8 results on '"Chirvasa, Mihaela"'
Search Results
2. Myocardial Strain Predicts Cardiovascular Morbidity and Death: A UK Biobank Cardiovascular Magnetic Resonance Study
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Chadalavada, Sucharitha, primary, Fung, Kenneth, additional, Rauseo, Elisa, additional, Lee, Aaron, additional, Amir-Khalili, Alborz, additional, Paiva, Jose, additional, Naderi, Hafiz, additional, Banik, Shantanu, additional, Chirvasa, Mihaela, additional, Jensen, Magnus, additional, Aung, Nay, additional, and Petersen, Steffen, additional
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- 2024
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3. Single and binary Black Holes and their active environment
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Biermann, Peter L., Chirvasa, Mihaela, Falcke, Heino, Markof, Sera, and Zier, Christian
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Astrophysics - Abstract
In this short review we describe some of the latest endeavours to understand the activity around Black Holes. First, it has been possible to demonstrate that a large part of the electromagnetic emission observed can be interpreted as arising from the jet; this explains at once all spectral features and their variability. Second we dwell on the concept that merging galaxies naturally lead to merging Black Holes. Here we emphasize two aspects: a) the torque exerted by the binary Black Holes carves a torus like distribution out of the stellar population near to the Black Hole binary; b) We consider the last stages of the Black Hole binary merger, taking into account the angle between the spin of the primary Black Hole, and the orbital spin of the second Black Hole. We show that the loss of orbital angular momentum is very strongly spin-dependent; for large angles between the two spins the angular momentum loss is strongly inhibited, allowing spin flip of the primary Black Hole which preserves a high angular momentum relative to the maximum allowed. This ensures that both before and after the merger the accretion disk may reach to very small distances from the central Black Hole, with very high local temperatures right near the base of the jet: This is especially interesting in the case that forming the jet requires the formation of an ADAF like ring near the inner edge of the disk, as suggested by some earlier work. It also may have consequences for the initial hadronic interactions right near the base of the jet. Finally, this may also have important implications for the discovery of gravitational radiation bursts from the merger of black holes; the spin dependence needs to be taken into account., Comment: 17 pages, 10 figures,"Invited lecture, Proceedings of the 7eme Colloquium Cosmologie, `High Energy Astrophysics from and for Space', Paris, June 2002, Eds. N. Sanchez and H. de Vega, in press"
- Published
- 2002
4. Kiosk 11R-TB-01 - Strain Calculation Validation Using Realistic Phantoms
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Werys, Konrad, Chirvasa, Mihaela, Sharma, Gulshan, Olbrechts, Annik, Delgado, Diego, Lee, Estee, Banik, Shantanu, and Amir-Khalili, Alborz
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- 2024
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5. CMR 4-144 - Myocardial Strain Predicts Cardiovascular Morbidity and Death: A UK Biobank Cardiovascular Magnetic Resonance Study
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Chadalavada, Sucharitha, Fung, Kenneth, Rauseo, Elisa, Lee, Aaron, Amir-Khalili, Alborz, Paiva, Jose, Naderi, Hafiz, Banik, Shantanu, Chirvasa, Mihaela, Jensen, Magnus, Aung, Nay, and Petersen, Steffen
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- 2024
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6. Finite Differenzen für hyperbolische Gleichungen erster Ordnung in der Zeit, zweiter Ordnung im Raum in der numerischen Relativitätstheorie
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Chirvasa, Mihaela
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Institut für Physik und Astronomie ,ddc:530 - Abstract
This thesis is concerned with the development of numerical methods using finite difference techniques for the discretization of initial value problems (IVPs) and initial boundary value problems (IBVPs) of certain hyperbolic systems which are first order in time and second order in space. This type of system appears in some formulations of Einstein equations, such as ADM, BSSN, NOR, and the generalized harmonic formulation. For IVP, the stability method proposed in [14] is extended from second and fourth order centered schemes, to 2n-order accuracy, including also the case when some first order derivatives are approximated with off-centered finite difference operators (FDO) and dissipation is added to the right-hand sides of the equations. For the model problem of the wave equation, special attention is paid to the analysis of Courant limits and numerical speeds. Although off-centered FDOs have larger truncation errors than centered FDOs, it is shown that in certain situations, off-centering by just one point can be beneficial for the overall accuracy of the numerical scheme. The wave equation is also analyzed in respect to its initial boundary value problem. All three types of boundaries - outflow, inflow and completely inflow that can appear in this case, are investigated. Using the ghost-point method, 2n-accurate (n = 1, 4) numerical prescriptions are prescribed for each type of boundary. The inflow boundary is also approached using the SAT-SBP method. In the end of the thesis, a 1-D variant of BSSN formulation is derived and some of its IBVPs are considered. The boundary procedures, based on the ghost-point method, are intended to preserve the interior 2n-accuracy. Numerical tests show that this is the case if sufficient dissipation is added to the rhs of the equations. Diese Doktorarbeit beschäftigt sich mit der Entwicklung numerischer Verfahren für die Diskretisierung des Anfangswertproblems und des Anfangs-Randwertproblems unter Einsatz von finite-Differenzen-Techniken für bestimmte hyperbolischer Systeme erster Ordnung in der Zeit und zweiter Ordnung im Raum. Diese Art von Systemen erscheinen in einigen Formulierungen der Einstein'schen-Feldgleichungen, wie zB. den ADM, BSSN oder NOR Formulierungen, oder der sogenanten verallgemeinerten harmonischen Darstellung. Im Hinblick auf das Anfangswertproblem untersuche ich zunächst tiefgehend die mathematischen Eigenschaften von finite-Differenzen-Operatoren (FDO) erster und zweiter Ordnung mit 2n-facher Genaugigkeit. Anschließend erweitere ich eine in der Literatur beschriebene Methode zur Stabilitätsanalyse für Systeme mit zentrierten FDOs in zweiter und vierter Genauigkeitsordung auf Systeme mit gemischten zentrierten und nicht zentrierten Ableitungsoperatoren 2n-facher Genauigkeit, eingeschlossen zusätzlicher Dämpfungsterme, wie sie bei numerischen Simulationen der allgemeinen Relativitätstheorie üblich sind. Bei der Untersuchung der einfachen Wellengleichung als Fallbeispiel wird besonderes Augenmerk auf die Analyse der Courant-Grenzen und numerischen Geschwindigkeiten gelegt. Obwohl unzentrierte, diskrete Ableitungsoperatoren größere Diskretisierungs-Fehler besitzen als zentrierte Ableitungsoperatoren, wird gezeigt, daß man in bestimmten Situationen eine Dezentrierung des numerischen Moleküls von nur einem Punkt bezüglich des zentrierten FDO eine höhere Genauigkeit des numerischen Systems erzielen kann. Die Wellen-Gleichung in einer Dimension wurde ebenfalls im Hinblick auf das Anfangswertproblem untersucht. In Abhängigkeit des Wertes des sogenannten Shift-Vektors, müssen entweder zwei (vollständig eingehende Welle), eine (eingehende Welle) oder keine Randbedingung (ausgehende Welle) definiert werden. In dieser Arbeit wurden alle drei Fälle mit Hilfe der 'Ghost-point-methode' numerisch simuliert und untersucht, und zwar auf eine Weise, daß alle diese Algorithmen stabil sind und eine 2n-Genauigkeit besitzen. In der 'ghost-point-methode' werden die Evolutionsgleichungen bis zum letzen Punkt im Gitter diskretisiert unter Verwendung von zentrierten FDOs und die zusätzlichen Punkte die am Rand benötigt werden ('Ghost-points') werden unter Benutzung von Randwertbedingungen und Extrapolationen abgeschätzt. Für den Zufluß-Randwert wurde zusätzlich noch eine andere Implementierung entwickelt, welche auf der sogenannten SBP-SAT (Summation by parts-simulatanous approximation term) basiert. In dieser Methode werden die diskreten Ableitungen durch Operatoren angenähert, welche die 'Summation-by-parts' Regeln erfüllen. Die Randwertbedingungen selber werden in zusätzlichen Termen integriert, welche zu den Evolutionsgleichnungen der Punkte nahe des Randes hinzuaddiert werden und zwar auf eine Weise, daß die 'summation-by-parts' Eigenschaften erhalten bleiben. Am Ende dieser Arbeit wurde noch eine eindimensionale (kugelsymmetrische) Version der BSSN Formulierung abgeleitet und einige physikalisch relevanten Anfangs-Randwertprobleme werden diskutiert. Die Randwert-Algorithmen, welche für diesen Fall ausgearbeitet wurden, basieren auf der 'Ghost-point-Methode' and erfüllen die innere 2n-Genauigkeit solange genügend Reibung in den Gleichungen zugefügt wird.
- Published
- 2010
7. Myocardial Strain Measured by Cardiac Magnetic Resonance Predicts Cardiovascular Morbidity and Death.
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Chadalavada, Sucharitha, Fung, Kenneth, Rauseo, Elisa, Lee, Aaron M., Khanji, Mohammed Y., Amir-Khalili, Alborz, Paiva, Jose, Naderi, Hafiz, Banik, Shantanu, Chirvasa, Mihaela, Jensen, Magnus T., Aung, Nay, and Petersen, Steffen E.
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CARDIAC magnetic resonance imaging , *HEART failure , *MYOCARDIAL infarction , *PROGNOSIS , *STROKE ,CARDIOVASCULAR disease related mortality - Abstract
Myocardial strain using cardiac magnetic resonance (CMR) is a sensitive marker for predicting adverse outcomes in many cardiac disease states, but the prognostic value in the general population has not been studied conclusively. The goal of this study was to assess the independent prognostic value of CMR feature tracking (FT)—derived LV global longitudinal (GLS), circumferential (GCS), and radial strain (GRS) metrics in predicting adverse outcomes (heart failure, myocardial infarction, stroke, and death). Participants from the UK Biobank population imaging study were included. Univariable and multivariable Cox models were used for each outcome and each strain marker (GLS, GCS, GRS) separately. The multivariable models were tested with adjustment for prognostically important clinical features and conventional global LV imaging markers relevant for each outcome. Overall, 45,700 participants were included in the study (average age 65 ± 8 years), with a median follow-up period of 3 years. All univariable and multivariable models demonstrated that lower absolute GLS, GCS, and GRS were associated with increased incidence of heart failure, myocardial infarction, stroke, and death. All strain markers were independent predictors (incrementally above some respective conventional LV imaging markers) for the morbidity outcomes, but only GLS predicted death independently: (HR: 1.18; 95% CI: 1.07-1.30). In the general population, LV strain metrics derived using CMR-FT in radial, circumferential, and longitudinal directions are strongly and independently predictive of heart failure, myocardial infarction, and stroke, but only GLS is independently predictive of death in an adult population cohort. [ABSTRACT FROM AUTHOR]
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- 2024
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8. Quality control of cardiac magnetic resonance imaging segmentation, feature tracking, aortic flow, and native T1 analysis using automated batch processing in the UK Biobank study.
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Chadalavada S, Rauseo E, Salih A, Naderi H, Khanji M, Vargas JD, Lee AM, Amir-Kalili A, Lockhart L, Graham B, Chirvasa M, Fung K, Paiva J, Sanghvi MM, Slabaugh GG, Jensen MT, Aung N, and Petersen SE
- Abstract
Aims: Automated algorithms are regularly used to analyse cardiac magnetic resonance (CMR) images. Validating data output reliability from this method is crucial for enabling widespread adoption. We outline a visual quality control (VQC) process for image analysis using automated batch processing. We assess the performance of automated analysis and the reliability of replacing visual checks with statistical outlier (SO) removal approach in UK Biobank CMR scans., Methods and Results: We included 1987 CMR scans from the UK Biobank COVID-19 imaging study. We used batch processing software (Circle Cardiovascular Imaging Inc.-CVI42) to automatically extract chamber volumetric data, strain, native T1, and aortic flow data. The automated analysis outputs (∼62 000 videos and 2000 images) were visually checked by six experienced clinicians using a standardized approach and a custom-built R Shiny app. Inter-observer variability was assessed. Data from scans passing VQC were compared with a SO removal QC method in a subset of healthy individuals ( n = 1069). Automated segmentation was highly rated, with over 95% of scans passing VQC. Overall inter-observer agreement was very good (Gwet's AC2 0.91; 95% confidence interval 0.84, 0.94). No difference in overall data derived from VQC or SO removal in healthy individuals was observed., Conclusion: Automated image analysis using CVI42 prototypes for UK Biobank CMR scans demonstrated high quality. Larger UK Biobank data sets analysed using these automated algorithms do not require in-depth VQC. SO removal is sufficient as a QC measure, with operator discretion for visual checks based on population or research objectives., Competing Interests: Conflict of interest: S.E.P. provides consultancy to Circle Cardiovascular Imaging, Inc., Calgary, Alberta, Canada. The remaining authors have nothing to disclose., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Cardiology.)
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- 2024
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