Biological samples are routinely analyzed for microbe concentration. The samples are diluted, loaded onto established host cell cultures, and incubated. If infectious agents are present in the samples, they form circular spots that do not contain the host cells. Each spot is assumed to be originated from a single microbial unit such as a bacterial colony forming unit or viral plaque forming unit. The undiluted sample concentration is estimated by counting the spots and back-calculating. Counting the number of spots by trained technicians is currently the gold standard but it is laborious, subjective, and hard to scale. This paper presents a new automated algorithm for spot counting, Localized and Sequential Thresholding (LoST). Validation studies showed that LoST performance was comparable with manual counting and outperformed several existing tools on images with overlapping spots. The LoST algorithm employs sequential thresholding through a two-stage segmentation and borrows information across all images from the same dilution series to fine-tune the count and identify right censoring. The algorithm increases the efficiency of the spot counting and the quality of the downstream analysis, especially when coupled with an appropriate statistical serial dilution model to enhance the undiluted sample concentration estimation procedure.

This paper describes an operating system (OS) interface for active routers. This interface allows code loaded into active routers to access the router's memory, communication, and computational resources on behalf of different packet flows. In addition to motivating and describing the interface, the paper also reports our experiences implementing the interface in three different OS environments: Scout, the OSKit, and the esokernel.

The special problems of software re-engineering and technologies and approaches that specifically address these re-engineering problems are considered. Particular attention is given to approaches for analyzing and abstracting the functionality of old code, converting software to work with new languages or dialects, translating large systems, defining appropriate roles for the user of highly automated tools, and identifying the automatable steps in a large-scale project to re-engineer assembly language code. An attempt is made to indicate on the basis of actual experience what aspects of the re-engineering process seem to be most amenable to automation and what productivity gains can be expected.>