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Load sensing (LS) is a dominant fluid power actuation technology in mobile machines, particularly in construction and agriculture. It has the advantage of guaranteeing good controllability in systems with multiple actuators while promoting higher energy efficiency. Several variants of LS systems have been proposed over the years, and research on cost-effective methods to further increase their efficiency is still of interest for original equipment manufacturers (OEMs) and the fluid power community. This article presents two solution, referred to as variable pump margin (VPM) and hybrid variable margin (HVM), suitable to improve the energy efficiency in pre-compensated LS systems such as those used in agricultural tractors. Both methods allow either downsizing the control valves or reducing the power consumption over the working range. Compared to a standard LS system, the VPM solution lowers the pump pressure using an electronic proportional pressure-reducing valve (ep-PRV), while the HVM solution uses a second ep-PRV in the compensator’s pilot line to further minimize the pressure differential across the LS valve. Simulation and experimental results show that, among the main working conditions, the VPM solution on average achieved 6.7% power saving over the standard LS system, while the model predicted an average improvement of 15.6% for the HVM solution. [ABSTRACT FROM AUTHOR]

External gear pumps are among the most popular fluid power positive displacement pumps, however they often suffer of excessive flow pulsation transmitted to the downstream circuit. To meet the increasing demand of quiet operation for modern fluid power system, a better understanding of the ripple source of gear pumps is desirable. This paper presents a novel approach for the analysis of the ripple source of gear pumps based on decomposition into a kinematic component and a pressurization component. The pump ripple can be regarded as the superposition of the displacement solution and the pressurization solution. The displacement solution is driven by the kinematic flow, and it can be derived from the kinematic flow theory; instead, the pressurization solution can be approximated by overlapping the pressurization flow for a single displacement chamber. Furthermore, in this way the changes of these two components with modification of the delivery circuit are determined in both analytical and numerical ways. The result of this analysis provides a good interpretation of the pulsation simulated by a detailed lumped-parameter simulation model, thus showing its validity. The result also indicates that the response of two ripple sources to the change of the loading in the downstream hydraulic circuit is very different. These findings reveal the limitation of the traditional experimental method for determining the pump ripple, that new experimental methods which are more physics-based can be potentially formulated based on this work. [ABSTRACT FROM AUTHOR]

In this paper, a novel approach for the simulation of cavitation and aeration in hydraulic systems using the lumped parameter method is presented. The presented approach called the Hybrid Rayleigh–Plesset Equation model is derived from the Rayleigh–Plesset Equation representative of bubble dynamics and overcomes several shortcomings present in existing lumped parameter based cavitation modeling approaches. Models based on static approximations do not consider the non-equilibrium effects of phase change on the system and incorrectly predict the system dynamics. On the other hand, the existing dynamic cavitation modeling strategies account for the non-equilibrium effects of phase change but express the evolution of phases through approximations of the Rayleigh–Plesset Equation (such as exclusion of nonlinear interactions in bubble dynamics), which often lead to physically unrealistic time-scales of bubble growth or dissolution. This paper presents a dynamic model for cavitation which is capable of predicting cavitation in hydraulic systems while preserving the nonlinear dynamics arising from the Rayleigh–Plesset Equation. The derived model determines the evolution of phases in terms of physically realizable parameters such as the bubble radius and the nuclei density, which can be estimated or determined experimentally. The paper demonstrates the effectiveness of the derived modeling approach with the help of numerical simulations of an External Gear Machine. Results from the simulations employing the proposed model are compared with an existing dynamic cavitation modeling approach and validated with experimental results over a range of dynamic parameters. [ABSTRACT FROM AUTHOR]

The author reflects on research efforts made by both the energy industry and academia to improve fluid power technology. It cites that topics of interest include reduction of oscillations and vibrations of fluid power machines, digital and switched fluid power systems, and new system configurations to reduce fuel consumption and increase productivity of fluid power machines.

Mechanical gearboxes have one of the highest failure rates of wind turbine components while being one of the most expensive parts to replace or service. They are easily fatigued and have a low power rating relative to their size and mass. In this article, hydraulic transmissions are proposed as an alternative to mechanical drive trains and their feasibility has been established, particularly for offshore wind turbine applications. Here, we provide an in-depth analysis regarding the techno-economic benefits of replacing the mechanical gearbox with a hydraulic transmission in an offshore system. Our analysis shows that hydraulic transmissions are particularly beneficial for offshore applications: (i) relocating 35.3% of the nacelle mass to the base, thus moving the center of gravity toward the ground level, (ii) diminishing operation and maintenance costs, and (iii) replacing now-redundant power electronics. These three benefits contribute to saving between 3.92 and 18.8% on the Levelized Cost of Electricity for average cost offshore wind turbines. • The failure-prone gearbox is replaced by a hydraulic pump and a ground-level motor. • The transfer of components to ground level leads to a 35% reduction of nacelle mass. • Ground-level components allow for easier access, lowering maintenance costs. • The transmission reduces the LCOE of an offshore wind turbine by 4–19%. [ABSTRACT FROM AUTHOR]

Mechanical gearboxes have one of the highest failure rates of wind turbine components while being one of the most expensive parts to replace or service. They are easily fatigued and have a low power rating relative to their size and mass. In this article, hydraulic transmissions are proposed as an alternative to mechanical drive trains and their feasibility has been established, particularly for offshore wind turbine applications. Here, we provide an in-depth analysis regarding the techno-economic benefits of replacing the mechanical gearbox with a hydraulic transmission in an offshore system. Our analysis shows that hydraulic transmissions are particularly beneficial for offshore applications: (i) relocating 35.3% of the nacelle mass to the base, thus moving the center of gravity toward the ground level, (ii) diminishing operation and maintenance costs, and (iii) replacing now-redundant power electronics. These three benefits contribute to saving between 3.92 and 18.8% on the Levelized Cost of Electricity for average cost offshore wind turbines. • The failure-prone gearbox is replaced by a hydraulic pump and a ground-level motor. • The transfer of components to ground level leads to a 35% reduction of nacelle mass. • Ground-level components allow for easier access, lowering maintenance costs. • The transmission reduces the LCOE of an offshore wind turbine by 4–19%. [ABSTRACT FROM AUTHOR]

• Developed is a two-layer model for non-isothermal film flow of power-law fluids on a porous incline. • An expression for the critical Reynolds number for long-wave instability is obtained. • A reduced dimensionality model is used to study the nonlinear effects. • Important correlation found between substrate filtration and thermocapillary instability. The stability of the steady uniform flow of a power–law fluid down an inclined porous layer heated from below is investigated by means of a two–layer model. Under the long-wave approximation, the flow model is deduced starting from the continuity and momentum equations in the fluid film, the continuity and the generalized Darcy's law in the porous layer, and the energy balances in both the film and the porous layer. The associated boundary conditions account for the surface tension and the Beavers-Joseph velocity slip at the film bottom. A linear stability analysis of both two–dimensional and one–dimensional, i.e. depth–integrated, formulations is performed to define the neutral stability conditions, separately analyzing the S- and H-mode contributions. The influence of all the dimensionless governing parameters on the stability is discussed. Finally, the numerical solution of the depth–integrated model allows for an investigation of the nonlinear growth of H-mode unstable perturbations up to the formation of permanent waves and a discussion of the role of the magnitude of thermocapillary effects on the wave shape. Present results, taken collectively, indicate that, similarly to the isothermal case, the presence of a porous medium strongly modifies the stability bounds even in non-isothermal conditions, suggesting its potentiality as a passive control for the themocapillary instability for both H- and S-modes. Moreover, it is found that the shear-thinning behaviour leads to flows which are less stable but also less susceptible to thermocapillary effects. [ABSTRACT FROM AUTHOR]

Highlights • A depth-averaged model with a power-law rheology is studied analytically. • Basic wave parameters and linearized response functions are derived. • The Full Dynamic Model is compared with Kinematic, Diffusion and Quasi-Steady Models. • The results indicate that the diffusive approximation is the most accurate one. • The analytical solutions may be used for testing numerical method performances. Abstract A depth-averaged model with a power-law rheology, usually adopted for debris flow of fine sediment-water mixtures, is analytically studied, considering the complete (Full Dynamic Model) and the simplified momentum equations, known as Kinematic, Diffusion, and Quasi-steady Models. Applying the Laplace transform to the linearized equations, the analytical first-order expressions of the upstream and downstream spatio-temporal channel response functions are derived for the full and the approximate models. Both shear-thinning and shear-thickening fluids have been considered in hypocritical and linearly stable conditions, to investigate the influence of the rheology on the wave propagation. The effect of the upstream and downstream boundary conditions is considered assuming a finite channel length. The analytic description of the various linearized approximations allows a multi-faceted comparison of the wave propagation. About the basic wave characteristics, in the entire investigated range of Froude numbers and for all the considered rheologies, the Kinematic and Diffusive models underestimate the primary wave celerity and the Quasi-steady model underestimates the wave round-trip time. However, the examination of the response function reveals that the approximate models may provide relatively accurate reproduction of the full dynamic response. Moreover, the analytical solutions in the Laplace variables permit a systematic analysis of some relevant shape factors of the response functions. Independently on the models and the rheology, the damping of the downstream response function is several orders of magnitude larger than that of the upstream one. The results of the shape factor analysis of the upstream response function indicate that the diffusive approximation is the most accurate one. The performed comparison among the wave characteristics of the different approximations provides indications on the applicability of the simplified models for predicting debris or mud flows. [ABSTRACT FROM AUTHOR]

Highlights • Bed-forms may appear on the bottom surface during fast geomorphic transients. • A two-phase gradually-varied flow model accounting for bottom curvature is proposed. • The prediction of antidune formation is investigated in the linear regime. • Unstable bed perturbations are found owing to the sediment dynamics description. • The bottom curvature correction is mandatory for proper antidune length selection. Abstract The paper explores the possibility of predicting the occurrence of antidunes in gradually-varied flows through non-equilibrium morphological models natively derived, under the long-wave approximation, for fast geomorphic transients. Starting from a recent two-phase gradually-varied flow model, an improved version, which partially accounts for the bottom curvature effects, is proposed and analyzed. The normal mode analysis carried out on the linearized gradually-varied flow model shows the existence of unstable conditions at moderate Froude numbers characterized by bed perturbations migrating in the upstream direction. However, a proper wavelength selection may be obtained only when the bottom curvature is accounted for. Direct numerical simulations in linear regime of the improved model indicate the existence of unstable dominant wavelengths, which comply with experimental evidences. Full non-linear simulations confirm the ability of the improved two-phase model in predicting the antidunes formation. [ABSTRACT FROM AUTHOR]

A two–sided model is proposed to investigate the stability problem of the steady uniform flow of a power–law fluid layer down an inclined porous layer. The governing equations for the clear fluid flow are coupled with the ones for the seepage in the porous layer, for which the generalized Darcy’s law is employed. A linear stability analysis of both two–dimensional and depth–integrated formulations is carried out in order to individuate the neutral stability conditions. The influence of the dimensionless governing parameters on the stability properties is deeply discussed. The nonlinear effects on the stability of the flow are finally investigated through the numerical solution of the depth–integrated model. [ABSTRACT FROM AUTHOR]

The paper investigates the applicability of Kinematic and Diffusive Wave models for mud-flows with a power-law shear-thinning rheology. In analogy with a well-known approach for turbulent clear-water flows, the study compares the steady flow depth profiles predicted by approximated models with those of the Full Dynamic Wave one. For all the models and assuming an infinitely wide channel, the analytical solution of the flow depth profiles, in terms of hypergeometric functions, is derived. The accuracy of the approximated models is assessed by computing the average, along the channel length, of the errors, for several values of the Froude and kinematic wave numbers. Assuming the threshold value of the error equal to 5%, the applicability conditions of the two approximations have been individuated for several values of the power-law exponent, showing a crucial role of the rheology. The comparison with the clear-water results indicates that applicability criteria for clear-water flows do not apply to shear-thinning fluids, potentially leading to an incorrect use of approximated models if the rheology is not properly accounted for. [ABSTRACT FROM AUTHOR]

Presents a corrected reprint of the article "Influence of Turbulence on Bed Load Sediment Transport’ ” by B. Mutlu Sumer, Lloyd H. C. Chua, N.-S. Cheng, and Jorgen Fedsoe," published in the January 2005, Volume 131 of the "Journal of Hydraulic Engineering".

• Electrification to increase off-highway vehicles efficiency. • Electro-hydraulic unit as a prime mover of off-highway vehicles. • Integrated hydraulic gear machine and permanent magnet synchronous electric machine. • Electric and hydraulic machines integration to increase compactness. • High rotational velocity operation to increase efficiency. In recent years, increasingly stringent emission regulations have spurred an electrification trend in off-highway vehicle technology. To address challenges such as the high cost of power electronics components, limited battery capacity, and the substantial modifications required for the vehicles, there is a pressing need to develop high-speed, cost-effective, compact, and efficient electro-hydraulic units capable of powering vehicle functions. In response to these demands, this paper introduces an innovative morphology for an electro-hydraulic unit and outlines the integration method for a crescent-type internal gear machine with a permanent magnet synchronous electric machine. The proposed morphology aims to minimize component count through a shaftless solution while incorporating a cooling system that utilizes the same working fluid as the hydraulic machine. The design approach utilizes a genetic algorithm optimization process to maximize overall energy efficiency and compactness. Insights gained from the optimization results shed light on the relationship between key design parameters and unit performance, enhancing the understanding of this electro-hydraulic unit. A prototype of the unit was manufactured and tested, demonstrating a volumetric efficiency ranging from 81 % to 97 % at a maximum rotational velocity of the pinion of 6000 rpm. These results validate both the morphology and the design approach, indicating the feasibility of designing compact electro-hydraulic units that leverage hydraulic machines with higher maximum rotational velocities than commercially available counterparts as a mean to enhance efficiency and compactness. [ABSTRACT FROM AUTHOR]

The adoption of the Diffusive Wave (DW) instead of the Full Dynamic (FD) model in the analysis of mud flood routing within the shallow-water framework may provide a significant reduction of the computational effort, and the knowledge of the conditions in which this approximation may be employed is therefore important. In this paper, the applicability of the DW approximation of a depth-integrated Herschel–Bulkley model is investigated through linear analysis. Assuming as the initial condition a steady hypocritical decelerated flow, induced by downstream backwater, the propagation characteristics of a small perturbation predicted by the DW and FD models are compared. The results show that the spatial variation on the initial profile may preclude the application of DW model with a prescribed accuracy. Whenever the method is applicable, the rising time of the mud flood must satisfy additional constraints, whose dependence on the flow depth, along with the Froude number and the rheological parameters, is deeply analyzed and discussed. [ABSTRACT FROM AUTHOR]

A common assumption in the analysis of swashplate type axial piston machines (APMs) is to consider the relative rotation between the piston and cylinder block almost equal to the shaft speed. While this effect has been observed experimentally and confirmed by simplified models, an in-depth study and confirmation of the causes has never been undertaken. To address this, the presented work performs a simulation study of the piston and slipper spin in APMs. For this purpose, this work first develops a strongly coupled simulation model considering the displacing action of the machine coupled - with asynchronous time stepping - with the detailed simulation of its lubricating interfaces. The proposed approach accounts for the dynamics of the floating bodies in these machines, the ball-socket friction which couples the dynamic of each piston and slipper, and the impact on the fluid-structure induced cavitation and mixed lubrication in their tribological interfaces. As a consequence, the mutual interaction between the slipper-swash plate interface and the piston-cylinder interface of the APM is taken into account. After validating this model on a reference commercial unit, the impacts of the operating parameters (such as instantaneous displacement, pressure and shaft speed) and of the ball socket friction on the behavior of the machine are explored. It can be observed from the simulation results that the relative piston rotary motion in the cylinder bore varies with the operating conditions and the swashplate angle is one of the most influential parameters. • A novel piston machine simulation tool that considers coupled physics across multiple lubricating interfaces. • Ball joint friction modeling and coupled piston and slipper dynamics. • Numerical analysis of piston spin at various operating conditions using the proposed fully coupled model. [ABSTRACT FROM AUTHOR]

The occurrence of roll-waves in mud-flows is investigated based on the formulation of the marginal stability threshold of a linearized onedimensional viscoplastic (shear-thinning) flow model. Since for this kind of non-Newtonian rheological models this threshold may occur in a hypocritical flow, the downstream boundary condition may have a nonnegligible effect on the spatial growth/decay of the perturbation. The paper presents the solution of the 1D linearized flow of a Herschel and Bulkley fluid in a channel of finite length, in the neighbourhood of a hypocritical base uniform flow. Both linearly stable and unstable conditions are considered. The analytical solution is found applying the Laplace transform method and obtaining the first-order analytical expressions of the upstream and downstream channel response functions in the time domain. The effects of both the yield stress and the rheological law exponent are discussed, recovering as particular cases both power-law and Bingham fluids. The theoretical achievements may be used to extend semi-empirical criteria commonly employed for predicting roll waves occurrence in clear water even to mud-flows. [ABSTRACT FROM AUTHOR]

In the present paper, an analytical expression of the Green's function of linearized Saint-Venant equations (LSVEs) for shallow water waves is provided and applied to analyse the propagation of a perturbation superposed to a uniform flow. Independently of the kinematic character of the base flow, i.e., subcritical or supercritical uniform flow, the effects of a non-uniform vertical velocity profile and a non-constant resistance coefficient are accounted for. The use of the Darcy-Weisbach friction law allows a unified treatment of both laminar and turbulent conditions. The influence on the wave evolution of the wall roughness and the fluid viscosity are finally discussed, showing that in turbulent regime the assumption of constant friction coefficient may lead to an underestimation of both amplification and damping factors on the wave fronts, especially at low Reynolds numbers. This conclusion has to be accounted for, particularly in describing hyper-concentrated suspensions or other kinds of Newtonian mixtures, for which the high values of the kinematic viscosity may lead to relatively low Reynolds numbers. [ABSTRACT FROM AUTHOR]

Abstract: Soils are characterized by an intrinsic variability through time and space at different scales of observation and are often affected by morphodynamic processes strictly interacting with pedogenesis, under changing (paleo)environmental/climatic conditions. We focus on exploring this interplay in modern soils and paleosols of southeast Sardinia (Italy), integrating two innovative techniques to a traditional pedological study: (i) laser ablation ICP-MS spot analyses applied to detect microscale distribution of trace elements in discrete soil features of organic-mineral (A) and argillic (Bt) horizons in thin sections, and (ii) radioactive disequilibria as tracers and chronometers of pedogenetic alteration and geomorphic dynamics. The Pleistocene paleosols developed mainly during interglacial periods, with important clay illuviation and rubification. The other soils are essentially characterized by organic matter incorporation into the profiles. Field discontinuities described within soil profiles, related to phases of sediment aggradation and/or surface erosion, are often supported by laboratory results, mainly micromorphological and geochemical data. LA-ICP-MS data show an overall trend of increase of most trace elements (REEs included) from skeletal rock fragments to both clayey and organic-rich soil matrix to clay coatings. This pathway is clearly controlled by the degree of weathering of primary minerals and by pedogenetic processes, where element adsorption onto reactive sites of organic matter and clay particles and clay illuviation play prominent roles. Recent trends of the studied soils/paleosols in terms of geomorphic stability (equilibrium) or morphodynamic processes (erosion/accumulation rates) are estimated using radionuclide disequilibria in the order of 1cm/a or lower. [Copyright &y& Elsevier]

The paper investigates the influence of the resistance coefficient variability onto the spatial development of roll-waves. Two models, based on time-asymptotic solutions of the linearized St. Venant equations, subject to either impulsive or oscillating perturbation, have been modified by including the dependence of the resistance coefficient on flow conditions, wall roughness, and fluid viscosity. Independently of the perturbation type, it has been shown that the hypothesis of constant resistance coefficient leads to underestimate the disturbance spatial growth. Theoretical predictions are finally compared with results of a fully nonlinear model and with literature experimental data for several combinations of Froude and Reynolds numbers and relative roughness values. The representation of variability of the resistance coefficient fundamentally improves the performance of minimum channel length criteria, whereas its neglect may lead to noncautious channel design. [ABSTRACT FROM AUTHOR]

Summary: This paper analyses conditions for roll-waves formation in homogeneous granular flows with the aim of predicting their occurrence in finite length channels. With reference to a wide class of constitutive equations of the flowing medium, the response of the linearized one-dimensional flow model to a pointwise instantaneous disturbance is studied and a closed form of the Green’s function, in both stable and unstable conditions, is provided. The exponential growth of the disturbance peak is used to predict the spatial evolution of roll-waves in dry flows of dense granular materials and a criterion for the minimum channel length necessary to appreciate roll-wave development is proposed. The comparison among theoretical and experimental data available in the literature appears promising. [Copyright &y& Elsevier]

This paper proposes a cost-effective, robustly practical solution for a high-efficient electro-hydraulic actuator (EHA) for linear drives. The solution addresses the challenges of high costs and limited efficiency that limit the application of EHA for the electrification of many off-road vehicles. Based on a variable-speed electric motor and a low-cost technology for a fixed-displacement pump, the proposed solution is suitable for a compact implementation and it is capable of energy regeneration under overrunning load conditions. Two different architectures—an open circuit and a closed circuit one—are considered to determine the most practical and efficient configuration as well as the control features. Both architectures minimize throttling losses associated with the conventional regulation of hydraulic actuators. Actuator velocities below the minimum and beyond the maximum allowable pump flow rate are achieved in both architectures using a proportional valve that bypasses the pump flow. The paper describes the design methodology as well as the simulation and experimental activities performed to verify the control strategies as well as energy efficiency. Considering an EHA system of about 20 kW, a complete efficiency map of the system is determined for all the possible four quadrants of operation thus including both resistive and overrunning loads, where energy recuperation is implemented. Simulation and experimental results show that the energy efficiency of the hydraulic systems can reach 84.7% in resistive phases. In assistive phases, the hydraulic system can recover up to 81.8% of the actuator energy. The comparison between open-circuit and closed-circuit structures shows the advantages of the former in terms of energy efficiency. The proposed solution is suitable for electrified hydraulic actuation systems, in both industrial and mobile applications. With the advantages of the low cost of the hydraulic unit and high energy efficiency, it is particularly suitable for mobile applications such as construction machines, that are recently experiencing a significant electrification trend. • A cost-effective electro-hydraulic actuator is proposed with high efficiency. • The solution uses fixed-displacement pump and variable-speed electric motor. • Low-speed actuation is allowed by the usage of bypass valve in the architecture. • The efficiency of the system is verified by both simulation and experiments. • Four-quadrant efficiency maps demonstrate energy performance. [ABSTRACT FROM AUTHOR]

The 2D shallow water equations are often solved through finite volume (FV) methods in the presence of irregular topography or in non-rectangular channels. The ability of FV schemes to preserve uniform flow conditions under these circumstances is herein analysed as a preliminary condition for more involved applications. The widely used standard Harten-Lax-Van Leer (HLL) and a well-balanced Roe method are considered, along with a scheme from the class of wave propagation methods. The results indicate that, differently from the other solvers, the standard HLL does not preserve the uniform condition. It is therefore suggested to benchmark numerical schemes under this condition to avoid inaccurate hydrodynamic simulations. The analysis of the discretized equations reveals an unbalance of the HLL transversal fluxes in the streamwise momentum equation. Finally, a modification of the HLL scheme, based on the auxiliary variable balance method, is proposed, which strongly improves the scheme performance. [ABSTRACT FROM AUTHOR]

• We assess landform and parent material influence on soil types and properties. • We predict the composition of mapping units in terms of principal soil types. • Soil spatial patterns are coherent with terrain attributes and parent materials. • Models are more reliable in predicting absence rather than presence of soil types. A soil map (1:50,000 scale) was recently produced in Sardinia (Italy) using a cost-effective GIS approach. In this study we aimed to verify, in two pilot areas and by means of statistical analysis, the effectiveness of the adopted methodology in representing and predicting the spatial distribution of soil types and properties. We focused on evaluation of 1) the influence of landforms and parent materials on soil types (WRB Reference Soil Groups) and selected soil properties and 2) the suitability of the adopted methodology for calibrating a model to predict land unit composition in terms of different soil types. Leptosols, Regosols and Cambisols were prevalent on slopes, with Leptosols being more frequent on convex slopes and Regosols and Cambisols on concave slopes. In flat areas, soil types mainly depended on the type and age of parent material, with Regosols and Cambisols prevailing on Holocene deposits and highly developed soils (mainly Luvisols) largely prevailing on Pleistocene deposits. On hard rock, Leptosols were very frequent on terrigenous metamorphic rock and frequent on granite. Besides Leptosols, Regosols occurred more frequently than Cambisols on both parent materials. Landforms strongly influenced soil depth and available water capacity. Soils on plains were deeper than those on slopes, where convex forms had shallower soils than concave forms. A similar trend applied to the available water capacity. The parent material had a significant effect on topsoil properties (thickness, texture, pH and organic carbon content) of soils belonging to the same WRB Reference Soil Group (analysis done on the most relevant WRB Reference Soil Groups, i.e. Leptosols, Regosols and Cambisols). We calibrated and tested stepwise multiple linear regressions (MLR) and general linear models (GLM) to predict the composition of map units in terms of different WRB Reference Soil Groups. The two models gave very similar results, with distinct distribution patterns that were coherent with the relationships observed between soil groups and specific combination of terrain attributes and parent materials. Results showed that both models were more reliable in predicting the absence rather than presence of a given soil type. [ABSTRACT FROM AUTHOR]

The authors comment on the article "Analysis of Dynamic Wave Model for Unsteady Flow in an Open Channel" by Maurizio Venutelli. They mentions the analytical expressions of phase and group speeds and wave amplitude that have been derived by studying the linearized shallow-water equations (SWEs). The author states that the result of the study allows assessing convergence and accuracy of numerical schemes commonly.

• The proposed simulation model evaluates different flow, force features of a Gerotor. • The model considers different fluid–structure interactions of the rotors. • Flow rate, pressure pulsation and mechanical efficiency are experimentally validated. • Torque losses are quantified, considering possible asymmetry of the axial gap. Gerotors are compact, inexpensive and robust pumps generally used in hydraulic systems. Owing to their characteristic operation at low pressure (up to 30 bar), these units can be modelled using relatively simple tools considering only their fluid dynamics aspects. However, some commercially available Gerotors operate at higher pressures so that material deformation effects cannot be neglected under such conditions. This paper presents an omni-comprehensive simulation approach for Gerotor units that considers the fluid–structure interaction effects at the lateral lubricating gaps and related to the contacts between the rotors. The numerical tool consists of different submodels which allow the evaluation of the fluid dynamic features of the flow through the pump considering micro-motion effects of the rotors. This paper particularly details the novel aspects of the simulation approach, which is the introduction of submodels that account for fluid–structure interaction effects: the lateral lubricating gap models and the rotor contact models, both based on the solution of the Reynolds equation considering the deformation of the solid parts. For the model validation, a commercially available pump able to operate above 100 bar was tested at the authors' research center. The comparison between the simulation results and the experimental data clearly show the good accuracy of the model, in terms of volumetric flow and port pressure pulsation. In particular, the model allows predicting both the volumetric and the torque efficiency of the unit. Furthermore, the simulation results permit to interpret the reasons for instances of wear present in the unit. [ABSTRACT FROM AUTHOR]

• A design parameterization of a helical/spur external gear machine was developed. • An optimization procedure was developed for design of helical and spur gear pumps. • Helical gears have more potential for better meshing stress ripple than spur. • Helical gears also have more potential for compactness and efficiency. • Spur gears offer more potential for flow ripple reduction than helical. This paper addresses the problem of determining the relative performance of spur and helical external gear pumps (EGPs) for fluid power applications. Helical EGPs are commonly considered as quieter units than spur ones; however, there is no specific study reported in literature that proves such claim. Similarly, it is hard to find data indicating which design is better in terms of compactness or energy performance. To tackle this problem, a procedure is developed for virtual design optimization of both helical and spur gear EGPs. This includes addressing the two fundamental challenges of the work, parameterizing a generic EGP design and quantifying its performance. By applying this procedure, a genetic algorithm can continue improving from generation to generation, until the pareto optimal set of designs is identified for both helical and spur units. In the comparison of these, the differences between the two configurations will be identified and the fundamental question of this work can be answered; are helical gears 'better' than spur gears? [ABSTRACT FROM AUTHOR]

In the context of improving energy efficiency and fuel consumption of mobile hydraulic equipment, it is important to analyze all the sources of power loss occurring within the hydraulic systems. While plenty of analyses have been performed on the working implements and the main transmission systems, very little attention has been paid to low-pressure (LP) systems until recently. LP systems are required on closed-circuit hydraulic systems to replenish losses, provide cooling flow, and maintain a pilot pressure necessary to operate hydraulic control valves and variable displacement units. It is shown that these circuits, which are often thought to have minimal impact on power consumption, actually cause significant, continuous power loss. A new method of power savings in these circuits is investigated through management of charge pump flow by application of an accumulator-sense pump-unloading (ASPU) valve. This work further proposes the combination of a split LP architecture with an ASPU valve. Three systems are simulated using Simcenter Amesim® and MATLAB/Simulink®. Using realistic duty cycles and unit loss models on a circuit for mobile off-road hydraulic equipment, it is shown that a standard LP system can consume about 5 kW of power. Power savings of up to 65% over a standard LP system are demonstrated by the proposed architecture. [ABSTRACT FROM AUTHOR]

Global climate change has discernible impacts on the quality of the landscapes of Hungary. Only a dynamic and spatially differentiated land evaluation methodology can properly reflect these changes. The provision level, rate of transformation and spatial distribution of ecosystem services (ESs) are fundamental properties of landscapes and have to be integral parts of an up-to-date land evaluation. For agricultural land capability assessment soil fertility is a major supporting ES, directly associated with climate change through greenhouse gas emissions and carbon sequestration as regulationg services. Since for Hungary aridification is the most severe consequence of climate change, water-related ESs, such as water retention and storage on and below the surface as well as control of floods, water pollution and soil erosion, are of increasing importance. The productivity of agricultural crops is enhanced by more atmospheric CO2 but restricted by higher drought susceptibility. The value of floodplain landscapes, i.e. their agroecological, nature conservation, tourism (aesthetic) and other potentials, however, will be increasingly controlled by their water supply, which is characterized by hydrometeorological parameters. Case studies are presented for the estimation of the value of two water-related regulating ESs (water retention and groundwater recharge capacities) in the floodplains of the Kapos and Drava rivers, Southwest Hungary. It is predictable that in the future land evaluation techniques based on the FAO framework will be more dynamic and integrated with the monetary valuation of ESs. The latter task, however, still involves numerous methodological problems to solve. [ABSTRACT FROM AUTHOR]

In this article, we present the Terrestrial intergrades from never or only few days submersed humipedons, without permanent hydromorphic signs, until humipedons with presence of signs of partial asphyxia. Specific terms are defined and diagnostic horizons illustrated, both with the help of text explanations and photographs. The article ends with a table working as a classification field key. [ABSTRACT FROM AUTHOR]

This article is an as simple as possible key of classification of terrestrial (aerobic, not submersed) topsoils (organic and organic-mineral series of soil horizons). Based on the introduction exposed in Humusica 1, article 1, and using vocabulary and definitions listed in article 4, a classification is proposed for better understanding the biological functioning of the soil, partially disclosing the process of litter digestion. Five types of terrestrial topsoils, called terrestrial humus systems, are described and illustrated with the help of photographs. Within each humus system, 3–4 humus forms are also revealed, corresponding to similar series of soil horizons generated in a relatively homogeneous environment whose range of ecological factors is not so large to overstep and cause the genesis of another different humus system. The article ends with a figure that shows the relationship between Tangel and Amphi humus systems, and a dichotomous key of classification that one can easily print and bring in the field for practicing humus classification. [ABSTRACT FROM AUTHOR]

Knowledge of a little number of specific terms is necessary to investigate and describe humipedons. This “new vocabulary” allows individuating and circumscribing particular diagnostic horizons, which are the fundamental bricks of the humipedon. Few “components” defined by specific terms characterize a specific “humipedon horizon”; few “humipedon horizons” compose a given “humus form” and some similar “humus forms” are grouped in a functional “humus system”. In this article, specific terms and humus horizons are listed and explained one by one. Field difficulties are illustrated and resolved. The aim of the article is to present in a manner as simple as possible how to distinguish in the field the soil structures allowing a morpho-functional classification of terrestrial (aerated, not submerged) humipedons. [ABSTRACT FROM AUTHOR]

The impact of a dam-break wave on an erodible embankment with a steep slope is studied in the paper using both experimental and numerical approaches. The laboratory experiments have been specifically designed and performed for a range of the storage water levels and the embankment elevations and slopes. The simulations were carried out using a recently-developed two-phase depth-integrated model, supplemented with a geofailure operator to account for the possible occurrence of geotechnical collapses. A comparison between numerical and experimental results indicates that the two-phase model reproduces the experimental free surface elevation well, with or without the geofailure operator. On the other hand, especially for high embankment slopes, this operator appears to be important for predicting the observed morphological evolution. The results also show that, due to the geotechnical collapses, water and sediment velocities may have opposite signs. While the models based on equal direction of the liquid and the solid motions cannot reproduce this effect, the proposed two-phase approach easily accounts for such a peculiarity of the investigated process. [ABSTRACT FROM AUTHOR]

Hydrostatic transmissions (HT) are widely applied to heavy-duty mobile applications because of the advantages of layout flexibility, power to weight ratio, and ease of control. Though applications of fluid power in light-duty vehicles face challenges, including the unavailability of off-the-shelf components suitable to the power scale, there are potential advantages for HTs in human-powered vehicles, such as bicycles, the most important one being the energy-saving advantage achievable through regenerative braking in a hybrid HT. This paper describes an innovative design for a hydraulic hybrid bicycle, i.e., the PurdueTracer. The PurdueTracer is an energy-efficient human-powered hydraulic bicycle with flexible operation and software aids. An open-circuit hydraulic hybrid transmission allows PurdueTracer to operate in four modes: Pedaling, Charging, Boost, and Regeneration, to satisfy users' need for different riding occasions. An aluminum chassis that also functions as a system reservoir was customized for the PurdueTracer to optimize the durability, riding comfort, and space for components. The selection of the hydraulic components was performed by creating a model of the bicycle in AMESim simulation software and conducting a numerical optimization based on the model. The electronic system equipped users with informative feedback showing the bicycle performance, intuitive execution of functions, and comprehensive guidance for operation. This paper describes the design approach and the main results of the PurdueTracer, which also won the 2017 National Fluid Power Association Fluid Power Vehicle Challenge. This championship serves to prove the excellence of this vehicle in terms of effectiveness, efficiency, durability, and novelty. [ABSTRACT FROM AUTHOR]

This article is an as simple as possible key of classification of terrestrial (aerobic, not submersed) topsoils (organic and organic-mineral series of soil horizons). Based on the introduction exposed in Humusica 1, article 1, and using vocabulary and definitions listed in article 4, a classification is proposed for better understanding the biological functioning of the soil, partially disclosing the process of litter digestion. Five types of terrestrial topsoils, called terrestrial humus systems, are described and illustrated with the help of photographs. Within each humus system, 3–4 humus forms are also revealed, corresponding to similar series of soil horizons generated in a relatively homogeneous environment whose range of ecological factors is not so large to overstep and cause the genesis of another different humus system. The article ends with a figure that shows the relationship between Tangel and Amphi humus systems, and a dichotomous key of classification that one can easily print and bring in the field for practicing humus classification. [ABSTRACT FROM AUTHOR]

In this article, we present the Terrestrial intergrades from never or only few days submersed humipedons, without permanent hydromorphic signs, until humipedons with presence of signs of partial asphyxia. Specific terms are defined and diagnostic horizons illustrated, both with the help of text explanations and photographs. The article ends with a table working as a classification field key. [ABSTRACT FROM AUTHOR]

This article is an as simple as possible key of classification of terrestrial (aerobic, not submersed) topsoils (organic and organic-mineral series of soil horizons). Based on the introduction exposed in Humusica 1, article 1, and using vocabulary and definitions listed in article 4, a classification is proposed for better understanding the biological functioning of the soil, partially disclosing the process of litter digestion. Five types of terrestrial topsoils, called terrestrial humus systems, are described and illustrated with the help of photographs. Within each humus system, 3–4 humus forms are also revealed, corresponding to similar series of soil horizons generated in a relatively homogeneous environment whose range of ecological factors is not so large to overstep and cause the genesis of another different humus system. The article ends with a figure that shows the relationship between Tangel and Amphi humus systems, and a dichotomous key of classification that one can easily print and bring in the field for practicing humus classification. [ABSTRACT FROM AUTHOR]

Knowledge of a little number of specific terms is necessary to investigate and describe humipedons. This “new vocabulary” allows individuating and circumscribing particular diagnostic horizons, which are the fundamental bricks of the humipedon. Few “components” defined by specific terms characterize a specific “humipedon horizon”; few “humipedon horizons” compose a given “humus form” and some similar “humus forms” are grouped in a functional “humus system”. In this article, specific terms and humus horizons are listed and explained one by one. Field difficulties are illustrated and resolved. The aim of the article is to present in a manner as simple as possible how to distinguish in the field the soil structures allowing a morpho-functional classification of terrestrial (aerated, not submerged) humipedons. [ABSTRACT FROM AUTHOR]

In this article, we present the Terrestrial intergrades from never or only few days submersed humipedons, without permanent hydromorphic signs, until humipedons with presence of signs of partial asphyxia. Specific terms are defined and diagnostic horizons illustrated, both with the help of text explanations and photographs. The article ends with a table working as a classification field key. [ABSTRACT FROM AUTHOR]

Some soil scientists or biologists (14, one preferring anonymity) answered the three following questions: (1. Introduction) 2. Why is organic food better (tastes better, is healthier, richer in nutrients, contains less pesticide, etc.) than food produced with hydroponic or intensive farming techniques? 3. In a humipedon, are soil functioning, biodiversity and carbon content three interdependent and intersected aspects of a single ecosystem? In other words, can we treat these aspects as if they were inseparable in a humipedon? 4. Are agriculture and civilization (the society, culture, and way of life) interconnected? All scientists expressed affirmative answers. Nuances or in depth information were also furnished. The article allows to understand the real “agronomic challenge” that the predicted Global Change might represent for humanity. [ABSTRACT FROM AUTHOR]

Knowledge of a little number of specific terms is necessary to investigate and describe humipedons. This “new vocabulary” allows individuating and circumscribing particular diagnostic horizons, which are the fundamental bricks of the humipedon. Few “components” defined by specific terms characterize a specific “humipedon horizon”; few “humipedon horizons” compose a given “humus form” and some similar “humus forms” are grouped in a functional “humus system”. In this article, specific terms and humus horizons are listed and explained one by one. Field difficulties are illustrated and resolved. The aim of the article is to present in a manner as simple as possible how to distinguish in the field the soil structures allowing a morpho-functional classification of terrestrial (aerated, not submerged) humipedons. [ABSTRACT FROM AUTHOR]

The bottom elevation at the midpoint of the interfaces, Graph HT ht and Graph HT ht , in the formulas are evaluated based on this assumption. Consistently with the lateralization technique used for the slope source term (Greco et al., [3]), the scheme considers a piecewise-constant distribution of the free-surface elevation Graph HT ht of the cell. Similarly, in the evaluation of the auxiliary variables Graph HT ht , interface-midpoint values of I h i are used for the first variable, cell values for the second and the third variables. [Extracted from the article]

• Mud-flows may cause serious damages to people and structures. • The evaluation of the impact of mud flows against obstacles is crucial for damage assessment. • The impact force depends on both the fluid rheology and the geometry. • In some conditions the peak force does not exceed the time-asymptotic hydrostatic value. • Useful indications on how to evaluate the peak force have been provided. Mud flows represent one of the major causes of natural hazards in mountain regions. Similarly to debris flows, they consist of a hyper-concentrated mixture of water and sediments flowing down a slope and may cause serious damages to people and structures. The present paper investigates the force produced by a dam-break wave of mud impacting against a rigid wall. A power-law shear-thinning model is used to describe the rheology of the hyper-concentrated mixture. A one-dimensional shallow water model is adopted and a second-order Finite Volume scheme is employed to numerically solve the governing equations. The results indicate that depending on the fluid rheological parameters and on the bottom slope, there exists a minimum value of the wall distance above which the peak force does not exceed the asymptotic value of the hydrostatic final condition. For two different values of the channel slope, the dimensionless value of this lower bound is individuated for several values of the power-law exponent and of a dimensionless Basal Drag coefficient. An estimation of the maximum peak force for wall distance smaller than the minimum value is also provided. [ABSTRACT FROM AUTHOR]

This paper investigates the spatial evolution of a disturbance in an open-channel flow of a power-law fluid at non-uniform accelerated and decelerated initial profiles, up to the occurrence of roll-waves in mild and steep slope channels. Both theoretical and numerical analyses are applied to the depth-averaged continuity and momentum conservation equations, deduced from the von Kármán's integral method. For the theoretical investigation, the nonlinear near-front expansion technique was applied. Then, the full nonlinear problem in its conservative formulation was numerically solved. Independently of the rheology of the flowing medium, non-uniform initial conditions strongly influence the perturbation celerity, the disturbance evolution and the roll-wave development. For mild slope channels, an initially decelerated profile of shear-thinning fluids has a stabilizing effect, while the opposite is found for accelerated profiles. For shear-thickening fluids, only the stabilizing effect caused by a decelerated profile is observed. In steep slope channels, independently of the fluid rheology, decelerated initial conditions promote roll-wave occurrence, while accelerated conditions inhibit the perturbation growth. Although experimental verifications are needed, the present results have to be properly accounted for in defining roll-wave prediction methods and in assigning appropriate boundary conditions to enhance or to reduce their formation. [ABSTRACT FROM AUTHOR]

Fast geomorphic transients may involve complex cenarios of sediment transport, occurring near the bottom as bed load (i.e., saltating, sliding, and rolling) or as suspended load in the upper portion of the flow. The two sediment transport modalities may even coexist or alternate each other during the same event, especially when the shear stress varies considerably. Modeling these processes is therefore a challenging task, for which the usual representation of the flow as a mixture may result in being unsatisfactory. In the present paper, a new two-phase depth-averaged model is presented that accounts for variable sediment concentration in both bed and suspended loads. Distinct phase velocities are considered for bed load, whereas the slip velocity between the two phases is neglected in the suspended load. It is shown that the resulting two-phase model is hyperbolic, and the analytical expression of the eigenvalues is provided. The entrainment/ deposition of sediment between the bottom and the bed load layer is based on a modified van Rijn transport parameter, whereas for the suspended sediment a first-order exchange law is considered. A numerical finite-volume method is used for the simulation of three dam break experiments found in the literature, which are effectively reproduced in terms of both free surface elevation and bottom deformation, confirming the key role played by the solid concentration variability even for two-phase models. [ABSTRACT FROM AUTHOR]

Field soil pore water monitoring was applied in a highly heavy-metal contaminated area in SW Sardinia, Italy, as a direct, realistic measure of heavy metal mobility. The main chemistry of pore waters well reflects the local characteristics of soils, ranging from Ca–SO 4 to (Ca)Mg–HCO 3 to Ca(Na)–SO 4 (Cl), with a wide range of conductivity. The mobility of Zn and Pb is apparently controlled by equilibrium with minerals such as hydrozincite or smithsonite, and cerussite, respectively. These results allow a correct estimate of the actual environmental risk associated with the presence of heavy metals in soils, and may serve as a supporting tool for phytoremediation planning. [ABSTRACT FROM AUTHOR]

This study was aimed to implement the understanding of the Sb behavior in near-surface environments, as a contribution to address appropriate mitigation actions at contaminated sites. For this purpose, geochemical data of soil (8 sites), water (29 sites), and plant (12 sites) samples were collected. The study area is located at Su Suergiu and surroundings in Sardinia (Italy), an abandoned mine area heavily contaminated with Sb, with relevant impact on water bodies that supply water for agriculture and domestic uses. Antimony in the soil horizons ranged from 19 to 4400 mg kg − 1 , with highest concentrations in soils located close to the mining-related wastes, and concentrations in the topsoil much higher than in the bedrock. The Sb readily available fraction was about 2% of the total Sb in the soil. Antimony in the pore water ranged from 23 to 1700 μg L − 1 , with highest values in the Sb-rich soils. The waters showed neutral to slightly alkaline pH, redox potential values indicating oxidizing conditions, electrical conductivity in the range of 0.2 to 3.7 mS cm − 1 , and dissolved organic carbon ≤ 2 mg L − 1 . The waters collected upstream of the mine have Ca-bicarbonate dominant composition, and median concentration of Sb(tot) of 1.7 μg L − 1 (that is total antimony determined in waters filtered through 0.45 μm), a value relatively high as compared with the background value (≤ 0.5 μg L − 1 Sb) estimated for Sardinian waters, but below the limits established by the European Union and the World Health Organization for drinking water (5 μg L − 1 Sb and 20 μg L − 1 Sb, respectively). The waters flowing in the mine area are characterized by Ca-sulfate dominant composition, and median concentrations of 7000 μg L − 1 Sb(tot). Extreme concentrations, up to 30,000 μg L − 1 Sb(tot), were observed in waters flowing out of the slag materials derived from the processing of Sb-ore. The Sb(III) was in the range of 0.8 to 760 μg L − 1 and represented up to 6% of Sb(tot). In the waters collected downstream of the mine, median Sb(tot) concentrations decreased as distance from the mine area increases: 1300 μg L − 1 Sb(tot) in the stream Rio Ciurixeda at 3 km distance, and 25 μg L − 1 Sb(tot) in the main River Flumendosa 15 km further downstream. Attenuation of Sb contamination was mainly due to dilution. Results of modeling, carried out by both EQ3 and Visual MINTEQ computer programs, suggest that sorption of dissolved Sb onto solid phases, and/or precipitation of Sb-bearing minerals, likely give a minor contribution to attenuation of Sb contamination. The slightly alkaline pH and oxidizing conditions might favor the persistence of inorganic Sb(V)-bearing species at long distance in the studied waters. Concentrations of Sb in the plants Pistacia lentiscus and Asparagus ranged from 0.1 to 22 mg kg − 1 , with maximum values in plants growing very close to the mining-related wastes. The P. lentiscus grows well on the soils highly contaminated with Sb at Su Suergiu and might be used for revegetation of the Sb-rich heaps, thus contributing to reduce the dispersion of contaminated materials. Major effects of contamination were observed on the water bodies located downstream of the Su Suergiu abandoned mine. The maximum load (16.6 kg Sb per day) to the Flumendosa, the main aquatic recipient, was observed after heavy rain events. Therefore, priorities of mitigation actions should be focused on minimizing the contact of rain and runoff waters on the heaps of mining wastes. [ABSTRACT FROM AUTHOR]

As bryophytes present the capacity to colonize a wide range of habitats, including extreme environments (e.g., mine areas), we first checked the global response of bryophytes to heavy metals (HM) by a systematic review. This analysis found i) the lack of studies in a polluted environment and ii) resulted in a global trend of photochemical efficiency decrease when bryophytes faced heavy metals. Secondly, we characterized the photoprotective responses of four metallicolous populations of mosses (Lewinskya rupestris , Polytrichum commune , Ptychostomum compactum and Rhynchostegium confertum) naturally growing in an abandoned mine area by an experimental field approach. As a result, we found markedly species-specific tolerance patterns: i) less tolerant species, presenting high pollutants content accompanied by marked dissipative and antioxidative strategies. This strategy was depicted by the species R. confertum that result to be a good sentinel species due to the high pollutant content and high physiological sensitivity.; ii) intermediate tolerant species presenting a medium content of pollutants and less marked photoprotective mechanisms, and iii) most tolerant species minimizing pollutants content and consequently presenting no changes in their physiological performance. This evidence support that species' bryological attributes have a key role in determining species' tolerance towards environmental heavy metals, and should be taken into consideration in future studies. The findings of this study also pointed out that the higher levels of γ + β-tocopherol in metallicolous populations could play a regulatory role in metal stress tolerance in mosses and it could be a suitable functional responsive trait for environmental response prediction to heavy metals in polluted environments. [Display omitted] • Bryophytes' adaptive mechanisms to metalliferous environments are poorly studied. • Photoprotective strategies are the result of species' bryological attributes and pollutant content. • Changes in photoprotective compounds levels mark bryophytes' tolerance to environmental heavy metals. • Increasing γ + β-tocopherol is a functional trait in mosses copying with heavy metals. [ABSTRACT FROM AUTHOR]

Abstract: Some of the weathering deposits that formed during the emersive phase, which in Sardinia lasted from Late Cretaceous to Palaeocene–Early Eocene, consist today of ferruginous palaeosols (ferricretes), sometimes overlain by palustrine limestones. In this article, the two outcrops at Nuxis and Guardia Pisano, containing a ferricrete composed of subspherical goethitic-hematitic concretions, are studied in detail. The main components are Fe, Al, Si, along with Ba, which is very abundant in the Nuxis outcrop. With the exception of the barite, the pisolithic ferricretes of Sardinia can be compared, for their chemical and mineralogical composition, with the pisoplinthites that form in modern tropical soils. They are also comparable with the pisolithic ferricretes cropping out in southern France, that formed around the K/T boundary. The pisolithic ferricretes of southern France and Sardinia can be interpreted as the weathering product of identical warm and humid climatic conditions and, reasonably, of the same climatic event. Therefore, they provide further evidence that Sardinia and southern France formed part of the same palaeogeographic province. A tropical environment is, on the other hand, consistent with the barite leaching from the Palaeozoic substratum and with its reprecipitation into the iron pisoliths. Micro- and nanostructures, observed using SEM analysis within and between the concentric layers of the pisoliths, are consistent with biological processes involving bacteria during their deposition. [Copyright &y& Elsevier]