Kenko Uchida

μ -synthesis of an electromagnetic suspension system

This paper deals with /spl mu/-synthesis of an electromagnetic suspension system. First, an issue of modeling a real physical electromagnetic suspension system is discussed. We derive a nominal model as well as a set of models in which the real system is assumed to reside. Different model structures and possible model parameter values are fully employed to determine unstructured additive plant perturbations, which directly yield uncertainty frequency weighting function. Second, based on the set of plant models, we setup robust performance control objectives. Third, we make use of the D-K iteration approach for the controller design. Finally, implementing the controller with a digital signal processor, experiments are carried out. With these experimental results, we show robust performance of the designed control system. >

Robust stabilization of a system with delays in control

A robust stabilization problem is discussed for a system with delays in control. The authors derive a robust stabilizing law against additive perturbations. Then, motivated by the feature of predictive controllers, they investigate the structure of robust stabilizing law and provide some interpretations on the relation between the value of time delay and the achievable margin of robust stabilizability. >

The linear-quadratic optimal control approach to feedback control design for systems with delay

Abstract A generalized linear-quadratic optimal control problem for systems with delay is formulated. The optimal solution is given as a state feedback form which requires a solution of coupled infinite-dimensional Riccati equations. It is shown that the closed-loop system formed by the optimal state feedback control has some desirable sensitivity and robustness properties. The generalization exists in the state quadratic form of the cost functional, which makes it possible to discuss a pole location problem within the framework of the linear-quadratic optimal control problem. It is also shown that the generalized cost functional contains a special class of cost functionals for which the optimal control can be realized by solving only a finite-dimensional Riccati equation. Based on these results about the generalized linear-quadratic optimal control, a design method of feedback controls is proposed and an illustrative example is then presented.

Aberrant molecular properties shared by familial Parkinson’s disease-associated mutant UCH-L1 and carbonyl-modified UCH-L1

Parkinsons disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons. The I93M mutation in ubiquitin C-terminal hydrolase L1 (UCH-L1) is associated with familial PD, and we have previously shown that the I93M UCH-L1-transgenic mice exhibit dopaminergic cell loss. Over 90% of neurodegenerative diseases, including PD, occur sporadically. However, the molecular mechanisms underlying sporadic PD as well as PD associated with I93M UCH-L1 are largely unknown. UCH-L1 is abundant (1-5% of total soluble protein) in the brain and is a major target of oxidative/carbonyl damage associated with sporadic PD. As well, abnormal microtubule dynamics and tubulin polymerization are associated with several neurodegenerative diseases including frontotemporal dementia and parkinsonism linked to chromosome 17. Here we show that familial PD-associated mutant UCH-L1 and carbonyl-modified UCH-L1 display shared aberrant properties: compared with wild-type UCH-L1, they exhibit increased insolubility and elevated interactions with multiple proteins, which are characteristics of several neurodegenerative diseases-linked mutants. Circular dichroism analyses suggest similar structural changes in both UCH-L1 variants. We further report that one of the proteins interacting with UCH-L1 is tubulin, and that aberrant interaction of mutant or carbonyl-modified UCH-L1 with tubulin modulates tubulin polymerization. These findings may underlie the toxic gain of function by mutant UCH-L1 in familial PD. Our results also suggest that the carbonyl modification of UCH-L1 and subsequent abnormal interactions of carbonyl-modified UCH-L1 with multiple proteins, including tubulin, constitute one of the causes of sporadic PD.

Discovery of a novel type of autophagy targeting RNA

Regulated degradation of cellular components by lysosomes is essential to maintain biological homeostasis. In mammals, three forms of autophagy, macroautophagy, microautophagy and chaperone-mediated autophagy (CMA), have been identified. Here, we showed a novel type of autophagy, in which RNA is taken up directly into lysosomes for degradation. This pathway, which we term “RNautophagy,” is ATP-dependent, and unlike CMA, is independent of HSPA8/Hsc70. LAMP2C, a lysosomal membrane protein, serves as a receptor for this pathway. The cytosolic tail of LAMP2C specifically binds to almost all total RNA derived from mouse brain. The cytosolic sequence of LAMP2C and its affinity for RNA are evolutionarily conserved from nematodes to humans. Our findings shed light on the mechanisms underlying RNA homeostasis in higher eukaryotes.

On the central controller: Characterizations via differential games and LEQG control problems

Abstract We provide a game-theoretic interpretation to the central controller, which plays a central role in characterizing all controllers achieving disturbance attenuation in the sense of the H ∞ - norm , in the imperfect observation case. We also establish a direct relation between the central controller and the stationary LEQG controller for continuous time systems.

Direct uptake and degradation of DNA by lysosomes

Lysosomes contain various hydrolases that can degrade proteins, lipids, nucleic acids and carbohydrates. We recently discovered “RNautophagy,” an autophagic pathway in which RNA is directly taken up by lysosomes and degraded. A lysosomal membrane protein, LAMP2C, a splice variant of LAMP2, binds to RNA and acts as a receptor for this pathway. In the present study, we show that DNA is also directly taken up by lysosomes and degraded. Like RNautophagy, this autophagic pathway, which we term “DNautophagy,” is dependent on ATP. The cytosolic sequence of LAMP2C also directly interacts with DNA, and LAMP2C functions as a receptor for DNautophagy, in addition to RNautophagy. Similarly to RNA, DNA binds to the cytosolic sequences of fly and nematode LAMP orthologs. Together with the findings of our previous study, our present findings suggest that RNautophagy and DNautophagy are evolutionarily conserved systems in Metazoa.

A new LMI approach to analysis of linear systems with scheduling parameter reduction to finite number of LMI conditions

In previous results on analysis and design of scheduled control for linear systems with scheduling parameter, parametrically-dependent LMI conditions characterize internal stability and L/sup 2/ gain performance. In this article, the parametrically-dependent LMI condition is reduced to a finite number of parametrically-independent LMI conditions. By applying this approach, actual analysis and actual design of the scheduled control for linear systems with scheduling parameter is feasible by means of a finite number of computations.

Memory state feedback control synthesis for linear systems with time delay via a finite number of linear matrix inequalities

Abstract In this paper, we consider a synthesis problem of delay-dependent memory state feedback control which stabilizes linear time-delay systems. First we derive conditions for stability analysis and controller synthesis in the form of infinite-dimensional (parameter-dependent) linear matrix inequalities (LMIs), while infinite dimensionality of the LMIs may lead to less conservative results, but makes the conditions difficult to use. Second we show a technique to reduce the infinite-dimensional LMIs to a finite number of LMIs. A numerical example is given to demonstrate out approach.

A new LMI approach to analysis of linear systems depending on scheduling parameter in polynomial forms

This paper proposes a new LMI approach to analysis of linear systems depending on scheduling parameter in polynomial forms: we first propose a method to reduce the parameter dependent LMI condition, which characterizes internal stability and L2 gain, to the finite number of LMI conditions by introducing a convex polyhedron which includes a polynomial curve parameterized by scheduling parameter; next we propose a systematic procedure to construct the convex polyhedron. Our approach enable us to analyze L2 gain of linear systems with scheduling parameter in polynomial forms through computation of the finite number of LMIs. To show efficacy of our approach, we finally make a numerical experiment of L2 gain analysis for a gasturbine engine model which is described as a linear system with a scheduling parameter in polynomial form of two degree.