Long pulse excitation thermographic non-destructive evaluation

A comprehensive analysis of the defect detection performance of long pulse excitation thermographic NDE is presented. An analytical procedure for predicting the thermal image contrasts of defects of specified size and depth is developed and validated by extensive experimental studies of test pieces having a wide range of thermal properties. Results obtained using long pulse (~5 s) excitation are compared with those obtained using traditional flash excitation. The conditions necessary for the success of the long pulse method are explained and illustrated by both modelling and experimental results. Practical advantages of long pulse excitation are discussed

Nonlinear imaging of damage in composite structures using sparse ultrasonic sensor arrays

In different engineering fields, there is a strong demand for diagnostic methods able to provide detailed information on material defects. Low velocity impact damage can considerably degrade the integrity of structural components and, if not detected, can result in catastrophic failures. This paper presents a nonlinear structural health monitoring imaging method, based on nonlinear elastic wave spectroscopy, for the detection and localisation of nonlinear signatures on a damaged composite structure. The proposed technique relies on the bispectral analysis of ultrasonic waveforms originated by a harmonic excitation and it allows for the evaluation of second order material nonlinearities due to the presence of cracks and delaminations. This nonlinear imaging technique was combined with a radial basis function approach in order to achieve an effective visualisation of the damage over the panel using only a limited number of acquisition points. The robustness of bispectral analysis was experimentally demonstrated on a damaged carbon fibre reinforced plastic (CFRP) composite panel, and the nonlinear source’s location was obtained with a high level of accuracy. Unlike other ultrasonic imaging methods for damage detection, this methodology does not require any baseline with the undamaged structure for the evaluation of the defect, nor a priori knowledge of the mechanical properties of the specimen

Nonlinear imaging of damage in composite structures using sparse ultrasonic sensor arrays

In different engineering fields, there is a strong demand for diagnostic methods able to provide detailed information on material defects. Low velocity impact damage can considerably degrade the integrity of structural components and, if not detected, can result in catastrophic failures. This paper presents a nonlinear structural health monitoring imaging method, based on nonlinear elastic wave spectroscopy, for the detection and localisation of nonlinear signatures on a damaged composite structure. The proposed technique relies on the bispectral analysis of ultrasonic waveforms originated by a harmonic excitation and it allows for the evaluation of second order material nonlinearities due to the presence of cracks and delaminations. This nonlinear imaging technique was combined with a radial basis function approach in order to achieve an effective visualisation of the damage over the panel using only a limited number of acquisition points. The robustness of bispectral analysis was experimentally demonstrated on a damaged carbon fibre reinforced plastic (CFRP) composite panel, and the nonlinear source’s location was obtained with a high level of accuracy. Unlike other ultrasonic imaging methods for damage detection, this methodology does not require any baseline with the undamaged structure for the evaluation of the defect, nor a priori knowledge of the mechanical properties of the specimen

Long pulse excitation thermographic non-destructive evaluation

A comprehensive analysis of the defect detection performance of long pulse excitation thermographic NDE is presented. An analytical procedure for predicting the thermal image contrasts of defects of specified size and depth is developed and validated by extensive experimental studies of test pieces having a wide range of thermal properties. Results obtained using long pulse (~5 s) excitation are compared with those obtained using traditional flash excitation. The conditions necessary for the success of the long pulse method are explained and illustrated by both modelling and experimental results. Practical advantages of long pulse excitation are discussed

Segue 2: A Prototype of the Population of Satellites of Satellites

We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope. From this, we derive a luminosity of M_v = -2.5, a half-light radius of 34 pc and a systemic velocity of -40$ km/s. Our MMT data also provides evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighboring fields. We resolve the velocity dispersion of Segue 2 as 3.4 km/s and the possible stream as about 7 km/s. This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites -- survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts z > 10 and are good candidates for fossils of the reionization epoch.Comment: MNRAS, Submitte

Blood pressure variability and cardiovascular risk in the PROspective study of pravastatin in the elderly at risk (PROSPER)

Variability in blood pressure predicts cardiovascular disease in young- and middle-aged subjects, but relevant data for older individuals are sparse. We analysed data from the PROspective Study of Pravastatin in the Elderly at Risk (PROSPER) study of 5804 participants aged 70–82 years with a history of, or risk factors for cardiovascular disease. Visit-to-visit variability in blood pressure (standard deviation) was determined using a minimum of five measurements over 1 year; an inception cohort of 4819 subjects had subsequent in-trial 3 years follow-up; longer-term follow-up (mean 7.1 years) was available for 1808 subjects. Higher systolic blood pressure variability independently predicted long-term follow-up vascular and total mortality (hazard ratio per 5 mmHg increase in standard deviation of systolic blood pressure = 1.2, 95% confidence interval 1.1–1.4; hazard ratio 1.1, 95% confidence interval 1.1–1.2, respectively). Variability in diastolic blood pressure associated with increased risk for coronary events (hazard ratio 1.5, 95% confidence interval 1.2–1.8 for each 5 mmHg increase), heart failure hospitalisation (hazard ratio 1.4, 95% confidence interval 1.1–1.8) and vascular (hazard ratio 1.4, 95% confidence interval 1.1–1.7) and total mortality (hazard ratio 1.3, 95% confidence interval 1.1–1.5), all in long-term follow-up. Pulse pressure variability was associated with increased stroke risk (hazard ratio 1.2, 95% confidence interval 1.0–1.4 for each 5 mmHg increase), vascular mortality (hazard ratio 1.2, 95% confidence interval 1.0–1.3) and total mortality (hazard ratio 1.1, 95% confidence interval 1.0–1.2), all in long-term follow-up. All associations were independent of respective mean blood pressure levels, age, gender, in-trial treatment group (pravastatin or placebo) and prior vascular disease and cardiovascular disease risk factors. Our observations suggest variability in diastolic blood pressure is more strongly associated with vascular or total mortality than is systolic pressure variability in older high-risk subjects

Long-range chemical sensitivity in the sulfur K-edge X-ray absorption spectra of substituted thiophenes

© 2014 American Chemical Society. Thiophenes are the simplest aromatic sulfur-containing compounds and are stable and widespread in fossil fuels. Regulation of sulfur levels in fuels and emissions has become and continues to be ever more stringent as part of governments' efforts to address negative environmental impacts of sulfur dioxide. In turn, more effective removal methods are continually being sought. In a chemical sense, thiophenes are somewhat obdurate and hence their removal from fossil fuels poses problems for the industrial chemist. Sulfur K-edge X-ray absorption spectroscopy provides key information on thiophenic components in fuels. Here we present a systematic study of the spectroscopic sensitivity to chemical modifications of the thiophene system. We conclude that while the utility of sulfur K-edge X-ray absorption spectra in understanding the chemical composition of sulfur-containing fossil fuels has already been demonstrated, care must be exercised in interpreting these spectra because the assumption of an invariant spectrum for thiophenic forms may not always be valid

POSIWID and determinism in design for behaviour change

Copyright @ 2012 Social Services Research GroupWhen designing to influence behaviour for social or environmental benefit, does designers' intent matter? Or are the effects on behaviour more important, regardless of the intent involved? This brief paper explores -- in the context of design for behaviour change -- some treatments of design, intentionality, purpose and responsibility from a variety of fields, including Stafford Beer's "The purpose of a system is what it does" and Maurice Broady's perspective on determinism. The paper attempts to extract useful implications for designers working on behaviour-related problems, in terms of analytical or reflective questions to ask during the design process