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An active mass driver has been designed for installation on the upper observation deck of the 310 m Nanjing TV transmission tower in China in order to reduce the acceleration response under strong wind gusts. In this paper, the linear quadratic Gaussian (LQG), [H.sup.[infinity]], and continuous sliding mode control (CSMC) strategies have been applied to the active mass driver system based on the acceleration feedbacks. Emphasis is placed on the practical applications of LQG, [H.sup.[infinity]], and CSMC controllers, including limitations on the actuator peak force and stroke, the limited number of sensors, and noise pollution. Further, a method for modulating the control effort for the CSMC controller is proposed in this paper to satisfy the practical constraints on the actuator. A state reduced-order system has been established to design the dynamic output feedback controllers. The wind loads acting on the tower are defined by the Davenport cross-power spectral density matrix. Simulation results demonstrate that, when designed appropriately, the LQG, [H.sup.[infinity]], and CSMC control strategies are suitable for full-scale implementations of the active mass driver, and their control performances are quite remarkable.

This study develops fuzzy control that is designed with sliding modes to achieve stability of the fuzzy controller. Fuzzy control is formulated in the form of variable structure system (VSS) control. In contrast to previous works in which Lyapunov functions are used to examine the stability, the current study investigates the stability of fuzzy control from the viewpoints of differential geometric methods and the sliding mode theory. Best values for parameters in fuzzy control rules are determined with the aid of sliding modes. In order to improve control performance, a tuning algorithm is executed to adjust parameters for dealing with uncertainties and disturbances. Both computer simulations and experiments with regard to an inverted pendulum hinged to a rotating disk are carried out to validate the proposed method. This apparatus can to some extent represent cornering motion of a motorcycle on which a rider leans to maintain stability. Effects of rider's leaning angle on both stability and handling control are examined according to Bode plots.

Recently, [H.sub.[infinity]] and sliding mode control methods have been investigated for applications to active/hybrid control of seismically excited structures. Numerical simulation results indicate that both control methods are quite promising for civil engineering applications. In the present paper, shaking table experimental tests were conducted to verify the [H.sub.[infinity]] and continuous sliding mode control methods. The test structure used was the three-story 1/4-scaled building model, equipped with an active tendon control system, which was used extensively at the State University of New York, Buffalo. Different earthquake records were used as the input excitations, including the El Centro, Pacoima, Hachinohe, and Taft. Both the full-state feedback controllers and the static output feedback controllers were used. Experimental data correlate satisfactorily with numerical simulation results. Extensive experimental results demonstrate that the [H.sub.[infinity]] and continuous sliding mode control methods, in particular the static output feedback controllers using only the measured information from a limited number of sensors installed at strategic locations without an observer, are quite promising for practical implementations of active control systems on seismically excited structures.

The use of a split-gate method aids in the formation of quantum waveguides with double-bend discontinuities in modulation-doped AlGaAs/GaAs heterojunctions. In the reduced temperature conductance of double bend quantum wires, resonance peaks are detected, which are enhanced with the enhancement in electron density and cavity. Length of the wire influences the transmission coefficient at resonance.

Controllable remanent states have been studied on the microstructured magnetic tunnel junction (MTJ) rings through magnetoresistance measurements. These rings were designed accordingly with an outer/inner diameter of 2/1 and 1/0.5 [micro]m to reveal two and one metastable states, respectively, during the magnetization reversal process on the free layer. The distinct magnetoresistance levels based on the tunneling magnetoresistance effect are associated with the relative alignment of magnetization of free layer and pinned layer. As a result, four and three controllable remanent magnetic states on the free layer were manipulated by ramping external magnetic fields, applied in the biasing direction, with various field ranges, giving rise to four and three stable mangetoresistance values at zero field. These results may provide a great potential in magnetic multibit memory applications using ring-shaped cells. Index Terms--Magnetic tunneling junction (MTJ), magnetoresistance, multibit application, ring-shaped cells.

Microstructured magnetic tunnel junction ring with outer/inner diameter of 2/1 [micro]m has been fabricated to investigate the angular dependence of magnetoresistance during magnetization reversal process. The minor loop of magnetoresistive curve reveals four distinct resistance levels associated with four magnetization configurations within the free layer throughout the magnetization reversal. The magnetoresistance decreases with increasing angle between applied external field and biasing direction, which is resulted from the relative alignment of total magnetization of pinned and free layer. An extra feature appeared in the minor loop when the external field is transverse to the biasing direction; this can be attributed to a vortex-pair formation/annihilation in the free layer. Furthermore, a series of schemes of magnetic configurations of pinned and free layers are illustrated to explain the routes of minor loops. Index Terms--Magnetization reversal, magnetoresistance, magnetoresistive devices.

A double-barrier-layer perpendicular magnetic tunneling junction (DpMTJ) structure consisting of Si substrate/Pt/GdFeCo/AlOx/GdFeCo/ FeCo/AlOx/FeCo/TbFeCo/Pt/Ti-cap was prepared by a direct current (dc) and radio frequency (RF) magnetron sputtering method. An elliptical DpMTJ element with 3.5 [micro]m x 2.5 [micro]m size was fabricated using a top-down technique. A conducting atomic force microscope (CAFM) was used to obtain I-V curves of DpMTJ structures. We obtained the magnetoresistance (MR) ratio value from measured I-V curves by applying two opposite magnetic fields value of [+ or -] 200 Oe perpendicular to the plane of film. The MR ratio was reached as high as 74% at zero applied bias voltage. Furthermore, the MR ratio decreased as bias voltage increased. It could make the DpMTJ structure to be used in the high-density MRAM devices. Index Terms--Magnetic tunneling junction (MTJ), magnetoresistance (MR).

A local magnetization reversal of Permalloy cross has been studied by using magnetoresistance measurement and magnetic force microscope. An extraordinary change of the transverse voltage correlated with the planar Hall Effect was presented and evidenced by a series of MFM images which indicates that the rotation of magnetization within the joint area contributes to the significant voltage alteration. Index Terms--Hall effect devices, magnetic force microscopy (MFM), magnetic recording, magnetoresistance.

Domain wall motion through current-induced Oersted field was investigated by magnetic force microscopy, magnetoresistance measurement, and micromagnetic simulation. Microstructured permalloy rings with nonmagnetic control leads were fabricated by means of electron beam lithography. Through variant arrangement of control lead, the generation of uniform and nonuniform Oersted fields on a single element becomes achievable. The movement of the walls within vortex-pair state, clockwise or counterclockwise, was controlled by the Oersted fields. Index Terms--Magnetic force microscopy, magnetic recording, magnetoresistance.

Microstructured magnetic tunnel junction rings have been fabricated by a top-down technique combining electron beam lithography and ion milling process. Four-terminal magnetoresistance measurements and magnetic force microscopy were used to successfully explore a four-transition process within the free layer throughout the magnetization reversal. Various magnetization configurations were identified to be the onion state, vortex-pair state, vortex state, vortex-core state, and reverse onion state. In addition, the various durations of each magnetic state observed in the magnetoresistance curve can be utilized for the study of a coupling effect between the pinned layer and the free layer. Index Terms--Fabrication, magnetic force microscopy (MFM), magnetization reversal, magnetoresistance.