IMECE2005-82037 ROBUST TIME-OPTIMAL COMMAND SHAPING FOR PIEZOELECTRIC ACTUATORS: STM APPLICATION

ABSTRACT A scanning tunneling microscope (STM) uses a piezoelectric actuator to perform constant-velocity scanning motion. Many feedback strategies have been proposed, but their achievable scan rate is substantially limited by the turnaround transients in the scan path. Therefore, a robust time-optimal command shaping technique with an iterative search procedure is introduced in this paper to improve the scan speed of piezoactuators, and is applicable to a general class of systems without rigid-body mode. Furthermore, a time-energy-optimal formulation is presented to reduce the in-maneuver oscillation. The hysteresis nonlinearity of piezoactuators is compensated using the proposed continuous numerical inversion algorithm. Finally, the closed-loop simulation shows the performance robustness in the presence of hysteresis cancellation error and natural frequency perturbation

Molecular velocity auto-correlation of simple liquids observed by NMR MGSE method

The velocity auto-correlation spectra of simple liquids obtained by the NMR method of modulated gradient spin echo show features in the low frequency range up to a few kHz, which can be explained reasonably well by a $t^{-3/2}$ long time tail decay only for non-polar liquid toluene, while the spectra of polar liquids, such as ethanol, water and glycerol, are more congruent with the model of diffusion of particles temporarily trapped in potential wells created by their neighbors. As the method provides the spectrum averaged over ensemble of particle trajectories, the initial non-exponential decay of spin echoes is attributed to a spatial heterogeneity of molecular motion in a bulk of liquid, reflected in distribution of the echo decays for short trajectories. While at longer time intervals, and thus with longer trajectories, heterogeneity is averaged out, giving rise to a spectrum which is explained as a combination of molecular self-diffusion and eddy diffusion within the vortexes of hydrodynamic fluctuations.Comment: 8 pages, 6 figur

Collusion Theory in Search of Robust Themes: A Comment on Switgard Feuerstein's Survey

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46450/1/10842_2005_Article_4870.pd

On economic growth and minimum wages

We offer an analysis of the existence of a positive relationship between minimum wages and economic growth in a simple one-sector overlapping generations economy where the usual Romer-typed knowledge spill-over mechanism in production represents the engine of endogenous growth, in the case of both homogeneous and heterogeneous (i.e., skilled and unskilled) labour. Assuming also the existence of unemployment benefits financed with consumption taxes not conditioned on age at a balanced budget, it is shown that minimum wages may stimulate economic growth and welfare despite the unemployment occurrence. Moreover, a growth-maximising minimum wage can exist. A straightforward message, therefore, is that a combination of minimum wage and unemployment benefit policies can appropriately be used to promote balanced growth and welfare