Lift-off Time Research Articles

A Useful Device to Measure Kinetics of Platelet Contraction.

Platelet contraction provides a minimally invasive source for physiologic information. In this article, we describe a device that directly measures the kinetics of platelet contraction. Whole blood is injected between acrylic plates and an adherent clot forms. The bottom plate is fixed, and the top plate is attached to a wire cantilever. Platelet contraction drives deflection of the wire cantilever which is captured by a camera. Force generated by the clot with time is derived using beam equations. Force derivations were verified using a microelectromechanical (MEMS) force sensor. Kinetics of clot contraction were defined, including maximum contraction force (FMAX), lift-off time (TLIFTOFF), and contraction rate (CR). Metrics were compared with optical aggregometry and thromboelastography. FMAX correlates with optical aggregometry maximal amplitude with a Spearman's rho of 0.7904 and p = 0.0195 and thromboelastography maximal amplitude with a Spearman's rho of 0.8857 and p = 0.0188. Lift-off time correlates with optical aggregometry lag time with a Spearman's rho of 0.9048 and p = 0.002. This preliminary study demonstrates the repeatability of a useful platelet contraction device and its correlation with thromboelastography and optical aggregometry, the gold standard platelet function test.

Internal stress-assisted epitaxial lift-off process for flexible thin film (In)GaAs solar cells on metal foil

Flexible thin film (In)GaAs solar cells are grown by metalorganic chemical vapor deposition on GaAs substrates and transferred to 30 μm thick Au foil by internal stress-assisted epitaxial lift-off processes. The internal stress is induced by replacing the solar cell epi-layers from GaAs to In0.015Ga0.985As, which has a slightly larger lattice constant. The compressive strained layer thickness was varied from 0 to 4.5 μm to investigate the influence of the internal stress on the epitaxial lift-off time. The etching time in the epitaxial lift-off process was reduced from 36 to 4 h by employing a GaAs/In0.015Ga0.985As heterojunction structure that has a compressive film stress of −59.0 MPa. We found that the partially strained epi-structure contributed to the much faster lateral etching rate with spontaneous bending. Although an efficiency degradation problem occurred in the strained solar cell, it was solved by optimizing the epitaxial growth conditions.

Morphology of drop impact on a superhydrophobic surface with macro-structures

Drop-surface interaction is predominant in nature as well as in many industrial applications. Superhydrophobic surfaces show potential for various applications as they show complete drop rebound. In a recent work, it has been reported that the drop lift-off time on a superhydrophobic substrate could be further reduced by introducing a macro-ridge. The macro-ridge introduces asymmetry on the morphology of drop spreading and retraction on the surface. This changes the hydrodynamics of drop retraction and reduces the lift-off time. Keeping practical applications in view, we decorate the surface with multiple ridges. The morphology of the hydrodynamic asymmetry is completely different for the drops impacting onto the tip of the ridges from those impacting onto the middle of the valley between the ridges. We show that the morphology forms the key to the lift-off time. We also show that the outward flow from the ridge triggers a Laplace pressure driven de-wetting on the tip of the ridge, thus aiding the lift-off time. At the end of this work, we propose a ridge to ridge separation that effectively reduces the lift-off times for impacts both at the tip of the ridge and offset from it.

Equilibrium Yield Curves and the Interest Rate Lower Bound

We study the term structure of default-free interest rates in a sticky-price model with an occasionally binding effective lower bound (ELB) constraint on interest rates and recursive preferences. The ELB constraint induces state-dependency in the dynamics of term premiums by affecting macroeconomic uncertainty and interest-rate sensitivity to economic activities. In a model calibrated to match key features of the aggregate economy and term structure dynamics in the U.S. above and at the ELB, we find that the ELB constraint typically lowers the absolute size of term premiums at the ELB and increases their volatility around the time of liftoff. The central bank's announcement to keep the policy rate at the ELB for longer than previously expected lowers the expected short rate path, but its effect on term premiums depends on the risk exposure of bonds to the macroeconomy; while the announcement increases term premiums if bonds are a hedge against economic downturns, it decreases them otherwise.

Sacrificial Structure for Effective Sapphire Substrate Liftoff Based on Photoelectrochemical Etching

The photoelectrochemical (PEC) liftoff results and the performances of fabricated vertical light-emitting diodes (LEDs) among four samples of different PEC etching sacrificial structures are compared. With a dopant-graded n-GaN sacrificial layer, the PEC liftoff time is decreased. With an n-AlGaN etching-stop layer, the roughness of PEC-etching surface is significantly reduced for simplifying the following device process. Illuminated by an ultraviolet LED array at 365 nm in emission wavelength, the PEC liftoff of a 2-in wafer with device isolation can be completed in 25 min. The performances of the fabricated vertical LEDs with different sacrificial structures are similar.

Analysis on the formation of a FRC by flux measurements and MHD simulations

The evolution of the separatrix and excluded flux radius was investigated in a mirror-less theta pinch with external magnetic and loop probes and by numerical simulation. In the numerical hybrid code the anomalous effect was taken as evolution of lower hybrid drift instability. At mid-plane of the coil the experimental and theoretical values of lift-off time, implosion time and equilibrium plasma radius were very close. The implosion time is 5 ± 1 cm/ps and the separatrix radius at mid-plane is around one half of the discharge tube radius. Within the experimental uncertainty the excluded flux radius has the same value along the coil, suggesting an elongated configuration with closed magnetic field lines.

EXPERIMENTAL STUDY OF BUBBLE DYNAMICS DURING NUCLEATE FLOW BOILING ON HORIZONTAL AND VERTICAL SURFACES

Knowledge of the physical mechanisms governing bubble dynamics and two-phase heat transfer is required to develop mechanistic models and to accurately predict and scale the performance of two-phase systems in reduced gravity environments. To better understand the effect of the magnitude of gravity on flow boiling, especially the dynamics of single bubbles under different levels of bulk liquid velocity, surface orientation at earth normal gravity and contact angle effects were studied in this work. A microfabricated nucleation site (10 mm in diameter) at the center of a flat heating surface was used to generate bubbles. Silicon and aluminum were used as substrate materials, with static contact angles of 56° and 19°, respectively, and water as the test liquid. Bulk liquid velocities ranged from 0 to 0.25 m/s, for horizontal and vertical surface orientations, in upflow conditions. Bulk liquid temperature was set close to saturation temperature, with bulk liquid subcooling less than 1°C, and wall superheat was maintained between 5.0°C and 6.0°C. The experimental results for bubble growth, departure diameter and time for departure, bubble sliding distance and velocity, bubble lift-off diameter and time for lift-off, and bubble base diameter are reported for vertical and horizontal orientations, as the system variables were varied parametrically. It is found that irrespective of orientation and contact angle, departure and lift-off diameters decrease with increase in bulk liquid velocity. At a given velocity, departure diameter decreases with increase in the component of gravity parallel to the heater surface. For a given bulk liquid velocity, increase in contact angle results in increase in bubble departure and lift-off diameters, for all orientations. For given conditions, bubble lift-off diameter increases with decrease in the component of gravity normal to the heater surface. The effect of gravity on lift-off diameter is reduced at high liquid bulk velocities. For given orientation and flow velocity, sliding distance decreases monotonically with decrease in contact angle. The bubble velocity at lift-off increases with increase in flow velocity and increase in the component of gravity parallel to heater surface.

Gait Transition of Quadruped Robot Using Time Sequence Control Based on Finite-State Machine

The adaptability of velocity changing of quadruped robot needs to be realized by gait transition. In this paper, a gait transition method of a quadruped robot based on changing the time sequence was investigated. The swing phase and the stance phase are separated by finite-state machine (FSM), and the locomotion gait involves breaking/enforcing synchronization or changing the order of leg liftoff events, it makes the duration time of liftoff and touchdown events variable. The gait transition from walk to trot is realized by the combination driving of time and event. The experiment is verified by interactive co-simulation among Matlab-Adams. The transition method satisfies the velocity changing of quadruped robot.

Observation of solar energetic particle (SEP) events associated with narrow CMEs

We report here on two proton energetic particle events observed by the Energetic and Relativistic Nuclei and Electron (ERNE) instrument on the Solar and Heliospheri- cal Observatory (SOHO). Both events were impulsive (SEP) events with intensities of > 10 3 cm 2 sr 1 s 1 MeV 1 at an energy range of tens of MeVs and were associated with CMEs of angular widths 800 kms 1 . In one of the events there was no associated solar flare, which indicates that the first injected protons were completely due to the associated CME and in the second event the associated solar flare was an impulsive M1.1 class flare and the calculated first injection time for protons of en- ergies 36 MeV and propagating along 1.2 AU path length, was close to the liftoff time of the CME. These observations are inconsistent with the view presented in some studies that narrow fast CME are not associated with SEP events.

Effect of Yoga on Motor Function in People with Parkinson’s Disease: A Randomized, Controlled Pilot Study

Yoga is a form of exercise that may be beneficial to those with Parkinson’s disease (PD). There have been no randomized control research studies investigating the effect of yoga on those with PD. The objective was to determine if yoga can improve motor function in people with PD using a randomized controlled small group design. The PD participants were randomized into a yoga intervention group or a control group of no intervention. Assessment of physical function included motor examination scores from the Unified Parkinson’s Disease Rating Scale, posture, measures of extremity ROM, flexibility and strength, and biomechanical measures of balance and gait that occurred at 3 time points: prior to starting the intervention, at 6 weeks of intervention, and immediately following 12 weeks of intervention. Thirteen adults with PD met the inclusion and exclusion criteria. All participants were unfamiliar with yoga. An Iyengar Hatha yoga program was tailored to fit participants with PD and designed to improve strength, flexibility, body alignment, and overall well-being. A 60-minute session, including physical postures, breathing, and meditation was implemented twice a week for 12 weeks. A significant improvement was found in motor UPDRS scores (p=0.004) and Berg Balance Scale scores (p=0.04) in the yoga group. A general trend of positive outcomes in the yoga group for strength, ROM and flexibility were noted with significant differences at p=0.05 in selected hip and ankle measurements. Qualitative improvements in posture were observed and there were significant improvements in the onset time of foot unloading and onset time of foot lift off. Findings suggest that yoga practice improves motor function which may be partially explained by improvements in balance, strength, posture and gait. Due to the progressive nature of PD yoga programs may offer a way to maintain wellness and perhaps quality of life.

Lesions of the dentate and interposed nuclei are associated with impaired prehension in cerebellar patients

In a recent study using voxel based lesion symptom mapping (VLSM) in cerebellar patients following stroke we found associations of prehensile deficits to lesions of the cerebellar cortex and dentate nucleus (DN). Associations to lesions of the interposed nucleus (IN), which has been shown to contribute to prehension in monkeys, could not be established. One possible reason was that the IN was largely unaffected in the stroke patients. To further address the question of IN involvement in prehension we performed VLSM in patients with surgical cerebellar lesions (n=20), exhibiting high lesion overlap in the medial and intermediate cerebellum including the IN. Prehensile deficits were quantified by analyses of movement kinematics and finger forces. In the patient population prehensile deficits comprised lower movement velocity in reaching and increased lift-off time in grasping. These were associated with lesions of the intermediate and lateral cerebellar cortex together with their output nuclei. Specifically, IN lesions were linked to increased lift-off time in grasping and not to slower reaching movements. Thus, our data support IN contribution particularly for the fluent production of grip forces during dexterous prehension in humans.

Numerical investigation on bubble dynamics during flow boiling using moving particle semi-implicit method

In the present study, two-dimensional numerical simulation of single bubble dynamics during nucleate flow boiling has been performed using moving particle semi-implicit (MPS) method. A set of moving particles was used to represent the liquid phase. The bubble–liquid interface was set to be a free surface boundary which can be captured according to the motion and location of interfacial particles. The interfacial heat transfer rate was determined by the energy variety of interfacial particles. The bulk liquid velocities investigated ranged from 0.07 to 0.3m/s. The surface orientations varied from vertical to horizontal through 60°, 45° and 30°. Bulk liquid subcooling varied from 0 to 6.5°C and wall superheat from 2.0 to 20.0°C. The computational results show that the bulk liquid velocity and surface orientation influenced the bubble diameter and liftoff time. Bubble would slide along the heater surface before lifting off and the sliding velocity at liftoff increased with an increase in bulk liquid velocity. Bubble dynamic was related to bulk liquid subcooling as well as wall superheat. The numerical results have been compared with the experimental data.

CME–flare association during the 23rd solar cycle

The relation between coronal mass ejections (CMEs) and solar flares are statistically studied. More than 10,000 CME events observed by SOHO/LASCO during the period 1996–2005 have been analyzed. The soft X-ray flux measurements provided by the Geostationary Operational Environmental Satellite (GOES), recorded more than 20,000 flares in the same time period. The data is filtered under certain temporal and spatial conditions to select the CME–flare associated events. The results show that CME–flare associated events are triggered with a lift-off time within the range 0.4–1.0h. We list a set of 41 CME–flare associated events satisfying the temporal and spatial conditions. The listed events show a good correlation between the CME energy and the X-ray flux of the CME–flare associated events with correlation coefficient of 0.76.

Launch windows for libration point missions

The four upcoming ESA missions to the collinear Lagrange points in the sun–Earth system, Herschel and Planck, GAIA, and LISA Pathfinder, will be launched from French Guiana by different Rockets, namely Ariane 5, Soyuz, and VEGA. Herschel and Planck will be launched together in 2008 on an Ariane 5. The launcher injects Herschel directly into the stable manifold of a large amplitude quasi-Halo orbit at L 2 . Departing from this launch orbit, Planck performs a three manoeuvre transfer to a Lissajous orbit, on which the sun–spacecraft–Earth angle remains below 15 ∘ . The daily and seasonal launch window for Herschel/Planck will be constrained by sun aspect angle conditions, by eclipse conditions, and by the propellant allocation on the Planck satellite. GAIA will be launched by Soyuz/Fregat end 2011. The target orbit at L 2 is similar to that of Planck, with a constrained sun–spacecraft–Earth angle. Initially, to reach a full year launch window, a launch scenario was preferred using a nearly circular parking orbit at 19 ∘ inclination, before igniting the Fregat upper stage to enter into the transfer. Recently alternative launch scenarios have been introduced, to guarantee a controlled re-entry of the Soyuz third stage, but leading to a reduction of the launch window. LISA Pathfinder will be delivered 2010 by the VEGA launcher to a low inclination elliptical orbit, with 1624 km apogee height. From there an apogee raising manoeuvre sequence, using a propulsion module connected to the spacecraft, reaches L 1 transfer conditions. Launch window calculations for these projects combine the choice of lift-off time and launch orbit conditions, with the selection of the target orbit at the Lagrange points and the minimisation of propellant to reach that orbit. For Herschel and LISA Pathfinder the target orbits have been chosen such that a transfer without deterministic manoeuvres is possible. Planck and GAIA both use a multiple manoeuvre fast transfer strategy reaching the Lissajous orbit at L 2 within 50 days.

Radio and White‐Light Coronal Signatures Associated with theRHESSIHard X‐Ray Event of 2002 July 23

Simultaneous radio, white-light, and hard X-ray (HXR) observations for the 2002 July 23 ?-ray flare event are used to establish the relationship of a complex type III-like burst to the corresponding coronal mass ejection (CME) and the coronal electron acceleration signatures observed in the decimeter/microwave (dm-cm) emissions and X-rays. We find that the onset of the type III-like emissions for this event is coincident with the impulsive RHESSI HXR event, the dm-cm radio emissions and with the linearly extrapolated liftoff time of the CME. The overall intensity-time characteristics of the complex type III-like burst resembles that of both the dm-cm flux and the HXR light curve that correspond to an electron acceleration event deep in the corona. Furthermore, the complex radiation characteristics of the type III-like emissions are found to be directly related to the CME kinematics, which is directly related to the frequency drift of the associated low-frequency (kilometric) type II emissions. The frequency-drift characteristics of the high-frequency (metric) type II emissions observed for this event, on the other hand, are not clearly related to the kilometric type II emissions and therefore to the observed CME height-time characteristics, indicating that these emissions may correspond to an independent coronal shock wave.

Chair rise strategies in older adults with functional limitations

Studies investigating chair rise (CR) strategies in older adults, including the identification of CR strategies in the clinical setting, are limited. We identified biomechanical differences between CR strategies performed by older adults. The "healthy" momentum transfer (MT), the exaggerated trunk flexion (ETF), and the dominant vertical rise (DVR) CR strategies were observed in 29 women and 17 men (64-88 yr) with functional limitations. The DVR strategy required the greatest knee torque (mean = 12.76 moment-% body weight). Maximum knee torque occurred significantly earlier for the ETF strategy (mean = 47% CR time). Lift-off time was earliest for the ETF strategy (mean = 32% CR time). Peak trunk flexion was the primary distinguishing biomechanical measure for classifying CR strategy. This finding may offer clinicians an easy method of identifying CR strategies during evaluation. Because of DVR and ETF movement timing and torque demands, we conclude that MT is the safest and most preferable CR strategy.

Benchmarking mean dispatch, lift-off and scene times in rotor-wing air medical transport scene flights

Introduction: Dispatch, lift-off and scene times are considered important parameters in rotor-wing air medical transport, balancing safety, reality and the needs of our patients and customers. Many programs track these times carefully as part of their ongoing quality assurance programs, yet there are no accepted industry-wide standards. Our goal is to establish dispatch, lift-off and scene time benchmarks for emergency rotor-wing scene flights.

SWERVING STICK INSECTS

Watch a stumbling toddler and you'll see that we struggle to learn how to control just two legs. But spare a thought for the humble stick insect; it has to coordinate 18 leg joints as it ambles around. Volker Dürr and Wiebke Ebeling at Bielefeld University analysed how stick insects negotiate bends to understand the behavioural coordination that underlies walking(p. 2237 and p. 2253).To see how stick insects initiate changes in direction during walking,Dürr and Ebeling examined the sequence of stick insects' leg movements during straight and curved walking. They tethered stick insects onto an air-cushioned Styrofoam ball and videotaped them as they sauntered across the top of the ball. At the same time, they recorded in which direction the insects walked by tracking the rotation and backward and sideward translations of the ball using motion sensors. They filmed the insects walking in a straight line and then rotated a black and white pattern around the insects– a visual motion stimulus that they knew would provoke the insects to start turning.To examine how quickly the insects adjusted their legs as they turned,Dürr and Ebeling measured the rate of change of 13 kinematic parameters per leg, including stride direction, length and duration, and lift-off and touch-down positions. Then they related the time course of these parameters to the insects' walking behaviour. The time at which Dürr and Ebeling recorded a change in an animal's walking path served as a reference point to identify which parameters change faster than the insect's change of direction. They reasoned that the parameters that change faster than the change in walking direction are the ones that actively initiate an insect's turn, and those that change at a slower rate than the insect's turn do not play an active role in turning.Dürr and Ebeling found that the movement parameters changed at different rates for each of the insects' six legs, so turning is a carefully orchestrated process in which each leg has a different function. They noticed that the two front legs change their step direction faster than the insect's turning response, and concluded that stick insects' front legs actively initiate turning. But they were surprised to find that the strongest changes were not necessarily the fastest ones. `A parameter's magnitude doesn't tell you everything,' Dürr concludes, `you also need to consider the time course of events.'So how do stick insects orchestrate their walking? `We can model it using simple coordination rules,' Dürr says. An insect's six legs coordinate their lift-off times by `telling' each other which state they are in. Examining his behavioural data, Dürr found that the strength of these signals is not constant between legs, but adapts depending on whether the insect is walking in a straight line or a curve. Dürr and his collaborators in Bielefeld will incorporate all of these behavioural findings into computer simulations of insect walking. By testing these updated algorithms on a 6-legged robot in the lab, they might eventually manage to adapt leg coordination to the environment's current demands, enabling such a robot to march across the rugged terrain that thwarts wheeled robots.

Effects of step length on stepping responses used to arrest a forward fall

This study investigated effects of step length on the stepping response used to arrest an impending forward fall. Twelve healthy young (mean age 22, S.D. 3.3 years) males participated by recovering balance with a single step following a forward lean-and-release. Participants were instructed to step to one of three floor targets representing small, natural, and large step lengths. The effect of step length was examined on the primary outcome variables: pushoff time, liftoff and landing time, swing duration, balance recovery time, landing impulse, and center of mass (COM) characteristics. Pushoff and liftoff times were not affected by step length, although swing phase duration, landing and recovery times and the anterior-posterior (AP) impulse at landing increased with increasing step length. The results support the idea of an invariant step preparation phase. Given that our participants naturally chose not to utilize a step as short as they were capable of employing, healthy young individuals do not minimize recovery time nor strength requirements when selecting their step length.

Instant of chair-rise lift-off can be predicted by foot–floor reaction forces

Objective: To develop a predictive model of the lift-off event during chair rise in healthy subjects, using foot–floor reaction forces. Background: An important event during chair rise is lift-off from the seat: the transition from the inherently stable three-point contact to the unstable two-point contact. There is no consistent or generally agreed upon method for estimating the time of lift-off when an instrumented seat is unavailable. Methods: Twenty healthy volunteers were divided into a testing set and training set. Each subject performed repeated chair rise trials at different speeds. Seat–floor and foot–floor forces, recorded with two force platforms, were used to develop a model of the lift-off event. Results: The magnitude of the vertical foot–floor reaction at lift-off (F0VF) was linearly related ( R 2=0.71, P<0.001) to the peak vertical foot–floor reaction force (FMVF). A linear model was developed for the training group, which enabled prediction of lift-off time for the testing group with an absolute average error of 6 ms (about 1 data frame at 150 Hz). The linear model derived for the entire sample was: F0VF=28.14+ FMVF ∗ (0.6434) . Conclusions: The lift-off event for healthy subjects performing chair rise can be accurately predicted from foot–floor reaction forces, without requiring an instrumented seat.