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Sample records for dynamically stabilized microtubules

  1. Structure of Dynamic, Taxol-Stabilized, and GMPPCP-Stabilized Microtubule.

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    Ginsburg, Avi; Shemesh, Asaf; Millgram, Abigail; Dharan, Raviv; Levi-Kalisman, Yael; Ringel, Israel; Raviv, Uri

    2017-09-14

    Microtubule (MT) is made of αβ-tubulin heterodimers that dynamically assemble into a hollow nanotube composed of straight protofilaments. MT dynamics is facilitated by hydrolysis of guanosine-5'-triphosphate (GTP) and can be inhibited by either anticancer agents like taxol or the nonhydrolyzable GTP analogues like GMPPCP. Using high-resolution synchrotron X-ray scattering, we have measured and analyzed the scattering curves from solutions of dynamic MT (in other words, in the presence of excess GTP and free of dynamic-inhibiting agents) and examined the effect of two MT stabilizers: taxol and GMPPCP. Previously, we have analyzed the structure of dynamic MT by docking the atomic model of tubulin dimer onto a 3-start left handed helical lattice, derived from the PDB ID 3J6F . 3J6F corresponds to a MT with 14 protofilaments. In this paper, we took into account the possibility of having MT structures containing between 12 and 15 protofilaments. MTs with 12 protofilaments were never observed. We determined the radii, the pitch, and the distribution of protofilament number that best fit the scattering data from dynamic MT or stabilized MT by taxol or GMPPCP. We found that the protofilament number distribution shifted when the MT was stabilized. Taxol increased the mass fraction of MT with 13 protofilaments and decreased the mass fraction of MT with 14 protofilaments. GMPPCP reduced the mass fraction of MT with 15 protofilaments and increased the mass fraction of MT with 14 protofilaments. The pitch, however, remained unchanged regardless of whether the MT was dynamic or stabilized. Higher tubulin concentrations increased the fraction of dynamic MT with 14 protofilaments.

  2. Microtubule dynamics: Caps, catastrophes, and coupled hydrolysis

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    Flyvbjerg, H.; Holy, T.E.; Leibler, S.

    1996-01-01

    An effective theory is formulated for the dynamics of the guanosine triphosphate (GTP) cap believed to stabilize growing microtubules. The theory provides a ''coarse-grained'' description of the cap's dynamics. ''Microscopic'' details, such as the microtubule lattice structure and the fate of its...

  3. Taxol crystals can masquerade as stabilized microtubules.

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    Margit Foss

    Full Text Available Taxol is a potent anti-mitotic drug used in chemotherapy, angioplastic stents, and cell biology research. By binding and stabilizing microtubules, Taxol inhibits their dynamics, crucial for cell division, motility, and survival. The drug has also been reported to induce formation of asters and bundles composed of stabilized microtubules. Surprisingly, at commonly used concentrations, Taxol forms crystals that rapidly bind fluorescent tubulin subunits, generating structures with an uncanny resemblance to microtubule asters and bundles. Kinetic and topological considerations suggest that tubulin subunits, rather than microtubules, bind the crystals. This sequestration of tubulin from the subunit pool would be expected to shift the equilibrium of free to polymerized tubulin to disfavor assembly. Our results imply that some previously reported Taxol-induced asters or bundles could include or be composed of tubulin-decorated Taxol crystals. Thus, reevaluation of certain morphological, chemical, and physical properties of Taxol-treated microtubules may be necessary. Moreover, our findings suggest a novel mechanism for chemotherapy-induced cytotoxicity in non-dividing cells, with far-reaching medical implications.

  4. Shaping the tracks : Regulation of microtubule dynamics by kinesins KIF21A and KIF21B

    NARCIS (Netherlands)

    van Riel, W.E.|info:eu-repo/dai/nl/338772634

    2016-01-01

    Control of microtubule dynamics is important for cell morphogenesis. Kinesins, motor proteins known to function in cargo transport, were recently also implicated in altering the microtubule network. Several kinesins are described to cause microtubule network reorganization or stabilization, either

  5. Griseofulvin stabilizes microtubule dynamics, activates p53 and inhibits the proliferation of MCF-7 cells synergistically with vinblastine

    International Nuclear Information System (INIS)

    Rathinasamy, Krishnan; Jindal, Bhavya; Asthana, Jayant; Singh, Parminder; Balaji, Petety V; Panda, Dulal

    2010-01-01

    Griseofulvin, an antifungal drug, has recently been shown to inhibit proliferation of various types of cancer cells and to inhibit tumor growth in athymic mice. Due to its low toxicity, griseofulvin has drawn considerable attention for its potential use in cancer chemotherapy. This work aims to understand how griseofulvin suppresses microtubule dynamics in living cells and sought to elucidate the antimitotic and antiproliferative action of the drug. The effects of griseofulvin on the dynamics of individual microtubules in live MCF-7 cells were measured by confocal microscopy. Immunofluorescence microscopy, western blotting and flow cytometry were used to analyze the effects of griseofulvin on spindle microtubule organization, cell cycle progression and apoptosis. Further, interactions of purified tubulin with griseofulvin were studied in vitro by spectrophotometry and spectrofluorimetry. Docking analysis was performed using autodock4 and LigandFit module of Discovery Studio 2.1. Griseofulvin strongly suppressed the dynamic instability of individual microtubules in live MCF-7 cells by reducing the rate and extent of the growing and shortening phases. At or near half-maximal proliferation inhibitory concentration, griseofulvin dampened the dynamicity of microtubules in MCF-7 cells without significantly disrupting the microtubule network. Griseofulvin-induced mitotic arrest was associated with several mitotic abnormalities like misaligned chromosomes, multipolar spindles, misegregated chromosomes resulting in cells containing fragmented nuclei. These fragmented nuclei were found to contain increased concentration of p53. Using both computational and experimental approaches, we provided evidence suggesting that griseofulvin binds to tubulin in two different sites; one site overlaps with the paclitaxel binding site while the second site is located at the αβ intra-dimer interface. In combination studies, griseofulvin and vinblastine were found to exert synergistic

  6. SAS-4 is recruited to a dynamic structure in newly forming centrioles that is stabilized by the gamma-tubulin-mediated addition of centriolar microtubules.

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    Dammermann, Alexander; Maddox, Paul S; Desai, Arshad; Oegema, Karen

    2008-02-25

    Centrioles are surrounded by pericentriolar material (PCM), which is proposed to promote new centriole assembly by concentrating gamma-tubulin. Here, we quantitatively monitor new centriole assembly in living Caenorhabditis elegans embryos, focusing on the conserved components SAS-4 and SAS-6. We show that SAS-4 and SAS-6 are coordinately recruited to the site of new centriole assembly and reach their maximum levels during S phase. Centriolar SAS-6 is subsequently reduced by a mechanism intrinsic to the early assembly pathway that does not require progression into mitosis. Centriolar SAS-4 remains in dynamic equilibrium with the cytoplasmic pool until late prophase, when it is stably incorporated in a step that requires gamma-tubulin and microtubule assembly. These results indicate that gamma-tubulin in the PCM stabilizes the nascent daughter centriole by promoting microtubule addition to its outer wall. Such a mechanism may help restrict new centriole assembly to the vicinity of preexisting parent centrioles that recruit PCM.

  7. GDP-tubulin incorporation into growing microtubules modulates polymer stability.

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    Valiron, Odile; Arnal, Isabelle; Caudron, Nicolas; Job, Didier

    2010-06-04

    Microtubule growth proceeds through the endwise addition of nucleotide-bound tubulin dimers. The microtubule wall is composed of GDP-tubulin subunits, which are thought to come exclusively from the incorporation of GTP-tubulin complexes at microtubule ends followed by GTP hydrolysis within the polymer. The possibility of a direct GDP-tubulin incorporation into growing polymers is regarded as hardly compatible with recent structural data. Here, we have examined GTP-tubulin and GDP-tubulin incorporation into polymerizing microtubules using a minimal assembly system comprised of nucleotide-bound tubulin dimers, in the absence of free nucleotide. We find that GDP-tubulin complexes can efficiently co-polymerize with GTP-tubulin complexes during microtubule assembly. GDP-tubulin incorporation into microtubules occurs with similar efficiency during bulk microtubule assembly as during microtubule growth from seeds or centrosomes. Microtubules formed from GTP-tubulin/GDP-tubulin mixtures display altered microtubule dynamics, in particular a decreased shrinkage rate, apparently due to intrinsic modifications of the polymer disassembly properties. Thus, although microtubules polymerized from GTP-tubulin/GDP-tubulin mixtures or from homogeneous GTP-tubulin solutions are both composed of GDP-tubulin subunits, they have different dynamic properties, and this may reveal a novel form of microtubule "structural plasticity."

  8. Stabilizing versus Destabilizing the Microtubules: A Double-Edge Sword for an Effective Cancer Treatment Option?

    Directory of Open Access Journals (Sweden)

    Daniele Fanale

    2015-01-01

    Full Text Available Microtubules are dynamic and structural cellular components involved in several cell functions, including cell shape, motility, and intracellular trafficking. In proliferating cells, they are essential components in the division process through the formation of the mitotic spindle. As a result of these functions, tubulin and microtubules are targets for anticancer agents. Microtubule-targeting agents can be divided into two groups: microtubule-stabilizing, and microtubule-destabilizing agents. The former bind to the tubulin polymer and stabilize microtubules, while the latter bind to the tubulin dimers and destabilize microtubules. Alteration of tubulin-microtubule equilibrium determines the disruption of the mitotic spindle, halting the cell cycle at the metaphase-anaphase transition and, eventually, resulting in cell death. Clinical application of earlier microtubule inhibitors, however, unfortunately showed several limits, such as neurological and bone marrow toxicity and the emergence of drug-resistant tumor cells. Here we review several natural and synthetic microtubule-targeting agents, which showed antitumor activity and increased efficacy in comparison to traditional drugs in various preclinical and clinical studies. Cryptophycins, combretastatins, ombrabulin, soblidotin, D-24851, epothilones and discodermolide were used in clinical trials. Some of them showed antiangiogenic and antivascular activity and others showed the ability to overcome multidrug resistance, supporting their possible use in chemotherapy.

  9. Tau can switch microtubule network organizations: from random networks to dynamic and stable bundles.

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    Prezel, Elea; Elie, Auréliane; Delaroche, Julie; Stoppin-Mellet, Virginie; Bosc, Christophe; Serre, Laurence; Fourest-Lieuvin, Anne; Andrieux, Annie; Vantard, Marylin; Arnal, Isabelle

    2018-01-15

    In neurons, microtubule networks alternate between single filaments and bundled arrays under the influence of effectors controlling their dynamics and organization. Tau is a microtubule bundler that stabilizes microtubules by stimulating growth and inhibiting shrinkage. The mechanisms by which tau organizes microtubule networks remain poorly understood. Here, we studied the self-organization of microtubules growing in the presence of tau isoforms and mutants. The results show that tau's ability to induce stable microtubule bundles requires two hexapeptides located in its microtubule-binding domain and is modulated by its projection domain. Site-specific pseudophosphorylation of tau promotes distinct microtubule organizations: stable single microtubules, stable bundles, or dynamic bundles. Disease-related tau mutations increase the formation of highly dynamic bundles. Finally, cryo-electron microscopy experiments indicate that tau and its variants similarly change the microtubule lattice structure by increasing both the protofilament number and lattice defects. Overall, our results uncover novel phosphodependent mechanisms governing tau's ability to trigger microtubule organization and reveal that disease-related modifications of tau promote specific microtubule organizations that may have a deleterious impact during neurodegeneration. © 2018 Prezel, Elie, et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

  10. The Drosophila Microtubule-Associated Protein Mars Stabilizes Mitotic Spindles by Crosslinking Microtubules through Its N-Terminal Region

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    Zhang, Gang; Beati, Hamze; Nilsson, Jakob; Wodarz, Andreas

    2013-01-01

    Correct segregation of genetic material relies on proper assembly and maintenance of the mitotic spindle. How the highly dynamic microtubules (MTs) are maintained in stable mitotic spindles is a key question to be answered. Motor and non-motor microtubule associated proteins (MAPs) have been reported to stabilize the dynamic spindle through crosslinking adjacent MTs. Mars, a novel MAP, is essential for the early development of Drosophila embryos. Previous studies showed that Mars is required for maintaining an intact mitotic spindle but did not provide a molecular mechanism for this function. Here we show that Mars is able to stabilize the mitotic spindle in vivo. Both in vivo and in vitro data reveal that the N-terminal region of Mars functions in the stabilization of the mitotic spindle by crosslinking adjacent MTs. PMID:23593258

  11. The Drosophila microtubule-associated protein mars stabilizes mitotic spindles by crosslinking microtubules through its N-terminal region.

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    Gang Zhang

    Full Text Available Correct segregation of genetic material relies on proper assembly and maintenance of the mitotic spindle. How the highly dynamic microtubules (MTs are maintained in stable mitotic spindles is a key question to be answered. Motor and non-motor microtubule associated proteins (MAPs have been reported to stabilize the dynamic spindle through crosslinking adjacent MTs. Mars, a novel MAP, is essential for the early development of Drosophila embryos. Previous studies showed that Mars is required for maintaining an intact mitotic spindle but did not provide a molecular mechanism for this function. Here we show that Mars is able to stabilize the mitotic spindle in vivo. Both in vivo and in vitro data reveal that the N-terminal region of Mars functions in the stabilization of the mitotic spindle by crosslinking adjacent MTs.

  12. The Drosophila microtubule-associated protein mars stabilizes mitotic spindles by crosslinking microtubules through its N-terminal region.

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    Zhang, Gang; Beati, Hamze; Nilsson, Jakob; Wodarz, Andreas

    2013-01-01

    Correct segregation of genetic material relies on proper assembly and maintenance of the mitotic spindle. How the highly dynamic microtubules (MTs) are maintained in stable mitotic spindles is a key question to be answered. Motor and non-motor microtubule associated proteins (MAPs) have been reported to stabilize the dynamic spindle through crosslinking adjacent MTs. Mars, a novel MAP, is essential for the early development of Drosophila embryos. Previous studies showed that Mars is required for maintaining an intact mitotic spindle but did not provide a molecular mechanism for this function. Here we show that Mars is able to stabilize the mitotic spindle in vivo. Both in vivo and in vitro data reveal that the N-terminal region of Mars functions in the stabilization of the mitotic spindle by crosslinking adjacent MTs.

  13. Dietary flavonoid fisetin binds to β-tubulin and disrupts microtubule dynamics in prostate cancer cells.

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    Mukhtar, Eiman; Adhami, Vaqar Mustafa; Sechi, Mario; Mukhtar, Hasan

    2015-10-28

    Microtubule targeting based therapies have revolutionized cancer treatment; however, resistance and side effects remain a major limitation. Therefore, novel strategies that can overcome these limitations are urgently needed. We made a novel discovery that fisetin, a hydroxyflavone, is a microtubule stabilizing agent. Fisetin binds to tubulin and stabilizes microtubules with binding characteristics far superior than paclitaxel. Surface plasmon resonance and computational docking studies suggested that fisetin binds to β-tubulin with superior affinity compared to paclitaxel. Fisetin treatment of human prostate cancer cells resulted in robust up-regulation of microtubule associated proteins (MAP)-2 and -4. In addition, fisetin treated cells were enriched in α-tubulin acetylation, an indication of stabilization of microtubules. Fisetin significantly inhibited PCa cell proliferation, migration, and invasion. Nudc, a protein associated with microtubule motor dynein/dynactin complex that regulates microtubule dynamics, was inhibited with fisetin treatment. Further, fisetin treatment of a P-glycoprotein overexpressing multidrug-resistant cancer cell line NCI/ADR-RES inhibited the viability and colony formation. Our results offer in vitro proof-of-concept for fisetin as a microtubule targeting agent. We suggest that fisetin could be developed as an adjuvant for treatment of prostate and other cancer types. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  14. Stable and dynamic microtubules coordinately shape the myosin activation zone during cytokinetic furrow formation

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    Foe, Victoria E.; von Dassow, George

    2008-01-01

    The cytokinetic furrow arises from spatial and temporal regulation of cortical contractility. To test the role microtubules play in furrow specification, we studied myosin II activation in echinoderm zygotes by assessing serine19-phosphorylated regulatory light chain (pRLC) localization after precisely timed drug treatments. Cortical pRLC was globally depressed before cytokinesis, then elevated only at the equator. We implicated cell cycle biochemistry (not microtubules) in pRLC depression, and differential microtubule stability in localizing the subsequent myosin activation. With no microtubules, pRLC accumulation occurred globally instead of equatorially, and loss of just dynamic microtubules increased equatorial pRLC recruitment. Nocodazole treatment revealed a population of stable astral microtubules that formed during anaphase; among these, those aimed toward the equator grew longer, and their tips coincided with cortical pRLC accumulation. Shrinking the mitotic apparatus with colchicine revealed pRLC suppression near dynamic microtubule arrays. We conclude that opposite effects of stable versus dynamic microtubules focuses myosin activation to the cell equator during cytokinesis. PMID:18955555

  15. Kinesin expands and stabilizes the GDP-microtubule lattice

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    Peet, Daniel R.; Burroughs, Nigel J.; Cross, Robert A.

    2018-05-01

    Kinesin-1 is a nanoscale molecular motor that walks towards the fast-growing (plus) ends of microtubules, hauling molecular cargo to specific reaction sites in cells. Kinesin-driven transport is central to the self-organization of eukaryotic cells and shows great promise as a tool for nano-engineering1. Recent work hints that kinesin may also play a role in modulating the stability of its microtubule track, both in vitro2,3 and in vivo4, but the results are conflicting5-7 and the mechanisms are unclear. Here, we report a new dimension to the kinesin-microtubule interaction, whereby strong-binding state (adenosine triphosphate (ATP)-bound and apo) kinesin-1 motor domains inhibit the shrinkage of guanosine diphosphate (GDP) microtubules by up to two orders of magnitude and expand their lattice spacing by 1.6%. Our data reveal an unexpected mechanism by which the mechanochemical cycles of kinesin and tubulin interlock, and so allow motile kinesins to influence the structure, stability and mechanics of their microtubule track.

  16. Xyloglucan Deficiency Disrupts Microtubule Stability and Cellulose Biosynthesis in Arabidopsis, Altering Cell Growth and Morphogenesis

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    Xiao, Chaowen; Zhang, Tian; Zheng, Yunzhen; Cosgrove, Daniel J.; Anderson, Charles T.

    2015-11-02

    Xyloglucan constitutes most of the hemicellulose in eudicot primary cell walls and functions in cell wall structure and mechanics. Although Arabidopsis (Arabidopsis thaliana) xxt1 xxt2 mutants lacking detectable xyloglucan are viable, they display growth defects that are suggestive of alterations in wall integrity. To probe the mechanisms underlying these defects, we analyzed cellulose arrangement, microtubule patterning and dynamics, microtubule- and wall-integrity-related gene expression, and cellulose biosynthesis in xxt1 xxt2 plants. We found that cellulose is highly aligned in xxt1 xxt2 cell walls, that its three-dimensional distribution is altered, and that microtubule patterning and stability are aberrant in etiolated xxt1 xxt2 hypocotyls. We also found that the expression levels of microtubule-associated genes, such as MAP70-5 and CLASP, and receptor genes, such as HERK1 and WAK1, were changed in xxt1 xxt2 plants and that cellulose synthase motility is reduced in xxt1 xxt2 cells, corresponding with a reduction in cellulose content. Our results indicate that loss of xyloglucan affects both the stability of the microtubule cytoskeleton and the production and patterning of cellulose in primary cell walls. These findings establish, to our knowledge, new links between wall integrity, cytoskeletal dynamics, and wall synthesis in the regulation of plant morphogenesis.

  17. An ELMO2-RhoG-ILK network modulates microtubule dynamics.

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    Jackson, Bradley C; Ivanova, Iordanka A; Dagnino, Lina

    2015-07-15

    ELMO2 belongs to a family of scaffold proteins involved in phagocytosis and cell motility. ELMO2 can simultaneously bind integrin-linked kinase (ILK) and RhoG, forming tripartite ERI complexes. These complexes are involved in promoting β1 integrin-dependent directional migration in undifferentiated epidermal keratinocytes. ELMO2 and ILK have also separately been implicated in microtubule regulation at integrin-containing focal adhesions. During differentiation, epidermal keratinocytes cease to express integrins, but ERI complexes persist. Here we show an integrin-independent role of ERI complexes in modulation of microtubule dynamics in differentiated keratinocytes. Depletion of ERI complexes by inactivating the Ilk gene in these cells reduces microtubule growth and increases the frequency of catastrophe. Reciprocally, exogenous expression of ELMO2 or RhoG stabilizes microtubules, but only if ILK is also present. Mechanistically, activation of Rac1 downstream from ERI complexes mediates their effects on microtubule stability. In this pathway, Rac1 serves as a hub to modulate microtubule dynamics through two different routes: 1) phosphorylation and inactivation of the microtubule-destabilizing protein stathmin and 2) phosphorylation and inactivation of GSK-3β, which leads to the activation of CRMP2, promoting microtubule growth. At the cellular level, the absence of ERI species impairs Ca(2+)-mediated formation of adherens junctions, critical to maintaining mechanical integrity in the epidermis. Our findings support a key role for ERI species in integrin-independent stabilization of the microtubule network in differentiated keratinocytes. © 2015 Jackson et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

  18. The Role of Molecular Microtubule Motors and the Microtubule Cytoskeleton in Stress Granule Dynamics

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    Kristen M. Bartoli

    2011-01-01

    Full Text Available Stress granules (SGs are cytoplasmic foci that appear in cells exposed to stress-induced translational inhibition. SGs function as a triage center, where mRNAs are sorted for storage, degradation, and translation reinitiation. The underlying mechanisms of SGs dynamics are still being characterized, although many key players have been identified. The main components of SGs are stalled 48S preinitiation complexes. To date, many other proteins have also been found to localize in SGs and are hypothesized to function in SG dynamics. Most recently, the microtubule cytoskeleton and associated motor proteins have been demonstrated to function in SG dynamics. In this paper, we will discuss current literature examining the function of microtubules and the molecular microtubule motors in SG assembly, coalescence, movement, composition, organization, and disassembly.

  19. Melanophores for microtubule dynamics and motility assays.

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    Ikeda, Kazuho; Semenova, Irina; Zhapparova, Olga; Rodionov, Vladimir

    2010-01-01

    Microtubules (MTs) are cytoskeletal structures essential for cell division, locomotion, intracellular transport, and spatial organization of the cytoplasm. In most interphase cells, MTs are organized into a polarized radial array with minus-ends clustered at the centrosome and plus-ends extended to the cell periphery. This array directs transport of organelles driven by MT-based motor proteins that specifically move either to plus- or to minus-ends. Along with using MTs as tracks for cargo, motor proteins can organize MTs into a radial array in the absence of the centrosome. Transport of organelles and motor-dependent radial organization of MTs require MT dynamics, continuous addition and loss of tubulin subunits at minus- and plus-ends. A unique experimental system for studying the role of MT dynamics in these processes is the melanophore, which provides a useful tool for imaging of both dynamic MTs and moving membrane organelles. Melanophores are filled with pigment granules that are synchronously transported by motor proteins in response to hormonal stimuli. The flat shape of the cell and the radial organization of MTs facilitate imaging of dynamic MT plus-ends and monitoring of their interaction with membrane organelles. Microsurgically produced cytoplasmic fragments of melanophores are used to study the centrosome-independent rearrangement of MTs into a radial array. Here we describe the experimental approaches to study the role of MT dynamics in intracellular transport and centrosome-independent MT organization in melanophores. We focus on the preparation of cell cultures, microsurgery and microinjection, fluorescence labeling, and live imaging of MTs. 2010 Elsevier Inc. All rights reserved.

  20. The Drosophila Microtubule-Associated Protein Mars Stabilizes Mitotic Spindles by Crosslinking Microtubules through Its N-Terminal Region

    DEFF Research Database (Denmark)

    Zhang, Gang; Beati, Hamze; Nilsson, Jakob

    2013-01-01

    Correct segregation of genetic material relies on proper assembly and maintenance of the mitotic spindle. How the highly dynamic microtubules (MTs) are maintained in stable mitotic spindles is a key question to be answered. Motor and non-motor microtubule associated proteins (MAPs) have been...

  1. Survivin counteracts the therapeutic effect of microtubule de-stabilizers by stabilizing tubulin polymers

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    Hsieh Hsing-Pang

    2009-07-01

    Full Text Available Abstract Background Survivin is a dual function protein. It inhibits the apoptosis of cells by inhibiting caspases, and also promotes cell growth by stabilizing microtubules during mitosis. Over-expression of survivin has been demonstrated to induce drug-resistance to various chemo-therapeutic agents such as cisplatin (DNA damaging agent and paclitaxel (microtubule stabilizer in cancers. However, survivin-induced resistance to microtubule de-stabilizers such as Vinca alkaloids and Combretastatin A-4 (CA-4-related compounds were seldom demonstrated in the past. Furthermore, the question remains as to whether survivin plays a dominant role in processing cytokinesis or inhibiting caspases activity in cells treated with anti-mitotic compounds. The purpose of this study is to evaluate the effect of survivin on the resistance and susceptibility of human cancer cells to microtubule de-stabilizer-induced cell death. Results BPR0L075 is a CA-4 analog that induces microtubule de-polymerization and subsequent caspase-dependent apoptosis. To study the relationship between the expression of survivin and the resistance to microtubule de-stabilizers, a KB-derived BPR0L075-resistant cancer cell line, KB-L30, was generated for this study. Here, we found that survivin was over-expressed in the KB-L30 cells. Down-regulation of survivin by siRNA induced hyper-sensitivity to BPR0L075 in KB cells and partially re-stored sensitivity to BPR0L075 in KB-L30 cells. Western blot analysis revealed that down-regulation of survivin induced microtubule de-stabilization in both KB and KB-L30 cells. However, the same treatment did not enhance the down-stream caspase-3/-7 activities in BPR0L075-treated KB cells. Translocation of a caspase-independent apoptosis-related molecule, apoptosis-inducing factor (AIF, from cytoplasm to the nucleus was observed in survivin-targeted KB cells under BPR0L075 treatment. Conclusion In this study, survivin plays an important role in the

  2. Stabilization, not polymerization, of microtubules inhibits the nuclear translocation of STATs in adipocytes

    International Nuclear Information System (INIS)

    Gleason, Evanna L.; Hogan, Jessica C.; Stephens, Jacqueline M.

    2004-01-01

    Signal transducers and activators of transcriptions (STATs) are a family of latent transcription factors which are activated by a variety of growth factors and cytokines in many cell types. However, the mechanism by which these transcription factors translocate to the nucleus is poorly understood. The goal of this study was to determine the requirement of microfilaments and microtubules for cytokine induced STAT activation in cultured adipocytes. We used seven different actin-specific and microtubule-specific agents that are well-established effectors of these cytoskeletal networks. Our results clearly demonstrate that inhibition of microfilaments or the prevention of microtubule polymerization has no effect on the ability of STATs to be tyrosine phosphorylated or to translocate to the nucleus. However, we observed that paclitaxel, a microtubule stabilizer, resulted in a significant decrease in the nuclear translocation of STATs without affecting the cytosolic tyrosine phosphorylation of these transcription factors. In summary, our results demonstrate that the dynamic instability, but not the polymerization, of microtubules contributes to nuclear translocation of STAT proteins in adipocytes

  3. Nonlinear dynamics of C-terminal tails in cellular microtubules

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    Sekulic, Dalibor L.; Sataric, Bogdan M.; Zdravkovic, Slobodan; Bugay, Aleksandr N.; Sataric, Miljko V.

    2016-07-01

    The mechanical and electrical properties, and information processing capabilities of microtubules are the permanent subject of interest for carrying out experiments in vitro and in silico, as well as for theoretical attempts to elucidate the underlying processes. In this paper, we developed a new model of the mechano-electrical waves elicited in the rows of very flexible C-terminal tails which decorate the outer surface of each microtubule. The fact that C-terminal tails play very diverse roles in many cellular functions, such as recruitment of motor proteins and microtubule-associated proteins, motivated us to consider their collective dynamics as the source of localized waves aimed for communication between microtubule and associated proteins. Our approach is based on the ferroelectric liquid crystal model and it leads to the effective asymmetric double-well potential which brings about the conditions for the appearance of kink-waves conducted by intrinsic electric fields embedded in microtubules. These kinks can serve as the signals for control and regulation of intracellular traffic along microtubules performed by processive motions of motor proteins, primarly from kinesin and dynein families. On the other hand, they can be precursors for initiation of dynamical instability of microtubules by recruiting the proper proteins responsible for the depolymerization process.

  4. Kinesin-8 effects on mitotic microtubule dynamics contribute to spindle function in fission yeast

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    Gergely, Zachary R.; Crapo, Ammon; Hough, Loren E.; McIntosh, J. Richard; Betterton, Meredith D.

    2016-01-01

    Kinesin-8 motor proteins destabilize microtubules. Their absence during cell division is associated with disorganized mitotic chromosome movements and chromosome loss. Despite recent work studying effects of kinesin-8s on microtubule dynamics, it remains unclear whether the kinesin-8 mitotic phenotypes are consequences of their effect on microtubule dynamics, their well-established motor activity, or additional, unknown functions. To better understand the role of kinesin-8 proteins in mitosis, we studied the effects of deletion of the fission yeast kinesin-8 proteins Klp5 and Klp6 on chromosome movements and spindle length dynamics. Aberrant microtubule-driven kinetochore pushing movements and tripolar mitotic spindles occurred in cells lacking Klp5 but not Klp6. Kinesin-8–deletion strains showed large fluctuations in metaphase spindle length, suggesting a disruption of spindle length stabilization. Comparison of our results from light microscopy with a mathematical model suggests that kinesin-8–induced effects on microtubule dynamics, kinetochore attachment stability, and sliding force in the spindle can explain the aberrant chromosome movements and spindle length fluctuations seen. PMID:27146110

  5. Nonlinear dynamics of C–terminal tails in cellular microtubules

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    Sekulic, Dalibor L., E-mail: dalsek@uns.ac.rs; Sataric, Bogdan M.; Sataric, Miljko V. [University of Novi Sad, Faculty of Technical Sciences, Novi Sad (Serbia); Zdravkovic, Slobodan [University of Belgrade, Institute of Nuclear Sciences Vinca, Belgrade (Serbia); Bugay, Aleksandr N. [Laboratory of Radiation Biology, Joint Institute for Nuclear Research, Dubna (Russian Federation)

    2016-07-15

    The mechanical and electrical properties, and information processing capabilities of microtubules are the permanent subject of interest for carrying out experiments in vitro and in silico, as well as for theoretical attempts to elucidate the underlying processes. In this paper, we developed a new model of the mechano–electrical waves elicited in the rows of very flexible C–terminal tails which decorate the outer surface of each microtubule. The fact that C–terminal tails play very diverse roles in many cellular functions, such as recruitment of motor proteins and microtubule–associated proteins, motivated us to consider their collective dynamics as the source of localized waves aimed for communication between microtubule and associated proteins. Our approach is based on the ferroelectric liquid crystal model and it leads to the effective asymmetric double-well potential which brings about the conditions for the appearance of kink–waves conducted by intrinsic electric fields embedded in microtubules. These kinks can serve as the signals for control and regulation of intracellular traffic along microtubules performed by processive motions of motor proteins, primarly from kinesin and dynein families. On the other hand, they can be precursors for initiation of dynamical instability of microtubules by recruiting the proper proteins responsible for the depolymerization process.

  6. Nonlinear dynamics of C–terminal tails in cellular microtubules

    International Nuclear Information System (INIS)

    Sekulic, Dalibor L.; Sataric, Bogdan M.; Sataric, Miljko V.; Zdravkovic, Slobodan; Bugay, Aleksandr N.

    2016-01-01

    The mechanical and electrical properties, and information processing capabilities of microtubules are the permanent subject of interest for carrying out experiments in vitro and in silico, as well as for theoretical attempts to elucidate the underlying processes. In this paper, we developed a new model of the mechano–electrical waves elicited in the rows of very flexible C–terminal tails which decorate the outer surface of each microtubule. The fact that C–terminal tails play very diverse roles in many cellular functions, such as recruitment of motor proteins and microtubule–associated proteins, motivated us to consider their collective dynamics as the source of localized waves aimed for communication between microtubule and associated proteins. Our approach is based on the ferroelectric liquid crystal model and it leads to the effective asymmetric double-well potential which brings about the conditions for the appearance of kink–waves conducted by intrinsic electric fields embedded in microtubules. These kinks can serve as the signals for control and regulation of intracellular traffic along microtubules performed by processive motions of motor proteins, primarly from kinesin and dynein families. On the other hand, they can be precursors for initiation of dynamical instability of microtubules by recruiting the proper proteins responsible for the depolymerization process.

  7. Ibuprofen regulation of microtubule dynamics in cystic fibrosis epithelial cells.

    Science.gov (United States)

    Rymut, Sharon M; Kampman, Claire M; Corey, Deborah A; Endres, Tori; Cotton, Calvin U; Kelley, Thomas J

    2016-08-01

    High-dose ibuprofen, an effective anti-inflammatory therapy for the treatment of cystic fibrosis (CF), has been shown to preserve lung function in a pediatric population. Despite its efficacy, few patients receive ibuprofen treatment due to potential renal and gastrointestinal toxicity. The mechanism of ibuprofen efficacy is also unclear. We have previously demonstrated that CF microtubules are slower to reform after depolymerization compared with respective wild-type controls. Slower microtubule dynamics in CF cells are responsible for impaired intracellular transport and are related to inflammatory signaling. Here, it is identified that high-dose ibuprofen treatment in both CF cell models and primary CF nasal epithelial cells restores microtubule reformation rates to wild-type levels, as well as induce extension of microtubules to the cell periphery. Ibuprofen treatment also restores microtubule-dependent intracellular transport monitored by measuring intracellular cholesterol transport. These effects are specific to ibuprofen as other cyclooxygenase inhibitors have no effect on these measures. Effects of ibuprofen are mimicked by stimulation of AMPK and blocked by the AMPK inhibitor compound C. We conclude that high-dose ibuprofen treatment enhances microtubule formation in CF cells likely through an AMPK-related pathway. These findings define a potential mechanism to explain the efficacy of ibuprofen therapy in CF. Copyright © 2016 the American Physiological Society.

  8. The engine of microtubule dynamics comes into focus.

    Science.gov (United States)

    Mitchison, T J

    2014-05-22

    In this issue, Alushin et al. report high-resolution structures of three states of the microtubule lattice: GTP-bound, which is stable to depolymerization; unstable GDP-bound; and stable Taxol and GDP-bound. By comparing these structures at near-atomic resolution, they are able to propose a detailed model for how GTP hydrolysis destabilizes the microtubule and thus powers dynamic instability and chromosome movement. Destabilization of cytoskeleton filaments by nucleotide hydrolysis is an important general principle in cell dynamics, and this work represents a major step forward on a problem with a long history. Copyright © 2014 Elsevier Inc. All rights reserved.

  9. Dietary flavonoid fisetin binds to β-tubulin and disrupts microtubule dynamics in prostate cancer cells

    OpenAIRE

    Mukhtar, Eiman; Adhami, Vaqar Mustafa; Sechi, Mario; Mukhtar, Hasan

    2015-01-01

    Microtubule targeting based therapies have revolutionized cancer treatment; however, resistance and side effects remain a major limitation. Therefore, novel strategies that can overcome these limitations are urgently needed. We made a novel discovery that fisetin, a hydroxyflavone, is a microtubule stabilizing agent. Fisetin binds to tubulin and stabilizes microtubules with binding characteristics far superior than paclitaxel. Surface plasmon resonance and computational docking studies sugges...

  10. Stabilization of microtubules by inorganic phosphate and its structural analogues, the fluoride complexes of aluminum and beryllium

    International Nuclear Information System (INIS)

    Carlier, M.F.; Didry, D.; Melki, R.; Chabre, M.; Pantaloni, D.

    1988-01-01

    In order to elucidate how the elementary reactions of GTP cleavage and subsequent inorganic phosphate (P/sub i/) release, which accompany microtubule assembly, regulate microtubule dynamics, the effect of P/sub i/ and of its structural analogues AlF 4 - and BeF 3 - on the stability of GDP-microtubules has been investigated. Inorganic phosphate binds to microtubules with a low affinity (K/sub D/ = 25 mM) and slows down the rate of GDP-subunit dissociation by about 2 orders of magnitude. AlF 4 - and BeF 3 - exhibit phosphate-like effects with 1000-fold higher affinity. Evidence has been obtained for direct binding of BeF 3 - to microtubules with a stoichiometry of 1 mol of BeF 3 - per mole of GDP-subunit and an equilibrium dissociation constant of 12-15 μM. AlF 4 - and P/sub i/ compete for this site. Phosphate analogues abolish oscillatory polymerization kinetics and slow down microtubule turnover at steady state. In view of these results, the authors propose that P/sub i/ and its structural analogues bind to the site of the γ-phosphate of GTP in the E site and reconstitute a GDP-P/sub i/-microtubule, from which tubulin subunits dissociate very slowly. They therefore understand that, following GTP cleavage on microtubules, P/sub i/ release in the medium is accompanied by a structural change resulting in a large destabilization of the polymer. A cap of slowly dissociating GDP-P/sub i/-subunits prevents depolymerization of the microtubule GDP-core at steady state. The similarity with the actin system is studied

  11. Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy.

    Science.gov (United States)

    Flex, Elisabetta; Niceta, Marcello; Cecchetti, Serena; Thiffault, Isabelle; Au, Margaret G; Capuano, Alessandro; Piermarini, Emanuela; Ivanova, Anna A; Francis, Joshua W; Chillemi, Giovanni; Chandramouli, Balasubramanian; Carpentieri, Giovanna; Haaxma, Charlotte A; Ciolfi, Andrea; Pizzi, Simone; Douglas, Ganka V; Levine, Kara; Sferra, Antonella; Dentici, Maria Lisa; Pfundt, Rolph R; Le Pichon, Jean-Baptiste; Farrow, Emily; Baas, Frank; Piemonte, Fiorella; Dallapiccola, Bruno; Graham, John M; Saunders, Carol J; Bertini, Enrico; Kahn, Richard A; Koolen, David A; Tartaglia, Marco

    2016-10-06

    Microtubules are dynamic cytoskeletal elements coordinating and supporting a variety of neuronal processes, including cell division, migration, polarity, intracellular trafficking, and signal transduction. Mutations in genes encoding tubulins and microtubule-associated proteins are known to cause neurodevelopmental and neurodegenerative disorders. Growing evidence suggests that altered microtubule dynamics may also underlie or contribute to neurodevelopmental disorders and neurodegeneration. We report that biallelic mutations in TBCD, encoding one of the five co-chaperones required for assembly and disassembly of the αβ-tubulin heterodimer, the structural unit of microtubules, cause a disease with neurodevelopmental and neurodegenerative features characterized by early-onset cortical atrophy, secondary hypomyelination, microcephaly, thin corpus callosum, developmental delay, intellectual disability, seizures, optic atrophy, and spastic quadriplegia. Molecular dynamics simulations predicted long-range and/or local structural perturbations associated with the disease-causing mutations. Biochemical analyses documented variably reduced levels of TBCD, indicating relative instability of mutant proteins, and defective β-tubulin binding in a subset of the tested mutants. Reduced or defective TBCD function resulted in decreased soluble α/β-tubulin levels and accelerated microtubule polymerization in fibroblasts from affected subjects, demonstrating an overall shift toward a more rapidly growing and stable microtubule population. These cells displayed an aberrant mitotic spindle with disorganized, tangle-shaped microtubules and reduced aster formation, which however did not alter appreciably the rate of cell proliferation. Our findings establish that defective TBCD function underlies a recognizable encephalopathy and drives accelerated microtubule polymerization and enhanced microtubule stability, underscoring an additional cause of altered microtubule dynamics with

  12. A computational framework for cortical microtubule dynamics in realistically shaped plant cells.

    Directory of Open Access Journals (Sweden)

    Bandan Chakrabortty

    2018-02-01

    Full Text Available Plant morphogenesis is strongly dependent on the directional growth and the subsequent oriented division of individual cells. It has been shown that the plant cortical microtubule array plays a key role in controlling both these processes. This ordered structure emerges as the collective result of stochastic interactions between large numbers of dynamic microtubules. To elucidate this complex self-organization process a number of analytical and computational approaches to study the dynamics of cortical microtubules have been proposed. To date, however, these models have been restricted to two dimensional planes or geometrically simple surfaces in three dimensions, which strongly limits their applicability as plant cells display a wide variety of shapes. This limitation is even more acute, as both local as well as global geometrical features of cells are expected to influence the overall organization of the array. Here we describe a framework for efficiently simulating microtubule dynamics on triangulated approximations of arbitrary three dimensional surfaces. This allows the study of microtubule array organization on realistic cell surfaces obtained by segmentation of microscopic images. We validate the framework against expected or known results for the spherical and cubical geometry. We then use it to systematically study the individual contributions of global geometry, cell-edge induced catastrophes and cell-face induced stability to array organization in a cuboidal geometry. Finally, we apply our framework to analyze the highly non-trivial geometry of leaf pavement cells of Arabidopsis thaliana, Nicotiana benthamiana and Hedera helix. We show that our simulations can predict multiple features of the microtubule array structure in these cells, revealing, among others, strong constraints on the orientation of division planes.

  13. A computational framework for cortical microtubule dynamics in realistically shaped plant cells

    KAUST Repository

    Chakrabortty, Bandan; Blilou, Ikram; Scheres, Ben; Mulder, Bela M.

    2018-01-01

    Plant morphogenesis is strongly dependent on the directional growth and the subsequent oriented division of individual cells. It has been shown that the plant cortical microtubule array plays a key role in controlling both these processes. This ordered structure emerges as the collective result of stochastic interactions between large numbers of dynamic microtubules. To elucidate this complex self-organization process a number of analytical and computational approaches to study the dynamics of cortical microtubules have been proposed. To date, however, these models have been restricted to two dimensional planes or geometrically simple surfaces in three dimensions, which strongly limits their applicability as plant cells display a wide variety of shapes. This limitation is even more acute, as both local as well as global geometrical features of cells are expected to influence the overall organization of the array. Here we describe a framework for efficiently simulating microtubule dynamics on triangulated approximations of arbitrary three dimensional surfaces. This allows the study of microtubule array organization on realistic cell surfaces obtained by segmentation of microscopic images. We validate the framework against expected or known results for the spherical and cubical geometry. We then use it to systematically study the individual contributions of global geometry, cell-edge induced catastrophes and cell-face induced stability to array organization in a cuboidal geometry. Finally, we apply our framework to analyze the highly non-trivial geometry of leaf pavement cells of Arabidopsis thaliana, Nicotiana benthamiana and Hedera helix. We show that our simulations can predict multiple features of the microtubule array structure in these cells, revealing, among others, strong constraints on the orientation of division planes.

  14. A computational framework for cortical microtubule dynamics in realistically shaped plant cells

    KAUST Repository

    Chakrabortty, Bandan

    2018-02-02

    Plant morphogenesis is strongly dependent on the directional growth and the subsequent oriented division of individual cells. It has been shown that the plant cortical microtubule array plays a key role in controlling both these processes. This ordered structure emerges as the collective result of stochastic interactions between large numbers of dynamic microtubules. To elucidate this complex self-organization process a number of analytical and computational approaches to study the dynamics of cortical microtubules have been proposed. To date, however, these models have been restricted to two dimensional planes or geometrically simple surfaces in three dimensions, which strongly limits their applicability as plant cells display a wide variety of shapes. This limitation is even more acute, as both local as well as global geometrical features of cells are expected to influence the overall organization of the array. Here we describe a framework for efficiently simulating microtubule dynamics on triangulated approximations of arbitrary three dimensional surfaces. This allows the study of microtubule array organization on realistic cell surfaces obtained by segmentation of microscopic images. We validate the framework against expected or known results for the spherical and cubical geometry. We then use it to systematically study the individual contributions of global geometry, cell-edge induced catastrophes and cell-face induced stability to array organization in a cuboidal geometry. Finally, we apply our framework to analyze the highly non-trivial geometry of leaf pavement cells of Arabidopsis thaliana, Nicotiana benthamiana and Hedera helix. We show that our simulations can predict multiple features of the microtubule array structure in these cells, revealing, among others, strong constraints on the orientation of division planes.

  15. Microtubules become more dynamic but not shorter during preprophase band formation: A possible "search-and-capture" mechanism for microtubule translocation

    NARCIS (Netherlands)

    Vos, J.W.; Dogterom, M.; Emons, A.M.C.

    2004-01-01

    The dynamic behavior of the microtubule cytoskeleton plays a crucial role in cellular organization, but the physical mechanisms underlying microtubule (re)organization in plant cells are poorly understood. We investigated microtubule dynamics in tobacco BY-2 suspension cells during interphase and

  16. Optical Tweezers-Based Measurements of Forces and Dynamics at Microtubule Ends.

    Science.gov (United States)

    Baclayon, Marian; Kalisch, Svenja-Marei; Hendel, Ed; Laan, Liedewij; Husson, Julien; Munteanu, E Laura; Dogterom, Marileen

    2017-01-01

    Microtubules are dynamic cytoskeletal polymers that polymerize and depolymerize while interacting with different proteins and structures within the cell. The highly regulated dynamic properties as well as the pushing and pulling forces generated by dynamic microtubule ends play important roles in processes such as in cell division. For instance, microtubule end-binding proteins are known to affect dramatically the dynamic properties of microtubules, and cortical dyneins are known to mediate pulling forces on microtubule ends. We discuss in this chapter our efforts to reconstitute these systems in vitro and mimic their interactions with structures within the cell using micro-fabricated barriers. Using an optical tweezers setup, we investigate the dynamics and forces of microtubules growing against functionalized barriers in the absence and presence of end-binding proteins and barrier-attached motor proteins. This setup allows high-speed as well as nanometer and piconewton resolution measurements on dynamic microtubules.

  17. EWSR1 regulates mitosis by dynamically influencing microtubule acetylation.

    Science.gov (United States)

    Wang, Yi-Long; Chen, Hui; Zhan, Yi-Qun; Yin, Rong-Hua; Li, Chang-Yan; Ge, Chang-Hui; Yu, Miao; Yang, Xiao-Ming

    2016-08-17

    EWSR1, participating in transcription and splicing, has been identified as a translocation partner for various transcription factors, resulting in translocation, which in turn plays crucial roles in tumorigenesis. Recent studies have investigated the role of EWSR1 in mitosis. However, the effect of EWSR1 on mitosis is poorly understood. Here, we observed that depletion of EWSR1 resulted in cell cycle arrest in the mitotic phase, mainly due to an increase in the time from nuclear envelope breakdown to metaphase, resulting in a high percentage of unaligned chromosomes and multipolar spindles. We also demonstrated that EWSR1 is a spindle-associated protein that interacts with α-tubulin during mitosis. EWSR1 depletion increased the cold-sensitivity of spindle microtubules, and decreased the rate of spindle assembly. EWSR1 regulated the level of microtubule acetylation in the mitotic spindle; microtubule acetylation was rescued in EWSR1-depleted mitotic cells following suppression of HDAC6 activity by its specific inhibitor or siRNA treatment. In summary, these results suggest that EWSR1 regulates the acetylation of microtubules in a cell cycle-dependent manner through its dynamic location on spindle MTs, and may be a novel regulator for mitosis progress independent of its translocation.

  18. A mutation of the fission yeast EB1 overcomes negative regulation by phosphorylation and stabilizes microtubules

    International Nuclear Information System (INIS)

    Iimori, Makoto; Ozaki, Kanako; Chikashige, Yuji; Habu, Toshiyuki; Hiraoka, Yasushi; Maki, Takahisa; Hayashi, Ikuko; Obuse, Chikashi; Matsumoto, Tomohiro

    2012-01-01

    Mal3 is a fission yeast homolog of EB1, a plus-end tracking protein (+ TIP). We have generated a mutation (89R) replacing glutamine with arginine in the calponin homology (CH) domain of Mal3. Analysis of the 89R mutant in vitro has revealed that the mutation confers a higher affinity to microtubules and enhances the intrinsic activity to promote the microtubule-assembly. The mutant Mal3 is no longer a + TIP, but binds strongly the microtubule lattice. Live cell imaging has revealed that while the wild type Mal3 proteins dissociate from the tip of the growing microtubules before the onset of shrinkage, the mutant Mal3 proteins persist on microtubules and reduces a rate of shrinkage after a longer pausing period. Consequently, the mutant Mal3 proteins cause abnormal elongation of microtubules composing the spindle and aster. Mal3 is phosphorylated at a cluster of serine/threonine residues in the linker connecting the CH and EB1-like C-terminal motif domains. The phosphorylation occurs in a microtubule-dependent manner and reduces the affinity of Mal3 to microtubules. We propose that because the 89R mutation is resistant to the effect of phosphorylation, it can associate persistently with microtubules and confers a stronger stability of microtubules likely by reinforcing the cylindrical structure. -- Highlights: ► We characterize a mutation (mal3-89R) in fission yeast homolog of EB1. ► The mutation enhances the activity to assemble microtubules. ► Mal3 is phosphorylated in a microtubule-dependent manner. ► The phosphorylation negatively regulates the Mal3 activity.

  19. A mutation of the fission yeast EB1 overcomes negative regulation by phosphorylation and stabilizes microtubules

    Energy Technology Data Exchange (ETDEWEB)

    Iimori, Makoto; Ozaki, Kanako [Graduate School of Biostudies, Kyoto University, Kitashirakawa-Oiwake cho, Sakyo ku, Kyoto, 606-8502 (Japan); Chikashige, Yuji [Kobe Advanced ICT Research Center, National Institute of Information and Communications Technology, Kobe, 651-2492 (Japan); Habu, Toshiyuki [Graduate School of Biostudies, Kyoto University, Kitashirakawa-Oiwake cho, Sakyo ku, Kyoto, 606-8502 (Japan); Radiation Biology Center, Kyoto University, Yoshida-Konoe cho, Sakyo ku, Kyoto, 606-8501 (Japan); Hiraoka, Yasushi [Kobe Advanced ICT Research Center, National Institute of Information and Communications Technology, Kobe, 651-2492 (Japan); Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, 565-0871 (Japan); Maki, Takahisa; Hayashi, Ikuko [Graduate School of Nanobioscience, Yokohama City University, Tsurumi, Yokohama, 230-0045 (Japan); Obuse, Chikashi [Graduate School of Life Science, Hokkaido University, Sapporo 001-0021 (Japan); Matsumoto, Tomohiro, E-mail: tmatsumo@house.rbc.kyoto-u.ac.jp [Graduate School of Biostudies, Kyoto University, Kitashirakawa-Oiwake cho, Sakyo ku, Kyoto, 606-8502 (Japan); Radiation Biology Center, Kyoto University, Yoshida-Konoe cho, Sakyo ku, Kyoto, 606-8501 (Japan)

    2012-02-01

    Mal3 is a fission yeast homolog of EB1, a plus-end tracking protein (+ TIP). We have generated a mutation (89R) replacing glutamine with arginine in the calponin homology (CH) domain of Mal3. Analysis of the 89R mutant in vitro has revealed that the mutation confers a higher affinity to microtubules and enhances the intrinsic activity to promote the microtubule-assembly. The mutant Mal3 is no longer a + TIP, but binds strongly the microtubule lattice. Live cell imaging has revealed that while the wild type Mal3 proteins dissociate from the tip of the growing microtubules before the onset of shrinkage, the mutant Mal3 proteins persist on microtubules and reduces a rate of shrinkage after a longer pausing period. Consequently, the mutant Mal3 proteins cause abnormal elongation of microtubules composing the spindle and aster. Mal3 is phosphorylated at a cluster of serine/threonine residues in the linker connecting the CH and EB1-like C-terminal motif domains. The phosphorylation occurs in a microtubule-dependent manner and reduces the affinity of Mal3 to microtubules. We propose that because the 89R mutation is resistant to the effect of phosphorylation, it can associate persistently with microtubules and confers a stronger stability of microtubules likely by reinforcing the cylindrical structure. -- Highlights: Black-Right-Pointing-Pointer We characterize a mutation (mal3-89R) in fission yeast homolog of EB1. Black-Right-Pointing-Pointer The mutation enhances the activity to assemble microtubules. Black-Right-Pointing-Pointer Mal3 is phosphorylated in a microtubule-dependent manner. Black-Right-Pointing-Pointer The phosphorylation negatively regulates the Mal3 activity.

  20. Plasma membrane factor XIIIA transglutaminase activity regulates osteoblast matrix secretion and deposition by affecting microtubule dynamics.

    Directory of Open Access Journals (Sweden)

    Hadil F Al-Jallad

    2011-01-01

    Full Text Available Transglutaminase activity, arising potentially from transglutaminase 2 (TG2 and Factor XIIIA (FXIIIA, has been linked to osteoblast differentiation where it is required for type I collagen and fibronectin matrix deposition. In this study we have used an irreversible TG-inhibitor to 'block -and-track' enzyme(s targeted during osteoblast differentiation. We show that the irreversible TG-inhibitor is highly potent in inhibiting osteoblast differentiation and mineralization and reduces secretion of both fibronectin and type I collagen and their release from the cell surface. Tracking of the dansyl probe by Western blotting and immunofluorescence microscopy demonstrated that the inhibitor targets plasma membrane-associated FXIIIA. TG2 appears not to contribute to crosslinking activity on the osteoblast surface. Inhibition of FXIIIA with NC9 resulted in defective secretory vesicle delivery to the plasma membrane which was attributable to a disorganized microtubule network and decreased microtubule association with the plasma membrane. NC9 inhibition of FXIIIA resulted in destabilization of microtubules as assessed by cellular Glu-tubulin levels. Furthermore, NC9 blocked modification of Glu-tubulin into 150 kDa high-molecular weight Glu-tubulin form which was specifically localized to the plasma membrane. FXIIIA enzyme and its crosslinking activity were colocalized with plasma membrane-associated tubulin, and thus, it appears that FXIIIA crosslinking activity is directed towards stabilizing the interaction of microtubules with the plasma membrane. Our work provides the first mechanistic cues as to how transglutaminase activity could affect protein secretion and matrix deposition in osteoblasts and suggests a novel function for plasma membrane FXIIIA in microtubule dynamics.

  1. Statistical mechanics provides novel insights into microtubule stability and mechanism of shrinkage.

    Directory of Open Access Journals (Sweden)

    Ishutesh Jain

    2015-02-01

    Full Text Available Microtubules are nano-machines that grow and shrink stochastically, making use of the coupling between chemical kinetics and mechanics of its constituent protofilaments (PFs. We investigate the stability and shrinkage of microtubules taking into account inter-protofilament interactions and bending interactions of intrinsically curved PFs. Computing the free energy as a function of PF tip position, we show that the competition between curvature energy, inter-PF interaction energy and entropy leads to a rich landscape with a series of minima that repeat over a length-scale determined by the intrinsic curvature. Computing Langevin dynamics of the tip through the landscape and accounting for depolymerization, we calculate the average unzippering and shrinkage velocities of GDP protofilaments and compare them with the experimentally known results. Our analysis predicts that the strength of the inter-PF interaction (E(s(m has to be comparable to the strength of the curvature energy (E(b(m such that E(s(m - E(b(m ≈ 1kBT, and questions the prevalent notion that unzippering results from the domination of bending energy of curved GDP PFs. Our work demonstrates how the shape of the free energy landscape is crucial in explaining the mechanism of MT shrinkage where the unzippered PFs will fluctuate in a set of partially peeled off states and subunit dissociation will reduce the length.

  2. Brassinosteroids regulate pavement cell growth by mediating BIN2-induced microtubule stabilization.

    Science.gov (United States)

    Liu, Xiaolei; Yang, Qin; Wang, Yuan; Wang, Linhai; Fu, Ying; Wang, Xuelu

    2018-02-23

    Brassinosteroids (BRs), a group of plant steroid hormones, play important roles in regulating plant development. The cytoskeleton also affects key developmental processes and a deficiency in BR biosynthesis or signaling leads to abnormal phenotypes similar to those of microtubule-defective mutants. However, how BRs regulate microtubule and cell morphology remains unknown. Here, using liquid chromatography-tandem mass spectrometry, we identified tubulin proteins that interact with Arabidopsis BRASSINOSTEROID INSENSITIVE2 (BIN2), a negative regulator of BR responses in plants. In vitro and in vivo pull-down assays confirmed that BIN2 interacts with tubulin proteins. High-speed co-sedimentation assays demonstrated that BIN2 also binds microtubules. The Arabidopsis genome also encodes two BIN2 homologs, BIN2-LIKE 1 (BIL1) and BIL2, which function redundantly with BIN2. In the bin2-3 bil1 bil2 triple mutant, cortical microtubules were more sensitive to treatment with the microtubule-disrupting drug oryzalin than in wild-type, whereas in the BIN2 gain-of-function mutant bin2-1, cortical microtubules were insensitive to oryzalin treatment. These results provide important insight into how BR regulates plant pavement cell and leaf growth by mediating the stabilization of microtubules by BIN2.

  3. An agent-based model contrasts opposite effects of dynamic and stable microtubules on cleavage furrow positioning.

    Science.gov (United States)

    Odell, Garrett M; Foe, Victoria E

    2008-11-03

    From experiments by Foe and von Dassow (Foe, V.E., and G. von Dassow. 2008. J. Cell Biol. 183:457-470) and others, we infer a molecular mechanism for positioning the cleavage furrow during cytokinesis. Computer simulations reveal how this mechanism depends on quantitative motor-behavior details and explore how robustly this mechanism succeeds across a range of cell sizes. The mechanism involves the MKLP1 (kinesin-6) component of centralspindlin binding to and walking along microtubules to stimulate cortical contractility where the centralspindlin complex concentrates. The majority of astral microtubules are dynamically unstable. They bind most MKLP1 and suppress cortical Rho/myosin II activation because the tips of unstable microtubules usually depolymerize before MKLP1s reach the cortex. A subset of astral microtubules stabilizes during anaphase, becoming effective rails along which MKLP1 can actually reach the cortex. Because stabilized microtubules aim statistically at the equatorial spindle midplane, that is where centralspindlin accumulates to stimulate furrow formation.

  4. Microtubules Nonlinear Models Dynamics Investigations through the exp(−Φ(ξ-Expansion Method Implementation

    Directory of Open Access Journals (Sweden)

    Nur Alam

    2016-02-01

    Full Text Available In this research article, we present exact solutions with parameters for two nonlinear model partial differential equations(PDEs describing microtubules, by implementing the exp(−Φ(ξ-Expansion Method. The considered models, describing highly nonlinear dynamics of microtubules, can be reduced to nonlinear ordinary differential equations. While the first PDE describes the longitudinal model of nonlinear dynamics of microtubules, the second one describes the nonlinear model of dynamics of radial dislocations in microtubules. The acquired solutions are then graphically presented, and their distinct properties are enumerated in respect to the corresponding dynamic behavior of the microtubules they model. Various patterns, including but not limited to regular, singular kink-like, as well as periodicity exhibiting ones, are detected. Being the method of choice herein, the exp(−Φ(ξ-Expansion Method not disappointing in the least, is found and declared highly efficient.

  5. NAD+ and SIRT3 control microtubule dynamics and reduce susceptibility to antimicrotubule agents

    Science.gov (United States)

    Harkcom, William T.; Ghosh, Ananda K.; Sung, Matthew S.; Matov, Alexandre; Brown, Kevin D.; Giannakakou, Paraskevi; Jaffrey, Samie R.

    2014-01-01

    Nicotinamide adenine dinucleotide (NAD+) is an endogenous enzyme cofactor and cosubstrate that has effects on diverse cellular and physiologic processes, including reactive oxygen species generation, mitochondrial function, apoptosis, and axonal degeneration. A major goal is to identify the NAD+-regulated cellular pathways that may mediate these effects. Here we show that the dynamic assembly and disassembly of microtubules is markedly altered by NAD+. Furthermore, we show that the disassembly of microtubule polymers elicited by microtubule depolymerizing agents is blocked by increasing intracellular NAD+ levels. We find that these effects of NAD+ are mediated by the activation of the mitochondrial sirtuin sirtuin-3 (SIRT3). Overexpression of SIRT3 prevents microtubule disassembly and apoptosis elicited by antimicrotubule agents and knockdown of SIRT3 prevents the protective effects of NAD+ on microtubule polymers. Taken together, these data demonstrate that NAD+ and SIRT3 regulate microtubule polymerization and the efficacy of antimicrotubule agents. PMID:24889606

  6. Cep169, a Novel Microtubule Plus-End-Tracking Centrosomal Protein, Binds to CDK5RAP2 and Regulates Microtubule Stability.

    Directory of Open Access Journals (Sweden)

    Yusuke Mori

    Full Text Available The centrosomal protein, CDK5RAP2, is a microcephaly protein that regulates centrosomal maturation by recruitment of a γ-tubulin ring complex (γ-TuRC onto centrosomes. In this report, we identified a novel human centrosomal protein, Cep169, as a binding partner of CDK5RAP2, a member of microtubule plus-end-tracking proteins (+TIPs. Cep169 interacts directly with CDK5RAP2 through CM1, an evolutionarily conserved domain, and colocalizes at the pericentriolar matrix (PCM around centrioles with CDK5RAP2. In addition, Cep169 interacts with EB1 through SxIP-motif responsible for EB1 binding, and colocalizes with CDK5RAP2 at the microtubule plus-end. EB1-binding-deficient Cep169 abolishes EB1 interaction and microtubule plus-end attachment, indicating Cep169 as a novel member of +TIPs. We further show that ectopic expression of either Cep169 or CDK5RAP2 induces microtubule bundling and acetylation in U2OS cells, and depletion of Cep169 induces microtubule depolymerization in HeLa cells, although Cep169 is not required for assembly of γ-tubulin onto centrosome by CDK5RAP2. These results show that Cep169 targets microtubule tips and regulates stability of microtubules with CDK5RAP2.

  7. Four-stranded mini microtubules formed by Prosthecobacter BtubAB show dynamic instability.

    Science.gov (United States)

    Deng, Xian; Fink, Gero; Bharat, Tanmay A M; He, Shaoda; Kureisaite-Ciziene, Danguole; Löwe, Jan

    2017-07-18

    Microtubules, the dynamic, yet stiff hollow tubes built from αβ-tubulin protein heterodimers, are thought to be present only in eukaryotic cells. Here, we report a 3.6-Å helical reconstruction electron cryomicroscopy structure of four-stranded mini microtubules formed by bacterial tubulin-like Prosthecobacter dejongeii BtubAB proteins. Despite their much smaller diameter, mini microtubules share many key structural features with eukaryotic microtubules, such as an M-loop, alternating subunits, and a seam that breaks overall helical symmetry. Using in vitro total internal reflection fluorescence microscopy, we show that bacterial mini microtubules treadmill and display dynamic instability, another hallmark of eukaryotic microtubules. The third protein in the btub gene cluster, BtubC, previously known as "bacterial kinesin light chain," binds along protofilaments every 8 nm, inhibits BtubAB mini microtubule catastrophe, and increases rescue. Our work reveals that some bacteria contain regulated and dynamic cytomotive microtubule systems that were once thought to be only useful in much larger and sophisticated eukaryotic cells.

  8. Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy

    NARCIS (Netherlands)

    Flex, Elisabetta; Niceta, Marcello; Cecchetti, Serena; Thiffault, Isabelle; Au, Margaret G.; Capuano, Alessandro; Piermarini, Emanuela; Ivanova, Anna A.; Francis, Joshua W.; Chillemi, Giovanni; Chandramouli, Balasubramanian; Carpentieri, Giovanna; Haaxma, Charlotte A.; Ciolfi, Andrea; Pizzi, Simone; Douglas, Ganka V.; Levine, Kara; Sferra, Antonella; Dentici, Maria Lisa; Pfundt, Rolph R.; Le Pichon, Jean-Baptiste; Farrow, Emily; Baas, Frank; Piemonte, Fiorella; Dallapiccola, Bruno; Graham, John M.; Saunders, Carol J.; Bertini, Enrico; Kahn, Richard A.; Koolen, David A.; Tartaglia, Marco

    2016-01-01

    Microtubules are dynamic cytoskeletal elements coordinating and supporting a variety of neuronal processes, including cell division, migration, polarity, intracellular trafficking, and signal transduction. Mutations in genes encoding tubulins and microtubule-associated proteins are known to cause

  9. Learning-induced and stathmin-dependent changes in microtubule stability are critical for memory and disrupted in ageing

    Science.gov (United States)

    Uchida, Shusaku; Martel, Guillaume; Pavlowsky, Alice; Takizawa, Shuichi; Hevi, Charles; Watanabe, Yoshifumi; Kandel, Eric R.; Alarcon, Juan Marcos; Shumyatsky, Gleb P.

    2014-01-01

    Changes in the stability of microtubules regulate many biological processes, but their role in memory remains unclear. Here we show that learning causes biphasic changes in the microtubule-associated network in the hippocampus. In the early phase, stathmin is dephosphorylated, enhancing its microtubule-destabilizing activity by promoting stathmin-tubulin binding, whereas in the late phase these processes are reversed leading to an increase in microtubule/KIF5-mediated localization of the GluA2 subunit of AMPA receptors at synaptic sites. A microtubule stabilizer paclitaxel decreases or increases memory when applied at the early or late phases, respectively. Stathmin mutations disrupt changes in microtubule stability, GluA2 localization, synaptic plasticity and memory. Aged wild-type mice show impairments in stathmin levels, changes in microtubule stability, and GluA2 localization. Blocking GluA2 endocytosis rescues memory deficits in stathmin mutant and aged wild-type mice. These findings demonstrate a role for microtubules in memory in young adult and aged individuals. PMID:25007915

  10. Microtubule catastrophe and rescue.

    Science.gov (United States)

    Gardner, Melissa K; Zanic, Marija; Howard, Jonathon

    2013-02-01

    Microtubules are long cylindrical polymers composed of tubulin subunits. In cells, microtubules play an essential role in architecture and motility. For example, microtubules give shape to cells, serve as intracellular transport tracks, and act as key elements in important cellular structures such as axonemes and mitotic spindles. To accomplish these varied functions, networks of microtubules in cells are very dynamic, continuously remodeling through stochastic length fluctuations at the ends of individual microtubules. The dynamic behavior at the end of an individual microtubule is termed 'dynamic instability'. This behavior manifests itself by periods of persistent microtubule growth interrupted by occasional switching to rapid shrinkage (called microtubule 'catastrophe'), and then by switching back from shrinkage to growth (called microtubule 'rescue'). In this review, we summarize recent findings which provide new insights into the mechanisms of microtubule catastrophe and rescue, and discuss the impact of these findings in regards to the role of microtubule dynamics inside of cells. Copyright © 2012 Elsevier Ltd. All rights reserved.

  11. Epothilones as lead structures for the synthesis-based discovery of new chemotypes for microtubule stabilization.

    Science.gov (United States)

    Feyen, Fabian; Cachoux, Frédéric; Gertsch, Jürg; Wartmann, Markus; Altmann, Karl-Heinz

    2008-01-01

    Epothilones are macrocyclic bacterial natural products with potent microtubule-stabilizing and antiproliferative activity. They have served as successful lead structures for the development of several clinical candidates for anticancer therapy. However, the structural diversity of this group of clinical compounds is rather limited, as their structures show little divergence from the original natural product leads. Our own research has explored the question of whether epothilones can serve as a basis for the development of new structural scaffolds, or chemotypes, for microtubule stabilization that might serve as a basis for the discovery of new generations of anticancer drugs. We have elaborated a series of epothilone-derived macrolactones whose overall structural features significantly deviate from those of the natural epothilone scaffold and thus define new structural families of microtubule-stabilizing agents. Key elements of our hypermodification strategy are the change of the natural epoxide geometry from cis to trans, the incorporation of a conformationally constrained side chain, the removal of the C3-hydroxyl group, and the replacement of C12 with nitrogen. So far, this approach has yielded analogs 30 and 40 that are the most advanced, the most rigorously modified, structures, both of which are potent antiproliferative agents with low nanomolar activity against several human cancer cell lines in vitro. The synthesis was achieved through a macrolactone-based strategy or a high-yielding RCM reaction. The 12-aza-epothilone ("azathilone" 40) may be considered a "non-natural" natural product that still retains most of the overall structural characteristics of a true natural product but is structurally unique, because it lies outside of the general scope of Nature's biosynthetic machinery for polyketide synthesis. Like natural epothilones, both 30 and 40 promote tubulin polymerization in vitro and at the cellular level induce cell cycle arrest in mitosis. These

  12. Deficiency of RITA results in multiple mitotic defects by affecting microtubule dynamics.

    Science.gov (United States)

    Steinhäuser, K; Klöble, P; Kreis, N-N; Ritter, A; Friemel, A; Roth, S; Reichel, J M; Michaelis, J; Rieger, M A; Louwen, F; Oswald, F; Yuan, J

    2017-04-01

    Deregulation of mitotic microtubule (MT) dynamics results in defective spindle assembly and chromosome missegregation, leading further to chromosome instability, a hallmark of tumor cells. RBP-J interacting and tubulin-associated protein (RITA) has been identified as a negative regulator of the Notch signaling pathway. Intriguingly, deregulated RITA is involved in primary hepatocellular carcinoma and other malignant entities. We were interested in the potential molecular mechanisms behind its involvement. We show here that RITA binds to tubulin and localizes to various mitotic MT structures. RITA coats MTs and affects their structures in vitro as well as in vivo. Tumor cell lines deficient of RITA display increased acetylated α-tubulin, enhanced MT stability and reduced MT dynamics, accompanied by multiple mitotic defects, including chromosome misalignment and segregation errors. Re-expression of wild-type RITA, but not RITA Δtub ineffectively binding to tubulin, restores the phenotypes, suggesting that the role of RITA in MT modulation is mediated via its interaction with tubulin. Mechanistically, RITA interacts with tubulin/histone deacetylase 6 (HDAC6) and its suppression decreases the binding of the deacetylase HDAC6 to tubulin/MTs. Furthermore, the mitotic defects and increased MT stability are also observed in RITA -/- mouse embryonic fibroblasts. RITA has thus a novel role in modulating MT dynamics and its deregulation results in erroneous chromosome segregation, one of the major reasons for chromosome instability in tumor cells.

  13. Microtubule dynamics. II. Kinetics of self-assembly

    DEFF Research Database (Denmark)

    Flyvbjerg, H.; Jobs, E.

    1997-01-01

    Inverse scattering theory describes the conditions necessary and sufficient to determine an unknown potential from known scattering data. No similar theory exists for when and how one may deduce the kinetics of an unknown chemical reaction from quantitative information about its final state and i...... to analyze the self-assembly of microtubules from tubulin are general, and many other reactions and processes may be studied as inverse problems with these methods when enough experimental data are available....

  14. Dictyoceratidan poisons: Defined mark on microtubule-tubulin dynamics.

    Science.gov (United States)

    Gnanambal K, Mary Elizabeth; Lakshmipathy, Shailaja Vommi

    2016-03-01

    Tubulin/microtubule assembly and disassembly is characterized as one of the chief processes during cell growth and division. Hence drugs those perturb these process are considered to be effective in killing fast multiplying cancer cells. There is a collection of natural compounds which disturb microtubule/tubulin dis/assemblage and there have been a lot of efforts concerted in the marine realm too, to surveying such killer molecules. Close to half the natural compounds shooting out from marine invertebrates are generally with no traceable definite mechanisms of action though may be tough anti-cancerous hits at nanogram levels, hence fatefully those discoveries conclude therein without a capacity of translation from laboratory to pharmacy. Astoundingly at least 50% of natural compounds which have definite mechanisms of action causing disorders in tubulin/microtubule kinetics have an isolation history from sponges belonging to the Phylum: Porifera. Poriferans have always been a wonder worker to treat cancers with a choice of, yet precise targets on cancerous tissues. There is a specific order: Dictyoceratida within this Phylum which has contributed to yielding at least 50% of effective compounds possessing this unique mechanism of action mentioned above. However, not much notice is driven to Dictyoceratidans alongside the order: Demospongiae thus dictating the need to know its select microtubule/tubulin irritants since the unearthing of avarol in the year 1974 till date. Hence this review selectively pinpoints all the compounds, noteworthy derivatives and analogs stemming from order: Dictyoceratida focusing on the past, present and future. Copyright © 2016 Elsevier Inc. All rights reserved.

  15. Microtubule-Organizing Centers.

    Science.gov (United States)

    Wu, Jingchao; Akhmanova, Anna

    2017-10-06

    The organization of microtubule networks is crucial for controlling chromosome segregation during cell division, for positioning and transport of different organelles, and for cell polarity and morphogenesis. The geometry of microtubule arrays strongly depends on the localization and activity of the sites where microtubules are nucleated and where their minus ends are anchored. Such sites are often clustered into structures known as microtubule-organizing centers, which include the centrosomes in animals and spindle pole bodies in fungi. In addition, other microtubules, as well as membrane compartments such as the cell nucleus, the Golgi apparatus, and the cell cortex, can nucleate, stabilize, and tether microtubule minus ends. These activities depend on microtubule-nucleating factors, such as γ-tubulin-containing complexes and their activators and receptors, and microtubule minus end-stabilizing proteins with their binding partners. Here, we provide an overview of the current knowledge on how such factors work together to control microtubule organization in different systems.

  16. TBCD links centriologenesis, spindle microtubule dynamics, and midbody abscission in human cells.

    Directory of Open Access Journals (Sweden)

    Mónica López Fanarraga

    2010-01-01

    Full Text Available Microtubule-organizing centers recruit alpha- and beta-tubulin polypeptides for microtubule nucleation. Tubulin synthesis is complex, requiring five specific cofactors, designated tubulin cofactors (TBCs A-E, which contribute to various aspects of microtubule dynamics in vivo. Here, we show that tubulin cofactor D (TBCD is concentrated at the centrosome and midbody, where it participates in centriologenesis, spindle organization, and cell abscission. TBCD exhibits a cell-cycle-specific pattern, localizing on the daughter centriole at G1 and on procentrioles by S, and disappearing from older centrioles at telophase as the protein is recruited to the midbody. Our data show that TBCD overexpression results in microtubule release from the centrosome and G1 arrest, whereas its depletion produces mitotic aberrations and incomplete microtubule retraction at the midbody during cytokinesis. TBCD is recruited to the centriole replication site at the onset of the centrosome duplication cycle. A role in centriologenesis is further supported in differentiating ciliated cells, where TBCD is organized into "centriolar rosettes". These data suggest that TBCD participates in both canonical and de novo centriolar assembly pathways.

  17. Integrins Regulate Apical Constriction via Microtubule Stabilization in the Drosophila Eye Disc Epithelium

    Directory of Open Access Journals (Sweden)

    Vilaiwan M. Fernandes

    2014-12-01

    Full Text Available During morphogenesis, extracellular signals trigger actomyosin contractility in subpopulations of cells to coordinate changes in cell shape. To illuminate the link between signaling-mediated tissue patterning and cytoskeletal remodeling, we study the progression of the morphogenetic furrow (MF, the wave of apical constriction that traverses the Drosophila eye imaginal disc preceding photoreceptor neurogenesis. Apical constriction depends on actomyosin contractility downstream of the Hedgehog (Hh and bone morphogenetic protein (BMP pathways. We identify a role for integrin adhesion receptors in MF progression. We show that Hh and BMP regulate integrin expression, the loss of which disrupts apical constriction and slows furrow progression; conversely, elevated integrins accelerate furrow progression. We present evidence that integrins regulate MF progression by promoting microtubule stabilization, since reducing microtubule stability rescues integrin-mediated furrow acceleration. Thus, integrins act as a genetic link between tissue-level signaling events and morphological change at the cellular level, leading to morphogenesis and neurogenesis in the eye.

  18. Microtubule heterogeneity of Ornithogalum umbellatum ovary epidermal cells: non-stable cortical microtubules and stable lipotubuloid microtubules.

    Science.gov (United States)

    Kwiatkowska, Maria; Stępiński, Dariusz; Polit, Justyna T; Popłońska, Katarzyna; Wojtczak, Agnieszka

    2011-01-01

    Lipotubuloids, structures containing lipid bodies and microtubules, are described in ovary epidermal cells of Ornithogalum umbellatum. Microtubules of lipotubuloids can be fixed in electron microscope fixative containing only buffered OsO(4) or in glutaraldehyde with OsO(4) post-fixation, or in a mixture of OsO(4) and glutaraldehyde. None of these substances fixes cortical microtubules of ovary epidermis of this plant which is characterized by dynamic longitudinal growth. However, cortical microtubules can be fixed with cold methanol according immunocytological methods with the use of β-tubulin antibodies and fluorescein. The existence of cortical microtubules has also been evidenced by EM observations solely after the use of taxol, microtubule stabilizer, and fixation in a glutaraldehyde/OsO(4) mixture. These microtubules mostly lie transversely, sometimes obliquely, and rarely parallel to the cell axis. Staining, using Ruthenium Red and silver hexamine, has revealed that lipotubuloid microtubules surface is covered with polysaccharides. The presumption has been made that the presence of a polysaccharide layer enhances the stability of lipotubuloid microtubules.

  19. KATNAL1 regulation of sertoli cell microtubule dynamics is essential for spermiogenesis and male fertility.

    Directory of Open Access Journals (Sweden)

    Lee B Smith

    Full Text Available Spermatogenesis is a complex process reliant upon interactions between germ cells (GC and supporting somatic cells. Testicular Sertoli cells (SC support GCs during maturation through physical attachment, the provision of nutrients, and protection from immunological attack. This role is facilitated by an active cytoskeleton of parallel microtubule arrays that permit transport of nutrients to GCs, as well as translocation of spermatids through the seminiferous epithelium during maturation. It is well established that chemical perturbation of SC microtubule remodelling leads to premature GC exfoliation demonstrating that microtubule remodelling is an essential component of male fertility, yet the genes responsible for this process remain unknown. Using a random ENU mutagenesis approach, we have identified a novel mouse line displaying male-specific infertility, due to a point mutation in the highly conserved ATPase domain of the novel KATANIN p60-related microtubule severing protein Katanin p60 subunit A-like1 (KATNAL1. We demonstrate that Katnal1 is expressed in testicular Sertoli cells (SC from 15.5 days post-coitum (dpc and that, consistent with chemical disruption models, loss of function of KATNAL1 leads to male-specific infertility through disruption of SC microtubule dynamics and premature exfoliation of spermatids from the seminiferous epithelium. The identification of KATNAL1 as an essential regulator of male fertility provides a significant novel entry point into advancing our understanding of how SC microtubule dynamics promotes male fertility. Such information will have resonance both for future treatment of male fertility and the development of non-hormonal male contraceptives.

  20. Mutations in Human Tubulin Proximal to the Kinesin-Binding Site Alter Dynamic Instability at Microtubule Plus- and Minus-Ends

    Energy Technology Data Exchange (ETDEWEB)

    Ti, Shih-Chieh; Pamula, Melissa C.; Howes, Stuart C.; Duellberg, Christian; Cade, Nicholas I.; Kleiner, Ralph E.; Forth, Scott; Surrey, Thomas; Nogales, Eva; Kapoor, Tarun M.

    2016-04-01

    The assembly of microtubule-based cellular structures depends on regulated tubulin polymerization and directional transport. In this research, we have purified and characterized tubulin heterodimers that have human β-tubulin isotype III (TUBB3), as well as heterodimers with one of two β-tubulin mutations (D417H or R262H). Both point mutations are proximal to the kinesin-binding site and have been linked to an ocular motility disorder in humans. Compared to wild-type, microtubules with these mutations have decreased catastrophe frequencies and increased average lifetimes of plus- and minus-end-stabilizing caps. Importantly, the D417H mutation does not alter microtubule lattice structure or Mal3 binding to growing filaments. Instead, this mutation reduces the affinity of tubulin for TOG domains and colchicine, suggesting that the distribution of tubulin heterodimer conformations is changed. Together, our findings reveal how residues on the surface of microtubules, distal from the GTP-hydrolysis site and inter-subunit contacts, can alter polymerization dynamics at the plus- and minus-ends of microtubules.

  1. Development of other microtubule-stabilizer families: the epothilones and their derivatives.

    Science.gov (United States)

    Brogdon, Cynthia F; Lee, Francis Y; Canetta, Renzo M

    2014-05-01

    Chemotherapy is the mainstay of treatment for numerous cancer types, but resistance to chemotherapy remains a major clinical issue and is one of the driving influences underlying the development of new anticancer medications. One of the most important classes of chemotherapy agents is the taxanes, which target the cytoskeleton and spindle apparatus of tumor cells by binding to the microtubules, thereby disrupting key cellular mechanisms, including mitosis. Taxane resistance, however, limits treatment options and creates a major challenge for clinicians. Ongoing research has identified several newer classes of microtubule-targeting chemotherapies that may retain activity despite clinical resistance to taxanes. Among these classes, the epothilones have been studied most extensively in the clinical setting. Like taxanes, epothilones stabilize microtubulin turnover, and they have properties favoring their development as anticancer agents. The most clinically advanced epothilone analog is ixabepilone, which is currently the only approved epothilone derivative. Ixabepilone is indicated for the treatment of metastatic or locally advanced breast cancer in combination with capecitabine after failure of an anthracycline and a taxane, or as monotherapy after failure of an anthracycline, a taxane, and capecitabine. In phase II and III trials, ixabepilone showed efficacy in several patient subgroups and in various stages of breast cancer. Common adverse reactions include peripheral sensory neuropathy and asthenia. This paper will discuss the preclinical and clinical development of epothilones and their derivatives across a variety of cancer types.

  2. Erucin, the major isothiocyanate in arugula (Eruca sativa, inhibits proliferation of MCF7 tumor cells by suppressing microtubule dynamics.

    Directory of Open Access Journals (Sweden)

    Olga Azarenko

    Full Text Available Consumption of cruciferous vegetables is associated with reduced risk of various types of cancer. Isothiocyanates including sulforaphane and erucin are believed to be responsible for this activity. Erucin [1-isothiocyanato-4-(methylthiobutane], which is metabolically and structurally related to sulforaphane, is present in large quantities in arugula (Eruca sativa, Mill., kohlrabi and Chinese cabbage. However, its cancer preventive mechanisms remain poorly understood. We found that erucin inhibits proliferation of MCF7 breast cancer cells (IC50 = 28 µM in parallel with cell cycle arrest at mitosis (IC50 = 13 µM and apoptosis, by a mechanism consistent with impairment of microtubule dynamics. Concentrations of 5-15 µM erucin suppressed the dynamic instability of microtubules during interphase in the cells. Most dynamic instability parameters were inhibited, including the rates and extents of growing and shortening, the switching frequencies between growing and shortening, and the overall dynamicity. Much higher erucin concentrations were required to reduce the microtubule polymer mass. In addition, erucin suppressed dynamic instability of microtubules reassembled from purified tubulin in similar fashion. The effects of erucin on microtubule dynamics, like those of sulforaphane, are similar qualitatively to those of much more powerful clinically-used microtubule-targeting anticancer drugs, including taxanes and the vinca alkaloids. The results suggest that suppression of microtubule dynamics by erucin and the resulting impairment of critically important microtubule-dependent cell functions such as mitosis, cell migration and microtubule-based transport may be important in its cancer preventive activities.

  3. Stability of dynamical systems

    CERN Document Server

    Liao, Xiaoxin; Yu, P 0

    2007-01-01

    The main purpose of developing stability theory is to examine dynamic responses of a system to disturbances as the time approaches infinity. It has been and still is the object of intense investigations due to its intrinsic interest and its relevance to all practical systems in engineering, finance, natural science and social science. This monograph provides some state-of-the-art expositions of major advances in fundamental stability theories and methods for dynamic systems of ODE and DDE types and in limit cycle, normal form and Hopf bifurcation control of nonlinear dynamic systems.ʺ Presents

  4. Daple Coordinates Planar Polarized Microtubule Dynamics in Ependymal Cells and Contributes to Hydrocephalus

    Directory of Open Access Journals (Sweden)

    Maki Takagishi

    2017-07-01

    Full Text Available Motile cilia in ependymal cells, which line the cerebral ventricles, exhibit a coordinated beating motion that drives directional cerebrospinal fluid (CSF flow and guides neuroblast migration. At the apical cortex of these multi-ciliated cells, asymmetric localization of planar cell polarity (PCP proteins is required for the planar polarization of microtubule dynamics, which coordinates cilia orientation. Daple is a disheveled-associating protein that controls the non-canonical Wnt signaling pathway and cell motility. Here, we show that Daple-deficient mice present hydrocephalus and their ependymal cilia lack coordinated orientation. Daple regulates microtubule dynamics at the anterior side of ependymal cells, which in turn orients the cilial basal bodies required for the directional cerebrospinal fluid flow. These results demonstrate an important role for Daple in planar polarity in motile cilia and provide a framework for understanding the mechanisms and functions of planar polarization in the ependymal cells.

  5. Microtubule Catastrophe and Rescue

    OpenAIRE

    Gardner, Melissa K.; Zanic, Marija; Howard, Jonathon

    2012-01-01

    Microtubules are long cylindrical polymers composed of tubulin subunits. In cells, microtubules play an essential role in architecture and motility. For example, microtubules give shape to cells, serve as intracellular transport tracks, and act as key elements in important cellular structures such as axonemes and mitotic spindles. To accomplish these varied functions, networks of microtubules in cells are very dynamic, continuously remodeling through stochastic length fluctuations at the ends...

  6. Active Erk Regulates Microtubule Stability in H-ras-Transformed Cells

    Directory of Open Access Journals (Sweden)

    Rene E. Harrison

    2001-01-01

    Full Text Available Increasing evidence suggests that activated erk regulates cell functions, at least in part, by mechanisms that do not require gene transcription. Here we show that the map kinase, erk, decorates microtubules (MTs and mitotic spindles in both parental and mutant active rastransfected 10T1 /2 fibroblasts and MCF10A breast epithelial cells. Approximately 20% of total cellular erk decorated MTs in both cell lines. A greater proportion of activated erk was associated with MTs in the presence of mutant active H-ras than in parental cells. Activation of erk by the ras pathway coincided with a decrease in the stability of MT, as detected by a stability marker. The MKK1 inhibitor, PD98059 and transfection of a dominant negative MKK1 blocked ras-induced instability of MTs but did not modify the association of erk with MTs or affect MT stability of the parental cells. These results indicate that the subset of active erk kinase that associates with MTs contributes to their instability in the presence of a mutant active ras. The MT-associated subset of active erk likely contributes to the enhanced invasive and proliferative abilities of cells containing mutant active H-ras.

  7. Mechanics of microtubules: effects of protofilament orientation.

    Science.gov (United States)

    Donhauser, Zachary J; Jobs, William B; Binka, Edem C

    2010-09-08

    Microtubules are hollow cylindrical polymers of the protein tubulin that play a number of important dynamic and structural roles in eukaryotic cells. Both in vivo and in vitro microtubules can exist in several possible configurations, differing in the number of protofilaments, helical rise of tubulin dimers, and protofilament skew angle with respect to the main tube axis. Here, finite element modeling is applied to examine the mechanical response of several known microtubule types when subjected to radial deformation. The data presented here provide an important insight into microtubule stiffness and reveal that protofilament orientation does not affect radial stiffness. Rather, stiffness is primarily dependent on the effective Young's modulus of the polymerized material and the effective radius of the microtubule. These results are also directly correlated to atomic force microscopy nanoindentation measurements to allow a more detailed interpretation of previous experiments. When combined with experimental data that show a significant difference between microtubules stabilized with a slowly hydrolyzable GTP analog and microtubules stabilized with paclitaxel, the finite element data suggest that paclitaxel increases the overall radial flexibility of the microtubule wall. Copyright 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  8. Combing and self-assembly phenomena in dry films of Taxol-stabilized microtubules

    Directory of Open Access Journals (Sweden)

    Rose Franck

    2007-01-01

    Full Text Available AbstractMicrotubules are filamentous proteins that act as a substrate for the translocation of motor proteins. As such, they may be envisioned as a scaffold for the self-assembly of functional materials and devices. Physisorption, self-assembly and combing are here investigated as a potential prelude to microtubule-templated self-assembly. Dense films of self-assembled microtubules were successfully produced, as well as patterns of both dendritic and non-dendritic bundles of microtubules. They are presented in the present paper and the mechanism of their formation is discussed.

  9. Noscapine alters microtubule dynamics in living cells and inhibits the progression of melanoma.

    Science.gov (United States)

    Landen, Jaren W; Lang, Roland; McMahon, Steve J; Rusan, Nasser M; Yvon, Anne-Marie; Adams, Ashley W; Sorcinelli, Mia D; Campbell, Ross; Bonaccorsi, Paola; Ansel, John C; Archer, David R; Wadsworth, Patricia; Armstrong, Cheryl A; Joshi, Harish C

    2002-07-15

    Cellular microtubules, polymers of tubulin, alternate relentlessly between phases of growth and shortening. We now show that noscapine, a tubulin-binding agent, increases the time that cellular microtubules spend idle in a paused state. As a result, most mammalian cell types observed arrest in mitosis in the presence of noscapine. We demonstrate that noscapine-treated murine melanoma B16LS9 cells do not arrest in mitosis but rather become polyploid followed by cell death, whereas primary melanocytes reversibly arrest in mitosis and resume a normal cell cycle after noscapine removal. Furthermore, in a syngeneic murine model of established s.c. melanoma, noscapine treatment resulted in an 85% inhibition of tumor volume on day 17 when delivered by gavage compared with untreated animals (P microtubule dynamics, with no detected toxicity to the host. Consequently, noscapine could be a valuable chemotherapeutic agent, alone or in combination, for the treatment of advanced melanoma.

  10. ATX-2, the C. elegans Ortholog of Human Ataxin-2, Regulates Centrosome Size and Microtubule Dynamics.

    Directory of Open Access Journals (Sweden)

    Michael D Stubenvoll

    2016-09-01

    Full Text Available Centrosomes are critical sites for orchestrating microtubule dynamics, and exhibit dynamic changes in size during the cell cycle. As cells progress to mitosis, centrosomes recruit more microtubules (MT to form mitotic bipolar spindles that ensure proper chromosome segregation. We report a new role for ATX-2, a C. elegans ortholog of Human Ataxin-2, in regulating centrosome size and MT dynamics. ATX-2, an RNA-binding protein, forms a complex with SZY-20 in an RNA-independent fashion. Depleting ATX-2 results in embryonic lethality and cytokinesis failure, and restores centrosome duplication to zyg-1 mutants. In this pathway, SZY-20 promotes ATX-2 abundance, which inversely correlates with centrosome size. Centrosomes depleted of ATX-2 exhibit elevated levels of centrosome factors (ZYG-1, SPD-5, γ-Tubulin, increasing MT nucleating activity but impeding MT growth. We show that ATX-2 influences MT behavior through γ-Tubulin at the centrosome. Our data suggest that RNA-binding proteins play an active role in controlling MT dynamics and provide insight into the control of proper centrosome size and MT dynamics.

  11. Interplay between microtubule bundling and sorting factors ensures acentriolar spindle stability during C. elegans oocyte meiosis.

    Directory of Open Access Journals (Sweden)

    Timothy J Mullen

    2017-09-01

    Full Text Available In many species, oocyte meiosis is carried out in the absence of centrioles. As a result, microtubule organization, spindle assembly, and chromosome segregation proceed by unique mechanisms. Here, we report insights into the principles underlying this specialized form of cell division, through studies of C. elegans KLP-15 and KLP-16, two highly homologous members of the kinesin-14 family of minus-end-directed kinesins. These proteins localize to the acentriolar oocyte spindle and promote microtubule bundling during spindle assembly; following KLP-15/16 depletion, microtubule bundles form but then collapse into a disorganized array. Surprisingly, despite this defect we found that during anaphase, microtubules are able to reorganize into a bundled array that facilitates chromosome segregation. This phenotype therefore enabled us to identify factors promoting microtubule organization during anaphase, whose contributions are normally undetectable in wild-type worms; we found that SPD-1 (PRC1 bundles microtubules and KLP-18 (kinesin-12 likely sorts those bundles into a functional orientation capable of mediating chromosome segregation. Therefore, our studies have revealed an interplay between distinct mechanisms that together promote spindle formation and chromosome segregation in the absence of structural cues such as centrioles.

  12. Cabazitaxel-induced stabilization of microtubules enhances radiosensitivity in ovarian cancer cells

    Directory of Open Access Journals (Sweden)

    Charles eKunos

    2013-09-01

    Full Text Available Background: Up to 40% of women with ovarian cancer have short disease-free intervals due to molecular mechanisms of chemotherapy resistance. New therapeutic strategies are sought. Ovarian cancers are sensitive to radiochemotherapy. The taxane cabazitaxel (XRP6258, Jevtana promotes tubulin assembly and stabilizes microtubules against depolymerization in cells, acting similarly in mechanism to paclitaxel. Here, sequences of cabazitaxel-radiation co-administration are tested for drug-alone cytotoxicity and optimal radiosensitization.Methods: SKOV3, OVCAR3, and TOV-112D ovarian cancer cells were administered cabazitaxel 24 h before (first, 18 h before (second, together (third, or 24 h after (fourth a single radiation dose, and then, investigated by clonogenic assay and flow cytometric assays. Radiation dose-cell survival data were fitted by two-stage multivariate analyses of variance. High content flow cytometry partitioned cabazitaxel effects into G2-phase versus M-phase events by DNA content, cyclin A2, and phospho-S10-histone H3 (PHH3. Paclitaxel served as a comparator. Findings: Cabazitaxel cytotoxicity and radiosensitization were dose dependent. Cabazitaxel added 24 h before radiation was the most lethal schedule. DNA content measurements by flow cytometry showed that cabazitaxel-treated cells accumulated in the radiosensitive G2/M 4C DNA complement compartment. Cytometry also showed that surviving cabazitaxel-induced cell cycle arrested cells resolve the arrest by entering 4C or by 8C DNA complement cell cycles.Interpretation: The radiosensitizing effect of cabazitaxel was schedule dependent, due to cell cycle redistribution, and best when cabazitaxel was given 24 h before radiation. Clinical trials of administering both cabazitaxel and radiation should be explored in women with chemoresistant ovarian cancer. Funding: Case Comprehensive Cancer Center and Sanofi-Aventis

  13. Effect of radiation on microtubule structure in cancer cells

    International Nuclear Information System (INIS)

    Tripath, Shambhoo Sharan; Panda, Dulal; Jayakumar, S.; Maikho, Thoh; Sandur, Santosh Kumar

    2017-01-01

    Microtubules (MT) are dynamic structural cellular components. In proliferating cells, they are essential components in cell division through the formation of the mitotic spindle. Radiotherapy is an integral part of cancer treatment for most of the solid cancers. Scanty data exists in the literature related to how ionizing radiation affects microtubule reorganization in tumor cells. In the present study, breast cancer cell line (MCF-7 cells) was exposed to different doses of radiation (2-10Gy). Cells were cultured for 24 h, fixed and stained with antitubulin antibody and subjected to immunofluorescence microscopy. In another experiment, cells were subjected to cold treatment for 5 min or 30 min for studying the disassembly of microtubules after 24 h of irradiation. Further, these cells were incubated at 37°C for 20 min for studying the reassembly of microtubules. Acetylation of microtubule was also examined after exposure of cells to radiation. Experiments were also performed by combining radiation with low concentration of CXI-Benzo 84 (MT destabilizing agent 1 and 2.5 uM). Exposure of MCF-7 cells to radiation lead to destabilization of microtubules. Interestingly, destabilization of microtubule was faster upon cold treatment in irradiated group as compared to control group. These cells failed to re-stabilize at 37°C. Radiation also reduced the acetylation level of microtubule. Combination treatment of CXI-Benzo 84 with radiation exhibited additive effect in terms of depolymerization of MT. Our results suggest that ionizing radiation indeed modulates microtubule dynamics. (author)

  14. Proteomics of cancer cell lines resistant to microtubule-stabilizing agents

    DEFF Research Database (Denmark)

    Albrethsen, Jakob; Angeletti, Ruth H; Horwitz, Susan Band

    2014-01-01

    Despite the clinical success of microtubule-interacting agents (MIA), a significant challenge for oncologists is the inability to predict the response of individual patients with cancer to these drugs. In the present study, six cell lines were compared by 2D DIGE proteomics to investigate cellula...

  15. An antitubulin agent BCFMT inhibits proliferation of cancer cells and induces cell death by inhibiting microtubule dynamics.

    Directory of Open Access Journals (Sweden)

    Ankit Rai

    Full Text Available Using cell based screening assay, we identified a novel anti-tubulin agent (Z-5-((5-(4-bromo-3-chlorophenylfuran-2-ylmethylene-2-thioxothiazolidin-4-one (BCFMT that inhibited proliferation of human cervical carcinoma (HeLa (IC(50, 7.2 ± 1.8 µM, human breast adenocarcinoma (MCF-7 (IC(50, 10.0 ± 0.5 µM, highly metastatic breast adenocarcinoma (MDA-MB-231 (IC(50, 6.0 ± 1 µM, cisplatin-resistant human ovarian carcinoma (A2780-cis (IC(50, 5.8 ± 0.3 µM and multi-drug resistant mouse mammary tumor (EMT6/AR1 (IC(50, 6.5 ± 1 µM cells. Using several complimentary strategies, BCFMT was found to inhibit cancer cell proliferation at G2/M phase of the cell cycle apparently by targeting microtubules. In addition, BCFMT strongly suppressed the dynamics of individual microtubules in live MCF-7 cells. At its half maximal proliferation inhibitory concentration (10 µM, BCFMT reduced the rates of growing and shortening phases of microtubules in MCF-7 cells by 37 and 40%, respectively. Further, it increased the time microtubules spent in the pause (neither growing nor shortening detectably state by 135% and reduced the dynamicity (dimer exchange per unit time of microtubules by 70%. In vitro, BCFMT bound to tubulin with a dissociation constant of 8.3 ± 1.8 µM, inhibited tubulin assembly and suppressed GTPase activity of microtubules. BCFMT competitively inhibited the binding of BODIPY FL-vinblastine to tubulin with an inhibitory concentration (K(i of 5.2 ± 1.5 µM suggesting that it binds to tubulin at the vinblastine site. In cultured cells, BCFMT-treatment depolymerized interphase microtubules, perturbed the spindle organization and accumulated checkpoint proteins (BubR1 and Mad2 at the kinetochores. BCFMT-treated MCF-7 cells showed enhanced nuclear accumulation of p53 and its downstream p21, which consequently activated apoptosis in these cells. The results suggested that BCFMT inhibits proliferation of several types of cancer cells including drug

  16. The dynamic interplay of plasma membrane domains and cortical microtubules in secondary cell wall patterning

    Directory of Open Access Journals (Sweden)

    Yoshihisa eOda

    2013-12-01

    Full Text Available Patterning of the cellulosic cell wall underlies the shape and function of plant cells. The cortical microtubule array plays a central role in the regulation of cell wall patterns. However, the regulatory mechanisms by which secondary cell wall patterns are established through cortical microtubules remain to be fully determined. Our recent study in xylem vessel cells revealed that a mutual inhibitory interaction between cortical microtubules and distinct plasma membrane domains leads to distinctive patterning in secondary cell walls. Our research revealed that the recycling of active and inactive ROP proteins by a specific GAP and GEF pair establishes distinct de novo plasma membrane domains. Active ROP recruits a plant-specific microtubule-associated protein, MIDD1, which mediates the mutual interaction between cortical microtubules and plasma membrane domains. In this mini review, we summarize recent research regarding secondary wall patterning, with a focus on the emerging interplay between plasma membrane domains and cortical microtubules through MIDD1 and ROP.

  17. The Kinesin Adaptor Calsyntenin-1 Organizes Microtubule Polarity and Regulates Dynamics during Sensory Axon Arbor Development

    Directory of Open Access Journals (Sweden)

    Mary C. Halloran

    2017-04-01

    Full Text Available Axon growth and branching, and development of neuronal polarity are critically dependent on proper organization and dynamics of the microtubule (MT cytoskeleton. MTs must organize with correct polarity for delivery of diverse cargos to appropriate subcellular locations, yet the molecular mechanisms regulating MT polarity remain poorly understood. Moreover, how an actively branching axon reorganizes MTs to direct their plus ends distally at branch points is unknown. We used high-speed, in vivo imaging of polymerizing MT plus ends to characterize MT dynamics in developing sensory axon arbors in zebrafish embryos. We find that axonal MTs are highly dynamic throughout development, and that the peripheral and central axons of sensory neurons show differences in MT behaviors. Furthermore, we show that Calsyntenin-1 (Clstn-1, a kinesin adaptor required for sensory axon branching, also regulates MT polarity in developing axon arbors. In wild type neurons the vast majority of MTs are directed in the correct plus-end-distal orientation from early stages of development. Loss of Clstn-1 causes an increase in MTs polymerizing in the retrograde direction. These misoriented MTs most often are found near growth cones and branch points, suggesting Clstn-1 is particularly important for organizing MT polarity at these locations. Together, our results suggest that Clstn-1, in addition to regulating kinesin-mediated cargo transport, also organizes the underlying MT highway during axon arbor development.

  18. Complementary activities of TPX2 and chTOG constitute an efficient importin-regulated microtubule nucleation module.

    Science.gov (United States)

    Roostalu, Johanna; Cade, Nicholas I; Surrey, Thomas

    2015-11-01

    Spindle assembly and function require precise control of microtubule nucleation and dynamics. The chromatin-driven spindle assembly pathway exerts such control locally in the vicinity of chromosomes. One of the key targets of this pathway is TPX2. The molecular mechanism of how TPX2 stimulates microtubule nucleation is not understood. Using microscopy-based dynamic in vitro reconstitution assays with purified proteins, we find that human TPX2 directly stabilizes growing microtubule ends and stimulates microtubule nucleation by stabilizing early microtubule nucleation intermediates. Human microtubule polymerase chTOG (XMAP215/Msps/Stu2p/Dis1/Alp14 homologue) only weakly promotes nucleation, but acts synergistically with TPX2. Hence, a combination of distinct and complementary activities is sufficient for efficient microtubule formation in vitro. Importins control the efficiency of the microtubule nucleation by selectively blocking the interaction of TPX2 with microtubule nucleation intermediates. This in vitro reconstitution reveals the molecular mechanism of regulated microtubule formation by a minimal nucleation module essential for chromatin-dependent microtubule nucleation in cells.

  19. Dynamic microtubule organization and mitochondrial transport are regulated by distinct Kinesin-1 pathways

    Directory of Open Access Journals (Sweden)

    Anna Melkov

    2015-12-01

    Full Text Available The microtubule (MT plus-end motor kinesin heavy chain (Khc is well known for its role in long distance cargo transport. Recent evidence showed that Khc is also required for the organization of the cellular MT network by mediating MT sliding. We found that mutations in Khc and the gene of its adaptor protein, kinesin light chain (Klc resulted in identical bristle morphology defects, with the upper part of the bristle being thinner and flatter than normal and failing to taper towards the bristle tip. We demonstrate that bristle mitochondria transport requires Khc but not Klc as a competing force to dynein heavy chain (Dhc. Surprisingly, we demonstrate for the first time that Dhc is the primary motor for both anterograde and retrograde fast mitochondria transport. We found that the upper part of Khc and Klc mutant bristles lacked stable MTs. When following dynamic MT polymerization via the use of GFP-tagged end-binding protein 1 (EB1, it was noted that at Khc and Klc mutant bristle tips, dynamic MTs significantly deviated from the bristle parallel growth axis, relative to wild-type bristles. We also observed that GFP-EB1 failed to concentrate as a focus at the tip of Khc and Klc mutant bristles. We propose that the failure of bristle tapering is due to defects in directing dynamic MTs at the growing tip. Thus, we reveal a new function for Khc and Klc in directing dynamic MTs during polarized cell growth. Moreover, we also demonstrate a novel mode of coordination in mitochondrial transport between Khc and Dhc.

  20. Recruitment of EB1, a Master Regulator of Microtubule Dynamics, to the Surface of the Theileria annulata Schizont

    KAUST Repository

    Woods, Kerry L.

    2013-05-09

    The apicomplexan parasite Theileria annulata transforms infected host cells, inducing uncontrolled proliferation and clonal expansion of the parasitized cell population. Shortly after sporozoite entry into the target cell, the surrounding host cell membrane is dissolved and an array of host cell microtubules (MTs) surrounds the parasite, which develops into the transforming schizont. The latter does not egress to invade and transform other cells. Instead, it remains tethered to host cell MTs and, during mitosis and cytokinesis, engages the cell\\'s astral and central spindle MTs to secure its distribution between the two daughter cells. The molecular mechanism by which the schizont recruits and stabilizes host cell MTs is not known. MT minus ends are mostly anchored in the MT organizing center, while the plus ends explore the cellular space, switching constantly between phases of growth and shrinkage (called dynamic instability). Assuming the plus ends of growing MTs provide the first point of contact with the parasite, we focused on the complex protein machinery associated with these structures. We now report how the schizont recruits end-binding protein 1 (EB1), a central component of the MT plus end protein interaction network and key regulator of host cell MT dynamics. Using a range of in vitro experiments, we demonstrate that T. annulata p104, a polymorphic antigen expressed on the schizont surface, functions as a genuine EB1-binding protein and can recruit EB1 in the absence of any other parasite proteins. Binding strictly depends on a consensus SxIP motif located in a highly disordered C-terminal region of p104. We further show that parasite interaction with host cell EB1 is cell cycle regulated. This is the first description of a pathogen-encoded protein to interact with EB1 via a bona-fide SxIP motif. Our findings provide important new insight into the mode of interaction between Theileria and the host cell cytoskeleton. 2013 Woods et al.

  1. Recruitment of EB1, a master regulator of microtubule dynamics, to the surface of the Theileria annulata schizont.

    Directory of Open Access Journals (Sweden)

    Kerry L Woods

    2013-05-01

    Full Text Available The apicomplexan parasite Theileria annulata transforms infected host cells, inducing uncontrolled proliferation and clonal expansion of the parasitized cell population. Shortly after sporozoite entry into the target cell, the surrounding host cell membrane is dissolved and an array of host cell microtubules (MTs surrounds the parasite, which develops into the transforming schizont. The latter does not egress to invade and transform other cells. Instead, it remains tethered to host cell MTs and, during mitosis and cytokinesis, engages the cell's astral and central spindle MTs to secure its distribution between the two daughter cells. The molecular mechanism by which the schizont recruits and stabilizes host cell MTs is not known. MT minus ends are mostly anchored in the MT organizing center, while the plus ends explore the cellular space, switching constantly between phases of growth and shrinkage (called dynamic instability. Assuming the plus ends of growing MTs provide the first point of contact with the parasite, we focused on the complex protein machinery associated with these structures. We now report how the schizont recruits end-binding protein 1 (EB1, a central component of the MT plus end protein interaction network and key regulator of host cell MT dynamics. Using a range of in vitro experiments, we demonstrate that T. annulata p104, a polymorphic antigen expressed on the schizont surface, functions as a genuine EB1-binding protein and can recruit EB1 in the absence of any other parasite proteins. Binding strictly depends on a consensus SxIP motif located in a highly disordered C-terminal region of p104. We further show that parasite interaction with host cell EB1 is cell cycle regulated. This is the first description of a pathogen-encoded protein to interact with EB1 via a bona-fide SxIP motif. Our findings provide important new insight into the mode of interaction between Theileria and the host cell cytoskeleton.

  2. Non-critical string theory formulation of microtubule dynamics and quantum aspects of brain function

    CERN Document Server

    Mavromatos, Nikolaos E

    1995-01-01

    Microtubule (MT) networks, subneural paracrystalline cytosceletal structures, seem to play a fundamental role in the neurons. We cast here the complicated MT dynamics in the form of a 1+1-dimensional non-critical string theory, thus enabling us to provide a consistent quantum treatment of MTs, including enviromental {\\em friction} effects. We suggest, thus, that the MTs are the microsites, in the brain, for the emergence of stable, macroscopic quantum coherent states, identifiable with the {\\em preconscious states}. Quantum space-time effects, as described by non-critical string theory, trigger then an {\\em organized collapse} of the coherent states down to a specific or {\\em conscious state}. The whole process we estimate to take {\\cal O}(1\\,{\\rm sec}), in excellent agreement with a plethora of experimental/observational findings. The {\\em microscopic arrow of time}, endemic in non-critical string theory, and apparent here in the self-collapse process, provides a satisfactory and simple resolution to the age...

  3. Microtubule plus end-tracking proteins play critical roles in directional growth of hyphae by regulating the dynamics of cytoplasmic microtubules in Aspergillus nidulans.

    Science.gov (United States)

    Zeng, Cui J Tracy; Kim, Hye-Ryun; Vargas Arispuro, Irasema; Kim, Jung-Mi; Huang, An-Chi; Liu, Bo

    2014-11-01

    Cytoplasmic microtubules (MTs) serve as a rate-limiting factor for hyphal tip growth in the filamentous fungus Aspergillus nidulans. We hypothesized that this function depended on the MT plus end-tracking proteins (+TIPs) including the EB1 family protein EBA that decorated the MT plus ends undergoing polymerization. The ebAΔ mutation reduced colony growth and the mutant hyphae appeared in an undulating pattern instead of exhibiting unidirectional growth in the control. These phenotypes were enhanced by a mutation in another +TIP gene clipA. EBA was required for plus end-tracking of CLIPA, the Kinesin-7 motor KipA, and the XMAP215 homologue AlpA. In addition, cytoplasmic dynein also depended on EBA to track on most polymerizing MT plus ends, but not for its conspicuous appearance at the MT ends near the hyphal apex. The loss of EBA reduced the number of cytoplasmic MTs and prolonged dwelling times for MTs after reaching the hyphal apex. Finally, we found that colonies were formed in the absence of EBA, CLIPA, and NUDA together, suggesting that they were dispensable for fundamental functions of MTs. This study provided a comprehensive delineation of the relationship among different +TIPs and their contributions to MT dynamics and unidirectional hyphal expansion in filamentous fungi. © 2014 John Wiley & Sons Ltd.

  4. Microtubule dynamics of the centrosome-like polar organizers from the basal land plant Marchantia polymorpha.

    Science.gov (United States)

    Buschmann, Henrik; Holtmannspötter, Michael; Borchers, Agnes; O'Donoghue, Martin-Timothy; Zachgo, Sabine

    2016-02-01

    The liverwort Marchantia employs both modern and ancestral devices during cell division: it forms preprophase bands and in addition it shows centrosome-like polar organizers. We investigated whether polar organizers and preprophase bands cooperate to set up the division plane. To this end, two novel green fluorescent protein-based microtubule markers for dividing cells of Marchantia were developed. Cells of the apical notch formed polar organizers first and subsequently assembled preprophase bands. Polar organizers were formed de novo from multiple mobile microtubule foci localizing to the nuclear envelope. The foci then became concentrated by bipolar aggregation. We determined the comet production rate of polar organizers and show that microtubule plus ends of astral microtubules polymerize faster than those found on cortical microtubules. Importantly, it was observed that conditions increasing polar organizer numbers interfere with preprophase band formation. The data show that polar organizers have much in common with centrosomes, but that they also have specialized features. The results suggest that polar organizers contribute to preprophase band formation and in this way are involved in controlling the division plane. Our analyses of the basal land plant Marchantia shed new light on the evolution of plant cell division. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

  5. Dynamic Stability of Maglev Systems,

    Science.gov (United States)

    1992-04-01

    AD-A259 178 ANL-92/21 Materials and Components Dynamic Stability of Technology Division Materials and Components Maglev Systems Technology Division...of Maglev Systems Y. Cai, S. S. Chen, and T. M. Mulcahy Materials and Components Technology Division D. M. Rote Center for Transportation Research...of Maglev System with L-Shaped Guideway ......................................... 6 3 Stability of M aglev System s

  6. Dynamic stability under sudden loads

    International Nuclear Information System (INIS)

    Simitses, G.J.

    1998-01-01

    The concept of dynamic stability of elastic structures subjected to sudden (step) loads is discussed. The various criteria and related methodologies for estimating critical conditions are presented with the emphasis on their similarities and differences. These are demonstrated by employing a simple mechanical model. Several structural configurations are analyzed, for demonstration purposes, with the intention of comparing critical dynamic loads to critical static loads. These configurations include shallow arches and shallow spherical caps, two bar frames, and imperfect cylindrical shells of metallic as well as laminated composite construction. In the demonstration examples, the effect of static pre loading on the dynamic critical load is presented

  7. CLASP2 interacts with p120-catenin and governs microtubule dynamics at adherens junctions

    DEFF Research Database (Denmark)

    Shahbazi, Marta N; Megias, Diego; Epifano, Carolina

    2013-01-01

    Classical cadherins and their connections with microtubules (MTs) are emerging as important determinants of cell adhesion. However, the functional relevance of such interactions and the molecular players that contribute to tissue architecture are still emerging. In this paper, we report that the ...

  8. Cyclin G2 is a centrosome-associated nucleocytoplasmic shuttling protein that influences microtubule stability and induces a p53-dependent cell cycle arrest

    International Nuclear Information System (INIS)

    Arachchige Don, Aruni S.; Dallapiazza, Robert F.; Bennin, David A.; Brake, Tiffany; Cowan, Colleen E.; Horne, Mary C.

    2006-01-01

    Cyclin G2 is an atypical cyclin that associates with active protein phosphatase 2A. Cyclin G2 gene expression correlates with cell cycle inhibition; it is significantly upregulated in response to DNA damage and diverse growth inhibitory stimuli, but repressed by mitogenic signals. Ectopic expression of cyclin G2 promotes cell cycle arrest, cyclin dependent kinase 2 inhibition and the formation of aberrant nuclei [Bennin, D. A., Don, A. S., Brake, T., McKenzie, J. L., Rosenbaum, H., Ortiz, L., DePaoli-Roach, A. A., and Horne, M. C. (2002). Cyclin G2 associates with protein phosphatase 2A catalytic and regulatory B' subunits in active complexes and induces nuclear aberrations and a G 1 /S-phase cell cycle arrest. J Biol Chem 277, 27449-67]. Here we report that endogenous cyclin G2 copurifies with centrosomes and microtubules (MT) and that ectopic G2 expression alters microtubule stability. We find exogenous and endogenous cyclin G2 present at microtubule organizing centers (MTOCs) where it colocalizes with centrosomal markers in a variety of cell lines. We previously reported that cyclin G2 forms complexes with active protein phosphatase 2A (PP2A) and colocalizes with PP2A in a detergent-resistant compartment. We now show that cyclin G2 and PP2A colocalize at MTOCs in transfected cells and that the endogenous proteins copurify with isolated centrosomes. Displacement of the endogenous centrosomal scaffolding protein AKAP450 that anchors PP2A at the centrosome resulted in the depletion of centrosomal cyclin G2. We find that ectopic expression of cyclin G2 induces microtubule bundling and resistance to depolymerization, inhibition of polymer regrowth from MTOCs and a p53-dependent cell cycle arrest. Furthermore, we determined that a 100 amino acid carboxy-terminal region of cyclin G2 is sufficient to both direct GFP localization to centrosomes and induce cell cycle inhibition. Colocalization of endogenous cyclin G2 with only one of two GFP-centrin-tagged centrioles, the

  9. Insight into microtubule destabilization mechanism of 3,4,5-trimethoxyphenyl indanone derivatives using molecular dynamics simulation and conformational modes analysis

    Science.gov (United States)

    Tripathi, Shubhandra; Srivastava, Gaurava; Singh, Aastha; Prakasham, A. P.; Negi, Arvind S.; Sharma, Ashok

    2018-03-01

    Colchicine site inhibitors are microtubule destabilizers having promising role in cancer therapeutics. In the current study, four such indanone derivatives (t1, t9, t14 and t17) with 3,4,5-trimethoxyphenyl fragment (ring A) and showing significant microtubule destabilization property have been explored. The interaction mechanism and conformational modes triggered by binding of these indanone derivatives and combretastatin at colchicine binding site (CBS) of αβ-tubulin dimer were studied using molecular dynamics (MD) simulation, principle component analysis and free energy landscape analysis. In the MD results, t1 showed binding similar to colchicine interacting in the deep hydrophobic core at the CBS. While t9, t14 and t17 showed binding conformation similar to combretastatin, with ring A superficially binding at the CBS. Results demonstrated that ring A played a vital role in binding via hydrophobic interactions and got anchored between the S8 and S9 sheets, H8 helix and T7 loop at the CBS. Conformational modes study revealed that twisting and bending conformational motions (as found in the apo system) were nearly absent in the ligand bound systems. Absence of twisting motion might causes loss of lateral contacts in microtubule, thus promoting microtubule destabilization. This study provides detailed account of microtubule destabilization mechanism by indanone ligands and combretastatin, and would be helpful for designing microtubule destabilizers with higher activity.

  10. Potent antiproliferative cembrenoids accumulate in tobacco upon infection with Rhodococcus fascians and trigger unusual microtubule dynamics in human glioblastoma cells.

    Directory of Open Access Journals (Sweden)

    Aminata P Nacoulma

    Full Text Available AIMS: Though plant metabolic changes are known to occur during interactions with bacteria, these were rarely challenged for pharmacologically active compounds suitable for further drug development. Here, the occurrence of specific chemicals with antiproliferative activity against human cancer cell lines was evidenced in hyperplasia (leafy galls induced when plants interact with particular phytopathogens, such as the Actinomycete Rhodococcus fascians. METHODS: We examined leafy galls fraction F3.1.1 on cell proliferation, cell division and cytoskeletal disorganization of human cancer cell lines using time-lapse videomicroscopy imaging, combined with flow cytometry and immunofluorescence analysis. We determined the F3.1.1-fraction composition by gas chromatography coupled to mass spectrometry. RESULTS: The leafy galls induced on tobacco by R. fascians yielded fraction F3.1.1 which inhibited proliferation of glioblastoma U373 cells with an IC50 of 4.5 µg/mL, F.3.1.1 was shown to increase cell division duration, cause nuclear morphological deformations and cell enlargement, and, at higher concentrations, karyokinesis defects leading to polyploidization and apoptosis. F3.1.1 consisted of a mixture of isomers belonging to the cembrenoids. The cellular defects induced by F3.1.1 were caused by a peculiar cytoskeletal disorganization, with the occurrence of fragmented tubulin and strongly organized microtubule aggregates within the same cell. Colchicine, paclitaxel, and cembrene also affected U373 cell proliferation and karyokinesis, but the induced microtubule rearrangement was very different from that provoked by F3.1.1. Altogether our data indicate that the cembrenoid isomers in F3.1.1 have a unique mode of action and are able to simultaneously modulate microtubule polymerization and stability.

  11. Antagonism between the dynein and Ndc80 complexes at kinetochores controls the stability of kinetochore-microtubule attachments during mitosis.

    Science.gov (United States)

    Amin, Mohammed A; McKenney, Richard J; Varma, Dileep

    2018-04-20

    Chromosome alignment and segregation during mitosis require kinetochore-microtubule (kMT) attachments that are mediated by the molecular motor dynein and the kMT-binding complex Ndc80. The Rod-ZW10-Zwilch (RZZ) complex is central to this coordination as it has an important role in dynein recruitment and has recently been reported to have a key function in the regulation of stable kMT attachments in Caenorhabditis elegans besides its role in activating the spindle assembly checkpoint (SAC). However, the mechanism by which these protein complexes control kMT attachments to drive chromosome motility during early mitosis is still unclear. Here, using in vitro total internal reflection fluorescence microscopy, we observed that higher concentrations of Ndc80 inhibited dynein binding to MTs, providing evidence that Ndc80 and dynein antagonize each other's function. High-resolution microscopy and siRNA-mediated functional disruption revealed that severe defects in chromosome alignment induced by depletion of dynein or the dynein adapter Spindly are rescued by codepletion of the RZZ component Rod in human cells. Interestingly, rescue of the chromosome alignment defects was independent of Rod function in SAC activation and was accompanied by a remarkable restoration of stable kMT attachments. Furthermore, the chromosome alignment rescue depended on the plus-end-directed motility of centromere protein E (CENP-E) because cells codepleted of CENP-E, Rod, and dynein could not establish stable kMT attachments or align their chromosomes properly. Our findings support the idea that dynein may control the function of the Ndc80 complex in stabilizing kMT attachments directly by interfering with Ndc80-MT binding or indirectly by controlling the Rod-mediated inhibition of Ndc80. © 2018 by The American Society for Biochemistry and Molecular Biology, Inc.

  12. Chromatin dynamics in genome stability

    DEFF Research Database (Denmark)

    Nair, Nidhi; Shoaib, Muhammad; Sørensen, Claus Storgaard

    2017-01-01

    Genomic DNA is compacted into chromatin through packaging with histone and non-histone proteins. Importantly, DNA accessibility is dynamically regulated to ensure genome stability. This is exemplified in the response to DNA damage where chromatin relaxation near genomic lesions serves to promote...... access of relevant enzymes to specific DNA regions for signaling and repair. Furthermore, recent data highlight genome maintenance roles of chromatin through the regulation of endogenous DNA-templated processes including transcription and replication. Here, we review research that shows the importance...... of chromatin structure regulation in maintaining genome integrity by multiple mechanisms including facilitating DNA repair and directly suppressing endogenous DNA damage....

  13. Dynamic release of nuclear RanGTP triggers TPX2-dependent microtubule assembly during the apoptotic execution phase.

    Science.gov (United States)

    Moss, David K; Wilde, Andrew; Lane, Jon D

    2009-03-01

    During apoptosis, the interphase microtubule network is dismantled then later replaced by a novel, non-centrosomal microtubule array. These microtubules assist in the peripheral redistribution of nuclear fragments in the apoptotic cell; however, the regulation of apoptotic microtubule assembly is not understood. Here, we demonstrate that microtubule assembly depends upon the release of nuclear RanGTP into the apoptotic cytoplasm because this process is blocked in apoptotic cells overexpressing dominant-negative GDP-locked Ran (T24N). Actin-myosin-II contractility provides the impetus for Ran release and, consequently, microtubule assembly is blocked in blebbistatin- and Y27632-treated apoptotic cells. Importantly, the spindle-assembly factor TPX2 (targeting protein for Xklp2), colocalises with apoptotic microtubules, and siRNA silencing of TPX2, but not of the microtubule motors Mklp1 and Kid, abrogates apoptotic microtubule assembly. These data provide a molecular explanation for the assembly of the apoptotic microtubule network, and suggest important similarities with the process of RanGTP- and TPX2-mediated mitotic spindle formation.

  14. C-terminal region of MAP7 domain containing protein 3 (MAP7D3 promotes microtubule polymerization by binding at the C-terminal tail of tubulin.

    Directory of Open Access Journals (Sweden)

    Saroj Yadav

    Full Text Available MAP7 domain containing protein 3 (MAP7D3, a newly identified microtubule associated protein, has been shown to promote microtubule assembly and stability. Its microtubule binding region has been reported to consist of two coiled coil motifs located at the N-terminus. It possesses a MAP7 domain near the C-terminus and belongs to the microtubule associated protein 7 (MAP7 family. The MAP7 domain of MAP7 protein has been shown to bind to kinesin-1; however, the role of MAP7 domain in MAP7D3 remains unknown. Based on the bioinformatics analysis of MAP7D3, we hypothesized that the MAP7 domain of MAP7D3 may have microtubule binding activity. Indeed, we found that MAP7 domain of MAP7D3 bound to microtubules as well as enhanced the assembly of microtubules in vitro. Interestingly, a longer fragment MDCT that contained the MAP7 domain (MD with the C-terminal tail (CT of the protein promoted microtubule polymerization to a greater extent than MD and CT individually. MDCT stabilized microtubules against dilution induced disassembly. MDCT bound to reconstituted microtubules with an apparent dissociation constant of 3.0 ± 0.5 µM. An immunostaining experiment showed that MDCT localized along the length of the preassembled microtubules. Competition experiments with tau indicated that MDCT shares its binding site on microtubules with tau. Further, we present evidence indicating that MDCT binds to the C-terminal tail of tubulin. In addition, MDCT could bind to tubulin in HeLa cell extract. Here, we report a microtubule binding region in the C-terminal region of MAP7D3 that may have a role in regulating microtubule assembly dynamics.

  15. Stability in dynamical systems I

    International Nuclear Information System (INIS)

    Courant, E.D.; Ruth, R.D.; Weng, W.T.

    1984-08-01

    We have reviewed some of the basic techniques which can be used to analyze stability in nonlinear dynamical systems, particularly in circular particle accelerators. We have concentrated on one-dimensional systems in the examples in order to simply illustrate the general techniques. We began with a review of Hamiltonian dynamics and canonical transformations. We then reviewed linear equations with periodic coefficients using the basic techniques from accelerator theory. To handle nonlinear terms we developed a canonical perturbation theory. From this we calculated invariants and the amplitude dependence of the frequency. This led us to resonances. We studied the cubic resonance in detail by using a rotating coordinate system in phase space. We then considered a general isolated nonlinear resonance. In this case we calculated the width of the resonance and estimated the spacing of resonances in order to use the Chirikov criterion to restrict the validity of the analysis. Finally the resonance equation was reduced to the pendulum equation, and we examined the motion on a separatrix. This brought us to the beginnings of stochastic behavior in the neighborhood of the separatrix. It is this complex behavior in the neighborhood of the separatrix which causes the perturbation theory used here to diverge in many cases. In spite of this the methods developed here have been and are used quite successfully to study nonlinear effects in nearly integrable systems. When used with caution and in conjunction with numerical work they give tremendous insight into the nature of the phase space structure and the stability of nonlinear differential equations. 14 references

  16. Model for the orientational ordering of the plant microtubule cortical array

    Science.gov (United States)

    Hawkins, Rhoda J.; Tindemans, Simon H.; Mulder, Bela M.

    2010-07-01

    The plant microtubule cortical array is a striking feature of all growing plant cells. It consists of a more or less homogeneously distributed array of highly aligned microtubules connected to the inner side of the plasma membrane and oriented transversely to the cell growth axis. Here, we formulate a continuum model to describe the origin of orientational order in such confined arrays of dynamical microtubules. The model is based on recent experimental observations that show that a growing cortical microtubule can interact through angle dependent collisions with pre-existing microtubules that can lead either to co-alignment of the growth, retraction through catastrophe induction or crossing over the encountered microtubule. We identify a single control parameter, which is fully determined by the nucleation rate and intrinsic dynamics of individual microtubules. We solve the model analytically in the stationary isotropic phase, discuss the limits of stability of this isotropic phase, and explicitly solve for the ordered stationary states in a simplified version of the model.

  17. Local Dynamic Stability Associated with Load Carrying

    Directory of Open Access Journals (Sweden)

    Jian Liu

    2013-03-01

    Conclusion: Current study confirmed the sensitivity of local dynamic stability measure in load carrying situation. It was concluded that load carrying tasks were associated with declined local dynamic stability, which may result in increased risk of fall accident. This finding has implications in preventing fall accidents associated with occupational load carrying.

  18. Cell cycle-dependent microtubule-based dynamic transport of cytoplasmic dynein in mammalian cells.

    Directory of Open Access Journals (Sweden)

    Takuya Kobayashi

    Full Text Available BACKGROUND: Cytoplasmic dynein complex is a large multi-subunit microtubule (MT-associated molecular motor involved in various cellular functions including organelle positioning, vesicle transport and cell division. However, regulatory mechanism of the cell-cycle dependent distribution of dynein has not fully been understood. METHODOLOGY/PRINCIPAL FINDINGS: Here we report live-cell imaging of cytoplasmic dynein in HeLa cells, by expressing multifunctional green fluorescent protein (mfGFP-tagged 74-kDa intermediate chain (IC74. IC74-mfGFP was successfully incorporated into functional dynein complex. In interphase, dynein moved bi-directionally along with MTs, which might carry cargos such as transport vesicles. A substantial fraction of dynein moved toward cell periphery together with EB1, a member of MT plus end-tracking proteins (+TIPs, suggesting +TIPs-mediated transport of dynein. In late-interphase and prophase, dynein was localized at the centrosomes and the radial MT array. In prometaphase and metaphase, dynein was localized at spindle MTs where it frequently moved from spindle poles toward chromosomes or cell cortex. +TIPs may be involved in the transport of spindle dyneins. Possible kinetochore and cortical dyneins were also observed. CONCLUSIONS AND SIGNIFICANCE: These findings suggest that cytoplasmic dynein is transported to the site of action in preparation for the following cellular events, primarily by the MT-based transport. The MT-based transport may have greater advantage than simple diffusion of soluble dynein in rapid and efficient transport of the limited concentration of the protein.

  19. Dynamic Stability Experiment of Maglev Systems,

    Science.gov (United States)

    1995-04-01

    This report summarizes the research performed on maglev vehicle dynamic stability at Argonne National Laboratory during the past few years. It also... maglev system, it is important to consider this phenomenon in the development of all maglev systems. This report presents dynamic stability experiments...on maglev systems and compares their numerical simulation with predictions calculated by a nonlinear dynamic computer code. Instabilities of an

  20. MVL-PLA2, a snake venom phospholipase A2, inhibits angiogenesis through an increase in microtubule dynamics and disorganization of focal adhesions.

    Directory of Open Access Journals (Sweden)

    Amine Bazaa

    Full Text Available Integrins are essential protagonists of the complex multi-step process of angiogenesis that has now become a major target for the development of anticancer therapies. We recently reported and characterized that MVL-PLA2, a novel phospholipase A2 from Macrovipera lebetina venom, exhibited anti-integrin activity. In this study, we show that MVL-PLA2 also displays potent anti-angiogenic properties. This phospholipase A2 inhibited adhesion and migration of human microvascular-endothelial cells (HMEC-1 in a dose-dependent manner without being cytotoxic. Using Matrigel and chick chorioallantoic membrane assays, we demonstrated that MVL-PLA2, as well as its catalytically inactivated form, significantly inhibited angiogenesis both in vitro and in vivo. We have also found that the actin cytoskeleton and the distribution of alphav beta3 integrin, a critical regulator of angiogenesis and a major component of focal adhesions, were disturbed after MVL-PLA2 treatment. In order to further investigate the mechanism of action of this protein on endothelial cells, we analyzed the dynamic instability behavior of microtubules in living endothelial cells. Interestingly, we showed that MVL-PLA2 significantly increased microtubule dynamicity in HMEC-1 cells by 40%. We propose that the enhancement of microtubule dynamics may explain the alterations in the formation of focal adhesions, leading to inhibition of cell adhesion and migration.

  1. Models for microtubule cargo transport coupling the Langevin equation to stochastic stepping motor dynamics: Caring about fluctuations.

    Science.gov (United States)

    Bouzat, Sebastián

    2016-01-01

    One-dimensional models coupling a Langevin equation for the cargo position to stochastic stepping dynamics for the motors constitute a relevant framework for analyzing multiple-motor microtubule transport. In this work we explore the consistence of these models focusing on the effects of the thermal noise. We study how to define consistent stepping and detachment rates for the motors as functions of the local forces acting on them in such a way that the cargo velocity and run-time match previously specified functions of the external load, which are set on the base of experimental results. We show that due to the influence of the thermal fluctuations this is not a trivial problem, even for the single-motor case. As a solution, we propose a motor stepping dynamics which considers memory on the motor force. This model leads to better results for single-motor transport than the approaches previously considered in the literature. Moreover, it gives a much better prediction for the stall force of the two-motor case, highly compatible with the experimental findings. We also analyze the fast fluctuations of the cargo position and the influence of the viscosity, comparing the proposed model to the standard one, and we show how the differences on the single-motor dynamics propagate to the multiple motor situations. Finally, we find that the one-dimensional character of the models impede an appropriate description of the fast fluctuations of the cargo position at small loads. We show how this problem can be solved by considering two-dimensional models.

  2. Microtubules self-repair in response to mechanical stress

    Science.gov (United States)

    Schaedel, Laura; John, Karin; Gaillard, Jérémie; Nachury, Maxence V.; Blanchoin, Laurent; Théry, Manuel

    2015-11-01

    Microtubules--which define the shape of axons, cilia and flagella, and provide tracks for intracellular transport--can be highly bent by intracellular forces, and microtubule structure and stiffness are thought to be affected by physical constraints. Yet how microtubules tolerate the vast forces exerted on them remains unknown. Here, by using a microfluidic device, we show that microtubule stiffness decreases incrementally with each cycle of bending and release. Similar to other cases of material fatigue, the concentration of mechanical stresses on pre-existing defects in the microtubule lattice is responsible for the generation of more extensive damage, which further decreases microtubule stiffness. Strikingly, damaged microtubules were able to incorporate new tubulin dimers into their lattice and recover their initial stiffness. Our findings demonstrate that microtubules are ductile materials with self-healing properties, that their dynamics does not exclusively occur at their ends, and that their lattice plasticity enables the microtubules' adaptation to mechanical stresses.

  3. Dynamic Recruitment of Cdc2 to Specific Microtubule Structures during Mitosis

    Czech Academy of Sciences Publication Activity Database

    Weingartner, M.; Binarová, Pavla; Dryková, Denisa; Achweighofer, A.; David, P.; Heberle, E.; Doonan, J.; Bogre, L.

    2001-01-01

    Roč. 13, - (2001), s. 1929-1943 ISSN 1040-4651 R&D Projects: GA AV ČR IAA5020803 Grant - others:XE(XC) GA QLRT-00454 Keywords : dynamic * recruitment * specific Subject RIV: EE - Microbiology, Virology Impact factor: 11.081, year: 2001

  4. Assembly and control of large microtubule complexes

    Science.gov (United States)

    Korolev, Kirill; Ishihara, Keisuke; Mitchison, Timothy

    Motility, division, and other cellular processes require rapid assembly and disassembly of microtubule structures. We report a new mechanism for the formation of asters, radial microtubule complexes found in very large cells. The standard model of aster growth assumes elongation of a fixed number of microtubules originating from the centrosomes. However, aster morphology in this model does not scale with cell size, and we found evidence for microtubule nucleation away from centrosomes. By combining polymerization dynamics and auto-catalytic nucleation of microtubules, we developed a new biophysical model of aster growth. The model predicts an explosive transition from an aster with a steady-state radius to one that expands as a travelling wave. At the transition, microtubule density increases continuously, but aster growth rate discontinuously jumps to a nonzero value. We tested our model with biochemical perturbations in egg extract and confirmed main theoretical predictions including the jump in the growth rate. Our results show that asters can grow even though individual microtubules are short and unstable. The dynamic balance between microtubule collapse and nucleation could be a general framework for the assembly and control of large microtubule complexes. NIH GM39565; Simons Foundation 409704; Honjo International 486 Scholarship Foundation.

  5. Biological Information Processing in Single Microtubules

    Science.gov (United States)

    2014-03-05

    generated by synchronized oscillations of microtubules, centrosomes and chromosomes regulate the dynamics of mitosis and meiosis, Yue Zhao and Qimin...of frequency by a single microtubule. Green arrows depict the peaks that appear in absorption and disappear in transmission. Purple arrows show

  6. GDP-to-GTP exchange on the microtubule end can contribute to the frequency of catastrophe.

    Science.gov (United States)

    Piedra, Felipe-Andrés; Kim, Tae; Garza, Emily S; Geyer, Elisabeth A; Burns, Alexander; Ye, Xuecheng; Rice, Luke M

    2016-11-07

    Microtubules are dynamic polymers of αβ-tubulin that have essential roles in chromosome segregation and organization of the cytoplasm. Catastrophe-the switch from growing to shrinking-occurs when a microtubule loses its stabilizing GTP cap. Recent evidence indicates that the nucleotide on the microtubule end controls how tightly an incoming subunit will be bound (trans-acting GTP), but most current models do not incorporate this information. We implemented trans-acting GTP into a computational model for microtubule dynamics. In simulations, growing microtubules often exposed terminal GDP-bound subunits without undergoing catastrophe. Transient GDP exposure on the growing plus end slowed elongation by reducing the number of favorable binding sites on the microtubule end. Slower elongation led to erosion of the GTP cap and an increase in the frequency of catastrophe. Allowing GDP-to-GTP exchange on terminal subunits in simulations mitigated these effects. Using mutant αβ-tubulin or modified GTP, we showed experimentally that a more readily exchangeable nucleotide led to less frequent catastrophe. Current models for microtubule dynamics do not account for GDP-to-GTP exchange on the growing microtubule end, so our findings provide a new way of thinking about the molecular events that initiate catastrophe. © 2016 Piedra et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

  7. Reliability Analysis of Dynamic Stability in Waves

    DEFF Research Database (Denmark)

    Søborg, Anders Veldt

    2004-01-01

    exhibit sufficient characteristics with respect to slope at zero heel (GM value), maximum leverarm, positive range of stability and area below the leverarm curve. The rule-based requirements to calm water leverarm curves are entirely based on experience obtained from vessels in operation and recorded......The assessment of a ship's intact stability is traditionally based on a semi-empirical deterministic concept that evaluates the characteristics of ship's calm water restoring leverarm curves. Today the ship is considered safe with respect to dynamic stability if its calm water leverarm curves...... accidents in the past. The rules therefore only leaves little room for evaluation and improvement of safety of a ship's dynamic stability. A few studies have evaluated the probability of ship stability loss in waves using Monte Carlo simulations. However, since this probability may be in the order of 10...

  8. Stabilization of Microtubule-Unbound Tau via Tau Phosphorylation at Ser262/356 by Par-1/MARK Contributes to Augmentation of AD-Related Phosphorylation and Aβ42-Induced Tau Toxicity.

    Directory of Open Access Journals (Sweden)

    Kanae Ando

    2016-03-01

    Full Text Available Abnormal accumulation of the microtubule-interacting protein tau is associated with neurodegenerative diseases including Alzheimer's disease (AD. β-amyloid (Aβ lies upstream of abnormal tau behavior, including detachment from microtubules, phosphorylation at several disease-specific sites, and self-aggregation into toxic tau species in AD brains. To prevent the cascade of events leading to neurodegeneration in AD, it is essential to elucidate the mechanisms underlying the initial events of tau mismetabolism. Currently, however, these mechanisms remain unclear. In this study, using transgenic Drosophila co-expressing human tau and Aβ, we found that tau phosphorylation at AD-related Ser262/356 stabilized microtubule-unbound tau in the early phase of tau mismetabolism, leading to neurodegeneration. Aβ increased the level of tau detached from microtubules, independent of the phosphorylation status at GSK3-targeted SP/TP sites. Such mislocalized tau proteins, especially the less phosphorylated species, were stabilized by phosphorylation at Ser262/356 via PAR-1/MARK. Levels of Ser262 phosphorylation were increased by Aβ42, and blocking this stabilization of tau suppressed Aβ42-mediated augmentation of tau toxicity and an increase in the levels of tau phosphorylation at the SP/TP site Thr231, suggesting that this process may be involved in AD pathogenesis. In contrast to PAR-1/MARK, blocking tau phosphorylation at SP/TP sites by knockdown of Sgg/GSK3 did not reduce tau levels, suppress tau mislocalization to the cytosol, or diminish Aβ-mediated augmentation of tau toxicity. These results suggest that stabilization of microtubule-unbound tau by phosphorylation at Ser262/356 via the PAR-1/MARK may act in the initial steps of tau mismetabolism in AD pathogenesis, and that such tau species may represent a potential therapeutic target for AD.

  9. Interaction of the Tobacco mosaic virus movement protein with microtubules during the cell cycle in tobacco BY-2 cells.

    Science.gov (United States)

    Boutant, Emmanuel; Fitterer, Chantal; Ritzenthaler, Christophe; Heinlein, Manfred

    2009-10-01

    Cell-to-cell movement of Tobacco mosaic virus (TMV) involves the interaction of virus-encoded 30-kDa movement protein (MP) with microtubules. In cells behind the infection front that accumulate high levels of MP, this activity is reflected by the formation of stabilized MP/microtubule complexes. The ability of MP to bind along and stabilize microtubules is conserved upon expression in mammalian cells. In mammalian cells, the protein also leads to inhibition of mitosis and cell division through a microtubule-independent process correlated with the loss of centrosomal gamma-tubulin and of centrosomal microtubule-nucleation activity. Since MP has the capacity to interact with plant factors involved in microtubule nucleation and dynamics, we used inducible expression in BY-2 cells to test whether MP expression inhibits mitosis and cell division also in plants. We demonstrate that MP:GFP associates with all plant microtubule arrays and, unlike in mammalian cells, does not interfere with mitosis. Thus, MP function and the interaction of MP with factors of the cytoskeleton do not entail an inhibition of mitosis in plants. We also report that the protein targets primary plasmodesmata in BY-2 cells immediately upon or during cytokinesis and that the accumulation of MP in plasmodesmata occurs in the presence of inhibitors of the cytoskeleton and the secretory pathway.

  10. Beam Stability and Nonlinear Dynamics. Proceedings

    International Nuclear Information System (INIS)

    Parsa, Z.

    1997-01-01

    These proceedings represent papers presented at the Beam Stability and Nonlinear Dynamics symposium held in Santa Barbara in December 1996. The symposium was sponsored by the National Science Foundation as part of the United States long term accelerator research. The focus of this symposium was on nonlinear dynamics and beam stability. The topics included single-particle and many-particle dynamics, and stability in large circular accelerators such as the Large Hadron Collider(LHC). Other subjects covered were spin dynamics, nonlinear aberration correction, collective effects in the LHC, sawtooth instability and Landau damping in the presence of strong nonlinearity. There were presentations concerning plasma physics including the effect of beam echo. There are 17 papers altogether in these proceedings and 8 of them have been abstracted for the Energy Science and Technology database

  11. Unifying dynamical and structural stability of equilibria

    Science.gov (United States)

    Arnoldi, Jean-François; Haegeman, Bart

    2016-09-01

    We exhibit a fundamental relationship between measures of dynamical and structural stability of linear dynamical systems-e.g. linearized models in the vicinity of equilibria. We show that dynamical stability, quantified via the response to external perturbations (i.e. perturbation of dynamical variables), coincides with the minimal internal perturbation (i.e. perturbations of interactions between variables) able to render the system unstable. First, by reformulating a result of control theory, we explain that harmonic external perturbations reflect the spectral sensitivity of the Jacobian matrix at the equilibrium, with respect to constant changes of its coefficients. However, for this equivalence to hold, imaginary changes of the Jacobian's coefficients have to be allowed. The connection with dynamical stability is thus lost for real dynamical systems. We show that this issue can be avoided, thus recovering the fundamental link between dynamical and structural stability, by considering stochastic noise as external and internal perturbations. More precisely, we demonstrate that a linear system's response to white-noise perturbations directly reflects the intensity of internal white-noise disturbance that it can accommodate before becoming stochastically unstable.

  12. Modeling microtubule oscillations

    DEFF Research Database (Denmark)

    Jobs, E.; Wolf, D.E.; Flyvbjerg, H.

    1997-01-01

    Synchronization of molecular reactions in a macroscopic volume may cause the volume's physical properties to change dynamically and thus reveal much about the reactions. As an example, experimental time series for so-called microtubule oscillations are analyzed in terms of a minimal model...... for this complex polymerization-depolymerization cycle. The model reproduces well the qualitatively different time series that result from different experimental conditions, and illuminates the role and importance of individual processes in the cycle. Simple experiments are suggested that can further test...... and define the model and the polymer's reaction cycle....

  13. Microtubule bundling plays a role in ethylene-mediated cortical microtubule reorientation in etiolated Arabidopsis hypocotyls.

    Science.gov (United States)

    Ma, Qianqian; Sun, Jingbo; Mao, Tonglin

    2016-05-15

    The gaseous hormone ethylene is known to regulate plant growth under etiolated conditions (the 'triple response'). Although organization of cortical microtubules is essential for cell elongation, the underlying mechanisms that regulate microtubule organization by hormone signaling, including ethylene, are ambiguous. In the present study, we demonstrate that ethylene signaling participates in regulation of cortical microtubule reorientation. In particular, regulation of microtubule bundling is important for this process in etiolated hypocotyls. Time-lapse analysis indicated that selective stabilization of microtubule-bundling structures formed in various arrays is related to ethylene-mediated microtubule orientation. Bundling events and bundle growth lifetimes were significantly increased in oblique and longitudinal arrays, but decreased in transverse arrays in wild-type cells in response to ethylene. However, the effects of ethylene on microtubule bundling were partially suppressed in a microtubule-bundling protein WDL5 knockout mutant (wdl5-1). This study suggests that modulation of microtubule bundles that have formed in certain orientations plays a role in reorienting microtubule arrays in response to ethylene-mediated etiolated hypocotyl cell elongation. © 2016. Published by The Company of Biologists Ltd.

  14. Moonlighting microtubule-associated proteins: regulatory functions by day and pathological functions at night.

    Science.gov (United States)

    Oláh, J; Tőkési, N; Lehotzky, A; Orosz, F; Ovádi, J

    2013-11-01

    The sensing, integrating, and coordinating features of the eukaryotic cells are achieved by the complex ultrastructural arrays and multifarious functions of the cytoskeletal network. Cytoskeleton comprises fibrous protein networks of microtubules, actin, and intermediate filaments. These filamentous polymer structures are highly dynamic and undergo constant and rapid reorganization during cellular processes. The microtubular system plays a crucial role in the brain, as it is involved in an enormous number of cellular events including cell differentiation and pathological inclusion formation. These multifarious functions of microtubules can be achieved by their decoration with proteins/enzymes that exert specific effects on the dynamics and organization of the cytoskeleton and mediate distinct functions due to their moonlighting features. This mini-review focuses on two aspects of the microtubule cytoskeleton. On the one hand, we describe the heteroassociation of tubulin/microtubules with metabolic enzymes, which in addition to their catalytic activities stabilize microtubule structures via their cross-linking functions. On the other hand, we focus on the recently identified moonlighting tubulin polymerization promoting protein, TPPP/p25. TPPP/p25 is a microtubule-associated protein and it displays distinct physiological or pathological (aberrant) functions; thus it is a prototype of Neomorphic Moonlighting Proteins. The expression of TPPP/p25 is finely controlled in the human brain; this protein is indispensable for the development of projections of oligodendrocytes that are responsible for the ensheathment of axons. The nonphysiological, higher or lower TPPP/p25 level leads to distinct CNS diseases. Mechanisms contributing to the control of microtubule stability and dynamics by metabolic enzymes and TPPP/p25 will be discussed. Copyright © 2013 Wiley Periodicals, Inc.

  15. Structural stability of nonlinear population dynamics.

    Science.gov (United States)

    Cenci, Simone; Saavedra, Serguei

    2018-01-01

    In population dynamics, the concept of structural stability has been used to quantify the tolerance of a system to environmental perturbations. Yet, measuring the structural stability of nonlinear dynamical systems remains a challenging task. Focusing on the classic Lotka-Volterra dynamics, because of the linearity of the functional response, it has been possible to measure the conditions compatible with a structurally stable system. However, the functional response of biological communities is not always well approximated by deterministic linear functions. Thus, it is unclear the extent to which this linear approach can be generalized to other population dynamics models. Here, we show that the same approach used to investigate the classic Lotka-Volterra dynamics, which is called the structural approach, can be applied to a much larger class of nonlinear models. This class covers a large number of nonlinear functional responses that have been intensively investigated both theoretically and experimentally. We also investigate the applicability of the structural approach to stochastic dynamical systems and we provide a measure of structural stability for finite populations. Overall, we show that the structural approach can provide reliable and tractable information about the qualitative behavior of many nonlinear dynamical systems.

  16. Structural stability of nonlinear population dynamics

    Science.gov (United States)

    Cenci, Simone; Saavedra, Serguei

    2018-01-01

    In population dynamics, the concept of structural stability has been used to quantify the tolerance of a system to environmental perturbations. Yet, measuring the structural stability of nonlinear dynamical systems remains a challenging task. Focusing on the classic Lotka-Volterra dynamics, because of the linearity of the functional response, it has been possible to measure the conditions compatible with a structurally stable system. However, the functional response of biological communities is not always well approximated by deterministic linear functions. Thus, it is unclear the extent to which this linear approach can be generalized to other population dynamics models. Here, we show that the same approach used to investigate the classic Lotka-Volterra dynamics, which is called the structural approach, can be applied to a much larger class of nonlinear models. This class covers a large number of nonlinear functional responses that have been intensively investigated both theoretically and experimentally. We also investigate the applicability of the structural approach to stochastic dynamical systems and we provide a measure of structural stability for finite populations. Overall, we show that the structural approach can provide reliable and tractable information about the qualitative behavior of many nonlinear dynamical systems.

  17. Vehicle lateral dynamics stabilization using active suspension

    Directory of Open Access Journals (Sweden)

    Drobný V.

    2008-12-01

    Full Text Available The paper deals with the investigation of active nonlinear suspension control in order to stabilize the lateral vehicle motion in similar way as systems like ESP do. The lateral stabilization of vehicle based on braking forces can be alternatively provided by the different setting of suspension forces. The basis of this control is the nonlinear property of the tyres. The vehicle has at least four wheels and it gives one or more redundant vertical forces that can be used for the different distribution of vertical suspension forces in such a way that resulting lateral and/or longitudinal forces create the required correction moment for lateral dynamic vehicle stabilization.

  18. Dynamic stabilization of imploding liquid metal liner

    International Nuclear Information System (INIS)

    Itoh, Yasuyuki; Fujiie, Yoichi

    1979-01-01

    The rotational stabilization has been proposed against the Rayleigh-Taylor instability of the imploding liquid metal liner. In this paper, the discussion is made on the possibility of the dynamic stabilization by applying the oscillating azimuthal magnetic field in addition to the axial field. In contrast to the rotational stabilization, the required (field) energy for this stabilization is also used for the liner driving or the plasma confinement. In the analysis, the liner subjected to the acceleration is assumed to be infinitely long, at rest and have the situation at the start of the implosion or turnaround. At turnaround, the existence of the plasma is taken into account. The perturbed motion of the liner is discussed with a linear stability analysis. Results are as follows: (1) The dynamic stabilization at the start of the implosion is possible if the distance from the conducting wall to the liner outer surface is comparable with or less than the liner thickness. (2) At turnaround, the stability is improved with decreasing the ratio of the plasma radius to that of the liner inner surface however the kink mode (m = 1) cannot be suppressed. (author)

  19. The use of compressive sensing and peak detection in the reconstruction of microtubules length time series in the process of dynamic instability.

    Science.gov (United States)

    Mahrooghy, Majid; Yarahmadian, Shantia; Menon, Vineetha; Rezania, Vahid; Tuszynski, Jack A

    2015-10-01

    Microtubules (MTs) are intra-cellular cylindrical protein filaments. They exhibit a unique phenomenon of stochastic growth and shrinkage, called dynamic instability. In this paper, we introduce a theoretical framework for applying Compressive Sensing (CS) to the sampled data of the microtubule length in the process of dynamic instability. To reduce data density and reconstruct the original signal with relatively low sampling rates, we have applied CS to experimental MT lament length time series modeled as a Dichotomous Markov Noise (DMN). The results show that using CS along with the wavelet transform significantly reduces the recovery errors comparing in the absence of wavelet transform, especially in the low and the medium sampling rates. In a sampling rate ranging from 0.2 to 0.5, the Root-Mean-Squared Error (RMSE) decreases by approximately 3 times and between 0.5 and 1, RMSE is small. We also apply a peak detection technique to the wavelet coefficients to detect and closely approximate the growth and shrinkage of MTs for computing the essential dynamic instability parameters, i.e., transition frequencies and specially growth and shrinkage rates. The results show that using compressed sensing along with the peak detection technique and wavelet transform in sampling rates reduces the recovery errors for the parameters. Copyright © 2015 Elsevier Ltd. All rights reserved.

  20. Dynamic stability of a seaplane in takeoff

    CSIR Research Space (South Africa)

    Dala, L

    2015-01-01

    Full Text Available This research is based on the investigation into the dynamic stability associated with seaplanes during take-off. Various forces acting on a hydroplaning hull form have been empirically defined. Such empirical data have shown that under a certain...

  1. An analytical method for solving exact solutions of a nonlinear evolution equation describing the dynamics of ionic currents along microtubules

    Directory of Open Access Journals (Sweden)

    Md. Nur Alam

    2017-11-01

    Full Text Available In this article, a variety of solitary wave solutions are observed for microtubules (MTs. We approach the problem by treating the solutions as nonlinear RLC transmission lines and then find exact solutions of Nonlinear Evolution Equations (NLEEs involving parameters of special interest in nanobiosciences and biophysics. We determine hyperbolic, trigonometric, rational and exponential function solutions and obtain soliton-like pulse solutions for these equations. A comparative study against other methods demonstrates the validity of the technique that we developed and demonstrates that our method provides additional solutions. Finally, using suitable parameter values, we plot 2D and 3D graphics of the exact solutions that we observed using our method. Keywords: Analytical method, Exact solutions, Nonlinear evolution equations (NLEEs of microtubules, Nonlinear RLC transmission lines

  2. Dynamic large eddy simulation: Stability via realizability

    Science.gov (United States)

    Mokhtarpoor, Reza; Heinz, Stefan

    2017-10-01

    The concept of dynamic large eddy simulation (LES) is highly attractive: such methods can dynamically adjust to changing flow conditions, which is known to be highly beneficial. For example, this avoids the use of empirical, case dependent approximations (like damping functions). Ideally, dynamic LES should be local in physical space (without involving artificial clipping parameters), and it should be stable for a wide range of simulation time steps, Reynolds numbers, and numerical schemes. These properties are not trivial, but dynamic LES suffers from such problems over decades. We address these questions by performing dynamic LES of periodic hill flow including separation at a high Reynolds number Re = 37 000. For the case considered, the main result of our studies is that it is possible to design LES that has the desired properties. It requires physical consistency: a PDF-realizable and stress-realizable LES model, which requires the inclusion of the turbulent kinetic energy in the LES calculation. LES models that do not honor such physical consistency can become unstable. We do not find support for the previous assumption that long-term correlations of negative dynamic model parameters are responsible for instability. Instead, we concluded that instability is caused by the stable spatial organization of significant unphysical states, which are represented by wall-type gradient streaks of the standard deviation of the dynamic model parameter. The applicability of our realizability stabilization to other dynamic models (including the dynamic Smagorinsky model) is discussed.

  3. Dynamical stability in fluid-structure interaction

    International Nuclear Information System (INIS)

    Planchard, J.; Thomas, B.

    1991-01-01

    The aim of the paper is to investigate the dynamical stability of a group of elastic tubes placed in a cross-flow which obeys to the Navier-Stokes equations. The stability of this coupled system is deduced from the study of a quadratic eigenvalue problem arising in the linearized equations. The instability occurs when the real part of one of the eigenvalues becomes positive; the steady state is then replaced by a time-periodic state which is stable (Hopf bifurcation phenomenon). Some numerical methods for solving the quadratic eigenvalue problem are described [fr

  4. SDF1 Reduces Interneuron Leading Process Branching through Dual Regulation of Actin and Microtubules

    Science.gov (United States)

    Lysko, Daniel E.; Putt, Mary

    2014-01-01

    Normal cerebral cortical function requires a highly ordered balance between projection neurons and interneurons. During development these two neuronal populations migrate from distinct progenitor zones to form the cerebral cortex, with interneurons originating in the more distant ganglionic eminences. Moreover, deficits in interneurons have been linked to a variety of neurodevelopmental disorders underscoring the importance of understanding interneuron development and function. We, and others, have identified SDF1 signaling as one important modulator of interneuron migration speed and leading process branching behavior in mice, although how SDF1 signaling impacts these behaviors remains unknown. We previously found SDF1 inhibited leading process branching while increasing the rate of migration. We have now mechanistically linked SDF1 modulation of leading process branching behavior to a dual regulation of both actin and microtubule organization. We find SDF1 consolidates actin at the leading process tip by de-repressing calpain protease and increasing proteolysis of branched-actin-supporting cortactin. Additionally, SDF1 stabilizes the microtubule array in the leading process through activation of the microtubule-associated protein doublecortin (DCX). DCX stabilizes the microtubule array by bundling microtubules within the leading process, reducing branching. These data provide mechanistic insight into the regulation of interneuron leading process dynamics during neuronal migration in mice and provides insight into how cortactin and DCX, a known human neuronal migration disorder gene, participate in this process. PMID:24695713

  5. SDF1 reduces interneuron leading process branching through dual regulation of actin and microtubules.

    Science.gov (United States)

    Lysko, Daniel E; Putt, Mary; Golden, Jeffrey A

    2014-04-02

    Normal cerebral cortical function requires a highly ordered balance between projection neurons and interneurons. During development these two neuronal populations migrate from distinct progenitor zones to form the cerebral cortex, with interneurons originating in the more distant ganglionic eminences. Moreover, deficits in interneurons have been linked to a variety of neurodevelopmental disorders underscoring the importance of understanding interneuron development and function. We, and others, have identified SDF1 signaling as one important modulator of interneuron migration speed and leading process branching behavior in mice, although how SDF1 signaling impacts these behaviors remains unknown. We previously found SDF1 inhibited leading process branching while increasing the rate of migration. We have now mechanistically linked SDF1 modulation of leading process branching behavior to a dual regulation of both actin and microtubule organization. We find SDF1 consolidates actin at the leading process tip by de-repressing calpain protease and increasing proteolysis of branched-actin-supporting cortactin. Additionally, SDF1 stabilizes the microtubule array in the leading process through activation of the microtubule-associated protein doublecortin (DCX). DCX stabilizes the microtubule array by bundling microtubules within the leading process, reducing branching. These data provide mechanistic insight into the regulation of interneuron leading process dynamics during neuronal migration in mice and provides insight into how cortactin and DCX, a known human neuronal migration disorder gene, participate in this process.

  6. TCS1, a Microtubule-Binding Protein, Interacts with KCBP/ZWICHEL to Regulate Trichome Cell Shape in Arabidopsis thaliana.

    Directory of Open Access Journals (Sweden)

    Liangliang Chen

    2016-10-01

    Full Text Available How cell shape is controlled is a fundamental question in developmental biology, but the genetic and molecular mechanisms that determine cell shape are largely unknown. Arabidopsis trichomes have been used as a good model system to investigate cell shape at the single-cell level. Here we describe the trichome cell shape 1 (tcs1 mutants with the reduced trichome branch number in Arabidopsis. TCS1 encodes a coiled-coil domain-containing protein. Pharmacological analyses and observations of microtubule dynamics show that TCS1 influences the stability of microtubules. Biochemical analyses and live-cell imaging indicate that TCS1 binds to microtubules and promotes the assembly of microtubules. Further results reveal that TCS1 physically associates with KCBP/ZWICHEL, a microtubule motor involved in the regulation of trichome branch number. Genetic analyses indicate that kcbp/zwi is epistatic to tcs1 with respect to trichome branch number. Thus, our findings define a novel genetic and molecular mechanism by which TCS1 interacts with KCBP to regulate trichome cell shape by influencing the stability of microtubules.

  7. Explaining the Microtubule Energy Balance: Contributions Due to Dipole Moments, Charges, van der Waals and Solvation Energy

    Directory of Open Access Journals (Sweden)

    Ahmed Taha Ayoub

    2017-09-01

    Full Text Available Microtubules are the main components of mitotic spindles, and are the pillars of the cellular cytoskeleton. They perform most of their cellular functions by virtue of their unique dynamic instability processes which alternate between polymerization and depolymerization phases. This in turn is driven by a precise balance between attraction and repulsion forces between the constituents of microtubules (MTs—tubulin dimers. Therefore, it is critically important to know what contributions result in a balance of the interaction energy among tubulin dimers that make up microtubules and what interactions may tip this balance toward or away from a stable polymerized state of tubulin. In this paper, we calculate the dipole–dipole interaction energy between tubulin dimers in a microtubule as part of the various contributions to the energy balance. We also compare the remaining contributions to the interaction energies between tubulin dimers and establish a balance between stabilizing and destabilizing components, including the van der Waals, electrostatic, and solvent-accessible surface area energies. The energy balance shows that the GTP-capped tip of the seam at the plus end of microtubules is stabilized only by − 9 kcal/mol, which can be completely reversed by the hydrolysis of a single GTP molecule, which releases + 14 kcal/mol and destabilizes the seam by an excess of + 5 kcal/mol. This triggers the breakdown of microtubules and initiates a disassembly phase which is aptly called a catastrophe.

  8. Trait diversity promotes stability of community dynamics

    DEFF Research Database (Denmark)

    Zhang, Lai; Thygesen, Uffe Høgsbro; Knudsen, Kim

    2013-01-01

    body size. The dynamic properties of the models are described by a stability analysis of equilibrium solutions and by the non-equilibrium dynamics. We find that the introduction of trait diversity expands the set of parameters for which the equilibrium is stable and, if the community is unstable, makes....... The analysis is performed by comparing the properties of two size spectrum models. The first model considers all individuals as belonging to the same “average” species, i.e., without a description of diversity. The second model introduces diversity by further considering individuals by a trait, here asymptotic...

  9. TIPsy tour guides: How microtubule plus-end tracking proteins (+TIPs facilitate axon guidance

    Directory of Open Access Journals (Sweden)

    Elizabeth A Bearce

    2015-06-01

    Full Text Available The growth cone is a dynamic cytoskeletal vehicle, which drives the end of a developing axon. It serves to interpret and navigate through the complex landscape and guidance cues of the early nervous system. The growth cone’s distinctive cytoskeletal organization offers a fascinating platform to study how extracellular cues can be translated into mechanical outgrowth and turning behaviors. While many studies of cell motility highlight the importance of actin networks in signaling, adhesion, and propulsion, both seminal and emerging works in the field have highlighted a unique and necessary role for microtubules in growth cone navigation. Here, we focus on the role of singular pioneer microtubules, which extend into the growth cone periphery and are regulated by a diverse family of microtubule plus-end tracking proteins (+TIPs. These +TIPs accumulate at the dynamic ends of microtubules, where they are well-positioned to encounter and respond to key signaling events downstream of guidance receptors, catalyzing immediate changes in microtubule stability and actin cross-talk, that facilitate both axonal outgrowth and turning events.

  10. YB-1 promotes microtubule assembly in vitro through interaction with tubulin and microtubules

    Directory of Open Access Journals (Sweden)

    Baconnais Sonia

    2008-09-01

    Full Text Available Abstract Background YB-1 is a major regulator of gene expression in eukaryotic cells. In addition to its role in transcription, YB-1 plays a key role in translation and stabilization of mRNAs. Results We show here that YB-1 interacts with tubulin and microtubules and stimulates microtubule assembly in vitro. High resolution imaging via electron and atomic force microscopy revealed that microtubules assembled in the presence of YB-1 exhibited a normal single wall ultrastructure and indicated that YB-1 most probably coats the outer microtubule wall. Furthermore, we found that YB-1 also promotes the assembly of MAPs-tubulin and subtilisin-treated tubulin. Finally, we demonstrated that tubulin interferes with RNA:YB-1 complexes. Conclusion These results suggest that YB-1 may regulate microtubule assembly in vivo and that its interaction with tubulin may contribute to the control of mRNA translation.

  11. Dynamic postural stability during advancing pregnancy.

    Science.gov (United States)

    McCrory, J L; Chambers, A J; Daftary, A; Redfern, M S

    2010-08-26

    Pregnant women are at an increased risk of experiencing a fall. Numerous anatomical, physiological, and hormonal alterations occur during pregnancy, but the influence of these factors on dynamic postural stability has not been explored. The purpose of this study was to examine dynamic postural stability in pregnant women during their second and third trimesters as well as in a group of non-pregnant control women. Eighty-one women (41 pregnant, 40 controls) participated stood on a force plate that translated anteroposteriorly at small, medium, and large magnitudes. Reaction time and center of pressure (COP) movement during the translations were analyzed. Trimester, perturbation direction, and perturbation magnitude were the independent variables in a mixed-model analysis of variance on each of the following dependent variables: reaction time, initial sway, total sway, and sway velocity. Reaction time to the perturbation was not significantly different between the groups. Initial sway, total sway, and sway velocity were significantly less during the third trimester than during the second trimester and when compared to the non-pregnant controls (Ppostural stability. 2010 Elsevier Ltd. All rights reserved.

  12. Rho-associated coiled-coil kinase (ROCK) protein controls microtubule dynamics in a novel signaling pathway that regulates cell migration.

    Science.gov (United States)

    Schofield, Alice V; Steel, Rohan; Bernard, Ora

    2012-12-21

    The two members of the Rho-associated coiled-coil kinase (ROCK1 and 2) family are established regulators of actin dynamics that are involved in the regulation of the cell cycle as well as cell motility and invasion. Here, we discovered a novel signaling pathway whereby ROCK regulates microtubule (MT) acetylation via phosphorylation of the tubulin polymerization promoting protein 1 (TPPP1/p25). We show that ROCK phosphorylation of TPPP1 inhibits the interaction between TPPP1 and histone deacetylase 6 (HDAC6), which in turn results in increased HDAC6 activity followed by a decrease in MT acetylation. As a consequence, we show that TPPP1 phosphorylation by ROCK increases cell migration and invasion via modulation of cellular acetyl MT levels. We establish here that the ROCK-TPPP1-HDAC6 signaling pathway is important for the regulation of cell migration and invasion.

  13. Microtubules Growth Rate Alteration in Human Endothelial Cells

    Directory of Open Access Journals (Sweden)

    Irina B. Alieva

    2010-01-01

    Full Text Available To understand how microtubules contribute to the dynamic reorganization of the endothelial cell (EC cytoskeleton, we established an EC model expressing EB3-GFP, a protein that marks microtubule plus-ends. Using this model, we were able to measure microtubule growth rate at the centrosome region and near the cell periphery of a single human EC and in the EC monolayer. We demonstrate that the majority of microtubules in EC are dynamic, the growth rate of their plus-ends is highest in the internal cytoplasm, in the region of the centrosome. Growth rate of microtubule plus-ends decreases from the cell center toward the periphery. Our data suggest the existing mechanism(s of local regulation of microtubule plus-ends growth in EC. Microtubule growth rate in the internal cytoplasm of EC in the monolayer is lower than that of single EC suggesting the regulatory effect of cell-cell contacts. Centrosomal microtubule growth rate distribution in single EC indicated the presence of two subpopulations of microtubules with “normal” (similar to those in monolayer EC and “fast” (three times as much growth rates. Our results indicate functional interactions between cell-cell contacts and microtubules.

  14. Dynamical stability of slip-stacking particles

    Energy Technology Data Exchange (ETDEWEB)

    Eldred, Jeffrey; Zwaska, Robert

    2014-09-01

    We study the stability of particles in slip-stacking configuration, used to nearly double proton beam intensity at Fermilab. We introduce universal area factors to calculate the available phase space area for any set of beam parameters without individual simulation. We find perturbative solutions for stable particle trajectories. We establish Booster beam quality requirements to achieve 97% slip-stacking efficiency. We show that slip-stacking dynamics directly correspond to the driven pendulum and to the system of two standing-wave traps moving with respect to each other.

  15. Beam stability & nonlinear dynamics. Formal report

    Energy Technology Data Exchange (ETDEWEB)

    Parsa, Z. [ed.

    1996-12-31

    his Report includes copies of transparencies and notes from the presentations made at the Symposium on Beam Stability and Nonlinear Dynamics, December 3-5, 1996 at the Institute for Theoretical Physics, University of California, Santa Barbara California, that was made available by the authors. Editing, reduction and changes to the authors contributions were made only to fulfill the printing and publication requirements. We would like to take this opportunity and thank the speakers for their informative presentations and for providing copies of their transparencies and notes for inclusion in this Report.

  16. Beam stability ampersand nonlinear dynamics. Formal report

    International Nuclear Information System (INIS)

    Parsa, Z.

    1996-01-01

    This report includes copies of transparencies and notes from the presentations made at the Symposium on Beam Stability and Nonlinear Dynamics, December 3-5, 1996 at the Institute for Theoretical Physics, University of California, Santa Barbara California, that was made available by the authors. Editing, reduction and changes to the authors contributions were made only to fulfill the printing and publication requirements. We would like to take this opportunity and thank the speakers for their informative presentations and for providing copies of their transparencies and notes for inclusion in this Report

  17. Stochastic Dynamics Underlying Cognitive Stability and Flexibility.

    Directory of Open Access Journals (Sweden)

    Kai Ueltzhöffer

    2015-06-01

    updating and dopaminergic modulation of cognitive flexibility. These results show that stochastic dynamical systems can implement the basic computations underlying cognitive stability and flexibility and explain neurobiological bases of individual differences.

  18. BWR stability using a reducing dynamical model

    International Nuclear Information System (INIS)

    Ballestrin Bolea, J. M.; Blazquez Martinez, J. B.

    1990-01-01

    BWR stability can be treated with reduced order dynamical models. When the parameters of the model came from dynamical models. When the parameters of the model came from experimental data, the predictions are accurate. In this work an alternative derivation for the void fraction equation is made, but remarking the physical structure of the parameters. As the poles of power/reactivity transfer function are related with the parameters, the measurement of the poles by other techniques such as noise analysis will lead to the parameters, but the system of equations is non-linear. Simple parametric calculation of decay ratio are performed, showing why BWRs become unstable when they are operated at low flow and high power. (Author)

  19. Dynamic stabilization of disruption precursors in tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Maoquan, Wang; Jianshan, Mao; Yuan, Pan [Academia Sinica, Hefei, AH (China). Inst. of Plasma Physics

    1994-12-01

    A method for dynamic stabilization of the disruption precursors in tokamak is proposed, that is a controlled ac current induced and added to the equilibrium current. The ac currents applied can be a sine alternative current with a relevant frequency, or a pulsed current with a suitable pulsed width {tau} and or a discontinuous pulsed current whose width {tau} is very shorter than the intervals between pulses, and or a `sawtooth` pulsed current with the time of ramp phase of the sawtooth is very much shorter than the sawtooth descending time, the ratio of them can be {<=}10{sup -3}. The physical model of the ac current drive is analyzed in detail. The suppression role of the ac current on the MHD perturbations was analyzed in theory and proved numerically. It is indicated that the ac current can make the discontinuous derivative, {Delta}`, more favorable for the tearing mode stabilities, and so, as long as the parameters of the applied ac currents are selected suitably, the MHD perturbations can be suppressed effectively, the perturbations will be in the zero-growing state, the profile of the plasma current and temperature remain in the initial states and not variate basically, the tokamak be in the stabilized operation state. (8 figs.).

  20. Dynamic stability of an aerodynamically efficient motorcycle

    Science.gov (United States)

    Sharma, Amrit; Limebeer, David J. N.

    2012-08-01

    Motorcycles exhibit two potentially dangerous oscillatory modes known as 'wobble' and 'weave'. The former is reminiscent of supermarket castor shimmy, while the latter is a low frequency 'fish-tailing' motion that involves a combination of rolling, yawing, steering and side-slipping motions. These unwanted dynamic features, which can occur when two-wheeled vehicles are operated at speed, have been studied extensively. The aim of this paper is to use mathematical analysis to identify important stability trends in the on-going design of a novel aerodynamically efficient motorcycle known as the ECOSSE Spirit ES1. A mathematical model of the ES1 is developed using a multi-body dynamics software package called VehicleSim [Anon, VehicleSim Lisp Reference Manual Version 1.0, Mechanical Simulation Corporation, 2008. Available at http://www.carsim.com]. This high-fidelity motorcycle model includes realistic tyre-road contact geometry, a comprehensive tyre model, tyre relaxation and a flexible frame. A parameter set representative of a modern high-performance machine and rider is used. Local stability is investigated via the eigenvalues of the linearised models that are associated with equilibrium points of interest. A comprehensive study of the effects of frame flexibilities, acceleration, aerodynamics and tyre variations is presented, and an optimal passive steering compensator is derived. It is shown that the traditional steering damper cannot be used to stabilise the ES1 over its entire operating speed range. A simple passive compensator, involving an inerter is proposed. Flexibility can be introduced deliberately into various chassis components to change the stability characteristics of the vehicle; the implications of this idea are studied.

  1. Novel Microtubule-Stabilizing Reagents

    National Research Council Canada - National Science Library

    Bulinski, Chloe J

    2005-01-01

    ... [1]. Taxanes are widely used to halt breast tumors, because they block mitosis and metastasis, and promote apoptosis, though some breast cancers are unpredictably refractory to taxanes, even at levels...

  2. ANALYSIS AND OPTIMISATION OF DYNAMIC STABILITY OF MOBILE WORKING MACHINES

    Directory of Open Access Journals (Sweden)

    Peter BIGOŠ

    2014-09-01

    Full Text Available This paper describes an investigation of the dynamic stability, which is specified for the mobile working machines. There are presented the basic theoretical principles of the stability theory together with an introduction of two illustrative examples of the dynamic stability analysis.

  3. BWR stability using a reduced dynamical model

    International Nuclear Information System (INIS)

    Ballestrin Bolea, J.M.; Blazquez, J.B.

    1990-01-01

    BWR stability can be treated with reduced order dynamical models. When the parameters of the model came from experimental data, the predictions are accurate. In this work an alternative derivation for the void fraction equation is made, but remarking the physical struct-ure of the parameters. As the poles of power/reactivity transfer function are related with the parameters, the measurement of the poles by other techniques such as noise analysis will lead to the parameters, but the system of equations in non-linear. Simple parametric calculat-ion of decay ratio are performed, showing why BWRs become unstable when they are operated at low flow and high power. (Author). 7 refs

  4. Microtubules: A network for solitary waves

    Directory of Open Access Journals (Sweden)

    Zdravković Slobodan

    2017-01-01

    Full Text Available In the present paper we deal with nonlinear dynamics of microtubules. The structure and role of microtubules in cells are explained as well as one of models explaining their dynamics. Solutions of the crucial nonlinear differential equation depend on used mathematical methods. Two commonly used procedures, continuum and semi-discrete approximations, are explained. These solutions are solitary waves usually called as kink solitons, breathers and bell-type solitons. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III45010

  5. Stability of molecular dynamics simulations of classical systems

    DEFF Research Database (Denmark)

    Toxværd, Søren

    2012-01-01

    The existence of a shadow Hamiltonian for discrete classical dynamics, obtained by an asymptotic expansion for a discrete symplectic algorithm, is employed to determine the limit of stability for molecular dynamics (MD) simulations with respect to the time-increment h of the discrete dynamics....... The investigation is based on the stability of the shadow energy, obtained by including the first term in the asymptotic expansion, and on the exact solution of discrete dynamics for a single harmonic mode. The exact solution of discrete dynamics for a harmonic potential with frequency ω gives a criterion...... for the limit of stability h ⩽ 2/ω. Simulations of the Lennard-Jones system and the viscous Kob-Andersen system show that one can use the limit of stability of the shadow energy or the stability criterion for a harmonic mode on the spectrum of instantaneous frequencies to determine the limit of stability of MD...

  6. Multiscale modeling and simulation of microtubule-motor-protein assemblies

    Science.gov (United States)

    Gao, Tong; Blackwell, Robert; Glaser, Matthew A.; Betterton, M. D.; Shelley, Michael J.

    2015-12-01

    Microtubules and motor proteins self-organize into biologically important assemblies including the mitotic spindle and the centrosomal microtubule array. Outside of cells, microtubule-motor mixtures can form novel active liquid-crystalline materials driven out of equilibrium by adenosine triphosphate-consuming motor proteins. Microscopic motor activity causes polarity-dependent interactions between motor proteins and microtubules, but how these interactions yield larger-scale dynamical behavior such as complex flows and defect dynamics is not well understood. We develop a multiscale theory for microtubule-motor systems in which Brownian dynamics simulations of polar microtubules driven by motors are used to study microscopic organization and stresses created by motor-mediated microtubule interactions. We identify polarity-sorting and crosslink tether relaxation as two polar-specific sources of active destabilizing stress. We then develop a continuum Doi-Onsager model that captures polarity sorting and the hydrodynamic flows generated by these polar-specific active stresses. In simulations of active nematic flows on immersed surfaces, the active stresses drive turbulent flow dynamics and continuous generation and annihilation of disclination defects. The dynamics follow from two instabilities, and accounting for the immersed nature of the experiment yields unambiguous characteristic length and time scales. When turning off the hydrodynamics in the Doi-Onsager model, we capture formation of polar lanes as observed in the Brownian dynamics simulation.

  7. Multiscale modeling and simulation of microtubule-motor-protein assemblies.

    Science.gov (United States)

    Gao, Tong; Blackwell, Robert; Glaser, Matthew A; Betterton, M D; Shelley, Michael J

    2015-01-01

    Microtubules and motor proteins self-organize into biologically important assemblies including the mitotic spindle and the centrosomal microtubule array. Outside of cells, microtubule-motor mixtures can form novel active liquid-crystalline materials driven out of equilibrium by adenosine triphosphate-consuming motor proteins. Microscopic motor activity causes polarity-dependent interactions between motor proteins and microtubules, but how these interactions yield larger-scale dynamical behavior such as complex flows and defect dynamics is not well understood. We develop a multiscale theory for microtubule-motor systems in which Brownian dynamics simulations of polar microtubules driven by motors are used to study microscopic organization and stresses created by motor-mediated microtubule interactions. We identify polarity-sorting and crosslink tether relaxation as two polar-specific sources of active destabilizing stress. We then develop a continuum Doi-Onsager model that captures polarity sorting and the hydrodynamic flows generated by these polar-specific active stresses. In simulations of active nematic flows on immersed surfaces, the active stresses drive turbulent flow dynamics and continuous generation and annihilation of disclination defects. The dynamics follow from two instabilities, and accounting for the immersed nature of the experiment yields unambiguous characteristic length and time scales. When turning off the hydrodynamics in the Doi-Onsager model, we capture formation of polar lanes as observed in the Brownian dynamics simulation.

  8. S. pombe kinesins-8 promote both nucleation and catastrophe of microtubules.

    Directory of Open Access Journals (Sweden)

    Muriel Erent

    Full Text Available The kinesins-8 were originally thought to be microtubule depolymerases, but are now emerging as more versatile catalysts of microtubule dynamics. We show here that S. pombe Klp5-436 and Klp6-440 are non-processive plus-end-directed motors whose in vitro velocities on S. pombe microtubules at 7 and 23 nm s(-1 are too slow to keep pace with the growing tips of dynamic interphase microtubules in living S. pombe. In vitro, Klp5 and 6 dimers exhibit a hitherto-undescribed combination of strong enhancement of microtubule nucleation with no effect on growth rate or catastrophe frequency. By contrast in vivo, both Klp5 and Klp6 promote microtubule catastrophe at cell ends whilst Klp6 also increases the number of interphase microtubule arrays (IMAs. Our data support a model in which Klp5/6 bind tightly to free tubulin heterodimers, strongly promoting the nucleation of new microtubules, and then continue to land as a tubulin-motor complex on the tips of growing microtubules, with the motors then dissociating after a few seconds residence on the lattice. In vivo, we predict that only at cell ends, when growing microtubule tips become lodged and their growth slows down, will Klp5/6 motor activity succeed in tracking growing microtubule tips. This mechanism would allow Klp5/6 to detect the arrival of microtubule tips at cells ends and to amplify the intrinsic tendency for microtubules to catastrophise in compression at cell ends. Our evidence identifies Klp5 and 6 as spatial regulators of microtubule dynamics that enhance both microtubule nucleation at the cell centre and microtubule catastrophe at the cell ends.

  9. Expansion and Polarity Sorting in Microtubule-Dynein Bundles(WHAT IS LIFE? THE NEXT 100 YEARS OF YUKAWA'S DREAM)

    OpenAIRE

    Assaf, ZEMEL; Alex, MOGILNER; Department of Neurobiology, Physiology and Behavior, University of California; Department of Neurobiology, Physiology and Behavior, University of California

    2008-01-01

    Interactions of multiple molecular motors with dynamic polymers, such as actin and microtubules, form the basis for many processes in the cell cytoskeleton. One example is the active 'sorting' of microtubule bundles by dynein molecular motors into aster-like arrays of microtubules; in these bundles dynein motors cross-link and slide neighboring microtubules apart. A number of models have been suggested to quantify the active dynamics of cross-linked bundles of polar filaments. In the case of ...

  10. Electrodynamic effects on microtubules

    Czech Academy of Sciences Publication Activity Database

    Kučera, Ondřej; Havelka, Daniel; Deriu, M.A.; Cifra, Michal

    2015-01-01

    Roč. 44, Jul (2015), s. 169-169 ISSN 0175-7571. [10th European-Biophysical-Societies-Association (EBSA) European Biophysics Congress. 18.07.2015-22.07.2015, Dresden] R&D Projects: GA ČR(CZ) GA15-17102S Institutional support: RVO:67985882 Keywords : Microtubules * Electric al polarity Subject RIV: JA - Electronics ; Optoelectronics, Electric al Engineering

  11. Microtubule's conformational cap

    DEFF Research Database (Denmark)

    Flyvbjerg, H.

    1999-01-01

    The molecular mechanisms that allow elongation of the unstable microtubule lattice remain unclear. It is usually thought that the GDP-liganded tubulin lattice is capped by a small layer of GTP- or GDP-P(i)-liganded molecules, the so called "GTP-cap". Here, we point-out that the elastic properties...

  12. Nanojets: Electrification, Energetics, Dynamics, Stability and Breakup

    National Research Council Canada - National Science Library

    Landman, Uzi

    2006-01-01

    Simulation methodologies, algorithms, and computer codes allowing molecular dynamics simulations of formation, propagation, and breakup processes of nanojets, generated either through the application...

  13. Learning and Understanding System Stability Using Illustrative Dynamic Texture Examples

    Science.gov (United States)

    Liu, Huaping; Xiao, Wei; Zhao, Hongyan; Sun, Fuchun

    2014-01-01

    System stability is a basic concept in courses on dynamic system analysis and control for undergraduate students with computer science backgrounds. Typically, this was taught using a simple simulation example of an inverted pendulum. Unfortunately, many difficult issues arise in the learning and understanding of the concepts of stability,…

  14. Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

    KAUST Repository

    Shroll, Andrew P.; Shanbhogue, Santosh J.; Ghoniem, Ahmed F.

    2012-01-01

    This work explores the dynamic stability characteristics of premixed CH 4/O 2/CO 2 mixtures in a 50 kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different dilution levels of carbon dioxide used

  15. The Microtubule Regulatory Protein Stathmin Is Required to Maintain the Integrity of Axonal Microtubules in Drosophila

    Science.gov (United States)

    Duncan, Jason E.; Lytle, Nikki K.; Zuniga, Alfredo; Goldstein, Lawrence S. B.

    2013-01-01

    Axonal transport, a form of long-distance, bi-directional intracellular transport that occurs between the cell body and synaptic terminal, is critical in maintaining the function and viability of neurons. We have identified a requirement for the stathmin (stai) gene in the maintenance of axonal microtubules and regulation of axonal transport in Drosophila . The stai gene encodes a cytosolic phosphoprotein that regulates microtubule dynamics by partitioning tubulin dimers between pools of soluble tubulin and polymerized microtubules, and by directly binding to microtubules and promoting depolymerization. Analysis of stai function in Drosophila , which has a single stai gene, circumvents potential complications with studies performed in vertebrate systems in which mutant phenotypes may be compensated by genetic redundancy of other members of the stai gene family. This has allowed us to identify an essential function for stai in the maintenance of the integrity of axonal microtubules. In addition to the severe disruption in the abundance and architecture of microtubules in the axons of stai mutant Drosophila , we also observe additional neurological phenotypes associated with loss of stai function including a posterior paralysis and tail-flip phenotype in third instar larvae, aberrant accumulation of transported membranous organelles in stai deficient axons, a progressive bang-sensitive response to mechanical stimulation reminiscent of the class of Drosophila mutants used to model human epileptic seizures, and a reduced adult lifespan. Reductions in the levels of Kinesin-1, the primary anterograde motor in axonal transport, enhance these phenotypes. Collectively, our results indicate that stai has an important role in neuronal function, likely through the maintenance of microtubule integrity in the axons of nerves of the peripheral nervous system necessary to support and sustain long-distance axonal transport. PMID:23840848

  16. Stability of large scale interconnected dynamical systems

    International Nuclear Information System (INIS)

    Akpan, E.P.

    1993-07-01

    Large scale systems modelled by a system of ordinary differential equations are considered and necessary and sufficient conditions are obtained for the uniform asymptotic connective stability of the systems using the method of cone-valued Lyapunov functions. It is shown that this model significantly improves the existing models. (author). 9 refs

  17. On atmospheric stability in the dynamic wake meandering model

    DEFF Research Database (Denmark)

    Keck, Rolf-Erik; de Mare, Martin Tobias; Churchfield, Matthew J.

    2014-01-01

    The present study investigates a new approach for capturing the effects of atmospheric stability on wind turbine wake evolution and wake meandering by using the dynamic wake meandering model. The most notable impact of atmospheric stability on the wind is the changes in length and velocity scales...... spectra and applied to the dynamic wake meandering model to capture the correct wake meandering behaviour. The ambient turbulence in all stability classes is generated using the Mann turbulence model, where the effects of non-neutral atmospheric stability are approximated by the selection of input...... in the computational domain. The changes in the turbulent length scales due to the various atmospheric stability states impact the wake meandering characteristics and thus the power generation by the individual turbines. The proposed method is compared with results from both large-eddy simulation coupled...

  18. Stability analysis of host dynamics for hiv

    Science.gov (United States)

    Geetha, V.; Balamuralitharan, S.

    2018-04-01

    The phenomenon of disease modeling can be easily accomplished through mathematical framework. In this paper the transmission of disease in human is represented mathematically as a nonlinear system. We think about the components of the Human Immunodeficiency Virus (HIV) among the beginning periods of illness. Throughout this paper we have determined those logical representation of a three-compartmental HIV demonstrate for their stability evaluation. We tend to likewise explore the stimulating behavior of the model and acquire those Steady states for the disease-free and the endemic agreement. The framework can be evaluated by reproduction number R0. We additionally clarify the numerical recreation and their outcomes.

  19. Microtubule and Cell Contact Dependency of ER-bound PTP1B Localization in Growth Cones

    Science.gov (United States)

    Fuentes, Federico

    2009-01-01

    PTP1B is an ER-bound protein tyrosine phosphatase implied in the regulation of cell adhesion. Here we investigated mechanisms involved in the positioning and dynamics of PTP1B in axonal growth cones and evaluated the role of this enzyme in axons. In growth cones, PTP1B consistently localizes in the central domain, and occasionally at the peripheral region and filopodia. Live imaging of GFP-PTP1B reveals dynamic excursions of fingerlike processes within the peripheral region and filopodia. PTP1B and GFP-PTP1B colocalize with ER markers and coalign with microtubules at the peripheral region and redistribute to the base of the growth cone after treatment with nocodazole, a condition that is reversible. Growth cone contact with cellular targets is accompanied by invasion of PTP1B and stable microtubules in the peripheral region aligned with the contact axis. Functional impairment of PTP1B causes retardation of axon elongation, as well as reduction of growth cone filopodia lifetime and Src activity. Our results highlight the role of microtubules and cell contacts in the positioning of ER-bound PTP1B to the peripheral region of growth cones, which may be required for the positive role of PTP1B in axon elongation, filopodia stabilization, and Src activity. PMID:19158394

  20. Synchronous Oscillations in Microtubule Polymerization

    Science.gov (United States)

    Carlier, M. F.; Melki, R.; Pantaloni, D.; Hill, T. L.; Chen, Y.

    1987-08-01

    Under conditions where microtubule nucleation and growth are fast (i.e., high magnesium ion and tubulin concentrations and absence of glycerol), microtubule assembly in vitro exhibits an oscillatory regime preceding the establishment of steady state. The amplitude of the oscillations can represent >50% of the maximum turbidity change and oscillations persist for up to 20 periods of 80 s each. Oscillations are accompanied by extensive length redistribution of microtubules. Preliminary work suggests that the oscillatory kinetics can be simulated using a model in which many microtubules undergo synchronous transitions between growing and rapidly depolymerizing phases, complicated by the kinetically limiting rate of nucleotide exchange on free tubulin.

  1. Effects of the KIF2C neck peptide on microtubules: lateral disintegration of microtubules and β-structure formation.

    Science.gov (United States)

    Shimizu, Youské; Shimizu, Takashi; Nara, Masayuki; Kikumoto, Mahito; Kojima, Hiroaki; Morii, Hisayuki

    2013-04-01

    Members of the kinesin-13 sub-family, including KIF2C, depolymerize microtubules. The positive charge-rich 'neck' region extending from the N-terminus of the catalytic head is considered to be important in the depolymerization activity. Chemically synthesized peptides, covering the basic region (A182-E200), induced a sigmoidal increase in the turbidity of a microtubule suspension. The increase was suppressed by salt addition or by reduction of basicity by amino acid substitutions. Electron microscopic observations revealed ring structures surrounding the microtubules at high peptide concentrations. Using the peptide A182-D218, we also detected free thin straight filaments, probably protofilaments disintegrated from microtubules. Therefore, the neck region, even without the catalytic head domain, may induce lateral disintegration of microtubules. With microtubules lacking anion-rich C-termini as a result of subtilisin treatment, addition of the peptide induced only a moderate increase in turbidity, and rings and protofilaments were rarely detected, while aggregations, also thought to be caused by lateral disintegration, were often observed in electron micrographs. Thus, the C-termini are not crucial for the action of the peptides in lateral disintegration but contribute to structural stabilization of the protofilaments. Previous structural studies indicated that the neck region of KIF2C is flexible, but our IR analysis suggests that the cation-rich region (K190-A204) forms β-structure in the presence of microtubules, which may be of significance with regard to the action of the neck region. Therefore, the neck region of KIF2C is sufficient to cause disintegration of microtubules into protofilaments, and this may contribute to the ability of KIF2C to cause depolymerization of microtubules. © 2013 The Authors Journal compilation © 2013 FEBS.

  2. Handbook of electrical power system dynamics modeling, stability, and control

    CERN Document Server

    Eremia, Mircea

    2013-01-01

    Complete guidance for understanding electrical power system dynamics and blackouts This handbook offers a comprehensive and up-to-date treatment of power system dynamics. Addressing the full range of topics, from the fundamentals to the latest technologies in modeling, stability, and control, Handbook of Electrical Power System Dynamics provides engineers with hands-on guidance for understanding the phenomena leading to blackouts so they can design the most appropriate solutions for a cost-effective and reliable operation. Focusing on system dynamics, the book details

  3. Dynamics and Stability of Permanent-Magnet Synchronous Motor

    OpenAIRE

    He, Ren; Han, Qingzhen

    2017-01-01

    The aim of this article is to explore the dynamic characteristics and stability of the permanent-magnet synchronous motor (PMSM). PMSM equilibrium local stability condition and Hopf  bifurcation condition, pitchfork bifurcation condition, and fold bifurcation condition have been derived by using the Routh-Hurwitz criterion and the bifurcation theory, respectively. Bifurcation curves of the equilibrium with single and double parameters are obtained by continuation method. Numerical simulations...

  4. Dynamic stability of passive dynamic walking on an irregular surface.

    Science.gov (United States)

    Su, Jimmy Li-Shin; Dingwell, Jonathan B

    2007-12-01

    Falls that occur during walking are a significant health problem. One of the greatest impediments to solve this problem is that there is no single obviously "correct" way to quantify walking stability. While many people use variability as a proxy for stability, measures of variability do not quantify how the locomotor system responds to perturbations. The purpose of this study was to determine how changes in walking surface variability affect changes in both locomotor variability and stability. We modified an irreducibly simple model of walking to apply random perturbations that simulated walking over an irregular surface. Because the model's global basin of attraction remained fixed, increasing the amplitude of the applied perturbations directly increased the risk of falling in the model. We generated ten simulations of 300 consecutive strides of walking at each of six perturbation amplitudes ranging from zero (i.e., a smooth continuous surface) up to the maximum level the model could tolerate without falling over. Orbital stability defines how a system responds to small (i.e., "local") perturbations from one cycle to the next and was quantified by calculating the maximum Floquet multipliers for the model. Local stability defines how a system responds to similar perturbations in real time and was quantified by calculating short-term and long-term local exponential rates of divergence for the model. As perturbation amplitudes increased, no changes were seen in orbital stability (r(2)=2.43%; p=0.280) or long-term local instability (r(2)=1.0%; p=0.441). These measures essentially reflected the fact that the model never actually "fell" during any of our simulations. Conversely, the variability of the walker's kinematics increased exponentially (r(2)>or=99.6%; psimulated conditions, the walker remained orbitally stable, while exhibiting substantial local instability. This was because very small initial perturbations diverged away from the limit cycle, while larger

  5. Dynamic stability and bifurcation analysis in fractional thermodynamics

    Science.gov (United States)

    Béda, Péter B.

    2018-02-01

    In mechanics, viscoelasticity was the first field of applications in studying geomaterials. Further possibilities arise in spatial non-locality. Non-local materials were already studied in the 1960s by several authors as a part of continuum mechanics and are still in focus of interest because of the rising importance of materials with internal micro- and nano-structure. When material instability gained more interest, non-local behavior appeared in a different aspect. The problem was concerned to numerical analysis, because then instability zones exhibited singular properties for local constitutive equations. In dynamic stability analysis, mathematical aspects of non-locality were studied by using the theory of dynamic systems. There the basic set of equations describing the behavior of continua was transformed to an abstract dynamic system consisting of differential operators acting on the perturbation field variables. Such functions should satisfy homogeneous boundary conditions and act as indicators of stability of a selected state of the body under consideration. Dynamic systems approach results in conditions for cases, when the differential operators have critical eigenvalues of zero real parts (dynamic stability or instability conditions). When the critical eigenvalues have non-trivial eigenspace, the way of loss of stability is classified as a typical (or generic) bifurcation. Our experiences show that material non-locality and the generic nature of bifurcation at instability are connected, and the basic functions of the non-trivial eigenspace can be used to determine internal length quantities of non-local mechanics. Fractional calculus is already successfully used in thermo-elasticity. In the paper, non-locality is introduced via fractional strain into the constitutive relations of various conventional types. Then, by defining dynamic systems, stability and bifurcation are studied for states of thermo-mechanical solids. Stability conditions and genericity

  6. Deciphering the imprint of topology on nonlinear dynamical network stability

    International Nuclear Information System (INIS)

    Nitzbon, J; Schultz, P; Heitzig, J; Kurths, J; Hellmann, F

    2017-01-01

    Coupled oscillator networks show complex interrelations between topological characteristics of the network and the nonlinear stability of single nodes with respect to large but realistic perturbations. We extend previous results on these relations by incorporating sampling-based measures of the transient behaviour of the system, its survivability, as well as its asymptotic behaviour, its basin stability. By combining basin stability and survivability we uncover novel, previously unknown asymptotic states with solitary, desynchronized oscillators which are rotating with a frequency different from their natural one. They occur almost exclusively after perturbations at nodes with specific topological properties. More generally we confirm and significantly refine the results on the distinguished role tree-shaped appendices play for nonlinear stability. We find a topological classification scheme for nodes located in such appendices, that exactly separates them according to their stability properties, thus establishing a strong link between topology and dynamics. Hence, the results can be used for the identification of vulnerable nodes in power grids or other coupled oscillator networks. From this classification we can derive general design principles for resilient power grids. We find that striving for homogeneous network topologies facilitates a better performance in terms of nonlinear dynamical network stability. While the employed second-order Kuramoto-like model is parametrised to be representative for power grids, we expect these insights to transfer to other critical infrastructure systems or complex network dynamics appearing in various other fields. (paper)

  7. Solar Dynamic Power System Stability Analysis and Control

    Science.gov (United States)

    Momoh, James A.; Wang, Yanchun

    1996-01-01

    The objective of this research is to conduct dynamic analysis, control design, and control performance test of solar power system. Solar power system consists of generation system and distribution network system. A bench mark system is used in this research, which includes a generator with excitation system and governor, an ac/dc converter, six DDCU's and forty-eight loads. A detailed model is used for modeling generator. Excitation system is represented by a third order model. DDCU is represented by a seventh order system. The load is modeled by the combination of constant power and constant impedance. Eigen-analysis and eigen-sensitivity analysis are used for system dynamic analysis. The effects of excitation system, governor, ac/dc converter control, and the type of load on system stability are discussed. In order to improve system transient stability, nonlinear ac/dc converter control is introduced. The direct linearization method is used for control design. The dynamic analysis results show that these controls affect system stability in different ways. The parameter coordination of controllers are recommended based on the dynamic analysis. It is concluded from the present studies that system stability is improved by the coordination of control parameters and the nonlinear ac/dc converter control stabilize system oscillation caused by the load change and system fault efficiently.

  8. Does dynamic stability govern propulsive force generation in human walking?

    Science.gov (United States)

    Browne, Michael G; Franz, Jason R

    2017-11-01

    Before succumbing to slower speeds, older adults may walk with a diminished push-off to prioritize stability over mobility. However, direct evidence for trade-offs between push-off intensity and balance control in human walking, independent of changes in speed, has remained elusive. As a critical first step, we conducted two experiments to investigate: (i) the independent effects of walking speed and propulsive force ( F P ) generation on dynamic stability in young adults, and (ii) the extent to which young adults prioritize dynamic stability in selecting their preferred combination of walking speed and F P generation. Subjects walked on a force-measuring treadmill across a range of speeds as well as at constant speeds while modulating their F P according to a visual biofeedback paradigm based on real-time force measurements. In contrast to improvements when walking slower, walking with a diminished push-off worsened dynamic stability by up to 32%. Rather, we find that young adults adopt an F P at their preferred walking speed that maximizes dynamic stability. One implication of these findings is that the onset of a diminished push-off in old age may independently contribute to poorer balance control and precipitate slower walking speeds.

  9. Capture of microtubule plus-ends at the actin cortex promotes axophilic neuronal migration by enhancing microtubule tension in the leading process.

    Science.gov (United States)

    Hutchins, B Ian; Wray, Susan

    2014-01-01

    Microtubules are a critical part of neuronal polarity and leading process extension, thus microtubule movement plays an important role in neuronal migration. However, the dynamics of microtubules during the forward movement of the nucleus into the leading process (nucleokinesis) is unclear and may be dependent on the cell type and mode of migration used. In particular, little is known about cytoskeletal changes during axophilic migration, commonly used in anteroposterior neuronal migration. We recently showed that leading process actin flow in migrating GnRH neurons is controlled by a signaling cascade involving IP3 receptors, CaMKK, AMPK, and RhoA. In the present study, microtubule dynamics were examined in GnRH neurons. Failure of the migration of these cells leads to the neuroendocrine disorder Kallmann Syndrome. Microtubules translocated forward along the leading process shaft during migration, but reversed direction and moved toward the nucleus when migration stalled. Blocking calcium release through IP3 receptors halted migration and induced the same reversal of microtubule translocation, while blocking cortical actin flow prevented microtubules from translocating toward the distal leading process. Super-resolution imaging revealed that microtubule plus-end tips are captured at the actin cortex through calcium-dependent mechanisms. This work shows that cortical actin flow draws the microtubule network forward through calcium-dependent capture in order to promote nucleokinesis, revealing a novel mechanism engaged by migrating neurons to facilitate movement.

  10. Innovation networking between stability and political dynamics

    DEFF Research Database (Denmark)

    Koch, Christian

    2004-01-01

    of the contribution is to challenge and transcend these notions and develop an understanding of innovation networks as an interplay between stable and dynamic elements, where political processes in innovation are much more than a disruptive and even a counterproductive feature. It reviews the growing number...... of studies that highlight the political aspect of innovation. The paper reports on a study of innovation processes conducted within the EU—TSER-programme and a study made under the banner of management of technology. Intensive field studies in two constellations of enterprises were carried out. One......This contribution views innovation as a social activity of building networks, using software product development in multicompany alliances and networks as example. Innovation networks are frequently understood as quite stable arrangements characterised by high trust among the participants. The aim...

  11. Sync in Complex Dynamical Networks: Stability, Evolution, Control, and Application

    OpenAIRE

    Li, Xiang

    2005-01-01

    In the past few years, the discoveries of small-world and scale-free properties of many natural and artificial complex networks have stimulated significant advances in better understanding the relationship between the topology and the collective dynamics of complex networks. This paper reports recent progresses in the literature of synchronization of complex dynamical networks including stability criteria, network synchronizability and uniform synchronous criticality in different topologies, ...

  12. PWL approximation of nonlinear dynamical systems, part I: structural stability

    International Nuclear Information System (INIS)

    Storace, M; De Feo, O

    2005-01-01

    This paper and its companion address the problem of the approximation/identification of nonlinear dynamical systems depending on parameters, with a view to their circuit implementation. The proposed method is based on a piecewise-linear approximation technique. In particular, this paper describes the approximation method and applies it to some particularly significant dynamical systems (topological normal forms). The structural stability of the PWL approximations of such systems is investigated through a bifurcation analysis (via continuation methods)

  13. Microtubules as mechanical force sensors.

    Science.gov (United States)

    Karafyllidis, Ioannis G; Lagoudas, Dimitris C

    2007-03-01

    Microtubules are polymers of tubulin subunits (dimers) arranged on a hexagonal lattice. Each tubulin dimer comprises two monomers, the alpha-tubulin and beta-tubulin, and can be found in two states. In the first state a mobile negative charge is located into the alpha-tubulin monomer and in the second into the beta-tubulin monomer. Each tubulin dimer is modeled as an electrical dipole coupled to its neighbors by electrostatic forces. The location of the mobile charge in each dimer depends on the location of the charges in the dimer's neighborhood. Mechanical forces that act on the microtubule affect the distances between the dimers and alter the electrostatic potential. Changes in this potential affect the mobile negative charge location in each dimer and the charge distribution in the microtubule. The net effect is that mechanical forces affect the charge distribution in microtubules. We propose to exploit this effect and use microtubules as mechanical force sensors. We model each dimer as a two-state quantum system and, following the quantum computation paradigm, we use discrete quantum random walk on the hexagonal microtubule lattice to determine the charge distribution. Different forces applied on the microtubule are modeled as different coin biases leading to different probability distributions of the quantum walker location, which are directly connected to different charge distributions. Simulation results show that there is a strong indication that microtubules can be used as mechanical force sensors and that they can also detect the force directions and magnitudes.

  14. TgICMAP1 is a novel microtubule binding protein in Toxoplasma gondii.

    Directory of Open Access Journals (Sweden)

    Aoife T Heaslip

    Full Text Available The microtubule cytoskeleton provides essential structural support for all eukaryotic cells and can be assembled into various higher order structures that perform drastically different functions. Understanding how microtubule-containing assemblies are built in a spatially and temporally controlled manner is therefore fundamental to understanding cell physiology. Toxoplasma gondii, a protozoan parasite, contains at least five distinct tubulin-containing structures, the spindle pole, centrioles, cortical microtubules, the conoid, and the intra-conoid microtubules. How these five structurally and functionally distinct sets of tubulin containing structures are constructed and maintained in the same cell is an intriguing problem. Previously, we performed a proteomic analysis of the T. gondii apical complex, a cytoskeletal complex located at the apical end of the parasite that is composed of the conoid, three ring-like structures, and the two short intra-conoid microtubules. Here we report the characterization of one of the proteins identified in that analysis, TgICMAP1. We show that TgICMAP1 is a novel microtubule binding protein that can directly bind to microtubules in vitro and stabilizes microtubules when ectopically expressed in mammalian cells. Interestingly, in T. gondii, TgICMAP1 preferentially binds to the intra-conoid microtubules, providing us the first molecular tool to investigate the intra-conoid microtubule assembly process during daughter construction.

  15. Arabidopsis FH1 Formin Affects Cotyledon Pavement Cell Shape by Modulating Cytoskeleton Dynamics.

    Science.gov (United States)

    Rosero, Amparo; Oulehlová, Denisa; Stillerová, Lenka; Schiebertová, Petra; Grunt, Michal; Žárský, Viktor; Cvrčková, Fatima

    2016-03-01

    Plant cell morphogenesis involves concerted rearrangements of microtubules and actin microfilaments. We previously reported that FH1, the main Arabidopsis thaliana housekeeping Class I membrane-anchored formin, contributes to actin dynamics and microtubule stability in rhizodermis cells. Here we examine the effects of mutations affecting FH1 (At3g25500) on cell morphogenesis and above-ground organ development in seedlings, as well as on cytoskeletal organization and dynamics, using a combination of confocal and variable angle epifluorescence microscopy with a pharmacological approach. Homozygous fh1 mutants exhibited cotyledon epinasty and had larger cotyledon pavement cells with more pronounced lobes than the wild type. The pavement cell shape alterations were enhanced by expression of the fluorescent microtubule marker GFP-microtubule-associated protein 4 (MAP4). Mutant cotyledon pavement cells exhibited reduced density and increased stability of microfilament bundles, as well as enhanced dynamics of microtubules. Analogous results were also obtained upon treatments with the formin inhibitor SMIFH2 (small molecule inhibitor of formin homology 2 domains). Pavement cell shape in wild-type (wt) and fh1 plants in some situations exhibited a differential response towards anti-cytoskeletal drugs, especially the microtubule disruptor oryzalin. Our observations indicate that FH1 participates in the control of microtubule dynamics, possibly via its effects on actin, subsequently influencing cell morphogenesis and macroscopic organ development. © The Author 2016. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.

  16. Criteria for stability of linear dynamical systems with multiple delays ...

    African Journals Online (AJOL)

    In this study we considered a linear Dynamical system with multiple delays and find suitable conditions on the systems parameters such that for a given initial function, we can define a mapping in a carefully chosen complete metric space on which the mapping has a unique fixed point. An asymptotic stability theory for the ...

  17. Stability of nanofluids: Molecular dynamic approach and experimental study

    International Nuclear Information System (INIS)

    Farzaneh, H.; Behzadmehr, A.; Yaghoubi, M.; Samimi, A.; Sarvari, S.M.H.

    2016-01-01

    Highlights: • Nanofluid stability is investigated and discussed. • A molecular dynamic approach, considering different forces on the nanoparticles, is adopted. • Stability diagrams are presented for different thermo-fluid conditions. • An experimental investigation is carried out to confirm the theoretical approach. - Abstract: Nanofluids as volumetric absorbent in solar energy conversion devices or as working fluid in different heat exchangers have been proposed by various researchers. However, dispersion stability of nanofluids is an important issue that must be well addressed before any industrial applications. Conditions such as severe temperature gradient, high temperature of heat transfer fluid, nanoparticle mean diameters and types of nanoparticles and base fluid are among the most effective parameters on the stability of nanofluid. A molecular dynamic approach, considering kinetic energy of nanoparticles and DLVO potential energy between nanoparticles, is adopted to study the nanofluid stability for different nanofluids at different working conditions. Different forces such as Brownian, thermophoresis, drag and DLVO are considered to introduce the stability diagrams. The latter presents the conditions for which a nanofluid can be stable. In addition an experimental investigation is carried out to find a stable nanofluid and to show the validity of the theoretical approach. There is a good agreement between the experimental and theoretical results that confirms the validity of our theoretical approach.

  18. Differentiable dynamical systems an introduction to structural stability and hyperbolicity

    CERN Document Server

    Wen, Lan

    2016-01-01

    This is a graduate text in differentiable dynamical systems. It focuses on structural stability and hyperbolicity, a topic that is central to the field. Starting with the basic concepts of dynamical systems, analyzing the historic systems of the Smale horseshoe, Anosov toral automorphisms, and the solenoid attractor, the book develops the hyperbolic theory first for hyperbolic fixed points and then for general hyperbolic sets. The problems of stable manifolds, structural stability, and shadowing property are investigated, which lead to a highlight of the book, the \\Omega-stability theorem of Smale. While the content is rather standard, a key objective of the book is to present a thorough treatment for some tough material that has remained an obstacle to teaching and learning the subject matter. The treatment is straightforward and hence could be particularly suitable for self-study. Selected solutions are available electronically for instructors only. Please send email to textbooks@ams.org for more informatio...

  19. Attitude Dynamics and Stability of a Simple Solar Photon Thruster

    Directory of Open Access Journals (Sweden)

    Anna D. Guerman

    2013-01-01

    Full Text Available This paper is dedicated to the development of a model of the attitude dynamics for a nonideal Simple Solar Photon Thruster (SSPT and to the analysis of sailcraft motions with respect to their centre of mass. Derivation of the expressions for force and torque due to solar radiation that is valid for the case, when there is a misalignment of the SSPT axis with the sun direction, is followed by study of sailcraft dynamics and stability properties. Analysis of stability shows that an ideally reflecting sail is unstable, while for a sailcraft with nonideal collector, the symmetry axis is stable with respect to the Sun direction for large variety of system parameters. The motion around symmetry axis is always unstable and requires an active stabilizer.

  20. A structural model for microtubule minus-end recognition and protection by CAMSAP proteins

    NARCIS (Netherlands)

    Atherton, Joseph; Jiang, Kai; Stangier, Marcel M.; Luo, Yanzhang; Hua, Shasha; Houben, Klaartje; Van Hooff, Jolien J.E.; Joseph, Agnel Praveen; Scarabelli, Guido; Grant, Barry J.; Roberts, Anthony J.; Topf, Maya; Steinmetz, Michel O.; Baldus, Marc; Moores, Carolyn A.; Akhmanova, Anna

    2017-01-01

    CAMSAP and Patronin family members regulate microtubule minus-end stability and localization and thus organize noncentrosomal microtubule networks, which are essential for cell division, polarization and differentiation. Here, we found that the CAMSAP C-terminal CKK domain is widely present among

  1. Stability theory for dynamic equations on time scales

    CERN Document Server

    Martynyuk, Anatoly A

    2016-01-01

    This monograph is a first in the world to present three approaches for stability analysis of solutions of dynamic equations. The first approach is based on the application of dynamic integral inequalities and the fundamental matrix of solutions of linear approximation of dynamic equations. The second is based on the generalization of the direct Lyapunovs method for equations on time scales, using scalar, vector and matrix-valued auxiliary functions. The third approach is the application of auxiliary functions (scalar, vector, or matrix-valued ones) in combination with differential dynamic inequalities. This is an alternative comparison method, developed for time continuous and time discrete systems. In recent decades, automatic control theory in the study of air- and spacecraft dynamics and in other areas of modern applied mathematics has encountered problems in the analysis of the behavior of solutions of time continuous-discrete linear and/or nonlinear equations of perturbed motion. In the book “Men of Ma...

  2. Dynamical behavior and Jacobi stability analysis of wound strings

    Science.gov (United States)

    Lake, Matthew J.; Harko, Tiberiu

    2016-06-01

    We numerically solve the equations of motion (EOM) for two models of circular cosmic string loops with windings in a simply connected internal space. Since the windings cannot be topologically stabilized, stability must be achieved (if at all) dynamically. As toy models for realistic compactifications, we consider windings on a small section of mathbb {R}^2, which is valid as an approximation to any simply connected internal manifold if the winding radius is sufficiently small, and windings on an S^2 of constant radius mathcal {R}. We then use Kosambi-Cartan-Chern (KCC) theory to analyze the Jacobi stability of the string equations and determine bounds on the physical parameters that ensure dynamical stability of the windings. We find that, for the same initial conditions, the curvature and topology of the internal space have nontrivial effects on the microscopic behavior of the string in the higher dimensions, but that the macroscopic behavior is remarkably insensitive to the details of the motion in the compact space. This suggests that higher-dimensional signatures may be extremely difficult to detect in the effective (3+1)-dimensional dynamics of strings compactified on an internal space, even if configurations with nontrivial windings persist over long time periods.

  3. Dynamical behavior and Jacobi stability analysis of wound strings

    Energy Technology Data Exchange (ETDEWEB)

    Lake, Matthew J. [Naresuan University, The Institute for Fundamental Study, ' ' The Tah Poe Academia Institute' ' , Phitsanulok (Thailand); Thailand Center of Excellence in Physics, Ministry of Education, Bangkok (Thailand); Harko, Tiberiu [Babes-Bolyai University, Department of Physics, Cluj-Napoca (Romania); University College London, Department of Mathematics, London (United Kingdom)

    2016-06-15

    We numerically solve the equations of motion (EOM) for two models of circular cosmic string loops with windings in a simply connected internal space. Since the windings cannot be topologically stabilized, stability must be achieved (if at all) dynamically. As toy models for realistic compactifications, we consider windings on a small section of R{sup 2}, which is valid as an approximation to any simply connected internal manifold if the winding radius is sufficiently small, and windings on an S{sup 2} of constant radius R. We then use Kosambi-Cartan-Chern (KCC) theory to analyze the Jacobi stability of the string equations and determine bounds on the physical parameters that ensure dynamical stability of the windings. We find that, for the same initial conditions, the curvature and topology of the internal space have nontrivial effects on the microscopic behavior of the string in the higher dimensions, but that the macroscopic behavior is remarkably insensitive to the details of the motion in the compact space. This suggests that higher-dimensional signatures may be extremely difficult to detect in the effective (3+1)-dimensional dynamics of strings compactified on an internal space, even if configurations with nontrivial windings persist over long time periods. (orig.)

  4. Dynamic postural stability in blind athletes using the biodex stability system.

    Science.gov (United States)

    Aydoğ, E; Aydoğ, S T; Cakci, A; Doral, M N

    2006-05-01

    Three systems affect the upright standing posture in humans - visual, vestibular, and somatosensory. It is well known that the visually impaired individuals have bad postural balance. On the other hand, it is a well documented fact that some sports can improve postural balance. Therefore, it is aimed in this study to evaluate the dynamic postural stability in goal-ball athletes. Twenty blind goal-ball players, 20 sighted and 20 sedentary blind controls were evaluated using the Biodex Stability System. Three adaptation trials and three test evaluations (a 20-second balance test at a platform stability of 8) were applied to the blind people, and to the sighted with eyes open and closed. Dynamic postural stability was measured on the basis of three indices: overall, anteroposterior, and mediolateral. Means of each test score were calculated. The tests results were compared for the blind athletes, sighted (with eyes open and closed) subjects, and sedentary blind people. There were significant differences between the results of the blind people and the sighted subjects with regards to all of the three indices. Although the stability of goal-ball players was better than sedentary blinds', only ML index values were statistically different (4.47 +/- 1.24 in the goal-ball players; 6.46 +/- 3.42 in the sedentary blind, p = 0.04). Dynamic postural stability was demonstrated to be affected by vision; and it was found that blind people playing goal-ball 1 - 2 days per week have higher ML stability than the sedentary sighted people.

  5. EML proteins in microtubule regulation and human disease.

    Science.gov (United States)

    Fry, Andrew M; O'Regan, Laura; Montgomery, Jessica; Adib, Rozita; Bayliss, Richard

    2016-10-15

    The EMLs are a conserved family of microtubule-associated proteins (MAPs). The founding member was discovered in sea urchins as a 77-kDa polypeptide that co-purified with microtubules. This protein, termed EMAP for echinoderm MAP, was the major non-tubulin component present in purified microtubule preparations made from unfertilized sea urchin eggs [J. Cell Sci. (1993) 104: , 445-450; J. Cell Sci. (1987) 87: (Pt 1), 71-84]. Orthologues of EMAP were subsequently identified in other echinoderms, such as starfish and sand dollar, and then in more distant eukaryotes, including flies, worms and vertebrates, where the name of ELP or EML (both for EMAP-like protein) has been adopted [BMC Dev. Biol. (2008) 8: , 110; Dev. Genes Evol. (2000) 210: , 2-10]. The common property of these proteins is their ability to decorate microtubules. However, whether they are associated with particular microtubule populations or exercise specific functions in different microtubule-dependent processes remains unknown. Furthermore, although there is limited evidence that they regulate microtubule dynamics, the biochemical mechanisms of their molecular activity have yet to be explored. Nevertheless, interest in these proteins has grown substantially because of the identification of EML mutations in neuronal disorders and oncogenic fusions in human cancers. Here, we summarize our current knowledge of the expression, localization and structure of what is proving to be an interesting and important class of MAPs. We also speculate about their function in microtubule regulation and highlight how the studies of EMLs in human diseases may open up novel avenues for patient therapy. © 2016 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

  6. On the dynamics of turbulent transport near marginal stability

    International Nuclear Information System (INIS)

    Diamond, P.H.; Hahm, T.S.

    1995-03-01

    A general methodology for describing the dynamics of transport near marginal stability is formulated. Marginal stability is a special case of the more general phenomenon of self-organized criticality. Simple, one field models of the dynamics of tokamak plasma self-organized criticality have been constructed, and include relevant features such as sheared mean flow and transport bifurcations. In such models, slow mode (i.e. large scale, low frequency transport events) correlation times determine the behavior of transport dynamics near marginal stability. To illustrate this, impulse response scaling exponents (z) and turbulent diffusivities (D) have been calculated for the minimal (Burgers) and sheared flow models. For the minimal model, z = 1 (indicating ballastic propagation) and D ∼(S 0 2 ) 1/3 , where S 0 2 is the noise strength. With an identically structured noise spectrum and flow with shearing rate exceeding the ambient decorrelation rate for the largest scale transport events, diffusion is recovered with z = 2 and D ∼ (S 0 2 ) 3/5 . This indicates a qualitative change in the dynamics, as well as a reduction in losses. These results are consistent with recent findings from ρ scaling scans. Several tokamak transport experiments are suggested

  7. Stabilization of computational procedures for constrained dynamical systems

    Science.gov (United States)

    Park, K. C.; Chiou, J. C.

    1988-01-01

    A new stabilization method of treating constraints in multibody dynamical systems is presented. By tailoring a penalty form of the constraint equations, the method achieves stabilization without artificial damping and yields a companion matrix differential equation for the constraint forces; hence, the constraint forces are obtained by integrating the companion differential equation for the constraint forces in time. A principal feature of the method is that the errors committed in each constraint condition decay with its corresponding characteristic time scale associated with its constraint force. Numerical experiments indicate that the method yields a marked improvement over existing techniques.

  8. The validity and reliability of a dynamic neuromuscular stabilization-heel sliding test for core stability.

    Science.gov (United States)

    Cha, Young Joo; Lee, Jae Jin; Kim, Do Hyun; You, Joshua Sung H

    2017-10-23

    Core stabilization plays an important role in the regulation of postural stability. To overcome shortcomings associated with pain and severe core instability during conventional core stabilization tests, we recently developed the dynamic neuromuscular stabilization-based heel sliding (DNS-HS) test. The purpose of this study was to establish the criterion validity and test-retest reliability of the novel DNS-HS test. Twenty young adults with core instability completed both the bilateral straight leg lowering test (BSLLT) and DNS-HS test for the criterion validity study and repeated the DNS-HS test for the test-retest reliability study. Criterion validity was determined by comparing hip joint angle data that were obtained from BSLLT and DNS-HS measures. The test-retest reliability was determined by comparing hip joint angle data. Criterion validity was (ICC2,3) = 0.700 (preliability was (ICC3,3) = 0.953 (pvalidity data demonstrated a good relationship between the gold standard BSLLT and DNS-HS core stability measures. Test-retest reliability data suggests that DNS-HS core stability was a reliable test for core stability. Clinically, the DNS-HS test is useful to objectively quantify core instability and allow early detection and evaluation.

  9. TONNEAU2/FASS Regulates the Geometry of Microtubule Nucleation and Cortical Array Organization in Interphase Arabidopsis Cells[C][W

    Science.gov (United States)

    Kirik, Angela; Ehrhardt, David W.; Kirik, Viktor

    2012-01-01

    Organization of microtubules into ordered arrays involves spatial and temporal regulation of microtubule nucleation. Here, we show that acentrosomal microtubule nucleation in plant cells involves a previously unknown regulatory step that determines the geometry of microtubule nucleation. Dynamic imaging of interphase cortical microtubules revealed that the ratio of branching to in-bundle microtubule nucleation on cortical microtubules is regulated by the Arabidopsis thaliana B′′ subunit of protein phosphatase 2A, which is encoded by the TONNEAU2/FASS (TON2) gene. The probability of nucleation from γ-tubulin complexes localized at the cell cortex was not affected by a loss of TON2 function, suggesting a specific role of TON2 in regulating the nucleation geometry. Both loss of TON2 function and ectopic targeting of TON2 to the plasma membrane resulted in defects in cell shape, suggesting the importance of TON2-mediated regulation of the microtubule cytoskeleton in cell morphogenesis. Loss of TON2 function also resulted in an inability for cortical arrays to reorient in response to light stimulus, suggesting an essential role for TON2 and microtubule branching nucleation in reorganization of microtubule arrays. Our data establish TON2 as a regulator of interphase microtubule nucleation and provide experimental evidence for a novel regulatory step in the process of microtubule-dependent nucleation. PMID:22395485

  10. Wood cell-wall structure requires local 2D-microtubule disassembly by a novel plasma membrane-anchored protein.

    Science.gov (United States)

    Oda, Yoshihisa; Iida, Yuki; Kondo, Yuki; Fukuda, Hiroo

    2010-07-13

    Plant cells have evolved cortical microtubules, in a two-dimensional space beneath the plasma membrane, that regulate patterning of cellulose deposition. Although recent studies have revealed that several microtubule-associated proteins facilitate self-organization of transverse cortical microtubules, it is still unknown how diverse patterns of cortical microtubules are organized in different xylem cells, which are the major components of wood. Using our newly established in vitro xylem cell differentiation system, we found that a novel microtubule end-tracking protein, microtubule depletion domain 1 (MIDD1), was anchored to distinct plasma membrane domains and promoted local microtubule disassembly, resulting in pits on xylem cell walls. The introduction of RNA interference for MIDD1 resulted in the failure of local microtubule depletion and the formation of secondary walls without pits. Conversely, the overexpression of MIDD1 reduced microtubule density. MIDD1 has two coiled-coil domains for the binding to microtubules and for the anchorage to plasma membrane domains, respectively. Combination of the two coils caused end tracking of microtubules during shrinkage and suppressed their rescue events. Our results indicate that MIDD1 integrates spatial information in the plasma membrane with cortical microtubule dynamics for determining xylem cell wall pattern. Copyright 2010 Elsevier Ltd. All rights reserved.

  11. Polyamine sharing between tubulin dimers favours microtubule nucleation and elongation via facilitated diffusion.

    Directory of Open Access Journals (Sweden)

    Alain Mechulam

    2009-01-01

    Full Text Available We suggest for the first time that the action of multivalent cations on microtubule dynamics can result from facilitated diffusion of GTP-tubulin to the microtubule ends. Facilitated diffusion can promote microtubule assembly, because, upon encountering a growing nucleus or the microtubule wall, random GTP-tubulin sliding on their surfaces will increase the probability of association to the target sites (nucleation sites or MT ends. This is an original explanation for understanding the apparent discrepancy between the high rate of microtubule elongation and the low rate of tubulin association at the microtubule ends in the viscous cytoplasm. The mechanism of facilitated diffusion requires an attraction force between two tubulins, which can result from the sharing of multivalent counterions. Natural polyamines (putrescine, spermidine, and spermine are present in all living cells and are potent agents to trigger tubulin self-attraction. By using an analytical model, we analyze the implication of facilitated diffusion mediated by polyamines on nucleation and elongation of microtubules. In vitro experiments using pure tubulin indicate that the promotion of microtubule assembly by polyamines is typical of facilitated diffusion. The results presented here show that polyamines can be of particular importance for the regulation of the microtubule network in vivo and provide the basis for further investigations into the effects of facilitated diffusion on cytoskeleton dynamics.

  12. Adaptive Dynamic Programming for Control Algorithms and Stability

    CERN Document Server

    Zhang, Huaguang; Luo, Yanhong; Wang, Ding

    2013-01-01

    There are many methods of stable controller design for nonlinear systems. In seeking to go beyond the minimum requirement of stability, Adaptive Dynamic Programming for Control approaches the challenging topic of optimal control for nonlinear systems using the tools of  adaptive dynamic programming (ADP). The range of systems treated is extensive; affine, switched, singularly perturbed and time-delay nonlinear systems are discussed as are the uses of neural networks and techniques of value and policy iteration. The text features three main aspects of ADP in which the methods proposed for stabilization and for tracking and games benefit from the incorporation of optimal control methods: • infinite-horizon control for which the difficulty of solving partial differential Hamilton–Jacobi–Bellman equations directly is overcome, and  proof provided that the iterative value function updating sequence converges to the infimum of all the value functions obtained by admissible control law sequences; • finite-...

  13. Dynamics and Stability of Permanent-Magnet Synchronous Motor

    Directory of Open Access Journals (Sweden)

    Ren He

    2017-01-01

    Full Text Available The aim of this article is to explore the dynamic characteristics and stability of the permanent-magnet synchronous motor (PMSM. PMSM equilibrium local stability condition and Hopf  bifurcation condition, pitchfork bifurcation condition, and fold bifurcation condition have been derived by using the Routh-Hurwitz criterion and the bifurcation theory, respectively. Bifurcation curves of the equilibrium with single and double parameters are obtained by continuation method. Numerical simulations not only confirm the theoretical analysis results but also show one kind of codimension-two-bifurcation points of the equilibrium. PMSM, with or without external load, can exhibit rich dynamic behaviors in different parameters regions. It is shown that if unstable equilibrium appears in the parameters regions, the PMSM may not be able to work stably. To ensure the PMSMs work stably, the inherent parameters should be designed in the region which has only one stable equilibrium.

  14. Direct Cytoplasmic Delivery and Nuclear Targeting Delivery of HPMA-MT Conjugates in a Microtubules Dependent Fashion.

    Science.gov (United States)

    Zhong, Jiaju; Zhu, Xi; Luo, Kui; Li, Lian; Tang, Manlin; Liu, Yanxi; Zhou, Zhou; Huang, Yuan

    2016-09-06

    As the hearts of tumor cells, the nucleus is the ultimate target of many chemotherapeutic agents and genes. However, nuclear drug delivery is always hampered by multiple intracellular obstacles, such as low efficiency of lysosome escape and insufficient nuclear trafficking. Herein, an N-(2-hydroxypropyl) methacrylamide (HPMA) polymer-based drug delivery system was designed, which could achieve direct cytoplasmic delivery by a nonendocytic pathway and transport into the nucleus in a microtubules dependent fashion. A special targeting peptide (MT), derived from an endogenic parathyroid hormone-related protein, was conjugated to the polymer backbone, which could accumulate into the nucleus a by microtubule-mediated pathway. The in vitro studies found that low temperature and NaN3 could not influence the cell internalization of the conjugates. Besides, no obvious overlay of the conjugates with lysosome demonstrated that the polymer conjugates could enter the tumor cell cytoplasm by a nonendocytic pathway, thus avoiding the drug degradation in the lysosome. Furthermore, after suppression of the microtubule dynamics with microtubule stabilizing docetaxel (DTX) and destabilizing nocodazole (Noc), the nuclear accumulation of polymeric conjugates was significantly inhibited. Living cells fluorescence recovery after photobleaching study found that the nuclear import rate of conjugates was 2-fold faster compared with the DTX and Noc treated groups. These results demonstrated that the conjugates transported into the nucleus in a microtubules dependent way. Therefore, in addition to direct cytoplasmic delivery, our peptide conjugated polymeric platform could simultaneously mediate nuclear drug accumulation, which may open a new path for further intracellular genes/peptides delivery.

  15. Synthesis and biological evaluation of structurally simplified noscapine analogues as microtubule binding agents

    Czech Academy of Sciences Publication Activity Database

    Ghaly, P.E.; Churchill, C.D.M.; Abou El-Magd, R.M.; Hájková, Zuzana; Dráber, Pavel; West, F.G.; Tuszyński, J.A.

    2017-01-01

    Roč. 95, č. 6 (2017), s. 649-655 ISSN 0008-4042 R&D Projects: GA ČR GA15-22194S Institutional support: RVO:68378050 Keywords : noscapine * microtubule * tubulin * cytotoxicity * microtubule dynamics * docking Subject RIV: EB - Genetics ; Molecular Biology OBOR OECD: Biochemistry and molecular biology Impact factor: 1.080, year: 2016

  16. Dynamic remedial action scheme using online transient stability analysis

    Science.gov (United States)

    Shrestha, Arun

    Economic pressure and environmental factors have forced the modern power systems to operate closer to their stability limits. However, maintaining transient stability is a fundamental requirement for the operation of interconnected power systems. In North America, power systems are planned and operated to withstand the loss of any single or multiple elements without violating North American Electric Reliability Corporation (NERC) system performance criteria. For a contingency resulting in the loss of multiple elements (Category C), emergency transient stability controls may be necessary to stabilize the power system. Emergency control is designed to sense abnormal conditions and subsequently take pre-determined remedial actions to prevent instability. Commonly known as either Remedial Action Schemes (RAS) or as Special/System Protection Schemes (SPS), these emergency control approaches have been extensively adopted by utilities. RAS are designed to address specific problems, e.g. to increase power transfer, to provide reactive support, to address generator instability, to limit thermal overloads, etc. Possible remedial actions include generator tripping, load shedding, capacitor and reactor switching, static VAR control, etc. Among various RAS types, generation shedding is the most effective and widely used emergency control means for maintaining system stability. In this dissertation, an optimal power flow (OPF)-based generation-shedding RAS is proposed. This scheme uses online transient stability calculation and generator cost function to determine appropriate remedial actions. For transient stability calculation, SIngle Machine Equivalent (SIME) technique is used, which reduces the multimachine power system model to a One-Machine Infinite Bus (OMIB) equivalent and identifies critical machines. Unlike conventional RAS, which are designed using offline simulations, online stability calculations make the proposed RAS dynamic and adapting to any power system

  17. Dynamical stability of the holographic system with two competing orders

    Energy Technology Data Exchange (ETDEWEB)

    Du, Yiqiang [School of Physics, University of Chinese Academy of Sciences,Beijing 100049 (China); Lan, Shan-Quan [Department of Physics, Beijing Normal University,Beijing 100875 (China); Tian, Yu [School of Physics, University of Chinese Academy of Sciences,Beijing 100049 (China); State Key Laboratory of Theoretical Physics,Institute of Theoretical Physics, Chinese Academy of Science,Beijing 100190 (China); Zhang, Hongbao [Department of Physics, Beijing Normal University,Beijing 100875 (China); Theoretische Natuurkunde, Vrije Universiteit Brussel and The International Solvay Institutes,Pleinlaan 2, B-1050 Brussels (Belgium)

    2016-01-04

    We investigate the dynamical stability of the holographic system with two order parameters, which exhibits competition and coexistence of condensations. In the linear regime, we have developed the gauge dependent formalism to calculate the quasi-normal modes by gauge fixing, which turns out be considerably convenient. Furthermore, by giving different Gaussian wave packets as perturbations at the initial time, we numerically evolve the full nonlinear system until it arrives at the final equilibrium state. Our results show that the dynamical stability is consistent with the thermodynamical stability. Interestingly, the dynamical evolution, as well as the quasi-normal modes, shows that the relaxation time of this model is generically much longer than the simplest holographic system. We also find that the late time behavior can be well captured by the lowest lying quasi-normal modes except for the non-vanishing order towards the single ordered phase. To our knowledge, this exception is the first counter example to the general belief that the late time behavior towards a final stable state can be captured by the lowest lying quasi-normal modes. In particular, a double relation is found for this exception in certain cases.

  18. Dynamics, stability, and statistics on lattices and networks

    International Nuclear Information System (INIS)

    Livi, Roberto

    2014-01-01

    These lectures aim at surveying some dynamical models that have been widely explored in the recent scientific literature as case studies of complex dynamical evolution, emerging from the spatio-temporal organization of several coupled dynamical variables. The first message is that a suitable mathematical description of such models needs tools and concepts borrowed from the general theory of dynamical systems and from out-of-equilibrium statistical mechanics. The second message is that the overall scenario is definitely reacher than the standard problems in these fields. For instance, systems exhibiting complex unpredictable evolution do not necessarily exhibit deterministic chaotic behavior (i.e., Lyapunov chaos) as it happens for dynamical models made of a few degrees of freedom. In fact, a very large number of spatially organized dynamical variables may yield unpredictable evolution even in the absence of Lyapunov instability. Such a mechanism may emerge from the combination of spatial extension and nonlinearity. Moreover, spatial extension allows one to introduce naturally disorder, or heterogeneity of the interactions as important ingredients for complex evolution. It is worth to point out that the models discussed in these lectures share such features, despite they have been inspired by quite different physical and biological problems. Along these lectures we describe also some of the technical tools employed for the study of such models, e.g., Lyapunov stability analysis, unpredictability indicators for “stable chaos,” hydrodynamic description of transport in low spatial dimension, spectral decomposition of stochastic dynamics on directed networks, etc

  19. Navier-Stokes Predictions of Dynamic Stability Derivatives: Evaluation of Steady-State Methods

    National Research Council Canada - National Science Library

    DeSpirito, James; Silton, Sidra I; Weinacht, Paul

    2008-01-01

    The prediction of the dynamic stability derivatives-roll-damping, Magnus, and pitch-damping moments-were evaluated for three spin-stabilized projectiles using steady-state computational fluid dynamic (CFD) calculations...

  20. On D-brane dynamics and moduli stabilization

    Science.gov (United States)

    Kitazawa, Noriaki

    2017-09-01

    We discuss the effect of the dynamics of D-branes on moduli stabilization in type IIB string theory compactifications, with reference to a concrete toy model of T6/Z 3 orientifold compactification with fractional D3-branes and anti-D3-branes at orbifold fixed points. The resulting attractive forces between anti-D3-branes and D3-branes, together with the repulsive forces between anti-D3-branes and O3-planes, can affect the stability of the compact space. There are no complex structure moduli in T6/Z 3 orientifold, which should thus capture some generic features of more general settings where all complex structure moduli are stabilized by three-form fluxes. The simultaneous presence of branes and anti-branes brings along the breaking of supersymmetry. Non-BPS combinations of this type are typical of “brane supersymmetry breaking” and are a necessary ingredient in the KKLT scenario for stabilizing the remaining Kähler moduli. The conclusion of our analysis is that, while mutual D-brane interactions sometimes help Kähler moduli stabilization, this is not always the case.

  1. Stability and chaotic dynamics of a perturbed rate gyro

    International Nuclear Information System (INIS)

    Chen, H.-H.

    2006-01-01

    An analysis of stability and chaotic dynamics is presented by a single-axis rate gyro subjected to linear feedback control loops. This rate gyro is supposed to be mounted on a space vehicle which undergoes an uncertain angular velocity ω Z (t) around its spin axis and simultaneously acceleration ω-bar X (t) occurs with respect to the output axis. The necessary and sufficient conditions of stability and degeneracy conditions for the autonomous case, whose vehicle undergoes a steady rotation, were provided by Routh-Hurwitz theory. The stability of the nonlinear nonautonomous system was investigated by Liapunov stability and instability theorems. As the electrical time constant is much smaller than the mechanical time constant, the singularly perturbed system can be obtained by the singular perturbation theory. The Liapunov stability of this system by studying the reduced and boundary-layer systems was also analyzed. Using the Melinikov technique, we can give criteria for the existence of chaos in the gyro motion when the vehicle undergoes perturbed harmonic rotation about its spin and output axes

  2. Transition from shod to barefoot alters dynamic stability during running.

    Science.gov (United States)

    Ekizos, Antonis; Santuz, Alessandro; Arampatzis, Adamantios

    2017-07-01

    Barefoot running recently received increased attention, with controversial results regarding its effects on injury risk and performance. Numerous studies examined the kinetic and kinematic changes between the shod and the barefoot condition. Intrinsic parameters such as the local dynamic stability could provide new insight regarding neuromuscular control when immediately transitioning from one running condition to the other. We investigated the local dynamic stability during the change from shod to barefoot running. We further measured biomechanical parameters to examine the mechanisms governing this transition. Twenty habitually shod, young and healthy participants ran on a pressure plate-equipped treadmill and alternated between shod and barefoot running. We calculated the largest Lyapunov exponents as a measure of errors in the control of the movement. Biomechanical parameters were also collected. Local dynamic stability decreased significantly (d=0.41; 2.1%) during barefoot running indicating worse control over the movement. We measured higher cadence (d=0.35; 2.2%) and total flight time (d=0.58; 19%), lower total contact time (d=0.58; -5%), total vertical displacement (d=0.39; -4%), and vertical impulse (d=1.32; 11%) over the two minutes when running barefoot. The strike index changed significantly (d=1.29; 237%) towards the front of the foot. Immediate transition from shod to the barefoot condition resulted in an increased instability and indicates a worst control over the movement. The increased instability was associated with biomechanical changes (i.e. foot strike patterns) of the participants in the barefoot condition. Possible reasons why this instability arises, might be traced in the stance phase and particularly in the push-off. The decreased stability might affect injury risk and performance. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. Dynamic postural stability differences between male and female players with and without ankle sprain

    NARCIS (Netherlands)

    Dallinga, Joan; van der Does, Henrike; Benjaminse, Anne; Lemmink, Koen

    2015-01-01

    Objectives: The strategy for dynamic postural stability might be different for male and female players. Additionally, dynamic and challenging tasks are recommended to measure differences in postural stability between injured and non-injured players. Therefore, the dynamic stability index (DSI) was

  4. The growth speed of microtubules with XMAP215-coated beads coupled to their ends is increased by tensile force

    Science.gov (United States)

    Trushko, Anastasiya; Schäffer, Erik; Howard, Jonathon

    2013-01-01

    The generation of pulling and pushing forces is one of the important functions of microtubules, which are dynamic and polarized structures. The ends of dynamic microtubules are able to form relatively stable links to cellular structures, so that when a microtubule grows it can exert a pushing force and when it shrinks it can exert a pulling force. Microtubule growth and shrinkage are tightly regulated by microtubule-associated proteins (MAPs) that bind to microtubule ends. Given their localization, MAPs may be exposed to compressive and tensile forces. The effect of such forces on MAP function, however, is poorly understood. Here we show that beads coated with the microtubule polymerizing protein XMAP215, the Xenopus homolog of Dis1 and chTOG, are able to link stably to the plus ends of microtubules, even when the ends are growing or shrinking; at growing ends, the beads increase the polymerization rate. Using optical tweezers, we found that tensile force further increased the microtubule polymerization rate. These results show that physical forces can regulate the activity of MAPs. Furthermore, our results show that XMAP215 can be used as a handle to sense and mechanically manipulate the dynamics of the microtubule tip. PMID:23964126

  5. Quantitative Analysis of Tau-Microtubule Interaction Using FRET

    Directory of Open Access Journals (Sweden)

    Isabelle L. Di Maïo

    2014-08-01

    Full Text Available The interaction between the microtubule associated protein, tau and the microtubules is investigated. A fluorescence resonance energy transfer (FRET assay was used to determine the distance separating tau to the microtubule wall, as well as the binding parameters of the interaction. By using microtubules stabilized with Flutax-2 as donor and tau labeled with rhodamine as acceptor, a donor-to-acceptor distance of 54 ± 1 Å was found. A molecular model is proposed in which Flutax-2 is directly accessible to tau-rhodamine molecules for energy transfer. By titration, we calculated the stoichiometric dissociation constant to be equal to 1.0 ± 0.5 µM. The influence of the C-terminal tails of αβ-tubulin on the tau-microtubule interaction is presented once a procedure to form homogeneous solution of cleaved tubulin has been determined. The results indicate that the C-terminal tails of α- and β-tubulin by electrostatic effects and of recruitment seem to be involved in the binding mechanism of tau.

  6. Strategy switching in the stabilization of unstable dynamics.

    Directory of Open Access Journals (Sweden)

    Jacopo Zenzeri

    Full Text Available In order to understand mechanisms of strategy switching in the stabilization of unstable dynamics, this work investigates how human subjects learn to become skilled users of an underactuated bimanual tool in an unstable environment. The tool, which consists of a mass and two hand-held non-linear springs, is affected by a saddle-like force-field. The non-linearity of the springs allows the users to determine size and orientation of the tool stiffness ellipse, by using different patterns of bimanual coordination: minimal stiffness occurs when the two spring terminals are aligned and stiffness size grows by stretching them apart. Tool parameters were set such that minimal stiffness is insufficient to provide stable equilibrium whereas asymptotic stability can be achieved with sufficient stretching, although at the expense of greater effort. As a consequence, tool users have two possible strategies for stabilizing the mass in different regions of the workspace: 1 high stiffness feedforward strategy, aiming at asymptotic stability and 2 low stiffness positional feedback strategy aiming at bounded stability. The tool was simulated by a bimanual haptic robot with direct torque control of the motors. In a previous study we analyzed the behavior of naïve users and we found that they spontaneously clustered into two groups of approximately equal size. In this study we trained subjects to become expert users of both strategies in a discrete reaching task. Then we tested generalization capabilities and mechanism of strategy-switching by means of stabilization tasks which consist of tracking moving targets in the workspace. The uniqueness of the experimental setup is that it addresses the general problem of strategy-switching in an unstable environment, suggesting that complex behaviors cannot be explained in terms of a global optimization criterion but rather require the ability to switch between different sub-optimal mechanisms.

  7. Algorithm for Stabilizing a POD-Based Dynamical System

    Science.gov (United States)

    Kalb, Virginia L.

    2010-01-01

    This algorithm provides a new way to improve the accuracy and asymptotic behavior of a low-dimensional system based on the proper orthogonal decomposition (POD). Given a data set representing the evolution of a system of partial differential equations (PDEs), such as the Navier-Stokes equations for incompressible flow, one may obtain a low-dimensional model in the form of ordinary differential equations (ODEs) that should model the dynamics of the flow. Temporal sampling of the direct numerical simulation of the PDEs produces a spatial time series. The POD extracts the temporal and spatial eigenfunctions of this data set. Truncated to retain only the most energetic modes followed by Galerkin projection of these modes onto the PDEs obtains a dynamical system of ordinary differential equations for the time-dependent behavior of the flow. In practice, the steps leading to this system of ODEs entail numerically computing first-order derivatives of the mean data field and the eigenfunctions, and the computation of many inner products. This is far from a perfect process, and often results in the lack of long-term stability of the system and incorrect asymptotic behavior of the model. This algorithm describes a new stabilization method that utilizes the temporal eigenfunctions to derive correction terms for the coefficients of the dynamical system to significantly reduce these errors.

  8. Evaluation of constraint stabilization procedures for multibody dynamical systems

    Science.gov (United States)

    Park, K. C.; Chiou, J. C.

    1987-01-01

    Comparative numerical studies of four constraint treatment techniques for the simulation of general multibody dynamic systems are presented, and results are presented for the example of a classical crank mechanism and for a simplified version of the seven-link manipulator deployment problem. The staggered stabilization technique (Park, 1986) is found to yield improved accuracy and robustness over Baumgarte's (1972) technique, the singular decomposition technique (Walton and Steeves, 1969), and the penalty technique (Lotstedt, 1979). Furthermore, the staggered stabilization technique offers software modularity, and the only data each solution module needs to exchange with the other is a set of vectors plus a common module to generate the gradient matrix of the constraints, B.

  9. Local stability of galactic discs in modified dynamics

    Science.gov (United States)

    Shenavar, Hossein; Ghafourian, Neda

    2018-04-01

    The local stability of stellar and fluid discs, under a new modified dynamical model, is surveyed by using WKB approximation. The exact form of the modified Toomre criterion is derived for both types of systems and it is shown that the new model is, in all situations, more locally stable than Newtonian model. In addition, it has been proved that the central surface density of the galaxies plays an important role in the local stability in the sense that low surface brightness (LSB) galaxies are more stable than high surface brightness (HSBs). Furthermore, the growth rate in the new model is found to be lower than the Newtonian one. We found that, according to this model, the local instability is related to the ratio of surface density of the disc to a critical surface density Σcrit. We provide observational evidence to support this result based on star formation rate in HSBs and LSBs.

  10. Identification of process dynamics. Stability monitoring in BWR type reactors

    International Nuclear Information System (INIS)

    Abrahamsson, P.; Hallgren, P.

    1991-06-01

    Identification of process dynamics is used for stability monitoring in nuclear reactors (Boiling Water Reactor). This report treats the problem of estimating a damping factor and a resonance frequency from the neutron flux as measured in the reactor. A new parametric online method for identification is derived and presented, and is shown to meet the requirements of stability monitoring. The technique for estimating the process parameters is based on a recursive lattice filter algorithm. The problem of time varying parameters and offset, as well as offline experiments and signal processing are treated. All parts are implemented in a realtime program, using the language C. In comparison with earlier identifications, the new way of estimating the damping factor is shown to work well. Estimates of both the damping factor and the resonance frequency show a stable and reliable behavior. Future development and improvements are also indicated. (au)

  11. Centriolar CPAP/SAS-4 Imparts Slow Processive Microtubule Growth

    NARCIS (Netherlands)

    Sharma, Ashwani; Aher, Amol; Dynes, Nicola J; Frey, Daniel; Katrukha, Eugene A; Jaussi, Rolf; Grigoriev, Ilya; Croisier, Marie; Kammerer, Richard A; Akhmanova, Anna; Gönczy, Pierre; Steinmetz, Michel O

    2016-01-01

    Centrioles are fundamental and evolutionarily conserved microtubule-based organelles whose assembly is characterized by microtubule growth rates that are orders of magnitude slower than those of cytoplasmic microtubules. Several centriolar proteins can interact with tubulin or microtubules, but how

  12. Centriole triplet microtubules are required for stable centriole formation and inheritance in human cells

    Science.gov (United States)

    Wang, Jennifer T; Kong, Dong; Hoerner, Christian R; Loncarek, Jadranka

    2017-01-01

    Centrioles are composed of long-lived microtubules arranged in nine triplets. However, the contribution of triplet microtubules to mammalian centriole formation and stability is unknown. Little is known of the mechanism of triplet microtubule formation, but experiments in unicellular eukaryotes indicate that delta-tubulin and epsilon-tubulin, two less-studied tubulin family members, are required. Here, we report that centrioles in delta-tubulin and epsilon-tubulin null mutant human cells lack triplet microtubules and fail to undergo centriole maturation. These aberrant centrioles are formed de novo each cell cycle, but are unstable and do not persist to the next cell cycle, leading to a futile cycle of centriole formation and disintegration. Disintegration can be suppressed by paclitaxel treatment. Delta-tubulin and epsilon-tubulin physically interact, indicating that these tubulins act together to maintain triplet microtubules and that these are necessary for inheritance of centrioles from one cell cycle to the next. PMID:28906251

  13. Centriole triplet microtubules are required for stable centriole formation and inheritance in human cells.

    Science.gov (United States)

    Wang, Jennifer T; Kong, Dong; Hoerner, Christian R; Loncarek, Jadranka; Stearns, Tim

    2017-09-14

    Centrioles are composed of long-lived microtubules arranged in nine triplets. However, the contribution of triplet microtubules to mammalian centriole formation and stability is unknown. Little is known of the mechanism of triplet microtubule formation, but experiments in unicellular eukaryotes indicate that delta-tubulin and epsilon-tubulin, two less-studied tubulin family members, are required. Here, we report that centrioles in delta-tubulin and epsilon-tubulin null mutant human cells lack triplet microtubules and fail to undergo centriole maturation. These aberrant centrioles are formed de novo each cell cycle, but are unstable and do not persist to the next cell cycle, leading to a futile cycle of centriole formation and disintegration. Disintegration can be suppressed by paclitaxel treatment. Delta-tubulin and epsilon-tubulin physically interact, indicating that these tubulins act together to maintain triplet microtubules and that these are necessary for inheritance of centrioles from one cell cycle to the next.

  14. Moduli stabilization and uplifting with dynamically generated F-terms

    International Nuclear Information System (INIS)

    Dudas, Emilian; Papineau, Chloe; Pokorski, Stefan

    2007-01-01

    We use the F-term dynamical supersymmetry breaking models with metastable vacua in order to uplift the vacuum energy in the KKLT moduli stabilization scenario. The main advantage compared to earlier proposals is the manifest supersymmetric treatment and the natural coexistence of a TeV gravitino mass with a zero cosmological constant. We argue that it is generically difficult to avoid anti de-Sitter supersymmetric minima, however the tunneling rate from the metastable vacuum with zero vacuum energy towards them can be very suppressed. We briefly comment on the properties of the induced soft terms in the observable sector

  15. Moduli stabilization and uplifting with dynamically generated F-terms

    Energy Technology Data Exchange (ETDEWEB)

    Dudas, Emilian [CERN Theory Division, CH-1211, Geneva 23 (Switzerland); Papineau, Chloe [CPhT, Ecole Polytechnique, F-91128 Palaiseau Cedex (France); Pokorski, Stefan [Institute of Theoretical Physics, Univ. of Warsaw, 00-681 Warsaw (Poland)

    2007-02-15

    We use the F-term dynamical supersymmetry breaking models with metastable vacua in order to uplift the vacuum energy in the KKLT moduli stabilization scenario. The main advantage compared to earlier proposals is the manifest supersymmetric treatment and the natural coexistence of a TeV gravitino mass with a zero cosmological constant. We argue that it is generically difficult to avoid anti de-Sitter supersymmetric minima, however the tunneling rate from the metastable vacuum with zero vacuum energy towards them can be very suppressed. We briefly comment on the properties of the induced soft terms in the observable sector.

  16. On the dynamical stability of the space 'monorail'

    Science.gov (United States)

    Bergamaschi, S.; Manni, D.

    The dynamical stability of 'monorail' tethered-satellite/elevator configurations being studied for the Space Station is investigated analytically, treating the end platforms and elevator as point masses, neglecting tether elasticity, and taking the Coriolis force and the complex gravitational field into account in analyzing the orbital-plane motion of the system. A mathematical model is constructed; the equations of motion are derived; and results obtained by numerical integration for platform masses 100,000 and 10,000 kg, elevator mass 5000 kg, and a 10-km-long 6-mm-diameter 4070-kg-mass tether are presented in graphs and briefly characterized.

  17. Stability mechanisms of a thermophilic laccase probed by molecular dynamics

    DEFF Research Database (Denmark)

    Christensen, Niels Johan; Kepp, Kasper Planeta

    2013-01-01

    Laccases are highly stable, industrially important enzymes capable of oxidizing a large range of substrates. Causes for their stability are, as for other proteins, poorly understood. In this work, multiple-seed molecular dynamics (MD) was applied to a Trametes versicolor laccase in response...... integrity by increasing persistent backbone hydrogen bonds by ∼4 across simulations, mainly via prevention of F(-) intrusion. Hydrogen-bond loss in distinct loop regions and ends of critical β-sheets suggest potential strategies for laboratory optimization of these industrially important enzymes....

  18. Dynamic modelling of tearing mode stabilization by RF current drive

    International Nuclear Information System (INIS)

    Giruzzi, G.; Zabiego, M.; Gianakon, T.A.; Garbet, X.; Bernabei, S.

    1998-01-01

    The theory of tearing mode stabilization in toroidal plasmas by RF-driven currents that are modulated in phase with the island rotation is investigated. A time scale analysis of the phenomena involved indicates that transient effects, such as finite time response of the driven currents, island rotation during the power pulses, and the inductive response of the plasma, are intrinsically important. A dynamic model of such effects is developed, based on a 3-D Fokker-Planck code coupled to both the electric field diffusion and the island evolution equations. Extensive applications to both Electron Cyclotron and Lower Hybrid current drive in ITER are presented. (author)

  19. Stability and dynamic of strain mediated adatom superlattices on Cu

    Science.gov (United States)

    Kappus, Wolfgang

    2013-03-01

    Substrate strain mediated adatom equilibrium density distributions have been calculated for Cu surfaces using two complementing methods. A hexagonal adatom superlattice in a coverage range up to 0.045 ML is derived for repulsive short range interactions. For zero short range interactions a hexagonal superstructure of adatom clusters is derived in a coverage range about 0.08 ML. Conditions for the stability of the superlattice against formation of dimers or clusters and degradation are analyzed using simple neighborhood models. Such models are also used to investigate the dynamic of adatoms within their superlattice neighborhood. Collective modes of adatom diffusion are proposed from the analogy with bulk lattice dynamics and methods for measurement are suggested. The recently put forward explanation of surface state mediated interactions for superstructures found in scanning tunneling microscopy experiments is put in question and strain mediated interactions are proposed as an alternative.

  20. Nonlinear flight dynamics and stability of hovering model insects

    Science.gov (United States)

    Liang, Bin; Sun, Mao

    2013-01-01

    Current analyses on insect dynamic flight stability are based on linear theory and limited to small disturbance motions. However, insects' aerial environment is filled with swirling eddies and wind gusts, and large disturbances are common. Here, we numerically solve the equations of motion coupled with the Navier–Stokes equations to simulate the large disturbance motions and analyse the nonlinear flight dynamics of hovering model insects. We consider two representative model insects, a model hawkmoth (large size, low wingbeat frequency) and a model dronefly (small size, high wingbeat frequency). For small and large initial disturbances, the disturbance motion grows with time, and the insects tumble and never return to the equilibrium state; the hovering flight is inherently (passively) unstable. The instability is caused by a pitch moment produced by forward/backward motion and/or a roll moment produced by side motion of the insect. PMID:23697714

  1. On the nature and shape of tubulin trails: implications on microtubule self-organization.

    Science.gov (United States)

    Glade, Nicolas

    2012-06-01

    Microtubules, major elements of the cell skeleton are, most of the time, well organized in vivo, but they can also show self-organizing behaviors in time and/or space in purified solutions in vitro. Theoretical studies and models based on the concepts of collective dynamics in complex systems, reaction-diffusion processes and emergent phenomena were proposed to explain some of these behaviors. In the particular case of microtubule spatial self-organization, it has been advanced that microtubules could behave like ants, self-organizing by 'talking to each other' by way of hypothetic (because never observed) concentrated chemical trails of tubulin that are expected to be released by their disassembling ends. Deterministic models based on this idea yielded indeed like-looking spatio-temporal self-organizing behaviors. Nevertheless the question remains of whether microscopic tubulin trails produced by individual or bundles of several microtubules are intense enough to allow microtubule self-organization at a macroscopic level. In the present work, by simulating the diffusion of tubulin in microtubule solutions at the microscopic scale, we measure the shape and intensity of tubulin trails and discuss about the assumption of microtubule self-organization due to the production of chemical trails by disassembling microtubules. We show that the tubulin trails produced by individual microtubules or small microtubule arrays are very weak and not elongated even at very high reactive rates. Although the variations of concentration due to such trails are not significant compared to natural fluctuations of the concentration of tubuline in the chemical environment, the study shows that heterogeneities of biochemical composition can form due to microtubule disassembly. They could become significant when produced by numerous microtubule ends located in the same place. Their possible formation could play a role in certain conditions of reaction. In particular, it gives a mesoscopic

  2. Dynamic plate osteosynthesis for fracture stabilization: how to do it

    Directory of Open Access Journals (Sweden)

    Juerg Sonderegger

    2010-01-01

    Full Text Available Plate osteosynthesis is one treatment option for the stabilization of long bones. It is widely accepted to achieve bone healing with a dynamic and biological fixation where the perfusion of the bone is left intact and micromotion at the fracture gap is allowed. The indications for a dynamic plate osteosynthesis include distal tibial and femoral fractures, some midshaft fractures, and adolescent tibial and femoral fractures with not fully closed growth plates. Although many lower limb shaft fractures are managed successfully with intramedullary nails, there are some important advantages of open-reduction-and-plate fixation: the risk of malalignment, anterior knee pain, or nonunion seems to be lower. The surgeon performing a plate osteosynthesis has the possibility to influence fixation strength and micromotion at the fracture gap. Long plates and oblique screws at the plate ends increase fixation strength. However, the number of screws does influence stiffness and stability. Lag screws and screws close to the fracture site reduce micromotion dramatically. Dynamic plate osteosynthesis can be achieved by applying some simple rules: long plates with only a few screws should be used. Oblique screws at the plate ends increase the pullout strength. Two or three holes at the fracture site should be omitted. Lag screws, especially through the plate, must be avoided whenever possible. Compression is not required. Locking plates are recommended only in fractures close to the joint. When respecting these basic concepts, dynamic plate osteosynthesis is a safe procedure with a high healing and a low complication rate. 

  3. Dynamics and stability of light-like tachyon condensation

    International Nuclear Information System (INIS)

    Barnaby, Neil; Robinson, Patrick; Mulryne, David J.; Nunes, Nelson J.

    2009-01-01

    Recently, Hellerman and Schnabl considered the dynamics of unstable D-branes in the background of a linear dilaton. Remarkably, they were able to construct light-like tachyon solutions which interpolate smoothly between the perturbative and nonperturbative vacua, without undergoing the wild oscillations that plague time-like solutions. In their analysis, however, the full structure of the initial value problem for the nonlocal dynamical equations was not considered. In this paper, therefore, we reexamine the nonlinear dynamics of light-like tachyon condensation using a combination of numerical and analytical techniques. We find that for the p-adic string the monotonic behaviour obtained previously relied on a special choice of initial conditions near the unstable maximum. For generic initial conditions the wild oscillations come back to haunt us. Interestingly, we find an 'island of stability' in initial condition space that leads to sensible evolution at late times. For the string field theory case, on the other hand, we find that the evolution is completely stable for generic choices of initial data. This provides an explicit example of a string theoretic system that admits infinitely many initial data but is nevertheless nonperturbatively stable. Qualitatively similar dynamics are obtained in nonlocal cosmologies where the Hubble damping plays a role very analogous to the dilaton gradient.

  4. Dynamics and stability of light-like tachyon condensation

    Science.gov (United States)

    Barnaby, Neil; Mulryne, David J.; Nunes, Nelson J.; Robinson, Patrick

    2009-03-01

    Recently, Hellerman and Schnabl considered the dynamics of unstable D-branes in the background of a linear dilaton. Remarkably, they were able to construct light-like tachyon solutions which interpolate smoothly between the perturbative and nonperturbative vacua, without undergoing the wild oscillations that plague time-like solutions. In their analysis, however, the full structure of the initial value problem for the nonlocal dynamical equations was not considered. In this paper, therefore, we reexamine the nonlinear dynamics of light-like tachyon condensation using a combination of numerical and analytical techniques. We find that for the p-adic string the monotonic behaviour obtained previously relied on a special choice of initial conditions near the unstable maximum. For generic initial conditions the wild oscillations come back to haunt us. Interestingly, we find an ``island of stability'' in initial condition space that leads to sensible evolution at late times. For the string field theory case, on the other hand, we find that the evolution is completely stable for generic choices of initial data. This provides an explicit example of a string theoretic system that admits infinitely many initial data but is nevertheless nonperturbatively stable. Qualitatively similar dynamics are obtained in nonlocal cosmologies where the Hubble damping plays a role very analogous to the dilaton gradient.

  5. Interactive domains in the molecular chaperone human alphaB crystallin modulate microtubule assembly and disassembly.

    Directory of Open Access Journals (Sweden)

    Joy G Ghosh

    2007-06-01

    Full Text Available Small heat shock proteins regulate microtubule assembly during cell proliferation and in response to stress through interactions that are poorly understood.Novel functions for five interactive sequences in the small heat shock protein and molecular chaperone, human alphaB crystallin, were investigated in the assembly/disassembly of microtubules and aggregation of tubulin using synthetic peptides and mutants of human alphaB crystallin.The interactive sequence (113FISREFHR(120 exposed on the surface of alphaB crystallin decreased microtubule assembly by approximately 45%. In contrast, the interactive sequences, (131LTITSSLSSDGV(142 and (156ERTIPITRE(164, corresponding to the beta8 strand and the C-terminal extension respectively, which are involved in complex formation, increased microtubule assembly by approximately 34-45%. The alphaB crystallin peptides, (113FISREFHR(120 and (156ERTIPITRE(164, inhibited microtubule disassembly by approximately 26-36%, and the peptides (113FISREFHR(120 and (131LTITSSLSSDGV(142 decreased the thermal aggregation of tubulin by approximately 42-44%. The (131LTITSSLSSDGV(142 and (156ERTIPITRE(164 peptides were more effective than the widely used anti-cancer drug, Paclitaxel, in modulating tubulinmicrotubule dynamics. Mutagenesis of these interactive sequences in wt human alphaB crystallin confirmed the effects of the alphaB crystallin peptides on microtubule assembly/disassembly and tubulin aggregation. The regulation of microtubule assembly by alphaB crystallin varied over a narrow range of concentrations. The assembly of microtubules was maximal at alphaB crystallin to tubulin molar ratios between 1:4 and 2:1, while molar ratios >2:1 inhibited microtubule assembly.Interactive sequences on the surface of human alphaB crystallin collectively modulate microtubule assembly through a dynamic subunit exchange mechanism that depends on the concentration and ratio of alphaB crystallin to tubulin. These are the first

  6. Stability and nonlinear dynamics of gyrotrons at cyclotron harmonics

    International Nuclear Information System (INIS)

    Saraph, G.P.; Nusinovich, G.S.; Antonsen, T.M. Jr.; Levush, B.

    1992-01-01

    Gyrotrons operating at higher harmonics of the cyclotron frequency can overcome the frequency limitations caused by achievable strength of the magnetic field. However, the excitation of modes at the fundamental frequency exhibit a major problem for stable operation of harmonic gyrotron at high power with high efficiency. Therefore the issues of stability of gyrotron operation at the cyclotron harmonics and nonlinear dynamics of mode interaction are of great importance. The results of the authors stability analysis and multimode simulation are presented here. A detailed nonlinear theory of steady state single mode operation at cyclotron harmonics has been presented previously, taking into account beam-wave coupling and nonlinear gain function at cyclotron harmonics. A set of equations describing low gain regime interaction of modes resonant at different cyclotron harmonics was studied before. The multifrequency time-dependent nonlinear analysis presented here is based on previous gyrotron studies and beam-wave interaction at cyclotron harmonics. The authors have determined the parameter space for stable single mode operation at the second harmonic. The nonlinear dynamics of mode evolution and mode interaction for a harmonic gyrotron is presented. A new nonlinear effect in which the parasite at the fundamental harmonic helps excite the operating mode at the second harmonic has been demonstrated

  7. Skipping Posterior Dynamic Transpedicular Stabilization for Distant Segment Degenerative Disease

    Directory of Open Access Journals (Sweden)

    Bilgehan Solmaz

    2012-01-01

    Full Text Available Objective. To date, there is still no consensus on the treatment of spinal degenerative disease. Current surgical techniques to manage painful spinal disorders are imperfect. In this paper, we aimed to evaluate the prospective results of posterior transpedicular dynamic stabilization, a novel surgical approach that skips the segments that do not produce pain. This technique has been proven biomechanically and radiologically in spinal degenerative diseases. Methods. A prospective study of 18 patients averaging 54.94 years of age with distant spinal segment degenerative disease. Indications consisted of degenerative disc disease (57%, herniated nucleus pulposus (50%, spinal stenosis (14.28%, degenerative spondylolisthesis (14.28%, and foraminal stenosis (7.1%. The Oswestry Low-Back Pain Disability Questionnaire and visual analog scale (VAS for pain were recorded preoperatively and at the third and twelfth postoperative months. Results. Both the Oswestry and VAS scores showed significant improvement postoperatively (P<0.05. We observed complications in one patient who had spinal epidural hematoma. Conclusion. We recommend skipping posterior transpedicular dynamic stabilization for surgical treatment of distant segment spinal degenerative disease.

  8. Electricity Market Stochastic Dynamic Model and Its Mean Stability Analysis

    Directory of Open Access Journals (Sweden)

    Zhanhui Lu

    2014-01-01

    Full Text Available Based on the deterministic dynamic model of electricity market proposed by Alvarado, a stochastic electricity market model, considering the random nature of demand sides, is presented in this paper on the assumption that generator cost function and consumer utility function are quadratic functions. The stochastic electricity market model is a generalization of the deterministic dynamic model. Using the theory of stochastic differential equations, stochastic process theory, and eigenvalue techniques, the determining conditions of the mean stability for this electricity market model under small Gauss type random excitation are provided and testified theoretically. That is, if the demand elasticity of suppliers is nonnegative and the demand elasticity of consumers is negative, then the stochastic electricity market model is mean stable. It implies that the stability can be judged directly by initial data without any computation. Taking deterministic electricity market data combined with small Gauss type random excitation as numerical samples to interpret random phenomena from a statistical perspective, the results indicate the conclusions above are correct, valid, and practical.

  9. Designing Inter-Organisational Collectivities for Dynamic Fit: Stability, maneuvrability and Application in Disaster Relief Endeavours

    Science.gov (United States)

    2011-01-01

    changed consumer preferences . Hence, static stability limits initial performance deviation (e.g., maintaining desired airplane altitude, maintaining...by changed consumer preferences . Hence, dynamic stability limits the duration of performance deviation (e.g., maintaining desired airplane altitude...altitude from wind gust. Initial resistance to deviation in profit level from change in consumer preferences . Dynamic stability Quickness of a

  10. Buckling analysis of orthotropic protein microtubules under axial and radial compression based on couple stress theory.

    Science.gov (United States)

    Beni, Yaghoub Tadi; Zeverdejani, M Karimi; Mehralian, Fahimeh

    2017-10-01

    Protein microtubules (MTs) are one of the important intercellular components and have a vital role in the stability and strength of the cells. Due to applied external loads, protein microtubules may be involved buckling phenomenon. Due to impact of protein microtubules in cell reactions, it is important to determine their critical buckling load. Considering nature of protein microtubules, various parameters are effective on microtubules buckling. The small size of microtubules and also lack of uniformity of MTs properties in different directions caused the necessity of accuracy in the analysis of these bio-structure. In fact, microtubules must be considered as a size dependent cylinder, which behave as an orthotropic material. Hence, in the present work using first-order shear deformation model (FSDT), the buckling equations of anisotropic MTs are derived based on new modified couple stress theory (NMCST). After solving the stability equations, the influences of various parameters are measured on the MTs critical buckling load. Copyright © 2017 Elsevier Inc. All rights reserved.

  11. Dynamic Stabilization of Metal Oxide–Water Interfaces

    Energy Technology Data Exchange (ETDEWEB)

    McBriarty, Martin E.; von Rudorff, Guido Falk; Stubbs, Joanne; Eng, Peter; Blumberger, Jochen; Rosso, Kevin M.

    2017-02-08

    Metal oxide growth, dissolution, and redox reactivity depend on the structure and dynamics at the interface with aqueous solution. We present the most definitive analysis to date of the hydrated naturally abundant r-cut (11$\\bar{0}$2) termination of the iron oxide hematite (α-Fe2O3). In situ synchrotron X-ray scattering analysis reveals a ridged lateral arrangement of adsorbed water molecules hydrogen bonded to terminal aquo groups. Large-scale hybrid-functional density functional theory-based molecular dynamics (DFT-MD) simulations show how this structure is dynamically stabilized by picosecond exchange between aquo groups and adsorbed water, even under nominally dry conditions. Surface pKa prediction based on bond valence analysis suggests that water exchange may influence the proton transfer reactions associated with acid/base reactivity at the interface. Our findings rectify inconsistencies between existing models and may be extended to resolving more complex electrochemical phenomena at metal oxide-water interfaces.

  12. Atmospheric stability analysis over statically and dynamically rough surfaces

    Science.gov (United States)

    Maric, Emina; Metzger, Meredith; Singha, Arindam; Sadr, Reza

    2011-11-01

    The ratio of buoyancy flux to turbulent kinetic energy production in the atmospheric surface layer is investigated experimentally for air flow over two types of surfaces characterized by static and dynamic roughness. In this study, ``static'' refers to the time-invariant nature of naturally-occurring roughness over a mud/salt playa; while, ``dynamic'' refers to the behavior of water waves along an air-water interface. In both cases, time-resolved measurements of the momentum and heat fluxes were acquired from synchronized 3D sonic anemometers mounted on a vertical tower. Field campaigns were conducted at two sites, representing the ``statically'' and ``dynamically'' rough surfaces, respectively: (1) the SLTEST facility in Utah's western desert, and (2) the new Doha airport in Qatar under construction along the coast of the Persian Gulf. Note, at site 2, anemometers were located directly above the water by extension from a tower secured to the end of a 1 km-long pier. Comparisons of the Monin-Obukhov length, flux Richardson number, and gradient Richardson number are presented, and discussed in the context of the observed evolution of the turbulent spectra in response to diurnal variations of atmospheric stability. Supported by the Qatar National Research Fund.

  13. A ROP2-RIC1 pathway fine-tunes microtubule reorganization for salt tolerance in Arabidopsis.

    Science.gov (United States)

    Li, Changjiang; Lu, Hanmei; Li, Wei; Yuan, Ming; Fu, Ying

    2017-07-01

    The reorganization of microtubules induced by salt stress is required for Arabidopsis survival under high salinity conditions. RIC1 is an effector of Rho-related GTPase from plants (ROPs) and a known microtubule-associated protein. In this study, we demonstrated that RIC1 expression decreased with long-term NaCl treatment, and ric1-1 seedlings exhibited a higher survival rate under salt stress. We found that RIC1 reduced the frequency of microtubule transition from shortening to growing status and knockout of RIC1 improved the reassembly of depolymerized microtubules caused by either oryzalin treatment or salt stress. Further investigation showed that constitutively active ROP2 promoted the reassembly of microtubules and the survival of seedlings under salt stress. A rop2-1 ric1-1 double mutant rescued the salt-sensitive phenotype of rop2-1, indicating that ROP2 functions in salt tolerance through RIC1. Although ROP2 did not regulate RIC1 expression upon salt stress, a quick but mild increase of ROP2 activity was induced, led to reduction of RIC1 on microtubules. Collectively, our study reveals an ROP2-RIC1 pathway that fine-tunes microtubule dynamics in response to salt stress in Arabidopsis. This finding not only reveals a new regulatory mechanism for microtubule reorganization under salt stress but also the importance of ROP signalling for salinity tolerance. © 2017 John Wiley & Sons Ltd.

  14. Stability of power systems coupled with market dynamics

    Science.gov (United States)

    Meng, Jianping

    This Ph.D. thesis presented here spans two relatively independent topics. The first part, Chapter 2 is self-contained, and is dedicated to studies of new algorithms for power system state estimation. The second part, encompassing the remaining chapters, is dedicated to stability analysis of power system coupled with market dynamics. The first part of this thesis presents improved Newton's methods employing efficient vectorized calculations of higher order derivatives in power system state estimation problems. The improved algorithms are proposed based on an exact Newton's method using the second order terms. By efficiently computing an exact gain matrix, combined with a special optimal multiplier method, the new algorithms show more reliable convergence compared with the existing methods of normal equations, orthogonal decomposition, and Hachtel's sparse tableau. Our methods are able to handle ill-conditioned problems, yet show minimal penalty in computational cost for well-conditioned cases. These claims are illustrated through the standard IEEE 118 and 300 bus test examples. The second part of the thesis focuses on stability analysis of market/power systems. The work presented is motivated by an emerging problem. As the frequency of market based dispatch updates increases, there will inevitably be interaction between the dynamics of markets determining the generator dispatch commands, and the physical response of generators and network interconnections, necessitating the development of stability analysis for such coupled systems. We begin with numeric tests using different market models, with detailed machine/exciter/turbine/governor dynamics, in the New England 39 bus test system. A progression of modeling refinements are introduced, including such non-ideal effects as time delays. Electricity market parameter identification algorithms are also studied based on real time data from the PJM electricity market. Finally our power market model is augmented by optimal

  15. Dynamic Stability Analysis Using High-Order Interpolation

    Directory of Open Access Journals (Sweden)

    Juarez-Toledo C.

    2012-10-01

    Full Text Available A non-linear model with robust precision for transient stability analysis in multimachine power systems is proposed. The proposed formulation uses the interpolation of Lagrange and Newton's Divided Difference. The High-Order Interpolation technique developed can be used for evaluation of the critical conditions of the dynamic system.The technique is applied to a 5-area 45-machine model of the Mexican interconnected system. As a particular case, this paper shows the application of the High-Order procedure for identifying the slow-frequency mode for a critical contingency. Numerical examples illustrate the method and demonstrate the ability of the High-Order technique to isolate and extract temporal modal behavior.

  16. Dynamical stability of a many-body Kapitza pendulum

    Energy Technology Data Exchange (ETDEWEB)

    Citro, Roberta, E-mail: citro@sa.infn.it [Dipartimento di Fisica “E. R. Caianiello” and Spin-CNR, Universita’ degli Studi di Salerno, Via Giovanni Paolo II, I-84084 Fisciano (Italy); Dalla Torre, Emanuele G., E-mail: emanuele.dalla-torre@biu.ac.il [Department of Physics, Bar Ilan University, Ramat Gan 5290002 (Israel); Department of Physics, Harvard University, Cambridge, MA 02138 (United States); D’Alessio, Luca [Department of Physics, The Pennsylvania State University, University Park, PA 16802 (United States); Department of Physics, Boston University, Boston, MA 02215 (United States); Polkovnikov, Anatoli [Department of Physics, Boston University, Boston, MA 02215 (United States); Babadi, Mehrtash [Department of Physics, Harvard University, Cambridge, MA 02138 (United States); Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, CA 91125 (United States); Oka, Takashi [Department of Applied Physics, University of Tokyo, Tokyo, 113-8656 (Japan); Demler, Eugene [Department of Physics, Harvard University, Cambridge, MA 02138 (United States)

    2015-09-15

    We consider a many-body generalization of the Kapitza pendulum: the periodically-driven sine–Gordon model. We show that this interacting system is dynamically stable to periodic drives with finite frequency and amplitude. This finding is in contrast to the common belief that periodically-driven unbounded interacting systems should always tend to an absorbing infinite-temperature state. The transition to an unstable absorbing state is described by a change in the sign of the kinetic term in the Floquet Hamiltonian and controlled by the short-wavelength degrees of freedom. We investigate the stability phase diagram through an analytic high-frequency expansion, a self-consistent variational approach, and a numeric semiclassical calculation. Classical and quantum experiments are proposed to verify the validity of our results.

  17. Manipulation and quantification of microtubule lattice integrity

    Directory of Open Access Journals (Sweden)

    Taylor A. Reid

    2017-08-01

    Full Text Available Microtubules are structural polymers that participate in a wide range of cellular functions. The addition and loss of tubulin subunits allows the microtubule to grow and shorten, as well as to develop and repair defects and gaps in its cylindrical lattice. These lattice defects act to modulate the interactions of microtubules with molecular motors and other microtubule-associated proteins. Therefore, tools to control and measure microtubule lattice structure will be invaluable for developing a quantitative understanding of how the structural state of the microtubule lattice may regulate its interactions with other proteins. In this work, we manipulated the lattice integrity of in vitro microtubules to create pools of microtubules with common nucleotide states, but with variations in structural states. We then developed a series of novel semi-automated analysis tools for both fluorescence and electron microscopy experiments to quantify the type and severity of alterations in microtubule lattice integrity. These techniques will enable new investigations that explore the role of microtubule lattice structure in interactions with microtubule-associated proteins.

  18. Dynamics of Stability of Orientation Maps Recorded with Optical Imaging.

    Science.gov (United States)

    Shumikhina, S I; Bondar, I V; Svinov, M M

    2018-03-15

    Orientation selectivity is an important feature of visual cortical neurons. Optical imaging of the visual cortex allows for the generation of maps of orientation selectivity that reflect the activity of large populations of neurons. To estimate the statistical significance of effects of experimental manipulations, evaluation of the stability of cortical maps over time is required. Here, we performed optical imaging recordings of the visual cortex of anesthetized adult cats. Monocular stimulation with moving clockwise square-wave gratings that continuously changed orientation and direction was used as the mapping stimulus. Recordings were repeated at various time intervals, from 15 min to 16 h. Quantification of map stability was performed on a pixel-by-pixel basis using several techniques. Map reproducibility showed clear dynamics over time. The highest degree of stability was seen in maps recorded 15-45 min apart. Averaging across all time intervals and all stimulus orientations revealed a mean shift of 2.2 ± 0.1°. There was a significant tendency for larger shifts to occur at longer time intervals. Shifts between 2.8° (mean ± 2SD) and 5° were observed more frequently at oblique orientations, while shifts greater than 5° appeared more frequently at cardinal orientations. Shifts greater than 5° occurred rarely overall (5.4% of cases) and never exceeded 11°. Shifts of 10-10.6° (0.7%) were seen occasionally at time intervals of more than 4 h. Our findings should be considered when evaluating the potential effect of experimental manipulations on orientation selectivity mapping studies. Copyright © 2018 IBRO. Published by Elsevier Ltd. All rights reserved.

  19. Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

    KAUST Repository

    Shroll, Andrew P.

    2012-01-01

    This work explores the dynamic stability characteristics of premixed CH 4/O 2/CO 2 mixtures in a 50 kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different dilution levels of carbon dioxide used to control the flame temperature (T ad). For the highest T ad\\'s, the combustor is unstable at the first harmonic of the combustor\\'s natural frequency. As the temperature is reduced, the combustor jumps to fundamental mode and then to a low-frequency mode whose value is well below the combustor\\'s natural frequency, before eventually reaching blowoff. Similar to the case of CH 4/air mixtures, the transition from one mode to another is predominantly a function of the T ad of the reactive mixture, despite significant differences in laminar burning velocity and/or strained flame consumption speed between air and oxy-fuel mixtures for a given T ad. High speed images support this finding by revealing similar vortex breakdown modes and thus similar turbulent flame geometries that change as a function of flame temperature. Copyright © 2012 American Society of Mechanical Engineers.

  20. Blowoff dynamics of bluff body stabilized turbulent premixed flames

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhuri, Swetaprovo; Kostka, Stanislav; Renfro, Michael W.; Cetegen, Baki M. [Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, U-3139, Storrs, CT 06269 (United States)

    2010-04-15

    This article concerns the flame dynamics of a bluff body stabilized turbulent premixed flame as it approaches lean blowoff. Time resolved chemiluminescence imaging along with simultaneous particle image velocimetry and OH planar laser-induced fluorescence were utilized in an axisymmetric bluff body stabilized, propane-air flame to determine the sequence of events leading to blowoff and provide a quantitative analysis of the experimental results. It was found that as lean blowoff is approached by reduction of equivalence ratio, flame speed decreases and the flame shape progressively changes from a conical to a columnar shape. For a stably burning conical flame away from blowoff, the flame front envelopes the shear layer vortices. Near blowoff, the columnar flame front and shear layer vortices overlap to induce high local stretch rates that exceed the extinction stretch rates instantaneously and in the mean, resulting in local flame extinction along the shear layers. Following shear layer extinction, fresh reactants can pass through the shear layers to react within the recirculation zone with all other parts of the flame extinguished. This flame kernel within the recirculation zone may survive for a few milliseconds and can reignite the shear layers such that the entire flame is reestablished for a short period. This extinction and reignition event can happen several times before final blowoff which occurs when the flame kernel fails to reignite the shear layers and ultimately leads to total flame extinguishment. (author)

  1. Effects of microtubule mechanics on hydrolysis and catastrophes

    International Nuclear Information System (INIS)

    Müller, N; Kierfeld, J

    2014-01-01

    We introduce a model for microtubule (MT) mechanics containing lateral bonds between dimers in neighboring protofilaments, bending rigidity of dimers, and repulsive interactions between protofilaments modeling steric constraints to investigate the influence of mechanical forces on hydrolysis and catastrophes. We use the allosteric dimer model, where tubulin dimers are characterized by an equilibrium bending angle, which changes from 0 ∘ to 22 ∘ by hydrolysis of a dimer. This also affects the lateral interaction and bending energies and, thus, the mechanical equilibrium state of the MT. As hydrolysis gives rise to conformational changes in dimers, mechanical forces also influence the hydrolysis rates by mechanical energy changes modulating the hydrolysis rate. The interaction via the MT mechanics then gives rise to correlation effects in the hydrolysis dynamics, which have not been taken into account before. Assuming a dominant influence of mechanical energies on hydrolysis rates, we investigate the most probable hydrolysis pathways both for vectorial and random hydrolysis. Investigating the stability with respect to lateral bond rupture, we identify initiation configurations for catastrophes along the hydrolysis pathways and values for a lateral bond rupture force. If we allow for rupturing of lateral bonds between dimers in neighboring protofilaments above this threshold force, our model exhibits avalanche-like catastrophe events. (papers)

  2. Dynamics of multiple nuclei in Ashbya gossypii hyphae depend on the control of cytoplasmic microtubules length by Bik1, Kip2, Kip3, and not on a capture/shrinkage mechanism.

    Science.gov (United States)

    Grava, Sandrine; Philippsen, Peter

    2010-11-01

    Ashbya gossypii has a budding yeast-like genome but grows exclusively as multinucleated hyphae. In contrast to budding yeast where positioning of nuclei at the bud neck is a major function of cytoplasmic microtubules (cMTs), A. gossypii nuclei are constantly in motion and positioning is not an issue. To investigate the role of cMTs in nuclear oscillation and bypassing, we constructed mutants potentially affecting cMT lengths. Hyphae lacking the plus (+)end marker Bik1 or the kinesin Kip2 cannot polymerize long cMTs and lose wild-type nuclear movements. Interestingly, hyphae lacking the kinesin Kip3 display longer cMTs concomitant with increased nuclear oscillation and bypassing. Polymerization and depolymerization rates of cMTs are 3 times higher in A. gossypii than in budding yeast and cMT catastrophes are rare. Growing cMTs slide along the hyphal cortex and exert pulling forces on nuclei. Surprisingly, a capture/shrinkage mechanism seems to be absent in A. gossypii. cMTs reaching a hyphal tip do not shrink, and cMT +ends accumulate in hyphal tips. Thus, differences in cMT dynamics and length control between budding yeast and A. gossypii are key elements in the adaptation of the cMT cytoskeleton to much longer cells and much higher degrees of nuclear mobilities.

  3. Modulation of microtubule assembly by the HIV-1 Tat protein is strongly dependent on zinc binding to Tat

    Directory of Open Access Journals (Sweden)

    Muller Sylviane

    2008-07-01

    Full Text Available Abstract Background During HIV-1 infection, the Tat protein plays a key role by transactivating the transcription of the HIV-1 proviral DNA. In addition, Tat induces apoptosis of non-infected T lymphocytes, leading to a massive loss of immune competence. This apoptosis is notably mediated by the interaction of Tat with microtubules, which are dynamic components essential for cell structure and division. Tat binds two Zn2+ ions through its conserved cysteine-rich region in vitro, but the role of zinc in the structure and properties of Tat is still controversial. Results To investigate the role of zinc, we first characterized Tat apo- and holo-forms by fluorescence correlation spectroscopy and time-resolved fluorescence spectroscopy. Both of the Tat forms are monomeric and poorly folded but differ by local conformational changes in the vicinity of the cysteine-rich region. The interaction of the two Tat forms with tubulin dimers and microtubules was monitored by analytical ultracentrifugation, turbidity measurements and electron microscopy. At 20°C, both of the Tat forms bind tubulin dimers, but only the holo-Tat was found to form discrete complexes. At 37°C, both forms promoted the nucleation and increased the elongation rates of tubulin assembly. However, only the holo-Tat increased the amount of microtubules, decreased the tubulin critical concentration, and stabilized the microtubules. In contrast, apo-Tat induced a large amount of tubulin aggregates. Conclusion Our data suggest that holo-Tat corresponds to the active form, responsible for the Tat-mediated apoptosis.

  4. Taking directions: the role of microtubule-bound nucleation in the self-organization of the plant cortical array

    International Nuclear Information System (INIS)

    Deinum, Eva E; Tindemans, Simon H; Mulder, Bela M

    2011-01-01

    The highly aligned cortical microtubule array of interphase plant cells is a key regulator of anisotropic cell expansion. Recent computational and analytical work has shown that the non-equilibrium self-organization of this structure can be understood on the basis of experimentally observed collisional interactions between dynamic microtubules attached to the plasma membrane. Most of these approaches assumed that new microtubules are homogeneously and isotropically nucleated on the cortical surface. Experimental evidence, however, shows that nucleation mostly occurs from other microtubules and under specific relative angles. Here, we investigate the impact of directed microtubule-bound nucleations on the alignment process using computer simulations. The results show that microtubule-bound nucleations can increase the degree of alignment achieved, decrease the timescale of the ordering process and widen the regime of dynamic parameters for which the system can self-organize. We establish that the major determinant of this effect is the degree of co-alignment of the nucleations with the parent microtubule. The specific role of sideways branching nucleations appears to allow stronger alignment while maintaining a measure of overall spatial homogeneity. Finally, we investigate the suggestion that observed persistent rotation of microtubule domains can be explained through a handedness bias in microtubule-bound nucleations, showing that this is possible only for an extreme bias and over a limited range of parameters

  5. Taking directions: the role of microtubule-bound nucleation in the self-organization of the plant cortical array

    Science.gov (United States)

    Deinum, Eva E.; Tindemans, Simon H.; Mulder, Bela M.

    2011-10-01

    The highly aligned cortical microtubule array of interphase plant cells is a key regulator of anisotropic cell expansion. Recent computational and analytical work has shown that the non-equilibrium self-organization of this structure can be understood on the basis of experimentally observed collisional interactions between dynamic microtubules attached to the plasma membrane. Most of these approaches assumed that new microtubules are homogeneously and isotropically nucleated on the cortical surface. Experimental evidence, however, shows that nucleation mostly occurs from other microtubules and under specific relative angles. Here, we investigate the impact of directed microtubule-bound nucleations on the alignment process using computer simulations. The results show that microtubule-bound nucleations can increase the degree of alignment achieved, decrease the timescale of the ordering process and widen the regime of dynamic parameters for which the system can self-organize. We establish that the major determinant of this effect is the degree of co-alignment of the nucleations with the parent microtubule. The specific role of sideways branching nucleations appears to allow stronger alignment while maintaining a measure of overall spatial homogeneity. Finally, we investigate the suggestion that observed persistent rotation of microtubule domains can be explained through a handedness bias in microtubule-bound nucleations, showing that this is possible only for an extreme bias and over a limited range of parameters.

  6. Dynamic Stabilization of Metal Oxide–Water Interfaces

    Energy Technology Data Exchange (ETDEWEB)

    McBriarty, Martin E.; von Rudorff, Guido Falk; Stubbs, Joanne E.; Eng, Peter J.; Blumberger, Jochen; Rosso, Kevin M.

    2017-02-08

    The interaction of water with metal oxide surfaces plays a crucial role in the catalytic and geochemical behavior of metal oxides. In a vast majority of studies, the interfacial structure is assumed to arise from a relatively static lowest energy configuration of atoms, even at room temperature. Using hematite (α-Fe2O3) as a model oxide, we show through a direct comparison of in situ synchrotron X-ray scattering with density functional theory-based molecular dynamics simulations that the structure of the (1102) termination is dynamically stabilized by picosecond water exchange. Simulations show frequent exchanges between terminal aquo groups and adsorbed water in locations and with partial residence times consistent with experimentally determined atomic sites and fractional occupancies. Frequent water exchange occurs even for an ultrathin adsorbed water film persisting on the surface under a dry atmosphere. The resulting time-averaged interfacial structure consists of a ridged lateral arrangement of adsorbed water molecules hydrogen bonded to terminal aquo groups. Surface pKa prediction based on bond valence analysis suggests that water exchange will influence the proton-transfer reactions underlying the acid/base reactivity at the interface. Our findings provide important new insights for understanding complex interfacial chemical processes at metal oxide–water interfaces.

  7. Dynamics of microresonator frequency comb generation: models and stability

    Directory of Open Access Journals (Sweden)

    Hansson Tobias

    2016-06-01

    Full Text Available Microresonator frequency combs hold promise for enabling a new class of light sources that are simultaneously both broadband and coherent, and that could allow for a profusion of potential applications. In this article, we review various theoretical models for describing the temporal dynamics and formation of optical frequency combs. These models form the basis for performing numerical simulations that can be used in order to better understand the comb generation process, for example helping to identify the universal combcharacteristics and their different associated physical phenomena. Moreover, models allow for the study, design and optimization of comb properties prior to the fabrication of actual devices. We consider and derive theoretical formalisms based on the Ikeda map, the modal expansion approach, and the Lugiato-Lefever equation. We further discuss the generation of frequency combs in silicon resonators featuring multiphoton absorption and free-carrier effects. Additionally, we review comb stability properties and consider the role of modulational instability as well as of parametric instabilities due to the boundary conditions of the cavity. These instability mechanisms are the basis for comprehending the process of frequency comb formation, for identifying the different dynamical regimes and the associated dependence on the comb parameters. Finally, we also discuss the phenomena of continuous wave bi- and multistability and its relation to the observation of mode-locked cavity solitons.

  8. Actin and microtubule networks contribute differently to cell response for small and large strains

    Science.gov (United States)

    Kubitschke, H.; Schnauss, J.; Nnetu, K. D.; Warmt, E.; Stange, R.; Kaes, J.

    2017-09-01

    Cytoskeletal filaments provide cells with mechanical stability and organization. The main key players are actin filaments and microtubules governing a cell’s response to mechanical stimuli. We investigated the specific influences of these crucial components by deforming MCF-7 epithelial cells at small (≤5% deformation) and large strains (>5% deformation). To understand specific contributions of actin filaments and microtubules, we systematically studied cellular responses after treatment with cytoskeleton influencing drugs. Quantification with the microfluidic optical stretcher allowed capturing the relative deformation and relaxation of cells under different conditions. We separated distinctive deformational and relaxational contributions to cell mechanics for actin and microtubule networks for two orders of magnitude of drug dosages. Disrupting actin filaments via latrunculin A, for instance, revealed a strain-independent softening. Stabilizing these filaments by treatment with jasplakinolide yielded cell softening for small strains but showed no significant change at large strains. In contrast, cells treated with nocodazole to disrupt microtubules displayed a softening at large strains but remained unchanged at small strains. Stabilizing microtubules within the cells via paclitaxel revealed no significant changes for deformations at small strains, but concentration-dependent impact at large strains. This suggests that for suspended cells, the actin cortex is probed at small strains, while at larger strains; the whole cell is probed with a significant contribution from the microtubules.

  9. Atomic-resolution structure of the CAP-Gly domain of dynactin on polymeric microtubules determined by magic angle spinning NMR spectroscopy.

    Science.gov (United States)

    Yan, Si; Guo, Changmiao; Hou, Guangjin; Zhang, Huilan; Lu, Xingyu; Williams, John Charles; Polenova, Tatyana

    2015-11-24

    Microtubules and their associated proteins perform a broad array of essential physiological functions, including mitosis, polarization and differentiation, cell migration, and vesicle and organelle transport. As such, they have been extensively studied at multiple levels of resolution (e.g., from structural biology to cell biology). Despite these efforts, there remain significant gaps in our knowledge concerning how microtubule-binding proteins bind to microtubules, how dynamics connect different conformational states, and how these interactions and dynamics affect cellular processes. Structures of microtubule-associated proteins assembled on polymeric microtubules are not known at atomic resolution. Here, we report a structure of the cytoskeleton-associated protein glycine-rich (CAP-Gly) domain of dynactin motor on polymeric microtubules, solved by magic angle spinning NMR spectroscopy. We present the intermolecular interface of CAP-Gly with microtubules, derived by recording direct dipolar contacts between CAP-Gly and tubulin using double rotational echo double resonance (dREDOR)-filtered experiments. Our results indicate that the structure adopted by CAP-Gly varies, particularly around its loop regions, permitting its interaction with multiple binding partners and with the microtubules. To our knowledge, this study reports the first atomic-resolution structure of a microtubule-associated protein on polymeric microtubules. Our approach lays the foundation for atomic-resolution structural analysis of other microtubule-associated motors.

  10. Stability Analysis for Rotating Stall Dynamics in Axial Flow Compressors

    Science.gov (United States)

    1999-01-01

    modes determines collectively local stability of the compressor model. Explicit conditions are obtained for local stability of rotating stall which...critical modes determines the stability for rotating stall collectively . We point out that although in a special case our stability condition for...strict crossing assumption implies that the zero solution changes its stability as ~, crosses ~’c. For instance, odk (yc ) > 0 implies that the zero

  11. Stability mechanisms of a thermophilic laccase probed by molecular dynamics.

    Directory of Open Access Journals (Sweden)

    Niels J Christensen

    Full Text Available Laccases are highly stable, industrially important enzymes capable of oxidizing a large range of substrates. Causes for their stability are, as for other proteins, poorly understood. In this work, multiple-seed molecular dynamics (MD was applied to a Trametes versicolor laccase in response to variable ionic strengths, temperatures, and glycosylation status. Near-physiological conditions provided excellent agreement with the crystal structure (average RMSD ∼0.92 Å and residual agreement with experimental B-factors. The persistence of backbone hydrogen bonds was identified as a key descriptor of structural response to environment, whereas solvent-accessibility, radius of gyration, and fluctuations were only locally relevant. Backbone hydrogen bonds decreased systematically with temperature in all simulations (∼9 per 50 K, probing structural changes associated with enthalpy-entropy compensation. Approaching T opt (∼350 K from 300 K, this change correlated with a beginning "unzipping" of critical β-sheets. 0 M ionic strength triggered partial denucleation of the C-terminal (known experimentally to be sensitive at 400 K, suggesting a general salt stabilization effect. In contrast, F(- (but not Cl(- specifically impaired secondary structure by formation of strong hydrogen bonds with backbone NH, providing a mechanism for experimentally observed small anion destabilization, potentially remedied by site-directed mutagenesis at critical intrusion sites. N-glycosylation was found to support structural integrity by increasing persistent backbone hydrogen bonds by ∼4 across simulations, mainly via prevention of F(- intrusion. Hydrogen-bond loss in distinct loop regions and ends of critical β-sheets suggest potential strategies for laboratory optimization of these industrially important enzymes.

  12. GLOBAL STABILITY AND PERIODIC SOLUTION OF A VIRAL DYNAMIC MODEL

    Directory of Open Access Journals (Sweden)

    Erhan COŞKUN

    2009-02-01

    Full Text Available Abstract:In this paper, we consider the classical viral dynamic mathematical model. Global dynamics of the model is rigorously established. We prove that, if the basic reproduction number, the HIV infection is cleared from the T-cell population; if , the HIV infection persists. For an open set of parameter values, the chronic-infection equilibrium can be unstable and periodic solutions may exist. We establish parameter regions for which is globally stable. Keywords: Global stability, HIV infection; CD4+ T cells; Periodic solution Mathematics Subject Classifications (2000: 65L10, 34B05 BİR VİRAL DİNAMİK MODELİN GLOBAL KARARLILIĞI VE PERİYODİK ÇÖZÜMÜ Özet: Bu makalede klasik viral dinamik modeli ele aldık. Modelin global dinamikleri oluşturuldu. Eğer temel üretim sayısı olur ise HIV enfeksiyonu T hücre nüfusundan çıkartılır, eğer olursa HIV enfeksiyonu çıkartılamaz. Parametre değerlerinin açık bir kümesi için kronik enfeksiyon dengesi kararsızdır ve periyodik çözüm oluşabilir. ın global kararlı olduğu parametre bölgeleri oluşturuldu. Anahtar Kelimeler: Global Kararlılık, HIV enfeksiyon, CD4+ T hücreler, Periyodik çözüm

  13. Effect of Footwear on Dynamic Stability during Single-leg Jump Landings.

    Science.gov (United States)

    Bowser, Bradley J; Rose, William C; McGrath, Robert; Salerno, Jilian; Wallace, Joshua; Davis, Irene S

    2017-06-01

    Barefoot and minimal footwear running has led to greater interest in the biomechanical effects of different types of footwear. The effect of running footwear on dynamic stability is not well understood. The purpose of this study was to compare dynamic stability and impact loading across 3 footwear conditions; barefoot, minimal footwear and standard running shoes. 25 injury free runners (21 male, 4 female) completed 5 single-leg jump landings in each footwear condition. Dynamic stability was assessed using the dynamic postural stability index and its directional components (mediolateral, anteroposterior, vertical). Peak vertical ground reaction force and vertical loadrates were also compared across footwear conditions. Dynamic stability was dependent on footwear type for all stability indices (ANOVA, pfootwear for the anteroposterior stability index (pfootwear (p≤0.05). Dynamic stability, peak vertical force, and average loadrates during single-leg jump landings appear to be affected by footwear type. The results suggest greater dynamic stability and lower impact loading when landing barefoot or in minimal footwear. © Georg Thieme Verlag KG Stuttgart · New York.

  14. The mathematical model of dynamic stabilization system for autonomous car

    Science.gov (United States)

    Saikin, A. M.; Buznikov, S. E.; Shabanov, N. S.; Elkin, D. S.

    2018-02-01

    Leading foreign companies and domestic enterprises carry out extensive researches and developments in the field of control systems for autonomous cars and in the field of improving driver assistance systems. The search for technical solutions, as a rule, is based on heuristic methods and does not always lead to satisfactory results. The purpose of this research is to formalize the road safety problem in the terms of modern control theory, to construct the adequate mathematical model for solving it, including the choice of software and hardware environment. For automatic control of the object, it is necessary to solve the problem of dynamic stabilization in the most complete formulation. The solution quality of the problem on a finite time interval is estimated by the value of the quadratic functional. Car speed, turn angle and additional yaw rate (during car drift or skidding) measurements are performed programmatically by the original virtual sensors. The limit speeds at which drift, skidding or rollover begins are calculated programmatically taking into account the friction coefficient identified in motion. The analysis of the results confirms both the adequacy of the mathematical models and the algorithms and the possibility of implementing the system in the minimal technical configuration.

  15. Theory of the dynamic stability of plasma systems

    International Nuclear Information System (INIS)

    Bud'ko, A.B.; Velikovich, A.L.; Kleev, A.I.; Liberman, M.A.; Felber, F.S.

    1989-01-01

    Internal instabilities of the plasma of a diffuse pinch result from the acceleration of the plasma in the course of its compression and the expansion of the current channel. The spectra of the growth rates σ m,k of the hydromagnetic instabilities responsible for the disruption of the initial cylindrical symmetry during compression are calculated. For a Z-pinch with a Gaussian density profile, the major instabilities in the course of the compression are the small-scale sausage and kink instabilities with kR >> 1 (R is a typical radius of the pinch). Superimposed on these small-scale instabilities is a filamentation instability with m >> 1, which develops more slowly. If the density instead has a power-law profile, the filamentation instabilities will develop more rapidly than the sausage and kink instabilities. Dynamic stabilization of a pinch by a longitudinal magnetic field makes it possible to maintain symmetry up to radial compressions of the plasma significantly higher than in the absence of a field

  16. Quantitative cell polarity imaging defines leader-to-follower transitions during collective migration and the key role of microtubule-dependent adherens junction formation.

    Science.gov (United States)

    Revenu, Céline; Streichan, Sebastian; Donà, Erika; Lecaudey, Virginie; Hufnagel, Lars; Gilmour, Darren

    2014-03-01

    The directed migration of cell collectives drives the formation of complex organ systems. A characteristic feature of many migrating collectives is a 'tissue-scale' polarity, whereby 'leader' cells at the edge of the tissue guide trailing 'followers' that become assembled into polarised epithelial tissues en route. Here, we combine quantitative imaging and perturbation approaches to investigate epithelial cell state transitions during collective migration and organogenesis, using the zebrafish lateral line primordium as an in vivo model. A readout of three-dimensional cell polarity, based on centrosomal-nucleus axes, allows the transition from migrating leaders to assembled followers to be quantitatively resolved for the first time in vivo. Using live reporters and a novel fluorescent protein timer approach, we investigate changes in cell-cell adhesion underlying this transition by monitoring cadherin receptor localisation and stability. This reveals that while cadherin 2 is expressed across the entire tissue, functional apical junctions are first assembled in the transition zone and become progressively more stable across the leader-follower axis of the tissue. Perturbation experiments demonstrate that the formation of these apical adherens junctions requires dynamic microtubules. However, once stabilised, adherens junction maintenance is microtubule independent. Combined, these data identify a mechanism for regulating leader-to-follower transitions within migrating collectives, based on the relocation and stabilisation of cadherins, and reveal a key role for dynamic microtubules in this process.

  17. Structural differences between yeast and mammalian microtubules revealed by cryo-EM

    Energy Technology Data Exchange (ETDEWEB)

    Howes, Stuart C. [Univ. of California, Berkeley, CA (United States). Biophysics Graduate Group; Geyer, Elisabeth A. [Univ. of Texas Southwestern Medical Center, Dallas, TX (United States). Dept. of Biophysics; Univ. of Texas Southwestern Medical Center, Dallas, TX (United States). Dept. of Biochemistry; LaFrance, Benjamin [Univ. of California, Berkeley, CA (United States). Molecular and Cell Biology Graduate Program; Zhang, Rui [Univ. of California, Berkeley, CA (United States). Howard Hughes Medical Inst.; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division; Kellogg, Elizabeth H. [Univ. of California, Berkeley, CA (United States). Howard Hughes Medical Inst.; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division; Westermann, Stefan [Univ. of Duisburg-Essen, Essen (Germany). Dept. of Molecular Genetics, Center for Medical Biotechnology; Rice, Luke M. [Univ. of Texas Southwestern Medical Center, Dallas, TX (United States). Dept. of Biophysics; Univ. of Texas Southwestern Medical Center, Dallas, TX (United States). Dept. of Biochemistry; Nogales, Eva [Univ. of California, Berkeley, CA (United States). Howard Hughes Medical Inst.; Univ. of California, Berkeley, CA (United States). Dept. of Molecular Biology and California Inst. for Quantitative Biosciences; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division

    2017-06-26

    Microtubules are polymers of αβ-tubulin heterodimers essential for all eukaryotes. Despite sequence conservation, there are significant structural differences between microtubules assembled in vitro from mammalian or budding yeast tubulin. Yeast MTs were not observed to undergo compaction at the interdimer interface as seen for mammalian microtubules upon GTP hydrolysis. Lack of compaction might reflect slower GTP hydrolysis or a different degree of allosteric coupling in the lattice. The microtubule plus end–tracking protein Bim1 binds yeast microtubules both between αβ-tubulin heterodimers, as seen for other organisms, and within tubulin dimers, but binds mammalian tubulin only at interdimer contacts. At the concentrations used in cryo-electron microscopy, Bim1 causes the compaction of yeast microtubules and induces their rapid disassembly. In conclusion, our studies demonstrate structural differences between yeast and mammalian microtubules that likely underlie their differing polymerization dynamics. These differences may reflect adaptations to the demands of different cell size or range of physiological growth temperatures.

  18. Hypothesis: NDL proteins function in stress responses by regulating microtubule organization.

    Science.gov (United States)

    Khatri, Nisha; Mudgil, Yashwanti

    2015-01-01

    N-MYC DOWNREGULATED-LIKE proteins (NDL), members of the alpha/beta hydrolase superfamily were recently rediscovered as interactors of G-protein signaling in Arabidopsis thaliana. Although the precise molecular function of NDL proteins is still elusive, in animals these proteins play protective role in hypoxia and expression is induced by hypoxia and nickel, indicating role in stress. Homology of NDL1 with animal counterpart N-MYC DOWNREGULATED GENE (NDRG) suggests similar functions in animals and plants. It is well established that stress responses leads to the microtubule depolymerization and reorganization which is crucial for stress tolerance. NDRG is a microtubule-associated protein which mediates the microtubule organization in animals by causing acetylation and increases the stability of α-tubulin. As NDL1 is highly homologous to NDRG, involvement of NDL1 in the microtubule organization during plant stress can also be expected. Discovery of interaction of NDL with protein kinesin light chain- related 1, enodomembrane family protein 70, syntaxin-23, tubulin alpha-2 chain, as a part of G protein interactome initiative encourages us to postulate microtubule stabilizing functions for NDL family in plants. Our search for NDL interactors in G protein interactome also predicts the role of NDL proteins in abiotic stress tolerance management. Based on published report in animals and predicted interacting partners for NDL in G protein interactome lead us to hypothesize involvement of NDL in the microtubule organization during abiotic stress management in plants.

  19. Microtubule nucleation and organization in dendrites

    Science.gov (United States)

    Delandre, Caroline; Amikura, Reiko; Moore, Adrian W.

    2016-01-01

    ABSTRACT Dendrite branching is an essential process for building complex nervous systems. It determines the number, distribution and integration of inputs into a neuron, and is regulated to create the diverse dendrite arbor branching patterns characteristic of different neuron types. The microtubule cytoskeleton is critical to provide structure and exert force during dendrite branching. It also supports the functional requirements of dendrites, reflected by differential microtubule architectural organization between neuron types, illustrated here for sensory neurons. Both anterograde and retrograde microtubule polymerization occur within growing dendrites, and recent studies indicate that branching is enhanced by anterograde microtubule polymerization events in nascent branches. The polarities of microtubule polymerization events are regulated by the position and orientation of microtubule nucleation events in the dendrite arbor. Golgi outposts are a primary microtubule nucleation center in dendrites and share common nucleation machinery with the centrosome. In addition, pre-existing dendrite microtubules may act as nucleation sites. We discuss how balancing the activities of distinct nucleation machineries within the growing dendrite can alter microtubule polymerization polarity and dendrite branching, and how regulating this balance can generate neuron type-specific morphologies. PMID:27097122

  20. Microtubule-targeting drugs rescue axonal swellings in cortical neurons from spastin knockout mice

    Directory of Open Access Journals (Sweden)

    Coralie Fassier

    2013-01-01

    Mutations in SPG4, encoding the microtubule-severing protein spastin, are responsible for the most frequent form of hereditary spastic paraplegia (HSP, a heterogeneous group of genetic diseases characterized by degeneration of the corticospinal tracts. We previously reported that mice harboring a deletion in Spg4, generating a premature stop codon, develop progressive axonal degeneration characterized by focal axonal swellings associated with impaired axonal transport. To further characterize the molecular and cellular mechanisms underlying this mutant phenotype, we have assessed microtubule dynamics and axonal transport in primary cultures of cortical neurons from spastin-mutant mice. We show an early and marked impairment of microtubule dynamics all along the axons of spastin-deficient cortical neurons, which is likely to be responsible for the occurrence of axonal swellings and cargo stalling. Our analysis also reveals that a modulation of microtubule dynamics by microtubule-targeting drugs rescues the mutant phenotype of cortical neurons. Together, these results contribute to a better understanding of the pathogenesis of SPG4-linked HSP and ascertain the influence of microtubule-targeted drugs on the early axonal phenotype in a mouse model of the disease.

  1. Stabilities and Dynamics of Protein Folding Nuclei by Molecular Dynamics Simulation

    Science.gov (United States)

    Song, Yong-Shun; Zhou, Xin; Zheng, Wei-Mou; Wang, Yan-Ting

    2017-07-01

    To understand how the stabilities of key nuclei fragments affect protein folding dynamics, we simulate by molecular dynamics (MD) simulation in aqueous solution four fragments cut out of a protein G, including one α-helix (seqB: KVFKQYAN), two β-turns (seqA: LNGKTLKG and seqC: YDDATKTF), and one β-strand (seqD: DGEWTYDD). The Markov State Model clustering method combined with the coarse-grained conformation letters method are employed to analyze the data sampled from 2-μs equilibrium MD simulation trajectories. We find that seqA and seqB have more stable structures than their native structures which become metastable when cut out of the protein structure. As expected, seqD alone is flexible and does not have a stable structure. Throughout our simulations, the native structure of seqC is stable but cannot be reached if starting from a structure other than the native one, implying a funnel-shape free energy landscape of seqC in aqueous solution. All the above results suggest that different nuclei have different formation dynamics during protein folding, which may have a major contribution to the hierarchy of protein folding dynamics. Supported by the National Basic Research Program of China under Grant No. 2013CB932804, the National Natural Science Foundation of China under Grant No. 11421063, and the CAS Biophysics Interdisciplinary Innovation Team Project

  2. Dissecting the nanoscale distributions and functions of microtubule-end-binding proteins EB1 and ch-TOG in interphase HeLa cells.

    Directory of Open Access Journals (Sweden)

    Satoko Nakamura

    Full Text Available Recently, the EB1 and XMAP215/TOG families of microtubule binding proteins have been demonstrated to bind autonomously to the growing plus ends of microtubules and regulate their behaviour in in vitro systems. However, their functional redundancy or difference in cells remains obscure. Here, we compared the nanoscale distributions of EB1 and ch-TOG along microtubules using high-resolution microscopy techniques, and also their roles in microtubule organisation in interphase HeLa cells. The ch-TOG accumulation sites protruded ∼100 nm from the EB1 comets. Overexpression experiments showed that ch-TOG and EB1 did not interfere with each other's localisation, confirming that they recognise distinct regions at the ends of microtubules. While both EB1 and ch-TOG showed similar effects on microtubule plus end dynamics and additively increased microtubule dynamicity, only EB1 exhibited microtubule-cell cortex attachment activity. These observations indicate that EB1 and ch-TOG regulate microtubule organisation differently via distinct regions in the plus ends of microtubules.

  3. Structural stability, dynamical stability, thermoelectric properties, and elastic properties of GeTe at high pressure

    Science.gov (United States)

    Kagdada, Hardik L.; Jha, Prafulla K.; Śpiewak, Piotr; Kurzydłowski, Krzysztof J.

    2018-04-01

    The stability of GeTe in rhombohedral (R 3 m ), face centred cubic (F m 3 m ), and simple cubic (P m 3 m ) phases has been studied using density functional perturbation theory. The rhombohedral phase of GeTe is dynamically stable at 0 GPa, while F m 3 m and P m 3 m phases are stable at 3.1 and 33 GPa, respectively. The pressure-dependent phonon modes are observed in F m 3 m and P m 3 m phases at Γ and M points, respectively. The electronic and the thermoelectric properties have been investigated for the stable phases of GeTe. The electronic band gap for rhombohedral and F m 3 m phases of GeTe has been observed as 0.66 and 0.17 eV, respectively, while the P m 3 m phase shows metallic behavior. We have used the Boltzmann transport equation under a rigid band approximation and constant relaxation time approximation as implemented in boltztrap code for the calculation of thermoelectric properties of GeTe. The metallic behavior of P m 3 m phase gives a very low value of Seebeck coefficient compared to the other two phases as a function of temperature and the chemical potential μ. It is observed that the rhombohedral phase of GeTe exhibits higher thermoelectric performance. Due to the metallic nature of P m 3 m phase, negligible thermoelectric performance is observed compared to R 3 m and F m 3 m -GeTe. The calculated lattice thermal conductivities are low for F m 3 m -GeTe and high for R 3 m -GeTe. At the relatively higher temperature of 1350 K, the figure of merit ZT is found to be 0.7 for rhombohedral GeTe. The elastic constants satisfy the Born stability criteria for all three phases. The rhombohedral and F m 3 m phases exhibits brittleness and the P m 3 m phase shows ductile nature.

  4. Katanin: A Sword Cutting Microtubules for Cellular, Developmental, and Physiological Purposes

    Directory of Open Access Journals (Sweden)

    Ivan Luptovčiak

    2017-11-01

    Full Text Available KATANIN is a well-studied microtubule severing protein affecting microtubule organization and dynamic properties in higher plants. By regulating mitotic and cytokinetic and cortical microtubule arrays it is involved in the progression of cell division and cell division plane orientation. KATANIN is also involved in cell elongation and morphogenesis during plant growth. In this way KATANIN plays critical roles in diverse plant developmental processes including the development of pollen, embryo, seed, meristem, root, hypocotyl, cotyledon, leaf, shoot, and silique. KATANIN-dependent microtubule regulation seems to be under the control of plant hormones. This minireview provides an overview on available KATANIN mutants and discusses advances in our understanding of KATANIN biological roles in plants.

  5. Obesity May Not Induce Dynamic Stability Disadvantage during Overground Walking among Young Adults.

    Science.gov (United States)

    Liu, Zhong-Qi; Yang, Feng

    2017-01-01

    Obesity has been related to postural instability during static standing. It remains unknown how obesity influences stability during dynamic movements like gait. The primary aim of this study was to investigate the effects of obesity on dynamic gait stability control in young adults during gait. Forty-four young adults (21 normal-weight and 23 obese) participated in this study. Participants walked five times at their self-selected gait speeds on a linear walkway. Their full-body kinematics were gathered by a motion capture system. Compared with normal-weight group, individuals with obesity walked more slowly with a shorter but wider step. People with obesity also spent an elongated double stance phase than those with normal weight. A reduced gait speed decreases the body center of mass's velocity relative to the base of support, leading to a reduction in dynamic stability. On the other hand, a shortened step in accompanying with a less backward-leaning trunk has the potential to bring the center of mass closer to the base of support, resulting in an increase in dynamic stability. As the result of these adaptive changes to the gait pattern, dynamic gait stability among people with obesity did not significantly differ from the one among people with normal weight. Obesity seems to not be inducing dynamic stability disadvantage in young adults during level overground walking. These findings could provide insight into the mechanisms of stability control among people affected by obesity during dynamic locomotion.

  6. Tubulin cofactor B regulates microtubule densities during microglia transition to the reactive states

    International Nuclear Information System (INIS)

    Fanarraga, M.L.; Villegas, J.C.; Carranza, G.; Castano, R.; Zabala, J.C.

    2009-01-01

    Microglia are highly dynamic cells of the CNS that continuously survey the welfare of the neural parenchyma and play key roles modulating neurogenesis and neuronal cell death. In response to injury or pathogen invasion parenchymal microglia transforms into a more active cell that proliferates, migrates and behaves as a macrophage. The acquisition of these extra skills implicates enormous modifications of the microtubule and actin cytoskeletons. Here we show that tubulin cofactor B (TBCB), which has been found to contribute to various aspects of microtubule dynamics in vivo, is also implicated in microglial cytoskeletal changes. We find that TBCB is upregulated in post-lesion reactive parenchymal microglia/macrophages, in interferon treated BV-2 microglial cells, and in neonate amoeboid microglia where the microtubule densities are remarkably low. Our data demonstrate that upon TBCB downregulation both, after microglia differentiation to the ramified phenotype in vivo and in vitro, or after TBCB gene silencing, microtubule densities are restored in these cells. Taken together these observations support the view that TBCB functions as a microtubule density regulator in microglia during activation, and provide an insight into the understanding of the complex mechanisms controlling microtubule reorganization during microglial transition between the amoeboid, ramified, and reactive phenotypes

  7. Luminal localization of α-tubulin K40 acetylation by cryo-EM analysis of fab-labeled microtubules.

    Directory of Open Access Journals (Sweden)

    Virupakshi Soppina

    Full Text Available The αβ-tubulin subunits of microtubules can undergo a variety of evolutionarily-conserved post-translational modifications (PTMs that provide functional specialization to subsets of cellular microtubules. Acetylation of α-tubulin residue Lysine-40 (K40 has been correlated with increased microtubule stability, intracellular transport, and ciliary assembly, yet a mechanistic understanding of how acetylation influences these events is lacking. Using the anti-acetylated tubulin antibody 6-11B-1 and electron cryo-microscopy, we demonstrate that the K40 acetylation site is located inside the microtubule lumen and thus cannot directly influence events on the microtubule surface, including kinesin-1 binding. Surprisingly, the monoclonal 6-11B-1 antibody recognizes both acetylated and deacetylated microtubules. These results suggest that acetylation induces structural changes in the K40-containing loop that could have important functional consequences on microtubule stability, bending, and subunit interactions. This work has important implications for acetylation and deacetylation reaction mechanisms as well as for interpreting experiments based on 6-11B-1 labeling.

  8. Influence of carbon nanotubes on the buckling of microtubule bundles in viscoelastic cytoplasm using nonlocal strain gradient theory

    Directory of Open Access Journals (Sweden)

    A. Farajpour

    Full Text Available Carbon nanotubes are a new class of microtubule-stabilizing agents since they interact with protein microtubules in living cells, interfering with cell division and inducing apoptosis. In the present work, a modified beam model is developed to investigate the effect of carbon nanotubes on the buckling of microtubule bundles in living cell. A realistic interaction model is employed using recent experimental data on the carbon nanotube-stabilized microtubules. Small scale and surface effects are taken into account applying the nonlocal strain gradient theory and surface elasticity theory. Pasternak model is used to describe the normal and shearing effects of enclosing filament matrix on the buckling behavior of the system. An exact solution is obtained for the buckling growth rates of the mixed bundle in viscoelastic surrounding cytoplasm. The present results are compared with those reported in the open literature for single microtubules and an excellent agreement is found. Finally, the effects of different parameters such as the size, chirality, position and surface energy of carbon nanotubes on the buckling growth rates of microtubule bundles are studied. It is found that the buckling growth rate may increase or decrease by adding carbon nanotubes, depending on the diameter and chirality of carbon nanotubes. Keywords: Microtubules, Carbon nanotubes, Buckling, Size effects

  9. Near-atomic model of microtubule-tau interactions.

    Science.gov (United States)

    Kellogg, Elizabeth H; Hejab, Nisreen M A; Poepsel, Simon; Downing, Kenneth H; DiMaio, Frank; Nogales, Eva

    2018-06-15

    Tau is a developmentally regulated axonal protein that stabilizes and bundles microtubules (MTs). Its hyperphosphorylation is thought to cause detachment from MTs and subsequent aggregation into fibrils implicated in Alzheimer's disease. It is unclear which tau residues are crucial for tau-MT interactions, where tau binds on MTs, and how it stabilizes them. We used cryo-electron microscopy to visualize different tau constructs on MTs and computational approaches to generate atomic models of tau-tubulin interactions. The conserved tubulin-binding repeats within tau adopt similar extended structures along the crest of the protofilament, stabilizing the interface between tubulin dimers. Our structures explain the effect of phosphorylation on MT affinity and lead to a model of tau repeats binding in tandem along protofilaments, tethering together tubulin dimers and stabilizing polymerization interfaces. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  10. Microtubule Regulation of Kv7 Channels Orchestrates cAMP-Mediated Vasorelaxations in Rat Arterial Smooth Muscle

    DEFF Research Database (Denmark)

    Lindman, Johanna; Khammy, Makhala M; Lundegaard, Pia R

    2018-01-01

    Microtubules can regulate GPCR (G protein-coupled receptor) signaling in various cell types. In vascular smooth muscle, activation of the β-adrenoceptor leads to production of cAMP to mediate a vasorelaxation. Little is known about the role of microtubules in smooth muscle, and given the importance...... of renal and mesenteric arteries that the microtubule stabilizer, paclitaxel, prevented. Sharp microelectrode experiments showed that colchicine treatment caused increased hyperpolarization of mesenteric artery segments in response to isoprenaline. Application of the Kv7 channel blocker, XE991, attenuated...

  11. Dynamic stability of a curved pipe bent in the arc of a circle on hinge ...

    Indian Academy of Sciences (India)

    of numerical solution of the dynamic stability of a pipe in its plane are developed. An example of a ... Most scientific researches in the area of vibrations of pipes conveying liquids are concerned with investigation of ..... is good coincidence. 5.

  12. Theory and analysis of nonlinear dynamics and stability in storage rings: A working group summary

    International Nuclear Information System (INIS)

    Chattopadhyay, S.; Audy, P.; Courant, E.D.

    1988-07-01

    A summary and commentary of the available theoretical and analytical tools and recent advances in the nonlinear dynamics, stability and aperture issues in storage rings are presented. 11 refs., 4 figs

  13. Short term outcome of posterior dynamic stabilization system in degenerative lumbar diseases

    Directory of Open Access Journals (Sweden)

    Mingyuan Yang

    2014-01-01

    Conclusion: Dynamic stabilization system treating lumbar degenerative disease showed clinical benefits with motion preservation of the operated segments, but does not have the significant advantage on motion preservation at adjacent segments, to avoid the degeneration of adjacent intervertebral disk.

  14. Dynamics, Stability, and Evolutionary Patterns of Mesoscale Intrathermocline Vortices

    Science.gov (United States)

    2016-12-01

    different manner from a dynamic eddy, which underscores inherent limitations of intrusion modeling in quiescent background states. Finally, it...of observed values. (3) A static eddy dissipates in a very different manner from a dynamic eddy, which underscores inherent limitations of...does not react to the environment in a physical manner . This establishes a need for future research on eddies to be modeled on a dynamically rotating

  15. Assessment of stability during gait in patients with spinal deformity-A preliminary analysis using the dynamic stability margin.

    Science.gov (United States)

    Simon, Anne-Laure; Lugade, Vipul; Bernhardt, Kathie; Larson, A Noelle; Kaufman, Kenton

    2017-06-01

    Daily living activities are dynamic, requiring spinal motion through space. Current assessment of spinal deformities is based on static measurements from full-spine standing radiographs. Tools to assess dynamic stability during gait might be useful to enhance the standard evaluation. The aim of this study was to evaluate gait dynamic imbalance in patients with spinal deformity using the dynamic stability margin (DSM). Twelve normal subjects and 17 patients with spinal deformity were prospectively recruited. A kinematic 3D gait analysis was performed for the control group (CG) and the spinal deformity group (SDG). The DSM (distance between the extrapolated center of mass and the base of support) and time-distance parameters were calculated for the right and left side during gait. The relationship between DSM and step length was assessed using three variables: gait stability, symmetry, and consistency. Variables' accuracy was validated by a discriminant analysis. Patients with spinal deformity exhibited gait instability according to the DSM (0.25m versus 0.31m) with decreased velocity (1.1ms -1 versus 1.3ms -1 ) and decreased step length (0.32m versus 0.38m). According to the discriminant analysis, gait stability was the more accurate variable (area under the curve AUC=0.98) followed by gait symmetry and consistency. However, gait consistency showed 100% of specificity, sensitivity, and accuracy of precision. The DSM showed that patients with spinal malalignment exhibit decreased gait stability, symmetry, and consistency besides gait time-distance parameter changes. Additional work is required to determine how to apply the DSM for preoperative and postoperative spinal deformity management. Copyright © 2017. Published by Elsevier B.V.

  16. The Effects of Core Stabilization Exercise on Dynamic Balance and Gait Function in Stroke Patients

    OpenAIRE

    Chung, Eun-Jung; Kim, Jung-Hee; Lee, Byoung-Hee

    2013-01-01

    [Purpose] The purpose of this study was to determine the effects of core stabilization exercise on dynamic balance and gait function in stroke patients. [Subjects] The subjects were 16 stroke patients, who were randomly divided into two groups: a core stabilization exercise group of eight subjects and control group of eight subjects. [Methods] Subjects in both groups received general training five times per week. Subjects in the core stabilization exercise group practiced an additional core s...

  17. Investigation of biomechanical behavior of lumbar vertebral segments with dynamic stabilization device using finite element approach

    Science.gov (United States)

    Deoghare, Ashish B.; Kashyap, Siddharth; Padole, Pramod M.

    2013-03-01

    Degenerative disc disease is a major source of lower back pain and significantly alters the biomechanics of the lumbar spine. Dynamic stabilization device is a remedial technique which uses flexible materials to stabilize the affected lumbar region while preserving the natural anatomy of the spine. The main objective of this research work is to investigate the stiffness variation of dynamic stabilization device under various loading conditions under compression, axial rotation and flexion. Three dimensional model of the two segment lumbar spine is developed using computed tomography (CT) scan images. The lumbar structure developed is analyzed in ANSYS workbench. Two types of dynamic stabilization are considered: one with stabilizing device as pedicle instrumentation and second with stabilization device inserted around the inter-vertebral disc. Analysis suggests that proper positioning of the dynamic stabilization device is of paramount significance prior to the surgery. Inserting the device in the posterior region indicates the adverse effects as it shows increase in the deformation of the inter-vertebral disc. Analysis executed by positioning stabilizing device around the inter-vertebral disc yields better result for various stiffness values under compression and other loadings. [Figure not available: see fulltext.

  18. Direct evidence for GTP and GDP-Pi intermediates in microtubule assembly

    International Nuclear Information System (INIS)

    Melki, R.; Carlier, M.F.; Pantaloni, D.

    1990-01-01

    Identification of the kinetic intermediates in GTP hydrolysis on microtubules and characterization of their assembly properties is essential in understanding microtubule dynamics. By using an improved glass filter assay that selectively traps microtubules with a dead time of 2 s and monitoring taxol-induced rapid assembly of microtubules from [γ- 32 P, 3 H]GTP-tubulin 1:1 complex, direct evidence has been obtained for GTP- and GDP-P i -microtubule transient states in the early stages of the polymerization process. A simple kinetic analysis of GTP hydrolysis on microtubules within two sequential pseudo-first-order processes led to apparent first-order rate constants of 0.065 s -1 for the cleavage of the γ-phosphate and 0.02 s -1 for the liberation of P i , assuming a simple random model. Apparent rate constants for GTP hydrolysis and P i release were independent of the composition of the buffer used to polymerize tubulin. The significance of these values with respect to those derived from previous studies from this and other laboratories and the possibility of a vectorial model for GTP hydrolysis are discussed

  19. Motivational Dynamics in Language Learning: Change, Stability, and Context

    Science.gov (United States)

    Waninge, Freerkien; Dörnyei, Zoltán; De Bot, Kees

    2014-01-01

    Motivation as a variable in L2 development is no longer seen as the stable individual difference factor it was once believed to be: Influenced by process-oriented models and principles, and especially by the growing understanding of how complex dynamic systems work, researchers have been focusing increasingly on the dynamic and changeable nature…

  20. Standard representation and unified stability analysis for dynamic artificial neural network models.

    Science.gov (United States)

    Kim, Kwang-Ki K; Patrón, Ernesto Ríos; Braatz, Richard D

    2018-02-01

    An overview is provided of dynamic artificial neural network models (DANNs) for nonlinear dynamical system identification and control problems, and convex stability conditions are proposed that are less conservative than past results. The three most popular classes of dynamic artificial neural network models are described, with their mathematical representations and architectures followed by transformations based on their block diagrams that are convenient for stability and performance analyses. Classes of nonlinear dynamical systems that are universally approximated by such models are characterized, which include rigorous upper bounds on the approximation errors. A unified framework and linear matrix inequality-based stability conditions are described for different classes of dynamic artificial neural network models that take additional information into account such as local slope restrictions and whether the nonlinearities within the DANNs are odd. A theoretical example shows reduced conservatism obtained by the conditions. Copyright © 2017. Published by Elsevier Ltd.

  1. Nonlinear dynamics near the stability margin in rotating pipe flow

    Science.gov (United States)

    Yang, Z.; Leibovich, S.

    1991-01-01

    The nonlinear evolution of marginally unstable wave packets in rotating pipe flow is studied. These flows depend on two control parameters, which may be taken to be the axial Reynolds number R and a Rossby number, q. Marginal stability is realized on a curve in the (R, q)-plane, and the entire marginal stability boundary is explored. As the flow passes through any point on the marginal stability curve, it undergoes a supercritical Hopf bifurcation and the steady base flow is replaced by a traveling wave. The envelope of the wave system is governed by a complex Ginzburg-Landau equation. The Ginzburg-Landau equation admits Stokes waves, which correspond to standing modulations of the linear traveling wavetrain, as well as traveling wave modulations of the linear wavetrain. Bands of wavenumbers are identified in which the nonlinear modulated waves are subject to a sideband instability.

  2. Profilin connects actin assembly with microtubule dynamics

    Czech Academy of Sciences Publication Activity Database

    Nejedla, M.; Sadi, S.; Sulimenko, Vadym; de Almeida, F.N.; Blom, H.; Dráber, Pavel; Aspenstrom, P.; Karlsson, R.

    2016-01-01

    Roč. 27, č. 15 (2016), s. 2381-2393 ISSN 1059-1524 R&D Projects: GA ČR GA16-25159S Institutional support: RVO:68378050 Keywords : cross-linked profilin * arp2/3 complex * f-actin * microfilament system * migrating cells * focal adhesions * cultured-cells * messenger-rna * living cells * protein Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 3.685, year: 2016

  3. Stability properties of nonlinear dynamical systems and evolutionary stable states

    Energy Technology Data Exchange (ETDEWEB)

    Gleria, Iram, E-mail: iram@fis.ufal.br [Instituto de Física, Universidade Federal de Alagoas, 57072-970 Maceió-AL (Brazil); Brenig, Leon [Faculté des Sciences, Université Libre de Bruxelles, 1050 Brussels (Belgium); Rocha Filho, Tarcísio M.; Figueiredo, Annibal [Instituto de Física and International Center for Condensed Matter Physics, Universidade de Brasília, 70919-970 Brasília-DF (Brazil)

    2017-03-18

    Highlights: • We address the problem of equilibrium stability in a general class of non-linear systems. • We link Evolutionary Stable States (ESS) to stable fixed points of square quasi-polynomial (QP) systems. • We show that an interior ES point may be related to stable interior fixed points of QP systems. - Abstract: In this paper we address the problem of stability in a general class of non-linear systems. We establish a link between the concepts of asymptotic stable interior fixed points of square Quasi-Polynomial systems and evolutionary stable states, a property of some payoff matrices arising from evolutionary games.

  4. Stability and stabilisation of a class of networked dynamic systems

    Science.gov (United States)

    Liu, H. B.; Wang, D. Q.

    2018-04-01

    We investigate the stability and stabilisation of a linear time invariant networked heterogeneous system with arbitrarily connected subsystems. A new linear matrix inequality based sufficient and necessary condition for the stability is derived, based on which the stabilisation is provided. The obtained conditions efficiently utilise the block-diagonal characteristic of system parameter matrices and the sparseness of subsystem connection matrix. Moreover, a sufficient condition only dependent on each individual subsystem is also presented for the stabilisation of the networked systems with a large scale. Numerical simulations show that these conditions are computationally valid in the analysis and synthesis of a large-scale networked system.

  5. Dynamical stability of the alpha and theta phases of alumina

    DEFF Research Database (Denmark)

    Lodziana, Zbigniew; Parlinski, K.

    2003-01-01

    Using density functional calculations the phonon dispersion relations, phonon density of states, and free energy of theta and alpha phases of alumina are investigated. The temperature dependence of the free energy indicates that entropy contributes to the destabilization of the alpha phase...... cations in alumina, and suggest that some other than entropic mechanism exists, which stabilizes transition aluminas up to 1400 K. The present calculations go beyond the ground state energy calculations [C. Wolverton and K.C. Hass, Phys. Rev. B 63, 24102 (2001)], and give an additional understanding...... of the stability of transition alumina at finite temperatures....

  6. A novel mechanism important for the alignment of microtubules.

    Science.gov (United States)

    Wightman, Raymond; Turner, Simon R

    2008-04-01

    Using a live-cell imaging approach to study individual micro-tubules, we have compared microtubule behavior between net-like and aligned cortical arrays. In contrast to previous studies, a steep angled collision between the growing end of a microtubule and a preexisting microtubule was found to favor crossover. Frequencies of microtubule crossovers, bundling and catastrophes are similar regardless of whether the cell exhibited a net-like or aligned microtubule array. In the predominantly aligned array of petiole cells, severing occurs at the sites of microtubule crossovers and serves to remove unaligned microtubules and to increase microtubule density. Severing was observed to be rare in net-like arrays. Microtubule severing is carried out by the katanin enzyme. In this addendum, we present new insights into the possible mechanism of crossing over and preliminary data looking at organization of the array in a katanin mutant.

  7. Dynamic stability of self-similar solutions for a plasma pinch

    International Nuclear Information System (INIS)

    Ma, Sifeng.

    1988-01-01

    Linear Magnetohydrodynamic (MHD) stability theory is applied to a class of self-similar solutions which describe implosion, expansion and oscillation of an infinitely conducting plasma column. The equations of perturbation are derived in the Lagrangian coordinate system. Numerical procedures via the finite-element method are formulated, and general aspects of dynamic stability are discussed, The dynamic stability of the column when it is oscillatory is studied in detail using the Floquet theory, and the characteristic exponent is calculated numerically. A-pinch configuration is examined. It is found that self-similar oscillations in general destabilize the continua in the MHD spectrum, and parametric instability results

  8. Stability Analysis on Sparsely Encoded Associative Memory with Short-Term Synaptic Dynamics

    Science.gov (United States)

    Xu, Muyuan; Katori, Yuichi; Aihara, Kazuyuki

    This study investigates the stability of sparsely encoded associative memory in a network composed of stochastic neurons. The incorporation of short-term synaptic dynamics significantly changes the stability with respect to synaptic properties. Various states including static and oscillatory states are found in the network dynamics. Specifically, the sparseness of memory patterns raises the problem of spurious states. A mean field model is used to analyze the detailed structure in the stability and show that the performance of memory retrieval is recovered by appropriate feedback.

  9. Dynamics, stability analysis and quantization of β-Fermi–Pasta ...

    Indian Academy of Sciences (India)

    We study the well-known one-dimensional problem of particles with nonlinear interaction. The -Fermi–Pasta–Ulam model is the special case of quadratic and quartic interaction potential among nearest neighbours. We enumerate and classify the simple periodic orbits for this system and find the stability zones, ...

  10. Stability and dynamic analysis of a service robot

    NARCIS (Netherlands)

    Bouten, J.T.; Alvarez Aguirre, A.; Derks, R.J.S.; Nijmeijer, H.

    2011-01-01

    A Remote Operated SErvice robot (ROSE) is built to assist elderly people in health care. The use of technology to assist the elderly and disabled is desirable to ease the burden on the decreasing working population in the Netherlands and all over Europe. In this report the stability of the ROSE

  11. Meteorological fluid dynamics asymptotic modelling, stability and chaotic atmospheric motion

    CERN Document Server

    Zeytounian, Radyadour K

    1991-01-01

    The author considers meteorology as a part of fluid dynamics. He tries to derive the properties of atmospheric flows from a rational analysis of the Navier-Stokes equations, at the same time analyzing various types of initial and boundary problems. This approach to simulate nature by models from fluid dynamics will be of interest to both scientists and students of physics and theoretical meteorology.

  12. A unifying energy-based approach to stability of power grids with market dynamics

    NARCIS (Netherlands)

    Stegink, Tjerk; De Persis, Claudio; van der Schaft, Arjan

    2017-01-01

    In this paper a unifying energy-based approach is provided to the modeling and stability analysis of power systems coupled with market dynamics. We consider a standard model of the power network with a third-order model for the synchronous generators involving voltage dynamics. By applying the

  13. Effect of soil stabilized by cement on dynamic response of machine foundations

    Directory of Open Access Journals (Sweden)

    Al-Wakel Saad

    2018-01-01

    Full Text Available Machine foundations require significant attention from designers. The main goal of the design of machine foundation is to limit the amplitude displacement and not disturb the people who work near the machine. In some cases, if the design of machine foundations does not satisfy the acceptable value of the dynamic response (such as maximum amplitude of displacement, the stabilization of soil under the machine foundation may be used to decrease the amplitude of displacement. This paper outlines effect of stabilized soil under the foundation by cement on the displacement response of machine foundations. Three-dimensional analyses by using finite element method are carried out to investigate the effect of depth of stabilized layer with different percentage of cement content on the dynamic response of the machine foundation. In addition, the effect of area stabilized by cement material on the dynamic response of machine foundation is investigated. The results shown that, the dynamic response of machine foundations generally decreases with increasing the depth of soil layer stabilized with cement. A significant decrease in the displacement of machine foundations is occurred for the stabilized soil layer with a depth of two times of the width of foundation, and the optimum percentage of cement for stabilizing is 6%.

  14. Research on Dynamics and Stability in the Stairs-Climbing of a Tracked Mobile Robot

    Directory of Open Access Journals (Sweden)

    Weijun Tao

    2012-10-01

    Full Text Available Aiming at the functional requirement of climbing up the stairs, the dynamics and stability during a tracked mobile robot's climbing of stairs is studied. First, from the analysis of its cross-country performance, the mechanical structure of the tracked mobile robot is designed and the hardware composition of its control system is given. Second, based on the analysis to its stairs-climbing process, the dynamical model of stairs-climbing is established by using the classical mechanics method. Next, the stability conditions for its stairs-climbing are determined and an evaluation method of its stairs-climbing stability is proposed, based on a mechanics analysis on the robot's backwards tumbling during the stairs-climbing process. Through simulation and experiments, the effectiveness of the dynamical model and the stability evaluation method of the tracked mobile robot in stairs-climbing is verified, which can provide design and analysis foundations for the tracked mobile robots' stairs-climbing.

  15. Microtubule array reorientation in response to hormones does not involve changes in microtubule nucleation modes at the periclinal cell surface

    Science.gov (United States)

    Atkinson, Samantha; Kirik, Angela; Kirik, Viktor

    2014-01-01

    Aligned microtubule arrays spatially organize cell division, trafficking, and determine the direction of cell expansion in plant cells. In response to changes in environmental and developmental signals, cells reorganize their microtubule arrays into new configurations. Here, we tested the role of microtubule nucleation during hormone-induced microtubule array reorientation. We have found that in the process of microtubule array reorientation the ratios between branching, parallel, and de-novo nucleations remained constant, suggesting that the microtubule reorientation mechanism does not involve changes in nucleation modes. In the ton2/fass mutant, which has reduced microtubule branching nucleation frequency and decreased nucleation activity of the γ-tubulin complexes, microtubule arrays were able to reorient. Presented data suggest that reorientation of microtubules into transverse arrays in response to hormones does not involve changes in microtubule nucleation at the periclinal cell surface PMID:25135522

  16. The dynamic stability of OPEC's oil price mechanism

    International Nuclear Information System (INIS)

    Hammoudeh, S.; Madan, V.

    1992-01-01

    This paper examines OPEC's long-lived mechanism which targets the oil price and adjusts the quality ceiling to meet the target. The stability of this controversial mechanism is compared to that of two alternatives: one requires quantity control without any price targeting and the other is a synthesis of quantity control and the OPEC mechanisms. All three mechanisms passed the stability test and the two alternatives give rise to some interesting policy implications. Practicality considerations which involve the availability of specific information make OPEC's mechanism the most appropriate in terms of achieved targeted revenues. The paper also offers a convergence strategy that speeds up the achievement of targeted revenues under OPEC's current mechanism. (author)

  17. Distributed-Order Dynamic Systems Stability, Simulation, Applications and Perspectives

    CERN Document Server

    Jiao, Zhuang; Podlubny, Igor

    2012-01-01

    Distributed-order differential equations, a generalization of fractional calculus, are of increasing importance in many fields of science and engineering from the behaviour of complex dielectric media to the modelling of nonlinear systems. This Brief will broaden the toolbox available to researchers interested in modeling, analysis, control and filtering. It contains contextual material outlining the progression from integer-order, through fractional-order to distributed-order systems. Stability issues are addressed with graphical and numerical results highlighting the fundamental differences between constant-, integer-, and distributed-order treatments. The power of the distributed-order model is demonstrated with work on the stability of noncommensurate-order linear time-invariant systems. Generic applications of the distributed-order operator follow: signal processing and viscoelastic damping of a mass–spring set up. A new general approach to discretization of distributed-order derivatives and integrals ...

  18. Dynamic Biological Functioning Important for Simulating and Stabilizing Ocean Biogeochemistry

    Science.gov (United States)

    Buchanan, P. J.; Matear, R. J.; Chase, Z.; Phipps, S. J.; Bindoff, N. L.

    2018-04-01

    The biogeochemistry of the ocean exerts a strong influence on the climate by modulating atmospheric greenhouse gases. In turn, ocean biogeochemistry depends on numerous physical and biological processes that change over space and time. Accurately simulating these processes is fundamental for accurately simulating the ocean's role within the climate. However, our simulation of these processes is often simplistic, despite a growing understanding of underlying biological dynamics. Here we explore how new parameterizations of biological processes affect simulated biogeochemical properties in a global ocean model. We combine 6 different physical realizations with 6 different biogeochemical parameterizations (36 unique ocean states). The biogeochemical parameterizations, all previously published, aim to more accurately represent the response of ocean biology to changing physical conditions. We make three major findings. First, oxygen, carbon, alkalinity, and phosphate fields are more sensitive to changes in the ocean's physical state. Only nitrate is more sensitive to changes in biological processes, and we suggest that assessment protocols for ocean biogeochemical models formally include the marine nitrogen cycle to assess their performance. Second, we show that dynamic variations in the production, remineralization, and stoichiometry of organic matter in response to changing environmental conditions benefit the simulation of ocean biogeochemistry. Third, dynamic biological functioning reduces the sensitivity of biogeochemical properties to physical change. Carbon and nitrogen inventories were 50% and 20% less sensitive to physical changes, respectively, in simulations that incorporated dynamic biological functioning. These results highlight the importance of a dynamic biology for ocean properties and climate.

  19. Nonlinear dynamics of human locomotion: effects of rhythmic auditory cueing on local dynamic stability

    Directory of Open Access Journals (Sweden)

    Philippe eTerrier

    2013-09-01

    Full Text Available It has been observed that times series of gait parameters (stride length (SL, stride time (ST and stride speed (SS, exhibit long-term persistence and fractal-like properties. Synchronizing steps with rhythmic auditory stimuli modifies the persistent fluctuation pattern to anti-persistence. Another nonlinear method estimates the degree of resilience of gait control to small perturbations, i.e. the local dynamic stability (LDS. The method makes use of the maximal Lyapunov exponent, which estimates how fast a nonlinear system embedded in a reconstructed state space (attractor diverges after an infinitesimal perturbation. We propose to use an instrumented treadmill to simultaneously measure basic gait parameters (time series of SL, ST and SS from which the statistical persistence among consecutive strides can be assessed, and the trajectory of the center of pressure (from which the LDS can be estimated. In 20 healthy participants, the response to rhythmic auditory cueing (RAC of LDS and of statistical persistence (assessed with detrended fluctuation analysis (DFA was compared. By analyzing the divergence curves, we observed that long-term LDS (computed as the reverse of the average logarithmic rate of divergence between the 4th and the 10th strides downstream from nearest neighbors in the reconstructed attractor was strongly enhanced (relative change +47%. That is likely the indication of a more dampened dynamics. The change in short-term LDS (divergence over one step was smaller (+3%. DFA results (scaling exponents confirmed an anti-persistent pattern in ST, SL and SS. Long-term LDS (but not short-term LDS and scaling exponents exhibited a significant correlation between them (r=0.7. Both phenomena probably result from the more conscious/voluntary gait control that is required by RAC. We suggest that LDS and statistical persistence should be used to evaluate the efficiency of cueing therapy in patients with neurological gait disorders.

  20. Predator interference and stability of predator-prey dynamics

    Czech Academy of Sciences Publication Activity Database

    Přibylová, L.; Berec, Luděk

    2015-01-01

    Roč. 71, č. 2 (2015), s. 301-323 ISSN 0303-6812 Grant - others:European Social Fund(CZ) CZ.1.07/2.2.00/15.0203 Institutional support: RVO:60077344 Keywords : population stability * functional response * intraspecific competition Subject RIV: EH - Ecology, Behaviour Impact factor: 1.716, year: 2015 http://link.springer.com/article/10.1007%2Fs00285-014-0820-9

  1. Drosophila homologue of Diaphanous 1 (DIAPH1) controls the metastatic potential of colon cancer cells by regulating microtubule-dependent adhesion.

    Science.gov (United States)

    Lin, Yuan-Na; Bhuwania, Ridhirama; Gromova, Kira; Failla, Antonio Virgilio; Lange, Tobias; Riecken, Kristoffer; Linder, Stefan; Kneussel, Matthias; Izbicki, Jakob R; Windhorst, Sabine

    2015-07-30

    Drosophila homologue of Diaphanous 1 (DIAPH1) regulates actin polymerization and microtubule (MT) stabilization upon stimulation with lysophosphatidic acid (LPA). Recently, we showed strongly reduced lung metastasis of DIAPH1-depleted colon cancer cells but we found accumulations of DIAPH1-depleted cells in bone marrow. Here, we analyzed possible organ- or tissue-specific metastasis of DIAPH1-depleted HCT-116 cells. Our data confirmed that depletion of DIAPH1 strongly inhibited lung metastasis and revealed that, in contrast to control cells, DIAPH1-depleted cells did not form metastases in further organs. Detailed mechanistic analysis on cells that were not stimulated with LPA to activate the cytoskeleton-modulating activity of DIAPH1, revealed that even under basal conditions DIAPH1 was essential for cellular adhesion to collagen. In non-stimulated cells DIAPH1 did not control actin dynamics but, interestingly, was essential for stabilization of microtubules (MTs). Additionally, DIAPH1 controlled directed vesicle trafficking and with this, local clustering of the adhesion protein integrin-β1 at the plasma membrane. Therefore, we conclude that under non-stimulating conditions DIAPH1 controls cellular adhesion by stabilizing MTs required for local clustering of integrin-β1 at the plasma membrane. Thus, blockade of DIAPH1-tubulin interaction may be a promising approach to inhibit one of the earliest steps in the metastatic cascade of colon cancer.

  2. Ionic wave propagation and collision in an excitable circuit model of microtubules

    Science.gov (United States)

    Guemkam Ghomsi, P.; Tameh Berinyoh, J. T.; Moukam Kakmeni, F. M.

    2018-02-01

    In this paper, we report the propensity to excitability of the internal structure of cellular microtubules, modelled as a relatively large one-dimensional spatial array of electrical units with nonlinear resistive features. We propose a model mimicking the dynamics of a large set of such intracellular dynamical entities as an excitable medium. We show that the behavior of such lattices can be described by a complex Ginzburg-Landau equation, which admits several wave solutions, including the plane waves paradigm. A stability analysis of the plane waves solutions of our dynamical system is conducted both analytically and numerically. It is observed that perturbed plane waves will always evolve toward promoting the generation of localized periodic waves trains. These modes include both stationary and travelling spatial excitations. They encompass, on one hand, localized structures such as solitary waves embracing bright solitons, dark solitons, and bisolitonic impulses with head-on collisions phenomena, and on the other hand, the appearance of both spatially homogeneous and spatially inhomogeneous stationary patterns. This ability exhibited by our array of proteinic elements to display several states of excitability exposes their stunning biological and physical complexity and is of high relevance in the description of the developmental and informative processes occurring on the subcellular scale.

  3. Phase stability and dynamics of entangled polymer-nanoparticle composites.

    KAUST Repository

    Mangal, Rahul

    2015-06-05

    Nanoparticle-polymer composites, or polymer-nanoparticle composites (PNCs), exhibit unusual mechanical and dynamical features when the particle size approaches the random coil dimensions of the host polymer. Here, we harness favourable enthalpic interactions between particle-tethered and free, host polymer chains to create model PNCs, in which spherical nanoparticles are uniformly dispersed in high molecular weight entangled polymers. Investigation of the mechanical properties of these model PNCs reveals that the nanoparticles have profound effects on the host polymer motions on all timescales. On short timescales, nanoparticles slow-down local dynamics of the host polymer segments and lower the glass transition temperature. On intermediate timescales, where polymer chain motion is typically constrained by entanglements with surrounding molecules, nanoparticles provide additional constraints, which lead to an early onset of entangled polymer dynamics. Finally, on long timescales, nanoparticles produce an apparent speeding up of relaxation of their polymer host.

  4. Phase stability and dynamics of entangled polymer-nanoparticle composites.

    KAUST Repository

    Mangal, Rahul; Srivastava, Samanvaya; Archer, Lynden A

    2015-01-01

    Nanoparticle-polymer composites, or polymer-nanoparticle composites (PNCs), exhibit unusual mechanical and dynamical features when the particle size approaches the random coil dimensions of the host polymer. Here, we harness favourable enthalpic interactions between particle-tethered and free, host polymer chains to create model PNCs, in which spherical nanoparticles are uniformly dispersed in high molecular weight entangled polymers. Investigation of the mechanical properties of these model PNCs reveals that the nanoparticles have profound effects on the host polymer motions on all timescales. On short timescales, nanoparticles slow-down local dynamics of the host polymer segments and lower the glass transition temperature. On intermediate timescales, where polymer chain motion is typically constrained by entanglements with surrounding molecules, nanoparticles provide additional constraints, which lead to an early onset of entangled polymer dynamics. Finally, on long timescales, nanoparticles produce an apparent speeding up of relaxation of their polymer host.

  5. Dynamic stability of a lightly damped column trapped by a ...

    African Journals Online (AJOL)

    In this paper we initiate an analytical approach for determining the dynamic buckling load of a finite viscously damped column acted upon by a harmonically slowly varying explicitly time dependent load. The viscous damping is considered light and the column rests on an elastic foundation that produces a nonlinear ...

  6. Protein kinesis: The dynamics of protein trafficking and stability

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1995-12-31

    The purpose of this conference is to provide a multidisciplinary forum for exchange of state-of-the-art information on protein kinesis. This volume contains abstracts of papers in the following areas: protein folding and modification in the endoplasmic reticulum; protein trafficking; protein translocation and folding; protein degradation; polarity; nuclear trafficking; membrane dynamics; and protein import into organelles.

  7. Identification and characterization of SSE15206, a microtubule depolymerizing agent that overcomes multidrug resistance

    KAUST Repository

    Manzoor, Safia

    2018-02-13

    Microtubules are highly dynamic structures that form spindle fibres during mitosis and are one of the most validated cancer targets. The success of drugs targeting microtubules, however, is often limited by the development of multidrug resistance. Here we describe the discovery and characterization of SSE15206, a pyrazolinethioamide derivative [3-phenyl-5-(3,4,5-trimethoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbothioamide] that has potent antiproliferative activities in cancer cell lines of different origins and overcomes resistance to microtubule-targeting agents. Treatment of cells with SSE15206 causes aberrant mitosis resulting in G2/M arrest due to incomplete spindle formation, a phenotype often associated with drugs that interfere with microtubule dynamics. SSE15206 inhibits microtubule polymerization both in biochemical and cellular assays by binding to colchicine site in tubulin as shown by docking and competition studies. Prolonged treatment of cells with the compound results in apoptotic cell death [increased Poly (ADP-ribose) polymerase cleavage and Annexin V/PI staining] accompanied by p53 induction. More importantly, we demonstrate that SSE15206 is able to overcome resistance to chemotherapeutic drugs in different cancer cell lines including multidrug-resistant KB-V1 and A2780-Pac-Res cell lines overexpressing MDR-1, making it a promising hit for the lead optimization studies to target multidrug resistance.

  8. Centromere Protein (CENP)-W Interacts with Heterogeneous Nuclear Ribonucleoprotein (hnRNP) U and May Contribute to Kinetochore-Microtubule Attachment in Mitotic Cells

    Science.gov (United States)

    Chun, Younghwa; Kim, Raehyung; Lee, Soojin

    2016-01-01

    Background Recent studies have shown that heterogeneous nuclear ribonucleoprotein U (hnRNP U), a component of the hnRNP complex, contributes to stabilize the kinetochore-microtubule interaction during mitosis. CENP-W was identified as an inner centromere component that plays crucial roles in the formation of a functional kinetochore complex. Results We report that hnRNP U interacts with CENP-W, and the interaction between hnRNP U and CENP-W mutually increased each other’s protein stability by inhibiting the proteasome-mediated degradation. Further, their co-localization was observed chiefly in the nuclear matrix region and at the microtubule-kinetochore interface during interphase and mitosis, respectively. Both microtubule-stabilizing and microtubule-destabilizing agents significantly decreased the protein stability of CENP-W. Furthermore, loss of microtubules and defects in microtubule organization were observed in CENP-W-depleted cells. Conclusion Our data imply that CENP-W plays an important role in the attachment and interaction between microtubules and kinetochore during mitosis. PMID:26881882

  9. Dynamic stability control in forward falls: postural corrections after muscle fatigue in young and older adults.

    Science.gov (United States)

    Mademli, Lida; Arampatzis, Adamantios; Karamanidis, Kiros

    2008-06-01

    Many studies report that muscle strength loss may alter the human system's capacity to generate rapid force for balance corrections after perturbations, leading to deficient recovery behaviours. Yet little is known regarding the effect of modifications in the neuromuscular system induced by fatigue on dynamic stability control during postural perturbations. This study investigates the effect of muscle strength decline induced by fatiguing contractions on the dynamic stability control of young and older adults during forward falls. Eleven young and eleven older male adults had to regain balance after sudden falls before and after submaximal fatiguing knee extension-flexion contractions. Young subjects had a higher margin of stability than older ones before and after the fatiguing task. This reflects their enhanced ability in using mechanisms for maintaining dynamic stability (i.e. a greater base of support). The margin of stability, the boundary of the base of support and the position of the extrapolated centre of mass, remained unaffected by the reduction in muscle strength induced by the fatiguing contractions, indicating an appropriate adjustment of the motor commands to compensate the deficit in muscle strength. Both young and older adults were able to counteract the decreased horizontal ground reaction forces after the fatiguing task by flexing their knee to a greater extent, leading to similar decreases in the horizontal velocity of centre of mass as in the pre fatigue condition. The results demonstrate the ability of the central nervous system to rapidly modify the execution of postural corrections including mechanisms for maintaining dynamic stability.

  10. Effect of speed on local dynamic stability of locomotion under different task constraints in running.

    Science.gov (United States)

    Mehdizadeh, Sina; Arshi, Ahmed Reza; Davids, Keith

    2014-01-01

    A number of studies have investigated effects of speed on local dynamic stability of walking, although this relationship has been rarely investigated under changing task constraints, such as during forward and backward running. To rectify this gap in the literature, the aim of this study was to investigate the effect of running speed on local dynamic stability of forward and backward running on a treadmill. Fifteen healthy male participants took part in this study. Participants ran in forward and backward directions at speeds of 80%, 100% and 120% of their preferred running speed. The three-dimensional motion of a C7 marker was recorded using a motion capture system. Local dynamic stability of the marker was quantified using short- and long-term largest finite-time Lyapunov exponents (LyE). Results showed that short-term largest finite-time LyE values increased with participant speed meaning that local dynamic stability decreased with increasing speed. Long-term largest finite-time LyEs, however, remained unaffected as speed increased. Results of this study indicated that, as in walking, slow running is more stable than fast running. These findings improve understanding of how stability is regulated when constraints on the speed of movements is altered. Implications for the design of rehabilitation or sport practice programmes suggest how task constraints could be manipulated to facilitate adaptations in locomotion stability during athletic training.

  11. Classification of Intact Stability Standards for Dynamically Supported Craft.

    Science.gov (United States)

    1979-10-01

    introduced (by the U.S. Navy) in the late 1950’s. Both military and commercial applications of this type have since proved very successful . From the... successful and safe planing craft have been built for military, commercial and private use. The stability of planing craft, however, is an extremely...forlces. Broaching- [ n I, 111, I ikeA LL) tOCCUr in suvvre following seas, when the Cr aft runs do L tht ! act of ort wav docd slope- ts bovw Ma’ thes

  12. Stability properties of a general class of nonlinear dynamical systems

    Science.gov (United States)

    Gléria, I. M.; Figueiredo, A.; Rocha Filho, T. M.

    2001-05-01

    We establish sufficient conditions for the boundedness of the trajectories and the stability of the fixed points in a class of general nonlinear systems, the so-called quasi-polynomial vector fields, with the help of a natural embedding of such systems in a family of generalized Lotka-Volterra (LV) equations. A purely algebraic procedure is developed to determine such conditions. We apply our method to obtain new results for LV systems, by a reparametrization in time variable, and to study general nonlinear vector fields, originally far from the LV format.

  13. Stability properties of a general class of nonlinear dynamical systems

    Energy Technology Data Exchange (ETDEWEB)

    Gleria, I.M. [Filho Instituto de Fisica, Universidade de Brasilia, Campus Universitario Darcy Ribeiro, Brasilia (Brazil). E-mail: iram@ucb.br; Figueiredo, A. [Filho Instituto de Fisica, Universidade de Brasilia, Campus Universitario Darcy Ribeiro, Brasilia (Brazil). E-mail: annibal@helium.fis.unb.br; Rocha, T.M. [Filho Instituto de Fisica, Universidade de Brasilia, Campus Universitario Darcy Ribeiro, Brasilia (Brazil). E-mail: marciano@helium.fis.unb.br

    2001-05-04

    We establish sufficient conditions for the boundedness of the trajectories and the stability of the fixed points in a class of general nonlinear systems, the so-called quasi-polynomial vector fields, with the help of a natural embedding of such systems in a family of generalized Lotka-Volterra (LV) equations. A purely algebraic procedure is developed to determine such conditions. We apply our method to obtain new results for LV systems, by a reparametrization in time variable, and to study general nonlinear vector fields, originally far from the LV format. (author)

  14. Use efficiency of dynamic stabilizer in the post-repair period of railways in Ukraine

    Directory of Open Access Journals (Sweden)

    O.V. Gubar

    2013-08-01

    Full Text Available Purpose. To analyze the interaction forces of the track and rolling stock at application of dynamic stabilizers, as well as the determination of the area, on which the track stabilization is necessary not only according to the technical indices but also according to the economic ones. Methodology.To achieve the research purpose the methods of analysis of material flows, peculiar to the places that need applications of dynamic stabilizers on railway transport tracks are used. Findings. Researches of relatively economic efficiency of dynamic stabilizers application, which were conducted by scientists during the last years, do not spread to comparison of cost of works on the track stabilizing and losses of railway for period of running. During the running period the trains move with a limited speed that causes corresponding financial losses. Speed limitation result in the both the motion time increase and in some occasions in the heavy consumption of fuel and energy resources. The more intensive track discord and expenses increase for its maintenance are observed in the sections of braking and acceleration immediately in front of and after the areas of limitation. The methodology relative to the estimation of economic efficiency of dynamic stabilizers application after completion of track repairs for the areas of Ukrainian railways with different operational conditions was developed. This methodology includes the losses calculation of railroad, which are predefined by extra motion time, heavy consumption of fuel and energy resources and charges for current maintenance. Originality. The methodology of cost effectiveness evaluating of the dynamic stabilizers application in the post-repair period was developed. Such an approach would allow one to take the rational decisions taking into account the features of the track sections, which were reconstructed. Practical value. The obtained results will rationally assign the works on the dynamic track

  15. Dynamic stabilization of D—T burn in Tokamak reactors

    Institute of Scientific and Technical Information of China (English)

    ShiBing-Ren; LongYong-Xing

    1997-01-01

    A simple,engineeringly feasible dynamic method is supposed to control the deuterium-tritium burn process in Tokamak reactors operated in an advanced scenario.The thermal transport of the D-T plasma is described by an anomalous thermal conduction which is a radially increasing function and the central conduction value is proportional to the central temperature of the plasma.The dynamic external heating power is selected to be inversely proportional to certain power function of this temperature,As a result,the D-T burn can undergo in controllable way in different temperature regimes with different power output.Anomalous alpha particle transport effect is taken into account.It can affect the resultant plasma equilibrium ,the reactor efficency,the operation mode and so on.

  16. STABILITY, BIFURCATIONS AND CHAOS IN UNEMPLOYMENT NON-LINEAR DYNAMICS

    Directory of Open Access Journals (Sweden)

    Pagliari Carmen

    2013-07-01

    Full Text Available The traditional analysis of unemployment in relation to real output dynamics is based on some empirical evidences deducted from Okun’s studies. In particular the so called Okun’s Law is expressed in a linear mathematical formulation, which cannot explain the fluctuation of the variables involved. Linearity is an heavy limit for macroeconomic analysis and especially for every economic growth study which would consider the unemployment rate among the endogenous variables. This paper deals with an introductive study about the role of non-linearity in the investigation of unemployment dynamics. The main idea is the existence of a non-linear relation between the unemployment rate and the gap of GDP growth rate from its trend. The macroeconomic motivation of this idea moves from the consideration of two concatenate effects caused by a variation of the unemployment rate on the real output growth rate. These two effects are concatenate because there is a first effect that generates a secondary one on the same variable. When the unemployment rate changes, the first effect is the variation in the level of production in consequence of the variation in the level of such an important factor as labour force; the secondary effect is a consecutive variation in the level of production caused by the variation in the aggregate demand in consequence of the change of the individual disposal income originated by the previous variation of production itself. In this paper the analysis of unemployment dynamics is carried out by the use of the logistic map and the conditions for the existence of bifurcations (cycles are determined. The study also allows to find the range of variability of some characteristic parameters that might be avoided for not having an absolute unpredictability of unemployment dynamics (deterministic chaos: unpredictability is equivalent to uncontrollability because of the total absence of information about the future value of the variable to

  17. Effect of arm swing strategy on local dynamic stability of human gait.

    Science.gov (United States)

    Punt, Michiel; Bruijn, Sjoerd M; Wittink, Harriet; van Dieën, Jaap H

    2015-02-01

    Falling causes long term disability and can even lead to death. Most falls occur during gait. Therefore improving gait stability might be beneficial for people at risk of falling. Recently arm swing has been shown to influence gait stability. However at present it remains unknown which mode of arm swing creates the most stable gait. To examine how different modes of arm swing affect gait stability. Ten healthy young male subjects volunteered for this study. All subjects walked with four different arm swing instructions at seven different gait speeds. The Xsens motion capture suit was used to capture gait kinematics. Basic gait parameters, variability and stability measures were calculated. We found an increased stability in the medio-lateral direction with excessive arm swing in comparison to normal arm swing at all gait speeds. Moreover, excessive arm swing increased stability in the anterior-posterior and vertical direction at low gait speeds. Ipsilateral and inphase arm swing did not differ compared to a normal arm swing. Excessive arm swing is a promising gait manipulation to improve local dynamic stability. For excessive arm swing in the ML direction there appears to be converging evidence. The effect of excessive arm swing on more clinically relevant groups like the more fall prone elderly or stroke survivors is worth further investigating. Excessive arm swing significantly increases local dynamic stability of human gait. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. Combined analytical and numerical approaches in Dynamic Stability analyses of engineering systems

    Science.gov (United States)

    Náprstek, Jiří

    2015-03-01

    Dynamic Stability is a widely studied area that has attracted many researchers from various disciplines. Although Dynamic Stability is usually associated with mechanics, theoretical physics or other natural and technical disciplines, it is also relevant to social, economic, and philosophical areas of our lives. Therefore, it is useful to occasionally highlight the general aspects of this amazing area, to present some relevant examples and to evaluate its position among the various branches of Rational Mechanics. From this perspective, the aim of this study is to present a brief review concerning the Dynamic Stability problem, its basic definitions and principles, important phenomena, research motivations and applications in engineering. The relationships with relevant systems that are prone to stability loss (encountered in other areas such as physics, other natural sciences and engineering) are also noted. The theoretical background, which is applicable to many disciplines, is presented. In this paper, the most frequently used Dynamic Stability analysis methods are presented in relation to individual dynamic systems that are widely discussed in various engineering branches. In particular, the Lyapunov function and exponent procedures, Routh-Hurwitz, Liénard, and other theorems are outlined together with demonstrations. The possibilities for analytical and numerical procedures are mentioned together with possible feedback from experimental research and testing. The strengths and shortcomings of these approaches are evaluated together with examples of their effective complementing of each other. The systems that are widely encountered in engineering are presented in the form of mathematical models. The analyses of their Dynamic Stability and post-critical behaviour are also presented. The stability limits, bifurcation points, quasi-periodic response processes and chaotic regimes are discussed. The limit cycle existence and stability are examined together with their

  19. Dynamic voltage stability constrained congestion management framework for deregulated electricity markets

    International Nuclear Information System (INIS)

    Amjady, Nima; Hakimi, Mahmood

    2012-01-01

    Highlights: ► A new congestion management method for electricity markets is proposed. ► The proposed method includes dynamic models of generators and loads. ► Dynamic voltage stability limits are properly modeled in the proposed method. ► The proposed method is compared with several other congestion management methods. ► It leads to a more robust power system with a lower congestion management cost. - Abstract: Congestion management is an important part of power system operation in today deregulated electricity markets. However, congestion management is traditionally performed based on static analysis tools, while these tools may not correctly capture dynamic voltage stability limits of a power system. In this paper, a new congestion management framework considering dynamic voltage stability boundary of power system is proposed. For this purpose, precise dynamic modeling of power system equipment, including generators and loads, is incorporated into the proposed congestion management framework. The proposed method alleviates congestion with a lower congestion management cost and more dynamic voltage stability margin, resulting in a more robust power system, compared with the previous congestion management methods. The validity of proposed congestion management framework is studied based on the New England 39-bus power system. The obtained results confirm the validity of the developed approach.

  20. Mto2 multisite phosphorylation inactivates non-spindle microtubule nucleation complexes during mitosis

    Science.gov (United States)

    Borek, Weronika E.; Groocock, Lynda M.; Samejima, Itaru; Zou, Juan; de Lima Alves, Flavia; Rappsilber, Juri; Sawin, Kenneth E.

    2015-01-01

    Microtubule nucleation is highly regulated during the eukaryotic cell cycle, but the underlying molecular mechanisms are largely unknown. During mitosis in fission yeast Schizosaccharomyces pombe, cytoplasmic microtubule nucleation ceases simultaneously with intranuclear mitotic spindle assembly. Cytoplasmic nucleation depends on the Mto1/2 complex, which binds and activates the γ-tubulin complex and also recruits the γ-tubulin complex to both centrosomal (spindle pole body) and non-centrosomal sites. Here we show that the Mto1/2 complex disassembles during mitosis, coincident with hyperphosphorylation of Mto2 protein. By mapping and mutating multiple Mto2 phosphorylation sites, we generate mto2-phosphomutant strains with enhanced Mto1/2 complex stability, interaction with the γ-tubulin complex and microtubule nucleation activity. A mutant with 24 phosphorylation sites mutated to alanine, mto2[24A], retains interphase-like behaviour even in mitotic cells. This provides a molecular-level understanding of how phosphorylation ‘switches off' microtubule nucleation complexes during the cell cycle and, more broadly, illuminates mechanisms regulating non-centrosomal microtubule nucleation. PMID:26243668

  1. Kindlin1 regulates microtubule function to ensure normal mitosis.

    Science.gov (United States)

    Patel, Hitesh; Stavrou, Ifigeneia; Shrestha, Roshan L; Draviam, Viji; Frame, Margaret C; Brunton, Valerie G

    2016-08-01

    Loss of Kindlin 1 (Kin1) results in the skin blistering disorder Kindler Syndrome (KS), whose symptoms also include skin atrophy and reduced keratinocyte proliferation. Kin1 binds to integrins to modulate their activation and more recently it has been shown to regulate mitotic spindles and cell survival in a Plk1-dependent manner. Here we report that short-term Kin1 deletion in mouse skin results in impaired mitosis, which is associated with reduced acetylated tubulin (ac-tub) levels and cell proliferation. In cells, impaired mitosis and reduced ac-tub levels are also accompanied by reduced microtubule stability, all of which are rescued by HDAC6 inhibition. The ability of Kin1 to regulate HDAC6-dependent cellular ac-tub levels is dependent on its phosphorylation by Plk1. Taken together, these data define a novel role for Kin1 in microtubule acetylation and stability and offer a mechanistic insight into how certain KS phenotypes, such as skin atrophy and reduced cell proliferation, arise. © The Author (2016). Published by Oxford University Press on behalf of Journal of Molecular Cell Biology, IBCB, SIBS, CAS.

  2. Finding the Cell Center by a Balance of Dynein and Myosin Pulling and Microtubule Pushing: A Computational Study

    Science.gov (United States)

    Zhu, Jie; Burakov, Anton; Rodionov, Vladimir

    2010-01-01

    The centrosome position in many types of interphase cells is actively maintained in the cell center. Our previous work indicated that the centrosome is kept at the center by pulling force generated by dynein and actin flow produced by myosin contraction and that an unidentified factor that depends on microtubule dynamics destabilizes position of the centrosome. Here, we use modeling to simulate the centrosome positioning based on the idea that the balance of three forces—dyneins pulling along microtubule length, myosin-powered centripetal drag, and microtubules pushing on organelles—is responsible for the centrosome displacement. By comparing numerical predictions with centrosome behavior in wild-type and perturbed interphase cells, we rule out several plausible hypotheses about the nature of the microtubule-based force. We conclude that strong dynein- and weaker myosin-generated forces pull the microtubules inward competing with microtubule plus-ends pushing the microtubule aster outward and that the balance of these forces positions the centrosome at the cell center. The model also predicts that kinesin action could be another outward-pushing force. Simulations demonstrate that the force-balance centering mechanism is robust yet versatile. We use the experimental observations to reverse engineer the characteristic forces and centrosome mobility. PMID:20980619

  3. DYMEL code for prediction of dynamic stability limits in boilers

    International Nuclear Information System (INIS)

    Deam, R.T.

    1980-01-01

    Theoretical and experimental studies of Hydrodynamic Instability in boilers were undertaken to resolve the uncertainties of the existing predictive methods at the time the first Advanced Gas Cooled Reactor (AGR) plant was commissioned. The experiments were conducted on a full scale electrical simulation of an AGR boiler and revealed inadequacies in existing methods. As a result a new computer code called DYMEL was developed based on linearisation and Fourier/Laplace Transformation of the one-dimensional boiler equations in both time and space. Beside giving good agreement with local experimental data, the DYMEL code has since shown agreement with stability data from the plant, sodium heated helical tubes, a gas heated helical tube and an electrically heated U-tube. The code is now used widely within the U.K. (author)

  4. The dynamics of CRM attitude change: Attitude stability

    Science.gov (United States)

    Gregorich, Steven E.

    1993-01-01

    Special training seminars in cockpit resource management (CRM) are designed to enhance crew effectiveness in multicrew air-transport cockpits. In terms of CRM, crew effectiveness is defined by teamwork rather than technical proficiency. These seminars are designed to promote factual learning, alter aviator attitudes, and motivate aviators to make use of what they have learned. However, measures of attitude change resulting from CRM seminars have been the most common seminar evaluation technique. The current investigation explores a broader range of attitude change parameters with specific emphasis on the stability of change between recurrent visits to the training center. This allows for a comparison of training program strengths in terms of seminar ability to effect lasting change.

  5. Interplay Between Energy-Market Dynamics and Physical Stability of a Smart Power Grid

    Science.gov (United States)

    Picozzi, Sergio; Mammoli, Andrea; Sorrentino, Francesco

    2013-03-01

    A smart power grid is being envisioned for the future which, among other features, should enable users to play the dual role of consumers as well as producers and traders of energy, thanks to emerging renewable energy production and energy storage technologies. As a complex dynamical system, any power grid is subject to physical instabilities. With existing grids, such instabilities tend to be caused by natural disasters, human errors, or weather-related peaks in demand. In this work we analyze the impact, upon the stability of a smart grid, of the energy-market dynamics arising from users' ability to buy from and sell energy to other users. The stability analysis of the resulting dynamical system is performed assuming different proposed models for this market of the future, and the corresponding stability regions in parameter space are identified. We test our theoretical findings by comparing them with data collected from some existing prototype systems.

  6. Stability of dynamical systems on the role of monotonic and non-monotonic Lyapunov functions

    CERN Document Server

    Michel, Anthony N; Liu, Derong

    2015-01-01

    The second edition of this textbook provides a single source for the analysis of system models represented by continuous-time and discrete-time, finite-dimensional and infinite-dimensional, and continuous and discontinuous dynamical systems.  For these system models, it presents results which comprise the classical Lyapunov stability theory involving monotonic Lyapunov functions, as well as corresponding contemporary stability results involving non-monotonicLyapunov functions.Specific examples from several diverse areas are given to demonstrate the applicability of the developed theory to many important classes of systems, including digital control systems, nonlinear regulator systems, pulse-width-modulated feedback control systems, and artificial neural networks.   The authors cover the following four general topics:   -          Representation and modeling of dynamical systems of the types described above -          Presentation of Lyapunov and Lagrange stability theory for dynamical sy...

  7. The effect of walking speed on local dynamic stability is sensitive to calculation methods

    DEFF Research Database (Denmark)

    Stenum, Jan; Bruijn, Sjoerd M; Jensen, Bente Rona

    2014-01-01

    Local dynamic stability has been assessed by the short-term local divergence exponent (λS), which quantifies the average rate of logarithmic divergence of infinitesimally close trajectories in state space. Both increased and decreased local dynamic stability at faster walking speeds have been...... reported. This might pertain to methodological differences in calculating λS. Therefore, the aim was to test if different calculation methods would induce different effects of walking speed on local dynamic stability. Ten young healthy participants walked on a treadmill at five speeds (60%, 80%, 100%, 120......% and 140% of preferred walking speed) for 3min each, while upper body accelerations in three directions were sampled. From these time-series, λS was calculated by three different methods using: (a) a fixed time interval and expressed as logarithmic divergence per stride-time (λS-a), (b) a fixed number...

  8. Magnolol Inhibits the Growth of Non-Small Cell Lung Cancer via Inhibiting Microtubule Polymerization

    Directory of Open Access Journals (Sweden)

    Jia Shen

    2017-07-01

    Full Text Available Background: The tubulin/microtubule system, which is an integral component of the cytoskeleton, plays an essential role in mitosis. Targeting mitotic progression by disturbing microtubule dynamics is a rational strategy for cancer treatment. Methods: Microtubule polymerization assay was performed to examine the effect of Magnolol (a novel natural phenolic compound isolated from Magnolia obovata on cellular microtubule polymerization in human non-small cell lung cancer (NSCLC cells. Cell cycle analysis, mitotic index assay, cell proliferation assay, colony formation assay, western blotting analysis of cell cycle regulators, Annexin V-FITC/PI staining, and live/dead viability staining were carried out to investigate the Magnolol’s inhibitory effect on proliferation and viability of NSCLS cells in vitro. Xenograft model of human A549 NSCLC tumor was used to determine the Magnolol’s efficacy in vivo. Results: Magnolol treatment effectively inhibited cell proliferation and colony formation of NSCLC cells. Further study proved that Magnolol induced the mitotic phase arrest and inhibited G2/M progression in a dose-dependent manner, which were mechanistically associated with expression alteration of a series of cell cycle regulators. Furthermore, Magnolol treatment disrupted the cellular microtubule organization via inhibiting the polymerization of microtubule. We also found treatment with NSCLC cells with Magnolol resulted in apoptosis activation through a p53-independent pathway, and autophgy induction via down-regulation of the Akt/mTOR pathway. Finally, Magnolol treatment significantly suppressed the NSCLC tumor growth in mouse xenograft model in vivo. Conclusion: These findings identify Magnolol as a promising candidate with anti-microtubule polymerization activity for NSCLC treatment.

  9. Molecular dynamics study of thermodynamic stability and dynamics of [Li(glyme)]+ complex in lithium-glyme solvate ionic liquids

    Science.gov (United States)

    Shinoda, Wataru; Hatanaka, Yuta; Hirakawa, Masashi; Okazaki, Susumu; Tsuzuki, Seiji; Ueno, Kazuhide; Watanabe, Masayoshi

    2018-05-01

    Equimolar mixtures of glymes and organic lithium salts are known to produce solvate ionic liquids, in which the stability of the [Li(glyme)]+ complex plays an important role in determining the ionic dynamics. Since these mixtures have attractive physicochemical properties for application as electrolytes, it is important to understand the dependence of the stability of the [Li(glyme)]+ complex on the ion dynamics. A series of microsecond molecular dynamics simulations has been conducted to investigate the dynamic properties of these solvate ionic liquids. Successful solvate ionic liquids with high stability of the [Li(glyme)]+ complex have been shown to have enhanced ion dynamics. Li-glyme pair exchange rarely occurs: its characteristic time is longer than that of ion diffusion by one or two orders of magnitude. Li-glyme pair exchange most likely occurs through cluster formation involving multiple [Li(glyme)]+ pairs. In this process, multiple exchanges likely take place in a concerted manner without the production of energetically unfavorable free glyme or free Li+ ions.

  10. Stability and dynamics of reactors with heterogeneously catalyzed reactions

    Energy Technology Data Exchange (ETDEWEB)

    Eigenberger, G [BASF A.G., Ludwigshafen am Rhein (Germany, F.R.)

    1978-12-01

    Our knowledge of causes and consequences of problems arising from instability and dynamic effects in reactors with heterogeneously catalyzed reactions has increased remarkably in recent years. Especially thermal effects, caused by the self-acceleration of an exothermic reaction in combination with heat and mass transport, are now well understood. In addition, kinetic effects, i.e. phenomena which have to be explained by the kinetic peculiarities of surface reactions, have attracted increasing interest. For both cases the state of the art will be reviewed, highlighting the physical and chemical causes of the observed phenomena.

  11. Nonlinear dynamics of a driven mode near marginal stability

    International Nuclear Information System (INIS)

    Berk, H.L.; Breizman, B.N.; Pekker, M.

    1995-09-01

    The nonlinear dynamics of a linearly unstable mode in a driven kinetic system is investigated to determine scaling of the saturated fields near the instability threshold. To leading order, this problem reduces to solving an integral equation with a temporally nonlocal cubic term. This equation can exhibit a self-similar solution that blows up in a finite time. When the blow-up occurs, higher nonlinearities become important and the mode saturates due to plateau formation arising from particle trapping in the wave. Otherwise, the simplified equation gives a regular solution that leads to a different saturation scaling reflecting the closeness to the instability threshold

  12. Constraints on dynamic stability during forward, backward and lateral locomotion in skilled football players.

    Science.gov (United States)

    Mehdizadeh, Sina; Arshi, Ahmed Reza; Davids, Keith

    2016-01-01

    The aim of this study was to investigate effects of speed and plane of motion on stability during locomotion in skilled football players. Ten male national-level football players participated in this study to run forward, backward and in lateral directions on a treadmill at 80%, 100% and 120% of their preferred running speeds. The coordinate data of passive reflective markers attached to body segments were recorded using motion capture systems. Time series data obtained from the ankle marker were used for further analyses. The largest finite-time Lyapunov exponent and maximum Floquet multiplier were adopted to quantify local and orbital dynamic stabilities, respectively. Results showed that speed did not significantly change local and orbital dynamic stabilities in any of running patterns. However, both local and orbital dynamic stability were significantly higher in the secondary plane of progression. Data revealed that in running, unlike walking, stability in the direction perpendicular to the direction of running is significantly higher, implying that less active control is required in the secondary plane of progression. The results of this study could be useful in sports training and rehabilitation programmes where development of fundamental exercise programmes that challenge both speed and the ability to maintain stability might produce a tangible enhancement of athletic skill level.

  13. The Comprehensive Biomechanics and Load-Sharing of Semirigid PEEK and Semirigid Posterior Dynamic Stabilization Systems

    Directory of Open Access Journals (Sweden)

    D. K. Sengupta

    2013-01-01

    Full Text Available Alternatives to conventional rigid fusion have been proposed for several conditions related to degenerative disc disease when nonoperative treatment has failed. Semirigid fixation, in the form of dynamic stabilization or PEEK rods, is expected to provide compression under loading as well as an intermediate level of stabilization. This study systematically examines both the load-sharing characteristics and kinematics of these two devices compared to the standard of internal rigid fixators. Load-sharing was studied by using digital pressure films inserted between an artificially machined disc and two loading fixtures. Rigid rods, PEEK rods, and the dynamic stabilization system were inserted posteriorly for stabilization. The kinematics were quantified on ten, human, cadaver lumbosacral spines (L3-S1 which were tested under a pure bending moment, in flexion-extension, lateral bending, and axial rotation. The magnitude of load transmission through the anterior column was significantly greater with the dynamic device compared to PEEK rods and rigid rods. The contact pressures were distributed more uniformly, throughout the disc with the dynamic stabilization devices, and had smaller maximum point-loading (pressures on any particular point within the disc. Kinematically, the motion was reduced by both semirigid devices similarly in all directions, with slight rigidity imparted by a lateral interbody device.

  14. Dynamics of bad-cavity-enhanced interaction with cold Sr atoms for laser stabilization

    DEFF Research Database (Denmark)

    Schäffer, S. A.; Christensen, B. T.R.; Henriksen, M. R.

    2017-01-01

    Hybrid systems of cold atoms and optical cavities are promising systems for increasing the stability of laser oscillators used in quantum metrology and atomic clocks. In this paper we map out the atom-cavity dynamics in such a system and demonstrate limitations as well as robustness of the approach....... We investigate the phase response of an ensemble of cold Sr88 atoms inside an optical cavity for use as an error signal in laser frequency stabilization. With this system we realize a regime where the high atomic phase shift limits the dynamical locking range. The limitation is caused by the cavity...

  15. Guidelines for Computing Longitudinal Dynamic Stability Characteristics of a Subsonic Transport

    Science.gov (United States)

    Thompson, Joseph R.; Frank, Neal T.; Murphy, Patrick C.

    2010-01-01

    A systematic study is presented to guide the selection of a numerical solution strategy for URANS computation of a subsonic transport configuration undergoing simulated forced oscillation about its pitch axis. Forced oscillation is central to the prevalent wind tunnel methodology for quantifying aircraft dynamic stability derivatives from force and moment coefficients, which is the ultimate goal for the computational simulations. Extensive computations are performed that lead in key insights of the critical numerical parameters affecting solution convergence. A preliminary linear harmonic analysis is included to demonstrate the potential of extracting dynamic stability derivatives from computational solutions.

  16. Dynamical stability for finite quantum spin chains against a time-periodic inhomogeneous perturbation

    International Nuclear Information System (INIS)

    Kudo, Kazue; Nakamura, Katsuhiro

    2009-01-01

    We investigate dynamical stability of the ground state against a time-periodic and spatially-inhomogeneous magnetic field for finite quantum XXZ spin chains. We use the survival probability as a measure of stability and demonstrate that it decays as P(t) ∝ t -1/2 under a certain condition. The dynamical properties should also be related to the level statistics of the XXZ spin chains with a constant spatially-inhomogeneous magnetic field. The level statistics depends on the anisotropy parameter and the field strength. We show how the survival probability depends on the anisotropy parameter, the strength and frequency of the field.

  17. Radio galaxies radiation transfer, dynamics, stability and evolution of a synchrotron plasmon

    CERN Document Server

    Pacholczyk, A G

    1977-01-01

    Radio Galaxies: Radiation Transfer, Dynamics, Stability and Evolution of a Synchrotron Plasmon deals with the physics of a region in space containing magnetic field and thermal and relativistic particles (a plasmon). The synchrotron emission and absorption of this region are discussed, along with the properties of its spectrum; its linear and circular polarization; transfer of radiation through such a region; its dynamics and expansion; and interaction with external medium.Comprised of eight chapters, this volume explores the stability, turbulence, and acceleration of particles in a synchrotro

  18. A heterogenous Cournot duopoly with delay dynamics: Hopf bifurcations and stability switching curves

    Science.gov (United States)

    Pecora, Nicolò; Sodini, Mauro

    2018-05-01

    This article considers a Cournot duopoly model in a continuous-time framework and analyze its dynamic behavior when the competitors are heterogeneous in determining their output decision. Specifically the model is expressed in the form of differential equations with discrete delays. The stability conditions of the unique Nash equilibrium of the system are determined and the emergence of Hopf bifurcations is shown. Applying some recent mathematical techniques (stability switching curves) and performing numerical simulations, the paper confirms how different time delays affect the stability of the economy.

  19. Ball lightning dynamics and stability at moderate ion densities

    International Nuclear Information System (INIS)

    Morrow, R

    2017-01-01

    A general mechanism is presented for the dynamics and structure of ball lightning and for the maintenance of the ball lightning structure for several seconds. Results are obtained using a spherical geometry for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions and negative ions coupled with Poisson’s equation. A lightning strike can generate conditions in the lightning channel with a majority of positive nitrogen ions, and a minority of negative oxygen ions and electrons. The calculations are initiated with electrons included; however, at the moderate ion densities chosen the electrons are rapidly lost to form negative ions, and after 1 µ s their influence on the ion dynamics is negligible. Further development after 1 µ s is followed using a simpler set of equations involving only positive ions and negative ions, but including ion diffusion. The space-charge electric field generated by the majority positive ions drives them from the centre of the distribution and drives the minority negative ions and electrons towards the centre of the distribution. In the central region the positive and negative ion distributions eventually overlap exactly and their space-charge fields cancel resulting in zero electric field, and the plasma ball formed is quite stable for a number of seconds. The formation of such plasma balls is not critically dependent on the initial diameter of the ion distributions, or the initial density of minority negative ions. The ion densities decrease relatively slowly due to mutual neutralization of positive and negative ions. The radiation from this neutralization process involving positive nitrogen ions and negative oxygen ions is not sufficient to account for the reported luminosity of ball lightning and some other source of luminosity is shown to be required; the plasma ball model used could readily incorporate other ions in order to account for the luminosity and range of colours reported for ball

  20. Ferritin associates with marginal band microtubules

    International Nuclear Information System (INIS)

    Infante, Anthony A.; Infante, Dzintra; Chan, M.-C.; How, P.-C.; Kutschera, Waltraud; Linhartova, Irena; Muellner, Ernst W.; Wiche, Gerhard; Propst, Friedrich

    2007-01-01

    We characterized chicken erythrocyte and human platelet ferritin by biochemical studies and immunofluorescence. Erythrocyte ferritin was found to be a homopolymer of H-ferritin subunits, resistant to proteinase K digestion, heat stable, and contained iron. In mature chicken erythrocytes and human platelets, ferritin was localized at the marginal band, a ring-shaped peripheral microtubule bundle, and displayed properties of bona fide microtubule-associated proteins such as tau. Red blood cell ferritin association with the marginal band was confirmed by temperature-induced disassembly-reassembly of microtubules. During erythrocyte differentiation, ferritin co-localized with coalescing microtubules during marginal band formation. In addition, ferritin was found in the nuclei of mature erythrocytes, but was not detectable in those of bone marrow erythrocyte precursors. These results suggest that ferritin has a function in marginal band formation and possibly in protection of the marginal band from damaging effects of reactive oxygen species by sequestering iron in the mature erythrocyte. Moreover, our data suggest that ferritin and syncolin, a previously identified erythrocyte microtubule-associated protein, are identical. Nuclear ferritin might contribute to transcriptional silencing or, alternatively, constitute a ferritin reservoir

  1. Dynamics and stability of charged clusters and droplets

    International Nuclear Information System (INIS)

    Manil, B.; Lebius, H.; Chandezon, F.; Huber, B.A.; Duft, D.; Leisner, T.; Guet, C.

    2002-01-01

    Lord Raleigh predicted (Phil. Mag. 14, 184(1982) ) that a charged, incompressible liquid droplet becomes unstable as soon as the cohesive forces, which create the surface tension and which try to keep the droplet in its spherical form, are equal to the Coulomb forces, which try to destabilise it. This means that that the Coulomb energy E c corresponds to twice the surface energy E s . The ratio X = E c / 2 E s (feasibility), thus characterising the Raleigh limit by X = 1. In order to test its validity, metal clusters were ionized in collisions with highly charged ions, allowing for the first time to prepare charged systems with a feasibility greater than 1. Multiply charged sodium clusters were produced through collisions of Ar 11+ or Xe 28+ with neutral sodium clusters. It was observed, with increasing cluster charge and consequently cluster size the detected system indeed approach the Raleigh limit (for q = 10 X = 0.85). However, it was not reached due to the initial cluster temperature and the energy transfer in the collision. Subsequent, the stability and the explosion of highly charge microdroplets which were injected into a Paul trap levitator were studied, specifically, glycol was irradiated with a HeNe laser. It was observed that a resonance phenomena appeared just before each explosion. As the resonance is linked to X ∼ 1, this is the first proof that the Coulomb instability of charge glycol microdroplets occurs at X ∼ 1, as predicted by Lord Raleigh. (nevyjel)

  2. STABILITY AND DYNAMICS OF SPATIO-TEMPORAL STRUCTURES

    Energy Technology Data Exchange (ETDEWEB)

    Hermann Riecke

    2005-10-21

    This document constitutes the final report for the grant. It provides a complete list of publications and presentations that arose from the project as well as a brief description of the highlights of the research results. The research funded by this grant has provided insights into the spontaneous formation of structures of increasing complexity in systems driven far from thermodynamic equilibrium. A classic example of such a system is thermally driven convection in a horizontal fluid layer. Highlights of the research are: (1) explanation of the localized traveling wave pulses observed in binary-mixture convection, (2) explanation of the localized waves in electroconvection, (3) introduction of a new diagnostics for spatially and temporally chaotic states, which is based on the statistics of defect trajectories, (4) prediction of complex states in thermally driven convection in rotating systems. Additional contributions provided insight into the localization mechanism for oscillons, the prediction of a new localization mechanism for traveling waves based on a resonant periodic forcing, and an analysis of the stability of quasi-periodic patterns.

  3. Verifying Stability of Dynamic Soft-Computing Systems

    Science.gov (United States)

    Wen, Wu; Napolitano, Marcello; Callahan, John

    1997-01-01

    Soft computing is a general term for algorithms that learn from human knowledge and mimic human skills. Example of such algorithms are fuzzy inference systems and neural networks. Many applications, especially in control engineering, have demonstrated their appropriateness in building intelligent systems that are flexible and robust. Although recent research have shown that certain class of neuro-fuzzy controllers can be proven bounded and stable, they are implementation dependent and difficult to apply to the design and validation process. Many practitioners adopt the trial and error approach for system validation or resort to exhaustive testing using prototypes. In this paper, we describe our on-going research towards establishing necessary theoretic foundation as well as building practical tools for the verification and validation of soft-computing systems. A unified model for general neuro-fuzzy system is adopted. Classic non-linear system control theory and recent results of its applications to neuro-fuzzy systems are incorporated and applied to the unified model. It is hoped that general tools can be developed to help the designer to visualize and manipulate the regions of stability and boundedness, much the same way Bode plots and Root locus plots have helped conventional control design and validation.

  4. Recent Advances in Heliogyro Solar Sail Structural Dynamics, Stability, and Control Research

    Science.gov (United States)

    Wilkie, W. Keats; Warren, Jerry E.; Horta, Lucas G.; Lyle, Karen H.; Juang, Jer-Nan; Gibbs, S. Chad; Dowell, Earl H.; Guerrant, Daniel V.; Lawrence, Dale

    2015-01-01

    Results from recent NASA sponsored research on the structural dynamics, stability, and control characteristics of heliogyro solar sails are summarized. Specific areas under investigation include coupled nonlinear finite element analysis of heliogyro membrane blade with solar radiation pressure effects, system identification of spinning membrane structures, and solarelastic stability analysis of heliogyro solar sails, including stability during blade deployment. Recent results from terrestrial 1-g blade dynamics and control experiments on "rope ladder" membrane blade analogs, and small-scale in vacuo system identification experiments with hanging and spinning high-aspect ratio membranes will also be presented. A low-cost, rideshare payload heliogyro technology demonstration mission concept is used as a mission context for these heliogyro structural dynamics and solarelasticity investigations, and is also described. Blade torsional dynamic response and control are also shown to be significantly improved through the use of edge stiffening structural features or inclusion of modest tip masses to increase centrifugal stiffening of the blade structure. An output-only system identification procedure suitable for on-orbit blade dynamics investigations is also developed and validated using ground tests of spinning sub-scale heliogyro blade models. Overall, analytical and experimental investigations to date indicate no intractable stability or control issues for the heliogyro solar sail concept.

  5. Nonlinear Slewing Spacecraft Control Based on Exergy, Power Flow, and Static and Dynamic Stability

    Science.gov (United States)

    Robinett, Rush D.; Wilson, David G.

    2009-10-01

    This paper presents a new nonlinear control methodology for slewing spacecraft, which provides both necessary and sufficient conditions for stability by identifying the stability boundaries, rigid body modes, and limit cycles. Conservative Hamiltonian system concepts, which are equivalent to static stability of airplanes, are used to find and deal with the static stability boundaries: rigid body modes. The application of exergy and entropy thermodynamic concepts to the work-rate principle provides a natural partitioning through the second law of thermodynamics of power flows into exergy generator, dissipator, and storage for Hamiltonian systems that is employed to find the dynamic stability boundaries: limit cycles. This partitioning process enables the control system designer to directly evaluate and enhance the stability and performance of the system by balancing the power flowing into versus the power dissipated within the system subject to the Hamiltonian surface (power storage). Relationships are developed between exergy, power flow, static and dynamic stability, and Lyapunov analysis. The methodology is demonstrated with two illustrative examples: (1) a nonlinear oscillator with sinusoidal damping and (2) a multi-input-multi-output three-axis slewing spacecraft that employs proportional-integral-derivative tracking control with numerical simulation results.

  6. Dynamic Stability of Columns Subjected to Follower Loads: a Survey

    Science.gov (United States)

    LANGTHJEM, M. A.; SUGIYAMA, Y.

    2000-12-01

    This paper offers a survey of simple, flexible structural elements subjected to non-conservative follower loads, such as those caused by the thrust of rocket- and jet engines, and by dry friction in automotive disk- and drum-brake systems. Emphasis is on the “canonical problems”, Beck's, Reut's, Leipholz's, and Hauger's columns. Beck's and Reut's columns have been realized experimentally, and very good agreement between theory and experiments has been found. Leipholz's column is basically realized in an automobile brake system, where noise due to dynamic or parametric instability (brake squeal) is a well-known environmental problem. It is attempted to give a broad overview, with emphasis on experimental works and the associated theoretical problems. Structural optimization is also included in the review, as many studies in that area have served an important purpose in the development of optimization techniques for practical, large-scale optimization problems with non-conservative forces, such as in aeroelasticity.

  7. Lateral motion and bending of microtubules studied with a new single-filament tracking routine in living cells.

    Science.gov (United States)

    Pallavicini, Carla; Levi, Valeria; Wetzler, Diana E; Angiolini, Juan F; Benseñor, Lorena; Despósito, Marcelo A; Bruno, Luciana

    2014-06-17

    The cytoskeleton is involved in numerous cellular processes such as migration, division, and contraction and provides the tracks for transport driven by molecular motors. Therefore, it is very important to quantify the mechanical behavior of the cytoskeletal filaments to get a better insight into cell mechanics and organization. It has been demonstrated that relevant mechanical properties of microtubules can be extracted from the analysis of their motion and shape fluctuations. However, tracking individual filaments in living cells is extremely complex due, for example, to the high and heterogeneous background. We introduce a believed new tracking algorithm that allows recovering the coordinates of fluorescent microtubules with ∼9 nm precision in in vitro conditions. To illustrate potential applications of this algorithm, we studied the curvature distributions of fluorescent microtubules in living cells. By performing a Fourier analysis of the microtubule shapes, we found that the curvatures followed a thermal-like distribution as previously reported with an effective persistence length of ∼20 μm, a value significantly smaller than that measured in vitro. We also verified that the microtubule-associated protein XTP or the depolymerization of the actin network do not affect this value; however, the disruption of intermediate filaments decreased the persistence length. Also, we recovered trajectories of microtubule segments in actin or intermediate filament-depleted cells, and observed a significant increase of their motion with respect to untreated cells showing that these filaments contribute to the overall organization of the microtubule network. Moreover, the analysis of trajectories of microtubule segments in untreated cells showed that these filaments presented a slower but more directional motion in the cortex with respect to the perinuclear region, and suggests that the tracking routine would allow mapping the microtubule dynamical organization in cells

  8. Dynamics and stability of directional jumps in the desert locust

    Directory of Open Access Journals (Sweden)

    Omer Gvirsman

    2016-09-01

    Full Text Available Locusts are known for their ability to jump large distances to avoid predation. The jump also serves to launch the adult locust into the air in order to initiate flight. Various aspects of this important behavior have been studied extensively, from muscle physiology and biomechanics, to the energy storage systems involved in powering the jump, and more. Less well understood are the mechanisms participating in control of the jump trajectory. Here we utilise video monitoring and careful analysis of experimental directional jumps by adult desert locusts, together with dynamic computer simulation, in order to understand how the locusts control the direction and elevation of the jump, the residual angular velocities resulting from the jump and the timing of flapping-flight initiation. Our study confirms and expands early findings regarding the instrumental role of the initial body position and orientation. Both real-jump video analysis and simulations based on our expanded dynamical model demonstrate that the initial body coordinates of position (relative to the hind-legs ground-contact points are dominant in predicting the jumps’ azimuth and elevation angles. We also report a strong linear correlation between the jumps’ pitch-angular-velocity and flight initiation timing, such that head downwards rotations lead to earlier wing opening. In addition to offering important insights into the bio-mechanical principles of locust jumping and flight initiation, the findings from this study will be used in designing future prototypes of a bio-inspired miniature jumping robot that will be employed in animal behaviour studies and environmental monitoring applications.

  9. Dynamics and stability of directional jumps in the desert locust.

    Science.gov (United States)

    Gvirsman, Omer; Kosa, Gabor; Ayali, Amir

    2016-01-01

    Locusts are known for their ability to jump large distances to avoid predation. The jump also serves to launch the adult locust into the air in order to initiate flight. Various aspects of this important behavior have been studied extensively, from muscle physiology and biomechanics, to the energy storage systems involved in powering the jump, and more. Less well understood are the mechanisms participating in control of the jump trajectory. Here we utilise video monitoring and careful analysis of experimental directional jumps by adult desert locusts, together with dynamic computer simulation, in order to understand how the locusts control the direction and elevation of the jump, the residual angular velocities resulting from the jump and the timing of flapping-flight initiation. Our study confirms and expands early findings regarding the instrumental role of the initial body position and orientation. Both real-jump video analysis and simulations based on our expanded dynamical model demonstrate that the initial body coordinates of position (relative to the hind-legs ground-contact points) are dominant in predicting the jumps' azimuth and elevation angles. We also report a strong linear correlation between the jumps' pitch-angular-velocity and flight initiation timing, such that head downwards rotations lead to earlier wing opening. In addition to offering important insights into the bio-mechanical principles of locust jumping and flight initiation, the findings from this study will be used in designing future prototypes of a bio-inspired miniature jumping robot that will be employed in animal behaviour studies and environmental monitoring applications.

  10. Collective behavior of minus-ended motors in mitotic microtubule asters gliding toward DNA

    International Nuclear Information System (INIS)

    Athale, Chaitanya A; Dinarina, Ana; Nedelec, Francois; Karsenti, Eric

    2014-01-01

    Microtubules (MTs) nucleated by centrosomes form star-shaped structures referred to as asters. Aster motility and dynamics is vital for genome stability, cell division, polarization and differentiation. Asters move either toward the cell center or away from it. Here, we focus on the centering mechanism in a membrane independent system of Xenopus cytoplasmic egg extracts. Using live microscopy and single particle tracking, we find that asters move toward chromatinized DNA structures. The velocity and directionality profiles suggest a random-walk with drift directed toward DNA. We have developed a theoretical model that can explain this movement as a result of a gradient of MT length dynamics and MT gliding on immobilized dynein motors. In simulations, the antagonistic action of the motor species on the radial array of MTs leads to a tug-of-war purely due to geometric considerations and aster motility resembles a directed random-walk. Additionally, our model predicts that aster velocities do not change greatly with varying initial distance from DNA. The movement of asymmetric asters becomes increasingly super-diffusive with increasing motor density, but for symmetric asters it becomes less super-diffusive. The transition of symmetric asters from superdiffusive to diffusive mobility is the result of number fluctuations in bound motors in the tug-of-war. Overall, our model is in good agreement with experimental data in Xenopus cytoplasmic extracts and predicts novel features of the collective effects of motor-MT interactions. (paper)

  11. Katanin localization requires triplet microtubules in Chlamydomonas reinhardtii.

    Directory of Open Access Journals (Sweden)

    Jessica M Esparza

    Full Text Available Centrioles and basal bodies are essential for a variety of cellular processes that include the recruitment of proteins to these structures for both centrosomal and ciliary function. This recruitment is compromised when centriole/basal body assembly is defective. Mutations that cause basal body assembly defects confer supersensitivity to Taxol. These include bld2, bld10, bld12, uni3, vfl1, vfl2, and vfl3. Flagellar motility mutants do not confer sensitivity with the exception of mutations in the p60 (pf19 and p80 (pf15 subunits of the microtubule severing protein katanin. We have identified additional pf15 and bld2 (ε-tubulin alleles in screens for Taxol sensitivity. Null pf15 and bld2 alleles are viable and are not essential genes in Chlamydomonas. Analysis of double mutant strains with the pf15-3 and bld2-6 null alleles suggests that basal bodies in Chlamydomonas may recruit additional proteins beyond katanin that affect spindle microtubule stability. The bld2-5 allele is a hypomorphic allele and its phenotype is modulated by nutritional cues. Basal bodies in bld2-5 cells are missing proximal ends. The basal body mutants show aberrant localization of an epitope-tagged p80 subunit of katanin. Unlike IFT proteins, katanin p80 does not localize to the transition fibers of the basal bodies based on an analysis of the uni1 mutant as well as the lack of colocalization of katanin p80 with IFT74. We suggest that the triplet microtubules are likely to play a key role in katanin p80 recruitment to the basal body of Chlamydomonas rather than the transition fibers that are needed for IFT localization.

  12. Stability and Control of Large-Scale Dynamical Systems A Vector Dissipative Systems Approach

    CERN Document Server

    Haddad, Wassim M

    2011-01-01

    Modern complex large-scale dynamical systems exist in virtually every aspect of science and engineering, and are associated with a wide variety of physical, technological, environmental, and social phenomena, including aerospace, power, communications, and network systems, to name just a few. This book develops a general stability analysis and control design framework for nonlinear large-scale interconnected dynamical systems, and presents the most complete treatment on vector Lyapunov function methods, vector dissipativity theory, and decentralized control architectures. Large-scale dynami

  13. Research on Dynamics and Stability in the Stairs-climbing of a Tracked Mobile Robot

    OpenAIRE

    Tao, Weijun; Ou, Yi; Feng, Hutian

    2012-01-01

    Aiming at the functional requirement of climbing up the stairs, the dynamics and stability during a tracked mobile robot's climbing of stairs is studied. First, from the analysis of its cross-country performance, the mechanical structure of the tracked mobile robot is designed and the hardware composition of its control system is given. Second, based on the analysis to its stairs-climbing process, the dynamical model of stairs-climbing is established by using the classical mechanics method. N...

  14. Asymptotic stability and blow up for a semilinear damped wave equation with dynamic boundary conditions

    KAUST Repository

    Gerbi, Sté phane; Said-Houari, Belkacem

    2011-01-01

    In this paper we consider a multi-dimensional wave equation with dynamic boundary conditions, related to the KelvinVoigt damping. Global existence and asymptotic stability of solutions starting in a stable set are proved. Blow up for solutions of the problem with linear dynamic boundary conditions with initial data in the unstable set is also obtained. © 2011 Elsevier Ltd. All rights reserved.

  15. Asymptotic stability and blow up for a semilinear damped wave equation with dynamic boundary conditions

    KAUST Repository

    Gerbi, Stéphane

    2011-12-01

    In this paper we consider a multi-dimensional wave equation with dynamic boundary conditions, related to the KelvinVoigt damping. Global existence and asymptotic stability of solutions starting in a stable set are proved. Blow up for solutions of the problem with linear dynamic boundary conditions with initial data in the unstable set is also obtained. © 2011 Elsevier Ltd. All rights reserved.

  16. Certain Actions from the Functional Movement Screen Do Not Provide an Indication of Dynamic Stability

    Science.gov (United States)

    Lockie, Robert G.; Callaghan, Samuel J.; Jordan, Corrin A.; Luczo, Tawni M.; Jeffriess, Matthew D.; Jalilvand, Farzad; Schultz, Adrian B.

    2015-01-01

    Dynamic stability is an essential physical component for team sport athletes. Certain Functional Movement Screen (FMS) exercises (deep squat; left- and right-leg hurdle step; left- and right-leg in-line lunge [ILL]; left- and right-leg active straight-leg raise; and trunk stability push-up [TSPU]) have been suggested as providing an indication of dynamic stability. No research has investigated relationships between these screens and an established test of dynamic stability such as the modified Star Excursion Balance Test (mSEBT), which measures lower-limb reach distance in posteromedial, medial, and anteromedial directions, in team sport athletes. Forty-one male and female team sport athletes completed the screens and the mSEBT. Participants were split into high-, intermediate-, and low-performing groups according to the mean of the excursions when both the left and right legs were used for the mSEBT stance. Any between-group differences in the screens and mSEBT were determined via a one-way analysis of variance with Bonferroni post hoc adjustment (p in any of the screens, and only two positive correlations between the screens and the mSEBT (TSPU and right stance leg posteromedial excursion, r = 0.37; left-leg ILL and left stance leg posteromedial excursion, r = 0.46). The mSEBT clearly indicated participants with different dynamic stability capabilities. In contrast to the mSEBT, the selected FMS exercises investigated in this study have a limited capacity to identify dynamic stability in team sport athletes. PMID:26557187

  17. Certain Actions from the Functional Movement Screen Do Not Provide an Indication of Dynamic Stability

    Directory of Open Access Journals (Sweden)

    Lockie Robert G.

    2015-09-01

    Full Text Available Dynamic stability is an essential physical component for team sport athletes. Certain Functional Movement Screen (FMS exercises (deep squat; left- and right-leg hurdle step; left- and right-leg in-line lunge [ILL]; left- and right-leg active straight-leg raise; and trunk stability push-up [TSPU] have been suggested as providing an indication of dynamic stability. No research has investigated relationships between these screens and an established test of dynamic stability such as the modified Star Excursion Balance Test (mSEBT, which measures lower-limb reach distance in posteromedial, medial, and anteromedial directions, in team sport athletes. Forty-one male and female team sport athletes completed the screens and the mSEBT. Participants were split into high-, intermediate-, and low-performing groups according to the mean of the excursions when both the left and right legs were used for the mSEBT stance. Any between-group differences in the screens and mSEBT were determined via a one-way analysis of variance with Bonferroni post hoc adjustment (p < 0.05. Data was pooled for a correlation analysis (p < 0.05. There were no between-group differences in any of the screens, and only two positive correlations between the screens and the mSEBT (TSPU and right stance leg posteromedial excursion, r = 0.37; left-leg ILL and left stance leg posteromedial excursion, r = 0.46. The mSEBT clearly indicated participants with different dynamic stability capabilities. In contrast to the mSEBT, the selected FMS exercises investigated in this study have a limited capacity to identify dynamic stability in team sport athletes.

  18. Convergence and Heterogeneity in Euro Based Economies: Stability and Dynamics

    Directory of Open Access Journals (Sweden)

    Philip Haynes

    2016-08-01

    Full Text Available Cluster analysis is used to explore the performance of key macroeconomic variables in European countries that share the euro, from the inception of the currency in 2002 through to 2013. An original applied statistical approach searches for a pattern synthesis across a matrix of macroeconomic data to examine if there is evidence for country clusters and whether there is convergence of the cluster patterns over time. A number of different clusters appear and these change over time as the economies of the member states dynamically interact. This includes some new countries joining the currency during the period of examination. As found in previous research, Southern European countries tend to remain separate from other countries. The new methods used, however, add to an understanding of some differences between Southern European countries, in addition to replicating their broad similarities. Hypotheses are formed about the country clusters existing in 2002, 2006 and 2013, at key points in time of the euro integration process. These hypotheses are tested using the rigour of a bivariate analysis and the multivariate method of Qualitative Comparative Analysis (QCA. The results confirm the hypotheses of cluster memberships in all three periods. The confirmation analysis provides evidence about which variables are most influencing cluster memberships at each time point. In 2002 and 2006, differences between countries are influenced by their different Harmonised Index of Consumer Prices (HICP and labour productivity scores. In 2013, after the crisis, there is a noticeable change. Long term interest rates and gross government debt become key determinants of differences, in addition to the continuing influence of labour productivity. The paper concludes that in the last decade the convergence of countries sharing the euro has been limited, by the joining of new countries and the circumstances of the global economic crisis. The financial crisis has driven

  19. Network Firewall Dynamics and the Subsaturation Stabilization of HIV.

    Science.gov (United States)

    Khan, Bilal; Dombrowski, Kirk; Saad, Mohamed; McLean, Katherine; Friedman, Samuel

    2013-01-01

    In 2001, Friedman et al. conjectured the existence of a "firewall effect" in which individuals who are infected with HIV, but remain in a state of low infectiousness, serve to prevent the virus from spreading. To evaluate this historical conjecture, we develop a new graph-theoretic measure that quantifies the extent to which Friedman's firewall hypothesis(FH)holds in a risk network. We compute this new measure across simulated trajectories of a stochastic discrete dynamical system that models a social network of 25,000 individuals engaging in risk acts over a period of 15 years. The model's parameters are based on analyses of data collected in prior studies of the real-world risk networks of people who inject drugs (PWID) in New York City. Analysis of system trajectories reveals the structural mechanisms by which individuals with mature HIV infections tend to partition the network into homogeneous clusters (with respect to infection status) and how uninfected clusters remain relatively stable (with respect to infection status) over long stretches of time. We confirm the spontaneous emergence of network firewalls in the system and reveal their structural role in the nonspreading of HIV.

  20. Dynamic stability calculations for power grids employing a parallel computer

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, K

    1982-06-01

    The aim of dynamic contingency calculations in power systems is to estimate the effects of assumed disturbances, such as loss of generation. Due to the large dimensions of the problem these simulations require considerable computing time and costs, to the effect that they are at present only used in a planning state but not for routine checks in power control stations. In view of the homogeneity of the problem, where a multitude of equal generator models, having different parameters, are to be integrated simultaneously, the use of a parallel computer looks very attractive. The results of this study employing a prototype parallel computer (SMS 201) are presented. It consists of up to 128 equal microcomputers bus-connected to a control computer. Each of the modules is programmed to simulate a node of the power grid. Generators with their associated control are represented by models of 13 states each. Passive nodes are complemented by 'phantom'-generators, so that the whole power grid is homogenous, thus removing the need for load-flow-iterations. Programming of microcomputers is essentially performed in FORTRAN.

  1. Stabilizing simulations of complex stochastic representations for quantum dynamical systems

    Energy Technology Data Exchange (ETDEWEB)

    Perret, C; Petersen, W P, E-mail: wpp@math.ethz.ch [Seminar for Applied Mathematics, ETH, Zurich (Switzerland)

    2011-03-04

    Path integral representations of quantum dynamics can often be formulated as stochastic differential equations (SDEs). In a series of papers, Corney and Drummond (2004 Phys. Rev. Lett. 93 260401), Deuar and Drummond (2001 Comput. Phys. Commun. 142 442-5), Drummond and Gardnier (1980 J. Phys. A: Math. Gen. 13 2353-68), Gardiner and Zoller (2004 Quantum Noise: A Handbook of Markovian and Non-Markovian Quantum Stochastic Methods with Applications to Quantum Optics (Springer Series in Synergetics) 3rd edn (Berlin: Springer)) and Gilchrist et al (1997 Phys. Rev. A 55 3014-32) and their collaborators have derived SDEs from coherent states representations for density matrices. Computationally, these SDEs are attractive because they seem simple to simulate. They can be quite unstable, however. In this paper, we consider some of the instabilities and propose a few remedies. Particularly, because the variances of the simulated paths typically grow exponentially, the processes become de-localized in relatively short times. Hence, the issues of boundary conditions and stable integration methods become important. We use the Bose-Einstein Hamiltonian as an example. Our results reveal that it is possible to significantly extend integration times and show the periodic structure of certain functionals.

  2. Microtubules move the nucleus to quiescence.

    Science.gov (United States)

    Laporte, Damien; Sagot, Isabelle

    2014-01-01

    The nucleus is a cellular compartment that hosts several macro-molecular machines displaying a highly complex spatial organization. This tight architectural orchestration determines not only DNA replication and repair but also regulates gene expression. In budding yeast microtubules play a key role in structuring the nucleus since they condition the Rabl arrangement in G1 and chromosome partitioning during mitosis through their attachment to centromeres via the kinetochore proteins. Recently, we have shown that upon quiescence entry, intranuclear microtubules emanating from the spindle pole body elongate to form a highly stable bundle that spans the entire nucleus. Here, we examine some molecular mechanisms that may underlie the formation of this structure. As the intranuclear microtubule bundle causes a profound re-organization of the yeast nucleus and is required for cell survival during quiescence, we discuss the possibility that the assembly of such a structure participates in quiescence establishment.

  3. Dynamic respiration index as a descriptor of the biological stability of organic wastes.

    Science.gov (United States)

    Adani, Fabrizio; Confalonieri, Roberto; Tambone, Fulvia

    2004-01-01

    Analytical methods applicable to different organic wastes are needed to establish the extent to which readily biodegradable organic matter has decomposed (i.e., biological stability). The objective of this study was to test a new respirometric method for biological stability determination of organic wastes. Dynamic respiration index (DRI) measurements were performed on 16 organic wastes of different origin, composition, and biological stability degree to validate the test method and result expression, and to propose biological stability limits. In addition, theoretical DRI trends were obtained by using a mathematical model. Each test lasted 96 h in a 148-L-capacity respirometer apparatus, and DRI was monitored every hour. The biological stability was expressed as both single and cumulative DRI values. Results obtained indicated that DRI described biological stability in relation to waste typology and age well, revealing lower-stability waste characterized by a well-pronounced DRI profile (a marked peak was evident) that became practically flat for samples with higher biological stability. Fitting indices showed good model prediction compared with the experimental data, indicating that the method was able to reproduce the aerobic process, providing a reliable indication of the biological stability. The DRI can therefore be proposed as a useful method to measure the biological stability of organic wastes, and DRI values, calculated as a mean of 24 h of the highest microbial activity, of 1000 and 500 mg O(2) kg(-1) volatile solids (VS) h(-1) are proposed to indicate medium (e.g., fresh compost) and high (e.g., mature compost) biological stabilities, respectively.

  4. Potential mechanisms of resistance to microtubule inhibitors.

    Science.gov (United States)

    Kavallaris, Maria; Annereau, Jean-Philippe; Barret, Jean-Marc

    2008-06-01

    Antimitotic drugs targeting the microtubules, such as the taxanes and vinca alkaloids, are widely used in the treatment of neoplastic diseases. Development of drug resistance over time, however, limits the efficacy of these agents and poses a clinical challenge to long-term improvement of patient outcomes. Understanding the mechanism(s) of drug resistance becomes paramount to allowing for alternative, if not improved, therapeutic options that might circumvent this challenge. Vinflunine, a novel microtubule inhibitor, has shown superior preclinical antitumor activity, and displays a different pattern of resistance, compared with other agents in the vinca alkaloid class.

  5. Operational Limitations of Arctic Waste Stabilization Ponds: Insights from Modeling Oxygen Dynamics and Carbon Removal

    DEFF Research Database (Denmark)

    Ragush, Colin M.; Gentleman, Wendy C.; Hansen, Lisbeth Truelstrup

    2018-01-01

    Presented here is a mechanistic model of the biological dynamics of the photic zone of a single-cell arctic waste stabilization pond (WSP) for the prediction of oxygen concentration and the removal of oxygen-demanding substances. The model is an exploratory model to assess the limiting environmen...

  6. Dynamic postural stability differences between male and female players with and without ankle sprain

    NARCIS (Netherlands)

    Dallinga, Joan M.; Does, van der Henrike T. D.; Benjaminse, Anne; Lemmink, Koen A. P. M.

    Objectives: To evaluate dynamic stability index (DSI) differences between males and females for different jump directions. To examine both preseason DSI differences between players with and without a history of ankle sprain, and between players with and without an ankle sprain during the subsequent

  7. Local dynamic stability and variability of gait are associated with fall history in elderly subjects

    NARCIS (Netherlands)

    Toebes, M.J.P.; Hoozemans, M.J.M.; Furrer, R.; Dekker, J.; van Dieen, J.H.

    2012-01-01

    Gait parameters that can be measured with simple instrumentation may hold promise for identifying individuals at risk of falling. Increased variability of gait is associated with increased risk of falling, but research on additional parameters indicates that local dynamic stability (LDS) of gait may

  8. Dynamic Stability Analysis of Autonomous Medium-Voltage Mixed-Source Microgrid

    DEFF Research Database (Denmark)

    Zhao, Zhuoli; Yang, Ping; Guerrero, Josep M.

    2015-01-01

    -space model of the autonomous MV mixed-source microgrid containing diesel generator set (DGS), grid-supporting battery energy storage system (BESS), squirrel cage induction generator (SCIG) wind turbine and network is developed. Sensitivity analysis is carried out to reveal the dynamic stability margin...

  9. Locomotor Stability in a Model Swimmer: Coupling Fluid Dynamics, Neurophysiology and Muscle Mechanics

    Science.gov (United States)

    2017-07-05

    SECURITY CLASSIFICATION OF: We use multiscale modeling and computational fluid dynamics to examine the stability of a swimming organism in the face of...information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and

  10. Small disturbance voltage stability assessment of power systems by modal analysis and dynamic simulation

    International Nuclear Information System (INIS)

    Amjady, Nima; Ansari, Mohammad Reza

    2008-01-01

    The introduction of liberalized electricity markets in many countries has resulted in more highly stressed power systems. On the other hand, operating points of a power system are acceptable in the feasible region, which is surrounded by the borders of different stabilities. Power system instability is critical for all participants of the electricity market. Determination of different stability margins can result in the optimum utilization of power system with minimum risk. This paper focuses on the small disturbance voltage stability, which is an important subset of the power system global stability. This kind of voltage stability is usually evaluated by static analysis tools such as continuation power flow, while it essentially has dynamic nature. Besides, a combination of linear and nonlinear analysis tools is required to correctly analyze it. In this paper, a hybrid evaluation method composed of static, dynamic, linear, and nonlinear analysis tools is proposed for this purpose. Effect of load scenario, generation pattern, branch and generator contingency on the small disturbance voltage stability are evaluated by the hybrid method. The test results are given for New England and IEEE68 bus test systems. (author)

  11. Dynamic Stability of Pipe Conveying Fluid with Crack and Attached Masses

    International Nuclear Information System (INIS)

    Ahn, Tae Soo; Yoon, Han Ik; Son, In Soo; Ahn, Sung Jin

    2007-01-01

    In this paper, the dynamic stability of a cracked simply supported pipe conveying fluid with an attached mass is investigated. Also, the effect of attached masses on the dynamic stability of a simply supported pipe conveying fluid is presented for the different positions and depth of the crack. Based on the Euler-Bernoulli beam theory, the equation of motion can be constructed by the energy expressions using extended Hamilton's principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of a fracture and to be always opened during the vibrations. Finally, the critical flow velocities and stability maps of the pipe conveying fluid are obtained by changing the attached masses and crack severity

  12. A direct comparison of spine rotational stiffness and dynamic spine stability during repetitive lifting tasks.

    Science.gov (United States)

    Graham, Ryan B; Brown, Stephen H M

    2012-06-01

    Stability of the spinal column is critical to bear loads, allow movement, and at the same time avoid injury and pain. However, there has been a debate in recent years as to how best to define and quantify spine stability, with the outcome being that different methods are used without a clear understanding of how they relate to one another. Therefore, the goal of the present study was to directly compare lumbar spine rotational stiffness, calculated with an EMG-driven biomechanical model, to local dynamic spine stability calculated using Lyapunov analyses of kinematic data, during a series of continuous dynamic lifting challenges. Twelve healthy male subjects performed 30 repetitive lifts under three varying load and three varying rate conditions. With an increase in the load lifted (constant rate) there was a significant increase in mean, maximum, and minimum spine rotational stiffness (pstiffness (pstiffness and a non-significant decrease in local dynamic stability (p>0.05). Weak linear relationships were found for the varying rate conditions (r=-0.02 to -0.27). The results suggest that spine rotational stiffness and local dynamic stability are closely related to one another, as they provided similar information when movement rate was controlled. However, based on the results from the changing lifting rate conditions, it is evident that both models provide unique information and that future research is required to completely understand the relationship between the two models. Using both techniques concurrently may provide the best information regarding the true effects of (in) stability under different loading and movement scenarios, and in comparing healthy and clinical populations. Copyright © 2012 Elsevier Ltd. All rights reserved.

  13. Dynamical investigation and parameter stability region analysis of a flywheel energy storage system in charging mode

    International Nuclear Information System (INIS)

    Zhang Wei-Ya; Li Yong-Li; Chang Xiao-Yong; Wang Nan

    2013-01-01

    In this paper, the dynamic behavior analysis of the electromechanical coupling characteristics of a flywheel energy storage system (FESS) with a permanent magnet (PM) brushless direct-current (DC) motor (BLDCM) is studied. The Hopf bifurcation theory and nonlinear methods are used to investigate the generation process and mechanism of the coupled dynamic behavior for the average current controlled FESS in the charging mode. First, the universal nonlinear dynamic model of the FESS based on the BLDCM is derived. Then, for a 0.01 kWh/1.6 kW FESS platform in the Key Laboratory of the Smart Grid at Tianjin University, the phase trajectory of the FESS from a stable state towards chaos is presented using numerical and stroboscopic methods, and all dynamic behaviors of the system in this process are captured. The characteristics of the low-frequency oscillation and the mechanism of the Hopf bifurcation are investigated based on the Routh stability criterion and nonlinear dynamic theory. It is shown that the Hopf bifurcation is directly due to the loss of control over the inductor current, which is caused by the system control parameters exceeding certain ranges. This coupling nonlinear process of the FESS affects the stability of the motor running and the efficiency of energy transfer. In this paper, we investigate into the effects of control parameter change on the stability and the stability regions of these parameters based on the averaged-model approach. Furthermore, the effect of the quantization error in the digital control system is considered to modify the stability regions of the control parameters. Finally, these theoretical results are verified through platform experiments. (interdisciplinary physics and related areas of science and technology)

  14. Dynamic Characteristics Analysis and Stabilization of PV-Based Multiple Microgrid Clusters

    DEFF Research Database (Denmark)

    Zhao, Zhuoli; Yang, Ping; Wang, Yuewu

    2018-01-01

    -based multiple microgrid clusters. A detailed small-signal model for PV-based microgrid clusters considering local adaptive dynamic droop control mechanism of the voltage-source PV system is developed. The complete dynamic model is then used to access and compare the dynamic characteristics of the single...... microgrid and interconnected microgrids. In order to enhance system stability of the PV microgrid clusters, a tie-line flow and stabilization strategy is proposed to suppress the introduced interarea and local oscillations. Robustly selecting of the key control parameters is transformed to a multiobjective......As the penetration of PV generation increases, there is a growing operational demand on PV systems to participate in microgrid frequency regulation. It is expected that future distribution systems will consist of multiple microgrid clusters. However, interconnecting PV microgrids may lead to system...

  15. Power system dynamics and stability with synchrophasor measurement and power system toolbox

    CERN Document Server

    Sauer, Peter W; Chow, Joe H

    2017-01-01

    This new edition addresses the needs of dynamic modeling and simulation relevant to power system planning, design, and operation, including a systematic derivation of synchronous machine dynamic models together with speed and voltage control subsystems. Reduced-order modeling based on integral manifolds is used as a firm basis for understanding the derivations and limitations of lower-order dynamic models. Following these developments, a multi-machine model interconnected through the transmission network is formulated and simulated using numerical simulation methods. Energy function methods are discussed for direct evaluation of stability. Small-signal analysis is used for determining the electromechanical modes and mode-shapes, and for power system stabilizer design. Time-synchronized high-sampling-rate phasor measurement units (PMUs) to monitor power system disturbances ave been implemented throughout North America and many other countries. In this second edition, new chapters on synchrophasor measurement ...

  16. Dynamic stability of running: The effects of speed and leg amputations on the maximal Lyapunov exponent

    International Nuclear Information System (INIS)

    Look, Nicole; Arellano, Christopher J.; Grabowski, Alena M.; Kram, Rodger; McDermott, William J.; Bradley, Elizabeth

    2013-01-01

    In this paper, we study dynamic stability during running, focusing on the effects of speed, and the use of a leg prosthesis. We compute and compare the maximal Lyapunov exponents of kinematic time-series data from subjects with and without unilateral transtibial amputations running at a wide range of speeds. We find that the dynamics of the affected leg with the running-specific prosthesis are less stable than the dynamics of the unaffected leg and also less stable than the biological legs of the non-amputee runners. Surprisingly, we find that the center-of-mass dynamics of runners with two intact biological legs are slightly less stable than those of runners with amputations. Our results suggest that while leg asymmetries may be associated with instability, runners may compensate for this effect by increased control of their center-of-mass dynamics

  17. Static and dynamic stability of pneumatic vibration isolators and systems of isolators

    Science.gov (United States)

    Ryaboy, Vyacheslav M.

    2014-01-01

    Pneumatic vibration isolation is the most widespread effective method for creating vibration-free environments that are vital for precise experiments and manufacturing operations in optoelectronics, life sciences, microelectronics, nanotechnology and other areas. The modeling and design principles of a dual-chamber pneumatic vibration isolator, basically established a few decades ago, continue to attract attention of researchers. On the other hand, behavior of systems of such isolators was never explained in the literature in sufficient detail. This paper covers a range of questions essential for understanding the mechanics of pneumatic isolation systems from both design and application perspectives. The theory and a model of a single standalone isolator are presented in concise form necessary for subsequent analysis. Then the dynamics of a system of isolators supporting a payload is considered with main attention directed to two aspects of their behavior: first, the static stability of payloads with high positions of the center of gravity; second, dynamic stability of the feedback system formed by mechanical leveling valves. The direct method of calculating the maximum stable position of the center of gravity is presented and illustrated by three-dimensional stability domains; analytic formulas are given that delineate these domains. A numerical method for feedback stability analysis of self-leveling valve systems is given, and the results are compared with the analytical estimates for a single isolator. The relation between the static and dynamic phenomena is discussed.

  18. On Stabilizing the Variance of Dynamic Functional Brain Connectivity Time Series.

    Science.gov (United States)

    Thompson, William Hedley; Fransson, Peter

    2016-12-01

    Assessment of dynamic functional brain connectivity based on functional magnetic resonance imaging (fMRI) data is an increasingly popular strategy to investigate temporal dynamics of the brain's large-scale network architecture. Current practice when deriving connectivity estimates over time is to use the Fisher transformation, which aims to stabilize the variance of correlation values that fluctuate around varying true correlation values. It is, however, unclear how well the stabilization of signal variance performed by the Fisher transformation works for each connectivity time series, when the true correlation is assumed to be fluctuating. This is of importance because many subsequent analyses either assume or perform better when the time series have stable variance or adheres to an approximate Gaussian distribution. In this article, using simulations and analysis of resting-state fMRI data, we analyze the effect of applying different variance stabilization strategies on connectivity time series. We focus our investigation on the Fisher transformation, the Box-Cox (BC) transformation and an approach that combines both transformations. Our results show that, if the intention of stabilizing the variance is to use metrics on the time series, where stable variance or a Gaussian distribution is desired (e.g., clustering), the Fisher transformation is not optimal and may even skew connectivity time series away from being Gaussian. Furthermore, we show that the suboptimal performance of the Fisher transformation can be substantially improved by including an additional BC transformation after the dynamic functional connectivity time series has been Fisher transformed.

  19. The Effect of the Loading on Dynamic Stability and Scapular Asymmetry

    Directory of Open Access Journals (Sweden)

    Mohammad Hassan Azarsa

    2014-03-01

    Full Text Available Background: Scapular stabilization and neuromuscular control provide an important parameter to characterize shoulder function during dynamic activities. Many studies have confirmed the effect of the loading on scapular position and scapulohumeral rhythm. Therefore, the evaluation of stabilizer muscles involvement in scapular asymmetry may assist in the development of clinical examination and rehabilitation program. The aim of this study was to evaluate the effect of loading on dynamic stability and scapular asymmetry in basketball players. Methods: Thirty healthy male basketball players aged between 20 to 31 years old were tested. The linear distance between scapular inferior angle and T7 spinous process was measured using a caliper in 90 degrees of unloaded scaption and with 1, 2 and 4 kg loading. The difference of distances of two sides in the above 4 positions was analyzed. Results: The amount of distances difference in two sides with 1 kg loading was minimal (9.36 mm. This difference increased to 10.19 mm and 12.22 mm, with increasing the loading to 2 and 4 kg respectively; although the 4 positions of the test did not show significant differences in distances difference (P>0.05. Conclusion: This study shows that dynamic stability of the scapula is dependent on the role of muscles, so that with increasing load on the muscles, the scapular asymmetry is more pronounced.

  20. Torsional Stiffness Effects on the Dynamic Stability of a Horizontal Axis Wind Turbine Blade

    Directory of Open Access Journals (Sweden)

    Min-Soo Jeong

    2013-04-01

    Full Text Available Aeroelastic instability problems have become an increasingly important issue due to the increased use of larger horizontal axis wind turbines. To maintain these large structures in a stable manner, the blade design process should include studies on the dynamic stability of the wind turbine blade. Therefore, fluid-structure interaction analyses of the large-scaled wind turbine blade were performed with a focus on dynamic stability in this study. A finite element method based on the large deflection beam theory is used for structural analysis considering the geometric nonlinearities. For the stability analysis, a proposed aerodynamic approach based on Greenberg’s extension of Theodorsen’s strip theory and blade element momentum method were employed in conjunction with a structural model. The present methods proved to be valid for estimations of the aerodynamic responses and blade behavior compared with numerical results obtained in the previous studies. Additionally, torsional stiffness effects on the dynamic stability of the wind turbine blade were investigated. It is demonstrated that the damping is considerably influenced by variations of the torsional stiffness. Also, in normal operating conditions, the destabilizing phenomena were observed to occur with low torsional stiffness.

  1. The effects of core stabilization exercise on dynamic balance and gait function in stroke patients.

    Science.gov (United States)

    Chung, Eun-Jung; Kim, Jung-Hee; Lee, Byoung-Hee

    2013-07-01

    [Purpose] The purpose of this study was to determine the effects of core stabilization exercise on dynamic balance and gait function in stroke patients. [Subjects] The subjects were 16 stroke patients, who were randomly divided into two groups: a core stabilization exercise group of eight subjects and control group of eight subjects. [Methods] Subjects in both groups received general training five times per week. Subjects in the core stabilization exercise group practiced an additional core stabilization exercise program, which was performed for 30 minutes, three times per week, during a period of four weeks. All subjects were evaluated for dynamic balance (Timed Up and Go test, TUG) and gait parameters (velocity, cadence, step length, and stride length). [Results] Following intervention, the core exercise group showed a significant change in TUG, velocity, and cadence. The only significant difference observed between the core group and control group was in velocity. [Conclusion] The results of this study suggest the feasibility and suitability of core stabilization exercise for stroke patients.

  2. Topics in Modeling of Cochlear Dynamics: Computation, Response and Stability Analysis

    Science.gov (United States)

    Filo, Maurice G.

    This thesis touches upon several topics in cochlear modeling. Throughout the literature, mathematical models of the cochlea vary according to the degree of biological realism to be incorporated. This thesis casts the cochlear model as a continuous space-time dynamical system using operator language. This framework encompasses a wider class of cochlear models and makes the dynamics more transparent and easier to analyze before applying any numerical method to discretize space. In fact, several numerical methods are investigated to study the computational efficiency of the finite dimensional realizations in space. Furthermore, we study the effects of the active gain perturbations on the stability of the linearized dynamics. The stability analysis is used to explain possible mechanisms underlying spontaneous otoacoustic emissions and tinnitus. Dynamic Mode Decomposition (DMD) is introduced as a useful tool to analyze the response of nonlinear cochlear models. Cochlear response features are illustrated using DMD which has the advantage of explicitly revealing the spatial modes of vibrations occurring in the Basilar Membrane (BM). Finally, we address the dynamic estimation problem of BM vibrations using Extended Kalman Filters (EKF). Due to the limitations of noninvasive sensing schemes, such algorithms are inevitable to estimate the dynamic behavior of a living cochlea.

  3. Local Dynamic Stability Assessment of Motion Impaired Elderly Using Electronic Textile Pants.

    Science.gov (United States)

    Liu, Jian; Lockhart, Thurmon E; Jones, Mark; Martin, Tom

    2008-10-01

    A clear association has been demonstrated between gait stability and falls in the elderly. Integration of wearable computing and human dynamic stability measures into home automation systems may help differentiate fall-prone individuals in a residential environment. The objective of the current study was to evaluate the capability of a pair of electronic textile (e-textile) pants system to assess local dynamic stability and to differentiate motion-impaired elderly from their healthy counterparts. A pair of e-textile pants comprised of numerous e-TAGs at locations corresponding to lower extremity joints was developed to collect acceleration, angular velocity and piezoelectric data. Four motion-impaired elderly together with nine healthy individuals (both young and old) participated in treadmill walking with a motion capture system simultaneously collecting kinematic data. Local dynamic stability, characterized by maximum Lyapunov exponent, was computed based on vertical acceleration and angular velocity at lower extremity joints for the measurements from both e-textile and motion capture systems. Results indicated that the motion-impaired elderly had significantly higher maximum Lyapunov exponents (computed from vertical acceleration data) than healthy individuals at the right ankle and hip joints. In addition, maximum Lyapunov exponents assessed by the motion capture system were found to be significantly higher than those assessed by the e-textile system. Despite the difference between these measurement techniques, attaching accelerometers at the ankle and hip joints was shown to be an effective sensor configuration. It was concluded that the e-textile pants system, via dynamic stability assessment, has the potential to identify motion-impaired elderly.

  4. EFFECT OF SHOULDER SIDE PACK ON DYNAMIC POSTURAL STABILITY IN YOUNG HEALTHY FEMALE

    Directory of Open Access Journals (Sweden)

    Enas ELsayed Mohamed Abutaleb

    2016-06-01

    Full Text Available Background: Control of balance is a complex motor skill that involves integration of sensory inputs and the planning and execution of flexible movement patterns. Carrying side packs is famous in our society especially shoulder side packs. Most students carry shoulder side packs and they don't care about the way to carry them to be more balanced. The purpose of the study is to investigate the effect of carrying shoulder side pack on dynamic postural stability and to determine the best way of carrying a shoulder side pack either on the dominant side or non-dominant side that doesn’t affect dynamic postural stability in young healthy female. Methods: Sixty female volunteers aged from 18 to 25 years old participated in the study. Biodex balance system was used to measure the dynamic postural stability in three different occasions (without carrying a shoulder side pack, with carrying a shoulder side pack on the dominant side, and on the non-dominant side with a rest period in between. Results: Repeated measure analysis of variance (ANOVA followed by Bonferroni post hoc test were used to compare dynamic posture balance without carrying and during carrying a shoulder side pack on dominant and non-dominant sides. Analysis revealed that overall, anteroposterior and mediolateral stability indexes reduced significantly (P<0.0001 when carrying shoulder side pack on dominant side in comparison with when carrying shoulder side pack on non-dominant side and without carrying bag. Conclusion: It was concluded that carrying a shoulder side pack on the non-dominant side didn't disturb the postural stability when compared to carrying on the dominant side so, we recommend the students to carry shoulder side packs on the non-dominant side.

  5. Dynamic trunk stabilization: a conceptual back injury prevention program for volleyball athletes.

    Science.gov (United States)

    Smith, Chad E; Nyland, John; Caudill, Paul; Brosky, Joseph; Caborn, David N M

    2008-11-01

    The sport of volleyball creates considerable dynamic trunk stability demands. Back injury occurs all too frequently in volleyball, particularly among female athletes. The purpose of this clinical commentary is to review functional anatomy, muscle coactivation strategies, assessment of trunk muscle performance, and the characteristics of effective exercises for the trunk or core. From this information, a conceptual progressive 3-phase volleyball-specific training program is presented to improve dynamic trunk stability and to potentially reduce the incidence of back injury among volleyball athletes. Phase 1 addresses low-velocity motor control, kinesthetic awareness, and endurance, with the clinician providing cues to teach achievement of biomechanically neutral spine alignment. Phase 2 focuses on progressively higher velocity dynamic multiplanar endurance, coordination, and strength-power challenges integrating upper and lower extremity movements, while maintaining neutral spine alignment. Phase 3 integrates volleyball-specific skill simulations by breaking down composite movement patterns into their component parts, with differing dynamic trunk stability requirements, while maintaining neutral spine alignment. Prospective research is needed to validate the efficacy of this program.

  6. The Effects of Core Stability Exercise on the Dynamic Balance of Volleyball Players

    Directory of Open Access Journals (Sweden)

    Hassan Sadeghi

    2013-12-01

    Full Text Available Dynamic balance is a key component of injury prevention and rehabilitation in sports. Training the core muscles has been hypothesized as an intervention for improving balance. However, there is a lack of current scientific evidence to support this claim. The purpose of this study was to evaluate the effects of a core stability program on dynamic balance of volleyball players as measured with the Star Excursion Balance Test (SEBT. Thirty healthy participants were divided into 2 groups: control and exercise groups. All participants performed the SEBT before and after 8-week exercise time. During the 8-week time, the exercise group performed a core stability program, whereas the control group abstained from any new exercise. These results also illustrated there was significant differences in the scores for pre-test and post-test of all direction according SEBT in the experimental group. An independent sample t-test was conducted to compare experimental and control group (F=43.573, Sig=0.000. These results were a significant difference in the scores for control and experimental groups. Maximum excursion distances improved for the exercise group, compared with the control group. This result justifies the hypothesis that core strengthening can improve dynamic postural control during landing of volleyball players significantly. Keywords: Core stabilization; volleyball player; dynamic balance; SEBT

  7. Stability of Intelligent Transportation Network Dynamics: A Daily Path Flow Adjustment considering Travel Time Differentiation

    Directory of Open Access Journals (Sweden)

    Ming-Chorng Hwang

    2015-01-01

    Full Text Available A theoretic formulation on how traffic time information distributed by ITS operations influences the trajectory of network flows is presented in this paper. The interactions between users and ITS operator are decomposed into three parts: (i travel time induced path flow dynamics (PFDTT; (ii demand induced path flow dynamics (PFDD; and (iii predicted travel time dynamics for an origin-destination (OD pair (PTTDOD. PFDTT describes the collective results of user’s daily route selection by pairwise comparison of path travel time provided by ITS services. The other two components, PTTDOD and PFDD, are concentrated on the evolutions of system variables which are predicted and observed, respectively, by ITS operators to act as a benchmark in guiding the target system towards an expected status faster. In addition to the delivered modelings, the stability theorem of the equilibrium solution in the sense of Lyapunov stability is also provided. A Lyapunov function is developed and employed to the proof of stability theorem to show the asymptotic behavior of the aimed system. The information of network flow dynamics plays a key role in traffic control policy-making. The evaluation of ITS-based strategies will not be reasonable without a well-established modeling of network flow evolutions.

  8. Static and dynamic stability of the guidance force in a side-suspended HTS maglev system

    Science.gov (United States)

    Zhou, Dajin; Cui, Chenyu; Zhao, Lifeng; Zhang, Yong; Wang, Xiqing; Zhao, Yong

    2017-02-01

    The static and dynamic stability of the guidance force in a side-suspended HTS-PMG (permanent magnetic guideway) system were studied theoretically and experimentally. It is found that there are two types of guidance force that exist in the HTS-PMG system, which are sensitive to the levitation gap and the arrangement of YBCO bulks around the central axis of the PMG. An optimized YBCO array was used to stabilize the system, which enabled a side-suspended HTS-PMG maglev vehicle to run stably at 102 km h-1 on a circular test track with 6.5 m in diameter.

  9. A new strategy for transient stability using augmented generator control and local dynamic braking

    Energy Technology Data Exchange (ETDEWEB)

    Dorsey, J; Jiang, H; Habetler, T [Georgia Inst. of Tech., Atlanta, GA (United States); Qu, Z [University of Central Florida, Orlando, FL (United States)

    1994-12-31

    A decentralized automatic control strategy for significantly improving the transient stability of a large power system is introduced. The strategy combines local dynamic braking and a straightforward augmentation of the existing turbine / governor control system that uses only local feedback. The brake resistor, which employs thick film, metal oxide technology, has no inductance and is of very low resistance, allowing its use during fault to show a generator`s acceleration. Simulation results using the 39 Bus New England system show that the strategy dramatically increases the global stability of a power system. (author) 15 refs., 7 figs., 1 tab.

  10. Classical linear-control analysis applied to business-cycle dynamics and stability

    Science.gov (United States)

    Wingrove, R. C.

    1983-01-01

    Linear control analysis is applied as an aid in understanding the fluctuations of business cycles in the past, and to examine monetary policies that might improve stabilization. The analysis shows how different policies change the frequency and damping of the economic system dynamics, and how they modify the amplitude of the fluctuations that are caused by random disturbances. Examples are used to show how policy feedbacks and policy lags can be incorporated, and how different monetary strategies for stabilization can be analytically compared. Representative numerical results are used to illustrate the main points.

  11. Stability and periodicity of solutions for delay dynamic systems on time scales

    Directory of Open Access Journals (Sweden)

    Zhi-Qiang Zhu

    2014-04-01

    Full Text Available This article concerns the stability and periodicity of solutions to the delay dynamic system $$ x^{\\triangle}(t=A(t x(t + F(t, x(t, x(g(t+C(t $$ on a time scale. By the inequality technique for vectors, we obtain some stability criteria for the above system. Then, by using the Horn fixed point theorem, we present some conditions under which our system is asymptotically periodic and its periodic solution is unique. In particular, the periodic solution is positive under proper assumptions.

  12. Linear stability analysis of detonations via numerical computation and dynamic mode decomposition

    KAUST Repository

    Kabanov, Dmitry; Kasimov, Aslan R.

    2018-01-01

    We introduce a new method to investigate linear stability of gaseous detonations that is based on an accurate shock-fitting numerical integration of the linearized reactive Euler equations with a subsequent analysis of the computed solution via the dynamic mode decomposition. The method is applied to the detonation models based on both the standard one-step Arrhenius kinetics and two-step exothermic-endothermic reaction kinetics. Stability spectra for all cases are computed and analyzed. The new approach is shown to be a viable alternative to the traditional normal-mode analysis used in detonation theory.

  13. Linear stability analysis of detonations via numerical computation and dynamic mode decomposition

    KAUST Repository

    Kabanov, Dmitry I.

    2017-12-08

    We introduce a new method to investigate linear stability of gaseous detonations that is based on an accurate shock-fitting numerical integration of the linearized reactive Euler equations with a subsequent analysis of the computed solution via the dynamic mode decomposition. The method is applied to the detonation models based on both the standard one-step Arrhenius kinetics and two-step exothermic-endothermic reaction kinetics. Stability spectra for all cases are computed and analyzed. The new approach is shown to be a viable alternative to the traditional normal-mode analysis used in detonation theory.

  14. Linear stability analysis of detonations via numerical computation and dynamic mode decomposition

    KAUST Repository

    Kabanov, Dmitry

    2018-03-20

    We introduce a new method to investigate linear stability of gaseous detonations that is based on an accurate shock-fitting numerical integration of the linearized reactive Euler equations with a subsequent analysis of the computed solution via the dynamic mode decomposition. The method is applied to the detonation models based on both the standard one-step Arrhenius kinetics and two-step exothermic-endothermic reaction kinetics. Stability spectra for all cases are computed and analyzed. The new approach is shown to be a viable alternative to the traditional normal-mode analysis used in detonation theory.

  15. FINANCIAL STABILITY OF SMALL BUSINESS: THE ESTIMATION AND DYNAMICS OF REGIONAL DEVELOPMENT

    Directory of Open Access Journals (Sweden)

    A.U. Makarova

    2008-03-01

    Full Text Available In clause the problem of an estimation of financial stability of the enterprises of small business is considered. It is offered to use traditional indicators of an estimation of the financial stability, describing it in the short-term period, and such indicators as equation of monetary streams, qualitative risk-management, a level äèâåðñèôèêàöèè business and competitive position of the company for an estimation of stability in the long-term period. On the basis of data of statistical supervision over small enterprises the estimation of dynamics of results of financial activity and financial stability of small enterprises of Sverdlovsk area is lead to 2001 – 2005 is drawn a conclusion about low parameters of solvency and financial stability of small enterprises of region in comparison with normative parameters and data on the large and average enterprises. The measures directed on increase of financial stability of the enterprises of small business are offered.

  16. Measurement of in vitro microtubule polymerization by turbidity and fluorescence.

    Science.gov (United States)

    Mirigian, Matthew; Mukherjee, Kamalika; Bane, Susan L; Sackett, Dan L

    2013-01-01

    Tubulin polymerization may be conveniently monitored by the increase in turbidity (optical density, or OD) or by the increase in fluorescence intensity of diamidino-phenylindole. The resulting data can be a quantitative measure of microtubule (MT) assembly, but some care is needed in interpretation, especially of OD data. Buffer formulations used for the assembly reaction significantly influence the polymerization, both by altering the critical concentration for polymerization and by altering the exact polymer produced-for example, by increasing the production of sheet polymers in addition to MT. Both the turbidity and the fluorescence methods are useful for demonstrating the effect of MT-stabilizing or -destabilizing additives. 2013 Published by Elsevier Inc.

  17. HSPB1 facilitates the formation of non-centrosomal microtubules.

    Directory of Open Access Journals (Sweden)

    Leonardo Almeida-Souza

    Full Text Available The remodeling capacity of microtubules (MT is essential for their proper function. In mammals, MTs are predominantly formed at the centrosome, but can also originate from non-centrosomal sites, a process that is still poorly understood. We here show that the small heat shock protein HSPB1 plays a role in the control of non-centrosomal MT formation. The HSPB1 expression level regulates the balance between centrosomal and non-centrosomal MTs. The HSPB1 protein can be detected specifically at sites of de novo forming non-centrosomal MTs, while it is absent from the centrosomes. In addition, we show that HSPB1 binds preferentially to the lattice of newly formed MTs in vitro, suggesting that its function occurs by stabilizing MT seeds. Our findings open new avenues for the understanding of the role of HSPB1 in the development, maintenance and protection of cells with specialized non-centrosomal MT arrays.

  18. Feedback control stabilization of critical dynamics via resource transport on multilayer networks: How glia enable learning dynamics in the brain

    Science.gov (United States)

    Virkar, Yogesh S.; Shew, Woodrow L.; Restrepo, Juan G.; Ott, Edward

    2016-10-01

    Learning and memory are acquired through long-lasting changes in synapses. In the simplest models, such synaptic potentiation typically leads to runaway excitation, but in reality there must exist processes that robustly preserve overall stability of the neural system dynamics. How is this accomplished? Various approaches to this basic question have been considered. Here we propose a particularly compelling and natural mechanism for preserving stability of learning neural systems. This mechanism is based on the global processes by which metabolic resources are distributed to the neurons by glial cells. Specifically, we introduce and study a model composed of two interacting networks: a model neural network interconnected by synapses that undergo spike-timing-dependent plasticity; and a model glial network interconnected by gap junctions that diffusively transport metabolic resources among the glia and, ultimately, to neural synapses where they are consumed. Our main result is that the biophysical constraints imposed by diffusive transport of metabolic resources through the glial network can prevent runaway growth of synaptic strength, both during ongoing activity and during learning. Our findings suggest a previously unappreciated role for glial transport of metabolites in the feedback control stabilization of neural network dynamics during learning.

  19. A new kymogram-based method reveals unexpected effects of marker protein expression and spatial anisotropy of cytoskeletal dynamics in plant cell cortex

    Czech Academy of Sciences Publication Activity Database

    Cvrčková, F.; Oulehlová, Denisa

    2017-01-01

    Roč. 13, MAR 27 (2017), č. článku 19. ISSN 1746-4811 Institutional support: RVO:61389030 Keywords : green fluorescent protein * cortical microtubule arrays * actin stochastic dynamics * arabidopsis-thaliana * epidermal-cells * quantitative-analysis * binding domain * gfp-tubulin * f-actin * microscopy * Actin * Microtubules * Lifeact * Variable angle fluorescence microscopy * Spinning disc confocal microscopy * Kymogram * Structure stability * Lateral mobility * Anisotropy * FH1 (At3g25500) Subject RIV: EB - Genetics ; Molecular Biology OBOR OECD: Cell biology Impact factor: 3.510, year: 2016

  20. Fast Dynamic Simulation-Based Small Signal Stability Assessment and Control

    Energy Technology Data Exchange (ETDEWEB)

    Acharya, Naresh [General Electric Company, Fairfield, CT (United States); Baone, Chaitanya [General Electric Company, Fairfield, CT (United States); Veda, Santosh [General Electric Company, Fairfield, CT (United States); Dai, Jing [General Electric Company, Fairfield, CT (United States); Chaudhuri, Nilanjan [General Electric Company, Fairfield, CT (United States); Leonardi, Bruno [General Electric Company, Fairfield, CT (United States); Sanches-Gasca, Juan [General Electric Company, Fairfield, CT (United States); Diao, Ruisheng [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Wu, Di [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Huang, Zhenyu [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Zhang, Yu [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Jin, Shuangshuang [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Zheng, Bin [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Chen, Yousu [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2014-12-31

    Power grid planning and operation decisions are made based on simulation of the dynamic behavior of the system. Enabling substantial energy savings while increasing the reliability of the aging North American power grid through improved utilization of existing transmission assets hinges on the adoption of wide-area measurement systems (WAMS) for power system stabilization. However, adoption of WAMS alone will not suffice if the power system is to reach its full entitlement in stability and reliability. It is necessary to enhance predictability with "faster than real-time" dynamic simulations that will enable the dynamic stability margins, proactive real-time control, and improve grid resiliency to fast time-scale phenomena such as cascading network failures. Present-day dynamic simulations are performed only during offline planning studies, considering only worst case conditions such as summer peak, winter peak days, etc. With widespread deployment of renewable generation, controllable loads, energy storage devices and plug-in hybrid electric vehicles expected in the near future and greater integration of cyber infrastructure (communications, computation and control), monitoring and controlling the dynamic performance of the grid in real-time would become increasingly important. The state-of-the-art dynamic simulation tools have limited computational speed and are not suitable for real-time applications, given the large set of contingency conditions to be evaluated. These tools are optimized for best performance of single-processor computers, but the simulation is still several times slower than real-time due to its computational complexity. With recent significant advances in numerical methods and computational hardware, the expectations have been rising towards more efficient and faster techniques to be implemented in power system simulators. This is a natural expectation, given that the core solution algorithms of most commercial simulators were developed

  1. Conceptual Design Optimization of an Augmented Stability Aircraft Incorporating Dynamic Response and Actuator Constraints

    Science.gov (United States)

    Welstead, Jason; Crouse, Gilbert L., Jr.

    2014-01-01

    Empirical sizing guidelines such as tail volume coefficients have long been used in the early aircraft design phases for sizing stabilizers, resulting in conservatively stable aircraft. While successful, this results in increased empty weight, reduced performance, and greater procurement and operational cost relative to an aircraft with optimally sized surfaces. Including flight dynamics in the conceptual design process allows the design to move away from empirical methods while implementing modern control techniques. A challenge of flight dynamics and control is the numerous design variables, which are changing fluidly throughout the conceptual design process, required to evaluate the system response to some disturbance. This research focuses on addressing that challenge not by implementing higher order tools, such as computational fluid dynamics, but instead by linking the lower order tools typically used within the conceptual design process so each discipline feeds into the other. In thisresearch, flight dynamics and control was incorporated into the conceptual design process along with the traditional disciplines of vehicle sizing, weight estimation, aerodynamics, and performance. For the controller, a linear quadratic regulator structure with constant gains has been specified to reduce the user input. Coupling all the disciplines in the conceptual design phase allows the aircraft designer to explore larger design spaces where stabilizers are sized according to dynamic response constraints rather than historical static margin and volume coefficient guidelines.

  2. Accuracy Enhanced Stability and Structure Preserving Model Reduction Technique for Dynamical Systems with Second Order Structure

    DEFF Research Database (Denmark)

    Tahavori, Maryamsadat; Shaker, Hamid Reza

    A method for model reduction of dynamical systems with the second order structure is proposed in this paper. The proposed technique preserves the second order structure of the system, and also preserves the stability of the original systems. The method uses the controllability and observability...... gramians within the time interval to build the appropriate Petrov-Galerkin projection for dynamical systems within the time interval of interest. The bound on approximation error is also derived. The numerical results are compared with the counterparts from other techniques. The results confirm...

  3. Dynamic Phasors-Based Modeling and Stability Analysis of Droop-Controlled Inverters for Microgrid Applications

    DEFF Research Database (Denmark)

    Guo, Xiaoqiang; Lu, Zhigang; Wang, Baocheng

    2014-01-01

    models fail to predict the system instabilities. In order to solve the problem, a new modeling approach for inverter-dominated microgrids by using dynamic phasors is presented in this paper. Our findings indicate that the proposed dynamic phasor model is able to predict accurately the stability margins...... of the system, while the conventional reduced-order small signal model fails. In addition, the virtual ω-E frame power control method, which deals with the power coupling caused by the line impedance X/R characteristic, has also been chosen as an application example of the proposed modeling technique....

  4. Stability of the Supply Chain Using System Dynamics Simulation and the Accumulated Deviations from Equilibrium

    Directory of Open Access Journals (Sweden)

    Luis Rabelo

    2011-01-01

    Full Text Available We propose and demonstrate a new methodology to stabilize systems with complex dynamics like the supply chain. This method is based on the accumulated deviations from equilibrium (ADE. It is most beneficial for controlling system dynamic models characterized by multiple types of delays, many interacting variables, and feedback processes. We employ the classical version of particle swarm optimization as the optimization approach due to its performance in multidimensional space, stochastic properties, and global reach. We demonstrate the effectiveness of our method based on ADE using a manufacturing-supply-chain case study.

  5. Dynamics of a stabilized motor defense conditioned reflex at different levels of motivation in irradiated rats

    Energy Technology Data Exchange (ETDEWEB)

    Shtemberg, A S

    1982-05-01

    Postradiation dynamics of strengthened motor-defense conditioned reflex in rats-males irradiated with the doses of 94.111 and 137 Gy was studied. Phase disturbances of conditioned-reflex activity increased with enhancing irradiation dose have been revealed. Rapid recovery of conditioned reflex after short primary aggravation was a characteristic peculiarity. At that, the dynamics of relation of main nervous processes in cortex was noted for significant instability increasing with radiation syndrome development. Enhancement of force of electro-defense support promoted more effective strengthening of temporary connections and conditioned high stability of trained-reflex reactions during serious functional disturbances resulted from sublethal dose irradiation.

  6. Dynamic Stability Study of Static Gas Bearing for Small Cryogenic Turbo-Expander

    International Nuclear Information System (INIS)

    Wang Xuemin; Zhuang Ming; Zhang Qiyong; Li Shanshan; Fu Bao

    2011-01-01

    An experimental method is presented to analyze the dynamic stability of the gas bearing for small cryogenic turbo-expanders. The rotation imbalance response and the shape of the rotor orbit were obtained for different speeds up to 110,000 rpm, and the critical speed of the rotor-bearing system was determined by a Bode diagram. An FFT signal analytical method was applied to identify the resonance frequency, and the waterfall plot was presented. During the whole process of speeding up to the designed speed of 110,000 rpm, the rotor-bearing works stably with no whirl instability, which is validated in a waterfall plot. Also, the tested rotor-bearing model was analyzed theoretically. It was proved that the experimental results were highly consistent with those of theoretical calculations. Thus the experimental method proposed here to analyze the dynamic stability of the gas bearing is feasible. (fusion engineering)

  7. Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Liang, Xiaogang; Hamid, Ilyar; Duan, Haiming, E-mail: dhm@xju.edu.cn [College of Physics Science and Technology. Xinjiang University, Urumqi 830046 (China)

    2016-06-15

    The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure). The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti) > (Cu, Fe, Co, Ni, Mg, Ag) > (Pb, Au, Pd, Pt, Rh, Ir), which correspond to the predicted formation ability of the quasicrystals. The differences of the sequences can be explained by analyzing the parameters of the Gupta-type many-body inter-atomic potentials.

  8. Advanced numerical methods for uncertainty reduction when predicting heat exchanger dynamic stability limits: Review and perspectives

    International Nuclear Information System (INIS)

    Longatte, E.; Baj, F.; Hoarau, Y.; Braza, M.; Ruiz, D.; Canteneur, C.

    2013-01-01

    Highlights: ► Proposal of hybrid computational methods for investigating dynamical system stability. ► Modeling turbulence disequilibrium due to interaction with moving solid boundaries. ► Providing computational procedure for large size system solution approximation through model reduction. -- Abstract: This article proposes a review of recent and current developments in the modeling and advanced numerical methods used to simulate large-size systems involving multi-physics in the field of mechanics. It addresses the complex issue of stability analysis of dynamical systems submitted to external turbulent flows and aims to establish accurate stability maps applicable to heat exchanger design. The purpose is to provide dimensionless stability limit modeling that is suitable for a variety of configurations and is as accurate as possible in spite of the large scale of the systems to be considered. The challenge lies in predicting local effects that may impact global systems. A combination of several strategies that are suited concurrently to multi-physics, multi-scale and large-size system computation is therefore required. Based on empirical concepts, the heuristic models currently used in the framework of standard stability analysis suffer from a lack of predictive capabilities. On the other hand, numerical approaches based on fully-coupled fluid–solid dynamics system computation remain expensive due to the multi-physics patterns of physics and the large number of degrees of freedom involved. In this context, since experimentation cannot be achieved and numerical simulation is unavoidable but prohibitive, a hybrid strategy is proposed in order to take advantage of both numerical local solutions and empirical global solutions

  9. Assessment of pipeline stability in the Gulf of Mexico during hurricanes using dynamic analysis

    Directory of Open Access Journals (Sweden)

    Yinghui Tian

    2015-03-01

    Full Text Available Pipelines are the critical link between major offshore oil and gas developments and the mainland. Any inadequate on-bottom stability design could result in disruption and failure, having a devastating impact on the economy and environment. Predicting the stability behavior of offshore pipelines in hurricanes is therefore vital to the assessment of both new design and existing assets. The Gulf of Mexico has a very dense network of pipeline systems constructed on the seabed. During the last two decades, the Gulf of Mexico has experienced a series of strong hurricanes, which have destroyed, disrupted and destabilized many pipelines. This paper first reviews some of these engineering cases. Following that, three case studies are retrospectively simulated using an in-house developed program. The study utilizes the offshore pipeline and hurricane details to conduct a Dynamic Lateral Stability analysis, with the results providing evidence as to the accuracy of the modeling techniques developed.

  10. Dynamic Voltage Stability Studies using a Modified IEEE 30-Bus System

    Directory of Open Access Journals (Sweden)

    Oluwafemi Emmanuel Oni

    2016-09-01

    Full Text Available Power System stability is an essential study in the planning and operation of an efficient, economic, reliable and secure electric power system because it encompasses all the facet of power systems operations, from planning, to conceptual design stages of the project as well as during the systems operating life span. This paper presents different scenario of power system stability studies on a modified IEEE 30-bus system which is subjected to different faults conditions. A scenario whereby the longest high voltage alternating current (HVAC line is replaced with a high voltage direct current (HVDC line was implemented. The results obtained show that the HVDC line enhances system stability more compared to the contemporary HVAC line. Dynamic analysis using RMS simulation tool was used on DigSILENT PowerFactory.

  11. Dynamic stability and failure modes of slopes in discontinuous rock mass

    International Nuclear Information System (INIS)

    Shimizu, Yasuhiro; Aydan, O.; Ichikawa, Yasuaki; Kawamoto, Toshikazu.

    1988-01-01

    The stability of rock slopes during earthquakes are of great concern in rock engineering works such as highway, dam, and nuclear power station constructions. As rock mass in nature is usually discontinuous, the stability of rock slopes will be geverned by the spatial distribution of discontinuities in relation with the geometry of slope and their mechanical properties rather than the rock element. The authors have carried out some model tests on discontinuous rock slopes using three different model tests techniques in order to investigate the dynamic behaviour and failure modes of the slopes in discontinuous rock mass. This paper describes the findings and observations made on model rock slopes with various discontinuity patterns and slope geometry. In addition some stability criterions are developed and the calculated results are compared with those of experiments. (author)

  12. Dynamic stability of a vertically excited non-linear continuous system

    Czech Academy of Sciences Publication Activity Database

    Náprstek, Jiří; Fischer, Cyril

    2015-01-01

    Roč. 155, July (2015), s. 106-114 ISSN 0045-7949 R&D Projects: GA ČR(CZ) GA15-01035S Institutional support: RVO:68378297 Keywords : non-linear systems * auto-parametric systems * semi-trivial solution * dynamic stability * system recovery * post- critical response Subject RIV: JM - Building Engineering Impact factor: 2.425, year: 2015 http://www.sciencedirect.com/science/article/pii/S0045794915000024

  13. On the internal stability of non-linear dynamic inversion: application to flight control

    Czech Academy of Sciences Publication Activity Database

    Alam, M.; Čelikovský, Sergej

    2017-01-01

    Roč. 11, č. 12 (2017), s. 1849-1861 ISSN 1751-8644 R&D Projects: GA ČR(CZ) GA17-04682S Institutional support: RVO:67985556 Keywords : flight control * non-linear dynamic inversion * stability Subject RIV: BC - Control Systems Theory OBOR OECD: Automation and control systems Impact factor: 2.536, year: 2016 http://library.utia.cas.cz/separaty/2017/TR/celikovsky-0476150.pdf

  14. Stability and Dynamic of strain mediated Adatom Superlattices on Cu<111>

    OpenAIRE

    Kappus, Wolfgang

    2012-01-01

    Substrate strain mediated adatom density distributions have been calculated for Cu surfaces. Complemented by Monte Carlo calculations a hexagonal close packaged adatom superlattice in a coverage range up to 0.045 ML is derived. Conditions for the stability of the superlattice against nucleation and degradation are analyzed using simple neighborhood models. Such models are also used to investigate the dynamic of adatoms within their superlattice neighborhood. Collective modes of adatom diffusi...

  15. Local dynamic stability and variability of gait are associated with fall history in elderly subjects

    OpenAIRE

    Toebes, M.J.P.; Hoozemans, M.J.M.; Furrer, R.; Dekker, J.; van Dieen, J.H.

    2012-01-01

    Gait parameters that can be measured with simple instrumentation may hold promise for identifying individuals at risk of falling. Increased variability of gait is associated with increased risk of falling, but research on additional parameters indicates that local dynamic stability (LDS) of gait may also be a predictor of fall risk. The objective of the present study was to assess the association between gait variability, LDS of gait and fall history in a large sample of elderly subjects.Subj...

  16. Dynamical Stability of Imaged Planetary Systems in Formation: Application to HL Tau

    OpenAIRE

    Tamayo, Daniel; Triaud, Amaury H. M. J.; Menou, Kristen; Rein, Hanno

    2015-01-01

    A recent ALMA image revealed several concentric gaps in the protoplanetary disk surrounding the young star HL Tau. We consider the hypothesis that these gaps are carved by planets, and present a general framework for understanding the dynamical stability of such systems over typical disk lifetimes, providing estimates for the maximum planetary masses. We collect these easily evaluated constraints into a workflow that can help guide the design and interpretation of new observational campaigns ...

  17. Investigation of elastic stability of the lower part of drill pipe string (dynamic problems)

    Energy Technology Data Exchange (ETDEWEB)

    Griguletskii, V.G.

    1981-12-01

    Based on V.V. Bolotin's results, the problem of dynamic stability of the lower part of a string of drill pipes in a vertical well is formulated (and solved in the first approximation). An investigation of the phenomena during the interaction between lengthwise and transverse oscillations of the bottom part of the drill pipe string is carried out. Excitation conditions are determined and the mechanism of the onset of parametric oscillations is explained. 20 refs.

  18. Voltage regulator for on-board CMS ECAL powering : dynamic stability of the feedback loop

    CERN Document Server

    Wertelaers, P

    2010-01-01

    Traditionally, a capacitor is parallelled to the load of the regulator. Its main function is to steer (limit) the loop bandwidth. An ideal capacitor would provoke near-to-no dynamic stability. A typical remedy, not always elegant, is to select a device with appreciable parasitic series resistance. In this Note, and alternative method is proposed. The CMS ECAL regulator is of adjustable type, and adding a small capacitor at the divider there, brings about a "lead" type control action.

  19. Intense field stabilization in circular polarization: Three-dimensional time-dependent dynamics

    International Nuclear Information System (INIS)

    Choi, Dae-Il; Chism, Will

    2002-01-01

    We investigate the stabilization of hydrogen atoms in a circularly polarized laser field. We use a three-dimensional, time-dependent approach to study the quantum dynamics of hydrogen atoms subject to high-intensity, short-wavelength, laser pulses. We find an enhanced survival probability as the field is increased under fixed envelope conditions. We also confirm wave packet behaviors previously seen in two-dimensional time-dependent computations

  20. Comparison of dynamic postural stability scores between athletes with and without chronic ankle instability during lateral jump landing.

    Science.gov (United States)

    Shiravi, Zeinab; Shadmehr, Azadeh; Moghadam, Saeed Talebian; Moghadam, Behrouz Attarbashi

    2017-01-01

    Many ankle injuries occur while participating in sports that require jumping and landing such as basketball, volleyball and soccer. Most recent studies have investigated dynamic postural stability of patients with chronic ankle instability after landing from a forward jump. The present study aimed to investigate the dynamic postural stability of the athletes who suffer from chronic ankle sprain while landing from a lateral jump. Twelve athletes with self-reported unilateral chronic ankle instability (4 females and 8 males) and 12 matched controls (3 females and 9 males) voluntarily participated in the study. Dynamic postural stability index and its directional indices were measured while performing lateral jump landing test. No differences were found between athletes with and without chronic ankle instability during our landing protocol by means of the dynamic postural stability index and its directional indices. Findings showed that in each group, medial/lateral stability index is significantly higher than anterior/posterior and vertical stability indexes. Findings showed that dynamic postural stability was not significantly different between the two groups. Future studies should examine chronic ankle instability patients with more severe disabilities and expose them to more challenging dynamic balance conditions to further explore postural stability. IIIa.

  1. The stability analysis of the nutrition restricted dynamic model of the microalgae biomass growth

    Science.gov (United States)

    Ratianingsih, R.; Fitriani, Nacong, N.; Resnawati, Mardlijah, Widodo, B.

    2018-03-01

    The biomass production is very essential in microalgae farming such that its growth rate is very important to be determined. This paper proposes the dynamics model of it that restricted by its nutrition. The model is developed by considers some related processes that are photosynthesis, respiration, nutrition absorption, stabilization, lipid synthesis and CO2 mobilization. The stability of the dynamical system that represents the processes is analyzed using the Jacobian matrix of the linearized system in the neighborhood of its critical point. There is a lipid formation threshold needed to require its existence. In such case, the absorption rate of respiration process has to be inversely proportional to the absorption rate of CO2 due to photosynthesis process. The Pontryagin minimal principal also shows that there are some requirements needed to have a stable critical point, such as the rate of CO2 released rate, due to the stabilization process that is restricted by 50%, and the threshold of its shifted critical point. In case of the rate of CO2 released rate due to the photosynthesis process is restricted in such interval; the stability of the model at the critical point could not be satisfied anymore. The simulation shows that the external nutrition plays a role in glucose formation such that sufficient for the biomass growth and the lipid production.

  2. Dynamic stabilization of the imploding-shell Rayleigh-Taylor instability

    International Nuclear Information System (INIS)

    Boris, J.P.

    1977-01-01

    A method for dynamic stabilization of the Rayleigh-Taylor (R-T) instability on the surface of an imploding fusion pellet is discussed. The driving laser beams are modulated in intensity so the ablation layer is subject to a rapidly and strongly oscillating acceleration. A substantial band of the Rayleigh-Taylor instability spectrum can be stabilized by this oscillation even though the time average acceleration vector lies in the destabilizing direction. By adjusting the frequency, structure, and amplitude of the modulation, the band of dynamically stabilized modes can be made to include the most unstable and dangerous modes. Thus considerably higher aspect ratio shells (i.e., thinner shells) could implode successfully than had been previously considered stable enough. Both theory and numerical simulations support this conclusion for the case of laser-driven pellet implosions. Similar modulation via transverse beam oscillations or parallel bunching should also work to stabilize the most dangerous surface Rayleigh-Taylor modes in relativistic electron-, ion- and heavy ion-pellet fusion schemes. (U.K.)

  3. Path to Stochastic Stability: Comparative Analysis of Stochastic Learning Dynamics in Games

    KAUST Repository

    Jaleel, Hassan

    2018-04-08

    Stochastic stability is a popular solution concept for stochastic learning dynamics in games. However, a critical limitation of this solution concept is its inability to distinguish between different learning rules that lead to the same steady-state behavior. We address this limitation for the first time and develop a framework for the comparative analysis of stochastic learning dynamics with different update rules but same steady-state behavior. We present the framework in the context of two learning dynamics: Log-Linear Learning (LLL) and Metropolis Learning (ML). Although both of these dynamics have the same stochastically stable states, LLL and ML correspond to different behavioral models for decision making. Moreover, we demonstrate through an example setup of sensor coverage game that for each of these dynamics, the paths to stochastically stable states exhibit distinctive behaviors. Therefore, we propose multiple criteria to analyze and quantify the differences in the short and medium run behavior of stochastic learning dynamics. We derive and compare upper bounds on the expected hitting time to the set of Nash equilibria for both LLL and ML. For the medium to long-run behavior, we identify a set of tools from the theory of perturbed Markov chains that result in a hierarchical decomposition of the state space into collections of states called cycles. We compare LLL and ML based on the proposed criteria and develop invaluable insights into the comparative behavior of the two dynamics.

  4. Gaze stability, dynamic balance and participation deficits in people with multiple sclerosis at fall-risk.

    Science.gov (United States)

    Garg, Hina; Dibble, Leland E; Schubert, Michael C; Sibthorp, Jim; Foreman, K Bo; Gappmaier, Eduard

    2018-05-05

    Despite the common complaints of dizziness and demyelination of afferent or efferent pathways to and from the vestibular nuclei which may adversely affect the angular Vestibulo-Ocular Reflex (aVOR) and vestibulo-spinal function in persons with Multiple Sclerosis (PwMS), few studies have examined gaze and dynamic balance function in PwMS. 1) Determine the differences in gaze stability, dynamic balance and participation measures between PwMS and controls, 2) Examine the relationships between gaze stability, dynamic balance and participation. Nineteen ambulatory PwMS at fall-risk and 14 age-matched controls were recruited. Outcomes included (a) gaze stability [angular Vestibulo-Ocular Reflex (aVOR) gain (ratio of eye to head velocity); number of Compensatory Saccades (CS) per head rotation; CS latency; gaze position error; Coefficient of Variation (CV) of aVOR gain], (b) dynamic balance [Functional Gait Assessment, FGA; four square step test], and (c) participation [dizziness handicap inventory; activities-specific balance confidence scale]. Separate independent t-tests and Pearson's correlations were calculated. PwMS were age = 53 ± 11.7yrs and had 4.2 ± 3.3 falls/yr. PwMS demonstrated significant (pbalance and participation measures compared to controls. CV of aVOR gain and CS latency were significantly correlated with FGA. Deficits and correlations across a spectrum of disability measures highlight the relevance of gaze and dynamic balance assessment in PwMS. This article is protected by copyright. All rights reserved. © 2018 Wiley Periodicals, Inc.

  5. THE WAYS AND METHODS OF MAINTENANCE OF ECONOMIC STABILITY OF BUILDING ENTERPRISE BY CAUSE OF DYNAMIC MODEL

    Directory of Open Access Journals (Sweden)

    A.M. Platonov

    2008-12-01

    Full Text Available It is considered in work what exactly is main base for construction of dynamic model of stability of the building enterprise. There are submitted normative requirements which provide economic stability and also normative parities of dynamics of the parameters that correspond to these requirements. The technique of providing of economic stability is submitted on examples of two building enterprises of Ekaterinburg in view of results of their work in years of 2005-2006. There are determined the ways of providing of economic stability on the results of the carried out calculation. There are also revealed reserves of the enterprises for growth of efficiency of their activity.

  6. Calcium-dependent depletion zones in the cortical microtubule array coincide with sites of, but do not regulate, wall ingrowth papillae deposition in epidermal transfer cells

    Science.gov (United States)

    Zhang, Hui-ming; Talbot, Mark J.; McCurdy, David W.; Patrick, John W.; Offler, Christina E.

    2015-01-01

    Trans-differentiation to a transfer-cell morphology is characterized by the localized deposition of wall ingrowth papillae that protrude into the cytosol. Whether the cortical microtubule array directs wall ingrowth papillae formation was investigated using a Vicia faba cotyledon culture system in which their adaxial epidermal cells were spontaneously induced to trans-differentiate to transfer cells. During deposition of wall ingrowth papillae, the aligned cortical microtubule arrays in precursor epidermal cells were reorganized into a randomized array characterized by circular depletion zones. Concurrence of the temporal appearance, spatial pattern, and size of depletion zones and wall ingrowth papillae was consistent with each papilla occupying a depletion zone. Surprisingly, microtubules appeared not to regulate construction of wall ingrowth papillae, as neither depolymerization nor stabilization of cortical microtubules changed their deposition pattern or morphology. Moreover, the size and spatial pattern of depletion zones was unaltered when the formation of wall ingrowth papillae was blocked by inhibiting cellulose biosynthesis. In contrast, the depletion zones were absent when the cytosolic calcium plumes, responsible for directing wall ingrowth papillae formation, were blocked or dissipated. Thus, we conclude that the depletion zones within the cortical microtubule array result from localized depolymerization of microtubules initiated by elevated cytosolic Ca2+ levels at loci where wall ingrowth papillae are deposited. The physiological significance of the depletion zones as a mechanism to accommodate the construction of wall ingrowth papillae without compromising maintenance of the plasma membrane–microtubule inter-relationship is discussed. PMID:26136268

  7. Tuning of tool dynamics for increased stability of parallel (simultaneous) turning processes

    Science.gov (United States)

    Ozturk, E.; Comak, A.; Budak, E.

    2016-01-01

    Parallel (simultaneous) turning operations make use of more than one cutting tool acting on a common workpiece offering potential for higher productivity. However, dynamic interaction between the tools and workpiece and resulting chatter vibrations may create quality problems on machined surfaces. In order to determine chatter free cutting process parameters, stability models can be employed. In this paper, stability of parallel turning processes is formulated in frequency and time domain for two different parallel turning cases. Predictions of frequency and time domain methods demonstrated reasonable agreement with each other. In addition, the predicted stability limits are also verified experimentally. Simulation and experimental results show multi regional stability diagrams which can be used to select most favorable set of process parameters for higher stable material removal rates. In addition to parameter selection, developed models can be used to determine the best natural frequency ratio of tools resulting in the highest stable depth of cuts. It is concluded that the most stable operations are obtained when natural frequency of the tools are slightly off each other and worst stability occurs when the natural frequency of the tools are exactly the same.

  8. Dinitroaniline herbicide resistance and the microtubule cytoskeleton.

    Science.gov (United States)

    Anthony; Hussey

    1999-03-01

    Dinitroaniline herbicides have been used for pre-emergence weed control for the past 25 years in cotton, soybean, wheat and oilseed crops. Considering their long persistence and extensive use, resistance to dinitroanilines is fairly rare. However, the most widespread dinitroaniline-resistant weeds, the highly resistant (R) and the intermediate (I) biotypes of the invasive goosegrass Eleusine indica, are now infesting more than 1000 cotton fields in the southern states of the USA. The molecular basis of this resistance has been identified, and found to be a point mutation in a major microtubule cytoskeletal protein, alpha-tubulin. These studies have served both to explain the establishment of resistance and to reveal fundamental properties of tubulin gene expression and microtubule structure.

  9. Dynamics and regulation at the tip : a high resolution view on microtubele assembly

    NARCIS (Netherlands)

    Munteanu, Laura

    2008-01-01

    Microtubules are highly dynamic protein polymers that and are essential for intracellular organization and fundamental processes like transport and cell division. In cells, a wide family of microtubule-associated proteins (MAPs) tightly regulates microtubule dynamics. The work presented in this

  10. Learning Probabilistic Models of Hydrogen Bond Stability from Molecular Dynamics Simulation Trajectories

    KAUST Repository

    Chikalov, Igor

    2011-04-02

    Hydrogen bonds (H-bonds) play a key role in both the formation and stabilization of protein structures. H-bonds involving atoms from residues that are close to each other in the main-chain sequence stabilize secondary structure elements. H-bonds between atoms from distant residues stabilize a protein’s tertiary structure. However, H-bonds greatly vary in stability. They form and break while a protein deforms. For instance, the transition of a protein from a nonfunctional to a functional state may require some H-bonds to break and others to form. The intrinsic strength of an individual H-bond has been studied from an energetic viewpoint, but energy alone may not be a very good predictor. Other local interactions may reinforce (or weaken) an H-bond. This paper describes inductive learning methods to train a protein-independent probabilistic model of H-bond stability from molecular dynamics (MD) simulation trajectories. The training data describes H-bond occurrences at successive times along these trajectories by the values of attributes called predictors. A trained model is constructed in the form of a regression tree in which each non-leaf node is a Boolean test (split) on a predictor. Each occurrence of an H-bond maps to a path in this tree from the root to a leaf node. Its predicted stability is associated with the leaf node. Experimental results demonstrate that such models can predict H-bond stability quite well. In particular, their performance is roughly 20% better than that of models based on H-bond energy alone. In addition, they can accurately identify a large fraction of the least stable H-bonds in a given conformation. The paper discusses several extensions that may yield further improvements.

  11. Floquet stability analysis of the longitudinal dynamics of two hovering model insects

    Science.gov (United States)

    Wu, Jiang Hao; Sun, Mao

    2012-01-01

    Because of the periodically varying aerodynamic and inertial forces of the flapping wings, a hovering or constant-speed flying insect is a cyclically forcing system, and, generally, the flight is not in a fixed-point equilibrium, but in a cyclic-motion equilibrium. Current stability theory of insect flight is based on the averaged model and treats the flight as a fixed-point equilibrium. In the present study, we treated the flight as a cyclic-motion equilibrium and used the Floquet theory to analyse the longitudinal stability of insect flight. Two hovering model insects were considered—a dronefly and a hawkmoth. The former had relatively high wingbeat frequency and small wing-mass to body-mass ratio, and hence very small amplitude of body oscillation; while the latter had relatively low wingbeat frequency and large wing-mass to body-mass ratio, and hence relatively large amplitude of body oscillation. For comparison, analysis using the averaged-model theory (fixed-point stability analysis) was also made. Results of both the cyclic-motion stability analysis and the fixed-point stability analysis were tested by numerical simulation using complete equations of motion coupled with the Navier–Stokes equations. The Floquet theory (cyclic-motion stability analysis) agreed well with the simulation for both the model dronefly and the model hawkmoth; but the averaged-model theory gave good results only for the dronefly. Thus, for an insect with relatively large body oscillation at wingbeat frequency, cyclic-motion stability analysis is required, and for their control analysis, the existing well-developed control theories for systems of fixed-point equilibrium are no longer applicable and new methods that take the cyclic variation of the flight dynamics into account are needed. PMID:22491980

  12. Effects of an attention demanding task on dynamic stability during treadmill walking

    Directory of Open Access Journals (Sweden)

    Troy Karen L

    2008-04-01

    Full Text Available Abstract Background People exhibit increased difficulty balancing when they perform secondary attention-distracting tasks while walking. However, a previous study by Grabiner and Troy (J. Neuroengineering Rehabil., 2005 found that young healthy subjects performing a concurrent Stroop task while walking on a motorized treadmill exhibited decreased step width variability. However, measures of variability do not directly quantify how a system responds to perturbations. This study re-analyzed data from Grabiner and Troy 2005 to determine if performing the concurrent Stroop task directly affected the dynamic stability of walking in these same subjects. Methods Thirteen healthy volunteers walked on a motorized treadmill at their self-selected constant speed for 10 minutes both while performing the Stroop test and during undisturbed walking. This Stroop test consisted of projecting images of the name of one color, printed in text of a different color, onto a wall and asking subjects to verbally identify the color of the text. Three-dimensional motions of a marker attached to the base of the neck (C5/T1 were recorded. Marker velocities were calculated over 3 equal intervals of 200 sec each in each direction. Mean variability was calculated for each time series as the average standard deviation across all strides. Both "local" and "orbital" dynamic stability were quantified for each time series using previously established methods. These measures directly quantify how quickly small perturbations grow or decay, either continuously in real time (local or discretely from one cycle to the next (orbital. Differences between Stroop and Control trials were evaluated using a 2-factor repeated measures ANOVA. Results Mean variability of trunk movements was significantly reduced during the Stroop tests compared to normal walking. Conversely, local and orbital stability results were mixed: some measures showed slight increases, while others showed slight decreases

  13. Novel mitochondrial extensions provide evidence for a link between microtubule-directed movement and mitochondrial fission

    International Nuclear Information System (INIS)

    Bowes, Timothy; Gupta, Radhey S.

    2008-01-01

    Mitochondrial dynamics play an important role in a large number of cellular processes. Previously, we reported that treatment of mammalian cells with the cysteine-alkylators, N-ethylmaleimide and ethacrynic acid, induced rapid mitochondrial fusion forming a large reticulum approximately 30 min after treatment. Here, we further investigated this phenomenon using a number of techniques including live-cell confocal microscopy. In live cells, drug-induced fusion coincided with a cessation of fast mitochondrial movement which was dependent on microtubules. During this loss of movement, thin mitochondrial tubules extending from mitochondria were also observed, which we refer to as 'mitochondrial extensions'. The formation of these mitochondrial extensions, which were not observed in untreated cells, depended on microtubules and was abolished by pretreatment with nocodazole. In this study, we provide evidence that these extensions result from of a block in mitochondrial fission combined with continued application of motile force by microtubule-dependent motor complexes. Our observations strongly suggest the existence of a link between microtubule-based mitochondrial trafficking and mitochondrial fission

  14. Vault mobility depends in part on microtubules and vaults can be recruited to the nuclear envelope

    International Nuclear Information System (INIS)

    Zon, Arend van; Mossink, Marieke H.; Houtsmuller, Adriaan B.; Schoester, Martijn; Scheffer, George L.; Scheper, Rik J.; Sonneveld, Pieter; Wiemer, Erik A.C.

    2006-01-01

    Vaults are ribonucleoproteins that may function in intracellular transport processes. We investigated the intracellular distribution and dynamics of vaults in non-small cell lung cancer cells in which vaults are labeled with the green fluorescent protein. Immunofluorescence experiments showed that vaults are dispersed throughout the cytoplasm; a small fraction is found in close proximity to microtubules. Immunoprecipitation experiments corroborated these results showing co-precipitation of MVP and β-tubulin. Using quantitative fluorescence-recovery after photobleaching (FRAP), we demonstrated that vault mobility over longer distances in part depends on intact microtubules; vaults moving slower when microtubules are depolymerized by nocodazole. Biochemical fractionation indicated a small fraction of MVP associated with the nucleus, however, no GFP-tagged vaults could be observed inside the nucleus. We observed an accumulation of vaults at the nuclear envelope upon treatment of cells with the protein synthesis inhibitor cycloheximide. Analysis of nucleo-cytoplasmic transport using a fluorescent substrate containing a classical NLS and NES expressed in MVP +/+ and MVP -/- mouse embryonic fibroblasts indicated no differences in nuclear import/export kinetics, suggesting no role for vaults in these processes. We hypothesize that a subset of vaults moves directionally via microtubules, possibly towards the nucleus

  15. Stability Result For Dynamic Inversion Devised to Control Large Flexible Aircraft

    Science.gov (United States)

    Gregory, Irene M.

    2001-01-01

    High performance aircraft of the future will be designed lighter, more maneuverable, and operate over an ever expanding flight envelope. One of the largest differences from the flight control perspective between current and future advanced aircraft is elasticity. Over the last decade, dynamic inversion methodology has gained considerable popularity in application to highly maneuverable fighter aircraft, which were treated as rigid vehicles. This paper is an initial attempt to establish global stability results for dynamic inversion methodology as applied to a large, flexible aircraft. This work builds on a previous result for rigid fighter aircraft and adds a new level of complexity that is the flexible aircraft dynamics, which cannot be ignored even in the most basic flight control. The results arise from observations of the control laws designed for a new generation of the High-Speed Civil Transport aircraft.

  16. Stability of a general delayed virus dynamics model with humoral immunity and cellular infection

    Science.gov (United States)

    Elaiw, A. M.; Raezah, A. A.; Alofi, A. S.

    2017-06-01

    In this paper, we investigate the dynamical behavior of a general nonlinear model for virus dynamics with virus-target and infected-target incidences. The model incorporates humoral immune response and distributed time delays. The model is a four dimensional system of delay differential equations where the production and removal rates of the virus and cells are given by general nonlinear functions. We derive the basic reproduction parameter R˜0 G and the humoral immune response activation number R˜1 G and establish a set of conditions on the general functions which are sufficient to determine the global dynamics of the models. We use suitable Lyapunov functionals and apply LaSalle's invariance principle to prove the global asymptotic stability of the all equilibria of the model. We confirm the theoretical results by numerical simulations.

  17. Dynamics and stability of radiation-driven double ablation front structures

    International Nuclear Information System (INIS)

    Drean, V.; Olazabal-Loume, M.; Tikhonchuk, V. T.; Sanz, J.

    2010-01-01

    The dynamics of double ablation front (DAF) structures is studied for planar targets with moderate atomic number ablators. These structures are obtained in hydrodynamic simulations for various materials and laser intensities and are qualitatively characterized during the acceleration stage of the target. The importance of the radiative transport for the DAF dynamics is then demonstrated. Simulated hydrodynamic profiles are compared with a theoretical model, showing the consistency of the model and the relevant parameters for the dynamics description. The stability of DAF structures with respect to two-dimensional perturbations is studied using two different approaches: one considers the assumptions of the theoretical model and the other one a more complete physics. The numerical simulations performed with both approaches demonstrate good agreement of dispersion curves.

  18. New Systematic CFD Methods to Calculate Static and Single Dynamic Stability Derivatives of Aircraft

    Directory of Open Access Journals (Sweden)

    Bai-gang Mi

    2017-01-01

    Full Text Available Several new systematic methods for high fidelity and reliability calculation of static and single dynamic derivatives are proposed in this paper. Angle of attack step response is used to obtain static derivative directly; then translation acceleration dynamic derivative and rotary dynamic derivative can be calculated by employing the step response motion of rate of the angle of attack and unsteady motion of pitching angular velocity step response, respectively. Longitudinal stability derivative calculations of SACCON UCAV are taken as test cases for validation. Numerical results of all cases achieve good agreement with reference values or experiments data from wind tunnel, which indicate that the proposed methods can be considered as new tools in the process of design and production of advanced aircrafts for their high efficiency and precision.

  19. Hybrid dynamic stabilization: a biomechanical assessment of adjacent and supraadjacent levels of the lumbar spine.

    Science.gov (United States)

    Mageswaran, Prasath; Techy, Fernando; Colbrunn, Robb W; Bonner, Tara F; McLain, Robert F

    2012-09-01

    The object of this study was to evaluate the effect of hybrid dynamic stabilization on adjacent levels of the lumbar spine. Seven human spine specimens from T-12 to the sacrum were used. The following conditions were implemented: 1) intact spine; 2) fusion of L4-5 with bilateral pedicle screws and titanium rods; and 3) supplementation of the L4-5 fusion with pedicle screw dynamic stabilization constructs at L3-4, with the purpose of protecting the L3-4 level from excessive range of motion (ROM) and to create a smoother motion transition to the rest of the lumbar spine. An industrial robot was used to apply continuous pure moment (± 2 Nm) in flexion-extension with and without a follower load, lateral bending, and axial rotation. Intersegmental rotations of the fused, dynamically stabilized, and adjacent levels were measured and compared. In flexion-extension only, the rigid instrumentation at L4-5 caused a 78% decrease in the segment's ROM when compared with the intact specimen. To compensate, it caused an increase in motion at adjacent levels L1-2 (45.6%) and L2-3 (23.2%) only. The placement of the dynamic construct at L3-4 decreased the operated level's ROM by 80.4% (similar stability as the fusion at L4-5), when compared with the intact specimen, and caused a significant increase in motion at all tested adjacent levels. In flexion-extension with a follower load, instrumentation at L4-5 affected only a subadjacent level, L5-sacrum (52.0%), while causing a reduction in motion at the operated level (L4-5, -76.4%). The dynamic construct caused a significant increase in motion at the adjacent levels T12-L1 (44.9%), L1-2 (57.3%), and L5-sacrum (83.9%), while motion at the operated level (L3-4) was reduced by 76.7%. In lateral bending, instrumentation at L4-5 increased motion at only T12-L1 (22.8%). The dynamic construct at L3-4 caused an increase in motion at T12-L1 (69.9%), L1-2 (59.4%), L2-3 (44.7%), and L5-sacrum (43.7%). In axial rotation, only the placement of

  20. Stabilization

    Directory of Open Access Journals (Sweden)

    Muhammad H. Al-Malack

    2016-07-01

    Full Text Available Fuel oil flyash (FFA produced in power and water desalination plants firing crude oils in the Kingdom of Saudi Arabia is being disposed in landfills, which increases the burden on the environment, therefore, FFA utilization must be encouraged. In the current research, the effect of adding FFA on the engineering properties of two indigenous soils, namely sand and marl, was investigated. FFA was added at concentrations of 5%, 10% and 15% to both soils with and without the addition of Portland cement. Mixtures of the stabilized soils were thoroughly evaluated using compaction, California Bearing Ratio (CBR, unconfined compressive strength (USC and durability tests. Results of these tests indicated that stabilized sand mixtures could not attain the ACI strength requirements. However, marl was found to satisfy the ACI strength requirement when only 5% of FFA was added together with 5% of cement. When the FFA was increased to 10% and 15%, the mixture’s strength was found to decrease to values below the ACI requirements. Results of the Toxicity Characteristics Leaching Procedure (TCLP, which was performed on samples that passed the ACI requirements, indicated that FFA must be cautiously used in soil stabilization.

  1. Conceptual Design Optimization of an Augmented Stability Aircraft Incorporating Dynamic Response Performance Constraints

    Science.gov (United States)

    Welstead, Jason

    2014-01-01

    This research focused on incorporating stability and control into a multidisciplinary de- sign optimization on a Boeing 737-class advanced concept called the D8.2b. A new method of evaluating the aircraft handling performance using quantitative evaluation of the sys- tem to disturbances, including perturbations, continuous turbulence, and discrete gusts, is presented. A multidisciplinary design optimization was performed using the D8.2b transport air- craft concept. The con guration was optimized for minimum fuel burn using a design range of 3,000 nautical miles. Optimization cases were run using xed tail volume coecients, static trim constraints, and static trim and dynamic response constraints. A Cessna 182T model was used to test the various dynamic analysis components, ensuring the analysis was behaving as expected. Results of the optimizations show that including stability and con- trol in the design process drastically alters the optimal design, indicating that stability and control should be included in conceptual design to avoid system level penalties later in the design process.

  2. Glucose regulated proteins 78 and 75 bind to the receptor for hyaluronan mediated motility in interphase microtubules

    International Nuclear Information System (INIS)

    Kuwabara, Hiroko; Yoneda, Masahiko; Hayasaki, Hana; Nakamura, Toshiya; Mori, Hiroshi

    2006-01-01

    The receptor for hyaluronan mediated motility (RHAMM), which is a hyaluronan-binding protein, is a centrosomal and microtubal protein. Here, we have identified two RHAMM-binding proteins, glucose regulated protein (GRP) 78 and GRP75, using co-immunoprecipitation analysis. These two proteins directly bound to glutathione-S-transferase-RHAMM fusion proteins. By double immunostaining, GRP78 and GRP75 colocalized with RHAMM in interphase microtubules, but were separated in mitotic spindles. Prevention of microtubule polymerization by TN-16 and vincristine sulfate induced RHAMM overexpression without a significant change in GRP78/75. Taken together, GRP78/75 and RHAMM complexes may stabilize microtubules in the interphase, associated with a downregulation of RHAMM. These results reveal a new biochemical activity of RHAMM

  3. Algorithm of dynamic stabilization system for a car 4x4 with a link rear axle

    Directory of Open Access Journals (Sweden)

    M. M. Jileikin

    2014-01-01

    Full Text Available The slow development of active safety systems of the automobile all-wheel drive vehicles is the cause of lack of researches in the field of power distribution under the specific conditions of movement. The purpose of work is to develop methods to control a curvilinear motion of 4x4 cars with a link to the rear axle that provides the increase in directional and trajectory stability of the car. The paper analyses the known methods to increase wheeled vehicles movement stability. It also offers a method for power flow redistribution in the transmission of the car 4x4 with a link to the rear axle, providing the increase in directional and trajectory stability of the car.To study the performance and effectiveness of the proposed method a mathematical model of the moving car 4x4 with a link to the rear axle is developed. Simulation methods allowed us to establish the following:1. for car 4x4 with redistribution of torque between the driving axles in the range of 100:0 - 50:50 and with redistribution of torque between the wheels of the rear axle in the range of 0:100 the most effective are the stabilization algorithms used in combination “Lowing power consumption of the engine +Creation of stabilizing the moment due to the redistribution of torque on different wheels", providing the increase in directional and trajectory stability by 12...93%;2. for car 4x4 with redistribution of torque between the driving axles in the range 100:0 - 0:100 and with redistribution of torque between the wheels of the rear axle in the range of 0:100 the best option is a combination of algorithms "Lowing power consumption of the engine + Creation of stabilizing moment due to redistribution of torques on different wheels", providing the increase in directional and trajectory stability by 27...93%.A comparative analysis of algorithms efficiency of dynamic stabilization system operation for two-axle wheeled vehicles depending on the torque redistribution between the driving

  4. Microtubules are organized independently of the centrosome in Drosophila neurons

    Directory of Open Access Journals (Sweden)

    Nguyen Michelle M

    2011-12-01

    Full Text Available Abstract Background The best-studied arrangement of microtubules is that organized by the centrosome, a cloud of microtubule nucleating and anchoring proteins is clustered around centrioles. However, noncentrosomal microtubule arrays are common in many differentiated cells, including neurons. Although microtubules are not anchored at neuronal centrosomes, it remains unclear whether the centrosome plays a role in organizing neuronal microtubules. We use Drosophila as a model system to determine whether centrosomal microtubule nucleation is important in mature neurons. Results In developing and mature neurons, centrioles were not surrounded by the core nucleation protein γ-tubulin. This suggests that the centrioles do not organize functional centrosomes in Drosophila neurons in vivo. Consistent with this idea, centriole position was not correlated with a specific region of the cell body in neurons, and growing microtubules did not cluster around the centriole, even after axon severing when the number of growing plus ends is dramatically increased. To determine whether the centrosome was required for microtubule organization in mature neurons, we used two approaches. First, we used DSas-4 centriole duplication mutants. In these mutants, centrioles were present in many larval sensory neurons, but they were not fully functional. Despite reduced centriole function, microtubule orientation was normal in axons and dendrites. Second, we used laser ablation to eliminate the centriole, and again found that microtubule polarity in axons and dendrites was normal, even 3 days after treatment. Conclusion We conclude that the centrosome is not a major site of microtubule nucleation in Drosophila neurons, and is not required for maintenance of neuronal microtubule organization in these cells.

  5. Network stability is a balancing act of personality, power, and conflict dynamics in rhesus macaque societies.

    Science.gov (United States)

    McCowan, Brenda; Beisner, Brianne A; Capitanio, John P; Jackson, Megan E; Cameron, Ashley N; Seil, Shannon; Atwill, Edward R; Fushing, Hsieh

    2011-01-01

    Stability in biological systems requires evolved mechanisms that promote robustness. Cohesive primate social groups represent one example of a stable biological system, which persist in spite of frequent conflict. Multiple sources of stability likely exist for any biological system and such robustness, or lack thereof, should be reflected and thus detectable in the group's network structure, and likely at multiple levels. Here we show how network structure and group stability are linked to the fundamental characteristics of the individual agents in groups and to the environmental and social contexts in which these individuals interact. Both internal factors (e.g., personality, sex) and external factors (e.g., rank dynamics, sex ratio) were considered from the level of the individual to that of the group to examine the effects of network structure on group stability in a nonhuman primate species. The results yielded three main findings. First, successful third-party intervention behavior is a mechanism of group stability in rhesus macaques in that successful interventions resulted in less wounding in social groups. Second, personality is the primary factor that determines which individuals perform the role of key intervener, via its effect on social power and dominance discrepancy. Finally, individuals with high social power are not only key interveners but also key players in grooming networks and receive reconciliations from a higher diversity of individuals. The results from this study provide sound evidence that individual and group characteristics such as personality and sex ratio influence network structures such as patterns of reconciliation, grooming and conflict intervention that are indicators of network robustness and consequent health and well-being in rhesus macaque societies. Utilizing this network approach has provided greater insight into how behavioral and social processes influence social stability in nonhuman primate groups.

  6. Network stability is a balancing act of personality, power, and conflict dynamics in rhesus macaque societies.

    Directory of Open Access Journals (Sweden)

    Brenda McCowan

    Full Text Available Stability in biological systems requires evolved mechanisms that promote robustness. Cohesive primate social groups represent one example of a stable biological system, which persist in spite of frequent conflict. Multiple sources of stability likely exist for any biological system and such robustness, or lack thereof, should be reflected and thus detectable in the group's network structure, and likely at multiple levels. Here we show how network structure and group stability are linked to the fundamental characteristics of the individual agents in groups and to the environmental and social contexts in which these individuals interact. Both internal factors (e.g., personality, sex and external factors (e.g., rank dynamics, sex ratio were considered from the level of the individual to that of the group to examine the effects of network structure on group stability in a nonhuman primate species. The results yielded three main findings. First, successful third-party intervention behavior is a mechanism of group stability in rhesus macaques in that successful interventions resulted in less wounding in social groups. Second, personality is the primary factor that determines which individuals perform the role of key intervener, via its effect on social power and dominance discrepancy. Finally, individuals with high social power are not only key interveners but also key players in grooming networks and receive reconciliations from a higher diversity of individuals. The results from this study provide sound evidence that individual and group characteristics such as personality and sex ratio influence network structures such as patterns of reconciliation, grooming and conflict intervention that are indicators of network robustness and consequent health and well-being in rhesus macaque societies. Utilizing this network approach has provided greater insight into how behavioral and social processes influence social stability in nonhuman primate groups.

  7. Auxin-dependent microtubule responses and seedling development are affected in a rice mutant resistant to EPC

    International Nuclear Information System (INIS)

    Nick, P.; Yatou, O.; Furuya, M.; Lambert, A.M.

    1994-01-01

    Mutants in rice (Oryza sativa L. cv. japonica) were used to study the role of the cytoskeleton in signal-dependent morphogenesis. Mutants obtained by gamma ray irradiation were selected that failed to show inhibition of coleoptile elongation by the anti microtubular drug ethyl-N-phenylcarbamate (EPC). The mutation EPC-Resistant 31 (ER31), isolated from such a screen, caused lethality in putatively homozygous embryos. Heterozygotes exhibited drug resistance, impaired development of crown roots, and characteristic changes in the pattern of cell elongation: cell elongation was enhanced in mesocotyls and leaf sheaths, but inhibited in coleoptiles. The orientation of cortical microtubules changed correspondingly: for etiolated seedlings, compared with the wild-type, they were more transverse with respect to the long cell axis in mesocotyls and leaf sheaths, but more longitudinal in coleoptiles. In mutant coleoptiles, in contrast to wild-type, microtubules did not reorient in response to auxin, and their response to microtubule-eliminating and microtubule-stabilizing drugs was conspicuously reduced. In contrast, they responded normally to other stimuli such as gibberellins or red light. Auxin sensitivity as assayed by the dose-response for callus induction did not show any significant differences between wild-type and mutant. The mutant phenotype is interpreted in terms of an interrupted link between auxin-triggered signal transduction and microtubule reorientation. (author)

  8. Influence of neuromuscular noise and walking speed on fall risk and dynamic stability in a 3D dynamic walking model.

    Science.gov (United States)

    Roos, Paulien E; Dingwell, Jonathan B

    2013-06-21

    Older adults and those with increased fall risk tend to walk slower. They may do this voluntarily to reduce their fall risk. However, both slower and faster walking speeds can predict increased risk of different types of falls. The mechanisms that contribute to fall risk across speeds are not well known. Faster walking requires greater forward propulsion, generated by larger muscle forces. However, greater muscle activation induces increased signal-dependent neuromuscular noise. These speed-related increases in neuromuscular noise may contribute to the increased fall risk observed at faster walking speeds. Using a 3D dynamic walking model, we systematically varied walking speed without and with physiologically-appropriate neuromuscular noise. We quantified how actual fall risk changed with gait speed, how neuromuscular noise affected speed-related changes in fall risk, and how well orbital and local dynamic stability measures predicted changes in fall risk across speeds. When we included physiologically-appropriate noise to the 'push-off' force in our model, fall risk increased with increasing walking speed. Changes in kinematic variability, orbital, and local dynamic stability did not predict these speed-related changes in fall risk. Thus, the increased neuromuscular variability that results from increased signal-dependent noise that is necessitated by the greater muscular force requirements of faster walking may contribute to the increased fall risk observed at faster walking speeds. The lower fall risk observed at slower speeds supports experimental evidence that slowing down can be an effective strategy to reduce fall risk. This may help explain the slower walking speeds observed in older adults and others. Copyright © 2013 Elsevier Ltd. All rights reserved.

  9. Molecular Dynamics Driven Design of pH-Stabilized Mutants of MNEI, a Sweet Protein.

    Directory of Open Access Journals (Sweden)

    Serena Leone

    Full Text Available MNEI is a single chain derivative of monellin, a plant protein that can interact with the human sweet taste receptor, being therefore perceived as sweet. This unusual physiological activity makes MNEI a potential template for the design of new sugar replacers for the food and beverage industry. Unfortunately, applications of MNEI have been so far limited by its intrinsic sensitivity to some pH and temperature conditions, which could occur in industrial processes. Changes in physical parameters can, in fact, lead to irreversible protein denaturation, as well as aggregation and precipitation. It has been previously shown that the correlation between pH and stability in MNEI derives from the presence of a single glutamic residue in a hydrophobic pocket of the protein. We have used molecular dynamics to study the consequences, at the atomic level, of the protonation state of such residue and have identified the network of intramolecular interactions responsible for MNEI stability at acidic pH. Based on this information, we have designed a pH-independent, stabilized mutant of MNEI and confirmed its increased stability by both molecular modeling and experimental techniques.

  10. Molecular Dynamics Driven Design of pH-Stabilized Mutants of MNEI, a Sweet Protein.

    Science.gov (United States)

    Leone, Serena; Picone, Delia

    2016-01-01

    MNEI is a single chain derivative of monellin, a plant protein that can interact with the human sweet taste receptor, being therefore perceived as sweet. This unusual physiological activity makes MNEI a potential template for the design of new sugar replacers for the food and beverage industry. Unfortunately, applications of MNEI have been so far limited by its intrinsic sensitivity to some pH and temperature conditions, which could occur in industrial processes. Changes in physical parameters can, in fact, lead to irreversible protein denaturation, as well as aggregation and precipitation. It has been previously shown that the correlation between pH and stability in MNEI derives from the presence of a single glutamic residue in a hydrophobic pocket of the protein. We have used molecular dynamics to study the consequences, at the atomic level, of the protonation state of such residue and have identified the network of intramolecular interactions responsible for MNEI stability at acidic pH. Based on this information, we have designed a pH-independent, stabilized mutant of MNEI and confirmed its increased stability by both molecular modeling and experimental techniques.

  11. Solutions Stability of Initial Boundary Problem, Modeling of Dynamics of Some Discrete Continuum Mechanical System

    Directory of Open Access Journals (Sweden)

    D. A. Eliseev

    2015-01-01

    Full Text Available The solution stability of an initial boundary problem for a linear hybrid system of differential equations, which models the rotation of a rigid body with two elastic rods located in the same plane is studied in the paper. To an axis passing through the mass center of the rigid body perpendicularly to the rods location plane is applied the stabilizing moment proportional to the angle of the system rotation, derivative of the angle, integral of the angle. The external moment provides a feedback. A method of studying the behavior of solutions of the initial boundary problem is proposed. This method allows to exclude from the hybrid system of differential equations partial differential equations, which describe the dynamics of distributed elements of a mechanical system. It allows us to build one equation for an angle of the system rotation. Its characteristic equation defines the stability of solutions of all the system. In the space of feedback-coefficients the areas that provide the asymptotic stability of solutions of the initial boundary problem are built up.

  12. Producing Conditional Mutants for Studying Plant Microtubule Function

    Energy Technology Data Exchange (ETDEWEB)

    Richard Cyr

    2009-09-29

    The cytoskeleton, and in particular its microtubule component, participates in several processes that directly affect growth and development in higher plants. Normal cytoskeletal function requires the precise and orderly arrangement of microtubules into several cell cycle and developmentally specific arrays. One of these, the cortical array, is notable for its role in directing the deposition of cellulose (the most prominent polymer in the biosphere). An understanding of how these arrays form, and the molecular interactions that contribute to their function, is incomplete. To gain a better understanding of how microtubules work, we have been working to characterize mutants in critical cytoskeletal genes. This characterization is being carried out at the subcellular level using vital microtubule gene constructs. In the last year of funding colleagues have discovered that gamma-tubulin complexes form along the lengths of cortical microtubules where they act to spawn new microtubules at a characteristic 40 deg angle. This finding complements nicely the finding from our lab (which was funded by the DOE) showing that microtubule encounters are angle dependent; high angles encounters results in catastrophic collisions while low angle encounters result in favorable zippering. The finding of a 40 deg spawn of new microtubules from extant microtubule, together with aforementioned rules of encounters, insures favorable co-alignment in the array. I was invited to write a New and Views essay on this topic and a PDF is attached (News and Views policy does not permit funding acknowledgments and so I was not allowed to acknowledge support from the DOE).

  13. Microjet Injection Strategies for Mitigating Dynamics in a Lean Premixed Swirl-Stabilized Combustor

    KAUST Repository

    LaBry, Zachary

    2011-01-04

    Combustion dynamics remain a challenge in the development of low-emission, air-breathing combustors for power generation and aircraft propulsion. In this paper, we presenta parametric study on the use of microjet injectors for suppressing or mitigating the combustion dynamics that energize the thermoacoustic instability in a swirl-stabilized, premixed combustor. Microjet injectors consist of small inlet ports intended to inject flow with high momentum at relatively low mass flow rates into the flame-anchoring region. The microjets were configured to inject flow either axially, into the outer recirculation zone, or radially into the inner recirculation zone. Additionally, different injectors were tested with different relative senses of swirl (signs of angular momentum)with respect to the main flow: co-swirling, not swirling, or counter-swirling. We observed that injecting air or premixed fuel/air into the inner recirculation zone via counter-swirling radial microjets, we were able to reduce the overall sound pressure level in the combustor by over 20 dB in the lean end of the operating range. Other injector configurations were not observed to positively influence the combust or stability. Detailed PIV measurements are used to examine possible mechanisms of how the microjets impact the combustion dynamics, and the technology implications of our experiments are discussed.

  14. Mathematical modeling of the dynamic stability of fluid conveying pipe based on integral equation formulations

    International Nuclear Information System (INIS)

    Elfelsoufi, Z.; Azrar, L.

    2016-01-01

    In this paper, a mathematical modeling of flutter and divergence analyses of fluid conveying pipes based on integral equation formulations is presented. Dynamic stability problems related to fluid pressure, velocity, tension, topography slope and viscoelastic supports and foundations are formulated. A methodological approach is presented and the required matrices, associated to the influencing fluid and pipe parameters, are explicitly given. Internal discretizations are used allowing to investigate the deformation, the bending moment, slope and shear force at internal points. Velocity–frequency, pressure-frequency and tension-frequency curves are analyzed for various fluid parameters and internal elastic supports. Critical values of divergence and flutter behaviors with respect to various fluid parameters are investigated. This model is general and allows the study of dynamic stability of tubes crossed by stationary and instationary fluid on various types of supports. Accurate predictions can be obtained and are of particular interest for a better performance and for an optimal safety of piping system installations. - Highlights: • Modeling the flutter and divergence of fluid conveying pipes based on RBF. • Dynamic analysis of a fluid conveying pipe with generalized boundary conditions. • Considered parameters fluid are the pressure, tension, slopes topography, velocity. • Internal support increase the critical velocity value. • This methodologies determine the fluid parameters effects.

  15. Microjet Injection Strategies for Mitigating Dynamics in a Lean Premixed Swirl-Stabilized Combustor

    KAUST Repository

    LaBry, Zachary; Shanbhogue, Santosh; Ghoniem, Ahmed

    2011-01-01

    Combustion dynamics remain a challenge in the development of low-emission, air-breathing combustors for power generation and aircraft propulsion. In this paper, we presenta parametric study on the use of microjet injectors for suppressing or mitigating the combustion dynamics that energize the thermoacoustic instability in a swirl-stabilized, premixed combustor. Microjet injectors consist of small inlet ports intended to inject flow with high momentum at relatively low mass flow rates into the flame-anchoring region. The microjets were configured to inject flow either axially, into the outer recirculation zone, or radially into the inner recirculation zone. Additionally, different injectors were tested with different relative senses of swirl (signs of angular momentum)with respect to the main flow: co-swirling, not swirling, or counter-swirling. We observed that injecting air or premixed fuel/air into the inner recirculation zone via counter-swirling radial microjets, we were able to reduce the overall sound pressure level in the combustor by over 20 dB in the lean end of the operating range. Other injector configurations were not observed to positively influence the combust or stability. Detailed PIV measurements are used to examine possible mechanisms of how the microjets impact the combustion dynamics, and the technology implications of our experiments are discussed.

  16. Polyhedral Lyapunov functions structurally ensure global asymptotic stability of dynamical networks iff the Jacobian is non-singular

    NARCIS (Netherlands)

    Blanchini, Franco; Giordano, G.

    2017-01-01

    For a vast class of dynamical networks, including chemical reaction networks (CRNs) with monotonic reaction rates, the existence of a polyhedral Lyapunov function (PLF) implies structural (i.e., parameter-free) local stability. Global structural stability is ensured under the additional

  17. Dynamic motion stabilization for front-wheel drive in-wheel motor electric vehicles

    Directory of Open Access Journals (Sweden)

    Jia-Sheng Hu

    2015-12-01

    Full Text Available This article presents a new dynamic motion stabilization approach to front-wheel drive in-wheel motor electric vehicles. The approach includes functions such as traction control system, electronic differential system, and electronic stability control. The presented electric vehicle was endowed with anti-skid performance in longitudinal accelerated start; smooth turning with less tire scrubbing; and safe driving experience in two-dimensional steering. The analysis of the presented system is given in numerical derivations. For practical verifications, this article employed a hands-on electric vehicle named Corsa-electric vehicle to carry out the tests. The presented approach contains an integrated scheme which can achieve the mentioned functions in a single microprocessor. The experimental results demonstrated the effectiveness and feasibility of the presented methodology.

  18. Simplified distributed parameters BWR dynamic model for transient and stability analysis

    International Nuclear Information System (INIS)

    Espinosa-Paredes, Gilberto; Nunez-Carrera, Alejandro; Vazquez-Rodriguez, Alejandro

    2006-01-01

    This paper describes a simplified model to perform transient and linear stability analysis for a typical boiling water reactor (BWR). The simplified transient model was based in lumped and distributed parameters approximations, which includes vessel dome and the downcomer, recirculation loops, neutron process, fuel pin temperature distribution, lower and upper plenums reactor core and pressure and level controls. The stability was determined by studying the linearized versions of the equations representing the BWR system in the frequency domain. Numerical examples are used to illustrate the wide application of the simplified BWR model. We concluded that this simplified model describes properly the dynamic of a BWR and can be used for safety analysis or as a first approach in the design of an advanced BWR

  19. Dynamics and stabilization of peak current-mode controlled buck converter with constant current load

    International Nuclear Information System (INIS)

    Leng Min-Rui; Zhou Guo-Hua; Zhang Kai-Tun; Li Zhen-Hua

    2015-01-01

    The discrete iterative map model of peak current-mode controlled buck converter with constant current load (CCL), containing the output voltage feedback and ramp compensation, is established in this paper. Based on this model the complex dynamics of this converter is investigated by analyzing bifurcation diagrams and the Lyapunov exponent spectrum. The effects of ramp compensation and output voltage feedback on the stability of the converter are investigated. Experimental results verify the simulation and theoretical analysis. The stability boundary and chaos boundary are obtained under the theoretical conditions of period-doubling bifurcation and border collision. It is found that there are four operation regions in the peak current-mode controlled buck converter with CCL due to period-doubling bifurcation and border-collision bifurcation. Research results indicate that ramp compensation can extend the stable operation range and transfer the operating mode, and output voltage feedback can eventually eliminate the coexisting fast-slow scale instability. (paper)

  20. In-Well Sediment Incubators to Evaluate Microbial Community Stability and Dynamics following Bioimmobilization of Uranium

    International Nuclear Information System (INIS)

    Baldwin, Brett R.; Peacock, Aaron D.; Gan, M.; Resch, Charles T.; Arntzen, Evan V.; Smithgall, A.N.; Pfiffner, S.; Freifeld, Barry M.; White, D.C.; Long, Philip E.

    2009-01-01

    An in-situ incubation device (ISI) was developed in order to investigate the stability and dynamics of sediment associated microbial communities to prevailing subsurface oxidizing or reducing conditions. Here we describe the use of these devices at the Old Rifle Uranium Mill Tailings Remedial Action (UMTRA) site. During the 7 month deployment oxidized Rifle aquifer background sediments (RABS) were deployed in previously biostimulated wells under iron reducing conditions, cell densities of known iron reducing bacteria including Geobacteraceae increased significantly showing the microbial community response to local subsurface conditions. PLFA profiles of RABS following in situ deployment were strikingly similar to those of adjacent sediment cores suggesting ISI results could be extrapolated to the native material of the test plots. Results for ISI deployed reduced sediments showed only slight changes in community composition and pointed toward the ability of the ISIs to monitor microbial community stability and response to subsurface conditions.

  1. Dynamical Stability of Imaged Planetary Systems in Formation: Application to HL Tau

    Science.gov (United States)

    Tamayo, D.; Triaud, A. H. M. J.; Menou, K.; Rein, H.

    2015-06-01

    A recent Atacama Large Millimeter/Submillimeter Array image revealed several concentric gaps in the protoplanetary disk surrounding the young star HL Tau. We consider the hypothesis that these gaps are carved by planets, and present a general framework for understanding the dynamical stability of such systems over typical disk lifetimes, providing estimates for the maximum planetary masses. We collect these easily evaluated constraints into a workflow that can help guide the design and interpretation of new observational campaigns and numerical simulations of gap opening in such systems. We argue that the locations of resonances should be significantly shifted in massive disks like HL Tau, and that theoretical uncertainties in the exact offset, together with observational errors, imply a large uncertainty in the dynamical state and stability in such disks. This presents an important barrier to using systems like HL Tau as a proxy for the initial conditions following planet formation. An important observational avenue to breaking this degeneracy is to search for eccentric gaps, which could implicate resonantly interacting planets. Unfortunately, massive disks like HL Tau should induce swift pericenter precession that would smear out any such eccentric features of planetary origin. This motivates pushing toward more typical, less massive disks. For a nominal non-resonant model of the HL Tau system with five planets, we find a maximum mass for the outer three bodies of approximately 2 Neptune masses. In a resonant configuration, these planets can reach at least the mass of Saturn. The inner two planets’ masses are unconstrained by dynamical stability arguments.

  2. How biological microtubules may avoid decoherence

    International Nuclear Information System (INIS)

    Hameroff, S.

    2005-01-01

    Full text: Entangled superpositions persisting for hundreds of milliseconds in protein assemblies such as microtubules (MTs) are proposed in biological functions, e.g. quantum computation relevant to consciousness in the Penrose-Hameroff 'Orch OR' model. Cylindrical polymers of the protein tubulin, MTs organize cell activities. The obvious question is how biological quantum states could avoid decoherence, e.g. in the brain at 37.6 degrees centigrade. Screening/sheelding: tubulin protein states/functions are governed by van der Waals London forces, quantum interactions among clouds of delocalizable electrons in nonpolar 'hydrophobic' intra-protein pockets screened from external van der Waals thermal interactions. Such pockets include amino acid resonance structures benzene and indole rings. (Anesthetic gases erase consciousness solely by interfering with London forces in hydrophobic pockets in various brain proteins). Hence tubulin states may act as superpositioned qubits also shielded at the MT level by counter-ion Debye plasma layers (due to charged C-termini tails on tubulin) and by water-ordering actin gels which embed MTs in a quasi-solid. Biological systems may also exploit thermodynamic gradients to give extremely low effective temperatures. Decoherence free subspaces: paradoxically, a system coupled strongly to its environment through certain degrees of freedom can effectively 'freeze' other degrees of freedom (quantum Zeno effect), enabling coherent superpositions and entanglement to persist. Metabolic energy supplied to MT collective dynamics (e.g. Froehlich coherence) can cause Bose-Einstein condenzation and counter decoherence as lasers avoid decoherence at room temperature. Topological quantum error correction: MT lattice structure reveals various helical winding paths through adjacent tubulins which follow the Fibonacci series. Propagation/interactions of quasi-particles along these paths may process information. As proposed by Kitaev (1997), various

  3. Dynamic aeroelastic stability of vertical-axis wind turbines under constant wind velocity

    Science.gov (United States)

    Nitzsche, Fred

    1994-05-01

    The flutter problem associated with the blades of a class of vertical-axis wind turbines called Darrieus is studied in detail. The spinning blade is supposed to be initially curved in a particular shape characterized by a state of pure tension at the blade cross section. From this equilibrium position a three-dimensional linear perturbation pattern is superimposed to determine the dynamic aeroelastic stability of the blade in the presence of free wind speed by means of the Floquet-Lyapunov theory for periodic systems.

  4. Brownian dynamics simulations of an order-disorder transition in sheared sterically stabilized colloidal suspensions

    International Nuclear Information System (INIS)

    Rigos, A.A.; Wilemski, G.

    1992-01-01

    The shear thinning behavior of a sterically stabilized nonaqueous colloidal suspension was investigated using nonequilibrium Brownian dynamics simulations of systems with 108 and 256 particles. At a volume fraction of 0.4, the suspension is thixotropic: it has a reversible shear thinning transition from a disordered state to an ordered, lamellar state with triangularly packed strings of particles. The time scale for the transition is set by the free particle diffusion constant. For the smaller system, the transition occurs gradually with increasing shear rate. For the larger system, the transition is sharp and discontinuous shear thinning is found. 34 refs., 9 figs., 1 tab

  5. Local dynamic stability during treadmill walking can detect children with developmental coordination disorder

    DEFF Research Database (Denmark)

    Speedtsberg, Merete Brink; Christensen, Sofie Bouschinger; Stenum, Jan

    2018-01-01

    -posterior directions were recorded with a sternum mounted accelerometer at 256Hz. Short term local dynamic stability (λs), root mean square (RMS) and relative root mean square (RMSR) were calculated from measures of orthogonal trunk accelerations. Receiver operating characteristic curve (ROC) analysis was performed...... between children with DCD and TD children in any direction. The ROC analysis of λs in separate directions and in two dimensions showed an excellent accuracy of discriminating between children with DCD and TD children. Anterior-posterior direction in combination with medio-lateral or vertical showed best...

  6. Dynamic stability of a cantilevered Timoshenko beam on partial elastic foundations subjected to a follower force

    International Nuclear Information System (INIS)

    Ryu, Bong Jo; Shin, Kwang Bok; Yim, Kyung Bin; Yoon, Young Sik

    2006-01-01

    This paper presents the dynamic stability of a cantilevered Timoshenko beam with a concentrated mass, partially attached to elastic foundations, and subjected to a follower force. Governing equations are derived from the extended Hamilton's principle, and FEM is applied to solve the discretized equation. The influence of some parameters such as the elastic foundation parameter, the positions of partial elastic foundations, shear deformations, the rotary inertia of the beam, and the mass and the rotary inertia of the concentrated mass on the critical flutter load is investigated. Finally, the optimal attachment ratio of partial elastic foundation that maximizes the critical flutter load is presented

  7. Transient Dynamics of Electric Power Systems: Direct Stability Assessment and Chaotic Motions

    Science.gov (United States)

    Chu, Chia-Chi

    A power system is continuously experiencing disturbances. Analyzing, predicting, and controlling transient dynamics, which describe transient behaviors of the power system following disturbances, is a major concern in the planning and operation of a power utility. Important conclusions and decisions are made based on the result of system transient behaviors. As today's power network becomes highly interconnected and much more complex, it has become essential to enhance the fundamental understanding of transient dynamics, and to develop fast and reliable computational algorithms. In this thesis, we emphasize mathematical rigor rather than physical insight. Nonlinear dynamical system theory is applied to study two fundamental topics: direct stability assessment and chaotic motions. Conventionally, power system stability is determined by calculating the time-domain transient behaviors for a given disturbance. In contrast, direct methods identify whether or not the system will remain stable once the disturbance is removed by comparing the corresponding energy value of the post-fault system to a calculated threshold value. Direct methods not only avoid the time-consuming numerical integration of the time domain approach, but also provide a quantitative measure of the degree of system stability. We present a general framework for the theoretical foundations of direct methods. Canonical representations of network-reduction models as well as network-preserving models are proposed to facilitate the analysis and the construction of energy functions of various power system models. An advanced and practical method, called the boundary of stability region based controlling unstable equilibrium point method (BCU method), of computing the controlling unstable equilibrium point is proposed along with its theoretical foundation. Numerical solution algorithms capable of supporting on-line applications of direct methods are provided. Further possible improvements and enhancements are

  8. The determination of temperature stability of silver nanotubes by the molecular dynamics simulation

    Science.gov (United States)

    Filatov, O.; Soldatenko, S.; Soldatenko, O.

    2018-04-01

    Molecular dynamics simulation using the embedded-atom method is applied to study thermal stability of silver nanotubes and its coefficient of linear thermal expansion. The correspondence of face centered cubic structure potential for this task is tested. Three types of nanotubes are modelled: scrolled from graphene-like plane, scrolled from plane with cubic structure and cut from cylinder. It is established that only the last two of them are stable. The last one describes in details. There is critical temperature when free ends of the nanotube close but the interior surface retains. At higher temperatures, the interior surface collapses and the nanotube is unstable.

  9. Study of the influence of imperfections on the dynamic stability of tanks

    International Nuclear Information System (INIS)

    Uras, R.A.; Liu, Wing Kam; Chen, Yi-Jung

    1990-01-01

    The influence of geometrical imperfections on the dynamic stability of liquid-filled shells under horizontal ground excitation is studied. Some basic concepts in the large deformation and large deformation thin shell theory are recalled. The work done by inertial and internal forces are given in the Gaussian surface coordinate system. A general imperfection pattern in the circumferential direction is introduced. The emphasis is particularly dedicated to the analysis of the geometrical stiffness term. Different patterns are studied to explain the occurrence of additional instability regions. 6 refs., 1 fig., 3 tabs

  10. Abl N-terminal cap stabilization of SH3 domain dynamics.

    Science.gov (United States)

    Chen, Shugui; Dumitrescu, Teodora Pene; Smithgall, Thomas E; Engen, John R

    2008-05-27

    Crystal structures and other biochemical data indicate that the N-terminal cap (NCap) region of the Abelson tyrosine kinase (c-Abl) is important for maintaining the downregulated conformation of the kinase domain. The exact contributions that the NCap makes in stabilizing the various intramolecular interactions within c-Abl are less clear. While the NCap appears to be important for locking the SH3 and SH2 domains to the back of the kinase domain, there may be other more subtle elements of regulation. Hydrogen exchange (HX) and mass spectrometry (MS) were used to determine if the NCap contributes to intramolecular interactions involving the Abl SH3 domain. Under physiological conditions, the Abl SH3 domain underwent partial unfolding and its unfolding half-life was slowed during binding to the SH2 kinase linker, providing a unique assay for testing NCap-induced stabilization of the SH3 domain in various constructs. The results showed that the NCap stabilizes the dynamics of the SH3 domain in certain constructs but does not increase the relative affinity of the SH3 domain for the native SH2 kinase linker. The stabilization effect was absent in constructs of just the NCap and SH3 but was obvious when the SH2 domain and the SH2 kinase linker were present. These results suggest that interactions between the NCap and the SH3 domain can contribute to c-Abl stabilization in constructs that contain at least the SH2 domain, an effect that may partially compensate for the absence of the negative regulatory C-terminal tail found in the related Src family of kinases.

  11. Dynamics and stability of a tethered centrifuge in low earth orbit

    Science.gov (United States)

    Quadrelli, B. M.; Lorenzini, E. C.

    1992-01-01

    The three-dimensional attitude dynamics of a spaceborne tethered centrifuge for artificial gravity experiments in low earth orbit is analyzed using two different methods. First, the tethered centrifuge is modeled as a dumbbell with a straight viscoelastic tether, point tip-masses, and sophisticated environmental models such as nonspherical gravity, thermal perturbations, and a dynamic atmospheric model. The motion of the centrifuge during spin-up, de-spin, and steady-rotation is then simulated. Second, a continuum model of the tether is developed for analyzing the stability of lateral tether oscillations. Results indicate that the maximum fluctuation about the 1-g radial acceleration level is less than 0.001 g; the time required for spin-up and de-spin is less than one orbit; and lateral oscillations are stable for any practical values of the system parameters.

  12. BWR stability using a reducing dynamical model; Estabilidad de un BWR con un modelo dinamico reducido

    Energy Technology Data Exchange (ETDEWEB)

    Ballestrin Bolea, J M; Blazquez Martinez, J B

    1990-07-01

    BWR stability can be treated with reduced order dynamical models. When the parameters of the model came from dynamical models. When the parameters of the model came from experimental data, the predictions are accurate. In this work an alternative derivation for the void fraction equation is made, but remarking the physical structure of the parameters. As the poles of power/reactivity transfer function are related with the parameters, the measurement of the poles by other techniques such as noise analysis will lead to the parameters, but the system of equations is non-linear. Simple parametric calculation of decay ratio are performed, showing why BWRs become unstable when they are operated at low flow and high power. (Author)

  13. Stability Analysis of an Advanced Persistent Distributed Denial-of-Service Attack Dynamical Model

    Directory of Open Access Journals (Sweden)

    Chunming Zhang

    2018-01-01

    Full Text Available The advanced persistent distributed denial-of-service (APDDoS attack is a fairly significant threat to cybersecurity. Formulating a mathematical model for accurate prediction of APDDoS attack is important. However, the dynamical model of APDDoS attack has barely been reported. This paper first proposes a novel dynamical model of APDDoS attack to understand the mechanisms of APDDoS attack. Then, the attacked threshold of this model is calculated. The global stability of attack-free and attacked equilibrium are both proved. The influences of the model’s parameters on attacked equilibrium are discussed. Eventually, the main conclusions of the theoretical analysis are examined through computer simulations.

  14. Dynamic Rocker-Bogie: Kinematical Analysis in a High-Speed Traversal Stability Enhancement

    Directory of Open Access Journals (Sweden)

    Sunxin Wang

    2016-01-01

    Full Text Available The rocker-bogie suspension system has robust capabilities to deal with uneven terrain because of its distributing of the payload over its six wheels uniformly, while there is one major shortcoming to high-speed traversal over the planar terrain. This paper proposes a new dynamic rocker-bogie suspension system with two modes of operation: it can expand the span of the rocker-bogie support polygon to increase travel rate when the terrain is planar; and it can switch to its original configuration to move by low speed when it is faced with rough terrain. The analysis on dynamic stability margin and kinematical simulation on the two operating modes of rocker-bogie are employed to analyze and verify the rationality and effectiveness of the modification in the structure.

  15. Duplication in the microtubule-actin cross-linking factor 1 gene causes a novel neuromuscular condition

    DEFF Research Database (Denmark)

    Jørgensen, Louise H; Mosbech, Mai-Britt; Færgeman, Nils J

    2014-01-01

    Spectrins and plakins are important communicators linking cytoskeletal components to each other and to cellular junctions. Microtubule-actin cross-linking factor 1 (MACF1) belongs to the spectraplakin family and is involved in control of microtubule dynamics. Complete knock out of MACF1 in mice...... muscles and diminished motor skills, with heterogeneous presentation among the affected family members. To corroborate these findings we used RNA interference to knock down the VAB-10 locus containing the MACF1 homologue in C. elegans, and we could show that this also causes movement disturbances...

  16. Calmodulin immunolocalization to cortical microtubules is calcium independent

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, D.D.; Cyr, R.J.

    1992-12-31

    Calcium affects the stability of cortical microtubules (MTs) in lysed protoplasts. This calmodulin (CaM)-mediated interaction may provide a mechanism that serves to integrate cellular behavior with MT function. To test the hypothesis that CaM associates with these MTs, monoclonal antibodies were produced against CaM, and one (designated mAb1D10), was selected for its suitability as an immunocytochemical reagent. It is shown that CaM associates with the cortical Mats of cultured carrot (Daucus carota L.) and tobacco (Nicotiana tobacum L.) cells. Inasmuch as CaM interacts with calcium and affects the behavior of these Mats, we hypothesized that calcium would alter this association. To test this, protoplasts containing taxol-stabilized Mats were lysed in the presence of various concentrations of calcium and examined for the association of Cam with cortical Mats. At 1 {mu}M calcium, many protoplasts did not have CaM in association with the cortical Mats, while at 3.6 {mu}M calcium, this association was completely abolished. The results are discussed in terms of a model in which CaM associates with Mats via two types of interactions; one calcium dependent and one independent.

  17. Calmodulin immunolocalization to cortical microtubules is calcium independent

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, D.D.; Cyr, R.J.

    1992-01-01

    Calcium affects the stability of cortical microtubules (MTs) in lysed protoplasts. This calmodulin (CaM)-mediated interaction may provide a mechanism that serves to integrate cellular behavior with MT function. To test the hypothesis that CaM associates with these MTs, monoclonal antibodies were produced against CaM, and one (designated mAb1D10), was selected for its suitability as an immunocytochemical reagent. It is shown that CaM associates with the cortical Mats of cultured carrot (Daucus carota L.) and tobacco (Nicotiana tobacum L.) cells. Inasmuch as CaM interacts with calcium and affects the behavior of these Mats, we hypothesized that calcium would alter this association. To test this, protoplasts containing taxol-stabilized Mats were lysed in the presence of various concentrations of calcium and examined for the association of Cam with cortical Mats. At 1 [mu]M calcium, many protoplasts did not have CaM in association with the cortical Mats, while at 3.6 [mu]M calcium, this association was completely abolished. The results are discussed in terms of a model in which CaM associates with Mats via two types of interactions; one calcium dependent and one independent.

  18. Modelling of gas-liquid reactors - stability and dynamic behaviour of gas-liquid mass transfer accompanied by irreversible reaction

    NARCIS (Netherlands)

    Elk, E.P. van; Borman, P.C.; Kuipers, J.A.M.; Versteeg, G.F.

    1999-01-01

    The dynamic behaviour and stability of single-phase reacting systems has been investigated thoroughly in the past and design rules for stable operation are available from literature. The dynamic behaviour of gas-liquid processes is considerably more complex and has received relatively little

  19. Modelling of gas-liquid reactors - stability and dynamic behaviour of gas-liquid mass transfer accompanied by irreversible reaction

    NARCIS (Netherlands)

    Elk, van E.P.; Borman, P.C.; Kuipers, J.A.M.; Versteeg, G.F.

    1999-01-01

    The dynamic behaviour and stability of single-phase reacting systems has been investigated thoroughly in the past and design rules for stable operation are available from literature. The dynamic behaviour of gas–liquid processes is considerably more complex and has received relatively little

  20. Optomechanical proposal for monitoring microtubule mechanical vibrations

    Czech Academy of Sciences Publication Activity Database

    Barzanjeh, Sh.; Salari, V.; Tuszynski, J. A.; Cifra, Michal; Simon, C.

    2017-01-01

    Roč. 96, č. 1 (2017), č. článku 012404. ISSN 2470-0045 R&D Projects: GA ČR(CZ) GA15-17102S Grant - others:AV ČR(CZ) SAV-15-22 Program:Bilaterální spolupráce Institutional support: RVO:67985882 Keywords : Vibrational modes * Microtubule * Resonance frequencies Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Optics (including laser optics and quantum optics) Impact factor: 2.366, year: 2016

  1. Emerging microtubule targets in glioma therapy

    Czech Academy of Sciences Publication Activity Database

    Katsetos, C.D.; Reginato, M.J.; Baas, P.W.; D'Agostino, L.; Legido, A.; Tuszynski, J. A.; Dráberová, Eduarda; Dráber, Pavel

    2015-01-01

    Roč. 22, č. 1 (2015), s. 49-72 ISSN 1071-9091 R&D Projects: GA MŠk LH12050; GA MZd NT14467 Grant - others:GA AV ČR M200521203PIPP; NIH(US) R01 NS028785; Philadelphia Health Education Corporation (PHEC)–St. Christopher’s Hospital for Children Reunified Endowment (C.D.K.)(US) 323256 Institutional support: RVO:68378050 Keywords : glioma tumorigenesis * glioblastoma * tubulin * microtubules Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 1.303, year: 2015

  2. Binding stability of peptides on major histocompatibility complex class I proteins: role of entropy and dynamics

    Science.gov (United States)

    Gul, Ahmet; Erman, Burak

    2018-03-01

    Prediction of peptide binding on specific human leukocyte antigens (HLA) has long been studied with successful results. We herein describe the effects of entropy and dynamics by investigating the binding stabilities of 10 nanopeptides on various HLA Class I alleles using a theoretical model based on molecular dynamics simulations. The fluctuational entropies of the peptides are estimated over a temperature range of 310-460 K. The estimated entropies correlate well with experimental binding affinities of the peptides: peptides that have higher binding affinities have lower entropies compared to non-binders, which have significantly larger entropies. The computation of the entropies is based on a simple model that requires short molecular dynamics trajectories and allows for approximate but rapid determination. The paper draws attention to the long neglected dynamic aspects of peptide binding, and provides a fast computation scheme that allows for rapid scanning of large numbers of peptides on selected HLA antigens, which may be useful in defining the right peptides for personal immunotherapy.

  3. In vivo FRET imaging revealed a regulatory role of RanGTP in kinetochore-microtubule attachments via Aurora B kinase.

    Directory of Open Access Journals (Sweden)

    Yoke-Peng Lee

    Full Text Available Under the fluctuating circumstances provided by the innate dynamics of microtubules and opposing tensions resulted from microtubule-associated motors, it is vital to ensure stable kinetochore-microtubule attachments for accurate segregation. However, a comprehensive understanding of how this regulation is mechanistically achieved remains elusive. Using our newly designed live cell FRET time-lapse imaging, we found that post-metaphase RanGTP is crucial in the maintenance of stable kinetochore-microtubule attachments by regulating Aurora B kinase via the NES-bearing Mst1. More importantly, our study demonstrates that by ensuring stable alignment of metaphase chromosomes prior to segregation, RanGTP is indispensible in governing the genomic integrity and the fidelity of cell cycle progression. Our findings suggest an additional role of RanGTP beyond its known function in mitotic spindle assembly during the prometaphase-metaphase transition.

  4. Effects of grab bar on utilized friction and dynamic stability when elderly people enter the bathtub.

    Science.gov (United States)

    Sekiguchi, Yusuke; Kato, Tomohisa; Honda, Keita; Kanetaka, Hiroyasu; Izumi, Shin-Ichi

    2017-08-01

    The effect of the grab bar on dynamic stability when elderly people enter the bathtub remains unclear. The purpose of the present study is to examine the age-related effect of the grab bar on dynamic stability during lateral stepping over an obstacle when entering bathtub. Sixteen young, healthy adults and sixteen elderly adults participated. The subjects performed lateral stepping over an obstacle with and without vertical and horizontal bars. Displacement and velocity of the center of mass and utilized friction, which is the required coefficient of friction to avoid slipping, were simultaneously measured by a three-dimensional motion analysis system and two force plates. A post hoc test for two-way ANOVA revealed that velocity of the center of mass in the vertical direction (pbar were significantly slower and smaller than those without the grab bar in young and elderly people. Moreover, the utilized friction at push off of the trailing leg with the vertical bar in elderly people was lower (pbar. The use of each grab bar while performing a lateral step over an obstacle may help maintaining balance in lateral and vertical directions. However, use of the vertical bar while lateral stepping over an object in elderly people may need low utilized friction to prevent slipping. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Dynamic behavior of tripolar hip endoprostheses under physiological conditions and their effect on stability.

    Science.gov (United States)

    Fabry, Christian; Kaehler, Michael; Herrmann, Sven; Woernle, Christoph; Bader, Rainer

    2014-01-01

    Tripolar systems have been implanted to reduce the risk of recurrent dislocation. However, there is little known about the dynamic behavior of tripolar hip endoprostheses under daily life conditions and achieved joint stability. Hence, the objective of this biomechanical study was to examine the in vivo dynamics and dislocation behavior of two types of tripolar systems compared to a standard total hip replacement (THR) with the same outer head diameter. Several load cases of daily life activities were applied to an eccentric and a concentric tripolar system by an industrial robot. During testing, the motion of the intermediate component was measured using a stereo camera system. Additionally, their behavior under different dislocation scenarios was investigated in comparison to a standard THR. For the eccentric tripolar system, the intermediate component demonstrated the shifting into moderate valgus-positions, regardless of the type of movement. This implant showed the highest resisting torque against dislocation in combination with a large range of motion. In contrast, the concentric tripolar system tended to remain in varus-positions and was primarily moved after stem contact. According to the results, eccentric tripolar systems can work well under in vivo conditions and increase hip joint stability in comparison to standard THRs. Copyright © 2013 IPEM. Published by Elsevier Ltd. All rights reserved.

  6. Local dynamic stability of lower extremity joints in lower limb amputees during slope walking.

    Science.gov (United States)

    Chen, Jin-Ling; Gu, Dong-Yun

    2013-01-01

    Lower limb amputees have a higher fall risk during slope walking compared with non-amputees. However, studies on amputees' slope walking were not well addressed. The aim of this study was to identify the difference of slope walking between amputees and non-amputees. Lyapunov exponents λS was used to estimate the local dynamic stability of 7 transtibial amputees' and 7 controls' lower extremity joint kinematics during uphill and downhill walking. Compared with the controls, amputees exhibited significantly lower λS in hip (P=0.04) and ankle (P=0.01) joints of the sound limb, and hip joints (P=0.01) of the prosthetic limb during uphill walking, while they exhibited significantly lower λS in knee (P=0.02) and ankle (P=0.03) joints of the sound limb, and hip joints (P=0.03) of the prosthetic limb during downhill walking. Compared with amputees level walking, they exhibited significantly lower λS in ankle joints of the sound limb during both uphill (P=0.01) and downhill walking (P=0.01). We hypothesized that the better local dynamic stability of amputees was caused by compensation strategy during slope walking.

  7. Diagonal recurrent neural network based adaptive control of nonlinear dynamical systems using lyapunov stability criterion.

    Science.gov (United States)

    Kumar, Rajesh; Srivastava, Smriti; Gupta, J R P

    2017-03-01

    In this paper adaptive control of nonlinear dynamical systems using diagonal recurrent neural network (DRNN) is proposed. The structure of DRNN is a modification of fully connected recurrent neural network (FCRNN). Presence of self-recurrent neurons in the hidden layer of DRNN gives it an ability to capture the dynamic behaviour of the nonlinear plant under consideration (to be controlled). To ensure stability, update rules are developed using lyapunov stability criterion. These rules are then used for adjusting the various parameters of DRNN. The responses of plants obtained with DRNN are compared with those obtained when multi-layer feed forward neural network (MLFFNN) is used as a controller. Also, in example 4, FCRNN is also investigated and compared with DRNN and MLFFNN. Robustness of the proposed control scheme is also tested against parameter variations and disturbance signals. Four simulation examples including one-link robotic manipulator and inverted pendulum are considered on which the proposed controller is applied. The results so obtained show the superiority of DRNN over MLFFNN as a controller. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

  8. Study of V-OTDR stability for dynamic strain measurement in piezoelectric vibration

    Science.gov (United States)

    Ren, Meiqi; Lu, Ping; Chen, Liang; Bao, Xiaoyi

    2016-09-01

    In a phase-sensitive optical-time domain reflectometry (Φ-OTDR) system, the challenge for dynamic strain measurement lies in large intensity fluctuations from trace to trace. The intensity fluctuation caused by stochastic characteristics of Rayleigh backscattering sets detection limit for the minimum strength of vibration measurement and causes the large measurement uncertainty. Thus, a trace-to-trace correlation coefficient is introduced to quantify intensity fluctuation of Φ-OTDR traces and stability of the sensor system theoretically and experimentally. A novel approach of measuring dynamic strain induced by various driving voltages of lead zirconate titanate (PZT) in Φ-OTDR is also demonstrated. Piezoelectric vibration signals are evaluated through analyzing peak values of fast Fourier transform spectra at the fundamental frequency and high-order harmonics based on Bessel functions. High trace-to-trace correlation coefficients varying from 0.824 to 0.967 among 100 measurements are obtained in experimental results, showing the good stability of our sensor system, as well as small uncertainty of measured peak values.

  9. Induced Unbalance as a Method for Improving the Dynamic Stability of High-Speed Turbochargers

    KAUST Repository

    Gordon Kirk, R.; Alsaeed, Ali A.

    2011-01-01

    The high-speed diesel engine turbocharger is known to have subsynchronous vibrations for a wide speed range. The bearing fluid-film instability is the main source of the vibration. The nonlinear forces inside the bearings are causing the rotor to whirl in a limit cycle. This study presents a new method for improving the dynamic stability by inducing the turbocharger rotor unbalance in order to suppress the subsynchronous vibration. The finite-element model of the turbocharger with floating-ring bearings is numerically solved for the nonlinear time-transient response. Both compressor and turbine added unbalance are induced and the dynamic stability is computed. The turbocharger model with linearized floating-ring bearings is also solved for eigenvalues to predict the modes of instability. The linear analysis demonstrates that the forward whirling mode of the floating-ring at the compressor end also becomes unstable at the higher turbocharger speeds, in addition to the unstable forward conical and cylindrical modes. The numerical predictions are also compared to the former experimental results of a similar turbocharger. The results of the study show that the subsynchronous frequency amplitude of the dominant first mode is reduced when inducing either the compressor or the turbine unbalance at a certain level. © 2011 R. Gordon Kirk and Ali A. Alsaeed.

  10. Modified TOV in gravity’s rainbow: properties of neutron stars and dynamical stability conditions

    Energy Technology Data Exchange (ETDEWEB)

    Hendi, S.H. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha (RIAAM),P.O. Box 55134-441, Maragha (Iran, Islamic Republic of); Bordbar, G.H. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Center for Excellence in Astronomy and Astrophysics (CEAA-RIAAM)-Maragha,P.O. Box 55134-441, Maragha 55177-36698 (Iran, Islamic Republic of); Panah, B. Eslam [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Panahiyan, S. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Physics Department, Shahid Beheshti University,Tehran 19839 (Iran, Islamic Republic of)

    2016-09-09

    In this paper, we consider a spherical symmetric metric to extract the hydrostatic equilibrium equation of stars in (3+1)-dimensional gravity’s rainbow in the presence of cosmological constant. Then, we generalize the hydrostatic equilibrium equation to d-dimensions and obtain the hydrostatic equilibrium equation for this gravity. Also, we obtain the maximum mass of neutron star using the modern equations of state of neutron star matter derived from the microscopic calculations. It is notable that, in this paper, we consider the effects of rainbow functions on the diagrams related to the mass-central mass density (M-ρ{sub c}) relation and also the mass-radius (M-R) relation of neutron star. We also study the effects of rainbow functions on the other properties of neutron star such as the Schwarzschild radius, average density, strength of gravity and gravitational redshift. Then, we apply the cosmological constant to this theory to obtain the diagrams of M-ρ{sub c} (or M-R) and other properties of these stars. Next, we investigate the dynamical stability condition for these stars in gravity’s rainbow and show that these stars have dynamical stability. We also obtain a relation between mass of neutron stars and Planck mass. In addition, we compare obtained results of this theory with the observational data.

  11. Lateral dynamic flight stability of a model hoverfly in normal and inclined stroke-plane hovering

    International Nuclear Information System (INIS)

    Xu, Na; Sun, Mao

    2014-01-01

    Many insects hover with their wings beating in a horizontal plane (‘normal hovering’), while some insects, e.g., hoverflies and dragonflies, hover with inclined stroke-planes. Here, we investigate the lateral dynamic flight stability of a hovering model hoverfly. The aerodynamic derivatives are computed using the method of computational fluid dynamics, and the equations of motion are solved by the techniques of eigenvalue and eigenvector analysis. The following is shown: The flight of the insect is unstable at normal hovering (stroke-plane angle equals 0) and the instability becomes weaker as the stroke-plane angle increases; the flight becomes stable at a relatively large stroke-plane angle (larger than about 24°). As previously shown, the instability at normal hovering is due to a positive roll-moment/side-velocity derivative produced by the ‘changing-LEV-axial-velocity’ effect. When the stroke-plane angle increases, the wings bend toward the back of the body, and the ‘changing-LEV-axial-velocity’ effect decreases; in addition, another effect, called the ‘changing-relative-velocity’ effect (the ‘lateral wind’, which is due to the side motion of the insect, changes the relative velocity of its wings), becomes increasingly stronger. This causes the roll-moment/side-velocity derivative to first decrease and then become negative, resulting in the above change in stability as a function of the stroke-plane angle. (paper)

  12. Dynamics of bluff-body-stabilized lean premixed syngas flames in a meso-scale channel

    KAUST Repository

    Lee, Bok Jik

    2016-07-15

    Direct numerical simulations are conducted to investigate the dynamics of lean premixed syngas flames stabilized by a bluff-body in a meso-scale channel at near blow-off conditions, in order to provide fundamental insights into the physical mechanisms responsible for the critical phenomena. Flames in a two-dimensional meso-scale channel with a square flame holder are adopted as the model configuration, and a syngas mixture at an equivalence ratio of 0.5 with the CO:H ratio of 1 is considered. As the inlet velocity is increased, the initially stable steady flames undergo a transition to an unsteady mode of regular asymmetric fluctuation. When the inlet velocity is further increased, the flame is eventually blown off. Between the regular fluctuation mode and blow-off limit, there exists a narrow range of the inlet velocity where the flames exhibit periodic local extinction and recovery. Approaching further to the blow-off limit, the recovery mode fails to occur but the flame survives as a short kernel attached to the base of the bluff-body, until it is completely extinguished as the attached flames are gradually shrunk towards the bluff-body. The results are systematically compared with the hydrogen flame results reported in our earlier study. Examination of the characteristic time scales of relevant processes provided understanding of key mechanisms responsible for the observed differences, thereby allowing improved description of the local extinction and re-ignition dynamics that are critical to flame stabilization.

  13. Structure, stability and ELM dynamics of the H-mode pedestal in DIII-D

    International Nuclear Information System (INIS)

    Fenstermacher, M.E.; Leonard, A.W.; Osborne, T.H.

    2005-01-01

    Experiments are described that have increased understanding of the transport and stability physics that set the H-mode edge pedestal width and height, determine the onset of Type-I edge localized modes (ELMs), and produce the nonlinear dynamics of the ELM perturbation in the pedestal and scrape-off layer (SOL). Predictive models now exist for the n e pedestal profile and the p e height at the onset of Type-I ELMs, and progress has been made toward predictive models of the T e pedestal width and nonlinear ELM evolution. Similarity experiments between DIII-D and JET suggested that neutral penetration physics dominates in the relationship between the width and height of the n e pedestal while plasma physics dominates in setting the T e pedestal width. Measured pedestal conditions including edge current at ELM onset agree with intermediate-n peeling-ballooning (P-B) stability predictions. Midplane ELM dynamics data show the predicted (P-B) structure at ELM onset, large rapid variations of the SOL parameters, and fast radial propagation in later phases, similar to features in nonlinear ELM simulations. (author)

  14. Stability of nanocrystalline Ni-based alloys: coupling Monte Carlo and molecular dynamics simulations

    Science.gov (United States)

    Waseda, O.; Goldenstein, H.; Silva, G. F. B. Lenz e.; Neiva, A.; Chantrenne, P.; Morthomas, J.; Perez, M.; Becquart, C. S.; Veiga, R. G. A.

    2017-10-01

    The thermal stability of nanocrystalline Ni due to small additions of Mo or W (up to 1 at%) was investigated in computer simulations by means of a combined Monte Carlo (MC)/molecular dynamics (MD) two-steps approach. In the first step, energy-biased on-lattice MC revealed segregation of the alloying elements to grain boundaries. However, the condition for the thermodynamic stability of these nanocrystalline Ni alloys (zero grain boundary energy) was not fulfilled. Subsequently, MD simulations were carried out for up to 0.5 μs at 1000 K. At this temperature, grain growth was hindered for minimum global concentrations of 0.5 at% W and 0.7 at% Mo, thus preserving most of the nanocrystalline structure. This is in clear contrast to a pure Ni model system, for which the transformation into a monocrystal was observed in MD simulations within 0.2 μs at the same temperature. These results suggest that grain boundary segregation of low-soluble alloying elements in low-alloyed systems can produce high-temperature metastable nanocrystalline materials. MD simulations carried out at 1200 K for 1 at% Mo/W showed significant grain boundary migration accompanied by some degree of solute diffusion, thus providing additional evidence that solute drag mostly contributed to the nanostructure stability observed at lower temperature.

  15. Dynamic Postural-Stability Deficits After Cryotherapy to the Ankle Joint.

    Science.gov (United States)

    Fullam, Karl; Caulfield, Brian; Coughlan, Garrett F; McGroarty, Mark; Delahunt, Eamonn

    2015-09-01

    Decreased postural stability is a primary risk factor for lower limb musculoskeletal injuries. During athletic competitions, cryotherapy may be applied during short breaks in play or during half-time; however, its effects on postural stability remain unclear. To investigate the acute effects of a 15-minute ankle-joint cryotherapy application on dynamic postural stability. Controlled laboratory study. University biomechanics laboratory. A total of 29 elite-level collegiate male field-sport athletes (age = 20.8 ± 1.12 years, height = 1.80 ± 0.06 m, mass = 81.89 ± 8.59 kg) participated. Participants were tested on the anterior (ANT), posterolateral (PL), and posteromedial (PM) reach directions of the Star Excursion Balance Test before and after a 15-minute ankle-joint cryotherapy application. Normalized reach distances; sagittal-plane kinematics of the hip, knee, and ankle joints; and associated mean velocity of the center-of-pressure path during performance of the ANT, PL, and PM reach directions of the Star Excursion Balance Test. We observed a decrease in reach-distance scores for the ANT, PL, and PM reach directions from precryotherapy to postcryotherapy (P .05). We noted a decrease in mean velocity of the center-of-pressure path from precryotherapy to postcryotherapy (P cryotherapy to the ankle joint.

  16. Spin dynamics and thermal stability in L10 FePt

    Science.gov (United States)

    Chen, Tianran; Toomey, Wahida

    Increasing the data storage density of hard drives remains one of the continuing goals in magnetic recording technology. A critical challenge for increasing data density is the thermal stability of the written information, which drops rapidly as the bit size gets smaller. To maintain good thermal stability in small bits, one should consider materials with high anisotropy energy such as L10 FePt. High anisotropy energy nevertheless implies high coercivity, making it difficult to write information onto the disk. This issue can be overcome by a new technique called heat-assisted magnetic recording, where a laser is used to locally heat the recording medium to reduce its coercivity while retaining relatively good thermal stability. Many of the microscopic magnetic properties of L10 FePt, however, have not been theoretically well understood. In this poster, I will focus on a single L10 FePt grain, typically of a few nanometers. Specifically, I will discuss its critical temperature, size effect and, in particular, spin dynamics in the writing process, a key to the success of heat-assisted magnetic recording. WCU URF16.

  17. Tuned dynamics stabilizes an idealized regenerative axial-torsional model of rotary drilling

    Science.gov (United States)

    Gupta, Sunit K.; Wahi, Pankaj

    2018-01-01

    We present an exact stability analysis of a dynamical system idealizing rotary drilling. This system comprises lumped parameter axial-torsional modes of the drill-string coupled via the cutting forces and torques. The kinematics of cutting is modeled through a functional description of the cut surface which evolves as per a partial differential equation (PDE). Linearization of this model is straightforward as opposed to the traditional state-dependent delay (SDDE) model and both the approaches result in the same characteristic equation. A systematic study on the key system parameters influencing the stability characteristics reveals that torsional damping is very critical and stable drilling is, in general, not possible in its absence. The stable regime increases as the natural frequency of the axial mode approaches that of the torsional mode and a 1:1 internal resonance leads to a significant improvement in the system stability. Hence, from a practical point of view, a drill-string with 1:1 internal resonance is desirable to avoid vibrations during rotary drilling. For the non-resonant case, axial damping reduces the stable range of operating parameters while for the resonant case, an optimum value of axial damping (equal to the torsional damping) results in the largest stable regime. Interestingly, the resonant (tuned) system has a significant parameter regime corresponding to stable operation even in the absence of damping.

  18. Dynamic stability requirements during gait and standing exergames on the wii fit® system in the elderly

    Directory of Open Access Journals (Sweden)

    Duclos Cyril

    2012-05-01

    Full Text Available Abstract Background In rehabilitation, training intensity is usually adapted to optimize the trained system to attain better performance (overload principle. However, in balance rehabilitation, the level of intensity required during training exercises to optimize improvement in balance has rarely been studied, probably due to the difficulty in quantifying the stability level during these exercises. The goal of the present study was to test whether the stabilizing/destabilizing forces model could be used to analyze how stability is challenged during several exergames, that are more and more used in balance rehabilitation, and a dynamic functional task, such as gait. Methods Seven healthy older adults were evaluated with three-dimensional motion analysis during gait at natural and fast speed, and during three balance exergames (50/50 Challenge, Ski Slalom and Soccer. Mean and extreme values for stabilizing force, destabilizing force and the ratio of the two forces (stability index were computed from kinematic and kinetic data to determine the mean and least level of dynamic, postural and overall balance stability, respectively. Results Mean postural stability was lower (lower mean destabilizing force during the 50/50 Challenge game than during all the other tasks, but peak postural instability moments were less challenging during this game than during any of the other tasks, as shown by the minimum destabilizing force values. Dynamic stability was progressively more challenged (higher mean and maximum stabilizing force from the 50/50 Challenge to the Soccer and Slalom games, to the natural gait speed task and to the fast gait speed task, increasing the overall stability difficulty (mean and minimum stability index in the same manner. Conclusions The stabilizing/destabilizing forces model can be used to rate the level of balance requirements during different tasks such as gait or exergames. The results of our study showed that postural stability

  19. Elderly fallers enhance dynamic stability through anticipatory postural adjustments during a choice stepping reaction time

    Directory of Open Access Journals (Sweden)

    Romain Tisserand

    2016-11-01

    Full Text Available In the case of disequilibrium, the capacity to step quickly is critical to avoid falling for elderly. This capacity can be simply assessed through the choice stepping reaction time test (CSRT, where elderly fallers (F take longer to step than elderly non-fallers (NF. However, reasons why elderly F elongate their stepping time remain unclear. The purpose of this study is to assess the characteristics of anticipated postural adjustments (APA that elderly F develop in a stepping context and their consequences on the dynamic stability. 44 community-dwelling elderly subjects (20 F and 22 NF performed a CSRT where kinematics and ground reaction forces were collected. Variables were analyzed using two-way repeated measures ANOVAs. Results for F compared to NF showed that stepping time is elongated, due to a longer APA phase. During APA, they seem to use two distinct balance strategies, depending on the axis: in the anteroposterior direction, we measured a smaller backward movement and slower peak velocity of the center of pressure (CoP; in the mediolateral direction, the CoP movement was similar in amplitude and peak velocity between groups but lasted longer. The biomechanical consequence of both strategies was an increased margin of stability (MoS at foot-off, in the respective direction. By elongating their APA, elderly F use a safer balance strategy that prioritizes dynamic stability conditions instead of the objective of the task. Such a choice in balance strategy probably comes from muscular limitations and/or a higher fear of falling and paradoxically indicates an increased risk of fall.

  20. The Microtubule Plus-End Tracking Protein CLASP2 Is Required for Hematopoiesis and Hematopoietic Stem Cell Maintenance

    Directory of Open Access Journals (Sweden)

    Ksenija Drabek

    2012-10-01

    Full Text Available Mammalian CLASPs are microtubule plus-end tracking proteins whose essential function as regulators of microtubule behavior has been studied mainly in cultured cells. We show here that absence of murine CLASP2 in vivo results in thrombocytopenia, progressive anemia, and pancytopenia, due to defects in megakaryopoiesis, in erythropoiesis, and in the maintenance of hematopoietic stem cell activity. Furthermore, microtubule stability and organization are affected upon attachment of Clasp2 knockout hematopoietic stem-cell-enriched populations, and these cells do not home efficiently toward their bone marrow niche. Strikingly, CLASP2-deficient hematopoietic stem cells contain severely reduced mRNA levels of c-Mpl, which encodes the thrombopoietin receptor, an essential factor for megakaryopoiesis and hematopoietic stem cell maintenance. Our data suggest that thrombopoietin signaling is impaired in Clasp2 knockout mice. We propose that the CLASP2-mediated stabilization of microtubules is required for proper attachment, homing, and maintenance of hematopoietic stem cells and that this is necessary to sustain c-Mpl transcription.