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See detailIsogeometric analysis: an overview and computer implementation aspects
Nguyen, Vinh-Phu; Anitescu, Cosmin; Bordas, Stéphane UL et al

in Mathematics and Computers in Simulation (2015)

Isogeometric analysis (IGA) represents a recently developed technology in computational mechanics that offers the possibility of integrating methods for analysis and Computer Aided Design (CAD) into a ... [more ▼]

Isogeometric analysis (IGA) represents a recently developed technology in computational mechanics that offers the possibility of integrating methods for analysis and Computer Aided Design (CAD) into a single, unified process. The implications to practical engineering design scenarios are profound, since the time taken from design to analysis is greatly reduced, leading to dramatic gains in efficiency. In this manuscript, through a self-contained Matlab⃝R implementation, we present an introduction to IGA applied to simple analysis problems and the related computer implementation aspects. Furthermore, implementation of the extended IGA which incorporates enrichment functions through the partition of unity method (PUM) is also presented, where several examples for both two-dimensional and three-dimensional fracture are illustrated. We also describe the use of IGA in the context of strong-form (collocation) formulations, which has been an area of research interest due to the potential for significant efficiency gains offered by these methods. The code which accompanies the present paper can be applied to one, two and three-dimensional problems for linear elasticity, linear elastic fracture mechanics, structural mechanics (beams/plates/shells including large displacements and rotations) and Poisson problems with or without enrichment. The B ́ezier extraction concept that allows the FE analysis to be performed efficiently on T-spline geometries is also incorporated. The article includes a summary of recent trends and developments within the field of IGA. [less ▲]

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See detailIsogeometric analysis: an overview and computer implementation aspects
Nguyen, Vinh-Phu; Anitescu, Cosmin; Bordas, Stéphane UL et al

Learning material (2013)

Isogeometric analysis (IGA) represents a recently developed technology in computational mechanics that offers the possibility of integrating methods for analysis and Computer Aided Design (CAD) into a ... [more ▼]

Isogeometric analysis (IGA) represents a recently developed technology in computational mechanics that offers the possibility of integrating methods for analysis and Computer Aided Design (CAD) into a single, unified process. The implications to practical engineering design scenarios are profound, since the time taken from design to analysis is greatly reduced, leading to dramatic gains in efficiency. The tight coupling of CAD and analysis within IGA requires knowledge from both fields and it is one of the goals of the present paper to outline much of the commonly used notation. In this manuscript, through a clear and simple Matlab⃝R implementation, we present an introduction to IGA applied to the Finite Element (FE) method and related computer implementation aspects. Furthermore, implemen- tation of the extended IGA which incorporates enrichment functions through the partition of unity method (PUM) is also presented, where several examples for both two-dimensional and three-dimensional fracture are illustrated. The open source Matlab⃝R code which accompanies the present paper can be applied to one, two and three-dimensional problems for linear elasticity, linear elastic fracture mechanics, structural mechanics (beams/plates/shells including large displacements and rotations) and Poisson problems with or without enrichment. The B ́ezier extraction concept that allows FE analysis to be performed efficiently on T-spline geometries is also incorporated. The article includes a summary of recent trends and developments within the field of IGA. [less ▲]

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See detailIsogeometric and multi-scale fracture
Bordas, Stéphane UL

Presentation (2015, July 31)

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See detailIsogeometric boundary element analysis using unstructured T-splines
Scott, M. A.; Simpson, R. N.; Evans, J. A. et al

in Computer Methods in Applied Mechanics & Engineering (2013), 254

We couple collocated isogeometric boundary element methods and unstructured analysis-suitable T-spline surfaces for linear elastostatic problems. We extend the definition of analysis-suitable T-splines to ... [more ▼]

We couple collocated isogeometric boundary element methods and unstructured analysis-suitable T-spline surfaces for linear elastostatic problems. We extend the definition of analysis-suitable T-splines to encompass unstructured control grids (unstructured meshes) and develop basis functions which are smooth (rational) polynomials defined in terms of the Bézier extraction framework and which pass standard patch tests. We then develop a collocation procedure which correctly accounts for sharp edges and corners, extraordinary points, and T-junctions. This approach is applied to several three-dimensional problems, including a real-world T-spline model of a propeller. We believe this work clearly illustrates the power of combining new analysis-suitable computer aided design technologies with established analysis methodologies, in this case, the boundary element method. © 2012 Elsevier B.V. [less ▲]

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See detailAn isogeometric boundary element method for elastostatic analysis: 2D implementation aspects
Simpson, R. N.; Bordas, Stéphane UL; Lian, H. et al

in Computers & Structures (2013), 118

The concept of isogeometric analysis, whereby the parametric functions that are used to describe CAD geometry are also used to approximate the unknown fields in a numerical discretisation, has progressed ... [more ▼]

The concept of isogeometric analysis, whereby the parametric functions that are used to describe CAD geometry are also used to approximate the unknown fields in a numerical discretisation, has progressed rapidly in recent years. This paper advances the field further by outlining an isogeometric boundary element Method (IGABEM) that only requires a representation of the geometry of the domain for analysis, fitting neatly with the boundary representation provided completely by CAD. The method circumvents the requirement to generate a boundary mesh representing a significant step in reducing the gap between engineering design and analysis. The current paper focuses on implementation details of 2D IGABEM for elastostatic analysis with particular attention paid towards the differences over conventional boundary element implementations. Examples of Matlab® code are given whenever possible to aid understanding of the techniques used. [less ▲]

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See detailAn isogeometric boundary element method for elastostatic analysis: 2D implementation aspects
Simpson, Robert; Bordas, Stéphane UL; Lian, Haojie et al

in Computers & Structures (2013), 118

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See detailAn isogeometric boundary element method for fracture modeling
Peng, Xuan; Atroshchenko, Elena; Bordas, Stéphane UL

Presentation (2015, May)

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See detailIsogeometric boundary element methods for linear elastic fracture mechanics
Peng, Xuan; Atroshchenko, Elena; Kerfriden, Pierre et al

Report (2016)

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See detailIsogeometric boundary element methods for three dimensional fatigue crack growth
Peng, Xuan; Atroshchenko, Elena; Kerfriden, Pierre et al

Report (2015)

The isogeometric boundary element method (IGABEM) based on NURBS is adopted to model fracture problem in 3D. The NURBS basis functions are used in both crack representation and physical quantity ... [more ▼]

The isogeometric boundary element method (IGABEM) based on NURBS is adopted to model fracture problem in 3D. The NURBS basis functions are used in both crack representation and physical quantity approximation. A stable quadrature scheme for singular integration is proposed to enhance the robustness of the method in dealing with highly distorted element. The convergence study in crack opening displacement is performed for penny-shaped crack and elliptical crack. Two ways to extract stress intensity factors (SIFs), the contour $M$ integral and virtual crack closure integral, are implemented based on the framework of dual integral equations. An algorithm is outlined and validated to be stable for fatigue crack growth, thanks to the smoothness not only in crack geometry but also in stress/SIFs solution brought by IGABEM. [less ▲]

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See detailIsogeometric boundary element methods for three dimensional static fracture and fatigue crack growth
Peng, Xuan; Atroshchenko, Elena; Kerfriden, Pierre et al

in Computer Methods in Applied Mechanics & Engineering (2016)

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See detailIsogeometric cohesive elements for two and three dimensional composite delamination analysis
Nguyen, VP; Kerfriden, Pierre; Bordas, Stéphane UL

in Composites : Part B, Engineering (2013)

Isogeometric cohesive elements are presented for modeling two and three dimensional delaminated composite structures. We exploit the knot insertion algorithm offered by NURBS (Non Uniform Rational B ... [more ▼]

Isogeometric cohesive elements are presented for modeling two and three dimensional delaminated composite structures. We exploit the knot insertion algorithm offered by NURBS (Non Uniform Rational B-splines) to generate cohesive ele- ments along delamination planes in an automatic fashion. A complete computational framework is presented including pre-processing, processing and post-processing. They are explained in details and implemented in MIGFEM–an open source Matlab Isogemetric Analysis code developed by the authors. The composite laminates are modeled using both NURBS solid and rotation-free shell elements. Several two and three dimensional examples ranging from standard delamination tests (the mixed mode bending test) to the L-shaped specimen with a fillet, three dimensional (3D) double cantilever beam and a 3D singly curved thick-walled laminate are provided. To the authors’ knowledge, it is the first time that NURBS-based isogeometric analysis for two/three dimensional delamination modeling is presented. IGA provides a bi-directional system in which one can go forward from CAD to analysis and backwards from analysis to CAD. This is believed to facilitate the design of composite structures. [less ▲]

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See detailIsogeometric finite element analysis of time-harmonic exterior acoustic scattering problems
Khajah, Tahsin; Antoine, Xavier; Bordas, Stéphane UL

E-print/Working paper (2016)

We present an isogeometric analysis of time-harmonic exterior acoustic problems. The infinite space is truncated by a fictitious boundary and (simple) absorbing boundary conditions are applied. The ... [more ▼]

We present an isogeometric analysis of time-harmonic exterior acoustic problems. The infinite space is truncated by a fictitious boundary and (simple) absorbing boundary conditions are applied. The truncation error is included in the exact solution so that the reported error is an indicator of the performance of the isogeometric analysis, in particular of the related pollution error. Numerical results performed with high-order basis functions (third or fourth orders) showed no visible pollution error even for very high frequencies. This property combined with exact geometrical representation makes isogeometric analysis a very promising platform to solve high-frequency acoustic problems. [less ▲]

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See detailIsogeometric finite element analysis using polynomial splines over hierarchical T-meshes
Nguyen-Thanh, Nhon; Nguyen-Xuan, Hung; Bordas, Stéphane UL et al

in IOP Conference Series: Materials Science and Engineering (2014), 10(1),

Isogeometric finite element analysis has become a powerful alternative to standard finite elements due to their flexibility in handling complex geometries. One major drawback of NURBS based isogeometric ... [more ▼]

Isogeometric finite element analysis has become a powerful alternative to standard finite elements due to their flexibility in handling complex geometries. One major drawback of NURBS based isogeometric finite elements is their less effectiveness of local refinement. In this study, we present an alternative to NURBS based isogeometric finite elements that allow for local refinement. The idea is based on polynomial splines and exploits the flexibility of T-meshes for local refinement. The shape functions satisfy important properties such as non-negativity, local support and partition of unity. We will demonstrate the efficiency of the proposed method by two numerical examples. [less ▲]

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See detailIsogeometric locking-free plate element: a simple first order shear deformation theory for functionally graded plates
Shuohui, Yin; Hale, Jack UL; Yu, Tiantang et al

in Composite Structures (2014), 118

An effective, simple, robust and locking-free plate formulation is proposed to analyze the static bending, buckling, and free vibration of homogeneous and functionally graded plates. The simple first ... [more ▼]

An effective, simple, robust and locking-free plate formulation is proposed to analyze the static bending, buckling, and free vibration of homogeneous and functionally graded plates. The simple first-order shear deformation theory (S-FSDT), which was recently presented in Thai and Choi (2013) [11], is naturally free from shear-locking and captures the physics of the shear-deformation effect present in the original FSDT, whilst also being less computationally expensive due to having fewer unknowns. The S-FSDT requires C1-continuity that is simple to satisfy with the inherent high-order continuity of the non-uniform rational B-spline (NURBS) basis functions, which we use in the framework of isogeometric analysis (IGA). Numerical examples are solved and the results are compared with reference solutions to confirm the accuracy of the proposed method. Furthermore, the effects of boundary conditions, gradient index, and geometric shape on the mechanical response of functionally graded plates are investigated. [less ▲]

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See detailIsolated myocardial cells: a new tool for the investigation of hypertensive heart disease.
Neyses, Ludwig UL; Vetter, H.

in Journal of hypertension. Supplement : official journal of the International Society of Hypertension (1990), 8(4), 99-102

Cardiac hypertrophy is characterized by marked abnormalities in the contraction/relaxation pattern of the heart. For example, delayed relaxation is a prominent feature, impairing ventricular filling and ... [more ▼]

Cardiac hypertrophy is characterized by marked abnormalities in the contraction/relaxation pattern of the heart. For example, delayed relaxation is a prominent feature, impairing ventricular filling and coronary flow. In intact heart preparations the relative contribution of fibrosis and of the myocardial cell itself to these abnormalities cannot be correctly assessed. Biochemical studies on the mechanisms of impaired contraction and relaxation and hypertensive heart failure are hampered by the fact that 75% of all heart cells are non-myocytes. We therefore established the model of the isolated calcium-tolerant, adult rat cardiomyocyte as a new approach to the investigation of these problems. Contractility was measured using a videomicroscope system with high time resolution (1 ms). Angiotensin II induced a marked relaxation delay in the cardiomyocyte from normotensive rats and showed a moderate positive inotropic effect, whereas isoproterenol had a strong positive inotropic effect but accelerated relaxation. Therefore, angiotensin II is capable of inducing a relaxation delay even in the absence of coronary ischaemia or hypertension. These first results show that the isolated cardiomyocyte model may be a useful approach to investigating the mechanisms of hypertensive heart disease. [less ▲]

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See detailIsolating First Order Equivalent Mutants via Second Order Mutation.
Kintis, Marinos; Papadakis, Mike UL; Malevris, Nicos

in ICST 2012 (2012)

Detailed reference viewed: 102 (6 UL)
Peer Reviewed
See detailIsolation and characterization of the C3b-binding entity of C3b-receptor from human erythrocytes.
Mussel, H. H.; Ehlen, T.; Schmitt, Michèle UL et al

in Immunology letters (1982), 4(1), 1-6

Applying 2 M KBr, membranes of Ehu were solubilized. By C3-affinity chromatography an activity could be isolated that inhibited the immune adherence reaction and C3b-dependent rosette formation. Since ... [more ▼]

Applying 2 M KBr, membranes of Ehu were solubilized. By C3-affinity chromatography an activity could be isolated that inhibited the immune adherence reaction and C3b-dependent rosette formation. Since this material did not agglutinate EAC14oxy23b we termed it monovalent C3b receptor (mC3bR). PAGE and SDS-PAGE and staining with Coomassie brilliant blue and PAS reagent revealed a single glycoprotein band with a mol. wt. of 55,000-60,000 daltons and an electrophoretic mobility comparable to ovalbumin. This mC3bR proved to be antigenetically related to gp 205 [17]. The potential of mC3bR to react with C3b-carrying particles was not destroyed by heat and trypsin treatment but by neuraminidase or periodic acid treatment suggesting that mC3bR reacted by its carbohydrate moiety with C3b. As by mC3bR, immune adherence could be inhibited by D-glucose and D-galactose but not by their optical antipodes, L-glucose and L-galactose. [less ▲]

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Peer Reviewed
See detailIsolation of measles virus from a naturally-immune, asymptomatically re-infected individual
Vardas, E. A B; Kreis, Stephanie UL

in Journal of Clinical Virology (1999), 13(3), 173-179

Background: The changing epidemiology of measles with mild measles cases increasingly being recognised in previously-vaccinated individuals, suggests that more asymptomatic or subclinical cases might be ... [more ▼]

Background: The changing epidemiology of measles with mild measles cases increasingly being recognised in previously-vaccinated individuals, suggests that more asymptomatic or subclinical cases might be occurring. Although this has been clearly documented in previously-vaccinated individuals, the frequency of these asymptomatic infections in individuals previously naturally-infected with measles is not known. Also, it is not known whether these asymptomatic or mildly-infected individuals who do not display the full range of clinical signs of measles are capable of transmitting the virus to other susceptible persons. Objectives: To demonstrate the isolation of measles virus (MV) from previously, naturally-immune individuals asymptomatically infected with measles while in close contact with acutely infected family members and to document the secondary immune responses (SIR) associated with asymptomatic measles infection. Study Design: Throat swab and urine specimens from five acute measles cases and their family contacts, taken within 5 days of onset of rash in each acute case, were used to isolate MV by tissue culture. Positive tissue culture results were confirmed by indirect immunofluorescence (IF) staining. Measles specific antibodies (IgG and IgM), IgG urea avidity and measles-neutralising antibodies were measured in the one family (index family) where an asymptomatic measles infection of a contact was demonstrated. Results: The acutely infected patient in the index family (T1/96) had a measles-neutralising antibody titre of < 1:10, measles IgG urea avidity of 24% and MV was isolated and confirmed by IF from urine and throat swab specimens. T1/96 represents acute measles infection after primary vaccine failure because he had a clear history of being vaccinated against measles as a child. MV was also successfully isolated from throat swab and urine specimens from the other four acute cases and from the urine but not the throat swab of an asymptomatically infected family contact in the index family (mother, T2/96). T2/96 had a history of natural measles infection as a child approximately 50 years ago. In addition to detectable MV in urine this contact also had a SIR with a rise in measles specific neutralising antibody titre. No virus was isolated from the other contact in the index family (father, T3/96) or from the contacts of the other four acute cases examined. Conclusions: This is the first report of a confirmed asymptomatic MV infection, by MV isolation and IF testing and a concurrent SIR, in a previously naturally-immune contact of an acute case. The importance of these findings to the epidemiology and control of MV as well as the diagnostic value of MV urine isolation and IF confirmation for mild or asymptomatic cases must be examined further. [less ▲]

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See detailIsolation of nucleic acids from low biomass samples: detection and removal of sRNA contaminants
Heintz-Buschart, Anna; Yusuf, Dilmurat; Kaysen, Anne UL et al

E-print/Working paper (2017)

Sequencing-based analyses of low-biomass samples are known to be prone to misinterpretation due to the potential presence of contaminating molecules derived from laboratory reagents and environments. Due ... [more ▼]

Sequencing-based analyses of low-biomass samples are known to be prone to misinterpretation due to the potential presence of contaminating molecules derived from laboratory reagents and environments. Due to its inherent instability, contamination with RNA is usually considered to be unlikely. Here we report the presence of small RNA (sRNA) contaminants in widely used microRNA extraction kits and means for their depletion. Sequencing of sRNAs extracted from human plasma samples was performed and significant levels of non-human (exogenous) sequences were detected. The source of the most abundant of these sequences could be traced to the microRNA extraction columns by qPCR-based analysis of laboratory reagents. The presence of artefactual sequences originating from the confirmed contaminants were furthermore replicated in a range of published datasets. To avoid artefacts in future experiments, several protocols for the removal of the contaminants were elaborated, minimal amounts of starting material for artefact-free analyses were defined, and the reduction of contaminant levels for identification of bona fide sequences using 'ultra-clean' extraction kits was confirmed. In conclusion, this is the first report of the presence of RNA molecules as contaminants in laboratory reagents. The described protocols should be applied in the future to avoid confounding sRNA studies. [less ▲]

Detailed reference viewed: 147 (2 UL)