Unlocked Conditions Research Articles

Motion Analysis of a Frontal Plane Adaptable Prosthetic Foot.

ABSTRACT Introduction An objective of designing a prosthetic foot is to achieve the natural adaptability of the foot and ankle on various surfaces and different forms of gait. Frontal plane position of the foot relative to the shank changes with many functional aspects of gait, such as turning, stairs, and walking on uneven ground. Prosthetic foot designs have variable frontal plane adaptability. An investigation foot with a linkage with ±10° of frontal plane motion was developed to improve frontal plane response under various conditions. The purpose of this study was to compare the kinematics of locked and unlocked conditions of a frontal plane adaptable prosthetic foot and the person’s usual foot while walking forward on a level surface, on an unstable rock surface, and sidestep, using a crossover design. These different conditions result in changes in frontal plane motion in the anatomical foot and ankle, and the current study evaluates whether there are similar trends in prosthetic feet. Materials and Methods People were included if they had a unilateral below-knee amputation, intact residual limb skin, were over 16 years old, and were able to walk more than 400 m on level ground without using a walking aid and without an increase in pain. The control group was people without amputations who completed the procedures once. Participants with amputations completed forward walking on level ground, on an unstable rock surface, and sidestep with their usual foot. Then after 2 weeks of accommodation, participants repeated these tests with the investigational foot unlocked and locked. Motion analysis data were collected with a 12-camera optically based system. Primary outcomes were sagittal and frontal plane motions of the foot relative to the shank. In addition, step length, step width, and stride velocity were obtained from the kinematic measures. Paired t-tests were used for statistical inference for individual participant comparisons. Unpaired t-tests were used for comparisons between the controls and people with amputations. Results Twenty-one people with amputations and 10 controls completed the tests. Participants with amputation had 16 different usual feet. There was a wide variation in usual foot motion during forward walking, whereas investigational foot conditions showed less variability. During level walking, control subjects had more frontal plane motion than any of the foot conditions, and the unlocked had more frontal plane motion than the usual foot and locked condition. Walking across an unstable rock surface showed similar trends, with control participants having more sagittal and frontal plane ankle motion compared with any prosthetic foot condition. Also, the unlocked had statistically greater frontal plane motion than the usual foot or locked condition. Sidestep results were also consistent with other gait tests. The control participants’ sagittal plane ankle range of motion was significantly more than the prosthetic sagittal plane motion for all foot conditions, whether the prosthetic side was leading or trailing. There was significantly more frontal plane motion with the unlocked than the usual foot and locked condition when the prosthetic foot was trailing or leading. Discussion and Conclusions Wide variation in usual foot range of motions in the frontal and sagittal planes confirmed the need for additional controls when considering the effect of the linkage alone. The unlocked had increased frontal plane ranges of motion compared with the locked and the majority of usual foot for all gait conditions, including level walking. This finding demonstrated that people with amputations were functionally using the additional range of motion provided by the linkage. However, control subjects used more range of motion in both the sagittal and frontal planes for the unstable rock surface and sidestepping. Increased frontal plane range of motion did not translate into improved stride length and velocity, step width, or center of mass deviations. Clinical Relevance The person-specific functional activities should be considered when choosing a prosthetic foot. A prosthesis with frontal plane motion may be applicable for a person who moves in a sidestep pattern or on uneven ground.

Lock-in phenomenon of tip clearance flow and its influence on aerodynamic damping under specified vibration on an axial transonic compressor rotor

In this study, the lock-in phenomenon of Tip Clearance Flow (TCF) instabilities and their relationship to blade vibration are investigated numerically on an axial transonic rotor with a large tip clearance. The capabilities of simulating instability flow and lock-in phenomenon are verified on a transonic rotor and a NACA0012 airfoil by comparing with the test data, respectively. The lock-in phenomenon is first numerically confirmed that may occur to TCF instabilities when its frequency is close to the blade vibration frequency. The lock-in region becomes wider with the vibration amplitude increasing, and it is also affected by modal shapes. For the rotor at the simulation conditions in this study, the bending mode results in a wider lock-in region than the torsional mode. In the lock-in region, the phase difference between the Tip Clearance Vortex (TCV) and the blade vibration changes with the flow condition and the frequency ratio of the blade vibration and the TCV instabilities. The frequency of the TCV instabilities reduces with the mass flow decreasing. Therefore, reducing mass flow and increasing frequency ratio have similar effects on the TCV phase, which causes a significant variation on the unsteady pressure amplitude in the blade tip area. Thus, the aerodynamic damping changes significantly with the TCV phase. The aerodynamic damping displays a nonlinear relationship with the vibration amplitude, and it changes from negative to positive with the vibration amplitude increasing at the same frequency ratio. The negative damping is mainly provided by the tip area of the blade. For unlocked conditions, the period of the TCF instabilities fluctuates over time, and it cannot be directly separated by their frequency features. Inter Blade Phase Angle (IBPA) also has an important influence on the feature of the TCV instabilities. The occurrence of frequency lock-in also requires “appropriate” IBPA. For the examined working conditions, the frequency lock-in occurs under 0 ND (Nodal Diameter), but not under 8 ND. However, no matter 0 ND or 8 ND, the phase of TCV always locks onto the IBPA at the examined conditions.

Standing on a sliding board affects generation of anticipatory and compensatory postural adjustments

Postural control is compromised in the presence of body instability. We studied anticipatory and compensatory postural adjustments people use to maintain balance while standing on an unstable surface and performing voluntary arm movements. Nine healthy participants stood on a sliding board (that was either locked and as such motionless or unlocked and as such free to move in the anterior-posterior direction) and performed fast bilateral arms flexion. Arm acceleration, bilateral electromyographic activity (EMG) of the trunk and lower extremity muscles and center of pressure (COP) displacements were recorded and analyzed within the intervals typical for the anticipatory (APAs) and compensatory (CPAs) postural adjustments. Peaks of acceleration of the arm movements were not different between the locked and unlocked conditions. Larger EMG integrals were seen in the muscles of the lower extremity in both APAs and CPAs when standing on the unlocked sliding board. No significant difference was observed in the trunk muscles. Larger maximum COP displacement was seen when participants stood on the locked board. The results demonstrated that when standing on a free to move sliding board and performing bilateral arm flexion, the central nervous system (CNS) does not slow down the arm movements; instead it modifies activation of the lower extremity muscles. The observed differences in APAs and CPAs between the locked and unlocked conditions suggest that the CNS employs similar strategy while controlling the focal part of the task and adjusts the activity of muscles that are close to the source of instability to control postural task.

Note: Digital laser frequency auto-locking for inter-satellite laser ranging.

We present a prototype of a laser frequency auto-locking and re-locking control system designed for laser frequency stabilization in inter-satellite laser ranging system. The controller has been implemented on field programmable gate arrays and programmed with LabVIEW software. The controller allows initial frequency calibrating and lock-in of a free-running laser to a Fabry-Pérot cavity. Since it allows automatic recovery from unlocked conditions, benefit derives to automated in-orbit operations. Program design and experimental results are demonstrated.

Analysis of Injection Pulling in Phase-Locked Loops With a New Modeling Technique

A new formulation is presented for the analysis of phase-locked loops (PLL). It is based on the use of a realistic reduced-order model for the voltage-controlled oscillator, extracted from harmonic-balance (HB) simulations. An HB formulation of the reduced-order PLL equations enables an efficient analysis of the PLL in unlocked conditions, and therefore, prediction of common hysteresis phenomena. The injection-pulling effects in the presence of interference signals are analyzed taking into account the nonlinearity of the phase detector. The interfered PLL in locked conditions is analyzed with a single-tone HB formulation of the reduced-order system, whereas a two-tone HB analysis is used for the analysis in unlocked conditions. The frequency-domain formulation enables an accurate and efficient prediction of the effect of the interferer on the hold-in and lock-in ranges, here investigated, to our knowledge, for the first time. The analysis has been successfully applied to a PLL operating at 5.3 GHz.

Wheelchair safety: Effect of locking or grasping the rear wheels during a rear tip

Objective: To test the hypothesis that, with the wheels locked (by the mechanical locks or by the user grasping the wheels), the rear wheels and the chair rotate slowly backwards during a fall, whereas with the wheels unlocked, the rear wheels rotate quickly forwards. Design: Before-after trial. Setting: Kinesiologic laboratory. Participants: Ten nondisabled adults, a sample of convenience. Intervention: In a single representative wheelchair, subjects were dropped from beyond their balance points onto a mat with the rear wheels locked (L), with two hands grasping the rear wheels (TH), and with the wheels unlocked (UL). Main Outcome Measures: From videorecordings, the horizontal displacement of the rear wheels, the rotation of the rear wheels, and the fall times were derived. Using an anthropomorphic test dummy (ATD) and a Kistler force platform, the impacts of the head with the floor were also recorded. Results: In both the L and TH conditions, the rear wheels moved and rotated backwards. The UL condition was significantly different than the L and TH conditions, with the rear wheels moving and rotating forwards and the fall occurring more quickly, with mean differences of 442 and 455mm, 84.0° and 87.1°, and .52 and .45 sec ( p ⩽ .0001). The forces on the ATD's occiput were 12,280 and 21,118N in the L and UL conditions, respectively, and lasted ∼20msec. Conclusion: Locking or grasping the rear wheels has a profound effect on the nature of rear-tipping incidents, a finding with important implications for the training of users in how to fall safely.

Aerodynamics of a circular cylinder in oscillatory flow.

Experimental investigations of the aerodynamics of a circular cylinder in oscillating flow have been made at Reynolds numbers of (1.1∼1.7)×104. The vortex-shedding frequencies, time mean and fluctuating pressure distributions on a cylinder in sinusoidal gusts with various frequencies and amplitudes have been obtained. Fluctuating fluid forces acting on a cylinder have been separated into two parts, i. e., and oscillating fluid force due to vortex shedding and that due to the flow oscillation, using a computer-aided flow visualization technique. The lock-on phenomena occur in the frequency ranges near the natural vortex-shedding frequency and at twice this value. The alternative nature of vortex shedding is maintained in both locked and unlocked conditions, but an appreciable increase in an oscillating lift force appears in locked-on ranges. The oscillating lift and drag forces due to flow oscillation are proportional to the gust velocity components in their individual directions.

An Experimental Study of Frequency and Power Stability of Phase-Locked Microwave Signal Sources

In setting up of microwave measurement standards of power attenuation, impedance, noise, etc. at the highest level of accuracy, high stability of frequency and power of the microwave signal source is an essential requirement. For this purpose, experimental investigations of frequency and power stabilization of microwave signals derived from klystrons and other sources under phase-locked and unlocked conditions have been carried out. The signals both locked and unlocked have been analyzed for their spectral purity, frequency drift etc. using microwave counter and spectrum analyzer. Phase-locked signals show better frequency stability, less residual FM and low noise-side bands. Source warm-up time is an important factor to achieve better frequency and power stability. Stability of the output power under locked condition improves to better than 0.1% as compared to 0.7 to 1.0% under unlocked condition. Such phase-locked microwave signal sources have been utilized for precision measurement of power, attenuatio...