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1

Measuring graphene's bending stiffness  

NASA Astrophysics Data System (ADS)

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. [1] A. Fasolino et al., Nat. Mater. (2007) [2] D. R. Nelson and L. Peliti, J Physique (1987) [3] F. L. Braghin and N. Hasselmann, Phys Rev B (2010)

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

2

Liver Stiffness Measurement among Patients with Chronic Hepatitis B and C: Results from a 5-Year Prospective Study  

PubMed Central

Liver stiffness measurement (LSM) is widely used to evaluate liver fibrosis, but longitudinal studies are rare. The current study was aimed to monitor LSM during follow-up, and to evaluate the association of LSM data with mortality and liver-related outcomes. We included all patients with chronic viral hepatitis and valid LSM using Fibroscan. Information about liver biopsy, antiviral treatment, and clinical outcome was obtained from medical records and national registers. The study included 845 patients: 597 (71%) with hepatitis C virus (HCV), 235 (28%) with hepatitis B virus (HBV) and 13 (2%) with dual infection. The initial LSM distribution (<7/7–9.9/10–16.9/?17 kPa) was 58%/16%/14%/12%. Among patients with initial LSM values of 7–9.9 kPa, 60% of HCV patients and 83% of HBV patients showed LSM values of <7 kPa at the latest follow-up. Progression rates (defined as >20% and >2 kPa increase, with one measure >7 kPa) were 3.4/100 person years (PY) for HCV and 1.5/100 PY for HBV infected patients. Patients with LSM values of ?17 kPa had the same liver-related complication incidence as patients with biopsy-proven cirrhosis (11.1 versus 12.1/100 PY). Thirteen liver-related deaths occurred among HCV patients (0.6/100 PY), but none among HBV patients. Among patients who died of liver-related causes, all but one had baseline LSM values of ?17 kPa. Overall, patients with LSM values <17 kPa were not associated with adverse outcomes. In contrast, LSM values ?17 kPa were associated with significant risk of liver-related problems. The results of the current study suggest that clinical decisions should not be taken based on a single LSM measurement. PMID:25369038

Christiansen, Karen M.; Mössner, Belinda K.; Hansen, Janne F.; Jarnbjer, Erik F.; Pedersen, Court; Christensen, Peer B.

2014-01-01

3

Autonomous mobile robot fast hybrid decision system DT-FAM based on laser system measurement LSM  

NASA Astrophysics Data System (ADS)

In this paper the new intelligent data processing system for mobile robot is described. The robot perception uses the LSM - Laser System Measurement. The innovative fast hybrid decision system is based on fuzzy ARTMAP supported by decision tree. The virtual laboratory of robotics was implemented to execute experiments.

B?dkowski, Janusz; Jankowski, Stanis?aw

2006-10-01

4

The Frequency and Determinants of Liver Stiffness Measurement Failure: A Retrospective Study of “Real-Life” 38,464 Examinations  

PubMed Central

Objective To investigate the frequency and determinants of liver stiffness measurement (LSM) failure by means of FibroScan in “real-life” Chinese patients. Methods A total of 38,464 “real-life” Chinese patients in 302 military hospital of China through the whole year of 2013, including asymptomatic carrier, chronic hepatitis B, chronic hepatitis C, liver cirrhosis (LC), alcoholic liver disease, autoimmune liver disease, hepatocellular carcinoma (HCC) and other, were enrolled, their clinical and biological parameters were retrospectively investigated. Liver fibrosis was evaluated by FibroScan detection. S probe (for children with height less than 1.20 m) and M probe (for adults) were used. LSM failure defined as zero valid shots (unsuccessful LSM), or the ratio of the interquartile range to the median of 10 measurements (IQR/M) greater than 0.30 plus median LSM greater or equal to 7.1 kPa (unreliable LSM). Results LSM failure occurred in 3.34% of all examinations (1286 patients out of 38,464), among them, there were 958 cases (2.49%) with unsuccessful LSM, and 328 patients (0.85%) with unreliable LSM. Statistical analyses showed that LSM failure was independently associated with body mass index (BMI) greater than 30 kg/m2, female sex, age greater than 50 years, intercostal spaces (IS) less than 9 mm, decompensated liver cirrhosis and HCC patients. There were no significant differences among other diseases. By changing another skilled operator, success was achieved on 301 cases out of 1286, which reduced the failure rate to 2.56%, the decrease was significant (P<0.0001). Conclusions The principal reasons of LSM failure are ascites, obesity and narrow of IS. The failure rates of HCC, decompensated LC, elder or female patients are higher. These results emphasize the need for adequate operator training, technological improvements and optimal criteria for specific patient subpopulations. PMID:25122123

Han, Ping; Li, Fan; Li, Bing; Zang, Hong; Niu, Xiaoxia; Li, Zhongbin; Xin, Shaojie; Chen, Guofeng

2014-01-01

5

The usefulness of non-invasive liver stiffness measurements in predicting clinically significant portal hypertension in cirrhotic patients: Korean data  

PubMed Central

Background/Aims Liver stiffness measurement (LSM) has been proposed as a non-invasive method for estimating the severity of fibrosis and the complications of cirrhosis. Measurement of the hepatic venous pressure gradient (HVPG) is the gold standard for assessing the presence of portal hypertension, but its invasiveness limits its clinical application. In this study we evaluated the relationship between LSM and HVPG, and the predictive value of LSM for clinically significant portal hypertension (CSPH) and severe portal hypertension in cirrhosis. Methods LSM was performed with transient elastography in 59 consecutive cirrhotic patients who underwent hemodynamic HVPG investigations. CSPH and severe portal hypertension were defined as HVPG ?10 and ?12 mmHg, respectively. Linear regression analysis was performed to evaluate the relationship between LSM and HVPG. Diagnostic values were analyzed based on receiver operating characteristic (ROC) curves. Results A strong positive correlation between LSM and HVPG was observed in the overall population (r2=0.496, P<0.0001). The area under the ROC curve (AUROC) for the prediction of CSPH (HVPG ?10 mmHg) was 0.851, and the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for an LSM cutoff value of 21.95 kPa were 82.5%, 73.7%, 86.8%, and 66.7%, respectively. The AUROC at prediction of severe portal hypertension (HVPG ?12 mmHg) was 0.877, and the sensitivity, specificity, PPV, and NPV at LSM cutoff value of 24.25 kPa were 82.9%, 70.8%, 80.6%, and 73.9%, respectively. Conclusions LSM exhibited a significant correlation with HVPG in patients with cirrhosis. LSM could be a non-invasive method for predicting CSPH and severe portal hypertension in Korean patients with liver cirrhosis. PMID:24459641

Hong, Won Ki; Baik, Soon Koo; Shin, Seung Yong; Kim, Jung Min; Kang, Yong Seok; Lim, Yoo Li; Kim, Young Ju; Cho, Youn Zoo; Hwang, Hye Won; Lee, Jin Hyung; Chae, Myeong Hun; Kim, Hyoun A; Kang, Hye Won; Kwon, Sang Ok

2013-01-01

6

Tectorial membrane. II: Stiffness measurements in vivo.  

PubMed

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

Zwislocki, J J; Cefaratti, L K

1989-11-01

7

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

SciTech Connect

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.

Kozlov, Valentin [Karlsruhe Institute of Technology, Institut für Kernphysik, Postfach 3640, 76021 Karlsruhe (Germany)] [Karlsruhe Institute of Technology, Institut für Kernphysik, Postfach 3640, 76021 Karlsruhe (Germany); Collaboration: EDELWEISS Collaboration

2013-08-08

8

Crystal Structures of Lsm3, Lsm4 and Lsm5/6/7 from Schizosaccharomyces pombe  

PubMed Central

Sm-like (Lsm) proteins are ubiquitous and function in many aspects of RNA metabolism, including pre-mRNA splicing, nuclear RNA processing, mRNA decay and miRNA biogenesis. Here three crystal structures including Lsm3, Lsm4 and Lsm5/6/7 sub-complex from S. pombe are reported. These structures show that all the five individual Lsm subunits share a conserved Sm fold, and Lsm3, Lsm4, and Lsm5/6/7 form a heptamer, a trimer and a hexamer within the crystal lattice, respectively. Analytical ultracentrifugation indicates that Lsm3 and Lsm5/6/7 sub-complex exist in solution as a heptamer and a hexamer, respectively while Lsm4 undergoes a dynamic equilibrium between monomer and trimer in solution. RNA binding assays show that Lsm2/3 and Lsm5/6/7 bind to oligo(U) whereas no RNA binding is observed for Lsm3 and Lsm4. Analysis of the inter-subunit interactions in Lsm5/6/7 reveals the organization order among Lsm5, Lsm6 and Lsm7. PMID:22615807

Bowler, Matthew W.; Song, Haiwei

2012-01-01

9

Measuring Interfacial Stiffness of Adhesively-Bonded Wood  

E-print Network

1 Measuring Interfacial Stiffness of Adhesively-Bonded Wood Edward A. Le FPInnovations - Engineered Interfacial Stiffness of Adhesively-Bonded Wood Abstract Future Abstract (100 to 150 words) 1. Introduction Adhesive bonds in wood composites have two roles. The first is to hold elements of the composite together

Nairn, John A.

10

Measurement of normal contact stiffness of fractal rough surfaces  

E-print Network

We investigate the effects of roughness and fractality on the normal contact stiffness of rough surfaces. Samples of isotropically roughened aluminium surfaces are considered. The roughness and fractal dimension were altered through blasting using different sized particles. Subsequently, surface mechanical attrition treatment (SMAT) was applied to the surfaces in order to modify the surface at the microscale. The surface topology was characterised by interferometry based profilometry. The normal contact stiffness was measured through nanoindentation with a flat tip utilising the partial unloading method. We focus on establishing the relationships between surface stiffness and roughness, combined with the effects of fractal dimension. The experimental results, for a wide range of surfaces, showed that the measured contact stiffness depended very closely on surfaces' root mean squared (RMS) slope and their fractal dimension, with correlation coefficients of around 90\\%, whilst a relatively weak correlation coefficient of 57\\% was found between the contact stiffness and RMS roughness.

Chongpu Zhai; Sébastien Bevand; Yixiang Gan; Dorian Hanaor; Gwénaëlle Proust; Bruno Guelorget; Delphine Retraint

2014-09-03

11

Measuring Ascending Aortic Stiffness In Vivo in Mice Using Ultrasound  

PubMed Central

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

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

12

The measurement of plain weft-knitted fabric stiffness  

NASA Astrophysics Data System (ADS)

A new instrument and a test method are presented in this paper that can evaluate the stiffness of plain weft-knitted fabrics. The WIRA Instrumentation Tester can measure torsion data for various flexible fibre assemblies whilst they are being twisted. The torsional properties of two types of fabrics, namely nonwoven and knitted fabrics, were analyzed. Then, comparisons between bending rigidity and torsional rigidity have been conducted using FAST-2, Shirley, Heart Loop and the new WIRA method for the assessment of fabric stiffness. The results show high correlation between bending rigidity and torsional rigidity in assessment of nonwoven fabric stiffness; they also reveal that the WIRA tester and torsional rigidity are more suitable for characterizing the stiffness of plain weft-knitted fabrics than the other test methods.

Haji Mohamad, Ayhan; Cassidy, Thomas; Brydon, Alan; Halley, Dave

2012-05-01

13

A simple method for measuring stiffness during running.  

PubMed

The spring-mass model, representing a runner as a point mass supported by a single linear leg spring, has been a widely used concept in studies on running and bouncing mechanics. However, the measurement of leg and vertical stiffness has previously required force platforms and high-speed kinematic measurement systems that are costly and difficult to handle in field conditions. We propose a new "sine-wave" method for measuring stiffness during running. Based on the modeling of the force-time curve by a sine function,this method allows leg and vertical stiffness to be estimated from just a few simple mechanical parameters: body mass, forward velocity, leg length, flight time, and contact time. We compared this method to force-platform-derived stiffness measurements for treadmill dynamometer and overground running conditions, at velocities ranging from 3.33 m.s-1 to maximal running velocity in both recreational and highly trained runners. Stiffness values calculated with the proposed method ranged from 0.67 % to 6.93 % less than the force platform method, and thus were judged to be acceptable. Furthermore, significant linear regressions (p < 0.01) close to the identity line were obtained between force platform and sine-wave model values of stiffness. Given the limits inherent in the use of the spring-mass model, it was concluded that this sine-wave method allows leg and stiffness estimates in running on the basis of a few mechanical parameters, and could be useful in further field measurements. PMID:16082017

Morin, Jean Benoît; Dalleau, Georges; Kyröläinen, Heikki; Jeannin, Thibault; Belli, Alain

2005-05-01

14

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

PubMed

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

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

2014-02-28

15

Relationship of Liver Stiffness and Controlled Attenuation Parameter Measured by Transient Elastography with Diabetes Mellitus in Patients with Chronic Liver Disease  

PubMed Central

High prevalence of diabetes mellitus in patients with liver cirrhosis has been reported in many studies. The aim of our study was to evaluate the relationship of hepatic fibrosis and steatosis assessed by transient elastography with diabetes in patients with chronic liver disease. The study population consisted of 979 chronic liver disease patients. Liver fibrosis and steatosis were assessed by liver stiffness measurement (LSM) and controlled attenuation parameter (CAP) on transient elastography. Diabetes was diagnosed in 165 (16.9%) of 979 patients. The prevalence of diabetes had significant difference among the etiologies of chronic liver disease. Higher degrees of liver fibrosis and steatosis, assessed by LSM and CAP score, showed higher prevalence of diabetes (F0/1 [14%], F2/3 [18%], F4 [31%], P<0.001; S0/1 [15%], S2 [17%], S3 [26%], P=0.021). Multivariate analysis showed that the independent predictive risk factors for diabetes were hypertension (OR, 1.98; P=0.001), LSM F4 (OR, 1.86; P=0.010), male gender (OR, 1.60; P=0.027), and age>50 yr (OR, 1.52; P=0.046). The degree of hepatic fibrosis but not steatosis assessed by transient elastography has significant relationship with the prevalence of diabetes in patients with chronic liver disease. Graphical Abstract PMID:25120322

Kim, So Hyun; Lee, Jun Hee; Cho, Ju Yeon; Sohn, Won; Gwak, Geum-Youn; Choi, Moon Seok; Lee, Joon Hyeok; Koh, Kwang Cheol; Paik, Seung Woon; Yoo, Byung Chul

2014-01-01

16

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

E-print Network

Multijoint Muscle Regulation Mechanisms Examined by Measured Human Arm Stiffness and EMG Signals stiffness and EMG signals. J. Neurophysiol. 81: 1458­1468, 1999. Stiffness properties of the musculo activation during static force control in the horizontal plane by means of surface electromyographic (EMG

Osu, Rieko

17

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

E-print Network

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

Gorassini, Monica

18

Bending stiffness measurements of magnetic tapes and substrates  

Microsoft Academic Search

Magnetic coatings are made up of either magnetic particles dispersed in a polymeric matrix or thin continuous films of magnetic material. Magnetic tape stiffness, in both the machine and transverse directions, influences the way in which tapes conform to magnetic heads in magnetic tape drives. For this reason tape stiffness plays an important role in the friction, stiction and wear

William W. Scott; Bharat Bhushan

1997-01-01

19

Fatigue Damage Evaluation through Stiffness Measurements in Boron-Epoxy Laminates  

Microsoft Academic Search

Stiffness reductions, resulting from fatigue damage, were measured for unnotched [±45]s, [0\\/90] s, and [0\\/90\\/ ±45 ] s boron\\/epoxy laminates. Deg radation in the various in-plane stiffnesses (Exx, Byy, Gxy) were measured using a combination of uniaxial tension, rail shear, and flexure tests. An attempt was made to predict stiffness loss at failure from a secant modulus criterion. Damage growth

T. Kevin OBrien; Kenneth L. Reifsnider

1981-01-01

20

Noninvasive assessment of portal hypertension in cirrhosis: Liver stiffness and beyond  

PubMed Central

Liver stiffness measurement (LSM) is a good, but still limited tool to noninvasively assess complications and prognosis in patients with advanced liver disease. This review aims to consider the role of LSM for the diagnosis of portal hypertension-related complications and for assessment of prognosis in cirrhotic patients, and to highlight the drawbacks as well as some alternatives for improving the performance. Hence, this field is far from being closed, and deserves more attention. There is still a place for more carefully designed studies to find new, innovative and reliable approaches. PMID:25492995

Stefanescu, Horia; Procopet, Bogdan

2014-01-01

21

Sources of Variability in Musculo-Articular Stiffness Measurement  

PubMed Central

The assessment of musculo-articular stiffness (MAS) with the free-oscillation technique is a popular method with a variety of applications. This study examined the sources of variability (load applied and frequency of oscillation) when MAS is assessed. Over two testing occasions, 14 healthy men (27.7±5.2 yr, 1.82±0.04 m, 79.5±8.4 kg) were measured for isometric maximum voluntary contraction and MAS of the knee flexors using submaximal loads relative to the individual's maximum voluntary contraction (MAS%MVC) and a single absolute load (MASABS). As assessment load increased, MAS%MVC (coefficient of variation (CV) ?=? 8.1–12.1%; standard error of measurement (SEM) ?=? 51.6–98.8 Nm?1) and frequency (CV ?=? 4.8–7.0%; SEM ?=? 0.060–0.075 s?1) variability increased consequently. Further, similar levels of variability arising from load (CV ?=? 6.7%) and frequency (CV ?=? 4.8–7.0%) contributed to the overall MAS%MVC variability. The single absolute load condition yielded better reliability scores for MASABS (CV ?=? 6.5%; SEM ?=? 40.2 Nm?1) and frequency (CV ?=? 3.3%; SEM ?=? 0.039 s?1). Low and constant loads for MAS assessment, which are particularly relevant in the clinical setting, exhibited superior reliability compared to higher loads expressed as a percentage of maximum voluntary contraction, which are more suitable for sporting situations. Appropriate sample size and minimum detectable change can therefore be determined when prospective studies are carried out. PMID:23667662

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

2013-01-01

22

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

23

Measurement of Equivalent Stiffness and Damping of Shock Absorbers Mohan D. Raoa  

E-print Network

1 Measurement of Equivalent Stiffness and Damping of Shock Absorbers Mohan D. Raoa and Scott methodology for obtaining equivalent linear stiffness and damping of automotive shock absorbers for use [1]. The physical models [2-4] attempt to calculate the shock absorber force as a function

Rao, Mohan

24

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

Microsoft Academic Search

In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. The Lamb\\u000a wave velocity is directly related to the material parameters, so an effective method exists to ascertain the stiffness of\\u000a composites by measuring the velocity of these waves. In this study, a Lamb wave measurement system was used to measure the\\u000a bending and

M. D. Seale; E. I. Madaras

1999-01-01

25

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

PubMed Central

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

Tian, Lian; Chesler, Naomi C.

2012-01-01

26

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

NASA Technical Reports Server (NTRS)

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.

Zheng, Yun; Su, Chanmin; Getty, Stephanie

2010-01-01

27

Non-contact stiffness measurement of a suspended single walled carbon nanotube devices  

NASA Astrophysics Data System (ADS)

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.

Zheng, Yun; Su, Chanmin; Getty, Stephanie

2010-08-01

28

Measuring the Characteristic Topography of Brain Stiffness with Magnetic Resonance Elastography  

PubMed Central

Purpose To develop a reliable magnetic resonance elastography (MRE)-based method for measuring regional brain stiffness. Methods First, simulation studies were used to demonstrate how stiffness measurements can be biased by changes in brain morphometry, such as those due to atrophy. Adaptive postprocessing methods were created that significantly reduce the spatial extent of edge artifacts and eliminate atrophy-related bias. Second, a pipeline for regional brain stiffness measurement was developed and evaluated for test-retest reliability in 10 healthy control subjects. Results This technique indicates high test-retest repeatability with a typical coefficient of variation of less than 1% for global brain stiffness and less than 2% for the lobes of the brain and the cerebellum. Furthermore, this study reveals that the brain possesses a characteristic topography of mechanical properties, and also that lobar stiffness measurements tend to correlate with one another within an individual. Conclusion The methods presented in this work are resistant to noise- and edge-related biases that are common in the field of brain MRE, demonstrate high test-retest reliability, and provide independent regional stiffness measurements. This pipeline will allow future investigations to measure changes to the brain’s mechanical properties and how they relate to the characteristic topographies that are typical of many neurologic diseases. PMID:24312570

Murphy, Matthew C.; Huston, John; Jack, Clifford R.; Glaser, Kevin J.; Senjem, Matthew L.; Chen, Jun; Manduca, Armando; Felmlee, Joel P.; Ehman, Richard L.

2013-01-01

29

Experimental measure of arm stiffness during single reaching movements with a time-frequency analysis  

PubMed Central

We tested an innovative method to estimate joint stiffness and damping during multijoint unfettered arm movements. The technique employs impulsive perturbations and a time-frequency analysis to estimate the arm's mechanical properties along a reaching trajectory. Each single impulsive perturbation provides a continuous estimation on a single-reach basis, making our method ideal to investigate motor adaptation in the presence of force fields and to study the control of movement in impaired individuals with limited kinematic repeatability. In contrast with previous dynamic stiffness studies, we found that stiffness varies during movement, achieving levels higher than during static postural control. High stiffness was associated with elevated reflexive activity. We observed a decrease in stiffness and a marked reduction in long-latency reflexes around the reaching movement velocity peak. This pattern could partly explain the difference between the high stiffness reported in postural studies and the low stiffness measured in dynamic estimation studies, where perturbations are typically applied near the peak velocity point. PMID:23945781

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

2013-01-01

30

Experimental measure of arm stiffness during single reaching movements with a time-frequency analysis.  

PubMed

We tested an innovative method to estimate joint stiffness and damping during multijoint unfettered arm movements. The technique employs impulsive perturbations and a time-frequency analysis to estimate the arm's mechanical properties along a reaching trajectory. Each single impulsive perturbation provides a continuous estimation on a single-reach basis, making our method ideal to investigate motor adaptation in the presence of force fields and to study the control of movement in impaired individuals with limited kinematic repeatability. In contrast with previous dynamic stiffness studies, we found that stiffness varies during movement, achieving levels higher than during static postural control. High stiffness was associated with elevated reflexive activity. We observed a decrease in stiffness and a marked reduction in long-latency reflexes around the reaching movement velocity peak. This pattern could partly explain the difference between the high stiffness reported in postural studies and the low stiffness measured in dynamic estimation studies, where perturbations are typically applied near the peak velocity point. PMID:23945781

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

2013-11-01

31

Towards a Method for Peripheral Nervous System Axonal Stiffness Measurements with MEMS-based Microgrippers  

Microsoft Academic Search

We present a novel method for measuring axonal axial stiffness in genetically and metabolically challenged peripheral nerve axons using MEMS-based microgrippers. Using microgrippers with an out of plane stiffness of 122 Newtons\\/meter, we propose to apply up to 1830 muNewtons of force on axons growing in 50 ng\\/ml 7s nerve growth factor (NGF) for 4-6 days, then replated on untreated

B. E. Layton; K. B. Allen; K. A. Myers; M. D. Stokes; P. W. Baas

2005-01-01

32

Measurement of passive ankle stiffness in subjects with chronic hemiparesis using a novel ankle robot  

PubMed Central

Our objective in this study was to assess passive mechanical stiffness in the ankle of chronic hemiparetic stroke survivors and to compare it with those of healthy young and older (age-matched) individuals. Given the importance of the ankle during locomotion, an accurate estimate of passive ankle stiffness would be valuable for locomotor rehabilitation, potentially providing a measure of recovery and a quantitative basis to design treatment protocols. Using a novel ankle robot, we characterized passive ankle stiffness both in sagittal and in frontal planes by applying perturbations to the ankle joint over the entire range of motion with subjects in a relaxed state. We found that passive stiffness of the affected ankle joint was significantly higher in chronic stroke survivors than in healthy adults of a similar cohort, both in the sagittal as well as frontal plane of movement, in three out of four directions tested with indistinguishable stiffness values in plantarflexion direction. Our findings are comparable to the literature, thus indicating its plausibility, and, to our knowledge, report for the first time passive stiffness in the frontal plane for persons with chronic stroke and older healthy adults. PMID:21346215

Roy, Anindo; Bever, Christopher T.; Forrester, Larry W.; Macko, Richard F.; Hogan, Neville

2011-01-01

33

Liver Stiffness Is Associated With Risk of Decompensation, Liver Cancer, and Death in Patients With Chronic Liver Diseases: A Systematic Review and Meta-analysis  

PubMed Central

BACKGROUND & AIMS Liver stiffness measurement (LSM), using elastography, can independently predict outcomes of patients with chronic liver diseases (CLDs). However, there is much variation in reporting and consistency of findings. We performed a systematic review and meta-analysis to evaluate the association between LSM and outcomes of patients with CLDs. METHODS We performed a systematic review of the literature, through February 2013, for studies that followed up patients with CLDs prospectively for at least 6 months and reported the association between baseline LSM and subsequent development of decompensated cirrhosis or hepatocellular carcinoma (HCC), as well as mortality. Summary relative risk (RR) estimates per unit of LSM and 95% confidence intervals (CIs) were estimated using the random effects model. RESULTS Our final analysis included 17 studies, reporting on 7058 patients with CLDs. Baseline LSM was associated significantly with risk of hepatic decompensation (6 studies; RR, 1.07; 95% CI, 1.03–1.11), HCC (9 studies; RR, 1.11; 95% CI, 1.05–1.18), death (5 studies; RR, 1.22; 95% CI, 1.05–1.43), or a composite of these outcomes (7 studies; RR, 1.32; 95% CI, 1.16–1.51). We observed considerable heterogeneity among studies—primarily in the magnitude of effect, rather than the direction of effect. This heterogeneity could not be explained by variations in study locations, etiologies and stages of CLD, techniques to measure liver stiffness, adjustment for covariates, or method of imputing relationship in the meta-analysis. CONCLUSIONS Based on a meta-analysis of cohort studies, the degree of liver stiffness is associated with risk of decompensated cirrhosis, HCC, and death in patients with CLDs. LSM therefore might be used in risk stratification. PMID:23954643

Singh, Siddharth; Fujii, Larissa L.; Murad, Mohammad Hassan; Wang, Zhen; Asrani, Sumeet K.; Ehman, Richard L.; Kamath, Patrick S.; Talwalkar, Jayant A.

2013-01-01

34

Slippage toughness measurement of soft interface between stiff thin films and elastomeric substrate  

NASA Astrophysics Data System (ADS)

Traditional interfacial toughness measurements for thin films on substrate are not appropriate to the structure composed of stiff films and soft substrate. This paper describes a new bending test system to measure the interfacial toughness for the soft interface between stiff films and elastomeric substrate. The experimental setup including the loading stages is easy to operate and scanning electron microscope is used to in situ monitor the interfacial slippage during loading. The proposed bending test is conducted for silicon film on poly(dimethylsiloxane) substrate. This method demonstrates the promising way to measure the slippage toughness of soft interface involving the flexible electronics and the bio-related fields.

Huang, Yin; Feng, Xue; Qu, Binrui

2011-10-01

35

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

SciTech Connect

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.

Seale, M.D.; Madaras, E.I. (NASA Langley Research Center, Hampton, VA (United States))

1999-08-01

36

Non-invasive assessment of arterial stiffness using oscillometric blood pressure measurement  

PubMed Central

Background Arterial stiffness is a major contributor to cardiovascular diseases. Because current methods of measuring arterial stiffness are technically demanding, the purpose of this study was to develop a simple method of evaluating arterial stiffness using oscillometric blood pressure measurement. Methods Blood pressure was conventionally measured in the left upper arm of 173 individuals using an inflatable cuff. Using the time series of occlusive cuff pressure and the amplitudes of pulse oscillations, we calculated local slopes of the curve between the decreasing cuff pressure and corresponding arterial volume. Whole pressure-volume curve was derived from numerical integration of the local slopes. The curve was fitted using an equation and we identified a numerical coefficient of the equation as an index of arterial stiffness (Arterial Pressure-volume Index, API). We also measured brachial-ankle (baPWV) PWV and carotid-femoral (cfPWV) PWV using a vascular testing device and compared the values with API. Furthermore, we assessed carotid arterial compliance using ultrasound images to compare with API. Results The slope of the calculated pressure-volume curve was steeper for compliant (low baPWV or cfPWV) than stiff (high baPWV or cfPWV) arteries. API was related to baPWV (r = -0.53, P < 0.05), cfPWV (r = -0.49, P < 0.05), and carotid arterial compliance (r = 0.32, P < 0.05). A stepwise multiple regression analysis demonstrated that baPWV and carotid arterial compliance were the independent determinants of API, and that API was the independent determinant of baPWV and carotid arterial compliance. Conclusions These results suggest that our method can simply and simultaneously evaluate arterial stiffness and blood pressure based on oscillometric measurements of blood pressure. PMID:22325084

2012-01-01

37

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

NASA Technical Reports Server (NTRS)

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.

Kufeld, Robert M.

2014-01-01

38

Optoelectronic tweezers for the measurement of the relative stiffness of erythrocytes  

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

39

Muscle stiffness at different force levels measured with two myotonometric devices.  

PubMed

Myotonometric measurements are quantitative methods of muscle tone assessment and may be used as an alternative for palpation evaluation. The objective of the study was to compare the measurements of brachioradialis muscle tone and stiffness using the Myoton-3 and the Myotonometer. The participants were young males (N = 17, mean age 21 ± 1 years). The skeletal muscle state was expressed by the Myoton-3 parameters stiffness (N m(-1)), frequency (Hz) and decrement (no unit) and the Myotonometer's area under the curve (AUC) parameter (area under the curve, no unit), when muscle was at rest and during activity at 25%, 50%, 80% and 100% of maximal voluntary contraction for elbow flexors. Pearson's correlation between AUC and stiffness is r = -0.89, AUC and frequency r = -0.84 and AUC and decrement r = 0.79, p < 0.01. When comparing the results from each experimental condition separately for frequency and AUC, the correlation was from -0.63 to -0.80, for stiffness and AUC it ranged from -0.25 to -0.75 and for decrement and AUC from 0.27 to 0.74. The degree of correlation between myotonometric measurements depends on whether the measured muscle is at rest or during contraction. The correlation is diverse among related parameters. PMID:22155969

Jarocka, Ewa; Marusiak, Jaros?aw; Kumorek, Martyna; Jaskólska, Anna; Jaskólski, Artur

2012-01-01

40

Measures of Obesity Are Associated With Vascular Stiffness in Young and Older Adults  

Microsoft Academic Search

Obesity has reached epidemic levels and carries a risk for cardiovascular disease. Obesity's effects on the vascular systems of young adults and African Americans have not been well characterized. The aim of this study was to assess the association between measures of obesity and aortic stiffness in 186 young adults (20 to 40 years, 50% African American) and 177 older

Rachel P. Wildman; Rachel H. Mackey; Andrew Bostom; Trina Thompson; Kim Sutton-Tyrrell

2009-01-01

41

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

42

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

PubMed

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. PMID:25408955

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

2014-11-01

43

Reproducibility of oscillometrically measured arterial stiffness indices: Results of the SAPALDIA 3 cohort study.  

PubMed

Abstract Background. There is an increasing interest in oscillometric arterial stiffness measurement for cardiovascular risk stratification. We assessed reproducibility of the cuff-based arterial stiffness measures cardio-ankle vascular index (CAVI), brachial-ankle pulse wave velocity (baPWV) and peripheral augmentation index (pAI) in a subsample of the second follow-up of the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults (SAPALDIA 3). Methods. CAVI, baPWV and pAI were measured twice within 90 days in a representative subsample (n = 105) of SAPALDIA 3 with a mean age of 63 years (52.4% female). Results. The mean coefficient of variation for CAVI was 4.4%, baPWV 3.9%, and pAI 7.4%. The intraclass correlation coefficient ranged from 0.6 for pAI to 0.8 for CAVI, and 0.9 for baPWV. The mixed linear model revealed that 68.7%/80.1%/55.0% of the CAVI/baPWV/pAI variance was accounted for by the subject, 5.2%/8.1%/ < 0.01% by the fieldworker, 6.7%/7.8%/28.5% by variation between measurement days, and 19.4%/4%/16.5% by measurement error. Bland-Altman plots showed no particular dispersion patterns except for pAI. Conclusions. Oscillometric arterial stiffness measurement by CAVI and baPWV has proved to be highly reproducible in Caucasians. Results of the pAI showed lower reproducibility. CAVI and baPWV can be implemented as easy-to-apply arterial stiffness measures in population wide cardiovascular risk assessment in Caucasians. PMID:25594797

Endes, Simon; Caviezel, Seraina; Dratva, Julia; Schaffner, Emmanuel; Schindler, Christian; Rothe, Thomas; Rochat, Thierry; Künzli, Nino; Probst-Hensch, Nicole; Schmidt-Trucksäss, Arno

2015-04-01

44

Reproducibility of liver stiffness measurements in hepatitis C virus (HCV)-infected patients in Egypt.  

PubMed

Elastometry has demonstrated good accuracy, but little is known about its reproducibility. The aim of this study was to assess the intra- and inter-operator reproducibility of liver stiffness measurement among hepatitis C virus (HCV)-infected patients in Egypt. The study was conducted among HCV-infected patients referred for treatment evaluation in two hepatitis treatment centres of Cairo. Two operators took liver stiffness measurement two times per patient the same day. Intra- and inter-reproducibility were estimated by different methods: Bland and Altman graphics, variation coefficient, intraclass correlation coefficient and Kappa coefficient; 7.1?kPa was used as the threshold of significant (?F2) fibrosis whenever needed. Fifty-eight patients were included in the study, and 216 measurements were taken. Failure rate was 7% and associated with overweight. For a value of 7.1?kPa, the inter-operator 95% limits of agreement were estimated at ±2.88?kPa. Intra- and inter-operator coefficients of variation ranged between 11% and 15%, intraclass correlation coefficients [95% confidence interval] between 0.94 [0.86-0.97] and 0.97 [0.95-0.99], and Kappa coefficients between 0.65 [0.44-0.88] and 0.92 [0.81-1.00]. The reliability of liver stiffness measurement is questionable when considering the decision to initiate antiviral therapy because of the percentage of discordance between measurements is notable, especially in the intermediate fibrosis stages. PMID:21692948

Vignier, N; Esmat, G; Elsharkawy, A; Hassany, M; Bonnard, P; Delarocque-Astagneau, E; Said, M; Raafat, R; El-Hoseiny, M; Fontanet, A; Mohamed, M K; Vray, M

2011-07-01

45

A simple indentation device for measuring micrometer-scale tissue stiffness  

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

46

A simple indentation device for measuring micrometer-scale tissue stiffness  

PubMed Central

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

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

2012-01-01

47

Role for LSM genes in the regulation of circadian rhythms  

PubMed Central

Growing evidence suggests that core spliceosomal components differentially affect RNA processing of specific genes; however, whether changes in the levels or activities of these factors control specific signaling pathways is largely unknown. Here we show that some SM-like (LSM) genes, which encode core components of the spliceosomal U6 small nuclear ribonucleoprotein complex, regulate circadian rhythms in plants and mammals. We found that the circadian clock regulates the expression of LSM5 in Arabidopsis plants and several LSM genes in mouse suprachiasmatic nucleus. Further, mutations in LSM5 or LSM4 in Arabidopsis, or down-regulation of LSM3, LSM5, or LSM7 expression in human cells, lengthens the circadian period. Although we identified changes in the expression and alternative splicing of some core clock genes in Arabidopsis lsm5 mutants, the precise molecular mechanism causing period lengthening remains to be identified. Genome-wide expression analysis of either a weak lsm5 or a strong lsm4 mutant allele in Arabidopsis revealed larger effects on alternative splicing than on constitutive splicing. Remarkably, large splicing defects were not observed in most of the introns evaluated using RNA-seq in the strong lsm4 mutant allele used in this study. These findings support the idea that some LSM genes play both regulatory and constitutive roles in RNA processing, contributing to the fine-tuning of specific signaling pathways. PMID:25288739

Perez-Santángelo, Soledad; Mancini, Estefanía; Francey, Lauren J.; Schlaen, Ruben Gustavo; Chernomoretz, Ariel; Hogenesch, John B.; Yanovsky, Marcelo J.

2014-01-01

48

Extraction of plate bending stiffness from coincidence angles of sound transmission measurements.  

PubMed

The bending stiffness in a homogeneous, isotropic, thin plate is experimentally derived from measurements of coincidence angles extracted from supercritical sound transmission versus frequency measurements. A computer controlled turn table rotates a plate sample and a receiver array, placed in the near field of the plate. The array is used to track the transmitted sound through the plate, generated by a far-field stationary source, using beam forming. The array technique enables measurement of plates measuring only one wavelength in width. Two examples are used for proof of concept, including an aluminum plate in air and an alumina plate under water. PMID:25618078

Anderson, Brian E; Shaw, Matthew D; Harker, Blaine M

2015-01-01

49

Measurements of the exchange stiffness of YIG films using broadband ferromagnetic resonance techniques  

NASA Astrophysics Data System (ADS)

Measurements of the exchange stiffness D and the exchange constant A of Yttrium Iron Garnet (YIG) films are presented. YIG films with thicknesses from 0.9 to 2.6 µm were investigated with a microwave setup in a wide frequency range from 5 to 40 GHz. The measurements were performed with the external static magnetic field applied in-plane and out-of-plane. The method of Schreiber and Frait (1996 Phys. Rev. B 54 6473), based on the analysis of the perpendicular standing spin wave mode frequency dependence on the applied out-of-plane magnetic field, was used to obtain the exchange stiffness D. This method was modified to avoid the influence of internal magnetic fields during the determination of the exchange stiffness. Furthermore, the method was also adapted for in-plane measurements. The results obtained using all methods are compared and values of D between (5.18 ± 0.01)· 10?17 T· m2 and (5.40 ± 0.02)· 10?17 T· m2 were obtained for different thicknesses. From this, the exchange constant was calculated to be A = (3.7 ± 0.4) pJ·m?1.

Klingler, S.; Chumak, A. V.; Mewes, T.; Khodadadi, B.; Mewes, C.; Dubs, C.; Surzhenko, O.; Hillebrands, B.; Conca, A.

2015-01-01

50

Ultrasound elastography: the new frontier in direct measurement of muscle stiffness.  

PubMed

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

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

2014-11-01

51

Measuring the stiffness of bacterial cells from growth rates in hydrogels of tunable elasticity  

PubMed Central

Summary Although bacterial cells are known to experience large forces from osmotic pressure differences and their local microenvironment, quantitative measurements of the mechanical properties of growing bacterial cells have been limited. We provide an experimental approach and theoretical framework for measuring the mechanical properties of live bacteria. We encapsulated bacteria in agarose with a user-defined stiffness, measured the growth rate of individual cells, and fit data to a thin-shell mechanical model to extract the effective longitudinal Young's modulus of the cell envelope of Escherichia coli (50–150 MPa), Bacillus subtilis (100–200 MPa), and Pseudomonas aeruginosa (100–200 MPa). Our data provide estimates of cell wall stiffness similar to values obtained via the more labor-intensive technique of atomic force microscopy. To address physiological perturbations that produce changes in cellular mechanical properties, we tested the effect of A22-induced MreB depolymerization on the stiffness of E. coli. The effective longitudinal Young's modulus was not significantly affected by A22 treatment at short time scales, supporting a model in which the interactions between MreB and the cell wall persist on the same time scale as growth. Our technique therefore enables the rapid determination of how changes in genotype and biochemistry affect the mechanical properties of the bacterial envelope. PMID:22548341

Tuson, Hannah H.; Auer, George K.; Renner, Lars D.; Hasebe, Mariko; Tropini, Carolina; Salick, Max; Crone, Wendy C.; Gopinathan, Ajay; Huang, Kerwyn Casey; Weibel, Douglas B.

2012-01-01

52

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

PubMed Central

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

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

2014-01-01

53

Measuring passive myocardial stiffness in Drosophila melanogaster to investigate diastolic dysfunction.  

PubMed

Aging is marked by a decline in LV diastolic function, which encompasses abnormalities in diastolic relaxation, chamber filling and/or passive myocardial stiffness. Genetic tractability and short life span make Drosophila melanogaster an ideal organism to study the effects of aging on heart function, including senescent-associated changes in gene expression and in passive myocardial stiffness. However, use of the Drosophila heart tube to probe deterioration of diastolic performance is subject to at least two challenges: the extent of genetic homology to mammals and the ability to resolve mechanical properties of the bilayered fly heart, which consists of a ventral muscle layer that covers the contractile cardiomyocytes. Here, we argue for widespread use of Drosophila as a novel myocardial aging model by (1) describing diastolic dysfunction in flies, (2) discussing how critical pathways involved in dysfunction are conserved across species and (3) demonstrating the advantage of an atomic force microscopy-based analysis method to measure stiffness of the multilayered Drosophila heart tube versus isolated myocytes from other model systems. By using powerful Drosophila genetic tools, we aim to efficiently alter changes observed in factors that contribute to diastolic dysfunction to understand how one might improve diastolic performance at advanced ages in humans. PMID:22225769

Kaushik, Gaurav; Zambon, Alexander C; Fuhrmann, Alexander; Bernstein, Sanford I; Bodmer, Rolf; Engler, Adam J; Cammarato, Anthony

2012-08-01

54

Prediction of stroke motor recovery using reflex stiffness measures at one month.  

PubMed

This study characterizes the recovery patterns of motor impairment after stroke, and uses neuromuscular measures of the elbow joint at one month after the event to predict the ensuing recovery patterns over 12 months. Motor impairment was assessed using the Fugl-Meyer Assessment (FMA) of the upper extremity at various intervals after stroke. A parallel-cascade system identification technique characterized the intrinsic and reflex stiffness at various elbow angles. We then used "growth-mixture" modeling to identify three distinct recovery classes for FMA. While class 1 and class 3 subjects both started with low FMA, those in class 1 increased FMA significantly over 12-month recovery period, whereas those in class 3 presented no improvement. Class 2 subjects started with high FMA and also exhibited significant FMA improvement, but over a smaller range and at a slower recovery rate than class 1. Our results showed that the one-month reflex stiffness was able to distinguish between classes 1 and 3 even though both showed similarly low month-1 FMA. These findings demonstrate that, using reflex stiffness, we were able to accurately predict arm function recovery in stroke subjects over one year and beyond. This information is clinically significant and can be helpful in developing targeted therapeutic interventions. PMID:22868634

Mirbagheri, Mehdi M; Niu, Xun; Varoqui, Deborah

2012-11-01

55

A Novel Technique to Measure In Vivo Uterine Suspensory Ligament Stiffness  

PubMed Central

Objective To describe a new computer-controlled research apparatus for measuring in vivo uterine ligament force-displacement behavior and stiffness and to present pilot data in women with and without prolapse. Study Design Seventeen women with varying uterine support underwent testing in the operating room (OR) after anesthetic induction. A tripod-mounted computer-controlled linear servoactuator was used to quantify force-displacement behavior of the cervix and supporting ligaments. The servoactuator applied a caudally-directed force to a tenaculum at 4 mm/s velocity until the traction force reached 17.8N (4 lbs.). Cervix location on POP-Q in clinic, in the OR at rest, and with minimal force (<1.1N), and maximum force (17.8N) was recorded. Ligament “stiffness” between minimum and maximum force was calculated. Results The mean (SD) subject age was 54.5 (12.7) years, parity 2.9 (1.1), BMI 29.0 (4.3) kg/m2, and POP-Q point C ?3.1 (3.9) cm. POP-Q point C was most strongly correlated with cervix location at maximum force (r=+0.68, p=.003) and at rest (r=+0.62, p=.009). Associations between cervix location at minimum force (r=+0.46, p=.059) and ligament stiffness (r= ?0.44,p=.079) were not statistically significant. Cervix location in the OR with minimal traction lay below the lowest point found on POP-Q for 13 women. Conclusions POP-Q point C was strongly correlated with cervix location at rest and at maximum traction force; however only 19% of the variation in POP-Q point C location was explained by ligament stiffness. The cervix location in the OR at minimal traction lay below POP-Q point C value in ¾ of women. PMID:23747493

Smith, Tovia M.; Luo, Jiajia; Hsu, Yvonne; Ashton-Miller, James A.; Delancey, John O.L.

2013-01-01

56

Review of MRI-based measurements of pulse wave velocity: a biomarker of arterial stiffness  

PubMed Central

Atherosclerosis is the leading cause of cardiovascular disease (CVD) in the Western world. In the early development of atherosclerosis, vessel walls remodel outwardly such that the vessel luminal diameter is minimally affected by early plaque development. Only in the late stages of the disease does the vessel lumen begin to narrow—leading to stenoses. As a result, angiographic techniques are not useful for diagnosing early atherosclerosis. Given the absence of stenoses in the early stages of atherosclerosis, CVD remains subclinical for decades. Thus, methods of diagnosing atherosclerosis early in the disease process are needed so that affected patients can receive the necessary interventions to prevent further disease progression. Pulse wave velocity (PWV) is a biomarker directly related to vessel stiffness that has the potential to provide information on early atherosclerotic disease burden. A number of clinical methods are available for evaluating global PWV, including applanation tonometry and ultrasound. However, these methods only provide a gross global measurement of PWV—from the carotid to femoral arteries—and may mitigate regional stiffness within the vasculature. Additionally, the distance measurements used in the PWV calculation with these methods can be highly inaccurate. Faster and more robust magnetic resonance imaging (MRI) sequences have facilitated increased interest in MRI-based PWV measurements. This review provides an overview of the state-of-the-art in MRI-based PWV measurements. In addition, both gold standard and clinical standard methods of computing PWV are discussed. PMID:24834415

Wentland, Andrew L.; Grist, Thomas M.

2014-01-01

57

Measuring multi-joint stiffness during single movements: numerical validation of a novel time-frequency approach.  

PubMed

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

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

2012-01-01

58

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

PubMed Central

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

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

2012-01-01

59

Measurement of elastic-stiffness tensor of an anisotropic thin film by electromagnetic acoustic resonance.  

PubMed

This paper presents a contactless methodology for determining all independent elastic-stiffness coefficients Cij of a transverse isotropic thin film: C11, C12, C13, C33, and C44. The electromagnetic-acoustic-resonance technique measures the acoustic resonance frequencies of a film-coated specimen with a high accuracy, better than 10(-5), which enables determining the film Cij with the known substrate Cij. The measurement takes two steps. First, through-thickness resonance frequencies of longitudinal and shear modes are measured to determine C33 and C44, and the film thickness. Then, remaining three coefficients are deduced from measurements of the free-vibration resonance frequencies of the layer parallelepiped specimen. Simulations and experiments with monocrystal copper and titanium confirm the reliability of the resultant film Cij within 5%, when the film thickness is more than 0.5% of the substrate. PMID:12159959

Ogi, Hirotsugu; Shimoike, Goh; Takashima, Kazuki; Hirao, Masahiko

2002-05-01

60

Instrument towards Faster Diagnosis and Treatment of Prostate Cancer – Resonance Sensor Stiffness Measurements on Human Prostate Tissue in vitro  

Microsoft Academic Search

\\u000a Prostate cancer is the most common cancer among men and the methods used to detect and diagnose prostate cancer are not sufficiently\\u000a accurate. Radical prostatectomy is a surgical treatment of prostate cancer where the whole prostate is removed from the patient.\\u000a Prostate tissue stiffness can be measured with a stiffness sensitive resonance sensor. The aim of this study was to

V. Jalkanen; B. M. Andersson; O. A. Lindahl

61

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

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

62

Electrophoretic deposition of bi-layered LSM/LSM-YSZ cathodes for solid oxide fuel cell  

NASA Astrophysics Data System (ADS)

Bi-layered cathodes with the LSM/LSM-YSZ structure for solid oxide fuel cells were successfully formed on the carbon-sputtered surface of a YSZ sheet by electrophoretic deposition (EPD). The thicknesses of the first layer of LSM-YSZ (LY) and the second layer of La0.8Sr0.2MnO3 (LSM) could be controlled by adjusting the deposition time in the EPD process. The cathodic properties of the bi-layered structures were superior to those of the mono-layered structures, and were dependent on the thickness of each layer. Decreasing the thickness of the first layer and increasing that of the second layer tended to reduce both polarization and ohmic resistances. The optimal thickness of the first layer at the operating temperature of 600 °C was 4 ?m, suggesting that an effective three-phase boundary was extended from the interface between the electrolyte and cathode film to around 4 ?m thickness.

Itagaki, Yoshiteru; Watanabe, Shinji; Yamaji, Tsuyoshi; Asamoto, Makiko; Yahiro, Hidenori; Sadaoka, Yoshihiko

2012-09-01

63

Functionalized AFM probes for force spectroscopy: eigenmode shapes and stiffness calibration through thermal noise measurements  

NASA Astrophysics Data System (ADS)

The functionalization of an atomic force microscope (AFM) cantilever with a colloidal bead is a widely used technique when the geometry between the probe and the sample must be controlled, particularly in force spectroscopy. But some questions remain: how does a bead glued at the end of a cantilever influence its mechanical response? And more importantly for quantitative measurements, can we still determine the stiffness of the AFM probe with traditional techniques? In this paper, the influence of the colloidal mass loading on the eigenmode shape and resonant frequency is investigated by measuring the thermal noise on rectangular AFM microcantilevers with and without beads attached at their extremities. The experiments are performed with a home-made ultra-sensitive AFM, based on differential interferometry. The focused beam from the interferometer probes the cantilever at different positions and the spatial shapes of the modes are determined up to the fifth resonance, without external excitation. The results clearly demonstrate that the first eigenmode is almost unchanged by mass loading. However the oscillation behavior of higher resonances presents a marked difference: with a particle glued at its extremity, the nodes of the modes are displaced towards the free end of the cantilever. These results are compared to an analytical model taking into account the mass and inertial moment of the load in an Euler-Bernoulli framework, where the normalization of the eigenmodes is explicitly worked out in order to allow a quantitative prediction of the thermal noise amplitude of each mode. A good agreement between the experimental results and the analytical model is demonstrated, allowing a clean calibration of the probe stiffness.

Laurent, Justine; Steinberger, Audrey; Bellon, Ludovic

2013-06-01

64

Force Spectroscopy with Dual-Trap Optical Tweezers: Molecular Stiffness Measurements and Coupled Fluctuations Analysis  

PubMed Central

Dual-trap optical tweezers are often used in high-resolution measurements in single-molecule biophysics. Such measurements can be hindered by the presence of extraneous noise sources, the most prominent of which is the coupling of fluctuations along different spatial directions, which may affect any optical tweezers setup. In this article, we analyze, both from the theoretical and the experimental points of view, the most common source for these couplings in dual-trap optical-tweezers setups: the misalignment of traps and tether. We give criteria to distinguish different kinds of misalignment, to estimate their quantitative relevance and to include them in the data analysis. The experimental data is obtained in a, to our knowledge, novel dual-trap optical-tweezers setup that directly measures forces. In the case in which misalignment is negligible, we provide a method to measure the stiffness of traps and tether based on variance analysis. This method can be seen as a calibration technique valid beyond the linear trap region. Our analysis is then employed to measure the persistence length of dsDNA tethers of three different lengths spanning two orders of magnitude. The effective persistence length of such tethers is shown to decrease with the contour length, in accordance with previous studies. PMID:23199920

Ribezzi-Crivellari, M.; Ritort, F.

2012-01-01

65

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

PubMed Central

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

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

2013-01-01

66

Ankle ROM and stiffness measured at rest and during gait in individuals with and without diabetic sensory neuropathy  

Microsoft Academic Search

Introduction: The purpose of our study was to examinethe relationship between ankledorsiflexion(DF) range of motion (ROM) and stiffness measured at rest (passively) and plantar loading during gait in individuals with and without diabetes mellitus (DM) and sensory neuropathy. Specifically, we sought to address three questions for this at-risk patient population: (1) Does peak passive DF ROM predict ankle DF ROM

Smita Rao; Charles Saltzman; H. John Yack

2006-01-01

67

Picosecond acoustic diffraction in anisotropic thin film (µm) application to the measurement of stiffness coefficients  

NASA Astrophysics Data System (ADS)

Investigation of thin metallic film properties by means of picosecond ultrasonics has been under the scope of several studies. Generation of longitudinal and shear waves with a wave vector normal to the film free surface has been demonstrated. Such measurements can not provide complete information about properties of anisotropic films. Acute focusing of the laser pump beam (approx 0.5 µm) on the sample surface has recently allowed us to provide evidence of picosecond acoustic diffraction in thin metallic films (approx1 µm) such as aluminum, gold, copper. Waveforms have been experimentally recorded in a gold layer (2 µm thick) for several distances between pump and probe on the sample surface. Due to acoustic diffraction, the acoustic wavefronts propagate at a group velocity which differs from phase velocity in the anisotropic film. However, a specified signal processing allows us analyzing the space repartition of the acoustic wave-vectors for both longitudinal and shear waves. Four stiffness coefficients of the anisotropic gold layer could thus be recovered accurately, demonstrating the feasibility of the measurement.

Audoin, B.; Perton, M.; Chigarev, N.; Rossignol, C.

2007-12-01

68

Leg stiffness in human running: Comparison of estimates derived from previously published models to direct kinematic-kinetic measures.  

PubMed

It is not presently clear whether mathematical models used to estimate leg stiffness during human running are valid. Therefore, leg stiffness during the braking phase of ground contact of running was calculated directly using synchronous kinematic (high-speed motion analysis) and kinetic (force platform) analysis, and compared to stiffness calculated using four previously published kinetic models. Nineteen well-trained male middle distance runners (age=21.1±4.1yr; VO(2max)=69.5±7.5mlO(2)kg(-1)min(-1)) completed a series of runs of increasing speed from 2.5 to 6.5ms(-1). Leg stiffness was calculated directly from kinetic-kinematic analysis using both vertical and horizontal forces to obtain the resultant force in the line of leg compression (Model 1). Values were also estimated using four previously published mathematical models where only force platform derived and anthropometric measures were required (Models 2-5; Morin et al., 2005, Morin et al., 2011, Blum et al., 2009, Farley et al., 1993, respectively). The greatest statistical similarity between leg stiffness values occurred with Models 1 and 2. The poorest similarity occurred when values from Model 4 were compared with Model 1. Analyses suggest that the poor correlation between Model 1 other models may have resulted from errors in the estimation in change in leg length during the braking phase. Previously published mathematical models did not provide accurate leg stiffness estimates, although Model 2, used by Morin et al. (2005), provided reasonable estimates that could be further improved by the removal of systematic error using a correction factor (K=1.0496K(Model2)). PMID:22682258

Coleman, David R; Cannavan, Dale; Horne, Sara; Blazevich, Anthony J

2012-07-26

69

Genetic determinants of arterial stiffness.  

PubMed

Stiffness of large arteries (called arteriosclerosis) is an independent predictor of cardiovascular morbidity and mortality. Although previous studies have shown that arterial stiffness is moderately heritable, genetic factors contributing to arterial stiffness are largely unknown. In this paper, we reviewed the available literature on genetic variants that are potentially related to arterial stiffness. Most variants have shown mixed depictions of their association with arterial stiffness across multiple studies. Various methods to measure arterial stiffness at different arterial sites can contribute to these inconsistent results. In addition, studies in patient populations with hypertension or atherosclerosis may overestimate the impact of genetic variants on arterial stiffness. Future studies are recommended to standardize current measures of arterial stiffness in different age groups. Studies conducted in normal healthy subjects may also provide better opportunities to find novel genetic variants of arterial stiffness. PMID:25472935

Logan, Jeongok G; Engler, Mary B; Kim, Hyungsuk

2015-02-01

70

Measuring the effects of aging and sex on regional brain stiffness with MR elastography in healthy older adults.  

PubMed

Changes in tissue composition and cellular architecture have been associated with neurological disease, and these in turn can affect biomechanical properties. Natural biological factors such as aging and an individual's sex also affect underlying tissue biomechanics in different brain regions. Understanding the normal changes is necessary before determining the efficacy of stiffness imaging for neurological disease diagnosis and therapy monitoring. The objective of this study was to evaluate global and regional changes in brain stiffness as a function of age and sex, using improved MRE acquisition and processing that have been shown to provide median stiffness values that are typically reproducible to within 1% in global measurements and within 2% for regional measurements. Furthermore, this is the first study to report the effects of age and sex over the entire cerebrum volume and over the full frontal, occipital, parietal, temporal, deep gray matter/white matter (insula, deep gray nuclei and white matter tracts), and cerebellum volumes. In 45 volunteers, we observed a significant linear correlation between age and brain stiffness in the cerebrum (P<.0001), frontal lobes (P<.0001), occipital lobes (P=.0005), parietal lobes (P=.0002), and the temporal lobes (P<.0001) of the brain. No significant linear correlation between brain stiffness and age was observed in the cerebellum (P=.74), and the sensory-motor regions (P=.32) of the brain, and a weak linear trend was observed in the deep gray matter/white matter (P=.075). A multiple linear regression model predicted an annual decline of 0.011±0.002kPa in cerebrum stiffness with a theoretical median age value (76years old) of 2.56±0.08kPa. Sexual dimorphism was observed in the temporal (P=.03) and occipital (P=.001) lobes of the brain, but no significant difference was observed in any of the other brain regions (P>.20 for all other regions). The model predicted female occipital and temporal lobes to be 0.23kPa and 0.09kPa stiffer than males of the same age, respectively. This study confirms that as the brain ages, there is softening; however, the changes are dependent on region. In addition, stiffness effects due to sex exist in the occipital and temporal lobes. PMID:25698157

Arani, Arvin; Murphy, Matthew C; Glaser, Kevin J; Manduca, Armando; Lake, David S; Kruse, Scott A; Jack, Clifford R; Ehman, Richard L; Huston, John

2015-05-01

71

Strain measurement on stiff structures: experimental evaluation of three integrated measurement principles  

NASA Astrophysics Data System (ADS)

This paper presents an experimental evaluation of three different strain measuring principles. Mounted on a steel beam resembling a car engine mount, metal foil strain gauges, piezoresistive silicon strain gauges and piezoelectric patches are investigated to measure structure-borne forces to control an active mounting structure. FEA simulation determines strains to be measured in the range of 10-8 up to 10-5 m × m-1. These low strains cannot be measured with conventional metal foil strain gauges, as shown in the experiment conducted. Both piezoresistive and piezoelectric gauges show good results compared to a conventional piezoelectric force sensor. Depending on bandwidth, overload capacity and primary electronic costs, these principles seem to be worth considering in an adaptronic system design. These parameters are described in detail for the principles investigated.

Rausch, J.; Hatzfeld, C.; Karsten, R.; Kraus, R.; Millitzer, J.; Werthschützky, R.

2012-06-01

72

Microfluidic acoustic trapping force and stiffness measurement using viscous drag effect  

PubMed Central

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 24 MHz 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 (Ftrapping) and the trap stiffness (or compliance k) are experimentally determined for a streaming droplet in a microfluidic channel. Ftrapping is calibrated to viscous drag force produced from syringe pumps. Chebyshev-windowed chirp coded excitation sequences sweeping the frequency range from 18 MHz to 30 MHz 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 (Fmin,trapping) required for initially immobilizing drifting droplets is determined as a function of pulse repetition frequency (PRF), duty factor (DTF), and input voltage amplitude (Vin) to the transducer. At PRF = 0.1 kHz and DTF = 30%, Fmin,trapping is increased from 2.2 nN for Vin = 22 Vpp to 3.8 nN for Vin = 54 Vpp. With a fixed Vin = 54 Vpp and DTF = 30%, Fmin,trapping can be varied from 3.8 nN at PRF = 0.1 kHz to 6.7 nN at PRF = 0.5 kHz. 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 (Ftrapping) corresponding to the displacement (x) of a droplet from the trap center. By plotting Ftrapping – x curves for certain values of Vin (22/38/54 Vpp) at DTF = 10% and PRF = 0.1 kHz, k is measured to be 0.09, 0.14, and 0.20 nN/?m, respectively. With variable PRF from 0.1 to 0.5 kHz at Vin = 54 Vpp, k is increased from 0.20 to 0.42 nN/?m. It is shown that a higher PRF leads to a more compliant trap formation (or a stronger Ftrapping) 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

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

2013-01-01

73

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

PubMed

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

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

2013-01-01

74

Design and Vibration Measurements of High Stiffness Massive Supports for the ESRF Nano-precision Engineering Platform Integration Laboratory  

Microsoft Academic Search

Within the framework of its nano-precision engineer ing platform, the ESRF has designed, built and commissioned two massive benches. These stiff suppo rt structures will serve for measurements of precise equipment in a controlled environment analo gous to that encountered on ESRF beamlines. The bases of the benches (1600x1000x540 mm) are mad e of concrete, for the first one, and

P. Van Vaerenbergh; M. Lesourd; L. Zhang; R. Barrett; L. Eybert; T. Mairs

75

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

76

Size dependence of shape and stiffness of single sessile oil nanodroplets as measured by atomic force microscopy.  

PubMed

This article presents results and guidelines on the quantitative analysis of size, shape, and stiffness of single sessile oil droplets in air and in water. Atomic force microscopy (AFM) facilitates the analysis of micro- and nanoscale droplets which are of growing importance for agrochemicals, cosmetics, or foodstuffs containing emulsions with nanoscale compartments or droplets. Measurement of droplet shape and stiffness provides information on the contact angle with the support surface as well as the interfacial tension of the liquid-liquid interface. In this study, micro- and nanoscale droplets were imaged both in amplitude modulation (AM) and force mapping modes. The effects of the AM mode set point ratio on the measured droplet shape are discussed, and a modified spherical cap model is suggested to extract the droplet-substrate contact angle. This model was applied to a population of different sized oil droplets imaged in water and led to the finding that the contact angle with the solid support varies with the droplet size. Force mapping was undertaken to measure the droplet stiffness as a function of the droplet size. Smaller droplets were found to be stiffer, in reasonable agreement with the Attard-Miklavcic model [Langmuir 2001, 17, 8217-8223] which describes the deformation of a sessile droplet in the nonwetting regime, i.e., by partial wrapping of the droplet around the probe surface. The model limitations are discussed in terms of the diverging droplet stiffness predicted for droplet radii similar to the probe radius as well as the error propagation associated with the droplet shape function. PMID:24660961

Munz, Martin; Mills, Tom

2014-04-22

77

Stiff Quantum Polymers  

E-print Network

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.

H. Kleinert

2007-05-01

78

Plasma Fluctuation Measurements in Ion Stiffness Experiments using Phase Contrast Imaging  

NASA Astrophysics Data System (ADS)

The Phase Contrast Imaging (PCI) diagnostic on the DIII-D tokamak has recently been modified to image density fluctuations near the plasma mid-radius, thus enabling the investigation of core turbulence. Results are presented on core fluctuations in experiments exploring ion profile stiffness [1], i.e. the degree of sensitivity of ion temperature profiles to heat flux variations. In these experiments, plasmas were heated by neutral beams (NBI) configured to provide both high and low input torque; the injected NBI power was varied at constant torque to evaluate profile stiffness. A preliminary analysis indicates a decreased stiffness at high rotation in the outer half of the plasma. The toroidal rotation depends primarly on torque, with little or no dependence on input power. The amplitude of fluctuations increases with decreasing rotation, and the power spectra at similar torque have quantitatively similar shapes and values with little dependence on input power. Correlation lengths depend neither on torque nor input power. PCI power spectra and correlation lengths are evaluated and compared to non-linear gyro-kinetic simulations using the GYRO code. 6pt [1] J.E. Kinsey, et al., Bull. Am. Phys. Soc. 56, 282 (2011).

Marinoni, A.; Rost, J. C.; Porkolab, M.; Burrell, K. H.; Candy, J.; Luce, T. C.

2012-10-01

79

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

80

A new bending stiffness measurement device to monitor the influence of different intramedullar implants during healing period.  

PubMed

To manage fractures in long bones, intramedullar implants, plates or external fixators are often used. In many cases, the implants are removed after bone consolidation. X-ray images are normally used to monitor bone formation and to determine the point of return to full load bearing and removal of the implants. However, plain radiographs give only inaccurate information about the degree of healing progress. Known quantitative methods as QCT, DEXA, etc. provide information about bone density which certainly contributes to the mechanical properties of healing bone, but they do not provide a direct measurement of the stiffness of the healing callus. In this study we present an in vivo 4-point-bending stiffness device for small animals which is designed to directly monitor the progression of the healing process. The device was tested in a bone-defect model with different test-specimens chosen to simulate the stiffness of bone at different stages of healing. To verify the results, it was tested in an animal fracture study in rabbits during the healing period with and without an intramedulary implant. Both the test-specimen and bones of the in vivo study were compared with data in a materials testing system (MTS) in four-point bending. The device was found to have a high precision and significant in vitro and in vivo correlation with the MTS. The results suggest that this measurement device has the ability to monitor the healing process of bone and to analyse the influence of degradable implants on the mechanical behaviour of bone or bone metabolism effecting pharmaceutics. PMID:18487859

Thorey, Fritz; Richter, Arne; Besdo, Silke; Hackenbroich, Christian; Meyer-Lindenberg, Andrea; Hurschler, Christof; Windhagen, Henning

2008-01-01

81

CHROMIUM POISONING OF COMPOSITE LSM/YSZ CATHODES  

E-print Network

CHROMIUM POISONING OF COMPOSITE LSM/YSZ CATHODES Janet J. Bentzen, Jørgen B. Bilde-Sørensen, Yi, during exposure at ~850°C to different chromium oxide vapour emitting materials and different current for ~1650 h, revealing a chromium containing phase at the cathode/YSZ pellet interface (dark grey phase

82

Feasibility study of superconducting LSM rocket launcher system  

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

83

Graduate School Life Science Munich (LSM) Biozentrum der Ludwig-Maximilians-  

E-print Network

Graduate School Life Science Munich (LSM) Biozentrum der Ludwig-Maximilians- Universität München 266 Subway U6 www.lsm.bio.lmu.de Graduate School Life Science Munich (LSM) Biocenter of the Ludwig LIFE SCIENCE MUNICH invites all to Thursday, November 29, 2012 at 2 pm Room B01.027, Biocenter PROGRAM

Kersting, Roland

84

Do higher dialysate calcium concentrations increase vascular stiffness in haemodialysis patients as measured by aortic pulse wave velocity?  

PubMed Central

Background Haemodialysis patients have an increased prevalence of hypertension and risk of cardiovascular mortality and stroke. Higher dialysate calcium concentrations have been reported to cause both an acute and chronic increase in arterial stiffness. We therefore looked at changes in arterial stiffness in established haemodialysis patients to determine whether there was a threshold effect of dialysate calcium concentration linked to change in arterial stiffness. Methods We performed pulse wave velocity measurements six months apart in patients dialysing with calcium concentrations of 1.0, 1.25, 1.35 and ?1.5 mmol/l. Results 289 patients, 62.2% male, mean age 65.5?±?15.7 years, weight body mass index 25.8?±?5.4 kg/m2 ,47.9% diabetic were studied. Systolic blood pressure (SBP) was 148.4?±?28.6 mmHg and diastolic blood pressure (DBP) 80.2?±?15.5 mmHg. Mean pulse wave velocity increased over time (9.66?±?2.0 vs 10.13?±?2.16 m/s; p?

2013-01-01

85

Stiff quantum polymers  

E-print Network

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.

H. Kleinert

2009-10-19

86

LSM-YSZ Cathodes with Reaction-Infiltrated Nanoparticles  

SciTech Connect

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.

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

2006-01-31

87

The Effect of Regular Exercise Training During Pregnancy on Postpartum Brachial-Ankle Pulse Wave Velocity, a Measure of Arterial Stiffness  

PubMed Central

The aim of our study was to use brachial-ankle pulse wave velocity (baPWV) measurements to noninvasively assess the effect of exercise training on arterial stiffness in normal pregnant women. Arterial stiffness was assessed at the beginning of the early second trimester of pregnancy and 1 month after delivery in 17 women with normal singleton pregnancies who exercised regularly throughout pregnancy: 81 matched controls were used for comparison. No significant differences were observed in baPWV between the exercise and control groups at the beginning of the second trimester. BaPWV 1 month after delivery (1160.2 ± 109.1 cm·second-1) was signifi-cantly higher than that in the early second trimester (1116.7 ± 87.9 cm·second-1) in the control group (indicating increased arterial stiffness), but not in the exercise group (1145.9 ± 88.1 cm/second vs 1122.7 ± 100.2 cm·second-1, respectively: not significant). The results indicated that regular maternal exercise training decreased arterial stiffness in normal pregnant women, which suggests that regular exercise may help prevent hypertensive disorders during pregnancy. Key pointsRegular maternal exercise training decreased arterial stiffness in normal pregnant women, which suggests that regular exercise may help prevent hypertensive disorders during pregnancy.Maternal exercise suggests that disturbances in arterial function during pregnancy may be prevented by regular exercise. PMID:24149358

Kawabata, Ikuno; Nakai, Akihito; Sekiguchi, Atsuko; Inoue, Yuko; Takeshita, Toshiyuki

2012-01-01

88

Preparation of LSM–YSZ composite powder for anode of solid oxide electrolysis cell and its activation mechanism  

Microsoft Academic Search

Sr-doped LaMnO3 and Yttria stabilized zirconia (LSM–YSZ) composite powder is synthesized by the preparation of LSM on submicron-sized YSZ particles using an in-situ glycin–nitrate combustion method for solid oxide electrolysis cells (SOEC) in this paper. LSM–YSZ composite powder and the relevant LSM powder are characterized by XRD and FESEM. The results show that LSM–YSZ is net-porous composite powder while YSZ

Mingde Liang; Bo Yu; Mingfen Wen; Jing Chen; Jingming Xu; Yuchun Zhai

2009-01-01

89

Fabrication of elastomer pillar arrays with modulated stiffness for cellular force measurements  

E-print Network

with their environment, it is important to control the mechanical properties of the cell's environment, and measure the forces exerted by the cell. Previous work has demonstrated the importance of the rigidity of the cell between normal and transformed cancerous cells. In addi- tion, Engler et al.7 showed that the rigidity

Hone, James

90

COMMUNICATION Stiffness of desiccating insect wings  

Microsoft Academic Search

The stiffness of insect wings is typically determined through experimental measurements. Such experiments are performed on wings removed from insects. However, the wings are subject to desiccation which typically leads to an increase in their stiffness. Although this effect of desiccation is well known, a comprehensive study of the rate of change in stiffness of desiccating insect wings would be

T. E. Mengesha; R. R. Vallance; R. Mittal

2011-01-01

91

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

92

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

SciTech Connect

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.

Brown, Eric [Los Alamos National Laboratory

2012-06-07

93

Influence of alumina impurities on microstructure of LSM–CeO 2 composites  

Microsoft Academic Search

A two-phase model composite of LSM–CeO2 was developed to simulate triple phase boundaries of SOFC and to study the impact of alumina impurities on the microstructure. Interfaces between cerium oxide and 10at.% strontium-doped lanthanum manganite (LSM) were characterized using X-ray diffraction, atomic-force microscopy, focused ion beam milling, field-emission scanning electron microscopy, X-ray energy dispersive spectroscopy and transmission electron microscopy. LSM,

Sanjit Bhowmick; Yuan Xue; Jonathan Winterstein; C. Barry Carter

2011-01-01

94

Diagnosis of GLDAS LSM based aridity index and dryland identification.  

PubMed

The identification of dryland areas is crucial for guiding policy aimed at intervening in water-stressed areas and addressing the perennial livelihood or food insecurity of these areas. However, the prevailing aridity indices (such as UNEP aridity index) have methodological limitations that restrict their use in delineating drylands and may be insufficient for decision-making frameworks. In this study, we propose a new aridity index based on based on 3 decades of soil moisture time series by accounting for site-specific soil and vegetation that partitions precipitation into the competing demands of evaporation and runoff. Our proposed aridity index is the frequency at which the dominant soil moisture value at a location is not exceeded by the dominant soil moisture values in all of the other locations. To represent the dominant spatial template of the soil moisture conditions, we extract the first eigenfunction from the empirical orthogonal function (EOF) analysis from 3 GLDAS land surface models (LSMs): VIC, MOSAIC and NOAH at 1 × 1 degree spatial resolution. The EOF analysis reveals that the first eigenfunction explains 33%, 43% and 47% of the VIC, NOAH and MOSAIC models, respectively. We compare each LSM aridity indices with the UNEP aridity index, which is created based on LSM data forcings. The VIC aridity index displays a pattern most closely resembling that of UNEP, although all of the LSM-based indices accurately isolate the dominant dryland areas. The UNEP classification identifies portions of south-central Africa, southeastern United States and eastern India as drier than predicted by all of the LSMs. The NOAH and MOSAIC LSMs categorize portions of southwestern Africa as drier than the other two classifications, while all of the LSMs classify portions of central India as wetter than the UNEP classification. We compare all aridity maps with the long-term average NDVI values. Results show that vegetation cover in areas that the UNEP index classifies as drier than the other three LSMs (NDVI values are mostly greater than 0). Finally, the unsupervised clustering of global land surface based on long-term mean temperature and precipitation, soil texture and land slope reveals that areas classified as dry by the UNEP index but not by the LSMs do not have dry region characteristics. The dominant cluster for these areas has high water holding capacity. We conclude that the LSM-based aridity index may identify dryland areas more effectively than the UNEP aridity index because the former incorporates the role of vegetation and soil in the partitioning of precipitation into evaporation, runoff and infiltration. PMID:23500019

Ghazanfari, Sadegh; Pande, Saket; Hashemy, Mehdy; Sonneveld, Ben

2013-04-15

95

Development of LSM\\/YSZ composite cathode for anode-supported solid oxide fuel cells  

Microsoft Academic Search

This paper presents the effect of (La,Sr)MnO3 (LSM) stoichiometry on the polarization behaviour of LSM\\/Y2O3-ZrO2 (YSZ) composite cathodes. The composite cathode made of A-site deficient (La0.85Sr0.15)0.9MnO3 (LSM-B) showed much lower electrode interfacial resistance and overpotential losses than that made of stoichiometric (La0.85Sr0.15)1.0MnO3 (LSM-A). The much poorer performance of the latter is believed to be due to the formation of resistive

Y. J. Leng; S. H. Chan; K. A. Khor; S. P. Jiang

2004-01-01

96

Stiffness of desiccating insect wings.  

PubMed

The stiffness of insect wings is typically determined through experimental measurements. Such experiments are performed on wings removed from insects. However, the wings are subject to desiccation which typically leads to an increase in their stiffness. Although this effect of desiccation is well known, a comprehensive study of the rate of change in stiffness of desiccating insect wings would be a significant aid in planning experiments as well as interpreting data from such experiments. This communication presents a comprehensive experimental analysis of the change in mass and stiffness of gradually desiccating forewings of Painted Lady butterflies (Vanessa?cardui). Mass and stiffness of the forewings of five butterflies were simultaneously measured every 10 min over a 24 h period. The averaged results show that wing mass declined exponentially by 21.1% over this time period with a time constant of 9.8 h, while wing stiffness increased linearly by 46.2% at a rate of 23.4 µN mm(-1) h(-1). For the forewings of a single butterfly, the experiment was performed over a period of 1 week, and the results show that wing mass declined exponentially by 52.2% with a time constant of 30.2 h until it reached a steady-state level of 2.00 mg, while wing stiffness increased exponentially by 90.7% until it reached a steady-state level of 1.70 mN mm(-1). PMID:21160117

Mengesha, T E; Vallance, R R; Mittal, R

2011-03-01

97

Tectorial Membrane Stiffness Gradients  

PubMed Central

The mammalian inner ear processes sound with high sensitivity and fine resolution over a wide frequency range. The underlying mechanism for this remarkable ability is the “cochlear amplifier”, which operates by modifying cochlear micromechanics. However, it is largely unknown how the cochlea implements this modification. Although gradual improvements in experimental techniques have yielded ever-better descriptions of gross basilar membrane vibration, the internal workings of the organ of Corti and of the tectorial membrane have resisted exploration. Although measurements of cochlear function in mice with a gene mutation for ?-tectorin indicate the tectorial membrane's key role in the mechanoelectrical transformation by the inner ear, direct experimental data on the tectorial membrane's physical properties are limited, and only a few direct measurements on tectorial micromechanics are available. Using the hemicochlea, we are able to show that a tectorial membrane stiffness gradient exists along the cochlea, similar to that of the basilar membrane. In artificial perilymph (but with low calcium), the transversal and radial driving point stiffnesses change at a rate of –4.0 dB/mm and ?4.9 dB/mm, respectively, along the length of the cochlear spiral. In artificial endolymph, the stiffness gradient for the transversal component was –3.4 dB/mm. Combined with the changes in tectorial membrane dimensions from base to apex, the radial stiffness changes would be able to provide a second frequency-place map in the cochlea. Young's modulus, which was obtained from measurements performed in the transversal direction, decreased by ?2.6 dB/mm from base to apex. PMID:17496047

Richter, Claus-Peter; Emadi, Gulam; Getnick, Geoffrey; Quesnel, Alicia; Dallos, Peter

2007-01-01

98

LSM Proteins Provide Accurate Splicing and Decay of Selected Transcripts to Ensure Normal Arabidopsis Development[W  

PubMed Central

In yeast and animals, SM-like (LSM) proteins typically exist as heptameric complexes and are involved in different aspects of RNA metabolism. Eight LSM proteins, LSM1 to 8, are highly conserved and form two distinct heteroheptameric complexes, LSM1-7 and LSM2-8,that function in mRNA decay and splicing, respectively. A search of the Arabidopsis thaliana genome identifies 11 genes encoding proteins related to the eight conserved LSMs, the genes encoding the putative LSM1, LSM3, and LSM6 proteins being duplicated. Here, we report the molecular and functional characterization of the Arabidopsis LSM gene family. Our results show that the 11 LSM genes are active and encode proteins that are also organized in two different heptameric complexes. The LSM1-7 complex is cytoplasmic and is involved in P-body formation and mRNA decay by promoting decapping. The LSM2-8 complex is nuclear and is required for precursor mRNA splicing through U6 small nuclear RNA stabilization. More importantly, our results also reveal that these complexes are essential for the correct turnover and splicing of selected development-related mRNAs and for the normal development of Arabidopsis. We propose that LSMs play a critical role in Arabidopsis development by ensuring the appropriate development-related gene expression through the regulation of mRNA splicing and decay. PMID:23221597

Perea-Resa, Carlos; Hernández-Verdeja, Tamara; López-Cobollo, Rosa; Castellano, María del Mar; Salinas, Julio

2012-01-01

99

Lase Ultrasonic Web Stiffness tester  

SciTech Connect

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.

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

2009-01-12

100

AFM characterization of nanopositioner in-plane stiffnesses  

Microsoft Academic Search

A versatile method for measurement of in-plane stiffness of micro-elements was developed and its usefulness has been demonstrated. The in-plane stiffness of a NIST nanopositioner has been measured directly using a colloidal probe in an AFM without any fixture. Using this method it was possible to measure the in-plane stiffness at different locations of the same micro-element. The in-plane stiffness

Seung Ho Yang; Yongsik Kim; Kavuri Premsagar Purushotham; Jae-Myung Yoo; Young-Man Choi; Nicholas Dagalakis

2010-01-01

101

Tenure in transition : case of the LSM Cooperative Housing Estate, Lublin, Poland  

E-print Network

This thesis explores various tenure models as a means to understand development in transition. The emergence of new markets, aspirations, needs and varied agendas of the actors in the LSM Cooperative Housing Estate in ...

Kumar, Sanjay M

1992-01-01

102

Effect of surface stress on the stiffness of micro/nanocantilevers: Nanowire elastic modulus measured by nano-scale tensile and vibrational techniques  

NASA Astrophysics Data System (ADS)

Surface stress induced stiffness change of micro/nanocantilevers is reviewed and rigorously examined in this work. The self-equilibrium strain field of micro/nanocantilevers carrying an inherent surface stress on substrate is derived by resorting to the generalized Young-Laplace equation. It is found that the mechanism responsible for the observed stiffness change of micro/nano cantilevers originating from surface stress cannot be attributed to the development of in-plane stress near the clamp. Based on the analysis, two loading modes used in the mechanical test experiments performed on nanowire (NW) are theoretically investigated in detail: tension and electrically-induced-vibration. Lattice distortions arising from surface stress, coupled with that induced by residual strain, are shown to play a significant role in the elastic modulus measurement of NWs using an electric-field-induced vibrational mode, but have no influences on the tensile testing mode. The analytical results are validated by comparisons with molecular dynamic simulations and experimental measurements. The present results are useful in interpreting differences in observed size-dependent elasticity of NWs and developing the nano- and micro-mechanical testing techniques.

Qiao, Li; Zheng, Xiaojing

2013-01-01

103

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 , MSc Stiffness from Quiet Stance: Applicability to Parkinson's Disease Abstract In previous studies, we developed this measure to patients with Parkinson's disease (PD). We correlated the postural stiffness measure

104

Improvement of LSM performance under co-sintering at high temperature via CeO2 addition  

NASA Astrophysics Data System (ADS)

This work proposes the use of CeO2 as additive for La0.8Sr0.2MnO3 cathodes (LSM) in order to increase both their thermal stability and electrochemical properties after co-sintering with YSZ-electrolyte at 1350°C. Results show that non CeO2-added LSM is instable at 1350°C, whereas in CeO2-added LSM cathodes the instability is drastically reduced. Besides, results show a correlation between CeO2 addition into LSM and the maximum power density obtained in an YSZ-electrolyte supported single cell (300 ?m thickness) with anode and cathode co-sintered at 1350°C. Single cells with non CeO2-added LSM cathodes produce only 7 mW/cm2 at 800°C whereas in CeO2-added (12 mol%) LSM the power density rises up to 117 mW/cm2. Results suggest that CeO2 could enhance the power density by at least two ways: CeO2 doping into LSM structure and by the modification of La2Zr2O7 formation at high temperature. Finally, the CeO2 addition into LSM approach provides the highest co-sintering temperature for LSM-YSZ with a reasonable a promising electrochemical performance and without use any barrier layer between LSM-cathode and YSZ-electrolyte.

Wiff, J. P.; Jono, K.; Suzuki, M.; Suda, S.; Hashimoto, F.

2011-06-01

105

The passive stiffness of the wrist and forearm  

PubMed Central

Because wrist rotation dynamics are dominated by stiffness (Charles SK, Hogan N. J Biomech 44: 614–621, 2011), understanding how humans plan and execute coordinated wrist rotations requires knowledge of the stiffness characteristics of the wrist joint. In the past, the passive stiffness of the wrist joint has been measured in 1 degree of freedom (DOF). Although these 1-DOF measurements inform us of the dynamics the neuromuscular system must overcome to rotate the wrist in pure flexion-extension (FE) or pure radial-ulnar deviation (RUD), the wrist rarely rotates in pure FE or RUD. Instead, understanding natural wrist rotations requires knowledge of wrist stiffness in combinations of FE and RUD. The purpose of this report is to present measurements of passive wrist stiffness throughout the space spanned by FE and RUD. Using a rehabilitation robot designed for the wrist and forearm, we measured the passive stiffness of the wrist joint in 10 subjects in FE, RUD, and combinations. For comparison, we measured the passive stiffness of the forearm (in pronation-supination), as well. Our measurements in pure FE and RUD agreed well with previous 1-DOF measurements. We have linearized the 2-DOF stiffness measurements and present them in the form of stiffness ellipses and as stiffness matrices useful for modeling wrist rotation dynamics. We found that passive wrist stiffness was anisotropic, with greater stiffness in RUD than in FE. We also found that passive wrist stiffness did not align with the anatomical axes of the wrist; the major and minor axes of the stiffness ellipse were rotated with respect to the FE and RUD axes by ?20°. The direction of least stiffness was between ulnar flexion and radial extension, a direction used in many natural movements (known as the “dart-thrower's motion”), suggesting that the nervous system may take advantage of the direction of least stiffness for common wrist rotations. PMID:22649208

Charles, Steven K.; Zollo, Loredana; Guglielmelli, Eugenio; Hogan, Neville; Krebs, Hermano I.

2012-01-01

106

Surface probe measurements of the elasticity of sectioned tissue, thin gels and polyelectrolyte multilayer films: Correlations between substrate stiffness and cell adhesion  

NASA Astrophysics Data System (ADS)

Surface probe measurements of the elasticity of thin film matrices as well as biological samples prove generally important to understanding cell attachment across such systems. To illustrate this, sectioned arteries were probed by atomic force microscopy (AFM) within the smooth muscle cell (SMC)-rich medial layer, yielding an apparent Young's modulus Emedia ˜ 5-8 kPa. Polyacrylamide gels with Egel spanning several-fold above and below this range were then cast 5-70 ?m thick and coated with collagen: SMC spreading shows a hyperbolic dependence in projected cell area versus Egel. The modulus that gives half-max spreading is E1/2-spread ˜ 8-10 kPa, proving remarkably close to Emedia. More complex, layer-by-layer microfilms of poly( L-lysine)/hyaluronic acid were also tested and show equivalent trends of increased SMC spreading with increased stiffness. Adhesive spreading of cells thus seems to correlate broadly with the effective stiffness of synthetic materials and tissues.

Engler, Adam J.; Richert, Ludovic; Wong, Joyce Y.; Picart, Catherine; Discher, Dennis E.

2004-10-01

107

Measurements of the stiffness and thickness of the pavement asphalt layer using the enhanced resonance search method.  

PubMed

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

Zakaria, Nur Mustakiza; Yusoff, Nur Izzi Md; Hardwiyono, Sentot; Nayan, Khairul Anuar Mohd; El-Shafie, Ahmed

2014-01-01

108

Pat1 contributes to the RNA binding activity of the Lsm1-7-Pat1 complex.  

PubMed

A major mRNA decay pathway in eukaryotes is initiated by deadenylation followed by decapping of the oligoadenylated mRNAs and subsequent 5'-to-3' exonucleolytic degradation of the capless mRNA. In this pathway, decapping is a rate-limiting step that requires the hetero-octameric Lsm1-7-Pat1 complex to occur at normal rates in vivo. This complex is made up of the seven Sm-like proteins, Lsm1 through Lsm7, and the Pat1 protein. It binds RNA and has a unique binding preference for oligoadenylated RNAs over polyadenylated RNAs. Such binding ability is crucial for its mRNA decay function in vivo. In order to determine the contribution of Pat1 to the function of the Lsm1-7-Pat1 complex, we compared the RNA binding properties of the Lsm1-7 complex purified from pat1? cells and purified Pat1 fragments with that of the wild-type Lsm1-7-Pat1 complex. Our studies revealed that both the Lsm1-7 complex and purified Pat1 fragments have very low RNA binding activity and are impaired in the ability to recognize the oligo(A) tail on the RNA. However, reconstitution of the Lsm1-7-Pat1 complex from these components restored these abilities. We also observed that Pat1 directly contacts RNA in the context of the Lsm1-7-Pat1 complex. These studies suggest that the unique RNA binding properties and the mRNA decay function of the Lsm1-7-Pat1 complex involve cooperation of residues from both Pat1 and the Lsm1-7 ring. Finally our studies also revealed that the middle domain of Pat1 is essential for the interaction of Pat1 with the Lsm1-7 complex in vivo. PMID:25035297

Chowdhury, Ashis; Kalurupalle, Swathi; Tharun, Sundaresan

2014-09-01

109

Stiffness Control of Surgical Continuum Manipulators  

PubMed Central

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

Mahvash, Mohsen; Dupont, Pierre E.

2013-01-01

110

Haptic Identification of Stiffness and Force Magnitude Steven A. Cholewiak,  

E-print Network

Haptic Identification of Stiffness and Force Magnitude Steven A. Cholewiak, 1 Hong Z. Tan, 1 investigated the channel capacity for transmitting information through stiffness or force magnitude. Specifically, we measured the number of stiffness or force- magnitude levels that can be reliably identified

Tan, Hong Z.

111

Theoretical analysis of segmented Wolter/LSM X-ray telescope systems  

NASA Technical Reports Server (NTRS)

The Segmented Wolter I/LSM X-ray Telescope, which consists of a Wolter I Telescope with a tilted, off-axis convex spherical Layered Synthetic Microstructure (LSM) optics placed near the primary focus to accommodate multiple off-axis detectors, has been analyzed. The Skylab ATM Experiment S056 Wolter I telescope and the Stanford/MSFC nested Wolter-Schwarzschild x-ray telescope have been considered as the primary optics. A ray trace analysis has been performed to calculate the RMS blur circle radius, point spread function (PSF), the meridional and sagittal line functions (LST), and the full width half maximum (PWHM) of the PSF to study the spatial resolution of the system. The effects on resolution of defocussing the image plane, tilting and decentrating of the multilayer (LSM) optics have also been investigated to give the mounting and alignment tolerances of the LSM optic. Comparison has been made between the performance of the segmented Wolter/LSM optical system and that of the Spectral Slicing X-ray Telescope (SSXRT) systems.

Shealy, D. L.; Chao, S. H.

1986-01-01

112

Arterial Stiffness and Cardiovascular Therapy  

PubMed Central

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

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

2014-01-01

113

Aortic stiffness: pathophysiology, clinical implications, and approach to treatment  

PubMed Central

Aortic stiffness is a hallmark of aging, and classic cardiovascular risk factors play a role in accelerating this process. Current changes in medicine, which focus on preventive care, have led to a growing interest in noninvasive evaluation of aortic stiffness. Aortic stiffness has emerged as a good tool for further risk stratification because it has been linked to increased risk of atherosclerotic heart disease, myocardial infarction, heart failure, and stroke. This has led to the invention and validation of multiple methods to measure aortic stiffness. Pulse wave velocity is emerging as the gold standard for evaluation of aortic stiffness. This review focuses on the pathophysiology involved in aortic stiffness, methods available for evaluation of aortic stiffness, the importance of central pressure as a predictor of future cardiovascular events, and therapies that affect aortic stiffness. PMID:24910511

Sethi, Salil; Rivera, Oscar; Oliveros, Rene; Chilton, Robert

2014-01-01

114

Stiffness analysis and experimental validation of robotic systems  

NASA Astrophysics Data System (ADS)

Stiffness can be considered of primary importance in order to guarantee the successful use of any robotic system for a given task. Therefore, this paper proposes procedures for carrying out both numerical and experimental estimations of stiffness performance for multibody robotic systems. The proposed numerical procedure is based on models with lumped parameters for deriving the Cartesian stiffness matrix. Stiffness performance indices are also proposed for comparing stiffness performance. Then, an experimental procedure for the evaluation stiffness performance is proposed as based on a new measuring system named as Milli-CATRASYS (Milli Cassino Tracking System) and on a trilateration technique. Cases of study are reported to show the soundness and engineering feasibility of both the proposed numerical formulation for stiffness analysis and experimental validation of stiffness performance.

Carbone, Giuseppe

2011-06-01

115

Model-based estimation of knee stiffness.  

PubMed

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

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

2012-09-01

116

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

NASA Astrophysics Data System (ADS)

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.

Shigeeda, Hidenori; Okui, Akinobu; Akagi, Hirofumi

117

Electromechanical Dynamics Simulations of Superconducting LSM Rocket Launcher System in Attractive-Mode  

NASA Technical Reports Server (NTRS)

Further feasibility study on a superconducting linear synchronous motor (LSM) rocket launcher system is presented on the basis of dynamic simulations of electric power, efficiency and power factor as well as the ascending motions of the launcher and rocket. The advantages of attractive-mode operation are found from comparison with repulsive-mode operation. It is made clear that the LSM rocket launcher system, of which the long-stator is divided optimally into 60 sections according to launcher speeds, can obtain high efficiency and power factor.

Yoshida, Kinjiro; Hayashi, Kengo; Takami, Hiroshi

1996-01-01

118

Abnormal Stress?Related Measures of Arterial Stiffness in Middle?Aged and Elderly Men and Women With Impaired Fasting Glucose at Risk for a First Episode of Symptomatic Heart Failure  

PubMed Central

Background Abnormal resting arterial stiffness is present in middle?aged and elderly persons with abnormalities of fasting glucose (diabetes or impaired fasting glucose) and is associated with exercise intolerance. We sought to determine whether these same persons exhibited stress?related abnormalities of arterial stiffness. Methods and Results We analyzed dobutamine magnetic resonance stress imaging results from 373 consecutively recruited persons aged 55 to 85 years with normal fasting glucose, impaired fasting glucose, or diabetes who were at risk for but without symptomatic heart failure. Personnel blinded to participant identifiers measured arterial stiffness (brachial pulse pressure/left ventricular stroke volume indexed to body surface area, the aortic elastance index [brachial end?systolic pressure/left ventricular stroke volume indexed to body surface area], and thoracic aortic distensibility) at 80% of the maximum predicted heart rate response for age. Participants averaged 69±8 years of age; 79% were white, 92% were hypertensive, and 66% were women. After accounting for hypertension, sex, coronary artery disease, smoking, medications, hypercholesterolemia, and visceral fat, we observed an effect of glycemic status for stress measures of arterial stiffness in those with diabetes and impaired fasting glucose relative to those with normal fasting glucose (P=0.002, P=0.02, and P=0.003, respectively). Conclusion Middle? and older?aged individuals with diabetes or impaired fasting glucose have higher stress measures of arterial stiffness than those with normal fasting glucose. These data emphasize the need for future studies with larger sample sizes to determine whether stress?related elevations in arterial stiffness are related to exercise intolerance and future episodes of heart failure experienced by those with abnormalities of fasting glucose. Clinical Trial Registration URL: http://clinicaltrials.gov/. Unique identifier: NCT00542503. PMID:25589534

Vasu, Sujethra; Morgan, Timothy M.; Kitzman, Dalane W.; Bertoni, Alain; Stacey, Richard B.; Hamilton, Craig; Chiles, Caroline; Thohan, Vinay; Hundley, W. Gregory

2015-01-01

119

Measurement of arterial stiffness in subjects with and without renal disease: Are changes in the vessel wall earlier and more sensitive markers of cardiovascular disease than intima media thickness and pulse pressure?  

PubMed Central

There is increased cardiovascular (CV) mortality in subjects with chronic kidney disease (CKD). Arterial stiffness in these subjects is increased when compared to a healthy population. Markers of arterial stiffness and intima media thickness (IMT) are predictors of CV mortality. The aim of this study was to investigate whether there is any difference in markers of arterial stiffness and IMT between subjects with normal renal function and those with mild renal disease. The arterial distension waveform, IMT, diameter, and brachial blood pressure were measured to calculate Young's modulus (E) and elastic modulus (Ep) in the common carotid arteries of subjects with normal kidney function (estimated glomerular filtration rate [eGFR] >90) and those mild CKD (stage 2, eGFR 89–60). Data were available for 15 patients with normal kidney function and 29 patients with mild CKD. The subjects with mild CKD were older, but other co-variables were not significantly different. Both arterial wall stiffness parameters (E and Ep), but not IMT were significantly higher in the mild CKD group. Logistic regression demonstrated that only the arterial wall stiffness parameters (Ep and E) were independently associated with mild renal disease compared with normal, in a model adjusting for sex, age and diabetes and history of cardiovascular disease (CVD). E and Ep may be early markers of CVD in subjects with mild CKD that may manifest change before other more recognized markers such as IMT and pulse pressure. PMID:25684868

Claridge, M.; Wilmink, T.; Ferring, M.; Dasgupta, I.

2015-01-01

120

The stiff elbow.  

PubMed

Elbow motion is essential for upper extremity function to position the hand in space. Unfortunately, the elbow joint is prone to stiffness following a multitude of traumatic and atraumatic etiologies. Elbow stiffness can be diagnosed with a complete history and physical exam, supplemented with appropriate imaging studies. The stiff elbow is challenging to treat, and thus, its prevention is of paramount importance. When this approach fails, non-operative followed by operative treatment modalities should be pursued. Upon initial presentation in those who have minimal contractures of 6-month duration or less, static and dynamic splinting, serial casting, continuous passive motion, occupational/physical therapy, and manipulation are non-operative treatment modalities that may be attempted. A stiff elbow that is refractory to non-operative management can be treated surgically, either arthroscopically or open, to eliminate soft tissue or bony blocks to motion. In the future, efforts to prevent and treat elbow stiffness may target the basic science mechanisms involved. Our purpose was to review the etiologies, classification, evaluation, prevention, operative, and non-operative treatment of the stiff elbow. PMID:19350328

Nandi, Sumon; Maschke, Steven; Evans, Peter J; Lawton, Jeffrey N

2009-12-01

121

Analysis of the magnetic field and force of LSM with permanent magnet Halbach array and ironless coil  

Microsoft Academic Search

The LSM, or linear synchronous motor, with permanent magnet Halbach array and ironless coil possesses the dominant advantages of direct linear movement and being energy-saving. To analytically investigate the characteristics of this innovative LSM, its magnetic field and magnetic force are analyzed in this work. Based on the magnetic field of a single surface current, the field of a single

Xiao Zhang; Yungang Li; Hengkun Liu

2011-01-01

122

Measurements of Drag Torque and Lift Off Speed and Identification of Stiffness and Damping in a Metal Mesh Foil Bearing  

E-print Network

) of the floating test MMFB with little frictional loses at increasing loads. The measured drag torque peaks when the rotor starts and stops, and drops significantly once the bearing is airborne. The estimated rotor speed for lift-off increases linearly...

Chirathadam, Thomas A.

2010-07-14

123

Theoretical analysis of Wolter/LSM X-ray telescope systems  

NASA Technical Reports Server (NTRS)

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.

Shealy, D. L.; Chao, S.

1985-01-01

124

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 ...

125

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

NASA Technical Reports Server (NTRS)

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.

Yoshida, Kinjiro; Egashira, Tatsuya; Hirai, Ryuichi

1996-01-01

126

Reflectional transformation for structural stiffness  

SciTech Connect

This paper presents a structural reflection-related transformation for structural stiffness. The stiffness transformation addresses reflection of a structure about any of the three coordinate planes and renders the desired stiffness matrix using a stiffness matrix for the same structure before reflection. This transformation is elegant and simple, provides an efficient and technically rigorous approach to derive the required stiffness matrix without structural remodeling, and can be readily programmed to quickly perform the required matrix manipulations. 2 figs.

Vashi, K.M.

1990-01-01

127

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

128

Exercise, Vascular Stiffness, and Tissue Transglutaminase  

PubMed Central

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

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

129

Arterial Stiffness, Its Assessment, Prognostic Value, and Implications for Treatment  

Microsoft Academic Search

Arterial stiffness has been known as a sign of cardiovascular risk since the 19th century. Despite this, accurate measurement and clinical utility have only emerged in recent times. Arterial stiffness and its hemodynamic consequences are now established as predictors of adverse cardiovascular outcome. They are easily and reliably measured using a range of noninvasive techniques, which can be used readily

Audrey Adji; Michael F. O'Rourke; Mayooran Namasivayam

2011-01-01

130

Contribution of anion-? interactions to the stability of Sm/LSm proteins.  

PubMed

We have analyzed the influence of anion-? interactions to the stability of Sm/LSm assemblies. The side chain of Glu is more likely to be in anion-? interactions than Asp. Phe has the highest occurrence in these interactions than the other two ? residues. Among the anion-? residue pairs, Glu-Phe residue pair showed the maximum number of anion-?. We have found hot-spot residues forming anion-? interactions, and Glu-Phe is the most common hot-spot interacting pair. The significant numbers of anion-? interacting residues identified in the dataset were involved in the formation of multiple anion-? interactions. More than half of the residues involved in these interactions are evolutionarily conserved. The anion-? interaction energies are distance and orientation dependent. It was found that anion-? interactions showed energy less than -15 kcal mol(-1), and most of them have energy in the range -2 to -9 kcal mol(-1). Solvent accessibility pattern of Sm/LSm proteins reveals that all of the interacting residues are preferred to be in buried regions. Most of the interacting residues preferred to be in strand. A significant percentage of anion-? interacting residues are located as stabilization centers and thus might provide additional stability to these proteins. The simultaneous interaction of anions and cations on different faces of the same ?-system has been observed. On the whole, the results presented in this work will be very useful for understanding the contribution of anion-? interaction to the stability of Sm/LSm proteins. PMID:25502146

Breberina, Luka M; Mil?i?, Miloš K; Nikoli?, Milan R; Stojanovi?, Sr?an ?

2015-04-01

131

Variable stiffness torsion springs  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

132

Variable stiffness torsion springs  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

133

Normal liver stiffness in healthy adults assessed by real-time shear wave elastography and factors that influence this method.  

PubMed

Real-time shear wave elastography (SWE) is a novel two-dimensional elastographic method that is used to estimate the severity of liver fibrosis. However, the normal range of liver stiffness (LS) and the possible factors that influence SWE are not well understood. The aims of the current study are to define the normal range of LS in healthy subjects and to explore the factors that may affect SWE. A total of 509 healthy subjects underwent SWE to determine the stiffness of their livers, and the effects of gender, age and body mass index (BMI) on LS were analyzed. The effects of different factors on SWE, including the testing position, measurement depth and size of the region of interest (ROI), were analyzed in 137 subjects. SWE imaging was successfully performed in 502 healthy subjects (98.6%, 502/509). The mean value of the SWE measurements in 502 individuals was 5.10 ± 1.02 kPa, and the 95% confidence interval was 5.02-5.19 kPa (range: 2.4-8.7 kPa). We found that the detective position within the liver had a significant impact on the liver stiffness measurement (LSM), and the lowest coefficient of variation (CV = 8%) was obtained for LSMs made at segment V. LS was greater at a depth >5 cm (5.78 ± 1.66 kPa) compared with depths ?5 cm (4.66 ± 0.77 kPa, p < 0.001); LS was also greater in men than in women (5.45 ± 1.02 kPa vs. 4.89 ± 0.96 kPa, p < 0.001). However, there were no significant differences in the LS values regarding the size of the ROI, age or BMI (all p > 0.05). The mean LS value in all 502 healthy subjects was 5.10 ± 1.02 kPa. The mean LS value obtained by SWE was not influenced by the size of the ROI, age or BMI, but the mean value was significantly influenced by the different segments of the liver, the detection depth and gender. PMID:25282481

Huang, Zeping; Zheng, Jian; Zeng, Jie; Wang, Xiaoli; Wu, Tao; Zheng, Rongqin

2014-11-01

134

Elasticity of stiff biopolymers.  

PubMed

We present a statistical mechanical study of stiff polymers, motivated by experiments on actin filaments and the considerable current interest in polymer networks. We obtain simple, approximate analytical forms for the force-extension relations and compare these with numerical treatments. We note the important role of boundary conditions in determining force-extension relations. The theoretical predictions presented here can be tested against single molecule experiments on neurofilaments and cytoskeletal filaments like actin and microtubules. Our work is motivated by the buckling of the cytoskeleton of a cell under compression, a phenomenon of interest to biology. PMID:18233859

Ghosh, Abhijit; Samuel, Joseph; Sinha, Supurna

2007-12-01

135

On Zero Stiffness  

E-print Network

tables [8], com- puter screens [9] (e.g. the Apple G4 iMac), supports for industrial pipes [10,11], and rehabilitation aids [12]. In robotics the use of static balancing enables ma- nipulators to become lighter and faster, as the weight of the links... . 501–511. 23 pr e p r i n t [63] Lin PY, Shieh WB, Chen DZ. A stiffness matrix approach for the design of statically balanced planar articulated manipulators. Mechanism and Machine Theory. 2010;45(12):1877–1891. [64] Park ST, Luu TT. Techniques...

Schenk, Mark; Guest, Simon D.

2013-11-17

136

Running with a load increases leg stiffness.  

PubMed

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

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

2015-04-13

137

Stability of cobalt oxide infiltrated LSM/TZ8Y cathode for solid oxide fuel cells at intermediate temperatures  

NASA Astrophysics Data System (ADS)

The performance of a La0.4Sr0.6MnO3/8wt% Y2O3-stabilized ZrO2 (LSM/YZ8Y) composite cathode was observed to increase by post-firing doping (infiltration) of cobalt nitrate into the pores of an LSM/TZ8Y cathode in solid oxide fuel cells. Results demonstrated that cobalt nitrate decomposed into nano-sized spinel structures of Co3O4 of sizes ranging from 40 to 60 nm. The stability of a Co3O4 infiltrated LSM/TZ8Y cathode was studied under both oxidizing and reducing environments at 700°C. This dissertation studied the coarsening effects of Co3O 4 nano-particles in the pores of LSM/TZ8Y cathodes and its chemical interaction between LSM and TZ8Y during 1000 hours of exposure to air. A scanning electron microscopy (SEM) was used to observe the microstructure. Polarization curves and electrochemical impedance spectroscopy were used to electrochemically characterize LSM/TZ8Y half cells (oxygen pump) with applied cathodic currents before and after Co3O4 infiltration. The chemical interactions of Co3O4 and an LSM/TZ8Y cathode were studied under the effects of a reducing atmosphere at various currents applied to the cathode, e.g., 500mA/cm2, 1500mA/cm2 and 3A/cm 2. The corresponding partial pressure of oxygen (P O2) at the cathode was observed and calculated from a built-in oxygen sensor which monitored applied cathodic currents. Chemical reactions were characterized through the use scanning transmission electron microscopy (STEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD) analysis.

Chen, Xuan

138

Arterial stiffness in diabetes mellitus.  

PubMed

Arterial stiffness is an age-related process that is a shared consequence of numerous diseases including diabetes mellitus (DM), and is an independent predictor of mortality both in this population and in the general population. While much has been published about arterial stiffness in patients with DM, a thorough review of the current literature is lacking. Using a systematic literature search strategy, we aimed to summarize our current understanding related to arterial stiffness in DM. We review key studies demonstrating that, among patients with established DM, arterial stiffness is closely related to the progression of complications of DM, including nephropathy, retinopathy, and neuropathy. It is also becoming clear that arterial stiffness can be increased even in pre-diabetic populations with impaired glucose tolerance, and in those with the metabolic syndrome (METS), well before the onset of overt DM. Some data suggests that arterial stiffness can predict the onset of DM. However, future work is needed to further clarify whether large artery stiffness and the pulsatile hemodynamic changes that accompany it are involved in the pathogenesis of DM, and whether interventions targeting arterial stiffness are associated with improved clinical outcomes in DM. We also review of the potential mechanisms of arterial stiffness in DM, with particular emphasis on the role of advanced glycation endproducts (AGEs) and nitric oxide dysregulation, and address potential future directions for research. PMID:25558032

Prenner, Stuart B; Chirinos, Julio A

2015-02-01

139

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

SciTech Connect

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.

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

2009-01-05

140

Elastin in large artery stiffness and hypertension  

PubMed Central

Large artery stiffness, as measured by pulse wave velocity (PWV), is correlated with high blood pressure and may be a causative factor in essential hypertension. The extracellular matrix components, specifically the mix of elastin and collagen in the vessel wall, determine the passive mechanical properties of the large arteries. Elastin is organized into elastic fibers in the wall during arterial development in a complex process that requires spatial and temporal coordination of numerous proteins. The elastic fibers last the lifetime of the organism, but are subject to proteolytic degradation and chemical alterations that change their mechanical properties. This review discusses how alterations in the amount, assembly, organization or chemical properties of the elastic fibers affect arterial stiffness and blood pressure. Strategies for encouraging or reversing alterations to the elastic fibers are addressed. Methods for determining the efficacy of these strategies, by measuring elastin amounts and arterial stiffness, are summarized. Therapies that have a direct effect on arterial stiffness through alterations to the elastic fibers in the wall may be an effective treatment for essential hypertension. PMID:22290157

Wagenseil, Jessica E.; Mecham, Robert P.

2012-01-01

141

Monitoring the Bending Stiffness of DNA  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

142

Association of Arterial Stiffness with Silent Cerebrovascular Lesions: The Ohasama Study  

Microsoft Academic Search

Background: Arterial stiffness is a risk factor for symptomatic stroke, and is associated with symptomatic cerebral infarction and cognitive impairment. Hence, we hypothesized that arterial stiffness would be a significant determinant of silent cerebrovascular lesions. Methods: The subjects were 363 individuals without symptomatic cerebrovascular lesions who had their arterial stiffness assessed by brachial-ankle pulse wave velocity (baPWV) measurement. The subjects

Rieko Hatanaka; Taku Obara; Daisuke Watabe; Tomofumi Ishikawa; Takeo Kondo; Kazuki Ishikura; Tomoyuki Aikawa; Yoko Aono; Azusa Hara; Hirohito Metoki; Kei Asayama; Masahiro Kikuya; Nariyasu Mano; Takayoshi Ohkubo; Shin-Ichi Izumi; Yutaka Imai

2011-01-01

143

Arterial stiffness and wave reflections in diabetes type 2 and normal subjects  

Microsoft Academic Search

Increase vascular stiffness may be associated with increased pulse wave velocity and with greater amplitude of reflected waves from the peripherical arteries. Diabetes is associated with increased arterial stiffness. We evaluated whether diabetics had an increased aortic stiffness and an increase of augmentation index calculated as a measure of arterial wave reflexion. Aortic pressure waveforms derived both from the radial

Joao Maldonado; Telmo Pereira; Jose A. Silva; Jorge J. Polonia

2002-01-01

144

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

NASA Technical Reports Server (NTRS)

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.

Lemoine, Sandra M.

1997-01-01

145

Boundary Stiffness Regulates Fibroblast Behavior in Collagen Gels  

PubMed Central

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

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

2010-01-01

146

Estimation of myocardial mechanical properties with dynamic transverse stiffness.  

PubMed

There are currently no validated methods for accurately estimating regional ventricular mechanical properties. We recently developed a dynamic indentation system that can determine dynamic transverse stiffness (the slope of the relation between the indentation stress and indentation strain during high frequency indentations) in as little as 10 msec. The apparatus consists of an indentation probe coupled to a linear-motor and a computerized control system. This indentation system was tested on beating, canine ventricular septa that were mounted in a biaxial system that could apply strains in the plane of the septum and measure the resulting in-plane stresses. The probe indented the septa with peak displacements of 0.1-0.5 mm at frequencies of 20 and 50 Hz. The transverse stiffness was shown to be related to the in-plane stress and stiffness in the isolated septa. Dynamic transverse stiffness was then used to study the effects of myocardial perfusion on passive tissue stiffness and on contractility. In addition, the transverse stiffness was studied in intact canine hearts during diastole, where it was related to the chamber stiffness. Thus, dynamic transverse stiffness appears to allow estimation of myocardial mechanical properties. PMID:8184749

Halperin, H R; Tsitlik, J E; Rayburn, B K; Resar, J R; Livingston, J Z; Yin, F C

1993-01-01

147

Nonlinear vibration of thick stiff fabric with small flexural stiffness  

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

148

Stiffness Corrections for the Vibration Frequency of a Stretched Wire  

ERIC Educational Resources Information Center

Discusses the need of introducing corrections due to wire stiffness arising from end constraints and wire axis distribution curvature in the measurement of ac electrical frequency by exciting transverse standing waves in a stretched steel wire. (SL)

Hornung, H. G.; Durie, M. J.

1977-01-01

149

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

NASA Astrophysics Data System (ADS)

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.

Pugachev, A. O.; Deckner, M.

2012-08-01

150

Electron profile stiffness and critical gradient studies  

SciTech Connect

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.

DeBoo, J. C.; Petty, C. C.; Burrell, K. H.; Smith, S. P. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); White, A. E. [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Doyle, E. J.; Hillesheim, J. C.; Rhodes, T. L.; Schmitz, L.; Wang, G.; Zeng, L. [University of California-Los Angeles, Los Angeles, California 90095-7099 (United States); Holland, C. [University of California-San Diego, La Jolla, California 92093-0417 (United States); McKee, G. R. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2012-08-15

151

Developments in plastic wire chambers operated in the limited streamer mode (LSM detectors)  

NASA Astrophysics Data System (ADS)

We have calculated the photon detection efficiency of a wire chamber constructed with conductive nylon-66 plastic as cathode material in the photon energy range of 100 keV-1 MeV. The calculated results are compared with the results obtained with a Monte Carlo simulation using the FLUKA [1] transport code and with experimental results. We have also calculated the efficiency for copper and compared these two cathode materials. The comparison shows that wire chambers with nylon and copper cathodes are equally efficient in detecting the 100 keV-1 MeV photons. Furthermore, we have studied the different physical processes contributing to photon detection as well as the detection efficiency as a function of cathode thickness. Finally, we report some results from the first LSM detector operational tests performed with our new wire chamber testing device.

Laakso, Mikko; Kurvinen, Kari; Orava, Risto

1988-12-01

152

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

PubMed Central

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

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

2013-01-01

153

Switchable stiffness scanning microscope probe  

E-print Network

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 ...

Mueller-Falcke, Clemens T. (Clemens Tobias)

2005-01-01

154

Stiff polymer in monomer ensemble  

E-print Network

We make use of the previously developed formalism for a monomer ensemble and include angular dependence of the segments of the polymer chains thus described. In particular we show how to deal with stiffness when the polymer chain is confined to certain regions. We investigate the stiffness from the perspectives of a differential equation, integral equations, or recursive relations for both continuum and lattice models. Exact analytical solutions are presented for two cases, whereas numerical results are shown for a third case.

K. K. Muller-Nedebock; H. L. Frisch; J. K. Percus

2002-01-18

155

Arterial stiffness estimation based photoplethysmographic pulse wave analysis  

NASA Astrophysics Data System (ADS)

Arterial stiffness is one of the indices of vascular healthiness. It is based on pulse wave analysis. In the case we decompose the pulse waveform for the estimation and determination of arterial elasticity. Firstly, optically measured with photoplethysmograph and then investigating means by four lognormal pulse waveforms for which we can find very good fit between the original and summed decomposed pulse wave. Several studies have demonstrated that these kinds of measures predict cardiovascular events. While dynamic factors, e.g., arterial stiffness, depend on fixed structural features of the vascular wall. Arterial stiffness is estimated based on pulse wave decomposition analysis in the radial and tibial arteries. Elucidation of the precise relationship between endothelial function and vascular stiffness awaits still further study.

Huotari, Matti; Maatta, Kari; Kostamovaara, Juha

2010-11-01

156

Active Trunk Stiffness Increases with Co-contraction  

PubMed Central

Trunk dynamics, including stiffness, mass and damping were quantified during trunk extension exertions with and without voluntary recruitment of antagonistic co-contraction. The objective of this study was to empirically evaluate the influence of co-activation on trunk stiffness. Muscle activity associated with voluntary co-contraction has been shown to increase joint stiffness in the ankle and elbow. Although biomechanical models assume co-active recruitment causes increase trunk stiffness it has never been empirically demonstrated. Small trunk displacements invoked by pseudorandom force disturbances during trunk extension exertions were recorded from 17 subjects at two co-contraction conditions (minimal and maximal voluntary co-contraction recruitment). EMG data were recorded from eight trunk muscles as a baseline measure of co-activation. Increased EMG activity confirms that muscle recruitment patterns were different between the two co-contraction conditions. Trunk stiffness was determined from analyses of impulse response functions (IRFs) of trunk dynamics wherein the kinematics were represented as a second-order behavior. Trunk stiffness increased 37.8% (p < 0.004) from minimal to maximal co-activation. Results support the assumption used in published models of spine biomechanics that recruitment of trunk muscle co-contraction increases trunk stiffness thereby supporting conclusions from those models that co-contraction may contribute to spinal stability. PMID:16099678

Lee, Patrick J.; Rogers, Ellen L.; Granata, Kevin P.

2006-01-01

157

Dynamic dorsoventral stiffness assessment of the ovine lumbar spine.  

PubMed

Posteroanterior spinal stiffness assessments are common in the evaluating patients with low back pain. The purpose of this study was to determine the effects of mechanical excitation frequency on dynamic lumbar spine stiffness. A computer-controlled voice coil actuator equipped with a load cell and LVDT was used to deliver an oscillatory dorsoventral (DV) mechanical force to the L3 spinous process of 15 adolescent Merino sheep. DV forces (48 N peak, approximately 10% body weight) were randomly applied at periodic excitation frequencies of 2.0, 6.0, 11.7 and a 0.5-19.7 Hz sweep. Force and displacement were recorded over a 13-22 s time interval. The in vivo DV stiffness of the ovine spine was frequency dependent and varied 3.7-fold over the 0.5-19.7 Hz mechanical excitation frequency range. Minimum and maximum DV stiffness (force/displacement) were 3.86+/-0.38 and 14.1+/-9.95 N/mm at 4.0 and 19.7 Hz, respectively. Stiffness values based on the swept-sine measurements were not significantly different from corresponding periodic oscillations (2.0 and 6.0 Hz). The mean coefficient of variation in the swept-sine DV dynamic stiffness assessment method was 15%, which was similar to the periodic oscillation method (10-16%). The results indicate that changes in mechanical excitation frequency and animal body mass modulate DV spinal stiffness. PMID:16376350

Keller, Tony S; Colloca, Christopher J

2007-01-01

158

In-situ fracture stiffness determination  

NASA Astrophysics Data System (ADS)

In-situ experiments to determine the hydrologic and mechanical characteristics of large naturally occurring fractures were conducted at the NAGRA test site in Grimsel, Switzerland. In addition to seismic measurements across a fracture zone in the FRI test area and flow measurements into the zone, deformation of the fracture resulting from pressurization of the zone was also measured. The deformation is modeled in three different ways: as a mathematical crack employing linear elastic fracture mechanics; as a mathematical crack with an additional restraining stiffness between the faces of the crack, and as a row of coplanar two-dimensional cracks.

Hesler, G. J., III; Zheng, Z.; Myer, L. R.

1990-01-01

159

Variable stiffness mechanisms with SMA actuators  

Microsoft Academic Search

Variable stiffness is a new branch of smart structures development with several applications related to aircraft. Previous research indicates that temporarily reducing the stiffness of an airplane wing can decrease control actuator sizing and improve aeroelastic roll performance. Some smart materials like shape memory alloys (SMA) can change their material stiffness properties, but they tend to gain stiffness in their

Damin J. Siler; Kimberly B. Demoret

1996-01-01

160

The P body protein LSm1 contributes to stimulation of hepatitis C virus translation, but not replication, by microRNA-122  

PubMed Central

The P body protein LSm1 stimulates translation and replication of hepatitis C virus (HCV). As the liver-specific microRNA-122 (miR-122) is required for HCV replication and is associated with P bodies, we investigated whether regulation of HCV by LSm1 involves miR-122. Here, we demonstrate that LSm1 contributes to activation of HCV internal ribosome entry site (IRES)-driven translation by miR-122. This role for LSm1 is specialized for miR-122 translation activation, as LSm1 depletion does not affect the repressive function of miR-122 at 3? untranslated region (UTR) sites, or miR-122–mediated cleavage at a perfectly complementary site. We find that LSm1 does not influence recruitment of the microRNA (miRNA)-induced silencing complex to the HCV 5?UTR, implying that it regulates miR-122 function subsequent to target binding. In contrast to the interplay between miR-122 and LSm1 in translation, we find that LSm1 is not required for miR-122 to stimulate HCV replication, suggesting that miR-122 regulation of HCV translation and replication have different requirements. For the first time, we have identified a protein factor that specifically contributes to activation of HCV IRES-driven translation by miR-122, but not to other activities of the miRNA. Our results enhance understanding of the mechanisms by which miR-122 and LSm1 regulate HCV. PMID:24141094

Roberts, Ashley P. E.; Doidge, Rachel; Tarr, Alexander W.; Jopling, Catherine L.

2014-01-01

161

Stiffness after total knee arthroplasty.  

PubMed

Stiffness after total knee arthroplasty (TKA) adversely affects outcome and impacts patient function. Various risk factors for stiffness after TKA have been identified, including reduced preoperative knee range of motion, history of prior knee surgery, etiology of arthritis, incorrect positioning or oversizing of components, and incorrect gap balancing. Mechanical and associated causes, such as infection, arthrofibrosis, complex regional pain syndrome, and heterotopic ossification, secondary gain issues have also been identified. Management of stiffness following TKA can be challenging. The condition needs to be assessed and treated in a staged manner. A nonsurgical approach is the first step. Manipulation under anesthesia may be considered within the first 3 months after the index TKA, if physical therapy fails to improve the range of motion. Beyond this point, consideration should be given to surgical intervention such as lysis of adhesions, either arthroscopically or by open arthrotomy. If the cause of stiffness is deemed to be surgical error, such as component malpositioning, revision arthroplasty is indicated. The purpose of this article is to evaluate the various aspects of management of stiffness after TKA. PMID:25513992

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

2015-04-01

162

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

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

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

2014-01-01

163

Stiff polymer in monomer ensemble  

NASA Astrophysics Data System (ADS)

We employ an ordered monomer ensemble formalism in order to develop techniques to investigate a stiff polymer chain which is confined to a certain region. In particular, we calculate the segment density for a given location and segment orientation distribution within the confining geometry. With this method the role of the stiffness can be examined by means of differential equations, integral equations, or recursive relations for both continuum and lattice models. A suitable choice of lattice model permits an exact analytical solution for the segment location and orientation density for a chain between two parallel plates. For the stiff polymer in a spherical cavity we develop an integral equation formalism which is treated numerically, and in the same spherical geometry, a different model of the polymer displays a solution of a differential equation.

Müller-Nedebock, K. K.; Frisch, H. L.; Percus, J. K.

2003-01-01

164

Stiff polymer in monomer ensemble.  

PubMed

We employ an ordered monomer ensemble formalism in order to develop techniques to investigate a stiff polymer chain which is confined to a certain region. In particular, we calculate the segment density for a given location and segment orientation distribution within the confining geometry. With this method the role of the stiffness can be examined by means of differential equations, integral equations, or recursive relations for both continuum and lattice models. A suitable choice of lattice model permits an exact analytical solution for the segment location and orientation density for a chain between two parallel plates. For the stiff polymer in a spherical cavity we develop an integral equation formalism which is treated numerically, and in the same spherical geometry, a different model of the polymer displays a solution of a differential equation. PMID:12636521

Müller-Nedebock, K K; Frisch, H L; Percus, J K

2003-01-01

165

Stiff muscle fibers in calf muscles of patients with cerebral palsy lead to high passive muscle stiffness.  

PubMed

Cerebral palsy (CP), caused by an injury to the developing brain, can lead to alterations in muscle function. Subsequently, increased muscle stiffness and decreased joint range of motion are often seen in patients with CP. We examined mechanical and biochemical properties of the gastrocnemius and soleus muscles, which are involved in equinus muscle contracture. Passive mechanical testing of single muscle fibers from gastrocnemius and soleus muscle of patients with CP undergoing surgery for equinus deformity showed a significant increase in fiber stiffness (p<0.01). Bundles of fibers that included their surrounding connective tissues showed no stiffness difference (p=0.28).). When in vivo sarcomere lengths were measured and fiber and bundle stiffness compared at these lengths, both fibers and bundles of patients with CP were predicted to be much stiffer in vivo compared to typically developing (TD) individuals. Interestingly, differences in fiber and bundle stiffness were not explained by typical biochemical measures such as titin molecular weight (a giant protein thought to impact fiber stiffness) or collagen content (a proxy for extracellular matrix amount). We suggest that the passive mechanical properties of fibers and bundles are thus poorly understood. PMID:25138654

Mathewson, Margie A; Chambers, Henry G; Girard, Paul J; Tenenhaus, Mayer; Schwartz, Alexandra K; Lieber, Richard L

2014-12-01

166

The Relationship of Magnetic Stiffness Between Single and Multiple YBCO Superconductors over Permanent Magnet Guideway  

NASA Astrophysics Data System (ADS)

For YBCO bulk levitating over a permanent magnet guideway (PMG), the magnetic stiffness is connected directly with the pinning properties of the measured sample. An experimental setup has been built to investigate the vertical and lateral magnetic stiffness of five high-temperature superconducting (HTS) bulk arrays over a PMG by two methods: the additive method, i.e., calculating the summation of the measured magnetic stiffness values of each HTS bulk in the array; the direct method, i.e., measuring directly the magnetic stiffness of the HTS bulk array. From the experimental results, it is found that the resultant magnetic stiffness of the HTS bulk array composing of multiple YBCO bulk is related with the magnetic stiffness of each individual single bulk, but the additive method does not predict the magnetic stiffness of the array very well because of the interaction between adjacent HTS bulk. The resultant magnetic stiffness of the HTS bulk array is less than the summation magnetic stiffness of each single HTS bulk. One numerical method is used to calculate the magnetic stiffness for comparing with experimental results. The results may be helpful to the design and optimization of the superconducting magnetic levitation system.

Lu, Yiyun; Lu, Bingjuan; Wang, Suyu

2011-09-01

167

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

NASA Astrophysics Data System (ADS)

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.

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

168

e-mail : {js.lee, robot91, lsm}@kitech.re.kr1 , btzhang@snu.ac.kr2  

E-print Network

Algorithm based Multi-Robot Cooperation Jaeseon Lee1 , Sang-Hoon Ji1 , Sang-Moo Lee1 , Byoung-Tak Zhang2-based Multi-robot Cooperative Exploration," Control and Automation, 2007. ICCA 2007. IEEE International 1 , 1 , 1 , 2 1 , 2 e-mail : {js.lee, robot91, lsm}@kitech.re.kr1 , btzhang@snu.ac.kr2 Memetic

Zhang, Byoung-Tak

169

Stiffness Dependent Separation of Cells in a Microfluidic Device  

PubMed Central

Abnormal cell mechanical stiffness can point to the development of various diseases including cancers and infections. We report a new microfluidic technique for continuous cell separation utilizing variation in cell stiffness. We use a microfluidic channel decorated by periodic diagonal ridges that compress the flowing cells in rapid succession. The compression in combination with secondary flows in the ridged microfluidic channel translates each cell perpendicular to the channel axis in proportion to its stiffness. We demonstrate the physical principle of the cell sorting mechanism and show that our microfluidic approach can be effectively used to separate a variety of cell types which are similar in size but of different stiffnesses, spanning a range from 210 Pa to 23 kPa. Atomic force microscopy is used to directly measure the stiffness of the separated cells and we found that the trajectories in the microchannel correlated to stiffness. We have demonstrated that the current processing throughput is 250 cells per second. This microfluidic separation technique opens new ways for conducting rapid and low-cost cell analysis and disease diagnostics through biophysical markers. PMID:24146787

Wang, Gonghao; Mao, Wenbin; Byler, Rebecca; Patel, Krishna; Henegar, Caitlin; Alexeev, Alexander; Sulchek, Todd

2013-01-01

170

Stiffness of compressed fiber mats  

Microsoft Academic Search

We investigate, using an analytical and a numerical model, the in-plane stiffness of fiber mats. A mat is modeled by randomly depositing thin linear-elastic fibers on top of each other under the influence of an external pressure. The external pressure has the effect of bending the fibers over each other. The fibers are assumed rigidly bonded at contacts. For a

H. Hirvonen; J. Timonen

2000-01-01

171

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

172

Visualizing the structural evolution of LSM/xYSZ composite cathodes for SOFC by in-situ neutron diffraction.  

PubMed

Thermal stability of composite cathodes for solid oxide fuel cells, the mixtures of (La0.8Sr0.2)0.95MnO(3-?) (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

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

2014-01-01

173

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

SciTech Connect

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.

Chen, Yan [ORNL] [ORNL; Yang, Ling [ORNL] [ORNL; Ren, Fei [ORNL] [ORNL; An, Ke [ORNL] [ORNL

2014-01-01

174

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

PubMed Central

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

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

2014-01-01

175

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

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

176

Chains of oscillators with negative stiffness elements  

NASA Astrophysics Data System (ADS)

Negative stiffness is not allowed by thermodynamics and hence materials and systems whose global behaviour exhibits negative stiffness are unstable. However the stability is possible when these materials/systems are elements of a larger system sufficiently stiff to stabilise the negative stiffness elements. In order to investigate the effect of stabilisation we analyse oscillations in a chain of n linear oscillators (masses and springs connected in series) when some of the springs' stiffnesses can assume negative values. The ends of the chain are fixed. We formulated the necessary stability condition: only one spring in the chain can have negative stiffness. Furthermore, the value of negative stiffness cannot exceed a certain critical value that depends upon the (positive) stiffnesses of other springs. At the critical negative stiffness the system develops an eigenmode with vanishing frequency. In systems with viscous damping vanishing of an eigenfrequency does not yet lead to instability. Further increase in the value of negative stiffness leads to the appearance of aperiodic eigenmodes even with light damping. At the critical negative stiffness the low dissipative mode becomes non-dissipative, while for the high dissipative mode the damping coefficient becomes as twice as high as the damping coefficient of the system. A special element with controllable negative stiffness is suggested for designing hybrid materials whose stiffness and hence the dynamic behaviour is controlled by the magnitude of applied compressive force.

Pasternak, Elena; Dyskin, Arcady V.; Sevel, Greg

2014-12-01

177

The electrochemical performance of LSM\\/zirconia–yttria interface as a function of a-site non-stoichiometry and cathodic current treatment  

Microsoft Academic Search

The adhesion and the electrochemical performance of Sr doped LaMnO3 (LSM) electrode with zirconia–yttria electrolyte has been investigated as a function of the A-site non-stoichiometry. In addition the effect of cathodic current treatment on the electrode resistance and the mechanism of oxygen reduction have been carefully studied. The LSM\\/electrolyte interface region was examined by SEM\\/EDS and XRD. The adhesion of

S. P Jiang; J. G Love; J. P Zhang; M Hoang; Y Ramprakash; A. E Hughes; S. P. S Badwal

1999-01-01

178

Relative stiffness of flat conductor cables  

NASA Technical Reports Server (NTRS)

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.

Hankins, J. D.

1976-01-01

179

Conservation Assessment for Groundcedar and Stiff  

E-print Network

;EXECUTIVE SUMMARY Stiff clubmoss (Lycopodium annotinum L.) and groundcedar (Lycopodium complanatum L.; synonym = Diphasiastrum complanatum [L.] Holub.) (Lycopodiaceae) are circumboreal clubmoss species events and invasion by noxious weeds and other invasive plants. Key words: Lycopodium, stiff clubmoss

180

Direct Stiffness Analysis of Lateral Buckling  

Microsoft Academic Search

A direct stiffness method of analyzing the elastic ftexural-torsional buckling of rigid-jointed plane frames composed of l-section members and subjected to in-plane loads is presented. The in-plane stiffness matrix and the fixed-end resultants are obtained from the member stiffness matrices derived from the in-plane differential equations. These member stiffness matrices are assembled and solved, and their solutions are used to

P. Vacharajittiphan; N. S. Trahair

1974-01-01

181

Direct Stiffness Analysis of Lateral Buckling  

Microsoft Academic Search

A direct stiffness method of analyzing the elastic ftexural-torsional buckling of rigid-jointed plane frames composed of l-section members and subjected to in-plane loads is presented. The in-plane stiffness matrix and the fixed-end resultants are obtained from the member stiffness matrices derived from the in-plane differential equations. These member stiffness matrices are assembled and solved, and their solutions are used to

P. Vacharajittiphan; N. S. Trahair

1994-01-01

182

Multi-fingered haptic palpation utilizing granular jamming stiffness feedback actuators  

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

183

Surface probe measurements of the elasticity of sectioned tissue, thin gels and polyelectrolyte multilayer films: Correlations between substrate stiffness and cell adhesion  

Microsoft Academic Search

Surface probe measurements of the elasticity of thin film matrices as well as biological samples prove generally important to understanding cell attachment across such systems. To illustrate this, sectioned arteries were probed by atomic force microscopy (AFM) within the smooth muscle cell (SMC)-rich medial layer, yielding an apparent Young’s modulus Emedia?5–8 kPa. Polyacrylamide gels with Egel spanning several-fold above and

Adam J. Engler; Ludovic Richert; Joyce Y. Wong; Catherine Picart; Dennis E. Discher

2004-01-01

184

Evaluating pulp stiffness from fibre bundles by ultrasound  

NASA Astrophysics Data System (ADS)

A non-destructive ultrasonic tester was developed to measure the stiffness of pulp bundles. The mechanical properties of pulp are important when estimating the behaviour of paper under stress. Currently available pulp tests are tedious and alter the fibres structurally and mechanically. The developed tester employs (933 ± 15) kHz tweezer-like ultrasonic transducers and time-of-flight measurement through (9.0 ± 2.5) mm long and (0.8 ± 0.1) mm thick fibre bundles kept at (19.1 ± 0.4) °C and (62 ± 1)% RH. We determined the stiffness of soft wood pulps produced by three kraft pulping modifications: standard kraft pulp, (5.2 ± 0.4) GPa, prehydrolysis kraft pulp, (4.3 ± 0.4) GPa, and alkali extracted prehydrolysis kraft pulp, (3.3 ± 0.4) GPa. Prehydrolysis and alkali extraction processes mainly lowered the hemicellulose content of the pulps, which essentially decreased the fibre-wall stiffness hence impairing the stiffness of the fibre networks. Our results indicate that the method allows ranking of pulps according to their stiffness determined from bundle-like samples taken at an early phase of the papermaking process.

Karppinen, Timo; Montonen, Risto; Määttänen, Marjo; Ekman, Axel; Myllys, Markko; Timonen, Jussi; Hæggström, Edward

2012-06-01

185

Estimation of Stiffness Parameter on the Common Carotid Artery  

NASA Astrophysics Data System (ADS)

The arteriosclerosis is on the increase with an aging or change of our living environment. For that reason, diagnosis of the common carotid artery using echocardiogram is doing to take precautions carebropathy. Up to the present, several methods to measure stiffness parameter of the carotid artery have been proposed. However, they have analyzed at the only one point of common carotid artery. In this paper, we propose the method of analysis extended over a wide area of common carotid artery. In order to measure stiffness parameter of common carotid artery from echocardiogram, it is required to detect two border curves which are boundaries between vessel wall and blood. The method is composed of two steps. The first step is the detection of border curves, and the second step is the calculation of stiffness parameter using diameter of common carotid artery. Experimental results show the validity of the proposed method.

Koya, Yoshiharu; Mizoshiri, Isao; Matsui, Kiyoaki; Nakamura, Takashi

186

Effect of surface stress on the stiffness of cantilever plates.  

PubMed

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

Lachut, Michael J; Sader, John E

2007-11-16

187

Arterial Stiffness and ?-Amyloid Progression in Nondemented Elderly Adults  

PubMed Central

IMPORTANCE Recent studies show that cerebral ?-amyloid (A?) deposition is associated with blood pressure and measures of arterial stiffness in nondemented individuals. OBJECTIVE To examine the association between measures of arterial stiffness and change in A? deposition over time. DESIGN, SETTING, AND PARTICIPANTS Deposition of A? was determined in a longitudinal observational study of aging by positron emission tomography using the Pittsburgh compound B twice 2 years apart in 81 nondemented individuals 83 years and older. Arterial stiffness was measured with a noninvasive and automated waveform analyzer at the time closest to the second positron emission tomography scan. All measures were performed under standardized conditions. Pulse wave velocity (PWV) was measured in the central (carotid-femoral and heart-femoral PWV), peripheral (femoral-ankle PWV), and mixed (brachial-ankle PWV) vascular beds. MAIN OUTCOMES AND MEASURES The change in A? deposition over 2 years was calculated from the 81 individuals with repeat A?-positron emission tomography. RESULTS The proportion of A?-positive individuals increased from 48% at baseline to 75% at follow-up. Brachial-ankle PWV was significantly higher among A?-positive participants at baseline and follow-up. Femoral-ankle PWV was only higher among A?-positive participants at follow-up. Measures of central stiffness and blood pressure were not associated with A? status at baseline or follow-up, but central stiffness was associated with a change in A? deposition over time. Each standard deviation increase in central stiffness (carotid-femoral PWV, P = .001; heart-femoral PWV, P = .004) was linked with increases in A? deposition over 2 years. CONCLUSIONS AND RELEVANCE This study showed that A? deposition increases with age in nondemented individuals and that arterial stiffness is strongly associated with the progressive deposition of A? in the brain, especially in this age group. The association between A? deposition changes over time and generalized arterial stiffness indicated a relationship between the severity of subclinical vascular disease and progressive cerebral A? deposition. PMID:24687165

Hughes, Timothy M.; Kuller, Lewis H.; Barinas-Mitchell, Emma J. M.; McDade, Eric M.; Klunk, William E.; Cohen, Ann D.; Mathis, Chester A.; DeKosky, Steven T.; Price, Julie C.; Lopez, Oscar L.

2014-01-01

188

Comparison of cervical spine stiffness in individuals with chronic nonspecific neck pain and asymptomatic individuals.  

PubMed

Study Design Clinical measurement, cross-sectional. Objective To determine if spinal joint stiffness is different in individuals with nonspecific neck pain, and whether stiffness magnitude is associated with pain intensity and disability. Background Manual therapists commonly evaluate spinal joint stiffness in patients presenting with nonspecific neck pain. However, a relationship between stiffness and neck pain has not yet been demonstrated. Methods Spinal stiffness at C7 was objectively measured in participants with chronic nonspecific neck pain whose symptomatic spinal level was identified as C7 (n = 12) and in age- and sex-matched asymptomatic controls (n = 12). Stiffness (slope of the linear region of the force-displacement curve) was quantified using a device that applied 5 standardized mechanical force cycles to the C7 spinous process, while concurrently measuring displacement and resistance to movement. Stiffness was compared between groups using an independent t test. Spearman rho and Pearson r were used to determine the extent to which stiffness magnitude was associated with pain intensity (visual analog scale) and level of disability (Neck Disability Index), respectively, in the group with neck pain. Results Participants with nonspecific neck pain had greater spinal joint stiffness at C7 compared with asymptomatic individuals (mean difference, 1.78 N/mm; 95% confidence interval: 0.28, 3.27; P = .022). However, stiffness magnitude in the group with neck pain was not associated (P>.05) with pain intensity or level of disability. Conclusion These preliminary results suggest that cervical spine stiffness may be greater in the presence of nonspecific neck pain. However, judgments regarding pain intensity and level of disability should not be inferred from examinations of spinal joint stiffness. J Orthop Sports Phys Ther 2015;45(3):162-169. Epub 27 Jan 2015. doi:10.2519/jospt.2015.5711. PMID:25627153

Ingram, Lewis A; Snodgrass, Suzanne J; Rivett, Darren A

2015-03-01

189

Boundary slip dependency on surface stiffness.  

PubMed

The paper investigates the effects of surface stiffness on the slip process aiming to obtain a better insight of the momentum transfer at nanoscale. The surface stiffness is modeled through the stiffness, ?, of spring potentials, which are employed to construct the thermal walls. It is shown that variations of stiffness, ?, influence the slip mechanism either toward slip or stick conditions. Increasing the values of ? alters the oscillation frequency and the mean displacement of the wall particles toward higher and lower values, respectively. Our results suggest that the amount of slip produced as a function of stiffness follows a common pattern that can be modeled through a fifth-order polynomial function. PMID:20866421

Asproulis, Nikolaos; Drikakis, Dimitris

2010-06-01

190

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

NASA Astrophysics Data System (ADS)

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.

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

2012-04-01

191

Increased Cardiovascular Stiffness and Impaired Age-related Functional Status.  

PubMed

Our objective was to determine if increased cardiovascular (CV) stiffness is associated with disability in middle-aged and older adults at risk for congestive heart failure. CV stiffness (brachial pulse pressure/left ventricular stroke volume indexed to body surface area) and total disability (the summed assessment of activities of daily living, mobility, and instrumental activities of daily living) were measured in 445 individuals. A subset of 109 randomly selected individuals also underwent physical function testing. Total disability was associated with CV stiffness (p = .01), driven by an association with mobility (p = .005), but not activities of daily living (p = .13) or instrumental activities of daily living (p = .61). After accounting for age, these correlations remained significant for men (p = .04), but not for women. CV stiffness was also associated with increased 400-m walk time (p = .02). In middle-aged and elderly men at risk for congestive heart failure, CV stiffness is associated with decreased mobility and physical function, and increased overall disability. PMID:24963155

Andersen, Mousumi M; Kritchevsky, Stephen B; Morgan, Timothy M; Hire, Don G; Vasu, Sujethra; Brinkley, Tina E; Kitzman, Dalane W; Hamilton, Craig A; Soots, Sandra; Hundley, William G

2015-05-01

192

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

193

Cell stiffness and receptors: evidence for cytoskeletal subnetworks Hayden Huang,1  

E-print Network

to the cytoskel- eton, while the other, the transferrin receptors, is not. Fibronectin- coated beads were used the beads to endocytose. For epithelial cells, transferrin-dependent stiffness and endocytosed bead the transferrin-dependent stiffness was lower. The conclusion of this study is that the measured cellular

Campbell, Kevin P.

194

Fracture stiffness as a guide to the management of tibial fractures  

Microsoft Academic Search

e have studied the progression of healing in 103 unstable fractures of the tibia. In 76 patients we removed the external fixator once the stiffness had reached 15 Nm\\/° in the sagittal plane. Deformity at the site of the fracture subsequently occurred in four patients. In a further 27, we measured stiffness in several planes and removed the fixator only

R. H. Wade; C. I. Moorcroft; P. B. M. Thomas

2001-01-01

195

INFLUENCES OF NONEQUILIBRIUM MOISTURE CONDITIONS ON THE IN-PLANE, ULTRASONIC STIFFNESSES OF CELLULOSE  

Microsoft Academic Search

Resonant and time-of-flight ultrasonic techniques were used to measure mass specific elastic stiffnesses and loss tangents for several papers and cellophanes during sorption, desorption, and at moisture equilibrium. When com- pared at equal moistures and temperatures, ultrasonic elastic stiffnesses and loss tangents obtained under nonequilibrium moisture conditions were identical to those at equilibrium. These results differ from published studies, which

C. C. Habeger

196

Dynamic phototuning of 3D hydrogel stiffness.  

PubMed

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

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

2015-02-17

197

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

SciTech Connect

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)

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

1985-01-01

198

A New Sampling Method for Spleen Stiffness Measurement Based on Quantitative Acoustic Radiation Force Impulse Elastography for Noninvasive Assessment of Esophageal Varices in Newly Diagnosed HCV-Related Cirrhosis  

PubMed Central

In our study, we evaluated the feasibility of a new sampling method for splenic stiffness (SS) measurement by Quantitative Acoustic Radiation Force Impulse Elastography (Virtual Touch Tissue Quantification (VTTQ)).We measured SS in 54 patients with HCV-related cirrhosis of whom 28 with esophageal varices (EV), 27 with Chronic Hepatitis C (CHC) F1–F3, and 63 healthy controls. VTTQ-SS was significantly higher among cirrhotic patients with EV (3.37?m/s) in comparison with controls (2.19?m/s, P < 0.001), CHC patients (2.37?m/s, P < 0.001), and cirrhotic patients without EV (2.7?m/s, P < 0.001). Moreover, VTTQ-SS was significantly higher among cirrhotic patients without EV in comparison with both controls (P < 0.001) and CHC patients (P < 0.01). The optimal VTTQ-SS cut-off value for predicting EV was 3.1?m/s (AUROC = 0.96, sensitivity 96.4%, specificity 88.5%, positive predictive value 90%, negative predictive value 96%, positive likelihood ratio 8.36, and negative likelihood ratio 0.04). In conclusion, VTTQ-SS is a promising noninvasive and reliable diagnostic tool to screen cirrhotic patients for EV and reduce the need for upper gastrointestinal endoscopy. By using our cut-off value of 3.1?m/s, we would avoid endoscopy in around 45% of cirrhotic subjects, with significant time and cost savings. PMID:24729970

Rizzo, Leonardo; Attanasio, Massimo; Berretta, Massimiliano; Malaguarnera, Michele; Morra, Aldo; L'Abbate, Luca; Balestreri, Luca; Nunnari, Giuseppe; Cacopardo, Bruno

2014-01-01

199

A new sampling method for spleen stiffness measurement based on quantitative acoustic radiation force impulse elastography for noninvasive assessment of esophageal varices in newly diagnosed HCV-related cirrhosis.  

PubMed

In our study, we evaluated the feasibility of a new sampling method for splenic stiffness (SS) measurement by Quantitative Acoustic Radiation Force Impulse Elastography (Virtual Touch Tissue Quantification (VTTQ)).We measured SS in 54 patients with HCV-related cirrhosis of whom 28 with esophageal varices (EV), 27 with Chronic Hepatitis C (CHC) F1-F3, and 63 healthy controls. VTTQ-SS was significantly higher among cirrhotic patients with EV (3.37?m/s) in comparison with controls (2.19?m/s, P<0.001), CHC patients (2.37?m/s, P<0.001), and cirrhotic patients without EV (2.7?m/s, P<0.001). Moreover, VTTQ-SS was significantly higher among cirrhotic patients without EV in comparison with both controls (P<0.001) and CHC patients (P<0.01). The optimal VTTQ-SS cut-off value for predicting EV was 3.1?m/s (AUROC=0.96, sensitivity 96.4%, specificity 88.5%, positive predictive value 90%, negative predictive value 96%, positive likelihood ratio 8.36, and negative likelihood ratio 0.04). In conclusion, VTTQ-SS is a promising noninvasive and reliable diagnostic tool to screen cirrhotic patients for EV and reduce the need for upper gastrointestinal endoscopy. By using our cut-off value of 3.1?m/s, we would avoid endoscopy in around 45% of cirrhotic subjects, with significant time and cost savings. PMID:24729970

Rizzo, Leonardo; Attanasio, Massimo; Pinzone, Marilia Rita; Berretta, Massimiliano; Malaguarnera, Michele; Morra, Aldo; L'Abbate, Luca; Balestreri, Luca; Nunnari, Giuseppe; Cacopardo, Bruno

2014-01-01

200

Composite Materials with Viscoelastic Stiffness Greater Than Diamond  

E-print Network

. Stone,3 R. S. Lakes4 * We show that composite materials can exhibit a viscoelastic modulus (Young of single foam cells (3). The elastic modulus, a stress/strain ratio, is a measure of material stiffness compressibility has been observed in small-cell foams (10). Negative compressibility differs from negative thermal

Lakes, Roderic

201

Modifiable Risk Factors for Increased Arterial Stiffness in Outpatient Nephrology  

PubMed Central

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

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

202

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

PubMed

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

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

2009-01-01

203

Elasticity of Stiff Biopolymer Networks  

NASA Astrophysics Data System (ADS)

The elasticity of cells is governed by the cytoskeleton, a partially crosslinked network of relatively stiff filaments forming a several 100 nm thick shell called the actin cortex. While the statistical properties of single cytoskeletal filaments are by now relatively well understood [1], theoretical concepts for the elasticity of stiff polymer networks are still evolving. One major open question is to understand how stresses and strains are transmitted in such networks. As a idealized model system we study the elasticity of a two-dimensional random network of rigid rods ("Mikado model")[2]. The essential features incorporated into the model are the anisotropic elasticity of the rods and the random geometry of the network. We show that there are three distinct scaling regimes, characterized by two distinct length scales on the elastic backbone. In addition to a critical rigidiy percolation region and a homogeneously elastic regime we find a novel intermediate scaling regime, where the elasticity is dominated by bending deformations. We discuss the application of these results to F-Actin and microtubule networks. [1] L. Le Goff, O. Hallatschek, E. Frey, F. Amblard, Phys. Rev. Lett. 89, 258101 (2002). [2] J. Wilhelm, and E. Frey, Phys. Rev. Lett. 91, 108103 (2003).

Wilhelm, Jan; Frey, Erwin

2004-03-01

204

Stiffness Simulation Using Non-linear FEA  

SciTech Connect

In this paper, Stamping-stiffness coupling simulation techniques are proposed, i.e., stamping, springback and stiffness is simulated with dynamic-explicit FE method, static-implicit FE method, and dynamic-explicit FE method continually. Carrying out process for three steps and some key technical factors are listed. The stiffness for double-curvature box parts is analyzed by this method.The simulation result is compared with experimental one, and satisfied calculation accuracy is obtained.

Xu, W.L.; Ai, J.; Lu, J.X.; Ying, B.H. [Baoshan Iron and Steel Co., LTD, R and D Center Customer Technology Research Center, Shanghai (China)

2005-08-05

205

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

NASA Technical Reports Server (NTRS)

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.

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

1976-01-01

206

Cardiovascular Health and Arterial Stiffness: The Maine Syracuse Longitudinal Study  

PubMed Central

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

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

2014-01-01

207

Mechanics and stiffness limitations of a variable stiffness actuator for use in prosthetic limbs  

Microsoft Academic Search

This paper examines an actuation system, intended for use in a prosthetic arm, that mimics the ability of antagonistic muscles in biological systems to modulate the stiffness and position of a joint. The system uses two physical nonlinear springs arranged antagonistically about a joint to generate control of both stiffness and movement. To decouple the net joint stiffness from joint

C. E. English; D. Russell

1999-01-01

208

Arthroscopic Treatment of Stiff Elbow  

PubMed Central

Contracture of the elbow represents a disabling condition that can impair a person's quality of life. Regardless of the event that causes an elbow contracture, the conservative or surgical treatment is usually considered technically difficult and associated with complications. When the conservative treatment fails to restore an acceptable range of motion in the elbow, open techniques have been shown to be successful options. More recently the use of arthroscopy has become more popular for several reasons. These reasons include better visualization of intra-articular structures, less tissue trauma from open incisions, and potentially the ability to begin early postoperative motion. The purpose of this paper is to review the indications, complications, and results of arthroscopic management of a stiff elbow. PMID:22084755

Blonna, Davide; Bellato, Enrico; Marini, Eleonora; Scelsi, Michele; Castoldi, Filippo

2011-01-01

209

Stiffness and damping characteristics of aluminum in creep  

NASA Technical Reports Server (NTRS)

Tensile creep tests conducted at 200 C were performed on annealed commercially pure aluminum specimens in order to measure the dominant elevated temperature dislocation processes. Testing consisted of applying small lateral loads to measure flexural stiffness, and vibrating the specimens laterally in order to measure dynamic modulus and internal damping. It was concluded that (1) the strain hardening increased static stiffness and decreased internal damping during early creep, and (2) the dynamic modulus remained essentially constant at the elastic value during creep. These results imply that primary creep may constitute a mechanism of recovery of dislocatory disorder induced by yielding the material during loading, and that the inelastic modulus utilized as a mathematical concept in several creep buckling theories is not a directly measurable material property.

Berkovits, A.

1977-01-01

210

Lamb wave assessment of stiffness degradation in fatigued composites  

Microsoft Academic Search

A Lamb wave scanning system that measures the elastic properties of a material was used to characterize fatigue damage in composites. The Lamb Wave Imager™ (LWI) uses a pulse\\/receive technique that excites a flexural Lamb mode and measure 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

Michael D. Seale; Eric I. Madaras

2000-01-01

211

Real Stiffness Augmentation for Haptic Augmented Reality  

Microsoft Academic Search

Haptic augmented reality (AR) mixes a real environment with computer-generated virtual haptic stimuli, enabling the system to modulate the haptic attributes of a real object to desired values. This paper reports our second study on this functionality, with stiffness as a goal modulation property. Our first study explored the potential of haptic AR by presenting an effective stiffness modulation system

Seokhee Jeon; Seungmoon Choi

2011-01-01

212

Zero Stiffness Tensegrity Structures M. Schenk a  

E-print Network

words, they remain neutrally stable, require no external work to de- form, and hence have zero stiffness-stress. These structures require specific external loads or states of self-stress to exhibit zero stiffness. The key-standing prestressed pin-jointed structures, which are in general both statically and kinematically indeterminate

Guest, Simon

213

Rolling Element Bearing Stiffness Matrix Determination (Presentation)  

SciTech Connect

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.

Guo, Y.; Parker, R.

2014-01-01

214

Stiffness of desiccating insect wings This article has been downloaded from IOPscience. Please scroll down to see the full text article.  

E-print Network

Stiffness of desiccating insect wings This article has been downloaded from IOPscience. Please.1088/1748-3182/6/1/014001 COMMUNICATION Stiffness of desiccating insect wings T E Mengesha1, R R Vallance1 and R Mittal2 1 Department The stiffness of insect wings is typically determined through experimental measurements. Such experiments

Mittal, Rajat

215

Effect of sprung (suspended) floor on lower extremity stiffness during a force-returning ballet jump.  

PubMed

Our objective in this study was to compare stiffness of bilateral lower extremities (LEs) in ballet dancers performing sauté on a low-stiffness "sprung floor" to that during the same movement on a high-stiffness floor (wood on concrete). LE stiffness was calculated as the ratio of vertical ground reaction force (in kN) to compression of the lower limb (in meters). Seven female dancers were measured for five repetitions each at the point of maximum leg compression while performing sauté on both of the surfaces, such that 43 ms of data were represented for each trial. The stiffness of bilateral LEs at the point of maximum compression was higher by a mean difference score of 2.48 ± 2.20 kN/m on the low-stiffness floor compared to a high-stiffness floor. Paired t-test analysis of the difference scores yielded a one-tailed probability of 0.012. This effect was seen in six out of seven participants (one participant showed no difference between floor conditions). The finding of increased stiffness of the LEs in the sprung floor condition suggests that some of the force of landing the jump was absorbed by the surface, and therefore did not need to be absorbed by the participants' LEs themselves. This in turn implies that a sprung dance floor may help to prevent dance-related injuries. PMID:22211195

Hackney, James; Brummel, Sara; Becker, Dana; Selbo, Aubrey; Koons, Sandra; Stewart, Meredith

2011-12-01

216

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

PubMed Central

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

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

2014-01-01

217

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

PubMed

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

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

2013-02-01

218

Association between arterial stiffness and variations in estrogen-related genes  

E-print Network

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 ...

Peter, Inga

219

Topology optimization under stochastic stiffness  

NASA Astrophysics Data System (ADS)

Topology optimization is a systematic computational tool for optimizing the layout of materials within a domain for engineering design problems. It allows variation of structural boundaries and connectivities. This freedom in the design space often enables discovery of new, high performance designs. However, solutions obtained by performing the optimization in a deterministic setting may be impractical or suboptimal when considering real-world engineering conditions with inherent variabilities including (for example) variabilities in fabrication processes and operating conditions. The aim of this work is to provide a computational methodology for topology optimization in the presence of uncertainties associated with structural stiffness, such as uncertain material properties and/or structural geometry. Existing methods for topology optimization under deterministic conditions are first reviewed. Modifications are then proposed to improve the numerical performance of the so-called Heaviside Projection Method (HPM) in continuum domains. Next, two approaches, perturbation and Polynomial Chaos Expansion (PCE), are proposed to account for uncertainties in the optimization procedure. These approaches are intrusive, allowing tight and efficient coupling of the uncertainty quantification with the optimization sensitivity analysis. The work herein develops a robust topology optimization framework aimed at reducing the sensitivity of optimized solutions to uncertainties. The perturbation-based approach combines deterministic topology optimization with a perturbation method for the quantification of uncertainties. The use of perturbation transforms the problem of topology optimization under uncertainty to an augmented deterministic topology optimization problem. The PCE approach combines the spectral stochastic approach for the representation and propagation of uncertainties with an existing deterministic topology optimization technique. The resulting compact representations for the response quantities allow for efficient and accurate calculation of sensitivities of response statistics with respect to the design variables. The proposed methods are shown to be successful at generating robust optimal topologies. Examples from topology optimization in continuum and discrete domains (truss structures) under uncertainty are presented. It is also shown that proposed methods lead to significant computational savings when compared to Monte Carlo-based optimization which involve multiple formations and inversions of the global stiffness matrix and that results obtained from the proposed method are in excellent agreement with those obtained from a Monte Carlo-based optimization algorithm.

Asadpoure, Alireza

220

A conserved Lsm-interaction motif in Prp24 required for efficient U4/U6 di-snRNP formation  

E-print Network

A conserved Lsm-interaction motif in Prp24 required for efficient U4/U6 di-snRNP formation STEPHEN the splicing factor Prp24. We have identified a family of Prp24 homologs that includes the human protein SART3 conservation among the Prp24 homologs reveals the existence of a fourth previously unidentified RNA recognition

Rader, Stephen

221

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

NASA Technical Reports Server (NTRS)

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.

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

2009-01-01

222

High performance composites with active stiffness control.  

PubMed

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

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

2013-09-25

223

Stiff Coatings on Compliant Biofibers  

PubMed Central

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

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

2009-01-01

224

Effective stiffness of cracked elastic solids  

SciTech Connect

This paper discusses the elastic stiffness reduction that accompanies cracking. Basic results are illustrated using simple examples and general approaches of determining the effective stiffness of cracked solids are reviewed. Various approximate methods of obtaining the effective stiffness of cracked solids are demonstrated for the case of aligned uniform cracks. These methods include the dilute approximation, self-consistent method, Mori-Tanaka`s method, differential scheme and shear lag model. Finally, recent numerical results of 3-D periodically cracked solids with high interaction are presented and discussed. 40 refs., 9 figs.

Fares, N. [Polytechnic Univ., Brooklyn, NY (United States)

1992-08-01

225

Threshold bracing stiffness of two story frames  

E-print Network

of an equa- tion relating the frame geometry and loading to the bracing stiffness is derived. The common practice of using a bracing area equal to 2g of the column area is investigated; the result indicated that the value of 2s resulted in a safe design... JOINTED FRAMES 24 General Bracing Stiffness Calculations. Limiting Values of the Bracing Stiffnesses. Numerical Example for the Pin Jointed Frames. Diagonal Bracing. Verification of the 2'-o Rule Conclusions 24 24 28 30 32 37 38 IV. BRACING...

Khader, Ghassan Sudki

1982-01-01

226

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

PubMed

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

Struzik, Artur; Zawadzki, Jerzy

2013-01-01

227

Bending stiffness of the lumbar spine subjected to posteroanterior manipulative force.  

PubMed

This study measured the bending stiffness of the spine when it is subjected to posteroanterior mobilization force. The lumbar spine was modeled as an initially curved beam column supported over the rib cage and the pelvis. Posteroanterior mobilization was assumed to be three-point bending of the beam. The mobilization force was measured by the mounting of a force plate onto the manipulation couch, where electromagnetic sensors measured the change in spinal curvature. The bending stiffness of the spine was derived from the force and curvature data. The technique developed in this study provided highly repeatable data. The theoretical analysis suggests that the pelvic rotation produced by mobilization may be used clinically to indicate the magnitude of the mobilization force. Future research may employ the present method to determine how back pain may affect the bending stiffness of the spine. The bending stiffness values reported in this study will be valuable to future modeling work. PMID:15944881

Lee, Raymond Y W; Tsung, Bonnie Y S; Tong, Pin; Evans, John

2005-01-01

228

Arterial stiffness is higher in older adults with increased perceived fatigue and fatigability during walking.  

PubMed

We investigated whether central and/or peripheral arterial stiffness contributes to increased perceived fatigue during walking in mobility-intact older adults. Arterial stiffness of the common carotid artery and superficial femoral artery (SFA) was measured using Doppler-ultrasound in 45 community-dwelling women and men (60-78yrs). The change in perceived fatigue was measured after a fast-pace 400meter walk test. Adults that rated feeling more tired after walking (n=10) had higher SFA stiffness (p<0.01), but not carotid artery stiffness, than adults that reported feeling more energetic after walking (n=22). The change in perceived fatigue rating was normalized to energy expenditure during walking to determine perceived fatigability. Adults were divided into lower and higher perceived fatigability groups (n=22 per group). Carotid artery stiffness was not different between perceived fatigability groups after adjusting for age, sex, body fat, systolic blood pressure, fasting blood glucose, daily physical activity levels, and resting diameter. However, SFA stiffness was significantly elevated in the higher as compared to lower perceived fatigability group (?-index: 20.7±1.3 vs. 15.3±1.4U; p=0.02) after adjusting for the abovementioned variables. Moreover, stepwise regression identified SFA ?-index to be an independent predictor of perceived fatigability (r(2)=0.38, p<0.01). These results suggest that peripheral arterial stiffness is independently associated with perceived fatigue and fatigability in older adults. PMID:25482474

Gonzales, Joaquin U; Wiberg, Matthew; Defferari, Elizabeth; Proctor, David N

2015-01-01

229

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

PubMed Central

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

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

2015-01-01

230

Reliabilities of leg and vertical stiffness during treadmill running.  

PubMed

The aim of this study was to determine the intra-participant variabilities (i.e. intra-day and inter-day reliabilities) in leg and vertical stiffness, as well as related kinematic parameters, during treadmill running using the sine-wave method. Twenty-two healthy men ran on a treadmill at 4.44 m/s, and the flight and contact times were measured with a high-speed video camera. Three 30-s running bouts with 2-min inter-bout rests were performed to examine the intra-day reliability, and single 30-s running bouts on three separate days with 24- to 48-h inter-bout intervals were performed to examine the inter-day reliability. The reliability statistics included repeated-measure analyses of variance, average inter-trial correlations, intra-class correlation coefficients (ICCs), Cronbach's ? reliability coefficient, and the coefficient of variation. Both leg and vertical stiffness produced high ICCs within 0.972 and 0.982, respectively, and between 0.922 and 0.873 days, respectively. High values were also observed for all of the reliability coefficients. Similar results were found regarding contact time, flight time, step length, and step rate. It was concluded that the measurements of leg and vertical stiffness, as well as related kinematic parameters, obtained using the sine-wave method during treadmill running at 4.44 m/s, were highly reliable, both within and across days. PMID:25438771

Pappas, Panagiotis; Paradisis, Giorgos; Tsolakis, Charilaos; Smirniotou, Athanasia; Morin, Jean-Benoit

2014-11-01

231

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

NASA Astrophysics Data System (ADS)

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.

Curà, Francesca; Mura, Andrea

2013-11-01

232

Programmable variable stiffness 2D surface design  

NASA Astrophysics Data System (ADS)

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.

Trabia, Sarah; Hwang, Taeseon; Yim, Woosoon

2014-03-01

233

49 CFR 213.359 - Track stiffness.  

Code of Federal Regulations, 2010 CFR

...STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness...generated at maximum permissible train speeds, cant deficiencies and surface...generated at maximum permissible train speeds, cant deficiencies and lateral...

2010-10-01

234

External mechanical compression reduces regional arterial stiffness  

Microsoft Academic Search

Acute aerobic and resistance exercise has been shown to reduce local muscular artery stiffness in the exercised limb while\\u000a having no effect on the non-exercised limb. The stimulus for these modulations may be related to local muscular compression\\u000a of underlying vasculature. The purpose of this study was to examine arterial stiffness before and after a series of locally\\u000a applied external

Kevin S. Heffernan; David G. Edwards; Lindy Rossow; Sae Young Jae; Bo Fernhall

2007-01-01

235

In-plane stiffness of wooden floor  

Microsoft Academic Search

The seismic response of existing un-reinforced masonry (URM) buildings is strongly dependent on the characteristics of wooden floors and in particular on their in- plane stiffness and on the quality of the connections between the floors and the URM elements. It is generally well-recognized that adequate in plane-stiffness and proper connections improves the three-dimensional response of the whole system and

A. Brignola; S. Podestà; S. Pampanin

236

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

PubMed Central

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

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

2014-01-01

237

Stiff limb syndrome: a case report  

PubMed Central

Introduction Stiff limb syndrome is a clinical feature of the stiff person syndrome, which is a rare and disabling neurologic disorder characterized by muscle rigidity and episodic spasms that involve axial and limb musculature. It is an autoimmune disorder resulting in a malfunction of aminobutyric acid mediated inhibitory networks in the central nervous system. We describe a patient diagnosed by neurological symptoms of stiff limb syndrome with a good outcome after treatment, and a review of the related literature. Case presentation A 49-year-old male patient presented with a progressive stiffness and painful spasms of his both legs resulting in a difficulty of standing up and walking. The diagnosis of stiff limb syndrome was supported by the dramatically positive response to treatment using diazepam 25 mg/day and baclofen 30 mg/day. Conclusion This clinical case highlights the importance of a therapeutic test to confirm the diagnosis of stiff limb syndrome especially when there is a high clinical suspicion with unremarkable electromyography PMID:20205913

2010-01-01

238

Finite element based nonlinear normalization of human lumbar intervertebral disc stiffness to account for its morphology.  

PubMed

Disc degeneration, usually associated with low back pain and changes of intervertebral stiffness, represents a major health issue. As the intervertebral disc (IVD) morphology influences its stiffness, the link between mechanical properties and degenerative grade is partially lost without an efficient normalization of the stiffness with respect to the morphology. Moreover, although the behavior of soft tissues is highly nonlinear, only linear normalization protocols have been defined so far for the disc stiffness. Thus, the aim of this work is to propose a nonlinear normalization based on finite elements (FE) simulations and evaluate its impact on the stiffness of human anatomical specimens of lumbar IVD. First, a parameter study involving simulations of biomechanical tests (compression, flexion/extension, bilateral torsion and bending) on 20 FE models of IVDs with various dimensions was carried out to evaluate the effect of the disc's geometry on its compliance and establish stiffness/morphology relations necessary to the nonlinear normalization. The computed stiffness was then normalized by height (H), cross-sectional area (CSA), polar moment of inertia (J) or moments of inertia (Ixx, Iyy) to quantify the effect of both linear and nonlinear normalizations. In the second part of the study, T1-weighted MRI images were acquired to determine H, CSA, J, Ixx and Iyy of 14 human lumbar IVDs. Based on the measured morphology and pre-established relation with stiffness, linear and nonlinear normalization routines were then applied to the compliance of the specimens for each quasi-static biomechanical test. The variability of the stiffness prior to and after normalization was assessed via coefficient of variation (CV). The FE study confirmed that larger and thinner IVDs were stiffer while the normalization strongly attenuated the effect of the disc geometry on its stiffness. Yet, notwithstanding the results of the FE study, the experimental stiffness showed consistently higher CV after normalization. Assuming that geometry and material properties affect the mechanical response, they can also compensate for one another. Therefore, the larger CV after normalization can be interpreted as a strong variability of the material properties, previously hidden by the geometry's own influence. In conclusion, a new normalization protocol for the intervertebral disc stiffness in compression, flexion, extension, bilateral torsion and bending was proposed, with the possible use of MRI and FE to acquire the discs' anatomy and determine the nonlinear relations between stiffness and morphology. Such protocol may be useful to relate the disc's mechanical properties to its degree of degeneration. PMID:24671515

Maquer, Ghislain; Laurent, Marc; Brandejsky, Vaclav; Pretterklieber, Michael L; Zysset, Philippe K

2014-06-01

239

Effects of substitution on the exchange stiffness and magnetization of Co films  

NASA Astrophysics Data System (ADS)

An antiferromagnetically coupled FM/NM/FM (FM = ferromagnet, NM = normal metal) trilayer structure responds to an external magnetic field by the formation of a magnetic-moment spring within the FM layers. We show that the exchange stiffness (Aex) of an FM layer can be determined by fitting the field-dependent magnetization, M (H ) , of the FM/NM/FM trilayer to a micromagnetic model. Using this method, we have measured the exchange stiffness of thin-film Co alloyed with Cr, Fe, Ni, Pd, Pt, and Ru. The results show that the rate at which a substituent element reduces the exchange stiffness is not directly related to its effect on the magnetization of the alloy. The observed trends have been understood by material-specific modeling based on density functional theory within the local density approximation. The stiffness measurements are in agreement with Brillouin light scattering carried out on thicker Co films.

Eyrich, C.; Zamani, A.; Huttema, W.; Arora, M.; Harrison, D.; Rashidi, F.; Broun, D.; Heinrich, B.; Mryasov, O.; Ahlberg, M.; Karis, O.; Jönsson, P. E.; From, M.; Zhu, X.; Girt, E.

2014-12-01

240

Biphasic response of cell invasion to matrix stiffness in three-dimensional biopolymer networks.  

PubMed

When cells come in contact with an adhesive matrix, they begin to spread and migrate with a speed that depends on the stiffness of the extracellular matrix. On a flat surface, migration speed decreases with matrix stiffness mainly due to an increased stability of focal adhesions. In a three-dimensional (3-D) environment, cell migration is thought to be additionally impaired by the steric hindrance imposed by the surrounding matrix. For porous 3-D biopolymer networks such as collagen gels, however, the effect of matrix stiffness on cell migration is difficult to separate from effects of matrix pore size and adhesive ligand density, and is therefore unknown. Here we used glutaraldehyde as a crosslinker to increase the stiffness of self-assembled collagen biopolymer networks independently of collagen concentration or pore size. Breast carcinoma cells were seeded onto the surface of 3-D collagen gels, and the invasion depth was measured after 3 days of culture. Cell invasion in gels with pore sizes >5 ?m increased with higher gel stiffness, whereas invasion in gels with smaller pores decreased with higher gel stiffness. These data show that 3-D cell invasion is enhanced by higher matrix stiffness, opposite to cell behavior in two dimensions, as long as the pore size does not fall below a critical value where it causes excessive steric hindrance. These findings may be important for optimizing the recellularization of soft tissue implants or for the design of 3-D invasion models in cancer research. PMID:25462839

Lang, Nadine R; Skodzek, Kai; Hurst, Sebastian; Mainka, Astrid; Steinwachs, Julian; Schneider, Julia; Aifantis, Katerina E; Fabry, Ben

2015-02-01

241

Increased liver stiffness denotes hepatic dysfunction and mortality risk in critically ill non-cirrhotic patients at a medical ICU  

PubMed Central

Introduction Hepatic dysfunction is a common finding in critically ill patients on the ICU and directly influences survival. Liver stiffness can be measured by the novel method of transient elastography (fibroscan) and is closely associated with hepatic fibrosis in patients with chronic liver disease, but also is increased in patients with acute hepatitis, acute liver failure and cholestasis. We investigated liver stiffness as a potentially useful tool for early detection of patients with hepatic deterioration and risk stratification with respect to short- and long-term mortality. Methods We prospectively evaluated 108 consecutive critically ill patients at our medical intensive care unit (ICU) with subsequent longitudinal liver stiffness measurements (admission, Day 3, Day 7 and weekly thereafter) during the course of ICU treatment. Outcome was followed after discharge (median observation time 237 days). Results Liver stiffness could be reliably measured in 71% of ICU patients at admission (65% at Day 3, 63% at Day 7). Critically ill patients (n = 108) had significantly increased liver stiffness compared to sex- and age-matched standard care patients (n = 25). ICU patients with decompensated cirrhosis showed highest liver stiffness, whereas other critical diseases (for example, sepsis) and comorbidities (for example, diabetes, obesity) did not impact stiffness values. At admission to the ICU, liver stiffness is closely related to hepatic damage (liver synthesis, cholestasis, fibrosis markers). During the course of ICU treatment, fluid overload (renal failure, volume therapy) and increased central venous pressure (mechanical ventilation, heart failure) were major factors determining liver stiffness. Liver stiffness values > 18 kilopascal (kPa) at ICU admission were associated with increased ICU and long-term mortality, even in non-cirrhotic patients. Conclusions Considering that liver stiffness cannot be validly measured in about 30% of ICU patients, transient elastography performed at ICU admission might be a useful tool to early identify liver dysfunction and predict mortality in critically ill patients at a medical ICU. PMID:22082207

2011-01-01

242

Analysis of stiffness loss in cross-ply composite laminates  

NASA Astrophysics Data System (ADS)

A constitutive model of the damage state for composite laminates, first proposed by Allen et al. (1987), is used with a damage evolution criterion based on strain energy to predict the stiffness loss due to matrix cracking in cross-ply laminated composite plates. Although the constitutive model does not require the determination of many constants, the state of damage is described by a vector of internal state variables (ISVs), which contains information on the crack geometry and fracture modes. The effects of relative ply thicknesses, crack density, and crack opening profile on the vector of ISVs are determined. The analysis results compare favorably with experimental measurements of progressive stiffness loss in damaged cross-ply graphite-epoxy laminates obtained from other studies.

Tay, T. E.; Lim, E. H.

243

Alterations in myocardial stiffness in elite athletes assessed by a new Doppler index  

Microsoft Academic Search

Background:In elite athletes left ventricular (LV) morphological changes are predicted to alter passive pressure\\/volume characteristics by reducing myocardial stiffness and increasing compliance.Objective:To investigate the utility of a new Doppler tissue index based on the pressure volume relation ((E\\/Ea)\\/LVEDD), which provides a measure of myocardial stiffness, and to assess its usefulness in detecting cardiac adaptation in elite rowers.Methods:Thirty-six international rowers who

G J King; R T Murphy; I Almuntaser; K Bennett; E Ho; A S Brown

2008-01-01

244

Effects of acute eccentric contractions on rat ankle joint stiffness  

Microsoft Academic Search

The sensation of joint stiffness is frequently observed after eccentric contractions (ECs) in human, but the joint stiffness of animals after ECs has not been examined previously. This study tested whether a bout of ECs affects rat ankle joint stiffness. We also evaluate muscle passive tension in the rat hindlimb to ex- amine the relationships of ankle joint stiffness with

Ochi Eisuke; Ishii Naokata; Nakazato Koichi

2007-01-01

245

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

PubMed

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

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

2015-04-13

246

Anterior Knee Stiffness Changes in Laxity “Responders” Versus “Nonresponders” Across the Menstrual Cycle  

PubMed Central

Context Although changes in anterior knee laxity (AKL) across the menstrual cycle have been reported, the effects of cyclic knee laxity changes on the underlying characteristics of the load-displacement (stiffness) curve generated during anterior loading of the tibia relative to the femur are relatively unknown. Objective To describe the anterior load-displacement curve during anterior loading of the tibia relative to the femur using incremental stiffnesses and to compare underlying stiffness measures between days of the cycle when AKL is at its minimum and maximum. Design Descriptive laboratory study. Setting University laboratory. Patients or Other Participants Fifty-seven recreationally active women. Main Outcome Measure(s) Anterior knee laxity and 6 incremental stiffness measures (N/mm) were obtained with an instrumented knee arthrometer on days 1–6 of menses and days 0–8 postovulation during 2 consecutive menstrual cycles. Participants were then classified in tertiles based on the maximum change (difference between maximum and minimum) in AKL, and incremental stiffness was compared on days of minimum versus maximum laxity between the lowest (<1.24 mm cyclic laxity change = laxity “nonresponders” [n = 19]) and highest (>1.75 mm cyclic laxity change = laxity “responders” [n = 19]) tertiles. Results All participants displayed decreasing stiffness initially (0–20 N > 20–40 N and 40–60 N), followed by incrementally increasing stiffness (40–60 N < 60–80 N < 80–100 N < 100–130 N) (P ? .05). Responders demonstrated decreased stiffness between the days of minimum and maximum AKL at the 10–130-N increment versus the 0–20-N and 20–40-N increments (P ? .05); nonresponders had no change in stiffness. Conclusions Participants who experienced larger magnitudes of cyclic changes in AKL also experienced decreases in terminal (100–130 N) stiffness during anterior knee joint loading. Decreases in incremental stiffness at higher anterior directed loads may adversely affect passive restraint systems, resulting in altered arthrokinematics during functional activity. PMID:23672324

Schmitz, Randy J; Shultz, Sandra J

2013-01-01

247

Tunable elastic stiffness of plasma-sprayed zirconia coatings  

NASA Astrophysics Data System (ADS)

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

Bamberg, Joachim; Schwaminger, Christian

1999-07-01

248

Normalized stiffness ratios for mechanical characterization of isotropic acoustic foams.  

PubMed

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

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

2013-12-01

249

The effects of thermal cycling on matrix cracking and stiffness changes in composite tubes  

NASA Technical Reports Server (NTRS)

The study investigated the accumulation of transverse matrix cracks and the resultant loss of torsional, extensional, and bending stiffnesses in 8 layer 0.5 in. diameter crossply tubes subjected to thermal cycling. The tubes were graphite-epoxy and the temperature range during cycling was -250 to 200 F. The effect of fiber and matrix properties was investigated through the use of T300 and P75S fibers and 934 and CE339 resins. The study considered 0, 10, 50, 100, 300, and 500 thermal cycles. Photomicrographs, X-rays, and edge replication were used to evaluate cracking. Special loading fixtures were used to measure stiffness changes. An important finding was that for the tubes studied, even with extensive cracking, the bending and extensional stiffnesses were not affected. The torsional stiffness, however, was strongly affected.

Cohen, D.; Hyer, M. W.; Tompkins, S. S.

1984-01-01

250

Effects of Isokinetic Passive Exercise and Isometric Muscle Contraction on Passive Stiffness  

PubMed Central

[Purpose] The purpose of this study was to investigate the effects of isokinetic passive exercise and motion velocity on passive stiffness. In addition, we also discuss the effects of the contraction of agonist and antagonist muscles on passive stiffness. [Subjects] The subjects were 20 healthy men with no bone or joint disease. [Methods] Isokinetic passive exercise and isometric muscle contraction were performed on an isokinetic dynamometer. The angular acceleration measured by the accelerometer was compared before and after each task. [Results] After the passive exercise, the angular acceleration increased in the phase of small damped oscillation. Moreover, the effect was higher at high-speed movement. The angular acceleration was decreased by the contraction of the agonist muscle. Conversely, the angular acceleration was increased by the contraction of the antagonist muscle. [Conclusion] Isokinetic passive exercise reduced passive stiffness. Our results suggest the possibility that passive stiffness is increased by agonist muscle contraction and decreased by antagonist muscle contraction. PMID:24259791

Terada, Shigeru; Miaki, Hiroichi; Uchiyama, Keita; Hayakawa, Shozo; Yamazaki, Toshiaki

2013-01-01

251

Lung Function Is Associated with Arterial Stiffness in Children  

PubMed Central

Background In older adults, an independent association exists between impaired lung function and cardiovascular disease. This interaction might be related to the effects of aging and/or smoking. In order to explore possible childhood antecedents to this association, we hypothesized that decreased lung function and vascular stiffness might be related, in early life. Objective To determine the relationship between lung function and carotid augmentation index (AIx), a measure of vascular stiffness, in 8-year old children. Methods Data on brachial blood pressure, lung function (FEV1, FVC, FEV1/FVC, obtained by spirometry) and carotid AIx75 (AIx standardised to an arbitrary heart rate of 75 beats per minute, obtained by applanation tonometry) was available in 249 community-based 8-year old children. These healthy children had been subjects in a randomised controlled trial of two interventions (omega-3 fatty acid supplementation and house-dust mite avoidance) to prevent asthma. Smoking in pregnancy and childhood environmental tobacco smoke (ETS) exposure was prospectively collected by questionnaire. The association between lung function and carotid AIx75 was assessed in multivariate models that included sex, height, smoking status during pregnancy, ETS exposure and randomisation groups (house dust mite avoidance and dietary intervention) as covariates. Results In the fully adjusted models, Carotid AIx75 was independently associated with FEV1 (standardised ??=??0.17,b?=??6.72, partial R2?=?.02, p?=?0.03), FVC (standardised ??=??0.29, b?=??9.31, partial R2?=?0.04, p<0.001) and FEV1/FVC (standardised ??=?.13, b?=?18.4, partial R2?=?0.02, p?=?0.04). Conclusion Lower lung volumes are associated with increased vascular stiffness at an early age. The interaction between lung function and vascular stiffness may thus represent more than just age-related alterations in both the pulmonary and vascular systems. PMID:22046271

Ayer, Julian G.; Belousova, Elena G.; Harmer, Jason A.; Toelle, Brett; Celermajer, David S.; Marks, Guy B.

2011-01-01

252

Association between arterial stiffness and peritoneal small solute transport rate.  

PubMed

While cardiovascular disease accounts for 40-50% of the mortality in dialysis patients, and while a high peritoneal transport in continuous ambulatory peritoneal dialysis (CAPD) is an independent predictor of outcome, it is unclear if there are any links. Aortic stiffness has become established as a cardiovascular risk factor. We thus studied pulse wave velocity (PWV) in CAPD patients to explore the possible link between peritoneal small solute transport and aortic stiffness. CAPD patients (n = 76, 27 M/49 F) in our center were included in the present study. Aortic stiffness was assessed by brachial pulse pressure (PP) and carotid-femoral PWV. Patients' peritoneal small solute transport rate was assessed by D/P(cr) at 4 h. Extracellular water over total body water (E/T ratio) was assessed by means of bioimpedance analysis. C-reactive protein was also measured. Carotid-femoral PWV was positively associated with patients' age (r = 0.555; P < 0.01), time on peritoneal dialysis (r = 0.332; P < 0.01), diabetic status (r = 0.319; P < 0.01), D/P(cr) (r = 0.241; P < 0.05), PP (r = 0.475; P < 0.01), and E/T (r = 0.606; P < 0.01). In a multivariate regression analysis, carotid-femoral PWV was independently determined by E/T (P < 0.01), PP (P < 0.01), age (P < 0.01), and D/P(cr) (P < 0.05). D/P(cr), in addition to E/T, age, and PP, was an independent predictor of elevated carotid-femoral PWV in CAPD patients, suggesting that there might be a link between high aortic stiffness and increased peritoneal small solute transport rate. PMID:18471172

Zhe, Xing-wei; Tian, Xin-kui; Chen, Wei; Guo, Li-juan; Gu, Yue; Chen, Hui-min; Tang, Li-jun; Wang, Tao

2008-05-01

253

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

254

Nanoscale directional motion towards regions of stiffness.  

PubMed

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

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

2015-01-01

255

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

PubMed

Hypertension and aging are both recognized to increase aortic stiffness, but their interactions are not completely understood. Most previous studies have attributed increased aortic stiffness to changes in extracellular matrix proteins that alter the mechanical properties of the vascular wall. Alternatively, we hypothesized that a significant component of increased vascular stiffness in hypertension is due to changes in the mechanical and adhesive properties of vascular smooth muscle cells, and that aging would augment the contribution from vascular smooth muscle cells when compared with the extracellular matrix. Accordingly, we studied aortic stiffness in young (16-week-old) and old (64-week-old) spontaneously hypertensive rats and Wistar-Kyoto wild-type controls. Systolic and pulse pressures were significantly increased in young spontaneously hypertensive rats when compared with young Wistar-Kyoto rats, and these continued to rise in old spontaneously hypertensive rats when compared with age-matched controls. Excised aortic ring segments exhibited significantly greater elastic moduli in both young and old spontaneously hypertensive rats versus Wistar-Kyoto rats. were isolated from the thoracic aorta, and stiffness and adhesion to fibronectin were measured by atomic force microscopy. Hypertension increased both vascular smooth muscle cell stiffness and vascular smooth muscle cell adhesion, and these increases were both augmented with aging. By contrast, hypertension did not affect histological measures of aortic collagen and elastin, which were predominantly changed by aging. These findings support the concept that stiffness and adhesive properties of vascular smooth muscle cells are novel mechanisms contributing to the increased aortic stiffness occurring with hypertension superimposed on aging. PMID:25452471

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

2015-02-01

256

Arterial stiffness, pulse pressure, and the kidney.  

PubMed

Classical studies indicate that the contribution of kidneys to hypertension is almost exclusively related to the association between mean arterial pressure (MAP) and vascular resistance. Recent reports including estimates of glomerular filtration rate (GFR) have shown that pulse pressure (PP) and pulse wave velocity, 2 major indices of arterial stiffness, now emerge as significant predictors of cardiovascular risk and age-associated decline in GFR. Such findings are mainly observed in patients with hypertension and renal failure and in atherosclerotic subjects undergoing coronary angiography. In such patients, amplification of PP between ascending and terminal aorta at the renal site is constantly increased over 10mm Hg (P < 0.001), whereas MAP level remains continuously unmodified. This PP amplification is significantly associated with presence of proteinuria. Furthermore, increases in plasma creatinine and aortic stiffness are independently and positively correlated (P < 0.001) both in cross-sectional and longitudinal studies. All these relationships associating PP, arterial stiffness, and renal function are mainly observed in patients 60 years of age or older. Furthermore, in renal transplant patients and their donors, subjects have been recruited for evaluations of arterial stiffness and posttransplant decline in GFR. Determinants of GFR decline were evaluated 1 and 9 years after transplantation. The first year GFR decline was related to smoking and acute rejection, whereas the later was significantly and exclusively associated with donor age and aortic stiffness. Thus, in hypertensive humans, the observed association between PP and GFR suggests that the 2 parameters are substantially mediated by arterial stiffness, not exclusively by vascular resistance. PMID:25480804

Safar, Michel E; Plante, Gérard E; Mimran, Albert

2015-05-01

257

Elastic Stiffness of a Skyrmion Crystal  

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

258

Contact Probe Based Stiffness Sensing of Human Eye by Considering Contact Area  

Microsoft Academic Search

The contact tonometer is commonly used for measuring the internal eye pressure to diagnose glaucoma. However, the conventional eye pressure measurement is valid only under the assumption that all subjects have the same structural eye stiffness. This paper challenges to measure the contact area between the probe and the cornea in addition to the corneal deformation for considering the individual

Yuichi Kurita; Yoshichika Iida; Roland Kempf; Makoto Kaneko; Hidetoshi Tsukamoto; Eiichiro Sugimoto; Seiki Katakura; Hiromu K. Mishima

2007-01-01

259

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

PubMed Central

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

2013-01-01

260

Stiffness and strain energy criteria to evaluate the threshold of injury to an intervertebral joint.  

PubMed

This study is focused to evaluate the threshold of injury to an intervertebral joint based on its mechanical response. The load-deflection behavior of the intervertebral joint indicated non-linear and sigmoidal characteristics with continuously changing stiffness (a measure of the ability to withstand external force). The load corresponding to the point of zero stiffness was identified, according to the classical theories of mechanics, as the maximum load carrying capacity. Further, the initiation of trauma was defined to occur at the point on the load-deflection curve at which the stiffness begins to decrease for the first time. The load, stiffness and energy absorbing capabilities of normal and degenerated intervertebral joints at the initiation of trauma was determined. Axial compressive load experiments were conducted on nine intervertebral joints of fresh human male cadavers and the resulting load-deflection responses were transformed into stiffness-deflection responses using the derivative principle. Energy characteristics were also derived. Load, stiffness and energy at the initiation of trauma were found to be 9.0 kN, 2850 N mm-1, and 10.2 J for normal and 4.4 kN, 1642 N mm-1, and 5.8 J for degenerated segments, respectively. The load and energy values at failure were 11.0 kN, and 18.0 J for normal and 5.3 kN and 5.7 J for degenerated intervertebral joints, respectively. PMID:2708393

Yoganandan, N; Ray, G; Pintar, F A; Myklebust, J B; Sances, A

1989-01-01

261

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

262

Influence of String Stiffness on Piano Tone  

E-print Network

Piano tones vary according to how pianist touches the keys. Many possible factors contribute to the relations between piano touch and tone. Focusing on the stiffness of string, we establish a model for vibration of a real piano string and derive a semi-analytical solution to the vibration equation.

Lai-Mei Nie

2010-12-02

263

Mandibular stiffness in humans: Numerical predictions  

Microsoft Academic Search

The chin is a feature unique to humans. This study evaluates the effect of mandibular symphyseal design on biomechanical masticatory effectiveness as determined by structural stiffness and stress developed under flexural and torsional loading. A simple model of three symphyseal shapes (chin, flat symphysis and lingual buttress), was built to represent human, Neanderthal and higher primate symphyses and these were

I. Ichim; M. V. Swain; J. A. Kieser

2006-01-01

264

Numerical simulations of stiff fluid gravitational singularities  

E-print Network

Numerical simulations of the approach to the singularity in spacetimes with stiff fluid matter are presented here. The spacetimes examined have no symmetries and can be regarded as representing the general behavior of singularities in the presence of such matter. It is found that the singularity is spacelike and that as it is approached, the spacetime dynamics becomes local and non-oscillatory.

Joshua Curtis; David Garfinkle

2005-06-21

265

Exploiting Variable Stiffness in Explosive Movement Tasks  

E-print Network

-specific impedance profile that leads to better performance is non-trivial. Here, we utilise optimal control) adding additional redundancy in the control (allowing robots to be stiff and accurate or compliant of the environment, is known as a duality principle in impedance control [2]. It is, however, not entirely clear how

Vijayakumar, Sethu

266

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

267

Photoinduced variable stiffness of spiropyran-based composites  

SciTech Connect

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.

Samoylova, E.; Ceseracciu, L.; Allione, M.; Diaspro, A.; Barone, A. C. [Istituto Italiano di Tecnologia, via Morego 30, Genova I-16163 (Italy); Athanassiou, A. [Istituto Italiano di Tecnologia, via Morego 30, Genova I-16163 (Italy); Center for Biomolecular Nanotechnologies-Unile, Istituto Italiano di Tecnologia, via Barsanti, Arnesano (Lecce) I-73010 (Italy)

2011-11-14

268

Scaling of Fluid Flow and Seismic Stiffness of Fractures  

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

269

Blood pressure and arterial stiffness in obese children and adolescents.  

PubMed

Obesity, elevated blood pressure (BP) and arterial stiffness are risk factors for cardiovascular disease. A strong relationship exists between obesity and elevated BP in both children and adults. Obesity and elevated BP in childhood track into adult life increasing the risk of cardiovascular disease in adulthood. Ambulatory BP is the most precise measure to evaluate the BP burden, whereas carotid-femoral pulse wave velocity (cfPWV) is regarded as the gold standard for evaluating arterial (i.e. aortic) stiffness. These measures might contribute to a better understanding of obesity's adverse impact on the cardiovascular system, and ultimately a better prevention and treatment of childhood obesity. The overall aim of the present PhD thesis is to investigate arterial stiffness and 24-hour BP in obese children and adolescents, and evaluate whether these measures are influenced by weight reduction. The present PhD thesis is based on four scientific papers.  In a cross-sectional design, 104 severe obese children and adolescents with an age of 10-18 years were recruited when newly referred to the Children's Obesity Clinic, Holbæk University Hospital, and compared to 50 normal weighted age and gender matched control individuals. Ambulatory BP was measured, and cfPWV was investigated in two ways in respect to the distance measure of aorta; the previously recommended length - the so called subtracted distance, and the currently recommended length - the direct distance. In a longitudinal design, the obese patients were re-investigated after one-year of lifestyle intervention at the Children's Obesity Clinic in purpose of reducing the degree of obesity. In the cross-sectional design, the obese group had higher measures of obesity, while matched for age, gender and height, when compared to the control group. In the longitudinal design, 74% of the 72 followed up obese patients experienced a significant weight reduction. CfPWV was dependent on the method used to measure the length of the aorta. The subtracted distance was not consistent in its relation to height in the obese and the control group. Opposite, the direct distance was consistent in its relation to height in the two groups. Therefore, cfPWV using the direct distance (cfPWV-direct) was regarded as the appropriate measure of arterial stiffness. CfPWV-direct was reduced in the obese group after adjustment for known confounders. In the longitudinal design, weight reduction across one year did not have an impact on cfPWV-direct in the obese patients. In fact, cfPWV-direct was higher at follow-up, which was explained by the increased age and partly by changes in BP and heart rate. The obese group had a relatively higher night- than day-time BP when compared to the control group. The obesity-related elevated night-time BP was independent of arterial stiffness and insulin resistance. Although night-time systolic BP was related to arterial stiffness and tended to be related to insulin resistance, insulin resistance and arterial stiffness were not related. In the longitudinal design, changes in anthropometric obesity measures across one year were associated with changes in 24-hour, day- and night-time BP, and consistent when evaluated in standardised values that accounted for growth. No association was found between changes in anthropometric obesity measures and changes in clinic BP. In conclusion, the results suggest that obesity in children is not "yet" associated with structural changes in aorta when evaluated with the appropriate new method of cfPWV. In this respect, weight reduction did not have an impact on arterial stiffness. The ambulatory BP, namely the night-time BP, was elevated in the obese patients, whereas changes in anthropometric obesity measures were related to changes in ambulatory BP but not to changes in clinic BP. In perspective, it is reassuring that weight changes are accompanied with a change in 24-hour BP as ambulatory BP is the most precise measure to evaluate the BP burden, and it emphasises the use of 24-hour ambulatory BP measurements in childr

Hvidt, Kristian Nebelin

2015-03-01

270

Haptic Stiffness Identification by Veterinarians and Novices: A Comparison  

E-print Network

Haptic Stiffness Identification by Veterinarians and Novices: A Comparison Neil Forrest 1 , Sarah compares the ability of practicing veterinarians and veterinary students to identify stiffness values veterinarians and 14 veterinary students show that the veterinarians performed significantly better than

Tan, Hong Z.

271

Design and characterization of tunable stiffness flexural bearings  

E-print Network

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 ...

Ramirez, Aaron Eduardo

2012-01-01

272

Effective Elastic Stiffness for Periodic Masonry Structures via Eigenstrain Homogenization  

E-print Network

, normally arranged periodically. Studying the in-plane load deformation characteristics of the masonryEffective Elastic Stiffness for Periodic Masonry Structures via Eigenstrain Homogenization Gang eigenstrain method is used to evaluate the effective elastic stiffness of periodic masonry structure

Li, Shaofan

273

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

E-print Network

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

Patton, Carl

274

A novel variable stiffness actuator: minimizing the energy requirements for the stiffness regulation.  

PubMed

The design of robots required to work in the close vicinity or physically interact with humans such as humanoids machines, rehabilitation or human performance augmentation systems should not follow the traditional design rule 'stiffer is better'. Safety is a particularly vital concern in these systems and to maximize it a different design approach should be used. The role of compliance in improving specific suspects of the robotic system, including safety and energy efficiency, has been studied and validated in many works. This work presents the design and realization of a new variable compliance actuator for robots physically interacting with humans, e.g. prosthesis devices and exoskeleton augmentation systems. The actuator can independently control the equilibrium position and stiffness using two motors. The main novelty of the proposed variable stiffness actuator is that the stiffness regulation is achieved not through the pretension of the elastic elements which needs the stiffness tuning actuator to act against the forces generated by the springs but by mechanically adjusting the fixation of the spring elements. As a result the stiffness actuator does not need to act against the spring forces reducing the energy required for the stiffness adjustment to minimal. PMID:21095917

Tsagarikis, Nikos G; Jafari, Amir; Caldwell, Darwin G

2010-01-01

275

Circulating Angiogenic Cell Populations, Vascular Function, and Arterial Stiffness  

PubMed Central

Objective Several bone marrow-derived cell populations have been identified that may possess angiogenic activity and contribute to vascular homeostasis in experimental studies. We examined the extent to which lower quantities of these circulating angiogenic cell phenotypes may be related to impaired vascular function and greater arterial stiffness. Methods We studied 1,948 Framingham Heart Study participants (mean age, 66±9 years; 54% women) who were phenotyped for circulating angiogenic cells: CD34+, CD34+/KDR+, and early outgrowth colony forming units (CFU). Participants underwent non-invasive assessments of vascular function including peripheral arterial tone (PAT), arterial tonometry, and brachial reactivity testing. Results In unadjusted analyses, higher CD34+ and CD34+/KDR+ concentrations were modestly associated with lower PAT ratio (?=?0.052±0.011, P<0.001 and ?=?0.030±0.011, P=0.008, respectively) and with higher carotid-brachial pulse wave velocity (?=0.144±0.043, P=0.001 and ?=0.112±0.043, P=0.009), but not with flow-mediated dilation; higher CD34+ was also associated with lower carotid-femoral pulse wave velocity (?=?0.229±0.094, P=0.015) However, only the association of lower CD34+ concentration with higher PAT ratio persisted in multivariable analyses that adjusted for standard cardiovascular risk factors. In all analyses, CFU was not associated with measures of vascular function or arterial stiffness. Conclusions In our large, community-based sample of men and women, circulating angiogenic cell phenotypes largely were not associated with measures of vascular function or arterial stiffness in analyses adjusting for traditional risk factors. PMID:22093724

Cheng, Susan; Wang, Na; Larson, Martin G.; Palmisano, Joseph N.; Mitchell, Gary F.; Benjamin, Emelia J.; Vasan, Ramachandran S; Levy, Daniel; McCabe, Elizabeth L.; Vita, Joseph A.; Wang, Thomas J.; Shaw, Stanley Y.; Cohen, Kenneth S.; Hamburg, Naomi M.

2011-01-01

276

Stiffness of glycerinated rabbit psoas fibers in the rigor state. Filament-overlap relation.  

PubMed Central

The stiffness of glycerinated rabbit psoas fibers in the rigor state was measured at various sarcomere lengths in order to determine the distribution of the sarcomere compliance between the cross-bridge and other structures. The stiffness was determined by measuring the tension increment at one end of a fiber segment while stretching the other end of the fiber. The contribution of the end compliance to the rigor segments was checked both by laser diffractometry of the sarcomere length change and by measuring the length dependence of the Young's modulus; the contribution was found to be small. The stiffness in the rigor state was constant at sarcomere lengths of 2.4 microns or less; at greater sarcomere lengths the stiffness, when corrected for the contribution of resting stiffness, scaled with the amount of overlap between the thick and thin filaments. These results suggest that the source of the sarcomere compliance of the rigor fiber at the full overlapping of filaments is mostly the cross-bridge compliance. Images FIGURE 2 FIGURE 5 PMID:6713072

Tawada, K; Kimura, M

1984-01-01

277

Gender differences in the passive stiffness of the human gastrocnemius muscle during stretch.  

PubMed

The aim of this study was to determine whether muscle stiffness measured in vivo was different between males and females. Distal displacement of the gastrocnemius medialis myotendinous junction was measured directly using ultrasonography during passive dorsiflexion in eight males and eight females (age range 19-28 years). Plantarflexion torque and myotendinous junction displacement were measured at 5° intervals, where 0° was with the foot at right angles to the tibia. Stiffness of the gastrocnemius medialis muscle was calculated between 0° and 25° of dorsiflexion, and defined as passive plantarflexion torque/distal displacement of the myotendinous junction (N m cm(-1)). Relative muscle stiffness was also calculated as distal displacement relative to resting muscle length, and as passive torque relative to plantarflexion maximal voluntary contraction torque. No significant gender difference was observed in passive dorsiflexion torque, or in passive torque/maximal voluntary torque throughout the range of motion. Distal displacement of the gastrocnemius myotendinous junction was 26% more in females than in males (P < 0.05). Myotendinous junction displacement was 5.0 ± 1.4% of resting gastrocnemius medialis length in females, and 3.9 ± 0.6% in males. Over 25° of passive dorsiflexion, gastrocnemius medialis muscle stiffness was greater in males than in females by 44% (P < 0.05). In conclusion, based on the in vivo assessment of myotendinous junction displacement, passive gastrocnemius medialis muscle stiffness is greater in males than in females. PMID:21298445

Morse, Christopher I

2011-09-01

278

Assessment of passive knee stiffness and viscosity in individuals with spinal cord injury using pendulum test.  

PubMed

Objective Stiffness and viscosity represent passive resistances to joint motion related with the structural properties of the joint tissue and of the musculotendinous complex. Both parameters can be affected in patients with spinal cord injury (SCI). The purpose of this study was to measure passive knee stiffness and viscosity in patients with SCI with paraplegia and healthy subjects using Wartenberg pendulum test. Design Non-experimental, cross-sectional, case-control design. Setting An outpatient physical therapy clinic, University of social welfare and Rehabilitation Science, Iran. Patients A sample of convenience sample of 30 subjects participated in the study. Subjects were categorized into two groups: individuals with paraplegic SCI (n = 15, age: 34.60 ± 9.18 years) and 15 able-bodied individuals as control group (n = 15, age: 30.66 ± 11.13 years). Interventions Not applicable. Main measures Passive pendulum test of Wartenberg was used to measure passive viscous-elastic parameters of the knee (stiffness, viscosity) in all subjects. Results Statistical analysis (independent t-test) revealed significant difference in the joint stiffness between healthy subjects and those with paraplegic SCI (P = 0.01). However, no significant difference was found in the viscosity between two groups (P = 0.17). Except for first peak flexion angle, all other displacement kinematic parameters exhibited no statistically significant difference between normal subjects and subjects with SCI. Conclusions Patients with SCI have significantly greater joint stiffness compared to able-bodied subjects. PMID:25437824

Joghtaei, Mahmoud; Arab, Amir Massoud; Hashemi-Nasl, Hamed; Joghataei, Mohammad Taghi; Tokhi, Mohammad Osman

2015-03-01

279

Lamb Wave Stiffness Characterization of Composites Undergoing Thermal-Mechanical Aging  

NASA Technical Reports Server (NTRS)

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.

Seale, Michael D.; Madaras, Eric I.

2004-01-01

280

Lifestyle Modification Decreases Arterial Stiffness in Overweight and Obese Men: Dietary Modification vs. Exercise Training.  

PubMed

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

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

2015-02-01

281

Effects of weight loss and insulin reduction on arterial stiffness in the SAVE trial  

PubMed Central

Background Chronic arterial stiffness contributes to the negative health effects of obesity and insulin resistance, which include hypertension, stroke, and increased cardiovascular and all-cause mortality. Weight loss and improved insulin sensitivity are individually associated with improved central arterial stiffness; however, their combined effects on arterial stiffness are poorly understood. The purpose of this study was to determine how insulin levels modify the improvements in arterial stiffness seen with weight loss in overweight and obese young adults. Methods To assess the effects of weight loss and decreased fasting insulin on vascular stiffness, we studied 339 participants in the Slow the Adverse Effects of Vascular Aging (SAVE) trial. At study entry, the participants were aged 20–45, normotensive, non-diabetic, and had a body-mass index of 25–39.9?kg/m2. Measures of pulse wave velocity (PWV) in the central (carotid-femoral (cfPWV)), peripheral (femoral-ankle (faPWV)), and mixed (brachial-ankle (baPWV)) vascular beds were collected at baseline and 6?months. The effects of 6-month change in weight and insulin on measures of PWV were estimated using multivariate regression. Results After adjustment for baseline risk factors and change in systolic blood pressure, 6-month weight loss and 6-month change in fasting insulin independently predicted improvement in baPWV but not faPWV or cfPWV. There was a significant interaction between 6-month weight change and change in fasting insulin when predicting changes in baPWV (p?stiffness. This improvement in vascular stiffness with weight loss and insulin declines may occur throughout the vasculature and may not be limited to individual vascular beds. Trial registration NCT00366990 PMID:22998737

2012-01-01

282

Representations of multi-joint stiffness for prosthetic limb design  

Microsoft Academic Search

Human limbs have inherent spring-like properties that have been shown to be important for posture and movement control. When an amputated limb is augmented with a powered prosthesis, the stiffness properties of the resulting limb-prosthesis combination are an important aspect of the performance of the system. Limb stiffness properties are typically represented as stiffness ellipses or isopotential ellipses at the

Chad E. English; Donald L. Russell

2008-01-01

283

The hydrostatic stiffness of flexible floating structures for linear hydroelasticity  

Microsoft Academic Search

The formulation of the hydrostatic stiffness for linear rigid body hydrodynamics is well known. An explicit formulation for an analogous hydrostatic stiffness in linear hydroelasticity, which is applicable to both rigid body and flexible displacement, is not as well-known. Three such formulations have been proposed previously in the literature, none of which is quite correct; all produce an unsymmetric stiffness

L. L. Huang; H. R. Riggs

2000-01-01

284

Stiffness tensor random fields through upscaling of planar random materials  

E-print Network

of media having the same random geometries) [1­3] to assess the in-plane stiffness tensor RF. OnceStiffness tensor random fields through upscaling of planar random materials Michael P. Sena: Random microstructure Random fields Stiffness tensor Compliance tensor Mesoscale Correlation structure

Ostoja-Starzewski, Martin

285

Active stiffness control of a manipulator in cartesian coordinates  

Microsoft Academic Search

A method of actively controlling the apparent stiffness of a manipulator end effecter is presented. The approach allows the programmer to specify the three transnational and three rotational stiffness of a frame located arbitrarily in hand coordinates. Control of the nominal position of the hand then permits simultaneous position and force control. Stiffness may be changed under program control to

J. Kenneth Salisbury

1980-01-01

286

Torque transmission mechanism with nonlinear passive stiffness using mechanical singularity  

Microsoft Academic Search

To introduce a passive compliant mechanism for robot joints is an effective way for impact absorption. However, because robot joints also require high torque transmission characteristic, the simultaneous implementation of stiffness and softness is a significant issue. In this paper, we develop a torque transmission mechanism with nonlinear passive stiffness that realizes from zero to extremely high stiffness based on

Masafumi Okada; Shintaro Kino

2008-01-01

287

A new configuration of the Zeiss LSM 510 for simultaneous optical separation of green and red fluorescent protein pairs.  

PubMed

The power and simplicity of genetically encoded fluorophores (fluorescent proteins, FPs) have drawn many molecular biologists to light microscopy. First generation FPs suffered from overlapping excitation and emission spectra, which limited their use together in pairs (Patterson et al., J Cell Sci 2001;114 (Part 5):837-838). Image acquisition and processing techniques, collectively known as linear unmixing, have been developed to separate overlapping fluorescence signals encountered in the imaging of FP pairs and also in FRET. These specialized techniques are not without their potential drawbacks, including limitations on sensitivity and time-resolution for live cell imaging, and the risk of artifact in the hands of nonspecialists. With the advent of a new generation of red-shifted FPs (Shaner et al., Nat Biotechnol 2004;22:1567-1572; Verkhusha and Lukyanov, Nat Biotechnol 2004;22:289-296) careful selection of excitation sources and emission filters obviate the need for linear unmixing when simple two channel imaging of FPs is required. Here we introduce a new configuration of the Zeiss LSM 510 laser scanning confocal microscope, optimized for live cell imaging of green fluorescent protein (GFP) together with spectral variants such as mRFP1 and mCherry using standard photo-multipliers. A 2 mW, 594 nm HeNe laser was chosen as the excitation source for the red FP. This wavelength efficiently excites the aforementioned red variants without limiting the detection range of GFP emission during simultaneous two-channel imaging. Compared to excitation of GFP and mCherry at 488 and 543 nm, excitation at 488 and 594 nm approximately doubles the sensitivity of GFP detection and eliminates bleed-through of GFP into the mCherry channel. However, sensitivity of mCherry detection is decreased by 30%, suggesting the need for red FPs having longer emission peaks. Practical advantages to the simultaneous optical separation of FPs with nonoverlapping emission spectra include simplicity, robustness, reduced risk of artifact, and increased sensitivity during live cell imaging. PMID:16969813

Anderson, Kurt I; Sanderson, Jeremy; Gerwig, Silke; Peychl, Jan

2006-08-01

288

The bizarre stiff hip. Possible idiopathic chondrolysis.  

PubMed

Idiopathic chondrolysis of the hip is characterized by pain and limp in adolescence, with progressive loss of articular cartilage space and stiffness of the hip. In our five cases, the best results were obtained in those patients immobilized in a position of function. Those cases in which range-of-motion exercises were carried out resulted in ankylosis in a position of excessive flexion. PMID:1172705

Duncan, J W; Schrantz, J L; Nasca, R J

1975-01-27

289

METHOD OF HYPERBOLIC SYSTEMS WITH STIFF RELAXATION  

SciTech Connect

Three methods are analyzed for solving a linear hyperbolic system that contains stiff relaxation. We show that the semi-discrete discontinuous Galerkin method, with a linear basis, is accurate when the relaxation time is unresolved (asymptotically preserving--AP). A recently developed central method is shown to be non-AP. To discriminate between AP and non-AP methods, we argue that one must study problems that are diffusion dominated.

R. B. LOWRIE; J. E. MOREL

2001-03-01

290

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

NASA Technical Reports Server (NTRS)

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

Wu, K. Chauncey; Gurdal, Zafer

2006-01-01

291

Multijoint arm stiffness during movements following stroke: implications for robot therapy.  

PubMed

Impaired arm movements in stroke appear as a set of stereotypical kinematic patterns, characterized by abnormal joint coupling, which have a direct consequence on arm mechanics and can be quantified by the net arm stiffness at the hand. The current available measures of arm stiffness during functional tasks have limited clinical use, since they require several repetitions of the same test movement in many directions. Such procedure is difficult to obtain in stroke survivors who have lower fatigue threshold and increased variability compared to unimpaired individuals. The present study proposes a novel, fast quantitative measure of arm stiffness during movements by means of a Time-Frequency technique and the use of a reassigned spectrogram, applied on a trial-by-trial basis with a single perturbation. We tested the technique feasibility during robot mediated therapy, where a robot helped stroke survivors to regain arm mobility by providing assistive forces during a hitting task to 13 targets covering the entire reachable workspace. The endpoint stiffness of the paretic arm was estimated at the end of each hitting movements by suddenly switching of the assistive forces and observing the ensuing recoil movements. In addition, we considered how assistive forces influence stiffness. This method will provide therapists with improved tools to target the treatment to the individual's specific impairment and to verify the effects of the proposed exercises. PMID:22275576

Piovesan, D; Casadio, M; Mussa-Ivaldi, F A; Morasso, P G

2011-01-01

292

Ethnic Differences in Bending Stiffness of the Ulna and Tibia  

NASA Technical Reports Server (NTRS)

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%.

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

293

Anomalies in stiffness and damping of a 2D discrete viscoelastic system due to negative stiffness components  

E-print Network

thin films with unusual in-plane mechanical properties. © 2006 Elsevier B.V. All rights reservedAnomalies in stiffness and damping of a 2D discrete viscoelastic system due to negative stiffness Available online 24 February 2006 Abstract The recent development of using negative stiffness inclusions

Lakes, Roderic

294

Nonaffine rubber elasticity for stiff polymer networks  

E-print Network

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.

C. Heussinger; B. Schaefer; E. Frey

2007-11-26

295

Servo-controlled indenter for determining the transverse stiffness of ventricular muscle.  

PubMed

Regional ventricular wall stress is a critical determinant of cardiac function. There are, however, no validated methods for accurately estimating this stress. We have shown in the isolated ventricular septum that, during steady-state indentations, the transverse stiffness (the ratio of indentation stress [pressure acting on indenter face] to indentation strain [amount of indentation/nonindented thickness]) can be used as an estimate of the in-plane wall stress. Because of the long acquisition time for those transverse stiffness determinations, it was not possible to follow changes in wall stress over a single contraction. We recently developed a dynamic indentation system that can determine transverse stiffness in as little as 10 ms, allowing estimation of wall stress over a single contraction cycle. The apparatus consists of an indentation probe coupled to a linear motor. This indentation system was tested on two beating canine ventricular septa that were mounted in a biaxial system the could apply strains in the plane of the septa and measure the resulting in-plane stresses. The probe indented the septa with peak displacements of 0.1-0.5 mm at frequencies of 20 and 50 Hz. The transverse stiffness was calculated as the slope of the relation between the indentation stress and indentation strain during each high-frequency indentation. Consistent with earlier studies, the transverse stiffness was related to the inplane stress. In contrast to earlier studies, however, these dynamic transverse stiffness determinations could be made during a single contraction. Thus, dynamic transverse stiffness determinations allow estimation of wall stress in the isolated septa by minimal surface contact, and may lead to methods for estimating wall stress in the intact heart. PMID:1879850

Halperin, H R; Tsitlik, J E; Gelfand, M; Downs, J; Yin, F C

1991-06-01

296

In vivo tibial stiffness is maintained by whole bone morphology and cross-sectional geometry in growing female mice  

PubMed Central

Whole bone morphology, cortical geometry, and tissue material properties modulate skeletal stresses and strains that in turn influence skeletal physiology and remodeling. Understanding how bone stiffness, the relationship between applied load and tissue strain, is regulated by developmental changes in bone structure and tissue material properties is important in implementing biophysical strategies for promoting healthy bone growth and preventing bone loss. The goal of this study was to relate developmental patterns of in vivo whole bone stiffness to whole bone morphology, cross-sectional geometry, and tissue properties using a mouse axial loading model. We measured in vivo tibial stiffness in three age groups (6wks, 10wks, 16wks old) of female C57Bl/6 mice during cyclic tibial compression. Tibial stiffness was then related to cortical geometry, longitudinal bone curvature, and tissue mineral density using microcomputed tomography (microCT). Tibial stiffness and the stresses induced by axial compression were generally maintained from 6 to 16wks of age. Growth-related increases in cortical cross-sectional geometry and longitudinal bone curvature had counteracting effects on induced bone stresses and, therefore, maintained tibial stiffness similarly with growth. Tissue mineral density increased slightly from 6 to 16wks of age, and although the effects of this increase on tibial stiffness were not directly measured, its role in the modulation of whole bone stiffness was likely minor over the age range examined. Thus, whole bone morphology, as characterized by longitudinal curvature, along with cortical geometry, plays an important role in modulating bone stiffness during development and should be considered when evaluating and designing in vivo loading studies and biophysical skeletal therapies. PMID:20673665

Main, Russell P.; Lynch, Maureen E.; van der Meulen, Marjolein C.H.

2010-01-01

297

The effect of sprung (suspended) floors on leg stiffness during grand jeté landings in ballet.  

PubMed

This study compared stiffness of the landing leg in ballet dancers performing grand jeté on a sprung floor to leg stiffness during the same movement on a hard floor (wood on concrete). Leg stiffness was calculated as the ratio of vertical ground reaction force (in Newtons) to compression of the lower limb (in meters). Thirteen female dancers were measured for five repetitions each at the point of maximum leg compression while landing grand jeté on both of the surfaces, such that 20 milliseconds of data were represented for each trial. The stiffness of the landing leg at the point of maximum compression was decreased by a mean difference score of 6168.0 N/m ± 11,519.5 N/m on the hard floor compared to the sprung floor. Paired t-test yielded a one-tailed probability of p = 0.038. This effect was seen in 11 of the 13 participants. The finding of increased stiffness of the landing leg in the sprung floor condition suggests that some of the force of landing the leap was absorbed by the surface, and therefore did not need to be absorbed by the landing leg itself. This in turn implies that a sprung dance floor may help to prevent dance-related injuries. PMID:22040759

Hackney, James; Brummel, Sara; Jungblut, Kara; Edge, Carissa

2011-09-01

298

Multicomponent supplement containing Chlorella decreases arterial stiffness in healthy young men.  

PubMed

Chlorella, a unicellular green alga, contains various antioxidants and other nutrients such as amino acids and fiber. Previous studies have reported that supplementation with multiple antioxidants reduces arterial stiffness, a well-established cardiovascular risk factor. We investigated the effects of Chlorella intake on arterial stiffness using a single-blinded, placebo-controlled crossover study design. Fourteen young men took placebo or Chlorella tablets for four weeks, with a 12-week washout period between trials, in a randomized order. Before and after each trial, blood pressure, heart rate, and brachial-ankle pulse wave velocity, an index of arterial stiffness, were measured. Treatment compliance was comparable between the two groups. There were no differences in blood pressure and heart rate before and after supplementation in both the placebo and Chlorella groups. Brachial-ankle pulse wave velocity decreased after Chlorella intake (before vs after intake; 11.6 ± 0.2 vs 11.1 ± 0.1 m/s, p = 0.01), but not after placebo intake (11.4 ± 0.2 vs 11.4 ± 0.2 m/s, p = 0.98). Multicomponent analysis of the Chlorella-containing tablet detected nutrients that can reduce arterial stiffness, such as antioxidant vitamins, arginine, potassium, calcium, and n-3 unsaturated fatty acids. These results suggest that intake of a Chlorella-containing multicomponent supplement can decrease arterial stiffness. PMID:24249971

Otsuki, Takeshi; Shimizu, Kazuhiro; Iemitsu, Motoyuki; Kono, Ichiro

2013-11-01

299

Matrix stiffness determines the fate of nucleus pulposus-derived stem cells.  

PubMed

Intervertebral disc (IVD) degeneration and consequent low-back pain present a major medical challenge. Nucleus pulposus-derived stem cells (NP-SCs) may lead to a novel therapy for this severe disease. It was recently shown that survival and function of mature NP cells are regulated in part by tissue stiffness. We hypothesized that modification of matrix stiffness will influence the ability of cultured NP-SCs to proliferate, survive, and differentiate into mature NP cells. NP-SCs were subcultured in three-dimensional matrices of varying degrees of stiffness as measured by the material's shear storage modulus. Cell survival, activity, and rate of differentiation toward the chondrogenic or osteogenic lineage were analyzed. NP-SCs were found to proliferate and differentiate in all matrices, irrespective of matrix stiffness. However, matrices with a low shear storage modulus (G' = 1 kPa) promoted significantly more proliferation and chondrogenic differentiation, whereas matrices with a high modulus (G' = 2 kPa) promoted osteogenic differentiation. Imaging performed via confocal and scanning electron microscopes validated cell survival and highlighted stiffness-dependent cell-matrix interactions. These results underscore the effect of the matrix modulus on the fate of NP-SCs. This research may facilitate elucidation of the complex cross-talk between NP-SCs and their surrounding matrix in healthy as well as pathological conditions. PMID:25725556

Navaro, Yosi; Bleich-Kimelman, Nadav; Hazanov, Lena; Mironi-Harpaz, Iris; Shachaf, Yonatan; Garty, Shai; Smith, Yoav; Pelled, Gadi; Gazit, Dan; Seliktar, Dror; Gazit, Zulma

2015-05-01

300

Animals prefer leg stiffness values that may reduce the energetic cost of locomotion.  

PubMed

Despite the neuromechanical complexity and wide diversity of running animals, most run with a center-of-mass motion that is similar to a simple mass bouncing on a spring. Further, when animals? effective leg stiffness is measured and normalized for size and weight, the resulting relative leg stiffness that most animals prefer lies in a narrow range between 7 and 27. Understanding why this nearly universal preference exists could shed light on how whole animal behaviors are organized. Here we show that the biologically preferred values of relative leg stiffness coincide with a theoretical minimal energetic cost of locomotion. This result strongly implies that animals select and regulate leg stiffness in order to reduce the energy required to move, thus providing animals an energetic advantage. This result also helps explain how high level control targets such as energy efficiency might influence overall physiological parameters and the underlying neuromechanics that produce it. Overall, the theory presented here provides an explanation for the existence of a nearly universal preferred leg stiffness. Also, the results of this work are beneficial for understanding the principles underlying human and animal locomotion, as well as for the development of prosthetic, orthotic and robotic devices. PMID:25234232

Shen, ZhuoHua; Seipel, Justin

2015-01-01

301

Hinge stiffness is a barrier to RNA folding  

PubMed Central

Cation-mediated RNA folding from extended to compact, biologically active conformations relies on a temporal balance of forces. The Mg2+-mediated folding of the Tetrahymena thermophila ribozyme is characterized by rapid non-specific collapse followed by tertiary contact induced compaction. This paper focuses on an autonomously folding portion of the Tetrahymena ribozyme, its P4–P6 domain, in order to probe one facet of the rapid collapse: chain flexibility. The time evolution of P4–P6 folding was followed by global and local measures as a function of Mg2+ concentration. While all concentrations of Mg2+ studied are sufficient to screen the charge on the helices, the rates of compaction and tertiary contact formation diverge as the concentration of Mg2+ increases; collapse is greatly accelerated by Mg2+ while tertiary contact formation is not. These studies highlight the importance of chain stiffness to RNA folding; at 10 mM Mg2+ a stiff hinge limits the rate of P4–P6 folding. At higher magnesium concentrations the rate limiting step shifts from hinge bending to tertiary contact formation. PMID:18471829

Schlatterer, Jörg C.; Kwok, Lisa W.; Lamb, Jessica S.; Park, Hye Yoon; Andresen, Kurt; Brenowitz, Michael; Pollack, Lois

2008-01-01

302

Characterization of superconducting magnetic bearings (dynamic stiffness and damping coefficient in axial direction)  

NASA Technical Reports Server (NTRS)

High T(sub c) superconductor as a stator and permanent magnets for a rotor were assembled into a superconducting magnetic bearing. The dynamic stiffness and the damping coefficient of the superconducting magnetic bearing in axial direction were measured. The dynamic stiffness depended on an axial gap between superconductor and permanent magnet. The superconducting magnetic bearings are advantageous for a passive bearing, because they have a vibration damping effect that a permanent magnet bearing does not have. The tendency of its vibration damping coefficient indicated an increase as the resonant frequency increased.

Takahata, Ryoichi; Ueyama, Hirochika; Yotsuya, Tsutom

1992-01-01

303

Assessments of Arterial Stiffness and Endothelial Function Using Pulse Wave Analysis  

PubMed Central

Conventionally, the assessments of endothelial function and arterial stiffness require different sets of equipment, making the inclusion of both tests impractical for clinical and epidemiological studies. Pulse wave analysis (PWA) provides useful information regarding the mechanical properties of the arterial tree and can also be used to assess endothelial function. PWA is a simple, valid, reliable, and inexpensive technique, offering great clinical and epidemiological potential. The current paper will outline how to measure arterial stiffness and endothelial function using this technique and include discussion of validity and reliability. PMID:22666595

Stoner, Lee; Young, Joanna M.; Fryer, Simon

2012-01-01

304

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

NASA Astrophysics Data System (ADS)

We study the aggregation transition of a finite theta-polymer system in dependence on the bending stiffness ? 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\\text-? 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.

Zierenberg, Johannes; Janke, Wolfhard

2015-01-01

305

Optical imaging of resting-state functional connectivity in a novel arterial stiffness model  

PubMed Central

This study aims to assess the impact of unilateral increases in carotid stiffness on cortical functional connectivity measures in the resting state. Using a novel animal model of induced arterial stiffness combined with optical intrinsic signals and laser speckle imaging, resting state functional networks derived from hemodynamic signals are investigated for their modulation by isolated changes in stiffness of the right common carotid artery. By means of seed-based analysis, results showed a decreasing trend of homologous correlation in the motor and cingulate cortices. Furthermore, a graph analysis indicated a randomization of the cortex functional networks, suggesting a loss of connectivity, more specifically in the motor cortex lateral to the treated carotid, which however did not translate in differentiated metabolic activity. PMID:24298398

Guevara, Edgar; Sadekova, Nataliya; Girouard, Hélène; Lesage, Frédéric

2013-01-01

306

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

PubMed Central

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

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

2013-01-01

307

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

E-print Network

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.

Johannes Zierenberg; Wolfhard Janke

2015-01-24

308

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

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

309

Angiopoietin-2-induced arterial stiffness in CKD.  

PubMed

The mechanism of vascular calcification in CKD is not understood fully, but may involve collagen deposition in the arterial wall upon osteo/chondrocytic transformation of vascular smooth muscle cells (VSMCs). Increased levels of circulating angiopoietin-2 correlate with markers of CKD progression and angiopoietin-2 regulate inflammatory responses, including intercellular and vascular adhesion and recruitment of VSMCs. Here, we investigate the potential role of angiopoietin-2 in the pathogenesis of arterial stiffness associated with CKD. In a cohort of 416 patients with CKD, the plasma level of angiopoietin-2 correlated independently with the severity of arterial stiffness assessed by pulse wave velocity. In mice subjected to 5/6 subtotal nephrectomy or unilateral ureteral obstruction, plasma levels of angiopoietin-2 also increased. Angiopoietin-2 expression markedly increased in tubular epithelial cells of fibrotic kidneys but decreased in other tissues, including aorta and lung, after 5/6 subtotal nephrectomy. Expression of collagen and profibrotic genes in aortic VSMCs increased in mice after 5/6 subtotal nephrectomy and in mice producing human angiopoietin-2. Angiopoietin-2 stimulated endothelial expression of chemokines and adhesion molecules for monocytes, increased Ly6C(low) macrophages in aorta, and increased the expression of the profibrotic cytokine TGF-?1 in aortic endothelial cells and Ly6C(low) macrophages. Angiopoietin-2 blockade attenuated expression of monocyte chemokines, profibrotic cytokines, and collagen in aorta of mice after 5/6 subtotal nephrectomy. This study identifies angiopoietin-2 as a link between kidney fibrosis and arterial stiffness. Targeting angiopoietin-2 to attenuate inflammation and collagen expression may provide a novel therapy for cardiovascular disease in CKD. PMID:24511140

Chang, Fan-Chi; Chiang, Wen-Chih; Tsai, Ming-Hsuan; Chou, Yu-Hsiang; Pan, Szu-Yu; Chang, Yu-Ting; Yeh, Pei-Ying; Chen, Yi-Ting; Chiang, Chih-Kang; Chen, Yung-Ming; Chu, Tzong-Shinn; Wu, Kwan-Dun; Lin, Shuei-Liong

2014-06-01

310

An improved spinning lens test to determine the stiffness of the human lens  

PubMed Central

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

Burd, H.J.; Wilde, G.S.; Judge, S.J.

2011-01-01

311

Relation Between Coronary Artery Disease, Aortic Stiffness, and Left Ventricular Structure in a Population Sample  

Microsoft Academic Search

To elucidate the relationship between coronary artery disease (CAD), aortic stiffness, and left ventricular structure, we recruited 55 subjects (33 men; average age, 6361 years) with previously unknown CAD from a healthy general population sample, as well as 55 control subjects matched for gender, age, and serum cholesterol level. We measured arterial blood pressure and the systolic expansion of the

Christoph D. Gatzka; James D. Cameron; Bronwyn A. Kingwell; Anthony M. Dart

312

Impact of Aortic Stiffness on Survival in End Stage Renal Disease  

Microsoft Academic Search

population, all-cause mortality-adjusted OR was 1.39 (95% CI, 1.19 to 1.62). Conclusions-These results provide the first direct evidence that in patients with ESRD, increased aortic stiffness determined by measurement of aortic PWV is a strong independent predictor of all-cause and mainly cardiovascular mortality. {Circulation. 1999;99:2434-2439.)

Jacques Blacher; Alain P. Guerin; Bruno Pannier; Sylvain I. Marchais; Michel E. Safar; Gerard M. London

313

ADAPTIVE ROBUST MOTION AND FORCE TRACKING CONTROL OF ROBOT MANIPULATORS IN CONTACT WITH STIFF SURFACES  

E-print Network

ADAPTIVE ROBUST MOTION AND FORCE TRACKING CONTROL OF ROBOT MANIPULATORS IN CONTACT WITH STIFF Abstract High performance robust motion and force tracking control of robot manipulators in contact controller is proposed, which needs measurements of position, velocity and interaction force only

Yao, Bin

314

The development of advanced materials: Negative Poisson's ratio materials, high damping and high stiffness materials, and composites with negative stiffness inclusions and their stability  

NASA Astrophysics Data System (ADS)

The manufacture of negative Poisson's ratio polymeric foams was based on a thermal transformation technique to convert the convex cell shape of conventional foams to a concave or re-entrant shape through triaxial compression and heating. Poisson's ratio measurements were performed with a laser-based setup for non-transparent materials with high accuracy. Contrary to the predictions of the theory of elasticity, we observed cell size influences on Poisson's ratio of conventional and transformed foams. The theoretical study of the contact problem involving materials with negative Poisson's ratios revealed a further reduction on contact pressure between the contacting two bodies in comparison with materials with positive Poisson's ratio. The classical Hertz contact theory and 3D elasticity solution in an asymptotic form for finite-thickness, layered media indented by an elastic spherical were used. As for advanced composite materials, theoretically, significant amplification was found in composites' mechanical, thermal, electrical or coupled field properties due to negative stiffness inclusions. Experimentally, we fabricated high damping and high stiffness composite materials, SiC-InSn, to obtain a realization of the prediction from composite theory. With the idea of using negative stiffness components, we manufactured Sn, Zn or Al composites with 1% VO2 particles by volume, where the transforming particles, VO 2, were used as a negative stiffness source, and observed anomalies both in overall stiffness and tan delta. Broadband viscoelastic spectroscopy (BVS) was used to measure mechanical properties. The transformation of the eutectoid ZnAl was studied with resonant ultrasound spectroscopy (RUS), and about a 30% increase in shear modulus and tan delta, respectively, were observed. To investigate the stability of systems with negative stiffness elements, several discrete viscoelastic models were analyzed. With the Lyapunov indirect stability theorem, we found that extreme high mechanical damping can exist in an unconditional stable manner. Equilibrium configurations corresponding to extreme high stiffness were metastable. The metastability was dominated by the viscosity of the systems. The observability of the metastable systems can be achieved when the rate of divergence was slower than the rate of switching states. Strong ellipticity and stability theorems in elasticity for continuum media were studied.

Wang, Yun-Che

315

On waveguide modeling of stiff piano strings.  

PubMed

Bensa et al. [J. Acoust. Soc. Am. 114, 1095-1107 (2003), Sec. IV] recently proposed a waveguide model for the transverse displacement of a stiff piano string. The study described here is an attempt to cast a complementary light on this topic, based on a common wave approach instead of a modal approach. A pair of weakly attenuated traveling waves and a pair of fast-decaying waves both satisfy the one-dimensional wave equation developed by Bensa et al. These solutions have to be carefully considered, however, for portions of string interacting with the hammer felt, the bridge, or the capo d'astro bar. PMID:16240835

Ducasse, Eric

2005-09-01

316

Arthrodiastasis for stiff hips in young patients.  

PubMed

Joint distraction (arthrodiastasis) with a unilateral fixator was used to treat 9 patients with stiffness of the hip which had followed Perthes' disease (3), epiphysiolysis (2), congenital dysplasia (2), tuberculosis (1) and idiopathic chondrolysis (1). Their average age was 14 years, and they all had pain, limp and shortening of the leg. Distraction of 0.5 to 1 cm was maintained for an average of 94 days. The average range of movement subsequently was 65 degrees compared with 20 degrees before. The articular space was widened by an average of 2.8 mm, and only 3 patients had pain on follow up. PMID:8407045

Cañadell, J; Gonzales, F; Barrios, R H; Amillo, S

1993-01-01

317

On waveguide modeling of stiff piano strings  

NASA Astrophysics Data System (ADS)

Bensa et al. [J. Acoust. Soc. Am. 114, 1095-1107 (2003), Sec. IV] recently proposed a waveguide model for the transverse displacement of a stiff piano string. The study described here is an attempt to cast a complementary light on this topic, based on a common wave approach instead of a modal approach. A pair of weakly attenuated traveling waves and a pair of fast-decaying waves both satisfy the one-dimensional wave equation developed by Bensa et al. These solutions have to be carefully considered, however, for portions of string interacting with the hammer felt, the bridge, or the capo d'astro bar.

Ducasse, Éric

2005-09-01

318

Discontinuous Galerkin for Stiff Hyperbolic Systems  

SciTech Connect

A Discontinuous Galerkin (DG) method is applied to hyperbolic systems that contain stiff relaxation terms. We demonstrate that when the relaxation time is under-resolved, DG is accurate in the sense that the method accurately represents the system's Chapman-Enskog (or ''diffusion'') approximation. Moreover, we demonstrate that a high-resolution, finite-volume method using the same time-integration method as DG is very inaccurate in the diffusion limit. Results for DG are presented for the hyperbolic heat equation, the Broadwell model of gas kinetics, and coupled radiation-hydrodynamics.

Lowrie, R.B.; Morel, J.E.

1999-06-27

319

EFFECT OF PASSIVE HEAT STRESS ON ARTERIAL STIFFNESS  

PubMed Central

Arterial compliance, the inverse of arterial stiffness, is a prognostic indicator of arterial health. Central and peripheral arterial compliance decrease with acute cold stress and may increase post exercise when exercise-induced elevations in core temperature are likely still present. Increased blood flow through the conduit arteries associated with elevated core temperature increases shear stress which in turn releases nitric oxide and other endothelial derived factors. These changes, in conjunction with supportive in vitro data, suggest that elevated core temperature may indirectly increase central and peripheral arterial compliance (i.e., decrease arterial stiffness). The purpose of this study was to test the hypothesis that increased core temperature decreases central and peripheral arterial stiffness, as measured with pulse wave velocity (PWV). Using Doppler ultrasound, carotid-femoral (central) and carotid-radial (peripheral) arterial PWVs were measured from eight subjects (age 37 ± 11 years; mass 68.8 ± 11.1 kg; height 171 ± 3 cm) before and during passive heat-stress induced increases in core temperature of 0.47 ± 0.05, 1.03 ± 0.12, and 1.52 ± 0.07°C (i.e., baseline, 0.5, 1.0, and 1.5°C, respectively). Changes in PWV were evaluated with a one-way repeated measures ANOVA. When analyzed as group means, neither central (677 ± 161, 617 ± 72, 659 ± 74, and 766 ± 207 cm/s; P=0.12) nor peripheral (855 ± 192, 772 ± 95, 759 ± 49, and 858 ± 247 cm/s; P=0.56) PWV changed as core temperature increased from baseline to 0.5, 1.0, and 1.5°C, respectively. However, individual changes in central (average r = ?0.89, P < 0.05) and peripheral (average r = ?0.93, P < 0.05) PWV with heat stress were significantly correlated with normothermic baseline PWV. In conclusion, these data suggest that the magnitude by which heat stress reduced PWV was predicated upon normothermic PWV, with the individuals having the highest normothermic PWV being most responsive to the heat stress-induced reductions in PWV. PMID:21685446

Ganio, Matthew S.; Brothers, R. Matthew; Shibata, Shigeki; Hastings, Jeffrey L.; Crandall, Craig G.

2011-01-01

320

Comparison of plantar flexor musculotendinous stiffness, geometry, and architecture in male runners with and without a history of tibial stress fracture.  

PubMed

Greater lower extremity joint stiffness may be related to the development of tibial stress fractures in runners. Musculotendinous stiffness is the largest contributor to joint stiffness, but it is unclear what factors contribute to musculotendinous stiffness. The purpose of this study was to compare plantar flexor musculotendinous stiffness, architecture, geometry, and Achilles tendon stiffness between male runners with and without a history of tibial stress fracture. Nineteen healthy runners (age = 21 ± 2.7 years; mass = 68.2 ± 9.3 kg; height = 177.3 ± 6.0 cm) and 19 runners with a history of tibial stress fracture (age = 21 ± 2.9 years; mass = 65.3 ± 6.0 kg; height = 177.2 ± 5.2 cm) were recruited from community running groups and the university's varsity and club cross-country teams. Plantar flexor musculotendinous stiffness was estimated from the damped frequency of oscillatory motion about the ankle follow perturbation. Ultrasound imaging was used to measure architecture and geometry of the medial gastrocnemius. Dependent variables were compared between groups via one-way ANOVAs. Previously injured runners had greater plantar flexor musculotendinous stiffness (P < .001), greater Achilles tendon stiffness (P = .004), and lesser Achilles tendon elongation (P = .003) during maximal isometric contraction compared with healthy runners. No differences were found in muscle thickness, pennation angle, or fascicle length. PMID:25320911

Pamukoff, Derek N; Blackburn, J Troy

2015-02-01

321

STIFF: Converting Scientific FITS Images to TIFF  

NASA Astrophysics Data System (ADS)

STIFF is a program that converts scientific FITS1 images to the more popular TIFF2 format for illustration purposes. Most FITS readers and converters do not do a proper job at converting FITS image data to 8 bits. 8-bit images stored in JPEG, PNG or TIFF files have the intensities implicitely stored in a non-linear way. Most current FITS image viewers and converters provide the user an incorrect translation of the FITS image content by simply rescaling linearly input pixel values. A first consequence is that the people working on astronomical images usually have to apply narrow intensity cuts or square-root or logarithmic intensity transformations to actually see something on their deep-sky images. A less obvious consequence is that colors obtained by combining images processed this way are not consistent across such a large range of surface brightnesses. Though with other software the user is generally afforded a choice of nonlinear transformations to apply in order to make the faint stuff stand out more clearly in the images, with the limited selection of choices provides, colors will not be accurately rendered, and some manual tweaking will be necessary. The purpose of STIFF is to produce beautiful pictures in an automatic and consistent way.

Bertin, Emmanuel

2011-10-01

322

Contact stiffness of randomly rough surfaces.  

PubMed

We investigate the contact stiffness of an elastic half-space and a rigid indenter with randomly rough surface having a power spectrum C2D(q)proportional q(-2H-2), where q is the wave vector. The range of H[symbol: see text] is studied covering a wide range of roughness types from white noise to smooth single asperities. At low forces, the contact stiffness is in all cases a power law function of the normal force with an exponent ?. For H > 2, the simple Hertzian behavior is observed . In the range of 0 < H < 2, the Pohrt-Popov behavior is valid (). For H < 0, a power law with a constant power of approximately 0.9 is observed, while the exact value depends on the number of modes used to produce the rough surface. Interpretation of the three regions is given both in the frame of the three dimensional contact mechanics and the method of dimensionality reduction (MDR). The influence of the long wavelength roll-off is investigated and discussed. PMID:24257034

Pohrt, Roman; Popov, Valentin L

2013-01-01

323

Early arthroscopic release in stiff shoulder  

PubMed Central

Purpose: To evaluate the results of early arthroscopic release in the patients of stiff shoulder Methods: Twenty patients of stiff shoulder, who had symptoms for at least three months and failed to improve with steroid injections and physical therapy of 6 weeks duration, underwent arthroscopic release. The average time between onset of symptoms and the time of surgery was 4 months and 2 weeks. The functional outcome was evaluated using ASES and Constant and Murley scoring systems. Results: All the patients showed significant improvement in the range of motion and relief of pain by end of three months following the procedure. At 12 months, mean improvement in ASES score is 38 points and Constant and Murley score is 4O.5 points. All patients returned to work by 3-5 months (average -4.5 months). Conclusion: Early arthroscopic release showed promising results with reliable increase in range of motion, early relief of symptoms and consequent early return to work. So it is highly recommended in properly selected patients. Level of evidence: Level IV PMID:20300309

Sabat, Dhananjaya; Kumar, Vinod

2008-01-01

324

Dynamics of a Gear System with Faults in Meshing Stiffness  

E-print Network

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.

Grzegorz Litak; Michael I. Friswell

2004-05-23

325

Rough set theory based robot stiffness tel-control  

Microsoft Academic Search

When the traditional robot stiffness control is applied into the internet environment, the uncertain time delay will bring a very austere problem of impact and stability to the system. So, a RST(rough set theory) based stiffness tel-controller was designed to solve the problem, and the result of experiment show that this controller can ensure the stability of the stiffness tel-control

Yunhong Lei; Jianxin Wang; Guanzhen Wu; Yongqing Zhou

2009-01-01

326

Human vertebral body apparent and hard tissue stiffness  

Microsoft Academic Search

Cancellous bone apparent stiffness and strength are dependent upon material properties at the tissue level and trabecular architecture. Microstructurally accurate, large-scale finite element (LS-FE) models were used to predict the experimental apparent stiffness of human vertebral cancellous bone and to estimate the trabecular hard tissue stiffness. Twenty-eight LS-FE models of cylindrical human vertebral cancellous bone specimens (8mm in diameter, 9.5mm

Fu J. Hou; Susan M. Lang; Susan J. Hoshaw; David A. Reimann; David P. Fyhrie

1998-01-01

327

Premature aortic stiffness in systemic lupus erythematosus by transesophageal echocardiography.  

PubMed

To assess aortic stiffness by transesophageal echocardiography (TEE) and to determine its clinical predictors and relation to age, blood pressure, renal function, and atherosclerosis, 50 patients with systemic lupus erythematosus (SLE), 94% women, with a mean age of 38 ± 12 years, and 22 age and gender-matched healthy controls underwent clinical and laboratory evaluations and multiplane TEE to assess stiffness, intima-media thickness (IMT), and plaques of the proximal, mid, and distal descending thoracic aorta. Stiffness at each level and overall aortic stiffness by the pressure-strain elastic modulus was higher in patients than in controls after adjusting for age (overall, 8.25 ± 4.13 versus 6.1 ± 2.5 Pascal units, p = 0.01). Patients had higher aortic stiffness than controls after adjusting both groups to the same mean age, blood pressure, creatinine, and aortic IMT (p = 0.005). Neither IMT nor plaques were predictors of aortic stiffness. Moreover, normotensive patients, those without aortic plaques, and non-smokers had higher stiffness than controls (all p < 0.05). Age at SLE diagnosis and non-neurologic damage score were the only SLE-specific independent predictors of aortic stiffness (both p ? 0.01). Thus, increased aortic stiffness is an early manifestation of lupus vasculopathy that seems to precede the development of hypertension and atherosclerosis. PMID:20813797

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

2010-12-01

328

Computation of grain boundary stiffness and mobility from boundary fluctuations.  

SciTech Connect

Grain boundary stiffness and mobility determine the kinetics of curvature-driven grain growth. Here the stiffness and mobility are computed using an analysis of fluctuations in the grain boundary position during molecular dynamics simulations. This work represents the first determination of grain boundary stiffness for a realistic three-dimensional system. The results indicate that the boundary stiffness for a given boundary plane has a strong dependence on the direction of the boundary distortion. The mobility deduced is comparable with that determined in previous computer simulation studies. The advantages and limitations of the fluctuation approach are discussed.

Hoyt, Jeffrey John; Foiles, Stephen Martin

2005-06-01

329

Towards ultra-stiff materials: Surface effects on nanoporous materials  

SciTech Connect

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.

Lu, Dingjie; Xie, Yi Min; Huang, Xiaodong; Zhou, Shiwei, E-mail: shiwei.zhou@rmit.edu.au [Centre for Innovative Structures and Materials, School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne 3001 (Australia); Li, Qing [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, New South Wales 2006 (Australia)

2014-09-08

330

The relationship between renal resistive index, arterial stiffness, and atherosclerotic burden: the link between macrocirculation and microcirculation.  

PubMed

The renal resistive index (RRI) measured by Doppler sonography is a marker of microvascular status that can be generalized to the whole of the arterial tree. Its association with large-vessel dysfunction, such as arterial stiffness or the atherosclerotic burden, can help to establish physiopathological associations between macrocirculation and microcirculation. The authors conducted a cross-sectional study of hypertensive patients (n=202) and a healthy control group (n=16). Stiffness parameters, atherosclerotic burden, and determination of the RRI in both kidneys were performed. The average RRI was 0.69±0.08 and was significantly greater in patients with diabetes and chronic kidney disease. Renal resistive index positively correlated with age, creatinine, and albuminuria. Positive correlations were found with arterial stiffness parameters (pulse wave velocity, ambulatory arterial stiffness index, and 24-hour pulse pressure), as well as atherosclerotic burden and endothelial dysfunction measured as asymmetric dimethylarginine in serum. In the multivariate analysis, independent factors for increased RRI were age, renal function, 24-hour diastolic blood pressure, and arterial stiffness. The authors concluded that there is an independent association between renal hemodynamics and arterial stiffness. This, together with the atherosclerotic burden and endothelial dysfunction, suggests that there is a physiopathologic relationship between macrovascular and microvascular impairment. PMID:24548343

Calabia, Jordi; Torguet, Pere; Garcia, Isabel; Martin, Nadia; Mate, Gerard; Marin, Adriana; Molina, Carolina; Valles, Marti

2014-03-01

331

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

PubMed Central

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

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

2014-01-01

332

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

SciTech Connect

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.

Kiracofe, Daniel; Raman, Arvind [Birck Nanotechnology Center and School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47904-2088 (United States)

2010-02-15

333

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

PubMed

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

Kancharala, A K; Philen, M K

2014-09-01

334

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

PubMed Central

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

2013-01-01

335

Determining cantilever stiffness from thermal noise.  

PubMed

We critically discuss the extraction of intrinsic cantilever properties, namely eigenfrequency f n , quality factor Q n and specifically the stiffness k n of the nth cantilever oscillation mode from thermal noise by an analysis of the power spectral density of displacement fluctuations of the cantilever in contact with a thermal bath. The practical applicability of this approach is demonstrated for several cantilevers with eigenfrequencies ranging from 50 kHz to 2 MHz. As such an analysis requires a sophisticated spectral analysis, we introduce a new method to determine k n from a spectral analysis of the demodulated oscillation signal of the excited cantilever that can be performed in the frequency range of 10 Hz to 1 kHz regardless of the eigenfrequency of the cantilever. We demonstrate that the latter method is in particular useful for noncontact atomic force microscopy (NC-AFM) where the required simple instrumentation for spectral analysis is available in most experimental systems. PMID:23616942

Lübbe, Jannis; Temmen, Matthias; Rahe, Philipp; Kühnle, Angelika; Reichling, Michael

2013-01-01

336

On-machine ultrasonic sensors for paper stiffness. Final report  

SciTech Connect

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.

Hall, Maclin S.; Jackson, Theodore G.; Brown, Ernest (Andy)

2000-04-01

337

Real time vision based cell stiffness evaluation toward 100% guarantee  

Microsoft Academic Search

Stiffness is an important index to know the quality of a cell. While there have been a couple of works to evaluate the cell stiffness in real time by combining a micro fluid chip with electric impedance based cell counters, we can not see what is really happening in the channel after all. The challenge of this paper is to

Makoto Kaneko; Yuki Hirose; Wataru Fukui; Mitsuru Higashimori; Tomohiro Kawahara; Yoko Yamanishi; Fumihito Arai

2011-01-01

338

Stiff, strong, and tough hydrogels with good chemical stability  

E-print Network

for oil packers require high stiffness, high strength, and chemical stability; they need to resist deformaStiff, strong, and tough hydrogels with good chemical stability Jianyu Li,a Zhigang Suoab and Joost an elastic modulus of 5 MPa, a strength of 2.5 MPa, and a fracture energy of 14 000 J mÃ?2 , while maintaining

Suo, Zhigang

339

Kinematic optimization for isotropic stiffness of redundantly actuated parallel manipulators  

Microsoft Academic Search

? Abstract— A kinematic optimization procedure for redundantly actuated parallel manipulator is developed to ensure the isotropic antagonistic stiffness in a workspace. The kinematic parameters of the mechanism are optimized to maximize and equal out antagonistic stiffness of the redundantly actuated manipulator when size and shape of the usable workspace are given but position in the entire workspace is not.

Hyunpyo Shin; SungCheul Lee; Jay I. Jeong; Jongwon Kim

2011-01-01

340

Forced Vibration Isolation System with Stiffness On-Off Control  

Microsoft Academic Search

Semi-active vibration systems expend a small amount of energy to change the system parameters such as damping and stiffness. The variable damping and stiffness semi-active systems with base excitations have demonstrated excellent performances in the resonant and high frequency regions. For a forced vibration, it plays an important role in describing a building system with wind loading or a vehicle

Yanqing Liu; Hiroshi Matsuhisa; Hideo Utsuno

2008-01-01

341

Extraordinary stiffness tunability through thermal expansion of nonlinear defect modes  

E-print Network

Incremental stiffness characterizes the variation of a material's force response to a small deformation change. Typically materials have an incremental stiffness that is fixed and positive, but recent technologies, such as super-lenses, low frequency band gap materials and acoustic cloaks, are based on materials with zero, negative or extremely high incremental stiffness. So far, demonstrations of this behavior have been limited either to a narrow range of frequencies, temperatures, stiffness or to specific deformations. Here we demonstrate a mechanism to tune the static incremental stiffness that overcomes those limitations. This tunability is achieved by driving a nonlinear defect mode in a lattice. As in thermal expansion, the defect's vibration amplitude affects the force at the boundary, hence the lattice's stiffness. By using the high sensitivities of nonlinear systems near bifurcation points, we tune the magnitude of the incremental stiffness over a wide range: from positive, to zero, to arbitrarily negative values. The particular deformation where the incremental stiffness is modified can be arbitrarily selected varying the defect's driving frequency. We demonstrate this experimentally in a compressed array of spheres and propose a general theoretical model.

Marc Serra-Garcia; Joseph Lydon; Chiara Daraio

2014-11-19

342

In-plane stiffness of shear walls with openings  

Microsoft Academic Search

In this paper, a new method is presented to determine the in-plane stiffness of shear walls with openings, in which the spandrels are assumed flexible, and can translate and rotate under lateral load. The in-plane stiffnesses of shear walls with openings obtained by using the new method are generally much different from the results obtained by the well known three

M. Qamaruddin

1998-01-01

343

Role of Inflammation in the Pathogenesis of Arterial Stiffness  

PubMed Central

Increased arterial stiffness is an independent predictor of cardiovascular disease independent from blood pressure. Recent studies have shed new light on the importance of inflammation on the pathogenesis of arterial stiffness. Arterial stiffness is associated with the increased activity of angiotensin II, which results in increased NADPH oxidase activity, reduced NO bioavailability and increased production of reactive oxygen species. Angiotensin II signaling activates matrix metalloproteinases (MMPs) which degrade TGF? precursors to produce active TGF?, which then results in increased arterial fibrosis. Angiotensin II signaling also activates cytokines, including monocyte chemoattractant protein-1, TNF-?, interleukin-1, interleukin-17 and interleukin-6. There is also ample clinical evidence that demonstrates the association of inflammation with increased arterial stiffness. Recent studies have shown that reductions in inflammation can reduce arterial stiffness. In patients with rheumatoid arthritis, increased aortic pulse wave velocity in patients was significantly reduced by anti tumor necrosis factor-? therapy. Among the major classes of anti hypertensive drugs, drugs that block the activation of the RAS system may be more effective in reducing the progression of arterial stiffness. Thus, there is rationale for targeting specific inflammatory pathways involved in arterial stiffness in the development of future drugs. Understanding the role of inflammation in the pathogenesis of arterial stiffness is important to understanding the complex puzzle that is the pathophysiology of arterial stiffening and may be important for future development of novel treatments. PMID:22318811

Park, Sungha

2012-01-01

344

Leg stiffness of sprinters using running-specific prostheses  

E-print Network

stiffness of the prosthesis coupled with differences in the limb posture required to run with the prosthesis forces during sprinting. Keywords: biomechanics; spring­mass model; stiffness; prosthesis; amputee springs that are attached to a socket, which surrounds the residual lower limb of a person

Herr, Hugh

345

Modeling and Control of Stiff Robots for Flexible Manufacturing  

E-print Network

Modeling and Control of Stiff Robots for Flexible Manufacturing #12;#12;Modeling and Control of Stiff Robots for Flexible Manufacturing Isolde Dressler Department of Automatic Control Lund University manufacturing. This thesis contributes to the development of robot concepts that fit the needs of SMEs. A major

346

Force and Stiffness of Passive Magnetic Bearings Using Permanent Magnets.  

E-print Network

1 Force and Stiffness of Passive Magnetic Bearings Using Permanent Magnets. Part 2 : Radial of the force and the stiffness between two ring permanent magnets whose polarization is radial. Such a configuration corresponds to a passive magnetic bearing. The magnetic force exerted between ring permanent

Paris-Sud XI, Université de

347

VAGINAL DEGENERATION FOLLOWING IMPLANTATION OF SYNTHETIC MESH WITH INCREASED STIFFNESS  

PubMed Central

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

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

2012-01-01

348

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

PubMed Central

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

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

2012-01-01

349

Effect of Lysyl Oxidase Inhibition on Angiotensin II-Induced Arterial Hypertension, Remodeling, and Stiffness  

PubMed Central

It is well accepted that angiotensin II (Ang II) induces altered vascular stiffness through responses including both structural and material remodeling. Concurrent with remodeling is the induction of the enzyme lysyl oxidase (LOX) through which ECM proteins are cross-linked. The study objective was to determine the effect of LOX mediated cross-linking on vascular mechanical properties. Three-month old mice were chronically treated with Ang II with or without the LOX blocker, ? -aminopropionitrile (BAPN), for 14 days. Pulse wave velocity (PWV) from Doppler measurements of the aortic flow wave was used to quantify in vivo vascular stiffness in terms of an effective Young’s modulus. The increase in effective Young’s modulus with Ang II administration was abolished with the addition of BAPN, suggesting that the material properties are a major controlling element in vascular stiffness. BAPN inhibited the Ang II induced collagen cross-link formation by 2-fold and PWV by 44% (P<0.05). Consistent with this observation, morphometric analysis showed that BAPN did not affect the Ang II mediated increase in medial thickness but significantly reduced the adventitial thickness. Since the hypertensive state contributes to the measured in vivo PWV stiffness, we removed the Ang II infusion pumps on Day 14 and achieved normal arterial blood pressures. With pump removal we observed a decrease of the PWV in the Ang II group to 25% above that of the control values (P=0.002), with a complete return to control values in the Ang II plus BAPN group. In conclusion, we have shown that the increase in vascular stiffness with 14 day Ang II administration results from a combination of hypertension-induced wall strain, adventitial wall thickening and Ang II mediated LOX ECM cross-linking, which is a major material source of vascular stiffening, and that the increased PWV was significantly inhibited with co-administration of BAPN. PMID:25875748

Eberson, Lance S.; Sanchez, Pablo A.; Majeed, Beenish A.; Tawinwung, Supannikar; Secomb, Timothy W.; Larson, Douglas F.

2015-01-01

350

Preperitoneal fat tissue may be associated with arterial stiffness in obese adolescents.  

PubMed

Vascular aging is a chronic process, and many negative effects of obesity in this process have been well defined. We assessed arterial stiffness in obese adolescents and evaluated the relationship between intra-abdominal fat distribution and arterial stiffness. Arterial stiffness parameters and pulse wave velocity (PWV) were evaluated in 61 obese adolescents and 58 healthy controls. Carotid-femoral PWV was calculated by arterial tonometry. Additionally, all obese children were evaluated for metabolic syndrome and insulin resistance. Intra-abdominal fat distribution, including subcutaneous, preperitoneal and visceral fat thicknesses, was assessed by ultrasonography. PWVs of obese children were significantly higher than those of healthy controls (5.0 ± 0.7 m/s vs. 4.7 ± 0.5 m/s). Parameters affecting PWV were evaluated by regression analysis. The independent variable in the regression analysis model was PWV, and the dependent variables were age, metabolic syndrome, body mass index and Homeostasis Model Assessment--Insulin Resistance, as well as subcutaneous, preperitoneal and visceral fat tissue thicknesses measured by ultrasonography. The only parameter associated with PWV was preperitoneal fat tissue thickness. Vascular changes related to obesity may begin in adolescence, as illustrated by the increased PWV. Preperitoneal fat tissue may be related to arterial stiffness. Intra-abdominal fat distributions obtained by ultrasonography may provide clinicians with valuable information needed to determine cardiovascular disease risk factors in obese adolescents. PMID:24462148

Hac?hamdio?lu, Bülent; Öçal, Gönül; Berbero?lu, Merih; S?klar, Zeynep; Fitöz, Suat; Tutar, Ercan; Nergiso?lu, Gökhan; Sava? Erdeve, Senay; Çamtosun, Emine

2014-05-01

351

Structural stiffness of the Hoffmann simple anterior tibial external fixation frame.  

PubMed

Tibial external fixation frames were constructed on aluminum tube simulating tibia bone. A 20-mm gap was left at the fracture site in order to measure the structural stiffness of the frame rather than the aluminum tube. The performance of the frames were experimentally evaluated and quantified using tests which simulated the loading conditions encountered in normal walking. These included axial compression, anteroposterior (AP) bending, lateral bending and torsional loading of the frame. The parameters studied were (a) number of fixation pins, (b) number of connecting rods and (c) location of clamps on the pins. Four constants were evaluated from these tests using various structural configurations of the frames; these resulted in four stiffness coefficients in compression, AP bending, lateral bending and torsion. Stiffnesses of various frames with different geometric configurations were compared by comparing their appropriate stiffness coefficients. Such comparison can set forth a quantitative guideline in selecting a suitable frame configuration for the type of injury and condition of fracture pattern. This type of quantitative analysis can also be useful in modifying the frame during the postoperative bone healing process. PMID:2729681

Vossoughi, J; Youm, Y; Bosse, M; Burgess, A R; Poka, A

1989-01-01

352

Negative hair-bundle stiffness betrays a mechanism for mechanical amplification by the hair cell.  

PubMed

Hearing and balance rely on the ability of hair cells in the inner ear to sense miniscule mechanical stimuli. In each cell, sound or acceleration deflects the mechanosensitive hair bundle, a tuft of rigid stereocilia protruding from the cell's apical surface. By altering the tension in gating springs linked to mechanically sensitive transduction channels, this deflection changes the channels' open probability and elicits an electrical response. To detect weak stimuli despite energy losses caused by viscous dissipation, a hair cell can use active hair-bundle movement to amplify its mechanical inputs. This amplificatory process also yields spontaneous bundle oscillations. Using a displacement-clamp system to measure the mechanical properties of individual hair bundles from the bullfrog's ear, we found that an oscillatory bundle displays negative slope stiffness at the heart of its region of mechanosensitivity. Offsetting the hair bundle's position activates an adaptation process that shifts the region of negative stiffness along the displacement axis. Modeling indicates that the interplay between negative bundle stiffness and the motor responsible for mechanical adaptation produces bundle oscillation similar to that observed. Just as the negative resistance of electrically excitable cells and of tunnel diodes can be embedded in a biasing circuit to amplify electrical signals, negative stiffness can be harnessed to amplify mechanical stimuli in the ear. PMID:11027302

Martin, P; Mehta, A D; Hudspeth, A J

2000-10-24

353

Damage Detection on Sudden Stiffness Reduction Based on Discrete Wavelet Transform  

PubMed Central

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

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

2014-01-01

354

Age, arterial stiffness, and components of blood pressure in Chinese adults.  

PubMed

Blood pressure (BP) changes with age. We conducted a cross-sectional study in rural Chinese adults to investigate: (1) what is the relationship between age, arterial stiffness, and BP in Chinese men and women; and (2) to what degree can the age-BP relationship be explained by arterial stiffness, controlling for other covariables. These analyses included a total of 1688 subjects (males/females: 623/1065), aged 40 to 88 years. Among them, 353 (20.9%) had hypertension (defined as systolic blood pressure (SBP) ? 140 mm Hg or diastolic blood pressure (DBP) ? 90 mm Hg). Arterial stiffness was measured by brachial-ankle pulse wave velocity (baPWV). baPWV appeared to be more strongly correlated with BP (including SBP, DBP, mean arterial pressure [MAP], pulse pressure [PP]) than age (P < 0.001 for comparisons between Spearman correlation coefficients). Furthermore, baPWV was associated with BP (including SBP, DBP, MAP, and PP) and risk of hypertension in a dose-response fashion, independent of age; in contrast, the age-BP associations were either attenuated or became negative after adjusting for baPWV. Arterial stiffness appears to be an independent contributor to hypertension, even after adjusting for age and other covariables. In contrast, age-BP associations became attenuated or negative after adjusting for baPWV. The utility of baPWV as a diagnostic, prognostic, and therapeutic indicator for hypertension warrants further investigation. PMID:25546666

Zheng, Meili; Xu, Xiping; Wang, Xiaobin; Huo, Yong; Xu, Xin; Qin, Xianhui; Tang, Genfu; Xing, Houxun; Fan, Fangfang; Cui, Wei; Yang, Xinchun

2014-12-01

355

Musculoskeletal stiffness during hopping and running does not change following downhill backwards walking.  

PubMed

Eccentric contractions that provide spring energy can also cause muscle damage. The aim of this study was to explore leg and vertical stiffness following muscle damage induced by an eccentric exercise protocol. Twenty active males completed 60 minutes of backward-walking on a treadmill at 0.67 m/s and a gradient of - 8.5° to induce muscle damage. Tests were performed immediately before; immediately post; and 24, 48, and 168 hours post eccentric exercise. Tests included running at 3.35 m/s and hopping at 2.2 Hz using single- and double-legged actions. Leg and vertical stiffness were measured from kinetic and kinematic data, and electromyography (EMG) of five muscles of the preferred limb were recorded during hopping. Increases in pain scores (over 37%) occurred post-exercise and 24 and 48 hours later (p < 0.001). A 7% decrease in maximal voluntary contraction occurred immediately post-exercise (p = 0.019). Changes in knee kinematics during single-legged hopping were observed 168 hours post (p < 0.05). No significant changes were observed in EMG, creatine kinase activity, leg, or vertical stiffness. Results indicate that knee mechanics may be altered to maintain consistent levels of leg and vertical stiffness when eccentric exercise-induced muscle damage is present in the lower legs. PMID:25325769

Joseph, Corey W; Bradshaw, Elizabeth J; Kemp, Justin; Clark, Ross A

2014-09-01

356

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

PubMed

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

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

2015-04-01

357

Muscle stiffness, strength loss, swelling and soreness following exercise-induced injury in humans.  

PubMed Central

1. In order to study injury-related changes in muscle stiffness, injury to the elbow flexors of thirteen human subjects was induced by a regimen of eccentric exercise. 2. Passive stiffness over an intermediate range of elbow angles was measured with a device which held the relaxed arm of the subject in the horizontal plane and stepped it through the range of elbow angles from 90 deg to near full extension at 180 deg. The relation between static torque and elbow angle was quite linear over the first 50 deg and was taken as stiffness. 3. Stiffness over this range of angles more than doubled immediately after exercise and remained elevated for about 4 days, and may result from low level myofibrillar activation induced by muscle stretch. 4. Arm swelling was biphasic; arm circumference increased by about 3% immediately after exercise, fell back toward normal, then increased by as much as 9% and remained elevated for as long as 9 days. 5. Ultrasound imaging showed most of the swelling immediately following the exercise to be localized to the flexor muscle compartment; subsequent swelling involved other tissue compartments as well. 6. Muscle strength declined by almost 40% after the exercise and recovery was only slight 10 days later; the half-time of recovery appeared to be as long as 5-6 weeks. PMID:8229798

Howell, J N; Chleboun, G; Conatser, R

1993-01-01

358

Anglepoise lamps, Zero Stiffness, Image ForcesAnglepoise lamps, Zero Stiffness, Image Forces andand EshelbyEshelby BendsBends  

E-print Network

-space Dislocations in infinite bodies feel no forces! #12;2 Image ForcesImage Forces A hypothetical negative1 Anglepoise lamps, Zero Stiffness, Image ForcesAnglepoise lamps, Zero Stiffness, Image ForcesNUtoQ/Sb1vcZjQWBI/AAAAAAAAAeU/ABGRV9DEsks/s400/glass+sphere+with+shadow+8+x+8.jpg Rigid body in neutral

Subramaniam, Anandh

359

Effects of varying machine stiffness and contact area in UltraForm Finishing  

NASA Astrophysics Data System (ADS)

UltraForm Finishing (UFF) is a deterministic, subaperture, computer numerically controlled, grinding and polishing platform designed by OptiPro Systems. UFF is used to grind and polish a variety optics from simple spherical to fully freeform, and numerous materials from glasses to optical ceramics. The UFF system consists of an abrasive belt around a compliant wheel that rotates and contacts the part to remove material. This work aims to measure the stiffness variations in the system and how it can affect material removal rates. The stiffness of the entire system is evaluated using a triaxial load cell to measure forces and a capacitance sensor to measure deviations in height. Because the wheel is conformal and elastic, the shapes of contact areas are also of interest. For the scope of this work, the shape of the contact area is estimated via removal spot. The measured forces and removal spot area are directly related to material removal rate through Preston's equation. Using our current testing apparatus, we will demonstrate stiffness measurements and contact areas for a single UFF belt during different states of its lifecycle and assess the material removal function from spot diagrams as a function of wear. This investigation will ultimately allow us to make better estimates of Preston's coefficient and develop spot-morphing models in an effort to more accurately predict instantaneous material removal functions throughout the lifetime of a belt.

Briggs, Dennis E.; Echaves, Samantha; Pidgeon, Brendan; Travis, Nathan; Ellis, Jonathan D.

2013-09-01

360

Quantitative evaluation of stiffness of commercial suture materials.  

PubMed

The bending stiffness of 22 commercial suture materials of varying size, chemical structure and physical form was quantitatively evaluated using a stiffness tester (Taber V-5, model 150B, Teledyne). The commercial sutures were Chromic catgut; Dexon (polyglycolic acid); Vicryl (polyglactin 910); PDS (polydioxanone); Maxon (polyglycolide-trimethylene carbonate); Silk (coated with silicone); Mersilene (polyester fiber); Tycron (polyester fiber); Ethibond (polyethylene terephthalate coated with polybutylene); Nurolon (nylon 66); Surgilon (nylon 66 coated with silicone); Ethilon (coated nylon 66), Prolene (polypropylene); Dermalene (polyethylene), and Gore-tex (polytetraflouroethylene). These are both natural and synthetic, absorbable and nonabsorbable and monofilament and multifilament sutures. All of these sutures were size 2-0, but Prolene sutures with sizes ranging from 1-0 to 9-0 were also tested to determine the effect of suture size on stiffness. The bending stiffness data obtained showed that a wide range of bending stiffness was observed among the 22 commercial sutures. The most flexible 2-0 suture was Gore-tex, followed by Dexon, Silk, Surgilon, Vicryl (uncoated), Tycron, Nurolon, Mersilene, Ethibond, Maxon, PDS, Ethilon, Prolene, Chromic catgut, coated Vicryl, and lastly, Dermalene. The large porous volume inherent in Gore-tex monofilament suture was the reason for its lowest flexural stiffness. Sutures with a braided structure were generally more flexible than those of a monofilament structure, irrespective of the chemical constituents. Coated sutures had significantly higher stiffness than the corresponding uncoated ones. This is particularly true when polymers rather than wax were used as the coating material. This increase in stiffness is attributable to the loss of mobility under bending force in the fibers and yarns that make up the sutures. An increase in the size of the suture significantly increased the stiffness, and the magnitude of increase depended on the chemical constituent of the suture. The flexural stiffness of sutures was also found to depend on the duration of bending in the test for stiffness. In general, monofilament sutures exhibited the largest time-dependent stiffness. This was most pronounced with the Gore-tex suture. Most braided sutures also showed less time-dependence in stiffness. Nylon sutures did not exhibit this time-dependent phenomenon regardless of physical form. PMID:2919353

Chu, C C; Kizil, Z

1989-03-01

361

An experimental and morphometric test of the relationship between vertebral morphology and joint stiffness in Nile crocodiles (Crocodylus niloticus).  

PubMed

Despite their semi-aquatic mode of life, modern crocodylians use a wide range of terrestrial locomotor behaviours, including asymmetrical gaits otherwise only found in mammals. The key to these diverse abilities may lie in the axial skeleton. Correlations between vertebral morphology and both intervertebral joint stiffness and locomotor behaviour have been found in other animals, but the vertebral mechanics of crocodylians have not yet been experimentally and quantitatively tested. We measured the passive mechanics and morphology of the thoracolumbar vertebral column in Crocodylus niloticus in order to validate a method to infer intervertebral joint stiffness based on morphology. Passive stiffness of eight thoracic and lumbar joints was tested in dorsal extension, ventral flexion and mediolateral flexion using cadaveric specimens. Fifteen measurements that we deemed to be potential correlates of stiffness were taken from each vertebra and statistically tested for correlation with joint stiffness. We found that the vertebral column of C. niloticus is stiffer in dorsoventral flexion than in lateral flexion and, in contrast to that of many mammals, shows an increase in joint stiffness in the lumbar region. Our findings suggest that the role of the axial column in crocodylian locomotion may be functionally different from that in mammals, even during analogous gaits. A moderate proportion of variation in joint stiffness (R(2)=0.279-0.520) was predicted by centrum width and height, neural spine angle and lamina width. These results support the possible utility of some vertebral morphometrics in predicting mechanical properties of the vertebral column in crocodiles, which also should be useful for forming functional hypotheses of axial motion during locomotion in extinct archosaurs. PMID:24574389

Molnar, Julia L; Pierce, Stephanie E; Hutchinson, John R

2014-03-01

362

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

PubMed Central

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

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

2013-01-01

363

Multi-size Scaling of Fluid Flow and Seismic Fracture Stiffness (Invited)  

NASA Astrophysics Data System (ADS)

Remote monitoring of any natural or anthropogenic process in the subsurface seeks to gain knowledge of the local fracture network geometry and the local fluid flow patterns. From the study of single fractures at laboratory scales, a clear understanding has emerged on how to interpret fracture specific stiffness from seismic data and how time-dependent processes (e.g., stress, geochemical interactions, fluid saturation) affect interpretation. However, an open challenge remains to determine if fracture specific stiffness is related to the hydraulic properties of a fracture and if this relationship holds across a broad range of scales. A finite-size scaling analysis was performed on fractures numerically simulated with weakly correlated random aperture distributions to explore whether a fundamental scaling relationship exists between fracture seismic stiffness and fracture flow behavior. Computational models were used to analyze fluid flow through a fracture undergoing deformation. The numerical methods included a stratified percolation approach to generate pore-scale fracture void geometry for fractures, a combined conjugate-gradient method and fast-multipole method for determining fracture deformation, and a flow network model for simulating fluid flow, fluid velocity and fluid pressures within a fracture. From the numerical simulations, fracture specific stiffness was determined to be a surrogate for fracture void area (traditionally used in percolation studies). Fracture specific stiffness captures the deformation of the fracture void geometry that includes both changes in contact area and aperture. This enabled a collapse of the numerical flow-stiffness data, simulated at multiple length scales, to a single scaling function. The scaling function displays two exponential regions above and below the transition into the critical regime. The transition point is governed by the multi-fractal spectrum of stress dependent flow paths. This spectrum reveals that the flow path geometry deforms from a sheet-like topology to a string-like topology. The resulting hydro-mechanical scaling function provides a link between fluid flow and the seismic response of a fracture, because fracture specific stiffness affects seismic wave attenuation and velocity, which are routinely measured in the field. Acknowledgment: The authors wish to acknowledge support of this work by the Geosciences Research Program, Office of Basic Energy Sciences US Department of Energy (DE-FG02-09ER16022), by the Geo-mathematical Imaging Group at Purdue University, and the Purdue Research Foundation.

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

2013-12-01

364

Dehydroepiandrosterone replacement therapy in older adults improves indices of arterial stiffness  

PubMed Central

Background Serum dehydroepiandrosterone (DHEA) concentrations decrease ~80% between ages 25 and 75 yr. Aging also results in an increase in arterial stiffness, which is an independent predictor of cardiovascular disease (CVD) risk and mortality. Therefore, it is conceivable that DHEA replacement in older adults could reduce arterial stiffness. We sought to determine if DHEA replacement therapy in older adults reduces carotid augmentation index (AI) and carotid-femoral pulse wave velocity (PWV) as indices of arterial stiffness. Methods A randomized, double-blind trial was conducted to study the effects of 50 mg/d DHEA replacement on AI (n=92) and PWV (n=51) in women and men aged 65–75 yr. Inflammatory cytokines and sex hormones were measured in fasting serum. Results AI decreased in the DHEA group but not in the placebo group (difference between groups, ?6±2 AI units, p=0.002). PWV also decreased (difference between groups, ?3.5±1.0 m/sec, p=0.001); however, after adjusting for baseline values, the between-group comparison became non-significant (p=0.20). The reductions in AI and PWV were accompanied by decreases in inflammatory cytokines (TNF? and IL-6, p<0.05) and correlated with increases in serum DHEAS (r = ?0.31 and ?0.37, respectively, p<0.05). The reductions in AI also correlated with free testosterone index (r = ?0.23, p=0.03). Conclusion DHEA replacement in elderly men and women improves indices of arterial stiffness. Arterial stiffness increases with age and is an independent risk factor for CVD. Therefore the improvements observed in the present study suggest that DHEA replacement might partly reverse arterial aging and reduce CVD risk. PMID:22712469

Weiss, Edward P.; Villareal, Dennis T.; Ehsani, Ali A.; Fontana, Luigi; Holloszy, John O.

2012-01-01

365

Inhomogeneity of local stiffness in the extracellular matrix scaffold of fibrotic mouse lungs.  

PubMed

Lung disease models are useful to study how cell engraftment, proliferation and differentiation are modulated in lung bioengineering. The aim of this work was to characterize the local stiffness of decellularized lungs in aged and fibrotic mice. Mice (2- and 24-month old; 14 of each) with lung fibrosis (N=20) and healthy controls (N=8) were euthanized after 11 days of intratracheal bleomycin (fibrosis) or saline (controls) infusion. The lungs were excised, decellularized by a conventional detergent-based (sodium-dodecyl sulfate) procedure and slices of the acellular lungs were prepared to measure the local stiffness by means of atomic force microscopy. The local stiffness of the different sites in acellular fibrotic lungs was very inhomogeneous within the lung and increased according to the degree of the structural fibrotic lesion. Local stiffness of the acellular lungs did not show statistically significant differences caused by age. The group of mice most affected by fibrosis exhibited local stiffness that were ~2-fold higher than in the control mice: from 27.2±1.64 to 64.8±7.1kPa in the alveolar septa, from 56.6±4.6 to 99.9±11.7kPa in the visceral pleura, from 41.1±8.0 to 105.2±13.6kPa in the tunica adventitia, and from 79.3±7.2 to 146.6±28.8kPa in the tunica intima. Since acellular lungs from mice with bleomycin-induced fibrosis present considerable micromechanical inhomogeneity, this model can be a useful tool to better investigate how different degrees of extracellular matrix lesion modulate cell fate in the process of organ bioengineering from decellularized lungs. PMID:24946269

Melo, Esther; Cárdenes, Nayra; Garreta, Elena; Luque, Tomas; Rojas, Mauricio; Navajas, Daniel; Farré, Ramon

2014-09-01

366

25-Hydroxyvitamin D status, arterial stiffness and the renin-angiotensin system in healthy humans.  

PubMed

Vitamin D deficiency is associated with increased arterial stiffness. We sought to clarify the influence of vitamin D in modulating angiotensin II-dependent arterial stiffness. Thirty-six healthy subjects (33 ± 2 years, 67% female, mean 25-hydroxyvitamin D 69 ± 4 nmol/L) were studied in high salt balance. Arterial stiffness, expressed as brachial pulse wave velocity (bPWV) and aortic augmentation index (AIx), was measured by tonometry at baseline and in response to angiotensin II infusion (3 ng/kg/min × 30 min then 6 ng/kg/min × 30 min). The primary outcome was change in bPWV after an angiotensin II challenge. Results were analyzed according to plasma 25-hydroxyvitamin D status: deficient (<50 nmol/L) and sufficient (? 50 nmol/L). There were no differences in baseline arterial stiffness between vitamin D deficient (25-hydroxyvitamin D 40 ± 2 nmol/L) and sufficient (25-hydroxyvitamin D 80 ± 4 nmol/L) groups. Compared with sufficient vitamin D status, vitamin D deficiency was associated with a decreased arterial response to angiotensin II challenge (?brachial pulse wave velocity: 0.48 ± 0.44 m/s versus 1.95 ± 0.22 m/s, p=0.004; ?aortic augmentation index: 9.4 ± 3.4% versus 14.2 ± 2.7%, p=0.3), which persisted for brachial pulse wave velocity response after adjustment for covariates (p=0.03). Vitamin D deficiency is associated with increased arterial stiffness in healthy humans, possibly through an angiotensin II-dependent mechanism. PMID:24164282

Abdi-Ali, Ahmed; Nicholl, David D M; Hemmelgarn, Brenda R; MacRae, Jennifer M; Sola, Darlene Y; Ahmed, Sofia B

2014-01-01

367

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

PubMed

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. PMID:25597833

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

2015-01-01

368

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

369

Robust time-domain identification of mass stiffness, and damping matrices  

NASA Technical Reports Server (NTRS)

Accurate estimates of the mass, stiffness, and damping characteristics of a structure is necessary for determining the control laws best suited for active control methodologies. There are several modal identification techniques available for determining the frequencies, damping ratios, and mode shapes of a structure. However, modal identification methods in both the frequency and time domains have difficulties for certain circumstances. Frequency domain techniques which utilize the steady-state response from various harmonic inputs often encounter difficulties when the frequencies are closely distributed, the structure exhibits a high degree of damping, or the steady-state condition is hard to establish. Time domain techniques have produced successful results, but lack robustness with respect to measurement noise. In this paper, two identification techniques and an estimation method are combined to form a time-domain technique to accurately identify the mass, stiffness, and damping matrices from noisy measurements.

Roemer, Michael J.; Mook, D. Joseph

1990-01-01

370

Stabilisation of a large rainfall induced landslide in stiff clay  

NASA Astrophysics Data System (ADS)

In December 2000, a 150,000m^3 landslide developed in the north face of a Gault clay cutting on one of Britains busiest motorways. The failure followed prolonged and heavy rainfall and the resulting mudslide was threatening closure of the motorway. Movement continued with further high rainfall, as an investigation began to determine the causes and design remedial measures. The landslide comprised irregular benches and steep slopes with a complex backscarp area that included a small graben. At the toe severe bulging caused heave of the hard shoulder and lateral mudstones were associated with seepage points. Geomorphological investigation showed the failure to be part reactivation of a fossil landslide, at at time when historical groundwater records were broken. Thorough ground investigation confirmed the ground conditions as stiff fissured clay with overlying head deposits. Near surface water levels were measured. Found to be 10m deep the failure was stabilised by a combination of large diameter shear piles and cut-off and counterfort drainage, all designed and installed within one year of the first movements. This would not have been achieved without excellent risk management and honest and open partnership between the Client, Designer and Contractor. Later high rainfall without movement indicated the successful stabilisation of the landslide.

Loyeridge, F. A.; Perry, J.; Spink, T. W.

2003-04-01

371

Short range stiffness elastic limit depends on joint velocity.  

PubMed

Muscles behave as elastic springs during the initial strain phase, indicated as short range stiffness (SRS). Beyond a certain amount of strain the muscle demonstrates a more viscous behavior. The strain at which the muscle transits from elastic- to viscous-like behavior is called the elastic limit and is believed to be the result of breakage of cross-bridges between the contractile filaments. The aim of this study was to test whether the elastic limit, measured in vivo at the wrist joint, depended on the speed of lengthening. Brief extension rotations were imposed to the wrist joint (n=8) at four different speeds and at three different levels of voluntary torque using a servo controlled electrical motor. Using a recently published identification scheme, we quantified the elastic limit from measured joint angle and torque. The results showed that the elastic limit significantly increased with speed in a linear way, indicating to a constant time of approximately 30 ms before cross-bridges break. The implications for movement control of the joint are discussed. PMID:21640995

de Vlugt, Erwin; van Eesbeek, Stijn; Baines, Patricia; Hilte, Joost; Meskers, Carel G M; de Groot, Jurriaan H

2011-07-28

372

Physiopathogenic Investigations in a Case of Familial Stiff-Skin Syndrome  

Microsoft Academic Search

Background: Stiff-skin syndrome (SSS) is a rare cutaneous syndrome characterized by stony-hard skin and limitation of joint mobility. Its cause is still unknown. Objective: Biological investigations were performed in a new case of SSS. Methods: Collagen production and DNA biosynthesis were studied from fibroblast culture. Proinflammatory cytokines (TNF-?, IL-6 and TGF-?2) were measured in the patient’s serum. Results were compared

M. A. Richard; J. J. Grob; N. Philip; J. Rey; A. Chamson; J. L. Mege; L. Andrac; F. Faure; N. Basseres; J. J. Bonerandi

1998-01-01

373

Stiffness Tuning with Bias Magnetic Fields in Ferromagnetic Shape Memory Ni-Mn-Ga  

Microsoft Academic Search

This article presents the dynamic characterization of mechanical stiffness changes under varied bias magnetic fields in single-crystal ferromagnetic shape memory Ni-Mn-Ga. The material is first converted to a single variant through the application and subsequent removal of a bias magnetic field. Mechanical base excitation is then used to measure the acceleration transmissibility across the sample, from where the resonance frequency

Neelesh N. Sarawate; Marcelo J. Dapino

2009-01-01

374

Noninvasive Evaluation of Hepatic Fibrosis using Acoustic Radiation Force-Based Shear Stiffness in Patients with Nonalcoholic Fatty Liver Disease  

PubMed Central

Background & Aims Nonalcoholic fatty liver disease (NAFLD), the most common form of chronic liver disease in developed countries, may progress to nonalcoholic steatohepatitis (NASH) in a minority of people. Those with NASH are at increased risk for cirrhosis and hepatocellular carcinoma. The potential risk and economic burden of utilizing liver biopsy to stage NAFLD in an overwhelmingly large at-risk population are enormous; thus, the discovery of sensitive, inexpensive, and reliable noninvasive diagnostic modalities is essential for population-based screening. Methods Acoustic Radiation Force Impulse (ARFI) shear wave imaging, a noninvasive method of assessing tissue stiffness, was used to evaluate liver fibrosis in 172 patients diagnosed with NAFLD. Liver shear stiffness measures in 3 different imaging locations were reconstructed and compared to the histologic features of NAFLD and AST-to-platelet ratio indices (APRI). Results Reconstructed shear stiffnesses were not associated with ballooned hepatocytes (p = 0.11), inflammation (p = 0.69), nor imaging location (p = 0.11). Using a predictive shear stiffness threshold of 4.24 kPa, shear stiffness distinguished low (fibrosis stage 0–2) from high (fibrosis stage 3–4) fibrosis stages with a sensitivity of 90% and a specificity of 90% (AUC of 0.90). Shear stiffness had a mild correlation with APRI (R2 = 0.22). BMI > 40 kg/m2 was not a limiting factor for ARFI imaging, and no correlation was noted between BMI and shear stiffness (R2 = 0.05). Conclusions ARFI imaging is a promising imaging modality for assessing the presence or absence of advanced fibrosis in patients with obesity-related liver disease. PMID:21256907

Palmeri, Mark L.; Wang, Michael H.; Rouze, Ned C.; Abdelmalek, Manal F.; Guy, Cynthia D.; Moser, Barry; Diehl, Anna Mae; Nightingale, Kathryn R.

2011-01-01

375

Arterial stiffness and blood flow adaptations following eight weeks of resistance exercise training in young and older women.  

PubMed

Resistance training is recommended for all adults of both sexes. The arterial stiffness and limb blood flow responses to resistance training in young and older women have not been well-studied. The purpose of this study was to examine arterial stiffness and blood flow adaptations to high-intensity resistance exercise training in young and older women. Young (aged 18-25) and older (aged 50-64) women performed full-body high-intensity resistance exercise three times per week for eight weeks. The following measurements were performed twice prior to training and once following training: carotid to femoral and femoral to tibialis posterior pulse wave velocity (PWV), blood pressure, heart rate, resting forearm blood flow and forearm reactive hyperemia. Data was analyzed by ANOVAs with alpha set at 0.05. Correlations were also examined between changes in arterial stiffness and baseline arterial stiffness values. Older subjects had higher carotid-femoral PWV than younger subjects. No significant effects were found for femoral-tibialis posterior PWV or for resting forearm blood flow. Changes in carotid-femoral and femoral-tibialis posterior PWV correlated significantly with their respective baseline values. Older subjects increased peak forearm blood flow while young subjects showed no change. Total hyperemia increased significantly in both groups. In conclusion, in both young and older women, eight weeks of high-intensity resistance training appeared to improve microvascular forearm function while not changing carotid-femoral or femoral-tibialis posterior arterial stiffness. However, a large degree of individual variation was found and arterial stiffness adaptations appeared positively related to the initial stiffness values. PMID:24566193

Rossow, Lindy M; Fahs, Christopher A; Thiebaud, Robert S; Loenneke, Jeremy P; Kim, Daeyeol; Mouser, James G; Shore, Erin A; Beck, Travis W; Bemben, Debra A; Bemben, Michael G

2014-05-01

376

Quantification of magnetically induced changes in ECM local apparent stiffness.  

PubMed

The stiffness of the extracellular matrix (ECM) is known to influence cell behavior. The ability to manipulate the stiffness of ECM has important implications in understanding how cells interact mechanically with their microenvironment. This article describes an approach to manipulating the stiffness ECM, whereby magnetic beads are embedded in the ECM through bioconjugation between the streptavidin-coated beads and the collagen fibers and then manipulated by an external magnetic field. It also reports both analytical results (obtained by formal modeling and numerical simulation) and statistically meaningful experimental results (obtained by atomic force microscopy) that demonstrate the effectiveness of this approach. These results clearly suggest the possibility of creating desired stiffness gradients in ECM in vitro to influence cell behavior. PMID:24411265

Herath, Sahan C B; Yue, Du; Hui, Shi; Kim, Min-Cheol; Wang, Dong-An; Wang, Qingguo; Van Vliet, Krystyn J; Asada, Harry; Chen, Peter C Y

2014-01-01

377

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

PubMed

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

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

2014-12-01

378

Evaluation of the stiffness tensor of a fractured medium with ...  

E-print Network

[Ch09] described anisotropic attenuation in a TI medium using Schoenberg's linear-slip ... to the static limit, which yields the desired static stiffnesses coefficients. ...... and S. A. Shapiro, 2007, Finite-difference modeling of wave propagation on ...

379

Evaluation of the stiffness tensor of a fractured medium with ...  

E-print Network

Jul 6, 2012 ... element approach to determine the complex stiffness coefficients of the TIV equivalent ... anisotropic medium, including attenuation, are ...... Shapiro, 2007, Finite-difference modeling of wave propagation on microscale:.

santos,,,

380

Operator-Based Preconditioning of Stiff Hyperbolic Systems  

SciTech Connect

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.

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

2009-02-09

381

Wing/store flutter with nonlinear pylon stiffness  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

382

Improved Equivalent Linearization Implementations Using Nonlinear Stiffness Evaluation  

NASA Technical Reports Server (NTRS)

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.

Rizzi, Stephen A.; Muravyov, Alexander A.

2001-01-01

383

The stiff total knee arthroplasty: causes and cures.  

PubMed

Stiffness following TKA can be related to patient factors, intraoperative technical errors, or postoperative surgical complications. The best management is prevention by providing thorough preoperative patient education, aggressive postoperative physiotherapy, and avoidance of technical errors. PMID:11570479

Dennis, D A

2001-09-01

384

Cornering stiffness estimation based on vehicle lateral dynamics  

Microsoft Academic Search

In this article, the cornering stiffness estimation problem based on the vehicle bicycle (one-track) model is studied. Both time-domain and frequency-domain-based methods are analyzed, aiming to estimate the effective cornering stiffness, defined as the ratio between the lateral force and the slip angle at the two axles. Several methods based on the bicycle model were developed, each having specific pros\\/cons

C. Sierra; E. Tseng; A. Jain; H. Peng

2006-01-01

385

On stiffness properties of square honeycombs and other unidirectional composites  

Microsoft Academic Search

In this paper we consider stiffness properties of square symmetric unidirectional two-phase composites with given volume fractions. First, we compare the effective moduli of the stiffest possible (or softest possible) of such materials which satisfy transverse isotropy or square isotropy with that of materials satisfying 3D-isotropy.Next, we present some numerical FEM computations of in-plane stiffness properties of square honeycombs. Our

Stein A. Berggren; Dag Lukkassen; Annette Meidell; Leon Simula

2001-01-01

386

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

PubMed

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

Feilich, Kara L; Lauder, George V

2015-01-01

387

Mesenchymal Stem Cell Durotaxis Depends on Substrate Stiffness Gradient Strength  

PubMed Central

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

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

2013-01-01

388

The pendulum test as a tool to evaluate passive knee stiffness and viscosity of patients with rheumatoid arthritis  

PubMed Central

Background The pendulum test of Wartenberg is a technique commonly used to measure passive knee motion with the aim to assess spasticity. We used this test to evaluate changes of the knee angular displacement, passive stiffness and viscosity in rheumatoid arthritis patients. Stiffness and viscosity represent passive resistances to joint motion associated with the structural properties of the joint tissue and of the muscular-tendon complex. Stiffness can be considered an intrinsic property of the tissues to resist deformation, while viscosity is related to cohesive forces between adjacent layers of tissues. Both parameters may influence the joint range of motion affecting angular displacement. Methods Nine women with rheumatoid arthritis were compared with a group of healthy women. With the subject half-lying, the relaxed knee was dropped from near-full extension and the characteristics of the ensuring damped unsustained knee oscillation evaluated. The kinematics of leg oscillations was recorded using ultrasonic markers (Zebris CMS HS 10) and the kinetic data were calculated from kinematic and anthropometric measures. Results Knee stiffness significantly increased (p < 0.001) in patients with respect to the control group, while differences in viscosity were not significant. Moreover, the amplitudes of first knee flexion (the maximal flexion excursion after knee release) and first knee extension (the maximal extension excursion after the first knee flexion) were significantly decreased (p < 0.001). A regression analysis showed that disease severity correlated moderately with stiffness (R2 = 0.68) and first flexion (R2 = 0.78). Using a multivariate regression, we found that increasing stiffness was the main factor for the reduction of flexion and extension motions. Conclusion We showed that the Wartenberg test can be considered a practical tool to measure mechanical changes of knee caused by rheumatoid arthritis. This novel application of Wartenberg test could be useful to follow up the effects of pharmacological and rehabilitative interventions in this disease. PMID:17134492

Valle, Maria S; Casabona, Antonino; Sgarlata, Rosaria; Garozzo, Rosaria; Vinci, Maria; Cioni, Matteo

2006-01-01

389

Dynamic regulation of genome-wide pre-mRNA splicing and stress tolerance by the Sm-like protein LSm5 in Arabidopsis  

PubMed Central

Background Sm-like proteins are highly conserved proteins that form the core of the U6 ribonucleoprotein and function in several mRNA metabolism processes, including pre-mRNA splicing. Despite their wide occurrence in all eukaryotes, little is known about the roles of Sm-like proteins in the regulation of splicing. Results Here, through comprehensive transcriptome analyses, we demonstrate that depletion of the Arabidopsis supersensitive to abscisic acid and drought 1 gene (SAD1), which encodes Sm-like protein 5 (LSm5), promotes an inaccurate selection of splice sites that leads to a genome-wide increase in alternative splicing. In contrast, overexpression of SAD1 strengthens the precision of splice-site recognition and globally inhibits alternative splicing. Further, SAD1 modulates the splicing of stress-responsive genes, particularly under salt-stress conditions. Finally, we find that overexpression of SAD1 in Arabidopsis improves salt tolerance in transgenic plants, which correlates with an increase in splicing accuracy and efficiency for stress-responsive genes. Conclusions We conclude that SAD1 dynamically controls splicing efficiency and splice-site recognition in Arabidopsis, and propose that this may contribute to SAD1-mediated stress tolerance through the metabolism of transcripts expressed from stress-responsive genes. Our study not only provides novel insights into the function of Sm-like proteins in splicing, but also uncovers new means to improve splicing efficiency and to enhance stress tolerance in a higher eukaryote. PMID:24393432

2014-01-01

390

Acute effects of submaximal endurance training on arterial stiffness in healthy middle- and long-distance runners.  

PubMed

Measures of arterial stiffness are indicators for cardiovascular health and predictors of cardiovascular events. Arterial stiffness is responsive to acute physiologic stressors such as exercise. However, the acute effects of intensive exercise and recovery on arterial stiffness are controversial. Thirty-seven healthy middle- and long-distance runners (33 men, mean age 26.5±6.6 years) underwent evaluation of their cardiovascular stiffness at rest, after a 15-minute warm-up, immediately after vigorous running 3 km at the pace of their 10-km personal best, and finally 30 minutes after terminating their workout. Peripheral and central systolic blood pressure, as well as augmentation index and pulse wave velocity (PWV), increased during exercise in comparison to baseline (P<.001, general linear model). Thirty minutes after terminating the workout, a drop in peripheral blood pressure (P<.001), central blood pressure (P<.001), and PWV (P=.001) below baseline was observed. Therefore, the authors found that exercise of either moderate or vigorous intensity causes a temporary increase in arterial stiffness in middle- and long-distance runners. PMID:25782686

Müller, Jan; Wilms, Michael; Oberhoffer, Renate

2015-05-01

391

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

PubMed

Compliance can increase the thrust generated by the fin of a bio-inspired underwater vehicle. To improve the performance of a compliant fin, the compliance should change with the operating conditions; a fin should become stiffer as the oscillating frequency increases. This paper presents a novel variable-stiffness flapping (VaSF) mechanism that can change its stiffness to maximize the thrust of a bio-inspired underwater robot. The mechanism is designed on the basis of an endoskeleton structure, composed of compliant and rigid segments alternately connected in series. To determine the attachment point of tendons, the anatomy of a dolphin's fluke is considered. Two tendons run through the mechanism to adjust the stiffness. The fluke becomes stiffer when the tendons are pulled to compress the structure. The thrust generated by a prototype mechanism is measured under different conditions to show that the thrust can be maximized by changing the stiffness. The thrust of the VaSF device can approximately triple at a certain frequency just by changing the stiffness. This VaSF mechanism can be used to improve the efficiency of a bio-inspired underwater robot that uses compliance. PMID:24584214

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

2014-09-01

392

Variations in varus/valgus and internal/external rotational knee laxity and stiffness across the menstrual cycle.  

PubMed

Cyclic variations in genu recurvatum (GR), general joint laxity (GJL), varus-valgus (VV), and internal-external (IER) rotational laxities and stiffnesses were examined in 64 females and 43 males at two time points during the females' menstrual cycle [days of minimum (T1) and maximum (T2) anterior knee laxity (AKL)]. Cyclic increases in AKL (9.5%), GR (37.5%), and GJL (13.6%) were observed in females but not males from T1 to T2 (p < 0.001). Cyclic increases in VV and IER laxity were negligible (1.5-3.2%, p > 0.320). Females compared to males had lower overall VV stiffness at T2 (F 37% stiffness (p = 0.452). Across both time points, females had consistently greater VV (30.2%) and IER (20%) laxity and less VV (32.5%) and IER (24.3%) incremental stiffness (p < 0.001). Low-to-moderate associations were observed between AKL, GR, and GJL with VV and IER laxities and stiffnesses in females as measured at T1 and the change in values from T1 to T2. Whether these findings reflect ligament-specific responses to hormone changes, or implicate changes in injury risk potential across the menstrual cycle requires further study. PMID:20882589

Shultz, Sandra J; Schmitz, Randy J; Beynnon, Bruce D

2011-03-01

393

Umbilical Stiffness Matrix Characterization and Testing for Microgravity Science Payloads  

NASA Technical Reports Server (NTRS)

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.

Engberg, Robert C.

2003-01-01

394

Ambulatory arterial stiffness index in children after kidney transplantation.  

PubMed

Given the increase in CV morbidity after RTx and the scarcity of CV events in pediatrics, surrogate markers should be assessed to characterize CV damage in this population. AASI is a marker of arterial stiffness in adults, predicting cardio- and cerebrovascular morbidity. Our aim was to assess the determinants of AASI in RTx children (n = 54, 15.5 ± 3.5 yr) and to examine its relationship to central PWV. AASI was calculated from 24 h ABPM. PWV was determined by applanation tonometry, body composition by multifrequency bioimpedance measurement. The dipping state, volume overload, and time on dialysis were the main predictors of AASI (p < 0.05). Children with established HT (n = 34) had increased AASI, extracellular body water, and BNP (p < 0.05). In contrast to AASI, PWV did not differ between HT and normotensive RTx patient groups. There was no correlation between AASI and PWV. PWV was increased in children who spent more than one yr on dialysis prior to RTx. In conclusion, increased AASI in HT RTx children better characterizes the actual volume- and pressure-dependent arterial rigidity rather than long-term morphological changes in large arteries as reflected by PWV. PMID:23855604

Dégi, Arianna; Kerti, Andrea; Cseprekál, Orsolya; Kis, Éva; Sallay, Péter; Szabó, Attila J; Reusz, George S

2013-11-01

395

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

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

396

Polyaxial locking and compression screws improve construct stiffness of acetabular cup fixation: a biomechanical study.  

PubMed

Bone ingrowth into uncemented acetabular components requires intimate cup-bone contact and rigid fixation, which can be difficult to achieve in revision hip arthroplasty. This study compares polyaxial compression locking screws with non-locked and cancellous screw constructs for acetabular cup fixation. An acetabular cup modified with screw holes to provide both compression and angular stability was implanted into a bone substitute. Coronal lever out, axial torsion and push-out tests were performed with an Instron testing machine, measuring load versus displacement. Polyaxial locking compression screws significantly improved construct stiffness compared with non-locked or cancellous screws. This increased construct stiffness will likely reduce interfacial micromotion. Further research is required to determine whether this will improve bone ingrowth in vivo and reduce cup failure. PMID:24360790

Milne, Lachlan P; Kop, Alan M; Kuster, Markus S

2014-05-01

397

Effect of treatment on strength and stiffness of Western Red Cedar utility poles  

SciTech Connect

Based on a survey of North American utilities, research organizations and manufacturers, the effect of preservative methods on strength and stiffness of new wood utility poles was found to be inconclusive. This is primarily due to the fact that no direct comparisons were made between the mechanical properties of the same poles before and after the treatment. Hence a systematic research program was carried out on thirty, forty-five foot long Western Red Cedar poles having different sizes. Two newly developed Nondestructive Evaluation instruments, based on ultrasonic principles, were used to grade and assure the quality of these poles, individually, at the green stage. Penetration resistances were quantified using an instrumented drill. The stiffness of the untreated poles were measured from full scale deflection tests. After these measurements, the poles were treated with chromate copper arsenate (CCA) wood preservatives. Change in strength, stiffness and penetration resistance due to the treatment was quantified for each pole using the above methods. This paper will summarize the results obtained from this research program.

Bhuyan, G.S. [Powertech Labs Inc., Surrey (Canada); Chetwynd, D.S. [B.C. Hydro, Burnaby (Canada)

1995-12-31

398

An Experimental Study on the Stiffness of Size-Isolated Microbubbles Using Atomic Force Microscopy  

PubMed Central

To fully assess contrast-enhanced acoustic bioeffects in diagnostic and therapeutic procedures, the mechanical properties of microbubbles need to be considered. In the present study, direct measurements of the microbubble stiffness were performed using atomic force microscopy by applying nanoscale compressions (up to 25 nN/s) on size-isolated, lipid-coated microbubbles (diameter ranges of 4 to 6 ?m and 6 to 8 ?m). The stiffness was found to lie between 4 and 22 mN/m and to decrease exponentially with the microbubble size within the diameter range investigated. No cantilever spring constant effect was found on the measured stiffness. The Young’s modulus of the size-isolated microbubbles used in our study ranged between 0.4 and 2 MPa. Microstructures on the surface of the microbubbles were found to influence the overall microbubble elasticity. Our results indicated that more detailed theoretical models are needed to account for the size-dependent microbubble mechanical properties to accurately predict their acoustic behavior. The findings provided useful insights into guidance of cavitation-induced drug and gene delivery and could be used as part of the framework in studies on the shear stresses induced on the blood vessel walls by oscillating microbubbles. PMID:23475918

Chen, Cherry C.; Wu, Shih-Ying; Finan, John D.; Morrison, Barclay; Konofagou, Elisa E.

2014-01-01

399

Contribution of Knee Flexor and Extensor Strength on Sex-Specific Energy Absorption and Torsional Joint Stiffness During Drop Jumping  

PubMed Central

Abstract Context: Lower extremity injury often occurs during abrupt deceleration when attempting to change the body's direction. Although sex-specific biomechanics have been implicated in the greater risk of acute knee injury in women than in men, it is unknown if sex differences in thigh strength affect sex-specific energy absorption and torsional joint stiffness patterns. Objective: To determine sex differences in energy absorption patterns and joint stiffnesses of the lower extremity during a drop jump and to determine if these sex differences were predicted by knee extensor and flexor strength. Design: Cross-sectional study. Setting: Laboratory environment. Patients or Other Participants: Recreationally active, college-aged students (41 women: age ?=? 22.1 ± 2.9 years, height ?=? 1.63 ± 0.07 m, mass ?=? 59.3 ± 8.0 kg; 40 men: age ?=? 22.4 ± 2.8 years, height ?=? 1.77 ± 0.1 m, mass ?=? 80.9 ± 14.1 kg). Intervention(s): Participants performed knee flexor and extensor maximal voluntary isometric contractions followed by double-leg drop-jump landings. Main Outcome Measure(s): Lower extremity joint energetics (J × N?1 × m?1) and torsional joint stiffnesses (Nm × N?1 × m?1 × degrees?1) were calculated for the hip, knee, and ankle during the initial landing phase. Body weight was measured in newtons and height was measured in meters. Sex comparisons were made and sex-specific regressions determined if thigh muscle strength (Nm/kg) predicted sagittal-plane landing energetics and stiffnesses. Results: Women absorbed 69% more knee energy and had 36% less hip torsional stiffness than men. In women, greater knee extensor strength predicted greater knee energy absorption (R2 ?=? 0.11, P ?=? .04), and greater knee flexor strength predicted greater hip torsional stiffness (R2 ?=? 0.12, P ?=? .03). Conclusions: Sex-specific biomechanics during the deceleration phase of a drop jump revealed that women used a strategy to attempt to decrease system stiffness. Additionally, only female strength values were predictive of landing energetics and stiffnesses. These findings collectively demonstrated that the task may have been more difficult for women, resulting in a different movement strategy among those with different levels of thigh strength to safely complete the task. Future researchers should look at other predictive factors of observed sex differences. PMID:20831388

Schmitz, Randy J.; Shultz, Sandra J.

2010-01-01

400

An investigation of angular stiffness and damping coefficients of an axial spline coupling in high-speed rotating machinery  

NASA Technical Reports Server (NTRS)

This paper provided an opportunity to quantify the angular stiffness and equivalent viscous damping coefficients of an axial spline coupling used in high-speed turbomachinery. A unique test methodology and data reduction procedures were developed. The bending moments and angular deflections transmitted across an axial spline coupling were measured while a nonrotating shaft was excited by an external shaker. A rotor dynamics computer program was used to simulate the test conditions and to correlate the angular stiffness and damping coefficients. In addition, sensitivity analyses were performed to show that the accuracy of the dynamic coefficients do not rely on the accuracy of the data reduction procedures.

Ku, C.-P. Roger; Walton, James F., Jr.; Lund, Jorgen W.

1994-01-01

401

Arabidopsis Floral Initiator SKB1 Confers High Salt Tolerance by Regulating Transcription and Pre-mRNA Splicing through Altering Histone H4R3 and Small Nuclear Ribonucleoprotein LSM4 Methylation[C][W  

PubMed Central

Plants adapt their growth and development in response to perceived salt stress. Although DELLA-dependent growth restraint is thought to be an integration of the plant’s response to salt stress, little is known about how histone modification confers salt stress and, in turn, affects development. Here, we report that floral initiator Shk1 kinase binding protein1 (SKB1) and histone4 arginine3 (H4R3) symmetric dimethylation (H4R3sme2) integrate responses to plant developmental progress and salt stress. Mutation of SKB1 results in salt hypersensitivity, late flowering, and growth retardation. SKB1 associates with chromatin and thereby increases the H4R3sme2 level to suppress the transcription of FLOWERING LOCUS C (FLC) and a number of stress-responsive genes. During salt stress, the H4R3sme2 level is reduced, as a consequence of SKB1 disassociating from chromatin to induce the expression of FLC and the stress-responsive genes but increasing the methylation of small nuclear ribonucleoprotein Sm-like4 (LSM4). Splicing defects are observed in the skb1 and lsm4 mutants, which are sensitive to salt. We propose that SKB1 mediates plant development and the salt response by altering the methylation status of H4R3sme2 and LSM4 and linking transcription to pre-mRNA splicing. PMID:21258002

Zhang, Zhaoliang; Zhang, Shupei; Zhang, Ya; Wang, Xin; Li, Dan; Li, Qiuling; Yue, Minghui; Li, Qun; Zhang, Yu-e; Xu, Yunyuan; Xue, Yongbiao; Chong, Kang; Bao, Shilai

2011-01-01

402

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

NASA Astrophysics Data System (ADS)

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.

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

403

Bending stiffness of two aesthetic orthodontic archwires: an in vitro comparative study.  

PubMed

The aims of the study were to quantify the transverse stiffness of two aesthetic orthodontic archwires (0018 inch Teflon-coated stainless steel and 0017 inch Optiflex) in a simulated clinical setting and to assess the influence of deflection direction on the bending stiffness. The aesthetic archwires were randomly divided into three equal groups: group 1, lingual deflection; group 2, labial deflection; and group 3, occlusal deflection. Each group consisted of six archwires of the same type. The control group consisting of eighteen 0014 inch stainless steel archwires were also subjected to the same grouping. A total of 54 archwires were tested in the study. The deflection of the archwires was measured with a travelling microscope and the load measured with a calibrated strain gauge ring transducer. The mean stiffnesses of the archwires in the lingual, labial and occlusal deflection groups were found to be 29, 08 and 25 mN/mm respectively for 0017 inch Optiflex (r = 09, P less than 0001), 132, 105 and 245 mN/mm respectively for 0018 inch Teflon-coated stainless steel (r = 09, P less than 0001) and 266, 164 and 323 mN/mm respectively for the control (r = 09, P less than 0001). Springback was found to be poor for Optiflex and the archwire remained bent upon deactivation. ANOVA showed that the influence of arch curvature on the bending stiffness was significantly different for Optiflex (P less than 005), Teflon-coated stainless steel (P less than 0005) and the control group (P <0005).(ABSTRACT TRUNCATED AT 250 WORDS) PMID:10147326

Lim, K F; Lew, K K; Toh, S L

1994-01-01

404

Exposure to wood smoke increases arterial stiffness and decreases heart rate variability in humans  

PubMed Central

Background Emissions from biomass combustion are a major source of indoor and outdoor air pollution, and are estimated to cause millions of premature deaths worldwide annually. Whilst adverse respiratory health effects of biomass exposure are well established, less is known about its effects on the cardiovascular system. In this study we assessed the effect of exposure to wood smoke on heart rate, blood pressure, central arterial stiffness and heart rate variability in otherwise healthy persons. Methods Fourteen healthy non-smoking subjects participated in a randomized, double-blind crossover study. Subjects were exposed to dilute wood smoke (mean particle concentration of 314±38 ?g/m3) or filtered air for three hours during intermittent exercise. Heart rate, blood pressure, central arterial stiffness and heart rate variability were measured at baseline and for one hour post-exposure. Results Central arterial stiffness, measured as augmentation index, augmentation pressure and pulse wave velocity, was higher after wood smoke exposure as compared to filtered air (p < 0.01 for all), and heart rate was increased (p < 0.01) although there was no effect on blood pressure. Heart rate variability (SDNN, RMSSD and pNN50; p = 0.003, p < 0.001 and p < 0.001 respectively) was decreased one hour following exposure to wood smoke compared to filtered air. Conclusions Acute exposure to wood smoke as a model of exposure to biomass combustion is associated with an immediate increase in central arterial stiffness and a simultaneous reduction in heart rate variability. As biomass is used for cooking and heating by a large fraction of the global population and is currently advocated as a sustainable alternative energy source, further studies are required to establish its likely impact on cardiovascular disease. Trial registration ClinicalTrials.gov, NCT01488500 PMID:23742058

2013-01-01

405

Analysis and Design of Variable Stiffness Composite Cylinders  

NASA Technical Reports Server (NTRS)

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

Tatting, Brian F.; Guerdal, Zafer

1998-01-01

406

The use of color Doppler imaging for the assessment of sacroiliac joint stiffness: a study on embalmed human pelvises  

Microsoft Academic Search

Purpose: The validity and reproducibility of an instrumented dynamic examination method to measure sacroiliac (SI) joint stiffness was tested in vitro. Methods: Four embalmed human female pelvises were excitated by a pelvic vibrator. A color Doppler imaging (CDI) scanner was used to image the amplitude of vibrations at different sites of the pelvis. Vibrations were applied to the anterior superior

H. Muzaffer Buyruk; Hendrik J. Stam; Christian J. Snijders; Adrian Vleeming; Johan S. Laméris; Wim P. J. Holland

1995-01-01

407

PREDICTING RUNOFF AND SOIL EROSION FROM A STIFF-STEMMED GRASS HEDGE SYSTEM IN A SMALL WATERSHED  

Technology Transfer Automated Retrieval System (TEKTRAN)

Planting of vegetative stiff-stemmed grass hedges as an erosion control practice may influence surface runoff by altering soil hydraulic properties. The objective of our study was to evaluate the effects of measured soil hydraulic properties as influenced by grass hedges on runoff and sediment yiel...

408

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

PubMed Central

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