Science.gov

Sample records for active variable stiffness

  1. 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

  2. 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

  3. 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.

  4. Gradual stiffness versus magnetic imaging-guided variable stiffness colonoscopes: A randomized noninferiority trial

    PubMed Central

    Wiig, Håvard; Hasund, Audun; Matre, Jon; Holme, Øyvind; Noraberg, Geir; Løberg, Magnus; Kalager, Mette; Adami, Hans-Olov; Bretthauer, Michael

    2016-01-01

    Background Colonoscopes with gradual stiffness have recently been developed to enhance cecal intubation. Objective We aimed to determine if the performance of gradual stiffness colonoscopes is noninferior to that of magnetic endoscopic imaging (MEI)-guided variable stiffness colonoscopes. Methods Consecutive patients were randomized to screening colonoscopy with Fujifilm gradual stiffness or Olympus MEI-guided variable stiffness colonoscopes. The primary endpoint was cecal intubation rate (noninferiority limit 5%). Secondary endpoints included cecal intubation time. We estimated absolute risk differences with 95% confidence intervals (CIs). Results We enrolled 475 patients: 222 randomized to the gradual stiffness instrument, and 253 to the MEI-guided variable stiffness instrument. Cecal intubation rate was 91.7% in the gradual stiffness group versus 95.6% in the variable stiffness group. The adjusted absolute risk for cecal intubation failure was 4.3% higher in the gradual stiffness group than in the variable stiffness group (upper CI border 8.1%). Median cecal intubation time was 13 minutes in the gradual stiffness group and 10 minutes in the variable stiffness group (p < 0.001). Conclusions The study is inconclusive with regard to noninferiority because the 95% CI for the difference in cecal intubation rate between the groups crosses the noninferiority margin. (ClinicalTrials.gov identifier: NCT01895504).

  5. A prototype of a novel energy efficient variable stiffness actuator.

    PubMed

    Visser, L C; Carloni, R; Klijnstra, F; Stramigioli, S

    2010-01-01

    In this work, we present a proof of concept of a novel variable stiffness actuator. The actuator design is based on the conceptual design proposed in earlier work, and is such that the apparent output stiffness of the actuator can be changed independently of the output position and without any energy cost. Experimental results show that the behavior of the prototype is in accordance with the theoretical results of the conceptual design, and thus show that energy efficient variable stiffness actuators can be realized.

  6. A novel energy-efficient rotational variable stiffness actuator.

    PubMed

    Rao, Shodhan; Carloni, Raffaella; Stramigioli, Stefano

    2011-01-01

    This paper presents the working principle, the design and realization of a novel rotational variable stiffness actuator, whose stiffness can be varied independently of its output angular position. This actuator is energy-efficient, meaning that the stiffness of the actuator can be varied by keeping constant the internal stored energy of the actuator. The principle of the actuator is an extension of the principle of translational energy-efficient actuator vsaUT. A prototype based on the principle has been designed, in which ball-bearings and linear slide guides have been used in order to reduce losses due to friction.

  7. Stiff substrates enhance cultured neuronal network activity.

    PubMed

    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

    2014-08-28

    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 Ca(2+) channel currents determined by patch-clamp recording were greater in neurons on stiff substrates than on soft substrates. Ca(2+) 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.

  8. Research on damping properties optimization of variable-stiffness plate

    NASA Astrophysics Data System (ADS)

    Wen-kai, QI; Xian-tao, YIN; Cheng, SHEN

    2016-09-01

    This paper investigates damping optimization design of variable-stiffness composite laminated plate, which means fibre paths can be continuously curved and fibre angles are distinct for different regions. First, damping prediction model is developed based on modal dissipative energy principle and verified by comparing with modal testing results. Then, instead of fibre angles, the element stiffness and damping matrixes are translated to be design variables on the basis of novel Discrete Material Optimization (DMO) formulation, thus reducing the computation time greatly. Finally, the modal damping capacity of arbitrary order is optimized using MMA (Method of Moving Asymptotes) method. Meanwhile, mode tracking technique is employed to investigate the variation of modal shape. The convergent performance of interpolation function, first order specific damping capacity (SDC) optimization results and variation of modal shape in different penalty factor are discussed. The results show that the damping properties of the variable-stiffness plate can be increased by 50%-70% after optimization.

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

    PubMed

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

    2016-04-08

    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.

  10. Analysis and Design of Variable Stiffness Composite Cylinders

    NASA Technical Reports Server (NTRS)

    Tatting, Brian F.; Guerdal, Zafer

    1998-01-01

    An investigation of the possible performance improvements of thin circular cylindrical shells through the use of the variable stiffness concept is presented. The variable stiffness concept implies that the stiffness parameters change spatially throughout the structure. This situation is achieved mainly through the use of curvilinear fibers within a fiber-reinforced composite laminate, though the possibility of thickness variations and discrete stiffening elements is also allowed. These three mechanisms are incorporated into the constitutive laws for thin shells through the use of Classical Lamination Theory. The existence of stiffness variation within the structure warrants a formulation of the static equilibrium equations from the most basic principles. The governing equations include sufficient detail to correctly model several types of nonlinearity, including the formation of a nonlinear shell boundary layer as well as the Brazier effect due to nonlinear bending of long cylinders. Stress analysis and initial buckling estimates are formulated for a general variable stiffness cylinder. Results and comparisons for several simplifications of these highly complex governing equations are presented so that the ensuing numerical solutions are considered reliable and efficient enough for in-depth optimization studies. Four distinct cases of loading and stiffness variation are chosen to investigate possible areas of improvement that the variable stiffness concept may offer over traditional constant stiffness and/or stiffened structures. The initial investigation deals with the simplest solution for cylindrical shells in which all quantities are constant around the circumference of the cylinder. This axisymmetric case includes a stiffness variation exclusively in the axial direction, and the only pertinent loading scenarios include constant loads of axial compression, pressure, and torsion. The results for these cases indicate that little improvement over traditional

  11. Thermal Testing of Tow-Placed, Variable Stiffness Panels

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey; Guerdal, Zafer

    2001-01-01

    Commercial systems for precise placement of pre-preg composite tows are enabling technology that allows fabrication of advanced composite structures in which the tows may be precisely laid down along curvilinear paths within a given ply. For laminates with curvilinear tow paths, the fiber orientation angle varies continuously throughout the laminate, and is not required to be straight and parallel in each ply as in conventional composite laminates. Hence, the stiffness properties vary as a function of location in the laminate, and the associated composite structure is called a "variable stiffness" composite structure.

  12. 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.

  13. Non-linear dynamic analysis of beams with variable stiffness

    NASA Astrophysics Data System (ADS)

    Katsikadelis, J. T.; Tsiatas, G. C.

    2004-03-01

    In this paper the analog equation method (AEM), a BEM-based method, is employed to the non-linear dynamic analysis of a Bernoulli-Euler beam with variable stiffness undergoing large deflections, under general boundary conditions which maybe non-linear. As the cross-sectional properties of the beam vary along its axis, the coefficients of the differential equations governing the dynamic equilibrium of the beam are variable. The formulation is in terms of the displacements. The governing equations are derived in both deformed and undeformed configuration and the deviations of the two approaches are studied. Using the concept of the analog equation, the two coupled non-linear hyperbolic differential equations with variable coefficients are replaced by two uncoupled linear ones pertaining to the axial and transverse deformation of a substitute beam with unit axial and bending stiffness, respectively, under fictitious time-dependent load distributions. A significant advantage of this method is that the time history of the displacements as well as the stress resultants are computed at any cross-section of the beam using the respective integral representations as mathematical formulae. Beams with constant and varying stiffness are analyzed under various boundary conditions and loadings to illustrate the merits of the method as well as its applicability, efficiency and accuracy.

  14. 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.

  15. Evaluation of feedforward and feedback contributions to hand stiffness and variability in multijoint arm control.

    PubMed

    He, Xin; Du, Yu-Fan; Lan, Ning

    2013-07-01

    The purpose of this study is to validate a neuromechanical model of the virtual arm (VA) by comparing emerging behaviors of the model to those of experimental observations. Hand stiffness of the VA model was obtained by either theoretical computation or simulated perturbations. Variability in hand position of the VA was generated by adding signal dependent noise (SDN) to the motoneuron pools of muscles. Reflex circuits of Ia, Ib and Renshaw cells were included to regulate the motoneuron pool outputs. Evaluation of hand stiffness and variability was conducted in simulations with and without afferent feedback under different patterns of muscle activations during postural maintenance. The simulated hand stiffness and variability ellipses captured the experimentally observed features in shape, magnitude and orientation. Steady state afferent feedback contributed significantly to the increase in hand stiffness by 35.75±16.99% in area, 18.37±7.80% and 16.15±7.15% in major and minor axes; and to the reduction of hand variability by 49.41±21.19% in area, 36.89±12.78% and 18.87±23.32% in major and minor axes. The VA model reproduced the neuromechanical behaviors that were consistent with experimental data, and it could be a useful tool for study of neural control of posture and movement, as well as for application to rehabilitation.

  16. Sources of variability in musculo-articular stiffness measurement.

    PubMed

    Ditroilo, Massimiliano; Watsford, Mark; Murphy, Aron; De Vito, Giuseppe

    2013-01-01

    The assessment of musculo-articular stiffness (MAS) with the free-oscillation technique is a popular method with a variety of applications. This study examined the sources of variability (load applied and frequency of oscillation) when MAS is assessed. Over two testing occasions, 14 healthy men (27.7±5.2 yr, 1.82±0.04 m, 79.5±8.4 kg) were measured for isometric maximum voluntary contraction and MAS of the knee flexors using submaximal loads relative to the individual's maximum voluntary contraction (MAS%MVC) and a single absolute load (MASABS). As assessment load increased, MAS%MVC (coefficient of variation (CV)  =  8.1-12.1%; standard error of measurement (SEM)  =  51.6-98.8 Nm⁻¹) and frequency (CV  =  4.8-7.0%; SEM  =  0.060-0.075 s⁻¹) variability increased consequently. Further, similar levels of variability arising from load (CV  =  6.7%) and frequency (CV  =  4.8-7.0%) contributed to the overall MAS%MVC variability. The single absolute load condition yielded better reliability scores for MASABS (CV  =  6.5%; SEM  =  40.2 Nm⁻¹) and frequency (CV  =  3.3%; SEM  =  0.039 s⁻¹). Low and constant loads for MAS assessment, which are particularly relevant in the clinical setting, exhibited superior reliability compared to higher loads expressed as a percentage of maximum voluntary contraction, which are more suitable for sporting situations. Appropriate sample size and minimum detectable change can therefore be determined when prospective studies are carried out.

  17. Enabling variable-stiffness hand rehabilitation orthoses with dielectric elastomer transducers.

    PubMed

    Carpi, Federico; Frediani, Gabriele; Gerboni, Carlo; Gemignani, Jessica; De Rossi, Danilo

    2014-02-01

    Patients affected by motor disorders of the hand and having residual voluntary movements of fingers or wrist can benefit from self-rehabilitation exercises performed with so-called dynamic hand splints. These systems consist of orthoses equipped with elastic cords or springs, which either provide a sustained stretch or resist voluntary movements of fingers or wrist. These simple systems are limited by the impossibility of modulating the mechanical stiffness. This limitation does not allow for customizations and real-time control of the training exercise, which would improve the rehabilitation efficacy. To overcome this limitation, 'active' orthoses equipped with devices that allow for electrical control of the mechanical stiffness are needed. Here, we report on a solution that relies on compact and light-weight electroactive elastic transducers that replace the passive elastic components. We developed a variable-stiffness transducer made of dielectric elastomers, as the most performing types of electromechanically active polymers. The transducer was manufactured with a silicone film and tested with a purposely-developed stiffness control strategy that allowed for electrical modulations of the force-elongation response. Results showed that the proposed new technology is a promising and viable solution to develop electrically controllable dynamic hand orthoses for hand rehabilitation.

  18. Variable stiffness property study on shape memory polymer composite tube

    NASA Astrophysics Data System (ADS)

    Chen, Yijin; Sun, Jian; Liu, Yanju; Leng, Jinsong

    2012-09-01

    As a typical smart material, shape memory polymers (SMPs) have the capability of variable stiffness in response to external stimuli, such as heat, electricity, magnetism and solvents. In this research, a shape memory polymer composite (SMPC) tube composed of multi-layered filament wound structures is investigated. The SMPC tube possesses considerable flexibility under high temperature and rigidity under low temperature. Significant changes in effective engineering modulus can be achieved through regulating the environment temperature. Based on the classical laminated-plate theory and Sun’s thick laminate analysis, a 3D theory method is used to study the effective engineering modulus and modulus ratio of the SMPC tube. The tensile test is conducted on the SMPC tube to verify the accuracy of the theoretical method. In addition, the effective engineering modulus and modulus ratio are discussed under different fiber-winding angles and fiber volume fractions of the SMPC tube. The presented analysis provides meaningful guidance to assist the design and manufacture of SMPC tubes in morphing skin applications.

  19. Concurrent design of a morphing aerofoil with variable stiffness bi-stable laminates

    NASA Astrophysics Data System (ADS)

    Kuder, I. K.; Fasel, U.; Ermanni, P.; Arrieta, A. F.

    2016-11-01

    Morphing systems able to efficiently adjust their characteristics to resolve the conflicting demands of changing operating conditions offer great potential for enhanced performance and functionality. The main practical challenge, however, consists in combining the desired compliance to accomplish radical reversible geometry modifications at reduced actuation effort with the requirement of high stiffness imposed by operational functions. A potential decoupling strategy entails combining the conformal shape adaptation benefits of distributed compliance with purely elastic stiffness variability provided by embedded bi-stable laminates. This selective compliance can allow for on-demand stiffness adaptation by switching between the stable states of the internal elements. The current paper considers the optimal positioning of the bi-stable components within the structure while assessing the energy required for morphing under aerodynamic loading. Compared to a time-invariant system, activating specific deformation modes permits decreasing the amount of actuation energy, and hence the amount of actuation material to be carried. A concurrent design and optimisation framework is implemented to develop selective configurations targeting different flight conditions. First, an aerodynamically favourable high-lift mode achieves large geometric changes due to reduced actuation demands. This is only possible by virtue of the internally tailored compliance, arising from the stable state switch of the embedded bi-stable components. A second, stiff configuration, targets operation under increased aerodynamic loading. The dynamic adequacy of the design is proved via high fidelity fluid-structure interaction simulations.

  20. Structural Response of Compression-Loaded, Tow-Placed, Variable Stiffness Panels

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey; Guerdal, Zafer; Starnes, James H., Jr.

    2002-01-01

    Results of an analytical and experimental study to characterize the structural response of two compression-loaded variable stiffness composite panels are presented and discussed. These variable stiffness panels are advanced composite structures, in which tows are laid down along precise curvilinear paths within each ply and the fiber orientation angle varies continuously throughout each ply. The panels are manufactured from AS4/977-3 graphite-epoxy pre-preg material using an advanced tow placement system. Both variable stiffness panels have the same layup, but one panel has overlapping tow bands and the other panel has a constant-thickness laminate. A baseline cross-ply panel is also analyzed and tested for comparative purposes. Tests performed on the variable stiffness panels show a linear prebuckling load-deflection response, followed by a nonlinear response to failure at loads between 4 and 53 percent greater than the baseline panel failure load. The structural response of the variable stiffness panels is also evaluated using finite element analyses. Nonlinear analyses of the variable stiffness panels are performed which include mechanical and thermal prestresses. Results from analyses that include thermal prestress conditions correlate well with measured variable stiffness panel results. The predicted response of the baseline panel also correlates well with measured results.

  1. Variable stiffness corrugated composite structure with shape memory polymer for morphing skin applications

    NASA Astrophysics Data System (ADS)

    Gong, Xiaobo; Liu, Liwu; Scarpa, Fabrizio; Leng, Jinsong; Liu, Yanju

    2017-03-01

    This work presents a variable stiffness corrugated structure based on a shape memory polymer (SMP) composite with corrugated laminates as reinforcement that shows smooth aerodynamic surface, extreme mechanical anisotropy and variable stiffness for potential morphing skin applications. The smart composite corrugated structure shows a low in-plane stiffness to minimize the actuation energy, but also possess high out-of-plane stiffness to transfer the aerodynamic pressure load. The skin provides an external smooth aerodynamic surface because of the one-sided filling with the SMP. Due to variable stiffness of the shape memory polymer the morphing skin exhibits a variable stiffness with a change of temperature, which can help the skin adjust its stiffness according different service environments and also lock the temporary shape without external force. Analytical models related to the transverse and bending stiffness are derived and validated using finite element techniques. The stiffness of the morphing skin is further investigated by performing a parametric analysis against the geometry of the corrugation and various sets of SMP fillers. The theoretical and numerical models show a good agreement and demonstrate the potential of this morphing skin concept for morphing aircraft applications. We also perform a feasibility study of the use of this morphing skin in a variable camber morphing wing baseline. The results show that the morphing skin concept exhibits sufficient bending stiffness to withstand the aerodynamic load at low speed (less than 0.3 Ma), while demonstrating a large transverse stiffness variation (up to 191 times) that helps to create a maximum mechanical efficiency of the structure under varying external conditions.

  2. Variable stiffness and recruitment using nylon actuators arranged in a pennate configuration

    NASA Astrophysics Data System (ADS)

    Kianzad, Soheil; Pandit, Milind; Lewis, Johnathan D.; Berlingeri, Alexander R.; Haebler, Karl J.; Madden, John D. W.

    2015-04-01

    In muscle variable impedance and ability to recruit fibers as needed helps enable actions such as walking and catching. A new biomimetic structure of nylon actuator is presented that imitates the human pennate muscle in structure, ability to vary stiffness and the ability to increase force by recruiting additional fibers. The actuator consists of 16 silver coated nylon coiled fibers attached to a central tendon at an angle of 20°. Each nylon coil produces 20 MPa of stress at constant length and nearly 20% strain at fixed load. Fibers are individually switched ON and OFF using transistors so that each element can be recruited, and the stiffness varied. The amount of input power is controlled with pulse width modulation (PWM) techniques. It is observed that the spring constant of the pennate structure varies from that of its passive state, 503 N/m and a resonance frequency of 1.4 Hz, to 1480 N/m with resonance frequency of 3.1 Hz in the active state where all the fibers are switched on under a 25 N load. Stiffness can be varied by a factor of 9.

  3. Substrate Stiffness Regulates Filopodial Activities in Lung Cancer Cells

    PubMed Central

    Liou, Yu-Ren; Torng, Wen; Kao, Yu-Chiu; Sung, Kung-Bin; Lee, Chau-Hwang; Kuo, Po-Ling

    2014-01-01

    Microenvironment stiffening plays a crucial role in tumorigenesis. While filopodia are generally thought to be one of the cellular mechanosensors for probing environmental stiffness, the effects of environmental stiffness on filopodial activities of cancer cells remain unclear. In this work, we investigated the filopodial activities of human lung adenocarcinoma cells CL1-5 cultured on substrates of tunable stiffness using a novel platform. The platform consists of an optical system called structured illumination nano-profilometry, which allows time-lapsed visualization of filopodial activities without fluorescence labeling. The culturing substrates were composed of polyvinyl chloride mixed with an environmentally friendly plasticizer to yield Young's modulus ranging from 20 to 60 kPa. Cell viability studies showed that the viability of cells cultured on the substrates was similar to those cultured on commonly used elastomers such as polydimethylsiloxane. Time-lapsed live cell images were acquired and the filopodial activities in response to substrates with varying degrees of stiffness were analyzed. Statistical analyses revealed that lung cancer cells cultured on softer substrates appeared to have longer filopodia, higher filopodial densities with respect to the cellular perimeter, and slower filopodial retraction rates. Nonetheless, the temporal analysis of filopodial activities revealed that whether a filopodium decides to extend or retract is purely a stochastic process without dependency on substrate stiffness. The discrepancy of the filopodial activities between lung cancer cells cultured on substrates with different degrees of stiffness vanished when the myosin II activities were inhibited by treating the cells with blebbistatin, which suggests that the filopodial activities are closely modulated by the adhesion strength of the cells. Our data quantitatively relate filopodial activities of lung cancer cells with environmental stiffness and should shed light

  4. 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.

  5. Constant and variable stiffness and damping of the leg joints in human hopping.

    PubMed

    Rapoport, Svetlana; Mizrahi, Joseph; Kimmel, Eitan; Verbitsky, Oleg; Isakov, Eli

    2003-08-01

    The present study deals with the stiffness and damping profiles of the leg joints during the ground-contact phase of hopping. A two-dimensional (sagittal plane) jumping model, consisting of four linked rigid segments and including the paired feet, shanks, thighs, and the head-arms-trunk segment, was developed. The segments were interconnected by damped torsional springs, representing the action of the muscles, tendons and ligaments across the joint and of the other joint tissues. A regressive function was used to express stiffness and damping, and included second-order dependence on angle and first-order dependence on angular velocity. By eliminating redundancies in the numerical solution using multicollinearity diagnostic algorithms, the model results revealed that the correct and sufficient nonlinearity for the joint stiffness is of the first order. Damping was found negligible. The stiffness profiles obtained were bell-shaped with a maximum near midstance and nonzero edge values. In predicting the joint moments, the obtained variable joint stiffnesses provided a closer agreement compared to a constant stiffness model. The maximal stiffness was found to be in linear correlation with the initial stiffness in each joint, providing support to the of muscles' preactivation strategy during the flight phase of hopping. All stiffnesses increased with increasing hopping frequency. The model presented provides an effective tool for future designing of artificial legs and robots and for the development of more accurate control strategies.

  6. Photoinduced variable stiffness of spiropyran-based composites

    SciTech Connect

    Samoylova, E.; Ceseracciu, L.; Allione, M.; Diaspro, A.; Barone, A. C.; Athanassiou, A.

    2011-11-14

    A quantitative demonstration of reversible stiffness upon appropriate light stimulus in a spiropyran-polymeric composite is presented. The polymeric films containing 3% wt. of the photochromic spiropyran were irradiated with alternating ultraviolet and visible light and the storage modulus was measured. A reversible change in modulus of about 7% was observed. The modulus change was attributed to an interaction of the polar merocyanine with the polymeric chains and/or to a variation of effective free volume induced by merocyanine aggregates formed in the polymer upon ultraviolet irradiation. The effect is fully reversed when the merocyanine isomers turn back to the spiropyran state after visible irradiation.

  7. Increased Thrust through Passively Variable Tail Stiffness in Fast Starting Fish

    NASA Astrophysics Data System (ADS)

    Currier, Todd; Ma, Ganzhong; Modarres-Sadeghi, Yahya

    2016-11-01

    An experimental study is conducted in the effect of tail stiffness on increased acceleration in mechanisms designed to emulate fast-start fish maneuvers. The variable stiffness is characterized by the directionality of loading. As load is applied in one direction on the fin the structure is flexible, simulating the preparatory stage of the maneuver, and as load is applied in the opposing direction the fin rigidly maintains its shape during the propulsive stage. A 3D printed fin structure is used to achieve the directional stiffness and is tested dynamically. Thrust is measured at various rates of rotation studying the influence of timing on peak acceleration.

  8. Composite laminates with spatially varying fiber orientations - 'Variable stiffness panel concept'

    NASA Technical Reports Server (NTRS)

    Guerdal, Zafer; Olmedo, Reynaldo

    1992-01-01

    A solution has been obtained to the plane elasticity problem for a symmetrically laminated composite panel with spatially varying fiber orientations. Since variation of the fiber angles along the length of a composite laminate results in stiffness properties that change as a function of location, the laminates are called variable stiffness panels. An analysis of the stiffness variation and its effect on the elastic response of the panel is presented here. A numerical solution has been obtained using an iterative collocation technique. Corresponding closed-form solutions are given for three different sets of boundary conditions. Two of the cases considered have exact solutions and thus serve to validate the numerical model.

  9. Variable Stiffness Panel Structural Analyses With Material Nonlinearity and Correlation With Tests

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey; Gurdal, Zafer

    2006-01-01

    Results from structural analyses of three tow-placed AS4/977-3 composite panels with both geometric and material nonlinearities are presented. Two of the panels have variable stiffness layups where the fiber orientation angle varies as a continuous function of location on the panel planform. One variable stiffness panel has overlapping tow bands of varying thickness, while the other has a theoretically uniform thickness. The third panel has a conventional uniform-thickness [plus or minus 45](sub 5s) layup with straight fibers, providing a baseline for comparing the performance of the variable stiffness panels. Parametric finite element analyses including nonlinear material shear are first compared with material characterization test results for two orthotropic layups. This nonlinear material model is incorporated into structural analysis models of the variable stiffness and baseline panels with applied end shortenings. Measured geometric imperfections and mechanical prestresses, generated by forcing the variable stiffness panels from their cured anticlastic shapes into their flatter test configurations, are also modeled. Results of these structural analyses are then compared to the measured panel structural response. Good correlation is observed between the analysis results and displacement test data throughout deep postbuckling up to global failure, suggesting that nonlinear material behavior is an important component of the actual panel structural response.

  10. Improving stability and curving passing performance for railway vehicles with a variable stiffness MRF rubber joint

    NASA Astrophysics Data System (ADS)

    Harris, B. J.; Sun, S. S.; Li, W. H.

    2017-03-01

    With the growing need for effective intercity transport, the need for more advanced rail vehicle technology has never been greater. The conflicting primary longitudinal suspension requirements of high speed stability and curving performance limit the development of rail vehicle technology. This paper presents a novel magnetorheological fluid based joint with variable stiffness characteristics for the purpose of overcoming this parameter conflict. Firstly, the joint design and working principle is developed. Following this, a prototype is tested by MTS to characterize its variable stiffness properties under a range of conditions. Lastly, the performance of the proposed MRF rubber joint with regard to improving train stability and curving performance is numerically evaluated.

  11. Engineering Tools for Variable Stiffness Vibration Suppression and Isolation

    DTIC Science & Technology

    2004-12-01

    A-1 Appendix B . Variation of Parameters for the Initial Value Variable Sti¤ness Constant Damping Problem... B -1 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BIB-1 Vita...Pan et. al. has approximated c0 and linearly as c0 = ca + cbV (2.32) = a + bV (2.33) where ca, cb, a, and b are constants and V is the input

  12. Quantifying the variability in stiffness and damping of an automotive vehicle's trim-structure mounts

    NASA Astrophysics Data System (ADS)

    Abolfathi, Ali; O'Boy, Dan J.; Walsh, Stephen J.; Dowsett, Amy; Fisher, Stephen A.

    2016-09-01

    Small plastic clips are used in large numbers in automotive vehicles to connect interior trims to vehicle structures. The variability in their properties can contribute to the overall variability in noise and vibration response of the vehicle. The variability arises due to their material and manufacturing tolerances and more importantly due to the boundary condition. To measure their stiffness and damping, a simple experimental rig is used where a mass is supported by the clip which is modelled as a single degree of freedom system. The rig is designed in a way that it simulates the boundary condition as those of the real vehicle. The variability in clip and also due to the boundary condition at the structure side is first examined which is 7% for stiffness and 8% for damping. To simulate the connection of the trim side, a mount is built using a 3D printer. Rattling occurs in the response of the clips with loose connections, however by preloading the mount the effective stiffness increases and the rattling is eliminated. The variability due to the boundary condition at the trim side was as large as 40% for stiffness and 52% for damping.

  13. Ti-Ni Rods with Variable Stiffness for Spine Stabilization: Manufacture and Biomechanical Evaluation

    NASA Astrophysics Data System (ADS)

    Brailovski, Vladimir; Facchinello, Yann; Brummund, Martin; Petit, Yvan; Mac-Thiong, Jean-Marc

    2016-03-01

    A new concept of monolithic spinal rods with variable flexural stiffness is proposed to reduce the risk of adjacent segment degeneration and vertebral fracture, while providing adequate stability to the spine. The variability of mechanical properties is generated by locally annealing Ti-Ni shape memory alloy rods. Ten-minute Joule effect annealing allows the restoration of the superelasticity in the heated portion of the rod. Such processing also generates a mechanical property gradient between the heated and the unheated zones. A numerical model simulating the annealing temperature and the distributions of the mechanical properties was developed to optimize the Joule-heating strategy and to modulate the rod's overall flexural stiffness. Subsequently, the rod model was included in a finite element model of a porcine lumbar spine to study the effect of the rod's stiffness profiles on the spinal biomechanics.

  14. Synthesis, Characterization, and Modeling of Nanotube Materials with Variable Stiffness Tethers

    NASA Technical Reports Server (NTRS)

    Frankland, S. J. V.; Herzog, M. N.; Odegard, G. M.; Gates, T. S.; Fay, C. C.

    2004-01-01

    Synthesis, mechanical testing, and modeling have been performed for carbon nanotube based materials. Tests using nanoindentation indicated a six-fold enhancement in the storage modulus when comparing the base material (no nanotubes) to the composite that contained 5.3 wt% of nanotubes. To understand how crosslinking the nanotubes may further alter the stiffness, a model of the system was constructed using nanotubes crosslinked with a variable stiffness tether (VST). The model predicted that for a composite with 5 wt% nanotubes at random orientations, crosslinked with the VST, the bulk Young's modulus was reduced by 30% compared to the noncrosslinked equivalent.

  15. 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.

  16. 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

  17. Magnetorheological elastomer with stiffness-variable characteristics based on induced current applied to differential mount of vehicles

    NASA Astrophysics Data System (ADS)

    Jeong, Un-Chang; Yoon, Ji-Hyun; Yang, In-Hyung; Jeong, Jae-Eun; Kim, Jin-Su; Chung, Kyung-Ho; Oh, Jae-Eung

    2013-11-01

    A differential mount with elastomers is installed to insulate vibration transmitted from the engine to the body through the propeller shaft. Since existing differential mounts adopt an elastomer of uniform stiffness, it is difficult to meet both the requirements for steering performance and driving comfort at the same time. In order to overcome this limitation, this study suggests a magnetorheological elastomer (MRE)-based stiffness-variable differential mount which allows the mount’s stiffness to vary reversibly or instantly. The stiffness-variable differential mount was designed with a new inner structure where a magnetic field can be induced in the MRE. Further, the geometry of the MRE was optimized by means of the response surface method to achieve a targeted level of stiffness. The variable performance of the stiffness-variable differential mount was evaluated with the dynamic stiffness when a current of 3 A (0.287 T) was applied. As a result, it was found that the average increase in dynamic stiffness was 4.41 kgf mm-1 over an excitation frequency range of 60-100 Hz, a critical point of variation for dynamic stiffness, and 3.60 kgf mm-1 over an excitation frequency range of less than 100 Hz.

  18. Optimal design of variable-stiffness fiber-reinforced composites using cellular automata

    NASA Astrophysics Data System (ADS)

    Setoodeh, Shahriar

    The growing number of applications of composite materials in aerospace and naval structures along with advancements in manufacturing technologies demand continuous innovations in the design of composite structures. In the traditional design of composite laminates, fiber orientation angles are constant for each layer and are usually limited to 0, 90, and +/-45 degrees. To fully benefit from the directional properties of composite laminates, such limitations have to be removed. The concept of variable-stiffness laminates allows the stiffness properties to vary spatially over the laminate. Through tailoring of fiber orientations and laminate thickness spatially in an optimal fashion, mechanical properties of a part can be improved. In this thesis, the optimal design of variable-stiffness fiber-reinforced composite laminates is studied using an emerging numerical engineering optimization scheme based on the cellular automata paradigm. A cellular automaton (CA) based design scheme uses local update rule for both field variables (displacements) and design variables (lay-up configuration and laminate density measure) in an iterative fashion to convergence to an optimal design. In the present work, the displacements are updated based on the principle of local equilibrium and the design variables are updated according to the optimality criteria for minimum compliance design. A closed form displacement update rule for constant thickness isotropic continua is derived, while for the general anisotropic continua with variable thickness a numeric update rule is used. Combined lay-up and topology design of variable-stiffness flat laminates is performed under the action of in-plane loads and bending loads. An optimality criteria based formulation is used to obtain local design rules for minimum compliance design subject to a volume constraint. It is shown that the design rule splits into a two step application. In the first step an optimal lay-up configuration is computed and in

  19. 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.

  20. Monolithic superelastic rods with variable flexural stiffness for spinal fusion: modeling of the processing-properties relationship.

    PubMed

    Facchinello, Yann; Brailovski, Vladimir; Petit, Yvan; Mac-Thiong, Jean-Marc

    2014-11-01

    The concept of a monolithic Ti-Ni spinal rod with variable flexural stiffness is proposed to reduce the risks associated with spinal fusion. The variable stiffness is conferred to the rod using the Joule-heating local annealing technique. The annealing temperature and the mechanical properties' distributions resulted from this thermal treatment are numerically modeled and experimentally measured. To illustrate the possible applications of such a modeling approach, two case studies are presented: (a) optimization of the Joule-heating strategy to reduce annealing time, and (b) modulation of the rod's overall flexural stiffness using partial annealing. A numerical model of a human spine coupled with the model of the variable flexural stiffness spinal rod developed in this work can ultimately be used to maximize the stabilization capability of spinal instrumentation, while simultaneously decreasing the risks associated with spinal fusion.

  1. Mean Platelet Volume and Arterial Stiffness – Clinical Relationship and Common Genetic Variability

    PubMed Central

    Panova-Noeva, Marina; Arnold, Natalie; Hermanns, M. Iris; Prochaska, Jürgen H.; Schulz, Andreas; Spronk, Henri M.; Binder, Harald; Pfeiffer, Norbert; Beutel, Manfred; Blankenberg, Stefan; Zeller, Tanja; Lotz, Johannes; Münzel, Thomas; Lackner, Karl J.; ten Cate, Hugo; Wild, Philipp S.

    2017-01-01

    Vessel wall stiffening is an important clinical parameter, but it is unknown whether platelets, key elements in the pathogenesis of arterial thrombosis, are associated with arterial stiffness. The present studies sought to determine whether mean platelet volume (MPV), a potential marker of platelet activation, is linked to vascular elasticity as assessed by the augmentation index (AIx), in 15,010 individuals from the population-based Gutenberg Health Study. Multivariable analysis showed that MPV in both males (β 0.776; 95thCI [0.250;1.16]; p = 0.0024) and females (β 0.881[0.328;1.43]; p = 0.0018) is strongly associated with AIx. Individuals with MPV and AIx above the sex-specific medians had worse survival. Association analysis between MPV-related genetic variants and arterial stiffness identified four genetic variants in males and one in females related with AIx. Cox regression analysis for mortality identified one of these joint genetic variants close to ring finger protein 145 gene (RNF145, rs10076782) linked with increased mortality (hazard ratio 2.02; 95thCI [1.35;3.02]; p = 0.00061). Thus, these population-based data demonstrate a close relation between platelet volume as a potential marker of platelet activation and arterial stiffness in both sexes. Further research is warranted to further elucidate the mechanisms underlying larger platelets‘ role in arterial stiffening including the role of shared common genetics. PMID:28059166

  2. Variability of recombination frequencies in the Iowa Stiff Stalk Synthetic (Zea mays L.).

    PubMed

    Fatmi, A; Poneleit, C G; Pfeiffer, T W

    1993-08-01

    Variability in recombination frequency has been reported in several plant populations. The objectives of the present research were to establish the range in variability in recombination among genotypes in the important corn population Iowa Stiff Stalk Synthetic and to identify individual genotypes which produced increased or decreased recombination frequencies. Approximately 150 individual S0 plants were testcrossed to measure male recombination frequency on three chromosomes: 4, sul-c2; 5, a2-btl-pr1; and 9, sh1-bz1-wx1. Although the variance component for individuals accounted for only 20-33% of the total variation, highly significant variability among individuals was present at all chromosome regions. Thus the environmental effects did not prevent measurement of differences between S0 individuals. At each chromosome region, individual genotypes with recombination frequencies at least two standard deviations above or below the population mean were isolated. Reports in the literature suggest that the variability reported here for the BSSS population should be representative of that present in other corn breeding populations. Recombination frequencies were positively correlated between adjacent regions of chromosome 9 and also between adjacent regions of chromosome 5. Recombination frequencies were positively correlated between both regions on chromosome 5 with the su1-c2 region of chromosome 4. Negative correlations were observed between chromosome 9 recombination and recombination in each region of chromosomes 4 and 5. Thus rankings of S0 individual recombination frequencies were not consistent for all three chromosomes.

  3. A variable stiffness transverse mode shape memory alloy actuator as a minimally invasive organ positioner

    NASA Astrophysics Data System (ADS)

    Anderson, W.; Eshghinejad, A.; Azadegan, R.; Cooper, C.; Elahinia, M.

    2013-09-01

    Smart materials have gained a great deal of attention in recent years because of their unique actuation properties. Actuators are needed in the medical field where space is limited. Presented within this work is an organ positioner used to position the esophagus away from the left atrium to avoid the development of an esophageal fistula during atrial fibrillation (afib) ablation procedures. Within this work, a subroutine was implemented into the finite element framework to predict the midspan load capacity of a near equiatomic NiTi specimen in both the super elastic and shape memory regimes. The purpose of the simulations and experimental results was to develop a design envelope for the organ positioning device. The transverse loading experiments were conducted at several different temperatures leading to the ability to design a variable stiffness actuator. This is essential because the actuator must not be too stiff to injure the organ it is positioning. Extended further, geometric perturbations were applied in the virtual model and the entire design envelope was developed. Further, nitinol was tested for safety in the radio-frequency environment (to ensure that local heating will not occur in the ablation environment). With the safety of the device confirmed, a primitive prototype was manufactured and successfully tested in a cadaver. The design of the final device is also presented. The contribution of this work is the presentation of a new type of positoning device for medical purposes (NiTiBOP). In the process a comprehensive model for transverse actuation of an SMA actuator was developed and experimentally verified.

  4. Elevation of serum urokinase plasminogen activator receptor and liver stiffness in postoperative biliary atresia

    PubMed Central

    Udomsinprasert, Wanvisa; Honsawek, Sittisak; Jirathanathornnukul, Napaphat; Chongsrisawat, Voranush; Poovorawan, Yong

    2016-01-01

    AIM To investigate serum urokinase-type plasminogen activator receptor (uPAR) and liver stiffness in biliary atresia (BA) and examine the correlation of circulating uPAR, liver stiffness, and clinical outcomes in postoperative BA children. METHODS Eighty-five postKasai BA children and 24 control subjects were registered. Circulating uPAR was measured using enzyme-linked immunosorbent essay. Liver stiffness was analyzed using transient elastography. RESULTS BA children had significantly greater circulating uPAR and liver stiffness scores than control subjects (P < 0.001). Circulating uPAR and liver stiffness were substantially higher in jaundiced BA children than non-jaundiced BA children (P < 0.001). In addition, circulating uPAR was positively associated with serum aspartate aminotransferase (r = 0.507, P < 0.001), alanine aminotransferase (r = 0.364, P < 0.001), total bilirubin (r = 0.559, P < 0.001), alkaline phosphatase (r = 0.325, P < 0.001), and liver stiffness scores (r = 0.508, P < 0.001). CONCLUSION Circulating uPAR and liver stiffness values were greater in BA children than healthy controls. The increased circulating uPAR was associated with liver dysfunction in BA. As a consequence, serum uPAR and liver stiffness may be used as noninvasive biomarkers indicating the progression of liver fibrosis in postKasai BA. PMID:27957246

  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. Bone volume fraction and fabric anisotropy are better determinants of trabecular bone stiffness than other morphological variables.

    PubMed

    Maquer, Ghislain; Musy, Sarah N; Wandel, Jasmin; Gross, Thomas; Zysset, Philippe K

    2015-06-01

    As our population ages, more individuals suffer from osteoporosis. This disease leads to impaired trabecular architecture and increased fracture risk. It is essential to understand how morphological and mechanical properties of the cancellous bone are related. Morphology-elasticity relationships based on bone volume fraction (BV/TV) and fabric anisotropy explain up to 98% of the variation in elastic properties. Yet, other morphological variables such as individual trabeculae segmentation (ITS) and trabecular bone score (TBS) could improve the stiffness predictions. A total of 743 micro-computed tomography (μCT) reconstructions of cubic trabecular bone samples extracted from femur, radius, vertebrae, and iliac crest were analyzed. Their morphology was assessed via 25 variables and their stiffness tensor (CFE) was computed from six independent load cases using micro finite element (μFE) analyses. Variance inflation factors were calculated to evaluate collinearity between morphological variables and decide upon their inclusion in morphology-elasticity relationships. The statistically admissible morphological variables were included in a multiple linear regression model of the dependent variable CFE. The contribution of each independent variable was evaluated (ANOVA). Our results show that BV/TV is the best determinant of CFE(r(2) adj  = 0.889), especially in combination with fabric anisotropy (r(2) adj  = 0.968). Including the other independent predictors hardly affected the amount of variance explained by the model (r(2) adj  = 0.975). Across all anatomical sites, BV/TV explained 87% of the variance of the bone elastic properties. Fabric anisotropy further described 10% of the bone stiffness, but the improvement in variance explanation by adding other independent factors was marginal (<1%). These findings confirm that BV/TV and fabric anisotropy are the best determinants of trabecular bone stiffness and show, against common belief, that other

  7. Design of a variable-stiffness flapping mechanism for maximizing the thrust of a bio-inspired underwater robot.

    PubMed

    Park, Yong-Jai; Huh, Tae Myung; Park, Daegeun; Cho, Kyu-Jin

    2014-09-01

    Compliance can increase the thrust generated by the fin of a bio-inspired underwater vehicle. To improve the performance of a compliant fin, the compliance should change with the operating conditions; a fin should become stiffer as the oscillating frequency increases. This paper presents a novel variable-stiffness flapping (VaSF) mechanism that can change its stiffness to maximize the thrust of a bio-inspired underwater robot. The mechanism is designed on the basis of an endoskeleton structure, composed of compliant and rigid segments alternately connected in series. To determine the attachment point of tendons, the anatomy of a dolphin's fluke is considered. Two tendons run through the mechanism to adjust the stiffness. The fluke becomes stiffer when the tendons are pulled to compress the structure. The thrust generated by a prototype mechanism is measured under different conditions to show that the thrust can be maximized by changing the stiffness. The thrust of the VaSF device can approximately triple at a certain frequency just by changing the stiffness. This VaSF mechanism can be used to improve the efficiency of a bio-inspired underwater robot that uses compliance.

  8. Aortic stiffness and blood pressure variability in young people: a multimodality investigation of central and peripheral vasculature

    PubMed Central

    Boardman, Henry; Lewandowski, Adam J.; Lazdam, Merzaka; Kenworthy, Yvonne; Whitworth, Polly; Zwager, Charlotte L.; Francis, Jane M.; Aye, Christina Y.L.; Williamson, Wilby; Neubauer, Stefan; Leeson, Paul

    2017-01-01

    Introduction: Increased blood pressure (BP) variability is a cardiovascular risk marker for young individuals and may relate to the ability of their aorta to buffer cardiac output. We used a multimodality approach to determine relations between central and peripheral arterial stiffness and BP variability. Methods: We studied 152 adults (mean age of 31 years) who had BP variability measures based on SD of awake ambulatory BPs, 24-h weighted SD and average real variability (ARV). Global and regional aortic distensibility was measured by cardiovascular magnetic resonance, arterial stiffness by cardio-ankle vascular index (CAVI) and pulse wave velocity (PWV) by SphygmoCor (carotid–femoral) and Vicorder (brachial–femoral). Results: In young people, free from overt cardiovascular disease, all indices of SBP and DBP variability correlated with aortic distensibility (global aortic distensibility versus awake SBP SD: r = −0.39, P < 0.001; SBP ARV: r = −0.34, P < 0.001; weighted 24-h SBP SD: r = −0.42, P < 0.001). CAVI, which closely associated with aortic distensibility, also related to DBP variability, as well as awake SBP SD (r = 0.19, P < 0.05) and weighted 24-h SBP SD (r = 0.24, P < 0.01), with a trend for SBP ARV (r = 0.17, P = 0.06). In contrast, associations with PWV were only between carotid–femoral PWV and weighted SD of SBP (r = 0.20, P = 0.03) as well as weighted and ARV of DBP. Conclusion: Greater BP variability in young people relates to increases in central aortic stiffness, strategies to measure and protect aortic function from a young age may be important to reduce cardiovascular risk. PMID:27846043

  9. Design of a variable-stiffness robotic hand using pneumatic soft rubber actuators

    NASA Astrophysics Data System (ADS)

    Nagase, Jun-ya; Wakimoto, Shuichi; Satoh, Toshiyuki; Saga, Norihiko; Suzumori, Koichi

    2011-10-01

    In recent years, Japanese society has been ageing, engendering a labor shortage of young workers. Robots are therefore expected to be useful in performing tasks such as day-to-day support for elderly people. In particular, robots that are intended for use in the field of medical care and welfare are expected to be safe when operating in a human environment because they often come into contact with people. Furthermore, robots must perform various tasks such as regrasping, grasping of soft objects, and tasks using frictional force. Given these demands and circumstances, a tendon-driven robot hand with a stiffness changing finger has been developed. The finger surface stiffness can be altered by adjusting the input pressure depending on the task. Additionally, the coefficient of static friction can be altered by changing the surface stiffness merely by adjusting the input air pressure. This report describes the basic structure, driving mechanism, and basic properties of the proposed robot hand.

  10. Proximal aortic stiffness is increased in systemic lupus erythematosus activity in children and adolescents.

    PubMed

    El Gamal, Yehia Mohamad; Elmasry, Ola Abd Elaziz; El Hadidi, Iman Saleh; Soliman, Ola Kamel

    2013-01-01

    Patients with systemic lupus erythematosus (SLE) are prone to premature atherosclerosis and are at risk for the development of cardiovascular disease. Increased arterial stiffness is emerging as a marker of subclinical atherosclerosis. Purpose. To measure proximal aortic stiffness in children and adolescents with SLE. Methods. We studied 16 patients with SLE in activity (mean age 15 ± 2.42 years; 16 females), 14 patients with SLE not in activity (mean age 15.7 ± 1.89 years; 4 males, 10 females), and 16 age- and sex-comparable healthy children and adolescents (15.5 ± 1.71 years; 4 males, 12 females). Disease activity was determined by the SLE disease activity index (SLEDAI). All subjects underwent echocardiography for assessment of proximal aortic pulse wave velocity (PWV) [Ao distance/Ao wave transit time in the aortic arch]. Venous blood samples were collected for ESR. Results. Patients in activity had significantly higher PWV values than controls (P < 0.05), while no significant difference was found between patients not in activity and controls. Conclusions. SLE patients with disease activity demonstrate increased PWV and arterial stiffness of the proximal aorta, while patients without disease activity do not. This suggests that inflammation secondary to SLE activity, and not subclinical atherosclerosis, is the major underlying cause for increased arterial stiffness in this age group.

  11. Semi-active control of helicopter vibration using controllable stiffness and damping devices

    NASA Astrophysics Data System (ADS)

    Anusonti-Inthra, Phuriwat

    Semi-active concepts for helicopter vibration reduction are developed and evaluated in this dissertation. Semi-active devices, controllable stiffness devices or controllable orifice dampers, are introduced; (i) in the blade root region (rotor-based concept) and (ii) between the rotor and the fuselage as semi-active isolators (in the non-rotating frame). Corresponding semi-active controllers for helicopter vibration reduction are also developed. The effectiveness of the rotor-based semi-active vibration reduction concept (using stiffness and damping variation) is demonstrated for a 4-bladed hingeless rotor helicopter in moderate- to high-speed forward flight. A sensitivity study shows that the stiffness variation of root element can reduce hub vibrations when proper amplitude and phase are used. Furthermore, the optimal semi-active control scheme can determine the combination of stiffness variations that produce significant vibration reduction in all components of vibratory hub loads simultaneously. It is demonstrated that desired cyclic variations in properties of the blade root region can be practically achieved using discrete controllable stiffness devices and controllable dampers, especially in the flap and lag directions. These discrete controllable devices can produce 35--50% reduction in a composite vibration index representing all components of vibratory hub loads. No detrimental increases are observed in the lower harmonics of blade loads and blade response (which contribute to the dynamic stresses) and controllable device internal loads, when the optimal stiffness and damping variations are introduced. The effectiveness of optimal stiffness and damping variations in reducing hub vibration is retained over a range of cruise speeds and for variations in fundamental rotor properties. The effectiveness of the semi-active isolator is demonstrated for a simplified single degree of freedom system representing the semi-active isolation system. The rotor

  12. Investigation of the biomechanical effect of variable stiffness shoe on external knee adduction moment in various dynamic exercises

    PubMed Central

    2013-01-01

    Background The growing ageing population and high prevalence of knee osteoarthritis (OA) in athletes across nations have created a strong demand for improved non-invasive therapeutic alternatives for knee OA. The aim of this study is to investigate the effect of the variable stiffness shoe (VSS), a new non-invasive therapeutic approach, on external knee adduction moment (EKAM) in various dynamic exercises. EKAM is believed to have positive correlation with the progression and development of knee OA. Methods Thirty young participants (16 male and 14 female; age 22.6 ± 1.9 years) from National University of Singapore were enrolled in this study. The tested activities were walking, running, drop-landing, and lateral hopping. All the dynamic exercises were recorded simultaneously by the 8-camera VICON Motion Systems (Oxford Metric, UK) with a sampling rate of 100 Hz. Results The results showed that the EKAM was reduced in all the dynamic exercises with the use of VSS. The VSS produced significant reductions in the peak EKAM during walking (4.97%, p = 0.039), running (11.15%, p = 0.011), drop-landing (11.18%, p = 0.038) and lateral hopping (17.34%, p = 0.023) as compared to the control shoe. Conclusions The reduction of EKAM with the use of VSS in various dynamic exercises demonstrates its potential in delaying the onset and the progression of knee OA in early stage of knee OA patients. PMID:24044429

  13. Visit-to-visit blood pressure variability, average BP level and carotid arterial stiffness in the elderly: a prospective study.

    PubMed

    Nagai, M; Dote, K; Kato, M; Sasaki, S; Oda, N; Kagawa, E; Nakano, Y; Yamane, A; Kubo, Y; Higashihara, T; Miyauchi, S; Harada, W; Masuda, H

    2016-10-20

    In a cross-sectional study, visit-to-visit blood pressure (BP) variability was shown to be associated with artery remodelling. Here, we investigated the impact of visit-to-visit BP variability and average BP on the carotid artery remodelling progression in high-risk elderly according to different classes of antihypertension medication use/non-use. BP measurements and carotid ultrasound were performed in the common carotid artery in 164 subjects (mean age 79.7 years at baseline, 74.7% females) with one or more cardiovascular risk factors. Based on 12 visits (1 × /month for 1 year), we calculated visit-to-visit BP variability expressed as the standard deviation (s.d.), coefficient of variation (CV), maximum BP, minimum BP and delta (maximum-minimum) BP. We measured mean intima-media thickness (IMT) as well as stiffness parameter β were measured at baseline and at the mean 4.2-year follow-up. In a multiple regression analysis, the maximum, minimum, s.d. and average of systolic BP (SBP) were significantly associated with a change in β-values between the baseline and follow-up after adjustment for age, smoking, lower high-density lipoprotein level, baseline β-value and follow-up period. There were no significant associations between the visit-to-visit BP variability measures and the change in mean IMT. Significant associations of maximum, minimum, s.d. and average SBP were found with increased β-values in the subjects without calcium channel blocker (CCB) use and in the subjects using renin-angiotensin system inhibitors (RASIs). Thus, exaggerated visit-to-visit SBP variability and a high average SBP level were significant predictors of progression in carotid arterial stiffness in high-risk elderly without CCBs use and in those using a RASI.Journal of Human Hypertension advance online publication, 20 October 2016; doi:10.1038/jhh.2016.77.

  14. Physical Activity Correlates with Arterial Stiffness in Community-dwelling Individuals with Stroke

    PubMed Central

    Tang, Ada; Eng, Janice J.; Brasher, Penelope M.; Madden, Kenneth M.; Mohammadi, Azam; Krassioukov, Andrei V.; Tsang, Teresa S. M.

    2013-01-01

    Background Physical inactivity contributes to atherosclerotic processes, which manifest as increased arterial stiffness. Arterial stiffness is associated with myocardial demand and coronary perfusion and is a risk factor for stroke and other adverse cardiac outcomes. Poststroke mobility limitations often lead to physical inactivity and sedentary behaviors. This exploratory study aimed to identify functional correlates, reflective of daily physical activity levels, with arterial stiffness in community-dwelling individuals >1 year poststroke. Methods Carotid–femoral pulse wave velocity (cfPWV) was measured in 35 participants (65% men; mean ± SD age 66.9 ± 6.9 years; median time poststroke 3.7 years). Multivariable regression analyses examined the relationships between cfPWV and factors associated with daily physical activity: aerobic capacity (VO2 peak), gait speed, and balance ability (Berg Balance Scale). Age and the use of antihypertensive medications, known to be associated with pulse wave velocity, were also included in the model. Results Mean cfPWV was 11.2 ± 2.4 m/s. VO2 peak and age were correlated with cfPWV (r = −0.45 [P = .006] and r = 0.46 [P = .004], respectively). In the multivariable regression analyses, age and the use of antihypertensive medication accounted for 20.4% of the variance of cfPWV, and the addition of VO2 peak explained an additional 4.5% of the variance (R2 = 0.249). Conclusions We found that arterial stiffness is elevated in community-dwelling, ambulatory individuals with stroke relative to healthy people. Multivariable regression analysis suggests that aerobic capacity (VO2 peak) may contribute to the variance of cfPWV after accounting for the effects of age and medication use. Whether intense risk modification and augmented physical activity will improve arterial stiffness in this population remains to be determined. PMID:23473623

  15. The Impact of Remote Ischemic Preconditioning on Arterial Stiffness and Heart Rate Variability in Patients with Angina Pectoris

    PubMed Central

    Zagidullin, Naufal; Scherbakova, Elena; Safina, Yuliana; Zulkarneev, Rustem; Zagidullin, Shamil

    2016-01-01

    Remote ischemic preconditioning (RIPC) is the set of ischemia episodes that protects against subsequent periods of prolonged ischemia through the cascade of adaptive responses; however, the mechanisms of RIPC are not entirely clear. Here, we aimed to study the impact of RIPC in patients with stable angina pectoris and compare it with healthy individuals with respect to arterial stiffness and heart rate variability. In the randomized, sham-controlled, crossover blind design study, a group of 30 coronary heart disease (CHD) patients (63.9 ± 1.6 years) with stable angina pectoris NYHA II-III and a control group of 20 healthy individuals (58.2 ± 2.49) were both randomly allocated for remote RIPC or sham RIPC. Arterial stiffness, pulse wave velocity (Spygmacor, Australia), and heart rate variability (HRV) were recorded before and after the procedure followed by the crossover examination. In the group of healthy individuals, RIPC showed virtually no impact on the cardiovascular parameters, while, in the CHD group, the systolic and central systolic blood pressure, central pulse pressure, and augmentation decreased, and total power of HRV improved. We conclude that ischemic preconditioning reduces not only systolic blood pressure, but also reduces central systolic blood pressure and improves arterial compliance and heart rate modulation reserve, which may be associated with the antianginal effect of preconditioning. PMID:27348009

  16. 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

  17. 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.

  18. Note: Vibration suppression using tunable vibration absorber based on stiffness variable magneto-rheological gel

    NASA Astrophysics Data System (ADS)

    Shin, Beom-Cheol; Yoon, Jung-Hwan; Kim, Young-Keun; Kim, Kyung-Soo

    2015-10-01

    This paper proposes a novel adaptive tunable vibration absorber (TVA) based on a smart material the magnetorheological gel (MRG) to achieve a wide range of tonal vibration suppression on the primary system to protect any connected sensitive device. The vibration suppression performance of the MRG TVA was analyzed by conducting a modal test of the primary system under different magnetic fields. The experiment verified that the proposed MRG TVA can be controlled to produce 379% of stiffness change or 115% of tuning frequency under just 200 mT magnetic field. The proposed MRG TVA was found to possess a wider tuning frequency range than the TVA based on other smart material such as magnetorheological elastomer.

  19. 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.

  20. Wing Torsional Stiffness Tests of the Active Aeroelastic Wing F/A-18 Airplane

    NASA Technical Reports Server (NTRS)

    Lokos, William A.; Olney, Candida D.; Crawford, Natalie D.; Stauf, Rick; Reichenbach, Eric Y.

    2002-01-01

    The left wing of the Active Aeroelastic Wing (AAW) F/A-18 airplane has been ground-load-tested to quantify its torsional stiffness. The test has been performed at the NASA Dryden Flight Research Center in November 1996, and again in April 2001 after a wing skin modification was performed. The primary objectives of these tests were to characterize the wing behavior before the first flight, and provide a before-and-after measurement of the torsional stiffness. Two streamwise load couples have been applied. The wing skin modification is shown to have more torsional flexibility than the original configuration has. Additionally, structural hysteresis is shown to be reduced by the skin modification. Data comparisons show good repeatability between the tests.

  1. Active Vitamin D and Accelerated Progression of Aortic Stiffness in Hemodialysis Patients: A Longitudinal Observational Study

    PubMed Central

    Fortier, Catherine; Mac-Way, Fabrice; De Serres, Sacha A.; Marquis, Karine; Douville, Pierre; Desmeules, Simon; Larivière, Richard

    2014-01-01

    BACKGROUND We hypothesized that high-dose active vitamin D therapy in the form of alphacalcidol (α-calcidol), used to treat secondary hyperparathyroidism in chronic kidney disease, could lead to vascular calcification and accelerated progression of aortic stiffness. METHODS We conducted an observational study in 85 patients on chronic hemodialysis, among which 70 were taking a weekly dose of α-calcidol of <2 µg and 15 were taking a weekly dose of ≥2 µg (pharmacological dose). Parathyroid hormone, 25-hydroxyvitamin D, fibroblast growth factor 23, and α-klotho were determined. Aortic stiffness was assessed by determination of carotid–femoral pulse wave velocity (cf-PWV) at baseline and after a mean follow-up of 1.2 years. A multivariable regression model was used to evaluate the impact of pharmacological dose of α-calcidol on the progression of aortic stiffness. RESULTS At baseline, clinical, biological, and hemodynamic parameters were similar. At follow-up, cf-PWV increased more in patients with pharmacological dose of α-calcidol (0.583±2.291 m/s vs. 1.948±1.475 m/s; P = 0.04). After adjustment for changes in mean blood pressure and duration of follow-up, pharmacological dose of α-calcidol was associated with a higher rate of progression of cf-PWV (0.969 m/s; 95% confidence interval = 0.111–1.827; P = 0.03), and this association persisted after further adjustments for parameters of mineral metabolism. CONCLUSIONS In this study, pharmacological dose of α-calcidol was associated with accelerated progression of aortic stiffness. This study suggest that the vascular safety of active vitamin D posology may need to be specifically addressed in the treatment of chronic kidney disease–related bone mineral disorder. PMID:24695980

  2. Substrate Stiffness Influences Doxorubicin-Induced p53 Activation via ROCK2 Expression

    PubMed Central

    Ebata, Takahiro; Mitsui, Yasumasa; Sugimoto, Wataru; Maeda, Miho; Machiyama, Hiroaki; Harada, Ichiro; Sawada, Yasuhiro; Fujita, Hideaki; Hirata, Hiroaki

    2017-01-01

    The physical properties of the extracellular matrix (ECM), such as stiffness, are involved in the determination of the characteristics of cancer cells, including chemotherapy sensitivity. Resistance to chemotherapy is often linked to dysfunction of tumor suppressor p53; however, it remains elusive whether the ECM microenvironment interferes with p53 activation in cancer cells. Here, we show that, in MCF-7 breast cancer cells, extracellular stiffness influences p53 activation induced by the antitumor drug doxorubicin. Cell growth inhibition by doxorubicin was increased in response to ECM rigidity in a p53-dependent manner. The expression of Rho-associated coiled coil-containing protein kinase (ROCK) 2, which induces the activation of myosin II, was significantly higher when cells were cultured on stiffer ECM substrates. Knockdown of ROCK2 expression or pharmacological inhibition of ROCK decreased doxorubicin-induced p53 activation. Our results suggest that a soft ECM causes downregulation of ROCK2 expression, which drives resistance to chemotherapy by repressing p53 activation. PMID:28191463

  3. Active pneumatic vibration isolation system using negative stiffness structures for a vehicle seat

    NASA Astrophysics Data System (ADS)

    Danh, Le Thanh; Ahn, Kyoung Kwan

    2014-02-01

    In this paper, an active pneumatic vibration isolation system using negative stiffness structures (NSS) for a vehicle seat in low excitation frequencies is proposed, which is named as an active system with NSS. Here, the negative stiffness structures (NSS) are used to minimize the vibratory attraction of a vehicle seat. Owing to the time-varying and nonlinear behavior of the proposed system, it is not easy to build an accurate dynamic for model-based controller design. Thus, an adaptive intelligent backstepping controller (AIBC) is designed to manage the system operation for high-isolation effectiveness. In addition, an auxiliary control effort is also introduced to eliminate the effect of the unpredictable perturbations. Moreover, a radial basis function neural network (RBFNN) model is utilized to estimate the optimal gain of the auxiliary control effort. Final control input and the adaptive law for updating coefficients of the approximate series can be obtained step by step using a suitable Lyapunov function. Afterward, the isolation performance of the proposed system is assessed experimentally. In addition, the effectiveness of the designed controller for the proposed system is also compared with that of the traditional backstepping controller (BC). The experimental results show that the isolation effectiveness of the proposed system is better than that of the active system without NSS. Furthermore, the undesirable chattering phenomenon in control effort is quite reduced by the estimation mechanism. Finally, some concluding remarks are given at the end of the paper.

  4. Activation of SIRT1 Attenuates Klotho Deficiency-Induced Arterial Stiffness and Hypertension by Enhancing AMP-Activated Protein Kinase Activity.

    PubMed

    Gao, Diansa; Zuo, Zhong; Tian, Jing; Ali, Quaisar; Lin, Yi; Lei, Han; Sun, Zhongjie

    2016-11-01

    Arterial stiffness is an independent risk factor for stroke and myocardial infarction. This study was designed to investigate the role of SIRT1, an important deacetylase, and its relationship with Klotho, a kidney-derived aging-suppressor protein, in the pathogenesis of arterial stiffness and hypertension. We found that the serum level of Klotho was decreased by ≈45% in patients with arterial stiffness and hypertension. Interestingly, Klotho haplodeficiency caused arterial stiffening and hypertension, as evidenced by significant increases in pulse wave velocity and blood pressure in Klotho-haplodeficient (KL(+/-)) mice. Notably, the expression and activity of SIRT1 were decreased significantly in aortic endothelial and smooth muscle cells in KL(+/-) mice, suggesting that Klotho deficiency downregulates SIRT1. Treatment with SRT1720 (15 mg/kg/d, IP), a specific SIRT1 activator, abolished Klotho deficiency-induced arterial stiffness and hypertension in KL(+/-) mice. Klotho deficiency was associated with significant decreases in activities of AMP-activated protein kinase α (AMPKα) and endothelial NO synthase (eNOS) in aortas, which were abolished by SRT1720. Furthermore, Klotho deficiency upregulated NADPH oxidase activity and superoxide production, increased collagen expression, and enhanced elastin fragmentation in the media of aortas. These Klotho deficiency-associated changes were blocked by SRT1720. In conclusion, this study provides the first evidence that Klotho deficiency downregulates SIRT1 activity in arterial endothelial and smooth muscle cells. Pharmacological activation of SIRT1 may be an effective therapeutic strategy for arterial stiffness and hypertension.

  5. The relationship between lower-body stiffness and dynamic performance.

    PubMed

    Pruyn, Elizabeth C; Watsford, Mark; Murphy, Aron

    2014-10-01

    Greater levels of lower-body stiffness have been associated with improved outcomes for a number of physical performance variables involving rapid stretch-shorten cycles. The aim of this study was to investigate the relationship between several measures of lower-body stiffness and physical performance variables typically evident during team sports in female athletes. Eighteen female athletes were assessed for quasi-static stiffness (myometry) for several isolated muscles in lying and standing positions. The muscles included the medial gastrocnemius (MedGast), lateral gastrocnemius, soleus, and Achilles tendon. Dynamic stiffness during unilateral hopping was also assessed. Participants were separated into relatively stiff and compliant groups for each variable. A number of significant differences in performance were evident between stiff and compliant subjects. When considering the quasi-static stiffness of the MedGast in lying and standing positions, relatively stiff participants recorded significantly superior results during agility, bounding, sprinting, and jumping activities. Stiffness as assessed by hopping did not discriminate between performance ability in any test. Relationships highlighted by MedGast results were supported by further significant differences in eccentric utilisation ratio and drop jump results between stiff and compliant groups for the lateral gastrocnemius and soleus in lying and standing positions. Higher levels of lower-body stiffness appear to be advantageous for females when performing rapid and (or) repeated stretch-shorten cycle movements, including sprinting, bounding, and jumping. Further, the stiffness of the MedGast is of particular importance during the performance of these activities. It is important for practitioners working with athletes in sports that rely upon these activities for success to consider stiffness assessment and modification.

  6. Effect of variable-stiffness walking shoes on knee adduction moment, pain, and function in subjects with medial compartment knee osteoarthritis after 1 year.

    PubMed

    Erhart-Hledik, Jennifer C; Elspas, Barbara; Giori, Nicholas J; Andriacchi, Thomas P

    2012-04-01

    This study investigated the load-modifying and clinical efficacy of variable-stiffness shoes after 12 months in subjects with medial compartment knee osteoarthritis. Subjects who completed a prior 6-month study were asked to wear their assigned constant-stiffness control or variable-stiffness intervention shoes during the remainder of the study. Changes in peak knee adduction moment, total Western Ontario and McMaster Universities (WOMAC), and WOMAC pain scores were assessed. Seventy-nine subjects were enrolled, and 55 completed the trial. Using an intention-to-treat analysis, the variable-stiffness shoes reduced the within-day peak knee adduction moment (-5.5%, p < 0.001) in the intervention subjects, while the constant-stiffness shoes increased the peak knee adduction moment in the control subjects (+3.1%, p = 0.015) at the 12-month visit. WOMAC pain and total scores for the intervention group were significantly reduced from baseline to 12 months (-32%, p = 0.002 and -35%, p = 0.007, respectively). The control group had a reduction of 27% in WOMAC pain score (p = 0.04) and no significant reduction in total WOMAC score. Reductions in WOMAC pain and total scores were similar between groups (p = 0.8 and p = 0.47, respectively). In the intervention group, reductions in adduction moment were related to improvements in pain and function (R(2)  = 0.11, p = 0.04). Analysis by disease severity revealed greater efficacy in adduction moment reduction in the less severe intervention group. While the long-term effects of the intervention shoes on pain and function did not differ from control, the data suggest wearing the intervention shoe reduces the within-day adduction moment after long-term wear, and thus should reduce loading on the affected medial compartment of the knee.

  7. Influence of recreational activity and muscle strength on ulnar bending stiffness in men

    NASA Technical Reports Server (NTRS)

    Myburgh, K. H.; Charette, S.; Zhou, L.; Steele, C. R.; Arnaud, S.; Marcus, R.

    1993-01-01

    Bone bending stiffness (modulus of elasticity [E] x moment of inertia [I]), a measure of bone strength, is related to its mineral content (BMC) and geometry and may be influenced by exercise. We evaluated the relationship of habitual recreational exercise and muscle strength to ulnar EI, width, and BMC in 51 healthy men, 28-61 yr of age. BMC and width were measured by single photon absorptiometry and EI by mechanical resistance tissue analysis. Maximum biceps strength was determined dynamically (1-RM) and grip strength isometrically. Subjects were classified as sedentary (S) (N = 13), moderately (M) (N = 18), or highly active (H) (N = 20) and exercised 0.2 +/- 0.2; 2.2 +/- 1.3; and 6.8 +/- 2.3 h.wk-1 (P < 0.001). H had greater biceps (P < 0.0005) and grip strength (P < 0.05), ulnar BMC (P < 0.05), and ulnar EI (P = 0.01) than M or S, who were similar. Amount of activity correlated with grip and biceps strength (r = 0.47 and 0.49; P < 0.001), but not with bone measurements, whereas muscle strength correlated with both EI and BMC (r = 0.40-0.52, P < 0.005). EI also correlated significantly with both BMC and ulnar width (P < 0.0001). Ulnar width and biceps strength were the only independent predictors of EI (r2 = 0.67, P < 0.0001). We conclude that levels of physical activity sufficient to increase arm strength influence ulnar bending stiffness.

  8. Active control of sound transmission through stiff lightweight composite fuselage constructions

    NASA Technical Reports Server (NTRS)

    Thomas, D. R.; Nelson, P. A.; Pinnington, R. J.; Elliott, S. J.

    1992-01-01

    Work was performed on the active control of sound transmission in composite structures. First, a model was outlined of a vibrating plate with arbitrary boundary conditions. Second, the far field was minimized to radiate acoustic power using secondary force inputs. Third, a model of a simple case of freely mounted stiff lightweight panels was used. Fourth, experimental results for aluminum honeycomb composite panels is presented. Fifth, experimental results are presented for the combination of a clamped steel plate and an aluminum honeycomb panel with secondary forces acting between the partitions. Finally, experimental results for the combination of a clamped steel plate with four secondary aluminum honeycomb panels is presented. All materials are shown in viewgraph format.

  9. Multi-DOF rotor model based measurement of stiffness and damping for active magnetic bearing using multi-frequency excitation

    NASA Astrophysics Data System (ADS)

    Jiang, Kejian; Zhu, Changsheng; Chen, Liangliang; Qiao, Xiaoli

    2015-08-01

    To represent the support characteristic of active magnetic bearings (AMB), the commonly used parameters are the equivalent stiffness and the equivalent damping, which inherit the parameters of the stiffness and the damping from traditional mechanical bearings. First, by analyzing the diversity and the similarity between traditional mechanical bearing and AMB, the prior condition for applying the parametric representation of equivalent stiffness and equivalent damping to AMB is illuminated. Then, a method for measuring the equivalent stiffness and the equivalent damping of AMB-rotor system is proposed with multi-frequency excitation. One of its outstanding features is that the proposed method is based on the multi-degree of freedom (DOF) rotor model, not the single- DOF model, because the single DOF model cannot be suitably applied to the multi-DOF AMB-rotor systems. Otherwise, in order to decrease the identification error, the multi-frequency excitation can achieve the lowest peak value by means of appropriate selection for the relative phasing of each component, so that the possibility of the rotor displacement exceeding clearances of AMB and the magnetic force reaching saturation is minimized. Finally, the experiments, which are carried out on an AMB-rotor test rig with a vertical shaft, indicate that the proposed method can efficiently reduce the peak value for the superimposed multi-frequency excitation and correctly identify the equivalent stiffness and equivalent damping of AMB-rotor system.

  10. Sex differences in associations between insulin resistance, heart rate variability, and arterial stiffness in healthy women and men: a physiology study.

    PubMed

    Rannelli, Luke Anthony; MacRae, Jennifer M; Mann, Michelle C; Ramesh, Sharanya; Hemmelgarn, Brenda R; Rabi, Doreen; Sola, Darlene Y; Ahmed, Sofia B

    2017-04-01

    Diabetes confers greater cardiovascular risk to women than to men. Whether insulin-resistance-mediated risk extends to the healthy population is unknown. Measures of insulin resistance (fasting insulin, homeostatic model assessment, hemoglobin A1c, quantitative insulin sensitivity check index, glucose) were determined in 48 (56% female) healthy subjects. Heart rate variability (HRV) was calculated by spectral power analysis and arterial stiffness was determined using noninvasive applanation tonometry. Both were measured at baseline and in response to angiotensin II infusion. In women, there was a non-statistically significant trend towards increasing insulin resistance being associated with an overall unfavourable HRV response and increased arterial stiffness to the stressor, while men demonstrated the opposite response. Significant differences in the associations between insulin resistance and cardiovascular physiological profile exist between healthy women and men. Further studies investigating the sex differences in the pathophysiology of insulin resistance in cardiovascular disease are warranted.

  11. Carotid Stiffness and Physical Activity in Elderly—A Short Report of the SAPALDIA 3 Cohort Study

    PubMed Central

    Caviezel, Seraina; Dratva, Julia; Schaffner, Emmanuel; Schindler, Christian; Endes, Simon; Autenrieth, Christine S.; Wanner, Miriam; Martin, Brian; de Groot, Eric; Gaspoz, Jean-Michel; Künzli, Nino; Probst-Hensch, Nicole; Schmidt-Trucksäss, Arno

    2015-01-01

    Introduction Regular physical activity has been shown to reduce cardiovascular disease risk in the general population. While smaller studies in specified groups (highly trained versus untrained individuals) indicate a certain dose-dependent effect of physical activity on the reduction of carotid stiffness (an indicator of subclinical vascular disease), it is unclear whether this association is present in a representative sample. Thus, we investigated this question cross-sectionally in participants from the population-based Swiss Cohort Study on Air Pollution And Lung and Heart Diseases In Adults (SAPALDIA). Methods Self-reported total, moderate and vigorous physical activity and distensibility as a measure of local arterial stiffness among 1636 participants aged 50 to 81 years without clinically manifest diseases were evaluated. Mixed regression models were used to examine associations of physical activity intensity with distensibility. Results Vigorous physical activity, but not total nor moderate physical activity, was significantly associated with increased distensibility (= reduced carotid stiffness) in univariate analyses (percent change in the geometric mean and 95% confidence interval per 1 standard deviation increment in vigorous physical activity = 2.54 (0.69; 4.43), p<0.01; in total physical activity = 1.62 (-0.22; 3.50), p = 0.08; in moderate physical activity = 0.70 (-1.12; 2.56), p = 0.45). These associations disappeared when we additionally adjusted for age. Conclusion After adjustment for the most important confounders and risk factors, we found no evidence for an association of physical activity with carotid stiffness in the general middle aged to elderly population. PMID:26035590

  12. Evolution of Stiffness and Permeability in Fractures Subject to - and Mechanically-Activated Dissolution

    NASA Astrophysics Data System (ADS)

    Faoro, I.; Elsworth, D.; Candela, T.

    2013-12-01

    Strong feedbacks link thermal gradients (T), hydrologic flow (H), chemical alteration (C) and mechanical deformation (M) in fractured rock. These processes are strongly interconnected since one process effects the initiation and progress of another. Dissolution and precipitation of minerals are affected by temperature and stress, and can result in significant changes in permeability and solute transport characteristics. Understanding these couplings is important for oil, gas, and geothermal reservoir engineering and for waste disposal in underground repositories and reservoirs. In order to experimentally investigate the interactions between THCM processes in a natural stressed fracture, we report on heated ( up to 150C) flow-through experiments on fractured core samples of Westerly granite. These experiments are performed to examine the influence of thermally and mechanically activated dissolution on the mechanical (stress/strain) and transport (permeability) characteristics of fractures. The evolutions of both the permeability and stiffness of the sample are recorded as the experimental thermal conditions change and chemical alteration progresses. Furthermore efflux of dissolved mineral mass is measured periodically to provide a record of the net mass removal, to correlate this with observed changes in fracture aperture, defined by the flow test. During the experiments the fracture shows high hydraulic sensitivity to the changing conditions of stress and temperature. Significant variation of the effluent fluid chemistry is observed. We argue that the formation of clay (Kaolinite) is the main mechanism responsible for the permanent change in permeability recorded at higher confining stresses (40 MPa).

  13. 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.

  14. The Variable Angle Hip Fracture Nail Relative to the Gamma 3: A Finite Element Analysis Illustrating the Same Stiffness and Fatigue Characteristics

    PubMed Central

    Matityahu, Amir; Schmidt, Andrew H.; Grantz, Alan; Clawson, Ben; Marmor, Meir; McClellan, R. Trigg

    2013-01-01

    Ten percent of the 250,000 proximal femur fractures that occur in the United States each year are malreduced into a varus position after treatment. Currently, there is no cephalomedullary nail available that allows the physician to dynamically change the lag-screw-to-nail angle. The Variable Angle Nail (VAN) was designed to allow movement of the lag screw relative to the shaft of the nail. This study compared the characteristics of the VAN to the Gamma 3 nail via finite element analysis (FEA) in stiffness and fatigue. The results of the FEA model with the same loading parameters showed the Gamma 3 and the VAN with lag-screw-to-nail angle of 120° to have essentially the same stiffness values ranging from 350 to 382 N/mm. The VAN with lag-screw-to-nail angles of 120°, 130°, and 140° should be able to withstand more than 1,000,000 cycles from 1,400 N to 1,500 N loading of the tip of the lag screw. The Gamma 3 should be able to last more than 1,000,000 cycles at 1,400 N. In summary, the VAN is superior or equivalent in stiffness and fatigue when compared to the Gamma 3 using FEA. PMID:23585970

  15. 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.

  16. Photochemical activation increases the porcine corneal stiffness and resistance to collagenase digestion.

    PubMed

    Wang, Ti; Peng, Yinbo; Shen, Nianci; Yu, Yan; Yao, Min; Zhu, Jingyin

    2014-06-01

    In this study, we explore the effect of photochemical activation induced corneal cross-linking, utilizing Rose Bengal (RB) and 532 nm green light irradiation (RB-PCL), on porcine corneal biomechanical rigidity and the biochemical resistance against collagenase digestion. A protocol with a wavelength of 532 nm and illumination intensity of 0.4W/cm(2) for 250 s to deliver a dose of 100 J/cm(2) was chosen. Using confocal microscopy, we demonstrated that the diffusion depth of RB into porcine cornea was approximately 150 μm and mostly localized in anterior stroma 25 min followed by RB application. After photochemical cross-linking, an increase in tensile strength (by average 200%) and Young's modulus (by average 200%) in porcine corneas was observed. The corneal buttons treated by RB-PCL showed doubling of collagenase digestion time from 10.8 ± 3.1 days in the blank group to 19.7 ± 6.2 days in the RB-PCL group, indicating increased resistance to enzymatic digestion. In conclusion, Collagen cross-linking by RB-PCL increased both the biomechanical stiffness and the biochemical resistance against collagenase digestion in porcine corneas, therefore to allow stabilizing and solidifier the cornea. The advantages and disadvantages of RB-PCL versus UVA/riboflavin cross-linking technique (UV-CXL) are fully explored. Due to the nature of minimal penetration of RB into corneal stroma, the RB-PCL method could potentially be used in patients with corneal thickness less than 400 μm where UV-CXL is limited.

  17. Modulation of tumor cell stiffness and migration by type IV collagen through direct activation of integrin signaling pathway.

    PubMed

    Chen, Sheng-Yi; Lin, Jo-Shi; Yang, Bei-Chang

    2014-08-01

    Excessive collagen deposition plays a critical role in tumor progression and metastasis. To understand how type IV collagen affects mechanical stiffness and migration, low-collagen-IV-expressing transfectants of B16F10, U118MG, and Huh7 (denoted shCol cells) were established by the lentiviral-mediated delivery of small interfering RNA against type IV-α1 collagen (Col4A1). Although having similar growth rates, shCol cells showed a flatter morphology compared to that of the corresponding controls. Notably, knocking down the Col4A1 gene conferred the cells with higher levels of elasticity and lower motility. Exposure to blocking antibodies against human β1 integrin or α2β1 integrin or the pharmacological inhibition of Src and ERK activity by PP1 and U0126, respectively, effectively reduced cell motility and raised cell stiffness. Reduced Src and ERK activities in shCol cells indicate the involvement of a collagen IV/integrin signaling pathway. The forced expression of β1 integrin significantly stimulated Src and ERK phosphorylation, reduced cell stiffness, and accelerated cell motility. In an experimental metastasis assay using C57BL/6 mice, B16F10 shCol cells formed significantly fewer and smaller lung nodules, confirming the contribution of collagen to metastasis. In summary, the integrin signaling pathway activated in a tumor environment with collagen deposition is responsible for low cell elasticity and high metastatic ability.

  18. Breaking the Meyer-Overton rule: predicted effects of varying stiffness and interfacial activity on the intrinsic potency of anesthetics.

    PubMed Central

    Cantor, R S

    2001-01-01

    Exceptions to the Meyer-Overton rule are commonly cited as evidence against indirect, membrane-mediated mechanisms of general anesthesia. However, another interpretation is possible within the context of an indirect mechanism in which solubilization of an anesthetic in the membrane causes a redistribution of lateral pressures in the membrane, which in turn shifts the conformational equilibrium of membrane proteins such as ligand-gated ion channels. It is suggested that compounds of different stiffness and interfacial activity have different intrinsic potencies, i.e., they cause widely different redistributions of the pressure profile (and thus different effects on protein conformational equilibria) per unit concentration of the compound in the membrane. Calculations incorporating the greater stiffness of perfluoromethylenic chains and the large interfacial attraction of hydroxyl groups predict the higher intrinsic potency of short alkanols than alkanes, the cutoffs in potency of alkanes and alkanols and the much shorter cutoffs for their perfluorinated analogues. Both effects, increased stiffness and interfacial activity, are present in unsaturated hydrocarbon solutes, and the intrinsic potencies are predicted to depend on the magnitude of both effects and on the number and locations of multiple bonds within the molecule. Most importantly, the intrinsic potencies of polymeric alkanols with regularly spaced hydroxyl groups are predicted to rise with increasing chain length, without cutoff; such molecules should serve to distinguish unambiguously between indirect mechanisms and direct binding mechanisms of anesthesia. PMID:11325730

  19. Active load path adaption in a simple kinematic load-bearing structure due to stiffness change in the structure's supports

    NASA Astrophysics Data System (ADS)

    Gehb, C. M.; Platz, R.; Melz, T.

    2016-09-01

    Load-bearing structures with kinematic functions enable and disable degrees of freedom and are part of many mechanical engineering applications. The relative movement between a wheel and the body of a car or a landing gear and an aircraft fuselage are examples for load-bearing systems with defined kinematics. In most cases, the load is transmitted through a predetermined load path to the structural support interfaces. However, unexpected load peaks or varying health condition of the system's supports, which means for example varying damping and stiffness characteristics, may require an active adjustment of the load path. However, load paths transmitted through damaged or weakened supports can be the reason for reduced comfort or even failure. In this paper a simplified 2D two mass oscillator with two supports is used to numerically investigate the potential of controlled adaptive auxiliary kinematic guidance elements in a load-bearing structure to adapt the load path depending on the stiffness change, representing damage of the supports. The aim is to provide additional forces in the auxiliary kinematic guidance elements for two reasons. On the one hand, one of the two supports that may become weaker through stiffness change will be relieved from higher loading. On the other hand, tilting due to different compliance in the supports will be minimized. Therefore, shifting load between the supports during operation could be an effective option.

  20. Effects of using an unstable inclined board on active and passive ankle range of motion in patients with ankle stiffness.

    PubMed

    Yoo, Won-Gyu

    2015-07-01

    [Purpose] The present study assessed the effects of using an unstable inclined board on the active and passive ankle range of motion in patients with ankle stiffness. [Subjects] The study included 10 young female patients with ankle stiffness. [Methods] The patients were divided into the following two groups: a group that performed ankle dorsiflexion stretching exercises using a wooden inclined board and a group that performed stretching exercises using an air-cushioned inclined board (unstable inclined board). Active and passive ankle dorsiflexion angles were measured bilaterally using a goniometer. [Results] Both inclined boards significantly increased active and passive ankle dorsiflexion. After performing ankle stretching exercises, active dorsiflexion significantly increased the unstable inclined board compared to that using the wooden inclined board. However, the passive dorsiflexion angles did not differ significantly between the two groups after ankle stretching exercises. [Conclusion] The use of an unstable inclined board might stimulate activation of the ankle dorsiflexors in addition to stretching muscle or tissue. Active ankle dorsiflexion was more effectively improved with stretching exercises using an unstable inclined board than with exercises using a wooden inclined board.

  1. Job rotation: Effects on muscular activity variability.

    PubMed

    Rodriguez, Andres C; Barrero, Lope H

    2017-04-01

    Job rotation strategies have been used for years as an administrative intervention to reduce the risk of musculoskeletal disorders. The benefits of job rotation have been hypothesized to occur via changes in muscular activity variability (MAV). However, the effect of job rotation on MAV has not been fully analyzed in a literature review. A wide search was conducted to identify studies testing the effect of different job rotation strategies on MAV. Twenty-six studies of acceptable quality were included. Several studies on different types of tasks supported the view that job rotation can increase muscular activity variability, particularly with strategies such as alternating tasks and pace changes. However, it remains uncertain whether such variability changes immediately translate into benefits for the worker because little evidence was found that showed simultaneous changes in different muscular groups. Additionally, variability was occasionally achieved at the expense of average activity in the assessed muscles.

  2. Programmed electromyographic activity and negative incremental muscle stiffness in monkeys jumping downward.

    PubMed Central

    Dyhre-Poulsen, P; Laursen, A M

    1984-01-01

    We trained monkeys to jump down from different heights, and recorded electromyograms (e.m.g.s) in arm muscles, and ground reaction forces. The landing movements were also recorded by high-speed cinematography. The e.m.g. of the triceps began about 80 ms before landing. The initial burst lasted until about 20 ms after ground contact and was succeeded by bursts of gradually declining amplitude. These discharges were not of reflex origin, because when the monkey was deceived by a collapsible platform, they were time-locked to the expected, not to the true landing. The amplitude of the e.m.g. in the triceps increased with the height of the jump, indicating adaptive control. The timing of the e.m.g. pattern was assumed to be programmed before take off, because it was unaffected by extinction of the light during the fall. The vertical ground reaction force produced by the arms had an inflexion on its rising phase which arose from the very rapid stretch of the muscles which control the wrist. Then came a sharp peak produced mainly by stretch of the triceps. The inflexion and the sharp peak were probably produced by short-range stiffness of the muscles of the upper arm. The torque acting on the elbow joint, and the elbow joint stiffness were calculated from the ground reaction forces and the movement of the arm. The torque was high at impact and gradually declined during the landing. The force produced by the triceps increased sharply, then decreased while it continued to lengthen. Thus, the elbow joint showed high initial stiffness, which then decreased, and finally became negative. This dynamic relation between length and tension was very different from the static length-tension characteristic of skeletal muscles. The observed behaviour of the muscles presumably takes advantage of the resistance of the musculo-skeletal system to transient forces. The observed negative stiffness occurs only during submaximal contractions. We propose that the segmented pattern in the e

  3. Programmed electromyographic activity and negative incremental muscle stiffness in monkeys jumping downward.

    PubMed

    Dyhre-Poulsen, P; Laursen, A M

    1984-05-01

    We trained monkeys to jump down from different heights, and recorded electromyograms (e.m.g.s) in arm muscles, and ground reaction forces. The landing movements were also recorded by high-speed cinematography. The e.m.g. of the triceps began about 80 ms before landing. The initial burst lasted until about 20 ms after ground contact and was succeeded by bursts of gradually declining amplitude. These discharges were not of reflex origin, because when the monkey was deceived by a collapsible platform, they were time-locked to the expected, not to the true landing. The amplitude of the e.m.g. in the triceps increased with the height of the jump, indicating adaptive control. The timing of the e.m.g. pattern was assumed to be programmed before take off, because it was unaffected by extinction of the light during the fall. The vertical ground reaction force produced by the arms had an inflexion on its rising phase which arose from the very rapid stretch of the muscles which control the wrist. Then came a sharp peak produced mainly by stretch of the triceps. The inflexion and the sharp peak were probably produced by short-range stiffness of the muscles of the upper arm. The torque acting on the elbow joint, and the elbow joint stiffness were calculated from the ground reaction forces and the movement of the arm. The torque was high at impact and gradually declined during the landing. The force produced by the triceps increased sharply, then decreased while it continued to lengthen. Thus, the elbow joint showed high initial stiffness, which then decreased, and finally became negative. This dynamic relation between length and tension was very different from the static length-tension characteristic of skeletal muscles. The observed behaviour of the muscles presumably takes advantage of the resistance of the musculo-skeletal system to transient forces. The observed negative stiffness occurs only during submaximal contractions. We propose that the segmented pattern in the e

  4. An analysis of the mechanisms for reducing the knee adduction moment during walking using a variable stiffness shoe in subjects with knee osteoarthritis.

    PubMed

    Jenkyn, Thomas R; Erhart, Jennifer C; Andriacchi, Thomas P

    2011-04-29

    Variable stiffness shoes that have a stiffer lateral than medial sole may reduce the external knee adduction moment (EKAM) and pain during walking in patients with medial compartment knee osteoarthritis (OA). However, the mechanism by which EKAM may be reduced in the OA knee with this intervention remains unclear. Three hypotheses were tested in this study: (1) The reduction in EKAM during walking with the variable stiffness shoe is associated with a reduction in GRF magnitude and/or (2) frontal plane lever arm. (3) A reduction in frontal plane lever arm occurs either by moving the center of pressure laterally under the shoe and/or by dynamically reducing the medial component of GRF. Thirty-two subjects (20 male, 12 female; age: 58.7 ± 9.3 years; height: 1.62 ± 0.08 m; mass: 81.3 ± 14.6 kg) with medial compartment knee osteoarthritis were studied walking in a gait laboratory. The frontal plane lever arm was significantly reduced (1.62%, 0.07%ht, p=0.02) on the affected side while the magnitude of the GRF was not significantly changed. The reduction in the lever arm was weakly correlated with a medial shift in the COP. However, the combined medial shift in the COP and reduction in the medial GRF explained 50% of the change of the frontal plane lever arm. These results suggest that the medial shift in the COP at the foot produced by the intervention shoe stimulates an adaptive dynamic response during gait that reduces the frontal plane lever arm.

  5. 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.

  6. Development of an Experimental Model to Study the Relationship Between Day-to-Day Variability in Blood Pressure and Aortic Stiffness.

    PubMed

    Bouissou-Schurtz, Camille; Lindesay, Georges; Regnault, Véronique; Renet, Sophie; Safar, Michel E; Molinie, Vincent; Dabire, Hubert; Bezie, Yvonnick

    2015-01-01

    We aimed to develop an animal model of long-term blood pressure variability (BPV) and to investigate its consequences on aortic damage. We hypothesized that day-to-day BPV produced by discontinuous treatment of spontaneously hypertensive rats (SHR) by valsartan may increase arterial stiffness. For that purpose, rats were discontinuously treated, 2 days a week, or continuously treated by valsartan (30 mg/kg/d in chow) or placebo. Telemetered BP was recorded during 2 min every 15 min, 3 days a week during 8 weeks to cover the full BP variations in response to the treatment schedule. Pulse wave velocity (PWV) and aortic structure evaluated by immunohistochemistry were investigated in a second set of rats treated under the same conditions. Continuous treatment with valsartan reduced systolic BP (SBP) and reversed the aortic structural alterations observed in placebo treated SHR (decrease of medial cross-sectional area). Discontinuous treatment with valsartan decreased SBP to a similar extent but increased the day-to-day BPV, short term BPV, diastolic blood pressure (DBP), and PWV as compared with continuous treatment. Despite no modifications in the elastin/collagen ratio and aortic thickness, an increase in PWV was observed following discontinuous treatment and was associated with a specific accumulation of fibronectin and its αv-integrin receptor compared with both groups of rats. Taken together the present results indicate that a discontinuous treatment with valsartan is able to induce a significant increase in day-to-day BPV coupled to an aortic phenotype close to that observed in hypertension. This experimental model should pave the way for future experimental and clinical studies aimed at assessing how long-term BPV increases aortic stiffness.

  7. Development of an Experimental Model to Study the Relationship Between Day-to-Day Variability in Blood Pressure and Aortic Stiffness

    PubMed Central

    Bouissou-Schurtz, Camille; Lindesay, Georges; Regnault, Véronique; Renet, Sophie; Safar, Michel E.; Molinie, Vincent; Dabire, Hubert; Bezie, Yvonnick

    2015-01-01

    We aimed to develop an animal model of long-term blood pressure variability (BPV) and to investigate its consequences on aortic damage. We hypothesized that day-to-day BPV produced by discontinuous treatment of spontaneously hypertensive rats (SHR) by valsartan may increase arterial stiffness. For that purpose, rats were discontinuously treated, 2 days a week, or continuously treated by valsartan (30 mg/kg/d in chow) or placebo. Telemetered BP was recorded during 2 min every 15 min, 3 days a week during 8 weeks to cover the full BP variations in response to the treatment schedule. Pulse wave velocity (PWV) and aortic structure evaluated by immunohistochemistry were investigated in a second set of rats treated under the same conditions. Continuous treatment with valsartan reduced systolic BP (SBP) and reversed the aortic structural alterations observed in placebo treated SHR (decrease of medial cross-sectional area). Discontinuous treatment with valsartan decreased SBP to a similar extent but increased the day-to-day BPV, short term BPV, diastolic blood pressure (DBP), and PWV as compared with continuous treatment. Despite no modifications in the elastin/collagen ratio and aortic thickness, an increase in PWV was observed following discontinuous treatment and was associated with a specific accumulation of fibronectin and its αv-integrin receptor compared with both groups of rats. Taken together the present results indicate that a discontinuous treatment with valsartan is able to induce a significant increase in day-to-day BPV coupled to an aortic phenotype close to that observed in hypertension. This experimental model should pave the way for future experimental and clinical studies aimed at assessing how long-term BPV increases aortic stiffness. PMID:26696902

  8. Assessing Stride Variables and Vertical Stiffness with GPS-Embedded Accelerometers: Preliminary Insights for the Monitoring of Neuromuscular Fatigue on the Field.

    PubMed

    Buchheit, Martin; Gray, Andrew; Morin, Jean-Benoit

    2015-12-01

    The aim of the present study was to examine the ability of a GPS-imbedded accelerometer to assess stride variables and vertical stiffness (K), which are directly related to neuromuscular fatigue during field-based high-intensity runs. The ability to detect stride imbalances was also examined. A team sport player performed a series of 30-s runs on an instrumented treadmill (6 runs at 10, 17 and 24 km·h(-1)) with or without his right ankle taped (aimed at creating a stride imbalance), while wearing on his back a commercially-available GPS unit with an embedded 100-Hz tri-axial accelerometer. Contact (CT) and flying (FT) time, and K were computed from both treadmill and accelerometers (Athletic Data Innovations) data. The agreement between treadmill (criterion measure) and accelerometer-derived data was examined. We also compared the ability of the different systems to detect the stride imbalance. Biases were small (CT and K) and moderate (FT). The typical error of the estimate was trivial (CT), small (K) and moderate (FT), with nearly perfect (CT and K) and large (FT) correlations for treadmill vs. accelerometer. The tape induced very large increase in the right - left foot ∆ in CT, FT and K measured by the treadmill. The tape effect on CT and K ∆ measured with the accelerometers were also very large, but of lower magnitude than with the treadmill. The tape effect on accelerometer-derived ∆ FT was unclear. Present data highlight the potential of a GPS-embedded accelerometer to assess CT and K during ground running. Key pointsGPS-embedded tri-axial accelerometers may be used to assess contact time and vertical stiffness during ground running.These preliminary results open new perspective for the field monitoring of neuromuscular fatigue and performance in run-based sports.

  9. Assessing Stride Variables and Vertical Stiffness with GPS-Embedded Accelerometers: Preliminary Insights for the Monitoring of Neuromuscular Fatigue on the Field

    PubMed Central

    Buchheit, Martin; Gray, Andrew; Morin, Jean-Benoit

    2015-01-01

    The aim of the present study was to examine the ability of a GPS-imbedded accelerometer to assess stride variables and vertical stiffness (K), which are directly related to neuromuscular fatigue during field-based high-intensity runs. The ability to detect stride imbalances was also examined. A team sport player performed a series of 30-s runs on an instrumented treadmill (6 runs at 10, 17 and 24 km·h-1) with or without his right ankle taped (aimed at creating a stride imbalance), while wearing on his back a commercially-available GPS unit with an embedded 100-Hz tri-axial accelerometer. Contact (CT) and flying (FT) time, and K were computed from both treadmill and accelerometers (Athletic Data Innovations) data. The agreement between treadmill (criterion measure) and accelerometer-derived data was examined. We also compared the ability of the different systems to detect the stride imbalance. Biases were small (CT and K) and moderate (FT). The typical error of the estimate was trivial (CT), small (K) and moderate (FT), with nearly perfect (CT and K) and large (FT) correlations for treadmill vs. accelerometer. The tape induced very large increase in the right - left foot ∆ in CT, FT and K measured by the treadmill. The tape effect on CT and K ∆ measured with the accelerometers were also very large, but of lower magnitude than with the treadmill. The tape effect on accelerometer-derived ∆ FT was unclear. Present data highlight the potential of a GPS-embedded accelerometer to assess CT and K during ground running. Key points GPS-embedded tri-axial accelerometers may be used to assess contact time and vertical stiffness during ground running. These preliminary results open new perspective for the field monitoring of neuromuscular fatigue and performance in run-based sports PMID:26664264

  10. The test bench for testing torsional stiffness of active anti-roll bar made of extended profiles with rectangular cross-section

    NASA Astrophysics Data System (ADS)

    Macikowski, K. R.; Kaszuba, S.

    2016-09-01

    The article describes the test bench constructed to determine the characteristics of torsional stiffness of extended rod elements, which can be used, for example, in cars as anti-roll bars. The bench has been designed so as to allow an examination of the samples with variable length and variable cross-sectional dimensions. It is possible to perform tests for different materials. The article contains a detailed description of the mentioned test bench and presentation of the results obtained from preliminary tests.

  11. Shoulder physical activity, functional disability and task difficulties in patients with stiff shoulders: interpretation from RT3 accelerator.

    PubMed

    Yang, Jing-Lan; Lin, Jiu-Jenq; Huang, Han-Yi; Huang, Tsun-Shun; Chao, Yu Wen

    2014-08-01

    We determined whether the degree of symptom-related functional disability was related to daily physical activity of the shoulder in subjects with stiff shoulders (SSs). Responsiveness and a clinically meaningful level of discrimination between improvement and non-improvement for shoulder physical activity (SPA) were determined. Twenty-six subjects with SSs participated. Shoulder physical activity was assessed by RT3 accelerometers fixed on the humerus during daily 14-h data collection periods twice a week for 2 weeks. A moderate correlation coefficient was found between SPA and functional disability (β = .47). Based on our cohort design and sample, we suggest that SPA (higher than 101.8 counts, hard-moderate or hard tasks) during daily activity are associated with (with at least 83% probability) non-improvement in an individual with SS. Compared to the non-improvement group, the improvement group had less duration of sedentary activity, less frequency and duration of hard tasks, and more frequency and duration of easy tasks (p < 0.01). Appropriate guidance on shoulder physical activities for subjects with SS is important to consider in rehabilitation strategies for these subjects. In our sample, a hard level of shoulder physical activity and sedentary activity should be cautious for these subjects. Further study is needed to validate therapeutic effect of physical activity on the course of patient improvement in subjects with SSs.

  12. Effect of High Impact or Non-impact Loading Activity on Bone Bending Stiffness and Mineral Density

    NASA Technical Reports Server (NTRS)

    Liang, Michael T. C.; Arnnud, Sara B.; Steele, Charles R.; Moreno, Alexjandro

    2003-01-01

    Material properties of conical bone, including mineral density (BMD) and its geometry is closely related to its load-carrying capacity. These two primary components determine the strength of conical bone. High impact loading involving acceleration and deceleration movements used in gymnastics induce higher BMD of the affected bone compared to the non-impact acceleration and deceleration movements used in swimming. Study of these two groups of athletes on bone bending stiffness has not been reported. The purpose of this study was to compare differences in bone bending stiffness and BMD between competitive female synchronized swimmers and female gymnasts. Thirteen world class female synchronized swimmers (SYN) and 8 female gymnasts (GYM), mean age 21 +/- 2.9 yr. were recruited for this study. We used a mechanical response tissue analyzer (Gaitscan, NJ) to calculate EI, where E is Young's modulus of elasticity and I is the cross-sectional moment of inertia. EI was obtained from tissue response to a vibration probe placed directly on the skin of the mid-region of tibia and ulna. BMD of the heel and wrist were measured with a probe densitometer (PIXI, Lunor, WI). The SYN were taller than (p < 0.05) the GYM but weighed the same as the GYM. EI obtained from tibia and ulna of the SYN (291 +/- 159 and 41 +/- 19.4, respectively) were not significantly different from thc GYM (285 +/- 140 and 44 +/- 18.3, respectively). BMD of the heel and wrist in GYM were higher than in SYN (p < 0.001). High impact weight-bearing activities promote similar bone strength but greater BMD response than non-impact activities performed in a buoyant environment.

  13. Stiff person syndrome.

    PubMed

    Hadavi, Shahrzad; Noyce, Alastair J; Leslie, R David; Giovannoni, Gavin

    2011-10-01

    Stiff person syndrome (SPS) is a rare disorder, characterised by fluctuating rigidity and stiffness of the axial and proximal lower limb muscles, with superimposed painful spasms and continuous motor unit activity on electromyography. Although rare in general neurology practice, once observed it is unforgettable. The general neurologist may see only one or two cases during his or her career and as such it remains underdiagnosed. Left untreated, SPS symptoms can progress to cause significant disability. Patients have a poor quality of life and an excess rate of comorbidity and mortality. The severity of symptoms and lack of public awareness of the condition create anxiety and uncertainty for people with the disease. This review aims to raise awareness of SPS and to improve the likelihood of its earlier diagnosis and treatment.

  14. Active region coronal loops - Structural and variability

    NASA Technical Reports Server (NTRS)

    Haisch, Bernhard M.; Strong, Keith T.; Harrison, Richard A.; Gary, G. A.

    1988-01-01

    X-ray images of a pair of active region loops are studied which show significant, short time-scale variability in the line fluxes of O VIII, Ne IX, and Mg XI and in the 3.5-11.5 keV soft X-ray bands. Vector magnetograms and high-resolution UV images were used to model the three-dimensional characteristics of the loops. X-ray light curves were generated spanning four consecutive orbits for both loops individually, and light curves of the loop tops and brightest points were also generated. The largest variations involve flux changes of up to several hundred percent on time scales of 10 minutes. No significant H-alpha flare activity is reported, and loop temperatures remain in the four to six million K range. The decay phases of the light curves indicate radiative cooling, inhibition of conduction, and some type of 'continued heating' due to ongoing, underlying activity at the microflare level.

  15. 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).

  16. Stiff person syndrome.

    PubMed

    Ciccoto, Giuseppe; Blaya, Maike; Kelley, Roger E

    2013-02-01

    Recognizing stiff person syndrome is clinically important. It is uncommon, characterized by body stiffness associated with painful muscle spasms, and varies in location and severity. It is subdivided into stiff trunk versus stiff limb presentation, and as a progressive encephalomyelitis. Stiff person-type syndrome also reflects a paraneoplastic picture. Most patients demonstrate exaggerated lumbar lordosis. Roughly 60% of patients have antiglutamic acid decarboxylase antibodies in the blood and the cerebrospinal fluid. The differential diagnosis includes many severe conditions. There are reports of response to muscle relaxants, immunosuppressants, intravenous gamma globulin, plasma exchange, a number of anticonvulsants, and botulinum toxin.

  17. The relative roles of collagen adhesive receptor DDR2 activation and matrix stiffness on the downregulation of focal adhesion kinase in vascular smooth muscle cells.

    PubMed

    Bhadriraju, Kiran; Chung, Koo-Hyun; Spurlin, Tighe A; Haynes, Ross J; Elliott, John T; Plant, Anne L

    2009-12-01

    Cells within tissues derive mechanical anchorage and specific molecular signals from the insoluble extracellular matrix (ECM) that surrounds them. Understanding the role of different cues that extracellular matrices provide cells is critical for controlling and predicting cell response to scaffolding materials. Using an engineered extracellular matrix of Type I collagen we examined how the stiffness, supramolecular structure, and glycosylation of collagen matrices influence the protein levels of cellular FAK and the activation of myosin II. Our results show that (1) cellular FAK is downregulated on collagen fibrils, but not on a non-fibrillar monolayer of collagen, (2) the downregulation of FAK is independent of the stiffness of the collagen fibrils, and (3) FAK levels are correlated with levels of tyrosine phosphorylation of the collagen adhesion receptor DDR2. Further, siRNA depletion of DDR2 blocks FAK downregulation. Our results suggest that the collagen receptor DDR2 is involved in the regulation of FAK levels in vSMC adhered to Type I collagen matrices, and that regulation of FAK levels in these cells appears to be independent of matrix stiffness.

  18. Stiffness is more than just duration and severity: a qualitative exploration in people with rheumatoid arthritis

    PubMed Central

    Dures, Emma; Kirwan, John; Pollock, Jon; Baker, Gill; Edmunds, Avis; Hewlett, Sarah

    2015-01-01

    Objective. Stiffness is internationally recognized as an important indicator of inflammatory activity in RA but is poorly understood and difficult to measure. The aim of this study was to explore the experience of stiffness from the patient perspective. Methods. Semi-structured interviews conducted with 16 RA patients were analysed independently by researchers and pat.ient partners using inductive thematic analysis. Results. Six themes were identified. Part of having RA identified stiffness as a normal consequence of RA, perceived as associated with disease-related aspects such as fluctuating disease activity, other RA symptoms and disease duration. Local and widespread highlighted stiffness occurring not only in joints, but also over the whole body, being more widespread during the morning or flare. Linked to behaviour and environment illustrated factors that influence stiffness, including movement, medications and weather. Highly variable captured the fluctuating nature of stiffness within and between patients and in relation to temporality, duration and intensity. Impacts on daily life emphasized the effect of stiffness on a range of domains, including physical function, quality of life, psychological well-being, activities of daily living and participation in work and leisure activities. Requires self-management detailed self-management strategies targeting both the symptom and its consequences. Conclusion. Patients’ experiences of stiffness were varied, complex and not exclusive to the morning period. Importantly, stiffness was reported in terms of impact rather than the traditional measurement concepts of severity or duration. Based on these findings, further research is needed to develop a patient-centred measure that adequately reflects inflammatory activity. PMID:25231178

  19. Arterial stiffness and inflammatory response to psychophysiological stress.

    PubMed

    Ellins, Elizabeth; Halcox, Julian; Donald, Ann; Field, Bryony; Brydon, Lena; Deanfield, John; Steptoe, Andrew

    2008-08-01

    The processes through which psychological stress influences cardiovascular disease are poorly understood, but may involve activation of hemodynamic, neuroendocrine and inflammatory responses. We assessed the relationship between carotid arterial stiffness and inflammatory responses to acute psychophysiologic stress. Participants were 155 healthy men and women aged 55.3, SD 2.7 years. Blood samples for the assessment of plasma fibrinogen, tumor necrosis factor (TNF) alpha and interleukin (IL) 6 were drawn at baseline, immediately following standardized behavioral tasks, and 45 min later. Carotid artery stiffness was measured ultrasonically three years later, and blood pressure and heart rate responses were recorded. The tasks induced substantial increases in blood pressure and heart rate, together with increased fibrinogen, TNFalpha and IL-6 concentration. Carotid stiffness was positively associated with body mass, waist/hip ratio, blood pressure, low density lipoprotein cholesterol, and C-reactive protein, and inversely with high density lipoprotein and grade of employment. Baseline levels of inflammatory variables were not related to carotid artery stiffness. But carotid stiffness was greater in participants with larger fibrinogen (p=0.037) and TNFalpha (p=0.036) responses to psychophysiological stress. These effects were independent of age, gender, grade of employment, smoking, body mass, waist/hip ratio, systolic and diastolic pressure, high and low density lipoprotein cholesterol, and C-reactive protein. There were no associations between carotid stiffness and stress responses in IL-6, blood pressure, or heart rate. We conclude that individual differences in inflammatory responses to psychophysiological stress are independently related to structural changes in artery walls that reflect increased cardiovascular disease risk.

  20. Materials with negative stiffness

    NASA Astrophysics Data System (ADS)

    Jaglinski, Tim

    Negative stiffness, or a reversal in the usual assumed direction between causal forces and ensuing deformations, has been proposed as a pathway to materials which exceed theoretical performance bounds. Negative stiffness, as a concept, represents a relaxation of tacitly assumed material behavior, but it violates no natural laws. Negative stiffness, normally unstable without constraint, is permissible for stability under special conditions, for example a rigid boundary constraint so long as the material satisfies strong ellipticity in the parlance of elasticity. Hence, negative stiffness is not observed in materials or structures which are not constrained. If negative stiffness is allowed for inclusions of material, which are surrounded by a stabilizing positive stiffness matrix, composite theory predicts large increases in the mechanical damping and composite stiffness. The work herein explores several material systems which possess negative stiffness, and seeks to characterize the composite mechanical properties of these systems. Two metal matrix composite systems, namely Sn-VO2 and Sn-BaTIO3, were investigated. Here, negative stiffness arises from the ferroelastic phase transformations in the ceramic inclusions; stability is imparted by the tin matrix. Polycrystalline In-Tl and BaTIO 3 were also studied. Here, the entire material volume is phase transforming. Constraint is imparted on a small volume fraction of crystallites by the surrounding material. Various manifestations of negative stiffness were observed. Thermally broad damping peaks which depended upon thermal cycling were observed in the Sn-VO2 composites. Furthermore, mechanical instabilities were seen in composites intentionally designed to be unstable. Negative stiffness was indicated in the In-Tl alloy by magnification of damping peaks over those observed in single crystals, increases in damping peaks with increased cooling rates, occurrence of damping peaks before the appearance of martensite and

  1. Subduction Variability Along the Active Chilean Margin

    NASA Astrophysics Data System (ADS)

    Reichert, C. J.; Barckhausen, U.; Bartsch, H.; Block, M.; Boennemann, C.; Diaz-Naveas, J. L.; Flueh, E. R.; Delisle, G.; Gaedicke, C.; Kopp, H.; Krawczyk, C. M.; Kus, J.; Ladage, S.; Ranero, C.; Schreckenberger, B.; Stoll, J. B.; Urbina, O.; Wiedicke-Hombach, M.

    2002-12-01

    The presence of different subduction modes in the convergence process between the Nazca and South-American plates along the Chilean margin is known from previous investigations. In order to study this variability in detail a comprehensive combined off- and onshore geo-scientific survey (SPOC) was recently conducted between Coquimbo and Valdivia in collaboration between a number of German and Chilean institutions. Major focus was also put on the structure of the sedimentary forearc basins and the distribution of gas hydrates along the slope. SPOC is the successor project to a similar experiment named CINCA that was earlier performed in the far north of Chile between Arica and Taltal. The SPOC results clearly show a change in subduction mode at about 33 deg S where the Juan Fernandez Ridge presently strikes the margin. North of that latitude, structural features such as extensional fracturing of the continental slope, very little or almost no sedimentary trench fill, intensive block faulting of the oceanic crust, a missing accretionary wedge, a very narrow shelf and other facts provide evidence for subduction erosion in that region. South of 33 deg S, we observed significantly steeper frontal slope angles and much less inclination of the oceanic crust toward the trench. In general, the topography of the oceanic crust is relatively smooth with the exception of several seamounts and fracture zones. Moreover, the width of the trench and of the shelf significantly widens toward the south, and pronounced forearc basins developed. Compared to the thick sedimentary trench fill of up to 2 km a very narrow accretionary wedge was encountered. Preliminary mass balancing combined with the assumption that the high present convergence rate occurred also in the past suggests that the bulk of the trench sediments is removed by subduction. Thus, accretionary processes can play only a subordinate or intermittent role. Geological seafloor samples support the assumption that small- to

  2. Physical inactivity and arterial stiffness in COPD

    PubMed Central

    Sievi, Noriane A; Franzen, Daniel; Kohler, Malcolm; Clarenbach, Christian F

    2015-01-01

    Background Arterial stiffness is an important predictor of cardiovascular risk besides classic cardiovascular risk factors. Previous studies showed that arterial stiffness is increased in patients with COPD compared to healthy controls and exercise training may reduce arterial stiffness. Since physical inactivity is frequently observed in patients with COPD and exercise training may improve arterial stiffness, we hypothesized that low daily physical activity may be associated with increased arterial stiffness. Methods In 123 patients with COPD (72% men; mean [standard deviation] age: 62 [7.5] years; median [quartile] forced expiratory volume in 1 second 35 [27/65] %predicted), arterial stiffness was assessed by augmentation index (AI). Daily physical activity level (PAL) was measured by an activity monitor (SenseWear Pro™) >1 week. The association between AI and PAL was investigated by univariate and multivariate regression analysis, taking into account disease-specific characteristics and comorbidities. Results Patients suffered from moderate (35%), severe (32%), and very severe (33%) COPD, and 22% were active smokers. Median (quartile) PAL was 1.4 (1.3/1.5) and mean (standard deviation) AI 26% (9.2%). PAL showed a negative association with AI (B=−9.32, P=0.017) independent of age, sex, blood pressure, and airflow limitation. Conclusion In COPD patients, a higher PAL seems to favorably influence arterial stiffness and therefore may reduce cardiovascular risk. Clinical Trial Registration http://www.ClinicalTrials.gov, NCT01527773 PMID:26392763

  3. Cardiovascular Health and Arterial Stiffness: The Maine Syracuse Longitudinal Study

    PubMed Central

    Crichton, Georgina E; Elias, Merrill F; Robbins, Michael A

    2014-01-01

    Ideal cardiovascular health is a recently defined construct by the American Heart Association (AHA) to promote cardiovascular disease reduction. Arterial stiffness is a major risk factor for cardiovascular disease. The extent to which the presence of multiple prevalent cardiovascular risk factors and health behaviors is associated with arterial stiffness is unknown. The aim of this study was to examine the association between the AHA construct of cardiovascular health and arterial stiffness, as indexed by pulse wave velocity and pulse pressure. The AHA health metrics, comprising of four health behaviors (smoking, body mass index, physical activity, and diet) and three health factors (total cholesterol, blood pressure, and fasting plasma glucose) were evaluated among 505 participants in the Maine-Syracuse Longitudinal Study. Outcome measures were carotid-femoral pulse wave velocity (PWV) and pulse pressure measured at 4 to 5-year follow-up. Better cardiovascular health, comprising both health factors and behaviors, was associated with lower arterial stiffness, as indexed by pulse wave velocity and pulse pressure. Those with at least five health metrics at ideal levels had significantly lower PWV (9.8 m/s) than those with two or less ideal health metrics (11.7 m/s) (P<0.001). This finding remained with the addition of demographic and PWV-related variables (P=0.004). PMID:24384629

  4. Activation of Yes-Associated Protein in Low-Grade Meningiomas Is Regulated by Merlin, Cell Density, and Extracellular Matrix Stiffness.

    PubMed

    Tanahashi, Kuniaki; Natsume, Atsushi; Ohka, Fumiharu; Motomura, Kazuya; Alim, Adiljan; Tanaka, Ichidai; Senga, Takeshi; Harada, Ichiro; Fukuyama, Ryuichi; Sumiyoshi, Naoyuki; Sekido, Yoshitaka; Wakabayashi, Toshihiko

    2015-07-01

    The NF2 gene product Merlin is a protein containing ezrin, radixin, and moesin domains; it is a member of the 4.1 protein superfamily associated with the membrane cytoskeleton and also interacts with cell surface molecules. The mammalian Hippo cascade, a downstream signaling cascade of merlin, inactivates the Yes-associated protein (YAP). Yes-associated protein is activated by loss of the NF2 gene and functions as an oncogene in meningioma cells; however, the factors controlling YAP expression, phosphorylation, and subcellular localization in meningiomas have not been fully elucidated. Here, we demonstrate that merlin expression is heterogeneous in 1 NF2 gene-negative and 3 NF2 gene-positive World Health Organization grade I meningiomas. In the NF2 gene-positive meningiomas, regions with low levels of merlin (tumor rims) had greater numbers of cells with nuclear YAP versus regions with high merlin levels (tumor cores). Merlin expression and YAP phosphorylation were also affected by cell density in the IOMM-Lee and HKBMM human meningioma cell lines; nuclear localization of YAP was regulated by cell density and extracellular matrix (ECM) stiffness in IOMM-Lee cells. These results suggest that cell density and ECM stiffness may contribute to the heterogeneous loss of merlin and increased nuclear YAP expression in human meningiomas.

  5. Investigating the Spectroscopic Variability and Magnetic Activity of Photometrically Variable M Dwarfs in SDSS

    NASA Astrophysics Data System (ADS)

    Ventura, Jean-Paul; Cid, Aurora; Schmidt, Sarah J.; Rice, Emily L.; Cruz, Kelle L.

    2017-01-01

    Magnetic activity, a wide range of observable phenomena produced in the outer atmospheres of stars, is currently not well understood for M dwarfs. In higher mass stars, magnetic activity is powered by a dynamo process involving the differential rotation of a star’s inner regions. This process generates a magnetic field, heats up regions in the atmosphere, and produces emission line radiation (H-alpha) from collisional excitation. Using the Sloan Digital Sky Survey’s (SDSS) Time Domain Spectroscopic Survey (TDSS), we will compare the H-alpha emission line strengths for a sample of 12,000 known photometrically variable M dwarfs observed in the PAN-STARRS1 survey with those of a known non-variable sample. This will be done in order to test whether photometric variability of the sample correlate with chromospheric H-alpha emission features and if not, explore the alternate reasons for that photometric variability, like binarity.

  6. 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

  7. Posttraumatic stiff elbow

    PubMed Central

    Mittal, Ravi

    2017-01-01

    Posttraumatic stiff elbow is a frequent and disabling complication and poses serious challenges for its management. In this review forty studies were included to know about the magnitude of the problem, causes, pathology, prevention, and treatment of posttraumatic stiff elbow. These studies show that simple measures such as internal fixation, immobilization in extension, and early motion of elbow joint are the most important steps that can prevent elbow stiffness. It also supports conservative treatment in selected cases. There are no clear guidelines about the choice between the numerous procedures described in literature. However, this review article disproves two major beliefs-heterotopic ossification is a bad prognostic feature, and passive mobilization of elbow causes elbow stiffness. PMID:28216745

  8. Spatial variability of the dehydrogenase activity in forest soils

    NASA Astrophysics Data System (ADS)

    Błońska, Ewa; Lasota, Jarosław

    2014-05-01

    The aim of this study was to assess the spatial variability of the dehydrogenase activity (DH) in forest soils using geostatistics. We have studied variability soil dehydrogenase and their relationship with variability of some physic-chemical properties. Two study areas (A and B) were set up in southern Poland in the Zlotoryja Forest District. Study areas were covered by different types of vegetation (A- broadleaf forest with beech, ash and sycamore), B- coniferous forest with Norway spruce). The soils were classified as Dystric Cambisols (WRB 2006). The samples for laboratory testing were collected from 49 places on each areas. 15 cm of surface horizon of soil were taken (with previously removed litter). Dehydrogenase activity was marked with Lenhard's method according to the Casida procedure. Soil pH, nitrogen (N) and soil organic carbon (C) content (by LECO CNS 2000 carbon analyzer) was marked. C/N ratio was calculated. Particle size composition was determined using laser diffraction. Statistical analysis were performed using STATISTICA 10 software. Geostatistical analysis and mapping were done by application of GS 9+ (Gamma Design) and Surfer 11 (Golden Software). The activity of DH ranged between 5,02 and 71,20 mg TPP• kg-1 •24 h-1 on the A area and between 0,94 and 16,47 mg TPP• kg-1 •24 h-1. Differences in spatial variability of the analised features were noted. The variability of dehydrogenase activity on the A study area was described by an exponential model, whereas on the B study area the spatial correlation has not been noted. The relationship of dehydrogenase activity with the remaining parameters of soil was noted only in the case of A study area. The variability of organic carbon content on the A and B study areas were described by an exponential model. The variability of nitrogen content on both areas were described by an spherical model.

  9. 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

  10. Can co-activation reduce kinematic variability? A simulation study.

    PubMed

    Selen, Luc P J; Beek, Peter J; van Dieën, Jaap H

    2005-11-01

    Impedance modulation has been suggested as a means to suppress the effects of internal 'noise' on movement kinematics. We investigated this hypothesis in a neuro-musculo-skeletal model. A prerequisite is that the muscle model produces realistic force variability. We found that standard Hill-type models do not predict realistic force variability in response to variability in stimulation. In contrast, a combined motor-unit pool model and a pool of parallel Hill-type motor units did produce realistic force variability as a function of target force, largely independent of how the force was transduced to the tendon. To test the main hypothesis, two versions of the latter model were simulated as an antagonistic muscle pair, controlling the position of a frictionless hinge joint, with a distal segment having realistic inertia relative to the muscle strength. Increasing the impedance through co-activation resulted in less kinematic variability, except for the lowest levels of co-activation. Model behavior in this region was affected by the noise amplitude and the inertial properties of the model. Our simulations support the idea that muscular co-activation is in principle an effective strategy to meet accuracy demands.

  11. 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.

  12. Individual Variability in Brain Activity: A Nuisance or an Opportunity?

    PubMed

    Van Horn, John Darrell; Grafton, Scott T; Miller, Michael B

    2008-12-01

    Functional imaging research has been heavily influenced by results based on population-level inference. However, group average results may belie the unique patterns of activity present in the individual that ordinarily are considered random noise. Recent advances in the evolution of MRI hardware have led to significant improvements in the stability and reproducibility of blood oxygen level dependent (BOLD) measurements. These enhancements provide a unique opportunity for closer examination of individual patterns of brain activity. Three objectives can be accomplished by considering brain scans at the individual level; (1) Mapping functional anatomy at a fine grained analysis; (2) Determining if an individual scan is normative with respect to a reference population; and (3) Understanding the sources of intersubject variability in brain activity. In this review, we detail these objectives, briefly discuss their histories and present recent trends in the analyses of individual variability. Finally, we emphasize the unique opportunities and challenges for understanding individual differences through international collaboration among Pacific Rim investigators.

  13. Functional Embedding Predicts the Variability of Neural Activity

    PubMed Central

    Mišić, Bratislav; Vakorin, Vasily A.; Paus, Tomáš; McIntosh, Anthony R.

    2011-01-01

    Neural activity is irregular and unpredictable, yet little is known about why this is the case and how this property relates to the functional architecture of the brain. Here we show that the variability of a region’s activity systematically varies according to its topological role in functional networks. We recorded the resting-state electroencephalogram (EEG) and constructed undirected graphs of functional networks. We measured the centrality of each node in terms of the number of connections it makes (degree), the ease with which the node can be reached from other nodes in the network (efficiency) and the tendency of the node to occupy a position on the shortest paths between other pairs of nodes in the network (betweenness). As a proxy for variability, we estimated the information content of neural activity using multiscale entropy analysis. We found that the rate at which information was generated was largely predicted by centrality. Namely, nodes with greater degree, betweenness, and efficiency were more likely to have high information content, while peripheral nodes had relatively low information content. These results suggest that the variability of regional activity reflects functional embedding. PMID:22164135

  14. Role of reflex dynamics in spinal stability: intrinsic muscle stiffness alone is insufficient for stability.

    PubMed

    Moorhouse, Kevin M; Granata, Kevin P

    2007-01-01

    Spinal stability is related to both the intrinsic stiffness of active muscle as well as neuromuscular reflex response. However, existing analyses of spinal stability ignore the role of the reflex response, focusing solely on the intrinsic muscle stiffness associated with voluntary activation patterns in the torso musculature. The goal of this study was to empirically characterize the role of reflex components of spinal stability during voluntary trunk extension exertions. Pseudorandom position perturbations of the torso and associated driving forces were recorded in 11 healthy adults. Nonlinear systems-identification analyses of the measured data provided an estimate of total systems dynamics that explained 81% of the movement variability. Proportional intrinsic response was less than zero in more than 60% of the trials, e.g. mean value of P(INT) during the 20% maximum voluntary exertion trunk extension exertions -415+/-354N/m. The negative value indicated that the intrinsic muscle stiffness was not sufficient to stabilize the spine without reflex response. Reflexes accounted for 42% of the total stabilizing trunk stiffness. Both intrinsic and reflex components of stiffness increased significantly with trunk extension effort. Results reveal that reflex dynamics are a necessary component in the stabilizing control of spinal stability.

  15. Role of Reflex Dynamics in Spinal Stability: Intrinsic Muscle Stiffness Alone is Insufficient for Stability

    PubMed Central

    Moorhouse, Kevin M.; Granata, Kevin P.

    2006-01-01

    Spinal stability is related to both the intrinsic stiffness of active muscle as well as neuromuscular reflex response. However, existing analyses of spinal stability ignore the role of the reflex response, focusing solely on the intrinsic muscle stiffness associated with voluntary activation patterns in the torso musculature. The goal of this study was to empirically characterize the role of reflex components of spinal stability during voluntary trunk extension exertions. Pseudorandom position perturbations of the torso and associated driving forces were recorded in 11 healthy adults. Nonlinear systems-identification analyses of the measured data provided an estimate of total systems dynamics that explained 81% of the movement variability. Proportional intrinsic response was less than zero in more than 60% of the trials, e.g. mean value of PINT during the 20% maximum voluntary exertion trunk extension exertions 415±354 N/m. The negative value indicated that the intrinsic muscle stiffness was not sufficient to stabilize the spine without reflex response. Reflexes accounted for 42% of the total stabilizing trunk stiffness. Both intrinsic and reflex components of stiffness increased significantly with trunk extension effort. Results reveal that reflex dynamics are a necessary component in the stabilizing control of spinal stability. PMID:16782106

  16. Objectively measured physical activity and sedentary-time are associated with arterial stiffness in Brazilian young adults

    PubMed Central

    Horta, Bernardo Lessa; Schaan, Beatriz D.; Bielemann, Renata Moraes; Vianna, Carolina Ávila; Gigante, Denise Petrucci; Barros, Fernando C.; Ekelund, Ulf; Hallal, Pedro Curi

    2015-01-01

    Objective To examine the associations between objectively measured physical activity and sedentary time with pulse wave velocity (PWV) in Brazilian young adults. Methods Cross-sectional analysis with participants of the 1982 Pelotas (Brazil) Birth Cohort who were followed-up from birth to 30 years of age. Overall physical activity (PA) assessed as the average acceleration (mg), time spent in moderate-to-vigorous physical activity (MVPA – min/day) and sedentary time (min/day) were calculated from acceleration data. Carotid-femoral PWV (m/s) was assessed using a portable ultrasound. Systolic and diastolic blood pressure (SBP/DBP), waist circumference (WC) and body mass index (BMI) were analyzed as possible mediators. Multiple linear regression and g-computation formula were used in the analyses. Results Complete data were available for 1241 individuals. PWV was significantly lower in the two highest quartiles of overall PA (0.26 m/s) compared with the lowest quartile. Participants in the highest quartile of sedentary time had 0.39 m/s higher PWV (95%CI: 0.20; 0.57) than those in the lowest quartile. Individuals achieving ≥30 min/day in MVPA had lower PWV (β = −0.35; 95%CI: −0.56; −0.14). Mutually adjusted analyses between MVPA and sedentary time and PWV changed the coefficients, although results from sedentary time remained more consistent. WC captured 44% of the association between MVPA and PWV. DBP explained 46% of the association between acceleration and PWV. Conclusions Physical activity was inversely related to PWV in young adults, whereas sedentary time was positively associated. Such associations were only partially mediated by WC and DBP. PMID:26386211

  17. Winter Eurasian Climate Variability: Role of Cyclone and Anticyclone Activity

    NASA Astrophysics Data System (ADS)

    Lu, C.; Zhang, X.; Guan, Z.

    2012-12-01

    This study investigates variability of extratropical Eurasian cyclone and anticyclone activity by using a modified automated cyclone and anticyclone identification and tracking algorithm. The cyclone and anticyclone activities are quantified by their regionally integrated intensity (CI and ACI) during 1978/79-2011/2012 winter seasons. We found that the time evolutions of the CI and ACI exhibit a general negative correlation of -0.7 between them at a significant level of 99.99%. This anticyclone (cyclone) variability contributes to the substantially large-scale sea level pressure variability over extratropical Eurasian continent, and explains the interannual fluctuation of surface air temperature over mid latitude Eurasia as well as the adjacent continents. The ACI swings from one phase to another, also producing large changes in snow cover extend, snow equivalent water as well as frequency of extreme cold events over the Eurasian continent. The strengthening of anticyclone intensity is preceded by retreated of the October sea-ice extent over Barents-Kara Sea, which associates tightly with an increasing stability at lower troposphere around the Ural Mountains and induces strengthening Eurasian anticyclones activity in the subsequent winter.

  18. Variability of mitomycin C adsorption by activated charcoal.

    PubMed

    Shah, I A; Lindup, W E; McCulloch, P G

    1998-03-01

    A saline suspension of mitomycin C adsorbed on activated charcoal and administered intraperitoneally has been reported to be safe and effective in the treatment of gastric carcinoma. Activated charcoal specifically targets tumour and lymph-node tissues and the sustained higher local drug concentration is thought to be beneficial. The charcoal particles used in these suspensions have varied in size from > 147 microm to < 20 nm in diameter, but no data have been published to show how this might affect drug adsorption and delivery. Any variability in drug adsorption could pose a serious clinical risk for drugs with a narrow therapeutic index. We have, therefore, investigated the adsorption of mitomycin C on activated charcoal in-vitro. Activated charcoal was ground and sieved to yield four size-fractions between 180 and 53 microm. Adsorption isotherms (n > or = 3) were constructed and applied to the Freundlich model with 0-l00 microg mL(-1) mitomycin C measured by HPLC with detection at 365 nm. Adsorption of mitomycin C by activated charcoal varied by a factor of three under identical conditions at room temperature (21 degrees C) and at 37 degrees C. The specific adsorption (microg mitomycin C (mg activated charcoal)(-1)) was generally higher at 37 degrees C than at room temperature. The variability of mitomycin C adsorption was greatly reduced by addition of the surface-active agent polyvinylpyrollidone, used to determine that adsorption of mitomycin C was independent of activated charcoal particle size. The characteristics of adsorption of mitomycin C by activated charcoal are complex and should be thoroughly investigated to discover the critical controlling factors before submitting the suspensions for further clinical evaluation.

  19. Microenvironment complexity and matrix stiffness regulate breast cancer cell activity in a 3D in vitro model

    PubMed Central

    Cavo, Marta; Fato, Marco; Peñuela, Leonardo; Beltrame, Francesco; Raiteri, Roberto; Scaglione, Silvia

    2016-01-01

    Three-dimensional (3D) cell cultures represent fundamental tools for the comprehension of cellular phenomena both in normal and in pathological conditions. In particular, mechanical and chemical stimuli play a relevant role on cell fate, cancer onset and malignant evolution. Here, we use mechanically-tuned alginate hydrogels to study the role of substrate elasticity on breast adenocarcinoma cell activity. The hydrogel elastic modulus (E) was measured via atomic force microscopy (AFM) and a remarkable range (150–4000 kPa) was obtained. A breast cancer cell line, MCF-7, was seeded within the 3D gels, on standard Petri and alginate-coated dishes (2D controls). Cells showed dramatic morphological differences when cultured in 3D versus 2D, exhibiting a flat shape in both 2D conditions, while maintaining a circular, spheroid-organized (cluster) conformation within the gels, similar to those in vivo. Moreover, we observed a strict correlation between cell viability and substrate elasticity; in particular, the number of MCF-7 cells decreased constantly with increasing hydrogel elasticity. Remarkably, the highest cellular proliferation rate, associated with the formation of cell clusters, occurred at two weeks only in the softest hydrogels (E = 150–200 kPa), highlighting the need to adopt more realistic and a priori defined models for in vitro cancer studies. PMID:27734939

  20. 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.

  1. Torso flexion modulates stiffness and reflex response.

    PubMed

    Granata, K P; Rogers, E

    2007-08-01

    Neuromuscular factors that contribute to spinal stability include trunk stiffness from passive and active tissues as well as active feedback from reflex response in the paraspinal muscles. Trunk flexion postures are a recognized risk factor for occupational low-back pain and may influence these stabilizing control factors. Sixteen healthy adult subjects participated in an experiment to record trunk stiffness and paraspinal muscle reflex gain during voluntary isometric trunk extension exertions. The protocol was designed to achieve trunk flexion without concomitant influences of external gravitational moment, i.e., decouple the effects of trunk flexion posture from trunk moment. Systems identification analyses identified reflex gain by quantifying the relation between applied force disturbances and time-dependent EMG response in the lumbar paraspinal muscles. Trunk stiffness was characterized from a second order model describing the dynamic relation between the force disturbances versus the kinematic response of the torso. Trunk stiffness increased significantly with flexion angle and exertion level. This was attributed to passive tissue contributions to stiffness. Reflex gain declined significantly with trunk flexion angle but increased with exertion level. These trends were attributed to correlated changes in baseline EMG recruitment in the lumbar paraspinal muscles. Female subjects demonstrated greater reflex gain than males and the decline in reflex gain with flexion angle was greater in females than in males. Results reveal that torso flexion influences neuromuscular factors that control spinal stability and suggest that posture may contribute to the risk of instability injury.

  2. Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei

    NASA Technical Reports Server (NTRS)

    Mushotzky, R. F.; Edelson, R.; Baumgartner, W. H.; Gandhi, P.

    2012-01-01

    Over three quarters in 2010 - 2011, Kepler monitored optical emission from four active galactic nuclei (AGN) with approx 30 min sampling, > 90% duty cycle and approx < 0.1% repeatability. These data determined the AGN optical fluctuation power spectral density functions (PSDs) over a wide range in temporal frequency. Fits to these PSDs yielded power law slopes of -2.6 to -3.3, much steeper than typically seen in the X-rays. We find evidence that individual AGN exhibit intrinsically different PSD slopes. The steep PSD fits are a challenge to recent AGN variability models but seem consistent with first order MRI theoretical calculations of accretion disk fluctuations.

  3. Variability and reliability of muscle activity measurements during chewing.

    PubMed

    Kravchenko, A; Weiser, A; Hugger, S; Kordass, B; Hugger, A; Wanke, E

    2014-01-01

    The objective of this study was to test masseter muscle activity and its variability and reliability in terms of repeatable measurements in fully dentate and healthy volunteers during habitual chewing and deliberate unilateral chewing. Three sessions were performed on three consecutive days, each time recording kinematic data and masseter muscle EMG activities through a series of defined jaw exercises, including maximum voluntary contraction, habitual chewing, and left and right unilateral chewing. Asymmetry index (AI) and deliberate chewing index (DCI) scores were used to evaluate the activities of the left and right masseter muscles, which were separately recorded during each of these chewing exercises. DCI scores were side-specific, including two sets of values for left and right unilateral chewing. Reproducibility testing of the values obtained for all parameters revealed good to excellent reproducibility of masseter muscle activity under standardized recording conditions across the consecutive study sessions, with intra-class correlation coefficients (ICCs) ranging from 0.68 to 0.93. Different individuals were found to utilize different strategies of bilateral masseter activation during both habitual chewing and deliberate unilateral chewing.

  4. Topology optimization under stochastic stiffness

    NASA Astrophysics Data System (ADS)

    Asadpoure, Alireza

    Topology optimization is a systematic computational tool for optimizing the layout of materials within a domain for engineering design problems. It allows variation of structural boundaries and connectivities. This freedom in the design space often enables discovery of new, high performance designs. However, solutions obtained by performing the optimization in a deterministic setting may be impractical or suboptimal when considering real-world engineering conditions with inherent variabilities including (for example) variabilities in fabrication processes and operating conditions. The aim of this work is to provide a computational methodology for topology optimization in the presence of uncertainties associated with structural stiffness, such as uncertain material properties and/or structural geometry. Existing methods for topology optimization under deterministic conditions are first reviewed. Modifications are then proposed to improve the numerical performance of the so-called Heaviside Projection Method (HPM) in continuum domains. Next, two approaches, perturbation and Polynomial Chaos Expansion (PCE), are proposed to account for uncertainties in the optimization procedure. These approaches are intrusive, allowing tight and efficient coupling of the uncertainty quantification with the optimization sensitivity analysis. The work herein develops a robust topology optimization framework aimed at reducing the sensitivity of optimized solutions to uncertainties. The perturbation-based approach combines deterministic topology optimization with a perturbation method for the quantification of uncertainties. The use of perturbation transforms the problem of topology optimization under uncertainty to an augmented deterministic topology optimization problem. The PCE approach combines the spectral stochastic approach for the representation and propagation of uncertainties with an existing deterministic topology optimization technique. The resulting compact representations

  5. VARIABILITY IN ACTIVE GALACTIC NUCLEI FROM PROPAGATING TURBULENT RELATIVISTIC JETS

    SciTech Connect

    Pollack, Maxwell; Pauls, David; Wiita, Paul J.

    2016-03-20

    We use the Athena hydrodynamics code to model propagating two-dimensional relativistic jets as approximations to the growth of radio-loud active galactic nuclei for various input jet velocities and jet-to-ambient matter density ratios. Using results from these simulations we estimate the changing synchrotron emission by summing the fluxes from a vertical strip of zones behind the reconfinement shock, which is nearly stationary, and from which a substantial portion of the flux variability should arise. We explore a wide range of timescales by considering two light curves from each simulation; one uses a relativistic turbulence code with bulk velocities taken from our simulations as input, while the other uses the bulk velocity data to compute fluctuations caused by variations in the Doppler boosting due to changes in the direction and the speed of the flow through all zones in the strip. We then calculate power spectral densities (PSDs) from the light curves for both turbulent and bulk velocity origins for variability. The range of the power-law slopes of the PSDs for the turbulence induced variations is −1.8 to −2.3, while for the bulk velocity produced variations this range is −2.1 to −2.9; these are in agreement with most observations. When superimposed, these power spectra span a very large range in frequency (about five decades), with the turbulent fluctuations yielding most of the shorter timescale variations and the bulk flow changes dominating the longer periods.

  6. Arterial stiffness in diabetes mellitus.

    PubMed

    Prenner, Stuart B; Chirinos, Julio A

    2015-02-01

    Arterial stiffness is an age-related process that is a shared consequence of numerous diseases including diabetes mellitus (DM), and is an independent predictor of mortality both in this population and in the general population. While much has been published about arterial stiffness in patients with DM, a thorough review of the current literature is lacking. Using a systematic literature search strategy, we aimed to summarize our current understanding related to arterial stiffness in DM. We review key studies demonstrating that, among patients with established DM, arterial stiffness is closely related to the progression of complications of DM, including nephropathy, retinopathy, and neuropathy. It is also becoming clear that arterial stiffness can be increased even in pre-diabetic populations with impaired glucose tolerance, and in those with the metabolic syndrome (METS), well before the onset of overt DM. Some data suggests that arterial stiffness can predict the onset of DM. However, future work is needed to further clarify whether large artery stiffness and the pulsatile hemodynamic changes that accompany it are involved in the pathogenesis of DM, and whether interventions targeting arterial stiffness are associated with improved clinical outcomes in DM. We also review of the potential mechanisms of arterial stiffness in DM, with particular emphasis on the role of advanced glycation endproducts (AGEs) and nitric oxide dysregulation, and address potential future directions for research.

  7. Structural changes in the myosin filament and cross-bridges during active force development in single intact frog muscle fibres: stiffness and X-ray diffraction measurements.

    PubMed

    Brunello, E; Bianco, P; Piazzesi, G; Linari, M; Reconditi, M; Panine, P; Narayanan, T; Helsby, W I; Irving, M; Lombardi, V

    2006-12-15

    Structural and mechanical changes occurring in the myosin filament and myosin head domains during the development of the isometric tetanus have been investigated in intact frog muscle fibres at 4 degrees C and 2.15 microm sarcomere length, using sarcomere level mechanics and X-ray diffraction at beamline ID2 of the European Synchrotron Radiation Facility (Grenoble, France). The time courses of changes in both the M3 and M6 myosin-based reflections were recorded with 5 ms frames using the gas-filled RAPID detector (MicroGap Technology). Following the end of the latent period (11 ms after the start of stimulation), force increases to the tetanus plateau value (T(0)) with a half-time of 40 ms, and the spacings of the M3 and M6 reflections (S(M3) and S(M6)) increase by 1.5% from their resting values, with time courses that lead that of force by approximately 10 and approximately 20 ms, respectively. These temporal relations are maintained when the increase of force is delayed by approximately 10 ms by imposing, from 5 ms after the first stimulus, 50 nm (half-sarcomere)(-1) shortening at the velocity (V(0)) that maintains zero force. Shortening at V(0) transiently reduces S(M3) following the latent period and delays the subsequent increase in S(M3), but only delays the S(M6) increase without a transient decrease. Shortening at V(0) imposed at the tetanus plateau causes an abrupt reduction of the intensity of the M3 reflection (I(M3)), whereas the intensity of the M6 reflection (I(M6)) is only slightly reduced. The changes in half-sarcomere stiffness indicate that the isometric force at each time point is proportional to the number of myosin heads bound to actin. The different sensitivities of the intensity and spacing of the M3 and M6 reflections to the mechanical responses support the view that the M3 reflection in active muscle originates mainly from the myosin heads attached to the actin filament and the M6 reflection originates mainly from a fixed structure in the

  8. Gear mesh stiffness and load sharing in planetary gearing

    NASA Technical Reports Server (NTRS)

    Kasuba, R.; August, R.

    1984-01-01

    An interactive computerized analysis was developed for determining load sharing among planetary gears. The load sharing is established as a function of transmitted torque, degree of sun gear fixity, component flexibility, gear tooth quality, and phasing of individual planet gears. A nonlinear variable gear tooth mesh stiffness model was used to simulate the sun/plant and planet/ring gear meshes. The determined load sharing and gear mesh stiffness parameters then can be used for the subsequent assessment of dynamic load factors.

  9. Effective leg stiffness in running.

    PubMed

    Blum, Yvonne; Lipfert, Susanne W; Seyfarth, Andre

    2009-10-16

    Leg stiffness is a common parameter used to characterize leg function during bouncing gaits, like running and hopping. In the literature, different methods to approximate leg stiffness based on kinetic and kinematic parameters are described. A challenging point in estimating leg stiffness is the definition of leg compression during contact. In this paper four methods (methods A-D) based on ground reaction forces (GRF) and one method (method E) relying on temporal parameters are described. Leg stiffness calculated by these five methods is compared with running patterns, predicted by the spring mass model. The best and simplest approximation of leg stiffness is method E. It requires only easily accessible parameters (contact time, flight time, resting leg length, body mass and the leg's touch down angle). Method D is of similar quality but additionally requires the time-dependent progression of the GRF. The other three methods show clear differences from the model predictions by over- or underestimating leg stiffness, especially at slow speeds. Leg stiffness is derived from a conceptual model of legged locomotion and does not exist without this model. Therefore, it is important to prove which experimental method is suited best for approximating the stiffness in a specific task. This will help to interpret the predictions of the conceptual model in comparison with experimental data.

  10. Jerking stiff-man syndrome.

    PubMed Central

    Alberca, R; Romero, M; Chaparro, J

    1982-01-01

    A female patient had permanent axial muscular rigidity similar to the "stiff-man syndrome", together with axial myoclonus triggered by stretch reflexes and by supramaximal stimulation of the supraorbital nerve. The disorder responded to treatment with diazepam and baclofen. This disorder bore a marked similarity to the so-called "jerking stiff-man syndrome". PMID:7161612

  11. 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.

  12. 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.

  13. Variability Analysis and the Structure of Active Galactic Nuclei

    NASA Technical Reports Server (NTRS)

    Krolik, Julian H.

    1998-01-01

    This five-year Long-Term Space Astrophysics grant provided the support for several major steps in advancing our knowledge of the internal structure of active galactic nuclei. The single largest portion of this program had to do with the development and application of techniques for "reverberation mapping", the use of spectral monitoring of several different bands related by radiation reprocessing to infer the internal geometry of sources. Major steps were taken in this regard, particularly in establishing the distribution in radius of emission line material, and in relating the apparent reprocessing of continuum bands to the underlying structure of the accretion disk. Another major effort built directly upon these results. Once the case for continuum reprocessing was made by the monitoring, it next behooved us to understand the spectral output of AGN as a result of this reprocessing. As a result, our view of continuum production in AGN is now much better focussed on the key problems. A third focus of effort had to do with the nature of X-ray variability in AGN, and what it can tell us about the dynamics of extremely hot material in the immediate outskirts of the supermassive black holes that form the central engines of active galactic nuclei. In addition to these primary efforts, this grant also supported many other, smaller projects. Several of these were demonstrations of how the material spewed out of AGN in relativistic.ets generate the radiation by which we observe them. J Finally, the portion of this study that had to do with continuum production by accretion disks in AGN led naturally to several papers in which new developments were presented having to do with "advection-dominated accretion disks", those disks in which accretion appears to proceed at a substantial rate, but in which radiation processes are weak.

  14. The Focal Adhesion: A Regulated Component of Aortic Stiffness

    PubMed Central

    Saphirstein, Robert J.; Gao, Yuan Z.; Jensen, Mikkel H.; Gallant, Cynthia M.; Vetterkind, Susanne; Moore, Jeffrey R.; Morgan, Kathleen G.

    2013-01-01

    Increased aortic stiffness is an acknowledged predictor and cause of cardiovascular disease. The sources and mechanisms of vascular stiffness are not well understood, although the extracellular matrix (ECM) has been assumed to be a major component. We tested here the hypothesis that the focal adhesions (FAs) connecting the cortical cytoskeleton of vascular smooth muscle cells (VSMCs) to the matrix in the aortic wall are a component of aortic stiffness and that this component is dynamically regulated. First, we examined a model system in which magnetic tweezers could be used to monitor cellular cortical stiffness, serum-starved A7r5 aortic smooth muscle cells. Lysophosphatidic acid (LPA), an activator of myosin that increases cell contractility, increased cortical stiffness. A small molecule inhibitor of Src-dependent FA recycling, PP2, was found to significantly inhibit LPA-induced increases in cortical stiffness, as well as tension-induced increases in FA size. To directly test the applicability of these results to force and stiffness development at the level of vascular tissue, we monitored mouse aorta ring stiffness with small sinusoidal length oscillations during agonist-induced contraction. The alpha-agonist phenylephrine, which also increases myosin activation and contractility, increased tissue stress and stiffness in a PP2- and FAK inhibitor 14-attenuated manner. Subsequent phosphotyrosine screening and follow-up with phosphosite-specific antibodies confirmed that the effects of PP2 and FAK inhibitor 14 in vascular tissue involve FA proteins, including FAK, CAS, and paxillin. Thus, in the present study we identify, for the first time, the FA of the VSMC, in particular the FAK-Src signaling complex, as a significant subcellular regulator of aortic stiffness and stress. PMID:23626821

  15. A Variable Light Domain Fluorogen Activating Protein Homodimerizes To Activate Dimethylindole Red

    SciTech Connect

    Senutovitch, Nina; Stanfield, Robyn L.; Bhattacharyya, Shantanu; Rule, Gordon S.; Wilson, Ian A.; Armitage, Bruce A.; Waggoner, Alan S.; Berget, Peter B.

    2012-07-11

    Novel fluorescent tools such as green fluorescent protein analogues and fluorogen activating proteins (FAPs) are useful in biological imaging for tracking protein dynamics in real time with a low fluorescence background. FAPs are single-chain variable fragments (scFvs) selected from a yeast surface display library that produce fluorescence upon binding a specific dye or fluorogen that is normally not fluorescent when present in solution. FAPs generally consist of human immunoglobulin variable heavy (V{sub H}) and variable light (V{sub L}) domains covalently attached via a glycine- and serine-rich linker. Previously, we determined that the yeast surface clone, V{sub H}-V{sub L} M8, could bind and activate the fluorogen dimethylindole red (DIR) but that the fluorogen activation properties were localized to the M8V{sub L} domain. We report here that both nuclear magnetic resonance and X-ray diffraction methods indicate the M8V{sub L} forms noncovalent, antiparallel homodimers that are the fluorogen activating species. The M8V{sub L} homodimers activate DIR by restriction of internal rotation of the bound dye. These structural results, together with directed evolution experiments with both V{sub H}-V{sub L} M8 and M8V{sub L}, led us to rationally design tandem, covalent homodimers of M8V{sub L} domains joined by a flexible linker that have a high affinity for DIR and good quantum yields.

  16. A Comparison of Total and Intrinsic Muscle Stiffness Among Flexors and Extensors of the Ankle, Knee and Elbow

    NASA Technical Reports Server (NTRS)

    Lemoine, Sandra M.

    1997-01-01

    This study examined 3 methods that assessed muscle stiffness. Muscle stiffness has been quantified by tissue reactive force (transverse stiffness), vibration, and force (or torque) over displacement. Muscle stiffness also has two components: reflex (due to muscle sensor activity) and intrinsic (tonic firing of motor units, elastic nature of actin and myosin cross bridges, and connective tissue). This study compared three methods of measuring muscle stiffness of agonist-antagonist muscle pairs of the ankle, knee and elbow.

  17. A Reply to Stiff and Boster.

    ERIC Educational Resources Information Center

    Petty, Richard E.; And Others

    1987-01-01

    Addresses the major errors and misconceptions perpetuated by Stiff and Boster's response to criticism of Stiff's 1986 article. Focuses on the major conceptual and methodological issues of Stiff's model. (NKA)

  18. The active liquid Earth - importance of temporal and spatial variability

    NASA Astrophysics Data System (ADS)

    Arheimer, Berit

    2016-04-01

    The Planet Earth is indeed liquid and active - 71 percent of its surface is water-covered and this water never rests. Thanks to the water cycle, our planet's water supply is constantly moving from one place to another and from one form to another. Only 2.5% of the water is freshwater and it exists in the air as water vapor; it hits the ground as rain and snow; it flows on the surface from higher to lower altitudes in rivers, lakes, and glaciers; and it flows in the ground in soil, aquifers, and in all living organisms until it reaches the sea. On its way over the Earth's crust, some returns quickly to vapor again, while some is trapped and exposed to many "fill and spill" situations for a long journey. The variability in the water balance is crucial for hydrological understanding and modelling. The water cycle may appear simple, but magnitudes and rates in fluxes are very different from one place to another, resulting from variable drivers such as solar energy, precipitation and gravity in co-evolution with geology, soil, vegetation and fauna. The historical evolution, the temporal fluxes and diversity in space continue to fascinate hydrological scientists. Specific physical processes may be well known, but their boundary conditions, interactions and rate often remain unknown at a specific site and are difficult to monitor in nature. This results in mysterious features where trends in drivers do not match runoff, like the Sahelian Paradox or discharge to the Arctic Ocean. Humans have always interfered with the water cycle and engineering is fundamental for water regulation and re-allocation. Some 80% of the river flow from the northern part of the Earth is affected by fragmentation of the river channels by dams. In water management, there is always a tradeoff between upstream and downstream activities, not only regarding total water quantities but also for temporal patterns and water quality aspects. Sharing a water resource can generate conflicts but geopolitical

  19. Can a soft robotic probe use stiffness control like a human finger to improve efficacy of haptic perception?

    PubMed

    Sornkarn, Nantachai; Nanayakkara, Thrishantha

    2016-10-19

    When humans are asked to palpate a soft tissue to locate a hard nodule, they regulate the stiffness, speed, and force of the finger during examination. If we understand the relationship between these behavioral variables and haptic information gain (transfer entropy) during manual probing, we can improve the efficacy of soft robotic probes for soft tissue palpation, such as in tumor localization in minimally invasive surgery. Here, we recorded the muscle co-contraction activity of the finger using EMG sensors to address the question as to whether joint stiffness control during manual palpation plays an important role in the haptic information gain. To address this question, we used a soft robotic probe with a controllable stiffness joint and a force sensor mounted at the base to represent the function of the tendon in a biological finger. Then, we trained a Markov chain using muscle co- contraction patterns of human subjects, and used it to control the stiffness of the soft robotic probe in the same soft tissue palpation task. The soft robotic experiments showed that haptic information gain about the depth of the hard nodule can be maximized by varying the internal stiffness of the soft probe.

  20. Significantly different coagulation factor activities underlying the variability of 'normal' activated partial thromboplastin time.

    PubMed

    Park, Kyoung-Jin; Kwon, Eui-Hoon; Ma, Youngeun; Park, In-Ae; Kim, Seon-Woo; Kim, Sun-Hee; Kim, Hee-Jin

    2012-01-01

    The activated partial thromboplastin time (aPTT) is a widely used coagulation screening test in routine laboratories. The aPTT level in the control population varies and is reflected by the reference interval. However, there have been no studies to investigate the coagulation status determining the variability of the aPTT. The aim of this study was to investigate the coagulation factor activities underlying the variability of aPTT in the population. The study participants were reference individuals with prothrombin time and aPTT within reference intervals. The aPTT was determined using STA-PTT Automate (Diagnostica Stago, Asnieres, France; local reference interval, 29.1-41.9 s). Those with aPTT within the marginal ranges of reference interval were selected for factor assays. We defined the lower marginal group as the lowest 10 percentile of reference interval (29.1-30.9 s) and the upper marginal group as the highest 10 percentile (38.0-41.9 s). Activities of factor II, V, VIII, IX, X, XI, and XII were determined in both groups. The lower marginal and upper marginal groups consisted of 220 and 209 individuals, respectively. All coagulation factors were significantly higher in the lower marginal than in the upper marginal group (P = 0.0127 for factor II and P < 0.0001 for the others). Multiple logistic regression analyses revealed factor XII and VIII were two strongest contributors determining the aPTT level, whereas factor XI was not significantly different between the groups (P = 0.095). This study firstly demonstrated significantly different coagulation factor activities underlying the variability of aPTT in reference individuals. The results suggested the possibility of disease association or phenotypic contribution of variable coagulation activities in the population.

  1. A comparison of muscle stiffness and musculoarticular stiffness of the knee joint in young athletic males and females.

    PubMed

    Wang, Dan; De Vito, Giuseppe; Ditroilo, Massimiliano; Fong, Daniel T P; Delahunt, Eamonn

    2015-06-01

    The objective of this study was to investigate the gender-specific differences in peak torque (PT), muscle stiffness (MS) and musculoarticular stiffness (MAS) of the knee joints in a young active population. Twenty-two male and twenty-two female recreational athletes participated. PT of the knee joint extensor musculature was assessed on an isokinetic dynamometer, MS of the vastus lateralis (VL) muscle was measured in both relaxed and contracted conditions, and knee joint MAS was quantified using the free oscillation technique. Significant gender differences were observed for all dependent variables. Females demonstrated less normalized PT (mean difference (MD)=0.4Nm/kg, p=0.005, η(2)=0.17), relaxed MS (MD=94.2N/m, p<.001, η(2)=0.53), contracted MS (MD=162.7N/m, p<.001, η(2)=0.53) and MAS (MD=422.1N/m, p<.001, η(2)=0.23) than males. MAS increased linearly with the external load in both genders with males demonstrating a significantly higher slope (p=0.019) than females. The observed differences outlined above may contribute to the higher knee joint injury incidence and prevalence in females when compared to males.

  2. Rho-kinase mediated cytoskeletal stiffness in skinned smooth muscle

    PubMed Central

    Lan, Bo; Wang, Lu; Zhang, Jenny; Pascoe, Chris D.; Norris, Brandon A.; Liu, Jeffrey C.-Y.; Solomon, Dennis; Paré, Peter D.; Deng, Linhong

    2013-01-01

    The structurally dynamic cytoskeleton is important in many cell functions. Large gaps still exist in our knowledge regarding what regulates cytoskeletal dynamics and what underlies the structural plasticity. Because Rho-kinase is an upstream regulator of signaling events leading to phosphorylation of many cytoskeletal proteins in many cell types, we have chosen this kinase as the focus of the present study. In detergent skinned tracheal smooth muscle preparations, we quantified the proteins eluted from the muscle cells over time and monitored the muscle's ability to respond to acetylcholine (ACh) stimulation to produce force and stiffness. In a partially skinned preparation not able to generate active force but could still stiffen upon ACh stimulation, we found that the ACh-induced stiffness was independent of calcium and myosin light chain phosphorylation. This indicates that the myosin light chain-dependent actively cycling crossbridges are not likely the source of the stiffness. The results also indicate that Rho-kinase is central to the ACh-induced stiffness, because inhibition of the kinase by H1152 (1 μM) abolished the stiffening. Furthermore, the rate of relaxation of calcium-induced stiffness in the skinned preparation was faster than that of ACh-induced stiffness, with or without calcium, suggesting that different signaling pathways lead to different means of maintenance of stiffness in the skinned preparation. PMID:24072407

  3. Stiffness of compressed fiber mats

    NASA Astrophysics Data System (ADS)

    Åström, J. A.; Mäkinen, J. P.; Hirvonen, H.; Timonen, J.

    2000-11-01

    We investigate, using an analytical and a numerical model, the in-plane stiffness of fiber mats. A mat is modeled by randomly depositing thin linear-elastic fibers on top of each other under the influence of an external pressure. The external pressure has the effect of bending the fibers over each other. The fibers are assumed rigidly bonded at contacts. For a low external pressure the stiffness of the mat deviates from that of its two-dimensional projection only by a geometrical factor, and the effective Poisson contraction is close to zero. For higher pressures, stiffness is governed by two competing effects and a maximum appears in the stiffness. The effective Poisson ratio is clearly negative in this range. An approximative analytical description is developed for the stiffness of mats formed under low external pressure. The stiffness is given as a function of only a few parameters: the degree of bonding, the dimensions of the fibers, the elastic constants of the fiber material, and the density of fibers.

  4. Active optics for high-dynamic variable curvature mirrors.

    PubMed

    Hugot, Emmanuel; Ferrari, Marc; Lemaitre, Gérard R; Madec, Fabrice; Vives, Sébastien; Chardin, Elodie; Le Mignant, David; Cuby, Jean-Gabriel

    2009-10-01

    Variable curvature mirrors of large amplitude are designed by using finite element analysis. The specific case studied reaches at least a 800 mum sag with an optical quality better than lambda/5 over a 120 mm clear aperture. We highlight the geometrical nonlinearity and the plasticity effect.

  5. 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

  6. Stiffness control of magnetorheological gels for adaptive tunable vibration absorber

    NASA Astrophysics Data System (ADS)

    Kim, Hyun Kee; Kim, Hye Shin; Kim, Young-Keun

    2017-01-01

    In this study, a stiffness feedback control system for magnetorheological (MR) gel—a smart material of variable stiffness—is proposed, toward the design of a tunable vibration absorber that can adaptively tune to a time varying disturbance in real time. A PID controller was designed to track the required stiffness of the MR gel by controlling the magnitude of the target external magnetic field pervading the MR gel. This paper proposes a novel magnetic field generator that could produce a variable magnetic field with low energy consumption. The performance of the MR gel stiffness control was validated through experiments that showed the MR gel absorber system could be automatically tuned from 56 Hz to 67 Hz under a field of 100 mT to minimize the vibration of the primary system.

  7. Leg stiffness of sprinters using running-specific prostheses.

    PubMed

    McGowan, Craig P; Grabowski, Alena M; McDermott, William J; Herr, Hugh M; Kram, Rodger

    2012-08-07

    Running-specific prostheses (RSF) are designed to replicate the spring-like nature of biological legs (bioL) during running. However, it is not clear how these devices affect whole leg stiffness characteristics or running dynamics over a range of speeds. We used a simple spring-mass model to examine running mechanics across a range of speeds, in unilateral and bilateral transtibial amputees and performance-matched controls. We found significant differences between the affected leg (AL) of unilateral amputees and both ALs of bilateral amputees compared with the bioL of non-amputees for nearly every variable measured. Leg stiffness remained constant or increased with speed in bioL, but decreased with speed in legs with RSPs. The decrease in leg stiffness in legs with RSPs was mainly owing to a combination of lower peak ground reaction forces and increased leg compression with increasing speeds. Leg stiffness is an important parameter affecting contact time and the force exerted on the ground. It is likely that the fixed stiffness of the prosthesis coupled with differences in the limb posture required to run with the prosthesis limits the ability to modulate whole leg stiffness and the ability to apply high vertical ground reaction forces during sprinting.

  8. Diagnostic for two-mode variable valve activation device

    SciTech Connect

    Fedewa, Andrew M

    2014-01-07

    A method is provided for diagnosing a multi-mode valve train device which selectively provides high lift and low lift to a combustion valve of an internal combustion engine having a camshaft phaser actuated by an electric motor. The method includes applying a variable electric current to the electric motor to achieve a desired camshaft phaser operational mode and commanding the multi-mode valve train device to a desired valve train device operational mode selected from a high lift mode and a low lift mode. The method also includes monitoring the variable electric current and calculating a first characteristic of the parameter. The method also includes comparing the calculated first characteristic against a predetermined value of the first characteristic measured when the multi-mode valve train device is known to be in the desired valve train device operational mode.

  9. 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

  10. Arterial Stiffness: Recommendations and Standardization

    PubMed Central

    Townsend, Raymond R.

    2017-01-01

    The use of arterial stiffness measurements in longitudinal cohorts of normal populations, hypertensive patients, diabetic patients, healthy elderly, and patients on hemodialysis have confirmed the value of this important measure of arterial health, and established its complementary role to measures of blood pressure. Its contribution to understanding cardiovascular and mortality risk beyond blood pressure measurements has moved measures of arterial stiffness into the ranks of factors such as elevated cholesterol, diabetes, and left ventricular hypertrophy in considering cardiovascular risk. The recent international collaboration's publication of reference ranges for normal people and those with hypertension, along with the American Heart Association's recent scientific statement on standardizing arterial stiffness measurements are important aspects to consider in future studies employing these valuable methods, particularly as interventions that not only lower blood pressure but improve arterial function are tested in the clinical arena. PMID:28275588

  11. Monitoring stiffness contrast in elastography

    NASA Astrophysics Data System (ADS)

    Kiss, Miklos; Bharat, Shyam; Varghese, Tomy; Techavipoo, Udomchai; Liu, Wu

    2005-03-01

    Elastography is an imaging modality used to image tissue strains resulting from external quasi-static compression of tissue. Therefore, elastograms can be used to study variations in the stiffness of thermally coagulated regions of tissue. In this study, the variations in stiffness contrast of lesions formed by radio frequency (RF) ablation of canine liver tissue have been investigated. RF ablation was performed on in vitro canine liver tissue over a range of temperatures from 70 - 100 degrees C, and over a range of ablation times from 1 -- 8 minutes. Elastography was then performed on these samples and on normal tissue. It was expected that stiffness contrast would increase with increasing lesion temperature and ablation duration, on the basis that higher temperature and greater ablation durations lead to increased protein denaturation. This increase was seen with ablation duration, but is not obvious with ablation temperature. These and other results will be discussed.

  12. 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

  13. Relationships Between Lower-Body Muscle Structure and, Lower-Body Strength, Explosiveness and Eccentric Leg Stiffness in Adolescent Athletes

    PubMed Central

    Secomb, Josh L.; Nimphius, Sophia; Farley, Oliver R.L.; Lundgren, Lina E.; Tran, Tai T.; Sheppard, Jeremy M.

    2015-01-01

    The purpose of the present study was to determine whether any relationships were present between lower-body muscle structure and, lower-body strength, variables measured during a countermovement jump (CMJ) and squat jump (SJ), and eccentric leg stiffness, in adolescent athletes. Thirty junior male (n = 23) and female (n = 7) surfing athletes (14.8 ± 1.7 y; 1.63 ± 0.09 m; 54.8 ± 12.1 kg) undertook lower-body muscle structure assessment with ultrasonography and performed a; CMJ, SJ and an isometric mid-thigh pull (IMTP). In addition, eccentric leg stiffness was calculated from variables of the CMJ and IMTP. Moderate to very large relationships (r = 0.46-0.73) were identified between the thickness of the vastus lateralis (VL) and lateral gastrocnemius (LG) muscles, and VL pennation angle and; peak force (PF) in the CMJ, SJ and IMTP. Additionally, moderate to large relationships (r = 0.37-0.59) were found between eccentric leg stiffness and; VL and LG thickness, VL pennation angle, and LG fascicle length, with a large relationship (r = 0.59) also present with IMTP PF. These results suggest that greater thickness of the VL and LG were related to improved maximal dynamic and isometric strength, likely due to increased hypertrophy of the extensor muscles. Furthermore, this increased thickness was related to greater eccentric leg stiffness, as the associated enhanced lower-body strength likely allowed for greater neuromuscular activation, and hence less compliance, during a stretch-shortening cycle. Key points Greater thickness of the VL and LG muscles were significantly related to an enhanced ability to express higher levels of isometric and dynamic strength, and explosiveness in adolescent athletes. Isometric strength underpinned performance in the CMJ and SJ in these athletes. Greater lower-body isometric strength was significantly related to eccentric leg stiffness, which is potentially the result of greater neuromuscular activation in the muscle-tendon unit. PMID

  14. Relationships Between Lower-Body Muscle Structure and, Lower-Body Strength, Explosiveness and Eccentric Leg Stiffness in Adolescent Athletes.

    PubMed

    Secomb, Josh L; Nimphius, Sophia; Farley, Oliver R L; Lundgren, Lina E; Tran, Tai T; Sheppard, Jeremy M

    2015-12-01

    The purpose of the present study was to determine whether any relationships were present between lower-body muscle structure and, lower-body strength, variables measured during a countermovement jump (CMJ) and squat jump (SJ), and eccentric leg stiffness, in adolescent athletes. Thirty junior male (n = 23) and female (n = 7) surfing athletes (14.8 ± 1.7 y; 1.63 ± 0.09 m; 54.8 ± 12.1 kg) undertook lower-body muscle structure assessment with ultrasonography and performed a; CMJ, SJ and an isometric mid-thigh pull (IMTP). In addition, eccentric leg stiffness was calculated from variables of the CMJ and IMTP. Moderate to very large relationships (r = 0.46-0.73) were identified between the thickness of the vastus lateralis (VL) and lateral gastrocnemius (LG) muscles, and VL pennation angle and; peak force (PF) in the CMJ, SJ and IMTP. Additionally, moderate to large relationships (r = 0.37-0.59) were found between eccentric leg stiffness and; VL and LG thickness, VL pennation angle, and LG fascicle length, with a large relationship (r = 0.59) also present with IMTP PF. These results suggest that greater thickness of the VL and LG were related to improved maximal dynamic and isometric strength, likely due to increased hypertrophy of the extensor muscles. Furthermore, this increased thickness was related to greater eccentric leg stiffness, as the associated enhanced lower-body strength likely allowed for greater neuromuscular activation, and hence less compliance, during a stretch-shortening cycle. Key pointsGreater thickness of the VL and LG muscles were significantly related to an enhanced ability to express higher levels of isometric and dynamic strength, and explosiveness in adolescent athletes.Isometric strength underpinned performance in the CMJ and SJ in these athletes.Greater lower-body isometric strength was significantly related to eccentric leg stiffness, which is potentially the result of greater neuromuscular activation in the muscle-tendon unit.

  15. Multi-Wavelength Time Variability of Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Chatterjee, Ritaban

    2009-01-01

    Due to their large distances, AGNs are not spatially resolved with current and near-future technologies except by radio interferometry. However, we can use time variability, one of the defining properties of AGNs, to probe the location and physical processes related to the emission at resolutions even finer than provided by VLBI. I use extensive multi-frequency monitoring data of the blazars 3C 279 and PKS 1510-089 (over 10 years long) and the radio galaxy 3C 120 ( 5 years), including well-sampled light curves (radiative flux vs. time) at X-ray energies (2-10 keV), optical wavelengths (R band), and radio frequencies (14.5 GHz and 37 GHz), as well as monthly images obtained with the Very Long Baseline Array (VLBA) at 43 GHz that follow changes in the emission structure of the jet on parsec scales. I have developed and applied a set of statistical tools to characterize the time variability of AGNs. This includes the power spectral density (PSD) and its uncertainties, discrete cross-correlation functions and their significance using random light curves simulated from the previously calculated PSDs, and decomposition of light curves into individual flares. I also model the time variable emission spectrum of an AGN jet using a numerical code that includes conical geometry, turbulent magnetic field and density, and energization of electrons due to a moving shock front. Comparing the results of the model calculations and the application of the above-mentioned statistical procedures on the real data, I draw conclusions about the location of the emission regions of these objects. I also identify the ongoing emission mechanisms and implications regarding the physics of jets. This work is supported by NASA through grants NNX08AJ64G (ADP) and NNX08AV65G (Fermi).

  16. Variable phase sine wave generator for active phased arrays

    NASA Astrophysics Data System (ADS)

    Waters, W. M.

    1992-09-01

    A waveform generator is provided for generating a high frequency waveform. A pulse generator provides a pulse train at a low frequency. A pulse converter converts the pulse train into an alternatingly positive and negative groups of pulses. A bandpass filter passes the alternatingly positive and negative groups of pulses in a frequency band centered at the high frequency to output the generated waveform at the high frequency. When the groups of pulses are a pair of pulses, a sine wave is output from the bandpass filter. A pulse delay circuit can be used to variably delay the pulse train and thereby cause a phase change in the generated waveform.

  17. Variability of the Lyman alpha flux with solar activity

    SciTech Connect

    Lean, J.L.; Skumanich, A.

    1983-07-01

    A three-component model of the solar chromosphere, developed from ground based observations of the Ca II K chromospheric emission, is used to calculate the variability of the Lyman alpha flux between 1969 and 1980. The Lyman alpha flux at solar minimum is required in the model and is taken as 2.32 x 10/sup 11/ photons/cm/sup 2//s. This value occurred during 1975 as well as in 1976 near the commencement of solar cycle 21. The model predicts that the Lyman alpha flux increases to as much as 5 x 10/sup 11/ photons/cm/sup 2//s at the maximum of the solar cycle. The ratio of the average fluxes for December 1979 (cycle maximum) and July 1976 (cycle minimum) is 1.9. During solar maximum the 27-day solar rotation is shown to cause the Lyman alpha flux to vary by as much as 40% or as little as 5%. The model also shows that the Lyman alpha flux varies over intermediate time periods of 2 to 3 years, as well as over the 11-year sunspot cycle. We conclude that, unlike the sunspot number and the 10.7-cm radio flux, the Lyman alpha flux had a variability that was approximately the same during each of the past three cycles. Lyman alpha fluxes calculated by the model are consistent with measurements of the Lyman alpha flux made by 11 of a total of 14 rocket experiments conducted during the period 1969--1980. The model explains satisfactorily the absolute magnitude, long-term trends, and the cycle variability seen in the Lyman alpha irradiances by the OSO 5 satellite experiment. The 27-day variability observed by the AE-E satellite experiment is well reproduced. However, the magntidue of the AE-E 1 Lyman alpha irradiances are higher than the model calculations by between 40% and 80%. We suggest that the assumed calibration of the AE-E irradiances is in error.

  18. 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.

  19. Relationship between two proprioceptive measures and stiffness at the ankle.

    PubMed

    Docherty, Carrie L; Arnold, Brent L; Zinder, Steven M; Granata, Kevin; Gansneder, Bruce M

    2004-06-01

    Previous research has investigated the role of proprioception and stiffness in the control of joint stability. However, to date, no research has been done on the relationship between proprioception and stiffness. Therefore, the purpose of this study was to determine the relationship between force sense, joint reposition sense, and stiffness at the ankle. A heterogeneous sample was obtained for this study; 20 of the 40 participants had a history of ankle sprains, and 13 of the 20 had been diagnosed by a physician (two mild ankle sprains, seven moderate sprains, four severe sprains). All subjects were asymptomatic and active at the time of the study. Active joint reposition sense was measured using a custom-built ankle goniometer, force sense was measured unilaterally and contralaterally with a load cell, and ankle muscle stiffness was measured via transient oscillation using a custom-built inversion-eversion cradle. We found no significant correlations between stiffness and joint reposition sense, with values of r ranging from 0.01 to 0.21. Significant correlations were found between stiffness and force sense. Specifically, contralateral force sense reproduction was significantly correlated to stiffness in the injured or "involved" ankle (r's ranging from 0.47 to 0.65; P< or =0.008). Whether the decreased ability to appropriately sense force (increased error) sends information to the central nervous system to increase muscle stiffness in response to an unexpected loss of stability, or whether these two phenomena function independently and both change concurrently as a result of injury to the system requires further investigation.

  20. Epidemiology of the arterial stiffness.

    PubMed

    Breithaupt-Grögler, K; Belz, G G

    1999-06-01

    Aortic stiffening is as much an important risk factor in cardiovascular morbidity and mortality, as it serves as reliable surrogate marker for clinical endpoints like myocardial and cerebrovascular incidents. Elevated aortic stiffness induces high systolic blood pressure, augmented pulse pressure with increased ventricular afterload, reduced subendocardial blood flow and augmented pulsatile stress in the peripheral arteries. Factors with relevant impact on the epidemiology of arterial stiffness are widely spread. 3 major groups of parameters influencing the stiffness of the aorta and the large arteries have been studied and described up to now: (i) physiological properties like age, gender, body height, pressure, hormonal state, genetic factors; (ii) environmental factors like nutrition (fish-, salt-, garlic consumption), smoking, performance of sports and aerobic capacity; (iii) diseases like hypertension, hypercholesterolemia, diabetes, coronary heart disease, cerebrovascular disease, renal failure, Marfan-syndrome, growth hormone deficiency. Close association between several of these factors impedes analyzing them independently from each other. Age and blood pressure were found to be the most prominent predictors of arterial stiffness in normal as well as in disease populations. Physiological and environmental factors can modulate these effects of aging, diseases generally seem to amplify them.

  1. 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

  2. Biofidelic Human Activity Modeling and Simulation with Large Variability

    DTIC Science & Technology

    2014-11-25

    capture data to replicate a human activity in 3D space. Since technologies for simultaneously capturing human motion and dynamic shapes are not yet ready...for practical use, a motion capture system can be used to capture markers on the body during motion and a 3D body scanner can be used to capture the...animation-capable model that can replicate a human activity in 3D space with the true shape and true motion of a human. Using this approach, a model

  3. Age-Related Variability in Cortical Activity during Language Processing

    ERIC Educational Resources Information Center

    Fridriksson, Julius; Morrow, K. Leigh; Moser, Dana; Baylis, Gordon C.

    2006-01-01

    Purpose: The present study investigated the extent of cortical activity during overt picture naming using functional magnetic resonance imaging (fMRI). Method: Participants comprised 20 healthy, adult participants with ages ranging from 20 to 82 years. While undergoing fMRI, participants completed a picture-naming task consisting of 60…

  4. Concept of variable activation energy and its validity in nonisothermal kinetics.

    PubMed

    Tan, Guanglei; Wang, Qi; Zheng, Hongxia; Zhao, Wei; Zhang, Song; Liu, Zhongsuo

    2011-06-09

    The concept of variable activation energy in solid-state kinetics under nonisothermal conditions has been suffering from doubt and controversy. Rate equations of nonisothermal kinetics of solid decomposition, which involve the factors of thermodynamics conditions, pressure of gaseous product, structure parameters of solid, and/or extent of conversion, are derived from the models of the interface reaction, the diffusion of gaseous product, and the nuclei growth of the solid product, respectively. The definition of the validity function in the rate equations represents the influence of the factors on the reaction rate. A function of variable activation energy depending on the validity function is also developed. The changing trend and degree of activation energy are extrapolated from the function of variable activation energy and based on the data of nonisothermal thermal decomposition of calcium carbonate. It is shown that the concept of variable activation energy is meaningfully applicable to solid-state reactions under nonisothermal conditions.

  5. Older women track and field athletes have enhanced calcaneal stiffness.

    PubMed

    Welch, J M; Rosen, C J

    2005-08-01

    Vigorous weight-bearing exercise is recommended to women as a method of osteoporosis prevention. This study examined older women athletes to see if they indeed were less likely to develop osteoporosis than those in the general population, and to investigate which factors could have contributed to these results. One hundred and thirty-nine women 40-88 years old, all competitors in a USA National Masters Track and Field Championships, volunteered for the study. Masters refers to competitors > or =40 years old. Their calcaneal stiffness (SI) was measured by a Lunar Achilles+ ultrasonometer. Subjects were also measured for height and weight, and completed a questionnaire on exercise history, diet, lifestyle factors, medical and menopausal issues, and use of hormone replacement therapy (HRT). The women, mean age 57.3 years, had an overall average SI of 99.5 (T-score = 0.04) which is equivalent to that of a 20-year-old woman and 20.8% higher than expected for women of their age. Their median SI remained not different from expected peak bone SI until the age of 70. For analysis, this cohort of women was divided into two groups: premenopausal and postmenopausal athletes. The SI of both groups was correlated with the earliest age at which they had first participated in sports or exercises that impart moderate to high strain rates to the lower limbs and with current participation in high impact track and field events. Variables correlated with SI in the general population, such as weight, HRT, previous fracture, hysterectomy, and current menopausal status, did not predict SI in this cohort. In conclusion, women competing in Masters track and field at the national level had calcaneal stiffness substantially higher than expected for women of their age in the general population, and their participation in vigorous sports and activities, either currently or at a younger age, was predictive of this association.

  6. Chemical Variability and Biological Activities of Eucalyptus spp. Essential Oils.

    PubMed

    Barbosa, Luiz Claudio Almeida; Filomeno, Claudinei Andrade; Teixeira, Robson Ricardo

    2016-12-07

    Many plant species produce mixtures of odorous and volatile compounds known as essential oils (EOs). These mixtures play important roles in Nature and have been utilized by mankind for different purposes, such as pharmaceuticals, agrochemicals, aromatherapy, and food flavorants. There are more than 3000 EOs reported in the literature, with approximately 300 in commercial use, including the EOs from Eucalyptus species. Most EOs from Eucalyptus species are rich in monoterpenes and many have found applications in pharmaceuticals, agrochemicals, food flavorants, and perfumes. Such applications are related to their diverse biological and organoleptic properties. In this study, we review the latest information concerning the chemical composition and biological activities of EOs from different species of Eucalyptus. Among the 900 species and subspecies of the Eucalyptus genus, we examined 68 species. The studies associated with these species were conducted in 27 countries. We have focused on the antimicrobial, acaricidal, insecticidal and herbicidal activities, hoping that such information will contribute to the development of research in this field. It is also intended that the information described in this study can be useful in the rationalization of the use of Eucalyptus EOs as components for pharmaceutical and agrochemical applications as well as food preservatives and flavorants.

  7. Anticorrelation of Variability Amplitude with X-Ray Luminosity for Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Bao, Gang; Abramowicz, Marek A.

    1996-07-01

    The bright-spot model for the short-term X-ray variability of active galactic nuclei predicts that, statistically, sources with larger luminosities should have smaller variability amplitudes. This quantitatively agrees with the analysis of the observational data from 12 high-quality EXOSAT long looks performed by Lawrence & Papadakis.

  8. Muscle Stiffness and Spinal Stretch Reflex Sensitivity in the Triceps Surae

    PubMed Central

    Blackburn, J. Troy; Padua, Darin A; Guskiewicz, Kevin M

    2008-01-01

    Context: Greater musculotendinous stiffness may enhance spinal stretch reflex sensitivity by improving mechanical coupling of the muscle spindle and the stretch stimulus. This heightened sensitivity would correspond with a shorter latency and higher-amplitude reflex response, potentially enhancing joint stability. Objective: To compare spinal stretch reflex latency and amplitude across groups that differed in musculotendinous stiffness. Design: Static group comparisons. Setting: Research laboratory. Patients or Other Participants: Forty physically active individuals (20 men, 20 women). Intervention(s): We verified a sex difference in musculotendinous stiffness and compared spinal stretch reflex latency and amplitude in high-stiffness (men) and low-stiffness (women) groups. We also evaluated relationships between musculotendinous stiffness and spinal stretch reflex latency and amplitude, respectively. Main Outcome Measure(s): Triceps surae musculotendinous stiffness and soleus spinal stretch reflex latency and amplitude were assessed at 30% of a maximal voluntary isometric plantar-flexion contraction. Results: The high-stiffness group demonstrated significantly greater stiffness (137.41 ± 26.99 N/cm) than the low-stiffness group did (91.06 ± 20.10 N/cm). However, reflex latency (high stiffness = 50.11 ± 2.07 milliseconds, low stiffness = 48.26 ± 2.40 milliseconds) and amplitude (high stiffness = 0.28% ± 0.12% maximum motor response, low stiffness = 0.31% ± 0.16% maximum motor response) did not differ significantly across stiffness groups. Neither reflex latency (r = .053, P = .746) nor amplitude (r = .073, P = .653) was related significantly to musculotendinous stiffness. Conclusions: A moderate level of pretension (eg, 30%) likely eliminates series elastic slack; thus, a greater change in force per unit-of-length change (ie, heightened stiffness) would have minimal effects on coupling of the muscle spindle and the stretch stimulus and, therefore, on spinal

  9. Stiffness characterisation of microcantilevers based on conducting polymers

    NASA Astrophysics Data System (ADS)

    Alici, Gursel; Higgins, Michael J.

    2008-12-01

    The object of this paper is to characterise the stiffness of microfabricated cantilevers consisting of two electroactive polymer (polypyrrole (PPy)) layers, and two gold layers with a negligible thickness and a layer of porous polyvinylidene fluoride (PVDF), which serves as a backing layer and electrolyte storage tank. This composite cantilever structure is used as polymer actuators or famously known as artificial muscles when tailored appropriately. The polymer microactuators considered in this study, which were fabricated using a laser ablation technique, could operate both in aqueous and non-aqueous media. The stiffness characterization of the microactuators is critical to assess their suitability to numerous applications including the micromanipulation of living cells, bio-analytical nanosystems, datastorage, labon- chip, microvalve, microswitch, microshutter, cantilever light modulators, micro-optical instrumentation, artificial muscles for micro and macro robotic sytems and similar. The stiffness measurement method followed in this study is a static deflection measurement method, using an atomic force microscope (AFM). The stiffness constants of the microactuators while they were in passive (no electrochemical activation) and active (electrochemically activated) states were measured separately, and their statistical comparison was provided. The possible error sources for the stiffness measurement method are elaborated.

  10. Physically Active Adults: An Analysis of the Key Variables That Keep Them Moving

    ERIC Educational Resources Information Center

    Downs, Andrew

    2016-01-01

    Background: A large proportion of adults are insufficiently physically active, and researchers have yet to determine the factors that enable individuals to maintain adequate levels of physical activity throughout adulthood. Purpose: This study sought to identify the key variables linked with consistent physical activity in adulthood as elucidated…

  11. Variability in affective activation predicts non-suicidal self-injury in eating disorders.

    PubMed

    Vansteelandt, Kristof; Claes, Laurence; Muehlenkamp, Jennifer; De Cuyper, Kathleen; Lemmens, Jos; Probst, Michel; Vanderlinden, Johan; Pieters, Guido

    2013-03-01

    We examined whether affective variability can predict non-suicidal self-injury (NSSI) in eating disorders. Affect was represented by valence (positive versus negative) and activation (high versus low). Twenty-one patients with anorexia nervosa-restricting type, 18 patients with anorexia nervosa-binge-purging type and 20 patients with bulimia nervosa reported their momentary affect at nine random times a day during a one week period using a hand-held computer. Affective variability was calculated as the within-person standard deviation of valence and activation over time. Results indicate that patients displaying greater variability in activation and using selective serotonin reuptake inhibitors have a higher probability to engage in lifetime NSSI after adjustment for depression and borderline personality disorder. Neither variability of valence nor mean level of valence and activation had any predictive association with engaging in NSSI. It is suggested that the treatment of NSSI should focus on affect stabilization rather than reducing negative affect.

  12. Exploratory factor analysis for differentiating sensory and mechanical variables related to muscle-tendon unit elongation

    PubMed Central

    Chagas, Mauro H.; Magalhães, Fabrício A.; Peixoto, Gustavo H. C.; Pereira, Beatriz M.; Andrade, André G. P.; Menzel, Hans-Joachim K.

    2016-01-01

    ABSTRACT Background Stretching exercises are able to promote adaptations in the muscle-tendon unit (MTU), which can be tested through physiological and biomechanical variables. Identifying the key variables in MTU adaptations is crucial to improvements in training. Objective To perform an exploratory factor analysis (EFA) involving the variables often used to evaluate the response of the MTU to stretching exercises. Method Maximum joint range of motion (ROMMAX), ROM at first sensation of stretching (FSTROM), peak torque (torqueMAX), passive stiffness, normalized stiffness, passive energy, and normalized energy were investigated in 36 participants during passive knee extension on an isokinetic dynamometer. Stiffness and energy values were normalized by the muscle cross-sectional area and their passive mode assured by monitoring the EMG activity. Results EFA revealed two major factors that explained 89.68% of the total variance: 53.13% was explained by the variables torqueMAX, passive stiffness, normalized stiffness, passive energy, and normalized energy, whereas the remaining 36.55% was explained by the variables ROMMAX and FSTROM. Conclusion This result supports the literature wherein two main hypotheses (mechanical and sensory theories) have been suggested to describe the adaptations of the MTU to stretching exercises. Contrary to some studies, in the present investigation torqueMAX was significantly correlated with the variables of the mechanical theory rather than those of the sensory theory. Therefore, a new approach was proposed to explain the behavior of the torqueMAX during stretching exercises. PMID:27437715

  13. Exploratory factor analysis for differentiating sensory and mechanical variables related to muscle-tendon unit elongation.

    PubMed

    Chagas, Mauro H; Magalhães, Fabrício A; Peixoto, Gustavo H C; Pereira, Beatriz M; Andrade, André G P; Menzel, Hans-Joachim K

    2016-03-22

    Background Stretching exercises are able to promote adaptations in the muscle-tendon unit (MTU), which can be tested through physiological and biomechanical variables. Identifying the key variables in MTU adaptations is crucial to improvements in training. Objective To perform an exploratory factor analysis (EFA) involving the variables often used to evaluate the response of the MTU to stretching exercises. Method Maximum joint range of motion (ROMMAX), ROM at first sensation of stretching (FSTROM), peak torque (torqueMAX), passive stiffness, normalized stiffness, passive energy, and normalized energy were investigated in 36 participants during passive knee extension on an isokinetic dynamometer. Stiffness and energy values were normalized by the muscle cross-sectional area and their passive mode assured by monitoring the EMG activity. Results EFA revealed two major factors that explained 89.68% of the total variance: 53.13% was explained by the variables torqueMAX, passive stiffness, normalized stiffness, passive energy, and normalized energy, whereas the remaining 36.55% was explained by the variables ROMMAX and FSTROM. Conclusion This result supports the literature wherein two main hypotheses (mechanical and sensory theories) have been suggested to describe the adaptations of the MTU to stretching exercises. Contrary to some studies, in the present investigation torqueMAX was significantly correlated with the variables of the mechanical theory rather than those of the sensory theory. Therefore, a new approach was proposed to explain the behavior of the torqueMAX during stretching exercises.

  14. Spatial variability of muscle activity during human walking: the effects of different EMG normalization approaches.

    PubMed

    Cronin, N J; Kumpulainen, S; Joutjärvi, T; Finni, T; Piitulainen, H

    2015-08-06

    Human leg muscles are often activated inhomogeneously, e.g. in standing. This may also occur in complex tasks like walking. Thus, bipolar surface electromyography (sEMG) may not accurately represent whole muscle activity. This study used 64-electrode high-density sEMG (HD-sEMG) to examine spatial variability of lateral gastrocnemius (LG) muscle activity during the stance phase of walking, maximal voluntary contractions (MVCs) and maximal M-waves, and determined the effects of different normalization approaches on spatial and inter-participant variability. Plantar flexion MVC, maximal electrically elicited M-waves and walking at self-selected speed were recorded in eight healthy males aged 24-34. sEMG signals were assessed in four ways: unnormalized, and normalized to MVC, M-wave or peak sEMG during the stance phase of walking. During walking, LG activity varied spatially, and was largest in the distal and lateral regions. Spatial variability fluctuated throughout the stance phase. Normalizing walking EMG signals to the peak value during stance reduced spatial variability within LG on average by 70%, and inter-participant variability by 67%. Normalizing to MVC reduced spatial variability by 17% but increased inter-participant variability by 230%. Normalizing to M-wave produced the greatest spatial variability (45% greater than unnormalized EMG) and increased inter-participant variability by 70%. Unnormalized bipolar LG sEMG may provide misleading results about representative muscle activity in walking due to spatial variability. For the peak value and MVC approaches, different electrode locations likely have minor effects on normalized results, whereas electrode location should be carefully considered when normalizing walking sEMG data to maximal M-waves.

  15. Objective measures of joint stiffness.

    PubMed

    Roberson, L; Giurintano, D J

    1995-01-01

    Objective measures of joint stiffness allow for the evaluation of the effectiveness of treatment modalities. Without this, the effectiveness of therapy is not quantifiable. Presently, joint stiffness can be quantified by either passive range of motion (PROM) measurement or torque range of motion (TqROM) measurement. PROM measurement does not control the force applied, nor does it require that the other joints in the kinematic chain be held fixed. Also, it demonstrates poor interrater reliability. An idealized device melding existing technologies of constant passive motion devices and computerized workstations is proposed to allow for easier measurement of TqROM angles for analysis data for the determination of the effectiveness of treatment modalities.

  16. Cryotherapy induces an increase in muscle stiffness.

    PubMed

    Point, Maxime; Guilhem, Gaël; Hug, François; Nordez, Antoine; Frey, Alain; Lacourpaille, Lilian

    2017-03-06

    Although cold application (i.e., cryotherapy) may be useful to treat sports injuries and to prevent muscle damage, it is unclear whether it has adverse effects on muscle mechanical properties. This study aimed to determine the effect of air-pulsed cryotherapy on muscle stiffness estimated using ultrasound shear wave elastography. Myoelectrical activity, ankle passive torque, shear modulus (an index of stiffness) and muscle temperature of the gastrocnemius medialis were measured before, during an air-pulsed cryotherapy (-30°) treatment of 4 sets of 4 minutes with 1 min recovery in between, and during a 40-min post-cryotherapy period. Muscle temperature significantly decreased after the second set of treatment (10 min: 32.3 ± 2.5°C; P < 0.001), peaked at 29 min (27.9 ± 2.2°C; P < 0.001) and remained below baseline values at 60 minutes (29.5 ± 2.0°C; P < 0.001). Shear modulus increased by +11.5 ± 11.8% after the second set (10 min; P = 0.011), peaked at 30 min (+34.7 ± 42.6%; P < 0.001) and remained elevated until the end of the post-treatment period (+25.4 ± 17.1%; P < 0.001). These findings provide evidence that cryotherapy induces an increase in muscle stiffness. This acute change in muscle mechanical properties may lower the amount of stretch that the muscle tissue is able to sustain without subsequent injury. This should be considered when using cryotherapy in athletic practice. This article is protected by copyright. All rights reserved.

  17. Coupled variability in primary sensory areas and the hippocampus during spontaneous activity

    PubMed Central

    de Vasconcelos, Nivaldo A. P.; Soares-Cunha, Carina; Rodrigues, Ana João; Ribeiro, Sidarta; Sousa, Nuno

    2017-01-01

    The cerebral cortex is an anatomically divided and functionally specialized structure. It includes distinct areas, which work on different states over time. The structural features of spiking activity in sensory cortices have been characterized during spontaneous and evoked activity. However, the coordination among cortical and sub-cortical neurons during spontaneous activity across different states remains poorly characterized. We addressed this issue by studying the temporal coupling of spiking variability recorded from primary sensory cortices and hippocampus of anesthetized or freely behaving rats. During spontaneous activity, spiking variability was highly correlated across primary cortical sensory areas at both small and large spatial scales, whereas the cortico-hippocampal correlation was modest. This general pattern of spiking variability was observed under urethane anesthesia, as well as during waking, slow-wave sleep and rapid-eye-movement sleep, and was unchanged by novel stimulation. These results support the notion that primary sensory areas are strongly coupled during spontaneous activity. PMID:28393914

  18. The Long-term Centimeter Variability of Active Galactic Nuclei: A New Relation between Variability Timescale and Accretion Rate

    NASA Astrophysics Data System (ADS)

    Park, Jongho; Trippe, Sascha

    2017-01-01

    We study the long-term (≈ 30 years) radio variability of 43 radio-bright active galactic nuclei (AGNs) by exploiting the database of the University of Michigan Radio Astronomy Observatory monitoring program. We model the periodograms (temporal power spectra) of the observed light curves as simple power-law noise (red noise, spectral power P(f)\\propto {f}-β ) using Monte Carlo simulations, taking into account windowing effects (red-noise leak, aliasing). The power spectra of 39 (out of 43) sources are in good agreement with the models, yielding a range in power spectral index (β) from ≈1 to ≈3. We fit a Gaussian function to each flare in a given light curve to obtain the flare duration. We discover a correlation between β and the median duration of the flares. We use the derivative of a light curve to obtain a characteristic variability timescale, which does not depend on the assumed functional form of the flares, incomplete fitting, and so on. We find that, once the effects of relativistic Doppler boosting are corrected for, the variability timescales of our sources are proportional to the accretion rate to the power of 0.25 ± 0.03 over five orders of magnitude in accretion rate, regardless of source type. We further find that modeling the periodograms of four of our sources requires the assumption of broken power-law spectra. From simulating light curves as superpositions of exponential flares, we conclude that strong overlap of flares leads to featureless simple power-law periodograms of AGNs at radio wavelengths in most cases. Based on observations obtained by the University of Michigan Radio Astronomy Observatory (UMRAO).

  19. Rapid X-Ray Variability of Active Galaxies. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Tennant, A. F., Jr.

    1983-01-01

    Active galactic nuclei are luminous sources of X-rays. The thesis that the X-rays are generated within 10 gravitational radii from the central object is tested. A very sensitive search for rapid ( 1 day) X-ray variability from active galaxies was made.

  20. Physical activity, functional capacity, and step variability during walking in people with lower-limb amputation.

    PubMed

    Lin, Suh-Jen; Winston, Katie D; Mitchell, Jill; Girlinghouse, Jacob; Crochet, Karleigh

    2014-01-01

    Physical activity is important for general health. For an individual with amputation to sustain physical activity, certain functional capacity might be needed. Gait variability is related to the incidence of falls. This study explored the relationship between physical activity and a few common performance measures (six-minute walk test, step length variability, step width variability, and comfortable walking speed) in individuals with unilateral lower-limb amputation. Twenty individuals completed the study (age: 50±11yrs). Twelve of them had transtibial amputation, seven had transfemoral amputation, and one had through-knee amputation. Gait data was collected by the GaitRite instrumented walkway while participants performed a 3-min comfortable walking trial followed by a six-minute walk test. Physical activity was indicated by the mean of 7-day step counts via a pedometer. Gait variability was calculated by the coefficient of variation. Pearson correlation analysis was conducted between physical activity level and the 4 performance measures. Significance level was set at 0.05. Physical activity correlates strongly to comfortable walking speed (r=0.76), six-minute walk distance (r=0.67), and correlates fairly to step width variability (r=0.44). On the contrary, physical activity is inversely related to step length variability of the prosthetic leg (r=-0.46) and of the sound leg (r=-0.47). Having better functional capacity and lateral stability might enable an individual with lower-limb amputation to engage in a higher physical activity level, or vise versa. However, our conclusions are only preliminary as limited by the small sample size.

  1. Variables associated with upper extremity function in patients with Duchenne muscular dystrophy.

    PubMed

    Janssen, Mariska M H P; Hendriks, Jan C M; Geurts, Alexander C H; de Groot, Imelda J M

    2016-09-01

    Preserving upper extremity (UE) function in patients with Duchenne muscular dystrophy (DMD) is extremely important as it is related to independence and quality of life. For clinical decision making, knowledge of variables associated with UE function is necessary. This knowledge is, however, limited. Therefore, this study aims to gain more insight into the variables associated with UE function in DMD. Data from an international web-based questionnaire on UE function, obtained from 213 DMD patients, were used. Six dependent variables regarding UE function were used in multivariable linear regression analyses. In addition, 26 independent variables regarding patient characteristics, medication, therapy, supportive aids, pain, stiffness and participation were used. Twelve independent variables showed a significant relation to UE function. Variables with a negative relation to UE function were: later disease stage, occurrence of scoliosis, higher age, use of UE splints, more frequent stiffness complaints, more limitations due to stiffness, more frequent elbow pain, and having physical therapy. A positive relation with UE function was seen for going to school or work, use of corticosteroids, higher BMI, and higher age at diagnosis. These variables explained 56-81 % of the variation of the different measures of UE function. Knowledge of variables associated with UE function is very important in the clinical management of DMD patients. The results of this study suggest that corticosteroid use and participation in school and work related activities are positively related to UE function in DMD patients, as well as reducing pain and stiffness and preventing scoliosis.

  2. The solar magnetic activity band interaction and instabilities that shape quasi-periodic variability

    PubMed Central

    McIntosh, Scott W.; Leamon, Robert J.; Krista, Larisza D.; Title, Alan M.; Hudson, Hugh S.; Riley, Pete; Harder, Jerald W.; Kopp, Greg; Snow, Martin; Woods, Thomas N.; Kasper, Justin C.; Stevens, Michael L.; Ulrich, Roger K.

    2015-01-01

    Solar magnetism displays a host of variational timescales of which the enigmatic 11-year sunspot cycle is most prominent. Recent work has demonstrated that the sunspot cycle can be explained in terms of the intra- and extra-hemispheric interaction between the overlapping activity bands of the 22-year magnetic polarity cycle. Those activity bands appear to be driven by the rotation of the Sun's deep interior. Here we deduce that activity band interaction can qualitatively explain the ‘Gnevyshev Gap'—a well-established feature of flare and sunspot occurrence. Strong quasi-annual variability in the number of flares, coronal mass ejections, the radiative and particulate environment of the heliosphere is also observed. We infer that this secondary variability is driven by surges of magnetism from the activity bands. Understanding the formation, interaction and instability of these activity bands will considerably improve forecast capability in space weather and solar activity over a range of timescales. PMID:25849045

  3. The solar magnetic activity band interaction and instabilities that shape quasi-periodic variability.

    PubMed

    McIntosh, Scott W; Leamon, Robert J; Krista, Larisza D; Title, Alan M; Hudson, Hugh S; Riley, Pete; Harder, Jerald W; Kopp, Greg; Snow, Martin; Woods, Thomas N; Kasper, Justin C; Stevens, Michael L; Ulrich, Roger K

    2015-04-07

    Solar magnetism displays a host of variational timescales of which the enigmatic 11-year sunspot cycle is most prominent. Recent work has demonstrated that the sunspot cycle can be explained in terms of the intra- and extra-hemispheric interaction between the overlapping activity bands of the 22-year magnetic polarity cycle. Those activity bands appear to be driven by the rotation of the Sun's deep interior. Here we deduce that activity band interaction can qualitatively explain the 'Gnevyshev Gap'—a well-established feature of flare and sunspot occurrence. Strong quasi-annual variability in the number of flares, coronal mass ejections, the radiative and particulate environment of the heliosphere is also observed. We infer that this secondary variability is driven by surges of magnetism from the activity bands. Understanding the formation, interaction and instability of these activity bands will considerably improve forecast capability in space weather and solar activity over a range of timescales.

  4. Long-term X-Ray Variability of Typical Active Galactic Nuclei in the Distant Universe

    NASA Astrophysics Data System (ADS)

    Yang, G.; Brandt, W. N.; Luo, B.; Xue, Y. Q.; Bauer, F. E.; Sun, M. Y.; Kim, S.; Schulze, S.; Zheng, X. C.; Paolillo, M.; Shemmer, O.; Liu, T.; Schneider, D. P.; Vignali, C.; Vito, F.; Wang, J.-X.

    2016-11-01

    We perform long-term (≈15 years, observed-frame) X-ray variability analyses of the 68 brightest radio-quiet active galactic nuclei (AGNs) in the 6 Ms Chandra Deep Field-South survey; the majority are in the redshift range of 0.6-3.1, providing access to penetrating rest-frame X-rays up to ≈10-30 keV. Of the 68 sources, 24 are optical spectral type I AGNs, and the rest (44) are type II AGNs. The timescales probed in this work are among the longest for X-ray variability studies of distant AGNs. Photometric analyses reveal widespread photon flux variability: 90% of AGNs are variable above a 95% confidence level, including many X-ray obscured AGNs and several optically classified type II quasars. We characterize the intrinsic X-ray luminosity ({L}{{X}}) and absorption ({N}{{H}}) variability via spectral fitting. Most (74%) sources show {L}{{X}} variability; the variability amplitudes are generally smaller for quasars. A Compton-thick candidate AGN shows variability of its high-energy X-ray flux, indicating the size of reflecting material to be ≲0.3 pc. {L}{{X}} variability is also detected in a broad absorption line quasar. The {N}{{H}} variability amplitude for our sample appears to rise as time separation increases. About 16% of sources show {N}{{H}} variability. One source transitions from an X-ray unobscured to obscured state, while its optical classification remains type I; this behavior indicates the X-ray eclipsing material is not large enough to obscure the whole broad-line region.

  5. 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

  6. Effects of reaction time variability and age on brain activity during Stroop task performance.

    PubMed

    Tam, Angela; Luedke, Angela C; Walsh, Jeremy J; Fernandez-Ruiz, Juan; Garcia, Angeles

    2015-09-01

    Variability in reaction time during task performance may reflect fluctuations in attention and cause reduced performance in goal-directed tasks, yet it is unclear whether the mechanisms behind this phenomenon change with age. Using fMRI, we tested young and cognitively healthy older adults with the Stroop task to determine whether aging affects the neural mechanisms underlying intra-individual reaction time variability. We found significant between-group differences in BOLD activity modulated by reaction time. In older adults, longer reaction times were associated with greater activity in frontoparietal attentional areas, while in younger adults longer reaction times were associated with greater activity in default mode network areas. Our results suggest that the neural correlates of reaction time variability change with healthy aging, reinforcing the concept of functional plasticity to maintain high cognitive function throughout the lifespan.

  7. Experimental stiffness of tapered bore seals

    NASA Technical Reports Server (NTRS)

    Fleming, D. P.

    1985-01-01

    The stiffness of tapered-bore ring seals was measured with air as the sealed fluid. Static stiffness agreed fairly well with results of a previous analysis. Cross-coupled stiffness due to shaft rotation was much less than predicted. It is suggested that part of the disparity may be due to simplifying assumptions in the analysis; however, these do not appear to account for the entire difference observed.

  8. Chromospherically active stars. II - HD 82558, a young single BY Draconis variable

    NASA Technical Reports Server (NTRS)

    Fekel, Francis C.; Bopp, Bernard W.; Africano, John L.; Goodrich, Bret D.; Palmer, Leigh Hunter

    1986-01-01

    It is presently noted that the HD 82558 chromospherically active star is a young and rapidly rotating K2 V single BY Draconis variable with very strong far-UV emission features and an H-alpha line filled to the continuum level by emission. HD 82558 has constant velocity and is not a member of the Hyades Supercluster. Its light curve behavior, which appears to have been stable for several hundred rotation cycles, is reminiscent of that of the young, rapidly rotating, single K V variable H II 1883 in the Pleiades; this stability may be characteristic of young, single, chromospherically active stars.

  9. Crumpling of a Stiff Tethered Membrane

    NASA Astrophysics Data System (ADS)

    Åström, J. A.; Timonen, J.; Karttunen, Mikko

    2004-12-01

    A first-principles numerical model for crumpling of a stiff tethered membrane is introduced. This model displays wrinkles, ridge formation, ridge collapse, and initiation of stiffness divergence. The amplitude and wavelength of the wrinkles and the scaling exponent of the stiffness divergence are consistent with both theory and experiment. Close to the stiffness divergence further buckling is hindered by the nonzero thickness of the membrane, and its elastic behavior becomes similar to that of dry granular media. No change in the distribution of contact forces can be observed at the crossover, implying that the network of ridges is then simultaneously a granular force-chain network.

  10. Ensemble spectral variability study of Active Galactic Nuclei from the XMM-Newton serendipitous source catalogue

    NASA Astrophysics Data System (ADS)

    Serafinelli, R.; Vagnetti, F.; Middei, R.

    2016-02-01

    The variability of the X-Ray spectra of active galactic nuclei (AGN) usually includes a change of the spectral slope. This has been investigated for a small sample of local AGNs by Sobolewska and Papadakis [1], who found that slope variations are well correlated with flux variations, and that the spectra are typically steeper in the bright phase (softer when brighter behaviour). Not much information is available for the spectral variability of high-luminosity AGNs and quasars. In order to investigate this phenomenon, we use data from the XMM-Newton Serendipitous Source Catalogue, Data Release 5, which contains X- Ray observations for a large number of active galactic nuclei in a wide luminosity and redshift range, for several different epochs. This allows to perform an ensemble analysis of the spectral variability for a large sample of quasars. We quantify the spectral variability through the spectral variability parameter β, defined by Trevese and Vagnetti [2] as the ratio between the change in spectral slope and the corresponding logarithmic flux variation. We find that the spectral variability of quasars has a softer when brighter behaviour, similarly to local AGNs.

  11. The Role of the Autonomic Nervous System in the Regulation of Aortic Stiffness

    PubMed Central

    Barrett, Sharon M.L.; Evans, Sarah V.; Cheriyan, Joseph; McEniery, Carmel M.; Wilkinson, Ian B.

    2016-01-01

    The autonomic nervous system is important in regulating blood pressure, but whether it regulates aortic stiffness is more contentious. We conducted 3 studies in young, healthy individuals to address this important question. Study 1 was a cross-sectional study of 347 subjects with detailed measurements of hemodynamics and heart rate variability. In study 2, 9 subjects were given a bolus of intravenous nicotinic ganglion blocker, pentolinium, or saline in a random order and hemodynamics and heart rate variability were assessed before and after. In study 3, changes in hemodynamics and heart rate variability were assessed during stimulation of the sympathetic nervous system with the use of isometric handgrip exercise in 12 subjects. Study 1: aortic pulse wave velocity (P=0.003) was lowest in the subjects with the highest parasympathetic activity, but after adjusting for mean arterial pressure, the effect was abolished (P=0.3). Study 2: after pentolinium, sympathetic and parasympathetic activity fell (P=0.001 for both), mean arterial pressure, and heart rate increased (P=0.004 and P=0.04, respectively), but there was no change in pulse wave velocity in comparison to placebo (P=0.1). Study 3: during handgrip exercise, sympathetic activity (P=0.003), mean arterial pressure (P<0.0001), and aortic pulse wave velocity increased (P=0.013). However, pulse wave velocity adjusted for mean arterial pressure did not change (P=0.1). The main finding of these studies is that in young healthy subjects, the autonomic nervous system does not have a pressure-independent role in the regulation of aortic stiffness. However, these findings may not apply to patients with increased sympathetic tone or hypertension. PMID:27672029

  12. Chromospheric activity in Delta Scuti stars - The suspected variable Tau Cygni

    NASA Technical Reports Server (NTRS)

    Fracassini, M.; Pasinetti Fracassini, L. E.; Mariani, A.; Pastori, L.; Teays, T. J.

    1991-01-01

    High-resolution IUE spectra of the suspected variable Tau Cyg were obtained to search for a possible variability of the Mg II h, k double-peaked emission. The observations, spanning an interval of about 6.3 h, have shown flux excursions within or just near 15 percent, a value suggested as the detection limit of actual variations with IUE spectra. A variability, difficult to explain, could be present in the ratios Fk2v/Fk2r. The emission fluxes seem to be higher than those of the Delta Scuti variables Rho Pup and Beta Cas. This comparison could give some insights on the possible role of the convection on the pulsational and chromospheric activities of Tau Cyg. A positive correlation between the total emission fluxes and the rotational velocities of these stars was found.

  13. Modifiable risk factors for increased arterial stiffness in outpatient nephrology.

    PubMed

    Elewa, Usama; Fernandez-Fernandez, Beatriz; Alegre, Raquel; Sanchez-Niño, Maria D; Mahillo-Fernández, Ignacio; Perez-Gomez, Maria Vanessa; El-Fishawy, Hussein; Belal, Dawlat; Ortiz, Alberto

    2015-01-01

    Arterial stiffness, as measured by pulse wave velocity (PWV), is an independent predictor of cardiovascular events and mortality. Arterial stiffness increases with age. However, modifiable risk factors such as smoking, BP and salt intake also impact on PWV. The finding of modifiable risk factors may lead to the identification of treatable factors, and, thus, is of interest to practicing nephrologist. We have now studied the prevalence and correlates of arterial stiffness, assessed by PWV, in 191 patients from nephrology outpatient clinics in order to identify modifiable risk factors for arterial stiffness that may in the future guide therapeutic decision-making. PWV was above normal levels for age in 85/191 (44.5%) patients. Multivariate analysis showed that advanced age, systolic BP, diabetes mellitus, serum uric acid and calcium polystyrene sulfonate therapy or calcium-containing medication were independent predictors of PWV. A new parameter, Delta above upper limit of normal PWV (Delta PWV) was defined to decrease the weight of age on PWV values. Delta PWV was calculated as (measured PWV) - (upper limit of the age-adjusted PWV values for the general population). Mean±SD Delta PWV was 0.76±1.60 m/sec. In multivariate analysis, systolic blood pressure, active smoking and calcium polystyrene sulfonate therapy remained independent predictors of higher delta PWV, while age, urinary potassium and beta blocker therapy were independent predictors of lower delta PWV. In conclusion, arterial stiffness was frequent in nephrology outpatients. Systolic blood pressure, smoking, serum uric acid, calcium-containing medications, potassium metabolism and non-use of beta blockers are modifiable factors associated with increased arterial stiffness in Nephrology outpatients.

  14. The discrete and localized nature of the variable emission from active regions

    NASA Technical Reports Server (NTRS)

    Arndt, Martina Belz; Habbal, Shadia Rifai; Karovska, Margarita

    1994-01-01

    Using data from the Extreme Ultraviolet (EUV) Spectroheliometer on Skylab, we study the empirical characteristics of the variable emission in active regions. These simultaneous multi-wavelength observations clearly confirm that active regions consist of a complex of loops at different temperatures. The variable emission from this complex has very well-defined properties that can be quantitatively summarized as follows: (1) It is localized predominantly around the footpoints where it occurs at discrete locations. (2) The strongest variability does not necessarily coincide with the most intense emission. (3) The fraction of the area of the footpoints, (delta n)/N, that exhibits variable emission, varies by +/- 15% as a function of time, at any of the wavelengths measured. It also varies very little from footpoint to footpoint. (4) This fractional variation is temperature dependent with a maximum around 10(exp 5) K. (5) The ratio of the intensity of the variable to the average background emission, (delta I)/(bar-I), also changes with temperature. In addition, we find that these distinctive characteristics persist even when flares occur within the active region.

  15. Tropical temperature variability and Kelvin-wave activity in the UTLS from GPS RO measurements

    NASA Astrophysics Data System (ADS)

    Scherllin-Pirscher, Barbara; Randel, William J.; Kim, Joowan

    2017-01-01

    Tropical temperature variability over 10-30 km and associated Kelvin-wave activity are investigated using GPS radio occultation (RO) data from January 2002 to December 2014. RO data are a powerful tool for quantifying tropical temperature oscillations with short vertical wavelengths due to their high vertical resolution and high accuracy and precision. Gridded temperatures from GPS RO show the strongest variability in the tropical tropopause region (on average 3 K2). Large-scale zonal variability is dominated by transient sub-seasonal waves (2 K2), and about half of sub-seasonal variance is explained by eastward-traveling Kelvin waves with periods of 4 to 30 days (1 K2). Quasi-stationary waves associated with the annual cycle and interannual variability contribute about a third (1 K2) to total resolved zonal variance. Sub-seasonal waves, including Kelvin waves, are highly transient in time. Above 20 km, Kelvin waves are strongly modulated by the quasi-biennial oscillation (QBO) in stratospheric zonal winds, with enhanced wave activity during the westerly shear phase of the QBO. In the tropical tropopause region, however, peaks of Kelvin-wave activity are irregularly distributed in time. Several peaks coincide with maxima of zonal variance in tropospheric deep convection, but other episodes are not evidently related. Further investigations of convective forcing and atmospheric background conditions are needed to better understand variability near the tropopause.

  16. Match-to-match variability of high-speed activities in premier league soccer.

    PubMed

    Gregson, W; Drust, B; Atkinson, G; Salvo, V D

    2010-04-01

    The aim of the present investigation was to determine the between-match variability of high-speed running activities completed by a large sample of elite players over an extended period of time. A further aim of the study was to determine the influence of playing position on the magnitude of this variability. Observations on individual match performance measures were undertaken on 485 outfield players (median of 10 games per player; range=2-57) competing in the English Premier League from 2003/2004 to 2005/2006 using a computerised tracking system (Prozone, Leeds, England). High-speed activities selected for analysis included total high-speed running distance (THSR), high-speed running (HSR), total sprint distance (TSD) and the total number of sprints undertaken. Total high-speed running distance in possession and without possession of the ball was also analysed. Match-to-match variability was generally high across all variables with a mean CV of 16.2+/-6.4% (95% CI=15.6-16.7%) and 30.8+/-11.2% (95% CI=29.9-31.7%) reported for HSR and TSD covered during a game. This variability was generally higher for central players (midfielders and defenders) and lower for wide midfielders and attackers. Greater variability was also noted when the team were in possession of the ball (approximately 30%) than when they did not have possession (approximately 23%). The findings of the present study indicate that match-to-match variability in performance characteristics of elite soccer players is high. This inherent variability means that research requires large sample sizes in order to detect real systematic changes in performance characteristics.

  17. Cycle-to-cycle variability of neuromuscular activity in Aplysia feeding behavior.

    PubMed

    Horn, Charles C; Zhurov, Yuriy; Orekhova, Irina V; Proekt, Alex; Kupfermann, Irving; Weiss, Klaudiusz R; Brezina, Vladimir

    2004-07-01

    Aplysia consummatory feeding behavior, a rhythmic cycling of biting, swallowing, and rejection movements, is often said to be stereotyped. Yet closer examination shows that cycles of the behavior are very variable. Here we have quantified and analyzed the variability at several complementary levels in the neuromuscular system. In reduced preparations, we recorded the motor programs produced by the central pattern generator, firing of the motor neurons B15 and B16, and contractions of the accessory radula closer (ARC) muscle while repetitive programs were elicited by stimulation of the esophageal nerve. In other similar experiments, we recorded firing of motor neuron B48 and contractions of the radula opener muscle. In intact animals, we implanted electrodes to record nerve or ARC muscle activity while the animals swallowed controlled strips of seaweed or fed freely. In all cases, we found large variability in all parameters examined. Some of this variability reflected systematic, slow, history-dependent changes in the character of the central motor programs. Even when these trends were factored out, however, by focusing only on the differences between successive cycles, considerable variability remained. This variability was apparently random. Nevertheless, it too was the product of central history dependency because regularizing merely the high-level timing of the programs also regularized many of the downstream neuromuscular parameters. Central motor program variability thus appears directly in the behavior. With regard to the production of functional behavior in any one cycle, the large variability may indicate broad tolerances in the operation of the neuromuscular system. Alternatively, some cycles of the behavior may be dysfunctional. Overall, the variability may be part of an optimal strategy of trial, error, and stabilization that the CNS adopts in an uncertain environment.

  18. Sources and magnitude of variability in pedometer-determined physical activity levels of youth

    PubMed Central

    Kim, So-Yeun; Park, Hye-Sang

    2015-01-01

    This study examined sources of variability in habitual physical activity of children, and the minimum number of days required for estimating children’s habitual physical activity levels using pedometers. A total of 31 children wore two pedometers during five weekdays and four weekend days. A two random facet completely crossed design was conducted with two-way analysis of variances across weekdays, weekends, and weekdays and weekend days combined. Moderate/high generalizability coefficients were estimated across all days. Primary sources of variability were variance components of the person and person by day interaction. Minimum numbers of days required for estimating habitual physical activity levels using a pedometer were five during weekdays. However, estimating habitual physical activity levels during weekends, and weekdays and weekend days combined was impractical. PMID:26730388

  19. Modes of hurricane activity variability in the eastern Pacific: Implications for the 2016 season

    NASA Astrophysics Data System (ADS)

    Boucharel, Julien; Jin, Fei-Fei; England, Matthew H.; Lin, I. I.

    2016-11-01

    A gridded product of accumulated cyclone energy (ACE) in the eastern Pacific is constructed to assess the dominant mode of tropical cyclone (TC) activity variability. Results of an empirical orthogonal function decomposition and regression analysis of environmental variables indicate that the two dominant modes of ACE variability (40% of the total variance) are related to different flavors of the El Niño-Southern Oscillation (ENSO). The first mode, more active during the later part of the hurricane season (September-November), is linked to the eastern Pacific El Niño through the delayed oceanic control associated with the recharge-discharge mechanism. The second mode, dominant in the early months of the hurricane season, is related to the central Pacific El Niño mode and the associated changes in atmospheric variability. A multilinear regression forecast model of the dominant principal components of ACE variability is then constructed. The wintertime subsurface state of the eastern equatorial Pacific (characterizing ENSO heat discharge), the east-west tilt of the thermocline (describing ENSO phase transition), the anomalous ocean surface conditions in the TC region in spring (portraying atmospheric changes induced by persistence of local surface anomalies), and the intraseasonal atmospheric variability in the western Pacific are found to be good predictors of TC activity. Results complement NOAA's official forecast by providing additional spatial and temporal information. They indicate a more active 2016 season ( 2 times the ACE mean) with a spatial expansion into the central Pacific associated with the heat discharge from the 2015/2016 El Niño.

  20. The Main Sources of Intersubject Variability in Neuronal Activation for Reading Aloud

    ERIC Educational Resources Information Center

    Kherif, Ferath; Josse, Goulven; Seghier, Mohamed L.; Price, Cathy J.

    2009-01-01

    The aim of this study was to find the most prominent source of intersubject variability in neuronal activation for reading familiar words aloud. To this end, we collected functional imaging data from a large sample of subjects (n = 76) with different demographic characteristics such as handedness, sex, and age, while reading. The…

  1. Leg stiffness during phases of countermovement and take-off in vertical jump.

    PubMed

    Struzik, Artur; Zawadzki, Jerzy

    2013-01-01

    With respect to cyclic movements such as human gait, running or hopping, leg stiffness is a little variable parameter. The aim of this study was to investigate changes in leg stiffness during the phase of countermovement and take-off when performing a single maximum counter-movement jump. Kistler force plates and a BTS SMART system for comprehensive motion analysis were employed in the study. The study covered a group of 12 athletes from university basketball teams. Leg stiffness was calculated in those parts of countermovement and take-off phases where its level is relatively constant and the relationship F(Δl) is similar to linear one. Mean total stiffness (±SD) in both legs in the countermovement phase amounted to 6.5 ± 1.5 kN/m, whereas during the take-off phase this value was 6.9 ± 1 kN/m. No statistically significant differences were found between leg stiffness during the countermovement phase and takeoff phase in the study group at the level of significance set at α = 0.05. This suggests that the leg stiffness in phase of countermovement and phase of take-off are much similar to each other, despite different function of both phases. Similar to cyclic movements, leg stiffness turned out relatively constant when performing a single vertical jump. There are also reported statistically significant correlations between body mass, body height, length of lower limbs and leg stiffness. The stiffness analysed by the authors should be understood as quasi-stiffness because the measurements of ΔF(Δl) were made during transient states where inertia and dumping forces are likely to affect the final result.

  2. Cerebral Small Vessel Disease and Arterial Stiffness: Tsunami Effect in the Brain?

    PubMed Central

    Saji, Naoki; Toba, Kenji; Sakurai, Takashi

    2016-01-01

    Background Cerebral small vessel diseases, including silent lacunar infarcts, white matter hyperintensities, and microbleeds, pose a risk for cerebrovascular disease, cognitive impairment, and the geriatric syndrome via effects on arterial stiffness. However, the vascular, physiological, and metabolic roles of arterial stiffness in cerebral small vessel diseases remain unclear. Summary Arterial stiffness can be assessed using various indicators such as the ankle-brachial index, pulse wave velocity, cardio-ankle vascular index, and augmentation index. Arterial stiffness is independently associated with all components of cerebral small vessel disease including silent lacunar infarcts, white matter hyperintensities, and microbleeds, although there are some methodological differences between the various surrogate markers. Evidence of arterial stiffness indicates microvessel arteriosclerosis presenting with vascular endothelial dysfunction. Further, vascular narrowing due to atherosclerosis and vascular stiffness due to lipohyalinosis can accelerate the pulse waves. This hemodynamic stress, pulsatile pressure, or blood pressure variability can cause a ‘tsunami effect’ towards the cerebral parenchyma and lead to cerebral small vessel disease. Previous studies have shown that silent lacunar infarcts and white matter hyperintensities are strongly associated with arterial stiffness. However, the association between microbleeds and arterial stiffness remains controversial, as there are two vessel mechanisms related to microbleeds: cerebral amyloid angiopathy and hypertensive small vessel disease. Key Messages Cerebral small vessel disease with associated arterial stiffness is a risk factor for silent cerebral lesions, stroke, and cognitive impairment. Improvement of the living environment, management of risk factors, and innovation and development of novel drugs that improve arterial stiffness may suppress the progression of cerebral small vessel disease, and may reduce

  3. 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…

  4. Stiff person syndrome: a case report.

    PubMed

    Kelly, Patricia A; Kuberski, Carolyn

    2014-08-01

    The case report features a patient who had a diagnosis of a common type of breast cancer with an uncommon neurologic syndrome. She had extreme pain and progressive stiffness with cognitive and functional decline. This article includes the pathogenesis and treatment options for a rare, but treatable, autoimmune disorder of malignancy called stiff person syndrome.

  5. Match-to-match variability in high-speed running activity in a professional soccer team.

    PubMed

    Carling, Christopher; Bradley, Paul; McCall, Alan; Dupont, Gregory

    2016-12-01

    This study investigated variability in competitive high-speed running performance in an elite soccer team. A semi-automated tracking system quantified running performance in 12 players over a season (median 17 matches per player, 207 observations). Variability [coefficient of variation (CV)] was compared for total sprint distance (TSD, >25.2 km/h), high-speed running (HSR, 19.8-25.2 km/h), total high-speed running (THSR, ≥19.8 km/h); THSR when the team was in and out of ball possession, in individual ball possession, in the peak 5 min activity period; and distance run according to individual maximal aerobic speed (MAS). Variability for % declines in THSR and distance covered at ≥80% MAS across halves, at the end of play (final 15 min vs. mean for all 15 min periods) and transiently (5 min period following peak 5 min activity period), was analysed. Collectively, variability was higher for TSD versus HSR and THSR and lowest for distance run at ≥80% MAS (CVs: 37.1%, 18.1%, 19.8% and 11.8%). THSR CVs when the team was in/out of ball possession, in individual ball possession and during the peak 5 min period were 31.5%, 26.1%, 60.1% and 23.9%. Variability in THSR declines across halves, at the end of play and transiently, ranged from 37.1% to 142.6%, while lower CVs were observed in these metrics for running at ≥80% MAS (20.9-53.3%).These results cast doubt on the appropriateness of general measures of high-speed activity for determining variability in an elite soccer team, although individualisation of HSR thresholds according to fitness characteristics might provide more stable indicators of running performance and fatigue occurrence.

  6. Paired changes in electromechanical delay and musculo-tendinous stiffness after endurance or plyometric training.

    PubMed

    Grosset, Jean-Francois; Piscione, Julien; Lambertz, Daniel; Pérot, Chantal

    2009-01-01

    When measured in vivo electromechanical delay (EMD) depends mainly on the elastic properties of the muscle-tendon unit. Recent studies have shown changes in stiffness of the triceps surae (TS) following a period of training. To confirm the influence of musculo-tendinous stiffness on EMD, this study investigates paired changes in these two parameters after a training period. Two types of training known to induce opposite changes in stiffness were analysed. EMD and musculo-tendinous stiffness were measured on adult subjects before and after 10 weeks of endurance (n = 21) or plyometric (n = 9) trainings. EMD was defined as the time lag between the TS M-wave latency and the onset of muscle twitch evoked at rest by supramaximal electrical stimulations of the posterior tibial nerve. Quick release tests were used to evaluate the musculo-tendinous stiffness of the ankle plantar flexors. The stiffness index was defined as the slope of the relationship between angular stiffness and external torque values. Endurance training, known to preferentially activate the slow, stiffer muscle fibers, leads to a decrease in EMD and to an increase in stiffness index. Following plyometric training, which specifically recruits fast, more compliant fibers, EMD and the stiffness index exhibited adaptations directionally opposite to those seen with endurance training. When pooling the data for the two subject groups, a correlation was found between changes in EMD and changes in musculo-tendinous stiffness indexes. Thus, changes in EMD values are proposed to indirectly link to changes in musculo-tendinous stiffness for subjects involved in muscle training.

  7. Combining Dynamic Stretch and Tunable Stiffness to Probe Cell Mechanobiology In Vitro

    PubMed Central

    Throm Quinlan, Angela M.; Sierad, Leslie N.; Capulli, Andrew K.; Firstenberg, Laura E.; Billiar, Kristen L.

    2011-01-01

    Cells have the ability to actively sense their mechanical environment and respond to both substrate stiffness and stretch by altering their adhesion, proliferation, locomotion, morphology, and synthetic profile. In order to elucidate the interrelated effects of different mechanical stimuli on cell phenotype in vitro, we have developed a method for culturing mammalian cells in a two-dimensional environment at a wide range of combined levels of substrate stiffness and dynamic stretch. Polyacrylamide gels were covalently bonded to flexible silicone culture plates and coated with monomeric collagen for cell adhesion. Substrate stiffness was adjusted from relatively soft (G′ = 0.3 kPa) to stiff (G′ = 50 kPa) by altering the ratio of acrylamide to bis-acrylamide, and the silicone membranes were stretched over circular loading posts by applying vacuum pressure to impart near-uniform stretch, as confirmed by strain field analysis. As a demonstration of the system, porcine aortic valve interstitial cells (VIC) and human mesenchymal stem cells (hMSC) were plated on soft and stiff substrates either statically cultured or exposed to 10% equibiaxial or pure uniaxial stretch at 1Hz for 6 hours. In all cases, cell attachment and cell viability were high. On soft substrates, VICs cultured statically exhibit a small rounded morphology, significantly smaller than on stiff substrates (p<0.05). Following equibiaxial cyclic stretch, VICs spread to the extent of cells cultured on stiff substrates, but did not reorient in response to uniaxial stretch to the extent of cells stretched on stiff substrates. hMSCs exhibited a less pronounced response than VICs, likely due to a lower stiffness threshold for spreading on static gels. These preliminary data demonstrate that inhibition of spreading due to a lack of matrix stiffness surrounding a cell may be overcome by externally applied stretch suggesting similar mechanotransduction mechanisms for sensing stiffness and stretch. PMID

  8. Stiffness Control of Surgical Continuum Manipulators

    PubMed Central

    Mahvash, Mohsen; Dupont, Pierre E.

    2013-01-01

    This paper introduces the first stiffness controller for continuum robots. The control law is based on an accurate approximation of a continuum robot’s coupled kinematic and static force model. To implement a desired tip stiffness, the controller drives the actuators to positions corresponding to a deflected robot configuration that produces the required tip force for the measured tip position. This approach provides several important advantages. First, it enables the use of robot deflection sensing as a means to both sense and control tip forces. Second, it enables stiffness control to be implemented by modification of existing continuum robot position controllers. The proposed controller is demonstrated experimentally in the context of a concentric tube robot. Results show that the stiffness controller achieves the desired stiffness in steady state, provides good dynamic performance, and exhibits stability during contact transitions. PMID:24273466

  9. Stiffness Control of Surgical Continuum Manipulators.

    PubMed

    Mahvash, Mohsen; Dupont, Pierre E

    2011-04-01

    This paper introduces the first stiffness controller for continuum robots. The control law is based on an accurate approximation of a continuum robot's coupled kinematic and static force model. To implement a desired tip stiffness, the controller drives the actuators to positions corresponding to a deflected robot configuration that produces the required tip force for the measured tip position. This approach provides several important advantages. First, it enables the use of robot deflection sensing as a means to both sense and control tip forces. Second, it enables stiffness control to be implemented by modification of existing continuum robot position controllers. The proposed controller is demonstrated experimentally in the context of a concentric tube robot. Results show that the stiffness controller achieves the desired stiffness in steady state, provides good dynamic performance, and exhibits stability during contact transitions.

  10. 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.

  11. Effects of repeated Achilles tendon vibration on triceps surae stiffness and reflex excitability.

    PubMed

    Lapole, Thomas; Pérot, Chantal

    2011-02-01

    Clinical studies frequently report an increase in stiffness and a loss of range of motion at joints placed in disuse or immobilization. This is notably the case for subjects maintained in bed for a long period, whilst their joints are not affected. Recently we documented on healthy subjects the benefit in terms of force and activation capacities of the triceps surae offered by vibrations applied to the Achilles tendon. Knowing that stiffness changes may contribute to force changes, the aim of the present study was to investigate the effects of tendon vibration on the triceps surae stiffness of healthy subjects. The vibration program consisted in 14 days of 1h daily Achilles tendon vibration applied at rest. Nineteen healthy students were involved in this study. Before and at the end of the vibration program, musculo-tendinous stiffness in active conditions was determined by use of a quick-release test. Passive stiffness was also analyzed by a flexibility test: passive torque-angle relationships were established from maximal plantar-flexion to maximal dorsiflexion. Passive stiffness indexes at 10°, 15° and 20° dorsiflexion were defined as the slope of the relationships at the corresponding angle. Tendinous reflex, influenced by stiffness values, was also investigated as well as the H reflex to obtain an index of the central reflex excitability. After the program, musculo-tendinous stiffness was significantly decreased (p=.01). At the same time, maximal passive dorsiflexion was increased (p=.005) and passive stiffness indexes at 10°, 15° and 20° dorsiflexion decreased (p<.001; p<.001 and p=.011, respectively). Tendinous reflex also significantly decreased. As the triceps surae parameters are diminished after the vibration program, it could be beneficial to immobilized persons as hypo-activity is known to increase muscular stiffness.

  12. Intersubject Variability in Fearful Face Processing: The Link Between Behavior and Neural Activation

    PubMed Central

    Doty, Tracy J.; Japee, Shruti; Ingvar, Martin; Ungerleider, Leslie G.

    2014-01-01

    Stimuli that signal threat show considerable variability in the extent to which they enhance behavior, even among healthy individuals. However, the neural underpinning of this behavioral variability is not well understood. By manipulating expectation of threat in an fMRI study of fearful vs. neutral face categorization, we uncovered a network of areas underlying variability in threat processing in healthy adults. We explicitly altered expectation by presenting face images at three different expectation levels: 80%, 50%, and 20%. Subjects were instructed to report as fast and as accurately as possible whether the face was fearful (signaled threat) or not. An uninformative cue preceded each face by 4 seconds (s). By taking the difference between response times (RT) to fearful compared to neutral faces, we quantified an overall fear RT bias (i.e. faster to fearful than neutral faces) for each subject. This bias correlated positively with late trial fMRI activation (8 s after the face) during unexpected fearful face trials in bilateral ventromedial prefrontal cortex, the left subgenual cingulate cortex, and the right caudate nucleus and correlated negatively with early trial fMRI activation (4 s after the cue) during expected neutral face trials in bilateral dorsal striatum and the right ventral striatum. These results demonstrate that the variability in threat processing among healthy adults is reflected not only in behavior but also in the magnitude of activation in medial prefrontal and striatal regions that appear to encode affective value. PMID:24841078

  13. NAO-related Variability in Arctic Storm Activity and its Effect on Cloud Cover

    NASA Astrophysics Data System (ADS)

    Previdi, M.; Veron, D. E.

    2005-12-01

    Variability in Arctic and sub-Arctic storm activity on intraseasonal, interannual and decadal timescales is associated primarily with the North Atlantic Oscillation (NAO). NAO-related changes in storminess affect a wide range of sensible weather, including air temperature, precipitation and wind. We focus on a less often examined climate impact of these storm changes, their effect on cloud cover. The NAO modulation of storminess in the high latitude North Atlantic is studied using composites of regional climate model simulations representative of NAO extremes. The associated changes in cloud cover and their role in producing the mean surface air temperature response to NAO variability are then discussed.

  14. Ensemble X-ray variability of active galactic nuclei at intermediate and long time lags

    NASA Astrophysics Data System (ADS)

    Vagnetti, Fausto; Middei, Riccardo

    2016-08-01

    We present a variability analysis for a sample of 2700 active galactic nuclei extracted from the latest release of the XMM-Newton serendipitous source catalogue. The structure function of this sample increases up to rest-frame time lags of about 5 years. Moreover, comparing observations performed by the XMM-Newton and ROSAT satellites, we are able to extend the X-ray structure function to 20 years rest-frame, showing a further increase of variability without any evidence of a plateau. Our results are compared with similar analyses in the optical band, and discussed in relation to the physical sizes of the emitting regions.

  15. Use of Variable Pressure Suits, Intermittent Recompression and Nitrox Breathing Mixtures during Lunar Extravehicular Activities

    NASA Technical Reports Server (NTRS)

    Gernhardt, Michael L.; Abercromby, Andrew F.

    2009-01-01

    This slide presentation reviews the use of variable pressure suits, intermittent recompression and Nitrox breathing mixtures to allow for multiple short extravehicular activities (EVAs) at different locations in a day. This new operational concept of multiple short EVAs requires short purge times and shorter prebreathes to assure rapid egress with a minimal loss of the vehicular air. Preliminary analysis has begun to evaluate the potential benefits of the intermittent recompression, and Nitrox breathing mixtures when used with variable pressure suits to enable reduce purges and prebreathe durations.

  16. The variability of co-activation pattern of antagonist muscles in human infant crawling.

    PubMed

    Xiong, Qi L; Wu, Xiao Y; Nong Xiao; Zeng, Si Y; Zheng, Xiao L; Di Wu; Hou, Wen S

    2016-08-01

    Infant crawling is part of normal human gross motor development, and a 4-beat gait that involves rhythmical flexion and extension of limbs and the underlying muscle co-activation of antagonist muscle around the joint. However, detection the co-activation pattern of antagonist muscle are sparse due to the general difficulty of measuring locomotion in human infants. In this paper, sEMG of antagonist muscles and the corresponding kinematics data of limbs were collected when infants were crawling on hands and knees at their self-selected speed. The infant's gross motor developmental status was assessed by the global Gross Motor Function Measure Scale (GMFM-88) as well. The method based on EMG-EMG plots was used to quantify the variability of co-activation pattern of antagonist muscle. After that, we observed that antagonist muscles of upper limb (triceps brachii and biceps brachii) showed less variability of co-activation pattern of muscles than lower limb(quadriceps femoris and hamstrings) during crawling, and this variability was also varied in different crawling phases (stance and swing). Furthermore, we found some varied behaviors in the co-activation patterns of antagonist muscles when gross motor developmental level increased. The preliminary work suggests that such adaptive changes may be related to the adjustment of neuromuscular in the early stage of gross motor development.

  17. Timing and Variability of Galactose Metabolic Gene Activation Depend on the Rate of Environmental Change.

    PubMed

    Nguyen-Huu, Truong D; Gupta, Chinmaya; Ma, Bo; Ott, William; Josić, Krešimir; Bennett, Matthew R

    2015-07-01

    Modulation of gene network activity allows cells to respond to changes in environmental conditions. For example, the galactose utilization network in Saccharomyces cerevisiae is activated by the presence of galactose but repressed by glucose. If both sugars are present, the yeast will first metabolize glucose, depleting it from the extracellular environment. Upon depletion of glucose, the genes encoding galactose metabolic proteins will activate. Here, we show that the rate at which glucose levels are depleted determines the timing and variability of galactose gene activation. Paradoxically, we find that Gal1p, an enzyme needed for galactose metabolism, accumulates more quickly if glucose is depleted slowly rather than taken away quickly. Furthermore, the variability of induction times in individual cells depends non-monotonically on the rate of glucose depletion and exhibits a minimum at intermediate depletion rates. Our mathematical modeling suggests that the dynamics of the metabolic transition from glucose to galactose are responsible for the variability in galactose gene activation. These findings demonstrate that environmental dynamics can determine the phenotypic outcome at both the single-cell and population levels.

  18. Interannual variability of tropical cyclone activity and regional Hadley circulation over the Northeastern Pacific

    NASA Astrophysics Data System (ADS)

    Zhang, Gan; Wang, Zhuo

    2015-04-01

    The interannual variability of the regional Hadley circulation (HC) and tropical cyclone (TC) activity over the Northeastern Pacific (NEP) was investigated. The interannual variability of the HC in the NEP hurricane season is found dominated by a mode (M1EP) regulating the strength and meridional extent of the Intertropical Convergence Zone. M1EP has a more robust correlation with NEP TC activity than the El Niño-Southern Oscillation sea surface temperature indices. The strong correlation is attributed to the impacts of M1EP on environmental conditions. In addition, the leading mode of the Atlantic HC, which has an anticorrelation with M1EP, also strongly impacts NEP TC activity. The findings, together with Zhang and Wang (2013), highlight the role of the HC in controlling the variability of TC activity as well as the interbasin connection between the NEP and the Atlantic. The regional HC is thus recommended as a useful metric to benchmark models in simulating TC activity.

  19. A method for accounting for test fixture compliance when estimating proximal femur stiffness.

    PubMed

    Rossman, Timothy; Dragomir-Daescu, Dan

    2016-09-06

    Fracture testing of cadaveric femora to obtain strength and stiffness information is an active area of research in developing tools for diagnostic prediction of bone strength. These measurements are often used in the estimation and validation of companion finite element models constructed from the femora CT scan data, therefore, the accuracy of the data is of paramount importance. However, experimental stiffness calculated from force-displacement data has largely been ignored by most researchers due to inherent error in the differential displacement measurement obtained when not accounting for testing apparatus compliance. However, having such information is necessary for validation of computational models. Even in the few cases when fixture compliance was considered the measurements showed large lab-to-lab variation due to lack of standardization in fixture design. We examined the compliance of our in-house designed cadaveric femur test fixture to determine the errors we could expect when calculating stiffness from the collected experimental force-displacement data and determined the stiffness of the test fixture to be more than 10 times the stiffness of the stiffest femur in a sample of 44 femora. When correcting the apparent femur stiffness derived from the original data, we found that the largest stiffness was underestimated by about 10%. The study confirmed that considering test fixture compliance is a necessary step in improving the accuracy of fracture test data for characterizing femur stiffness, and highlighted the need for test fixture design standardization for proximal femur fracture testing.

  20. Musculotendinous stiffness of triceps surae, maximal rate of force development, and vertical jump performance.

    PubMed

    Driss, Tarak; Lambertz, Daniel; Rouis, Majdi; Jaafar, Hamdi; Vandewalle, Henry

    2015-01-01

    The relationships between ankle plantar flexor musculotendinous stiffness (MTS) and performance in a countermovement vertical jump (CMJ) and maximal rate of torque development (MRTD) were studied in 27 active men. MTS was studied by means of quick releases at 20 (S0.2), 40 (S0.4), 60 (S0.6), and 80% (S0.8) of maximal voluntary torque (T(MVC)). CMJ was not correlated with strength indices but was positively correlated with MRTD/BM, S 0.4/BM. The slope α 2 and intercept β 2 of the torque-stiffness relationships from 40 to 80% T(MVC) were correlated negatively (α 2) and positively (β 2) with CMJ. The different stiffness indices were not correlated with MRTD. The prediction of CMJ was improved by the introduction of MRTD in multiple regressions between CMJ and stiffness. CMJ was also negatively correlated with indices of curvature of the torque-stiffness relationship. The subjects were subdivided in 3 groups in function of CMJ (groups H, M, and L for high, medium, and low performers, resp.). There was a downward curvature of the torque-stiffness relationship at high torques in group H or M and the torque-stiffness regression was linear in group L only. These results suggested that torque-stiffness relationships with a plateau at high torques are more frequent in the best jumpers.

  1. Three-Dimensional Stiff Graphene Scaffold on Neural Stem Cells Behavior.

    PubMed

    Ma, Qinqin; Yang, Lingyan; Jiang, Ziyun; Song, Qin; Xiao, Miao; Zhang, Dong; Ma, Xun; Wen, Tieqiao; Cheng, Guosheng

    2016-12-21

    Physical cues of the scaffolds, elasticity, and stiffness significantly guide adhesion, proliferation, and differentiation of stem cells. In addressable microenvironments constructed by three-dimensional graphene foams (3D-GFs), neural stem cells (NSCs) interact with and respond to the structural geometry and mechanical properties of porous scaffolds. Our studies aim to investigate NSC behavior on the various stiffness of 3D-GFs. Two kinds of 3D-GFs scaffolds present soft and stiff properties with elasticity moduli of 30 and 64 kPa, respectively. Stiff scaffold enhanced NSC attachment and proliferation with vinculin and integrin gene expression were up-regulated by 2.3 and 1.5 folds, respectively, compared with the soft one. Meanwhile, up-regulated Ki67 expression and almost no variation of nestin expression in a group of the stiff scaffold were observed, implying that the stiff substrate fosters NSC growth and keeps the cells in an active stem state. Furthermore, NSCs grown on stiff scaffold exhibited enhanced differentiation to astrocytes. Interestingly, differentiated neurons on stiff scaffold are suppressed since growth associated protein-43 expression was significantly improved by 5.5 folds.

  2. Ensemble X-ray variability of active galactic nuclei. II. Excess variance and updated structure function

    NASA Astrophysics Data System (ADS)

    Vagnetti, F.; Middei, R.; Antonucci, M.; Paolillo, M.; Serafinelli, R.

    2016-09-01

    Context. Most investigations of the X-ray variability of active galactic nuclei (AGN) have been concentrated on the detailed analyses of individual, nearby sources. A relatively small number of studies have treated the ensemble behaviour of the more general AGN population in wider regions of the luminosity-redshift plane. Aims: We want to determine the ensemble variability properties of a rich AGN sample, called Multi-Epoch XMM Serendipitous AGN Sample (MEXSAS), extracted from the fifth release of the XMM-Newton Serendipitous Source Catalogue (XMMSSC-DR5), with redshift between ~0.1 and ~5, and X-ray luminosities in the 0.5-4.5 keV band between ~1042 erg/s and ~1047 erg/s. Methods: We urge caution on the use of the normalised excess variance (NXS), noting that it may lead to underestimate variability if used improperly. We use the structure function (SF), updating our previous analysis for a smaller sample. We propose a correction to the NXS variability estimator, taking account of the light curve duration in the rest frame on the basis of the knowledge of the variability behaviour gained by SF studies. Results: We find an ensemble increase of the X-ray variability with the rest-frame time lag τ, given by SF ∝ τ0.12. We confirm an inverse dependence on the X-ray luminosity, approximately as SF ∝ LX-0.19. We analyse the SF in different X-ray bands, finding a dependence of the variability on the frequency as SF ∝ ν-0.15, corresponding to a so-called softer when brighter trend. In turn, this dependence allows us to parametrically correct the variability estimated in observer-frame bands to that in the rest frame, resulting in a moderate (≲15%) shift upwards (V-correction). Conclusions: Ensemble X-ray variability of AGNs is best described by the structure function. An improper use of the normalised excess variance may lead to an underestimate of the intrinsic variability, so that appropriate corrections to the data or the models must be applied to prevent

  3. Long-term variability of active galactic nuclei from the "Planck" catalog

    NASA Astrophysics Data System (ADS)

    Volvach, A. E.; Kardashev, N. S.; Larionov, M. G.; Volvach, L. N.

    2016-07-01

    A complete sample of 104 bright active galactic nuclei (AGNs) from the "Planck" catalog (early results) were observed at 36.8 GHz with the 22-m radio telescope of the Crimean Astrophysical Observatory (CrAO).Variability indices of the sources at this frequency were determined based on data from theWMAP space observatory, theMetsa¨ hovi RadioObservatory (Finland), and the CrimeanAstrophysical Observatory. New observational results confirm that the variability of these AGNs is stronger in the millimeter than at other radio wavelengths. The variability indices probably change as a result of the systematic decrease in the AGN flux densities in the transition to the infrared. Some radio sources demonstrate significant flux-density variations, including decreases, which sometimes cause them to fall out of the analysed sample. The change of the variability index in the millimeter is consistent with the suggestion that this variability is due to intrinsic processes in binary supermassive black holes at an evolutionary stage close to coalescence. All 104 of the sources studied are well known objects that are included in various radio catalogs and have flux densities exceeding 1 Jy at 36.8 GHz.

  4. Physical activity levels of older community-dwelling adults are influenced by summer weather variables.

    PubMed

    Brandon, Caitlin A; Gill, Dawn P; Speechley, Mark; Gilliland, Jason; Jones, Gareth R

    2009-04-01

    Adequate daily physical activity (PA) is important for maintaining functional capacity and independence in older adults. However, most older adults in Canada do not engage in enough PA to sustain fitness and functional independence. Environmental influences, such as warmer daytime temperatures, may influence PA participation; however, few studies have examined the effect of summertime temperatures on PA levels in older adults. This investigation measured the influence of summertime weather variables on PA in 48 community-dwelling older adults who were randomly recruited from a local seniors' community centre. Each participant wore an accelerometer for a single 7-consecutive-day period (between 30 May and 9 August 2006) during waking hours, and completed a PA logbook to remark on major daily PA events. Local weather variables were collected from a national weather service and compared with PA counts per minute. Regression analysis revealed a curvilinear relationship between log-transformed PA and mean daily temperature (r2 = 0.025; p < 0.05). Linear mixed effects models that accounted for repeated measures nested within individuals were performed for monthly periods, meteorological variables, sex, age, and estimated maximal oxygen consumption, with PA as the dependent variable. Age and Air Quality Index remained significant variables within the model. Higher fitness levels had no effect on allowing individuals to perform more vigorous PA in warmer temperatures.

  5. Ultraviolet and X-ray variability of active galactic nuclei with Swift

    NASA Astrophysics Data System (ADS)

    Buisson, D. J. K.; Lohfink, A. M.; Alston, W. N.; Fabian, A. C.

    2017-01-01

    We analyse a sample of 21 active galactic nuclei using data from the Swift satellite to study the variability properties of the population in the X-ray, UV and optical band. We find that the variable part of the UV-optical emission has a spectrum consistent with a power law, with an average index of -2.21 ± 0.13, as would be expected from central illumination of a thin disc (index of -7/3). We also calculate the slope of a power law from UV to X-ray variable emission, αOX, Var; the average for this sample is αOX, Var = -1.06 ± 0.04. The anticorrelation of αOX with the UV luminosity, LUV, previously found in the average emission is also present in the variable part: αOX, Var = ( - 0.177 ± 0.083)log (Lν, Var(2500 Å)) + (3.88 ± 2.33). Correlated variability between the emission in X-rays and UV is detected significantly for 9 of the 21 sources. All these cases are consistent with the UV lagging the X-rays, as would be seen if the correlated UV variations were produced by the reprocessing of X-ray emission. The observed UV lags are tentatively longer than expected for a standard thin disc.

  6. RMS Spectral Modelling - a powerful tool to probe the origin of variability in Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Mallick, Labani; Dewangan, Gulab chand; Misra, Ranjeev

    2016-07-01

    The broadband energy spectra of Active Galactic Nuclei (AGN) are very complex in nature with the contribution from many ingredients: accretion disk, corona, jets, broad-line region (BLR), narrow-line region (NLR) and Compton-thick absorbing cloud or TORUS. The complexity of the broadband AGN spectra gives rise to mean spectral model degeneracy, e.g, there are competing models for the broad feature near 5-7 keV in terms of blurred reflection and complex absorption. In order to overcome the energy spectral model degeneracy, the most reliable approach is to study the RMS variability spectrum which connects the energy spectrum with temporal variability. The origin of variability could be pivoting of the primary continuum, reflection and/or absorption. The study of RMS (Root Mean Square) spectra would help us to connect the energy spectra with the variability. In this work, we study the energy dependent variability of AGN by developing theoretical RMS spectral model in ISIS (Interactive Spectral Interpretation System) for different input energy spectra. In this talk, I would like to present results of RMS spectral modelling for few radio-loud and radio-quiet AGN observed by XMM-Newton, Suzaku, NuSTAR and ASTROSAT and will probe the dichotomy between these two classes of AGN.

  7. Controls on interannual variability in lightning-caused fire activity in the western US

    NASA Astrophysics Data System (ADS)

    Abatzoglou, John T.; Kolden, Crystal A.; Balch, Jennifer K.; Bradley, Bethany A.

    2016-04-01

    Lightning-caused wildfires account for a majority of burned area across the western United States (US), yet lightning remains among the more unpredictable spatiotemporal aspects of the fire environment and a challenge for both modeling and managing fire activity. A data synthesis of cloud-to-ground lightning strikes, climate and fire data across the western US from 1992 to 2013 was conducted to better understand geographic variability in lightning-caused wildfire and the factors that influence interannual variability in lightning-caused wildfire at regional scales. Distinct geographic variability occurred in the proportion of fires and area burned attributed to lightning, with a majority of fires in the interior western US attributed to lightning. Lightning ignition efficiency was highest across the western portion of the region due to the concomitance of peak lightning frequency and annual nadir in fuel moisture in mid-to-late summer. For most regions the number of total and dry lightning strikes exhibited strong interannual correlation with the number of lightning-caused fires, yet were a poor predictor of area burned at regional scales. Commonality in climate-fire relationships for regional annual area burned by lightning- versus human-ignited fires suggests climate conditions, rather than lightning activity, are the predominant control of interannual variability in area burned by lightning-caused fire across much of the western US.

  8. The effect of short-term isometric training on core/torso stiffness.

    PubMed

    Lee, Benjamin; McGill, Stuart

    2016-09-26

    "Core" exercise is a basic part of many physical training regimens with goals ranging from rehabilitation of spine and knee injuries to improving athletic performance. Core stiffness has been proposed to perform several functions including reducing pain by minimising joint micro-movements, and enhancing strength and speed performance. This study probes the links between a training approach and immediate but temporary changes in stiffness. Passive and active stiffness was measured on 24 participants; 12 having little to no experience in core training (inexperienced), and the other 12 being athletes experienced to core training methods; before and after a 15 min bout of isometric core exercises. Passive stiffness was assessed on a "frictionless" bending apparatus and active stiffness assessed via a quick release mechanism. Short-term isometric core training increased passive and active stiffness in most directions for both inexperienced and experienced participants, passive left lateral bend among experienced participants being the exception (P < 0.05). There was no difference between the inexperienced and experienced groups. The results confirm that the specific isometric training exercise approach tested here can induce immediate changes in core stiffness, in this case following a single session. This may influence performance and injury resilience for a brief period.

  9. A computational model of the response of adherent cells to stretch and changes in substrate stiffness.

    PubMed

    Parameswaran, Harikrishnan; Lutchen, Kenneth R; Suki, Béla

    2014-04-01

    Cells in the body exist in a dynamic mechanical environment where they are subject to mechanical stretch as well as changes in composition and stiffness of the underlying extracellular matrix (ECM). However, the underlying mechanisms by which cells sense and adapt to their dynamic mechanical environment, in particular to stretch, are not well understood. In this study, we hypothesized that emergent phenomena at the level of the actin network arising from active structural rearrangements driven by nonmuscle myosin II molecular motors play a major role in the cellular response to both stretch and changes in ECM stiffness. To test this hypothesis, we introduce a simple network model of actin-myosin interactions that links active self-organization of the actin network to the stiffness of the network and the traction forces generated by the network. We demonstrate that such a network replicates not only the effect of changes in substrate stiffness on cellular traction and stiffness and the dependence of rate of force development by a cell on the stiffness of its substrate, but also explains the physical response of adherent cells to transient and cyclic stretch. Our results provide strong indication that network phenomena governed by the active reorganization of the actin-myosin structure plays an important role in cellular mechanosensing and response to both changes in ECM stiffness and externally applied mechanical stretch.

  10. 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

  11. A time to search: finding the meaning of variable activation energy.

    PubMed

    Vyazovkin, Sergey

    2016-07-28

    This review deals with the phenomenon of variable activation energy frequently observed when studying the kinetics in the liquid or solid phase. This phenomenon commonly manifests itself through nonlinear Arrhenius plots or dependencies of the activation energy on conversion computed by isoconversional methods. Variable activation energy signifies a multi-step process and has a meaning of a collective parameter linked to the activation energies of individual steps. It is demonstrated that by using appropriate models of the processes, the link can be established in algebraic form. This allows one to analyze experimentally observed dependencies of the activation energy in a quantitative fashion and, as a result, to obtain activation energies of individual steps, to evaluate and predict other important parameters of the process, and generally to gain deeper kinetic and mechanistic insights. This review provides multiple examples of such analysis as applied to the processes of crosslinking polymerization, crystallization and melting of polymers, gelation, and solid-solid morphological and glass transitions. The use of appropriate computational techniques is discussed as well.

  12. 3D Printing Variable Stiffness Foams Using Viscous Thread Instability

    PubMed Central

    Lipton, Jeffrey I.; Lipson, Hod

    2016-01-01

    Additive manufacturing of cellular structures has numerous applications ranging from fabrication of biological scaffolds and medical implants, to mechanical weight reduction and control over mechanical properties. Various additive manufacturing processes have been used to produce open regular cellular structures limited only by the resolution of the printer. These efforts have focused on printing explicitly designed cells or explicitly planning offsets between strands. Here we describe a technique for producing cellular structures implicitly by inducing viscous thread instability when extruding material. This process allows us to produce complex cellular structures at a scale that is finer than the native resolution of the printer. We demonstrate tunable effective elastic modulus and density that span two orders of magnitude. Fine grained cellular structures allow for fabrication of foams for use in a wide range of fields ranging from bioengineering, to robotics to food printing. PMID:27503148

  13. 3D Printing Variable Stiffness Foams Using Viscous Thread Instability.

    PubMed

    Lipton, Jeffrey I; Lipson, Hod

    2016-08-09

    Additive manufacturing of cellular structures has numerous applications ranging from fabrication of biological scaffolds and medical implants, to mechanical weight reduction and control over mechanical properties. Various additive manufacturing processes have been used to produce open regular cellular structures limited only by the resolution of the printer. These efforts have focused on printing explicitly designed cells or explicitly planning offsets between strands. Here we describe a technique for producing cellular structures implicitly by inducing viscous thread instability when extruding material. This process allows us to produce complex cellular structures at a scale that is finer than the native resolution of the printer. We demonstrate tunable effective elastic modulus and density that span two orders of magnitude. Fine grained cellular structures allow for fabrication of foams for use in a wide range of fields ranging from bioengineering, to robotics to food printing.

  14. 3D Printing Variable Stiffness Foams Using Viscous Thread Instability

    NASA Astrophysics Data System (ADS)

    Lipton, Jeffrey I.; Lipson, Hod

    2016-08-01

    Additive manufacturing of cellular structures has numerous applications ranging from fabrication of biological scaffolds and medical implants, to mechanical weight reduction and control over mechanical properties. Various additive manufacturing processes have been used to produce open regular cellular structures limited only by the resolution of the printer. These efforts have focused on printing explicitly designed cells or explicitly planning offsets between strands. Here we describe a technique for producing cellular structures implicitly by inducing viscous thread instability when extruding material. This process allows us to produce complex cellular structures at a scale that is finer than the native resolution of the printer. We demonstrate tunable effective elastic modulus and density that span two orders of magnitude. Fine grained cellular structures allow for fabrication of foams for use in a wide range of fields ranging from bioengineering, to robotics to food printing.

  15. Cross-Linked Nanotube Materials with Variable Stiffness Tethers

    NASA Technical Reports Server (NTRS)

    Frankland, Sarah-Jane V.; Odegard, Gregory M.; Herzog, Matthew N.; Gates, Thomas S.; Fay, Catherine C.

    2004-01-01

    The constitutive properties of a cross-linked single-walled carbon nanotube material are predicted with a multi-scale model. The material is modeled as a transversely isotropic solid using concepts from equivalent-continuum modeling. The elastic constants are determined using molecular dynamics simulation. Some parameters of the molecular force field are determined specifically for the cross-linker from ab initio calculations. A demonstration of how the cross-linked nanotubes may affect the properties of a nanotube/polyimide composite is included using a micromechanical analysis.

  16. Assessing the impact of climate variability and human activities on streamflow variation

    NASA Astrophysics Data System (ADS)

    Chang, Jianxia; Zhang, Hongxue; Wang, Yimin; Zhu, Yuelu

    2016-04-01

    Water resources in river systems have been changing under the impact of both climate variability and human activities. Assessing the respective impact on decadal streamflow variation is important for water resource management. By using an elasticity-based method and calibrated TOPMODEL and VIC hydrological models, we quantitatively isolated the relative contributions that human activities and climate variability made to decadal streamflow changes in the Jinghe basin, located in the northwest of China. This is an important watershed of the Shaanxi province that supplies drinking water for a population of over 6 million people. The results showed that the maximum value of the moisture index (E0/P) was 1.91 and appeared in 1991-2000, and the decreased speed of streamflow was higher since 1990 compared with 1960-1990. The average annual streamflow from 1990 to 2010 was reduced by 26.96 % compared with the multiyear average value (from 1960 to 2010). The estimates of the impacts of climate variability and human activities on streamflow decreases from the hydrological models were similar to those from the elasticity-based method. The maximum contribution value of human activities was 99 % when averaged over the three methods, and appeared in 1981-1990 due to the effects of soil and water conservation measures and irrigation water withdrawal. Climate variability made the greatest contribution to streamflow reduction in 1991-2000, the values of which was 40.4 %. We emphasized various source of errors and uncertainties that may occur in the hydrological model (parameter and structural uncertainty) and elasticity-based method (model parameter) in climate change impact studies.

  17. Assessing the impact of climate variability and human activities on streamflow variation

    NASA Astrophysics Data System (ADS)

    Chang, J.; Zhang, H.; Wang, Y.; Zhu, Y.

    2015-12-01

    Water resources in river systems have been changing under the impact of both climate variability and human activities. Assessing the respective impact on decadal streamflow variation is important for water resource management. By using an elasticity-based method and calibrated TOPMODEL and VIC hydrological models, we quantitatively isolated the relative contributions that human activities and climate variability made to decadal streamflow changes in Jinghe basin, located in the northwest of China. This is an important watershed of Shaanxi Province that supplies drinking water for a population of over 6 million people. The results showed that the maximum value of the moisture index (E0/P) was 1.91 and appeared in 1991-2000 and that the decreased speed of streamflow was higher since 1990. The average annual streamflow from 1990 to 2010 was reduced by 26.96 % compared with the multi-year average value. The estimates of climate variability and the impact of human activities on streamflow decreases from the hydrological models were similar to those from the elasticity-based method. The maximum contribution value of human activities was appeared in 1981-1990 due to the effects of soil and water conservation measures and irrigation water withdrawal. Climate variability made the greatest contribution to reduction in 1991-2000, the values of which were 99 and 40.4 % when averaged over the three methods. We emphasized various source of errors and uncertainties that may occur in the hydrological model (parameter and structural uncertainty) and elasticity-based method (model parameter) in climate change impact studies.

  18. Characteristics of high-stiffness superconducting bearing

    SciTech Connect

    Okano, M.; Tamada, N.; Fuchino, S.; Ishii, I.

    1996-07-01

    Magnetic bearings using a high-Tc superconductor have been studied. Generally the bearing makes use of the pinning effects to get the levitation force. The stiffness of the bearing, however, is extremely low as compared with industrial-scale conventional one. To improve the bearing stiffness the authors propose a disc-type repulsive superconducting thrust bearing with a slit for the restraint of the flux. Both theoretical and experimental evaluation on the load performance was carried out, and it is clarified that the proposed superconducting bearing has higher stiffness.

  19. An Energy-Based Method for Computing Radial Stiffness of Single Archimedes Spiral Plane Supporting Spring

    NASA Astrophysics Data System (ADS)

    Zheng, Enlai; Jia, Fang; Lu, Changhui; Chen, He; Ji, Xin

    With space-based adaptive performance of lower stiffness and greater deformation energy, the plane supporting spring finds its wide application in fields like aeronautics, astronautics, etc. In the current study, the radial stiffness formula of a single Archimedes spiral plane supporting spring is derived by means of energy approach, with three key parameters of the supporting spring as independent variables. A series of the supporting spring FEA models are established via APDL speedy modeling. According to the isolation requirements of electronic equipment for a fighter, an example is presented in the form of finite element analysis. The theoretical calculation and analysis data are studied and fitted by MATLAB using the least-square method to obtain the discipline of the radial stiffness of single spiral plane supporting spring with the changes of its three key parameters. The validity of energy-based radial stiffness formula of the spring is confirmed by the comparison between the theoretical calculation and finite element analysis results.

  20. Active galactic nucleus X-ray variability in the XMM-COSMOS survey

    SciTech Connect

    Lanzuisi, G.; Ponti, G.; Salvato, M.; Brusa, M.; Nandra, P. K.; Merloni, A.; Rosario, D.; Hasinger, G.; Sanders, D.; Cappelluti, N.; Comastri, A.; Gilli, R.; Bongiorno, A.; Lusso, E.; Steinhardt, C.; Silverman, J.; Schramm, M.; Trump, J.; and others

    2014-02-01

    We used the observations carried out by XMM in the COSMOS field over 3.5 yr to study the long term variability of a large sample of active galactic nuclei (AGNs) (638 sources) in a wide range of redshifts (0.1 < z < 3.5) and X-ray luminosities (10{sup 41} < L {sub 0.5-10} <10{sup 45.5}). Both a simple statistical method to assess the significance of variability and the Normalized Excess Variance (σ{sub rms}{sup 2}) parameter were used to obtain a quantitative measurement of the variability. Variability is found to be prevalent in most AGNs, whenever we have good statistics to measure it, and no significant differences between type 1 and type 2 AGNs were found. A flat (slope –0.23 ± 0.03) anti-correlation between σ{sub rms}{sup 2} and X-ray luminosity is found when all significantly variable sources are considered together. When divided into three redshift bins, the anti-correlation becomes stronger and evolving with z, with higher redshift AGNs being more variable. We prove, however, that this effect is due to the pre-selection of variable sources: when considering all of the sources with an available σ{sub rms}{sup 2} measurement, the evolution in redshift disappears. For the first time, we were also able to study long term X-ray variability as a function of M {sub BH} and Eddington ratio for a large sample of AGNs spanning a wide range of redshifts. An anti-correlation between σ{sub rms}{sup 2} and M {sub BH} is found, with the same slope of anti-correlation between σ{sub rms}{sup 2} and X-ray luminosity, suggesting that the latter may be a by-product of the former. No clear correlation is found between σ{sub rms}{sup 2} and the Eddington ratio in our sample. Finally, no correlation is found between the X-ray σ{sub rms}{sup 2} and optical variability.

  1. 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

  2. Active optics: variable curvature mirrors for ELT laser guide star refocusing systems

    NASA Astrophysics Data System (ADS)

    Challita, Zalpha; Hugot, Emmanuel; Madec, Fabrice; Ferrari, Marc; Le Mignant, David; Vivès, Sébastien; Cuby, Jean-Gabriel

    2011-10-01

    The future generation of Extremely Large Telescopes will require a complex combination of technologies for adaptive optics (AO) systems assisted by laser guide stars (LGS). In this context, the distance from the LGS spot to the telescope pupil ranges from about 80 to 200 km, depending on the Sodium layer altitude and the elevation of the telescope. This variation leads to a defocusing effect on the LGS wave-front sensor which needs to be compensated. We propose an active mirror able to compensate for this variation, based on an original optical design including this active optics component. This LGS Variable Curvature Mirror (LGS-VCM) is a 120 mm spherical active mirror able to achieve 820 μm deflection sag with an optical quality better than 150 nm RMS, allowing the radius of curvature variation from F/12 to F/2. Based on elasticity theory, the deformation of the metallic mirror is provided by an air pressure applied on a thin meniscus with a variable thickness distribution. In this article, we detail the analytical development leading to the specific geometry of the active component, the results of finite element analysis and the expected performances in terms of surface error versus the range of refocalisation. Three prototypes have been manufactured to compare the real behavior of the mirror and the simulations data. Results obtained on the prototypes are detailed, showing that the deformation of the VCM is very close to the simulation, and leads to a realistic active concept.

  3. Inferior frontal cortex activity is modulated by reward sensitivity and performance variability.

    PubMed

    Fuentes-Claramonte, Paola; Ávila, César; Rodríguez-Pujadas, Aina; Costumero, Víctor; Ventura-Campos, Noelia; Bustamante, Juan Carlos; Rosell-Negre, Patricia; Barrós-Loscertales, Alfonso

    2016-02-01

    High reward sensitivity has been linked with motivational and cognitive disorders related with prefrontal and striatal brain function during inhibitory control. However, few studies have analyzed the interaction among reward sensitivity, task performance and neural activity. Participants (N=57) underwent fMRI while performing a Go/No-go task with Frequent-go (77.5%), Infrequent-go (11.25%) and No-go (11.25%) stimuli. Task-associated activity was found in inhibition-related brain regions, with different activity patterns for right and left inferior frontal gyri (IFG): right IFG responded more strongly to No-go stimuli, while left IFG responded similarly to all infrequent stimuli. Reward sensitivity correlated with omission errors in Go trials and reaction time (RT) variability, and with increased activity in right and left IFG for No-go and Infrequent-go stimuli compared with Frequent-go. Bilateral IFG activity was associated with RT variability, with reward sensitivity mediating this association. These results suggest that reward sensitivity modulates behavior and brain function during executive control.

  4. Modeling inter-subject variability in fMRI activation location: A Bayesian hierarchical spatial model

    PubMed Central

    Xu, Lei; Johnson, Timothy D.; Nichols, Thomas E.; Nee, Derek E.

    2010-01-01

    Summary The aim of this work is to develop a spatial model for multi-subject fMRI data. There has been extensive work on univariate modeling of each voxel for single and multi-subject data, some work on spatial modeling of single-subject data, and some recent work on spatial modeling of multi-subject data. However, there has been no work on spatial models that explicitly account for inter-subject variability in activation locations. In this work, we use the idea of activation centers and model the inter-subject variability in activation locations directly. Our model is specified in a Bayesian hierarchical frame work which allows us to draw inferences at all levels: the population level, the individual level and the voxel level. We use Gaussian mixtures for the probability that an individual has a particular activation. This helps answer an important question which is not addressed by any of the previous methods: What proportion of subjects had a significant activity in a given region. Our approach incorporates the unknown number of mixture components into the model as a parameter whose posterior distribution is estimated by reversible jump Markov Chain Monte Carlo. We demonstrate our method with a fMRI study of resolving proactive interference and show dramatically better precision of localization with our method relative to the standard mass-univariate method. Although we are motivated by fMRI data, this model could easily be modified to handle other types of imaging data. PMID:19210732

  5. A new method of measuring the stiffness of astronauts' EVA gloves

    NASA Astrophysics Data System (ADS)

    Mousavi, Mehdi; Appendino, Silvia; Battezzato, Alessandro; Bonanno, Alberto; Chen Chen, Fai; Crepaldi, Marco; Demarchi, Danilo; Favetto, Alain; Pescarmona, Francesco

    2014-04-01

    Hand fatigue is one of the most important problems of astronauts during their missions to space. This fatigue is due to the stiffness of the astronauts' gloves known as Extravehicular Activity (EVA) gloves. The EVA glove has a multilayered, bulky structure and is pressurized against the vacuum of space. In order to evaluate the stiffness of EVA gloves, different methods have been proposed in the past. In particular, the effects of wearing an EVA glove on the performance of the hands have been published by many researchers to represent the stiffness of the EVA glove. In this paper, a new method for measuring the stiffness of EVA gloves is proposed. A tendon-actuated finger probe is designed and used as an alternative to the human index finger in order to be placed inside an EVA glove and measure its stiffness. The finger probe is equipped with accelerometers, which work as tilt sensors, to measure the angles of its phalanges. The phalanges are actuated by applying different amount of torque using the tendons of the finger probe. Moreover, a hypobaric glove box is designed and realized to simulate the actual operating pressure of the EVA glove and to measure its stiffness in both pressurized and non-pressurized conditions. In order to prove the right performance of the proposed finger probe, an Orlam-DM EVA glove is used to perform a number of tests. The equation of stiffness for the PIP joint of this glove is extracted from the results acquired from the tests. This equation presents the torque required to flex the middle phalanx of the glove. Then, the effect of pressurization on the stiffness is highlighted in the last section. This setup can be used to measure the stiffness of different kinds of EVA gloves and allows direct, numerical comparison of their stiffness.

  6. Magnetic bearing stiffness control using frequency band filtering

    NASA Technical Reports Server (NTRS)

    Chen, H. Ming

    1989-01-01

    Active magnetic bearings can be implemented with frequency band-reject filtering that decreases the bearing stiffness and damping at a small bandwidth around a chosen frequency. The control scheme was used for reducing a rotor dynamic force, such as an imbalance force, transmitted to the bearing stator. The scheme creates additional system vibration modes at the same frequency. It also shows that the amount of force reduction is limited by the stability requirement of these modes.

  7. Compact, Stiff, Remotely-Actuable Quick-Release Clamp

    NASA Technical Reports Server (NTRS)

    Tsai, Ted W. (Inventor)

    2000-01-01

    The present invention provides a clamp that is compact and lightweight, yet provides high holding strength and stiffness or rigidity. The clamp uses a unique double slant interface design which provides mechanical advantages to resist forces applied to the clamp member as the load increases. The clamp allows for rapid and remote-activated release of the clamp jaws by applying only a small operating force to an over-center lock/release mechanism, such as by pulling a manual tether.

  8. Stiffness and Confinement Ratios of SMA Wire Jackets for Confining Concrete

    NASA Astrophysics Data System (ADS)

    Choi, Eunsoo; Kim, Dong Joo; Youn, Heejung

    2014-07-01

    This article discusses the effects of the stiffness and confinement ratios of shape memory alloy (SMA) wire jackets on the behavior of confined concrete. SMA wire jackets are an effective confining material to improve concrete behavior; for example, by increasing peak strength and failure strain. The stiffness and confinement ratios of fiber-reinforced polymer jackets have been extensively discussed and their effects are well known. However, assessment of the stiffness and confinement ratios of SMA wire jackets has not previously been conducted. In this study, we investigate the effects of the stiffness and confinement ratios of steel jackets, and then compare the results with those of SMA wire jackets. In general, the stiffness ratios of SMA wire jackets are relatively smaller than those of steel jackets, and most of them have lower stiffness ratios because the Young's moduli of the SMAs are relatively small. The active confining pressure of the SMA wires does not improve the lower stiffness-ratio effect since the amount of active confining pressure is not sufficiently large.

  9. Effect of long-term isometric training on core/torso stiffness.

    PubMed

    Lee, Benjamin C Y; McGill, Stuart M

    2015-06-01

    Although core stiffness enhances athletic performance traits, controversy exists regarding the effectiveness of isometric vs. dynamic core training methods. This study aimed to determine whether long-term changes in stiffness can be trained, and if so, what is the most effective method. Twenty-four healthy male subjects (23 ± 3 years; 1.8 ± 0.06 m; 77.5 ± 10.8 kg) were recruited for passive and active stiffness measurements before and after a 6-week core training intervention. Twelve subjects (22 ± 2 years; 1.8 ± 0.08 m; 78.3 ± 12.3 kg) were considered naive to physical and core exercise. The other 12 subjects (24 ± 3 years; 1.8 ± 0.05 m; 76.8 ± 9.7 kg) were Muay Thai athletes (savvy). A repeated-measures design compared core training methods (isometric vs. dynamic, with a control group) and subject training experience (naive vs. savvy) before and after a 6-week training period. Passive stiffness was assessed on a "frictionless" bending apparatus and active stiffness assessed through a quick release mechanism. Passive stiffness increased after the isometric training protocol. Dynamic training produced a smaller effect, and as expected, there was no change in the control group. Active stiffness did not change in any group. Comparisons between subject and training groups did not reveal any interactions. Thus, an isometric training approach was superior in terms of enhancing core stiffness. This is important since increased core stiffness enhances load bearing ability, arrests painful vertebral micromovements, and enhances ballistic distal limb movement. This may explain the efficacy reported for back and knee injury reduction.

  10. Macroscopic Stiffness of Breast Tumors Predicts Metastasis

    PubMed Central

    Fenner, Joseph; Stacer, Amanda C.; Winterroth, Frank; Johnson, Timothy D.; Luker, Kathryn E.; Luker, Gary D.

    2014-01-01

    Mechanical properties of tumors differ substantially from normal cells and tissues. Changes in stiffness or elasticity regulate pro-metastatic behaviors of cancer cells, but effects have been documented predominantly in isolated cells or in vitro cell culture systems. To directly link relative stiffness of tumors to cancer progression, we combined a mouse model of metastatic breast cancer with ex vivo measurements of bulk moduli of freshly excised, intact tumors. We found a high, inverse correlation between bulk modulus of resected tumors and subsequent local recurrence and metastasis. More compliant tumors were associated with more frequent, larger local recurrences and more extensive metastases than mice with relatively stiff tumors. We found that collagen content of resected tumors correlated with bulk modulus values. These data establish that relative differences in tumor stiffness correspond with tumor progression and metastasis, supporting further testing and development of tumor compliance as a prognostic biomarker in breast cancer. PMID:24981707

  11. A NEW COSMOLOGICAL DISTANCE MEASURE USING ACTIVE GALACTIC NUCLEUS X-RAY VARIABILITY

    SciTech Connect

    Franca, Fabio La; Bianchi, Stefano; Branchini, Enzo; Matt, Giorgio; Ponti, Gabriele

    2014-05-20

    We report the discovery of a luminosity distance estimator using active galactic nuclei (AGNs). We combine the correlation between the X-ray variability amplitude and the black hole (BH) mass with the single-epoch spectra BH mass estimates which depend on the AGN luminosity and the line width emitted by the broad-line region. We demonstrate that significant correlations do exist that allow one to predict the AGN (optical or X-ray) luminosity as a function of the AGN X-ray variability and either the Hβ or the Paβ line widths. In the best case, when the Paβ is used, the relationship has an intrinsic dispersion of ∼0.6 dex. Although intrinsically more disperse than supernovae Ia, this relation constitutes an alternative distance indicator potentially able to probe, in an independent way, the expansion history of the universe. With respect to this, we show that the new mission concept Athena should be able to measure the X-ray variability of hundreds of AGNs and then constrain the distance modulus with uncertainties of 0.1 mag up to z ∼ 0.6. We also discuss how our estimator has the prospect of becoming a cosmological probe even more sensitive than the current supernovae Ia samples by using a new dedicated wide-field X-ray telescope able to measure the variability of thousands of AGNs.

  12. Optimal strategies for observation of active galactic nuclei variability with Imaging Atmospheric Cherenkov Telescopes

    NASA Astrophysics Data System (ADS)

    Giomi, Matteo; Gerard, Lucie; Maier, Gernot

    2016-07-01

    Variable emission is one of the defining characteristic of active galactic nuclei (AGN). While providing precious information on the nature and physics of the sources, variability is often challenging to observe with time- and field-of-view-limited astronomical observatories such as Imaging Atmospheric Cherenkov Telescopes (IACTs). In this work, we address two questions relevant for the observation of sources characterized by AGN-like variability: what is the most time-efficient way to detect such sources, and what is the observational bias that can be introduced by the choice of the observing strategy when conducting blind surveys of the sky. Different observing strategies are evaluated using simulated light curves and realistic instrument response functions of the Cherenkov Telescope Array (CTA), a future gamma-ray observatory. We show that strategies that makes use of very small observing windows, spread over large periods of time, allows for a faster detection of the source, and are less influenced by the variability properties of the sources, as compared to strategies that concentrate the observing time in a small number of large observing windows. Although derived using CTA as an example, our conclusions are conceptually valid for any IACTs facility, and in general, to all observatories with small field of view and limited duty cycle.

  13. A SEARCH FOR FAST X-RAY VARIABILITY FROM ACTIVE GALACTIC NUCLEI USING SWIFT

    SciTech Connect

    Pryal, Matthew; Falcone, Abe; Stroh, Michael

    2015-03-20

    Blazars are a class of active galactic nuclei (AGNs) known for their very rapid variabilty in the high energy regions of the electromagnetic spectrum. Despite this known fast variability, X-ray observations have generally not revealed variability in blazars with rate doubling or halving timescales less than approximately 15 minutes. Since its launch, the Swift X-ray Telescope has obtained 0.2–10 keV X-ray data on 143 AGNs, including blazars, through intense target of opportunity observations that can be analyzed in a multiwavelength context and used to model jet parameters, particularly during flare states. We have analyzed this broad Swift data set in a search for short timescale variability in blazars that could limit the size of the emission region in the blazar jet. While we do find several low-significance possible flares with potential indications of rapid variability, we find no strong evidence for rapid (<15 minutes) doubling or halving times in flares in the soft X-ray energy band for the AGNs analyzed.

  14. X-ray flux variability of active galactic nuclei observed using NuSTAR

    NASA Astrophysics Data System (ADS)

    Rani, Priyanka; Stalin, C. S.; Rakshit, Suvendu

    2017-04-01

    We present results of a systematic study of flux variability on hourly time-scales in a large sample of active galactic nuclei (AGN) in the 3-79 keV band using data from Nuclear Spectroscopic Telescope Array. Our sample consists of four BL Lac objects (BL Lacs), three flat spectrum radio quasars (FSRQs) 24 Seyfert 1, 42 Seyfert 2 and eight narrow line Seyfert 1 (NLSy1) galaxies. We find that in the 3-79 keV band, about 65 per cent of the sources in our sample show significant variations on hourly time-scales. Using the Mann-Whitney U-test and the Kolmogorov-Smirnov test, we find no difference in the variability behaviour between Seyfert 1 and 2 galaxies. The blazar sources (FSRQs and BL Lacs) in our sample are more variable than Seyfert galaxies that include Seyfert 1 and Seyfert 2 in the soft (3-10 keV), hard (10-79 keV) and total (3-79 keV) bands. NLSy1 galaxies show the highest duty cycle of variability (87 per cent), followed by BL Lacs (82 per cent), Seyfert galaxies (56 per cent) and FSRQs (23 per cent). We obtained flux doubling/halving time in the hard X-ray band less than 10 min in 11 sources. The flux variations between the hard and soft bands in all the sources in our sample are consistent with zero lag.

  15. BROAD Hβ EMISSION-LINE VARIABILITY IN A SAMPLE OF 102 LOCAL ACTIVE GALAXIES

    SciTech Connect

    Runco, Jordan N.; Cosens, Maren; Bennert, Vardha N.; Scott, Bryan; Komossa, S.; Malkan, Matthew A.; Treu, Tommaso; Lazarova, Mariana S.; Auger, Matthew W.; Park, Daeseong E-mail: mcosens@calpoly.edu E-mail: malkan@astro.ucla.edu E-mail: lazarovam2@unk.edu E-mail: daeseongpark@kasi.re.kr

    2016-04-10

    A sample of 102 local (0.02 ≤ z ≤ 0.1) Seyfert galaxies with black hole masses M{sub BH} > 10{sup 7}M{sub ⊙} was selected from the Sloan Digital Sky Survey (SDSS) and observed using the Keck 10 m telescope to study the scaling relations between M{sub BH} and host galaxy properties. We study profile changes of the broad Hβ emission line within the three to nine year time frame between the two sets of spectra. The variability of the broad Hβ emission line is of particular interest, not only because it is used to estimate M{sub BH}, but also because its strength and width are used to classify Seyfert galaxies into different types. At least some form of broad-line variability (in either width or flux) is observed in the majority (∼66%) of the objects, resulting in a Seyfert-type change for ∼38% of the objects, likely driven by variable accretion and/or obscuration. The broad Hβ line virtually disappears in 3/102 (∼3%) extreme cases. We discuss potential causes for these changing look active galactic nuclei. While similar dramatic transitions have previously been reported in the literature, either on a case-by-case basis or in larger samples focusing on quasars at higher redshifts, our study provides statistical information on the frequency of Hβ line variability in a sample of low-redshift Seyfert galaxies.

  16. Seasonal and interannual variability of mesospheric gravity wave activity at high and mid-latitudes

    NASA Astrophysics Data System (ADS)

    Hoffmann, Peter; Singer, Werner; Becker, Erich; Latteck, Ralph; Keuer, Dieter

    The seasonal variation and interannual variability of the gravity wave activity in the mesosphere/lower thermosphere (MLT) region at high and mid-latitudes is investigated. Variations of the gravity wave activity are examined in relation to the filtering processes due to the changes of the background winds, tides and planetary waves. Our studies are basing on wind measurements from meteor and MF radars at Andenes (69° N, 16° E) and Juliusruh (55° N, 13° E). These measurements are supplemented by mesospheric temperatures derived from meteor decay times. Additionally, turbulent energy dissipation rates have been estimated from spectral width measurements using a 3 MHz Doppler radar near Andenes. Particular attention is directed to the influence of the solar activity on the gravity wave activity during the summer months when the mesospheric winds show the strongest correlation with the solar activity. Possible dependencies between the occurrence rates of polar mesospheric summer echoes (PMSE) and the gravity wave activity are discussed. Furthermore, the activity of gravity waves and their dissipation are investigated in winter in relation with wind changes during sudden stratospheric warming (SSW) events. The summer/ winter behavior of the gravity wave activity will be compared to simulations with the simple general circulation model KMCM (K¨hlungsborn Mechanistic u Circulation Model) that extends up to 100 km. In all cases, the percentage rates of the kinetic energy of defined period ranges in relation to the total variances of the horizontal wind fluctuations are estimated.

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

    PubMed Central

    Chu, Shin-Ying; Kieweg, Douglas; Lee, Jaehoon

    2010-01-01

    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 (ΔF) and interangle span (ΔX), 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. PMID:20185131

  18. Variable expression of activation-linked surface antigens on human mast cells in health and disease.

    PubMed

    Valent, P; Schernthaner, G H; Sperr, W R; Fritsch, G; Agis, H; Willheim, M; Bühring, H J; Orfao, A; Escribano, L

    2001-02-01

    Mast cells (MC) are multipotent effector cells of the immune system. They contain an array of biologically active mediator substances in their granules. MC also express a number of functionally important cell surface antigens, including stem cell factor receptor (SCFR=kit=CD117), high affinity IgER (FcepsilonRI), or CSaR (CD88). Respective ligands can induce or promote degranulation, migration, or cytokine production. Other integral surface molecules can mediate adhesion or cell aggregation. Recent data suggest that a number of critical molecules are variably expressed on the surface of human MC. In fact, depending on the environment (organ), stage of cell maturation, type of disease, and other factors, MC express variable amounts of activation-linked antigens (CD25, CD63, CD69, CD88), cell recognition molecules (CD2, CD11, CD18, CD50, CD54), or cytokine receptors. At present, however, little is known about the mechanisms and regulation of expression of such antigens. The present article gives an overview of MC phenotypes in health and disease, and attempts to provide explanations for the phenotypic variability of MC.

  19. Impairment variables predicting activity limitation in individuals with lower limb amputation.

    PubMed

    Raya, Michele A; Gailey, Robert S; Fiebert, Ira M; Roach, Kathyrn E

    2010-03-01

    The purpose of this study was to determine whether measures of impairment (i.e., muscle strength, balance), personal factors (i.e., comorbidities, demographic information) and amputation specific variables (i.e., time since amputation, cause of amputation, level of amputation) were able to predict performance on the six-minute walk test, a measure of activity limitation, in individuals with lower limb amputation. A total of 72 individuals with lower limb amputation ranging in age from 21-83 were tested for balance, limb muscle strength and function. Medical comorbidities were recorded and activity limitation was measured using the six-minute walk test. Data were analyzed and multivariate relationships were examined using multiple linear regression. Impairment variables of strength, balance, subject demographics, time since amputation, cause of amputation and level of amputation were all significant predictors and explained 72% of the variance in the outcome variable. Strength of the hip extensors was the strongest predictor, accounting for 30.9% of the total variance. Multiple factors impact six minute walk scores in individuals with lower limb amputation. Impairments in hip strength and balance appear to be the two most significant. The findings of this study support the use of the six-minute walk test to underscore impairments of the musculoskeletal system that can affect ambulation ability in the amputee.

  20. Revisiting a possible relationship between solar activity and Earth rotation variability

    NASA Astrophysics Data System (ADS)

    Abarca del Rio, R.; Gambis, D.

    2011-10-01

    A variety of studies have searched to establish a possible relationship between the solar activity and earth variations (Danjon, 1958-1962; Challinor, 1971; Currie, 1980, Gambis, 1990). We are revisiting previous studies (Bourget et al, 1992, Abarca del Rio et al, 2003, Marris et al, 2004) concerning the possible relationship between solar activity variability and length of day (LOD) variations at decadal time scales. Assuming that changes in AAM for the entire atmosphere are accompanied by equal, but opposite, changes in the angular momentum of the earth it is possible to infer changes in LOD from global AAM time series, through the relation : delta (LOD) (ms) = 1.68 10^29 delta(AAM) (kgm2/s) (Rosen and Salstein, 1983), where δ(LOD) is given in milliseconds. Given the close relationship at seasonal to interannual time's scales between LOD and the Atmospheric Angular Momentum (AAM) (see Abarca del Rio et al., 2003) it is possible to infer from century long atmospheric simulations what may have been the variability in the associated LOD variability throughout the last century. In the absence of a homogeneous century long LOD time series, we take advantage of the recent atmospheric reanalyzes extending since 1871 (Compo, Whitaker and Sardeshmukh, 2006). The atmospheric data (winds) of these reanalyzes allow computing AAM up to the top of the atmosphere; though here only troposphere data (up to 100 hPa) was taken into account.

  1. Stiffness transition in anisotropic fiber nets

    NASA Astrophysics Data System (ADS)

    Åström, J. A.; Sunil Kumar, P. B.; Karttunen, Mikko

    2012-08-01

    We demonstrate the existence of a percolationlike stiffness transition in fiber networks with a bidisperse orientation distribution and with fiber densities clearly above the geometrical and the ordinary stiffness transition. The fibers are oriented parallel and perpendicular to a strain direction and they have a large fiber aspect ratio. The stiffness K of the fiber nets can be described by a scaling relation, K∝ταg[(ɛ-ɛc)/τ-β], where τ is the fraction of fibers parallel to strain. g is a scaling function that is roughly described by a power law g(x)∝xγ for stiffness above the transition and by a constant below the transition. The transition point is characterized by qualitative changes in the distribution of the elastic deformation energy of the fibers, the deformation mode of the fibers, the effective Poisson ratio of the nets, the distribution of elastic energy on fibers and cross links, and the ratio of elastic and viscous dissipation energy. This transition opens the possibility of extreme stiffness variations with minimal mesh manipulations in the vicinity of the transition (i.e., a stiffness gate). It is possible that this transition affects the mechanical behavior of the cytoskeleton in cells.

  2. 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.

  3. Spatio-temporal variability in the GDH activity to ammonium excretion ratio in epipelagic marine zooplankton

    NASA Astrophysics Data System (ADS)

    Fernández-Urruzola, I.; Osma, N.; Packard, T. T.; Maldonado, F.; Gómez, M.

    2016-11-01

    Glutamate dehydrogenase (GDH) activities have been widely used in oceanographic research as an index of in situ NH4+ excretion rates (RNH4+) in zooplankton. Here we study the variability in the relationship between the enzymatic rates and the actual rates measured in epipelagic marine zooplankton between several marine ecosystems. Although both measures were significantly correlated across zooplankton assemblages, the regression models yielded different GDH/RNH4+ ratios across ecosystems. Accordingly, the error of a general equation increased up to ±42.5 % when regressing all our data together. Aside from possible interspecific differences, some of the variability was explained by the unequal allometric relation that each rate maintained with protein. Scaling exponents were 1.38 for GDH activities and 0.87 for RNH4+, which would induce uncertainties in the GDH/RNH4+ ratios when organisms with different sizes were considered. Nevertheless, the main factor causing divergence between GDH activities and RNH4+ was the potential prey availability. We compared the excretory metabolism of the zooplankton community at different productivity periods in waters off Gran Canaria, and observed an important decrease in the RNH4+ during stratification. A similar decrease was found in the internal pool of glutamate, which may be critical in the regulation of in vivo rates. Strengthening our knowledge of the relationship between GDH activities and the RNH4+ will lead to more meaningful predictions of phytoplankton regeneration and community nitrogen fluxes across large spatial scales.

  4. Non-stiff anti-amphiphysin syndrome: clinical manifestations and outcome after immunotherapy.

    PubMed

    Moon, Jangsup; Lee, Soon-Tae; Shin, Jung-Won; Byun, Jung-Ick; Lim, Jung-Ah; Shin, Yong-Won; Kim, Tae-Joon; Lee, Keon-Joo; Park, Kyung-Il; Jung, Keun-Hwa; Jung, Ki-Young; Lee, Sang Kun; Chu, Kon

    2014-09-15

    Amphiphysin antibody causes paraneoplastic stiff-person syndrome and can also result in a variety of neurological manifestations. Here, we investigated the clinical spectrum of 20 patients with non-stiff anti-amphiphysin syndrome and their responses to immunotherapy. The most common neurological manifestation was limbic encephalitis (n=10), followed by dysautonomia (n=9), and cerebellar dysfunction (n=6). Cancer was detected in only seven patients. Intravenous immunoglobulin or steroid treatment was effective in most patients, but three improved only after rituximab treatment. Our study suggests that anti-amphiphysin syndrome can manifest as non-stiff encephalomyelitis and is only partially associated with cancer. Active immunotherapy, including rituximab, would be beneficial.

  5. Variability and Stability in Daily Moderate-to-Vigorous Physical Activity among 10 Year Old Children

    PubMed Central

    Pereira, Sara; Gomes, Thayse Natacha; Borges, Alessandra; Santos, Daniel; Souza, Michele; dos Santos, Fernanda K.; Chaves, Raquel N.; Katzmarzyk, Peter T.; Maia, José A. R.

    2015-01-01

    Day-to-day variability and stability of children’s physical activity levels across days of the week are not well understood. Our aims were to examine the day-to-day variability of moderate-to-vigorous physical activity (MVPA), to determine factors influencing the day-to-day variability of MVPA and to estimate stability of MVPA in children. The sample comprises 686 Portuguese children (10 years of age). MVPA was assessed with an accelerometer, and BMI was computed from measured height and weight. Daily changes in MVPA and their correlates (gender, BMI, and maturity) were modeled with a multilevel approach, and tracking was calculated using Foulkes & Davies γ. A total of 51.3% of boys and 26.2% of girls achieved 60 min/day of MVPA on average. Daily MVPA was lower during the weekend (23.6% of boys and 13.6% of girls comply with the recommended 60 min/day of MVPA) compared to weekdays (60.8% and 35.4%, boys and girls, respectively). Normal weight children were more active than obese children and no effect was found for biological maturation. Tracking is low in both boys (γ = 0.59 ± 0.01) and girls (γ = 0.56 ± 0.01). Children’s MVPA levels during a week are highly unstable. In summary, boys are more active than girls, maturation does not affect their MVPA, and obese children are less likely to meet 60 min/day of MVPA. These results highlight the importance of providing opportunities for increasing children’s daily MVPA on all days of week, especially on the weekend. PMID:26262632

  6. Design of a multilevel Active Power Filter for More Electrical Airplane variable frequency systems

    NASA Astrophysics Data System (ADS)

    Guerreiro, Joel Filipe; Pomilio, Jose Antenor; Busarello, Tiago Davi Curi

    This paper presents the design and simulation of an Aeronautical Active Power Filter (AAPF) for a Variable Speed Variable Frequency (VSVF) advanced aircraft electric power system. The purposes of the AAPF are to mitigate current harmonics, to improve the source power factor and to mitigate the effects of unbalanced loads. Regarding the fact that the Aircraft Electrical Power System (AEPS) frequency may vary between 360 Hz and 900 Hz, and the load dynamics is often modified, an enhanced filtering technique is required. The designed AAPF topology is an asymmetrical multilevel inverter (AMI), which control strategy is based on the Conservative Power Theory (CPT) and synchronized by a Kalman Filter Phase-Locked Loop (KF-PLL). The above configuration renders the AAPF very robust and effective to its purpose. Accurate simulation results on Matlab/Simulink platform verify the feasibility of the proposed AAPF and the high performance of the control strategy during steady-state and dynamic operations.

  7. The photometric variability of the chromospherically active binary star HD 80715

    NASA Technical Reports Server (NTRS)

    Strassmeier, Klaus G.; Hooten, James T.; Hall, Douglas S.; Fekel, Francis C.

    1989-01-01

    Differential UBVRI photometry of the double-lined BY Dra system HD 80715 (K3 V + K3 V) obtained in December 1987 is presented. The star is found to be a variable with a full amplitude of 0.06 mag in V and a period similar or equal to the orbital period of 3.804 days. The mechanism of the variability is interpreted as rotational modulation due to dark starspots. In an attempt to detect chromospheric activity, high-resolution CCD spectra were obtained at Ca II H and K and at Fe I 6430 A and Ca I 6439 A, the photospheric lines normally used for Doppler imaging. HD 80715 shows double H and K emission features at a constant flux level for each component.

  8. Bubble mass center and fluid feedback force fluctuations activated by constant lateral impulse with variable thrust

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Long, Y. T.

    1995-01-01

    Sloshing dynamics within a partially filled rotating dewar of superfluid helium 2 are investigated in response to constant lateral impulse with variable thrust. The study, including how the rotating bubble of superfluid helium 2 reacts to the constant impulse with variable time period of thrust action in microgravity, how amplitudes of bubble mass center fluctuates with growth and decay of disturbances, and how fluid feedback forces fluctuates in activating on the rotating dewar through the dynamics of sloshing waves are investigated. The numerical computation of sloshing dynamics is based on the non-inertial frame spacecraft bound coordinate with lateral impulses actuating on the rotating dewar in both inertial and non-inertial frames of thrust. Results of the simulations are illustrated.

  9. Temporal and spatial variability of soil biological activity at European scale

    NASA Astrophysics Data System (ADS)

    Mallast, Janine; Rühlmann, Jörg

    2015-04-01

    The CATCH-C project aims to identify and improve the farm-compatibility of Soil Management Practices including to promote productivity, climate change mitigation and soil quality. The focus of this work concentrates on turnover conditions for soil organic matter (SOM). SOM is fundamental for the maintenance of quality and functions of soils while SOM storage is attributed a great importance in terms of climate change mitigation. The turnover conditions depend on soil biological activity characterized by climate and soil properties. Soil biological activity was investigated using two model concepts: a) Re_clim parameter within the ICBM (Introductory Carbon Balance Model) (Andrén & Kätterer 1997) states a climatic factor summarizing soil water storage and soil temperature and its influence on soil biological activity. b) BAT (biological active time) approach derived from model CANDY (CArbon and Nitrogen Dynamic) (Franko & Oelschlägel 1995) expresses the variation of soil moisture, soil temperature and soil aeration as a time scale and an indicator of biological activity for soil organic matter (SOM) turnover. During an earlier stage both model concepts, Re_clim and BAT, were applied based on a monthly data to assess spatial variability of turnover conditions across Europe. This hampers the investigation of temporal variability (e.g. intra-annual). The improved stage integrates daily data of more than 350 weather stations across Europe presented by Klein Tank et al. (2002). All time series data (temperature, precipitation and potential evapotranspiration and soil texture derived from the European Soil Database (JRC 2006)), are used to calculate soil biological activity in the arable layer. The resulting BAT and Re_clim values were spatio-temporal investigated. While "temporal" refers to a long-term trend analysis, "spatial" includes the investigation of soil biological activity variability per environmental zone (ENZ, Metzger et al. 2005 representing similar

  10. Social desirability is associated with some physical activity, psychosocial variables and sedentary behavior but not self-reported physical activity among adolescent males

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study examined whether controlling for social desirability improved the association between self-reported and objectively measured physical activity among adolescent males and the extent that psychosocial variables predict physical activity after controlling for social desirability. Participant...

  11. Impacts of Climate Change/Variability and Human Activities on Contemporary Vegetation Productivity across Africa

    NASA Astrophysics Data System (ADS)

    Ugbaje, S. U.; Odeh, I. A.; Bishop, T.

    2015-12-01

    Vegetation productivity is increasingly being impacted upon by climate change/variability and anthropogenic activities, especially in developing countries, where many livelihoods depend on the natural resource base. Despite these impacts, the individual and combined roles of climate and anthropogenic factors on vegetation dynamics have rarely been quantified in many ecosystems and regions of the world. This paper analyzes recent trend in vegetation productivity across Africa and quantified the relative roles of climate change/variability and human activities in driving this trend over 2000-2014 using net primary productivity (NPP) as an indicator. The relative roles of these factors to vegetation productivity change were quantified by comparing the trend slope (p<0.1) and total change in interannual actual NPP (NPPA), potential NPP (NPPP), and human appropriated NPP (NPPH). NPP significantly increased across Africa relative to NPP decline, though the extent of NPP decline is also quite appreciable. Whereas estimated NPP declined by 207 Tg C over 140 X 104 km of land area, vegetation productivity was estimated to improve by 1415 Tg C over 786 X 104 km of land area. NPP improvement is largely concentrated in equatorial and northern hemispheric Africa, while subequatorial Africa exhibited the most NPP decline. Generally, anthropogenic activities dominated climate change/variability in improving or degrading vegetation productivity. Of the estimated total NPP gained over the study period, 32.6, 8.8, and 58.6 % were due to individual human, climate and combined impacts respectively. The contributions of the factors to NPP decline in the same order are: 50.7, 16.0 and 33.3 %. The Central Africa region is where human activities had the greatest impact on NPP improvement; whereas the Sahel and the coastlines of west northern Africa are areas associated with the greatest influence of climate-driven NPP gain. Areas with humans dominating NPP degradation include eastern

  12. A Variable Active Site Residue Influences the Kinetics of Response Regulator Phosphorylation and Dephosphorylation.

    PubMed

    Immormino, Robert M; Silversmith, Ruth E; Bourret, Robert B

    2016-10-04

    Two-component regulatory systems, minimally composed of a sensor kinase and a response regulator protein, are common mediators of signal transduction in microorganisms. All response regulators contain a receiver domain with conserved active site residues that catalyze the signal activating and deactivating phosphorylation and dephosphorylation reactions. We explored the impact of variable active site position T+1 (one residue C-terminal to the conserved Thr/Ser) on reaction kinetics and signaling fidelity, using wild type and mutant Escherichia coli CheY, CheB, and NarL to represent the three major sequence classes observed across response regulators: Ala/Gly, Ser/Thr, and Val/Ile/Met, respectively, at T+1. Biochemical and structural data together suggested that different amino acids at T+1 impacted reaction kinetics by altering access to the active site while not perturbing overall protein structure. A given amino acid at position T+1 had similar effects on autodephosphorylation in each protein background tested, likely by modulating access of the attacking water molecule to the active site. Similarly, rate constants for CheY autophosphorylation with three different small molecule phosphodonors were consistent with the steric constraints on access to the phosphorylation site arising from combination of specific phosphodonors with particular amino acids at T+1. Because other variable active site residues also influence response regulator phosphorylation biochemistry, we began to explore how context (here, the amino acid at T+2) affected the influence of position T+1 on CheY autocatalytic reactions. Finally, position T+1 affected the fidelity and kinetics of phosphotransfer between sensor kinases and response regulators but was not a primary determinant of their interaction.

  13. Comparing citrated native, kaolin-activated, and tissue factor-activated samples and determining intraindividual variability for feline thromboelastography.

    PubMed

    Banerjee, Amrita; Blois, Shauna L; Wood, R Darren

    2011-11-01

    Thromboelastography (TEG) is a point-of-care whole blood test of hemostasis. While TEG is becoming more widely used in veterinary medicine, few studies describe the use of TEG in cats. The objectives of the current study were to: 1) document the range of TEG variables produced in healthy cats using 3 sample types (citrated native, kaolin-activated, and tissue factor-activated), and 2) determine if there was a significant difference between 2 separate samples obtained from individual healthy cats on the same day. Jugular venipuncture was performed in 20 cats, and citrated blood collected for TEG. TEG analysis was performed on citrated native, kaolin-activated, and tissue factor-activated blood for each sample. Two hours later, the procedure was repeated from the opposite jugular vein, yielding a total of 120 analyses. Reaction time (R), alpha angle (α), kappa value (κ), and maximum amplitude (MA) were recorded from each tracing. No significant differences were found between TEG tracings from the first and second venipuncture samples. Significant differences were found between sample types for R, α, κ, and MA. Means for citrated native/kaolin-activated/tissue factor-activated methods were R = 4.1/3.7/0.6 min; κ = 2.5/1.8/2.2 min; α = 59.9/65.1/70.4 degrees; MA = 47.4/49.9/44.7 mm. A limitation of this study was the small number of cats used. Thromboelastography analysis may be a suitable method of evaluating hemostasis in cats.

  14. Intra-Individual Variability of Physical Activity in Older Adults With and Without Mild Alzheimer’s Disease

    PubMed Central

    Hoffman, Lesa; Templin, Jonathan

    2016-01-01

    Physical activity shows promise for protection against cognitive decline in older adults with and without Alzheimer’s disease (AD). To better understand barriers to adoption of physical activity in this population, a clear understanding of daily and weekly activity patterns is needed. Most accelerometry studies report average physical activity over an entire wear period without considering the potential importance of the variability of physical activity. This study evaluated individual differences in the amount and intra-individual variability of physical activity and determined whether these differences could be predicted by AD status, day of wear, age, gender, education, and cardiorespiratory capacity. Physical activity was measured via accelerometry (Actigraph GT3X+) over one week in 86 older adults with and without AD (n = 33 and n = 53, respectively). Mixed-effects location-scale models were estimated to evaluate and predict individual differences in the amount and intra-individual variability of physical activity. Results indicated that compared to controls, participants with AD averaged 21% less activity, but averaged non-significantly greater intra-individual variability. Women and men averaged similar amounts of physical activity, but women were significantly less variable. The amount of physical activity differed significantly across days of wear. Increased cardiorespiratory capacity was associated with greater average amounts of physical activity. Investigation of individual differences in the amount and intra-individual variability of physical activity provided insight into differences by AD status, days of monitor wear, gender, and cardiovascular capacity. All individuals regardless of AD status were equally consistent in their physical activity, which may have been due to a highly sedentary sample and/or the early disease stage of those participants with AD. These results highlight the value of considering individual differences in both the amount

  15. Dielectrophoresis-Mediated Electrodeformation as a Means of Determining Individual Platelet Stiffness

    PubMed Central

    Leung, Siu Ling; Lu, Yi; Bluestein, Danny; Slepian, Marvin J.

    2015-01-01

    Platelets, essential for hemostasis, are easily activated via biochemical and mechanical stimuli. Cell stiffness is a vital parameter modulating the mechano-transduction of exogenous mechanical stimuli. While methods exist to measure cell stiffness, no ready method exists for measuring platelet stiffness that is both minimally-contacting, imparting minimal exogenous force and non-activating. We developed a minimal-contact methodology capable of trapping and measuring the stiffness of individual platelets utilizing dielectrophoresis (DEP)-mediated electrodeformation. Parametric studies demonstrate a non-uniform electric field in the MHz frequency range (0.2–20 MHz) is required for generating effective DEP forces on platelets, suspended in isotonic buffer with conductivity ~100–200 μS/cm. A nano-Newton DEP force (0.125–4.5 nN) was demonstrated to be essential for platelet electrodeformation, which could be generated with an electric field with strength of 1.5–9 V/μm. Young’s moduli of platelets were calculated using a Maxwell stress tensor model and stress-deformation relationship. Platelet stiffness was determined to be in the range of 3.5 ± 1.4 and 8.5 ± 1.5 kPa for resting and 0.4% paraformaldehydetreated cells, respectively. The developed methodology fills a gap in approaches of measuring individual platelet stiffness, free of inadvertent platelet activation, which will facilitate further studies of mechanisms involved in mechanically-mediated platelet activation. PMID:26202677

  16. Modeling and simulating the neuromuscular mechanisms regulating ankle and knee joint stiffness during human locomotion

    PubMed Central

    Maculan, Marco; Pizzolato, Claudio; Reggiani, Monica; Farina, Dario

    2015-01-01

    This work presents an electrophysiologically and dynamically consistent musculoskeletal model to predict stiffness in the human ankle and knee joints as derived from the joints constituent biological tissues (i.e., the spanning musculotendon units). The modeling method we propose uses electromyography (EMG) recordings from 13 muscle groups to drive forward dynamic simulations of the human leg in five healthy subjects during overground walking and running. The EMG-driven musculoskeletal model estimates musculotendon and resulting joint stiffness that is consistent with experimental EMG data as well as with the experimental joint moments. This provides a framework that allows for the first time observing 1) the elastic interplay between the knee and ankle joints, 2) the individual muscle contribution to joint stiffness, and 3) the underlying co-contraction strategies. It provides a theoretical description of how stiffness modulates as a function of muscle activation, fiber contraction, and interacting tendon dynamics. Furthermore, it describes how this differs from currently available stiffness definitions, including quasi-stiffness and short-range stiffness. This work offers a theoretical and computational basis for describing and investigating the neuromuscular mechanisms underlying human locomotion. PMID:26245321

  17. Big bang nucleosynthesis with a stiff fluid

    SciTech Connect

    Dutta, Sourish; Scherrer, Robert J.

    2010-10-15

    Models that lead to a cosmological stiff fluid component, with a density {rho}{sub S} that scales as a{sup -6}, where a is the scale factor, have been proposed recently in a variety of contexts. We calculate numerically the effect of such a stiff fluid on the primordial element abundances. Because the stiff fluid energy density decreases with the scale factor more rapidly than radiation, it produces a relatively larger change in the primordial helium-4 abundance than in the other element abundances, relative to the changes produced by an additional radiation component. We show that the helium-4 abundance varies linearly with the density of the stiff fluid at a fixed fiducial temperature. Taking {rho}{sub S10} and {rho}{sub R10} to be the stiff fluid energy density and the standard density in relativistic particles, respectively, at T=10 MeV, we find that the change in the primordial helium abundance is well-fit by {Delta}Y{sub p}=0.00024({rho}{sub S10}/{rho}{sub R10}). The changes in the helium-4 abundance produced by additional radiation or by a stiff fluid are identical when these two components have equal density at a 'pivot temperature', T{sub *}, where we find T{sub *}=0.55 MeV. Current estimates of the primordial {sup 4}He abundance give the constraint on a stiff fluid energy density of {rho}{sub S10}/{rho}{sub R10}<30.

  18. 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.

  19. Estimation of axial stiffness of plant fibres from compaction of non-woven mats

    NASA Astrophysics Data System (ADS)

    Gamstedt, E. K.; Bommier, E.; Madsen, B.

    2014-03-01

    Plant fibres are known to show a large variability in stiffness, which makes it time-consuming to experimentally characterize this property by conventional tensile testing. In this work, an alternative method is used, where the average fibre stiffness is back-calculated from compaction tests of in-plane randomly oriented fibre mats. The model by Toll is used to relate the load-displacement curve from the test to the Young modulus of the fibre, taking into account the natural variability in fibre cross section. Several tests have been performed on hemp fibre mats and compared with results from single-fibre tensile testing. The average back-calculated Young's modulus of the fibres was 45 GPa, whereas the average value from tensile testing ranged from 30 to 60 GPa. The straightforward compaction test can be useful in ranking of fibre stiffness, provided that the mat is composed of well-separated fibres and not of twisted yarns.

  20. Variability in AIRS CO2 during active and break phases of Indian summer monsoon.

    PubMed

    Revadekar, J V; Ravi Kumar, K; Tiwari, Yogesh K; Valsala, Vinu

    2016-01-15

    Due to human activities, the atmospheric concentration of Carbon Dioxide (CO2) has been rising extensively since the Industrial Revolution. Indian summer monsoon (ISM) has a dominant westerly component from ocean to land with a strong tendency to ascend and hence may have role in CO2 distribution in lower and middle troposphere over Indian sub-continent. A substantial component of ISM variability arises from the fluctuations on the intra-seasonal scale between active and break phases which correspond to strong and weak monsoon circulation. In view of the above, an attempt is made in this study to examine the AIRS/AQUA satellite retrieved CO2 distribution in response to atmospheric circulation with focus on active and break phase. Correlation analysis indicates the increase in AIRS CO2 linked with strong monsoon circulation. Study also reveals that anomalous circulation pattern during active and break phase show resemblance with high and low values of AIRS CO2. Homogeneous monsoon regions of India show substantial increase in CO2 levels during active phase. Hilly regions of India show strong contrast in CO2 and vertical velocity during active and break phases.

  1. Investigation of In Vivo skin stiffness anisotropy in breast cancer related lymphoedema.

    PubMed

    Coutts, L V; Miller, N R; Mortimer, P S; Bamber, J C

    2016-01-04

    There is a limited range of suitable measurement techniques for detecting and assessing breast cancer related lymphoedema (BCRL). This study investigated the suitability of using skin stiffness measurements, with a particular focus on the variation in stiffness with measurement direction (known as anisotropy). In addition to comparing affected tissue with the unaffected tissue on the corresponding site on the opposite limb, volunteers without BCRL were tested to establish the normal variability in stiffness anisotropy between these two corresponding regions of skin on each opposite limb. Multi-directional stiffness was measured with an Extensometer, within the higher stiffness region that skin typically displays at high applied strains, using a previously established protocol developed by the authors. Healthy volunteers showed no significant difference in anisotropy between regions of skin on opposite limbs (mean decrease of 4.7 +/-2.5% between non-dominant and dominant arms), whereas BCRL sufferers showed a significant difference between limbs (mean decrease of 51.0+/-16.3% between unaffected and affected arms). A large difference in anisotropy was apparent even for those with recent onset of the condition, indicating that the technique may have potential to be useful for early detection. This difference also appeared to increase with duration since onset. Therefore, measurement of stiffness anisotropy has potential value for the clinical assessment and diagnosis of skin conditions such as BCRL. The promising results justify a larger study with a larger number of participants.

  2. A New Extensive Catalog of Optically Variable Active Galactic Nuclei in the GOODS Fields and a New Statistical Approach to Variability Selection

    NASA Astrophysics Data System (ADS)

    Villforth, Carolin; Koekemoer, Anton M.; Grogin, Norman A.

    2010-11-01

    Variability is a property shared by practically all active galactic nuclei (AGNs). This makes variability selection a possible technique for identifying AGNs. Given that variability selection makes no prior assumption about spectral properties, it is a powerful technique for detecting both low-luminosity AGNs in which the host galaxy emission is dominating and AGNs with unusual spectral properties. In this paper, we will discuss and test different statistical methods for the detection of variability in sparsely sampled data that allow full control over the false positive rates. We will apply these methods to the GOODS North and South fields and present a catalog of variable sources in the z band in both GOODS fields. Out of the 11,931 objects checked, we find 155 variable sources at a significance level of 99.9%, corresponding to about 1.3% of all objects. After rejection of stars and supernovae, 139 variability-selected AGNs remain. Their magnitudes reach down as faint as 25.5 mag in z. Spectroscopic redshifts are available for 22 of the variability-selected AGNs, ranging from 0.046 to 3.7. The absolute magnitudes in the rest-frame z band range from ~-18 to -24, reaching substantially fainter than the typical luminosities probed by traditional X-ray and spectroscopic AGN selection in these fields. Therefore, this is a powerful technique for future exploration of the evolution of the faint end of the AGN luminosity function up to high redshifts. Based on observations obtained with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.

  3. Severity and Diurnal Improvement of Morning Stiffness Independently Associate with Tenosynovitis in Patients with Rheumatoid Arthritis

    PubMed Central

    Kobayashi, Yoshihisa; Nakamura, Takayuki; Yamagata, Mieko; Nakazawa, Takuya; Tanaka, Shigeru; Furuta, Shunsuke; Umibe, Takeshi; Nakajima, Hiroshi

    2016-01-01

    Background and objectives Although morning stiffness has long been recognized as a characteristic feature of rheumatoid arthritis (RA), it is no more included in the 2010 ACR/EULAR Classification Criteria or in the current major instruments for evaluating disease activity of RA. In this cross-sectional study, we aimed to determine the independent value and the optimal measurement of morning stiffness by clarifying the associations between morning stiffness and synovial inflammation. Patients and methods We enrolled 76 consecutive RA patients who underwent musculoskeletal ultrasound examination and agreed to participate in the study. In addition to asking the duration of morning stiffness, we asked patients to complete a diagram which represents the time course of their morning stiffness in the dominant hand. Based on this diagram, we calculated the severity and the diurnal improvement of morning stiffness. We also determined the activity of intra-articular synovitis in 11 joints and tenosynovitis in 8 tendons/tendon compartments in the same hand by using power Doppler (PD) ultrasound with a semiquantitative score (0–3). Results For intra-articular synovitis, swollen/tender joint counts more strongly correlated with total PD scores (ρ = 0.379–0.561, p ≤ 0.001) than did any parameters of morning stiffness (ρ = 0.217–0.314, p = 0.006–0.021). For tenosynovitis, however, the severity on awakening and the improvement of morning stiffness more strongly correlated with total PD scores (ρ = 0.503–0.561, p < 0.001) than did swollen/tender joint counts (ρ = 0.276–0.388, p = 0.001–0.016). Multivariate analyses identified the severity on awakening and the improvement but not the duration of morning stiffness as factors that independently associate with the total tenosynovial PD score. Conclusions Our data demonstrate a pathophysiological link between morning stiffness and tenosynovitis and also give an insight into the optimal measurement of morning

  4. Social desirability is associated with some physical activity, psychosocial variables and sedentary behavior but not self-reported physical activity among adolescent males.

    PubMed

    Jago, Russell; Baranowski, Tom; Baranowski, Janice C; Cullen, Karen W; Thompson, Debbe I

    2007-06-01

    This study examined whether controlling for social desirability improved the association between self-reported and objectively measured physical activity among adolescent males and the extent that psychosocial variables predict physical activity after controlling for social desirability. Participants (n=447) were 10- to 14-year old Houston Boy Scouts. Participants completed self-reports of physical activity, sedentary behavior, preferences, self-efficacy and social desirability and wore an MTI accelerometer for 3 days. Correlations were conducted among variables. Regression models were performed to examine the relationships between objectively measured (accelerometer) and self-reported physical activity, objectively measured physical activity and psychosocial variables and self-reports of physical activity and psychosocial variables. All models controlled for social desirability. There were weak associations between self-reported and objectively measured physical activity measures that were slightly improved after controlling for social desirability. Psychosocial variables were strongly associated with self-reports of physical activity, but weakly associated with accelerometer physical activity. Social desirability was positively associated with physical activity preferences (r=0.169) and self-efficacy (r=0.118) and negatively associated (r=-0.158) with self-reported sedentary behavior. Differences in the strength of relationships between self-reported and objectively measured physical activity and psychosocial variables were not a function of social desirability.

  5. A higher baseline plasma uric acid level is an independent predictor of arterial stiffness

    PubMed Central

    Ding, Xiao-Han; Wang, Xiaona; Cao, Ruihua; Yang, Xu; Xiao, Wenkai; Zhang, Yun; Bai, Yongyi; Wu, Hongmei; Ye, Ping

    2017-01-01

    Abstract Hyperuricemia has been demonstrated to be a risk factor for cardiovascular diseases. Though the association between uric acid (UA) and arterial stiffness has been investigated previously in patients with basic diseases, the predictive value of baseline UA level for arterial stiffness has not been conducted. We aimed at identifying the predictive role of UA for arterial stiffness prospectively. A longitudinal follow-up study in a routine health check-up population was performed with an average follow-up of 4.8 years. The demographic information, baseline and follow-up anthropometric parameters, arterial stiffness (pulse-wave velocity, PWV), and biomarker variables including UA have been measured and analyzed. A total of 1447 valid follow-ups were available for the final analysis. Both of the baseline and follow-up UA levels were significantly higher in the arterial stiffness groups than that in the nonarterial stiffness groups (all P values <0.001). The follow-up carotid-femoral PWV [(cf-PWV), r = 0.161, P < 0.001] was strongly correlated with baseline UA. At the follow-up cross-section, cf-PWV was also closely associated with UA (r = 0.101, P < 0.001). Logistic regressions revealed that a higher baseline UA level was an independent predictor of follow-up arterial stiffness assessed by cf-PWV [odds ratio (OR): 1.824; P = 0.046]. A higher baseline level of UA is closely related to arterial stiffness and is an independent predictor of arterial stiffening. PMID:28178136

  6. Performance variation due to stiffness in a tuna-inspired flexible foil model.

    PubMed

    Rosic, Mariel-Luisa N; Thornycroft, Patrick J M; Feilich, Kara L; Lucas, Kelsey N; Lauder, George V

    2017-01-17

    Tuna are fast, economical swimmers in part due to their stiff, high aspect ratio caudal fins and streamlined bodies. Previous studies using passive caudal fin models have suggested that while high aspect ratio tail shapes such as a tuna's generally perform well, tail performance cannot be determined from shape alone. In this study, we analyzed the swimming performance of tuna-tail-shaped hydrofoils of a wide range of stiffnesses, heave amplitudes, and frequencies to determine how stiffness and kinematics affect multiple swimming performance parameters for a single foil shape. We then compared the foil models' kinematics with published data from a live swimming tuna to determine how well the hydrofoil models could mimic fish kinematics. Foil kinematics over a wide range of motion programs generally showed a minimum lateral displacement at the narrowest part of the foil, and, immediately anterior to that, a local area of large lateral body displacement. These two kinematic patterns may enhance thrust in foils of intermediate stiffness. Stiffness and kinematics exhibited subtle interacting effects on hydrodynamic efficiency, with no one stiffness maximizing both thrust and efficiency. Foils of intermediate stiffnesses typically had the greatest coefficients of thrust at the highest heave amplitudes and frequencies. The comparison of foil kinematics with tuna kinematics showed that tuna motion is better approximated by a zero angle of attack foil motion program than by programs that do not incorporate pitch. These results indicate that open questions in biomechanics may be well served by foil models, given appropriate choice of model characteristics and control programs. Accurate replication of biological movements will require refinement of motion control programs and physical models, including the creation of models of variable stiffness.

  7. 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

  8. ACTIVE LEARNING TO OVERCOME SAMPLE SELECTION BIAS: APPLICATION TO PHOTOMETRIC VARIABLE STAR CLASSIFICATION

    SciTech Connect

    Richards, Joseph W.; Starr, Dan L.; Miller, Adam A.; Bloom, Joshua S.; Butler, Nathaniel R.; Berian James, J.; Brink, Henrik; Long, James P.; Rice, John

    2012-01-10

    Despite the great promise of machine-learning algorithms to classify and predict astrophysical parameters for the vast numbers of astrophysical sources and transients observed in large-scale surveys, the peculiarities of the training data often manifest as strongly biased predictions on the data of interest. Typically, training sets are derived from historical surveys of brighter, more nearby objects than those from more extensive, deeper surveys (testing data). This sample selection bias can cause catastrophic errors in predictions on the testing data because (1) standard assumptions for machine-learned model selection procedures break down and (2) dense regions of testing space might be completely devoid of training data. We explore possible remedies to sample selection bias, including importance weighting, co-training, and active learning (AL). We argue that AL-where the data whose inclusion in the training set would most improve predictions on the testing set are queried for manual follow-up-is an effective approach and is appropriate for many astronomical applications. For a variable star classification problem on a well-studied set of stars from Hipparcos and Optical Gravitational Lensing Experiment, AL is the optimal method in terms of error rate on the testing data, beating the off-the-shelf classifier by 3.4% and the other proposed methods by at least 3.0%. To aid with manual labeling of variable stars, we developed a Web interface which allows for easy light curve visualization and querying of external databases. Finally, we apply AL to classify variable stars in the All Sky Automated Survey, finding dramatic improvement in our agreement with the ASAS Catalog of Variable Stars, from 65.5% to 79.5%, and a significant increase in the classifier's average confidence for the testing set, from 14.6% to 42.9%, after a few AL iterations.

  9. Substrate Stiffness Controls Osteoblastic and Chondrocytic Differentiation of Mesenchymal Stem Cells without Exogenous Stimuli

    PubMed Central

    Hyzy, Sharon L.; Doroudi, Maryam; Williams, Joseph K.; Gall, Ken; Boyan, Barbara D.; Schwartz, Zvi

    2017-01-01

    Stem cell fate has been linked to the mechanical properties of their underlying substrate, affecting mechanoreceptors and ultimately leading to downstream biological response. Studies have used polymers to mimic the stiffness of extracellular matrix as well as of individual tissues and shown mesenchymal stem cells (MSCs) could be directed along specific lineages. In this study, we examined the role of stiffness in MSC differentiation to two closely related cell phenotypes: osteoblast and chondrocyte. We prepared four methyl acrylate/methyl methacrylate (MA/MMA) polymer surfaces with elastic moduli ranging from 0.1 MPa to 310 MPa by altering monomer concentration. MSCs were cultured in media without exogenous growth factors and their biological responses were compared to committed chondrocytes and osteoblasts. Both chondrogenic and osteogenic markers were elevated when MSCs were grown on substrates with stiffness <10 MPa. Like chondrocytes, MSCs on lower stiffness substrates showed elevated expression of ACAN, SOX9, and COL2 and proteoglycan content; COMP was elevated in MSCs but reduced in chondrocytes. Substrate stiffness altered levels of RUNX2 mRNA, alkaline phosphatase specific activity, osteocalcin, and osteoprotegerin in osteoblasts, decreasing levels on the least stiff substrate. Expression of integrin subunits α1, α2, α5, αv, β1, and β3 changed in a stiffness- and cell type-dependent manner. Silencing of integrin subunit beta 1 (ITGB1) in MSCs abolished both osteoblastic and chondrogenic differentiation in response to substrate stiffness. Our results suggest that substrate stiffness is an important mediator of osteoblastic and chondrogenic differentiation, and integrin β1 plays a pivotal role in this process. PMID:28095466

  10. 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.

  11. 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

  12. Effects of inorganic phosphate analogues on stiffness and unloaded shortening of skinned muscle fibres from rabbit.

    PubMed Central

    Chase, P B; Martyn, D A; Kushmerick, M J; Gordon, A M

    1993-01-01

    1. We examined the effects of aluminofluoride (AlFx) and orthovanadate (Vi), tightly binding analogues of orthophosphate (Pi), on the mechanical properties of glycerinated fibres from rabbit psoas muscle. Maximum Ca(2+)-activated force, stiffness, and unloaded shortening velocity (Vus) were measured under conditions of steady-state inhibition (up to 1 mM of inhibitor) and during the recovery from inhibition. 2. Stiffness was measured using either step or sinusoidal (1 kHz) changes in fibre length. Sarcomere length was monitored continuously by helium-neon laser diffraction during maximum Ca2+ activation. Stiffness was determined from the changes in sarcomere length and the corresponding changes in force. Vus was measured using the slack test method. 3. AlF chi and Vi each reversibly inhibited force, stiffness and Vus. Actively cycling cross-bridges were required for reversal of these inhibitory effects. Recovery from inhibition by AlF chi was 3- to 4-fold slower than that following removal of V1. 4. At various degrees of inhibition, AlF chi and Vi both inhibited steady-state isometric force more than either Vus or stiffness. For both AlF chi and Vi, the relatively greater inhibition of force over stiffness persisted during recovery from steady-state inhibition. We interpret these results to indicate that the cross-bridges with AlF chi or Vi bound are analogous to those which occur early in the cross-bridge cycle. PMID:8487194

  13. Nonparticipatory Stiffness in the Male Perioral Complex

    PubMed Central

    Chu, Shin-Ying; Lee, Jaehoon

    2008-01-01

    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 computer-controlled linear motor servo programmed to impose a series of tensile displacements over a span of approximately 24 mm at the oral angle in 20 healthy young male adults. Perioral electromyograms were simultaneously sampled to confirm nonparticipation or passive muscle state. Perioral stiffness, derived as a quotient from resultant force (ΔF) and oral span (ΔX), was modeled with regression techniques, and subsequently compared to previously reported perioral stiffness data for female adults. Results Multilevel regression analysis revealed a significant quadratic relation between the perioral stiffness and interangle span; however, no significant difference was found between adult males and females. Conclusion These normative measures will have application to future studies designed to objectively assess the effects of pathology (i.e., progressive neuromotor disease, traumatic brain insult) and intervention (pharmacologic, neurosurgical, and reconstructive surgery of the face [i.e., cleft lip, trauma, missile injuries]) on facial animation and speech kinematics. PMID:19717655

  14. 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.

  15. [Stiff-person syndrome and related autoantibodies].

    PubMed

    Tomioka, Ryo; Tanaka, Keiko

    2013-04-01

    Central nervous system hyperexcitability disorders, known as stiff-man/person syndrome (SPS), are thought to be related to the regulatory disturbance of inhibitory synaptic transmission of motor neurons in the brainstem and spinal cord. SPS is characterized by stiffness and spasms of the axis and limbs and is divided into two clinical subgroups: classic SPS, which affects the lumbar, trunk, and proximal limb muscles, and SPS-plus syndrome. The latter comprises (1) the stiff-limb subtype, in which symptom is limited to the lower limbs; (2) jerking stiff-man syndrome, characterized by chronically progressive stiffness and myoclonus; and (3) acute-onset and progressive encephalomyelitis with rigidity and myoclonus. Almost 80% of patients with classic SPS harbor autoantibodies against glutamic acid decarboxylase 65 (GAD65). In approximately 30-40% of patients, SPS accompanies type I diabetes, and anti-GAD65 antibodies are detected frequently in type I diabetes. However, the antibody-recognizing epitopes might be different between SPS and diabetes. Other autoantibodies against glycine receptor α1 (12% of patients with SPS) and GABA(A)-receptor associated protein (70% of patients with SPS) have been reported. In paraneoplastic SPS, anti-amphiphysin antibodies have been shown in patients with breast cancer or small cell lung cancer. One case of mediastinal tumor with anti-gephyrin antibodies has also been reported. However, the roles of these autoantibodies in the pathomechanisms of SPS have not yet been elucidated.

  16. Motor activity as an unbiased variable to assess anaphylaxis in allergic rats.

    PubMed

    Abril-Gil, Mar; Garcia-Just, Alba; Cambras, Trinitat; Pérez-Cano, Francisco J; Castellote, Cristina; Franch, Àngels; Castell, Margarida

    2015-10-01

    The release of mediators by mast cells triggers allergic symptoms involving various physiological systems and, in the most severe cases, the development of anaphylactic shock compromising mainly the nervous and cardiovascular systems. We aimed to establish variables to objectively study the anaphylactic response (AR) after an oral challenge in an allergy model. Brown Norway rats were immunized by intraperitoneal injection of ovalbumin with alum and toxin from Bordetella pertussis. Specific immunoglobulin (Ig) E antibodies were developed in immunized animals. Forty days after immunization, the rats were orally challenged with the allergen, and motor activity, body temperature and serum mast cell protease concentration were determined. The anaphylaxis induced a reduction in body temperature and a decrease in the number of animal movements, which was inversely correlated with serum mast cell protease release. In summary, motor activity is a reliable tool for assessing AR and also an unbiased method for screening new anti-allergic drugs.

  17. Essential Oil Composition of Phagnalon sordidum (L.) from Corsica, Chemical Variability and Antimicrobial Activity.

    PubMed

    Brunel, Marion; Vitrac, Caroline; Costa, Jean; Mzali, Fatima; Vitrac, Xavier; Muselli, Alain

    2016-03-01

    The chemical composition of Phagnalon sordidum (L.) essential oil was investigated for the first time using gas chromatography and chromatography/mass spectrometry. Seventy-six compounds, which accounted for 87.9% of the total amount, were identified in a collective essential oil of P. sordidum from Corsica. The main essential oil components were (E)-β-caryophyllene (14.4%), β-pinene (11.0%), thymol (9.0%), and hexadecanoic acid (5.3%). The chemical compositions of essential oils from 19 Corsican locations were investigated. The study of the chemical variability using statistical analysis allowed identifying direct correlation between the three populations of P. sordidum widespread in Corsica and the essential oil compositions they produce. The in vitro antimicrobial activity of P. sordidum essential oil was evaluated and it exhibited a notable activity on a large panel of clinically significant microorganisms.

  18. C15078. Essential oil composition of Phagnalon sordidum (L.) from Corsica, chemical variability and antimicrobial activity.

    PubMed

    Brunel, Marion; Vitrac, Caroline; Costa, Jean; Mzali, Fatima; Vitrac, Xavier; Muselli, Alain

    2016-02-10

    The chemical composition of Phagnalon sordidum (L.) essential oil was investigated for the first time using gas chromatography and chromatography-mass spectrometry. Seventy-six compounds, which accounted for 87.9% of the total amount, were identified in a collective essential oil of P. sordidum from Corsica. The main essential oil components were (E)-β-caryophyllene (14.4%), β-pinene (11.0%), thymol (9.0%), and hexadecanoic acid (5.3%). The chemical compositions of essential oils from 19 Corsican locations were investigated. The study of the chemical variability using statistical analysis allowed identifying direct correlation between the three populations of P. sordidum widespread in Corsica and the essential oil compositions they produce. The in vitro antimicrobial activity of P. sordidum essential oil was evaluated and exhibited a notable activity on a large panel of clinically significant microorganisms. This article is protected by copyright. All rights reserved.

  19. Variable Camber Continuous Aerodynamic Control Surfaces and Methods for Active Wing Shaping Control

    NASA Technical Reports Server (NTRS)

    Nguyen, Nhan T. (Inventor)

    2016-01-01

    An aerodynamic control apparatus for an air vehicle improves various aerodynamic performance metrics by employing multiple spanwise flap segments that jointly form a continuous or a piecewise continuous trailing edge to minimize drag induced by lift or vortices. At least one of the multiple spanwise flap segments includes a variable camber flap subsystem having multiple chordwise flap segments that may be independently actuated. Some embodiments also employ a continuous leading edge slat system that includes multiple spanwise slat segments, each of which has one or more chordwise slat segment. A method and an apparatus for implementing active control of a wing shape are also described and include the determination of desired lift distribution to determine the improved aerodynamic deflection of the wings. Flap deflections are determined and control signals are generated to actively control the wing shape to approximate the desired deflection.

  20. Characterizing biological variability in livestock blood cholinesterase activity for biomonitoring organophosphate nerve agent exposure

    SciTech Connect

    Halbrook, R.S.; Shugart, L.R.; Watson, A.P.; Munro, N.B.; Linnabary, R.D. )

    1992-09-01

    A biomonitoring protocol, using blood cholinesterase (ChE) activity in livestock as a monitor of potential organophosphate nerve agent exposure during the planned destruction of US unitary chemical warfare agent stockpiles, is described. The experimental design included analysis of blood ChE activity in individual healthy sheep, horses, and dairy and beef cattle during a 10- to 12-month period. Castrated and sexually intact males, pregnant and lactating females, and adult and immature animals were examined through at least one reproductive cycle. The same animals were used throughout the period of observation and were not exposed to ChE-inhibiting organophosphate or carbamate compounds. A framework for an effective biomonitoring protocol within a monitoring area includes establishing individual baseline blood ChE activity for a sentinel group of 6 animals on the bases of blood samples collected over a 6-month period, monthly collection of blood samples for ChE-activity determination during monitoring, and selection of adult animals as sentinels. Exposure to ChE-inhibiting compounds would be suspected when all blood ChE activity of all animals within the sentinel group are decreased greater than 20% from their own baseline value. Sentinel species selection is primarily a logistical and operational concern; however, sheep appear to be the species of choice because within-individual baseline ChE activity and among age and gender group ChE activity in sheep had the least variability, compared with data from other species. This protocol provides an effective and efficient means for detecting abnormal depressions in blood ChE activity in livestock and can serve as a valuable indicator of the extent of actual plume movement and/or deposition in the event of organophosphate nerve agent release.

  1. Changes in the Hurst Exponent of Heart Rate Variability during Physical Activity

    NASA Astrophysics Data System (ADS)

    Aoyagi, Naoko; Kiyono, Ken; Struzik, Zbigniew R.; Yamamoto, Yoshiharu

    2005-08-01

    We examine fractal scaling properties of heart rate variability using detrended fluctuation analysis (DFA), during physical activity in healthy subjects. We analyze 11 records of healthy subjects, which include both usual daily activity and experimental exercise. The subjects were asked to ride on a bicycle ergometer for 2.5 hours, and maintained a heartbeat interval of 500-600 ms. In order to estimate the long-range correlation in the series of heartbeat intervals during controlled physical activity, we apply DFA to the data set with the third-order polynomial trend removed. For all records during exercise, we observe a characteristic crossover phenomenon at ≈ 300 beats. The scaling exponent in the range > 300 beats (> 3 minutes) during exercise decreases and tends to be closer to white noise (≈ 0.5), which corresponds to uncorrelated behavior. The long-range scaling exponent during exercise is significantly lower than that during daily activity in this range. Contrary to the currently held view, our results indicate a breakdown in long-range correlations and 1/f-like scaling, rather than the increase in the Hurst exponent characteristic of a (congestive) increase in afterload and observed, e.g., in congestive heart failure (CHF) patients. Further, our results suggest an increased load imbalance induced departure from critical-like behavior, which has recently been reported in healthy human heart rate during daily activity.

  2. Effect of process variables on the production of Polyhydroxyalkanoates by activated sludge

    PubMed Central

    2012-01-01

    Polyhydroxyalkanoates are known to be temporarily stored by microorganisms in activated sludge, especially in anaerobic-aerobic processes. Due to the problems resulted from the disposals of plastic wastes and excess sludge of wastewater treatment plants, the production of polyhydroxyalkanoates by treating activated sludge and determining the effect of process variables were the main issues of this paper. In this research, an anaerobic-aerobic sequencing batch reactor was used to make microorganism adapted and a batch aerobic reactor was used for enriching them. The variables affecting polyhydroxyalkanoates production including aeration time, sludge retention time, and volatile fatty acids concentration of the influent in sequencing batch reactor, and also carbon to nitrogen ratio and cultivation time in polymer production reactor, were investigated using Taguchi statistical approach to determine optimum conditions. The maximum polymer production of 29% was achieved at sludge retention time of 5–10 days, aeration time of 2 hours, supplementation of 40% of volatile fatty acids in the influent and increasing of carbon to nitrogen ratio of polymer production reactor to above 25 g/g. Based on the results, in optimum conditions, the volatile fatty acids concentration which increased the production of polyhydroxyalkanoates up to 49% was the most effective variable. Carbon to nitrogen ratio, sludge retention time and aeration time were ranked as the next affecting parameters. Although the polyhydroxyalkanoates content achieved in present study is much lower than that by pure culture, but the proposed method may still serve well as an environmental friendly means to convert waste into valuable product. PMID:23369512

  3. The variability of the trunk forward bending in standing activities during work vs. leisure time.

    PubMed

    Villumsen, Morten; Madeleine, Pascal; Jørgensen, Marie Birk; Holtermann, Andreas; Samani, Afshin

    2017-01-01

    High level of occupational physical activity (PA), contrary to leisure time activities, is generally associated with detrimental health outcomes. We hypothesized that this contrast may be associated with a different pattern of exposure variability in PA, e.g., forward bending of the trunk. The study was conducted on 657 blue-collar workers. Two accelerometers were used to identify the body posture and forward bending of the trunk during work and leisure time. The pattern of forward bending was analyzed using exposure variation analysis (EVA). The recordings comprised of 2.6 ± 0.97 working days in average, with 19.9 ± 8.1 h work and 22.9 ± 8.9 h leisure. The standard deviation and entropy of the EVA profile indicated 11% and 6% (for about 80% of subjects) less variable pattern during work compared with the leisure time, respectively. These new findings contribute to the understanding the paradoxical outcomes of PA during work and leisure.

  4. Physical activity, mindfulness meditation, or heart rate variability biofeedback for stress reduction: a randomized controlled trial.

    PubMed

    van der Zwan, Judith Esi; de Vente, Wieke; Huizink, Anja C; Bögels, Susan M; de Bruin, Esther I

    2015-12-01

    In contemporary western societies stress is highly prevalent, therefore the need for stress-reducing methods is great. This randomized controlled trial compared the efficacy of self-help physical activity (PA), mindfulness meditation (MM), and heart rate variability biofeedback (HRV-BF) in reducing stress and its related symptoms. We randomly allocated 126 participants to PA, MM, or HRV-BF upon enrollment, of whom 76 agreed to participate. The interventions consisted of psycho-education and an introduction to the specific intervention techniques and 5 weeks of daily exercises at home. The PA exercises consisted of a vigorous-intensity activity of free choice. The MM exercises consisted of guided mindfulness meditation. The HRV-BF exercises consisted of slow breathing with a heart rate variability biofeedback device. Participants received daily reminders for their exercises and were contacted weekly to monitor their progress. They completed questionnaires prior to, directly after, and 6 weeks after the intervention. Results indicated an overall beneficial effect consisting of reduced stress, anxiety and depressive symptoms, and improved psychological well-being and sleep quality. No significant between-intervention effect was found, suggesting that PA, MM, and HRV-BF are equally effective in reducing stress and its related symptoms. These self-help interventions provide easily accessible help for people with stress complaints.

  5. Observing Campaign to Monitor Magnetically-Active Dwarfs for Long-Term Variability

    NASA Astrophysics Data System (ADS)

    Templeton, Matthew R.

    2009-10-01

    Dr. Styliani (Stella) Kafka of the Department of Terrestrial Magnetism, Carnegie Institute of Washington, requests AAVSO observers to perform long-term photometric monitoring on a number of magnetically active dwarf stars, with an observing frequency of one observation every three days taken with one or more filters. When multiple filters are available, the preferred observations are (in order of precedence): Rc, V, Ic, and B. Please observe such that you obtain a signal to noise of at least 50 (100 or higher is preferred). These objects are all nearby dwarfs known or suspected to have magnetic activity, primarily of the UV Ceti (flare star) or BY Draconis subtypes. Long-term photometric monitoring of these objects will be used in conjunction with other multiwavelength observations from ground-based facilities including the Magellan 6.5-meter and DuPont 2.5-meter telescopes in Chile to understand the long-term magnetic activity cycles of these stars. Such a study can reveal information about the physical natures of these stars, but also about their near space environments and habitability for life. These objects are red, and the variability amplitudes are low, often well below 0.1 magnitudes. The long-term variability due to stellar activity cycles may be much lower. Photometric accuracy rather than the number of observations are key to the success of this project. Unaccounted-for atmospheric effects such as extinction will likely overwhelm any long-term signal from these stars. Observers are strongly urged to fully calibrate their systems and to carefully reduce and transform their photometry to standard photometric passbands, including corrections for airmass/atmospheric extinction. Parameters for 40 objects are given. Observations should be submitted to the AAVSO International Database.

  6. Comparison of kinetic variables and muscle activity during a squat vs. a box squat.

    PubMed

    McBride, Jeffrey M; Skinner, Jared W; Schafer, Patrick C; Haines, Tracie L; Kirby, Tyler J

    2010-12-01

    The purpose of this investigation was to determine if there was a difference in kinetic variables and muscle activity when comparing a squat to a box squat. A box squat removes the stretch-shortening cycle component from the squat, and thus, the possible influence of the box squat on concentric phase performance is of interest. Eight resistance trained men (Height: 179.61 ± 13.43 cm; Body Mass: 107.65 ± 29.79 kg; Age: 24.77 ± 3.22 years; 1 repetition maximum [1RM]: 200.11 ± 58.91 kg) performed 1 repetition of squats and box squats using 60, 70, and 80% of their 1RM in a randomized fashion. Subjects completed the movement while standing on a force plate and with 2 linear position transducers attached to the bar. Force and velocity were used to calculate power. Peak force and peak power were determined from the force-time and power-time curves during the concentric phase of the lift. Muscle activity (electromyography) was recorded from the vastus lateralis, vastus medialis, biceps femoris, and longissimus. Results indicate that peak force and peak power are similar between the squat and box squat. However, during the 70% of 1RM trials, the squat resulted in a significantly lower peak force in comparison to the box squat (squat = 3,269 ± 573 N, box squat = 3,364 ± 575 N). In addition, during the 80% of 1RM trials, the squat resulted in significantly lower peak power in comparison to the box squat (squat = 2,050 ± 486 W, box squat = 2,197 ± 544 W). Muscle activity was generally higher during the squat in comparison to the box squat. In conclusion, minimal differences were observed in kinetic variables and muscle activity between the squat and box squat. Removing the stretch-shortening cycle during the squat (using a box) appears to have limited negative consequences on performance.

  7. Collar height and heel counter-stiffness for ankle stability and athletic performance in basketball.

    PubMed

    Liu, Hui; Wu, Zitian; Lam, Wing-Kai

    2017-01-25

    This study examined the effects of collar height and heel counter-stiffness of basketball shoes on ankle stability during sidestep cutting and athletic performance. 15 university basketball players wore customized shoes with different collar heights (high and low) and heel counter-stiffness (regular, stiffer and stiffest) for this study. Ankle stability was evaluated in sidestep cutting while athletic performance evaluated in jumping and agility tasks. All variables were analysed using two-way repeated ANOVA. Results showed shorter time to peak ankle inversion for both high collar and stiff heel counter conditions (P < 0.05), while smaller initial ankle inversion angle, peak inversion velocity and total range of inversion for wearing high collar shoes (P < 0.05). No shoe differences were found for performance variables. These findings imply that the collar height might play a larger role in lateral stability than heel counter-stiffness, while both collar height and counter-stiffness have no effect on athletic performance.

  8. Dynamic stiffness model of spherical parallel robots

    NASA Astrophysics Data System (ADS)

    Cammarata, Alessandro; Caliò, Ivo; D`Urso, Domenico; Greco, Annalisa; Lacagnina, Michele; Fichera, Gabriele

    2016-12-01

    A novel approach to study the elastodynamics of Spherical Parallel Robots is described through an exact dynamic model. Timoshenko arches are used to simulate flexible curved links while the base and mobile platforms are modelled as rigid bodies. Spatial joints are inherently included into the model without Lagrangian multipliers. At first, the equivalent dynamic stiffness matrix of each leg, made up of curved links joined by spatial joints, is derived; then these matrices are assembled to obtain the Global Dynamic Stiffness Matrix of the robot at a given pose. Actuator stiffness is also included into the model to verify its influence on vibrations and modes. The latter are found by applying the Wittrick-Williams algorithm. Finally, numerical simulations and direct comparison to commercial FE results are used to validate the proposed model.

  9. Electrochemical stiffness in lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Tavassol, Hadi; Jones, Elizabeth M. C.; Sottos, Nancy R.; Gewirth, Andrew A.

    2016-11-01

    Although lithium-ion batteries are ubiquitous in portable electronics, increased charge rate and discharge power are required for more demanding applications such as electric vehicles. The high-rate exchange of lithium ions required for more power and faster charging generates significant stresses and strains in the electrodes that ultimately lead to performance degradation. To date, electrochemically induced stresses and strains in battery electrodes have been studied only individually. Here, a new technique is developed to probe the chemomechanical response of electrodes by calculating the electrochemical stiffness via coordinated in situ stress and strain measurements. We show that dramatic changes in electrochemical stiffness occur due to the formation of different graphite-lithium intercalation compounds during cycling. Our analysis reveals that stress scales proportionally with the lithiation/delithiation rate and strain scales proportionally with capacity (and inversely with rate). Electrochemical stiffness measurements provide new insights into the origin of rate-dependent chemomechanical degradation and the evaluation of advanced battery electrodes.

  10. Seasonal Variability in Boreal Wildfire Activity Associated with Landscape Patterns of Burned Area

    NASA Astrophysics Data System (ADS)

    Barrett, K. M.; Kasischke, E. S.

    2012-12-01

    Wildfire is the most prominent disturbance in the boreal forest, effecting changes in stand age and vegetation composition often over thousands of square kilometers. The effect of wildfire on ecosystem structure and function depends heavily on the seasonality of the burn, and periods of seasonally high fire activity are highly sporadic. The majority of area in Alaska that burns in a fire season does so during relatively short periods of high fire activity. These periods, which can be determined from active fire detections or fire management agency data records, are caused by elevated air temperatures and low precipitation which decrease fuel moisture and encourage the spread of fire. While fire fronts dominate during periods of low fire activity, more active periods have a higher proportion of residual burning which remains after a front has passed through. Residual burning is likely responsible for the extensive combustion of surface organic materials in the boreal forest, which can lead to post-fire changes in dominant vegetation type. Seasonal variations in fire activity are therefore an important factor in the mosaic of severity conditions across large burned areas and shifts in land cover over successional time scales. The purpose of this study is to characterize the temporal and spatial variability in periods of seasonal high fire activity that influence patterns of burned area. In large burns, unburned areas within a fire scar may serve as an important seed stock during post-fire recruitment. These areas may also feedback to future fire regimes through the preservation of more fire-resistant vegetation in unburned "islands".

  11. Application of a local linearization technique for the solution of a system of stiff differential equations associated with the simulation of a magnetic bearing assembly

    NASA Technical Reports Server (NTRS)

    Kibler, K. S.; Mcdaniel, G. A.

    1981-01-01

    A digital local linearization technique was used to solve a system of stiff differential equations which simulate a magnetic bearing assembly. The results prove the technique to be accurate, stable, and efficient when compared to a general purpose variable order Adams method with a stiff option.

  12. Structures of glycosylated mammalian glutaminyl cyclases reveal conformational variability near the active center.

    PubMed

    Ruiz-Carrillo, David; Koch, Birgit; Parthier, Christoph; Wermann, Michael; Dambe, Tresfore; Buchholz, Mirko; Ludwig, Hans-Henning; Heiser, Ulrich; Rahfeld, Jens-Ulrich; Stubbs, Milton T; Schilling, Stephan; Demuth, Hans-Ulrich

    2011-07-19

    Formation of N-terminal pyroglutamate (pGlu or pE) from glutaminyl or glutamyl precursors is catalyzed by glutaminyl cyclases (QC). As the formation of pGlu-amyloid has been linked with Alzheimer's disease, inhibitors of QCs are currently the subject of intense development. Here, we report three crystal structures of N-glycosylated mammalian QC from humans (hQC) and mice (mQC). Whereas the overall structures of the enzymes are similar to those reported previously, two surface loops in the neighborhood of the active center exhibit conformational variability. Furthermore, two conserved cysteine residues form a disulfide bond at the base of the active center that was not present in previous reports of hQC structure. Site-directed mutagenesis suggests a structure-stabilizing role of the disulfide bond. At the entrance to the active center, the conserved tryptophan residue, W(207), which displayed multiple orientations in previous structure, shows a single conformation in both glycosylated human and murine QCs. Although mutagenesis of W(207) into leucine or glutamine altered substrate conversion significantly, the binding constants of inhibitors such as the highly potent PQ50 (PBD150) were minimally affected. The crystal structure of PQ50 bound to the active center of murine QC reveals principal binding determinants provided by the catalytic zinc ion and a hydrophobic funnel. This study presents a first comparison of two mammalian QCs containing typical, conserved post-translational modifications.

  13. Human single-chain variable fragment antibody inhibits macrophage migration inhibitory factor tautomerase activity.

    PubMed

    Tarasuk, Mayuri; Poungpair, Ornnuthchar; Ungsupravate, Duangporn; Bangphoomi, Kunan; Chaicumpa, Wanpen; Yenchitsomanus, Pa-Thai

    2014-03-01

    Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine, secreted from a variety of immune cells, that regulates innate and adaptive immune responses. Elevation of MIF levels in plasma correlates with the severity of inflammatory diseases in humans. Inhibition of MIF or its tautomerase activity ameliorates disease severity by reducing inflammatory responses. In this study, the human single-chain variable fragment (HuScFv) antibody specific to MIF was selected from the human antibody phage display library by using purified recombinant full-length human MIF (rMIF) as the target antigen. Monoclonal HuScFv was produced from phage-transformed bacteria and tested for their binding activities to rMIF by indirect enzyme-linked immunosorbent assay as well as to native MIF by western blot analysis and immunofluorescence assay. The HuScFv with highest binding signal to rMIF also inhibited the tautomerase activities of both rMIF and native MIF in human monoblastic leukemia (U937) cells in a dose-dependent manner. Mimotope searching and molecular docking concordantly demonstrated that the HuScFv interacted with Lys32 and Ile64 in the MIF tautomerase active site. To the best of our knowledge, this is the first study to focus on MIF-specific fully-human antibody fragment with a tautomerase-inhibitory effect that has potential to be developed as anti-inflammatory biomolecules for human use.

  14. Geographic Variability and Anti-Staphylococcal Activity of the Chrysophaentins and Their Synthetic Fragments

    PubMed Central

    Keffer, Jessica L.; Hammill, Jared T.; Lloyd, John R.; Plaza, Alberto; Wipf, Peter; Bewley, Carole A.

    2012-01-01

    Drug-resistant Staphylococcus aureus is a continuing public health concern, both in the hospital and community settings. Antibacterial compounds that possess novel structural scaffolds and are effective against multiple S. aureus strains, including current drug-resistant ones, are needed. Previously, we have described the chrysophaentins, a family of bisdiarylbutene macrocycles from the chrysophyte alga Chrysophaeum taylori that inhibit the growth of S. aureus and methicillin-resistant S. aureus (MRSA). In this study we have analyzed the geographic variability of chrysophaentin production in C. taylori located at different sites on the island of St. John, U.S. Virgin Islands, and identified two new linear chrysophaentin analogs, E2 and E3. In addition, we have expanded the structure activity relationship through synthesis of fragments comprising conserved portions of the chrysophaentins, and determined the antimicrobial activity of natural chrysophaentins and their synthetic analogs against five diverse S. aureus strains. We find that the chrysophaentins show similar activity against all S. aureus strains, regardless of their drug sensitivity profiles. The synthetic chrysophaentin fragments indeed mimic the natural compounds in their spectrum of antibacterial activity, and therefore represent logical starting points for future medicinal chemistry studies of the natural products and their analogs. PMID:22822360

  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. Vinculin promotes nuclear localization of TAZ to inhibit ECM stiffness-dependent differentiation into adipocytes.

    PubMed

    Kuroda, Mito; Wada, Hiroki; Kimura, Yasuhisa; Ueda, Kazumitsu; Kioka, Noriyuki

    2017-03-01

    Extracellular matrix (ECM) stiffness regulates the lineage commitment of mesenchymal stem cells (MSCs). Although cells sense ECM stiffness through focal adhesions, how cells sense ECM stiffness and regulate ECM stiffness-dependent differentiation remains largely unclear. In this study, we show that the cytoskeletal focal adhesion protein vinculin plays a critical role in the ECM stiffness-dependent adipocyte differentiation of MSCs. ST2 mouse MSCs differentiate into adipocytes and osteoblasts in an ECM stiffness-dependent manner. We find that a rigid ECM increases the amount of cytoskeleton-associated vinculin and promotes the nuclear localization and activity of the transcriptional coactivator paralogs Yes-associated protein (YAP, also known as YAP1) and transcriptional coactivator with a PDZ-binding motif (TAZ, also known as WWTR1) (hereafter YAP/TAZ). Vinculin is necessary for enhanced nuclear localization and activity of YAP/TAZ on the rigid ECM but it does not affect the phosphorylation of the YAP/TAZ kinase LATS1. Furthermore, vinculin depletion promotes differentiation into adipocytes on rigid ECM, while it inhibits differentiation into osteoblasts. Finally, TAZ knockdown was less effective at promoting adipocyte differentiation in vinculin-depleted cells than in control cells. These results suggest that vinculin promotes the nuclear localization of transcription factor TAZ to inhibit the adipocyte differentiation on rigid ECM.

  17. Interhourly Variability Index of Geomagnetic Activity and Its Use in Deriving the Long-Term Variation of Solar Wind Speed

    DTIC Science & Technology

    2007-10-31

    CONTRACT NUMBER Interhourly variability index of geomagnetic activity and its use in deriving the long-term variation of solar wind speed 5b...detailed derivation of the interhourly variability (IHP) index of geomagnetic activity. The LHV index for a given geomagnetic element is mechanically... index is derived separately for stations in both hemispheres within six longitude sectors spanning the Earth using only local night hours. It is

  18. Differentiation between non-neural and neural contributors to ankle joint stiffness in cerebral palsy

    PubMed Central

    2013-01-01

    Background Spastic paresis in cerebral palsy (CP) is characterized by increased joint stiffness that may be of neural origin, i.e. improper muscle activation caused by e.g. hyperreflexia or non-neural origin, i.e. altered tissue viscoelastic properties (clinically: “spasticity” vs. “contracture”). Differentiation between these components is hard to achieve by common manual tests. We applied an assessment instrument to obtain quantitative measures of neural and non-neural contributions to ankle joint stiffness in CP. Methods Twenty-three adolescents with CP and eleven healthy subjects were seated with their foot fixated to an electrically powered single axis footplate. Passive ramp-and-hold rotations were applied over full ankle range of motion (RoM) at low and high velocities. Subject specific tissue stiffness, viscosity and reflexive torque were estimated from ankle angle, torque and triceps surae EMG activity using a neuromuscular model. Results In CP, triceps surae reflexive torque was on average 5.7 times larger (p = .002) and tissue stiffness 2.1 times larger (p = .018) compared to controls. High tissue stiffness was associated with reduced RoM (p < .001). Ratio between neural and non-neural contributors varied substantially within adolescents with CP. Significant associations of SPAT (spasticity test) score with both tissue stiffness and reflexive torque show agreement with clinical phenotype. Conclusions Using an instrumented and model based approach, increased joint stiffness in CP could be mainly attributed to higher reflexive torque compared to control subjects. Ratios between contributors varied substantially within adolescents with CP. Quantitative differentiation of neural and non-neural stiffness contributors in CP allows for assessment of individual patient characteristics and tailoring of therapy. PMID:23880287

  19. MEASURING X-RAY VARIABILITY IN FAINT/SPARSELY SAMPLED ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Allevato, V.; Paolillo, M.; Papadakis, I.; Pinto, C.

    2013-07-01

    We study the statistical properties of the normalized excess variance of variability process characterized by a ''red-noise'' power spectral density (PSD), as in the case of active galactic nuclei (AGNs). We perform Monte Carlo simulations of light curves, assuming both a continuous and a sparse sampling pattern and various signal-to-noise ratios (S/Ns). We show that the normalized excess variance is a biased estimate of the variance even in the case of continuously sampled light curves. The bias depends on the PSD slope and on the sampling pattern, but not on the S/N. We provide a simple formula to account for the bias, which yields unbiased estimates with an accuracy better than 15%. We show that the normalized excess variance estimates based on single light curves (especially for sparse sampling and S/N < 3) are highly uncertain (even if corrected for bias) and we propose instead the use of an ''ensemble estimate'', based on multiple light curves of the same object, or on the use of light curves of many objects. These estimates have symmetric distributions, known errors, and can also be corrected for biases. We use our results to estimate the ability to measure the intrinsic source variability in current data, and show that they could also be useful in the planning of the observing strategy of future surveys such as those provided by X-ray missions studying distant and/or faint AGN populations and, more in general, in the estimation of the variability amplitude of sources that will result from future surveys such as Pan-STARRS and LSST.

  20. LONG-TERM OPTICAL CONTINUUM COLOR VARIABILITY OF NEARBY ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Sakata, Yu; Minezaki, Takeo; Yoshii, Yuzuru; Uchimoto, Yuka Katsuno; Sugawara, Shota; Kobayashi, Yukiyasu; Koshida, Shintaro; Aoki, Tsutomu; Tomita, Hiroyuki; Enya, Keigo; Suganuma, Masahiro

    2010-03-01

    We examine whether the spectral energy distribution of optical continuum emission of active galactic nuclei (AGNs) changes during flux variation, based on accurate and frequent monitoring observations of 11 nearby Seyfert galaxies and QSOs carried out in the B, V, and I bands for seven years by the MAGNUM telescope. The multi-epoch flux data in any two different bands obtained on the same night show a very tight linear flux-to-flux relationship for all target AGNs. The flux of the host galaxy within the photometric aperture is carefully estimated by surface brightness fitting to available high-resolution Hubble Space Telescope images and MAGNUM images. The flux of narrow emission lines in the photometric bands is also estimated from available spectroscopic data. We find that the non-variable component of the host galaxy plus narrow emission lines for all target AGNs is located on the fainter extension of the linear regression line of multi-epoch flux data in the flux-to-flux diagram. This result strongly indicates that the spectral shape of AGN continuum emission in the optical region ({approx}4400-7900 A) does not systematically change during flux variation. The trend of spectral hardening that optical continuum emission becomes bluer as it becomes brighter, which has been reported by many studies, is therefore interpreted as the domination of the variable component of the nearly constant spectral shape of an AGN as it brightens over the non-variable component of the host galaxy plus narrow lines, which is usually redder than AGN continuum emission.

  1. The variability in DMSP content and DMSP lyase activity in marine dinoflagellates

    NASA Astrophysics Data System (ADS)

    Caruana, Amandine M. N.; Malin, Gill

    2014-01-01

    More than 20 years ago Maureen Keller and co-workers published a study that identified dinoflagellates as an important marine phytoplankton group with respect to the production of dimethylsulphoniopropionate (DMSP). Here, we present a synthesis and analysis of all the DMSP and DMSP lyase activity (DLA) measurements currently available for dinoflagellates. The data cover 110 species and strains and reveal over 6 orders of magnitude variability in intracellular DMSP concentrations and substantial variations in DLA in 23 strains. Inter-specific variability was explored with reference to a range of biological characteristics. The presence of a theca did not appear to be related to DMSP concentration but there was a potential relationship with toxicity (P = 0.06) and bioluminescent species produced significantly lower concentrations (P < 0.01) than non-bioluminescent ones. DMSP concentrations were related to plastid types (P < 0.05); dinoflagellates with haptophyte-like plastids contained lower amounts of DMSP than those with peridinin plastids (P < 0.01), whereas those containing cryptomonad-like plastids tended to have higher DMSP concentrations. Heterotrophic dinoflagellates were also considered given their importance in the natural environment. They are the only heterotrophs known to synthesise DMSP and this ability may support the theory that they are of photosynthetic origin. However, the heterotrophic species investigated so far suggest wide variability in DMSP content and the species Oxyrrhis marina had no detectable DMSP. The oceanic province of origin significantly affected the DMSP concentrations (P < 0.05) with higher DMSP content observed in dinoflagellates from the Mediterranean province, the Kuroshio Current province and the East Coastal Australian province. Overall this study supports the concept that DMSP-containing dinoflagellates are an important potential source of DMS to the global atmosphere and highlights current gaps in knowledge.

  2. Modulation of fixation stiffness from flexible to stiff in a rat model of bone healing

    PubMed Central

    Bartnikowski, Nicole; Claes, Lutz E; Koval, Lidia; Glatt, Vaida; Bindl, Ronny; Steck, Roland; Ignatius, Anita; Schuetz, Michael A; Epari, Devakara R

    2017-01-01

    Background and purpose Constant fixator stiffness for the duration of healing may not provide suitable mechanical conditions for all stages of bone repair. We therefore investigated the influence of stiffening fixation on callus stiffness and morphology in a rat diaphyseal osteotomy model to determine whether healing time was shortened and callus stiffness increased through modulation of fixation from flexible to stiff. Material and methods An external unilateral fixator was applied to the osteotomized femur and stiffened by decreasing the offset of the inner fixator bar at 3, 7, 14, and 21 days after operation. After 5 weeks, the rats were killed and healing was evaluated with mechanical, histological, and microcomputed tomography methods. Constant fixation stiffness control groups with either stiff or flexible fixation were included for comparison. Results The callus stiffness of the stiff group and all 4 experimental groups was greater than in the flexible group. The callus of the flexible group was larger but contained a higher proportion of unmineralized tissue and cartilage. The stiff and modulated groups (3, 7, 14, and 21 days) all showed bony bridging at 5 weeks, as well as signs of callus remodeling. Stiffening fixation at 7 and 14 days after osteotomy produced the highest degree of callus bridging. Bone mineral density in the fracture gap was highest in animals in which the fixation was stiffened after 14 days. Interpretation The predicted benefit of a large robust callus formed through early flexible fixation could not be shown, but the benefits of stabilizing a flexible construct to achieve timely healing were demonstrated at all time points. PMID:27841708

  3. Modulation of fixation stiffness from flexible to stiff in a rat model of bone healing.

    PubMed

    Bartnikowski, Nicole; Claes, Lutz E; Koval, Lidia; Glatt, Vaida; Bindl, Ronny; Steck, Roland; Ignatius, Anita; Schuetz, Michael A; Epari, Devakara R

    2016-11-14

    Background and purpose - Constant fixator stiffness for the duration of healing may not provide suitable mechanical conditions for all stages of bone repair. We therefore investigated the influence of stiffening fixation on callus stiffness and morphology in a rat diaphyseal osteotomy model to determine whether healing time was shortened and callus stiffness increased through modulation of fixation from flexible to stiff. Material and methods - An external unilateral fixator was applied to the osteotomized femur and stiffened by decreasing the offset of the inner fixator bar at 3, 7, 14, and 21 days after operation. After 5 weeks, the rats were killed and healing was evaluated with mechanical, histological, and microcomputed tomography methods. Constant fixation stiffness control groups with either stiff or flexible fixation were included for comparison. Results - The callus stiffness of the stiff group and all 4 experimental groups was greater than in the flexible group. The callus of the flexible group was larger but contained a higher proportion of unmineralized tissue and cartilage. The stiff and modulated groups (3, 7, 14, and 21 days) all showed bony bridging at 5 weeks, as well as signs of callus remodeling. Stiffening fixation at 7 and 14 days after osteotomy produced the highest degree of callus bridging. Bone mineral density in the fracture gap was highest in animals in which the fixation was stiffened after 14 days. Interpretation - The predicted benefit of a large robust callus formed through early flexible fixation could not be shown, but the benefits of stabilizing a flexible construct to achieve timely healing were demonstrated at all time points.

  4. Photosynthetic activity, photoprotection and photoinhibition in intertidal microphytobenthos as studied in situ using variable chlorophyll fluorescence

    NASA Astrophysics Data System (ADS)

    Serôdio, João; Vieira, Sónia; Cruz, Sónia

    2008-06-01

    The photosynthetic activity of microphytobenthos biofilms was studied in situ on an intertidal mudflat of the Ria de Aveiro, Portugal. Time series of physical variables characterizing the microenvironment at the sediment photic zone (incident solar irradiance, temperature, salinity), photophysiological parameters and productive biomass of undisturbed microalgal assemblages were measured during daytime low-tide periods along one spring-neap tidal cycle, with the objective of (1) characterizing the short-term variability in photosynthetic activity in situ, (2) relating it with the changing environmental conditions and (3) with the operation of physiologically (xanthophyll cycle) and behaviorally (vertical migration) based photoprotective processes, and (4) assessing the occurrence of photoinhibition. Pulse Amplitude Modulated (PAM) fluorometry was applied to measure photosynthetic activity (the effective and maximum quantum yield of photosystem II, Δ F/ Fm' and Fv/ Fm; the photosynthesis index EFY; rapid light-response curves (RLC)), the photoprotective operation of the xanthophyll cycle and photoinhibition (non-photochemical quenching, NPQ; quantum efficiency of open RCs, Fv'/ Fm'), and vertical migration (productive biomass, Fo). The photosynthetic activity was found to be strongly affected by the cumulative light dose received during the morning low-tide periods. The fluorescence indices Δ F/ Fm', EFY, Fv'/ Fm' and RLC parameters were more depressed under high irradiances when clear sky was present during the morning low tide than when foggy conditions reduced the light dose received during a comparable period. Productive biomass exhibited maximum values in the first hours of the morning, followed by a steep decrease when irradiance reached moderate levels, due to the downward migration of the microalgae. This photophobic migratory response appeared to display a photoprotective role, allowing Δ F/ Fm' to remain near optimum values until irradiance reached

  5. Effect of highly active antiretroviral therapy on incident AIDS using calendar period as an instrumental variable.

    PubMed

    Cain, Lauren E; Cole, Stephen R; Greenland, Sander; Brown, Todd T; Chmiel, Joan S; Kingsley, Lawrence; Detels, Roger

    2009-05-01

    Human immunodeficiency virus (HIV) researchers often use calendar periods as an imperfect proxy for highly active antiretroviral therapy (HAART) when estimating the effect of HAART on HIV disease progression. The authors report on 614 HIV-positive homosexual men followed from 1984 to 2007 in 4 US cities. During 5,321 person-years, 268 of 614 men incurred acquired immunodeficiency syndrome, 49 died, and 90 were lost to follow-up. Comparing the pre-HAART calendar period (<1996) with the HAART calendar period (>or=1996) resulted in a naive rate ratio of 3.62 (95% confidence limits: 2.67, 4.92). However, this estimate is likely biased because of misclassification of HAART use by calendar period. Simple calendar period approaches may circumvent confounding by indication at the cost of inducing exposure misclassification. To correct this misclassification, the authors propose an instrumental-variable estimator analogous to ones previously used for noncompliance corrections in randomized clinical trials. When the pre-HAART calendar period was compared with the HAART calendar period, the instrumental-variable rate ratio was 5.02 (95% confidence limits: 3.45, 7.31), 39% higher than the naive result. Weighting by the inverse probability of calendar period given age at seroconversion, race/ethnicity, and time since seroconversion did not appreciably alter the results. These methods may help resolve discrepancies between observational and randomized evidence.

  6. Single-trial prediction of reaction time variability from MEG brain activity

    PubMed Central

    Ohata, Ryu; Ogawa, Kenji; Imamizu, Hiroshi

    2016-01-01

    Neural activity prior to movement onset contains essential information for predictive assistance for humans using brain-machine-interfaces (BMIs). Even though previous studies successfully predicted different goals for upcoming movements, it is unclear whether non-invasive recording signals contain the information to predict trial-by-trial behavioral variability under the same movement. In this paper, we examined the predictability of subsequent short or long reaction times (RTs) from magnetoencephalography (MEG) signals in a delayed-reach task. The difference in RTs was classified significantly above chance from 550 ms before the go-signal onset using the cortical currents in the premotor cortex. Significantly above-chance classification was performed in the lateral prefrontal and the right inferior parietal cortices at the late stage of the delay period. Thus, inter-trial variability in RTs is predictable information. Our study provides a proof-of-concept of the future development of non-invasive BMIs to prevent delayed movements. PMID:27250872

  7. Investigating the variability of active galactic nuclei using combined multi-quarter Kepler data

    SciTech Connect

    Revalski, Mitchell; Nowak, Dawid; Wiita, Paul J.; Wehrle, Ann E.; Unwin, Stephen C.

    2014-04-10

    We used photometry from the Kepler satellite to characterize the variability of four radio-loud active galactic nuclei (AGNs) on timescales from years to minutes. The Kepler satellite produced nearly continuous high precision data sets which provided better temporal coverage than possible with ground based observations. We have now accumulated 11 quarters of data, eight of which were reported in our previous paper. In addition to constructing power spectral densities (PSDs) and characterizing the variability of the last three quarters, we have linked together the individual quarters using a multiplicative scaling process, providing data sets spanning ∼2.8 yr with >98% coverage at a 30 minute sampling rate. We compute PSDs on these connected data sets that yield power law slopes at low frequencies in the approximate range of –1.5 to –2.0, with white noise seen at higher frequencies. These PSDs are similar to those of both the individual quarters and to those of ground-based optical observations of other AGNs. We also have explored a PSD binning method intended to reduce a bias toward shallow slope fits by evenly distributing the points within the PSDs. This tends to steepen the computed PSD slopes, especially when the low frequencies are relatively poorly fit. We detected flares lasting several days in which the brightness increased by ∼15%-20% in one object, as well a smaller flare in another. Two AGNs showed only small, ∼1%-2%, fluctuations in brightness.

  8. Chemical variability, antifungal and antioxidant activity of Eucalyptus camaldulensis essential oil from Sardinia.

    PubMed

    Barra, Andrea; Coroneo, Valentina; Dessi, Sandro; Cabras, Paolo; Angioni, Alberto

    2010-02-01

    Essential oil (EO) from aerial parts of Eucalyptus camaldulensis Dehnh., growing wild in different localities of Sardinia (Italy), was extracted by steam distillation and analyzed by gas chromatography (GC) FID and GC-ion trap mass spectrometry (ITMS). The yields of EO (v/dry wt) ranged between 0.2-0.5%. Samples were harvested between April and December to study the seasonal chemical variability of the EO. The chemical composition varied depending on the different origins and showed strong fluctuation during the vegetative stage. Thirty-seven compounds, accounting for at least 97.7% of the total EOs were identified, the major components being p-cymene (27.8-42.7%), 1,8-cineole (4.1-39.5%), beta-phellandrene (3.9-23.8%), spathulenol (2.1-15.5%) and cryptone (3.2-10.2%). The oils possessed moderate amounts (1.4-4.7%) of two uncommon aldehydes, cuminal and phellandral. The essential oils were screened for their antifungal activities against common phytopathogenic fungi using the paper disk diffusion method and they showed activity at low doses against the fungi tested. The antioxidant activity, assessed by DPPH-test and expressed as Trolox equivalent antioxidant capacity, showed values ranging between 0.5 and 5.8 mmol/L.

  9. Chemical Variability and Biological Activities of Essential Oils of Micromeria inodora (Desf.) Benth. from Algeria.

    PubMed

    Benomari, Fatima Zahra; Djabou, Nassim; Medbouhi, Ali; Khadir, Abdelmounaim; Bendahou, Mourad; Selles, Chaouki; Desjobert, Jean-Marie; Costa, Jean; Muselli, Alain

    2016-11-01

    The chemical composition of the essential oils isolated from the aerial parts of Micromeria inodora (Desf.) Benth. collected in 24 Algerian localities was investigated from the first time using GC-FID, GC/MS and (13) C-NMR. Altogether, 83 components which accounted for 94.7% of the total oil composition were identified. The main compounds were trans-sesquisabinene hydrate (1; 20.9%), α-terpinyl acetate (2; 19.8%), globulol (3; 4.9%), caryophyllene oxide (4; 4.3%), β-bisabolol (5; 2.9%) and trans-7-epi-sesquisabinene hydrate (6; 2.6%). Comparison with the literature highlighted the originality of the Algerian M. inodora oil and indicated that 1 might be used as taxonomical marker. The study of the chemical variability allowed the discrimination of two main clusters confirming that there is a relation between the essential-oil compositions and the soil nature of the harvest locations. Biological activity of M. inodora essential oil was assessed against fourteen species of microorganisms involved in nosocomial infections using paper disc diffusion and dilution agar assays. The in vitro study demonstrated a good activity against Gram-positive strains such as Staphylococcus aureus, Bacillus cereus, Bacillus subtilis, and Enterococcus faecalis, and moderate activity against Candida albicans. These results might be useful for the future commercial valorization of M. inodora essential oil as a promising source of natural products with potential against various nosocomial community and toxinic infections.

  10. Active notch filter network with variable notch depth, width and frequency

    NASA Technical Reports Server (NTRS)

    Black, J. M. (Inventor)

    1980-01-01

    An active notch filter having independently adjustable notch frequency, width, and depth is provided by three equal capacitors connected in series with an operational amplifier (connected in a voltage follower configuration), a potentiometer across the series connected capacitors for notch depth adjustment, and a potentiometer (for notch frequency connected across the center capacitor); with its tap connected to receive a voltage feedback signal from a variable voltage divider comprised of another potentiometer for notch width. Adjusting the voltage dividing potentiometer will independently set the notch width, and adjusting the tap on the potentiometer across the center capacitor will independently adjust the notch frequency of the filter. A second operational amplifier connected in a voltage follower configuration may be used to connect the voltage divider output to the adjustable tap of the potentiometer across the center capacitor.

  11. Decadal variability of European sea level extremes in relation to the solar activity

    NASA Astrophysics Data System (ADS)

    Martínez-Asensio, Adrián.; Tsimplis, Michael N.; Calafat, Francisco Mir

    2016-11-01

    This study investigates the relationship between decadal changes in solar activity and sea level extremes along the European coasts and derived from tide gauge data. Autumn sea level extremes vary with the 11 year solar cycle at Venice as suggested by previous studies, but a similar link is also found at Trieste. In addition, a solar signal in winter sea level extremes is also found at Venice, Trieste, Marseille, Ceuta, Brest, and Newlyn. The influence of the solar cycle is also evident in the sea level extremes derived from a barotropic model with spatial patterns that are consistent with the correlations obtained at the tide gauges. This agreement indicates that the link to the solar cycle is through modulation of the atmospheric forcing. The only atmospheric regional pattern that showed variability at the 11 year period was the East Atlantic pattern.

  12. A flexible active and reactive power control strategy for a variable speed constant frequency generating system

    SciTech Connect

    Tang, Y.; Xu, L.

    1995-07-01

    Variable-speed constant-frequency generating systems are used in wind power, hydro power, aerospace, and naval power generations to enhance efficiency and reduce friction. In these applications, an attractive candidate is the slip power recovery system comprising of doubly excited induction machine or doubly excited brushless reluctance machine and PWM converters with a dc link. In this paper, a flexible active and reactive power control strategy is developed, such that the optimal torque-speed profile of the turbine can be followed and overall reactive power can be controlled, while the machine copper losses have been minimized. At the same time, harmonics injected into the power network has also been minimized. In this manner, the system can function as both a high-efficient power generator and a flexible reactive power compensator.

  13. The role of physical activity and heart rate variability for the control of work related stress.

    PubMed

    Tonello, Laís; Rodrigues, Fábio B; Souza, Jeniffer W S; Campbell, Carmen S G; Leicht, Anthony S; Boullosa, Daniel A

    2014-01-01

    Physical activity (PA) and exercise are often used as tools to reduce stress and therefore the risk for developing cardiovascular diseases (CVD). Meanwhile, heart rate variability (HRV) has been utilized to assess both stress and PA or exercise influences. The objective of the present review was to examine the current literature in regards to workplace stress, PA/exercise and HRV to encourage further studies. We considered original articles from known databases (PubMed, ISI Web of Knowledge) over the last 10 years that examined these important factors. A total of seven studies were identified with workplace stress strongly associated with reduced HRV in workers. Longitudinal workplace PA interventions may provide a means to improve worker stress levels and potentially cardiovascular risk with mechanisms still to be clarified. Future studies are recommended to identify the impact of PA, exercise, and fitness on stress levels and HRV in workers and their subsequent influence on cardiovascular health.

  14. Seasonal and solar activity variability of D-region electron density at 69°N

    NASA Astrophysics Data System (ADS)

    Singer, Werner; Latteck, Ralph; Friedrich, Martin; Wakabayashi, Makato; Rapp, Markus

    2011-06-01

    A narrow beam Doppler radar operating at 3.17 MHz and installed close to the Andøya Rocket Range in Andenes, Norway, (69.3°N, 16.0°E) has been providing electron densities in the lower ionosphere since summer 2003. The experiment utilizes partial reflection of ordinary and extraordinary component waves from scatterers in the altitude range 50-95 km to estimate electron densities from differential absorption and differential phase measurements. These ground-based observations are in good agreement with concurrent rocket-borne radio wave propagation measurements at Andenes. Results of the diurnal and seasonal variability of electron densities and the response of D-region electron densities to solar activity storms are presented.

  15. Multiwavelength temporal variability of the blazar 3C 454.3 during 2014 activity phase

    NASA Astrophysics Data System (ADS)

    Kushwaha, Pankaj; Gupta, Alok C.; Misra, Ranjeev; Singh, K. P.

    2017-01-01

    We present a multiwavelength temporal analysis of the blazar 3C 454.3 during the high γ-ray active period from May to December, 2014. Except for X-rays, the period is well sampled at near-infrared (NIR)-optical by the Small and Moderate Aperture Research Telescope System (SMARTS) facility, and the source is detected continuously on daily time-scale in the Fermi-Large Area Telescope γ-ray band. The source exhibits diverse levels of variability with many flaring/active states in the continuously sampled γ-ray light curve which are also reflected in the NIR-optical light curves and the sparsely sampled X-ray light curve by the Swift-XRT. Multiband correlation analysis of this continuous segment during different activity periods shows a change of state from no lags between IR and γ-ray, optical and γ-ray, and IR and optical to a state where γ-ray lags the IR/optical by ˜3 d. The results are consistent with the previous studies of the same during various γ-ray flaring and active episodes of the source. This consistency, in turn, suggests an extended localized emission region with almost similar conditions during various γ-ray activity states. On the other hand, the delay of γ-ray with respect to IR/optical and a trend similar to IR/optical in X-rays along with strong broad-band correlations favour magnetic field related origin with X-ray and γ-ray being inverse Comptonization of IR/optical photons and external radiation field, respectively.

  16. 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...

  17. 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...

  18. 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...

  19. Monitoring the Bending Stiffness of DNA

    NASA Astrophysics Data System (ADS)

    Yuan, Chongli; Lou, Xiongwen; Rhoades, Elizabeth; Chen, Huimin; Archer, Lynden

    2007-03-01

    In eukaryotic cells, the accessibility of genomic sequences provides an inherent regulation mechanism for gene expression through variations in bending stiffness encoded by the nucleic acid sequence. Cyclization of dsDNA is the prevailing method for determining DNA bending stiffness. Recent cyclization data for short dsDNA raises several fundamental questions about the soundness of the cyclization method, particularly in cases where the probability of highly bent DNA conformations is low. We herein evaluate the role of T4 DNA ligase in the cyclization reaction by inserting an environmental sensitive base analogue, 2-amino purine, to the DNA molecule. By monitoring the 2-AP fluorescence under standard cyclization conditions, it is found that in addition to trapping highly-bent cyclic DNA conformations, T4 DNA ligase enhances the apparent base pair flip out rate, thus exaggerating the measured flexibility. This result is further confirmed using fluorescence anisotropy experiments. We show that fluorescence resonance energy transfer (FRET) measurements on suitably labeled dsDNA provides an alternative approach for quantifying the bending stiffness of short fragments. DNA bending stiffness results obtained using FRET are compared with literature values.

  20. 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...

  1. 49 CFR 213.359 - Track stiffness.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ..., 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...

  2. Improved Stiff ODE Solvers for Combustion CFD

    NASA Astrophysics Data System (ADS)

    Imren, A.; Haworth, D. C.

    2016-11-01

    Increasingly large chemical mechanisms are needed to predict autoignition, heat release and pollutant emissions in computational fluid dynamics (CFD) simulations of in-cylinder processes in compression-ignition engines and other applications. Calculation of chemical source terms usually dominates the computational effort, and several strategies have been proposed to reduce the high computational cost associated with realistic chemistry in CFD. Central to most strategies is a stiff ordinary differential equation (ODE) solver to compute the change in composition due to chemical reactions over a computational time step. Most work to date on stiff ODE solvers for computational combustion has focused on backward differential formula (BDF) methods, and has not explicitly considered the implications of how the stiff ODE solver couples with the CFD algorithm. In this work, a fresh look at stiff ODE solvers is taken that includes how the solver is integrated into a turbulent combustion CFD code, and the advantages of extrapolation-based solvers in this regard are demonstrated. Benefits in CPU time and accuracy are demonstrated for homogeneous systems and compression-ignition engines, for chemical mechanisms that range in size from fewer than 50 to more than 7,000 species.

  3. Stiff directed lines in random media.

    PubMed

    Boltz, Horst-Holger; Kierfeld, Jan

    2013-07-01

    We investigate the localization of stiff directed lines with bending energy by a short-range random potential. We apply perturbative arguments, Flory scaling arguments, a variational replica calculation, and functional renormalization to show that a stiff directed line in 1+d dimensions undergoes a localization transition with increasing disorder for d>2/3. We demonstrate that this transition is accessible by numerical transfer matrix calculations in 1+1 dimensions and analyze the properties of the disorder-dominated phase in detail. On the basis of the two-replica problem, we propose a relation between the localization of stiff directed lines in 1+d dimensions and of directed lines under tension in 1+3d dimensions, which is strongly supported by identical free-energy distributions. This shows that pair interactions in the replicated Hamiltonian determine the nature of directed line localization transitions with consequences for the critical behavior of the Kardar-Parisi-Zhang equation. We support the proposed relation to directed lines via multifractal analysis, revealing an analogous Anderson transition-like scenario and a matching correlation length exponent. Furthermore, we quantify how the persistence length of the stiff directed line is reduced by disorder.

  4. [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.

  5. Can Indian Ocean SST variability impact TC activity in the South Pacific? A Spatial Analysis

    NASA Astrophysics Data System (ADS)

    Magee, Andrew D.; Verdon-Kidd, Danielle C.; Kiem, Anthony S.

    2015-04-01

    Tropical Cyclones (TCs) represent a significant natural hazard to the 15 island nations and 2.7 million inhabitants of the South Pacific, accounting for 76% of reported disasters in the region since 1950. This vast area, dominated by the coupled ocean-atmosphere interactions of the South Pacific fuels the highly variable nature of TCs (both spatially and temporally), leading to difficulties in planning for and responding to these extreme events. While it is well known that the El Niño/Southern Oscillation (ENSO) plays a significant role in modulating the background state on which TCs form, there are other large-scale climate drivers operating on annual timescales or longer within the South Pacific (e.g. ENSO Modoki and the Interdecadal Pacific Oscillation) and outside the Pacific Basin (e.g. the Indian Ocean Dipole and the Southern Annular Mode) that may also influence TC formation. In response to this issue, the impact of these large-scale climate drivers upon the spatial characteristics of tropical cyclogenesis is assessed for the South Pacific region (5o-35oS, 145oE-130oW) over a 67-year period (1945-2011). It is shown, that in addition to the impact of 'Pacific-centric' climate drivers, eastern Indian Ocean sea surface temperatures significantly impact the spatial characteristics of tropical cyclogenesis in the South Pacific. In particular, warming (cooling) in the eastern Indian Ocean is found to result in an eastward (westward) shift in the average location of tropical cyclogenesis in the South Pacific (up to 712km between extreme phases). One mechanism that may account for this east/west modulation of TC activity in the South Pacific is the propagation of warmer water from the Timor Sea through the Coral Sea to the Pacific, resulting in a strengthening of the Pacific Warm Pool and associated meteorological characteristics connected with tropical cyclogenesis. Understanding how other large-scale climate modes interact with Indian Ocean processes is important

  6. Frequency-Dependent Fracture Specific Stiffness

    NASA Astrophysics Data System (ADS)

    Pyrak-Nolte, L. J.; Folz, M. A.; Acosta-Colon, A.

    2003-12-01

    Monitoring the hydraulic properties of fractures remotely through their seismic signatures is an important goal for field hydrology. Empirical studies have shown that the hydraulic properties of a fracture are implicitly related to the fracture specific stiffness through the amount and distribution of contact area and apertures that arise from two rough surfaces in contact. Complicating this simple picture are seismic measurements that indicate frequency-dependent stiffness, i.e., a scale-dependent fracture stiffness where the scale is set by the wavelength. Thus relating the hydraulic properties of fractures to seismic measurements becomes a scale dependent problem. We have performed laboratory experiments to examine the phenomenon of frequency dependent fracture specific stiffness to aid in the assessment of the hydraulic properties of a fracture using seismic techniques. To this end, we have developed a photolithographic technique with which we can construct synthetic fractures of known fracture geometry with feature sizes controlled over several orders of magnitude. The synthetic fracture (and the control non-fractured samples) are made from acrylic cylinders that measure 15.0 cm in diameter by 7.7 cm in height. The diameter of the samples enables us to sample the acoustic properties of the fracture using acoustic lens over regions that range in scale from 10 mm to 60 mm. A confinement cell controls the normal stress on the fracture. Seismic measurements were made with broadband compressional-mode piezoelectric transducers enabling one-order of magnitude in frequency. We found that when the wavelength is smaller than the asperity size, a linear dependence of fracture specific stiffness on frequency occurs. In this geometric ray regime the asymptotic value of the transmission function provides a direct measure of the contact area of the fracture. On the other hand, when the asperity spacing is less than an eighth of a wavelength, the fracture behaves as a

  7. Physical Activity Is Linked to Greater Moment-To-Moment Variability in Spontaneous Brain Activity in Older Adults

    PubMed Central

    Burzynska, Agnieszka Z.; Wong, Chelsea N.; Voss, Michelle W.; Cooke, Gillian E.; Gothe, Neha P.; Fanning, Jason; McAuley, Edward; Kramer, Arthur F.

    2015-01-01

    Higher cardiorespiratory fitness (CRF) and physical activity (PA) in old age are associated with greater brain structural and functional integrity, and higher cognitive functioning. However, it is not known how different aspects of lifestyle such as sedentariness, light PA (LI-PA), or moderate-to-vigorous physical activity (MV-PA) relate to neural activity in aging. In addition, it is not known whether the effects of PA on brain function differ or overlap with those of CRF. Here, we objectively measured CRF as oxygen consumption during a maximal exercise test and measured PA with an accelerometer worn for 7 days in 100 healthy but low active older adults (aged 60–80 years). We modeled the relationships between CRF, PA, and brain functional integrity using multivariate partial least squares analysis. As an index of functional brain integrity we used spontaneous moment-to-moment variability in the blood oxygenation level-dependent signal (SDBOLD), known to be associated with better cognitive functioning in aging. We found that older adults who engaged more in LI-PA and MV-PA had greater SDBOLD in brain regions that play a role in integrating segregated functional domains in the brain and benefit from greater CRF or PA, such as precuneus, hippocampus, medial and lateral prefrontal, and temporal cortices. Our results suggest that engaging in higher intensity PA may have protective effects on neural processing in aging. Finally, we demonstrated that older adults with greater overall WM microstructure were those showing more LI-PA and MV-PA and greater SDBOLD. We conclude that SDBOLD is a promising correlate of functional brain health in aging. Future analyses will evaluate whether SDBOLD is modifiable with interventions aimed to increase PA and CRF in older adults. PMID:26244873

  8. ON THE STIFFNESS OF DEMINERALIZED DENTIN MATRICES

    PubMed Central

    Ryou, Heonjune; Turco, Gianluca; Breschi, Lorenzo; Tay, Franklin R.; Pashley, David H.; Arola, Dwayne

    2015-01-01

    Resin bonding to dentin requires the use of self-etching primers or acid etching to decalcify the surface and expose a layer of collagen fibrils of the dentin matrix. Acid-etching reduces the stiffness of demineralized dentin from approximately 19 GPa to 1 MPa, requiring that it floats in water to prevent it from collapsing during bonding procedures. Several publications show that crosslinking agents like gluteraladehyde, carbodiimide or grape seed extract can stiffen collagen and improve resin-dentin bond strength. Objective The objective was to assess a new approach for evaluating the changes in stiffness of decalcified dentin by polar solvents and a collagen cross-linker. Methods Fully demineralized dentin beams and sections of etched coronal dentin were subjected to indentation loading using a cylindrical flat indenter in water, and after treatment with ethanol or ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). The stiffness was measured as a function of strain and as a function of loading rate from 1 to 50 µm/sec. Results At a strain of 0.25% the elastic modulus of the fully demineralized dentin was approximately 0.20 MPa. It increased to over 0.90 MPa at strains of 1%. Exposure to ethanol caused an increase in elastic modulus of up to four times. Increasing the loading rate from 1 to 50 µm/sec caused an increase in the apparent modulus of up to three times in both water and ethanol. EDC treatment caused increases in the stiffness in fully demineralized samples and in acid-etched demineralized dentin surfaces in situ. Significance Changes in the mechanical behavior of demineralized collagen matrices can be measured effectively under hydration via indentation with cylindrical flat indenters. This approach can be used for quantifying the effects of bonding treatments on the properties of decalcified dentin after acid etching, as well as to follow the loss of stiffness over time due to enzymatic degradation. PMID:26747822

  9. Stiffness of lipid monolayers with phase coexistence.

    PubMed

    Caruso, Benjamín; Mangiarotti, Agustín; Wilke, Natalia

    2013-08-27

    The surface dilational modulus--or compressibility modulus--has been previously studied for monolayers composed of pure materials, where a jump in this modulus was related with the onset of percolation as a result of the establishment of a connected structure at the molecular level. In this work, we focused on monolayers composed of two components of low lateral miscibility. Our aim was to investigate the compressibility of mixed monolayers at pressures and compositions in the two-phase region of the phase diagram, in order to analyze the effect of the mechanical properties of each phase on the stiffness of the composite. In nine different systems with distinct molecular dipoles and charges, the stiffness of each phase and the texture at the plane of the monolayer were studied. In this way, we were able to analyze the general compressibility of two-phase lipid monolayers, regardless of the properties of their constituent parts. The results are discussed in the light of the following two hypotheses: first, the stiffness of the composite could be dominated by the stiffness of each phase as a weighted sum according to the percentage of each phase area, regardless of the distribution of the phases in the plane of the monolayer. Alternatively, the stiffness of the composite could be dominated by the mechanical properties of the continuous phase. Our results were better explained by this latter proposal, as in all the analyzed mixtures it was found that the mechanical properties of the percolating phase were the determining factors. The value of the compression modulus was closer to the value of the connected phase than to that of the dispersed phase, indicating that the bidimensional composites displayed mechanical properties that were related to the properties of each phases in a rather complex manner.

  10. Relationship between sympathetic baroreflex sensitivity and arterial stiffness in elderly men and women.

    PubMed

    Okada, Yoshiyuki; Galbreath, M Melyn; Shibata, Shigeki; Jarvis, Sara S; VanGundy, Tiffany B; Meier, Rhonda L; Vongpatanasin, Wanpen; Levine, Benjamin D; Fu, Qi

    2012-01-01

    Previous human studies have shown that large-artery stiffness contributes to an age-related decrease in cardiovagal baroreflex sensitivity. Whether this is also true with sympathetic baroreflex sensitivity is unknown. We tested the hypothesis that sympathetic baroreflex sensitivity is associated with the stiffness of baroreceptor segments (the carotid artery and the aorta) in elderly individuals and that sex affects this relationship. Sympathetic baroreflex sensitivity was assessed from the spontaneous changes in beat-by-beat diastolic pressure and corresponding muscle sympathetic nerve activity (microneurography) during supine rest in 30 men (mean±SEM: 69±1 years) and 31 women (68±1 years). Carotid artery stiffness (B-mode ultrasonography) and aortic stiffness (MRI) were also determined. We found that elderly women had lower sympathetic baroreflex sensitivity than elderly men (-2.33±0.25 versus -3.32±0.25 bursts · 100 beats(-1) · mm Hg(-1); P=0.007). β-Stiffness indices of the carotid artery and the aorta were greater in elderly women than in men (6.68±0.48 versus 5.10±0.50 and 4.03±0.47 versus 2.68±0.42; both P<0.050). Sympathetic baroreflex sensitivity was inversely correlated with carotid artery stiffness in both men and women (r=0.49 and 0.50; both P<0.05), whereas this relation was shifted in parallel upward (toward a reduced sensitivity) in women with no changes in the slope (0.26 versus 0.24 arbitrary units). Sympathetic baroreflex sensitivity and aortic stiffness showed similar trends. Thus, barosensory artery stiffness seems to be one independent determinant of sympathetic baroreflex sensitivity in elderly men and women. The lower sympathetic baroreflex sensitivity in elderly women may predispose them to an increased prevalence of hypertension.

  11. Mechanical phenotype of cancer cells: cell softening and loss of stiffness sensing.

    PubMed

    Lin, Hsi-Hui; Lin, Hsiu-Kuan; Lin, I-Hsuan; Chiou, Yu-Wei; Chen, Horn-Wei; Liu, Ching-Yi; Harn, Hans I-Chen; Chiu, Wen-Tai; Wang, Yang-Kao; Shen, Meng-Ru; Tang, Ming-Jer

    2015-08-28

    The stiffness sensing ability is required to respond to the stiffness of the matrix. Here we determined whether normal cells and cancer cells display distinct mechanical phenotypes. Cancer cells were softer than their normal counterparts, regardless of the type of cancer (breast, bladder, cervix, pancreas, or Ha-RasV12-transformed cells). When cultured on matrices of varying stiffness, low stiffness decreased proliferation in normal cells, while cancer cells and transformed cells lost this response. Thus, cancer cells undergo a change in their mechanical phenotype that includes cell softening and loss of stiffness sensing. Caveolin-1, which is suppressed in many tumor cells and in oncogene-transformed cells, regulates the mechanical phenotype. Caveolin-1-upregulated RhoA activity and Y397FAK phosphorylation directed actin cap formation, which was positively correlated with cell elasticity and stiffness sensing in fibroblasts. Ha-RasV12-induced transformation and changes in the mechanical phenotypes were reversed by re-expression of caveolin-1 and mimicked by the suppression of caveolin-1 in normal fibroblasts. This is the first study to describe this novel role for caveolin-1, linking mechanical phenotype to cell transformation. Furthermore, mechanical characteristics may serve as biomarkers for cell transformation.

  12. Aging impairs smooth muscle-mediated regulation of aortic stiffness: a defect in shock absorption function?

    PubMed

    Gao, Yuan Z; Saphirstein, Robert J; Yamin, Rina; Suki, Bela; Morgan, Kathleen G

    2014-10-15

    Increased aortic stiffness is an early and independent biomarker of cardiovascular disease. Here we tested the hypothesis that vascular smooth muscle cells (VSMCs) contribute significantly to aortic stiffness and investigated the mechanisms involved. The relative contributions of VSMCs, focal adhesions (FAs), and matrix to stiffness in mouse aorta preparations at optimal length and with confirmed VSMC viability were separated by the use of small-molecule inhibitors and activators. Using biomechanical methods designed for minimal perturbation of cellular function, we directly quantified changes with aging in aortic material stiffness. An alpha adrenoceptor agonist, in the presence of N(G)-nitro-l-arginine methyl ester (l-NAME) to remove interference of endothelial nitric oxide, increases stiffness by 90-200% from baseline in both young and old mice. Interestingly, increases are robustly suppressed by the Src kinase inhibitor PP2 in young but not old mice. Phosphotyrosine screening revealed, with aging, a biochemical signature of markedly impaired agonist-induced FA remodeling previously associated with Src signaling. Protein expression measurement confirmed a decrease in Src expression with aging. Thus we report here an additive model for the in vitro biomechanical components of the mouse aortic wall in which 1) VSMCs are a surprisingly large component of aortic stiffness at physiological lengths and 2) regulation of the VSMC component through FA signaling and hence plasticity is impaired with aging, diminishing the aorta's normal shock absorption function in response to stressors.

  13. Aging impairs smooth muscle-mediated regulation of aortic stiffness: a defect in shock absorption function?

    PubMed Central

    Gao, Yuan Z.; Saphirstein, Robert J.; Yamin, Rina; Suki, Bela

    2014-01-01

    Increased aortic stiffness is an early and independent biomarker of cardiovascular disease. Here we tested the hypothesis that vascular smooth muscle cells (VSMCs) contribute significantly to aortic stiffness and investigated the mechanisms involved. The relative contributions of VSMCs, focal adhesions (FAs), and matrix to stiffness in mouse aorta preparations at optimal length and with confirmed VSMC viability were separated by the use of small-molecule inhibitors and activators. Using biomechanical methods designed for minimal perturbation of cellular function, we directly quantified changes with aging in aortic material stiffness. An alpha adrenoceptor agonist, in the presence of NG-nitro-l-arginine methyl ester (l-NAME) to remove interference of endothelial nitric oxide, increases stiffness by 90–200% from baseline in both young and old mice. Interestingly, increases are robustly suppressed by the Src kinase inhibitor PP2 in young but not old mice. Phosphotyrosine screening revealed, with aging, a biochemical signature of markedly impaired agonist-induced FA remodeling previously associated with Src signaling. Protein expression measurement confirmed a decrease in Src expression with aging. Thus we report here an additive model for the in vitro biomechanical components of the mouse aortic wall in which 1) VSMCs are a surprisingly large component of aortic stiffness at physiological lengths and 2) regulation of the VSMC component through FA signaling and hence plasticity is impaired with aging, diminishing the aorta's normal shock absorption function in response to stressors. PMID:25128168

  14. Pneumatic Variable Series Elastic Actuator.

    PubMed

    Zheng, Hao; Wu, Molei; Shen, Xiangrong

    2016-08-01

    Inspired by human motor control theory, stiffness control is highly effective in manipulation and human-interactive tasks. The implementation of stiffness control in robotic systems, however, has largely been limited to closed-loop control, and suffers from multiple issues such as limited frequency range, potential instability, and lack of contribution to energy efficiency. Variable-stiffness actuator represents a better solution, but the current designs are complex, heavy, and bulky. The approach in this paper seeks to address these issues by using pneumatic actuator as a variable series elastic actuator (VSEA), leveraging the compressibility of the working fluid. In this work, a pneumatic actuator is modeled as an elastic element with controllable stiffness and equilibrium point, both of which are functions of air masses in the two chambers. As such, for the implementation of stiffness control in a robotic system, the desired stiffness/equilibrium point can be converted to the desired chamber air masses, and a predictive pressure control approach is developed to control the timing of valve switching to obtain the desired air mass while minimizing control action. Experimental results showed that the new approach in this paper requires less expensive hardware (on-off valve instead of proportional valve), causes less control action in implementation, and provides good control performance by leveraging the inherent dynamics of the actuator.

  15. Cell stiffness is a biomarker of the metastatic potential of ovarian cancer cells

    NASA Astrophysics Data System (ADS)

    Xu, Wenwei; Mezencev, Roman; Kim, Byungkyu; Wang, Lijuan; McDonald, John; Sulchek, Todd; Sulchek Team; McDonald Team

    2013-03-01

    The metastatic potential of cells is an important parameter in the design of optimal strategies for the personalized treatment of cancer. Using atomic force microscopy (AFM), we show that ovarian cancer cells are generally softer and display lower intrinsic variability in cell stiffness than non-malignant ovarian epithelial cells. A detailed study of highly invasive ovarian cancer cells (HEY A8) and their less invasive parental cells (HEY), demonstrates that deformability can serve as an accurate biomarker of metastatic potential. Comparative gene expression profiling indicate that the reduced stiffness of highly metastatic HEY A8 cells is associated with actin cytoskeleton remodeling, microscopic examination of actin fiber structure in these cell lines is consistent with this prediction. Our results indicate that cell stiffness not only distinguishes ovarian cancer cells from non-malignant cells, but may also be a useful biomarker to evaluate the relative metastatic potential of ovarian and perhaps other types of cancer cells.

  16. Stiffness, resilience, compressibility. Atomic scale force spectroscopy of biomolecules

    NASA Astrophysics Data System (ADS)

    Leu, Bogdan M.; Sage, J. Timothy

    2016-12-01

    The flexibility of a protein is an important component of its functionality. We use nuclear resonance vibrational spectroscopy (NRVS) to quantify the flexibility of the heme iron environment in the electron-carrying protein cytochrome c by measuring the stiffness and the resilience. These quantities are sensitive to structural differences between the active sites of different proteins, as illustrated by a comparative analysis with myoglobin. The elasticity of the entire protein, on the other hand, can be probed quantitatively from NRVS and high energy-resolution inelastic X-ray scattering (IXS) measurements, an approach that we used to extract the bulk modulus of cytochrome c.

  17. Mapping stiffness perception in the brain with an fMRI-compatible particle-jamming haptic interface.

    PubMed

    Menon, Samir; Stanley, Andrew A; Zhu, Jack; Okamura, Allison M; Khatib, Oussama

    2014-01-01

    We demonstrate reliable neural responses to changes in haptic stiffness perception using a functional magnetic resonance imaging (fMRI) compatible particle-jamming haptic interface. Our haptic interface consists of a silicone tactile surface whose stiffness we can control by modulating air-pressure in a sub-surface pouch of coarsely ground particles. The particles jam together as the pressure decreases, which stiffens the surface. During fMRI acquisition, subjects performed a constant probing task, which involved continuous contact between the index fingertip and the interface and rhythmic increases and decreases in fingertip force (1.6 Hz) to probe stiffness. Without notifying subjects, we randomly switched the interface's stiffness (switch time, 300-500 ms) from soft (200 N/m) to hard (1400 N/m). Our experiment design's constant motor activity and cutaneous tactile sensation helped disassociate neural activation for both from stiffness perception, which helped localized it to a narrow region in somatosensory cortex near the supra-marginal gyrus. Testing different models of neural activation, we found that assuming indepedent stiffness-change responses at both soft-hard and hard-soft transitions provides the best explanation for observed fMRI measurements (three subjects; nine four-minute scan runs each). Furthermore, we found that neural activation related to stiffness-change and absolute stiffness can be localized to adjacent but disparate anatomical locations. We also show that classical finger-tapping experiments activate a swath of cortex and are not suitable for localizing stiffness perception. Our results demonstrate that decorrelating motor and sensory neural activation is essential for characterizing somatosensory cortex, and establish particle-jamming haptics as an attractive low-cost method for fMRI experiments.

  18. A novel smart rotor support with shape memory alloy metal rubber for high temperatures and variable amplitude vibrations

    NASA Astrophysics Data System (ADS)

    Ma, Yanhong; Zhang, Qicheng; Zhang, Dayi; Scarpa, Fabrizio; Liu, Baolong; Hong, Jie

    2014-12-01

    The work describes the design, manufacturing and testing of a smart rotor support with shape memory alloy metal rubber (SMA-MR) elements, able to provide variable stiffness and damping characteristics with temperature, motion amplitude and excitation frequency. Differences in damping behavior and nonlinear stiffness between SMA-MR and more traditional metal rubber supports are discussed. The mechanical performance shown by the prototype demonstrates the feasibility of using the SMA-MR concept for active vibration control in rotordynamics, in particular at high temperatures and large amplitude vibrations.

  19. The geovisualisation window of the temporal and spatial variability for Volunteered Geographic Information activities

    NASA Astrophysics Data System (ADS)

    Medynska-Gulij, Beata; Myszczuk, Miłosz

    2012-11-01

    This study presents an attempt to design geographical visualisation tools that allow to tackle the immensity of spatial data provided by Volunteered Geographic Information (VGI), both in terms of temporal and spatial aspects. In accordance with the assumptions made at the conceptual stage, the final action was the implementation of the window entitled ‘Geovisualisation of the Panoramio.com Activities in District of Poznan 2011’ into the web browser. The concept has been based on a division of the geovisualisation window into three panels, of which the most important - in order to capture spatial variability - have statistical maps at the general level (dot map and choropleth map), while at the detailed level - a dot map on a topographic reference map or tourist map. For two ranges, temporal variability is presented by graphs, while a review of attributes of individual activities of the social website in question is set forward in the table panel. The element that visually interlinks all of the panels is the emphasised individual activity. Problemem podjetym w tych badaniach stało sie wykorzystanie metod z nurtu geograficznej wizualizacji do wskazania cech fenomenu VGI w zakresie zmiennosci czasowo-przestrzennej. Zgodnie z załozeniami poczynionymi w etapie koncepcyjnym finalnym działaniem stało sie zaimplementowanie do przegladarki internetowej okna pod tytułem: ”Geowizualizacja aktywnosci społecznosci Panoramio.com w powiecie poznanskim w 2011 roku”. Koncepcja została oparta na podziale okna geowizualizacji na trzy panele, z których najwazniejsze znaczenie dla uchwycenia zmiennosci przestrzennej na poziomie ogólnym ma kartogram, natomiast na poziomie szczegółowym mapa kropkowa wyswietlana na podkładzie mapy topograficznej lub turystycznej. Zmiennosc czasowa w dwóch zakresach prezentuja wykresy, a przeglad atrybutów poszczególnych aktywnosci prezentowanego portalu społecznosciowego zapewnia tabela. Elementem spajajacym wizualnie wszystkie

  20. Variability in Saponin Content, Cancer Antiproliferative Activity and Physicochemical Properties of Concentrated Agave Sap.

    PubMed

    Santos-Zea, Liliana; Rosas-Pérez, Aratza Mireya; Leal-Díaz, Ana María; Gutiérrez-Uribe, Janet A

    2016-08-01

    Concentrated agave sap (CAS) has gained popularity as an unrefined sweetener. It is obtained by boiling "aguamiel" that contains phytochemicals with diverse bioactivities. Saponins have been the most widely studied agave phytochemicals due to their cancer antiproliferative effect but their concentration may vary due to maturity of the agave plant and collection site. In this study, 18 CAS samples produced in different states of Mexico were analyzed using multivariate methods to determine which physicochemical or phytochemical parameters were responsible for variation. Additionally, extracts with different saponin profiles were tested to determine possible correlations with antiproliferative activity. Total soluble solids, pH, and water activity were similar to those reported for other agave sweeteners. Antioxidant capacity of samples was correlated to browning index. Eleven steroidal saponins were found in CAS samples and they were the main source of variability. Magueyoside B, a kammogenin tetraglycoside, was the most abundant saponin in all samples. With respect to bioactivity, multivariate analysis indicated that magueyoside B and a gentrogenin tetraglycoside were compounds strongly related with bioactivity. CAS from Hidalgo, Puebla, and Veracruz had higher concentration of magueyoside B than from the other kamogenin tetraglycoside found in the samples from other Mexican states. These results could be used as a first approach to characterize and standardize CAS to validate the potential health benefits derived from its consumption.

  1. Roche tomography of cataclysmic variables - VII. The long-term magnetic activity of AE Aqr

    NASA Astrophysics Data System (ADS)

    Hill, C. A.; Watson, C. A.; Steeghs, D.; Dhillon, V. S.; Shahbaz, T.

    2016-06-01

    We present a long-term study of the secondary star in the cataclysmic variable AE Aqr, using Roche tomography to indirectly image starspots on the stellar surface spanning 8 years of observations. The seven maps show an abundance of spot features at both high and low latitudes. We find that all maps have at least one large high-latitude spot region, and we discuss its complex evolution between maps, as well as its compatibility with current dynamo theories. Furthermore, we see the apparent growth in fractional spot coverage, fs, around 45° latitude over the duration of observations, with a persistently high fs near latitudes of 20°. These bands of spots may form as part of a magnetic activity cycle, with magnetic flux tubes emerging at different latitudes, similar to the `butterfly' diagram for the Sun. We discuss the nature of flux tube emergence in close binaries, as well as the activity of AE Aqr in the context of other stars.

  2. Moment to moment variability in functional brain networks during cognitive activity in EEG data.

    PubMed

    Dasari, Naga M; Nandagopal, Nanda D; Ramasamy, Vijayalaxmi; Cocks, Bernadine; Thomas, Bruce H; Dahal, Nabaraj; Gaertner, Paul

    2015-09-01

    Functional brain networks (FBNs) are gaining increasing attention in computational neuroscience due to their ability to reveal dynamic interdependencies between brain regions. The dynamics of such networks during cognitive activity between stimulus and response using multi-channel electroencephalogram (EEG), recorded from 16 healthy human participants are explored in this research. Successive EEG segments of 500[Formula: see text]ms duration starting from the onset of cognitive stimulation have been used to analyze and understand the cognitive dynamics. The approach employs a combination of signal processing techniques, nonlinear statistical measures and graph-theoretical analysis. The efficacy of this approach in detecting and tracking cognitive load induced changes in EEG data is clearly demonstrated using graph metrics. It is revealed that most cognitive activity occurs within approximately 500[Formula: see text]ms of the stimulus presentation in addition to temporal variability in the FBNs. It is shown that mutual information (MI), a nonlinear measure, produces good correlations between the EEG channels thus enabling the construction of FBNs which are sensitive to cognitive load induced changes in EEG. Analyses of the dynamics of FBNs and the visualization approach reveal hard to detect subtle changes in cognitive function and hence may lead to a better understanding of cognitive processing in the brain. The techniques exploited have the potential to detect human cognitive dysfunction (impairments).

  3. Activity Pattern Profiles: Relationship With Affect, Daily Functioning, Impairment, and Variables Related to Life Goals.

    PubMed

    Esteve, Rosa; López-Martínez, Alicia E; Peters, Madelon L; Serrano-Ibáñez, Elena R; Ruíz-Párraga, Gema T; González-Gómez, Henar; Ramírez-Maestre, Carmen

    2017-01-04

    The aim of this cross-sectional study was to identify subgroups of patients on the basis of their activity patterns and to investigate their relationship with life goals, optimism, affect, and functioning. The sample was comprised of 276 patients with chronic musculoskeletal pain. Hierarchical cluster analysis was performed on the activity pattern variables and the resulting clusters were compared using 1-way analysis of variance. The 4-cluster was the optimal solution. The 4 clusters comprised: 1) avoiders: patients with high levels of avoidance and low levels of persistence, who use pacing to reduce pain, 2) doers: patients with high levels of persistence and low levels of pacing and avoidance, 3) extreme cyclers: patients with high levels of avoidance and persistence and low levels of pacing, and 4) medium cyclers: patients with moderately high levels of avoidance and persistence and high levels of pacing. Comparison of the clusters showed that doers had the most adaptive profile, whereas avoiders, followed by extreme cyclers, had unhealthy profiles. Doers showed a high level of optimism and a good balance between goal value, expectancy, and conflict.

  4. Spatial and temporal variability in microbial activities of coastal acid saline soils of Goa, India

    NASA Astrophysics Data System (ADS)

    Mahajan, G. R.; Manjunath, B. L.; Latare, A. M.; D'Souza, R.; Vishwakarma, S.; Singh, N. P.

    2015-11-01

    The aim of the present investigation was to study the spatio-temporal variability of the microbial activities in coastal saline soils (locally called Khazan) of Goa, India (west coast region). The coastal soil salinity is a major constraint for reduced crop yields and abandonment of farming in these areas. Three replicated global positioning based soil samples (0-0.20 m depth) from each of four salinity groups i.e. non-saline (EC=0.08±0.06 dS m-1), weakly saline (EC=2.04±0.06 dS m-1), moderately saline (EC=3.50±0.57 dS m-1) and strongly saline (EC=5.49±0.49 dS m-1) during three seasons-monsoon, post-monsoon and pre-monsoon were collected. Soil microbial activity in terms of soil microbial carbon (MBC), MBC as a fraction of soil organic carbon (SOC) (MBC/SOC), basal soil respiration (BSR), metabolic quotient (qCO2) and soil enzyme activities-dehydrogenase, phosphatase and urease was tested. In all the seasons, the soil cationic composition depended significantly (p<0.01) on salinity levels and the exchangeable sodium (Na) was the second most dominant among the tested cations. The MBC, MBC/SOC and BSR reduced significantly with increasing salinity, whereas qCO2 increased with increased salinity levels. In general, MBC, MBC/SOC and BSR and soil enzyme activities were observed as: salinity levels-strongly saline < moderately saline < weakly saline < non-saline and season-post-monsoon > monsoon > during pre-monsoon season. The mean MBC and MBC/SOC of non-saline soils were 1.61 and 2.28 times higher than that of strongly saline soils, whereas qCO2 of strongly saline soils was 2.4 times higher than that of non-saline soils. This indirectly indicates the salinity stress on the soil microorganisms. Irrespective of season, the soil enzyme activities decreased significantly (p<0.05) with increasing salinity levels. Suitable countermeasures needs to be taken up to alleviate the depressive salinity effect on the microbial and activity for the sustainable crop production in

  5. Actively Heated Fiber Optics for Distributed Soil Moisture Measurements: Addressing Field Calibration and Spatial Variability

    NASA Astrophysics Data System (ADS)

    Sayde, C.; Moreno, D.; Benitez-buelga, J.; Dong, J.; Ochsner, T. E.; Steele-Dunne, S. C.; Rodriguez-Sinobas, L.; Selker, J. S.

    2015-12-01

    The Actively Heated Fiber Optics (AHFO) method has the potential to measure soil water content at high temporal (<1hr) and spatial (every 0.25 m) resolutions along buried fiber optics (FO) cables multiple kilometers in length. This game-changing method can capture soil water dynamics over four orders of magnitude in spatial scale (0.1-1000 m). However, many challenges remain to resolve for the practical applicability of the AHFO at the field scale. In particular, cost effective distributed calibration method that accounts for the spatial variability of the soil thermal properties is still lacking. In fact, AHFO infers soil water content from observing the thermal response of the soil to a heat pulse injected along the fiber optic cable. For a particular location, the temporal variation of the soil thermal response depends mainly on the soil moisture content. Across the field the variability of thermal response will also be a function of the soil thermal properties which change with the soil mineralogy and bulk density. Here we present various strategies for distributed calibration of the AHFO method based on numerical simulation, direct field observation, and/or laboratory experimentation. In particular we will present a novel approach for mapping the soil thermal behavior by conducting AHFO measurements at strategic soil water conditions such as near saturation and dry conditions. We will show results from a large scale deployment at the MOISST site in Stillwater, Oklahoma where 4900 m of fiber optic soil moisture sensing cables are providing daily soil moisture measurements at >39,000 locations in the field. The material is based upon work supported by NASA under award NNX12AP58G, with equipment and assistance also provided by CTEMPs.org with support from the National Science Foundation under Grant Number 1129003. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views

  6. Drivers of Time-Activity Budget Variability during Breeding in a Pelagic Seabird

    PubMed Central

    Rishworth, Gavin M.; Tremblay, Yann; Green, David B.; Connan, Maëlle; Pistorius, Pierre A.

    2014-01-01

    During breeding, animal behaviour is particularly sensitive to environmental and food resource availability. Additionally, factors such as sex, body condition, and offspring developmental stage can influence behaviour. Amongst seabirds, behaviour is generally predictably affected by local foraging conditions and has therefore been suggested as a potentially useful proxy to indicate prey state. However, besides prey availability and distribution, a range of other variables also influence seabird behavior, and these need to be accounted for to increase the signal-to-noise ratio when assessing specific characteristics of the environment based on behavioural attributes. The aim of this study was to use continuous, fine-scale time-activity budget data from a pelagic seabird (Cape gannet, Morus capensis) to determine the influence of intrinsic (sex and body condition) and extrinsic (offspring and time) variables on parent behaviour during breeding. Foraging trip duration and chick provisioning rates were clearly sex-specific and associated with chick developmental stage. Females made fewer, longer foraging trips and spent less time at the nest during chick provisioning. These sex-specific differences became increasingly apparent with chick development. Additionally, parents in better body condition spent longer periods at their nests and those which returned later in the day had longer overall nest attendance bouts. Using recent technological advances, this study provides new insights into the foraging behaviour of breeding seabirds, particularly during the post-guarding phase. The biparental strategy of chick provisioning revealed in this study appears to be an example where the costs of egg development to the female are balanced by paternal-dominated chick provisioning particularly as the chick nears fledging. PMID:25551620

  7. 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.

  8. WILLIAMS SYNDROME PREDISPOSES TO VASCULAR STIFFNESS MODIFIED BY ANTI-HYPERTENSIVE USE AND COPY NUMBER CHANGES IN NCF1

    PubMed Central

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

    2014-01-01

    Williams syndrome, is caused by the deletion of 26-28 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 persons 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 NAD(P)H 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 Williams children. 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 anti-hypertension 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 anti-hypertensives and/or agents inhibiting oxidative stress may be important in managing patients with this condition, potentially even those who are not overtly hypertensive. PMID:24126171

  9. Microbial contribution to carbon biogeochemistry in the Central Mediterranean Sea: Variability of activities and biomass

    NASA Astrophysics Data System (ADS)

    La Ferla, Rosabruna; Azzaro, Filippo; Azzaro, Maurizio; Caruso, Gabriella; Decembrini, Franco; Leonardi, Marcella; Maimone, Giovanna; Monticelli, Luis S.; Raffa, Francesco; Santinelli, Chiara; Zaccone, Renata; Ribera d'Alcalà, Maurizio

    2005-08-01

    This paper concerns the current debate as to whether oceans are heterotrophic or autotrophic environments. Microbes are responsible for the assimilation and remineralization of CO 2 in the sea and microbial processes are involved in the Earth climatic change. The variability of microbial biomass and activities were studied in the Mediterranean Sea which represents a suitable basin for mapping the trophic regimes by the study of biogeochemical processes. The surveys were carried out in the epi-, meso- and bathy-pelagic zones of the Central Mediterranean Sea from 1996 to 2002. Bacterial abundance, leucine aminopeptidase (LAP) and β-glucosidase (β-GLU) activities, bacterial carbon production (BCP), community respiration (R) and primary production (PP) were the main parameters investigated. Biomass and activities seasonally varied in epipelagic and, to some extent, in meso- and bathy-pelagic layers too and several trophic ratios were determined, showing different scenarios in the different areas and seasons. In the euphotic layer, bacterial growth efficiency (BGE) widely ranged between 4% and 50% showing a decreasing trend from estuaries towards pelagic areas in alignment with the trophic gradient from the Northern Adriatic to the Ionian Sea. However, BGE did not correlate to PP and temperature. The Central Mediterranean Sea showed different trophic regimes in the examined areas and seasons. In the Northern Adriatic Sea in winter, the trophic balance appeared to move towards autotrophy and a positive C budget resulted. An opposite scenario happened in summer when the trophic balance moved to heterotrophy and a negative C budget occurred. In the Ionian Sea, the overall balance turned always towards remineralization. However, on annual time scale, the Central Mediterranean Sea seems to show a tendency towards a heterotrophic system.

  10. The passive stiffness of the wrist and forearm

    PubMed Central

    Charles, Steven K.; Zollo, Loredana; Guglielmelli, Eugenio; Hogan, Neville; Krebs, Hermano I.

    2012-01-01

    Because wrist rotation dynamics are dominated by stiffness (Charles SK, Hogan N. J Biomech 44: 614–621, 2011), understanding how humans plan and execute coordinated wrist rotations requires knowledge of the stiffness characteristics of the wrist joint. In the past, the passive stiffness of the wrist joint has been measured in 1 degree of freedom (DOF). Although these 1-DOF measurements inform us of the dynamics the neuromuscular system must overcome to rotate the wrist in pure flexion-extension (FE) or pure radial-ulnar deviation (RUD), the wrist rarely rotates in pure FE or RUD. Instead, understanding natural wrist rotations requires knowledge of wrist stiffness in combinations of FE and RUD. The purpose of this report is to present measurements of passive wrist stiffness throughout the space spanned by FE and RUD. Using a rehabilitation robot designed for the wrist and forearm, we measured the passive stiffness of the wrist joint in 10 subjects in FE, RUD, and combinations. For comparison, we measured the passive stiffness of the forearm (in pronation-supination), as well. Our measurements in pure FE and RUD agreed well with previous 1-DOF measurements. We have linearized the 2-DOF stiffness measurements and present them in the form of stiffness ellipses and as stiffness matrices useful for modeling wrist rotation dynamics. We found that passive wrist stiffness was anisotropic, with greater stiffness in RUD than in FE. We also found that passive wrist stiffness did not align with the anatomical axes of the wrist; the major and minor axes of the stiffness ellipse were rotated with respect to the FE and RUD axes by ∼20°. The direction of least stiffness was between ulnar flexion and radial extension, a direction used in many natural movements (known as the “dart-thrower's motion”), suggesting that the nervous system may take advantage of the direction of least stiffness for common wrist rotations. PMID:22649208

  11. Evaluation of the stiffnesses of the Achilles tendon and soleus from the apparent stiffness of the triceps surae.

    PubMed

    París-García, Federico; Barroso, Alberto; Doblaré, Manuel; Cañas, José; París, Federico

    2015-01-01

    The triceps surae plays an important role in the performance of many sports. Although the apparent average mechanical properties of the triceps surae may be a satisfactory parameter for estimating the training level of an athlete, a knowledge of the mechanical properties of the individual constituents of the triceps surae (in particular the Achilles tendon and soleus) permits a more detailed and in-depth control of the effects of training from more physically based parameters. The objective of this work is therefore the estimation of the individual viscoelastic properties (stiffness and viscosity) of soleus and Achilles tendon from the apparent properties of the triceps surae obtained by free vibration techniques. Different procedures have been developed and discussed, showing a high degree of robustness in the predictions. The results obtained for a non-oriented set of subjects present a high level of variability, depending on the training conditions and anthropometric features, although the corresponding average values compare well with data previously reported in the literature, particularly those associated with the tendon stiffness.

  12. Chain stiffness regulates entropy-templated perfect mixing at single-nanoparticle level

    NASA Astrophysics Data System (ADS)

    Huang, Zihan; Lu, Ce; Dong, Bojun; Xu, Guoxi; Ji, Chengcheng; Zhao, Kongyin; Yan, Li-Tang

    2015-12-01

    The mixing on a single-particle level of chemically incompatible nanoparticles is an outstanding challenge for many applications. Burgeoning research activity suggests that entropic templating is a potential strategy to address this issue. Herein, using systematic computer simulations of model nanoparticle systems, we show that the entropy-templated interfacial organization of nanoparticles significantly depends on the stiffness of tethered chains. Unexpectedly, the optimal chain stiffness can be identified wherein a system exhibits the most perfect mixing for a certain compression ratio. Our simulations demonstrate that entropic templating regulated by chain stiffness precisely reflects various entropic repulsion states that arise from typical conformation regimes of semiflexible chains. The physical mechanism of the chain stiffness effect is revealed by analyzing the entropic repulsion states of tethered chains and quantitatively estimating the resulting entropy penalties, which provides direct evidence that supports the key role of entropic transition in the entropic templating strategy, as suggested in experiments. Moreover, the model nanoparticle systems are found to evolve into binary nanoparticle superlattices by remixing at extremely high stiffness. The findings facilitate the wide application of the entropic templating strategy in creating interfacially reactive nanomaterials with ordered structures on the single-nanoparticle level as well as mechanomutable responses.The mixing on a single-particle level of chemically incompatible nanoparticles is an outstanding challenge for many applications. Burgeoning research activity suggests that entropic templating is a potential strategy to address this issue. Herein, using systematic computer simulations of model nanoparticle systems, we show that the entropy-templated interfacial organization of nanoparticles significantly depends on the stiffness of tethered chains. Unexpectedly, the optimal chain stiffness can

  13. Titin stiffness modifies the force-generating region of muscle sarcomeres

    PubMed Central

    Li, Yong; Lang, Patrick; Linke, Wolfgang A.

    2016-01-01

    The contractile units of striated muscle, the sarcomeres, comprise the thick (myosin) and thin (actin) filaments mediating active contraction and the titin filaments determining “passive” elasticity. We hypothesized that titin may be more active in muscle contraction by directly modulating thick-filament properties. We used single-myofibril mechanical measurements and atomic force microscopy of individual sarcomeres to quantify the effects of sarcomere strain and titin spring length on both the inter-filament lattice spacing and the lateral stiffness of the actin-myosin overlap zone (A-band). We found that strain reduced the lattice spacing similarly in sarcomeres with stiff (rabbit psoas) or compliant titin (rabbit diaphragm), but increased A-band lateral stiffness much more in psoas than in diaphragm. The strain-induced alterations in A-band stiffness that occur independently of lattice spacing effects may be due to titin stiffness-sensing by A-band proteins. This mechanosensitivity could play a role in the physiologically important phenomenon of length-dependent activation of striated muscle. PMID:27079135

  14. Titin stiffness modifies the force-generating region of muscle sarcomeres.

    PubMed

    Li, Yong; Lang, Patrick; Linke, Wolfgang A

    2016-04-15

    The contractile units of striated muscle, the sarcomeres, comprise the thick (myosin) and thin (actin) filaments mediating active contraction and the titin filaments determining "passive" elasticity. We hypothesized that titin may be more active in muscle contraction by directly modulating thick-filament properties. We used single-myofibril mechanical measurements and atomic force microscopy of individual sarcomeres to quantify the effects of sarcomere strain and titin spring length on both the inter-filament lattice spacing and the lateral stiffness of the actin-myosin overlap zone (A-band). We found that strain reduced the lattice spacing similarly in sarcomeres with stiff (rabbit psoas) or compliant titin (rabbit diaphragm), but increased A-band lateral stiffness much more in psoas than in diaphragm. The strain-induced alterations in A-band stiffness that occur independently of lattice spacing effects may be due to titin stiffness-sensing by A-band proteins. This mechanosensitivity could play a role in the physiologically important phenomenon of length-dependent activation of striated muscle.

  15. Holocene activity of an alpine debris-flow catchment: does climate control erosion rate variability?

    NASA Astrophysics Data System (ADS)

    Savi, S.; Norton, K. P.; Brardinoni, F.; Akçar, N.; Kubik, P.; Picotti, V.; Schlunegger, F.

    2012-12-01

    The Zielbach catchment is located in the central-eastern Italian Alps. It covers an area of ca. 40 km2 and is characterized by fluvial sediment transport along the main drainage basin, and by the supply of sediment through debris flows, derived from a ca. 10 km2 tributary catchment. A debris-flow database demonstrates that nowadays this latter tributary dominates the sediment budget of the entire Zielbach. In this study, we analyze modern and paleo-erosion rates of the catchment through the application of the cosmogenic nuclides technique. For modern erosion rate, samples of river-born sand were taken from the main river and tributaries along the entire drainage system, while paleo-erosion rates are calculated thanks to cores' samples, which were collected on the alluvial fan and which were likewise dated based on 14C measurements of organic matter. Results obtained from the modern drainage system reveal the spatial erosion rate variability that characterizes the catchment nowadays (values ranging from 2.6 to 0.15 mm/yr). This spatial pattern is characterized by a generally increasing trend of 10Be values where hillslope contributions predominate and by a decreasing concentration trend where sediment has been supplied by debris flows. Results obtained from the cores allow the reconstruction of the Zielbach Holocene evolution and the assignment of the climate role on the temporal erosion rate variability (values ranging between 21 and 0.43 mm/yr). 14C concentrations of organic material collected from the core material indicate a lowermost age of 10'000 yr at ca. 35 m depth. The sedimentary fabric of the deposits indicates that the fan is built up by alternation of alluvial and debris-flow deposits, where the latter ones dominate in volumes. The stratigraphic architecture also infers that alluvial deposits correspond to periods of low activity of the debris-flow catchment. Most important, however, paleo-erosion rates indicate a decreasing trend for the debris

  16. Familial influences on the full range of variability in attention and activity levels during adolescence: A longitudinal twin study.

    PubMed

    Peng, Chun-Zi; Grant, Julia D; Heath, Andrew C; Reiersen, Angela M; Mulligan, Richard C; Anokhin, Andrey P

    2016-05-01

    To investigate familial influences on the full range of variability in attention and activity across adolescence, we collected maternal ratings of 339 twin pairs at ages 12, 14, and 16, and estimated the transmitted and new familial influences on attention and activity as measured by the Strengths and Weaknesses of Attention-Deficit/Hyperactivity Disorder Symptoms and Normal Behavior Scale. Familial influences were substantial for both traits across adolescence: genetic influences accounted for 54%-73% (attention) and 31%-73% (activity) of the total variance, and shared environmental influences accounted for 0%-22% of the attention variance and 13%-57% of the activity variance. The longitudinal stability of individual differences in attention and activity was largely accounted for by familial influences transmitted from previous ages. Innovations over adolescence were also partially attributable to familial influences. Studying the full range of variability in attention and activity may facilitate our understanding of attention-deficit/hyperactivity disorder's etiology and intervention.

  17. Hydrothermal activity at slow-spreading ridges: variability and importance of magmatic controls

    NASA Astrophysics Data System (ADS)

    Escartin, Javier

    2016-04-01

    Hydrothermal activity along mid-ocean ridge axes is ubiquitous, associated with mass, chemical, and heat exchanges between the deep lithosphere and the overlying envelopes, and sustaining chemiosynthetic ecosystems at the seafloor. Compared with hydrothermal fields at fast-spreading ridges, those at slow spreading ones show a large variability as their location and nature is controlled or influenced by several parameters that are inter-related: a) tectonic setting, ranging from 'volcanic systems' (along the rift valley floor, volcanic ridges, seamounts), to 'tectonic' ones (rift-bounding faults, oceanic detachment faults); b) the nature of the host rock, owing to compositional heterogeneity of slow-spreading lithosphere (basalt, gabbro, peridotite); c) the type of heat source (magmatic bodies at depth, hot lithosphere, serpentinization reactions); d) and the associated temperature of outflow fluids (high- vs.- low temperature venting and their relative proportion). A systematic review of the distribution and characteristics of hydrothermal fields along the slow-spreading Mid-Atlantic Ridge suggests that long-lived hydrothermal activity is concentrated either at oceanic detachment faults, or along volcanic segments with evidence of robust magma supply to the axis. A detailed study of the magmatically robust Lucky Strike segment suggests that all present and past hydrothermal activity is found at the center of the segment. The association of these fields to central volcanos, and the absence of indicators of hydrothermal activity along the remaining of the ridge segment, suggests that long-lived hydrothermal activity in these volcanic systems is maintained by the enhanced melt supply and the associated magma chamber(s) required to build these volcanic edifices. In this setting, hydrothermal outflow zones at the seafloor are systematically controlled by faults, indicating that hydrothermal fluids in the shallow crust exploit permeable fault zones to circulate. While

  18. Where’s the Noise? Key Features of Spontaneous Activity and Neural Variability Arise through Learning in a Deterministic Network

    PubMed Central

    Hartmann, Christoph; Lazar, Andreea; Nessler, Bernhard; Triesch, Jochen

    2015-01-01

    Even in the absence of sensory stimulation the brain is spontaneously active. This background “noise” seems to be the dominant cause of the notoriously high trial-to-trial variability of neural recordings. Recent experimental observations have extended our knowledge of trial-to-trial variability and spontaneous activity in several directions: 1. Trial-to-trial variability systematically decreases following the onset of a sensory stimulus or the start of a motor act. 2. Spontaneous activity states in sensory cortex outline the region of evoked sensory responses. 3. Across development, spontaneous activity aligns itself with typical evoked activity patterns. 4. The spontaneous brain activity prior to the presentation of an ambiguous stimulus predicts how the stimulus will be interpreted. At present it is unclear how these observations relate to each other and how they arise in cortical circuits. Here we demonstrate that all of these phenomena can be accounted for by a deterministic self-organizing recurrent neural network model (SORN), which learns a predictive model of its sensory environment. The SORN comprises recurrently coupled populations of excitatory and inhibitory threshold units and learns via a combination of spike-timing dependent plasticity (STDP) and homeostatic plasticity mechanisms. Similar to balanced network architectures, units in the network show irregular activity and variable responses to inputs. Additionally, however, the SORN exhibits sequence learning abilities matching recent findings from visual cortex and the network’s spontaneous activity reproduces the experimental findings mentioned above. Intriguingly, the network’s behaviour is reminiscent of sampling-based probabilistic inference, suggesting that correlates of sampling-based inference can develop from the interaction of STDP and homeostasis in deterministic networks. We conclude that key observations on spontaneous brain activity and the variability of neural responses can be

  19. Chain stiffness of elastin-like polypeptides

    PubMed Central

    Fluegel, Sabine; Fischer, Karl; McDaniel, Jonathan R.; Chilkoti, Ashutosh; Schmidt, Manfred

    2010-01-01

    The hydrodynamic radii of a series of genetically engineered monodisperse elastin like polypeptides (ELP) was determined by dynamic light scattering in aqueous solution as function of molar mass. Utilizing the known theoretical expression for the hydrodynamic radius of wormlike chains, the Kuhn statistical segment length was determined to be lk = 2.1 nm, assuming that the length of the peptide repeat unit was b = 0.365 nm, a value derived for a coiled conformation of ELP. The resulting chain stiffness is significantly larger than previously reported by force-distance curve analysis (lk < 0.4 nm). The possible occurrence of superstructures, such as hairpins or helices, would reduce the contour length of the ELP, further increasing lk. Accordingly, the value lk = 2.1 nm reported here represents a lower limit of the chain stiffness for ELP. PMID:20961120

  20. [Stiff person syndrome--case report].

    PubMed

    Tomczykiewicz, Kazimierz; Pastuszak, Zanna; Staszewski, Jacek; Stepień, Adam

    2014-01-01

    Stiff person syndrome (SPS) is the rare disease and cause great inefficient. It is characterized by progressive stiffness muscles of trunk and the limbs on which the cramps of muscles overlap. In the electrophysiological investigation of the patients the involuntary discharge of motor unit potentials find and also simultaneous contraction agonistic and antagonistic muscles. SPS is presented with insulin-dependent diabetes mellitus often or is the symptom of the paraneoplastic syndrome. It is commonly associated with high anti-glutamic acid decarboxylaze (GAD) antibody titters in the serum of the blood of patients. Establishing the diagnosis can cause difficulties. We observed the patient in the last period about the atypical course the disease. The diagnosis was confirmed occurrences of the high titters of antibodies anti-GAD, the discharge of motor unit potential in paraspinal muscles in the rest and good response the treatment with diazepamem.

  1. 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.

  2. 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.

  3. 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.

  4. The variability of coronal holes during two last cycles of solar activity

    NASA Astrophysics Data System (ADS)

    Prosovetsky, Dmitry

    Coronal holes (CH) well known as open magnetic field area are the important factor of space weather variability and geomagnetic disturbances in the Earth's magnetosphere. The properties of CH as well as related with them high-speed solar wind streams are defined by features of a configuration of a magnetic field and an atmosphere structure above. However, till now it is not clear, how these parameters vary during different cycles of solar activity and different phases of cycle development. In this paper the comparative examination of CH properties is carried out for minima of 22 and 23 cycles of solar activity. The observations data of UV and microwave emission at four frequencies together with measuring of a magnetic field and its extrapolation on high levels were studied. Some significant features were founded. It was noticed the middle-latitude and equatorial CH with largest area exists during large time of a cycle with an identical configuration of a large-scale magnetic field. CH of an identical configuration (e.g. elephant trunk) are observed in both various cycles of solar activity that reflects identical mechanisms of a global magnetic field formation in a cycle. Brightness temperatures at levels of chromosphere and the low corona in a CH of a cycle 23 minimum, on the average, are 50 percents less than temperature during cycle 22 minimum. It is found, that the large-scale magnetic field of the Sun in activity minimums is segmented by alternating areas of different polarity, and the magnetic fields of CH are one of segments. In cycle 22 minimum the meridional segments of the magnetic field related with CH were dominated. On the other hand during 23 cycle the latitudinal segments were dominated. Features of CH with the closed configuration of a magnetic field perhaps not are visible in UV and microwave emission. Visibility requirements of CH as dark features in UV concerning the quiet Sun are quasi-radiality of a magnetic field and its value ¿5 Gs were

  5. The influence of desk and display design on posture and muscle activity variability whilst performing information technology tasks.

    PubMed

    Straker, L; Burgess-Limerick, R; Pollock, C; Maslen, B

    2009-09-01

    Desk design and computer display height can affect posture and muscle activation during computer use. Amplitudes of postural variables and muscle activity during computer use do not explain the results from epidemiological studies of musculoskeletal discomfort and disorders related to computer use. The purpose of this study was to assess variability of posture and muscle activity during work with two computer display heights and book/paper, in conjunction with a curved desk designed to provide forearm support and a traditional, straight desk. 18 male and 18 female participants performed 10-min tasks involving keying, mousing, reading and writing in six desk/display conditions. 3D posture and surface emg were assessed for the final 2 min of each task. The curved desk resulted in greater postural and muscle activity variation, suggesting an advantage of this supportive surface over the straight desk. There was little difference in variability associated with the two display heights. However, greater variability of posture and muscle activity was evident with the book/paper condition. Non-touch typists had greater neck flexion variation. The design of information technology tasks and workstations can influence the short term variation in posture and muscle activity. Variation is influenced independently of mean postures and muscle amplitudes and therefore needs to be considered to adequately assess the risk of musculoskeletal disorders.

  6. Temporal variability of glucocorticoid receptor activity is functionally important for the therapeutic action of fluoxetine in the hippocampus.

    PubMed

    Lee, M-S; Kim, Y-H; Park, W-S; Park, O-K; Kwon, S-H; Hong, K S; Rhim, H; Shim, I; Morita, K; Wong, D L; Patel, P D; Lyons, D M; Schatzberg, A F; Her, S

    2016-02-01

    Previous studies have shown inconsistent results regarding the actions of antidepressants on glucocorticoid receptor (GR) signalling. To resolve these inconsistencies, we used a lentiviral-based reporter system to directly monitor rat hippocampal GR activity during stress adaptation. Temporal GR activation was induced significantly by acute stress, as demonstrated by an increase in the intra-individual variability of the acute stress group compared with the variability of the non-stress group. However, the increased intra-individual variability was dampened by exposure to chronic stress, which was partly restored by fluoxetine treatment without affecting glucocorticoid secretion. Immobility in the forced-swim test was negatively correlated with the intra-individual variability, but was not correlated with the quantitative GR activity during fluoxetine therapy; this highlights the temporal variability in the neurobiological links between GR signalling and the therapeutic action of fluoxetine. Furthermore, we demonstrated sequential phosphorylation between GR (S224) and (S232) following fluoxetine treatment, showing a molecular basis for hormone-independent nuclear translocation and transcriptional enhancement. Collectively, these results suggest a neurobiological mechanism by which fluoxetine treatment confers resilience to the chronic stress-mediated attenuation of hypothalamic-pituitary-adrenal axis activity.

  7. Population variability in the Active Brownian Particle model of Daphnia motions

    NASA Astrophysics Data System (ADS)

    Moss, Frank; Erdmann, Udo; Schimansky-Geier, Lutz; Ordmann, Anke

    2004-03-01

    Three characteristic motions of foraging biological agents are predicted by the Active Brownian Particle model [1]. These are random motions about the minimum of a central attracting potential, a bifurcation to bidirectional circular motions about the axis of symmetry of the potential, and a transition to vortex motion. All three can be observed in swarms of the zooplankton Daphnia swimming in light fields. Here we focus on the bidirectional circular motions in 2-D space [1]. The mean radii, as well as other characteristics of the paths, are determined by three strength parameters appropriate to individual Daphnia: energy uptake from the medium, metabolistic drain, and dissipation due to movement. It is shown that individual variability can be represented by distributions of these strength parameters. Conditions for which the experimental data are best described by the model are discussed. [1] U. Erdmann, W. Ebeling and V. S. Anishchenko, Excitation of rotational modes in two-dimensional systems of driven Brownian particles. Phys. Rev. E 65, 061106 (2002)

  8. Variability of the lipolytic activity in Yarrowia lipolytica strains in pork fat.

    PubMed

    Patrignani, Francesca; Vannini, Lucia; Gardini, Fausto; Guerzoni, M Elisabetta; Lanciotti, Rosalba

    2011-08-01

    This work studied the variability in lipolytic activity in 35 strains of Yarrowia lipolytica inoculated in pork fat after 7 and 21 days of storage at 15 °C. The strains were able to generate three different hydrolysis profiles. In particular, the strains PO10, PO14, RO1, RO5, Y15, Y16A, Y20, B5, 7B, 7B3, 16B and 21C caused an increase with time in concentrations of C16:0, C18:0, C18:1, C18:1(Δ11) and C18:2 which were the predominant free fatty acids (FFAs). On the contrary, the strains PO1, PO19, PO23, RO22, Y12, B4, B74, GB, 5B, 5D, 27D and W29 showed an opposite trend, while the remaining ones induced no change. Because the released FFAs can be considered precursors for flavour development, the results suggest the potential use of some Y. lipolytica strains in sausage making to improve the overall aroma.

  9. Non-linear modelling and control of semi-active suspensions with variable damping

    NASA Astrophysics Data System (ADS)

    Chen, Huang; Long, Chen; Yuan, Chao-Chun; Jiang, Hao-Bin

    2013-10-01

    Electro-hydraulic dampers can provide variable damping force that is modulated by varying the command current; furthermore, they offer advantages such as lower power, rapid response, lower cost, and simple hardware. However, accurate characterisation of non-linear f-v properties in pre-yield and force saturation in post-yield is still required. Meanwhile, traditional linear or quarter vehicle models contain various non-linearities. The development of a multi-body dynamics model is very complex, and therefore, SIMPACK was used with suitable improvements for model development and numerical simulations. A semi-active suspension was built based on a belief-desire-intention (BDI)-agent model framework. Vehicle handling dynamics were analysed, and a co-simulation analysis was conducted in SIMPACK and MATLAB to evaluate the BDI-agent controller. The design effectively improved ride comfort, handling stability, and driving safety. A rapid control prototype was built based on dSPACE to conduct a real vehicle test. The test and simulation results were consistent, which verified the simulation.

  10. Low solar activity variability and IRI 2007 predictability of equatorial Africa GPS TEC

    NASA Astrophysics Data System (ADS)

    Adewale, A. O.; Oyeyemi, E. O.; Cilliers, P. J.; McKinnell, L. A.; Adeloye, A. B.

    2012-01-01

    Diurnal, seasonal and latitudinal variations of Vertical Total Electron Content (VTEC) over the equatorial region of the African continent and a comparison with IRI-2007 derived TEC (IRI-TEC), using all three options (namely; NeQuick, IRI01-corr and IRI-2001), are presented in this paper. The variability and comparison are presented for 2009, a year of low solar activity, using data from thirteen Global Positioning System (GPS) receivers. VTEC values were grouped into four seasons namely March Equinox (February, March, April), June Solstice (May, June, July), September Equinox (August, September, October), and December Solstice (November, December, January). VTEC generally increases from 06h00 LT and reaches its maximum value at approximately 15h00-17h00 LT during all seasons and at all locations. The NeQuick and IRI01-corr options of the IRI model predict reasonably well the observed diurnal and seasonal variation patterns of VTEC values. However, the IRI-2001 option gave a relatively poor prediction when compared with the other options. The post-midnight and post-sunset deviations between modeled and observed VTEC could arise because NmF2 or the shape of the electron density profile, or both, are not well predicted by the model; hence some improvements are still required in order to obtain improved predictions of TEC over the equatorial region of the Africa sector.

  11. LOW-MASS ACTIVE GALACTIC NUCLEI WITH RAPID X-RAY VARIABILITY

    SciTech Connect

    Ho, Luis C.; Kim, Minjin

    2016-04-10

    We present a detailed study of the optical spectroscopic properties of 12 active galactic nuclei (AGNs) with candidate low-mass black holes (BHs) selected by Kamizasa et al. through rapid X-ray variability. The high-quality, echellette Magellan spectra reveal broad Hα emission in all the sources, allowing us to estimate robust virial BH masses and Eddington ratios for this unique sample. We confirm that the sample contains low-mass BHs accreting at high rates: the median M{sub BH} = 1.2 × 10{sup 6} M{sub ⊙} and median L{sub bol}/L{sub Edd} = 0.44. The sample follows the M{sub BH}–σ{sub *} relation, within the considerable scatter typical of pseudobulges, the probable hosts of these low-mass AGNs. Various lines of evidence suggest that ongoing star formation is prevalent in these systems. We propose a new strategy to estimate star formation rates in AGNs hosted by low-mass, low-metallicity galaxies, based on modification of an existing method using the strength of [O ii] λ3727, [O iii] λ5007, and X-rays.

  12. OBLIQUE SHOCKS AS THE ORIGIN OF RADIO TO GAMMA-RAY VARIABILITY IN ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Hughes, Philip A.; Aller, Margo F.; Aller, Hugh D. E-mail: mfa@umich.edu

    2011-07-10

    The 'shock in jet' model for centimeter-waveband blazar variability is revisited, allowing for arbitrary shock orientation with respect to the jet flow direction, and both random and ordered magnetic field. It is shown that oblique shocks can explain events with swings in polarization position angle much less than the 90{sup 0} associated with transverse structures, while retaining the general characteristics of outbursts, including spectral behavior and level of peak percentage polarization. Models dominated by a force-free, minimum energy magnetic field configuration (essentially helical) display a shallow rise in percentage polarization and frequency-dependent swing in polarization position angle not in agreement with the results of single-dish monitoring observations, implying that the field is predominantly random in the quiescent state. Outbursts well explained by the 'shock in jet' model are present during {gamma}-ray flaring in several sources, supporting the idea that shock events are responsible for activity from the radio to {gamma}-ray bands.

  13. Ticks elicit variable f ibrinogenolytic activities upon feeding on hosts with different immune backgrounds

    PubMed Central

    Vora, Ashish; Taank, Vikas; Dutta, Sucharita M.; Anderson, John F.; Fish, Durland; Sonenshine, Daniel E.; Catravas, John D.; Sultana, Hameeda; Neelakanta, Girish

    2017-01-01

    Ticks secrete several anti-hemostatic factors in their saliva to suppress the host innate and acquired immune defenses against infestations. Using Ixodes scapularis ticks and age-matched mice purchased from two independent commercial vendors with two different immune backgrounds as a model, we show that ticks fed on immunodeficient animals demonstrate decreased fibrinogenolytic activity in comparison to ticks fed on immunocompetent animals. Reduced levels of D-dimer (fibrin degradation product) were evident in ticks fed on immunodeficient animals in comparison to ticks fed on immunocompetent animals. Increased engorgement weights were noted for ticks fed on immunodeficient animals in comparison to ticks fed on immunocompetent animals. Furthermore, the LC-MS/MS and quantitative real-time-PCR analysis followed by inhibitor and antibody-blocking assays revealed that the arthropod HSP70-like molecule contributes to differential fibrinogenolysis during tick feeding. Collectively, these results not only indicate that ticks elicit variable fibrinogenolysis upon feeding on hosts with different immune backgrounds but also provide insights for the novel role of arthropod HSP70-like molecule in fibrinogenolysis during blood feeding. PMID:28300174

  14. Heart rate variability and muscle sympathetic nerve activity response to acute stress: the effect of breathing

    PubMed Central

    DeBeck, Lindsay D.; Petersen, Stewart R.; Jones, Kelvin E.; Stickland, Michael K.

    2016-01-01

    Previous research has suggested a relationship between low-frequency power of heart rate variability (HRV; LF in normalized units, LFnu) and muscle sympathetic nerve activity (MSNA). However, investigations have not systematically controlled for breathing, which can modulate both HRV and MSNA. Accordingly, the aims of this experiment were to investigate the possibility of parallel responses in MSNA and HRV (LFnu) to selected acute stressors and the effect of controlled breathing. After data were obtained at rest, 12 healthy males (28 ± 5 yr) performed isometric handgrip exercise (30% maximal voluntary contraction) and the cold pressor test in random order, and were then exposed to hypoxia (inspired fraction of O2 = 0.105) for 7 min, during randomly assigned spontaneous and controlled breathing conditions (20 breaths/min, constant tidal volume, isocapnic). MSNA was recorded from the peroneal nerve, whereas HRV was calculated from ECG. At rest, controlled breathing did not alter MSNA but decreased LFnu (P < 0.05 for all) relative to spontaneous breathing. MSNA increased in response to all stressors regardless of breathing. LFnu increased with exercise during both breathing conditions. During cold pressor, LFnu decreased when breathing was spontaneous, whereas in the controlled breathing condition, LFnu was unchanged from baseline. Hypoxia elicited increases in LFnu when breathing was controlled, but not during spontaneous breathing. The parallel changes observed during exercise and controlled breathing during hypoxia suggest that LFnu may be an indication of sympathetic outflow in select conditions. However, since MSNA and LFnu did not change in parallel with all stressors, a cautious approach to the use of LFnu as a marker of sympathetic activity is warranted. PMID:20410469

  15. Heart rate variability and muscle sympathetic nerve activity response to acute stress: the effect of breathing.

    PubMed

    DeBeck, Lindsay D; Petersen, Stewart R; Jones, Kelvin E; Stickland, Michael K

    2010-07-01

    Previous research has suggested a relationship between low-frequency power of heart rate variability (HRV; LF in normalized units, LFnu) and muscle sympathetic nerve activity (MSNA). However, investigations have not systematically controlled for breathing, which can modulate both HRV and MSNA. Accordingly, the aims of this experiment were to investigate the possibility of parallel responses in MSNA and HRV (LFnu) to selected acute stressors and the effect of controlled breathing. After data were obtained at rest, 12 healthy males (28 +/- 5 yr) performed isometric handgrip exercise (30% maximal voluntary contraction) and the cold pressor test in random order, and were then exposed to hypoxia (inspired fraction of O(2) = 0.105) for 7 min, during randomly assigned spontaneous and controlled breathing conditions (20 breaths/min, constant tidal volume, isocapnic). MSNA was recorded from the peroneal nerve, whereas HRV was calculated from ECG. At rest, controlled breathing did not alter MSNA but decreased LFnu (P < 0.05 for all) relative to spontaneous breathing. MSNA increased in response to all stressors regardless of breathing. LFnu increased with exercise during both breathing conditions. During cold pressor, LFnu decreased when breathing was spontaneous, whereas in the controlled breathing condition, LFnu was unchanged from baseline. Hypoxia elicited increases in LFnu when breathing was controlled, but not during spontaneous breathing. The parallel changes observed during exercise and controlled breathing during hypoxia suggest that LFnu may be an indication of sympathetic outflow in select conditions. However, since MSNA and LFnu did not change in parallel with all stressors, a cautious approach to the use of LFnu as a marker of sympathetic activity is warranted.

  16. Regional Heat Sources and the Active and Break Phases of Boreal Summer Intraseasonal Variability

    SciTech Connect

    Annamalai, H; Sperber, K R

    2003-12-15

    The boreal summer intraseasonal variability (BSISV) associated with the 30-50 day mode is represented by the co-existence of three components, poleward propagation of convection over the Indian and tropical west Pacific longitudes and eastward propagation along the equator. The hypothesis that the three components influence each other has been investigated using observed OLR, NCEP-NCAR reanalysis, and solutions from an idealized linear model. The null hypothesis is that the three components are mutually independent. Cyclostationary EOF (CsEOF) analysis is applied on filtered OLR to extract the life-cycle of the BSISV. The dominant mode of CsEOF is significantly tied to observed rainfall over the Indian subcontinent. The components of the heating patterns from CsEOF analysis serve as prescribed forcings for the linear model. This allows us to ascertain which heat sources and sinks are instrumental in driving the large-scale monsoon circulation during the BSISV life-cycle. We identify three new findings: (1) the circulation anomalies that develop as a Rossby wave response to suppressed convection over the equatorial Indian Ocean associated with the previous break phase of the BSISV precondition the ocean-atmosphere system in the western Indian Ocean and trigger the next active phase of the BSISV, (2) the development of convection over the tropical west Pacific forces descent anomalies to the west. This, in conjunction with the weakened cross-equatorial flow due to suppressed convective anomalies over the equatorial Indian Ocean reduce the tropospheric moisture over the Arabian Sea, and promote westerly wind anomalies that do not recurve over India. As a result the low-level cyclonic vorticity shifts from India to southeast Asia and break conditions are initiated over India, and (3) the circulation anomalies forced by equatorial Indian Ocean convective anomalies significantly influence the active/break phases over the tropical west Pacific. Our model solutions support

  17. Nonaffine rubber elasticity for stiff polymer networks.

    PubMed

    Heussinger, Claus; Schaefer, Boris; Frey, Erwin

    2007-09-01

    We present a theory for the elasticity of cross-linked stiff polymer networks. Stiff polymers, unlike their flexible counterparts, are highly anisotropic elastic objects. Similar to mechanical beams, stiff polymers easily deform in bending, while they are much stiffer with respect to tensile forces ("stretching"). Unlike in previous approaches, where network elasticity is derived from the stretching mode, our theory properly accounts for the soft bending response. A self-consistent effective medium approach is used to calculate the macroscopic elastic moduli starting from a microscopic characterization of the deformation field in terms of "floppy modes"-low-energy bending excitations that retain a high degree of nonaffinity. The length scale characterizing the emergent nonaffinity is given by the "fiber length" lf, defined as the scale over which the polymers remain straight. The calculated scaling properties for the shear modulus are in excellent agreement with the results of recent simulations obtained in two-dimensional model networks. Furthermore, our theory can be applied to rationalize bulk rheological data in reconstituted actin networks.

  18. An improved spinning lens test to determine the stiffness of the human lens

    PubMed Central

    Burd, H.J.; Wilde, G.S.; Judge, S.J.

    2011-01-01

    It is widely accepted that age-related changes in lens stiffness are significant for the development of presbyopia. However, precise details on the relative importance of age-related changes in the stiffness of the lens, in comparison with other potential mechanisms for the development of presbyopia, have not yet been established. One contributing factor to this uncertainty is the paucity and variability of experimental data on lens stiffness. The available published data generally indicate that stiffness varies spatially within the lens and that stiffness parameters tend to increase with age. However, considerable differences exist between these published data sets, both qualitatively and quantitatively. The current paper describes new and improved methods, based on the spinning lens approach pioneered by Fisher, R.F. (1971) ‘The elastic constants of the human lens’, Journal of Physiology, 212, 147–180, to make measurements on the stiffness of the human lens. These new procedures have been developed in an attempt to eliminate, or at least substantially reduce, various systematic errors in Fisher’s original experiment. An improved test rig has been constructed and a new modelling procedure for determining lens stiffness parameters from observations made during the test has been devised. The experiment involves mounting a human lens on a vertical rotor so that the lens spins on its optical axis (typically at 1000 rpm). An automatic imaging system is used to capture the outline of the lens, while it is rotating, at pre-determined angular orientations. These images are used to quantify the deformations developed in the lens as a consequence of the centripetal forces induced by the rotation. Lens stiffness is inferred using axisymmetric finite element inverse analysis in which a nearly-incompressible neo-Hookean constitutive model is used to represent the mechanics of the lens. A numerical optimisation procedure is used to determine the stiffness parameters

  19. Variability Selected Low-Luminosity Active Galactic Nuclei in the 4 Ms Chandra Deep Field-South

    NASA Technical Reports Server (NTRS)

    Young, M.; Brandt, W. N.; Xue, Y. Q.; Paolillo, D. M.; Alexander, F. E.; Bauer, F. E.; Lehmer, B. D.; Luo, B.; Shemmer, O.; Schneider, D. P.; Vignail, C.

    2012-01-01

    The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGN). However, cosmologically distant low-luminosity AGN (LLAGN) have remained a challenge to identify due to significant contribution from the host galaxy. We identify long-term X ray variability (approx. month years, observed frame) in 20 of 92 CDF-S galaxies spanning redshifts approx equals 00.8 - 1.02 that do not meet other AGN selection criteria. We show that the observed variability cannot be explained by X-ray binary populations or ultraluminous X-ray sources, so the variability is most likely caused by accretion onto a supermassive black hole. The variable galaxies are not heavily obscured in general, with a stacked effective power-law photon index of Gamma(sub Stack) approx equals 1.93 +/- 0.13, and arc therefore likely LLAGN. The LLAGN tend to lie it factor of approx equal 6-89 below the extrapolated linear variability-luminosity relation measured for luminous AGN. This may he explained by their lower accretion rates. Variability-independent black-hole mass and accretion-rate estimates for variable galaxies show that they sample a significantly different black hole mass-accretion-rate space, with masses a factor of 2.4 lower and accretion rates a factor of 22.5 lower than variable luminous AGNs at the same redshift. We find that an empirical model based on a universal broken power-law power spectral density function, where the break frequency depends on SMBH mass and accretion rate, roughly reproduces the shape, but not the normalization, of the variability-luminosity trends measured for variable galaxies and more luminous AGNs.

  20. Arterial stiffness is not increased in patients with short duration rheumatoid arthritis and ankylosing spondylitis.

    PubMed

    Dzieża-Grudnik, Anna; Sulicka, Joanna; Strach, Magdalena; Siga, Olga; Klimek, Ewa; Korkosz, Mariusz; Grodzicki, Tomasz

    2017-04-01

    Patients with rheumatoid arthritis (RA) and ankylosing spondylitis (AS) have increased cardiovascular (CV) morbidity and mortality. Arterial stiffness is an independent predictor of CV events. The aim of the study was to assess arterial stiffness and inflammatory markers in patients with short duration chronic arthritis. We assessed carotid-femoral pulse wave velocity (PWV), augmentation index (AIx), traditional CV risk factors and inflammatory and endothelial markers in 71 chronic arthritis patients (RA and AS) and in 29 healthy controls. We did not find differences in PWV (for RA, AS and controls, respectively: 10 [8.8-10.9] versus 10.7 [9.1-11.8] versus 9.2 [8.3-11.4] m/s; p = .14) and AIx (for RA, AS and controls, respectively: 24.3 ± 11.5 versus 5.7 ± 12.4 versus 10 ± 12.8%; p = .22). Both groups of arthritis patients had active disease with significantly elevated inflammatory markers compared to controls. There were no correlations between endothelial and inflammatory markers and parameters of arterial stiffness in arthritis patients. When analyzing arthritis patients according to median of PVW, there were no significant differences in inflammatory and endothelial markers. We found that in patients with short duration active RA and AS arterial stiffness was not increased and furthermore, there was no association between markers of systemic inflammation and arterial stiffness.

  1. CURious Variables Experiment (CURVE): CCD photometry of active dwarf nova DI Ursae Majoris

    NASA Astrophysics Data System (ADS)

    Rutkowski, A.; Olech, A.; Wiśniewski, M.; Pietrukowicz, P.; Pala, J.; Poleski, R.

    2009-04-01

    Context: We report an analysis of photometric behaviour of DI UMa, an extremely active dwarf nova. The observational campaign (completed in 2007) covers five superoutbursts and four normal outbursts. Aims: We examined principal parameters of the system to understand peculiarities of DI UMa, and other active cataclysmic variables. Methods: Based on precise photometric measurements, temporal light curve behaviour, O-C analysis, and power spectrum analysis, we investigated physical parameters of the system. Results: We found that the period of the supercycle now equals 31.45 ± 0.3 days. Observations during superoutbursts infer that the period of superhumps equals P_sh = 0.055318(11) days (79.66± 0.02 min). During quiescence, the light curve reveals a modulation of period P_orb = 0.054579(6) days (78.59 ± 0.01 min), which we interpret as the orbital period of the binary system. The values obtained allowed us to determine a fractional period excess of 1.35% ± 0.02%, which is surprisingly small compared to the usual value for dwarf novae (2%-5%). A detailed O-C analysis was performed for two superoutbursts with the most comprehensive coverage. In both cases, we detected an increase in the superhump period with a mean rate of dot P/P_sh = 4.4(1.0)× 10-5. Conclusions: Based on these measurements, we confirm that DI UMa is probably a period bouncer, an old system that reached its period minimum a long time ago, has a secondary that became a degenerate brown dwarf, the entire system evolving now toward longer periods. DI UMa is an extremely interesting object because we know only one more active ER UMa star with similar characteristics (IX Dra). Photometric data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/497/437

  2. Vascular Smooth Muscle Cell Stiffness as a Mechanism for Increased Aortic Stiffness with Aging

    PubMed Central

    Qiu, Hongyu; Zhu, Yi; Sun, Zhe; Trzeciakowski, Jerome P.; Gansner, Meredith; Depre, Christophe; Resuello, Ranillo R.G.; Natividad, Filipinas F.; Hunter, William C.; Genin, Guy M.; Elson, Elliot L.; Vatner, Dorothy E.; Meininger, Gerald A.; Vatner, Stephen F.

    2010-01-01

    Rationale Increased aortic stiffness, an important feature of many vascular diseases, e.g., aging, hypertension, atherosclerosis and aortic aneurysms, is assumed due to changes in extracellular matrix (ECM). Objective We tested the hypothesis that the mechanisms also involve intrinsic stiffening of vascular smooth muscle cells (VSMCs). Methods and Results Stiffness was measured in vitro both by atomic force microscopy (AFM) and in a reconstituted tissue model, using VSMCs from aorta of young versus old male monkeys (Macaca fascicularis, n=7/group), where aortic stiffness increases by 200 % in vivo. The apparent elastic modulus was increased (P<0.05) in old VSMCs (41.7±0.5 kPa) versus young (12.8±0.3 kPa), but not after disassembly of the actin cytoskeleton with cytochalasin D. Stiffness of the VSMCs in the reconstituted tissue model was also higher (P<0.05) in old (23.3±3.0 kPa) than in young (13.7±2.4 kPa). Conclusions These data support the novel concept, not appreciated previously, that increased vascular stiffness with aging is due not only to changes in ECM, but also to intrinsic changes in VSMCs. PMID:20634486

  3. 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

  4. Assessment of the variability of vastii myoelectric activity in young healthy females during walking: a statistical gait analysis.

    PubMed

    Di Nardo, Francesco; Maranesi, Elvira; Mengarelli, Alessandro; Ghetti, Giacomo; Burattini, Laura; Fioretti, Sandro

    2015-10-01

    The study was designed to assess the natural variability of the activation modalities of vastus medialis (VM) and vastus lateralis (VL) during walking at a self-selected speed and cadence of 30 young, healthy, females. This was achieved by conducting statistical gait analysis on the surface electromyographic signals from hundreds of strides for each subject. Results revealed variability in the number of activations, occurrence frequency, and onset-offset instants across the thousands of strides analyzed. However, despite the variability, there was one activation occurrence which remained consistent across subjects for both VM and VL. This occurred from terminal swing to the following loading response (observed in 100% of strides). A second, less frequent, activation occurred between mid-stance up to pre-swing (observed in 39.3±22.4% of strides for VM and in 35.1±20.6% for VL). No significant differences (p>0.05) were observed in the onset-offset instants or in the occurrence frequency, which suggest a simultaneous recruitment of VM and VL. This "normality" pattern represents the first attempt at developing a reference frame for vastii sEMG activity during walking, that is able to include the physiological variability of the phenomenon and control the confounding effects of age and gender.

  5. Identification of Active Galactic Nuclei through HST optical variability in the GOODS South field

    NASA Astrophysics Data System (ADS)

    Pouliasis, Ektoras; Georgantopoulos; Bonanos, A.; HCV Team

    2016-08-01

    This work aims to identify AGN in the GOODS South deep field through optical variability. This method can easily identify low-luminosity AGN. In particular, we use images in the z-band obtained from the Hubble Space Telescope with the ACS/WFC camera over 5 epochs separated by ~45 days. Aperture photometry has been performed using SExtractor to extract the lightcurves. Several variability indices, such as the median absolute deviation, excess variance, and sigma were applied to automatically identify the variable sources. After removing artifacts, stars and supernovae from the variable selected sample and keeping only those sources with known photometric or spectroscopic redshift, the optical variability was compared to variability in other wavelengths (X-rays, mid-IR, radio). This multi-wavelength study provides important constraints on the structure and the properties of the AGN and their relation to their hosts. This work is a part of the validation of the Hubble Catalog of Variables (HCV) project, which has been launched at the National Observatory of Athens by ESA, and aims to identify all sources (pointlike and extended) showing variability, based on the Hubble Source Catalog (HSC, Whitmore et al. 2015). The HSC version 1 was released in February 2015 and includes 80 million sources imaged with the WFPC2, ACS/WFC, WFC3/UVIS and WFC3/IR cameras.

  6. WASTE SOLIDIFICATION BUILDING BENCH SCALE HIGH ACTIVITY WASTE SIMULANT VARIABILITY STUDY FY2008

    SciTech Connect

    Hansen, E; Timothy Jones, T; Tommy Edwards, T; Alex Cozzi, A

    2009-03-20

    The primary objective of this task was to perform a variability study of the high activity waste (HAW) acidic feed to determine the impact of feed variability on the quality of the final grout and on the mixability of the salt solution into the dry powders. The HAW acidic feeds were processed through the neutralization/pH process, targeting a final pH of 12. These fluids were then blended with the dry materials to make the final waste forms. A secondary objective was to determine if elemental substitution for cost prohibitive or toxic elements in the simulant affects the mixing response, thus providing a more economical simulant for use in full scale tests. Though not an objective, the HAW simulant used in the full scale tests was also tested and compared to the results from this task. A statistically designed test matrix was developed based on the maximum molarity inputs used to make the acidic solutions. The maximum molarity inputs were: 7.39 HNO{sub 3}, 0.11618 gallium, 0.5423 silver, and 1.1032 'other' metals based on their NO{sub 3}{sup -} contribution. Substitution of the elements aluminum for gallium and copper for silver was also considered in this test matrix, resulting in a total of 40 tests. During the NaOH addition, the neutralization/pH adjustment process was controlled to a maximum temperature of 60 C. The neutralized/pH adjusted simulants were blended with Portland cement and zircon flour at a water to cement mass ratio of 0.30. The mass ratio of zircon flour to Portland cement was 1/12. The grout was made using a Hobart N-50 mixer running at low speed for two minutes to incorporate and properly wet the dry solids with liquid and at medium speed for five minutes for mixing. The resulting fresh grout was measured for three consecutive yield stress measurements. The cured grout was measured for set, bleed, and density. Given the conditions of preparing the grout in this task, all of the grouts were visually well mixed prior to preparing the grouts for

  7. Nonlinear effects on the stiffness of bolted joints

    SciTech Connect

    Lehnhoff, T.F.; Wistehuff, W.E.

    1996-02-01

    Axisymmetric finite element modeling of bolted joints was performed to show the effects of the magnitude and position of the external load, member thickness, and member material on the bolt and member stiffnesses. The member stiffness of the bolted joint was found to decrease 10 to 42 percent for the 20-mm to 8-mm bolts, respectively, as the magnitude of the external load was increased. Member stiffness appears to be independent of the radial location of the external load and increases as the member thickness decreases. Member stiffness decreased by a factor of 2.5 to 3 with a change in the member material from steel to aluminum. The cast iron members had a decrease in member stiffness of a factor of 1.7 to 1.9. The aluminum over cast iron combination had a member stiffness between the aluminum and cast iron alone. Bolt stiffnesses varied by less than two percent for changes in the magnitude of the external load for all bolt sizes and member materials, except for the 8-mm bolt where stiffness increased by approximately 11 percent. Changes in radial position of the external load had no effect on the bolt stiffness. A 3 to 13-percent decrease in the bolt stiffness was found when changing from steel to aluminum members. A 2 to 3-percent bolt stiffness decrease resulted when the member material was changed from steel to cast iron and similarly from steel to the aluminum over cast iron combination.

  8. 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.

  9. 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

  10. Effect of RGD-functionalization and stiffness modulation of polyelectrolyte multilayer films on muscle cell differentiation

    PubMed Central

    Gribova, Varvara; Gauthier-Rouvière, Cécile; Albigès-Rizo, Corinne; Auzely-Velty, Rachel; Picart, Catherine

    2014-01-01

    Skeletal muscle tissue engineering holds promise for the replacement of muscle due to an injury and for the treatment of muscle diseases. Although RGD substrates have been widely explored in tissue engineering, there is no study aimed at investigating the combined effects of RGD nanoscale presentation and matrix stiffness on myogenesis. In the present work, we use polyelectrolyte multilayer films made of poly(L-lysine) (PLL) and poly(L-glutamic) acid (PGA) as substrates of tunable stiffness that can be functionalized by a RGD adhesive peptide to investigate important events in myogenesis, including adhesion, migration, proliferation and differentiation. C2C12 myoblasts were used as cellular models. RGD presentation on soft films and increased film stiffness could both induce cell adhesion, but integrins involved in adhesion were different in case of soft and stiff films. Moreover, soft films with RGD peptide appeared to be the most appropriate substrate for myogenic differentiation while the stiff PLL/PGA films significantly induced cell migration, proliferation and inhibited myogenic differentiation. The ROCK kinase was found to be involved in myoblast response to the different films. Indeed, its inhibition was sufficient to rescue the differentiation on stiff films, but no significant changes were observed on stiff films with the RGD peptide. These results suggest that different signaling pathways may be activated depending on mechanical and biochemical properties of the multilayer films. This study emphasizes the superior advantage of the soft PLL/PGA films presenting the RGD peptide in terms of myogenic differentiation. This soft RGD-presenting film may be further used as coating of various polymeric scaffolds for muscle tissue engineering. PMID:23261924

  11. Interannual variability of the frontal activity in the Southern Hemisphere: relationship with atmospheric circulation and precipitation over southern South America

    NASA Astrophysics Data System (ADS)

    Blázquez, Josefina; Solman, Silvina A.

    2016-06-01

    The interannual variability of the frontal activity over the western Southern Hemisphere and its linkage with the variability of the atmospheric circulation and precipitation over southern South America is studied. The analysis is focused on the austral winter and spring seasons. The frontal activity is represented by an index defined as the product between the horizontal gradient of temperature and the relative vorticity at 850 hPa (FI) and is computed from the ERA Interim and NCEP2 reanalysis. For the two seasons the main mode of variability of FI, as depicted by the first Empirical Orthogonal Function, presents centres of action located in the southern part of the western Southern Hemisphere. This pattern is present in the two reanalysis datasets. The correlation coefficients between the principal component of the leading mode of FI and the two main modes of the 500 hPa geopotential height indicate that both the ENSO-mode and the SAM modulate the leading pattern of FI in winter while during the spring season the ENSO-mode controls the FI variability. The variability of the FI has a robust influence on the interannual variability of precipitation over southern South America and adjacent oceans. Over the continent, it was found that the pattern of precipitation anomalies associated with the variability of the FI depicts significant signals over southeastern South America (SESA), centre and south of Chile for winter and over SESA and southeastern Brazil for spring and agrees with the pattern of the leading mode of precipitation variability over southern South America.

  12. Muscular contributions to dynamic dorsoventral lumbar spine stiffness

    PubMed Central

    Colloca, Christopher J.; Harrison, Deed E.; Moore, Robert J.; Gunzburg, Robert

    2006-01-01

    Spinal musculature plays a major role in spine stability, but its importance to spinal stiffness is poorly understood. We studied the effects of graded trunk muscle stimulation on the in vivo dynamic dorsoventral (DV) lumbar spine stiffness of 15 adolescent Merino sheep. Constant voltage supramaximal electrical stimulation was administered to the L3–L4 interspinous space of the multifidus muscles using four stimulation frequencies (2.5, 5, 10, and 20 Hz). Dynamic stiffness was quantified at rest and during muscle stimulation using a computer-controlled testing apparatus that applied variable frequency (0.46–19.7 Hz) oscillatory DV forces (13-N preload to 48-N peak) to the L3 spinous process of the prone-lying sheep. Five mechanical excitation trials were randomly performed, including four muscle stimulation trials and an unstimulated or resting trial. The secant stiffness (ky = DV force/L3 displacement, kN/m) and loss angle (phase angle, deg) were determined at 44 discrete mechanical excitation frequencies. Results indicated that the dynamic stiffness varied 3.7-fold over the range of mechanical excitation frequencies examined (minimum resting ky = 3.86 ± 0.38 N/mm at 4.0 Hz; maximum ky = 14.1 ± 9.95 N/mm at 19.7 Hz). Twenty hertz muscle stimulation resulted in a sustained supramaximal contraction that significantly (P < 0.05) increased ky up to twofold compared to rest (mechanical excitation at 3.6 Hz). Compared to rest, ky during the 20 Hz muscle stimulation was significantly increased for 34 of 44 mechanical excitation frequencies (mean increase = 55.1%, P < 0.05), but was most marked between 2.55 and 4.91 Hz (mean increase = 87.5%, P < 0.05). For lower frequency, sub-maximal muscle stimulation, there was a graded change in ky, which was significantly increased for 32/44 mechanical excitation frequencies (mean increase = 40.4%, 10 Hz stimulus), 23/44 mechanical excitation frequencies (mean increase = 10.5%, 5 Hz stimulus

  13. Radiofrequency exposure in the French general population: band, time, location and activity variability.

    PubMed

    Viel, Jean-François; Cardis, Elisabeth; Moissonnier, Monika; de Seze, René; Hours, Martine

    2009-11-01

    Information on the exposure of individual persons to radiofrequency (RF) fields is scarce, although such data are crucial in order to develop a suitable exposure assessment method, and frame the hypothesis and design of future epidemiological studies. The main goal of this survey is to assess individual RF exposure on a population basis, while clarifying the relative contribution of different sources to the total exposure. A total of 377 randomly selected people were analyzed. Each participant was supplied with a personal exposure meter for 24-hour measurements (weekday), and kept a time-location-activity diary. Electric field strengths were recorded in 12 different RF bands every 13s. Summary statistics were calculated with the robust regression on order statistics method. Most of the time, recorded field strengths were not detectable with the exposure meter. Total field, cordless phones, WiFi-microwave, and FM transmitters stood apart with a proportion above the detection threshold of 46.6%, 17.2%, 14.1%, and 11.0%, respectively. The total field mean value was 0.201V/m, higher in urban areas, during daytime, among adults, and when moving. When focusing on specific channels, the highest mean exposure resulted from FM sources (0.044V/m), followed by WiFi-microwaves (0.038V/m), cordless phones (0.037V/m), and mobile phones (UMTS: 0.036V/m, UMTS: 0.037V/m). Various factors, however, contributed to a high variability in RF exposure assessment. These population-based estimates should therefore be confirmed by further surveys to better characterize the exposure situation in different microenvironments.

  14. Solar activity variability in the IRI at high latitudes: Comparisons with GPS total electron content

    NASA Astrophysics Data System (ADS)

    Themens, David R.; Jayachandran, P. T.

    2016-04-01

    Total electron content (TEC) measurements from 10 dual-frequency GPS receivers in the Canadian High Arctic Ionospheric Network (CHAIN) are used to evaluate the performance of International Reference Ionosphere (IRI)-2007 within the Canadian sector. Throughout the region, we see systematic underestimation of daytime TEC, particularly at solar maximum, where summer and equinox root-mean-square errors reach as high as 14 total electron content units, 1 TECU = 1016 el m-2 (TECU). It is also shown that the use of a monthly IG index, in place of the IRI's standard IG12 index, leads to an improvement in TEC specification by up to 3 TECU in the polar cap and up to 6 TECU in the subauroral region during periods of short-term, large amplitude changes in solar activity. On diurnal timescales, variability in TEC is found to be underestimated by the IRI, during equinox periods, by up to 40% at subauroral latitudes and up to 70% in the polar cap region. During the winter, diurnal variations are overestimated by up to 40% in the subauroral region and are underestimated within the polar cap by up to 80%. Using collocated ionosonde data, we find IRI bottomside TEC to be within 1 TECU of observation with errors largest during the equinoxes. For the topside we find good agreement during the winter but significant underestimation of topside TEC by the IRI during summer and equinox periods, exceeding 6 TECU at times. By ingesting measured NmF2 into the IRI, we show that the topside thickness parameterization is the source of the bulk of the observed TEC errors.

  15. Antagonistic active knee prosthesis. A metabolic cost of walking comparison with a variable-damping prosthetic knee.

    PubMed

    Martinez-Villalpando, Ernesto C; Mooney, Luke; Elliott, Grant; Herr, Hugh

    2011-01-01

    This paper examines the impact of a biomimetic active knee prosthesis on the metabolic costs associated with a unilateral transfemoral amputee walking at self selected speed. In this study we compare the antagonistic active knee prosthesis developed at MIT to an electronically controlled, variable-damping commercial knee prosthesis, the Otto Bock C-leg. Use of the active knee prosthesis resulted in both, a 17% increase in an amputee's average self selected walking speed from 1.12 m/s to 1.31 m/s, and a 6.8% reduction in metabolic cost. The results of this study suggest that an agonist-antagonist active knee prosthesis design with variable impedance control can offer walking energetic advantages over commercially available systems.

  16. A novel online method to monitor autonomic nervous activity based on arterial wall impedance and heart rate variability.

    PubMed

    Kutluk, Abdugheni; Tsuji, Toshio; Ukawa, Teiji; Nakamura, Ryuji; Saeki, Noboru; Yoshizumi, Masao; Kawamoto, Masashi

    2010-04-01

    This paper proposes a new method of evaluating autonomic nervous activity using the mechanical impedance of arterial walls and heart rate variability. The cardiovascular system is indispensable to life maintenance functions, and homeostasis is maintained by the autonomic nervous system. Accordingly, it is very important to be able to make diagnosis based on autonomic nervous activity within the body's circulation. The proposed method was evaluated in surgical operations; the mechanical impedance of the arterial wall was estimated from arterial blood pressure and a photoplethysmogram, and heart rate variability was estimated using electrocardiogram R-R interval spectral analysis. In this paper, we monitored autonomic nervous system activity using the proposed system during endoscopic transthoracic sympathetic block surgery in eight patients with hyperhidrosis. The experimental results indicated that the proposed system can be used to estimate autonomic nervous activity in response to events during operations.

  17. Attributing runoff changes to climate variability and human activities: uncertainty analysis using four monthly water balance models

    SciTech Connect

    Li, Shuai; Xiong, Lihua; Li, Hong-Yi; Leung, L. Ruby; Demissie, Yonas

    2015-05-26

    Hydrological simulations to delineate the impacts of climate variability and human activities are subjected to uncertainties related to both parameter and structure of the hydrological models. To analyze the impact of these uncertainties on the model performance and to yield more reliable simulation results, a global calibration and multimodel combination method that integrates the Shuffled Complex Evolution Metropolis (SCEM) and Bayesian Model Averaging (BMA) of four monthly water balance models was proposed. The method was applied to the Weihe River Basin (WRB), the largest tributary of the Yellow River, to determine the contribution of climate variability and human activities to runoff changes. The change point, which was used to determine the baseline period (1956-1990) and human-impacted period (1991-2009), was derived using both cumulative curve and Pettitt’s test. Results show that the combination method from SCEM provides more skillful deterministic predictions than the best calibrated individual model, resulting in the smallest uncertainty interval of runoff changes attributed to climate variability and human activities. This combination methodology provides a practical and flexible tool for attribution of runoff changes to climate variability and human activities by hydrological models.

  18. Implications of Rural Environmental Variables Associated with the Participation of Children in Farming Activities: A Lesson from Rural Southwestern Nigeria

    ERIC Educational Resources Information Center

    Ajayi, A. O.; Jibowo, A. A.

    2006-01-01

    This study aimed at investigating the relationship between the participation of rural children in farming activities and selected social, school, and physical environment related variables. Data were collected from four hundred and fifty eight children selected through stage-wise random sampling procedure from the four agricultural zones in Oyo…

  19. Functional aortic stiffness: role of CD4(+) T lymphocytes.

    PubMed

    Majeed, Beenish A; Eberson, Lance S; Tawinwung, Supannikar; Larmonier, Nicolas; Secomb, Timothy W; Larson, Douglas F

    2015-01-01

    The immune system is suggested to be essential in vascular remodeling and stiffening. To study the dependence upon lymphocytes in vascular stiffening, we compared an angiotensin II-model of vascular stiffening in normal C57BL/6J mice with lymphocyte-deficient RAG 1(-/-) mice and additionally characterized the component of vascular stiffness due to vasoconstriction vs. vascular remodeling. Chronic angiotensin II increased aortic pulse wave velocity, effective wall stiffness, and effective Young's modulus in C57BL/6J mice by three-fold but caused no change in the RAG 1(-/-) mice. These functional measurements were supported by aortic morphometric analysis. Adoptive transfer of CD4(+) T helper lymphocytes restored the angiotensin II-mediated aortic stiffening in the RAG 1(-/-) mice. In order to account for the hydraulic vs. material effects of angiotensin II on pulse wave velocity, subcutaneous osmotic pumps were removed after 21 days of angiotensin II-infusion in the WT mice to achieve normotensive values. The pulse wave velocity (PWV) decreased from three- to two-fold above baseline values up to 7 days following pump removal. This study supports the pivotal role of the CD4(+) T-lymphocytes in angiotensin II-mediated vascular stiffening and that angiotensin II-mediated aortic stiffening is due to the additive effect of active vascular smooth muscle vasoconstriction and vascular remodeling.

  20. Morning stiffness and other patient-reported outcomes of rheumatoid arthritis in clinical practice.

    PubMed

    Sokka, T

    2011-01-01

    Morning stiffness has been recognized in traditional approaches to assessment of disease activity in rheumatoid arthritis (RA). Although morning stiffness is not specific to RA, changes in morning stiffness for an individual patient are helpful when monitoring health status. Health professionals can ask about morning stiffness but the most accurate and consistent approach to assessment from one visit to the next appears to be a patient self-report questionnaire. However, quantitative measures of patient-reported data are not an integral part of clinical monitoring in most clinics. No single measure is adequate for all individual patients, so quantitative measurement of patient-reported data should include many elements such as pain, functional status, fatigue, sleep, morning stiffness, work capacity, and physical and emotional well-being. In daily clinical practice, patient-reported outcomes can be collected easily using a standard questionnaire that patients can complete with pencil and paper or electronically on a touch screen in the waiting room. The results are then immediately available to the rheumatologists, to facilitate doctor-patient communication to improve the quality of patient care, leading to better patient outcomes.

  1. Interplay between Heightened Temporal Variability of Spontaneous Brain Activity and Task-Evoked Hyperactivation in the Blind

    PubMed Central

    Dai, Rui; Huang, Zirui; Tu, Huihui; Wang, Luoyu; Tanabe, Sean; Weng, Xuchu; He, Sheng; Li, Dongfeng

    2016-01-01

    The brain's functional organization can be altered by visual deprivation. This is observed by comparing blind and sighted people's activation response to tactile discrimination tasks, like braille reading. Where, the blind have higher activation than the sighted upon tactile discrimination tasks, especially high activation difference is seen in ventral occipitotemporal (vOT) cortex. However, it remains unknown, whether this vOT hyperactivation is related to alteration of spontaneous activity. To address this question, we examined 16 blind subjects, 19 low-vision individuals, and 21 normally sighted controls using functional magnetic resonance imaging (fMRI). Subjects were scanned in resting-state and discrimination tactile task. In spontaneous activity, when compared to sighted subjects, we found both blind and low vision subjects had increased local signal synchronization and increased temporal variability. During tactile tasks, compared to sighted subjects, blind and low-vision subject's vOT had stronger tactile task-induced activation. Furthermore, through inter-subject partial correlation analysis, we found temporal variability is more related to tactile-task activation, than local signal synchronization's relation to tactile-induced activation. Our results further support that vision impairment induces vOT cortical reorganization. The hyperactivation in the vOT during tactile stimulus processing in the blind may be related to their greater dynamic range of spontaneous activity. PMID:28066206

  2. Searching for Short Term Variable Active Galactic Nuclei: A Vital Step Towards Using AGN as Standard Candles

    NASA Astrophysics Data System (ADS)

    Kilts, Kelly; Gorjian, Varoujan; Rutherford, Thomas; Kohrs, Russell; Urbanowski, Vincent; Bellusci, Nina; Horton, Savannah; Jones, Dana; Jones, Kaytlyn; Pawelski, Peter; Tranum, Haley; Zhang, Emily

    2017-01-01

    Current models for accretion disk sizes of active galactic nuclei (AGN) do not match the limited observational data available, so there is an active need from the modeling community for many more accretion disk/dusty torus reverberation mapping campaigns with which to better calibrate models. Since short term variable AGN can be more easily monitored for reverberation mapping than long term variable AGN, they can begin to provide data more quickly. This project looked for short term variable AGN in the Young Stellar Object Variability (YSOVAR) survey conducted using the Spitzer Space Telescope. The YSOVAR survey targeted 12 nearby star forming regions for repeated observations. Potential AGN from the YSOVAR data were first selected by color ([3.6] - [4.5] > 0.4) and then by magnitude (m < 14) based on previous Spitzer surveys of known AGN. Since AGN share some similar color characteristics with young stars, images of each YSOVAR region were viewed to remove potential objects near concentrations of known young stellar objects since these were likely also YSOs. The spectral energy distribution (SED) for each remaining potential AGN was then examined for AGN like characteristics. Several potential short term variable AGN were found.

  3. Serial Liver Stiffness Measurements and Monitoring of Liver-Transplanted Patients in a Real-Life Clinical Practice

    PubMed Central

    Rinaldi, Luca; Valente, Giovanna; Piai, Guido

    2016-01-01

    Background Liver transplanted patients need close surveillance for early signs of graft disease. Objectives Transient elastography can safely be repeated over time, offering serial liver stiffness measurement values. Serial stiffness measurements were compared to single baseline stiffness measurements in predicting the appearance of liver-related clinical events and guiding subsequent clinical decisions. Methods One hundred and sixty liver transplanted patients were observed for three years in our real-life practice. Results Liver stiffness measurements were stable in 75% of patients, decreased in 4% of patients, and increased in 21% of patients. The pattern of increased stiffness measurements was associated with both HCV-RNA positive status and the presence of an active biliary complication of liver transplantation and was more predictive of a clinically significant event resulting from any disease of the transplanted liver when compared to a stable pattern or to a single liver stiffness measurement. The procedures that were consequently performed were often diagnostic for unexpected situations, both in HCV-RNA positive and HCV-RNA negative patients. Conclusions The pattern of longitudinally increased liver stiffness measurements efficiently supported clinical decisions for individualized management strategies. Repeated transient elastography in real-life clinical practice appears to have a practical role in monitoring liver transplanted patients. PMID:28123442

  4. TIME VARIABILITY OF EMISSION LINES FOR FOUR ACTIVE T TAURI STARS. I. OCTOBER-DECEMBER IN 2010

    SciTech Connect

    Chou, Mei-Yin; Takami, Michihiro; Karr, Jennifer L.; Shang Hsien; Liu, Hauyu Baobab; Manset, Nadine; Beck, Tracy; Pyo, Tae-Soo; Chen, Wen-Ping; Panwar, Neelam

    2013-04-15

    We present optical spectrophotometric monitoring of four active T Tauri stars (DG Tau, RY Tau, XZ Tau, RW Aur A) at high spectral resolution (R {approx}> 1 Multiplication-Sign 10{sup 4}), to investigate the correlation between time variable mass ejection seen in the jet/wind structure of the driving source and time variable mass accretion probed by optical emission lines. This may allow us to constrain the understanding of the jet/wind launching mechanism, the location of the launching region, and the physical link with magnetospheric mass accretion. In 2010, observations were made at six different epochs to investigate how daily and monthly variability might affect such a study. We perform comparisons between the line profiles we observed and those in the literature over a period of decades and confirm the presence of time variability separate from the daily and monthly variability during our observations. This is so far consistent with the idea that these line profiles have a long-term variability (3-20 yr) related to episodic mass ejection suggested by the structures in the extended flow components. We also investigate the correlations between equivalent widths and between luminosities for different lines. We find that these correlations are consistent with the present paradigm of steady magnetospheric mass accretion and emission line regions that are close to the star.

  5. Rotor/bearing system dynamic stiffness measurements

    NASA Technical Reports Server (NTRS)

    Muszynska, A.

    1985-01-01

    Sweep perturbation testing as used in Modal Analysis when applied to a rotating machine has to take into consideration the machine dynamic state of equilibrium at its operational rotative speed. This stands in contrasts to a static equilibrium of nonrotating structures. The rotational energy has a significant influence on rotor dynamic characteristics. The best perturbing input for rotating machines is a forward or reverse rotating, circular force applied directly to the shaft. Determination of Dynamic Stiffness Characteristics of the rotor bearing system by nonsynchronous perturbation of a symmetric rotating shaft supported in one relatively rigid and one oil lubricated bearing.

  6. Deterministic Folding in Stiff Elastic Membranes

    NASA Astrophysics Data System (ADS)

    Tallinen, T.; Åström, J. A.; Timonen, J.

    2008-09-01

    Crumpled membranes have been found to be characterized by complex patterns of spatially seemingly random facets separated by narrow ridges of high elastic energy. We demonstrate by numerical simulations that compression of stiff elastic membranes with small randomness in their initial configurations leads to either random ridge configurations (high entropy) or nearly deterministic folds (low elastic energy). For folding with symmetric ridge configurations to appear in part of the crumpling processes, the crumpling rate must be slow enough. Folding stops when the thickness of the folded structure becomes important, and crumpling continues thereafter as a random process.

  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. Discontinuous Galerkin for Stiff Hyperbolic Systems

    SciTech Connect

    Lowrie, R.B.; Morel, J.E.

    1999-06-27

    A Discontinuous Galerkin (DG) method is applied to hyperbolic systems that contain stiff relaxation terms. We demonstrate that when the relaxation time is under-resolved, DG is accurate in the sense that the method accurately represents the system's Chapman-Enskog (or ''diffusion'') approximation. Moreover, we demonstrate that a high-resolution, finite-volume method using the same time-integration method as DG is very inaccurate in the diffusion limit. Results for DG are presented for the hyperbolic heat equation, the Broadwell model of gas kinetics, and coupled radiation-hydrodynamics.

  9. Vascular Stiffness in Children With Chronic Kidney Disease.

    PubMed

    Savant, Jonathan D; Betoko, Aisha; Meyers, Kevin E C; Mitsnefes, Mark; Flynn, Joseph T; Townsend, Raymond R; Greenbaum, Larry A; Dart, Allison; Warady, Bradley; Furth, Susan L

    2017-05-01

    Carotid-femoral pulse wave velocity (cfPWV) is a measure of arterial stiffness associated with cardiovascular events in the general population and in adults with chronic kidney disease. However, few data exist regarding cfPWV in children with chronic kidney disease. We compared observed cfPWV assessed via applanation tonometry in children enrolled in the CKiD cohort study (Chronic Kidney Disease in Children) to normative data in healthy children and examined risk factors associated with elevated cfPWV. cfPWV Z score for height/gender and age/gender was calculated from and compared with published pediatric norms. Multivariable linear regression was used to assess the relationship between cfPWV and age, gender, race, body mass index, diagnosis, urine protein-creatinine ratio, mean arterial pressure, heart rate, number of antihypertensive medications, uric acid, and serum low-density lipoprotein. Of the 95 participants with measured cfPWV, 60% were male, 19% were black, 46% had glomerular cause of chronic kidney disease, 22% had urine protein-creatinine ratio 0.5 to 2.0 mg/mg and 9% had >2.0 mg/mg, mean age was 15.1 years, average mean arterial pressure was 80 mm Hg, and median glomerular filtration rate was 63 mL/min per 1.73 m(2) Mean cfPWV was 5.0 m/s (SD, 0.8 m/s); mean cfPWV Z score by height/gender norms was -0.1 (SD, 1.1). cfPWV increased significantly with age, mean arterial pressure, and black race in multivariable analysis; no other variables, including glomerular filtration rate, were independently associated with cfPWV. In this pediatric cohort with mild kidney dysfunction, arterial stiffness was comparable to that of normal children. Future research is needed to examine the impact of chronic kidney disease progression on arterial stiffness and associated cardiovascular parameters in children.

  10. Optical imaging of resting-state functional connectivity in a novel arterial stiffness model.

    PubMed

    Guevara, Edgar; Sadekova, Nataliya; Girouard, Hélène; Lesage, Frédéric

    2013-01-01

    This study aims to assess the impact of unilateral increases in carotid stiffness on cortical functional connectivity measures in the resting state. Using a novel animal model of induced arterial stiffness combined with optical intrinsic signals and laser speckle imaging, resting state functional networks derived from hemodynamic signals are investigated for their modulation by isolated changes in stiffness of the right common carotid artery. By means of seed-based analysis, results showed a decreasing trend of homologous correlation in the motor and cingulate cortices. Furthermore, a graph analysis indicated a randomization of the cortex functional networks, suggesting a loss of connectivity, more specifically in the motor cortex lateral to the treated carotid, which however did not translate in differentiated metabolic activity.

  11. Stiff Person syndrome and other anti-GAD-associated neurologic disorders.

    PubMed

    Dayalu, Praveen; Teener, James W

    2012-11-01

    Antibodies directed against glutamic acid decarboxylase (GAD) are present in many patients with stiff person syndrome and increasingly found in patients with other symptoms indicative of central nervous system (CNS) dysfunction, such as ataxia. The classic clinical features of stiff person syndrome include muscular stiffness with superimposed painful muscular spasms. Gait is often impaired. Other CNS disorders associated with GAD antibodies include progressive encephalomyelitis with rigidity and myoclonus (PERM), limbic encephalitis, and even epilepsy. Glutamic acid decarboxylase is the rate-limiting enzyme in the production of gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter. Presumably, antibodies directed against GAD impair GABA production, but the precise pathogenic mechanism of GAD-antibody-related neurologic disorders is uncertain. Many patients respond to treatment with immunomodulating therapy. Symptomatic treatment with agents that enhance GABA activity, such as benzodiazepines and baclofen, is also helpful for many patients.

  12. Revealing unobserved factors underlying cortical activity with a rectified latent variable model applied to neural population recordings.

    PubMed

    Whiteway, Matthew R; Butts, Daniel A

    2017-03-01

    The activity of sensory cortical neurons is not only driven by external stimuli but also shaped by other sources of input to the cortex. Unlike external stimuli, these other sources of input are challenging to experimentally control, or even observe, and as a result contribute to variability of neural responses to sensory stimuli. However, such sources of input are likely not "noise" and may play an integral role in sensory cortex function. Here we introduce the rectified latent variable model (RLVM) in order to identify these sources of input using simultaneously recorded cortical neuron populations. The RLVM is novel in that it employs nonnegative (rectified) latent variables and is much less restrictive in the mathematical constraints on solutions because of the use of an autoencoder neural network to initialize model parameters. We show that the RLVM outperforms principal component analysis, factor analysis, and independent component analysis, using simulated data across a range of conditions. We then apply this model to two-photon imaging of hundreds of simultaneously recorded neurons in mouse primary somatosensory cortex during a tactile discrimination task. Across many experiments, the RLVM identifies latent variables related to both the tactile stimulation as well as nonstimulus aspects of the behavioral task, with a majority of activity explained by the latter. These results suggest that properly identifying such latent variables is necessary for a full understanding of sensory cortical function and demonstrate novel methods for leveraging large population recordings to this end.NEW & NOTEWORTHY The rapid development of neural recording technologies presents new opportunities for understanding patterns of activity across neural populations. Here we show how a latent variable model with appropriate nonlinear form can be used to identify sources of input to a neural population and infer their time courses. Furthermore, we demonstrate how these sources are

  13. 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

  14. Stability with large step sizes for multistep discretizations of stiff ordinary differential equations

    NASA Technical Reports Server (NTRS)

    Majda, George

    1986-01-01

    One-leg and multistep discretizations of variable-coefficient linear systems of ODEs having both slow and fast time scales are investigated analytically. The stability properties of these discretizations are obtained independent of ODE stiffness and compared. The results of numerical computations are presented in tables, and it is shown that for large step sizes the stability of one-leg methods is better than that of the corresponding linear multistep methods.

  15. Low intraindividual variability of activated partial thromboplastin time revealed in a population of 10,487 control individuals.

    PubMed

    Ma, Youngeun; Huh, Hee Jae; Kim, Sun-Hee; Kim, Hee-Jin

    2013-10-01

    The activated partial thromboplastin time (aPTT) is a routine coagulation test that reflects the activities of multiple coagulation proteins. Given the known genetic elements underlying the different coagulation factor activities, a low intraindividual variability is expected in aPTT values, but has not been demonstrated in a large population. In this regard, we evaluated the intraindividual variability of aPTT by analyzing serial aPTTs from a large population. The study population consisted of control individuals who had three or more consecutive aPTT values at at least 6-month intervals at a single institution. The coefficient of variation of serial aPTT values was determined in each control individual, and the mean value of the coefficient of variations in the control population was calculated. The aPTT values from a total of 10,487 individuals [mean age 57 years (range 21-93 years); male-to-female ratio 1 : 0.9] were included. The mean value of the coefficient of variation of aPTTs in those individuals was 3.75%, which indicates a very low intraindividual variability. This is the first study to demonstrate a low intraindividual variability of aPTT in a large population. The result supports the previous notion that aPTT is a genetically determined parameter and has potential clinical implications.

  16. Solar EUV Variability from FISM and SDO/EVE During Solar Minimum, Active, and Flaring Time Periods

    NASA Technical Reports Server (NTRS)

    Chamberlin, Phillip C.

    2011-01-01

    The Living With a Star (LWS) Focus Science Team has identified three periods of different solar activity levels for which they will be determining the Earth's Ionosphere and Thermosphere response. Not only will the team be comparing individual models (e.g. FLIP, T1MEGCM, GLOW) outcome driven by the various levels of solar activity, but the models themselves will also be compared. These models all rely on the input solar EUV (0.1 -190 nm) irradiance to drive the variability. The Flare Irradiance Spectral Model (FISM) and the EUV Variability Experiment (EVE) onboard provide the Solar Dynamics Observatory (SDO) provide the most accurate quantification of these irradiances. Presented and discussed are how much the solar EUV irradiance changes during these three scenarios, both as a function of activity and wavelength.

  17. Effects of human activities and climate variability on water resources in the Saveh plain, Iran.

    PubMed

    Mohammadi Ghaleni, M; Ebrahimi, K

    2015-02-01

    Quantity and quality distribution of surface water and groundwater are changing under the impacts of both climate variability and human activities. The main goal of this paper is to evaluate the abovementioned impacts on the water resources in the Saveh plain, central Iran. To achieve this aim, spatial and temporal changes of the surface and groundwater quality and quantity have been analyzed, using hydrometric and meteorological data. The nonparametric Mann-Kendall test was used to identify trends and change points in the annual rainfall and runoff for the period of 1946 to 2011. In order to analyze the impacts of the Saveh Dam on runoff, the dam operation year, 1994, was considered as a change point. Mann-Kendall test results show that rainfall time series was divided into two parts, namely, 1966-1989 and 1990-2007, and averages of annual rainfall in five stations increase from 10 to 21 %. Also, runoff time series was divided into two parts, namely, 1946-1995 and 1996-2007 and averages of annual runoff in four stations decrease from 8 to 83 %. Results show that rainfall changes in Shahabasi, Razin, Jalayer, Emamabad, and Ahmadabad stations increased from 9 to 33 % before and after 1994. Nevertheless, runoff decreased from 24 to 81 %. The results indicate that the greatest lack of runoff between stations is at Shahabasi station and one important reason for the severe lack is operation of the Saveh Dam in 1994. Highest groundwater level decline, about 168.67 cm, occurred in 1994 that is the operation year of the Saveh Dam. Trend analysis of surface water quality show that electrical conductivity increased 957.34 μmho/cm before and after 1994. Also, the Wilcox water quality classification method has been reduced from C3-S1 to C4-S2. Average groundwater electrical conductivity (EC) during 1999-2003 and 2004-2009 increased to 89.6 μmho/cm. Also, the groundwater quality indices for agricultural usages are classified in four classes including, C4-S2 16, C4-S1 46, C3-S

  18. Effects of an Obesity Intervention Integrating Physical Activity and Psychological Strategy on BMI, Physical Activity, and Psychological Variables in Male Obese Adolescents.

    PubMed

    Lee, HakGweon; Kim, YoungHo

    2015-01-01

    The current study investigated the effect of an obesity intervention incorporating physical activity and behavior-based motivational enhancement intervention on BMI, physical activity levels, and psychological variables toward physical activity in male obese adolescents. Single group study without having a control group was carried out in Korea. Sixty-eight obese male adolescents who had BMI greater than 25 kg/m(2) participated in the 16-week obesity intervention. During this period, the study participants' BMI, physical activity levels, self-efficacy, and perceived benefits and barriers were measured at the three time point (baseline, after week 8, and after week 16). Results indicated that obese adolescents' BMI significantly decreased (F = 3.51, p = .03) and physical activity (F = 4.01, p = .02) significantly increased over the 16-week obesity intervention. In addition, Exercise self-efficacy (F = 5.02) and perceived benefits toward physical activity (F = 5.34) significantly increased but perceived barriers of physical activity (F = 5.10) gradually decreased over the intervention. This study suggests that an obesity intervention combining physical activity and behavior-based motivational enhancement intervention significantly contributed to decreased BMI, increased physical activity, and positively changed psychological variables related to physical activity. This first application has resulted in preliminary support for this intervention modality within non-western obese adolescents.

  19. 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.

  20. 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

    2016-07-06

    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.

  1. Elastic metamaterial beam with remotely tunable stiffness

    SciTech Connect

    Qian, Wei; Yu, Zhengyue; Wang, Xiaole; Lai, Yun; Yellen, Benjamin B.

    2016-02-07

    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.

  2. Moderate and heavy metabolic stress interval training improve arterial stiffness and heart rate dynamics in humans.

    PubMed

    Rakobowchuk, Mark; Harris, Emma; Taylor, Annabelle; Cubbon, Richard M; Birch, Karen M

    2013-04-01

    Traditional continuous aerobic exercise training attenuates age-related increases of arterial stiffness, however, training studies have not determined whether metabolic stress impacts these favourable effects. Twenty untrained healthy participants (n = 11 heavy metabolic stress interval training, n = 9 moderate metabolic stress interval training) completed 6 weeks of moderate or heavy intensity interval training matched for total work and exercise duration. Carotid artery stiffness, blood pressure contour analysis, and linear and non-linear heart rate variability were assessed before and following training. Overall, carotid arterial stiffness was reduced (p < 0.01), but metabolic stress-specific alterations were not apparent. There was a trend for increased absolute high-frequency (HF) power (p = 0.10) whereas both absolute low-frequency (LF) power (p = 0.05) and overall power (p = 0.02) were increased to a similar degree following both training programmes. Non-linear heart rate dynamics such as detrended fluctuation analysis [Formula: see text] also improved (p > 0.05). This study demonstrates the effectiveness of interval training at improving arterial stiffness and autonomic function, however, the metabolic stress was not a mediator of this effect. In addition, these changes were also independent of improvements in aerobic capacity, which were only induced by training that involved a high metabolic stress.

  3. Stiffness, intralimb coordination, and joint modulation during a continuous vertical jump test.

    PubMed

    Dal Pupo, Juliano; Dias, Jonathan Ache; Gheller, Rodrigo Ghedini; Detanico, Daniele; dos Santos, Saray Giovana

    2013-09-01

    This study analysed the modulation of jump performance, vertical stiffness as well as joint and intralimb coordination throughout a 30-s vertical jump test. Twenty male athletes performed the test on a force plate while undergoing kinematic analysis. Jump height, power output, ground contact time, vertical stiffness, maximum knee and hip flexion angles, and coordination by continuous relative phase (CRP) were analysed. Analysis of variance was used to compare variables within deciles, and t-tests were used to compare CRP data between the initial and final jumps. Results showed reduction in jump height, power output, and vertical stiffness, with an increase in contact time found during the test. Maximum knee and hip flexion angles declined, but hip angle decreased earlier (10-20% of the test) than knee angle (90-100%). No changes were observed in CRP for thigh-leg coupling when comparing initial and final jumps, but the trunk-thigh coupling was more in-phase near the end of the test. We conclude that fatigue causes reduction in jump performance, as well as changes in stiffness and joint angles. Furthermore, changes in intralimb coordination appear at the last 10% of the test, suggesting a neuromotor mechanism to counterbalance the loss of muscle strength.

  4. Population activity statistics dissect subthreshold and spiking variability in V1.

    PubMed

    Bányai, Mihály; Koman, Zsombor; Orbán, Gergő

    2017-03-15

    Response variability, as measured by fluctuating responses upon repeated performance of trials, is a major component of neural responses, and its characterization is key to interpret high dimensional population recordings. Response variability and covariability display predictable changes upon changes in stimulus and cognitive or behavioral state, providing an opportunity to test the predictive power of models of neural variability. Still, there is little agreement on which model to use as a building block for population-level analyses, and models of variability are often treated as a subject of choice. We investigate two competing models, the Doubly Stochastic Poisson (DSP) model assuming stochasticity at spike generation, and the Rectified Gaussian (RG) model tracing variability back to membrane potential variance, to analyze stimulus-dependent modulation of both single-neuron and pairwise response statistics. Using a pair of model neurons, we demonstrate that the two models predict similar single-cell statistics. However, DSP and RG models have contradicting predictions on the joint statistics of spiking responses. In order to test the models against data, we build a population model to simulate stimulus change-related modulations in pairwise response statistics. We use single-unit data from the primary visual cortex (V1) of monkeys to show that while model predictions for variance are qualitatively similar to experimental data, only the RG model's predictions are compatible with joint statistics. These results suggest that models using Poisson-like variability might fail to capture important properties of response statistics. We argue that membrane potential-level modelling of stochasticity provides an efficient strategy to model correlations.

  5. Salivary aldehyde dehydrogenase - temporal and population variability, correlations with drinking and smoking habits and activity towards aldehydes contained in food.

    PubMed

    Giebułtowicz, Joanna; Dziadek, Marta; Wroczyński, Piotr; Woźnicka, Katarzyna; Wojno, Barbara; Pietrzak, Monika; Wierzchowski, Jacek

    2010-01-01

    Fluorimetric method based on oxidation of the fluorogenic 6-methoxy-2-naphthaldehyde was applied to evaluate temporal and population variability of the specific activity of salivary aldehyde dehydrogenase (ALDH) and the degree of its inactivation in healthy human population. Analyzed was also its dependence on drinking and smoking habits, coffee consumption, and its sensitivity to N-acetylcysteine. Both the specific activity of salivary ALDH and the degree of its inactivation were highly variable during the day, with the highest activities recorded in the morning hours. The activities were also highly variable both intra- and interpersonally, and negatively correlated with age, and this correlation was stronger for the subgroup of volunteers declaring abstinence from alcohol and tobacco. Moderately positive correlations of salivary ALDH specific activity with alcohol consumption and tobacco smoking were also recorded (r(s) ~0.27; p=0.004 and r(s) =0.30; p=0.001, respectively). Moderate coffee consumption correlated positively with the inactivation of salivary ALDH, particularly in the subgroup of non-drinking and non-smoking volunteers. It was found that mechanical stimulation of the saliva flow increases the specific activity of salivary ALDH. The specific activity of the salivary ALDH was strongly and positively correlated with that of superoxide dismutase, and somewhat less with salivary peroxidase. The antioxidant-containing drug N-acetylcysteine increased activity of salivary ALDH presumably by preventing its inactivation in the oral cavity. Some food-related aldehydes, mainly cinnamic aldehyde and anisaldehyde, were excellent substrates of the salivary ALDH3A1 enzyme, while alkenals, particularly those with short chain, were characterized by lower affinity towards this enzyme but high catalytic constants. The protective role of salivary ALDH against aldehydes in food and those found in the cigarette smoke is discussed, as well as its participation in

  6. DEPENDENCE OF THE OPTICAL/ULTRAVIOLET VARIABILITY ON THE EMISSION-LINE PROPERTIES AND EDDINGTON RATIO IN ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Ai, Y. L.; Yuan, W.; Wang, J. G.

    2010-06-10

    The dependence of the long-term optical/UV variability on the spectral and fundamental physical parameters for radio-quiet active galactic nuclei (AGNs) is investigated. The multi-epoch-repeated photometric scanning data in the Stripe-82 region of the Sloan Digital Sky Survey (SDSS) are exploited for two comparative AGN samples (mostly quasars) selected therein: a broad-line Seyfert 1 (BLS1) type sample and a narrow-line Seyfert 1 (NLS1) type AGN sample within redshifts 0.3-0.8. Their spectral parameters are derived from the SDSS spectroscopic data. It is found that on rest-frame timescales of several years the NLS1-type AGNs show systematically smaller variability compared to the BLS1-type AGNs. In fact, the variability amplitude is found to correlate, though only moderately, with the eigenvector 1 parameters, i.e., the smaller the H{beta} linewidth, the weaker the [O III] and the stronger the Fe II emission, the smaller the variability amplitude. Moreover, an interesting inverse correlation is found between the variability and the Eddington ratio, which is perhaps more fundamental. The previously known dependence of the variability on luminosity is not significant, and the dependence on black hole mass-as claimed in recent papers and also present in our data-fades out when controlling for the Eddington ratio in the correlation analysis, though these may be partly due to the limited ranges of luminosity and black hole mass of our samples. Our result strongly supports that an accretion disk is likely to play a major role in producing the optical/UV variability.

  7. Multiple anesthetics for a patient with stiff-person syndrome.

    PubMed

    Cassavaugh, Jessica M; Oravitz, Todd M

    2016-06-01

    Stiff-person syndrome is a progressive disease of muscle rigidity and spasticity due to a deficiency in the production of γ-aminobutyric acid. Because of the rarity of the condition, little is known about effects of anesthesia on patients with stiff-person syndrome. This report describes the clinical course for a single patient with stiff-person syndrome who received general anesthesia on 3 separate occasions. Her anesthetics included use of both neuromuscular blockade and volatile agents. Unlike several previous reports regarding anesthesia and stiff-person syndrome, the postoperative period for this patient did not require prolonged intubation or result in any residual weakness.

  8. Blending stiffness and strength disorder can stabilize fracture

    NASA Astrophysics Data System (ADS)

    Karpas, Ehud D.; Kun, Ferenc

    2016-03-01

    Quasibrittle behavior, where macroscopic failure is preceded by stable damaging and intensive cracking activity, is a desired feature of materials because it makes fracture predictable. Based on a fiber-bundle model with global load sharing we show that blending strength and stiffness disorder of material elements leads to the stabilization of fracture, i.e., samples that are brittle when one source of disorder is present become quasibrittle as a consequence of blending. We derive a condition of quasibrittle behavior in terms of the joint distribution of the two sources of disorder. Breaking bursts have a power-law size distribution of exponent 5 /2 without any crossover to a lower exponent when the amount of disorder is gradually decreased. The results have practical relevance for the design of materials to increase the safety of constructions.

  9. Dynamic blocked transfer stiffness method of characterizing the magnetic field and frequency dependent dynamic viscoelastic properties of MRE

    NASA Astrophysics Data System (ADS)

    Poojary, Umanath R.; Hegde, Sriharsha; Gangadharan, K. V.

    2016-11-01

    Magneto rheological elastomer (MRE) is a potential resilient element for the semi active vibration isolator. MRE based isolators adapt to different frequency of vibrations arising from the source to isolate the structure over wider frequency range. The performance of MRE isolator depends on the magnetic field and frequency dependent characteristics of MRE. Present study is focused on experimentally evaluating the dynamic stiffness and loss factor of MRE through dynamic blocked transfer stiffness method. The dynamic stiffness variations of MRE exhibit strong magnetic field and mild frequency dependency. Enhancements in dynamic stiffness saturate with the increase in magnetic field and the frequency. The inconsistent variations of loss factor with the magnetic field substantiate the inability of MRE to have independent control over its damping characteristics.

  10. Long-term variability and impact on human health of biologically active UV radiation in Moscow

    NASA Astrophysics Data System (ADS)

    Zhdanova, Ekaterina; Chubarova, Natalia

    2014-05-01

    Measurements of erythemally weighted UV irradiance (Qer) have been performed at the Meteorological Observatory of Moscow State University since 1999 with the UVB-1 YES pyranometers. These types of devices are broadband with a spectral sensitivity curve close to the action spectrum of erythema. Main uncertainties of UVB-1 YES measurements include the difference in spectral curves of the instrument and the action spectrum of erythema, as well as the deviation from the cosine law. These uncertainties were taken into account in the database of Qer measurements (Chubarova, 2008. Additional corrections of UVB-1 measurements at low ambient temperatures have been made. We analyze interannual, seasonal and diurnal Qer changes over the time period 1999-2012. In addition, the comparisons with the results of UV reconstruction model (Chubarova, 2008) are made. This model allows us to evaluate relative changes in Qer due to variations in total ozone, effective cloud amount transmission, aerosol and cloud optical thickness since 1968. It is important to note that the main reason for UV irradiance monitoring development is the strong influence of UV irradiance on the biosphere and especially on human health mainly on human skin (CIE, 1993, CIE, 2006) and eyes (Oriowo, M. et al., 2001). Based on the detailed studies we have shown the possibility of utilizing UVB-1 pyranometers for measuring the eye-damage UV radiation. Parallel measurements by the Bentham DTM-300 spectrometer and the UVB-1 YES pyranometer at the Innsbruck Medical University (Austria) have provided us the calibration factor in eye-damage units for this broadband instrument. Influence of main geophysical factors on different types of UV irradiance is estimated by means the RAF ideology (Booth, Madronich, 1994). We discuss the responses of different types of biologically active UV radiation to the impact of various atmospheric factors. The UV conditions (deficiency, optimum, excess for human) are analyzed according to

  11. 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

  12. Field-scale tracking of active methane-oxidizing communities in a landfill cover soil reveals spatial and seasonal variability.

    PubMed

    Henneberger, Ruth; Chiri, Eleonora; Bodelier, Paul E L; Frenzel, Peter; Lüke, Claudia; Schroth, Martin H

    2015-05-01

    Aerobic methane-oxidizing bacteria (MOB) in soils mitigate methane (CH4 ) emissions. We assessed spatial and seasonal differences in active MOB communities in a landfill cover soil characterized by highly variable environmental conditions. Field-based measurements of CH4 oxidation activity and stable-isotope probing of polar lipid-derived fatty acids (PLFA-SIP) were complemented by microarray analysis of pmoA genes and transcripts, linking diversity and function at the field scale. In situ CH4 oxidation rates varied between sites and were generally one order of magnitude lower in winter compared with summer. Results from PLFA-SIP and pmoA transcripts were largely congruent, revealing distinct spatial and seasonal clustering. Overall, active MOB communities were highly diverse. Type Ia MOB, specifically Methylomonas and Methylobacter, were key drivers for CH4 oxidation, particularly at a high-activity site. Type II MOB were mainly active at a site showing substantial fluctuations in CH4 loading and soil moisture content. Notably, Upland Soil Cluster-gamma-related pmoA transcripts were also detected, indicating concurrent oxidation of atmospheric CH4 . Spatial separation was less distinct in winter, with Methylobacter and uncultured MOB mediating CH4 oxidation. We propose that high diversity of active MOB communities in this soil is promoted by high variability in environmental conditions, facilitating substantial removal of CH4 generated in the waste body.

  13. Reciprocal relationship between plasma ghrelin level and arterial stiffness in hypertensive subjects.

    PubMed

    Zhao, Yin-Tao; Yang, Hai-Bo; Li, Ling; Gao, Ke; Li, Peng-Fei; Xie, Wei-Wei

    2013-11-01

    Arterial stiffness, considered an independent predictor of cardiovascular morbidity and mortality, is closely associated with hypertension. Futhermore, the role of ghrelin in the development of hypertension has been widely recognized. The purpose of the present study was to explore the potential relationship between circulating ghrelin and arterial stiffness in hypertensive subjects. A total of 192 patients with primary hypertension and 107 normotensive (NT) control subjects were enrolled in the present cross-sectional study. Plasma ghrelin was determined by ELISA. Arterial stiffness was assessed by brachial-ankle pulse wave velocity (baPWV) and the augmentation index (AIx). Both baPWV and AIx values were markedly higher in the hypertensive compared with NT group (P < 0.01). In contrast, plasma ghrelin concentrations were significantly lower in hypertensive patients compared with NT subjects (P < 0.01). Plasma ghrelin concentrations were negatively correlated with age (odds ratio (OR) -1.836; P < 0.001), smoking (OR -1.347; P = 0.042), baPWV (OR -1.762; P < 0.001) and AIx (OR -1.516; P = 0.005), but positively associated with fasting plasma glucose (OR 1.293; P = 0.047) and HbA1c (OR 1.413; P = 0.025). The inverse correlation between circulating ghrelin and the extent of arterial stiffness suggests that ghrelin is an independent determinant of arterial stiffness, even after adjustment for confounding cardiovascular risk factors, and it actively participates in the pathophysiology of arterial stiffness in hypertensive subjects.

  14. Evaluation of Multifunctional Polysaccharide Hydrogels with Varying Stiffness for Bone Tissue Engineering

    PubMed Central

    Zuidema, Jonathan M.; Venuto, Kathryn N.; Macione, James; Dai, Guohao; Gilbert, Ryan J.; Kotha, Shiva P.

    2013-01-01

    The use of hydrogels for bone regeneration has been limited due to their inherent low modulus to support cell adhesion and proliferation as well as their susceptibility to bacterial infections at the wound site. To overcome these limitations, we evaluated multifunctional polysaccharide hydrogels of varying stiffness to obtain the optimum stiffness at which the gels (1) induce proliferation of human dermal fibroblasts, human umbilical vascular endothelial cells (HUVECs), and murine preosteoblasts (MC3T3-E1), (2) induce osteoblast differentiation and mineralization, and (3) exhibit an antibacterial activity. Rheological studies demonstrated that the stiffness of hydrogels made of a polysaccharide blend of methylcellulose, chitosan, and agarose was increased by crosslinking the chitosan component to different extents with increasing amounts of genipin. The gelation time decreased (from 210 to 60 min) with increasing genipin concentrations. Proliferation of HUVECs decreased by 10.7 times with increasing gel stiffness, in contrast to fibroblasts and osteoblasts, where it increased with gel stiffness by 6.37 and 7.8 times, respectively. At day 14 up to day 24, osteoblast expression of differentiation markers—osteocalcin, osteopontin—and early mineralization marker—alkaline phosphatase, were significantly enhanced in the 0.5% (w/v) crosslinked gel, which also demonstrated enhanced mineralization by day 25. The antibacterial efficacy of the hydrogels decreased with the increasing degree of crosslinking as demonstrated by biofilm formation experiments, but gels crosslinked with 0.5% (w/v) genipin still demonstrated significant bacterial inhibition. Based on these results, gels crosslinked with 0.5% (w/v) genipin, where 33% of available groups on chitosan were crosslinked, exhibited a stiffness of 502±64.5 Pa and demonstrated the optimal characteristics to support bone regeneration. PMID:23724786