A case study on the seismic performance of earth dams

The seismic non-linear behaviour of earth dams is investigated by using a well-documented case study and employing advanced static and dynamic coupled-consolidation finite-element analysis. The static part of the analysis considers the layered construction, reservoir impoundment and consolidation, whereas the dynamic part considers the response of the dam to two earthquakes of different magnitude, duration and frequency content. The results of the analysis are compared with the recorded response of the dam and exhibit a generally good agreement. The effects of the narrow canyon geometry, the reservoir impoundment and the elasto-plastic soil behaviour on the seismic dam behaviour are investigated. Finally the implications of the adopted constitutive modelling assumptions on the predicted response are discussed

Outbreak detection algorithms for seasonal disease data: a case study using ross river virus disease

<p>Abstract</p> <p>Background</p> <p>Detection of outbreaks is an important part of disease surveillance. Although many algorithms have been designed for detecting outbreaks, few have been specifically assessed against diseases that have distinct seasonal incidence patterns, such as those caused by vector-borne pathogens.</p> <p>Methods</p> <p>We applied five previously reported outbreak detection algorithms to Ross River virus (RRV) disease data (1991-2007) for the four local government areas (LGAs) of Brisbane, Emerald, Redland and Townsville in Queensland, Australia. The methods used were the Early Aberration Reporting System (EARS) C1, C2 and C3 methods, negative binomial cusum (NBC), historical limits method (HLM), Poisson outbreak detection (POD) method and the purely temporal SaTScan analysis. Seasonally-adjusted variants of the NBC and SaTScan methods were developed. Some of the algorithms were applied using a range of parameter values, resulting in 17 variants of the five algorithms.</p> <p>Results</p> <p>The 9,188 RRV disease notifications that occurred in the four selected regions over the study period showed marked seasonality, which adversely affected the performance of some of the outbreak detection algorithms. Most of the methods examined were able to detect the same major events. The exception was the seasonally-adjusted NBC methods that detected an excess of short signals. The NBC, POD and temporal SaTScan algorithms were the only methods that consistently had high true positive rates and low false positive and false negative rates across the four study areas. The timeliness of outbreak signals generated by each method was also compared but there was no consistency across outbreaks and LGAs.</p> <p>Conclusions</p> <p>This study has highlighted several issues associated with applying outbreak detection algorithms to seasonal disease data. In lieu of a true gold standard, a quantitative comparison is difficult and caution should be taken when interpreting the true positives, false positives, sensitivity and specificity.</p

Experimental and numerical investigation on soft soil tunnels under impact loading condition

Background: Tunnels extend the use of underground space for special applications such as transportation, mine development and civil defense. These structures could become susceptible to severe dynamic loads such as traffic loads, pile driving, impact and blast loads. Methodology: In this context, the experiment and simulations were conducted on semi-cylindrical tunnels of dimensions 1.2 m length × ∅ 0.5 m center-to-center and 0.05 m lining thickness under impact loading. The drop height was kept at 3.0 m and the burial depths of the soil cushion were varied as 0, 0.05, 0.10 and 0.15 m to study the effect of the cushion layer under repeated impact load. The experimental results were obtained in terms of damage to the tunnel and displacements in the tunnel under repeated impacts. Results: It was observed that the impact resistance of tunnels increased significantly when the natural burial depth increased from 0.05 to 0.10 m. It was concluded that the tunnel with 0.15 m burial depth was able to resist up to nine impacts as compared to the tunnel without cushion which offered resistance against two impact only. The numerical investigations were performed for each tunnel under repeated impacts using ABAQUS/Explicit. The numerical results were found to be in good agreement with the experimental results in terms of strain in rebar and mid displacement. The parametric study was performed for the influence of mass and velocity of the impactor in terms of crack pattern, impact force, displacement and energy absorption capacity in the tunnel. On increasing the mass of the impactor from 150 (4.41 kJ) to 400 kg (11.77 kJ), the energy absorption capacity was found to increase from 7.8% to 48.7%; however, on increasing the height of drop from 5 (5.1 kJ) to 20 m (20.40 kJ), the energy absorption capacity of the tunnel was increased from 8.1 to 48.6%. Conclusions: It was concluded that under the low-velocity impact, energy absorption in the tunnel is more sensitive to the mass of the impactor as compared to drop height. It was observed that Yang Qixin's algorithm was the best predicting algorithm among others when comparing peak impact force with the numerical result.</p

Distribué fibre optique des infrastructures du CERN dans la région des molasse

The European Centre for Nuclear Research (CERN) is a large underground laboratory and it is home to two large particle accelerators, including the «Large Hadron Collider» (LHC). The particles travel at the speed of light through a series of tunnels which must comply with the high serviceability requirements. However, the underground facilities have expanded over a period of 40 years with new tunnels, shafts and caverns. Structural ageing and deterioration of the infrastructure can alter the drainage conditions around tunnels and this can cause, in turn, excess deformation of the tunnels and serviceability issue for the particle accelerators. A remote monitoring system based on distributed fibre-optic strain sensing technology has been implemented in some of the concrete-lined tunnels in order to gain insight in the long-term mechanical behaviour of the underground system. This paper presents the results of the monitoring programme and the results show a slow development of ovalisation of the tunnel over a period of three years.Le Centre Européen pour la Recherche Nucléaire (CERN) est un grand laboratoire souterrain qui héberge deux accélérateurs de particules dont le « Large Hadron Collider » (LHC). Les particules se déplacent à la vitesse de la lumière à travers un réseau de tunnels qui doivent répondre à des exigences élevées de service. L’infrastructure souterraine du CERN s’est étendue sur une période de 40 ans avec la construction de nouveaux tunnels, puits et cavernes. Le vieillissement des matériaux et la détérioration structurelles des ouvrages peuvent altérer les conditions de drainage autour des tunnels ce qui peut engendrer, à son tour, des déformations excessives et atteindre la limite de service des accélérateurs de particules. Un système de monitoring à distance avec des câbles en fibre optique a été mis en place dans certains tunnels afin d’étudier le comportement à long terme. Cet article présente les résultats de la compagne de monitoring et démontre une ovalisation des tunnels sur une période de trois ans

Monitoring bridge degradation using dynamic strain, acoustic emission and environmental data

This paper studies the long term structural behaviour of a Victorian railway viaduct under train loading and temperature variation. A multi-sensing, self-sustaining and remotely controlled data acquisition system combines fibre Bragg grating strain sensors with acoustic emission sensors for the study of both global dynamic deformation and local masonry deterioration. A statistical analysis of fibre Bragg grating signals reveals regions with permanent change in the dynamic deformation of the bridge over the last two years, whereas in other locations the deformation follows a seasonal cyclic pattern. In order to decouple changes in structural behaviour due to real mechanical damage from normal seasonal effect, the paper studies the ambient temperature effect on the dynamic deformation of the bridge, showing a clear linear dependence. In particular, when temperature increases, the dynamic strain due to train loading decreases uniformly in the longitudinal direction. In the transverse direction, where the thermal expansion is not constrained, the decrease is smaller. Decoupling damage from normal seasonal effect is of critical importance for the development of reliable early warning structural alert systems for infrastructure networks. The paper further studies local masonry deterioration at four critical location by combining data from the two sensing technologies: fibre optic and acoustic emission sensors.This work is being funded by the Lloyd’s Register Foundation, EPSRC and Innovate UK through the Data-Centric Engineering programme of the Alan Turing Institute and through the Cambridge Centre for Smart Infrastructure and Construction. Funding for the monitoring installation was provided by EPSRC under the Ref. EP/N021614/1 grant and by Innovate UK under the Ref. 920035 grant

Identification of optimal epitopes for Plasmodium falciparum rapid diagnostic tests that target histidine-rich proteins 2 and 3

Rapid diagnostic tests (RDTs) represent important tools to diagnose malaria infection. To improve understanding of the variable performance of RDTs that detect the major target in Plasmodium falciparum, namely, histidine-rich protein 2 (HRP2), and to inform the design of better tests, we undertook detailed mapping of the epitopes recognized by eight HRP-specific monoclonal antibodies (MAbs). To investigate the geographic skewing of this polymorphic protein, we analyzed the distribution of these epitopes in parasites from geographically diverse areas. To identify an ideal amino acid motif for a MAb to target in HRP2 and in the related protein HRP3, we used a purpose-designed script to perform bioinformatic analysis of 448 distinct gene sequences from pfhrp2 and from 99 sequences from the closely related gene pfhrp3. The frequency and distribution of these motifs were also compared to the MAb epitopes. Heat stability testing of MAbs immobilized on nitrocellulose membranes was also performed. Results of these experiments enabled the identification of MAbs with the most desirable characteristics for inclusion in RDTs, including copy number and coverage of target epitopes, geographic skewing, heat stability, and match with the most abundant amino acid motifs identified. This study therefore informs the selection of MAbs to include in malaria RDTs as well as in the generation of improved MAbs that should improve the performance of HRP-detecting malaria RDTs. Copyright © 2012, American Society for Microbiology

Distributed fiber optic sensing of axially loaded bored piles

Instrumented pile tests are vital to establish the performance of a pile and validate the assumptions made during initial design. Conventional instrumentation includes vibrating wire strain gauges and extensometers to measure the change in strain or displacements within a pile. Although these strain and displacement gauges are very accurate, they only provide strain/displacement readings at discrete locations at which they are installed. It is therefore common to interpolate between two consecutive points to obtain values corresponding to the data gaps between points; in practice, these discrete instrumented points could be tens of meters apart, at depths corresponding to different soil layers, and hence simple interpolation between the measurement points remains questionable. The Brillouin optical time-domain reflectometry fiber optic strain sensing system is able to provide distributed strain sensing along the entire length of the cable, enabling the full strain profile to be measured during a maintained pile load test. The strain data can also be integrated to obtain the displacement profile. This paper presents three case studies which investigate the performance of three concrete bored piles in London using both conventional vibrating wire strain gauges and distributed fiber optic strain sensing during maintained pile load tests, which enable comparisons made between the two instrumentation systems. In addition, finite-element analyses show that the ability to measure the full strain profiles for each pile is highly advantageous in understanding the performance of the pile and in detecting any abnormalities in the pile behavior.This research was conducted within the Centre for Smart Infrastructure and Construction (CSIC) of the University of Cambridge, funded by EPSRC and Innovate U.K

Dengue disease outbreak definitions are implicitly variable.

Infectious diseases rarely exhibit simple dynamics. Outbreaks (defined as excess cases beyond response capabilities) have the potential to cause a disproportionately high burden due to overwhelming health care systems. The recommendations of international policy guidelines and research agendas are based on a perceived standardised definition of an outbreak characterised by a prolonged, high-caseload, extra-seasonal surge. In this analysis we apply multiple candidate outbreak definitions to reported dengue case data from Brazil to test this assumption. The methods identify highly heterogeneous outbreak characteristics in terms of frequency, duration and case burden. All definitions identify outbreaks with characteristics that vary over time and space. Further, definitions differ in their timeliness of outbreak onset, and thus may be more or less suitable for early intervention. This raises concerns about the application of current outbreak guidelines for early warning/identification systems. It is clear that quantitatively defining the characteristics of an outbreak is an essential prerequisite for effective reactive response. More work is needed so that definitions of disease outbreaks can take into account the baseline capacities of treatment, surveillance and control. This is essential if outbreak guidelines are to be effective and generalisable across a range of epidemiologically different settings