Robust non-fragile LQ controllers: The static state feedback case

This paper describes the synthesis of non-fragile or resilient regulators for linear systems. A general framework for fragility is described using state-space methodologies, and the LQ/H₂ static state-feedback problem is examined in detail. We discuss the multiplicative structured uncertainties case, and propose remedies of the fragility problem using an optimization programming framework via matrix inequalities. A special case that leads to a convex optimization framework via linear matrix inequalities (LMIs) will be considered. The benchmark problem is taken as an example to show how special controller gain variations can affect the performance of the closed-loop system.     

Non-linear impulsive dynamical systems. Part II: Stability of feedback interconnections and optimality

In a companion paper (Nonlinear Impulsive Dynamical Systems. Part I: Stability and Dissipativity) Lyapunov and invariant set stability theorems and dissipativity theory were developed for non-linear impulsive dynamical systems. In this paper we build on these results to develop general stability criteria for feedback interconnections of non-linear impulsive systems. In addition, a unified framework for hybrid feedback optimal and inverse optimal control involving a hybrid non-linear-non-quadratic performance functional is developed. It is shown that the hybrid cost functional can be evaluated in closed-form as long as the cost functional considered is related in a specific way to an underlying Lyapunov function that guarantees asymptotic stability of the non-linear closed-loop impulsive system. Furthermore, the Lyapunov function is shown to be a solution of a steady-state, hybrid Hamilton‐Jacobi‐Bellman equation.     

Multi-month memory effects on early summer vegetative activity in semi-arid South Africa and their spatial heterogeneity

In semi-arid African regions (annual rainfall between 200 and 600 mm), variability of vegetative activity is mainly due to the rainfall of the current rainy season. In most of South Africa, the rainy season occurs from October to March. On average, vegetative activity lags rainfall by 1 to 2 months. The interannual variability in early summer (December to September) normalized difference vegetation index (NDVI) depends primarily on precipitation at the beginning (October to November) of the rainy season. However, once this primary control is removed, the residual interannual variability in NDVI highlights a double memory effect: a 1-year effect, referred to as Mem₁, and a 7- to 10-month effect, referred to as Mem₂. This article aims at better describing the influence of soil and vegetation characteristics on these two memory effects. The data sets used in this study are as follows: (1) a 19-year NDVI time series from National Oceanic and Atmospheric Administration (NOAA) satellites, (2) rainfall records from a network of 1160 rain-gauge stations compiled by the Water Research Commission (WRC), (3) vegetation types from Global Land Cover (GLC) 2000 and (4) soil characteristics from the soil and terrain database for Southern Africa (SOTERSAF). Results indicate that among 20–30% of NDVI variance that is not explained by the concurrent rainfall, one-third is explained by the two memory effects. Mem₁ is found to have maximum effect in the northwest of our study domain, near the Botswana boundary, in the South Kalahari. Associated conditions are open grasslands growing on Arenosols. Mem₁ is less important in the southeast, particularly in open grassland with shrubs growing on Cambisols. Thus, Mem₁ mainly depends on soil texture. Mem₂ is more widespread and its influence is the greatest in the centre, the south and the east of our domain. It is related to rainfall from January to April, which controls, beyond the intervening dry season, the interannual variations of NDVI (December to September) at the beginning of the next rainy season. Through these new findings, this article emphasizes again the high potential of remote-sensing techniques to monitor and understand the dynamics of semi-arid environments.     

Synthesis and characterization of chloro-sulphide glass-ceramics containing neodymium(III) ions

In this paper, we describe the preparation of Nd³⁺ doped glass-ceramics in the (GeS₂)₇₀-(Ga₂S₃)₂₀-(CsCl)₁₀ system. Neodymium has been introduced as metallic powder or incorporated as sulphide. Appropriate heat treatments of the base-glass lead to glass-ceramics with controllable crystal sizes that are transparent in the visible and infrared spectral ranges. X-ray diffraction as well as electron diffraction techniques were used to investigate the crystallization process. Differential scanning calorimetry indicates that neodymium ions are poor nucleating agents in this glass compared to erbium ions. Luminescence measurements were also performed and point out that although the ceramization process increases significantly the luminescence efficiency, the neodymium ions are only partially incorporated in the nanocrystals.     

Effects of five natural gonadotropin-releasing hormones on cell suspensions of marine bivalve gonad: stimulation of gonial DNA synthesis

Gonadotropin-releasing hormones (GnRH) constitute a family of neuropeptides which are important regulators of reproduction in vertebrates. The effect of mammalian GnRH (mGnRH), salmon GnRH, chicken GnRH-I, chicken GnRH-II, and lamprey GnRH-I on [3H]thymidine incorporation into DNA of dissociated gonadal cells of marine bivalves has been studied. The incorporation of [3H]thymidine is linear between 1.5 and 8 h of incubation. All five GnRHs significantly increased DNA synthesis in gonial cells of Crassostrea gigas. The maximal activation was about of 135-140% above control. The activation is dose dependent, over the range 10(-11) to 10(-6) M, but is modulated by the physiological condition of the cells and the stage of sexual maturity of the gonad. mGnRH has also a mitogenic effect in dissociated mantle cells of Mytilus edulis. The effect of mGnRH is blocked by a GnRH antagonist ([D-pGlu1,D-Phe2, D-Trp3,6]GnRH, 5 x 10(-6)M) in C. gigas as well as in M. edulis, suggesting that the GnRH action in the gonad is mediated by specific receptors for GnRH or GnRH-like peptides. The existence of GnRH-immunoreactive neurons and fibers in the cerebral and pedal ganglia of M. edulis was demonstrated by immunocytochemistry. They are located principally in the anterior internal area of the cerebral ganglia, close to the cerebral commissure and in the posterior part of the pedal ganglia. The presence of GnRH-responsive cells and GnRH-like immunoreactive material suggests that peptides of the GnRH-like family are present and functional in bivalve molluscs.     

Learning correct responses and errors in the Hebb repetition effect: Two faces of the same coin.

In a serial recall task, the Hebb repetition effect occurs when recall performance improves for a sequence repeated throughout the experimental session. This phenomenon has been replicated many times. Nevertheless, such cumulative learning seldom leads to perfect recall of the whole sequence, and errors persist. Here the authors report evidence that there is another side to the Hebb repetition effect that involves learning errors produced in a repeated sequence. A learning measure based on past recalls (correct or incorrect) shows that the probability of a given response increases with the number of prior occurrences of that response. The pattern of results reveals another manifestation of the Hebb repetition effect and speaks to the nature of implicit learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuroadaptive output feedback control for nonlinear nonnegative dynamical systems with actuator amplitude and integral constraints

A neuroadaptive output feedback control architecture for nonlinear nonnegative dynamical systems with input amplitude and integral constraints is developed. Specifically, the neuroadaptive controller guarantees that the control amplitude as well as the integral of the control input over a given time interval are constrained, and the physical system states remain in the nonnegative orthant of the state space. The proposed approach is used to control the infusion of the anesthetic drug propofol for maintaining a desired constant level of depth of anesthesia for noncardiac surgery in the face of infusion rate constraints and an integral drug dosing constraint over a specified time period. Copyright © 2010 John Wiley & Sons, Ltd.     

Bake induced charge gain in NOR flash cells

Charge gain, caused by localized defects in the tunnel oxide of floating gate devices, is one of the central reliability concerns of flash memory. In this work, we show that charge motion in the poly sidewall spacers of flash cells can also result in substantial charge gain, for nonoptimized processes. Data showing the time, temperature, and field dependencies of this charge gain mechanism are presented. It is shown that the threshold voltage shift caused by charge motion in the poly sidewall spacers follows the simple factorial expression: ΔV _th=C·V_fg·t^α ·e^-ϵ(a)kT/