Large roots dominate the contribution of trees to slope stability

Tree roots provide surface erosion protection and improve slope stability through highly complex interactions with the soil due to the nature of root systems. Root reinforcement estimation is usually performed by in situ pullout tests, in which roots are pulled out of the soil to reliably estimate the root strength of compact soils. However, this test is not suitable for the scenario where a soil progressively fails in a series of slump blocks – for example, in unsupported soils near streambanks and road cuts where the soil has no compressive resistance at the base of the hillslope. The scenario where a soil is unsupported on its downslope extent and progressively deforms at a slow strain rate has received little attention, and we are unaware of any study on root reinforcement that estimates the additional strength provided by roots in this situation. We therefore designed two complementary laboratory experiments to compare the force required to pull the root out. The results indicate that the force required to pull out roots is reduced by up to 50% when the soil fails as slump blocks compared to pullout tests. We also found that, for slump block failure, roots had a higher tendency to slip than to break, showing the importance of active earth pressure on root reinforcement behaviour, which contributes to reduced friction between soil and roots. These results were then scaled up to a full tree and tree stand using the root bundle and field-measured spatial distributions of root density. Although effects on the force mobilized in small roots can be relevant, small roots have virtually no effect on root reinforcement at the tree or stand scale on hillslopes. When root distribution has a wide range of diameters, the root reinforcement results are controlled by large roots, which hold much more force than small roots. © 2019 John Wiley & Sons, Ltd.     

Correction to: Geochemical Prospectivity Mapping Through a Feature Extraction–Selection Classification Scheme

Natural Resources Research - The original version of this article unfortunately contained a mistake in the second part of Table 3. The data in last four rows of Table 3, i.e.,...     

Assessment of Various Fuzzy c-Mean Clustering Validation Indices for Mapping Mineral Prospectivity: Combination of Multifractal Geochemical Model and Mineralization Processes

This paper describes the application of an unsupervised clustering method, fuzzy c-means (FCM), to generate mineral prospectivity models for Cu?±?Au?±?Fe mineralization in the Feizabad District of NE Iran. Various evidence layers relevant to indicators or potential controls on mineralization, including geochemical data, geological–structural maps and remote sensing data, were used. The FCM clustering approach was employed to reduce the dimensions of nine key attribute vectors derived from different exploration criteria. Multifractal inverse distance weighting interpolation coupled with factor analysis was used to generate enhanced multi-element geochemical signatures of areas with Cu?±?Au?±?Fe mineralization. The GIS-based fuzzy membership function MSLarge was used to transform values of the different evidence layers, including geological–structural controls as well as alteration, into a [0–1] range. Four FCM-based validation indices, including Bezdek’s partition coefficient (V_Pc) and partition entropy (V_Pe) indices, the Fukuyama and Sugeno (V_FS) index and the Xie and Beni (V_XB) index, were employed to derive the optimum number of clusters and subsequently generate prospectivity maps. Normalized density indices were applied for quantitative evaluation of the classes of the FCM prospectivity maps. The quantitative evaluation of the results demonstrates that the higher favorability classes derived from V_FS and V_XB (N_d?=?9.19) appear more reliable than those derived from V_Pc and V_Pe (N_d?=?6.12) in detecting existing mineral deposits and defining new zones of potential Cu?±?Au?±?Fe mineralization in the study area.

     

Bursting and quenching in massive galaxies without major mergers or AGNs

In this work, we study the formation and evolution of dark matter haloes by means of the spherical infalling model with shell-crossing. We present a framework to tackle this effect properly based on the numerical follow-up, with time, of that individual shell of matter that contains always the same fraction of mass with respect to the total mass. In this first step, we do not include angular momentum, velocity dispersion or triaxiality. Within this framework – named as the spherical shell tracker – we investigate the dependence of the evolution of the halo with virial mass, with the adopted mass fraction of the shell, and for different cosmologies. We find that our results are very sensitive to a variation of the halo virial mass or the mass fraction of the shell that we consider. However, we obtain a negligible dependence on cosmology. Furthermore, we show that the effect of shell-crossing plays a crucial role in the way that the halo reaches the stabilization in radius and the virial equilibrium. We find that the values currently adopted in the literature for the actual density contrast at the moment of virialization,  δ_vir  , may not be accurate enough. In this context, we stress the problems related to the definition of a virial mass and a virial radius for the halo. The question of whether the results found here may be obtained by tracking the shells with an analytic approximation remains to be explored.     

Pulsar magnetosphere

Pulsars are presently believed to be rotating neutron stars with large frozen-in magnetic fields normally assumed to be dipole fields. It has been shown that such a star must possess a magnetosphere if it rotates sufficiently rapidly. By assuming that the magnetic field is dipolar, and unaffected by the trapped particles in the magnetosphere, and that the field dipole axis is parallel to the rotation axis, Goldreich and Julian determined many of the properties of the magnetosphere. In this paper is given a self-consistent model of the closed field lines of a pulsar magnetosphere. Using this model, it is shown that, close to the star, the above assumptions of Goldreich and Julian are justified. Their results are extended to the oblique rotator as well as to stars with magnetic multipoles of arbitrary order and arbitrary orientation.Supported in part by the U.S. Atomic Energy Commission under Grant 2171T.     

Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: I. An introduction to the project

We investigated paleolimnological records from a series of river deltas around the northeastern rim of Lake Tanganyika, East Africa (Tanzania and Burundi) in order to understand the history of anthropogenic activity in the lakes catchment over the last several centuries, and to determine the impact of these activities on the biodiversity of littoral and sublittoral lake communities. Sediment pollution caused by increased rates of soil erosion in deforested watersheds has caused significant changes in aquatic communities along much of the lakes shoreline. We analyzed the effects of sediment discharge on biodiversity around six deltas or delta complexes on the east coast of Lake Tanganyika: the Lubulungu River delta, Kabesi River delta, Nyasanga/Kahama River deltas, and Mwamgongo River delta in Tanzania; and the Nyamuseni River delta and Karonge/Kirasa River deltas in Burundi. Collectively, these deltas and their associated rivers were chosen to represent a spectrum of drainage-basin sizes and disturbance levels. By comparing deltas that are similar in watershed attributes (other than disturbance levels), our goal was to explore a series of historical experiments at the watershed scale, with which we could more clearly evaluate hypotheses of land use or other effects on nearshore ecosystems. Here we discuss these deltas, their geologic and physiographic characteristics, and the field procedures used for coring and sampling the deltas, and various indicators of anthropogenic impact.     

Local music policies within a global music industry: cultural quarters in Manchester and Sheffield

This paper will explore the relationship between the local and the global in the music industry through the lens of place-based cultural policies.The first part of the paper will outline current debates around the complex interaction of the local and the global in culture in general and the popular music industry in particular. Alongside the continuous expansion of globalisation has been a reassertion of ‘place', of ‘locality'. Whilst this has been investigated to some extent at the level of local music scenes it has never been fully addressed in terms of music industry policy as part of an economic development strategy. Yet it is here that the particular values of ‘place' are asserted in the face of some ‘global' music industry with a view to developing (or at least retaining some of the benefits of) a local music industry.Whilst situating itself within these debates about the relationship of local and global musical production and consumption, the paper explores the different strategies of two northern English cities and their attempts to promote culture, and music, within each cities ‘cultural quarter': Sheffield's Cultural Industries Quarter and Manchester's Northern Quarter. The paper analyses the role and appropriateness of local authority policy intervention, the importance of ‘soft' networks within local music scenes and the different ways in which authorities in each example have tried to overcome dichotomies of art and industry, cultural and economy.     

Ecosystem specific yield for estimating evapotranspiration and groundwater exchange from diel surface water variation

The White method, routinely used to estimate phreatophyte transpiration from diel groundwater variation, also provides measures of total evapotranspiration (ET) and groundwater fluxes in surface waters. Such applications remain rare, however, and critically require accurate representation of stage‐dependent variation in specific yield (S_y). High‐resolution stage data from three Florida swamps were used to evaluate different relationships between S_y and stage (ecosystem specific yield, ESY). A discretized form, ESY_D, assumes constant S_y near unity for inundated conditions, applying soil S_y for belowground stage and open water S_y (S_y,OW ≈ 1.0) for aboveground stage. A mixture approach, ESY_M, applies a stage‐dependent interpolation between S_y,Soil and S_y,OW using stage‐area relationships and assumes rapid lateral equilibration between inundated and non‐inundated wetland areas. Finally, an empirical formulation, ESY_RR, uses measured ratios of rain to rise to estimate stage‐specific S_y. All formulations yielded reasonable ET rates (ET ≈ PET) at high stage; ESY_D markedly overestimated ET (ET/PET > 3) at intermediate stage, whereas ESY_M and ESY_RR maintained ET/PET near 1.0. Estimated groundwater fluxes using ESY_M and ESY_RR correlated well with Darcy‐estimated flows, but were larger, likely due to uncertainties in Darcy parameters. Well transects across wetlands documented equal water elevation and diel variation across inundated and non‐inundated areas, verifying rapid equilibration that reduces S_y and explaining overestimation by ESY_D. However, equilibration area varied within and among wetlands, explaining observed differences between ESY_M and ESY_RR, and suggesting ESY_RR may be preferred. Stage histograms followed the shape of ESY_RR, highlighting reciprocal influences of ESY on stage stability. Copyright © 2012 John Wiley & Sons, Ltd.     

摩擦滑动起始的动力学特征

摩擦界面的失效方式对于我们从根本上认识工程学至地震学领域中的失效过程非常关键.摩擦运动起始于将两个剪切体分离的薄界面内传播的破裂前沿.通过测定沿界面的剪切应力和法向应力,结合随后的实际接触面积动态学特性,我们发现剪切应力与法向应力之比在局部可远远超过没有发生突然滑动的静摩擦系数.而且,系统所选的不同破裂模式与局部应力比...