Structural incorporation of Cm(III) in trioctahedral smectite hectorite: A time-resolved laser fluorescence spectroscopy (TRLFS) study     

Heike Brandt  Dirk Bosbach  Petra J. Panak 《Geochimica et cosmochimica acta》2007,71(1):145-154

Structural incorporation of the actinide curium in the octahedral layer of the trioctahedral Mg-rich smectite hectorite was studied using time-resolved laser fluorescence spectroscopy. Organo-hectorite nanoparticles were synthesized at 90 °C in the presence of Cm(III). Within 120 h, hectorite particles were formed. Time-resolved laser fluorescence spectroscopy was used to identify Cm(III) species during various synthesis steps and to characterize the structural incorporation mechanism. The formation of a Cm-containing Mg hydroxide precursor and the reaction with aqueous silica in a pH range of 9-10 to form TOT layers were identified to be key steps for trivalent actinide incorporation in hectorite via coprecipitation.  相似文献   

Tree Species Composition in European Pristine Forests: Comparison of Stand Data to Model Predictions   总被引：1，自引：0，他引：1  

Franz-W. Badeck  Heike Lischke  Harald Bugmann  Thomas Hickler  Karl Hönninger  Petra Lasch  Manfred J. Lexer  Florent Mouillot  Jörg Schaber  Benjamin Smith 《Climatic change》2001,51(3-4):307-347

The degree of general applicability across Europe currently achieved with several forest succession models is assessed, data needs and steps for further model development are identified and the role physiology based models can play in this process is evaluated. To this end, six forest succession models (DISCFORM, ForClim, FORSKA-M, GUESS, PICUS v1.2, SIERRA) are applied to simulate stand structure and species composition at 5 European pristine forest sites in different climatic regions. The models are initialized with site-specific soil information and driven with climate data from nearby weather stations. Predicted species composition and stand structure are compared to inventory data. Similarity and dissimilarity in the model results under current climatic conditions as well as the predicted responses to six climate change scenarios are discussed. All models produce good results in the prediction of the right tree functional types. In about half the cases, the dominating species are predicted correctly under the current climate. Where deviations occur, they often represent a shift of the species spectrum towards more drought tolerant species. Results for climate change scenarios indicate temperature driven changes in the alpine elevational vegetation belts at humid sites and a high sensitivity of forest composition and biomass of boreal and temperate deciduous forests to changes in precipitation as mediated by summer drought. Restricted generality of the models is found insofar as models originally developed for alpine conditions clearly perform better at alpine sites than at boreal sites, and vice versa. We conclude that both the models and the input data need to be improved before the models can be used for a robust evaluation of forest dynamics under climate change scenarios across Europe. Recommendations for model improvements, further model testing and the use of physiology based succession models are made.  相似文献   

Effect of N content and soil texture on the decomposition of organic matter in forest soils as revealed by solid-state CPMAS NMR spectroscopy     

Marie-France Dignac  Heike Knicker  Ingrid Kgel-Knabner 《Organic Geochemistry》2002,33(12):157

N has a controlling effect on litter biodegradation in the forest floor, while stabilization of organic matter in the mineral soil may be influenced by physical parameters related to soil texture. In this study, in order to understand the processes involved in soil organic matter (SOM) formation, the chemical composition of SOM was followed and evaluated with regards to N contents and soil texture. Samples were taken on sites covered with Norway spruce and displaying contrasting values of C/N ratios in the forest floor. The chemical structure of OM was characterized using solid-state CPMAS ¹³C and ¹⁵N nuclear magnetic resonance (NMR) spectroscopy, along with Proton Spin Relaxation Editing (PSRE) sequences. Four groups of sampling sites were defined based on the NMR spectra of Oh and A horizons. In each group displaying similar NMR characteristics, N content and soil texture could be highly different among sites. Some Oh horizons with similar NMR spectra had very different N contents. Highly humified OM in Oh horizons were observed mainly on sites with low N contents. Some A horizons with different soil texture displayed similar OM chemical structure. High contents of O-alkyl C in some A horizons could originate from higher fresh root material input.  相似文献   

Concentration variations of anthropogenic and biogenic organic substances in the German Bight due to changing meteorological conditions     

Dr. Heinrich Hühnerfuss  Heike Dannhauer  Jörn Faller  Peter Ludwig 《Ocean Dynamics》1990,43(5):253-272

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Lithostratigraphy of the Kalahari Group in northeastern Namibia     

Heike Wanke  Ansgar Wanke   《Journal of African Earth Sciences》2007,48(5):314-328

The Kalahari Group in northeastern Namibia consists of terrestrial sediments deposited in a tectonically active basin that was formed by flexural uplift of the African continental margin and independent structures related to rifting. The thickness of the sequence varies from a few meters to around 400 m. Greatest thicknesses occur where the NW–SE trending Kalahari basin axis conjugates with NE–SW trending grabens.Repeated phases of flooding and desiccation dominate the depositional environments of the Kalahari Group in northeastern Namibia. Associations of lithofacies allow recognition of distinct depositional settings such as proximal debris flows, braided streams and sand fans, and pans and sandflats.The northeastern Namibian Kalahari Group rests unconformable on the pre-Kalahari surface which showed a relatively pronounced relief in the Epukiro area. The succession starts with conglomerates, breccias and pebbly sandstones, followed by carbonates, sandstones of various maturities, and silcretes. Ferruginous sandstones and ferricretes occur locally. The onset of Kalahari Group deposition was likely a basin-wide event and therefore the basal lithostratigraphic units can be correlated with confidence. Conversely, the correlation of the succeeding lithostratigraphic units remains fairly speculative.  相似文献   

UV‐Irradiation of the Antibiotic Sulfathiazole Surprisingly Leads to Former Antituberculotic Promizole          下载免费PDF全文

Astrid Spielmeyer  Myriam Heer  Siegrun A.I. Mohring  Heike Hausmann  Jessica Stahl  Manfred Kietzmann  Sebastian Dold  Bernhard Spengler  Gerd Hamscher 《洁净——土壤、空气、水》2015,43(4):490-495

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Regionale Meeresschutzkooperation und die EU-Gratwanderung der Helsinki-Kommission imOsterweiterungsprozess der EU     

Imhoff  Heike 《Ocean Dynamics》1999,51(10):109-115

Ocean Dynamics - Der Vortrag bezweckt, die Rolle der regionalen Meeresschutzkooperationen im Gefüge der internationalen Zusammenarbeit zu beschreiben; es soll nachgewiesen werden, dass die...  相似文献   

The 1995–2002 Long-Term Monitoring of Comet C/1995 O1 (HALE–BOPP) at Radio Wavelength     

Biver  Nicolas  Bockelée-Morvan  Dominique  Colom  Pierre  Crovisier  Jacques  Henry  Florence  Lellouch  Emmanuel  Winnberg  Anders  Johansson  Lars E.B.  Gunnarsson  Marcus  Rickman  Hans  Rantakyrö  Fredrik  Davies  John K.  Dent  William R.F.  Paubert  Gabriel  Moreno  Raphaël  Wink  Jörn  Despois  Didier  Benford  Dominic J.  Gardner  Matt  Lis  Dariusz C.  Mehringer  David  Phillips  Thomas G.  Rauer  Heike 《Earth, Moon, and Planets》2002,90(1-4):5-14

The bright comet Hale–Bopp provided the first opportunity to follow the outgassing rates of a number of molecular species over a large range of heliocentric distances. We present the results of our observing campaign at radio wavelengths which began in August 1995 and ended in January 2002. The observations were carried out with the telescopes of Nançay, IRAM, JCMT, CSO and, since September 1997, SEST. The lines of nine molecules (OH, CO, HCN, CH₃OH, H₂CO, H₂S, CS, CH₃CN and HNC) were monitored. CS, H₂S, H₂CO, CH₃CN were detected up to r_h= 3–4 AU from the Sun, while HCN and CH₃OH were detected up to 6 AU. CO, which is the main driver of cometary activity at heliocentric distances larger than 3–4 AU, was last detected in August 2001, at r_h= 14 AU. The gas production rates obtained from this programme contain important information on the nature of cometary ices, their thermal properties and sublimation mechanisms.Line shapes allow to measure gas expansion velocities, which, at large heliocentric distances, might be directly connected to the temperature of the nucleus surface. Inferred expansion velocity of the gas varied as r_h ^-0.4 within 7 AU from the Sun, but remained close to 0.4 km s^-1 further away. The CO spectra obtained at large r_hare strongly blueshifted and indicative of an important day-to-night asymmetry in outgassing and expansion velocity. The kinetic temperature of the coma, estimated from the relative intensities of the CH₃OH and CO lines, increased with decreasing r_h, from about 10 K at 7 AU to 110 K around perihelion.  相似文献   

Tracking and orbit determination performance of the GRAS instrument on MetOp-A   总被引：8，自引：3，他引：5  

Oliver Montenbruck  Yago Andres  Heike Bock  Tom van Helleputte  Jose van den Ijssel  Marc Loiselet  Christian Marquardt  Pierluigi Silvestrin  Pieter Visser  Yoke Yoon 《GPS Solutions》2008,12(4):289-299

The global navigation satellite system receiver for atmospheric sounding (GRAS) on MetOp-A is the first European GPS receiver providing dual-frequency navigation and occultation measurements from a spaceborne platform on a routine basis. The receiver is based on ESA’s AGGA-2 correlator chip, which implements a high-quality tracking scheme for semi-codeless P(Y) code tracking on the L1 and L2 frequency. Data collected with the zenith antenna on MetOp-A have been used to perform an in-flight characterization of the GRAS instrument with focus on the tracking and navigation performance. Besides an assessment of the receiver noise and systematic measurement errors, the study addresses the precise orbit determination accuracy achievable with the GRAS receiver. A consistency on the 5 cm level is demonstrated for reduced dynamics orbit solutions computed independently by four different agencies and software packages. With purely kinematic solutions, 10 cm accuracy is obtained. As a part of the analysis, an empirical antenna offset correction and preliminary phase center correction map are derived, which notably reduce the carrier phase residuals and improve the consistency of kinematic orbit determination results.

Oliver MontenbruckEmail:

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Cometary nuclear magnitudes from sky survey observations     

Michael Weiler  Heike Rauer  Christiaan Sterken 《Icarus》2011,212(1):351-366

The determination of the nuclear magnitudes of comets, and with it nuclear size frequency distributions, is strongly complicated by cometary activity. By now, only nuclear size frequency distributions for Jupiter Family comets are available, and they are still subject of uncertainties. For comets of other dynamical classes, nuclear magnitudes are known for only a few comets. The size frequency distributions are thus not well constrained.In this work we study whether nuclear magnitudes of comets can be constrained from sky survey observations as published by the Minor Planet Center. Observations from sky survey programs in which the comet was classified as a point-like source are analyzed in this respect.From the available published observations from 1998 to 2008, we derive nuclear magnitudes, as well as nuclear radii, for 84 comets. Among these are comets of the Jupiter Family, dynamically old and new isotropic comets, Halley-type comets and Centaurs. For Jupiter Family comets and for isotropic comets, the size frequency distributions are presented.Uncertainties of derived nuclear magnitudes arise from photometry and from potentially undetected activity. However, a comparison with objects with well known nuclear parameters shows that, despite substantial observational uncertainties, nuclear magnitudes are constrained to ±0.6 mag, thereby providing first indications for nuclear sizes. This is particularly relevant for isotropic comets with so far ill-constrained size distributions. Exponents of the differential size frequency distributions of for Jupiter Family comets and for isotropic comets are presented. The values derived here form a basis for future, dedicated observational studies which provide higher measurement accuracy.  相似文献