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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 36 (1998), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The concentrations of tritium, helium isotopes, and neon have been measured in ground water from a fractured bedrock aquifer in a densely populated suburban area near New York City. Samples were obtained from heavily pumped production wells of a regional water supply company. Helium and neon concentrations exceed the values for air-saturated water, which is explained by the addition of unfractionated atmospheric air, radiogenic helium, and tritiogenic 3He. The identification of the composition of these excess components allows reliable separation of the tritiogenic 3He concentration, and hence the calculation of the 3H/3He ages of the ground water. Comparison of the combined tritium plus tritiogenic 3He concentrations with the historical record of tritium input from precipitation confirms that the 3H/3He data are self-consistent and provides constraints on the degree of mixing or helium loss. The distribution of 3H/3He ages is related to the large-scale topography of the study area and the depth of the wells. Furthermore, correlations between the 3H/3He ages and concentrations of total dissolved solids and total CO2 show that the ages contain meaningful information related to the temporal changes of the ground water chemistry.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: 3H, He, 4He, and Ne data were obtained from a shallow ground-water system being recharged by bank infiltration from the Danube River in northwestern Hungary. After correting for excess air, 4He and Ne concentrations reflect a recharge temperature of about 9° C., close to the mean annual temperature of the Danube (10.4° C). Values of H plus 3Hetrit (“initial tritium”) as a function of the tritium/He age are consistent with time series measurements of tritium in the Danube. Tritium/ He ages increase linearly as a function of distance from the Danube along ground-water flow lines. A horizontal flow velocity of about 530 m yr1 was derived from the age gradient. Most of the deviations between measured Danube tritium data and ground-water tritium/He data can be explained by dispersive mixing.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 89 (1988), S. 353-362 
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 94 (1989), S. 245-256 
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 342 (1989), S. 908-912 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] All continental ground waters contain small amounts of dissolved helium, often considerably in excess of the equilibrium saturation value. Most of this helium is generated by radioactivity and other nuclear processes within the crust. Such helium is characterized by its isotopic composition, ...
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  Palaeodata in synthesis form are needed as benchmarks for the Palaeoclimate Modelling Intercomparison Project (PMIP). Advances since the last synthesis of terrestrial palaeodata from the last glacial maximum (LGM) call for a new evaluation, especially of data from the tropics. Here pollen, plant-macrofossil, lake-level, noble gas (from groundwater) and δ18O (from speleothems) data are compiled for 18±2 ka (14C), 32 °N–33 °S. The reliability of the data was evaluated using explicit criteria and some types of data were re-analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month (MTCO), mean annual temperature (MAT), plant available moisture (PAM) and runoff (P-E). Cold-month temperature (MAT) anomalies from plant data range from −1 to −2 K near sea level in Indonesia and the S Pacific, through −6 to −8 K at many high-elevation sites to −8 to −15 K in S China and the SE USA. MAT anomalies from groundwater or speleothems seem more uniform (−4 to −6 K), but the data are as yet sparse; a clear divergence between MAT and cold-month estimates from the same region is seen only in the SE USA, where cold-air advection is expected to have enhanced cooling in winter. Regression of all cold-month anomalies against site elevation yielded an estimated average cooling of −2.5 to −3 K at modern sea level, increasing to ≈−6 K by 3000 m. However, Neotropical sites showed larger than the average sea-level cooling (−5 to −6 K) and a non-significant elevation effect, whereas W and S Pacific sites showed much less sea-level cooling (−1 K) and a stronger elevation effect. These findings support the inference that tropical sea-surface temperatures (SSTs) were lower than the CLIMAP estimates, but they limit the plausible average tropical sea-surface cooling, and they support the existence of CLIMAP-like geographic patterns in SST anomalies. Trends of PAM and lake levels indicate wet LGM conditions in the W USA, and at the highest elevations, with generally dry conditions elsewhere. These results suggest a colder-than-present ocean surface producing a weaker hydrological cycle, more arid continents, and arguably steeper-than-present terrestrial lapse rates. Such linkages are supported by recent observations on freezing-level height and tropical SSTs; moreover, simulations of “greenhouse” and LGM climates point to several possible feedback processes by which low-level temperature anomalies might be amplified aloft.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  Seventeen simulations of the Last Glacial Maximum (LGM) climate have been performed using atmospheric general circulation models (AGCM) in the framework of the Paleoclimate Modeling Intercomparison Project (PMIP). These simulations use the boundary conditions for CO2, insolation and ice-sheets; surface temperatures (SSTs) are either (a) prescribed using CLIMAP data set (eight models) or (b) computed by coupling the AGCM with a slab ocean (nine models). The present-day (PD) tropical climate is correctly depicted by all the models, except the coarser resolution models, and the simulated geographical distribution of annual mean temperature is in good agreement with climatology. Tropical cooling at the LGM is less than at middle and high latitudes, but greatly exceeds the PD temperature variability. The LGM simulations with prescribed SSTs underestimate the observed temperature changes except over equatorial Africa where the models produce a temperature decrease consistent with the data. Our results confirm previous analyses showing that CLIMAP (1981) SSTs only produce a weak terrestrial cooling. When SSTs are computed, the models depict a cooling over the Pacific and Indian oceans in contrast with CLIMAP and most models produce cooler temperatures over land. Moreover four of the nine simulations, produce a cooling in good agreement with terrestrial data. Two of these model results over ocean are consistent with new SST reconstructions whereas two models simulate a homogeneous cooling. Finally, the LGM aridity inferred for most of the tropics from the data, is globally reproduced by the models with a strong underestimation for models using computed SSTs.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-1076
    Keywords: Ventricular septal defect ; Colour Doppler ; Neonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Between January 1987 and July 1989 a ventricular septal defect (VSD) as a single cardiac lesion was detected in 269 small infants aged less than 1 year. The diagnosis was achieved by two-dimensional echocardiography and Doppler colour flow mapping using subcostal, parasternal, apical, and suprasternal views. VSDs were divided into perimembraneous, muscular, malalignment, and subpulmonary defects. Septal defects in complex lesions and atrioventricular defects were excluded. In group 1 (174 infants up to 4 weeks of age, mean 10 days) 125 muscular (71.8%), 35 (20.1%) perimembraneous, 12 (6.9%) malalignment, and 2 (1.1%) subpulmonary defects were diagnosed. One baby had a combined perimembraneous and muscular defect. In another baby a malalignment defect was associated with an av-canal. In group 2 (95 infants aged 4 weeks to 1 year, mean 4.0 months), 57 (60%) muscular, 32 (33.6%) perimembraneous and 6 (6.3%) malalignment defects were found. Within the maximum observation period of 13 months, spontaneous closure occurred in 72 (42.6%) of 169 infants who had a sufficient follow up. Sixty-four had a muscular (88.9%) and 8 (11.1%) a perimembraneous defect. Surgical intervention was required in 11 patients: five perimembraneous defects were closed, one was palliated. Five infants with a malalignment defect were palliated. The malalignment defect frequently needed surgical intervention even in newborns; it never closed spontaneously. About 10% of patients with perimembraneous septal defect required surgery. Spontaneous closure rarely occurred in early infancy. Muscular VSDs were most frequent but virtually never required therapy. Spontaneous closure rate was about 50% during the 1st year of life.
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 2014-03-25
    Description: Disc winds originating from the inner parts of accretion discs are considered as the basic component of magnetically collimated outflows. The only available analytical magnetohydrodynamic (MHD) solutions to describe disc-driven jets are those characterized by the symmetry of radial self-similarity. However, radially self-similar MHD jet models, in general, have three geometrical shortcomings: (i) a singularity at the jet axis, (ii) the necessary assumption of axisymmetry and (iii) the non-existence of an intrinsic radial scale, i.e. the jets formally extend to radial infinity. Hence, numerical simulations are necessary to extend the analytical solutions towards the axis, by solving the full three-dimensional equations of MHD and impose a termination radius at finite radial distance. We focus here on studying the effects of relaxing the (ii) assumption of axisymmetry, i.e. of performing full 3D numerical simulations of a disc wind crossing all MHD critical surfaces. We compare the results of these runs with previous axisymmetric 2.5D simulations. The structure of the flow in all simulations shows strong similarities. The 3D runs reach a steady state and stay close to axisymmetry for most of the physical quantities, except for the poloidal magnetic field and the toroidal velocity which slightly deviate from axisymmetry. The latter quantities show signs of instabilities, which, however, are confined to the region inside the fast magnetosonic separatrix surface. The forces present in the flow, both of collimating and accelerating nature, are in good agreement in both the 2.5D and the 3D runs. We conclude that the analytical solution behaves well also after relaxing the basic assumption of axisymmetry.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 10
    Publication Date: 2013-04-03
    Description: Chronic exposure to arsenic (As) by drinking shallow groundwater causes widespread disease in Bangladesh and neighboring countries. The release of As naturally present in sediment to groundwater has been linked to the reductive dissolution of iron oxides coupled to the microbial respiration of organic carbon (OC). The source of OC...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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