Untersuchung zur Frage der Entstehung der Eisphase aus unterkühlten Wassertropfen

Zusammenfassung Auf verschiedenen Metallspiegeln wurden durch Kondensation Tröpfchen mit Durchmessern zwischen 5 und 25 erzeugt und so lange unterkühlt, bis ihr Gefrierpunkt beobachtet werden konnte. Die Auswertung ergibt, daß der Erstarrungsvorgang an den Tropfen bei –10° C einsetzt und sich ab etwa –15° C verstärkt. Die Temperatur des häufigsten Umschlags von Wasser zu Eis liegt im Bereich zwischen –20°C und –24° C. In Übereinstimmung mitJacobi wird festgestellt, daß metallische Unterlagen das Gefrieren begünstigen, wofür zum Teil deren hohe Wärmeleitfähigkeit verantwortlich gemacht wird. Eine Abhängigkeit der beobachteten Gefriertemperatur von Tropfengröße oder Kühlgeschwindigkeit besteht nicht.

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Summary Droplets of 5 to 25 diameter have been produced by condensation on different metallic mirrors and supercooled until congelation, which begins at –10° C and increases from –15° on with a maximum between –20° and –24°. In concert withJacobi metal support favours the freezing process, probably because of its high thermal conductivity. The freezing temperature depends neither on the size of the droplets nor on the speed of refrigeration.

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Résumé On a obtenu par condensation sur différents miroirs métalliques des gouttelettes avec des diamètres de 5 à 25 et on les a refroidies jusqu'à congélation. Celle-ci commence à –10° C et se renforce à partir de –15° environ; elle se produit de préférence entre –20° et –24°. Le support métallique favorise, en concordance avec les résultats deJacobi, le processus de congélation en vertu probablement de sa grande conductibilité calorifique. La température de congélation ne dépend pas de la grosseur des gouttelettes ni de la vitesse de refroidissement.

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Mit 9 Textabbildungen     

Application of the water balance model J2000 to estimate groundwater recharge in a semi-arid environment: a case study in the Zarqa River catchment, NW-Jordan

Pollution and overexploitation of scarce groundwater resources is a serious problem in the Zarqa River catchment, Jordan. To estimate this resource’s potential, the amount and spatial distribution of groundwater recharge was calculated by applying the hydrological model J2000. The simulation period is composed of daily values gathered over a 30-year period (July 1977 to June 2007). The figure finally obtained for estimated groundwater recharge of the Zarqa River catchment is 105 × 10⁶ m³ per year (21 mm a^?1). This is 19 % higher than the value previously assumed to be correct by most Jordanian authorities. The average ratio of precipitation to groundwater recharge is 9.5 %. To directly validate modelled groundwater recharge, two independent methods were applied in spring catchments: (1) alteration of stable isotope signatures (δ¹⁸O, δ²H) between precipitation and groundwater and (2) the chloride mass balance method. Recharge rates determined by isotopic investigations are 25 % higher, and recharge rates determined by chloride mass balance are 9 % higher than the modelled results for the corresponding headwater catchments. This suggests a reasonably modelled safe yield estimation of groundwater resources.     

The nature of the luminous X-ray emission of NGC 6240

We briefly review and extend our discussion of the ROSAT detectionof the extraordinarily luminous (>10⁴² erg/s) partly extended(>30 kpc diameter) X-ray emission from the ultraluminous infrared galaxy NGC 6240.The `standard'-model of starburst outflow is contrasted with alternatives and a comparison with the X-ray properties of ellipticals is performed.     

Evidence of Spatio-Temporal Variations in Contaminants Discharging to a Peri-Urban Stream

Xenobiotic organic compounds can be discharged from contaminated groundwater inflow and may seep into streams from multiple pathways with very different dynamics, some not fully understood. In this study, we investigated the spatio-temporal variation of chlorinated ethenes discharging from a former industrial site (with two main contaminant sources, A and B) into a stream system in a heterogeneous clay till setting in eastern Denmark. The investigated reach and near-stream surroundings are representative of peri-urban settings, with a mix of high channel alteration and more natural stream environment. We therefore propose an approach for risk assessing impacts arising from such complex contamination patterns, accounting for potential spatio-temporal fluctuations and presence of multiple pathways. Our study revealed substantial variations in pathway contributions and overall contaminant mass discharge to the stream. Variable contaminant contributions arising from both groundwater seepage and urban drains were identified in the channelized part of the north stream, primarily from source A. Furthermore, variations in the hyporheic and shallow groundwater flows were found to enhance contaminant transport from source B. These processes result in an increase of the overall mass of contaminant discharged, correlating with the channels' flow. Thus, an in-stream control plane approach was found to be an effective method for integrating multiple and variable discharge contributions quantitatively, although information on specific contaminant sources is lost. This study highlights the complexity and variability of contaminant fluxes occurring at the interface between groundwater and peri-urban streams, and calls for the consideration of these variations when designing monitoring programs and remedial actions for contaminated sites with the potential to impact streams.     

Coal mine workers' pneumoconiosis

 The fibrogenic and cytotoxic potential of coal mine dust is independent of the amount of quartz and other inorganic parameters. Results of coal petrographical and organic geochemical investigations of coals and coal mine dust from the Ruhr and Ibbenbüren Region of Germany demonstrate variations of organic dust amount possibly influencing these noxious properties. Coal mine dust of high rank coals is characterized by a pronounced fibrogenic risk. This risk, independent of the quantity of quartz, is probably based on shape variations of different coal macerals. With increasing coalification of the corresponding seam, the vitrinite is enriched in its dust; however, lower concentrations have been determined for inertinite. Vitrinite shows constant shapes and sizes independent of the rank of coal. Inertinite particles with elongated to fibrous shapes tend to larger sizes with increasing coalification. Strikingly, coal mine dust from miners' lungs with high degrees of coal mine workers' pneumoconiosis (CWP) is enriched in inertinite. In contrast, high cytotoxicities in cell tests are known for coal mine dust from low coalified coals. High concentrations of phenolic compounds can be extracted by dichloromethane from low coalified coal mine dust. These compounds, which are characterized by a high water solubility and therefore high bioavailability, explain the high cytotoxicities of coal mine dust. Contamination of dust by diesel emissions in the coal mine can act as additionally supporting parameters for extended cytotoxicities. Received: 18 August 1995 · Accepted: 15 October 1995     

Quantum statistical cluster abundances in hot nuclear matter and elemental composition of cosmic-ray sources

A simple model for superluminal double radio sources is presented. A relativistic electron-positron beam drives the expansion of an elongated magnetic loop configuration. This is treated using basic conservation laws. Relativistically expanding radio components on a scale of parsecs result for plausible physical parameters.     

Desert Potholes: Ephemeral Aquatic Microsystems

An enigma of the Colorado Plateau high desert is the “pothole”, which ranges from shallow ephemeral puddles to deeply carved pools. The existence of prokaryotic to eukaryotic organisms within these pools is largely controlled by the presence of collected rainwater. Multivariate statistical analysis of physical and chemical limnologic data variables measured from potholes indicates spatial and temporal variations, particularly in water depth, manganese, iron, nitrate and sulfate concentrations and salinity. Variation in water depth and salinity are likely related to the amount of time since the last precipitation, whereas the other variables may be related to redox potential. The spatial and temporal variations in water chemistry affect the distribution of organisms, which must adapt to daily and seasonal extremes of fluctuating temperature (0–60 °C), pH changes of as much as 5 units over 12 days, and desiccation. For example, many species become dormant when potholes dry, in order to endure intense heat, UV radiation, desiccation and freezing, only to flourish again upon rehydration. But the pothole organisms also have a profound impact on the potholes. Through photosynthesis and respiration, pothole organisms affect redox potential, and indirectly alter the water chemistry. Laboratory examination of dried biofilm from the potholes revealed that within 2 weeks of hydration, the surface of the desiccated, black biofilm became green from cyanobacterial growth, which supported significant growth in heterotrophic bacterial populations. This complex biofilm is persumably responsible for dissolving the cement between the sandstone grains, allowing the potholes to enlarge, and for sealing the potholes, enabling them to retain water longer than the surrounding sandstone. Despite the remarkable ability of life in potholes to persist, desert potholes may be extremely sensitive to anthropogenic effects. The unique limnology and ecology of Utah potholes holds great scientific value for understanding water–rock–biological interactions with possible applications to life on other planetary bodies.     

Analysis of Gable-Roofed Building Signature in Multiaspect InSAR Data

The spatial resolution of state-of-the-art synthetic aperture radar sensors enables the structure analysis of urban areas. The appearance of buildings in magnitude images in settlements is dominated by the effects of the inherent oblique scene illumination. In urban residential districts, salient pairs of parallel lines of bright magnitude are often caused by direct reflection and double-bounce signal at gable-roofed buildings. In this letter, the magnitude and interferometric phase signature of gable-roofed buildings are discussed to extract reliable building features for reconstruction. The analysis contains signature changes by varying illumination and building geometry. The presented approach is aiming at the reconstruction of gable-roofed buildings by a knowledge-based analysis considering the discussed effects. The reconstruction results are assessed by using a high-resolution LIDAR surface model as ground truth.      

Provenance of Austroalpine basement metasediments: tightening up Early Palaeozoic connections between peri-Gondwanan domains of central Europe and Northern Africa

International Journal of Earth Sciences - New U–Pb and Lu–Hf detrital zircon data together with whole-rock geochemical and Sm–Nd data were obtained for paragneisses of the...     

Enigmatic clastic pipe swarms and implications for fluidization dynamics in aeolian deposits

Soft‐sediment deformation of contorted and massive sandstone is common throughout much of the siliciclastic record, but clastic pipes represent a distinctive class of pressurized synsedimentary features. Remarkable centimetre to metre‐scale clastic pipe exposures in the Jurassic Navajo Sandstone of Utah (USA) establish a range of pipe sizes, expressions and relationships to the host rock in an erg margin setting, traditionally thought to be just a dry desert system. In particular, the field and laboratory characterizations of cylindrical pipes show internal concentric, annular rings that imply water fluidization, with alignment of long grain axes due to shear flow along pipe margins. Central interior parts of decimetre‐scale pipes appear massive in plan view, but display weakly developed pseudobedding from post‐pressure release, gravitational settling in the cross‐sectional view. Deformation features of conjugate fractures, ring faults, hypotrochoid patterns (geometric arcs and circles) and breccia in the host material reflect both brittle and ductile behaviour in response to the fluidization and injection of the clastic pipes. The stratigraphic context of individual pipes and the stratabound intervals of pipe features imply dynamic deformation nearly coincident with deposition in this Early Jurassic aeolian system related to multiple factors of groundwater expulsion, timing and local host sediment properties that influenced pipe development. Although the pipe features might be easily overlooked as a smaller scale feature of soft‐sediment deformation in dune deposits, these are valuable environmental indications of disrupted fluid pathways within porous, reservoir quality sands, associated with possible combinations of periodic springs, high water‐table conditions and strong ground‐motion events. These pipe examples may be important analogues where exposures are not so clear, with applications to diverse modern and ancient clastic settings internationally on Earth as well as in planetary explorations such as on Mars.