Proximity effects on semiconducting mineral surfaces II:: Distance dependence of indirect interactions     

Kevin M. Rosso  Udo Becker 《Geochimica et cosmochimica acta》2003,67(5):941-953

In a previous study, we described proximity effects on surfaces of the semiconducting minerals galena and pyrite, whereby a chemical reaction at one surface site modifies the reactivity of a remote surface site several Ångstroms or even nanometers away (Becker et al., 2001). The modification of interest does not arise because of a direct “through space” interaction between the two sites, but rather an indirect interaction via the electronic structure of the substrate. Here we investigate the distance and direction dependence of proximity effects using quantum mechanical modeling. The direct and indirect interactions between co-adsorbed oxygen atoms and between adsorbed oxygen atoms and point defects on vacuum-terminated galena (100) surfaces were modeled. Density functional theory cluster and plane wave pseudopotential calculations were used to calculate the modifications to the adsorption energy as a function of separation. Energy-distance plots indicate that the proximity effect energy can become very strong at separations decreasing below about 5 to 6 Å, and persist at increasing separations up to 12 Å in a slowly decaying form. A strong attractive indirect interaction out-competes direct electrostatic repulsion for O-vacancy interactions. An oscillatory asymptotic behavior is found for co-adsorbed O-O indirect interactions, which indicates that the proximity effect energy can vary with surface crystallographic direction. It implies the presence of a strong organizing force on like adatoms that may explain the progressive oxidation of certain sulfide minerals by patchwork growth. These findings begin to pave the way for improved adsorption isotherms and extended surface complexation models that will include the specific influence of semiconductor-type proximity effects.  相似文献   

Beschreibung einer Methode zur Bestimmung von Dieldrin,p.p′-DDT und PCB's in Seewasser und Werte für die Deutsche Bucht, 1974     

Dr. Dieter Stadler  Udo Ziebarth 《Ocean Dynamics》1975,28(6):263-273

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Dating of Dissolved Iodine in Pore Waters from the Gas Hydrate Occurrence Offshore Shimokita Peninsula,Japan: 129I Results from the D/V Chikyu Shakedown Cruise     

Hitoshi Tomaru  Udo Fehn  Zunli Lu  Rika Takeuchi  Fumio Inagaki  Hiroyuki Imachi  Ryosuke Kotani  Ryo Matsumoto  Kan Aoike 《Resource Geology》2009,59(4):359-373

Iodine concentration and radioisotopic composition (¹²⁹I/I) were measured in the pore waters from the gas hydrate occurrence in the forearc basin offshore Shimokita Peninsula, north-eastern Japan, to determine the source formation of I and accompanying hydrocarbons. Iodine concentrations correlate well with the alkalinity and SO₄ patterns, reflecting degradation stages of I-rich buried organic matter, rapidly increasing in the sulfate reduction interval, and becoming constant below 250 meters below the seafloor with an upwelling flux of 1.5 × 10⁻¹¹ µmol cm⁻² year⁻¹. The ¹²⁹I/I ratios of 300 × 10⁻¹⁵–400 × 10⁻¹⁵ in deep pore waters suggest ages for iodine and hydrocarbon sources as old as 40 Ma. These ages correlate well with the coaly source formations of the Eocene age thought to be responsible for the conventional natural gas deposits underlying the gas hydrate stability zone. Similar profiles are observed in ¹²⁹I/I ratios of pore waters in the gas hydrate stability zone from the forearc basin in the eastern Nankai Trough, offshore central Japan, where pore waters are enriched in I and reach ages as old as ∼50 Ma through the sediment column. At the outer ridge site along the trough, on the other hand, relatively younger I are more frequently delivered probably through thrusts/faults associated with subduction. The nature of source formations of I and hydrocarbons in the offshore Shimokita Peninsula has a more terrestrial contribution compared with those in the Nankai Trough, but these formations are also considerably older than the host sediments, suggesting long-term transport of I and hydrocarbons for the accumulation of gas hydrates in both locations.  相似文献   

A new towed marine vector magnetometer: methods and results from a Central Pacific cruise   总被引：1，自引：0，他引：1  

Martin Engels  Udo Barckhausen  Jeffrey S. Gee 《Geophysical Journal International》2008,172(1):115-129

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Volatile Organic Compounds in Various Marine Organisms From the Southern North Sea     

Patrick Roose  Udo A. Th. Brinkman 《Marine pollution bulletin》2000,40(12):1167-1177

The concentration levels of 12 priority volatile organic compounds (VOCs) were determined in two species of vertebrates and four species of invertebrates from sampling stations in the southern North Sea, using a modified Tekmar LSC 2000 purge and trap system coupled to gas chromatograph–mass spectrometer (GC–MS). In general, concentration levels of VOCs found in this study were of the same order of magnitude as those previously reported in the literature. The concentrations of the chlorinated hydrocarbons (CHCs), with the exception of chloroform, tended to be lower than those of the monocyclic aromatic hydrocarbons (MAHs). The experimental data were statistically evaluated using both cluster analysis and principal component analysis (PCA). From the results of cluster analysis and PCA, no specific groups could be distinguished on the basis of geographical, temporal or biological parameters. However, based on the cluster analysis and the PCA, the VOCs could be divided into three groups, C₂-substituted benzenes, CHCs and benzene plus toluene. This division could be related to different types of sources. Finally, it was shown that organisms can be used to monitor the presence of VOCs in the marine environment and the observed concentrations levels were compared with proposed safety levels.  相似文献   

Backshore coarsening processes triggered by wave‐induced sand transport: the critical role of storm events     

Keiko Udo  Akira Mano 《地球表面变化过程与地形》2010,35(11):1269-1280

Spatial backshore processes were investigated through field observations of topography and median sand grain size at a sandy beach facing the Pacific Ocean in Japan. A comparison of the backshore profile and cross‐shore distribution of the median sand grain size in 1999 and 2004 revealed an unusual sedimentary process in which sand was coarsened in a depositional area in the 5‐year period, although sediment is generally coarsened in erosional areas. In support of these observations, monthly spatial field analyses carried out in 2004 demonstrated a remarkable backshore coarsening process triggered by sedimentation in the seaward part of the backshore during a storm event. In order to elucidate mechanisms involved in the backshore coarsening process, thresholds of movable sand grain size under wave and wind actions (a uniform parameter for both these cases) in the onshore and offshore directions were estimated using wave, tide, and wind data. The cross‐shore distributions of the estimated thresholds provided reasonable values and demonstrated a coarsening mechanism involving the intermediate zone around the shoreline under alternating wave and wind actions as a result of which coarse sand was transported toward the seaward part of the backshore by large waves during storms and then toward the landward part by strong onshore winds. The 5‐year backshore coarsening is most certainly explained by repetition of short‐term coarsening mechanisms caused by wave‐induced sand transport occurring from the nearshore to the intermediate zone. Copyright © 2010 John Wiley & Sons, Ltd  相似文献   

Vegetation-based bioindication of humus forms in coniferous mountain forests     

Kerstin Anschlag  Dylan Tatti  Niels Hellwig  Giacomo Sartori  Jean-Michel Gobat  Gabriele Broll 《山地科学学报》2017,14(4):662-673

Humus forms, especially the occurrence and the thickness of the horizon of humified residues(OH), provide valuable information on site conditions.In mountain forest soils, humus forms show a high spatial variability and data on their spatial patterns is often scarce. Our aim was to test the applicability of various vegetation features as proxy for OH thickness.Subalpine coniferous forests dominated by Picea abies(L.) H. Karst. and Larix decidua Mill. were studied in the Province of Trento, Italian Alps,between ca. 900 and 2200 m a.s.l. Braun-Blanquet vegetation relevés and OH thickness were recorded at152 plots. The vegetation parameters, tested for their suitability as indicators of OH thickness,encompassed mean Landolt indicator values of the herb layer(both unweighted and cover-weighted means) as well as parameters of vegetation structure(cover values of plant species groups) calculated from the relevés. To our knowledge, the predictive power of Landolt indicator values(LIVs) for humus forms had not been tested before. Correlations between OH thickness and mean LIVs were strongest for the soil reaction value, but indicator values for humus,nutrients, temperature and light were also significantly correlated with OH thickness. Generally,weighting with species cover reduced the indicator quality of mean LIVs for OH thickness. The strongest relationships between OH thickness and vegetation structure existed in the following indicators: the cover of forbs(excluding graminoids and ferns) and the cover of Ericaceae in the herb layer. Regression models predicting OH thickness based on vegetation structure had almost as much predictive power as models based on LIVs. We conclude that LIVs analysis can produce fairly reliable information regarding the thickness of the OH horizon and, thus,the humus form. If no relevé data are readily available,a field estimation of the cover values of certain easily distinguishable herb layer species groups is much faster than a vegetation survey with consecutive indicator value analysis, and might be a feasible way of quickly indicating the humus form.  相似文献