This Letter reports a technique for the imaging of acoustic nonlinearity. By contrasting the energy of the diffuse field produced through the focusing of an ultrasonic array by delayed parallel ...element transmission with that produced by postprocessing of sequential transmission data, acoustic nonlinearity local to the focal point is measured. Spatially isolated wave distortion is inferred without requiring interrogation of the wave at the inspection point, thereby allowing nonlinear imaging through depth.
Multiple sclerosis is increasingly being recognized as a neurodegenerative disease that is triggered by inflammatory attack of the CNS. As yet there is no satisfactory treatment. Using experimental ...allergic encephalo myelitis (EAE), an animal model of multiple sclerosis, we demonstrate that the cannabinoid system is neuroprotective during EAE. Mice deficient in the cannabinoid receptor CB1 tolerate inflammatory and excito toxic insults poorly and develop substantial neurodegeneration following immune attack in EAE. In addition, exogenous CB1 agonists can provide significant neuroprotection from the consequences of inflammatory CNS disease in an experimental allergic uveitis model. Therefore, in addition to symptom management, cannabis may also slow the neurodegenerative processes that ultimately lead to chronic disability in multiple sclerosis and probably other diseases.
Ultrasonic phased arrays have produced major benefits in a range of fields, from medical imaging to non-destructive evaluation. The maximum information, which can be measured by an array, corresponds ...to the Full Matrix Capture (FMC) data acquisition technique and contains all possible combinations of transmitter–receiver signals. However, this method is not fast enough for some applications and can result in a very large volume of data. In this paper, the problem of optimal array data acquisition strategy is considered, that is, how to make the minimum number of array measurements without loss of information. The main result is that under the single scattering assumption the FMC dataset has a specific sparse structure, and this property can be used to design an optimal data acquisition method. An analytical relationship between the minimum number of array firings, maximum steering angle and signal-to-noise ratio is derived, and validated experimentally. An important conclusion is that the optimal number of emissions decreases when the angular aperture of the array increases. It is also shown that plane wave imaging data are equivalent to the FMC dataset, but requires up to an order of magnitude fewer array firings.
This article reports a technique for near-surface ultrasonic array imaging. Information equivalent to an undelayed full matrix of inter-element responses is produced through cross-correlation of a ...later time diffuse full matrix. This reconstructed full matrix lacks the nonlinear effects of early time saturation present in a directly acquired response. Consequently the near-surface material information usually obscured by this effect is retrieved. Furthermore it is shown that a hybrid full matrix formed through a temporally weighted sum of coherent and reconstructed matrices allows for effective near-surface and bulk material imaging from a single direct-contact experimental realisation.
Ultrasonic guided wave propagation in anisotropic attenuative materials like CFRP (carbon fibre reinforced polymer) is much more complicated than in isotropic materials. Propagation phenomena need to ...be understood and quantified before reliable NDE (Non-destructive Evaluation)/SHM (Structural Health Monitoring) inspection systems can be realized. The propagation characteristics: energy velocity, dispersion, mode coupling, energy focusing factor and attenuation are considered in this paper. Concepts of minimum resolvable distance and sensitivity maps are extended to anisotropic attenuative materials in order to provide the means for comparison of different guided wave modes in composite materials. The paper is intended to serve as a framework for evaluating and comparing different modes and choosing the optimum operating conditions (frequency, sensor layout) for possible NDE/SHM applications on composite materials. Fundamental guided wave modes in the low frequency regime for highly anisotropic CFRP plates are investigated experimentally and theoretically and the implications for NDE/SHM are discussed.
•Temperature response of guided wave propagation in CFRP materials was investigated.•Investigations focused on highly anisotropic CFRP materials.•Model for predicting subtraction performance in SHM ...on such materials was developed.•Results produced by the model generally agreed with experimental measurements.
Carbon Fibre Reinforced Polymer (CFRP) materials are lightweight and corrosion-resistant and therefore are increasingly used in aerospace, automotive and construction industries. In Structural Health Monitoring (SHM) applications of CFRP materials, ultrasonic guided waves potentially offer large area inspection or inspection from a remote location. This paper addresses the effect of temperature variation on guided wave propagation in highly anisotropic CFRP materials. Temperature variations cause changes in guided wave velocity that can in turn compromise the baseline subtraction procedures employed by many SHM systems for damage detection. A simple model that describes the dependence of elastic properties of the CFRP plates on temperature is presented in this paper. The model can be used to predict anisotropic velocity changes and baseline subtraction performance under varying thermal conditions. The results produced by the model for unidirectional and 0/90 CFRP plates are compared with experimental measurements.
This paper uses a simple separated flow model based on the classical work of
Davidson (1961) to describe the complex dynamics in bubbling fluidized beds. It shows that this application is robust and ...independent of geometry and gas flow conditions. The model successfully simulates the pressure measurements made in a bubbling fluidized bed and it is shown that the single measurement of pressure can be used to characterise the entire fluidized bed. The successful application of the Davidson model suggests that the flow field and hence pressure field in a bubbling fluidized bed is dominated by the size and location of voids, and once given this, particle–particle or complex particle–fluid interactions make a minor direct contribution to the pressure field.
Strategies for guided-wave structural health monitoring Croxford, A.J; Wilcox, P.D; Drinkwater, B.W ...
Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences,
11/2007, Letnik:
463, Številka:
2087
Journal Article
Recenzirano
Structural health monitoring (SHM) using guided waves is one of the only ways in which damage anywhere in a structure can be detected using a sparse array of permanently attached sensors. To ...distinguish damage from structural features, some form of comparison with damage-free reference data is essential, and here subtraction is considered. The detectability of damage is determined by the amplitude of residual signals from structural features remaining after the subtraction of reference data. These are non-zero due to changing environmental conditions such as temperature. In this paper, the amplitude of the residual signals is quantified for different guided-wave SHM strategies. Comparisons are made between two methods of reference signal subtraction and between two candidate sensor configurations. These studies allow estimates to be made of the number of sensors required per unit area to reliably detect a prescribed type of damage. It is shown that the number required is prohibitively high, even in the presence of modest temperature fluctuations, hence some form of temperature compensation is absolutely essential for guided-wave SHM systems to be viable. A potential solution is examined and shown to provide an improvement in signal suppression of approximately 30 dB, which corresponds to two orders of magnitude reduction in the number of sensors required.
Objectives
In recent years, new technologies and new approaches to scale up HIV testing have emerged. The objective of this paper was to synthesize the body of recent evidence on strategies aimed at ...increasing the uptake and coverage of HIV testing outside of health care settings in the European Union (EU)/European Economic Area (EEA).
Methods
Systematic searches to identify studies describing effective HIV testing interventions and barriers to testing were run in five databases (2010–2017) with no language restrictions; the grey literature was searched for similar unpublished studies (2014–2017). Study selection, data extraction and critical appraisal were performed by two independent reviewers following Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines.
Results
Eighty studies on HIV testing in non‐health care settings were identified, the majority set in Northern Europe. Testing was implemented in 65 studies, with men who have sex with men the risk group most often targeted. Testing coverage and positivity/reactivity rates varied widely by setting and population group. However, testing in community and outreach settings was effective at reaching people who had never previously been tested and acceptability of HIV testing, particularly rapid testing, outside of health care settings was found to be high. Other interventions aimed to increase HIV testing identified were: campaigns (n = 8), communication technologies (n = 2), education (n = 3) and community networking (n = 1).
Conclusions
This review has identified several strategies with potential to achieve high HIV testing coverage outside of health care settings. However, the geographical spread of studies was limited, and few intervention studies reported before and after data, making it difficult to evaluate the impact of interventions on test coverage.
Objectives
Despite the availability of HIV testing guidelines to facilitate prompt diagnosis, late HIV diagnosis remains high across Europe. The study synthesizes recent evidence on HIV testing ...strategies adopted in health care settings in the European Union/European Economic Area (EU/EEA).
Methods
Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines were followed and systematic searches were run in five databases (2010–2017) to identify studies describing HIV testing interventions in health care settings in the EU/EEA. The grey literature was searched for unpublished studies (2014–2017). Two reviewers independently performed study selection, data extraction and critical appraisal.
Results
One hundred and thirty intervention and/or feasibility studies on HIV testing in health care settings were identified. Interventions included testing provision (n = 94), campaigns (n = 14) and education and training for staff and patients (n = 20). HIV test coverage achieved through testing provision varied: 2.9–94% in primary care compared to 3.9–66% in emergency departments. HIV test positivity was lower in emergency departments (0–1.3%) and antenatal services (0–0.05%) than in other hospital departments (e.g. inpatients: 0–5.3%). Indicator condition testing programmes increased HIV test coverage from 3.9–72% before to 12–85% after their implementation, with most studies reporting a 10–20% increase. There were 51 feasibility and/or acceptability studies that demonstrated that HIV testing interventions were generally acceptable to patients and providers in health care settings (e.g. general practitioner testing acceptable: 77–93%).
Conclusions
This review has identified several strategies that could be adopted to achieve high HIV testing coverage across a variety of health care settings and populations in the EU/EEA. Very few studies compared the intervention under investigation to a baseline, but, where this was assessed, data suggested increases in testing.
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