Remote-scope Promotion: Clarified, Rectified, and Verified

Modern accelerator programming frameworks, such as OpenCL, organise threads into work-groups. Remote-scope promotion (RSP) is a language extension recently proposed by AMD researchers that is designed to enable applications, for the first time, both to optimise for the common case of intra-work-group communication (using memory scopes to provide consistency only within a work-group) and to allow occasional inter-work-group communication (as required, for instance, to support the popular load-balancing idiom of work stealing). We present the first formal, axiomatic memory model of OpenCL extended with RSP. We have extended the Herd memory model simulator with support for OpenCL kernels that exploit RSP, and used it to discover bugs in several litmus tests and a work-stealing queue, that have been used previously in the study of RSP. We have also formalised the proposed GPU implementation of RSP. The formalisation process allowed us to identify bugs in the description of RSP that could result in well-synchronised programs experiencing memory inconsistencies. We present and prove sound a new implementation of RSP that incorporates bug fixes and requires less non-standard hardware than the original implementation. This work, a collaboration between academia and industry, clearly demonstrates how, when designing hardware support for a new concurrent language feature, the early application of formal tools and techniques can help to prevent errors, such as those we have found, from making it into silicon

Wavelet analysis on pressure stimulated currents emitted by marble samples

International audienceThis paper presents a wavelet based method of analysis of experimentally recorded weak electric signals from marble specimens which have undergone successive abrupt step loadings. Experimental results verify the existence of "memory effects" in rocks, as far as the current emission is concerned, akin to the "Kaiser effect" in acoustic emissions, which accompany rock fracturing. Macroscopic signal processing shows similarities and differences between the currents emitted during successive loading and wavelet analysis can reveal significant differences between the currents of each loading cycle that contain valuable information for the micro and macro cracks in the specimen as well as information for the remaining strength of the material. Wavelets make possible the time localization of the energy of the electric signal emitted by stressed specimens and can serve as method to differentiate between compressed and uncompressed samples, or to determine the deformation level of specimens

Variance reduction and signal-to-noise ratio: Reducing uncertainty in spectral ratios

This paper uses an unusually large dataset to study scatter in site-effect estimation, focusing on how the events that increase uncertainty can be removed from the dataset. Four hundred seventy-three weak motion earthquake records from the surface and bedrock of a 178-m-deep borehole in Aegion, Gulf of Corinth, Greece, are used to evaluate spectral ratios. A simple statistical tool, variance reduction (VR), is first used to identify two groups of events that lie closest and farthest from the average, which is considered here as the initial best estimate of the site response. The scatter in the original dataset is found to be due to the group of events with smallest VR. These events can be removed from the dataset in order to compute a more reliable site response. However, VR is not normally used to choose records for site-effect studies, and it cannot be applied to the usual small datasets available. The signal-to-noise ratio (SNR) is normally used to this end, for which reason we investigate whether SNR can be used to achieve similar results as VR. Signal-to-noise ratio is estimated using different definitions. Data selection based on SNR is then compared to that using VR in order to define an SNR-based criterion that discriminates against events that, according to VR, increase scatter. We find that defining the SNR of a surface record as the mean value over a frequency range around the resonant peak (here, 0.5–1.5 Hz) and using a cutoff value of 5 may be used in this case to exclude most events for which VR is small. This process is also applied to the downhole station, where we obtain similar results for a cutoff value of 3

Demography and disorders of German Shepherd Dogs under primary veterinarycare in the UK

The German Shepherd Dog (GSD) has been widely used for a variety of working roles. However, concerns for the health and welfare of the GSD have been widely aired and there is evidence that breed numbers are now in decline in the UK. Accurate demographic and disorder data could assist with breeding and clinical prioritisation. The VetCompassTM Programme collects clinical data on dogs under primary veterinary care in the UK. This study included all VetCompassTM dogs under veterinary care during 2013. Demographic, mortality and clinical diagnosis data on GSDs were extracted and reported

The wealth effects, mood and outcome of UK takeover bids: An empirical analysis using a simultaneous equations approach

The primary objective of this thesis is to investigate whether or not UK takeover bids create wealth gains for the shareholders of the companies involved and what determines the size of these gains. However, as previous empirical research has shown one of the factors influencing the creation of wealth is the mood of a bid, in other words if the bid is hostile or friendly. Due to the fact that previous empirical evidence also suggests the existence of an interdependence among wealth, mood and outcome of bids we develop a simultaneous equations model whereby we explore the determinants of these three factors. Thus, the other two goals of this thesis are to find what determines the mood and outcome of takeover bids. A large sample of 354 completed and failed takeover bids during the 1963-1989 period was initially used to generate the wealth gains measured in the form of abnormal returns and estimated by event study methodology. Then we used multiple regression analysis to test a range of hypotheses selected from the industrial economics and finance literature with respect to the main objectives of this thesis. The results obtained show first that target shareholders capture large gains, while bidder shareholders experience small losses around the period of bids announcement. This leads to a small increase of the value of the combined firm. Second, we detect that short run factors reflecting characteristics of the bid process, such as the mood, explain better the wealth created in takeovers than long term strategic factors. However, we find some evidence of managerial and financial synergies. Third, we find that the wealth and mood variables are mutually dependent on each other thereby justifying our simultaneous equations approach. Fourth, we discover that the agency problem exists on both target and bidder but its impact is mitigated by disciplinary bids. This finding gives some support for the argument that hostile bids reflect the disciplinary device that the market uses to correct managerial failure. Fifth, our results suggest that the mood, the level of managerial ownership in the target company and the size of bid premium are crucial in determining the outcome of bids

Assessment of groundwater pollution in relation to heavy metals of the alluvial aquifer of Thriasion Plain (NW Attica)

Στην παρούσα εργασία παρουσιάζονται τα υδρογεωλογικά και υδροχημικά χαρακτηριστικά της περιοχής του Θριάσιου Πεδίου, εστιάζοντας κυρίως στην παρουσία των βαρέων μετάλλων στα υπόγεια νερά του προσχωματικού υδροφορέα. Στην περιοχή εντοπίζονται δυο ευδιάκριτες μεταξύ τους υδροφορίες, η καρστική υδροφορία που αναπτύσσεται εντός των καρστικοποιημένων ανθρακικών σχηματισμών, οι οποίοι δομούν τα περιθώρια και το υπόβαθρο της προσχωματικής λεκάνης και η φρεάτια υδροφορία που αναπτύσσεται εντός των Τεταρτογενών αποθέσεων. Η άμεση επικοινωνία των υδροφόρων με τη θάλασσα έχει ως αποτέλεσμα την έντονη υφαλμύρωση τους. Η υδροχημική έρευνα έδειξε, υψηλά επίπεδα αλατότητας και σκληρότητας, υψηλές συγκεντρώσεις στα κύρια στοιχεία Na+, Cl-, SO4 2-, NO3 -, NH4 + και PO4 3- και στα βαρέα μέταλλα Cd, Cu, Fe, Mn, Ni, Pb, Sr και Zn, τα οποία αντικατοπτρίζουν τις ποικίλες γεωγενείς και ανθρωπογενείς επιδράσεις που υφίσταται ο εκμεταλλευόμενος υδροφορέας. Η άναρχη ανθρωπογενής δραστηριότητα που συντελείται στο Θριάσιο Πεδίο, σε συνδυασμό με την θαλάσσια διείσδυση, έχουν συμβάλλει στη συνεχή υποβάθμιση της ποιότητας των υπόγειων νερών με αποτέλεσμα το περιορισμό της δυνατότητας εκμετάλλευσης τους, όχι μόνον για την ανθρώπινη κατανάλωση αλλά και για πολλές άλλες χρήσεις.In this study the hydrogeological and hydrochemical characteristics of Thriasion Plain are presented focusing mainly on the presence of heavy metals in the alluvial aquifer. Two main aquifer systems exist in the study area: a) the karst aquifer hosted in the karstified carbonate formations, which structure the bedrock and the margins of the alluvial basin and b) the phreatic aquifer within the Quaternary deposits of the Thriasion Plain. Coastal and submarine groundwater discharges show the direct connection of the aquifers with the sea causing intense salinization in both aquifers. The phreatic aquifer is characterized by high levels of TDS (483 – 13,067 mg/l) and correspondingly high degree of hardness (15.7 to 165.7 odH). High concentrations of Na+, Cl-, SO4 2-, NO3 -, NH4 + and PO4 3- reflect the diverse anthropogenic influences on the aquifer. The strong presence of heavy metals, Cd, Cu, Fe, Mn, Ni, Pb, Sr and Zn has been determined in the most of the samples. Their origin is associated with geogenic factors, such as the occurrences of bauxites, oxides derived from the alteration of rocks, especially shischts, organic matter within the Plio-Pleistocene sediments of the region, as well as with intense pressures from anthropogenic activities. In some cases the groundwater is improper not only for human consumption but also for many other uses

Understanding single-station ground motion variability and uncertainty (sigma) – Lessons learnt from EUROSEISTEST

Accelerometric data from the well-studied valley EUROSEISTEST are used to investigate ground motion uncertainty and variability. We define a simple local ground motion prediction equation (GMPE) and investigate changes in standard deviation (σ) and its components, the between-event variability (τ) and within-event variability (φ). Improving seismological metadata significantly reduces τ (30-50%), which in turn reduces the total σ. Improving site information reduces the systematic site-to-site variability, φS2S (20-30%), in turn reducing φ, and ultimately, σ. Our values of standard deviations are lower than global values from literature, and closer to path-specific than site-specific values. However, our data have insufficient azimuthal coverage for single-path analysis. Certain stations have higher ground-motion variability, possibly due to topography, basin edge or downgoing wave effects. Sensitivity checks show that 3 recordings per event is a sufficient data selection criterion, however, one of the dataset’s advantages is the large number of recordings per station (9-90) that yields good site term estimates. We examine uncertainty components binning our data with magnitude from 0.01 to 2 s; at smaller magnitudes, τ decreases and φSS increases, possibly due to κ and source-site trade-offs Finally, we investigate the alternative approach of computing φSS using existing GMPEs instead of creating an ad hoc local GMPE. This is important where data are insufficient to create one, or when site-specific PSHA is performed. We show that global GMPEs may still capture φSS, provided that: 1. the magnitude scaling errors are accommodated by the event terms; 2. there are no distance scaling errors (use of a regionally applicable model). Site terms (φS2S) computed by different global GMPEs (using different site-proxies) vary significantly, especially for hard-rock sites. This indicates that GMPEs may be poorly constrained where they are sometimes most needed, i.e. for hard rock