Effect of depositional method on the undrained behavior and microstructure of sand with silt     

Jerry A. Yamamuro  Fletcher M. Wood 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):751

It has been known for many years that depositional method plays an important part in the results of laboratory testing of clean sands. In this paper, undrained triaxial compression tests were performed on specimens composed of Nevada sand with 20% non-plastic silt content using a variety of depositional methods that include slurry deposition, water sedimentation, air pluviation, mixed dry deposition, and dry funnel deposition. It was found that there was a marked difference in the undrained behavior even though the density and stress conditions were identical. The conclusion was that the soil fabric was responsible for this result. Using the scanning electron microscope, a method was developed to examine and quantify the microstructure of silty sand. These results appear to indicate that there are internal particle structures in sand with silt and their relative quantities correlate with the observed macroscopic undrained behavior.  相似文献   

Planetary sciences: Imke de Pater and Jack J. Lissauer, Cambridge University Press, 2001, 528 pp., GBP 50 (ISBN 0-521-48219-4)     

B.P. Glass 《Geochimica et cosmochimica acta》2003,67(2):323-324

  相似文献   

Riverine quality at the Anthropocene: Propositions for global space and time analysis,illustrated by the Seine River   总被引：4，自引：0，他引：4  

Michel Meybeck 《Aquatic Sciences - Research Across Boundaries》2002,64(4):376-393

The control of riverine quality (water, particulates) by human-related pressures is now a major feature of the Anthropocene era. A set of general typologies and approaches to address the complex relationships between pressures, environmental impacts and some of the related social responses is proposed here on the basis of various examples, among others the Seine basin. Riverine quality management is described through a dozen major types illustrated by river fluxes and riverine quality trends (>> 10 years). A successful restoration cycle, still seldom documented, is used as an example of the decomposition of the multiple social, societal and hydrological inertia and time lags, generally spanning several decades. Human impacts can also be described by finer temporal analysis, over hourly to year-on-year scales, and spatial analysis including classical longitudinal profiles, stream-order ranking and sediment pathways. The Seine river example illustrates the pressures from intensive agriculture, industrialisation, hydrological regulation and urbanisation with the impact of the World's second largest treated urban sewer discharge (from 8 million people in greater Paris). The impacts of the Paris megalopolis are much more widely spread than might be expected and include retro-impacts (in upstream reaches), distal (> 100 km) and external impacts (outside of watershed). They are illustrated by specific spatial distributions of indicators of each particular phenomenon (organic pollution, metal contamination, xenobiotic occurrence, nitrate pollution, eutrophication). Although not comprehensive (acidification and salinization are not addressed here), such typologies should facilitate the comparisons between basins and phenomena at the regional and global scales.  相似文献   

Application of the sine-Poisson equation in solar magnetostatics     

G. M. Webb  G. P. Zank 《Solar physics》1990,127(2):229-252

Solutions of the sine-Poisson equation are used to construct a class of isothermal magnetostatic atmospheres, with one ignorable coordinate corresponding to a uniform gravitational field in a plane geometry. The distributed current in the model j is directed along the x-axis, where x is the horizontal ignorable coordinate. The current j varies as the sine of the magnetostatic potential and falls off exponentially with distance vertical to the base with an e-folding distance equal to the gravitational scale height. We investigate in detail solutions for the magnetostatic potential A corresponding to the one-soliton, two soliton, and breather solutions of the sine-Gordon equation. Depending on the values of the free parameters in the soliton solutions, horizontally, periodic magnetostatic structures are obtained possessing either (a) a single X-type neutral point, (b) multiple neutral X-points, or (c) solutions without X-points. The solution cases (b) and (c) contain two families of intersecting current sheets, in which the line of intersection forms flux concentration points (or singularities) for the magnetic field. The solutions illustrate the contribution of the anisotropic J × B force (B, magnetic field induction), the gravitational force, and the gas pressure gradient to the force balance.  相似文献   

Linear free energy relationships for metal-ligand complexation: Monodentate binding to negatively-charged oxygen donor atoms     

Richard F. Carbonaro  Dominic M. Di Toro 《Geochimica et cosmochimica acta》2007,71(16):3958-3968

The analysis presented below suggests that the following equation models monodentate binding to negatively-charged oxygen donor atoms with no distinction between phenolic, carboxylic or inorganic hydroxide functional groups: log K_ML = α_O log K_HL + β_O; where K_ML is the metal-ligand formation constant, K_HL is the corresponding proton-ligand formation constant, and α_O and β_O are termed the Irving-Rossotti slope and intercept, respectively. Linear free energy relationships (LFERs) of this type are presented for 24 different metal ions complexing to negatively-charged oxygen donor atoms. Ligands selected for use in LFERs meet the following criteria: (i) they contain negatively-charged oxygen donor atoms (e.g., carboxylic acids and phenols), (ii) they are capable of only monodentate binding to metal ions, (iii) steric hindrances are not expected to influence the extent of metal-ligand binding, and (iv) the negatively-charged oxygen donor atom is the only functional group that imparts charge. The intercept of all LFERs was nearly zero for all metal ions investigated (β_O ≈ 0). The magnitude of α_O indicates the relative preference of metal binding to negatively-charged oxygen donor atoms and to the proton. Values of α_O can be used in QSARs (quantitative structure activity relationships) to estimate metal-NOM (natural organic matter) binding constants employed in the Windermere Humic Aqueous Model (WHAM) version V.  相似文献   

1.3 Billion years of acritarch history: An empirical morphospace approach     

《Precambrian Research》2006,144(1-2):52-68

Acritarchs are a group of organic-walled vesicular microfossils interpreted as protists, and are among the first eukaryotes preserved in the fossil record. Taxonomic inconsistencies amongst acritarch workers have made it difficult to address the evolutionary history of this group through more traditional methods (i.e., biodiversity through species counts). We have constructed an empirical morphospace to examine the first 1.3 billion years of acritarch evolution. We show that protist morphologic evolution is broadly correlated with major environmental and biologic revolutions in Earth history such as late Neoproterozoic global glaciations, the first appearance of the Ediacaran metazoans and the Cambrian explosion. Our results also show that protist morphologic expansion precedes their taxonomic diversification; this pattern, similar to that seen in Phanerozoic animal clades, suggests that early morphospace saturation and convergence are common occurrences in eukaryote macroevolution. In addition, our data do not support a monotonic increase in maximum diameter of acritarch vesicles through the Proterozoic; instead, maximum vesicle diameter appears to fluctuate in the Proterozoic before decreasing significantly in the early Cambrian.  相似文献   

Non-hydrostatic modeling of surf zone wave dynamics     

《Coastal Engineering》2014

Non-hydrostatic models such as Surface WAves till SHore (SWASH) resolve many of the relevant physics in coastal wave propagation such as dispersion, shoaling, refraction, dissipation and nonlinearity. However, for efficiency, they assume a single-valued surface and therefore do not resolve some aspects of breaking waves such as wave overturning, turbulence generation, and air entrainment. To study the ability of such models to represent nonlinear wave dynamics and statistics in a dissipative surf zone, we compare simulations with SWASH to flume observations of random, unidirectional waves, incident on a 1:30 planar beach. The experimental data includes a wide variation in the incident wave fields, so that model performance can be studied over a large range of wave conditions. Our results show that, without specific calibration, the model accurately predicts second-order bulk parameters such as wave height and period, the details of the spectral evolution, and higher-order statistics, such as skewness and asymmetry of the waves. Monte Carlo simulations show that the model can capture the principal features of the wave probability density function in the surf zone, and that the spectral distribution of dissipation in SWASH is proportional to the frequency squared, which is consistent with observations reported by earlier studies. These results show that relatively efficient non-hydrostatic models such as SWASH can be successfully used to parametrize surf zone wave processes.  相似文献   

Calibration and evaluation of a carbonate microsensor for studies of the marine inorganic carbon system     

Chenhua Han  Wei-Jun Cai  Yongchen Wang  Ying Ye 《Journal of Oceanography》2014,70(5):425-433

Accurate and rapid determination of inorganic carbon constituents in ocean environments is important for understanding the carbon cycle, especially in the context of ocean-acidification research. A microsensor capable of directly measuring carbonate ion (CO₃ ^2–) concentrations would be desirable. In this study, a carbonate microsensor with a polymeric liquid membrane was fabricated, and two calibration methods were used to evaluate its performance. The first method was based on continuous titration. Small increments of HCl were added to seawater or Na₂CO₃ solution to adjust the total alkalinity and pH values and thus obtain a series of carbonate concentrations. The second method used a series of discrete standards. Varying amounts of HCl or NaOH were added to separate seawater aliquots, and the CO₃ ^2– concentration of each standard was calculated from the resulting total alkalinity and total dissolved inorganic carbon. Both methods were found to be adequate for achieving accurate calibration of the CO₃ ^2– sensor, and both are suitable for field work. The discrete standards method, however, is more convenient and may provide a better linear range at low CO₃ ^2– concentrations (detection range: 2–300 μmol/kg) than the continuous titration method in seawater (detection range: 10–250 μmol/kg). This CO₃ ^2– microsensor can be used for 5–7 d and detects changes in carbonate concentration as low as 2 μmol/kg in the inorganic carbon constituents of the environments where marine calcareous organisms grow. The CO₃ ^2– microelectrode was further assessed by applying it to the measurement of pore-water CO₃ ^2– concentration profiles in a marine sediment core.  相似文献   

Surface currents and winds at the Delaware Bay mouth   总被引：1，自引：0，他引：1  

P.A. Muscarella  N.P. BartonB.L. Lipphardt Jr.  D.E. VeronK.C. Wong  A.D. Kirwan Jr. 《Continental Shelf Research》2011,31(12):1282-1293

Knowledge of the circulation of estuaries and adjacent shelf waters has relied on hydrographic measurements, moorings, and local wind observations usually removed from the region of interest. Although these observations are certainly sufficient to identify major characteristics, they lack both spatial resolution and temporal coverage. High-resolution synoptic observations are required to identify important coastal processes at smaller scales. Long observation periods are needed to properly sample low-frequency processes that may also be important. The introduction of high-frequency (HF) radar measurements and regional wind models for coastal studies is changing this situation. Here we analyze synoptic, high-resolution surface winds and currents in the Delaware Bay mouth over an 8-month period (October 2007 through May 2008). The surface currents were measured by two HF radars while the surface winds were extracted from a data-assimilating regional wind model. To illustrate the utility of these monitoring tools we focus on two 45-day periods which previously were shown to present contrasting pictures of the circulation. One, the low-outflow period is from 1 October through 14 November 2007; the other is the high-outflow period from 3 March through 16 April 2008. The large-scale characteristics noted by previous workers are clearly corroborated. Specifically the M2 tide dominates the surface currents, and the Delaware Bay outflow plume is clearly evident in the low frequency currents. Several new aspects of the surface circulation were also identified. These include a map of the spatial variability of the M2 tide (validating an earlier model study), persistent low-frequency cross-mouth flow, and a rapid response of the surface currents to a changing wind field. However, strong wind episodes did not persist long enough to set up a sustained Ekman response.  相似文献   

Linear Free Energy Relationships for Metal-Ligand Complexation: Bidentate Binding to Negatively-Charged Oxygen Donor Atoms     

Carbonaro RF  Atalay YB  Di Toro DM 《Geochimica et cosmochimica acta》2011,75(9):2499-10090

Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log K_ML = χ_OO(α_O log K_HL,1 + α_O log K_HL,2) where K_ML is the metal-ligand stability constant for a 1:1 complex, K_HL,1 and K_HL,2 are the proton-ligand stability constants (the ligand pK_a values), and α_O is the Irving-Rossotti slope. The parameter χ_OO is metal specific and has slightly different values for five and six membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log K_ML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, α-hydroxycarboxylic acids, and α-ketocarboxylic acids, a modification of the LFER where log K_HL,2 is set equal to zero is required. The chemical interpretation of χ_OO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu-NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log K_ML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log K_ML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems.  相似文献