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RISS 인기검색어
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- 저자 : Uhlar, Courtney (검색결과 3 건)
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Energy-consistent integration of multibody systems with friction
Stefan Uhlar,Peter Betsch 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.4
The main goal of the present contribution is to establish an energy consistent time integration procedure for multibody systems with friction. Based upon a rotationless formulation for multibody systems, we use the coordinate augmentation technique in order to implement frictional phenomena such as joint friction. Within this contribution we use the viscous friction assumption as a classical friction model incorporated in the joints. We start with a classical ad hoc model for damping and extend the formulation to multibody systems, dealing finally with an underactuated control problem of a three bar linkage with applied joint friction.
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Mitochondrial dysfunction and calcium deregulation by the RanBP9-cofilin pathway
Roh, Seung-Eon,Woo, Jung A.,Lakshmana, Madepalli K.,Uhlar, Courtney,Ankala, Vinishaa,Boggess, Taylor,Liu, Tian,Hong, Yun-Hwa,Mook-Jung, Inhee,Kim, Sang Jeong,Kang, David E. The Federation of American Societies for Experimen 2013 The FASEB Journal Vol.27 No.12
<P>Mitochondrial dysfunction and synaptic damage are important features of Alzheimer's disease (AD) associated with amyloid β (Aβ) and tau. We reported previously that the scaffolding protein RanBP9, which is overall increased in brains of patients with AD and in mutant APP transgenic mice, simultaneously promotes Aβ generation and focal adhesion disruption by accelerating the endocytosis of APP and β1-integrin, respectively. Moreover, RanBP9 induces neurodegeneration <I>in vitro</I> and <I>in vivo</I> and mediates Aβ-induced neurotoxicity. Here we show in primary hippocampal neurons that RanBP9 potentiates Aβ-induced reactive oxygen species (ROS) overproduction, apoptosis, and calcium deregulation. Analyses of calcium-handling measures demonstrate that RanBP9 selectively delays the clearance of cytosolic Ca<SUP>2+</SUP> mediated by the mitochondrial calcium uniporter through a process involving the translocation of cofilin into mitochondria and oxidative mechanisms. Further, RanBP9 retards the anterograde axonal transport of mitochondria in primary neurons and decreases synaptic mitochondrial activity in brain. These data indicate that RanBP9, cofilin, and Aβ mimic and potentiate each other to produce mitochondrial dysfunction, ROS overproduction, and calcium deregulation, which leads to neurodegenerative changes reminiscent of those seen in AD.—Roh. S.-E., Woo, J. A., Lakshmana, M. K., Uhlar, C., Ankala, V., Boggess, T., Liu, T., Hong, Y.-H., Mook-Jung, I., Kim, S. J., Kang, D. E. Mitochondrial dysfunction and calcium deregulation by the RanBP9-cofilin pathway.</P>
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Numerical integration of discrete mechanical systems with mixed holonomic and control constraints
Peter Betsch,Mahmud Quasem,Stefan Uhlar 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.4
The present work aims to incorporate control (or servo) constraints into finite-dimensional mechanical systems subject to holonomic constraints. In particular, we focus on underactuated systems, defined as systems in which the number of degrees of freedom exceeds the number of inputs. The corresponding equations of motion can be written in the form of differential-algebraic equations (DAEs) with a mixed set of holonomic and control constraints. Apart from closed-loop multibody systems, the present formulation accommodates the so-called rotationless formulation of multibody dynamics. The rotationless formulation has proven to be especially well-suited for the design of energy and momentum conserving schemes, which typically exhibit superior numerical stability properties (see [4, 7, 10]). Subsequent to the incorporation of the servo constraints, we deal with a reformulation of the underlying DAEs, which is amenable to a direct numerical discretization. To this end, we apply a specific projection method to the DAEs in terms of redundant coordinates. A similar projection approach has been previously developed in the framework of generalized coordinates by Blajer & Kolodziejczyk [12]. A numerical example is presented, which deals with a 3D rotary crane.
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