The Shallow Weathered Fracture Layer in the Near–Stream Zone     

W. J. Gburek  J. B. Urban 《Ground water》1990,28(6):875-883

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Correlation of Plio-Pleistocene deposits of the Lower Rhine Basin (North-West Germany) and the Valle Ricca pits (Central Italy)     

Claudio Arias  Giulio Bigazzi  Francescopaolo Bonadonna  Karl Brunnacker  Brigitte Urban 《Quaternary Science Reviews》1984,3(1):73-89

Biostratigraphic and palaeomagnetic research has been carried out on selected profiles in North-Western Germany and Central Italy in order to correlate Plio-Pleistocene sections.Around the Réunion subchronozone, vegetation in the Valle Ricca was dominated by a mountain forest type pointing to cool climatic conditions. In the Lower Rhine Basin vegetation had a slightly warmer character, but was also dominated strongly by a mountain type of forest vegetation, characteristic of cooler summers and higher precipitation than at present.Two warmer periods have been determined in the Central Italian profiles; the youngest around the Olduvai reversal, should correspond to the youngest Tiglian beds of the Lower Rhine Basin.Deposits older than the Réunion subzone have not been found in the Valle Ricca. In the Lower Rhine Basin, on the other hand, the Gauss-Matuyama boundary is located between the uppermost Pliocene, the Reuverian C and the Praetiglian.  相似文献   

Selection criteria for continuous channel electron multipliers in space applications     

A. Urban 《Astrophysics and Space Science》1982,83(1-2):3-14

Criteria for selecting continuous channel electron multipliers were applied to fifteen Mullard units without significantly affecting their overall lifetime. The gain fatigue vs accumulated counts, the change of the pulse height distribution during lifetime, the gain degradation vs count rates as well as the gain vs operating voltage and the resolution vs operating voltage have been investigated using a tritium source. The results provide several criteria to determine good, marginal and poor multipliers. From all tested devices 25% had a very low gain and did not operate satisfactory at the end of their lifetime investigations (4×10⁹ accumulated counts). 40% of all devices could be classified as good multipliers. Their main characteristic was a gain recovery phenomenon after 3×10⁹ accumulated counts with a progressive gain stabilizing. Multipliers classified as marginal exhibited some unexpected behaviour during the lifetime but a gain recovery phase and gain plateau region could be identified. Furthermore, the relative efficiency of the multipliers vs electron energy as a function of the operating voltage has been measured by using a near monoenergetic electron beam.Originally submitted to the journalSpace Science Instrumentation.  相似文献   

Transboundary impacts on regional ground water modeling in Texas   总被引：1，自引：0，他引：1  

Rainwater K  Stovall J  Frailey S  Urban L 《Ground water》2005,43(5):706-716

Recent legislation required regional grassroots water resources planning across the entire state of Texas. The Texas Water Development Board (TWDB), the state's primary water resource planning agency, divided the state into 16 planning regions. Each planning group developed plans to manage both ground water and surface water sources and to meet future demands of various combinations of domestic, agricultural, municipal, and industrial water consumers. This presentation describes the challenges in developing a ground water model for the Llano Estacado Regional Water Planning Group (LERWPG), whose region includes 21 counties in the Southern High Plains of Texas. While surface water is supplied to several cities in this region, the vast majority of the regional water use comes from the High Plains aquifer system, often locally referred to as the Ogallala Aquifer. Over 95% of the ground water demand is for irrigated agriculture. The LERWPG had to predict the impact of future TWDB-projected water demands, as provided by the TWDB, on the aquifer for the period 2000 to 2050. If detrimental impacts were noted, alternative management strategies must be proposed. While much effort was spent on evaluating the current status of the ground water reserves, an appropriate numerical model of the aquifer system was necessary to demonstrate future impacts of the predicted withdrawals as well as the effects of the alternative strategies. The modeling effort was completed in the summer of 2000. This presentation concentrates on the political, scientific, and nontechnical issues in this planning process that complicated the modeling effort. Uncertainties in data, most significantly in distribution and intensity of recharge and withdrawals, significantly impacted the calibration and predictive modeling efforts. Four predictive scenarios, including baseline projections, recurrence of the drought of record, precipitation enhancement, and reduced irrigation demand, were simulated to identify counties at risk of low final ground water storage volume or low levels of satisfied demand by 2050.  相似文献   

Wave Flow Simulations Over Arctic Leads     

Thorsten?MauritsenEmail author  Gunilla?Svensson  Branko?Grisogono 《Boundary-Layer Meteorology》2005,117(2):259-273

We investigate the flow over Arctic leads using a mesoscale numerical model, typical of both summer and winter, under idealised conditions. We find that Arctic leads may be the source of standing atmospheric internal gravity waves during both seasons. The summertime wave may be compared with the wave generated by a small ridge, though with the phase reversed. The mechanism for exciting the wave is found to be the internal boundary layer developing due to horizontal variations in surface temperature and roughness length. During the more exploratory wintertime simulations, with substantial temperature difference between the lead and the ice surface, we find that secondary circulations and intermittent wave-breaking may occur. The effects of the lead appear far downstream.  相似文献   

Violations of Gutenberg–Richter Relation in Anthropogenic Seismicity     

Pawel Urban  Stanislaw Lasocki  Patrick Blascheck  Aderson Farias do Nascimento  Nguyen Van Giang  Grzegorz Kwiatek 《Pure and Applied Geophysics》2016,173(5):1517-1537

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Combined Ozone and Biological Treatment of Oak Wood Leachate          下载免费PDF全文

Henric Svensson  Henrik Hansson  William Hogland 《洁净——土壤、空气、水》2015,43(4):598-604

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Spatial organization of seismicity and fracture pattern in NE Italy and W Slovenia     

G.?Bressan  M.?Ponton  G.?RossiEmail author  S.?Urban 《Journal of Seismology》2016,20(2):511-534

The study focuses on the spatial organization of seismicity and the relation between fracture pattern and earthquakes in the Friuli (north-eastern Italy) and western Slovenia seismic regions. The structural setting is characterized by a complex structure resulting from the superposition of several tectonic phases that generated NW-SE trending Dinaric faults and about E-W trending Alpine faults. The upper crust is characterized by lithological and mechanical heterogeneities. The fractal analysis shows that, in general, the seismicity only partially fills a plane. Only in a few cases, the earthquakes distribute on planar structures. The orientation of planes that fit through the hypocentres shows a different disposition at the two depth intervals analysed. The shallower interval (0–10 km) is characterized by planes with highly variable orientations. The spatial seismicity is investigated in the context of a general damage model, represented by the crack density distribution. The results evidence that the seismicity appears mostly located along sharp transition areas from low crack density to higher crack density, i.e., from zones of low damage to zones of intermediate damage. These zones are characterized by high heterogeneity due to the superposition of different tectonic phases and by the maximum interference between Dinaric and Alpine domains. The orientation of the planes fitting the seismicity at 10–20-km depth appears less dispersed, coinciding with the trend of Dinaric sub-vertical faults in the northern and eastern parts of the study area, and with Alpine low-angle faults in the western and southern parts.  相似文献   

The simulation of Arctic clouds and their influence on the winter surface temperature in present-day climate in the CMIP3 multi-model dataset   总被引：1，自引：1，他引：0  

Johannes Karlsson  Gunilla Svensson 《Climate Dynamics》2011,36(3-4):623-635

We investigate the influence of clouds on the surface energy budget and surface temperature in the sea-ice covered parts of the ocean north of the Arctic circle in present-day climate in nine global climate models participating in the Coupled Model Intercomparison Project phase 3, CMIP3. Monthly mean simulated surface skin temperature, radiative fluxes and cloud parameters are evaluated using retrievals from the extended AVHHR Polar Pathfinder (APP-x) product. We analyzed the annual cycle but the main focus is on the winter, in which large parts of the region experience polar night. We find a smaller across-model spread as well as better agreement with observations during summer than during winter in the simulated climatological annual cycles of total cloudiness and surface skin temperature. The across-model spread in liquid and ice water paths is substantial during the whole year. These results qualitatively agree with earlier studies on the present-day Arctic climate in GCMs. The climatological ensemble model mean annual cycle of surface cloud forcing shows good agreement with observations in summer. However, during winter the insulating effect of clouds tends to be underestimated in models. During winter, most of the models as well as the observations show higher monthly mean total cloud fractions, associated with larger positive surface cloud forcing. Most models also show good correlation between the surface cloud forcing and the vertically integrated ice and liquid cloud condensate. The wintertime ensemble model mean total cloud fraction (69%) shows excellent agreement with observations. The across-model spread in the winter mean cloudiness is substantial (36?C94%) however and several models significantly underestimate the cloud liquid water content. If the two models not showing any relationship between cloudiness and surface cloud forcing are disregarded, a tentative across-model relation exists, in such a way that models that simulate large winter mean cloudiness also show larger surface cloud forcing. Even though the across-model spread in wintertime surface cloud forcing is large, no clear relation to the surface temperature is found. This indicates that other processes, not explicitly cloud related, are important for the simulated across-model spread in surface temperature.  相似文献   

Palaeoecological analysis of a Late Quaternary sediment profile in northern Oman     

B. Urban  A. Buerkert 《Journal of Arid Environments》2009,73(3):296-305

High resolution palaeoecological studies of the Arabian Peninsula for the late Quaternary period are scarce. Consequently, little is known about time-dependent relationships between vegetation, environment and the development of human settlements in this area. To help fill this gap for the arid Hajar mountains of northern Oman, a 20 m deep profile in a sediment-filled depression near an oasis settlement was analysed for its physico-chemical properties, pollen and spores and other palynomorphs. Charcoal frequencies in combination with geochemical data provided evidence of an Early Holocene increase of rainfall. The onset of dryer conditions at about 8 ka was indicated by charcoal frequencies and geochemical data as were previously unrecognised short humid periods dated to 5.7, 5 and 4.4 ka. The upper 4 m of sediments contained a 4300 year-old pollen profile reaching into the archaeologically important Umm al-Nar period characterized by increased settlement activities throughout Oman. Variation in mollusc shell frequency and periodic peaks of NH₄-N suggested only minor local variations of rainfall throughout the last 2000 years. The sudden appearance of Olea spec., Ziziphus and Fabaceae pollen since about 500 years ago points to a late onset of oasis agriculture nearby.  相似文献