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Passive Control (passive + control)

Distribution by Scientific Domains

Engineering	62%
Medical Sciences	37%

Selected Abstracts

Passive control of the flow around a square cylinder using porous media

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2004
Charles-Henri Bruneau
Abstract The passive control of bluff body flows using porous media is investigated by means of the penalization method. This method is used to create intermediate porous media between solid obstacles and the fluid in order to modify the boundary layer behaviour. The study covers a wide range of two-dimensional flows from low transitional flow to fully established turbulence by direct numerical simulation of incompressible Navier,Stokes equations. A parametric study is performed to illustrate the effect of the porous layer permeability and thickness on the passive control. The numerical results reveal the ability of porous media to both regularize the flow and to reduce the drag forces up to 30%. Copyright © 2004 John Wiley & Sons, Ltd. [source]

The effects of acute exercise on attentional bias towards smoking-related stimuli during temporary abstinence from smoking

ADDICTION, Issue 11 2009
Kate Janse Van Rensburg
ABSTRACT Rationale Attentional bias towards smoking-related cues is increased during abstinence and can predict relapse after quitting. Exercise has been found to reduce cigarette cravings and desire to smoke during temporary abstinence and attenuate increased cravings in response to smoking cues. Objective To assess the acute effects of exercise on attentional bias to smoking-related cues during temporary abstinence from smoking. Method In a randomized cross-over design, on separate days regular smokers (n = 20) undertook 15 minutes of exercise (moderate intensity stationary cycling) or passive seating following 15 hours of nicotine abstinence. Attentional bias was measured at baseline and post-treatment. The percentage of dwell time and direction of initial fixation was assessed during the passive viewing of a series of paired smoking and neutral images using an Eyelink II eye-tracking system. Self-reported desire to smoke was recorded at baseline, mid- and post-treatment and post-eye-tracking task. Results There was a significant condition × time interaction for desire to smoke, F(1,18) = 10.67, P = 0.004, eta2 = 0.36, with significantly lower desire to smoke at mid- and post-treatment following the exercise condition. The percentage of dwell time and direction of initial fixations towards smoking images were also reduced significantly following the exercise condition compared with the passive control. Conclusion Findings support previous research that acute exercise reduces desire to smoke. This is the first study to show that exercise appears to also influence the salience and attentional biases towards cigarettes. [source]

Passive control of the flow around a square cylinder using porous media

Cost-Effectiveness of Preventive Occupational Therapy for Independent-Living Older Adults

JOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 8 2002
Joel Hay PhD
OBJECTIVES: To evaluate the cost-effectiveness of a 9-month preventive occupational therapy (OT) program in the Well-Elderly Study: a randomized trial in independent-living older adults that found significant health, function, and quality of life benefits attributable to preventive OT. DESIGN: A randomized trial. SETTING: Two government-subsidized apartment complexes. PARTICIPANTS: One hundred sixty-three culturally diverse volunteers aged 60 and older. INTERVENTION: An OT group, a social activity group (active control), and a nontreatment group (passive control). MEASUREMENTS: Use of healthcare services was determined by telephone interview during and after the treatment phase. A conversion algorithm was applied to the RAND 36-item Short Form Health Survey to derive a preference-based health-related quality of life index, quality-adjusted life years (QALYs), and the incremental cost-effectiveness ratio for preventive OT relative to the combined control group. RESULTS: Costs for the 9-month OT program averaged $548 per subject. Postintervention healthcare costs were lower for the OT group ($967) than for the active control group ($1,726), the passive control group ($3,334), or a combination of the control groups ($2,593). The quality of life index showed a 4.5% QALY differential (OT vs combined control), P < .001. The cost per QALY estimates for the OT group was $10,666 (95% confidence interval = $6,747,$25,430). For the passive and active control groups, the corresponding costs per QALY were $13,784 and $7,820, respectively. CONCLUSION: In this study, preventive OT demonstrated cost-effectiveness in conjunction with a trend toward decreased medical expenditures. [source]

Virtual passive control of flexible arms with collocated and noncollocated feedback

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11 2001
Shang-Teh Wu
A novel approach to the control of flexible manipulators is proposed. The controller includes both joint-variable and tip-deflection feedback. It is shown that tip-deflection feedback transforms the original structure into new system in which the structure parameters are virtually scaled up or down. The new system can hence be easily stabilized via a strictly passive feedback law. A co-hub, lumped-parameter structure with multiple massless links is first investigated and stability conditions are developed. The results are then applied to a distributed-parameter flexible arm, which is decomposed into an equivalent lumped-parameter structure via a set of modal functions normalized in a particular way. Tip-deflection feedback is shown to be capable of enhancing control performance on a flexible arm, and stability is ensured as long as the gain associated with the noncollocated feedback satisfies a simple inequality. The stability criteria re valid independent of high-order flexible modes. © 2001 John Wiley & Sons, Inc. [source]

Delay-dependent robust passive control for a class of nonlinear systems with time-varying delays

OPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 5 2008
Jiqing Qiu
Abstract In this paper, the problem of robust passive control for a class of nonlinear systems with time-varying delays is considered. The uncertainties investigated in this paper are norm bounded and time varying, and they enter all system matrices. Based on the Lyapunov,Krasovskii functionals approach, a new robust passive control criterion is proposed in terms of linear matrix inequalities, which is dependent on the size of time delay. We also design a state feedback controller that guarantees a robust asymptotically stable and strictly passive closed-loop system for all admissible uncertainties. Finally, two numerical examples are given to illustrate the effectiveness of the developed techniques. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Optimizing the Response From a Passively Controlled Biventricular Assist Device

ARTIFICIAL ORGANS, Issue 5 2010
Nicholas Richard Gaddum
Abstract Recent studies into rotary biventricular support have indicated that inadequate left/right flow balancing may lead to vascular congestion and/or ventricular suckdown. The implementation of a passive controller that automatically adjusts left/right flow during total and partial cardiac support would improve physiological interaction. This has encouraged the development of a biventricular assist device (BiVAD) prototype that achieves passive control of the two rotary pumps' hydraulic output by way of a nonrotating double pressure plate configuration, the hub, suspended between the ventricular assist device (VAD) impellers. Fluctuations in either the VAD's inlet or outlet pressure will cause the hub to translate, and in doing so, affect each pump's hydraulic outputs. In order to achieve partial support, the floating assembly needed to respond to pathologic blood pressure signals while being insensitive to residual ventricular function. An incorporated mechanical spring,mass,damper assembly affects the passive response to optimize the dynamic interaction between the prototype and the supported cardiovascular system. It was found that increasing the damping from a medium to a high level was effective in filtering out the higher frequency ventricular pressure signals, reducing a modified amplitude ratio by up to 72%. A spring response was also identified as being inherent in the passive response and was characterized as being highly nonlinear at the extremes of the floating assembly's translation range. The results from this study introduce a new means of BiVAD control as well as the characterization of a fully passive mechanical physiological controller. [source]