6 research outputs found
System and Application Performance Analysis Patterns Using Software Tracing
Software systems have become increasingly complex, which makes it difficult to detect the root causes of performance degradation. Software tracing has been used extensively to analyze the system at run-time to detect performance issues and uncover the causes. There exist several studies that use tracing and other dynamic analysis techniques for performance analysis. These studies focus on specific system characteristics such as latency, performance bugs, etc. In this thesis, we review the literature to build a catalogue of performance analysis patterns that can be detected using trace data. The goal is to help developers debug run-time and performance issues more efficiently. The patterns are formalized and implemented so that they can be readily referred to by developers while analyzing large execution traces. The thesis focuses on the traces of system calls generated by the Linux kernel. This is because no application is an island and that we cannot ignore the complex interactions that an application has with the operating system kernel if we are to detect potential performance issues
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Next generation computational tools for extreme-scale simulation of dynamic fracture and fragmentation in three dimensions
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 211-221).The accurate modeling of dynamic fracture and fragmentation remains one of the most difficult challenges in computational mechanics research. As part of this thesis, a scalable algorithm for modeling dynamic fracture and fragmentation of solids in three dimensions is developed. The method is based on the combination of a discontinuous Galerkin (DG) formulation of the continuum problem and Cohesive Zone Models (CZM) of fracture. Prior to fracture, the flux and stabilization terms arising from the DG formulation at interelement boundaries are enforced via interface elements, much like in conventional approaches based on CZM. Upon the onset of fracture, the traction-separation law (TSL) governing the fracture process becomes operative without the need to propagate topological changes in the mesh as cracks and fragments develop. This enables the indistinctive treatment of crack propagation across processor boundaries and, thus, scalability in parallel computations. Upon crack closure, the reinstatement of the DG terms guarantees the proper description of compressive waves across closed crack surfaces. Another advantage of the method is that it preserves consistency and stability in the uncracked interfaces, thus avoiding issues with wave propagation typical of many CZM-based approaches. The new method is applied in this thesis to conduct the first systematic largescale 3D simulation study of projectile impact damage in brittle plates using CZMs. Utilizing full machine access to supercomputers from the DoD Supercomputing Resource Center (DSRC), we conduct a series of impact simulations at an unprecedented scale aimed at investigating the fundamental physics governing the fracture and fragmentation of brittle plates subjected to normal impact loads. Using the full-field description provided by the simulations, we identify the driving forces for different fracture mechanisms as a function of key problem parameters such as impact speed and plate geometry. In order to validate the computational approach, we also simulate several edge-on impact experiments and compare the simulated cracking patterns directly to experimental results. Another important contribution of this thesis is the first large-scale study of convergence of the fracture patterns predicted in 3D simulations, for which we complete full runs on up to 17,264 processors using meshes comprising up to 2.4 billion degrees of freedom. In addition to the simulation studies, we also develop a fracture mechanics-based model for characterizing radial cracking patterns in thin plates subjected to contact loads. To this end, we derive an approximate closed-form expression for the number of radial cracks which will propagate in an elastic membrane subjected to time-invariant axisymmetric tranverse loads. The model elucidates some of the basic physics governing the radial cracking process and proves useful as a tool for predicting the number of radial cracks in three-dimensional problems involving contact loads.by Andrew Nathan Seagraves.Ph.D
Evolutionary genomics : statistical and computational methods
This open access book addresses the challenge of analyzing and understanding the evolutionary dynamics of complex biological systems at the genomic level, and elaborates on some promising strategies that would bring us closer to uncovering of the vital relationships between genotype and phenotype. After a few educational primers, the book continues with sections on sequence homology and alignment, phylogenetic methods to study genome evolution, methodologies for evaluating selective pressures on genomic sequences as well as genomic evolution in light of protein domain architecture and transposable elements, population genomics and other omics, and discussions of current bottlenecks in handling and analyzing genomic data. Written for the highly successful Methods in Molecular Biology series, chapters include the kind of detail and expert implementation advice that lead to the best results. Authoritative and comprehensive, Evolutionary Genomics: Statistical and Computational Methods, Second Edition aims to serve both novices in biology with strong statistics and computational skills, and molecular biologists with a good grasp of standard mathematical concepts, in moving this important field of study forward
Evolutionary Genomics
This open access book addresses the challenge of analyzing and understanding the evolutionary dynamics of complex biological systems at the genomic level, and elaborates on some promising strategies that would bring us closer to uncovering of the vital relationships between genotype and phenotype. After a few educational primers, the book continues with sections on sequence homology and alignment, phylogenetic methods to study genome evolution, methodologies for evaluating selective pressures on genomic sequences as well as genomic evolution in light of protein domain architecture and transposable elements, population genomics and other omics, and discussions of current bottlenecks in handling and analyzing genomic data. Written for the highly successful Methods in Molecular Biology series, chapters include the kind of detail and expert implementation advice that lead to the best results. Authoritative and comprehensive, Evolutionary Genomics: Statistical and Computational Methods, Second Edition aims to serve both novices in biology with strong statistics and computational skills, and molecular biologists with a good grasp of standard mathematical concepts, in moving this important field of study forward