Efficacy of the SU(3) scheme for ab initio large-scale calculations beyond the lightest nuclei

We report on the computational characteristics of ab initio nuclear structure calculations in a symmetry-adapted no-core shell model (SA-NCSM) framework. We examine the computational complexity of the current implementation of the SA-NCSM approach, dubbed LSU3shell, by analyzing ab initio results for 6Li and 12C in large harmonic oscillator model spaces and SU(3)-selected subspaces. We demonstrate LSU3shell's strong-scaling properties achieved with highly-parallel methods for computing the many-body matrix elements. Results compare favorably with complete model space calculations and significant memory savings are achieved in physically important applications. In particular, a well-chosen symmetry-adapted basis affords memory savings in calculations of states with a fixed total angular momentum in large model spaces while exactly preserving translational invariance.Comment: 11 pages, 8 figure

HyperPRAW : architecture-aware hypergraph restreaming partition to improve performance of parallel applications running on high performance computing systems

High Performance Computing (HPC) demand is on the rise, particularly for large distributed computing. HPC systems have, by design, very heterogeneous architectures, both in computation and in communication bandwidth, resulting in wide variations in the cost of communications between compute units. If large distributed applications are to take full advantage of HPC, the physical communication capabilities must be taken into consideration when allocating workload. Hypergraphs are good at modelling total volume of communication in parallel and distributed applications. To the best of our knowledge, there are no hypergraph partitioning algorithms to date that are architecture-aware. We propose a novel restreaming hypergraph partitioning algorithm (HyperPRAW) that takes advantage of peer to peer physical bandwidth profiling data to improve distributed applications performance in HPC systems. Our results show that not only the quality of the partitions achieved by our algorithm is comparable with state-of-the-art multilevel partitioning, but that the runtime performance in a synthetic benchmark is significantly reduced in 10 hypergraph models tested, with speedup factors of up to 14x

Collective Modes in Light Nuclei from First Principles

Results for ab initio no-core shell model calculations in a symmetry-adapted SU(3)-based coupling scheme demonstrate that collective modes in light nuclei emerge from first principles. The low-lying states of 6Li, 8Be, and 6He are shown to exhibit orderly patterns that favor spatial configurations with strong quadrupole deformation and complementary low intrinsic spin values, a picture that is consistent with the nuclear symplectic model. The results also suggest a pragmatic path forward to accommodate deformation-driven collective features in ab initio analyses when they dominate the nuclear landscape.Comment: 5 pages 3 figures, accepted to Physical Review Letter

BlueGene/L Applications: Parallelism on a Massive Scale

BlueGene/L (BG/L), developed through a partnership between IBM and Lawrence Livermore National Laboratory (LLNL), is currently the world's largest system both in terms of scale with 131,072 processors and absolute performance with a peak rate of 367 TFlop/s. BG/L has led the Top500 list the last four times with a Linpack rate of 280.6 TFlop/s for the full machine installed at LLNL and is expected to remain the fastest computer in the next few editions. However, the real value of a machine like BG/L derives from the scientific breakthroughs that real applications can produce by successfully using its unprecedented scale and computational power. In this paper, we describe our experiences with eight large scale applications on BG/L from several application domains, ranging from molecular dynamics to dislocation dynamics and turbulence simulations to searches in semantic graphs. We also discuss the challenges we faced when scaling these codes and present several successful optimization techniques. All applications show excellent scaling behavior, even at very large processor counts, with one code even achieving a sustained performance of more than 100 TFlop/s, clearly demonstrating the real success of the BG/L design

A Matrix Partitioning Interface to PaToH in MATLAB

Cataloged from PDF version of article.We present the PaToH MATLAB Matrix Partitioning Interface. The interface provides support for hypergraph-based sparse matrix partitioning methods which are used for efficient parallelization of sparse matrix-vector multiplication operations. The interface also offers tools for visualizing and measuring the quality of a given matrix partition. We propose a novel, multilevel, 20 coarsening-based 20 matrix partitioning method and implement it using the interface. We have performed extensive comparison of the proposed method against our implementation of orthogonal recursive bisection and fine-grain methods on a large set of publicly available test matrices. The conclusion of the experiments is that the new method can compete with the fine-grain method while also suggesting new research directions. (C) 2010 Elsevier BM. All rights reserved

A new closure technique for limited thoracotomy where the ribs are spread minimally

An alternative closure technique for limited thoracotomy incisions is described below. This technique consists of fixing the intercostal muscles with horizontal matress sutures. Also the described technique can be applied where the ribs are spread minimally in such limited thoracotomy incisions

Transthoracic Colour Doppler Ultrasonography in the Evaluation of Internal Thoracic Artery Bypass Graft Patency

The internal thoracic artery (ITA) is the most important conduit for coronary artery bypass grafting. The quality of the anastomosis joining the ITA to the left anterior descending coronary artery has a major impact on left ventricular perfusion. The rapid detection of flow disturbances due to sub-optimal anastomosis is, therefore, of great prognostic significance. In this study, 47 coronary bypass patients were examined using colour Doppler ultrasonography peri-operatively and 4 - 6 months post-operatively. Findings were correlated with clinical observations and a treadmill exercise test. The pre-operative ITA flow pattern was normally triphasic, but changed post-operatively to simulate the normal biphasic flow pattern of left anterior descending coronary artery. A 35-case-control group was used to compare pre-operative ITA flow characteristics. The authors conclude that Doppler parameters, clinical findings and the treadmill test can be used in combination for the routine evaluation of graft potency, and to select cases that require more invasive coronary angiography

Transthoracic colour Doppler ultrasonography in the evaluation of internal thoracic artery bypass graft patency

The internal thoracic artery (ITA) is the most important conduit for coronary artery bypass grafting. The quality of the anastomosis joining the ITA to the left anterior descending coronary artery has a major impact on left ventricular perfusion. The rapid detection of flow disturbances due to sub-optimal anastomosis is, therefore, of great prognostic significance. In this study, 47 coronary bypass patients were examined using colour Doppler ultrasonography peri-operatively and 4 - 6 months post-operatively. Findings were correlated with clinical observations and a treadmill exercise test. The pre-operative ITA flow pattern was normally triphasic, but changed post-operatively to simulate the normal biphasic flow pattern of left anterior descending coronary artery. A 35-case-control group was used to compare pre-operative ITA flow characteristics. The authors conclude that Doppler parameters, clinical findings and the treadmill test can be used in combination for the routine evaluation of graft potency, and to select cases that require more invasive coronary angiography