Modeling Geochemically Caused Permanent Stratification in Lake Waldsee (Germany)     

Santiago Moreira  Bertram Boehrer  Martin Schultze  Severine Dietz  Javier Samper 《Aquatic Geochemistry》2011,17(3):265-280

A geochemical model was incorporated into a stratification model for lakes to create the model package: DYCD-CORE, a numerical code that couples the thermal and hydrodynamic capabilities of DYRESM and the geochemical capabilities of the reactive transport model CORE^2D V4. Based on the chemical composition of solutes calculated in each node for each time step, density was computed using specific partial molal volumes of all considered solutes and fed back into the stratification module of the program package. The density calculated each time step leads to a strong coupling of hydrodynamics and hydrogeochemistry and reflects the complex interaction as it is present in all lakes. To demonstrate the functionality of the numerical approach, an example of an iron-meromictic lake was chosen, where the reactivity of the dissolved iron kept the water body perennially stratified. To critically validate the model results, temperatures were continously measured at high vertical and temporal resolution in a field investigation of Waldsee (near Döbern, Germany). Multiparameterprobe profiles and water samples confirmed the continous chemical stratification and served as initial and boundary conditions for the simulation period. The model package DYCD-CORE could reproduce the permanent stratification as it were in the lake. A demonstration run using the standard UNESCO equation for density, and hence assuming non-reactive solutes, failed entirely. Hence, stratification models using salinity for density are not suited for simulating density created by lake-internal geochemical transformation of solutes. However, density can be based directly on the simultaneous numerical simulation of lake geochemistry. Predictive modeling of changing lake circulation in a variable climate or considering change of use will require a proper inclusion of the geochemistry as demonstrated in this paper.  相似文献   

Molecular Gas in the Abell 262 Cluster Galaxy Ugc 1347     

Thomas Bertram  Andreas Eckart  Melanie Krips  Johannes Staguhn 《Astrophysics and Space Science》2005,295(1-2):303-308

We present the results of ¹²CO(1-0) and ¹²CO(2-1) observations on UGC 1347 obtained with BIMA and the IRAM 30 m telescope. UGC 1347 is a member of the Abell 262 cluster. In Abell 262, a nearby spiral rich cluster, the signs of galaxy interaction and therefore the mechanisms which play an important role in galaxy evolution within clusters can be studied with high spatial resolution. Aside from its bright central region, UGC 1347 features a second prominent source at the southern tip of the bar, which has been identified as region with recent enhanced star formation. The CO observations prove the existence of reservoirs of cold molecular gas at the positions of both bright regions.  相似文献   

Reconstructing basin evolution from sedimentary thickness; the importance of palaeobathymetric control, with reference to the North Sea     

G. T. Bertram  N. J. Milton 《Basin Research》1988,1(4):247-257

Abstract The structural evolution of a basin cannot be reconstructed from sedimentary thicknesses alone without data on palaeobathymetry. Two classes of geological horizons, are defined, profiles and traces. Profiles are time-lines and bound depositional units. Traces were formed at a known water depth and contain implicit palaeobathymetric data.
Rock units bounded by traces are diachronous lithostratigraphic units, and the thicknesses of such units are controlled directly by subsidence, while the thicknesses of profile-bounded units may be unaffected by the subsidence or even the palaeotopography of the basin.
Dating fault movement from thickness variations in profile-bounded units is difficult without prior knowledge of the palaeobathymetry, and it is impossible to distinguish between synsedimentary fault movement and onlap to a pre-existing fault scarp from thickness alone.
Reconstruction of the basin history of the North Sea is difficult due to the lack of trace-bounded units in the post-Jurassic. The validity of previously published studies depends largely on the quality and quantity of palaeobathymetric data included. An alternative basin history is proposed based on the few trace-bounded units in the North Viking Graben. This includes rifting episodes in the Triassic and Late Jurassic, and a period of uplift in the Palaeocene.  相似文献   

On a vibronic origin for the diffuse band spectrum     

Joseph A. Nuth  Bertram Donn 《Astrophysics and Space Science》1983,95(1):209-212

Duley (1982) has proposed that many of the diffuse interstellar bands in the wavelength interval 677 nm>λ>542 nm arise from vibronic transitions of Cr³⁺ ions in MgO grains. No explanation has been offered for the fact that as many as 85 of the possible 108 transitions of this system have not been observed in the interstellar medium. Moreover, the relative intensities of the diffuse bands which are observed appear to be inconsistent with their assignment. We therefore conclude that this model is not consistent with the observations.  相似文献   

Studies of proton-irradiated cometary-type ice mixtures     

Marla H. Moore  Bertram Donn  Raj Khanna  Michael F. A&#x;Hearn 《Icarus》1983,54(3):388-405

Radiation synthesis has been proposed as a mechanism for changing the nature of the outer few meters of ice in a comet stored 4.6 billion years in the Oort cloud and may explain some of the differences observed between new and more evolved comets. Cometary-type ice mixtures were studied in a laboratory experiment designed to approximately simulate the expected temperature, pressure, and radiation environment of the interstellar Oort cloud region. The 2.5- to 15-μm infrared absorption features of thin ice films were analyzed near 20°K before and after 1 MeV proton irradiation. Various ice mixtures included the molecules H₂O, NH₃, CH₄, N₂, C₃H₈, CO, and CO₂. All experiments confirm the synthesis of new molecular species in solid phase mixtures at 20°K. The synthesized molecules, identified by their infrared signatures, are C₂H₆, CO₂, CO, N₂O, NO, and CH₄ (weak). Synthesized molecules, identified by gas chromatographic (GC) analysis of the volatile fraction of the warmed irradiated ice mixture, are C₂H₄ or C₂H₆, and C₃H₈. When CH₄ is present in the irradiated ice mixture, long-chained volatile hydrocarbons and CO₂ are synthesized along with high-molecular-weight carbon compounds present in the room temperature residue. Irradiated mixtures containing CO and H₂O synthesize CO₂ and those CO₂ and H₂O synthesize CO. Due to radiation synthesis, ～1% of the ice was converted into a nonvolatile residue containing complicated carbon compounds not present in blank samples. These results suggest that irrespective of the composition of newly accreted comets, initial molecular abundances can be altered and new species created as a result of radiation synthesis. Irradiated mixtures exhibited thermoluminescence and pressure enhancements during warming; these phenomena suggest irradiation synthesis of reactive species. Ourbursts in new comets resulting from similar radiation induced exothermic activity would be expected to occur beginning at distances of the order of 100 AU.  相似文献   

Some aspects of condensation in clouds     

Bertram Donn 《Astrophysics and Space Science》1979,65(1):167-171

Several general features of nucleation characteristics of low density cosmic clouds are discussed. These are: (1) tendency for metastable condensates to form, (2) non-occurrence of nominal refractory molecule in the gas, (3) a strong temperature dependence of condensation at relatively low temperatures, and (4) significant vibrational disequilibrium in cosmic clouds. These support previous analyses by the author which indicate that equilibrium calculations have restricted applicability. A kinetic treatment of condensation is required for cosmic grains and the possibility of formulating such an analysis is pointed out.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space Medium, held at the Lunar and Planetary Institute, Houston, 6–8 September, 1978.  相似文献   

New Zealand since 1984: Elite succession, income distribution and economic growth in a small trading economy     

Geoff Bertram 《GeoJournal》2004,59(2):93-106

Four interrelated patterns of structural change in the New Zealand economy since 1980 are identified and analysed, against the backdrop of a growth rate which fell substantially behind the rest of the OECD in the late 1980s and early 1990s before recovering, but without catchup, from 1993. The changes discussed are: a shift in sharemarket capitalization from formerly-dominant productive activities in agriculture, manufacturing and construction to the current predominance of utilities, transport and finance; a sharp increase in overseas investors' share of the economic surplus, from around 20% to over half of post-tax corporate profits; a steady rise in international indebtedness at the same time as sovereign foreign-currency debt was eliminated; hence overseas debt was successfully privatized; a weakening of regulatory control over monopoly profits, opening the way for a surge of rent-seeking activity during the 1990s. The neoliberal reform programme has achieved fiscal and monetary sustainability, increased market flexibility, and insulated the economy against external shocks. At the same time it has led to denationalisation of economic surplus, ongoing current account deficits, and a significant diversion of resources from productive use into rent-seeking. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Relationship of concretions and chlorite-muscovite porphyroblasts to the development of domainal cleavage in low-grade metamorphic deformed rocks from north-central Wales,Great Britain     

Bertram G. Woodland 《Journal of Structural Geology》1985,7(2):205-215

Spaced or domainal cleavage is widespread in deformed rocks of low metamorphic grade. This study presents evidence on the origin of spaced cleavage in deformed pelites from Silurian turbidite sequences in north-central Wales. The variable development of cleavage folia is related to the presence of concretions, which served to concentrate strain effects of well-developed cleavage folia in the matrix in some zones and to produce ‘strain shadows’ (few or no cleavage folia) in others. Compositional differences between matrix, narrow transition zones, and concretions also influenced the development of cleavage folia. Chlorite-muscovite porphyroblast growth was initiated before cleavage formation, but its further growth and development took place during cleavage formation. The relationship of cleavage to the concretions and to the chlorite-muscovite porphyroblasts indicates that cleavage developed in a matrix that must have been in an advanced state of lithification (anchimetamorphic to lowermost greenschist facies of metamorphism) and not during soft-sediment deformation.  相似文献   

Implications of weak near-term climate policies on long-term mitigation pathways     

Gunnar?LudererEmail author  Christoph?Bertram  Katherine?Calvin  Enrica?De?Cian  Elmar?Kriegler 《Climatic change》2016,135(1):127-141

While the international community has agreed on the long-term target of limiting global warming to no more than 2 °C above pre-industrial levels, only a few concrete climate policies and measures to reduce greenhouse gas (GHG) emissions have been implemented. We use a set of three global integrated assessment models to analyze the implications of current climate policies on long-term mitigation targets. We define a weak-policy baseline scenario, which extrapolates the current policy environment by assuming that the global climate regime remains fragmented and that emission reduction efforts remain unambitious in most of the world’s regions. These scenarios clearly fall short of limiting warming to 2 °C. We investigate the cost and achievability of the stabilization of atmospheric GHG concentrations at 450 ppm CO₂e by 2100, if countries follow the weak policy pathway until 2020 or 2030 before pursuing the long-term mitigation target with global cooperative action. We find that after a deferral of ambitious action the 450 ppm CO₂e is only achievable with a radical up-scaling of efforts after target adoption. This has severe effects on transformation pathways and exacerbates the challenges of climate stabilization, in particular for a delay of cooperative action until 2030. Specifically, reaching the target with weak near-term action implies (a) faster and more aggressive transformations of energy systems in the medium term, (b) more stranded investments in fossil-based capacities, (c) higher long-term mitigation costs and carbon prices and (d) stronger transitional economic impacts, rendering the political feasibility of such pathways questionable.  相似文献   

A note on the composition and structure of interstellar grains     

Joseph A. Nuth  Bertram Donn 《Astrophysics and Space Science》1983,95(1):175-178

Gürtleret al. (1981) argue that SiO could not be the material responsible for the interstellar 10 micron feature as had been proposed by Duleyet al. (1979). While Millar (1982) has quite successfully refuted the arguments of Gürtleret al. (1981), we present here some additional considerations which indicate that the model of Duleyet al. (1979) requires appreciable modification to be consistent with recent experimental results.  相似文献