A Method for Constrained Multiobjective Optimization Based on SQP Techniques

We propose a method for constrained and unconstrained nonlinear multiobjective optimization problems that is based on an SQP-type approach. The proposed algorithm maintains a list of nondominated points that is improved both for spread along the Pareto front and optimality by solving single-objective constrained optimization problems. These single-objective problems are derived as SQP problems based on the given nondominated points.Under appropriate differentiability assumptions we discuss convergence to local optimal Pareto points. We provide numerical results for a set of unconstrained and constrained multiobjective optimization problems in the form of performance and data profiles, where several performance metrics are used. The numerical results confirm the superiority of the proposed algorithm against a state-of-the-art multiobjective solver and a classical scalarization approach, both in the quality of the approximated Pareto front and in the computational effort necessary to compute the approximation.<br/

BOLD fMRI Correlation Reflects Frequency-Specific Neuronal Correlation

SummaryThe brain-wide correlation of hemodynamic signals as measured with BOLD fMRI is widely studied as a proxy for integrative brain processes [1–3]. However, the relationship between hemodynamic correlation structure and neuronal correlation structure [4–6] remains elusive. We investigated this relation using BOLD fMRI and spatially co-registered, source-localized MEG in resting humans. We found that across the entire cortex BOLD correlation reflected the co-variation of frequency-specific neuronal activity. Resolving the relation between electrophysiological and hemodynamic correlation structures locally in cortico-cortical connection space, we found that this relation was subject specific and even persisted on the centimeter scale. At first sight, this relation was strongest in the alpha to beta frequency range (8–32 Hz). However, correcting for differences in signal-to-noise ratios across electrophysiological frequencies, we found that the relation extended over a broad frequency range from 2 to 128 Hz. Moreover, we found that the frequency with the tightest link to BOLD correlation varied across cortico-cortical space. For every cortico-cortical connection, we show which specific correlated oscillations were most related to BOLD correlations. Our work provides direct evidence for the neuronal origin of BOLD correlation structure. Moreover, our work suggests that, across the brain, BOLD correlation reflects correlation of different types of neuronal network processes and that frequency-specific electrophysiological correlation provides information about large-scale neuronal interactions complementary to BOLD fMRI

Cosmic Structure Traced by Precision Measurements of the X-Ray Brightest Galaxy Clusters in the Sky

The current status of our efforts to trace cosmic structure with 10^6 galaxies (2MASS), 10^3 galaxy clusters (NORAS II cluster survey), and precision measurements for 10^2 galaxy clusters (HIFLUGCS) is given. The latter is illustrated in more detail with results on the gas temperature and metal abundance structure for 10^0 cluster (A1644) obtained with XMM-Newton.Comment: 4 pages; to be published in the Proceedings of the Conference: The Emergence of Cosmic Structure, College Park, MD (2002), editors: S.S. Holt and C. Reynolds; also available at http://www.reiprich.ne

A single Streptomyces symbiont makes multiple antifungals to support the fungus farming ant Acromyrmex octospinosus

Attine ants are dependent on a cultivated fungus for food and use antibiotics produced by symbiotic Actinobacteria as weedkillers in their fungus gardens. Actinobacterial species belonging to the genera Pseudonocardia, Streptomyces and Amycolatopsis have been isolated from attine ant nests and shown to confer protection against a range of microfungal weeds. In previous work on the higher attine Acromyrmex octospinosus we isolated a Streptomyces strain that produces candicidin, consistent with another report that attine ants use Streptomyces-produced candicidin in their fungiculture. Here we report the genome analysis of this Streptomyces strain and identify multiple antibiotic biosynthetic pathways. We demonstrate, using gene disruptions and mass spectrometry, that this single strain has the capacity to make candicidin and multiple antimycin compounds. Although antimycins have been known for > 60 years we report the sequence of the biosynthetic gene cluster for the first time. Crucially, disrupting the candicidin and antimycin gene clusters in the same strain had no effect on bioactivity against a co-evolved nest pathogen called Escovopsis that has been identified in similar to 30% of attine ant nests. Since the Streptomyces strain has strong bioactivity against Escovopsis we conclude that it must make additional antifungal(s) to inhibit Escovopsis. However, candicidin and antimycins likely offer protection against other microfungal weeds that infect the attine fungal gardens. Thus, we propose that the selection of this biosynthetically prolific strain from the natural environment provides A. octospinosus with broad spectrum activity against Escovopsis and other microfungal weeds.Publisher PDFPeer reviewe

Label-free electrical quantification of the dielectrophoretic response of DNA

A purely electrical sensing scheme is presented that determines the concentration of macromolecules in solution by measuring the capacitance between planar microelectrodes. Concentrations of DNA in the ng/mL range have been used in samples of 1 microL volume. The method has been applied to the characterisation of the dielectrophoretic response of DNA without the need for any chemical modifications. The influence of electrical parameters like duty cycle, voltage and frequency has been investigated. The results are in good agreement with data from dielectrophoretic studies on fluorescently labelled DNA. Extension of the method down to the single molecule level appears feasible.Comment: 12 pages, 7 figure

Selenium and tellurium concentrations of Carboniferous British coals

The authors wish to thank Kier Group, the British Coal Utilisation Research Association (BCURA) and Uniper (E.On) for kindly providing coal samples. The authors are grateful to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS) for supporting this study. The authors are grateful for the thorough and constructive comments from two anonymous reviewers, as well as the careful editorial handling of Prof. Ian Somerville. This work was supported by the NERC under Grant number NE/L001764/1.Peer reviewedPublisher PD