iPregel: Strategies to Deal with an Extreme Form of Irregularity in Vertex-Centric Graph Processing

Over the last decade, the vertex-centric programming model has attracted significant attention in the world of graph processing, resulting in the emergence of a number of vertex-centric frameworks. Its simple programming interface, where computation is expressed from a vertex point of view, offers both ease of programming to the user and inherent parallelism for the underlying framework to leverage. However, vertex-centric programs represent an extreme form of irregularity, both inter and intra core. This is because they exhibit a variety of challenges from a workload that may greatly vary across supersteps, through fine-grain synchronisations, to memory accesses that are unpredictable both in terms of quantity and location. In this paper, we explore three optimisations which address these irregular challenges; a hybrid combiner carefully coupling lock-free and lock-based combinations, the partial externalisation of vertex structures to improve locality and the shift to an edge-centric representation of the workload. The optimisations were integrated into the iPregel vertex-centric framework, enabling the evaluation of each optimisation in the context of graph processing across three general purpose benchmarks common in the vertex-centric community, each run on four publicly available graphs covering all orders of magnitude from a million to a billion edges. The result of this work is a set of techniques which we believe not only provide a significant performance improvement in vertex-centric graph processing, but are also applicable more generally to irregular applications.Comment: Preprint of paper submitted to 9th Workshop on Irregular Applications: Architectures and Algorithms (IA3

Moving Beyond the “Lump-Sum”: A Case Study of Partnership for Positive Social Change

Based on a foundation of an integrated sport program for positive social change and health promotion, this paper presents a case study of the relationship between a corporate sponsor (JP Morgan), and a community-based health promotion/social change organization (Football United). The paper articulates the various issues that arise in management of such a program, and the involvement of sponsors in its operation. Illustrated through the JP Morgan - Football United case study, the paper explores: the difficulties of maintaining a program that remains faithful to the expectations and demands of each stakeholder group involved; the challenges involved in harnessing support for a program when moving beyond the one-dimensional transfer of funds; the different needs and expectations of/for volunteers this type of complex health promotion intervention. This case study has been written to propose that an “integrated partnership” between a corporate body and a social change organization can produce significant advantages beyond the scope of uncomplicated financial contribution The key feature documented is that corporate investment can move beyond abstract “lump-sum” social responsibility, towards targeted contributions to detailed outcomes through sustainable and meaningful involvement in a health promotion framework. This in turn equates to funding stability and a more empowering partnership for the health promotion/social change organization

Ammonium Fluoride as a Hydrogen-disordering Agent for Ice

The removal of residual hydrogen disorder from various phases of ice with acid or base dopants at low temperatures has been a focus of intense research for many decades. As an antipode to these efforts, we now show using neutron diffraction that ammonium fluoride (NH4F) is a hydrogen-disordering agent for the hydrogen-ordered ice VIII. Cooling its hydrogen-disordered counterpart ice VII doped with 2.5 mol% ND4F under pressure leads to a hydrogen-disordered ice VIII with ~31% residual hydrogen disorder illustrating the long-range hydrogen-disordering effect of ND4F. The doped ice VII could be supercooled by ~20 K with respect to the hydrogen-ordering temperature of pure ice VII after which the hydrogen-ordering took place slowly over a ~60 K temperature window. These findings demonstrate that ND4F-doping slows down the hydrogen-ordering kinetics quite substantially. The partial hydrogen order of the doped sample is consistent with the antiferroelectric ordering of pure ice VIII. Yet, we argue that local ferroelectric domains must exist between ionic point defects of opposite charge. In addition to the long-range effect of NH4F-doping on hydrogen-ordered water structures, the design principle of using topological charges should be applicable to a wide range of other 'ice-rule' systems including spin ices and related polar materials.Comment: 23 pages, 4 figures, 2 table

The Anatomy of Quantum Many-Body Scars: Origins and Implementations

Quantum many-body scars (QMBS) are a mechanism for many-body interacting systems to resist thermalisation. QMBS systems host a subset of atypical, non thermal eigenstates which are responsible for coherent oscillatory dynamics when these systems are prepared in special initial states. There exist two categories of QMBS. Firstly, there are `exact scars', which arise due to spectrum generating algebras (SGA), resulting in perfect oscillations for all times. On the other hand, there exist `approximate scars', which have been observed in experiment and are responsible for decaying oscillatory dynamics. The purpose of this thesis is to explain the origin of approximate scars, make predictions of new models expected to host them, and to realise approximate scarred dynamics experimentally. We show approximate scars arise due to algebraic structures analogous to SGA. These structures are known as `broken' Lie algebras. Understanding approximate scars at the level of a Lie algebra allows us to systematically derive higher order corrections which interpolate between approximate scarring and exact scarring. In addition, for models with a single revival frequency, indicative of some su(2) algebraic structure, we introduce a complementary approach of studying embedded hypercubic structures contained within the adjacency graph of the scarred Hamiltonian. Inspired by the notions of approximate algebraic relations and embedded graph structures, we introduce a general method of constructing scarred models via kinetic constraints. Finally, by utilising the suppressed entropy growth typical of QMBS models, we implement scarred dynamics on a quantum computer

Macroeconomic Modeling of Tax Policy: A Comparison of Current Methodologies

The macroeconomic effects of tax reform are a subject of significant discussion and controversy. In 2015, the House of Representatives adopted a new “dynamic scoring” rule requiring a point estimate within the budget window of the deficit effect due to the macroeconomic response to certain proposed tax legislation. The revenue estimates provided by the staff of the Joint Committee on Taxation (JCT) for major tax bills often play a critical role in Congressional deliberations and public discussion of those bills. The JCT has long had macroeconomic analytic capability, and in recent years, responding to Congress’ interest in macrodynamic estimates for purposes of scoring legislation, outside think tank groups — notably the Tax Policy Center and the Tax Foundation — have also developed macrodynamic estimation models. The May 2017 National Tax Association (NTA) Spring Symposium brought together the JCT with the Tax Foundation and the Tax Policy Center for a panel discussion regarding their respective macrodynamic estimating approaches. This paper reports on that discussion. Below each organization provides a general description of their macrodynamic modeling methodology and answers five questions posed by the convening authors

Thermodynamic study of CsCaCl₃ using neutron diffraction

The pressure and temperature phase diagram of the halide-based perovskite, CsCaCl3 is investigated using neutron diffraction. At ambient pressure, it undergoes a cubic to tetragonal phase transition at approximately 95 K. The structural evolution is characterised by changes in Cs and Ca coordination, bond lengths, and polyhedral volumes. Heat capacity measurements reveal a discontinuity at the phase transition, where we use a two-term Debye model to show the presence of two distinct contributions. Under pressure, CsCaCl3 exhibits phase transitions from cubic to tetragonal to rhombohedral symmetry, which can be understood when comparing the relative compressibilites of the CaCl6 and CsCln (where n = 12 for the cubic and 8 for the tetragonal and rhombohedral phases). Overall, this study provides experimentally derived thermodynamic properties and a tentative phase diagram of CsCaCl3 as a function of pressure and temperature.</p