Shear localization as a mesoscopic stress-relaxation mechanism in fused silica glass at high strain rates

Molecular dynamics (MD) simulations of fused silica glass deforming in pressure-shear, while revealing useful insights into processes unfolding at the atomic level, fail spectacularly in that they grossly overestimate the magnitude of the stresses relative to those observed, e. g., in plate-impact experiments. We interpret this gap as evidence of relaxation mechanisms that operate at mesoscopic lengthscales and which, therefore, are not taken into account in atomic-level calculations. We specifically hypothesize that the dominant mesoscopic relaxation mechanism is shear banding. We evaluate this hypothesis by first generating MD data over the relevant range of temperature and strain rate and then carrying out continuum shear-banding calculations in a plate-impact configuration using a critical-state plasticity model fitted to the MD data. The main outcome of the analysis is a knock-down factor due to shear banding that effectively brings the predicted level of stress into alignment with experimental observation, thus resolving the predictive gap of MD calculations

Spin Physics at COMPASS

The COMPASS experiment is a fixed target experiment at the CERN SPS using muon and hadron beams for the investigation of the spin structure of the nucleon and hadron spectroscopy. The main objective of the muon physics program is the study of the spin of the nucleon in terms of its constituents, quarks and gluons. COMPASS has accumulated data during 6 years scattering polarized muons off a longitudinally or a transversely polarized deuteron (6LiD) or proton (NH3) target. Results for the gluon polarization are obtained from longitudinal double spin cross section asymmetries using two different channels, open charm production and high transverse momentum hadron pairs, both proceeding through the photon-gluon fusion process. Also, the longitudinal spin structure functions of the proton and the deuteron were measured in parallel as well as the helicity distributions for the three lightest quark flavors. With a transversely polarized target, results were obtained with proton and deuteron targets for the Collins and Sivers asymmetries for charged hadrons as well as for identified kaons and pions. The Collins asymmetry is sensitive to the transverse spin structure of the nucleon, while the Sivers asymmetry reflects correlations between the quark transverse momentum and the nucleon spin. Recently, a new proposal for the COMPASS II experiment was accepted by the CERN SPS which includes two new topics: Exclusive reactions like DVCS and DVMP using the muon beam and a hydrogen target to study generalized parton distributions and Drell-Yan measurements using a pion beam and a polarized NH3 target to study transverse momentum dependent distributions.Comment: Proceedings of the Rutherford conference, Manchester, August 2011. Changes due to referees comments implemente

Possible natural fluid pathways from gravity pseudo-tomography in the geothermal fields of Northern Alsace (Upper Rhine Graben)

Background This study aims on investigating the regional flow field of the Soultz and adjacent geothermal fields located on the western side of the central Upper Rhine Graben and thus to provide insight into the origin of the 70% of the geothermal fluid coming from the regional inflow in the deep reservoir of the Soultz site. In an integrative approach, we consolidate conceptual models on fluid flow in the central Upper Rhine Graben. Methods Based on a 3D geological model and a new 3D temperature interpolation, we tackle the relation between tectonic structures and the occurrence of advection/convection along favourably oriented fault zones. Using sequential Butterworth filters, we study the distribution of negative residual anomalies in a pseudo-tomography down to a depth of about 6 to 8 km. Results We derived N-S-striking V-shaped negative anomalies that are consistent with the orientation of fault zones revealing major temperature anomalies to their east. Conclusions Following the concept of negative anomalies revealing zones of increased fracture porosity, and in agreement with fluid-chemistry, our findings suggest infiltration of meteoric water through the graben boundary fault and along preferential flow pathways that merge at intermediate depth. Up-flow of thermal water mixed most likely with brine from the deeper eastern part of the graben occurs along W-dipping typically rather steep structures

Shear localization as a mesoscopic stress-relaxation mechanism in fused silica glass at high strain rates

Molecular dynamics (MD) simulations of fused silica glass deforming in pressure-shear, while revealing useful insights into processes unfolding at the atomic level, fail spectacularly in that they grossly overestimate the magnitude of the stresses relative to those observed, e. g., in plate-impact experiments. We interpret this gap as evidence of relaxation mechanisms that operate at mesoscopic lengthscales and which, therefore, are not taken into account in atomic-level calculations. We specifically hypothesize that the dominant mesoscopic relaxation mechanism is shear banding. We evaluate this hypothesis by first generating MD data over the relevant range of temperature and strain rate and then carrying out continuum shear-banding calculations in a plate-impact configuration using a critical-state plasticity model fitted to the MD data. The main outcome of the analysis is a knock-down factor due to shear banding that effectively brings the predicted level of stress into alignment with experimental observation, thus resolving the predictive gap of MD calculations

Perceptual and conceptual sources of priming on a word generation task

Repetition of any number of cognitive processes can facilitate subsequent performance (i.e., repetition priming). In this study, we explored several candidate mechanisms that could account for repetition priming on a word generation task. In Experiment 1, we examined whether repetition of semantic processing is necessary for priming on this task. In Experiment 2, we examined whether repetition of semantic processing is sufficient for priming on this task. In both experiments, we additionally examined the effect of changing the specific nature of the semantic retrieval task (i.e., from visual to functional, and vice versa) on performance. The results from these experiments indicated that repetition of semantic processing is both necessary and sufficient to produce a facilitation effect on the word generation task. However, semantic processing of the same attribute does not need to be repeated for facilitation effects to occur. Implications of these findings for theories of the representation and retrieval of semantic knowledge are discussed

Case 12 : Prioritizing Emerging and Re-Emerging Non-enteric Zoonotic Infectious Diseases: What Should we be Afraid of Next?

As time progresses, new zoonoses make their way to the forefront in the media, in healthcare systems, in government projects, and in the daily lives of Canadians. Prioritization exercises carried out by public health experts can provide an indication for which zoonoses we should be most afraid of next, and ultimately most prepared for, especially in light of impeding changes in climate. Blake O’Neil and Brock Jansen have recently transitioned to new positions with the Health Professionals Guidance Unit at the Centre for Food-borne, Environmental, and Zoonotic Infectious Diseases. Together, they plan to develop health professional guidance documents and tools to aid in the prevention, early diagnosis, and clinical management of various emerging and re-emerging non-enteric zoonotic infectious diseases. To maintain efficiency when creating guidance documents and tools, Blake and Brock have commenced a prioritization exercise to determine which emerging and re-emerging non-enteric zoonotic infectious diseases are of the greatest threat to the health of Canadians as a result of climate change. To date, Blake and Brock have reviewed previously conducted internal and external prioritization exercises; received consultation from the National Microbiology Lab in Winnipeg, Manitoba; undertaken a literature review to explore zoonoses relevant to the Canadian context; and organized an advisory committee composed of external stakeholders from various healthrelated specialties. With the results from the literature review and the input from various stakeholder organizations, Blake and Brock have developed a list of zoonoses to be included in the prioritization exercise. The upcoming federal election tenders a very constrained timeframe for Blake and Brock, specifically for engaging with stakeholders external to the Public Health Agency of Canada. As public servants, Blake and Brock need to ensure government resources are not used for partisan advantage. Therefore, any stakeholder engagement would need to be paused when electoral campaigning begins until a Prime Minister is elected and the Senate and House of Commons resume. Furthermore, prior to the federal election, Blake and Brock must produce a list of priority emerging and re-emerging non-enteric zoonotic infectious diseases so they can begin developing health professional guidance documents and tools. The pair has only been able to identify two prioritization criteria thus far: measuring the number of incident cases within Canada for each zoonosis and measuring the severity of illness associated with each zoonosis. However, because severity of illness is relatively challenging to define, the pair continues to search for a unit of analysis that adequately represents the criterion. In addition, they must tailor the incidence formula to sufficiently capture the status of the zoonoses in Canada. Blake and Brock are now at a standstill in terms of identifying three additional prioritization criteria, defining what each criterion entails, and how each criterion will be measured

Conceptual Representations of Action in the Lateral Temporal Cortex

Retrieval of conceptual information from action pictures causes greater activation than from object pictures bilaterally in human motion areas (MT/MST) and nearby temporal regions. By contrast, retrieval of conceptual information from action words causes greater activation in left middle and superior temporal gyri, anterior and dorsal to the MT/MST. We performed two fMRI experiments to replicate and extend these findings regarding action words. In the first experiment, subjects performed conceptual judgments of action and object words under conditions that stressed visual semantic information. Under these conditions, action words again activated posterior temporal regions close to, but not identical with, the MT/MST. In the second experiment, we included conceptual judgments of manipulable object words in addition to judgments of action and animal words. Both action and manipulable object judgments caused greater activity than animal judgments in the posterior middle temporal gyrus. Both of these experiments support the hypothesis that middle temporal gyrus activation is related to accessing conceptual information about motion attributes, rather than alternative accounts on the basis of lexical or grammatical factors. Furthermore, these experiments provide additional support for the notion of a concrete to abstract gradient of motion representations with the lateral occipitotemporal cortex, extending anterior and dorsal from the MT/MST towards the peri-sylvian cortex