Science.gov

Sample records for aileron control stiffness

  1. Aileron controls for wind turbine applications

    NASA Technical Reports Server (NTRS)

    Miller, D. R.; Putoff, R. L.

    1984-01-01

    Horizontal axis wind turbines which utilize partial or full variable blade pitch to regulate rotor speed were examined. The weight and costs of these systems indicated a need for alternate methods of rotor control. Aileron control is an alternative which has potential to meet this need. Aileron control rotors were tested on the Mod-O wind turbine to determine their power regulation and shutdown characteristics. Test results for a 20 and 38% chord aileron control rotor are presented. Test is shown that aileron control is a viable method for safety for safely controlling rotor speed, following a loss of general load.

  2. Flutter prediction for a wing with active aileron control

    NASA Technical Reports Server (NTRS)

    Penning, K.; Sandlin, D. R.

    1983-01-01

    A method for predicting the vibrational stability of an aircraft with an analog active aileron flutter suppression system (FSS) is expained. Active aileron refers to the use of an active control system connected to the aileron to damp vibrations. Wing vibrations are sensed by accelerometers and the information is used to deflect the aileron. Aerodynamic force caused by the aileron deflection oppose wing vibrations and effectively add additional damping to the system.

  3. Charts for the Determination of Wing Torsional Stiffness Required for Specified Rolling Characteristics or Aileron Reversal Speed

    NASA Technical Reports Server (NTRS)

    Pearson, Henry A; Aiken, William S , Jr

    1944-01-01

    A series of charts are presented by which the wing torsional stiffness required to meet a given standard of rolling effectiveness may be quickly determined. The charts may also be used to obtain quickly the aileron reversal speed and the variation of the loss in rolling effectiveness with airspeed. The charts apply to linearly tapered wings and elliptical wings of tubular-shell construction having various aspect ratios with aileron span and location of ailerons as variables. In the derivation of the charts, induced lift effects have been taken into account and the form of the wing-torsional-stiffness curve has been assumed.

  4. Summary of NASA/DOE Aileron-Control Development Program for Wind Turbines

    NASA Technical Reports Server (NTRS)

    Miller, D. R.

    1986-01-01

    The development of aileron-control for wind turbines is discussed. Selected wind tunnel test results and full-scale rotor test results are presented for various types of ailerons. Finally, the current status of aileron-control development is discussed. Aileron-control was considered as a method of rotor control for use on wind turbines based on its potential to reduce rotor weight and cost. Following an initial feasibility study, a 20 percent chord aileron-control rotor was fabricated and tested on the NASA/DOE Mod-0 experimental wind turbine. Results from these tests indicated that the 20 percent chord ailerons regulated power and provided overspeed protection, but only over a very limited windspeed range. The next aileron-control rotor to be tested on the Mod-0 had 38 percent chord ailerons and test results showed these ailerons provided overspeed protection and power regulation over the Mod-0's entire operational windspeed range.

  5. Feasibility of power and teeter control using ailerons

    SciTech Connect

    Pierce, K.; Hansen, C.

    1995-12-31

    In recent years the complexity of wind turbine systems has increased dramatically. Many new turbines, and proposed designs, use aerodynamic controls, and/or power electronics to improve efficiency, eliminate overloading, and reduce fatigue loads. ADAMS, coupled with AeroDyn aerodynamic routines, developed at the University of Utah, allow for very general modeling of these systems. ADAMS allows general modeling of the dynamic system and controls, while AeroDyn allows general modeling of the aerodynamic characteristics, and wind inputs. This report presents preliminary results on the use of ailerons for regulating produced power, limiting teeter amplitude, and reducing fatigue loads on an upwind teetering rotor. For this preliminary study controllers were developed by classical methods. These controllers were then implemented in both ADAMS coupled with AeroDyn, and a modified version of YawDyn. Effect of the power control on low speed shaft power and flap moments are presented as time series and rain flow counts. Results from the implementation of the teeter control are presented as time series. It is evident from the simulations that the ailerons are capable of reducing fatigue loads, controlling produced power, and reducing teeter amplitude.

  6. Feasibility study of aileron and spoiler control systems for large horizontal axis wind turbines

    NASA Technical Reports Server (NTRS)

    Wentz, W. H., Jr.; Snyder, M. H.; Calhoun, J. T.

    1980-01-01

    The feasibility of using aileron or spoiler controls as alternates to pitch control for large horizontal axis wind turbines was studied. The NASA Mod-0 100 kw machine was used as the basis for the study. Specific performance studies were conducted for 20% chord ailerons over the outboard 30% span, and for 10% chord spoilers over the same portion of the span. Both control systems utilized control deflections up to 60 deg. Results of the study show that either ailerons or spoilers can provide the control necessary to limit turbine power in high wind conditions. The aileron system, as designed, provides overspeed protection at hurricane wind speeds, low wind speed starting torque of 778 N-m (574 ft. lb) at 3.6 m/sec, and a 1.3 to 1.5% increase in annual energy compared to a fixed pitch rotor. The aileron control system preliminary design study includes aileron loads analysis and the design of a failsafe flyweight actuator for overspeed protection in the event of a hydraulic system failure.

  7. Flight Investigation of the Effectiveness of an Automatic Aileron Trim Control Device for Personal Airplanes

    NASA Technical Reports Server (NTRS)

    Phillips, William H; Kuehnel, Helmut A; Whitten, James B

    1957-01-01

    A flight investigation to determine the effectiveness of an automatic aileron trim control device installed in a personal airplane to augment the apparent spiral stability has been conducted. The device utilizes a rate-gyro sensing element in order to switch an on-off type of control that operates the ailerons at a fixed rate through control centering springs. An analytical study using phase-plane and analog-computer methods has been carried out to determine a desirable method of operation for the automatic trim control.

  8. Aeroelastic stability of wind turbine blade/aileron systems

    NASA Technical Reports Server (NTRS)

    Strain, J. C.; Mirandy, L.

    1995-01-01

    Aeroelastic stability analyses have been performed for the MOD-5A blade/aileron system. Various configurations having different aileron torsional stiffness, mass unbalance, and control system damping have been investigated. The analysis was conducted using a code recently developed by the General Electric Company - AILSTAB. The code extracts eigenvalues for a three degree of freedom system, consisting of: (1) a blade flapwise mode; (2) a blade torsional mode; and (3) an aileron torsional mode. Mode shapes are supplied as input and the aileron can be specified over an arbitrary length of the blade span. Quasi-steady aerodynamic strip theory is used to compute aerodynamic derivatives of the wing-aileron combination as a function of spanwise position. Equations of motion are summarized herein. The program provides rotating blade stability boundaries for torsional divergence, classical flutter (bending/torsion) and wing/aileron flutter. It has been checked out against fixed-wing results published by Theodorsen and Garrick. The MOD-5A system is stable with respect to divergence and classical flutter for all practical rotor speeds. Aileron torsional stiffness must exceed a minimum critical value to prevent aileron flutter. The nominal control system stiffness greatly exceeds this minimum during normal operation. The basic system, however, is unstable for the case of a free (or floating) aileron. The instability can be removed either by the addition of torsional damping or mass-balancing the ailerons. The MOD-5A design was performed by the General Electric Company, Advanced Energy Program Department under Contract DEN3-153 with NASA Lewis Research Center and sponsored by the Department of Energy.

  9. Performance and power regulation characteristics of two aileron-controlled rotors and a pitchable tip-controlled rotor on the Mod-O turbine

    NASA Technical Reports Server (NTRS)

    Corrigan, Robert D.; Ensworth, Clinton B. F., III; Miller, Dean R.

    1987-01-01

    Tests were conducted on the DOE/NASA mod-0 horizontal axis wind turbine to compare and evaluate the performance and the power regulation characteristics of two aileron-controlled rotors and a pitchable tip-controlled rotor. The two aileron-controlled rotor configurations used 20 and 38 percent chord ailerons, while the tip-controlled rotor had a pitchable blade tip. The ability of the control surfaces to regulate power was determined by measuring the change in power caused by an incremental change in the deflection angle of the control surface. The data shows that the change in power per degree of deflection angle for the tip-controlled rotor was four times the corresponding value for the 2- percent chord ailerons. The root mean square power deviation about a power setpoint was highest for the 20 percent chord aileron, and lowest for the 38 percent chord aileron.

  10. Flight Measurements of the Lateral Control Characteristics of Narrow-Chord Ailerons on the Trailing Edge of a Full-Span Slotted Flap

    NASA Technical Reports Server (NTRS)

    Sawyer, Richard H

    1947-01-01

    Results are presented of light tests made to determine the effect of flap deflection on the lateral control characteristics of a modified brewster f2a-2 airplane equipped with partial-span narrow-chord ailerons on the trailing edge of a full-span NACA slotted flap. The investigation included determination of the rolling and yawing characteristics of the airplane in abrupt aileron rolls with the slotted flap at various settings ranging from 0 degree to about 40 degrees. The results showed that the effectiveness of the ailerons was greatly reduced at flap deflections greater than about 20 degrees. For flap deflections up to about 20 degrees, the aileron effectiveness was about the same as with flaps retracted, but the adverse yawing velocity developed in the abrupt aileron rolls was somewhat increased.

  11. Effect of Aspect Ratio on the Low-Speed Lateral Control Characteristics of Untapered Low-Aspect-Ratio Wings Equipped with Flap and with Retractable Ailerons

    NASA Technical Reports Server (NTRS)

    Fischel, Jack; Naeseth, Rodger L; Hagerman, John R; O'Hare, William M

    1952-01-01

    A low-speed wind-tunnel investigation was made to determine the lateral control characteristics of a series of untapered low-aspect-ratio wings. Sealed flap ailerons of various spans and spanwise locations were investigated on unswept wings of aspect ratios 1.13, 1.13, 4.13, and 6.13; and various projections of 0.60-semispan retractable ailerons were investigated on the unsweptback wings of aspect ratios 1.13, 2.13, and 4.13 and on a 45 degree sweptback wing. The retractable ailerons investigated on the unswept wings spanned the outboard stations of each wing; whereas the plain and stepped retractable ailerons investigated on the sweptback wing were located at various spanwise stations. Design charts based on experimental results are presented for estimating the flap aileron effectiveness for low-aspect-ratio, untapered, unswept.

  12. Wind turbine rotor aileron

    DOEpatents

    Coleman, Clint; Kurth, William T.

    1994-06-14

    A wind turbine has a rotor with at least one blade which has an aileron which is adjusted by an actuator. A hinge has two portions, one for mounting a stationary hinge arm to the blade, the other for coupling to the aileron actuator. Several types of hinges can be used, along with different actuators. The aileron is designed so that it has a constant chord with a number of identical sub-assemblies. The leading edge of the aileron has at least one curved portion so that the aileron does not vent over a certain range of angles, but vents if the position is outside the range. A cyclic actuator can be mounted to the aileron to adjust the position periodically. Generally, the aileron will be adjusted over a range related to the rotational position of the blade. A method for operating the cyclic assembly is also described.

  13. Advanced wind turbine with lift-destroying aileron for shutdown

    DOEpatents

    Coleman, Clint; Juengst, Theresa M.; Zuteck, Michael D.

    1996-06-18

    An advanced aileron configuration for wind turbine rotors featuring an aileron with a bottom surface that slopes upwardly at an angle toward the nose region of the aileron. The aileron rotates about a center of rotation which is located within the envelope of the aileron, but does not protrude substantially into the air flowing past the aileron while the aileron is deflected to angles within a control range of angles. This allows for strong positive control of the rotation of the rotor. When the aileron is rotated to angles within a shutdown range of deflection angles, lift-destroying, turbulence-producing cross-flow of air through a flow gap, and turbulence created by the aileron, create sufficient drag to stop rotation of the rotor assembly. The profile of the aileron further allows the center of rotation to be located within the envelope of the aileron, at or near the centers of pressure and mass of the aileron. The location of the center of rotation optimizes aerodynamically and gyroscopically induced hinge moments and provides a fail safe configuration.

  14. Wind tunnel research concerning lateral control devices, particularly at high angles of attack VII : Handley Page tip and full-span slots with ailerons and spoilers

    NASA Technical Reports Server (NTRS)

    Weick, Fred E; Wenzinger, Carl J

    1933-01-01

    Tests were made with ordinary ailerons and different sizes of spoilers on rectangular Clark Y wing models with Handley Page tip and full span slots. The tests showed the effect of the control devices on the general performance of the wings as well as on the lateral control and lateral stability characteristics.

  15. Advanced composite aileron for L-1011 transport aircraft: Aileron manufacture

    NASA Technical Reports Server (NTRS)

    Dunning, E. G.; Cobbs, W. L.; Legg, R. L.

    1981-01-01

    The fabrication activities of the Advanced Composite Aileron (ACA) program are discussed. These activities included detail fabrication, manufacturing development, assembly, repair and quality assurance. Five ship sets of ailerons were manufactured. The detail fabrication effort of ribs, spar and covers was accomplished on male tools to a common cure cycle. Graphite epoxy tape and fabric and syntactic epoxy materials were utilized in the fabrication. The ribs and spar were net cured and required no post cure trim. Material inconsistencies resulted in manufacturing development of the front spar during the production effort. The assembly effort was accomplished in subassembly and assembly fixtures. The manual drilling system utilized a dagger type drill in a hydraulic feed control hand drill. Coupon testing for each detail was done.

  16. Advanced wind turbine with lift cancelling aileron for shutdown

    DOEpatents

    Coleman, Clint; Juengst, Theresa M.; Zuteck, Michael D.

    1996-06-18

    An advanced aileron configuration for wind turbine rotors featuring an independent, lift generating aileron connected to the rotor blade. The aileron has an airfoil profile which is inverted relative to the airfoil profile of the main section of the rotor blade. The inverted airfoil profile of the aileron allows the aileron to be used for strong positive control of the rotation of the rotor while deflected to angles within a control range of angles. The aileron functions as a separate, lift generating body when deflected to angles within a shutdown range of angles, generating lift with a component acting in the direction opposite the direction of rotation of the rotor. Thus, the aileron can be used to shut down rotation of the rotor. The profile of the aileron further allows the center of rotation to be located within the envelope of the aileron, at or near the centers of pressure and mass of the aileron. The location of the center of rotation optimizes aerodynamically and gyroscopically induced hinge moments and provides a fail safe configuration.

  17. Flight Evaluation of an Aircraft with Side and Center Stick Controllers and Rate-Limited Ailerons

    NASA Technical Reports Server (NTRS)

    Deppe, P. R.; Chalk, C. R.; Shafer, M. F.

    1996-01-01

    As part of an ongoing government and industry effort to study the flying qualities of aircraft with rate-limited control surface actuators, two studies were previously flown to examine an algorithm developed to reduce the tendency for pilot-induced oscillation when rate limiting occurs. This algorithm, when working properly, greatly improved the performance of the aircraft in the first study. In the second study, however, the algorithm did not initially offer as much improvement. The differences between the two studies caused concern. The study detailed in this paper was performed to determine whether the performance of the algorithm was affected by the characteristics of the cockpit controllers. Time delay and flight control system noise were also briefly evaluated. An in-flight simulator, the Calspan Learjet 25, was programmed with a low roll actuator rate limit, and the algorithm was programmed into the flight control system. Side- and center-stick controllers, force and position command signals, a rate-limited feel system, a low-frequency feel system, and a feel system damper were evaluated. The flight program consisted of four flights and 38 evaluations of test configurations. Performance of the algorithm was determined to be unaffected by using side- or center-stick controllers or force or position command signals. The rate-limited feel system performed as well as the rate-limiting algorithm but was disliked by the pilots. The low-frequency feel system and the feel system damper were ineffective. Time delay and noise were determined to degrade the performance of the algorithm.

  18. Preliminary Results of a Free-Flight Investigation of the Static Stability and Aileron Control Characteristics of 1/6 Scale Models of the Bell MX-776

    NASA Technical Reports Server (NTRS)

    Michal, David H.; Mitcham, Grady L.

    1949-01-01

    An investigation of the static longitudinal stability, static directional stability, and aileron control characteristics at transonic and supersonic speeds is being made of 1/6 scale rocket-propelled model of the Bell MX-776. A stability investigation has been made of two symmetrical models with controls undeflected and centers of gravity one-half and one-body diameter, respectively, ahead of the equivalent design center-of-gravity location of the full-scale version. Both models developed large normal-force coefficients in both the subsonic and supersonic ranges which indicated longitudinal instability at low angles of attack. The side-force coefficients were small for both models and indicated that the models were directionally stable. A possible tendency toward dynamic directional instability in the transonic region was indicated by short-period oscillations of the side forces. The results showed a partial-span inboard aileron to be ineffective or to cause negative control in the the transonic region when deflected approximately 5 deg but not when deflected 10 deg. An investigation of drag showed it to increase with a rearward movement of the center of gravity. This indicates an increase in the trim angle of attack as could be caused by a decrease in static stability.

  19. High performance composites with active stiffness control.

    PubMed

    Tridech, Charnwit; Maples, Henry A; Robinson, Paul; Bismarck, Alexander

    2013-09-25

    High performance carbon fiber reinforced composites with controllable stiffness could revolutionize the use of composite materials in structural applications. Here we describe a structural material, which has a stiffness that can be actively controlled on demand. Such a material could have applications in morphing wings or deployable structures. A carbon fiber reinforced-epoxy composite is described that can undergo an 88% reduction in flexural stiffness at elevated temperatures and fully recover when cooled, with no discernible damage or loss in properties. Once the stiffness has been reduced, the required deformations can be achieved at much lower actuation forces. For this proof-of-concept study a thin polyacrylamide (PAAm) layer was electrocoated onto carbon fibers that were then embedded into an epoxy matrix via resin infusion. Heating the PAAm coating above its glass transition temperature caused it to soften and allowed the fibers to slide within the matrix. To produce the stiffness change the carbon fibers were used as resistance heating elements by passing a current through them. When the PAAm coating had softened, the ability of the interphase to transfer load to the fibers was significantly reduced, greatly lowering the flexural stiffness of the composite. By changing the moisture content in PAAm fiber coating, the temperature at which the PAAm softens and the composites undergo a reduction in stiffness can be tuned. PMID:23978266

  20. Numerical design of an adaptive aileron

    NASA Astrophysics Data System (ADS)

    Amendola, Gianluca; Dimino, Ignazio; Concilio, Antonio; Magnifico, Marco; Pecora, Rosario

    2016-04-01

    The study herein described is aimed at investigating the feasibility of an innovative full-scale camber morphing aileron device. In the framework of the "Adaptive Aileron" project, an international cooperation between Italy and Canada, this goal was carried out with the integration of different morphing concepts in a wing-tip prototype. As widely demonstrated in recent European projects such as Clean Sky JTI and SARISTU, wing trailing edge morphing may lead to significant drag reduction (up to 6%) in off-design flight points by adapting chord-wise camber variations in cruise to compensate A/C weight reduction following fuel consumption. Those researches focused on the flap region as the most immediate solution to implement structural adaptations. However, there is also a growing interest in extending morphing functionalities to the aileron region preserving its main functionality in controlling aircraft directional stability. In fact, the external region of the wing seems to be the most effective in producing "lift over drag" improvements by morphing. Thus, the objective of the presented research is to achieve a certain drag reduction in off-design flight points by adapting wing shape and lift distribution following static deflections. In perspective, the developed device could also be used as a load alleviation system to reduce gust effects, augmenting its frequency bandwidth. In this paper, the preliminary design of the adaptive aileron is first presented, assessed on the base of the external aerodynamic loads. The primary structure is made of 5 segmented ribs, distributed along 4 bays, each splitted into three consecutive parts, connected with spanwise stringers. The aileron shape modification is then implemented by means of an actuation system, based on a classical quick-return mechanism, opportunely suited for the presented application. Finite element analyses were assessed for properly sizing the load-bearing structure and actuation systems and for

  1. Vibration Control via Stiffness Switching of Magnetostrictive Transducers

    NASA Technical Reports Server (NTRS)

    Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.

    2016-01-01

    This paper presents a computational study of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magnetomechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.25; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping.

  2. Stiffness control of balance in quiet standing.

    PubMed

    Winter, D A; Patla, A E; Prince, F; Ishac, M; Gielo-Perczak, K

    1998-09-01

    Our goal was to provide some insights into how the CNS controls and maintains an upright standing posture, which is an integral part of activities of daily living. Although researchers have used simple performance measures of maintenance of this posture quite effectively in clinical decision making, the mechanisms and control principles involved have not been clear. We propose a relatively simple control scheme for regulation of upright posture that provides almost instantaneous corrective response and reduces the operating demands on the CNS. The analytic model is derived and experimentally validated. A stiffness model was developed for quiet standing. The model assumes that muscles act as springs to cause the center-of-pressure (COP) to move in phase with the center-of-mass (COM) as the body sways about some desired position. In the sagittal plane this stiffness control exists at the ankle plantarflexors, in the frontal plane by the hip abductors/adductors. On the basis of observations that the COP-COM error signal continuously oscillates, it is evident that the inverted pendulum model is severely underdamped, approaching the undamped condition. The spectrum of this error signal is seen to match that of a tuned mass, spring, damper system, and a curve fit of this "tuned circuit" yields omega n the undamped natural frequency of the system. The effective stiffness of the system, Ke, is then estimated from Ke = I omega n2, and the damping B is estimated from B = BW X I, where BW is the bandwidth of the tuned response (in rad/s), and I is the moment of inertia of the body about the ankle joint. Ten adult subjects were assessed while standing quietly at three stance widths: 50% hip-to-hip distance, 100 and 150%. Subjects stood for 2 min in each position with eyes open; the 100% stance width was repeated with eyes closed. In all trials and in both planes, the COP oscillated virtually in phase (within 6 ms) with COM, which was predicted by a simple 0th order spring

  3. The Reduction of Aileron Operating Force by Differential Linkage

    NASA Technical Reports Server (NTRS)

    Jones, Robert T; Nerken, Albert I

    1936-01-01

    It is shown that the control force of ordinary ailerons may be reduced to zero over a range of deflections and at a given flight condition by the use of an appropriate differential movement. Approximations to the ideal motion obtainable with a simple linkage are discussed and a chart that enables the selection of an appropriate crank arrangement is presented. Various aspects of the practical application of the system are discussed and it is concluded that a small fixed tab, deflected to trim both ailerons upward, would be advantageous.

  4. Wind-Tunnel Investigation of a Plain Aileron with Various Trailing-Edge Modifications on a Tapered Wing III : Ailerons with Simple and Spring-Linked Balancing Tabs

    NASA Technical Reports Server (NTRS)

    Purser, Paul E.; Rogallo, F.M.

    1943-01-01

    Aerodynamics data are obtained for the design of linked balancing tabs and effect of varied tab span and location to produce suitable lateral control characteristics with reasonable stick pressures for high-speed aircraft. Simple and spring-linked balancing tabs may considerably reduce control pressures if aileron system is designed for low maximum aileron deflection. Spring-linked tabs also decrease variation of stick pressure with speed and impart better controlllability at low speeds.

  5. Vibration control via stiffness switching of magnetostrictive transducers

    NASA Astrophysics Data System (ADS)

    Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.

    2016-04-01

    In this paper, a computational study is presented of structural vibration control that is realized by switching a magneto-strictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magneto-strictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magneto-strictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magneto-mechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.13; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magneto-strictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magneto-strictive shunt damping. For the cases considered, optimal resistive shunt damping performed considerably better than both voltage- and shunt-controlled stiffness switching.

  6. Vibration Control via Stiffness Switching of Magnetostrictive Transducers

    NASA Technical Reports Server (NTRS)

    Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.

    2016-01-01

    In this paper, a computational study is presented of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magneto-mechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.13; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping. For the cases considered, optimal resistive shunt damping performed considerably better than both voltage- and shunt-controlled stiffness switching.

  7. Aerodynamic Tests of a Full-scale TBF-1 Aileron Installation in the Langley 16-foot High-Speed Tunnel

    NASA Technical Reports Server (NTRS)

    Becker, John V; Korycinski, Peter F

    1944-01-01

    The failure of wing panels on a number of TBF-1 and TBM-1 airplanes in flight has prompted several investigations of the possible causes of failure. This report describes tests in the Langley 16-foot high-speed tunnel to determine whether these failures could be attributed to changes in the aerodynamic characteristics of the ailerons at high speeds. The tests were made of a 12-foot-span section including the tip and aileron of the right wing of a TBF-1 airplane. Hinge moments, control-link stresses due to aerodynamic buffeting, and fabric-deflection photographs were obtained at true airspeeds ranging from 110 to 365 miles per hour. The aileron hinge-moment coefficients were found to vary only slightly with airspeed in spite of the large fabric deflections that developed as the speed was increased. An analysis of these results indicated that the resultant hinge moment of the ailerons as installed in the airplane would tend to restore the ailerons to their neutral position for all the high-speed flight conditions covered in the tests. Serious aerodynamic buffeting occurred at up aileron angles of -10 degrees or greater because of stalling of the sharp projecting lip of the Frise aileron. The peak stresses set up in the aileron control linkages in the buffeting condition were as high as three times the mean stress. During the hinge-moment investigation, flutter of the test installation occurred at airspeeds of about 150 miles per hour. This flutter condition was investigated in some detail and slow-motion pictures were made of the motion of the wing tip and aileron. The flutter was found to involve simultaneous normal bending and chordwise oscillation of the wing and flapping of the aileron. The aileron motion appeared to be coupled with this flutter condition and was investigated in some detail and slow-motion pictures were made of the motion of the wing tip and aileron. The flutter was found to involve simultaneous normal bending and chordwise oscillation of the

  8. 14 CFR 23.455 - Ailerons.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... Devices § 23.455 Ailerons. (a) The ailerons must be designed for the loads to which they are subjected— (1) In the neutral position during symmetrical flight conditions; and (2) By the following deflections (except as limited by pilot effort), during unsymmetrical flight conditions: (i) Sudden...

  9. 14 CFR 23.455 - Ailerons.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... Devices § 23.455 Ailerons. (a) The ailerons must be designed for the loads to which they are subjected— (1) In the neutral position during symmetrical flight conditions; and (2) By the following deflections (except as limited by pilot effort), during unsymmetrical flight conditions: (i) Sudden...

  10. Properties of the grasp stiffness matrix and conservative control strategies

    SciTech Connect

    Kao, I.; Ngo, C.

    1999-02-01

    In this paper, the authors present fundamental properties of stiffness matrices as applied in analysis of grasping and dexterous manipulation in configuration spaces and linear Euclidean R{sup 3x3} space without rotational components. A conservative-stiffness matrix in such spaces needs to satisfy both symmetric and exact differential criteria. Two types of stiffness matrices are discussed: constant and configuration-dependent matrices are discussed: constant and configuration-dependent matrices. The symmetric part of a constant-stiffness matrix can be derived from a conservative quadratic potential function in the Hermitian form; while the skew-symmetric part is a function of the nonconservative curl vector field of the grasp. A configuration-dependent stiffness matrix needs to be symmetric and must simultaneously satisfy the exact differential condition to be conservative. The theory is most relevant to the Cartesian stiffness control, where the stiffness of the end effector is usually constant, such as that in RCC wrists. Conservative control strategies are proposed for a configuration-dependent stiffness matrix. One of the most important results of this paper is the nonconservative congruence mapping of stiffness between the joint and Cartesian spaces. In general, the congruence transformation (or its inverse transformation), K{sub {theta}} = J{sub {theta}}{sup T}K{sub p}J{sub {theta}}, is a nonconservative mapping over finite paths for a configuration-dependent Jacobian. Thus, to obtain a conservative system with respect to the Cartesian space, one has to either find the corresponding K{sub {theta}} at every configuration due to the constant and symmetric Cartesian stiffness matrix, or determine symmetric yet configuration-varying K{sub {theta}} at every configuration due to the constant and symmetric Cartesian stiffness matrix, or determine the symmetric yet configuration-varying K{sub {theta}} which makes the resulting configuration-dependent K{sub p

  11. Acoustic tests of the MOD-O/5A wind turbine rotor with two different ailerons

    NASA Technical Reports Server (NTRS)

    Shepherd, K. P.; Hubbard, H. H.

    1984-01-01

    The noise of a MOD-O wind turbine generator rotor equipped with plain and balanced partial span ailerons for lift and drag control was measured. Data were obtained for a wide range of aileron deflection angles and for limited ranges of wind velocity and power output. Noise levels increased as deflection angles increased and were higher in the upwind than in the downwind direction. The plain aileron exhibited a howling noise in the frequency range 400-800 Hz at deflection angles for which flow induced cavity resonances were significant.

  12. Robust Position Control of End-Effector Considering Gear Stiffness and Arm Stiffness for Industrial Robot

    NASA Astrophysics Data System (ADS)

    Tungpataratanawong, Somsawas; Chitbanchong, Satit; Miyazaki, Toshimasa; Katsura, Seiichiro; Ohishi, Kiyoshi

    Industrial robot with two-inertia model and resonant vibration suppression by using parameters from resonant identification method are addressed in this paper. By using only D-PD control with vibration suppression scheme for two-inertia model of flexible joint robot, the end-effector position does not perfectly reach the desired position owing to the effect of external force to the elastic arm. However, only gear stiffness parameter of two-inertia model is not enough, the new equivalent spring constant parameter including the stiffness of link and gear of the robot is introduced as the total arm spring constant. The novel load-side disturbance compensation considering total arm elasticity is proposed in this paper. The proposed control system is based on inner-loop vibration suppression feedback control and load-side disturbance suppression which motivates the simple consideration of the elastic joint under external torque. Moreover, the experimental results show the effectiveness of the proposed robust position control of end-effector with disturbance compensation considering total arm stiffness. The experimentation on workspace impedance control with inner-loop disturbance suppression implementing on the three degree-of-freedom (3-DOF) robot manipulator is also presented and discussed. The performance and feasibility of the proposed position control of end-effector is confirmed to apply to industrial robot manipulator without additional device.

  13. Novel Control Effectors for Truss Braced Wing

    NASA Technical Reports Server (NTRS)

    White, Edward V.; Kapania, Rakesh K.; Joshi, Shiv

    2015-01-01

    At cruise flight conditions very high aspect ratio/low sweep truss braced wings (TBW) may be subject to design requirements that distinguish them from more highly swept cantilevered wings. High aspect ratio, short chord length and relative thinness of the airfoil sections all contribute to relatively low wing torsional stiffness. This may lead to aeroelastic issues such as aileron reversal and low flutter margins. In order to counteract these issues, high aspect ratio/low sweep wings may need to carry additional high speed control effectors to operate when outboard ailerons are in reversal and/or must carry additional structural weight to enhance torsional stiffness. The novel control effector evaluated in this study is a variable sweep raked wing tip with an aileron control surface. Forward sweep of the tip allows the aileron to align closely with the torsional axis of the wing and operate in a conventional fashion. Aft sweep of the tip creates a large moment arm from the aileron to the wing torsional axis greatly enhancing aileron reversal. The novelty comes from using this enhanced and controllable aileron reversal effect to provide roll control authority by acting as a servo tab and providing roll control through intentional twist of the wing. In this case the reduced torsional stiffness of the wing becomes an advantage to be exploited. The study results show that the novel control effector concept does provide roll control as described, but only for a restricted class of TBW aircraft configurations. For the configuration studied (long range, dual aisle, Mach 0.85 cruise) the novel control effector provides significant benefits including up to 12% reduction in fuel burn.

  14. Reflection plane tests of a wind turbine blade tip section with ailerons

    NASA Technical Reports Server (NTRS)

    Savino, J. M.; Nyland, T. W.; Birchenough, A. G.; Jordan, F. L.; Campbell, N. K.

    1985-01-01

    Tests were conducted in the NASA Langley 30 by 60 foot Wind Tunnel on a full scale 7.31 m (24 ft) long tip section of a wind turbine rotor blade. The blade tip section was built with ailerons on the trailing edge. The ailerons, which spanned a length of 6.1 m (20 ft), were designed so that two types could be evaluated: the plain and the balanced. The ailerons were hinged on the suction surface at the 0.62 X chord station behind the leading edge. The purpose of the tests was to measure the aerodynamic characteristics of the blade section for: an angle of attack range from 0 deg to 90 deg aileron deflections from 0 deg to -90 deg, and Reynolds numbers of 0.79 and 1.5 x 10 to the 6th power. These data were then used to determine which aileron configuration had the most desirable rotor control and aerodynamic braking characteristics. Tests were also run to determine the effects of vortex generators, leading edge roughness, and the gaps between the aileron sections on the lift, drag, and chordwise force coefficients of the blade tip section.

  15. A theoretical investigation of the rolling oscillations of an airplane with ailerons free

    NASA Technical Reports Server (NTRS)

    Cohen, Doris

    1944-01-01

    An analysis is made of the stability of an airplane with ailerons free, with particular attention to the motions when the ailerons have a tendency to float against the wind. The present analysis supersedes the aileron investigation contained in NACA Technical Report no. 709. The equations of motion are first written to include yawing and sideslipping, and it is demonstrated that the principal effects of freeing the ailerons can be determined without regard to these motions. If the ailerons tend to float against the wind and have a high degree of aerodynamic balance, rolling oscillations, in addition to the normal lateral oscillations, are likely to occur. On the basis of the equations including only the rolling motion and the aileron deflection, formulas derived for the stability and damping of the rolling oscillations in terms of the hinge-moment derivatives are also presented showing the oscillatory regions and stability boundaries for a fictitious airplane of conventional proportion. The effects of friction in the control system are investigated and discussed.

  16. Dynamically tuned magnetostrictive spring with electrically controlled stiffness

    NASA Astrophysics Data System (ADS)

    Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.

    2016-03-01

    This paper presents the design and testing of an electrically controllable magnetostrictive spring that has a dynamically tunable stiffness (i.e., a magnetostrictive Varispring). The device enables in situ stiffness tuning or stiffness switching for vibration control applications. Using a nonlinear electromechanical transducer model and an analytical solution of linear, mechanically induced magnetic diffusion, Terfenol-D is shown to have a faster rise time to stepped voltage inputs and a significantly higher magnetic diffusion cut-off frequency relative to Galfenol. A Varispring is manufactured using a laminated Terfenol-D rod. Further rise time reductions are achieved by minimizing the rod’s diameter and winding the electromagnet with larger wire. Dynamic tuning of the Varispring’s stiffness is investigated by measuring the Terfenol-D rod’s strain response to dynamic, compressive, axial forces in the presence of sinusoidal or square wave control currents. The Varispring’s rise time is \\lt 1 ms for 1 A current switches. Continuous modulus changes up to 21.9 GPa and 500 Hz and square wave modulus changes (dynamic {{Δ }}E effect) up to 12.3 GPa and 100 Hz are observed. Stiffness tunability and tuning bandwidth can be considerably increased by operating about a more optimal bias stress and improving the control of the electrical input.

  17. Controlled Unusual Stiffness of Mechanical Metamaterials.

    PubMed

    Lee, Wooju; Kang, Da-Young; Song, Jihwan; Moon, Jun Hyuk; Kim, Dongchoul

    2016-02-03

    Mechanical metamaterials that are engineered with sub-unit structures present unusual mechanical properties depending on the loading direction. Although they show promise, their practical utility has so far been somewhat limited because, to the best of our knowledge, no study about the potential of mechanical metamaterials made from sophisticatedly tailored sub-unit structures has been made. Here, we present a mechanical metamaterial whose mechanical properties can be systematically designed without changing its chemical composition or weight. We study the mechanical properties of triply periodic bicontinuous structures whose detailed sub-unit structure can be precisely fabricated using various sub-micron fabrication methods. Simulation results show that the effective wave velocity of the structures along with different directions can be designed to introduce the anisotropy of stiffness by changing a volume fraction and aspect ratio. The ratio of Young's modulus to shear modulus can be increased by up to at least 100, which is a 3500% increase over that of isotropic material (2.8, acrylonitrile butadiene styrene). Furthermore, Poisson's ratio of the constituent material changes the ratio while Young's modulus does not influence it. This study presents the promising potential of mechanical metamaterials for versatile industrial and biomedical applications.

  18. Controlled Unusual Stiffness of Mechanical Metamaterials

    PubMed Central

    Lee, Wooju; Kang, Da-Young; Song, Jihwan; Moon, Jun Hyuk; Kim, Dongchoul

    2016-01-01

    Mechanical metamaterials that are engineered with sub-unit structures present unusual mechanical properties depending on the loading direction. Although they show promise, their practical utility has so far been somewhat limited because, to the best of our knowledge, no study about the potential of mechanical metamaterials made from sophisticatedly tailored sub-unit structures has been made. Here, we present a mechanical metamaterial whose mechanical properties can be systematically designed without changing its chemical composition or weight. We study the mechanical properties of triply periodic bicontinuous structures whose detailed sub-unit structure can be precisely fabricated using various sub-micron fabrication methods. Simulation results show that the effective wave velocity of the structures along with different directions can be designed to introduce the anisotropy of stiffness by changing a volume fraction and aspect ratio. The ratio of Young’s modulus to shear modulus can be increased by up to at least 100, which is a 3500% increase over that of isotropic material (2.8, acrylonitrile butadiene styrene). Furthermore, Poisson’s ratio of the constituent material changes the ratio while Young’s modulus does not influence it. This study presents the promising potential of mechanical metamaterials for versatile industrial and biomedical applications. PMID:26837466

  19. Controlled Unusual Stiffness of Mechanical Metamaterials

    NASA Astrophysics Data System (ADS)

    Lee, Wooju; Kang, Da-Young; Song, Jihwan; Moon, Jun Hyuk; Kim, Dongchoul

    2016-02-01

    Mechanical metamaterials that are engineered with sub-unit structures present unusual mechanical properties depending on the loading direction. Although they show promise, their practical utility has so far been somewhat limited because, to the best of our knowledge, no study about the potential of mechanical metamaterials made from sophisticatedly tailored sub-unit structures has been made. Here, we present a mechanical metamaterial whose mechanical properties can be systematically designed without changing its chemical composition or weight. We study the mechanical properties of triply periodic bicontinuous structures whose detailed sub-unit structure can be precisely fabricated using various sub-micron fabrication methods. Simulation results show that the effective wave velocity of the structures along with different directions can be designed to introduce the anisotropy of stiffness by changing a volume fraction and aspect ratio. The ratio of Young’s modulus to shear modulus can be increased by up to at least 100, which is a 3500% increase over that of isotropic material (2.8, acrylonitrile butadiene styrene). Furthermore, Poisson’s ratio of the constituent material changes the ratio while Young’s modulus does not influence it. This study presents the promising potential of mechanical metamaterials for versatile industrial and biomedical applications.

  20. Morphological Computation of Haptic Perception of a Controllable Stiffness Probe

    PubMed Central

    Sornkarn, Nantachai; Dasgupta, Prokar; Nanayakkara, Thrishantha

    2016-01-01

    When people are asked to palpate a novel soft object to discern its physical properties such as texture, elasticity, and even non-homogeneity, they not only regulate probing behaviors, but also the co-contraction level of antagonistic muscles to control the mechanical impedance of fingers. It is suspected that such behavior tries to enhance haptic perception by regulating the function of mechanoreceptors at different depths of the fingertips and proprioceptive sensors such as tendon and spindle sensors located in muscles. In this paper, we designed and fabricated a novel two-degree of freedom variable stiffness indentation probe to investigate whether the regulation of internal stiffness, indentation, and probe sweeping velocity (PSV) variables affect the accuracy of the depth estimation of stiff inclusions in an artificial silicon phantom using information gain metrics. Our experimental results provide new insights into not only the biological phenomena of haptic perception but also new opportunities to design and control soft robotic probes. PMID:27257814

  1. Morphological Computation of Haptic Perception of a Controllable Stiffness Probe.

    PubMed

    Sornkarn, Nantachai; Dasgupta, Prokar; Nanayakkara, Thrishantha

    2016-01-01

    When people are asked to palpate a novel soft object to discern its physical properties such as texture, elasticity, and even non-homogeneity, they not only regulate probing behaviors, but also the co-contraction level of antagonistic muscles to control the mechanical impedance of fingers. It is suspected that such behavior tries to enhance haptic perception by regulating the function of mechanoreceptors at different depths of the fingertips and proprioceptive sensors such as tendon and spindle sensors located in muscles. In this paper, we designed and fabricated a novel two-degree of freedom variable stiffness indentation probe to investigate whether the regulation of internal stiffness, indentation, and probe sweeping velocity (PSV) variables affect the accuracy of the depth estimation of stiff inclusions in an artificial silicon phantom using information gain metrics. Our experimental results provide new insights into not only the biological phenomena of haptic perception but also new opportunities to design and control soft robotic probes. PMID:27257814

  2. Acute Achilles tendinopathy: effect of pain control on leg stiffness.

    PubMed

    Maquirriain, J; Kokalj, A

    2014-03-01

    Tendinopathies are a major cause of disability in the athletic population; the main purpose of the treatment of these injuries is to reduce pain and improve function. The aim of this study was to evaluate the effect of NSAIDs on leg stiffness of patients suffering acute unilateral Achilles tendinopathy. Twenty-eight eligible male athletes (aged 39.1 ± 10.3 y) suffering acute Achilles tendinopathy were treated with etoricoxib (120 mg oral once daily) during 7 days. Pain (100-mm visual analogue scale-VAS), analgesic effect (percentage of 100-mm VAS reduction), and leg stiffness were evaluated pre- and post- anti-inflammatory treatment. Results of this study showed that over the 7-day treatment period, etoricoxib provided significant relief of Achilles tendon pain (VAS) compared to that experienced at baseline: 54.5 ± 21.6 and 24.5 ± 24.8, respectively (p<0.001). Leg stiffness showed a significant improvement after one-week NSAID therapy: LSR 0.89 ± 0.1 vs. 0.97 ± 0.1; (p=0.02). In conclusion, findings of this study demonstrated that patients suffering acute unilateral Achilles tendinopathy increased their leg stiffness of the affected side after oral anti-inflammatory therapy. Effective control of tendon pain in the acute phase of such sports-related injuries may contribute to improve capabilities associated with high performance like leg stiffness. PMID:24583548

  3. Dynamic Estimation of Environmental Stiffness by Bilateral Control

    NASA Astrophysics Data System (ADS)

    Takei, Takayoshi; Shimono, Tomoyuki; Ohnishi, Kouhei

    Recently, minimally invasive surgery (MIS) has become apparent. Research has been performed on surgical robots needed in MIS. In the case of MIS, it is effective to express environmental impedance as numerical data in order to preserve it for establishing standard reference values of the conditions of internal organs. In this paper, we propose a novel method for the estimation of stiffness in real environments in which bilaterally controlled robots are needed. By using the proposed method, environmental stiffness can be estimated dynamically regardless of the initial position of slave system. The viability of the proposed method is confirmed from the experimental results.

  4. Nanostructured conducting polymers for stiffness controlled cell adhesion

    NASA Astrophysics Data System (ADS)

    Moyen, Eric; Hama, Adel; Ismailova, Esma; Assaud, Loic; Malliaras, George; Hanbücken, Margrit; Owens, Roisin M.

    2016-02-01

    We propose a facile and reproducible method, based on ultra thin porous alumina membranes, to produce cm2 ordered arrays of nano-pores and nano-pillars on any kind of substrates. In particular our method enables the fabrication of conducting polymers nano-structures, such as poly[3,4-ethylenedioxythiophene]:poly[styrene sulfonate] (PEDOT:PSS). Here, we demonstrate the potential interest of those templates with controlled cell adhesion studies. The triggering of the eventual fate of the cell (proliferation, death, differentiation or migration) is mediated through chemical cues from the adsorbed proteins and physical cues such as surface energy, stiffness and topography. Interestingly, as well as through material properties, stiffness modifications can be induced by nano-topography, the ability of nano-pillars to bend defining an effective stiffness. By controlling the diameter, length, depth and material of the nano-structures, one can possibly tune the effective stiffness of a (nano) structured substrate. First results indicate a possible change in the fate of living cells on such nano-patterned devices, whether they are made of conducting polymer (soft material) or silicon (hard material).

  5. Controllable-stiffness components based on magnetorheological elastomers

    NASA Astrophysics Data System (ADS)

    Ginder, John M.; Nichols, Mark E.; Elie, Larry D.; Clark, Seamus M.

    2000-06-01

    So-called magnetorheological (MR) elastomers, comprising rubbery polymers loaded with magnetizable particles that are aligned in a magnetic field, possess dynamic stiffness and damping that can subsequently be controlled by applied fields. Tunable automotive bushings and mounts incorporating these materials and an embedded magnetic field source have been constructed. In this article, the response of these components to dynamic mechanical loading is described. They behave essentially as elastomeric springs with stiffness and damping that is increased by tens of percent with an applied electrical current. Their time of response to a change in current is less than ten milliseconds. In addition to a tunable spring or force generator, these components may also serve as deflection sensors.

  6. The aileron as an aid to recovery from the spin

    NASA Technical Reports Server (NTRS)

    Neihouse, A I

    1940-01-01

    As part of a general investigation by the NACA of factors that affect the spin, the use of the aileron as an aid to recovery from the spin was studied. Tests of 10 different models, covering a wide range of mass distribution, were made in the NACA free-spinning tunnel to determine the effects of a large downward deflection of the outboard aileron and of normal angular deflections of the ailerons upon recovery characteristics. The results indicate that the direction of aileron setting, with or against the spin, which will aid recovery from the spin depends upon the airplane weight distribution. For monoplanes and for biplanes with lower-wing ailerons, ailerons with the spin will be favorable when the weight is distributed chiefly along the fuselage (single-engine airplanes) and ailerons against the spin will be favorable when the weight is distributed chiefly along the wings (multi engine airplanes). Downward movement of the outboard aileron through a large angle will not always be effective in aiding recovery, the effectiveness of such a movement also being dependent upon the weight distribution of the airplane.

  7. Experimental characterization of an adaptive aileron: lab tests and FE correlation

    NASA Astrophysics Data System (ADS)

    Amendola, Gianluca; Dimino, Ignazio; Amoroso, Francesco; Pecora, Rosario

    2016-04-01

    Like any other technology, morphing has to demonstrate system level performance benefits prior to implementation onto a real aircraft. The current status of morphing structures research efforts (as the ones, sponsored by the European Union) involves the design of several subsystems which have to be individually tested in order to consolidate their general performance in view of the final integration into a flyable device. This requires a fundamental understanding of the interaction between aerodynamic, structure and control systems. Important worldwide research collaborations were born in order to exchange acquired experience and better investigate innovative technologies devoted to morphing structures. The "Adaptive Aileron" project represents a joint cooperation between Canadian and Italian research centers and leading industries. In this framework, an overview of the design, manufacturing and testing of a variable camber aileron for a regional aircraft is presented. The key enabling technology for the presented morphing aileron is the actuation structural system, integrating a suitable motor and a load-bearing architecture. The paper describes the lab test campaign of the developed device. The implementation of a distributed actuation system fulfills the actual tendency of the aeronautical research to move toward the use of electrical power to supply non-propulsive systems. The aileron design features are validated by targeted experimental tests, demonstrating both its adaptive capability and robustness under operative loads and its dynamic behavior for further aeroelastic analyses. The experimental results show a satisfactory correlation with the numerical expectations thus validating the followed design approach.

  8. Results of differential elevon/aileron deflection for lateral control optimization and elevon hinge moment investigations on an 0.015-scale model (49-0) of the space shuttle orbiter in the NASA/Langley Research Center 8 foot TPT (OA116)

    NASA Technical Reports Server (NTRS)

    Lindsey, A. I.; Milam, M. D.

    1974-01-01

    Aerodynamic investigations were conducted in a transonic pressure tunnel on an 0.015 scale model of the space shuttle orbiter. Major test objectives were to determine: (1) transonic differential elevon/aileron lateral control optimization; (2) transonic elevon hinge moments; (3) transonic effects of the baseline 6 inch elevon/elevon and elevon/fuselage gaps; and (4) transonic effects of the short OMS pods. Six-component aerodynamic force and moment, and elevon hinge moment data, were recorded over an angle-of-attack range form -2 to +22 degrees.

  9. Comparative wind tunnel test at high Reynolds numbers of NACA 64 621 airfoils with two aileron configurations

    NASA Technical Reports Server (NTRS)

    Gregorek, G. M.

    1995-01-01

    An experimental program to measure the aerodynamic characteristics of the NACA 64-621 airfoil when equipped with plain ailerons of 0.38 chord and 0.30 chord and with 0.38 chord balanced aileron has been conducted in the pressurized O.S.U. 6 x 12 ft High Reynolds Number Wind Tunnel. Surface pressures were measured and integrated to yield lift and pressure drag coefficients for angles of attack from -3 to +42 deg and for selected aileron deflections from 0 to -90 deg at nominal Mach and Reynolds numbers of 0.25 and 5 x 10(exp 6). When resolved into thrust coefficient for wind turbine aerodynamic control applications, the data indicated the anticipated decrease in thrust coefficient with negative aileron deflection at low angles of attack; however, as angle of attack increased, thrust coefficients eventually became positive. All aileron configurations, even at -90 deg deflections showed this trend. Hinge moments for each configuration complete the data set.

  10. Wind-Tunnel Investigation of Wings with Ordinary Ailerons and Full-Span External-Airfoil Flaps

    NASA Technical Reports Server (NTRS)

    Platt, Robert C; Shortal, Joseph A

    1937-01-01

    Report presents an investigation carried out in the NACA 7- by 10-foot wind tunnel of an NACA 23012 airfoil equipped, first, with a full-span NACA 23012 external-airfoil flap having a chord 0.20 of the main airfoil chord and with a full-span aileron with a chord 0.12 of the main airfoil chord on the trailing edge of the main airfoil and equipped second, with a 0.30-chord full-span NACA 23012 external-airfoil flap and a 0.13-chord full-span aileron. The results are arranged in three groups, the first two of which deal with the airfoil characteristics of the two airfoil-flap combinations and with the internal-control characteristics of the airfoil-flap-aileron combinations. The third group of tests deals with several means for balancing ailerons mounted on a special large-chord NACA 23012 external-airfoil flap. The tests included an ordinary aileron, a curtained-nose balance, a frise balance, and a tab.

  11. Advanced composite aileron for L-1011 transport aircraft

    NASA Technical Reports Server (NTRS)

    1978-01-01

    Design and evaluation of alternate concepts for the major subcomponents of the advanced composite aileron (ACA) was completed. From this array of subcomponents, aileron assemblies were formulated and evaluated. Based on these analyses a multirib assembly with graphite tape/syntactic core covers, a graphite tape front spar, and a graphite fabric rib was selected for development. A weight savings of 29.1 percent (40.8 pounds per aileron) is predicted. Engineering cost analyses indicate that the production cost of the ACA will be 7.3 percent less than the current aluminum aileron. Fabrication, machining, and testing of the material evaluation specimens for the resin screening program was completed. The test results lead to the selection of Narmco 5208 resin for the ACA. Other activities completed include: the detailed design of the ACA, construction of a three dimensional finite element model for structural analysis, and formulation of detail plans for material verification and process development.

  12. Integrated, proportionally controlled, and naturally compliant universal joint actuator with controllable stiffness

    DOEpatents

    Borenstein, Johann; Granosik, Grzegorz

    2005-03-22

    An apparatus for traversing obstacles having an elongated, round, flexible body that includes a plurality of segments interconnected by an integrated joint actuator assembly. The integrated joint actuator assembly includes a plurality of bellows-type actuators individually coupling adjacent segments to permit pivotal actuation of the apparatus therebetween. A controller is employed to maintain proper positional control and stiffness control while minimize air flow.

  13. Full-scale Wind-tunnel and Flight Test of a Fairchild 22 Airplane Equipped with a Zap Flap and Zap Ailerons

    NASA Technical Reports Server (NTRS)

    Dearborn, C H; Soule, H A

    1937-01-01

    A wing equipped with a Zap flap and Zap ailerons was tested on a Fairchild 22 airplane in the full-scale wind tunnel and in flight to determine the effect of the flaps and ailerons on the performance and the control characteristics of the airplane. The flaps were 0.30 of the wing chord and 0.83 of the wing span. Two sets of ailerons having equal areas but different proportions were tested, one set being 0.56 of the semispan and 0.18 of the chord and the other set being 0.46 of the semispan and 0.22 of the chord. The wind-tunnel tests showed that, when the ailerons and horizontal tail surfaces were removed, the flaps increased the maximum lift coefficient from 1.48 to 2.39. In flight, the fully deflected flaps decreased the minimum speed from 48.2 to 38.8 miles per hour. The take-off and landing distances were both reduced by the flaps. The wind-tunnel tests showed the ailerons to increase the drag coefficient, at a lift coefficient and Reynolds Number corresponding to the high speed of the airplane, from 0.0432 to 0.0498 and 0.0514, the 0.46 semispan ailerons giving the highest drag. In the flight tests both sets of ailerons were found to give satisfactory rolling action in the normal-flight range. They required relatively large stick forces for their operation, however, and the variation of the forces with aileron deflection was not linear.

  14. Variable stiffness and damping semi-active vibration control technology based on magnetorheological fluids

    NASA Astrophysics Data System (ADS)

    Zhao, Shiyu; Deng, Huaxia; Zhang, Jin; Sun, ShuaiShuai; Li, Weihua; Wang, Lei

    2013-10-01

    Vibration is a source to induce uncertainty for the measurement. The traditional passive vibration control method has low efficiency and limited working conditions. The active vibration control method is not practical for its power demanding, complexity and instability. In this paper, a novel semi-active vibration control technology based on magnetorheological (MR) fluid is presented with dual variable stiffness and damping capability. Because of the rheological behavior depending on the magnetic field intensity, MR fluid is used in many damping semi-active vibration control systems. The paper proposed a structure to allow the both overall damping and stiffness variable. The equivalent damping and stiffness of the structure are analyzed and the influences of the parameters on the stiffness and damping changing are further discussed.

  15. Vibration isolation and reduction by spring-stiffness control based on theory of variable structure systems

    SciTech Connect

    Yamaguchi, H.; Shioya, S.; Oda, M.

    1995-12-31

    By controlling spring stiffness, vibration reduction and isolation for the mass-spring system are achieved in this paper. The control algorithm of the spring stiffness is based on the variable structure systems (VSS) theory. The stiffness-controllable spring is achieved by using two straight bars that are hinged to the mass in a line perpendicular to the direction of mass motion and are applied axial force. Since the axial force causes restoring force equivalent to the spring, the stiffness is controlled by the axial force. In the numerical simulations and experiments, the settling time of the impulse response and the displacement transmissibility are investigated. The results show that the proposed method is effective in suppressing shock motion and isolating vibration transmitted from the floor.

  16. Design and Testing of a Dynamically-Tuned Magnetostrictive Spring with Electrically-Controlled Stiffness

    NASA Technical Reports Server (NTRS)

    Scheidler, Justin; Asnani, Vivake M.; Dapino, Marcelo J.

    2015-01-01

    This paper details the development of an electrically-controlled, variable-stiffness spring based on magnetostrictive materials. The device, termed a magnetostrictive Varispring, can be applied as a semi-active vibration isolator or switched stiffness vibration controller for reducing transmitted vibrations. The Varispring is designed using 1D linear models that consider the coupled electrical response, mechanically-induced magnetic diffusion, and the effect of internal mass on dynamic stiffness. Modeling results illustrate that a Terfenol-D-based Varispring has a rise time almost an order of magnitude smaller and a magnetic diffusion cut-off frequency over two orders of magnitude greater than a Galfenol-based Varispring. The results motivate the use of laminated Terfenol-D rods for a greater stiffness tuning range and increased bandwidth. The behavior of a prototype Varispring is examined under vibratory excitation up to 6 MPa and 25 Hz using a dynamic load frame. For this prototype, stiffness is indirectly varied by controlling the excitation current. Preliminary measurements of continuous stiffness tuning via sinusoidal currents up to 1 kHz are presented. The measurements demonstrate that the Young's modulus of the Terfenol-D rod inside the Varispring can be continuously varied by up to 21.9 GPa. The observed stiffness tuning range is relatively constant up to 500 Hz, but significantly decreases thereafter. The stiffness tuning range can be greatly increased by improving the current and force control such that a more consistent current can be applied and the Varispring can be accurately tested at a more optimal bias stress.

  17. Real-time control of geometry and stiffness in adaptive structures

    NASA Technical Reports Server (NTRS)

    Ramesh, A. V.; Utku, S.; Wada, B. K.

    1991-01-01

    The basic theory is presented for the geometry, stiffness, and damping control of adaptive structures, with emphasis on adaptive truss structures. Necessary and sufficient conditions are given for stress-free geometry control in statically determinate and indeterminate adaptive discrete structures. Two criteria for selecting the controls are proposed, and their use in real-time control is illustrated by numerical simulation results. It is shown that the stiffness and damping control of adaptive truss structures for vibration suppression is possible by elongation and elongation rate dependent feedback forces from the active elements.

  18. Measurement of the UH-60A Hub Large Rotor Test Apparatus Control System Stiffness

    NASA Technical Reports Server (NTRS)

    Kufeld, Robert M.

    2014-01-01

    This purpose of this report is to provides details of the measurement of the control system stiffness of the UH-60A rotor hub mounted on the Large Rotor Test Apparatus (UH-60A/LRTA). The UH-60A/LRTA was used in the 40- by 80-Foot Wind Tunnel to complete the full-scale wind tunnel test portion of the NASA / ARMY UH-60A Airloads Program. This report describes the LRTA control system and highlights the differences between the LRTA and UH-60A aircraft. The test hardware, test setup, and test procedures are also described. Sample results are shown, including the azimuthal variation of the measured control system stiffness for three different loadings and two different dynamic actuator settings. Finally, the azimuthal stiffness is converted to fixed system values using multi-blade transformations for input to comprehensive rotorcraft prediction codes.

  19. Neural control of leg stiffness during hopping in boys and men.

    PubMed

    Oliver, J L; Smith, P M

    2010-10-01

    The purpose of the study was to investigate whether boys and men utilise different control strategies whilst hopping. Eleven boys (11-12yr old) and ten men completed hopping at 1.5Hz, 3.0Hz and at their preferred frequency. A footswitch measured contact and flight times, from which leg stiffness was calculated. Simultaneously, surface electromyograms (EMGs) of selected lower limb muscles were recorded and quantified for each 30ms period during the first 120ms post-ground contact. At 1.5Hz there were no differences between the groups in relative stiffness or muscle activity. At 3.0Hz men had significantly shorter contact times (P=0.013), longer flight times (P=0.002), greater relative stiffness (P=0.01) and significantly greater soleus (P=0.012) and vastus lateralis (P<0.001) activity during the initial 30ms post-ground contact. At the preferred frequency men hopped significantly faster than the boys (P=0.007), with greater leg stiffness (P<0.01) and with more extensor activity in most time periods. Boys and men demonstrated similar control strategies when hopping at a slow frequency, but when hopping frequency increased men were able to better increase feedforward and reflex muscle activity to hop with greater relative stiffness.

  20. Seismic Response Control Of Structures Using Semi-Active and Passive Variable Stiffness Devices

    NASA Astrophysics Data System (ADS)

    Salem, Mohamed M. A.

    Controllable devices such as Magneto-Rheological Fluid Dampers, Electro-Rheological Dampers, and controllable friction devices have been studied extensively with limited implementation in real structures. Such devices have shown great potential in reducing seismic demands, either as smart base isolation systems, or as smart devices for multistory structures. Although variable stiffness devices can be used for seismic control of structures, the vast majority of research effort has been given to the control of damping. The primary focus of this dissertation is to evaluate the seismic control of structures using semi-active and passive variable stiffness characteristics. Smart base isolation systems employing variable stiffness devices have been studied, and two semi-active control strategies are proposed. The control algorithms were designed to reduce the superstructure and base accelerations of seismically isolated structures subject to near-fault and far-field ground motions. Computational simulations of the proposed control algorithms on the benchmark structure have shown that excessive base displacements associated with the near-fault ground motions may be better mitigated with the use of variable stiffness devices. However, the device properties must be controllable to produce a wide range of stiffness changes for an effective control of the base displacements. The potential of controllable stiffness devices in limiting the base displacement due to near-fault excitation without compromising the performance of conventionally isolated structures, is illustrated. The application of passive variable stiffness devices for seismic response mitigation of multistory structures is also investigated. A stiffening bracing system (SBS) is proposed to replace the conventional bracing systems of braced frames. An optimization process for the SBS parameters has been developed. The main objective of the design process is to maintain a uniform inter-story drift angle over the

  1. Wind tunnel force and pressure tests of a 21% thick general aviation airfoil with 20% aileron, 25% slotted flap and 10% slot-lip spoiler

    NASA Technical Reports Server (NTRS)

    Wentz, W. H., Jr.; Fiscko, K. A.

    1979-01-01

    Force and surface pressure distributions were measured for the 21% LS(1)-0421 modified airfoil fitted with 20% aileron, 25% slotted flap and 10% slot lip spoiler. All tests were conducted at a Reynolds number of 2.2 x 10 to the 6th power and a Mach number of 0.13. The lift, drag, pitching moments, control surface normal force and hinge moments, and surface pressure distributions are included in the results. Incremental performance of flap and aileron are discussed and compared to the GA(W)-2 airfoil. Spoiler control which shows a slight reversal tendency at high alpha, is examined.

  2. Human motor control consequences of thixotropic changes in muscular short-range stiffness.

    PubMed

    Axelson, H W; Hagbarth, K E

    2001-08-15

    nervous system in its control of voluntary movements takes account of and compensates for the history-dependent degree of inherent short-range stiffness of the muscles antagonistic to the prime movers.

  3. Advantages and disadvantages of stiffness instructions when studying postural control.

    PubMed

    Bonnet, Cédrick T

    2016-05-01

    To understand the maintenance of upright stance, researchers try to discover the fundamental mechanisms and attentional resources devoted to postural control and eventually to the performance of other tasks (e.g., counting in the head). During their studies, some researchers require participants to stand as steady as possible and other simply ask participants to stand naturally. Surprisingly, a clear and direct explanation of the usefulness of the steadiness requirement seems to be lacking, both in experimental and methodological discussions. Hence, the objective of the present note was to provide advantages and disadvantages of this steadiness requirement in studies of postural control. The advantages may be to study fundamental postural control, to eliminate useless postural variability, to control spurious body motions and to control the participants' thoughts. As disadvantages, this steadiness requirement only leads to study postural control in unnatural upright stance, it changes the focus of attention (internal vs. external) and the nature of postural control (unconscious vs. conscious), it increases the difficulty of a supposedly easy control task and it eliminates or reduces the opportunity to record exploratory behaviors. When looking carefully at the four advantages of the steadiness requirement, one can believe that they are, in fact, more disadvantageous than advantageous. Overall therefore, this requirement seems illegitimate and it is proposed that researchers should not use it in the study of postural control. They may use this requirement only if they search to know the limit until which participants can consciously reduce their postural sway.

  4. Semi-active variable stiffness vibration control of vehicle seat suspension using an MR elastomer isolator

    NASA Astrophysics Data System (ADS)

    Du, Haiping; Li, Weihua; Zhang, Nong

    2011-10-01

    This paper presents a study on continuously variable stiffness control of vehicle seat suspension using a magnetorheological elastomer (MRE) isolator. A concept design for an MRE isolator is proposed in the paper and its behavior is experimentally evaluated. An integrated seat suspension model, which includes a quarter-car suspension and a seat suspension with a driver body model, is used to design a sub-optimal H_{\\infty } controller for an active isolator. The desired control force generated by this active isolator is then emulated by the MRE isolator through its continuously variable stiffness property when the actuating condition is met. The vibration control effect of the MRE isolator is evaluated in terms of driver body acceleration responses under both bump and random road conditions. The results show that the proposed control strategy achieves better vibration reduction performance than conventional on-off control.

  5. Evaluation of a game controller using human stiffness estimated from electromyogram.

    PubMed

    Watanabe, Masato; Yamamoto, Taisuke; Kambara, Hiroyuki; Koike, Yasuharu

    2010-01-01

    A motion controller which has an acceleration sensor increases reality and intuitiveness in sports games. But we adjust not only visible posture but also invisible force like stiffness and viscosity when we play sports. We propose a game controller using player's movement and force by using acceleration and electromyogram(EMG). In this research, we compared conventional motion controller and proposed method by using a golf game. The score was the distance between cup position and carried ball position. For beginner of video games, proposed method is superior than conventional. For well-trained video game players conventional button type controller wins on accurate input. Because it was difficult to keep arm stiffness constant than button. Using coarsely-quantized EMG might resolve this problem, then achieve intuitive and easy-to-use game controller.

  6. A new active variable stiffness suspension system using a nonlinear energy sink-based controller

    NASA Astrophysics Data System (ADS)

    Anubi, Olugbenga Moses; Crane, Carl D.

    2013-10-01

    This paper presents the active case of a variable stiffness suspension system. The central concept is based on a recently designed variable stiffness mechanism which consists of a horizontal control strut and a vertical strut. The horizontal strut is used to vary the load transfer ratio by actively controlling the location of the point of attachment of the vertical strut to the car body. The control algorithm, effected by a hydraulic actuator, uses the concept of nonlinear energy sink (NES) to effectively transfer the vibrational energy in the sprung mass to a control mass, thereby reducing the transfer of energy from road disturbance to the car body at a relatively lower cost compared to the traditional active suspension using the skyhook concept. The analyses and simulation results show that a better performance can be achieved by subjecting the point of attachment of a suspension system, to the chassis, to the influence of a horizontal NES system.

  7. Advanced composite aileron for L-1011 transport aircraft: Design and analysis

    NASA Technical Reports Server (NTRS)

    Griffin, C. F.; Fogg, L. D.; Dunning, E. G.

    1981-01-01

    Detail design of the composite aileron has been completed. The aileron design is a multi-rib configuration with single piece upper and lower covers mechanically fastened to the substructure. Covers, front, spar and ribs are fabricated with graphite/epoxy tape or fabric composite material. The design has a weight savings of 23 percent compared to the aluminum aileron. The composite aileron has 50 percent fewer fasteners and parts than the metal aileron and is predicted to be cost competitive. Structural integrity of the composite aileron was verified by structural analysis and an extensive test program. Static, failsafe, and vibration analyses have been conducted on the composite aileron using finite element models and specialized computer programs for composite material laminates. The fundamental behavior of the composite materials used in the aileron was determined by coupon tests for a variety of environmental conditions. Critical details of the design were interrogated by static and fatigue tests on full-scale subcomponents and subassemblies of the aileron.

  8. Comparative wind tunnel tests of NACA 23024 airfoils with several aileron and spoiler configurations

    NASA Technical Reports Server (NTRS)

    Wentz, W. H., Jr.; Snyder, M. H.

    1995-01-01

    This paper reviews research efforts at Wichita State University sponsored by NASA Lewis Research Center to design and evaluate aerodynamic braking devices which will be smaller and lighter than full-chord blade pitch control. Devices evaluated include a variety of aileron configurations, and spoilers located at both trailing edge and near the leading edge. The paper discusses analytical modeling, wind tunnel tests, and for some configurations, full-scale rotor tests. Current designs have not provided adequate control power at high angles of attack (low tip-speed-ratios). The reasons for these limitations are discussed. Analysis and wind tunnel test data indicate that several options are available to the designer to provide aerodynamic slowdown without full-chord pitch control. Three options are suggested; adding venting in front of the control surface hingeline, using spoilers located near the leading edge, and using a two-piece control combining downward deflection inboard with upward deflection outboard.

  9. Regulation of astrocyte activity via control over stiffness of cellulose acetate electrospun nanofiber.

    PubMed

    Min, Seul Ki; Jung, Sang Myung; Ju, Jung Hyeon; Kwon, Yeo Seon; Yoon, Gwang Heum; Shin, Hwa Sung

    2015-10-01

    Astrocytes are involved in neuron protection following central nervous system (CNS) injury; accordingly, engineered astrocytes have been investigated for their usefulness in cell therapy for CNS injury. Nanofibers have attracted a great deal of attention in neural tissue engineering, but their mechanical properties greatly influence physiology. Cellulose acetate (CA) has been studied for use in scaffolds owing to its biocompatibility, biodegradability, and good thermal stability. In this study, stiffness of CA nanofibers controlled by heat treatment was shown to regulate astrocyte activity. Adhesion and viability increased in culture as substrate became stiffer but showed saturation at greater than 2 MPa of tensile strength. Astrocytes became more active in terms of increasing intermediate filament glial fibrillary acidic protein (GFAP). The results of this study demonstrate the effects of stiffness alone on cellular behaviors in a three-dimensional culture and highlight the efficacy of heat-treated CA for astrocyte culture in that the simple treatment enables control of astrocyte activity. PMID:26091629

  10. Damping control in a spring and suspension with sign-changing stiffness

    NASA Astrophysics Data System (ADS)

    Lee, C.-M.; Goverdovskiy, V. N.

    2016-07-01

    Vibration isolation in a range as close to zero frequency as possible is important for human and sensitive high-precision equipment. Springs with variable sign-changing stiffness can cancel the stiffness and provide perfect vibration isolation. However, it is possible in certain damping conditions. This paper presents an approach of damping control in suspensions with such springs. A model of the mode of deformation is formulated and validated for analysis of structural damping in the springs. A vibration model is formulated to estimate a maximum efficiency of a soft suspension in the infra frequency range and predict a reasonable level of slip damping. Novel materials and designs are demonstrated for control and minimization of the damping. Validity of the approach is illustrated with numeric and measured data obtained from development test of the springs and suspensions equipped with such springs.

  11. Regulation of astrocyte activity via control over stiffness of cellulose acetate electrospun nanofiber.

    PubMed

    Min, Seul Ki; Jung, Sang Myung; Ju, Jung Hyeon; Kwon, Yeo Seon; Yoon, Gwang Heum; Shin, Hwa Sung

    2015-10-01

    Astrocytes are involved in neuron protection following central nervous system (CNS) injury; accordingly, engineered astrocytes have been investigated for their usefulness in cell therapy for CNS injury. Nanofibers have attracted a great deal of attention in neural tissue engineering, but their mechanical properties greatly influence physiology. Cellulose acetate (CA) has been studied for use in scaffolds owing to its biocompatibility, biodegradability, and good thermal stability. In this study, stiffness of CA nanofibers controlled by heat treatment was shown to regulate astrocyte activity. Adhesion and viability increased in culture as substrate became stiffer but showed saturation at greater than 2 MPa of tensile strength. Astrocytes became more active in terms of increasing intermediate filament glial fibrillary acidic protein (GFAP). The results of this study demonstrate the effects of stiffness alone on cellular behaviors in a three-dimensional culture and highlight the efficacy of heat-treated CA for astrocyte culture in that the simple treatment enables control of astrocyte activity.

  12. Failure Analysis of T-38 Aircraft Burst Hydraulic Aileron Return Line

    NASA Technical Reports Server (NTRS)

    Martinez, J. E.; Figert, J. D.; Paton, R. M.; Nguyen, S. D.; Flint, A.

    2012-01-01

    During maintenance troubleshooting for fluctuating hydraulic pressures, a technician found that a right hand aileron return line, on the flight hydraulic side, was ruptured (Fig. 1, 2). This tubing is part of the Hydraulic Flight Control Aileron Return Reducer to Aileron Manifold and is suspected to be original to the T-38 Talon trainer aircraft. Ailerons are small hinged sections on the outboard portion of a wing used to generate rolling motion thereby banking the aircraft. The ailerons work by changing the effective shape of the airfoil of the outer portion of the wing [1]. The drawing, Northrop P/N 3-43033-55 (6/1960), specifies that the line is made from 0.375 inch OD, aluminum 5052-0 tubing with a 0.049 inch wall thickness. WW-T-787 requires the tube shall be seamless and uniform in quality and temper [2]. The test pressure for this line is 3000 psi, and the operational pressure for this line is estimated to be between 45 psi and 1500 psi based on dynamic loading during flight. Examination of the fracture surface found evidence of arrest bands originating on the inner diameter (Fig 3). Ductile dimples are observed on the tube fractures (Fig. 4). The etched cross-section revealed thinning and work-hardening in the burst region (Fig. 5). The wall thickness just outside the work-hardened fracture region measured 0.035". Barlow's Formula: P = 2St/D, where P is burst pressure, S is allowable stress, t is wall thickness and D is the outer diameter of tube. Using the ultimate tensile strength of 28 ksi and a measured wall thickness of 0.035 inches at burst, P = 5.2 ksi (burst pressure). Using the yield of 13 ksi (YS) for aluminum 5052-0, plastic deformation will happen at P = 2.4 ksi suggesting plastic deformation occurred at a proof pressure of 3.0 ksi. Conclusion: The burst resulted from high stress, low-cycle fatigue. Evidence of arrest bands originating on the inner diameter. Fracture is predominately shear dimples, characteristic of high load ductile fractures

  13. Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption

    PubMed Central

    Inouye, Joshua M.; Valero-Cuevas, Francisco J.

    2016-01-01

    Much debate has arisen from research on muscle synergies with respect to both limb impedance control and energy consumption. Studies of limb impedance control in the context of reaching movements and postural tasks have produced divergent findings, and this study explores whether the use of synergies by the central nervous system (CNS) can resolve these findings and also provide insights on mechanisms of energy consumption. In this study, we phrase these debates at the conceptual level of interactions between neural degrees of freedom and tasks constraints. This allows us to examine the ability of experimentally-observed synergies—correlated muscle activations—to control both energy consumption and the stiffness component of limb endpoint impedance. In our nominal 6-muscle planar arm model, muscle synergies and the desired size, shape, and orientation of endpoint stiffness ellipses, are expressed as linear constraints that define the set of feasible muscle activation patterns. Quadratic programming allows us to predict whether and how energy consumption can be minimized throughout the workspace of the limb given those linear constraints. We show that the presence of synergies drastically decreases the ability of the CNS to vary the properties of the endpoint stiffness and can even preclude the ability to minimize energy. Furthermore, the capacity to minimize energy consumption—when available—can be greatly affected by arm posture. Our computational approach helps reconcile divergent findings and conclusions about task-specific regulation of endpoint stiffness and energy consumption in the context of synergies. But more generally, these results provide further evidence that the benefits and disadvantages of muscle synergies go hand-in-hand with the structure of feasible muscle activation patterns afforded by the mechanics of the limb and task constraints. These insights will help design experiments to elucidate the interplay between synergies and the

  14. Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption.

    PubMed

    Inouye, Joshua M; Valero-Cuevas, Francisco J

    2016-02-01

    Much debate has arisen from research on muscle synergies with respect to both limb impedance control and energy consumption. Studies of limb impedance control in the context of reaching movements and postural tasks have produced divergent findings, and this study explores whether the use of synergies by the central nervous system (CNS) can resolve these findings and also provide insights on mechanisms of energy consumption. In this study, we phrase these debates at the conceptual level of interactions between neural degrees of freedom and tasks constraints. This allows us to examine the ability of experimentally-observed synergies--correlated muscle activations--to control both energy consumption and the stiffness component of limb endpoint impedance. In our nominal 6-muscle planar arm model, muscle synergies and the desired size, shape, and orientation of endpoint stiffness ellipses, are expressed as linear constraints that define the set of feasible muscle activation patterns. Quadratic programming allows us to predict whether and how energy consumption can be minimized throughout the workspace of the limb given those linear constraints. We show that the presence of synergies drastically decreases the ability of the CNS to vary the properties of the endpoint stiffness and can even preclude the ability to minimize energy. Furthermore, the capacity to minimize energy consumption--when available--can be greatly affected by arm posture. Our computational approach helps reconcile divergent findings and conclusions about task-specific regulation of endpoint stiffness and energy consumption in the context of synergies. But more generally, these results provide further evidence that the benefits and disadvantages of muscle synergies go hand-in-hand with the structure of feasible muscle activation patterns afforded by the mechanics of the limb and task constraints. These insights will help design experiments to elucidate the interplay between synergies and the mechanisms

  15. Aircraft wing structural detail design (wing, aileron, flaps, and subsystems)

    NASA Technical Reports Server (NTRS)

    Downs, Robert; Zable, Mike; Hughes, James; Heiser, Terry; Adrian, Kenneth

    1993-01-01

    The goal of this project was to design, in detail, the wing, flaps, and ailerons for a primary flight trainer. Integrated in this design are provisions for the fuel system, the electrical system, and the fuselage/cabin carry-through interface structure. This conceptual design displays the general arrangement of all major components in the wing structure, taking into consideration the requirements set forth by the appropriate sections of Federal Aviation Regulation Part 23 (FAR23) as well as those established in the statement of work.

  16. Shape control of structures with semi-definite stiffness matrices for adaptive wings

    NASA Astrophysics Data System (ADS)

    Austin, Fred; Van Nostrand, William C.; Rossi, Michael J.

    1993-09-01

    Maintaining an optimum-wing cross section during transonic cruise can dramatically reduce the shock-induced drag and can result in significant fuel savings and increased range. Our adaptive-wing concept employs actuators as truss elements of active ribs to reshape the wing cross section by deforming the structure. In our previous work, to derive the shape control- system gain matrix, we developed a procedure that requires the inverse of the stiffness matrix of the structure without the actuators. However, this method cannot be applied to designs where the actuators are required structural elements since the stiffness matrices are singular when the actuator are removed. Consequently, a new method was developed, where the order of the problem is reduced and only the inverse of a small nonsingular partition of the stiffness matrix is required to obtain the desired gain matrix. The procedure was experimentally validated by achieving desired shapes of a physical model of an aircraft-wing rib. The theory and test results are presented.

  17. Formation of composite polyacrylamide and silicone substrates for independent control of stiffness and strain

    PubMed Central

    Simmons, Chelsey S.; Ribeiro, Alexandre J. S.; Pruitt, Beth L.

    2013-01-01

    Cells that line major tissues in the body such as blood vessels, lungs and gastrointestinal tract experience deformation from mechanical strain with our heartbeat, breathing, and other daily activities. Tissues also remodel in both development and disease, changing their mechanical properties. Taken together, cells can experience vastly different mechanical cues resulting from the combination of these interdependent stimuli. To date, most studies of cellular mechanotransduction have been limited to assays in which variations in substrate stiffness and strain were not combined. Here, we address this technological gap by implementing a method that can simultaneously tune both substrate stiffness and mechanical strain. Substrate stiffness is controlled with different monomer and crosslinker ratios during polyacrylamide gel polymerization, and strain is transferred from the underlying silicone platform when stretched. We demonstrate this platform with polyacrylamide gels with elastic moduli at 6 kPa and 20 kPa in combination with two different silicone formulations. The gels remain attached with up to 50% applied strains. To validate strain transfer through the gels into cells, we employ particle-tracking methods and observe strain transmission via cell morphological changes. PMID:23287818

  18. Stiffness and Adhesivity Control Aortic Valve Interstitial Cell Behavior within Hyaluronic Acid Based Hydrogels

    PubMed Central

    Duan, Bin; Hockaday, Laura A.; Kapetanovic, Edi; Kang, Kevin H.; Butcher, Jonathan T.

    2013-01-01

    Bioactive and biodegradable hydrogels that mimic the extracellular matrix and regulate valve interstitial cells (VIC) behavior are of great interest as three dimensional (3D) model systems for understanding mechanisms of valvular heart disease pathogenesis in vitro and the basis for regenerative templates for tissue engineering. However, the role of stiffness and adhesivity of hydrogels in VIC behavior remains poorly understood. This study reports synthesis of oxidized and methacrylated hyaluronic acid (Me-HA and MOHA) and subsequent development of hybrid hydrogels based on modified HA and methacrylated gelatin (Me-Gel) for VIC encapsulation. The mechanical stiffness and swelling ratio of the hydrogels were tunable with molecular weight of HA and concentration/composition of precursor solution. The encapsulated VIC in pure HA hydrogels with lower mechanical stiffness showed more spreading morphology comparing to stiffer counterparts and dramatically upregulated alpha smooth muscle actin expression indicating more activated myofibroblast properties. The addition of Me-Gel in Me-HA facilitated cell spreading, proliferation and VIC migration from encapsulated spheroids and better maintained VIC fibroblastic phenotype. The VIC phenotype transition during migration from encapsulated spheroids in both Me-HA and Me-HA/Me-Gel hydrogel matrix was also observed. These findings are important for the rational design of hydrogels for controlling VIC morphology, and for regulating VIC phenotype and function. The Me-HA/Me-Gel hybrid hydrogels accommodated with VIC are promising as valve tissue engineering scaffolds and 3D model for understanding valvular pathobiology. PMID:23648571

  19. Effects of Allopurinol on Arterial Stiffness: A Meta-Analysis of Randomized Controlled Trials

    PubMed Central

    Deng, Gang; Qiu, Zhandong; Li, Dayong; Fang, Yu; Zhang, Suming

    2016-01-01

    Background Several studies have tested the effects of allopurinol on arterial stiffness, but the results have been inconclusive. We aimed to conduct a meta-analysis to investigate the impacts of allopurinol treatment on arterial stiffness, as measured by pulse wave velocity (PWV) and augmentation index (AIx). Material/Methods Randomized controlled trials (RCTs) assessing the effects of allopurinol on arterial stiffness were identified through searching PubMed, Web of Science, EMBASE, the Cochrane Library for Central Register of Clinical Trials, and China National Knowledge Infrastructure up to December 2015. The primary endpoints were the change of PWV and AIx after allopurinol treatment. The weighted mean difference (WMD) or standardized mean difference (SMD) and the 95% confidence interval (CI) of each study were pooled for meta-analysis. Results A total of 11 RCTs met the inclusion criteria and were included in the final meta-analysis. Eight RCTs with 1,111 patients were pooled for PWV; eight RCTs with 397 patients were pooled for PWV. Allopurinol administration did not significantly change PWV (WMD=−0.19 m/s, 95% CI: −0.49 to 0.12, Z=1.21, p=0.23), but significantly reduced AIx (SMD=−0.34, 95% CI: −0.54 to −0.14, Z=3.35, p=0.0008). Conclusions Although our meta-analysis showed some favorable effects of allopurinol treatment on improving AIx, its impact on arterial stiffness must be tested in more large-scale RCTs. PMID:27110924

  20. Arterial stiffness in periodontitis patients and controls. A case–control and pilot intervention study.

    PubMed

    Houcken, W; Teeuw, W J; Bizzarro, S; Alvarez Rodriguez, E; Mulders, T A; van den Born, B-Jh; Loos, B G

    2016-01-01

    Increased arterial stiffness (AS) is an important indicator for atherosclerotic cardiovascular disease (ACVD). Epidemiologically, periodontitis and ACVD are associated. Therefore, we aimed to investigate AS in periodontitis patients and controls. In addition, we explored the effect of periodontal therapy on AS in a sub-group of cases. Pulse-wave velocity (PWV), a non-invasive chair-side function test for AS, was measured in periodontitis patients (n=57; mean age 46.6 years) and compared with a reference group (n=48; mean age 45.5 years). In addition, 45 cases (mean age 46.9 years) were 6 months followed after periodontal treatment, to explore a possible effect on arterial function. Periodontitis patients showed a significantly increased PWV compared with the reference group (8.01±0.20 vs. 7.36±0.22 m s(-1) respectively; P=0.029) and this remained significant after adjustments for ACVD risk factors (P=0.019). After periodontal therapy, no significant reduction in PWV was seen (8.00±1.8 to 7.82±1.6 m s(-1); P=0.13), but systolic blood pressure (SBP) was significantly reduced (119.8±14.6 to 116.9±15.1 mm Hg; P=0.040). It can be concluded that periodontitis is associated with increased AS. This confirms with a new parameter the association of periodontitis with ACVD. Although periodontal treatment did not lower AS significantly, a modest reduction of SBP after 6 months was observed.

  1. Arterial stiffness in periodontitis patients and controls. A case–control and pilot intervention study.

    PubMed

    Houcken, W; Teeuw, W J; Bizzarro, S; Alvarez Rodriguez, E; Mulders, T A; van den Born, B-Jh; Loos, B G

    2016-01-01

    Increased arterial stiffness (AS) is an important indicator for atherosclerotic cardiovascular disease (ACVD). Epidemiologically, periodontitis and ACVD are associated. Therefore, we aimed to investigate AS in periodontitis patients and controls. In addition, we explored the effect of periodontal therapy on AS in a sub-group of cases. Pulse-wave velocity (PWV), a non-invasive chair-side function test for AS, was measured in periodontitis patients (n=57; mean age 46.6 years) and compared with a reference group (n=48; mean age 45.5 years). In addition, 45 cases (mean age 46.9 years) were 6 months followed after periodontal treatment, to explore a possible effect on arterial function. Periodontitis patients showed a significantly increased PWV compared with the reference group (8.01±0.20 vs. 7.36±0.22 m s(-1) respectively; P=0.029) and this remained significant after adjustments for ACVD risk factors (P=0.019). After periodontal therapy, no significant reduction in PWV was seen (8.00±1.8 to 7.82±1.6 m s(-1); P=0.13), but systolic blood pressure (SBP) was significantly reduced (119.8±14.6 to 116.9±15.1 mm Hg; P=0.040). It can be concluded that periodontitis is associated with increased AS. This confirms with a new parameter the association of periodontitis with ACVD. Although periodontal treatment did not lower AS significantly, a modest reduction of SBP after 6 months was observed. PMID:25972093

  2. Introducing a new semi-active engine mount using force controlled variable stiffness

    NASA Astrophysics Data System (ADS)

    Azadi, Mojtaba; Behzadipour, Saeed; Faulkner, Gary

    2013-05-01

    This work introduces a new concept in designing semi-active engine mounts. Engine mounts are under continuous development to provide better and more cost-effective engine vibration control. Passive engine mounts do not provide satisfactory solution. Available semi-active and active mounts provide better solutions but they are more complex and expensive. The variable stiffness engine mount (VSEM) is a semi-active engine mount with a simple ON-OFF control strategy. However, unlike available semi-active engine mounts that work based on damping change, the VSEM works based on the static stiffness change by using a new fast response force controlled variable spring. The VSEM is an improved version of the vibration mount introduced by the authors in their previous work. The results showed significant performance improvements over a passive rubber mount. The VSEM also provides better vibration control than a hydromount at idle speed. Low hysteresis and the ability to be modelled by a linear model in low-frequency are the advantages of the VSEM over the vibration isolator introduced earlier and available hydromounts. These specifications facilitate the use of VSEM in the automotive industry, however, further evaluation and developments are needed for this purpose.

  3. Matrix stiffness exerts biphasic control over monocyte-endothelial adhesion via Rho-mediated ICAM-1 clustering.

    PubMed

    Scott, Harry A; Quach, Boi; Yang, Xiao; Ardekani, Soroush; Cabrera, Andrea P; Wilson, Randall; Messaoudi-Powers, Ilhem; Ghosh, Kaustabh

    2016-08-01

    Leukocyte-endothelial adhesion is a critical early step in chronic vascular inflammation associated with diabetes, emphysema, and aging. Importantly, these conditions are also marked by abnormal subendothelial matrix crosslinking (stiffness). Yet, whether and how abnormal matrix stiffness contributes to leukocyte-endothelial adhesion remains poorly understood. Using a co-culture of human monocytic cells and human microvascular endothelial cells (ECs) grown on matrices of tunable stiffness, we demonstrate that matrix stiffness exerts biphasic control over monocyte-EC adhesion, with both matrix softening and stiffening eliciting a two-fold increase in this adhesive interaction. This preferential endothelial adhesivity on softer and stiffer matrices was consistent with a significant increase in α-actinin-4-associated endothelial ICAM-1 clustering, a key determinant of monocyte-EC adhesion. Further, the enhanced ICAM-1 clustering on soft and stiff matrices correlated strongly with an increase in Rho activity and ROCK2 expression. Importantly, inhibition of Rho/ROCK activity blocked the effects of abnormal matrix stiffness on ICAM-1 clustering and monocyte-EC adhesion. Thus, these findings implicate matrix stiffness-dependent ICAM-1 clustering as an important regulator of vascular inflammation and provide the rationale for closely examining mechanotransduction pathways as new molecular targets for anti-inflammatory therapy.

  4. Matrix stiffness exerts biphasic control over monocyte-endothelial adhesion via Rho-mediated ICAM-1 clustering.

    PubMed

    Scott, Harry A; Quach, Boi; Yang, Xiao; Ardekani, Soroush; Cabrera, Andrea P; Wilson, Randall; Messaoudi-Powers, Ilhem; Ghosh, Kaustabh

    2016-08-01

    Leukocyte-endothelial adhesion is a critical early step in chronic vascular inflammation associated with diabetes, emphysema, and aging. Importantly, these conditions are also marked by abnormal subendothelial matrix crosslinking (stiffness). Yet, whether and how abnormal matrix stiffness contributes to leukocyte-endothelial adhesion remains poorly understood. Using a co-culture of human monocytic cells and human microvascular endothelial cells (ECs) grown on matrices of tunable stiffness, we demonstrate that matrix stiffness exerts biphasic control over monocyte-EC adhesion, with both matrix softening and stiffening eliciting a two-fold increase in this adhesive interaction. This preferential endothelial adhesivity on softer and stiffer matrices was consistent with a significant increase in α-actinin-4-associated endothelial ICAM-1 clustering, a key determinant of monocyte-EC adhesion. Further, the enhanced ICAM-1 clustering on soft and stiff matrices correlated strongly with an increase in Rho activity and ROCK2 expression. Importantly, inhibition of Rho/ROCK activity blocked the effects of abnormal matrix stiffness on ICAM-1 clustering and monocyte-EC adhesion. Thus, these findings implicate matrix stiffness-dependent ICAM-1 clustering as an important regulator of vascular inflammation and provide the rationale for closely examining mechanotransduction pathways as new molecular targets for anti-inflammatory therapy. PMID:27444067

  5. Management of acute Achilles tendinopathy: effect of etoricoxib on pain control and leg stiffness.

    PubMed

    Maquirriain, Javier; Kokalj, Antonio

    2013-09-01

    Tendinopathies are a major cause of disability in the athletic population; the main purpose of the treatment of these injuries is to reduce pain and improve function promptly. The objective of this randomized, active comparator controlled, blinded study was to evaluate etoricoxib efficacy in pain control and leg stiffness in athletes suffering acute unilateral Achilles tendinopathy. Fifty-six eligible male athletes (mean age 37.5 ± 11.0 y) suffering acute Achilles tendinopathy were randomized to receive either etoricoxib 120 mg oral once daily (n=28) or diclofenac 100 mg oral once daily (n=28). Pain (100-mm visual analogue scale-VAS), analgesic effect (percentage of 100-mm VAS reduction), satisfaction with pain management (PGART), and leg stiffness (LSR) were evaluated after one week of anti-inflammatory treatment. Over the 7-day treatment period, both etoricoxib and diclofenac provided significantly relief of Achilles tendon pain compared to that experienced at baseline (mean VAS 26.7 ± 2.2 and 56.4 ± 1.8, respectively; p<.001). Analgesic effect averaged 53.7 ± 38.1% (etoricoxib= 56.4% and diclofenac 50.6%, p=0.64). Patients referred high level of satisfaction with anti-inflammatory treatment (PGART = 2.0 ± 1.3), while leg stiffness showed a significant improvement after one-week therapy (LSR 0.89 ± 0.1 vs. 0.95 ± 0.1; p=0.038). PGART and LSR values within etoricoxib and diclofenac groups were not significant (p=0.46, and p=0.37, respectively). Both drugs were generally well tolerated; patients receiving etoricoxib reported significantly less side effects than those in the diclofenac group (0% and 14,2%, respectively, p=0.037). Etoricoxib is clinically effective in treatment of acute Achilles tendinopathy providing a magnitude of effect comparable to that of diclofenac with fewer side effects. Effective control of tendon pain in the acute phase of such sports-related injuries may be helpful to reduce morbidity and improve capabilities associated with high

  6. Advanced composite aileron for L-1011 transport aircraft, task 1

    NASA Technical Reports Server (NTRS)

    Griffin, C. F.; Fogg, L. D.; Stone, R. L.; Dunning, E. G.

    1978-01-01

    Structural design and maintainability criteria were established and used as a guideline for evaluating a variety of configurations and materials for each of the major subcomponents. From this array of subcomponent designs, several aileron assemblies were formulated and analyzed. The selected design is a multirib configuration with sheet skin covers mechanically fastened to channel section ribs and spars. Qualitative analysis of currently available composite material systems led to the selection of three candidate materials on which comparative structural tests were conducted to measure the effects of environment and impact damage on mechanical property retention. In addition, each system was evaluated for producibility characteristics. From these tests, Thornel 300/5208 unidirectional tape was selected for the front spar and covers, and Thornel 300 fabric/5208 was chosen for the ribs.

  7. Stimulation of PPC Affects the Mapping between Motion and Force Signals for Stiffness Perception But Not Motion Control

    PubMed Central

    Mawase, Firas; Karniel, Amir; Donchin, Opher; Rothwell, John; Nisky, Ilana; Davare, Marco

    2016-01-01

    How motion and sensory inputs are combined to assess an object's stiffness is still unknown. Here, we provide evidence for the existence of a stiffness estimator in the human posterior parietal cortex (PPC). We showed previously that delaying force feedback with respect to motion when interacting with an object caused participants to underestimate its stiffness. We found that applying theta-burst transcranial magnetic stimulation (TMS) over the PPC, but not the dorsal premotor cortex, enhances this effect without affecting movement control. We explain this enhancement as an additional lag in force signals. This is the first causal evidence that the PPC is not only involved in motion control, but also has an important role in perception that is disassociated from action. We provide a computational model suggesting that the PPC integrates position and force signals for perception of stiffness and that TMS alters the synchronization between the two signals causing lasting consequences on perceptual behavior. SIGNIFICANCE STATEMENT When selecting an object such as a ripe fruit or sofa, we need to assess the object's stiffness. Because we lack dedicated stiffness sensors, we rely on an as yet unknown mechanism that generates stiffness percepts by combining position and force signals. Here, we found that the posterior parietal cortex (PPC) contributes to combining position and force signals for stiffness estimation. This finding challenges the classical view about the role of the PPC in regulating position signals only for motion control because we highlight a key role of the PPC in perception that is disassociated from action. Altogether this sheds light on brain mechanisms underlying the interaction between action and perception and may help in the development of better teleoperation systems and rehabilitation of patients with sensory impairments. PMID:27733607

  8. Force control compensation method with variable load stiffness and damping of the hydraulic drive unit force control system

    NASA Astrophysics Data System (ADS)

    Kong, Xiangdong; Ba, Kaixian; Yu, Bin; Cao, Yuan; Zhu, Qixin; Zhao, Hualong

    2016-05-01

    Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit (HDU), and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this

  9. Tongue Stiffness is Lower in Patients with Obstructive Sleep Apnea during Wakefulness Compared with Matched Control Subjects

    PubMed Central

    Brown, Elizabeth C.; Cheng, Shaokoon; McKenzie, David K.; Butler, Jane E.; Gandevia, Simon C.; Bilston, Lynne E.

    2015-01-01

    Study Objectives: This study aimed to determine whether tongue stiffness (shear modulus) in patients with obstructive sleep apnea (OSA) is different for controls matched for age, sex, and body mass index (BMI), and to investigate the effect of continuous positive airway pressure (CPAP) on stiffness. Design: Controlled experimental study. Setting: Medical research institute. Participants: Patients with OSA and age-, sex-, and BMI-matched healthy controls. Measurements: Magnetic resonance elastography was performed in nine patients with OSA (apnea-hypopnea index (AHI) > 15 events/h) and seven controls (AHI < 10 events/h) matched for age, sex, and BMI. Six of these OSA subjects were also scanned while 10 cmH2O CPAP was applied. Mean isotropic shear modulus and anisotropic shear moduli parallel and perpendicular to the muscle fascicles in the tongue were calculated. Results: Tongue shear modulus in patients with OSA was lower than that in matched controls (2.68 ± 0.35 (mean ± standard deviation) kPa versus 2.98 ± 0.44 kPa, P < 0.001). Shear modulus decreased with increasing AHI (R = −0.496, P = 0.043), but not age, BMI, or percentage tongue fat. Anisotropic analysis revealed that reduction in stiffness was greatest parallel to the muscle fibers. CPAP had no significant effect on tongue shear modulus. Conclusions: In awake subjects with obstructive sleep apnea, the tongue is less stiff than in similar healthy subjects and this difference occurs in the muscle fiber direction. CPAP did not significantly reduce tongue stiffness. Thus, any change in neural drive to genioglossus during wakefulness is insufficient to restore normal tongue stiffness. Citation: Brown EC, Cheng S, McKenzie DK, Butler JE, Gandevia SC, Bilston LE. Tongue stiffness is lower in patients with obstructive sleep apnea during wakefulness compared with matched control subjects. SLEEP 2015;38(4):537–544. PMID:25409103

  10. Temperature compensation method for the resonant frequency of a differential vibrating accelerometer using electrostatic stiffness control

    NASA Astrophysics Data System (ADS)

    Lee, Jungshin; Rhim, Jaewook

    2012-09-01

    Differential vibrating accelerometer (DVA) is a resonant-type sensor which detects the change in the resonant frequency in the presence of acceleration input, i.e. inertial loading. However, the resonant frequency of micromachined silicon resonators is sensitive to the temperature change as well as the input acceleration. Therefore, to design a high-precision vibrating accelerometer, the temperature sensitivity of the resonant frequency has to be predicted and compensated accurately. In this study, a temperature compensation method for resonant frequency is proposed which controls the electrostatic stiffness of the dual-ended tuning fork (DETF) using the temperature-dependent dc voltage between the parallel plate electrodes. To do this, the electromechanical model is derived first to predict the change in the electrostatic stiffness and the resonant frequency resulting from the dc voltage between the resonator and the electrodes. Next, the temperature sensitivity of the resonant frequency is modeled, estimated and compared with the measured values. Then it is shown that the resonant frequency of the DETF can be kept constant in the operating temperature range by applying the temperature-dependent driving voltage to the parallel plate electrodes. The proposed method is validated through experiment.

  11. Theoretical span loading and moments of tapered wings produced by aileron deflection

    NASA Technical Reports Server (NTRS)

    Pearson, H A

    1937-01-01

    The effect of tapered ailerons on linearly tapered wings is theoretically determined. Four different aileron spans are considered for each of three wing aspect ratios and each of four wing taper ratios. The change in lift on one half of the wing, the rolling moment, the additional induced drag, and the yawing moment, due to aileron deflection, are represented by non dimensional coefficients. Similar coefficients are given for the damping and yawing moments, the additional drag, and the change in lift, due to rolling. It was found possible to effect a fairly close agreement between the theoretical and experimental rolling moments by introducing into the theoretical expression for the rolling moment an effective change in angle of attack obtained from an analysis of flap data. The theoretical curves show that the highly tapered wing with long ailerons has a lower ratio of yawing to rolling moment and a lower additional induced drag than wings with less taper.

  12. Design development of an advanced composite aileron. [graphite-epoxy structure for L-1011

    NASA Technical Reports Server (NTRS)

    Griffin, C. F.

    1979-01-01

    This paper summarizes the design development of an advanced composite inboard aileron for the L-1011 commercial transport aircraft. Design details of the composite aileron are reported. Results of tests which substantiate the structural integrity of the design are also presented. The composite aileron is a multi-rib assembly with graphite/epoxy tape-syntactic core sandwich covers, a graphite/epoxy tape front spar, and graphite/epoxy fabric ribs. This structure is a direct replacement for the current metal aileron with a weight savings of 28.7 percent (40.3 lb.). Engineering cost estimates indicate that the composite structure will be cost competitive with the metal structure it is replacing.

  13. Stiff railguns

    NASA Astrophysics Data System (ADS)

    Weldon, W. F.; Bacon, J. L.; Weeks, D. A.; Zowarka, R. C., Jr.

    1991-01-01

    Stiff guns have been operated with both plasma and solid armatures. A performance gain was seen in the plasma railgun as stiffness was increased. A stiff gun will help to maintain the bore shape and preserve the integrity of the seam between rail and insulator under the extreme asymmetric loads sustained during high-pressure operation. The hydraulically preloaded moly and ceramic gun has been fired six times at pressures as high as 87 ksi, and the bore still holds roughing vacuum up to two hours after the test. The elimination of seam leakage helps control bore erosion associated with plasma reconstitution from the rail and plasma perturbation that might result in loss-initiating instabilities. Reduced rail deflection allows solid and transitioning armatures to track the bore surface. An analysis of the strain energy associated with the deflection of the railgun structure is presented, and this mechanism is found to be a small fraction of the energy associated with armature loss and the rail resistive loss.

  14. Arterial stiffness in kidney transplantation: a single center case-control study comparing belatacept versus calcineurin inhibitor immunosuppressive based regimen.

    PubMed

    Melilli, Edoardo; Bestard-Matamoros, Oriol; Manonelles-Montero, Anna; Sala-Bassa, Neus; Mast, Richard; Grinyó-Boira, Josep M; Cruzado, Josep M

    2015-01-01

    Arterial stiffness is nowadays a well-accepted predictor of cardiovascular mortality in general population; as well as in kidney transplant recipient population. The femoral-carotid pulse wave velocity (cf-PWV) is the widest used method to assess the arterial stiffness. The aim of this study was to test whether CNI-free immunosuppression based on belatacept was associated with lower cf-PWV, as a surrogate marker of arterial stiffness, than CNI. This was a retrospective case-control study. We included all the cases treated with belatacept as a maintenance immunosuppression in our center (n=20). An appropriate control group of patients (n=20) treated with CNI was selected to achieve match for key factors associated with arterial stiffness. After a follow-up of 5 years after transplantation, the Belatacept group had a reduced prevalence of patients with a cf-PWV higher than 8.1m/s (50% in BLC vs. 25% in CNI, p=0.08). At multivariate logistic regression analysis, the risk of high cf-PWV was correlated with age (OR 1.24; p<0.03) and renal resistive index (OR 1.25; p<0.05). Belatacept treatment was associated with a significant reduction in risk of cf-PWV (OR 0.008; P=0.045). Belatacept-based maintenance immunosuppression could improve kidney transplant recipient’s survival by reducing cardiovascular events related to stiffness. PMID:25611834

  15. The Role of Monitoring Arterial Stiffness with Cardio-Ankle Vascular Index in the Control of Lifestyle-Related Diseases.

    PubMed

    Shirai, Kohji; Saiki, Atsuhito; Nagayama, Daiji; Tatsuno, Ichiro; Shimizu, Kazuhiro; Takahashi, Mao

    2015-09-01

    Arteriosclerosis is a major contributor to cardiovascular diseases. One of the difficulties in controlling those diseases is the lack of a suitable indicator of arteriosclerosis or arterial injury in routine clinical practice. Arterial stiffness was supposed to be one of the monitoring indexes of arteriosclerosis. Cardio-ankle vascular index (CAVI) is reflecting the stiffness of the arterial tree from the origin of the aorta to the ankle, and one of the features of CAVI is independency from blood pressure at a measuring time. When doxazosin, an α1-adrenergic blocker, was administered, CAVI decreased, indicating that arterial stiffness is composed of both organic stiffness and functional stiffness, which reflects the contraction of arterial smooth muscle. CAVI shows a high value with aging and in many arteriosclerotic diseases, and is also high in persons possessing main coronary risk factors such as diabetes mellitus, metabolic syndrome, hypertension and smoking. Furthermore, when the most of those risk factors were controlled by proper methods, CAVI improved. Furthermore, the co-relationship between CAVI and heart function was demonstrated during treatment of heart failure. This paper reviews the principle and rationale of CAVI, and discusses the meaning of monitoring CAVI in following up so-called lifestyle-related diseases and cardiac dysfunction in routine clinical practice. PMID:26587461

  16. Active noise control using noise source having adaptive resonant frequency tuning through stiffness variation

    NASA Technical Reports Server (NTRS)

    Pla, Frederic G. (Inventor); Rajiyah, Harindra (Inventor); Renshaw, Anthony A. (Inventor); Hedeen, Robert A. (Inventor)

    1995-01-01

    A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by a plurality of force transmitting mechanisms which contact the noise radiating element. Each one of the force transmitting mechanisms includes an expandable element and a spring in contact with the noise radiating element so that excitation of the element varies the spring force applied to the noise radiating element. The elements are actuated by a controller which receives input of a signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the spring force applied to the noise radiating element to be varied. The force transmitting mechanisms can be arranged to either produce bending or linear stiffness variations in the noise radiating element.

  17. Effect of a tart cherry juice supplement on arterial stiffness and inflammation in healthy adults: a randomised controlled trial.

    PubMed

    Lynn, Anthony; Mathew, Shilpa; Moore, Chris T; Russell, Jean; Robinson, Emma; Soumpasi, Vithleem; Barker, Margo E

    2014-06-01

    Tart cherries are a particularly rich source of anthocyanins. Evidence indicates that dietary intake of anthocyanins is inversely associated with arterial stiffness. We conducted an open-label randomised placebo controlled study to determine whether a tart cherry juice concentrate (Cherry Active) reduced arterial stiffness, inflammation and risk markers for cardiovascular disease in 47 healthy adults (30-50 years). Participants consumed 30 ml of cherry concentrate diluted to a volume of 250 ml with water or the same volume of an energy matched control drink daily for six weeks. Measurements were taken at baseline and at the end of the intervention. There was no effect of the intervention on arterial stiffness (P = 0.218), c-reactive protein (P = 0.220), systolic blood pressure (P = 0.163), diastolic blood pressure (P = 0.121), total cholesterol (P = 0.342) and high density lipoprotein cholesterol (P = 0.127). At the end of the intervention, plasma antioxidant capacity (measured as the ferric reducing ability of plasma (FRAP)) was significantly higher in the intervention group than the control group (P = 0.012). We conclude that a tart cherry juice concentrate rich in anthocyanins has no effect on arterial stiffness, c-reactive protein and risk markers for cardiovascular disease, but evokes a minor increase in antioxidant status in healthy adults. PMID:24570273

  18. An Investigation of the Aerodynamic Characteristics of an 0.08-Scale Model of the Chance Vought XF7U-1 Airplane in the Langley High-Speed 7- by 10-Foot Tunnel. Part IV - Aileron Characteristics TED No. NACA DE308. Part 4; Aileron Characteristics, TED No. NACA DE308

    NASA Technical Reports Server (NTRS)

    Goodson, Kenneth W.; Myers, Boyd C., II

    1947-01-01

    Tests have been conducted in the Langley high-speed 7- by 10-foot tunnel over a Mach number range from 0.40 to 0.91 to determine the stability and control characteristics of an 0.08-scale model of the Chance Vought XF7U-1 airplane. The aileron characteristics of the complete model are presented in the present report with a very limited analysis of the results.

  19. Substrate stiffness and matrix composition coordinately control the differentiation of liver progenitor cells.

    PubMed

    Kourouklis, Andreas P; Kaylan, Kerim B; Underhill, Gregory H

    2016-08-01

    Recent approaches have utilized microfabricated platforms to examine combinations of microenvironmental signals that regulate stem and progenitor cell differentiation. However, the majority of these efforts have focused on the biochemical properties of extracellular matrix (ECM) or soluble factors without simultaneously exploring the biomechanical effects of cell-substrate interactions. To address this need, we combined a high-throughput approach for the analysis of combinatorial ECM cues with substrates of modular stiffness and traction force microscopy. This integrated approach enabled the characterization of cell-generated traction stress and phenotypic expression in response to ECM cues. We investigated the impact of substrate stiffness and ECM composition on the differentiation of bipotential mouse embryonic liver (BMEL) progenitor cells. We observed that hepatocyte differentiation was primarily regulated by ECM composition, and cholangiocyte differentiation was cooperatively influenced by ECM proteins and stiffness properties. In particular, stiffness-mediated cholangiocyte differentiation was observed for cells cultured on fibronectin, while collagen IV promoted differentiation independent of substrate stiffness. We demonstrated the influence of cell contractility and traction stress in early cholangiocyte specification and further uncovered the roles of ERK and ROCK in this differentiation process. Overall, these findings illustrate the involvement of biomechanical signals in liver progenitor differentiation. Further, this approach could enable investigations for a broad range of cell types and ECM proteins, providing an integrated platform for evaluating the combinatorial effects of biochemical and biophysical signals in cell differentiation.

  20. Extracellular Matrix Stiffness Controls VEGF Signaling and Processing in Endothelial Cells.

    PubMed

    Sack, Kelsey D; Teran, Madelane; Nugent, Matthew A

    2016-09-01

    Vascular endothelial growth factor A (VEGF) drives endothelial cell maintenance and angiogenesis. Endothelial cell behavior is altered by the stiffness of the substrate the cells are attached to suggesting that VEGF activity might be influenced by the mechanical cellular environment. We hypothesized that extracellular matrix (ECM) stiffness modifies VEGF-cell-matrix tethering leading to altered VEGF processing and signaling. We analyzed VEGF binding, internalization, and signaling as a function of substrate stiffness in endothelial cells cultured on fibronectin (Fn) linked polyacrylamide gels. Cell produced extracellular matrices on the softest substrates were least capable of binding VEGF, but the cells exhibited enhanced VEGF internalization and signaling compared to cells on all other substrates. Inhibiting VEGF-matrix binding with sucrose octasulfate decreased cell-internalization of VEGF and, inversely, heparin pre-treatment to enhance Fn-matrix binding of VEGF increased cell-internalization of VEGF regardless of matrix stiffness. β1 integrins, which connect cells to Fn, modulated VEGF uptake in a stiffness dependent fashion. Cells on hard surfaces showed decreased levels of activated β1 and inhibition of β1 integrin resulted in a greater proportional decrease in VEGF internalization than in cells on softer matrices. Extracellular matrix binding is necessary for VEGF internalization. Stiffness modifies the coordinated actions of VEGF-matrix binding and β1 integrin binding/activation, which together are critical for VEGF internalization. This study provides insight into how the microenvironment may influence tissue regeneration and response to injury and disease. J. Cell. Physiol. 231: 2026-2039, 2016. © 2016 Wiley Periodicals, Inc.

  1. Nonstationary flow about a wing-aileron-tab combination including aerodynamic balance

    NASA Technical Reports Server (NTRS)

    Theodorsen, Theodore; Garrick, I E

    1942-01-01

    This paper presents a continuation of the work published in Technical Report no. 496. The results of that paper have been extended to include the effect of aerodynamic balance and the effect of a tab added to the aileron. The aerodynamic coefficients are presented in a form convenient for application to the flutter problem.

  2. Molecular Mechanism Responsible for Fibronectin-controlled Alterations in Matrix Stiffness in Advanced Chronic Liver Fibrogenesis.

    PubMed

    Iwasaki, Ayumi; Sakai, Keiko; Moriya, Kei; Sasaki, Takako; Keene, Douglas R; Akhtar, Riaz; Miyazono, Takayoshi; Yasumura, Satoshi; Watanabe, Masatoshi; Morishita, Shin; Sakai, Takao

    2016-01-01

    Fibrosis is characterized by extracellular matrix (ECM) remodeling and stiffening. However, the functional contribution of tissue stiffening to noncancer pathogenesis remains largely unknown. Fibronectin (Fn) is an ECM glycoprotein substantially expressed during tissue repair. Here we show in advanced chronic liver fibrogenesis using a mouse model lacking Fn that, unexpectedly, Fn-null livers lead to more extensive liver cirrhosis, which is accompanied by increased liver matrix stiffness and deteriorated hepatic functions. Furthermore, Fn-null livers exhibit more myofibroblast phenotypes and accumulate highly disorganized/diffuse collagenous ECM networks composed of thinner and significantly increased number of collagen fibrils during advanced chronic liver damage. Mechanistically, mutant livers show elevated local TGF-β activity and lysyl oxidase expressions. A significant amount of active lysyl oxidase is released in Fn-null hepatic stellate cells in response to TGF-β1 through canonical and noncanonical Smad such as PI3 kinase-mediated pathways. TGF-β1-induced collagen fibril stiffness in Fn-null hepatic stellate cells is significantly higher compared with wild-type cells. Inhibition of lysyl oxidase significantly reduces collagen fibril stiffness, and treatment of Fn recovers collagen fibril stiffness to wild-type levels. Thus, our findings indicate an indispensable role for Fn in chronic liver fibrosis/cirrhosis in negatively regulating TGF-β bioavailability, which in turn modulates ECM remodeling and stiffening and consequently preserves adult organ functions. Furthermore, this regulatory mechanism by Fn could be translated for a potential therapeutic target in a broader variety of chronic fibrotic diseases.

  3. Matrix stiffness modulates formation and activity of neuronal networks of controlled architectures.

    PubMed

    Lantoine, Joséphine; Grevesse, Thomas; Villers, Agnès; Delhaye, Geoffrey; Mestdagh, Camille; Versaevel, Marie; Mohammed, Danahe; Bruyère, Céline; Alaimo, Laura; Lacour, Stéphanie P; Ris, Laurence; Gabriele, Sylvain

    2016-05-01

    The ability to construct easily in vitro networks of primary neurons organized with imposed topologies is required for neural tissue engineering as well as for the development of neuronal interfaces with desirable characteristics. However, accumulating evidence suggests that the mechanical properties of the culture matrix can modulate important neuronal functions such as growth, extension, branching and activity. Here we designed robust and reproducible laminin-polylysine grid micropatterns on cell culture substrates that have similar biochemical properties but a 100-fold difference in Young's modulus to investigate the role of the matrix rigidity on the formation and activity of cortical neuronal networks. We found that cell bodies of primary cortical neurons gradually accumulate in circular islands, whereas axonal extensions spread on linear tracks to connect circular islands. Our findings indicate that migration of cortical neurons is enhanced on soft substrates, leading to a faster formation of neuronal networks. Furthermore, the pre-synaptic density was two times higher on stiff substrates and consistently the number of action potentials and miniature synaptic currents was enhanced on stiff substrates. Taken together, our results provide compelling evidence to indicate that matrix stiffness is a key parameter to modulate the growth dynamics, synaptic density and electrophysiological activity of cortical neuronal networks, thus providing useful information on scaffold design for neural tissue engineering.

  4. Semi-active damping with negative stiffness for multi-mode cable vibration mitigation: approximate collocated control solution

    NASA Astrophysics Data System (ADS)

    Weber, F.; Distl, H.

    2015-11-01

    This paper derives an approximate collocated control solution for the mitigation of multi-mode cable vibration by semi-active damping with negative stiffness based on the control force characteristics of clipped linear quadratic regulator (LQR). The control parameters are derived from optimal modal viscous damping and corrected in order to guarantee that both the equivalent viscous damping coefficient and the equivalent stiffness coefficient of the semi-active cable damper force are equal to their desired counterparts. The collocated control solution with corrected control parameters is numerically validated by free decay tests of the first four cable modes and combinations of these modes. The results of the single-harmonic tests demonstrate that the novel approach yields 1.86 times more cable damping than optimal modal viscous damping and 1.87 to 2.33 times more damping compared to a passive oil damper whose viscous damper coefficient is optimally tuned to the targeted mode range of the first four modes. The improvement in case of the multi-harmonic vibration tests, i.e. when modes 1 and 3 and modes 2 and 4 are vibrating at the same time, is between 1.55 and 3.81. The results also show that these improvements are obtained almost independent of the cable anti-node amplitude. Thus, the proposed approximate real-time applicable collocated semi-active control solution which can be realized by magnetorheological dampers represents a promising tool for the efficient mitigation of stay cable vibrations.

  5. Analysis of Effect of Rolling Pull-Outs on Wing and Aileron Loads of a Fighter Airplane

    NASA Technical Reports Server (NTRS)

    Pearson, Henry A.; Aiken, William S.

    1946-01-01

    An analysis was made to determine the effect of rolling pull-out maneuvers on the wing and aileron loads of a typical fighter airplane, the P-47B. The results obtained indicate that higher loads are imposed upon wings and ailerons because of the rolling pull-out maneuver, than would be obtained by application of the loading requirements to which the airplane was designed. An increase of 102 lb or 15 percent of wing weight would be required if the wing were designed for rolling pull-out maneuver. It was also determined that the requirements by which the aileron was originally designed were inadequate.

  6. Pilot-model measurements of pilot responses in a lateral-directional control task

    NASA Technical Reports Server (NTRS)

    Adams, J. J.

    1976-01-01

    Pilot response during an aircraft bank-angle compensatory control task was measured by using an adaptive modeling technique. In the main control loop, which is the bank angle to aileron command loop, the pilot response was the same as that measured previously in single-input, single-output systems. The pilot used a rudder to aileron control coordination that canceled up to 80 percent of the vehicle yawing moment due to aileron deflection.

  7. Finger Stiffness.

    PubMed

    Oosterhoff, Thijs C H; Nota, Sjoerd P F T; Ring, David

    2015-06-01

    Background Finger stiffness varies substantially in patients with hand and upper extremity illness and can be notably more than expected for a given pathophysiology. In prior studies, pain intensity and magnitude of disability consistently correlate with coping strategies such as catastrophic thinking and kinesiophobia, which can be characterized as overprotectiveness. In this retrospective study we address the primary research question whether patients with finger stiffness are more often overprotective when the primary pathology is outside the hand (e.g. distal radius fracture) than when it is located within the hand. Methods In an orthopaedic hand surgery department 160 patients diagnosed with more finger stiffness than expected for a given pathophysiology or time point of recovery between December 2006 and September 2012 were analyzed to compare the proportion of patients characterized as overprotective for differences by site of pathology: (1) inside the hand, (2) outside the hand, and (3) psychiatric etiology (e.g. clenched fist). Results Among 160 subjects with more finger stiffness than expected, 132 (82 %) were characterized as overprotective including 88 of 108 (81 %) with pathology in the hand, 39 of 44 (89 %) with pathology outside the hand, and 5 of 8 (63 %) with psychiatric etiology. These differences were not significant. Conclusions Overprotectiveness is common in patients with more finger stiffness than expected regardless the site and type of primary pathology. It seems worthwhile to recognize and treat maladaptive coping strategies early during recovery to limit impairment, symptoms, and disability. PMID:26078497

  8. Effects of sodium and potassium supplementation on blood pressure and arterial stiffness: a fully controlled dietary intervention study.

    PubMed

    Gijsbers, L; Dower, J I; Mensink, M; Siebelink, E; Bakker, S J L; Geleijnse, J M

    2015-10-01

    We performed a randomised, placebo-controlled, crossover study to examine the effects of sodium and potassium supplementation on blood pressure (BP) and arterial stiffness in untreated (pre)hypertensive individuals. During the study, subjects were on a fully controlled diet that was relatively low in sodium and potassium. After a 1-week run-in period, subjects received capsules with supplemental sodium (3 g d(-1), equals 7.6 g d(-1) of salt), supplemental potassium (3 g d(-1)) or placebo, for 4 weeks each, in random order. Fasting office BP, 24-h ambulatory BP and measures of arterial stiffness were assessed at baseline and every 4 weeks. Of 37 randomized subjects, 36 completed the study. They had a mean pre-treatment BP of 145/81 mm Hg and 69% had systolic BP ⩾140 mm Hg. Sodium excretion was increased by 98 mmol per 24 h and potassium excretion by 63 mmol per 24 h during active interventions, compared with placebo. During sodium supplementation, office BP was significantly increased by 7.5/3.3 mm Hg, 24-h BP by 7.5/2.7 mm Hg and central BP by 8.5/3.6 mm Hg. During potassium supplementation, 24-h BP was significantly reduced by 3.9/1.6 mm Hg and central pulse pressure by 2.9 mm Hg. Pulse wave velocity and augmentation index were not significantly affected by sodium or potassium supplementation. In conclusion, increasing the intake of sodium caused a substantial increase in BP in subjects with untreated elevated BP. Increased potassium intake, on top of a relatively low-sodium diet, had a beneficial effect on BP. Arterial stiffness did not materially change during 4-week interventions with sodium or potassium.

  9. Center of gravity motions and ankle joint stiffness control in upright undisturbed stance modeled through a fractional Brownian motion framework.

    PubMed

    Rougier, P; Caron, O

    2000-12-01

    The authors modeled the center of gravity vertical projection (CG(v)) and the difference, CP - CG(v), which, combined, constitute the center of pressure (CP) trajectory, as fractional Brownian motion in order to investigate their relative contributions and their spatiotemporal articulation. The results demonstrated that CG(v) and CP - CG(v) motions are both endowed in complementary fashion with strong stochastic and part-deterministic behaviors. In addition, if the temporal coordinates remain similar for all 3 trajectories by definition, the switch between the successive control mechanisms appears for shorter displacements for CP - CG(v) and CG(v) than for CP trajectories. Results deduced from both input (CG(v)) and muscular stiffness (CP - CG(v)) thus provide insight into the way the central nervous system regulates stance control and in particular how CG and CP - CG are controlled. PMID:11114233

  10. Controlling matrix stiffness and topography for the study of tumor cell migration

    PubMed Central

    Kraning-Rush, Casey M.; Reinhart-King, Cynthia A.

    2012-01-01

    Cellular studies have long been performed on the bench top, within Petri dishes and flasks that expose cells to surroundings that differ greatly from their native environment. The complexity of a human tissue is such that to truly replicate a cell’s physiologic microenvironment in vitro is currently impossible. It is nevertheless important to determine how various factors of the microenvironment interact to drive cell behavior, particularly with regard to disease states, such as cancer. Here we focus on two key elements of the cellular microenvironment, matrix stiffness and architecture, in the context of tumor cell behavior. We discuss recent work focusing on the effects of these individual properties on cancer cell migration and describe one technique developed by our lab that could be applied to dissect the effects of specific structural and mechanical cues, and which may lead to useful insights into the potentially synergistic effects of these properties on tumor cell behavior. PMID:22863740

  11. Dynamic control of muscle stiffness and H reflex modulation during hopping and jumping in man.

    PubMed Central

    Dyhre-Poulsen, P; Simonsen, E B; Voigt, M

    1991-01-01

    1. The objective of the study was to evaluate the functional effects of reflexes on muscle mechanics during natural voluntary movements. The excitability of the H (Hoffmann) reflex was used as a measure of the excitability of the central component of the stretch reflex. 2. We recorded EMG, ground reaction forces and the H reflex in the soleus muscle in humans while landing from a downward jump, during drop jumping and during hopping. The movements were also recorded by high-speed cinematography. 3. The EMG pattern was adapted to the motor task. When landing the EMG in the soleus muscle and in the anterior tibial muscle showed preinnervation and alternating activity after touch down. When hopping there was little preinnervation in the soleus muscle, and the activity was initiated about 45 ms after touch down by a peak and continued unbroken until lift off. In the drop jumps the EMG pattern depended on the jumping style used by the subject. 4. The H reflex in the soleus muscle was strongly modulated in a manner appropriate to the requirements of the motor task. During landing from a downward jump the H reflex was low at touch down whereas while hopping it was high at touch down. During drop jumping it was variable and influenced by the jumping technique. 5. Muscle stiffness in the ankle joint was negative after touch down when landing, but always positive when hopping. 6. It is suggested that during landing the alternating EMG pattern after touch down was programmed and little influenced by reflexes. During hopping reflexes could contribute to the initial peak and the EMG during lift off. 7. The programmed EMG activity and the suppression of the H reflex while landing probably contribute to the development of the negative stiffness and change the muscles from a spring to a damping unit. PMID:1890636

  12. Hierarchies of plant stiffness.

    PubMed

    Brulé, Veronique; Rafsanjani, Ahmad; Pasini, Damiano; Western, Tamara L

    2016-09-01

    Plants must meet mechanical as well as physiological and reproductive requirements for survival. Management of internal and external stresses is achieved through their unique hierarchical architecture. Stiffness is determined by a combination of morphological (geometrical) and compositional variables that vary across multiple length scales ranging from the whole plant to organ, tissue, cell and cell wall levels. These parameters include, among others, organ diameter, tissue organization, cell size, density and turgor pressure, and the thickness and composition of cell walls. These structural parameters and their consequences on plant stiffness are reviewed in the context of work on stems of the genetic reference plant Arabidopsis thaliana (Arabidopsis), and the suitability of Arabidopsis as a model system for consistent investigation of factors controlling plant stiffness is put forward. Moving beyond Arabidopsis, the presence of morphological parameters causing stiffness gradients across length-scales leads to beneficial emergent properties such as increased load-bearing capacity and reversible actuation. Tailoring of plant stiffness for old and new purposes in agriculture and forestry can be achieved through bioengineering based on the knowledge of the morphological and compositional parameters of plant stiffness in combination with gene identification through the use of genetics.

  13. Hierarchies of plant stiffness.

    PubMed

    Brulé, Veronique; Rafsanjani, Ahmad; Pasini, Damiano; Western, Tamara L

    2016-09-01

    Plants must meet mechanical as well as physiological and reproductive requirements for survival. Management of internal and external stresses is achieved through their unique hierarchical architecture. Stiffness is determined by a combination of morphological (geometrical) and compositional variables that vary across multiple length scales ranging from the whole plant to organ, tissue, cell and cell wall levels. These parameters include, among others, organ diameter, tissue organization, cell size, density and turgor pressure, and the thickness and composition of cell walls. These structural parameters and their consequences on plant stiffness are reviewed in the context of work on stems of the genetic reference plant Arabidopsis thaliana (Arabidopsis), and the suitability of Arabidopsis as a model system for consistent investigation of factors controlling plant stiffness is put forward. Moving beyond Arabidopsis, the presence of morphological parameters causing stiffness gradients across length-scales leads to beneficial emergent properties such as increased load-bearing capacity and reversible actuation. Tailoring of plant stiffness for old and new purposes in agriculture and forestry can be achieved through bioengineering based on the knowledge of the morphological and compositional parameters of plant stiffness in combination with gene identification through the use of genetics. PMID:27457986

  14. Reynolds Number Effects on the Performance of Ailerons and Spoilers (Invited)

    NASA Technical Reports Server (NTRS)

    Mineck, R. E.

    2001-01-01

    The influence of Reynolds number on the performance of outboard spoilers and ailerons was investigated on a generic subsonic transport configuration in the National Transonic Facility over a chord Reynolds number range from 3 to 30 million and a Mach number range from 0.70 to 0.94. Spoiler deflection angles of 0, 10, and 20 degrees and aileron deflection angles of -10, 0, and 10 degrees were tested. Aeroelastic effects were minimized by testing at constant normalized dynamic pressure conditions over intermediate Reynolds number ranges. Results indicated that the increment in rolling moment due to spoiler deflection generally becomes more negative as the Reynolds number increases from 3 x 10(exp 6) to 22 x 10 (exp 6) with only small changes between Reynolds numbers of 22 x 10(exp 6) and 30 x 10(exp 6). The change in the increment in rolling moment coefficient with Reynolds number for the aileron deflected configuration is generally small with a general trend of increasing magnitude with increasing Reynolds number.

  15. Dynamically variable negative stiffness structures.

    PubMed

    Churchill, Christopher B; Shahan, David W; Smith, Sloan P; Keefe, Andrew C; McKnight, Geoffrey P

    2016-02-01

    Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness-based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771

  16. 77 FR 12173 - Airworthiness Directives; Bombardier, Inc. Airplanes

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-29

    ... aileron control stiffness. This AD requires revising the maintenance program to incorporate the discard task for outboard wing aileron pulleys. We are issuing this AD to prevent aileron control stiffness... specified products. That NPRM was published in the Federal Register on November 8, 2011 (76 FR 69161)....

  17. Nanoconfinement controls stiffness, strength and mechanical toughness of β-sheet crystals in silk

    NASA Astrophysics Data System (ADS)

    Keten, Sinan; Xu, Zhiping; Ihle, Britni; Buehler, Markus J.

    2010-04-01

    Silk features exceptional mechanical properties such as high tensile strength and great extensibility, making it one of the toughest materials known. The exceptional strength of silkworm and spider silks, exceeding that of steel, arises from β-sheet nanocrystals that universally consist of highly conserved poly-(Gly-Ala) and poly-Ala domains. This is counterintuitive because the key molecular interactions in β-sheet nanocrystals are hydrogen bonds, one of the weakest chemical bonds known. Here we report a series of large-scale molecular dynamics simulations, revealing that β-sheet nanocrystals confined to a few nanometres achieve higher stiffness, strength and mechanical toughness than larger nanocrystals. We illustrate that through nanoconfinement, a combination of uniform shear deformation that makes most efficient use of hydrogen bonds and the emergence of dissipative molecular stick-slip deformation leads to significantly enhanced mechanical properties. Our findings explain how size effects can be exploited to create bioinspired materials with superior mechanical properties in spite of relying on mechanically inferior, weak hydrogen bonds.

  18. Comparison of decentralized velocity feedback control for thin homogeneous and stiff sandwich panels using electrodynamic proof-mass actuators

    NASA Astrophysics Data System (ADS)

    Rohlfing, J.; Gardonio, P.; Thompson, D. J.

    2011-02-01

    Theoretical and experimental work is presented to compare the effect of decentralised velocity feedback control on thin homogeneous and sandwich panels. The decentralised control system consists of five control units, which are composed of a proof-mass electrodynamic actuator with an accelerometer underneath its footprint and an analogue controller. The stability of the feedback loops is analysed by considering the sensor-actuator open-loop frequency response function of each control unit and the eigenvalues of the fully populated matrix of open-loop frequency response functions between the five sensors and five actuators. The control performance is then analysed in terms of the time-averaged total kinetic energy and total sound power radiated by the two panels. The results show that for a stiff sandwich panel higher stable feedback gains can be implemented than on a thin homogeneous panel of comparable weight per unit area. Moreover the implementation of decentralised velocity feedback can offset some of the undesirable sound transmission properties of lightweight sandwich structures by efficiently reducing structural vibration and sound power radiation in the mid audio frequency range.

  19. A self-assembling peptide matrix used to control stiffness and binding site density supports the formation of microvascular networks in three dimensions

    PubMed Central

    Stevenson, M.D.; Piristine, H.; Hogrebe, N.J.; Nocera, T.M.; Boehm, M.W.; Reen, R.K.; Koelling, K.W.; Agarwal, G.; Sarang-Sieminski, A.L.; Gooch, K.J.

    2015-01-01

    A three-dimensional (3-D) cell culture system that allows control of both substrate stiffness and integrin binding density was created and characterized. This system consisted of two self-assembling peptide (SAP) sequences that were mixed in different ratios to achieve the desired gel stiffness and adhesiveness. The specific peptides used were KFE ((acetyl)-FKFEFKFE-CONH2), which has previously been reported not to support cell adhesion or MVN formation, and KFE-RGD ((acetyl)-GRGDSP-GG-FKFEFKFE-CONH2), which is a similar sequence that incorporates the RGD integrin binding site. Storage modulus for these gels ranged from ~60 to 6000 Pa, depending on their composition and concentration. Atomic force microscopy revealed ECM-like fiber microarchitecture of gels consisting of both pure KFE and pure KFE-RGD as well as mixtures of the two peptides. This system was used to study the contributions of both matrix stiffness and adhesiveness on microvascular network (MVN) formation of endothelial cells and the morphology of human mesenchymal stem cells (hMSC). When endothelial cells were encapsulated within 3-D gel matrices without binding sites, little cell elongation and no network formation occurred, regardless of the stiffness. In contrast, matrices containing the RGD binding site facilitated robust MVN formation, and the extent of this MVN formation was inversely proportional to matrix stiffness. Compared with a matrix of the same stiffness with no binding sites, a matrix containing RGD-functionalized peptides resulted in a ~2.5-fold increase in the average length of network structure, which was used as a quantitative measure of MVN formation. Matrices with hMSC facilitated an increased number and length of cellular projections at higher stiffness when RGD was present, but induced a round morphology at every stiffness when RGD was absent. Taken together, these results demonstrate the ability to control both substrate stiffness and binding site density within 3-D cell

  20. Dynamically variable negative stiffness structures

    PubMed Central

    Churchill, Christopher B.; Shahan, David W.; Smith, Sloan P.; Keefe, Andrew C.; McKnight, Geoffrey P.

    2016-01-01

    Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness–based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771

  1. Applied Joint-Space Torque and Stiffness Control of Tendon-Driven Fingers

    NASA Technical Reports Server (NTRS)

    Abdallah, Muhammad E.; Platt, Robert, Jr.; Wampler, Charles W.; Hargrave, Brian

    2010-01-01

    Existing tendon-driven fingers have applied force control through independent tension controllers on each tendon, i.e. in the tendon-space. The coupled kinematics of the tendons, however, cause such controllers to exhibit a transient coupling in their response. This problem can be resolved by alternatively framing the controllers in the joint-space of the manipulator. This work presents a joint-space torque control law that demonstrates both a decoupled and significantly faster response than an equivalent tendon-space formulation. The law also demonstrates greater speed and robustness than comparable PI controllers. In addition, a tension distribution algorithm is presented here to allocate forces from the joints to the tendons. It allocates the tensions so that they satisfy both an upper and lower bound, and it does so without requiring linear programming or open-ended iterations. The control law and tension distribution algorithm are implemented on the robotic hand of Robonaut-2.

  2. Rubber to rigid, clamped to undamped: toward composite materials with wide-range controllable stiffness and damping

    NASA Astrophysics Data System (ADS)

    Kornbluh, Roy D.; Prahlad, Harsha; Pelrine, Ron; Stanford, Scott; Rosenthal, Marcus A.; von Guggenberg, Philip A.

    2004-07-01

    Composite materials have increased the range of mechanical properties available to the design engineer compared with the range afforded by single component materials, leading to a revolution in capabilities. Nearly all commonly used engineering materials, including these composite materials, however, have a great limitation; that is, once their mechanical properties are set they cannot be changed. Imagine a material that could, under electric control, change from rubbery to rigid. Such composite "meta-materials" with stiffness and damping properties that can be electrically controlled over a wide range would find widespread application in areas such as morphing structures, tunable and conformable devices for human interaction, and greatly improved vibration control. Such a technology is a breakthrough capability because it fundamentally changes the paradigm of composite materials having a fixed set of mechanical properties. These electronically controllable composites may be the basis of discrete devices with tunable impedance. The composites can also be multifunctional materials: They can minimize size and mass by acting not only as a tunable impedance device, but also as a supporting structure or protective skin. Current approaches to controllable mechanical properties include composites with materials that have intrinsically variable properties such as shape memory alloys or polymers, or magnetorheological fluids, or composites that have active materials such as piezoelectrics, magnetostrictives, and newly emerging electroactive polymers. Each of these materials is suitable for some applications, but no single technology is capable of fast and efficient response that can produce a very wide range of stiffness and damping with a high elongation capability, that is, go from rubber to rigid. Such a material would be capable of a change in its maximum elastic energy of deformation of 50,000 J/cm3. No existing material is within three orders of magnitude of this

  3. Arterial Stiffness

    PubMed Central

    Avolio, Alberto

    2013-01-01

    Stiffness of large arteries has been long recognized as a significant determinant of pulse pressure. However, it is only in recent decades, with the accumulation of longitudinal data from large and varied epidemiological studies of morbidity and mortality associated with cardiovascular disease, that it has emerged as an independent predictor of cardiovascular risk. This has generated substantial interest in investigations related to intrinsic causative and associated factors responsible for the alteration of mechanical properties of the arterial wall, with the aim to uncover specific pathways that could be interrogated to prevent or reverse arterial stiffening. Much has been written on the haemodynamic relevance of arterial stiffness in terms of the quantification of pulsatile relationships of blood pressure and flow in conduit arteries. Indeed, much of this early work regarded blood vessels as passive elastic conduits, with the endothelial layer considered as an inactive lining of the lumen and as an interface to flowing blood. However, recent advances in molecular biology and increased technological sophistication for the detection of low concentrations of biochemical compounds have elucidated the highly important regulatory role of the endothelial cell affecting vascular function. These techniques have enabled research into the interaction of the underlying passive mechanical properties of the arterial wall with the active cellular and molecular processes that regulate the local environment of the load-bearing components. This review addresses these emerging concepts. PMID:26587425

  4. A general method for the layout of ailerons and elevators of gliders and motorplanes

    NASA Technical Reports Server (NTRS)

    Hiller, M. H.

    1979-01-01

    A method is described which allows the layout of the spatial driving mechanism of the aileron for a glider or a motorplane to be performed in a systematic manner. In particular, a prescribed input-output behavior of the mechanism can be realized by variation of individual parameters of the spatial four-bar mechanisms which constitute the entire driving mechanism. By means of a sensitivity analysis, a systematic choice of parameters is possible. At the same time the forces acting in the mechanism can be limited by imposing maximum values of the forces as secondary conditions during the variation process.

  5. Acoustic droplet-hydrogel composites for spatial and temporal control of growth factor delivery and scaffold stiffness.

    PubMed

    Fabiilli, Mario L; Wilson, Christopher G; Padilla, Frédéric; Martín-Saavedra, Francisco M; Fowlkes, J Brian; Franceschi, Renny T

    2013-07-01

    Wound healing is regulated by temporally and spatially restricted patterns of growth factor signaling, but there are few delivery vehicles capable of the "on-demand" release necessary for recapitulating these patterns. Recently we described a perfluorocarbon double emulsion that selectively releases a protein payload upon exposure to ultrasound through a process known as acoustic droplet vaporization (ADV). In this study, we describe a delivery system composed of fibrin hydrogels doped with growth factor-loaded double emulsion for applications in tissue regeneration. Release of immunoreactive basic fibroblast growth factor (bFGF) from the composites increased up to 5-fold following ADV and delayed release was achieved by delaying exposure to ultrasound. Releasates of ultrasound-treated materials significantly increased the proliferation of endothelial cells compared to sham controls, indicating that the released bFGF was bioactive. ADV also triggered changes in the ultrastructure and mechanical properties of the fibrin as bubble formation and consolidation of the fibrin in ultrasound-treated composites were accompanied by up to a 22-fold increase in shear stiffness. ADV did not reduce the viability of cells suspended in composite scaffolds. These results demonstrate that an acoustic droplet-hydrogel composite could have broad utility in promoting wound healing through on-demand control of growth factor release and/or scaffold architecture. PMID:23535233

  6. Acoustic droplet–hydrogel composites for spatial and temporal control of growth factor delivery and scaffold stiffness

    PubMed Central

    Fabiilli, Mario L.; Wilson, Christopher G.; Padilla, Frédéric; Martín-Saavedra, Francisco M.; Fowlkes, J. Brian; Franceschi, Renny T.

    2013-01-01

    Wound healing is regulated by temporally and spatially restricted patterns of growth factor signaling, but there are few delivery vehicles capable of the “on-demand” release necessary for recapitulating these patterns. Recently we described a perfluorocarbon double emulsion that selectively releases a protein payload upon exposure to ultrasound through a process known as acoustic droplet vaporization (ADV). In this study, we describe a delivery system composed of fibrin hydrogels doped with growth factor-loaded double emulsion for applications in tissue regeneration. Release of immunoreactive basic fibroblast growth factor (bFGF) from the composites increased up to 5-fold following ADV and delayed release was achieved by delaying exposure to ultrasound. Releasates of ultrasound-treated materials significantly increased the proliferation of endothelial cells compared to sham controls, indicating that the released bFGF was bioactive. ADV also triggered changes in the ultrastructure and mechanical properties of the fibrin as bubble formation and consolidation of the fibrin in ultrasound-treated composites were accompanied by up to a 22-fold increase in shear stiffness. ADV did not reduce the viability of cells suspended in composite scaffolds. These results demonstrate that an acoustic droplet–hydrogel composite could have broad utility in promoting wound healing through on-demand control of growth factor release and/or scaffold architecture. PMID:23535233

  7. Description of an experimental (hydrogen peroxide) rocket system and its use in measuring aileron and rudder effectiveness of a light airplane

    NASA Technical Reports Server (NTRS)

    Obryan, T. C.; Goode, M. W.; Gregory, F. D.; Mayo, M. H.

    1980-01-01

    A hydrogen peroxide fueled rocket system, which is to be used as a research tool in flight studies of stall and spin maneuvers, was installed on a light, four place general aviation airplane. The pilot controlled rocket system produces moments about either the roll or the yaw body axis to augment or oppose the aerodynamic forces and inertial moments acting on the airplane during various flight maneuvers, including the spin. These controlled moments of a known magnitude can be used in various ways to help analyze and interpret the importance of the various factors which influence airplane maneuvers. The rocket system and its installation in the airplane are described, and the results of flight rests used to measure rudder and aileron effectiveness at airspeeds above the stall are presented. These tests also serve to demonstrate the operational readiness of the rocket system for future research operations.

  8. Towards a fibrous composite with dynamically controlled stiffness: lessons from echinoderms.

    PubMed

    Trotter, J A; Tipper, J; Lyons-Levy, G; Chino, K; Heuer, A H; Liu, Z; Mrksich, M; Hodneland, C; Dillmore, W S; Koob, T J; Koob-Emunds, M M; Kadler, K; Holmes, D

    2000-01-01

    Sea urchins and sea cucumbers, like other echinoderms, control the tensile properties of their connective tissues by regulating stress transfer between collagen fibrils. The collagen fibrils are spindle-shaped and up to 1 mm long with a constant aspect ratio of approx. 2000. They are organized into a tissue by an elastomeric network of fibrillin microfibrils. Interactions between the fibrils are regulated by soluble macromolecules that are secreted by local, neurally controlled, effector cells. We are characterizing the non-linear viscoelastic properties of sea cucumber dermis under different conditions, as well as the structures, molecules and molecular interactions that determine its properties. In addition, we are developing reagents that will bind covalently to fibril surfaces and reversibly form cross-links with other reagents, resulting in a chemically controlled stress-transfer capacity. The information being developed will lead to the design and construction of a synthetic analogue composed of fibres in an elastomeric matrix that contains photo- or electro-sensitive reagents that reversibly form interfibrillar cross-links.

  9. The relationship between trunk muscle activation and trunk stiffness: examining a non-constant stiffness gain.

    PubMed

    Brown, Stephen H M; McGill, Stuart M

    2010-12-01

    The relationship between muscle activation, force and stiffness needs to be known to interpret the stability state of the spine. To test the relationship between these variables, a quick release approach was used to match quantified torso stiffness with an EMG activation-based estimate of individual muscle stiffnesses. The relationship between activation, force and stiffness was modelled as k = q x F/l, where k, F and l are muscle stiffness, force and length, respectively, and q is the dimensionless stiffness gain relating these variables. Under the tested experimental scenario, the 'stiffness gain', q, which linked activation with stiffness, demonstrated a decreasing trend with increasing levels of torso muscle activation. This highlights the likelihood that the choice of a single q value may be over simplistic to relate force to stiffness in muscles that control the spine. This has implications for understanding the potential for spine instability in situations requiring high muscular demand.

  10. Further wind tunnel investigation of the SM701 airfoil with aileron and turbulators

    NASA Technical Reports Server (NTRS)

    Steen, Gregory; Nicks, Oran; Heffner, Michael

    1992-01-01

    Wind tunnel tests were performed on a two-dimensional model of the SM701 airfoil designed for use on the World Class gliders. The test covered a range of Reynolds numbers from 500,000 to 1.7 million. Aerodynamic forces and moments were measured with an external balance. Momentum loss method measurements of the section drag coefficient were also made. Flow visualization techniques provided information on transition from laminar to turbulent flow. Lift, drag, and pitching moment were analyzed and comparisons were made with predicted and previously obtained experimental data. The effects of V-tape turbulators for use in turbulent drag reduction were studied. The performance of a 25 percent chord aileron deflected through plus or minus 20 degrees was researched. The model was designed, constructed, and tested by students at Texas A&M University.

  11. Rapid non-contact inspection of composite ailerons using air-coupled ultrasound

    NASA Astrophysics Data System (ADS)

    Panda, Rabi Sankar; Karpenko, Oleksii; Udpa, Lalita; Haq, Mahmoodul; Rajagopal, Prabhu; Balasubramaniam, Krishnan

    2016-02-01

    This paper demonstrates an approach for rapid non-contact air-coupled ultrasonic inspection of composite ailerons with complex cross-sectional profile including thickness changes, curvature and the presence of a number of stiffeners. Low-frequency plate guided ultrasonic modes are used in B-scan mode for the measurements in pitch-catch mode. Appropriate probe holder angles suitable for generating and receiving lower order guided wave modes are discussed. Different embodiments of the pitch-catch tandem positions along and across stiffener and curved regions of the test sample enable a rapid test campaign capturing the feature-rich sample profile. Techniques to distinguish special features in the stiffener are presented.

  12. 76 FR 69161 - Airworthiness Directives; Bombardier, Inc. Airplanes

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-08

    ...: A number of reports of aileron control stiffness have been received on Bombardier Regional Jet... determined that an additional maintenance task is required. * * * ileron control stiffness during flight... number of reports of aileron control stiffness have been received on Bombardier Regional Jet...

  13. Dynamic phototuning of 3D hydrogel stiffness

    PubMed Central

    Stowers, Ryan S.; Allen, Shane C.; Suggs, Laura J.

    2015-01-01

    Hydrogels are widely used as in vitro culture models to mimic 3D cellular microenvironments. The stiffness of the extracellular matrix is known to influence cell phenotype, inspiring work toward unraveling the role of stiffness on cell behavior using hydrogels. However, in many biological processes such as embryonic development, wound healing, and tumorigenesis, the microenvironment is highly dynamic, leading to changes in matrix stiffness over a broad range of timescales. To recapitulate dynamic microenvironments, a hydrogel with temporally tunable stiffness is needed. Here, we present a system in which alginate gel stiffness can be temporally modulated by light-triggered release of calcium or a chelator from liposomes. Others have shown softening via photodegradation or stiffening via secondary cross-linking; however, our system is capable of both dynamic stiffening and softening. Dynamic modulation of stiffness can be induced at least 14 d after gelation and can be spatially controlled to produce gradients and patterns. We use this system to investigate the regulation of fibroblast morphology by stiffness in both nondegradable gels and gels with degradable elements. Interestingly, stiffening inhibits fibroblast spreading through either mesenchymal or amoeboid migration modes. We demonstrate this technology can be translated in vivo by using deeply penetrating near-infrared light for transdermal stiffness modulation, enabling external control of gel stiffness. Temporal modulation of hydrogel stiffness is a powerful tool that will enable investigation of the role that dynamic microenvironments play in biological processes both in vitro and in well-controlled in vivo experiments. PMID:25646417

  14. Minimum stiffness location of point support for control of fundamental natural frequency of rectangular plate by Rayleigh-Ritz method

    NASA Astrophysics Data System (ADS)

    Wang, D.; Yang, Z. C.; Yu, Z. G.

    2010-07-01

    The Rayleigh-Ritz method is employed to determine the minimum stiffness location of the elastic point support for raising the fundamental natural frequency of a rectangular plate to the second frequency of the unsupported plate, which usually is the upper limit of the first frequency for a single support. Based on the optimal design of the support position, the minimum stiffness can be obtained numerically by solving a characteristic eigenvalue sub-problem. In the Rayleigh-Ritz procedure the boundary characteristic orthogonal polynomials are used for the admissible functions. Several typical examples of plate structures with the additional point supports are analyzed in detail, and the results prove that the proposed method is very effective in the solution to the optimal design of the supports. It will be shown that elastic supports can be designed like rigid ones for the purpose of increasing the fundamental natural frequency of a rectangular plate.

  15. Comparison of Pitching Moments Produced by Plain Flaps and by Spoilers and Some Aerodynamic Characteristics of an NACA 23012 Airfoil with Various Types of Aileron

    NASA Technical Reports Server (NTRS)

    Purser, Paul E.; Mckinney, Elizabeth G.

    1945-01-01

    Sectional characteristics of airfoil having retractable slotted flap with plain, slot-lip, or retractable ailerons are presented for a large range of aileron deflections. The analysis indicated that pitching moments produced by spoilers were less positive than those produced by plain flaps of equal effectiveness, also that pitching moments created by the spoiler increased less with the Mach number than similar moments produced by plain flaps. Positive values of pitching moment decreased as devices were located nearer airfoil leading edge.

  16. Effect of Variation of Chord and Span of Ailerons on Rolling and Yawing Moments at Several Angles of Pitch

    NASA Technical Reports Server (NTRS)

    Heald, R H; Strother, D H; Monish, B H

    1931-01-01

    This report presents the results of an extension to higher angles of attack of the investigation of the rolling and yawing moments due to ailerons of various chords and spans on two airfoils having the Clark Y and U. S. A. 27 wings. The measurements were made at various angles of pitch but at zero angle of roll and yaw, the wing chord being set at an angle of +4 degrees to the fuselage axis. In the case of the Clark Y airfoil the measurements have been extended to a pitch angle of 40 degrees, using ailerons of span equal to 67 per cent of the wing semispan and chord equal to 20 and 30 per cent of the wing chord. The work was conducted on wing models of 60-inch span and 10-inch chord.

  17. The Total In-Flight Simulator (TIFS) aerodynamics and systems: Description and analysis. [maneuver control and gust alleviators

    NASA Technical Reports Server (NTRS)

    Andrisani, D., II; Daughaday, H.; Dittenhauser, J.; Rynaski, E.

    1978-01-01

    The aerodynamics, control system, instrumentation complement and recording system of the USAF Total In/Flight Simulator (TIFS) airplane are described. A control system that would allow the ailerons to be operated collectively, as well as, differentially to entrance the ability of the vehicle to perform the dual function of maneuver load control and gust alleviation is emphasized. Mathematical prediction of the rigid body and the flexible equations of longitudinal motion using the level 2.01 FLEXSTAB program are included along with a definition of the vehicle geometry, the mass and stiffness distribution, the calculated mode frequencies and mode shapes, and the resulting aerodynamic equations of motion of the flexible vehicle. A complete description of the control and instrumentation system of the aircraft is presented, including analysis, ground test and flight data comparisons of the performance and bandwidth of the aerodynamic surface servos. Proposed modification for improved performance of the servos are also presented.

  18. The Difference between Stiffness and Quasi-stiffness in the Context of Biomechanical Modeling

    PubMed Central

    Rouse, Elliott J.; Gregg, Robert D.; Hargrove, Levi J.; Sensinger, Jonathon W.

    2014-01-01

    The ankle contributes the majority of mechanical power during walking and is a frequently studied joint in biomechanics. Specifically, researchers have extensively investigated the torque-angle relationship for the ankle during dynamic tasks, such as walking and running. The slope of this relationship has been termed the “quasi-stiffness.” However, over time, researchers have begun to interchange the concepts of quasi-stiffness and stiffness. This is an especially important distinction as researchers currently begin to investigate the appropriate control systems for recently developed powered prosthetic legs. The quasi-stiffness and stiffness are distinct concepts in the context of powered joints, and are equivalent in the context of passive joints. The purpose of this paper is to demonstrate the difference between the stiffness and quasi-stiffness using a simple impedance controlled inverted pendulum model and a more sophisticated biped walking model, each with the ability to modify the trajectory of an impedance controller’s equilibrium angle position. In both cases, stiffness values are specified by the controller and the quasi-stiffness are shown during a single step. Both models have widely varying quasi-stiffness but each have a single stiffness value. Therefore, from this simple modeling approach, the differences and similarities between these two concepts are elucidated. PMID:23212310

  19. Acupuncture at Houxi (SI 3) acupoint for acute neck pain caused by stiff neck: study protocol for a pilot randomised controlled trial

    PubMed Central

    Sun, Zhong-ren; Yue, Jin-huan; Tian, Hong-zhao; Zhang, Qin-hong

    2014-01-01

    Introduction The use of acupuncture has been suggested for the treatment of acute neck pain caused by stiff neck in China. However, current evidence is insufficient to draw any conclusions about its efficacy. Therefore this pilot study was designed to evaluate the feasibility and efficacy of acupuncture at the Houxi (SI3) acupoint for treatment of acute neck pain. Methods/analysis This pilot study will be a two-parallel-group, assessor-blinded, randomised controlled trial. Thirty-six stiff neck participants with acute neck pain will be recruited and randomly divided into two groups in a 1:1 ratio. Participants in the control group will receive massage on the local neck region (5 min each session, three times a day for 3 days). In addition to massage, patients in the treatment group will receive acupuncture (one session a day for 3 days). Measures will be taken at 0, 3 and 15 days. The primary outcome is the Northwick Park Neck Pain Questionnaire (NPQ). The secondary outcome is the Short Form of the McGill Pain Questionnaire (SF-MPQ). Ethics/dissemination The protocol for this pilot randomised clinical trial has undergone ethics scrutiny and been approved by the ethics review boards of the First Affiliated Hospital of Heilongjiang University of Traditional Chinese Medicine (Permission number: HZYLL201303502). The findings of this study will provide important clinical evidence on the feasibility and efficacy of acupuncture treatment for stiff neck patients with acute neck pain. In addition, it will explore the feasibility of further acupuncture research. Trial registration number ChiCTR-TRC-13003911. PMID:25537784

  20. Concept for design of variable stiffness damper

    NASA Technical Reports Server (NTRS)

    Lohr, J. J.

    1967-01-01

    Damping mechanism, containing polymeric-like materials is applicable to a wide range of shock and vibration. The polymeric-like material changes from a relatively stiff material to a relatively soft, rubbery material in the region of their glass transition temperatures. The energy absorption characteristics and stiffness are controllable with temperature.

  1. 14 CFR 25.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    .... Controls Motion and effect Aileron Right (clockwise) for right wing down. Elevator Rearward for nose up. Rudder Right pedal forward for nose right. (2) Secondary. Controls Motion and effect Flaps (or...

  2. 14 CFR 25.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    .... Controls Motion and effect Aileron Right (clockwise) for right wing down. Elevator Rearward for nose up. Rudder Right pedal forward for nose right. (2) Secondary. Controls Motion and effect Flaps (or...

  3. 14 CFR 25.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    .... Controls Motion and effect Aileron Right (clockwise) for right wing down. Elevator Rearward for nose up. Rudder Right pedal forward for nose right. (2) Secondary. Controls Motion and effect Flaps (or...

  4. Vehicle dynamics control of four in-wheel motor drive electric vehicle using gain scheduling based on tyre cornering stiffness estimation

    NASA Astrophysics Data System (ADS)

    Xiong, Lu; Yu, Zhuoping; Wang, Yang; Yang, Chen; Meng, Yufeng

    2012-06-01

    This paper focuses on the vehicle dynamic control system for a four in-wheel motor drive electric vehicle, aiming at improving vehicle stability under critical driving conditions. The vehicle dynamics controller is composed of three modules, i.e. motion following control, control allocation and vehicle state estimation. Considering the strong nonlinearity of the tyres under critical driving conditions, the yaw motion of the vehicle is regulated by gain scheduling control based on the linear quadratic regulator theory. The feed-forward and feedback gains of the controller are updated in real-time by online estimation of the tyre cornering stiffness, so as to ensure the control robustness against environmental disturbances as well as parameter uncertainty. The control allocation module allocates the calculated generalised force requirements to each in-wheel motor based on quadratic programming theory while taking the tyre longitudinal/lateral force coupling characteristic into consideration. Simulations under a variety of driving conditions are carried out to verify the control algorithm. Simulation results indicate that the proposed vehicle stability controller can effectively stabilise the vehicle motion under critical driving conditions.

  5. Stiff Person Syndrome.

    PubMed

    Saigal, Renu; Goyal, Laxmikant; Yadav, Rn; Agrawal, Abhishek; Mital, Pradeep; Patel, Bhavesh

    2015-08-01

    Stiff-person syndrome or Moersch-Woltmann is a very rare and disabling neurologic disorder characterized by muscle rigidity and episodic spasms involving axial and limb musculature. It is an autoimmune disorder resulting in a malfunction of aminobutyric acid mediated inhibitory networks in the central nervous system. We describe a patient of stiff person syndrome. PMID:27604442

  6. Curvature dependent modulation of fish fin stiffness

    NASA Astrophysics Data System (ADS)

    Nguyen, Khoi; Yu, Ning; Bandi, Mahesh; Venkadesan, Madhusudhan; Mandre, Shreyas

    Propulsion and maneuvering ability of fishes depends on the stiffness of their fins. However, increasing stiffness by simply adding material to thicken the fin would incur a substantial energetic cost associated with flapping the fin. We propose that fishes increase stiffness of the fin not by building thicker fins, but by geometrically coupling out-of-plane bending of the fin's rays with in-plane stretching of a stiff membrane that connects the rays. We present a model of fin elasticity for ray-finned fish, where we decompose the fin into a series of elastic beams (rays) with springy interconnections (membrane). In one limit, where the membranes are infinitely extensible, the fin's stiffness is no more than the sum of the stiffness of individual rays. At the other limit of an inextensible membrane, fin stiffness reaches an asymptotic maximum. The asymptote value increases monotonically with curvature. We propose that musculature at the base of the fin controls fin curvature, and thereby modulates stiffness.

  7. Control of dynamic foot-ground interactions in male and female soccer athletes: Females exhibit reduced dexterity and higher limb stiffness during landing

    PubMed Central

    Lyle, Mark A.; Valero-Cuevas, Francisco J.; Gregor, Robert J.; Powers, Christopher M.

    2014-01-01

    Controlling dynamic interactions between the lower limb and ground is important for skilled locomotion and may influence injury risk in athletes. It is well known that female athletes sustain anterior cruciate ligament (ACL) tears at higher rates than male athletes, and exhibit lower extremity biomechanics thought to increase injury risk during sport maneuvers. The purpose of this study was to examine whether lower extremity dexterity (LED) – the ability to dynamically control endpoint force magnitude and direction as quantified by compressing an unstable spring with the lower limb at submaximal forces – is a potential contributing factor to the “at-risk” movement behavior exhibited by female athletes. We tested this hypothesis by comparing LED-test performance and single-limb drop jump biomechanics between 14 female and 14 male high school soccer players. We found that female athletes exhibited reduced LED-test performance (p=0.001) and higher limb stiffness during landing (p=0.008) calculated on average within 51 ms of foot contact. Females also exhibited higher coactivation at the ankle (p=0.001) and knee (p=0.02) before landing. No sex differences in sagittal plane joint angles and center of mass velocity at foot contact were observed. Collectively, our results raise the possibility that the higher leg stiffness observed in females during landing is an anticipatory behavior due in part to reduced lower extremity dexterity. The reduced lower extremity dexterity and compensatory stiffening strategy may contribute to the heightened risk of ACL injury in this population. PMID:24275440

  8. Arterial Stiffness Gradient

    PubMed Central

    Fortier, Catherine; Agharazii, Mohsen

    2016-01-01

    Background Aortic stiffness is a strong predictor of cardiovascular mortality in various clinical conditions. The aim of this review is to focus on the arterial stiffness gradient, to discuss the integrated role of medium-sized muscular conduit arteries in the regulation of pulsatile pressure and organ perfusion and to provide a rationale for integrating their mechanical properties into risk prediction. Summary The physiological arterial stiffness gradient results from a higher degree of vascular stiffness as the distance from the heart increases, creating multiple reflective sites and attenuating the pulsatile nature of the forward pressure wave along the arterial tree down to the microcirculation. The stiffness gradient hypothesis simultaneously explains its physiological beneficial effects from both cardiac and peripheral microcirculatory points of view. The loss or reversal of stiffness gradient leads to the transmission of a highly pulsatile pressure wave into the microcirculation. This suggests that a higher degree of stiffness of medium-sized conduit arteries may play a role in protecting the microcirculation from a highly pulsatile forward pressure wave. Using the ratio of carotid-femoral pulse wave velocity (PWV) to carotid-radial PWV, referred to as PWV ratio, a recent study in a dialysis cohort has shown that the PWV ratio is a better predictor of mortality than the classical carotid-femoral PWV. Key Messages Theoretically, the use of the PWV ratio seems more logical for risk determination than aortic stiffness as it provides a better estimation of the loss of stiffness gradient, which is the unifying hypothesis that explains the impact of aortic stiffness both on the myocardium and on peripheral organs. PMID:27195235

  9. A compilation of the pressures measured on a wing and aileron with various amounts of sweep in the Langley 8-foot high-speed tunnel

    NASA Technical Reports Server (NTRS)

    Whitcomb, Richard T

    1948-01-01

    A compilation is made in tabular form of all the pressures measured on a thin high-aspect-ratio wing and aileron with no sweep and with 30 degree and 45 degree of sweepback and sweepforward at high subsonic Mach numbers in the Langley 8-foot high-speed tunnel.

  10. Dynamic behavior of stay cables with passive negative stiffness dampers

    NASA Astrophysics Data System (ADS)

    Shi, Xiang; Zhu, Songye; Li, Jin-Yang; Spencer, Billie F., Jr.

    2016-07-01

    This paper systematically investigates the dynamic behavior of stay cables with passive negative stiffness dampers (NSD) installed close to the cable end. A passive NSD is modeled as a combination of a negative stiffness spring and a viscous damper. Through both analytical and numerical approaches, parametric analysis of negative stiffness and viscous damping are conducted to systematically evaluate the vibration control performance of passive NSD on stay cables. Since negative stiffness is an unstable element, the boundary of passive negative stiffness for stay cables to maintain stability is also derived. Results reveal that the asymptotic approach is only applicable to passive dampers with positive or moderate negative stiffness, and loses its accuracy when a passive NSD possesses significant negative stiffness. It has been found that the performance of passive NSD can be much better than those of conventional viscous dampers. The superior control performance of passive NSD in cable vibration mitigation is validated through numerical simulations of a full-scale stay cable.

  11. Variable stiffness materials for reconfigurable surface applications

    NASA Astrophysics Data System (ADS)

    McKnight, Geoff; Henry, Chris

    2005-05-01

    Reconfigurable and morphing structures can potentially provide a range of new functionalities including system optimization over broad operational conditions and multi-mission capability. Previous efforts in morphing surfaces have generally focused on small deformation of high stiffness structural materials (e.g. aluminum, CFRP) or large deformation of low stiffness non-structural materials (e.g. elastomers). This paper introduces a new approach to achieving large strains in materials with high elastic moduli (5 to 30+ GPa). The work centers on creating variable stiffness composite materials which exhibit a controllable change in elastic modulus (bending or axial) and large reversible strains (5-15%). Several prototype materials were prepared using a commercial shape memory polymer, and measurements on these materials indicate a controllable change in stiffness as a function of temperature along with large reversible strain accommodation. We have fabricated and tested several design variations of laminar morphing materials which exhibit structural stiffness values of 8-12 GPa, changes in modulus of 15-77x, and large reversible bending strain and recovery of 2% area change in specific sample types. Results indicate that significant controllable changes in stiffness are possible.

  12. Pressure Distributions for the GA(W)-2 Airfoil with 20% Aileron, 25% Slotted Flap and 30% Fowler Flap

    NASA Technical Reports Server (NTRS)

    Wentz, W. H., Jr.; Fiscko, K. A.

    1978-01-01

    Surface pressure distributions were measured for the 13% thick GA(W)-2 airfoil section fitted with 20% aileron, 25% slotted flap and 30% Fowler flap. All tests were conducted at a Reynolds number of 2.2 x 10 to the 6th power and a Mach number of 0.13. Pressure distribution and force and moment coefficient measurements are compared with theoretical results for a number of cases. Agreement between theory and experiment is generally good for low angles of attack and small flap deflections. For high angles and large flap deflections where regions of separation are present, the theory is inadequate. Theoretical drag predictions are poor for all flap-extended cases.

  13. Determination of ball bearing dynamic stiffness

    NASA Technical Reports Server (NTRS)

    Beatty, R. F.; Rowan, B. F.

    1982-01-01

    The dynamic radial stiffness characteristics of rolling element bearings are currently determined by analytical methods that have not been experimentally verified. These bearing data are vital to rotating machinery design integrity because accurate critical speeds and rotor stability predictions are highly dependent on the bearing stiffness. A tester was designed capable of controlling the bearing axial preload, speed, and rotor unbalance. The rotor and support structures were constructed to permit critical speeds that are predominantly determined by a 57 mm test bearing. A curve of calculated critical speed versus stiffness was used to determine the actual bearing stiffness from the empirical data. The results of extensive testing are used to verify analytical predictions, increase confidence in existing bearing computer programs, and to serve as a data base for efforts to correct these programs.

  14. Effects of different types of antihypertensive agents on arterial stiffness: a systematic review and meta-analysis of randomized controlled trials

    PubMed Central

    Chen, Xiahuan; Huang, Bo; Li, Xueying

    2015-01-01

    Background This system review and meta-analysis was conducted to systematically review and analyze the clinical benefits of different antihypertensive agents in improving arterial stiffness in hypertensive patients. Methods PubMed database was searched for randomized controlled trials (RCTs) evaluating the effects of angiotensin receptor blockers (ARB) or other types of antihypertensive agents on pulse wave velocity (PWV). The main indicators were the improvements of PWV and augmentation index (AI) before and after randomized treatments with antihypertensive agents. For the studies that only provided the mean and standard deviation of the indicators before and after randomization, the standardized mean difference (SMD) method was directly applied to combine the mean and standard deviation of various indicators after the treatment. For the studies provided the mean and standard deviation of the changes of the indicators, the weighted mean difference (MD) method was applied to combine the mean and standard deviation of the therapeutic effect. Results Ten RCT studies were included and the sample sizes range from 40 to 201 (total: 938). Four studies provided the changes of PWV before and after randomization, the pooled analysis showed that the changes of PWV in ARB group were not significantly higher than other antihypertensive agents [MD: 125.76, 95% confidence interval (CI): −78.70 to 330.23, P=0.23]; 4 studies provided the PWV values before and after randomization, the PWV values in ARB group were not significantly superior (SMD: 0.04, 95% CI: −0.16 to 0.24, P=0.71). Three studies provided the changes of AI before and after randomization, the ability of ARB to lower the level of the AI was superior to other antihypertensive agents (MD: 8.94, 95% CI: 2.18–5.71, P=0.01); 2 studies provided the AI value after randomization, the abilities of ARB and other anti-hypertensive agents to improve the AI were similar (SMD: 0.03, 95% CI: −1.20 to 1.26, P=0

  15. Hypertension and arterial stiffness in heart transplantation patients

    PubMed Central

    de Souza-Neto, João David; de Oliveira, Ítalo Martins; Lima-Rocha, Hermano Alexandre; Oliveira-Lima, José Wellington; Bacal, Fernando

    2016-01-01

    OBJECTIVES: Post-transplantation hypertension is prevalent and is associated with increased cardiovascular morbidity and subsequent graft dysfunction. The present study aimed to identify the factors associated with arterial stiffness as measured by the ambulatory arterial stiffness index. METHODS: The current study used a prospective, observational, analytical design to evaluate a group of adult heart transplantation patients. Arterial stiffness was obtained by monitoring ambulatory blood pressure and using the ambulatory arterial stiffness index as the surrogate outcome. Multivariate logistic regression analyses were performed to control confounding. RESULTS: In a group of 85 adult heart transplantation patients, hypertension was independently associated with arterial stiffness (OR 4.98, CI 95% 1.06-23.4) as well as systolic and diastolic blood pressure averages and nighttime descent. CONCLUSIONS: Measurement of ambulatory arterial stiffness index is a new, non-invasive method that is easy to perform, may contribute to better defining arterial stiffness prognosis and is associated with hypertension.

  16. Hypertension and arterial stiffness in heart transplantation patients

    PubMed Central

    de Souza-Neto, João David; de Oliveira, Ítalo Martins; Lima-Rocha, Hermano Alexandre; Oliveira-Lima, José Wellington; Bacal, Fernando

    2016-01-01

    OBJECTIVES: Post-transplantation hypertension is prevalent and is associated with increased cardiovascular morbidity and subsequent graft dysfunction. The present study aimed to identify the factors associated with arterial stiffness as measured by the ambulatory arterial stiffness index. METHODS: The current study used a prospective, observational, analytical design to evaluate a group of adult heart transplantation patients. Arterial stiffness was obtained by monitoring ambulatory blood pressure and using the ambulatory arterial stiffness index as the surrogate outcome. Multivariate logistic regression analyses were performed to control confounding. RESULTS: In a group of 85 adult heart transplantation patients, hypertension was independently associated with arterial stiffness (OR 4.98, CI 95% 1.06-23.4) as well as systolic and diastolic blood pressure averages and nighttime descent. CONCLUSIONS: Measurement of ambulatory arterial stiffness index is a new, non-invasive method that is easy to perform, may contribute to better defining arterial stiffness prognosis and is associated with hypertension. PMID:27652829

  17. Sensitivity of overall vehicle stiffness to local joint stiffness

    NASA Technical Reports Server (NTRS)

    Chon, Choon T.

    1987-01-01

    How overall vehicle stiffness is affected by local joint stiffness is discussed. By using the principle of virtual work and the minimum strain energy theorem, a closed form expression for the sensitivity coefficient was derived. The insensitivity of the vehicle stiffness to a particular joint, when its stiffness exceeds a certain value (or threshold value), was proven mathematically. In order to investigate the sensitivity of the structure to the joint stiffness, a so-called stick model was created, and the modeling technique is briefly described. Some data on joint stiffness of tested vehicles are also presented.

  18. Right Ventricular Myocardial Stiffness in Experimental Pulmonary Arterial Hypertension

    PubMed Central

    Rain, Silvia; Andersen, Stine; Najafi, Aref; Gammelgaard Schultz, Jacob; da Silva Gonçalves Bós, Denielli; Handoko, M. Louis; Bogaard, Harm-Jan; Vonk-Noordegraaf, Anton; Andersen, Asger; van der Velden, Jolanda; Ottenheijm, Coen A.C.

    2016-01-01

    Background— The purpose of this study was to determine the relative contribution of fibrosis-mediated and myofibril-mediated stiffness in rats with mild and severe right ventricular (RV) dysfunction. Methods and Results— By performing pulmonary artery banding of different diameters for 7 weeks, mild RV dysfunction (Ø=0.6 mm) and severe RV dysfunction (Ø=0.5 mm) were induced in rats. The relative contribution of fibrosis- and myofibril-mediated RV stiffness was determined in RV trabecular strips. Total myocardial stiffness was increased in trabeculae from both mild and severe RV dysfunction in comparison to controls. In severe RV dysfunction, increased RV myocardial stiffness was explained by both increased fibrosis-mediated stiffness and increased myofibril-mediated stiffness, whereas in mild RV dysfunction, only myofibril-mediated stiffness was increased in comparison to control. Histological analyses revealed that RV fibrosis gradually increased with severity of RV dysfunction, whereas the ratio of collagen I/III expression was only elevated in severe RV dysfunction. Stiffness measurements in single membrane-permeabilized RV cardiomyocytes demonstrated a gradual increase in RV myofibril stiffness, which was partially restored by protein kinase A in both mild and severe RV dysfunction. Increased expression of compliant titin isoforms was observed only in mild RV dysfunction, whereas titin phosphorylation was reduced in both mild and severe RV dysfunction. Conclusions— RV myocardial stiffness is increased in rats with mild and severe RV dysfunction. In mild RV dysfunction, stiffness is mainly determined by increased myofibril stiffness. In severe RV dysfunction, both myofibril- and fibrosis-mediated stiffness contribute to increased RV myocardial stiffness. PMID:27370069

  19. Knee stiffness following anterior cruciate ligament reconstruction: the incidence and associated factors of knee stiffness following anterior cruciate ligament reconstruction.

    PubMed

    Robertson, G A J; Coleman, S G S; Keating, J F

    2009-08-01

    We reviewed 100 patients retrospectively following primary ACL reconstruction with quadruple hamstring autografts to evaluate the incidence and factors associated with postoperative stiffness. Stiffness was defined as any loss of motion using the contra-lateral leg as a control. The median delay between injury and operation was 15 months. The incidence of stiffness was 12% at 6 months post-reconstruction. Both incomplete attendance at physiotherapy (p<0.005) and previous knee surgery (p<0.005) were the strongest predictors of the stiffness. Anterior knee pain was also associated with the stiffness (p<0.029). Factors that failed to show a significant association with the stiffness included associated MCL sprain at injury (p=0.32), post-injury stiffness (p=1.00) and concomitant menisectomy at reconstruction (p=0.54). Timing of surgery also did not appear to influence the onset of stiffness (median delays: 29 months for stiff patients; 14 months for non-stiff patients). The rate of stiffness fell to 5% at 12 months postreconstruction, without operative intervention.

  20. Present Status of Lateral-Control Devices for use with Split Flaps, Special Report

    NASA Technical Reports Server (NTRS)

    Weick, Fred E.

    1933-01-01

    The increased use of split flaps for the dual purpose of reducing the landing speed and shortening the landing glide of airplanes has established as acute the problem of obtaining satisfactory lateral control to be used in conjunction with the flaps with out the sacrifice of any of the effectiveness of the flaps. A large amount of work is being done on this problem by various organizations and individuals. Several of the devices developed seem usable, some of them unquestionably so. The present paper attempts to summarize the most promising results obtained to date. Topics covered include ordinary ailerons, external ailerons, floating ailerons, upper-surface ailerons, and spoilers. Although the external ailerons above the trailing edge of the wing and the spoilers at the rear of the wing appear quite promising, it would seem that probably the most satisfactory immediate solution of the problem, including the obtaining of light and smoothly graduated control forces, would in most cases be obtained by the use of the arrangement in which the flap is retracted ahead of ordinary narrow-chord ailerons and is deflected to the rear as well as downward when in use.

  1. Premature aortic stiffness in systemic lupus erythematosus by transesophageal echocardiography.

    PubMed

    Roldan, C A; Joson, J; Qualls, C R; Sharrar, J; Sibbitt, W L

    2010-12-01

    To assess aortic stiffness by transesophageal echocardiography (TEE) and to determine its clinical predictors and relation to age, blood pressure, renal function, and atherosclerosis, 50 patients with systemic lupus erythematosus (SLE), 94% women, with a mean age of 38 ± 12 years, and 22 age and gender-matched healthy controls underwent clinical and laboratory evaluations and multiplane TEE to assess stiffness, intima-media thickness (IMT), and plaques of the proximal, mid, and distal descending thoracic aorta. Stiffness at each level and overall aortic stiffness by the pressure-strain elastic modulus was higher in patients than in controls after adjusting for age (overall, 8.25 ± 4.13 versus 6.1 ± 2.5 Pascal units, p = 0.01). Patients had higher aortic stiffness than controls after adjusting both groups to the same mean age, blood pressure, creatinine, and aortic IMT (p = 0.005). Neither IMT nor plaques were predictors of aortic stiffness. Moreover, normotensive patients, those without aortic plaques, and non-smokers had higher stiffness than controls (all p < 0.05). Age at SLE diagnosis and non-neurologic damage score were the only SLE-specific independent predictors of aortic stiffness (both p ≤ 0.01). Thus, increased aortic stiffness is an early manifestation of lupus vasculopathy that seems to precede the development of hypertension and atherosclerosis.

  2. Calculations on the forces and moments for an oscillating wing-aileron combination in two-dimensional potential flow at sonic speed

    NASA Technical Reports Server (NTRS)

    Nelson, Herbert C; Berman, Julian H

    1953-01-01

    The linearized theory for compressible unsteady flow is used, as suggested in recent contributions to the subject, to obtain the velocity potential and the lift and moment for a thin harmonically oscillating, two-dimensional wing-aileron combination moving at sonic speed. The velocity potential is derived by considering the sonic case as the limit of the linearized supersonic theory. From the velocity potential explicit expressions for the lift and moment are developed for vertical translation and pitching of the wing and rotation of the aileron. The sonic results are compared and found to be consistent with previously obtained subsonic and supersonic results. Several figures are presented showing the variation of lift and moment with reduced frequency and Mach number and the influence of Mach number on some cases of bending-torsion flutter.

  3. Cancer Cell Stiffness: Integrated Roles of Three-Dimensional Matrix Stiffness and Transforming Potential

    PubMed Central

    Baker, Erin L.; Lu, Jing; Yu, Dihua; Bonnecaze, Roger T.; Zaman, Muhammad H.

    2010-01-01

    While significant advances have been made toward revealing the molecular mechanisms that influence breast cancer progression, much less is known about the associated cellular mechanical properties. To this end, we use particle-tracking microrheology to investigate the interplay among intracellular mechanics, three-dimensional matrix stiffness, and transforming potential in a mammary epithelial cell (MEC) cancer progression series. We use a well-characterized model system where human-derived MCF10A MECs overexpress either ErbB2, 14-3-3ζ, or both ErbB2 and 14-3-3ζ, with empty vector as a control. Our results show that MECs possessing ErbB2 transforming potential stiffen in response to elevated matrix stiffness, whereas non-transformed MECs or those overexpressing only 14-3-3ζ do no exhibit this response. We further observe that overexpression of ErbB2 alone is associated with the highest degree of intracellular sensitivity to matrix stiffness, and that the effect of transforming potential on intracellular stiffness is matrix-stiffness-dependent. Moreover, our intracellular stiffness measurements parallel cell migration behavior that has been previously reported for these MEC sublines. Given the current knowledge base of breast cancer mechanobiology, these findings suggest that there may be a positive relationship among intracellular stiffness sensitivity, cell motility, and perturbed mechanotransduction in breast cancer. PMID:20923638

  4. Cancer cell stiffness: integrated roles of three-dimensional matrix stiffness and transforming potential.

    PubMed

    Baker, Erin L; Lu, Jing; Yu, Dihua; Bonnecaze, Roger T; Zaman, Muhammad H

    2010-10-01

    While significant advances have been made toward revealing the molecular mechanisms that influence breast cancer progression, much less is known about the associated cellular mechanical properties. To this end, we use particle-tracking microrheology to investigate the interplay among intracellular mechanics, three-dimensional matrix stiffness, and transforming potential in a mammary epithelial cell (MEC) cancer progression series. We use a well-characterized model system where human-derived MCF10A MECs overexpress either ErbB2, 14-3-3ζ, or both ErbB2 and 14-3-3ζ, with empty vector as a control. Our results show that MECs possessing ErbB2 transforming potential stiffen in response to elevated matrix stiffness, whereas non-transformed MECs or those overexpressing only 14-3-3ζ do no exhibit this response. We further observe that overexpression of ErbB2 alone is associated with the highest degree of intracellular sensitivity to matrix stiffness, and that the effect of transforming potential on intracellular stiffness is matrix-stiffness-dependent. Moreover, our intracellular stiffness measurements parallel cell migration behavior that has been previously reported for these MEC sublines. Given the current knowledge base of breast cancer mechanobiology, these findings suggest that there may be a positive relationship among intracellular stiffness sensitivity, cell motility, and perturbed mechanotransduction in breast cancer.

  5. Effect of Rg3-enriched Korean red ginseng (Panax ginseng) on arterial stiffness and blood pressure in healthy individuals: a randomized controlled trial.

    PubMed

    Jovanovski, Elena; Bateman, Emma A; Bhardwaj, Jyoti; Fairgrieve, Chris; Mucalo, Iva; Jenkins, Alexandra L; Vuksan, Vladimir

    2014-08-01

    Ginsenoside Rg3, present in steamed ginseng (Panax Ginseng C.A. Meyer), is thought to be a potent modulator of vascular function. Our objective was to clinically evaluate acute effects of ginsenoside Rg3-enriched Korean red ginseng (Rg3-KRG) on measures of arterial stiffness and peripheral and central blood pressure (BP) parameters in healthy volunteers. Using a double-blind, randomized, crossover design, 23 individuals (9 males:14 females; age, 25 ± 2 years; body mass index, 22 ± 0.6 kg/m(2); systolic BP/diastolic BP, 113 ± 3/70 ± 2 mm Hg) were administered 400-mg Rg3-KRG extract or 400-mg wheat bran control on two separate visits with a 7-day washout period. Aortic augmentation index and central BP were measured using applanation tonometry by radial pulse wave analysis, and peripheral BP was evaluated oscillometrically. Measurements were taken at baseline and at 1, 2, and 3 hours after intervention. Compared with control, there were significant reductions in augmentation index (-4.3 ± 8.9%, P = .03), central (-4.8 ± 6.8 mm Hg, P = .01) and brachial mean arterial pressure (-4.4 ± 6.6 mm Hg, P = .01), central systolic (-5.0 ± 7.9 mm Hg, P = .01) and diastolic BP (-3.9 ± 6.6 mm Hg, P = .01), and brachial systolic (-4.4 ± 10.0 mm Hg, P = .048) and diastolic BP (-3.6 ± 6.4 mm Hg, P = .01) at 3 hours after intervention compared with control. This study is the first to demonstrate Rg3-KRG extract acutely lowers central and peripheral arterial pressures in healthy adults. Further clinical evaluation is desired to quantify efficacy in higher risk individuals and in long-term settings.

  6. Variable stiffness torsion springs

    NASA Technical Reports Server (NTRS)

    Alhorn, Dean C. (Inventor); Polites, Michael E. (Inventor)

    1994-01-01

    In a torsion spring the spring action is a result of the relationships between the torque applied in twisting the spring, the angle through which the torsion spring twists, and the modulus of elasticity of the spring material in shear. Torsion springs employed industrially have been strips, rods, or bars, generally termed shafts, capabable of being flexed by twisting their axes. They rely on the variations in shearing forces to furnish an internal restoring torque. In the torsion springs herein the restoring torque is external and therefore independent of the shearing modulus of elasticity of the torsion spring shaft. Also provided herein is a variable stiffness torsion spring. This torsion spring can be so adjusted as to have a given spring constant. Such variable stiffness torsion springs are extremely useful in gimballed payloads such as sensors, telescopes, and electronic devices on such platforms as a space shuttle or a space station.

  7. Variable stiffness torsion springs

    NASA Technical Reports Server (NTRS)

    Alhorn, Dean C. (Inventor); Polites, Michael E. (Inventor)

    1995-01-01

    In a torsion spring the spring action is a result of the relationships between the torque applied in twisting the spring, the angle through which the torsion spring twists, and the modulus of elasticity of the spring material in shear. Torsion springs employed industrially have been strips, rods, or bars, generally termed shafts, capabable of being flexed by twisting their axes. They rely on the variations in shearing forces to furnish an internal restoring torque. In the torsion springs herein the restoring torque is external and therefore independent of the shearing modulus of elasticity of the torsion spring shaft. Also provided herein is a variable stiffness torsion spring. This torsion spring can be so adjusted as to have a given spring constant. Such variable stiffness torsion springs are extremely useful in gimballed payloads such as sensors, telescopes, and electronic devices on such platforms as a space shuttle or a space station.

  8. Association between bone stiffness and nutritional biomarkers combined with weight-bearing exercise, physical activity, and sedentary time in preadolescent children. A case-control study.

    PubMed

    Herrmann, Diana; Pohlabeln, Hermann; Gianfagna, Francesco; Konstabel, Kenn; Lissner, Lauren; Mårild, Staffan; Molnar, Dénes; Moreno, Luis A; Siani, Alfonso; Sioen, Isabelle; Veidebaum, Toomas; Ahrens, Wolfgang

    2015-09-01

    Physical activity (PA) and micronutrients such as calcium (Ca), vitamin D (25OHD), and phosphate (PO) are important determinants of skeletal development. This case-control study examined the association of these nutritional biomarkers and different PA behaviours, such as habitual PA, weight-bearing exercise (WBE) and sedentary time (SED) with bone stiffness (SI) in 1819 2-9-year-old children from the IDEFICS study (2007-2008). SI was measured on the calcaneus using quantitative ultrasound. Serum and urine Ca and PO and serum 25OHD were determined. Children's sports activities were reported by parents using a standardised questionnaire. A subsample of 1089 children had accelerometer-based PA data (counts per minute, cpm). Moderate-to-vigorous PA (MVPA) and SED were estimated. Children with poor SI (below the 15th age-/sex-/height-specific percentile) were defined as cases (N=603). Randomly selected controls (N=1216) were matched by age, sex, and country. Odds ratios (OR) for poor SI were calculated by conditional logistic regression for all biomarkers and PA behaviour variables separately and combined (expressed as tertiles and dichotomised variables, respectively). ORs were adjusted for fat-free mass, dairy product consumption, and daylight duration. We observed increased ORs for no sports (OR=1.39, p<0.05), PA levels below 524 cpm (OR=1.85, p<0.05) and MVPA below 4.2% a day (OR=1.69, p<0.05) compared to WBE, high PA levels (<688 cpm) and high MVPA (6.7%), respectively. SED was not associated with SI. ORs were moderately elevated for low serum Ca and 25OHD. However, biomarkers were not statistically significantly associated with SI and did not modify the association between PA behaviours and SI. Although nutritional biomarkers appear to play a minor role compared to the osteogenic effect of PA and WBE, it is noteworthy that the highest risk for poor SI was observed for no sports or low MVPA combined with lower serum Ca (<2.5 mmol/l) or lower 25OHD (<43.0 nmol/l).

  9. Effect of Spinach, a High Dietary Nitrate Source, on Arterial Stiffness and Related Hemodynamic Measures: A Randomized, Controlled Trial in Healthy Adults.

    PubMed

    Jovanovski, Elena; Bosco, Laura; Khan, Kashif; Au-Yeung, Fei; Ho, Hoang; Zurbau, Andreea; Jenkins, Alexandra L; Vuksan, Vladimir

    2015-07-01

    Diets rich in fruits and vegetables reduce risk of adverse cardiovascular events. However, the constituents responsible for this effect have not been well established. Lately, the attention has been brought to vegetables with high nitrate content with evidence that this might represent a source of vasoprotective nitric oxide. We hypothesized that short-term consumption of spinach, a vegetable having high dietary nitrate content, can affect the arterial waveform indicative of arterial stiffness, as well as central and peripheral blood pressure (BP). Using a placebo-controlled, crossover design, 27 healthy participants were randomly assigned to receive either a high-nitrate (spinach; 845 mg nitrate/day) or low-nitrate soup (asparagus; 0.6 mg nitrate/day) for 7 days with a 1-week washout period. On days 1 and 7, profiles of augmentation index, central, and brachial BP were obtained over 180 min post-consumption in 4 fasted visits. A postprandial reduction in augmentation index was observed at 180 min on high-nitrate compared to low-nitrate intervention (-6.54 ± 9.7% vs. -0.82 ± 8.0%, p = 0.01) on Day 1, and from baseline on Day 7 (-6.93 ± 8.7%, p < 0.001; high vs. low: -2.28 ± 12.5%, p = 0.35), suggesting that the nitrate intervention is not associated with the development of tolerance for at least 7 days of continued supplementation. High vs. low-nitrate intervention also reduced central systolic (-3.39 ± 5.6 mmHg, p = 0.004) and diastolic BP (-2.60 ± 5.8 mmHg, p = 0.028) and brachial systolic BP (-3.48 ± 7.4 mmHg, p = 0.022) at 180 min following 7-day supplementation only. These findings suggest that dietary nitrate from spinach may contribute to beneficial hemodynamic effects of vegetable-rich diets and highlights the potential of developing a targeted dietary approach in the management of elevated BP. PMID:26251834

  10. Effects of lanthanum carbonate versus calcium carbonate on vascular stiffness and bone mineral metabolism in hemodialysis patients with type 2 diabetes mellitus: a randomized controlled trial

    PubMed Central

    Wada, Kentaro; Wada, Yuko; Uchida, Haruhito Adam; Tsuruoka, Shuichi

    2015-01-01

    Background Vascular calcification contributes to cardiovascular disease in hemodialysis (HD) patients with diabetes. The randomized controlled trial reported here compared the effects of lanthanum carbonate (LC) and calcium carbonate (CC) on vascular stiffness assessed using brachial-ankle pulse wave velocity (ba-PWV), intima-media thickness (IMT), bone mineral density (BMD), and serum markers of chronic kidney disease – mineral and bone disorder in such patients. Methods Ba-PWV, IMT, BMD, and the biomarkers osteocalcin (OC) and bone alkaline phosphatase (BAP) were examined in 43 type 2 diabetes HD patients treated with LC (n=21) or CC (n=22) for 2 years. Results Forty-one patients completed the study (19, LC; 22, CC). The mean ba-PWV significantly increased only in the CC group (median: 2,280.5 to 2,402.5 cm/s, P<0.05), after 24-month treatment; it remained unchanged in the LC group (median: 1,830.5 to 2,018.3 cm/s). However, the difference between the groups did not reach statistical significance. Changes in IMT and BMD were not different between the two groups. Changes in serum phosphorus, corrected calcium, and intact parathyroid hormone levels were similar between the groups. The incidence of fracture was 0% (0/19) in the LC group, and 13.6% (3/22) in the CC group (P=0.2478). The OC/BAP ratio increased significantly in the LC group (median: 0.83 to 2.47), compared with in the CC group (median: 0.77 to 1.40) (P=0.036). Conclusion From this study, in Japanese type 2 diabetes HD patients, we conclude that 2-year treatment with LC might have slowed the progression of ba-PWV; however, it did not cause a difference in ba-PWV, IMT, BMD, or fracture, compared with CC. Further, LC increased the OC/BAP ratio to a greater extent than CC. PMID:26346335

  11. Effect of Spinach, a High Dietary Nitrate Source, on Arterial Stiffness and Related Hemodynamic Measures: A Randomized, Controlled Trial in Healthy Adults

    PubMed Central

    Jovanovski, Elena; Bosco, Laura; Khan, Kashif; Au-Yeung, Fei; Ho, Hoang; Zurbau, Andreea; Jenkins, Alexandra L.

    2015-01-01

    Diets rich in fruits and vegetables reduce risk of adverse cardiovascular events. However, the constituents responsible for this effect have not been well established. Lately, the attention has been brought to vegetables with high nitrate content with evidence that this might represent a source of vasoprotective nitric oxide. We hypothesized that short-term consumption of spinach, a vegetable having high dietary nitrate content, can affect the arterial waveform indicative of arterial stiffness, as well as central and peripheral blood pressure (BP). Using a placebo-controlled, crossover design, 27 healthy participants were randomly assigned to receive either a high-nitrate (spinach; 845 mg nitrate/day) or low-nitrate soup (asparagus; 0.6 mg nitrate/day) for 7 days with a 1-week washout period. On days 1 and 7, profiles of augmentation index, central, and brachial BP were obtained over 180 min post-consumption in 4 fasted visits. A postprandial reduction in augmentation index was observed at 180 min on high-nitrate compared to low-nitrate intervention (-6.54 ± 9.7% vs. -0.82 ± 8.0%, p = 0.01) on Day 1, and from baseline on Day 7 (-6.93 ± 8.7%, p < 0.001; high vs. low: -2.28 ± 12.5%, p = 0.35), suggesting that the nitrate intervention is not associated with the development of tolerance for at least 7 days of continued supplementation. High vs. low-nitrate intervention also reduced central systolic (-3.39 ± 5.6 mmHg, p = 0.004) and diastolic BP (-2.60 ± 5.8 mmHg, p = 0.028) and brachial systolic BP (-3.48 ± 7.4 mmHg, p = 0.022) at 180 min following 7-day supplementation only. These findings suggest that dietary nitrate from spinach may contribute to beneficial hemodynamic effects of vegetable-rich diets and highlights the potential of developing a targeted dietary approach in the management of elevated BP. PMID:26251834

  12. The Effect of High Dose Cholecalciferol on Arterial Stiffness and Peripheral and Central Blood Pressure in Healthy Humans: A Randomized Controlled Trial

    PubMed Central

    Bressendorff, Iain; Brandi, Lisbet; Schou, Morten; Nygaard, Birgitte; Frandsen, Niels Erik; Rasmussen, Knud; Ødum, Lars; Østergaard, Ove Vyff; Hansen, Ditte

    2016-01-01

    Background Low levels of serum 25-hydroxy vitamin D are associated with increased arterial stiffness and hypertension. Supplementation with vitamin D precursors has been proposed as a treatment option for these conditions. We examined the effect of oral cholecalciferol on arterial stiffness and blood pressure in healthy normotensive adults. Methods 40 healthy adults were randomised in this double-blinded study to either oral cholecalciferol 3000 IU/day or matching placebo and were followed for 16 weeks to examine any effects on pulse wave velocity (PWV), augmentation index (AIx), peripheral and central blood pressure and 24-hour ambulatory blood pressure. Results 22 subjects in the cholecalciferol arm and 18 subjects in the placebo arm completed the 16 weeks of follow-up. There was no difference in changes in PWV, AIx corrected for heart rate or central or peripheral blood pressure between the two groups. There was no correlation between serum 25-hydroxy vitamin D and any of these parameters. Conclusions Oral cholecalciferol 3000 IU/day does not affect arterial stiffness or blood pressure after 16 weeks of treatment in healthy normotensive adults. Trial Registration ClinicalTrials.gov NCT00952562 PMID:27509187

  13. Cockpit control system conceptual design

    NASA Technical Reports Server (NTRS)

    Meholic, Greg; Brown, Rhonda; Hall, Melissa; Harvey, Robert; Singer, Michael; Tella, Gustavo

    1993-01-01

    The purpose of this project was to provide a means for operating the ailerons, elevator, elevator trim, rudder, nosewheel steering, and brakes in the Triton primary flight trainer. The main design goals under consideration were to illustrate system and subsystem integration, control function ability, and producibility. Weight and maintenance goals were addressed.

  14. Supplementary Investigation in the Free-Spinning Tunnel of a 1/24-Scale Model of the Grumman F9F-6 Airplane Incorporating only Flaperons for Lateral Control, TED No. NACA DE 364

    NASA Technical Reports Server (NTRS)

    Klinar, Walter J.; Lee, Henry A.

    1954-01-01

    A supplementary investigation was conducted in the Langley 20-foot free-spinning tunnel on a 1/24-scale model of the Grumman F9F-6 airplane. The primary purpose of the investigation was to reevaluate the spin-recovery characteristics of the airplane in view of the fact that the ailerons had been eliminated from the flaperon-aileron lateral control system of the airplane. A spin-tunnel investigation on a model of the earlier version of the F9F-6 airplane had indicated that use of ailerons with the spin (stick right in a right spin) was essential to insure recovery. The results indicate that with.ailerons eliminated, it may be difficult to obtain an erect developed spin but if a fully developed spin is obtained on the airplane, recovery therefrom may be difficult or impossible. Flaperon deflection should have little effect on spins or recoveries.

  15. Effects of control inputs on the estimation of stability and control parameters of a light airplane

    NASA Technical Reports Server (NTRS)

    Cannaday, R. L.; Suit, W. T.

    1977-01-01

    The maximum likelihood parameter estimation technique was used to determine the values of stability and control derivatives from flight test data for a low-wing, single-engine, light airplane. Several input forms were used during the tests to investigate the consistency of parameter estimates as it relates to inputs. These consistencies were compared by using the ensemble variance and estimated Cramer-Rao lower bound. In addition, the relationship between inputs and parameter correlations was investigated. Results from the stabilator inputs are inconclusive but the sequence of rudder input followed by aileron input or aileron followed by rudder gave more consistent estimates than did rudder or ailerons individually. Also, square-wave inputs appeared to provide slightly improved consistency in the parameter estimates when compared to sine-wave inputs.

  16. The Effect of Blunt-Trailing-Edge Modifications on the High-Speed Stability and Control Characteristics of a Swept-Wing Fighter Airplane

    NASA Technical Reports Server (NTRS)

    Sadoff, Melvin; Matteson, Frederick H.; Van Dyke, Rudolph D., Jr.

    1954-01-01

    An investigation was conducted on a 35 deg swept-wing fighter airplane to determine the effects of several blunt-trailing-edge modifications to the wing and tail on the high-speed stability and control characteristics and tracking performance. The results indicated significant improvement in the pitch-up characteristics for the blunt-aileron configuration at Mach numbers around 0.90. As a result of increased effectiveness of the blunt-trailing-edge aileron, the roll-off, customarily experienced with the unmodified airplane in wings-level flight between Mach numbers of about 0.9 and 1.0 was eliminated, The results also indicated that the increased effectiveness of the blunt aileron more than offset the large associated aileron hinge moment, resulting in significant improvement in the rolling performance at Mach numbers between 0.85 and 1.0. It appeared from these results that the tracking performance with the blunt-aileron configuration in the pitch-up and buffeting flight region at high Mach numbers was considerably improved over that of the unmodified airplane; however, the tracking errors of 8 to 15 mils were definitely unsatisfactory. A drag increment of about O.OOl5 due to the blunt ailerons was noted at Mach numbers to about 0.85. The drag increment was 0 at Mach numbers above 0.90.

  17. Arterial stiffness, as monitored by cardio–ankle vascular index, is affected by obstructive sleep apnea, blood glucose control, and body weight – a case with 8 years follow up

    PubMed Central

    Shimizu, Kazuhiro; Yamamoto, Tomoyuki; Shirai, Kohji

    2016-01-01

    The cardio–ankle vascular index (CAVI) is an indicator of arterial stiffness from the heart to the ankles. The CAVI increases as arteriosclerosis progresses, but it can be decreased by appropriate treatment. There are several risk factors for coronary artery disease, however, the degree of stress caused by each separate risk factor to arteries cannot be assessed. CAVI increases with age and according to the severity of atherosclerosis. We found that CAVI also changes in response to the control of risk factors, which may be associated with the functional stiffness of arteries. CAVI can be a useful indicator of risk control for coronary artery disease. We followed a patient aged 71 years who had diabetes mellitus and obstructive sleep apnea (OSA) by measuring CAVI for 8 years from age 63. He underwent coronary artery bypass grafting due to angina pectoris when he was 63 years old. Before coronary artery bypass grafting, CAVI was 11.8 on the right and 11.5 on the left. Three years later he was found to have OSA and received treatment with continuous positive airway pressure. There was a marked improvement in CAVI after continuous positive airway pressure (age 68; right 10.4, left 10.2). However, following a gradual increase in body weight and worsening of diabetes mellitus, CAVI showed an increasing trend. CAVI decreased with biguanides treatment, but increased again with an increase in body weight. In conclusion, CAVI responded to the patient’s conditions including obesity, diabetes mellitus, and OSA. CAVI is not only a marker of arterial stiffness, but can also be a useful indicator of physiological status; it may be effective in total risk control for coronary artery disease. PMID:27563259

  18. Arterial stiffness, as monitored by cardio-ankle vascular index, is affected by obstructive sleep apnea, blood glucose control, and body weight - a case with 8 years follow up.

    PubMed

    Shimizu, Kazuhiro; Yamamoto, Tomoyuki; Shirai, Kohji

    2016-01-01

    The cardio-ankle vascular index (CAVI) is an indicator of arterial stiffness from the heart to the ankles. The CAVI increases as arteriosclerosis progresses, but it can be decreased by appropriate treatment. There are several risk factors for coronary artery disease, however, the degree of stress caused by each separate risk factor to arteries cannot be assessed. CAVI increases with age and according to the severity of atherosclerosis. We found that CAVI also changes in response to the control of risk factors, which may be associated with the functional stiffness of arteries. CAVI can be a useful indicator of risk control for coronary artery disease. We followed a patient aged 71 years who had diabetes mellitus and obstructive sleep apnea (OSA) by measuring CAVI for 8 years from age 63. He underwent coronary artery bypass grafting due to angina pectoris when he was 63 years old. Before coronary artery bypass grafting, CAVI was 11.8 on the right and 11.5 on the left. Three years later he was found to have OSA and received treatment with continuous positive airway pressure. There was a marked improvement in CAVI after continuous positive airway pressure (age 68; right 10.4, left 10.2). However, following a gradual increase in body weight and worsening of diabetes mellitus, CAVI showed an increasing trend. CAVI decreased with biguanides treatment, but increased again with an increase in body weight. In conclusion, CAVI responded to the patient's conditions including obesity, diabetes mellitus, and OSA. CAVI is not only a marker of arterial stiffness, but can also be a useful indicator of physiological status; it may be effective in total risk control for coronary artery disease. PMID:27563259

  19. A Randomized Controlled Trial of the Effects of Vitamin D Supplementation on Arterial Stiffness and Aortic Blood Pressure in Native American Women

    PubMed Central

    Gepner, Adam D.; Haller, Irina V.; Krueger, Diane C.; Korcarz, Claudia E.; Binkley, Neil; Stein, James H.

    2015-01-01

    Objective It is unclear if vitamin D supplementation improves central blood pressure or arterial stiffness in Native American (NA) women. Methods Healthy postmenopausal NA women were randomized to receive 400 IU or 2,500 IU of vitamin D for 6 months. Central systolic blood pressure (cSBP), central pulse pressure (cPP) and aortic augmentation index (AIx) were estimated by tonometry at baseline and after 6 months. Results Study volunteers (n=98) were 61 (7.3) years old. 25(OH)D was 26.4 (11.0) ng/mL. 25(OH)D was similar between the two treatment groups (p=0.291), as were baseline cSBP, cPP, and CVD risk factors (all p>0.1). Treatment with 2,500 IU of daily vitamin D3 did not affect cSBP, cPP, or AIx (all p>0.1) compared to 400 IU daily. Conclusions Despite low serum 25(OH)D at baseline, 6 months of vitamin D supplementation did not improve central blood pressure parameters or arterial stiffness in NA women. PMID:25955191

  20. Effects of Renal Sympathetic Denervation on Arterial Stiffness and Blood Pressure Control in Resistant Hypertensive Patients: A Single Centre Prospective Study.

    PubMed

    Baroni, Matteo; Nava, Stefano; Giupponi, Luca; Meani, Paolo; Panzeri, Francesco; Varrenti, Marisa; Maloberti, Alessandro; Soriano, Francesco; Agrati, Antonio Maria; Ferraro, Giovanni; Colombo, Fabrizio; Rampoldi, Antonio; Mancia, Giuseppe; Colombo, Paola; Klugmann, Silvio; Giannattasio, Cristina

    2015-12-01

    Renal denervation (RD) is an intriguing treatment strategy for resistant hypertension. However, limited data are available about its long time efficacy as well as its effects on intermediate phenotypes like arterial stiffness and carotid IMT. 12 patients (9 males, mean 69 years) with resistant hypertension underwent bilateral RDN (Medtronic System) since April 2012 in Niguarda Ca' Granda Hospital (Milan). Patients were studied before intervention, and at 1, 3, 6 and 12 months after RD. Carotid intima media thickness (Esaote Mylab) and carotid-femoral pulse wave velocity (Complior, Alam medical) were assessed at each step. Compared to baseline, patients showed a marked reduction of office systolic blood pressure at each follow-up step (p < 0.05 versus baseline for all steps) as well as pulse wave velocity (p < 0.01 at 1 year versus baseline). Moreover, reduction in pulse wave velocity was higher than the expected value obtained only considering blood pressure drop. Conversely, no significant effect was observed on diastolic blood pressure as well as carotid intima-media thickness. In our study, renal denervation was a safe and effective procedure. The BP lowering effect was maintained during follow-up and a beneficial effect on arterial stiffness was observed, which implies that this effect can't passively originate from the BP fall but rather from an improvement of arterial mechanical properties, possibly related to a reduced sympathetic arterial drive.

  1. Arterial Stiffness in Children: Pediatric Measurement and Considerations

    PubMed Central

    Savant, Jonathan D.; Furth, Susan L.; Meyers, Kevin E.C.

    2014-01-01

    Background Arterial stiffness is a natural consequence of aging, accelerated in certain chronic conditions, and predictive of cardiovascular events in adults. Emerging research suggests the importance of arterial stiffness in pediatric populations. Methods There are different indices of arterial stiffness. The present manuscript focuses on carotid-femoral pulse wave velocity and pulse wave analysis, although other methodologies are discussed. Also reviewed are specific measurement considerations for pediatric populations and the literature describing arterial stiffness in children with certain chronic conditions (primary hypertension, obesity, diabetes, chronic kidney disease, hypercholesterolemia, genetic syndromes involving vasculopathy, and solid organ transplant recipients). Conclusions The measurement of arterial stiffness in children is feasible and, under controlled conditions, can give accurate information about the underlying state of the arteries. This potentially adds valuable information about the functionality of the cardiovascular system in children with a variety of chronic diseases well beyond that of the brachial artery blood pressure. PMID:26587447

  2. The dynamic effect of muscle activation on knee stiffness.

    PubMed

    Ludvig, Daniel; Perreault, Eric J

    2014-01-01

    Adapting limb mechanics in a task and environment dependent manner is one component of human motor control. Joint mechanics have been extensively studied under static postural conditions, but less so under time-varying movement conditions. The limited studies that have investigated joint mechanics during movement, have found a drop in joint stiffness during movement, however the source of this decrease in stiffness remains unknown. Here in this paper we investigate whether time-varying muscle activation, which occurs during volitional movement, can lead to the drop in stiffness seen during movement. We found that under time-varying isometric conditions stiffness dropped when subjects transitioned from extension to flexion and vice-versa, a phenomenon that could not be explained by simply superimposing extension and flexion contractions. These findings suggest that dynamics of muscle activation may be responsible for the complex pattern of stiffness changes seen during simple movements. Furthermore, these results imply that EMG-based estimates of stiffness, which work well for steady-state postural conditions, will need to be augmented to account for the highly non-linear relationship between muscle activation and stiffness before they can also be used to estimate stiffness during dynamic contractions.

  3. Substrate stiffness regulates cellular uptake of nanoparticles.

    PubMed

    Huang, Changjin; Butler, Peter J; Tong, Sheng; Muddana, Hari S; Bao, Gang; Zhang, Sulin

    2013-04-10

    Nanoparticle (NP)-bioconjugates hold great promise for more sensitive disease diagnosis and more effective anticancer drug delivery compared with existing approaches. A critical aspect in both applications is cellular internalization of NPs, which is influenced by NP properties and cell surface mechanics. Despite considerable progress in optimization of the NP-bioconjugates for improved targeting, the role of substrate stiffness on cellular uptake has not been investigated. Using polyacrylamide (PA) hydrogels as model substrates with tunable stiffness, we quantified the relationship between substrate stiffness and cellular uptake of fluorescent NPs by bovine aortic endothelial cells (BAECs). We found that a stiffer substrate results in a higher total cellular uptake on a per cell basis, but a lower uptake per unit membrane area. To obtain a mechanistic understanding of the cellular uptake behavior, we developed a thermodynamic model that predicts that membrane spreading area and cell membrane tension are two key factors controlling cellular uptake of NPs, both of which are modulated by substrate stiffness. Our experimental and modeling results not only open up new avenues for engineering NP-based cancer cell targets for more effective in vivo delivery but also contribute an example of how the physical environment dictates cellular behavior and function.

  4. 14 CFR 25.397 - Control system loads.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ..., are assumed to act at the appropriate control grips or pads (in a manner simulating flight conditions... effort effects. In the control surface flight loading condition, the air loads on movable surfaces and... aileron control system must be designed for a single tangential force with a limit value equal to...

  5. 14 CFR 25.397 - Control system loads.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ..., are assumed to act at the appropriate control grips or pads (in a manner simulating flight conditions... effort effects. In the control surface flight loading condition, the air loads on movable surfaces and... aileron control system must be designed for a single tangential force with a limit value equal to...

  6. Nonlinear vibration of thick stiff fabric with small flexural stiffness

    NASA Astrophysics Data System (ADS)

    Chen, J.-P.; Wang, S.-Z.; Wu, W.-Y.; Gu, H.-B.

    2008-02-01

    Dynamic behaviour of fabric is very complex during weaving, dyeing and finishing processes. Thick stiff fabric vibration has great influence not only on the fabric itself but also on the performance of machine. The theoretic analysis for the nonlinear free vibration of thick stiff fabric with small flexural stiffness is put forward in the paper. The nonlinear partial differential equation is derived by applying the flexible thin plate theory, and then transformed into nonlinear ordinary differential equation by the Galerkin method. The approximate analytical solution is obtained by the homotopy perturbation method.

  7. Comparison of pressure distributions on model and full-scale NACA 64-621 airfoils with ailerons for wind turbine application

    NASA Technical Reports Server (NTRS)

    Gregorek, G. M.; Kuniega, R. J.; Nyland, T. W.

    1988-01-01

    The aerodynamic similarity between a small (4-inch chord) wind tunnel model and a full-scale wind turbine blade (24-foot tip section with a 36-inch chord) was evaluated by comparing selected pressure distributions around the geometrically similar cross sections. The airfoils were NACA 64-621 sections, including trailing-edge ailerons with a width equal to 38 percent of the airfoil chord. The model airfoil was tested in the OSU 6- by 12-inch High Reynolds Number Wind Tunnel; the full-scale blade section was tested in the NASA Langley Research Center 30- by 60-foot Subsonic Wind Tunnel. The model airfoil contained 61 pressure taps connected by embedded tubes to pressure transducers. A belt containing 29 pressure taps was fixed to the full-scale section at midspan to obtain surface pressure data. Lift coefficients were obtained by integrating pressures, and corrections were made for the 3-D effects of blade twist and downwash in the blade tip section. The results of the two different experimental methods correlated well for angles of attack from minus 4 to 36 degrees and aileron reflections from 0 to 90 degrees.

  8. 14 CFR 23.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Motion and effect of cockpit controls. 23... Construction Personnel and Cargo Accommodations § 23.779 Motion and effect of cockpit controls. Cockpit...) Aerodynamic controls: Motion and effect (1) Primary controls: Aileron Right (clockwise) for right wing...

  9. 14 CFR 23.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Motion and effect of cockpit controls. 23... Construction Personnel and Cargo Accommodations § 23.779 Motion and effect of cockpit controls. Cockpit...) Aerodynamic controls: Motion and effect (1) Primary controls: Aileron Right (clockwise) for right wing...

  10. 14 CFR 23.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Motion and effect of cockpit controls. 23... Construction Personnel and Cargo Accommodations § 23.779 Motion and effect of cockpit controls. Cockpit...) Aerodynamic controls: Motion and effect (1) Primary controls: Aileron Right (clockwise) for right wing...

  11. 14 CFR 23.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Motion and effect of cockpit controls. 23... Construction Personnel and Cargo Accommodations § 23.779 Motion and effect of cockpit controls. Cockpit...) Aerodynamic controls: Motion and effect (1) Primary controls: Aileron Right (clockwise) for right wing...

  12. Arterial stiffness and its clinical implications in women.

    PubMed

    Coutinho, Thais

    2014-07-01

    The burden of cardiovascular disease (CVD) in women is increasing, and CVD presently kills more North American women than men, highlighting the need for sex-specific research aimed at disentangling the complex interactions between sex, aging, and cardiovascular health. In the past decade, arterial stiffness has emerged as an independent predictor of adverse cardiovascular events and mortality, and its noninvasive, safe evaluation makes it an attractive tool for a snapshot assessment of cardiovascular health. An increasing number of reports have documented greater aortic stiffness in older women than men, which appears to have close relationships with blood pressure control, diastolic dysfunction, impaired ventricular coupling, and left ventricular remodelling in women. Thus, arterial stiffness is thought to play a role in the female predominance of several diseases such as isolated systolic hypertension, refractory hypertension, heart failure with preserved ejection fraction, and paradoxical low-flow, low-gradient, normal ejection fraction severe aortic stenosis. Furthermore, greater arterial stiffness is a common characteristic of women who develop hypertensive complications of pregnancy. Thus, better understanding sex differences in arterial stiffness and aging might provide valuable insights into CVD in women, and help identify novel risk stratification tools and therapeutic targets. To this end, the present review aims at describing sex differences in arterial stiffness, exploring the potential role of sex hormones and menopause on arterial aging, and highlighting the role of arterial stiffness in specific CVDs that preferentially affect women.

  13. MIGRAINE, CAROTID STIFFNESS AND GENETIC POLYMORPHISM.

    PubMed

    Kes, Vanja Basić; Jurasić, Miljenka-Jelena; Zavoreo, Iris; Corić, Lejla; Rotim, Kresimir

    2015-12-01

    Recently migraine has been associated with increased arterial stiffness, procoagulant state, increased incidence of cerebral white matter lesions (WML) and stroke. Our aim was to compare the characteristics of migraineurs to headache free controls regarding their functional carotid ultrasound parameters. Sixty patients (45 women) with migraine (mean age 40.42 ± 10.61 years) were compared with 45 controls (30 women) with no prior history of repeating headache (mean age 38.94 ± 5.46 years) using E-tracking software on Alpha 10 ultrasound platform. Student's t-test was used on statistical analysis with alpha < 0.05. All tested carotid vascular parameters were worse in patients with migraine including increased intima-media thickness, greater carotid diameter and carotid diameter change, as well as several arterial stiffness indices. Additionally, patients with migraine had greater incidence of homozygous mutations for procoagulant genes (MTHFR (C677T), PAI-1 and ACE I/D) than expected. Computed tomography and magnetic resonance imaging of the brain showed WML in 11 patients, four of them migraine with aura patients. Since we established increased carotid stiffness and higher frequency of procoagulant gene mutations in migraineurs, we propose prospective ultrasound monitoring in such patients, especially those with detected WML, in order to timely commence more active and specific preventive stroke management strategies.

  14. Adaptive Failure Compensation for Aircraft Tracking Control Using Engine Differential Based Model

    NASA Technical Reports Server (NTRS)

    Liu, Yu; Tang, Xidong; Tao, Gang; Joshi, Suresh M.

    2006-01-01

    An aircraft model that incorporates independently adjustable engine throttles and ailerons is employed to develop an adaptive control scheme in the presence of actuator failures. This model captures the key features of aircraft flight dynamics when in the engine differential mode. Based on this model an adaptive feedback control scheme for asymptotic state tracking is developed and applied to a transport aircraft model in the presence of two types of failures during operation, rudder failure and aileron failure. Simulation results are presented to demonstrate the adaptive failure compensation scheme.

  15. Stiffness after total knee arthroplasty.

    PubMed

    Manrique, Jorge; Gomez, Miguel M; Parvizi, Javad

    2015-04-01

    Stiffness after total knee arthroplasty (TKA) adversely affects outcome and impacts patient function. Various risk factors for stiffness after TKA have been identified, including reduced preoperative knee range of motion, history of prior knee surgery, etiology of arthritis, incorrect positioning or oversizing of components, and incorrect gap balancing. Mechanical and associated causes, such as infection, arthrofibrosis, complex regional pain syndrome, and heterotopic ossification, secondary gain issues have also been identified. Management of stiffness following TKA can be challenging. The condition needs to be assessed and treated in a staged manner. A nonsurgical approach is the first step. Manipulation under anesthesia may be considered within the first 3 months after the index TKA, if physical therapy fails to improve the range of motion. Beyond this point, consideration should be given to surgical intervention such as lysis of adhesions, either arthroscopically or by open arthrotomy. If the cause of stiffness is deemed to be surgical error, such as component malpositioning, revision arthroplasty is indicated. The purpose of this article is to evaluate the various aspects of management of stiffness after TKA.

  16. Extracellular matrix stiffness and composition jointly regulate the induction of malignant phenotypes in mammary epithelium.

    PubMed

    Chaudhuri, Ovijit; Koshy, Sandeep T; Branco da Cunha, Cristiana; Shin, Jae-Won; Verbeke, Catia S; Allison, Kimberly H; Mooney, David J

    2014-10-01

    In vitro models of normal mammary epithelium have correlated increased extracellular matrix (ECM) stiffness with malignant phenotypes. However, the role of increased stiffness in this transformation remains unclear because of difficulties in controlling ECM stiffness, composition and architecture independently. Here we demonstrate that interpenetrating networks of reconstituted basement membrane matrix and alginate can be used to modulate ECM stiffness independently of composition and architecture. We find that, in normal mammary epithelial cells, increasing ECM stiffness alone induces malignant phenotypes but that the effect is completely abrogated when accompanied by an increase in basement-membrane ligands. We also find that the combination of stiffness and composition is sensed through β4 integrin, Rac1, and the PI3K pathway, and suggest a mechanism in which an increase in ECM stiffness, without an increase in basement membrane ligands, prevents normal α6β4 integrin clustering into hemidesmosomes.

  17. Extracellular matrix stiffness and composition jointly regulate the induction of malignant phenotypes in mammary epithelium

    NASA Astrophysics Data System (ADS)

    Chaudhuri, Ovijit; Koshy, Sandeep T.; Branco da Cunha, Cristiana; Shin, Jae-Won; Verbeke, Catia S.; Allison, Kimberly H.; Mooney, David J.

    2014-10-01

    In vitro models of normal mammary epithelium have correlated increased extracellular matrix (ECM) stiffness with malignant phenotypes. However, the role of increased stiffness in this transformation remains unclear because of difficulties in controlling ECM stiffness, composition and architecture independently. Here we demonstrate that interpenetrating networks of reconstituted basement membrane matrix and alginate can be used to modulate ECM stiffness independently of composition and architecture. We find that, in normal mammary epithelial cells, increasing ECM stiffness alone induces malignant phenotypes but that the effect is completely abrogated when accompanied by an increase in basement-membrane ligands. We also find that the combination of stiffness and composition is sensed through β4 integrin, Rac1, and the PI3K pathway, and suggest a mechanism in which an increase in ECM stiffness, without an increase in basement membrane ligands, prevents normal α6β4 integrin clustering into hemidesmosomes.

  18. Black Raspberry Extract Increased Circulating Endothelial Progenitor Cells and Improved Arterial Stiffness in Patients with Metabolic Syndrome: A Randomized Controlled Trial.

    PubMed

    Jeong, Han Saem; Kim, Sohyeon; Hong, Soon Jun; Choi, Seung Cheol; Choi, Ji-Hyun; Kim, Jong-Ho; Park, Chi-Yeon; Cho, Jae Young; Lee, Tae-Bum; Kwon, Ji-Wung; Joo, Hyung Joon; Park, Jae Hyoung; Yu, Cheol Woong; Lim, Do-Sun

    2016-04-01

    Administration of black raspberry (Rubus occidentalis) is known to improve vascular endothelial function in patients at a high risk for cardiovascular (CV) disease. We investigated short-term effects of black raspberry on circulating endothelial progenitor cells (EPCs) and arterial stiffness in patients with metabolic syndrome. Patients with metabolic syndrome (n = 51) were prospectively randomized into the black raspberry group (n = 26, 750 mg/day) and placebo group (n = 25) during the 12-week follow-up. Central blood pressure, augmentation index, and EPCs, such as CD34/KDR(+), CD34/CD117(+), and CD34/CD133(+), were measured at baseline and at 12-week follow-up. Radial augmentation indexes were significantly decreased in the black raspberry group compared to the placebo group (-5% ± 10% vs. 3% ± 14%, P < .05). CD34/CD133(+) cells at 12-week follow-up were significantly higher in the black raspberry group compared to the placebo group (19 ± 109/μL vs. -28 ± 57/μL, P < .05). Decreases from the baseline in interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were significantly greater in the black raspberry group compared to the placebo group (-0.5 ± 1.4 pg/mL vs. -0.1 ± 1.1 pg/mL, P < .05 and -5.4 ± 4.5 pg/mL vs. -0.8 ± 4.0 pg/mL, P < .05, respectively). Increases from the baseline in adiponectin levels (2.9 ± 2.1 μg/mL vs. -0.2 ± 2.5 μg/mL, P < .05) were significant in the black raspberry group. The use of black raspberry significantly lowered the augmentation index and increased circulating EPCs, thereby improving CV risks in patients with metabolic syndrome during the 12-week follow-up.

  19. Black Raspberry Extract Increased Circulating Endothelial Progenitor Cells and Improved Arterial Stiffness in Patients with Metabolic Syndrome: A Randomized Controlled Trial.

    PubMed

    Jeong, Han Saem; Kim, Sohyeon; Hong, Soon Jun; Choi, Seung Cheol; Choi, Ji-Hyun; Kim, Jong-Ho; Park, Chi-Yeon; Cho, Jae Young; Lee, Tae-Bum; Kwon, Ji-Wung; Joo, Hyung Joon; Park, Jae Hyoung; Yu, Cheol Woong; Lim, Do-Sun

    2016-04-01

    Administration of black raspberry (Rubus occidentalis) is known to improve vascular endothelial function in patients at a high risk for cardiovascular (CV) disease. We investigated short-term effects of black raspberry on circulating endothelial progenitor cells (EPCs) and arterial stiffness in patients with metabolic syndrome. Patients with metabolic syndrome (n = 51) were prospectively randomized into the black raspberry group (n = 26, 750 mg/day) and placebo group (n = 25) during the 12-week follow-up. Central blood pressure, augmentation index, and EPCs, such as CD34/KDR(+), CD34/CD117(+), and CD34/CD133(+), were measured at baseline and at 12-week follow-up. Radial augmentation indexes were significantly decreased in the black raspberry group compared to the placebo group (-5% ± 10% vs. 3% ± 14%, P < .05). CD34/CD133(+) cells at 12-week follow-up were significantly higher in the black raspberry group compared to the placebo group (19 ± 109/μL vs. -28 ± 57/μL, P < .05). Decreases from the baseline in interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were significantly greater in the black raspberry group compared to the placebo group (-0.5 ± 1.4 pg/mL vs. -0.1 ± 1.1 pg/mL, P < .05 and -5.4 ± 4.5 pg/mL vs. -0.8 ± 4.0 pg/mL, P < .05, respectively). Increases from the baseline in adiponectin levels (2.9 ± 2.1 μg/mL vs. -0.2 ± 2.5 μg/mL, P < .05) were significant in the black raspberry group. The use of black raspberry significantly lowered the augmentation index and increased circulating EPCs, thereby improving CV risks in patients with metabolic syndrome during the 12-week follow-up. PMID:26891216

  20. ARTHROSCOPIC TREATMENT OF ELBOW STIFFNESS

    PubMed Central

    Vieira, Luis Alfredo Gómez; Dal Molin, Fabio Farina; Visco, Adalberto; Fernandes, Luis Filipe Daneu; dos Santos, Murilo Cunha Rafael; Cardozo Filho, Nivaldo Souza; Gómez Cordero, Nicolas Gerardo

    2015-01-01

    To present the arthroscopic surgical technique and the evaluation of the results from this technique for treating elbow stiffness. Methods: Between April 2007 and January 2010, ten elbows of ten patients with elbow stiffness underwent arthroscopic treatment to release the range of motion. The minimum follow-up was 11 months, with an average of 27 months. All the patients were male and their average age was 32.8 years (ranging from 22 to 48 years). After the arthroscopic treatment, they were followed up weekly in the first month and every three months thereafter. The clinical evaluation was made using the criteria of the University of California at Los Angeles (UCLA). Results: All the patients were satisfied with the results from the arthroscopic treatment. The average UCLA score was 33.8 points. Conclusion: Arthroscopic treatment for elbow stiffness is a minimally invasive surgical technique that was shown to be efficient for treating this complication. PMID:27027027

  1. Lase Ultrasonic Web Stiffness tester

    SciTech Connect

    Tim Patterson, Ph.D., IPST at Ga Tech

    2009-01-12

    The objective is to provide a sensor that uses non-contact, laser ultrasonics to measure the stiffness of paper during the manufacturing process. This will allow the manufacturer to adjust the production process in real time, increase filler content, modify fiber refining and as result produce a quality product using less energy. The sensor operates by moving back and forth across the paper web, at pre-selected locations firing a laser at the sheet, measuring the out-of-plane velocity of the sheet then using that measurement to calculate sheet stiffness.

  2. Aortic stiffness and distensibility among hypertensives.

    PubMed

    Meenakshisundaram, R; Kamaraj, K; Murugan, S; Thirumalaikolundusubramanian, P

    2009-09-01

    Hypertension is one among many factors that contribute to aortic stiffness, which has repercussions mainly on the heart. To assess aortic stiffness among essential hypertensives of South India and its relationship with gender. An analytical study was designed to assess aortic stiffness among 60 nonobese, nonalcoholic, nonsmoking, and non-caffeine consuming essential hypertensives without any overt illness or infection, and compared with 30 healthy age- and sex-matched nonhypertensives. They were assessed clinically and also by laboratory means. Their left ventricular mass (LV) and left ventricular ejection fraction (LVEF) were measured using Transthoracic echocardiogram. Aortic systolic and diastolic diameters were measured by using M-mode echocardiography during consecutive beats and averaged for each case. Finally, aortic stiffness was calculated. The data were analyzed statistically. Hypertensives were divided into Group I, consisting of patients with hypertension at least for 5 years, who were not adherent to medication, and Group II, consisting of patients with hypertension of duration between 6 months and 1 year. There were 20 males and 10 females in each group. There was no significant difference between the hypertensive groups and a control, normotensive, group with regard to BMI or total cholesterol. The means of LV mass (in grams), systolic BP (in mmHg), diastolic BP (in mmHg), aortic systolic diameter (in mm), aortic diastolic diameter (in mm), aortic distensibility (in mm), and aortic stiffness found in Group I, Group II, and controls were 105.8 +/- 23.8, 101.5 +/- 21, and 84 +/- 9.8; 138 +/- 14.2, 153 +/- 17.1, and 120 +/- 8.3; 90.5 +/- 11.6, 101.7 +/- 17.1, and 76.5 +/- 5; 30.85 +/- 2.6, 28.7 +/- 2.6, and 27.7 +/- 2.4; 28.7 +/- 2.2, 25.8 +/- 2.5, and 24.2 +/- 2.5; 2.14 +/- 0.3, 2.84 +/- 0.5, and 3.5 +/- 0.6; and 1.31 +/- 0.09, 1.14 +/- 0.1, and 1.04 +/- 0.08, respectively. The differences between the hypertensive groups and the control group were

  3. Direct measurement of human ankle stiffness during quiet standing: the intrinsic mechanical stiffness is insufficient for stability

    PubMed Central

    Loram, Ian D; Lakie, Martin

    2002-01-01

    During quiet standing the human ‘inverted pendulum’ sways irregularly. In previous work where subjects balanced a real inverted pendulum, we investigated what contribution the intrinsic mechanical ankle stiffness makes to achieve stability. Using the results of a plausible model, we suggested that intrinsic ankle stiffness is inadequate for providing stability. Here, using a piezo-electric translator we applied small, unobtrusive mechanical perturbations to the foot while the subject was standing freely. These short duration perturbations had a similar size and velocity to movements which occur naturally during quiet standing, and they produced no evidence of any stretch reflex response in soleus, or gastrocnemius. Direct measurement confirms our earlier conclusion; intrinsic ankle stiffness is not quite sufficient to stabilise the body or pendulum. On average the directly determined intrinsic stiffness is 91 ± 23 % (mean ± s.d.) of that necessary to provide minimal stabilisation. The stiffness was substantially constant, increasing only slightly with ankle torque. This stiffness cannot be neurally regulated in quiet standing. Thus we attribute this stiffness to the foot, Achilles’ tendon and aponeurosis rather than the activated calf muscle fibres. Our measurements suggest that the triceps surae muscles maintain balance via a spring-like element which is itself too compliant to guarantee stability. The implication is that the brain cannot set ankle stiffness and then ignore the control task because additional modulation of torque is required to maintain balance. We suggest that the triceps surae muscles maintain balance by predictively controlling the proximal offset of the spring-like element in a ballistic-like manner. PMID:12482906

  4. Model-Based Estimation of Active Knee Stiffness

    PubMed Central

    Pfeifer, Serge; Hardegger, Michael; Vallery, Heike; List, Renate; Foresti, Mauro; Riener, Robert; Perreault, Eric J.

    2013-01-01

    Knee joint impedance varies substantially during physiological gait. Quantifying this modulation is critical for the design of transfemoral prostheses that aim to mimic physiological limb behavior. Conventional methods for quantifying joint impedance typically involve perturbing the joint in a controlled manner, and describing impedance as the dynamic relationship between applied perturbations and corresponding joint torques. These experimental techniques, however, are difficult to apply during locomotion without impeding natural movements. In this paper, we propose a method to estimate the elastic component of knee joint impedance that depends on muscle activation, often referred to as active knee stiffness. The method estimates stiffness using a musculoskeletal model of the leg and a model for activation-dependent short-range muscle stiffness. Muscle forces are estimated from measurements including limb kinematics, kinetics and muscle electromyograms. For isometric validation, we compare model estimates to measurements involving joint perturbations; measured stiffness is 17% lower than model estimates for extension, and 42% lower for flexion torques. We show that sensitivity of stiffness estimates to common approaches for estimating muscle force is small in isometric conditions. We also make initial estimates of how knee stiffness is modulated during gait, illustrating how this approach may be used to obtain parameters relevant to the design of transfemoral prostheses. PMID:22275672

  5. Arterial Stiffness and Cardiovascular Therapy

    PubMed Central

    Janić, Miodrag; Lunder, Mojca; Šabovič, Mišo

    2014-01-01

    The world population is aging and the number of old people is continuously increasing. Arterial structure and function change with age, progressively leading to arterial stiffening. Arterial stiffness is best characterized by measurement of pulse wave velocity (PWV), which is its surrogate marker. It has been shown that PWV could improve cardiovascular event prediction in models that included standard risk factors. Consequently, it might therefore enable better identification of populations at high-risk of cardiovascular morbidity and mortality. The present review is focused on a survey of different pharmacological therapeutic options for decreasing arterial stiffness. The influence of several groups of drugs is described: antihypertensive drugs (angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers, beta-blockers, diuretics, and nitrates), statins, peroral antidiabetics, advanced glycation end-products (AGE) cross-link breakers, anti-inflammatory drugs, endothelin-A receptor antagonists, and vasopeptidase inhibitors. All of these have shown some effect in decreasing arterial stiffness. Nevertheless, further studies are needed which should address the influence of arterial stiffness diminishment on major adverse cardiovascular and cerebrovascular events (MACCE). PMID:25170513

  6. 14 CFR 23.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...) Aerodynamic controls: Motion and effect (1) Primary controls: Aileron Right (clockwise) for right wing down... auxiliary lift devices) Forward or up for flaps up or auxiliary device stowed; rearward or down for flaps down or auxiliary device deployed. Trim tabs (or equivalent) Switch motion or mechanical rotation...

  7. 14 CFR 25.779 - Motion and effect of cockpit controls.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    .... Controls Motion and effect Aileron Right (clockwise) for right wing down. Elevator Rearward for nose up... lift devices) Forward for flaps up; rearward for flaps down. Trim tabs (or equivalent) Rotate to...) Auxiliary. Controls Motion and effect Landing gear Down to extend....

  8. Wind turbine control systems: Dynamic model development using system identification and the fast structural dynamics code

    SciTech Connect

    Stuart, J.G.; Wright, A.D.; Butterfield, C.P.

    1996-10-01

    Mitigating the effects of damaging wind turbine loads and responses extends the lifetime of the turbine and, consequently, reduces the associated Cost of Energy (COE). Active control of aerodynamic devices is one option for achieving wind turbine load mitigation. Generally speaking, control system design and analysis requires a reasonable dynamic model of {open_quotes}plant,{close_quotes} (i.e., the system being controlled). This paper extends the wind turbine aileron control research, previously conducted at the National Wind Technology Center (NWTC), by presenting a more detailed development of the wind turbine dynamic model. In prior research, active aileron control designs were implemented in an existing wind turbine structural dynamics code, FAST (Fatigue, Aerodynamics, Structures, and Turbulence). In this paper, the FAST code is used, in conjunction with system identification, to generate a wind turbine dynamic model for use in active aileron control system design. The FAST code is described and an overview of the system identification technique is presented. An aileron control case study is used to demonstrate this modeling technique. The results of the case study are then used to propose ideas for generalizing this technique for creating dynamic models for other wind turbine control applications.

  9. Effect of Improving Dietary Quality on Arterial Stiffness in Subjects with Type 1 and Type 2 Diabetes: A 12 Months Randomised Controlled Trial

    PubMed Central

    Petersen, Kristina S.; Clifton, Peter M.; Lister, Natalie; Keogh, Jennifer B.

    2016-01-01

    People with diabetes have accelerated arterial stiffening. The aim of this study was to determine the effect of increasing fruit, vegetable and dairy intake for 12 months on carotid femoral pulse wave velocity (cfPWV), augmentation index (AIx), and central blood pressure (cBP), compared to a usual diet control, in people with type 1 and type 2 diabetes. In a 12 months randomised controlled trial, cfPWV, AIx and cBP were measured every 3 months. The intervention group received dietary counselling to increase consumption of fruit (+1 serving/day; 150 g/day), vegetables (+2 servings/day; 150 g/day) and dairy (+1 serving/day; 200–250 g/day) at baseline, 1, 3, 6 and 9 months. The control group continued on their usual diet. One hundred and nine participants were randomised and 92 (intervention n = 45; control n = 47) completed. At 3 months, fruit (184 g/day; p = 0.001) and dairy (83 g/day; p = 0.037) intake increased in the intervention group compared with the control group but this increase was not maintained at 12 months. After adjustment for baseline measurements there was no time by treatment effect for central systolic or diastolic BP, AIx or cfPWV. A time effect existed for AIx which modestly increased over time. Peripheral diastolic BP and central pulse pressure were improved in the intervention group compared with the control group at 12 months. In the cohort with type 1 and type 2 diabetes, improving dietary quality by increasing consumption of fruit, vegetables and dairy did not improve cBP, AIx or cfPWV, compared with a control group continuing on their usual diet, after 12 months. PMID:27338467

  10. Variable stiffness sandwich panels using electrostatic interlocking core

    NASA Astrophysics Data System (ADS)

    Heath, Callum J. C.; Bond, Ian P.; Potter, Kevin D.

    2016-04-01

    Structural topology has a large impact on the flexural stiffness of a beam structure. Reversible attachment between discrete substructures allows for control of shear stress transfer between structural elements, thus stiffness modulation. Electrostatic adhesion has shown promise for providing a reversible latching mechanism for controllable internal connectivity. Building on previous research, a thin film copper polyimide laminate has been used to incorporate high voltage electrodes to Fibre Reinforced Polymer (FRP) sandwich structures. The level of electrostatic holding force across the electrode interface is key to the achievable level of stiffness modulation. The use of non-flat interlocking core structures can allow for a significant increase in electrode contact area for a given core geometry, thus a greater electrostatic holding force. Interlocking core geometries based on cosine waves can be Computer Numerical Control (CNC) machined from Rohacell IGF 110 Foam core. These Interlocking Core structures could allow for enhanced variable stiffness functionality compared to basic planar electrodes. This novel concept could open up potential new applications for electrostatically induced variable stiffness structures.

  11. Aerobic, resistance and combined exercise training on arterial stiffness in normotensive and hypertensive adults: A review.

    PubMed

    Li, Yanlei; Hanssen, Henner; Cordes, Mareike; Rossmeissl, Anja; Endes, Simon; Schmidt-Trucksäss, Arno

    2015-01-01

    Exercise training has different effects on arterial stiffness according to training modalities. The optimal exercise modality for improvement of arterial function in normotensive and hypertensive individuals has not been well established. In this review, we aim to evaluate the effects of aerobic, resistance and combined aerobic and resistance training on arterial stiffness in individuals with and without hypertension. We systematically searched the Pubmed and Web of Science database from 1985 until December 2013 for relevant randomised controlled trials (RCTs). The data were extracted by one investigator and checked by a second investigator. The training effects on arterial stiffness were estimated using weighted mean differences of the relative changes (%) with 95% confidence intervals (CIs). We finally reviewed the results from 17 RCTs. The available evidence indicates that aerobic exercise tends to have a beneficial effect on arterial stiffness in normotensive and hypertensive patients, but does not affect arterial stiffness in patients with isolated systolic hypertension. Resistance exercise has differing effects on arterial stiffness depending on type and intensity. Vigorous resistance training is associated with an increase in arterial stiffness. There seem to be no unfavourable effects on arterial stiffness if the training is of low intensity, in a slow eccentric manner or with lower limb in healthy individuals. Combined training has neutral or even a beneficial effect on arterial stiffness. In conclusion, our review shows that exercise training has varying effects on arterial stiffness depending on the exercise modalities.

  12. Aerobic, resistance and combined exercise training on arterial stiffness in normotensive and hypertensive adults: A review.

    PubMed

    Li, Yanlei; Hanssen, Henner; Cordes, Mareike; Rossmeissl, Anja; Endes, Simon; Schmidt-Trucksäss, Arno

    2015-01-01

    Exercise training has different effects on arterial stiffness according to training modalities. The optimal exercise modality for improvement of arterial function in normotensive and hypertensive individuals has not been well established. In this review, we aim to evaluate the effects of aerobic, resistance and combined aerobic and resistance training on arterial stiffness in individuals with and without hypertension. We systematically searched the Pubmed and Web of Science database from 1985 until December 2013 for relevant randomised controlled trials (RCTs). The data were extracted by one investigator and checked by a second investigator. The training effects on arterial stiffness were estimated using weighted mean differences of the relative changes (%) with 95% confidence intervals (CIs). We finally reviewed the results from 17 RCTs. The available evidence indicates that aerobic exercise tends to have a beneficial effect on arterial stiffness in normotensive and hypertensive patients, but does not affect arterial stiffness in patients with isolated systolic hypertension. Resistance exercise has differing effects on arterial stiffness depending on type and intensity. Vigorous resistance training is associated with an increase in arterial stiffness. There seem to be no unfavourable effects on arterial stiffness if the training is of low intensity, in a slow eccentric manner or with lower limb in healthy individuals. Combined training has neutral or even a beneficial effect on arterial stiffness. In conclusion, our review shows that exercise training has varying effects on arterial stiffness depending on the exercise modalities. PMID:25251989

  13. Performance Assessment of a New Variable Stiffness Probing System for Micro-CMMs.

    PubMed

    Alblalaihid, Khalid; Kinnell, Peter; Lawes, Simon; Desgaches, Dorian; Leach, Richard

    2016-01-01

    When designing micro-scale tactile probes, a design trade-off must be made between the stiffness and flexibility of the probing element. The probe must be flexible enough to ensure sensitive parts are not damaged during contact, but it must be stiff enough to overcome attractive surface forces, ensure it is not excessively fragile, easily damaged or sensitive to inertial loads. To address the need for a probing element that is both flexible and stiff, a novel micro-scale tactile probe has been designed and tested that makes use of an active suspension structure. The suspension structure is used to modulate the probe stiffness as required to ensure optimal stiffness conditions for each phase of the measurement process. In this paper, a novel control system is presented that monitors and controls stiffness, allowing two probe stiffness values ("stiff" and "flexible") to be defined and switched between. During switching, the stylus tip undergoes a displacement of approximately 18 µm, however, the control system is able ensure a consistent flexible mode tip deflection to within 12 nm in the vertical axis. The overall uncertainty for three-dimensional displacement measurements using the probing system is estimated to be 58 nm, which demonstrates the potential of this innovative variable stiffness micro-scale probe system. PMID:27070611

  14. Measurement of Flying Qualities of a Dehavilland Mosquito F-8 Airplane (AAF No. 43-334960) I: Lateral and Directional Stability and Control Characteristics

    NASA Technical Reports Server (NTRS)

    Gray, W.E.; Talmage, D.B.; Crane, H.L.

    1945-01-01

    The data presented have no bearing on performance characteristics of airplane, which were considered exceptionally good in previous tests. Some of the undesirable features of lateral and directional stability and control characteristics of the F-8 are listed. Directional stability, with rudder fixed, did not sufficiently restrict aileron yaw; rudder control was inadequate during take-off and landing, and was insufficient to fly airplane with one engine; in clean condition, power of ailerons was slightly below minimum value specified; it was difficult to trim airplane in rough air.

  15. β3 integrin–mediated spreading induced by matrix-bound BMP-2 controls Smad signaling in a stiffness-independent manner

    PubMed Central

    Fourel, Laure; Valat, Anne; Faurobert, Eva; Guillot, Raphael; Bourrin-Reynard, Ingrid; Ren, Kefeng; Lafanechère, Laurence; Planus, Emmanuelle; Albiges-Rizo, Corinne

    2016-01-01

    Understanding how cells integrate multiple signaling pathways to achieve specific cell differentiation is a challenging question in cell biology. We have explored the physiological presentation of BMP-2 by using a biomaterial that harbors tunable mechanical properties to promote localized BMP-2 signaling. We show that matrix-bound BMP-2 is sufficient to induce β3 integrin–dependent C2C12 cell spreading by overriding the soft signal of the biomaterial and impacting actin organization and adhesion site dynamics. In turn, αvβ3 integrin is required to mediate BMP-2–induced Smad signaling through a Cdc42–Src–FAK–ILK pathway. β3 integrin regulates a multistep process to control first BMP-2 receptor activity and second the inhibitory role of GSK3 on Smad signaling. Overall, our results show that BMP receptors and β3 integrin work together to control Smad signaling and tensional homeostasis, thereby coupling cell adhesion and fate commitment, two fundamental aspects of developmental biology and regenerative medicine. PMID:26953352

  16. β3 integrin-mediated spreading induced by matrix-bound BMP-2 controls Smad signaling in a stiffness-independent manner.

    PubMed

    Fourel, Laure; Valat, Anne; Faurobert, Eva; Guillot, Raphael; Bourrin-Reynard, Ingrid; Ren, Kefeng; Lafanechère, Laurence; Planus, Emmanuelle; Picart, Catherine; Albiges-Rizo, Corinne

    2016-03-14

    Understanding how cells integrate multiple signaling pathways to achieve specific cell differentiation is a challenging question in cell biology. We have explored the physiological presentation of BMP-2 by using a biomaterial that harbors tunable mechanical properties to promote localized BMP-2 signaling. We show that matrix-bound BMP-2 is sufficient to induce β3 integrin-dependent C2C12 cell spreading by overriding the soft signal of the biomaterial and impacting actin organization and adhesion site dynamics. In turn, αvβ3 integrin is required to mediate BMP-2-induced Smad signaling through a Cdc42-Src-FAK-ILK pathway. β3 integrin regulates a multistep process to control first BMP-2 receptor activity and second the inhibitory role of GSK3 on Smad signaling. Overall, our results show that BMP receptors and β3 integrin work together to control Smad signaling and tensional homeostasis, thereby coupling cell adhesion and fate commitment, two fundamental aspects of developmental biology and regenerative medicine.

  17. Composite sizing and ply orientation for stiffness requirements using a large finite element structural model

    NASA Technical Reports Server (NTRS)

    Radovcich, N. A.; Gentile, D. P.

    1989-01-01

    A NASTRAN bulk dataset preprocessor was developed to facilitate the integration of filamentary composite laminate properties into composite structural resizing for stiffness requirements. The NASCOMP system generates delta stiffness and delta mass matrices for input to the flutter derivative program. The flutter baseline analysis, derivative calculations, and stiffness and mass matrix updates are controlled by engineer defined processes under an operating system called CBUS. A multi-layered design variable grid system permits high fidelity resizing without excessive computer cost. The NASCOMP system uses ply layup drawings for basic input. The aeroelastic resizing for stiffness capability was used during an actual design exercise.

  18. Mechanism of leg stiffness adjustment for hopping on surfaces of different stiffnesses.

    PubMed

    Farley, C T; Houdijk, H H; Van Strien, C; Louie, M

    1998-09-01

    When humans hop in place or run forward, leg stiffness is increased to offset reductions in surface stiffness, allowing the global kinematics and mechanics to remain the same on all surfaces. The purpose of the present study was to determine the mechanism for adjusting leg stiffness. Seven subjects hopped in place on surfaces of different stiffnesses (23-35,000 kN/m) while force platform, kinematic, and electromyographic data were collected. Leg stiffness approximately doubled between the most stiff surface and the least stiff surface. Over the same range of surfaces, ankle torsional stiffness increased 1.75-fold, and the knee became more extended at the time of touchdown (2.81 vs. 2.65 rad). We used a computer simulation to examine the sensitivity of leg stiffness to the observed changes in ankle stiffness and touchdown knee angle. Our model consisted of four segments (foot, shank, thigh, head-arms-trunk) interconnected by three torsional springs (ankle, knee, hip). In the model, an increase in ankle stiffness 1.75-fold caused leg stiffness to increase 1.7-fold. A change in touchdown knee angle as observed in the subjects caused leg stiffness to increase 1.3-fold. Thus both joint stiffness and limb geometry adjustments are important in adjusting leg stiffness to allow similar hopping on different surfaces.

  19. On the development of planar actuators for variable stiffness devices

    NASA Astrophysics Data System (ADS)

    Henke, Markus; Gerlach, Gerald

    2013-04-01

    This contribution describes the development, the potential and the limitations of planar actuators for controlling bending devices with variable stiffness. Such structures are supposed to be components of new smart, self-sensing and -controlling composite materials for lightweight constructions. To realize a proper stiffness control, it is necessary to develop reliable actuators with high actuation capabilities based on smart materials. Several actuator designs driven by electroactive polymers (EAPs) are presented and discussed regarding to their applicability in such structures. To investigate the actuators, variable-flexural stiffness devices based on the control of its area moment of inertia were developed. The devices consist of a multi-layer stack of thin, individual plates. Stiffness variation is caused by planar actuators which control the sliding behavior between the layers by form closure structures. Previous investigations have shown that actuators with high actuation potential are needed to ensure reliable connections between the layers. For that reason, two kinds of EAPs Danfoss PolyPower and VHB 4905 by 3M, have been studied as driving unit. These EAP-driven actuators will be compared based on experimental measurements and finite element analyses.

  20. Relationship between QT Interval Length and Arterial Stiffness in Systemic Lupus Erythematosus (SLE): A Cross-Sectional Case-Control Study

    PubMed Central

    Rivera-López, Ricardo; Jiménez-Jáimez, Juan; Sabio, José Mario; Zamora-Pasadas, Mónica; Vargas-Hitos, José Antonio; Martínez-Bordonado, Josefina; Navarrete-Navarrete, Nuria; Fernández, Ricardo Rivera; Sanchez-Cantalejo, E.; Jiménez-Alonso, Juan

    2016-01-01

    Introduction and Objectives The QT interval on the electrocardiogram has been shown to be longer in patients with systemic lupus erythematosus (SLE) compared to that of the general population. The clinical significance of this finding is unknown. The aim of this study was to assess the relationship between QT interval and subclinical atherosclerosis, measured by carotid-femoral pulse-wave velocity. Material and Methods 93 patients with SLE and 109 healthy women with similar basal characteristics were studied. All patients underwent a 12- lead electrocardiogram, and corrected QT interval (QTc) was measured using the Bazett’s formula. The presence of atherosclerosis was evaluated by carotid-femoral pulse-wave velocity. Results Clinical basal characteristics were similar in both groups. QTc interval was 415±21.4 milliseconds in all patients, and 407±19.1 milliseconds in the control group (p = 0.007). There was a positive correlation between QTc interval and carotid-femoral pulse-wave velocity (r = 0.235; p = 0.02) in patients with SLE. This association was independent of hypertension and age in a multivariate analysis. Conclusion QTc interval measured by electrocardiogram is prolonged in SLE patients; it is related to subclinical atherosclerosis, measured by carotid-femoral pulse-wave velocity. This measure may help stratify risk in routine clinical practice and select the patients that might benefit from a more aggressive therapy in the prevention of cardiovascular events. PMID:27064990

  1. Stiffness Feedback for Myoelectric Forearm Prostheses Using Vibrotactile Stimulation.

    PubMed

    Witteveen, Heidi J B; Luft, Frauke; Rietman, Johan S; Veltink, Peter H

    2014-01-01

    The ability to distinguish object stiffness is a very important aspect in object handling, but completely lacking in current myoelectric prostheses. In human hands both tactile and proprioceptive sensory information are required for stiffness determination. Therefore, it was investigated whether it is possible to distinguish object stiffness with vibrotactile feedback of hand opening and grasping force. Three configurations consisting of an array of coin motors and a single miniature vibrotactile transducer were investigated. Ten healthy subjects and seven subjects with upper limb loss due to amputation or congenital defects performed virtual grasping tasks, in which they controlled hand opening and grasping force. They were asked to determine the stiffness of a grasped virtual object from four options. With hand opening feedback alone or in combination with grasping force feedback, correct stiffness determination was achieved in around 60% of the cases and significantly higher than the 25% achieved without feedback or grasping force feedback alone. Despite the equal performance results, the combination of hand opening and grasping force feedback was preferred by the subjects over the hand opening feedback alone. No differences between feedback configurations and between subjects with upper limb loss and healthy subjects were found.

  2. Severity of Osteoarthritis Is Associated with Increased Arterial Stiffness

    PubMed Central

    Kals, Jaak; Zilmer, Mihkel; Paapstel, Kaido; Märtson, Aare

    2016-01-01

    Objective. Osteoarthritis (OA) is associated with increased cardiovascular comorbidity and mortality. Evidence is lacking about whether arterial stiffness is involved in OA. The objective of our study was to find out associations between OA, arterial stiffness, and adipokines. Design. Seventy end-stage knee and hip OA patients (age 62 ± 7 years) and 70 asymptomatic controls (age 60 ± 7 years) were investigated using the applanation tonometry to determine their parameters of arterial stiffness. Serum adiponectin, leptin, and matrix metalloproteinase 3 (MMP-3) levels were determined using the ELISA method. Correlation between variables was determined using Spearman's rho. Multiple regression analysis with a stepwise selection procedure was employed. Results. Radiographic OA grade was positively associated with increased carotid-femoral pulse wave velocity (cf-PWV) (r = 0.272, p = 0.023). We found that OA grade was also associated with leptin and MMP-3 levels (rho = −0.246, p = 0.040 and rho = 0.235, p = 0.050, resp.). In addition, serum adiponectin level was positively associated with augmentation index and inversely with large artery elasticity index (rho = 0.293, p = 0.006 and rho = −0.249, p = 0.003, resp.). Conclusions. Our results suggest that OA severity is independently associated with increased arterial stiffness and is correlated with expression of adipokines. Thus, increased arterial stiffness and adipokines might play an important role in elevated cardiovascular risk in end-stage OA. PMID:27493667

  3. Variable stiffness material and structural concepts for morphing applications

    NASA Astrophysics Data System (ADS)

    Kuder, Izabela K.; Arrieta, Andres F.; Raither, Wolfram E.; Ermanni, Paolo

    2013-11-01

    Morphing, understood as the ability to undergo pronounced shape adaptations to optimally respond to a diversity of operational conditions, has been singled out as a future direction in the pursuit of maximised efficiency of lightweight structures. Whereas a certain degree of adaptivity can be accomplished conventionally by means of mechanical systems, compliance allowing for substantial reversible deformability exhibits far more potential as a morphing strategy. A promising solution to the inherent contradiction between high stiffness and reversible deformation capacity posed by morphing is offered by introducing variable stiffness components. This notion indicates the provision of a controllable range of deformation resistance levels in place of fixed properties, as required by real-time shape adaptation dictated by maximum efficiency under changing external conditions. With special emphasis on the morphing context, the current review aims to identify the main tendencies, undertaking a systematic classification of existing approaches involving stiffness variability. Four broad categories in which variable stiffness has been applied to morphing are therefore distinguished and detailed: material engineering, active mechanical design, semi-active techniques and elastic structural behaviour. Adopting a wide perspective, the study highlights key capabilities, limitations and challenges. The need for attention directed to the variable stiffness strategy is recognised and the significance of intensive research activities in a highly integrated and multidisciplinary environment emphasised if higher maturity stages of the concepts are to be reached. Finally, the potential of emerging directions of semi-active design involving electro-bonded laminates and multi-stable structures is brought into focus.

  4. Effect of Hybridization on Stiffness Properties of Woven Textile Composites

    NASA Astrophysics Data System (ADS)

    Bejan, Liliana; Taranu, Nicolae; Sîrbu, Adriana

    2013-04-01

    The present study focuses on stiffness properties of woven textile reinforced polymeric composites with respect to hybridization, and geometry of reinforcement. The analyzed composites represent combinations of different fibre materials (E-glass, Kevlar 49, carbon HM) in a predetermined fabric geometry (a plane weave embedded in thermosetting polymeric resin) serving controlled properties and required performance. The effects of hybridization on the stiffness properties of woven textile composites have been studied with respect to the fibres materials, the unbalancing degree of fabrics, and the variation of compactness and undulation of yarns. Some undesirable effects in fabric geometry can be overcome by the combined effects of hybridization and compactness.

  5. Variable Stiffness Spar Wind-Tunnel Model Development and Testing

    NASA Technical Reports Server (NTRS)

    Florance, James R.; Heeg, Jennifer; Spain, Charles V.; Ivanco, Thomas G.; Wieseman, Carol D.; Lively, Peter S.

    2004-01-01

    The concept of exploiting wing flexibility to improve aerodynamic performance was investigated in the wind tunnel by employing multiple control surfaces and by varying wing structural stiffness via a Variable Stiffness Spar (VSS) mechanism. High design loads compromised the VSS effectiveness because the aerodynamic wind-tunnel model was much stiffer than desired in order to meet the strength requirements. Results from tests of the model include stiffness and modal data, model deformation data, aerodynamic loads, static control surface derivatives, and fuselage standoff pressure data. Effects of the VSS on the stiffness and modal characteristics, lift curve slope, and control surface effectiveness are discussed. The VSS had the most effect on the rolling moment generated by the leading-edge outboard flap at subsonic speeds. The effects of the VSS for the other control surfaces and speed regimes were less. The difficulties encountered and the ability of the VSS to alter the aeroelastic characteristics of the wing emphasize the need for the development of improved design and construction methods for static aeroelastic models. The data collected and presented is valuable in terms of understanding static aeroelastic wind-tunnel model development.

  6. Wind-tunnel investigation at Mach numbers from 1.90 to 2.86 of a canard-controlled missile with ram-air-jet spoiler roll control. [in the Langley Unitary Plan Wind Tunnel

    NASA Technical Reports Server (NTRS)

    Blair, A. B., Jr.

    1978-01-01

    The efficacy of using a ram-air-jet spoiler roll control device on a typical canard-controlled missile configuration was investigated. For roll control comparisons, conventional aileron controls on the tail fins were also tested. The results indicate that the roll control of the ram-air-jet spoiler tail fins at the highest free-stream Mach number compared favorably with that of the conventional 11-70 area-ratio tail fin ailerons, each deflected 10 deg. The roll control of the tail fin ailerons decreased while that of the ram-air-jet spoiler increased with free-stream Mach number. The addition of the ram-air-jet spoiler tail fins or flow-through tip chord nacelles on the tail fins resulted in only small changes in basic missile longitudinal stability. The axial force coefficient of the operating ram-air-jet spoiler is significantly larger than that of conventional ailerons and results primarily from the total pressure behind a normal shock in front of the nacelle inlets.

  7. Leg and Joint Stiffness in Children with Spastic Diplegic Cerebral Palsy during Level Walking

    PubMed Central

    Wang, Ting-Ming; Huang, Hsing-Po; Li, Jia-Da; Hong, Shih-Wun; Lo, Wei-Ching; Lu, Tung-Wu

    2015-01-01

    Individual joint deviations are often identified in the analysis of cerebral palsy (CP) gait. However, knowledge is limited as to how these deviations affect the control of the locomotor system as a whole when striving to meet the demands of walking. The current study aimed to bridge the gap by describing the control of the locomotor system in children with diplegic CP in terms of their leg stiffness, both skeletal and muscular components, and associated joint stiffness during gait. Twelve children with spastic diplegia CP and 12 healthy controls walked at a self-selected pace in a gait laboratory while their kinematic and forceplate data were measured and analyzed during loading response, mid-stance, terminal stance and pre-swing. For calculating the leg stiffness, each of the lower limbs was modeled as a non-linear spring, connecting the hip joint center and the corresponding center of pressure, with varying stiffness that was calculated as the slope (gradient) of the axial force vs. the deformation curve. The leg stiffness was further decomposed into skeletal and muscular components considering the alignment of the lower limb. The ankle, knee and hip of the limb were modeled as revolute joints with torsional springs whose stiffness was calculated as the slope of the moment vs. the angle curve of the joint. Independent t-tests were performed for between-group comparisons of all the variables. The CP group significantly decreased the leg stiffness but increased the joint stiffness during stance phase, except during terminal stance where the leg stiffness was increased. They appeared to rely more on muscular contributions to achieve the required leg stiffness, increasing the muscular demands in maintaining the body posture against collapse. Leg stiffness plays a critical role in modulating the kinematics and kinetics of the locomotor system during gait in the diplegic CP. PMID:26629700

  8. Leg and Joint Stiffness in Children with Spastic Diplegic Cerebral Palsy during Level Walking.

    PubMed

    Wang, Ting-Ming; Huang, Hsing-Po; Li, Jia-Da; Hong, Shih-Wun; Lo, Wei-Ching; Lu, Tung-Wu

    2015-01-01

    Individual joint deviations are often identified in the analysis of cerebral palsy (CP) gait. However, knowledge is limited as to how these deviations affect the control of the locomotor system as a whole when striving to meet the demands of walking. The current study aimed to bridge the gap by describing the control of the locomotor system in children with diplegic CP in terms of their leg stiffness, both skeletal and muscular components, and associated joint stiffness during gait. Twelve children with spastic diplegia CP and 12 healthy controls walked at a self-selected pace in a gait laboratory while their kinematic and forceplate data were measured and analyzed during loading response, mid-stance, terminal stance and pre-swing. For calculating the leg stiffness, each of the lower limbs was modeled as a non-linear spring, connecting the hip joint center and the corresponding center of pressure, with varying stiffness that was calculated as the slope (gradient) of the axial force vs. the deformation curve. The leg stiffness was further decomposed into skeletal and muscular components considering the alignment of the lower limb. The ankle, knee and hip of the limb were modeled as revolute joints with torsional springs whose stiffness was calculated as the slope of the moment vs. the angle curve of the joint. Independent t-tests were performed for between-group comparisons of all the variables. The CP group significantly decreased the leg stiffness but increased the joint stiffness during stance phase, except during terminal stance where the leg stiffness was increased. They appeared to rely more on muscular contributions to achieve the required leg stiffness, increasing the muscular demands in maintaining the body posture against collapse. Leg stiffness plays a critical role in modulating the kinematics and kinetics of the locomotor system during gait in the diplegic CP. PMID:26629700

  9. Leg and Joint Stiffness in Children with Spastic Diplegic Cerebral Palsy during Level Walking.

    PubMed

    Wang, Ting-Ming; Huang, Hsing-Po; Li, Jia-Da; Hong, Shih-Wun; Lo, Wei-Ching; Lu, Tung-Wu

    2015-01-01

    Individual joint deviations are often identified in the analysis of cerebral palsy (CP) gait. However, knowledge is limited as to how these deviations affect the control of the locomotor system as a whole when striving to meet the demands of walking. The current study aimed to bridge the gap by describing the control of the locomotor system in children with diplegic CP in terms of their leg stiffness, both skeletal and muscular components, and associated joint stiffness during gait. Twelve children with spastic diplegia CP and 12 healthy controls walked at a self-selected pace in a gait laboratory while their kinematic and forceplate data were measured and analyzed during loading response, mid-stance, terminal stance and pre-swing. For calculating the leg stiffness, each of the lower limbs was modeled as a non-linear spring, connecting the hip joint center and the corresponding center of pressure, with varying stiffness that was calculated as the slope (gradient) of the axial force vs. the deformation curve. The leg stiffness was further decomposed into skeletal and muscular components considering the alignment of the lower limb. The ankle, knee and hip of the limb were modeled as revolute joints with torsional springs whose stiffness was calculated as the slope of the moment vs. the angle curve of the joint. Independent t-tests were performed for between-group comparisons of all the variables. The CP group significantly decreased the leg stiffness but increased the joint stiffness during stance phase, except during terminal stance where the leg stiffness was increased. They appeared to rely more on muscular contributions to achieve the required leg stiffness, increasing the muscular demands in maintaining the body posture against collapse. Leg stiffness plays a critical role in modulating the kinematics and kinetics of the locomotor system during gait in the diplegic CP.

  10. Aerobic exercise training increases plasma Klotho levels and reduces arterial stiffness in postmenopausal women.

    PubMed

    Matsubara, Tomoko; Miyaki, Asako; Akazawa, Nobuhiko; Choi, Youngju; Ra, Song-Gyu; Tanahashi, Koichiro; Kumagai, Hiroshi; Oikawa, Satoshi; Maeda, Seiji

    2014-02-01

    The Klotho gene is a suppressor of the aging phenomena, and the secretion as well as the circulation of Klotho proteins decrease with aging. Although habitual exercise has antiaging effects (e.g., a decrease in arterial stiffness), the relationship between Klotho and habitual exercise remains unclear. In the present study, we investigated the effect of habitual exercise on Klotho, with a particular focus on arterial stiffness. First, we examined the correlation between plasma Klotho concentration and arterial stiffness (carotid artery compliance and β-stiffness index) or aerobic exercise capacity [oxygen uptake at ventilatory threshold (VT)] in 69 healthy, postmenopausal women (50-76 years old) by conducting a cross-sectional study. Second, we tested the effects of aerobic exercise training on plasma Klotho concentrations and arterial stiffness. A total of 19 healthy, postmenopausal women (50-76 years old) were divided into two groups: control group and exercise group. The exercise group completed 12 wk of moderate aerobic exercise training. In the cross-sectional study, plasma Klotho concentrations positively correlated with carotid artery compliance and VT and negatively correlated with the β-stiffness index. In the interventional study, aerobic exercise training increased plasma Klotho concentrations and carotid artery compliance and decreased the β-stiffness index. Moreover, the changes in plasma Klotho concentration and arterial stiffness were found to be correlated. These results suggest a possible role for secreted Klotho in the exercise-induced modulation of arterial stiffness.

  11. Performance Assessment of a New Variable Stiffness Probing System for Micro-CMMs

    PubMed Central

    Alblalaihid, Khalid; Kinnell, Peter; Lawes, Simon; Desgaches, Dorian; Leach, Richard

    2016-01-01

    When designing micro-scale tactile probes, a design trade-off must be made between the stiffness and flexibility of the probing element. The probe must be flexible enough to ensure sensitive parts are not damaged during contact, but it must be stiff enough to overcome attractive surface forces, ensure it is not excessively fragile, easily damaged or sensitive to inertial loads. To address the need for a probing element that is both flexible and stiff, a novel micro-scale tactile probe has been designed and tested that makes use of an active suspension structure. The suspension structure is used to modulate the probe stiffness as required to ensure optimal stiffness conditions for each phase of the measurement process. In this paper, a novel control system is presented that monitors and controls stiffness, allowing two probe stiffness values (“stiff” and “flexible”) to be defined and switched between. During switching, the stylus tip undergoes a displacement of approximately 18 µm, however, the control system is able ensure a consistent flexible mode tip deflection to within 12 nm in the vertical axis. The overall uncertainty for three-dimensional displacement measurements using the probing system is estimated to be 58 nm, which demonstrates the potential of this innovative variable stiffness micro-scale probe system. PMID:27070611

  12. Rolling bearing stiffness in arbitrary direction

    NASA Astrophysics Data System (ADS)

    Luo, Zhusan; Sun, Xinde; Wu, Linfeng

    1992-06-01

    This paper presents a new concept of rolling bearing stiffness in arbitrary direction, which is necessary to the investigation of rotor-bearing dynamics. It includes the axial stiffness and the arbitrary radial stiffness of the rolling bearing. Based on elasticity theory and the geometrical parameters of the bearing, the approximate formulas of the axial stiffness, the arbitrary radial stiffness, and the inner ring displacements are derived. Furthermore, the paper also discusses the effects of the loads, the radial clearance, and the load distribution parameters on the rolling bearing stiffness. In order to verify the model and the computer program, an example of a ball bearing is analyzed in detail. It shows that the model and the program are reliable and the results are consistent with the data supplied by the U.S. Air Force Aeropropulsion Laboratory.

  13. Performance analysis of a semi-active mount made by a new variable stiffness spring

    NASA Astrophysics Data System (ADS)

    Azadi, Mojtaba; Behzadipour, Saeed; Faulkner, Garry

    2011-06-01

    A new variable stiffness mount (VSM), is created and its performance is experimentally measured and analyzed. VSMs have extensive applications in the vibration control of machineries including automotive industry. The variable stiffness in this design is realized by the prestress stiffness of a cable-based mechanism at a singular configuration. Changing the prestress, through a piezo actuator and a simple on-off controller, results in significant stiffness change in short time and at low energy costs. The stiffness of the VSM is characterized through static and dynamic tests. The performance of the VSM is then evaluated and compared with an equivalent passive mount in two main areas of transmissibility and shock absorption. The response time of the semi-active VSM is also measured in a realistic scenario. A summary of the performance tests are presented at the end.

  14. Analysis and Design of Variable Stiffness Composite Cylinders

    NASA Technical Reports Server (NTRS)

    Tatting, Brian F.; Guerdal, Zafer

    1998-01-01

    involve the nonlinear phenomenon of long tubes under bending. Though this scenario is not as applicable to fuselage structures as the previous problems, the mechanisms that produce the nonlinear effect are ideally suited to be controlled by the variable stiffness concept. This is due to the fact that the dominating influence for long cylinders under bending is the ovalization of the cross-section, which is governed mainly by the stiffness parameters of the cylindrical shell. Possible improvement of the critical buckling moments for these structures is investigated using either a circumferential or axial stiffness variation. For the circumferential case involving infinite length cylinders, it is found that slight improvements can be observed by designing structures that resist the cross-sectional deformation yet do not detract from the buckling resistance at the critical location. The results also indicate that buckling behavior is extremely dependent on cylinder length. This effect is most easily seen in the solution of finite length cylinders under bending that contain an axial stiffness variation. For these structures, the only mechanism that exhibits improved response are those that effectively shorten the length of the cylinder, thus reducing the cross-sectional deformation due to the forced restraint at the ends. It was found that the use of curvilinear fibers was not able to achieve this effect in sufficient degree to resist the deformation, but that ring stiffeners produced the desired response admirably. Thus, it is shown that the variable stiffness concept is most effective at improving the bending response of long cylinders through the use of a circumferential stiffness variation.

  15. Leg stiffness measures depend on computational method.

    PubMed

    Hébert-Losier, Kim; Eriksson, Anders

    2014-01-01

    Leg stiffness is often computed from ground reaction force (GRF) registrations of vertical hops to estimate the force-resisting capacity of the lower-extremity during ground contact, with leg stiffness values incorporated in a spring-mass model to describe human motion. Individual biomechanical characteristics, including leg stiffness, were investigated in 40 healthy males. Our aim is to report and discuss the use of 13 different computational methods for evaluating leg stiffness from a double-legged repetitive hopping task, using only GRF registrations. Four approximations for the velocity integration constant were combined with three mathematical expressions, giving 12 methods for computing stiffness using double integrations. One frequency-based method that considered ground contact times was also trialled. The 13 methods thus defined were used to compute stiffness in four extreme cases, which were the stiffest, and most compliant, consistent and variable subjects. All methods provided different stiffness measures for a given individual, but the between-method variations in stiffness were consistent across the four atypical subjects. The frequency-based method apparently overestimated the actual stiffness values, whereas double integrations' measures were more consistent. In double integrations, the choice of the integration constant and mathematical expression considerably affected stiffness values, as variations during hopping were more or less emphasized. Stating a zero centre of mass position at take-off gave more consistent results, and taking a weighted-average of the force or displacement curve was more forgiving to variations in performance. In any case, stiffness values should always be accompanied by a detailed description of their evaluation methods, as our results demonstrated that computational methods affect calculated stiffness. PMID:24188972

  16. Arterial Stiffness in Nonhypertensive Type 2 Diabetes Patients in Ghana

    PubMed Central

    Antwi, Daniel A.; Gyan, Ben

    2016-01-01

    Background. Increased arterial stiffness is an independent cardiovascular risk factor in diabetes patients and general population. However, the contribution of diabetes to arterial stiffness is often masked by coexistent obesity and hypertension. In this study, we assessed arterial stiffness in nonhypertensive, nonobese type 2 diabetes (T2DM) patients in Ghana. Methods. In case-control design, 166 nonhypertensive, nonobese participants, comprising 96 T2DM patients and 70 nondiabetes controls, were recruited. Peripheral and central blood pressure (BP) indices were measured, and arterial stiffness was assessed as aortic pulse wave velocity (PWVao), augmentation index (AIx), cardioankle vascular index (CAVI), and heart-ankle pulse wave velocity (haPWV). Results. With similar peripheral and central BP indices, T2DM patients had higher PWVao (8.3 ± 1 versus 7.8 ± 1.3, p = 0.044) and CAVI (7.9 ± 1.2 versus 6.9 ± 0.7, p = 0.021) than nondiabetic control. AIx and haPWV were similar between T2DM and nondiabetic controls. Multiple regression models showed that, in the entire study participants, the major determinants of PWVao were diabetes status, age, gender, systolic BP, and previous smoking status (β = 0.22, 0.36, 0.48, 0.21, and 0.25, resp.; all p < 0.05); the determinants of CAVI were diabetes status, age, BMI, heart rate, HbA1c, total cholesterol, HDL cholesterol, and previous smoking status (β = 0.21, 0.38, 0.2, 0.18, 0.24. 0.2, −0.19, and 0.2, resp.; all p < 0.05). Conclusion. Our findings suggest that nonhypertensive, nonobese T2DM patients have increased arterial stiffness without appreciable increase in peripheral and central pressure indices. PMID:27774104

  17. Multiple-input, multiple-output system identification for characterization of limb stiffness dynamics.

    PubMed

    Perreault, E J; Kirsch, R F; Acosta, A M

    1999-05-01

    This study presents time-domain and frequency-domain, multiple-input, multiple-output (MIMO) linear system identification techniques that can be used to estimate the dynamic endpoint stiffness of a multijoint limb. The stiffness of a joint or limb arises from a number of physiological mechanisms and is thought to play a fundamental role in the control of posture and movement. Estimates of endpoint stiffness can therefore be used to characterize its modulation during physiological tasks and may provide insight into how the nervous system normally controls motor behavior. Previous MIMO stiffness estimates have focused upon the static stiffness components only or assumed simple parametric models with elastic, viscous, and inertial components. The method presented here captures the full stiffness dynamics during a relatively short experimental trial while assuming only that the system is linear for small perturbations. Simulation studies were performed to investigate the performance of this approach under typical experimental conditions. It was found that a linear MIMO description of endpoint stiffness dynamics was sufficient to describe the displacement responses to small stochastic force perturbations. Distortion of these linear estimates by nonlinear centripetal and Coriolis forces was virtually undetectable for these perturbations. The system identification techniques were also found to be robust in the presence of significant output measurement noise and input coupling. These results indicate that the approach described here will allow the estimation of endpoint stiffness dynamics in an experimentally efficient manner with minimal assumptions about the specific form of these properties. PMID:10365425

  18. Variable stiffness and damping suspension system for train

    NASA Astrophysics Data System (ADS)

    Sun, Shuaishuai; Deng, Huaxia; Li, Weihua

    2014-03-01

    As the vibration of high speed train becomes fierce when the train runs at high speed, it is crucial to develop a novel suspension system to negotiate train's vibration. This paper presents a novel suspension based on Magnetorheological fluid (MRF) damper and MRF based smart air spring. The MRF damper is used to generate variable damping while the smart air spring is used to generate field-dependent stiffness. In this paper, the two kind smart devices, MRF dampers and smart air spring, are developed firstly. Then the dynamic performances of these two devices are tested by MTS. Based on the testing results, the two devices are equipped to a high speed train which is built in ADAMS. The skyhook control algorithm is employed to control the novel suspension. In order to compare the vibration suppression capability of the novel suspension with other kind suspensions, three other different suspension systems are also considered and simulated in this paper. The other three kind suspensions are variable damping with fixed stiffness suspension, variable stiffness with fixed damping suspension and passive suspension. The simulation results indicate that the variable damping and stiffness suspension suppresses the vibration of high speed train better than the other three suspension systems.

  19. The posttraumatic stiff elbow: an update.

    PubMed

    Mellema, Jos J; Lindenhovius, Anneluuk L C; Jupiter, Jesse B

    2016-06-01

    Posttraumatic elbow stiffness is a disabling condition that remains challenging to treat despite improvement of our understanding of the pathogenesis of posttraumatic contractures and new treatment regimens. This review provides an update and overview of the etiology of posttraumatic elbow stiffness, its classification, evaluation, nonoperative and operative treatment, and postoperative management.

  20. Nonparticipatory Stiffness in the Male Perioral Complex

    ERIC Educational Resources Information Center

    Chu, Shin-Ying; Barlow, Steven M.; Lee, Jaehoon

    2009-01-01

    Purpose: The objective of this study was to extend previous published findings in the authors' laboratory using a new automated technology to quantitatively characterize nonparticipatory perioral stiffness in healthy male adults. Method: Quantitative measures of perioral stiffness were sampled during a nonparticipatory task using a…

  1. Running in the real world: adjusting leg stiffness for different surfaces.

    PubMed Central

    Ferris, D P; Louie, M; Farley, C T

    1998-01-01

    A running animal coordinates the actions of many muscles, tendons, and ligaments in its leg so that the overall leg behaves like a single mechanical spring during ground contact. Experimental observations have revealed that an animal's leg stiffness is independent of both speed and gravity level, suggesting that it is dictated by inherent musculoskeletal properties. However, if leg stiffness was invariant, the biomechanics of running (e.g. peak ground reaction force and ground contact time) would change when an animal encountered different surfaces in the natural world. We found that human runners adjust their leg stiffness to accommodate changes in surface stiffness, allowing them to maintain similar running mechanics on different surfaces. These results provide important insight into mechanics and control of animal locomotion and suggest that incorporating an adjustable leg stiffness in the design of hopping and running robots is important if they are to match the agility and speed of animals on varied terrain. PMID:9675909

  2. A variable transverse stiffness sandwich structure using fluidic flexible matrix composites (F2MC)

    NASA Astrophysics Data System (ADS)

    Li, Suyi; Lotfi, Amir; Shan, Ying; Wang, K. W.; Rahn, Christopher D.; Bakis, Charles E.

    2008-03-01

    Presented in this paper is the development of a novel honeycomb sandwich panel with variable transverse stiffness. In this structure, the traditional sandwich face sheets are replaced by the fluidic flexible matrix composite (F2MC) tube layers developed in recent studies. The F2MC layers, combined with the anisotropic honeycomb core material properties, provide a new sandwich structure with variable stiffness properties for transverse loading. In this research, an analytical model is derived based on Lekhitskii's anisotropic pressurized tube solution and Timoshenko beam theory. Experimental investigations are also conducted to verify the analytical findings. A segmented multiple-F2MC-tube configuration is synthesized to increase the variable stiffness range. The analysis shows that the new honeycomb sandwich structure using F2MC tubes of 10 segments can provide a high/low transverse stiffness ratio of 60. Segmentation and stiffness control can be realized by an embedded valve network, granting a fast response time.

  3. Research on a novel high stiffness axial passive magnetic bearing for DGMSCMG

    NASA Astrophysics Data System (ADS)

    Sun, Jinji; Wang, Chun'e.; Le, Yun

    2016-08-01

    To increase the displacement stiffness and decrease power loss of double gimbals magnetically suspended control momentum gyro (DGMSCMG), this paper researches a new structure of axial passive magnetic bearing (APMB). Different from the existing APMB, the proposed APMB is composed of segmented permanent magnets and magnetic rings. The displacement stiffness and angular stiffness expressions are derived by equivalent magnetic circuit method and infinitesimal method based on the end magnetic flux. The relationships are analyzed between stiffness and structure parameters such as length of air gap, length of permanent magnet, height of permanent magnet and end length of magnetic ring. Besides, the axial displacement stiffness measurement method of the APMB is proposed, and it verified the correctness of proposed theoretical method. The DGMSCMG prototype is manufactured and the slow-down characteristic experiment is carried out, and the experimental result reflects the low power loss feature of the APMB.

  4. Running in the real world: adjusting leg stiffness for different surfaces

    NASA Technical Reports Server (NTRS)

    Ferris, D. P.; Louie, M.; Farley, C. T.

    1998-01-01

    A running animal coordinates the actions of many muscles, tendons, and ligaments in its leg so that the overall leg behaves like a single mechanical spring during ground contact. Experimental observations have revealed that an animal's leg stiffness is independent of both speed and gravity level, suggesting that it is dictated by inherent musculoskeletal properties. However, if leg stiffness was invariant, the biomechanics of running (e.g. peak ground reaction force and ground contact time) would change when an animal encountered different surfaces in the natural world. We found that human runners adjust their leg stiffness to accommodate changes in surface stiffness, allowing them to maintain similar running mechanics on different surfaces. These results provide important insight into mechanics and control of animal locomotion and suggest that incorporating an adjustable leg stiffness in the design of hopping and running robots is important if they are to match the agility and speed of animals on varied terrain.

  5. Rolling Element Bearing Stiffness Matrix Determination (Presentation)

    SciTech Connect

    Guo, Y.; Parker, R.

    2014-01-01

    Current theoretical bearing models differ in their stiffness estimates because of different model assumptions. In this study, a finite element/contact mechanics model is developed for rolling element bearings with the focus of obtaining accurate bearing stiffness for a wide range of bearing types and parameters. A combined surface integral and finite element method is used to solve for the contact mechanics between the rolling elements and races. This model captures the time-dependent characteristics of the bearing contact due to the orbital motion of the rolling elements. A numerical method is developed to determine the full bearing stiffness matrix corresponding to two radial, one axial, and two angular coordinates; the rotation about the shaft axis is free by design. This proposed stiffness determination method is validated against experiments in the literature and compared to existing analytical models and widely used advanced computational methods. The fully-populated stiffness matrix demonstrates the coupling between bearing radial, axial, and tilting bearing deflections.

  6. Acute exercise modifies titin phosphorylation and increases cardiac myofilament stiffness

    PubMed Central

    Müller, Anna E.; Kreiner, Matthias; Kötter, Sebastian; Lassak, Philipp; Bloch, Wilhelm; Suhr, Frank; Krüger, Martina

    2014-01-01

    Titin-based myofilament stiffness is largely modulated by phosphorylation of its elastic I-band regions N2-Bus (decreases passive stiffness, PT) and PEVK (increases PT). Here, we tested the hypothesis that acute exercise changes titin phosphorylation and modifies myofilament stiffness. Adult rats were exercised on a treadmill for 15 min, untrained animals served as controls. Titin phosphorylation was determined by Western blot analysis using phosphospecific antibodies to Ser4099 and Ser4010 in the N2-Bus region (PKG and PKA-dependent. respectively), and to Ser11878 and Ser 12022 in the PEVK region (PKCα and CaMKIIδ-dependent, respectively). Passive tension was determined by step-wise stretching of isolated skinned cardiomyocytes to sarcomere length (SL) ranging from 1.9 to 2.4 μm and showed a significantly increased PT from exercised samples, compared to controls. In cardiac samples titin N2-Bus phosphorylation was significantly decreased by 40% at Ser4099, however, no significant changes were observed at Ser4010. PEVK phosphorylation at Ser11878 was significantly increased, which is probably mediated by the observed exercise-induced increase in PKCα activity. Interestingly, relative phosphorylation of Ser12022 was substantially decreased in the exercised samples. Surprisingly, in skeletal samples from acutely exercised animals we detected a significant decrease in PEVK phosphorylation at Ser11878 and an increase in Ser12022 phosphorylation; however, PKCα activity remained unchanged. In summary, our data show that a single exercise bout of 15 min affects titin domain phosphorylation and titin-based myocyte stiffness with obviously divergent effects in cardiac and skeletal muscle tissues. The observed changes in titin stiffness could play an important role in adapting the passive and active properties of the myocardium and the skeletal muscle to increased physical activity. PMID:25477822

  7. A FAK-Cas-Rac-Lamellipodin Signaling Module Transduces Extracellular Matrix Stiffness into Mechanosensitive Cell Cycling

    PubMed Central

    Bae, Yong Ho; Mui, Keeley L.; Hsu, Bernadette Y.; Liu, Shu-Lin; Cretu, Alexandra; Razinia, Ziba; Xu, Tina; Puré, Ellen; Assoian, Richard K.

    2015-01-01

    Tissue and extracellular matrix (ECM) stiffness is transduced into intracellular stiffness, signaling, and changes in cellular behavior. Integrins and several of their associated focal adhesion proteins have been implicated in sensing ECM stiffness. We investigated how an initial sensing event is translated into intracellular stiffness and a biologically interpretable signal. We found that a pathway consisting of focal adhesion kinase (FAK), the adaptor protein p130Cas (Cas), and the guanosine triphosphatase Rac selectively transduced ECM stiffness into stable intracellular stiffness, increased abundance of the cell cycle protein cyclin D1, and promoted S phase entry. Rac-dependent intracellular stiffening involved its binding partner lamellipodin, a protein that transmits Rac signals to the cytoskeleton during cell migration. Our findings establish that mechanotransduction by a FAK-Cas-Rac-lamellipodin signaling module converts the external information encoded by ECM stiffness into stable intracellular stiffness and mechanosensitive cell cycling. Thus, lamellipodin is not only important in controlling cellular migration, but also for regulating the cell cycle in response to mechanical signals. PMID:24939893

  8. Interplay of Matrix Stiffness and Cell-Cell Contact in Regulating Differentiation of Stem Cells.

    PubMed

    Ye, Kai; Cao, Luping; Li, Shiyu; Yu, Lin; Ding, Jiandong

    2016-08-31

    Stem cells are capable of sensing and responding to the mechanical properties of extracellular matrixes (ECMs). It is well-known that, while osteogenesis is promoted on the stiff matrixes, adipogenesis is enhanced on the soft ones. Herein, we report an "abnormal" tendency of matrix-stiffness-directed stem cell differentiation. Well-defined nanoarrays of cell-adhesive arginine-glycine-aspartate (RGD) peptides were modified onto the surfaces of persistently nonfouling poly(ethylene glycol) (PEG) hydrogels to achieve controlled specific cell adhesion and simultaneously eliminate nonspecific protein adsorption. Mesenchymal stem cells were cultivated on the RGD-nanopatterned PEG hydrogels with the same RGD nanospacing but different hydrogel stiffnesses and incubated in the induction medium to examine the effect of matrix stiffness on osteogenic and adipogenic differentiation extents. When stem cells were kept at a low density during the induction period, the differentiation tendency was consistent with the previous reports in the literature; however, both lineage commitments were favored on the stiff matrices at a high cell density. We interpreted such a complicated stiffness effect at a high cell density in two-dimensional culture as the interplay of matrix stiffness and cell-cell contact. As a result, this study strengthens the essence of the stiffness effect and highlights the combinatory effects of ECM cues and cell cues on stem cell differentiation.

  9. A FAK-Cas-Rac-lamellipodin signaling module transduces extracellular matrix stiffness into mechanosensitive cell cycling.

    PubMed

    Bae, Yong Ho; Mui, Keeley L; Hsu, Bernadette Y; Liu, Shu-Lin; Cretu, Alexandra; Razinia, Ziba; Xu, Tina; Puré, Ellen; Assoian, Richard K

    2014-06-17

    Tissue and extracellular matrix (ECM) stiffness is transduced into intracellular stiffness, signaling, and changes in cellular behavior. Integrins and several of their associated focal adhesion proteins have been implicated in sensing ECM stiffness. We investigated how an initial sensing event is translated into intracellular stiffness and a biologically interpretable signal. We found that a pathway consisting of focal adhesion kinase (FAK), the adaptor protein p130Cas (Cas), and the guanosine triphosphatase Rac selectively transduced ECM stiffness into stable intracellular stiffness, increased the abundance of the cell cycle protein cyclin D1, and promoted S-phase entry. Rac-dependent intracellular stiffening involved its binding partner lamellipodin, a protein that transmits Rac signals to the cytoskeleton during cell migration. Our findings establish that mechanotransduction by a FAK-Cas-Rac-lamellipodin signaling module converts the external information encoded by ECM stiffness into stable intracellular stiffness and mechanosensitive cell cycling. Thus, lamellipodin is important not only in controlling cellular migration but also for regulating the cell cycle in response to mechanical signals.

  10. PolyMUMPs MEMS device to measure mechanical stiffness of single cells in aqueous media

    NASA Astrophysics Data System (ADS)

    Warnat, S.; King, H.; Forbrigger, C.; Hubbard, T.

    2015-02-01

    A method of experimentally determining the mechanical stiffness of single cells by using differential displacement measurements in a two stage spring system is presented. The spring system consists of a known MEMS reference spring and an unknown cellular stiffness: the ratio of displacements is related to the ratio of stiffness. A polyMUMPs implementation for aqueous media is presented and displacement measurements made from optical microphotographs using a FFT based displacement method with a repeatability of ~20 nm. The approach was first validated on a MEMS two stage spring system of known stiffness. The measured stiffness ratios of control structures (i) MEMS spring systems and (ii) polystyrene microspheres were found to agree with theoretical values. Mechanical tests were then performed on Saccharomyces cerevisiae (Baker’s yeast) in aqueous media. Cells were placed (using a micropipette) inside MEMS measuring structures and compressed between two jaws using an electrostatic actuator and displacements measured. Tested cells showed stiffness values between 5.4 and 8.4 N m-1 with an uncertainty of 11%. In addition, non-viable cells were tested by exposing viable cells to methanol. The resultant mean cell stiffness dropped by factor of 3 × and an explicit discrimination between viable and non-viable cells based on mechanical stiffness was seen.

  11. Clipped viscous damping with negative stiffness for semi-active cable damping

    NASA Astrophysics Data System (ADS)

    Weber, F.; Boston, C.

    2011-04-01

    This paper investigates numerically and experimentally clipped viscous damping with negative stiffness for semi-active cable damping. From simulations it is concluded that unclipped and clipped viscous damping with negative stiffness is equivalent to unclipped and clipped LQR. It is shown that optimized unclipped viscous damping with negative stiffness generates critical cable damping by an anti-node at the actuator position. The resulting curvature at the actuator position is larger than the curvature close to the anchors due to the disturbance forces which may lead to premature cable fatigue at the actuator position. Optimized clipped viscous damping with negative stiffness does not show this drawback, can be implemented using a semi-active damper and produces twice as much cable damping as optimal viscous damping. Close to the optimal tuning, it leads to approximately the same control force as optimal semi-active friction damping with negative stiffness, which explains the superior cable damping. The superior damping results from the negative stiffness that increases the damper motion. Clipped viscous damping with negative stiffness is validated on a strand cable with a magneto-rheological damper. The measured cable damping is twice that achieved by emulated viscous damping, which confirms the numerical results. A tuning rule for clipped viscous damping with negative stiffness of real cables with flexural rigidity is given.

  12. Interplay of Matrix Stiffness and Cell-Cell Contact in Regulating Differentiation of Stem Cells.

    PubMed

    Ye, Kai; Cao, Luping; Li, Shiyu; Yu, Lin; Ding, Jiandong

    2016-08-31

    Stem cells are capable of sensing and responding to the mechanical properties of extracellular matrixes (ECMs). It is well-known that, while osteogenesis is promoted on the stiff matrixes, adipogenesis is enhanced on the soft ones. Herein, we report an "abnormal" tendency of matrix-stiffness-directed stem cell differentiation. Well-defined nanoarrays of cell-adhesive arginine-glycine-aspartate (RGD) peptides were modified onto the surfaces of persistently nonfouling poly(ethylene glycol) (PEG) hydrogels to achieve controlled specific cell adhesion and simultaneously eliminate nonspecific protein adsorption. Mesenchymal stem cells were cultivated on the RGD-nanopatterned PEG hydrogels with the same RGD nanospacing but different hydrogel stiffnesses and incubated in the induction medium to examine the effect of matrix stiffness on osteogenic and adipogenic differentiation extents. When stem cells were kept at a low density during the induction period, the differentiation tendency was consistent with the previous reports in the literature; however, both lineage commitments were favored on the stiff matrices at a high cell density. We interpreted such a complicated stiffness effect at a high cell density in two-dimensional culture as the interplay of matrix stiffness and cell-cell contact. As a result, this study strengthens the essence of the stiffness effect and highlights the combinatory effects of ECM cues and cell cues on stem cell differentiation. PMID:26600563

  13. Substrate stiffness affects skeletal myoblast differentiation in vitro

    NASA Astrophysics Data System (ADS)

    Romanazzo, Sara; Forte, Giancarlo; Ebara, Mitsuhiro; Uto, Koichiro; Pagliari, Stefania; Aoyagi, Takao; Traversa, Enrico; Taniguchi, Akiyoshi

    2012-12-01

    To maximize the therapeutic efficacy of cardiac muscle constructs produced by stem cells and tissue engineering protocols, suitable scaffolds should be designed to recapitulate all the characteristics of native muscle and mimic the microenvironment encountered by cells in vivo. Moreover, so not to interfere with cardiac contractility, the scaffold should be deformable enough to withstand muscle contraction. Recently, it was suggested that the mechanical properties of scaffolds can interfere with stem/progenitor cell functions, and thus careful consideration is required when choosing polymers for targeted applications. In this study, cross-linked poly-ɛ-caprolactone membranes having similar chemical composition and controlled stiffness in a supra-physiological range were challenged with two sources of myoblasts to evaluate the suitability of substrates with different stiffness for cell adhesion, proliferation and differentiation. Furthermore, muscle-specific and non-related feeder layers were prepared on stiff surfaces to reveal the contribution of biological and mechanical cues to skeletal muscle progenitor differentiation. We demonstrated that substrate stiffness does affect myogenic differentiation, meaning that softer substrates can promote differentiation and that a muscle-specific feeder layer can improve the degree of maturation in skeletal muscle stem cells.

  14. How crouch gait can dynamically induce stiff-knee gait.

    PubMed

    van der Krogt, Marjolein M; Bregman, Daan J J; Wisse, Martijn; Doorenbosch, Caroline A M; Harlaar, Jaap; Collins, Steven H

    2010-04-01

    Children with cerebral palsy frequently experience foot dragging and tripping during walking due to a lack of adequate knee flexion in swing (stiff-knee gait). Stiff-knee gait is often accompanied by an overly flexed knee during stance (crouch gait). Studies on stiff-knee gait have mostly focused on excessive knee muscle activity during (pre)swing, but the passive dynamics of the limbs may also have an important effect. To examine the effects of a crouched posture on swing knee flexion, we developed a forward-dynamic model of human walking with a passive swing knee, capable of stable cyclic walking for a range of stance knee crouch angles. As crouch angle during stance was increased, the knee naturally flexed much less during swing, resulting in a 'stiff-knee' gait pattern and reduced foot clearance. Reduced swing knee flexion was primarily due to altered gravitational moments around the joints during initial swing. We also considered the effects of increased push-off strength and swing hip flexion torque, which both increased swing knee flexion, but the effect of crouch angle was dominant. These findings demonstrate that decreased knee flexion during swing can occur purely as the dynamical result of crouch, rather than from altered muscle function or pathoneurological control alone.

  15. Torsion stiffness of a protein pair determined by magnetic particles.

    PubMed

    Janssen, X J A; van Noorloos, J M; Jacob, A; van Ijzendoorn, L J; de Jong, A M; Prins, M W J

    2011-05-01

    We demonstrate the ability to measure torsion stiffness of a protein complex by applying a controlled torque on a magnetic particle. As a model system we use protein G bound to an IgG antibody. The protein pair is held between a magnetic particle and a polystyrene substrate. The angular orientation of the magnetic particle shows an oscillating behavior upon application of a rotating magnetic field. The amplitude of the oscillation increases with a decreasing surface coverage of antibodies on the substrate and with an increasing magnitude of the applied field. For decreasing antibody coverage, the torsion spring constant converges to a minimum value of 1.5 × 10(3) pN·nm/rad that corresponds to a torsion modulus of 4.5 × 10(4) pN·nm(2). This torsion stiffness is an upper limit for the molecular bond between the particle and the surface that is tentatively assigned to a single protein G-IgG protein pair. This assignment is supported by interpreting the measured stiffness with a simple mechanical model that predicts a two orders of magnitude larger stiffness for the protein G-IgG complex than values found for micrometer length dsDNA. This we understand from the structural properties of the molecules, i.e., DNA is a long and flexible chain-like molecule, whereas the antibody-antigen couple is orders of magnitude smaller and more globular in shape due to the folding of the molecules.

  16. Acute benefits of the microbial-derived isoflavone metabolite equol on arterial stiffness in men prospectively recruited according to equol producer phenotype: a double-blind randomized controlled trial12

    PubMed Central

    Hazim, Sara; Curtis, Peter J; Schär, Manuel Y; Ostertag, Luisa M; Kay, Colin D; Minihane, Anne-Marie; Cassidy, Aedín

    2016-01-01

    Background: There is much speculation with regard to the potential cardioprotective benefits of equol, a microbial-derived metabolite of the isoflavone daidzein, which is produced in the large intestine after soy intake in 30% of Western populations. Although cross-sectional and retrospective data support favorable associations between the equol producer (EP) phenotype and cardiometabolic health, few studies have prospectively recruited EPs to confirm this association. Objective: The aim was to determine whether the acute vascular benefits of isoflavones differ according to EP phenotype and subsequently investigate the effect of providing commercially produced S-(–)equol to non-EPs. Design: We prospectively recruited male EPs and non-EPs (n = 14/group) at moderate cardiovascular risk into a double-blind, placebo-controlled crossover study to examine the acute effects of soy isoflavones (80-mg aglycone equivalents) on arterial stiffness [carotid-femoral pulse-wave velocity (cfPWV)], blood pressure, endothelial function (measured by using the EndoPAT 2000; Itamar Medical), and nitric oxide at baseline (0 h) and 6 and 24 h after intake. In a separate assessment, non-EPs consumed 40 mg S-(–)equol with identical vascular measurements performed 2 h after intake. Results: After soy intake, cfPWV significantly improved in EPs at 24 h (cfPWV change from 0 h: isoflavone, −0.2 ± 0.2 m/s; placebo, 0.6 ± 0.2 m/s; P < 0.01), which was significantly associated with plasma equol concentrations (R = −0.36, P = 0.01). No vascular effects were observed in EPs at 6 h or in non-EPs at any time point. Similarly, no benefit of commercially produced S-(–)equol was observed in non-EPs despite mean plasma equol concentrations reaching 3.2 μmol/L. Conclusions: Acute soy intake improved cfPWV in EPs, equating to an 11–12% reduced risk of cardiovascular disease if sustained. However, a single dose of commercially produced equol had no cardiovascular benefits in non-EPs. These

  17. Sway‐dependent changes in standing ankle stiffness caused by muscle thixotropy

    PubMed Central

    Sakanaka, Tania E.; Lakie, Martin

    2016-01-01

    Key points The passive stiffness of the calf muscles contributes to standing balance, although the properties of muscle tissue are highly labile.We investigated the effect of sway history upon intrinsic ankle stiffness and demonstrated reductions in stiffness of up to 43% during conditions of increased baseline sway.This sway dependence was most apparent when using low amplitude stiffness‐measuring perturbations, and the short‐range stiffness component was smaller during periods of high sway.These characteristics are consistent with the thixotropic properties of the calf muscles causing the observed changes in ankle stiffness.Periods of increased sway impair the passive stabilization of standing, demanding more active neural control of balance. Abstract Quiet standing is achieved through a combination of active and passive mechanisms, consisting of neural control and intrinsic mechanical stiffness of the ankle joint, respectively. The mechanical stiffness is partly determined by the calf muscles. However, the viscoelastic properties of muscle are highly labile, exhibiting a strong dependence on movement history. By measuring the effect of sway history upon ankle stiffness, the present study determines whether this lability has consequences for the passive stabilization of human standing. Ten subjects stood quietly on a rotating platform whose axis was collinear with the ankle joint. Ankle sway was increased by slowly tilting this platform in a random fashion, or decreased by fixing the body to a board. Ankle stiffness was measured by using the same platform to simultaneously apply small, brief perturbations (<0.6 deg; 140 ms) at the same time as the resulting torque response was recorded. The results show that increasing sway reduces ankle stiffness by up to 43% compared to the body‐fixed condition. Normal quiet stance was associated with intermediate values. The effect was most apparent when using smaller perturbation amplitudes to measure stiffness (0

  18. "Contact" of nanoscale stiff films.

    PubMed

    Yang, Fut K; Zhang, Wei; Han, Yougun; Yoffe, Serge; Cho, Yungchi; Zhao, Boxin

    2012-06-26

    We investigated the contact behaviors of a nanoscopic stiff thin film bonded to a compliant substrate and derived an analytical solution for determining the elastic modulus of thin films. Microscopic contact deformations of the gold and polydopamine thin films (<200 nm) coated on polydimethylsiloxane elastomers were measured by indenting a soft tip and analyzed in the framework of the classical plate theory and Johnson-Kendall-Roberts (JKR) contact mechanics. The analysis of this thin film contact mechanics focused on the bending and stretching resistance of thin films and is fundamentally different from conventional indentation measurements where the focus is on the fracture and compression of the films. The analytical solution of the elastic modulus of nanoscopic thin films was validated experimentally using 50 and 100 nm gold thin films coated on polydimethylsiloxane elastomers. The technical application of this analysis was further demonstrated by measuring the elastic modulus of thin films of polydopamine, a recently discovered biomimetic universal coating material. Furthermore, the method presented here is able to quantify the contact behaviors of nanoscopic thin films, effectively providing fundamental design parameters, the elastic modulus, and the work of adhesion, crucial for transferring them effectively into practical applications. PMID:22616836

  19. Model-based estimation of knee stiffness.

    PubMed

    Pfeifer, Serge; Vallery, Heike; Hardegger, Michael; Riener, Robert; Perreault, Eric J

    2012-09-01

    During natural locomotion, the stiffness of the human knee is modulated continuously and subconsciously according to the demands of activity and terrain. Given modern actuator technology, powered transfemoral prostheses could theoretically provide a similar degree of sophistication and function. However, experimentally quantifying knee stiffness modulation during natural gait is challenging. Alternatively, joint stiffness could be estimated in a less disruptive manner using electromyography (EMG) combined with kinetic and kinematic measurements to estimate muscle force, together with models that relate muscle force to stiffness. Here we present the first step in that process, where we develop such an approach and evaluate it in isometric conditions, where experimental measurements are more feasible. Our EMG-guided modeling approach allows us to consider conditions with antagonistic muscle activation, a phenomenon commonly observed in physiological gait. Our validation shows that model-based estimates of knee joint stiffness coincide well with experimental data obtained using conventional perturbation techniques. We conclude that knee stiffness can be accurately estimated in isometric conditions without applying perturbations, which presents an important step toward our ultimate goal of quantifying knee stiffness during gait.

  20. Model-Based Estimation of Knee Stiffness

    PubMed Central

    Pfeifer, Serge; Vallery, Heike; Hardegger, Michael; Riener, Robert; Perreault, Eric J.

    2013-01-01

    During natural locomotion, the stiffness of the human knee is modulated continuously and subconsciously according to the demands of activity and terrain. Given modern actuator technology, powered transfemoral prostheses could theoretically provide a similar degree of sophistication and function. However, experimentally quantifying knee stiffness modulation during natural gait is challenging. Alternatively, joint stiffness could be estimated in a less disruptive manner using electromyography (EMG) combined with kinetic and kinematic measurements to estimate muscle force, together with models that relate muscle force to stiffness. Here we present the first step in that process, where we develop such an approach and evaluate it in isometric conditions, where experimental measurements are more feasible. Our EMG-guided modeling approach allows us to consider conditions with antagonistic muscle activation, a phenomenon commonly observed in physiological gait. Our validation shows that model-based estimates of knee joint stiffness coincide well with experimental data obtained using conventional perturbation techniques. We conclude that knee stiffness can be accurately estimated in isometric conditions without applying perturbations, which presents an important step towards our ultimate goal of quantifying knee stiffness during gait. PMID:22801482

  1. Stiff substrates enhance cultured neuronal network activity

    PubMed Central

    Zhang, Quan-You; Zhang, Yan-Yan; Xie, Jing; Li, Chen-Xu; Chen, Wei-Yi; Liu, Bai-Lin; Wu, Xiao-an; Li, Shu-Na; Huo, Bo; Jiang, Lin-Hua; Zhao, Hu-Cheng

    2014-01-01

    The mechanical property of extracellular matrix and cell-supporting substrates is known to modulate neuronal growth, differentiation, extension and branching. Here we show that substrate stiffness is an important microenvironmental cue, to which mouse hippocampal neurons respond and integrate into synapse formation and transmission in cultured neuronal network. Hippocampal neurons were cultured on polydimethylsiloxane substrates fabricated to have similar surface properties but a 10-fold difference in Young's modulus. Voltage-gated Ca2+ channel currents determined by patch-clamp recording were greater in neurons on stiff substrates than on soft substrates. Ca2+ oscillations in cultured neuronal network monitored using time-lapse single cell imaging increased in both amplitude and frequency among neurons on stiff substrates. Consistently, synaptic connectivity recorded by paired recording was enhanced between neurons on stiff substrates. Furthermore, spontaneous excitatory postsynaptic activity became greater and more frequent in neurons on stiff substrates. Evoked excitatory transmitter release and excitatory postsynaptic currents also were heightened at synapses between neurons on stiff substrates. Taken together, our results provide compelling evidence to show that substrate stiffness is an important biophysical factor modulating synapse connectivity and transmission in cultured hippocampal neuronal network. Such information is useful in designing instructive scaffolds or supporting substrates for neural tissue engineering. PMID:25163607

  2. Reduction of hinge moments of airplane control surfaces by tabs

    NASA Technical Reports Server (NTRS)

    Harris, Thomas A

    1936-01-01

    This report presents the results of an investigation conducted in the NACA 7 by 10-foot wind tunnel of control surfaces equipped with tabs for reducing the control forces or trimming the aircraft. Two sizes of ordinary ailerons with several sizes of attached and inset tabs were tested on a Clark y wing. Tabs were also tested in combination with auxiliary balances of the horn and paddle types, and with a frise balance aileron. A tail-surface model of symmetrical section, equipped with tabs, was tested with 40 percent of the area movable (elevator) when used as a horizontal tail and 60 percent of the area movable (rudder) when used as a vertical tail. The half-span tail-surface model was tested with and without a reflection plane. The results of the tests indicated that inset tabs were superior to attached tabs for the same ratio of tab/control surface deflection.

  3. Physiotherapy assessment of shoulder stiffness and how it influences management

    PubMed Central

    Russell, Sarah

    2015-01-01

    Common causes of shoulder stiffness include osteoarthritis, trauma, rheumatological conditions and stiffness secondary to soft tissue adaptation. Physiotherapy assessment of the stiff shoulder aims to ascertain the key causative factors of stiffness to inform effective management planning. Identification of whether a patient presents with pain or stiffness as their predominant symptom further guides treatment selection. The current evidence base underpins a management algorithm which has been developed to guide the assessment and management of patients presenting with shoulder stiffness. PMID:27582980

  4. Aortic Stiffness, Cerebrovascular Dysfunction, and Memory

    PubMed Central

    Cooper, Leroy L.; Mitchell, Gary F.

    2016-01-01

    Background Aortic stiffness is associated with cardiovascular and cerebrovascular events and cognitive decline. This mini-review focuses on relations of aortic stiffness with microvascular dysfunction and discusses the contribution of abnormal pulsatile hemodynamics to cerebrovascular damage and cognitive decline. We also provide a rationale for considering aortic stiffness as a putative and important contributor to memory impairment in older individuals. Summary Aging is associated with stiffening of the aorta but not the muscular arteries, which reduces wave reflection and increases the transmission of pulsatility into the periphery. Aortic stiffening thereby impairs a protective mechanism that shields the peripheral microcirculation from excessive pulsatility within downstream target organs. Beyond midlife, aortic stiffness increases rapidly and exposes the cerebral microcirculation to abnormal pulsatile mechanical forces that are associated with microvascular damage and remodeling in the brain. Aortic stiffening and high-flow pulsatility are associated with alterations in the microvasculature of the brain; however, a mechanistic link between aortic stiffness and memory has not been established. We showed that in a community-based sample of older individuals, cerebrovascular resistance and white matter hyperintensities - markers of cerebrovascular remodeling and damage - mediated the relation between higher aortic stiffness and lower performance on memory function tests. These data suggest that microvascular and white matter damage associated with excessive aortic stiffness contribute to impaired memory function with advancing age. Key Messages Increasing evidence suggests that vascular etiologies - including aortic stiffness and microvascular damage - contribute to memory impairment and the pathogenesis of dementia, including Alzheimer's disease. Interventions that reduce aortic stiffness may delay memory decline among older individuals. PMID:27752478

  5. Liver stiffness is associated with monocyte activation in HIV-infected Ugandans without viral hepatitis.

    PubMed

    Redd, Andrew D; Wendel, Sarah K; Grabowski, Mary K; Ocama, Ponsiano; Kiggundu, Valerian; Bbosa, Francis; Boaz, Iga; Balagopal, Ashwin; Reynolds, Steven J; Gray, Ronald H; Serwadda, David; Kirk, Gregory D; Quinn, Thomas C; Stabinski, Lara

    2013-07-01

    A high prevalence of liver stiffness, as determined by elevated transient elastography liver stiffness measurement, was previously found in a cohort of HIV-infected Ugandans in the absence of chronic viral hepatitis. Given the role of immune activation and microbial translocation in models of liver disease, a shared immune mechanism was hypothesized in the same cohort without other overt causes of liver disease. This study examined whether HIV-related liver stiffness was associated with markers of immune activation or microbial translocation (MT). A retrospective case-control study of subjects with evidence of liver stiffness as defined by a transient elastography stiffness measurement ≥9.3 kPa (cases=133) and normal controls (n=133) from Rakai, Uganda was performed. Cases were matched to controls by age, gender, HIV, hepatitis B virus (HBV), and highly active antiretroviral therapy (HAART) status. Lipopolysaccharide (LPS), endotoxin IgM antibody, soluble CD14 (sCD14), C-reactive protein (CRP), and D-dimer levels were measured. Conditional logistic regression was used to estimate adjusted matched odds ratios (adjMOR) and 95% confidence intervals. Higher sCD14 levels were associated with a 19% increased odds of liver stiffness (adjMOR=1.19, p=0.002). In HIV-infected individuals, higher sCD14 levels were associated with a 54% increased odds of having liver stiffness (adjMOR=1.54, p<0.001); however, the opposite was observed in HIV-negative individuals (adjMOR=0.57, p=0.001). No other biomarker was significantly associated with liver stiffness, and only one subject was found to have detectable LPS. Liver stiffness in HIV-infected Ugandans is associated with increased sCD14 indicative of monocyte activation in the absence of viral hepatitis or microbial translocation, and suggests that HIV may be directly involved in liver disease.

  6. Liver Stiffness Is Associated With Monocyte Activation in HIV-Infected Ugandans Without Viral Hepatitis

    PubMed Central

    Wendel, Sarah K.; Grabowski, Mary K.; Ocama, Ponsiano; Kiggundu, Valerian; Bbosa, Francis; Boaz, Iga; Balagopal, Ashwin; Reynolds, Steven J.; Gray, Ronald H.; Serwadda, David; Kirk, Gregory D.; Quinn, Thomas C.; Stabinski, Lara

    2013-01-01

    Abstract A high prevalence of liver stiffness, as determined by elevated transient elastography liver stiffness measurement, was previously found in a cohort of HIV-infected Ugandans in the absence of chronic viral hepatitis. Given the role of immune activation and microbial translocation in models of liver disease, a shared immune mechanism was hypothesized in the same cohort without other overt causes of liver disease. This study examined whether HIV-related liver stiffness was associated with markers of immune activation or microbial translocation (MT). A retrospective case-control study of subjects with evidence of liver stiffness as defined by a transient elastography stiffness measurement ≥9.3 kPa (cases=133) and normal controls (n=133) from Rakai, Uganda was performed. Cases were matched to controls by age, gender, HIV, hepatitis B virus (HBV), and highly active antiretroviral therapy (HAART) status. Lipopolysaccharide (LPS), endotoxin IgM antibody, soluble CD14 (sCD14), C-reactive protein (CRP), and D-dimer levels were measured. Conditional logistic regression was used to estimate adjusted matched odds ratios (adjMOR) and 95% confidence intervals. Higher sCD14 levels were associated with a 19% increased odds of liver stiffness (adjMOR=1.19, p=0.002). In HIV-infected individuals, higher sCD14 levels were associated with a 54% increased odds of having liver stiffness (adjMOR=1.54, p<0.001); however, the opposite was observed in HIV-negative individuals (adjMOR=0.57, p=0.001). No other biomarker was significantly associated with liver stiffness, and only one subject was found to have detectable LPS. Liver stiffness in HIV-infected Ugandans is associated with increased sCD14 indicative of monocyte activation in the absence of viral hepatitis or microbial translocation, and suggests that HIV may be directly involved in liver disease. PMID:23548102

  7. Materials analogue of zero-stiffness structures

    NASA Astrophysics Data System (ADS)

    Kumar, Arun; Subramaniam, Anandh

    2011-04-01

    Anglepoise lamps and certain tensegrities are examples of zero-stiffness structures. These structures are in a state of neutral equilibrium with respect to changes in configuration of the system. Using Eshelby's example of an edge dislocation in a thin plate that can bend, we report the discovery of a non-trivial new class of material structures as an analogue to zero-stiffness structures. For extended positions of the edge dislocation in these structures, the dislocation experiences a zero image force. Salient features of these material structures along with the key differences from conventional zero-stiffness structures are pointed out.

  8. The relationship between fibroblast growth and the dynamic stiffnesses of a DNA crosslinked hydrogel.

    PubMed

    Jiang, Frank X; Yurke, Bernard; Schloss, Rene S; Firestein, Bonnie L; Langrana, Noshir A

    2010-02-01

    The microenvironment of cells is dynamic and undergoes remodeling with time. This is evident in development, aging, pathological processes, and at tissue-biomaterial interfaces. But in contrast, the majority of the biomimetic materials have static properties. Here, we show that a previously developed DNA crosslinked hydrogel circumvents the need of environmental factors and undergoes controlled stiffness change via DNA delivery, a feasible approach to initiate property changes in vivo, different from previous attempts. Two types of fibroblasts, L929 and GFP, were subject to the alterations in substrate rigidity presented in the hydrogels. Our results show that exogenous DNA does not cause appreciable cell shape change. Cells do respond to mechanical alterations as demonstrated in the cell projection area and polarity (e.g., Soft vs. Soft-->Medium), and the responses vary depending on magnitude (e.g., Soft-->Medium vs. Soft-->Stiff) and range of stiffness changes (e.g., Soft-->Medium vs. Medium-->Stiff). The two types of fibroblasts share specific responses in common (e.g., Soft-->Medium), while differ in others (e.g., Medium-->Stiff). For each cell type, the projection area and polarity respond differently. This approach provides insight into pathology (e.g., cancer) and tissue functioning, and assists in designing biomaterials with controlled dynamic stiffness by choosing the range and magnitude of stiffness change.

  9. “Smooth Muscle Cell Stiffness Syndrome”—Revisiting the Structural Basis of Arterial Stiffness

    PubMed Central

    Sehgel, Nancy L.; Vatner, Stephen F.; Meininger, Gerald A.

    2015-01-01

    In recent decades, the pervasiveness of increased arterial stiffness in patients with cardiovascular disease has become increasingly apparent. Though, this phenomenon has been well documented in humans and animal models of disease for well over a century, there has been surprisingly limited development in a deeper mechanistic understanding of arterial stiffness. Much of the historical literature has focused on changes in extracellular matrix proteins—collagen and elastin. However, extracellular matrix changes alone appear insufficient to consistently account for observed changes in vascular stiffness, which we observed in our studies of aortic stiffness in aging monkeys. This led us to examine novel mechanisms operating at the level of the vascular smooth muscle cell (VSMC)—that include increased cell stiffness and adhesion to extracellular matrix—which that may be interrelated with other mechanisms contributing to arterial stiffness. We introduce these observations as a new concept—the Smooth Muscle Cell Stiffness Syndrome (SMCSS)—within the field of arterial stiffness and posit that stiffening of vascular cells impairs vascular function and may contribute stiffening to the vasculature with aging and cardiovascular disease. Importantly, this review article revisits the structural basis of arterial stiffness in light of these novel findings. Such classification of SMCSS and its contextualization into our current understanding of vascular mechanics may be useful in the development of strategic therapeutics to directly target arterial stiffness. PMID:26635621

  10. Evaluation of aortic stiffness in children with chronic renal failure.

    PubMed

    Bakiler, Ali Rahmi; Yavascan, Onder; Harputluoglu, Nilgun; Kara, Orhan Deniz; Aksu, Nejat

    2007-11-01

    The measurement of aortic stiffness (As) [aortic strain (S), pressure strain elastic modulus (Ep) and pressure strain normalized by diastolic pressure (Ep*)] is suggested as an excellent marker of subclinical arterial sclerosis. We aimed to investigate the presence of As and to determine the relationship between As and some risk factors in children with chronic renal failure (CRF). Twenty-six pre-dialysis (PreD) [female/male (F/M) 7/19] patients and 23 chronic peritoneal dialysis (CPD) (F/M 13/10) patients were assessed. Twenty-nine healthy children were selected as a control group (F/M 14/15). We determined anemia, abnormal calcium/phosphate metabolism, hypertension, diastolic dysfunction, increased left ventricular mass (LVM), hypertriglyceridemia, increased stiffness (Ep, Ep*), and decreased strain (S) in the CRF (PreD and CPD) group compared with the controls (P < 0.05). Presence of renal disease, LVM and usage of angiotensin-converting enzyme inhibitor (ACE-I) in all groups; female gender, duration of disease and the usage of anti-hypertensive drug therapy in CRF patients; and LVM and LVM index in healthy children were found to be independent predictors for aortic stiffness and/or strain. In conclusion, CRF is associated with significant arterial functional abnormalities in uremic children and not controlled by dialysis treatment. These results suggest that, even in young children, uremia has a profound impact on arterial function.

  11. Is passive metatarsophalangeal joint stiffness related to leg stiffness, vertical stiffness and running economy during sub-maximal running?

    PubMed

    Man, Hok Sum; Lam, Wing Kai; Lee, Justin; Capio, Catherine M; Leung, Aaron Kam Lun

    2016-09-01

    This study examined whether passive metatarsophalangeal joints (MPJ) stiffness was associated with leg stiffness (Kleg) vertical stiffness (Kvert) and running economy (RE) during sub-maximal running. Nine male experienced runners underwent passive MPJ stiffness measurements in standing and sitting positions followed by sub-maximal running on an instrumented treadmill. With the individual foot position properly aligned, the MPJ passive stiffness in both sitting (MPJsit) and standing positions (MPJstand) were measured with a computerized dynamometer. Data were collected at a running speed of 2.78m/s, representing a stabilized level of energy expenditure. Pedar pressure insole was used to determine the contact time (tc) and peak reaction force for the calculation of Kleg and Kvert. A respiratory gas analysis system was used to estimate the RE. Bivariate correlation test was performed to examine the correlation among MPJ stiffness, contact time, Kleg, Kvert, and RE. The results showed that MPJsit and MPJstand were inversely correlated with RE (p=0.04, r=-0.68 to -0.69), suggesting that stiffer MPJ improves RE. In addition, MPJsit was correlated positively with Kleg (p<0.01, r=0.87),Kvert (p=0.03, r=0.70) but inversely with tc (p=0.02, r=-0.76), while MPJstand was correlated positively with the Kvert (p=0.02, r=0.77). These findings suggested that strength of toe plantar flexors provides stability and agility in the stance phase for more effective and faster forward movement.

  12. On a high-potential variable flexural stiffness device

    NASA Astrophysics Data System (ADS)

    Henke, Markus; Gerlach, Gerald

    2013-05-01

    There are great efforts in developing effective composite structures for lightweight constructions for nearly every field of engineering. This concerns for example aeronautics and spacecrafts, but also automotive industry and energy harvesting applications. Modern concepts of lightweight components try to make use of structures with properties which can be adjusted in a controllable was. However, classic composite materials can only slightly adapt to varying environmental conditions because most materials, like carbon or glass-fiber composites show properties which are time-constant and not changeable. This contribution describes the development, the potential and the limitations of novel smart, self-controlling structures which can change their mechanical properties - e.g. their flexural stiffness - by more then one order of magnitude. These structures use a multi-layer approach with a 10-layer stack of 0.75 mm thick polycarbonate. The set-up is analytically described and its mechanical behavior is predicted by finite element analysis done with ABAQUS. The layers are braided together by an array of shape memory alloy (SMA) wires, which can be activated independently. Depending on the temperature applied by the electrical current flowing through the wires and the corresponding contraction the wires can tightly clamp the layers so that they cannot slide against each other due to friction forces. In this case the multilayer acts as rigid beam with high stiffness. If the friction-induced shear stress is smaller than a certain threshold, then the layers can slide over each other and the multilayer becomes compliant under bending load. The friction forces between the layers and, hence, the stiffness of the beam is controlled by the electrical current through the wires. The more separate parts of SMA wires the structure has the larger is the number of steps of stiffness changes of the flexural beam.

  13. Arterial Stiffness in Patients Taking Second-generation Antipsychotics

    PubMed Central

    Fındıklı, Ebru; Gökçe, Mustafa; Nacitarhan, Vedat; Camkurt, Mehmet Akif; Fındıklı, Hüseyin Avni; Kardaş, Selçuk; Şahin, Merve Coşgun; Karaaslan, Mehmet Fatih

    2016-01-01

    Objective That treatment with second-generation antipsychotics (SGAs) causes metabolic side effects and atherosclerosis in patients with schizophrenia and bipolar disorder (BD) is well-known. Increased arterial stiffness is an important marker of arteriosclerosis and has been identified as an independent risk factor for cardiovascular diseases. We measured pulse wave velocity (PWV) as a marker of arteriosclerosis in patients with schizophrenia and BD who use SGAs. Methods Patients and controls were collected from our psychiatry outpatient clinics or family medicine. Mental illness was diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition. Mean age, gender, systolic and diastolic blood pressure, body mass index, Framingham risk score (FRS), etc. were determined. Simultaneous electrocardiography and pulse wave were recorded with an electromyography device. The photo-plethysmographic method was used to record the pulse wave. Inclusion criteria included use of SGAs for at least the last six months. Patients with diseases that are known to cause stiffness and the use of typical antipsychotics were excluded. Results Ninety-six subject (56 patients, 40 controls) were included in our study. There were 49 females, 47 males. Patients had schizophrenia (n=17) and BD (n=39). Their treatments were quetiapine (n=15), risperidone (n=13), olanzapine (n=15), and aripiprazole (n=13). Although differences in mean age, gender, and FRS in the patient and control groups were not statistically significant (p=1), PWV was greater in patients in the antipsychotic group (p=0.048). Conclusion This study supported the liability to stiffness in patients with schizophrenia and BD. Using SGAs may contribute to arterial stiffness in these patients. PMID:27776389

  14. Exercise, Vascular Stiffness, and Tissue Transglutaminase

    PubMed Central

    Steppan, Jochen; Sikka, Gautam; Jandu, Simran; Barodka, Viachaslau; Halushka, Marc K.; Flavahan, Nicholas A.; Belkin, Alexey M.; Nyhan, Daniel; Butlin, Mark; Avolio, Alberto; Berkowitz, Dan E.; Santhanam, Lakshmi

    2014-01-01

    Background Vascular aging is closely associated with increased vascular stiffness. It has recently been demonstrated that decreased nitric oxide (NO)‐induced S‐nitrosylation of tissue transglutaminase (TG2) contributes to age‐related vascular stiffness. In the current study, we tested the hypothesis that exercise restores NO signaling and attenuates vascular stiffness by decreasing TG2 activity and cross‐linking in an aging rat model. Methods and Results Rats were subjected to 12 weeks of moderate aerobic exercise. Aging was associated with diminished phosphorylated endothelial nitric oxide synthase and phosphorylated vasodilator‐stimulated phosphoprotein abundance, suggesting reduced NO signaling. TG2 cross‐linking activity was significantly increased in old animals, whereas TG2 abundance remained unchanged. These alterations were attenuated in the exercise cohort. Simultaneous measurement of blood pressure and pulse wave velocity (PWV) demonstrated increased aortic stiffness in old rats, compared to young, at all values of mean arterial pressure (MAP). The PWV‐MAP correlation in the old sedentary and old exercise cohorts was similar. Tensile testing of the vessels showed increased stiffness of the aorta in the old phenotype with a modest restoration of mechanical properties toward the young phenotype with exercise. Conclusions Increased vascular stiffness during aging is associated with decreased TG2 S‐nitrosylation, increased TG2 cross‐linking activity, and increased vascular stiffness likely the result of decreased NO bioavailability. In this study, a brief period of moderate aerobic exercise enhanced NO signaling, attenuated TG cross‐linking activity, and reduced ex vivo tensile properties, but failed to reverse functional vascular stiffness in vivo, as measured by PWV. PMID:24721796

  15. [A contribution to "stiff man" syndrome].

    PubMed

    Belian, T; Harms, L

    1990-05-01

    A patient with the clinical symptoms of the "Stiff-man"-syndrome, but an atypical course was introduced. Symptoms and course were compared with similar cases mentioned in literature. The "Stiff-man"-syndrome is probably a disease of central origin affecting the relationship between inhibitory and excitatory regulation of the muscle tonus, especially the exteroceptive reflex mechanisms. Several pathological processes of the CNS can be held responsible for the disturbance of the balance in this regulatory system. PMID:2167489

  16. OroSTIFF: Face-referenced measurement of perioral stiffness in health and disease.

    PubMed

    Chu, Shin-Ying; Barlow, Steven M; Kieweg, Douglas; Lee, Jaehoon

    2010-05-28

    A new device and automated measurement technology known as OroSTIFF is described to characterize non-participatory perioral stiffness in healthy adults for eventual application to patients with orofacial movement disorders associated with neuromotor disease, traumatic injury, or congenital clefts of the upper lip. Previous studies of perioral biomechanics required head stabilization for extended periods of time during measurement, which precluded sampling patients with involuntary body/head movements (dyskinesias), or pediatric subjects. The OroSTIFF device is face-referenced and avoids the complications associated with head-restraint. Supporting data of non-participatory perioral tissue stiffness using OroSTIFF are included from 10 male and 10 female healthy subjects. The OroSTIFF device incorporates a pneumatic glass air cylinder actuator instrumented for pressure, and an integrated subminiature displacement sensor to encode lip aperture. Perioral electromyograms were simultaneously sampled to confirm passive muscle state for the superior and inferior divisions of the orbicularis oris muscles. Perioral stiffness, derived as a quotient from resultant force (DeltaF) and interangle span (DeltaX), was modeled with multilevel regression techniques. Real-time calculation of the perioral stiffness function demonstrated a significant quadratic relation between imposed interangle stretch and resultant force. This stiffness growth function also differed significantly between males and females. This study demonstrates the OroSTIFF 'proof-of-concept' for cost-effective non-invasive stimulus generation and derivation of perioral stiffness in a group of healthy unrestrained adults, and a case study to illustrate the dose-dependent effects of Levodopa on perioral stiffness in an individual with advanced Parkinson's disease who exhibited marked dyskinesia and rigidity.

  17. Effect of in vitro aging on the stiffness of bioabsorbable fixation plates.

    PubMed

    Zinelis, Spiros; Venetis, Gregory; Eliades, Theodoros; Dimitrakopoulos, Ioannis; Eliades, Georgios

    2011-01-01

    The purpose of this study was to investigate the effect of in vitro aging on the stiffness of bioabsorbable fixation plates. Twenty-four polylactic/polyglycolic acid plates (LactoSorb; Lorenz, Jacksonville, FL) were divided in 3 groups of 8 specimens each. Group A served as control, and groups B and C were immersed in 0.1 M lactic acid for 15 and 30 days, respectively. All specimens were subjected to a 3-point bending test, using a universal testing machine, and the stiffness of each specimen was estimated. When analyzed with one-way analysis of variance, no difference was observed for the control and in vitro-aged specimens with regard to stiffness. Long-term (30 d) in vitro aging of poly-L-lactic acid bioabsorbable fixation plates does not seem to significantly affect the stiffness of the material as derived from a 3-point bending test.

  18. Roll stabilisation of road vehicles using a variable stiffness suspension system

    NASA Astrophysics Data System (ADS)

    Anubi, Olugbenga Moses; Crane, Carl D., III

    2013-12-01

    A variable stiffness architecture is used in the suspension system to counteract the body roll moment, thereby enhancing the roll stability of the vehicle. The variation of stiffness concept uses the 'reciprocal actuation' to effectively transfer energy between a vertical traditional strut and a horizontal oscillating control mass, thereby improving the energy dissipation of the overall suspension. The lateral dynamics of the system is developed using a bicycle model. The accompanying roll dynamics are also developed and validated using experimental data. The positions of the left and right control masses are sequentially allocated to reduce the effective body roll and roll rate. Simulation results show that the resulting variable stiffness suspension system has more than 50% improvement in roll response over the traditional constant stiffness counterparts. The simulation scenarios examined is the fishhook manoeuvre.

  19. Numerical assessment of the stiffness index.

    PubMed

    Epstein, Sally; Vergnaud, Anne-Claire; Elliott, Paul; Chowienczyk, Phil; Alastruey, Jordi

    2014-01-01

    Elevated systemic vascular stiffness is associated with increased risk of cardiovascular disease. It has been suggested that the time difference between the two characteristic peaks of the digital volume pulse (DVP) measured at the finger using photoplethysmography is related to the stiffness of the arterial tree, and inversely proportional to the stiffness index (SI). However, the precise physical meaning of the SI and its relation to aortic pulse wave velocity (aPWV) is yet to be ascertained. In this study we investigated numerically the effect of changes in arterial wall stiffness, peripheral resistances, peripheral compliances or peripheral wave reflections on the SI and aPWV. The SI was calculated from the digital area waveform simulated using a nonlinear one-dimensional model of pulse wave propagation in a 75-artery network, which includes the larger arteries of the hand. Our results show that aPWV is affected by changes in aortic stiffness, but the SI is primarily affected by changes in the stiffness of all conduit vessels. Thus, the SI is not a direct substitute for aPWV. Moreover, our results suggest that peripheral reflections in the upper body delay the time of arrival of the first peak in the DVP. The second peak is predominantly caused by the impedance mismatch within the 75 arterial segments, rather than by peripheral reflections.

  20. Stiffness of Railway Soil-Steel Structures

    NASA Astrophysics Data System (ADS)

    Machelski, Czesław

    2015-12-01

    The considerable influence of the soil backfill properties and that of the method of compacting it on the stiffness of soil-steel structures is characteristic of the latter. The above factors (exhibiting randomness) become apparent in shell deformation measurements conducted during construction and proof test loading. A definition of soil-shell structure stiffness, calculated on the basis of shell deflection under the service load, is proposed in the paper. It is demonstrated that the stiffness is the inverse of the deflection influence function used in structural mechanics. The moving load methodology is shown to be useful for testing, since it makes it possible to map the shell deflection influence line also in the case of group loads (concentrated forces), as in bridges. The analyzed cases show that the shell's span, geometry (static scheme) and the height of earth fill influence the stiffness of the structure. The soil-steel structure's characteristic parameter in the form of stiffness k is more suitable for assessing the quality of construction works than the proposed in code geometric index ω applied to beam structures. As shown in the given examples, parameter k is more effective than stiffness parameter λ used to estimate the deformation of soil-steel structures under construction. Although the examples concern railway structures, the methodology proposed in the paper is suitable also for road bridges.

  1. Role of three-dimensional matrix stiffness in regulating the chemoresistance of hepatocellular carcinoma cells.

    PubMed

    Liu, Chang; Liu, Yang; Xie, Hong-Guo; Zhao, Shan; Xu, Xiao-Xi; Fan, Li-Xin; Guo, Xin; Lu, Ting; Sun, Guang-Wei; Ma, Xiao-Jun

    2015-01-01

    Hepatocellular carcinoma (HCC) was the most common primary liver cancer, and its resistance to anti-tumor drugs often caused the death of patients suffering with HCC. Matrix stiffness was reported to be closely related to tumor chemoresistance; however, the relationship between HCC drug resistance and three-dimensional (3D) matrix stiffness is still unclear at present. In this study, alginate gel (ALG) beads with controllable matrix stiffness were used to mimic tumor tissue rigidity, and the role of 3D matrix stiffness in regulating the chemoresistance of HCC cells was investigated by using these ALG beads. It was found that HCC cells in ALG beads with 105 kPa stiffness had highest resistance to paclitaxel, 5-FU, and cisplatin. Although the mechanism was still uncovered, ABC transporters and endoplasmic reticulum stress-related molecules were highly expressed in ALG bead-encapsulated HCC cells compared with two-dimensional-cultured cells, which suggested a very complex mechanism underlying HCC drug resistance in 3D culture conditions. In addition, to mimic the specific stiffness of HCC tumor tissue, or other tumor tissues in vivo, response surface methodology (RSM) was used to build up a prediction mathematical model so that ALG beads with desired matrix stiffness could be prepared by simply changing three factors: molecular weight, G content, and alginate concentration.

  2. Plyometric training effects on Achilles tendon stiffness and dissipative properties.

    PubMed

    Fouré, Alexandre; Nordez, Antoine; Cornu, Christophe

    2010-09-01

    The aim of this study was to determine the effects of 14 wk of plyometric training on mechanical properties of the Achilles tendon. Nineteen subjects were randomly assigned to trained or control group. Cross-sectional area (CSA), stiffness, and dissipation coefficient of the Achilles tendon were measured before and after the training period. In the trained group, a decrease in dissipation coefficient (-35.0%; P<0.05) and an upward trend in stiffness (+24.1%) of the Achilles tendon was found, without any changes in Achilles tendon CSA (P>0.05). Plyometric training enhances the muscular tension transmission mainly through a reduction in energy dissipated by the tendon. The lack of changes in the Achilles tendon CSA indicates that changes in mechanical properties would mainly result from a qualitative change in tendinous tissues rather than from changes in the geometry of the Achilles tendon.

  3. Dense brushes of stiff polymers or filaments in fluid flow

    NASA Astrophysics Data System (ADS)

    Römer, F.; Fedosov, D. A.

    2015-03-01

    Dense filamentous brush-like structures are present in many biological interfacial systems (e.g., glycocalyx layer in blood vessels) to control their surface properties. Such structures can regulate the softness of a surface and modify fluid flow. In this letter, we propose a theoretical model which predicts quantitatively flow-induced deformation of a dense brush of stiff polymers or filaments, whose persistence length is larger or comparable to their contour length. The model is validated by detailed mesoscopic simulations and characterizes different contributions to brush deformation including hydrodynamic friction due to flow and steric excluded-volume interactions between grafted filaments. This theoretical model can be used to describe the effect of a stiff-polymer brush on fluid flow and to aid in the quantification of experiments.

  4. Tunable elastic stiffness of plasma-sprayed zirconia coatings

    NASA Astrophysics Data System (ADS)

    Bamberg, Joachim; Schwaminger, Christian

    1999-07-01

    Plasma-sprayed zirconia is widely used in aero-engines as thermal barrier coating material. The material has an open porosity and a network of very thin microcracks. The porosity and the microcracks give rise to the low elastic stiffness. When the plasm sprayed zirconia is immersed in a liquid the microcracks can be filled with the liquid by capillary forces. Although there is only a small amount of infiltrated material the zirconia shows a strong increase in elastic stiffness. We have measured the elastic behavior after infiltration and as function of temperature by ultrasonic pulse echo technique. It could be observed that the solidification of the infiltrated fluid at lower temperatures leads to a further increase of the elastic stiffness. The temperature controlled liquid-solid phase transition can therefore be used to change reversibly the elastic properties of this ceramic material. The desired switching temperature can be chosen by appropriate fluids. A possible application of this material is the vibration damping of coated structures by temperature controlled changing of resonance frequencies.

  5. Conceptual study of the damping of large space structures using large-stroke adaptive stiffness cables

    NASA Technical Reports Server (NTRS)

    Thorwald, Gregory; Mikulas, Martin M., Jr.

    1992-01-01

    The concept of a large-stroke adaptive stiffness cable-device for damping control of space structures with large mass is introduced. The cable is used to provide damping in several examples, and its performance is shown through numerical simulation results. Displacement and velocity information of how the structure moves is used to determine when to modify the cable's stiffness in order to provide a damping force.

  6. Joint stiffness of the ankle and the knee in running.

    PubMed

    Günther, Michael; Blickhan, Reinhard

    2002-11-01

    The spring-mass model is a valid fundament to understand global dynamics of fast legged locomotion under gravity. The underlying concept of elasticity, implying leg stiffness as a crucial parameter, is also found on lower motor control levels, i.e. in muscle-reflex and muscle-tendon systems. Therefore, it seems reasonable that global leg stiffness emerges from local elasticity established by appropriate joint torques. A recently published model of an elastically operating, segmented leg predicts that proper adjustment of joint elasticities to the leg geometry and initial conditions of ground contact provides internal leg stability. Another recent study suggests that in turn the leg segmentation and the initial conditions may be a consequence of metabolic and bone stress constraints. In this study, the theoretical predictions were verified experimentally with respect to initial conditions and elastic joint characteristics in human running. Kinematics and kinetics were measured and the joint torques were estimated by inverse dynamics. Stiffnesses and elastic nonlinearities describing the resulting joint characteristics were extracted from parameter fits. Our results clearly support the theoretical predictions: the knee joint is always stiffer and more extended than the ankle joint. Moreover, the knee torque characteristic on the average shows the higher nonlinearity. According to literature, the leg geometry is a consequence of metabolic and material stress limitations. Adapted to this given geometry, the initial joint angle conditions in fast locomotion are a compromise between metabolic and control effort minimisation. Based on this adaptation, an appropriate joint stiffness ratio between ankle and knee passively safeguards the internal leg stability. The identified joint nonlinearities contribute to the linearisation of the leg spring.

  7. Chronic intrauterine pulmonary hypertension increases main pulmonary artery stiffness and adventitial remodeling in fetal sheep

    PubMed Central

    Morgan, Matthew R.; Galambos, Csaba; Hunter, Kendall S.; Abman, Steven H.

    2014-01-01

    Persistent pulmonary hypertension of the newborn (PPHN) is a clinical syndrome that is characterized by high pulmonary vascular resistance due to changes in lung vascular growth, structure, and tone. PPHN has been primarily considered as a disease of the small pulmonary arteries (PA), but proximal vascular stiffness has been shown to be an important predictor of morbidity and mortality in other diseases associated with pulmonary hypertension (PH). The objective of this study is to characterize main PA (MPA) stiffness in experimental PPHN and to determine the relationship of altered biomechanics of the MPA with changes in extracellular matrix (ECM) content and orientation of collagen and elastin fibers. MPAs were isolated from control and PPHN fetal sheep model and were tested by planar biaxial testing to measure stiffness in circumferential and axial vessel orientations. Test specimens were fixed for histological assessments of the vascular wall ECM constituents collagen and elastin. MPAs from PPHN sheep had increased mechanical stiffness (P < 0.05) and altered ECM remodeling compared with control MPA. A constitutive mathematical model and histology demonstrated that PPHN vessels have a smaller contribution of elastin and a greater role for collagen fiber engagement compared with the control arteries. We conclude that exposure to chronic hemodynamic stress in late-gestation fetal sheep increases proximal PA stiffness and alters ECM remodeling. We speculate that proximal PA stiffness further contributes to increased right ventricular impedance in experimental PPHN, which contributes to abnormal transition of the pulmonary circulation at birth. PMID:25326575

  8. Medial Tibiofemoral-Joint Stiffness in Males and Females Across the Lifespan

    PubMed Central

    Aronson, Patricia; Rijke, Arie; Hertel, Jay; Ingersoll, Christopher D.

    2014-01-01

    Context: Analyzing ligament stiffness between males and females at 3 maturational stages across the lifespan may provide insight into whether changes in ligament behavior with aging may contribute to joint laxity. Objective: To compare the stiffness of the medial structures of the tibiofemoral joint and the medial collateral ligament to determine if there are differences at 3 distinct ages and between the sexes. Design: Cross-sectional study. Setting: Laboratory. Patients or Other Participants: A total of 108 healthy and physically active volunteers with no previous knee surgery, no acute knee injury, and no use of exogenous hormones in the past 6 months participated. They were divided into 6 groups based on sex and age (8–10, 18–40, 50–75 years). Main Outcome Measure(s): Ligament stiffness of the tibiofemoral joint was measured with an arthrometer in 0° and 20° of tibiofemoral-joint flexion. The slope values of the force-strain line that represents stiffness of the medial tibiofemoral joint at 0° and the medial collateral ligament at 20° of flexion were obtained. Results: When height and mass were controlled, we found a main effect (P < .001) for age group: the 8- to 10-year olds were less stiff than both the 18- to 40- and the 50- to 75-year-old groups. No effects of sex or tibiofemoral-joint position on stiffness measures were noted when height and mass were included as covariates. Conclusions: Prepubescent medial tibiofemoral-joint stiffness was less than postpubescent knee stiffness. Medial tibiofemoral-joint stiffness was related to height and mass after puberty in men and women. PMID:24955624

  9. Medial Tibiofemoral-Joint Stiffness in Males and Females Across the Lifespan.

    PubMed

    Aronson, Patricia; Rijke, Arie; Hertel, Jay; Ingersoll, Christopher D

    2014-02-12

    Context : Analyzing ligament stiffness between males and females at 3 maturational stages across the lifespan may provide insight into whether changes in ligament behavior with aging may contribute to joint laxity. Objective : To compare the stiffness of the medial structures of the tibiofemoral joint and the medial collateral ligament to determine if there are differences at 3 distinct ages and between the sexes. Design : Cross-sectional study. Setting : Laboratory. Patients or Other Participants : A total of 108 healthy and physically active volunteers with no previous knee surgery, no knee injury, and no use of exogenous hormones in the past 6 months participated. They were divided into 6 groups based on sex and age (8-10, 18-40, 50-75 years). Main Outcome Measure(s) : Ligament stiffness of the tibiofemoral joint was measured with an arthrometer in 0° and 20° of tibiofemoral-joint flexion. The slope values of the force-strain line that represents stiffness of the medial tibiofemoral joint at 0° and the medial collateral ligament at 20° of flexion were obtained. Results : When height and mass were controlled, we found a main effect (P < .001) for age group: the 8- to 10-year olds were less stiff than both the 18- to 40- and the 50- to 75-year-old groups. No effects of sex or tibiofemoral-joint position on stiffness measures were noted when height and mass were included as covariates. Conclusions : Prepubescent medial tibiofemoral-joint stiffness was less than postpubescent knee stiffness. Medial tibiofemoral-joint stiffness was related to height and mass after puberty in men and women.

  10. Waves in geomaterials exhibiting negative stiffness behaviour

    NASA Astrophysics Data System (ADS)

    Esin, Maxim; Dyskin, Arcady; Pasternak, Elena

    2016-04-01

    Negative stiffness denotes the type of material behaviour when the force applied to the body decreases the body's deformation increases. Some geomaterials, for instance, rocks, demonstrate behaviour of this type at certain loads: during the compression tests the loading curves exhibit descending branch (post-peak softening). One of the possible mechanisms of the negative stiffness appearance in geomaterials is rotation of non-spherical grains. It is important to emphasize that in this case the descending branch may be reversible given that the testing machine is stiff enough (in general case it means an importance of boundary conditions). Existence of geomaterials with a negative modulus associated with rotations may have significant importance. In particular, important is understanding of the wave propagation in such materials. We study the stability of geomaterials with negative stiffness inclusions and wave propagation in it using two approaches: Cosserat continuum and discrete mass-spring models. In both cases we consider the rotational degrees of freedom in addition to the conventional translational ones. We show that despite non positiveness of the energy the materials with negative stiffness elements can be stable if certain conditions are met. In the case of Cosserat continuum the Cosserat shear modulus (the modulus relating the non-symmetrical part of shear stress and internal rotations) is allowed to assume negative values as long as its value does not exceed the value of the standard (positive) shear modulus. In the case of discrete mass-spring systems (with translational and rotational springs) the concentration of negative stiffness springs and the absolute values of negative spring stiffness are limited. The critical concentration when the system loses stability and the amplitude of the oscillations tends to infinity is equal to 1/2 and 3/5 for two- and three-dimensional cases respectively.

  11. Stiff-person syndrome with amphiphysin antibodies

    PubMed Central

    Murinson, Beth B.; Guarnaccia, Joseph B.

    2008-01-01

    Background: Stiff-person syndrome (SPS), formerly Stiff-man syndrome, is a rare autoimmune disease usually exhibiting severe spasms and thoracolumbar stiffness, with very elevated glutamic acid decarboxylase antibodies (GAD Ab). A paraneoplastic variant, less well characterized, is associated with amphiphysin antibodies (amphiphysin Ab). The objective of this study was to identify distinctive clinical features of amphiphysin Ab-associated SPS. Methods: Records associated with 845 sera tested in the Yale SPS project were examined, and 621 patients with clinically suspected SPS were included in the study. Clinical characteristics were assessed with correction for multiple comparisons. Results: In all, 116 patients had GAD antibodies and 11 patients had amphiphysin Ab; some clinical information was available for 112 and 11 of these patients, respectively. Patients with amphiphysin Ab-associated SPS were exclusively female; mean age was 60. All except one had breast cancer; none had diabetes. Compared to patients with GAD Ab-associated SPS, those with amphiphysin Ab were older (p = 0.02) and showed a dramatically different stiffness pattern (p < 0.0000001) with cervical involvement more likely, p ≤ 0.001. Electromyography showed continuous motor unit activity or was reported positive in eight. Benzodiazepines at high dose (average 50 mg/day diazepam) were partially effective. Four patients were steroid responsive and tumor excision with chemotherapy produced marked clinical improvement in three of five patients. Conclusions: Amphiphysin Ab-associated stiff-person syndrome is strongly associated with cervical region stiffness, female sex, breast cancer, advanced age, EMG abnormalities, and benzodiazepine responsiveness. The condition may respond to steroids and can dramatically improve with cancer treatment. GLOSSARY EAE = experimental autoimmune encephalitis; GAD Ab = glutamic acid decarboxylase antibodies; ICC = immunocytochemistry; PERM = progressive variant with

  12. Does short-term whole-body vibration training affect arterial stiffness in chronic stroke? A preliminary study.

    PubMed

    Yule, Christie E; Stoner, Lee; Hodges, Lynette D; Cochrane, Darryl J

    2016-03-01

    [Purpose] Previous studies have shown that stroke is associated with increased arterial stiffness that can be diminished by a program of physical activity. A novel exercise intervention, whole-body vibration (WBV), is reported to significantly improve arterial stiffness in healthy men and older sedentary adults. However, little is known about its efficacy in reducing arterial stiffness in chronic stroke. [Subjects and Methods] Six participants with chronic stroke were randomly assigned to 4 weeks of WBV training or control followed by cross-over after a 2-week washout period. WBV intervention consisted of 3 sessions of 5 min intermittent WBV per week for 4 weeks. Arterial stiffness (carotid arterial stiffness, pulse wave velocity [PWV], pulse and wave analysis [PWA]) were measured before/after each intervention. [Results] No significant improvements were reported with respect to carotid arterial stiffness, PWV, and PWA between WBV and control. However, carotid arterial stiffness showed a decrease over time following WBV compared to control, but this was not significant. [Conclusion] Three days/week for 4 weeks of WBV seems too short to elicit appropriate changes in arterial stiffness in chronic stroke. However, no adverse effects were reported, indicating that WBV is a safe and acceptable exercise modality for people with chronic stroke.

  13. Does short-term whole-body vibration training affect arterial stiffness in chronic stroke? A preliminary study

    PubMed Central

    Yule, Christie E.; Stoner, Lee; Hodges, Lynette D.; Cochrane, Darryl J.

    2016-01-01

    [Purpose] Previous studies have shown that stroke is associated with increased arterial stiffness that can be diminished by a program of physical activity. A novel exercise intervention, whole-body vibration (WBV), is reported to significantly improve arterial stiffness in healthy men and older sedentary adults. However, little is known about its efficacy in reducing arterial stiffness in chronic stroke. [Subjects and Methods] Six participants with chronic stroke were randomly assigned to 4 weeks of WBV training or control followed by cross-over after a 2-week washout period. WBV intervention consisted of 3 sessions of 5 min intermittent WBV per week for 4 weeks. Arterial stiffness (carotid arterial stiffness, pulse wave velocity [PWV], pulse and wave analysis [PWA]) were measured before/after each intervention. [Results] No significant improvements were reported with respect to carotid arterial stiffness, PWV, and PWA between WBV and control. However, carotid arterial stiffness showed a decrease over time following WBV compared to control, but this was not significant. [Conclusion] Three days/week for 4 weeks of WBV seems too short to elicit appropriate changes in arterial stiffness in chronic stroke. However, no adverse effects were reported, indicating that WBV is a safe and acceptable exercise modality for people with chronic stroke. PMID:27134400

  14. Matrix stiffness reverses the effect of actomyosin tension on cell proliferation

    PubMed Central

    Mih, Justin D.; Marinkovic, Aleksandar; Liu, Fei; Sharif, Asma S.; Tschumperlin, Daniel J.

    2012-01-01

    Summary The stiffness of the extracellular matrix exerts powerful effects on cell proliferation and differentiation, but the mechanisms transducing matrix stiffness into cellular fate decisions remain poorly understood. Two widely reported responses to matrix stiffening are increases in actomyosin contractility and cell proliferation. To delineate their relationship, we modulated cytoskeletal tension in cells grown across a physiological range of matrix stiffnesses. On both synthetic and naturally derived soft matrices, and across a panel of cell types, we observed a striking reversal of the effect of inhibiting actomyosin contractility, switching from the attenuation of proliferation on rigid substrates to the robust promotion of proliferation on soft matrices. Inhibiting contractility on soft matrices decoupled proliferation from cytoskeletal tension and focal adhesion organization, but not from cell spread area. Our results demonstrate that matrix stiffness and actomyosin contractility converge on cell spreading in an unexpected fashion to control a key aspect of cell fate. PMID:23097048

  15. Improvement of bias stability for a micromachined gyroscope based on dynamic electrical balancing of coupling stiffness

    NASA Astrophysics Data System (ADS)

    Su, Jianbin; Xiao, Dingbang; Wu, Xuezhong; Hou, Zhanqiang; Chen, Zhihua

    2013-07-01

    We present a dynamic electrical balancing of coupling stiffness for improving the bias stability of micromachined gyroscopes, which embeds the coupling stiffness in a closed-loop system to make the micromachined gyroscope possess more robust bias stability by suppressing the variation of coupling stiffness. The effect of the dynamic electrical balancing control is theoretically analyzed and implemented using a silicon micromachined gyroscope as an example case. It has been experimentally shown that, comparing with open loop detection, the proposed method increased the stability of the amplitude of the mechanical quadrature signal by 38 times, and therefore improved the bias stability by 5.2 times from 89 to 17 deg/h, and the temperature stability of scale factor by 2.7 times from 622 to 231 ppm/°C. Experimental results effectively indicated the theoretical model of dynamic electrical balancing of coupling stiffness.

  16. Post-traumatic knee stiffness: surgical techniques.

    PubMed

    Pujol, N; Boisrenoult, P; Beaufils, P

    2015-02-01

    Post-traumatic knee stiffness and loss of range of motion is a common complication of injuries to the knee area. The causes of post-traumatic knee stiffness can be divided into flexion contractures, extension contractures, and combined contractures. Post-traumatic stiffness can be due to the presence of dense intra-articular adhesions and/or fibrotic transformation of peri-articular structures. Various open and arthroscopic surgical treatments are possible. A precise diagnosis and understanding of the pathology is mandatory prior to any surgical treatment. Failure is imminent if all pathologies are not addressed correctly. From a general point of view, a flexion contracture is due to posterior adhesions and/or anterior impingement. On the other hand, extension contractures are due to anterior adhesions and/or posterior impingement. This overview will describe the different modern surgical techniques for treating post-traumatic knee stiffness. Any bony impingements must be treated before soft tissue release is performed. Intra-articular stiff knees with a loss of flexion can be treated by an anterior arthroscopic arthrolysis. Extra-articular pathology causing a flexion contracture can be treated by open or endoscopic quadriceps release. Extension contractures can be treated by arthroscopic or open posterior arthrolysis. Postoperative care (analgesia, rehabilitation) is essential to maintaining the range of motion obtained intra-operatively.

  17. Leg stiffness: comparison between unilateral and bilateral hopping tasks.

    PubMed

    Brauner, Torsten; Sterzing, Thorsten; Wulf, Mathias; Horstmann, Thomas

    2014-02-01

    Leg stiffness is a predictor of athletic performance and injury and typically evaluated during bilateral hopping. The contribution of each limb to bilateral leg stiffness, however, is not well understood. This study investigated leg stiffness during unilateral and bilateral hopping to address the following research questions: (1) does the magnitude and variability of leg stiffness differ between dominant and non-dominant legs? (2) Does unilateral leg stiffness differ from bilateral leg stiffness? and (3) Is bilateral leg stiffness determined by unilateral leg stiffness? Thirty-two physically active males performed repeated hopping tests on a force platform for each of the three conditions: bilateral hopping, unilateral hopping on the dominant leg, and unilateral hopping on the non-dominant leg. Leg stiffness was estimated as the ratio of the peak vertical force and the maximum displacement using a simple 1-D mass-spring model. Neither the magnitude nor variability of leg stiffness differed between dominant and non-dominant limbs. Unilateral leg stiffness was 24% lower than bilateral stiffness and showed less variability between consecutive hops and subjects. Unilateral leg stiffness explained 76% of the variance in bilateral leg stiffness. We conclude that leg stiffness estimates during unilateral hopping are preferable for intervention studies because of their low variability. PMID:24290613

  18. Contact stiffness and damping identification for hardware-in-the-loop contact simulator with measurement delay compensation

    NASA Astrophysics Data System (ADS)

    Qi, Chenkun; Zhao, Xianchao; Gao, Feng; Ren, Anye; Sun, Qiao

    2016-06-01

    The hardware-in-the-loop (HIL) contact simulator is to simulate the contact process of two flying objects in space. The contact stiffness and damping are important parameters used for the process monitoring, compliant contact control and force compensation control. In this study, a contact stiffness and damping identification approach is proposed for the HIL contact simulation with the force measurement delay. The actual relative position of two flying objects can be accurately measured. However, the force measurement delay needs to be compensated because it will lead to incorrect stiffness and damping identification. Here, the phase lead compensation is used to reconstruct the actual contact force from the delayed force measurement. From the force and position data, the contact stiffness and damping are identified in real time using the recursive least squares (RLS) method. The simulations and experiments are used to verify that the proposed stiffness and damping identification approach is effective.

  19. Hamstrings Stiffness and Landing Biomechanics Linked to Anterior Cruciate Ligament Loading

    PubMed Central

    Blackburn, J. Troy; Norcross, Marc F.; Cannon, Lindsey N.; Zinder, Steven M.

    2013-01-01

    Context: Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks. Objective: To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury. Design: Cross-sectional study. Setting: Research laboratory. Patients or Other Participants: A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg). Intervention(s): Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests. Main Outcome Measure(s): Hamstrings stiffness was normalized to body mass (N/m·kg−1). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height. Results: Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t22 range = 1.729–2.224, P < .05). Conclusions: Greater hamstrings stiffness was associated with landing

  20. Seismic response of torsionally coupled building with passive and semi-active stiffness dampers

    NASA Astrophysics Data System (ADS)

    Mevada, Snehal V.; Jangid, R. S.

    2015-03-01

    The seismic response of single-storey, one-way asymmetric building with passive and semi-active variable stiffness dampers is investigated. The governing equations of motion are derived based on the mathematical model of asymmetric building. The seismic response of the system is obtained by numerically solving the equations of motion using state-space method under different system parameters. The switching and resetting control laws are considered for the semi-active devices. The important parameters considered are eccentricity ratio of superstructure, uncoupled lateral time period and ratio of uncoupled torsional to lateral frequency. The effects of these parameters are investigated on peak lateral, torsional and edge displacements and accelerations as well as on damper control forces. The comparative performance is investigated for asymmetric building installed with passive stiffness and semi-active stiffness dampers. It is shown that the semi-active stiffness dampers reduce the earthquake-induced displacements and accelerations significantly as compared to passive stiffness dampers. Also, the effects of torsional coupling on effectiveness of passive dampers in reducing displacements and accelerations are found to be more significant to the variation of eccentricity as compared to semi-active stiffness dampers.

  1. Local dynamic stability of spine muscle activation and stiffness patterns during repetitive lifting.

    PubMed

    Graham, Ryan B; Brown, Stephen H M

    2014-12-01

    To facilitate stable trunk kinematics, humans must generate appropriate motor patterns to effectively control muscle force and stiffness and respond to biomechanical perturbations and/or neuromuscular control errors. Thus, it is important to understand physiological variables such as muscle force and stiffness, and how these relate to the downstream production of stable spine and trunk movements. This study was designed to assess the local dynamic stability of spine muscle activation and rotational stiffness patterns using Lyapunov analyses, and relationships to the local dynamic stability of resulting spine kinematics, during repetitive lifting and lowering at varying combinations of lifting load and rate. With an increase in the load lifted at a constant rate there was a trend for decreased local dynamic stability of spine muscle activations and the muscular contributions to spine rotational stiffness; although the only significant change was for the full state space muscle activation stability (p < 0.05). With an increase in lifting rate with a constant load there was a significant decrease in the local dynamic stability of spine muscle activations and the muscular contributions to spine rotational stiffness (p ≤ 0.001 for all measures). These novel findings suggest that the stability of motor inputs and the muscular contributions to spine rotational stiffness can be altered by external task demands (load and lifting rate), and therefore are important variables to consider when assessing the stability of the resulting kinematics.

  2. Elucidating the Role of Matrix Stiffness in 3D Cell Migration and Remodeling

    PubMed Central

    Ehrbar, M.; Sala, A.; Lienemann, P.; Ranga, A.; Mosiewicz, K.; Bittermann, A.; Rizzi, S.C.; Weber, F.E.; Lutolf, M.P.

    2011-01-01

    Reductionist in vitro model systems which mimic specific extracellular matrix functions in a highly controlled manner, termed artificial extracellular matrices (aECM), have increasingly been used to elucidate the role of cell-ECM interactions in regulating cell fate. To better understand the interplay of biophysical and biochemical effectors in controlling three-dimensional cell migration, a poly(ethylene glycol)-based aECM platform was used in this study to explore the influence of matrix cross-linking density, represented here by stiffness, on cell migration in vitro and in vivo. In vitro, the migration behavior of single preosteoblastic cells within hydrogels of varying stiffness and susceptibilities to degradation by matrix metalloproteases was assessed by time-lapse microscopy. Migration behavior was seen to be strongly dependent on matrix stiffness, with two regimes identified: a nonproteolytic migration mode dominating at relatively low matrix stiffness and proteolytic migration at higher stiffness. Subsequent in vivo experiments revealed a similar stiffness dependence of matrix remodeling, albeit less sensitive to the matrix metalloprotease sensitivity. Therefore, our aECM model system is well suited to unveil the role of biophysical and biochemical determinants of physiologically relevant cell migration phenomena. PMID:21244824

  3. Vibration isolation using six degree-of-freedom quasi-zero stiffness magnetic levitation

    NASA Astrophysics Data System (ADS)

    Zhu, Tao; Cazzolato, Benjamin; Robertson, William S. P.; Zander, Anthony

    2015-12-01

    In laboratories and high-tech manufacturing applications, passive vibration isolators are often used to isolate vibration sensitive equipment from ground-borne vibrations. However, in traditional passive isolation devices, where the payload weight is supported by elastic structures with finite stiffness, a design trade-off between the load capacity and the vibration isolation performance is unavoidable. Low stiffness springs are often required to achieve vibration isolation, whilst high stiffness is desired for supporting payload weight. In this paper, a novel design of a six degree of freedom (six-dof) vibration isolator is presented, as well as the control algorithms necessary for stabilising the passively unstable maglev system. The system applies magnetic levitation as the payload support mechanism, which realises inherent quasi-zero stiffness levitation in the vertical direction, and zero stiffness in the other five dofs. While providing near zero stiffness in multiple dofs, the design is also able to generate static magnetic forces to support the payload weight. This negates the trade-off between load capacity and vibration isolation that often exists in traditional isolator designs. The paper firstly presents the novel design concept of the isolator and associated theories, followed by the mechanical and control system designs. Experimental results are then presented to demonstrate the vibration isolation performance of the proposed system in all six directions.

  4. A novel magnetorheological elastomer isolator with negative changing stiffness for vibration reduction

    NASA Astrophysics Data System (ADS)

    Yang, J.; Sun, S. S.; Du, H.; Li, W. H.; Alici, G.; Deng, H. X.

    2014-10-01

    Magneto-rheological elastomers (MREs) have attracted notable credits in the development of smart isolators and absorbers due to their controllable stiffness and damping properties. For the purpose of mitigating unwanted structural and/or machinery vibrations, the traditional MRE-based isolators have been generally proven effective because the MR effect can increase the stiffness when the magnetic field is strengthened. This study presents a novel MRE isolator that experienced reduced stiffness when the applied current was increased. This innovative work was accomplished by applying a hybrid magnet (electromagnet and permanent magnets) onto a multilayered MRE structure. To characterise this negative changing stiffness concept, a multilayered MRE isolator with a hybrid magnet was first designed, fabricated and then tested to measure its properties. An obvious reduction of the effective stiffness and natural frequency of the proposed MRE isolator occurred when the current was continuously adjusted. This device could also work as a conventional MRE isolator as its effective stiffness and natural frequency also increased when a negative current was applied. Further testing was carried out on a one-degree-of-freedom system to assess how effectively this device could isolate vibration. In this experiment, two cases were considered; in each case, the vibration of the primary system was obviously attenuated under ON-OFF control logic, thus demonstrating the feasibility of this novel design as an alternative adaptive vibration isolator.

  5. Hyper-damping properties of a stiff and stable linear oscillator with a negative stiffness element

    NASA Astrophysics Data System (ADS)

    Antoniadis, I.; Chronopoulos, D.; Spitas, V.; Koulocheris, D.

    2015-06-01

    A simple, stiff, statically and dynamically stable linear oscillator incorporating a negative stiffness element is used as a template to provide a generic theoretical basis for a novel vibration damping and isolation concept. This oscillator is designed to present the same overall static stiffness, the same mass and to use the same damping element as a reference classical linear SDoF oscillator. Thus, no increase of the structure mass or the viscous damping is needed, as in the case of a traditional linear isolator, no decrease of the overall structure stiffness is required as in the case of 'zero-stiffness' oscillators with embedded negative stiffness elements. The difference from these two templates consists entirely in the proper redistribution and reallocation of the stiffness and the damping elements of the system. Once such an oscillator is optimally designed, it is shown to exhibit an extraordinary apparent damping ratio, which is even several orders of magnitude higher than that of the original SDoF system, especially in cases where the original damping of the SDoF system is extremely low. This extraordinary damping behavior is a result of the phase difference between the positive and the negative stiffness elastic forces, which is in turn a consequence of the proper redistribution of the stiffness and the damping elements. This fact ensures that an adequate level of elastic forces exists throughout the entire frequency range, able to counteract the inertial and the excitation forces. Consequently, a resonance phenomenon, which is inherent in the original linear SDoF system, cannot emerge in the proposed oscillator. The optimal parameter selection for the design of the negative stiffness oscillator is discussed. To further exhibit the advantages that such a design can generate, the suggested oscillator is implemented within a periodic acoustic metamaterial structure, inducing a radical increase in the damping of the propagating acoustic waves. The concept

  6. Augmented vascular smooth muscle cell stiffness and adhesion when hypertension is superimposed on aging.

    PubMed

    Sehgel, Nancy L; Sun, Zhe; Hong, Zhongkui; Hunter, William C; Hill, Michael A; Vatner, Dorothy E; Vatner, Stephen F; Meininger, Gerald A

    2015-02-01

    Hypertension and aging are both recognized to increase aortic stiffness, but their interactions are not completely understood. Most previous studies have attributed increased aortic stiffness to changes in extracellular matrix proteins that alter the mechanical properties of the vascular wall. Alternatively, we hypothesized that a significant component of increased vascular stiffness in hypertension is due to changes in the mechanical and adhesive properties of vascular smooth muscle cells, and that aging would augment the contribution from vascular smooth muscle cells when compared with the extracellular matrix. Accordingly, we studied aortic stiffness in young (16-week-old) and old (64-week-old) spontaneously hypertensive rats and Wistar-Kyoto wild-type controls. Systolic and pulse pressures were significantly increased in young spontaneously hypertensive rats when compared with young Wistar-Kyoto rats, and these continued to rise in old spontaneously hypertensive rats when compared with age-matched controls. Excised aortic ring segments exhibited significantly greater elastic moduli in both young and old spontaneously hypertensive rats versus Wistar-Kyoto rats. were isolated from the thoracic aorta, and stiffness and adhesion to fibronectin were measured by atomic force microscopy. Hypertension increased both vascular smooth muscle cell stiffness and vascular smooth muscle cell adhesion, and these increases were both augmented with aging. By contrast, hypertension did not affect histological measures of aortic collagen and elastin, which were predominantly changed by aging. These findings support the concept that stiffness and adhesive properties of vascular smooth muscle cells are novel mechanisms contributing to the increased aortic stiffness occurring with hypertension superimposed on aging.

  7. The Development of a Lateral-control System for Use with Large-span Flaps

    NASA Technical Reports Server (NTRS)

    Ashkenas, I L

    1946-01-01

    A spoiler-type lateral-control system has been developed for use on the Northrop P-61 airplane. The lateral-control system is to be used with large-span flaps and consists of a thin circular arc spoiler, linked with a short-span plain aileron located just outboard of the spoiler. This unconventional lateral-control system has been accepted with enthusiasm by the pilots who have flown the airplane. The particularly appreciate its characteristic at high speed. The combination of light forges, favorable yawing moment, and low wing torsional moments, make it a very effective, easily applied control. The control available at and through the stall is also remarkably good, although this characteristic may be attributed, in part, to an exceptionally good wing stalling pattern rather than entirely to the use of the spoiler-type aileron. In the landing configuration, the lateral-control effectiveness increases automatically with the extension of wing flaps so that powerful control is available during the approach. There is, however, a decrease in effectiveness for the first 5 percent of the wheel travel with a resultant tendency for inexperienced pilots to overcontrol slightly at low speeds. The fact that the aileron can be fully used at the stall, however, more than compensates for this loss of effectiveness with flaps down and greatly enhances the airplane's landing performance.

  8. Running with a load increases leg stiffness.

    PubMed

    Silder, Amy; Besier, Thor; Delp, Scott L

    2015-04-13

    Spring-mass models have been used to characterize running mechanics and leg stiffness in a variety of conditions, yet it remains unknown how running while carrying a load affects running mechanics and leg stiffness. The purpose of this study was to test the hypothesis that running with a load increases leg stiffness. Twenty-seven subjects ran at a constant speed on a force-measuring treadmill while carrying no load, and while wearing weight vests loaded with 10%, 20%, and 30% of body weight. We measured lower extremity motion and created a scaled musculoskeletal model of each subject, which we used to estimate lower extremity joint angles and leg length. We estimated dimensionless leg stiffness as the ratio of the peak vertical ground reaction force (normalized to body weight) and the change in stance phase leg length (normalized to leg length at initial foot contact). Leg length was calculated as the distance from the center of the pelvis to the center-of-pressure under the foot. We found that dimensionless leg stiffness increased when running with load (p=0.001); this resulted from an increase in the peak vertical ground reaction force (p<0.001) and a smaller change in stance phase leg length (p=0.025). When running with load, subjects had longer ground contact times (p<0.020), greater hip (p<0.001) and knee flexion (p=0.048) at the time of initial foot contact, and greater peak stance phase hip, knee, and ankle flexion (p<0.05). Our results reveal that subjects run in a more crouched posture and with higher leg stiffness to accommodate an added load.

  9. Running with a load increases leg stiffness.

    PubMed

    Silder, Amy; Besier, Thor; Delp, Scott L

    2015-04-13

    Spring-mass models have been used to characterize running mechanics and leg stiffness in a variety of conditions, yet it remains unknown how running while carrying a load affects running mechanics and leg stiffness. The purpose of this study was to test the hypothesis that running with a load increases leg stiffness. Twenty-seven subjects ran at a constant speed on a force-measuring treadmill while carrying no load, and while wearing weight vests loaded with 10%, 20%, and 30% of body weight. We measured lower extremity motion and created a scaled musculoskeletal model of each subject, which we used to estimate lower extremity joint angles and leg length. We estimated dimensionless leg stiffness as the ratio of the peak vertical ground reaction force (normalized to body weight) and the change in stance phase leg length (normalized to leg length at initial foot contact). Leg length was calculated as the distance from the center of the pelvis to the center-of-pressure under the foot. We found that dimensionless leg stiffness increased when running with load (p=0.001); this resulted from an increase in the peak vertical ground reaction force (p<0.001) and a smaller change in stance phase leg length (p=0.025). When running with load, subjects had longer ground contact times (p<0.020), greater hip (p<0.001) and knee flexion (p=0.048) at the time of initial foot contact, and greater peak stance phase hip, knee, and ankle flexion (p<0.05). Our results reveal that subjects run in a more crouched posture and with higher leg stiffness to accommodate an added load. PMID:25728581

  10. Non-axial muscle stress and stiffness.

    PubMed

    Zahalak, G I

    1996-09-01

    A generalization is developed of the classic two-state Huxley cross-bridge model to account for non-axial active stress and stiffness. The main ingredients of the model are: (i) a relation between the general three-dimensional deformation of an element of muscle and the deformations of the cross-bridges, that assumes macroscopic deformation is transmitted to the myofibrils, (ii) radial as well as axial cross-bridge stiffness, and (iii) variations of the attachment and detachment rates with lateral filament spacing. The theory leads to a generalized Huxley rate equation on the bond-distribution function, n(zeta, theta, t), of the form [equation: see text] where the Dij are the components of the relative velocity gradient and rho and ñ are functions of the polar angle, theta, and time that describe, respectively, the deformation of the myofilament lattice and the distribution of accessible actin sites (both of these functions can be calculated from the macroscopic deformation). Explicit expressions, in terms of n, are derived for the nine components of the active stress tensor, and the 21 non-vanishing components of the active stiffness tensor; the active stress tensor is found to be unsymmetric. The theory predicts that in general non-axial deformations will modify active axial stress and stiffness, and also give rise to non-axial (e.g., shearing) components. Under most circumstances the magnitudes of the non-axial stress and stiffness components will be small compared with the axial and, further, the effects of non-axial deformation rates will be small compared with those of the axial rate. Large transverse deformations may, however, greatly reduce the axial force and stiffness. The theory suggests a significant mechanical role for the non-contractile proteins in muscle, namely that of equilibrating the unsymmetric active stresses. Some simple applications of the theory are provided to illustrate its physical content. PMID:8917737

  11. Flight investigation of the effect of control centering springs on the apparent spiral stability of a personal-owner airplane

    NASA Technical Reports Server (NTRS)

    Campbell, John P; Hunter, Paul A; Hewes, Donald E; Whitten, James B

    1952-01-01

    Report presents the results of a flight investigation conducted on a typical high-wing personal-owner airplane to determine the effect of control centering springs on apparent spiral stability. Apparent spiral stability is the term used to describe the spiraling tendencies of an airplane in uncontrolled flight as affected both by the true spiral stability of the perfectly trimmed airplane and by out-of-trim control settings. Centering springs were used in both the aileron and rudder control systems to provide both a positive centering action and a means of trimming the airplane. The springs were preloaded so that when they were moved through neutral they produced a nonlinear force gradient sufficient to overcome the friction in the control surface at the proper setting for trim. The ailerons and rudder control surfaces did not have trim tabs that could be adjusted in flight.

  12. Multi-layer beam with variable stiffness based on electroactive polymers

    NASA Astrophysics Data System (ADS)

    Henke, Markus; Sorber, Jörg; Gerlach, Gerald

    2012-04-01

    The contribution describes a new kind of multi-layer beam with a variable stiffness based on electroactive polymers (EAP). These structures are supposed to be components of new smart, self-sensing and -controlling composite materials for lightweight constructions. Dielectric Elastomer foils from Danfoss PolyPower are used to control the beam's stiffness. The basic idea is to change the area moment of inertia of bending beams. These beams are built up as multi-layer stacks of thin metal or PMMA plates. Its internal structure can be changed by the use of the electroactive polymers for controlling the area moment of inertia. So it is possible to strongly change the stiffness of bending beams up to two orders of magnitude. Thereby, the magnitude of varying the stiffness can be scaled by the number of layers and the number and type of electroactive polymer elements used within the bending beam. The mechanisms for controlling the area moment of inertia are described in detail. Modeling of the mechanical structure including the EAP uses a pseudo rigid-body model, a strain energy model as well as a finite element analysis. The theoretical calculations are verified by experiments. The prototype described here consists of two structural layers. First results show the feasibility of the proposed structure for mechanical components with stiffness control.

  13. Selected advanced aerodynamics and active controls technology concepts development on a derivative B-747

    NASA Technical Reports Server (NTRS)

    1980-01-01

    The feasibility of applying wing tip extensions, winglets, and active control wing load alleviation to the Boeing 747 is investigated. Winglet aerodynamic design methods and high speed wind tunnel test results of winglets and of symmetrically deflected ailerons are presented. Structural resizing analyses to determine weight and aeroelastic twist increments for all the concepts and flutter model test results for the wing with winglets are included. Control law development, system mechanization/reliability studies, and aileron balance tab trade studies for active wing load alleviation systems are discussed. Results are presented in the form of incremental effects on L/D, structural weight, block fuel savings, stability and control, airplane price, and airline operating economics.

  14. Adaptive Failure Compensation for Aircraft Flight Control Using Engine Differentials: Regulation

    NASA Technical Reports Server (NTRS)

    Yu, Liu; Xidong, Tang; Gang, Tao; Joshi, Suresh M.

    2005-01-01

    The problem of using engine thrust differentials to compensate for rudder and aileron failures in aircraft flight control is addressed in this paper in a new framework. A nonlinear aircraft model that incorporates engine di erentials in the dynamic equations is employed and linearized to describe the aircraft s longitudinal and lateral motion. In this model two engine thrusts of an aircraft can be adjusted independently so as to provide the control flexibility for rudder or aileron failure compensation. A direct adaptive compensation scheme for asymptotic regulation is developed to handle uncertain actuator failures in the linearized system. A design condition is specified to characterize the system redundancy needed for failure compensation. The adaptive regulation control scheme is applied to the linearized model of a large transport aircraft in which the longitudinal and lateral motions are coupled as the result of using engine thrust differentials. Simulation results are presented to demonstrate the effectiveness of the adaptive compensation scheme.

  15. Elastic-Stiffness Coefficients of Titanium Diboride

    PubMed Central

    Ledbetter, Hassel; Tanaka, Takaho

    2009-01-01

    Using resonance ultrasound spectroscopy, we measured the monocrystal elastic-stiffness coefficients, the Voigt Cij, of TiB2. With hexagonal symmetry, TiB2 exhibits five independent Cij: C11, C33, C44, C12, C13. Using Voigt-Reuss-Hill averaging, we converted these monocrystal values to quasiisotropic (polycrystal) elastic stiffnesses. Briefly, we comment on effects of voids. From the Cij, we calculated the Debye characteristic temperature, the Grüneisen parameter, and various sound velocities. Our study resolves the enormous differences between two previous reports of TiB2’s Cij. PMID:27504232

  16. Elastic Stiffness of a Skyrmion Crystal

    NASA Astrophysics Data System (ADS)

    Nii, Y.; Kikkawa, A.; Taguchi, Y.; Tokura, Y.; Iwasa, Y.

    2014-12-01

    We observe the elastic stiffness and ultrasonic absorption of a Skyrmion crystal in the chiral-lattice magnet MnSi. The Skyrmion crystal lattice exhibits a stiffness 3 orders of magnitude smaller than that of the atomic lattice of MnSi, being as soft as the flux line lattice in type-II superconductors. The observed anisotropic elastic responses are consistent with the cylindrical shape of the Skyrmion spin texture. Phenomenological analysis reveals that the spin-orbit coupling is responsible for the emergence of anisotropic elasticity in the Skyrmion lattice.

  17. Feedback control laws for highly maneuverable aircraft

    NASA Technical Reports Server (NTRS)

    Garrard, William L.; Balas, Gary J.

    1995-01-01

    During this year, we concentrated our efforts on the design of controllers for lateral/directional control using mu synthesis. This proved to be a more difficult task than we anticipated and we are still working on the designs. In the lateral-directional control problem, the inputs are pilot lateral stick and pedal commands and the outputs are roll rate about the velocity vector and side slip angle. The control effectors are ailerons, rudder deflection, and directional thrust vectoring vane deflection which produces a yawing moment about the body axis. Our math model does not contain any provision for thrust vectoring of rolling moment. This has resulted in limitations of performance at high angles of attack. During 1994-95, the following tasks for the lateral-directional controllers were accomplished: (1) Designed both inner and outer loop dynamic inversion controllers. These controllers are implemented using accelerometer outputs rather than an a priori model of the vehicle aerodynamics; (2) Used classical techniques to design controllers for the system linearized by dynamics inversion. These controllers acted to control roll rate and Dutch roll response; (3) Implemented the inner loop dynamic inversion and classical controllers on the six DOF simulation; (4) Developed a lateral-directional control allocation scheme based on minimizing required control effort among the ailerons, rudder, and directional thrust vectoring; and (5) Developed mu outer loop controllers combined with classical inner loop controllers.

  18. Arterial Stiffness, Lipoprotein Particle Size, and Lipoprotein Particle Concentration in Children with Type 1 Diabetes

    PubMed Central

    Gallo, Lisa M; Silverstein, Janet H.; Shuster, Jonathan J; Haller, Michael J.

    2013-01-01

    OBJECTIVE To determine if lipoprotein particle abnormalities correlate with arterial stiffness in children with type 1 diabetes (T1D). STUDY DESIGN In this case-control study, we evaluated 70 children, 35 with T1D and 35 controls, ages 10–18 years, matched for age, sex, race, and BMI. Arterial stiffness was assessed by radial tonometry (AI75) and blood was collected for lipoprotein subclass analysis. RESULTS T1D subjects had increased AI75, decreased small LDL particle concentration (P=0.0067), increased large LDL particle concentration (P=0.007), increased large HDL particle concentration (P=0.0012), increased mean LDL particle size (P=0.0028), and increased mean HDL particle size (P<0.0001) compared to controls. No significant correlations were found between lipoprotein subclasses and arterial stiffness in T1D subjects. CONCLUSIONS T1D subjects have increased arterial stiffness when compared to controls, despite a less pro-atherogenic lipoprotein profile, indicating the need to identify other risk factors that correlate with arterial stiffness in T1D youth. PMID:20857838

  19. Nonlinear model of space manipulator joint considering time-variant stiffness and backlash

    NASA Astrophysics Data System (ADS)

    Yang, Tianfu; Yan, Shaoze; Han, Zengyao

    2015-04-01

    Modeling of space manipulator joints has been studied for years but accurate positioning control is still unsatisfactory. One of the primary reasons is that, in the past researches, effects of the high-ratio reducers in the joints have usually been neglected. In this paper, a nonlinear dynamic model of the manipulator joint with planetary gear train transmission is developed by considering time-variant joint stiffness, backlash and reduction ratio. Based on the gear parameters and meshing phase relationship, the stiffness of the joint model is presented, in which the time-variant stiffness of 2K-H planetary gear train and the backlash are taken into consideration. The backlash effect is modeled as an alternate engagement mechanism, and the transmitted torque is defined as a dead zone function. This model is simulated on a two-link space manipulator system. The results show that the time-variant stiffness effect can be simplified as a constant value in most cases when other shafting parts are flexible, while if the total stiffness is approximate to the nonlinear stiffness, the positioning accuracy is reduced if neglecting the time-variant part. On the other hand, the backlash is the main source of positioning error and impact. Minimizing backlash is the most effective way to improve positioning accuracy and avoid the impact in the gearing system.

  20. Identification of dynamic stiffness matrices of elastomeric joints using direct and inverse methods

    NASA Astrophysics Data System (ADS)

    Noll, Scott; Dreyer, Jason T.; Singh, Rajendra

    2013-08-01

    New experiments are designed to permit direct comparison between direct and inverse identification methods of the dynamic stiffness matrices of elastomeric joints, including non-diagonal terms. The joints are constructed with combinations of inclined elastomeric cylinders to control non-diagonal terms in the stiffness matrix. The inverse experiment consists of an elastic metal beam end-supported by elastomeric joints coupling the in-plane transverse and longitudinal beam motion. A prior method is extended to identify the joint dynamic stiffness matrices of dimension 3 from limited modal measurements of the beam. The dynamic stiffness and loss factors of the elastomeric cylinders are directly measured in a commercial elastomer test machine in shear, compression, and inclined configurations and a coordinate transformation is used to estimate the kinematic non-diagonal stiffness terms. Agreement is found for both dynamic stiffness and loss factors between the direct and inverse methods at small displacements. Further, the identified joint properties are employed in a model that successfully predicts the modal parameters and accelerance spectra of the inverse experiment. This article provides valuable insight on the difficulties encountered when comparing system and elastomeric component test results.

  1. Matrix Stiffness and Nanoscale Spatial Organization of Cell-Adhesive Ligands Direct Stem Cell Fate.

    PubMed

    Ye, Kai; Wang, Xuan; Cao, Luping; Li, Shiyu; Li, Zhenhua; Yu, Lin; Ding, Jiandong

    2015-07-01

    One of the breakthroughs in biomaterials and regenerative medicine in the latest decade is the finding that matrix stiffness affords a crucial physical cue of stem cell differentiation. This statement was recently challenged by another understanding that protein tethering on material surfaces instead of matrix stiffness was the essential cue to regulate stem cells. Herein, we employed nonfouling poly(ethylene glycol) (PEG) hydrogels as the matrix to prevent nonspecific protein adsorption, and meanwhile covalently bound cell-adhesive arginine-glycine-aspartate (RGD) peptides onto the hydrogel surfaces in the form of well-defined nanoarrays to control specific cell adhesion. This approach enables the decoupling of the effects of matrix stiffness and surface chemistry. Mesenchymal stem cells (MSCs) were cultured on four substrates (two compressive moduli of the PEG hydrogels multiplied by two RGD nanospacings) and incubated in the mixed osteogenic and adipogenic medium. The results illustrate unambiguously that matrix stiffness is a potent regulator of stem cell differentiation. Moreover, we reveal that RGD nanospacing affects spreading area and differentiation of rat MSCs, regardless of the hydrogel stiffness. Therefore, both matrix stiffness and nanoscale spatial organization of cell-adhesive ligands direct stem cell fate.

  2. Musculoskeletal stiffness changes linearly in response to increasing load during walking gait.

    PubMed

    Caron, Robert R; Lewis, Cara L; Saltzman, Elliot; Wagenaar, Robert C; Holt, Kenneth G

    2015-04-13

    Development of biologically inspired exoskeletons to assist soldiers in carrying load is a rapidly expanding field. Understanding how the body modulates stiffness in response to changing loads may inform the development of these exoskeletons and is the purpose of the present study. Seventeen subjects walked on a treadmill at a constant preferred walking velocity while nine different backpack loading conditions ranging from 12.5% to 40% bodyweight (BW) were introduced in an ascending and then descending order. Kinematic data were collected using Optotrak, a 3D motion analysis system, and used to estimate the position of the center of mass (COM). Two different estimates of stiffness were computed for the stance phase of gait. Both measures of stiffness were positively and linearly related to load magnitudes, with the slopes of the relationships being larger for the descending than the ascending conditions. These results indicate that changes in mechanical stiffness brought about in the musculoskeletal system vary systematically during increases in load to ensure that critical kinematic variables measured in a previous publication remain invariant (Caron et al., 2013). Changes in stiffness and other kinematics measured at the 40% BW condition suggest a boundary in which gait stiffness control limit is reached and a new gait pattern is required. Since soldiers are now carrying up to 96% of body weight, the need for research with even heavier loads is warranted. These findings have implications on the development of exoskeletons to assist in carrying loads. PMID:25678200

  3. Jumping Mechanism for Asteroid Rover with the Use of Resonance and Electrical Stiffness Switching

    NASA Astrophysics Data System (ADS)

    Sugawara, Yoshiki; Mizuguchi, Kou; Kobayashi, Nobuyuki

    It is not easy for asteroid rover with wheels to move on the surface of asteroids because such an astral body has two special features. One feature is that there is no air and it induces vacuum metalizing of metal slide components. The other feature is that their quite small gravity induces bad controllability of rover with wheels which requires enough frictional force between ground and wheels. Therefore, it is preferable for rover to use jumping mechanism without metal slide component and with low energy consumption. In this paper, a jumping mechanism is proposed and the mechanism uses a energy which is stored by resonance of flexible part. However, simply giving resonance results in low height of jumping. Therefore, electrical stiffness switching system is implemented to realize a effective jumping. Electrical stiffness switching is realized by piezoelectric element and external capacitor which is connected to them. Two method of stiffness switching are introduced. One is stiffness hardening and the other is stiffness softening which solve the problem of stiffness hardening. To validate the proposed mechanisms, numerical analyses are carried out and feasibilities of application for asteroid rover are studied.

  4. Sagittal rotational stiffness and damping increase in a porcine lumbar spine with increased or prolonged loading.

    PubMed

    Zondervan, Robert L; Popovich, John M; Radcliffe, Clark J; Pathak, Pramod K; Reeves, N Peter

    2016-02-29

    While the impact of load magnitude on spine dynamic parameters (stiffness and damping) has been reported, it is unclear how load history (exposure to prolonged loading) affects spine dynamic parameters in sagittal rotation. Furthermore, it is unknown if both spine stiffness and damping are equally affected to prolonged loading. Using a pendulum testing apparatus, the effect of load magnitude and load history on spine sagittal rotational stiffness and damping was assessed. Nine porcine lumbar functional spine units (FSUs) were tested in an increasing compressive load phase (ICP: 44.85, 68.55, 91.75, 114.6kg) and then a decreasing compressive load phase (DCP: 91.75, 68.55, and 44.85kg). Each trial consisted of flexing the FSU 5° and allowing it to oscillate unconstrained. During the ICP, both stiffness and damping linearly increased with load. However, in the DCP, stiffness and damping values were significantly higher than the identical load collected during the ICP, suggesting load history affects sagittal rotational dynamic parameters. In addition, spine damping was more affected by load history than spine stiffness. These results highlight the importance of controlling load magnitude and history when assessing spine dynamic parameters. PMID:26892899

  5. Matrix Stiffness and Nanoscale Spatial Organization of Cell-Adhesive Ligands Direct Stem Cell Fate.

    PubMed

    Ye, Kai; Wang, Xuan; Cao, Luping; Li, Shiyu; Li, Zhenhua; Yu, Lin; Ding, Jiandong

    2015-07-01

    One of the breakthroughs in biomaterials and regenerative medicine in the latest decade is the finding that matrix stiffness affords a crucial physical cue of stem cell differentiation. This statement was recently challenged by another understanding that protein tethering on material surfaces instead of matrix stiffness was the essential cue to regulate stem cells. Herein, we employed nonfouling poly(ethylene glycol) (PEG) hydrogels as the matrix to prevent nonspecific protein adsorption, and meanwhile covalently bound cell-adhesive arginine-glycine-aspartate (RGD) peptides onto the hydrogel surfaces in the form of well-defined nanoarrays to control specific cell adhesion. This approach enables the decoupling of the effects of matrix stiffness and surface chemistry. Mesenchymal stem cells (MSCs) were cultured on four substrates (two compressive moduli of the PEG hydrogels multiplied by two RGD nanospacings) and incubated in the mixed osteogenic and adipogenic medium. The results illustrate unambiguously that matrix stiffness is a potent regulator of stem cell differentiation. Moreover, we reveal that RGD nanospacing affects spreading area and differentiation of rat MSCs, regardless of the hydrogel stiffness. Therefore, both matrix stiffness and nanoscale spatial organization of cell-adhesive ligands direct stem cell fate. PMID:26027605

  6. Williams syndrome predisposes to vascular stiffness modified by antihypertensive use and copy number changes in NCF1.

    PubMed

    Kozel, Beth A; Danback, Joshua R; Waxler, Jessica L; Knutsen, Russell H; de Las Fuentes, Lisa; Reusz, Gyorgy S; Kis, Eva; Bhatt, Ami B; Pober, Barbara R

    2014-01-01

    Williams syndrome is caused by the deletion of 26 to 28 genes, including elastin, on human chromosome 7. Elastin insufficiency leads to the cardiovascular hallmarks of this condition, namely focal stenosis and hypertension. Extrapolation from the Eln(+/-) mouse suggests that affected people may also have stiff vasculature, a risk factor for stroke, myocardial infarction, and cardiac death. NCF1, one of the variably deleted Williams genes, is a component of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex and is involved in the generation of oxidative stress, making it an interesting candidate modifier for vascular stiffness. Using a case-control design, vascular stiffness was evaluated by pulse wave velocity in 77 Williams cases and matched controls. Cases had stiffer conducting vessels than controls (P<0.001), with increased stiffness observed in even the youngest children with Williams syndrome. Pulse wave velocity increased with age at comparable rates in cases and controls, and although the degree of vascular stiffness varied, it was seen in both hypertensive and normotensive Williams participants. Use of antihypertensive medication and extension of the Williams deletion to include NCF1 were associated with protection from vascular stiffness. These findings demonstrate that vascular stiffness is a primary vascular phenotype in Williams syndrome and that treatment with antihypertensives or agents inhibiting oxidative stress may be important in managing patients with this condition, potentially even those who are not overtly hypertensive.

  7. [Anaesthetic management of Stiff Man syndrome].

    PubMed

    Marín, T; Hernando, D; Kinast, N; Churruca, I; Sabate, S

    2015-04-01

    Stiff Man syndrome or stiff-person syndrome is a rare autoimmune disorder. It is characterized by increased axial muscular tone and limb musculature, and painful spasms triggered by stimulus. The case is presented of a 44-year-old man with stiff-person syndrome undergoing an injection of botulinum toxin in the urethral sphincter under sedation. Before induction, all the surgical team were ready in order to minimise the anaesthetic time. The patient was monitored by continuous ECG, SpO2 and non-invasive blood pressure. He was induced with fractional dose of propofol 150 mg, fentanyl 50 μg and midazolam 1mg. Despite careful titration, the patient had an O2 saturation level of 90%,which was resolved by manual ventilation. There was no muscle rigidity or spasm during the operation. Post-operative recovery was uneventful and the patient was discharged 2 days later. A review of other cases is presented. The anaesthetic concern in patients with stiff-person syndrome is the interaction between the anaesthetic agents, the preoperative medication, and the GABA system. For a safe anaesthetic management, total intravenous anaesthesia is recommended instead of inhalation anaesthetics, as well as the close monitoring of the respiratory function and the application of the electrical nerve stimulator when neuromuscular blockers are used. PMID:25060949

  8. Vibrating Beam With Spatially Periodic Stiffness

    NASA Technical Reports Server (NTRS)

    Townsend, John S.

    1989-01-01

    Report presents theoretical analysis of vibrations of simply supported beam, bending stiffness varying about steady value, sinusoidally with position along length. Problem of practical importance because related to vibrations of twisted-pair electric-power transmission lines. Twists promote nonuniform shedding of vortexes and prevents resonant accumulation of vibrational energy from wind.

  9. Elastin in large artery stiffness and hypertension.

    PubMed

    Wagenseil, Jessica E; Mecham, Robert P

    2012-06-01

    Large artery stiffness, as measured by pulse wave velocity, is correlated with high blood pressure and may be a causative factor in essential hypertension. The extracellular matrix components, specifically the mix of elastin and collagen in the vessel wall, determine the passive mechanical properties of the large arteries. Elastin is organized into elastic fibers in the wall during arterial development in a complex process that requires spatial and temporal coordination of numerous proteins. The elastic fibers last the lifetime of the organism but are subject to proteolytic degradation and chemical alterations that change their mechanical properties. This review discusses how alterations in the amount, assembly, organization, or chemical properties of the elastic fibers affect arterial stiffness and blood pressure. Strategies for encouraging or reversing alterations to the elastic fibers are addressed. Methods for determining the efficacy of these strategies, by measuring elastin amounts and arterial stiffness, are summarized. Therapies that have a direct effect on arterial stiffness through alterations to the elastic fibers in the wall may be an effective treatment for essential hypertension.

  10. Biaxial strain and variable stiffness in aponeuroses

    PubMed Central

    Azizi, Emanuel; Roberts, Thomas J

    2009-01-01

    The elastic structures of many muscles include both an extramuscular free tendon as well as a sheet-like aponeurosis. An important distinguishing feature of aponeuroses is that these tendinous structures function as the attachment and insertion surfaces of muscle fascicles and therefore surround a substantial portion of the muscle belly. As a result, aponeuroses must expand both parallel (longitudinal) and perpendicular (transverse) to a muscle's line of action when contracting muscles bulge to maintain a constant volume. In this study, we use biplanar high-speed fluoroscopy to track the strain patterns of the turkey lateral gastrocnemius aponeurosis during active and passive force production in situ. We find that the behaviour of the aponeurosis during passive force production is consistent with uniaxial loading, as aponeuroses stretch only in the longitudinal direction. By contrast, our results show that aponeuroses are stretched in both longitudinal and transverse directions during active force production and that transverse strains are on average 4 times greater than longitudinal strains. Biaxial loading of aponeuroses appears to effectively modulate longitudinal stiffness, as we find the measured stiffness in the longitudinal direction varies in proportion to transverse strain. We conclude that biaxial strain during active force production distinguishes aponeuroses from free tendons and may function to dynamically modulate stiffness along the axis of muscle force production. It is likely that consideration of strains measured only in the longitudinal direction result in an underestimation of aponeurosis stiffness as well as its capacity for elastic energy storage. PMID:19596897

  11. [Anaesthetic management of Stiff Man syndrome].

    PubMed

    Marín, T; Hernando, D; Kinast, N; Churruca, I; Sabate, S

    2015-04-01

    Stiff Man syndrome or stiff-person syndrome is a rare autoimmune disorder. It is characterized by increased axial muscular tone and limb musculature, and painful spasms triggered by stimulus. The case is presented of a 44-year-old man with stiff-person syndrome undergoing an injection of botulinum toxin in the urethral sphincter under sedation. Before induction, all the surgical team were ready in order to minimise the anaesthetic time. The patient was monitored by continuous ECG, SpO2 and non-invasive blood pressure. He was induced with fractional dose of propofol 150 mg, fentanyl 50 μg and midazolam 1mg. Despite careful titration, the patient had an O2 saturation level of 90%,which was resolved by manual ventilation. There was no muscle rigidity or spasm during the operation. Post-operative recovery was uneventful and the patient was discharged 2 days later. A review of other cases is presented. The anaesthetic concern in patients with stiff-person syndrome is the interaction between the anaesthetic agents, the preoperative medication, and the GABA system. For a safe anaesthetic management, total intravenous anaesthesia is recommended instead of inhalation anaesthetics, as well as the close monitoring of the respiratory function and the application of the electrical nerve stimulator when neuromuscular blockers are used.

  12. 49 CFR 213.359 - Track stiffness.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...

  13. 49 CFR 213.359 - Track stiffness.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...

  14. 49 CFR 213.359 - Track stiffness.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...

  15. 49 CFR 213.359 - Track stiffness.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...

  16. Arterial Stiffness and Chronic Kidney Disease

    PubMed Central

    Garnier, Anne-Sophie; Briet, Marie

    2016-01-01

    Chronic kidney disease (CKD) is a major public health concern due to the high prevalence of associated cardiovascular (CV) disease. CV mortality is 10-30 times higher in end-stage renal disease patients than in the age-adjusted general population. The last 20 years have been marked by a huge effort in the characterization of the vascular remodeling process associated with CKD and its consequences on the renal, CV and general prognosis. By comparison with patients with normal renal function, with or without hypertension, an increase in large artery stiffness has been described in end-stage renal disease as well as in CKD stages 2-5. Most clinical studies are consistent with the observation that damage to large arteries may contribute to the high incidence of CV disease. By contrast, the impact of large artery stiffening and remodeling on CKD progression is still a matter of debate. Concomitant exposure to other CV risk factors, including diabetes, seems to play a major role in the association between aortic stiffness and estimated GFR. The conflicting results obtained from longitudinal studies designed to evaluate the impact of baseline aortic stiffness on GFR progression are detailed in the present review. Only pulse pressure, central and peripheral, is almost constantly associated with incident CKD and GFR decline. Kidney transplantation improves patients’ CV prognosis, but its impact on arterial stiffness is still controversial. Donor age, living kidney donation and mean blood pressure appear to be the main determinants of improvement in aortic stiffness after kidney transplantation. PMID:27195244

  17. Assessment of Liver and Spleen Stiffness in Patients With Myelofibrosis Using FibroScan and Shear Wave Elastography.

    PubMed

    Webb, Muriel; Shibolet, Oren; Halpern, Zamir; Nagar, Meital; Amariglio, Ninette; Levit, Stella; Steinberg, David M; Santo, Erwin; Salomon, Ophira

    2015-09-01

    Liver stiffness and spleen stiffness in patients with myelofibrosis have traditionally been assessed through manual palpation and thus influenced by interobserver variability. In this article, for the first time, liver stiffness and spleen stiffness of patients with myelofibrosis were evaluated through FibroScan and shear wave elastography (SWE). Nine patients with myelofibrosis comprised the study group. They were compared with 11 patients with liver cirrhosis and 8 healthy volunteers. Before the FibroScan study, all patients underwent ultrasound study to delineate the left intercostal space for validated measurements. In patients with myelofibrosis, the mean stiffness of the spleen was 41.3 and 32.9 kilopascals (kPa) through FibroScan and SWE, respectively. The mean stiffness of the liver was 7.8 kPa through FibroScan and 10.4 kPa through SWE. The stiffness of the spleen in patients with cirrhosis was even higher, reaching a mean of 58.5 kPa through FibroScan and 40.5 kPa through SWE. The means were considerably lower among the healthy controls (13.5 and 18.1 kPa, respectively). The correlation between spleen stiffness among the patients with cirrhosis is negative and opposite in direction (r = -0.35) in comparison with the patients with myelofibrosis (r = 0.78). Among the patients with liver cirrhosis and myelofibrosis, spleen size was weakly related to spleen stiffness as assessed through SWE (r = 0.49) but had almost no relation to the FibroScan measure (r = 0.13). The FibroScan and SWE of the spleen have little ability to distinguish between the patients with myelofibrosis and cirrhosis, but they do differentiate both patient groups from the healthy controls. The stiffness of spleen and liver as measured through FibroScan and SWE was not correlated to the longevity of myelofibrosis.

  18. A co-culture device with a tunable stiffness to understand combinatorial cell-cell and cell-matrix interactions.

    PubMed

    Rao, Nikhil; Grover, Gregory N; Vincent, Ludovic G; Evans, Samantha C; Choi, Yu Suk; Spencer, Katrina H; Hui, Elliot E; Engler, Adam J; Christman, Karen L

    2013-11-01

    Cell behavior on 2-D in vitro cultures is continually being improved to better mimic in vivo physiological conditions by combining niche cues including multiple cell types and substrate stiffness, which are well known to impact cell phenotype. However, no system exists in which a user can systematically examine cell behavior on a substrate with a specific stiffness (elastic modulus) in culture with a different cell type, while maintaining distinct cell populations. We demonstrate the modification of a silicon reconfigurable co-culture system with a covalently linked hydrogel of user-defined stiffness. This device allows the user to control whether two separate cell populations are in contact with each other or only experience paracrine interactions on substrates of controllable stiffness. To illustrate the utility of this device, we examined the role of substrate stiffness combined with myoblast co-culture on adipose derived stem cell (ASC) differentiation and found that the presence of myoblasts and a 10 kPa substrate stiffness increased ASC myogenesis versus co-culture on stiff substrates. As this example highlights, this technology better controls the in vitro microenvironment, allowing the user to develop a more thorough understanding of the combined effects of cell-cell and cell-matrix interactions.

  19. A co-culture device with a tunable stiffness to understand combinatorial cell-cell and cell-matrix interactions

    PubMed Central

    Rao, Nikhil; Grover, Gregory N.; Vincent, Ludovic G.; Evans, Samantha C.; Choi, Yu Suk; Vincent, Ludovic G.; Spencer, Katrina H.; Hui, Elliot E.; Engler, Adam J.; Christman, Karen L.

    2013-01-01

    Cell behavior on 2-D in vitro cultures is continually being improved to better mimic in vivo physiological conditions by combining niche cues including multiple cell types and substrate stiffness, which are well known to impact cell phenotype. However, no system exists in which a user can systematically examine cell behavior on a substrate with a specific stiffness (elastic modulus) in culture with a different cell type, while maintaining distinct cell populations. We demonstrate the modification of a silicon reconfigurable co-culture system with a covalently linked hydrogel of user-defined stiffness. This device allows the user to control whether two separate cell populations are in contact with each other or only experience paracrine interactions on substrates of controllable stiffness. To illustrate the utility of this device, we examined the role of substrate stiffness combined with myoblast co-culture on adipose derived stem cell (ASC) differentiation and found that the presence of myoblasts and a 10 kPa substrate stiffness increased ASC myogenesis versus co-culture on stiff substrates. As this example highlights, this technology better controls the in vitro microenvironment, allowing the user to develop a more thorough understanding of the combined effects of cell-cell and cell-matrix interactions. PMID:24061208

  20. A review on in situ stiffness adjustment methods in MEMS

    NASA Astrophysics Data System (ADS)

    de Laat, M. L. C.; Pérez Garza, H. H.; Herder, J. L.; Ghatkesar, M. K.

    2016-06-01

    In situ stiffness adjustment in microelectromechanical systems is used in a variety of applications such as radio-frequency mechanical filters, energy harvesters, atomic force microscopy, vibration detection sensors. In this review we provide designers with an overview of existing stiffness adjustment methods, their working principle, and possible adjustment range. The concepts are categorized according to their physical working principle. It is concluded that the electrostatic adjustment principle is the most applied method, and narrow to wide ranges in stiffness can be achieved. But in order to obtain a wide range in stiffness change, large, complex devices were designed. Mechanical stiffness adjustment is found to be a space-effective way of obtaining wide changes in stiffness, but these methods are often discrete and require large tuning voltages. Stiffness adjustment through stressing effects or change in Young’s modulus was used only for narrow ranges. The change in second moment of inertia was used for stiffness adjustment in the intermediate range.

  1. Lateral and Directional Stability and Control Characteristics of a C-54D Airplane

    NASA Technical Reports Server (NTRS)

    Talmage, Donald B; Reeder, John P

    1949-01-01

    Data are presented showing compliance of C-54D with Army and Navy lateral and directional stability and control specifications. The airplane met requirements except for the rolling effectiveness pb/2V, the aileron forces in rolling, and the rudder forces in the asymmetric power conditions which were marginal. Also, the results of special tests concerning asymmetric power, asymmetric loading, and pitch due to yaw requested by the Airplane Handling Qualities Subcommittee of the Air Transport Association are presented.

  2. Stiffness and mass matrices for shells of revolution (SAMMSOR II)

    NASA Technical Reports Server (NTRS)

    Tillerson, J. R.; Haisler, W. E.

    1974-01-01

    Utilizing element properties, structural stiffness and mass matrices are generated for as many as twenty harmonics and stored on magnetic tape. Matrices generated constitute input data to be used by other stiffness of revolution programs. Variety of boundary and loading conditions can be employed without having to create new mass and stiffness matrices for each case.

  3. Increased arterial stiffness in South Dakota American Indian children.

    PubMed

    Litz, Andrew M; Van Guilder, Gary P

    2016-02-01

    Arterial stiffness has been observed in white American obese children, yet there are no data in American Indian youth, who are affected disproportionately by the cardiovascular consequences of childhood obesity and its accompanying risk factors. The purpose of this study was to determine the association of childhood overweight-obesity and cardiometabolic risk factors with arterial stiffness in South Dakota white American and American Indian children. Thirty-six (28 white American and 8 American Indian) children (age, 13 ± 1 years; grades 6-8) from a rural South Dakota elementary and middle school were studied: 18 had a healthy weight (body mass index (BMI), 19.5 ± 1.9 kg/m(2)) and 18 were overweight-obese (BMI, 26.8 ± 3.5 kg/m(2)). Arterial stiffness was assessed using applanation tonometry via pulse wave analysis to determine carotid-radial pulse wave velocity (crPWV) and aortic augmentation index (AIx). There were no differences (P = 0.94) in crPWV between healthy weight (7.1 ± 1.4 m/s) and overweight-obese (7.3 ± 1.0 m/s) children, even after controlling for risk factors. However, crPWV was markedly elevated (P = 0.002) in overweight-obese American Indian children (7.7 ± 1.1 m/s) compared with white American children (6.8 ± 0.5 m/s), and these differences remained after controlling for blood pressure and more severe obesity in the American Indians. An obesity-matched subgroup analysis indicated that crPWV (7.7 ± 1.1 vs 6.8 ± 0.4 m/s) remained significantly greater in the American Indians (P = 0.03). There were no between-group differences in aortic AIx. These findings indicate an adverse influence of American Indian ethnicity on arterial stiffening in children with elevated adiposity. Arterial stiffness in American Indian children may accelerate early adulthood vascular disease. PMID:26761621

  4. A new hybrid gyroscope with electrostatic negative stiffness tuning.

    PubMed

    Yang, Bo; Guan, Yumei; Wang, Shourong; Zou, Qi; Chu, Xian; Xue, Haiyan

    2013-05-30

    A variety of gyroscopes have been extensively studied due to their capability of precision detection of rotation rates and extensive applications in navigation, guidance and motion control. In this work, a new Hybrid Gyroscope (HG) which combines the traditional Dynamically Tuned Gyroscope (DTG) with silicon micromachined technology is investigated. The HG not only has the potentiality of achieving the same high precision as the traditional DTG, but also features a small size and low cost. The theoretical mechanism of the HG with a capacitance transducer and an electrostatic torquer is derived and the influence of the installation errors from the capacitance plate and the disc rotor module is investigated. A new tuning mechanism based on negative stiffness rather than the traditional dynamic tuning is proposed. The experimental results prove that the negative stiffness tuning is practicable and a tuning voltage of as high as 63 V is demonstrated. Due to the decreased installation error, the non-linearity of the scale factor is reduced significantly from 11.78% to 0.64%, as well as the asymmetry from 93.3% to 1.56% in the open loop condition. The rebalancing close-loop control is simulated and achieved experimentally, which proves that the fundamental principle of the HG is feasible.

  5. A New Hybrid Gyroscope with Electrostatic Negative Stiffness Tuning

    PubMed Central

    Yang, Bo; Guan, Yumei; Wang, Shourong; Zou, Qi; Chu, Xian; Xue, Haiyan

    2013-01-01

    A variety of gyroscopes have been extensively studied due to their capability of precision detection of rotation rates and extensive applications in navigation, guidance and motion control. In this work, a new Hybrid Gyroscope (HG) which combines the traditional Dynamically Tuned Gyroscope (DTG) with silicon micromachined technology is investigated. The HG not only has the potentiality of achieving the same high precision as the traditional DTG, but also features a small size and low cost. The theoretical mechanism of the HG with a capacitance transducer and an electrostatic torquer is derived and the influence of the installation errors from the capacitance plate and the disc rotor module is investigated. A new tuning mechanism based on negative stiffness rather than the traditional dynamic tuning is proposed. The experimental results prove that the negative stiffness tuning is practicable and a tuning voltage of as high as 63 V is demonstrated. Due to the decreased installation error, the non-linearity of the scale factor is reduced significantly from 11.78% to 0.64%, as well as the asymmetry from 93.3% to 1.56% in the open loop condition. The rebalancing close-loop control is simulated and achieved experimentally, which proves that the fundamental principle of the HG is feasible. PMID:23722826

  6. Massage induces an immediate, albeit short-term, reduction in muscle stiffness.

    PubMed

    Eriksson Crommert, M; Lacourpaille, L; Heales, L J; Tucker, K; Hug, F

    2015-10-01

    Using ultrasound shear wave elastography, the aims of this study were: (a) to evaluate the effect of massage on stiffness of the medial gastrocnemius (MG) muscle and (b) to determine whether this effect (if any) persists over a short period of rest. A 7-min massage protocol was performed unilaterally on MG in 18 healthy volunteers. Measurements of muscle shear elastic modulus (stiffness) were performed bilaterally (control and massaged leg) in a moderately stretched position at three time points: before massage (baseline), directly after massage (follow-up 1), and following 3 min of rest (follow-up 2). Directly after massage, participants rated pain experienced during the massage. MG shear elastic modulus of the massaged leg decreased significantly at follow-up 1 (-5.2 ± 8.8%, P = 0.019, d = -0.66). There was no difference between follow-up 2 and baseline for the massaged leg (P = 0.83) indicating that muscle stiffness returned to baseline values. Shear elastic modulus was not different between time points in the control leg. There was no association between perceived pain during the massage and stiffness reduction (r = 0.035; P = 0.89). This is the first study to provide evidence that massage reduces muscle stiffness. However, this effect is short lived and returns to baseline values quickly after cessation of the massage.

  7. Resume and analysis of NACA lateral control research

    NASA Technical Reports Server (NTRS)

    Weick, F. E.; Jones, R. T.

    1976-01-01

    An analysis of the principal results of recent lateral control research is made. Two things are considered of primary importance in judging the effectiveness of different control devices: The (calculated) banking and yawing motion of a typical small airplane caused by a deflection of the control, and the stick force required to produce this deflection. The report includes a table in which a number of different lateral control devices are compared on these bases. Test flights demonstrated that satisfactory lateral control at high angles of attack depends as much on the retention of stability as on aileron effectiveness.

  8. Effect of chain stiffness on polymer properties

    NASA Astrophysics Data System (ADS)

    Luettmer-Strathmann, Jutta

    2008-03-01

    Static and dynamic properties of polymers are affected by the stiffness of the chains. In this work, we investigate structural and thermodynamic properties of a lattice model for semiflexible polymer chains. The model is an extension of Shaffer's bond- fluctuation model and includes attractive interactions between monomers and an adjustable bending penalty that determines the Kuhn segment length. For isolated chains, a competition between monomer-monomer interactions and bending penalties determines the chain conformations at low temperatures. For dense melts, packing effects play an important role in the structure and thermodynamics of the polymeric liquid. In order to investigate static properties as a function of temperature and chain stiffness, we perform Wang-Landau type simulations and construct densities of states over the two-dimensional state space of monomer-monomer and bending contributions to the internal energy.

  9. Light weight high-stiffness stage platen

    DOEpatents

    Spence, Paul A.

    2001-01-01

    An improved light weight, stiff stage platen for photolithography is provided. The high stiffness of the stage platen is exemplified by a relatively high first resonant vibrational mode as determined, for instance, by finite element modal analysis. The stage platen can be employed to support a chuck that is designed to secure a mask or wafer. The stage platen includes a frame that has interior walls that define an interior region and that has exterior walls wherein the outer surfaces of at least two adjacent walls are reflective mirror surfaces; and a matrix of ribs within the interior region that is connected to the interior walls wherein the stage platen exhibits a first vibrational mode at a frequency of greater than about 1000 Hz.

  10. Electron profile stiffness and critical gradient studies

    NASA Astrophysics Data System (ADS)

    DeBoo, J. C.; Petty, C. C.; White, A. E.; Burrell, K. H.; Doyle, E. J.; Hillesheim, J. C.; Holland, C.; McKee, G. R.; Rhodes, T. L.; Schmitz, L.; Smith, S. P.; Wang, G.; Zeng, L.

    2012-08-01

    Electron profile stiffness was studied in DIII-D L-mode discharges by systematically varying the heat flux in a narrow region with electron cyclotron heating and measuring the local change produced in ∇Te. Electron stiffness was found to slowly increase with toroidal rotation velocity. A critical inverse temperature gradient scale length 1/LC ˜ 3 m-1 was identified at ρ =0.6 and found to be independent of rotation. Both the heat pulse diffusivity and the power balance diffusivity, the latter determined by integrating the measured dependence of the heat pulse diffusivity on -∇Te, were fit reasonably well by a model containing a critical inverse temperature gradient scale length and varying linearly with 1/LT above the threshold.

  11. Gyrokinetic Transport Stiffness Calculations on Stellarator Geometries

    NASA Astrophysics Data System (ADS)

    Faber, B. J.; Mynick, H.; Weir, G. M.; Likin, K. M.; Talmadge, J. N.

    2012-10-01

    A significant, unanswered question in plasma physics is the difference in transport ``stiffness'' between tokamaks and stellarators. In an effort to shed light on this issue, presented are nonlinear gyrokinetic calculations on various machine geometries: the Helically Symmetric Experiment, the National Compact Stellarator Experiment and an equivalent tokamak configuration. Nonlinear gyrokinetic fluxes have been compared directly to experimental fluxes observed in HSX power modulation experiments. Linear calculations on HSX reveal large growth rates due to both ion temperature gradient and trapped electron turbulence, necessitating a kinetic treatment of electrons; one of the first calculations of its kind for stellarators. A comparison of transport stiffness profiles computed through nonlinear gyrokinetic calculations of ion temperature gradient turbulence for the different machine configurations will be presented.

  12. Electron profile stiffness and critical gradient studies

    SciTech Connect

    DeBoo, J. C.; Petty, C. C.; Burrell, K. H.; Smith, S. P.; White, A. E.; Doyle, E. J.; Hillesheim, J. C.; Rhodes, T. L.; Schmitz, L.; Wang, G.; Zeng, L.; Holland, C.; McKee, G. R.

    2012-08-15

    Electron profile stiffness was studied in DIII-D L-mode discharges by systematically varying the heat flux in a narrow region with electron cyclotron heating and measuring the local change produced in {nabla}T{sub e}. Electron stiffness was found to slowly increase with toroidal rotation velocity. A critical inverse temperature gradient scale length 1/L{sub C} {approx} 3 m{sup -1} was identified at {rho}=0.6 and found to be independent of rotation. Both the heat pulse diffusivity and the power balance diffusivity, the latter determined by integrating the measured dependence of the heat pulse diffusivity on -{nabla}T{sub e}, were fit reasonably well by a model containing a critical inverse temperature gradient scale length and varying linearly with 1/L{sub T} above the threshold.

  13. Material Stiffness Effects on Neurite Alignment to Photopolymerized Micropatterns

    PubMed Central

    2015-01-01

    The ability to direct neurite growth into a close proximity of stimulating elements of a neural prosthesis, such as a retinal or cochlear implant (CI), may enhance device performance and overcome current spatial signal resolution barriers. In this work, spiral ganglion neurons (SGNs), which are the target neurons to be stimulated by CIs, were cultured on photopolymerized micropatterns with varied matrix stiffnesses to determine the effect of rigidity on neurite alignment to physical cues. Micropatterns were generated on methacrylate thin film surfaces in a simple, rapid photopolymerization step by photomasking the prepolymer formulation with parallel line–space gratings. Two methacrylate series, a nonpolar HMA-co-HDDMA series and a polar PEGDMA-co-EGDMA series, with significantly different surface wetting properties were evaluated. Equivalent pattern periodicity was maintained across each methacrylate series based on photomask band spacing, and the feature amplitude was tuned to a depth of 2 μm amplitude for all compositions using the temporal control afforded by the UV curing methodology. The surface morphology was characterized by scanning electron microscopy and white light interferometry. All micropatterned films adsorb similar amounts of laminin from solution, and no significant difference in SGN survival was observed when the substrate compositions were compared. SGN neurite alignment significantly increases with increasing material modulus for both methacrylate series. Interestingly, SGN neurites respond to material stiffness cues that are orders of magnitude higher (GPa) than what is typically ascribed to neural environments (kPa). The ability to understand neurite response to engineered physical cues and mechanical properties such as matrix stiffness will allow the development of advanced biomaterials that direct de novo neurite growth to address the spatial signal resolution limitations of current neural prosthetics. PMID:25211120

  14. Stiff modes in spinvalve simulations with OOMMF

    NASA Astrophysics Data System (ADS)

    Mitropoulos, Spyridon; Tsiantos, Vassilis; Ovaliadis, Kyriakos; Kechrakos, Dimitris; Donahue, Michael

    2016-04-01

    Micromagnetic simulations are an important tool for the investigation of magnetic materials. Micromagnetic software uses various techniques to solve differential equations, partial or ordinary, involved in the dynamic simulations. Euler, Runge-Kutta, Adams, and BDF (Backward Differentiation Formulae) are some of the methods used for this purpose. In this paper, spinvalve simulations are investigated. Evidence is presented showing that these systems have stiff modes, and that implicit methods such as BDF are more effective than explicit methods in such cases.

  15. METHOD OF HYPERBOLIC SYSTEMS WITH STIFF RELAXATION

    SciTech Connect

    R. B. LOWRIE; J. E. MOREL

    2001-03-01

    Three methods are analyzed for solving a linear hyperbolic system that contains stiff relaxation. We show that the semi-discrete discontinuous Galerkin method, with a linear basis, is accurate when the relaxation time is unresolved (asymptotically preserving--AP). A recently developed central method is shown to be non-AP. To discriminate between AP and non-AP methods, we argue that one must study problems that are diffusion dominated.

  16. Stiff-Person Syndrome: Case Series

    PubMed Central

    Jung, Yu Jin; Jeong, Han G.; Kim, Ryul; Kim, Han-Joon; Jeon, Beom S.

    2014-01-01

    Stiff-person syndrome (SPS) is a rare disorder, characterized by progressive fluctuating muscular rigidity and spasms. Glutamic acid decarboxylase (GAD) antibody is primarily involved in the pathogenesis of SPS and SPS is strongly associated with other autoimmune disease. Here we report three cases of patients with classical SPS finally confirmed by high serum level of GAD antibodies. All of our patients respond favorably to gamma amino butyric acid-enhancing drugs and immunotherapies. PMID:24926406

  17. The stiffness tailoring of megawatt wind turbine

    NASA Astrophysics Data System (ADS)

    Li, Z. M.; Li, C.; Ye, Z.; Wu, P.; Lu, Y. F.

    2013-12-01

    Wind power has developed rapidly in recently years, the wind turbine's blades determine the performance of the device and the power. In this paper, we used integrated tailoring aimed at institutional characteristics of horizontal axis wind turbine with the composite laminated plate theory, then analyzed the composite blades of wind turbine by combining experimental analysis and finite elements method, and finally studied the influences that composite material properties on stiffness tailoring with changes in the number of different layers.

  18. Extreme damping in composite materials with negative-stiffness inclusions.

    PubMed

    Lakes, R S; Lee, T; Bersie, A; Wang, Y C

    2001-03-29

    When a force deforms an elastic object, practical experience suggests that the resulting displacement will be in the same direction as the force. This property is known as positive stiffness. Less familiar is the concept of negative stiffness, where the deforming force and the resulting displacement are in opposite directions. (Negative stiffness is distinct from negative Poisson's ratio, which refers to the occurrence of lateral expansion upon stretching an object.) Negative stiffness can occur, for example, when the deforming object has stored (or is supplied with) energy. This property is usually unstable, but it has been shown theoretically that inclusions of negative stiffness can be stabilized within a positive-stiffness matrix. Here we describe the experimental realization of this composite approach by embedding negative-stiffness inclusions of ferroelastic vanadium dioxide in a pure tin matrix. The resulting composites exhibit extreme mechanical damping and large anomalies in stiffness, as a consequence of the high local strains that result from the inclusions deforming more than the composite as a whole. Moreover, for certain temperature ranges, the negative-stiffness inclusions are more effective than diamond inclusions for increasing the overall composite stiffness. We expect that such composites could be useful as high damping materials, as stiff structural elements or for actuator-type applications. PMID:11279490

  19. Regional brain stiffness changes across the Alzheimer's disease spectrum☆

    PubMed Central

    Murphy, Matthew C.; Jones, David T.; Jack, Clifford R.; Glaser, Kevin J.; Senjem, Matthew L.; Manduca, Armando; Felmlee, Joel P.; Carter, Rickey E.; Ehman, Richard L.; Huston, John

    2015-01-01

    Magnetic resonance elastography (MRE) is an MRI-based technique to noninvasively measure tissue stiffness. Currently well established for clinical use in the liver, MRE is increasingly being investigated to measure brain stiffness as a novel biomarker of a variety of neurological diseases. The purpose of this work was to apply a recently developed MRE pipeline to measure regional brain stiffness changes in human subjects across the Alzheimer's disease (AD) spectrum, and to gain insights into the biological processes underlying those stiffness changes by correlating stiffness with existing biomarkers of AD. The results indicate that stiffness changes occur mostly in the frontal, parietal and temporal lobes, in accordance with the known topography of AD pathology. Furthermore, stiffness in those areas correlates with existing imaging biomarkers of AD including hippocampal volumes and amyloid PET. Additional analysis revealed preliminary but significant evidence that the relationship between brain stiffness and AD severity is nonlinear and non-monotonic. Given that similar relationships have been observed in functional MRI experiments, we used task-free fMRI data to test the hypothesis that brain stiffness was sensitive to structural changes associated with altered functional connectivity. The analysis revealed that brain stiffness is significantly and positively correlated with default mode network connectivity. Therefore, brain stiffness as measured by MRE has potential to provide new and essential insights into the temporal dynamics of AD, as well as the relationship between functional and structural plasticity as it relates to AD pathophysiology. PMID:26900568

  20. Regional brain stiffness changes across the Alzheimer's disease spectrum.

    PubMed

    Murphy, Matthew C; Jones, David T; Jack, Clifford R; Glaser, Kevin J; Senjem, Matthew L; Manduca, Armando; Felmlee, Joel P; Carter, Rickey E; Ehman, Richard L; Huston, John

    2016-01-01

    Magnetic resonance elastography (MRE) is an MRI-based technique to noninvasively measure tissue stiffness. Currently well established for clinical use in the liver, MRE is increasingly being investigated to measure brain stiffness as a novel biomarker of a variety of neurological diseases. The purpose of this work was to apply a recently developed MRE pipeline to measure regional brain stiffness changes in human subjects across the Alzheimer's disease (AD) spectrum, and to gain insights into the biological processes underlying those stiffness changes by correlating stiffness with existing biomarkers of AD. The results indicate that stiffness changes occur mostly in the frontal, parietal and temporal lobes, in accordance with the known topography of AD pathology. Furthermore, stiffness in those areas correlates with existing imaging biomarkers of AD including hippocampal volumes and amyloid PET. Additional analysis revealed preliminary but significant evidence that the relationship between brain stiffness and AD severity is nonlinear and non-monotonic. Given that similar relationships have been observed in functional MRI experiments, we used task-free fMRI data to test the hypothesis that brain stiffness was sensitive to structural changes associated with altered functional connectivity. The analysis revealed that brain stiffness is significantly and positively correlated with default mode network connectivity. Therefore, brain stiffness as measured by MRE has potential to provide new and essential insights into the temporal dynamics of AD, as well as the relationship between functional and structural plasticity as it relates to AD pathophysiology.

  1. Nanocharacterization of the negative stiffness of ferroelectric materials

    NASA Astrophysics Data System (ADS)

    Alipour Skandani, A.; Ctvrtlik, R.; Al-Haik, M.

    2014-08-01

    Phase changing materials such as ferroelectric materials could exhibit negative stiffness under certain thermomechanical environments. This negative stiffness is embodied by a deflection along the opposite direction of the applied load. So far negative stiffness materials were investigated with the specific morphology of embedded inclusions in stiff matrices then the resulting composite is studied to measure the behavior of each constituent indirectly. In this study, a modified nonisothermal nanoindentation method is developed to measure the negative stiffness of triglycine sulfate single crystal directly. This in-situ method is intended to first demonstrate the feasibility of detecting the negative stiffness via nanoindentation and nanocreep of a ferroelectric material at its Curie point and then to quantify the negative stiffness without the need for embedding the crystal within a stiffer matrix.

  2. Muscle short-range stiffness can be used to estimate the endpoint stiffness of the human arm

    PubMed Central

    Hu, Xiao; Murray, Wendy M.

    2011-01-01

    The mechanical properties of the human arm are regulated to maintain stability across many tasks. The static mechanics of the arm can be characterized by estimates of endpoint stiffness, considered especially relevant for the maintenance of posture. At a fixed posture, endpoint stiffness can be regulated by changes in muscle activation, but which activation-dependent muscle properties contribute to this global measure of limb mechanics remains unclear. We evaluated the role of muscle properties in the regulation of endpoint stiffness by incorporating scalable models of muscle stiffness into a three-dimensional musculoskeletal model of the human arm. Two classes of muscle models were tested: one characterizing short-range stiffness and two estimating stiffness from the slope of the force-length curve. All models were compared with previously collected experimental data describing how endpoint stiffness varies with changes in voluntary force. Importantly, muscle properties were not fit to the experimental data but scaled only by the geometry of individual muscles in the model. We found that force-dependent variations in endpoint stiffness were accurately described by the short-range stiffness of active arm muscles. Over the wide range of evaluated arm postures and voluntary forces, the musculoskeletal model incorporating short-range stiffness accounted for 98 ± 2, 91 ± 4, and 82 ± 12% of the variance in stiffness orientation, shape, and area, respectively, across all simulated subjects. In contrast, estimates based on muscle force-length curves were less accurate in all measures, especially stiffness area. These results suggest that muscle short-range stiffness is a major contributor to endpoint stiffness of the human arm. Furthermore, the developed model provides an important tool for assessing how the nervous system may regulate endpoint stiffness via changes in muscle activation. PMID:21289133

  3. Increasing matrix stiffness upregulates vascular endothelial growth factor expression in hepatocellular carcinoma cells mediated by integrin β1.

    PubMed

    Dong, Yinying; Xie, Xiaoying; Wang, Zhiming; Hu, Chao; Zheng, Qiongdan; Wang, Yaohui; Chen, Rongxin; Xue, Tongchun; Chen, Jie; Gao, Dongmei; Wu, Weizhong; Ren, Zhenggang; Cui, Jiefeng

    2014-02-14

    Matrix stiffness as a novel regulation factor involves in modulating the pathogenesis of hepatocellular carcinoma (HCC) invasion or metastasis. However, the mechanism by which matrix stiffness modulates HCC angiogenesis remains unknown. Here, using buffalo rat HCC models with different liver matrix stiffness backgrounds and an in vitro cell culture system of mechanically tunable Collagen1 (COL1)-coated polyacrylamide gel, we investigated the effects of different matrix stiffness levels on vascular endothelial growth factor (VEGF) expression in HCC cells and explored its regulatory mechanism for controlling HCC angiogenesis. Tissue microarray analysis showed that the expression levels of VEGF and CD31 were gradually upregulated in tumor tissues with increasing COL1 and lysyl oxidase (LOX) expression, indicating a positive correlation between tumor angiogenesis and matrix rigidity. The expression of VEGF and the phosphorylation levels of PI3K and Akt were all upregulated in HCC cells on high-stiffness gel than on low-stiffness gel. Meanwhile, alteration of intergrin β1 expression was found to be the most distinctive, implying that it might mediate the response of HCC cells to matrix stiffness simulation. After integrin β1 was blocked in HCC cells using specific monoclonal antibody, the expression of VEGF and the phosphorylation levels of PI3K and Akt at different culture times were accordingly suppressed and downregulated in the treatment group as compared with those in the control group. All data suggested that the extracellular matrix stiffness stimulation signal was transduced into HCC cells via integrin β1, and this signal activated the PI3K/Akt pathway and upregulated VEGF expression. This study unveils a new paradigm in which matrix stiffness as initiators to modulate HCC angiogenesis.

  4. Cosmology with a stiff matter era

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri

    2015-11-01

    We consider the possibility that the Universe is made of a dark fluid described by a quadratic equation of state P =K ρ2 , where ρ is the rest-mass density and K is a constant. The energy density ɛ =ρ c2+K ρ2 is the sum of two terms: a rest-mass term ρ c2 that mimics "dark matter" (P =0 ) and an internal energy term u =K ρ2=P that mimics a "stiff fluid" (P =ɛ ) in which the speed of sound is equal to the speed of light. In the early universe, the internal energy dominates and the dark fluid behaves as a stiff fluid (P ˜ɛ , ɛ ∝a-6). In the late universe, the rest-mass energy dominates and the dark fluid behaves as pressureless dark matter (P ≃0 , ɛ ∝a-3). We provide a simple analytical solution of the Friedmann equations for a universe undergoing a stiff matter era, a dark matter era, and a dark energy era due to the cosmological constant. This analytical solution generalizes the Einstein-de Sitter solution describing the dark matter era, and the Λ CDM model describing the dark matter era and the dark energy era. Historically, the possibility of a primordial stiff matter era first appeared in the cosmological model of Zel'dovich where the primordial universe is assumed to be made of a cold gas of baryons. A primordial stiff matter era also occurs in recent cosmological models where dark matter is made of relativistic self-gravitating Bose-Einstein condensates (BECs). When the internal energy of the dark fluid mimicking stiff matter is positive, the primordial universe is singular like in the standard big bang theory. It expands from an initial state with a vanishing scale factor and an infinite density. We consider the possibility that the internal energy of the dark fluid is negative (while, of course, its total energy density is positive), so that it mimics anti-stiff matter. This happens, for example, when the BECs have an attractive self-interaction with a negative scattering length. In that case, the primordial universe is nonsingular and

  5. An in-flight investigation of nonlinear roll control

    NASA Technical Reports Server (NTRS)

    Ellis, D. R.; Tilak, N. W.

    1975-01-01

    An in-flight simulation was undertaken to study the piloting problems associated with a type of nonlinear control effectiveness which is characteristic of spoiler roll control systems. Typically, the initial response is small or even zero, followed by a narrow region of highly effective control, and a final one of moderate effectiveness. Results for the landing flare and touchdown, which turned out to be the critical flight phase, indicate that a substantial amount of dead zone and changing effectiveness can be tolerated, but the best level of handling is obtained with linear, aileron-like control.

  6. A Comprehensive Robust Adaptive Controller for Gust Load Alleviation

    PubMed Central

    Quagliotti, Fulvia

    2014-01-01

    The objective of this paper is the implementation and validation of an adaptive controller for aircraft gust load alleviation. The contribution of this paper is the design of a robust controller that guarantees the reduction of the gust loads, even when the nominal conditions change. Some preliminary results are presented, considering the symmetric aileron deflection as control device. The proposed approach is validated on subsonic transport aircraft for different mass and flight conditions. Moreover, if the controller parameters are tuned for a specific gust model, even if the gust frequency changes, no parameter retuning is required. PMID:24688411

  7. Exploring bird aerodynamics using radio-controlled models.

    PubMed

    Hoey, Robert G

    2010-12-01

    A series of radio-controlled glider models was constructed by duplicating the aerodynamic shape of soaring birds (raven, turkey vulture, seagull and pelican). Controlled tests were conducted to determine the level of longitudinal and lateral-directional static stability, and to identify the characteristics that allowed flight without a vertical tail. The use of tail-tilt for controlling small bank-angle changes, as observed in soaring birds, was verified. Subsequent tests, using wing-tip ailerons, inferred that birds use a three-dimensional flow pattern around the wing tip (wing tip vortices) to control adverse yaw and to create a small amount of forward thrust in gliding flight.

  8. Fuzzy Logic Decoupled Lateral Control for General Aviation Airplanes

    NASA Technical Reports Server (NTRS)

    Duerksen, Noel

    1997-01-01

    It has been hypothesized that a human pilot uses the same set of generic skills to control a wide variety of aircraft. If this is true, then it should be possible to construct an electronic controller which embodies this generic skill set such that it can successfully control different airplanes without being matched to a specific airplane. In an attempt to create such a system, a fuzzy logic controller was devised to control aileron or roll spoiler position. This controller was used to control bank angle for both a piston powered single engine aileron equipped airplane simulation and a business jet simulation which used spoilers for primary roll control. Overspeed, stall and overbank protection were incorporated in the form of expert systems supervisors and weighted fuzzy rules. It was found that by using the artificial intelligence techniques of fuzzy logic and expert systems, a generic lateral controller could be successfully used on two general aviation aircraft types that have very different characteristics. These controllers worked for both airplanes over their entire flight envelopes. The controllers for both airplanes were identical except for airplane specific limits (maximum allowable airspeed, throttle ]ever travel, etc.). This research validated the fact that the same fuzzy logic based controller can control two very different general aviation airplanes. It also developed the basic controller architecture and specific control parameters required for such a general controller.

  9. Blood pressure and arterial stiffness in obese children and adolescents.

    PubMed

    Hvidt, Kristian Nebelin

    2015-03-01

    Obesity, elevated blood pressure (BP) and arterial stiffness are risk factors for cardiovascular disease. A strong relationship exists between obesity and elevated BP in both children and adults. Obesity and elevated BP in childhood track into adult life increasing the risk of cardiovascular disease in adulthood. Ambulatory BP is the most precise measure to evaluate the BP burden, whereas carotid-femoral pulse wave velocity (cfPWV) is regarded as the gold standard for evaluating arterial (i.e. aortic) stiffness. These measures might contribute to a better understanding of obesity's adverse impact on the cardiovascular system, and ultimately a better prevention and treatment of childhood obesity. The overall aim of the present PhD thesis is to investigate arterial stiffness and 24-hour BP in obese children and adolescents, and evaluate whether these measures are influenced by weight reduction. The present PhD thesis is based on four scientific papers.  In a cross-sectional design, 104 severe obese children and adolescents with an age of 10-18 years were recruited when newly referred to the Children's Obesity Clinic, Holbæk University Hospital, and compared to 50 normal weighted age and gender matched control individuals. Ambulatory BP was measured, and cfPWV was investigated in two ways in respect to the distance measure of aorta; the previously recommended length - the so called subtracted distance, and the currently recommended length - the direct distance. In a longitudinal design, the obese patients were re-investigated after one-year of lifestyle intervention at the Children's Obesity Clinic in purpose of reducing the degree of obesity. In the cross-sectional design, the obese group had higher measures of obesity, while matched for age, gender and height, when compared to the control group. In the longitudinal design, 74% of the 72 followed up obese patients experienced a significant weight reduction. CfPWV was dependent on the method used to measure the

  10. New method to improve dynamic stiffness of electro-hydraulic servo systems

    NASA Astrophysics Data System (ADS)

    Bai, Yanhong; Quan, Long

    2013-09-01

    Most current researches working on improving stiffness focus on the application of control theories. But controller in closed-loop hydraulic control system takes effect only after the controlled position is deviated, so the control action is lagged. Thus dynamic performance against force disturbance and dynamic load stiffness can’t be improved evidently by advanced control algorithms. In this paper, the elementary principle of maintaining piston position unchanged under sudden external force load change by charging additional oil is analyzed. On this basis, the conception of raising dynamic stiffness of electro hydraulic position servo system by flow feedforward compensation is put forward. And a scheme using double servo valves to realize flow feedforward compensation is presented, in which another fast response servo valve is added to the regular electro hydraulic servo system and specially utilized to compensate the compressed oil volume caused by load impact in time. The two valves are arranged in parallel to control the cylinder jointly. Furthermore, the model of flow compensation is derived, by which the product of the amplitude and width of the valve’s pulse command signal can be calculated. And determination rules of the amplitude and width of pulse signal are concluded by analysis and simulations. Using the proposed scheme, simulations and experiments at different positions with different force changes are conducted. The simulation and experimental results show that the system dynamic performance against load force impact is largely improved with decreased maximal dynamic position deviation and shortened settling time. That is, system dynamic load stiffness is evidently raised. This paper proposes a new method which can effectively improve the dynamic stiffness of electro-hydraulic servo systems.

  11. Analysis and design of a nonlinear stiffness and damping system with a scissor-like structure

    NASA Astrophysics Data System (ADS)

    Sun, Xiuting; Jing, Xingjian

    2016-01-01

    An n-layer Scissor-Like Structured (SLS) vibration isolation platform is studied in this paper, focusing on the analysis and design of nonlinear stiffness, friction forces and damping characteristics for an advantageous vibration isolation performance. The system nonlinear stiffness and damping characteristics are theoretically investigated by considering the influence incurred by different structural parameters, friction forces and link inertia. Since stiffness and damping properties are both asymmetrical nonlinear functions, and Coulomb friction is piecewise nonlinear function, Perturbation Method (PM) and Average Method (AM) are applied together to achieve better solutions. The vibration isolation performance of the SLS platform is compared with known quasi-zero-stiffness vibration isolators in the literature, and a typical application case study as a vehicle seat suspension is also conducted, subjected to different load masses, and base excitations. The results show that much better vibration isolation performance and loading capacity can be easily achieved with the SLS platform by designing structural parameters, and the scissor-like structure provides a very powerful, practical and passive solution to design and realization of beneficial nonlinear stiffness and damping characteristics in vibration control.

  12. Tuning 3D Collagen Matrix Stiffness Independently of Collagen Concentration Modulates Endothelial Cell Behavior

    PubMed Central

    Mason, Brooke N.; Starchenko, Alina; Williams, Rebecca M.; Bonassar, Lawrence J.; Reinhart-King, Cynthia A.

    2012-01-01

    Numerous studies have described the effects of matrix stiffening on cell behavior using two dimensional (2D) synthetic surfaces; however less is known about the effects of matrix stiffening on cells embedded in three dimensional (3D) in vivo-like matrices. A primary limitation in investigating the effects of matrix stiffness in 3D is the lack of materials that can be tuned to control stiffness independently of matrix density. Here, we use collagen-based scaffolds where the mechanical properties are tuned using non-enzymatic glycation of the collagen in solution, prior to polymerization. Collagen solutions glycated prior to polymerization result in collagen gels with a 3-fold increase in compressive modulus without significant changes to the collagen architecture. Using these scaffolds, we show that endothelial cell spreading increases with matrix stiffness, as does the number and length of angiogenic sprouts and the overall spheroid outgrowth. Differences in sprout length are maintained even when the receptor for advanced glycation endproducts is inhibited. Our results demonstrate the ability to de-couple matrix stiffness from matrix density and structure in collagen gels, and that increased matrix stiffness results in increased sprouting and outgrowth. PMID:22902816

  13. Effect of Polyelectrolyte Film Stiffness on Endothelial Cells During Endothelial-to-Mesenchymal Transition.

    PubMed

    Zhang, He; Chang, Hao; Wang, Li-mei; Ren, Ke-feng; Martins, M Cristina L; Barbosa, Mário A; Ji, Jian

    2015-11-01

    Endothelial-to-mesenchymal transition (EndMT), during which endothelial cells (ECs) transdifferentiate into mesenchymal phenotype, plays a key role in the development of vascular implant complications such as endothelium dysfunction and in-stent restenosis. Substrate stiffness has been confirmed as a key factor to influence EC behaviors; however, so far, the relationship between substrate stiffness and EndMT has been rarely studied. Here, ECs were cultured on the (poly(L-lysine)/hyaluronate acid) (PLL/HA) multilayer films with controlled stiffness for 2 weeks, and their EndMT behaviors were studied. We demonstrated that ECs lost their markers (vWf and CD31) in a stiffness-dependent manner even without supplement of growth factors, and the softer film favored the maintaining of EC phenotype. Further, induced by transforming growth factor β1 (TGF-β1), ECs underwent EndMT, as characterized by losing their typical cobblestone morphology and markers and gaining smooth muscle cell markers (α-smooth muscle actin and calponin). Interestingly, stronger EndMT was observed when ECs were cultured on the stiffer film. Collectively, our findings suggest that substrate stiffness has significant effects on EndMT, and a softer substrate is beneficial to ECs by keeping their phenotype and inhibiting EndMT, which presents a new strategy for surface design of vascular implant materials. PMID:26477358

  14. Collagen Substrate Stiffness Anisotropy Affects Cellular Elongation, Nuclear Shape, and Stem Cell Fate toward Anisotropic Tissue Lineage.

    PubMed

    Islam, Anowarul; Younesi, Mousa; Mbimba, Thomas; Akkus, Ozan

    2016-09-01

    Rigidity of substrates plays an important role in stem cell fate. Studies are commonly carried out on isotropically stiff substrate or substrates with unidirectional stiffness gradients. However, many native tissues are anisotropically stiff and it is unknown whether controlled presentation of stiff and compliant material axes on the same substrate governs cytoskeletal and nuclear morphology, as well as stem cell differentiation. In this study, electrocompacted collagen sheets are stretched to varying degrees to tune the stiffness anisotropy (SA) in the range of 1 to 8, resulting in stiff and compliant material axes orthogonal to each other. The cytoskeletal aspect ratio increased with increasing SA by about fourfold. Such elongation was absent on cellulose acetate replicas of aligned collagen surfaces indicating that the elongation was not driven by surface topography. Mesenchymal stem cells (MSCs) seeded on varying anisotropy sheets displayed a dose-dependent upregulation of tendon-related markers such as Mohawk and Scleraxis. After 21 d of culture, highly anisotropic sheets induced greater levels of production of type-I, type-III collagen, and thrombospondin-4. Therefore, SA has direct effects on MSC differentiation. These findings may also have ramifications of stem cell fate on other anisotropically stiff tissues, such as skeletal/cardiac muscles, ligaments, and bone.

  15. Collagen Substrate Stiffness Anisotropy Affects Cellular Elongation, Nuclear Shape, and Stem Cell Fate toward Anisotropic Tissue Lineage.

    PubMed

    Islam, Anowarul; Younesi, Mousa; Mbimba, Thomas; Akkus, Ozan

    2016-09-01

    Rigidity of substrates plays an important role in stem cell fate. Studies are commonly carried out on isotropically stiff substrate or substrates with unidirectional stiffness gradients. However, many native tissues are anisotropically stiff and it is unknown whether controlled presentation of stiff and compliant material axes on the same substrate governs cytoskeletal and nuclear morphology, as well as stem cell differentiation. In this study, electrocompacted collagen sheets are stretched to varying degrees to tune the stiffness anisotropy (SA) in the range of 1 to 8, resulting in stiff and compliant material axes orthogonal to each other. The cytoskeletal aspect ratio increased with increasing SA by about fourfold. Such elongation was absent on cellulose acetate replicas of aligned collagen surfaces indicating that the elongation was not driven by surface topography. Mesenchymal stem cells (MSCs) seeded on varying anisotropy sheets displayed a dose-dependent upregulation of tendon-related markers such as Mohawk and Scleraxis. After 21 d of culture, highly anisotropic sheets induced greater levels of production of type-I, type-III collagen, and thrombospondin-4. Therefore, SA has direct effects on MSC differentiation. These findings may also have ramifications of stem cell fate on other anisotropically stiff tissues, such as skeletal/cardiac muscles, ligaments, and bone. PMID:27377355

  16. Influence of visual feedback in the regulation of arm stiffness following stroke.

    PubMed

    Piovesan, Davide; Casadio, Maura; Morasso, Pietro; Giannoni, Psiche

    2011-01-01

    Stroke survivors strongly rely on visual feedback to control their movements, since segmental reflexes are characterized by an inherent hyper-excitability. To test the effect of visual feedback on the modulation of arm stability we estimated the stiffness of the paretic arm in nine stroke survivors during robot mediated therapy, where subjects trained with and without vision. While several studies found a negligible effect in unimpaired individuals, our results highlighted a marked reduction of stroke survivors' arm stiffness in absence of visual feedback.

  17. Arterial stiffness & Sri Lankan chronic kidney disease of unknown origin

    PubMed Central

    Gifford, Fiona; Kimmitt, Robert; Herath, Chula; Webb, David J; Melville, Vanessa; Siribaddana, Sisira; Eddleston, Michael; Dhaun, Neeraj

    2016-01-01

    Chronic kidney disease (CKD) is common and independently associated with cardiovascular disease (CVD). Arterial stiffness contributes to CVD risk in CKD. In many developing countries a considerable proportion of CKD remains unexplained, termed CKDu. We assessed arterial stiffness in subjects with Sri Lankan CKDu, in matched controls without CKD and in those with defined CKD. Aortic blood pressure (BP), pulse wave velocity (PWV) and augmentation index (AIx) were assessed in 130 subjects (50 with CKDu, 45 with CKD and 35 without CKD) using the validated TensioMed™ Arteriograph monitor. Brachial and aortic BP was lower in controls than in CKDu and CKD subjects but no different between CKDu and CKD. Controls had a lower PWV compared to subjects with CKDu and CKD. Despite equivalent BP and renal dysfunction, CKDu subjects had a lower PWV than those with CKD (8.7 ± 1.5 vs. 9.9 ± 2.2 m/s, p < 0.01). Excluding diabetes accentuated the differences in PWV seen between groups (controls vs. CKDu vs. CKD: 6.7 ± 0.9 vs. 8.7 ± 1.5 vs. 10.4 ± 1.5 m/s, p < 0.001 for all). Sri Lankan CKDu is associated with less arterial stiffening than defined causes of CKD. Whether this translates to lower cardiovascular morbidity and mortality long term is unclear and should be the focus of future studies. PMID:27586642

  18. Arterial stiffness & Sri Lankan chronic kidney disease of unknown origin

    NASA Astrophysics Data System (ADS)

    Gifford, Fiona; Kimmitt, Robert; Herath, Chula; Webb, David J.; Melville, Vanessa; Siribaddana, Sisira; Eddleston, Michael; Dhaun, Neeraj

    2016-09-01

    Chronic kidney disease (CKD) is common and independently associated with cardiovascular disease (CVD). Arterial stiffness contributes to CVD risk in CKD. In many developing countries a considerable proportion of CKD remains unexplained, termed CKDu. We assessed arterial stiffness in subjects with Sri Lankan CKDu, in matched controls without CKD and in those with defined CKD. Aortic blood pressure (BP), pulse wave velocity (PWV) and augmentation index (AIx) were assessed in 130 subjects (50 with CKDu, 45 with CKD and 35 without CKD) using the validated TensioMed™ Arteriograph monitor. Brachial and aortic BP was lower in controls than in CKDu and CKD subjects but no different between CKDu and CKD. Controls had a lower PWV compared to subjects with CKDu and CKD. Despite equivalent BP and renal dysfunction, CKDu subjects had a lower PWV than those with CKD (8.7 ± 1.5 vs. 9.9 ± 2.2 m/s, p < 0.01). Excluding diabetes accentuated the differences in PWV seen between groups (controls vs. CKDu vs. CKD: 6.7 ± 0.9 vs. 8.7 ± 1.5 vs. 10.4 ± 1.5 m/s, p < 0.001 for all). Sri Lankan CKDu is associated with less arterial stiffening than defined causes of CKD. Whether this translates to lower cardiovascular morbidity and mortality long term is unclear and should be the focus of future studies.

  19. Arterial stiffness &Sri Lankan chronic kidney disease of unknown origin.

    PubMed

    Gifford, Fiona; Kimmitt, Robert; Herath, Chula; Webb, David J; Melville, Vanessa; Siribaddana, Sisira; Eddleston, Michael; Dhaun, Neeraj

    2016-01-01

    Chronic kidney disease (CKD) is common and independently associated with cardiovascular disease (CVD). Arterial stiffness contributes to CVD risk in CKD. In many developing countries a considerable proportion of CKD remains unexplained, termed CKDu. We assessed arterial stiffness in subjects with Sri Lankan CKDu, in matched controls without CKD and in those with defined CKD. Aortic blood pressure (BP), pulse wave velocity (PWV) and augmentation index (AIx) were assessed in 130 subjects (50 with CKDu, 45 with CKD and 35 without CKD) using the validated TensioMed™ Arteriograph monitor. Brachial and aortic BP was lower in controls than in CKDu and CKD subjects but no different between CKDu and CKD. Controls had a lower PWV compared to subjects with CKDu and CKD. Despite equivalent BP and renal dysfunction, CKDu subjects had a lower PWV than those with CKD (8.7 ± 1.5 vs. 9.9 ± 2.2 m/s, p < 0.01). Excluding diabetes accentuated the differences in PWV seen between groups (controls vs. CKDu vs. CKD: 6.7 ± 0.9 vs. 8.7 ± 1.5 vs. 10.4 ± 1.5 m/s, p < 0.001 for all). Sri Lankan CKDu is associated with less arterial stiffening than defined causes of CKD. Whether this translates to lower cardiovascular morbidity and mortality long term is unclear and should be the focus of future studies. PMID:27586642

  20. Myo1g is an active player in maintaining cell stiffness in B-lymphocytes.

    PubMed

    López-Ortega, O; Ovalle-García, E; Ortega-Blake, I; Antillón, A; Chávez-Munguía, B; Patiño-López, G; Fragoso-Soriano, R; Santos-Argumedo, L

    2016-05-01

    B-lymphocytes are migrating cells that specialize in antigen presentation, antibody secretion, and endocytosis; these processes implicate the modulation of plasma membrane elasticity. Cell stiffness is a force generated by the interaction between the actin-cytoskeleton and the plasma membrane, which requires the participation of several proteins. These proteins include class I myosins, which are now considered to play a role in controlling membrane-cytoskeleton interactions. In this study, we identified the motor protein Myosin 1g (Myo1g) as a mediator of this phenomenon. The absence of Myo1g decreased the cell stiffness, affecting cell adhesion, cell spreading, phagocytosis, and endocytosis in B-lymphocytes. The results described here reveal a novel molecular mechanism by which Myo1g mediates and regulates cell stiffness in B-lymphocytes. © 2016 Wiley Periodicals, Inc. PMID:27106882

  1. Myo1g is an active player in maintaining cell stiffness in B-lymphocytes.

    PubMed

    López-Ortega, O; Ovalle-García, E; Ortega-Blake, I; Antillón, A; Chávez-Munguía, B; Patiño-López, G; Fragoso-Soriano, R; Santos-Argumedo, L

    2016-05-01

    B-lymphocytes are migrating cells that specialize in antigen presentation, antibody secretion, and endocytosis; these processes implicate the modulation of plasma membrane elasticity. Cell stiffness is a force generated by the interaction between the actin-cytoskeleton and the plasma membrane, which requires the participation of several proteins. These proteins include class I myosins, which are now considered to play a role in controlling membrane-cytoskeleton interactions. In this study, we identified the motor protein Myosin 1g (Myo1g) as a mediator of this phenomenon. The absence of Myo1g decreased the cell stiffness, affecting cell adhesion, cell spreading, phagocytosis, and endocytosis in B-lymphocytes. The results described here reveal a novel molecular mechanism by which Myo1g mediates and regulates cell stiffness in B-lymphocytes. © 2016 Wiley Periodicals, Inc.

  2. Aortic Compliance and Stiffness Among Severe Longstanding Hypertensive and Non-hypertensive

    PubMed Central

    Kamberi, Lulzim Selim; Gorani, Daut Rashit; Hoxha, Teuta Faik; Zahiti, Bedri Faik

    2013-01-01

    Introduction Abnormal aortic function in hypertension is generally attributed to accelerated breakdown of elastin in the aorta, leading to dilatation of the lumen and stiffening of the wall as elastin is replaced with stiffer collagen. Aortic stiffness is an independent predictor of cardiovascular risk and all-cause and cardiovascular mortality. Vascular stiffening can activate endothelium which in turn may promote atherogenesis. Modulation of arterial stiffness has been shown to be successfully managed via changes in lifestyle and put under control of hypertension pharmacologically with antihypertensive drugs and statins. Methods Hundred and forty four patients have been enrolled in this study. They have been divided in two groups, with hypertension and group of control. Groups were with no age difference. Results Group with hypertension were with reduced aortic strain, distensibility (compliance) and have higher stiffness than control group; GrHTA =9.3 compared to GC=5.4. After successful treatment of hypertension with antihypertensives and statins, for two years, these parameters showed improvement, but still remain out of normal range compared to control group; 7.6 vs. 5.38. Conclusions Hypertensive patients have reduced aortic elasticity and increased stiffness which can be stopped and improved after treatment with antihypertensive and statin. PMID:23572854

  3. Relative control effectiveness technique with application to airplane control coordination

    NASA Technical Reports Server (NTRS)

    Lallman, F. J.

    1985-01-01

    A method to select optimal combinations of the control variables of a linear system is reported. The combinations are chosen so that the control channels have their principal influences on selected fundamental modes of the system. A series of algebraic maximization problems is used to maximize the effects of the control channels on selected modes while simultaneously minimizing the effects on the remaining modes. The method is applied to the lateral and directional control of a linearized airplane model having ailerons, a rudder, and differential tail surfaces. Integration of these control eliminates oscillations present in the roll rate for a step lateral-control input and improves the sideslip response with reduced rolling motions for a step directional-control input. Inclusion of thrust-vectoring engine nozzles improves the roll rate capability of the airplane.

  4. Autonomous Flying Controls Testbed

    NASA Technical Reports Server (NTRS)

    Motter, Mark A.

    2005-01-01

    The Flying Controls Testbed (FLiC) is a relatively small and inexpensive unmanned aerial vehicle developed specifically to test highly experimental flight control approaches. The most recent version of the FLiC is configured with 16 independent aileron segments, supports the implementation of C-coded experimental controllers, and is capable of fully autonomous flight from takeoff roll to landing, including flight test maneuvers. The test vehicle is basically a modified Army target drone, AN/FQM-117B, developed as part of a collaboration between the Aviation Applied Technology Directorate (AATD) at Fort Eustis,Virginia and NASA Langley Research Center. Several vehicles have been constructed and collectively have flown over 600 successful test flights.

  5. Catching a ball: contributions of intrinsic muscle stiffness, reflexes, and higher order responses.

    PubMed

    Bennett, D J; Gorassini, M; Prochazka, A

    1994-05-01

    In three sets of experiments in nine normal subjects and a patient with a percutaneous wrist-stabilizing splint, we quantified the open-loop gain (OLG) of the stretch reflex acting about the elbow. The subjects exerted a steady mean flexing force and were instructed not to intervene (i.e., not to resist actively) when force or displacement perturbations were imposed on the forearm. The method was either to reconstruct transmission around the entire loop in a two-part experiment, or to use the attenuation of external perturbations in normal and electrically stimulated muscle to compute gain. Across all experiments, the mean magnitude of stretch reflex OLG was close to unity in the frequency range 1-2 Hz, and declined at higher frequencies, as required to ensure stability, given that the phase lag approached 180 degrees at 5 Hz. Inherent muscle stiffness was approximately equal to reflex stiffness. In functional terms, an OLG of 1 means that the yield caused by a force perturbation is approximately halved by reflex action (prevailing inherent muscle stiffness is doubled). Automatic scaling of reflex transmission at Ia/alpha-motoneuronal synapses ensures that the OLG remains close to unity as inherent stiffness increases. Trials in the patient with the wrist fixator gave similar results, indicating that the reflexes were proprioceptive ly mediated. In a fourth experiment in which the task was to catch a heavy ball, we compared the efficacy of inherent muscle stiffness and reflexes alone, with the subject's intentional reactions, which included predictive and voluntary components of response. The latter were far more effective in maintaining the position of the hand after the ball was caught than inherent and reflex stiffnesses alone. We conclude that stability requirements limit the extent to which stretch reflexes can augment inherent muscle stiffness. When inherent muscle stiffness is low, such as in our ball-catching task, the reflex stiffness is also low, and

  6. Laser application on haptics: Tactile stiffness measurement

    NASA Astrophysics Data System (ADS)

    Scalise, L.; Memeo, M.; Cannella, F.; Valente, M.; Caldwell, D. G.; Tomasini, E. P.

    2012-06-01

    There is a great interest in exploring the proprieties of the sense of the touch, its detailed knowledge in fact is a key issue in the area of robotics, haptics and human-machine interaction. In this paper, the authors focus their attention on a novel measurement method for the assessment of the tactile stiffness based on a original test rig; tactile stiffness is defined as the ratio between force, exerted by the finger, and the displacement of the finger tip operated during the test. To reach this scope, the paper describes a specific experimental test-rig used for the evaluation of subject tactile sensitivity, where finger force applied during tests as well as displacement and velocity of displacement, operated by the subject under investigation, are measured. Results show that tactile stiffness is linear respect to stimuli spatial difference (which is proportional to the difficulty to detect the variation of them). In particular, it has been possible to relate the force and displacement measured during the tests. The relationship between the response of the subject to the grating, velocity and force is determined. These results permit to carry out the further experimental tests on the same subject avoiding the use of a load cell and therefore simplifying the measurement test rig and data post-processing. Indeed, the first aspect (use of a load cell) can be relevant, because the grating positions are different, requiring a specific re-calibration and setting before each trial; while the second aspect allows simplify the test rig complexity and the processing algorithm.

  7. POST-TRAUMATIC STIFFNESS OF THE ELBOW

    PubMed Central

    Filh, Geraldo Motta; Galvão, Marcus Vinicius

    2015-01-01

    Elbow stiffness is a common problem after joint trauma, causing functional impairment of the upper limb. The severity of the dysfunction depends on the nature of the initial trauma and the treatment used. Appropriate clinical evaluation and complementary examinations are essential for therapeutic planning. Several surgical techniques are now available and the recommendation must be made in accordance with patient characteristics, degree of joint limitation and the surgeon's skill. Joint incongruence and degeneration have negative effects on the prognosis, but heterotrophic ossification alone has been correlated with a favorable surgical prognosis. PMID:27022563

  8. On waveguide modeling of stiff piano strings

    NASA Astrophysics Data System (ADS)

    Ducasse, Éric

    2005-09-01

    Bensa et al. [J. Acoust. Soc. Am. 114, 1095-1107 (2003), Sec. IV] recently proposed a waveguide model for the transverse displacement of a stiff piano string. The study described here is an attempt to cast a complementary light on this topic, based on a common wave approach instead of a modal approach. A pair of weakly attenuated traveling waves and a pair of fast-decaying waves both satisfy the one-dimensional wave equation developed by Bensa et al. These solutions have to be carefully considered, however, for portions of string interacting with the hammer felt, the bridge, or the capo d'astro bar.

  9. Changes in aortic stiffness related to elastic fiber network anomalies in the Brown Norway rat during maturation and aging.

    PubMed

    Osborne-Pellegrin, Mary; Labat, Carlos; Mercier, Nathalie; Challande, Pascal; Lacolley, Patrick

    2010-07-01

    Adult Brown Norway (BN) rats exhibit numerous internal elastic lamina (IEL) ruptures in the abdominal aorta (AA) and a lower aortic elastin-to-collagen ratio (E/C) compared with other strains. We studied here AA mechanical properties in BN compared with control strains. AA stiffness (assessed by plotting elastic modulus/wall-stress curves obtained under anesthesia), thoracic aorta elastin and collagen contents, and IEL ruptures in AA were measured in male BN and LOU rats aged 6, 10, and 15 wk. The Long Evans (LE) control strain was compared with BN at more advanced ages (15, 28, and 64 wk). At all ages, aortic E/C was lower in BN than in control strains. At 6 wk, AA stiffness was greater in BN than in LOU. In both strains, AA stiffness decreased between 6 and 10 wk, more so in BN than in LOU, and then increased, reaching similar values at 15 wk. BN AA stiffness was not different from that of LE at 15 and 28 wk, but was significantly lower at 64 wk. The increased stiffness in young BN rat AA may be due to the decreased E/C. IEL rupture onset in the BN around 7-8 wk, which decreases stiffness, as suggested by its pharmacological modulation, abolished such differences by 15 wk. Thereafter, age-related AA stiffness increased less in BN than in LE, likely due to the numerous IEL ruptures. We conclude that, in the BN rat, the lower E/C and the presence of IEL ruptures have opposing effects on arterial stiffness.

  10. Myocardial Stiffness in Patients with Heart Failure and a Preserved Ejection Fraction: Contributions of Collagen and Titin

    PubMed Central

    Zile, Michael R.; Baicu, Catalin F.; Ikonomidis, John; Stroud, Robert E.; Nietert, Paul J.; Bradshaw, Amy D.; Slater, Rebecca; Palmer, Bradley M.; Van Buren, Peter; Meyer, Markus; Redfield, Margaret; Bull, David; Granzier, Henk; LeWinter, Martin M.

    2015-01-01

    Background The purpose of this study was to determine whether patients with heart failure and a preserved ejection fraction (HFpEF) have an increase in passive myocardial stiffness and the extent to which discovered changes are dependent on changes in extracellular matrix fibrillar collagen and/or cardiomyocyte titin. Methods and Results Seventy patients undergoing coronary artery bypass grafting underwent an echocardiogram, plasma biomarker determination, and intra-operative left ventricular (LV) epicardial anterior wall biopsy. Patients were divided into 3 groups: referent control (n=17, no hypertension or diabetes), hypertension (HTN) without(-) HFpEF (n=31), and HTN with(+) HFpEF (n=22). One or more of the following studies were performed on the biopsies: passive stiffness measurements to determine total, collagen-dependent and titin-dependent stiffness (differential extraction assay), collagen assays (biochemistry or histology), or titin isoform and phosphorylation assays. Compared with controls, patients with HTN(-)HFpEF had no change in LV end diastolic pressure (LVEDP), myocardial passive stiffness, collagen, or titin phosphorylation but had an increase in biomarkers of inflammation (CRP, sST2, TIMP-1). Compared with both control and HTN(-)HFpEF, patients with HTN(+)HFpEF had increased LVEDP, left atrial volume, NT-proBNP, total, collagen-dependent and titin-dependent stiffness, insoluble collagen, increased titin phosphorylation on PEVK S11878(S26), reduced phosphorylation on N2B S4185(S469), and increased biomarkers of inflammation. Conclusions Hypertension in the absence of HFpEF, did not alter passive myocardial stiffness. Patients with HTN(+)HFpEF had a significant increase in passive myocardial stiffness; collagen-dependent and titin-dependent stiffness were increased. These data suggest that the development of HFpEF is dependent on changes in both collagen and titin homeostasis. PMID:25637629

  11. Accelerated development and flight evaluation of active controls concepts for subsonic transport aircraft. Volume 1: Load alleviation/extended span development and flight tests

    NASA Technical Reports Server (NTRS)

    Johnston, J. F.

    1979-01-01

    Active wing load alleviation to extend the wing span by 5.8 percent, giving a 3 percent reduction in cruise drag is covered. The active wing load alleviation used symmetric motions of the outboard ailerons for maneuver load control (MLC) and elastic mode suppression (EMS), and stabilizer motions for gust load alleviation (GLA). Slow maneuvers verified the MLC, and open and closed-loop flight frequency response tests verified the aircraft dynamic response to symmetric aileron and stabilizer drives as well as the active system performance. Flight tests in turbulence verified the effectiveness of the active controls in reducing gust-induced wing loads. It is concluded that active wing load alleviation/extended span is proven in the L-1011 and is ready for application to airline service; it is a very practical way to obtain the increased efficiency of a higher aspect ratio wing with minimum structural impact.

  12. Simple polyacrylamide-based multiwell stiffness assay for the study of stiffness-dependent cell responses.

    PubMed

    Syed, Sana; Karadaghy, Amin; Zustiak, Silviya

    2015-03-25

    Currently, most of the in vitro cell research is performed on rigid tissue culture polystyrene (~1 GPa), while most cells in the body are attached to a matrix that is elastic and much softer (0.1-100 kPa). Since such stiffness mismatch greatly affects cell responses, there is a strong interest in developing hydrogel materials that span a wide range of stiffness to serve as cell substrates. Polyacrylamide gels, which are inexpensive and cover the stiffness range of all soft tissues in the body, are the hydrogel of choice for many research groups. However, polyacrylamide gel preparation is lengthy, tedious, and only suitable for small batches. Here, we describe an assay which by utilizing a permanent flexible plastic film as a structural support for the gels, enables the preparation of polyacrylamide gels in a multiwell plate format. The technique is faster, more efficient, and less costly than current methods and permits the preparation of gels of custom sizes not otherwise available. As it doesn't require any specialized equipment, the method could be easily adopted by any research laboratory and would be particularly useful in research focused on understanding stiffness-dependent cell responses.

  13. Simple polyacrylamide-based multiwell stiffness assay for the study of stiffness-dependent cell responses.

    PubMed

    Syed, Sana; Karadaghy, Amin; Zustiak, Silviya

    2015-01-01

    Currently, most of the in vitro cell research is performed on rigid tissue culture polystyrene (~1 GPa), while most cells in the body are attached to a matrix that is elastic and much softer (0.1-100 kPa). Since such stiffness mismatch greatly affects cell responses, there is a strong interest in developing hydrogel materials that span a wide range of stiffness to serve as cell substrates. Polyacrylamide gels, which are inexpensive and cover the stiffness range of all soft tissues in the body, are the hydrogel of choice for many research groups. However, polyacrylamide gel preparation is lengthy, tedious, and only suitable for small batches. Here, we describe an assay which by utilizing a permanent flexible plastic film as a structural support for the gels, enables the preparation of polyacrylamide gels in a multiwell plate format. The technique is faster, more efficient, and less costly than current methods and permits the preparation of gels of custom sizes not otherwise available. As it doesn't require any specialized equipment, the method could be easily adopted by any research laboratory and would be particularly useful in research focused on understanding stiffness-dependent cell responses. PMID:25866916

  14. Substrate stiffness regulates solubility of cellular vimentin

    PubMed Central

    Murray, Maria E.; Mendez, Melissa G.; Janmey, Paul A.

    2014-01-01

    The intermediate filament protein vimentin is involved in the regulation of cell behavior, morphology, and mechanical properties. Previous studies using cells cultured on glass or plastic substrates showed that vimentin is largely insoluble. Although substrate stiffness was shown to alter many aspects of cell behavior, changes in vimentin organization were not reported. Our results show for the first time that mesenchymal stem cells (hMSCs), endothelial cells, and fibroblasts cultured on different-stiffness substrates exhibit biphasic changes in vimentin detergent solubility, which increases from nearly 0 to 67% in hMSCs coincident with increases in cell spreading and membrane ruffling. When imaged, the detergent-soluble vimentin appears to consist of small fragments the length of one or several unit-length filaments. Vimentin detergent solubility decreases when these cells are subjected to serum starvation, allowed to form cell–cell contacts, after microtubule disruption, or inhibition of Rac1, Rho-activated kinase, or p21-activated kinase. Inhibiting myosin or actin assembly increases vimentin solubility on rigid substrates. These data suggest that in the mechanical environment in vivo, vimentin is more dynamic than previously reported and its assembly state is sensitive to stimuli that alter cellular tension and morphology. PMID:24173714

  15. Multifunctional Stiff Carbon Foam Derived from Bread.

    PubMed

    Yuan, Ye; Ding, Yujie; Wang, Chunhui; Xu, Fan; Lin, Zaishan; Qin, Yuyang; Li, Ying; Yang, Minglong; He, Xiaodong; Peng, Qingyu; Li, Yibin

    2016-07-01

    The creation of stiff yet multifunctional three-dimensional porous carbon architecture at very low cost is still challenging. In this work, lightweight and stiff carbon foam (CF) with adjustable pore structure was prepared by using flour as the basic element via a simple fermentation and carbonization process. The compressive strength of CF exhibits a high value of 3.6 MPa whereas its density is 0.29 g/cm(3) (compressive modulus can be 121 MPa). The electromagnetic interference (EMI) shielding effectiveness measurements (specific EMI shielding effectiveness can be 78.18 dB·cm(3)·g(-1)) indicate that CF can be used as lightweight, effective shielding material. Unlike ordinary foam structure materials, the low thermal conductivity (lowest is 0.06 W/m·K) with high resistance to fire makes CF a good candidate for commercial thermal insulation material. These results demonstrate a promising method to fabricate an economical, robust carbon material for applications in industry as well as topics regarding environmental protection and improvement of energy efficiency. PMID:27295106

  16. Multifunctional Stiff Carbon Foam Derived from Bread.

    PubMed

    Yuan, Ye; Ding, Yujie; Wang, Chunhui; Xu, Fan; Lin, Zaishan; Qin, Yuyang; Li, Ying; Yang, Minglong; He, Xiaodong; Peng, Qingyu; Li, Yibin

    2016-07-01

    The creation of stiff yet multifunctional three-dimensional porous carbon architecture at very low cost is still challenging. In this work, lightweight and stiff carbon foam (CF) with adjustable pore structure was prepared by using flour as the basic element via a simple fermentation and carbonization process. The compressive strength of CF exhibits a high value of 3.6 MPa whereas its density is 0.29 g/cm(3) (compressive modulus can be 121 MPa). The electromagnetic interference (EMI) shielding effectiveness measurements (specific EMI shielding effectiveness can be 78.18 dB·cm(3)·g(-1)) indicate that CF can be used as lightweight, effective shielding material. Unlike ordinary foam structure materials, the low thermal conductivity (lowest is 0.06 W/m·K) with high resistance to fire makes CF a good candidate for commercial thermal insulation material. These results demonstrate a promising method to fabricate an economical, robust carbon material for applications in industry as well as topics regarding environmental protection and improvement of energy efficiency.

  17. Elastic metamaterial beam with remotely tunable stiffness

    NASA Astrophysics Data System (ADS)

    Qian, Wei; Yu, Zhengyue; Wang, Xiaole; Lai, Yun; Yellen, Benjamin B.

    2016-02-01

    We demonstrate a dynamically tunable elastic metamaterial, which employs remote magnetic force to adjust its vibration absorption properties. The 1D metamaterial is constructed from a flat aluminum beam milled with a linear array of cylindrical holes. The beam is backed by a thin elastic membrane, on which thin disk-shaped permanent magnets are mounted. When excited by a shaker, the beam motion is tracked by a Laser Doppler Vibrometer, which conducts point by point scanning of the vibrating element. Elastic waves are unable to propagate through the beam when the driving frequency excites the first elastic bending mode in the unit cell. At these frequencies, the effective mass density of the unit cell becomes negative, which induces an exponentially decaying evanescent wave. Due to the non-linear elastic properties of the membrane, the effective stiffness of the unit cell can be tuned with an external magnetic force from nearby solenoids. Measurements of the linear and cubic static stiffness terms of the membrane are in excellent agreement with experimental measurements of the bandgap shift as a function of the applied force. In this implementation, bandgap shifts by as much as 40% can be achieved with ˜30 mN of applied magnetic force. This structure has potential for extension in 2D and 3D, providing a general approach for building dynamically tunable elastic metamaterials for applications in lensing and guiding elastic waves.

  18. STIFF: Converting Scientific FITS Images to TIFF

    NASA Astrophysics Data System (ADS)

    Bertin, Emmanuel

    2011-10-01

    STIFF is a program that converts scientific FITS1 images to the more popular TIFF2 format for illustration purposes. Most FITS readers and converters do not do a proper job at converting FITS image data to 8 bits. 8-bit images stored in JPEG, PNG or TIFF files have the intensities implicitely stored in a non-linear way. Most current FITS image viewers and converters provide the user an incorrect translation of the FITS image content by simply rescaling linearly input pixel values. A first consequence is that the people working on astronomical images usually have to apply narrow intensity cuts or square-root or logarithmic intensity transformations to actually see something on their deep-sky images. A less obvious consequence is that colors obtained by combining images processed this way are not consistent across such a large range of surface brightnesses. Though with other software the user is generally afforded a choice of nonlinear transformations to apply in order to make the faint stuff stand out more clearly in the images, with the limited selection of choices provides, colors will not be accurately rendered, and some manual tweaking will be necessary. The purpose of STIFF is to produce beautiful pictures in an automatic and consistent way.

  19. Is tendon stiffness correlated to the dissipation coefficient?

    PubMed

    Fouré, A; Cornu, C; Nordez, A

    2012-01-01

    The assessment of Achilles tendon mechanical properties in vivo has received much attention in the literature. Many studies investigated mechanical properties by assessing tendon stiffness. Despite tendon dissipative properties being representative of a storage-recoil process, its determination has received minimal attention in the literature. The aim of this study was to determine if Achilles tendon stiffness is associated with dissipative properties. The cross-sectional area, stiffness and dissipation coefficient of the Achilles tendon were measured in 35 subjects. No significant correlation was found between stiffness and the dissipation coefficient, irrespective of stiffness normalization with cross-sectional area (P > 0.05). Thus, it appears that both stiffness and dissipative properties must be assessed to determine the storage-recoil process capacities of the Achilles tendon in order to precisely characterize changes in the tendon mechanical properties after chronic interventions or rehabilitation programs.

  20. Influence of the stiffness of three-dimensional alginate/collagen-I interpenetrating networks on fibroblast biology.

    PubMed

    Branco da Cunha, Cristiana; Klumpers, Darinka D; Li, Weiwei A; Koshy, Sandeep T; Weaver, James C; Chaudhuri, Ovijit; Granja, Pedro L; Mooney, David J

    2014-10-01

    Wound dressing biomaterials are increasingly being designed to incorporate bioactive molecules to promote healing, but the impact of matrix mechanical properties on the biology of resident cells orchestrating skin repair and regeneration remains to be fully understood. This study investigated whether tuning the stiffness of a model wound dressing biomaterial could control the behavior of dermal fibroblasts. Fully interpenetrating networks (IPNs) of collagen-I and alginate were fabricated to enable gel stiffness to be tuned independently of gel architecture, polymer concentration or adhesion ligand density. Three-dimensional cultures of dermal fibroblasts encapsulated within matrices of different stiffness were shown to promote dramatically different cell morphologies, and enhanced stiffness resulted in upregulation of key-mediators of inflammation such as IL-10 and COX-2. These findings suggest that simply modulating the matrix mechanical properties of a given wound dressing biomaterial deposited at the wound site could regulate the progression of wound healing.

  1. A ram-air-spoiler roll stabilization device for forward control cruciform missiles

    NASA Technical Reports Server (NTRS)

    Blair, A. B., Jr.; Sawyer, W. C.; Jackson, C. M., Jr.

    1978-01-01

    An experimental investigation has been made at supersonic Mach numbers to determine the feasibility of using a ram-air-spoiler roll control device on a typical canard control missile configuration. As a basis for roll control comparisons, conventional aileron controls on the tail fins were also tested. Results are presented which indicate that the addition of nacelles on the missile tail fins resulted in satisfactory roll control effectiveness and only small changes in basic missile stability. The ram-air-spoiler roll control effectiveness is relatively constant over the range of vehicle attitudes and Mach numbers investigated.

  2. Quantitative Elastography for Cervical Stiffness Assessment during Pregnancy

    PubMed Central

    Fruscalzo, A.; Londero, A. P.; Fröhlich, C.; Möllmann, U.; Schmitz, R.

    2014-01-01

    Aim. Feasibility and reliability of tissue Doppler imaging-(TDI-) based elastography for cervical quantitative stiffness assessment during all three trimesters of pregnancy were evaluated. Materials and Methods. Prospective case-control study including seventy-four patients collected between the 12th and 42nd weeks of gestation. The tissue strain (TS) was measured by two independent operators as natural strain. Intra- and interoperator intraclass correlation coefficient (ICC) agreements were evaluated. Results. TS measurement was always feasible and exhibited a high performance in terms of reliability (intraoperator ICC-agreement = 0.93; interoperator ICC agreement = 0.89 and 0.93 for a single measurement and for the average of two measurements, resp.). Cervical TS showed also a significant correlation with gestational age, cervical length, and parity. Conclusions. TS measurement during pregnancy demonstrated high feasibility and reliability. Furthermore, TS significantly correlated with gestational age, cervical length, and parity. PMID:24734246

  3. Stiff-system problems and solutions at LLNL

    SciTech Connect

    Hindmarsh, A.C.

    1982-03-01

    Difficult stiff system problems encountered at LLNL are typified by those arising from various atmospheric kinetics models, which include reaction kinetics and transport in up to two space dimensions. Approaches devised for these problems resulted in several general purpose stiff system solvers. These have since evolved into a new systematized collection of solvers, called ODEPACK, based on backward differentiation formulas in the stiff case. A model kinetics-transport problem is used to illustrate the various solvers.

  4. Letter to the Editor: On "Advantages and disadvantages of stiffness instructions when studying postural control" by C.T. Bonnet: You just can't win: Advantages and disadvantages of the postural stability requirement.

    PubMed

    Lajoie, Y; Richer, N; Jehu, D A; Polskaia, N; Saunders, D

    2016-05-01

    In the examination of postural control, instructions to stand as still as possible are common and promote a relatively unnatural sway pattern. The validity of the stability requirement is discussed in the present commentary in response to the discussion initiated by Cedrick T. Bonnet. The advantages of using the stability requirement include: evaluating unbiased postural control, reducing variability in postural sway, manipulating focus of attention, examining the ability to maintain an upright stance, and ecological validity of testing. The disadvantages include: constraining natural postural sway, increasing the complexity of the control condition, promoting an internal focus of attention, and reducing the ability to detect exploratory behaviour. After evaluating the aforementioned advantages and disadvantages, the present commentary suggests that researchers should strive to provide specific instructions to maintain feet, arm and eye position without specifically requiring participants to reduce their postural sway.

  5. Usefulness of liver stiffness measurement during acute cellular rejection in liver transplantation.

    PubMed

    Crespo, Gonzalo; Castro-Narro, Graciela; García-Juárez, Ignacio; Benítez, Carlos; Ruiz, Pablo; Sastre, Lydia; Colmenero, Jordi; Miquel, Rosa; Sánchez-Fueyo, Alberto; Forns, Xavier; Navasa, Miquel

    2016-03-01

    Liver stiffness measurement (LSM) is a useful method to estimate liver fibrosis and portal hypertension. The inflammatory process that takes place in post-liver transplant acute cellular rejection (ACR) may also increase liver stiffness. We aimed to explore the association between liver stiffness and the severity of ACR, as well as to assess the relationship between liver stiffness and response to rejection treatment in a prospective study that included 27 liver recipients with biopsy-proven ACR, 30 stable recipients with normal liver tests, and 30 hepatitis C virus (HCV)-infected LT recipients with histologically diagnosed HCV recurrence. Patients with rejection were stratified into 2 groups (mild and moderate/severe) according to the severity of rejection evaluated with the Banff score. Routine biomarkers and LSM with FibroScan were performed at the time of liver biopsy (baseline) and at 7, 30, and 90 days in patients with rejection and at baseline in control patients. Median baseline liver stiffness was 5.9 kPa in the mild rejection group, 11 kPa in the moderate/severe group (P = 0.001), 4.2 kPa in stable recipients (P = 0.02 versus mild rejection), and 13.6 kPa in patients with recurrent HCV (P = 0.17 versus moderate/severe rejection). The area under the receiver operator characteristic curve of LSM to discriminate mild versus moderate/severe ACR was 0.924, and a LSM value of 8.5 kPa yielded a positive predictive value of 100% to diagnose moderate/severe rejection. Liver stiffness improved in 7%, 21%, and 64% of patients with moderate/severe rejection at 7, 30, and 90 days. In conclusion, according to the results of this exploratory study, LSM is associated with the severity of ACR in liver transplantation and thus may be of help in its assessment. PMID:26609794

  6. A planar shock isolation system with high-static-low-dynamic-stiffness characteristic based on cables

    NASA Astrophysics Data System (ADS)

    Ma, Yanhui; He, Minghua; Shen, Wenhou; Ren, Gexue

    2015-12-01

    In this paper, a simple and designable shock isolation system with ideal high-static-low-dynamic-stiffness (HSLDS) is proposed, which is intended for the horizontal plane shock isolation application. In this system, the isolated object is suspended by several bearing cables and constrained by a number of uniformly distributed pretensioned cables in the horizontal plane, where the low dynamic stiffness of the system is main controlled by the pretension of the planar cables, whilst the high static stiffness is determined by the axial stiffness of the planar cables and their geometric settings. To obtain the HSLDS characteristic of the system, a brief theoretical description of the relationship between the restoring force and displacement is derived. By obtaining the three-order Taylor expansion with sufficient accuracy of the restoring force, influence of planar cable parameters on the low dynamic and high static stiffness is thus given, therefore, the required HSLDS isolator can be easily designed by adjusting the planar cable length, pretension and tensile stiffness. Finally, the isotropy characteristic of the restoring force of the system with different numbers of planar cables is investigated. To evaluate the performance of the system, a rigid isolated object and flexible cables coupling simulation model considering the contacts of the system is established by using multibody dynamics approach. In this model, flexible cables are simulated by 3-node cable element based on the absolute nodal coordinate formulation; the contact between cable and isolated object is simulated based on Hertz contact theory. Finally, the time-domain shock excitation is converted from the design shock spectrum on the basis of BV043/85 criterion. The design procedure of this isolator and some useful guidelines for choosing cable parameters are presented. In addition, a summary about the performance of the isolators with different numbers of cables shocking in an arbitrary direction is

  7. Optoelectronic tweezers for the measurement of the relative stiffness of erythrocytes

    NASA Astrophysics Data System (ADS)

    Neale, Steven L.; Mody, Nimesh; Selman, Colin; Cooper, Jonathan M.

    2012-10-01

    In this paper we describe the first use of Optoelectronic Tweezers (OET), an optically controlled micromanipulation method, to measure the relative stiffness of erythrocytes in mice. Cell stiffness is an important measure of cell health and in the case of erythrocytes, the most elastic cells in the body, an increase in cell stiffness can indicate pathologies such as type II diabetes mellitus or hypertension (high blood pressure). OET uses a photoconductive device to convert an optical pattern into and electrical pattern. The electrical fields will create a dipole within any polarisable particles in the device, such as cells, and non-uniformities of the field can be used to place unequal forces onto each side of the dipole thus moving the particle. In areas of the device where there are no field gradients, areas of constant illumination, the force on each side of the dipole will be equal, keeping the cell stationary, but as there are opposing forces on each side of the cell it will be stretched. The force each cell will experience will differ slightly so the stretching will depend on the cells polarisability as well as its stiffness. Because of this a relative stiffness rather than absolute stiffness is measured. We show that with standard conditions (20Vpp, 1.5MHz, 10mSm-1 medium conductivity) the cell's diameter changes by around 10% for healthy mouse erythrocytes and we show that due to the low light intensities required for OET, relative to conventional optical tweezers, multiple cells can be measured simultaneously.

  8. Evaluation of Arterial Stiffness in Patients with Behçet's Disease by Using Noninvasive Radiological Methods such as Intima-Media Thickness of the Carotid, Ankle-Brachial Pressure Index, Coronary Artery Calcium Scoring, and Their Relation to Serum Fetuin-A Levels: A Case-Control Study

    PubMed Central

    Solak, Aynur; Genç, Berhan; Akyıldız, Muhittin; Şahin, Neslin; Uyar, İhsan Sami; Saklamaz, Ali

    2015-01-01

    Background Behçet's disease (BD) is a chronic, recurrent inflammatory systemic vasculitis. Evidence for increased atherosclerosis in BD has been observed. The relation between cardiovascular risk factors and increased atherosclerosis in patients with BD is still controversial. Objective We performed this study to evaluate arterial stiffness in patients with BD by using noninvasive radiological methods such as carotid artery intima-media thickness (CIMT), ankle-brachial pressure index (ABPI), coronary artery calcium score (CACaS), and their relation to serum fetuin-A levels, which was recently found to be important in vascular calcification. Methods This prospective study included 26 patients with BD and 25 control subjects. In all patients, the CIMT, ABPI, CACaS, and serum fetuin-A levels were examined. Results The CIMT and CACaS were statistically higher and the ABPI was statistically lower in BD patients than in the control group. All p-values were <0.001. Positive correlations were found between the CACaS and CIMT, and negative correlations were found between the CACaS and ABPI. Although the values of fetuin-A were higher in BD, the difference was not statistically significant (p=0.064). However, the correlations found between fetuin-A levels and CIMT and between fetuin-A levels and CACaS were significant. Conclusion The CIMT, CACaS, and ABPI are all useful in detecting structural and functional vascular damage in BD. PMID:26719639

  9. Cholesterol depletion increases membrane stiffness of aortic endothelial cells.

    PubMed

    Byfield, Fitzroy J; Aranda-Espinoza, Helim; Romanenko, Victor G; Rothblat, George H; Levitan, Irena

    2004-11-01

    This study has investigated the effect of cellular cholesterol on membrane deformability of bovine aortic endothelial cells. Cellular cholesterol content was depleted by exposing the cells to methyl-beta-cyclodextrin or enriched by exposing the cells to methyl-beta-cyclodextrin saturated with cholesterol. Control cells were treated with methyl-beta-cyclodextrin-cholesterol at a molar ratio that had no effect on the level of cellular cholesterol. Mechanical properties of the cells with different cholesterol contents were compared by measuring the degree of membrane deformation in response to a step in negative pressure applied to the membrane by a micropipette. The experiments were performed on substrate-attached cells that maintained normal morphology. The data were analyzed using a standard linear elastic half-space model to calculate Young elastic modulus. Our observations show that, in contrast to the known effect of cholesterol on membrane stiffness of lipid bilayers, cholesterol depletion of bovine aortic endothelial cells resulted in a significant decrease in membrane deformability and a corresponding increase in the value of the elastic coefficient of the membrane, indicating that cholesterol-depleted cells are stiffer than control cells. Repleting the cells with cholesterol reversed the effect. An increase in cellular cholesterol to a level higher than that of normal cells, however, had no effect on the elastic properties of bovine aortic endothelial cells. We also show that although cholesterol depletion had no apparent effect on the intensity of F-actin-specific fluorescence, disrupting F-actin with latrunculin A abrogated the stiffening effect. We suggest that cholesterol depletion increases the stiffness of the membrane by altering the properties of the submembrane F-actin and/or its attachment to the membrane.

  10. Effect of Substrate Stiffness on Early Mouse Embryo Development

    PubMed Central

    Kolahi, Kevin S.; Donjacour, Annemarie; Liu, Xiaowei; Lin, Wingka; Simbulan, Rhodel K.; Bloise, Enrrico; Maltepe, Emin; Rinaudo, Paolo

    2012-01-01

    It is becoming increasingly clear that cells are remarkably sensitive to the biophysical cues of their microenvironment and that these cues play a significant role in influencing their behaviors. In this study, we investigated whether the early pre-implantation embryo is sensitive to mechanical cues, i.e. the elasticity of the culture environment. To test this, we have developed a new embryo culture system where the mechanical properties of the embryonic environment can be precisely defined. The contemporary standard environment for embryo culture is the polystyrene petri dish (PD), which has a stiffness (1 GPa) that is six orders of magnitude greater than the uterine epithelium (1 kPa). To approximate more closely the mechanical aspects of the in vivo uterine environment we used polydimethyl-siloxane (PDMS) or fabricated 3D type I collagen gels (1 kPa stiffness, Col-1k group). Mouse embryo development on alternate substrates was compared to that seen on the petri dish; percent development, hatching frequency, and cell number were observed. Our results indicated that embryos are sensitive to the mechanical environment on which they are cultured. Embryos cultured on Col-1k showed a significantly greater frequency of development to 2-cell (68±15% vs. 59±18%), blastocyst (64±9.1% vs. 50±18%) and hatching blastocyst stages (54±25% vs. 21±16%) and an increase in the number of trophectodermal cell (TE,65±13 vs. 49±12 cells) compared to control embryos cultured in PD (mean±S.D.; p<.01). Embryos cultured on Col-1k and PD were transferred to recipient females and observed on embryonic day 12.5. Both groups had the same number of fetuses, however the placentas of the Col-1k fetuses were larger than controls, suggesting a continued effect of the preimplantation environment. In summary, characteristics of the preimplantation microenvironment affect pre- and post-implantation growth. PMID:22860009

  11. Towards ultra-stiff materials: Surface effects on nanoporous materials

    SciTech Connect

    Lu, Dingjie; Xie, Yi Min; Huang, Xiaodong; Zhou, Shiwei; Li, Qing

    2014-09-08

    The significant rise in the strength and stiffness of porous materials at nanoscale cannot be described by conventional scaling laws. This letter investigates the effective Young's modulus of such materials by taking into account surface effect in a microcellular architecture designed for an ultralight material whose stiffness is an order of magnitude higher than most porous materials. We find that by considering the surface effects the predicted stiffness using Euler-Bernoulli beam theory compares well to experimental data for spongelike nanoporous gold with random microstructures. Analytical results show that, of the two factors influencing the effective Young's modulus, the residual stress is more important than the surface stiffness.

  12. Optimal chordwise stiffness profiles of self-propelled flapping fins.

    PubMed

    Kancharala, A K; Philen, M K

    2016-01-01

    The versatility of fish to adapt to different swimming requirements is attributed to their complex muscular system. Fish modulate their fin stiffness and shape for maximized performance. In this paper, optimal chordwise stiffness profiles that maximize the propulsive performance have been predicted using theoretical studies. An experimental setup has been fabricated to measure the stiffness profiles of real fish caudal fins. Chordwise varying stiffness robotic fins fabricated using carbon fiber reinforced composites (CFRC) have been tested in the water tunnel to evaluate their performance over constant stiffness fins. It is observed that the varying stiffness fins produce larger thrusts and efficiencies compared to constant stiffness fins for all the operating conditions considered in this work. A comparison of the digital image correlation (DIC) measured deformations of the fins showed that the better performance of varying stiffness fins is due to their larger curvatures and trailing edge amplitudes. These theoretical and experimental studies provide a greater understanding of the role of stiffness in fish fins for locomotion. PMID:27627992

  13. The effects of long-term FES-assisted walking on intrinsic and reflex dynamic stiffness in spastic spinal-cord-injured subjects.

    PubMed

    Mirbagheri, Mehdi M; Ladouceur, Michel; Barbeau, Hugues; Kearney, Robert E

    2002-12-01

    The effects of long-term functional electrical stimulation (FES)-assisted walking on ankle dynamic stiffness were examined in spinal cord-injured (SCI) subjects with incomplete motor function loss. A parallel-cascade system identification method was used to identify intrinsic and reflex contributions to dynamic ankle stiffness at different ankle positions while subjects remained relaxed. Intrinsic stiffness dynamics were well modeled by a linear second-order model relating intrinsic torque to joint position. Reflex stiffness dynamics were accurately described by a linear third-order model relating halfwave rectified velocity to reflex torque. We examined four SCI subjects before and after long-term FES-assisted walking (> 16 mo). Another SCI subject, who used FES for only five months was examined 12 mo latter to serve as a non-FES, SCI control. Reflex stiffness decreased in FES subjects by an average of 53% following FES-assisted walking, intrinsic stiffness also dropped by 45%. In contrast, both reflex and intrinsic stiffness increased in the non-FES, SCI control. These findings suggest that FES-assisted walking may have therapeutic effects, helping to reduce abnormal joint stiffness.

  14. Cell-stiffness-induced mechanosignaling - a key driver of leukocyte transendothelial migration.

    PubMed

    Schaefer, Antje; Hordijk, Peter L

    2015-07-01

    The breaching of cellular and structural barriers by migrating cells is a driving factor in development, inflammation and tumor cell metastasis. One of the most extensively studied examples is the extravasation of activated leukocytes across the vascular endothelium, the inner lining of blood vessels. Each step of this leukocyte transendothelial migration (TEM) process is regulated by distinct endothelial adhesion receptors such as the intercellular adhesion molecule 1 (ICAM1). Adherent leukocytes exert force on these receptors, which sense mechanical cues and transform them into localized mechanosignaling in endothelial cells. In turn, the function of the mechanoreceptors is controlled by the stiffness of the endothelial cells and of the underlying substrate representing a positive-feedback loop. In this Commentary, we focus on the mechanotransduction in leukocytes and endothelial cells, which is induced in response to variations in substrate stiffness. Recent studies have described the first key proteins involved in these mechanosensitive events, allowing us to identify common regulatory mechanisms in both cell types. Finally, we discuss how endothelial cell stiffness controls the individual steps in the leukocyte TEM process. We identify endothelial cell stiffness as an important component, in addition to locally presented chemokines and adhesion receptors, which guides leukocytes to sites that permit TEM.

  15. Functionalizable hydrogel microparticles of tunable size and stiffness for soft-tissue filler applications

    PubMed Central

    Chan, Ka Man Carmen; Li, Randolph H.; Chapman, Joseph W.; Trac, Eric M.; Kobler, James B.; Zeitels, Steven M.; Langer, Robert; Karajanagi, Sandeep S.

    2014-01-01

    Particle size, stiffness and surface functionality are important in determining the injection site, safety and efficacy of injectable soft-tissue fillers. Methods to produce soft injectable biomaterials with controlled particle characteristics are therefore desirable. Here we report a method based on suspension photopolymerization and semi-interpenetrating network (semi-IPN) to synthesize soft, functionalizable, spherical hydrogel microparticles (MP) of independently tunable size and stiffness. MP were prepared using acrylated forms of polyethylene glycol (PEG), gelatin and hyaluronic acid. Semi-IPN MP of PEG-diacrylate and PEG were used to study the effect of process parameters on particle characteristics. The process parameters were systematically varied to produce MP with size ranging from 115 to 515 μm and stiffness ranging from 190 to 1600 Pa. In vitro studies showed that the MP thus prepared were cytocompatible. The ratio and identity of the polymers used to make the semi-IPN MP were varied to control their stiffness and to introduce amine groups for potential functionalization. Slow-release polymeric particles loaded with Rhodamine or dexamethasone were incorporated in the MP as a proof-of-principle of drug incorporation and release from the MP. This work has implications in preparing injectable biomaterials of natural or synthetic polymers for applications as soft-tissue fillers. PMID:24561708

  16. Quantification of plaque stiffness by Brillouin microscopy in experimental thin cap fibroatheroma.

    PubMed

    Antonacci, Giuseppe; Pedrigi, Ryan M; Kondiboyina, Avinash; Mehta, Vikram V; de Silva, Ranil; Paterson, Carl; Krams, Rob; Török, Peter

    2015-11-01

    Plaques vulnerable to rupture are characterized by a thin and stiff fibrous cap overlaying a soft lipid-rich necrotic core. The ability to measure local plaque stiffness directly to quantify plaque stress and predict rupture potential would be very attractive, but no current technology does so. This study seeks to validate the use of Brillouin microscopy to measure the Brillouin frequency shift, which is related to stiffness, within vulnerable plaques. The left carotid artery of an ApoE(-/-)mouse was instrumented with a cuff that induced vulnerable plaque development in nine weeks. Adjacent histological sections from the instrumented and control arteries were stained for either lipids or collagen content, or imaged with confocal Brillouin microscopy. Mean Brillouin frequency shift was 15.79 ± 0.09 GHz in the plaque compared with 16.24 ± 0.15 (p < 0.002) and 17.16 ± 0.56 GHz (p < 0.002) in the media of the diseased and control vessel sections, respectively. In addition, frequency shift exhibited a strong inverse correlation with lipid area of -0.67 ± 0.06 (p < 0.01) and strong direct correlation with collagen area of 0.71 ± 0.15 (p < 0.05). This is the first study, to the best of our knowledge, to apply Brillouin spectroscopy to quantify atherosclerotic plaque stiffness, which motivates combining this technology with intravascular imaging to improve detection of vulnerable plaques in patients.

  17. An infinitely-stiff elastic system via a tuned negative-stiffness component stabilized by rotation-produced gyroscopic forces

    NASA Astrophysics Data System (ADS)

    Kochmann, D. M.; Drugan, W. J.

    2016-06-01

    An elastic system containing a negative-stiffness element tuned to produce positive-infinite system stiffness, although statically unstable as is any such elastic system if unconstrained, is proved to be stabilized by rotation-produced gyroscopic forces at sufficiently high rotation rates. This is accomplished in possibly the simplest model of a composite structure (or solid) containing a negative-stiffness component that exhibits all these features, facilitating a conceptually and mathematically transparent, completely closed-form analysis.

  18. Arterial stiffness: pathophysiology and clinical impact.

    PubMed

    London, Gérard M; Marchais, Sylvain J; Guerin, Alain P; Pannier, Bruno

    2004-01-01

    The ill effects of hypertension are usually attributed to a reduction in the caliber or the number of arterioles, resulting in an increase in total peripheral resistance (TPR). This definition does not take into account the fact that BP is a cyclic phenomenon with systolic and diastolic BP being the limits of these oscillations. The appropriate term to define the arterial factor(s) opposing LV ejection is aortic input impedance which depends on TPR, arterial distensibility (D), and wave reflections (WR). D defines the capacitive properties of arterial stiffness, whose role is to dampen pressure and flow oscillations and to transform pulsatile flow and pressure in arteries into a steady flow and pressure in peripheral tissues. Stiffness is the reciprocal value of D. These parameters are BP dependent, and arteries become stiffer at high pressure. In to D which provides information about the of artery as a hollow structure, the elastic incremental modulus (Einc) characterizes the properties of the arterial wall biomaterials, independently of vessel geometry. As an alternative, arterial D can be evaluated by measuring the pulse wave velocity (PWV) which increases with the stiffening of arteries. Arterial stiffening increases left ventricular (LV) afterload and alters the coronary perfusion. With increased PWV, the WR impacts on the aorta during systole, increasing systolic pressures and myocardial oxygen consumption, and decreasing diastolic BP and coronary flow. The arterial stiffness is altered primarily in association with increased collagen content and alterations of extracellular matrix (arteriosclerosis) as classically observed during aging or in arterial hypertension. The arterial stiffening estimated by changes in aortic PWV and intensity of WR are independent predictors of survival in end stage renal disease (ESRD) and general population. Improvement of arterial stiffening could be obtained by antihypertensive treatmen as observed with the calcium

  19. Cellular mechanoadaptation to substrate mechanical properties: contributions of substrate stiffness and thickness to cell stiffness measurements using AFM.

    PubMed

    Vichare, Shirish; Sen, Shamik; Inamdar, Mandar M

    2014-02-28

    Mechanosensing by adherent cells is usually studied by quantifying cell responses on hydrogels that are covalently linked to a rigid substrate. Atomic force microscopy (AFM) represents a convenient way of characterizing the mechanoadaptation response of adherent cells on hydrogels of varying stiffness and thickness. Since AFM measurements reflect the effective cell stiffness, therefore, in addition to measuring real cytoskeletal alterations across different conditions, these measurements might also be influenced by the geometry and physical properties of the substrate itself. To better understand how the physical attributes of the gel influence AFM stiffness measurements of cells, we have used finite element analysis to simulate the indentation of cells of various spreads resting on hydrogels of varying stiffness and thickness. Consistent with experimental results, our simulation results indicate that for well spread cells, stiffness values are significantly over-estimated when experiments are performed on cells cultured on soft and thin gels. Using parametric studies, we have developed scaling relationships between the effective stiffness probed by AFM and the bulk cell stiffness, taking cell and tip geometry, hydrogel properties, nuclear stiffness and cell contractility into account. Finally, using simulated mechanoadaptation responses, we have demonstrated that a cell stiffening response may arise purely due to the substrate properties. Collectively, our results demonstrate the need to take hydrogel properties into account while estimating cell stiffness using AFM indentation. PMID:24651595

  20. Scaling of the flow-stiffness relationship in weakly correlated single fractures

    NASA Astrophysics Data System (ADS)

    Petrovitch, Christopher L.

    The remote characterization of the hydraulic properties of fractures in rocks is important in many subsurface projects. Fractures create uncertainty in the hydraulic properties of the subsurface in that their topology controls the amount of flow that can occur in addition to that from the matrix. In turn, the fracture topology is also affected by stress which alters the topology as the stress changes directly. This alteration of fracture topology with stress is captured by fracture specific stiffness. The specific stiffness of a single fracture can be remotely probed from the attenuation and velocity of seismic waves. The hydromechanical coupling of single fractures, i.e. the relationship between flow and stiffness, holds the key to finding a method to remotely characterize a fractures hydraulic properties. This thesis is separated into two parts: (1) a description of the hydromechanical coupling of fractures based on numerical models used to generate synthetic fractures, compute the flow through a fracture, and deform fracture topologies to unravel the scaling function that is fundamental to the hydromechanical coupling of single fractures; (2) a Discontinuous Galerkin (DG) method was developed to accurately simulate the scattered seismic waves from realistic fracture topologies. The scaling regimes of fluid flow and specific stiffness in weakly correlated fractures are identified by using techniques from Percolation Theory and initially treating the two processes separately. The fixed points associated with fluid flow were found to display critical scaling while the fixed points for specific stiffness were trivial. The two processes could be indirectly related because the trivial scaling of the mechanical properties allowed the specific stiffness to be used as surrogate to the void area fraction. The dynamic transport exponent was extracted at threshold by deforming fracture geometries within the effective medium regime (near the ``cubic law'' regime) to the

  1. Stiff-knee gait in cerebral palsy: how do patients adapt to uneven ground?

    PubMed

    Böhm, Harald; Hösl, Matthias; Schwameder, Hermann; Döderlein, Leonhard

    2014-04-01

    Patients with cerebral palsy frequently experience foot dragging and tripping during walking due to reduced toe clearance mostly caused by a lack of adequate knee flexion in swing (stiff-knee gait). The aim of this study was to investigate adaptive mechanism to an uneven surface in stiff-knee walkers with cerebral palsy. Sixteen patients with bilateral cerebral palsy, GMFCS I-II and stiff-knee gait, mean age 14.1 (SD=6.2) years, were compared to 13 healthy controls with mean age 13.5 (SD=4.8) years. Gait analysis including EMG was performed under even and uneven surface conditions. Similar strategies to improve leg clearance were found in patients as well as in controls. Both adapted with significantly reduced speed and cadence, increased outward foot rotation, knee and hip flexion as well as anterior pelvic tilt. Therefore cerebral palsy and stiff-knee gait did not affect the adaptation capacity on the uneven surface. On the uneven surface an average increase in knee flexion of 7° (SD=3°) and 12° (SD=5°) was observed in controls and patients with cerebral palsy, respectively. Although rectus femoris activity was increased in patients with cerebral palsy, they were able to increase their knee flexion during swing. The results of this study suggest that walking on uneven surface has the potential to improve knee flexion in stiff-knee walkers. Therefore training on uneven surface could be used as a conservative treatment regime alone, in combination with Botulinum neurotoxin or in the rehabilitation of surgery.

  2. Effect of Lysyl Oxidase Inhibition on Angiotensin II-Induced Arterial Hypertension, Remodeling, and Stiffness

    PubMed Central

    Eberson, Lance S.; Sanchez, Pablo A.; Majeed, Beenish A.; Tawinwung, Supannikar; Secomb, Timothy W.; Larson, Douglas F.

    2015-01-01

    It is well accepted that angiotensin II (Ang II) induces altered vascular stiffness through responses including both structural and material remodeling. Concurrent with remodeling is the induction of the enzyme lysyl oxidase (LOX) through which ECM proteins are cross-linked. The study objective was to determine the effect of LOX mediated cross-linking on vascular mechanical properties. Three-month old mice were chronically treated with Ang II with or without the LOX blocker, β -aminopropionitrile (BAPN), for 14 days. Pulse wave velocity (PWV) from Doppler measurements of the aortic flow wave was used to quantify in vivo vascular stiffness in terms of an effective Young’s modulus. The increase in effective Young’s modulus with Ang II administration was abolished with the addition of BAPN, suggesting that the material properties are a major controlling element in vascular stiffness. BAPN inhibited the Ang II induced collagen cross-link formation by 2-fold and PWV by 44% (P<0.05). Consistent with this observation, morphometric analysis showed that BAPN did not affect the Ang II mediated increase in medial thickness but significantly reduced the adventitial thickness. Since the hypertensive state contributes to the measured in vivo PWV stiffness, we removed the Ang II infusion pumps on Day 14 and achieved normal arterial blood pressures. With pump removal we observed a decrease of the PWV in the Ang II group to 25% above that of the control values (P=0.002), with a complete return to control values in the Ang II plus BAPN group. In conclusion, we have shown that the increase in vascular stiffness with 14 day Ang II administration results from a combination of hypertension-induced wall strain, adventitial wall thickening and Ang II mediated LOX ECM cross-linking, which is a major material source of vascular stiffening, and that the increased PWV was significantly inhibited with co-administration of BAPN. PMID:25875748

  3. Inhomogeneity of local stiffness in the extracellular matrix scaffold of fibrotic mouse lungs.

    PubMed

    Melo, Esther; Cárdenes, Nayra; Garreta, Elena; Luque, Tomas; Rojas, Mauricio; Navajas, Daniel; Farré, Ramon

    2014-09-01

    Lung disease models are useful to study how cell engraftment, proliferation and differentiation are modulated in lung bioengineering. The aim of this work was to characterize the local stiffness of decellularized lungs in aged and fibrotic mice. Mice (2- and 24-month old; 14 of each) with lung fibrosis (N=20) and healthy controls (N=8) were euthanized after 11 days of intratracheal bleomycin (fibrosis) or saline (controls) infusion. The lungs were excised, decellularized by a conventional detergent-based (sodium-dodecyl sulfate) procedure and slices of the acellular lungs were prepared to measure the local stiffness by means of atomic force microscopy. The local stiffness of the different sites in acellular fibrotic lungs was very inhomogeneous within the lung and increased according to the degree of the structural fibrotic lesion. Local stiffness of the acellular lungs did not show statistically significant differences caused by age. The group of mice most affected by fibrosis exhibited local stiffness that were ~2-fold higher than in the control mice: from 27.2±1.64 to 64.8±7.1kPa in the alveolar septa, from 56.6±4.6 to 99.9±11.7kPa in the visceral pleura, from 41.1±8.0 to 105.2±13.6kPa in the tunica adventitia, and from 79.3±7.2 to 146.6±28.8kPa in the tunica intima. Since acellular lungs from mice with bleomycin-induced fibrosis present considerable micromechanical inhomogeneity, this model can be a useful tool to better investigate how different degrees of extracellular matrix lesion modulate cell fate in the process of organ bioengineering from decellularized lungs.

  4. Large strain variable stiffness composites for shear deformations with applications to morphing aircraft skins

    NASA Astrophysics Data System (ADS)

    McKnight, G. P.; Henry, C. P.

    2008-03-01

    Morphing or reconfigurable structures potentially allow for previously unattainable vehicle performance by permitting several optimized structures to be achieved using a single platform. The key to enabling this technology in applications such as aircraft wings, nozzles, and control surfaces, are new engineered materials which can achieve the necessary deformations but limit losses in parasitic actuation mass and structural efficiency (stiffness/weight). These materials should exhibit precise control of deformation properties and provide high stiffness when exercised through large deformations. In this work, we build upon previous efforts in segmented reinforcement variable stiffness composites employing shape memory polymers to create prototype hybrid composite materials that combine the benefits of cellular materials with those of discontinuous reinforcement composites. These composites help overcome two key challenges for shearing wing skins: the resistance to out of plane buckling from actuation induced shear deformation, and resistance to membrane deflections resulting from distributed aerodynamic pressure loading. We designed, fabricated, and tested composite materials intended for shear deformation and address out of plane deflections in variable area wing skins. Our designs are based on the kinematic engineering of reinforcement platelets such that desired microstructural kinematics is achieved through prescribed boundary conditions. We achieve this kinematic control by etching sheets of metallic reinforcement into regular patterns of platelets and connecting ligaments. This kinematic engineering allows optimization of materials properties for a known deformation pathway. We use mechanical analysis and full field photogrammetry to relate local scale kinematics and strains to global deformations for both axial tension loading and shear loading with a pinned-diamond type fixture. The Poisson ratio of the kinematically engineered composite is ~3x higher than

  5. Three-dimensional stiffness of the carpal arch.

    PubMed

    Gabra, Joseph N; Li, Zong-Ming

    2016-01-01

    The carpal arch of the wrist is formed by irregularly shaped carpal bones interconnected by numerous ligaments, resulting in complex structural mechanics. The purpose of this study was to determine the three-dimensional stiffness characteristics of the carpal arch using displacement perturbations. It was hypothesized that the carpal arch would exhibit an anisotropic stiffness behavior with principal directions that are oblique to the conventional anatomical axes. Eight (n=8) cadavers were used in this study. For each specimen, the hamate was fixed to a custom stationary apparatus. An instrumented robot arm applied three-dimensional displacement perturbations to the ridge of trapezium and corresponding reaction forces were collected. The displacement-force data were used to determine a three-dimensional stiffness matrix using least squares fitting. Eigendecomposition of the stiffness matrix was used to identify the magnitudes and directions of the principal stiffness components. The carpal arch structure exhibited anisotropic stiffness behaviors with a maximum principal stiffness of 16.4±4.6N/mm that was significantly larger than the other principal components of 3.1±0.9 and 2.6±0.5N/mm (p<0.001). The principal direction of the maximum stiffness was pronated within the cross section of the carpal tunnel which is accounted for by the stiff transverse ligaments that tightly bind distal carpal arch. The minimal principal stiffness is attributed to the less constraining articulation between the trapezium and scaphoid. This study provides advanced characterization of the wrist׳s three-dimensional structural stiffness for improved insight into wrist biomechanics, stability, and function.

  6. Tachocline dynamics: convective overshoot at stiff interfaces

    NASA Astrophysics Data System (ADS)

    Brown, Benjamin; Lecoanet, Daniel; Oishi, Jeffrey S.; Burns, Keaton; Vasil, Geoffrey M.

    2016-05-01

    The solar tachocline lies at the base of the solar convection zone. At this internal interface, motions from the unstable convection zone above overshoot and penetrate downward into the stiffly stable radiative zone below, driving gravity waves, mixing, and possibly pumping and storing magnetic fields. Here we study the dynamics of convective overshoot across very stiff interfaces with some properties similar to the internal boundary layer within the Sun. We use the Dedalus pseudospectral framework and study fully compressible dynamics at moderate to high Peclet number and low Mach number, probing a regime where turbulent transport is important. In this preliminary work, we find that the depth of convective overshoot is well described by a simple buoyancy equilibration model, and we consider implications for dynamics at the solar tachocline.

  7. Stiff-person syndrome treated with rituximab

    PubMed Central

    Lobo, Marcelo Evangelista; Araújo, Marx Lincoln Barros; Tomaz, Carlos Alberto Bezerra; Allam, Nasser

    2010-01-01

    Stiff-person syndrome (SPS) is a rare neurological condition consisting of progressive and fluctuating rigidity of the axial muscles combined with painful spasms. The pathophysiology of SPS is not fully understood, but there seems to be an autoimmune component. The use of rituximab, a chimeric monoclonal antibody targeting CD20 protein in the surface of mature B cells, for the treatment of SPS is a recent therapeutical approach showing promising results. The authors present a case report of a 41-year-old female patient diagnosed with SPS who was treated with rituximab in a public hospital in Brasília, Brazil, showing a good and safe response to the treatment so far. Our data go along with some recent articles published in the literature. PMID:22802263

  8. Hydrogels with Differential and Patterned Mechanics to Study Stiffness-Mediated Myofibroblastic Differentiation of Hepatic Stellate Cells

    PubMed Central

    Guvendiren, Murat; Perepelyuk, Maryna; Wells, Rebecca G.; Burdick, Jason A.

    2014-01-01

    The differentiation of hepatic stellate cells (HSCs) into myofbroblasts is a key event in liver fibrosis. Due to the local stiffening of the extracellular matrix (ECM) during fibrosis, it is of great interest to develop mimics that can be used to investigate the cellular response to changes in mechanics. Here, we used a step-wise hydrogel crosslinking technique, where macromolecules are crosslinked using a sequence of addition then UV light-mediated radical crosslinking, to generate hydrogels with tunable stiffness. Freshly isolated HSCs remained rounded with lipid droplets and high levels of PPARγ expression on soft substrates (E~2 kPa); however, HSCs spread, lost their lipid droplets, and expressed high levels of α-smooth muscle actin (α-SMA) and type I collagen on stiff substrates (E~ 24 kPa). Similarly, fully differentiated cells reverted to a quiescent state when plated on soft substrates. Stiffness-induced differentiation of HSCs was enhanced in the presence of exogenous TGF-β1, a dominant signal in fibrosis. When the UV-induced secondary crosslinking was restricted with a photomask to spatially control mechanics, HSCs responded based on the local hydrogel stiffness, although they remained quiescent on stiff substrates if the stiff feature size was not sufficient to allow cell spreading. This hydrogel system permits the investigation of HSC response to materials with diverse levels and spatially heterogeneous mechanical properties. PMID:24361340

  9. Modulation of 3D Fibrin Matrix Stiffness by Intrinsic Fibrinogen–Thrombin Compositions and by Extrinsic Cellular Activity

    PubMed Central

    Duong, Haison; Wu, Benjamin

    2009-01-01

    Fibrin is a substance formed through catalytic conversion of coagulation constituents: fibrinogen and thrombin. The kinetics of the two constituents determines the structural properties of the fibrin architecture. We have shown previously that changing the fibrinogen and thrombin concentrations in the final three-dimensional (3D) fibrin matrix influenced cell proliferation and differentiation. In this study, we further examined the effect of changing fibrinogen and thrombin concentrations in the absence or presence of fibroblasts on the structural modulus or stiffness of 3D fibrin matrices. We have prepared fibroblast-free and fibroblast-embedded 3D fibrin matrices of different fibrinogen and thrombin formulations, and tested the stiffness of these constructs using standard mechanical testing assays. Results showed that there was a corresponding increase in stiffness with increasing thrombin and fibrinogen concentrations; the increase was more notable with fibrinogen and to a lesser degree with thrombin. The effect of fibroblasts on the stiffness of the fibrin construct was also examined. We have observed a small increase in the stiffness of the fibroblast-incorporated fibrin construct as they proliferated and exhibited spreading morphology. To our knowledge, this is the first comprehensive report detailing the relationship between fibrinogen and thrombin concentrations, cell proliferation, and stiffness in 3D fibrin matrices. The data obtained may lead to optimally design suitable bioscaffolds where we can control both cell proliferation and structural integrity for a variety of tissue engineering applications. PMID:19309239

  10. Effect of increased quadriceps tensile stiffness on peak anterior cruciate ligament strain during a simulated pivot landing.

    PubMed

    Lipps, David B; Oh, Youkeun K; Ashton-Miller, James A; Wojtys, Edward M

    2014-03-01

    ACL injury prevention programs often involve strengthening the knee muscles. We posit that an unrecognized benefit of such training is the associated increase in the tensile stiffness of the hypertrophied muscle. We tested the hypothesis that an increased quadriceps tensile stiffness would reduce peak anteromedial bundle (AM-)ACL relative strain in female knees. Twelve female cadaver knees were subjected to compound impulsive two-times body weight loads in compression, flexion, and internal tibial torque beginning at 15° flexion. Knees were equipped with modifiable custom springs to represent the nonlinear rapid stretch behavior of a normal and increased stiffness female quadriceps (i.e., 33% greater stiffness). Peak AM-ACL relative strain was measured using an in situ transducer while muscle forces and tibiofemoral kinematics and kinetics were recorded. A 3D ADAMS™ dynamic biomechanical knee model was used in silico to interpret the experimental results which were analyzed using a repeated-measures Wilcoxon test. Female knees exhibited a 16% reduction in peak AM-ACL relative strain and 21% reduction in change in flexion when quadriceps tensile stiffness was increased by 33% (mean (SD) difference: 0.97% (0.65%), p = 0.003). We conclude that increased quadriceps tensile stiffness reduces peak ACL strain during a controlled study simulating a pivot landing.

  11. VAGINAL DEGENERATION FOLLOWING IMPLANTATION OF SYNTHETIC MESH WITH INCREASED STIFFNESS

    PubMed Central

    Liang, Rui; Abramowitch, Steven; Knight, Katrina; Palcsey, Stacy; Nolfi, Alexis; Feola, Andrew; Stein, Susan; Moalli, Pamela A.

    2012-01-01

    Objective To compare the impact of the prototype prolapse mesh Gynemesh PS to that of two new generation lower stiffness meshes, UltraPro and SmartMesh, on vaginal morphology and structural composition. Design A mechanistic study employing a non-human primate (NHP) model. Setting Magee-Womens Research Institute at the University of Pittsburgh. Population Parous rhesus macaques, with similar age, weight, parity and POP-Q scores. Methods Following IACUC approval, 50 rhesus macaques were implanted with Gynemesh PS (n=12), UltraPro with its blue line perpendicular to the longitudinal axis of vagina (n=10), UltraPro with its blue line parallel to the longitudinal axis of vagina (n=8) and SmartMesh (n=8) via sacrocolpopexy following hysterectomy. Sham operated animals (n=12) served as controls. Main Outcome Measures The mesh-vagina complex (MVC) was removed after 12 weeks and analyzed for histomorphology, in situ cell apoptosis, total collagen, elastin, glycosaminoglycan content and total collagenase activity. Appropriate statistics and correlation analyses were performed accordingly. Results Relative to sham and the two lower stiffness meshes, Gynemesh PS had the greatest negative impact on vaginal histomorphology and composition. Compared to sham, implantation with Gynemesh PS caused substantial thinning of the smooth muscle layer (1557 ± 499μm vs 866 ± 210 μm, P=0.02), increased apoptosis particularly in the area of the mesh fibers (P=0.01), decreased collagen and elastin content (20% (P=0.03) and 43% (P=0.02), respectively) and increased total collagenase activity (135% (P=0.01)). GAG (glycosaminoglycan), a marker of tissue injury, was the highest with Gynemesh PS compared to sham and other meshes (P=0.01). Conclusion Mesh implantation with the stiffer mesh Gynemesh PS induced a maladaptive remodeling response consistent with vaginal degeneration. PMID:23240802

  12. Muscle stiffness measured under conditions simulating natural sound production.

    PubMed

    Dobrunz, L E; Pelletier, D G; McMahon, T A

    1990-08-01

    Isolated whole frog gastrocnemius muscles were electrically stimulated to peak twitch tension while held isometrically in a bath at 4 degrees C. A quartz hydrophone detected vibrations of the muscle by measuring the pressure fluctuations caused by muscle movement. A small steel collar was slipped over the belly of the muscle. Transient forces including plucks and steady sinusoidal driving were applied to the collar by causing currents to flow in a coil held near the collar. The instantaneous resonant frequencies measured by the pluck and driving techniques were the same at various times during a twitch contraction cycle. The strain produced by the plucking technique in the outermost fibers was less than 1.6 x 10(-4%), a strain three orders of magnitude less than that required to drop the tension to zero in quick-length-change experiments. Because the pressure transients recorded by the hydrophone during plucks and naturally occurring sounds were of comparable amplitude, strains in the muscle due to naturally occurring sound must also be of the order 10(-3%). A simple model assuming that the muscle is an elastic bar under tension was used to calculate the instantaneous elastic modulus E as a function of time during a twitch, given the tension and resonant frequency. The result for Emax, the peak value of E during a twitch, was typically 2.8 x 10(6) N/m2. The methods used here for measuring muscle stiffness are unusual in that the apparatus used for measuring stiffness is separate from the apparatus controlling and measuring force and length. PMID:2207252

  13. Mechanically stiff, electrically conductive composites of polymers and carbon nanotubes

    SciTech Connect

    Worsley, Marcus A.; Kucheyev, Sergei O.; Baumann, Theodore F.; Kuntz, Joshua D.; Satcher, Jr., Joe H.; Hamza, Alex V.

    2015-07-21

    Using SWNT-CA as scaffolds to fabricate stiff, highly conductive polymer (PDMS) composites. The SWNT-CA is immersing in a polymer resin to produce a SWNT-CA infiltrated with a polymer resin. The SWNT-CA infiltrated with a polymer resin is cured to produce the stiff and electrically conductive composite of carbon nanotube aerogel and polymer.

  14. Boundary Stiffness Regulates Fibroblast Behavior in Collagen Gels

    PubMed Central

    John, Jeffrey; Quinlan, Angela Throm; Silvestri, Chiara; Billiar, Kristen

    2010-01-01

    Recent studies have illustrated the profound dependence of cellular behavior on the stiffness of 2D culture substrates. The goal of this study was to develop a method to alter the stiffness cells experience in a standard 3D collagen gel model without affecting the physiochemical properties of the extracellular matrix. A device was developed utilizing compliant anchors (0.048–0.64 N m−1) to tune the boundary stiffness of suspended collagen gels in between the commonly utilized free and fixed conditions (zero and infinite stiffness boundary stiffness). We demonstrate the principle of operation with finite element analyses and a wide range of experimental studies. In all cases, boundary stiffness has a strong influence on cell behavior, most notably eliciting higher basal tension and activated force (in response to KCl) and more pronounced remodeling of the collagen matrix at higher boundary stiffness levels. Measured equibiaxial forces for gels seeded with 3 million human foreskin fibroblasts range from 0.05 to 1 mN increasing monotonically with boundary stiffness. Estimated force per cell ranges from 17 to 100 nN utilizing representative volume element analysis. This device provides a valuable tool to independently study the effect of the mechanical environment of the cell in a 3D collagen matrix. PMID:20012205

  15. Extracellular Matrix Stiffness Regulates Osteogenic Differentiation through MAPK Activation

    PubMed Central

    Hwang, Jun-Ha; Byun, Mi Ran; Kim, A. Rum; Kim, Kyung Min; Cho, Hang Jun; Lee, Yo Han; Kim, Juwon; Jeong, Mi Gyeong; Hwang, Eun Sook; Hong, Jeong-Ho

    2015-01-01

    Mesenchymal stem cell (MSC) differentiation is regulated by the extracellular matrix (ECM) through activation of intracellular signaling mediators. The stiffness of the ECM was shown to be an important regulatory factor for MSC differentiation, and transcriptional coactivator with PDZ-binding motif (TAZ) was identified as an effector protein for MSC differentiation. However, the detailed underlying mechanism regarding the role of ECM stiffness and TAZ in MSC differentiation is not yet fully understood. In this report, we showed that ECM stiffness regulates MSC fate through ERK or JNK activation. Specifically, a stiff hydrogel matrix stimulates osteogenic differentiation concomitant with increased nuclear localization of TAZ, but inhibits adipogenic differentiation. ERK and JNK activity was significantly increased in cells cultured on a stiff hydrogel. TAZ activation was induced by ERK or JNK activation on a stiff hydrogel because exposure to an ERK or JNK inhibitor significantly decreased the nuclear localization of TAZ, indicating that ECM stiffness-induced ERK or JNK activation is important for TAZ-driven osteogenic differentiation. Taken together, these results suggest that ECM stiffness regulates MSC differentiation through ERK or JNK activation. PMID:26262877

  16. Extracellular Matrix Stiffness Regulates Osteogenic Differentiation through MAPK Activation.

    PubMed

    Hwang, Jun-Ha; Byun, Mi Ran; Kim, A Rum; Kim, Kyung Min; Cho, Hang Jun; Lee, Yo Han; Kim, Juwon; Jeong, Mi Gyeong; Hwang, Eun Sook; Hong, Jeong-Ho

    2015-01-01

    Mesenchymal stem cell (MSC) differentiation is regulated by the extracellular matrix (ECM) through activation of intracellular signaling mediators. The stiffness of the ECM was shown to be an important regulatory factor for MSC differentiation, and transcriptional coactivator with PDZ-binding motif (TAZ) was identified as an effector protein for MSC differentiation. However, the detailed underlying mechanism regarding the role of ECM stiffness and TAZ in MSC differentiation is not yet fully understood. In this report, we showed that ECM stiffness regulates MSC fate through ERK or JNK activation. Specifically, a stiff hydrogel matrix stimulates osteogenic differentiation concomitant with increased nuclear localization of TAZ, but inhibits adipogenic differentiation. ERK and JNK activity was significantly increased in cells cultured on a stiff hydrogel. TAZ activation was induced by ERK or JNK activation on a stiff hydrogel because exposure to an ERK or JNK inhibitor significantly decreased the nuclear localization of TAZ, indicating that ECM stiffness-induced ERK or JNK activation is important for TAZ-driven osteogenic differentiation. Taken together, these results suggest that ECM stiffness regulates MSC differentiation through ERK or JNK activation.

  17. ECM stiffness primes the TGFβ pathway to promote chondrocyte differentiation

    PubMed Central

    Allen, Jessica L.; Cooke, Margaret E.; Alliston, Tamara

    2012-01-01

    Cells encounter physical cues such as extracellular matrix (ECM) stiffness in a microenvironment replete with biochemical cues. However, the mechanisms by which cells integrate physical and biochemical cues to guide cellular decision making are not well defined. Here we investigate mechanisms by which chondrocytes generate an integrated response to ECM stiffness and transforming growth factor β (TGFβ), a potent agonist of chondrocyte differentiation. Primary murine chondrocytes and ATDC5 cells grown on 0.5-MPa substrates deposit more proteoglycan and express more Sox9, Col2α1, and aggrecan mRNA relative to cells exposed to substrates of any other stiffness. The chondroinductive effect of this discrete stiffness, which falls within the range reported for articular cartilage, requires the stiffness-sensitive induction of TGFβ1. Smad3 phosphorylation, nuclear localization, and transcriptional activity are specifically increased in cells grown on 0.5-MPa substrates. ECM stiffness also primes cells for a synergistic response, such that the combination of ECM stiffness and exogenous TGFβ induces chondrocyte gene expression more robustly than either cue alone through a p38 mitogen-activated protein kinase–dependent mechanism. In this way, the ECM stiffness primes the TGFβ pathway to efficiently promote chondrocyte differentiation. This work reveals novel mechanisms by which cells integrate physical and biochemical cues to exert a coordinated response to their unique cellular microenvironment. PMID:22833566

  18. Neuromuscular and stiffness adaptations in division I collegiate baseball players.

    PubMed

    Thomas, Stephen J; Swanik, Charles B; Higginson, Jill S; Kaminski, Thomas W; Swanik, Kathleen A; Kelly, John D; Nazarian, Levon N

    2013-02-01

    To compare bi-lateral shoulder EMG, active and short range glenohumeral stiffness, and examine its correlation to posterior capsule thickness (PCT) in collegiate baseball players. Surface and fine wire EMG was recorded on shoulder and scapular musculature during stiffness testing. Posterior capsule thickness was assessed separately using a diagnostic ultrasound. Serratus anterior EMG area and peak on the dominant arm was significantly greater compared to the non-dominant arm. The dominant arm had significantly greater active and short range glenohumeral stiffness compared to the non-dominant arm. Active glenohumeral stiffness was significantly correlated with PCT, however short range glenohumeral stiffness was not significantly correlated with PCT. Healthy collegiate baseball players present with adaptations of their stiffness regulation strategies. There were also correlations between stiffness and morphologic changes. Our results support the theory that PCT has an impact on the energy absorption capabilities of the shoulder during the deceleration phase of throwing. It also seems that tightening of the series elastic component within the posterior rotator cuff may be causing the increase in short range stiffness on the dominant arm.

  19. Neuromuscular and stiffness adaptations in division I collegiate baseball players.

    PubMed

    Thomas, Stephen J; Swanik, Charles B; Higginson, Jill S; Kaminski, Thomas W; Swanik, Kathleen A; Kelly, John D; Nazarian, Levon N

    2013-02-01

    To compare bi-lateral shoulder EMG, active and short range glenohumeral stiffness, and examine its correlation to posterior capsule thickness (PCT) in collegiate baseball players. Surface and fine wire EMG was recorded on shoulder and scapular musculature during stiffness testing. Posterior capsule thickness was assessed separately using a diagnostic ultrasound. Serratus anterior EMG area and peak on the dominant arm was significantly greater compared to the non-dominant arm. The dominant arm had significantly greater active and short range glenohumeral stiffness compared to the non-dominant arm. Active glenohumeral stiffness was significantly correlated with PCT, however short range glenohumeral stiffness was not significantly correlated with PCT. Healthy collegiate baseball players present with adaptations of their stiffness regulation strategies. There were also correlations between stiffness and morphologic changes. Our results support the theory that PCT has an impact on the energy absorption capabilities of the shoulder during the deceleration phase of throwing. It also seems that tightening of the series elastic component within the posterior rotator cuff may be causing the increase in short range stiffness on the dominant arm. PMID:22898532

  20. In vivo measurement of bending stiffness in fracture healing

    PubMed Central

    Hente, Reiner; Cordey, Jacques; Perren, Stephan M

    2003-01-01

    Background Measurement of the bending stiffness a healing fracture represents a valid variable in the assessment of fracture healing. However, currently available methods typically have high measurement errors, even for mild pin loosening. Furthermore, these methods cannot provide actual values of bending stiffness, which precludes comparisons among individual fractures. Thus, even today, little information is available with regards to the fracture healing pattern with respect to actual values of bending stiffness. Our goals were, therefore: to develop a measurement device that would allow accurate and sensitive measurement of bending stiffness, even in the presence of mild pin loosening; to describe the course of healing in individual fractures; and help to evaluate whether the individual pattern of bending stiffness can be predicted at an early stage of healing. Methods A new measurement device has been developed to precisely measure the bending stiffness of the healing fracture by simulating four-point-bending. The system was calibrated on aluminum models and intact tibiae. The influence of pin loosening on measurement error was evaluated. The system was tested at weekly intervals in an animal experiment to determine the actual bending stiffness of the fracture. Transverse fractures were created in the right tibia of twelve sheep, and then stabilized with an external fixator. At ten weeks, bending stiffness of the tibiae were determined in a four-point-bending test device to validate the in-vivo-measurement data. Results In-vivo bending stiffness can be measured accurately and sensitive, even in the early phase of callus healing. Up to a bending stiffness of 10 Nm/degree, measurement error was below 3.4% for one pin loose, and below 29.3% for four pins loose, respectively. Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but

  1. Assessment of passive knee stiffness and viscosity in individuals with spinal cord injury using pendulum test

    PubMed Central

    Joghtaei, Mahmoud; Arab, Amir Massoud; Hashemi-Nasl, Hamed; Joghataei, Mohammad Taghi; Tokhi, Mohammad Osman

    2015-01-01

    Objective Stiffness and viscosity represent passive resistances to joint motion related with the structural properties of the joint tissue and of the musculotendinous complex. Both parameters can be affected in patients with spinal cord injury (SCI). The purpose of this study was to measure passive knee stiffness and viscosity in patients with SCI with paraplegia and healthy subjects using Wartenberg pendulum test. Design Non-experimental, cross-sectional, case–control design. Setting An outpatient physical therapy clinic, University of social welfare and Rehabilitation Science, Iran. Patients A sample of convenience sample of 30 subjects participated in the study. Subjects were categorized into two groups: individuals with paraplegic SCI (n = 15, age: 34.60 ± 9.18 years) and 15 able-bodied individuals as control group (n = 15, age: 30.66 ± 11.13 years). Interventions Not applicable. Main measures Passive pendulum test of Wartenberg was used to measure passive viscous-elastic parameters of the knee (stiffness, viscosity) in all subjects. Results Statistical analysis (independent t-test) revealed significant difference in the joint stiffness between healthy subjects and those with paraplegic SCI (P = 0.01). However, no significant difference was found in the viscosity between two groups (P = 0.17). Except for first peak flexion angle, all other displacement kinematic parameters exhibited no statistically significant difference between normal subjects and subjects with SCI. Conclusions Patients with SCI have significantly greater joint stiffness compared to able-bodied subjects. PMID:25437824

  2. Elastomeric and mechanically stiff nanocomposites from poly(glycerol sebacate) and bioactive nanosilicates.

    PubMed

    Kerativitayanan, Punyavee; Gaharwar, Akhilesh K

    2015-10-01

    Poly(glycerol sebacate) (PGS) has been proposed for tissue engineering applications owing to its tough elastomeric mechanical properties, biocompatibility and controllable degradation. However, PGS shows limited bioactivity and thus constraining its utilization for musculoskeletal tissue engineering. To address this issue, we developed bioactive, highly elastomeric, and mechanically stiff nanocomposites by covalently reinforcing PGS network with two-dimensional (2D) nanosilicates. Nanosilicates are ultrathin nanomaterials and can induce osteogenic differentiation of human stem cells in the absence of any osteogenic factors such as dexamethasone or bone morphogenetic proteins-2 (BMP2). The addition of nanosilicate to PGS matrix significantly enhances the mechanical stiffness without affecting the elastomeric properties. Moreover, nanocomposites with higher amount of nanosilicates have higher in vitro stability as determined by degradation kinetics. The increase in mechanical stiffness and in vitro stability is mainly attributed to enhanced interactions between nanosilicates and PGS. We evaluated the in vitro bioactivity of nanocomposite using preosteoblast cells. The addition of nanosilicates significantly enhances the cell adhesion, support cell proliferation, upregulate alkaline phosphates and mineralized matrix production. Overall, the combination of high mechanically stiffness and elastomericity, tailorable degradation profile, and the ability to promote osteogenic differentiation of PGS-nanosilicate can be used for regeneration of bone. PMID:26297886

  3. Passive stiffness of hindlimb muscles in anurans with distinct locomotor specializations.

    PubMed

    Danos, Nicole; Azizi, Emanuel

    2015-08-01

    Anurans (frogs and toads) have been shown to have relatively compliant skeletal muscles. Using a meta-analysis of published data we have found that muscle stiffness is negatively correlated with joint range of motion when examined across mammalian, anuran and bird species. Given this trend across a broad phylogenetic sample, we examined whether the relationship held true within anurans. We identified four species that differ in preferred locomotor mode and hence joint range of motion (Lithobates catesbeianus, Rhinella marina, Xenopus laevis and Kassina senegalensis) and hypothesized that smaller in vivo angles (more flexed) at the knee and ankle joint would be associated with more compliant extensor muscles. We measured passive muscle tension during cyclical stretching (20%) around L0 (sarcomere lengths of 2.2 μm) in fiber bundles extracted from cruralis and plantaris muscles. We found no relationship between muscle stiffness and range of motion for either muscle-joint complex. There were no differences in the passive properties of the cruralis muscle among the four species, but the plantaris muscles of the Xenopus and Kassina were significantly stiffer than those of the other two species. Our results suggest that in anurans the stiffness of muscle fibers is a relatively minor contributor to stiffness at the level of joints and that variation in other anatomical properties including muscle-tendon architecture and joint mechanics as well as active control likely contribute more significantly to range of motion during locomotion.

  4. A new pre-loaded beam geometric stiffness matrix with full rigid body capabilities

    NASA Technical Reports Server (NTRS)

    Bosela, P. A.; Fertis, D. G.; Shaker, F. J.

    1992-01-01

    Space structures, such as the Space Station solar arrays, must be extremely light-weight, flexible structures. Accurate prediction of the natural frequencies and mode shapes is essential for determining the structural adequacy of components, and designing a controls system. The tension pre-load in the 'blanket' of photovoltaic solar collectors, and the free/free boundary conditions of a structure in space, causes serious reservations on the use of standard finite element techniques of solution. In particular, a phenomenon known as 'grounding', or false stiffening, of the stiffness matrix occurs during rigid body rotation. The authors have previously shown that the grounding phenomenon is caused by a lack of rigid body rotational capability, and is typical in beam geometric stiffness matrices formulated by others, including those which contain higher order effects. The cause of the problem was identified as the force imbalance inherent in the formulations. In this paper, the authors develop a beam geometric stiffness matrix for a directed force problem, and show that the resultant global stiffness matrix contains complete rigid body mode capabilities, and performs very well in the diagonalization methodology customarily used in dynamic analysis.

  5. Assessment of Arterial Stiffness Using the Cardio-Ankle Vascular Index

    PubMed Central

    Miyoshi, Toru; Ito, Hiroshi

    2016-01-01

    Background Arterial stiffness is an independent predictor of outcomes for patients with cardiovascular disease. Although measurement of pulse wave velocity is a widely accepted, noninvasive approach for the assessment of arterial stiffness, its accuracy is affected by changes in blood pressure. Summary The cardio-ankle vascular index (CAVI) is an index of the overall stiffness of the artery from the origin of the aorta to the ankle and is theoretically independent of blood pressure at the time of measurement. CAVI increases linearly with age and is elevated even in mild arteriosclerotic disease. It can identify differences in the degree of arteriosclerosis among patients with severe arteriosclerotic disease and better reflects the severity of disease of the coronary artery than does brachial-ankle pulse wave velocity. Patients with higher CAVI values show a poor prognosis compared with those with lower CAVI values. Furthermore, CAVI can be lowered by controlling diabetes mellitus and hypertension. Key Messages The primary aims of assessing arterial stiffness using CAVI are to assist in the early detection of arteriosclerosis, allowing timely treatment and lifestyle modification, and to quantitatively evaluate the progression of disease and the effectiveness of treatment. Whether CAVI-guided therapy can improve prognosis in high-risk patients needs to be further examined to confirm the clinical usefulness of this measure. PMID:27493899

  6. Vertical and leg stiffness and stretch-shortening cycle changes across maturation during maximal sprint running.

    PubMed

    Rumpf, Michael C; Cronin, John B; Oliver, Jon L; Hughes, Michael G

    2013-08-01

    The purpose of this study was to investigate whether vertical and leg stiffness, and stretch-shortening cycle (SSC) ability differed in developing athletes of various maturity status during maximal sprint running. Seventy-four male participants between 8 and 16 years of age were categorized into pre-, mid- or post-peak height velocity (PHV) and sprinted for 30 meters on a non-motorized treadmill. Dimensionless vertical stiffness increased significantly (p<.05) from pre-, to mid- and post-PHV state, while dimensionless leg stiffness was significantly higher in post- compared to mid- (18.4%) and pre-PHV participants (44.5%). Eccentric power was significantly lower in pre- compared to the mid- and post-PHV participants. Concentric power increased from pre- to mid- and post-PHV state. An analysis of covariance revealed no significant differences between all groups in dimensionless vertical and leg stiffness, eccentric and concentric time and power when controlling for years from PHV (maturation). Eccentric or concentric power, were found to be the best predictors of maximum velocity across all maturation groups (r2=.37-.68). It seems that maturation affects the ability to absorb and produce power and furthermore these variables are important predictors of maximal running velocity.

  7. Leg stiffness adjustment during hopping at different intensities and frequencies.

    PubMed

    Mrdakovic, Vladimir; Ilic, Dusko; Vulovic, Radun; Matic, Milan; Jankovic, Nenad; Filipovic, Nenad

    2014-01-01

    Understanding leg and joint stiffness adjustment during maximum hopping may provide important information for developing more effective training methods. It has been reported that ankle stiffness has major influence on stable spring-mass dynamics during submaximal hopping, and that knee stiffness is a major determinant for hopping performance during maximal hopping task. Furthermore, there are no reports on how the height of the previous hop could affect overall stiffness modulation of the subsequent maximum one. The purpose of the present study was to determine whether and how the jump height of the previous hop affects leg and joint stiffness for subsequent maximum hop. Ten participants completed trials in which they repeatedly hopped as high as possible (MX task) and trials in which they were instructed to perform several maximum hops with 3 preferred (optimal) height hops between each of them (P3MX task). Both hopping tasks were performed at 2.2 Hz hopping frequency and at the participant's preferred (freely chosen) frequency as well. By comparing results of those hopping tasks, we found that ankle stiffness at 2.2 Hz ( p = 0.041) and knee stiffness at preferred frequency ( p = 0.045) was significantly greater for MX versus P3MX tasks. Leg stiffness for 2.2 Hz hopping is greater than for the preferred frequency. Ankle stiffness is greater for 2.2 Hz than for preferred frequencies; opposite stands for knee stiffness. The results of this study suggest that preparatory hop height can be considered as an important factor for modulation of maximum hop. PMID:25308379

  8. An in-flight simulation of lateral control nonlinearities. [for general aviation aircraft

    NASA Technical Reports Server (NTRS)

    Ellis, D. R.; Tilak, N. W.

    1975-01-01

    An in-flight simulation program was conducted to explore, in a generalized way, the influence of spoiler-type roll-control nonlinearities on handling qualities. The roll responses studied typically featured a dead zone or very small effectiveness for small control inputs, a very high effectiveness for mid-range deflections, and low effectiveness again for large inputs. A linear force gradient with no detectable breakout force was provided. Given otherwise good handling characteristics, it was found that moderate nonlinearities of the types tested might yield acceptable roll control, but the best level of handling qualities is obtained with linear, aileron-like control.

  9. Low-intensity functional electrical stimulation can increase multidirectional trunk stiffness in able-bodied individuals during sitting.

    PubMed

    Vette, Albert H; Wu, Noel; Masani, Kei; Popovic, Milos R

    2015-08-01

    The inability to voluntarily control the trunk musculature is a major problem following spinal cord injury as it can compromise functional independence and produce unwanted secondary complications. Recent developments suggest that neuroprostheses utilizing functional electrical stimulation (FES) may be able to facilitate or restore trunk control during sitting, standing, and other tasks involving postural control. In spite of these efforts, no study to date has used low-intensity FES to increase multidirectional trunk stiffness and damping in an attempt to bolster stability while minimizing muscle fatigue. Therefore, we set out to investigate how multidirectional trunk stiffness changes in response to low-intensity FES of a few selected trunk muscles. Fifteen healthy participants sitting naturally were randomly perturbed in eight horizontal directions. Trunk stiffness and damping during natural and FES-supported sitting conditions were quantified using force and trunk kinematics in combination with two models of a mass-spring-damper system. Our results indicate that low-intensity FES can increase trunk stiffness in healthy individuals, and this specifically for directions associated with the stimulated muscles. In contrast, trunk damping was not found to be altered during FES. The presented results suggest that low-intensity FES is a simple and effective method for increasing trunk stiffness on demand. PMID:26071025

  10. Low-intensity functional electrical stimulation can increase multidirectional trunk stiffness in able-bodied individuals during sitting.

    PubMed

    Vette, Albert H; Wu, Noel; Masani, Kei; Popovic, Milos R

    2015-08-01

    The inability to voluntarily control the trunk musculature is a major problem following spinal cord injury as it can compromise functional independence and produce unwanted secondary complications. Recent developments suggest that neuroprostheses utilizing functional electrical stimulation (FES) may be able to facilitate or restore trunk control during sitting, standing, and other tasks involving postural control. In spite of these efforts, no study to date has used low-intensity FES to increase multidirectional trunk stiffness and damping in an attempt to bolster stability while minimizing muscle fatigue. Therefore, we set out to investigate how multidirectional trunk stiffness changes in response to low-intensity FES of a few selected trunk muscles. Fifteen healthy participants sitting naturally were randomly perturbed in eight horizontal directions. Trunk stiffness and damping during natural and FES-supported sitting conditions were quantified using force and trunk kinematics in combination with two models of a mass-spring-damper system. Our results indicate that low-intensity FES can increase trunk stiffness in healthy individuals, and this specifically for directions associated with the stimulated muscles. In contrast, trunk damping was not found to be altered during FES. The presented results suggest that low-intensity FES is a simple and effective method for increasing trunk stiffness on demand.

  11. Anterior Glenohumeral Laxity and Stiffness After a Shoulder-Strengthening Program in Collegiate Cheerleaders

    PubMed Central

    Laudner, Kevin G; Metz, Betsy; Thomas, David Q

    2013-01-01

    Context Approximately 62% of all cheerleaders sustain some type of orthopaedic injury during their cheerleading careers. Furthermore, the occurrence of such injuries has led to inquiry regarding optimal prevention techniques. One possible cause of these injuries may be related to inadequate conditioning in cheerleaders. Objective To determine whether a strength and conditioning program produces quantifiable improvements in anterior glenohumeral (GH) laxity and stiffness. Design Descriptive laboratory study. Setting University laboratory. Patients or Other Participants A sample of 41 collegiate cheerleaders (24 experimental and 17 control participants) volunteered. No participants had a recent history (in the past 6 months) of upper extremity injury or any history of upper extremity surgery. Intervention(s) The experimental group completed a 6-week strength and conditioning program between the pretest and posttest measurements; the control group did not perform any strength training between tests. Main Outcome Measure(s) We measured anterior GH laxity and stiffness with an instrumented arthrometer. We conducted a group × time analysis of variance with repeated measures on time (P < .05) to determine differences between groups. Results A significant interaction was demonstrated, with the control group having more anterior GH laxity at the posttest session than the strengthening group (P = .03, partial η2 = 0.11). However, no main effect for time (P = .92) or group (P = .97) was observed. In another significant interaction, the control group had less anterior GH stiffness at the posttest session than the strengthening group (P = .03, partial η2 = 0.12). Main effects for time (P = .02) and group (P = .004) were also significant. Conclusions Cheerleaders who participate in a shoulder-strengthening program developed less anterior GH laxity and more stiffness than cheerleaders in the control group. PMID:23672322

  12. Effects of non-uniform stiffness on the swimming performance of a passively-flexing, fish-like foil model.

    PubMed

    Lucas, Kelsey N; Thornycroft, Patrick J M; Gemmell, Brad J; Colin, Sean P; Costello, John H; Lauder, George V

    2015-10-01

    Simple mechanical models emulating fish have been used recently to enable targeted study of individual factors contributing to swimming locomotion without the confounding complexity of the whole fish body. Yet, unlike these uniform models, the fish body is notable for its non-uniform material properties. In particular, flexural stiffness decreases along the fish's anterior-posterior axis. To identify the role of non-uniform bending stiffness during fish-like propulsion, we studied four foil model configurations made by adhering layers of plastic sheets to produce discrete regions of high (5.5 × 10(-5) Nm(2)) and low (1.9 × 10(-5) Nm(2)) flexural stiffness of biologically-relevant magnitudes. This resulted in two uniform control foils and two foils with anterior regions of high stiffness and posterior regions of low stiffness. With a mechanical flapping foil controller, we measured forces and torques in three directions and quantified swimming performance under both heaving (no pitch) and constant 0° angle of attack programs. Foils self-propelled at Reynolds number 21 000-115 000 and Strouhal number ∼0.20-0.25, values characteristic of fish locomotion. Although previous models have emphasized uniform distributions and heaving motions, the combination of non-uniform stiffness distributions and 0° angle of attack pitching program was better able to reproduce the kinematics of freely-swimming fish. This combination was likewise crucial in maximizing swimming performance and resulted in high self-propelled speeds at low costs of transport and large thrust coefficients at relatively high efficiency. Because these metrics were not all maximized together, selection of the 'best' stiffness distribution will depend on actuation constraints and performance goals. These improved models enable more detailed, accurate analyses of fish-like swimming. PMID:26447541

  13. Stiffness nanotomography of human epithelial cancer cells

    NASA Astrophysics Data System (ADS)

    Staunton, Jack R.; Doss, Bryant L.; Gilbert, C. Michael; Kasas, Sandor; Ros, Robert

    2012-02-01

    The mechanical stiffness of individual cells is important in both cancer initiation and metastasis. We present atomic force microscopy (AFM) based nanoindentation experiments on various human mammary and esophagus cell lines covering the spectrum from normal immortalized cells to highly metastatic ones. The combination of an AFM with a confocal fluorescence lifetime imaging microscope (FLIM) in conjunction with the ability to move the sample and objective independently allow for precise alignment of AFM probe and laser focus with an accuracy down to a few nanometers. This enables us to correlate the mechanical properties with the point of indentation in the FLIM image. We are using force-volume measurements as well as force indentation curves on distinct points on the cells to compare the elastic moduli of the nuclei, nucleoli, and the cytoplasm, and how they vary within and between individual cells and cell lines. Further, a detailed analysis of the force-indentation curves allows study of the cells' mechanical properties at different indentation depths and to generate 3D elasticity maps.

  14. Simvastatin Ameliorates Matrix Stiffness-Mediated Endothelial Monolayer Disruption.

    PubMed

    Lampi, Marsha C; Faber, Courtney J; Huynh, John; Bordeleau, Francois; Zanotelli, Matthew R; Reinhart-King, Cynthia A

    2016-01-01

    Arterial stiffening accompanies both aging and atherosclerosis, and age-related stiffening of the arterial intima increases RhoA activity and cell contractility contributing to increased endothelium permeability. Notably, statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors whose pleiotropic effects include disrupting small GTPase activity; therefore, we hypothesized the statin simvastatin could be used to attenuate RhoA activity and inhibit the deleterious effects of increased age-related matrix stiffness on endothelial barrier function. Using polyacrylamide gels with stiffnesses of 2.5, 5, and 10 kPa to mimic the physiological stiffness of young and aged arteries, endothelial cells were grown to confluence and treated with simvastatin. Our data indicate that RhoA and phosphorylated myosin light chain activity increase with matrix stiffness but are attenuated when treated with the statin. Increases in cell contractility, cell-cell junction size, and indirect measurements of intercellular tension that increase with matrix stiffness, and are correlated with matrix stiffness-dependent increases in monolayer permeability, also decrease with statin treatment. Furthermore, we report that simvastatin increases activated Rac1 levels that contribute to endothelial barrier enhancing cytoskeletal reorganization. Simvastatin, which is prescribed clinically due to its ability to lower cholesterol, alters the endothelial cell response to increased matrix stiffness to restore endothelial monolayer barrier function, and therefore, presents a possible therapeutic intervention to prevent atherogenesis initiated by age-related arterial stiffening.

  15. Simvastatin Ameliorates Matrix Stiffness-Mediated Endothelial Monolayer Disruption

    PubMed Central

    Lampi, Marsha C.; Faber, Courtney J.; Huynh, John; Bordeleau, Francois; Zanotelli, Matthew R.; Reinhart-King, Cynthia A.

    2016-01-01

    Arterial stiffening accompanies both aging and atherosclerosis, and age-related stiffening of the arterial intima increases RhoA activity and cell contractility contributing to increased endothelium permeability. Notably, statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors whose pleiotropic effects include disrupting small GTPase activity; therefore, we hypothesized the statin simvastatin could be used to attenuate RhoA activity and inhibit the deleterious effects of increased age-related matrix stiffness on endothelial barrier function. Using polyacrylamide gels with stiffnesses of 2.5, 5, and 10 kPa to mimic the physiological stiffness of young and aged arteries, endothelial cells were grown to confluence and treated with simvastatin. Our data indicate that RhoA and phosphorylated myosin light chain activity increase with matrix stiffness but are attenuated when treated with the statin. Increases in cell contractility, cell-cell junction size, and indirect measurements of intercellular tension that increase with matrix stiffness, and are correlated with matrix stiffness-dependent increases in monolayer permeability, also decrease with statin treatment. Furthermore, we report that simvastatin increases activated Rac1 levels that contribute to endothelial barrier enhancing cytoskeletal reorganization. Simvastatin, which is prescribed clinically due to its ability to lower cholesterol, alters the endothelial cell response to increased matrix stiffness to restore endothelial monolayer barrier function, and therefore, presents a possible therapeutic intervention to prevent atherogenesis initiated by age-related arterial stiffening. PMID:26761203

  16. Substrate stiffness regulates extracellular matrix deposition by alveolar epithelial cells

    PubMed Central

    Eisenberg, Jessica L; Safi, Asmahan; Wei, Xiaoding; Espinosa, Horacio D; Budinger, GR Scott; Takawira, Desire; Hopkinson, Susan B; Jones, Jonathan CR

    2012-01-01

    Aim The aim of the study was to address whether a stiff substrate, a model for pulmonary fibrosis, is responsible for inducing changes in the phenotype of alveolar epithelial cells (AEC) in the lung, including their deposition and organization of extracellular matrix (ECM) proteins. Methods Freshly isolated lung AEC from male Sprague Dawley rats were seeded onto polyacrylamide gel substrates of varying stiffness and analyzed for expression and organization of adhesion, cytoskeletal, differentiation, and ECM components by Western immunoblotting and confocal immunofluorescence microscopy. Results We observed that substrate stiffness influences cell morphology and the organization of focal adhesions and the actin cytoskeleton. Surprisingly, however, we found that substrate stiffness has no influence on the differentiation of type II into type I AEC, nor does increased substrate stiffness lead to an epithelial–mesenchymal transition. In contrast, our data indicate that substrate stiffness regulates the expression of the α3 laminin subunit by AEC and the organization of both fibronectin and laminin in their ECM. Conclusions An increase in substrate stiffness leads to enhanced laminin and fibronectin assembly into fibrils, which likely contributes to the disease phenotype in the fibrotic lung. PMID:23204878

  17. Robust time-domain identification of mass stiffness, and damping matrices

    NASA Technical Reports Server (NTRS)

    Roemer, Michael J.; Mook, D. Joseph

    1990-01-01

    Accurate estimates of the mass, stiffness, and damping characteristics of a structure is necessary for determining the control laws best suited for active control methodologies. There are several modal identification techniques available for determining the frequencies, damping ratios, and mode shapes of a structure. However, modal identification methods in both the frequency and time domains have difficulties for certain circumstances. Frequency domain techniques which utilize the steady-state response from various harmonic inputs often encounter difficulties when the frequencies are closely distributed, the structure exhibits a high degree of damping, or the steady-state condition is hard to establish. Time domain techniques have produced successful results, but lack robustness with respect to measurement noise. In this paper, two identification techniques and an estimation method are combined to form a time-domain technique to accurately identify the mass, stiffness, and damping matrices from noisy measurements.

  18. Three-dimensional Macroscopic Scaffolds With a Gradient in Stiffness for Functional Regeneration of Interfacial Tissues

    PubMed Central

    Singh, Milind; Dormer, Nathan; Salash, Jean R.; Christian, Jordan M.; Moore, David S.; Berkland, Cory; Detamore, Michael S.

    2010-01-01

    A novel approach has been demonstrated to construct biocompatible, macroporous 3-D tissue engineering scaffolds containing a continuous macroscopic gradient in composition that yields a stiffness gradient along the axis of the scaffold. Polymeric microspheres, made of poly(d,l-lactic-co-glycolic acid) (PLGA), and composite microspheres encapsulating a higher stiffness nano-phase material (PLGA encapsulating CaCO3 or TiO2 nanoparticles) were used for the construction of microsphere-based scaffolds. Using controlled infusion of polymeric and composite microspheres, gradient scaffolds displaying an anisotropic macroscopic distribution of CaCO3/TiO2 were fabricated via an ethanol sintering technique. The controllable mechanical characteristics and biocompatible nature of these scaffolds warrants further investigation for interfacial tissue engineering applications. PMID:20336753

  19. Gelatin-Hyaluronic Acid Hydrogels with Tuned Stiffness to Counterbalance Cellular Forces and Promote Cell Differentiation.

    PubMed

    Poveda-Reyes, Sara; Moulisova, Vladimira; Sanmartín-Masiá, Esther; Quintanilla-Sierra, Luis; Salmerón-Sánchez, Manuel; Ferrer, Gloria Gallego

    2016-09-01

    Cells interact mechanically with their environment, exerting mechanical forces that probe the extracellular matrix (ECM). The mechanical properties of the ECM determine cell behavior and control cell differentiation both in 2D and 3D environments. Gelatin (Gel) is a soft hydrogel into which cells can be embedded. This study shows significant 3D Gel shrinking due to the high traction cellular forces exerted by the cells on the matrix, which prevents cell differentiation. To modulate this process, Gel with hyaluronic acid (HA) has been combined in an injectable crosslinked hydrogel with controlled Gel-HA ratio. HA increases matrix stiffness. The addition of small amounts of HA leads to a significant reduction in hydrogel shrinking after cell encapsulation (C2C12 myoblasts). We show that hydrogel stiffness counterbalanced traction forces of cells and this was decisive in promoting cell differentiation and myotube formation of C2C12 encapsulated in the hybrid hydrogels.

  20. Equivalent Dynamic Stiffness Mapping technique for identifying nonlinear structural elements from frequency response functions

    NASA Astrophysics Data System (ADS)

    Wang, X.; Zheng, G. T.

    2016-02-01

    A simple and general Equivalent Dynamic Stiffness Mapping technique is proposed for identifying the parameters or the mathematical model of a nonlinear structural element with steady-state primary harmonic frequency response functions (FRFs). The Equivalent Dynamic Stiffness is defined as the complex ratio between the internal force and the displacement response of unknown element. Obtained with the test data of responses' frequencies and amplitudes, the real and imaginary part of Equivalent Dynamic Stiffness are plotted as discrete points in a three dimensional space over the displacement amplitude and the frequency, which are called the real and the imaginary Equivalent Dynamic Stiffness map, respectively. These points will form a repeatable surface as the Equivalent Dynamic stiffness is only a function of the corresponding data as derived in the paper. The mathematical model of the unknown element can then be obtained by surface-fitting these points with special functions selected by priori knowledge of the nonlinear type or with ordinary polynomials if the type of nonlinearity is not pre-known. An important merit of this technique is its capability of dealing with strong nonlinearities owning complicated frequency response behaviors such as jumps and breaks in resonance curves. In addition, this technique could also greatly simplify the test procedure. Besides there is no need to pre-identify the underlying linear parameters, the method uses the measured data of excitation forces and responses without requiring a strict control of the excitation force during the test. The proposed technique is demonstrated and validated with four classical single-degree-of-freedom (SDOF) numerical examples and one experimental example. An application of this technique for identification of nonlinearity from multiple-degree-of-freedom (MDOF) systems is also illustrated.

  1. Computer-based assessment of left ventricular wall stiffness in patients with ischemic dilated cardiomyopathy

    NASA Astrophysics Data System (ADS)

    Su, Y.; Teo, S. K.; Tan, R. S.; Lim, C. W.; Zhong, L.

    2013-02-01

    Ischemic dilated cardiomyopathy (IDCM) is a degenerative disease of the myocardial tissue accompanied by left ventricular (LV) structural changes such as interstitial fibrosis. This can induce increased passive stiffness of the LV wall. However, quantification of LV passive wall stiffness in vivo is extremely difficult, particularly in ventricles with complex geometry. Therefore, we sought to (i) develop a computer-based assessment of LV passive wall stiffness from cardiac magnetic resonance (CMR) imaging in terms of a nominal stiffness index (E*); and (ii) investigate whether E* can offer an insight into cardiac mechanics in IDCM. CMR scans were performed in 5 normal subjects and 5 patients with IDCM. For each data sample, an in-house software was used to generate a 1-to-1 corresponding mesh pair of the LV from the ED and ES phases. The E* values are then computed as a function of local ventricular wall strain. We found that E* in the IDCM group (40.66 - 215.12) was at least one order of magnitude larger than the normal control group (1.00 - 6.14). In addition, the IDCM group revealed much higher inhomogeneity of E* values manifested by a greater spread of E* values throughout the LV. In conclusion, there is a substantial elevated ventricular stiffness index in IDCM. This would suggest that E* could be used as discriminator for early detection of disease state. The computational performance per data sample took approximately 25 seconds, which demonstrates its clinical potential as a real-time cardiac assessment tool.

  2. Effect of Reduced Stiffness Dance Flooring on Lower Extremity Joint Angular Trajectories During a Ballet Jump.

    PubMed

    Hackney, James; Brummel, Sara; Newman, Mary; Scott, Shannon; Reinagel, Matthew; Smith, Jennifer

    2015-09-01

    We carried out a study to investigate how low stiffness flooring may help prevent overuse injuries of the lower extremity in dancers. It was hypothesized that performing a ballet jump (sauté) on a reduced stiffness dance floor would decrease maximum joint flexion angles and negative angular velocities at the hips, knees, or ankles compared to performing the same jump on a harder floor. The participants were 15 young adult female dancers (age range 18 to 28, mean = 20.89 ± 2.93 years) with at least 5 years of continuous ballet experience and without history of serious lower body injury, surgery, or recent pain. They performed sautés on a (low stiffness) Harlequin ® WoodSpring Floor and on a vinyl-covered hardwood on concrete floor. Maximum joint flexion angles and negative velocities at bilateral hips, knees, and ankles were measured with the "Ariel Performance Analysis System" (APAS). Paired one-tailed t-tests yielded significant decreases in maximum knee angle (average decrease = 3.4° ± 4.2°, p = 0.026) and angular negative velocity of the ankles (average decrease = 18.7°/sec ± 27.9°/sec, p = 0.009) with low stiffness flooring. If the knee angle is less acute, then the length of the external knee flexion moment arm will also be shorter and result in a smaller external knee flexion moment, given an equal landing force. Also, high velocities of eccentric muscle contraction, which are necessary to control negative angular velocity of the ankle joint, are associated with higher risk of musculotendinous injury. Hence, our findings indicate that reduced floor stiffness may indeed help decrease the likelihood of lower extremity injuries. PMID:26349504

  3. Idiopathic hypertonicity as a cause of stiffness after surgery for developmental dysplasia of the hip☆

    PubMed Central

    Akgül, Turgut; Göksan, Süleyman Bora; Eren, İlker

    2014-01-01

    INTRODUCTION There are various complications reported with surgical treatment of DDH. Most studied complication is avascular necrosis of the femoral head and hip stiffness. The purpose of this report was to describe a case with severe stiffness of the hip due to hypertonicity in periarticular muscles after it was treated for developmental dysplasia of the hip (DDH). PRESENTATION OF CASE Three-year-old patient referred to our institution with bilateral DDH. Two hips were operated separately in one year with anterior open reduction, femoral shortening osteotomy. Third month after last surgery, limited right hip range of motion and limb length discrepency identified. Clinical examination revealed that patient had limited range of motion (ROM) in the right hip and compensated this with pelvis obliquity. Gluteus medius, sartorius and iliofemoral band release performed after examination under general anesthesia. Symptoms were persisted at 3rd week control and examination of the patient in general anesthesia revealed full ROM without increased tension. For the identified hypertonicity, ultrasound guided 100 IU botulinum toxin A injection performed to abductor group and iliopsoas muscles. Fifth month later, no flexor or abductor tension observed, and there was no pelvic obliquity. DISCUSSION Stiffness as a complication is rare and is usually resolved without treatment or simple physical therapy. Usually it is related with immobilization or surgery associated joint contracture, and spontaneous recovery reported. Presented case is diagnosed as hip stiffness due to underlying local hypertonicity. That is resolved with anesthesia and it was treated after using botulinum toxin A injection. CONCLUSION Hypertonicity with hip stiffness after surgical treatment of DDH differ from spontaneous recovering hip range of motion limitation and treatment can only be achieved by reduction of the muscle hypertonicity by neuromuscular junction blockage. PMID:24568944

  4. Effect of Reduced Stiffness Dance Flooring on Lower Extremity Joint Angular Trajectories During a Ballet Jump.

    PubMed

    Hackney, James; Brummel, Sara; Newman, Mary; Scott, Shannon; Reinagel, Matthew; Smith, Jennifer

    2015-09-01

    We carried out a study to investigate how low stiffness flooring may help prevent overuse injuries of the lower extremity in dancers. It was hypothesized that performing a ballet jump (sauté) on a reduced stiffness dance floor would decrease maximum joint flexion angles and negative angular velocities at the hips, knees, or ankles compared to performing the same jump on a harder floor. The participants were 15 young adult female dancers (age range 18 to 28, mean = 20.89 ± 2.93 years) with at least 5 years of continuous ballet experience and without history of serious lower body injury, surgery, or recent pain. They performed sautés on a (low stiffness) Harlequin ® WoodSpring Floor and on a vinyl-covered hardwood on concrete floor. Maximum joint flexion angles and negative velocities at bilateral hips, knees, and ankles were measured with the "Ariel Performance Analysis System" (APAS). Paired one-tailed t-tests yielded significant decreases in maximum knee angle (average decrease = 3.4° ± 4.2°, p = 0.026) and angular negative velocity of the ankles (average decrease = 18.7°/sec ± 27.9°/sec, p = 0.009) with low stiffness flooring. If the knee angle is less acute, then the length of the external knee flexion moment arm will also be shorter and result in a smaller external knee flexion moment, given an equal landing force. Also, high velocities of eccentric muscle contraction, which are necessary to control negative angular velocity of the ankle joint, are associated with higher risk of musculotendinous injury. Hence, our findings indicate that reduced floor stiffness may indeed help decrease the likelihood of lower extremity injuries.

  5. Cardiac Fibroblast-Dependent Extracellular Matrix Accumulation Is Associated with Diastolic Stiffness in Type 2 Diabetes

    PubMed Central

    Hutchinson, Kirk R.; Lord, C. Kevin; West, T. Aaron; Stewart, James A.

    2013-01-01

    Cardiovascular complications are a leading cause of death in patients with type 2 diabetes mellitus (T2DM). Diastolic dysfunction is one of the earliest manifestations of diabetes-induced changes in left ventricular (LV) function, and results from a reduced rate of relaxation and increased stiffness. The mechanisms responsible for increased stiffness are not completely understood. Chronic hyperglycemia, advanced glycation endproducts (AGEs), and increased levels of proinflammatory and profibrotic cytokines are molecular pathways known to be involved in regulating extracellular matrix (ECM) synthesis and accumulation resulting in increased LV diastolic stiffness. Experiments were conducted using a genetically-induced mouse model of T2DM generated by a point mutation in the leptin receptor resulting in nonfunctional leptin receptors (db/db murine model). This study correlated changes in LV ECM and stiffness with alterations in basal activation of signaling cascades and expression of profibrotic markers within primary cultures of cardiac fibroblasts from diabetic (db/db) mice with nondiabetic (db/wt) littermates as controls. Primary cultures of cardiac fibrobroblasts were maintained in 25 mM glucose (hyperglycemic-HG; diabetic db/db) media or 5 mM glucose (normoglycemic-NG, nondiabetic db/wt) media. The cells then underwent a 24-hour exposure to their opposite (NG; diabetic db/db) media or 5 mM glucose (HG, nondiabetic db/wt) media. Protein analysis demonstrated significantly increased expression of type I collagen, TIMP-2, TGF-β, PAI-1 and RAGE in diabetic db/db cells as compared to nondiabetic db/wt, independent of glucose media concentration. This pattern of protein expression was associated with increased LV collagen accumulation, myocardial stiffness and LV diastolic dysfunction. Isolated diabetic db/db fibroblasts were phenotypically distinct from nondiabetic db/wt fibroblasts and exhibited a profibrotic phenotype in normoglycemic conditions. PMID:23991045

  6. Cross-Linking in Collagen by Nonenzymatic Glycation Increases the Matrix Stiffness in Rabbit Achilles Tendon

    PubMed Central

    2004-01-01

    Nonenzymatic glycation of connective tissue matrix proteins is a major contributor to the pathology of diabetes and aging. Previously the author and colleagues have shown that nonenzymatic glycation significantly enhances the matrix stability in the Achilles tendon (Reddy et al., 2002, Arch. Biochem. Biophys., 399, 174–180). The present study was designed to gain further insight into glycation-induced collagen cross-linking and its relationship to matrix stiffness in the rabbit Achilles tendon. The glycation process was initiated by incubating the Achilles tendons (n = 6) in phosphate-buffered saline containing ribose, whereas control tendons (n = 6) were incubated in phosphate-buffered saline without ribose. Eight weeks following glycation, the biomechanical attributes as well as the degree of collagen cross-linking were determined to examine the potential associations between matrix stiffness and molecular properties of collagen. Compared to nonglycated tendons, the glycated tendons showed increased maximum load, stress, strain, Young's modulus of elasticity, and toughness indicating that glycation increases the matrix stiffness in the tendons. Glycation of tendons resulted in a considerable decrease in soluble collagen content and a significant increase in insoluble collagen and pentosidine. Analysis of potential associations between the matrix stiffness and degree of collagen cross-linking showed that both insoluble collagen and pentosidine exhibited a significant positive correlation with the maximum load, stress, and strain, Young's modulus of elasticity, and toughness (r values ranging from .61 to .94) in the Achilles tendons. However, the soluble collagen content present in neutral salt buffer, acetate buffer, and acetate buffer containing pepsin showed an inverse relation with the various biomechanical attributes tested (r values ranging from .22 to .84) in the Achilles tendons. The results of the study demonstrate that glycation-induced collagen cross

  7. Preload substantially influences the intervertebral disc stiffness in loading-unloading cycles of compression.

    PubMed

    Schmidt, Hendrik; Shirazi-Adl, Aboulfazl; Schilling, Christoph; Dreischarf, Marcel

    2016-06-14

    Disc hydration is controlled by fluid imbibition and exudation and hence by applied load magnitude and history, internal osmotic pressure and disc conditions. It affects both the internal load distribution and external load-bearing of a disc while variations therein give rise to the disc time-dependent characteristics. This study aimed to evaluate the effect of changes in compression preload magnitude on the disc axial cyclic compression stiffness under physiological loading. After 20h of free hydration, effects of various preload magnitudes (no preload, 0.06 and 0.28MPa, applied for eight hours) and disc-bone preparation conditions on disc height and axial stiffness were investigated using 36 disc-bone and 24 isolated disc (without bony endplates) bovine specimens. After preloading, specimens were subjected to ten loading/unloading cycles each of 7.5min compression at 0.5MPa followed by 7.5min at 0.06MPa. Under 0.06MPa preload, the specimen height losses during high loading periods of cyclic loading were greater than corresponding height recoveries during low loading phases. This resulted in a progressive reduction in the specimen height and increase in its stiffness. Differences between disc height losses in high cyclic loads and between stiffness in both load increase and release phases were significant for 0 and 0.06MPa vs. 0.28MPa preload. Results highlight the significant role of disc preload magnitude/history and hence disc height and hydration on disc stiffness in loading/unloading and disc height loss in loading periods. Proper preconditioning and hence hydration level should be achieved if recovery in height loss similar to in vivo conditions is expected. PMID:27209550

  8. Impact of blood pressure perturbations on arterial stiffness.

    PubMed

    Lim, Jisok; Pearman, Miriam E; Park, Wonil; Alkatan, Mohammed; Machin, Daniel R; Tanaka, Hirofumi

    2015-12-15

    Although the associations between chronic levels of arterial stiffness and blood pressure (BP) have been fairly well studied, it is not clear whether and how much arterial stiffness is influenced by acute perturbations in BP. The primary aim of this study was to determine magnitudes of BP dependence of various measures of arterial stiffness during acute BP perturbation maneuvers. Fifty apparently healthy subjects, including 25 young (20-40 yr) and 25 older adults (60-80 yr), were studied. A variety of BP perturbations, including head-up tilt, head-down tilt, mental stress, isometric handgrip exercise, and cold pressor test, were used to encompass BP changes induced by physical, mental, and/or mechanical stimuli. When each index of arterial stiffness was plotted with mean BP, all arterial stiffness indices, including cardio-ankle vascular index or CAVI (r = 0.50), carotid-femoral pulse wave velocity or cfPWV (r = 0.51), brachial-ankle pulse wave velocity or baPWV (r = 0.61), arterial compliance (r = -0.42), elastic modulus (r = 0.52), arterial distensibility (r = -0.32), β-stiffness index (r = 0.19), and Young's modulus (r = 0.35) were related to mean BP (all P < 0.01). Changes in CAVI, cfPWV, baPWV, and elastic modulus were significantly associated with changes in mean BP in the pooled conditions, while changes in arterial compliance, arterial distensibility, β-stiffness index, and Young's modulus were not. In conclusion, this study demonstrated that BP changes in response to various forms of pressor stimuli were associated with the corresponding changes in arterial stiffness indices and that the strengths of associations with BP varied widely depending on what arterial stiffness indices were examined. PMID:26468262

  9. Impact of blood pressure perturbations on arterial stiffness.

    PubMed

    Lim, Jisok; Pearman, Miriam E; Park, Wonil; Alkatan, Mohammed; Machin, Daniel R; Tanaka, Hirofumi

    2015-12-15

    Although the associations between chronic levels of arterial stiffness and blood pressure (BP) have been fairly well studied, it is not clear whether and how much arterial stiffness is influenced by acute perturbations in BP. The primary aim of this study was to determine magnitudes of BP dependence of various measures of arterial stiffness during acute BP perturbation maneuvers. Fifty apparently healthy subjects, including 25 young (20-40 yr) and 25 older adults (60-80 yr), were studied. A variety of BP perturbations, including head-up tilt, head-down tilt, mental stress, isometric handgrip exercise, and cold pressor test, were used to encompass BP changes induced by physical, mental, and/or mechanical stimuli. When each index of arterial stiffness was plotted with mean BP, all arterial stiffness indices, including cardio-ankle vascular index or CAVI (r = 0.50), carotid-femoral pulse wave velocity or cfPWV (r = 0.51), brachial-ankle pulse wave velocity or baPWV (r = 0.61), arterial compliance (r = -0.42), elastic modulus (r = 0.52), arterial distensibility (r = -0.32), β-stiffness index (r = 0.19), and Young's modulus (r = 0.35) were related to mean BP (all P < 0.01). Changes in CAVI, cfPWV, baPWV, and elastic modulus were significantly associated with changes in mean BP in the pooled conditions, while changes in arterial compliance, arterial distensibility, β-stiffness index, and Young's modulus were not. In conclusion, this study demonstrated that BP changes in response to various forms of pressor stimuli were associated with the corresponding changes in arterial stiffness indices and that the strengths of associations with BP varied widely depending on what arterial stiffness indices were examined.

  10. Moving a hand-held object: Reconstruction of referent coordinate and apparent stiffness trajectories

    PubMed Central

    Ambike, Satyajit; Zhou, Tao; Zatsiorsky, Vladimir M.; Latash, Mark L.

    2015-01-01

    This study used the framework of the referent configuration hypothesis and slow changes in the external conditions during vertical oscillation of a hand-held object to infer the characteristics of hypothetical control variables. The study had two main objectives: (1) to show that hypothetical control variables, namely, referent coordinates and apparent stiffness of vertical hand position and grip force can be measured in an experiment; and (2) to establish relation(s) between these control variables that yield the classic grip-force-load-force coupling. Healthy subjects gripped a handle and performed vertical oscillations between visual targets at one of five metronome-prescribed frequencies. A Hapticmaster robot was used to induce slow changes in the vertical force applied to the handle, while the size of the handle was changed slowly leading to changes in the grip aperture. The subjects were instructed not to react to possible changes in the external forces. A linear, second-order model was used to reconstruct the referent coordinate and apparent stiffness values for each phase of the vertical oscillation cycle using across-cycle regressions. The reconstructed time profiles of the referent coordinates and apparent stiffness showed consistent trends across subjects and movement frequencies. To validate the method, these values were used to predict the vertical force and the grip force applied to the handle for movement cycles that were not utilized in the reconstruction process. Analysis of the coupling between the four variables, two referent coordinates and two apparent stiffness values, revealed a single strong constraint reflecting the coupling between the grip force and vertical force. We view these data as providing experimental support for the idea of controlling natural, multi-muscle actions with shifts in a low-dimensional set of referent coordinates. PMID:25896800

  11. Moving a hand-held object: Reconstruction of referent coordinate and apparent stiffness trajectories.

    PubMed

    Ambike, S; Zhou, T; Zatsiorsky, V M; Latash, M L

    2015-07-01

    This study used the framework of the referent configuration hypothesis and slow changes in the external conditions during vertical oscillation of a hand-held object to infer the characteristics of hypothetical control variables. The study had two main objectives: (1) to show that hypothetical control variables, namely, referent coordinates and apparent stiffness of vertical hand position and grip force can be measured in an experiment; and (2) to establish relation(s) between these control variables that yield the classic grip-force-load-force coupling. Healthy subjects gripped a handle and performed vertical oscillations between visual targets at one of five metronome-prescribed frequencies. A HapticMaster robot was used to induce slow changes in the vertical force applied to the handle, while the size of the handle was changed slowly leading to changes in the grip aperture. The subjects were instructed not to react to possible changes in the external forces. A linear, second-order model was used to reconstruct the referent coordinate and apparent stiffness values for each phase of the vertical oscillation cycle using across-cycle regressions. The reconstructed time profiles of the referent coordinates and apparent stiffness showed consistent trends across subjects and movement frequencies. To validate the method, these values were used to predict the vertical force and the grip force applied to the handle for movement cycles that were not utilized in the reconstruction process. Analysis of the coupling between the four variables, two referent coordinates and two apparent stiffness values, revealed a single strong constraint reflecting the coupling between the grip force and vertical force. We view these data as providing experimental support for the idea of controlling natural, multi-muscle actions with shifts in a low-dimensional set of referent coordinates.

  12. Moving a hand-held object: Reconstruction of referent coordinate and apparent stiffness trajectories.

    PubMed

    Ambike, S; Zhou, T; Zatsiorsky, V M; Latash, M L

    2015-07-01

    This study used the framework of the referent configuration hypothesis and slow changes in the external conditions during vertical oscillation of a hand-held object to infer the characteristics of hypothetical control variables. The study had two main objectives: (1) to show that hypothetical control variables, namely, referent coordinates and apparent stiffness of vertical hand position and grip force can be measured in an experiment; and (2) to establish relation(s) between these control variables that yield the classic grip-force-load-force coupling. Healthy subjects gripped a handle and performed vertical oscillations between visual targets at one of five metronome-prescribed frequencies. A HapticMaster robot was used to induce slow changes in the vertical force applied to the handle, while the size of the handle was changed slowly leading to changes in the grip aperture. The subjects were instructed not to react to possible changes in the external forces. A linear, second-order model was used to reconstruct the referent coordinate and apparent stiffness values for each phase of the vertical oscillation cycle using across-cycle regressions. The reconstructed time profiles of the referent coordinates and apparent stiffness showed consistent trends across subjects and movement frequencies. To validate the method, these values were used to predict the vertical force and the grip force applied to the handle for movement cycles that were not utilized in the reconstruction process. Analysis of the coupling between the four variables, two referent coordinates and two apparent stiffness values, revealed a single strong constraint reflecting the coupling between the grip force and vertical force. We view these data as providing experimental support for the idea of controlling natural, multi-muscle actions with shifts in a low-dimensional set of referent coordinates. PMID:25896800

  13. Leg stiffness and joint stiffness while running to and jumping over an obstacle.

    PubMed

    Mauroy, G; Schepens, B; Willems, P A

    2014-01-22

    During running, muscles of the lower limb act like a linear spring bouncing on the ground. When approaching an obstacle, the overall stiffness of this leg-spring system (k(leg)) is modified during the two steps preceding the jump to enhance the movement of the center of mass of the body while leaping the obstacle. The aim of the present study is to understand how k(leg) is modified during the running steps preceding the jump. Since k(leg) depends on the joint torsional stiffness and on the leg geometry, we analyzed the changes in these two parameters in eight subjects approaching and leaping a 0.65 m-high barrier at 15 km h(-1). Ground reaction force (F) was measured during 5-6 steps preceding the obstacle using force platform and the lower limb movements were recorded by camera. From these data, the net muscular moment (M(j)), the angular displacement (θ(j)) and the lever arm of F were evaluated at the hip, knee and ankle. At the level of the hip, the M(j)-θ(j) relation shows that muscles are not acting like torsional springs. At the level of the knee and ankle, the M(j)-θ(j) relation shows that muscles are acting like torsional springs: as compared to steady-state running, the torsional stiffness k(j) decreases from ~1/3 two contacts before the obstacle, and increases from ~2/3 during the last contact. These modifications in k(j) reflect in changes in the magnitude of F but also to changes in the leg geometry, i.e. in the lever arms of F.

  14. Hormones and arterial stiffness in patients with chronic kidney disease.

    PubMed

    Gungor, Ozkan; Kircelli, Fatih; Voroneanu, Luminita; Covic, Adrian; Ok, Ercan

    2013-01-01

    Cardiovascular disease constitutes the major cause of mortality in patients with chronic kidney disease. Arterial stiffness is an important contributor to the occurrence and progression of cardiovascular disease. Various risk factors, including altered hormone levels, have been suggested to be associated with arterial stiffness. Based on the background that chronic kidney disease predisposes individuals to a wide range of hormonal changes, we herein review the available data on the association between arterial stiffness and hormones in patients with chronic kidney disease and summarize the data for the general population.

  15. Variable stiffness actuated prosthetic knee to restore knee buckling during stance: a modeling study.

    PubMed

    Wentink, E C; Koopman, H F J M; Stramigioli, S; Rietman, J S; Veltink, P H

    2013-06-01

    Most modern intelligent knee prosthesis use dampers to modulate dynamic behavior and prevent excessive knee flexion, but they dissipate energy and do not assist in knee extension. Energy efficient variable stiffness control (VSA) can reduce the energy consumption yet effectively modulate the dynamic behavior and use stored energy during flexion to assist in subsequent extension. A principle design of energy efficient VSA in a prosthetic knee is proposed and analyzed for the specific case of rejection of a disturbed stance phase. The concept is based on the principle that the output stiffness of a spring can be changed without changing the energy stored in the elastic elements of the spring. The usability of this concept to control a prosthetic knee is evaluated using a model. Part of the stance phase of the human leg was modeled by a double pendulum. Specifically the rejection of a common disturbance of transfemoral prosthetic gait, an unlocked knee at heel strike, was evaluated. The ranges of spring stiffnesses were determined such that the angular characteristics of a normal stance phase were preserved, but disturbances could also be rejected. The simulations predicted that energy efficient VSA can be useful for the control of prosthetic knees. PMID:23000012

  16. Summary of lateral-control research

    NASA Technical Reports Server (NTRS)

    Toll, Thomas A

    1947-01-01

    A summary has been made of the available information on lateral control. A discussion is given of the criterions used in lateral-control specifications, of the factors involved in obtaining satisfactory lateral control, and of the methods employed in making lateral-control investigations in flight and in wind tunnels. The available data on conventional flap-type ailerons having various types of aerodynamic balance are presented in a form convenient for use in design. The characteristics of spoiler devices and booster mechanisms are discussed. The effects of Mach number, boundary layer, and distortion of the wing or of the lateral-control system are considered insofar as the available information permits. An example is included to illustrate the use of the design data. The limitations of the available information and some of the lateral-control problems that remain to be solved are indicated.

  17. Quaternion representations of stiffness and momentum of the forces, acting in vibration isolating systems with stiffness compensators

    NASA Astrophysics Data System (ADS)

    Gurova, E. G.

    2016-04-01

    This research is devoted to development of the spatial vibration isolation devices. The description of the vibration isolation systems has been presented through quaternions of the forces, momentums, and stiffness. The considered method allows taking into account the stochastic vibrations and describes it with the help of the hypercomplex numbers. The theory suggests the development of the vibration isolation devices, which have traction characteristics with zero stiffness area. To obtain such area in traction characteristic, a spatial vibration isolator is presented as a resilient element and the stiffness compensator, which is connected in parallel with it.

  18. Stiffness of Carpentry Connections - Numerical Modelling vs. Experimental Test

    NASA Astrophysics Data System (ADS)

    Kekeliak, Miloš; Gocál, Jozef; Vičan, Josef

    2015-12-01

    In this paper, numerical modelling of the traditional carpentry connection with mortise and tenon is presented. Numerical modelling is focused on its stiffness and the results are compared to results of experimental tests carried out by (Feio, 2005) [6]. To consider soft behaviour of wood in carpentry connections, which are related to its surface roughness and geometrical accuracy of the contact surfaces, the characteristics of the normal contact stiffness, determined experimentally, are introduced in the numerical model. Parametric study by means of numerical modelling with regard to the sensitivity of connection stiffness to contact stiffness is presented. Based on the study results, in conclusion there are presented relevant differences between the results of numerical modelling and experimental tests (Feio, 2005) [6].

  19. Molecular Cues Guiding Matrix Stiffness in Liver Fibrosis

    PubMed Central

    Saneyasu, Takaoki; Akhtar, Riaz

    2016-01-01

    Tissue and matrix stiffness affect cell properties during morphogenesis, cell growth, differentiation, and migration and are altered in the tissue remodeling following injury and the pathological progression. However, detailed molecular mechanisms underlying alterations of stiffness in vivo are still poorly understood. Recent engineering technologies have developed powerful techniques to characterize the mechanical properties of cell and matrix at nanoscale levels. Extracellular matrix (ECM) influences mechanical tension and activation of pathogenic signaling during the development of chronic fibrotic diseases. In this short review, we will focus on the present knowledge of the mechanisms of how ECM stiffness is regulated during the development of liver fibrosis and the molecules involved in ECM stiffness as a potential therapeutic target for liver fibrosis. PMID:27800489

  20. Hyperekplexia and stiff-baby syndrome: an identical neurological disorder?

    PubMed

    Cioni, G; Biagioni, E; Bottai, P; Castellacci, A M; Paolicelli, P B

    1993-03-01

    Hyperekplexia (startle disease) is an unusual, familial, neurological disorder characterized by abnormally enhanced startle response, followed in most cases by momentary generalized muscular stiffness. These attacks may cause the patients to fall rigidly, while remaining fully conscious. Startle symptomatology has generally an onset in infancy and is often accompanied, during the first years of life, by rigidity, sleep myoclonus, motor delay, regurgitation and apneic spells, which may cause sudden death. Stiff-baby syndrome is a familial disorder characterized by marked rigidity, with neonatal onset and gradual reduction during infancy, regurgitations, motor delay and attacks of stiffness. We report 4 new cases of hyperekplexia from two different families and another infant with stiff-baby syndrome discussing clinical, electrophysiological and genetic aspects of both neurological disorders in relation to other reported cases. We suggest a continuum between these familial syndromes, which are often misinterpreted as epilepsy or other disorders.

  1. Improved Equivalent Linearization Implementations Using Nonlinear Stiffness Evaluation

    NASA Technical Reports Server (NTRS)

    Rizzi, Stephen A.; Muravyov, Alexander A.

    2001-01-01

    This report documents two new implementations of equivalent linearization for solving geometrically nonlinear random vibration problems of complicated structures. The implementations are given the acronym ELSTEP, for "Equivalent Linearization using a STiffness Evaluation Procedure." Both implementations of ELSTEP are fundamentally the same in that they use a novel nonlinear stiffness evaluation procedure to numerically compute otherwise inaccessible nonlinear stiffness terms from commercial finite element programs. The commercial finite element program MSC/NASTRAN (NASTRAN) was chosen as the core of ELSTEP. The FORTRAN implementation calculates the nonlinear stiffness terms and performs the equivalent linearization analysis outside of NASTRAN. The Direct Matrix Abstraction Program (DMAP) implementation performs these operations within NASTRAN. Both provide nearly identical results. Within each implementation, two error minimization approaches for the equivalent linearization procedure are available - force and strain energy error minimization. Sample results for a simply supported rectangular plate are included to illustrate the analysis procedure.

  2. Portal frame inertia and stiffness matrices by substructure synthesis

    NASA Astrophysics Data System (ADS)

    Morales, C. A.

    2005-05-01

    Generic expressions of mass and stiffness matrices of the portal frame are presented. These are derived by means of the substructure synthesis method. This method is exceptionally characterised by low-order eigenvalue problems and highly accurate eigensolutions.

  3. Arterial stiffness estimation based photoplethysmographic pulse wave analysis

    NASA Astrophysics Data System (ADS)

    Huotari, Matti; Maatta, Kari; Kostamovaara, Juha

    2010-11-01

    Arterial stiffness is one of the indices of vascular healthiness. It is based on pulse wave analysis. In the case we decompose the pulse waveform for the estimation and determination of arterial elasticity. Firstly, optically measured with photoplethysmograph and then investigating means by four lognormal pulse waveforms for which we can find very good fit between the original and summed decomposed pulse wave. Several studies have demonstrated that these kinds of measures predict cardiovascular events. While dynamic factors, e.g., arterial stiffness, depend on fixed structural features of the vascular wall. Arterial stiffness is estimated based on pulse wave decomposition analysis in the radial and tibial arteries. Elucidation of the precise relationship between endothelial function and vascular stiffness awaits still further study.

  4. Operator-Based Preconditioning of Stiff Hyperbolic Systems

    SciTech Connect

    Reynolds, Daniel R.; Samtaney, Ravi; Woodward, Carol S.

    2009-02-09

    We introduce an operator-based scheme for preconditioning stiff components encoun- tered in implicit methods for hyperbolic systems of partial differential equations posed on regular grids. The method is based on a directional splitting of the implicit operator, followed by a char- acteristic decomposition of the resulting directional parts. This approach allows for solution to any number of characteristic components, from the entire system to only the fastest, stiffness-inducing waves. We apply the preconditioning method to stiff hyperbolic systems arising in magnetohydro- dynamics and gas dynamics. We then present numerical results showing that this preconditioning scheme works well on problems where the underlying stiffness results from the interaction of fast transient waves with slowly-evolving dynamics, scales well to large problem sizes and numbers of processors, and allows for additional customization based on the specific problems under study.

  5. Arterial Stiffness and Renal Replacement Therapy: A Controversial Topic

    PubMed Central

    Fischer, Edmundo Cabrera; Zócalo, Yanina; Galli, Cintia; Bia, Daniel

    2015-01-01

    The increase of arterial stiffness has been to have a significant impact on predicting mortality in end-stage renal disease patients. Pulse wave velocity (PWV) is a noninvasive, reliable parameter of regional arterial stiffness that integrates the vascular geometry and arterial wall intrinsic elasticity and is capable of predicting cardiovascular mortality in this patient population. Nevertheless, reports on PWV in dialyzed patients are contradictory and sometimes inconsistent: some reports claim the arterial wall stiffness increases (i.e., PWV increase), others claim that it is reduced, and some even state that it augments in the aorta while it simultaneously decreases in the brachial artery pathway. The purpose of this study was to analyze the literature in which longitudinal or transversal studies were performed in hemodialysis and/or peritoneal dialysis patients, in order to characterize arterial stiffness and the responsiveness to renal replacement therapy. PMID:26064684

  6. [Impact of aortic stiffness on central hemodynamics and cardiovascular system].

    PubMed

    Bulas, J; Potočárová, M; Filková, M; Simková, A; Murín, J

    2013-06-01

    Arterial stiffness increases as a result of degenerative processes accelerated by aging and many risk factors, namely arterial hypertension. Basic clinical examination reveals increased pulse pressure as its hemodynamic manifestation. The most serious consequence of increased vascular stiffness, which cannot be revealed by clinical examination, is a change of central hemodynamics leading to increased load of left ventricle, left ventricular hypertrophy, diastolic dysfunction and to overall increase of cardiovascular risk. This review aimed to point at some patophysiological mechanisms taking part in the development of vascular stiffness, vascular remodeling and hemodynamic consequences of these changes. This work also gives an overview of noninvasive examination methods and their characteristics enabling to evaluate the local, regional and systemic arterial stiffness and central pulse wave analysis and their meaning for central hemodynamics and heart workload. PMID:23808736

  7. Stiffness Corrections for the Vibration Frequency of a Stretched Wire

    ERIC Educational Resources Information Center

    Hornung, H. G.; Durie, M. J.

    1977-01-01

    Discusses the need of introducing corrections due to wire stiffness arising from end constraints and wire axis distribution curvature in the measurement of ac electrical frequency by exciting transverse standing waves in a stretched steel wire. (SL)

  8. A Novel Echocardiographic Method for Assessing Arterial Stiffness in Obstructive Sleep Apnea Syndrome

    PubMed Central

    Akyol, Aytac; Cakmak, Huseyin Altug; Gunbatar, Hulya; Asker, Muntecep; Babat, Naci; Tosu, Aydin Rodi; Yaman, Mehmet; Gumrukcuoglu, Hasan Ali

    2015-01-01

    Background and Objectives Obstructive sleep apnea syndrome (OSAS) is associated with increased arterial stiffness and cardiovascular complications. The objective of this study was to assess whether the color M-mode-derived propagation velocity of the descending thoracic aorta (aortic velocity propagation, AVP) was an echocardiographic marker for arterial stiffness in OSAS. Subjects and Methods The study population included 116 patients with OSAS and 90 age and gender-matched control subjects. The patients with OSAS were categorized according to their apnea hypopnea index (AHI) as follows: mild to moderate degree (AHI 5-30) and severe degree (AHI≥30). Aortofemoral pulse wave velocity (PWV), carotid intima-media thickness (CIMT), brachial artery flow-mediated dilatation (FMD), and AVP were measured to assess arterial stiffness. Results AVP and FMD were significantly decreased in patients with OSAS compared to controls (p<0.001). PWV and CIMT were increased in the OSAS group compared to controls (p<0.001). Moreover, AVP and FMD were significantly decreased in the severe OSAS group compared to the mild to moderate OSAS group (p<0.001). PWV and CIMT were significantly increased in the severe group compared to the mild to moderate group (p<0.001). AVP was significantly positively correlated with FMD (r=0.564, p<0.001). However, it was found to be significantly inversely related to PWV (r=-0.580, p<0.001) and CIMT (r=-0.251, p<0.001). Conclusion The measurement of AVP is a novel and practical echocardiographic method, which may be used to identify arterial stiffness in OSAS. PMID:26617653

  9. Bending stiffness of two aesthetic orthodontic archwires: an in vitro comparative study.

    PubMed

    Lim, K F; Lew, K K; Toh, S L

    1994-01-01

    The aims of the study were to quantify the transverse stiffness of two aesthetic orthodontic archwires (0018 inch Teflon-coated stainless steel and 0017 inch Optiflex) in a simulated clinical setting and to assess the influence of deflection direction on the bending stiffness. The aesthetic archwires were randomly divided into three equal groups: group 1, lingual deflection; group 2, labial deflection; and group 3, occlusal deflection. Each group consisted of six archwires of the same type. The control group consisting of eighteen 0014 inch stainless steel archwires were also subjected to the same grouping. A total of 54 archwires were tested in the study. The deflection of the archwires was measured with a travelling microscope and the load measured with a calibrated strain gauge ring transducer. The mean stiffnesses of the archwires in the lingual, labial and occlusal deflection groups were found to be 29, 08 and 25 mN/mm respectively for 0017 inch Optiflex (r = 09, P less than 0001), 132, 105 and 245 mN/mm respectively for 0018 inch Teflon-coated stainless steel (r = 09, P less than 0001) and 266, 164 and 323 mN/mm respectively for the control (r = 09, P less than 0001). Springback was found to be poor for Optiflex and the archwire remained bent upon deactivation. ANOVA showed that the influence of arch curvature on the bending stiffness was significantly different for Optiflex (P less than 005), Teflon-coated stainless steel (P less than 0005) and the control group (P <0005).(ABSTRACT TRUNCATED AT 250 WORDS) PMID:10147326

  10. Intrinsic, reflex and voluntary contributions to task-dependent joint stiffness.

    PubMed

    Ludvig, Daniel; Kearney, Robert E

    2010-01-01

    Dynamic joint stiffness defines the dynamic relationship between the position of the joint and the torque acting about it. Joint stiffness consists of two components: intrinsic and reflex stiffness. Previous work from our lab has shown that subjects can alter their reflex stiffness voluntarily and independently of intrinsic stiffness. Numerous studies have investigated whether reflex stiffness is altered in a task-dependent fashion; however the results of these studies are inconclusive. We designed an experimental paradigm where subjects were faced with 3 tasks: one task where joint stiffness aided subjects, a second where joint stiffness hindered the subjects and a third where joint stiffness had no effect. We found that subjects did not alter their joint stiffness to perform the different tasks. Rather, they performed the tasks by voluntarily producing the appropriate torque based on visual feedback. Thus, with the paradigm used in this study, reflex stiffness was not modulated in a task-dependent manner.

  11. Pediatric stiff-person syndrome with renal failure

    PubMed Central

    Kumar, M. Veerendra; Savida, P.

    2016-01-01

    Stiff-person syndrome (SPS) is an autoimmune neuronitis with progressive myoclonus and stiffness. It is a rare but treatable disorder with few case reports in children. SPS is due to autoantibodies against the enzyme glutamic acid decarboxylase which is present in neuronal and nonneuronal tissues. This is the case report of an 8-year-old boy with clinical and investigational features suggestive of SPS with associated myoglobin-induced renal failure, who completely recovered with treatment. PMID:26933366

  12. The relationships between active extensibility, and passive and active stiffness of the knee flexors.

    PubMed

    Blackburn, J Troy; Padua, Darin A; Riemann, Bryan L; Guskiewicz, Kevin M

    2004-12-01

    Insufficient active knee flexor stiffness may predispose the anterior cruciate ligament to injury. Insufficient passive stiffness may result in insufficient active stiffness. Similarly, higher levels of musculotendinous extensibility may inhibit active and passive muscle stiffness, potentially contributing to an increased risk of injury. The literature is both limited and inconsistent concerning relationships between extensibility, passive stiffness, and active stiffness. Extensibility was measured as the maximal active knee extension angle from a supine position with the hip flexed to 90 degrees . Passive stiffness was calculated as the slope of the moment-angle curve resulting from passive knee extension. Active stiffness was assessed via acceleration associated with damped oscillatory motion about the knee. Stepwise multiple regression indicated that passive stiffness accounted for 25% of active muscle stiffness variance. The linear combination of extensibility and passive stiffness explained only 2% more variance compared to passive stiffness alone. Musculotendinous extensibility was moderately related to passive muscle stiffness, and weakly related to active muscle stiffness. The moderate relationship observed between active and passive stiffness emphasizes the dependence of active muscle stiffness on cross-bridge formation, and the relatively smaller contribution from parallel elastic tissues. Additionally, heightened extensibility does not appear to be a predisposing factor for reduced muscle stiffness. PMID:15491843

  13. Modulation of Huh7.5 Spheroid Formation and Functionality Using Modified PEG-Based Hydrogels of Different Stiffness

    PubMed Central

    Lee, Bae Hoon; Kim, Myung Hee; Lee, Jae Ho; Seliktar, Dror; Cho, Nam-Joon; Tan, Lay Poh

    2015-01-01

    Physical cues, such as cell microenvironment stiffness, are known to be important factors in modulating cellular behaviors such as differentiation, viability, and proliferation. Apart from being able to trigger these effects, mechanical stiffness tuning is a very convenient approach that could be implemented readily into smart scaffold designs. In this study, fibrinogen-modified poly(ethylene glycol)-diacrylate (PEG-DA) based hydrogels with tunable mechanical properties were synthesized and applied to control the spheroid formation and liver-like function of encapsulated Huh7.5 cells in an engineered, three-dimensional liver tissue model. By controlling hydrogel stiffness (0.1–6 kPa) as a cue for mechanotransduction representing different stiffness of a normal liver and a diseased cirrhotic liver, spheroids ranging from 50 to 200 μm were formed over a three week time-span. Hydrogels with better compliance (i.e. lower stiffness) promoted formation of larger spheroids. The highest rates of cell proliferation, albumin secretion, and CYP450 expression were all observed for spheroids in less stiff hydrogels like a normal liver in a healthy state. We also identified that the hydrogel modification by incorporation of PEGylated-fibrinogen within the hydrogel matrix enhanced cell survival and functionality possibly owing to more binding of autocrine fibronectin. Taken together, our findings establish guidelines to control the formation of Huh7.5 cell spheroids in modified PEGDA based hydrogels. These spheroids may serve as models for applications such as screening of pharmacological drug candidates. PMID:25692976

  14. Therapeutic modification of arterial stiffness: An update and comprehensive review

    PubMed Central

    Wu, Ching-Fen; Liu, Pang-Yen; Wu, Tsung-Jui; Hung, Yuan; Yang, Shih-Ping; Lin, Gen-Min

    2015-01-01

    Arterial stiffness has been recognized as a marker of cardiovascular disease and associated with long-term worse clinical outcomes in several populations. Age, hypertension, smoking, and dyslipidemia, known as traditional vascular risk factors, as well as diabetes, obesity, and systemic inflammation lead to both atherosclerosis and arterial stiffness. Targeting multiple modifiable risk factors has become the main therapeutic strategy to improve arterial stiffness in patients at high cardiovascular risk. Additionally to life style modifications, long-term ω-3 fatty acids (fish oil) supplementation in diet may improve arterial stiffness in the population with hypertension or metabolic syndrome. Pharmacological treatment such as renin-angiotensin-aldosterone system antagonists, metformin, and 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors were useful in individuals with hypertension and diabetes. In obese population with obstructive sleep apnea, weight reduction, aerobic exercise, and continuous positive airway pressure treatment may also improve arterial stiffness. In the populations with chronic inflammatory disease such as rheumatoid arthritis, a use of antibodies against tumor necrosis factor-alpha could work effectively. Other therapeutic options such as renal sympathetic nerve denervation for patients with resistant hypertension are investigated in many ongoing clinical trials. Therefore our comprehensive review provides knowledge in detail regarding many aspects of pathogenesis, measurement, and management of arterial stiffness in several populations, which would be helpful for physicians to make clinical decision. PMID:26635922

  15. Non-crossbridge stiffness in active muscle fibres.

    PubMed

    Colombini, Barbara; Nocella, Marta; Bagni, Maria Angela

    2016-01-01

    Stretching of an activated skeletal muscle induces a transient tension increase followed by a period during which the tension remains elevated well above the isometric level at an almost constant value. This excess of tension in response to stretching has been called 'static tension' and attributed to an increase in fibre stiffness above the resting value, named 'static stiffness'. This observation was originally made, by our group, in frog intact muscle fibres and has been confirmed more recently, by us, in mammalian intact fibres. Following stimulation, fibre stiffness starts to increase during the latent period well before crossbridge force generation and it is present throughout the whole contraction in both single twitches and tetani. Static stiffness is dependent on sarcomere length in a different way from crossbridge force and is independent of stretching amplitude and velocity. Static stiffness follows a time course which is distinct from that of active force and very similar to the myoplasmic calcium concentration time course. We therefore hypothesize that static stiffness is due to a calcium-dependent stiffening of a non-crossbridge sarcomere structure, such as the titin filament. According to this hypothesis, titin, in addition to its well-recognized role in determining the muscle passive tension, could have a role during muscle activity. PMID:26792325

  16. Therapeutic modification of arterial stiffness: An update and comprehensive review.

    PubMed

    Wu, Ching-Fen; Liu, Pang-Yen; Wu, Tsung-Jui; Hung, Yuan; Yang, Shih-Ping; Lin, Gen-Min

    2015-11-26

    Arterial stiffness has been recognized as a marker of cardiovascular disease and associated with long-term worse clinical outcomes in several populations. Age, hypertension, smoking, and dyslipidemia, known as traditional vascular risk factors, as well as diabetes, obesity, and systemic inflammation lead to both atherosclerosis and arterial stiffness. Targeting multiple modifiable risk factors has become the main therapeutic strategy to improve arterial stiffness in patients at high cardiovascular risk. Additionally to life style modifications, long-term ω-3 fatty acids (fish oil) supplementation in diet may improve arterial stiffness in the population with hypertension or metabolic syndrome. Pharmacological treatment such as renin-angiotensin-aldosterone system antagonists, metformin, and 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors were useful in individuals with hypertension and diabetes. In obese population with obstructive sleep apnea, weight reduction, aerobic exercise, and continuous positive airway pressure treatment may also improve arterial stiffness. In the populations with chronic inflammatory disease such as rheumatoid arthritis, a use of antibodies against tumor necrosis factor-alpha could work effectively. Other therapeutic options such as renal sympathetic nerve denervation for patients with resistant hypertension a