Variations in dissolved CO2 and CH4 in a first‐order stream and catchment: an investigation of soil–stream linkages

Spatial and seasonal variations in CO₂ and CH₄ concentrations in streamwater and adjacent soils were studied at three sites on Brocky Burn, a headwater stream draining a peatland catchment in upland Britain. Concentrations of both gases in the soil atmosphere were significantly higher in peat and riparian soils than in mineral soils. Peat and riparian soil CO₂ concentrations varied seasonally, showing a positive correlation with air and soil temperature. Streamwater CO₂ concentrations at the upper sampling site, which mostly drained deep peats, varied from 2·8 to 9·8 mg l^?1 (2·5 to 11·9 times atmospheric saturation) and decreased markedly downstream. Temperature‐related seasonal variations in peat and riparian soil CO₂ were reflected in the stream at the upper site, where 77% of biweekly variation was explained by an autoregressive model based on: (i) a negative log‐linear relationship with stream flow; (ii) a positive linear relationship with soil CO₂ concentrations in the shallow riparian wells; and (iii) a negative linear relationship with soil CO₂ concentrations in the shallow peat wells, with a significant 2‐week lag term. These relationships changed markedly downstream, with an apparent decrease in the soil–stream linkage and a switch to a positive relationship between stream flow and stream CO₂. Streamwater CH₄ concentrations also declined sharply downstream, but were much lower (<0·01 to 0·12 mg l^?1) than those of CO₂ and showed no seasonal variation, nor any relationship with soil atmospheric CH₄ concentrations. However, stream CH₄ was significantly correlated with stream flow at the upper site, which explained 57% of biweekly variations in dissolved concentrations. We conclude that stream CO₂ can be a useful integrative measure of whole catchment respiration, but only at sites where the soil–stream linkage is strong. Copyright © 2004 John Wiley & Sons, Ltd.     

Effect of soil interaction on the performance of liquid column dampers for seismic applications

The effects of soil–structure interaction (SSI) while designing the liquid column damper (LCD) for seismic vibration control of structures have been presented in this study. The formulation for the input–output relation of a flexible‐base structure with attached LCD has been presented. The superstructure has been modelled by a single‐degree‐of‐freedom (SDOF) system. The non‐linearity in the orifice damping of the LCD has been replaced by equivalent linear viscous damping by using equivalent linearization technique. The force–deformation relationships and damping characteristics of the foundation have been described by complex valued impedance functions. Through a numerical stochastic study in the frequency domain, the various aspects of SSI on the functioning of the LCD have been illustrated. A simpler approach for studying the LCD performance considering SSI, using an equivalent SDOF model for the soil–structure system available in literature by Wolf (Dynamic Soil–Structure Interaction. International Series in Civil Engineering and Engineering Mechanics. Prentice‐Hall: Englewood Cliffs, NJ, 1985) has also been presented. Copyright © 2005 John Wiley & Sons, Ltd.     

Amino‐acid geochronology and the British Pleistocene: secure stratigraphical framework or a case of circular reasoning?

Aminostratigraphy is central to the recently revised correlation of Quaternary deposits in the British Isles, providing a link between terrestrial deposits and marine Oxygen Isotope Stages. The central tenet of British aminostratigraphy, however, that shells from the same interglacial yield very similar ratios, so that the characteristic ratios from different interglacials are distinct, remains uncertain. The data available suggest that amino‐acid ratios from different interglacials do not fall into discrete groups, but overlap considerably. It is therefore not valid to assign individual shells to Oxygen Isotope Stages simply on the basis of their amino‐acid ratios, which means that filtering data to remove high or low values, on the assumption that they represent reworked shells, is unacceptable. The range of ‘characteristic ratios’ assigned to British warm stages may have been underestimated and the degree of separation between them overestimated. Amino‐acid ratios should be treated as sample data that are naturally variable. Copyright © 2002 John Wiley & Sons, Ltd.     

Stresses due to vertical subsurface loading for an inhomogeneous cross‐anisotropic half‐space

In this article, we present the solutions for the stresses induced by four different loads associated with an axially loaded pile in a continuously inhomogeneous cross‐anisotropic half‐space. The planes of cross‐anisotropy are parallel to the horizontal surface of the half‐space, and the Young's and shear moduli are assumed to vary exponentially with depth. The four loading types are: an embedded point load for an end‐bearing pile, uniform skin friction, linear variation of skin friction, and non‐linear parabolic variation of skin friction for a friction pile. The solutions for the stresses due to the pile load are expressed in terms of the Hankel integral and are obtained from the point load solutions of the same inhomogeneous cross‐anisotropic half‐space which were derived recently by the authors (Int. J. Rock Mech. Min. Sci. 2003; 40 (5):667–685). A numerical procedure is proposed to carry out the integral. For the special case of homogeneous isotropic and cross‐anisotropic half‐space, the stresses predicted by the numerical procedure agree well with the solutions of Geddes and Wang (Geotechnique 1966; 16 (3):231–255; Soils Found. 2003; 43 (5):41–52). An illustrative example is also given to investigate the effect of soil inhomogeneity, the type and degree of soil anisotropy, and the four different loading types on the vertical normal stress. The presented solutions are more realistic in simulating the actual stratum of loading problem in many areas of engineering practice. Copyright © 2004 John Wiley & Sons, Ltd.     

论网络生产力的结构层次

网络生产力是一个复杂的系统，它包括构成要素层次，渗透性因素层次与组合性因素层次而有别于一般生产力的新质。     

A hybrid Bayesian back‐propagation neural network approach to multivariate modelling

There is growing interest in the use of back‐propagation neural networks to model non‐linear multivariate problems in geotehnical engineering. To overcome the shortcomings of the conventional back‐propagation neural network, such as overfitting, where the neural network learns the spurious details and noise in the training examples, a hybrid back‐propagation algorithm has been developed. The method utilizes the genetic algorithms search technique and the Bayesian neural network methodology. The genetic algorithms enhance the stochastic search to locate the global minima for the neural network model. The Bayesian inference procedures essentially provide better generalization and a statistical approach to deal with data uncertainty in comparison with the conventional back‐propagation. The uncertainty of data can be indicated using error bars. Two examples are presented to demonstrate the convergence and generalization capabilities of this hybrid algorithm. Copyright © 2003 John Wiley & Sons, Ltd.     

Source signature and elastic waves in a half‐space under a momentary shear line impulse

The transient deformation of an elastic half‐space under a line‐concentrated impulsive vector shear load applied momentarily is disclosed in this paper. While in an earlier work, the author gave an analytical–numerical method for the solution to this transient boundary‐value problem, here, the resultant response of the half‐space is presented and interpreted. In particular, a probe is set up for the kinematics of the source signature and wave fronts, both explicitly revealed in the strained half‐space by the solution method. The source signature is the imprint of the spatiotemporal configuration of the excitation source in the resultant response. Fourteen wave fronts exist behind the precursor shear wave S: four concentric cylindrical, eight plane, and two relativistic cylindrical initiated at propagating centres that are located on the stationary boundaries of the solution domain. A snapshot of the stressed half‐space reveals that none of the 14 wave fronts fully extend laterally. Instead, each is enclosed within point bounds. These wave arresting points and the two propagating centres of the relativistic waves constitute the source signature. The obtained 14 wave fronts are further combined into 11 disparate wave fronts that are grouped into four categories: an axis of symmetry wave—so named here by reason of being a wave front that is contiguous to the axis of symmetry, three body waves, five surface waves and two inhibitor waves—so named here by reason that beyond them the material motion dies out. Of the three body waves, the first is an unloading shear wave, the second is a diffracted wave and the third is a reflected longitudinal two‐branch wave. Of the two inhibitor waves, the first is a two‐joint relativistic wave, while the second is a two‐branch wave. The wave system, however, is not the same for all the dependent variables; a wave front that appears in the behaviour of one dependent variable may not exist in the behaviour of another. It is evident from this work that Saint–Venant's principle for wave propagation problems cannot be formulated. Therefore, the above results are valid for the particular proposed model for the momentary line‐concentrated shear load. The formulation of the source signature, the wave system, and their role in the half‐space transient deformation are presented here. Copyright © 2003 John Wiley & Sons, Ltd.     

Palaeoecological evidence of changes in vegetation and climate during the Holocene in the pre‐Polar Urals,northeast European Russia

This study investigated Holocene tree‐line history and climatic change in the pre‐Polar Urals, northeast European Russia. A sediment core from Mezhgornoe Lake situated at the present‐day alpine tree‐line was studied for pollen, plant macrofossils, Cladocera and diatoms. A peat section from Vangyr Mire in the nearby mixed mountain taiga zone was analysed for pollen. The results suggest that the study area experienced a climatic optimum in the early Holocene and that summer temperatures were at least 2°C warmer than today. Tree birch immigrated to the Mezhgornoe Lake area at the onset of the Holocene. Mixed spruce forests followed at ca. 9500–9000 ¹⁴C yr BP. Climate was moist and the water level of Mezhgornoe Lake rose rapidly. The hypsithermal phase lasted until ca. 5500–4500 ¹⁴C yr BP, after which the mixed forest withdrew from the Mezhgornoe catchment as a result of the climate cooling. The gradual altitudinal downward shift of vegetation zones resulted in the present situation, with larch forming the tree‐line. Copyright © 2003 John Wiley & Sons, Ltd.     

Numerical solutions for flow in porous media

A numerical approach is proposed to model the flow in porous media using homogenization theory. The proposed concept involves the analyses of micro‐true flow at pore‐level and macro‐seepage flow at macro‐level. Macro‐seepage and microscopic characteristic flow equations are first derived from the Navier–Stokes equation at low Reynolds number through a two‐scale homogenization method. This homogenization method adopts an asymptotic expansion of velocity and pressure through the micro‐structures of porous media. A slightly compressible condition is introduced to express the characteristic flow through only characteristic velocity. This characteristic flow is then numerically solved using a penalty FEM scheme. Reduced integration technique is introduced for the volumetric term to avoid mesh locking. Finally, the numerical model is examined using two sets of permeability test data on clay and one set of permeability test data on sand. The numerical predictions agree well with the experimental data if constraint water film is considered for clay and two‐dimensional cross‐connection effect is included for sand. Copyright © 2003 John Wiley & Sons, Ltd.