Instability analysis and improvement of robustness of adaptive control

The effects of unmodeled high frequency dynamics and bounded disturbances on stability and performance of adaptive control schemes are analyzed. Five possible types of instability mechanisms—parameter drift, ‘linear’ instability, ‘fast adaptation’ instability, ‘high frequency’ instability, and ‘throughput’ instability—are analyzed using simple examples. A procedure is used to construct Lyapunov-like functions for a modified adaptive controller applied to a dominant plant of relative degree one, in the presence of parasitics and disturbances, and obtain sufficient conditions under which none of the five types of instability can occur. The modified scheme is robust in the sense that it guarantees the existence of a large region of attraction from which all the trajectories remain bounded and the state errors converge exponentially to a much smaller residual set. The size of the region of attraction depends on the speed of parasitics in such a way that as the parasitics become infinitely fast, the region of attraction becomes the whole space.     

Branch Network and Modular Service Optimization for Community Banking

In the information society, what is clearly changing is the role and image of bank branches in order to satsify in a more efficient way customers' needs. This paper develops an integrated approach to assist the bank's management in reconfiguring a branch network according to the dictates of the market. We are seeking the optimum number of branches and the optimum mix of services that each branch should offer in order to maximize the revenue–generating measures of the branches within a community. The problem is modeled using a linear program that accounts for community performance as a function of performance variables that are explained by a set of external and internal factors, which reflect community characteristics and modular branch banking parameters, respectively. The relationships between factor and performance variables are identified using regression analysis. An iterative algorithm allows convergence to a solution that provides the best configuration of branches after all possible branch mergers and modular branch adjustments are accomplished.     

Properties of ultra-thin wafer-bonded silicon-on-insulator MOSFET's

Strong interface coupling effects on the subthreshold and transconductance characteristics have been experimentally observed and analytically modeled. For total depletion, the subthreshold swing reaches a nearly ideal value. The front channel subthreshold slope of ultrathin MOSFETs is very sensitive to the density of states at the buried Si-SiO₂ interface so that a thicker fully depleted film is preferable when the quality of this interface is poor. The transconductance reaches a maximum for total depletion. Simple theoretical models are proposed which explain the substantial variations of the transconductance and subthreshold slope as the opposite interface is scanned from inversion to total depletion and accumulation. These MOSFETs behave very well and demonstrate that high carrier mobilities and low densities of defects can be obtained at both interfaces even in ultrathin silicon-on-insulator (SOI) structures     

Effect of Floating-Body and Stress Bias on NBTI and HCI on 65-nm SOI pMOSFETs

Grounded-body (GB) core-logic/high-speed (HS) and input/output (I/O) silicon-on-insulator pMOSFETs from 65-nm technology are shown to degrade more than floating-body (FB) devices under negative bias temperature instability (NBTI) stress. However, in both cases, worst case degradation occurs when stressed under equal gate and drain voltages (V_g = V_d), whereby degradation is simultaneously induced by both NBTI and hot carrier injection (HCI) simultaneously ("concurrent HCI-NBTI"), the relative importance of each mechanism depending on the type of device and the bias level. The degradation of I/O pMOSFETs stressed under V_g = V_d at room temperature shows predominantly NBTI-like behavior at higher stress voltages, whereas it shows concurrent HCI-NBTI behavior at lower stress voltages. By contrast, the degradation of HS pMOSFETs stressed under V_g = V_d shows concurrent HCI-NBTI behavior over the entire stress bias range. In both cases, FB devices degrade more than GB devices for higher stress voltage values, but the FB effects weaken and the degradations become comparable for lower stress bias.     

Inclusive access to emergency services: an action research project focused on hearing-impaired citizens

Universal Access in the Information Society - In case of emergency, hearing-impaired people are not always able to access emergency services, and hence, they do not have equal access to social...     

SEM—EBIC studies of boron implanted silicon

Known SEM-EBIC techniques based on Schottky diode and p-n junction charge collectors are modified or further developed in order to study the radiation damage and the minority carrier diffusion length and lifetime in boron implanted silicon, and their annealing behaviour.     

Adaptive control of linear time-varying plants: a new modelreference controller structure

The problem of developing a control law which can force the output of a linear time-varying plant to track the output of a stable linear time-invariant reference model is discussed. It is shown that the standard model reference controller, used for linear time-invariant plants, cannot guarantee zero tracking error in general when the plant is time-varying. A new model reference controller is proposed which guarantees stability and zero tracking error for a general class of linear time-varying plants with known parameters. When the time-varying plant parameters are unknown but vary slowly with time, it is shown that the new controller can be combined with a suitable adaptive law so that all the signals in the closed loop remain bounded for any bounded initial conditions and the tracking error is small in the mean. The assumption of slow parameter variations in the adaptive case can be relaxed if some information about the frequency or the form of the fast varying parameters is available a priori. Such information can be incorporated in an appropriately designed adaptive law so that stability and improved tracking performance is guaranteed for a class of plants with fast varying parameters     

Improving Endurance and Range of a UGV with Gimballed Landing Platform for Launching Small Unmanned Helicopters

Design specifications for a high-endurance and range unmanned ground vehicle (UGV) with a gimballed landing platform on top of it for takeoff/landing, transporting to the target area and recharging of small/miniature unmanned helicopters are presented and justified. Specification constraints include UGV strict payload limitations, limited free space affecting power supply availability that impacts on-board available energy, limited endurance and operational range, as well as limitations and restrictions related to electric and non-electric small unmanned vertical takeoff and landing (VTOL) vehicles, similar to those of UGV with the most important being limited flying time. Focusing on the All Terrain Robot Vehicle (ATRV-Jr) UGV and a helicopter of the size of the Maxi Joker 2 as a testbed, a detailed analysis of component power consumption reveals reasons for reduced runtime and operational range. After a comparative study of state of the art power supply and battery technologies, a hybrid battery configuration is proposed that improves more than 500% the manufacturer-specified ATRV-Jr endurance (or 1,000% the currently used custom-made ATRV-Jr endurance) by considering: (1) optimum design with weight, volume, runtime and rechargeability being major restrictions and concerns, and (2) use of lower power sensors and processors without affecting UGV functionality and operability. A sun-tracking solar array that collects and stores energy is integrated with the UGV gimballed landing platform. Simulations demonstrate the validity of the design. Although the testbed is specific, the design itself is generic enough and suitable for other UGV/VTOL vehicles. This work was supported by the US Army Research Office, Grant Number W91-11NF-06-1-0069 and SPAWAR, Grant Number N00039-06-C-0062.