University of Bremen

About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Glacial period. The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

Retrieval of aerosol optical thickness over land surfaces from top-of-atmosphere radiance

Abstract: [1] Aerosol remote sensing requires techniques enabling the determination of aerosol optical thickness (AOT) over land surfaces, because the most important sources (continental aerosols, anthropogenic aerosols, biomass burning, desert dust, volcano eruptions and others) are on continents. Here a retrieval method for the AOT over land surfaces from top-of-atmosphere (TOA) radiance using nadir looking instruments of the ocean color type (like Ocean Color and Temperature Sensor (OCTS), Sea viewing Wide Field Sensor (SeaWiFS), Moderate resolution Imaging Sensor (MODIS) or Medium Resolution Imaging Sensor (MERIS)) is presented. It is scheduled as an off-line procedure for the ENVISAT radiometers SCIAMACHY and MERIS. The method is based on lookup tables (LUT) between the AOT and the aerosol reflectance for wavelength <0.67 μm. The aerosol reflectance is obtained from TOA reflectance accounting for Rayleigh path reflectance and the apparent spectral surface reflectance. Over land the surface reflectance is estimated by a mixing model of bare soil and green vegetation spectra, tuned by the normalized differential vegetation index (NDVI) of the satellite scene. The method has been tested and validated with SeaWiFS data and with aerosol properties of the closure experiment LACE-98 (Lindenberg Aerosol Charactrization Experiment). For short wave channels (0.412–510 μm) an agreement between the retrieved and ground-based data of 20% is achieved. Thus the method enables the investigation of AOT over land, yielding the regional turbidity situation as well as the identification of aerosol sources like large cities, large fire plumes, haze, small scale dynamical events and also thin cirrus clouds.

Nonequilibrium clumped isotope signals in microbial methane

Abstract: Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted "clumped" isotopologues (for example, (13)CH3D) has recently emerged as a proxy for determining methane-formation temperatures. However, the effect of biological processes on methane's clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on (13)CH3D abundances and results in anomalously elevated formation-temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.

Copper: effects of deficiency and overload.

Abstract: Copper is an essential trace metal that is required for the catalysis of several important cellular enzymes. However, since an excess of copper can also harm cells due to its potential to catalyze the generation of toxic reactive oxygen species, transport of copper and the cellular copper content are tightly regulated. This chapter summarizes the current knowledge on the importance of copper for cellular processes and on the mechanisms involved in cellular copper uptake, storage and export. In addition, we will give an overview on disturbances of copper homeostasis that are characterized by copper overload or copper deficiency or have been connected with neurodegenerative disorders.

Opinion Dynamics Driven by Various Ways of Averaging

Abstract: The paper treats opinion dynamics under bounded confidence when agents employ, beside an arithmetic mean, means like a geometric mean, a power mean or a random mean in aggregating opinions. The different kinds of collective dynamics resulting from these various ways of averaging are studied and compared by simulations. Particular attention is given to the random mean which is a new concept introduced in this paper. All those concrete means are just particular cases of a partial abstract mean, which also is a new concept. This comprehensive concept of averaging opinions is investigated also analytically and it is shown in particular, that the dynamics driven by it always stabilizes in a certain pattern of opinions.