution, chain reactions occur when DPBF is used as chemical quencher in the photo-oxidative process. This problem ...

ATMOSPHERIC REMOTE-SENSING REFERENCE DATA FROM GOME: PART 1. TEMPERATURE-DEPENDENT ABSORPTION CROSS-SECTIONS OF NO2 IN THE 231–794 nm RANGE

Abstract: Absorption cross sections of O3 in the 231–794 nm range have been measured at temperatures between 202 and 293 K using the Global Ozone Monitoring Experiment (GOME) Flight-Model (FM) satellite spectrometer. The GOME FM spectra have a spectral resolution of about 0.2 nm below 400 nm and of about 0.3 nm above 400 nm, and were recorded covering simultaneously the Hartley, Huggins, and Chappuis bands centered around 255, 340, and 610 nm, respectively. The variation of the O3 absorption cross sections was investigated over the entire spectral range 231–794 nm. The new cross sections are important as reference data for atmospheric remote-sensing of O3 and other trace gases.

Continuation of the Mozambique Belt Into East Antarctica: Grenville‐Age Metamorphism and Polyphase Pan‐African High‐Grade Events in Central Dronning Maud Land

Abstract: The about 500 km long coastal stretch of central Dronning Maud Land (DML), East Antarctica, is critical for understanding both Gondwana and Rodinia assembly. In common Gondwana reconstructions central DML lies at the potential southern extension of the Mozambique Belt. We report the first extensive geochronological study of magmatic and metamorphic rocks from the area. These new U‐Pb SHRIMP zircon and Sm‐Nd‐data of rocks sampled during the German international GeoMaud 1995/96 expedition indicate that the oldest rocks in central DML are Mesoproterozoic in age. The crystallization ages of metavolcanic rocks were determined at c. 1130 Ma. Syn‐tectonic granite sheets and plutons give ages of c. 1080 Ma, contemporaneous with metamorphic zircon growth at granulite facies conditions. An anorthosite intrusion and a charnockite are dated at c. 600 Ma. Subsequent metamorphism is recorded for at least two different episodes at c. 570–550 Ma and between 530 to 515 Ma. The latter metamorphic event reached granulite fa...

GOME observations of tropospheric BrO in northern hemispheric spring and summer 1997

Abstract: Measurements from the Global Ozone Monitoring Experiment GOME have been analysed for tropospheric BrO in the northern hemispheric spring and summer 1997. Tropospheric excess columns have been determined by subtracting measurements from a longitude range which is assumed to represent background conditions. From February until the end of May enhanced tropospheric BrO columns are observed over the Hudson Bay area and parts of the Canadian Arctic. This large and persistent event has not been reported before and can only be explained by a large local source of bromine. In addition, from March to May other smaller and shorter tropospheric BrO events are detectable along the coast lines of the Arctic Sea and over the polar ice. They correspond to the ground-based observations of enhanced tropospheric BrO reported from several stations in the high Arctic.

Gender cultures and the gender arrangement—a theoretical framework for cross‐national gender research

Abstract: How can the marked national differences in the rates of women's participation in the labour market, and in their involvement in part‐time work, be explained? While institutional conditions, for example childcare policy, can have a contextual importance, these are not adequate for understanding women's different orientations and practices in combining paid and unpaid work. Rather, we must examine the idea that the social practice of women is heavily influenced by predominant norms and values about the ‘correct’ gender division of labour. Culture must therefore be included in any explanation of cross‐national differences in employment patterns. This is the task of this paper. After briefly examining the limitations of pre‐existing explanations, the paper goes on to present an alternative theorization which conceptualizes the links between gendered natures, structures and action. This new theoretical approach is then applied to a comparative analysis of changing employment patterns in Finland, Germa...

Covalent DNA-Streptavidin Conjugates as Building Blocks for Novel Biometallic Nanostructures.

Abstract: Supramolecular aggregates of DNA, RNA, streptavidin, immunoglobulin, and nanocrystalline metal clusters can be generated by self-assembly on the basis of oligonucleotide hybridization (shown schematically). Following selective immunosorption on surface-immobilized antigen, the biometallic hybrid is detectable by electron microscopy.

Transnational social spaces out of international migration: evolution, significance and future prospects

Abstract: Transnational social spaces denote the circular flow of persons, goods, information and symbols across countries that have been triggered in the course of international labor migration and refugee flows. The question is how such transnational phenomena can be described, catagorued and explained. What are the implications for the adaptation of international migrants and their descendants in the economic, political and cultural realms in the countries of setdement? First, this discussion clarifies basic concepts, such as transnational social space and the main resources involved, such as various forms of social capital, the norm of reciprocity, solidarity, information and control. Second, the analysis outlines some causal macro-factors that may have opened up opportunities for migrants to build transnational spaces to a greater extent than before World War Two. Third, a few forays into the empirical realm serve to sketch the lineaments of the German-Turkish transnational social spaces: the emergence of Turkish niche businesses in Germany and transnational businesses spanning both countries; efforts of some Kurdish organizations to establish a homeland called ‘Kurdistan’; and collective identity among secondgeneration German-Turks in the religions realm, involving Islamic thought and organizations, but also secular forms of everyday culture. The article concludes with a discussion of factors that may limit the future growth of transnational social spaces.

Tropospheric sulfur dioxide observed by the ERS-2 GOME instrument

Abstract: Since July 1995, the Global Ozone Monitoring Experiment (GOME) onboard ESA's 2nd European Remote Sensing Satellite (ERS-2) provides continuous spectral mea- surements of nadir backscattered earth radiances and so- lar irradiances in the UV/visible wavelength range. From these, column amounts of sulfur dioxide have been derived for the December 1996 eruption of Nyamuragira volcano, Zaire, and the ongoing activity of Popocat epetl volcano, Mexico. Maximal column densities of 33 DU for Nyamura- gira and 6 DU for Popocat epetl have been found. Popo- cat epetl results compare well with the activity reported for this volcano. Furthermore, GOME observed enhanced SO2 over Southeast Europe which is attributed to lignite com- bustion in local power plants. The results demonstrate a high sensitivity and specicity of this new sensor for sulfur dioxide. For cloud-free scenes at low solar zenith angles, the detection limit for SO2 is estimated to be 0.4 DU.

Ring effect: impact of rotational raman scattering on radiative transfer in earth’s atmosphere

Abstract: One significant limitation to the accuracy of the remote sensing of trace gas constituents in the atmosphere, using UV-visible spectroscopy and scattered sunlight, has often been a reliable knowledge of the so-called Ring effect. In this study it is demonstrated that the filling-in of Fraunhofer and gas absorption features, resulting from Rotational Raman scattering (RRS), explains to high accuracy the Ring effect. A radiative transfer model has been adapted to include RRS and carefully validated by comparison with Ring effect data by other models and from ground-based and satellite data. The analysis of the principle components of the simulated Ring spectra enabled the Fraunhofer and gas absorption filling-in to be separated. This yields a simple, and therefore computational fast, parameterization of the Ring effect suitable for trace gas retrievals. This approach was tested for the retrieval of NO 2 which is considered to be a worst case with respect to absorption feature filling-in for a trace gas retrieved from scattered light. Analysis of the errors in the vertical column of NO 2 derived using differential optical absorption spectroscopy (DOAS) technique indicate that they are dependent on the amount of NO 2 present in the atmosphere when regarding the experimental Ring spectra. This implies that calculated Ring spectra may be superior for DOAS retrievals, compared to the experimentally determined Ring spectra.

On Formalizing the UML Object Constraint Language OCL

Abstract: We present a formal semantics for the Object Constraint Language (OCL) which is part of the Unified Modeling Language (UML) – an emerging standard language and notation for object-oriented analysis and design. In context of information systems modeling, UML class diagrams can be utilized for describing the overall structure, whereas additional integrity constraints and queries are specified with OCL expressions. By using OCL, constraints and queries can be specified in a formal yet comprehensible way. However, the OCL itself is currently defined only in a semi-formal way. Thus the semantics of constraints is in general not precisely defined. Our approach gives precise meaning to OCL concepts and to some central aspects of UML class models. A formal semantics facilitates verification, validation and simulation of models and helps to improve the quality of models and software designs.

A learning pathway in high‐school level quantum atomic physics

Abstract: In this paper, one student's learning process in a course on quantum atomic physics in grade 13 of a German gymnasium (secondary school) is described. The course lasted 16 weeks for a total of approximately 80 lessons. The aim of the present study is to elaborate the student's cognitive system for atomic physics as a hypothetical pragmatic model to describe, analyse and explain his thinking and learning while interacting with the teaching input. In this paper, the student's learning pathway is described as a sequence of several meta‐stable conceptions of the atom, starting from a planetary model. His final cognitive element ‘atom’ following teaching is displayed as an association of three parallel conceptions including his initial planetary model, a state‐electron model and an electron‐cloud model. These different conceptions influence his thinking in different ‘strengths’ and ‘status’. In addition, the student's meta‐cognitive beliefs on physics and the way they are affected by a quantum world view are b...

Restricted diffusion and exchange of intracellular water: theoretical modelling and diffusion time dependence of 1H NMR measurements on perfused glial cells.

Abstract: Intracellular diffusion properties of water in F98 glioma cells immobilized in basement membrane gel threads, are investigated with a pulsed-field-gradient spin-echo NMR technique at diffusion times from 6 to 2000 ms and at different temperatures. In extended model calculations the concept of 'restricted intracellular diffusion at permeable boundaries' is described by a combined Tanner-Karger formula. Signal components in a series of ct experiments (constant diffusion time) are separated due to different diffusion properties (Gaussian and restricted diffusion), and physiological as well as morphological cell parameters are extracted from the experimental data. The intracellular apparent diffusion coefficients strongly depend on the diffusion time and are up to two orders of magnitude smaller than the self diffusion constant of water. Propagation lengths are found to be in the range of 4-7 microns. Hereby intracellular signals of compartments with a characteristic diameter could be selected by an appropriate gradient strength. With cg experiments (constant gradient) a mean intracellular residence time for water is determined to be about 50 ms, and the intrinsic intracellular diffusion constant is estimated to 1 x 10(-3)mm2/s. Studying the water diffusion in glial cells provides basic understanding of the intracellular situation in brain tissue and may elucidate possible influences on the changes in the diffusion contrast during ischemic conditions.

Error resilience support in H.263

Abstract: Version 2 of ITU Recommendation H.263, better known as H.263+, includes a number of new mechanisms to improve coding efficiency and support various types of networks more efficiently. This paper provides an overview of the error resilience optional modes of H.263+ and describes the use of such modes in various multimedia network scenarios.

Intercomparison of Simulated Global Vegetation Distributions in Response to 6 kyr BP Orbital Forcing

Abstract: The response of ten atmospheric general circulation models to orbital forcing at 6 kyr BP has been investigated using the BIOME model, which predicts equilibrium vegetation distribution, as a diagnostic. Several common features emerge: (a) reduced tropical rain forest as a consequence of increased aridity in the equatorial zone, (b) expansion of moisture-demanding vegetation in the Old World subtropics as a consequence of the expansion of the Afro–Asian monsoon, (c) an increase in warm grass/shrub in the Northern Hemisphere continental interiors in response to warming and enhanced aridity, and (d) a northward shift in the tundra–forest boundary in response to a warmer growing season at high northern latitudes. These broadscale features are consistent from model to model, but there are differences in their expression at a regional scale. Vegetation changes associated with monsoon enhancement and high-latitude summer warming are consistent with palaeoenvironmental observations, but the simulated sh...

The Rise of International Environmental Politics: A Review of Current Research

Abstract: This review article identifies five research themes in the study of international environmental politics. Among them, the research on regime effectiveness and on transnational networks has the greatest potential for becoming a driving force in the search for new avenues in the analysis of international relations. Although at the moment less is known about regime consequences and the role of transnational networks in international environmental politics than about regime formation, the former two have recently produced research questions and strategies that seem to be promising. However, the study of regime effectiveness and transnational networks requires more sophisticated research strategies in order to realize its full potential. Although the concept of causal mechanisms used in this research strand seems to be an extremely innovative and promising approach, it needs to be developed in more detail and backed up by comparative designs.

A numerically stable, structure preserving method for computing the eigenvalues of real Hamiltonian or symplectic pencils

Abstract: A new method is presented for the numerical computation of the generalized eigenvalues of real Hamiltonian or symplectic pencils and matrices. The method is numerically backward stable and preserves the structure (i.e., Hamiltonian or symplectic). In the case of a Hamiltonian matrix the method is closely related to the square reduced method of Van Loan, but in contrast to that method which may suffer from a loss of accuracy of order \(\sqrt{\varepsilon}\), where \(\varepsilon \) is the machine precision, the new method computes the eigenvalues to full possible accuracy.

Readiness of Zebrafish Brain Neurons to Regenerate a Spinal Axon Correlates with Differential Expression of Specific Cell Recognition Molecules

Abstract: We analyzed changes in the expression of mRNAs for the axonal growth-promoting cell recognition molecules L1.1, L1.2, and neural cell adhesion molecule (NCAM) after a rostral (proximal) or caudal (distal) spinal cord transection in adult zebrafish. One class of cerebrospinal projection nuclei (represented by the nucleus of the medial longitudinal fascicle, the intermediate reticular formation, and the magnocellular octaval nucleus) showed a robust regenerative response after both types of lesions as determined by retrograde tracing and/or in situ hybridization for GAP-43. A second class (represented by the nucleus ruber, the nucleus of the lateral lemniscus, and the tangential nucleus) showed a regenerative response only after proximal lesion. After distal lesion, upregulation of L1.1 and L1.2 mRNAs, but not NCAM mRNA expression, was observed in the first class of nuclei. The second class of nuclei did not show any changes in their mRNA expression after distal lesion. After proximal lesion, both classes of brain nuclei upregulated L1.1 mRNA expression (L1.2 and NCAM were not tested after proximal lesion). In the glial environment distal to the spinal lesion, labeling for L1.2 mRNA but not L1.1 or NCAM mRNAs was increased. These results, combined with findings in the lesioned retinotectal system of zebrafish ([Bernhardt et al., 1996][1]), indicate that the neuron-intrinsic regulation of cell recognition molecules after axotomy depends on the cell type as well as on the proximity of the lesion to the neuronal soma. Glial reactions differ for different regions of the CNS. [1]: #ref-13

Comparison of Models Used for UV Index Calculations

Abstract: Eighteen radiative transfer models in use for calculation of UV index are compared with respect to their results for more than 100 cloud-free atmospheres, which describe present, possible future and extreme conditions. The comparison includes six multiple-scattering spectral models, eight fast spectral models and four empirical models. Averages of the results of the six participating multiple-scattering spectral models are taken as a basis for assessment. The agreement among the multiple-scattering models is within ±0.5 UV index values for more than 80% of chosen atmospheric parameters. The fast spectral models have very different agreement, between ±1 and up to 12 UV index values. The results of the empirical models agree reasonably well with the reference models but only for the atmospheres for which they have been developed. The data to describe the atmospheric conditions, which are used for the comparison, together with the individual results of all participating models and model descriptions are available on the Internet: http://www.meteo.physik.uni-muenchen.de/strahlung/cost/.