Design and nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.     

Fault identification for robot manipulators

Several factors must be considered for robotic task execution in the presence of a fault, including: detection, identification, and accommodation for the fault. In this paper, a nonlinear observer is used to identify a class of actuator faults once the fault has been detected by some other method. Advantages of the proposed fault-identification method are that it is based on the nonlinear dynamic model of a robot manipulator (and hence, can be extended to a number of general Euler Lagrange systems), it does not require acceleration measurements, and it is independent from the controller. A Lyapunov-based analysis is provided to prove that the developed fault observer converges to the actual fault. Experimental results are provided to illustrate the performance of the identification method.     

Schottky barrier formation at nonpolar Au/GaN epilayer interfaces

A new approach to studying Schottky barrier formation on a nanometer scale is demonstrated using both Auger electron spectroscopy core level shift and secondary electron threshold work function measurements on cleaved epilayers. Band bending induced by metallization of cleaved epilayer surfaces can be investigated without introducing defects due to chemical or ion beam surface cleaning. For GaN epilayers, this approach also avoids complications due to piezoelectric effects on polar-axis growth surfaces. Initial investigations of Au and Ag Schottky contact formation on GaN in ultrahigh vacuum reveal the presence of a pinning level ∼1.7 eV above the valence band edge.     

Lime-Soda Softening Process Modifications for Enhanced NOM Removal

In this research, a number of process modifications to the lime-soda softening process were examined, including utilization of high Mg-content lime, addition of MgCl2, and the recycling of softening sludge, in order to improve the removal of natural organic matter (NOM) and reduce the formation of disinfection byproducts (DBPs). Jar test results showed that dissolved organic carbon (DOC) removal increased and trihalomethane (THM) formation was reduced as the magnesium in hydrated lime increased, and was directly correlated with the amount of magnesium removed from the system. However, a dolomitic quick lime hydrated under atmospheric conditions resulted in less effective DOC removal due to a lack of available Mg, and subsequently, less co-precipitation of Mg(OH)2-NOM complexes. The addition of MgCl2 to the raw water also increased DOC removal and reduced THM formation in both the presence and absence of softening sludge, with DOC removal increasing as softening sludge and magnesium dosages increased. As high as 43% removal of DOC was achieved at the stoichoimetric lime-soda ash dose in the presence of 457 mg/L sludge and 7.5 mg/L MgCl2, as compared to only 13% removal in the absence of sludge and MgCl2. The recycling of softening sludge had little or no effect on the hardness and the level of inorganic elements in treated water. The results presented here provide new approaches for improving DBP precursor removal during lime-soda softening without significantly increasing lime and soda ash dosage or the generation of waste sludge.     

Practical Kinematics for Real-Time Implementation of Continuum Robots

This paper introduces three algorithms which are essential for the practical, real-time implementation of continuum robots. Continuum robots lack the joints and links which compose traditional and high-degree-of-freedom robots, instead relying on finite actuation mechanisms to shape the robot into a smooth curve. Actuator length limits shape the configuration or joint space of continuum manipulators, introducing couplings analyzed in this paper which must be understood to make effective use of continuum robot hardware. Based on the new understanding of the configuration space uncovered, this paper then derives the workspace of continuum robots when constrained by actuator length limits. Finally, a tangle/untangle algorithm correctly computes the shape of the distal segments of multisection tendon-actuated continuum robots. These contributions are essential for effective use of a wide range of continuum robots, and have been implemented and tested on two different types of continuum robots. Results and insight gained from this implementation are presented     

IDDQ test: will it survive the DSM challenge?

Deep-submicron technologies pose difficult challenges for I_DDQ testing in the future. The low threshold voltage used by DSM devices decreases the defect resolution of I_DDQ. However, because I_DDQ is a valuable test method, researchers are working to augment with other test parameters to prolong its effectiveness     

In-chair movement: validity, reliability and implications for measuring sitting discomfort

Sitting discomfort is traditionally evaluated with subjective rating scales which are referenced to an objective correlate (e.g. sitting posture) measured on a static (i.e. non-continuous) basis. Since sitting discomfort is dynamic in nature, it requires continuous, objective measurement. We therefore adapted an interface pressure mat to continuously record in-chair movement (ICM) as an indirect measurement of sitting discomfort by tracking the center of pressure (COP) at the buttock-chair interface. Here we report on two phases in the development of the COP system: laboratory validity and field reliability. In the laboratory study we confirmed system validity by simultaneously tracking ICM with the mat and a force platform (r2 > 0.80) and by comparing subjects' COP movement with their gross trunk movements (r2 > 0.86). In our field study we used the intraclass correlation coefficient to establish a data sampling (i.e. selection) protocol that was reliable. We collected ICM data on seated telecommunications Directory Assistance operators during 2 h field tests. Results showed that using a minimum sampling time of 5 min and then averaging a series of 5 min samples of ICM was more reliable than single discrete samples. Using the averaging protocol, we also showed that ICM increased significantly over 2 h and that ICM did not differ between trials.     

Performance and design of InGaAs /InP photodiodes for single-photon counting at 1.55 microm

The performance of selected, commercially available InGaAs/InP avalanche photodiodes operating in a photon-counting mode at an incident wavelength of 1.55 mum is described. A discussion on the optimum operating conditions and their relationship to the electric field distribution within the device is presented.     

Observation of transient disorder during myosin subfragment-1 binding to actin by stopped-flow fluorescence and millisecond time resolution electron cryomicroscopy: evidence that the start of the crossbridge power stroke in muscle has variable geometry

The mechanism of binding of myosin subfragment-1 (S1) to actin in the absence of nucleotides was studied by a combination of stopped-flow fluorescence and ms time resolution electron microscopy. The fluorescence data were obtained by using pyrene-labeled actin and exhibit a lag phase. This demonstrates the presence of a transient intermediate after the collision complex and before the formation of the stable "rigor" complex. The transient intermediate predominates 2-15 ms after mixing, whereas the rigor complex predominates at time >50 ms. Electron microscopy of acto-S1 frozen 10 ms after mixing revealed disordered binding. Acto-S1 frozen at 50 ms or longer showed the "arrowhead" appearance characteristic of rigor. The most likely explanation of the disorder of the transient intermediate is that the binding is through one or more flexible loops on the surfaces of the proteins. The transition from disordered to ordered binding is likely to be part of the force-generating step in muscle.     

Applications of differential forms to boundary integral equations

In this paper we discuss the application of differential forms to integral equations arising in the study of electromagnetic wave propagation. The usual Stratton-Chu integral equations are derived in terms of differential forms and corresponding Galerkin formulations are constructed. All numerical schemes require the specification of basis functions and the use of differential forms provides a very general method for the construction of arbitrary order basis functions on curvilinear geometries. It is noted that the lowest order approximations on flat geometries reduce to forms essential equivalent to the standard Rao-Wilton-Glisson functions. The effect on accuracy is investigated for electric field integral equation and magnetic field integral equation formulations for a range of bases. Hierarchical classes of functions are also developed, as are transition elements useful in p-adaptive schemes where variable orders of approximation are sought.