Effect inference for deterministic parallelism

In this report we sketch a polymorphic type and effect inference system for ensuring deterministic execution of parallel programs containing shared mutable state. It differs from that of Gifford and Lucassen in being based on Hindley Milner polymorphism and in formalizing the operational semantics of parallel and sequential computation

A Comparison of some recent Task-based Parallel Programming Models

The need for parallel programming models that are simple to use and at the same time efficient for current ant future parallel platforms has led to recent attention to task-based models such as Cilk++, Intel TBB and the task concept in OpenMP version 3.0. The choice of model and implementation can have a major impact on the final performance and in order to understand some of the trade-offs we have made a quantitative study comparing four implementations of OpenMP (gcc, Intel icc, Sun studio and the research compiler Mercurium/nanos mcc), Cilk++ and Wool, a high-performance task-based library developed at SICS. Abstract. We use microbenchmarks to characterize costs for task-creation and stealing and the Barcelona OpenMP Tasks Suite for characterizing application performance. By far Wool and Cilk++ have the lowest overhead in both spawning and stealing tasks. This is reflected in application performance when many tasks with small granularity are spawned where Cilk++ and, in particular, has the highest performance. For coarse granularity applications, the OpenMP implementations have quite similar performance as the more light-weight Cilk++ and Wool except for one application where mcc is superior thanks to a superior task scheduler. Abstract. The OpenMP implemenations are generally not yet ready for use when the task granularity becomes very small. There is no inherent reason for this, so we expect future implementations of OpenMP to focus on this issue

Translational and rotational friction on a colloidal rod near a wall

We present particulate simulation results for translational and rotational friction components of a shish-kebab model of a colloidal rod with aspect ratio (length over diameter) $L/D = 10$ in the presence of a planar hard wall. Hydrodynamic interactions between rod and wall cause an overall enhancement of the friction tensor components. We find that the friction enhancements to reasonable approximation scale inversely linear with the closest distance $d$ between the rod surface and the wall, for $d$ in the range between $D/8$ and $L$. The dependence of the wall-induced friction on the angle $\theta$ between the long axis of the rod and the normal to the wall is studied and fitted with simple polynomials in $\cos \theta$.Comment: 8 pages, 8 figure

Oscillations and translation of a free cylinder in a confined flow

An oscillatory instability has been observed experimentally on an horizontal cylinder free to move and rotate between two parallel vertical walls of distance H; its characteristics differ both from vortex shedding driven oscillations and from those of tethered cylinders in the same geometry. The vertical motion of the cylinder, its rotation about its axis and its transverse motion across the gap have been investigated as a function of its diameter D, its density s, of the mean vertical velocity U of the fluid and of its viscosity. For a blockage ratio D/H above 0.5 and a Reynolds number Re larger then 14, oscillations of the rolling angle of the cylinder about its axis and of its transverse coordinate in the gap are observed together with periodic variations of the vertical velocity. Their frequency f is the same for the sedimentation of the cylinder in a static fluid (U = 0) and for a non-zero mean flow (U 6= 0). The Strouhal number St associated to the oscillation varies as 1/Re with : St.Re = 3 $\pm$ 0.15. The corresponding period 1/f is then independent of U and corresponds to a characteristic viscous diffusion time over a distance ~ D, implying a strong influence of the viscosity. These characteristics differ from those of vortex shedding and tethered cylinders for which St is instead roughly constant with Re and higher than here

Noise and Inertia-Induced Inhomogeneity in the Distribution of Small Particles in Fluid Flows

The dynamics of small spherical neutrally buoyant particulate impurities immersed in a two-dimensional fluid flow are known to lead to particle accumulation in the regions of the flow in which rotation dominates over shear, provided that the Stokes number of the particles is sufficiently small. If the flow is viewed as a Hamiltonian dynamical system, it can be seen that the accumulations occur in the nonchaotic parts of the phase space: the Kolmogorov--Arnold--Moser tori. This has suggested a generalization of these dynamics to Hamiltonian maps, dubbed a bailout embedding. In this paper we use a bailout embedding of the standard map to mimic the dynamics of impurities subject not only to drag but also to fluctuating forces modelled as white noise. We find that the generation of inhomogeneities associated with the separation of particle from fluid trajectories is enhanced by the presence of noise, so that they appear in much broader ranges of the Stokes number than those allowing spontaneous separation

Hydrodynamic interactions of spherical particles in Poiseuille flow between two parallel walls

We study hydrodynamic interactions of spherical particles in incident Poiseuille flow in a channel with infinite planar walls. The particles are suspended in a Newtonian fluid, and creeping-flow conditions are assumed. Numerical results, obtained using our highly accurate Cartesian-representation algorithm [Physica A xxx, {\bf xx}, 2005], are presented for a single sphere, two spheres, and arrays of many spheres. We consider the motion of freely suspended particles as well as the forces and torques acting on particles adsorbed at a wall. We find that the pair hydrodynamic interactions in this wall-bounded system have a complex dependence on the lateral interparticle distance due to the combined effects of the dissipation in the gap between the particle surfaces and the backflow associated with the presence of the walls. For immobile particle pairs we have examined the crossover between several far-field asymptotic regimes corresponding to different relations between the particle separation and the distances of the particles from the walls. We have also shown that the cumulative effect of the far-field flow substantially influences the force distribution in arrays of immobile spheres. Therefore, the far-field contributions must be included in any reliable algorithm for evaluating many-particle hydrodynamic interactions in the parallel-wall geometry.Comment: submitted to Physics of Fluid

Heart failure : role of metabolic biomarkers, ejection fraction, and sex

Background: Heart failure (HF) is common and associated with impaired quality of life (QoL) and poor prognosis. There is a ternary classification of HF based on ejection fraction (EF): HF with preserved(HFpEF), mid-range EF(HFmrEF), and reduced EF(HFrEF). How to treat the syndrome of HFpEF, and the extent to which HFpEF and HFrEF are similar, still remain elusive. Likewise, despite the fact that half of the patients with HF are women, the role of sex in HF is often overlooked. Aims: (1) To investigate whether HFpEF and HFrEF share features of anabolic impairment regarding insulin-like growth factor 1 (IGF-1) and IGF binding protein-1 (IGFBP-1). (2) To assess levels of the obesity related peptides, leptin and adiponectin, and whether the obesity paradox exists in HFpEF. (3) To investigate potential sex-specific differences in QoL in HFpEF. (4) To assess the impact of sex on N-terminal B-type natriuretic peptide (NT-proBNP) in chronic HF across the EF spectrum. Results: The IGF-1 axis in HFpEF and HFrEF Serum IGF-1and IGFBP-1 concentrations and their associations with other biomarkers and outcomes were analysed in patients with HFpEF and HFrEF. IGF-1 concentrations were lower and associated with poor prognosis in HFrEF only. However, IGFBP-1 was increased and associated with NTproBNP in both HF phenotypes. This suggests inhibition of the IGF-1-axis in both syndromes and a possible mechanistic link between IGFBP-1 and natriuretic peptides in HF. Leptin and adiponectin in HFpEF and HFrEF Serum leptin and adiponectin concentrations and their associations with other biomarkers and outcomes in patients with HFpEF and HFrEF were analysed. Our findings indicate that the two HF phenotypes share elevated levels of leptin and adiponectin. The obesity paradox regarding leptin, with higher levels being associated with better outcome was nevertheless only demonstrated in HFrEF, pointing towards a more conventional metabolic profile in HFpEF. Sex and quality of life in HFpEF We assessed QoL in HFpEF through generic and HF specific QoL instruments. Women with HFpEF express worse global QoL than men. Overall, QoL was only weakly associated with measures of HF severity and the associations were weaker in women. In men only, poor QoL was associated with worse outcome. Overall, this suggests, that in order to improve QoL in HFpEF patients, in particular in women, other factors than HF must be addressed. Impact of sex on NT-proBNP across HF phenotypes We analysed concentrations of NT-proBNP, and associations with clinical characteristics and outcomes in the three HF phenotypes, by sex. Women with chronic HF across the entire EF spectrum have higher NT-proBNP concentrations than men. However, associations between NT-proBNP concentrations and clinical characteristics as well as outcomes are largely similar. This supports the current use of NT-proBNP for prognostic purposes across HF phenotypes but the impact of sexdifferences in the lower NT-proBNP range warrants further investigation. Conclusion: HFpEF and HFrEF display important similarities and differences related to metabolic biomarkers, natriuretic peptides, and sex. The impact of these factors on the pathogenesis of and in manifest HF, and as potential therapeutic targets warrants further investigation

Lace: non-blocking split deque for work-stealing

Work-stealing is an efficient method to implement load balancing in fine-grained task parallelism. Typically, concurrent deques are used for this purpose. A disadvantage of many concurrent deques is that they require expensive memory fences for local deque operations.\ud \ud In this paper, we propose a new non-blocking work-stealing deque based on the split task queue. Our design uses a dynamic split point between the shared and the private portions of the deque, and only requires memory fences when shrinking the shared portion.\ud \ud We present Lace, an implementation of work-stealing based on this deque, with an interface similar to the work-stealing library Wool, and an evaluation of Lace based on several common benchmarks. We also implement a recent approach using private deques in Lace. We show that the split deque and the private deque in Lace have similar low overhead and high scalability as Wool

Acoustic radiation- and streaming-induced microparticle velocities determined by micro-PIV in an ultrasound symmetry plane

We present micro-PIV measurements of suspended microparticles of diameters from 0.6 um to 10 um undergoing acoustophoresis in an ultrasound symmetry plane in a microchannel. The motion of the smallest particles are dominated by the Stokes drag from the induced acoustic streaming flow, while the motion of the largest particles are dominated by the acoustic radiation force. For all particle sizes we predict theoretically how much of the particle velocity is due to radiation and streaming, respectively. These predictions include corrections for particle-wall interactions and ultrasonic thermoviscous effects, and they match our measurements within the experimental uncertainty. Finally, we predict theoretically and confirm experimentally that the ratio between the acoustic radiation- and streaming-induced particle velocities is proportional to the square of the particle size, the actuation frequency and the acoustic contrast factor, while it is inversely proportional to the kinematic viscosity.Comment: 11 pages, 9 figures, RevTex 4-

Structure and Properties of Traces for Functional Programs

The tracer Hat records in a detailed trace the computation of a program written in the lazy functional language Haskell. The trace can then be viewed in various ways to support program comprehension and debugging. The trace was named the augmented redex trail. Its structure was inspired by standard graph rewriting implementations of functional languages. Here we describe a model of the trace that captures its essential properties and allows formal reasoning. The trace is a graph constructed by graph rewriting but goes beyond simple term graphs. Although the trace is a graph whose structure is independent of any rewriting strategy, we define the trace inductively, thus giving us a powerful method for proving its properties