Analysis and transformation of legacy code

Hardware evolves faster than software. While a hardware system might need replacement every one to five years, the average lifespan of a software system is a decade, with some instances living up to several decades. Inevitably, code outlives the platform it was developed for and may become legacy: development of the software stops, but maintenance has to continue to keep up with the evolving ecosystem. No new features are added, but the software is still used to fulfil its original purpose. Even in the cases where it is still functional (which discourages its replacement), legacy code is inefficient, costly to maintain, and a risk to security. This thesis proposes methods to leverage the expertise put in the development of legacy code and to extend its useful lifespan, rather than to throw it away. A novel methodology is proposed, for automatically exploiting platform specific optimisations when retargeting a program to another platform. The key idea is to leverage the optimisation information embedded in vector processing intrinsic functions. The performance of the resulting code is shown to be close to the performance of manually retargeted programs, however with the human labour removed. Building on top of that, the question of discovering optimisation information when there are no hints in the form of intrinsics or annotations is investigated. This thesis postulates that such information can potentially be extracted from profiling the data flow during executions of the program. A context-aware data dependence profiling system is described, detailing previously overlooked aspects in related research. The system is shown to be essential in surpassing the information that can be inferred statically, in particular about loop iterators. Loop iterators are the controlling part of a loop. This thesis describes and evaluates a system for extracting the loop iterators in a program. It is found to significantly outperform previously known techniques and further increases the amount of information about the structure of a program that is available to a compiler. Combining this system with data dependence profiling improves its results even more. Loop iterator recognition enables other code modernising techniques, like source code rejuvenation and commutativity analysis. The former increases the use of idiomatic code and as a result increases the maintainability of the program. The latter can potentially drive parallelisation and thus dramatically improve runtime performance

Which effective viscosity?

Magmas undergoing shear are prime examples of flows that involve the transport of solids and gases by a separate (silicate melt) carrier phase. Such flows are called multiphase, and have attracted much attention due to their important range of engineering applications. Where the volume fraction of the dispersed phase (crystals) is large, the influence of particles on the fluid motion becomes significant and must be taken into account in any explanation of the bulk behaviour of the mixture. For congested magma deforming well in excess of the dilute limit (particle concentrations >40% by volume), sudden changes in the effective or relative viscosity can be expected. The picture is complicated further by the fact that the melt phase is temperature- and shear-rate-dependent. In the absence of a constitutive law for the flow of congested magma under an applied force, it is far from clear which of the many hundreds of empirical formulae devised to predict the rheology of suspensions as the particle fraction increases with time are best suited. Some of the more commonly used expressions in geology and engineering are reviewed with an aim to home in on those variables key to an improved understanding of magma rheology. These include a temperature, compositional and shear-rate dependency of viscosity of the melt phase with the shear-rate dependency of the crystal (particle) packing arrangement. Building on previous formulations, a new expression for the effective (relative) viscosity of magma is proposed that gives users the option to define a packing fraction range as a function of shear stress. Comparison is drawn between processes (segregation, clustering, jamming), common in industrial slurries, and structures seen preserved in igneous rocks. An equivalence is made such that congested magma, viewed in purely mechanical terms as a high-temperature slurry, is an inherently non-equilibrium material where flow at large Péclet numbers may result in shear thinning and spontaneous development of layering

Resource Management Optimization in Multi-Processor Platforms

Proceedings of: Third International Workshop on Sustainable Ultrascale Computing Systems (NESUS 2016). Sofia (Bulgaria), October, 6-7, 2016.The modern high-performance computing systems (HPCS) are composed of hundreds of thousand computational nodes. An effective resource allocation in HPCS is a subject for many scientific research investigations. Many programming models for effective resources allocation have been proposed. The main purpose of those models is to increase the parallel performance of the HPCS. This paper investigates the efficiency of parallel algorithm for resource management optimization based on Artificial Bee Colony (ABC) metaheuristic while solving a package of NP-complete problems on multi-processor platform.In order to achieve minimal parallelization overhead in each cluster node, a multi-level hybrid programming model is proposed that combines coarse-grain and fine-grain parallelism. Coarse-grain parallelism is achieved through domain decomposition by message passing among computational nodes using Message Passing Interface (MPI) and fine-grain parallelism is obtained by loop-level parallelism inside each computation node by compiler-based thread parallelization via Intel TBB. Parallel communications profiling is made and parallel performance parameters are evaluated on the basis of experimental results

Analysis of vibration impact on stability of dewetting thin liquid film

Dynamics of a thin dewetting liquid film on a vertically oscillating substrate is considered. We assume moderate vibration frequency and large (compared to the mean film thickness) vibration amplitude. Using the lubrication approximation and the averaging method, we formulate the coupled sets of equations governing the pulsatile and the averaged fluid flows in the film, and then derive the nonlinear amplitude equation for the averaged film thickness. We show that there exists a window in the frequency-amplitude domain where the parametric and shear-flow instabilities of the pulsatile flow do not emerge. As a consequence, in this window the averaged description is reasonable and the amplitude equation holds. The linear and nonlinear analyses of the amplitude equation and the numerical computations show that such vibration stabilizes the film against dewetting and rupture.Comment: 19 pages, 11 figure

Analysis of the performance of a particle velocity sensor between two cylindrical obstructions

The performance of an acoustic particle velocity sensor that is placed between two cylindrical objects has been analyzed both analytically and by means of finite volume simulations on fluid dynamics. The results are compared with acoustic experiments that show a large magnification of the output signal of the particle velocity sensor due to the mounting of the sensor between two cylinders. The influences of this construction consist of an attenuation of particle velocities at frequencies below a few hertz, whereas signals in the higher frequency range are amplified, up to approximately three times 10 dB in a frequency range between 50 and 1000 Hz. The theoretical analysis is based on the derivation of the stream function for the situation of two long cylinders immersed in an oscillating incompressible viscous fluid, at low Reynolds numbers. The results lead to an improved insight into the effects of viscosity and fluid flow that play a role in acoustic measurements and open the way for further optimization of the sensitivity of the sensor

Обтекание со сверхзвуковой скоростью закругленных обратных конусов

[Zapryanov Zapryan; Запрянов Запрян]Bulgarian. Russian, English summar

The cult of reputation: deterrent or a cause of war?

A reputation for resolve, used to predict an actor’s future intentions with reasonable accuracy based on his past actions, is central to many deterrence theories. The assumption is that states use other actors’ past behavior as a learning schema for generating expectations, and act according to such expectations. However, there are other powerful determinants in international politics—military capabilities, distribution of power, and interests at stake, etc.—that shape states’ policies. Nonetheless, decision makers assign to their states’ reputation the status of symbolic capital, in order to add credibility to their future threats and commitments, or to credibly deter adversaries’ future threats. They generally believe that their allies and adversaries infer the state’s resolve from its past behavior. In this paper we analyze how this belief and the consequent quest for building, preserving, and/or restoring reputation can push decision-makers into the vortex of conflicts.http://archive.org/details/thecultofreputat1094544557Lieutenant Colonel, Pakistan ArmyCaptain, Bulgarian Army Special ForcesApproved for public release; distribution is unlimited

Why I became a doctor

Prof. Dr. Nikola Zapryanov graduated as a medical doctor in Plovdiv in 1955. His research interests are in the field of social medicine and the history of medicine. He has authored more than 300 scientific publications and reports. At MU Plovdiv he was elected Dean and Vice Rector