Recent development and perspectives of machines for lattice QCD

I highlight recent progress in cluster computer technology and assess status and prospects of cluster computers for lattice QCD with respect to the development of QCDOC and apeNEXT. Taking the LatFor test case, I specify a 512-processor QCD-cluster better than 1$/Mflops.Comment: 14 pages, 17 figures, Lattice2003(plenary

Pattern recognition systems design on parallel GPU architectures for breast lesions characterisation employing multimodality images

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.The aim of this research was to address the computational complexity in designing multimodality Computer-Aided Diagnosis (CAD) systems for characterising breast lesions, by harnessing the general purpose computational potential of consumer-level Graphics Processing Units (GPUs) through parallel programming methods. The complexity in designing such systems lies on the increased dimensionality of the problem, due to the multiple imaging modalities involved, on the inherent complexity of optimal design methods for securing high precision, and on assessing the performance of the design prior to deployment in a clinical environment, employing unbiased system evaluation methods. For the purposes of this research, a Pattern Recognition (PR)-system was designed to provide highest possible precision by programming in parallel the multiprocessors of the NVIDIA’s GPU-cards, GeForce 8800GT or 580GTX, and using the CUDA programming framework and C++. The PR-system was built around the Probabilistic Neural Network classifier and its performance was evaluated by a re-substitution method, for estimating the system’s highest accuracy, and by the external cross validation method, for assessing the PR-system’s unbiased accuracy to new, “unseen” by the system, data. Data comprised images of patients with histologically verified (benign or malignant) breast lesions, who underwent both ultrasound (US) and digital mammography (DM). Lesions were outlined on the images by an experienced radiologist, and textural features were calculated. Regarding breast lesion classification, the accuracies for discriminating malignant from benign lesions were, 85.5% using US-features alone, 82.3% employing DM-features alone, and 93.5% combining US and DM features. Mean accuracy to new “unseen” data for the combined US and DM features was 81%. Those classification accuracies were about 10% higher than accuracies achieved on a single CPU, using sequential programming methods, and 150-fold faster. In addition, benign lesions were found smoother, more homogeneous, and containing larger structures. Additionally, the PR-system design was adapted for tackling other medical problems, as a proof of its generalisation. These included classification of rare brain tumours, (achieving 78.6% for overall accuracy (OA) and 73.8% for estimated generalisation accuracy (GA), and accelerating system design 267 times), discrimination of patients with micro-ischemic and multiple sclerosis lesions (90.2% OA and 80% GA with 32-fold design acceleration), classification of normal and pathological knee cartilages (93.2% OA and 89% GA with 257-fold design acceleration), and separation of low from high grade laryngeal cancer cases (93.2% OA and 89% GA, with 130-fold design acceleration). The proposed PR-system improves breast-lesion discrimination accuracy, it may be redesigned on site when new verified data are incorporated in its depository, and it may serve as a second opinion tool in a clinical environment

The South African print media, 1994-2004 : an application and critique of comparative media systems theory

Includes bibliographical references (leaves 226-237)Daniel C Hallin and Paolo Mancini's Comparing Media Systems (2004) has been hailed as an important contribution to understanding the inter-relationship between the media and political systems. The work was, however, based on a study of 18 stable, mature and highly developed democracies either in Europe or in North America. As an emerging democracy that has recently undergone dramatic change in both its political system and its media, South Africa's inclusion poses particular challenges to Hallin and Mancini's Three Models paradigm. This thesis focuses on the South African print media and tests both the paradigm's theoretical underpinnings as well as its four principle dimensions of analysis: political parallelism, state intervention, development of a mass market and journalistic professionalisation. A range of insights and a number of modifications are proposed. This thesis is based on interviews with South Africa's most senior media executives and editors, a comprehensive study of the relevant literature and 15 years of personal experience as a political analyst, columnist and parliamentary correspondent covering South Africa's transition from apartheid to democracy. The thesis sheds new light on the functioning and applicability of the Three Models comparative paradigm as well as on the development and future trajectory of South African print media journalism

JIT-based cost models for adaptive parallelism

Parallel programming is extremely challenging. Worse yet, parallel architectures evolve quickly, and parallel programs must often be refactored for each new architecture. It is highly desirable to provide performance portability, so programs developed on one architecture can deliver good performance on other architectures. This thesis is part of the AJITPar project that investigates a novel approach for achieving performance portability by the development of suitable cost models to inform scheduling decisions with dynamic information about computational and communication costs on the target architecture. The main artifact of the AJITPar project is the Adaptive Skeleton Library (ASL) that pro- vides a distributed-memory master-worker implementation of a set of Algorithmic Skeletons i.e. programming patterns that abstract away the low-level intricacies of parallelism. After JIT warm-up, ASL uses a computational cost model applied to JIT trace information from the Pycket compiler, a tracing JIT implementation of the Racket language, to transform the skeletons. The execution time of an ASL task is primarily determined by computation and communication costs. The Pycket compiler is extended to enable runtime access to JIT traces, both the sequences of instructions and frequency of execution. Crucially for dynamic, adaption these are obtained with minimal overhead. A low cost, dynamic computation cost model for estimating the runtime of JIT compiled Pycket programs, Γ, is developed and validated. This is believed to be the first such model. The design explores the challenges of estimating execution time from JIT trace instructions and presents three increasingly sophisticated cost models. The cost model predicts execution time based on the PyPy JIT instructions present in compiled JIT traces. The final abstract cost model applies weightings for 5 different classes of trace instructions and also proposes a method for aggregating the cost models for single traces into a cost model for an entire program. Execution time is measured, and traces generated are recorded, from a suite of 41 benchmarks. Linear regression is used to determine the weightings for the abstract cost model from this data. The final cost model reveals that allocation operations count most for execution time, followed by guards and numeric operations. The suitability of Γ for predicting the effect of ASL program transformations is investigated. The real utility of Γ is not in absolute predictions of execution times for different programs, but in predicting the effects of applying program transformations on parallel programs. A linear relationship between the actual computational cost for a task, and that predicted by Γ for five benchmarks on two architectures is demonstrated. A series of increasingly accurate low cost, dynamic cost models for estimating the communi- cation costs of ASL programs, K, are developed and validated. Predicting the optimum task size in ASL not only relies on computational cost predictions, but also predictions of the over- head of communicating tasks to worker nodes and results back to the master. The design and iterative development of a cost model which predicts the serialisation, deserialisation, and network send times of spawning a task in ASL is presented. Linear regression of communication timings are used to determine the appropriate weighting parameters for each. K is shown to be valid for predicting other, arbitrary data structures by demonstrating an additive property of the model. The model K is validated by showing a linear relationship between the combined predicted costs of the simple types in instances of aggregated data structures, and measured communication time. This validation is performed on five benchmarks on two platforms. Finally, a low cost dynamic cost model, T , that predicts a good ASL task size by combining information from the computation and communication cost models (Γand K) is developed and validated. The key insight in the design in this model is to balance the communications cost on the master node with the computational and communications cost on the worker nodes. The predictive power of T is tested model using six benchmarks, and it is shown to more accurately predict the optimal task size, reducing total program runtimes when compared with the default ASL prototype

Poetry and Politics in Post-Apartheid South Africa

This thesis explores the ability of poetry to articulate political critique in Post-Apartheid South Africa. The aim of the project is to evaluate the extent to which poetry provides criticism of a contemporary political climate marked by government corruption, rising social inequality and widespread immiseration. I argue that both ‘poetry’ and ‘post-Apartheid’ are developing and contested concepts that acquire meaning in concrete circumstances and continue to take on fresh resonance in South Africa today. I contend that poetry does not passively reflect historical circumstances nor docilely take its place in a post-Apartheid political climate. Instead, it actively engages with the milieu within which it finds itself and contributes in a meaningful way to our understanding of what the post-Apartheid era actually means. My study focuses on six poets who represent the innovative and politically charged character of post-Apartheid poetry. The writers I choose to examine are Ari Sitas, Seitlhamo Motsapi, Lesego Rampolokeng, Mxolisi Nyezwa, Vonani Bila, and Angifi Dladla. All of these poets lived through Apartheid and were young, or of middle age, at the dawn of liberation. Eager and able citizens willing to build a new democracy, these artists have been bitterly disappointed by the African National Congress’s abandonment of South Africa’s black majority. The poets in question have set about bearing witness to unrelenting social ills through drawing upon the dynamism of poetry in order to rejuvenate public language, dialogue and debate. Confronted with the over-simplification of information in an epoch of late-capitalism, the poets in this thesis seek to revitalise language, through innovative use of form, in order to fashion new perceptions of the world in which they live. All of the writers in this thesis have been involved in politics or activism and make a point of incorporating these real world experiences into their work. Thus, Sitas invokes worker chants from his time spent in Durban’s labour movement and Dladla remains fascinated by the Gauteng prisons where he has taught creative writing. The poetry I examine is moulded by the active public life of its writers and in turn seeks to participate in a wider world. In this line of thought, many of these poets have started their own literary journals and publishing initiatives, often with strong ties to social justice movements and grass-roots communities. Here, one can mention Nyezwa’s development of the English/isiXhosa multicultural arts journal Kotaz in the Eastern Cape and Bila’s Timbila publishing in the Limpopo province. Through autonomous methods of poetic production and distribution, poets are able to create spaces in which non-commercial and potentially revolutionary art can be heard. My doctorate spotlights the artistic and political victories of a pioneering group of poets, who are little known both locally and abroad. My research underscores the politically critical qualities of poetic form and thus has resonance beyond a narrowly South African context. Indeed, I believe my PhD can contribute in a valuable way to debates pertaining to the social relevance of poetry in the world today.Gates Cambridge Trus