161 research outputs found
GPTIPS 2: an open-source software platform for symbolic data mining
GPTIPS is a free, open source MATLAB based software platform for symbolic
data mining (SDM). It uses a multigene variant of the biologically inspired
machine learning method of genetic programming (MGGP) as the engine that drives
the automatic model discovery process. Symbolic data mining is the process of
extracting hidden, meaningful relationships from data in the form of symbolic
equations. In contrast to other data-mining methods, the structural
transparency of the generated predictive equations can give new insights into
the physical systems or processes that generated the data. Furthermore, this
transparency makes the models very easy to deploy outside of MATLAB. The
rationale behind GPTIPS is to reduce the technical barriers to using,
understanding, visualising and deploying GP based symbolic models of data,
whilst at the same time remaining highly customisable and delivering robust
numerical performance for power users. In this chapter, notable new features of
the latest version of the software are discussed with these aims in mind.
Additionally, a simplified variant of the MGGP high level gene crossover
mechanism is proposed. It is demonstrated that the new functionality of GPTIPS
2 (a) facilitates the discovery of compact symbolic relationships from data
using multiple approaches, e.g. using novel gene-centric visualisation analysis
to mitigate horizontal bloat and reduce complexity in multigene symbolic
regression models (b) provides numerous methods for visualising the properties
of symbolic models (c) emphasises the generation of graphically navigable
libraries of models that are optimal in terms of the Pareto trade off surface
of model performance and complexity and (d) expedites real world applications
by the simple, rapid and robust deployment of symbolic models outside the
software environment they were developed in.Comment: 26 pages, accepted for publication in the Springer Handbook of
Genetic Programming Applications (2015, in press
Structural and magneto-transport properties of electrodeposited bismuth nanowires
Arrays of semimetallic Bi nanowires have been successfully fabricated by electrodeposition. Each nanowire consists of elongated Bi grains along the wire direction. Very large positive magnetoresistance of 300% at low temperatures and 70% at room temperature with quasilinear field dependence has been observed. These features are desirable for wide-range field sensing applications. © 1998 American Institute of Physics
Relaxation of Surface Profiles by Evaporation Dynamics
We present simulations of the relaxation towards equilibrium of one
dimensional steps and sinusoidal grooves imprinted on a surface below its
roughening transition. We use a generalization of the hypercube stacking model
of Forrest and Tang, that allows for temperature dependent
next-nearest-neighbor interactions. For the step geometry the results at T=0
agree well with the t^(1/4) prediction of continuum theory for the spreading of
the step. In the case of periodic profiles we modify the mobility for the tips
of the profile and find the approximate solution of the resulting free boundary
problem to be in reasonable agreement with the T=0 simulations.Comment: 6 pages, Revtex, 5 Postscript figures, to appear in PRB 15, October
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Fundamental studies of passivity and passivity breakdown
This report summarizes the findings of our fundamental research program on passivity and passivity breakdown. During the past three and one half years in this program (including the three year incrementally-funded grant prior to the present grant), we developed and experimentally tested various physical models for the growth and breakdown of passive films on metal surfaces. These models belong to a general class termed point defects models'' (PDMs), in which the growth and breakdown of passive films are described in terms of the movement of anion and cation vacancies
A global ocean atlas of eukaryotic genes
While our knowledge about the roles of microbes and viruses in the ocean has increased tremendously due to recent advances in genomics and metagenomics, research on marine microbial eukaryotes and zooplankton has benefited much less from these new technologies because of their larger genomes, their enormous diversity, and largely unexplored physiologies. Here, we use a metatranscriptomics approach to capture expressed genes in open ocean Tara Oceans stations across four organismal size fractions. The individual sequence reads cluster into 116 million unigenes representing the largest reference collection of eukaryotic transcripts from any single biome. The catalog is used to unveil functions expressed by eukaryotic marine plankton, and to assess their functional biogeography. Almost half of the sequences have no similarity with known proteins, and a great number belong to new gene families with a restricted distribution in the ocean. Overall, the resource provides the foundations for exploring the roles of marine eukaryotes in ocean ecology and biogeochemistry
Finite-size effects in bismuth nanowires
Arrays of semimetallic Bi nanowires, fabricated by electrodeposition, exhibit strong finite-size effects in transport properties as the carrier mean-free path is limited by the wire dimensions. We have observed a resistivity enhancement, a very large positive magnetoresistance, and a resistance maximum that depends on the strength and orientation of the magnetic field and the nanowire diameter. These results demonstrate electrodeposited Bi nanowires as a new medium for studying the intricate physics in Bi nanostructures. © 1998 The American Physical Society
Large Magnetoresistance and Finite-Size Effects in Electrodeposited Single-Crystal Bi Thin Films
Trigonal-axis oriented single-crystal Bi thin films have been made by electrodeposition followed by suitable annealing. Very large magnetoresistance with ratios as much as 1500 at 5 K and 2.9 at 300 K under 5 T, Shubnikov-de Haas oscillations, and finite-size effects have been observed. © 1999 The American Physical Society
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