1,720,966 research outputs found
Mapping Britain's underworld. BBC Radio 4, May 25th 2012
No full textFour million holes are dug every year in the UK. Five billion pounds are lost through the economic effects of disruption and traffic hold ups, while hitting a utility pipe or cable can prove fatal for those working on the road. Adam Hart-Davis reports on a major research project which is trying to solve the problems.He takes us underground from his ancient ice house at the bottom of his Devon garden to report on Mapping the Underworld, the £3.5m programme involving universities throughout Britain. The aim is to improve how we locate the increasingly confusing and complex array of pipes, cables and sewers beneath our streets, and assess their condition - as well as ultimately providing a better map of what is beneath our cities to improve planning both above and below ground.At the moment it's often difficult to know where such utilities are - an estimated one in four of all holes are dug in the wrong place. Maps may not be accurate because original records of where the pipes and cables are located often use reference points on the surface which have long since gone.Existing sensors may have problems finding what is underground because of soil or weather conditions, while modern materials such as plastic or fibre optics pose a challenge to existing technologies.Adam Hart-Davis tries out the prototype of a multi-sensor cart where four different sensors operate together to produce an all-in-one solution, so if one technology doesn't work well in certain conditions and with particular materials, another one will. It is not an easy undertaking for the research teams or, as it turns out, for Adam testing the multi-sensor cart
Tree root detection from ground surface vibration measurements
No full textRapid development of urban infrastructure in past decades together with a relatively recent growth of awareness of its impact on the natural environment result in an increased interest in non-destructive ground interrogation methods. Tree root damage is a very well known issue in civil engineering and can emerge as road surface fracture, building foundations disintegration or pipe penetration, among others. In this paper we investigate the feasibility of using a vibroacoustic method for tree root mapping. The core of the idea is that the mechanical waves induced by an excitation mechanism acting on the tree trunk propagate to the roots and then radiate into the surrounding soil. Owing to that, the response measured at the ground surface contains the contribution of waves radiating from roots and can be used for mapping their extent. In this paper, we report a set of field experiments on a 'purpose-built' root-trunk model buried underground. These preliminary results both demonstrate the technique and shed light on related challenges and limitations.</p
Improving acoustic methods of pipeline leak location with distributed sensing
No full textLeaks in water distribution mains are a big problem, with around 20% of supplied potable water lost to leaks during transport. Correlation-based acoustic techniques have provided an accurate and non-invasive way of detecting and locating these leaks for a few decades. These methods have almost exclusively been using two sensors, and so this paper presents work aiming to explore leak detection and location with multiple sensors distributed along a pipe. Beamforming is a well-established method for using arrays of sensors to locate sources, among other purposes. With this premise, the present work adopts an array processing algorithm (MUSIC) in the context of water leak detection, intending to develop a framework for detecting multiple leaks using a sensor array. The concept, processing and implementation details are first supported with numerical simulations using existing acoustic models of water pipes. Then, experiments are presented on a short section of water-filled pipe with leak-like disturbances. These are captured with an array of accelerometers and processed using an implementation of the algorithm, testing the impact of real-world effects studied in simulations. The study considers several aspects of practical interest: (i) the effect of noise, both correlated and uncorrelated; (ii) the effect of reflections from discontinuities, such as pipe fittings and connections; (iii) the number and the distribution of sensors; as well as (iv) the presence of multiple leaks. The results pave the way for implementing this algorithm on practical installation designs, including the rod method developed during a wider research project associated with this study
Wavelet-based and data-adaptive methods for time delay estimation in acoustic leak detection
No full textLeakages in water distribution networks are a common issue encountered in the water industry. The acoustic cross-correlation method is generally employed for detecting and locating leaks in water pipes. One important factor that determines the effectiveness of this method is the accuracy of the time delay estimate which is usually obtained from the cross-correlation function (CCF) of two signals measured on the pipe. However, in some practical situations, accurate time delay estimate cannot be obtained using existing correlation-based time delay estimation (TDE) methods without first filtering the signals prior to calculating the CCF. Incorrect choice of filter cut-off frequencies limits the effectiveness of these methods. To deal with this issue, this paper proposes a scheme based on multi-resolution decomposition for accurately estimating time delays between leak signals. The proposed scheme first decomposes the signals at different scales using a shift-invariant wavelet transform or data-adaptive decomposition and then determines the time delay from the decomposed signals. Simulation and experimental results demonstrate the higher effectiveness of the proposed method compared to the commonly used basic and generalised cross-correlation TDE methods
Limits for leak noise detection in gas pipes using cross correlation
No full textThe cross correlation method is widely used in leak detection and location for pipes. The model of the cross correlation function of the leak noise for water pipes has been established in an earlier study, while there is no such model for gas pipes. In this study, a model of the correlation function of the leak noise in gas pipes is developed. The characteristics of wave propagation in gas pipes, combined with the leak noise spectrum, are incorporated into the model to consider the effects of physical parameters, i.e., turbulence parameters, pipe parameters and flow parameters, on the cross correlation function. This model is capable of describing the main features of the correlation results in gas pipes. Moreover, the model gives an estimation of the detection limits of the leak noise in the absence of noise, which is crucial to the deployment of sensors in real gas pipelines. The findings of this study provide theoretical insight and experimental evidence for optimizing the cross correlation method when conducting leak detection and location in gas pipes
Acoustic leak localisation based on multipath identification
No full textThis paper proposes a method for estimating wave speed and locating leaks in water pipes using multipath identification techniques. The wave speed and leak location are determined simultaneously from the relative arrival times of reflections in acoustic leak signals. Two multipath identification techniques based on the autocorrelation function and power cepstrum are derived and analysed for identifying reflections. Results show that the power cepstral technique is more robust and accurate than the autocorrelation technique. Analysis of simulation and experimental data acquired on a leakage test rig demonstrates that the proposed method is effective for locating leaks, outperforming the commonly used cross-correlation method in some cases. A practical advantage of the proposed method is capability to locate leaks without a priori knowledge of the wave speed
Midlumbar lateral flexion stability measured in healthy volunteers by in vivo fluoroscopy
No full textStudy Design: prospective fluoroscopic and electromyographic study of coronal plane lumbar spine motion in healthy male volunteers.Objectives: assess the intervertebral motion profiles in healthy volunteers for symmetry, regularity, and neutral zone laxity during passive recumbent lateral bending motion.Summary of background data: previous continuous in vivo motion studies of the lumbar spine have mainly been limited to active, weight-bearing, flexion-extension (sagittal plane) motion. No data are available for passive lateral bending or to indicate the motion profiles when muscle activity is minimized.Methods: thirty asymptomatic male volunteers underwent video-fluoroscopy of their lumbar spines during passive, recumbent lumbar lateral bending through 80° using a motor-driven motion table. Approximately 120 consecutive images of segments L2–L5 were captured, and the position of each vertebra was tracked throughout the sequence using automated frame-to-frame registration. Reference intervals for intervertebral motion parameters were calculated. Surface electromyography recordings of erector spinae were obtained in a similar group of volunteers using the same protocol without fluoroscopy to determine to what extent the motion was completely passive.Results: correlations between intervertebral and lumbar motion were always positive in controls and asymmetry was less than 55% of intervertebral range. The upper reference interval for the slope of intervertebral rotation in the first 10° of trunk motion did not exceed 0.46 for any level. Muscle electrical activity during the motionwas very low. Examples from patient studies showed markedly different results.Conclusion: these results suggest that reference limits from asymptomatic data for coronal plane passive recumbent intervertebral motion may be a useful resource forinvestigating the relationship between symptoms of chronic (nonspecific) low back pain and biomechanics and in the clinical assessment of patients and interventionsthat target the passive holding elements of the spine. Data pooling from multiple studies would be necessary to establish a complete database<br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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