The F-12 series aircraft approach to design for control system reliability

The F-12 series aircraft control system design philosophy is reviewed as it pertains to functional reliability. The basic control system, i.e., cables, mixer, feel system, trim devices, and hydraulic systems are described and discussed. In addition, the implementation of the redundant stability augmentation system in the F-12 aircraft is described. Finally, the functional reliability record that has been achieved is presented

Aspectos gerais da fotossensibilizacao hepatogena em bovinos.

A sensibilização da pele a luz devido, geralmente, a ação de certas doenças, plantas ou outras substancias, e denominada fotossensibilizacao (Stedman's Medical 1972). O primeiro registro sobre a ocorrência de fotossensibilizacao hepatogena em bovinos mantidos em pastagens de Brachiaria decumbens, na América do Sul, foi feito na Venezuela (Centro Internacional de Agricultura Tropical 1975), onde a doença ocasionou a morte de doze garrotes nos primeiros dias de pastejo. No Brasil, Hutton (s.d.lL) fez observações sobre casos desta doença no gado Nelore, em pastagens de B. decumbens, em Rio Verde de Goiás. O surto acometeu, principalmente, bezerros antes e depois da desmama. Alem desta primeira constatação, vários outros autores descreveram esta doença em bovinos em pastagem de B. decumbens.bitstream/item/138531/1/COT-19.pdfCNPG

Virtual Testing of Experimental Continuation

We present a critical advance in experimental testing of nonlinear structures. Traditional quasi-static experimental methods control the displacement or force at one or more load-introduction points on a structure. This approach is unable to traverse limit points in the control parameter, as the immediate equilibrium beyond these points is statically unstable, causing the structure to snap to another equilibrium. As a result, unstable equilibria---observed numerically---are yet to be verified experimentally. Based on previous experimental work, and a virtual testing environment developed herein, we propose a new experimental continuation method that can path-follow along unstable equilibria and traverse limit points. To support these developments, we provide insightful analogies between a fundamental building block of our technique---shape control---and analysis concepts such as the principle of virtual work and Galerkin's method. The proposed testing method will enable the validation of an emerging class of nonlinear structures that exploit instabilities for novel functionality

Shape Control for Experimental Continuation

An experimental method has been developed to locate unstable equilibria of nonlinear structures quasi-statically. The technique involves loading a structure by application of either a force or a displacement at a main actuation point, while simultaneously controlling the overall shape using additional probe points. The method is applied to a shallow arch, and unstable segments of its equilibrium path are identified experimentally for the first time. Shape control is a fundamental building block for the experimental---as opposed to numerical---continuation of nonlinear structures, which will significantly expand our ability to measure their mechanical response.Comment: Updated Figure 6 experimental results with correct calibration factor for linear transducer. Updated Figure 6 finite element results with correct load multiplier for half-model. Updated paper text to reflect these changes. 5 pages, 6 figure

A mathematical model of wheelchair racing

Wheelchair racing strokes are very complicated movements, which involve a coupling between the athlete and his or her racing chair. Each body segment, as well as the wheel, follows a distinct trajectory as the motion is performed. Understanding the kinematics and kinetics of various stroke techniques would provide the athletes and their coaches with information, which could help guide the racers toward improved performances. In this thesis, a mathematical model is developed, which is capable of providing such valuable kinematic and kinetic information. This two-dimensional model represents the body segments as a coupled pendulum system of point masses and the wheel as a distributed-mass disk. Furthermore, the model incorporates several fundamental assumptions, including that the stroke cycle can be divided into an arbitrary number of consecutive ballistic phases such that segment positions are continuous at phase boundaries. Each phase is mathematically a second-order, nonlinear ordinary boundary value problem (BVP). Numerical methods are used to solve the BVPs independently, resulting in velocity discontinuities at the phase boundaries. These instantaneous velocity increases or decreases must be caused by impulsive forces. In turn, these impulsive forces are interpreted as muscular input and/or physical impacts. In this research, the model is used to produce numerous stroke techniques, which are consistent with a given racer\u27s structural parameters and prescribed stroke characteristics (racing speed, cycle time, recovery cycle time, the athlete\u27s orientation in the racing chair, and wheel contact and release angles). The kinematics of these different techniques are contrasted. In addition, the muscular mechanical energy costs of these strokes are determined and an interpretation as to the mechanical energy efficiency of each technique is given. The model is used to provide insight into the intricacies of an actual wheelchair racing stroke. In this thesis, the kinematics and energetics of model-produced techniques guide the analysis of these characteristics of an empirical stroke. One conclusion of this analysis is that this model may be able to provide more mechanically efficient alternative strokes from which the athlete can choose. Finally, suggestions are offered toward improving the model

Consequences of Secondary Calibrations on Divergence Time Estimates

Secondary calibrations (calibrations based on the results of previous molecular dating studies) are commonly applied in divergence time analyses in groups that lack fossil data; however, the consequences of applying secondary calibrations in a relaxed-clock approach are not fully understood. I tested whether applying the posterior estimate from a primary study as a prior distribution in a secondary study results in consistent age and uncertainty estimates. I compared age estimates from simulations with 100 randomly replicated secondary trees. On average, the 95% credible intervals of node ages for secondary estimates were significantly younger and narrower than primary estimates. The primary and secondary age estimates were significantly different in 97% of the replicates after Bonferroni corrections. Greater error in magnitude was associated with deeper than shallower nodes, but the opposite was found when standardized by median node age, and a significant positive relationship was determined between the number of tips/age of secondary trees and the total amount of error. When two secondary calibrated nodes were analyzed, estimates remained significantly different, and although the minimum and median estimates were associated with less error, maximum age estimates and credible interval widths had greater error. The shape of the prior also influenced error, in which applying a normal, rather than uniform, prior distribution resulted in greater error. Secondary calibrations, in summary, lead to a false impression of precision and the distribution of age estimates shift away from those that would be inferred by the primary analysis. These results suggest that secondary calibrations should not be applied as the only source of calibration in divergence time analyses that test time-dependent hypotheses until the additional error associated with secondary calibrations is more properly modeled to take into account increased uncertainty in age estimates

Prometheus en Demeter

Rede Wageninge

Collision-free inverse kinematics of a 7 link cucumber picking robot

The paper presents results of research on inverse kinematics algorithms to be used in a functional model of a cucumber harvesting robot consisting of a redundant manipulator with one prismatic and six rotational joints (P6R). Within a first generic approach, the inverse kinematics problem was reformulated as a non-linear programming problem and solved with a generic algorithm. Solutions were easily obtained, but the considerable calculation time needed to solve the problem prevented on line implementation. To circumvent this problem, a second, less generic approach was developed consisting of a mixed numerical-analytic solution of the inverse kinematics problem exploiting the particular structure of the P6R manipulator. This approach facilitated rapid and robust calculation of the inverse kinematics of the cucumber harvester. During the early stages of the cucumber harvesting project, this inverse kinematics algorithm was used to off-line evaluate the ability of the robot to harvest cucumbers using 3D-information of a cucumber crop obtained in a real greenhouse. Thereafter, the algorithm was employed successfully in a functional model of the cucumber harvester to determine if cucumbers were hanging within the reachable workspace of the robot and to determine a collision-free harvest posture to be used for motion control of the manipulator during harvesting

Avoiding unseen obstacles : Subcortical vision is not sufficient to maintain normal obstacle avoidance behaviour during reaching

Acknowledgement This work was funded by the RS MacDonald Charitable Trust (awarded to C. Hesse in June 2013). T. Schenk was supported by a grant from the German Research Council (DFG – SCHE 735/3-1). The authors would like to thank Dr Stefanie Biehl for her valuable advice on lesion localisation based on the CT and MRI scans of the patients. We would also like to thank all the patients for taking part in our experiments and for giving up so much of their free time.Peer reviewedPostprin