We present a computer supported tool for cooperative work in interdisciplinary fields, which we tested within the area of astrobiology. Our document classification and visualization system is fully automated and data driven, based on unsupervised learning algorithms and network visualization tools. A new feature selection algorithm was created to aid this process that indicates which words should be used for mutual information-based clustering. Our system can extract information about collaborations from unstructured databases with no meta-data and reveals structure that can aid the planning of collaborative research. We analyzed publications produced by researchers from NASA's Astrobiology Institute. We presented this analysis as a cultural probe and recorded reactions from researchers that indicated that our method can help scientists from different disciplines to work together. We have made an interactive version of our visualization and analysis available as a website for long-term use.

We address the duality between adaptive filtering in C and R2and provide a comparison between the well understood dual channel real valued least mean square (DCRLMS) algorithm in R2and the corresponding algorithms in C. These include the complex LMS (CLMS) and the recently introduced augmented CLMS (ACLMS), a widely linear algorithm designed for the processing of noncircular complex valued signals. The analysis shows that the standard CLMS and DCRLMS in general provide different adaptive filtering solutions, whereas the ACLMS and DCRLMS are isomoprhic and can be made equivalent. The analysis is supported by simulations on noncircular real world signals.

We present a neuromorphic pattern generator for controlling the walking gaits of four-legged robots which is inspired by central pattern generators found in the nervous system and which is implemented as a very large scale integrated (VLSI) chip. The chip contains oscillator circuits that mimic the output of motor neurons in a strongly simplified way. We show that four coupled oscillators can produce rhythmic patterns with phase relationships that are appropriate to generate all four-legged animal walking gaits. These phase relationships together with frequency and duty cycle of the oscillators determine the walking behavior of a robot driven by the chip, and they depend on a small set of stationary bias voltages. We give analytic expressions for these dependencies. This chip reduces the complex, dynamic inter-leg control problem associated with walking gait generation to the problem of setting a few stationary parameters. It provides a compact and low power solution for walking gait control in robots.

Clustering provides a common means of identifying structure in complex data, and there is renewed interest in clustering as a tool for the analysis of large data sets in many fields. A natural question is how many clusters are appropriate for the description of a given system. Traditional approaches to this problem are based on either a framework in which clusters of a particular shape are assumed as a model of the system or on a two-step procedure in which a clustering criterion determines the optimal assignments for a given number of clusters and a separate criterion measures the goodness of the classification to determine the number of clusters. In a statistical mechanics approach, clustering can be seen as a trade-off between energy- and entropy-like terms, with lower temperature driving the proliferation of clusters to provide a more detailed description of the data. For finite data sets, we expect that there is a limit to the meaningful structure that can be resolved and therefore a minimum temperature beyond which we will capture sampling noise. This suggests that correcting the clustering criterion for the bias that arises due to sampling errors will allow us to find a clustering solution at a temperature that is optimal in the sense that we capture maximal meaningful structure--without having to define an external criterion for the goodness or stability of the clustering. We show that in a general information-theoretic framework, the finite size of a data set determines an optimal temperature, and we introduce a method for finding the maximal number of clusters that can be resolved from the data in the hard clustering limit.

We argue that K–means and deterministic annealing algorithms for geo- metric clustering can be derived from the more general Information Bot- tleneck approach. If we cluster the identities of data points to preserve information about their location, the set of optimal solutions is massively degenerate. But if we treat the equations that define the optimal solution as an iterative algorithm, then a set of “smooth” initial conditions selects solutions with the desired geometrical properties. In addition to concep- tual unification, we argue that this approach can be more efficient and robust than classic algorithms.

To control the walking gaits of a four-legged robot we present a novel neuromorphic VLSI chip that coordinates the relative phasing of the robot's legs similar to how spinal Central Pattern Generators are believed to control vertebrate locomotion [3]. The chip controls the leg move(cid:173) ments by driving motors with time varying voltages which are the out(cid:173) puts of a small network of coupled oscillators. The characteristics of the chip's output voltages depend on a set of input parameters. The rela(cid:173) tionship between input parameters and output voltages can be computed analytically for an idealized system. In practice, however, this ideal re(cid:173) lationship is only approximately true due to transistor mismatch and off(cid:173) sets. Fine tuning of the chip's input parameters is done automatically by the robotic system, using an unsupervised Support Vector (SV) learning algorithm introduced recently [7]. The learning requires only that the description of the desired output is given. The machine learns from (un(cid:173) labeled) examples how to set the parameters to the chip in order to obtain a desired motor behavior.