On the modelling of ultrasonic testing using boundary integral equation methods

Ultrasonic nondestructive testing has important applications in, for example, the nuclear power and aerospace industries, where it is used to inspect safety-critical parts for flaws. For safe and reliable testing, mathematical models of the ultrasonic measurement systems are invaluable tools. In this thesis such measurement models are developed for the ultrasonic testing for defects located near non-planar surfaces. The applications in mind are the testing of nuclear power plant components such as thick-walled pipes with diameter transitions, pipe connections, etc. The models use solution methods based on frequency domain boundary integral equation methods, with a focus on analytical approaches for the defects and regularized boundary element methods for the non-planar surfaces. A major benefit of the solution methods is the ability to provide accurate results both for low, intermediate and high frequencies. The solution methods are incorporated into a framework of transmitting probe models based on prescribing the traction underneath the probe and receiving probe models based on electromechanical reciprocity. Time traces are obtained by applying inverse temporal Fourier transforms, and it is also shown how calibration and effects of material damping can be included in the models

Elastic wave scattering by a rectangular crack near a non-planar back surface

A 3D model of non-destructive ultrasonic testing for cracks near a non-planar back surface is presented. The scattering by an interior rectangular crack in a thick-walled component with a back surface of general geometry is considered. The 3D wave scattering problem is solved using boundary integral equation methods (BIEMs): the boundary element method (BEM) for the back surface displacement is combined with an analytical technique for the hypersingular traction boundary integral equation for the crack opening displacement. The solution method generates many unknowns, but by applying a threshold criterion a sparse approximation of the system matrix is obtained such that a fast sparse solver may be used. The computations are accelerated further using the stationary phase approximation for the computation of probe field integrals. The action of ultrasonic probes in transmission and reception, calibration by side-drilled holes and effects of material damping are taken into account in the model, and a few numerical examples illustrate the influence of the back surface geometry

A hybrid T matrix/boundary element method for elastic wave scattering from a defect near a non-planar surface

The in-plane P-SV scattering of elastic waves bya defect and a close non-planar surface is considered. A hybrid T matrix/boundary element approach is used, where a boundary integral equation is used for the non-planar surface and the Green’s tensor in this integral equation is chosen as the one for the defect and thus incorporates the transition (T ) matrix of the defect. The integral equation is iscretized by the boundary element method in a standard way. Also models of ultrasonic probes in transmission and reception are included. In the numerical examples the defect is for simplicity chosen as a circular cavity. This cavity is located close to a non-planar surface, which is planar except for a smooth transition between two planar parts. It is illustrated that the scattering by the cavity and the non-planar surface becomes quite complicated, and that shielding and masking may appear

White matter disturbances in major depressive disorder : a coordinated analysis across 20 international cohorts in the ENIGMA MDD working group

Altres ajuts: The ENIGMA-Major Depressive Disorder working group gratefully acknowledges support from the NIH Big Data to Knowledge (BD2K) award (U54 EB020403 to PMT) and NIH grant R01 MH116147 (PMT). LS is supported by an NHMRC MRFF Career Development Fellowship (APP1140764). We wish to acknowledge the patients and control subjects that have particiaped int the study. We thank Rosa Schirmer, Elke Schreiter, Reinhold Borschke and Ines Eidner for image acquisition and data preparation, and Anna Oliynyk for quality checks. We thank Dorothee P. Auer and F. Holsboer for initiation of the RUD study. We wish to acknowledge the patients and control subjects that have particiaped int the study. We thank Rosa Schirmer, Elke Schreiter, Reinhold Borschke and Ines Eidner for image acquisition and data preparation, and Anna Oliynyk for quality checks. We thank Dorothee P. Auer and F. Holsboer for initiation of the RUD study. NESDA: The infrastructure for the NESDA study (www.nesda.nl) is funded through the Geestkracht program of the Netherlands Organisation for Health Research and Development (Zon-Mw, grant number 10-000-1002) and is supported by participating universities (VU University Medical Center, GGZ inGeest, Arkin, Leiden University Medical Center, GGZ Rivierduinen, University Medical Center Groningen) and mental health care organizations, see www.nesda.nl. M-JvT was supported by a VENI grant (NWO grant number 016.156.077). UCSF: This work was supported by the Brain and Behavior Research Foundation (formerly NARSAD) to TTY; the National Institute of Mental Health (R01MH085734 to TTY; K01MH117442 to TCH) and by the American Foundation for Suicide Prevention (PDF-1-064-13) to TCH. Stanford: This work was supported by NIMH Grants R01MH59259 and R37101495 to IHG. MS is partially supported by an award funded by the Phyllis and Jerome Lyle Rappaport Foundation. Muenster: This work was funded by the German Research Foundation (SFB-TRR58, Projects C09 and Z02 to UD) and the Interdisciplinary Center for Clinical Research (IZKF) of the medical faculty of Münster (grant Dan3/012/17 to UD). Marburg: This work was funded by the German Research Foundation (DFG, grant FOR2107 DA1151/5-1 and DA1151/5-2 to UD; KI 588/ 14-1, KI 588/14-2 to TK; KR 3822/7-1, KR 3822/7-2 to AK; JA 1890/ 7-1, JA 1890/7-2 to AJ). IMH-MDD: This work was supported by the National Healthcare Group Research Grant (SIG/15012) awarded to KS. Barcelona: This study was funded by two grants of the Fondo de Investigación Sanitaria from the Instituto de Salud Carlos III, by the Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM). The author is funded through 'Miguel Servet' research contract (CP16-0020), co-financed by the European Regional Development Fund (ERDF) (2016-2019). QTIM: We thank the twins and singleton siblings who gave generously of their time to participate in the QTIM study. We also thank the many research assistants, radiographers, and IT support staff for data acquisition and DNA sample preparation. This study was funded by White matter disturbances in major depressive disorder: a coordinated analysis across 20 international. . . 1521 the National Institute of Child Health & Human Development (RO1 HD050735); National Institute of Biomedical Imaging and Bioengineering (Award 1U54EB020403-01, Subaward 56929223); National Health and Medical Research Council, Australia (Project Grants 496682, 1009064). NIH ENIGMA-BD2K U54 EB020403 (Thompson); R01 MH117601 (Jahanshad/Schmaal). Magdeburg: M.L. and M.W. are funded by SFB 779. Bipolar Family Study: This study has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013). This paper reflects only the author's views and the European Union is not liable for any use that may be made of the information contained therein. This work was also supported by a Wellcome Trust Strategic Award (104036/Z/14/Z). Minnesota Adolescent Depression Study: The study was funded by the National Institute of Mental Health (K23MH090421), the National Alliance for Research on Schizophrenia and Depression, the University of Minnesota Graduate School, the Minnesota Medical Foundation, and the Biotechnology Research Center (P41 RR008079 to the Center for Magnetic Resonance Research), University of Minnesota, and the Deborah E. Powell Center for Women's Health Seed Grant, University of Minnesota. Dublin: This study was supported by Science Foundation Ireland through a Stokes Professorhip grant to TF. MPIP: The MPIP Sample comprises patients included in the Recurrent Unipolar Depression (RUD) Case-Control study at the clinic of the Max Planck Institute of Psychiatry, Munich, German. The RUD study was supported by GlaxoSmithKline.Alterations in white matter (WM) microstructure have been implicated in the pathophysiology of major depressive disorder (MDD). However, previous findings have been inconsistent, partially due to low statistical power and the heterogeneity of depression. In the largest multi-site study to date, we examined WM anisotropy and diffusivity in 1305 MDD patients and 1602 healthy controls (age range 12-88 years) from 20 samples worldwide, which included both adults and adolescents, within the MDD Working Group of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) consortium. Processing of diffusion tensor imaging (DTI) data and statistical analyses were harmonized across sites and effects were meta-analyzed across studies. We observed subtle, but widespread, lower fractional anisotropy (FA) in adult MDD patients compared with controls in 16 out of 25 WM tracts of interest (Cohen's d between 0.12 and 0.26). The largest differences were observed in the corpus callosum and corona radiata. Widespread higher radial diffusivity (RD) was also observed (all Cohen's d between 0.12 and 0.18). Findings appeared to be driven by patients with recurrent MDD and an adult age of onset of depression. White matter microstructural differences in a smaller sample of adolescent MDD patients and controls did not survive correction for multiple testing. In this coordinated and harmonized multisite DTI study, we showed subtle, but widespread differences in WM microstructure in adult MDD, which may suggest structural disconnectivity in MDD

Modelling of ultrasonic testing for cracks near a non-planar surface

Nondestructive testing using ultrasound has important applications in e.g. the nuclear power and aerospace industries, where it is used to inspect safety-critical parts for flaws. For reliable inspections a proper adaptation to the specific testing situation is crucial, and in this process a mathematical model of nondestructive ultrasonic testing is a valuable tool. In this thesis a two-dimensional mathematical model of ultrasonic nondestructive testing for cracks near a non-planar surface is developed, with applications in the testing of thick-walled pipes with diameter transitions, pipe connections, etc. In the first part of the thesis the 2D anti-plane wave scattering problem is considered. The solution method employed is based on reformulating the problem as two coupled boundary integral equations (BIE): a displacement BIE for the back surface displacement and a traction BIE for the crack opening displacement. In order to avoid numerical integration of singular integrals a regularization approach is employed for the displacement BIE. The integral equations are subsequently solved simultaneously using a combination of a series expansion of the crack-opening displacement and a boundary element discretization of the back surface. The transmitting ultrasonic contact probe is modelled by prescribing the traction beneath it. To model the action of the receiving probe an electromechanical reciprocity relation is used. An inverse temporal Fourier transform is applied to obtain the time traces, and a few numerical examples are given to illustrate the model and the influence of the back surface. In the second part of the thesis the solution method developed in the first part for anti-plane wave scattering is adapted and applied to the in-plane wave scattering problem, featuring coupled P and SV waves. The action of the transmitting ultrasonic contact probe is modelled also for this case by prescribing the traction beneath the probe, but in order to realistically model both P and SV probes two different tractions are considered. The model also takes into account the influence of a couplant applied between the probe and component. The action of the receiving probe is again modelled using reciprocity. Finally, a few numerical examples are given

On the modelling of ultrasonic testing using boundary integral equation methods

Ultrasonic nondestructive testing has important applications in, for example, the nuclearpower and aerospace industries, where it is used to inspect safety-critical parts for flaws.For safe and reliable testing, mathematical models of the ultrasonic measurement systemsare invaluable tools. In this thesis such measurement models are developed for the ultrasonictesting for defects located near non-planar surfaces. The applications in mind arethe testing of nuclear power plant components such as thick-walled pipes with diametertransitions, pipe connections, etc. The models use solution methods based on frequencydomain boundary integral equation methods, with a focus on analytical approaches for thedefects and regularized boundary element methods for the non-planar surfaces. A majorbenefit of the solution methods is the ability to provide accurate results both for low, intermediateand high frequencies. The solution methods are incorporated into a frameworkof transmitting probe models based on prescribing the traction underneath the probe andreceiving probe models based on electromechanical reciprocity. Time traces are obtainedby applying inverse temporal Fourier transforms, and it is also shown how calibration andeffects of material damping can be included in the models

2D SH modelling of ultrasonic testing for cracks near a non-planar surface

A model of 2D SH ultrasonic nondestructive testing for interior strip-like cracks near a non-planar back surface in a thick-walled elastic solid is presented. The model employs a Green\u27s function to reformulate the 2D antiplane wave scattering problem as two coupled boundary integral equations (BIE): a displacement BIE for the back surface displacement and a hypersingular traction BIE for the crack opening displacement (COD). The integral equations are solved by performing a boundary element discretization of the back surface and expanding the COD in a series of Chebyshev functions which incorporate the correct behaviour at the crack edges. The transmitting ultrasonic probe is modelled by prescribing the traction underneath it, enabling the consequent calculation of the incident field. An electromechanical reciprocity relation is used to model the action of the receiving probe. A few numerical examples which illustrate the influence of the non-planar back surface are given

2D SH modeling of ultrasonic testing for cracks near a non-planar back surface

A model of 2D SH ultrasonic nondestructive testing for interior strip-like cracks near a non-planar back surface in a thick-walled component is presented. The wave scattering problem is solved using a combination of the boundary element method (BEM) and an analytical hypersingular integral equation technique. The model takes into account the action of the ultrasonic transmitter and receiver, and a few numerical examples illustrating the influence of the non-planar back surface are given

2D SH modelling of ultrasonic testing for cracks near a non-planar surface

A model of 2D SH ultrasonic nondestructive testing for interior strip-like cracks near a non-planar back surface in a thick-walled elastic solid is presented. The model employs a Green's function to reformulate the 2D antiplane wave scattering problem as two coupled boundary integral equations (BIE): a displacement BIE for the back surface displacement and a hypersingular traction BIE for the crack opening displacement (COD). The integral equations are solved by performing a boundary element discretization of the back surface and expanding the COD in a series of Chebyshev functions which incorporate the correct behaviour at the crack edges. The transmitting ultrasonic probe is modelled by prescribing the traction underneath it, enabling the consequent calculation of the incident field. An electromechanical reciprocity relation is used to model the action of the receiving probe. A few numerical examples which illustrate the influence of the non-planar back surface are given

Aktierekommendationers påverkan på abnormal avkastning : En studie av Stockholmsbörsen 2017

Denna studie berör aktierekommendationers påverkan på abnormal avkastning. Studien undersöker rekommendationer utgivna under 2017 av professionella analytiker för aktier på Stockholmsbörsen och diskuterar skillnader mellan positiva och negativa rekommendationer, samt skillnader mellan marknader med olika stor konkurrens bland analytiker. Studien visar att abnormal avkastning uppstår på publiceringsdagen för både positiva och negativa rekommendationer. Den abnormala avkastningen som uppstår vid publicering av positiva rekommendationer halveras inom 20 dagar efter publicering, i enlighet med prispresshypotesen, medan den är beständig för negativa rekommendationer. Betydande skillnader i informationsinnehåll konstateras således utifrån om rekommendationerna har ett positivt eller negativt innehåll. Inga betydande skillnader kan konstateras mellan rekommendationers påverkan på Stockholmsbörsen och resultat från amerikanska studier, trots en förväntan om större svårigheter för analytiker att identifiera felvärderade aktier på den lägre konkurrensutsatta Stockholmsbörsen