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Clovis De Arruda Martins - One of the best experts on this subject based on the ideXlab platform.
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Simplified Finite Element Models to Study the Wet Collapse of Straight and Curved Flexible Pipes
Journal of Offshore Mechanics and Arctic Engineering, 2017Co-Authors: Alfredo Gay Neto, Clovis De Arruda Martins, Eduardo Ribeiro Malta, Rafael Loureiro Tanaka, Carlos Alberto Ferreira GodinhoAbstract:When the External Sheath of flexible pipes experiences damage, seawater floods the annulus. Then, the External pressure is applied directly on the internal polymeric layer, and the load is transferred to the interlocked carcass, the innermost layer. In this situation, the so-called wet collapse failure of the interlocked carcass can occur. Simplified methodologies to address such a scenario, using restricted three-dimensional (3D) finite element models, are presented in this work. They are compared with full 3D models, studying both straight and curved flexible pipes scenarios. The curvature of the flexible pipe is shown to be important for wet collapse pressure predictions.
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Simplified Finite Element Models to Study the Dry Collapse of Straight and Curved Flexible Pipes
Journal of Offshore Mechanics and Arctic Engineering, 2016Co-Authors: Clovis De Arruda Martins, Eduardo Ribeiro Malta, Rafael Loureiro Tanaka, Carlos Alberto Ferreira GodinhoAbstract:Dry collapse is one of the possible failure modes of flexible pipes. It refers to the situation in which no damage occurs in the flexible pipe External Sheath. In this scenario, all layers of the pipe withstand the External pressure loading in a deep-water application. Such a situation is addressed in this work, which proposes some simplified modeling techniques to represent straight and curved flexible pipes subjected to External pressure, undergoing dry collapse during simulation procedure. The results of the proposed models are compared to other reference results, from a fully three-dimensional (3D) finite element model. Good agreement has been got, even with the proposed simplifications with a large reduction in computational cost when compared to full 3D model.
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flexible pipes influence of the pressure armor in the wet collapse resistance
Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme, 2014Co-Authors: Clovis De Arruda MartinsAbstract:When submitted to high External pressure, flexible pipes may collapse. If the External Sheath is damaged, all the External pressure is directly applied on the internal polymeric layer that transmits the loading to the carcass layer, which can fail due to this effect, leading to wet collapse. This failure mode must be taken into account in a flexible pipe design. A model can be set up neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to include the pressure armor effect in the numerical prediction of wet collapse. The main contribution of the pressure armor to the flexible pipe resistance to collapse is to be a constraint to the radial displacement of the carcass and the internal polymeric layers. Two models were developed to find the wet collapse pressure in flexible pipes. A first study was done using a ring approximation three-dimensional (3D) finite element method (FEM) model. Comparisons are made with more simplified models using a 3D FEM equivalent ring approximation. The aim is to clarify the mechanical behavior of the pressure armor in the wet collapse scenario. Parametric studies of initial ovalization of carcass and initial gaps and interference between polymeric layer and pressure armor are made and discussed.
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Finite Element Analysis of Flexible Pipes Under Compression
Volume 6A: Pipeline and Riser Technology, 2014Co-Authors: Eduardo Ribeiro Malta, Clovis De Arruda MartinsAbstract:Axial compressive loads can appear in several situations during the service life of a flexible pipe, due to pressure variations during installation or due to surface vessel heave. The tensile armor withstands well tension loads, but under compression, instability may occur. A Finite Element model is constructed using Abaqus in order to study a flexible pipe compound by External Sheath, two layers of tensile armor, a high strength tape and a rigid nucleus. This model is fully tridimensional and takes into account all kinds of nonlinearities involved in this phenomenon, including contacts, gaps, friction, plasticity and large displacements. It also has no symmetry or periodical limitations, thus permitting each individual wire of the tensile armor do displace in any direction. Case studies were performed and their results discussed.© 2014 ASME
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Flexible Pipe Modeling Using Finite Macro-Elements
Volume 6A: Pipeline and Riser Technology, 2014Co-Authors: Rodrigo Provasi, Clovis De Arruda MartinsAbstract:Modeling flexible pipes in the local level is not a trivial task and many authors have employed a great amount of time in such task. The non-triviality arises from the various layers and their interaction, which are pretty tough to correctly model. The possible approaches to solve the problem are divided in to major categories: analytical models and numerical models. The analytical ones rely on a great number of hypotheses and, after a great effort, result in a system of algebraic equations. The numerical ones can be further differentiated in the ones developed using commercial software and the other ones using proprietary models.The authors choose the second way to approach the problem and presented in previous works a group of elements called macro-elements, including a cylindrical element for orthotropic layers, a three dimensional curved beam for helical elements, a rigid connection and a contact element, both dealing with different node displacement natures. These elements take into account the physical and geometrical characteristics of the components. In this paper a pipe model, with a flexible internal core, two tensile armors and an External Sheath, will be simulated and its the results will be checked against commercial software and commented.Copyright © 2014 by ASME
John Mccann - One of the best experts on this subject based on the ideXlab platform.
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Catheter policies for management of long term voiding problems in adults with neurogenic bladder disorders.
The Cochrane database of systematic reviews, 2013Co-Authors: Jim Jamison, Suzanne Maguire, John MccannAbstract:Management of the neurogenic bladder has the primary objectives of maintaining continence, ensuring low bladder pressure (to avoid renal damage) and avoiding or minimising infection. Options include intermittent urethral catheterisation, indwelling urethral or suprapubic catheterisation, timed voiding, use of External catheter (for men), drug treatment, augmentation cystoplasty and urinary diversion. The primary objective was to determine the effects of different methods of managing long-term voiding problems (persisting after three months) with catheters in patients with neurogenic bladder.Specific hypotheses to be addressed included:1. that intermittent catheterisation is better than indwelling catheterisation;2. that indwelling urethral catheterisation is better than suprapubic catheterisation;3. that External (Sheath) catheters are better than indwelling or intermittent urethral catheters;4. that External (Sheath) catheters are better than suprapubic catheters;5. that intermittent catheterisation is better than timed voiding. We searched the Cochrane Incontinence Group Specialised Register (searched 3 July 2013), which contains trials identified from the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and MEDLINE in process, and handsearched journals and conference proceedings. We sought additional trials from other sources such as the reference lists of relevant articles and by contacting consultants in Spinal Cord Injury Centres throughout the United Kingdom. All randomised and quasi-randomised controlled trials comparing methods of using catheters to manage urinary voiding in people with neurogenic bladder. Abstracts were independently inspected by the reviewers and full papers were obtained where necessary. Approximately 400 studies were scrutinised. No trials were found that met the inclusion criteria, and five studies were excluded from the review. Despite a comprehensive search no evidence from randomised or quasi-randomised controlled trials was found. It was not possible to draw any conclusions regarding the use of different types of catheter in managing the neurogenic bladder.
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The Cochrane Library - Catheter policies for management of long term voiding problems in adults with neurogenic bladder disorders
The Cochrane database of systematic reviews, 2011Co-Authors: Jim Jamison, Suzanne Maguire, John MccannAbstract:Background Management of the neurogenic bladder has the primary objectives of maintaining continence, ensuring low bladder pressure (to avoid renal damage) and avoiding or minimising infection. Options include intermittent urethral catheterisation, indwelling urethral or suprapubic catheterisation, timed voiding, use of External catheter (for men), drug treatment, augmentation cystoplasty and urinary diversion. Objectives The primary objective was to determine the effects of different methods of managing long-term voiding problems (persisting after three months) with catheters in patients with neurogenic bladder. Specific hypotheses to be addressed included: 1. that intermittent catheterisation is better than indwelling catheterisation; 2. that indwelling urethral catheterisation is better than suprapubic catheterisation; 3. that External (Sheath) catheters are better than indwelling or intermittent urethral catheters; 4. that External (Sheath) catheters are better than suprapubic catheters; 5. that intermittent catheterisation is better than timed voiding. Search methods We searched the Cochrane Incontinence Group Specialised Register (searched 3 July 2013), which contains trials identified from the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and MEDLINE in process, and handsearched journals and conference proceedings. We sought additional trials from other sources such as the reference lists of relevant articles and by contacting consultants in Spinal Cord Injury Centres throughout the United Kingdom. Selection criteria All randomised and quasi-randomised controlled trials comparing methods of using catheters to manage urinary voiding in people with neurogenic bladder. Data collection and analysis Abstracts were independently inspected by the reviewers and full papers were obtained where necessary. Main results Approximately 400 studies were scrutinised. No trials were found that met the inclusion criteria, and five studies were excluded from the review. Authors' conclusions Despite a comprehensive search no evidence from randomised or quasi-randomised controlled trials was found. It was not possible to draw any conclusions regarding the use of different types of catheter in managing the neurogenic bladder.
Gianni D Angelini - One of the best experts on this subject based on the ideXlab platform.
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long term reduction of medial and intimal thickening in porcine saphenous vein grafts with a polyglactin biodegradable External Sheath
Journal of Vascular Surgery, 2004Co-Authors: Viswanadha Vijaya, Jaso L Johnso, P Gadsdo, Nilima Shukla, Frank C T Smith, Gianni D Angelini, R N Aird, Jamie Y JeremyAbstract:Objectives The development of neointimal hyperplasia with subsequent atherosclerotic deposition has been proposed to cause most late vein graft failures. Our unit has previously demonstrated that placement of a macroporous, loose-fitting polyester External stent prevents neointimal thickening in porcine vein grafts, and has been proposed as a therapeutic strategy to prevent late vein graft failure. To reduce any potential long-term complications of the permanent polyester stent, a study was undertaken to investigate the effect of a biodegradable External stent on porcine vein graft thickening at 1 month and to identify its longer term effects at 6 months. Methods Bilateral saphenous vein to common carotid artery interposition grafting was performed in Large White pigs (25-32 kg; n=6 per time course group) according to UK Home Office guidelines. A commercially constructed loose-fitting 8-mm-diameter polyglactin stent was placed Externally around the vein graft on one side, and the contralateral side remained unstented to serve as control. The External stent was designed to biodegrade and hence disappear within 90 days. Grafts were left in situ for 1 month in 1 group of animals, and for up to 6 months in the other group, before explantation. Graft morphometric features were assessed with computer-aided planimetry. Results At 1 month the vein grafts fitted with the polyglactin stent demonstrated a statistically significant decrease in neointimal thickening (0.038 mm; interquartile range [IQR], 0.035-0.039 mm) compared with the unstented control grafts (0.13 mm; IQR; 0.11-0.19; P = .0012), and also in medial thickening (0.09 mm; IQR, 0.086-0.093) compared with unSheathed control grafts (0.302 mm; IQR, 0.272-0.414; P = .0012). The 6-month polyglactin stented grafts also demonstrated a statistically significant reduction in neointimal thickening (0.049 mm; IQR, 0.047-0.07; P = .0012) compared with control grafts (0.178 mm; IQR, 0.164-0.19), and also in medial thickening (0.105 mm; IQR, 0.095-0.143) compared with unstented grafts (0.421 mm; IQR, 0.35-0.44; P = .0012, Mann-Whitney U test). Conclusion The loose-fitting biodegradable polyglactin External stent reduces porcine vein graft thickening at 1 month, which persists in the long term, even after degradation of the stent itself. This effective removal of the stent may therefore reduce the long-term risks for infection and mechanical complications associated with implanted prosthetic material while still eliciting the primary objective of preventing graft thickening over the long term. Biodegradable External stents therefore have potential advantages over permanent stent material in clinical application.
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a bioabsorbable polyglactin nonrestrictive External Sheath inhibits porcine saphenous vein graft thickening
The Journal of Thoracic and Cardiovascular Surgery, 2004Co-Authors: Jamie Y Jeremy, Richard Ulbulia, Jaso L Johnso, P Gadsdo, Viswanadha Vijaya, Nilima Shukla, Frank C T Smith, Gianni D AngeliniAbstract:Abstract Objective External, nonrestrictive, macro-porous polyester stents prevent neointima formation in porcine vein grafts and have been proposed as a therapeutic approach to the prevention of late vein graft failure. These stents are nonbiodegradable and therefore may promote long-term foreign body problems including infection and inflammation. The effect of External macro-porous biodegradable (polyglactin) Sheaths on neointimal and medial thickening in porcine vein grafts was therefore investigated. Methods Bilateral saphenous vein–carotid artery interposition grafting was performed in white Landrace pigs (n = 8) with External placement of polyglactin (Vicryl) Sheaths (8 mm in diameter) on 1 side, with the contralateral side acting as a control. One month after surgery, grafts were explanted and wall dimensions measured on histological sections using computer-aided planimetry, and an immunocytochemical appraisal was carried out. Results All grafts were patent at explantation. Polyglactin Sheaths significantly reduced intimal thickness, medial thickness, and the percentage of proliferating cells compared with unSheathed controls. There was a pronounced accumulation of macrophages, giant cells, endothelial cells, and microvessels within and surrounding the biodegradable Sheath compared with controls. Conclusions A nonrestrictive, biodegradable (polyglactin), External Sheath reduces medial and intimal thickening in experimental saphenous vein grafts, possibly through inflammatory cell–mediated angiogenesis. If subsequent long-term studies confirm preservation of this beneficial effect, once the Sheath biodegrades, this approach may have an advantage over the permanent polyester stent when applied clinically.
Jamie Y Jeremy - One of the best experts on this subject based on the ideXlab platform.
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long term reduction of medial and intimal thickening in porcine saphenous vein grafts with a polyglactin biodegradable External Sheath
Journal of Vascular Surgery, 2004Co-Authors: Viswanadha Vijaya, Jaso L Johnso, P Gadsdo, Nilima Shukla, Frank C T Smith, Gianni D Angelini, R N Aird, Jamie Y JeremyAbstract:Objectives The development of neointimal hyperplasia with subsequent atherosclerotic deposition has been proposed to cause most late vein graft failures. Our unit has previously demonstrated that placement of a macroporous, loose-fitting polyester External stent prevents neointimal thickening in porcine vein grafts, and has been proposed as a therapeutic strategy to prevent late vein graft failure. To reduce any potential long-term complications of the permanent polyester stent, a study was undertaken to investigate the effect of a biodegradable External stent on porcine vein graft thickening at 1 month and to identify its longer term effects at 6 months. Methods Bilateral saphenous vein to common carotid artery interposition grafting was performed in Large White pigs (25-32 kg; n=6 per time course group) according to UK Home Office guidelines. A commercially constructed loose-fitting 8-mm-diameter polyglactin stent was placed Externally around the vein graft on one side, and the contralateral side remained unstented to serve as control. The External stent was designed to biodegrade and hence disappear within 90 days. Grafts were left in situ for 1 month in 1 group of animals, and for up to 6 months in the other group, before explantation. Graft morphometric features were assessed with computer-aided planimetry. Results At 1 month the vein grafts fitted with the polyglactin stent demonstrated a statistically significant decrease in neointimal thickening (0.038 mm; interquartile range [IQR], 0.035-0.039 mm) compared with the unstented control grafts (0.13 mm; IQR; 0.11-0.19; P = .0012), and also in medial thickening (0.09 mm; IQR, 0.086-0.093) compared with unSheathed control grafts (0.302 mm; IQR, 0.272-0.414; P = .0012). The 6-month polyglactin stented grafts also demonstrated a statistically significant reduction in neointimal thickening (0.049 mm; IQR, 0.047-0.07; P = .0012) compared with control grafts (0.178 mm; IQR, 0.164-0.19), and also in medial thickening (0.105 mm; IQR, 0.095-0.143) compared with unstented grafts (0.421 mm; IQR, 0.35-0.44; P = .0012, Mann-Whitney U test). Conclusion The loose-fitting biodegradable polyglactin External stent reduces porcine vein graft thickening at 1 month, which persists in the long term, even after degradation of the stent itself. This effective removal of the stent may therefore reduce the long-term risks for infection and mechanical complications associated with implanted prosthetic material while still eliciting the primary objective of preventing graft thickening over the long term. Biodegradable External stents therefore have potential advantages over permanent stent material in clinical application.
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a bioabsorbable polyglactin nonrestrictive External Sheath inhibits porcine saphenous vein graft thickening
The Journal of Thoracic and Cardiovascular Surgery, 2004Co-Authors: Jamie Y Jeremy, Richard Ulbulia, Jaso L Johnso, P Gadsdo, Viswanadha Vijaya, Nilima Shukla, Frank C T Smith, Gianni D AngeliniAbstract:Abstract Objective External, nonrestrictive, macro-porous polyester stents prevent neointima formation in porcine vein grafts and have been proposed as a therapeutic approach to the prevention of late vein graft failure. These stents are nonbiodegradable and therefore may promote long-term foreign body problems including infection and inflammation. The effect of External macro-porous biodegradable (polyglactin) Sheaths on neointimal and medial thickening in porcine vein grafts was therefore investigated. Methods Bilateral saphenous vein–carotid artery interposition grafting was performed in white Landrace pigs (n = 8) with External placement of polyglactin (Vicryl) Sheaths (8 mm in diameter) on 1 side, with the contralateral side acting as a control. One month after surgery, grafts were explanted and wall dimensions measured on histological sections using computer-aided planimetry, and an immunocytochemical appraisal was carried out. Results All grafts were patent at explantation. Polyglactin Sheaths significantly reduced intimal thickness, medial thickness, and the percentage of proliferating cells compared with unSheathed controls. There was a pronounced accumulation of macrophages, giant cells, endothelial cells, and microvessels within and surrounding the biodegradable Sheath compared with controls. Conclusions A nonrestrictive, biodegradable (polyglactin), External Sheath reduces medial and intimal thickening in experimental saphenous vein grafts, possibly through inflammatory cell–mediated angiogenesis. If subsequent long-term studies confirm preservation of this beneficial effect, once the Sheath biodegrades, this approach may have an advantage over the permanent polyester stent when applied clinically.
Jeff Errington - One of the best experts on this subject based on the ideXlab platform.
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Wall proficient E-coli capable of sustained growth in the absence of the Z-ring division machine
Nature Microbiology, 2016Co-Authors: Romain Mercier, Yoshikazu Kawai, Jeff ErringtonAbstract:The peptidoglycan cell wall is a major protective External Sheath in bacteria and a key target for antibiotics(1). Peptidoglycan is present in virtually all bacteria, suggesting that it was probably present in the last bacterial common ancestor(2). Cell wall expansion is orchestrated by cytoskeletal proteins related to actin (MreB) and tubulin (FtsZ)(3). FtsZ is a key essential player in a highly organized division machine that directs an invaginating annulus of cell wall peptidoglycan. The recent discovery that cell-wall-less bacteria (L-forms) can grow and divide independently of FtsZ(4,5,) provided a means of generating an ftsZ null mutant of Escherichia coli. Remarkably, we have been able to isolate variants of E. coli that lack FtsZ but are capable of efficient growth in a walled state. Genetic analysis reveals that a combination of mutations is needed for this phenotype. Importantly, the suppressive mutations lead to a major cell shape change, from the normal cylindrical shape to a branched and bulging, ramified shape, which we call `coli-flower'. The results highlight the versatility of bacterial cells and illustrate possible evolutionary routes leading to the emergence of specialized bacteria, such as pathogenic Chlamydia or aquatic Planctomycetes, that lack FtsZ but retain the cell wall(6-8).
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Wall proficient E. coli capable of sustained growth in the absence of the Z-ring division machine
Nature Microbiology, 2016Co-Authors: Romain Mercier, Yoshikazu Kawai, Jeff ErringtonAbstract:Branched growth and division of bacteria with a cell wall but without a Z-ring may shed light on the evolution of bacterial morphogenesis. The peptidoglycan cell wall is a major protective External Sheath in bacteria and a key target for antibiotics^ 1 . Peptidoglycan is present in virtually all bacteria, suggesting that it was probably present in the last bacterial common ancestor^ 2 . Cell wall expansion is orchestrated by cytoskeletal proteins related to actin (MreB) and tubulin (FtsZ)^ 3 . FtsZ is a key essential player in a highly organized division machine that directs an invaginating annulus of cell wall peptidoglycan. The recent discovery that cell-wall-less bacteria (L-forms) can grow and divide independently of FtsZ^ 4 , 5 , provided a means of generating an ftsZ null mutant of Escherichia coli . Remarkably, we have been able to isolate variants of E. coli that lack FtsZ but are capable of efficient growth in a walled state. Genetic analysis reveals that a combination of mutations is needed for this phenotype. Importantly, the suppressive mutations lead to a major cell shape change, from the normal cylindrical shape to a branched and bulging, ramified shape, which we call ‘coli-flower’. The results highlight the versatility of bacterial cells and illustrate possible evolutionary routes leading to the emergence of specialized bacteria, such as pathogenic Chlamydia or aquatic Planctomycetes, that lack FtsZ but retain the cell wall^ 6 – 8 .
