Stabilization of Cascaded Two-Port Networked Systems Against Nonlinear Perturbations

A networked control system (NCS) consisting of cascaded two-port communication channels between the plant and controller is modeled and analyzed. Towards this end, the robust stability of a standard closed-loop system in the presence of conelike perturbations on the system graphs is investigated. The underlying geometric insights are then exploited to analyze the two-port NCS. It is shown that the robust stability of the two-port NCS can be guaranteed when the nonlinear uncertainties in the transmission matrices are sufficiently small in norm. The stability condition, given in the form of "arcsin" of the uncertainty bounds, is both necessary and sufficient.Comment: 8 pages, in preparation for journal submissio

Generation of Choline for Acetylcholine Synthesis by Phospholipase D Isoforms

DEDICATION: This article is dedicated to the memory of Sue Kim Hanson, a graduate student in the department of Pathology and Laboratory Medicine at Boston University School of Medicine, who perished in the terrorist attacks of September 11, 2001. BACKGROUND: In cholinergic neurons, the hydrolysis of phosphatidylcholine (PC) by a phospholipase D (PLD)-type enzyme generates some of the precursor choline used for the synthesis of the neurotransmitter acetylcholine (ACh). We sought to determine the molecular identity of the relevant PLD using murine basal forebrain cholinergic SN56 cells in which the expression and activity of the two PLD isoforms, PLD1 and PLD2, were experimentally modified. ACh levels were examined in cells incubated in a choline-free medium, to ensure that their ACh was synthesized entirely from intracellular choline. RESULTS: PLD2, but not PLD1, mRNA and protein were detected in these cells and endogenous PLD activity and ACh synthesis were stimulated by phorbol 12-myristate 13-acetate (PMA). Introduction of a PLD2 antisense oligonucleotide into the cells reduced PLD2 mRNA and protein expression by approximately 30%. The PLD2 antisense oligomer similarly reduced basal- and PMAstimulated PLD activity and ACh levels. Overexpression of mouse PLD2 by transient transfection increased basal- (by 74%) and PMA-stimulated (by 3.2-fold) PLD activity. Moreover, PLD2 transfection increased ACh levels by 26% in the absence of PMA and by 2.1-fold in the presence of PMA. Overexpression of human PLD1 by transient transfection increased PLD activity by 4.6-fold and ACh synthesis by 2.3-fold in the presence of PMA as compared to controls. C: These data identify PLD2 as the endogenous enzyme that hydrolyzes PC to generate choline for ACh synthesis in cholinergic cells, and indicate that in a model system choline generated by PLD1 may also be used for this purpose.National Institute on Aging (AG09525

Robust multi-clue face tracking system

In this paper we present a multi-clue face tracking system, based on the combination of a face detector and two independent trackers. The detector, a variant of the Viola-Jones algorithm, is set to generate very low false positive error rate. It initiates the tracking system and updates its state. The trackers, based on 3DRS and optical flow respectively, have been chosen to complement each other in different conditions. The main focus of this work is the integration of the two trackers and the design of a closed loop detector-tracker system, aiming at achieving superior robustness at real-time operation on a PC platform. Tests were carried out to assess the actual performance of the system. With an average of about 95% correct face location rate and no significant false positives, the proposed approach appears to be particularly robust to complex backgrounds, ambient light variation, face orientation and scale changes, partial occlusions, different\ud facial expressions and presence of other unwanted faces

Accurate and stable numerical methods for solving micro heat transfer models in an N-carrier system in spherical coordinates

Energy exchange between electrons and phonons in metal provides the best example in describing non-equilibrium heating during the ultrafast transient. In times comparable to the thermalization and relaxation time of electrons and phonons, which are in the range of a few to several tens of picoseconds, heat continuously flows from hot electrons to cold phonons through mutual collisions. Consequently, electron temperature continuously decreases whereas phonon temperature continuously increases until thermal equilibrium is reached. Tien developed the well-known parabolic two-step model for describing the non-equilibrium heating in the electron-phonon system in 1992, and Tzou developed the parabolic model for the non-equilibrium heating in an N-carrier system in one-dimensional (1D) Cartesian coordinates in 2009. In the early 1990s, it was discovered that biological tissue, along with a number of other common materials, exhibits a relatively long thermal relaxation (or lag) time before equilibrium heating. Because a biological cell may contain proteins, water, and dissolved minerals, the non-equilibrium heating may also exist in the biological cell when exposed to ultrafast heating. This dissertation considers the generalized micro heat transfer models in an N-carrier system with the Neumann boundary condition in 1D and three-dimensional (3D) spherical coordinates, which can be applied to describe the non-equilibrium in biological cells. The generalized models in 1D and 3D spherical coordinates are shown to be well-posed. An improved unconditionally stable Crank-Nicholson (CN) scheme is presented for solving the generalized model in 1D spherical coordinates, where a second-order accurate finite difference scheme for the Neumann boundary condition is developed so that the overall truncation error of the 1D improved CN scheme is second-order. Two improved unconditionally stable CN schemes are then presented for solving the generalized model in 3D spherical coordinates. In particular, two second-order accurate finite difference schemes for the Neumann boundary condition are developed so that overall truncation errors of 3D improved CN schemes are second-order with respect to the spatial variable r. The stability of the 1D improved CN scheme and two 3D improved CN schemes is proved. The convergence rates of the solution of the 1D improved CN scheme are calculated by a numerical example. Results show that the convergence rates of the 1D improved CN scheme are about 2 with respect to both spatial and temporal variables respectively, while the convergence rates of the CN scheme with the convectional scheme for the Neumann boundary condition are about 1 and about 2 with respect to the spatial and temporal variables, respectively. The convergence rates of the numerical solution of two 3D improved CN schemes are calculated by two examples. Results show that the convergence rate of both 3D improved CN schemes are about 2 with respect to the spatial variable r, while the convergence rate of the 3D CN scheme is about 1 with respect to the spatial variable r