Shaping the Polypropionate Biosynthesis in the Solar‐Powered Mollusc Elysia viridis

Polypropionates that incorporate pyrones are a family of polyketides featuring the chemistry of a few marine molluscs capable of phototrophic CO₂ fixation as a result of storing viable symbiotic chloroplasts in their bodies. The role and origin of these molecules is poorly investigated, although the unusual biological activities and chemistry of these natural products have recently received renewed interest. Here, we report the results of in vivo studies on production of γ‐pyrone‐containing polypropionates in the Mediterranean mollusc Elysia viridis. Biosynthesis of the metabolites in the sacoglossan is shown to proceed through condensation of eight intact C₃ units by polyketide synthase assembly. LC–MS and NMR spectroscopic studies demonstrate that the process involves a pyrone tetraene ( 10 ) as key intermediate, whereas the levels of the final polypropionates ( 6 , 7 and 9 ) are related to each other and show a significant dependence upon light conditions.     

A reuse business model

This paper summarizes the decision framework for forming reuse business models and offers the Expert Services Model as a preferred first application of that framework. The Expert Services Model is only one possible approach, but one that we found is a good starting point. The framework for setting up a reuse plan consists of four major steps: define reuse, populate a library of reusable assets, share reusable assets, and maintain reusable assets.     

Scheduling Space–Ground Communications for the Air Force Satellite Control Network

We present the first coupled formal and empirical analysis of the Satellite Range Scheduling application. We structure our study as a progression; we start by studying a simplified version of the problem in which only one resource is present. We show that the simplified version of the problem is equivalent to a well-known machine scheduling problem and use this result to prove that Satellite Range Scheduling is NP-complete. We also show that for the one-resource version of the problem, algorithms from the machine scheduling domain outperform a genetic algorithm previously identified as one of the best algorithms for Satellite Range Scheduling. Next, we investigate if these performance results generalize for the problem with multiple resources. We exploit two sources of data: actual request data from the U.S. Air Force Satellite Control Network (AFSCN) circa 1992 and data created by our problem generator, which is designed to produce problems similar to the ones currently solved by AFSCN. Three main results emerge from our empirical study of algorithm performance for multiple-resource problems. First, the performance results obtained for the single-resource version of the problem do not generalize: the algorithms from the machine scheduling domain perform poorly for the multiple-resource problems. Second, a simple heuristic is shown to perform well on the old problems from 1992; however it fails to scale to larger, more complex generated problems. Finally, a genetic algorithm is found to yield the best overall performance on the larger, more difficult problems produced by our generator.     

Electrical measurement of cross-sectional position of particles flowing through a microchannel

The first high-throughput system for the electrical detection of cross-sectional position and velocity of individual particles flowing through a rectangular microchannel is presented. Lateral position (along channel width) and vertical position (along channel height) are measured using two different sets of coplanar electrodes. In particular, the ratio of travel times measured with electrodes generating a current flow transverse or oblique with respect to particle trajectory yields lateral position. The relative prominence and transit time of a bipolar double-Gaussian signal obtained with a suited electrode configuration, respectively, supply vertical position and velocity. The operating principle is presented by means of finite element numerical simulations. The method is experimentally validated by comparing the electrical estimates of position and velocity of polystyrene beads with optical estimates obtained by processing high-speed images. The system is used to observe bead focusing at different particle Reynolds numbers. This system, providing a fully electrical characterization of single-particle motion, represents a powerful tool, e.g. to understand fluid motion at the microscale, in particle separation studies, or to assess the performance of particle focusing devices. Moreover, it can be simultaneously used to perform single-cell impedance spectroscopy, thus achieving an unprecedented multiparamteric characterization.     

Archetypal Analysis

Archetypal analysis represents each individual in a data set as a mixture of individuals of pure type or archetypes. The archetypes themselves are restricted to being mixtures of the individuals in the data set. Archetypes are selected by minimizing the squared error in representing each individual as a mixture of archetypes. The usefulness of archetypal analysis is illustrated on several data sets. Computing the archetypes is a nonlinear least squares problem, which is solved using an alternating minimizing algorithm.     

Addressing real-time constraints in the design of autonomous agents

The Phoenix project is an experiment in the design of autonomous agents for a complex environment. The project consists of a simulator of the environment, a basic agent architecture, and specific implementation of agents based on real-time techniques; the first two parts have been constructed, the third is on-going. The facets of Phoenix that facilitate real-time research are: a simulator parameterized for varying environmental conditions and instrumented to record behaviors, an agent architecture designed to support adaptable planning and scheduling, and methods for reasoning about real-time constraints.This research has been supported by DARPA, # F30602-85-C-0014; the Office of Naval Research, under a University Research Initiative grant, N00014-86-K-0764; the Office of Naval Research, # N00014-88-K0009, and a grant from the Digital Equipment Corporation. We wish to thank Mike Greenberg for his keen understanding of design issues and mastery of programming that made Phoenix what it is today. We also wish to thank Paul Silvey and David Westbrook for their help.