Interaction of Guided Waves with Cracks in an Embedded Multilayered Anisotropic Plate by Using a Boundary Element Approach

In this work, the interaction of a transient guided elastic wave with a planar crack is studied by using a Boundary Finite Element approach on the crack. The originality of this work is to use the numerical Green functions of the multilayered plate. So, the key point of the method is to calculate rapidly and accurately these Green functions for such complex plane structures. For the space variables related to the plate surface, the fields are transformed in the 2D Fourier associated to the wave-vectors on this surface, and they are expressed in the partial-wave basis [1]. To ensure causality, the time dependence is dealt with in the Laplace domain. Surprisingly, this method, that involves 2D Fourier transform on the surface coupled with Laplace transform, has been rarely used in the ultrasonic community, while it is a useful tool which complements the much used technique based on generalized Lamb wave decomposition. By avoiding mode analysis, which can be problematic in some cases, exact numerical calculations of Green functions can be made in a relatively short time for immersed plates made of a stack of anisotropic viscoelastic layers. Even for 3D cases, numerical costs are relatively low. Numerical results show the effectiveness of this method. The examples presented emphasize the quality of the model and the robustness of the algorithm. Comparisons with Finite Element show excellent agreement. This approach is fast and low memory consuming for planar defects in arbitrary layered media, and can be extended to arbitrary shapes and boundary conditions for, of course, a higher computational cost. It is valid in 3D, however only the 2D case is considered in this work

Aneurysm of the Pancreaticoduodenal Arteries Associated with a Cœliac Artery Lesion

IntroductionA ruptured aneurysm of the pancreaticoduodenalarteries without acute or chronic pancreatitis butassociated with a median arcuate ligament divisionis an exceptional event described in only 11 cases. Thecase of a ruptured pancreaticoduodenal artery aneur-ysm, associated with a cœliac artery lesion which wedescribe, illustrates the difficulty in diagnosing theserare events promptly and in instituting urgent treat-ment to arrest the bleeding followed by an electiveprocedure to prevent recurrence.Case ReportA 54-year-old man with no history of vascular diseasewas admitted to a district hospital for investigation ofvague abdominal pain mainly affecting the rightabdomen, hypotension corrected by infusion ofcrystalloid and no fever. Laboratory blood chemicalfindings including a normal hemoglobin, raisedleukocyte count and high C-reactive protein concen-tration. This presentation raised the suspicion of a gallbladder infection and the patient was kept under closeobservation overnight. The next day, hypotensiondeveloped and the patient complained of pain in theright iliac quadrant. An abdominal ultrasound scanshowed a large iliac fluid collection, but no lesionsinvolving the gall bladder or liver. Appendicitis wasdiagnosed and the patient underwent a McBurneyoperation. During surgery blood was found in theabdomen. An exploratory laparotomy revealed a largeretroperitoneal hematoma. The patient was trans-ferred to our vascular surgery unit. A CT scan aftercontrast injection revealed an intact retroperitonealhematoma (16 £ 9 £ 15 cm), with no bleeding from theaorta or the visceral arteries, and a median arcuateligament division that compressed the origin of thecœliac trunk. Because these findings suggested aruptured pancreaticoduodenal artery aneurysm arter-iography was planned to confirm the diagnosis andtreat the aneurysm by embolization. The patient, whowas by now haemodynamically stable, was kept underobservation in the ITU and transferred to the vascularsurgical unit. On day 1, a CT scan showed that thehematoma had enlarged. The patient was kept undersurveillance in the vascular unit and arteriographywas planned for the following day. During the night,the patient collapsed but responded to more IVcrystalloid and was immediately transferred to theradiological unit. While the patient was being pre-pared for arteriography, a new CT scan showed thehematoma had now increased in size and had spreadto the intraperitoneal space, filling the peri-hepaticand peri-splenic areas as well as the pelvis.The patient underwent selective arteriography tovisualize the stenosis caused by compression of thecœliac axis, to localize the bleeding pancreaticoduo-denal artery aneurysm and to proceed to treatment byembolization. Under local anesthesia, a 5-F introduce

Imagerie topologique de plaques par ondes ultrasonores guidées

Le travail présenté traite de l’application de l’imagerie topologique aux ondes guidées dans les plaques. Les ondes guidées peuvent se propager sur de grandes distances et sont donc adaptées à l’inspection rapide de grandes structures. L’imagerie topologique est une méthode expérimentale récente qui s’appuie sur deux simulations physiques du milieu et qui est issue de recherches en mathématiques appliquées. Elle bénéficie des propriétés de refocalisation du retournement temporel pour tous les objets du milieu simultanément. Jusqu’ici appliquée aux ondes de volumes dans les fluides et les solides, elle permet une résolution élevée malgré un unique éclairage ultrasonore du milieu inspecté. La méthode d’imagerie dans les deux dimensions du plan de la plaque présentée ici s’appuie sur la propagation d’un seul mode guidé à la fois. Les deux simulations physiques nécessaires à la méthode sont réalisées à l’aide d’un modèle de propagation semi-analytique habituellement utilisé pour les ondes de volumes et ici adapté aux ondes guidées. Des résultats expérimentaux sont présentés pour une plaque d’aluminium inspectée à l’aide du mode de Lamb S0 et d’un réseau linéaire de 128 transducteurs dont la fréquence centrale est 500 kHz. Les défauts à imager sont ici des trous traversants. Bien que les mesures aient été réalisées sur une plage de fréquence où le mode S0 est fortement dispersif, les résolutions latérale et axiale sont très satisfaisantes. De plus, quelques secondes de calcul suffisent à l’obtention de l’image de toute la plaque

Ultrasonic imaging of buried defects in rails

The present work addresses the ultrasonic NDT of rails, more precisely of the rail foot. The practical constraint is that transducers must be located on the rail head, whereas the region of interest is the rail foot. Thus, there is no direct acoustic path between the transducers and the region of interest. As classical delay and sum methods cannot be applied to such cases, the goal of the paper is to numerically assess the potentiality of the topological imaging method to investigate the rail foot. Three specific typical rail foot defects are investigated, namely, longitudinal vertical cracks, corrosion pits and rail injuries. Simulating eight transducers with different polarizations, the images obtained show that the detection and approximate location of the various defects are possible

A systematic review of covered balloon-expandable stents for treating aortoiliac occlusive disease

Objective: To evaluate and compare studies reporting the outcomes of the use of covered balloon-expandable (CBE) stents for the treatment of aortoiliac occlusive disease. Methods: A systematic literature search was conducted to identify studies that investigated the use of CBE stents for the treatment of aortoiliac occlusive disease and were published between 2000 and 2019. Baseline demographic data, procedural variables, and long-term outcomes were extracted from publications for analysis. Results: A total of 15 published articles about 14 studies were included in the review. Of these, eight studies were prospective clinical trials and six studies were retrospective real-world studies. The articles included data regarding five different CBE stents, namely, the iCast/Advanta V12, Viabahn VBX, BeGraft, LifeStream, and JOSTENT. Lesion severity was higher in real-world studies, with more TransAtlantic Inter-Society Consensus Classification class D lesions and a higher percentage of occlusions. All studies showed high rates of technical success and patency over the course of 12 months. Long-term data were only available for the iCast/Advanta V12 device, which had a primary patency rate of 74.7% at 5 years. Conclusions: CBE stents are a viable treatment option for patients with complex aortoiliac lesions because of their high rates of technical success and favorable patency across all devices at 12 months. However, long-term data are only available for a single device, the iCast/Advanta V12. The results of using this device were favorable over the course of 5 years

Can Peto\u27s paradox be used as the null hypothesis to identify the role of evolution in natural resistance to cancer? A critical review

BACKGROUND: Carcinogenesis affects not only humans but almost all metazoan species. Understanding the rules driving the occurrence of cancers in the wild is currently expected to provide crucial insights into identifying how some species may have evolved efficient cancer resistance mechanisms. Recently the absence of correlation across species between cancer prevalence and body size (coined as Peto\u27s paradox) has attracted a lot of attention. Indeed, the disparity between this null hypothesis, where every cell is assumed to have an identical probability to undergo malignant transformation, and empirical observations is particularly important to understand, due to the fact that it could facilitate the identification of animal species that are more resistant to carcinogenesis than expected. Moreover it would open up ways to identify the selective pressures that may be involved in cancer resistance. However, Peto\u27s paradox relies on several questionable assumptions, complicating the interpretation of the divergence between expected and observed cancer incidences. DISCUSSIONS: Here we review and challenge the different hypotheses on which this paradox relies on with the aim of identifying how this null hypothesis could be better estimated in order to provide a standard protocol to study the deviation between theoretical/theoretically predicted and observed cancer incidence. We show that due to the disproportion and restricted nature of available data on animal cancers, applying Peto\u27s hypotheses at species level could result in erroneous conclusions, and actually assume the existence of a paradox. Instead of using species level comparisons, we propose an organ level approach to be a more accurate test of Peto\u27s assumptions. SUMMARY: The accuracy of Peto\u27s paradox assumptions are rarely valid and/or quantifiable, suggesting the need to reconsider the use of Peto\u27s paradox as a null hypothesis in identifying the influence of natural selection on cancer resistance mechanisms

First Results of the 140^{140}Ce(n,γ)141^{141}Ce Cross-Section Measurement at n_TOF

An accurate measurement of the $^{140}$Ce(n,γ) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the $^{140}$Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in $^{140}$Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the $^{140}$Ce Maxwellian-averaged cross-section

First Results of the 140^{140}Ce(n,γ)141^{141}Ce Cross-Section Measurement at n_TOF

An accurate measurement of the $^{140}$Ce(n,γ) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the $^{140}$Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in $^{140}$Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the $^{140}$Ce Maxwellian-averaged cross-section

Cardiovasc Diabetol

Lower-extremity arterial disease (LEAD) is a major endemic disease with an alarming increased prevalence worldwide. It is a common and severe condition with excess risk of major cardiovascular events and death. It also leads to a high rate of lower-limb adverse events and non-traumatic amputation. The American Diabetes Association recommends a widespread medical history and clinical examination to screen for LEAD. The ankle brachial index (ABI) is the first non-invasive tool recommended to diagnose LEAD although its variable performance in patients with diabetes. The performance of ABI is particularly affected by the presence of peripheral neuropathy, medial arterial calcification, and incompressible arteries. There is no strong evidence today to support an alternative test for LEAD diagnosis in these conditions. The management of LEAD requires a strict control of cardiovascular risk factors including diabetes, hypertension, and dyslipidaemia. The benefit of intensive versus standard glucose control on the risk of LEAD has not been clearly established. Antihypertensive, lipid-lowering, and antiplatelet agents are obviously worthfull to reduce major cardiovascular adverse events, but few randomised controlled trials (RCTs) have evaluated the benefits of these treatments in terms of LEAD and its related adverse events. Smoking cessation, physical activity, supervised walking rehabilitation and healthy diet are also crucial in LEAD management. Several advances have been achieved in endovascular and surgical revascularization procedures, with obvious improvement in LEAD management. The revascularization strategy should take into account several factors including anatomical localizations of lesions, medical history of each patients and operator experience. Further studies, especially RCTs, are needed to evaluate the interest of different therapeutic strategies on the occurrence and progression of LEAD and its related adverse events in patients with diabetes