Three-dimensional brittle shear fracturing by tensile crack interaction

Faults in brittle rock are shear fractures formed through the interaction and coalescence of many tensile microcracks. The geometry of these microcracks and their surrounding elastic stress fields control the orientation of the final shear fracture surfaces. The classic Coulomb-Mohr failure criterion predicts the development of two conjugate (bimodal) shear planes that are inclined at an acute angle to the axis of maximum compressive stress. This criterion, however, is incapable of explaining the three-dimensional polymodal fault patterns that are widely observed in rocks. Here we show that the elastic stress around tensile microcracks in three dimensions promotes a mutual interaction that produces brittle shear planes oriented obliquely to the remote principal stresses, and can therefore account for observed polymodal fault patterns. Our microcrack interaction model is based on the three-dimensional solution of Eshelby, unlike previous models that employed two-dimensional approximations. Our model predicts that shear fractures formed by the coalescence of interacting mode I cracks will be inclined at a maximum of 26 degrees to the axes of remote maximum and intermediate compression. An improved understanding of brittle shear failure in three dimensions has important implications for earthquake seismology and rock-mass stability, as well as fluid migration in fractured rocks.     

Synaptic scaling mediated by glial TNF-alpha

Two general forms of synaptic plasticity that operate on different timescales are thought to contribute to the activity-dependent refinement of neural circuitry during development: (1) long-term potentiation (LTP) and long-term depression (LTD), which involve rapid adjustments in the strengths of individual synapses in response to specific patterns of correlated synaptic activity, and (2) homeostatic synaptic scaling, which entails uniform adjustments in the strength of all synapses on a cell in response to prolonged changes in the cell's electrical activity. Without homeostatic synaptic scaling, neural networks can become unstable and perform suboptimally. Although much is known about the mechanisms underlying LTP and LTD, little is known about the mechanisms responsible for synaptic scaling except that such scaling is due, at least in part, to alterations in receptor content at synapses. Here we show that synaptic scaling in response to prolonged blockade of activity is mediated by the pro-inflammatory cytokine tumour-necrosis factor-alpha (TNF-alpha). Using mixtures of wild-type and TNF-alpha-deficient neurons and glia, we also show that glia are the source of the TNF-alpha that is required for this form of synaptic scaling. We suggest that by modulating TNF-alpha levels, glia actively participate in the homeostatic activity-dependent regulation of synaptic connectivity.     

Fishing elevates variability in the abundance of exploited species

The separation of the effects of environmental variability from the impacts of fishing has been elusive, but is essential for sound fisheries management. We distinguish environmental effects from fishing effects by comparing the temporal variability of exploited versus unexploited fish stocks living in the same environments. Using the unique suite of 50-year-long larval fish surveys from the California Cooperative Oceanic Fisheries Investigations we analyse fishing as a treatment effect in a long-term ecological experiment. Here we present evidence from the marine environment that exploited species exhibit higher temporal variability in abundance than unexploited species. This remains true after accounting for life-history effects, abundance, ecological traits and phylogeny. The increased variability of exploited populations is probably caused by fishery-induced truncation of the age structure, which reduces the capacity of populations to buffer environmental events. Therefore, to avoid collapse, fisheries must be managed not only to sustain the total viable biomass but also to prevent the significant truncation of age structure. The double jeopardy of fishing to potentially deplete stock sizes and, more immediately, to amplify the peaks and valleys of population variability, calls for a precautionary management approach.     

First record of the genus Tanaostigma (Hymenoptera,Chalcidoidea, Tanaostigmatidae) from the Afrotropical region with description of three new species

ABSTRACT

The genus Tanaostigma is newly recorded from the Afrotropical region and three new species are described: Tanaostigma lasallei van Noort sp. nov. (South Africa), Tanaostigma mulu van Noort sp. nov. (Kenya) and Tanaostigma ukumbusho van Noort sp. nov. (Kenya). We provide comprehensive images of the holotypes and an illustrated identification key to the African species. New country distribution records are provided for Tanaostigmodes tambotis Prinsloo & LaSalle, 1995. All images presented here as well as supplementary images and online keys are available on www.waspweb.org

www.zoobank.org/urn:lsid:zoobank.org:pub:61D1A59D-3702-480A-B146-73067C29CD82     

In Search of Resonance

In this paper I explore the possibility of a complementary relationship between action research and the management and systems sciences. A range of purposes that action researchers and management and systems scientists pursue is initially set out. The paper then explores whether this diversity of purposes and the ways they recommend people to proceed may come together in a new whole that is greater than the sum of its parts. A potentially useful realization of this for practice is a reflexive process of critique, choice, and action, which is elaborated on. The paper then investigates what view of holism arises from the preceeding discussions.     

Localization of iron-reducing activity in paddy soil by profile studies

The aim of this contribution is to analyze the difficulties and possible inconsistencies one may encounter when attempting to integrate substance philosophy and process philosophy. I argue that it is impossible to avoid these problems, and offer a typology that helps to understand the tensions involved in attempts to integrate these two worldviews. This revised version was published online in July 2006 with corrections to the Cover Date.     

The impact of seasonal constants on forecasting seasonally cointegrated time series

In this paper we focus on the effect of (i) deleting, (ii) restricting or (iii) not restricting seasonal intercept terms on forecasting sets of seasonally cointegrated macroeconomic time series for Austria, Germany and the UK. A first empirical result is that the number of cointegrating vectors as well as the relevant estimated parameter values vary across the three models. A second result is that the quality of out-of-sample forecasts critically depends on the way seasonal constants are treated. In most cases, predictive performance can be improved by restricting the effects of seasonal constants. However, we find that the relative advantages and disadvantages of each of the three methods vary across the data sets and may depend on sample-specific features. © 1998 John Wiley & Sons, Ltd.     

An intelligent business forecaster for strategic business planning

In this paper an intelligent business forecaster for strategic business planning is presented. The forecaster is basically a multi‐layered fuzzy rule‐based neural network which integrates the basic elements and functions of a traditional fuzzy logic inference into a neural network structure. It has also been shown to be superior to two commercially available business forecasters in terms of learning speed and forecasting accuracy. This paper presents the architectural design of the intelligent business forecaster and the results of a study that has been carried out to compare its performance with that of the others. Copyright © 1999 John Wiley & Sons, Ltd.