2020 [ to top ]

• 
  Zhou, H., Gracia, J., Zhou, N., Schneider, R.: Collectives in hybrid MPI+MPI code: Design, practice and performance. Parallel Computing. 99, 102669 (2020).
  [ URL ]
   
• 
  Klüsener, S., Schneider, R., Rosenbaum-Feldbrügge, M., Dudel, C., Loichinger, E., Sander, N., Backhaus, A., Fava, E.D., Esins, J., Fischer, M., Grabenhenrich, L., Grigoriev, P., Grow, A.'e, Hilton, J., Koller, B., Myrskylä, M., Scalone, F., Wolkewitz, M., Zagheni, E., Resch, M.M.: Forecasting intensive care unit demand during the COVID-19 pandemic: A spatial age-structured microsimulation model. (2020).
  [ URL ]
   
• 
  Koller, B., Schneider, R., Ruopp, A., Liparas, D.: Mastering Exascale Challenges for Engineering Applications. In: Resch, M.M., Kovalenko, Y., Bez, W., Focht, E., und Kobayashi, H. (Hrsg.) Sustained Simulation Performance 2018 and 2019. S. 13--22. Sustained Simulation Performance 2018 and 2019, Cham (2020).
  [ Abstract ]
   
  This chapter will present the European approach for establishing Centres of Excellence in High-Performance Computing (HPC) applications, ensuring best synergies between participants in the different European countries. Those Centres are user-centric and thus driven by the needs of the respective community stakeholders.

2019 [ to top ]

• 
  Schneider, R., Kouros, J.: Effiziente Programmierung sozialwissenschaftlicher Modelle. In: Saam, N.J., Resch, M., und Kaminski, A. (Hrsg.) Simulieren und Entscheiden: Entscheidungsmodellierung, Modellierungsentscheidungen, Entscheidungsunterstützung. S. 231--256. Simulieren und Entscheiden: Entscheidungsmodellierung, Modellierungsentscheidungen, Entscheidungsunterstützung, Wiesbaden (2019).
  [ Abstract ] [ URL ]
   
  In diesem Artikel werden wir die praktischen und technischen Aspekte von unterschiedlichen Ans"atzen zur Entwicklung sozialwissenschaftlicher Computersimulationen am Beispiel eines Modells zur sozialen Diffusion betrachten. Wir vergleichen die Verwendung von NetLogo, C++ und Anglican. NetLogo ist ein Programmiersystem, das vergleichsweise geringe Programmierkenntisse vorraussetzt und weite Verbreitung gefunden hat. C++ dagegen ist eine Programmiersprache, die besonders da benutzt wird, wo rechenintensive Programme performant implementiert werden sollen. Anglican ist eine relativ junge probabilistische Programmiersprache aus dem Bereich der k"unstlichen Intelligenz1. Im Vergleich zu NetLogo erfordert die Programierung in C++ oder Anglican deutlich mehr Vorkenntnisse auf Seiten der Nutzer. Wir wollen zeigen, dass die Zeit und Arbeit, welche f"ur das Erlernen und die Entwicklung von Simulationen in diesen Programmiersprachen aufgewendet werden muss, sich dennoch lohnen kann, weil dadurch komplexere Modelle performant implementiert werden k"onnen.
• 
  Zhou, H., Gracia, J.'e, Schneider, R.: MPI Collectives for Multi-core Clusters: Optimized Performance of the Hybrid MPI+ MPI Parallel Codes. Proceedings of the 48th International Conference on Parallel Processing: Workshops. S. 18:1-18:10. Proceedings of the 48th International Conference on Parallel Processing: Workshops, Kyoto, Japan (2019).
  [ Abstract ] [ URL ]
   
  The advent of multi-/many-core processors in clusters advocates hybrid parallel programming, which combines Message Passing Interface (MPI) for inter-node parallelism with a shared memory model for on-node parallelism. Compared to the traditional hybrid approach of MPI plus OpenMP, a new, but promising hybrid approach of MPI plus MPI-3 shared-memory extensions (MPI+MPI) is gaining attraction. We describe an algorithmic approach for collective operations (with allgather and broadcast as concrete examples) in the context of hybrid MPI+MPI, so as to minimize memory consumption and memory copies. With this approach, only one memory copy is maintained and shared by on-node processes. This allows the removal of unnecessary on-node copies of replicated data that are required between MPI processes when the collectives are invoked in the context of pure MPI. We compare our approach of collectives for hybrid MPI+MPI and the traditional one for pure MPI, and also have a discussion on the synchronization that is required to guarantee data integrity. The performance of our approach has been validated on a Cray XC40 system (Cray MPI) and NEC cluster (Open MPI), showing that it achieves comparable or better performance for allgather operations. We have further validated our approach with a standard computational kernel, namely distributed matrix multiplication, and a Bayesian Probabilistic Matrix Factorization code.

2017 [ to top ]

• 
  Ruopp, A., Schneider, R.: MRI-Based Computational Hemodynamics in Patients. In: Resch, M.M., Bez, W., Focht, E., Gienger, M., und Kobayashi, H. (Hrsg.) Sustained Simulation Performance 2017. S. 165--178. Sustained Simulation Performance 2017, Cham (2017).
  [ Abstract ]
   
  The target of this research was to develop a simulation process chain for the analysis of arterial hemodynamics in patients with automatic calibration of all boundary conditions for the physiological correct treatment of flow rates in transient blood flows with multiple bifurcations. The developed methodology uses stationary simulations at peak systolic acceleration and minimizes the error of target and simulated outflow conditions by means of a parallel genetic optimization approach. The target inflow and outflow conditions at peak systole are extracted from 4D phase contrast magnetic resonance imaging (4D PC-MRI). The flow resistance of the arterial system lying downstream of the simulation domain's outlets is modelled via porous media with velocity dependent loss coefficients. In the analysis of the subsequent transient simulations, it will be shown that the proposed calibration method shows to work suitable for three different types of patients including one healthy patient, a patient suffering from an aneurysm as well as one with a coarctation. Additionally the local effects of mapping the measured transient 4D PC-MRI data onto the aortic valve inlet in comparison to the usage of block inlet profiles will be shown.
• 
  Küster, U., Schneider, R., Ruopp, A.: The Numerical Approximation of Koopman Modes of a Nonlinear Operator Along a Trajectory. In: Resch, M.M., Bez, W., Focht, E., Gienger, M., und Kobayashi, H. (Hrsg.) Sustained Simulation Performance 2017. S. 27--51. Sustained Simulation Performance 2017, Cham (2017).
  [ Abstract ]
   
  The spectral theory of linear operators enables the analysis of their properties on stable subspaces. The Koopman operator allows to extend these approaches to a large class of nonlinear operators in a surprising way. This is even applicable for numerical analysis of time dependent data of simulations and measurements. We give here some remarks on the numerical approach, link it to spectral analysis by the Herglotz-Bochner theorem and are doing some steps for significance for partial differential equations.

2016 [ to top ]

• 
  Patel, N., Schneider, R., Küster, U.: Adaptive application of spatial filters on raw CT images. 2016 IEEE Southwest Symposium on Image Analysis and Interpretation (SSIAI). S. 157-160. 2016 IEEE Southwest Symposium on Image Analysis and Interpretation (SSIAI) (2016).
   
• 
  Schneider, R.: Analysis of continuum mechanical, anisotropic material parameters by direct mechanical simulationPhD dissertation, Stuttgarthttp://dx.doi.org/10.18419/opus-8752 (2016).
  [ URL ]
   

2014 [ to top ]

• 
  Schneider, R., Resch, M.M.: Calculation of the Discrete Effective Stiffness of Cancellous Bone by Direct Mechanical Simulations. In: Garbey, M., Bass, B.L., Berceli, S., Collet, C., und Cerveri, P. (Hrsg.) Computational Surgery and Dual Training. S. 351-361. Computational Surgery and Dual Training (2014).
  [ URL ]
   

2013 [ to top ]

• 
  Helwig, P., Hindenlang, U., Hirschmüller, A., Konstantinidis, L., Südkamp, N., Schneider, R.: A femoral model with all relevant muscles and hip capsule ligaments. Computer Methods in Biomechanics and Biomedical Engineering. 16, 669-677 (2013).
  [ URL ]
   
• 
  Kipp, A., Schneider, R., Schubert, L.: Encapsulation of Complex HPC Services. In: Rückemann, C.-P. (Hrsg.) Integrated Information and Computing Systems for Natural, Spatial, and Social Sciences. S. 153--176. Integrated Information and Computing Systems for Natural, Spatial, and Social Sciences, Hershey, PA, USA (2013).
  [ Abstract ] [ URL ]
   
  Developing and providing complex IT services typically enforces the cooperation of several experts from different domains. Beside the domain specific knowledge of every involved expert this typically enforces a profound knowledge of the underlying IT service infrastructures. In this chapter, the authors show how a complex (HPC) IT service product can be provided in an easy-to-use fashion via a service virtualisation infrastructure by referring to a complex medical simulation use case. In particular, they highlight how such a complex IT service can be integrated in a holistic virtual organisation environment and show how different experts from different domains can concentrate on their specific domain whilst being enabled to take advantage of the services provided by other experts / domains in a SOA like fashion.
• 
  Schneider, R.: Storage and Indexing of Fine Grain, Large Scale Data Sets. In: Resch, M.M., Bez, W., Focht, E., Kobayashi, H., und Kovalenko, Y. (Hrsg.) Sustained Simulation Performance 2013. S. 89-104. Sustained Simulation Performance 2013 (2013).
  [ URL ]
   

2011 [ to top ]

• 
  Schneider, R., Hindenlang, U., Copf, P.: Dynamic Finite Element Analysis of Cancellous Bone Micro Structure. In: Krause, E., Shokin, Y., Resch, M., Kröner, D., und Shokina, N. (Hrsg.) Computational Science and High Performance Computing IV. S. 339-347. Computational Science and High Performance Computing IV (2011).
  [ URL ]
   

2010 [ to top ]

• 
  Schneider, R.: Identification of Anisotropic Elastic Material Properties by Direct Mechanical Simulations: Estimation of Process Chain Resource Requirements. In: Resch, M., Benkert, K., Wang, X., Galle, M., Bez, W., Kobayashi, H., und Roller, S. (Hrsg.) High Performance Computing on Vector Systems 2010. S. 149-159. High Performance Computing on Vector Systems 2010 (2010).
  [ URL ]
   

2009 [ to top ]

• 
  Helwig, P., Faust, G., Hindenlang, U., Hirschmüller, A., Konstantinidis, L., Bahrs, C., Südkamp, N., Schneider, R.: Finite element analysis of four different implants inserted in different positions to stabilize an idealized trochanteric femoral fracture. Injury. 40, 288 - 295 (2009).
  [ Abstract ] [ URL ]
   
  Biomechanical analysis of the ideal placement of new intramedullary implants for stabilization of trochanteric fractures is not currently available. The aim of the presented study is to determine to what extent four intermedullary nails (Gliding-Nail, Gamma-Nail, PFN-A and Targon-PF), inserted in different positions, differ mechanically. A proximal femur was reconstructed on the basis of clinical \CT data as a surface model. Load application equivalent to the one-leg stance phase during gait was assumed, taking into account a limited number of active muscle forces. The four implants were inserted cranially and caudally into the bone structure and a model of a trochanteric fracture was created. Criteria with point ratings were introduced to quantify a favourable fracture healing situation. Finite element simulation showed clear differences between the different implants with regard to the distributions of stress and strain at the two fracture surfaces in the model and the von Mises stress in the implant itself. It was apparent for three implants under investigation that the caudal position generated better fracture healing conditions than the cranial position. Only the Targon \PF demonstrated better fracture healing conditions in the cranial position. Evaluation based on the point rating system revealed that the caudal position was the ideal position for the PFN-A, Gamma-Nail and Gliding-Nail. The Targon-PF demonstrated some advantages over the other implants in the caudal position.
• 
  Schneider, R., Faust, G., Hindenlang, U., Helwig, P.: Inhomogeneous, orthotropic material model for the cortical structure of long bones modelled on the basis of clinical CT or density data. Computer Methods in Applied Mechanics and Engineering. 198, 2167 - 2174 (2009).
  [ Abstract ] [ URL ]
   
  For the simulation of stabilisation systems in femoral fractures with finite elements three factors are essential: (1) the geometry of the bone, (2) the loading of the acting muscle forces in combination with the body weight and (3) the inhomogeneously distributed orthotropic behaviour of the bone material must be known. This study will focus on the third condition. A technique is presented for transferring the density distributions gained from clinical computer tomographies to inhomogeneous, orthotropic material distributions suitable for finite element calculations. First, the algorithm for determining the orthotropy directions from the local variation of the density field is explained phenomenologically. Subsequently, a function for setting up the orthotropic elasticity matrices from the absolute \CT field values is derived. Finally, the validation procedure for the cortical bone is presented in principle.

2008 [ to top ]

• 
  Schneider, R., Faust, G., Hindenlang, U., Resch, M.M., Helwig, P.: Finite element analysis of a bone-implant system with comparison of isotropic and orthotropic material models generated by means of clinical CT-data. The Finite Element Method in Biomedical Engineering, Biomechanics and Related Fields. S. 71-85. The Finite Element Method in Biomedical Engineering, Biomechanics and Related Fields, Albert-Einstein-Allee 11 D-89081 Ulm (2008).
  [ URL ]
   

2007 [ to top ]

• 
  Schneider, R.: Modellierung des inhomogenen orthotropen Materialverhaltens der kortikalen Femurstruktur auf der Basis klinischer CT- bzw. Dichte-DatenUniversität Stuttgarthttps://puma.ub.uni-stuttgart.de/documents/67bd659c2b168a03f4c69bd4f527bc31/ralfschneider/Studienarbeit-Ralf_Schneider.pdf (2007).
  [ URL ]