Artificial Neural Networks: A Solution to the Ambiguity in Prediction of Engineering Properties of Fine-Grained Soils

Determination of soaked california bearing ratio (CBR) and compaction characteristics of soils in the laboratory require considerable time and effort. To make a preliminary assessment of the suitability of soils required for a project, prediction models for these engineering properties on the basis of laboratory tests—which are quick to perform, less time consuming and cheap—such as the tests for index properties of soils, are preferable. Nevertheless researchers hold divergent views regarding the most influential parameters to be taken into account for prediction of soaked CBR and compaction characteristics of fine-grained soils. This could be due to the complex behaviour of soils—which, by their very nature, exhibit extreme variability. However this disagreement is a matter of concern as it affects the dependability of prediction models. This study therefore analyses the ability of artificial neural networks and multiple regression to handle different influential parameters simultaneously so as to make accurate predictions on soaked CBR and compaction characteristics of fine-grained soils. The results of simple regression analyses included in this study indicate that optimum moisture content (OMC) and maximum dry density (MDD) of fine-grained soils bear better correlation with soaked CBR of fine-grained soils than plastic limit and liquid limit. Simple regression analyses also indicate that plastic limit has stronger correlation with compaction characteristics of fine-grained soils than liquid limit. On the basis of these correlations obtained using simple regression analyses, neural network prediction models and multiple regression prediction models—with varying number of input parameters are developed. The results reveal that neural network models have more ability to utilize relatively less influential parameters than multiple regression models. The study establishes that in the case of neural network models, the relatively less powerful parameters—liquid limit and plastic limit can also be used effectively along with MDD and OMC for better prediction of soaked CBR of fine-grained soils. Also with the inclusion of less significant parameter—liquid limit along with plastic limit the predictions on compaction characteristics of fine-grained soils using neural network analysis improves considerably. Thus in the case of neural network analysis, the use of relatively less influential input parameters along with stronger parameters is definitely beneficial, unlike conventional statistical methods—for which, the consequence of this approach is unpredictable—giving sometimes not so favourable results. Very weak input parameters alone need to be avoided for neural network analysis. Consequently, when there is ambiguity regarding the most influential input parameters, neural network analysis is quite useful as all such influential parameters can be taken to consideration simultaneously, which will only improve the performance of neural network models. As soils by their very nature, exhibit extreme complexity, it is necessary to include maximum number of influential parameters—as can be determined easily using simple laboratory tests—in the prediction models for soil properties, so as to improve the reliability of these models—for which, use of neural networks is more desirable.     

Dust motions in quasi-statically charged binary asteroid systems

In this paper, we discuss dust motion and investigate possible mass transfer of charged particles in a binary asteroid system, in which the asteroids are electrically charged due to solar radiation. The surface potential of the asteroids is assumed to be a piecewise function, with positive potential on the sunlit half and negative potential on the shadow half. We derive the nonautonomous equations of motion for charged particles and an analytic representation for their lofting conditions. Particle trajectories and temporary relative equilibria are examined in relation to their moving forbidden regions, a concept we define and discuss. Finally, we use a Monte Carlo simulation for a case study on mass transfer and loss rates between the asteroids.     

Mobilisation and transport of dissolved organic carbon and iron in peat catchments—Insights from the Lehstenbach stream in Germany using generalised additive models

During the last decades, increasing exports of both dissolved organic carbon (DOC) and iron were observed from peat catchments in North America and Europe with potential consequences for water quality of streamwater and carbon storages of soils. As mobilisation and transport processes of DOC and iron in peat catchments are only partly understood, the purpose of this study was to elucidate these processes in an intensively monitored and studied system. Specifically, it was hypothesised that dissimilatory iron reduction in riparian peatland soils mobilises DOC initially adsorbed to iron minerals. During stormflow conditions, both DOC and iron will be transported into the stream network. Ferrous iron may be reoxidised at redox interfaces on its way to the stream, and subsequently, ferric iron could be transported together with DOC as complexes. To test these hypotheses, generalised additive models (GAMs) were applied to 14 years of weekly time series of discharge and concentrations of selected solutes measured in a German headwater stream called Lehstenbach. This stream drains a 4.19‐km² forested mountain catchment; one third of which is covered by riparian peatland soils. We interpreted results of different types of GAM in the way that (a) iron reduction drove the mobilisation of DOC from peatland soils and that (b) both iron and DOC were transported as complexes after their joint mobilisation to and within the steam. It was speculated that low nitrate availability in the uppermost wetland soil layer, particularly during the growing season, promoted iron reduction and thus the mobilisation of DOC. However, the influence of nitrate on the DOC mobilisation remains relatively uncertain. This influence could be further investigated using methods similar to the GAM analysis conducted here for other catchments with long‐term data as well as detailed measurements of the relevant species in riparian wetland soils and the adjacent stream network.     

Radio and Meteor Science Outcomes From Comparisons of Meteor Radar Observations at AMISR Poker Flat, Sondrestrom, and Arecibo

Radio science and meteor physics issues regarding meteor “head-echo” observations with high power, large aperture (HPLA) radars, include the frequency and latitude dependency of the observed meteor altitude, speed, and deceleration distributions. We address these issues via the first ever use and analysis of meteor observations from the Poker Flat AMISR (PFISR: 449.3 MHz), Sondrestrom (SRF: 1,290 MHz), and Arecibo (AO: 430 MHz) radars. The PFISR and SRF radars are located near the Arctic Circle while AO is in the tropics. The meteors observed at each radar were detected and analyzed using the same automated FFT periodic micrometeor searching algorithm. Meteor parameters (event altitude, velocity, and deceleration distributions) from all three facilities are compared revealing a clearly defined altitude “ceiling effect” in the 1,290 MHz results relative to the 430/449.3 MHz results. This effect is even more striking in that the Arecibo and PFISR distributions are similar even though the two radars are over 2,000 times different in sensitivity and at very different latitudes, thus providing the first statistical evidence that HPLA meteor radar observations are dominated by the incident wavelength, regardless of the other radar parameters. We also offer insights into the meteoroid fragmentation and “terminal” process.     

On the IAU 2000/2006 precession–nutation and comparison with other models and VLBI observations

In this paper, we discuss the fundamental aspects of the semi-analytical precession–nutation models that were adopted by IAU Resolutions in 2000 and 2006. We show that no significant discrepancies appear between those models (Mathews et al., J Geophys Res 107:B4, ETG 3-1–3-26, 2002, Capitaine et al., Astron Astrophys 412:567– 586, 2003) and other semi-analytical solutions or the INPOP06 numerical integration (Fienga et al., Astron Astrophys 477:315–327, 2008), especially for the quadratic terms. We also report on the most recent comparisons of the models with VLBI observations. We have employed different empirical models to fit the residuals, in attempting to characterize the nature of the observed curvature. The efficiencies of those empirical models are compared and their interpretations in terms of physical mechanisms are discussed. We show that a combination of linear and 18.6-year corrections is the most credible model for explaining the currently observed residuals, but that a longer span of observations is required before the true character of the effect can be determined. We note that the predictions from the ERA-2005 theory (Krasinsky, Celest Mech Dyn Astron 96:169–217, 2006) have diverged from recent VLBI results and suggest that the empirical nature of the ERA model is responsible.     

Three-dimensional carbon dioxide-induced strain distribution within a confined bituminous coal

Sequestration of carbon dioxide in unmineable coal seams is an option to reduce carbon dioxide emissions. It is well known that the interaction of carbon dioxide with unconfined coal induces swelling. This paper contributes three-dimensional strain distribution in confined coal at microstructural level using high-resolution X-ray computerized tomography data and image analysis. Swelling and compression/compaction of regions in the coal matrix occurs with CO₂ uptake. Normal strain varies between ? 1.15% and 0.93%, ? 3.11% and 0.94%, ? 0.43% and 0.30% along x, y and z axes respectively. Volumetric strain varies between ? 4.25% and 1.25%. The positive strains reported are consistent with typical range for unconstrained swelling. However, the average volumetric strains value (? 0.34%) reflect overall volume reduction. Overall swelling is apparently influenced by the confining stresses. The magnitudes of normal strains are heterogeneous and anisotropic. The swelling vs. compression/compaction observed after CO₂ uptake is localized and likely lithotype dependant.     

Relation between n-alkane distributions and effective coalification temperatures in some Permian shales

In Permian shales of the Sydney Basin, Australia, n-alkane distributions have been compared with effective coalification temperatures (ECTs) estimated from vitrinite reflectivities. The upper, non-marine part of the section shows evidence of progressive cracking (shift of n-alkane maximum toward shorter chains and tendency to eliminate longer chains) as depth and ECT increase; but this trend is not maintained in the underlying marine section.All samples show lack of a maximum in the longer-chain n-alkane distribution. Possible reasons discussed are (i) a cracking rate of long chains greater than their formation rate; (ii) a need for higher temperatures than the rock has so far undergone to produce a new crop of long chains; or (iii) exhaustion of the straight-chain generating potential of the kerogen. Pyrolysis experiments may be effective in testing these possibilities.The linking of ECTs to alteration stages of sediment hydrocarbons opens the possibility of comparing these stages among formations which differ in age and organic and inorganic composition, and among basins of diverse geological history.     

Stalagmites from caves in the Bahamas: Indicators of low sea level stand

Presently submerged Bahaman stalagmites can be used to date Pleistocene low sea level stands. Good precision was obtained using both ¹⁴C and ²³⁰Th-/²³⁴U-methods. The respective dates obtained were 21,900 ± 600 and 22,000 ± 350 YBP.     

Trace metal geochemistry of peat under a sanitary landfill-a reconnaissance

Core samples were taken at two sites from a peat deposit buried by a sanitary landfill operated by the city of Vancouver since the 1960s and from a third site where the same peat bed is not covered by landfill. Twenty-nine subsamples from the three cores were analyzed by a variety of techniques to determine the concentration of as many as 34 constituents. The content of heavy metals, the principal object of this investigation, is highest in the lower part of the peat succession, in which there is a significant amount of interbedded inorganic sediment, rather than in the upper clean bog peat. Individual layers as little as 2.5 cm thick can hold concentrations of heavy metals ten times that of the nearby layers. The heavy metal contents show a high positive correlation with those of iron and manganese and a very low correlation with sulfur. Iron from the landfill has been transported by downward percolating groundwater in solution or colloidal suspension into the lower layers of peat deposit where the passing heavy metals were sorbed. A comparison of the amounts of heavy metals stored in the peat alone with the amount leaving the whole landfill annually suggests that some metals, notably lead and arsenic, might be retained in the peat for very long periods, whereas other metals such as zinc and mercury might be quickly lost.     

Effect of refraction of sound on bistatic doppler sodar measurements of wind profiles

Comparisons of wind profiles measured with bistatic Doppler sodars below 100 m with in-situ measurements have shown that these sodars underestimate the winds. The possibility of refracted sound contaminating the scattered signals has been investigated both experimentally and theoretically. It was found that it is unlikely that refraction of the initial sound burst is the cause of the underestimation of winds at low levels.