Variable-delay feedback control of unstable steady states in retarded time-delayed systems

We study the stability of unstable steady states in scalar retarded time-delayed systems subjected to a variable-delay feedback control. The important aspect of such a control problem is that time-delayed systems are already infinite-dimensional before the delayed feedback control is turned on. When the frequency of the modulation is large compared to the system's dynamics, the analytic approach consists of relating the stability properties of the resulting variable-delay system with those of an analogous distributed delay system. Otherwise, the stability domains are obtained by a numerical integration of the linearized variable-delay system. The analysis shows that the control domains are significantly larger than those in the usual time-delayed feedback control, and that the complexity of the domain structure depends on the form and the frequency of the delay modulation.Comment: 13 pages, 8 figures, RevTeX, accepted for publication in Physical Review

Dutch Nao Team: Team description paper: Standard Platform League: German Open 2010

This is the debut of the Dutch Nao Team in the Standard Platform League. The team is a recreation of the Dutch Aibo Team, which was active in the predecessor of the SPL (2004-2006). This year participation is mainly intended to gain experience. As basis for the competition the code release of B-Human is used, with two modifications. The first modification is improved kicking behavior to accommodate the new ball. The second modification is two use both Nao camera’s (one for ball control and one for localization)

Water table fluctuations and carbon accumulation of a fen and a bog in the James Bay Lowlands of Quebec, Canada

An important work regarding northern hemisphere peatland modeling is currently being processed. One of the first steps of this work is to understand the relationship between different components of the peatland system and to analyse the way unspecific peatland systems react to water table fluctuations in terms of accumulation and decomposition that we present in this article. We chose distinct sampling sites within a large region including boreal and subarctic ecosystems in the Bay James lowlands, northern Québec, Canada. Two fens were selected in the subarctic region and two bogs in the boreal region. These sites have different geographical, climatological and ecological features (ex. pH, nutrient availability and species compositions). Fens and bogs behaviours in matter of decomposition and accumulation thus follow different patterns. The analyses of cores for theses sites allow the comparison and the quantification of the differences between subarctic and boreal sites. Five cores were analysed against Testate amoebae every 2cm for the short cores and every 4cm for the long core. These cores are also dated with 210 Pb and 14C. Loss on ignition analysis was performed with the resolution of 1cm for each core. The use of a transfer function with the results of the Testate amoebae analysis allowed reconstruction of water table fluctuations from 7500 years BP to the present. This reconstruction gives us an insight into the humidity regime of the system. This information is compared to the carbon accumulation sequences to evaluate the response of the system to changes in water table position. This research shows response range between sites and quantifies the range of the water table fluctuation inducing an imbalance of the system. This information will be of significant importance for the development of the peatland dynamics modeling

pavarotti encodes a kinesin-like protein required to organize the central spindle and contractile ring for cytokinesis

Mutations in the Drosophila gene pavarotti result in the formation of abnormally large cells in the embryonic nervous system. In mitotic cycle 16, cells of pav mutant embryos undergo normal anaphase but then develop an abnormal telophase spindle and fail to undertake cytokinesis. We show that the septin Peanut, actin, and the actin-associated protein Anillin, do not become correctly localized in pav mutants. pav encodes a kinesin-like protein, PAV–KLP, related to the mammalian MKLP-1. In cellularized embryos, the protein is localized to centrosomes early in mitosis, and to the midbody region of the spindle in late anaphase and telophase. We show that Polo kinase associates with PAV–KLP with which it shows an overlapping pattern of subcellular localization during the mitotic cycle and this distribution is disrupted in pavmutants. We suggest that PAV–KLP is required both to establish the structure of the telophase spindle to provide a framework for the assembly of the contractile ring, and to mobilize mitotic regulator proteins

pavarotti encodes a kinesin-like protein required to organize the central spindle and contractile ring for cytokinesis

Mutations in the Drosophila gene pavarotti result in the formation of abnormally large cells in the embryonic nervous system. In mitotic cycle 16, cells of pav mutant embryos undergo normal anaphase but then develop an abnormal telophase spindle and fail to undertake cytokinesis. We show that the septin Peanut, actin, and the actin-associated protein Anillin, do not become correctly localized in pav mutants. pav encodes a kinesin-like protein, PAV–KLP, related to the mammalian MKLP-1. In cellularized embryos, the protein is localized to centrosomes early in mitosis, and to the midbody region of the spindle in late anaphase and telophase. We show that Polo kinase associates with PAV–KLP with which it shows an overlapping pattern of subcellular localization during the mitotic cycle and this distribution is disrupted in pavmutants. We suggest that PAV–KLP is required both to establish the structure of the telophase spindle to provide a framework for the assembly of the contractile ring, and to mobilize mitotic regulator proteins

Synthesizing SystemC Code from Delay Hybrid CSP

Delay is omnipresent in modern control systems, which can prompt oscillations and may cause deterioration of control performance, invalidate both stability and safety properties. This implies that safety or stability certificates obtained on idealized, delay-free models of systems prone to delayed coupling may be erratic, and further the incorrectness of the executable code generated from these models. However, automated methods for system verification and code generation that ought to address models of system dynamics reflecting delays have not been paid enough attention yet in the computer science community. In our previous work, on one hand, we investigated the verification of delay dynamical and hybrid systems; on the other hand, we also addressed how to synthesize SystemC code from a verified hybrid system modelled by Hybrid CSP (HCSP) without delay. In this paper, we give a first attempt to synthesize SystemC code from a verified delay hybrid system modelled by Delay HCSP (dHCSP), which is an extension of HCSP by replacing ordinary differential equations (ODEs) with delay differential equations (DDEs). We implement a tool to support the automatic translation from dHCSP to SystemC

A Screen for Genes Expressed in the Olfactory Organs of Drosophila melanogaster Identifies Genes Involved in Olfactory Behaviour

BACKGROUND: For insects the sense of smell and associated olfactory-driven behaviours are essential for survival. Insects detect odorants with families of olfactory receptor proteins that are very different to those of mammals, and there are likely to be other unique genes and genetic pathways involved in the function and development of the insect olfactory system. METHODOLOGY/PRINCIPAL FINDINGS: We have performed a genetic screen of a set of 505 Drosophila melanogaster gene trap insertion lines to identify novel genes expressed in the adult olfactory organs. We identified 16 lines with expression in the olfactory organs, many of which exhibited expression of the trapped genes in olfactory receptor neurons. Phenotypic analysis showed that six of the lines have decreased olfactory responses in a behavioural assay, and for one of these we showed that precise excision of the P element reverts the phenotype to wild type, confirming a role for the trapped gene in olfaction. To confirm the identity of the genes trapped in the lines we performed molecular analysis of some of the insertion sites. While for many lines the reported insertion sites were correct, we also demonstrated that for a number of lines the reported location of the element was incorrect, and in three lines there were in fact two pGT element insertions. CONCLUSIONS/SIGNIFICANCE: We identified 16 new genes expressed in the Drosophila olfactory organs, the majority in neurons, and for several of the gene trap lines demonstrated a defect in olfactory-driven behaviour. Further characterisation of these genes and their roles in olfactory system function and development will increase our understanding of how the insect olfactory system has evolved to perform the same essential function to that of mammals, but using very different molecular genetic mechanisms

Retrograde semaphorin-plexin signalling drives homeostatic synaptic plasticity.

Homeostatic signalling systems ensure stable but flexible neural activity and animal behaviour. Presynaptic homeostatic plasticity is a conserved form of neuronal homeostatic signalling that is observed in organisms ranging from Drosophila to human. Defining the underlying molecular mechanisms of neuronal homeostatic signalling will be essential in order to establish clear connections to the causes and progression of neurological disease. During neural development, semaphorin-plexin signalling instructs axon guidance and neuronal morphogenesis. However, semaphorins and plexins are also expressed in the adult brain. Here we show that semaphorin 2b (Sema2b) is a target-derived signal that acts upon presynaptic plexin B (PlexB) receptors to mediate the retrograde, homeostatic control of presynaptic neurotransmitter release at the neuromuscular junction in Drosophila. Further, we show that Sema2b-PlexB signalling regulates presynaptic homeostatic plasticity through the cytoplasmic protein Mical and the oxoreductase-dependent control of presynaptic actin. We propose that semaphorin-plexin signalling is an essential platform for the stabilization of synaptic transmission throughout the developing and mature nervous system. These findings may be relevant to the aetiology and treatment of diverse neurological and psychiatric diseases that are characterized by altered or inappropriate neural function and behaviour