Active versus passive damping in large flexible structures

Optimal passive and active damping control can be considered in the context of a general control/structure optimization problem. Using a mean square output response approach, it is shown that the weight sensitivity of the active and passive controllers can be used to determine an optimal mix of active and passive elements in a flexible structure

A disturbance based control/structure design algorithm

Some authors take a classical approach to the simultaneous structure/control optimization by attempting to simultaneously minimize the weighted sum of the total mass and a quadratic form, subject to all of the structural and control constraints. Here, the optimization will be based on the dynamic response of a structure to an external unknown stochastic disturbance environment. Such a response to excitation approach is common to both the structural and control design phases, and hence represents a more natural control/structure optimization strategy than relying on artificial and vague control penalties. The design objective is to find the structure and controller of minimum mass such that all the prescribed constraints are satisfied. Two alternative solution algorithms are presented which have been applied to this problem. Each algorithm handles the optimization strategy and the imposition of the nonlinear constraints in a different manner. Two controller methodologies, and their effect on the solution algorithm, will be considered. These are full state feedback and direct output feedback, although the problem formulation is not restricted solely to these forms of controller. In fact, although full state feedback is a popular choice among researchers in this field (for reasons that will become apparent), its practical application is severely limited. The controller/structure interaction is inserted by the imposition of appropriate closed-loop constraints, such as closed-loop output response and control effort constraints. Numerical results will be obtained for a representative flexible structure model to illustrate the effectiveness of the solution algorithms

The effects of extended wear soft contact lenses on contrast sensitivity

This study was conducted to evaluate the long-term effects of soft contact lens extended wear on visual function as measured by contrast sensitivity . Contrast sensitivity measurements were taken at 6 spatial frequencies on 39 subjects when corrected with spectacle lenses and extended wear so f t lenses . The three types of contact lenses used (CS I-T, Hydrocurve II-55, Permaflex) represented low (38%), medium (55%), and high (74%) water content s . Measured amounts of residual refractive error were corrected using a trial frame and lenses and a Clason slide and projector was used to obtain a more precise determination of Snellen acuity. All subjects had vision correctable to 20/20 or better. Data were taken on nine occasions during a five month period to investigate the effect of time upon contrast sensitivity. Two way analysis of variance for repeated measures revealed statistically significant decreases in contrast sensitivity at several of the spatial frequencies tested, or all three lens types used. Although a combined effect of the cornea and the contact lens was present in some cases, the chief cause for this decrease was the cornea

Atmospheric and wind modeling for ATC

The section on atmospheric modeling covers the following topics: the standard atmosphere, atmospheric variations, atmosphere requirements for ATC, and implementation of a software model for Center/Tracon Advisory System (CTAS). The section on wind modeling covers the following topics: wind data -- NOAA profiler system; wind profile estimation; incorporation of various data types into filtering scheme; spatial and temporal variation; and software implementation into CTAS. The appendices contain Matlab codes for atmospheric routines and for wind estimation

Groundspeed filtering for CTAS

Ground speed is one of the radar observables which is obtained along with position and heading from NASA Ames Center radar. Within the Center TRACON Automation System (CTAS), groundspeed is converted into airspeed using the wind speeds which CTAS obtains from the NOAA weather grid. This airspeed is then used in the trajectory synthesis logic which computes the trajectory for each individual aircraft. The time history of the typical radar groundspeed data is generally quite noisy, with high frequency variations on the order of five knots, and occasional 'outliers' which can be significantly different from the probable true speed. To try to smooth out these speeds and make the ETA estimate less erratic, filtering of the ground speed is done within CTAS. In its base form, the CTAS filter is a 'moving average' filter which averages the last ten radar values. In addition, there is separate logic to detect and correct for 'outliers', and acceleration logic which limits the groundspeed change in adjacent time samples. As will be shown, these additional modifications do cause significant changes in the actual groundspeed filter output. The conclusion is that the current ground speed filter logic is unable to track accurately the speed variations observed on many aircraft. The Kalman filter logic however, appears to be an improvement to the current algorithm used to smooth ground speed variations, while being simpler and more efficient to implement. Additional logic which can test for true 'outliers' can easily be added by looking at the difference in the a priori and post priori Kalman estimates, and not updating if the difference in these quantities is too large

North American Fauna 80

Summary of extensive surveys on Florida mangrove landbirds conducted during 2008-2011, with results quantifying distribution and estimating breeding-season abundance of mangrove landbirds

Redox stratification drives enhanced growth in a deposit-feeding invertebrate: Implications for aquaculture bioremediation

Effective and affordable treatment of waste solids is a key sustainability challenge for the aquaculture industry. Here, we investigated the potential for a deposit-feeding sea cucumber, Holothuria scabra, to provide a remediation service whilst concurrently yielding a high-value secondary product in a land-based recirculating aquaculture system (RAS). The effect of sediment depth, particle size and redox regime were examined in relation to changes in the behaviour, growth and biochemical composition of juvenile sea cucumbers cultured for 81 d in manipulated sediment systems, describing either fully oxic or stratified (oxic-anoxic) redox regimes. The redox regime was the principal factor affecting growth, biochemical composition and behaviour, while substrate depth and particle size did not significantly affect growth rate or biomass production. Animals cultured under fully oxic conditions exhibited negative growth and had higher lipid and carbohydrate contents, potentially due to compensatory feeding in response to higher micro - phyto benthic production. In contrast, animals in the stratified treatments spent more time feeding, generated faster growth and produced significantly higher biomass yields (626.89 ± 35.44 g m-2 versus 449.22 ± 14.24 g m-2; mean ± SE). Further, unlike in oxic treatments, growth in the stratified treatments did not reach maximum biomass carrying capacity, indicating that stratified sediment is more suitable for culturing sea cucumbers. However, the stratified sediments may exhibit reduced bioremediation ability relative to the oxic sediment, signifying a trade-off between remediation efficiency and exploitable biomass yiel

Effect of Training Phase on Physical and Physiological Parameters of Male Powerlifters

Longitudinal research on training and dietary practices of natural powerlifters is limited. This study investigated the effect of phases of training on physical and physiological parameters in male natural powerlifters. Nine participants completed testing at two time points: (i) preparatory phase (~3 months prior to a major competition) and (ii) competition phase (1–2 weeks from a major competition). No significant changes between training phases were found for muscle strength and power. A trend for significance was found for decreased muscle endurance of the lower body (−24.4%, p = 0.08). A significant increase in leg lean mass was found at the competition phase (2.3%, p = 0.04), although no changes for other body composition measures were observed. No change was observed for any health marker except a trend for increased urinary creatinine clearance at the competition phase (12.5%, p = 0.08). A significant reduction in training volume for the lower body (−75.0%, p = 0.04) and a trend for a decrease in total energy intake (−17.0%, p = 0.06) was observed during the competition phase. Despite modifications in training and dietary practices, it appears that muscle performance, body composition, and health status remain relatively stable between training phases in male natural powerlifters