35 results on '"Martin Grabe"'
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2. STG-CT: High-vacuum plume test facility for chemical thrusters
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Martin Grabe
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Technology - Abstract
The STG-CT, operated by the DLR Institute for Aerodynamics and Flow Technology in Göttingen, is a vacuum facility specically designed to provide and maintain a space-like vacuum environment for researching plume flow and plume impingement from satellite reaction control thrusters. Its unique liquid-helium driven cryopump of 30m2 allows maintaining a background pressure
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- 2016
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3. The Effect of Impingement Angle on Bipropellant Thruster Plume Degradation of Spacecraft Materials
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Courtney Steagall, Crystal Quiroz, Brian Tulaba, Frederick Lutfy, Leonard Suess, Katie Fox, Alvin Huang, Carlos Soares, and Martin Grabe
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Spacecraft Propulsion and Power - Abstract
Unburned and partially combusted liquid propellant present in bipropellant thruster plumes can contaminate and damage external spacecraft materials. Microscopic impact features due to high-speed droplet impacts have been observed on space shuttle flight experiments and International Space Station (ISS) returned flight hardware. Analytical results have shown that particle impingement angle greatly affects surface damage, with normal impacts being the most severe and highly oblique impacts being more benign. The effect of thruster plume impingement angle on material degradation has now been further studied following a bipropellant thruster plume test performed at the high-vacuum plume test facility for chemical thrusters at DLR Göttingen, STG-CT. Several spacecraft material samples were exposed to the freely expanding pulsed thruster plume at a range of impingement angles (from 0 to 75 deg). Results of post-test evaluations and potential spaceflight applications are summarized.
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- 2024
4. Master equation approach for modeling diatomic gas flows with a kinetic Fokker-Planck algorithm.
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Christian Hepp, Martin Grabe, and Klaus Hannemann
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- 2020
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5. The evolving value assessment of cancer therapies: Results from a modified Delphi study
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Myrto Lee, Hugo Larose, Martin Gräbeldinger, Jon Williams, Anne-Marie Baird, Susan Brown, Johannes Bruns, Russell Clark, Javier Cortes, Giuseppe Curigliano, Andrea Ferris, Louis P. Garrison, Y.K. Gupta, Ravindran Kanesvaran, Gary Lyman, Luca Pani, Zack Pemberton-Whiteley, Tomas Salmonson, Peter Sawicki, Barry Stein, Dong-Churl Suh, Galina Velikova, and Jens Grueger
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Public aspects of medicine ,RA1-1270 - Abstract
The move toward early detection and treatment of cancer presents challenges for value assessment using traditional endpoints. Current cancer management rarely considers the full economic and societal benefits of therapies. Our study used a modified Delphi process to develop principles for defining and assessing value of cancer therapies that aligns with the current trajectory of oncology research and reflects broader notions of value. 24 experts participated in consensus-building activities across 5 months (16 took part in structured interactions, including a survey, plenary sessions, interviews, and off-line discussions, while 8 participated in interviews). Discussion focused on: 1) which oncology-relevant endpoints should be used for assessing treatments for early-stage cancer and access decisions for early-stage treatments, and 2) the importance of additional value components and how these can be integrated in value assessments. The expert group reached consensus on 4 principles in relation to the first area (consider oncology-relevant endpoints other than overall survival; build evidence for endpoints that provide earlier indication of efficacy; develop evidence for the next generation of predictive measures; use managed entry agreements supported by ongoing evidence collection to address decision-maker evidence needs) and 3 principles in relation to the second (routinely use patient reported outcomes in value assessments; assess broad economic impact of new medicines; consider other value aspects of relevance to patients and society).
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- 2024
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6. Flow characteristics of monopropellant micro-scale planar nozzles
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Klaus Hannemann, Martin Grabe, and Daniel T. Banuti
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Overall pressure ratio ,Propellant ,0209 industrial biotechnology ,Materials science ,Nozzle ,Flow (psychology) ,Aerospace Engineering ,Thrust ,02 engineering and technology ,Mechanics ,Propulsion ,Rocket engine ,7. Clean energy ,01 natural sciences ,010305 fluids & plasmas ,MEMS ,020901 industrial engineering & automation ,Satellite ,0103 physical sciences ,Hydrazine ,Cube sat ,Specific impulse ,Knudsen number ,Microscale chemistry - Abstract
We investigate the flow in planar microscale nozzles and find that design and analysis paradigms based on the assumption of a dominant isentropic core with moderate viscosity corrections are not valid. Instead, the flow downstream of the throat is dominated by boundary layers that may choke the flow to subsonic velocities. The geometrical expansion ratio is found to be essentially irrelevant, instead, the length from throat to exit plane is found to be a much more important design parameter. Full 3D simulations are required to predict the flow topology; thermophysical modeling of the expanding gas has a noticeable impact on predicted performance. An analytical estimation of the Knudsen number in the expanding flow is given, allowing to determine its values from the expansion pressure ratio. An axial thrust analysis suggests truncation of the nozzle, resulting in a predicted 30% increase in thrust and 30% increase in specific impulse compared to the baseline configuration. The work has been carried out within the European Commission co-funded PRECISE project which was focused on designing and testing a micro chemical propulsion system thruster prototype using catalytically decomposed hydrazine as propellant.
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- 2019
7. Left Ventricular Reverse Remodeling after Surgical Aortic Valve Replacement for Aortic Regurgitation—An Explorative Study
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Zsuzsanna Arnold, Alexander Elnekheli, Daniela Geisler, Thomas Aschacher, Verena Lenz, Bernhard Winkler, Reinhard Moidl, and Martin Grabenwöger
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reverse remodeling ,aortic regurgitation ,biological valve ,mechanical valve ,Medicine - Abstract
Background: The timing of treatment for chronic aortic valve regurgitation (AR), especially in asymptomatic patients, is gaining attention since less invasive strategies have become available. The aim of the present study was to evaluate left ventricular reverse remodeling after aortic valve replacement (AVR) for severe AR. Methods: Patients (n = 25) who underwent surgical AVR for severe AR with left ventricular ejection fraction (LVEF) less than 55% were included in this study. Preprocedural and follow-up clinical and echocardiographic measurements of LVEF and left ventricular (LV) diameters were retrospectively analyzed. Results: Mean LVEF increased significantly following surgical AVR (p < 0.0001). LV diameters showed a clear regression (p = 0.0088). Younger patients and those receiving a mechanical valve tended to have less improved LVEF on follow-up than patients over 60 years or the ones who were implanted with a biological prosthesis (p = 0.0239 and p = 0.069, respectively). Gender had no effect on the degree of LVEF improvement (p = 0.4908). Conclusions: We demonstrated significant LV reverse remodeling following AVR for AR. However, more data are needed on LV functional and geometrical improvement comparing the different types of valve prostheses to provide an optimal treatment strategy.
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- 2024
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8. Europa Lander mission concept plume-induced contamination: Experimental testing and computational analysis
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William A. Hoey, Carlos E. Soares, Martin Grabe, and Anthony T. Wong
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Contamination control ,Experimental testing ,business.industry ,Environmental science ,Computational analysis ,Direct simulation Monte Carlo ,Contamination ,Aerospace engineering ,business ,Jet propulsion ,Monopropellant ,Plume - Abstract
The Jet Propulsion Laboratory (JPL) has pursued a multi-disciplinary effort to experimentally characterize and computationally simulate the effects of powered descent onto the Europan surface. As part of the proposed Europa Lander technology development and maturation activities, JPL Contamination Control and the German Aerospace Center (DLR) are conducting a test program to characterize monopropellant plume-induced contamination, the preliminary results of which are showcased in this presentation. These measurements have been used in the further development of JPL’s computational physics simulations of descent engine plumes interacting with the Europan surface with direct simulation Monte Carlo (DSMC) techniques, and in broader support of contamination control strategies for the proposed Europa Lander mission.
- Published
- 2020
9. Cubic Fokker–Planck method for rarefied monatomic gas flow through a slit and an orifice
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Klaus Hannemann, Eunji Jun, and Martin Grabe
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Overall pressure ratio ,Monatomic gas ,General Computer Science ,Vacuum Flows ,01 natural sciences ,FP-DSMC Hybrid ,Mathematics::Numerical Analysis ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,symbols.namesake ,0103 physical sciences ,Rarefied Gas Dynamics ,0101 mathematics ,DSMC ,Physics ,Stochastic process ,Fokker-Planck (FP) ,General Engineering ,Mechanics ,Collision ,010101 applied mathematics ,Boltzmann constant ,symbols ,Fokker–Planck equation ,Direct simulation Monte Carlo ,SPARTA ,Body orifice - Abstract
The flow through a thin slit and a thin orifice is studied with the Direct Simulation Monte Carlo (DSMC), cubic Fokker–Planck (FP), and a coupled FP-DSMC hybrid method. Pressure driven monatomic gas flows through a slit and an orifice with various values of degree of rarefaction and pressure ratio are computed. The DSMC method is physically accurate for all flow regimes; however it is computationally expensive in high density, near continuum regions. An alternative stochastic particle scheme, the cubic FP kinetic model has addressed this issue by approximating the particle collisions involved in the Boltzmann collision integral with continuous stochastic processes. The ability of the cubic FP method to reproduce breakdown of translational equilibrium is discussed. In addition, a coupled FP-DSMC hybrid scheme is employed aiming at an efficient and accurate solution. The FP-DSMC hybrid scheme employs DSMC in rarefied regions and FP method in near continuum flow regions. Numerical procedures of the cubic FP method are implemented within the framework of an existing DSMC-solver, SPARTA. The FP-DSMC hybrid solution reproduces pure DSMC solution with improved computational efficiency up to a factor of eight for vacuum flow through a thin slit.
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- 2018
10. Consensus statement—graft treatment in cardiovascular bypass graft surgery
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Maximilian Y. Emmert, Johannes Bonatti, Etem Caliskan, Mario Gaudino, Martin Grabenwöger, Martin T. Grapow, Paul Phillip Heinisch, Teresa Kieser-Prieur, Ki-Bong Kim, Attila Kiss, Fatima Mouriquhe, Markus Mach, Adrianna Margariti, John Pepper, Louis P. Perrault, Bruno K. Podesser, John Puskas, David P. Taggart, Om P. Yadava, and Bernhard Winkler
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CABG ,endothelium ,heart ,radial artery ,VEST ,Diseases of the circulatory (Cardiovascular) system ,RC666-701 - Abstract
Coronary artery bypass grafting (CABG) is and continues to be the preferred revascularization strategy in patients with multivessel disease. Graft selection has been shown to influence the outcomes following CABG. During the last almost 60 years saphenous vein grafts (SVG) together with the internal mammary artery have become the standard of care for patients undergoing CABG surgery. While there is little doubt about the benefits, the patency rates are constantly under debate. Despite its acknowledged limitations in terms of long-term patency due to intimal hyperplasia, the saphenous vein is still the most often used graft. Although reendothelialization occurs early postoperatively, the process of intimal hyperplasia remains irreversible. This is due in part to the persistence of high shear forces, the chronic localized inflammatory response, and the partial dysfunctionality of the regenerated endothelium. “No-Touch” harvesting techniques, specific storage solutions, pressure controlled graft flushing and external stenting are important and established methods aiming to overcome the process of intimal hyperplasia at different time levels. Still despite the known evidence these methods are not standard everywhere. The use of arterial grafts is another strategy to address the inferior SVG patency rates and to perform CABG with total arterial revascularization. Composite grafting, pharmacological agents as well as latest minimal invasive techniques aim in the same direction. To give guide and set standards all graft related topics for CABG are presented in this expert opinion document on graft treatment.
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- 2024
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11. Non-equilibrium parameter for a hybrid Fokker-Planck/ DSMC scheme
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Christian Hepp, Klaus Hannemann, and Martin Grabe
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Physics ,Hypersonic speed ,Direct Simulation Monte Carlo (DSMC) ,Particle number ,Raumfahrzeuge, GO ,Cylinder ,Kinetic energy ,Hypersonic Flow ,Weighting ,Mathematics::Numerical Analysis ,Physics::Fluid Dynamics ,Fokker–Planck equation ,Statistical physics ,Knudsen number ,Direct simulation Monte Carlo ,Fokker-Planck ,Magnetosphere particle motion - Abstract
In this work we investigate the kinetic Fokker-Planck (FP) model [1, 2] concerning its applicability to simulate hyper-sonic, rarefied gas flow. As in the direct simulation Monte Carlo (DSMC) algorithm, the FP model simulates the stochastic motion of a set of particles through the computational domain which results in a simple coupling of both methods. No collisions must be calculated in the FP approach and so larger cell and time step sizes than by DSMC calculations can be used. Because of this, the FP model holds the potential to be more efficient than DSMC where the Knudsen number is small. Further we present and investigate a hybridisation scheme for the FP and DSMC algorithms. We derive a non-equilibrium parameter from the Fokker-Planck- and Boltzmann-operator which indicates the validity of the FP model. In hybrid simulations this parameter is used to partition the computational domain in DSMC and FP regions. The particle motion is processed similarly in both regions, only the procedure for assigning new particle velocities differs. To achieve an equal number of particles per cell, weighting factors depended on the cell size are used. The hybridisation scheme is tested for one-dimensional shock and two-dimensional cylinder flows and gives results in agreement to pure DSMC simulations. An efficiency study shows, that the hybrid scheme is roughly five times faster than a pure DSMC simulation for a hypersonic cylinder flow test case.
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- 2019
12. Cubic Fokker-Planck-DSMC hybrid method for diatomic gas flow through a slit
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Eunji Jun, Klaus Hannemann, and Martin Grabe
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Plume ,Physics ,Direct Simulation Monte Carlo (DSMC) ,Flow (mathematics) ,Quantum electrodynamics ,Fokker–Planck equation ,Fokker-Planck ,Orifice ,Slit ,Diatomic molecule - Published
- 2019
13. Effect of source geometry on fully expanding free jets
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Christian Hepp, Klaus Hannemann, Georg Dettleff, and Martin Grabe
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Plume ,Physics ,Mass flux ,Impact pressure ,Ultra-high vacuum ,Reynolds number ,Geometry ,Conical surface ,Physics::Fluid Dynamics ,symbols.namesake ,symbols ,Cylinder ,STG-CT ,Orifice ,Body orifice - Abstract
The impact of two geometric configurations of sonic orifices on the free plume expansion into high vacuum is studied both experimentally and numerically. One configuration is a flat-faced cylinder, into whose face a square edged orifice is centrally machined. This simple type of orifice is often used for ease of manufacturing. The other source features a sharp-edged orifice, whose outer walls are inclined backwards 135o from the axis. Nitrogen plumes emanating at two source Reynolds numbers, Re* ∈ {3850, 15400}, are compared here. Mass flux measurements with a free-molecular impact pressure probe (“Patterson probe”) show, that the plume originating from the flat-faced orifice expands freely within about 45 o from the axis. Numerical analysis of the plume near-field suggests, that molecules scattered back from the walls of a conical orifice only affect the plume expansion at angles greater than about 80o from the axis.The impact of two geometric configurations of sonic orifices on the free plume expansion into high vacuum is studied both experimentally and numerically. One configuration is a flat-faced cylinder, into whose face a square edged orifice is centrally machined. This simple type of orifice is often used for ease of manufacturing. The other source features a sharp-edged orifice, whose outer walls are inclined backwards 135o from the axis. Nitrogen plumes emanating at two source Reynolds numbers, Re* ∈ {3850, 15400}, are compared here. Mass flux measurements with a free-molecular impact pressure probe (“Patterson probe”) show, that the plume originating from the flat-faced orifice expands freely within about 45 o from the axis. Numerical analysis of the plume near-field suggests, that molecules scattered back from the walls of a conical orifice only affect the plume expansion at angles greater than about 80o from the axis.
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- 2019
14. A kinetic Fokker–Planck approach for modeling variable hard-sphere gas mixtures
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Klaus Hannemann, Christian Hepp, and Martin Grabe
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010302 applied physics ,Physics ,None equilibrium flows ,Raumfahrzeuge, GO ,General Physics and Astronomy ,Fokker-Planck equation ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Kinetic energy ,01 natural sciences ,Stochastic solution ,Kinetic particle method ,lcsh:QC1-999 ,Interaction potential ,Test case ,0103 physical sciences ,Particle ,Fokker–Planck equation ,Statistical physics ,Direct simulation Monte Carlo ,Multi species flow ,0210 nano-technology ,DSMC ,lcsh:Physics ,Variable (mathematics) - Abstract
Kinetic Fokker–Planck (FP) methods for modeling rarefied gas flows have received increasing attention over the last few years. However, formulating such models for realistic multi-species gases is still an open subject of research. Therefore, in this letter, we develop a kinetic FP model for describing gas mixtures with particles interacting according to the variable hard-sphere interaction potential. In accordance with the kinetic FP framework, a stochastic solution algorithm is employed in order to solve the model on a particle level. Different test cases are carried out, and the performance of the proposed method is compared with the direct simulation Monte Carlo algorithm.
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- 2020
15. A kinetic Fokker–Planck approach to model hard-sphere gas mixtures
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Klaus Hannemann, Martin Grabe, and Christian Hepp
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Fluid Flow and Transfer Processes ,Physics ,None equilibrium flows ,Stochastic process ,Mechanical Engineering ,Monte Carlo method ,Raumfahrzeuge, GO ,Computational Mechanics ,Fokker-Planck equation ,Condensed Matter Physics ,Kinetic energy ,Collision ,Kinetic particle method ,01 natural sciences ,Boltzmann equation ,010305 fluids & plasmas ,Mechanics of Materials ,0103 physical sciences ,Stochastic simulation ,Fokker–Planck equation ,Statistical physics ,Multi species flow ,DSMC ,010306 general physics ,Ansatz - Abstract
Since its first introduction, it has always been a subject of research to find models for a meaningful approximation of the highly accurate but complex Boltzmann equation. In the kinetic Fokker-Planck (FP) approach, a FP operator in velocity space is employed to approximate the collision integral of the Boltzmann equation. Instead of directly solving the resulting FP equation, a Monte Carlo technique is used to model an associated random process. This approach leads to an efficient stochastic solution algorithm. In recent years, the FP ansatz has become increasingly popular. Nevertheless, the modeling of gas mixtures in the context of kinetic FP has so far only been addressed in a very few papers. This article introduces a kinetic FP model that is capable of describing gas mixtures with particles interacting according to the hard-sphere collision model. The model is constructed to reproduce Grad's 13 moment equations on a Navier-Stokes level of accuracy for gas mixtures with an arbitrary number of constituents. A stochastic simulation algorithm is derived that ensures a correct evolution of the species diffusion velocities and the species temperatures for a homogeneous gas, regardless of the applied time step size. It is shown that the proposed model is capable of correctly predicting shear stresses, heat fluxes, and diffusion velocities for different test cases, employing a He-Ar mixture.
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- 2020
16. Wie funktioniert Psychotherapie? (Wissen & Leben) : Ein Buch aus der Praxis für alle, die es wissen wollen
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Martin Grabe and Martin Grabe
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Viel bunte Erfahrung statt graue Theorie. Selten wurde ein Buch so konsequent aus der Praxiserfahrung heraus geschrieben: Dr. Martin Grabe, Leiter eines psychotherapeutischen Weiterbildungsinstitutes und Chefarzt einer psychosomatischen Abteilung, schildert fern jeglicher grauer Theorie, wie erfahrene Therapeutinnen und Therapeuten arbeiten und Psychotherapie gelingt. - Auf welchem Weg werden Änderungen angestoßen? - Wie gelangt man zu Modellen über die jeweilige Störung der Patientin/des Patienten? - Was geht in der Therapeutin/im Therapeuten vor, während sie/er mit der Patientin/dem Patienten spricht? Ein Buch für Psychologinnen und Psychologen und Ärztinnen und Ärzte in psychotherapeutischer Weiterbildung, wie es wirklich benötigt wird. Ein Buch für Patientinnen und Patienten und deren Angehörige, die einmal wissen möchten, was sich in einer Psychotherapie abspielt, zwischenmenschlich und in deren Innenleben. Ein Buch für alle, die mehr wissen wollen über die Wirkung von Psychotherapie. Therapieschulen-übergreifend, durch zahlreiche Exkurse höchst erhellend – und immer frei heraus. Dieses Buch richtet sich an: - Psychologinnen und Psychologen - Ärztinnen und Ärzte in psychotherapeutischer Weiterbildung - Patientinnen und Patienten und deren Angehörige; alle, die mehr wissen wollen über die Wirkung von Psychotherapie Aus dem Inhalt Wie innere Konflikte das Leben einengen und wo Therapie ansetzen kann | Wie findet man den zentralen Beziehungskonflikt? | Die Therapeutische Beziehung | Verstrickungen lösen und Entscheidungen treffen | Psychotherapie und Spiritualität | Therapieschulen im Überblick | Spezielle Störungsbilder
- Published
- 2018
17. Impact of CytoSorb® on interleukin-6 in cardiac surgery
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Daniela Geisler, Noemi Arleth, Johannes Grabenwöger, Zsuzsanna Arnold, Thomas Aschacher, Bernhard Winkler, Markus Mach, and Martin Grabenwöger
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IL-6 ,cytokine storm ,CytoSorb® ,hemadsorption ,cardiac surgery ,Diseases of the circulatory (Cardiovascular) system ,RC666-701 - Abstract
ObjectiveCardiac surgery is known to activate a cascade of inflammatory mediators leading to a systemic inflammatory response. Hemadsorption (HA) devices such as CytoSorb® have been postulated to mitigate an overshooting immune response, which is associated with increased morbidity and mortality, and thus improve outcome. We aimed to investigate the effect of CytoSorb® on interleukin (IL)-6 levels in patients undergoing complex cardiac surgery in comparison to a control group.MethodsA total of 56 patients (28 CytoSorb®, 28 control) undergoing acute and elective cardiac surgery between January 2020 and February 2021 at the Department of Cardiac and Vascular Surgery, Clinic Floridsdorf, Vienna, were retrospectively analyzed. The primary endpoint was the difference in IL-6 levels between the CytoSorb® and control group. Secondary endpoint was periprocedural mortality.ResultsCytoSorb®, installed in the bypass circuit, had no significant effect on IL-6 levels. IL-6 peaked on the first postoperative day (HA: 775.3 ± 838.4 vs. control: 855.5 ± 1,052.9 pg/ml, p = 0.856). In total, three patients died in the HA group, none in the control (logistic regression model, p = 0.996). Patients with an increased Euroscore II of 7 or more showed a reduced IL-6 response compared to patients with an Euroscore II below 7 (178.3 ± 63.1 pg/ml vs. 908.6 ± 972.6 pg/ml, p-value = 0.00306).ConclusionsNo significant reduction of IL-6 levels or periprocedural mortality through intraoperative HA with CytoSorb® in patients undergoing cardiac surgery was observed. However, this study was able to show a reduced immunologic response in patients with a high Euroscore II. The routine application of CytoSorb® in cardiac surgery to reduce inflammatory mediators has to be scrutinized in future prospective randomized studies.
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- 2023
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18. Impact of nozzle separation on the plumes of two parallel thrusters
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Martin Grabe, Klaus Hannemann, and Georg Dettleff
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Mass flux ,Physics ,Stagnation temperature ,business.industry ,Nozzle ,Rarefaction ,Reynolds number ,Inflow ,Mechanics ,Plume interaction ,Plume ,symbols.namesake ,symbols ,backflow ,Direct simulation Monte Carlo ,Aerospace engineering ,DSMC ,business - Abstract
Two identical, interacting plumes emanating from model thrusters with parallel axes separated from 50 to 150 throat diameters are studied numerically. The nozzle throat Reynolds number is set to nearly 15, 000 to match that of a small bi-propellant attitude control thruster, but the simulated gas is nitrogen with a stagnation temperature of 300 K. The near-isentropic, dense plume core is computed with the DLR Navier-Stokes solver TAU and the conditions at a suitably defined interface are then used on the inflow boundary of a separately conducted direct simulation Monte Carlo (DSMC) simulation. The results are shown to agree favorably with particle flux measurements performed in the DLR high-vacuum plume test facility for chemical thrusters (STG-CT). Varying the nozzle separation distance alters the degree of rarefaction in the interaction plane, and by tagging DSMC particles according to their origin, the effect on the individual plume may be investigated. The impact of nozzle axis separation on mass flux...
- Published
- 2016
19. Early and midterm results of frozen elephant trunk operation with Evita open stent-graft in patients with Marfan syndrome: results of a multicentre study
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Kazimierz Jan Widenka, Monika Kosiorowska, Heinz Jakob, Davide Pacini, Wolfgang Hemmer, Martin Grabenwoeger, Thanos Sioris, Anton Moritz, and Konstantinos Tsagakis
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Frozen elephant trunk ,International E-vita Open Registry ,Marfan syndrome ,Diseases of the circulatory (Cardiovascular) system ,RC666-701 - Abstract
Abstract Background Endovascular treatment of patients with Marfan syndrome (MFS) is not recommended. Hybrid procedures such as frozen elephant trunk (FET), which combines stent-graft deployment with an integrated non-stented fabric graft for proximal grafting and suturing, have not been previously evaluated. The aim of this study was to assess the safety and feasibility of FET operation in patients with MFS. Methods Patients enrolled in the International E-vita Open Registry (IEOR) who underwent FET procedure between January 2001 and February 2020 meeting Ghent criteria for MFS were included in the study. Early and midterm results were retrospectively analyzed. Preoperative, postoperative and follow-up computed tomography angiography scans were analysed. Results We analyzed 37 patients [mean age 38 ± 11 years, 65% men]. Acute or chronic aortic dissection was present in 35 (95%) patients (14 and 21 patients respectively). Two (5%) patients had an aneurysm without dissection. Malperfusion syndrome was present in 4 patients. Twenty-nine (78%) patients had history of aortic surgical interventions. The 30-day and in-hospital mortality amounted to 8 and 14% respectively. False lumen exclusion was present in 73% in stented segment in last postoperative CT. The overall 5-year survival was 71% and freedom from reintervention downstream was 58% at 5 years. Of the nine patients who required reintervention for distal aortic disease, one patient died. Conclusions FET operation for patients with MFS can be performed with acceptable mortality and morbidity. In long-term follow-up no reinterventions on the aortic arch were required. FET allows for easier second stage operations providing platform for surgical and endovascular reinterventions.
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- 2022
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20. Intrapersonal Conflict in Goals and Values of Patients with Unipolar Depression
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Ulrich Stangier, Martin Grabe, Wolf Lauterbach, Uwe Ukrow, and Karin Schermelleh-Engel
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Adult ,Male ,Personality Inventory ,Psychometrics ,Social Values ,Models, Psychological ,Social value orientations ,Developmental psychology ,Conflict, Psychological ,Interpersonal relationship ,Social cognition ,Cognitive dissonance ,Humans ,Interpersonal Relations ,Problem Solving ,Applied Psychology ,Depression (differential diagnoses) ,Depressive Disorder, Major ,Cognitive vulnerability ,Reproducibility of Results ,General Medicine ,Middle Aged ,Achievement ,Social relation ,Psychiatry and Mental health ,Clinical Psychology ,Female ,Dysthymic Disorder ,Psychology ,Goals ,Cognitive Dissonance ,Intrapersonal communication - Abstract
Background: Although increased conflicts between attitudes and beliefs about certain goals or values are often discussed as important factors in depression, there are only few empirical studies investigating these relations among patients with depressive disorders. Methods: In the present study, we used the Intrapersonal Conflict Test to assess cognitive inconsistencies in goals or values. A total of 53 inpatients with unipolar depression and 24 nondepressed controls (inpatients of an internal and a surgery ward) participated in the study. In addition to the Intrapersonal Conflict Test, patients completed the Beck Depression Inventory, the Dysfunctional Attitude Scale, the Inventory of Interpersonal Problems as well as the Problem Solving Inventory. Results: Compared with controls, patients with depressive disorders showed significantly higher scores for global inconsistencies, inconsistencies within different goals/values, as well as between goals/values and their perceived realization. Significant correlations were found between conflict measures and the Inventory of Interpersonal Problems, as well as the Problem Solving Inventory. Path analyses show that group differences in intrapersonal conflicts were partially mediated by interpersonal problems but not by depressive symptoms or cognitive vulnerability factors. Conclusions: Given the cross-sectional design of the study, the findings of this exploratory study do not allow for conclusions regarding the role of intrapersonal conflicts in the development and course of depression. Nevertheless, the high levels of intrapersonal conflicts observed in the study suggest that inconsistencies in goals or values should be considered in the psychological treatment of depression.
- Published
- 2007
21. Flow Characteristics of Micro-Scale Planar Nozzles
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Daniel T. Banuti, Klaus Hannemann, and Martin Grabe
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Engineering ,nozzle ,business.industry ,Nozzle ,Choke ,Structural engineering ,Mechanics ,Aspect ratio (image) ,MEMS ,Cross section (physics) ,Boundary layer ,Planar ,Flow (mathematics) ,Inviscid flow ,CFD ,business - Abstract
Flow in micro chemical propulsion systems (µCPS) based on etched silicon deviates strongly from its conventional, macroscopic counterparts. This paper reports on peculiarities of small scale planar nozzles with a high aspect ratio, rectangular cross section. Design and analysis paradigms based on the assumption of rationally symmetric flow with a dominant isentropic core are shown to be no longer valid. We will point out insufficiencies of treating planar nozzles as two dimensional, inviscid, or assessing their performance with classical analytical isentropic 1D analysis. Instead, the resulting low Reynolds number flow is boundary layer dominated. Boundary layer build-up from the top and bottom walls threaten to choke the expansion. The geometrical expansion ratio is found to be essentially irrelevant, the length from throat to exit plane is found to be a much more important design parameter. The work has been carried out within the European PRECISE project which is focused on designing and testing a prototype using catalytically decomposed hydrazine as propellant.
- Published
- 2014
22. Numerical Investigation of Two Interacting Parallel Thruster-Plumes and Comparison to Experiment
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Martin Grabe, André Holz, Stefan Ziegenhagen, and Klaus Hannemann
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Engineering ,Impact pressure ,Spacecraft ,business.industry ,Thrust ,Mechanics ,Plume ,Plume interaction ,Attitude control ,symbols.namesake ,Mach number ,Control theory ,Redundancy (engineering) ,symbols ,Patterson probe ,business ,DSMC ,Body orifice - Abstract
Clusters of orbital thrusters are an attractive option to achieve graduated thrust levels and increased redundancy with available hardware, but the heavily under-expanded plumes of chemical attitude control thrusters placed in close proximity will interact, leading to a local amplification of downstream fluxes and of back-flow onto the spacecraft. The interaction of two similar, parallel, axi-symmetric cold-gas model thrusters has recently been studied in the DLR High-Vacuum Plume Test Facility STG under space-like vacuum conditions, employing a Patterson-type impact pressure probe with slot orifice. We reproduce a selection of these experiments numerically, and emphasise that a comparison of numerical results to the measured data is not straight-forward. The signal of the probe used in the experiments must be interpreted according to the degree of rarefaction and local flow Mach number, and both vary dramatically thoughout the flow-field. We present a procedure to reconstruct the probe signal by post-processing the numerically obtained flow-field data and show that agreement to the experimental results is then improved. Features of the investigated cold-gas thruster plume interaction are discussed on the basis of the numerical results.
- Published
- 2014
23. Mediterranean lichens on‐line
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Martin Grabe and Pier Luigi Nimis
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Mediterranean climate ,Geography ,Oceanography ,Plant Science ,Line (text file) ,Lichen ,Ecology, Evolution, Behavior and Systematics - Published
- 1997
24. Response of the Patterson probe in the transition flow regime
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Martin Grabe
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experimental procedures ,Computer simulation ,business.industry ,Angle of attack ,Thermodynamics ,Context (language use) ,Mach numbers ,Monte Carlo methods ,Mechanics ,Computational fluid dynamics ,Environmental impacts ,transition regime ,Knudsen flow ,symbols.namesake ,High pressure ,transition flow regime ,Flow (mathematics) ,Mach number ,symbols ,Free-molecular pressure probe ,Direct Simulation Monte Carlo ,Knudsen number ,Patterson probe ,business ,Mathematics - Abstract
The free-molecular impact pressure probe, also known as Patterson probe, is known and applied for more than half a century now to deduce the number flux of a single species in highly rarefied inert flow. While the working principle is conceptually simple, interpretation of the gauge readings may not be, but approximate formulas for evaluation exist. In the context of cold-gas plume flow and interaction experiments with the obvious large variations in Mach and Knudsen numbers, it may not be clear initially, whether the signals measured with the Patterson probe are obtained in free-molecular flow environment, and hence, whether the mentioned evaluation techniques may be employed. A series of numerical experiments have been conducted using the Direct Simulation Monte-Carlo method, to study the response of the Patterson probe to prescribed free-stream conditions in the transitional flow regime. From the computational results we infer analytical expressions that describe the probe response in transitional regime at zero angle of attack.
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- 2012
25. A Voronoi Grid and a Particle Tracking Algorithm for DSMC
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Martin Grabe and Frank Stollmeier
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Computer simulation ,Discretization ,Numerical analysis ,Probabilistic logic ,Tracking (particle physics) ,Grid ,Raumfahrzeuge ,particle tracking ,Polyhedron ,mesh ,Voronoi diagram ,DSMC ,Algorithm ,Mathematics - Abstract
The DSMC method simulates a gas by three uncoupled steps: moving representative particles through a physical domain, performing probabilistic collisions and estimating the macroscopic state by ensemble averaging. In order to ease computational treatment of these three steps it is convenient to discretize the space with a grid that fits into the boundaries of the physical domain. For efficient particle tracking it is useful that the cells of this grid are convex polyhedra which preferably have no indirect neighbors. To reduce discretization errors in the collision step and to take reasonable averages the cells should be nearly isotropic, whereas their volume is primarily determined by the local flow gradients. Especially the latter condition requires the density of the grid to be continuously adaptable in space and time. We show that grids derived from Voronoi diagrams fulfill these requirements very well.
- Published
- 2011
26. Steady Shock Refraction in Hypersonic Ramp Flow
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Daniel T. Banuti, Martin Grabe, and Klaus Hannemann
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Hypersonic speed ,Engineering ,business.industry ,Mechanics ,Computational fluid dynamics ,Mach wave ,Compressible flow ,Raumfahrzeuge ,Physics::Fluid Dynamics ,symbols.namesake ,Boundary layer ,Refraction ,Optics ,Mach number ,Hypersonics ,symbols ,Oblique shock ,Gasdynamics ,business ,Choked flow ,Shocks - Abstract
This paper discusses features of a supersonic flow with a transversal Mach number stratification when encountering a ramp. A flow of this nature can occur for a variety of reasons around a hypersonic vehicle. Formation of a heated wall boundary layer, external fuel injection on the compression ramp, energy deposition, and film or transpiration cooling are just some of the processes that will establish a flow where a wall near layer features a distinct difference in Mach number compared to the outer flow. This paper will introduce a flow topology framework that will help to understand phenomena associated with this stratification. Shock refraction is identified as the main mechanism which causes a redirection of the flow additional to the ramp deflection. It will be shown how, depending on the Mach number ratios between the layers, shocks or expansion fans will be created that will interact with the surface. This can be the cause for undesired or unexpected temperature and pressure distributions along the wall when shock refraction is not taken into account. As a possible application, it will be shown how shock refraction can act as a virtual external compression ramp. CFD computations are performed using the DLR TAU code, a finite volume, second order accuracy, compressible flow solver.
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- 2011
27. Graft preservation confers myocardial protection during coronary artery bypass grafting
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Philipp Szalkiewicz, Maximilian Y. Emmert, Paul P. Heinisch, Zsuzsanna Arnold, Ingo Crailsheim, Markus Mach, Thomas Aschacher, Martin Grabenwöger, and Bernhard Winkler
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vein graft preservation ,storage solutions ,myocardium ,protection ,coronary artery ,Diseases of the circulatory (Cardiovascular) system ,RC666-701 - Abstract
BackgroundDuring on-pump coronary artery bypass grafting (ONCAB), graft flushing for distal anastomoses testing also perfuses the downstream myocardium. This single-center retrospective study evaluated the impact of specific preservation solutions on myocardial protection during ONCAB.Materials and methodsBetween July 2019 and March 2020 either DuraGraft (DG) or 0.9% Saline/Biseko (SB) was applied to 272 ONCAB. Overall, 166 patients were propensity-matched into two groups. Cardiac enzymes [high-sensitive Troponin I (hs-TnI) and creatine kinase (CK)] were evaluated 7 days post-surgery.ResultsPost-surgery, hs-TnI values were significantly lower from 3 to 6 h (h) up to 4 days in the DG group: 3–6 h: 4,034 ng/L [IQR 1,853–8,654] vs. 5,532 ng/L [IQR 3,633—8,862], p = 0.05; 12–24 h: 2,420 ng/L [IQR 1,408–5,782] vs. 4,166 [IQR 2,052–8,624], p < 0.01; 2 days: 1,095 ng/L [IQR 479–2,311] vs. 1,564 ng/L [IQR 659–5,057], p = 0.02 and at 4 days: 488 ng/L [IQR 232–1,061] vs. 745 ng/L [IQR 319–1,820], p = 0.03. The maximum value: 4,151 ng/L [IQR 2,056–8,621] vs. 6,349 ng/L [IQR 4,061–12,664], p < 0.01 and the median area under the curve (AUC): 6,146 ng/L/24 h [IQR 3,121–13,248] vs. 10,735 ng/L/24 h [IQR 4,859–21,484], p = 0.02 were lower in the DG group. CK values were not significantly different between groups: maximum value 690 [IQR 417–947] vs. 631 [464–979], p = 0.61 and AUC 1,986 [1,226–2,899] vs. 2,081 [1,311–3,063], p = 0.37.ConclusionRepeated graft flushing with DG resulted in lower Troponin values post-surgery suggesting enhanced myocardial protection compared to SB. Additional studies are warranted to further assess the myocardial protection properties of DG.
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- 2022
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28. Characterization of a Free-Molecular Pressure Probe employing Gas-Kinetic Simulation
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Martin Grabe, Georg Dettleff, Rolf-Detlef Boettcher, Klaus Hannemann, Dillmann, Andreas, Heller, Gerd, Kreplin, Hans-Peter, Nitsche, Wolfgang, and Peltzer, Inken
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Free-molecule flow ,Patterson-probe ,Chemistry ,Angle of attack ,Numerical analysis ,rarefied flow ,Flow (psychology) ,Analytical chemistry ,Mechanics ,Kinetic energy ,Raumfahrzeuge ,Plume ,Characterization (materials science) ,Physics::Fluid Dynamics ,free-molecular ,Patterson probe ,DSMC ,Body orifice ,pressure probe ,Backflow - Abstract
Free-molecular pressure probes are employed to deduce particle flux in highly rarefied flow fields, such as the farfield or the backflow region of a plume expanding into vacuum. Analytical approaches to model the probe behavior are known in the literature for some time now. Numerical methods such as DSMC however allow to conduct investigations into the probe response in regimes inaccessible to analytical approaches. Besides, the numerical results may be compared to the analytical models in order to test their fidelity. We computed the response of a probe with slot orifice to a highly rarefied, parallel flow with varying molecular speed ratio. We confirmed the negligible influence of the speed ratio on probe response for low angles of attack, but observed significant deviations from analytical models as the angle of attack approaches 90°.
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- 2010
29. Numerical Simulation of Nozzle Flow into High Vacuum Using Kinetic and Continuum Approaches
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Stefanos Fasoulas, Rolf-Detlef Boettcher, Martin Grabe, Klaus Hannemann, Dillmann, Andreas, Heller, Gerd, Klaas, Michael, Kreplin, Hans-Peter, Nitsche, Wolfgang, and Schröder, Wolfgang
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Hypersonic speed ,Computer simulation ,Chemistry ,business.industry ,Nozzle ,Laminar flow ,Conical surface ,Mechanics ,Computational fluid dynamics ,Solver ,Raumfahrzeuge ,Physics::Fluid Dynamics ,Classical mechanics ,rarefied ,plume expansion ,Boundary value problem ,business ,DSMC - Abstract
Laminar nitrogen flow expanding through a conical nozzle into high vacuum is to be numerically reproduced and compared to available experimental data. As the gas density varies quickly by several orders of magnitude, leading to high rarefaction and thermal non-equilibrium, standard (continuum) CFD tools are not sufficient to accurately model the expanding flow. In the work presented here, the efficiency of Navier-Stokes solvers is to be exploited where applicable, supplying the boundary conditions for a kinetic Direct Simulation Monte Carlo (DSMC) solver to handle the domain of rarefaction and non-equilibrium. The hypersonic character of the flow suggests to attempt a pure downstream coupling. The validity of this approach is to be verified.
- Published
- 2010
30. The Technological Basis of a Balloon-Expandable TAVR System: Non-occlusive Deployment, Anchorage in the Absence of Calcification and Polymer Leaflets
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Harish Appa, Kenneth Park, Deon Bezuidenhout, Braden van Breda, Bruce de Jongh, Jandré de Villiers, Reno Chacko, Jacques Scherman, Chima Ofoegbu, Justiaan Swanevelder, Michael Cousins, Paul Human, Robin Smith, Ferdinand Vogt, Bruno K. Podesser, Christoph Schmitz, Lenard Conradi, Hendrik Treede, Holger Schröfel, Theodor Fischlein, Martin Grabenwöger, Xinjin Luo, Heather Coombes, Simon Matskeplishvili, David F. Williams, and Peter Zilla
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balloon-expandable ,plastic deformation ,aortic regurgitations ,polymer leaflets ,rheumatic heart disease ,Diseases of the circulatory (Cardiovascular) system ,RC666-701 - Abstract
Leaflet durability and costs restrict contemporary trans-catheter aortic valve replacement (TAVR) largely to elderly patients in affluent countries. TAVR that are easily deployable, avoid secondary procedures and are also suitable for younger patients and non-calcific aortic regurgitation (AR) would significantly expand their global reach. Recognizing the reduced need for post-implantation pacemakers in balloon-expandable (BE) TAVR and the recent advances with potentially superior leaflet materials, a trans-catheter BE-system was developed that allows tactile, non-occlusive deployment without rapid pacing, direct attachment of both bioprosthetic and polymer leaflets onto a shape-stabilized scallop and anchorage achieved by plastic deformation even in the absence of calcification. Three sizes were developed from nickel-cobalt-chromium MP35N alloy tubes: Small/23 mm, Medium/26 mm and Large/29 mm. Crimp-diameters of valves with both bioprosthetic (sandwich-crosslinked decellularized pericardium) and polymer leaflets (triblock polyurethane combining siloxane and carbonate segments) match those of modern clinically used BE TAVR. Balloon expansion favors the wing-structures of the stent thereby creating supra-annular anchors whose diameter exceeds the outer diameter at the waist level by a quarter. In the pulse duplicator, polymer and bioprosthetic TAVR showed equivalent fluid dynamics with excellent EOA, pressure gradients and regurgitation volumes. Post-deployment fatigue resistance surpassed ISO requirements. The radial force of the helical deployment balloon at different filling pressures resulted in a fully developed anchorage profile of the valves from two thirds of their maximum deployment diameter onwards. By combining a unique balloon-expandable TAVR system that also caters for non-calcific AR with polymer leaflets, a powerful, potentially disruptive technology for heart valve disease has been incorporated into a TAVR that addresses global needs. While fulfilling key prerequisites for expanding the scope of TAVR to the vast number of patients of low- to middle income countries living with rheumatic heart disease the system may eventually also bring hope to patients of high-income countries presently excluded from TAVR for being too young.
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- 2022
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31. Durability of bioprosthetic aortic valves in patients under the age of 60 years – rationale and design of the international INDURE registry
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Bart Meuris, Michael A. Borger, Thierry Bourguignon, Matthias Siepe, Martin Grabenwöger, Günther Laufer, Konrad Binder, Gianluca Polvani, Pierluigi Stefano, Enrico Coscioni, Wouter van Leeuwen, Philippe Demers, Francois Dagenais, Sergio Canovas, Alexis Theron, Thierry Langanay, Jean-Christian Roussel, Olaf Wendler, Giovanni Mariscalco, Renzo Pessotto, Beate Botta, Peter Bramlage, and Ruggero de Paulis
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Aortic valve disease ,Surgical aortic valve replacement ,SAVR ,INSPIRIS RESILIA ,Structural valve degeneration ,Valve durability ,Surgery ,RD1-811 ,Anesthesiology ,RD78.3-87.3 - Abstract
Abstract Background There is an ever-growing number of patients requiring aortic valve replacement (AVR). Limited data is available on the long-term outcomes and structural integrity of bioprosthetic valves in younger patients undergoing surgical AVR. Methods The INSPIRIS RESILIA Durability Registry (INDURE) is a prospective, open-label, multicentre, international registry with a follow-up of 5 years to assess clinical outcomes of patients younger than 60 years who undergo surgical AVR using the INSPIRIS RESILIA aortic valve. INDURE will be conducted across 20–22 sites in Europe and Canada and intends to enrol minimum of 400 patients. Patients will be included if they are scheduled to undergo AVR with or without concomitant root replacement and/or coronary bypass surgery. The primary objectives are to 1) determine VARC-2 defined time-related valve safety at one-year (depicted as freedom from events) and 2) determine freedom from stage 3 structural valve degeneration (SVD) presenting as morphological abnormalities and severe haemodynamic valve degeneration at 5 years. Secondary objectives include the assessment of the haemodynamic performance of the valve, all stages of SVD, potential valve-in-valve procedures, clinical outcomes (in terms of New York Heart Association [NYHA] function class and freedom from valve-related rehospitalisation) and change in patient quality-of-life. Discussion INDURE is a prospective, multicentre registry in Europe and Canada, which will provide much needed data on the long-term performance of bioprosthetic valves in general and the INSPIRIS RESILIA valve in particular. The data may help to gather a deeper understanding of the longevity of bioprosthetic valves and may expand the use of bioprosthetic valves in patients under the age of 60 years. Trial registration ClinicalTrials.gov identifier: NCT03666741 (registration received September, 12th, 2018).
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- 2020
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32. Impacts of Telomeric Length, Chronic Hypoxia, Senescence, and Senescence-Associated Secretory Phenotype on the Development of Thoracic Aortic Aneurysm
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Thomas Aschacher, Daniela Geisler, Verena Lenz, Olivia Aschacher, Bernhard Winkler, Anne-Kristin Schaefer, Andreas Mitterbauer, Brigitte Wolf, Florian K. Enzmann, Barbara Messner, Günther Laufer, Marek P. Ehrlich, Martin Grabenwöger, and Michael Bergmann
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telomere ,aneurysm ,DNA damage ,senescence-associated secretory phenotype ,cell death ,thoracic aorta ,Biology (General) ,QH301-705.5 ,Chemistry ,QD1-999 - Abstract
Thoracic aortic aneurysm (TAA) is an age-related and life-threatening vascular disease. Telomere shortening is a predictor of age-related diseases, and its progression is associated with premature vascular disease. The aim of the present work was to investigate the impacts of chronic hypoxia and telomeric DNA damage on cellular homeostasis and vascular degeneration of TAA. We analyzed healthy and aortic aneurysm specimens (215 samples) for telomere length (TL), chronic DNA damage, and resulting changes in cellular homeostasis, focusing on senescence and apoptosis. Compared with healthy thoracic aorta (HTA), patients with tricuspid aortic valve (TAV) showed telomere shortening with increasing TAA size, in contrast to genetically predisposed bicuspid aortic valve (BAV). In addition, TL was associated with chronic hypoxia and telomeric DNA damage and with the induction of senescence-associated secretory phenotype (SASP). TAA-TAV specimens showed a significant difference in SASP-marker expression of IL-6, NF-κB, mTOR, and cell-cycle regulators (γH2AX, Rb, p53, p21), compared to HTA and TAA-BAV. Furthermore, we observed an increase in CD163+ macrophages and a correlation between hypoxic DNA damage and the number of aortic telocytes. We conclude that chronic hypoxia is associated with telomeric DNA damage and the induction of SASP in a diseased aortic wall, promising a new therapeutic target.
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- 2022
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33. A High-Throughput Fluorescence Polarization-Based Assay for the SH2 Domain of STAT4
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Angela Berg, Martin Gräber, Sebastian Schmutzler, Ralf Hoffmann, and Thorsten Berg
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assay development ,fluorescence polarization ,protein-protein interactions ,SH2 domain ,STAT4 ,Biology (General) ,QH301-705.5 - Abstract
The signal transducer and activation of transcription (STAT) proteins are a family of Src homology 2 (SH2) domain-containing transcription factors. The family member STAT4 is a mediator of IL-12 signalling and has been implicated in the pathogenesis of multiple autoimmune diseases. The activity of STAT4 requires binding of phosphotyrosine-containing motifs to its SH2 domain. Selective inhibitors of the STAT4 SH2 domain have not been published to date. Here, we present a fluorescence polarization-based assay for the identification of inhibitors of the STAT4 SH2 domain. The assay is based on the interaction between the STAT4 SH2 domain and the fluorophore-labelled peptide 5-carboxyfluorescein-GpYLPQNID (Kd = 34 ± 4 nM). The assay is stable with respect to DMSO concentrations of up to 10% and incubation times of at least 8 h. The Z’-value of 0.85 ± 0.01 indicates that the assay is suited for use in high-throughput screening campaigns aimed at identifying new therapeutic modalities for the treatment of autoimmune diseases.
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- 2022
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34. Specific Graft Treatment Solution Enhances Vascular Endothelial Function
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Attila Kiss, Petra Lujza Szabo, Christopher Dostal, Zsuzsanna Arnold, Daniela Geisler, Ingo Crailsheim, Sandra Folkmann, Martin Grabenwöger, Bruno Karl Podesser, and Bernhard Winkler
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vein graft ,preservation solution ,endothelium ,coronary artery bypass grafting ,myograph ,Diseases of the circulatory (Cardiovascular) system ,RC666-701 - Abstract
Background: Saline is still the most widely used storage and rinsing solution for vessel grafts during cardiac surgery despite knowing evidence of its negative influence on the human endothelial cell function. Aim of this study was to assess the effect of DuraGraft©, an intraoperative graft treatment solution, on human saphenous vein segments and further elaborate the vasoprotective effect on rat aortic segments in comparison to saline. Methods: Human Saphenous vein (HSV) graft segments from patients undergoing aortocoronary bypass surgery (n = 15), were randomized to DuraGraft© (n = 15) or saline (n = 15) solution before intraoperative storage. Each segment was divided into two subsegmental parts for evaluation. These segments as well as rat aortic segments stored in DuraGraft© underwent assessment of vascular function in a multichamber isometric myograph system in comparison to Krebs-Henseleit solution (KHS), a physiologic organ buffer solution. Results: Potassium-Chloride (KCL)-induced contraction depicted a tendency towards increase when treated with DuraGraft© compared to saline preservation of HSV segments (23.02 ± 14.77 vs 14.44 ± 9.13 mN, p = 0.0571). Vein segments preserved with DuraGraft© showed a significant improvement of endothelium-dependent vasorelaxation in response to cumulative concentrations of bradykinin compared to saline treated segments (p < 0.05). Rat aortic segments stored in saline showed significantly impaired vasoconstriction (3.59 ± 4.20, p < 0.0001) and vasorelaxation when compared to KHS and DuraGraft© (p < 0.0001). Conclusions: DuraGraft© demonstrated a favorable effect on graft relaxation and contraction indicating preservation of vascular endothelial function. Clinical Trial Registration Number: NCT04614077.
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- 2022
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35. The Role of Telocytes and Telocyte-Derived Exosomes in the Development of Thoracic Aortic Aneurysm
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Thomas Aschacher, Olivia Aschacher, Katy Schmidt, Florian K. Enzmann, Eva Eichmair, Bernhard Winkler, Zsuzsanna Arnold, Felix Nagel, Bruno K. Podesser, Andreas Mitterbauer, Barbara Messner, Martin Grabenwöger, Günther Laufer, Marek P. Ehrlich, and Michael Bergmann
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telocytes ,aorta ,thoracic ascending aortic aneurysms ,exosomes ,cellular senescence ,miRNA ,Biology (General) ,QH301-705.5 ,Chemistry ,QD1-999 - Abstract
A hallmark of thoracic aortic aneurysms (TAA) is the degenerative remodeling of aortic wall, which leads to progressive aortic dilatation and resulting in an increased risk for aortic dissection or rupture. Telocytes (TCs), a distinct type of interstitial cells described in many tissues and organs, were recently observed in the aortic wall, and studies showed the potential regulation of smooth muscle cell (SMC) homeostasis by TC-released shed vesicles. The purpose of the present work was to study the functions of TCs in medial degeneration of TAA. During aneurysmal formation an increase of aortic TCs was identified in human surgical specimens of TAA-patients, compared to healthy thoracic aortic (HTA)-tissue. We found the presence of epithelial progenitor cells in the adventitial layer, which showed increased infiltration in TAA samples. For functional analysis, HTA- and TAA-telocytes were isolated, characterized, and compared by their protein levels, mRNA- and miRNA-expression profiles. We detected TC and TC-released exosomes near SMCs. TAA-TC-exosomes showed a significant increase of the SMC-related dedifferentiation markers KLF-4-, VEGF-A-, and PDGF-A-protein levels, as well as miRNA-expression levels of miR-146a, miR-221 and miR-222. SMCs treated with TAA-TC-exosomes developed a dedifferentiation-phenotype. In conclusion, the study shows for the first time that TCs are involved in development of TAA and could play a crucial role in SMC phenotype switching by release of extracellular vesicles.
- Published
- 2022
- Full Text
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