TY - JOUR A1 - Neumaier, Felix A1 - Weiss, Miriam A1 - Veldeman, Michael A1 - Kotliar, Konstantin A1 - Wiesmann, Martin A1 - Schulze-Steinen, Henna A1 - Höllig, Anke A1 - Clusmann, Hans A1 - Schubert, Gerrit Alexander A1 - Albanna, Walid T1 - Changes in endogenous daytime melatonin levels after aneurysmal subarachnoid hemorrhage – preliminary findings from an observational cohort study JF - Clinical Neurology and Neurosurgery N2 - Aneurysmal subarachnoid hemorrhage (aSAH) is associated with early and delayed brain injury due to several underlying and interrelated processes, which include inflammation, oxidative stress, endothelial, and neuronal apoptosis. Treatment with melatonin, a cytoprotective neurohormone with anti-inflammatory, anti-oxidant and anti-apoptotic effects, has been shown to attenuate early brain injury (EBI) and to prevent delayed cerebral vasospasm in experimental aSAH models. Less is known about the role of endogenous melatonin for aSAH outcome and how its production is altered by the pathophysiological cascades initiated during EBI. In the present observational study, we analyzed changes in melatonin levels during the first three weeks after aSAH. KW - constructive alignment KW - examination KW - long-term retention KW - multimodal KW - practical learning Y1 - 2021 U6 - http://dx.doi.org/10.1016/j.clineuro.2021.106870 SN - 0303-8467 VL - 208 IS - Article No.: 106870 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Nguyen, N.-H. A1 - Raatschen, Hans-Jürgen A1 - Staat, Manfred T1 - A hyperelastic model of biological tissue materials in tubular organs Y1 - 2010 N1 - ECCM 2010, IV European Conference on Computational Mechanics, Paris, France, May 16-21, 2010. SP - 1 EP - 12 ER - TY - JOUR A1 - Nguyen, Nhu Huynh A1 - Duong, Minh Tuan A1 - Tran, Thanh Ngoc A1 - Pham, Phu Tinh A1 - Grottke, O. A1 - Tolba, R. A1 - Staat, Manfred T1 - Influence of a freeze–thaw cycle on the stress–stretch curves of tissues of porcine abdominal organs JF - Journal of Biomechanics N2 - The paper investigates both fresh porcine spleen and liver and the possible decomposition of these organs under a freeze–thaw cycle. The effect of tissue preservation condition is an important factor which should be taken into account for protracted biomechanical tests. In this work, tension tests were conducted for a large number of tissue specimens from twenty pigs divided into two groups of 10. Concretely, the first group was tested in fresh state; the other one was tested after a freeze-thaw cycle which simulates the conservation conditions before biomechanical experiments. A modified Fung model for isotropic behavior was adopted for the curve fitting of each kind of tissues. Experimental results show strong effects of the realistic freeze–thaw cycle on the capsule of elastin-rich spleen but negligible effects on the liver which virtually contains no elastin. This different behavior could be explained by the autolysis of elastin by elastolytic enzymes during the warmer period after thawing. Realistic biomechanical properties of elastin-rich organs can only be expected if really fresh tissue is tested. The observations are supported by tests of intestines. KW - Autolysis KW - Decomposition KW - Freeze–thaw process KW - Spleen KW - Liver Y1 - 2012 U6 - http://dx.doi.org/10.1016/j.jbiomech.2012.07.008 SN - 1873-2380 VL - 45 IS - 14 SP - 2382 EP - 2386 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Nguyen-Xuan, H. A1 - Rabczuk, T. A1 - Nguyen-Thoi, T. A1 - Tran, Thanh Ngoc A1 - Nguyen-Thanh, N. T1 - Computation of limit and shakedown loads using a node-based smoothed finite element method JF - International Journal for Numerical Methods in Engineering N2 - This paper presents a novel numerical procedure for computing limit and shakedown loads of structures using a node-based smoothed FEM in combination with a primal–dual algorithm. An associated primal–dual form based on the von Mises yield criterion is adopted. The primal-dual algorithm together with a Newton-like iteration are then used to solve this associated primal–dual form to determine simultaneously both approximate upper and quasi-lower bounds of the plastic collapse limit and the shakedown limit. The present formulation uses only linear approximations and its implementation into finite element programs is quite simple. Several numerical examples are given to show the reliability, accuracy, and generality of the present formulation compared with other available methods. Y1 - 2011 U6 - http://dx.doi.org/10.1002/nme.3317 SN - 1097-0207 VL - 90 IS - 3 SP - 287 EP - 310 PB - Wiley CY - Weinheim ER - TY - JOUR A1 - Niedermeyer, Angela A1 - Zhou, Bei A1 - Dursun, Gözde A1 - Temiz Artmann, Aysegül A1 - Markert, Bernd T1 - An examination of tissue engineered scaffolds in a bioreactor JF - Proceedings in Applied Mathematics and Mechanics PAMM N2 - Replacement tissues, designed to fill in articular cartilage defects, should exhibit the same properties as the native material. The aim of this study is to foster the understanding of, firstly, the mechanical behavior of the material itself and, secondly, the influence of cultivation parameters on cell seeded implants as well as on cell migration into acellular implants. In this study, acellular cartilage replacement material is theoretically, numerically and experimentally investigated regarding its viscoelastic properties, where a phenomenological model for practical applications is developed. Furthermore, remodeling and cell migration are investigated. Y1 - 2016 U6 - http://dx.doi.org/10.1002/pamm.201610038 SN - 1617-7061 N1 - Joint Annual Meeting of DMV and GAMM 2016, 87th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM) and Deutsche Mathematiker-Vereinigung (DMV), Braunschweig, DE, Mar 7-11, 2016 VL - 16 IS - 1 SP - 99 EP - 100 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Nomdedeu, Mar Monsonis A1 - Willen, Christine A1 - Schieffer, Andre A1 - Arndt, Hartmut T1 - Temperature-dependent ranges of coexistence in a model of a two-prey-one-predator microbial food web JF - Marine Biology N2 - The objective of our study was to analyze the effects of temperature on the population dynamics of a three-species food web consisting of two prey bacteria (Pedobacter sp. and Acinetobacter johnsonii) and a protozoan predator (Tetrahymena pyriformis) as model organisms. We assessed the effects of temperature on the growth rates of all three species with the objective of developing a model with four differential equations based on the experimental data. The following hypotheses were tested at a theoretical level: Firstly, temperature changes can affect the dynamic behavior of a system by temperature-dependent parameters and interactions and secondly, food web response to temperature cannot be derived from the single species temperature response. The main outcome of the study is that temperature changes affect the parameter range where coexistence is possible within all three species. This has significant consequences on our ideas regarding the evaluation of effects of global warming. Y1 - 2012 U6 - http://dx.doi.org/10.1007/s00227-012-1966-x SN - 1432-1793 VL - 159 IS - 11 SP - 2423 EP - 2430 PB - Springer CY - Berlin ER - TY - JOUR A1 - Novacek, V. A1 - Tran, Thanh Ngoc A1 - Klinge, U. A1 - Tolba, R. H. A1 - Staat, Manfred A1 - Bronson, D. G. A1 - Miesse, A. M. A1 - Whiffen, J. A1 - Turquier, F. T1 - Finite element modelling of stapled colorectal end-to-end anastomosis : Advantages of variable height stapler design JF - Journal of Biomechanics N2 - The impact of surgical staplers on tissues has been studied mostly in an empirical manner. In this paper, finite element method was used to clarify the mechanics of tissue stapling and associated phenomena. Various stapling modalities and several designs of circular staplers were investigated to evaluate the impact of the device on tissues and mechanical performance of the end-to-end colorectal anastomosis. Numerical simulations demonstrated that a single row of staples is not adequate to resist leakage due to non-linear buckling and opening of the tissue layers between two adjacent staples. Compared to the single staple row configuration, significant increase in stress experienced by the tissue at the inner staple rows was observed in two and three rows designs. On the other hand, adding second and/or third staple row had no effect on strain in the tissue inside the staples. Variable height design with higher staples in outer rows significantly reduced the stresses and strains in outer rows when compared to the same configuration with flat cartridge. KW - Variable height stapler design KW - Anastomotic leakage KW - Finite element modelling KW - End-to-end colorectal anastomosis KW - Surgical staplers Y1 - 2012 U6 - http://dx.doi.org/10.1016/j.jbiomech.2012.07.021 SN - 1873-2380 VL - 45 IS - 115 SP - 2693 EP - 2697 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Nurispahic, A. A1 - Kotliar, Konstantin A1 - Lanzl, I. T1 - Messung der Akkommodation mittels optischer Biometrie JF - Der Ophthalmologe Y1 - 2008 SN - 1433-0423 VL - 105 IS - 4 SP - 369 EP - 375 PB - - ER - TY - JOUR A1 - Peloni, Alessandro A1 - Ceriotti, Matteo A1 - Dachwald, Bernd T1 - Solar-sail trajectory design for a multiple near-earth-asteroid rendezvous mission JF - Journal of Guidance, Control, and Dynamics N2 - The scientific interest for near-Earth asteroids as well as the interest in potentially hazardous asteroids from the perspective of planetary defense led the space community to focus on near-Earth asteroid mission studies. A multiple near-Earth asteroid rendezvous mission with close-up observations of several objects can help to improve the characterization of these asteroids. This work explores the design of a solar-sail spacecraft for such a mission, focusing on the search of possible sequences of encounters and the trajectory optimization. This is done in two sequential steps: a sequence search by means of a simplified trajectory model and a set of heuristic rules based on astrodynamics, and a subsequent optimization phase. A shape-based approach for solar sailing has been developed and is used for the first phase. The effectiveness of the proposed approach is demonstrated through a fully optimized multiple near-Earth asteroid rendezvous mission. The results show that it is possible to visit five near-Earth asteroids within 10 years with near-term solar-sail technology. Y1 - 2016 U6 - http://dx.doi.org/10.2514/1.G000470 SN - 0731-5090 VL - 39 IS - 12 SP - 2712 EP - 2724 PB - AIAA CY - Reston, Va. ER - TY - JOUR A1 - Peloni, Alessandro A1 - Dachwald, Bernd A1 - Ceriotti, Matteo T1 - Multiple near-earth asteroid rendezvous mission: Solar-sailing options JF - Advances in Space Research Y1 - 2017 U6 - http://dx.doi.org/10.1016/j.asr.2017.10.017 SN - 0273-1177 IS - In Press, Corrected Proof PB - Elsevier CY - Amsterdam ER -