Finite-element approximation of a nonlinear degenerate parabolic system describing bacterial pattern formation

Accepted versio

The scanning electron microscope as a tool in space biology

Normal erythrocytes are disc-shaped and are referred to here descriptively as discocytes. Several morphologically variant forms occur nomally but in rather small amounts, usually less than one percent of total. It has been shown though, that spiculed variant forms referred to as echinocytes are generated in significant amounts at zero g. Normal red cells have been stressed in vitro in an effort to duplicate the observed discocyte-echinocyte transformation at zero g. The significance of this transformation to extended stay in space and some of the plausible reasons for this transformation are discussed

Pipes and Connections

This document describes the low-level Pipe and ConnectionManager objects of the Mesh- Router system. The overall MeshRouter framework provides a general scheme for interest- limited communications among a number of client processes. This generality is achieved by a carefully factorized, object-oriented software implementation. Within this framework, the Pipe and ConnectionManager (base) classes dened in this note specify the interfaces for i) ac- tual `bits on the wire' communications and ii) dynamic client insertions during overall system execution. Two specic implementations of the Pipe class are described in detail: a `Memo- ryPipe' linking objects instanced on a single processor and a more general 'rtisPipe' providing inter-processor communications built entirely from the standard RTI-s library used in current JSAF applications. Initialization procedures within the overall MeshRouter system are dis- cussed, with particular attention given to dynamic management of inter-processor connections. Prototype RTI-s router processes are discussed, and simple extensions of the standard system conguration data les are presented

Improving Performance of Iterative Methods by Lossy Checkponting

Iterative methods are commonly used approaches to solve large, sparse linear systems, which are fundamental operations for many modern scientific simulations. When the large-scale iterative methods are running with a large number of ranks in parallel, they have to checkpoint the dynamic variables periodically in case of unavoidable fail-stop errors, requiring fast I/O systems and large storage space. To this end, significantly reducing the checkpointing overhead is critical to improving the overall performance of iterative methods. Our contribution is fourfold. (1) We propose a novel lossy checkpointing scheme that can significantly improve the checkpointing performance of iterative methods by leveraging lossy compressors. (2) We formulate a lossy checkpointing performance model and derive theoretically an upper bound for the extra number of iterations caused by the distortion of data in lossy checkpoints, in order to guarantee the performance improvement under the lossy checkpointing scheme. (3) We analyze the impact of lossy checkpointing (i.e., extra number of iterations caused by lossy checkpointing files) for multiple types of iterative methods. (4)We evaluate the lossy checkpointing scheme with optimal checkpointing intervals on a high-performance computing environment with 2,048 cores, using a well-known scientific computation package PETSc and a state-of-the-art checkpoint/restart toolkit. Experiments show that our optimized lossy checkpointing scheme can significantly reduce the fault tolerance overhead for iterative methods by 23%~70% compared with traditional checkpointing and 20%~58% compared with lossless-compressed checkpointing, in the presence of system failures.Comment: 14 pages, 10 figures, HPDC'1