Minimalist's Linux Cluster

Using barebone PC components and NIC's, we construct a linux cluster which has 2-dimensional mesh structure. This cluster has smaller footprint, is less expensive, and use less power compared to conventional linux cluster. Here, we report our experience in building such a machine and discuss our current lattice project on the machine.Comment: 3 pages, 2 figures, Proceedings of the Lattice 03 Conference (Tsukuba, Japan

Rigidity of noncompact complete Bach-flat manifolds

Let $(M,g)$ be a noncompact complete Bach-flat manifold with positive Yamabe constant. We prove that $(M,g)$ is flat if $(M, g)$ has zero scalar curvature and sufficiently small $L_{2}$ bound of curvature tensor. When $(M, g)$ has nonconstant scalar curvature, we prove that $(M, g)$ is conformal to the flat space if $(M, g)$ has sufficiently small $L_2$ bound of curvature tensor and $L_{4/3}$ bound of scalar curvature.Comment: 10 pages, To appear J. Geom. Physic

A dark matter solution from the supersymmetric axion model

We study the effect of the late decaying saxino (the scalar superpartner of the axion) and find out that there is a possible dark matter solution from a class of supersymmetric extensions of the invisible axion model. In this class of models, the saxino which decays into two axions acts as the late decaying particle which reconciles the cold dark matter model with high values of the Hubble constant. Recent observations of the Hubble constant are converging to $H_0=70\!-\!80\,{\rm km}\,{\rm sec}^{-1}\,{\rm Mpc}^{-1}$, which would be inconsistent with the standard mixed dark matter model. This class of models provides a plausible framework for the alternative cold dark matter plus late decaying particle model, with the interesting possibility that both cold dark matter and the extra radiation consist of axion.Comment: 11 pages, no figure, REVTEX 3.

Parallelizing non-vectorizable loops for MIMD machines

Parallelizing a loop for MIMD machines can be described as a process of partitioning it into a number of relatively independent subloops. Previous approaches to partitioning non-vectorizable loops were mainly based on iteration pipelining which partitioned a loop based on iteration number and exploited parallelism by overlapping the execution of iterations. However, the amount of parallelism exploited this way is limited because the parallelism inside iterations has been ignored. In this paper, we present a new loop partitioning technique which can exploit both forms of parallelism - inside and across iterations. While inspired by the VLIW approach, our method is designed for more general, asynchronous, MIMD machines. In particular, our schedule takes the cost of communication into account, and attempts to balance it with respect to parallelism. We show our method is correct, efficient, and produces better schedules than previous iteration level approaches