Online identification and nonlinear control of the electrically stimulated quadriceps muscle

A new approach for estimating nonlinear models of the electrically stimulated quadriceps muscle group under nonisometric conditions is investigated. The model can be used for designing controlled neuro-prostheses. In order to identify the muscle dynamics (stimulation pulsewidth-active knee moment relation) from discrete-time angle measurements only, a hybrid model structure is postulated for the shank-quadriceps dynamics. The model consists of a relatively well known time-invariant passive component and an uncertain time-variant active component. Rigid body dynamics, described by the Equation of Motion (EoM), and passive joint properties form the time-invariant part. The actuator, i.e. the electrically stimulated muscle group, represents the uncertain time-varying section. A recursive algorithm is outlined for identifying online the stimulated quadriceps muscle group. The algorithm requires EoM and passive joint characteristics to be known a priori. The muscle dynamics represent the product of a continuous-time nonlinear activation dynamics and a nonlinear static contraction function described by a Normalised Radial Basis Function (NRBF) network which has knee-joint angle and angular velocity as input arguments. An Extended Kalman Filter (EKF) approach is chosen to estimate muscle dynamics parameters and to obtain full state estimates of the shank-quadriceps dynamics simultaneously. The latter is important for implementing state feedback controllers. A nonlinear state feedback controller using the backstepping method is explicitly designed whereas the model was identified a priori using the developed identification procedure

Interstate Differences in Employer Tax Costs and Worker Benefits of Unemployment Insurance: A Micro-Simulation Approach

This study compares employer unemployment insurance (UI) tax costs and worker UI benefits across the 28 largest industrial states for 1988. The comparison is done using a detailed computerized micro-simulation model which computes the worker UI benefits and employer UI taxes for each state. Assumed characteristics of employers and employees are held constant across the states so that differences in UI costs and benefits among the states can be attributed entirely to differences in UI statutes. The principal findings of this study are: (1) the UI system can be modeled fruitfully at the firm level, (2) there are significant UI tax differentials across states attributable to statutory provisions, (3) UI tax differentials vary by type of employer, and (4) there is at least one significant regional difference: UI taxes are generally lower in Southern states

First time determination of the microscopic structure of a stripe phase: Low temperature NMR in La2NiO4.17

The experimental observations of stripes in superconducting cuprates and insulating nickelates clearly show the modulation in charge and spin density. However, these have proven to be rather insensitive to the harmonic structure and (site or bond) ordering. Using 139La NMR in La2NiO4.17, we show that in the 1/3 hole doped nickelate below the freezing temperature the stripes are strongly solitonic and site ordered with Ni3+ ions carrying S=1/2 in the domain walls and Ni2+ ions with S=1 in the domains.Comment: 4 pages including 4 figure

Job Growth in Early Transition: Comparing Two Paths

Small start-up firms are the engine of job creation in early transition and yet little is known about the characteristics of this new sector. We seek to identify patterns of job growth in this sector in terms of niches left from central planning and ask about differences in job creation across two different transition economies: Estonia, which experienced rapid destruction of the pre-existing firms, and the Czech Republic, which reduced the old sector gradually. We find job growth within industries to be quantitatively more important than job growth due to across-industry reallocation. Furthermore, the industrial composition of startups is strikingly similar in the two countries. We offer convergence to "western" industry firm-size distributions as an explanation. We also find regularities in wage evolution across new and old firms, including small differences in job quality across the two transition paths.http://deepblue.lib.umich.edu/bitstream/2027.42/39888/3/wp503.pd

Creep and Creep-Recovery Models for Wood Under High Stress Levels

Forty small clear southern pine specimens were loaded under third-point bending to examine creep and creep-recovery behavior for wood under high stress levels. Stress levels of between 69% and 91% of the predicted static strength were applied for 23 h with 1 h allowed for recovery, and the resulting deflection vs. time behavior was studied. The experimental creep and creep-recovery behavior was modeled using modified power law functions. The results indicate that these functions provide the best fit to both primary and secondary experimental data. The empirical models can be used to simulate the viscoelastic behavior of wood under high stress levels. The simulation will provide a useful tool in future studies to examine duration-of-load (DOL) effect, which is one of the more important factors in wood structural design

Spatial patterns of desynchronization bursts in networks

We adapt a previous model and analysis method (the {\it master stability function}), extensively used for studying the stability of the synchronous state of networks of identical chaotic oscillators, to the case of oscillators that are similar but not exactly identical. We find that bubbling induced desynchronization bursts occur for some parameter values. These bursts have spatial patterns, which can be predicted from the network connectivity matrix and the unstable periodic orbits embedded in the attractor. We test the analysis of bursts by comparison with numerical experiments. In the case that no bursting occurs, we discuss the deviations from the exactly synchronous state caused by the mismatch between oscillators