Zum jahreszeitlichen Nitratgehalt und zur Nitratauswaschung von landwirtschaftlich genutzten Böden in Baden-Württemberg

Seasonal nitrate content in, and nitrate leaching from, agricultural soils of Baden-Wuerttemberg The behavior of soil nitrate was investigated at five field locations in the State of Baden-Wuerttemberg between 1984 and 1987. It was found that the amount of nitrate in the upper 90 cm of soil was not a constant, but fluctuated throughout the year with maxima in the spring and in the fall. Additionally, it was found that the amount of nitrate leaching during winter (from November through April) was correlated to, but not identical with the mineral nitrogen content of the previous fall. It further appeared that nitrate leaching in light sandy soils is mainly a mixing process, whereas in heavy soils it seems to be more a miscible displacement phenomenon.     

Trace organics in septic tank effluent

This paper reviews the available information and presents the results of a study undertaken to estimate the presence and level of certain trace organics in wastewater samples collected from a septic tank in an individual household, from a lift station, and from a waste treatment lagoon near Regina, Canada. Out of 11 priority pollutants analyzed, 6 priority pollutants — chloroform, bromodichloromethane, toluene, benzene, methylene chloride and tetrachloroethylene — were detected in the samples. Benzene and bromodichloromethane were dominant. Methylene chloride and tetrachloroethylene could not be quantified at the low concentrations present. Chloroform was present in the lagoon effluent sample once at a concentration of 0.03 μg L^?1. Toluene was not present either in the septic tank effluent or in the lagoon effluent. Benzene was present in the septic tank effluent (max. value 450 μg L^?1) and in the lagoon effluent (max. value 120 μg L^?1). Bromodichloromethane was present in the septic tank effluent and lagoon effluent at concentrations lower than 1.10 μg L^?1. The trace organics in the septic tank effluent and lagoon effluent at these comparatively low concentrations may not pose any significant risk either to aquatic life or to public health, taking into account the attentuation capacity of the soil and the dilution usually available.     

The formation and fragmentation of disks around primordial protostars

The very first stars to form in the universe heralded an end to the cosmic dark ages and introduced new physical processes that shaped early cosmic evolution. Until now, it was thought that these stars lived short, solitary lives, with only one extremely massive star, or possibly a very wide binary system, forming in each dark-matter minihalo. Here we describe numerical simulations that show that these stars were, to the contrary, often members of tight multiple systems. Our results show that the disks that formed around the first young stars were unstable to gravitational fragmentation, possibly producing small binary and higher-order systems that had separations as small as the distance between Earth and the Sun.     

An ion balance for ultra-high-precision atomic mass measurements

We have developed the analog of a double-pan balance for determining the masses of single molecular ions from the ratio of their two cyclotron frequencies. By confining two different ions on the same magnetron orbit in a Penning trap, we balance out many sources of noise and error (such as fluctuations of the magnetic field). To minimize the systematic error associated with the Coulomb interaction between the two ions, they are kept about 1 millimeter apart from each other, resulting in fractional uncertainty below 1 x 10(-11). Such precision opens the door to numerous applications of mass spectrometry, including metrology, fundamental physics, and weighing chemical bonds.     

Sulfur diagenesis in everglades peat and origin of pyrite in coal

The pattern of sulfur transformation in peat across the Everglades basin indicates that pyrite formation in organic-rich swamps depends on the use of organic oxysulfur compounds in dissimilatory respiration by sulfur-reducing bacteria. This paragenesis explains the primary distribution of sulfur compounds in low-sulfur coals and possibly in most coals and many organic-rich soils and sediments. It also accounts for the occurrence of framboidal pyrite bound in fossil tissue in coal and sediments.     

Hematopoietic cell regulation by Rac1 and Rac2 guanosine triphosphatases

The Rho guanosine triphosphatases (GTPases) Rac1 and Rac2 are critical signaling regulators in mammalian cells. The deletion of both Rac1 and Rac2 murine alleles leads to a massive egress of hematopoietic stem/progenitor cells (HSC/Ps) into the blood from the marrow, whereas Rac1-/- but not Rac2-/- HSC/Ps fail to engraft in the bone marrow of irradiated recipient mice. In contrast, Rac2, but not Rac1, regulates superoxide production and directed migration in neutrophils, and in each cell type, the two GTPases play distinct roles in actin organization, cell survival, and proliferation. Thus, Rac1 and Rac2 regulate unique aspects of hematopoietic development and function.