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Sample records for stiffness measurement lsm

  1. Measuring graphene's bending stiffness

    NASA Astrophysics Data System (ADS)

    Blees, Melina; Barnard, Arthur; Roberts, Samantha; Kevek, Joshua W.; Ruyack, Alexander; Wardini, Jenna; Ong, Peijie; Zaretski, Aliaksandr; Wang, Siping; McEuen, Paul L.

    2013-03-01

    Graphene's unusual combination of in-plane strength and out-of-plane flexibility makes it promising for mechanical applications. A key value is the bending stiffness, which microscopic theories and measurements of phonon modes in graphite put at ?0 = 1.2 eV.1 However, theories of the effects of thermal fluctuations in 2D membranes predict that the bending stiffness at longer length scales could be orders of magnitude higher.2,3 This macroscopic value has not been measured. Here we present the first direct measurement of monolayer graphene's bending stiffness, made by mechanically lifting graphene off a surface in a liquid and observing both motion induced by thermal fluctuations and the deflection caused by gravity's effect on added weights. These experiments reveal a value ?eff = 12 keV at room temperature -- four orders of magnitude higher than ?0. These results closely match theoretical predictions of the effects of thermally-induced fluctuations which effectively thicken the membrane, dramatically increasing its bending stiffness at macroscopic length scales.

  2. Tectorial membrane. II: Stiffness measurements in vivo.

    PubMed

    Zwislocki, J J; Cefaratti, L K

    1989-11-01

    The tectorial membrane is assumed to play a crucial role in the stimulation of the cochlear hair cells and was thought for decades to serve as a stiff anchor for the tips of the hair-cell stereocilia, particularly those belonging to the OHCs. Yet, its stiffness has never been measured under conditions approximating its normal environment in live animals. We have developed a method for doing this. The tectorial membrane is approached through the lateral wall of scala media. The bony cochlear capsule is removed along scala media over somewhat less than 1/4 turn, and the underlying spiral ligament and stria vascularis are carefully reflected. With the help of a three axial hydraulic manipulator, a flexible micropipette filled with isotonic KCl is inserted into the tectorial membrane at one of two different angles and moved either transversally, away from the basilar membrane, or radially, toward or away from the modiolus. This causes the tectorial membrane to be deformed and the micropipette to bend. The micropipette stiffness is calibrated on an instrument of a new kind, so as to convert the bend into force. The calibration allows us to determine the point stiffness of the tectorial membrane from the amount of micropipette bend. The stiffness of the tectorial membrane per unit length has been calculated from the point stiffness with the help of the deformation pattern. Transversal and radial stiffness magnitudes have been determined in the second cochlear turn in Mongolian gerbils. Both are smaller by almost an order of magnitude than the corresponding aggregate stiffness of the OHC stereocilia. As a consequence, the tectorial membrane cannot act as a stiff anchor for the stereocilia but only as a mass load, except at relatively low sound frequencies where mass effects are negligible. This means that the classical model of shear motion between the tectorial membrane and the reticular lamina must be replaced. PMID:2606804

  3. Laser application on haptics: Tactile stiffness measurement

    NASA Astrophysics Data System (ADS)

    Scalise, L.; Memeo, M.; Cannella, F.; Valente, M.; Caldwell, D. G.; Tomasini, E. P.

    2012-06-01

    There is a great interest in exploring the proprieties of the sense of the touch, its detailed knowledge in fact is a key issue in the area of robotics, haptics and human-machine interaction. In this paper, the authors focus their attention on a novel measurement method for the assessment of the tactile stiffness based on a original test rig; tactile stiffness is defined as the ratio between force, exerted by the finger, and the displacement of the finger tip operated during the test. To reach this scope, the paper describes a specific experimental test-rig used for the evaluation of subject tactile sensitivity, where finger force applied during tests as well as displacement and velocity of displacement, operated by the subject under investigation, are measured. Results show that tactile stiffness is linear respect to stimuli spatial difference (which is proportional to the difficulty to detect the variation of them). In particular, it has been possible to relate the force and displacement measured during the tests. The relationship between the response of the subject to the grating, velocity and force is determined. These results permit to carry out the further experimental tests on the same subject avoiding the use of a load cell and therefore simplifying the measurement test rig and data post-processing. Indeed, the first aspect (use of a load cell) can be relevant, because the grating positions are different, requiring a specific re-calibration and setting before each trial; while the second aspect allows simplify the test rig complexity and the processing algorithm.

  4. Measurement and modeling of muon-induced neutrons in LSM in application for direct dark matter searches

    SciTech Connect

    Kozlov, Valentin; Collaboration: EDELWEISS Collaboration

    2013-08-08

    Due to a very low event rate expected in direct dark matter search experiments, a good understanding of every background component is crucial. Muon-induced neutrons constitute a prominent background, since neutrons lead to nuclear recoils and thus can mimic a potential dark matter signal. EDELWEISS is a Ge-bolometer experiment searching for WIMP dark matter. It is located in the Laboratoire Souterrain de Modane (LSM, France). We have measured muon-induced neutrons by means of a neutron counter based on Gd-loaded liquid scintillator. Studies of muon-induced neutrons are presented and include development of the appropriate MC model based on Geant4 and analysis of a 1000-days measurement campaign in LSM. We find a good agreement between measured rates of muon-induced neutrons and those predicted by the developed model with full event topology. The impact of the neutron background on current EDELWEISS data-taking as well as for next generation experiments such as EURECA is briefly discussed.

  5. Arterial Stiffness in Children: Pediatric Measurement and Considerations

    PubMed Central

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

    2014-01-01

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

  6. Measuring Ascending Aortic Stiffness In Vivo in Mice Using Ultrasound

    PubMed Central

    Kuo, Maggie M.; Barodka, Viachaslau; Abraham, Theodore P.; Steppan, Jochen; Shoukas, Artin A.; Butlin, Mark; Avolio, Alberto; Berkowitz, Dan E.; Santhanam, Lakshmi

    2014-01-01

    We present a protocol for measuring in vivo aortic stiffness in mice using high-resolution ultrasound imaging. Aortic diameter is measured by ultrasound and aortic blood pressure is measured invasively with a solid-state pressure catheter. Blood pressure is raised then lowered incrementally by intravenous infusion of vasoactive drugs phenylephrine and sodium nitroprusside. Aortic diameter is measured for each pressure step to characterize the pressure-diameter relationship of the ascending aorta. Stiffness indices derived from the pressure-diameter relationship can be calculated from the data collected. Calculation of arterial compliance is described in this protocol. This technique can be used to investigate mechanisms underlying increased aortic stiffness associated with cardiovascular disease and aging. The technique produces a physiologically relevant measure of stiffness compared to ex vivo approaches because physiological influences on aortic stiffness are incorporated in the measurement. The primary limitation of this technique is the measurement error introduced from the movement of the aorta during the cardiac cycle. This motion can be compensated by adjusting the location of the probe with the aortic movement as well as making multiple measurements of the aortic pressure-diameter relationship and expanding the experimental group size. PMID:25489936

  7. Stiffness measurement using terahertz and acoustic waves for biological samples.

    PubMed

    Yoon, Jong-Hyun; Yang, Young-Joong; Park, Jinho; Son, Heyjin; Park, Hochong; Park, Gun-Sik; Ahn, Chang-Beom

    2015-12-14

    A method is proposed to measure sample stiffness using terahertz wave and acoustic stimulation. The stiffness-dependent vibration is measured using terahertz wave (T-ray) during an acoustic stimulation. To quantify the vibration, time of the peak amplitude of the reflected T-ray is measured. In our experiment, the T-ray is asynchronously applied during the period of the acoustic stimulation, and multiple measurements are taken to use the standard deviation and the maximum difference in the peak times to estimate the amplitude of the vibration. Some preliminary results are shown using biological samples. PMID:26699056

  8. Confocal Laser Scanning Microscope"LSM710" "LSM710"

    E-print Network

    Park, Byungwoo

    Confocal Laser Scanning Microscope"LSM710" "LSM710" National Center for Inter separation and ultimate stability Principle : Confocal Laser Scanning Microscope that is reflected/emitted from others than the focal plane. The laser scanning microscope scans the sample

  9. Cellular mechanoadaptation to substrate mechanical properties: contributions of substrate stiffness and thickness to cell stiffness measurements using AFM.

    PubMed

    Vichare, Shirish; Sen, Shamik; Inamdar, Mandar M

    2014-02-28

    Mechanosensing by adherent cells is usually studied by quantifying cell responses on hydrogels that are covalently linked to a rigid substrate. Atomic force microscopy (AFM) represents a convenient way of characterizing the mechanoadaptation response of adherent cells on hydrogels of varying stiffness and thickness. Since AFM measurements reflect the effective cell stiffness, therefore, in addition to measuring real cytoskeletal alterations across different conditions, these measurements might also be influenced by the geometry and physical properties of the substrate itself. To better understand how the physical attributes of the gel influence AFM stiffness measurements of cells, we have used finite element analysis to simulate the indentation of cells of various spreads resting on hydrogels of varying stiffness and thickness. Consistent with experimental results, our simulation results indicate that for well spread cells, stiffness values are significantly over-estimated when experiments are performed on cells cultured on soft and thin gels. Using parametric studies, we have developed scaling relationships between the effective stiffness probed by AFM and the bulk cell stiffness, taking cell and tip geometry, hydrogel properties, nuclear stiffness and cell contractility into account. Finally, using simulated mechanoadaptation responses, we have demonstrated that a cell stiffening response may arise purely due to the substrate properties. Collectively, our results demonstrate the need to take hydrogel properties into account while estimating cell stiffness using AFM indentation. PMID:24651595

  10. Automated Liver Stiffness Measurements with Magnetic Resonance Elastography

    PubMed Central

    Dzyubak, Bogdan; Glaser, Kevin; Yin, Meng; Talwalkar, Jayant; Chen, Jun; Manduca, Armando; Ehman, Richard L.

    2012-01-01

    Purpose To provide a fully-automated algorithm for obtaining stiffness measurements from hepatic MR Elastography images that are consistent with measurements performed by expert readers. Materials and Methods An initial liver contour was found using an adaptive threshold and expanded using an active contour to select a homogeneous area of the liver. The confidence map generated during the stiffness calculation was used to select a region of reliable wave propagation. The average stiffness within the automatically-generated ROI was compared to measurements by two trained readers in a set of 88 clinical test cases ranging from healthy to severely fibrotic. Results The stiffness measurements reported by the readers differed by ?6.76% ± 22.8 % (95% confidence) and had an ICC of 0.972 (p<0.05).The algorithm and the more experienced reader differed by 4.32% ± 14.9 with an ICC of 0.987. Conclusion The automated algorithm performed reliably, even though MRE acquisitions often have motion artifacts present. The correlation between the automated measurements and those from the trained readers was superior to the correlation between the readers. PMID:23281171

  11. Microtensile measurements of single trabeculae stiffness in human femur.

    PubMed

    Bini, Fabiano; Marinozzi, Andrea; Marinozzi, Franco; Patanè, Federico

    2002-11-01

    In this paper, the authors perform microtensile tests of single trabeculae excised from a human femur head. One of the main issues of this work is to establish some experimental procedures for preparing and testing the specimens. The use of a well-characterized microtensile apparatus allows for a low intraspecimen dispersion of the measured stiffness. Tensile/compressive tests were chosen because they appear less sensitive to errors in the cross-sectional area measurements with respect to bending tests. By these considerations, some tensile/compressive tests of plate-like trabecular specimens have been carried out. Typical stiffness values are 74.2+/-0.7Nmm(-1) for tensile tests, and 58.9+/-0.6Nmm(-1) for compressive test. Another compressive test performed on a shorter specimen yielded a stiffness value of 148.3+/-5.3Nmm(-1). The maximum applied load was about 0.5N. Rough measurements of specimens sizes yielded a Young's modulus value ranging from 1.41 to 1.89GPa. PMID:12413971

  12. Assessment of a portable device for the quantitative measurement of ankle joint stiffness in spastic individuals

    E-print Network

    Gorassini, Monica

    Assessment of a portable device for the quantitative measurement of ankle joint stiffness-rater reliability. The device could easily distinguish between stiff and control ankle joints. A portable device can be a useful diagnostic tool to obtain reliable information of stiffness for the ankle joint. a b

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  14. Extending Bell's Model: How Force Transducer Stiffness Alters Measured Unbinding Forces and Kinetics of Molecular Complexes

    E-print Network

    Van Vliet, Krystyn J.

    Extending Bell's Model: How Force Transducer Stiffness Alters Measured Unbinding Forces of the force transducer k can significantly perturb the energy landscape and the apparent unbinding force of the complex for sufficiently stiff force transducers. Additionally, at least 20% variation in unbinding force

  15. 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.

  16. Single cell stiffness measurement at various humidity conditions by nanomanipulation of a nano-needle.

    PubMed

    Shen, Yajing; Nakajima, Masahiro; Yang, Zhan; Tajima, Hirotaka; Najdovski, Zoran; Homma, Michio; Fukuda, Toshio

    2013-04-12

    This paper presents a method for single cell stiffness measurement based on a nano-needle and nanomanipulation. The nano-needle with a buffering beam was fabricated from an atomic force microscope cantilever by the focused ion beam etching technique. Wild type yeast cells (W303) were prepared and placed on the sample stage inside an environmental scanning electron microscope (ESEM) chamber. The nanomanipulator actuated the nano-needle to press against a single yeast cell. As a result, the deformation of the cell and nano-needle was observed by the ESEM system in real-time. Finally, the stiffness of the single cell was determined based on this deformation information. To reveal the relationship between the cell stiffness and the environmental humidity conditions, the cell stiffness was measured at three different humidity conditions, i.e. 40, 70 and 100%, respectively. The results show that the stiffness of a single cell is reduced with increasing humidity. PMID:23507613

  17. In vivo and in vitro measurements of pulmonary arterial stiffness: A brief review

    PubMed Central

    Tian, Lian; Chesler, Naomi C.

    2012-01-01

    During the progression of pulmonary hypertension (PH), proximal pulmonary arteries (PAs) undergo remodeling such that they become thicker and the elastic modulus increases. Both of these changes increase the vascular stiffness. The increase in pulmonary vascular stiffness contributes to increased right ventricular (RV) afterload, which causes RV hypertrophy and eventually failure. Studies have found that proximal PA stiffness or its inverse, compliance, is strongly related to morbidity and mortality in patients with PH. Therefore, accurate in vivo measurement of PA stiffness is useful for prognoses in patients with PH. It is also important to understand the structural changes in PAs that occur with PH that are responsible for stiffening. Here, we briefly review the most common parameters used to quantify stiffness and in vivo and in vitro methods for measuring PA stiffness in human and animal models. For in vivo approaches, we review invasive and noninvasive approaches that are based on measurements of pressure and inner or outer diameter or cross-sectional area. For in vitro techniques, we review several different testing methods that mimic one, two or several aspects of physiological loading (e.g., uniaxial and biaxial testing, dynamic inflation-force testing). Many in vivo and in vitro measurement methods exist in the literature, and it is important to carefully choose an appropriate method to measure PA stiffness accurately. Therefore, advantages and disadvantages of each approach are discussed. PMID:23372936

  18. Non-Contact Stiffness Measurement of a Suspended Single Walled Carbon Nanotube Device

    NASA Technical Reports Server (NTRS)

    Zheng, Yun; Su, Chanmin; Getty, Stephanie

    2010-01-01

    A new nanoscale electric field sensor was developed for studying triboelectric charging in terrestrial and Martian dust devils. This sensor is capable to measure the large electric fields for large dust devils without saturation. However, to quantify the electric charges and the field strength it is critical to calibrate the mechanical stiffness of the sensor devices. We performed a technical feasibility study of the Nano E-field Sensor stiffness by a non-contact stiffness measurement method. The measurement is based on laser Doppler vibrometer measurement of the thermal noise due to energy flunctuations in the devices. The experiment method provides a novel approach to acquire data that is essential in analyzing the quantitative performance of the E-field Nano Sensor. To carry out the non-contact stiffness measurement, we fabricated a new Single-Walled Carbon Nanotube (SWCNT) E-field sensor with different SWCNTs suspension conditions. The power spectra of the thermal induced displacement in the nano E-field sensor were measured at the accuracy of picometer. The power spectra were then used to derive the mechanical stiffness of the sensors. Effect of suspension conditions on stiffness and sensor sensitivty was discussed. After combined deformation and resistivity measurement, we can compare with our laboratory testing and field testing results. This new non-contact measurement technology can also help to explore to other nano and MEMS devices in the future.

  19. Stiffness modeling of flexible suspension structure for displacement measurement probing sensors

    NASA Astrophysics Data System (ADS)

    Cui, Junning; Bian, Xingyuan; Sun, Tao; Li, Leilei

    2015-02-01

    In order to solve the problem of performance analysis and optimal design of flexible suspension structure for displacement measurement probing sensors, a novel theoretical model of stiffness with high accuracy is proposed. Both displacements constraint and angle constraint of elastic diaphragms are considered during modeling, and a stiffness equation including all dimensional parameters and material characteristics of elastic diaphragms is obtained. Thus the stiffness of the flexible suspension structure is modeled theoretically and accurately, and the influence on performance of probing sensors by each parameter can be analyzed. Simulations results show that the theoretical model of stiffness proposed is more accurate than existing models, and performance analysis and optimal design of probing sensors can be carried out based on it.

  20. Integration of Acoustic Radiation Force and Optical Imaging for Blood Plasma Clot Stiffness Measurement

    PubMed Central

    Wang, Caroline W.; Perez, Matthew J.; Helmke, Brian P.; Viola, Francesco; Lawrence, Michael B.

    2015-01-01

    Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood’s transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF) to induce micron-scaled displacements (1-500 ?m) on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample) to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich) clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties. PMID:26042775

  1. A Laplacian-based SNR measure: shear stiffness estimation in MR elastography

    NASA Astrophysics Data System (ADS)

    Eon, Rehman S.; Huynh, Khang T.; Lake, David S.; Manduca, Armando

    2015-03-01

    Magnetic resonance elastography (MRE) is a phase-contrast MRI based technique that allows quantitative, noninvasive assessment of the mechanical properties of tissues by the introduction of shear waves into the body and measurement of the resulting displacements. In MRE, the calculated stiffness values are affected by noise, which is amplified by the inversion process. It would be useful to know that beyond some SNR threshold, the stiffness values are accurate within some confidence limit. The most common methods to calculate SNR values in MRE are variations of displacement SNR, which estimate the noise in the measured displacement. However, the accuracy of stiffness determination depends not only on the displacement SNR, but also on the wavelength of the shear wave, in turn dependent on the stiffness of the underlying material. More recently, the SNR of the octahedral shear strain (OSS) has been proposed as a more appropriate measure, since shear deformation is the signal in MRE. We also propose here another measure based on the SNR of the Laplacian of the data, since this is the most noise sensitive quantity calculated when performing direct inversion of the Helmholtz equation. The three SNR measures were compared on simulated data for materials of different stiffness with varying amounts of noise using three inversion algorithms commonly used in MRE (phase gradient, local frequency estimation, and direct inversion). We demonstrate that the proper SNR measure for MRE depends on the inversion algorithm used, and, more precisely, on the order of derivatives used in the inversion process.

  2. Ultrasonic measurements of stiffness in thermal-mechanically fatigued IM7/5260 composites

    SciTech Connect

    Seale, M.D.; Madaras, E.I. )

    1999-08-01

    In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. The Lamb wave velocity is directly related to the material parameters, so an effective method exists to ascertain the stiffness of composites by measuring the velocity of these waves. In this study, a Lamb wave measurement system was used to measure the bending and out-of-plane stiffness coefficients of thermoset composite laminates undergoing thermal-mechanical loading. A series of 16 ply and 32 ply composite laminates were subjected to thermal-mechanical fatigue (TMF) in load frames equipped with special environmental chambers. The composite system studied was a graphite fiber-reinforced bismaleimide thermoset, IM7/5260. The samples were subjected to both high and low temperature profiles as well as high-strain and low-strain profiles. The bending and out-of-plane stiffnesses for composite samples that have undergone over 6,000 cycles of combined thermal and mechanical fatigue are reported. The Lamb wave generated elastic stiffness results have shown decreases of up to 64% at 4,706 cycles for samples subjected to TMF at high temperatures and less than a 10% decrease at over 6,000 cycles for samples subjected to TMF at low temperatures.

  3. Multijoint Muscle Regulation Mechanisms Examined by Measured Human Arm Stiffness and EMG Signals

    E-print Network

    Osu, Rieko

    Multijoint Muscle Regulation Mechanisms Examined by Measured Human Arm Stiffness and EMG Signals, Rieko and Hiroaki Gomi. Multijoint muscle regulation mech- anisms examined by measured human arm- skeletal system can be controlled by regulating muscle activation and neural feedback gain. To understand

  4. Piezoelectric Sensor to Measure Soft and Hard Stiffness with High Sensitivity for Ultrasonic Transducers

    PubMed Central

    Li, Yan-Rui; Su, Chih-Chung; Lin, Wen-Jin; Chang, Shuo-Hung

    2015-01-01

    During dental sinus lift surgery, it is important to monitor the thickness of the remaining maxilla to avoid perforating the sinus membrane. Therefore, a sensor should be integrated into ultrasonic dental tools to prevent undesirable damage. This paper presents a piezoelectric (PZT) sensor installed in an ultrasonic transducer to measure the stiffness of high and low materials. Four design types using three PZT ring materials and a split PZT for actuator and sensor ring materials were studied. Three sensor locations were also examined. The voltage signals of the sensor and the displacement of the actuator were analyzed to distinguish the low and high stiffness. Using sensor type T1 made of the PZT-1 material and the front location A1 provided a high sensitivity of 2.47 Vm/kN. The experimental results demonstrated that our design can measure soft and hard stiffness. PMID:26110400

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

    NASA Technical Reports Server (NTRS)

    Kufeld, Robert M.

    2014-01-01

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

  6. Optoelectronic tweezers for the measurement of the relative stiffness of erythrocytes

    NASA Astrophysics Data System (ADS)

    Neale, Steven L.; Mody, Nimesh; Selman, Colin; Cooper, Jonathan M.

    2012-10-01

    In this paper we describe the first use of Optoelectronic Tweezers (OET), an optically controlled micromanipulation method, to measure the relative stiffness of erythrocytes in mice. Cell stiffness is an important measure of cell health and in the case of erythrocytes, the most elastic cells in the body, an increase in cell stiffness can indicate pathologies such as type II diabetes mellitus or hypertension (high blood pressure). OET uses a photoconductive device to convert an optical pattern into and electrical pattern. The electrical fields will create a dipole within any polarisable particles in the device, such as cells, and non-uniformities of the field can be used to place unequal forces onto each side of the dipole thus moving the particle. In areas of the device where there are no field gradients, areas of constant illumination, the force on each side of the dipole will be equal, keeping the cell stationary, but as there are opposing forces on each side of the cell it will be stretched. The force each cell will experience will differ slightly so the stretching will depend on the cells polarisability as well as its stiffness. Because of this a relative stiffness rather than absolute stiffness is measured. We show that with standard conditions (20Vpp, 1.5MHz, 10mSm-1 medium conductivity) the cell's diameter changes by around 10% for healthy mouse erythrocytes and we show that due to the low light intensities required for OET, relative to conventional optical tweezers, multiple cells can be measured simultaneously.

  7. BME 315 Biomechanics Measurement of bone strength and stiffness via 3 point bending

    E-print Network

    Lakes, Roderic

    BME 315 Biomechanics Measurement of bone strength and stiffness via 3 point bending Preliminaries: Review your studies of bending. Also, review beam equations pertaining to 3 point bending. Experiment details and background are provided on the class web site; paper copies will be available in the lab

  8. Direct Measurement of the Passive Stiffness of Rat Sperm and Implications to

    E-print Network

    Lindemann, Charles

    Direct Measurement of the Passive Stiffness of Rat Sperm and Implications to the Mechanism of the flagella of Triton X-100-extracted rat sperm models. The sperm models were treated with 50 M sodium . Rat sperm models exposed to greater than 10 5 M calcium ions exhibit a strong bend in the basal 40 m

  9. Differentiating untreated and cross-linked porcine corneas of the same measured stiffness with optical coherence elastography

    NASA Astrophysics Data System (ADS)

    Li, Jiasong; Han, Zhaolong; Singh, Manmohan; Twa, Michael D.; Larin, Kirill V.

    2014-11-01

    Structurally degenerative diseases, such as keratoconus, can significantly alter the stiffness of the cornea, directly affecting the quality of vision. Ultraviolet-induced collagen cross-linking (CXL) effectively increases corneal stiffness and is applied clinically to treat keratoconus. However, measured corneal stiffness is also influenced by intraocular pressure (IOP). Therefore, experimentally measured changes in corneal stiffness may be attributable to the effects of CXL, changes in IOP, or both. We present a noninvasive measurement method using phase-stabilized swept-source optical coherence elastography to distinguish between CXL and IOP effects on measured corneal stiffness. This method compared the displacement amplitude attenuation of a focused air-pulse-induced elastic wave. The damping speed of the displacement amplitudes at each measurement position along the wave propagation were compared for different materials. This method was initially tested on gelatin and agar phantoms of the same stiffness for validation. Consequently, untreated and CXL-treated porcine corneas of the same measured stiffness, but at different IOPs, were also evaluated. The results suggest that this noninvasive method may have the potential to detect the early stages of ocular diseases such as keratoconus or may be applied during CLX procedures by factoring in the effects of IOP on the measured corneal stiffness.

  10. Identification of substructure properties of railway tracks by dynamic stiffness measurements and simulations

    NASA Astrophysics Data System (ADS)

    Berggren, Eric G.; Kaynia, Amir M.; Dehlbom, Björn

    2010-09-01

    A new vehicle has been developed to measure dynamic vertical track stiffness while in motion. This technique allows the resonance behaviour of the track below 50 Hz to be measured. Soft soils like clay and peat are the main causes of resonance below 20 Hz. By means of simulation studies with the software VibTrain, soft soil resonance behaviour may be characterized using a few key parameters originating from track stiffness measurements, such as the minimum phase delay and corresponding frequency of the receptance transfer function. Statistical models are built to relate these key parameters with substructure properties, such as embankment thickness, shear wave velocity and thickness of the soft soil layer using pattern recognition methods. Two case studies are used to show the methodology, and the results are verified using Ground Penetration Radar (GPR) measurements and borehole investigations. Models are also developed from the statistical relationship between GPR-data and stiffness measurements. It is shown that embankment thickness is the easiest quantity to estimate, but indicative results are also presented for the other quantities (shear wave velocity and thickness of soil layer).

  11. A simple indentation device for measuring micrometer-scale tissue stiffness

    PubMed Central

    Levental, I; Levental, K R; Klein, E A; Assoian, R; Miller, R T; Wells, R G; Janmey, P A

    2012-01-01

    Mechanical properties of cells and extracellular matrices are critical determinants of function in contexts including oncogenic transformation, neuronal synapse formation, hepatic fibrosis and stem cell differentiation. The size and heterogeneity of biological specimens and the importance of measuring their mechanical properties under conditions that resemble their environments in vivo present a challenge for quantitative measurement. Centimeter-scale tissue samples can be measured by commercial instruments, whereas properties at the subcellular (nm) scale are accessible by atomic force microscopy, optical trapping, or magnetic bead microrheometry; however many tissues are heterogeneous on a length scale between micrometers and millimeters which is not accessible to most current instrumentation. The device described here combines two commercially available technologies, a micronewton resolution force probe and a micromanipulator for probing soft biological samples at sub-millimeter spatial resolution. Several applications of the device are described. These include the first measurement of the stiffness of an intact, isolated mouse glomerulus, quantification of the inner wall stiffness of healthy and diseased mouse aortas, and evaluation of the lateral heterogeneity in the stiffness of mouse mammary glands and rat livers with correlation of this heterogeneity with malignant or fibrotic pathology as evaluated by histology. PMID:21386443

  12. A simple indentation device for measuring micrometer-scale tissue stiffness

    NASA Astrophysics Data System (ADS)

    Levental, I.; Levental, K. R.; Klein, E. A.; Assoian, R.; Miller, R. T.; Wells, R. G.; Janmey, P. A.

    2010-05-01

    Mechanical properties of cells and extracellular matrices are critical determinants of function in contexts including oncogenic transformation, neuronal synapse formation, hepatic fibrosis and stem cell differentiation. The size and heterogeneity of biological specimens and the importance of measuring their mechanical properties under conditions that resemble their environments in vivo present a challenge for quantitative measurement. Centimeter-scale tissue samples can be measured by commercial instruments, whereas properties at the subcellular (nm) scale are accessible by atomic force microscopy, optical trapping, or magnetic bead microrheometry; however many tissues are heterogeneous on a length scale between micrometers and millimeters which is not accessible to most current instrumentation. The device described here combines two commercially available technologies, a micronewton resolution force probe and a micromanipulator for probing soft biological samples at sub-millimeter spatial resolution. Several applications of the device are described. These include the first measurement of the stiffness of an intact, isolated mouse glomerulus, quantification of the inner wall stiffness of healthy and diseased mouse aortas, and evaluation of the lateral heterogeneity in the stiffness of mouse mammary glands and rat livers with correlation of this heterogeneity with malignant or fibrotic pathology as evaluated by histology.

  13. Ultrasound Elastography: The New Frontier in Direct Measurement of Muscle Stiffness

    PubMed Central

    Brandenburg, Joline E.; Eby, Sarah F.; Song, Pengfei; Zhao, Heng; Brault, Jeffrey S.; Chen, Shigao; An, Kai-Nan

    2014-01-01

    The use of brightness-mode ultrasound and Doppler ultrasound in physical medicine and rehabilitation has increased dramatically. The continuing evolution of ultrasound technology has also produced ultrasound elastography, a cutting-edge technology that can directly measure the mechanical properties of tissue, including muscle stiffness. Its real-time and direct measurements of muscle stiffness can aid the diagnosis and rehabilitation of acute musculoskeletal injuries and chronic myofascial pain. It can also help monitor outcomes of interventions affecting muscle in neuromuscular and musculoskeletal diseases, and it can better inform the functional prognosis. This technology has implications for even broader use of ultrasound in physical medicine and rehabilitation practice, but more knowledge about its uses and limitations is essential to its appropriate clinical implementation. In this review, we describe different ultrasound elastography techniques for studying muscle stiffness, including strain elastography, acoustic radiation force impulse imaging, and shear-wave elastography. We discuss the basic principles of these techniques, including the strengths and limitations of their measurement capabilities. We review the current muscle research, discuss physiatric clinical applications of these techniques, and note directions for future research. PMID:25064780

  14. Direct measurement of molecular stiffness and damping in confined water layers

    E-print Network

    Steve Jeffery; Peter M. Hoffmann; John B. Pethica; Chandra Ramanujan; H. Özgür Özer; Ahmet Oral

    2003-10-09

    We present {\\em direct} and {\\em linear} measurements of the normal stiffness and damping of a confined, few molecule thick water layer. The measurements were obtained by use of a small amplitude (0.36 $\\textrm{\\AA}$), off-resonance Atomic Force Microscopy (AFM) technique. We measured stiffness and damping oscillations revealing up to 7 layers separated by 2.56 $\\pm$ 0.20 $\\textrm{\\AA}$. Relaxation times could also be calculated and were found to indicate a significant slow-down of the dynamics of the system as the confining separation was reduced. We found that the dynamics of the system is determined not only by the interfacial pressure, but more significantly by solvation effects which depend on the exact separation of tip and surface. Thus ` solidification\\rq seems to not be merely a result of pressure and confinement, but depends strongly on how commensurate the confining cavity is with the molecule size. We were able to model the results by starting from the simple assumption that the relaxation time depends linearly on the film stiffness.

  15. Comparison of liver stiffness, fibrotest and liver biopsy for assessment of liver fibrosis in kidney-transplant patients with chronic viral hepatitis.

    PubMed

    Alric, Laurent; Kamar, Nassim; Bonnet, Delphine; Danjoux, Marie; Abravanel, Florence; Lauwers-Cances, Valérie; Rostaing, Lionel

    2009-05-01

    To assess the accuracy of the noninvasive tools, fibrotest (FT) and liver stiffness measurement (LSM) for assessing liver fibrosis in kidney-transplant patients with chronic hepatitis virus B (HBV) or C (HCV) infection. Thirty-eight consecutive kidney-transplant patients with HCV (n = 26) or HBV (n = 12) underwent liver biopsies followed by a FT and LSM. Liver biopsies gave the following fibrosis-grade distribution using METAVIR scores: F0/F1, n = 10 (26.9%); F2, n = 14 (36.8%), F3, n = 7 (18.42%); F4, n = 7 (18.4%). The area under the receiver-operating characteristic curve for mild fibrosis stage LSM; for severe fibrosis stage F3-F4, they were 0.55 (0.35-0.76) for the FT and 0.69 (0.50-0.87) for LSM. Eighty to 90% of patients with no significant liver fibrosis (LSM. Diagnosis of patients with severe liver fibrosis (F3/F4) by FT and LSM differed by 38.4% from the liver biopsy data. The FT and LSM are acceptably accurate for diagnosing mild liver fibrosis in kidney-transplant patients with chronic HCV or HBV infections, but their diagnostic value for predicting severe liver disease needs to be confirmed. PMID:19196449

  16. Pulmonary Vascular Stiffness: Measurement, Modeling, and Implications in Normal and Hypertensive Pulmonary Circulations

    PubMed Central

    Hunter, Kendall S.; Lammers, Steven R.; Shandas, Robin

    2014-01-01

    This article introduces the concept of pulmonary vascular stiffness, discusses its increasingly recognized importance as a diagnostic marker in the evaluation of pulmonary vascular disease, and describes methods to measure and model it clinically, experimentally, and computationally. It begins with a description of systems-level methods to evaluate pulmonary vascular compliance and recent clinical efforts in applying such techniques to better predict patient outcomes in pulmonary arterial hypertension. It then progresses from the systems-level to the local level, discusses proposed methods by which upstream pulmonary vessels increase in stiffness, introduces concepts around vascular mechanics, and concludes by describing recent work incorporating advanced numerical methods to more thoroughly evaluate changes in local mechanical properties of pulmonary arteries. PMID:23733649

  17. Measuring Multi-Joint Stiffness during Single Movements: Numerical Validation of a Novel Time-Frequency Approach

    PubMed Central

    Piovesan, Davide; Pierobon, Alberto; DiZio, Paul; Lackner, James R.

    2012-01-01

    This study presents and validates a Time-Frequency technique for measuring 2-dimensional multijoint arm stiffness throughout a single planar movement as well as during static posture. It is proposed as an alternative to current regressive methods which require numerous repetitions to obtain average stiffness on a small segment of the hand trajectory. The method is based on the analysis of the reassigned spectrogram of the arm's response to impulsive perturbations and can estimate arm stiffness on a trial-by-trial basis. Analytic and empirical methods are first derived and tested through modal analysis on synthetic data. The technique's accuracy and robustness are assessed by modeling the estimation of stiffness time profiles changing at different rates and affected by different noise levels. Our method obtains results comparable with two well-known regressive techniques. We also test how the technique can identify the viscoelastic component of non-linear and higher than second order systems with a non-parametrical approach. The technique proposed here is very impervious to noise and can be used easily for both postural and movement tasks. Estimations of stiffness profiles are possible with only one perturbation, making our method a useful tool for estimating limb stiffness during motor learning and adaptation tasks, and for understanding the modulation of stiffness in individuals with neurodegenerative diseases. PMID:22448233

  18. Profile stiffness measurements in the Helically Symmetric experiment and comparison to nonlinear gyrokinetic calculations

    SciTech Connect

    Weir, G. M.; Faber, B. J.; Likin, K. M.; Talmadge, J. N.; Anderson, D. T.; Anderson, F. S. B.

    2015-05-15

    Stiffness measurements are presented in the quasi-helically symmetric experiment (HSX), in which the neoclassical transport is comparable to that in a tokamak and turbulent transport dominates throughout the plasma. Electron cyclotron emission is used to measure the local electron temperature response to modulated electron cyclotron resonant heating. The amplitude and phase of the heat wave through the steep electron temperature gradient (ETG) region of the plasma are used to determine a transient electron thermal diffusivity that is close to the steady-state diffusivity. The low stiffness in the region between 0.2???r/a???0.4 agrees with the scaling of the steady-state heat flux with temperature gradient in this region. These experimental results are compared to gyrokinetic calculations in a flux-tube geometry using the gyrokinetic electromagnetic numerical experiment code with two kinetic species. Linear simulations show that the ETG mode may be experimentally relevant within r/a???0.2, while the Trapped Electron Mode (TEM) is the dominant long-wavelength microturbulence instability across most of the plasma. The TEM is primarily driven by the density gradient. Non-linear calculations of the saturated heat flux driven by the TEM and ETG bracket the experimental heat flux.

  19. Experimental measurements of hydrodynamic radial forces and stiffness matrices for a centrifugal pump-impeller

    NASA Technical Reports Server (NTRS)

    Chamieh, D. S.; Acosta, A. J.; Brennen, C. E.; Caughey, T. K.

    1985-01-01

    Measurements of the steady-state hydrodynamic forces on a centrifugal pump impeller are presented as a function of position within two geometrically different volutes. These correspond to the forces experienced by the impeller at zero whirl frequency. The hydrodynamic force matrices derived from these measurements exhibit both diagonal and off-diagonal terms of substantial magnitude. These terms are of the form which would tend to excite a whirl motion in a rotordynamic analysis of the pump; this may be the cause of 'rough running' reported in many pumps. Static pressure measurements in the impeller discharge flow show that the hydrodynamic force on the impeller contains a substantial component due to the nonisotropy of the net momentum flux leaving the impeller. A similar breakdown of the contributions to the stiffness matrices reveals that the major component of these matrices results from the nonisotropy of the momentum flux.

  20. Experimental measurements of hydrodynamic stiffness matrices for a centrifugal pump impeller

    NASA Technical Reports Server (NTRS)

    Chamieh, D. S.; Acosta, A. J.; Brennen, C. E.; Caughey, T. K.; Franz, R.

    1982-01-01

    The objective of the Rotor Force Test Facility at the California Institute of Technology is to artificially orbit the center of rotation of an impeller enclosed within a volute over a range of frequencies from zero to synchronous and to measure the resulting forces on the impeller. Preliminary data from the first stage experiments in which the shaft is orbited at low frequency is reported. Steady volute forces along with stiffness matrices due to the change in position of the rotor center are measured. Static pressure taps around the volute are used to obtain volute pressure distributions for various fixed positions of the impeller center and for various flow rates. Static pressure forces are calculated from these pressure distributions allowing a more complete analysis of the components of the impeller forces. Comparison is made with various existing theoretical and experimental results.

  1. Analysis, Design and Testing of a Novel Quasi-Zero-Stiffness based Sensor System for Measurement of Absolute Vibration Motion

    E-print Network

    Wang, Yu

    2015-01-01

    This study presents the analysis and design of a novel quasi-zero-stiffness (QZS) based vibration sensor system for measuring absolute displacement of vibrating platforms/objects. The sensor system is constructed by using positive and negative-stiffness springs, which makes it possible to achieve an equivalent QZS and consequently to create a broadband vibration-free point for absolute displacement measurement in vibrating platforms. Theoretic analysis is conducted for the analysis and design of the influence of structure parameters on system measurement performance. A prototype is designed which can avoid the drawback of instability in existing QZS systems with negative stiffness, and the corresponding data-processing software is developed to fulfill time domain and frequency domain measurements simultaneously. Both simulation and experiment results verify the effectiveness of this novel sensor system.

  2. Intracardiac Echocardiography (ICE) Measurement of Dynamic Myocardial Stiffness with Shear Wave Velocimetry

    PubMed Central

    Hollender, Peter J.; Wolf, Patrick D.; Goswami, Robi; Trahey, Gregg E.

    2012-01-01

    Acoustic Radiation Force (ARF)-based methods have been demonstrated to be a viable tool for noninvasively estimating tissue elastic properties, and shear wave velocimetry has been used to quantitatively measure the stiffening and relaxation of myocardial tissue in open-chest experiments. Dynamic stiffness metrics may prove to be indicators for certain cardiac diseases, but a clinically-viable means of remotely generating and tracking transverse wave propagation in myocardium is needed. Intracardiac echocardiography (ICE) catheter-tip transducers are demonstrated here as a viable tool for making this measurement. ICE probes achieve favorable proximity to the myocardium, enabling the use of shear wave velocimetry from within the right ventricle throughout the cardiac cycle. This work describes the techniques used to overcome the challenges of using a small probe to perform ARF-driven shear wave velocimetry, and presents in vivo porcine data showing the effectiveness of this method in the interventricular septum. Acoustic Radiation Force (ARF)-based methods have been demonstrated to be a viable tool for noninvasively estimating tissue elastic properties, and shear wave velocimetry has been used to quantitatively measure the stiffening and relaxation of myocardial tissue in open-chest experiments. Dynamic stiffness metrics may prove to be indicators for certain cardiac diseases, but a clinically-viable means of remotely generating and tracking transverse wave propagation in myocardium is needed. Intracardiac echocardiography (ICE) catheter-tip transducers are demonstrated here as a viable tool for making this measurement. ICE probes achieve favorable proximity to the myocardium, enabling the use of shear wave velocimetry from within the right ventricle throughout the cardiac cycle. This work describes the techniques used to overcome the challenges of using a small probe to perform ARF-driven shear wave velocimetry, and presents in vivo porcine data showing the effectiveness of this method in the interventricular septum. PMID:22579544

  3. Association of HIV Infection, Hepatitis C Virus Infection, and Metabolic Factors With Liver Stiffness Measured by Transient Elastography

    PubMed Central

    Bailony, M. Rami; Scherzer, Rebecca; Huhn, Gregory; Plankey, Michael W.; Peters, Marion G.; Tien, Phyllis C.

    2013-01-01

    Background.?Few studies have examined the relationship of human immunodeficiency virus (HIV) monoinfection and its associated perturbations with liver fibrosis. Methods.?Using multivariable linear regression, we examined the demographic, behavioral, metabolic and viral factors associated with transient elastography–measured liver stiffness in 314 participants (165 HIV positive/hepatitis C virus [HCV] negative, 78 HIV positive/HCV positive, 14 HIV negative/HCV positive, 57 HIV negative/HCV negative) in the Women's Interagency HIV Study. Results.?Compared with HIV negative/HCV negative women, HIV positive/HCV positive women had higher median liver stiffness values (7.1 vs 4.4 kPa; P < .001); HIV positive/HCV negative and HIV negative/HCV negative women had similar liver stiffness values (both 4.4 kPa; P = .94). HIV/HCV coinfection remained associated with higher liver stiffness values (74% higher; 95% confidence interval [CI], 49–104) even after multivariable adjustment. Among HCV positive women, waist circumference (per 10-cm increase) was associated with 18% (95% CI, 7.5%–30%) higher liver stiffness values after multivariable adjustment; waist circumference showed little association among HIV positive/HCV negative or HIV negative/HCV negative women. Among HIV positive/HCV negative women, history of AIDS (13%; 95% CI, 4% –27%) and HIV RNA (7.3%; 95% CI, 1.59%–13.3%, per 10-fold increase) were associated with greater liver stiffness. Conclusions.?HCV infection but not HIV infection is associated with greater liver stiffness when infected women are compared with those with neither infection. Our finding that waist circumference, a marker of central obesity, is associated with greater liver stiffness in HIV/HCV-coinfected but not HIV-monoinfected or women with neither infection suggests that in the absence of HCV-associated liver injury the adverse effects of obesity are lessened. PMID:23901097

  4. [Clinical value and measurement of arterial stiffness for the assessment of cardiovascular risk in light of recent results].

    PubMed

    Nemcsik, János; Tislér, András; Kiss, István

    2015-02-01

    Cardiovascular risk stratification is fundamental for the development of effective prevention and therapeutic strategies. Although there are numerous scores and risk tables available, a difference still exists between the estimated and real number of cardiovascular events. Measurement of arterial stiffness can provide additional information to risk stratification. The most widely accepted parameter of arterial stiffness is aortic pulse wave velocity, which has been included in the guideline of the European Society of Hypertension in 2007 and 2013, although American guidelines still omit it. In this review the authors summarize the evidence with regards to the different steps required for clinical application of arterial stiffness measurement and they also discuss the questions that evolved from the methodological variability of different measurement techniques. PMID:25639634

  5. The effect of the respiratory cycle on liver stiffness values as measured by transient elastography.

    PubMed

    Yun, M H; Seo, Y S; Kang, H S; Lee, K G; Kim, J H; An, H; Yim, H J; Keum, B; Jeen, Y T; Lee, H S; Chun, H J; Um, S H; Kim, C D; Ryu, H S

    2011-09-01

    The findings of several studies suggest that liver stiffness values can be affected by the degree of intrahepatic congestion respiration influence intrahepatic blood volume and may affect liver stiffness. We evaluated the influence of respiration on liver stiffness. Transient elastography (TE) was performed at the end of inspiration and at the end of expiration in patients with chronic liver disease. The median values obtained during the inspiration set and during the expiration set were defined as inspiratory and expiratory liver stiffness, respectively. A total of 123 patients with chronic liver disease were enrolled (mean age 49years; 64.2% men). Liver cirrhosis coexisted in 29 patients (23.6%). Expiratory liver stiffness was significantly higher than inspiratory liver stiffness (8.7 vs 7.9kPa, P=0.001), while the expiratory interquartile range/median ratio (IQR ratio) did not differ from the inspiratory IQR ratio. Expiratory liver stiffness was significantly higher than inspiratory liver stiffness in 49 (39.8%) patients (HE group), expiratory liver stiffness was significantly lower than inspiratory stiffness in 15 (12.2%) patients, and there was no difference in 59 (48.0%) patients. Liver cirrhosis was more frequent in those who had a lower liver stiffness reading in expiration, and only the absence of liver cirrhosis was significantly associated with a higher reading in expiration in multivariate analysis. In conclusion, liver stiffness was significantly elevated during expiration especially in patients without liver cirrhosis. The effect of respiration should be kept in mind during TE readings. PMID:21029256

  6. Nonalcoholic Fatty Liver Disease as a Risk Factor of Arterial Stiffness Measured by the Cardioankle Vascular Index

    PubMed Central

    Chung, Goh Eun; Choi, Su-Yeon; Kim, Donghee; Kwak, Min-Sun; Park, Hyo Eun; Kim, Min-Kyung; Yim, Jeong Yoon

    2015-01-01

    Abstract Nonalcoholic fatty liver disease (NAFLD) is associated with risk factors for cardiovascular disease. The cardioankle vascular index (CAVI), a new measure of arterial stiffness, was recently developed and is independent of blood pressure. We investigated whether NAFLD is associated with arterial stiffness as measured using the CAVI in an apparently healthy population. A total of 2954 subjects without any known liver diseases were enrolled. NAFLD was diagnosed via typical ultrasonography. The clinical characteristics examined included age, sex, body mass index (BMI), waist circumference (WC), and the levels of aspartate aminotransferase, alanine aminotransferase, total cholesterol, high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol triglycerides, and glucose. Arterial stiffness was defined using an age- and sex-specific threshold of the upper quartile of the CAVI. NAFLD was found in 1249 (42.3%) of the analyzed subjects. Using an age-, sex-, and BMI-adjusted model, NAFLD was associated with a 42% increase in the risk for arterial stiffness (highest quartile of the CAVI). The risk for arterial stiffness increased according to the severity of NAFLD (adjusted odds ratio [95% confidence interval], 1.27 [1.02???1.57] vs 1.78 [1.37???2.31], mild vs moderate-to-severe, respectively). When adjusted for other risk factors, including BMI, WC, smoking status, diabetes, and hypertension, these relationships remained statistically significant. Patients with NAFLD are at a high risk for arterial stiffness regardless of classical risk factors. The presence of cardiometabolic risk factors may attenuate the prediction of arterial stiffness by means of NAFLD presence. Thus, physicians should carefully assess subjects with NAFLD for atherosclerosis and associated comorbidities. PMID:25816034

  7. Biomechanics of hair cell kinocilia: experimental measurement of kinocilium shaft stiffness and base rotational stiffness with Euler–Bernoulli and Timoshenko beam analysis

    PubMed Central

    Spoon, Corrie; Grant, Wally

    2011-01-01

    Vestibular hair cell bundles in the inner ear contain a single kinocilium composed of a 9+2 microtubule structure. Kinocilia play a crucial role in transmitting movement of the overlying mass, otoconial membrane or cupula to the mechanotransducing portion of the hair cell bundle. Little is known regarding the mechanical deformation properties of the kinocilium. Using a force-deflection technique, we measured two important mechanical properties of kinocilia in the utricle of a turtle, Trachemys (Pseudemys) scripta elegans. First, we measured the stiffness of kinocilia with different heights. These kinocilia were assumed to be homogenous cylindrical rods and were modeled as both isotropic Euler–Bernoulli beams and transversely isotropic Timoshenko beams. Two mechanical properties of the kinocilia were derived from the beam analysis: flexural rigidity (EI) and shear rigidity (kGA). The Timoshenko model produced a better fit to the experimental data, predicting EI=10,400 pN ?m2 and kGA=247 pN. Assuming a homogenous rod, the shear modulus (G=1.9 kPa) was four orders of magnitude less than Young's modulus (E=14.1 MPa), indicating that significant shear deformation occurs within deflected kinocilia. When analyzed as an Euler–Bernoulli beam, which neglects translational shear, EI increased linearly with kinocilium height, giving underestimates of EI for shorter kinocilia. Second, we measured the rotational stiffness of the kinocilium insertion (?) into the hair cell's apical surface. Following BAPTA treatment to break the kinocilial links, the kinocilia remained upright, and ? was measured as 177±47 pN ?m rad–1. The mechanical parameters we quantified are important for understanding how forces arising from head movement are transduced and encoded by hair cells. PMID:21307074

  8. Face-Referenced Measurement of Perioral Stiffness and Speech Kinematics in Parkinson's Disease

    ERIC Educational Resources Information Center

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

    2015-01-01

    Purpose: Perioral biomechanics, labial kinematics, and associated electromyographic signals were sampled and characterized in individuals with Parkinson's disease (PD) as a function of medication state. Method: Passive perioral stiffness was sampled using the OroSTIFF system in 10 individuals with PD in a medication ON and a medication OFF state…

  9. Evaluation of Stiffness Changes in a High-Rise Building by Measurements of Lateral Displacements Using GPS Technology

    PubMed Central

    Choi, Se Woon; Kim, Ill Soo; Park, Jae Hwan; Kim, Yousok; Sohn, Hong Gyoo; Park, Hyo Seon

    2013-01-01

    The outrigger truss system is one of the most frequently used lateral load resisting structural systems. However, little research has been reported on the effect of installation of outrigger trusses on improvement of lateral stiffness of a high-rise building through full-scale measurements. In this paper, stiffness changes of a high-rise building due to installation of outrigger trusses have been evaluated by measuring lateral displacements using a global positioning system (GPS). To confirm the error range of the GPS measurement system used in the full-scale measurement tests, the GPS displacement monitoring system is investigated through a free vibration test of the experimental model. Then, for the evaluation of lateral stiffness of a high-rise building under construction, the GPS displacement monitoring system is applied to measurements of lateral displacements of a 66-story high-rise building before and after installation of outrigger truss. The stiffness improvement of the building before and after the installation is confirmed through the changes of the natural frequencies and the ratios of the base shear forces to the roof displacements. PMID:24233025

  10. Biomechanical measurements of stiffness and strength for five types of whole human and artificial humeri.

    PubMed

    Aziz, Mina S R; Nicayenzi, Bruce; Crookshank, Meghan C; Bougherara, Habiba; Schemitsch, Emil H; Zdero, Radovan

    2014-05-01

    The human humerus is the third largest longbone and experiences 2-3% of all fractures. Yet, almost no data exist on its intact biomechanical properties, thus preventing researchers from obtaining a full understanding of humerus behavior during injury and after being repaired with fracture plates and nails. The aim of this experimental study was to compare the biomechanical stiffness and strength of "gold standard" fresh-frozen humeri to a variety of humerus models. A series of five types of intact whole humeri were obtained: human fresh-frozen (n?=?19); human embalmed (n?=?18); human dried (n?=?15); artificial "normal" (n?=?12); and artificial "osteoporotic" (n?=?12). Humeri were tested under "real world" clinical loading modes for shear stiffness, torsional stiffness, cantilever bending stiffness, and cantilever bending strength. After removing geometric effects, fresh-frozen results were 585.8?±?181.5?N/mm2 (normalized shear stiffness); 3.1?±?1.1?N/(mm2 deg) (normalized torsional stiffness); 850.8?±?347.9?N/mm2 (normalized cantilever stiffness); and 8.3?±?2.7?N/mm2 (normalized cantilever strength). Compared to fresh-frozen values, statistical equivalence (p ? 0.05) was obtained for all four test modes (embalmed humeri), 1 of 4 test modes (dried humeri), 1 of 4 test modes (artificial "normal" humeri), and 1 of 4 test modes (artificial "osteoporotic" humeri). Age and bone mineral density versus experimental results had Pearson linear correlations ranging from R?=?-0.57 to 0.80. About 77% of human humeri failed via a transverse or oblique distal shaft fracture, whilst 88% of artificial humeri failed with a mixed transverse?+?oblique fracture. To date, this is the most comprehensive study on the biomechanics of intact human and artificial humeri and can assist researchers to choose an alternate humerus model that can substitute for fresh-frozen humeri. PMID:24598846

  11. Microfluidic acoustic trapping force and stiffness measurement using viscous drag effect.

    PubMed

    Lee, Jungwoo; Jeong, Jong Seob; Shung, K Kirk

    2013-01-01

    It has recently been demonstrated that it was possible to individually trap 70?m droplets flowing within a 500?m wide microfluidic channel by a 24MHz single element piezo-composite focused transducer. In order to further develop this non-invasive approach as a microfluidic particle manipulation tool of high precision, the trapping force needs to be calibrated to a known force, i.e., viscous drag force arising from the fluid flow in the channel. However, few calibration studies based on fluid viscosity have been carried out with focused acoustic beams for moving objects in microfluidic environments. In this paper, the acoustic trapping force (F(trapping)) and the trap stiffness (or compliance k) are experimentally determined for a streaming droplet in a microfluidic channel. F(trapping) is calibrated to viscous drag force produced from syringe pumps. Chebyshev-windowed chirp coded excitation sequences sweeping the frequency range from 18MHz to 30MHz is utilized to drive the transducer, enabling the beam transmission through the channel/fluid interface for interrogating the droplets inside the channel. The minimum force (F(min,trapping)) required for initially immobilizing drifting droplets is determined as a function of pulse repetition frequency (PRF), duty factor (DTF), and input voltage amplitude (V(in)) to the transducer. At PRF=0.1kHz and DTF=30%, F(min,trapping) is increased from 2.2nN for V(in)=22V(pp) to 3.8nN for V(in)=54V(pp). With a fixed V(in)=54V(pp) and DTF=30%, F(min,trapping) can be varied from 3.8nN at PRF=0.1kHz to 6.7nN at PRF=0.5kHz. These findings indicate that both higher driving voltage and more frequent beam transmission yield stronger traps for holding droplets in motion. The stiffness k can be estimated through linear regression by measuring the trapping force (F(trapping)) corresponding to the displacement (x) of a droplet from the trap center. By plotting F(trapping) - x curves for certain values of V(in) (22/38/54V(pp)) at DTF=10% and PRF=0.1kHz, k is measured to be 0.09, 0.14, and 0.20nN/?m, respectively. With variable PRF from 0.1 to 0.5kHz at V(in)=54 V(pp), k is increased from 0.20 to 0.42nN/?m. It is shown that a higher PRF leads to a more compliant trap formation (or a stronger F(trapping)) for a given displacement x. Hence the results suggest that this acoustic trapping method has the potential as a noninvasive manipulation tool for individual moving targets in microfluidics by adjusting the transducer's excitation parameters. PMID:22824623

  12. Assessing the small-strain soil stiffness for offshore wind turbines based on in situ seismic measurements

    NASA Astrophysics Data System (ADS)

    Versteijlen, W. G.; van Dalen, K. N.; Metrikine, A. V.; Hamre, L.

    2014-06-01

    The fundamental natural frequency as measured on installed offshore wind turbines is significantly higher than its designed value, and it is expected that the explanation for this can be found in the currently adopted modeling of soil-structure interaction. The small-strain soil stiffness is an important design parameter, as it has a defining influence on the first natural frequency of these structures. In this contribution, in situ seismic measurements are used to derive the small-strain shear modulus of soil as input for 3D soil-structure interaction models to assess the initial soil stiffness at small strains for offshore wind turbine foundations. A linear elastic finite element model of a half-space of solids attached to a pile is used to derive an equivalent first mode shape of the foundation. The second model extends the first one by introducing contact elements between pile and soil, to take possible slip and gap-forming into account. The deflections derived with the 3D models are smaller than those derived with the p- y curve design code. This higher stiffness is in line with the higher measured natural frequencies. Finally a method is suggested to translate the response of 3D models into 1D engineering models of a beam laterally supported by uncoupled distributed springs.

  13. Face-Referenced Measurement of Perioral Stiffness and Speech Kinematics in Parkinson's Disease

    PubMed Central

    Barlow, Steven M.; Lee, Jaehoon

    2015-01-01

    Purpose Perioral biomechanics, labial kinematics, and associated electromyographic signals were sampled and characterized in individuals with Parkinson's disease (PD) as a function of medication state. Method Passive perioral stiffness was sampled using the OroSTIFF system in 10 individuals with PD in a medication ON and a medication OFF state and compared to 10 matched controls. Perioral stiffness, derived as the quotient of resultant force and interoral angle span, was modeled with regression techniques. Labial movement amplitudes and integrated electromyograms from select lip muscles were evaluated during syllable production using a 4-D computerized motion capture system. Results Multilevel regression modeling showed greater perioral stiffness in patients with PD, consistent with the clinical correlate of rigidity. In the medication-OFF state, individuals with PD manifested greater integrated electromyogram levels for the orbicularis oris inferior compared to controls, which increased further after consumption of levodopa. Conclusions This study illustrates the application of biomechanical, electrophysiological, and kinematic methods to better understand the pathophysiology of speech motor control in PD. PMID:25629806

  14. Stiff Quantum Polymers

    E-print Network

    H. Kleinert

    2007-05-01

    At ultralow temperatures, polymers exhibit quantum behavior, which is calculated here for the moments and of the end-to-end distribution in the large-stiffness regime. The result should be measurable for polymers in wide optical traps.

  15. Correlation of Arterial Stiffness and Bone Mineral Density by Measuring Brachial-Ankle Pulse Wave Velocity in Healthy Korean Women

    PubMed Central

    Kim, Nam-Lee

    2015-01-01

    Background An association between arterial stiffness and osteoporosis has previously been reported. Therefore, we investigated the relationship between arterial stiffness, measured by brachial-ankle pulse wave velocity, and bone mineral density in a sample of healthy women undergoing routine medical checkup. Methods We retrospectively reviewed the medical charts of 135 women who had visited the Health Promotion Center (between May 2009 and December 2012). Brachial-ankle pulse wave velocity was measured using an automatic wave analyzer. Bone mineral density of the lumbar spine (L1-L4) and femur was measured by dual-energy X-ray absorptiometry. Metabolic syndrome was defined according to National Cholesterol Education Program-Adult Treatment Panel III criteria, using body mass index >25 kg/m2 instead of waist circumference >88.9 cm. Results Pearson's correlation analysis revealed significant inverse relationships between pulse wave velocity and bone mineral density of the lumbar spine (r=-0.335, P<0.001), femur neck (r=-0.335, P<0.001), and total femur (r=-0.181, P=0.04). Pulse wave velocity showed the strongest association with age (r=0.586, P<0.001). Multiple regression analysis identified an independent relationship between pulse wave velocity and lumbar spine bone mineral density in women after adjusting for age, metabolic syndrome, body mass index, smoking status, alcohol intake, and exercise (r=-0.229, P=0.01). Conclusion This study confirmed an association between arterial stiffness and bone mineral density in women. PMID:26634100

  16. Comparison of the Reliability of Acoustic Radiation Force Impulse Imaging and Supersonic Shear Imaging in Measurement of Liver Stiffness.

    PubMed

    Woo, Hyunsik; Lee, Jae Young; Yoon, Jeong Hee; Kim, Won; Cho, Belong; Choi, Byung Ihn

    2015-12-01

    Purpose To compare the reliability of acoustic radiation force impulse (ARFI) imaging and supersonic shear imaging (SSI) in measurement of liver stiffness. Materials and Methods This study was approved by the institutional review board, and written informed consent was obtained for all patients. Seventy-nine patients (25 healthy patients, 26 with Child-Pugh class A, and 28 with Child-Pugh class B or C) were enrolled and analyzed from April 2012 to April 2013. In each patient, three abdominal radiologists performed nine measurements of hepatic shear-wave speed with both ARFI imaging and SSI on the same day. Four weeks later, a second session was performed with the same protocol. Interobserver and intraobserver agreements were calculated by using intraclass correlation coefficients. Technical failures and measurement time were evaluated. Results There were four technical failures in the SSI group and one in the ARFI group (P = .375). The overall interobserver agreement of ARFI imaging was significantly higher than that of SSI (0.941 vs 0.828, P < .001). The overall intraobserver agreement of ARFI imaging was significantly higher than that of SSI (0.915 vs 0.829, P < .001). The overall shear-wave speed measured with SSI was higher than that measured with ARFI imaging (2.04 m/sec ± 0.88 vs 1.80 m/sec ± 0.81, P < .001). The measurement time of SSI was longer than that of ARFI imaging (310.8 seconds ± 88.5 vs 84.5 seconds ± 15.4, P < .001). Conclusion ARFI imaging was more reliable than SSI in measurement of liver stiffness. The hepatic shear-wave speed measured with SSI was higher than that measured with ARFI imaging, which means that the shear-wave speeds measured with ARFI imaging and SSI cannot be used interchangeably. (©) RSNA, 2015. PMID:26147680

  17. Growth, spectral, thermal, optical, mechanical and etching studies of L-lysine semi-maleate (L-LSM) single crystals

    NASA Astrophysics Data System (ADS)

    Vasudevan, V.; Renuka, N.; Ramesh Babu, R.; Ramamurthi, K.

    2015-02-01

    Organic nonlinear optical material, L-lysine semi-maleate (L-LSM) single crystals were grown by slow cooling solution growth technique. The crystal system of grown L-LSM was confirmed by single crystal and powder X-ray diffraction analyzes. Functional groups of the grown crystal have been identified by Fourier Transform Infrared spectral analysis. The proton and carbon NMR spectral studies confirm the presence of hydrogen and carbon in the grown L-LSM. The melting and thermal decomposition temperatures of the crystal were determined using thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. Optical transparency, second harmonic generation efficiency, micro hardness, dielectric constant and loss, refractive index and birefringence have also been measured. Further, the growth patterns and dislocations present in the grown crystal are studied.

  18. High temperature oxidation behavior of interconnect coated with LSCF and LSM for solid oxide fuel cell by screen printing

    NASA Astrophysics Data System (ADS)

    Lee, Shyong; Chu, Chun-Lin; Tsai, Ming-Jui; Lee, Jye

    2010-01-01

    The current study examined the effect of La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) and La 0.7Sr 0.3MnO 3 (LSM) coatings on the electrical properties and oxidation resistance of Crofer22 APU at 800 °C hot air. LSCF and LSM were coated on Crofer22 APU by screen printing and sintered over temperatures ranging from 1000 to 1100 °C in N 2. The coated alloy was first checked for compositions, morphology and interface conditions and then treated in a simulated oxidizing environment at 800 °C for 200 h. After measuring the long-term electrical resistance, the area specific resistance (ASR) at 800 °C for the alloy coated with LSCF was less than its counterpart coated with LSM. This work used LSCF coating as a metallic interconnect to reduce working temperature for the solid oxide fuel cell.

  19. Growth, spectral, thermal, optical, mechanical and etching studies of l-lysine semi-maleate (l-LSM) single crystals.

    PubMed

    Vasudevan, V; Renuka, N; Ramesh Babu, R; Ramamurthi, K

    2014-10-31

    Organic nonlinear optical material, l-lysine semi-maleate (l-LSM) single crystals were grown by slow cooling solution growth technique. The crystal system of grown l-LSM was confirmed by single crystal and powder X-ray diffraction analyzes. Functional groups of the grown crystal have been identified by Fourier Transform Infrared spectral analysis. The proton and carbon NMR spectral studies confirm the presence of hydrogen and carbon in the grown l-LSM. The melting and thermal decomposition temperatures of the crystal were determined using thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. Optical transparency, second harmonic generation efficiency, micro hardness, dielectric constant and loss, refractive index and birefringence have also been measured. Further, the growth patterns and dislocations present in the grown crystal are studied. PMID:25467679

  20. Evaluation of Noah-LSM for soil hydrology parameters in the Indian summer monsoon conditions

    NASA Astrophysics Data System (ADS)

    Patil, M. N.; Kumar, Manoj; Waghmare, R. T.; Dharmaraj, T.; Mahanty, N. C.

    2014-10-01

    The micrometeorological observations, collected over a station in Ranchi (23°45'N, 85°30'E) which is under the monsoon trough region of India, were used in the Noah-LSM (NCEP, OSU, Air Force and Office of Hydrology Land Surface Model) to investigate the model performance in wet (2009 and 2011) and dry (2010) conditions during the south-west summer monsoon season. With this analysis, it is seen that the Noah-LSM has simulated the diurnal cycle of heat fluxes (sensible and ground) reasonably. The simulated heat fluxes were compared with its direct measurements by sonic anemometer and soil heat flux plate. The net radiation and sensible heat flux are simulated well by the model, but the simulation of ground heat flux was found to be poor in both dry as well as wet conditions. The soil temperature simulations were also found to be poor in 0-5- and 5-10-cm layers compared to other deeper layers. The observations were also correlated with the Modern Era Retrospective-analysis for Research and Applications (MERRA) data. The correlation between the observations and ground heat flux was better in MERRA dataset than that of the Noah-LSM simulation.

  1. Variation in within-bone stiffness measured by nanoindentation in mice bred for high levels of voluntary wheel running.

    PubMed

    Middleton, Kevin M; Goldstein, Beth D; Guduru, Pradeep R; Waters, Julie F; Kelly, Scott A; Swartz, Sharon M; Garland, T

    2010-01-01

    The hierarchical structure of bone, involving micro-scale organization and interaction of material components, is a critical determinant of macro-scale mechanics. Changes in whole-bone morphology in response to the actions of individual genes, physiological loading during life, or evolutionary processes, may be accompanied by alterations in underlying mineralization or architecture. Here, we used nanoindentation to precisely measure compressive stiffness in the femoral mid-diaphysis of mice that had experienced 37 generations of selective breeding for high levels of voluntary wheel running (HR). Mice (n = 48 total), half from HR lines and half from non-selected control (C) lines, were divided into two experimental groups, one with 13-14 weeks of access to a running wheel and one housed without wheels (n = 12 in each group). At the end of the experiment, gross and micro-computed tomography (microCT)-based morphometric traits were measured, and reduced elastic modulus (E(r)) was estimated separately for four anatomical quadrants of the femoral cortex: anterior, posterior, lateral, and medial. Two-way, mixed-model analysis of covariance (ancova) showed that body mass was a highly significant predictor of all morphometric traits and that structural change is more apparent at the microCT level than in conventional morphometrics of whole bones. Both line type (HR vs. C) and presence of the mini-muscle phenotype (caused by a Mendelian recessive allele and characterized by a approximately 50% reduction in mass of the gastrocnemius muscle complex) were significant predictors of femoral cortical cross-sectional anatomy. Measurement of reduced modulus obtained by nanoindentation was repeatable within a single quadrant and sensitive enough to detect inter-individual differences. Although we found no significant effects of line type (HR vs. C) or physical activity (wheel vs. no wheel) on mean stiffness, anterior and posterior quadrants were significantly stiffer (P < 0.0001) than medial and lateral quadrants (32.67 and 33.09 GPa vs. 29.78 and 30.46 GPa, respectively). Our findings of no significant difference in compressive stiffness in the anterior and posterior quadrants agree with previous results for mice, but differ from those for large mammals. Integrating these results with others from ongoing research on these mice, we hypothesize that the skeletons of female HR mice may be less sensitive to the effects of chronic exercise, due to decreased circulating leptin levels and potentially altered endocannabinoid signaling. PMID:20402827

  2. Feasibility study of superconducting LSM rocket launcher system

    NASA Technical Reports Server (NTRS)

    Yoshida, Kinjiro; Ohashi, Takaaki; Shiraishi, Katsuto; Takami, Hiroshi

    1994-01-01

    A feasibility study is presented concerning an application of a superconducting linear synchronous motor (LSM) to a large-scale rocket launcher, whose acceleration guide tube of LSM armature windings is constructed 1,500 meters under the ground. The rocket is released from the linear launcher just after it gets to a peak speed of about 900 kilometers per hour, and it flies out of the guide tube to obtain the speed of 700 kilometers per hour at the height of 100 meters above ground. The linear launcher is brought to a stop at the ground surface for a very short time of 5 seconds by a quick control of deceleration. Very large current variations in the single-layer windings of the LSM armature, which are produced at the higher speed region of 600 to 900 kilometers per hour, are controlled successfully by adopting the double-layer windings. The proposed control method makes the rocket launcher ascend stably in the superconducting LSM system, controlling the Coriolis force.

  3. Stiff quantum polymers

    E-print Network

    H. Kleinert

    2009-10-19

    At ultralow temperatures, polymers exhibit quantum behavior, which is calculated here for the second and fourth moments of the end-to-end distribution in the large-stiffness regime. The result should be measurable for polymers in wide optical traps.

  4. Arterial Stiffness

    PubMed Central

    Avolio, Alberto

    2013-01-01

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

  5. In situ measurements of human articular cartilage stiffness by means of a scanning force microscope

    NASA Astrophysics Data System (ADS)

    Imer, Raphaël; Akiyama, Terunobu; de Rooij, Nico F.; Stolz, Martin; Aebi, Ueli; Kilger, Robert; Friederich, Niklaus F.; Wirz, Dieter; Daniels, A. U.; Staufer, Urs

    2007-03-01

    Osteoarthritis is a painful and disabling progressive joint disease, characterized by degradation of articular cartilage. In order to study this disease at early stages, we have miniaturized and integrated a complete scanning force microscope into a standard arthroscopic device fitting through a standard orthopedic canula. This instrument will allow orthopedic surgeons to measure the mechanical properties of articular cartilage at the nanometer and micrometer scale in-vivo during a standard arthroscopy. An orthopedic surgeon assessed the handling of the instrument. First measurements of the elasticity-modulus of human cartilage were recorded in a cadaver knee non minimal invasive. Second, minimally invasive experiments were performed using arthroscopic instruments. Load-displacement curves were successfully recorded.

  6. Magnetization measurements reveal the local shear stiffness of hydrogels probed by ferromagnetic nanorods

    NASA Astrophysics Data System (ADS)

    Bender, P.; Tschöpe, A.; Birringer, R.

    2014-12-01

    The local mechanical coupling of ferromagnetic nanorods in hydrogels was characterized by magnetization measurements. Nickel nanorods were synthesized by the AAO-template method and embedded in gelatine hydrogels with mechanically soft or hard matrix properties determined by the gelatine weight fraction. By applying a homogeneous magnetic field during gelation the nanorods were aligned along the field resulting in uniaxially textured ferrogels. The magnetization curves of the soft ferrogel exhibited not only important similarities but also characteristic differences as compared to the hard ferrogel. The hystereses measured in a field parallel to the texture axis were almost identical for both samples indicating effective coupling of the nanorods with the polymer network. By contrast, measurements in a magnetic field perpendicular to the texture axis revealed a much higher initial susceptibility of the soft as compared to the hard ferrogel. This difference was attributed to the additional rotation of the nanorods allowed by the reduced shear modulus in the soft ferrogel matrix. Two methods for data analysis were presented which enabled us to determine the shear modulus of the gelatine matrix which was interpreted as a local rather than macroscopic quantity in consideration of the nanoscale of the probe particles.

  7. Beetle adhesive hairs differ in stiffness and stickiness: in vivo adhesion measurements on individual setae

    NASA Astrophysics Data System (ADS)

    Bullock, James M. R.; Federle, Walter

    2011-05-01

    Leaf beetles are able to climb on smooth and rough surfaces using arrays of micron-sized adhesive hairs (setae) of varying morphology. We report the first in vivo adhesive force measurements of individual setae in the beetle Gastrophysa viridula, using a smooth polystyrene substrate attached to a glass capillary micro-cantilever. The beetles possess three distinct adhesive pads on each leg which differ in function and setal morphology. Visualisation of pull-offs allowed forces to be measured for each tarsal hair type. Male discoidal hairs adhered with the highest forces (919 ± 104 nN, mean ± SE), followed by spatulate (582 ± 59 nN) and pointed (127 ± 19 nN) hairs. Discoidal hairs were stiffer in the normal direction (0.693 ± 0.111 N m-1) than spatulate (0.364 ± 0.039 N m-1) or pointed (0.192 ± 0.044 N m-1) hairs. The greater adhesion on smooth surfaces and the higher stability of discoidal hairs help male beetles to achieve strong adhesion on the elytra of females during copulation. A comparison of pull-off forces measured for single setae and whole pads (arrays) revealed comparable levels of adhesive stress. This suggests that beetles are able to achieve equal load sharing across their adhesive pads so that detachment through peeling is prevented.

  8. Inverse measurement of stiffness by the normalization technique for J-integral fracture toughness

    SciTech Connect

    Brown, Eric

    2012-06-07

    The single specimen normalization technique for J-integral fracture toughness has been successfully employed by several researchers to study the strongly non-linear fracture response of ductile semicrystalline polymers. As part of the normalization technique the load and the plastic component of displacement are normalized. The normalized data is then fit with a normalization function that approximates a power law for small displacements that are dominated by blunting and smoothly transitions to a linear relationship for large displacements that are dominated by stable crack extension. Particularly for very ductile polymers the compliance term used to determine the plastic displacement can dominate the solution and small errors in determining the elastic modulus can lead to large errors in the normalization or even make it ill-posed. This can be further complicated for polymers where the elastic modulus is strong strain rate dependent and simply using a 'quasistatic' modulus from a dogbone measurement may not equate to the dominant strain rate in the compact tension specimen. The current work proposes directly measuring the compliance of the compact tension specimen in the solution of J-integral fracture toughness and then solving for the elastic modulus. By comparison with a range of strain rate data the dominant strain rate can then be determined.

  9. LSM-YSZ Cathodes with Reaction-Infiltrated Nanoparticles

    SciTech Connect

    Lu, Chun; Sholklapper, Tal Z.; Jacobson, Craig P.; Visco, StevenJ.; De Jonghe, Lutgard C.

    2006-01-31

    To improve the LSM-YSZ cathode performance of intermediate temperature solid oxide fuel cells (SOFCs), Sm0.6Sr0.4CoO3-sigma (SSC) perovskite nanoparticles are incorporated into the cathodes by a reaction-infiltration process. The SSC particles are {approx}20 to 80nm in diameter, and intimately adhere to the pore walls of the preformed LSM-YSZ cathodes. The SSC particles dramatically enhance single-cell performance with a 97 percent H2+3 percent H2O fuel, between 600 C and 800 C. Consideration of a simplified TPB (triple phase boundary) reaction geometry indicates that the enhancement may be attributed to the high electrocatalytic activity of SSC for electrochemical reduction of oxygen in a region that can be located a small distance away from the strict triple phase boundaries. The implication of this work for developing high-performance electrodes is also discussed.

  10. Impact of liver steatosis on the correlation between liver stiffness and fibrosis measured by transient elastography in patients coinfected with human immunodeficiency virus and hepatitis C virus.

    PubMed

    Sánchez-Conde, M; Montes Ramírez, M L; Bellón Cano, J M; Caminoa, A; Alvarez Rodríguez, F; González Garcia, J; Miralles Martín, P; Bernardino de la Serna, I; Bernardo de Quirós, J C López; Arribas López, J R; Cosín Ochaíta, J; Pascual Pareja, J F; Alvarez, E; Berenguer, J B

    2011-07-01

    We assessed the effect of different hepatic conditions such as fibrosis, steatosis and necroinflammatory activity on liver stiffness as measured by transient elastography in HIV/HCV-coinfected patients. We studied all consecutive HIV/HCV-coinfected patients who underwent liver biopsy and elastography between January 2007 and December 2008. Liver fibrosis was staged following METAVIR Cooperative Study Group criteria. Steatosis was categorized according to the percentage of affected hepatocytes as low (?10%), moderate (<25%) and severe (?25%). A total of 110 patients were included. Fibrosis was distributed by stage as follows: F0, n?=?13; F1, n?=?47; F2, n?=?29; F3, n?=?18; and F4, n?=?3. Liver biopsy revealed the presence of hepatic steatosis in 68 patients (low to moderate, n?=?53; and severe n?=?15). By univariate regression analysis, fibrosis, necroinflammatory activity, and the degree of steatosis were correlated with liver stiffness. However, in a multiple regression analysis, steatosis and fibrosis were the only independent variables significantly associated with liver stiffness. With a cut-off of 9.5?kPa to distinguish patients with F???2 from F???3, elastography led to a significantly higher number of misclassification errors (25%vs 5%; P?=?0.014), most of which were false positives for F???3. Our study suggests that the correlation between liver stiffness and fibrosis as estimated by transient elastography may be affected by the presence of hepatic steatosis in HIV/HCV-coinfected patients. PMID:21129129

  11. A novel method of measuring leaf epidermis and mesophyll stiffness shows the ubiquitous nature of the sandwich structure of leaf laminas in broad-leaved angiosperm species.

    PubMed

    Onoda, Yusuke; Schieving, Feike; Anten, Niels P R

    2015-05-01

    Plant leaves commonly exhibit a thin, flat structure that facilitates a high light interception per unit mass, but may increase risks of mechanical failure when subjected to gravity, wind and herbivory as well as other stresses. Leaf laminas are composed of thin epidermis layers and thicker intervening mesophyll layers, which resemble a composite material, i.e. sandwich structure, used in engineering constructions (e.g. airplane wings) where high bending stiffness with minimum weight is important. Yet, to what extent leaf laminas are mechanically designed and behave as a sandwich structure remains unclear. To resolve this issue, we developed and applied a novel method to estimate stiffness of epidermis- and mesophyll layers without separating the layers. Across a phylogenetically diverse range of 36 angiosperm species, the estimated Young's moduli (a measure of stiffness) of mesophyll layers were much lower than those of the epidermis layers, indicating that leaf laminas behaved similarly to efficient sandwich structures. The stiffness of epidermis layers was higher in evergreen species than in deciduous species, and strongly associated with cuticle thickness. The ubiquitous nature of sandwich structures in leaves across studied species suggests that the sandwich structure has evolutionary advantages as it enables leaves to be simultaneously thin and flat, efficiently capturing light and maintaining mechanical stability under various stresses. PMID:25675956

  12. 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.

  13. 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.

  14. The measurement of A0 and S0 lamb wave attenuation to determine the normal and shear stiffnesses of a compressively loaded interface.

    PubMed

    Drinkwater, Bruce W; Castaings, Michel; Hosten, Bernard

    2003-06-01

    Guided waves in an elastic plate surrounded by air propagate with very low attenuation. This paper describes the effect on this propagation of compressively loading an elastomer with high internal damping against one surface of the elastic plate. The propagation of both A0 and S0 Lamb modes is considered. The principal effect is shown to be increased attenuation of the guided waves. This attenuation is caused by leakage of energy from the plate into the elastomer, where it is dissipated due to high viscoelastic damping. It is shown that the increase in attenuation is strongly dependent on the compressive load applied across the solid-solid interface. This interface is represented as a spring layer in a continuum model of the system. Both normal and shear stiffnesses of the interface are quantified from the attenuation of A0 and S0 Lamb waves measured at each step of the compressive loading. The normal stiffness is also measured independently by normal incidence, bulk longitudinal wave ultrasound. The resulting predictions of wave propagation behavior, such as attenuation, obtained by the model are in excellent agreement with those measured experimentally. PMID:12822788

  15. The measurement of A0 and S0 Lamb wave attenuation to determine the normal and shear stiffnesses of a compressively loaded interface

    NASA Astrophysics Data System (ADS)

    Drinkwater, Bruce W.; Castaings, Michel; Hosten, Bernard

    2003-06-01

    Guided waves in an elastic plate surrounded by air propagate with very low attenuation. This paper describes the effect on this propagation of compressively loading an elastomer with high internal damping against one surface of the elastic plate. The propagation of both A0 and S0 Lamb modes is considered. The principal effect is shown to be increased attenuation of the guided waves. This attenuation is caused by leakage of energy from the plate into the elastomer, where it is dissipated due to high viscoelastic damping. It is shown that the increase in attenuation is strongly dependent on the compressive load applied across the solid-solid interface. This interface is represented as a spring layer in a continuum model of the system. Both normal and shear stiffnesses of the interface are quantified from the attenuation of A0 and S0 Lamb waves measured at each step of the compressive loading. The normal stiffness is also measured independently by normal incidence, bulk longitudinal wave ultrasound. The resulting predictions of wave propagation behavior, such as attenuation, obtained by the model are in excellent agreement with those measured experimentally.

  16. Cytoplasmic LSM-1 protein regulates stress responses through the insulin/IGF-1 signaling pathway in Caenorhabditis elegans.

    PubMed

    Cornes, Eric; Porta-De-La-Riva, Montserrat; Aristizábal-Corrales, David; Brokate-Llanos, Ana María; García-Rodríguez, Francisco Javier; Ertl, Iris; Díaz, Mònica; Fontrodona, Laura; Reis, Kadri; Johnsen, Robert; Baillie, David; Muñoz, Manuel J; Sarov, Mihail; Dupuy, Denis; Cerón, Julián

    2015-09-01

    Genes coding for members of the Sm-like (LSm) protein family are conserved through evolution from prokaryotes to humans. These proteins have been described as forming homo- or heterocomplexes implicated in a broad range of RNA-related functions. To date, the nuclear LSm2-8 and the cytoplasmic LSm1-7 heteroheptamers are the best characterized complexes in eukaryotes. Through a comprehensive functional study of the LSm family members, we found that lsm-1 and lsm-3 are not essential for C. elegans viability, but their perturbation, by RNAi or mutations, produces defects in development, reproduction, and motility. We further investigated the function of lsm-1, which encodes the distinctive protein of the cytoplasmic complex. RNA-seq analysis of lsm-1 mutants suggests that they have impaired Insulin/IGF-1 signaling (IIS), which is conserved in metazoans and involved in the response to various types of stress through the action of the FOXO transcription factor DAF-16. Further analysis using a DAF-16::GFP reporter indicated that heat stress-induced translocation of DAF-16 to the nuclei is dependent on lsm-1. Consistent with this, we observed that lsm-1 mutants display heightened sensitivity to thermal stress and starvation, while overexpression of lsm-1 has the opposite effect. We also observed that under stress, cytoplasmic LSm proteins aggregate into granules in an LSM-1-dependent manner. Moreover, we found that lsm-1 and lsm-3 are required for other processes regulated by the IIS pathway, such as aging and pathogen resistance. PMID:26150554

  17. 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…

  18. Spinal stiffness changes throughout the respiratory cycle.

    PubMed

    Shirley, D; Hodges, P W; Eriksson, A E M; Gandevia, S C

    2003-10-01

    Posteroanterior stiffness of the lumbar spine is influenced by factors, including trunk muscle activity and intra-abdominal pressure (IAP). Because these factors vary with breathing, this study investigated whether stiffness is modulated in a cyclical manner with respiration. A further aim was to investigate the relationship between stiffness and IAP or abdominal and paraspinal muscle activity. Stiffness was measured from force-displacement responses of a posteroanterior force applied over the spinous process of L2 and L4. Recordings were made of IAP and electromyographic activity from L4/L2 erector spinae, abdominal muscles, and chest wall. Stiffness was measured with the lung volume held at the extremes of tidal volume and at greater and lesser volumes. Stiffness at L4 and L2 increased above base-level values at functional residual capacity (L2 14.9 N/mm and L4 15.3 N/mm) with both inspiratory and expiratory efforts. The increase was related to the respiratory effort and was greatest during maximum expiration (L2 24.9 N/mm and L4 23.9 N/mm). The results indicate that changes in trunk muscle activity and IAP with respiratory efforts modulate spinal stiffness. In addition, the diaphragm may augment spinal stiffness via attachment of its crural fibers to the lumbar vertebrae. PMID:12970374

  19. Measurements of the Stiffness and Thickness of the Pavement Asphalt Layer Using the Enhanced Resonance Search Method

    PubMed Central

    Zakaria, Nur Mustakiza; Yusoff, Nur Izzi Md.; Hardwiyono, Sentot; Mohd Nayan, Khairul Anuar

    2014-01-01

    Enhanced resonance search (ERS) is a nondestructive testing method that has been created to evaluate the quality of a pavement by means of a special instrument called the pavement integrity scanner (PiScanner). This technique can be used to assess the thickness of the road pavement structure and the profile of shear wave velocity by using the principle of surface wave and body wave propagation. In this study, the ERS technique was used to determine the actual thickness of the asphaltic pavement surface layer, while the shear wave velocities obtained were used to determine its dynamic elastic modulus. A total of fifteen locations were identified and the results were then compared with the specifications of the Malaysian PWD, MDD UKM, and IKRAM. It was found that the value of the elastic modulus of materials is between 3929?MPa and 17726?MPa. A comparison of the average thickness of the samples with the design thickness of MDD UKM showed a difference of 20 to 60%. Thickness of the asphalt surface layer followed the specifications of Malaysian PWD and MDD UKM, while some of the values of stiffness obtained are higher than the standard. PMID:25276854

  20. Stiffness has different meanings, I think, to everyone”. Examining Stiffness from the Perspective of People Living with Rheumatoid Arthritis

    PubMed Central

    Orbai, Ana-Maria; Smith, Katherine C.; Bartlett, Susan J.; De Leon, Elaine; Bingham, Clifton O.

    2014-01-01

    Objective Stiffness is a well-recognized symptom of Rheumatoid Arthritis (RA). It is frequently queried during clinic visits as an indicator of disease activity, and was included in the 1961 and 1987 RA classification criteria. Little is known about how people with RA experience stiffness and its impact on their lives. Methods We conducted 4 focus groups with 20 people with RA (4-6 participants per group), from one academic clinical practice and one private practice, to generate accounts of stiffness experiences. Qualitative inductive thematic data analysis was conducted. Results Five overarching themes were identified: 1. Relationship of stiffness with other symptoms; 2. Exacerbating or alleviating factors and self-management; 3. Stiffness timing and location; 4. Individual meanings of stiffness experiences; 5. Impact of stiffness on daily life. Conclusion Focus group discussions revealed individual stiffness experiences as diverse and complex. Several stiffness features were endorsed by a majority of participants, but few, if any, were universally experienced, thus the significance of stiffness as an expression of the disease varied widely. Discussions yielded descriptions of how individual limits imposed by RA in general and stiffness in particular, may change over time and were intertwined with adaptations to preserve participation in valued life activities. These results concerning the diversity of the stiffness experience, consequential adaptations, and its impact suggest a more individualized approach to stiffness measurement may be needed in order to improve stiffness assessments. PMID:24891304

  1. Prognostic Significance of Regional Arterial Stiffness for Stroke in Hypertension

    PubMed Central

    Kubozono, Takuro; Ohishi, Mitsuru

    2015-01-01

    Background Hypertension is strongly associated with cardiovascular disease. It has been reported that arterial stiffness is related to cardiovascular mortality and morbidity in hypertensive patients and that the physiological evaluation of arterial stiffness may assist clinicians in the early detection of atherosclerosis. Summary It has been demonstrated that increased arterial stiffness is an independent predictor of cardiovascular disease, including stroke. Arterial stiffness is associated with structural changes in the brain. However, the stiffness responses of muscular arteries are different from those of elastic arteries, and so the impact of arterial stiffness and the conclusions to be drawn may be different depending on the region in which the measurement is taken. Key Messages In this review, we summarize the current literature describing the association between arterial stiffness, including carotid-femoral and brachial-ankle pulse wave velocity and cardio-ankle vascular index, and cardiovascular disease, specifically stroke. We discuss the utility and prognostic significance of regional arterial stiffness measurements.

  2. 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

  3. Relationship Between Urinary Cross-Linked N-Telopeptide of Type-I Collagen and Heel Stiffness Index Measured by Quantitative Ultrasound in Middle-Aged and Elderly Men.

    PubMed

    Nishimura, Takayuki; Arima, Kazuhiko; Abe, Yasuyo; Kanagae, Mitsuo; Mizukami, Satoshi; Okabe, Takuhiro; Tomita, Yoshihito; Goto, Hisashi; Horiguchi, Itsuko; Aoyagi, Kiyoshi

    2015-11-01

    The aim of the present study was to investigate the age-related patterns and the relationship between levels of urinary cross-linked N-telopeptide of type-I collagen (NTx) and heel stiffness index measured by quantitative ultrasound (QUS) in men with a special reference to age groups of aged 40 to 59 years and ?60 years.A total of 379 men participated in this study. Heel stiffness index (bone mass) was measured by QUS. Spot urine samples were collected, and urinary NTx was measured. The values were corrected for creatinine (Cre) concentration.Stiffness index was significantly lower in men aged ?60 years compared with men aged 40 to 59 years (P?stiffness index after adjusting for age and body mass index in men aged ?60 years, but not in men aged 40 to 59 years.Higher rates of bone resorption were associated with lower stiffness index only in elderly men. Our results may indicate a different mechanism of low bone mass among different age groups. PMID:26554777

  4. Athletic Footwear, Leg Stiffness, and Running Kinematics

    PubMed Central

    Bishop, Mark; Fiolkowski, Paul; Conrad, Bryan; Brunt, Denis; Horodyski, MaryBeth

    2006-01-01

    Context: The leg acts as a linear spring during running and hopping and adapts to the stiffness of the surface, maintaining constant total stiffness of the leg-surface system. Introducing a substance (eg, footwear) may affect the stiffness of the leg in response to changes in surface stiffness. Objective: To determine if the type of athletic footwear affects the regulation of leg stiffness in dynamic activities. Design: Repeated-measures design. Setting: Motion analysis laboratory. Patients or Other Participants: Nine healthy adults (age = 28 ± 6.8 years, mass = 71.6 ± 12.9 kg) free from lower extremity injuries. Intervention(s): Subjects hopped at 2.2 Hz on a forceplate under 3 footwear conditions (barefoot, low-cost footwear, high-cost footwear). Subjects ran on a treadmill at 2 speeds (2.23 m/s, 3.58 m/s) under the same footwear conditions. Main Outcome Measure(s): Limb stiffness was calculated from forceplate data. Kinematic data (knee and ankle angles at initial contact and peak joint excursion after contact) were collected during running. We calculated 1-way repeated-measures (stiffness) and 2-way (speed by footwear) repeated-measures analyses of variance (running kinematics) to test the dependent variables. Results: A significant increase in leg stiffness from the barefoot to the “cushioned” shoe condition was noted during hopping. When running shod, runners landed in more dorsiflexion but had less ankle motion than when running barefoot. No differences were seen between the types of shoes. The primary kinematic difference was identified as running speed increased: runners landed in more knee flexion. At the ankle, barefoot runners increased ankle motion to a significantly greater extent than did shod runners as speed increased. Conclusions: Footwear influences the maintenance of stiffness in the lower extremity during hopping and joint excursion at the ankle in running. Differences in cushioning properties of the shoes tested did not appear to be significant. PMID:17273463

  5. Arterial Stiffness and Cardiovascular Therapy

    PubMed Central

    Jani?, Miodrag; Lunder, Mojca; Šabovi?, Mišo

    2014-01-01

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

  6. LSm1-7 complexes bind to specific sites in viral RNA genomes and regulate their translation and replication

    PubMed Central

    Galão, Rui Pedro; Chari, Ashwin; Alves-Rodrigues, Isabel; Lobão, Daniela; Mas, Antonio; Kambach, Christian; Fischer, Utz; Díez, Juana

    2010-01-01

    LSm1-7 complexes promote cellular mRNA degradation, in addition to translation and replication of positive-strand RNA viruses such as the Brome mosaic virus (BMV). Yet, how LSm1-7 complexes act on their targets remains elusive. Here, we report that reconstituted recombinant LSm1-7 complexes directly bind to two distinct RNA-target sequences in the BMV genome, a tRNA-like structure at the 3?-untranslated region and two internal A-rich single-stranded regions. Importantly, in vivo analysis shows that these sequences regulate the translation and replication of the BMV genome. Furthermore, both RNA-target sequences resemble those found for Hfq, the LSm counterpart in bacteria, suggesting conservation through evolution. Our results provide the first evidence that LSm1-7 complexes interact directly with viral RNA genomes and open new perspectives in the understanding of LSm1-7 functions. PMID:20181739

  7. Magnetic negative stiffness dampers

    NASA Astrophysics Data System (ADS)

    Shi, Xiang; Zhu, Songye

    2015-07-01

    This communication presents the design principle and experimental validation of two novel configurations of magnetic negative stiffness dampers (MNSDs), both of which are composed of several permanent magnets arranged in a conductive pipe. The MNSD, as a passive device, efficiently integrates negative stiffness and eddy-current damping in a simple and compact design, in which the negative stiffness behavior depends on the different arrangements of the permanent magnets. When applied to structural vibration control, passive MNSD may achieve a performance comparable with semi-active or active control in some applications. Laboratory experiments of small-scale prototypes successfully verified the proposed MNSD design concept.

  8. 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

  9. 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

  10. Effect of seasonal dynamics of vegetation cover on land surface models: a case study of NOAH LSM over a savanna farm land in eastern Burkina Faso, West Africa

    NASA Astrophysics Data System (ADS)

    Bagayoko, F.; Yonkeu, S.; van de Giesen, N. C.

    2006-09-01

    The sensitivity of the land surface model of the National Centers for Environmental Prediction (NCEP), the Oregon State University, the Air Force and the Hydrologic Research Lab (NOAH LSM) was evaluated with respect to the seasonal dynamics of the vegetation cover in the savanna area under intensive agriculture in the eastern part of Burkina Faso, West Africa. The data collected during the first long-term measurement of the surface fluxes in this mentioned region was used for this purpose. The choice of NOAH LSM was motivated by the fact that it has already been tested in different environments in West Africa, especially in Ghana. The sensitivity was tested by comparing the simulated surfaces fluxes using a fixed values of the roughness length for momentum as a standard in the model and the true seasonal value of this variable. The results show that NOAH LSM was not sensitive to the change of the roughness length for momentum neither on a seasonal basis nor on a daily basis, which was found to be abnormal. The formulation of the coefficient (Bc) coupling the dry canopy transpiration to the atmosphere was found to be the main reason for this. An improved formulation for this coefficient was given to solve this insensitivity and to improve the performance of the model. Recommendations are also given to enhance the performance of the model in the West African savanna environment.

  11. BIOMECHANICS OF DOLPHIN HEARING: A COMPARISON OF MIDDLE AND INNER EAR STIFFNESS WITH OTHER MAMMALIAN

    E-print Network

    BIOMECHANICS OF DOLPHIN HEARING: A COMPARISON OF MIDDLE AND INNER EAR STIFFNESS WITH OTHER was to measure both middle ear stiffness and basilar membrane stiffness for the bottlenose dolphin (Tursiops that the point stiffness of the bottlenose dolphin basilar membrane has a gradient from 20 N/m near the base to 1

  12. Harmonic Analysis of the Output Voltage of a Third-Harmonic-Injected Inverter for LSM Drives

    NASA Astrophysics Data System (ADS)

    Shigeeda, Hidenori; Okui, Akinobu; Akagi, Hirofumi

    The superconducting magnetic levitation railway system (MAGLEV) under development in Japan uses a pulse-width-modulation (PWM) inverter for driving a linear synchronous motor (LSM). The inverter output voltage contains non-negligible harmonics which cause harmonic resonances in the LSM system, and therefore harmonics of the output voltage have been analyzed in order to control such harmonic resonances. This paper applies a third-harmonic injection method to the inverter for the purpose of enhancing the output voltage without changing the circuit configuration. It performs harmonic analysis of the output voltage of the inverter based on the third-harmonic injection. Validity of the harmonic analysis is verified by computer simulation.

  13. 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

  14. Sensitivity of overall vehicle stiffness to local joint stiffness

    NASA Technical Reports Server (NTRS)

    Chon, Choon T.

    1987-01-01

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

  15. 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 (? = ?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

  16. Lipoprotein(a) and Arterial Stiffness Parameters

    PubMed Central

    Sorokin, Alexander; Kotani, Kazuhiko

    2015-01-01

    Background Circulating lipoprotein(a) [Lp(a)] and arterial stiffness are markers associated with the atherosclerotic processes. With regard to cardiovascular outcomes, the relationship between Lp(a) and arterial stiffness has not been sufficiently summarized. The present review focuses on the existing association between Lp(a) and arterial stiffness parameters. Summary This review included human clinical studies that were published between 1980 and 2015. The metrics of arterial stiffness parameters, ‘pulse wave velocity’ (PWV) and ‘cardio-ankle vascular index’ (CAVI), were used for this search, which yielded only 4 cross-sectional studies on this topic. Of these 4 studies, 3 reports were based on the use of PWV, while 1 study was based on the use of CAVI. Three studies (including the study using CAVI) reported that high Lp(a) levels were positively associated with arterial stiffness. Conclusion The present review indicates a positive association between Lp(a) and arterial stiffness, as assessed by PWV and CAVI. To definitively establish these findings, there is a need for further prospective outcome studies that simultaneously measure Lp(a) and the oxidative form of Lp(a) (as a pathological marker) as well as PWV and CAVI.

  17. Benchmarking LSM root-zone soil mositure predictions using satellite-based vegetation indices

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The application of modern land surface models (LSMs) to agricultural drought monitoring is based on the premise that anomalies in LSM root-zone soil moisture estimates can accurately anticipate the subsequent impact of drought on vegetation productivity and health. In addition, the water and energy ...

  18. UPDATES AND EVALUATION OF THE PX-LSM IN MM5

    EPA Science Inventory

    Starting with Version 3.4, there is a new land surface model known as the Pleim-Xiu LSM available in the MM5 system. Pleim and Xiu (1995) described the initial development and testing of this land surface and workshop proceedings provided a basic description of the model and s...

  19. Log of Changes to the UW Laboratory Safety Manual (LSM) As of November, 2014

    E-print Network

    Brown, Sally

    Log of Changes to the UW Laboratory Safety Manual (LSM) As of November, 2014 Date Change Location; Renumbered following paragraphs and revised them for clarity Section 3.F.3, Waste Treatment Log Changed title typographical errors #12;Sept 27, 2013 Preface Revised cover page: Updated Log of Changes; Removed Director

  20. Theoretical analysis of Wolter/LSM X-ray telescope systems

    NASA Technical Reports Server (NTRS)

    Shealy, D. L.; Chao, S.

    1985-01-01

    A ray tracing analysis has been performed for the spectral slicing zoom X-ray telescope for configurations in which a convex layered synthetic microstructure (LSM) optic is placed in front of the prime focus or a concave LSM optic is placed behind the prime focus. The analysis has considered the geometrical shape of the LSM optic to be either a hyperboloid, sphere, ellipsoid or constant optical path aspheric element for two configurations of the glancing incidence X-ray telescope: the ATM Experimental S-056 Wolter I system and the Stanford/MSFC Wolter-Schwarzchild nested system. For the different systems the RMS blur circle radii, the point spread function (PSF), the full width half maximum (FWHM) of the PSF have been evaluated as a function of field angle and magnification of the secondary to determine resolution of the system. The effects of decentration and tilt of the selected LSM element on the performance of the system have been studied to determine mounting and alignment tolerances.

  1. Regardless-of-Speed Superconducting LSM Controlled-Repulsive MAGLEV Vehicle

    NASA Technical Reports Server (NTRS)

    Yoshida, Kinjiro; Egashira, Tatsuya; Hirai, Ryuichi

    1996-01-01

    This paper proposes a new repulsive Maglev vehicle which a superconducting linear synchronous motor (LSM) can levitate and propel simultaneously, independently of the vehicle speeds. The combined levitation and propulsion control is carried out by controlling mechanical-load angle and armature-current. Dynamic simulations show successful operations with good ride-quality by using a compact control method proposed here.

  2. Experiments on dynamic stiffness and damping of tapered bore seals

    NASA Technical Reports Server (NTRS)

    Fleming, David P.

    1987-01-01

    Stiffness and damping were measured in tapered bore ring seals with air as the sealed fluid. Excitation was provided by a known unbalance in the shaft which rotated in the test seals. Results were obtained for various seal supply pressures, clearances, unbalance amounts, and shaft speeds. Stiffness and damping varied little with unbalance level, indicating linearity of the seal. Greater variation was observed with speed and particularly supply pressure. A one-dimensional analysis predicted stiffness fairly well, but considerably overestimated damping.

  3. On Zero Stiffness

    E-print Network

    Schenk, Mark; Guest, Simon D.

    2013-11-17

    review by Ibrahim [18] covers a wide range of non-linear passive vibration isolators, including mechanical structures such as postbuckled beams, as well as magnetic quasi-zero stiffness systems [20]. For most vibration isolation applications, the use of a... Technical Conferences and Computers and Infor- mation in Engineering Conference (IDETC/CIE2009). DETC2009-87451. San Diego, California, USA; 2009. p. 313–323. [18] Ibrahim RA. Recent advances in nonlinear passive vibration isolators. Jour- nal of Sound...

  4. Stiffness Dependent Separation of Cells in a Microfluidic Device

    NASA Astrophysics Data System (ADS)

    Sulchek, Todd; Wang, Gonghao; Mao, Wenbin; Henegar, Caitlin; Alexeev, Alexander

    2012-02-01

    Abnormal cell mechanical stiffness can point to the development of various diseases including cancers and infections. We report a new high-throughput technique for continuous cell separation utilizing variation in cell stiffness. We use a microfluidic channel decorated by periodic diagonal ridges to separate K562 lymphoblastic cell line modified to different mechanical stiffness values. Diagonal ridges within the microfluidic flow channel compress and deform the cells in rapid succession to translate each cell perpendicular to the channel axis in proportion to its stiffness. Atomic force microscopy (AFM) was used to directly measure the Young's modulus of modified K562 cells to verify the stiffness variation. We demonstrate that soft cells can be separated from stiff cells at physiological concentrations with a fivefold enrichment of cell populations. This microfluidic device opens the way for conducting rapid and low-cost cell analysis and purification through physical markers.

  5. The human LSm1-7 proteins colocalize with the mRNA-degrading enzymes Dcp1/2 and Xrnl in distinct cytoplasmic foci.

    PubMed Central

    Ingelfinger, Dierk; Arndt-Jovin, Donna J; Lührmann, Reinhard; Achsel, Tilmann

    2002-01-01

    Sm and Sm-like (LSm) proteins form heptameric complexes that are involved in various steps of RNA metabolism. In yeast, the Lsm1-7 complex functions in mRNA degradation and is associated with several enzymes of this pathway, while the complex LSm2-8, the composition of which largely overlaps with that of LSm1-7, has a role in pre-mRNA splicing. A human gene encoding an LSm1 homolog has been identified, but its role in mRNA degradation has yet to be elucidated. We performed subcellular localization studies and found hLSm1 predominantly in the cytoplasm. However, it is not distributed evenly; rather, it is highly enriched in small, discrete foci. The endogenous hLSm4 is similarly localized, as are the overexpressed proteins hLSm1-7, but not hLSm8. The foci also contain two key factors in mRNA degradation, namely the decapping enzyme hDcp1/2 and the exonuclease hXrn1. Moreover, coexpression of wild-type and mutant LSm proteins, as well as fluorescence resonance energy transfer (FRET) studies, indicate that the mammalian proteins hLSm1-7 form a complex similar to the one found in yeast, and that complex formation is required for enrichment of the proteins in the cytoplasmic foci. Therefore, the foci contain a partially or fully assembled machinery for the degradation of mRNA. PMID:12515382

  6. Serum Mimecan Is Associated With Arterial Stiffness in Hypertensive Patients

    PubMed Central

    Gu, Xiaosong; Zhao, Liangping; Zhu, Jing; Gu, Haibo; Li, Hui; Wang, Luchen; Xu, Weiting; Chen, Jianchang

    2015-01-01

    Background Mimecan plays an important role in endothelial and vascular smooth muscle cell integrity and may be involved the pathology of arterial stiffness. However, the role of mimecan in arterial stiffness in patients with hypertension is not well defined. Methods and Results A total of 116 hypertension patients and 54 healthy controls were enrolled in the investigation. Hypertensive patients were divided into 2 groups: the with arterial stiffness group (brachial-ankle pulse wave velocity [baPWV] ?1400 cm/s; n=83) and the without arterial stiffness group (baPWV <1400 cm/s; n=33). A noninvasive measure of vascular stiffness was performed using pulse wave velocity (PWV) measurement of baPWV. Hypertensive patients had higher baPWV, mimecan, and endothelin 1 (ET-1) than healthy controls. The arterial stiffness group had higher mimecan and endothelin 1 (ET-1) and lower ankle-brachial pressure index (ABI) than those without stiffness. In hypertensive patients, mimecan was inversely correlated with ABI (P<0.05) and positively correlated with baPWV, ET-1, and total cholesterol. On multivariable logistic regression analysis, diastolic blood pressure, mimecan, ET-1, and creatinine were independent predictors of arterial stiffness in hypertensive patients (P<0.05). Conclusions Mimecan levels are higher in hypertensive patients than in healthy controls. Increased plasma mimecan levels are independently associated with increased arterial stiffness as assessed by baPWV. PMID:26206738

  7. NEM1 acts as a suppressor of apoptotic phenotypes in LSM4 yeast mutants.

    PubMed

    Palermo, Vanessa; Stirpe, Mariarita; Torella, Mirko; Falcone, Claudio; Mazzoni, Cristina

    2015-11-01

    Saccharomyces cerevisiae mutants in the essential gene LSM4, involved in messenger RNA decapping, and expressing a truncated form of the LSM4 gene of the yeast Kluyveromyces lactis (Kllsm4?1), show premature aging accompanied by the presence of typical markers of apoptosis and high sensitivity to oxidative stressing agents. We isolated multicopy extragenic suppressors of these defects, transforming the Kllsm4?1 mutant with a yeast DNA library and selecting clones showing resistance to acetic acid. Here we present one of these clones, carrying a DNA fragment containing the NEM1 gene (Nuclear Envelope Morphology protein 1), which encodes the catalytic subunit of the Nem1p-Spo7p phosphatase holoenzyme. Nem1p regulates nuclear growth by controlling phospholipid biosynthesis and it is required for normal nuclear envelope morphology and sporulation. The data presented here correlate the mRNA metabolism with the biosynthesis of phospholipids and with the functionality of the endoplasmic reticulum. PMID:26316593

  8. RESEARCH PAPER Stress-induced anisotropy in granular materials: fabric, stiffness,

    E-print Network

    Salzman, Daniel

    RESEARCH PAPER Stress-induced anisotropy in granular materials: fabric, stiffness, and permeability arrangement (fabric) and of the material's strength, incremental stiffness, and permeability. Thirteen measures of fabric anisotropy are developed, which are arranged in four categories: as preferred orien

  9. Running with a load increases leg stiffness.

    PubMed

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

    2015-04-13

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

  10. Development of engineering prototype of Life Support Module (LSM)

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The development of an engineering prototype of a life support system is discussed. The module consists of an electrocardiogram, a defibrillator, a resuscitator, and an aspirator, as well as body temperature and blood pressure measuring instruments. A drug kit is included.

  11. The compressive stiffness of human pediatric heads.

    PubMed

    Loyd, Andre Matthew; Nightingale, Roger W; Luck, Jason F; Song, Yin; Fronheiser, Lucy; Cutcliffe, Hattie; Myers, Barry S; Dale Bass, Cameron R

    2015-11-01

    Head injury is a persistent and costly problem for both children and adults. Globally, approximately 10 million people are hospitalized each year for head injuries. Knowing the structural properties of the head is important for modeling the response of the head in impact, and for providing insights into mechanisms of head injury. Hence, the goal of this study was to measure the sub-injurious structural stiffness of whole pediatric heads. 12 cadaveric pediatric (20-week-gestation to 16 years old) heads were tested in a battery of viscoelastic compression tests. The heads were compressed in both the lateral and anterior-posterior directions to 5% of gauge length at normalized deformation rates of 0.0005/s, 0.01/s, 0.1/s, and 0.3/s. Because of the non-linear nature of the response, linear regression models were used to calculate toe region (<2.5%) and elastic region (>2.5%) stiffness separately so that meaningful comparisons could be made across rate, age, and direction. The results showed that age was the dominant factor in predicting the structural stiffness of the human head. A large and statistically significant increase in the stiffness of both the toe region and the elastic region was observed with increasing age (p<0.0001), but no significant difference was seen across direction or normalized deformation rate. The stiffness of the elastic region increased from as low as 5N/mm in the neonate to >4500N/mm in the 16 year old. The changes in stiffness with age may be attributed to the disappearance of soft sutures and the thickening of skull bones with age. PMID:26476760

  12. Intra-abdominal pressure increases stiffness of the lumbar spine.

    PubMed

    Hodges, Paul W; Eriksson, A E Martin; Shirley, Debra; Gandevia, Simon C

    2005-09-01

    Intra-abdominal pressure (IAP) increases during many tasks and has been argued to increase stability and stiffness of the spine. Although several studies have shown a relationship between the IAP increase and spinal stability, it has been impossible to determine whether this augmentation of mechanical support for the spine is due to the increase in IAP or the abdominal muscle activity which contributes to it. The present study determined whether spinal stiffness increased when IAP increased without concurrent activity of the abdominal and back extensor muscles. A sustained increase in IAP was evoked by tetanic stimulation of the phrenic nerves either unilaterally or bilaterally at 20 Hz (for 5 s) via percutaneous electrodes in three subjects. Spinal stiffness was measured as the force required to displace an indentor over the L4 or L2 spinous process with the subjects lying prone. Stiffness was measured as the slope of the regression line fitted to the linear region of the force-displacement curve. Tetanic stimulation of the diaphragm increased IAP by 27-61% of a maximal voluntary pressure increase and increased the stiffness of the spine by 8-31% of resting levels. The increase in spinal stiffness was positively correlated with the size of the IAP increase. IAP increased stiffness at L2 and L4 level. The results of this study provide evidence that the stiffness of the lumbar spine is increased when IAP is elevated. PMID:16023475

  13. 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.

  14. Boundary Stiffness Regulates Fibroblast Behavior in Collagen Gels

    PubMed Central

    John, Jeffrey; Quinlan, Angela Throm; Silvestri, Chiara; Billiar, Kristen

    2010-01-01

    Recent studies have illustrated the profound dependence of cellular behavior on the stiffness of 2D culture substrates. The goal of this study was to develop a method to alter the stiffness cells experience in a standard 3D collagen gel model without affecting the physiochemical properties of the extracellular matrix. A device was developed utilizing compliant anchors (0.048–0.64 N m?1) to tune the boundary stiffness of suspended collagen gels in between the commonly utilized free and fixed conditions (zero and infinite stiffness boundary stiffness). We demonstrate the principle of operation with finite element analyses and a wide range of experimental studies. In all cases, boundary stiffness has a strong influence on cell behavior, most notably eliciting higher basal tension and activated force (in response to KCl) and more pronounced remodeling of the collagen matrix at higher boundary stiffness levels. Measured equibiaxial forces for gels seeded with 3 million human foreskin fibroblasts range from 0.05 to 1 mN increasing monotonically with boundary stiffness. Estimated force per cell ranges from 17 to 100 nN utilizing representative volume element analysis. This device provides a valuable tool to independently study the effect of the mechanical environment of the cell in a 3D collagen matrix. PMID:20012205

  15. Effect of Pressure on Liver Stiffness During the Development of Liver Fibrosis in Rabbits.

    PubMed

    Tang, Wen Bo; Xu, Qing Hua; Jiao, Zi Yu; Wu, Rong; Song, Qing; Luo, Yu Kun

    2016-01-01

    This study was designed to investigate whether hepatic arterial pressure and portal pressure have an effect on liver stiffness during the development of liver fibrosis. Liver fibrosis was induced in 50 healthy New Zealand white rabbits. Laparotomy was performed to measure liver stiffness, and the portal vein and hepatic artery were successively ligated to repeat the measurements. A significant difference was observed among liver stiffness values measured at different time points (F = 22.82, p < 0.001). Differences between original liver stiffness and liver stiffness measured after portal ligation were positively correlated with portal pressure (r = 0.801, p < 0.001). In animals with grade 4 liver fibrosis, the increase in liver stiffness caused by pressure was greater than that caused by extracellular matrix accumulation (p = 0.002). In conclusion, hepatic arterial pressure and portal pressure have a significant effect on liver stiffness during the development of liver fibrosis. PMID:26497767

  16. Dynamic Changes in LSM Nanoparticles on YSZ: A Model System for Non-stationary SOFC Cathode Behavior

    SciTech Connect

    Woo, L Y; Glass, R S; Gorte, R J; Orme, C A; Nelson, A J

    2009-01-05

    The interaction between nanoparticles of strontium-doped lanthanum manganite (LSM) and single crystal yttria-stabilized zirconia (YSZ) was investigated using atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM)/energy-dispersive x-ray spectroscopy (EDX). Nanoparticles of LSM were deposited directly onto single crystal YSZ substrates (100) using an ultrasonic spray nozzle. As samples were annealed from 850 C to 1250 C, nanoparticles gradually decreased in height and eventually disappeared completely. Subsequent reduction in H{sub 2}/H{sub 2}O at 700 C resulted in the reappearance of nanoparticles. Studies were carried out on identical regions of the sample allowing the same nanoparticles to be characterized at different temperatures. Morphological changes indicate the formation of a thin layer of LSM, and XPS results support the observation by indicating an increase in signal from the La and Sr and a decrease in signal from the Y and Zr with increasing temperature. SEM/EDX was used to verify that the nanoparticles in the reduced sample contained La. The changes in the LSM/YSZ morphology may be important in explaining the non-stationary behavior observed in operating fuel cells. The thin layer of LSM initially results in poor cathode performance; reducing conditions then lead to film disruptions, indicating nano/microporosity, that increase oxygen ion diffusion and performance.

  17. Experimental and theoretical rotordynamic stiffness coefficients for a three-stage brush seal

    NASA Astrophysics Data System (ADS)

    Pugachev, A. O.; Deckner, M.

    2012-08-01

    Experimental and theoretical results are presented for a multistage brush seal. Experimental stiffness is obtained from integrating circumferential pressure distribution measured in seal cavities. A CFD analysis is used to predict seal performance. Bristle packs are modeled by the porous medium approach. Leakage is predicted well by the CFD method. Theoretical stiffness coefficients are in reasonable agreement with the measurements. Experimental results are also compared with a three-teeth-on-stator labyrinth seal. The multistage brush seal gives about 60% leakage reduction over the labyrinth seal. Rotordynamic stiffness coefficients are also improved: the brush seal has positive direct stiffness and smaller cross-coupled stiffness.

  18. 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.

  19. 3D image registration is critical to ensure accurate detection of longitudinal changes in trabecular bone density, microstructure, and stiffness measurements in rat tibiae by in vivo microcomputed tomography (?CT).

    PubMed

    Lan, Shenghui; Luo, Shiming; Huh, Beom Kang; Chandra, Abhishek; Altman, Allison R; Qin, Ling; Liu, X Sherry

    2013-09-01

    In the recent decade, in vivo ?CT scanners have become available to monitor temporal changes in rodent bone in response to diseases and treatments. We investigated short-term and long-term precision of in vivo ?CT measurements of trabecular bone density, microstructure and stiffness of rat tibiae and tested whether they can be improved by 3D image registration. Rats in the short-term precision group underwent baseline and follow-up scans within the same day (n = 15) and those in the long-term precision group were scanned at day 0 and day 14 (n = 16) at 10.5 ?m voxel size. A 3D image-registration scheme was applied to register the trabecular bone compartments of baseline and follow-up scans. Prior to image registration, short-term precision ranged between 0.85% and 2.65% in bone volume fraction (BV/TV), trabecular number, thickness, and spacing (Tb.N*, Tb.Th*, Tb.Sp*), trabecular bone mineral density and tissue mineral density (Tb.BMD, and Tb.TMD), and was particularly high in structure model index (SMI), connectivity density (Conn.D), and stiffness (4.29%-8.83%). Image registration tended to improve the short-term precision, but the only statistically significant improvement was in Tb.N*, Tb.TMD, and stiffness. On the other hand, unregistered comparisons between day-0 and day-14 scans suggested significant increases in BV/TV, Tb.N*, Tb.Th*, Conn.D, and Tb.BMD and decrease in Tb.Sp* and SMI. However, the percent change in each parameter from registered comparisons was significantly different from unregistered comparisons. Registered results suggested a significant increase in BV/TV, Tb.BMD, and stiffness over 14 days, primarily caused by increased Tb.Th* and Tb.TMD. Due to the continuous growth of rodents, the direct comparisons between the unregistered baseline and follow-up scans were driven by changes due to global bone modeling instead of local remodeling. Our results suggested that 3D image registration is critical for detecting changes due to bone remodeling activities in rodent trabecular bone by in vivo ?CT imaging. PMID:23727434

  20. Switchable stiffness scanning microscope probe

    E-print Network

    Mueller-Falcke, Clemens T. (Clemens Tobias)

    2005-01-01

    Atomic Force Microscopy (AFM) has rapidly gained widespread utilization as an imaging device and micro/nano-manipulator during recent years. This thesis investigates the new concept of a dual stiffness scanning probe with ...

  1. Effect of ECM Stiffness on Integrin-Ligand Binding Strength

    NASA Astrophysics Data System (ADS)

    Thomas, Gawain; Wen, Qi

    2014-03-01

    Many studies have shown that cells respond to the stiffness of their extracellular matrix (ECM). However, the mechanism of this stiffness sensing is not fully understood. We believe that cells probe stiffness by applying intracellular force to the ECM via the integrin-mediated adhesions. The linkage of integrins to the cytoskeleton has been modeled as a slip clutch, which has been shown to affect focal adhesion formation and hence force transmission in a stiffness dependent manner. In contrast, the bonds between integrins and ECM have been characterized as ``catch bonds.'' It is unclear how ECM viscoelasticity affects these catch bonds. We report, for the first time, the effects of ECM stiffness on the binding strength of integrins to ECM ligands by measuring the rupture force of individual integrin-ligand bonds of cells on collagen-coated polyacrylamide gels. Results show that the integrin-collagen bonds of 3T3 fibroblasts are nearly four times stronger on a stiff (30 kPa) gel than on a soft (3 kPa) gel. The stronger integrin bonds on stiffer substrates can promote focal adhesion formation. This suggests that the substrate stiffness regulates the cell-ECM adhesions not only by affecting the cytoskeleton-integrin links but also by modulating the binding of integrins to the ECM.

  2. Microfinish As A Function Of Machine Stiffness

    NASA Astrophysics Data System (ADS)

    Watt, Gordon J.

    1987-01-01

    Stiffness of a machine must be known between the tip of the cutting tool and the surface being machined in order to correlate with microfinish. Signature of the machine tool and its environs are registered on the micro-machined surface. Imperfections are triggered by disturbances which may originate off the machine, from the machine, or by reaction between the tool and the workpiece. The machine transfer function is a complex mechanical system with many input points and resonance frequencies to be contended with. This paper deals with recognizable surface imperfections which are related back to mechanical parameters in and between the machine elements. To be complete, one must include spindles, slides, supports, vibration isolators, tool holders, tools, fixtures, and the workpiece itself. Their relation to sources of disturbance is discussed and examples are given of surface measurements made which identify the relation between machine stiffness and microfinish signatures.

  3. Impact of blood pressure perturbations on arterial stiffness.

    PubMed

    Lim, Jisok; Pearman, Miriam E; Park, Wonil; Alkatan, Mohammed; Machin, Daniel R; Tanaka, Hirofumi

    2015-12-15

    Although the associations between chronic levels of arterial stiffness and blood pressure (BP) have been fairly well studied, it is not clear whether and how much arterial stiffness is influenced by acute perturbations in BP. The primary aim of this study was to determine magnitudes of BP dependence of various measures of arterial stiffness during acute BP perturbation maneuvers. Fifty apparently healthy subjects, including 25 young (20-40 yr) and 25 older adults (60-80 yr), were studied. A variety of BP perturbations, including head-up tilt, head-down tilt, mental stress, isometric handgrip exercise, and cold pressor test, were used to encompass BP changes induced by physical, mental, and/or mechanical stimuli. When each index of arterial stiffness was plotted with mean BP, all arterial stiffness indices, including cardio-ankle vascular index or CAVI (r = 0.50), carotid-femoral pulse wave velocity or cfPWV (r = 0.51), brachial-ankle pulse wave velocity or baPWV (r = 0.61), arterial compliance (r = -0.42), elastic modulus (r = 0.52), arterial distensibility (r = -0.32), ?-stiffness index (r = 0.19), and Young's modulus (r = 0.35) were related to mean BP (all P < 0.01). Changes in CAVI, cfPWV, baPWV, and elastic modulus were significantly associated with changes in mean BP in the pooled conditions, while changes in arterial compliance, arterial distensibility, ?-stiffness index, and Young's modulus were not. In conclusion, this study demonstrated that BP changes in response to various forms of pressor stimuli were associated with the corresponding changes in arterial stiffness indices and that the strengths of associations with BP varied widely depending on what arterial stiffness indices were examined. PMID:26468262

  4. Effects of age and diabetes on scleral stiffness.

    PubMed

    Coudrillier, Baptiste; Pijanka, Jacek; Jefferys, Joan; Sorensen, Thomas; Quigley, Harry A; Boote, Craig; Nguyen, Thao D

    2015-07-01

    The effects of diabetes on the collagen structure and material properties of the sclera are unknown but may be important to elucidate whether diabetes is a risk factor for major ocular diseases such as glaucoma. This study provides a quantitative assessment of the changes in scleral stiffness and collagen fiber alignment associated with diabetes. Posterior scleral shells from five diabetic donors and seven non-diabetic donors were pressurized to 30?mm Hg. Three-dimensional surface displacements were calculated during inflation testing using digital image correlation (DIC). After testing, each specimen was subjected to wide-angle X-ray scattering (WAXS) measurements of its collagen organization. Specimen-specific finite element models of the posterior scleras were generated from the experimentally measured geometry. An inverse finite element analysis was developed to determine the material properties of the specimens, i.e., matrix and fiber stiffness, by matching DIC-measured and finite element predicted displacement fields. Effects of age and diabetes on the degree of fiber alignment, matrix and collagen fiber stiffness, and mechanical anisotropy were estimated using mixed effects models accounting for spatial autocorrelation. Older age was associated with a lower degree of fiber alignment and larger matrix stiffness for both diabetic and non-diabetic scleras. However, the age-related increase in matrix stiffness was 87% larger in diabetic specimens compared to non-diabetic controls and diabetic scleras had a significantly larger matrix stiffness (p?=?0.01). Older age was associated with a nearly significant increase in collagen fiber stiffness for diabetic specimens only (p?=?0.06), as well as a decrease in mechanical anisotropy for non-diabetic scleras only (p?=?0.04). The interaction between age and diabetes was not significant for all outcomes. This study suggests that the age-related increase in scleral stiffness is accelerated in eyes with diabetes, which may have important implications in glaucoma. PMID:25751456

  5. A Modification to the NOAH LSM to Simulate Heat Mitigation Strategies in the New York City Metropolitan Area

    E-print Network

    A Modification to the NOAH LSM to Simulate Heat Mitigation Strategies in the New York City (1968) observed the occurrence of the 1 Current affiliation: Weather It is, Ltd., Efrat, Israel, NY 10025. E-mail: barry-lynn@weather-it-is.com FEBRUARY 2009 L Y N N E T A L . 199 DOI: 10

  6. An Efficient Design and Implementation of LSM-Tree based Key-Value Store on Open-Channel SSD

    E-print Network

    Jiang, Song

    relational database systems. The log-structured merge tree (LSM-tree) based KV stores have attracted growing are widely deployed to support Internet-wide services. To store the ultra-large-scale data and service high-concurrent ac- cess, the use of traditional relational database management systems (RDBMS) as data storage may

  7. A bipolar functionality of Q/N-rich proteins: Lsm4 amyloid causes clearance of yeast prions

    PubMed Central

    Oishi, Keita; Kurahashi, Hiroshi; Pack, Chan-Gi; Sako, Yasushi; Nakamura, Yoshikazu

    2013-01-01

    Prions are epigenetic modifiers that cause partially loss-of-function phenotypes of the proteins in Saccharomyces cerevisiae. The molecular chaperone network that supports prion propagation in the cell has seen a great progress in the last decade. However, the cellular machinery to activate or deactivate the prion states remains an enigma, largely due to insufficient knowledge of prion-regulating factors. Here, we report that overexpression of a [PSI+]-inducible Q/N-rich protein, Lsm4, eliminates the three major prions [PSI+], [URE3], and [RNQ+]. Subcloning analysis revealed that the Q/N-rich region of Lsm4 is responsible for the prion loss. Lsm4 formed an amyloid in vivo, which seemed to play a crucial role in the prion elimination. Fluorescence correlation spectroscopy analysis revealed that in the course of the Lsm4-driven [PSI+] elimination, the [PSI+] aggregates undergo a size increase, which ultimately results in the formation of conspicuous foci in otherwise [psi?]-like mother cells. We also found that the antiprion activity is a general property of [PSI+]-inducible factors. These data provoked a novel “unified” model that explains both prion induction and elimination by a single scheme. PMID:23512891

  8. Theoretical analysis of Wolter/LSM x-ray telescope systems. Final report, 1 October 1984-26 May 1985

    SciTech Connect

    Shealy, D.L.; Chao, S.

    1985-05-01

    A ray tracing analysis has been performed for the spectral slicing zoom x-ray telescope for configurations in which a convex layered synthetic microstructure (LSM) optic is placed in front of the prime focus or a concave LSM optic is placed behind the prime focus. The analysis has considered the geometrical shape of the LSM optic to be either a hyperboloid, sphere, ellipsoid or constant optical path aspheric element for two configurations of the glancing incidence x-ray telescope: the ATM Experimental S-056 Wolter I system and the Stanford/MSFC Wolter-Schwarzchild nested system. For the different systems the RMS blur circle radii, the point spread function (PSF), the full width half maximum (FWHM) of the PSF have been evaluated as a function of field angle and magnification of the secondary to determine resolution of the system. The effects of decentration and tilt of the selected LSM element on the performance of the system have been studied to determine mounting and alignment tolerances.

  9. Positive Association Between Adipose Tissue and Bone Stiffness.

    PubMed

    Berg, R M; Wallaschofski, H; Nauck, M; Rettig, R; Markus, M R P; Laqua, R; Friedrich, N; Hannemann, A

    2015-07-01

    Obesity is often considered to have a protective effect against osteoporosis. On the other hand, several recent studies suggest that adipose tissue may have detrimental effects on bone quality. We therefore aimed to investigate the associations between body mass index (BMI), waist circumference (WC), visceral adipose tissue (VAT) or abdominal subcutaneous adipose tissue (SAT), and bone stiffness. The study involved 2685 German adults aged 20-79 years, who participated in either the second follow-up of the population-based Study of Health in Pomerania (SHIP-2) or the baseline examination of the SHIP-Trend cohort. VAT and abdominal SAT were quantified by magnetic resonance imaging. Bone stiffness was assessed by quantitative ultrasound (QUS) at the heel (Achilles InSight, GE Healthcare). The individual risk for osteoporotic fractures was determined based on the QUS-derived stiffness index and classified in low, medium, and high risk. Linear regression models, adjusted for sex, age, physical activity, smoking status, risky alcohol consumption, diabetes, and height (in models with VAT or abdominal SAT as exposure), revealed positive associations between BMI, WC, VAT or abdominal SAT, and the QUS variables broadband-ultrasound attenuation or stiffness index. Moreover, BMI was positively associated with speed of sound. Our study shows that all anthropometric measures including BMI and, WC as well as abdominal fat volume are positively associated with bone stiffness in the general population. As potential predictors of bone stiffness, VAT and abdominal SAT are not superior to easily available measures like BMI or WC. PMID:25929703

  10. Arterial Stiffness, Kidney Function, and Chronic Kidney Disease Progression

    PubMed Central

    Townsend, Raymond R.; Tomiyama, Hirofumi

    2013-01-01

    Arterial stiffness can nowadays be measured easily and noninvasively around the globe. Although well established as an independent predictor of cardiovascular events, less is known about the role of arterial stiffness in the progressive loss of kidney function once chronic kidney disease (CKD) is established. In addition to measures of arterial stiffness, a number of devices now noninvasively record the pulse profile from sites such as the radial artery and, using internal algorithms, are able to estimate central pressure profiles. Although these devices have generated much data on the prediction of cardiovascular events, e.g. measures of arterial stiffness, there is much less known about the predictive utility of these measures in CKD progression. In this review, we cover approaches to arterial stiffness as measured by pulse wave velocity and discuss measures of the systolic and diastolic contour of the pulse waveform vis-à-vis their relationship to declines in kidney function over time. We restrict our coverage to studies that have longitudinal data, but we also include a table of studies, which, to our knowledge, have only published cross-sectional data at this time.

  11. Rationale and study design of the Prospective comparison of Angiotensin Receptor neprilysin inhibitor with Angiotensin receptor blocker MEasuring arterial sTiffness in the eldERly (PARAMETER) study

    PubMed Central

    Williams, Bryan; Cockcroft, John R; Kario, Kazuomi; Zappe, Dion H; Cardenas, Pamela; Hester, Allen; Brunel, Patrick; Zhang, Jack

    2014-01-01

    Introduction Hypertension in elderly people is characterised by elevated systolic blood pressure (SBP) and increased pulse pressure (PP), which indicate large artery ageing and stiffness. LCZ696, a first-in-class angiotensin receptor neprilysin inhibitor (ARNI), is being developed to treat hypertension and heart failure. The Prospective comparison of Angiotensin Receptor neprilysin inhibitor with Angiotensin receptor blocker MEasuring arterial sTiffness in the eldERly (PARAMETER) study will assess the efficacy of LCZ696 versus olmesartan on aortic stiffness and central aortic haemodynamics. Methods and analysis In this 52-week multicentre study, patients with hypertension aged ?60?years with a mean sitting (ms) SBP ?150 to <180 and a PP>60?mm?Hg will be randomised to once daily LCZ696 200?mg or olmesartan 20?mg for 4?weeks, followed by a forced-titration to double the initial doses for the next 8?weeks. At 12–24?weeks, if the BP target has not been attained (msSBP <140? and ms diastolic BP <90?mm?Hg), amlodipine (2.5–5?mg) and subsequently hydrochlorothiazide (6.25–25?mg) can be added. The primary and secondary endpoints are changes from baseline in central aortic systolic pressure (CASP) and central aortic PP (CAPP) at week 12, respectively. Other secondary endpoints are the changes in CASP and CAPP at week 52. A sample size of 432 randomised patients is estimated to ensure a power of 90% to assess the superiority of LCZ696 over olmesartan at week 12 in the change from baseline of mean CASP, assuming an SD of 19?mm?Hg, the difference of 6.5?mm?Hg and a 15% dropout rate. The primary variable will be analysed using a two-way analysis of covariance. Ethics and dissemination The study was initiated in December 2012 and final results are expected in 2015. The results of this study will impact the design of future phase III studies assessing cardiovascular protection. Clinical trials identifier EUDract number 2012-002899-14 and ClinicalTrials.gov NCT01692301. PMID:24496699

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

    PubMed

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

    2015-07-01

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

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

    PubMed Central

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

    2015-01-01

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

  14. Accurate spring constant calibration for very stiff atomic force microscopy cantilevers

    SciTech Connect

    Grutzik, Scott J.; Zehnder, Alan T.; Gates, Richard S.; Gerbig, Yvonne B.; Smith, Douglas T.; Cook, Robert F.

    2013-11-15

    There are many atomic force microscopy (AFM) applications that rely on quantifying the force between the AFM cantilever tip and the sample. The AFM does not explicitly measure force, however, so in such cases knowledge of the cantilever stiffness is required. In most cases, the forces of interest are very small, thus compliant cantilevers are used. A number of methods have been developed that are well suited to measuring low stiffness values. However, in some cases a cantilever with much greater stiffness is required. Thus, a direct, traceable method for calibrating very stiff (approximately 200 N/m) cantilevers is presented here. The method uses an instrumented and calibrated nanoindenter to determine the stiffness of a reference cantilever. This reference cantilever is then used to measure the stiffness of a number of AFM test cantilevers. This method is shown to have much smaller uncertainty than previously proposed methods. An example application to fracture testing of nanoscale silicon beam specimens is included.

  15. Therapeutic modification of arterial stiffness: An update and comprehensive review

    PubMed Central

    Wu, Ching-Fen; Liu, Pang-Yen; Wu, Tsung-Jui; Hung, Yuan; Yang, Shih-Ping; Lin, Gen-Min

    2015-01-01

    Arterial stiffness has been recognized as a marker of cardiovascular disease and associated with long-term worse clinical outcomes in several populations. Age, hypertension, smoking, and dyslipidemia, known as traditional vascular risk factors, as well as diabetes, obesity, and systemic inflammation lead to both atherosclerosis and arterial stiffness. Targeting multiple modifiable risk factors has become the main therapeutic strategy to improve arterial stiffness in patients at high cardiovascular risk. Additionally to life style modifications, long-term ?-3 fatty acids (fish oil) supplementation in diet may improve arterial stiffness in the population with hypertension or metabolic syndrome. Pharmacological treatment such as renin-angiotensin-aldosterone system antagonists, metformin, and 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors were useful in individuals with hypertension and diabetes. In obese population with obstructive sleep apnea, weight reduction, aerobic exercise, and continuous positive airway pressure treatment may also improve arterial stiffness. In the populations with chronic inflammatory disease such as rheumatoid arthritis, a use of antibodies against tumor necrosis factor-alpha could work effectively. Other therapeutic options such as renal sympathetic nerve denervation for patients with resistant hypertension are investigated in many ongoing clinical trials. Therefore our comprehensive review provides knowledge in detail regarding many aspects of pathogenesis, measurement, and management of arterial stiffness in several populations, which would be helpful for physicians to make clinical decision. PMID:26635922

  16. Deletion of the Sm1 encoding motif in the lsm gene results in distinct changes in the transcriptome and enhanced swarming activity of Haloferax cells.

    PubMed

    Maier, Lisa-Katharina; Benz, Juliane; Fischer, Susan; Alstetter, Martina; Jaschinski, Katharina; Hilker, Rolf; Becker, Anke; Allers, Thorsten; Soppa, Jörg; Marchfelder, Anita

    2015-10-01

    Members of the Sm protein family are important for the cellular RNA metabolism in all three domains of life. The family includes archaeal and eukaryotic Lsm proteins, eukaryotic Sm proteins and archaeal and bacterial Hfq proteins. While several studies concerning the bacterial and eukaryotic family members have been published, little is known about the archaeal Lsm proteins. Although structures for several archaeal Lsm proteins have been solved already more than ten years ago, we still do not know much about their biological function, however one can confidently propose that the archaeal Lsm proteins will also be involved in RNA metabolism. Therefore, we investigated this protein in the halophilic archaeon Haloferax volcanii. The Haloferax genome encodes a single Lsm protein, the lsm gene overlaps and is co-transcribed with the gene for the ribosomal L37.eR protein. Here, we show that the reading frame of the lsm gene contains a promoter which regulates expression of the overlapping rpl37R gene. This rpl37R specific promoter ensures high expression of the rpl37R gene in exponential growth phase. To investigate the biological function of the Lsm protein we generated a lsm deletion mutant that had the coding sequence for the Sm1 motif removed but still contained the internal promoter for the downstream rpl37R gene. The transcriptome of this deletion mutant was compared to the wild type transcriptome, revealing that several genes are down-regulated and many genes are up-regulated in the deletion strain. Northern blot analyses confirmed down-regulation of two genes. In addition, the deletion strain showed a gain of function in swarming, in congruence with the up-regulation of transcripts encoding proteins required for motility. PMID:25754521

  17. Bending Stiffness of Multiwall Sandwich

    NASA Technical Reports Server (NTRS)

    Blosser, M. L.

    1983-01-01

    An analytical and experimental study was carried out to understand the extensional and flexural behavior of multiwall sandwich, a metallic insulation composed of alternate layers of flat and dimpled foil. The multiwall sandwich was structurally analyzed by using several simplifying assumptions combined with a finite element analysis. The simplifying assumptions made in this analysis were evaluated by bending and tensile tests. Test results validate the assumption that flat sheets in compression do not significantly contribute to the flexural stiffness of multiwall sandwich for the multiwall geometry tested. However, calculations show that thicker flat sheets may contribute significantly to bending stiffness and cannot be ignored. Results of this analytical approach compare well with test data; both show that the extensional stiffness of the dimpled sheet in he 0 deg direction is about 30 percent of that for a flat sheet, and that in the 45 deg direction, it is about 10 percent. The analytical and experimental multiwall bending stiffness showed good agreement for the particular geometry tested.

  18. Relative stiffness of flat conductor cables

    NASA Technical Reports Server (NTRS)

    Hankins, J. D.

    1976-01-01

    The measurement of the bending moment required to obtain a given deflection in short lengths of flat conductor cable (FCC) is presented in this report. Experimental data were taken on 10 different samples of FCC and normalized to express all bending moments (relative stiffness factor) in terms of a cable 5.1 cm (2.0 in.) in width. Data are presented in tabular and graphical form for the covenience of designers who may be interested in finding torques exerted on critical components by short lengths of FCC.

  19. Hydration Status Is Associated with Aortic Stiffness, but Not with Peripheral Arterial Stiffness, in Chronically Hemodialysed Patients

    PubMed Central

    Bia, Daniel; Galli, Cintia; Valtuille, Rodolfo; Zócalo, Yanina; Wray, Sandra A.; Armentano, Ricardo L.; Cabrera Fischer, Edmundo I.

    2015-01-01

    Background. Adequate fluid management could be essential to minimize high arterial stiffness observed in chronically hemodialyzed patients (CHP). Aim. To determine the association between body fluid status and central and peripheral arterial stiffness levels. Methods. Arterial stiffness was assessed in 65 CHP by measuring the pulse wave velocity (PWV) in a central arterial pathway (carotid-femoral) and in a peripheral pathway (carotid-brachial). A blood pressure-independent regional arterial stiffness index was calculated using PWV. Volume status was assessed by whole-body multiple-frequency bioimpedance. Patients were first observed as an entire group and then divided into three different fluid status-related groups: normal, overhydration, and dehydration groups. Results. Only carotid-femoral stiffness was positively associated (P < 0.05) with the hydration status evaluated through extracellular/intracellular fluid, extracellular/Total Body Fluid, and absolute and relative overhydration. Conclusion. Volume status and overload are associated with central, but not peripheral, arterial stiffness levels with independence of the blood pressure level, in CHP. PMID:26167301

  20. Multi-fingered haptic palpation utilizing granular jamming stiffness feedback actuators

    NASA Astrophysics Data System (ADS)

    Li, Min; Ranzani, Tommaso; Sareh, Sina; Seneviratne, Lakmal D.; Dasgupta, Prokar; Wurdemann, Helge A.; Althoefer, Kaspar

    2014-09-01

    This paper describes a multi-fingered haptic palpation method using stiffness feedback actuators for simulating tissue palpation procedures in traditional and in robot-assisted minimally invasive surgery. Soft tissue stiffness is simulated by changing the stiffness property of the actuator during palpation. For the first time, granular jamming and pneumatic air actuation are combined to realize stiffness modulation. The stiffness feedback actuator is validated by stiffness measurements in indentation tests and through stiffness discrimination based on a user study. According to the indentation test results, the introduction of a pneumatic chamber to granular jamming can amplify the stiffness variation range and reduce hysteresis of the actuator. The advantage of multi-fingered palpation using the proposed actuators is proven by the comparison of the results of the stiffness discrimination performance using two-fingered (sensitivity: 82.2%, specificity: 88.9%, positive predicative value: 80.0%, accuracy: 85.4%, time: 4.84 s) and single-fingered (sensitivity: 76.4%, specificity: 85.7%, positive predicative value: 75.3%, accuracy: 81.8%, time: 7.48 s) stiffness feedback.

  1. Stiffness threshold of randomly distributed carbon nanotube networks

    NASA Astrophysics Data System (ADS)

    Chen, Yuli; Pan, Fei; Guo, Zaoyang; Liu, Bin; Zhang, Jianyu

    2015-11-01

    For carbon nanotube (CNT) networks, with increasing network density, there may be sudden changes in the properties, such as the sudden change in electrical conductivity at the electrical percolation threshold. In this paper, the change in stiffness of the CNT networks is studied and especially the existence of stiffness threshold is revealed. Two critical network densities are found to divide the stiffness behavior into three stages: zero stiffness, bending dominated and stretching dominated stages. The first critical network density is a criterion to judge whether or not the network is capable of carrying load, defined as the stiffness threshold. The second critical network density is a criterion to measure whether or not most of the CNTs in network are utilized effectively to carry load, defined as bending-stretching transitional threshold. Based on the geometric probability analysis, a theoretical methodology is set up to predict the two thresholds and explain their underlying mechanisms. The stiffness threshold is revealed to be determined by the statical determinacy of CNTs in the network, and can be estimated quantitatively by the stabilization fraction of network, a newly proposed parameter in this paper. The other threshold, bending-stretching transitional threshold, which signs the conversion of dominant deformation mode, is verified to be well evaluated by the proposed defect fraction of network. According to the theoretical analysis as well as the numerical simulation, the average intersection number on each CNT is revealed as the only dominant factor for the electrical percolation and the stiffness thresholds, it is approximately 3.7 for electrical percolation threshold, and 5.2 for the stiffness threshold of 2D networks. For 3D networks, they are 1.4 and 4.4. And it also affects the bending-stretching transitional threshold, together with the CNT aspect ratio. The average intersection number divided by the fourth root of CNT aspect ratio is found to be an invariant at the bending-stretching transitional threshold, which is 6.7 and 6.3 for 2D and 3D networks, respectively. Based on this study, a simple piecewise expression is summarized to describe the relative stiffness of CNT networks, in which the relative stiffness of networks depends on the relative network density as well as the CNT aspect ratio. This formula provides a solid theoretical foundation for the design optimization and property prediction of CNT networks.

  2. Effect of surface stress on the stiffness of cantilever plates.

    PubMed

    Lachut, Michael J; Sader, John E

    2007-11-16

    Measurements over the past 30 years have indicated that surface stress can significantly affect the stiffness of microcantilever plates. Several one-dimensional models based on beam theory have been proposed to explain this phenomenon, but are found to be in violation of Newton's third law, in spite of their good agreement with measurements. In this Letter, we review this work and rigorously examine the effect of surface stress on the stiffness of cantilever plates using a full three-dimensional model. This study establishes the relationship between surface stress and cantilever stiffness, and in so doing elucidates its scaling behavior with cantilever dimensions. The use of short nanoscale cantilevers thus presents the most promising avenue for future investigations. PMID:18233163

  3. Simulating floodplain extent and inland water storage in the Amazon basin from a multi LSM perspective

    NASA Astrophysics Data System (ADS)

    Getirana, A.; Dutra, E. N.; Decharme, B.; Guimberteau, M.; Li, H.; Beaudoing, H.; Kam, J.; Toure, A. M.; Zhang, Z.; Drapeau, G.; Papa, F.; Kumar, S.; Peters-Lidard, C. D.; Balsamo, G.; Rodell, M.; Ronchail, J.; Sheffield, J.; Xue, Y.; Arsenault, K. R.

    2013-12-01

    Several modeling attempts have been conducted trying to improve the simulation of floods at several temporal and spatial scales worldwide. These attempts consider different modeling approaches and forcings, which can have a non-negligible impact on streamflows, inland water storage and floodplain extent. In the framework of the Global Land Water Cycle Benchmarking (GLWCB), the capability of simulating water and energy budgets by state-of-the-art land surface models (LSMs) and their impacts on predicting floods are evaluated. Fifteen LSMs were run for the 1980-2008 period using Princeton's meteorological forcings on a 3-hourly time step and at a 1° resolution. Three experiments are performed using Princeton's precipitation dataset rescaled to match monthly global GPCC and GPCP datasets and a daily dataset (HOP) specially developed for the basin. Surface and sub-surface runoffs derived from LSMs are used to force the Hydrological Modeling and Analysis Platform (HyMAP) river routing scheme (RRS) and simulated discharges are compared against observations at 146 gauges in the Amazon basin. Simulated floodplain extent and surface water storage are also compared against satellite-based products. Results show that simulated streamflows vary significantly as a function of both the LSM and precipitation used. It is also noted that floodplain extent is highly dependent on RRS parameters and further calibration must be performed.

  4. Visualizing the Structural Evolution of LSM/xYSZ Composite Cathodes for SOFC by in-situ Neutron Diffraction

    SciTech Connect

    Chen, Yan; Yang, Ling; Ren, Fei; An, Ke

    2014-01-01

    Composite cathodes for solid oxide fuel cells, the mixtures of (La0.8Sr0.2)0.95MnO3- (LSM) and (Y2O3)x(ZrO2)1-x (xYSZ, x = 3, 6, 8 and 10), have the thermal stability unraveled at elevated temperatures by using in-situ neutron diffraction. The Rietveld refinement analysis of neutron diffraction visualizes the phase evolutions and the ion activities in the material systems. The phase transition of tetragonal YSZ at T > 900 C leads to a heterogeneous redistribution of Mn ions. The reaction of LSM and YSZ occurring at T > 1100 C was revealed as a three-stage process, yielding La2Zr2O7, SrZrO3 and MnO. The activities of Y, Mn and La ions at elevated temperatures are derived by the structural analysis, and the three-stage reaction of YSZ and LSM was found strongly correlated to ions behaviors.

  5. Visualizing the Structural Evolution of LSM/xYSZ Composite Cathodes for SOFC by in-situ Neutron Diffraction

    PubMed Central

    Chen, Yan; Yang, Ling; Ren, Fei; An, Ke

    2014-01-01

    Thermal stability of composite cathodes for solid oxide fuel cells, the mixtures of (La0.8Sr0.2)0.95MnO3?? (LSM) and (Y2O3)x(ZrO2)1?x (xYSZ, x = 3, 6, 8 and 10), is determined using in-situ neutron diffraction. Thanks to the most advanced high flux neutron source, our work highlights the visualization of the phase evolutions in heterogeneous material systems at high temperatures, along with the analysis of the diffusion activities of transition metal ions that reveal the reaction mechanism and kinetics. It is found that the tetragonal-to-cubic phase transition in YSZ at T > 900°C leads to a heterogeneous redistribution of Mn ions. The subsequent reaction of LSM and YSZ occurring at T > 1100°C is revealed as a three-stage kinetic process, yielding La2Zr2O7, SrZrO3 and MnO. The diffusion activities of Y, Mn and La ions in the heterogeneous systems at elevated temperatures are derived by the structural analysis, and the three-stage reaction of YSZ and LSM is found strongly correlated to ions' behaviors as functions of temperature. PMID:24899139

  6. LV wall segmentation using the variational level set method (LSM) with additional shape constraint for oedema quantification

    NASA Astrophysics Data System (ADS)

    Kadir, K.; Gao, H.; Payne, A.; Soraghan, J.; Berry, C.

    2012-10-01

    In this paper an automatic algorithm for the left ventricle (LV) wall segmentation and oedema quantification from T2-weighted cardiac magnetic resonance (CMR) images is presented. The extent of myocardial oedema delineates the ischaemic area-at-risk (AAR) after myocardial infarction (MI). Since AAR can be used to estimate the amount of salvageable myocardial post-MI, oedema imaging has potential clinical utility in the management of acute MI patients. This paper presents a new scheme based on the variational level set method (LSM) with additional shape constraint for the segmentation of T2-weighted CMR image. In our approach, shape information of the myocardial wall is utilized to introduce a shape feature of the myocardial wall into the variational level set formulation. The performance of the method is tested using real CMR images (12 patients) and the results of the automatic system are compared to manual segmentation. The mean perpendicular distances between the automatic and manual LV wall boundaries are in the range of 1-2 mm. Bland-Altman analysis on LV wall area indicates there is no consistent bias as a function of LV wall area, with a mean bias of -121 mm2 between individual investigator one (IV1) and LSM, and -122 mm2 between individual investigator two (IV2) and LSM when compared to two investigators. Furthermore, the oedema quantification demonstrates good correlation when compared to an expert with an average error of 9.3% for 69 slices of short axis CMR image from 12 patients.

  7. Synchrotron based measurements of the soft x-ray performance of thin film multilayer structures

    SciTech Connect

    Kania, D.R.; Bartlett, R.J.; Trela, W.J.

    1985-01-01

    Using synchrotron radiation, measuring system has been developed to test the performance of layered synthetic microstructures (LSMs) from 50 to 500 eV. The measurement techniques are reviewed, and results are compared to theoretical predictions of LSM performance. (LEW)

  8. THE STIFFNESS OF THE FLAGELLA OF IMPALED BULL SPERM

    E-print Network

    Lindemann, Charles

    methylsulfonate, 0.163 M sucrose, 0.005 M magnesium sulfate, 2-5 uM calcium chloride, 0.007 M sodium lactate direct analytical treatment of the experimental system. The effects of external ATP and ADP were measured, 1971, 1972 a and c). The effect of ATP and ADP on stiffness is presently reported. METHODS Bull semen

  9. Modifiable Risk Factors for Increased Arterial Stiffness in Outpatient Nephrology

    PubMed Central

    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. PMID:25880081

  10. The differential effects of gender, anthropometry, and prior hormonal state on frontal plane knee joint stiffness

    PubMed Central

    Cammarata, Martha L.; Dhaher, Yasin Y.

    2012-01-01

    Background Gender differences in passive frontal plane knee stiffness may contribute to the increased anterior cruciate ligament injury rate in females. Gender-based stiffness differences have been attributed to anthropometric variations, but little data exist describing this relationship. Furthermore, sex hormone levels appear to influence joint stiffness, but the differential effects of instantaneous and prior hormonal concentrations remain unknown. This study sought to explore the effect of gender, prior hormonal status, and anthropometry on passive frontal plane knee joint stiffness. Methods Twelve males and 31 females participated. Females were grouped by hormonal contraceptive use (non users [n=11], monophasic contraceptive users [n=11], and triphasic contraceptive users [n=9]) and tested at the same point in the menstrual cycle. Subjects’ right knee was passively stretched ±7° in the frontal plane at 3°/s. Stiffness was estimated at three loading levels and normalized by body size to minimize anthropometric biases. A 4 (group) × 3 (load) repeated measures analysis of variance was performed for both raw and normalized stiffness. Linear regression analyses were preformed between stiffness estimates and knee diameter and quadriceps femoris angle. Findings Males displayed significantly greater (P<0.05) frontal plane stiffness than females. When normalized, males displayed significantly greater stiffness in valgus (P<0.05), but not varus (P>0.05) than females. No significant effect (P>0.05) of prior hormonal state was found; however, when normalized, varus stiffness was significantly less for triphasic contraceptive users than the other female groups (P<0.05). Quadriceps femoris angle was negatively correlated and knee diameter was positively correlated to knee stiffness. Interpretation Consistent with earlier in vitro findings, our data may indicate that ligament material properties are gender specific. A deficit in passive knee joint stiffness may place a larger burden on the neuromuscular system to resist frontal plane loading in females. PMID:18479791

  11. Comparison of a manual and motorized stiffness meter to quantify bone regeneration in distraction osteogenesis.

    PubMed

    Thorey, Fritz; Floerkemeier, Thilo; Wellmann, Matthias; Windhagen, Henning

    2009-01-01

    To assess bone healing and investigate the influence of different pharmaceutics (e.g. growth factors) on bone stiffness and strength in-vivo, new quantitative methods are necessary. Therefore, a new manual and motorized stiffness meter to quantify bone regeneration in a model of distraction osteogenesis were compared. The design, equipment, and improvements of the measurement devices are described. Furthermore, their difference in precision and accuracy in comparison to tests from a material testing system, used as "gold standard", were evaluated. Both devices were able to assess regenerate stiffness: the accuracy ranged between +/- 9% for the manual and +/-5% for the motorized version for stiffness data over 0.1 Nm/ degrees; precision between +/- 3.8% for the manual and +/- 3.2% for the motorized device. In summary, the two stiffness measurement devices described in this study have the power to monitor the beginning of bone healing and therefore predict the load bearing capacity of regenerating bone. The motorized version showed advantages over the manual device when investigating and monitoring the stiffness of bone during a consolidation period: (1) better accuracy in both stiffness below and above 0.1 Nm/ degrees, (2) a better precision in the stiffness range of interest, (3) easier handling, and (4) standardisation of the measurement process using the stepper motor and definition of the maximums of torque, angulation and rotation speed. PMID:20051616

  12. Rolling bearing stiffness in arbitrary direction

    NASA Astrophysics Data System (ADS)

    Luo, Zhusan; Sun, Xinde; Wu, Linfeng

    1992-06-01

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

  13. WAVE OF STIFFNESS PROPAGATING ALONG THE SURFACE OF THE NEWT EGG DURING CLEAVAGE

    PubMed Central

    Sawai, Tsuyoshi; Yoneda, Mitsuki

    1974-01-01

    In the eggs of the newt, Cynops (Triturus) pyrrhogaster, change in stiffness of the cortex was measured in various regions at the time of the cleavage. Measurements were performed by Mitchison and Swann's cell elastimeter method with a modification, in which two fine pipettes were attached to the surface of one egg at the same time, in order to compare the rigidity of two regions. The stiffness of the cortex changed very little before the start of the first cleavage. However, just before the appearance of the first cleavage furrow, the stiffness increased rapidly at the animal pole region, which later returned to the former level. As the cleavage furrow progressed, a wave of high stiffness travelled meridionally as a belt along the surface from the animal pole region toward the vegetal region. At second cleavage, the cycle of change in stiffness was repeated. PMID:4809240

  14. Experimental dynamic stiffness and damping of externally pressurized gas-lubricated journal bearings

    NASA Technical Reports Server (NTRS)

    Fleming, D. P.; Thayer, W. J.; Cunningham, R. E.

    1976-01-01

    A rigid vertical shaft was operated with known amounts of unbalance at speeds to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. The measured stiffness was proportional to the supply pressure, while damping was little affected by supply pressure. Damping dropped rapidly as the fractional frequency whirl threshold was approached. A small-eccentricity analysis overpredicted the stiffness by 20 to 70 percent. Predicted damping was lower than measured at low speeds but higher at high speeds.

  15. Passive Apaptive Damping for High Stiffness-low Mass Materials Incorporating Negative Stiffness Elements 

    E-print Network

    Cha, Gene

    2013-11-07

    High stiffness / low mass materials or structures reduce structure weight in transportation, but show little inherent damping. A new composite material that exhibits high stiffness and high damping might reduce issues with ...

  16. Diagnosis of GLDAS LSM based aridity index and dryland identification for socioeconomic aspect of water resources management

    NASA Astrophysics Data System (ADS)

    Ghazanfari, S.; Pande, S.; Hashemy, M.; Naseri M., M.

    2012-04-01

    Water resources scarcity plays an important role in socioeconomic aspect of livelihood pattern in dryland areas. Hydrological perspective of aridity is required for social and economic coping Strategies. Identification of dryland areas is crucial to guide policy aimed at intervening in water stressed areas and addressing its perennial livelihood or food insecurity. Yet, prevailing aridity indices are beset with methodological limitations that restrict their use in delineating drylands and, might be insuffient for decision making frameworks. Palmer's Drought Severity index (PDSI) reports relative soil moisture deviations from long term means, which does not allow cross comparisons, while UNEP's aridity index, the ratio of annual evaporative demand to rainfall supply, ignores site specific soil and vegetation characteristics that are needed for appropriate water balance assessment. We propose to refine UNEP's aridity index by accounting for site specific soil and vegetation to partition precipitation into competing demands of evaporation and runoff. We create three aridity indices at a 1 x 1 degree spatial resolution based on 3 decades of soil moisture time series from three GLDAS Land Surface Models (LSM's): VIC, MOSAIC and NOAH. We compare each LSM model aridity map with the UNEP aridity map which was created based on LSM data forcing. Our approach is to extract the first Eigen function from Empirical Orthogonal Function (EOF) analysis that represents the dominant spatial template of soil moisture conditions of the three LSM's. Frequency of non-exceedence of this dominant soil moisture mode for a location by all other locations is used as our proposed aridity index. The EOF analysis reveals that the first Eigen function explains, respectively, 33%, 43% and 47% of the VIC, NOAH and MOSAIC models. The temporal coefficients associated with the first OF (Orthogonal Function) for all three LSMS clearly show seasonality with a discrete jump in trend around the year 1999 for NOAH and MOSAIC. The VIC aridity index displays a pattern most closely resembling that of UNEP though all LSM based indices isolate dominant dryland areas, correctly. The UNEP classification identifies some parts of south central Africa, southeast United States and eastern India as drier than all LSMs. NOAH and MOSAIC categorize parts of SouthWestern Africa drier than the other two classifications, while all LSMs classify parts of central India wetter than the UNEP classification. We find long term average NDVI values showing vegetation cover in areas that UNEP classifies drier than other three LSMs. Finally, based on unsupervised clustering of global land surface based on long term mean temperature and precipitation, soil texture and land slope, areas classified as dry by UNEP but wet by LSMs have relatively wet characteristics while areas classified as wet by UNEP but dry by LSMs have dry characteristics. We conclude that LSM based aridity index identifies dryland areas other than UNEP aridity index since the former also incorporates the role of vegetation and soil in partitioning of precipitation into evaporation, runoff and infiltration.

  17. Impact of Irrigation Methods on LSM Spinup and Initialization of WRF Forecasts

    NASA Astrophysics Data System (ADS)

    Lawston, P.; Santanello, J. A.; Zaitchik, B. F.; Beaudoing, H.

    2013-12-01

    In the United States, irrigation represents the largest consumption of fresh water and accounts for approximately one-third of all water usage. Irrigation has been shown to modify local hydrology and regional climate through a repartitioning of water at the surface and through the atmosphere, and can in some cases drastically change the terrestrial energy budget in agricultural areas during the growing season. Vegetation cover and soil moisture primarily control water and energy fluxes from the surface so accurate representation of the land surface characteristics is key to determining and predicting atmospheric conditions. This study utilizes NASA's Land Information System (LIS) and the NASA Unified Weather Research and Forecasting (NU-WRF) model to investigate changes in land-atmosphere interactions resulting from drip, flood, and sprinkler irrigation methods. The study area encompasses a 500 km x 600 km region of the Central Great Plains including portions of Nebraska, Kansas, Iowa, and Missouri. This area provides a steep irrigation gradient, as much of the western region is heavily irrigated while minimal irrigation occurs in the eastern section. Five-year irrigated LIS spinups were used to initialize two-day, 1-km WRF forecasts. Two forecast periods were chosen, one in a drier than normal year (2006) and one in a wetter than normal year (2008) to evaluate the sensitivity of the irrigation approaches and impacts to the background climate conditions. The offline and coupled simulation results show that both LIS spinups and NU-WRF forecasts are sensitive to irrigation and irrigation methods, as exhibited by significant changes to temperature, soil moisture, boundary layer height, and the partitioning of latent and sensible heat fluxes. Dry year impacts are greater than those in the wet year suggesting that the magnitude of these changes is dependent on the existing precipitation regime. Sprinkler and flood irrigation schemes impact the NU-WRF forecast the most, while drip irrigation has a comparatively small effect. Evaluation of the irrigation schemes using observations of soil moisture, fluxes, and meteorological state variables shows that a realistic characterization of the land surface in terms of land cover classification, soil type, and soil moisture anomalies via a LSM spinup are critical to producing a proper simulation of irrigation in land surface and coupled models.

  18. 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

  19. A novel cell-stiffness-fingerprinting analysis by scanning atomic force microscopy: comparison of fibroblasts and diverse cancer cell lines.

    PubMed

    Zoellner, Hans; Paknejad, Navid; Manova, Katia; Moore, Malcolm A S

    2015-12-01

    Differing stimuli affect cell stiffness while cancer metastasis is associated with reduced cell stiffness. Cell stiffness determined by atomic force microscopy has been limited by measurement over nuclei to avoid spurious substratum effects in thin cytoplasmic domains, and we sought to develop a more complete approach including cytoplasmic areas. Ninety ?m square fields were recorded from ten separate sites of cultured human dermal fibroblasts (HDF) and three sites each for melanoma (MM39, WM175, and MeIRMu), osteosarcoma (SAOS-2 and U2OS), and ovarian carcinoma (COLO316 and PEO4) cell lines, each site providing 1024 measurements as 32 × 32 square grids. Stiffness recorded below 0.8 ?m height was occasionally influenced by substratum, so only stiffness recorded above 0.8 ?m was analysed, but all sites were included for height and volume analysis. COLO316 had the lowest cell height and volume, followed by HDF (p < 0.0001) and then PEO4, SAOS-2, MeIRMu, WM175, U2OS, and MM39. HDF were more stiff than all other cells (p < 0.0001), while in descending order of stiffness were PEO4, COLO316, WM175, SAOS-2, U2OS, MM39, and MeIRMu (p < 0.02). Stiffness fingerprints comprised scattergrams of stiffness values plotted against the height at which each stiffness value was recorded and appeared unique for each cell type studied, although in most cases the overall form of fingerprints was similar, with maximum stiffness at low height measurements and a second lower peak occurring at high-height levels. We suggest that our stiffness-fingerprint analytical method provides a more nuanced description than previously reported and will facilitate study of the stiffness response to cell stimulation. PMID:26357955

  20. Relative stiffness of flat-conductor cable

    NASA Technical Reports Server (NTRS)

    Hankins, J. D.

    1977-01-01

    Bending moment data were taken on ten different cable samples and normalized to express all stiffness factors in terms of cable 5.1 cm in width. Relative stiffness data and nominal physical characteristics are tabulated and presented in graphical form for designers who may be interested in finding torques exerted on critical components by short lengths of cable.

  1. 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.

  2. Spontaneous wrinkle branching by gradient stiffness

    NASA Astrophysics Data System (ADS)

    Ni, Yong; Yang, Dong; He, Linghui

    2012-09-01

    The concept of coherency loss is proposed to understand wrinkle branching as a pathway toward hierarchical wrinkling pattern formation in a compressed film-substrate system with gradient stiffness of the film or substrate. A simple model indicates that the wrinkle branching arises when the characteristic length of the stiffness inhomogeneity zone is larger than the coherency persistent length, which depends on the amplitude of the stiffness inhomogeneity. Numerical simulations of nonlinear wrinkles based on the model of the Föppl-von Kármán plate on compliant substrates show how regulating the size and amplitude of the stiffness inhomogeneities results in branched wrinkles in striking agreement with the existing observations. The paper reveals the origin of such kinds of branched wrinkles and may provide a guideline for controllable hierarchical wrinkles by patterning the stiffness gradient.

  3. Spontaneous wrinkle branching by gradient stiffness.

    PubMed

    Ni, Yong; Yang, Dong; He, Linghui

    2012-09-01

    The concept of coherency loss is proposed to understand wrinkle branching as a pathway toward hierarchical wrinkling pattern formation in a compressed film-substrate system with gradient stiffness of the film or substrate. A simple model indicates that the wrinkle branching arises when the characteristic length of the stiffness inhomogeneity zone is larger than the coherency persistent length, which depends on the amplitude of the stiffness inhomogeneity. Numerical simulations of nonlinear wrinkles based on the model of the Föppl-von Kármán plate on compliant substrates show how regulating the size and amplitude of the stiffness inhomogeneities results in branched wrinkles in striking agreement with the existing observations. The paper reveals the origin of such kinds of branched wrinkles and may provide a guideline for controllable hierarchical wrinkles by patterning the stiffness gradient. PMID:23030926

  4. Non-cross-bridge calcium-dependent stiffness in frog muscle fibers.

    PubMed

    Bagni, M A; Colombini, B; Geiger, P; Berlinguer Palmini, R; Cecchi, G

    2004-06-01

    At the end of the force transient elicited by a fast stretch applied to an activated frog muscle fiber, the force settles to a steady level exceeding the isometric level preceding the stretch. We showed previously that this excess of tension, referred to as "static tension," is due to the elongation of some elastic sarcomere structure, outside the cross bridges. The stiffness of this structure, "static stiffness," increased upon stimulation following a time course well distinct from tension and roughly similar to intracellular Ca(2+) concentration. In the experiments reported here, we investigated the possible role of Ca(2+) in static stiffness by comparing static stiffness measurements in the presence of Ca(2+) release inhibitors (D600, Dantrolene, (2)H(2)O) and cross-bridge formation inhibitors [2,3-butanedione monoxime (BDM), hypertonicity]. Both series of agents inhibited tension; however, only D600, Dantrolene, and (2)H(2)O decreased at the same time static stiffness, whereas BDM and hypertonicity left static stiffness unaltered. These results indicate that Ca(2+), in addition to promoting cross-bridge formation, increases the stiffness of an (unidentified) elastic structure of the sarcomere. This stiffness increase may help in maintaining the sarcomere length uniformity under conditions of instability. PMID:14749216

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

    PubMed

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

    1999-05-01

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

  6. The effects of isometric and isotonic training on hamstring stiffness and anterior cruciate ligament loading mechanisms.

    PubMed

    Blackburn, J Troy; Norcross, Marc F

    2014-02-01

    Greater hamstring musculotendinous stiffness is associated with lesser ACL loading mechanisms. Stiffness is enhanced via training, but previous investigations evaluated tendon rather than musculotendinous stiffness, and none involved the hamstrings. We evaluated the effects of isometric and isotonic training on hamstring stiffness and ACL loading mechanisms. Thirty-six healthy volunteers were randomly assigned to isometric, isotonic, and control groups. Isometric and isotonic groups completed 6 weeks of training designed to enhance hamstring stiffness. Stiffness, anterior tibial translation, and landing biomechanics were measured prior to and following the interventions. Hamstring stiffness increased significantly with isometric training (15.7%; p=0.006), but not in the isotonic (13.5%; p=0.089) or control (0.4%; p=0.942) groups. ACL loading mechanisms changed in manners consistent with lesser loading, but these changes were not statistically significant. These findings suggest that isometric training may be an important addition to ACL injury prevention programs. The lack of significant changes in ACL loading mechanisms and effects of isotonic training were likely due to the small sample sizes per group and limited intervention duration. Future research using larger sample sizes and longer interventions is necessary to determine the effects of enhancing hamstring stiffness on ACL loading and injury risk. PMID:24268874

  7. The difference between stiffness and quasi-stiffness in the context of biomechanical modeling.

    PubMed

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

    2013-02-01

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

  8. Investigation on Prototype Superconducting Linear Synchronous Motor (LSM) for 600-km/h Wheel-Type Railway

    NASA Astrophysics Data System (ADS)

    Eom, Beomyong; Lee, Changhyeong; Kim, Seokho; Lee, Changyoung; Yun, Sangwon

    The existing wheel-type high-speed railway with a rotatable motor has a limit of 600 km/h speed. The normal conducting electromagnet has several disadvantages to realize 600 km/h speed. Several disadvantages are the increased space and weight, and the decreased electric efficiency to generate the required high magnetic field. In order to reduce the volume and weight, superconducting electromagnets can be considered for LSM (Linear Synchronous Motor). Prior to the fabrication of the real system, a prototype demo-coil is designed and fabricated using 2G high temperature superconducting wire. The prototype HTS coil is cooled by the conduction using a GM cryocooler. To reduce the heat penetration, thermal design was performed for the current leads, supporting structure and radiation shield considering the thermal stress. The operating temperature and current are 30?40 K and 100 A. The coil consists of two double pancake coils (N, S pole, respectively) and it is driven on a test rail, which is installed for the test car. This paper describes the design and test results of the prototype HTS LSM system. Thermal characteristics are investigated with additional dummy thermal mass on the coil after turning off the cryocooler.

  9. Association between arterial stiffness and variations in estrogen-related genes

    E-print Network

    Peter, Inga

    Increased arterial stiffness and wave reflection have been identified as cardiovascular disease risk factors. In light of significant sex differences and the moderate heritability of vascular function measures, we hypothesized ...

  10. Stiff Coatings on Compliant Biofibers

    PubMed Central

    Holten-Andersen, Niels; Zhao, Hua; Waite, J. Herbert

    2009-01-01

    For lasting holdfast attachment, the mussel Mytilus californianus coats its byssal threads with a protective cuticle 2-5 ?m thick that is 4-6 times stiffer than the underlying collagen fibers. Although cuticle hardness (0.1 GPa) and stiffness (2 GPa) resemble those observed in related mussels, a more effective dispersion of microdamage enables M. californianus byssal threads to sustain strains to almost 120% before cuticle rupture occurs. Underlying factors for the superior damage tolerance of the byssal cuticle were explored in its microarchitecture and in the cuticular protein, mcfp-1. Cuticle microstructure was distinctly granular, with granule diameters (?200 nm) only a quarter of those in M. galloprovincialis cuticle, for example. Compared with homologous proteins in related mussel species, mcfp-1 from M. californianus had a similar mass (?92 kDa) and number of tandemly repeated decapeptides, and contained the same post-translational modifications, namely, trans-4-hydroxyproline, trans-2,3-cis-3,4-dihydroxyproline, and 3,4-dihydroxyphenylalanine (Dopa). The prominence of isoleucine in mcfp-1, however, distinguished it from homologues in other species. The complete protein sequence deduced from cDNAs for two related variants revealed a highly conserved consensus decapeptide PKISYPPTYK that is repeated 64 times and differs slightly from the consensus peptide (AKPSYPPTYK) of both M. galloprovincialis and M. edulis proteins. PMID:19220048

  11. Stiffness analysis for the micromagnetic standard problem No. 4

    SciTech Connect

    Tsiantos, Vassilios D.; Suess, Dieter; Schrefl, Thomas; Fidler, Josef

    2001-06-01

    In this article solutions to micromagnetic standard problem No. 4, a 500-nm{times}125-nm-wide NiFe film, are presented. A three-dimensional-finite element simulation based on the solution of the Gilbert equation has been used. The simulations show that two different reversal mechanisms occur for the two different applied fields. For a field at 170{degree} counterclockwise from the saturation direction there is a nonuniform rotation of magnetization towards the direction of the applied field, with the magnetization at the ends rotating faster than the magnetization in the center. For a field at 190{degree} counterclockwise from the saturation direction the magnetization at the ends and in the center rotate in opposite directions leading to the formation of a 360{degree} wall after 0.22 ns associated with a peak in the exchange energy. Moreover, the time for the magnetization component parallel to the long axis to cross the zero is 0.136 and 0.135 ns for field 1 and field 2, respectively. The stiffness of the problem has been investigated solving the system of ordinary differential equations with a nonstiff method (Adams) and a stiff one (backward differentiation formula, BDF). For the measure of stiffness the ratio of the total number of time steps (nst) taken by the two solvers, that is nst(Adams)/nst(BDF), has been used. This ratio is 0.784 for field 1 and 0.593 for field 2, which means that the nonstiff method (Adams) uses larger time steps than the stiff method (BDF) and consequently the systems are not stiff. The average time step for the Adams method was 0.2 ps for both fields. {copyright} 2001 American Institute of Physics.

  12. An acoustic startle alters knee joint stiffness and neuromuscular control.

    PubMed

    DeAngelis, A I; Needle, A R; Kaminski, T W; Royer, T R; Knight, C A; Swanik, C B

    2015-08-01

    Growing evidence suggests that the nervous system contributes to non-contact knee ligament injury, but limited evidence has measured the effect of extrinsic events on joint stability. Following unanticipated events, the startle reflex leads to universal stiffening of the limbs, but no studies have investigated how an acoustic startle influences knee stiffness and muscle activation during a dynamic knee perturbation. Thirty-six individuals were tested for knee stiffness and muscle activation of the quadriceps and hamstrings. Subjects were seated and instructed to resist a 40-degree knee flexion perturbation from a relaxed state. During some trials, an acoustic startle (50?ms, 1000?Hz, 100?dB) was applied 100?ms prior to the perturbation. Knee stiffness, muscle amplitude, and timing were quantified across time, muscle, and startle conditions. The acoustic startle increased short-range (no startle: 0.044?±?0.011?N·m/deg/kg; average startle: 0.047?±?0.01?N·m/deg/kg) and total knee stiffness (no startle: 0.036?±?0.01?N·m/deg/kg; first startle 0.027?±?0.02?N·m/deg/kg). Additionally, the startle contributed to decreased [vastus medialis (VM): 13.76?±?33.6%; vastus lateralis (VL): 6.72?±?37.4%] but earlier (VM: 0.133?±?0.17?s; VL: 0.124?±?0.17?s) activation of the quadriceps muscles. The results of this study indicate that the startle response can significantly disrupt knee stiffness regulation required to maintain joint stability. Further studies should explore the role of unanticipated events on unintentional injury. PMID:25212407

  13. High air-bearing stiffness slider design

    NASA Astrophysics Data System (ADS)

    Han, Y. F.; Liu, B.; Huang, X. Y.

    2006-08-01

    This paper discusses the approach to design air bearing surface (ABS), which can achieve high air bearing (AB) stiffness and high air pressure (AP). Generally, in order to reduce flying height variation and improve the slider's flying stability, high AB stiffness and high AP are preferred. AB stiffness and AP is very sensitive to the slider's ABS design. The flying height and flying attitude of slider is realized by ABS design. According to our study, flying stability of slider is also affected by ABS design. The slider has higher AB stiffness and higher air pressure; it is going to fly more stable. [E.M. Jayson, J. Murphy, P.W. Smith, F.E. Talke. J. Tribol. 125 (2003) 343; W.C. Choi, Y.H. Shin, J.H. Choi. JSME Int. J. 44 (2001) 470.] In order to increase highly the AB stiffness and AP, a dual shallow step structure in a slider is explored. It proved that the dual shallow step structure-increases the air bearing stiffness and the AP on the head area significantly. The structure of central trailing pad is found to have much higher influences on the AB stiffness and AP than the other pads. Optimizing the structure of central trailing pad in the dual shallow step structure slider can further increase the AB stiffness and AP. Finally, the optimized dual shallow step structure slider has much higher AB stiffness and much greater AP on the head area than the normal single shallow step slider. Therefore, the flying stability of the slider with optimized dual shallow step structure should be better.

  14. Evidence That Breast Tissue Stiffness Is Associated with Risk of Breast Cancer

    PubMed Central

    Boyd, Norman F.; Li, Qing; Melnichouk, Olga; Huszti, Ella; Martin, Lisa J.; Gunasekara, Anoma; Mawdsley, Gord; Yaffe, Martin J.; Minkin, Salomon

    2014-01-01

    Background Evidence from animal models shows that tissue stiffness increases the invasion and progression of cancers, including mammary cancer. We here use measurements of the volume and the projected area of the compressed breast during mammography to derive estimates of breast tissue stiffness and examine the relationship of stiffness to risk of breast cancer. Methods Mammograms were used to measure the volume and projected areas of total and radiologically dense breast tissue in the unaffected breasts of 362 women with newly diagnosed breast cancer (cases) and 656 women of the same age who did not have breast cancer (controls). Measures of breast tissue volume and the projected area of the compressed breast during mammography were used to calculate the deformation of the breast during compression and, with the recorded compression force, to estimate the stiffness of breast tissue. Stiffness was compared in cases and controls, and associations with breast cancer risk examined after adjustment for other risk factors. Results After adjustment for percent mammographic density by area measurements, and other risk factors, our estimate of breast tissue stiffness was significantly associated with breast cancer (odds ratio?=?1.21, 95% confidence interval?=?1.03, 1.43, p?=?0.02) and improved breast cancer risk prediction in models with percent mammographic density, by both area and volume measurements. Conclusion An estimate of breast tissue stiffness was associated with breast cancer risk and improved risk prediction based on mammographic measures and other risk factors. Stiffness may provide an additional mechanism by which breast tissue composition is associated with risk of breast cancer and merits examination using more direct methods of measurement. PMID:25010427

  15. Steady-state stiffness of utricular hair cells depends on macular location and hair bundle structure

    PubMed Central

    Spoon, Corrie; Moravec, W. J.; Rowe, M. H.; Grant, J. W.

    2011-01-01

    Spatial and temporal properties of head movement are encoded by vestibular hair cells in the inner ear. One of the most striking features of these receptors is the orderly structural variation in their mechanoreceptive hair bundles, but the functional significance of this diversity is poorly understood. We tested the hypothesis that hair bundle structure is a significant contributor to hair bundle mechanics by comparing structure and steady-state stiffness of 73 hair bundles at varying locations on the utricular macula. Our first major finding is that stiffness of utricular hair bundles varies systematically with macular locus. Stiffness values are highest in the striola, near the line of hair bundle polarity reversal, and decline exponentially toward the medial extrastriola. Striolar bundles are significantly more stiff than those in medial (median: 8.9 ?N/m) and lateral (2.0 ?N/m) extrastriolae. Within the striola, bundle stiffness is greatest in zone 2 (106.4 ?N/m), a band of type II hair cells, and significantly less in zone 3 (30.6 ?N/m), which contains the only type I hair cells in the macula. Bathing bundles in media that break interciliary links produced changes in bundle stiffness with predictable time course and magnitude, suggesting that links were intact in our standard media and contributed normally to bundle stiffness during measurements. Our second major finding is that bundle structure is a significant predictor of steady-state stiffness: the heights of kinocilia and the tallest stereocilia are the most important determinants of bundle stiffness. Our results suggest 1) a functional interpretation of bundle height variability in vertebrate vestibular organs, 2) a role for the striola in detecting onset of head movement, and 3) the hypothesis that differences in bundle stiffness contribute to diversity in afferent response dynamics. PMID:21918003

  16. 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(?l) 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 ? = 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 ?F(?l) were made during transient states where inertia and dumping forces are likely to affect the final result. PMID:23952196

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

    PubMed Central

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

    2015-01-01

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

  18. The viscoelastic stiffness model of seismicity

    NASA Technical Reports Server (NTRS)

    Cohen, S. C.

    1978-01-01

    A viscoelastic stiffness model of seismicity is developed by introducing a viscoelastic element into the stiffness model for fault dynamics. The introduction of this element permits modeling of transient anelastic deformations in response to stress loading and relaxation and provides a mechanism for partial stress recovery following an earthquake. As a consequence, several phenomena not present in elastic stiffness theory emerge. These include postseismic creep, foreshocks, and aftershocks. Numerical simulations of fault motion also reveal episodes of stable sliding, tertiary creep preceeding earthquakes, and long-term aseismic creep.

  19. 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.

  20. Stiffness map of the grasping contact areas of the human hand.

    PubMed

    Pérez-González, Antonio; Vergara, Margarita; Sancho-Bru, Joaquin L

    2013-10-18

    The elasticity and damping of the soft tissues of the hand contribute to dexterity while grasping and also help to stabilise the objects in manipulation tasks. Although some previous works have studied the force-displacement response of the fingertips, the responses in all other regions of the hand that usually participate in grasping have not been analysed to date. In this work we performed experimental measurements in 20 subjects to obtain a stiffness map of the different grasping contact areas of the human hand. A force-displacement apparatus was used to simultaneously measure force and displacement at 39 different points on the hand at six levels of force ranging from 1N to 6N. A non-linear force-displacement response was found for all points, with stiffness increasing with the amount of force applied. Mean stiffness for the different points and force levels was within the range from 0.2N/mm to 7.7N/mm. However, the stiffness range and variation with level of force were found to be different from point to point. A total of 13 regions with similar stiffness behaviours were identified. The stiffness in the fingertips increased linearly with the amount of force applied, while in the palm it remained more constant for the range of forces considered. It is hypothesised that the differences in the stiffness behaviour from one region to another allow these regions to play different roles during grasping. PMID:24063886

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

    PubMed Central

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

    2013-01-01

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

  2. Clinical Significance of Pre-Transplant Arterial Stiffness and the Impact of Kidney Transplantation on Arterial Stiffness

    PubMed Central

    Kim, Hyun Seon; Seung, Jaeho; Lee, Ju Hyun; Chung, Byung Ha; Yang, Chul Woo

    2015-01-01

    Background Arterial stiffness is closely associated with cardiovascular disease (CVD) in end stage renal disease (ESRD) patients. However, the clinical significance of pre-transplant arterial stiffness and the impact of kidney transplantation (KT) on arterial stiffness have not yet been determined. Method We measured the brachial-ankle pulse wave velocity (baPWV) before KT and one year after KT. We evaluated the potential utility of pre-transplant baPWV as a screening test to predict CVD. The impact of KT on progression of arterial stiffness was evaluated according to changes in baPWV after KT. The factors that influence the change of baPWV after KT were also examined. Result The mean value of pre-transplant baPWV was 1508 ± 300 cm/s in ESRD patients; 93.4% had a higher baPWV value than healthy controls. Pre-transplant baPWV was higher in patients with CVD than in those without CVD (1800 ± 440 vs. 1491 ± 265 cm/s, p<0.05), and was a strong predictive factor of CVD (OR 1.003, p<0.05). The optimal cut-off value of baPWV for the detection of CVD was 1591 cm/s, and this value was an independent predictor of CVD in KT recipients (OR 6.3, p<0.05). The post-transplant baPWV was significantly decreased compared to that of pre-transplant rates (1418 ± 235 vs. 1517 ± 293 cm/s, p<0.05), and progression of arterial stiffness was not observed in 86.9% patients. Logistic regression analysis revealed that higher body mass index and the degree of increase in calcium levels were independent risk factors that affected baPWV after KT. Conclusions Evaluation of arterial stiffness with baPWV is a useful screening test for predicting CVD after KT, and KT is effective in preventing the progression of arterial stiffness in ESRD patients. PMID:26406607

  3. Experimental procedure for the evaluation of tooth stiffness in spline coupling including angular misalignment

    NASA Astrophysics Data System (ADS)

    Curà, Francesca; Mura, Andrea

    2013-11-01

    Tooth stiffness is a very important parameter in studying both static and dynamic behaviour of spline couplings and gears. Many works concerning tooth stiffness calculation are available in the literature, but experimental results are very rare, above all considering spline couplings. In this work experimental values of spline coupling tooth stiffness have been obtained by means of a special hexapod measuring device. Experimental results have been compared with the corresponding theoretical and numerical ones. Also the effect of angular misalignments between hub and shaft has been investigated in the experimental planning.

  4. Vascular stiffness in insulin resistance and obesity

    PubMed Central

    Jia, Guanghong; Aroor, Annayya R.; DeMarco, Vincent G.; Martinez-Lemus, Luis A.; Meininger, Gerald A.; Sowers, James R.

    2015-01-01

    Obesity, insulin resistance, and type 2 diabetes are associated with a substantially increased prevalence of vascular fibrosis and stiffness, with attendant increased risk of cardiovascular and chronic kidney disease. Although the underlying mechanisms and mediators of vascular stiffness are not well understood, accumulating evidence supports the role of metabolic and immune dysregulation related to increased adiposity, activation of the renin angiotensin aldosterone system, reduced bioavailable nitric oxide, increased vascular extracellular matrix (ECM) and ECM remodeling in the pathogenesis of vascular stiffness. This review will give a brief overview of the relationship between obesity, insulin resistance and increased vascular stiffness to provide a contemporary understanding of the proposed underlying mechanisms and potential therapeutic strategies. PMID:26321962

  5. 49 CFR 213.359 - Track stiffness.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 2011-10-01 2011-10-01 false Track stiffness. 213.359 Section 213.359...ADMINISTRATION, DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track...

  6. 49 CFR 213.359 - Track stiffness.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 2010-10-01 2010-10-01 false Track stiffness. 213.359 Section 213.359...ADMINISTRATION, DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track...

  7. Programmable variable stiffness 2D surface design

    NASA Astrophysics Data System (ADS)

    Trabia, Sarah; Hwang, Taeseon; Yim, Woosoon

    2014-03-01

    Variable stiffness features can contribute to many engineering applications ranging from robotic joints to shock and vibration mitigation. In addition, variable stiffness can be used in the tactile feedback to provide the sense of touch to the user. A key component in the proposed device is the Biased Magnetorheological Elastomer (B-MRE) where iron particles within the elastomer compound develop a dipole interaction energy. A novel feature of this device is to introduce a field induced shear modulus bias via a permanent magnet which provides an offset with a current input to the electromagnetic control coil to change the compliance or modulus of a base elastomer in both directions (softer or harder). The B-MRE units can lead to the design of a variable stiffness surface. In this preliminary work, both computational and experimental results of the B-MRE are presented along with a preliminary design of the programmable variable stiffness surface design.

  8. Long Sleep Duration Associated With a Higher Risk of Increased Arterial Stiffness in Males

    PubMed Central

    Tsai, Tsai-Chen; Wu, Jin-Shang; Yang, Yi-Ching; Huang, Ying-Hsiang; Lu, Feng-Hwa; Chang, Chih-Jen

    2014-01-01

    Study Objectives: We aimed to examine the association between sleep duration and arterial stiffness among adults of different ages, because to date there has been only one study on this relationship, which was confined to middle-aged civil servants. Design: Cross-sectional study. Setting: A health examination center in National Cheng Kung University Hospital, Taiwan. Participants: A total of 3,508 subjects, age 20–87 y, were enrolled after excluding those with a history of cerebrovascular events, coronary artery disease, peripheral artery disease, and taking lipid-lowering drugs, antihypertensives, hypoglycemic agents, and anti-inflammatory drugs, from October 2006 to August 2009. Interventions: N/A. Measurements and Results: Sleep duration was classified into three groups: short (< 6 h), normal (6–8 h) and long (> 8 h). Arterial stiffness was measured by brachial-ankle pulse-wave velocity (baPWV), and increased arterial stiffness was defined as baPWV ? 1400 cm/sec. The sleep duration was different for subjects with and without increased arterial stiffness in males, but not in females. In the multivariate analysis for males, long sleepers (odds ratio [OR] 1.75, P = 0.034) but not short sleepers (OR 0.98, P = 0.92) had a higher risk of increased arterial stiffness. In addition, age, estimated glomerular filtration rate, hypertension, diabetes, total cholesterol/high-density lipoprotein cholesterol ratio, cigarette smoking, and exercise were also independently associated factors. However, in females, neither short nor long sleep duration was associated with increased arterial stiffness. Conclusions: Long sleep duration was associated with a higher risk of increased arterial stiffness in males. Short sleepers did not exhibit a significant risk of increased arterial stiffness in either sex. Citation: Tsai TC, Wu JS, Yang YC, Huang YH, Lu FH, Chang CJ. Long sleep duration associated with a higher risk of increased arterial stiffness in males. SLEEP 2014;37(8):1315-1320. PMID:25083011

  9. An analysis of traction drive torsional stiffness

    NASA Technical Reports Server (NTRS)

    Rohn, D. A.; Loewenthal, S. H.

    1983-01-01

    The tangential compliance of elastic bodies in concentrated contact applied to traction drive elements to determine their torsional stiffness was analyzed. Static loading and rotating conditions are considered. The effects of several design variables are shown. The theoretical torsional stiffness of a fixed ratio multiroller drive is computed and compared to experimental values. It is shown that the torsional compliance of the traction contacts themselves is a relatively small portion of the overall drive system compliance.

  10. Proceedings of the 2012 Workshop on Language in Social Media (LSM 2012), pages 918, Montreal, Canada, June 7, 2012. c 2012 Association for Computational Linguistics

    E-print Network

    to interaction effects. 1 Introduction Many people today deal with depression, post- traumatic stress disorderProceedings of the 2012 Workshop on Language in Social Media (LSM 2012), pages 9­18, Montr-distressed Affect States in Short Forum Texts Michael Thaul Lehrman Cecilia Ovesdotter Alm Rubén A. Proaño Rochester

  11. Fluid damping and fluid stiffness of tube arrays in crossflow

    SciTech Connect

    Chen, S.S.; Zhu, S.; Jendrzejczyk, J.A.

    1994-06-01

    Motion-dependent fluid forces acting on a tube array were measured as a function of excitation frequency, excitation amplitude, and flow velocity. Fluid-damping and fluid-stiffness coefficients were obtained from measured motion-dependent fluid forces as a function of reduced flow velocity and excitation amplitude. The water channel and test setup provide a sound facility for obtaining key coefficients for fluidelastic instability of tube arrays in crossflow. Once the motion-dependent fluid-force coefficients have been measured, a reliable design guideline, based on the unsteady flow theory, can be developed for fluidelastic instability of tube arrays in crossflow.

  12. Quantifying Parameter Sensitivity, Interaction and Transferability in Hydrologically Enhanced Versions of Noah-LSM over Transition Zones

    NASA Technical Reports Server (NTRS)

    Rosero, Enrique; Yang, Zong-Liang; Wagener, Thorsten; Gulden, Lindsey E.; Yatheendradas, Soni; Niu, Guo-Yue

    2009-01-01

    We use sensitivity analysis to identify the parameters that are most responsible for shaping land surface model (LSM) simulations and to understand the complex interactions in three versions of the Noah LSM: the standard version (STD), a version enhanced with a simple groundwater module (GW), and version augmented by a dynamic phenology module (DV). We use warm season, high-frequency, near-surface states and turbulent fluxes collected over nine sites in the US Southern Great Plains. We quantify changes in the pattern of sensitive parameters, the amount and nature of the interaction between parameters, and the covariance structure of the distribution of behavioral parameter sets. Using Sobol s total and first-order sensitivity indexes, we show that very few parameters directly control the variance of the model output. Significant parameter interaction occurs so that not only the optimal parameter values differ between models, but the relationships between parameters change. GW decreases parameter interaction and appears to improve model realism, especially at wetter sites. DV increases parameter interaction and decreases identifiability, implying it is overparameterized and/or underconstrained. A case study at a wet site shows GW has two functional modes: one that mimics STD and a second in which GW improves model function by decoupling direct evaporation and baseflow. Unsupervised classification of the posterior distributions of behavioral parameter sets cannot group similar sites based solely on soil or vegetation type, helping to explain why transferability between sites and models is not straightforward. This evidence suggests a priori assignment of parameters should also consider climatic differences.

  13. Effect of heat treatment on stiffness and damping of Sic/Ti-15-3

    NASA Technical Reports Server (NTRS)

    Grady, Joseph E.; Lerch, Bradley A.

    1992-01-01

    The effect of heat treatment on material properties of Sic/Ti-15-3 was measured by vibration tests. Heat treatment changes the microstructure, which stiffens the matrix and reduces its damping capacity. Test results illustrate how the changes in matrix material affect the stiffness and damping properties of the composite. Damping was found to be more sensitive than stiffness to microstructural changes in the matrix. Effects of heat treatment temperature and exposure time are presented.

  14. IEEE JOURNAL OF OCEANIC ENGINEERING, VOL. 31, NO. 1, JANUARY 2006 87 Middle-Ear Stiffness of the Bottlenose Dolphin

    E-print Network

    of the Bottlenose Dolphin Tursiops truncatus Brian S. Miller, Aleks L. Zosuls, Darlene R. Ketten, and David C was to measure the middle-ear stiffness for the bottlenose dolphin (Tursiops truncatus), a species specialized-ear stiffness in ten dolphin ears was 1.37 N m, which is considerably higher than that reported for most

  15. Spectral analysis of irregular roughness artifacts measured by atomic force microscopy and laser scanning microscopy.

    PubMed

    Chen, Yuhang; Luo, Tingting; Ma, Chengfu; Huang, Wenhao; Gao, Sitian

    2014-12-01

    Atomic force microscopy (AFM) and laser scanning microscopy (LSM) measurements on a series of specially designed roughness artifacts were performed and the results characterized by spectral analysis. As demonstrated by comparisons, both AFM and LSM can image the complex structures with high resolution and fidelity. When the surface autocorrelation length increases from 200 to 500 nm, the cumulative power spectral density spectra of the design, AFM and LSM data reach a better agreement with each other. The critical wavelength of AFM characterization is smaller than that of LSM, and the gap between the measured and designed critical wavelengths is reduced with an increase in the surface autocorrelation length. Topography measurements of surfaces with a near zero or negatively skewed height distribution were determined to be accurate. However, obvious discrepancies were found for surfaces with a positive skewness owing to more severe dilations of either the solid tip of the AFM or the laser tip of the LSM. Further surface parameter evaluation and template matching analysis verified that the main distortions in AFM measurements are tip dilations while those in LSM are generally larger and more complex. PMID:25339140

  16. Development of a variable stiffness spring for adaptive vibration isolators

    NASA Astrophysics Data System (ADS)

    Cronje, Johan M.; Heyns, P. S.; Theron, Nico J.; Loveday, Philip W.

    2004-07-01

    Variable stiffness springs allow vibration absorbers and isolators to adapt to changing operating conditions. This paper describes the development of such a spring. The spring was a compound leaf spring and variable stiffness was achieved by separating the two leaf springs using a wax actuator. In the selected design, each spring consisted of an outer (220mm in diameter) and an inner ring connected by three radial beams. A paraffin wax actuator was chosen to affect the separation of the leaf springs. This actuator consisted of a small copper cup containing paraffin wax. When the wax is heated, it changes from a solid to a liquid with an associated volume change that is used to drive an output shaft. A hot-air gun was used to heat and cool the wax actuator. It was found that the wax actuator could produce an 8mm separation of the springs, which increased the stiffness of the spring by 2.7 times, exceeding the typical requirement for adaptive absorbers and isolators. The loss factor, of the variable stiffness spring, was less than 0.12. The measured response times for the open-loop system were 82s and 109s for heating and cooling respectively. A linear sliding potentiometer was used to measure the spring separation and proportional and derivative feedback control was used to control the current supplied to the heating element thus reducing the response time to less than 30s for small step changes. Further improvement in response time could be achieved by more directly heating and cooling of the paraffin wax in the actuator.

  17. Empirical Investigations A Stiffness Discrimination Experiment Including Analysis of Palpation

    E-print Network

    Williams II, Robert L.

    stiffness discrimination between multiple objects. (Sim Healthcare 5:000­000, 2010) Key Words: StiffnessEmpirical Investigations A Stiffness Discrimination Experiment Including Analysis of Palpation discrimination program to train and test users in finding subtle differences in human tissue stiffness

  18. Effects of the decellularization method on the local stiffness of acellular lungs.

    PubMed

    Melo, Esther; Garreta, Elena; Luque, Tomas; Cortiella, Joaquin; Nichols, Joan; Navajas, Daniel; Farré, Ramon

    2014-05-01

    Lung bioengineering, a novel approach to obtain organs potentially available for transplantation, is based on decellularizing donor lungs and seeding natural scaffolds with stem cells. Various physicochemical protocols have been used to decellularize lungs, and their performance has been evaluated in terms of efficient decellularization and matrix preservation. No data are available, however, on the effect of different decellularization procedures on the local stiffness of the acellular lung. This information is important since stem cells directly sense the rigidity of the local site they are engrafting to during recellularization, and it has been shown that substrate stiffness modulates cell fate into different phenotypes. The aim of this study was to assess the effects of the decellularization procedure on the inhomogeneous local stiffness of the acellular lung on five different sites: alveolar septa, alveolar junctions, pleura, and vessels' tunica intima and tunica adventitia. Local matrix stiffness was measured by computing Young's modulus with atomic force microscopy after decellularizing the lungs of 36 healthy rats (Sprague-Dawley, male, 250-300 g) with four different protocols with/without perfusion through the lung circulatory system and using two different detergents (sodium dodecyl sulfate [SDS] and 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate [CHAPS]). The local stiffness of the acellular lung matrix significantly depended on the site within the matrix (p<0.001), ranging from ? 15 kPa at the alveolar septum to ? 60 kPa at the tunica intima. Acellular lung stiffness (p=0.003) depended significantly, albeit modestly, on the decellularization process. Whereas perfusion did not induce any significant differences in stiffness, the use of CHAPS resulted in a ? 35% reduction compared with SDS, the influence of the detergent being more important in the tunica intima. In conclusion, lung matrix stiffness is considerably inhomogeneous, and conventional decellularization procedures do not result in substantially different local stiffness in the acellular lung. PMID:24083889

  19. The influence of bearing stiffness on the vibration properties of statically overdetermined gearboxes

    NASA Astrophysics Data System (ADS)

    Razpotnik, M.; Bischof, T.; Boltežar, M.

    2015-09-01

    In the design process of every modern car, the appropriate acoustic behaviour of each integral part is of great importance. This is particularly so for gearboxes. The stiffness of a rolling-element bearing is one of the main contributors to the transmission of vibrations from the interior of the gearbox to the housing. Many methods have been proposed to determine the bearing stiffness; this stiffness is related to the load in a nonlinear way. In this article, a new method for defining the proper bearing stiffness of statically overdetermined gearboxes is proposed. To achieve this an iterative process is conducted, with an initial guess for the loads on the bearings, which provides the initial values for their stiffnesses. The calculated stiffnesses are then inserted into a finite element method (FEM) model of a gearbox, where the new load vectors on the bearings are calculated. The described process runs until the convergence of the loads on the bearings is reached. Afterwards, the frequency-response functions (FRFs) are numerically calculated. As a reference point for our calculations, the measured FRFs are obtained. The measurements were performed on a simple, but statically overdetermined, gearbox with the option for moment adjustments between the two shafts. The calculated results in the form of FRFs are compared with the measurements.

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

    PubMed

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

    2015-04-13

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

  1. 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

  2. The cross-sectional association of sitting time with carotid artery stiffness in young adults

    PubMed Central

    Huynh, Quan L; Blizzard, Christopher L; Sharman, James E; Magnussen, Costan G; Dwyer, Terence; Venn, Alison J

    2014-01-01

    Objectives Physical activity is negatively associated with arterial stiffness. However, the relationship between sedentary behaviour and arterial stiffness is poorly understood. In this study, we aimed to investigate the association of sedentary behaviour with arterial stiffness among young adults. Design Cross-sectional. Setting 34 study clinics across Australia during 2004–2006. Participants 2328 participants (49.4% male) aged 26–36?years who were followed up from a nationally representative sample of Australian schoolchildren in 1985. Measurements Arterial stiffness was measured by carotid ultrasound. Sitting time per weekday and weekend day, and physical activity were self-reported by questionnaire. Cardiorespiratory fitness was estimated as physical work capacity at a heart rate of 170?bpm. Anthropometry, blood pressure, resting heart rate and blood biochemistry were measured. Potential confounders, including strength training, education, smoking, diet, alcohol consumption and parity, were self-reported. Rank correlation was used for analysis. Results Sitting time per weekend day, but not per weekday, was correlated with arterial stiffness (males r=0.11 p<0.01, females r=0.08, p<0.05) and cardiorespiratory fitness (males r?=??0.14, females r?=??0.08, p<0.05), and also with fatness and resting heart rate. One additional hour of sitting per weekend day was associated with 5.6% (males p=0.046) and 8.6% (females p=0.05) higher risk of having metabolic syndrome. These associations were independent of physical activity and other potential confounders. The association of sitting time per weekend day with arterial stiffness was not mediated by resting heart rate, fatness or metabolic syndrome. Conclusions Our study demonstrates a positive association of sitting time with arterial stiffness. The greater role of sitting time per weekend day in prediction of arterial stiffness and cardiometabolic risk than that of sitting time per weekday may be due to better reflection of discretionary sitting behaviour. PMID:24604484

  3. Conformational Analysis of Stiff Chiral Polymers with End-Constraints

    PubMed Central

    Kim, Jin Seob; Chirikjian, Gregory S.

    2010-01-01

    We present a Lie-group-theoretic method for the kinematic and dynamic analysis of chiral semi-flexible polymers with end constraints. The first is to determine the minimum energy conformations of semi-flexible polymers with end constraints, and the second is to perform normal mode analysis based on the determined minimum energy conformations. In this paper, we use concepts from the theory of Lie groups and principles of variational calculus to model such polymers as inextensible or extensible chiral elastic rods with coupling between twisting and bending stiffnesses, and/or between twisting and extension stiffnesses. This method is general enough to include any stiffness and chirality parameters in the context of elastic filament models with the quadratic elastic potential energy function. As an application of this formulation, the analysis of DNA conformations is discussed. We demonstrate our method with examples of DNA conformations in which topological properties such as writhe, twist, and linking number are calculated from the results of the proposed method. Given these minimum energy conformations, we describe how to perform the normal mode analysis. The results presented here build both on recent experimental work in which DNA mechanical properties have been measured, and theoretical work in which the mechanics of non-chiral elastic rods has been studied. PMID:20198114

  4. Normalized stiffness ratios for mechanical characterization of isotropic acoustic foams.

    PubMed

    Sahraoui, Sohbi; Brouard, Bruno; Benyahia, Lazhar; Parmentier, Damien; Geslain, Alan

    2013-12-01

    This paper presents a method for the mechanical characterization of isotropic foams at low frequency. The objective of this study is to determine the Young's modulus, the Poisson's ratio, and the loss factor of commercially available foam plates. The method is applied on porous samples having square and circular sections. The main idea of this work is to perform quasi-static compression tests of a single foam sample followed by two juxtaposed samples having the same dimensions. The load and displacement measurements lead to a direct extraction of the elastic constants by means of normalized stiffness and normalized stiffness ratio which depend on Poisson's ratio and shape factor. The normalized stiffness is calculated by the finite element method for different Poisson ratios. The no-slip boundary conditions imposed by the loading rigid plates create interfaces with a complex strain distribution. Beforehand, compression tests were performed by means of a standard tensile machine in order to determine the appropriate pre-compression rate for quasi-static tests. PMID:25669274

  5. Stiffness Control of a Continuum Manipulator in Contact with a Soft Environment

    PubMed Central

    Mahvash, Mohsen; Dupont, Pierre E.

    2010-01-01

    Stiffness control of a continuum robot can prevent excessive contact forces during robot navigation inside delicate, uncertain and confined environments. Furthermore, it enables the selection of tip stiffnesses that match varying task requirements. This paper introduces a computationally-efficient approach to continuum-robot stiffness control that is based on writing the forward kinematic model as the product of two transformations. The first transformation calculates the non-contact kinematics of the robot and can be formulated based on the specific type of continuum robot under consideration. The second transformation calculates the tip deflection due to applied forces and is efficiently computed using the special Cosserat rod model. To implement a desired tip stiffness, the two transformations are used to solve for the actuator positions that deform the manipulator so as to generate the required tip force at the measured tip position. The efficacy of the proposed controller is demonstrated experimentally on a concentric-tube continuum robot. PMID:21399719

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  7. Quantification of Myocardial Stiffness using Magnetic Resonance Elastography in Right Ventricular Hypertrophy: Initial Feasibility in Dogs

    PubMed Central

    da Silveira, Juliana S; Scansen, Brian A; Wassenaar, Peter A; Raterman, Brian; Eleswarpu, Chethan; Jin, Ning; Mo, Xiaokui; White, Richard D; Bonagura, John D; Kolipaka, Arunark

    2015-01-01

    Introduction Myocardial stiffness is an important determinant of cardiac function and is currently invasively and indirectly assessed by catheter angiography. This study aims to demonstrate the feasibility of quantifying right ventricular (RV) stiffness noninvasively using cardiac magnetic resonance elastography (CMRE) in dogs with severe congenital pulmonary valve stenosis (PVS) causing RV hypertrophy, and compare it to remote myocardium in the left ventricle (LV). Additionally, correlations between stiffness and selected pathophysiologic indicators from transthoracic echocardiography (TTE) and cardiac magnetic resonance imaging were explored. Methods In-vivo CMRE was performed on nine dogs presenting severe congenital PVS using a 1.5T MRI scanner. T1-MOLLI, T2-prepared-bSSFP, gated-cine GRE-MRE and LGE (PSIR) sequences were used to acquire a basal short-axis slice. RV and LV-free-wall (FW) stiffness measurements were compared against each other and also correlated to ventricular mass, RV and LV FW thickness, T1 and T2 relaxation times, and extracellular volume fraction (ECV). Peak transpulmonary pressure gradient and myocardial strain were also acquired on eight dogs by TTE and correlated to RV-FW systolic stiffness. Potential correlations were evaluated by Spearman’s rho (rs). Results RV-FW stiffness was found to be significantly higher than the LV-FW stiffness both during end-systole (ES) (p=0.002) and end-diastole (ED) (p=0.029). Significant correlations were observed between RV-FW ES and LV-FW ED stiffness versus ECV (rs=0.75; p-value=0.05). Non-significant moderate correlations were found between LV-FW ES (rs=0.54) and RV-FW ED (rs=0.61) versus ECV. Furthermore, non-significant correlations were found between RV or LV-FW stiffness and the remaining variables (rs<0.54; p-value>0.05). Conclusion This study demonstrates the feasibility of determining RV stiffness. The positive correlations between stiffness and ECV might indicate some interdependence between stiffness and myocardial extracellular matrix alterations. However, further studies are warranted to validate our initial observations. PMID:26471513

  8. A new strategy for stiffness evaluation of sheet metal parts

    NASA Astrophysics Data System (ADS)

    Cai, Q.; Volk, W.; Düster, A.; Rank, E.

    2011-08-01

    In the automotive industry, surfaces of styling models are shaped very often in physical models. For example, in the styling process of a car body important design work is realized by clay models and the resulting geometry information typically comes from optical scans. The scanned data is given in the form of point clouds which is then utilized in the virtual planning process for engineering work, e.g. to evaluate the load-carrying capacity. This is an important measure for the stiffness of the car body panels. In this contribution, the following two issues are discussed: what is the suitable geometric representation of the stiffness of the car body and how it is computed if only discrete point clouds exist. In the first part, the suitable geometric representation is identified by constructing continuous CAD models with different geometric parameters, e.g. Gaussian curvature and mean curvature. The stiffness of models is then computed in LS-DYNA and the influence of different geometric parameters is presented based on the simulation result. In the second part, the point clouds from scanned data, rather than continuous CAD models, are directly utilized to estimate the Gaussian curvature, which is normally derived from continuous surfaces. The discrete Gauss-Bonnet algorithm is applied to estimate the Gaussian curvature of the point clouds and the sensitivity of the algorithm with respect to the mesh quality is analyzed. In this way, the stiffness evaluation process in an early stage can be accelerated since the transformation from discrete data to continuous CAD data is labor-intensive. The discrete Gauss-Bonnet algorithm is finally applied to a sheet metal model of the BMW 3 series.

  9. Effect of metatarsal phalangeal joint extension on plantar soft tissue stiffness and thickness

    PubMed Central

    Garcia, Christopher A.; Goebel, Shannon L.; Hastings, Mary K.; Klaesner, Joseph W.; Mueller, Michael J.

    2008-01-01

    Background Plantar soft tissue stiffness and thickness are important biomechanical variables to understand stress concentrations that may contribute to tissue injury. Objective The purpose of this study was to determine the effects of passive metatarsal phalangeal joint (MPJ) extension on plantar soft tissue stiffness and thickness. Methods Seventeen healthy participants (7 male, 10 female, mean age 25.3 y, SD 4.4 y, mean BMI 24.7 kg/m2, SD 3.2 kg/m2) were tested. Plantar soft tissue stiffness and thickness were measured at the metatarsal heads, midfoot and heel using a custom-built indentor device and an ultrasound machine. Results Indicators of soft tissue stiffness (K1 values) at the metatarsal heads and midfoot showed increases in stiffness of 81–88% (SD 20–33%) in the MPJ extension position compared with the MPJ neutral position. Soft tissue thickness measures at the metatarsal heads with the MPJ in neutral ranged from a mean of 8.9–13.5 mm and decreased, on average, by 8.8% (SD 2.9%) with MPJ extension. Conclusions MPJ extension has a profound effect on increasing forefoot plantar soft tissue stiffness and a consistent but minimal effect on reducing soft tissue thickness. These changes may help transform the foot into a rigid lever at push-off consistent with the theory of the windlass mechanism. PMID:19492011

  10. Use of reflectance interference contrast microscopy to characterize the endothelial glycocalyx stiffness

    PubMed Central

    Job, Kathleen M.; Dull, Randal O.

    2012-01-01

    Reflectance interference contrast microscopy (RICM) was used to study the mechanics of the endothelial glycocalyx. This technique tracks the vertical position of a glass microsphere probe that applies very light fluctuating loads to the outermost layer of the bovine lung microvascular endothelial cell (BLMVEC) glycocalyx. Fluctuations in probe vertical position are used to estimate the effective stiffness of the underlying layer. Stiffness was measured before and after removal of specific glycocalyx components. The mean stiffness of BLMVEC glycocalyx was found to be ?7.5 kT/nm2 (or ?31 pN/nm). Enzymatic digestion of the glycocalyx with pronase or hyaluronan with hyaluronidase increased the mean effective stiffness of the glycocalyx; however, the increase of the mean stiffness on digestion of heparan sulfate with heparinase III was not significant. The results imply that hyaluronan chains act as a cushioning layer to distribute applied forces to the glycocalyx structure. Effective stiffness was also measured for the glycocalyx exposed to 0.1%, 1.0%, and 4.0% BSA; glycocalyx compliance increased at two extreme BSA concentrations. The RICM images indicated that glycocalyx thickness increases with BSA concentrations. Results demonstrate that RICM is sensitive to detect the subtle changes of glycocalyx compliance at the fluid-fiber interface. PMID:22505668

  11. Comparative study of a muscle stiffness sensor and electromyography and mechanomyography under fatigue conditions.

    PubMed

    Han, Hyonyoung; Jo, Sungho; Kim, Jung

    2015-07-01

    This paper proposes the feasibility of a stiffness measurement for muscle contraction force estimation under muscle fatigue conditions. Bioelectric signals have been widely studied for the estimation of the contraction force for physical human-robot interactions, but the correlation between the biosignal and actual motion is decreased under fatigue conditions. Muscle stiffness could be a useful contraction force estimator under fatigue conditions because it measures the same physical quantity as the muscle contraction that generates the force. Electromyography (EMG), mechanomyography (MMG), and a piezoelectric resonance-based active muscle stiffness sensor were used to analyze the biceps brachii under isometric muscle fatigue conditions with reference force sensors at the end of the joint. Compared to EMG and MMG, the change in the stiffness signal was smaller (p < 0.05) in the invariable contraction force generation test until failure. In addition, in the various contraction level force generation tests, the stiffness signal under the fatigue condition changed <10% (p < 0.05) compared with the signal under non-fatigue conditions. This result indicates that the muscle stiffness signal is less sensitive to muscle fatigue than other biosignals. This investigation provides insights into methods of monitoring and compensating for muscle fatigue. PMID:25752771

  12. Magnetic levitation and stiffness in melt-textured Y-Ba-Cu-O

    SciTech Connect

    Hull, J.R.; Mulcahy, T.M. ); Salama, K.; Selvamanickam, V. ); Weinberger, B.R.; Lynds, L. )

    1992-09-01

    Magnetic levitation and stiffness have been measured in several systems composed of a permanent magnet elastically suspended above a stationary melt-textured sample of Y-Ba-Cu-O. The levitation force and vertical stiffness have been calculated on the basis of magnetization measurements of the same system, and the calculated results showed excellent agreement with the experimental measurements. Based on the force and magnetization measurements, it is predicted that the same Y-Ba-Cu-O material configured in a geometry suitable for magnetic bearings could produce a levitation pressure of 100--400 kPa at 20 K.

  13. 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.

  14. Nanoscale directional motion towards regions of stiffness.

    PubMed

    Chang, Tienchong; Zhang, Hongwei; Guo, Zhengrong; Guo, Xingming; Gao, Huajian

    2015-01-01

    How to induce nanoscale directional motion via some intrinsic mechanisms pertaining to a nanosystem remains a challenge in nanotechnology. Here we show via molecular dynamics simulations that there exists a fundamental driving force for a nanoscale object to move from a region of lower stiffness toward one of higher stiffness on a substrate. Such nanoscale directional motion is induced by the difference in effective van der Waals potential energy due to the variation in stiffness of the substrate; i.e., all other conditions being equal, a nanoscale object on a stiffer substrate has lower van der Waals potential energy. This fundamental law of nanoscale directional motion could lead to promising routes for nanoscale actuation and energy conversion. PMID:25615480

  15. Cosmology with a stiff matter era

    E-print Network

    Pierre-Henri Chavanis

    2014-11-27

    We provide a simple analytical solution of the Friedmann equations for a universe made of stiff matter, dust matter, and dark energy. A stiff matter era is present in the cosmological model of Zel'dovich (1972) where the primordial universe is assumed to be made of a cold gas of baryons. It also occurs in certain cosmological models where dark matter is made of relativistic self-gravitating Bose-Einstein condensates (BECs). When the energy density of the stiff matter is positive, the primordial universe is singular. It starts from a state with a vanishing scale factor and an infinite density. We consider the possibility that the energy density of the stiff matter is negative (anti-stiff matter). This happens, for example, when the BECs have an attractive self-interaction. In that case, the primordial universe is non-singular. It starts from a state in which the scale factor is finite and the energy density is equal to zero. For the sake of generality, we consider a cosmological constant of arbitrary sign. When the cosmological constant is positive, the universe asymptotically reaches a de Sitter phase where the scale factor increases exponentially rapidly. This can account for the accelerating expansion of the universe that we observe at present. When the cosmological constant is negative (anti-de Sitter), the evolution of the universe is cyclic. Therefore, depending on the sign of the energy density of the stiff matter and of the dark energy, we obtain singular and non-singular expanding or cyclic universes.

  16. In vivo Assessment of MR Elastography-Derived Effective End-Diastolic Myocardial Stiffness under Different Loading Conditions

    PubMed Central

    Kolipaka, Arunark; McGee, Kiaran P.; Manduca, Armando; Anavekar, Nandan; Ehman, Richard L.; Araoz, Philip A.

    2011-01-01

    Purpose To compare magnetic resonance elastography (MRE) effective stiffness to end-diastolic pressure at different loading conditions to demonstrate a relationship between myocardial MRE effective stiffness and end-diastolic left ventricular (LV) pressure. Methods MRE was performed on 4 pigs to measure the end-diastolic effective stiffness under different loading conditions. End-diastolic pressure was increased by infusing dextran-40 (20% of blood volume). For each infusion of dextran-40, end-diastolic pressure was recorded and end-diastolic effective stiffness was measured using MRE. In each pig, least-square linear regression was performed to determine the correlation between end-diastolic effective stiffness and end-diastolic LV pressure. Results A linear correlation was found between end-diastolic LV pressure and end-diastolic effective stiffness with R2 ranging from 0.73–0.9. A linear correlation with R2 = 0.26 was found between end-diastolic LV pressure and end-diastolic effective stiffness when pooling data points from all pigs. Conclusion End-diastolic effective myocardial stiffness increases linearly with end-diastolic LV pressure. PMID:21509882

  17. Elastic stiffness of a Skyrmion crystal.

    PubMed

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

    2014-12-31

    We observe the elastic stiffness and ultrasonic absorption of a Skyrmion crystal in the chiral-lattice magnet MnSi. The Skyrmion crystal lattice exhibits a stiffness 3 orders of magnitude smaller than that of the atomic lattice of MnSi, being as soft as the flux line lattice in type-II superconductors. The observed anisotropic elastic responses are consistent with the cylindrical shape of the Skyrmion spin texture. Phenomenological analysis reveals that the spin-orbit coupling is responsible for the emergence of anisotropic elasticity in the Skyrmion lattice. PMID:25615379

  18. Arterial stiffness in periodontitis patients and controls.

    PubMed

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

    2016-01-01

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

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

    PubMed

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

    2015-09-01

    Liver stiffness and spleen stiffness in patients with myelofibrosis have traditionally been assessed through manual palpation and thus influenced by interobserver variability. In this article, for the first time, liver stiffness and spleen stiffness of patients with myelofibrosis were evaluated through FibroScan and shear wave elastography (SWE). Nine patients with myelofibrosis comprised the study group. They were compared with 11 patients with liver cirrhosis and 8 healthy volunteers. Before the FibroScan study, all patients underwent ultrasound study to delineate the left intercostal space for validated measurements. In patients with myelofibrosis, the mean stiffness of the spleen was 41.3 and 32.9 kilopascals (kPa) through FibroScan and SWE, respectively. The mean stiffness of the liver was 7.8 kPa through FibroScan and 10.4 kPa through SWE. The stiffness of the spleen in patients with cirrhosis was even higher, reaching a mean of 58.5 kPa through FibroScan and 40.5 kPa through SWE. The means were considerably lower among the healthy controls (13.5 and 18.1 kPa, respectively). The correlation between spleen stiffness among the patients with cirrhosis is negative and opposite in direction (r = -0.35) in comparison with the patients with myelofibrosis (r = 0.78). Among the patients with liver cirrhosis and myelofibrosis, spleen size was weakly related to spleen stiffness as assessed through SWE (r = 0.49) but had almost no relation to the FibroScan measure (r = 0.13). The FibroScan and SWE of the spleen have little ability to distinguish between the patients with myelofibrosis and cirrhosis, but they do differentiate both patient groups from the healthy controls. The stiffness of spleen and liver as measured through FibroScan and SWE was not correlated to the longevity of myelofibrosis. PMID:26366688

  20. Basic study of intrinsic elastography: Relationship between tissue stiffness and propagation velocity of deformation induced by pulsatile flow

    NASA Astrophysics Data System (ADS)

    Nagaoka, Ryo; Iwasaki, Ryosuke; Arakawa, Mototaka; Kobayashi, Kazuto; Yoshizawa, Shin; Umemura, Shin-ichiro; Saijo, Yoshifumi

    2015-07-01

    We proposed an estimation method for a tissue stiffness from deformations induced by arterial pulsation, and named this proposed method intrinsic elastography (IE). In IE, assuming that the velocity of the deformation propagation in tissues is closely related to the stiffness, the propagation velocity (PV) was estimated by spatial compound ultrasound imaging with a high temporal resolution of 1 ms. However, the relationship between tissue stiffness and PV has not been revealed yet. In this study, the PV of the deformation induced by the pulsatile pump was measured by IE in three different poly(vinyl alcohol) (PVA) phantoms of different stiffnesses. The measured PV was compared with the shear wave velocity (SWV) measured by shear wave imaging (SWI). The measured PV has trends similar to the measured SWV. These results obtained by IE in a healthy male show the possibility that the mechanical properties of living tissues could be evaluated by IE.

  1. 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

  2. Arterial stiffness variations by gender in African-American and Caucasian children.

    PubMed Central

    Hlaing, WayWay M.; Prineas, Ronald J.

    2006-01-01

    OBJECTIVE: Most arterial stiffness studies have been conducted in adult populations as a part of the aging process in the arterial system. Arterial stiffness is an important early marker of disease identification that may lead to improved cardiovascular health. The aim of this study was to assess the gender and ethnic differences in the arterial stiffness levels among children and adolescents. DESIGN: From a subgroup of schoolchildren who participated in a prospective cohort study in Minnesota, Caucasian and African-American children who completed 16 timed visits were included in this report (n=487). The participants were followed from 1978 (7.68 +/- 0.72 years) to 1987 (16.65 +/- 0.71 years). A surrogate measure of arterial stiffness-arterial pulse pressure (APP in mmHg)--was used. RESULTS: Adjusted APP differences started to appear around 12.67 years and persisted throughout the study. Boys consistently had higher APP levels than the girls. Ethnic differences in adjusted APP levels were observed at an earlier age (7.68 years) but did not persist after age 10. CONCLUSION: APP levels were different between gender and ethnic groups in youth. These early indications of arterial stiffness warrant further exploration of arterial stiffness etiology. PMID:16708504

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  4. Exploiting Variable Stiffness in Explosive Movement Tasks

    E-print Network

    Vijayakumar, Sethu

    Exploiting Variable Stiffness in Explosive Movement Tasks David J. Braun, Matthew Howard and Sethu actuation is advantageous to robot control once high-performance, explosive tasks, such as throwing, hitting highly dynamic, explosive movements. Such movements are characterised by a large release of energy over

  5. [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 ?g and midazolam 1mg. Despite careful titration, the patient had an O2 saturation level of 90%,which was resolved by manual ventilation. There was no muscle rigidity or spasm during the operation. Post-operative recovery was uneventful and the patient was discharged 2 days later. A review of other cases is presented. The anaesthetic concern in patients with stiff-person syndrome is the interaction between the anaesthetic agents, the preoperative medication, and the GABA system. For a safe anaesthetic management, total intravenous anaesthesia is recommended instead of inhalation anaesthetics, as well as the close monitoring of the respiratory function and the application of the electrical nerve stimulator when neuromuscular blockers are used. PMID:25060949

  6. The 5' and 3' domains of yeast U6 snRNA: Lsm proteins facilitate binding of Prp24 protein to the U6 telestem region.

    PubMed Central

    Ryan, Daniel E; Stevens, Scott W; Abelson, John

    2002-01-01

    The 5' and 3' domains of yeast U6 snRNA contain sequences that are thought to be important for binding to Prp24 and Lsm proteins. By extensive mutational analysis of yeast U6 snRNA, we confirmed that the 3' terminal uridine tract of U6 snRNA is important for U6 binding to Lsm proteins in yeast. Binding of Prp24 protein to U6 RNA is dependent on or is strongly enhanced by U6 binding of Lsm proteins. This supports a model for U6 snRNP assembly in which U6 RNA binds to the Lsm2-8 core prior to binding Prp24 protein. Using compensatory base-pairing analysis, we show that at least half of the recently identified U6 telestem as well as a nucleotide sequence in the other half of the telestem are important for binding of U6 RNA to Prp24 protein. Surprisingly, disruption of base pairing in the unconfirmed half of the telestem enhanced U6-Prp24 binding. Truncation of the entire 3' terminal domain or nearly the entire 5' terminal domain of yeast U6 allowed for detectable levels of splicing to proceed in vitro. In addition to gaining knowledge of the function of the 5' and 3' domains of yeast U6, our results help define the minimal set of requirements for yeast U6 RNA function in splicing. We present a revised secondary structural model of yeast U6 snRNA in free U6 snRNPs. PMID:12212846

  7. 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.

  8. Stress-Induced Variations in the Stiffness of Micro- and Nanocantilever Beams

    PubMed Central

    Karabalin, R. B.; Villanueva, L. G.; Matheny, M. H.; Sader, J. E.; Roukes, M. L.

    2013-01-01

    The effect of surface stress on the stiffness of cantilever beams remains an outstanding problem in the physical sciences. While numerous experimental studies report significant stiffness change due to surface stress, theoretical predictions are unable to rigorously and quantitatively reconcile these observations. In this Letter, we present the first controlled measurements of stress-induced change in cantilever stiffness with commensurate theoretical quantification. Simultaneous measurements are also performed on equivalent clamped-clamped beams. All experimental results are quantitatively and accurately predicted using elasticity theory. We also present conclusive experimental evidence for invalidity of the longstanding and unphysical axial force model, which has been widely applied to interpret measurements using cantilever beams. Our findings will be of value in the development of micro- and nanoscale resonant mechanical sensors. PMID:23003973

  9. Scaling of Fluid Flow and Seismic Stiffness of Fractures

    NASA Astrophysics Data System (ADS)

    Petrovitch, C.; Nolte, D.; Pyrak-Nolte, L. J.

    2011-12-01

    A firm understanding of the relationship between the hydraulic and mechanical properties of fractures has been long sought. Seismic techniques probe the mechanical properties of fractures, e.g. fracture specific stiffness. Providing a connection between fluid flow and fracture stiffness would enable remote estimation of the flow properties in the subsurface. Linking theses two properties would improve society's ability to assess the risk related to the extraction of drinkable water, oil production, and the storage of CO2 in subsurface reservoirs. This relationship is complicated because the subsurface is composed of a hierarchy of structures and processes that span a large range of length and time scales. A scaling approach enables researchers to translate laboratory measurements towards the field scale and vise a versa. We performed a computational study of the scaling of the flow-stiffness relationship for planar fractures with uncorrelated aperture distributions. Three numerical models were required to study the scaling properties of the flow-stiffness relationship for single fractures. Firstly, the fracture topologies where constructed using a stratified continuum percolation method. Only uncorrelated fracture geometries were considered to provide a baseline of understanding for the different interacting critical thresholds occurring in the hydraulic and mechanical properties. Secondly, fracture stiffness was calculated by modeling the deformation of asperities and a deformable half space. This model computed the displacement-stress curves for a given fracture, from which the stiffness was extracted. Thirdly, due to the sensitive nature of the critical phenomena associated with fluid flow through fractures, two network flow models were used for verification. The fractures were first modeled as a network of elliptical pipes and the corresponding linear system of equations was solved. The second method consisted of using a lattice grid network, where the flow is computed using the "cubic law." Fractures were generated at five sizes (1, 0.5, 0.25, 0.125, and 0.0625m) to provide an order of magnitude variation. Each fracture was constructed such that the contact area ranged from approximately 5% to 30%. The rocks were given the properties of granite and stressed to a maximum load of 70MPa. The deformation solver was given 50 steps to reach the final load so that its flow rate could be monitored during each loading step. The results clearly showed a dependence on scale. Under low loads flow-stiffness was in an effective medium regime. However as the load increased, a distinct scale dependence emerged. This occurs because as the load increases there is an overall increase in contact area, which in turn moves the flow dynamics into a critical regime. From this finite size scaling effect, we analyzed how the uncorrelated topologies length scales changed under load to compute the flow exponents for the system. Acknowledgments: Geosciences Research Program, Office of Basic Energy Sciences US Department of Energy (DE-FG02-09ER16022), the Geo-mathematical Imaging Group at Purdue University, and the Purdue Research Foundation.

  10. 3494 IEEETRANSACTIONS ON MAGNETICS, VOL. MAG-23, NO. 5 , SEPTEMBER 1987 BRILLOUIN LIGHT SCATTERING STUDYOr' THE SPIN WAVE STIFFNESS PARAMETERIN

    E-print Network

    Patton, Carl

    STUDYOr' THE SPIN WAVE STIFFNESS PARAMETERIN SC-SUBSTITUTED LUTETIUM-YTTRIUM IRON GARNET J . G . Booth, G measured for a seriesof Sc substituted lutetium-yttrium iron garnet(YIG) liquid phase epitaxy thin films

  11. Magnetic Resonance Elastography as a Method for the Assessment of Effective Myocardial Stiffness throughout the Cardiac Cycle

    PubMed Central

    Kolipaka, Arunark; Araoz, Philip A.; McGee, Kiaran P.; Manduca, Armando; Ehman, Richard L.

    2011-01-01

    Magnetic resonance elastography (MRE) is a noninvasive technique in which images of externally generated waves propagating in tissue are used to measure stiffness. The first aim is to determine, from a range of driver configurations the optimal driver for the purpose of generating waves within the heart in vivo. The second aim is to quantify the shear stiffness of normal myocardium throughout the cardiac cycle using MRE and to compare MRE stiffness to left ventricular (LV) chamber pressure in an in vivo pig model. MRE was performed in 6-pigs with 6-different driver setups including no motion, 3-noninvasive drivers and 2-invasive drivers. MRE wave displacement amplitudes were calculated for each driver. During the same MRI examination, LV pressure and MRI-measured LV volume were obtained, and MRE myocardial stiffness was calculated for 20 phases of the cardiac cycle. No discernible waves were imaged when no external motion was applied, and a single pneumatic drum driver produced higher amplitude waves than the other noninvasive drivers (P <0.05). Pressure-volume loops overlaid onto stiffness-volume loops showed good visual agreement. Pressure and MRE-measured effective stiffness showed good correlation (R2 = 0.84). MRE shows potential as a noninvasive method for estimating effective myocardial stiffness throughout the cardiac cycle. PMID:20578052

  12. Design and characterization of tunable stiffness flexural bearings

    E-print Network

    Ramirez, Aaron Eduardo

    2012-01-01

    Compressed flexures have a downwards-tunable stiffness in their compliant directions; their stiffness can theoretically be reduced by up to four orders of magnitude. The compression-stiffiness relation is linear for most ...

  13. Vitamin E reduces liver stiffness in nonalcoholic fatty liver disease

    PubMed Central

    Fukui, Aiko; Kawabe, Naoto; Hashimoto, Senju; Murao, Michihito; Nakano, Takuji; Shimazaki, Hiroaki; Kan, Toshiki; Nakaoka, Kazunori; Ohki, Masashi; Takagawa, Yuka; Takamura, Tomoki; Kamei, Hiroyuki; Yoshioka, Kentaro

    2015-01-01

    AIM: To evaluate the efficacy of vitamin E treatment on liver stiffness in nonalcoholic fatty liver disease (NAFLD). METHODS: Thirty-eight NAFLD patients were administered vitamin E for > 1 year. The doses of vitamin E were 150, 300, or 600 mg; three times per day after each meal. Responses were assessed by liver enzyme levels [aspartate aminotransferase (AST), alanine aminotranferease (ALT), and ?-glutamyl transpeptidase (?-GTP)], noninvasive scoring systems of hepatic fibrosis-4 [FIB-4 index and aspartate aminotransferase-to-platelet index (APRI)], and liver stiffness [velocity of shear wave (Vs)] measured by acoustic radiation force impulse elastography. Vs measurements were performed at baseline and 12 mo after baseline. The patients were genotyped for the patatin-like phospholipase domain containing 3 (PNPLA3) polymorphisms and then divided into either the CC/CG or GG group to examine each group’s responses to vitamin E treatment. RESULTS: We found marked differences in the platelet count, serum albumin levels, alkaline phosphatase levels, FIB-4 index, APRI, and Vs at baseline depending on the PNPLA3 polymorphism. AST, ALT, and ?-GTP levels (all P < 0.001); FIB-4 index (P = 0.035); APRI (P < 0.001); and Vs (P < 0.001) significantly decreased from baseline to 12 mo in the analysis of all patients. In the subset analyses of PNPLA3 genotypes, AST levels (P = 0.011), ALT levels (P < 0.001), ?-GTP levels (P = 0.005), APRI (P = 0.036), and Vs (P = 0.029) in genotype GG patients significantly improved, and AST and ALT levels (both P < 0.001), ?-GTP levels (P = 0.003), FIB-4 index (P = 0.017), and APRI (P < 0.001) in genotype CC/CG patients. CONCLUSION: One year of vitamin E treatment improved noninvasive fibrosis scores and liver stiffness in NAFLD patients. The responses were similar between different PNPLA3 genotypes. PMID:26644818

  14. Lamb Wave Stiffness Characterization of Composites Undergoing Thermal-Mechanical Aging

    NASA Technical Reports Server (NTRS)

    Seale, Michael D.; Madaras, Eric I.

    2004-01-01

    The introduction of new, advanced composite materials into aviation systems requires a thorough understanding of the long term effects of combined thermal and mechanical loading upon those materials. Analytical methods investigating the effects of intense thermal heating combined with mechanical loading have been investigated. The damage mechanisms and fatigue lives were dependent on test parameters as well as stress levels. Castelli, et al. identified matrix dominated failure modes for out-of-phase cycling and fiber dominated damage modes for in-phase cycling. In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. To help evaluate the effect of aging, a suitably designed Lamb wave measurement system is being used to obtain bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system works by exciting an antisymmetric Lamb wave and calculating the velocity at each frequency from the known transducer separation and the measured time-of-flight. The same peak in the waveforms received at various distances is used to measure the time difference between the signals. The velocity measurements are accurate and repeatable to within 1% resulting in reconstructed stiffness values repeatable to within 4%. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. A mechanical scanner is used to move the sensors over the surface to map the time-of-flight, velocity, or stiffnesses of the entire specimen. Access to only one side of the material is required and no immersion or couplants are required because the sensors are dry coupled to the surface of the plate. In this study, the elastic stiffnesses D(sub 11), D(sub 22), A(sub 44), and A(sub 55) as well as time-of-flight measurements for composite samples that have undergone combined thermal and mechanical aging for a duration of 10,000 hours are reported.

  15. Dynamic Voltage Scaling for Commercial FPGAs , L.S.M. Tsui1

    E-print Network

    Luk, Wayne

    measurement circuit (LDMC) is used to determine the speed of an inverter chain for various operating and temperatures to demon- strate its utility and robustness. Power savings between 4% and 54% for the VINT supply- ing, power aware CAD (Computer-Aided Design) algo- rithms and power aware coding of finite state

  16. Lifestyle modification decreases arterial stiffness in overweight and obese men: dietary modification vs. exercise training.

    PubMed

    Maeda, Seiji; Zempo-Miyaki, Asako; Sasai, Hiroyuki; Tsujimoto, Takehiko; So, Rina; Tanaka, Kiyoji

    2015-02-01

    Obesity and increased arterial stiffness are independent risk factors for cardiovascular disease. Arterial stiffness is increased in obese individuals than in age-matched nonobese individuals. We demonstrated that dietary modification and exercise training are effective in reducing arterial stiffness in obese persons. However, the differences in the effect on arterial stiffness between dietary modification and exercise training are unknown. The purpose of the current study was to compare the effect of dietary modification and aerobic exercise training on arterial stiffness and endothelial function in overweight and obese persons. Forty-five overweight and obese men (48 ± 1 year) completed either a dietary modification (well-balanced nutrient, 1680 kcal/day) or an exercise-training program (walking, 40-60 min/day, 3 days/week) for 12 weeks. Before and after the intervention, all participants underwent anthropometric measurements. Arterial stiffness was measured based on carotid arterial compliance, brachial-ankle pulse wave velocity (baPWV), and endothelial function was determined by circulating level of endothelin-1 (ET-1) and nitric oxide metabolite (nitrites/nitrate as metabolite: NOx). Body mass and waist circumference significantly decreased after both intervention programs. Weight loss was greater after dietary modification than after exercise training (-10.1 ± 0.6 kg vs. -3.6 ± 0.5 kg, p < .01). Although arterial stiffness and the plasma levels of ET-1 and NOx were improved after dietary modification or exercise training, there were no differences in those improvements between the 2 types of interventions. Exercise training improves arterial function in obese men without as much weight loss as after dietary modification. PMID:25029200

  17. Assessing Muscle Stiffness from Quiet Stance in Parkinson's Disease

    E-print Network

    Assessing Muscle Stiffness from Quiet Stance in Parkinson's Disease Michael Lauk 1;2;4 , MSc­761­203­7700, email: lauk@fdm.uni­freiburg.de Running head: Assessing stiffness in parkinsonism. #12; Assessing Muscle Stiffness from Quiet Stance: Applicability to Parkinson's Disease Abstract In previous studies, we developed

  18. Cocoa intake and arterial stiffness in subjects with cardiovascular risk factors

    PubMed Central

    2012-01-01

    Background To analyze the relationship of cocoa intake to central and peripheral blood pressure, arterial stiffness, and carotid intima-media thickness in subjects with some cardiovascular risk factor. Findings Design: A cross-sectional study of 351 subjects (mean age 54.76 years, 62.4% males). Measurements: Intake of cocoa and other foods using a food frequency questionnaire, central and peripheral (ambulatory and office) blood pressure, central and peripheral augmentation index, pulse wave velocity, ambulatory arterial stiffness index, carotid intima-media thickness, and ankle-brachial index. Results: Higher pulse wave velocity and greater cardiovascular risk were found in non-cocoa consumers as compared to high consumers (p < 0.05). In a multivariate analysis, these differences disappeared after adjusting for age, gender, the presence of diabetes, systolic blood pressure and antihypertensive and lipid-lowering drug use. All other arterial stiffness measures (central and peripheral augmentation index, ambulatory arterial stiffness index, ankle-brachial index, and carotid intima-media thickness) showed no differences between the different consumption groups. Conclusions In subjects with some cardiovascular risk factors, cocoa consumption does not imply improvement in the arterial stiffness values. Trial Registration Clinical Trials.gov Identifier: NCT01325064. PMID:22325068

  19. An Integrated Indenter-ARFI Imaging System for Tissue Stiffness Quantification

    PubMed Central

    Zhai, Liang; Palmeri, Mark L.; Bouchard, Richard R.; Nightingale, Roger W.; Nightingale, Kathryn R.

    2008-01-01

    The goal of this work is to develop and characterize an integrated indenter-ARFI (acoustic radiation force impulse) imaging system. This system is capable of acquiring matched datasets of ARFI images and stiffness profiles from ex vivo tissue samples, which will facilitate correlation of ARFI images of tissue samples with independently-characterized material properties. For large and homogeneous samples, the indenter can be used to measure the Young's moduli by using Boussinesq's solution for a load on the surface of a semi-infinite isotropic elastic medium. Experiments and finite element method (FEM) models were designed to determine the maximum indentation depth and minimum sample size for accurate modulus reconstruction using this solution. Applying these findings, indentation measurements were performed on three calibrated commercial tissue-mimicking phantoms and the results were in good agreement with the calibrated stiffness. For heterogeneous tissue samples, indentation can be used independently to characterize relative stiffness variation across the sample surface, which can then be used to validate the stiffness variation in registered ARFI images. Tests were performed on heterogeneous phantoms and freshly-excised colon cancer specimens to detect the relative stiffness and lesion sizes using the combined system. Normalized displacement curves across the lesion surface were calculated and compared. Good agreement of the lesion profiles was observed between indentation and ARFI imaging. PMID:18939611

  20. Lower Body vs. Upper Body Resistance Training and Arterial Stiffness in Young Men.

    PubMed

    Li, Y; Bopp, M; Botta, F; Nussbaumer, M; Schäfer, J; Roth, R; Schmidt-Trucksäss, A; Hanssen, H

    2015-11-01

    Resistance training has been shown to increase arterial stiffness. The purpose of the present study was to examine and compare the systemic arterial stiffness responses to acute lower body (LRT) and upper body (URT) resistance training. 20 healthy young men [median age: 26 years (interquartile range 23, 32)] underwent LRT, URT and whole body resistance training (WRT). Before and immediately after, as well as 20, 40 and 60?min after each training session, we measured the cardio-ankle vascular index (CAVI) and brachial-ankle pulse wave velocity (baPWV) using VaSera VS-1500?N. We used mixed models for repeated measurements to estimate the post-exercise differences in CAVI and baPWV between the 3 resistance training modes. Immediately after exercise cessation, both CAVI and baPWV were lower for LRT compared with URT [CAVI: -?0.93 (95% confidence interval [CI] -?1.15, -?0.70); baPWV: -?2.08?m/s (95% CI -?2.48, -?1.67)]. Differences between LRT and URT gradually decreased during follow-up. Compared with WRT, LRT induced a decrease and URT an increase in arterial stiffness across all time points. In conclusion, LRT presents more favorable post-exercise arterial stiffness than URT. Our results suggest that LRT or WRT may be preferred over URT in individuals with impaired arterial stiffness. PMID:26212244

  1. Light weight high-stiffness stage platen

    DOEpatents

    Spence, Paul A. (Pleasanton, CA)

    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. Ethnic Differences in Bending Stiffness of the Ulna and Tibia

    NASA Technical Reports Server (NTRS)

    Arnaud, S. B.; Liang, M. T. C.; Bassin, S.; Braun, W.; Dutto, D.; Plesums, K.; Huvnh, H. T.; Cooper, D.; Wong, N.

    2004-01-01

    There is considerable information about the variations in bone mass associated with different opportunity to compare a mechanical property of bone in young college women of Caucasian, Hispanic and Asian descent who gave informed consent to participate in an exercise study. The subjects were sedentary, in good health, eumenorrheic, non-smokers and had body mass indices (BMI) less than 30. Measurements acquired were body weight, kg, and height, cm, calcaneal and wrist bone density, g/square cm (PIXI, Lunar GE) and bending stiffness (EI, Nm(exp 2)) in the ulna and tibia. E1 was determined non-invasively with an instrument called the Mechanical Response Tissue Analyzer (MRTA) that delivers a vibratory stimulus to the center of the ulna or tibia and analyzes the response curve based on the equation E1 = k(sub b) L(exp 3)/48 where k, is lateral bending stiffness, L is the length of the bone, E is Young's modulus of elasticity and I, the bending moment of inertia. The error of the test (CV) based on measurements of an aluminum rod with a known E1 was 4.8%, of calcaneal BMD, 0.54%, and of wrist bone density, 3.45%.

  3. Nonaffine rubber elasticity for stiff polymer networks

    E-print Network

    C. Heussinger; B. Schaefer; E. Frey

    2007-11-26

    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 non-affinity. The length-scale characterizing the emergent non-affinity is given by the ``fiber length'' $l_f$, 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.

  4. Coupling Multiple Stiff Processes in Reactive Flows

    NASA Astrophysics Data System (ADS)

    Boris, Jay P.; Oran, Elaine S.; Patnaik, Gopal

    1999-11-01

    This paper describes a new, Compenstated Operator-Split (COS) methodology for coupling several distinct, mathematically stiff, reactive flow processes into a dynamic simulation model. Operator-splitting (also called process-splitting or timestep-splitting) is the simplest way to build detailed numerical models containing a number of different reactive flow processes and allows use of optimal algorithms for each of the processes individually [Oran and Boris, 1987]. However, explicit operator-splitting performs poorly in situations where two or more of the processes are ``stiff'' and thus require unacceptably small timesteps. Global implicit coupling can in principle be used for these cases, but the computational cost becomes prohibitive, the programming is often complex, there are serious algorithmic restrictions, and the accuracy can be quite low. We describe how operator-splitting can be extended to a broad class of problems with interacting stiff processes without the limitations of a global implicit framework. (Work Sponsored by ONR through the Naval Research Laboratory.)

  5. WRF tests on sensitivity to PBL and LSM schemes during atmospheric transition periods: validation with BLLAST case study

    NASA Astrophysics Data System (ADS)

    Sastre, Mariano; Steeneveld, Gert-Jan; Yagüe, Carlos; Román-Cascón, Carlos; Maqueda, Gregorio

    2014-05-01

    The structure and properties at a certain time of the atmospheric or planetary boundary layer (PBL) has a major importance in land-atmosphere interaction and exchange processes, i.e. in pollutants concentration, humidity or different energy vertical fluxes. Transition periods at this part of the troposphere are found difficult to properly interpret, as far as among all the processes taking place at that timing, it is not clearly stated the predominance of just one of them; moreover, a drastic change in the motion scales present in the lower atmosphere is sometimes produced. Atmospheric global models fail at representing transitional events in the PBL, mainly because of sub-grid scale phenomena. These micrometeorological processes require to be better simulated. Weather Research and Forecast (WRF) mesoscale model offers a considerable amount of physical options and parameterizations, including different PBL and land surface model (LSM) schemes. This fact justifies a model experiment to evaluate its behavior and try to understand the differences in model performance for transition periods in the atmosphere, specifically when it moves on from a convective to a stratified stable structure at its lower region. The Boundary Layer Late Afternoon and Sunset Turbulent (BLLAST) project organized and conducted a field campaign [1] during summer 2011 in Lannemezan (France), getting together a wide amount of meteorological instrumentation. The available extensive experimental dataset from that campaign offers an excellent opportunity for model validation. Results of WRF sensitivity tests are presented, comparing simulations among themselves and validating them with the observational data. Different atmospheric variables involved in the late afternoon and evening transition processes are considered, both at surface (i.e. energy balance) and at higher levels (thermodynamic vertical structure), in order to obtain a wider view of the problem. [1] Lothon, M. and co-authors (2012): The Boundary-Layer Late Afternoon and Sunset Turbulence field experiment. Paper 14B.1, 20th Symposium on Boundary-Layers and turbulence, Boston, MA, Amer. Meteor. Soc., 12 pp.

  6. Arterial stiffness in adult patients after Fontan procedure

    PubMed Central

    2014-01-01

    Objectives Increased arterial stiffness is a risk factor of atherosclerosis and cardio-vascular complications. The aim of the study was to determine whether peripheral vascular function might be an early marker of impaired health status in patients with a single ventricle after Fontan procedure. Methods and results Twenty five consecutive adults (11 women and 14 men) aged 24.7?±?6.2 years after the Fontan procedure and 25 sex, age and BMI match healthy volunteers underwent physical examination, blood analysis, transthoracic echocardiography and noninvasive assessment of aortic stiffness. Augmented pressure and Augmentation Index (AIx) were both significantly elevated in Fontan when compared to the controls (6,08?±?0,7 vs. 2,0?±?3,7; p?=?0.002 and 17,01?±?3,3 vs. 6,05?±?11; p?stiffness assessed by a noninvasive technique. Low arterial oxygen saturation postoperative time, age at surgery, white blood cells, TNF? and bilirubin level are associated with arterial stiffening in these patients. The combination of blood parameters of the hepatic function and noninvasive measurements of arterial stiffness could be helpful in comprehensive care of patients with Fontan circulation. PMID:24716671

  7. 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 ?2 , where ? is the rest-mass density and K is a constant. The energy density ? =? c2+K ?2 is the sum of two terms: a rest-mass term ? c2 that mimics "dark matter" (P =0 ) and an internal energy term u =K ?2=P that mimics a "stiff fluid" (P =? ) 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 ˜? , ? ?a-6). In the late universe, the rest-mass energy dominates and the dark fluid behaves as pressureless dark matter (P ?0 , ? ?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 ? 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 bouncing like in loop quantum cosmology. At t =0 , the scale factor is finite and the energy density is equal to zero. The universe first has a phantom behavior where the energy density increases with the scale factor, then a normal behavior where the energy density decreases with the scale factor. For the sake of generality, we consider a cosmological constant of arbitrary sign. When the cosmological constant is positive, the Universe asymptotically reaches a de Sitter regime where the scale factor increases exponentially rapidly with time. This can account for the accelerating expansion of the Universe that we observe at present. When the cosmological constant is negative (anti-de Sitter), the evolution of the Universe is cyclic. Therefore, depending on the sign of the internal energy of the dark fluid and on the sign of the cosmological constant, we obtain analytical solutions of the Friedmann equations describing singular and nonsingular expanding, bouncing, or cyclic universes.

  8. Quantitative characterization of adhesion and stiffness of corneal lens of Drosophila melanogaster using atomic force microscopy.

    PubMed

    Lavanya Devi, A L; Nongthomba, Upendra; Bobji, M S

    2016-01-01

    Atomic force Microscopy (AFM) has become a versatile tool in biology due to its advantage of high-resolution imaging of biological samples close to their native condition. Apart from imaging, AFM can also measure the local mechanical properties of the surfaces. In this study, we explore the possibility of using AFM to quantify the rough eye phenotype of Drosophila melanogaster through mechanical properties. We have measured adhesion force, stiffness and elastic modulus of the corneal lens using AFM. Various parameters affecting these measurements like cantilever stiffness and tip geometry are systematically studied and the measurement procedures are standardized. Results show that the mean adhesion force of the ommatidial surface varies from 36nN to 16nN based on the location. The mean stiffness is 483±5N/m, and the elastic modulus is 3.4±0.05GPa (95% confidence level) at the center of ommatidia. These properties are found to be different in corneal lens of eye expressing human mutant tau gene (mutant). The adhesion force, stiffness and elastic modulus are decreased in the mutant. We conclude that the measurement of surface and mechanical properties of D. melanogaster using AFM can be used for quantitative evaluation of 'rough eye' surface. PMID:26327451

  9. Massage induces an immediate, albeit short-term, reduction in muscle stiffness.

    PubMed

    Eriksson Crommert, M; Lacourpaille, L; Heales, L J; Tucker, K; Hug, F

    2015-10-01

    Using ultrasound shear wave elastography, the aims of this study were: (a) to evaluate the effect of massage on stiffness of the medial gastrocnemius (MG) muscle and (b) to determine whether this effect (if any) persists over a short period of rest. A 7-min massage protocol was performed unilaterally on MG in 18 healthy volunteers. Measurements of muscle shear elastic modulus (stiffness) were performed bilaterally (control and massaged leg) in a moderately stretched position at three time points: before massage (baseline), directly after massage (follow-up 1), and following 3?min of rest (follow-up 2). Directly after massage, participants rated pain experienced during the massage. MG shear elastic modulus of the massaged leg decreased significantly at follow-up 1 (-5.2?±?8.8%, P?=?0.019, d?=?-0.66). There was no difference between follow-up 2 and baseline for the massaged leg (P?=?0.83) indicating that muscle stiffness returned to baseline values. Shear elastic modulus was not different between time points in the control leg. There was no association between perceived pain during the massage and stiffness reduction (r?=?0.035; P?=?0.89). This is the first study to provide evidence that massage reduces muscle stiffness. However, this effect is short lived and returns to baseline values quickly after cessation of the massage. PMID:25487283

  10. Body fat is associated with reduced aortic stiffness until middle age.

    PubMed

    Corden, Ben; Keenan, Niall G; de Marvao, Antonio S M; Dawes, Timothy J W; Decesare, Alain; Diamond, Tamara; Durighel, Giuliana; Hughes, Alun D; Cook, Stuart A; O'Regan, Declan P

    2013-06-01

    Obesity is a major risk factor for cardiometabolic disease, but the effect of body composition on vascular aging and arterial stiffness remains uncertain. We investigated relationships among body composition, blood pressure, age, and aortic pulse wave velocity in healthy individuals. Pulse wave velocity in the thoracic aorta, an indicator of central arterial stiffness, was measured in 221 volunteers (range, 18-72 years; mean, 40.3±13 years) who had no history of cardiovascular disease using cardiovascular MRI. In univariate analyses, age (r=0.78; P<0.001) and blood pressure (r=0.41; P<0.001) showed a strong positive association with pulse wave velocity. In multivariate analysis, after adjustment for age, sex, and mean arterial blood pressure, elevated body fat% was associated with reduced aortic stiffness until the age of 50 years, thereafter adiposity had an increasingly positive association with aortic stiffness (?=0.16; P<0.001). Body fat% was positively associated with cardiac output when age, sex, height, and absolute lean mass were adjusted for (?=0.23; P=0.002). These findings suggest that the cardiovascular system of young adults may be capable of adapting to the state of obesity and that an adverse association between body fat and aortic stiffness is only apparent in later life. PMID:23608657

  11. Functional aortic stiffness: role of CD4+ T lymphocytes

    PubMed Central

    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. PMID:26379554

  12. Ambient vibration testing for story stiffness estimation of a heritage timber building.

    PubMed

    Min, Kyung-Won; Kim, Junhee; Park, Sung-Ah; Park, Chan-Soo

    2013-01-01

    This paper investigates dynamic characteristics of a historic wooden structure by ambient vibration testing, presenting a novel estimation methodology of story stiffness for the purpose of vibration-based structural health monitoring. As for the ambient vibration testing, measured structural responses are analyzed by two output-only system identification methods (i.e., frequency domain decomposition and stochastic subspace identification) to estimate modal parameters. The proposed methodology of story stiffness is estimation based on an eigenvalue problem derived from a vibratory rigid body model. Using the identified natural frequencies, the eigenvalue problem is efficiently solved and uniquely yields story stiffness. It is noteworthy that application of the proposed methodology is not necessarily confined to the wooden structure exampled in the paper. PMID:24227999

  13. Ambient Vibration Testing for Story Stiffness Estimation of a Heritage Timber Building

    PubMed Central

    Min, Kyung-Won; Kim, Junhee; Park, Sung-Ah; Park, Chan-Soo

    2013-01-01

    This paper investigates dynamic characteristics of a historic wooden structure by ambient vibration testing, presenting a novel estimation methodology of story stiffness for the purpose of vibration-based structural health monitoring. As for the ambient vibration testing, measured structural responses are analyzed by two output-only system identification methods (i.e., frequency domain decomposition and stochastic subspace identification) to estimate modal parameters. The proposed methodology of story stiffness is estimation based on an eigenvalue problem derived from a vibratory rigid body model. Using the identified natural frequencies, the eigenvalue problem is efficiently solved and uniquely yields story stiffness. It is noteworthy that application of the proposed methodology is not necessarily confined to the wooden structure exampled in the paper. PMID:24227999

  14. From amorphous aggregates to polymer bundles: The role of stiffness on structural phases in polymer aggregation

    E-print Network

    Johannes Zierenberg; Wolfhard Janke

    2015-01-24

    We study the aggregation transition of a finite theta-polymer system in dependence on the bending stiffness $\\kappa$ with the help of parallel multicanonical simulations. In order to distinguish amorphous aggregates from polymer bundles we introduce an order parameter, measuring the correlation of the end-to-end vectors. With the help of this order parameter, we construct generic $T$-$\\kappa$ phase diagrams for systems with $2$ and $8$ polymers and discuss the occurring phases from amorphous aggregates to bundle structures. For an intermediate stiffness range we find multiple aggregated phases which change with increasing number of polymers and discuss their nature with the help of microcanonical analyses. We show that the stiffness of semiflexible theta polymers is the distinguishing parameter for the emergent structural motifs.

  15. Dynamic Stiffness and Damping Characteristics of a High-Temperature Air Foil Journal Bearing

    NASA Technical Reports Server (NTRS)

    Howard, Samuel A.; DellaCorte, Christopher; Valco, Mark J.; Prahl, Joseph M.; Heshmat, Hooshang

    2001-01-01

    Using a high-temperature optically based displacement measurement system, a foil air bearing's stiffness and damping characteristics were experimentally determined. Results were obtained over a range of modified Sommerfeld Number from 1.5E6 to 1.5E7, and at temperatures from 25 to 538 C. An Experimental procedure was developed comparing the error in two curve fitting functions to reveal different modes of physical behavior throughout the operating domain. The maximum change in dimensionless stiffness was 3.0E-2 to 6.5E-2 over the Sommerfeld Number range tested. Stiffness decreased with temperature by as much as a factor of two from 25 to 538 C. Dimensionless damping was a stronger function of Sommerfeld Number ranging from 20 to 300. The temperature effect on damping being more qualitative, showed the damping mechanism shifted from viscous type damping to frictional type as temperature increased.

  16. Somatic stiffness of cochlear outer hair cells is voltage-dependent.

    PubMed

    He, D Z; Dallos, P

    1999-07-01

    The mammalian cochlea depends on an amplification process for its sensitivity and frequency-resolving capability. Outer hair cells are responsible for providing this amplification. It is usually assumed that the membrane-potential-driven somatic shape changes of these cells are the basis of the amplifying process. It is of interest to see whether mechanical reactance changes of the cells might accompany their changes in cell shape. We now show that the cylindrical outer hair cells change their axial stiffness as their membrane potential is altered. Cell stiffness was determined by optoelectronically measuring the amplitude of motion of a flexible vibrating fiber as it was loaded by the isolated cell. Voltage commands to the cell were delivered in a tight-seal whole-cell configuration. Cell stiffness was decreased by depolarization and increased by hyperpolarization. PMID:10393976

  17. Position and Velocity Estimation for Two-Inertia System with Nonlinear Stiffness Based on Acceleration Sensor.

    PubMed

    Nam, Kyung-Tae; Lee, Seung-Joon; Kuc, Tae-Yong; Kim, Hyungjong

    2015-01-01

    In this paper, we consider the state estimation problem for flexible joint manipulators that involve nonlinear characteristics in their stiffness. The two key ideas of our design are that (a) an accelerometer is used in order that the estimation error dynamics do not depend on nonlinearities at the link part of the manipulators and (b) the model of the nonlinear stiffness is indeed a Lipschitz function. Based on the measured acceleration, we propose a nonlinear observer under the Lipschitz condition of the nonlinear stiffness. In addition, in order to effectively compensate for the estimation error, the gain of the proposed observer is chosen from the ARE (algebraic Riccati equations) which depend on the Lipschitz constant. Comparative experimental results verify the effectiveness of the proposed method. PMID:26729125

  18. Effect of end-ring stiffness on buckling of pressure-loaded stiffened conical shells

    NASA Technical Reports Server (NTRS)

    Davis, R. C.; Williams, J. G.

    1977-01-01

    Buckling studies were conducted on truncated 120 deg conical shells having large end rings and many interior reinforcing rings that are typical of aeroshells used as spacecraft decelerators. Changes in base-end-ring stiffness were accomplished by simply machining away a portion of the base ring between successive buckling tests. Initial imperfection measurements from the test cones were included in the analytical model.

  19. Platelet mechanosensing of substrate stiffness during clot formation mediates adhesion, spreading,

    E-print Network

    Kumar, Sanjay

    August 28, 2014 (received for review December 11, 2013) As platelets aggregate and activate at the site on stiffer substrates also leads to higher levels of platelet activation, as measured by integrin IIb3 and actomyosin activity mediate substrate stiffness-dependent platelet adhesion, spreading, and activation

  20. 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 that provide a best fit between the finite element model and the experimental data. Sample results are presented for a human lens of age 33 years. PMID:21040722

  1. 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. PMID:25570387

  2. Arterial stiffness is not associated with bone parameters in an elderly hyperhomocysteinemic population.

    PubMed

    van Dijk, S C; de Jongh, R T; Enneman, A W; Ham, A C; Swart, K M A; van Wijngaarden, J P; van der Zwaluw, N L; Brouwer-Brolsma, E M; van Schoor, N M; Dhonukshe-Rutten, R A M; Lips, P; de Groot, C P G M; Smulders, Y M; Blom, H J; Feskens, E J; Geleijnse, J M; van den Meiracker, A H; Mattace Raso, F U S; Uitterlinden, A G; Zillikens, M C; van der Velde, N

    2016-01-01

    Several studies have observed positive associations between bone disease and cardiovascular disease. A potential common pathway is hyperhomocysteinemia; however, to date, there is a lack of data regarding hyperhomocysteinemic populations. Therefore, we examined both cross-sectionally and longitudinally, whether there is an association between bone parameters and arterial stiffness in a hyperhomocysteinemic population, and investigated the potential common role of homocysteine (hcy) level on these associations. Cross-sectional and longitudinal data of the B-PROOF study were used (n = 519). At both baseline and 2-year follow-up we determined bone measures-incident fractures and history of fractures, bone-mineral density (BMD) and quantitative ultrasound (QUS) measurement. We also measured arterial stiffness parameters at baseline-pulse wave velocity, augmentation index and aortic pulse pressure levels with applanation tonometry. Linear regression analysis was used to examine these associations and we tested for potential interaction of hcy level. The mean age of the study population was 72.3 years and 44.3 % were female. Both cross-sectionally and longitudinally there was no association between arterial stiffness measures and BMD or QUS measurements or with incident fractures (n = 16) within the 2-3 years of follow-up. Hcy level did not modify the associations and adjustment for hcy did not change the results. Arterial stiffness was not associated with bone parameters and fractures, and hcy neither acted as a pleiotropic factor nor as a mediator. The potential association between bone and arterial stiffness is therefore not likely to be driven by hyperhomocysteinemia. PMID:25804313

  3. Postprandial effects on arterial stiffness parameters in healthy young adults.

    PubMed

    Murray, Tyler; Yang, Eric Y; Brunner, Gerd; Kumar, Anirudh; Lakkis, Nasser; Misra, Arunima; Virani, Salim S; Hartley, Craig J; Morrisett, Joel D; Ballantyne, Christie M; Nambi, Vijay

    2015-12-01

    Postprandial lipemia has been associated with acute endothelial dysfunction. Endothelial dysfunction, in turn, is associated with increased arterial stiffness. However, the relationship between postprandial lipemia and acute changes in arterial stiffness has not been extensively investigated. Therefore, we conducted a pilot study on the effects of postprandial lipemia on arterial stiffness in 19 healthy young adults before and after consumption of a high-fat mixed meal. Arterial stiffness was assessed locally with echo-tracking carotid arterial strain (CAS) and globally with carotid-femoral pulse wave velocity (PWV). As assessed by these two benchmark parameters, arterial stiffness did not differ significantly postprandially. However, the arterial distension period (ADP) was significantly lower 2 hours after mixed meal ingestion. In addition, slopes of carotid artery area (CAA) curves were significantly steeper postprandially. Therefore, we concluded that ADP may be a more sensitive marker of arterial stiffness in healthy young adults when compared to PWV and CAS. PMID:26060082

  4. 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. PMID:25128020

  5. Dynamics of a Gear System with Faults in Meshing Stiffness

    E-print Network

    Grzegorz Litak; Michael I. Friswell

    2004-05-23

    Gear box dynamics is characterised by a periodically changing stiffness. In real gear systems, a backlash also exists that can lead to a loss in contact between the teeth. Due to this loss of contact the gear has piecewise linear stiffness characteristics, and the gears can vibrate regularly and chaotically. In this paper we examine the effect of tooth shape imperfections and defects. Using standard methods for nonlinear systems we examine the dynamics of gear systems with various faults in meshing stiffness.

  6. Effect of passive heat stress on arterial stiffness in smokers versus non-smokers

    NASA Astrophysics Data System (ADS)

    Moyen, N. E.; Ganio, M. S.; Burchfield, J. M.; Tucker, M. A.; Gonzalez, M. A.; Dougherty, E. K.; Robinson, F. B.; Ridings, C. B.; Veilleux, J. C.

    2015-08-01

    In non-smokers, passive heat stress increases shear stress and vasodilation, decreasing arterial stiffness. Smokers, who reportedly have arterial dysfunction, may have similar improvements in arterial stiffness with passive heat stress. Therefore, we examined the effects of an acute bout of whole-body passive heat stress on arterial stiffness in smokers vs. non-smokers. Thirteen smokers (8.8 ± 5.5 [median = 6] cigarettes per day for >4 years) and 13 non-smokers matched for age, mass, height, and exercise habits (27 ± 8 years; 78.8 ± 15.4 kg; 177.6 ± 6.7 cm) were passively heated to 1.5 °C core temperature (T C) increase. At baseline and each 0.5 °C T C increase, peripheral (pPWV) and central pulse wave velocity (cPWV) were measured via Doppler ultrasound. No differences existed between smokers and non-smokers for any variables (all p > 0.05), except cPWV slightly increased from baseline (526.7 ± 81.7 cm · s-1) to 1.5 °C ?T C (579.7 ± 69.8 cm · s-1; p < 0.005), suggesting heat stress acutely increased central arterial stiffness. pPWV did not change with heating (grand mean: baseline = 691.9 ± 92.9 cm · s-1; 1.5 °C ?T C = 691.9 ± 79.5 cm · s-1; p > 0.05). Changes in cPWV and pPWV during heating correlated (p < 0.05) with baseline PWV in smokers (cPWV: r = -0.59; pPWV: r = -0.62) and non-smokers (cPWV: r = -0.45; pPWV: r = -0.77). Independent of smoking status, baseline stiffness appears to mediate the magnitude of heating-induced changes in arterial stiffness.

  7. Arterial stiffness is increased in American adolescents compared to Japanese counterparts.

    PubMed

    Collins, R Thomas; Somes, Grant W; Alpert, Bruce S

    2009-08-01

    Cardiovascular disease is increased in US groups versus Japanese counterparts. Increased arterial stiffness is an important predictor of cardiovascular risk. Pulse wave velocity correlates well with arterial stiffness. Gender and ethnic differences in biracial US adolescent groups have been described. No data are available evaluating differences in arterial stiffness between US and Japanese subjects. Previously published data from an adolescent (12-17 years of age) Japanese cohort were used as an historical control and were compared to an adolescent cohort from the United States. The same simple noninvasive oscillometric technique was used in each cohort to measure brachial-ankle pulse wave velocity (baPWV) as an index of arterial stiffness. The US group was a cross-sectional, biracial (64% African American, 56% female) sample of 162 subjects. The Japanese group was a cross-sectional (48% female) sample of 820 Japanese subjects. All subjects in both cohorts were normotensive (BP < 95% for gender, height, and age) adolescents (12-17 years of age). Subjects were analyzed in four groups on the basis of gender and age (12-14 and 15-17 years of age). In both individual cohorts, the mean baPWV was higher in males versus females and the baPWV increased with age. The mean baPWV was higher in all US groups versus Japanese counterparts (p < 0.0001). The mean systolic and diastolic blood pressures were higher in all Japanese groups versus US counterparts (p < 0.005). Differences in arterial stiffness are present and detectable between normotensive US and Japanese adolescent subjects. Increased arterial stiffness among these adolescent groups correlates with known adult risk for cardiovascular events among the same ethnic and gender groups. PMID:19357905

  8. Towards ultra-stiff materials: Surface effects on nanoporous materials

    SciTech Connect

    Lu, Dingjie; Xie, Yi Min; Huang, Xiaodong; Zhou, Shiwei; Li, Qing

    2014-09-08

    The significant rise in the strength and stiffness of porous materials at nanoscale cannot be described by conventional scaling laws. This letter investigates the effective Young's modulus of such materials by taking into account surface effect in a microcellular architecture designed for an ultralight material whose stiffness is an order of magnitude higher than most porous materials. We find that by considering the surface effects the predicted stiffness using Euler-Bernoulli beam theory compares well to experimental data for spongelike nanoporous gold with random microstructures. Analytical results show that, of the two factors influencing the effective Young's modulus, the residual stress is more important than the surface stiffness.

  9. Common Carotid Artery Stiffness Is Associated with Left Ventricular Structure and Function and Predicts First Hospitalization for Acute Heart Failure

    PubMed Central

    Sung, Shih-Hsien; Liao, Jo-Nan; Yu, Wen-Chung; Cheng, Hao-Min; Chen, Chen-Huan

    2014-01-01

    Aims Proximal aortic stiffness may be more important than carotid-femoral pulse wave velocity (cf-PWV) in the pathogenesis of heart failure. The present study investigated the associations of common carotid artery (CCA) stiffness, which might be a surrogate for proximal aortic stiffness, with left ventricular (LV) structure and function, and the development of acute heart failure (AHF). Methods and Results Outpatients without a history of heart failure (114 subjects aged 63.5 ± 17.5 years) were enrolled for comprehensive noninvasive cardiovascular examinations. The LV mass index, the LV ejection fraction (EF), and the ratio of the early diastolic transmitral flow velocity to the early septal mitral annular diastolic velocity (E/E’) were measured by echocardiography. CCA mechanical properties, including the incremental elastic modulus (Einc), ? stiffness index, CCA distensibility (CD) and circumferential strain (CS), were assessed by carotid artery ultrasonography. cf-PWV was measured by arterial tonometry. CD was significantly associated with the LV mass index, and all CCA stiffness indices were significantly associated with EF and E/E’ independently of age, mean blood pressure, and cf-PWV. During a mean follow-up of 265 ± 106 days, 9 patients presented with AHF. Einc (hazard ratio 6.56, 95% confidence interval 1.64-26.26, by quartile analysis), CS (6.82, 1.70-27.35), and ? stiffness index (3.91, 1.05-14.57) but not cf-PWV (1.62, 0.41-6.51) significantly predicted the events. Conclusions In patients at risk for heart failure, CCA stiffness was significantly associated with LV structure and function independently of cf-PWV. In addition, CCA stiffness but not cf-PWV predicted first AHF.

  10. Metabolic syndrome is associated with change in subclinical arterial stiffness - A community-based Taichung Community Health Study

    PubMed Central

    2011-01-01

    Background The aim of this study was to evaluate the effect of MetS on arterial stiffness in a longitudinal study. Methods Brachial-ankle pulse wave velocity (baPWV), a measurement interpreted as arterial stiffness, was measured in 1518 community-dwelling persons at baseline and re-examined within a mean follow-up period of 3 years. Multivariate linear regression with generalized estimating equations (GEE) were used to examine the longitudinal relationship between MetS and its individual components and baPWV, while multivariate logistic regression with GEE was used to examine the longitudinal relationship between MetS and its individual components and the high risk group with arterial stiffness. Results Subjects with MetS showed significantly greater baPWV at the end point than those without MetS, after adjusting for age, gender, education, hypertension medication and mean arterial pressure (MAP). MetS was associated with the top quartile of baPWV (the high-risk group of arterial stiffness, adjusted odds ratio [95% confidence interval] 1.52 [1.21-1.90]), and a significant linear trend of risk for the number of components of MetS was found (p for trend < 0.05). In further considering the individual MetS component, elevated blood pressure and fasting glucose significantly predicted a high risk of arterial stiffness (adjusted OR [95% CI] 3.72 [2.81-4.93] and 1.35 [1.08-1.68], respectively). Conclusions MetS affects the subject's progression to arterial stiffness. Arterial stiffness increased as the number of MetS components increased. Management of MetS is important for preventing the progression to advanced arterial stiffness. PMID:21999611

  11. The passive, human calf muscles in relation to standing: the short range stiffness lies in the contractile component

    PubMed Central

    Loram, Ian D; Maganaris, Constantinos N; Lakie, Martin

    2007-01-01

    Using short duration perturbations, previous attempts to measure the intrinsic ankle stiffness during human standing have revealed a substantial stabilizing contribution (65–90% normalized to load stiffness ‘mgh’). Others regard this method as unsuitable for the low-frequency conditions of quiet standing and believe the passive contribution to be small (10–15%). This latter view, consistent with a linear Hill-type model, argues that during standing, the contractile portion of the muscle is much less stiff than the tendon. Here, for upright subjects, we settle this issue by measuring the stiffness of the contractile portion of the passive calf muscles using low-frequency ankle rotations. Using ultrasound we tracked the changes in muscle contractile length and partitioned the ankle rotation into contractile and extra-contractile (series elastic) portions. Small ankle rotations of 0.15 and 0.4 deg show a contractile to series elastic stiffness ratio (Kce/Kse) of 12 ± 9 and 6.3 ± 10, respectively, with both elements displaying predominantly elastic behaviour. Larger, 7 deg rotations reveal the range of this ratio. It declines in a non-linear way from a high value (Kce/Kse= 18 ± 11) to a low value (Kce/Kse= 1 ± 0.4) as rotation increases from 0.1 to 7 deg. There is a marked transition at around 0.5 deg. The series elastic stiffness (Kse/mgh) remains largely constant (77 ± 13%) demonstrating the contractile component origin of passive, short range stiffness. The linear Hill-type model does not describe the range-related stiffness relevant to the progression from quiet standing to perturbed balance and movement and can lead to inaccurate predictions regarding human balance. PMID:17823208

  12. Quantification of plaque stiffness by Brillouin microscopy in experimental thin cap fibroatheroma.

    PubMed

    Antonacci, Giuseppe; Pedrigi, Ryan M; Kondiboyina, Avinash; Mehta, Vikram V; de Silva, Ranil; Paterson, Carl; Krams, Rob; Török, Peter

    2015-11-01

    Plaques vulnerable to rupture are characterized by a thin and stiff fibrous cap overlaying a soft lipid-rich necrotic core. The ability to measure local plaque stiffness directly to quantify plaque stress and predict rupture potential would be very attractive, but no current technology does so. This study seeks to validate the use of Brillouin microscopy to measure the Brillouin frequency shift, which is related to stiffness, within vulnerable plaques. The left carotid artery of an ApoE(-/-)mouse was instrumented with a cuff that induced vulnerable plaque development in nine weeks. Adjacent histological sections from the instrumented and control arteries were stained for either lipids or collagen content, or imaged with confocal Brillouin microscopy. Mean Brillouin frequency shift was 15.79 ± 0.09 GHz in the plaque compared with 16.24 ± 0.15 (p < 0.002) and 17.16 ± 0.56 GHz (p < 0.002) in the media of the diseased and control vessel sections, respectively. In addition, frequency shift exhibited a strong inverse correlation with lipid area of -0.67 ± 0.06 (p < 0.01) and strong direct correlation with collagen area of 0.71 ± 0.15 (p < 0.05). This is the first study, to the best of our knowledge, to apply Brillouin spectroscopy to quantify atherosclerotic plaque stiffness, which motivates combining this technology with intravascular imaging to improve detection of vulnerable plaques in patients. PMID:26559685

  13. Study of flexible fin and compliant joint stiffness on propulsive performance: theory and experiments.

    PubMed

    Kancharala, A K; Philen, M K

    2014-09-01

    The caudal fin is a major source of thrust generation in fish locomotion. Along with the fin stiffness, the stiffness of the joint connecting the fish body to the tail plays a major role in the generation of thrust. This paper investigates the combined effect of fin and joint flexibility on propulsive performance using theoretical and experimental studies. For this study, fluid-structure interaction of the fin has been modeled using the 2D unsteady panel method coupled with nonlinear Euler-Bernoulli beam theory. The compliant joint has been modeled as a torsional spring at the leading edge of the fin. A comparison of self-propelled speed and efficiency with parameters such as heaving and pitching amplitude, oscillation frequency, flexibility of the fin and the compliant joint is reported. The model also predicts the optimized stiffnesses of the compliant joint and the fin for maximum efficiency. Experiments have been carried out to determine the effect of fin and joint stiffness on propulsive performance. Digital image correlation has been used to measure the deformation of the fins and the measured deformation is coupled with the hydrodynamic model to predict the performance. The predicted theoretical performance behavior closely matches the experimental values. PMID:24737004

  14. Cell prestress. I. Stiffness and prestress are closely associated in adherent contractile cells

    NASA Technical Reports Server (NTRS)

    Wang, Ning; Tolic-Norrelykke, Iva Marija; Chen, Jianxin; Mijailovich, Srboljub M.; Butler, James P.; Fredberg, Jeffrey J.; Stamenovic, Dimitrije; Ingber, D. E. (Principal Investigator)

    2002-01-01

    The tensegrity hypothesis holds that the cytoskeleton is a structure whose shape is stabilized predominantly by the tensile stresses borne by filamentous structures. Accordingly, cell stiffness must increase in proportion with the level of the tensile stress, which is called the prestress. Here we have tested that prediction in adherent human airway smooth muscle (HASM) cells. Traction microscopy was used to measure the distribution of contractile stresses arising at the interface between each cell and its substrate; this distribution is called the traction field. Because the traction field must be balanced by tensile stresses within the cell body, the prestress could be computed. Cell stiffness (G) was measured by oscillatory magnetic twisting cytometry. As the contractile state of the cell was modulated with graded concentrations of relaxing or contracting agonists (isoproterenol or histamine, respectively), the mean prestress ((t)) ranged from 350 to 1,900 Pa. Over that range, cell stiffness increased linearly with the prestress: G (Pa) = 0.18(t) + 92. While this association does not necessarily preclude other interpretations, it is the hallmark of systems that secure shape stability mainly through the prestress. Regardless of mechanism, these data establish a strong association between stiffness of HASM cells and the level of tensile stress within the cytoskeleton.

  15. Evaluation of Compressive Strength and Stiffness of Grouted Soils by Using Elastic Waves

    PubMed Central

    Lee, In-Mo; Kim, Jong-Sun; Yoon, Hyung-Koo; Lee, Jong-Sub

    2014-01-01

    Cement grouted soils, which consist of particulate soil media and cementation agents, have been widely used for the improvement of the strength and stiffness of weak ground and for the prevention of the leakage of ground water. The strength, elastic modulus, and Poisson's ratio of grouted soils have been determined by classical destructive methods. However, the performance of grouted soils depends on several parameters such as the distribution of particle size of the particulate soil media, grouting pressure, curing time, curing method, and ground water flow. In this study, elastic wave velocities are used to estimate the strength and elastic modulus, which are generally obtained by classical strength tests. Nondestructive tests by using elastic waves at small strain are conducted before and during classical strength tests at large strain. The test results are compared to identify correlations between the elastic wave velocity measured at small strain and strength and stiffness measured at large strain. The test results show that the strength and stiffness have exponential relationship with elastic wave velocities. This study demonstrates that nondestructive methods by using elastic waves may significantly improve the strength and stiffness evaluation processes of grouted soils. PMID:25025082

  16. The intrinsic stiffness of human trabecular meshwork cells increases with senescence

    PubMed Central

    Chang, Yow-Ren; Murphy, Christopher J.; Russell, Paul

    2015-01-01

    Dysfunction of the human trabecular meshwork (HTM) plays a central role in the age-associated disease glaucoma, a leading cause of irreversible blindness. The etiology remains poorly understood but cellular senescence, increased stiffness of the tissue, and the expression of Wnt antagonists such as secreted frizzled related protein-1 (SFRP1) have been implicated. However, it is not known if senescence is causally linked to either stiffness or SFRP1 expression. In this study, we utilized in vitro HTM senescence to determine the effect on cellular stiffening and SFRP1 expression. Stiffness of cultured cells was measured using atomic force microscopy and the morphology of the cytoskeleton was determined using immunofluorescent analysis. SFRP1 expression was measured using qPCR and immunofluorescent analysis. Senescent cell stiffness increased 1.88±0.14 or 2.57±0.14 fold in the presence or absence of serum, respectively. This was accompanied by increased vimentin expression, stress fiber formation, and SFRP1 expression. In aggregate, these data demonstrate that senescence may be a causal factor in HTM stiffening and elevated SFRP1 expression, and contribute towards disease progression. These findings provide insight into the etiology of glaucoma and, more broadly, suggest a causal link between senescence and altered tissue biomechanics in aging-associated diseases. PMID:25915531

  17. On eigenmodes, stiffness, and sensitivity of atomic force microscope cantilevers in air versus liquids

    SciTech Connect

    Kiracofe, Daniel; Raman, Arvind

    2010-02-15

    The effect of hydrodynamic loading on the eigenmode shapes, modal stiffnesses, and optical lever sensitivities of atomic force microscope (AFM) microcantilevers is investigated by measuring the vibrations of such microcantilevers in air and water using a scanning laser Doppler vibrometer. It is found that for rectangular tipless microcantilevers, the measured fundamental and higher eigenmodes and their equivalent stiffnesses are nearly identical in air and in water. However, for microcantilevers with a tip mass or for picket shaped cantilevers, there is a marked difference in the second (and higher) eigenmode shapes between air and water that leads to a large decrease in their modal stiffness in water as compared to air as well as a decrease in their optical lever sensitivity. These results are explained in terms of hydrodynamic interactions of microcantilevers with nonuniform mass distribution. The results clearly demonstrate that tip mass and hydrodynamic loading must be taken into account in stiffness calibration and optical lever sensitivity calibration while using higher-order eigenmodes in dynamic AFM.

  18. Impact of diabetes mellitus on arterial stiffness in a representative sample of an urban Brazilian population

    PubMed Central

    2013-01-01

    Background Independent of other cardiovascular (CV) risk factors, increased arterial stiffness has been established as a predictor of morbidity and mortality. The main aim of this study was to investigate the impact of diabetes on arterial stiffness in a representative sample of an urban Brazilian population plus Amerindians. Methods A total of 1,415 individuals from the general population were randomly selected plus 588 Amerindians from a native community in Brazil. In addition, a sub-sample of 380 individuals from the general population had 5-year follow-up data. Pulse wave velocity (PWV) was measured with a non-invasive automatic device (Complior, Colson; Garges les Gonesses, France) and increased arterial stiffness was defined as PWV???12 m/s. Results In the overall group, diabetic individuals had higher frequencies of increased arterial stiffness and hypertension. They also had higher values of PWV, body mass index, total cholesterol, triglycerides, systolic and diastolic blood pressures compared to non-diabetic individuals (p?stiffness frequency were higher in diabetic individuals in both groups (hypertensive and non-hypertensive) (p?stiffness was observed in the diabetic individuals from the overall group (OR?=?2.27; CI?=?1.47-3.52, p?stiffness compared to non-diabetic individuals. Both diabetic and non-diabetic individuals had higher PWV values after 5 years. There was no significant difference in the 5-year PWV progression in diabetic compared to non-diabetic individuals. Conclusions These results confirm, in a sample of Brazilian population, that the presence of diabetes is associated with increased arterial stiffness and it may contribute in part to increased cardiovascular risk in diabetic patients. PMID:23965633

  19. On-machine ultrasonic sensors for paper stiffness. Final report

    SciTech Connect

    Hall, Maclin S.; Jackson, Theodore G.; Brown, Ernest

    2000-04-01

    This final report presents the results of a 5-year effort by the Institute of Paper Science and Technology (IPST) and its participating partners. The objective of this work was to develop and demonstrate sensors capable of measuring the velocity of ultrasound in the out-of-plane (ZD) and in-plane directions of paper as it is being produced on a commercial paper machine. On-machine ultrasonic measurements can be used to determine various mechanical properties of paper and to monitor process status and product quality. This report first presents a review of the background and potential benefits of on-machine ultrasonic measurements, then summarizes the results of previous work. The ZD measurement system involving the use of ultrasonic transducers in fluid-filled wheels is described in detail, including the method of measurement, the wheel mounting hardware, the on-machine operation, and an overview of the system software. Mill-trial results from two bump tests when producing 69{number_sign} and 55{number_sign} linearboard are presented. For the 69{number_sign} trial the correlation of ZD transit time with plybond and with ZDT (Z-direction tensile or internal bond strength) was greater than 0.8 (R squared). Also observed were ZD stiffness responses to refining and to calendering. ABB Industrial Systems Inc. was responsible for the in-plane sensor. A paper describing ABB's sensor and mill experience is appended.

  20. Transverse shear stiffness of laminated anisotropic shells

    NASA Technical Reports Server (NTRS)

    Cohen, G. A.

    1978-01-01

    Equations are derived for the transverse shear stiffness of laminated anisotropic shells. Without making assumptions for thickness distribution for either transverse shear stresses or strains, constitutive equations for the transverse shear deformation theory of anisotropic heterogeneous shells are found. The equations are based on Taylor series expansions about a generic point for stress resultants and couples, identically satisfying plate equilibrium equations. These equations are used to find statically correct expressions for in-surface stresses, transverse shear stresses, and the area density of transverse shear strain energy, in terms of transverse shear stress resultants and redundants. The application of Castigliano's theorem of least work minimizes shear strain energy with respect to the redundants. Examples are presented for several laminated walls. Good agreement is found between the results and those of exact three-dimensional elasticity solutions for the cylindrical bending of a plate.

  1. Stiffness of ? subunit of F(1)-ATPase.

    PubMed

    Okuno, Daichi; Iino, Ryota; Noji, Hiroyuki

    2010-11-01

    F(1)-ATPase is a molecular motor in which the ? subunit rotates inside the ?(3)?(3) ring upon adenosine triphosphate (ATP) hydrolysis. Recent works on single-molecule manipulation of F(1)-ATPase have shown that kinetic parameters such as the on-rate of ATP and the off-rate of adenosine diphosphate (ADP) strongly depend on the rotary angle of the ? subunit (Hirono-Hara et al. 2005; Iko et al. 2009). These findings provide important insight into how individual reaction steps release energy to power F(1) and also have implications regarding ATP synthesis and how reaction steps are reversed upon reverse rotation. An important issue regarding the angular dependence of kinetic parameters is that the angular position of a magnetic bead rotation probe could be larger than the actual position of the ? subunit due to the torsional elasticity of the system. In the present study, we assessed the stiffness of two different portions of F(1) from thermophilic Bacillus PS3: the internal part of the ? subunit embedded in the ?(3)?(3) ring, and the complex of the external part of the ? subunit and the ?(3)?(3) ring (and streptavidin and magnetic bead), by comparing rotational fluctuations before and after crosslinkage between the rotor and stator. The torsional stiffnesses of the internal and remaining parts were determined to be around 223 and 73 pNnm/radian, respectively. Based on these values, it was estimated that the actual angular position of the internal part of the ? subunit is one-fourth of the magnetic bead position upon stalling using an external magnetic field. The estimated elasticity also partially explains the accommodation of the intrinsic step size mismatch between F(o) and F(1)-ATPase. PMID:20549499

  2. Effects of proprioceptive neuromuscular facilitation stretching on stiffness and force-producing characteristics of the ankle in active women.

    PubMed

    Rees, Sven S; Murphy, Aron J; Watsford, Mark L; McLachlan, Ken A; Coutts, Aaron J

    2007-05-01

    The purpose of this study was to examine the effect of proprioceptive neuromuscular facilitation (PNF) stretching on musculotendinous unit (MTU) stiffness of the ankle joint. Twenty active women were assessed for maximal ankle range of motion, maximal strength of planter flexors, rate of force development, and ankle MTU stiffness. Subjects were randomly allocated into an experimental (n = 10) group or control group (n = 10). The experimental group performed PNF stretching on the ankle joint 3 times per week for 4 weeks, with physiological testing performed before and after the training period. After training, the experimental group significantly increased ankle range of motion (7.8%), maximal isometric strength (26%), rate of force development (25%), and MTU stiffness (8.4%) (p < 0.001). Four weeks of PNF stretching contributed to an increase in MTU stiffness, which occurred concurrently with gains to ankle joint range of motion. The results confirm that MTU stiffness and joint range of motion measurements appear to be separate entities. The increased MTU stiffness after the training period is explained by adaptations to maximal isometric muscle contractions, which were a component of PNF stretching. Because a stiffer MTU system is linked with an improved the ability to store and release elastic energy, PNF stretching would benefit certain athletic performance due to a reduced contraction time or greater mechanical efficiency. The results of this study suggest PNF stretching is a useful modality at increasing a joint's range of motion and its strength. PMID:17530973

  3. Hepatic and Splenic Stiffness Augmentation Assessed with MR Elastography in an in vivo Porcine Portal Hypertension Model

    PubMed Central

    Yin, Meng; Kolipaka, Arunark; Woodrum, David A.; Glaser, Kevin J.; Romano, Anthony J; Manduca, Armando; Talwalkar, Jayant A.; Araoz, Philip A.; McGee, Kiaran P.; Anavekar, Nandan S.; Ehman, Richard L.

    2013-01-01

    Purpose To investigate the influence of portal pressure on the shear stiffness of the liver and spleen in a well-controlled in vivo porcine model with MR Elastography (MRE). A significant correlation between portal pressure and tissue stiffness could be used to noninvasively assess increased portal venous pressure (portal hypertension), which is a frequent clinical condition caused by cirrhosis of the liver and is responsible for the development of many lethal complications. Materials and Methods During multiple intra-arterial infusions of Dextran-40 in three adult domestic pigs in vivo, 3-D abdominal MRE was performed with left ventricle and portal catheters measuring blood pressure simultaneously. Least-squares linear regressions were used to analyze the relationship between tissue stiffness and portal pressure. Results Liver and spleen stiffness have a dynamic component that increases significantly following an increase in portal or left ventricular pressure. Correlation coefficients with the linear regressions between stiffness and pressure exceeded 0.8 in most cases. Conclusion The observed stiffness-pressure relationship of the liver and spleen could provide a promising noninvasive method for assessing portal pressure. Using MRE to study the tissue mechanics associated with portal pressure may provide new insights into the natural history and pathophysiology of hepatic diseases and may have significant diagnostic value in the future. PMID:23418135

  4. VAGINAL DEGENERATION FOLLOWING IMPLANTATION OF SYNTHETIC MESH WITH INCREASED STIFFNESS

    PubMed Central

    Liang, Rui; Abramowitch, Steven; Knight, Katrina; Palcsey, Stacy; Nolfi, Alexis; Feola, Andrew; Stein, Susan; Moalli, Pamela A.

    2012-01-01

    Objective To compare the impact of the prototype prolapse mesh Gynemesh PS to that of two new generation lower stiffness meshes, UltraPro and SmartMesh, on vaginal morphology and structural composition. Design A mechanistic study employing a non-human primate (NHP) model. Setting Magee-Womens Research Institute at the University of Pittsburgh. Population Parous rhesus macaques, with similar age, weight, parity and POP-Q scores. Methods Following IACUC approval, 50 rhesus macaques were implanted with Gynemesh PS (n=12), UltraPro with its blue line perpendicular to the longitudinal axis of vagina (n=10), UltraPro with its blue line parallel to the longitudinal axis of vagina (n=8) and SmartMesh (n=8) via sacrocolpopexy following hysterectomy. Sham operated animals (n=12) served as controls. Main Outcome Measures The mesh-vagina complex (MVC) was removed after 12 weeks and analyzed for histomorphology, in situ cell apoptosis, total collagen, elastin, glycosaminoglycan content and total collagenase activity. Appropriate statistics and correlation analyses were performed accordingly. Results Relative to sham and the two lower stiffness meshes, Gynemesh PS had the greatest negative impact on vaginal histomorphology and composition. Compared to sham, implantation with Gynemesh PS caused substantial thinning of the smooth muscle layer (1557 ± 499?m vs 866 ± 210 ?m, P=0.02), increased apoptosis particularly in the area of the mesh fibers (P=0.01), decreased collagen and elastin content (20% (P=0.03) and 43% (P=0.02), respectively) and increased total collagenase activity (135% (P=0.01)). GAG (glycosaminoglycan), a marker of tissue injury, was the highest with Gynemesh PS compared to sham and other meshes (P=0.01). Conclusion Mesh implantation with the stiffer mesh Gynemesh PS induced a maladaptive remodeling response consistent with vaginal degeneration. PMID:23240802

  5. Mechanically stiff, electrically conductive composites of polymers and carbon nanotubes

    DOEpatents

    Worsley, Marcus A.; Kucheyev, Sergei O.; Baumann, Theodore F.; Kuntz, Joshua D.; Satcher, Jr., Joe H.; Hamza, Alex V.

    2015-07-21

    Using SWNT-CA as scaffolds to fabricate stiff, highly conductive polymer (PDMS) composites. The SWNT-CA is immersing in a polymer resin to produce a SWNT-CA infiltrated with a polymer resin. The SWNT-CA infiltrated with a polymer resin is cured to produce the stiff and electrically conductive composite of carbon nanotube aerogel and polymer.

  6. Accelerated Stochastic Simulation of the Stiff Enzyme-Substrate Reaction

    E-print Network

    Cao, Yang

    1 Accelerated Stochastic Simulation of the Stiff Enzyme-Substrate Reaction Yang Cao a) Dept into a product is a common reaction motif in cellular chemical systems. In the three reactions that comprise constituents than to produce a product molecule. This condition makes the reaction set mathematically "stiff

  7. Leg stiffness of sprinters using running-specific prostheses

    E-print Network

    Herr, Hugh

    stiffness of the prosthesis coupled with differences in the limb posture required to run with the prosthesisLeg stiffness of sprinters using running-specific prostheses Craig P. McGowan1,*, Alena M, USA Running-specific prostheses (RSF) are designed to replicate the spring-like nature of biologi- cal

  8. Differential Spring Stiffness Design for Finger Therapy Exercise Device

    E-print Network

    , middle and proximal phalanges and metacarpus. Suitable spring stiffness for DIP, PIP and MCP joints and proximal phalanges. Upon achieving desired posture, actuator was deactivated and the springs returned at distal, middle and proximal phalanges, coupled with differential spring stiffness design, allowed

  9. Characterization of the bending stiffness of large space structure joints

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey

    1989-01-01

    A technique for estimating the bending stiffness of large space structure joints is developed and demonstrated for an erectable joint concept. Experimental load-deflection data from a three-point bending test was used as input to solve a closed-form expression for the joint bending stiffness which was derived from linear beam theory. Potential error sources in both the experimental and analytical procedures are identified and discussed. The bending stiffness of a mechanically preloaded erectable joint is studied at three applied moments and seven joint orientations. Using this technique, the joint bending stiffness was bounded between 6 and 17 percent of the bending stiffness of the graphite/epoxy strut member.

  10. Stiffness coupling application to modal synthesis program, users guide

    NASA Technical Reports Server (NTRS)

    Kuhar, E. J.

    1976-01-01

    A FORTRAN IV computer program used to perform modal synthesis of structures by stiffness coupling, using the dynamic transformation method is described. The program was named SCAMP (Stiffness Coupling Approach Modal-Synthesis Program). The program begins with the entry of a substructure's physical mode shapes and eigenvalues or a substructure's mass and stiffness matrix. If the mass and stiffness matrices are entered, the eigen problem for the individual substructure is solved. Provisions are included for a maximum of 20 substructures which are coupled by stiffness matrix springs. Each substructure has a number degrees of freedom (DOF), except that for DOF greater than 100; vector sets having maximum row and column size of 100 were generated prior to entering SCAMP. The substructures are then coupled together via coupling springs, and the dynamic transformation is used to reduce the size of the eigen problem.

  11. An experimental nonlinear low dynamic stiffness device for shock isolation

    NASA Astrophysics Data System (ADS)

    Francisco Ledezma-Ramirez, Diego; Ferguson, Neil S.; Brennan, Michael J.; Tang, Bin

    2015-07-01

    The problem of shock generated vibration is very common in practice and difficult to isolate due to the high levels of excitation involved and its transient nature. If not properly isolated it could lead to large transmitted forces and displacements. Typically, classical shock isolation relies on the use of passive stiffness elements to absorb energy by deformation and some damping mechanism to dissipate residual vibration. The approach of using nonlinear stiffness elements is explored in this paper, focusing in providing an isolation system with low dynamic stiffness. The possibilities of using such a configuration for a shock mount are studied experimentally following previous theoretical models. The model studied considers electromagnets and permanent magnets in order to obtain nonlinear stiffness forces using different voltage configurations. It is found that the stiffness nonlinearities could be advantageous in improving shock isolation in terms of absolute displacement and acceleration response when compared with linear elastic elements.

  12. DETERIORATION IN BIOMECHANICAL PROPERTIES OF THE VAGINA FOLLOWING IMPLANTATION OF A HIGH STIFFNESS PROLAPSE MESH

    PubMed Central

    Feola, Andrew; Abramowitch, Steven; Jallah, Zegbeh; Stein, Suzan; Barone, William; Palcsey, Stacy; Moalli, Pamela

    2012-01-01

    Objective Define the impact of prolapse mesh on the biomechanical properties of the vagina by comparing the prototype Gynemesh PS (Ethicon, Somerville, NJ) to 2 new generation lower stiffness meshes, SmartMesh (Coloplast, Minneapolis, MN) and UltraPro (Ethicon). Design A study employing a non-human primate model Setting University of Pittsburgh Population 45 parous rhesus macaques Methods Meshes were implanted via sacrocolpexy after hysterectomy and compared to Sham. Because its stiffness is highly directional UltraPro was implanted in two directions: UltraPro Perpendicular (less stiff) and UltraPro Parallel (more stiff), with the indicated direction referring to the blue orientation lines. The mesh-vaginal complex (MVC) was excised en toto after 3 months. Main Outcome Measures Active mechanical properties were quantified as contractile force generated in the presence of 120 mM KCl. Passive mechanical properties (a tissues ability to resist an applied force) were measured using a multi-axial protocol. Results Vaginal contractility decreased 80% following implantation with the Gynemesh PS (p=0.001), 48% after SmartMesh (p=0.001), 68% after UltraPro parallel (p=0.001) and was highly variable after UltraPro perpendicular (p =0.16). The tissue contribution to the passive mechanical behavior of the MVC was drastically reduced for Gynemesh PS (p=0.003) but not SmartMesh (p=0.9) or UltraPro independent of the direction of implantation (p=0.68 and p=0.66, respectively). Conclusions Deterioration of the mechanical properties of the vagina was highest following implantation with the stiffest mesh, Gynemesh PS. Such a decrease associated with implantation of a device of increased stiffness is consistent with findings from other systems employing prostheses for support. PMID:23240801

  13. Acute Effect on Arterial Stiffness after Performing Resistance Exercise by Using the Valsalva Manoeuvre during Exertion

    PubMed Central

    Mak, Wai Yip Vincent; Lai, Wai Keung Christopher

    2015-01-01

    Background. Performing resistance exercise could lead to an increase in arterial stiffness. Objective. We investigate the acute effect on arterial stiffness by performing Valsalva manoeuvre during resistance exercise. Materials and Methods. Eighteen healthy young men were assigned to perform bicep curls by using two breathing techniques (exhalation and Valsalva manoeuvre during muscle contraction) on two separate study days. Carotid pulsed wave velocity (cPWV) was measured as an indicator to reflect the body central arterial stiffness using a high-resolution ultrasound system, and its value was monitored repeatedly at three predefined time intervals: before resistance exercise, immediately after exercise, and 15 minutes after exercise. Results. At the 0th minute after resistance exercise was performed using the Valsalva manoeuvre during exertion, a significant increase in cPWV (4.91?m/s ± 0.52) compared with the baseline value (4.67?m/s ± 0.32, P = 0.008) was observed, and then it nearly returned to its baseline value at the 15th minute after exercise (4.66?m/s ± 0.44, P = 0.010). These findings persisted after adjusting for age, body mass index, and systolic blood pressure. Conclusion. Our result suggests short duration of resistance exercise may provoke a transient increase in central arterial stiffness in healthy young men. PMID:26539481

  14. Influence of wheel configuration on wheelchair basketball performance: wheel stiffness, tyre type and tyre orientation.

    PubMed

    Mason, B S; Lemstra, M; van der Woude, L H V; Vegter, R; Goosey-Tolfrey, V L

    2015-04-01

    The aim of the current investigation was to explore the lateral stiffness of different sports wheelchair wheels available to athletes in 'new' and 'used' conditions and to determine the effect of (a) stiffness, (b) tyre type (clincher vs. tubular) and (c) tyre orientation on the physiological and biomechanical responses to submaximal and maximal effort propulsion specific to wheelchair basketball. Eight able-bodied individuals participated in the laboratory-based testing, which took place on a wheelchair ergometer at two fixed speeds (1.1 and 2.2 m s(-1)). Outcome measures were power output and physiological demand (oxygen uptake and heart rate). Three participants with experience of over-ground sports wheelchair propulsion also performed 2 × 20 m sprints in each wheel configuration. Results revealed that wheels differed significantly in lateral stiffness with the 'new' Spinergy wheel shown to be the stiffest (678.2 ± 102.1 N mm(-1)). However the effects of stiffness on physiological demand were minimal compared to tyre type whereby tubular tyres significantly reduced the rolling resistance and power output in relation to clincher tyres. Therefore tyre type (and subsequently inflation pressure) remains the most important aspect of wheel specification for athletes to consider and monitor when configuring a sports wheelchair. PMID:25726151

  15. Muscle stiffness estimation using a system identification technique applied to evoked mechanomyogram during cycling exercise.

    PubMed

    Uchiyama, Takanori; Saito, Kaito; Shinjo, Katsuya

    2015-12-01

    The aims of this study were to develop a method to extract the evoked mechanomyogram (MMG) during cycling exercise and to clarify muscle stiffness at various cadences, workloads, and power. Ten young healthy male participants were instructed to pedal a cycle ergometer at cadences of 40 and 60rpm. The loads were 4.9, 9.8, 14.7, and 19.6N, respectively. One electrical stimulus per two pedal rotations was applied to the vastus lateralis muscle at a knee angle of 80° in the down phase. MMGs were measured using a capacitor microphone, and the MMGs were divided into stimulated and non-stimulated sequences. Each sequence was synchronously averaged. The synchronously averaged non-stimulated MMG was subtracted from the synchronously averaged stimulated MMG to extract an evoked MMG. The evoked MMG system was identified and the poles of the transfer function were calculated. The poles and mass of the vastus lateralis muscle were used to estimate muscle stiffness. Results showed that muscle stiffness was 186-626N/m and proportional to the workloads and power. In conclusion, our method can be used to assess muscle stiffness proportional to the workload and power. PMID:26493234

  16. Damage Detection on Sudden Stiffness Reduction Based on Discrete Wavelet Transform

    PubMed Central

    Chen, Bo; Chen, Zhi-wei; Wang, Gan-jun; Xie, Wei-ping

    2014-01-01

    The sudden stiffness reduction in a structure may cause the signal discontinuity in the acceleration responses close to the damage location at the damage time instant. To this end, the damage detection on sudden stiffness reduction of building structures has been actively investigated in this study. The signal discontinuity of the structural acceleration responses of an example building is extracted based on the discrete wavelet transform. It is proved that the variation of the first level detail coefficients of the wavelet transform at damage instant is linearly proportional to the magnitude of the stiffness reduction. A new damage index is proposed and implemented to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. Numerical simulation using a five-story shear building under different types of excitation is carried out to assess the effectiveness and reliability of the proposed damage index for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also investigated. The made observations demonstrate that the proposed damage index can accurately identify the sudden damage events if the noise intensity is limited. PMID:24991647

  17. 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

  18. Leg stiffness adjustment during hopping at different intensities and frequencies.

    PubMed

    Mrdakovic, Vladimir; Ilic, Dusko; Vulovic, Radun; Matic, Milan; Jankovic, Nenad; Filipovic, Nenad

    2014-01-01

    Understanding leg and joint stiffness adjustment during maximum hopping may provide important information for developing more effective training methods. It has been reported that ankle stiffness has major influence on stable spring-mass dynamics during submaximal hopping, and that knee stiffness is a major determinant for hopping performance during maximal hopping task. Furthermore, there are no reports on how the height of the previous hop could affect overall stiffness modulation of the subsequent maximum one. The purpose of the present study was to determine whether and how the jump height of the previous hop affects leg and joint stiffness for subsequent maximum hop. Ten participants completed trials in which they repeatedly hopped as high as possible (MX task) and trials in which they were instructed to perform several maximum hops with 3 preferred (optimal) height hops between each of them (P3MX task). Both hopping tasks were performed at 2.2 Hz hopping frequency and at the participant's preferred (freely chosen) frequency as well. By comparing results of those hopping tasks, we found that ankle stiffness at 2.2 Hz ( p = 0.041) and knee stiffness at preferred frequency ( p = 0.045) was significantly greater for MX versus P3MX tasks. Leg stiffness for 2.2 Hz hopping is greater than for the preferred frequency. Ankle stiffness is greater for 2.2 Hz than for preferred frequencies; opposite stands for knee stiffness. The results of this study suggest that preparatory hop height can be considered as an important factor for modulation of maximum hop. PMID:25308379

  19. Stiffness characteristics of airfoils under pulse loading

    NASA Astrophysics Data System (ADS)

    Turner, Kevin Eugene

    The turbomachinery industry continually struggles with the adverse effects of contact rubs between airfoils and casings. The key parameter controlling the severity of a given rub event is the contact load produced when the airfoil tips incur into the casing. These highly non-linear and transient forces are difficult to calculate and their effects on the static and rotating components are not well understood. To help provide this insight, experimental and analytical capabilities have been established and exercised through an alliance between GE Aviation and The Ohio State University Gas Turbine Laboratory. One of the early findings of the program is the influence of blade flexibility on the physics of rub events. The core focus of the work presented in this dissertation is to quantify the influence of airfoil flexibility through a novel modeling approach that is based on the relationship between applied force duration and maximum tip deflection. This relationship is initially established using a series of forward, non-linear and transient analyses in which simulated impulse rub loads are applied. This procedure, although effective, is highly inefficient and costly to conduct by requiring numerous explicit simulations. To alleviate this issue, a simplified model, named the pulse magnification model, is developed that only requires a modal analysis and a static analyses to fully describe how the airfoil stiffness changes with respect to load duration. Results from the pulse magnification model are compared to results from the full transient simulation method and to experimental results, providing sound verification for the use of the modeling approach. Furthermore, a unique and highly efficient method to model airfoil geometries was developed and is outlined in this dissertation. This method produces quality Finite Element airfoil definitions directly from a fully parameterized mathematical model. The effectiveness of this approach is demonstrated by comparing modal properties of the simulated geometries to modal properties of various current airfoil designs. Finally, this modeling approach was used in conjunction with the pulse magnification model to study the effects of various airfoil geometric features on the stiffness of the blade under impulsive loading.

  20. Anterior Glenohumeral Laxity and Stiffness After a Shoulder-Strengthening Program in Collegiate Cheerleaders

    PubMed Central

    Laudner, Kevin G; Metz, Betsy; Thomas, David Q

    2013-01-01

    Context Approximately 62% of all cheerleaders sustain some type of orthopaedic injury during their cheerleading careers. Furthermore, the occurrence of such injuries has led to inquiry regarding optimal prevention techniques. One possible cause of these injuries may be related to inadequate conditioning in cheerleaders. Objective To determine whether a strength and conditioning program produces quantifiable improvements in anterior glenohumeral (GH) laxity and stiffness. Design Descriptive laboratory study. Setting University laboratory. Patients or Other Participants A sample of 41 collegiate cheerleaders (24 experimental and 17 control participants) volunteered. No participants had a recent history (in the past 6 months) of upper extremity injury or any history of upper extremity surgery. Intervention(s) The experimental group completed a 6-week strength and conditioning program between the pretest and posttest measurements; the control group did not perform any strength training between tests. Main Outcome Measure(s) We measured anterior GH laxity and stiffness with an instrumented arthrometer. We conducted a group × time analysis of variance with repeated measures on time (P < .05) to determine differences between groups. Results A significant interaction was demonstrated, with the control group having more anterior GH laxity at the posttest session than the strengthening group (P = .03, partial ?2 = 0.11). However, no main effect for time (P = .92) or group (P = .97) was observed. In another significant interaction, the control group had less anterior GH stiffness at the posttest session than the strengthening group (P = .03, partial ?2 = 0.12). Main effects for time (P = .02) and group (P = .004) were also significant. Conclusions Cheerleaders who participate in a shoulder-strengthening program developed less anterior GH laxity and more stiffness than cheerleaders in the control group. PMID:23672322

  1. A new method for accurately determining the modal equivalent stiffness ratio of bonded piezoelectric structures

    NASA Astrophysics Data System (ADS)

    Yamada, Keisuke; Matsuhisa, Hiroshi; Utsuno, Hideo

    2012-07-01

    This paper describes new methods for measuring the modal equivalent stiffness ratios and modal electromechanical coupling coefficients of piezoelectric elements attached to a host structure such as a beam. Modal equivalent stiffness ratios and modal electromechanical coupling coefficients are essential for estimating the performance and determining an optimum design of active vibration control and passive vibration suppression systems that use piezoelectric elements. Accurate determination of these modal parameters is also useful for other systems including piezoelectric sensors and energy generators. This paper not only describes the measurement methods but also presents the theoretical formulations derived by taking into account the effect of adhesive bonds. The formulations in this paper demonstrate the necessity of experimental measurements and the accuracy enhancements that the theoretical estimations can provide. Conventional methods for obtaining the modal equivalent stiffness ratios are sensitive to measurement errors, which result in the loss of accuracy, rendering these methods unreliable for many practical applications. The proposed methods use an inductor instead of an open circuit to address the abovementioned issue and, thereby, provide significant improvement in the accuracy. Because the loss factors of the experimental apparatus tend to compromise the accuracy of the proposed methods, a method using a negative resistor is proposed, theoretically analyzed, and confirmed to eliminate some of the errors introduced by loss factors. The advantages of the proposed methods and the effectiveness of theoretical analysis, considering the effect of adhesive bonds, are verified experimentally.

  2. What drives the translocation of stiff chains?

    PubMed Central

    Zandi, Roya; Reguera, David; Rudnick, Joseph; Gelbart, William M.

    2003-01-01

    We study the dynamics of the passage of a stiff chain through a pore into a cell containing particles that bind reversibly to it. Using Brownian molecular dynamics simulations we investigate the mean first-passage time as a function of the length of the chain inside for different concentrations of binding particles. As a consequence of the interactions with these particles, the chain experiences a net force along its length whose calculated value from the simulations accounts for the velocity at which it enters the cell. This force can in turn be obtained from the solution of a generalized diffusion equation incorporating an effective Langmuir adsorption free energy for the chain plus binding particles. These results suggest a role of binding particles in the translocation process that is in general quite different from that of a Brownian ratchet. Furthermore, nonequilibrium effects contribute significantly to the dynamics; e.g., the chain often enters the cell faster than particle binding can be saturated, resulting in a force several times smaller than the equilibrium value. PMID:12851462

  3. Aging affects passive stiffness and spindle function of the rat soleus muscle.

    PubMed

    Rosant, Cédric; Nagel, Marie-Danielle; Pérot, Chantal

    2007-04-01

    Aging affects many motor functions, notably the spinal stretch reflexes and muscle spindle sensitivity. Spindle activation also depends on the elastic properties of the structures linked to the proprioceptive receptors. We have calculated a spindle efficacy index, SEI, for old rats. This index relates the spindle sensitivity, deduced from electroneurograms recording (ENG), to the passive stiffness of the muscle. Spindle sensitivity and passive incremental stiffness were calculated during ramp and hold stretches imposed on pseudo-isolated soleus muscles of control rats (aged 4 months, n=12) and old rats (aged 24 months, n=16). SEI were calculated for the dynamic and static phases of ramp (1-80 mm/s) and for hold (0.5-2mm) stretches imposed at two reference lengths: length threshold for spindle afferents discharges, L(n) (neurogram length) and slack length, L(s). The passive incremental stiffness was calculated from the peak and steady values of passive tension, measured under the stretch conditions used for the ENG recordings, and taking into account the muscle cross-sectional area. The pseudo-isolated soleus muscles were also stretched to establish the stress-strain relationship and to calculate muscle stiffness constant. The contralateral muscle was used to count muscle spindles and spindle fibers (ATPase staining) and immunostained to identify MyHC isoforms. L(n) and L(s) lengths were not significantly different in the control group, while L(n) was significantly greater than L(s) in old muscles. Under dynamic conditions, the SEI of old muscles was the same as in controls at L(s), but it was significantly lower than in controls at L(n) due to increased passive incremental stiffness under the stretch conditions used to analyze the ENG. Under static conditions, the SEI of old muscles was significantly lower than control values at all the stretch amplitudes and threshold lengths tested, due to increased passive incremental stiffness and decreased spindle sensitivity at L(s). The muscle stiffness constant values were greater in old muscles than in controls, confirming the changes in elastic properties under passive conditions due to aging. Aging also altered the intrafusal fibers: it increased the mean number of intrafusal fibers and the contents in the slow, neonatal and developmental isoforms intrafusal of MyHC have been modified. These structural modifications do not seem great enough to counteract the loss of the spindle sensitivity or the spindle efficacy under passive conditions and after the nerve was severed. However, they may help to maintain the spindle afferent message under natural conditions and under fusimotor control. PMID:17118602

  4. Roles of Arterial Stiffness and Blood Pressure in Hypertension-Associated Cognitive Decline in Healthy Adults.

    PubMed

    Hajjar, Ihab; Goldstein, Felicia C; Martin, Greg S; Quyyumi, Arshed A

    2016-01-01

    Although there is strong evidence that hypertension leads to cognitive decline, especially in the executive domain, the relationship between blood pressure and cognition has been conflicted. Hypertension is characterized by blood pressure elevation and increased arterial stiffness. We aimed at investigating whether arterial stiffness would be superior to blood pressure in predicting cognitive decline and explaining the hypertension-executive decline association. A randomly selected asymptomatic population (n=591, age=49.2 years, 70% women, 27% black, and education=18 years) underwent annual vascular and cognitive assessments. Cognition was assessed using computerized versions commonly used cognitive tests, and principal component analysis was used for deriving cognitive scores for executive function, memory, and working memory. Arterial stiffness was measured by carotid-femoral pulse wave velocity (PWV). Higher PWV, but not blood pressure, was associated with a steeper decline in executive (P=0.0002), memory (P=0.05), and working memory (P=0.02) scores after adjusting for demographics, education, and baseline cognitive performance. This remained true after adjusting for hypertension. Hypertension was associated with greater decline in executive score (P=0.0029) and those with combined hypertension and elevated PWV (>7 m/s) had the greatest decline in executive score (P value hypertension×PWV=0.02). PWV explained the association between hypertension and executive function (P value for hypertension=0.0029 versus 0.24 when adjusting for PWV). In healthy adults, increased arterial stiffness is superior to blood pressure in predicting cognitive decline in all domains and in explaining the hypertension-executive function association. Arterial stiffness, especially in hypertension, may be a target in the prevention of cognitive decline. PMID:26527049

  5. Biomechanical constraints on the feedforward regulation of endpoint stiffness

    PubMed Central

    Murray, Wendy M.; Perreault, Eric J.

    2012-01-01

    Although many daily tasks tend to destabilize arm posture, it is still possible to have stable interactions with the environment by regulating the multijoint mechanics of the arm in a task-appropriate manner. For postural tasks, this regulation involves the appropriate control of endpoint stiffness, which represents the stiffness of the arm at the hand. Although experimental studies have been used to evaluate endpoint stiffness control, including the orientation of maximal stiffness, the underlying neural strategies remain unknown. Specifically, the relative importance of feedforward and feedback mechanisms has yet to be determined due to the difficulty separately identifying the contributions of these mechanisms in human experiments. This study used a previously validated three-dimensional musculoskeletal model of the arm to quantify the degree to which the orientation of maximal endpoint stiffness could be changed using only steady-state muscle activations, used to represent feedforward motor commands. Our hypothesis was that the feedforward control of endpoint stiffness orientation would be significantly constrained by the biomechanical properties of the musculoskeletal system. Our results supported this hypothesis, demonstrating substantial biomechanical constraints on the ability to regulate endpoint stiffness throughout the workspace. The ability to regulate stiffness orientation was further constrained by additional task requirements, such as the need to support the arm against gravity or exert forces on the environment. Together, these results bound the degree to which slowly varying feedforward motor commands can be used to regulate the orientation of maximum arm stiffness and provide a context for better understanding conditions in which feedback control may be needed. PMID:22832565

  6. Substrate stiffness-modulated registry phase correlations in cardiomyocytes map structural order to coherent beating

    NASA Astrophysics Data System (ADS)

    Dasbiswas, K.; Majkut, S.; Discher, D. E.; Safran, Samuel A.

    2015-01-01

    Recent experiments show that both striation, an indication of the structural registry in muscle fibres, as well as the contractile strains produced by beating cardiac muscle cells can be optimized by substrate stiffness. Here we show theoretically how the substrate rigidity dependence of the registry data can be mapped onto that of the strain measurements. We express the elasticity-mediated structural registry as a phase-order parameter using a statistical physics approach that takes the noise and disorder inherent in biological systems into account. By assuming that structurally registered myofibrils also tend to beat in phase, we explain the observed dependence of both striation and strain measurements of cardiomyocytes on substrate stiffness in a unified manner. The agreement of our ideas with experiment suggests that the correlated beating of heart cells may be limited by the structural order of the myofibrils, which in turn is regulated by their elastic environment.

  7. Energy cost of running and Achilles tendon stiffness in man and woman trained runners

    PubMed Central

    Fletcher, Jared R.; Pfister, Ted R.; MacIntosh, Brian R.

    2013-01-01

    Abstract The energy cost of running (Erun), a key determinant of distance running performance, is influenced by several factors. Although it is important to express Erun as energy cost, no study has used this approach to compare similarly trained men and women. Furthermore, the relationship between Achilles tendon (AT) stiffness and Erun has not been compared between men and women. Therefore, our purpose was to determine if sex?specific differences in Erun and/or AT stiffness existed. Erun (kcal kg?1 km?1) was determined by indirect calorimetry at 75%, 85%, and 95% of the speed at lactate threshold (sLT) on 11 man (mean ± SEM, 35 ± 1 years, 177 ± 1 cm, 78 ± 1 kg, 1 = 56 ± 1 mL kg?1 min?1) and 18 woman (33 ± 1 years, 165 ± 1 cm, 58 ± 1 kg, 2 = 50 ± 0.3 mL kg?1 min?1) runners. AT stiffness was measured using ultrasound with dynamometry. Man Erun was 1.01 ± 0.06, 1.04 ± 0.07, and 1.07 ± 0.07 kcal kg?1 km?1. Woman Erun was 1.05 ± 0.10, 1.07 ± 0.09, and 1.09 ± 0.10 kcal kg?1 km?1. There was no significant sex effect for Erun or RER, but both increased with speed (P < 0.01) expressed relative to sLT. High?range AT stiffness was 191 ± 5.1 N mm?1 for men and 125 ± 5.5 N mm?1, for women (P < 0.001). The relationship between low?range AT stiffness and Erun was significant at all measured speeds for women (r2 = 0.198, P < 0.05), but not for the men. These results indicate that when Erun is measured at the same relative intensity, there are no sex?specific differences in Erun or substrate use. Furthermore, differences in Erun cannot be explained solely by differences in AT stiffness. PMID:24744857

  8. Measuring Interfacial Stiffness of Adhesively-Bonded Edward A. Le

    E-print Network

    Nairn, John A.

    and the final load at failure is recorded. Some common strength tests are lap shear testing (ASTM 2008a), shear block testing (ASTM 2008b), and internal bond testing (ASTM 2008c). Adhesive bonds are tested for fracture toughness (Kut- nar, Kamke, and Sernek, 2008; ASTM 2005; ASTM E2006), but these are also probing

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

    PubMed Central

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

    2015-01-01

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

  10. Effects of non-uniform stiffness on the swimming performance of a passively-flexing, fish-like foil model.

    PubMed

    Lucas, Kelsey N; Thornycroft, Patrick J M; Gemmell, Brad J; Colin, Sean P; Costello, John H; Lauder, George V

    2015-10-01

    Simple mechanical models emulating fish have been used recently to enable targeted study of individual factors contributing to swimming locomotion without the confounding complexity of the whole fish body. Yet, unlike these uniform models, the fish body is notable for its non-uniform material properties. In particular, flexural stiffness decreases along the fish's anterior-posterior axis. To identify the role of non-uniform bending stiffness during fish-like propulsion, we studied four foil model configurations made by adhering layers of plastic sheets to produce discrete regions of high (5.5 × 10(-5) Nm(2)) and low (1.9 × 10(-5) Nm(2)) flexural stiffness of biologically-relevant magnitudes. This resulted in two uniform control foils and two foils with anterior regions of high stiffness and posterior regions of low stiffness. With a mechanical flapping foil controller, we measured forces and torques in three directions and quantified swimming performance under both heaving (no pitch) and constant 0° angle of attack programs. Foils self-propelled at Reynolds number 21 000-115 000 and Strouhal number ?0.20-0.25, values characteristic of fish locomotion. Although previous models have emphasized uniform distributions and heaving motions, the combination of non-uniform stiffness distributions and 0° angle of attack pitching program was better able to reproduce the kinematics of freely-swimming fish. This combination was likewise crucial in maximizing swimming performance and resulted in high self-propelled speeds at low costs of transport and large thrust coefficients at relatively high efficiency. Because these metrics were not all maximized together, selection of the 'best' stiffness distribution will depend on actuation constraints and performance goals. These improved models enable more detailed, accurate analyses of fish-like swimming. PMID:26447541

  11. Improved Equivalent Linearization Implementations Using Nonlinear Stiffness Evaluation

    NASA Technical Reports Server (NTRS)

    Rizzi, Stephen A.; Muravyov, Alexander A.

    2001-01-01

    This report documents two new implementations of equivalent linearization for solving geometrically nonlinear random vibration problems of complicated structures. The implementations are given the acronym ELSTEP, for "Equivalent Linearization using a STiffness Evaluation Procedure." Both implementations of ELSTEP are fundamentally the same in that they use a novel nonlinear stiffness evaluation procedure to numerically compute otherwise inaccessible nonlinear stiffness terms from commercial finite element programs. The commercial finite element program MSC/NASTRAN (NASTRAN) was chosen as the core of ELSTEP. The FORTRAN implementation calculates the nonlinear stiffness terms and performs the equivalent linearization analysis outside of NASTRAN. The Direct Matrix Abstraction Program (DMAP) implementation performs these operations within NASTRAN. Both provide nearly identical results. Within each implementation, two error minimization approaches for the equivalent linearization procedure are available - force and strain energy error minimization. Sample results for a simply supported rectangular plate are included to illustrate the analysis procedure.

  12. Torque-stiffness-controlled dynamic walking with central pattern generators.

    PubMed

    Huang, Yan; Vanderborght, Bram; Van Ham, Ronald; Wang, Qining

    2014-12-01

    Walking behavior is modulated by controlling joint torques in most existing passivity-based bipeds. Controlled Passive Walking with adaptable stiffness exhibits controllable natural motions and energy efficient gaits. In this paper, we propose torque-stiffness-controlled dynamic bipedal walking, which extends the concept of Controlled Passive Walking by introducing structured control parameters and a bio-inspired control method with central pattern generators. The proposed walking paradigm is beneficial in clarifying the respective effects of the external actuation and the internal natural dynamics. We present a seven-link biped model to validate the presented walking. Effects of joint torque and joint stiffness on gait selection, walking performance and walking pattern transitions are studied in simulations. The work in this paper develops a new solution of motion control of bipedal robots with adaptable stiffness and provides insights of efficient and sophisticated walking gaits of humans. PMID:25128320

  13. Stiffness mapping of compliant parallel mechanisms in a serial arrangement

    E-print Network

    Florida, University of

    Stiffness mapping of compliant parallel mechanisms in a serial arrangement Hyun K. Jung a , Carl D.: +1 352 392 9461; fax: +1 352 392 1071. E-mail addresses: hyunkwon.jung@gmail.com (H.K. Jung), ccrane

  14. STIFFNESS MAPPING OF PLANAR COMPLIANT PARALLEL MECHANISMS IN A

    E-print Network

    Florida, University of

    , Carl D. Crane III University of Florida Department of Mechanical and Aerospace Engineering hyunkwon.jungSTIFFNESS MAPPING OF PLANAR COMPLIANT PARALLEL MECHANISMS IN A SERIAL ARRANGEMENT Hyun K. Jung

  15. Operator-Based Preconditioning of Stiff Hyperbolic Systems

    SciTech Connect

    Reynolds, Daniel R.; Samtaney, Ravi; Woodward, Carol S.

    2009-02-09

    We introduce an operator-based scheme for preconditioning stiff components encoun- tered in implicit methods for hyperbolic systems of partial differential equations posed on regular grids. The method is based on a directional splitting of the implicit operator, followed by a char- acteristic decomposition of the resulting directional parts. This approach allows for solution to any number of characteristic components, from the entire system to only the fastest, stiffness-inducing waves. We apply the preconditioning method to stiff hyperbolic systems arising in magnetohydro- dynamics and gas dynamics. We then present numerical results showing that this preconditioning scheme works well on problems where the underlying stiffness results from the interaction of fast transient waves with slowly-evolving dynamics, scales well to large problem sizes and numbers of processors, and allows for additional customization based on the specific problems under study.

  16. Wing/store flutter with nonlinear pylon stiffness

    NASA Technical Reports Server (NTRS)

    Desmarais, R. N.; Reed, W. H., III

    1980-01-01

    Recent wind tunnel tests and analytical studies show that a store mounted on a pylon with soft pitch stiffness provides substantial increase in flutter speed of fighter aircraft and reduces dependency of flutter on mass and inertia of the store. This concept, termed the decoupler pylon, utilizes a low frequency control system to maintain pitch alignment of the store during maneuvers and changing flight conditions. Under rapidly changing transient loads, however, the alignment control system may allow the store to momentarily bottom against a relatively stiff backup structure in which case the pylon stiffness acts as a hardening nonlinear spring. Such structural nonlinearities are known to affect not only the flutter speed but also the basic behavior of the instability. The influence of pylon stiffness nonlinearities or the flutter characteristics of wing mounted external stores is examined.

  17. Knee joint stiffness and function following total knee arthroplasty 

    E-print Network

    Lane, Judith

    2010-01-01

    Introduction: Studies show that Total Knee Arthroplasty (TKA) is successful for the majority of patients however some continue to experience some functional limitations and anecdotal evidence indicates that stiffness is ...

  18. Arterial Stiffness and Renal Replacement Therapy: A Controversial Topic

    PubMed Central

    Fischer, Edmundo Cabrera; Zócalo, Yanina; Galli, Cintia; Bia, Daniel

    2015-01-01

    The increase of arterial stiffness has been to have a significant impact on predicting mortality in end-stage renal disease patients. Pulse wave velocity (PWV) is a noninvasive, reliable parameter of regional arterial stiffness that integrates the vascular geometry and arterial wall intrinsic elasticity and is capable of predicting cardiovascular mortality in this patient population. Nevertheless, reports on PWV in dialyzed patients are contradictory and sometimes inconsistent: some reports claim the arterial wall stiffness increases (i.e., PWV increase), others claim that it is reduced, and some even state that it augments in the aorta while it simultaneously decreases in the brachial artery pathway. The purpose of this study was to analyze the literature in which longitudinal or transversal studies were performed in hemodialysis and/or peritoneal dialysis patients, in order to characterize arterial stiffness and the responsiveness to renal replacement therapy. PMID:26064684

  19. Passive mechanical models of fish caudal fins: effects of shape and stiffness on self-propulsion.

    PubMed

    Feilich, Kara L; Lauder, George V

    2015-06-01

    Fishes are found in a great variety of body forms with tail shapes that vary from forked tuna-like tails to the square-shaped tails found in some deep-bodied species. Hydrodynamic theory suggests that a fish's body and tail shape affects undulatory swimming performance. For example, a narrow caudal peduncle is believed to reduce drag, and a tuna-like tail to increase thrust. Despite the prevalence of these assertions, there is no experimental verification of the hydrodynamic mechanisms that may confer advantages on specific forms. Here, we use a mechanically-actuated flapping foil model to study how two aspects of shape, caudal peduncle depth and presence or absence of a forked caudal fin, may affect different aspects of swimming performance. Four different foil shapes were each made of plastics of three different flexural stiffnesses, permitting us to study how shape might interact with stiffness to produce swimming performance. For each foil, we measured the self-propelling swimming speed. In addition, we measured the forces, torques, cost of transport and power coefficient of each foil swimming at its self-propelling speed. There was no single 'optimal' foil exhibiting the highest performance in all metrics, and for almost all measures of swimming performance, foil shape and flexural stiffness interacted in complicated ways. Particle image velocimetry of several foils suggested that stiffness might affect the relative phasing of the body trailing edge and the caudal fin leading edge, changing the flow incident to the tail, and affecting hydrodynamics of the entire foil. The results of this study of a simplified model of fish body and tail morphology suggest that considerable caution should be used when inferring a swimming performance advantage from body and tail shape alone. PMID:25879846

  20. 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.

  1. Study of flexural stiffness in delaminated composite plates

    NASA Astrophysics Data System (ADS)

    Kwon, Y. W.; Weiseman, K.

    This paper studied the effect of delamination on the flexural stiffness of laminated composite plates using the FEM. A plate bending element, which has displacements as degrees of freedom at nodes but not rotations, was used. The plate bending element includes the transverse shear deformation. Both angle-ply (+/- theta deg) and cross-ply (0/90 deg) laminates were considered with delamination between the two layers. The reduction in flexural stiffness was calculated by comparing deflections.

  2. Rotator cuff lesions with shoulder stiffness: updated pathomechanisms and management.

    PubMed

    Ko, Jih-Yang; Wang, Feng-Sheng

    2011-01-01

    Few previous studies have investigated the pathomechanism and managements of rotator cuff lesions with shoulder stiffness. Based on observations by Codman in 1934, frozen shoulder presumably relates to rotator cuff tendenitis. In the past six decades, tended to discriminate primary frozen shoulder from secondary shoulder stiffness due to shoulder disorders such as rotator cuff lesions or trauma. Intrinsic degeneration and outlet acromial spur impingement are reported as pathogenic causes of rotator cuff lesion. Although patients with rotator cuff lesions with shoulder stiffness or adhesive capsulitis (frozen shoulder) may have similar complaints about pain and motion limitation, the pathological reactions in these disorders remain unclear. In our investigation of clinical vignettes of shoulder stiffness, inflammation-mediated adhesions in the subacromial bursa in rotator cuff lesions, and changes in inflammatory cytokine levels have been linked to myofibroblast recruitment in the subacromial bursa. Our study provides the first indication that increased interleukin -1? expression and myofibroblast recruitment in the subacromial bursa are correlated with rotator cuff lesions with shoulder stiffness. Increased inflammatory cytokine concentrations in the lesions also provide new molecular insight into the pathological role of the subacromial bursa in the development of shoulder stiffness in rotator cuff lesions. Although rotator cuff repair is a shoulder-tightening procedure and is not recommended until resolution of the shoulder stiffness in rotator cuff lesions with stiff shoulder, our clinical evidence-based survey suggests that a combined procedure of manipulation, lysis of adhesions, acromioplasty, and rotator cuff repair is a useful procedure if the symptoms do not improve 3 months of aggressive rehabilitation. PMID:21880187

  3. A Multiwell Platform for Studying Stiffness-Dependent Cell Biology

    PubMed Central

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

    2011-01-01

    Adherent cells are typically cultured on rigid substrates that are orders of magnitude stiffer than their tissue of origin. Here, we describe a method to rapidly fabricate 96 and 384 well platforms for routine screening of cells in tissue-relevant stiffness contexts. Briefly, polyacrylamide (PA) hydrogels are cast in glass-bottom plates, functionalized with collagen, and sterilized for cell culture. The Young's modulus of each substrate can be specified from 0.3 to 55 kPa, with collagen surface density held constant over the stiffness range. Using automated fluorescence microscopy, we captured the morphological variations of 7 cell types cultured across a physiological range of stiffness within a 384 well plate. We performed assays of cell number, proliferation, and apoptosis in 96 wells and resolved distinct profiles of cell growth as a function of stiffness among primary and immortalized cell lines. We found that the stiffness-dependent growth of normal human lung fibroblasts is largely invariant with collagen density, and that differences in their accumulation are amplified by increasing serum concentration. Further, we performed a screen of 18 bioactive small molecules and identified compounds with enhanced or reduced effects on soft versus rigid substrates, including blebbistatin, which abolished the suppression of lung fibroblast growth at 1 kPa. The ability to deploy PA gels in multiwell plates for high throughput analysis of cells in tissue-relevant environments opens new opportunities for the discovery of cellular responses that operate in specific stiffness regimes. PMID:21637769

  4. Mesenchymal Stem Cell Durotaxis Depends on Substrate Stiffness Gradient Strength

    PubMed Central

    Vincent, Ludovic G.; Choi, Yu Suk; Alonso-Latorre, Baldomero; del Álamo, Juan C.; Engler, Adam J.

    2013-01-01

    Mesenchymal stem cells (MSCs) respond to niche elasticity, which varies between and within tissues. Stiffness gradients result from pathological conditions but also occur through normal variation, e.g. muscle. MSCs undergo directed migration even in response to shallow stiffness gradients before differentiating. More refined gradients of both stiffness range and strength are needed to better understand mechanical regulation of migration in normal and disease pathologies. We describe polyacrylamide stiffness gradient fabrication using three distinct systems that generate stiffness gradients of physiological (1 Pa/µm), pathological (10 Pa/µm), and step (? 100Pa/um) strength spanning physiologically relevant stiffness for most soft tissue, i.e. 1–12 kPa. MSCs migrated to the stiffest region for each gradient. Time-lapse microscopy revealed that migration velocity scaled directly with gradient strength. Directed migration was reduced in the presence of the contractile agonist lysophosphatidic acid (LPA) and cytoskeletal-perturbing drugs nocodazole and cytochalasin; LPA- and nocodazole-treated cells remained spread and protrusive, while cytochalasin-treated cells did not. Untreated and nocodazole-treated cells spread in a similar manner, but nocodazole-treated cells had greatly diminished traction forces. These data suggest that actin is required for migration whereas microtubules are required for directed migration. The data also imply that in vivo, MSCs may have a more significant contribution to repairs in stiffer regions where they may preferentially accumulate. PMID:23390141

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

    PubMed Central

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

    2015-01-01

    Arteriosclerosis is a major contributor to cardiovascular diseases. One of the difficulties in controlling those diseases is the lack of a suitable indicator of arteriosclerosis or arterial injury in routine clinical practice. Arterial stiffness was supposed to be one of the monitoring indexes of arteriosclerosis. Cardio-ankle vascular index (CAVI) is reflecting the stiffness of the arterial tree from the origin of the aorta to the ankle, and one of the features of CAVI is independency from blood pressure at a measuring time. When doxazosin, an ?1-adrenergic blocker, was administered, CAVI decreased, indicating that arterial stiffness is composed of both organic stiffness and functional stiffness, which reflects the contraction of arterial smooth muscle. CAVI shows a high value with aging and in many arteriosclerotic diseases, and is also high in persons possessing main coronary risk factors such as diabetes mellitus, metabolic syndrome, hypertension and smoking. Furthermore, when the most of those risk factors were controlled by proper methods, CAVI improved. Furthermore, the co-relationship between CAVI and heart function was demonstrated during treatment of heart failure. This paper reviews the principle and rationale of CAVI, and discusses the meaning of monitoring CAVI in following up so-called lifestyle-related diseases and cardiac dysfunction in routine clinical practice. PMID:26587461

  6. Identification of sudden stiffness changes in the acceleration response of a bridge to moving loads using ensemble empirical mode decomposition

    NASA Astrophysics Data System (ADS)

    Aied, H.; González, A.; Cantero, D.

    2016-01-01

    The growth of heavy traffic together with aggressive environmental loads poses a threat to the safety of an aging bridge stock. Often, damage is only detected via visual inspection at a point when repairing costs can be quite significant. Ideally, bridge managers would want to identify a stiffness change as soon as possible, i.e., as it is occurring, to plan for prompt measures before reaching a prohibitive cost. Recent developments in signal processing techniques such as wavelet analysis and empirical mode decomposition (EMD) have aimed to address this need by identifying a stiffness change from a localised feature in the structural response to traffic. However, the effectiveness of these techniques is limited by the roughness of the road profile, the vehicle speed and the noise level. In this paper, ensemble empirical mode decomposition (EEMD) is applied by the first time to the acceleration response of a bridge model to a moving load with the purpose of capturing sudden stiffness changes. EEMD is more adaptive and appears to be better suited to non-linear signals than wavelets, and it reduces the mode mixing problem present in EMD. EEMD is tested in a variety of theoretical 3D vehicle-bridge interaction scenarios. Stiffness changes are successfully identified, even for small affected regions, relatively poor profiles, high vehicle speeds and significant noise. The latter is due to the ability of EEMD to separate high frequency components associated to sudden stiffness changes from other frequency components associated to the vehicle-bridge interaction system.

  7. A Novel Shape Memory Plate Osteosynthesis for Noninvasive Modulation of Fixation Stiffness in a Rabbit Tibia Osteotomy Model

    PubMed Central

    Müller, Christian W.; Pfeifer, Ronny; Meier, Karen; Decker, Sebastian; Reifenrath, Janin; Gösling, Thomas; Wesling, Volker; Krettek, Christian; Hurschler, Christof; Krämer, Manuel

    2015-01-01

    Nickel-titanium shape memory alloy (NiTi-SMA) implants might allow modulating fracture healing, changing their stiffness through alteration of both elastic modulus and cross-sectional shape by employing the shape memory effect (SME). Hypotheses: a novel NiTi-SMA plate stabilizes tibia osteotomies in rabbits. After noninvasive electromagnetic induction heating the alloy exhibits the SME and the plate changes towards higher stiffness (inverse dynamization) resulting in increased fixation stiffness and equal or better bony healing. In 14 rabbits, 1.0?mm tibia osteotomies were fixed with our experimental plate. Animals were randomised for control or induction heating at three weeks postoperatively. Repetitive X-ray imaging and in vivo measurements of bending stiffness were performed. After sacrifice at 8 weeks, macroscopic evaluation, µCT, and post mortem bending tests of the tibiae were carried out. One death and one early implant dislocation occurred. Following electromagnetic induction heating, radiographic and macroscopic changes of the implant proved successful SME activation. All osteotomies healed. In the treatment group, bending stiffness increased over time. Differences between groups were not significant. In conclusion, we demonstrated successful healing of rabbit tibia osteotomies using our novel NiTi-SMA plate. We demonstrated shape-changing SME in-vivo through transcutaneous electromagnetic induction heating. Thus, future orthopaedic implants could be modified without additional surgery. PMID:26167493

  8. Cytoskeletal prestress regulates nuclear shape and stiffness in cardiac myocytes.

    PubMed

    Lee, Hyungsuk; Adams, William J; Alford, Patrick W; McCain, Megan L; Feinberg, Adam W; Sheehy, Sean P; Goss, Josue A; Parker, Kevin Kit

    2015-11-01

    Mechanical stresses on the myocyte nucleus have been associated with several diseases and potentially transduce mechanical stimuli into cellular responses. Although a number of physical links between the nuclear envelope and cytoplasmic filaments have been identified, previous studies have focused on the mechanical properties of individual components of the nucleus, such as the nuclear envelope and lamin network. The mechanical interaction between the cytoskeleton and chromatin on nuclear deformability remains elusive. Here, we investigated how cytoskeletal and chromatin structures influence nuclear mechanics in cardiac myocytes. Rapid decondensation of chromatin and rupture of the nuclear membrane caused a sudden expansion of DNA, a consequence of prestress exerted on the nucleus. To characterize the prestress exerted on the nucleus, we measured the shape and the stiffness of isolated nuclei and nuclei in living myocytes during disruption of cytoskeletal, myofibrillar, and chromatin structure. We found that the nucleus in myocytes is subject to both tensional and compressional prestress and its deformability is determined by a balance of those opposing forces. By developing a computational model of the prestressed nucleus, we showed that cytoskeletal and chromatin prestresses create vulnerability in the nuclear envelope. Our studies suggest the cytoskeletal-nuclear-chromatin interconnectivity may play an important role in mechanics of myocyte contraction and in the development of laminopathies by lamin mutations. PMID:25908635

  9. Modulating surface stiffness of polydimethylsiloxane (PDMS) with kiloelectronvolt ion patterning

    NASA Astrophysics Data System (ADS)

    Liu, Boyin; Fu, Jing

    2015-06-01

    This study is to investigate the modulated surface properties of polydimethylsiloxane (PDMS) with kiloelectronvolt ions. By irradiating the PDMS surface with a focused ion beam (FIB, keV Ga+), nano/microscale patterns of controlled stiffness can be fabricated with ion fluence ranging from 0.1-20?pC?µm-2. The following nanoindentation measurements with an atomic force microscope (AFM) revealed that Young’s modulus increased exponentially with the increase of ion fluence and reached 2?GPa. The stiffening was found to be less significant with irradiation at a higher ion incident angle and lower accelerating voltage. Raman spectroscopy results also confirmed that disordering caused by cross-linking and hydrogen release occurred on the target PDMS surface. By modelling and experimenting on PDMS-Si3N4 bilayer structures, the volume reduction ratios of PDMS with ion beam and electron beam irradiation were estimated. The proposed site specific modulating method and understanding of detailed governing mechanisms will allow the tuning of the PDMS surface with great accuracy and flexibility towards future applications in tissue engineering and microfabrication.

  10. Umbilical Stiffness Matrix Characterization and Testing for Microgravity Science Payloads

    NASA Technical Reports Server (NTRS)

    Engberg, Robert C.

    2003-01-01

    This paper describes efforts of testing and analysis of various candidate cables and umbilicals for International Space Station microgravity science payloads. The effects of looping, large vs. small displacements, and umbilical mounting configurations were assessed. A 3-DOF stepper motor driven fixture was used to excite the umbilicals. Forces and moments were directly measured in all three axes with a 6-DOF load cell in order to derive suitable stiffness matrices for design and analysis of vibration isolation controllers. Data obtained from these tests were used to help determine the optimum type and configuration of umbilical cables for the International Space Station microgravity science glovebox (MSG) vibration isolation platform. The data and procedures can also be implemented into control algorithm simulations to assist in validation of actively controlled vibration isolation systems. The experimental results of this work are specific in support of the Glovebox Integrated Microgravity Isolation Technology (g-LIMIT) isolation platform, to be located in the microgravity science glovebox aboard the U.S. Destiny Laboratory Module.

  11. 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.

  12. Shear horizontal guided wave modes to infer the shear stiffness of adhesive bond layers.

    PubMed

    Le Crom, Bénédicte; Castaings, Michel

    2010-04-01

    This paper presents a non-destructive, ultrasonic technique to evaluate the quality of bonds between substrates. Shear-horizontally polarized (SH) wave modes are investigated to infer the shear stiffness of bonds, which is necessarily linked to the shear resistance that is a critical parameter for bonded structures. Numerical simulations are run for selecting the most appropriate SH wave modes, i.e., with higher sensitivity to the bond than to other components, and experiments are made for generating-detecting pre-selected SH wave modes and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the shear stiffness modulus of a bond layer at different curing times between a metallic plate and a composite patch, such assembly being investigated in the context of repair of aeronautical structures. PMID:20370003

  13. Investigation of interfacial stiffnesses of a tri-layer using Zero-Group Velocity Lamb modes.

    PubMed

    Mezil, Sylvain; Bruno, Francois; Raetz, Samuel; Laurent, Jérôme; Royer, Daniel; Prada, Claire

    2015-11-01

    Zero-Group Velocity (ZGV) Lamb waves are studied in a structure composed of two plates bonded by an adhesive layer. The dispersion curves are calculated for a Duralumin/epoxy/Duralumin sample, where the adhesion is modeled by a normal and a tangential spring at both interfaces. Several ZGV modes are identified and their frequency dependence on interfacial stiffnesses and on the bonding layer thickness is numerically studied. Then, experiments achieved with laser ultrasonic techniques are presented. Local resonances are measured using a superimposed source and probe. Knowing the thicknesses and elastic constants of the Duralumin and epoxy layers, the comparison between theoretical and experimental ZGV resonances leads to an evaluation of the interfacial stiffnesses. A good agreement with theoretical dispersion curves confirms the identification of the resonances and the parameter estimations. This non-contact technique is promising for the local evaluation of bonded structures. PMID:26627794

  14. Laser ultrasonics in copy paper: bending stiffness dependence on temperature and moisture content.

    PubMed

    Cornwell, Matthew A; Berthelot, Yves H

    2002-12-01

    The A0 Lamb mode in copy paper is generated and detected by using laser ultrasonics. The frequency dependence of the group velocity of the A0 mode is found from the wavelet transform of the measured signal. A best fit of the dispersion curve against predictions based on orthotropic plate theory yields an estimate of the bending stiffness of the sample. The sample is enclosed in an environmental chamber so that the effects of temperature and humidity can be controlled. Results indicate that the bending stiffness decreases with increasing temperature at an approximate rate of 4 x 10(-6) N m/degrees C, and that it decreases with increasing percent moisture content (PMC) at an approximate rate of 2 x 10(-5) (N m)/PMC. PMID:12508996

  15. Sh Guided Waves to Infer the Shear Stiffness of Adhesive Bonds

    NASA Astrophysics Data System (ADS)

    Castaings, M.; Crom, B. Le

    2011-06-01

    Composite patches adhesively bonded onto metallic components are more and more used for repairing Aeronautical structures. The shear resistance of such adhesive bonds is of great importance to guarantee the efficiency of the repair. To non-destructively assess the shear stiffness of bonds, which is necessarily linked to their shear resistance, shear-horizontally polarized (SH), ultrasonic, wave modes are investigated. Numerical simulations are first run for selecting the most appropriate SH modes, i.e. with higher sensitivity to the bond than to other components. Then, experiments are made for generating-detecting pre-selected SH wave modes, and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the shear stiffness modulus of a bond layer at different curing times between an aluminium plate and a Carbon-Epoxy patch.

  16. Relationships among cell morphology, intrinsic cell stiffness and cell-substrate interactions.

    PubMed

    Chiang, Martin Y M; Yangben, Yanzi; Lin, Nancy J; Zhong, Julia L; Yang, Li

    2013-12-01

    Cell modulus (stiffness) is a critical cell property that is important in normal cell functions and increasingly associated with disease states, yet most methods to characterize modulus may skew results. Here we show strong evidence indicating that the fundamental nature of free energies associated with cell/substrate interactions regulates adherent cell morphology and can be used to deduce cell modulus. These results are based on a mathematical model of biophysics and confirmed by the measured morphology of normal and cancerous liver cells adhered on a substrate. Cells select their final morphology by minimizing the total free energy in the cell/substrate system. The key mechanism by which substrate stiffness influences cell morphology is the energy tradeoff between the stabilizing influence of the cell-substrate interfacial adhesive energy and the destabilizing influence of the total elastic energies in the system. Using these findings, we establish a noninvasive methodology to determine the intrinsic modulus of cells by observing global changes in cell morphology in response to substrate stiffness. We also highlight the importance of selecting a relevant morphological index, cell roundness, that reflects the interchange between forms of energy governing cell morphology. Thus, cell-substrate interactions can be rationalized by the underlying biophysics, and cell modulus is easily measured. PMID:24075411

  17. Mass and stiffness estimation using mobile devices for structural health monitoring

    NASA Astrophysics Data System (ADS)

    Le, Viet; Yu, Tzuyang

    2015-04-01

    In the structural health monitoring (SHM) of civil infrastructure, dynamic methods using mass, damping, and stiffness for characterizing structural health have been a traditional and widely used approach. Changes in these system parameters over time indicate the progress of structural degradation or deterioration. In these methods, capability of predicting system parameters is essential to their success. In this paper, research work on the development of a dynamic SHM method based on perturbation analysis is reported. The concept is to use externally applied mass to perturb an unknown system and measure the natural frequency of the system. Derived theoretical expressions for mass and stiffness prediction are experimentally verified by a building model. Dynamic responses of the building model perturbed by various masses in free vibration were experimentally measured by a mobile device (cell phone) to extract the natural frequency of the building model. Single-degreeof- freedom (SDOF) modeling approach was adopted for the sake of using a cell phone. From the experimental result, it is shown that the percentage error of predicted mass increases when the mass ratio increases, while the percentage error of predicted stiffness decreases when the mass ratio increases. This work also demonstrated the potential use of mobile devices in the health monitoring of civil infrastructure.

  18. Offset of rotation centers creates a bias in isokinetics: a virtual model including stiffness or friction.

    PubMed

    Deslandes, Samuel; Mariot, Jean-Pierre; Serveto, Sébastien

    2008-07-19

    The present paper deals with a virtual model devoted to isokinetics and isometrics assessment of a human muscular group in the common joints, knee, ankle, hip, shoulder, cervical spine, etc. This virtual model with an analytical analysis followed by a numerical simulation is able to predict measurement errors of the joint torque due to offset of rotation centers between the body segment and the ergometer arm. As soon as offset is present, errors increase due to the influence of inertial effects, gravity effects, stiffness due to the limb strapping on the ergometer arm or Coulomb friction between limb and ergometer. The analytical model is written in terms of Lagrange formalism and the numerical model uses ADAMS software adapted to multi-body dynamics simulations. Results of models show a maximal relative error of 11%, for a 10% relative offset between the rotation centers. Inertial contributions are found to be negligible but gravity effects must be discussed in regard to the measured torque. Stiffness or friction effects may also increase the torque error; in particular when offset occurs, it is shown that errors due to friction have to be considered for all torque level while only stiffness effects have to be considered for torque less than 25Nm. This study also emphasizes the influence of the angular range of motion at a given angular position. PMID:18556002

  19. Pulmonary vascular wall stiffness: An important contributor to the increased right ventricular afterload with pulmonary hypertension

    PubMed Central

    Wang, Zhijie; Chesler, Naomi C.

    2011-01-01

    Pulmonary hypertension (PH) is associated with structural and mechanical changes in the pulmonary vascular bed that increase right ventricular (RV) afterload. These changes, characterized by narrowing and stiffening, occur in both proximal and distal pulmonary arteries (PAs). An important consequence of arterial narrowing is increased pulmonary vascular resistance (PVR). Arterial stiffening, which can occur in both the proximal and distal pulmonary arteries, is an important index of disease progression and is a significant contributor to increased RV afterload in PH. In particular, arterial narrowing and stiffening increase the RV afterload by increasing steady and oscillatory RV work, respectively. Here we review the current state of knowledge of the causes and consequences of pulmonary arterial stiffening in PH and its impact on RV function. We review direct and indirect techniques for measuring proximal and distal pulmonary arterial stiffness, measures of arterial stiffness including elastic modulus, incremental elastic modulus, stiffness coefficient ? and others, the changes in cellular function and the extracellular matrix proteins that contribute to pulmonary arterial stiffening, the consequences of PA stiffening for RV function and the clinical implications of pulmonary vascular stiffening for PH progression. Future investigation of the relationship between PA stiffening and RV dysfunction may facilitate new therapies aimed at improving RV function and thus ultimately reducing mortality in PH. PMID:22034607

  20. Stabilizing the central part of tropomyosin increases the bending stiffness of the thin filament.

    PubMed

    Nabiev, Salavat R; Ovsyannikov, Denis A; Kopylova, Galina V; Shchepkin, Daniil V; Matyushenko, Alexander M; Koubassova, Natalia A; Levitsky, Dmitrii I; Tsaturyan, Andrey K; Bershitsky, Sergey Y

    2015-07-21

    A two-beam optical trap was used to measure the bending stiffness of F-actin and reconstructed thin filaments. A dumbbell was formed by a filament segment attached to two beads that were held in the two optical traps. One trap was static and held a bead used as a force transducer, whereas an acoustooptical deflector moved the beam holding the second bead, causing stretch of the dumbbell. The distance between the beads was measured using image analysis of micrographs. An exact solution to the problem of bending of an elastic filament attached to two beads and subjected to a stretch was used for data analysis. Substitution of noncanonical residues in the central part of tropomyosin with canonical ones, G126R and D137L, and especially their combination, caused an increase in the bending stiffness of the thin filaments. The data confirm that the effect of these mutations on the regulation of actin-myosin interactions may be caused by an increase in tropomyosin stiffness. PMID:26200873

  1. Associations between bicycling and carotid arterial stiffness in adolescents: The European Youth Hearts Study.

    PubMed

    Ried-Larsen, M; Grøntved, A; Østergaard, L; Cooper, A R; Froberg, K; Andersen, L B; Møller, N C

    2015-10-01

    The aim of the study was to investigate the associations between bicycling and carotid arterial stiffness, independent of objectively measured moderate-and-vigorous physical activity. This cross-sectional study included 375 adolescents (age 15.7?±?0.4 years) from the Danish site of the European Youth Heart Study. Total frequency of bicycle usage was assessed by self-report, and carotid arterial stiffness was assessed using B-mode ultrasound. After adjusting for pubertal status, body height, and objectively measured physical activity and other personal lifestyle and demographic factors, boys using their bicycle every day of the week displayed a higher carotid arterial compliance {standard beta 0.47 [95% confidence interval (CI) 0.07-0.87]} and distension [standard beta 0.38 (95% CI -0.04 to 0.81)]. Boys using their bicycle every day of the week furthermore displayed a lower Young's elastic modulus [standard beta -0.48 (95% CI -0.91 to -0.06)]. Similar trends were observed when investigating the association between commuter bicycling and carotid arterial stiffness. These associations were not observed in girls. Our observations suggest that increasing bicycling in adolescence may be beneficial to carotid arterial health among boys. PMID:25156494

  2. The Relationship Between the Changes in Local Stiffness of Chicken Myofibril and the Tenderness of Muscle During Postmortem Aging

    NASA Astrophysics Data System (ADS)

    Iwasaki, T.; Hasegawa, Y.; Yamamoto, K.; Nakamura, K.

    We have investigated that the relationship between the stiffness of myofibrils and the tenderness of muscle during postmortem aging. The stiffness (elasticity) of A and I bands as well as Z-line of chicken myofibrils during postmortem aging were measured by atomic force microscope. The stiffness of all regions increased till 12 hr of postmortem, then it decreased to 96 hr. This tendency was the same as the changes of shear force value of whole muscle during postmortem aging. The elasticity of the Z-line of chicken myofibrils treated with calcium ions in the presence of protease inhibitor decreased with treating time. This indicates that the nonenzymatic structural changes of myofibrils is one of the causes of meat tenderization.

  3. A Novel Echocardiographic Method for Assessing Arterial Stiffness in Obstructive Sleep Apnea Syndrome

    PubMed Central

    Akyol, Aytac; Cakmak, Huseyin Altug; Gunbatar, Hulya; Asker, Muntecep; Babat, Naci; Tosu, Aydin Rodi; Yaman, Mehmet; Gumrukcuoglu, Hasan Ali

    2015-01-01

    Background and Objectives Obstructive sleep apnea syndrome (OSAS) is associated with increased arterial stiffness and cardiovascular complications. The objective of this study was to assess whether the color M-mode-derived propagation velocity of the descending thoracic aorta (aortic velocity propagation, AVP) was an echocardiographic marker for arterial stiffness in OSAS. Subjects and Methods The study population included 116 patients with OSAS and 90 age and gender-matched control subjects. The patients with OSAS were categorized according to their apnea hypopnea index (AHI) as follows: mild to moderate degree (AHI 5-30) and severe degree (AHI?30). Aortofemoral pulse wave velocity (PWV), carotid intima-media thickness (CIMT), brachial artery flow-mediated dilatation (FMD), and AVP were measured to assess arterial stiffness. Results AVP and FMD were significantly decreased in patients with OSAS compared to controls (p<0.001). PWV and CIMT were increased in the OSAS group compared to controls (p<0.001). Moreover, AVP and FMD were significantly decreased in the severe OSAS group compared to the mild to moderate OSAS group (p<0.001). PWV and CIMT were significantly increased in the severe group compared to the mild to moderate group (p<0.001). AVP was significantly positively correlated with FMD (r=0.564, p<0.001). However, it was found to be significantly inversely related to PWV (r=-0.580, p<0.001) and CIMT (r=-0.251, p<0.001). Conclusion The measurement of AVP is a novel and practical echocardiographic method, which may be used to identify arterial stiffness in OSAS. PMID:26617653

  4. Acute Effects of a Mixed Meal on Arterial Stiffness and Central Hemodynamics in Healthy Adults

    PubMed Central

    2014-01-01

    BACKGROUND Elevated central pressures and arterial stiffness are associated with increased peripheral resistance and higher sympathetic nervous system activity. Additionally, consumption of a meal is known to be sympathoexcitatory. However, the acute effects of a meal on aortic wave reflection and stiffness are unknown. Therefore, we tested the hypothesis that aortic wave reflection and stiffness would increase after a meal. METHODS We examined these effects using high-fidelity radial arterial pressure waveforms and carotid–femoral pulse wave velocity measured noninvasively by applanation tonometry before and 60 and 180 minutes after ingestion of a liquid mixed meal (Ensure; 40% of daily energy expenditure) in 17 healthy adults (9 men/8 women; aged 29±2 years). Additionally, we measured sympathetic activity by microneurography at baseline and up to 60 minutes after the meal. RESULTS Although sympathetic activity increased after the meal, both peripheral and central pressures were reduced at 180 minutes from baseline (all P < 0.05). Contrary to our hypothesis, augmentation index (14% ± 3% vs. 2% ± 3% vs. 8% ± 3%), augmentation index normalized for heart rate (8% ± 3% vs. ?3% ± 3% vs. 3% ± 3%), augmented pressure (5±1mm Hg vs. 1±1mm Hg vs. 3±1mm Hg), and pulse wave velocity (7.1±0.2 m/s vs. 6.7±0.2 m/s vs. 6.7±0.1 m/s) were substantially reduced at 60 and 180 minutes after the meal (all P < 0.05). CONCLUSIONS Taken together, our results suggest that a liquid mixed meal acutely decreases central hemodynamics and arterial stiffness in healthy adults, which may be a result of meal-related increases in insulin and/or visceral vasodilation. PMID:24242825

  5. Effects of isometric squat training on the tendon stiffness and jump performance.

    PubMed

    Kubo, Keitaro; Yata, Hideaki; Kanehisa, Hiroaki; Fukunaga, Tetsuo

    2006-02-01

    The present study aimed to investigate the effect of isometric squat training on human tendon stiffness and jump performances. Eight subjects completed 12 weeks (4 days/week) of isometric squat training, which consisted of bilateral leg extension at 70% of maximum voluntary contraction (MVC) for 15 s per set (10 sets/day). Before and after training, the elongations of the tendon-aponeurosis complex in the vastus lateralis muscle and patella tendon were directly measured using ultrasonography while the subjects performed ramp isometric knee extension up to MVC. The relationship between the estimated muscle force and tendon elongation was fitted to a linear regression, the slope of which was defined as stiffness. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The training significantly increased the volume (P < 0.01) and MVC torque (P < 0.01) of the quadriceps femoris muscle. The stiffness of the tendon-aponeurosis complex increased significantly from 51 +/- 22 (mean +/- SD) to 59 +/- 24 N/mm (P = 0.04), although that of the patella tendon did not change (P = 0.48). The SJ height increased significantly after training (P = 0.03), although the CMJ height did not (P = 0.45). In addition, the relative difference in jump height between SJ and CMJ decreased significantly after training (P = 0.02). These results suggest that isometric squat training changes the stiffness of human tendon-aponeurosis complex in knee extensors to act negatively on the effects of pre-stretch during stretch-shortening cycle exercises. PMID:16328192

  6. Liver and spleen stiffness and other noninvasive methods to assess portal hypertension in cirrhotic patients: a review of the literature.

    PubMed

    Colecchia, Antonio; Marasco, Giovanni; Taddia, Martina; Montrone, Lucia; Eusebi, Leonardo H; Mandolesi, Daniele; Schiumerini, Ramona; Di Biase, Anna R; Festi, Davide

    2015-09-01

    Portal hypertension (PH) is one of the most important causes of morbidity and mortality in patients with chronic liver disease. PH measurement is crucial to stage and predict the clinical outcome of liver cirrhosis. Measurement of hepatic vein pressure gradient is considered the gold standard for assessment of the degree of PH; however, it is an invasive method and has not been used widely. Thus, noninvasive methods have been proposed recently. We critically evaluated serum markers, abdominal ultrasonography, and particularly liver and spleen stiffness measurement, which represent the more promising methods to stage PH degree and to assess the presence/absence of esophageal varices (EV). A literature search was carried out on MEDLINE, EMBASE, Web of Science, and Scopus for articles and abstracts. The search terms used included 'liver cirrhosis', 'portal hypertension', 'liver stiffness', 'spleen stiffness', 'ultrasonography', and 'portal hypertension serum biomarker'. The articles cited were selected on the basis of their relevance to the objective of the review. The results of available studies indicate that individually, these methods have a mild accuracy in predicting the presence of EV, and thus they cannot substitute endoscopy to predict EV. When these tests were used in combination, their accuracy increased. In addition to the PH staging, several serum markers and spleen stiffness measurement can predict the clinical outcome of liver cirrhosis with a good accuracy, comparable to that of hepatic vein pressure gradient. In the future, noninvasive methods could be used to select patients requiring further investigations to identify the best tailored clinical management. PMID:26020376

  7. Infarcted myocardium-like stiffness contributes to endothelial progenitor lineage commitment of bone marrow mononuclear cells.

    PubMed

    Zhang, Shuning; Sun, Aijun; Ma, Hong; Yao, Kang; Zhou, Ning; Shen, Li; Zhang, Chunyu; Zou, Yunzeng; Ge, Junbo

    2011-10-01

    Optimal timing of cell therapy for myocardial infarction (MI) appears during 5 to 14 days after the infarction. However, the potential mechanism requires further investigation. This work aimed to verify the hypothesis that myocardial stiffness within a propitious time frame might provide a most beneficial physical condition for cell lineage specification in favour of cardiac repair. Serum vascular endothelial growth factor (VEGF) levels and myocardial stiffness of MI mice were consecutively detected. Isolated bone marrow mononuclear cells (BMMNCs) were injected into infarction zone at distinct time-points and cardiac function were measured 2 months after infarction. Polyacrylamide gel substrates with varied stiffness were used to mechanically mimic the infarcted myocardium. BMMNCs were plated on the flexible culture substrates under different concentrations of VEGF. Endothelial progenitor lineage commitment of BMMNCs was verified by immunofluorescent technique and flow cytometry. Our results demonstrated that the optimal timing in terms of improvement of cardiac function occurred during 7 to 14 days after MI, which was consistent with maximized capillary density at this time domains, but not with peak VEGF concentration. Percentage of double-positive cells for DiI-labelled acetylated low-density lipoprotein uptake and fluorescein isothiocyanate (FITC)-UEA-1 (ulex europaeus agglutinin I lectin) binding had no significant differences among the tissue-like stiffness in high concentration VEGF. With the decrease of VEGF concentration, the benefit of 42 kPa stiffness, corresponding to infarcted myocardium at days 7 to 14, gradually occurred and peaked when it was removed from culture medium. Likewise, combined expressions of VEGFR2(+) , CD133(+) and CD45(-) remained the highest level on 42 kPa substrate in conditions of lower concentration VEGF. In conclusion, the optimal efficacy of BMMNCs therapy at 7 to 14 days after MI might result from non-VEGF dependent angiogenesis, and myocardial stiffness at this time domains was more suitable for endothelial progenitor lineage specification of BMMNCs. The results here highlight the need for greater attention to mechanical microenvironments in cell culture and cell therapy. PMID:21091632

  8. 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 laminates exists through the use of curvilinear fibers, mainly due to the presence of a weak link area within the stiffness variation that limits the ultimate load that the structure can withstand. Rigorous optimization studies reveal that even though slight increases in the critical loads can be produced for designs with an arbitrary variation of the fiber orientation angle, the improvements are not significant when compared to traditional design techniques that utilize ring stiffeners and frames. The second problem that is studied involves arbitrary loading of a cylinder with a stiffness variation that changes only in the circumferential direction. The end effects of the cylinder are ignored, so that the problem takes the form of an analysis of a cross-section for a short cylinder segment. Various load cases including axial compression, pressure, torsion, bending, and transverse shear forces are investigated. It is found that the most significant improvements in load-carrying capability exist for cases which involve loads that also vary around the circumference of the shell, namely bending and shear forces. The stiffness variation of the optimal designs contribute to the increased performance in two ways: lowering the stresses in the critical areas through redistribution of the stresses; and providing a relatively stiff region that alters the buckling behavior of the structure. These results lead to an in-depth optimization study involving weight optimization of a fuselage structure subjected to typical design constraints. Comparisons of the curvilinear fiber format to traditional stiffened structures constructed of isotropic and composite materials are included. It is found that standard variable stiffness designs are quite comparable in terms of weight and load-carrying capability yet offer the added advantage of tailorability of distinct regions of the structure that experience drastically different loading conditions. The last two problems presented in this work involve the nonlinear phenomenon of long tubes under bending. Though this scenario is not as applic

  9. In Vivo Dynamics of the Musculoskeletal System Cannot Be Adequately Described Using a Stiffness-Damping-Inertia Model

    PubMed Central

    Kistemaker, Dinant A.; Rozendaal, Leonard A.

    2011-01-01

    Background Visco-elastic properties of the (neuro-)musculoskeletal system play a fundamental role in the control of posture and movement. Often, these properties are described and identified using stiffness-damping-inertia (KBI) models. In such an approach, perturbations are applied to the (neuro-)musculoskeletal system and subsequently KBI-model parameters are optimized to obtain a best fit between simulated and experimentally observed responses. Problems with this approach may arise because a KBI-model neglects critical aspects of the real musculoskeletal system. Methodology/Principal Findings The purpose of this study was to analyze the relation between the musculoskeletal properties and the stiffness and damping estimated using a KBI-model, to analyze how this relation is affected by the nature of the perturbation and to assess the sensitivity of the estimated stiffness and damping to measurement errors. Our analyses show that the estimated stiffness and damping using KBI-models do not resemble any of the dynamical parameters of the underlying system, not even when the responses are very accurately fitted by the KBI-model. Furthermore, the stiffness and damping depend non-linearly on all the dynamical parameters of the underlying system, influenced by the nature of the perturbation and the time interval over which the KBI-model is optimized. Moreover, our analyses predict a very high sensitivity of estimated parameters to measurement errors. Conclusions/Significance The results of this study suggest that the usage of stiffness-damping-inertia models to investigate the dynamical properties of the musculoskeletal system under control by the CNS should be reconsidered. PMID:21637750

  10. Analysis and design of variable stiffness composite cylinders

    NASA Astrophysics Data System (ADS)

    Tatting, Brian Frederick

    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. The governing static equilibrium 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. Four distinct cases of loading and stiffness variation are chosen to investigate. The initial investigation deals 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 laminates exists through the use of curvilinear fibers. The second problem involves arbitrary loading of a cylinder with a stiffness variation only in the circumferential direction. The problem takes the form of an analysis of a cross-section for a short cylinder segment. It is found that the most significant improvements in load-carrying capability exist for loads that also vary around the circumference of the shell, namely bending and shear forces. The stiffness variation of the optimal designs contribute to the increased performance in two ways: lowering the stresses in the critical areas through redistribution; and providing a relatively stiff region that alters the buckling behavior of the structure. These results led to an in-depth optimization study involving weight optimization of a fuselage structure subjected to typical design constraints. It is found that standard variable stiffness designs a offer the added advantage of tailorability of distinct regions of the structure that experience drastically different loading conditions. The last two problems work involve the nonlinear phenomenon of long tubes under bending. The dominating influence for long cylinders under bending is the ovalization of the cross-section. Possible improvement of the critical buckling moments for these structures is investigated using either a circumferential or axial stiffness variation. For the circumferential case involving infinite length cylinders, slight improvements can be observed by designing structures that resist the cross-sectional deformation yet do not detract from the buckling resistance at the critical location. The results also indicate that buckling behavior is extremely dependent on cylinder length. For finite length cylinders contain an axial stiffness variation, the only mechanism that exhibits improved response are those that effectively shorten the length of the cylinder. The use of curvilinear fibers was not able to achieve this effect in sufficient degree to resist the deformation, but ring stiffeners produced the desired response. Thus the variable stiffness concept is most effective at improving the bending response of long cylinders through the use of a circumferential stiffness variation. (Abstract shortened by UMI.)

  11. Comparative Analysis of the Flexural Stiffness of Pinniped Vibrissae

    PubMed Central

    Ginter Summarell, Carly C.; Ingole, Sudeep; Fish, Frank E.; Marshall, Christopher D.

    2015-01-01

    Vibrissae are important components of the mammalian tactile sensory system and are used to detect vibrotactile stimuli in the environment. Pinnipeds have the largest and most highly innervated vibrissae among mammals, and the hair shafts function as a biomechanical filter spanning the environmental stimuli and the neural mechanoreceptors deep in the follicle-sinus complex. Therefore, the material properties of these structures are critical in transferring vibrotactile information to the peripheral nervous system. Vibrissae were tested as cantilever beams and their flexural stiffness (EI) was measured to test the hypotheses that the shape of beaded vibrissae reduces EI and that vibrissae are anisotropic. EI was measured at two locations on each vibrissa, 25% and 50% of the overall length, and at two orientations to the point force. EI differed in orientations that were normal to each other, indicating a functional anisotropy. Since vibrissae taper from base to tip, the second moment of area (I) was lower at 50% than 25% of total length. The anterior orientation exhibited greater EI values at both locations compared to the dorsal orientation for all species. Smooth vibrissae were generally stiffer than beaded vibrissae. The profiles of beaded vibrissae are known to decrease the amplitude of vibrations when protruded into a flow field. The lower EI values of beaded vibrissae, along with the reduced vibrations, may function to enhance the sensitivity of mechanoreceptors to detection of small changes in flow from swimming prey by increasing the signal to noise ratio. This study builds upon previous morphological and hydrodynamic analyses of vibrissae and is the first comparative study of the mechanical properties of pinniped vibrissae. PMID:26132102

  12. Performance Comparison of Ultrasound-Based Methods to Assess Aortic Diameter and Stiffness in Normal and Aneurysmal Mice

    PubMed Central

    Trachet, Bram; Fraga-Silva, Rodrigo A.; Londono, Francisco J.; Swillens, Abigaïl; Stergiopulos, Nikolaos; Segers, Patrick

    2015-01-01

    Objective Several ultrasound-based methods are currently used to assess aortic diameter, circumferential strain and stiffness in mice, but none of them is flawless and a gold standard is lacking. We aimed to assess the validity and sensitivity of these methods in control animals and animals developing dissecting abdominal aortic aneurysm. Methods and Results We first compared systolic and diastolic diameters as well as local circumferential strains obtained in 47 Angiotensin II-infused ApoE -/- mice with three different techniques (BMode, short axis MMode, long axis MMode), at two different abdominal aortic locations (supraceliac and paravisceral), and at three different time points of abdominal aneurysm formation (baseline, 14 days and 28 days). We found that short axis BMode was preferred to assess diameters, but should be avoided for strains. Short axis MMode gave good results for diameters but high standard deviations for strains. Long axis MMode should be avoided for diameters, and was comparable to short axis MMode for strains. We then compared pulse wave velocity measurements using global, ultrasound-based transit time or regional, pressure-based transit time in 10 control and 20 angiotensin II-infused, anti-TGF-Beta injected C57BL/6 mice. Both transit-time methods poorly correlated and were not able to detect a significant difference in PWV between controls and aneurysms. However, a combination of invasive pressure and MMode diameter, based on radio-frequency data, detected a highly significant difference in local aortic stiffness between controls and aneurysms, with low standard deviation. Conclusions In small animal ultrasound the short axis view is preferred over the long axis view to measure aortic diameters, local methods are preferred over transit-time methods to measure aortic stiffness, invasive pressure-diameter data are preferred over non-invasive strains to measure local aortic stiffness, and the use of radiofrequency data improves the accuracy of diameter, strain as well as stiffness measurements. PMID:26023786

  13. Use of Guided Acoustic Waves to Assess the Effects of Thermal-Mechanical Cycling on Composite Stiffness

    NASA Technical Reports Server (NTRS)

    Seale, Michael D.; Madaras, Eric I.

    2000-01-01

    The introduction of new, advanced composite materials into aviation systems requires it thorough understanding of the long-term effects of combined thermal and mechanical loading. As part of a study to evaluate the effects of thermal-mechanical cycling, it guided acoustic (Lamb) wave measurement system was used to measure the bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system uses a pulse/receive technique that excites an antisymmetric Lamb mode and measures the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the velocity dispersion curve. A series of 16 and 32-ply composite laminates were subjected to it thermal-mechanical loading profile in load frames equipped with special environmental chambers. The composite systems studied were it graphite fiber reinforced amorphous thermoplastic polyimide and it graphite fiber reinforced bismaleimide thermoset. The samples were exposed to both high and low temperature extremes its well as high and low strain profiles. The bending and out-of-plane stiffnesses for composite sample that have undergone over 6,000 cycles of thermal-mechanical loading are reported. The Lamb wave generated elastic stiffness results have shown decreases of up to 20% at 4,936 loading cycles for the graphite/thermoplastic samples and up to 64% at 4,706 loading cycles for the graphite/thermoset samples.

  14. Variable stiffness material and structural concepts for morphing applications

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  15. Pharmacological bronchodilation is partially mediated by reduced airway wall stiffness

    PubMed Central

    Ansell, T K; Noble, P B; Mitchell, H W; McFawn, P K

    2014-01-01

    Background and Purpose In asthmatic patients, airflow limitation is at least partly reversed by administration of pharmacological bronchodilators, typically ?2-adrenoceptor agonists. In addition to receptor-mediated bronchodilation, the dynamic mechanical environment of the lung itself can reverse bronchoconstriction. We have now explored the possibility that bronchodilators exert a synergistic effect with oscillatory loads by virtue of reducing airway wall stiffness, and therefore, enhancing the bronchodilatory response to breathing manoeuvres. Experimental Approach Whole porcine bronchial segments in vitro were contracted to carbachol and relaxed to the non-specific ?-adrenoceptor agonist, isoprenaline, under static conditions or during simulated breathing manoeuvres. Key Results The bronchodilatory response to isoprenaline was greater during breathing manoeuvres compared with the response under static conditions. As the bronchodilatory response to breathing manoeuvres is dependent upon airway smooth muscle (ASM) strain, and therefore, airway wall stiffness, our findings are likely to be explained by the effect of isoprenaline on reducing airway wall stiffness, which increased ASM strain, producing greater bronchodilation. Conclusions and Implications A contribution of reduced airway stiffness and increased ASM strain to the bronchodilator action of isoprenaline is shown, suggesting that oscillatory loads act synergistically with pharmacologically mediated bronchodilation. The implications for the treatment of asthma are that reducing airway wall stiffness represents a potential target for novel pharmacological agents. PMID:24846164

  16. Substrate stiffness regulates cadherin-dependent collective migration through myosin-II contractility

    PubMed Central

    Ng, Mei Rosa; Besser, Achim

    2012-01-01

    The mechanical microenvironment is known to influence single-cell migration; however, the extent to which mechanical cues affect collective migration of adherent cells is not well understood. We measured the effects of varying substrate compliance on individual cell migratory properties in an epithelial wound-healing assay. Increasing substrate stiffness increased collective cell migration speed, persistence, and directionality as well as the coordination of cell movements. Dynamic analysis revealed that wounding initiated a wave of motion coordination from the wound edge into the sheet. This was accompanied by a front-to-back gradient of myosin-II activation and establishment of cell polarity. The propagation was faster and farther reaching on stiff substrates, indicating that substrate stiffness affects the transmission of directional cues. Manipulation of myosin-II activity and cadherin–catenin complexes revealed that this transmission is mediated by coupling of contractile forces between neighboring cells. Thus, our findings suggest that the mechanical environment integrates in a feedback with cell contractility and cell–cell adhesion to regulate collective migration. PMID:23091067

  17. Quantitative assessment of sample stiffness and sliding friction from force curves in atomic force microscopy

    SciTech Connect

    Pratt, Jon R.; Shaw, Gordon A.; Kumanchik, Lee; Burnham, Nancy A.

    2010-02-15

    It has long been recognized that the angular deflection of an atomic force microscope (AFM) cantilever under ''normal'' loading conditions can be profoundly influenced by the friction between the tip and the surface. It is shown here that a remarkably quantifiable hysteresis occurs in the slope of loading curves whenever the normal flexural stiffness of the AFM cantilever is greater than that of the sample. This situation arises naturally in cantilever-on-cantilever calibration, but also when trying to measure the stiffness of nanomechanical devices or test structures, or when probing any type of surface or structure that is much more compliant along the surface normal than in transverse directions. Expressions and techniques for evaluating the coefficient of sliding friction between the cantilever tip and sample from normal force curves, as well as relations for determining the stiffness of a mechanically compliant specimen are presented. The model is experimentally supported by the results of cantilever-on-cantilever spring constant calibrations. The cantilever spring constants determined here agree with the values determined using the NIST electrostatic force balance within the limits of the largest uncertainty component, which had a relative value of less than 2.5%. This points the way for quantitative testing of micromechanical and nanomechanical components, more accurate calibration of AFM force, and provides nanotribologists access to information about contact friction from normal force curves.

  18. Increased tissue transglutaminase activity contributes to central vascular stiffness in eNOS knockout mice

    PubMed Central

    Jung, Sung Mee; Jandu, Simran; Steppan, Jochen; Belkin, Alexey; An, Steven S.; Pak, Alina; Choi, Eric Y.; Nyhan, Daniel; Butlin, Mark; Viegas, Kayla; Avolio, Alberto; Berkowitz, Dan E.

    2013-01-01

    Nitric oxide (NO) can modulate arterial stiffness by regulating both functional and structural changes in the arterial wall. Tissue transglutaminase (TG2) has been shown to contribute to increased central aortic stiffness by catalyzing the cross-linking of matrix proteins. NO S-nitrosylates and constrains TG2 to the cytosolic compartment and thereby holds its cross-linking function latent. In the present study, the role of endothelial NO synthase (eNOS)-derived NO in regulating TG2 function was studied using eNOS knockout mice. Matrix-associated TG2 and TG2 cross-linking function were higher, whereas TG2 S-nitrosylation was lower in the eNOS?/? compared with wild-type (WT) mice. Pulse-wave velocity (PWV) and blood pressure measured noninvasively were elevated in the eNOS?/? compared with WT mice. Intact aortas and decellularized aortic tissue scaffolds of eNOS?/? mice were significantly stiffer, as determined by tensile testing. The carotid arteries of the eNOS?/? mice were also stiffer, as determined by pressure-dimension analysis. Invasive methods to determine the PWV-mean arterial pressure relationship showed that PWV in eNOS?/? and WT diverge at higher mean arterial pressure. Thus eNOS-derived NO regulates TG2 localization and function and contributes to vascular stiffness. PMID:23873798

  19. A new method to assess passive and active ankle stiffness during quiet upright stance.

    PubMed

    Zhang, Hongbo; Nussbaum, Maury A; Agnew, Michael J

    2015-12-01

    Both passive and active ankle torque contribute to postural stability during quiet upright stance, yet directly measuring their relative contributions is difficult. Here, a new method was developed to estimate passive and active ankle stiffness (ST) and damping (DA). In contrast to earlier approaches, the proposed method does not require external mechanical or sensory perturbations. Instead, the method is based on the assumption that upright stance is intermittently controlled, and that active ankle torque is in-phase coherent with ankle angular acceleration. Thus, identifying the local maxima of ankle angular accelerations facilitates the identification of time windows that include substantial active ankle torque. After identifying these local maxima and associated windows, estimates of passive and active ankle ST and DA were obtained using linear regression analyses. Consistent with earlier work, passive ankle torque was estimated to account for 94-97% of the total ankle torque, and to have linear relationships with ankle angle and angular velocity. Predicted values of passive and active ankle stiffness were also consistent with earlier reports. This new approach may be a useful tool to efficiently investigate passive and active joint stiffness during quiet upright stance. PMID:26547842

  20. Preliminary study on the effect of stiffness on lamb wave propagation in bovine corneas.

    PubMed

    Zhang, Xin-Yu; Yin, Yin; Guo, Yan-Rong; Diao, Xian-Fen; Chen, Xin

    2013-01-01

    The viscoelastic properties of human cornea could provide valuable information for various clinical applications. Particularly, it will be helpful to achieve a patient-specific biomechanical optimization in LASIK refractive surgery, early detection of corneal ecstatic disease or improved accuracy of intraocular pressure (IOP) measurement. However, there are few techniques that are capable of accurately assessing the corneal elasticity in situ in a nondestructive fashion. In order to develop a quantitative method for assessing both elasticity and viscosity of the cornea, we use ultrasound radiation force to excite Lamb waves in cornea, and a pulse echo transducer to track the tissue vibration. The fresh postmortem bovine eyes were treated via collagen cross-linking to make the cornea stiff. The effect of stiffness was studied by comparing the propagation of Lamb waves in normal and treated corneas. It was found that the waveform of generated Lamb waves changed significantly due to the increase in higher modes in treated corneas. This result indicated that the generated waveform was a complex of multiple harmonics and the varied stiffness will affect the energy distribution over different components. Therefore, it is important for assessing the viscoelastic properties of the cornea to know the components of Lamb wave and calculate the phase velocity appropriately. PMID:24109889

  1. Effect of heat treatment on stiffness and damping of SiC/Ti-15-3

    NASA Technical Reports Server (NTRS)

    Grady, Joseph E.; Lerch, Bradley A.

    1992-01-01

    The effect of heat treatment on material properties of SiC/Ti-15-3 was measured by vibration tests. Heat treatment changes the microstructure, which was found to stiffen the matrix and reduce its damping capacity. Test results indicate how these changes in the matrix affect the corresponding properties of the composite. Measurements show that heat treatment affects damping properties of the composite to a greater extent than stiffness properties. The extent of change in mechanical properties is shown to depend on heat treatment temperature and exposure time.

  2. Arterial stiffness after glucose ingestion in exercise-trained versus untrained men.

    PubMed

    Kobayashi, Ryota; Yoshida, Shou; Okamoto, Takanobu

    2015-11-01

    Postprandial hyperglycemia increases arterial stiffness. Arterial stiffness and insulin resistance are lower in exercise-trained humans than in untrained humans. However, the effect of exercise on arterial stiffness after glucose ingestion in young adults remains unknown. The present study investigates the effect of regular aerobic exercise on arterial stiffness after glucose ingestion in young males. Ten exercise-trained males (age, 20.8 ± 0.2 years; ETR) and 9 healthy untrained males (age, 22.2 ± 0.7 years; UTR) participated in this study. Carotid-femoral (aortic) pulse wave velocity (PWV), femoral-ankle (leg) PWV, carotid augmentation index (AIx) (applanation tonometry), brachial and ankle blood pressure (BP), heart rate (oscillometric device and electrocardiography), and blood glucose (glucose oxidase method) were measured at 30 min before (baseline) and 30, 60, and 120 min after a 75-g oral glucose tolerance test. Leg PWV at 30 min after glucose ingestion was significantly higher (P < 0.01) in the UTR group than in the ETR group. Ankle systolic BP at 30 min after glucose ingestion was also significantly higher in the UTR group than in the ETR group (P < 0.05). Blood glucose increased from baseline at 30 min (P < 0.01) and 60 min (P < 0.05) after glucose ingestion in both groups. Aortic PWV, carotid AIx, and brachial systolic BP did not change from baseline after glucose ingestion in both groups. The present findings indicate that leg PWV and ankle systolic BP after glucose ingestion were significantly lower in the ETR group than in the UTR group. PMID:26444929

  3. Experimental investigation of the influence of the aortic stiffness on hemodynamics in the ascending aorta.

    PubMed

    Gülan, Utku; Lüthi, Beat; Holzner, Markus; Liberzon, Alex; Tsinober, Arkady; Kinzelbach, Wolfgang

    2014-11-01

    A three-dimensional (3-D) pulsatile aortic flow in a human ascending aorta is studied to investigate the effect of the aortic stiffness on the flow field and turbulent fluctuating velocities in the ascending aorta. A nonintrusive optical measurement technique, 3-D particle tracking velocimetry (3D-PTV), has been applied to anatomically accurate phantoms under clinically realistic conditions. A compliant silicon phantom was used to mimic the healthy aorta, and a rigid model was used to imitate the pathological case that appears in aortas for example as a result of aging. The realistic models are transparent which allows optical access to the investigation domain, and the index of refraction was matched to avoid optical distortions. Our results revealed that the aortic stiffness leads to an increase in systolic velocity and a decrease in the Windkessel effect, which is associated with the diastolic blood pressure. Furthermore, we found that the turbulent kinetic energy is about an order of magnitude higher for the rigid aorta, that is, an increase in aortic stiffness increases the magnitude of turbulent fluctuating velocities. The spatial distribution of the flow velocity showed that the flow is more organized and coherent spiraling patterns develop for the compliant aorta which helps to dampen the influence of disturbed flow. Finally, we observed higher Lagrangian acceleration and hence higher instantaneous forces acting on blood particles in the stiff case which implies that aging and hence arterial stiffening provokes distinctive alterations in blood flow, and these alterations may cause pathological symptoms in the cardiovascular system. PMID:24833608

  4. Comparative study of methods to calibrate the stiffness of a single-beam gradient-force optical tweezers over various laser trapping powers

    PubMed Central

    Sarshar, Mohammad; Wong, Winson T.; Anvari, Bahman

    2014-01-01

    Abstract. Optical tweezers have become an important instrument in force measurements associated with various physical, biological, and biophysical phenomena. Quantitative use of optical tweezers relies on accurate calibration of the stiffness of the optical trap. Using the same optical tweezers platform operating at 1064 nm and beads with two different diameters, we present a comparative study of viscous drag force, equipartition theorem, Boltzmann statistics, and power spectral density (PSD) as methods in calibrating the stiffness of a single beam gradient force optical trap at trapping laser powers in the range of 0.05 to 1.38 W at the focal plane. The equipartition theorem and Boltzmann statistic methods demonstrate a linear stiffness with trapping laser powers up to 355 mW, when used in conjunction with video position sensing means. The PSD of a trapped particle’s Brownian motion or measurements of the particle displacement against known viscous drag forces can be reliably used for stiffness calibration of an optical trap over a greater range of trapping laser powers. Viscous drag stiffness calibration method produces results relevant to applications where trapped particle undergoes large displacements, and at a given position sensing resolution, can be used for stiffness calibration at higher trapping laser powers than the PSD method. PMID:25375348

  5. Migration in Confined 3D Environments Is Determined by a Combination of Adhesiveness, Nuclear Volume, Contractility, and Cell Stiffness.

    PubMed

    Lautscham, Lena A; Kämmerer, Christoph; Lange, Janina R; Kolb, Thorsten; Mark, Christoph; Schilling, Achim; Strissel, Pamela L; Strick, Reiner; Gluth, Caroline; Rowat, Amy C; Metzner, Claus; Fabry, Ben

    2015-09-01

    In cancer metastasis and other physiological processes, cells migrate through the three-dimensional (3D) extracellular matrix of connective tissue and must overcome the steric hindrance posed by pores that are smaller than the cells. It is currently assumed that low cell stiffness promotes cell migration through confined spaces, but other factors such as adhesion and traction forces may be equally important. To study 3D migration under confinement in a stiff (1.77 MPa) environment, we use soft lithography to fabricate polydimethylsiloxane (PDMS) devices consisting of linear channel segments with 20 ?m length, 3.7 ?m height, and a decreasing width from 11.2 to 1.7 ?m. To study 3D migration in a soft (550 Pa) environment, we use self-assembled collagen networks with an average pore size of 3 ?m. We then measure the ability of four different cancer cell lines to migrate through these 3D matrices, and correlate the results with cell physical properties including contractility, adhesiveness, cell stiffness, and nuclear volume. Furthermore, we alter cell adhesion by coating the channel walls with different amounts of adhesion proteins, and we increase cell stiffness by overexpression of the nuclear envelope protein lamin A. Although all cell lines are able to migrate through the smallest 1.7 ?m channels, we find significant differences in the migration velocity. Cell migration is impeded in cell lines with larger nuclei, lower adhesiveness, and to a lesser degree also in cells with lower contractility and higher stiffness. Our data show that the ability to overcome the steric hindrance of the matrix cannot be attributed to a single cell property but instead arises from a combination of adhesiveness, nuclear volume, contractility, and cell stiffness. PMID:26331248

  6. Nonintrusive estimation of anisotropic stiffness maps of heterogeneous steel welds for the improvement of ultrasonic array inspection.

    PubMed

    Fan, Zheng; Mark, Alison F; Lowe, Michael J S; Withers, Philip J

    2015-08-01

    It is challenging to inspect austenitic welds nondestructively using ultrasonic waves because the spatially varying elastic anisotropy of weld microstructures can lead to the deviation of ultrasound. Models have been developed to predict the propagation of ultrasound in such welds once the weld stiffness heterogeneity is known. Consequently, it is desirable to have a means of measuring the variation in elastic anisotropy experimentally so as to be able to correct for deviations in ultrasonic pathways for the improvement of weld inspection. This paper investigates the use of external nonintrusive ultrasonic array measurements to construct such weld stiffness maps, representing the orientation of the stiffness tensor according to location in the weld cross section. An inverse model based on a genetic algorithm has been developed to recover a small number of key parameters in an approximate model of the weld map, making use of ultrasonic array measurements. The approximate model of the weld map uses the Modeling of anIsotropy based on Notebook of Arcwelding (MINA) formulation, which is one of the representations that has been proposed by other researchers to provide a simple, yet physically based, description of the overall variations of orientations of the stiffness tensors over the weld cross section. The choice of sensitive ultrasonic modes as well as the best monitoring positions have been discussed to achieve a robust inversion. Experiments have been carried out on a 60-mm-thick multipass tungsten inert gas (TIG) weld to validate the findings of the modeling, showing very good agreement. This work shows that ultrasonic array measurements can be used on a single side of a butt-welded plate, such that there is no need to access the remote side, to construct an approximate but useful weld map of the spatial variations in anisotropic stiffness orientation that occur within the weld. PMID:26276961

  7. Tissue Stiffness Dictates Development, Homeostasis, and Disease Progression

    PubMed Central

    Handorf, Andrew M; Zhou, Yaxian; Halanski, Matthew A; Li, Wan-Ju

    2015-01-01

    Abstract Tissue development is orchestrated by the coordinated activities of both chemical and physical regulators. While much attention has been given to the role that chemical regulators play in driving development, researchers have recently begun to elucidate the important role that the mechanical properties of the extracellular environment play. For instance, the stiffness of the extracellular environment has a role in orienting cell division, maintaining tissue boundaries, directing cell migration, and driving differentiation. In addition, extracellular matrix stiffness is important for maintaining normal tissue homeostasis, and when matrix mechanics become imbalanced, disease progression may ensue. In this article, we will review the important role that matrix stiffness plays in dictating cell behavior during development, tissue homeostasis, and disease progression. PMID:25915734

  8. Design and experiment of a high-static-low-dynamic stiffness isolator using a negative stiffness magnetic spring

    NASA Astrophysics Data System (ADS)

    Zheng, Yisheng; Zhang, Xinong; Luo, Yajun; Yan, Bo; Ma, Chicheng

    2016-01-01

    To improve the vibration isolation performance under low frequency excitation, a negative stiffness magnetic spring (NSMS) is employed to reduce the resonance frequency of the linear isolator. The NSMS comprising a pair of coaxial ring permanent magnets is installed in parallel with the mechanical spring to counteract its positive stiffness. The major feature of the isolator is that it has high static low dynamic stiffness (HSLDS). In this paper, the model of the HSLDS isolator and the NSMS is analyzed firstly; and the magnetic force and stiffness exerted between the inner magnet and the outer magnet is then calculated based on the Amperian current model. After analyzing the effect of the geometric parameters of the magnets on the stiffness characteristic of the NSMS, a designing procedure for the NSMS is proposed. Then the nonlinear dynamic equation of the isolator is established and numerical simulation is performed to obtain the transmissibility. Finally, the detailed design of the HSLDS isolator is given and an experimental setup is proposed. The experimental results demonstrate that the NSMS can reduce the resonance frequency of the isolator indeed; and the isolation performance of the proposed isolator is improved accordingly.

  9. Micropipette Aspiration of Substrate-attached Cells to Estimate Cell Stiffness

    PubMed Central

    Oh, Myung-Jin; Kuhr, Frank; Byfield, Fitzroy; Levitan, Irena

    2012-01-01

    Growing number of studies show that biomechanical properties of individual cells play major roles in multiple cellular functions, including cell proliferation, differentiation, migration and cell-cell interactions. The two key parameters of cellular biomechanics are cellular deformability or stiffness and the ability of the cells to contract and generate force. Here we describe a quick and simple method to estimate cell stiffness by measuring the degree of membrane deformation in response to negative pressure applied by a glass micropipette to the cell surface, a technique that is called Micropipette Aspiration or Microaspiration. Microaspiration is performed by pulling a glass capillary to create a micropipette with a very small tip (2-50 ?m diameter depending on the size of a cell or a tissue sample), which is then connected to a pneumatic pressure transducer and brought to a close vicinity of a cell under a microscope. When the tip of the pipette touches a cell, a step of negative pressure is applied to the pipette by the pneumatic pressure transducer generating well-defined pressure on the cell membrane. In response to pressure, the membrane is aspirated into the pipette and progressive membrane deformation or "membrane projection" into the pipette is measured as a function of time. The basic principle of this experimental approach is that the degree of membrane deformation in response to a defined mechanical force is a function of membrane stiffness. The stiffer the membrane is, the slower the rate of membrane deformation and the shorter the steady-state aspiration length.The technique can be performed on isolated cells, both in suspension and substrate-attached, large organelles, and liposomes. Analysis is performed by comparing maximal membrane deformations achieved under a given pressure for different cell populations or experimental conditions. A "stiffness coefficient" is estimated by plotting the aspirated length of membrane deformation as a function of the applied pressure. Furthermore, the data can be further analyzed to estimate the Young's modulus of the cells (E), the most common parameter to characterize stiffness of materials. It is important to note that plasma membranes of eukaryotic cells can be viewed as a bi-component system where membrane lipid bilayer is underlied by the sub-membrane cytoskeleton and that it is the cytoskeleton that constitutes the mechanical scaffold of the membrane and dominates the deformability of the cellular envelope. This approach, therefore, allows probing the biomechanical properties of the sub-membrane cytoskeleton. PMID:23051713

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

    NASA Astrophysics Data System (ADS)

    Bejan, Liliana; Taranu, Nicolae; Sîrbu, Adriana

    2013-04-01

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

  11. Aortic and Carotid Arterial Stiffness and Epigenetic Regulator Gene Expression Changes Precede Blood Pressure Rise in Stroke-Prone Dahl Salt-Sensitive Hypertensive Rats

    PubMed Central

    Herrera, Victoria L.; Decano, Julius L.; Giordano, Nicholas; Moran, Ann Marie; Ruiz-Opazo, Nelson

    2014-01-01

    Multiple clinical studies show that arterial stiffness, measured as pulse wave velocity (PWV), precedes hypertension and is an independent predictor of hypertension end organ diseases including stroke, cardiovascular disease and chronic kidney disease. Risk factor studies for arterial stiffness implicate age, hypertension and sodium. However, causal mechanisms linking risk factor to arterial stiffness remain to be elucidated. Here, we studied the causal relationship of arterial stiffness and hypertension in the Na-induced, stroke-prone Dahl salt-sensitive (S) hypertensive rat model, and analyzed putative molecular mechanisms. Stroke-prone and non-stroke-prone male and female rats were studied at 3- and 6-weeks of age for arterial stiffness (PWV, strain), blood pressure, vessel wall histology, and gene expression changes. Studies showed that increased left carotid and aortic arterial stiffness preceded hypertension, pulse pressure widening, and structural wall changes at the 6-week time-point. Instead, differential gene induction was detected implicating molecular-functional changes in extracellular matrix (ECM) structural constituents, modifiers, cell adhesion, and matricellular proteins, as well as in endothelial function, apoptosis balance, and epigenetic regulators. Immunostaining testing histone modifiers Ep300, HDAC3, and PRMT5 levels confirmed carotid artery-upregulation in all three layers: endothelial, smooth muscle and adventitial cells. Our study recapitulates observations in humans that given salt-sensitivity, increased Na-intake induced arterial stiffness before hypertension, increased pulse pressure, and structural vessel wall changes. Differential gene expression changes associated with arterial stiffness suggest a molecular mechanism linking sodium to full-vessel wall response affecting gene-networks involved in vascular ECM structure-function, apoptosis balance, and epigenetic regulation. PMID:25229245

  12. Digital Photoplethysmography for Assessment of Arterial Stiffness: Repeatability and Comparison with Applanation Tonometry

    PubMed Central

    Östling, Gerd; Nilsson, Peter M.

    2015-01-01

    Introduction Arterial stiffness is an independent risk factor for cardiovascular morbidity and can be assessed by applanation tonometry by measuring pulse wave velocity (PWV) and augmentation index (AIX) by pressure pulse wave analysis (PWA). As an inexpensive and operator independent alternative, photoelectric plethysmography (PPG) has been introduced with analysis of the digital volume pulse wave (DPA) and its second derivatives of wave reflections. Objective The objective was to investigate the repeatability of arterial stiffness parameters measured by digital pulse wave analysis (DPA) and the associations to applanation tonometry parameters. Methods and Results 112 pregnant and non-pregnant individuals of different ages and genders were examined with SphygmoCor arterial wall tonometry and Meridian DPA finger photoplethysmography. Coefficients of repeatability, Bland-Altman plots, intraclass correlation coefficients and correlations to heart rate (HR) and body height were calculated for DPA variables, and the DPA variables were compared to tonometry variables left ventricular ejection time (LVET), PWV and AIX. No DPA variable showed any systematic measurement error or excellent repeatability, but dicrotic index (DI), dicrotic dilatation index (DDI), cardiac ejection elasticity index (EEI), aging index (AI) and second derivatives of the crude pulse wave curve, b/a and e/a, showed good repeatability. Overall, the correlations to AIX were better than to PWV, with correlations coefficients >0.70 for EEI, AI and b/a. Considering the level of repeatability and the correlations to tonometry, the overall best DPA parameters were EEI, AI and b/a. The two pansystolic time parameters, ejection time compensated (ETc) by DPA and LVET by tonometry, showed a significant but weak correlation. Conclusion For estimation of the LV function, ETc, EEI and b/a are suitable, for large artery stiffness EEI, and for small arteries DI and DDI. The only global parameter, AI, showed a high repeatability and the overall best correlations with AIX and PWV. PMID:26291079

  13. Arterial Stiffness Estimation by Shear Wave Elastography: Validation in Phantoms with Mechanical Testing.

    PubMed

    Maksuti, Elira; Widman, Erik; Larsson, David; Urban, Matthew W; Larsson, Matilda; Bjällmark, Anna

    2016-01-01

    Arterial stiffness is an independent risk factor found to correlate with a wide range of cardiovascular diseases. It has been suggested that shear wave elastography (SWE) can be used to quantitatively measure local arterial shear modulus, but an accuracy assessment of the technique for arterial applications has not yet been performed. In this study, the influence of confined geometry on shear modulus estimation, by both group and phase velocity analysis, was assessed, and the accuracy of SWE in comparison with mechanical testing was measured in nine pressurized arterial phantoms. The results indicated that group velocity with an infinite medium assumption estimated shear modulus values incorrectly in comparison with mechanical testing in arterial phantoms (6.7 ± 0.0 kPa from group velocity and 30.5 ± 0.4 kPa from mechanical testing). To the contrary, SWE measurements based on phase velocity analysis (30.6 ± 3.2 kPa) were in good agreement with mechanical testing, with a relative error between the two techniques of 8.8 ± 6.0% in the shear modulus range evaluated (40-100 kPa). SWE by phase velocity analysis was validated to accurately measure stiffness in arterial phantoms. PMID:26454623

  14. Differential effects of nebivolol and metoprolol on arterial stiffness, circulating progenitor cells, and oxidative stress.

    PubMed

    Hayek, Salim S; Poole, Joseph C; Neuman, Robert; Morris, Alanna A; Khayata, Mohamed; Kavtaradze, Nino; Topel, Matthew L; Binongo, Jose G; Li, Qunna; Jones, Dean P; Waller, Edmund K; Quyyumi, Arshed A

    2015-03-01

    Unlike traditional beta receptor antagonists, nebivolol activates nitric oxide. We hypothesized that therapy with nebivolol compared with metoprolol would improve arterial stiffness, increase levels of circulating progenitor cells (PC), and decrease oxidative stress (OS). In a randomized, double-blind, cross-over study, 30 hypertensive subjects received either once daily nebivolol or metoprolol succinate for 3 months each. Pulse wave velocity and augmentation index were measured using tonometry. Flow cytometry was used to measure circulating PC. OS was measured as plasma aminothiols. Measurements were performed at baseline, and repeated at 3 and 6 months. No significant differences were present between the levels of OS, arterial stiffness, and PC numbers during treatment with metoprolol compared with nebivolol. In subgroup analyses of beta-blocker naïve subjects (n = 19), nebivolol reduced pulse wave velocity significantly compared with metoprolol (-1.4 ± 1.9 vs. -0.1 ± 2.2; P = .005). Both nebivolol and metoprolol increased circulating levels of CD34+/CD133 + PC similarly (P = .05), suggesting improved regenerative capacity. PMID:25681236

  15. 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.

  16. Flexural stiffness of feather shafts: geometry rules over material properties.

    PubMed

    Bachmann, Thomas; Emmerlich, Jens; Baumgartner, Werner; Schneider, Jochen M; Wagner, Hermann

    2012-02-01

    Flight feathers of birds interact with the flow field during flight. They bend and twist under aerodynamic loads. Two parameters are mainly responsible for flexibility in feathers: the elastic modulus (Young's modulus, E) of the material (keratin) and the geometry of the rachises, more precisely the second moment of area (I). Two independent methods were employed to determine Young's modulus of feather rachis keratin. Moreover, the second moment of area and the bending stiffness of feather shafts from fifth primaries of barn owls (Tyto alba) and pigeons (Columba livia) were calculated. These species of birds are of comparable body mass but differ in wing size and flight style. Whether their feather material (keratin) underwent an adaptation in stiffness was previously unknown. This study shows that no significant variation in Young's modulus between the two species exists. However, differences in Young's modulus between proximal and distal feather regions were found in both species. Cross-sections of pigeon rachises were particularly well developed and rich in structural elements, exemplified by dorsal ridges and a well-pronounced transversal septum. In contrast, cross-sections of barn owl rachises were less profiled but had a higher second moment of area. Consequently, the calculated bending stiffness (EI) was higher in barn owls as well. The results show that flexural stiffness is predominantly influenced by the geometry of the feathers rather than by local material properties. PMID:22246249

  17. Design of a Stiff Steerable Grasper for Sinus Surgery

    E-print Network

    Design of a Stiff Steerable Grasper for Sinus Surgery Andria A. Remirez, Ray A. Lathrop, Paul T Background With the advent of endoscopic sinus surgery in the late 1980's [1], a completely new surgical of the sinuses. Today, functional endoscopic sinus surgery (FESS) is commonly used to improve the sinuses

  18. Damping and Stiffness of Particulate SiCInSn Composite

    E-print Network

    Swan Jr., Colby Corson

    is the product of stiffness (Young's modulus E or shear modulus G) and damping (tan ; the loss tangent, which 100 Hz. Composite shear modulus was almost a factor two greater than matrix for 40% and a factor such as high specific modulus, strength, and thermal stability, yet composite design with consideration

  19. Riparian Sediment Delivery Ratio: Stiff Diagrams and Artifical Neural Networks

    EPA Science Inventory

    Various methods are used to estimate sediment transport through riparian buffers and grass jilters with the sediment delivery ratio having been the most widely applied. The U.S. Forest Service developed a sediment delivery ratio using the stiff diagram and a logistic curve to int...

  20. Residual-based Stiffness Estimation in Robots with Flexible Transmissions

    E-print Network

    De Luca, Alessandro

    only the knowledge of the dynamic parameters of the motors. In particular, no extra force/torque generates a residual signal that is a first-order filtered version of the flexibility torque), display nonlinear deformation-torque characteris- tics, or be part of a nonlinear variable stiffness

  1. Difference methods for stiff delay differential equations. [DDESUB, in FORTRAN

    SciTech Connect

    Roth, Mitchell G.

    1980-12-01

    Delay differential equations of the form y'(t) = f(y(t), z(t)), where z(t) = (y/sub 1/(..cap alpha../sub 1/(y(t))),..., y/sub n/(..cap alpha../sub n/(y(t))))/sup T/ and ..cap alpha../sub i/(y(t)) less than or equal to t, arise in many scientific and engineering fields when transport lags and propagation times are physically significant in a dynamic process. Difference methods for approximating the solution of stiff delay systems require special stability properties that are generalizations of those employed for stiff ordinary differential equations. By use of the model equation y'(t) = py(t) + qy(t-1), with complex p and q, the definitions of A-stability, A( )-stability, and stiff stability have been generalize to delay equations. For linear multistep difference formulas, these properties extend directly from ordinary to delay equations. This straight forward extension is not true for implicit Runge-Kutta methods, as illustrated by the midpoint formula, which is A-stable for ordinary equations, but not for delay equations. A computer code for stiff delay equations was developed using the BDF. 24 figures, 5 tables.

  2. Stiff, strong, and tough hydrogels with good chemical stability

    E-print Network

    Suo, Zhigang

    water content of the resulting gels increased with acrylamide content, while the coefficient of friction require high stiffness (1 MPa), high toughness (1000 J m�2 ), and high water content (60­ 80%).5 Materials- tion, sustain sealing pressure (up to 34 MPa) and be stable in saline water.3 Materials for articial

  3. Design optimization of a twist compliant mechanism with nonlinear stiffness

    NASA Astrophysics Data System (ADS)

    Tummala, Y.; Frecker, M. I.; Wissa, A. A.; Hubbard, J. E., Jr.

    2014-10-01

    A contact-aided compliant mechanism called a twist compliant mechanism (TCM) is presented in this paper. This mechanism has nonlinear stiffness when it is twisted in both directions along its axis. The inner core of the mechanism is primarily responsible for its flexibility in one twisting direction. The contact surfaces of the cross-members and compliant sectors are primarily responsible for its high stiffness in the opposite direction. A desired twist angle in a given direction can be achieved by tailoring the stiffness of a TCM. The stiffness of a compliant twist mechanism can be tailored by varying thickness of its cross-members, thickness of the core and thickness of its sectors. A multi-objective optimization problem with three objective functions is proposed in this paper, and used to design an optimal TCM with desired twist angle. The objective functions are to minimize the mass and maximum von-Mises stress observed, while minimizing or maximizing the twist angles under specific loading conditions. The multi-objective optimization problem proposed in this paper is solved for an ornithopter flight research platform as a case study, with the goal of using the TCM to achieve passive twisting of the wing during upstroke, while keeping the wing fully extended and rigid during the downstroke. Prototype TCMs have been fabricated using 3D printing and tested. Testing results are also presented in this paper.

  4. Substrate stiffness affects skeletal myoblast differentiation in vitro

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  5. ANISOTROPIC STEP STIFFNESS FROM A KINETIC MODEL OF EPITAXIAL GROWTH

    E-print Network

    Ferguson, Thomas S.

    . In epitax- ial growth, crystal surface features such as thin films, which are building blocks of solidANISOTROPIC STEP STIFFNESS FROM A KINETIC MODEL OF EPITAXIAL GROWTH RUSSEL E. CAFLISCH of the step edge orientation angle, . Basic ingredients of the model are: (i) the diffusion of point defects

  6. Variable stiffness and damping suspension system for train

    NASA Astrophysics Data System (ADS)

    Sun, Shuaishuai; Deng, Huaxia; Li, Weihua

    2014-03-01

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

  7. Torsional stiffness degradation and aerostatic divergence of suspension bridge decks

    NASA Astrophysics Data System (ADS)

    Zhang, Z. T.; Ge, Y. J.; Yang, Y. X.

    2013-07-01

    The mechanism of aerostatic torsional divergence (ATD) of long-span suspension bridges is investigated. A theoretical analysis on the basis of a generalized model is presented, showing that the vertical motion of a bridge deck is crucial to the torsional stiffness of the whole suspended system, and that the vertical motion of either cable with a magnitude beyond a certain threshold could result in a sudden degradation of the torsional stiffness of the system. This vertical motion-induced degradation of stiffness is recognized as the main reason for the ATD. Long-span suspension bridges are susceptible to such a type of divergence, especially when they are immersed in turbulent wind fields. The divergences that occur in turbulent wind fields differ significantly from those in smooth wind fields, and the difference is well explained by the generalized model that the loosening of any one cable could result in the vanishing of the part of stiffness provided by the whole cable system. The mechanism revealed in this paper leads to a definition of the critical wind speed of the ATD in a turbulent flow; that is, the one resulting in a vertical motion so large as to loosen either cable to a stressless state. Numerical results from the nonlinear finite-element (FE) analysis of the Xihoumen suspension bridge, in conjunction with observations from wind tunnel tests on an aero-elastic full bridge model, are in support of the viewpoint presented in this study.

  8. Magnetorheological brush - a soft structure with highly tuneable stiffness.

    PubMed

    Huang, Xiao; Mohla, Akshi; Hong, Wei; Bastawros, Ashraf F; Feng, Xi-Qiao

    2014-03-14

    By combining the field-stiffening effect of magnetorheological (MR) elastomers and the Euler buckling mechanism, we developed a brush-like magneto-active structure with highly tuneable stiffness. When the applied mechanical load is within a certain range, the effective stiffness of the structure can be tuned by several orders of magnitude with the applied magnetic field. The performance of the structure and its dependence on various synthesis parameters, such as the curing field and filler concentration, were investigated experimentally. It is found that the increase in the critical load for buckling is more than the contribution from the stiffening of the MR elastomer. To unravel the relationship between the stiffness increase and the applied field, a theoretical model with coupled mechanical deformation and magnetic field is established. The prediction of the model agrees well with experimental results. The theory may also be used to model the behaviour of other similar materials, such as MR gels. The MR brush developed in this research holds promise for potential applications in smart structures or devices that require mechanical stiffness to be tuneable in a relatively large range. As the amplification mechanism is independent of the base material, it could be used in conjunction with emerging MR materials for further enhanced performance. PMID:24652105

  9. Predictors of Postoperative Finger Stiffness in Unstable Proximal Phalangeal Fractures

    PubMed Central

    Onishi, Tadanobu; Shimizu, Takamasa; Fujitani, Ryotaro; Shigematsu, Koji; Tanaka, Yasuhito

    2015-01-01

    Background: The purpose of this study was to determine the risk factors for postoperative finger stiffness after open reduction and internal fixation of unstable proximal phalangeal fractures using a low-profile plate and/or screw system. We hypothesized that dorsal plate placement is a risk factor for postoperative finger stiffness. Methods: Seventy consecutive patients (50 men, 20 women; average age, 40 years) with 75 unstable proximal phalangeal fractures were treated with titanium plates and/or screws and evaluated at a minimum follow-up of 1 year. Thirty-six comminuted fractures and 24 intra-articular fractures were included, and 16 fractures had associated soft-tissue injuries. Plate fixation was performed in 59 fractures, and the remaining 16 were fixed with screws only. The implants were placed in a dorsal location in 33 fractures and in a lateral or volar location in 42 fractures. Finger stiffness was defined as a total active range of finger motion <80% for the treated finger. Univariate and multivariate analyses were performed on 8 variables: patient characteristics (age and sex), fracture characteristics (fracture comminution, joint involvement, and associated soft-tissue injury), and surgical characteristics (type and location of implants and removal of the implants). Results: Postoperative finger stiffness occurred in 38 fractures. The multivariate analysis indicated that plate fixation (odds ratio, 5.9; 95% confidence interval, 1.5–24.0; P = 0.01) and dorsal placement (odds ratio, 3.0; 95% confidence interval, 1.1–8.3; P = 0.03) were independent risk factors for finger stiffness. Conclusion: We recommend the use of screw fixation as much as possible for unstable proximal phalangeal fractures using a midlateral approach. PMID:26180732

  10. Evaluation of stiffness and plastic deformation of active ceramic self-ligating bracket clips after repetitive opening and closure movements

    PubMed Central

    Carneiro, Grace Kelly Martins; Roque, Juliano Alves; Segundo, Aguinaldo Silva Garcez; Suzuki, Hideo

    2015-01-01

    OBJECTIVE: The aim of this study was to assess whether repetitive opening and closure of self-ligating bracket clips can cause plastic deformation of the clip. METHODS: Three types of active/interactive ceramic self-ligating brackets (n = 20) were tested: In-Ovation C, Quicklear and WOW. A standardized controlled device performed 500 cycles of opening and closure movements of the bracket clip with proper instruments and techniques adapted as recommended by the manufacturer of each bracket type. Two tensile tests, one before and one after the repetitive cycles, were performed to assess the stiffness of the clips. To this end, a custom-made stainless steel 0.40 x 0.40 mm wire was inserted into the bracket slot and adapted to the universal testing machine (EMIC DL2000), after which measurements were recorded. On the loading portion of the loading-unloading curve of clips, the slope fitted a first-degree equation curve to determine the stiffness/deflection rate of the clip. RESULTS: The results of plastic deformation showed no significant difference among bracket types before and after the 500 cycles of opening and closure (p = 0.811). There were significant differences on stiffness among the three types of brackets (p = 0.005). The WOW bracket had higher mean values, whereas Quicklear bracket had lower values, regardless of the opening/closure cycle. CONCLUSION: Repetitive controlled opening and closure movements of the clip did not alter stiffness or cause plastic deformation. PMID:26352844

  11. Loss of an actin crosslinker uncouples cell spreading from cell stiffening on gels with a gradient of stiffness

    NASA Astrophysics Data System (ADS)

    Wen, Qi; Byfield, Fitzroy J.; Nordstrom, Kerstin; Arratia, Paulo E.; Miller, R. Tyler; Janmey, Paul A.

    2009-03-01

    We use microfluidics techniques to produce gels with a gradient of stiffness to show the essential function of the actin crosslinker filamin A in cell responses to mechanical stimuli. M2 melanoma cells null for filamin A do not alter their adherent area in response to increased substrate stiffness when they link to the substrate only through collagen receptors, but change adherent area normally when bound through fibronectin receptors. In contrast, filamin A-replete A7 cells change adherent area on both substrates and respond more strongly to collagen 1-coated gels than to fibronectin-coated gels. A7 cells alter their stiffness, as measured by atomic force microscopy, to match the elastic modulus of the substrate immediately adjacent to them on the gradient. M2 cells, in contrast, maintain a constant stiffness on all substrates that is as low as that of A7 cells on the softest gels achievable (1000 Pa). By contrasting the responses of these cell types to different adhesive substrates, cell spreading can be dissociated from stiffening.

  12. Association between plasma sLOX-1 concentration and arterial stiffness in middle-aged and older individuals

    PubMed Central

    Otsuki, Takeshi; Maeda, Seiji; Mukai, Jun; Ohki, Makoto; Nakanishi, Mamoru; Yoshikawa, Toshikazu

    2015-01-01

    Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is implicated in vascular endothelial function. Vascular endothelial function is a potent regulator of arterial stiffness, an independent risk factor for cardiovascular disease. However, it is unknown whether LOX-1 is associated with arterial stiffness. Plasma concentrations of soluble LOX-1 (sLOX-1) and brachial-ankle pulse wave velocity (baPWV, an index of arterial stiffness) were measured in 143 individuals between 51 and 83 years of age. Plasma sLOX-1 concentration was correlated with baPWV (r = 0.288, p = 0.0005). In stepwise regression analysis, plasma sLOX-1 concentration was associated with baPWV, after adjusting for age; body mass index; blood pressure; heart rate; blood levels of cholesterol, triglycerides, glucose, hemoglobin A1c, and insulin; sex; and use of antihypertensives, lipid-lowering agents, and other medications (R2 = 0.575, p<0.0001). Multiple logistic regression demonstrated that plasma sLOX-1 concentration was independently associated with elevated baPWV (?14.0 m/s; odds ratio, 1.01; 95% confidence interval, 1.00–1.03; p = 0.03). These results suggest that LOX-1 is associated with arterial stiffness. PMID:26388674

  13. Muscle short-range stiffness can be used to1 estimate the endpoint stiffness of the human arm2

    E-print Network

    Perreault, Eric J.

    , Chicago, IL, USA9 4 Research Service, Edward Hines, Jr. VA Hospital, Hines, IL, USA10 11 12 Running title relevant for the maintenance of posture. At a fixed posture, endpoint32 stiffness can be regulated range of43 evaluated arm postures and voluntary forces, the musculoskeletal model incorporating44 short

  14. Helix versus coil polypeptide macromers: gel networks with decoupled stiffness and permeability

    E-print Network

    Oelker, Abigail M.

    As a platform for investigating the individual effects of substrate stiffness, permeability, and ligand density on cellular behavior, we developed a set of hydrogels with stiffness tuned by polymer backbone rigidity, ...

  15. jamSheets: Thin Interfaces with Tunable Stiffness Enabled by Layer Jamming

    E-print Network

    Ou, Jifei

    This works introduces layer jamming as an enabling technology for designing deformable, stiffness-tunable, thin sheet interfaces. Interfaces that exhibit tunable stiffness properties can yield dynamic haptic feedback and ...

  16. Effects of mechanical forces on cytoskeletal remodeling and stiffness of cultured smooth muscle cells 

    E-print Network

    Na, Sungsoo

    2009-06-02

    that disruption of the actin filaments can reduce the stiffness substantially, whereas there can be little contribution to the overall cell stiffness by the microtubules or intermediate filaments. To investigate the effect of mechanical stretching on cytoskeletal...

  17. A piezoelectric-based infinite stiffness generation method for strain-type load sensors

    NASA Astrophysics Data System (ADS)

    Zhang, Shuwen; Shao, Shubao; Chen, Jie; Xu, Minglong

    2015-11-01

    Under certain application conditions like nanoindentation technology and the mechanical property measurement of soft materials, the elastic deformation of strain-type load sensors affects their displacement measurement accuracy. In this work, a piezoelectric-based infinite stiffness generation method for strain-type load sensors that compensates for this elastic deformation is presented. The piezoelectric material-based deformation compensation method is proposed. An Hottinger Baldwin Messtechnik GmbH (HBM) Z30A/50N load sensor acts as the foundation of the method presented in this work. The piezoelectric stack is selected based on its size, maximum deformation value, blocking force and stiffness. Then, a clamping and fixing structure is designed to integrate the HBM sensor with the piezoelectric stack. The clamping and fixing structure, piezoelectric stack and HBM load sensor comprise the sensing part of the enhanced load sensor. The load-deformation curve and the voltage-deformation curve of the enhanced load sensor are then investigated experimentally. Because a hysteresis effect exists in the piezoelectric structure, the relationship between the control signal and the deformation value of the piezoelectric material is nonlinear. The hysteresis characteristic in a quasi-static condition is studied and fitted using a quadratic polynomial, and its coefficients are analyzed to enable control signal prediction. Applied arithmetic based on current theory and the fitted data is developed to predict the control signal. Finally, the experimental effects of the proposed method are presented. It is shown that when a quasi-static load is exerted on this enhanced strain-type load sensor, the deformation is reduced and the equivalent stiffness appears to be almost infinite.

  18. Arterial Stiffness and Carotid Intima-Media Thickness in Diabetic Peripheral Neuropathy

    PubMed Central

    Avci, Ahmet; Demir, Kenan; Kaya, Zeynettin; Marakoglu, Kamile; Ceylan, Esra; Ekmekci, Ahmet Hakan; Yilmaz, Ahmet; Demir, Aysegul; Altunkeser, Bulent Behlul

    2014-01-01

    Background We investigated the relationship between peripheral neuropathy and parameters of arterial stiffness and carotid intima media thickness (CIMT) in patients with type 2 diabetes mellitus (T2DM). Material/Methods The study included 161 patients (80 females and 81 males), 69 of whom had peripheral neuropathy. All patients underwent 24-h blood pressure monitoring, and arterial stiffness parameters were measured. The CIMT was measured using B-mode ultrasonography and patients also underwent transthoracic echocardiographic examination. Results Patients with peripheral neuropathy, compared with those without it, were older (54.68±8.35 years vs. 51.04±7.89 years; p=0.005) and had T2DM for longer periods (60 vs. 36 months; p=0.004). Glycated hemoglobin (HbA1c) values (8.55±1.85 mg/dL vs. 7.30±1.51 mg/dL; p<0.001), pulse wave velocity (PWV) (7.74±1.14 m/s vs. 7.15±1.10 m/s; p=0.001), CIMT (anterior 0.74±0.15 mm vs. 0.67±0.13 mm; p=0.01), and left ventricular mass (LVM) index (98.68±26.28 g/m2 vs. 89.71±19.70 g/m2; p=0.02) were all significantly increased in the group with peripheral neuropathy compared to the group without peripheral neuropathy. We determined that duration of diabetes, HbA1c, and LVM index were predictors of peripheral neuropathy. Conclusions A significant relationship was found between diabetic neuropathy and increased PWV, a parameter of arterial stiffness, as well as CIMT, a marker of systemic atherosclerosis. Diabetic peripheral neuropathy may be a determinant of subclinical atherosclerosis in T2DM. PMID:25351260

  19. Stiff diamond/buckypaper carbon hybrids.

    PubMed

    Holz, T; Mata, D; Santos, N F; Bdikin, I; Fernandes, A J S; Costa, F M

    2014-12-24

    Given the specific properties of each carbon allotrope such as high electrical/thermal conductivity of multiwall carbon nanotubes (MWCNT) and extreme hardness and high inertness of nanocrystalline diamond (NCD), the integration of both carbon phases is highly desirable. Therefore, in the present work, buckypapers were produced from MWCNT suspensions and were used as free-standing substrates to be coated with NCD by microwave plasma chemical vapor deposition (MPCVD). The integration of both allotropes was successfully achieved, the CNTs being preserved after diamond growth as confirmed by ?-Raman spectroscopy and scanning electron microscopy (SEM). Additionally, a good linkage was observed, the CNTs remaining embedded within the NCD matrix, thus reinforcing the interface of the resulting hybrid structure. This was corroborated by bending tests in a modified nanohardness tester. The increase of the Young's modulus from 0.3 to 300 GPa after NCD growth enables the use of this material in a wide range of applications including microelectromechanical systems (MEMS). Additionally, a highly anisotropic electrical resistivity behavior was confirmed: low in-plane values were found for the CNT layer (1.39 × 10(-2) ?.cm), while high transverse ones were measured for both the NCD coated and uncoated CNT buckypapers (8.13 × 10(5) and 6.18 × 10(2) ?.cm, respectively). PMID:25412196

  20. Longitudinal relaxation of initially straight flexible and stiff polymers

    NASA Astrophysics Data System (ADS)

    Dimitrakopoulos, Panagiotis; Dissanayake, Inuka

    2004-11-01

    The present talk considers the relaxation of a single flexible or stiff polymer chain from an initial straight configuration in a viscous solvent. This problem commonly arises when strong flows are turned off in both industrial and biological applications. The problem is also motivated by recent experiments with single biopolymer molecules relaxing after being fully extended by applied forces as well as by the recent development of micro-devices involving stretched tethered biopolymers. Our results are applicable to a wide array of synthetic polymers such as polyacrylamides, Kevlar and polyesters as well as biopolymers such as DNA, actin filaments, microtubules and MTV. In this talk we discuss the mechanism of the polymer relaxation as was revealed through Brownian Dynamics simulations covering a broad range of time scales and chain stiffness. After the short-time free diffusion, the chain's longitudinal reduction at early intermediate times is shown to constitute a universal behavior for any chain stiffness caused by a quasi-steady relaxation of tensions associated with the deforming action of the Brownian forces. Stiff chains are shown to exhibit a late intermediate-time longitudinal reduction associated with a relaxation of tensions affected by the deforming Brownian and the restoring bending forces. The longitudinal and transverse relaxations are shown to obey different laws, i.e. the chain relaxation is anisotropic at all times. In the talk, we show how from the knowledge of the relaxation mechanism, we can predict and explain the polymer properties including the polymer stress and the solution birefringence. In addition, a generalized stress-optic law is derived valid for any time and chain stiffness. All polymer properties which depend on the polymer length are shown to exhibit two intermediate-time behaviors with the early one to constitute a universal behavior for any chain stiffness. This work was supported in part by the Minta Martin Research Fund. The computations were performed on multiprocessor computers provided by the National Center for Supercomputing Applications (NCSA) in Illinois (grant DMR000003), and by an Academic Equipment Grant from Sun Microsystems Inc.

  1. Arterial stiffness identification of the human carotid artery using the stressstrain relationship in vivo

    E-print Network

    Konofagou, Elisa E.

    Arterial stiffness identification of the human carotid artery using the stress­strain relationship in revised form 20 September 2011 Accepted 20 September 2011 Available online xxxx Keywords: Arterial stiffness Carotid artery Collagen Elastin Stress­strain relationship a b s t r a c t Arterial stiffness

  2. Intracellular nanomanipulation by a photonic-force microscope with real-time acquisition of a 3D stiffness matrix.

    PubMed

    Bertseva, E; Singh, A S G; Lekki, J; Thévenaz, P; Lekka, M; Jeney, S; Gremaud, G; Puttini, S; Nowak, W; Dietler, G; Forró, L; Unser, M; Kulik, A J

    2009-07-15

    A traditional photonic-force microscope (PFM) results in huge sets of data, which requires tedious numerical analysis. In this paper, we propose instead an analog signal processor to attain real-time capabilities while retaining the richness of the traditional PFM data. Our system is devoted to intracellular measurements and is fully interactive through the use of a haptic joystick. Using our specialized analog hardware along with a dedicated algorithm, we can extract the full 3D stiffness matrix of the optical trap in real time, including the off-diagonal cross-terms. Our system is also capable of simultaneously recording data for subsequent offline analysis. This allows us to check that a good correlation exists between the classical analysis of stiffness and our real-time measurements. We monitor the PFM beads using an optical microscope. The force-feedback mechanism of the haptic joystick helps us in interactively guiding the bead inside living cells and collecting information from its (possibly anisotropic) environment. The instantaneous stiffness measurements are also displayed in real time on a graphical user interface. The whole system has been built and is operational; here we present early results that confirm the consistency of the real-time measurements with offline computations. PMID:19550007

  3. 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:26664263

  4. Stiffness of carbodiimide-crosslinked glycerinated muscle fibres in rigor and relaxing solutions at high salt concentrations.

    PubMed

    Tawada, K; Kimura, M

    1986-08-01

    In this article, we have applied a crosslinking technique with a water-soluble carbodiimide to single glycerol-extracted muscle fibres from the rabbit. We have measured the stiffness of the fibres in a relaxing solution at high salt concentration. These fibres were crosslinked to varying extents in the rigor state. The relaxing solution caused uncrosslinked crossbridge heads (S1) to detach. High salt concentrations were used because the fibres were not activated by the crosslinked crossbridges under these conditions, although they were at physiological ionic strength. We found a linear correlation between the extent of S1 crosslinking to thin filaments and the stiffness and that the stiffness in the relaxing solution of muscle fibres with all the S1 heads crosslinked to thin filaments was the same as the rigor stiffness of the fibres before crosslinking. We conclude that the sarcomere compliance is mostly a property of the crossbridges (with more than 65% of the crossbridge compliance in the S1 portions and less than 35% in the S2 portion) and little of other sarcomere structures. In an earlier paper [Kimura & Tawada, Biophys. J. 45, 603-10 (1984)], we demonstrated that the S2 portion of the crossbridge was stiff. It then follows that the crossbridge compliance, and thus the sarcomere compliance, is a property of the S1 heads. Assuming that the S1 portion of the crossbridges in rigor strained muscle fibres is bent, we calculated the Young's modulus of the S1 portion and found that it is about 10(2) MN m-2. Because this order of magnitude is reasonable in terms of globular protein elasticity, bending is likely to be the nature of the S1 compliance in rigor muscle fibres. PMID:3760153

  5. On the role of CFRP reinforcement for wood beams stiffness

    NASA Astrophysics Data System (ADS)

    Ianasi, A. C.

    2015-11-01

    In recent years, carbon fiber composites have been increasingly used in different ways in reinforcing structural elements. Specifically, the use of composite materials as a reinforcement for wood beams under bending loads requires paying attention to several aspects of the problem such as the number of the composite layers applied on the wood beams. Study consolidation of composites revealed that they are made by bonding fibrous material impregnated with resin on the surface of various elements, to restore or increase the load carrying capacity (bending, cutting, compression or torque) without significant damage of their rigidity. Fibers used in building applications can be fiberglass, aramid or carbon. Items that can be strengthened are concrete, brick, wood, steel and stone, and in terms of structural beams, walls, columns and floors. This paper describes an experimental study which was designed to evaluate the effect of composite material on the stiffness of the wood beams. It proposes a summary of the fundamental principles of analysis of composite materials and the design and use. The type of reinforcement used on the beams is the carbon fiber reinforced polymer (CFRP) sheet and plates and also an epoxy resin for bonding all the elements. Structural epoxy resins remain the primary choice of adhesive to form the bond to fiber-reinforced plastics and are the generally accepted adhesives in bonded CFRP-wood connections. The advantages of using epoxy resin in comparison to common wood-laminating adhesives are their gap-filling qualities and the low clamping pressures that are required to form the bond between carbon fiber plates or sheets and the wood beams. Mechanical tests performed on the reinforced wood beams showed that CFRP materials may produce flexural displacement and lifting increases of the beams. Observations of the experimental load-displacement relationships showed that bending strength increased for wood beams reinforced with CFRP composite plates and sheets compared to those without CFRP reinforcement. The main conclusion of the tests is that the tensioning forces allow beam taking a maximum load for a while, something that is particularly useful when we consider a real construction, so in case of excess lift beam, we have time to take strengthening measures and when is about a catastrophic request (earthquake) the construction remain partially functional. The experiments have shown that the method of increasing resistance of wood constructions with composite materials is good for it. The solution is easy to implement and has low costs.

  6. Lamb wave characterization of the effects of long-term thermal-mechanical aging on composite stiffness

    NASA Technical Reports Server (NTRS)

    Seale, M. D.; Madaras, E. I.

    1999-01-01

    Lamb waves offer a promising method of evaluating damage in composite materials. The Lamb wave velocity is directly related to the material parameters, so an effective tool exists to monitor damage in composites by measuring the velocity of these waves. The Lamb Wave Imager (LWI) uses a pulse/receive technique that excites an antisymmetric Lamb mode and measures the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. In this study, the time-of-flight as well as the elastic stiffnesses D11, D22, A44, and A55 for composite samples which have undergone combined thermal and mechanical aging are obtained. The samples examined include a baseline specimen with 0 cycles, specimens which have been aged 2350 and 3530 cycles at high strain levels, and one specimen aged 3530 cycles at low strain levels.

  7. 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 the second step the density measure is obtained. The spatial lay-up design problem is formulated using both fiber angles and lamination parameters as design variables. A weighted average formulation is used to handle multiple load case designs. Numerical studies investigate the performance of the proposed design methodology. The optimal lay-up configuration is independent of the lattice density with more details emerging as the density is increased. Moreover, combined topology and lay-up designs are free of checkerboard patterns. (Abstract shortened by UMI.)

  8. Vibration in Planetary Gear Systems with Unequal Planet Stiffnesses

    NASA Technical Reports Server (NTRS)

    Frater, J. L.; August, R.; Oswald, F. B.

    1982-01-01

    An algorithm suitable for a minicomputer was developed for finding the natural frequencies and mode shapes of a planetary gear system which has unequal stiffnesses between the Sun/planet and planet/ring gear meshes. Mode shapes are represented in the form of graphical computer output that illustrates the lateral and rotational motion of the three coaxial gears and the planet gears. This procedure permits the analysis of gear trains utilizing nonuniform mesh conditions and user specified masses, stiffnesses, and boundary conditions. Numerical integration of the equations of motion for planetary gear systems indicates that this algorithm offers an efficient means of predicting operating speeds which may result in high dynamic tooth loads.

  9. Stabilized multilevel Monte Carlo method for stiff stochastic differential equations

    SciTech Connect

    Abdulle, Assyr Blumenthal, Adrian

    2013-10-15

    A multilevel Monte Carlo (MLMC) method for mean square stable stochastic differential equations with multiple scales is proposed. For such problems, that we call stiff, the performance of MLMC methods based on classical explicit methods deteriorates because of the time step restriction to resolve the fastest scales that prevents to exploit all the levels of the MLMC approach. We show that by switching to explicit stabilized stochastic methods and balancing the stabilization procedure simultaneously with the hierarchical sampling strategy of MLMC methods, the computational cost for stiff systems is significantly reduced, while keeping the computational algorithm fully explicit and easy to implement. Numerical experiments on linear and nonlinear stochastic differential equations and on a stochastic partial differential equation illustrate the performance of the stabilized MLMC method and corroborate our theoretical findings.

  10. Effects of Various Antihypertensive Drugs on Arterial Stiffness and Wave Reflections

    PubMed Central

    Liu, Ming; Li, Ge-Le; Li, Yan; Wang, Ji-Guang

    2013-01-01

    We reviewed trials that tested the efficacy of antihypertensive drugs in reducing arterial stiffness and wave reflections as assessed by pulse wave velocity and augmentation index, respectively. Regardless of cross-over or parallel-group comparison design, placebo-controlled trials demonstrated that antihypertensive drugs were effective in reducing pulse wave velocity. In actively-controlled parallel-group comparison studies, this effect on arterial stiffness was more evident for angiotensin-converting enzyme inhibitors or angiotensin receptor blockers than other classes of antihypertensive drugs, particularly when brachial-ankle pulse wave velocity was measured. Regardless of cross-over or parallel-group comparison or placebo- or actively-controlled design, the reviewed trials showed that ?-blockers were inferior to all the other classes of antihypertensive drugs in reducing augmentation index. However, these studies had a small sample size and a short follow-up time and did not link the changes in measurements of arterial function with cardiovascular events. Whether the superiority or inferiority is clinically relevant for cardiovascular protection and prevention remains to be investigated.

  11. Impact of opioid pharmacotherapy on arterial stiffness and vascular ageing: cross-sectional and longitudinal studies.

    PubMed

    Reece, Albert Stuart; Hulse, Gary Kenneth

    2013-09-01

    Whilst there is a small literature on the cardiovascular toxicity of opiates, there is no detailed antemortem data on non-cardiovascular patient populations. A cross-sectional and longitudinal naturalistic observational study was performed comparing methadone (N = 71)-, buprenorphine (N = 593)-, naltrexone (N = 23)-treated patients with controls (N = 576) on indices of arterial stiffness and vascular age by Pulse Wave Analysis in primary care, 2006-2011. Controls were younger 29.96 ± 0.45 (mean ± SEM) vs. 34.00 ± 0.34-39.22 ± 1.11 years (all P < 0.005) and had fewer smokers (15.9 % vs. 86.9 %-92.96 %, all P < 0.0001). The sex ratio was similar (69.6 vs. 67.7 % male, P = 0.46). These baseline differences were controlled for by multiple regression. Linear regression of vascular age, central augmentation pressure, central augmentation index and other measures against chronologic age showed significant protective effects by treatment group against the treatment standard of methadone, in both sexes in additive and interactive models (all P < 0.02). Interactive terms in treatment type remained significant including all conventional risk factors accounting for differing opiate exposures. The principal findings from multiple regression were confirmed in the time series analysis up to 5 years by repeated measures nonlinear regression. These studies show that the deleterious impact of chronic opiate pharmacotherapy on vascular age and arterial stiffness varies significantly by treatment type. PMID:23456431

  12. Acute effect of caffeine on arterial stiffness and aortic pressure waveform.

    PubMed

    Mahmud, A; Feely, J

    2001-08-01

    Caffeine acutely increases blood pressure and peripheral vascular resistance, in part because of sympathetic stimulation. Its effects on large artery properties are largely unknown. In a double-blind crossover study, 7 healthy subjects 26+/-2.6 years of age (mean+/-SEM) were studied for 90 minutes while in the supine position on 2 occasions separated by a week in random order after ingestion of 250 mL caffeinated (150 mg) and decaffeinated (<2 mg) coffee. Compared with baseline, arterial stiffness measured by carotid femoral pulse wave velocity increased progressively from 7.2+/-0.41 to 8.0+/-0.6 m/s (P<0.05) at 90 minutes after caffeine intake, an effect that may be independent of changes in blood pressure. In addition, arterial wave reflection, measured by applanation tonometry from the aortic pressure waveform, also increased from -5.7+/-7.6% to 5.28%+/-5.6 (P<0.01). No such changes were seen with decaffeinated coffee intake. Although the integral of the brachial systolic and diastolic blood pressure values over the 90 minutes was larger (P<0.05) after caffeinated than decaffeinated coffee intake, the effect on aortic systolic and diastolic blood pressures was more pronounced (P<0.05) than on the brachial artery. These results show a significant effect of caffeine intake on arterial tone and function and suggest that caffeine acutely increases arterial stiffness. PMID:11509481

  13. Nanomechanical mass sensing and stiffness spectrometry based on two-dimensional vibrations of resonant nanowires.

    PubMed

    Gil-Santos, Eduardo; Ramos, Daniel; Martínez, Javier; Fernández-Regúlez, Marta; García, Ricardo; San Paulo, Alvaro; Calleja, Montserrat; Tamayo, Javier

    2010-09-01

    One-dimensional nanomechanical resonators based on nanowires and nanotubes have emerged as promising candidates for mass sensors. When the resonator is clamped at one end and the atoms or molecules being measured land on the other end (which is free to vibrate), the resonance frequency of the device decreases by an amount that is proportional to the mass of the atoms or molecules. However, atoms and molecules can land at any position along the resonator, and many biomolecules have sizes that are comparable to the size of the resonator, so the relationship between the added mass and the frequency shift breaks down. Moreover, whereas resonators fabricated by top-down methods tend to vibrate in just one dimension because they are usually shaped like diving boards, perfectly axisymmetric one-dimensional nanoresonators can support flexural vibrations with the same amplitude and frequency in two dimensions. Here, we propose a new approach to mass sensing and stiffness spectroscopy based on the fact that the nanoresonator will enter a superposition state of two orthogonal vibrations with different frequencies when this symmetry is broken. Measuring these frequencies allows the mass, stiffness and azimuthal arrival direction of the adsorbate to be determined. PMID:20693990

  14. Stiffness Study of Wound-Filament Pressure Vessels

    NASA Technical Reports Server (NTRS)

    Verderaime, V.

    1986-01-01

    Report presents theoretical and experimental study of stiffness of lightweight, jointed pressure vessels made of wound graphite fibers and epoxy. Specimens fabricated from layers of graphite fibers, wet with epoxy, on aluminum mandrel. Segment ends thickened with interspersed layers of axially oriented fibers to reduce pinhole bearing stresses and local deformations. Segments cured at 390 degrees F (199 degrees C). Report presents results of vibrational tests of one-quarter-scale models of wound-filament pressure vessels.

  15. 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.

  16. High stiffness seals for rotor critical speed control

    NASA Technical Reports Server (NTRS)

    Fleming, D. P.

    1977-01-01

    An annular seal is analyzed in which the inlet clearance is larger than the outlet clearance; the flow path may be either stepped or tapered. This design produces radial stiffness 1.7 to 14 times that of a constant clearance seal having the same minimum clearance. When sealing high pressure fluids, such a seal improves rotor stability and can be used to shift troublesome critical speeds to a more suitable location.

  17. High stiffness seals for rotor critical speed control

    NASA Technical Reports Server (NTRS)

    Fleming, D. P.

    1977-01-01

    An annular seal is analyzed in which the inlet clearance is larger than the outlet clearance; the flow path may be either stepped or tapered. This design produces radial stiffnesses 1.7 to 14 times that of a constant-clearance seal having the same minimum clearance. When sealing high-pressure fluids, such as a seal can improve rotor stability and can be used to shift troublesome critical speeds to a more suitable location.

  18. Unexpected swelling of stiff DNA in a polydisperse crowded environment

    E-print Network

    Hongsuk Kang; Ngo Minh Toan; Changbong Hyeon; D. Thirumalai

    2015-08-13

    We investigate the conformations of DNA-like stiff chains, characterized by contour length ($L$) and persistence length ($l_p$), in a variety of crowded environments containing mono disperse soft spherical (SS) and spherocylindrical (SC) particles, mixture of SS and SC, and a milieu mimicking the composition of proteins in $E. coli.$ cytoplasm. The stiff chain, whose size modestly increases in SS crowders up to $\\phi\\approx 0.1$, is considerably more compact at low volume fractions ($\\phi \\leq 0.2$) in monodisperse SC particles than in a medium containing SS particles. A 1:1 mixture of SS and SC crowders induces greater chain compaction than the pure SS or SC crowders at the same $\\phi$ with the effect being highly non-additive. We also discover a counter-intuitive result that polydisperse crowding environment, mimicking the composition of a cell lysate, swells the DNA-like polymer, which is in stark contrast to the size reduction of flexible polymer in the same milieu. Trapping of the stiff chain in a fluctuating tube-like environment created by large-sized crowders explains the dramatic increase in size and persistence length of the stiff chain. In the polydisperse medium, mimicking the cellular environment, the size of the DNA (or related RNA) is determined by $L/l_p$. At low $L/l_p$ the size of the polymer is unaffected whereas there is a dramatic swelling at intermediate value of $L/l_p$. We use these results to provide insights into recent experiments on crowding effects on RNA, and also make testable predictions.

  19. Iron Stores, Hepcidin, and Aortic Stiffness in Individuals with Hypertension

    PubMed Central

    Valenti, Luca; Maloberti, Alessandro; Signorini, Stefano; Milano, Marta; Cesana, Francesca; Cappellini, Fabrizio; Dongiovanni, Paola; Porzio, Marianna; Soriano, Francesco; Brambilla, Maura; Cesana, Giancarlo; Brambilla, Paolo

    2015-01-01

    Background & Aims Iron accumulation within the arterial wall has been hypothesized to promote atherosclerosis progression. Aim of this study was to evaluate whether the hormone hepcidin and iron stores are associated with arterial stiffness in subjects with essential hypertension. Methods Circulating hepcidin, ferritin, and mutations in the hemochromatosis gene were compared between subjects included in the first vs. third tertile (n=284 each) of carotid-femoral pulse wave velocity (PWV) in an unselected cohort of patients with arterial hypertension. Results At univariate logistic regression analysis, high PWV was associated with higher ferritin levels (p=0.010), but lower hepcidin (p=0.045), and hepcidin ferritin/ratio (p<0.001). Hemochromatosis mutations predisposing to iron overload were associated with high PWV (p=0.025). At multivariate logistic regression analysis, high aortic stiffness was associated with older age, male sex, lower BMI, higher systolic blood pressure and heart rate, hyperferritinemia (OR 2.05, 95% c.i. 1.11-3.17 per log ng/ml; p=0.022), and lower circulating hepcidin concentration (OR 0.29, 95% c.i. 0.16-0.51 per log ng/ml; p<0.001). In subgroup analyses, high PWV was associated with indices of target organ damage, including micro-albuminuria (n=125, p=0.038), lower ejection fraction (n=175, p=0.031), cardiac diastolic dysfunction (p=0.004), and lower S wave peak systolic velocity (p<0.001). Ferritin was associated with cardiac diastolic dysfunction, independently of confounders (p=0.006). Conclusions In conclusion, hyperferritinemia is associated with high aortic stiffness and cardiac diastolic dysfunction, while low circulating hepcidin with high aortic stiffness. PMID:26244503

  20. Low-Friction, High-Stiffness Joint for Uniaxial Load Cell

    NASA Technical Reports Server (NTRS)

    Lewis, James L.; Le, Thang; Carroll, Monty B.

    2007-01-01

    A universal-joint assembly has been devised for transferring axial tension or compression to a load cell. To maximize measurement accuracy, the assembly is required to minimize any moments and non-axial forces on the load cell and to exhibit little or no hysteresis. The requirement to minimize hysteresis translates to a requirement to maximize axial stiffness (including minimizing backlash) and a simultaneous requirement to minimize friction. In practice, these are competing requirements, encountered repeatedly in efforts to design universal joints. Often, universal-joint designs represent compromises between these requirements. The improved universal-joint assembly contains two universal joints, each containing two adjustable pairs of angular-contact ball bearings. One might be tempted to ask why one could not use simple ball-and-socket joints rather than something as complex as universal joints containing adjustable pairs of angularcontact ball bearings. The answer is that ball-and-socket joints do not offer sufficient latitude to trade stiffness versus friction: the inevitable result of an attempt to make such a trade in a ball-and-socket joint is either too much backlash or too much friction. The universal joints are located at opposite ends of an axial subassembly that contains the load cell. The axial subassembly includes an axial shaft, an axial housing, and a fifth adjustable pair of angular-contact ball bearings that allows rotation of the axial housing relative to the shaft. The preload on each pair of angular-contact ball bearings can be adjusted to obtain the required stiffness with minimal friction, tailored for a specific application. The universal joint at each end affords two degrees of freedom, allowing only axial force to reach the load cell regardless of application of moments and non-axial forces. The rotational joint on the axial subassembly affords a fifth degree of freedom, preventing application of a torsion load to the load cell.

  1. Arterial stiffness in obese children: Role of adiposity and physical activity

    PubMed Central

    Pandit, Deepa S.; Khadilkar, Anuradha V.; Chiplonkar, Shashi A.; Khadilkar, Vaman V.; Kinare, Arun S.

    2014-01-01

    Objective: To explore association of adiposity and physical activity with arterial stiffness and to propose optimal waist circumference cutoffs, corresponding to 90th percentile of NHANES (National Health and Nutrition Examination Survey) for Indian children and adolescents. Materials and Methods: Data on weight, height, waist circumference, physical activity and right Carotid artery Intima-Media-Thickness (CIMT), pulse wave velocity (PWV), elasticity modulus (Ep), stiffness index(?), arterial compliance (AC) were assessed in 250 children (72 normal-weight and 178 overweight/obese) aged 6-17 years from Pune city, India. Body composition was measured using Dual energy X-ray absorptiometry. Results: Total, 37.1% normal-weight and 98.2% overweight/obese children had high adiposity (>95th body fat percentile). Positive association of PWV and Ep (r = 0.5) also ?(r = 0.25) with BMI (Body Mass Index), waist circumference and body fat (P < 0.05) was observed. Physical activity was inversely associated with PWV (r =-0.2), ?(r =-0.13), Ep (r =-0.12) and positively with AC (r = 0.12) (P < 0.05). PWV significantly increased with increasing body fat for each tertile of physical activity (P < 0.05). Regression analysis revealed waist circumference, BMI, body fat and physical activity as independent associates for PWV after adjusting for age (P < 0.05). The cutoff of waist circumference yielding sensitivity and specificity for predicting the risk of high PWV was (?0.43, ?0.44) for boys and girls with sensitivity in boys (girls) of 78% (87%) and specificity in boys (girls) 51% (70%). The observed cutoffs are less than the NHANES-III cutoff values of waist circumference for 90th percentiles according to age and sex. Conclusion: High adiposity and low physical activity are adversely related to arterial stiffness in Indian children. PMID:24701433

  2. Arterial stiffness and endothelial inflammation in prediabetes and newly diagnosed diabetes patients.

    PubMed

    Çakar, Mustafa; Balta, ?evket; ?arlak, Hakan; Akhan, Muharrem; Demirkol, Sait; Karaman, Murat; Ay, Seyit Ahmet; Kurt, Ömer; Çayci, Tuncer; ?nal, Sat?lm??; Demirba?, ?eref

    2015-10-01

    ObjectiveThere is a growing body of data supporting the association between diabetes and microcirculatory disfunction. We aimed to study e-selectin levels, and their associations with serum markers of inflammation and arterial stiffness in prediabetes and newly diagnosed diabetes patients in this study.Subjects and methodsSixty patients (25 females) with a newly established elevated fasting serum glucose [20 impaired fasting glucose (IFG), 20 impaired glucose tolerance (IGT), 20 newly diagnosed diabetes (T2DM)] and 17 healthy controls (13 females) were included in the study. Serum e-selectin and hs-CRP levels, and arterial stiffness parameters of the patients were studied.ResultsFasting serum glucose was the most important predictor of serum e-selectin levels. Pulse wave velocity and central aortic pressures were significantly higher in IFG, IGT and T2DM groups, compared to controls (p = 0.001, < 0.001, 0.013 and 0.015, 0.002, 0.009, respectively). The mean arterial pressure did not show any significant association with serum e-selectin and hs-CRP levels (? coefficient: 0.092, p = 0.358; and ? coefficient: 0.189, p = 0.362, respectively).ConclusionPrediabetes patients have increasing e-selectin levels through the diagnosis of T2DM. E-selectin is associated with serum glucose levels. Prediabetic and newly diagnosed diabetics have higher arterial stiffness measurements. Serum e-selectin may be a good marker of endothelial inflammation and dysfunction increasing in parallel with serum glucose levels, predicting future cardiovascular events. PMID:26201008

  3. The impact of angiotensin receptor blockers on arterial stiffness: a meta-analysis.

    PubMed

    Peng, Feng; Pan, Hongming; Wang, Bin; Lin, Jinxiu; Niu, Wenquan

    2015-09-01

    Some studies reported a protective role of angiotensin receptor blockers (ARBs) against arterial stiffness. Therefore, we performed a meta-analysis of published clinical trials to systematically assess the impact of ARBs on arterial stiffness as measured by using pulse wave velocity (PWV). Eligible articles were identified by searching PubMed, EMBASE, Cochrane, Wanfang and CNKI databanks before 31 July 2014. The data were extracted independently and in duplicate. Forty articles including 53 clinical trials qualified, including 1650 and 1659 subjects in ARB treatment and control groups, respectively. Overall reductions in carotid-femoral PWV (cfPWV) and brachial-ankle PWV (baPWV) were statistically significant, with an average of -42.52?cm?s(-1) (95% CI: -81.82 to -3.21; P=0.034) and -107.08?cm?s(-1) (95% CI: -133.98 to -80.18; P<0.0005), respectively, after receiving ARBs. Subgroup analysis by ARB type revealed that telmisartan (weighted mean difference or WMD=-100.82?cm?s(-1); P<0.0005) and valsartan (WMD=-104.59?cm?s(-1); P<0.0005) significantly reduced baPWV, but only valsartan reduced cfPWV (WMD=-65.58; P=0.030). cfPWV was significantly reduced in comparisons of ARBs with placebo (WMD=-79.65?cm?s(-1); P=0.001), and baPWV was significantly reduced with calcium channel blockers (WMD=-130.74?cm?s(-1); P<0.0005). There were low probabilities of publication bias. Taken together, our findings support the important role of ARB treatment in improving arterial stiffness. PMID:25854987

  4. Manipulation under Anesthesia for Stiffness after Total Knee Arthroplasty

    PubMed Central

    Yoo, Ju-Hyung; Oh, Jin-Cheol; Park, Sang-Hoon

    2015-01-01

    Purpose This study evaluated the incidence of manipulation under anesthesia (MUA) for stiffness after total knee arthroplasty (TKA) and the degree of joint motion recovery after MUA. Materials and Methods A total of 4,449 TKAs (2,973 patients) were performed between March 2000 and August 2014. Cases that underwent MUA for stiffness after TKA were reviewed. TKAs were performed using the conventional procedure in 329 cases and using the minimally invasive procedure in 4,120 cases. The preoperative range of joint motion, timing of manipulation, diagnosis and the range of joint motion before and after MUA were retrospectively investigated. Results MUA was carried out in 22 cases (16 patients), resulting in the incidence of 0.5%. The incidence after the conventional procedure was 1.2% and 0.4% after the minimally invasive procedure. In the manipulated knees, the preoperative range of motion (ROM) was 102.5°±26.7°, and the preoperative diagnosis was osteoarthritis in 19 cases, rheumatoid arthritis in two, and infection sequela in one. MUA was performed 4.7±3.0 weeks after TKA. The average ROM was 64.5°±13.5° before manipulation. At an average of 64.3±41.3 months after manipulation, the ROM was recovered to 113.4°±31.2°, which was an additional 49.9° improvement in flexion. Conclusions The satisfactory recovery of joint movement was achieved when MUA for stiffness was performed relatively early after TKA. PMID:26676186

  5. Origami tubes assembled into stiff, yet reconfigurable structures and metamaterials.

    PubMed

    Filipov, Evgueni T; Tachi, Tomohiro; Paulino, Glaucio H

    2015-10-01

    Thin sheets have long been known to experience an increase in stiffness when they are bent, buckled, or assembled into smaller interlocking structures. We introduce a unique orientation for coupling rigidly foldable origami tubes in a "zipper" fashion that substantially increases the system stiffness and permits only one flexible deformation mode through which the structure can deploy. The flexible deployment of the tubular structures is permitted by localized bending of the origami along prescribed fold lines. All other deformation modes, such as global bending and twisting of the structural system, are substantially stiffer because the tubular assemblages are overconstrained and the thin sheets become engaged in tension and compression. The zipper-coupled tubes yield an unusually large eigenvalue bandgap that represents the unique difference in stiffness between deformation modes. Furthermore, we couple compatible origami tubes into a variety of cellular assemblages that can enhance mechanical characteristics and geometric versatility, leading to a potential design paradigm for structures and metamaterials that can be deployed, stiffened, and tuned. The enhanced mechanical properties, versatility, and adaptivity of these thin sheet systems can provide practical solutions of varying geometric scales in science and engineering. PMID:26351693

  6. Arterial Stiffness, Oxidative Stress, and Smoke Exposure in Wildland Firefighters

    PubMed Central

    Gaughan, Denise M.; Siegel, Paul D.; Hughes, Michael D.; Chang, Chiung-Yu; Law, Brandon F.; Campbell, Corey R.; Richards, Jennifer C.; Kales, Stefanos F.; Chertok, Marcia; Kobzik, Lester; Nguyen, Phuongson; O’Donnell, Carl R.; Kiefer, Max; Wagner, Gregory R.; Christiani, David C.

    2015-01-01

    Objectives To assess the association between exposure, oxidative stress, symptoms, and cardiorespiratory function in wildland firefighters. Methods We studied two Interagency Hotshot Crews with questionnaires, pulse wave analysis for arterial stiffness, spirometry, urinary 8-iso-prostaglandin F2? (8-isoprostane) and 8-hydroxy-2?-deoxyguanosine (8-OHdG), and the smoke exposure marker (urinary levoglucosan). Arterial stiffness was assessed by examining levels of the aortic augmentation index, expressed as a percentage. An oxidative stress score comprising the average of z-scores created for 8-OHdG and 8-isoprostane was calculated. Results Mean augmentation index % was higher for participants with higher oxidative stress scores after adjusting for smoking status. Specifically for every one unit increase in oxidative stress score the augmentation index % increased 10.5% (95% CI: 2.5, 18.5%). Higher mean lower respiratory symptom score was associated with lower percent predicted forced expiratory volume in one second/forced vital capacity. Conclusions Biomarkers of oxidative stress may serve as indicators of arterial stiffness in wildland firefighters. PMID:24909863

  7. Active stiffness modulation of fins using macro fiber composites

    NASA Astrophysics Data System (ADS)

    Kancharala, Ashok K.; Philen, Michael K.

    2013-04-01

    Studies on the role of body flexibility in propulsion suggest that fish have the ability to control or modulate the stiffness of the fin for optimized propulsive performance. Fins with certain stiffness might be efficient for a particular set of operating parameters but may be inefficient for other parameters. Therefore active stiffness modulation of a fin can improve the propulsive performance for a range of operating conditions. This paper discusses the preliminary experimental work on the open loop active deformation control of heaving flexible fins using Macro Fiber Composites (MFCs). The effect of important parameters such as oscillation frequency, flexibility of the fin, applied voltage and the phase difference between applied voltage and heaving on propulsive performance are studied and reported. The results indicate that propulsive performance can be improved by active control of the fins. The mean thrust improved by 30- 38% for the fins used in the experiments. The phase difference of ~90° is found to be optimal for maximized propulsive performance for the parameters considered in the study. Furthermore, there exists an optimal voltage magnitude at which the propulsive performance is a maximum for the range of operating conditions.

  8. Explicit Integration of Extremely Stiff Reaction Networks: Asymptotic Methods

    SciTech Connect

    Guidry, Mike W; Budiardja, R.; Feger, E.; Billings, J. J.; Hix, William Raphael; Messer, O.E.B.; Roche, K. J.; McMahon, E.; He, M.

    2013-01-01

    We show that, even for extremely stiff systems, explicit integration may compete in both accuracy and speed with implicit methods if algebraic methods are used to stabilize the numerical integration. The stabilizing algebra differs for systems well removed from equilibrium and those near equilibrium. This paper introduces a quantitative distinction between these two regimes and addresses the former case in depth, presenting explicit asymptotic methods appropriate when the system is extremely stiff but only weakly equilibrated. A second paper [1] examines quasi-steady-state methods as an alternative to asymptotic methods in systems well away from equilibrium and a third paper [2] extends these methods to equilibrium conditions in extremely stiff systems using partial equilibrium methods. All three papers present systematic evidence for timesteps competitive with implicit methods. Because explicit methods can execute a timestep faster than an implicit method, our results imply that algebraically stabilized explicit algorithms may offer a means to integration of larger networks than have been feasible previously in various disciplines.

  9. The consequences of short-range stiffness and fluctuating muscle activity for proprioception of postural joint rotations: the relevance to human standing.

    PubMed

    Loram, Ian D; Lakie, Martin; Di Giulio, Irene; Maganaris, Constantinos N

    2009-07-01

    Proprioception comes from muscles and tendons. Tendon compliance, muscle stiffness, and fluctuating activity complicate transduction of joint rotation to a proprioceptive signal. These problems are acute in postural regulation because of tiny joint rotations and substantial short-range muscle stiffness. When studying locomotion or perturbed balance these problems are less applicable. We recently measured short-range stiffness in standing and considered the implications for load stability. Here, using an appropriately simplified model we analyze the conversion of joint rotation to spindle input and tendon tension while considering the effect of short-range stiffness, tendon compliance, fluctuating muscle activity, and fusimotor activity. Basic principles determine that when muscle stiffness and tendon compliance are high, fluctuating muscle activity is the greatest factor confounding registration of postural movements, such as ankle rotations during standing. Passive and isoactive muscle, uncomplicated by active length fluctuations, enable much better registration of joint rotation and require fewer spindles. Short-range muscle stiffness is a degrading factor for spindle input and enhancing factor for Golgi input. Constant fusimotor activity does not enhance spindle registration of postural joint rotations in actively modulated muscle: spindle input remains more strongly associated with muscle activity than joint rotation. A hypothesized rigid alpha-gamma linkage could remove this association with activity but would require large numbers of spindles in active postural muscles. Using microneurography, the existence of a rigid alpha-gamma linkage could be identified from the correlation between spindle output and muscle activity. Basic principles predict a proprioceptive "dead zone" in the active agonist muscle that is related to the short-range muscle stiffness. PMID:19420127

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    In vitro models of normal mammary epithelium have correlated increased extracellular matrix (ECM) stiffness with malignant phenotypes. However, the role of increased stiffness in this transformation remains unclear because of difficulties in controlling ECM stiffness, composition and architecture independently. Here we demonstrate that interpenetrating networks of reconstituted basement membrane matrix and alginate can be used to modulate ECM stiffness independently of composition and architecture. We find that, in normal mammary epithelial cells, increasing ECM stiffness alone induces malignant phenotypes but that the effect is completely abrogated when accompanied by an increase in basement-membrane ligands. We also find that the combination of stiffness and composition is sensed through ?4 integrin, Rac1, and the PI3K pathway, and suggest a mechanism in which an increase in ECM stiffness, without an increase in basement membrane ligands, prevents normal ?6?4 integrin clustering into hemidesmosomes.

  11. Effects of aging on the association between cerebrovascular responses to visual stimulation, hypercapnia and arterial stiffness

    PubMed Central

    Flück, Daniela; Beaudin, Andrew E.; Steinback, Craig D.; Kumarpillai, Gopukumar; Shobha, Nandavar; McCreary, Cheryl R.; Peca, Stefano; Smith, Eric E.; Poulin, Marc J.

    2014-01-01

    Aging is associated with decreased vascular compliance and diminished neurovascular- and hypercapnia-evoked cerebral blood flow (CBF) responses. However, the interplay between arterial stiffness and reduced CBF responses is poorly understood. It was hypothesized that increased cerebral arterial stiffness is associated with reduced evoked responses to both, a flashing checkerboard visual stimulation (i.e., neurovascular coupling), and hypercapnia. To test this hypothesis, 20 older (64 ± 8 year; mean ± SD) and 10 young (30 ± 5 year) subjects underwent a visual stimulation (VS) and a hypercapnic test. Blood velocity through the posterior (PCA) and middle cerebral (MCA) arteries was measured concurrently using transcranial Doppler ultrasound (TCD). Cerebral and systemic vascular stiffness were calculated from the cerebral blood velocity and systemic blood pressure waveforms, respectively. Cerebrovascular (MCA: young = 76 ± 15%, older = 98 ± 19%, p = 0.004; PCA: young = 80 ± 16%, older = 106 ± 17%, p < 0.001) and systemic (young = 59 ± 9% and older = 80 ± 9%, p < 0.001) augmentation indices (AI) were higher in the older group. CBF responses to VS (PCA: p < 0.026) and hypercapnia (PCA: p = 0.018; MCA: p = 0.042) were lower in the older group. A curvilinear model fitted to cerebral AI and age showed AI increases until ~60 years of age, after which the increase levels off (PCA: R2 = 0.45, p < 0.001; MCA: R2 = 0.31, p < 0.001). Finally, MCA, but not PCA, hypercapnic reactivity was inversely related to cerebral AI (MCA: R2 = 0.28, p = 0.002; PCA: R2 = 0.10, p = 0.104). A similar inverse relationship was not observed with the PCA blood flow response to VS (R2 = 0.06, p = 0.174). In conclusion, older subjects had reduced neurovascular- and hypercapnia-mediated CBF responses. Furthermore, lower hypercapnia-mediated blood flow responses through the MCA were associated with increased vascular stiffness. These findings suggest the reduced hypercapnia-evoked CBF responses through the MCA, in older individuals may be secondary to vascular stiffening. PMID:24600398

  12. Changes in arterial stiffness and nitric oxide production with Chlorella-derived multicomponent supplementation in middle-aged and older individuals

    PubMed Central

    Otsuki, Takeshi; Shimizu, Kazuhiro; Maeda, Seiji

    2015-01-01

    Chlorella is a unicellular green alga, which contains a variety of nutrients including amino acids, dietary fibers, n-3 unsaturated fatty acid, vitamins, and minerals. We previously demonstrated that Chlorella-derived multicomponent supplementation decreases arterial stiffness in young men. However, mechanisms underlying the reduction in arterial stiffness by Chlorella-derived supplementation and the effect in middle-aged and older individuals have remained unexplored. This study tested our hypothesis that Chlorella-derived supplementation improves arterial stiffness via an increase in nitric oxide (NO, a endothelium-derived relaxing factor) production in middle-aged and older individuals. Thirty-two subjects between 45 and 75 years of age assigned to placebo and Chlorella groups in a double-blinded manner and took respective tablets for 4 weeks. Before and after the supplementations, brachial-ankle pulse wave velocity (baPWV, an index of arterial stiffness) and plasma nitrite/nitrate (NOx, end product of NO) concentration were measured. There was no difference in baPWV between before and after the placebo intake, but baPWV decreased after the Chlorella supplementation. Changes in baPWV with the Chlorella supplementation were correlated with those in plasma NOx concentration. We concluded that Chlorella-derived multicomponent supplementation decreases arterial stiffness in middle-aged and older individuals. It may be associated with increase in NO production by vascular endothelium. PMID:26566309

  13. Changes in arterial stiffness and nitric oxide production with Chlorella-derived multicomponent supplementation in middle-aged and older individuals.

    PubMed

    Otsuki, Takeshi; Shimizu, Kazuhiro; Maeda, Seiji

    2015-11-01

    Chlorella is a unicellular green alga, which contains a variety of nutrients including amino acids, dietary fibers, n-3 unsaturated fatty acid, vitamins, and minerals. We previously demonstrated that Chlorella-derived multicomponent supplementation decreases arterial stiffness in young men. However, mechanisms underlying the reduction in arterial stiffness by Chlorella-derived supplementation and the effect in middle-aged and older individuals have remained unexplored. This study tested our hypothesis that Chlorella-derived supplementation improves arterial stiffness via an increase in nitric oxide (NO, a endothelium-derived relaxing factor) production in middle-aged and older individuals. Thirty-two subjects between 45 and 75 years of age assigned to placebo and Chlorella groups in a double-blinded manner and took respective tablets for 4 weeks. Before and after the supplementations, brachial-ankle pulse wave velocity (baPWV, an index of arterial stiffness) and plasma nitrite/nitrate (NOx, end product of NO) concentration were measured. There was no difference in baPWV between before and after the placebo intake, but baPWV decreased after the Chlorella supplementation. Changes in baPWV with the Chlorella supplementation were correlated with those in plasma NOx concentration. We concluded that Chlorella-derived multicomponent supplementation decreases arterial stiffness in middle-aged and older individuals. It may be associated with increase in NO production by vascular endothelium. PMID:26566309

  14. The Role of Systemic Arterial Stiffness in Open-Angle Glaucoma with Diabetes Mellitus

    PubMed Central

    Shim, Seong Hee; Kim, Chan Yun; Kim, Joon Mo; Kim, Da Yeong; Kim, Yang Jae; Bae, Jeong Hun; Sung, Ki Chul

    2015-01-01

    Purpose. To investigate the role of systemic arterial stiffness in glaucoma patients with diabetes mellitus (DM). Design. Retrospective, cross-sectional study. Participants. DM subjects who underwent brachial-ankle pulse wave velocity (baPWV) were recruited. Methods. Glaucoma patients (n = 75) and age-matched control subjects (n = 92) were enrolled. Systemic examination including BaPWV and detailed eye examination were performed. The glaucoma group was divided into subgroups of normal tension glaucoma (NTG, n = 55) and primary open-angle glaucoma (POAG) based on an IOP of 21?mmHg. BaPWV was used to stratify the population into 4 groups based on the rate. Stepwise multiple logistic regression analysis by baPWV quartiles was used to compare the glaucoma group with the control group. Main Outcome Measures. BaPWV in glaucoma with DM patients. Results. Faster baPWV was positively associated with glaucoma (odds ratio: 3.74; 95% CI: 1.03–13.56, stepwise multiple logistic regression analysis) in patients with DM. Increasing baPWV was also positively associated with glaucoma (p for trend = 0.036). The NTG subgroup showed similar results to those of the glaucoma group. Conclusions. In this study, increased arterial stiffness was shown to be associated with glaucoma and may contribute to the pathogenesis of glaucoma in DM patients. PMID:26557669

  15. A New Z-axis Resonant Micro-Accelerometer Based on Electrostatic Stiffness

    PubMed Central

    Yang, Bo; Wang, Xingjun; Dai, Bo; Liu, Xiaojun

    2015-01-01

    Presented in the paper is the design, the simulation, the fabrication and the experiment of a new z-axis resonant accelerometer based on the electrostatic stiffness. The new z-axis resonant micro-accelerometer, which consists of a torsional accelerometer and two plane resonators, decouples the sensing movement of the accelerometer from the oscillation of the plane resonators by electrostatic stiffness, which will improve the performance. The new structure and the sensitive theory of the acceleration are illuminated, and the equation of the scale factor is deduced under ideal conditions firstly. The Ansys simulation is implemented to verify the basic principle of the torsional accelerometer and the plane resonator individually. The structure simulation results prove that the effective frequency of the torsional accelerometer and the plane resonator are 0.66 kHz and 13.3 kHz, respectively. Then, the new structure is fabricated by the standard three-mask deep dry silicon on glass (DDSOG) process and encapsulated by parallel seam welding. Finally, the detecting and control circuits are designed to achieve the closed-loop self-oscillation, to trace the natural frequency of resonator and to measure the system frequency. Experimental results show that the new z-axis resonant accelerometer has a scale factor of 31.65 Hz/g, a bias stability of 727 ?g and a dynamic range of over 10 g, which proves that the new z-axis resonant micro-accelerometer is practicable. PMID:25569748

  16. Solving the Bateman equations in CASMO5 using implicit ode numerical methods for stiff systems

    SciTech Connect

    Hykes, J. M.; Ferrer, R. M.

    2013-07-01

    The Bateman equations, which describe the transmutation of nuclides over time as a result of radioactive decay, absorption, and fission, are often numerically stiff. This is especially true if short-lived nuclides are included in the system. This paper describes the use of implicit numerical methods for o D Es applied to the stiff Bateman equations, specifically employing the Backward Differentiation Formulas (BDF) form of the linear multistep method. As is true in other domains, using an implicit method removes or lessens the (sometimes severe) step-length constraints by which explicit methods must abide. To gauge its accuracy and speed, the BDF method is compared to a variety of other solution methods, including Runge-Kutta explicit methods and matrix exponential methods such as the Chebyshev Rational Approximation Method (CRAM). A preliminary test case was chosen as representative of a PWR lattice depletion step and was solved with numerical libraries called from a Python front-end. The Figure of Merit (a combined measure of accuracy and efficiency) for the BDF method was nearly identical to that for CRAM, while explicit methods and other matrix exponential approximations trailed behind. The test case includes 319 nuclides, in which the shortest-lived nuclide is {sup 98}Nb with a half-life of 2.86 seconds. Finally, the BDF and CRAM methods were compared within CASMO5, where CRAM had a FOM about four times better than BDF, although the BDF implementation was not fully optimized. (authors)

  17. Experimental Investigation of Composite Pressure Vessel Performance and Joint Stiffness for Pyramid and Inverted Pyramid Joints

    NASA Technical Reports Server (NTRS)

    Verhage, Joseph M.; Bower, Mark V.; Gilbert, Paul A. (Technical Monitor)

    2001-01-01

    The focus of this study is on the suitability in the application of classical laminate theory analysis tools for filament wound pressure vessels with adhesive laminated joints in particular: pressure vessel wall performance, joint stiffness and failure prediction. Two 18-inch diameter 12-ply filament wound pressure vessels were fabricated. One vessel was fabricated with a 24-ply pyramid laminated adhesive double strap butt joint. The second vessel was fabricated with the same number of plies in an inverted pyramid joint. Results from hydrostatic tests are presented. Experimental results were used as input to the computer programs GENLAM and Laminate, and the output compared to test. By using the axial stress resultant, the classical laminate theory results show a correlation within 1% to the experimental results in predicting the pressure vessel wall pressure performance. The prediction of joint stiffness for the two adhesive joints in the axial direction is within 1% of the experimental results. The calculated hoop direction joint stress resultant is 25% less than the measured resultant for both joint configurations. A correction factor is derived and used in the joint analysis. The correction factor is derived from the hoop stress resultant from the tank wall performance investigation. The vessel with the pyramid joint is determined to have failed in the joint area at a hydrostatic pressure 33% value below predicted failure. The vessel with the inverted pyramid joint failed in the wall acreage at a hydrostatic pressure within 10% of the actual failure pressure.

  18. Computational local stiffness analysis of biological cell: High aspect ratio single wall carbon nanotube tip.

    PubMed

    TermehYousefi, Amin; Bagheri, Samira; Shahnazar, Sheida; Rahman, Md Habibur; Kadri, Nahrizul Adib

    2016-02-01

    Carbon nanotubes (CNTs) are potentially ideal tips for atomic force microscopy (AFM) due to the robust mechanical properties, nanoscale diameter and also their ability to be functionalized by chemical and biological components at the tip ends. This contribution develops the idea of using CNTs as an AFM tip in computational analysis of the biological cells. The proposed software was ABAQUS 6.13 CAE/CEL provided by Dassault Systems, which is a powerful finite element (FE) tool to perform the numerical analysis and visualize the interactions between proposed tip and membrane of the cell. Finite element analysis employed for each section and displacement of the nodes located in the contact area was monitored by using an output database (ODB). Mooney-Rivlin hyperelastic model of the cell allows the simulation to obtain a new method for estimating the stiffness and spring constant of the cell. Stress and strain curve indicates the yield stress point which defines as a vertical stress and plan stress. Spring constant of the cell and the local stiffness was measured as well as the applied force of CNT-AFM tip on the contact area of the cell. This reliable integration of CNT-AFM tip process provides a new class of high performance nanoprobes for single biological cell analysis. PMID:26652417

  19. Constitutive properties of hypertrophied myocardium: cellular contribution to changes in myocardial stiffness

    NASA Technical Reports Server (NTRS)

    Harris, Todd S.; Baicu, Catalin F.; Conrad, Chester H.; Koide, Masaaki; Buckley, J. Michael; Barnes, Mary; Cooper, George 4th; Zile, Michael R.

    2002-01-01

    Recent studies have suggested that pressure overload hypertrophy (POH) alters the viscoelastic properties of individual cardiocytes when studied in isolation. However, whether these changes in cardiocyte properties contribute causally to changes in the material properties of the cardiac muscle as a whole is unknown. Accordingly, a selective, isolated, acute change in cardiocyte constitutive properties was imposed in an in vitro system capable of measuring the resultant effect on the material properties of the composite cardiac muscle. POH caused an increase in both myocardial elastic stiffness, from 20.5 +/- 1.3 to 28.4 +/- 1.8, and viscous damping, from 15.2 +/- 1.1 to 19.8 +/- 1.5 s (normal vs. POH, P < 0.05), respectively. Recent studies have shown that cardiocyte constitutive properties could be acutely altered by depolymerizing the microtubules with colchicine. Colchicine caused a significant decrease in the viscous damping in POH muscles (19.8 +/- 1.5 s at baseline vs. 14.7 +/- 1.3 s after colchicine, P < 0.05). Therefore, myocardial material properties can be altered by selectively changing the constitutive properties of one element within this muscle tissue, the cardiocyte. Changes in the constitutive properties of the cardiocytes themselves contribute to the abnormalities in myocardial stiffness and viscosity that develop during POH.

  20. Experimental Study on Shear Fatigue Behavior and Stiffness Performance of Warm Mix Asphalt by adding Synthetic Wax

    E-print Network

    Christophe Petit; Anne Millien; Francesco Canestrari; Valter Pannunzio; Amadeo Virgili

    2012-03-13

    Synthetic waxes produced by standard and registered processes may be used to manufacture Warm Mix Asphalt (WMA), which is a modified asphalt concrete produced, applied and compacted at temperatures below those typically required. This feature leads to environmental benefits, such as reduced energy consumption, gas and fume emissions, as well as to economic/operational advantages, such as lower production costs and greater hauling distances for extended construction seasons with tighter schedules. The present article serves to compare the mechanical performance of a WMA produced by adding synthetic wax with a traditional Hot Mix Asphalt (HMA) specimen, in terms of shear fatigue response and both complex and stiffness moduli. The experimental results and related modeling work demonstrate that adding synthetic wax into the WMA composition does not hinder either the destructive or non-destructive performance of an HMA, and this finding is corroborated by respectively measuring fatigue life and stiffness.

  1. Experimental Study on Shear Fatigue Behavior and Stiffness Performance of Warm Mix Asphalt by adding Synthetic Wax

    E-print Network

    Petit, Christophe; Canestrari, Francesco; Pannunzio, Valter; Virgili, Amadeo

    2012-01-01

    Synthetic waxes produced by standard and registered processes may be used to manufacture Warm Mix Asphalt (WMA), which is a modified asphalt concrete produced, applied and compacted at temperatures below those typically required. This feature leads to environmental benefits, such as reduced energy consumption, gas and fume emissions, as well as to economic/operational advantages, such as lower production costs and greater hauling distances for extended construction seasons with tighter schedules. The present article serves to compare the mechanical performance of a WMA produced by adding synthetic wax with a traditional Hot Mix Asphalt (HMA) specimen, in terms of shear fatigue response and both complex and stiffness moduli. The experimental results and related modeling work demonstrate that adding synthetic wax into the WMA composition does not hinder either the destructive or non-destructive performance of an HMA, and this finding is corroborated by respectively measuring fatigue life and stiffness.

  2. Mapping the Longitudinal Wall Stiffness Heterogeneities within Intact Canine Aortas using Pulse Wave Imaging (PWI) Ex Vivo

    PubMed Central

    Shahmirzadi, Danial; Narayanan, Prathyush; Li, Ronny X.; Qaqish, William W.; Konofagou, Elisa E.

    2014-01-01

    The aortic stiffness has been found to be a useful independent indicator of several cardiovascular diseases such as hypertension and aneurysms. Existing methods to estimate the aortic stiffness are either invasive, e.g. catheterization, or yield average global measurements which could be inaccurate, e.g., tonometry. Alternatively, the aortic pulse wave velocity (PWV) has been shown to be a reliable marker for estimating the wall stiffness based on the Moens–Korteweg (M–K) formulation. Pulse Wave Imaging (PWI) is a relatively new, ultrasound-based imaging method for noninvasive and regional estimation of PWV. The present study aims at showing the application of PWI in obtaining localized wall mechanical properties by making PWV measurements on several adjacent locations along the ascending thoracic to the suprarenal abdominal aortic trunk in its intact vessel form. The PWV estimates were used to calculate the regional wall modulus based on the M-K relationship and were compared against conventional mechanical testing. The findings indicated that for the anisotropic aortic wall, the PWI estimates of the modulus are smaller than the circumferential modulus by an average of ?32.22% and larger than the longitudinal modulus by an average of 25.83%. Ongoing work is focused on the in vivo applications of PWI in normal and pathological aortas with future implications in the clinical applications of the technique. PMID:23764176

  3. Approximate analysis of effects of large deflections and initial twist on torsional stiffness of a cantilever plate subjected to thermal stresses

    NASA Technical Reports Server (NTRS)

    Heldenfels, Richard R; Vosteen, Louis F

    1958-01-01

    An approximate analysis of the nonlinear effects of initial twist and large deflections on the torsional stiffness of a cantilever plate subjected to a nonuniform temperature distribution is presented. The Von Karman large-deflection equations are satisfied through the use of a variational principle. The results show that initial twist and applied moments can have significant effects on the changes in stiffness produced by nonuniform heating, particularly in the region of the buckling temperature difference. Results calculated by this approximate analysis are in satisfactory agreement with measured torsional deformations and changes in natural frequency. (author)

  4. Development of procedures for calculating stiffness and damping properties of elastomers. Part 3: The effects of temperature, dissipation level and geometry

    NASA Technical Reports Server (NTRS)

    Smalley, A. J.; Tessarzik, J. M.

    1975-01-01

    Effects of temperature, dissipation level and geometry on the dynamic behavior of elastomer elements were investigated. Force displacement relationships in elastomer elements and the effects of frequency, geometry and temperature upon these relationships are reviewed. Based on this review, methods of reducing stiffness and damping data for shear and compression test elements to material properties (storage and loss moduli) and empirical geometric factors are developed and tested using previously generated experimental data. A prediction method which accounts for large amplitudes of deformation is developed on the assumption that their effect is to increase temperature through the elastomers, thereby modifying the local material properties. Various simple methods of predicting the radial stiffness of ring cartridge elements are developed and compared. Material properties were determined from the shear specimen tests as a function of frequency and temperature. Using these material properties, numerical predictions of stiffness and damping for cartridge and compression specimens were made and compared with corresponding measurements at different temperatures, with encouraging results.

  5. The Scd6/Lsm14 protein xRAPB has properties different from RAP55 in selecting mRNA for early translation or intracellular distribution in Xenopus oocytes.

    PubMed

    Ladomery, Michael; Sommerville, John

    2015-11-01

    Oocytes accumulate mRNAs in the form of maternal ribonucleoprotein (RNP) particles, the protein components of which determine the location and stability of individual mRNAs prior to translation. Scd6/Lsm14 proteins, typified by RAP55, function in a wide range of eukaryotes in repressing translation and relocating mRNPs to processing bodies and stress granules. In Xenopus laevis, the RAP55 orthologue xRAPA fulfils these functions. Here we describe the properties of a variant of xRAPA, xRAPB, which is a member of the Lsm14B group. xRAPB differs from xRAPA in various respects: it is expressed at high concentration earlier in oogenesis; it interacts specifically with the DDX6 helicase Xp54; it is detected in polysomes and stalled translation initiation complexes; its over-expression leads to selective binding to translatable mRNA species without evidence of translation repression or mRNA degradation. Since both Xp54 and xRAPA are repressors of translation, activation appears to be effected through targeting of xRAPB/Xp54. PMID:26455898

  6. Association of Insulin Resistance, Arterial Stiffness and Telomere Length in Adults Free of Cardiovascular Diseases

    PubMed Central

    Strazhesko, Irina; Tkacheva, Olga; Boytsov, Sergey; Akasheva, Dariga; Dudinskaya, Ekaterina; Vygodin, Vladimir; Skvortsov, Dmitry; Nilsson, Peter

    2015-01-01

    Background Chronic inflammation and oxidative stress might be considered the key mechanisms of aging. Insulin resistance (IR) is a phenomenon related to inflammatory and oxidative stress. We tested the hypothesis that IR may be associated with cellular senescence, as measured by leukocyte telomere length (LTL), and arterial stiffness (core feature of arterial aging), as measured by carotid-femoral pulse wave velocity (c-f PWV). Methods The study group included 303 subjects, mean age 51.8 ±13.3 years, free of known cardiovascular diseases and regular drug consumption. For each patient, blood pressure was measured, blood samples were available for biochemical parameters, and LTL was analyzed by real time q PCR. C-f PWV was measured with the help of SphygmoCor. SAS 9.1 was used for statistical analysis. Results Through multiple linear regression analysis, c-f PWV is independently and positively associated with age (p = 0.0001) and the homeostasis model assessment of insulin resistance (HOMA-IR; p = 0.0001) and independently negatively associated with LTL (p = 0.0378). HOMA-IR seems to have a stronger influence than SBP on arterial stiffness. In all subjects, age, HOMA-IR, LTL, and SBP predicted 32% of the variance in c-f PWV. LTL was inversely associated with HOMA-IR (p = 0.0001) and age (p = 0.0001). In all subjects, HOMA-IR, age, sex, and SBP predicted 16% of the variance in LTL. Conclusions These data suggest that IR is associated with cell senescence and arterial aging and could, therefore, become the main target in preventing accelerated arterial aging, besides blood pressure control. Research in telomere biology may reveal new ways of estimating cardiovascular aging and risk. PMID:26308091

  7. Infant Arterial Stiffness and Maternal Iron Status in Pregnancy: A UK Birth Cohort (Baby VIP Study)

    PubMed Central

    Alwan, Nisreen A.; Cade, Janet E.; McArdle, Harry J.; Greenwood, Darren C.; Hayes, Helen E.; Ciantar, Etienne; Simpson, Nigel A.B.

    2015-01-01

    Background In animal studies, iron deficiency during pregnancy has been linked to increased offspring cardiovascular risk. No previous population studies have measured arterial stiffness early in life to examine its association with maternal iron status. Objective This study aimed to examine the association between maternal iron status in early pregnancy with infant brachio-femoral pulse wave velocity (PWV). Methods The Baby VIP (Baby's Vascular Health and Iron in Pregnancy) study is a UK-based birth cohort which recruited 362 women after delivery from the Leeds Teaching Hospitals postnatal wards. Ferritin and transferrin receptor levels were measured in maternal serum samples previously obtained in the first trimester. Infant brachio-femoral PWV was measured during a home visit at 2–6 weeks. Results Iron depletion (ferritin <15 µg/l) was detected in 79 (23%) women in early pregnancy. Infant PWV (mean = 6.7 m/s, SD = 1.3, n = 284) was neither associated with maternal ferritin (adjusted change per 10 µg/l = 0.02, 95% CI: ?0.01, 0.1), nor with iron depletion (adjusted change = ?0.2, 95% CI: ?0.6, 0.2). No evidence of association was observed between maternal serum transferrin receptor level and its ratio to ferritin with infant PWV. Maternal anaemia (<11 g/dl) at <20 weeks’ gestation was associated with a 1.0-m/s increase in infant PWV (adjusted 95% CI: 0.1, 1.9). Conclusion This is the largest study to date which has assessed peripheral PWV as a measure of arterial stiffness in infants. There was no evidence of an association between markers of maternal iron status early in pregnancy and infant PWV. PMID:25790854

  8. The Role of Stiffness in the Dynamics of Frictional Stick-Slip Failure: Insights from Laboratory Experiments

    NASA Astrophysics Data System (ADS)

    Leeman, J.; Scuderi, M.; Marone, C.; Saffer, D. M.

    2014-12-01

    Frictional stick-slip is considered to be the mechanism of shallow earthquakes, in which elastic energy slowly accumulates and is released during dynamic failure. Frictional materials can fail via stick-slip or stable sliding. In the context of rate-and-state friction, the transition between these behaviors is a Hopf bifurcation. However, laboratory and field observations suggest that more complicated behavior occurs, manifested by a range of slip modes that include slow earthquakes and slow slip transients. In the laboratory, these behaviors arise in materials exhibiting two-state variable friction behavior, or in systems with more complex elastic coupling than 1D interactions for a spring and rigid slider. To explore this problem, we conducted shearing tests on layers of quartz powder with a mean grain size of 10 ?m in a double-direct-shear geometry. Elastic stiffness of the loading system was varied by changing the central forcing block and the applied normal stress. Experiments were run at room temperature under a controlled relative humidity of 100%. Shear loading velocity was fixed at 10 ?m/s. We unloaded and reloaded the shear stress at fixed intervals during experiments to measure the aggregate system stiffness at multiple strains. For more compliant systems we observe slow stick-slip behavior, with slip durations on the order of seconds. Stiffer loading systems exhibit linearly stable behavior, even to velocity perturbations of an order of magnitude. The critical stiffness boundary suggested by rate-and-state friction appears to be a good first order predictor of the system, but does not capture its behavior completely. Our observations suggest that the interplay between loading stiffness and friction constitutive properties can in some cases produce an extended transition between stable and unstable sliding as a function of net slip in a given experiment, including a regime of complex slip behavior with slow stick-slip. This transition is caused by systematic changes in both gouge layer stiffness and friction as a function of accumulated strain, possibly related to shear localization. Our results suggest that the behavior of tectonic faults may evolve with accumulated slip that drives changes in stiffness, its spatial distribution along the fault, and frictional parameters.

  9. Material Stiffness Effects on Neurite Alignment to Photopolymerized Micropatterns

    PubMed Central

    2015-01-01

    The ability to direct neurite growth into a close proximity of stimulating elements of a neural prosthesis, such as a retinal or cochlear implant (CI), may enhance device performance and overcome current spatial signal resolution barriers. In this work, spiral ganglion neurons (SGNs), which are the target neurons to be stimulated by CIs, were cultured on photopolymerized micropatterns with varied matrix stiffnesses to determine the effect of rigidity on neurite alignment to physical cues. Micropatterns were generated on methacrylate thin film surfaces in a simple, rapid photopolymerization step by photomasking the prepolymer formulation with parallel line–space gratings. Two methacrylate series, a nonpolar HMA-co-HDDMA series and a polar PEGDMA-co-EGDMA series, with significantly different surface wetting properties were evaluated. Equivalent pattern periodicity was maintained across each methacrylate series based on photomask band spacing, and the feature amplitude was tuned to a depth of 2 ?m amplitude for all compositions using the temporal control afforded by the UV curing methodology. The surface morphology was characterized by scanning electron microscopy and white light interferometry. All micropatterned films adsorb similar amounts of laminin from solution, and no significant difference in SGN survival was observed when the substrate compositions were compared. SGN neurite alignment significantly increases with increasing material modulus for both methacrylate series. Interestingly, SGN neurites respond to material stiffness cues that are orders of magnitude higher (GPa) than what is typically ascribed to neural environments (kPa). The ability to understand neurite response to engineered physical cues and mechanical properties such as matrix stiffness will allow the development of advanced biomaterials that direct de novo neurite growth to address the spatial signal resolution limitations of current neural prosthetics. PMID:25211120

  10. Material stiffness effects on neurite alignment to photopolymerized micropatterns.

    PubMed

    Tuft, Bradley W; Zhang, Lichun; Xu, Linjing; Hangartner, Austin; Leigh, Braden; Hansen, Marlan R; Guymon, C Allan

    2014-10-13

    The ability to direct neurite growth into a close proximity of stimulating elements of a neural prosthesis, such as a retinal or cochlear implant (CI), may enhance device performance and overcome current spatial signal resolution barriers. In this work, spiral ganglion neurons (SGNs), which are the target neurons to be stimulated by CIs, were cultured on photopolymerized micropatterns with varied matrix stiffnesses to determine the effect of rigidity on neurite alignment to physical cues. Micropatterns were generated on methacrylate thin film surfaces in a simple, rapid photopolymerization step by photomasking the prepolymer formulation with parallel line-space gratings. Two methacrylate series, a nonpolar HMA-co-HDDMA series and a polar PEGDMA-co-EGDMA series, with significantly different surface wetting properties were evaluated. Equivalent pattern periodicity was maintained across each methacrylate series based on photomask band spacing, and the feature amplitude was tuned to a depth of 2 ?m amplitude for all compositions using the temporal control afforded by the UV curing methodology. The surface morphology was characterized by scanning electron microscopy and white light interferometry. All micropatterned films adsorb similar amounts of laminin from solution, and no significant difference in SGN survival was observed when the substrate compositions were compared. SGN neurite alignment significantly increases with increasing material modulus for both methacrylate series. Interestingly, SGN neurites respond to material stiffness cues that are orders of magnitude higher (GPa) than what is typically ascribed to neural environments (kPa). The ability to understand neurite response to engineered physical cues and mechanical properties such as matrix stiffness will allow the development of advanced biomaterials that direct de novo neurite growth to address the spatial signal resolution limitations of current neural prosthetics. PMID:25211120

  11. Kinematic Characterization of Left Ventricular Chamber Stiffness and Relaxation

    NASA Astrophysics Data System (ADS)

    Mossahebi, Sina

    Heart failure is the most common cause of hospitalization today, and diastolic heart failure accounts for 40-50% of cases. Therefore, it is critical to identify diastolic dysfunction at a subclinical stage so that appropriate therapy can be administered before ventricular function is further, and perhaps irreversibly impaired. Basic concepts in physics such as kinematic modeling provide a unique method with which to characterize cardiovascular physiology, specifically diastolic function (DF). The advantage of an approach that is standard in physics, such as the kinematic modeling is its causal formulation that functions in contrast to correlative approaches traditionally utilized in the life sciences. Our research group has pioneered theoretical and experimental quantitative analysis of DF in humans, using both non-invasive (echocardiography, cardiac MRI) and invasive (simultaneous catheterization-echocardiography) methods. Our group developed and validated the Parametrized Diastolic Filling (PDF) formalism which is motivated by basic physiologic principles (LV is a mechanical suction pump at the mitral valve opening) that obey Newton's Laws. PDF formalism is a kinematic model of filling employing an equation of motion, the solution of which accurately predicts all E-wave contours in accordance with the rules of damped harmonic oscillatory motion. The equation's lumped parameters---ventricular stiffness, ventricular viscoelasticity/relaxation and ventricular load---are obtained by solving the 'inverse problem'. The parameters' physiologic significance and clinical utility have been repeatedly demonstrated in multiple clinical settings. In this work we apply our kinematic modeling approach to better understand how the heart works as it fills in order to advance the relationship between physiology and mathematical modeling. Through the use of this modeling, we thereby define and validate novel, causal indexes of diastolic function such as early rapid filling energy, diastatic stiffness, and relaxation and stiffness components of E-wave deceleration time.

  12. On modeling hydraulic fracture in proper variables: stiffness, accuracy, sensitivity

    E-print Network

    Mishuris, Gennady; Linkov, Alexander

    2012-01-01

    The problem of hydraulic fracture propagation is considered by using its recently suggested modified formulation in terms of the particle velocity, the opening in the proper degree, appropriate spatial coordinates and $\\varepsilon$-regularization. We show that the formulation may serve for significant increasing the efficiency of numerical tracing the fracture propagation. Its advantages are illustrated by re-visiting the Nordgren problem. It is shown that the modified formulation facilitates (i) possibility to have various stiffness of differential equations resulting after spatial discretization, (ii) obtaining highly accurate and stable numerical results with moderate computational effort, and (iii) sensitivity analysis. The exposition is extensively illustrated by numerical examples.

  13. Material selection for acoustic radiators that are light and stiff.

    PubMed

    Porter, S P; Markley, D C; Van Tol, D J; Meyer, R J

    2011-01-01

    The headmass is a key element in tonpilz transducer design. As an acoustic radiator, a successful headmass must be built from a material that is both light and stiff. To assess the suitability of ceramics for this application, the authors used the mechanical properties of candidate materials to perform a theoretical comparison based on the flexural behavior of square plates. Although not a comprehensive metric for identifying the best headmass materials, the headmass flexure may be usefully employed as a first-level selection criteria. A software routine based on thin plate and thick plate theory was created to evaluate the flexural behavior in candidate materials. PMID:21302996

  14. Elastomeric substrates with embedded stiff platforms for stretchable electronics

    NASA Astrophysics Data System (ADS)

    Romeo, Alessia; Liu, Qihan; Suo, Zhigang; Lacour, Stéphanie P.

    2013-04-01

    Stretchable electronics typically integrate hard, functional materials on soft substrates. Here we report on engineered elastomeric substrates designed to host stretchable circuitry. Regions of a stiff material, patterned using photolithography, are embedded within a soft elastomer leaving a smooth surface. We present the associated design rules to produce stretchable circuits based on experimental as well as modeling data. We demonstrate our approach with thin-film electronic materials. The "customized" elastomeric substrates may also be used as a generic elastic substrate for stretchable circuits prepared with alternative technologies, such as transfer-printing of inorganic, thinned devices.

  15. EPS composition and calcification potential of tufa-dominating cyanobacteria investigated by Scanning Transmission X-ray Microscopy (STXM) and Laser Scanning Microscopy (LSM)

    NASA Astrophysics Data System (ADS)

    Zippel, Barbara; Dynes, James J.; Obst, Martin; Lawrence, John R.; Neu, Thomas R.

    2010-05-01

    Tufa deposits in freshwater habitats are the result of calcium carbonate precipitation within interfacial microbial ecosystems. Calcite precipitation is influenced by the saturation index and the occurrence of extracellular polymeric substances (EPS) which are produced by a variety of microorganisms. In theory, the first important step of biologically induced calcification processes is the adsorption of calcium ions by extracellular polymeric substances (EPS) produced by cyanobacteria. In the present study we take advantage of Laser Scanning Microscopy (LSM) and combine it with Synchrotron imaging using Scanning Transmission X-ray Microscopy (STXM). STXM represents a technique that allows simultaneous analysis of inorganic and organic constituents as a scale of 50 nm. By means of STXM it is possible to differentiate between calcium carbonate phases at the Ca L-edge. Furthermore, STXM has also been used at the C K-edge to map the major biomolecules (proteins, lipids, and polysaccharides). The purpose of this study is to find out if there are differences in calcium adsorption depending on specific composition of the EPS produced by filamentous cyanobacteria isolated from a German hard water creek (Westerhöfer Bach, Harz Mountains). The goal was to elucidate the potential of biofilms constituents, including microbial cell surfaces as well as extracellular polymeric substances, in triggering the formation of calcium carbonate in tufa systems. For this purpose three filamentous cyanobacteria (Pseudanabaena sp., Leptolyngbya sp. and Nostoc sp.) were cultivated in creek-adapted as well as standard media (BG11) on polycarbonate slides. In situ EPS composition was detected by means of fluorescence lectin-binding approach (FLBA) using 23 commercially available lectins with different specificities for mono- and disaccharides and amino sugars. For CaCO3 nucleation experiments cyanobacterial biofilms grown on polycarbonate slides were deposited in NaHCO3/CaCl2 solutions supersaturated 10 times with respect to calcite for 48, 72 and 144 hours. For the STXM experiment on beamline 10-ID1 at the Canadian Light Source (CLS), the biofilm samples were scrapped off, suspended in a slurry and deposited carefully on a Si3N4 window. In order to obtain quantitative speciation maps of cyanobacterial sheath EPS, image sequences (stacks) were recorded at the C-1s (280-320 eV) and Ca-2p (340-360 eV) edges. Data analysis was done by using the software aXis2000, and energy spectra were fitted with available reference spectra. Nearly the same lectins specific for fucose, mannose, N-acetylgalactosamine and N-acetylglucosamine, as well as sialic acid bound preferentially to the EPS of cyanobacterial sheaths of Pseudanabaena sp. and Leptolyngbya sp. Surprisingly, in case of Nostoc sp. only two lectins specific for fucose, and N-acetylgalactosamine showed a clear binding to the EPS of sheaths. Qualitative, lectin-specific EPS composition was not influenced by nutrient concentrations within the medium during cultivation. In order to biochemically characterize the CaCO3 nucleation sites within the sheaths of the cyanobacteria investigated, carbon maps of the most abundant organic components were derived from C-1s image sequences. The sheaths of the cyanobacteria contained mainly polysaccharides followed by proteins, and a small amount of lipids. The highest amount of polysaccharides was detected in EPS produced by Pseudanabaena sp., whereas in Nostoc sp. only one-fifth was found. All samples investigated contained spectral signatures of Ca2+ adsorbed to EPS. Aragonite-like CaCO3 was detected in close association with the cell surface of Leptolyngbya sp. only. Highest amount of adsorbed Ca to EPS was found in Pseudanabaena sp., whereas only one-third was detected within the EPS of sheaths in Leptolyngbya sp. and Nostoc sp. Results of this combined approach show that the cyanobacteria investigated are may be involved in calcification processes to different degrees.

  16. 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.

  17. Mechanosensitive Kinases Regulate Stiffness-Induced Cardiomyocyte Maturation

    PubMed Central

    Young, Jennifer L.; Kretchmer, Kyle; Ondeck, Matthew G.; Zambon, Alexander C.; Engler, Adam J.

    2014-01-01

    Cells secrete and assemble extracellular matrix throughout development, giving rise to time-dependent, tissue-specific stiffness. Mimicking myocardial matrix stiffening, i.e. ~10-fold increase over 1 week, with a hydrogel system enhances myofibrillar organization of embryonic cardiomyocytes compared to static hydrogels, and thus we sought to identify specific mechanosensitive proteins involved. Expression and/or phosphorylation state of 309 unique protein kinases were examined in embryonic cardiomyocytes plated on either dynamically stiffening or static mature myocardial stiffness hydrogels. Gene ontology analysis of these kinases identified cardiogenic pathways that exhibited time-dependent up-regulation on dynamic versus static matrices, including PI3K/AKT and p38 MAPK, while GSK3?, a known antagonist of cardiomyocyte maturation, was down-regulated. Additionally, inhibiting GSK3? on static matrices improved spontaneous contraction and myofibril organization, while inhibiting agonist AKT on dynamic matrices reduced myofibril organization and spontaneous contraction, confirming its role in mechanically-driven maturation. Together, these data indicate that mechanically-driven maturation is at least partially achieved via active mechanosensing at focal adhesions, affecting expression and phosphorylation of a variety of protein kinases important to cardiomyogenesis. PMID:25236849

  18. Methods for evaluating changes in cartilage stiffness following electromechanical reshaping

    NASA Astrophysics Data System (ADS)

    Lim, Amanda; Protsenko, Dmitriy E.; Wong, Brian J. F.

    2010-02-01

    One common component of otolaryngological surgeries is the reshaping of cartilage. Previous studies have demonstrated the efficient achievement of this procedure through electromechanical reshaping (EMR), a technique that involves the direct application of voltage to cartilage that is mechanically deformed in a jig. Two main parameters, voltage and application time, may be regulated to achieve varying degrees of shape change. Although prior research has correlated these EMR parameters with degree of shape change, it remains necessary to correlate the same parameters with the degree of change in the mechanical properties of tissue. Once this is accomplished, an ideal balance may be determined, in which shape change is maximized while intrinsic tissue damage is minimized This study satisfies this need by providing comprehensive data on the pre- and post-EMR stiffness of both septal and auricular cartilage over a range of voltages (2-8V) with constant application time (2 min for septal, 3 min for auricular). EMR was applied using flat platinum electrodes to one of two 15 mm X 5 mm samples obtained from the same cartilage specimen, while the second sample was maintained as a control. Following a 15 min re-hydration period, the Young's modulus of the tissue was calculated for both the control and experimental sample from data obtained through a uniaxial tension test. A general reduction in stiffness was observed beginning at 3V, with the magnitude of reduction increasing at 6V.

  19. Influence of Polyelectrolyte Film Stiffness on Bacterial Growth

    PubMed Central

    Saha, Naresh; Monge, Claire; Dulong, Virginie; Picart, Catherine; Glinel, Karine

    2015-01-01

    Photo-crosslinkable polyelectrolyte films whose nanomechanical properties can be varied under UV light illumination, were prepared from poly(L-lysine) (PLL) and a hyaluronan derivative modified with photoreactive vinylbenzyl groups (HAVB). The adhesion and the growth of two model bacteria, namely Escherichia coli and Lactococcus lactis, were studied on non-crosslinked and crosslinked films to investigate how the film stiffness influences the bacterial behavior. While the Gram positive L. lactis was shown to grow slowly on both films, independently of their rigidity, the Gram negative E. coli exhibited a more rapid growth on non-crosslinked softer films compared to the stiffer ones. Experiments performed on photo-patterned films showing both soft and stiff regions, confirmed a faster development of E. coli colonies on softer regions. Interestingly, this behavior is opposite to the one reported before for mammalian cells. Therefore, the photo-crosslinked (PLL/HAVB) films are interesting coatings for tissue engineering since they promote the growth of mammalian cells while limiting the bacterial colonization. PMID:23289403

  20. Functional bacterial amyloid increases Pseudomonas biofilm hydrophobicity and stiffness

    PubMed Central

    Zeng, Guanghong; Vad, Brian S.; Dueholm, Morten S.; Christiansen, Gunna; Nilsson, Martin; Tolker-Nielsen, Tim; Nielsen, Per H.; Meyer, Rikke L.; Otzen, Daniel E.

    2015-01-01

    The success of Pseudomonas species as opportunistic pathogens derives in great part from their ability to form stable biofilms that offer protection against chemical and mechanical attack. The extracellular matrix of biofilms contains numerous biomolecules, and it has recently been discovered that in Pseudomonas one of the components includes ?-sheet rich amyloid fibrils (functional amyloid) produced by the fap operon. However, the role of the functional amyloid within the biofilm has not yet been investigated in detail. Here we investigate how the fap-based amyloid produced by Pseudomonas affects biofilm hydrophobicity and mechanical properties. Using atomic force microscopy imaging and force spectroscopy, we show that the amyloid renders individual cells more resistant to drying and alters their interactions with hydrophobic probes. Importantly, amyloid makes Pseudomonas more hydrophobic and increases biofilm stiffness 20-fold. Deletion of any one of the individual members of in the fap operon (except the putative chaperone FapA) abolishes this ability to increase biofilm stiffness and correlates with the loss of amyloid. We conclude that amyloid makes major contributions to biofilm mechanical robustness. PMID:26500638

  1. Explicit Integration of Extremely Stiff Reaction Networks: Partial Equilibrium Methods

    SciTech Connect

    Guidry, Mike W; Billings, J. J.; Hix, William Raphael

    2013-01-01

    In two preceding papers [1,2] we have shown that, when reaction networks are well removed from equilibrium, explicit asymptotic and quasi-steady-state approximations can give algebraically stabilized integration schemes that rival standard implicit methods in accuracy and speed for extremely stiff systems. However, we also showed that these explicit methods remain accurate but are no longer competitive in speed as the network approaches equilibrium. In this paper we analyze this failure and show that it is associated with the presence of fast equilibration timescales that neither asymptotic nor quasi-steady-state approximations are able to remove efficiently from the numerical integration. Based on this understanding, we develop a partial equilibrium method to deal effectively with the new partial equilibrium methods, give an integration scheme that plausibly can deal with the stiffest networks, even in the approach to equilibrium, with accuracy and speed competitive with that of implicit methods. Thus we demonstrate that algebraically stabilized explicit methods may offer alternatives to implicit integration of even extremely stiff systems, and that these methods may permit integration of much larger networks than have been feasible previously in a variety of fields.

  2. Cerebrovascular Damage Mediates Relations Between Aortic Stiffness and Memory.

    PubMed

    Cooper, Leroy L; Woodard, Todd; Sigurdsson, Sigurdur; van Buchem, Mark A; Torjesen, Alyssa A; Inker, Lesley A; Aspelund, Thor; Eiriksdottir, Gudny; Harris, Tamara B; Gudnason, Vilmundur; Launer, Lenore J; Mitchell, Gary F

    2016-01-01

    Aortic stiffness is associated with cognitive decline. Here, we examined the association between carotid-femoral pulse wave velocity and cognitive function and investigated whether cerebrovascular remodeling and parenchymal small vessel disease damage mediate the relation. Analyses were based on 1820 (60% women) participants in the Age, Gene/Environment Susceptibility-Reykjavik Study. Multivariable linear regression models adjusted for vascular and demographic confounders showed that higher carotid-femoral pulse wave velocity was related to lower memory score (standardized ?: -0.071±0.023; P=0.002). Cerebrovascular resistance and white matter hyperintensities were each associated with carotid-femoral pulse wave velocity and memory (P<0.05). Together, cerebrovascular resistance and white matter hyperintensities (total indirect effect: -0.029; 95% CI, -0.043 to -0.017) attenuated the direct relation between carotid-femoral pulse wave velocity and memory (direct effect: -0.042; 95% CI, -0.087 to 0.003; P=0.07) and explained ?41% of the observed effect. Our results suggest that in older adults, associations between aortic stiffness and memory are mediated by pathways that include cerebral microvascular remodeling and microvascular parenchymal damage. PMID:26573713

  3. ??? Cross-Links Increase Fibrin Fiber Elasticity and Stiffness

    PubMed Central

    Helms, Christine C.; Ariëns, Robert A.S.; Uitte de Willige, S.; Standeven, Kristina F.; Guthold, Martin

    2012-01-01

    Fibrin fibers, which are ?100 nm in diameter, are the major structural component of a blood clot. The mechanical properties of single fibrin fibers determine the behavior of a blood clot and, thus, have a critical influence on heart attacks, strokes, and embolisms. Cross-linking is thought to fortify blood clots; though, the role of ?–? cross-links in fibrin fiber assembly and their effect on the mechanical properties of single fibrin fibers are poorly understood. To address this knowledge gap, we used a combined fluorescence and atomic force microscope technique to determine the stiffness (modulus), extensibility, and elasticity of individual, uncross-linked, exclusively ?–? cross-linked (?Q398N/Q399N/K406R fibrinogen variant), and completely cross-linked fibrin fibers. Exclusive ?–? cross-linking results in 2.5× stiffer and 1.5× more elastic fibers, whereas full cross-linking results in 3.75× stiffer, 1.2× more elastic, but 1.2× less extensible fibers, as compared to uncross-linked fibers. On the basis of these results and data from the literature, we propose a model in which the ?-C region plays a significant role in inter- and intralinking of fibrin molecules and protofibrils, endowing fibrin fibers with increased stiffness and elasticity. PMID:22225811

  4. Plasma homocysteine levels are independently associated with alterations of large artery stiffness in men but not in women

    PubMed Central

    Sheng, Li; Wu, Cai; Bai, Yong-Yi; Xiao, Wen-Kai; Feng, Dan; Ye, Ping

    2015-01-01

    Objectives To investigate the associations of the plasma homocysteine levels with the alterations in arterial stiffness in a community-based cohort. The gender differences in these associations were examined. Methods We evaluated the relationship between plasma homocysteine levels to three measures of vascular function [carotid-femoral pulse wave velocity (CF-PWV), carotid-ankle PWV (CA-PWV) and heart rate corrected augmentation index (AI)] in 1680 participants (mean age: 61.5 years; 709 men, 971 women) from communities of Beijing, China. Results In univariate analysis, plasma homocysteine levels was positively related to the CF-PWV (r = 0.211, P < 0.0001) and CA-PWV (r = 0.148, P < 0.0001), whereas inversely associated with AI (r = ?0.052, P = 0.016). In multiple linear regression models adjusting for covariants, plasma homocysteine remained positively related to the CF-PWV (standardized ? = 0.065, P = 0.007) in total cases. When the groups of men and women were examined separately, plasma homocysteine remained positively associated with the CF-PWV (standardized ? = 0.082, P = 0.023) in men, whereas the relations between homocysteine and any of the arterial stiffness indices were not further present in women. Conclusions In Chinese population, plasma homocysteine levels are independently associated with alterations of large artery stiffness in men but not in women. PMID:26089849

  5. Exact solutions for free vibration of shear-type structures with arbitrary distribution of mass or stiffness.

    PubMed

    Li, Q S

    2001-10-01

    In this paper, shear-type structures such as frame buildings, etc., are treated as nonuniform shear beams (one-dimensional systems) in free-vibration analysis. The expression for describing the distribution of shear stiffness of a shear beam is arbitrary, and the distribution of mass is expressed as a functional relation with the distribution of shear stiffness, and vice versa. Using appropriate functional transformation, the governing differential equations for free vibration of nonuniform shear beams are reduced to Bessel's equations or ordinary differential equations with constant coefficients for several functional relations. Thus, classes of exact solutions for free vibrations of the shear beam with arbitrary distribution of stiffness or mass are obtained. The effect of taper on natural frequencies of nonuniform beams is investigated. Numerical examples show that the calculated natural frequencies and mode shapes of shear-type structures are in good agreement with the field measured data and those determined by the finite-element method and Ritz method. PMID:11681376

  6. Stiffness alterations of single cells induced by UV in the presence of nanoTiO2.

    PubMed

    Vileno, Bertrand; Lekka, Ma?gorzata; Sienkiewicz, Andrzej; Jeney, Sylvia; Stoessel, Gabriela; Lekki, Janusz; Forró, László; Stachura, Zbigniew

    2007-07-15

    Nanocrystalline titanium dioxide (nanoTiO2) has been reported to generate reactive oxygen species (ROS) under UV illumination. In our studies, changes in mechanical properties of human skin fibroblasts, exposed to the oxidative stress induced in the presence of nanoTiO2 and UV light, were studied using atomic force microscopy (AFM). The exposure of cells to the action of ROS was performed at low TiO2 concentration (4 microg/mL) and under illumination with low-intensity UVA (8 and 20 mW/cm2) or UVC (0.1 mW/ cm2). AFM measurements of the cell stiffness were carried out immediately after exposure of cells to the oxidative stress. The data suggest that under illumination with low-intensity UVA nanoTiO2 generates ROS, which, in turn, damage cellular and subcellular structures. This process was detected by AFM as a marked drop in the cellular stiffness of ca. 30-75%, which occurred rapidly, in the time frame of 1 min. The photo-oxidative stress inducing the decrease of cell stiffness was cancelled in the presence of a well-established antioxidant, beta-carotene. The results highlight the sensitivity of AFM to detect early changes in mechanical properties of cells exposed to oxidative stress. PMID:17711237

  7. Evaluation of Stiffness of the Spastic Lower Extremity Muscles in Early Spinal Cord Injury by Acoustic Radiation Force Impulse Imaging

    PubMed Central

    Cho, Kang Hee

    2015-01-01

    Objective To investigate intrinsic viscoelastic changes using shear wave velocities (SWVs) of spastic lower extremity muscles in patients with early spinal cord injury (SCI) via acoustic radiation force impulse (ARFI) imaging and to evaluate correlation between the SWV values and spasticity. Methods Eighteen patients with SCI within 3 months and 10 healthy adults participated. We applied the ARFI technique to measure SWV of gastrocnemius muscle (GCM) and long head of biceps femoris muscle. Spasticity of ankle and knee joint was assessed by original Ashworth Scale. Results Ten patients with SCI had spasticity. Patients with spasticity had significantly faster SWV for GCM and biceps femoris muscle than those without spasticity (Mann-Whitney U test, p=0.007 and p=0.008) and normal control (p=0.011 and p=0.037, respectively). The SWV values of GCM correlated with the ankle spasticity (Spearman rank teat, p=0.026). There was significant correlation between the SWV values for long head of biceps femoris muscle and knee spasticity (Spearman rank teat, p=0.022). Conclusion ARFI demonstrated a difference in muscle stiffness in the GCM between patients with spastic SCI and those without spasticity. This finding suggested that stiffness of muscles increased in spastic lower extremity of early SCI patients. ARFI imaging is a valuable tool for noninvasive assessment of the stiffness of the spastic muscle and has the potential to identify pathomechanical changes of the tissue associated with SCI. PMID:26161345

  8. Using Micro-CT Derived Bone Microarchitecture to Analyze Bone Stiffness – A Case Study on Osteoporosis Rat Bone

    PubMed Central

    Wu, Yuchin; Adeeb, Samer; Doschak, Michael R.

    2015-01-01

    Micro-computed tomography (Micro-CT) images can be used to quantitatively represent bone geometry through a range of computed attenuation-based parameters. Nonetheless, those parameters remain indirect indices of bone microarchitectural strength and require further computational tools to interpret bone structural stiffness and potential for mechanical failure. Finite element analysis (FEA) can be applied to measure trabecular bone stiffness and potentially predict the location of structural failure in preclinical animal models of osteoporosis, although that procedure from image segmentation of Micro-CT derived bone geometry to FEA is often challenging and computationally expensive, resulting in failure of the model to build. Notably, the selection of resolution and threshold for bone segmentation are key steps that greatly affect computational complexity and validity. In the following study, we evaluated an approach whereby Micro-CT derived grayscale attenuation and segmentation data guided the selection of trabecular bone for analysis by FEA. We further correlated those FEA results to both two- and three-dimensional bone microarchitecture from sham and ovariectomized (OVX) rats (n?=?10/group). A virtual cylinder of vertebral trabecular bone 40% in length from the caudal side was selected for FEA, because Micro-CT based image analysis indicated the largest differences in microarchitecture between the two groups resided there. Bone stiffness was calculated using FEA and statistically correlated with the three-dimensional values of bone volume/tissue volume, bone mineral density, fractal dimension, trabecular separation, and trabecular bone pattern factor. Our method simplified the process for the assessment of trabecular bone stiffness by FEA from Micro-CT images and highlighted the importance of bone microarchitecture in conferring significantly increased bone quality capable of resisting failure due to increased mechanical loading. PMID:26042089

  9. Extensional, bending and twisting stiffness of Titanium Multiwall Thermal Protection System (TPS)

    NASA Technical Reports Server (NTRS)

    Meaney, J. E.

    1982-01-01

    A test program which determines the extensional, bending and torsional stiffness of various titanium multiwall sandwich configurations is described. It is shown that unlike honeycomb core, the dimpled core is a significant contributor to the stiffness and strength of the sandwich. the extensional stiffness test shows irregularities which are attributed to foil thickness variations and to the difficulty to determine linear values from nonlinear tests.

  10. Amino Acid Intakes Are Inversely Associated with Arterial Stiffness and Central Blood Pressure in Women12

    PubMed Central

    Jennings, Amy; MacGregor, Alex; Welch, Ailsa; Chowienczyk, Phil; Spector, Tim; Cassidy, Aedín

    2015-01-01

    Background: Although data suggest that intakes of total protein and specific amino acids (AAs) reduce blood pressure, data on other cardiovascular disease risk factors are limited. Objective: We examined associations between intakes of AAs with known mechanistic links to cardiovascular health and direct measures of arterial stiffness, central blood pressure, and atherosclerosis. Methods: In a cross-sectional study of 1898 female twins aged 18–75 y from the TwinsUK registry, intakes of 7 cardioprotective AAs (arginine, cysteine, glutamic acid, glycine, histidine, leucine, and tyrosine) were calculated from food-frequency questionnaires. Direct measures of arterial stiffness and atherosclerosis included central systolic blood pressure (cSBP), mean arterial pressure (MAP), augmentation index (AI), pulse wave velocity (PWV), and intima–media thickness (IMT). ANCOVA was used to assess the associations between endpoints of arterial stiffness and intake (per quintile), adjusting for potential confounders. Results: In multivariable analyses, higher intakes of total protein and 7 potentially cardioprotective AAs were associated with lower cSBP, MAP, and PWV. Higher intakes of glutamic acid, leucine, and tyrosine were most strongly associated with PWV, with respective differences of ?0.4 ± 0.2 m/s (P-trend = 0.02), ?0.4 ± 0.2 m/s (P-trend = 0.03), and ?0.4 ± 0.2 m/s (P-trend = 0.03), comparing extreme quintiles. There was a significant interaction between AA intakes and protein source, and higher intakes of AAs from vegetable sources were associated with lower central blood pressure and AI. Higher intakes of glutamic acid, leucine, and tyrosine from animal sources were associated with lower PWV. Conclusions: These data provide evidence to suggest that intakes of several AAs are associated with cardiovascular benefits beyond blood pressure reduction in healthy women. The magnitude of the observed associations was similar to those previously reported for other lifestyle factors. Increasing intakes of these AAs could be an important and readily achievable way to reduce cardiovascular disease risk. PMID:26203100

  11. Stroke volume-to-wall stress ratio as a load-adjusted and stiffness-adjusted indicator of ventricular systolic performance in chronic loading.

    PubMed

    Chemaly, Elie R; Chaanine, Antoine H; Sakata, Susumu; Hajjar, Roger J

    2012-10-15

    Load-adjusted measures of left ventricle (LV) systolic performance are limited by dependence on LV stiffness and afterload. To our knowledge, no stiffness-adjusted and afterload-adjusted indicator was tested in models of pressure (POH) and volume overload hypertrophy (VOH). We hypothesized that wall stress reflects changes in loading, incorporating chamber stiffness and afterload; therefore, stroke volume-to-wall stress ratio more accurately reflects systolic performance. We used rat models of POH (ascending aortic banding) and VOH (aorto-cava shunt). Animals underwent echocardiography and pressure-volume analysis at baseline and dobutamine challenge. We achieved extreme bidirectional alterations in LV systolic performance, end-systolic elastance (Ees), passive stiffness, and arterial elastance (Ea). In POH with LV dilatation and failure, some load-independent indicators of systolic performance remained elevated compared with controls, while some others failed to decrease with wide variability. In VOH, most, but not all indicators, including LV ejection fraction, were significantly reduced compared with controls, despite hyperdynamic circulation, lack of heart failure, and preserved contractile reserve. We related systolic performance to Ees adjusted for Ea and LV passive stiffness in multivariate models. Calculated residual Ees was not reduced in POH with heart failure and was reduced in VOH, while it positively correlated to dobutamine dose. Conversely, stroke volume-to-wall stress ratio was normal in compensated POH, markedly decreased in POH with heart failure, and, in contrast with LV ejection fraction, normal in VOH. Our results support stroke volume-to-wall stress ratio as a load-adjusted and stiffness-adjusted indicator of systolic function in models of POH and VOH. PMID:22923502

  12. Biomechanical Effects of Stiffness in Parallel With the Knee Joint During Walking.

    PubMed

    Shamaei, Kamran; Cenciarini, Massimo; Adams, Albert A; Gregorczyk, Karen N; Schiffman, Jeffrey M; Dollar, Aaron M

    2015-10-01

    The human knee behaves similarly to a linear torsional spring during the stance phase of walking with a stiffness referred to as the knee quasi-stiffness. The spring-like behavior of the knee joint led us to hypothesize that we might partially replace the knee joint contribution during stance by utilizing an external spring acting in parallel with the knee joint. We investigated the validity of this hypothesis using a pair of experimental robotic knee exoskeletons that provided an external stiffness in parallel with the knee joints in the stance phase. We conducted a series of experiments involving walking with the exoskeletons with four levels of stiffness, including 0%, 33%, 66%, and 100% of the estimated human knee quasi-stiffness, and a pair of joint-less replicas. The results indicated that the ankle and hip joints tend to retain relatively invariant moment and angle patterns under the effects of the exoskeleton mass, articulation, and stiffness. The results also showed that the knee joint responds in a way such that the moment and quasi-stiffness of the knee complex (knee joint and exoskeleton) remains mostly invariant. A careful analysis of the knee moment profile indicated that the knee moment could fully adapt to the assistive moment; whereas, the knee quasi-stiffness fully adapts to values of the assistive stiffness only up to ?80%. Above this value, we found biarticular consequences emerge at the hip joint. PMID:25955513

  13. Vanishing spin stiffness in the spin-1/2 Heisenberg chain for any nonzero temperature

    NASA Astrophysics Data System (ADS)

    Carmelo, J. M. P.; Prosen, T.; Campbell, D. K.

    2015-10-01

    Whether at the zero spin density m =0 and finite temperatures T >0 the spin stiffness of the spin-1 /2 X X X chain is finite or vanishes remains an unsolved and controversial issue, as different approaches yield contradictory results. Here we explicitly compute the stiffness at m =0 and find strong evidence that it vanishes. In particular, we derive an upper bound on the stiffness within a canonical ensemble at any fixed value of spin density m that is proportional to m2L in the thermodynamic limit of chain length L ?? , for any finite, nonzero temperature, which implies the absence of ballistic transport for T >0 for m =0 . Although our method relies in part on the thermodynamic Bethe ansatz (TBA), it does not evaluate the stiffness through the second derivative of the TBA energy eigenvalues relative to a uniform vector potential. Moreover, we provide strong evidence that in the thermodynamic limit the upper bounds on the spin current and stiffness used in our derivation remain valid under string deviations. Our results also provide strong evidence that in the thermodynamic limit the TBA method used by X. Zotos [Phys. Rev. Lett. 82, 1764 (1999), 10.1103/PhysRevLett.82.1764] leads to the exact stiffness values at finite temperature T >0 for models whose stiffness is finite at T =0 , similar to the spin stiffness of the spin-1 /2 Heisenberg chain but unlike the charge stiffness of the half-filled 1D Hubbard model.

  14. Stiff Man Syndrome: A Diagnostic Dilemma in a Young Female with Diabetes Mellitus and Thyroiditis

    PubMed Central

    Enuh, Hilary; Park, Michael; Ghodasara, Arjun; Arsura, Edward; Nfonoyim, Jay

    2014-01-01

    Stiff Person Syndrome (SPS), is a very rare neuroimmunologic disorder characterized by progressive muscle pain, rigidity, stiffness, and spasms. It can be very debilitating if misdiagnosed or not recognized in time. Herein we discuss a case of a female in her 20s who presented with an unsteady gait, lower extremity weakness, persistent leg pain, and stiffness few weeks after uncomplicated childbirth. She has type 1 diabetes mellitus (DM) and was diagnosed with thyroiditis in the course of her illness. The triad of thyroiditis, DM, and stiffness with normal neuroimaging in a young female patient is an unusual occurrence. PMID:25525403

  15. Review of ‘the potential role of arterial stiffness in the pathogenesis of Alzheimer’s disease’

    PubMed Central

    Hughes, Timothy M; Craft, Suzanne; Lopez, Oscar L

    2015-01-01

    SUMMARY Arterial stiffness is emerging as an important risk marker for poor brain aging and dementia through its associations with cerebral small vessel disease, stroke, ?-amyloid deposition, brain atrophy and cognitive impairment. Arterial stiffness directly relates the detrimental effects of hypertension on peripheral organs with dire consequences for the extensive microvasculature structure of the kidneys and brain. In this review, we discuss the evidence linking arterial stiffness, hypertension and brain structural abnormalities in older adults. In particular, we discuss the potential mechanisms linking arterial stiffness to brain ?-amyloid deposition and dementia and potential therapeutic strategies to prevent hypertension’s adverse effects on the brain. PMID:25894876

  16. Impact of morning stiffness on working behaviour and performance in people with rheumatoid arthritis.

    PubMed

    Mattila, Kalle; Buttgereit, Frank; Tuominen, Risto

    2014-12-01

    Work disability remains a considerable problem for many patients with rheumatoid arthritis (RA). Morning stiffness is a symptom of RA associated with early retirement from work and with impaired functional ability. We aimed to explore the patient's perception of the impact of morning stiffness on the working life of patients with RA. A survey was conducted in 11 European countries. Patients of working age, with RA for ?6 months and morning stiffness ?3 mornings a week, were interviewed by telephone using a structured questionnaire. Responses were assessed in the total sample and in subgroups defined by severity and duration of morning stiffness and by country. A total of 1,061 respondents completed the survey, 534 were working, 224 were retired and the rest were, i.e. homemakers and unemployed. Among the 534 working respondents, RA-related morning stiffness affected work performance (47 %), resulted in late arrival at work (33 %) and required sick leave in the past month (15 %). Of the 224 retired respondents, 159 (71 %) stopped working earlier than their expected retirement age, with 64 % giving RA-related morning stiffness as a reason. There was a differential impact of increasing severity and increasing duration of morning stiffness on the various parameters studied. There were notable inter-country differences in the impact of RA-related morning stiffness on ability to work and on retirement. This large survey showed that from the patient's perspective, morning stiffness reduces the ability to work in patients with RA and contributes to early retirement. PMID:24871158

  17. Stress phase angle depicts differences in arterial stiffness: phantom and in vivo study

    NASA Astrophysics Data System (ADS)

    Niu, Lili; Meng, Long; Xu, Lisheng; Liu, Jia; Wang, Qiwen; Xiao, Yang; Qian, Ming; Zheng, Hairong

    2015-06-01

    The endothelial cells (ECs) lining of a blood vessel wall are exposed to both the wall shear stress (WSS) of blood flow and the circumferential strain (CS) of pulsing artery wall motion. Both WSS and CS keep involved in the modulation of ECs’ biochemical response and function and the temporal phase angle between the two is called stress phase angle (SPA). Previous studies at the cellular level have indicated that SPA is highly negative at sites that are prone to atherosclerosis, and hypothesized that large SPA may contribute to atherogenesis. Till now, there is no experimental data to support this hypothesis, probably due to the lack of a proper tool for measuring WSS and CS simultaneously and real time. In this study, a non-invasive ultrasonic biomechanics method was utilized to quantitatively calculate the SPA and experimentally evaluate the role of SPA in predicting early atherosclerosis. Three silicon tubes with a stiffness of 1.15, 3.62, 9.38?MPa were assembled in a pulsatile flow circuit and the values of SPA were measured to be -101.86 ± 3.65°,-170.19 ± 17.77° and -260.63 ± 18.62°, respectively. For the PVA-c phantoms, stiffness was 162.45, 235.68 and 374.24?kPa, the SPA corresponding to -170.32 ± 17.55°,-207.56 ± 10.78° and -261.08 ± 10.90°, respectively. Both phantom studies results demonstrated that SPA was highly negative in stiffer arteries. Further, experiments were taken in healthy living rats as control group (n = 3), atherosclerotic model group (n = 3), and drug treated group (n = 3), and the results showed that SPA was most negative in the model group, and SPA was least negative in the control group. Together, this study suggested that highly negative SPA appeared to be a prominent mechanical feature of vessels prone to atherosclerotic disease.

  18. Assessment of Pulmonary Artery Stiffness of Repaired Congenital Heart Disease Patients

    NASA Astrophysics Data System (ADS)

    Lee, Namheon; Banerjee, Rajit; Taylor, Michael; Hor, Kan

    2012-10-01

    Surgical correction or palliation of congenital heart disease (CHD) often requires augmenting the main pulmonary artery (MPA) with non-native material or placing a cylindrical graft. The degree to which this intervention affects PA compliance is largely unknown. In this study, the MPA stiffness characteristics were assessed by its compliance, distensibility, and pressure-strain modulus. Coregistered velocity encoded phase-contrast MRI and cardiac catheterization data were available for a cohort of repaired CHD patients (n=8) and controls (n=3). All patients were repaired with either an RV-PA conduit or a RV outflow tract patch. We measured the MPA area change by MRI and MPA pressure during the cath. The measurements were taken through or just distal to the conduit. The MPA compliance and distensibility for the patients were significantly lower than the controls: compliance (9.8±10.8 vs 28.3±7.7mm^2/mmHg, p<0.05), distensibility (2.2±1.5 vs 6.6±2.1%Area change/mmHg, p=0.05). The patients had a significantly higher pressure-strain modulus (152.3±116.4mmHg, p<0.05) than the controls (35.8±10.6mmHg). The abnormally elevated PA stiffness due to the rigidity of the conduit or patch material may cause a compliance mismatch resulting in high stress levels contributing to the observed progressive PA dilatation. This may be a factor in the progressive RV dilatation seen in this cohort of repaired CHD patients.

  19. Surrogates of Large Artery versus Small Artery Stiffness and Ankle-Brachial Index

    PubMed Central

    Korhonen, Päivi; Syvänen, Kari; Aarnio, Pertti

    2011-01-01

    Peripheral artery tonometry (PAT) is a novel method for assessing arterial stiffness of small digital arteries. Pulse pressure can be regarded as a surrogate of large artery stiffness. When ankle-brachial index (ABI) is calculated using the higher of the two ankle systolic pressures as denominator (ABI-higher), leg perfusion can be reliably estimated. However, using the lower of the ankle pressures to calculate ABI (ABI-lower) identifies more patients with isolated peripheral arterial disease (PAD) in ankle arteries. We aimed to compare the ability of PAT, pulse pressure, and different calculations of ABI to detect atherosclerotic disease in lower extremities. We examined PAT, pulse pressure, and ABI in 66 cardiovascular risk subjects in whom borderline PAD (ABI 0.91 to 1.00) was diagnosed 4 years earlier. Using ABI-lower to diagnose PAD yielded 2-fold higher prevalence of PAD than using ABI-higher. Endothelial dysfunction was diagnosed in 15/66 subjects (23%). In a bivariate correlation analysis, pulse pressure was negatively correlated with ABI-higher (r?=??0.347, p?=?0.004) and with ABI-lower (r?=??0.424, p?Measurement of ABI using the lower of the two ankle pressures is an efficient method to identify patients with clinical or subclinical atherosclerosis and worth performing on subjects with pulse pressure above 65 mm Hg. The usefulness of PAT measurement in detecting PAD is vague. PMID:22942632

  20. Optimal design of the hydrodynamic multi-arc bearing in a centrifugal blood pump for the improvement of bearing stiffness and hemolysis level.

    PubMed

    Yasui, Kazuya; Kosaka, Ryo; Nishida, Masahiro; Maruyama, Osamu; Kawaguchi, Yasuo; Yamane, Takashi

    2013-09-01

    The purpose of the present study is to establish an optimal design of the multi-arc hydrodynamic bearing in a centrifugal blood pump for the improvement of bearing stiffness and hemolysis level. The multi-arc bearing was designed to fulfill the required specifications: (i) ensuring the uniform bearing stiffness for various bearing angles; (ii) ensuring a higher bearing stiffness than the centrifugal force to prevent impeller whirl; and (iii) adjusting the bearing clearance as much as possible to reduce hemolysis. First, a numerical analysis was performed to optimize three design parameters of the multi-arc bearing: number of arcs N, bearing clearance C, and groove depth H. To validate the accuracy of the numerical analysis, the impeller trajectories for six pump models were measured. Finally, an in vitro hemolysis test was conducted to evaluate the hemolytic property of the multi-arc bearing. As a result of the numerical analysis, the optimal parameter combination was determined as follows: N=4, C=100 ?m, and H ? 100 ?m. In the measurements of the impeller trajectory, the optimal parameter combination was found to be as follows: N=4, C=90 ?m, and H=100 ?m. This result demonstrated the high reliability of the numerical analysis. In the hemolysis test, the parameter combination that achieved the smallest hemolysis was obtained as follows: N=4, C=90 ?m, and H=100 ?m. In conclusion, the multi-arc bearing could be optimized for the improvement of bearing stiffness and hemolysis level. PMID:23980526

  1. Astaxanthin vs placebo on arterial stiffness, oxidative stress and inflammation in renal transplant patients (Xanthin): a randomised controlled trial

    PubMed Central

    Fassett, Robert G; Healy, Helen; Driver, Ritza; Robertson, Iain K; Geraghty, Dominic P; Sharman, James E; Coombes, Jeff S

    2008-01-01

    Background There is evidence that renal transplant recipients have accelerated atherosclerosis manifest by increased cardiovascular morbidity and mortality. The high incidence of atherosclerosis is, in part, related to increased arterial stiffness, vascular dysfunction, elevated oxidative stress and inflammation associated with immunosuppressive therapy. The dietary supplement astaxanthin has shown promise as an antioxidant and anti-inflammatory therapeutic agent in cardiovascular disease. The aim of this trial is to investigate the effects of astaxanthin supplementation on arterial stiffness, oxidative stress and inflammation in renal transplant patients. Method and Design This is a randomised, placebo controlled clinical trial. A total of 66 renal transplant recipients will be enrolled and allocated to receive either 12 mg/day of astaxanthin or an identical placebo for one-year. Patients will be stratified into four groups according to the type of immunosuppressant therapy they receive: 1) cyclosporine, 2) sirolimus, 3) tacrolimus or 4) prednisolone+/-azathioprine, mycophenolate mofetil or mycophenolate sodium. Primary outcome measures will be changes in 1) arterial stiffness measured by aortic pulse wave velocity (PWV), 2) oxidative stress assessed by plasma isoprostanes and 3) inflammation by plasma pentraxin 3. Secondary outcomes will include changes in vascular function assessed using the brachial artery reactivity (BAR) technique, carotid artery intimal medial thickness (CIMT), augmentation index (AIx), left ventricular afterload and additional measures of oxidative stress and inflammation. Patients will undergo these measures at baseline, six and 12 months. Discussion The results of this study will help determine the efficacy of astaxanthin on vascular structure, oxidative stress and inflammation in renal transplant patients. This may lead to a larger intervention trial assessing cardiovascular morbidity and mortality. Trial Registration ACTRN12608000159358 PMID:19091127

  2. A rotor unbalance response based approach to the identification of the closed-loop stiffness and damping coefficients of active magnetic bearings

    NASA Astrophysics Data System (ADS)

    Zhou, Jin; Di, Long; Cheng, Changli; Xu, Yuanping; Lin, Zongli

    2016-01-01

    The stiffness and damping coefficients of active magnetic bearings (AMBs) have direct influence on the dynamic response of a rotor bearing system, including the bending critical speeds, modes of vibrations and stability. Rotor unbalance response is informative in the identification of these bearing support parameters. In this paper, we propose a method for identifying closed-loop AMB stiffness and damping coefficients based on the rotor unbalance response. We will use a flexible rotor-AMB test rig to help describe the proposed method as well as to validate the identification results. First, based on a rigid body model of the rotor, a formula is derived that computes the nominal values of the bearing stiffness and damping coefficients at a given rotating speed from the experimentally measured rotor unbalance response at the given speed. Then, based on a finite element model of the rotor, an error response surface is constructed for each parameter to estimate the identification errors induced by the rotor flexibility. The final identified values of the stiffness and damping coefficients equal the sums of the nominal values initially computed from the unbalance response and the identification errors determined by the error response surfaces. The proposed identification method is carried out on the rotor-AMB test rig. In order to validate the identification results, the identified values of the closed-loop AMB stiffness and damping coefficients are combined with the finite element model of the rotor to form a full model of the rotor-AMB test rig, from which the model unbalance responses at various rotating speeds are determined through simulation and compared with the experimental measurements. The close agreements between the simulation results and the measurements validate the proposed identification method.

  3. On the difference between stiff and soft membranes: Capillary Waves

    E-print Network

    Jaksch, Sebastian; Ohl, Michael; Frielinghaus, Henrich

    2015-01-01

    One problem of non-crystalline condensed matter (soft matter) is creating the right equilibrium between elasticity and viscosity, referred to as viscoelasticity. Manifestations of that can be found in everyday live, where the viscoelasticity in a tire needs to be balanced so it is still flexible and can dissipate shock-energy, yet hard enough for energy-saving operation. Similarly, the cartilage in joints needs to absorb shocks while operating at low- level friction with high elasticity. Two such examples with a biological applicability are stiff membranes, which allow for the sliding of joints and therefore maintain their function over the lifetime of the corresponding individual (decades) and the softening of cell membranes, for example for antimicrobial effects by dissolution in the case of bacteria (seconds). While the first should allow for low- friction operation at high elasticity, in the second scenario energy dissipated into the membrane eventually leads to membrane destruction. Here we address the i...

  4. Cell stiffness, contractile stress and the role of extracellular matrix

    SciTech Connect

    An, Steven S.; Kim, Jina; Ahn, Kwangmi; Trepat, Xavier; Drake, Kenneth J.; Kumar, Sarvesh; Ling, Guoyu; Purington, Carolyn; Rangasamy, Tirumalai; Kensler, Thomas W.; Mitzner, Wayne; Fredberg, Jeffrey J.; Biswal, Shyam; Division of Pulmonary and Critical Care Medicine, Johns Hopkins School of Medicine, Baltimore, MD 21205

    2009-05-15

    Here we have assessed the effects of extracellular matrix (ECM) composition and rigidity on mechanical properties of the human airway smooth muscle (ASM) cell. Cell stiffness and contractile stress showed appreciable changes from the most relaxed state to the most contracted state: we refer to the maximal range of these changes as the cell contractile scope. The contractile scope was least when the cell was adherent upon collagen V, followed by collagen IV, laminin, and collagen I, and greatest for fibronectin. Regardless of ECM composition, upon adherence to increasingly rigid substrates, the ASM cell positively regulated expression of antioxidant genes in the glutathione pathway and heme oxygenase, and disruption of a redox-sensitive transcription factor, nuclear erythroid 2 p45-related factor (Nrf2), culminated in greater contractile scope. These findings provide biophysical evidence that ECM differentially modulates muscle contractility and, for the first time, demonstrate a link between muscle contractility and Nrf2-directed responses.

  5. The ocular phenotype of stiff-skin syndrome.

    PubMed

    Chamney, S; Cartmill, B; Earley, O; McConnell, V; Willoughby, C E

    2016-01-01

    PurposeStiff skin syndrome (SSS; MIM#184900) is a rare autosomal dominantly inherited Mendelian disorder characterised by thickened and stone-hard indurations of the skin, mild hypertrichosis, and limitation of joint mobility with flexion contractures. It is autosomal dominant with high penetrance and results from mutations in the fibrillin 1 (FBN1; MIM*134797) gene. Here we present the associated ocular phenotype in a two generation nonconsanguineous Northern Irish family.MethodsThe affected patients underwent complete ophthalmic and orthoptic assessment and genetic testing.ResultsAll three patients had ophthalmoplegia of varying degrees. Direct sequencing of the FBN1 gene detected a heterozygous pathogenic mutation (c.4710G>C; p.Trp1570Cys) in all affected patients.ConclusionsThis is the first report of ophthalmoplegia in association with SSS. PMID:26471116

  6. Underwater MASW to evaluate stiffness of water-bottom sediments

    USGS Publications Warehouse

    Park, C.B.; Miller, R.D.; Xia, J.; Ivanov, J.; Sonnichsen, G.V.; Hunter, J.A.; Good, R.L.; Burns, R.A.; Christian, H.

    2005-01-01

    The multichannel analysis of surface waves (MASW) is initially intended as a land survey method to investigate the near-surface materials for their elastic properties. The acquired data are first analyzed for dispersion characteristics and, from these the shear-wave velocity is estimated using an inversion technique. Land applications show the potential of the MASW method to map 2D bedrock surface, zones of low strength, Poisson's ratio, voids, as well as to generate shear-wave profiles for various othe geotechnical problems. An overview is given of several underwater applications of the MASW method to characterize stiffness distribution of water-bottom sediments. The first application details the survey under shallow-water (1-6 m) in the Fraser River (Canada). The second application is an innovative experimental marine seismic survey in the North Atlantic Ocean near oil fields in Grand Bank offshore Newfoundland.

  7. Arterial Stiffness: A Nexus between Cardiac and Renal Disease

    PubMed Central

    Jia, Guanghong; Aroor, Annayya R.; Sowers, James R.

    2014-01-01

    Vascular disease is the leading cause of morbidity and mortality in the Western world, and vascular function is determined by structural and functional properties of the arterial vascular wall. Cardiorenal metabolic syndrome such as obesity, diabetes, hypertension, kidney disease, and aging are conditions that predispose to arterial stiffening, which is a pathological alteration of the vascular wall and ultimately results in target organ damage in heart and kidney. In this review, we provide new insights on the interactions between arterial stiffness, vascular resistance and pulse wave velocity as well as final end-organ damage in heart and kidney. Better understanding of the mechanisms of arterial functional and hemodynamic alteration may help in developing more refined therapeutic strategies aimed to reduce cardiovascular and chronic kidney diseases. PMID:24847335

  8. Effect of Bearing Dynamic Stiffness on Gear Vibration

    NASA Technical Reports Server (NTRS)

    Fleming, David P.

    2002-01-01

    Noise is a major consideration in the design of high performance geared transmissions, such as for helicopters. Transmission error, that is, the accuracy with which the driven gear follows the driver gear, is a common indicator of noise generation. It is well known that bearing properties have a strong influence on shaft dynamics. However, up to now the contribution of bearings to transmission error has received little attention. In this paper, a torsional-axial-lateral geared rotor analysis is used to determine dynamic transmission error as a function of bearing stiffness and damping. Bearings have a similar effect as found in shaft dynamics; transmission error can be reduced more than 10 decibels by appropriate selection of bearing properties.

  9. The role of pulmonary arterial stiffness in COPD.

    PubMed

    Weir-McCall, Jonathan R; Struthers, Allan D; Lipworth, Brian J; Houston, J Graeme

    2015-11-01

    COPD is the second most common cause of pulmonary hypertension, and is a common complication of severe COPD with significant implications for both quality of life and mortality. However, the use of a rigid diagnostic threshold of a mean pulmonary arterial pressure (mPAP) of ?25mHg when considering the impact of the pulmonary vasculature on symptoms and disease is misleading. Even minimal exertion causes oxygen desaturation and elevations in mPAP, with right ventricular hypertrophy and dilatation present in patients with mild to moderate COPD with pressures below the threshold for diagnosis of pulmonary hypertension. This has significant implications, with right ventricular dysfunction associated with poorer exercise capability and increased mortality independent of pulmonary function tests. The compliance of the pulmonary artery (PA) is a key component in decoupling the right ventricle from the pulmonary bed, allowing the right ventricle to work at maximum efficiency and protecting the microcirculation from large pressure gradients. PA stiffness increases with the severity of COPD, and correlates well with the presence of exercise induced pulmonary hypertension. A curvilinear relationship exists between PA distensibility and mPAP and pulmonary vascular resistance (PVR) with marked loss of distensibility before a rapid rise in mPAP and PVR occurs with resultant right ventricular failure. This combination of features suggests PA stiffness as a promising biomarker for early detection of pulmonary vascular disease, and to play a role in right ventricular failure in COPD. Early detection would open this up as a potential therapeutic target before end stage arterial remodelling occurs. PMID:26095859

  10. On the difference between stiff and soft membranes: Capillary Waves

    E-print Network

    Sebastian Jaksch; Olaf Holderer; Michael Ohl; Henrich Frielinghaus

    2015-08-14

    One problem of non-crystalline condensed matter (soft matter) is creating the right equilibrium between elasticity and viscosity, referred to as viscoelasticity. Manifestations of that can be found in everyday live, where the v