Tree-Based Overlay Networks for Scalable Applications

The increasing availability of high-performance computing systems with thousands, tens of thousands, and even hundreds of thousands of computational nodes is driving the demand for programming models and infrastructures that allow effective use of such large-scale environments. Tree-based Overlay Networks (TBŌNs) have proven to provide such a model for distributed tools like performance profilers, parallel debuggers, system monitors and system administration tools. We demonstrate that the extensibility and flexibility of the TBŌN distributed computing model, along with its performance characteristics, make it surprisingly general, particularly for applications outside the tool domain. We describe many interesting applications and commonly-used algorithms for which TBŌNs are well-suited and provide a new (non-tool) case study, a distributed implementation of the mean-shift algorithm commonly used in computer vision to delineate arbitrarily shaped clusters in complex, multi-modal feature spaces. 1

On the unconstrained expansion of a spherical plasma cloud turning collisionless : case of a cloud generated by a nanometer dust grain impact on an uncharged target in space

Nano and micro meter sized dust particles travelling through the heliosphere at several hundreds of km/s have been repeatedly detected by interplanetary spacecraft. When such fast moving dust particles hit a solid target in space, an expanding plasma cloud is formed through the vaporisation and ionisation of the dust particles itself and part of the target material at and near the impact point. Immediately after the impact the small and dense cloud is dominated by collisions and the expansion can be described by fluid equations. However, once the cloud has reached micro-m dimensions, the plasma may turn collisionless and a kinetic description is required to describe the subsequent expansion. In this paper we explore the late and possibly collisionless spherically symmetric unconstrained expansion of a single ionized ion-electron plasma using N-body simulations. Given the strong uncertainties concerning the early hydrodynamic expansion, we assume that at the time of the transition to the collisionless regime the cloud density and temperature are spatially uniform. We do also neglect the role of the ambient plasma. This is a reasonable assumption as long as the cloud density is substantially higher than the ambient plasma density. In the case of clouds generated by fast interplanetary dust grains hitting a solid target some 10^7 electrons and ions are liberated and the in vacuum approximation is acceptable up to meter order cloud dimensions. ..

Forward Flux Sampling for rare event simulations

Rare events are ubiquitous in many different fields, yet they are notoriously difficult to simulate because few, if any, events are observed in a conventiona l simulation run. Over the past several decades, specialised simulation methods have been developed to overcome this problem. We review one recently-developed class of such methods, known as Forward Flux Sampling. Forward Flux Sampling uses a series of interfaces between the initial and final states to calculate rate constants and generate transition paths, for rare events in equilibrium or nonequilibrium systems with stochastic dynamics. This review draws together a number of recent advances, summarizes several applications of the method and highlights challenges that remain to be overcome.Comment: minor typos in the manuscript. J.Phys.:Condensed Matter (accepted for publication

Adam Smith and Colonialism

In the context of debates about liberalism and colonialism, the arguments of Adam Smith have been taken as illustrative of an important line of anti-colonial liberal thought. The reading of Smith presented here challenges this interpretation. It argues that Smith’s opposition to colonial rule derived largely from its impact on the metropole, rather than on its impact on the conquered and colonised; that Smith recognised colonialism had brought ‘improvement’ in conquered territories and that Smith struggled to balance recognition of moral diversity with a universal moral framework and a commitment to a particular interpretation of progress through history. These arguments have a wider significance as they point towards some of the issues at stake in liberal anti-colonial arguments more generally

Information theoretic approach to interactive learning

The principles of statistical mechanics and information theory play an important role in learning and have inspired both theory and the design of numerous machine learning algorithms. The new aspect in this paper is a focus on integrating feedback from the learner. A quantitative approach to interactive learning and adaptive behavior is proposed, integrating model- and decision-making into one theoretical framework. This paper follows simple principles by requiring that the observer's world model and action policy should result in maximal predictive power at minimal complexity. Classes of optimal action policies and of optimal models are derived from an objective function that reflects this trade-off between prediction and complexity. The resulting optimal models then summarize, at different levels of abstraction, the process's causal organization in the presence of the learner's actions. A fundamental consequence of the proposed principle is that the learner's optimal action policies balance exploration and control as an emerging property. Interestingly, the explorative component is present in the absence of policy randomness, i.e. in the optimal deterministic behavior. This is a direct result of requiring maximal predictive power in the presence of feedback.Comment: 6 page

1950: Abilene Christian College Bible Lectures - Full Text

Introduction We offer with interest and pleasure another volume of a great series of discourses delivered at Abilene Christian College. The following were given in February, 1950. The first of these Lectureships was held in the year 1919, and was published by the Firm Foundation Publishing House in book form. With little exception they have appeared each year since that time. The printing was done by others a few times. Those who are fortunate enough to have a complete set of these fine gospel sermons are possessed of a treasure in religious literature. Only a few of the later years can now be supplied. The rest are numbered among the “rare books” and we frequently have calls for them, but of course cannot supply them. Any reader having a copy for sale is requested to write the office of the Firm Foundation at Austin, Texas. The “Lectureship” of Abilene Christian College has become a great annual affair to the churches of Christ; thousands are in attendance, many of them coming from Canada and other countries besides all over the United States. This annual “mass meeting” must not be understood to be a “Convention” of the churches of Christ. We have no such conventions and do not endorse them. The Lectureship is simply a feature in the work of Abilene Christian College, a series of gospel sermons to which friends and patrons of the school and others are invited. It is our hope that the contents of this book may enrich the life, and strengthen the faith of the reader. G. H. F. SHOWALTER Austin, Texas August 20, 195

Investigation of the flow past finite wedges of 20 deg. and 40 deg. apex angle at subsonic and supersonic speeds, using a Mach-Zehnder interferometer with appendix: sensitivity and accuracy of the interference method applied to pressure measurements

An investigation has been made in the high-speed wind tunnel A 7 of the Luftfahrtforschungsanstalt. Brunswick, of the flow past finite wedges of 20 deg. and 40 deg. apex angle at both subsonic and supersonic speeds, the Mach numbers lying between 0.6 and 0.85 on the one hand, and between 1.4 and 2.8 on the other. The pressure distributions on the models have been evaluated from photographs of density contours obtained by the use of a Mach- Zehnder interferometer. The interferometer technique is briefly described, and also the method of evaluation of the photographs. The results are discussed in detail, and are compared with the theoretical predictions of Maccoll and Codd. A selection of photographs, and a number of diagrams showing the pressure distribution, are included. In the Appendix, the sensitivity and accuracy of the interference method applied to pressure measurements are discussed. It is shown that requirements for both, in the particular case of the A 7 tunnel, are satisfied in a range of Mach numbers between 0.5 and 3.0

Boundary Conditions on Internal Three-Body Wave Functions

For a three-body system, a quantum wave function $\Psi^\ell_m$ with definite $\ell$ and $m$ quantum numbers may be expressed in terms of an internal wave function $\chi^\ell_k$ which is a function of three internal coordinates. This article provides necessary and sufficient constraints on $\chi^\ell_k$ to ensure that the external wave function $\Psi^\ell_m$ is analytic. These constraints effectively amount to boundary conditions on $\chi^\ell_k$ and its derivatives at the boundary of the internal space. Such conditions find similarities in the (planar) two-body problem where the wave function (to lowest order) has the form $r^{|m|}$ at the origin. We expect the boundary conditions to prove useful for constructing singularity free three-body basis sets for the case of nonvanishing angular momentum.Comment: 41 pages, submitted to Phys. Rev.

Density functional study of the adsorption of K on the Ag(111) surface

Full-potential gradient corrected density functional calculations of the adsorption of potassium on the Ag(111) surface have been performed. The considered structures are Ag(111) (root 3 x root 3) R30degree-K and Ag(111) (2 x 2)-K. For the lower coverage, fcc, hcp and bridge site; and for the higher coverage all considered sites are practically degenerate. Substrate rumpling is most important for the top adsorption site. The bond length is found to be nearly identical for the two coverages, in agreement with recent experiments. Results from Mulliken populations, bond lengths, core level shifts and work functions consistently indicate a small charge transfer from the potassium atom to the substrate, which is slightly larger for the lower coverage.Comment: to appear in Phys Rev