The three stages of stress relaxation - Observations for the time-dependent behaviour of brittle rocks based on laboratory testing

Underground openings can experience time-dependent deformations and stress changes. Studying time-dependent rock behaviour is commonly done with static load (creep) tests in the laboratory which typically exhibit three distinct stages of behaviour. In this study relaxation tests were conducted to examine if three stages also exist under constant strain boundary conditions and to understand how the relaxation behaviour changes as the driving stress to strength ratio is increased. Tests were conducted on two types of limestone. At different load levels similar stress-time responses were measured indicating three distinct stages of stress relaxation. The first stage of stress relaxation (RI) where the stress relaxes with a decreasing rate is followed by the second stage (RII) in which the stress decrease approaches a constant rate and in the third stage (RIII) no further stress relaxation takes place. In the first stage 55% to 95% of the total stress relaxation takes place. The test results are compared with literature data to understand the influence of the stiffness on the magnitude and time to reach the maximum stress relaxation. Relaxation tests could be used to derive numerical model inputs to describe the time-dependent behaviour in a manner similar to static load tests

Functional diversification of Argonautes in nematodes:an expanding universe

In the last decade, many diverse RNAi (RNA interference) pathways have been discovered that mediate gene silencing at epigenetic, transcriptional and post-transcriptional levels. The diversity of RNAi pathways is inherently linked to the evolution of Ago (Argonaute) proteins, the central protein component of RISCs (RNA-induced silencing complexes). An increasing number of diverse Agos have been identified in different species. The functions of most of these proteins are not yet known, but they are generally assumed to play roles in development, genome stability and/or protection against viruses. Recent research in the nematode Caenorhabditis elegans has expanded the breadth of RNAi functions to include transgenerational epigenetic memory and, possibly, environmental sensing. These functions are inherently linked to the production of secondary siRNAs (small interfering RNAs) that bind to members of a clade of WAGOs (worm-specific Agos). In the present article, we review briefly what is known about the evolution and function of Ago proteins in eukaryotes, including the expansion of WAGOs in nematodes. We postulate that the rapid evolution of WAGOs enables the exceptional functional plasticity of nematodes, including their capacity for parasitism

Comments on the Sanef media audit: a new news culture is facing the media and journalism educators: the time to act is now!

This omnibus article deals with some of the comments received by the authors of the Sanef media audit (see p. 11) of the edition of Ecquid Novi). As Mark Deuze, one of the commentators puts it: The threats and challenges to contemporary journalism have caused scholars, publics, journalists, and thus journalism educators, to reconsider their approaches, definitions, roles, and function in community and society. Widely recognized as the four main changes or challenges facing education programmes in journalism are: the multicultural society; the rise and establishment of infotainment genres; the convergence of existing and new media technologies (cf. multimedia); and the internationalization or ‘glocalization’ of the media and journalism playing field. The four mentioned challenges and developments could be seen as reflected in the 2002 Sanef audit. The report particularly stresses the ‘new culture’ within which journalists are expected to do their work. This is a culture determined by fragmented audiences; a widening gap between journalists and their publics; and an increased need for quality information. It is also a culture of enhanced interactivity and media accountability; intercultural communication; recognition of cultural diversity; and dealing with ‘nonhierarchical’ management styles. Journalism education, in other words, is gearing up to face a tough challenge: keeping the best practices of the teaching context and practical skills courses on the one hand, and including cultural and critical reflective didactics on the other. This is not the traditional theory versus skills debate of old—this is definitely something ‘new’—as is clearly shown in the Sanef audit. In this respect the Sanef audit stands out for its discourse of emphasizing changes in journalism and news culture, rather than simply advocating more or less theory- or skills-based curricula

Ternary structure reveals mechanism of a membrane diacylglycerol kinase

Diacylglycerol kinase catalyses the ATP-dependent conversion of diacylglycerol to phosphatidic acid in the plasma membrane of Escherichia coli. The small size of this integral membrane trimer, which has 121 residues per subunit, means that available protein must be used economically to craft three catalytic and substrate-binding sites centred about the membrane/cytosol interface. How nature has accomplished this extraordinary feat is revealed here in a crystal structure of the kinase captured as a ternary complex with bound lipid substrate and an ATP analogue. Residues, identified as essential for activity by mutagenesis, decorate the active site and are rationalized by the ternary structure. The g-phosphate of the ATP analogue is positioned for direct transfer to the primary hydroxyl of the lipid whose acyl chain is in the membrane. A catalytic mechanism for this unique enzyme is proposed. The active site architecture shows clear evidence of having arisen by convergen

Novel Avian Influenza H7N3 Strain Outbreak, British Columbia

Genome sequences of chicken (low pathogenic avian influenza [LPAI] and highly pathogenic avian influenza [HPAI]) and human isolates from a 2004 outbreak of H7N3 avian influenza in Canada showed a novel insertion in the HA0 cleavage site of the human and HPAI isolate. This insertion likely occurred by recombination between the hemagglutination and matrix genes in the LPAI virus

The Mechanical Analysis and Interpretation of the EDZ Formation around Deep Tunnels within Massive Rockmasses Using a Hybrid Finite-Discrete Element Approach: The case of the AECL URL Test Tunnel

The construction of an underground opening leads to changes in the in situ stress regime surrounding the excavation. The opening influences the rockmass due to the redistribution of the stresses and results in the disturbance of the surrounding ground. At great depths, massive to relatively slightly or moderately fractured rockmasses are usually encountered and under high stresses they are more likely to behave in a brittle manner during an excavation. While constitutive models have been developed and proposed for the numerical simulation of such excavations using continuum mechanics, this brittle response cannot be simulated accurately enough since the material behaviour is governed by fracture initiation and propagation. On the contrary, discontinuum approaches are more suitable in such cases. For the purposes of this paper, the brittle behaviour of hard, massive rockmasses and the associated spalling failure mechanisms were simulated by employing a Finite Element Method/Discrete Element Method (FDEM) approach using the Irazu software. The generated numerical model was utilized in order to replicate field conditions based on the observations at the AECL-URL Test Tunnel located in Pinawa, Manitoba, Canada. The model results are compared to field observation data in order to explicitly demonstrate the suitability of the method.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Tunnel support for stress induced failures in Hawkesbury Sandstone

Underlying much of Sydney, Australia is a composite rock formation known as the Hawkesbury Sandstone. This unit is composed of clastic layers of variable competency including a number of thick and strong layers. The presence of very high horizontal stresses within these layers is widely accepted. Deep excavations such as basements or open cuts in Hawkesbury Sandstone often experience moderate horizontal movements in excess of 1 mm per metre of rock excavation. These movements can result in various scales of damage and excess loads on supporting elements. Stress induced failures in tunnels and underground excavations have also been observed in a number of projects and include crushing, spalling and or slabbing of intact rock blocks or shear failures associated with planes of weakness. While most design approaches in ground engineering account for shear failure mechanisms, the assessment of brittle failure is less common and less well understood. Conventional models and failure criteria do not appropriately describe such behaviour and consequently the impacts on ground support may not always be appropriately addressed. This paper presents some discussions on the modelling and assessment of brittle failure in Hawkesbury Sandstone and some of the impacts of high in-situ stresses on tunnel support design