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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

Assessment of impact factors on shear wave based liver stiffness measurement.  

PubMed

Shear wave based ultrasound elastographies have been implemented as non-invasive methods for quantitative assessment of liver stiffness. Nonetheless, there are only a few studies that have investigated impact factors on liver stiffness measurement (LSM). Moreover, standard examination protocols for LSM are still lacking in clinical practice. Our study aimed to assess the impact factors on LSM to establish its standard examination protocols in clinical practice. We applied shear wave based elastography point quantification (ElastPQ) in 21 healthy individuals to determine the impact of liver location (segments I-VIII), breathing phase (end-inspiration and end-expiration), probe position (sub-costal and inter-costal position) and examiner on LSM. Additional studies in 175 healthy individuals were also performed to determine the influence of gender and age on liver stiffness. We found significant impact of liver location on LSM, while the liver segment V displayed the lowest coefficient of variation (CV 21%). The liver stiffness at the end-expiration was significantly higher than that at the end-inspiration (P=2.1E-05). The liver stiffness was 8% higher in men than in women (3.8 ± 0.7 kPa vs. 3.5 ± 0.4 kPa, P=0.0168). In contrast, the liver stiffness was comparable in the different probe positions, examiners and age groups (P>0.05). In conclusion, this study reveals significant impact from liver location, breathing phase and gender on LSM, while furthermore strengthening the necessity for the development of standard examination protocols on LSM. PMID:23116805

Ling, Wenwu; Lu, Qiang; Quan, Jierong; Ma, Lin; Luo, Yan

2013-02-01

3

Measurement of liver stiffness as a non-invasive method for diagnosis of non-alcoholic fatty liver disease.  

PubMed

Non-alcoholic fatty liver disease (NAFLD) is one of the major causes of liver disease worldwide. To detect early stages of NAFLD and start treatment or to monitor the changes in trials of new drugs, non-invasive diagnostic methods are needed, such as biochemical markers or liver stiffness measurement (LSM). LSM with transient elastography (TE) and acoustic radiation force impulse (ARFI) has been shown to be useful in NAFLD, although the cut-off values have varied among reports. Magnetic resonance elastography and real-time tissue elastography also can be useful for the diagnosis of NAFLD, although the number of studies is limited. Fibrosis is absent in 8-40% of patients with non-alcoholic steatohepatitis (NASH), making it difficult to diagnose NASH by LSM because LSM is usually associated with fibrotic stage. The presence of inflammation or hepatocyte ballooning may affect LSM and aid the diagnosis of NASH without fibrosis. However, obesity significantly increases the failure of LSM and its interference is more conspicuous in TE than in ARFI. The newly implemented XL probe of TE has overcome the difficulty to some degree. Nonetheless, the effects of obesity, hepatocyte ballooning, steatosis and inflammation on LSM values have not yet been adequately investigated, although they are likely to affect LSM values. Further studies are needed to establish the clinical utility of LSM in NAFLD. PMID:25040931

Yoshioka, Kentaro; Hashimoto, Senju; Kawabe, Naoto

2015-01-01

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

Liver Stiffness Measurement, Better than APRI, Fibroindex, Fib-4, and NBI Gastroscopy, Predicts Portal Hypertension in Patients with Cirrhosis.  

PubMed

Liver stiffness measurement (LSM) is frequently used as non-invasive alternative for liver fibrosis including cirrhosis, which can lead to portal hypertension. This study was conducted to evaluate the predictive value of LSM in cirrhosis-induced portal hypertension patients. Between July 2011 and December 2013, 153 participants were enrolled into a single-center, prospective, cross-sectional study. Each subject received both gastroscopy and LSM. Baseline biochemical, APRI, Fibroindex, and Fib-4 were also performed. LSM of cirrhosis patients with portal hypertension was significantly higher compared to those without portal hypertension (P < 0.05). A LSM ? 13.6 kPa had a sensitivity of 83.87 % and a specificity of 72.53 % with an accuracy of 77.1 for the prediction of portal hypertension, which are higher than those of APRI, Fib-4, and Fibroscan separately. A combination of Fibroscan combined with Fib-4 achieved a maximum AUC of 0.833 and accuracy of 77.8. Discriminant and internal validation analysis showed that Fibroscan plus APRI obtained a lower false negative rate compared to Fibroscan plus Fib-4 and Fibroscan plus Fibroindex (9.68, 17.74, and 11.29 %, respectively). A good relationship was found between LSM and NBI mean optical density both by linear and polynomial correlation analysis (r = 0.5533 and r = 0.7349, both P < 0.001). There was a trend toward a better performance of LSM for assessing portal hypertension compared with NBI gastroscopy mean optical density (P = 0.028 and P = 0.05, respectively). Better than APRI, Fibroindex, Fib-4, and NBI gastroscopy, LSM can predict portal hypertension in cirrhosis patients. A LSM of 13.6 kPa can be considered to be the predictive value for portal hypertension. PMID:25417057

Zhang, Wei; Wang, Liqiong; Wang, Lei; Li, Gang; Huang, Aoshuang; Yin, Ping; Yang, Zhenhua; Ling, Changquan; Wang, Lingtai

2014-11-23

6

Leg stiffness measures depend on computational method.  

PubMed

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

Hébert-Losier, Kim; Eriksson, Anders

2014-01-01

7

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

8

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

9

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

PubMed Central

A new device and automated measurement technology known as OroSTIFF is described to characterize non-participatory perioral stiffness in healthy adults for eventual application to patients with orofacial movement disorders associated with neuromotor disease, traumatic injury, or congenital clefts of the upper lip. Previous studies of perioral biomechanics required head stabilization for extended periods of time during measurement which precluded sampling patients with involuntary body/head movements (dyskinesias), or pediatric subjects. The OroSTIFF device is face-referenced and avoids the complications associated with head-restraint. Supporting data of non-participatory perioral tissue stiffness using OroSTIFF are included from 10 male and 10 female healthy subjects. The OroSTIFF device incorporates a pneumatic glass air cylinder actuator instrumented for pressure, and an integrated subminiature displacement sensor to encode lip aperture. Perioral electromyograms were simultaneously sampled to confirm passive muscle state for the superior and inferior divisions of the orbicularis oris muscles. Perioral stiffness, derived as a quotient from resultant force (?F) and interangle span (?X), was modeled with multilevel regression techniques. Real-time calculation of the perioral stiffness function demonstrated a significant quadratic relation between imposed interangle stretch and resultant force. This stiffness growth function also differed significantly between males and females. This study demonstrates the OroSTIFF ‘proof-of-concept’ for cost-effective non-invasive stimulus generation and derivation of perioral stiffness in a group of healthy unrestrained adults, and a case study to illustrate the dose-dependent effects of Levodopa on perioral stiffness in an individual with advanced Parkinson’s disease who exhibited marked dyskinesia and rigidity. PMID:20185131

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

2010-01-01

10

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

11

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.

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

Development of continuous stiffness measurement technique for composite magnetic tapes  

SciTech Connect

Studying mechanical properties of materials on the nanoscale has received much attention in recent years as the properties are size dependent. Continuous measurements of mechanical properties of these materials during indentation are greatly needed. A continuous stiffness measurement (CSM) technique allows the contact stiffness to be measured at any point along the loading curve and not just at the point of unloading. In the present investigation, an analytical methodology of CSM technique used for characterizing nonuniform materials is developed and applied to nanocomposite magnetic tapes. The contact stiffness, elastic modulus and hardness of fused silica, polytetrafluoroethylene (PTFE) and metal-particle (MP) tapes were measured as a function of indentation depth using the CSM technique. For the first time, the graded material characteristics of MP tapes are reported.

Li, X.; Bhushan, B.

2000-05-10

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

Nanomechanical measurement of astrocyte stiffness correlated with cytoskeletal maturation.  

PubMed

Astrocytes are known to serve as scaffolding cells that shape the brain. The physical properties of astrocytes, such as stiffness, are important for their scaffolding function. These properties may be altered in certain pathological conditions, such as in brain cancer. However, actual stiffness of astrocytes is not yet well understood. Here, we report that the astrocyte stiffness is positively correlated with the density of cytoskeletal proteins, such as actin filaments, microtubules, and intermediate filaments. The value of the stiffness of astrocytes as measured by atomic force microscopy (AFM) increases 38-fold in five-week-old rats compared to postnatal-day zero pups. Using multicolor confocal microscopy, we found that the complexity of cytoskeletal proteins, such as actin filaments, microtubules, and intermediate filaments, increase as the animal gets older. Our findings indicate that the change of stiffness positively correlates with the maturation of cytoskeletal proteins, and suggest that AFM can be useful as an analytical and diagnostic tool for neuroscience. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 365-370, 2015. PMID:24665040

Lee, Sang-Myung; Nguyen, Thi-Huong; Na, Kyounghwan; Cho, Il-Joo; Woo, Dong Ho; Oh, Jae-Eung; Lee, C Justin; Yoon, Eui-Sung

2015-01-01

17

Dependence of elbow joint stiffness measurements on speed, angle, and muscle contraction level.  

PubMed

Elbow joint stiffness is critical to positioning the hand. Abnormal elbow joint stiffness may affect a person's ability to participate in activities of daily living. In this work, elbow joint stiffness was measured in ten healthy young adults with a device adapted from one previously used to measure stiffness in other joints. Measurements of elbow stiffness involved applying a constant-velocity rotational movement to the elbow and measuring the resultant displacement, torque, and acceleration. Elbow stiffness was then computed using a previously-established model for joint stiffness. Measurements were made at two unique elbow joint angles, two speeds, and two forearm muscle contraction levels. The results indicate that the elbow joint stiffness is significantly affected by both rotational speed and forearm muscle contraction level. PMID:24433667

Kuxhaus, Laurel; Zeng, Sisi; Robinson, Charles J

2014-03-21

18

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

PubMed Central

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

Loram, Ian D; Lakie, Martin

2002-01-01

19

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

20

UNIVERSITY OF CALIFORNIA, Stiffness and grip force measurement using  

E-print Network

basic elements: eccentric mass dc motor, skin mechanical impedance, system mass and muscle stiffness level 100%, we have a muscle stiffness of 816.1 N/m. Graph taken from [4], Fig. 4, subject B. ............................................................................................................................13 Figure 6: scheme showing skin mechanical impedance. Composed of a mass component (M), a damper

Paris-Sud XI, Université de

21

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

22

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

23

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

24

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

25

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

26

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

27

A novel mechatronic system for measuring end-point stiffness: mechanical design and preliminary tests.  

PubMed

Measuring arm stiffness is of great interest for many disciplines from biomechanics to medicine especially because modulation of impedance represents one of the main mechanism underlying control of movement and interaction with external environment. Previous works have proposed different methods to identify multijoint hand stiffness by using planar or even tridimensional haptic devices, but the associated computational burden makes them not easy to implement. We present a novel mechanism conceived for measuring multijoint planar stiffness by a single measurement and in a reduced execution time. A novel mechanical rotary device applies cyclic radial perturbation to human arm of a known displacement and the force is acquired by means of a 6-axes commercial load cell. The outcomes suggest that the system is not only reliable but allows obtaining a bi-dimensional estimation of arm stiffness in reduced amount of time and the results are comparable with those reported in previous researches. PMID:22275711

Masia, L; Sandini, G; Morasso, P G

2011-01-01

28

Stiffness matrix determination of composite materials using lamb wave group velocity measurements  

NASA Astrophysics Data System (ADS)

The use of Lamb waves in Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) is gaining popularity due to their ability to travel long distances without significant attenuation, therefore offering large area inspections with a small number of sensors. The design of a Lamb-wave-based NDE/SHM system for composite materials is more complicated than for metallic materials due to the directional dependence of Lamb wave propagation characteristics such as dispersion and group velocity. Propagation parameters can be theoretically predicted from known material properties, specifically the stiffness matrix and density. However, in practice it is difficult to obtain the stiffness matrix of a particular material or structure with high accuracy, hence introducing errors in theoretical predictions and inaccuracies in the resulting propagation parameters. Measured Lamb wave phase velocities can be used to infer the stiffness matrix, but the measurements are limited to the principal directions due to the steering effect (different propagation directions of phase and corresponding group velocities). This paper proposes determination of the stiffness matrix from the measured group velocities, which can be unambiguously measured in any direction. A highly anisotropic carbon-fibre-reinforced polymer plate is chosen for the study. The influence of different stiffness matrix elements on the directional group velocity profile is investigated. Thermodynamic Simulated Annealing (TSA) is used as a tool for inverse, multi variable inference of the stiffness matrix. A good estimation is achieved for particular matrix elements.

Putkis, O.; Croxford, A. J.

2013-04-01

29

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

30

Turtle utricle dynamic behavior using a combined anatomically accurate model and experimentally measured hair bundle stiffness.  

PubMed

Anatomically correct turtle utricle geometry was incorporated into two finite element models. The geometrically accurate model included appropriately shaped macular surface and otoconial layer, compact gel and column filament (or shear) layer thicknesses and thickness distributions. The first model included a shear layer where the effects of hair bundle stiffness was included as part of the shear layer modulus. This solid model's undamped natural frequency was matched to an experimentally measured value. This frequency match established a realistic value of the effective shear layer Young's modulus of 16 Pa. We feel this is the most accurate prediction of this shear layer modulus and fits with other estimates (Kondrachuk, 2001b). The second model incorporated only beam elements in the shear layer to represent hair cell bundle stiffness. The beam element stiffness's were further distributed to represent their location on the neuroepithelial surface. Experimentally measured striola hair cell bundles mean stiffness values were used in the striolar region and the mean extrastriola hair cell bundles stiffness values were used in this region. The results from this second model indicated that hair cell bundle stiffness contributes approximately 40% to the overall stiffness of the shear layer-hair cell bundle complex. This analysis shows that high mass saccules, in general, achieve high gain at the sacrifice of frequency bandwidth. We propose the mechanism by which this can be achieved is through increase the otoconial layer mass. The theoretical difference in gain (deflection per acceleration) is shown for saccules with large otoconial layer mass relative to saccules and utricles with small otoconial layer mass. Also discussed is the necessity of these high mass saccules to increase their overall system shear layer stiffness. Undamped natural frequencies and mode shapes for these sensors are shown. PMID:25445820

Davis, J L; Grant, J W

2014-12-01

31

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

32

Live-cell subcellular measurement of cell stiffness using a microengineered stretchable micropost array membrane  

PubMed Central

Forces are increasingly recognized as major regulators of cell structure and function, and the mechanical properties of cells, such as cell stiffness, are essential to the mechanisms by which cells sense forces, transmit them to the cell interior or to other cells, and transduce them into chemical signals that impact a spectrum of cellular responses. Here we reported a new whole-cell cell stiffness measurement technique with a subcellular spatial resolution. This technique was based on a novel cell stretching device that allowed for quantitative control and real-time measurements of mechanical stimuli and cellular biomechanical responses. Our strategy involved a microfabricated array of silicone elastomeric microposts integrated onto a stretchable elastomeric membrane. Using a computer-controlled vacuum, this micropost array membrane (mPAM) was activated to apply equibiaxial cell stretching forces to adherent cells attached on the tops of the microposts. The micropost top positions before and after mPAM stretches were recorded using fluorescence microscopy and further utilized to quantify local cell stretching forces and cell area increments. A robust computation scheme was developed and implemented for subcellular quantifications of cell stiffness using the data of local cell stretching forces and cell area increments generated from mPAM cell stretch assays. Our cell stiffness studies using the mPAM revealed strong positive correlations among cell stiffness, cellular traction force, and cell spread area, and illustrated the important functional roles of actin polymerization and myosin II-mediated cytoskeleton contractility in regulating cell stiffness. Collectively, our work reported a new approach for whole-cell cell stiffness measurements with a subcellular spatial resolution, which would likely help explain the complex biomechanical functions and force-sensing mechanisms of cells and design better materials for cell and tissue engineering and other applications in vivo. PMID:22935822

Lam, Raymond H. W.; Weng, Shinuo; Lu, Wei; Fu, Jianping

2014-01-01

33

Nanoindentation of wood cell walls: Continuous stiffness and hardness measurements q  

E-print Network

Nanoindentation of wood cell walls: Continuous stiffness and hardness measurements q W.T.Y. Tze a 37831-6116, USA d Department of Wood and Paper Science, North Carolina State University, Raleigh, NC The objective of this study was to measure the mechanical properties of individual, native wood fibers using

Wang, Siqun

34

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

35

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

36

Contact-flatted measurement of eye stiffness based on force-displacement relationship  

NASA Astrophysics Data System (ADS)

This paper presents a noninvasive approach in vivo measurement of eye stiffness based on a force-displacement relationship, which is based on a new contact-probe method of simultaneously measuring the static force and displacement. First, a simple spherical eye model is introduced for deriving analytical eye stiffness when a static force is applied to an eye. Next, a measurement system for simultaneously measuring force and displacement when a probe is pressed onto the eye is presented. Static eye stiffness is defined which based on the measured force-displacement relationship. A photoelectric probe transducer acts as displacement detector. A 16-bit single-chip microprocessor with E2PROM in the electronic circuit played the role of a nucleus, which stored the program instructions and the interrelated data. Laboratory experiments were carried out on a simulated eyeball connected to a hydraulic manometer to obtain intraocular pressure at different levels. The experimental results show that the measured eye stiffness nicely matches the analytical result.

Zhang, Jin; Ma, Jianguo; Zhang, Xueyong

2011-12-01

37

Controlling and measuring substrate stiffness for cell motility studies  

NASA Astrophysics Data System (ADS)

Cell motility and differentiation is generally considered to be controlled by mostly chemical cues. However, recent evidence has shown that mechanical cues may be just as important. Here, we present a study to create patterned substrates that allow to test the hypothesis that cells prefer substrates of certain mechanical moduli and will migrate towards these substrates. In this context, we present a discussion of optimal methods to measure substrate moduli at the local level and compare different methods with respect to ease of implementation, data interpretation and reliability.

Runyan, Lindsay; Hoffmann, Peter; Beningo, Karen

2009-03-01

38

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

39

Role for LSM genes in the regulation of circadian rhythms.  

PubMed

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

2014-10-21

40

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

41

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

42

Within- and between-day reliability of spinal stiffness measurements obtained using a computer controlled mechanical indenter in individuals with and without low back pain.  

PubMed

Instrumented spinal stiffness measurements have shown high test-retest reliability. However, factors that may affect reliability have yet to be investigated. The objective of this study was to compare the: 1) within- and between-day reliability of a mechanical indentation device (MID) in measuring spinal stiffness, 2) measurement precision of averaging multiple measurements, and 3) reliability of stiffness measurements between individuals with and without low back pain (LBP). The spinal stiffness of 26 volunteers with and without LBP was measured 3 times by MID in each of two visits 1-4 days apart. Two stiffness measures were calculated from the resulting force-displacement data: global stiffness and terminal stiffness. Intraclass correlation coefficients (ICCs) were used to estimate reliability. Measurement precision was measured by minimal detectable changes, bias and 95% limits of agreement. Using the mean of three spinal stiffness measurements, the measurement precision was improved by 33.7% over a single measurement. Averaging three measurements, the within- and between-day reliability point estimates of both global and terminal stiffness were 0.99 and 0.98, respectively. The reliability estimates of spinal stiffness measurement using MID were not significantly altered by the participants' LBP status across all circumstances (95% confidence intervals overlapped). With our experimental protocol, averaging three spinal stiffness measurements using MID produces reliable stiffness measurements regardless of individuals' LBP status. PMID:23465962

Wong, Arnold Y L; Kawchuk, Greg; Parent, Eric; Prasad, Narasimha

2013-10-01

43

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

44

Experimental validation of arthroscopic cartilage stiffness measurement using enzymatically degraded cartilage samples  

NASA Astrophysics Data System (ADS)

In order to evaluate the ability of the arthroscopic indentation instrument, originally developed for the measurement of cartilage stiffness during arthroscopy, to detect cartilage degeneration, we compared changes in the stiffness with the structural and constitutional alterations induced by enzymes on the tissue in vitro. The culturing of osteochondral plugs on Petri dishes was initiated in Minimum Essential Medium with Earle's salts and the baseline stiffness was measured. Then, the experimental specimens were digested using trypsin for 24 h, chondroitinase ABC or purified collagenase (type VII) for 24 h or 48 h ( n = 8-15 per group). The control specimens were incubated in the medium. After the enzyme digestion, the end-point stiffness was measured and the specimens for the microscopic analyses were processed. The proteoglycan (PG) distribution was analysed using quantitative microspectrophotometry and the quantitative evaluation of the collagen network was made using a computer-based polarized light microscopy analysis. Decrease of cartilage stiffness was found after 24 h trypsin (36%) and 48 h chondroitinase ABC (24%) digestion corresponding to a decrease of up to 80% and up to 30% in the PG content respectively. Decrease of the superficial zone collagen content or arrangement (78%, ) after 48 h collagenase digestion also induced a decrease (30%, ) in cartilage stiffness. We conclude that our instrument is capable of detecting early structural and compositional changes related to cartilage degeneration.

Lyyra, T.; Arokoski, J. P. A.; Oksala, N.; Vihko, A.; Hyttinen, M.; Jurvelin, J. S.; Kiviranta, I.

1999-02-01

45

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

46

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

47

Simultaneous measurement of real contact area and fault normal stiffness during frictional sliding  

NASA Astrophysics Data System (ADS)

The tectonic stresses that lead to earthquake slip are concentrated in small regions of solid contact between asperities or gouge particles within the fault. Fault strength is proportional to the contact area within the shearing portion of the fault zone and many fault properties of interest to earthquake hazard research, e.g., occurrence time, recurrence interval, precursory slip, triggered earthquake slip, are controlled by processes acting at the highly stressed contact regions. Unfortunately the contact-scale physical processes controlling earthquake occurrence cannot be easily observed or measured directly. In this pilot study we simultaneously directly measure contact area using transmitted light intensity (LI) [Dieterich and Kilgore, 1994; 1996] and continuously monitor the normal stiffness of the fault using acoustic wave transmission (AT) [Nagata et al., 2008]. The objective of our study is to determine relations amongst contacting area, stiffness, strength, normal stress, shear displacement, and time of contact during sliding. Interface stiffness is monitored using acoustic compressive waves transmitted across the fault. Because the fault is more compliant in compression than the surrounding rock, the fault has an elastic wave transmission coefficient that depends on the fault normal stiffness. Contact area is measured by LI: regions in contact transmit light efficiently while light is scattered elsewhere; therefore transmitted light intensity is presumed proportional to contact area. LI and AT are expected to be correlated; e.g., an elastic contact model suggests that stiffness goes as the square root of contact area. We observe LI and AT for sliding at slip speeds between 0.01 and 10 microns/s and normal stresses between 1 and 2.5 MPa while conducting standard velocity-step, normal stress-step and slide-hold-slide tests. AT and LI correlate during all tests, at all conditions. If the physical relationship, or even an empirical calibration between AT and LI can be established for rough fault surfaces, contact area could be measured with AT for non-transparent materials and at higher normal stresses than in the present experiments.

Beeler, N. M.; Nagata, K.; Kilgore, B. D.; Nakatani, M.

2010-12-01

48

Nanoindentation and contact stiffness measurement using force modulation with a capacitive load-displacement transducer  

NASA Astrophysics Data System (ADS)

We have implemented a force modulation technique for nanoindentation using a three-plate capacitive load-displacement transducer. The stiffness sensitivity of the instrument is ˜0.1 N/m. We show that the sensitivity of this instrument is sufficient to detect long-range surface forces and to locate the surface of a specimen. The low spring mass (236 mg), spring constant (116 N/m), and damping coefficient (0.008 Ns/m) of the transducer allows measurement of the damping losses for nanoscale contacts. We present the experimental technique, important specimen mounting information, and system calibration for nanomechanical property measurement.

Asif, S. A. Syed; Wahl, K. J.; Colton, R. J.

1999-05-01

49

Cardiovascular outcome associations among cardiovascular magnetic resonance measures of arterial stiffness: the Dallas heart study  

PubMed Central

Background Cardiovascular magnetic resonance (CMR) has been validated for the noninvasive assessment of total arterial compliance and aortic stiffness, but their associations with cardiovascular outcomes is unknown. The purpose of this study was to evaluate associations of CMR measures of total arterial compliance and two CMR measures of aortic stiffness with respect to future cardiovascular events. Methods The study consisted of 2122 Dallas Heart Study participants without cardiovascular disease who underwent CMR at 1.5 Tesla. Aortic stiffness was measured by CMR-derived ascending aortic distensibility and aortic arch pulse wave velocity. Total arterial compliance was calculated by dividing left ventricular stroke volume by pulse pressure. Participants were monitored for cardiovascular death, non-fatal cardiac events, and non-fatal extra-cardiac vascular events over 7.8?±?1.5 years. Cox proportional hazards regression was used to assess for associations between CMR measures and cardiovascular events. Results Age, systolic blood pressure, and resting heart rate were independently associated with changes in ascending aortic distensibility, arch pulse wave velocity, and total arterial compliance (all p?measures of arterial stiffness are associated with future cardiovascular events. Total arterial compliance and aortic distensibility may be stronger predictors of nonfatal cardiac events, while pulse wave velocity may be a stronger predictor of nonfatal extra-cardiac vascular events. PMID:24886531

2014-01-01

50

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

51

Measurement of sacroiliac joint stiffness in peripartum pelvic pain patients with Doppler imaging of vibrations (DIV)  

Microsoft Academic Search

Objectives. The research question of the present study was: are sacroiliac joint stiffness levels of peripartum pelvic pain patients different from those of healthy subjects?Study design. A cross-sectional comparative sacroiliac joint stiffness analysis of peripartum pelvic pain patients with healthy subjects. In previous studies we introduced a new technique, Doppler imaging of vibrations (DIV), to assess sacroiliac joint stiffness using

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

1999-01-01

52

A Mixture of Experts Model for the Diagnosis of Liver Cirrhosis by Measuring the Liver Stiffness  

PubMed Central

Objectives The mixture-of-experts (ME) network uses a modular type of neural network architecture optimized for supervised learning. This model has been applied to a variety of areas related to pattern classification and regression. In this research, we applied a ME model to classify hidden subgroups and test its significance by measuring the stiffness of the liver as associated with the development of liver cirrhosis. Methods The data used in this study was based on transient elastography (Fibroscan) by Kim et al. We enrolled 228 HBsAg-positive patients whose liver stiffness was measured by the Fibroscan system during six months. Statistical analysis was performed by R-2.13.0. Results A classical logistic regression model together with an expert model was used to describe and classify hidden subgroups. The performance of the proposed model was evaluated in terms of the classification accuracy, and the results confirmed that the proposed ME model has some potential in detecting liver cirrhosis. Conclusions This method can be used as an important diagnostic decision support mechanism to assist physicians in the diagnosis of liver cirrhosis in patients. PMID:22509471

Chang, Ji Hong; Song, Kijun

2012-01-01

53

Non-Contact Measurements of Stiffness in Confined PS Films by Fluorescence and XPCS  

NASA Astrophysics Data System (ADS)

Fluorescence is used to detect stiffness in confined polystyrene (PS) films through the intensity ratio (I3/I1) of the dye molecule pyrene. Free-standing PS films show a softening (an increase in I3/I1) when the film thickness decreases below 400 nm, and a stiffening (a decrease in I3/I1) below thicknesses of 200 nm. Silica- and PDMS-supported PS films show no softening but report stiffening for films less than 200 nm thick, a result not in accord with the Tg reductions seen for PS on silica. X-ray photon correlation spectroscopy (XPCS) also reports stiffening in PS on silica through the relaxation times of capillary waves at the polymer surface. A two order of magnitude increase in relaxation time is observed for small in-plane wavevectors (q) in a 30 nm PS film compared to a 120 nm film. Bilayer films of PS supported on various bulk underlayers studied by XPCS indicate that lower substrate modulus leads to faster PS surface relaxation times. These are the first reported non-contact measurements related to stiffness in confined PS on silica.

Evans, Christopher; Narayanan, Suresh; Jiang, Zhang; Torkelson, John

2011-03-01

54

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

PubMed Central

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

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

2012-01-01

55

Diabetes increases stiffness of live cardiomyocytes measured by atomic force microscopy nanoindentation.  

PubMed

Stiffness of live cardiomyocytes isolated from control and diabetic mice was measured using the atomic force microscopy nanoindentation method. Type 1 diabetes was induced in mice by streptozotocin administration. Histological images of myocardium from mice that were diabetic for 3 mo showed disorderly lineup of myocardial cells, irregularly sized cell nuclei, and fragmented and disordered myocardial fibers with interstitial collagen accumulation. Phalloidin-stained cardiomyocytes isolated from diabetic mice showed altered (i.e., more irregular and diffuse) actin filament organization compared with cardiomyocytes from control mice. Sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a) pump expression was reduced in homogenates obtained from the left ventricle of diabetic animals compared with age-matched controls. The apparent elastic modulus (AEM) for live control or diabetic isolated cardiomyocytes was measured using the atomic force microscopy nanoindentation method in Tyrode buffer solution containing 1.8 mM Ca(2+) and 5.4 mM KCl (physiological condition), 100 nM Ca(2+) and 5.4 mM KCl (low extracellular Ca(2+) condition), or 1.8 mM Ca(2+) and 140 mM KCl (contraction condition). In the physiological condition, the mean AEM was 112% higher for live diabetic than control isolated cardiomyocytes (91 ± 14 vs. 43 ± 7 kPa). The AEM was also significantly higher in diabetic than control cardiomyocytes in the low extracellular Ca(2+) and contraction conditions. These findings suggest that the material properties of live cardiomyocytes were affected by diabetes, resulting in stiffer cells, which very likely contribute to high diastolic LV stiffness, which has been observed in vivo in some diabetes mellitus patients. PMID:25163520

Benech, Juan C; Benech, Nicolás; Zambrana, Ana I; Rauschert, Inés; Bervejillo, Verónica; Oddone, Natalia; Damián, Juan P

2014-11-15

56

Transient micro-elastography: A novel non-invasive approach to measure liver stiffness in mice  

PubMed Central

AIM: To develop and validate a transient micro-elastography device to measure liver stiffness (LS) in mice. METHODS: A novel transient micro-elastography (TME) device, dedicated to LS measurements in mice with a range of measurement from 1-170 kPa, was developed using an optimized vibration frequency of 300 Hz and a 2 mm piston. The novel probe was validated in a classical fibrosis model (CCl4) and in a transgenic murine model of systemic amyloidosis. RESULTS: TME could be successfully performed in control mice below the xiphoid cartilage, with a mean LS of 4.4 ± 1.3 kPa, a mean success rate of 88%, and an excellent intra-observer agreement (0.98). Treatment with CCl4 over seven weeks drastically increased LS as compared to controls (18.2 ± 3.7 kPa vs 3.6 ± 1.2 kPa). Moreover, fibrosis stage was highly correlated with LS (Spearman coefficient = 0.88, P < 0.01). In the amyloidosis model, much higher LS values were obtained, reaching maximum values of > 150 kPa. LS significantly correlated with the amyloidosis index (0.93, P < 0.0001) and the plasma concentration of mutant hapoA-II (0.62, P < 0.005). CONCLUSION: Here, we have established the first non-invasive approach to measure LS in mice, and have successfully validated it in two murine models of high LS. PMID:21448348

Bastard, Cécile; Bosisio, Matteo R; Chabert, Michèle; Kalopissis, Athina D; Mahrouf-Yorgov, Meriem; Gilgenkrantz, Hélène; Mueller, Sebastian; Sandrin, Laurent

2011-01-01

57

A piconewton force transducer and its application to measurement of the bending stiffness of phospholipid membranes.  

PubMed

The bending stiffness of a phospholipid bilayer (Kc) was measured by forming thin bilayer cylinders (tethers) from giant phospholipid vesicles. Based on the balance of forces, the tether force was expected to be proportional to the square root of the membrane tension, with a constant of proportionality containing Kc. The membrane tension was controlled via the aspiration pressure in a micropipette used to hold the vesicle. The force on the tether was generated by an electromagnet acting on a paramagnetic bead attached to the vesicle surface. The magnitude of the force was determined from measurements of the magnet current, which was adjusted to maintain the position of the bead. Measurements were performed on vesicles composed of stearoyl-oleoyl-phosphatidylcholine plus 5% (by mole) biotinylated phosphatidylethanolamine to mediate adhesion to streptavidin-coated beads. From each vesicle, tethers were formed repeatedly at different values of the membrane tension. The expected relationship between membrane tension and tether force was observed. The mean value of Kc for 10 different vesicles was 1.17 x 10(-19) J (SD = 0.08 x 10(-19) J). The precision of these data demonstrates the reliability of this approach, which avoids uncertainties of interpretation and measurement that may be associated with other methods for determining Kc. PMID:8886240

Heinrich, V; Waugh, R E

1996-01-01

58

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

59

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

2014-12-01

60

SHORT REPORT ABSTRACT: In previous studies, we developed a postural stiffness mea-sure that is extracted from foot center-of-pressure (COP) trajectories from  

E-print Network

Parkinson's Disease Rating Scale. These results provide further evidence that a higher intrinsic muscle. Muscle Nerve 22: 635­639, 1999 ASSESSING MUSCLE STIFFNESS FROM QUIET STANCE IN PARKINSON'S DISEASE's disease; UP- DRS, Unified Parkinson's Disease Rating Scale Key words: measurement; muscle stiffness

Collins, James J.

61

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

62

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

PubMed

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

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

2014-10-31

63

Comparison of Posteroanterior Spinal Stiffness Measures to Clinical and Demographic Findings at Baseline in Patients Enrolled in a Clinical Study of Spinal Manipulation for Low Back Pain  

PubMed Central

Objective A system for measuring posterior-to-anterior spinal stiffness (PAS) was developed for use in clinical trials of manipulation for low back pain (LBP). The current report is an analysis of the baseline PAS data, with particular emphasis on relationships between PAS and clinical and demographic characteristics. Methods Posterior-to-anterior spinal stiffness measurements were recorded over the spinous processes of the lumbar spines from patients who had LBP. The system uses electronic sensors to record displacement and force, whereas a human operator provides the force of indentation. Clinical and outcome measures were compared with spinal stiffness. Results We recruited 192 patients (89 female and 103 male; average age, 40.0 years; SD, 9.4 years). The average Roland-Morris score was 9.7 (SD, 3.2) on a 24-point scale. The Visual Analog Scale pain scores were 55.7 (SD, 20.9) on a 100-mm scale. Stiffness values ranged from 4.16 to 39.68 N/mm (mean, 10.80 N/mm; SD, 3.72 N/mm). Females’ lumbar spines were, on the average, 2 N/mm more compliant than males (P < .001). Conclusions The PAS system of computer-monitored equipment with human operation performed well in this clinical study of LBP. Spinal stiffness was found to be different between males and females, and age and body mass index were related to PAS. We found no significant relationship between the severity or chronicity of the LBP complaint and spinal stiffness. There was little agreement between the stiff or tender segments identified by the clinicians using palpation and the segment that measured most stiff using the PAS device. PMID:17870417

Owens, Edward F.; DeVocht, James W.; Gudavalli, M. Ram; Wilder, David G.; Meeker, William C.

2008-01-01

64

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

65

Zeiss LSM 510 Laser Scanning Confocal Microscope User Guide  

E-print Network

Iron Man Zeiss LSM 510 Laser Scanning Confocal Microscope User Guide v. 1.3 (11 of the microscope 13 APPENDIX C ­ Configuring the Light Path 14 #12;Iron Man User Guide v. 1.3 3 Quick) Leave the microscope on a low power objective for next user. If someone is signed up within

Pace, Norman

66

Does hemodiafiltration reduce vascular stiffness measured by aortic pulse wave velocity compared with high-flux hemodialysis?  

PubMed

Hemodialfiltration (HDF) has been reported to reduce the frequency of intradialytic hypotension compared with hemodialysis (HD). We wished to determine whether HDF resulted in improvement of arterial stiffness compared with HD. We reviewed peripheral blood pressure and pulse wave velocity measurements in a cross-sectional analysis of stable HDF and HD outpatients. One hundred forty-one HDF patients were matched to 148 HD patients in terms of age, sex, prevalence of diabetes, peripheral blood pressure, and body mass. Pulse wave velocity was not different between the HD and HDF cohorts (median 9.1 [8.0-10.7] m/s vs. 9.7 [8.5-11.6] m/s). Similarly, there were no differences in central aortic pressure (149.2 ± 30.9 mmHg vs. 151.9 ± 35.2 mmHg), or aortic (39 [25.1-51.2]% vs. 38.6 [25.8-51.4]%) and brachial (3.8 [-24.3 to 26.9]% vs. 3 [-22.4 to 27.1]%) augmentation indices, respectively. Pulse wave velocity did not differ between adult patients treated by HD and HDF, and similarly, there were no differences in central aortic pressure, aortic or brachial augmentation indices, and cardiac diastolic perfusion. Our study suggests that HDF does not appear to offer any benefit over HD in terms of vascular stiffness. PMID:24299472

Charitaki, Evangelia; Davenport, Andrew

2014-04-01

67

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

PubMed Central

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

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

2010-01-01

68

3-D FEM field analysis in controlled-PM LSM for Maglev vehicle  

SciTech Connect

The magnetic fields in the controlled-PM LSM for Maglev vehicle, of which the width is not only finite with lateral edges, but also an effective electric-airgap is very large, are accurately analyzed by using 3-D FEM. The lateral airgap-flux due to lateral edges of the machine is made clear and its effects on thrust and lift forces are evaluated quantitatively from the comparison with 2-D FEA. The accuracy of 3-D FEA is verified by comparing the calculated results with the measured values.

Yoshida, Kinjiro; Lee, J. [Kyushu Univ., Fukuoka (Japan). Dept. of Electrical Engineering] [Kyushu Univ., Fukuoka (Japan). Dept. of Electrical Engineering; Kim, Y.J. [Korea Academy of Industrial Technology, Seoul (Korea, Republic of)] [Korea Academy of Industrial Technology, Seoul (Korea, Republic of)

1997-03-01

69

CHROMIUM POISONING OF COMPOSITE LSM/YSZ CATHODES  

E-print Network

Rp/Rp0 after 200 hours Rp/Rp0 after 700 hours Rp/Rp0 after1000 hours Polarization resistance, Rp densities; - given as Rp/Rp0 - evaluated values normalized to the polarization resistance at time 0. (The electron image of the LSM/YSZ cathode sample exposed to Fe22Cr with unsintered cobaltite coating at ~850°C

70

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

71

Elbow Stiffness  

Microsoft Academic Search

The elbow is affected more frequently than any other joint by post-traumatic loss of motion. It is not clear why the elbow\\u000a tends to develop stiffness after trauma. Its anatomic complexity certainly plays a relevant role:\\u000a \\u000a \\u000a \\u000a \\u000a – \\u000a \\u000a • the presence of the three most congruous joints in a single capsule and a synovial space;\\u000a \\u000a \\u000a \\u000a \\u000a – \\u000a \\u000a • the lateral collateral ligament

Andrea Celli; Luigi Celli

72

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

73

The measurements of sacroiliac joint stiffness with colour Doppler imaging: A study on healthy subjects  

Microsoft Academic Search

Rationale and objectives: Primary peripartum pelvic and low back pain is a common complaint of females. The etiologic relation between pain and pelvic stability has been shown in previous studies, but at present there is no objective clinical testing method to evaluate pelvic stability. Methods: In this study, a dynamic measurement method using sonoelasticity to assess the sacroiliac joint (SI)

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

1995-01-01

74

The pipette aspiration applied to the local stiffness measurement of soft tissues.  

PubMed

A simple method of identifying the initial slope of the stress-strain curve (i.e., Young's modulus of the soft tissue) by introducing the pipette aspiration technique is presented. The tissue was assumed to be isotropic and macroscopically homogeneous. Numerical simulations by the linear finite element analysis were performed for the axisymmetric model to survey the effects of friction at the tissue-pipette contact boundary, pipette cross-sectional geometry, relative size of the specimen to the pipette, and the layered inhomogeneity of the specimen tissue. The friction at the contact region had little effect on the measurement of Young's modulus. The configuration of the pipette was shown to affect the measurement for small pipette wall thickness. The measurement also depended on the relative size of the specimen to the pipette for relatively small specimens. The extent of the region contributing to the measurement was roughly twice the inside radius of the pipette. In this region, the maximum stress did not exceed the level of the aspiration pressure, with only minor exceptional locations. Calculation of strain energy components indicated that the major contributions to the deformation under pipette aspiration were by the normal extension and shear deformation in pipette axial direction. Experimental verification of the present method for the isotropic, homogeneous artificial material is also presented. PMID:9146811

Aoki, T; Ohashi, T; Matsumoto, T; Sato, M

1997-01-01

75

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

Microsoft Academic Search

Forced unbinding of complementary macromolecules such as ligand-receptor complexes can reveal energetic and kinetic details governing physiological processes ranging from cellular adhesion to drug metabolism. Although molecular-level experiments have enabled sampling of individual ligand-receptor complex dissociation events, disparities in measured unbinding force FR among these methods lead to marked variation in inferred binding energetics and kinetics at equilibrium. These discrepancies

Emily B. Walton; Sunyoung Lee; Krystyn J. Van Vliet

2008-01-01

76

The measurement of stiffness of uterine smooth muscle tumor by elastography.  

PubMed

Leiomyoma shows various diagnostic images, often making it difficult to differentiate from leiomyosarcoma. Recently, the utility of elastography has been reported for the differentiation of superficial tumors. We attempted to diagnose two cases of uterine smooth muscle tumors by elastography. One case was strongly suspected of leiomyosarcoma, and the other case had been diagnosed with leiomyoma. We preoperatively performed virtual tissue imaging (VTI) and virtual tissue quantification (VTQ). In VTQ, we measured shear wave velocity (Vs) five times at each point that ROI was placed. In case of suspected leiomyosarcoma, we attached the tip of convex probe 2 cm below the navel, perpendicular to the floor and measured Vs. In case of leiomyoma, we placed four ROIs randomly in leiomyomas for VTQ. For the case of suspected leiomyosarcoma, Vs and pathological findings from the VTQ were comparably examined. Significant differences were observed in the Vs in the leiomyosarcoma case, whereas not in the leiomyoma case. The comparison of VTQ and pathological findings for the case of leiomyosarcoma indicated high viability in the region where the highest Vs was measured, and strong necrosis in the region with the lowest Vs. These findings suggest that VTQ is useful for diagnosing uterine smooth muscle tumors. PMID:25019043

Furukawa, Shigenori; Soeda, Shu; Watanabe, Takafumi; Nishiyama, Hiroshi; Fujimori, Keiya

2014-01-01

77

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

78

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

79

Optimal Selection of Measurement Configurations for Stiffness Model Calibration of Anthropomorphic Manipulators  

NASA Astrophysics Data System (ADS)

The paper is devoted to the elastostatic calibration of industrial robots, which is used for precise machining of large-dimensional parts made of composite materials. In this technological process, the interaction between the robot and the workpiece causes essential elastic deflections of the manipulator components that should be compensated by the robot controller using relevant elastostatic model of this mechanism. To estimate parameters of this model, an advanced calibration technique is applied that is based on the non-linear experiment design theory, which is adopted for this particular application. In contrast to previous works, it is proposed a concept of the user-defined test-pose, which is used to evaluate the calibration experiments quality. In the frame of this concept, the related optimization problem is defined and numerical routines are developed, which allow generating optimal set of manipulator configurations and corresponding forces/torques for a given number of the calibration experiments. Some specific kinematic constraints are also taken into account, which insure feasibility of calibration experiments for the obtained configurations and allow avoiding collision between the robotic manipulator and the measurement equipment. The efficiency of the developed technique is illustrated by an application example that deals with elastostatic calibration of the serial manipulator used for robot-based machining.

Klimchik, Alexandr; Wu, Yier; Pashkevich, Anatol; Caro, Stéphane; Furet, Benoît

2012-03-01

80

Formation and confinement of FRCs in FRX-C/LSM  

SciTech Connect

The Large Source Modification of FRX-C (FRX-C/LSM) consists of a 50% increase in radius without a commensurate increase in either the coil length or capacitor bank energy. Previous studies in FRX-C/LSM compared tearing and nontearing formation in a coil arrangement which included passive mirrors and auxiliary cusp coils. The present studies use a straight coil (0.35 m radius, 2.0 m length) without passive mirrors; in this case, the cusp coils promote nontearing formation and provide mirror fields to inhibit axial drifting. This arrangement increases the length (from 1.3--2.0 m) and the length-to-diameter ratio (from 1.7--2.9) of the uniform field region. It also increases the implosion electric field from 28 to 32 kV/m. These changes tend to produce more elongated FRCs, but in all cases the axial equilibrium appears not to be influenced by the mirror fields. The FRCs are formed using a deuterium static fill varying from 2--10 mtorr, a bias field varying from 0.05--0.10 T, and preionization consisting of a zero-crossing ringing theta-pinch discharge aided by a 10 MHz RF generator. 10 refs., 2 figs.

Chrien, R.E.; Crawford, E.A.; Hugrass, W.N.; Okada, S.; Rej, D.J.; Siemon, R.E.; Taggart, D.P.; Tuszewski, M.; Webster, R.B.; Wright, B.L.

1988-01-01

81

Effect of alcohol consumption on liver stiffness measured by transient elastography  

PubMed Central

AIM: To determine the evolution of transient elastography (TE) in patients with alcoholic liver disease according to alcohol cessation or continuation. METHODS: We retrospectively selected in our local database all patients who had two TE between June 2005 and November 2010 with chronic alcohol excessive consumption and excluded those with associated cause of liver disease. TE was performed at least one week apart by senior operator. TE examinations with less than ten successful measures or with an interquartile range above 30% were excluded. We retrospectively reviewed file of all patients to include only patient followed up by trained addictologist and for which definite information on alcohol consumption was available. Concomitant biological parameters [aspartate amino transferase (AST), alanine amino transferase and gamma-glutamyl transpeptidase (GGT)] within 4 wk of initial and final TE were recorded. Putative fibrosis score according to initial and final TE were determined with available cut-off for alcoholic liver disease and hepatitis C. Initial and final putative fibrosis score were compared according to alcohol consumption during follow-up. RESULTS: During the study period 572 patients had TE examination for alcoholic liver disease and 79 of them had at least two examinations. Thirty-seven patients met our criteria with a median follow-up of 32.5 wk. At the end of the study, 13 (35%) were abstinent, and 24 (65%) relapsers. Eight patients had liver biopsy during follow-up. TE decreased significantly during follow-up in 85% of abstinent patients [median (range): -4.9 (-6.1,-1.9)], leading to a modification of the putative fibrosis stage in 28%-71% of patient according to different cut-off value. In relapsers TE increased in 45% and decreased in 54% of patient. There was no statistical difference between initial and final TE in relapsers. In the overall population, using 22.6 kPa as cut-off for cirrhosis, 4 patients had cirrhosis at initial TE and 3 patients had cirrhosis at final TE. Using 19.5 kPa as cut-off for cirrhosis, 7 patients had cirrhosis at initial TE and 5 patients had cirrhosis at final TE. Using 12.5 kPa as cut-off for cirrhosis, 16 patients had cirrhosis at initial TE and 15 patients had cirrhosis at final TE. Evolution of biological data was in accordance with the relapse or abstinent status: abstinence ratio (duration of abstinence/duration follow-up) was correlated with AST ratio (r = -0.465, P = 0.007) and GGT ratio (r = -0.662, P < 0.0001). GGT was correlated with initial (r = 0.488, P = 0.002) and final TE (r = 0.49, P < 0.005). Final TE was correlated with AST (r = 0.362, P < 0.05). Correlation between TE ratio and AST ratio (r = 0.44, P = 0.01) revealed that TE varied proportionally to AST for all patients irrespective of their alcohol status. The same relationship was observed between TE ratio and GGT ratio (r = 0.65, P < 0.0001). Evolution of TE was significantly correlated with the ratio of time of abstinence to observation time (r = -0.387, P = 0.016) and the evolution of liver enzymes. CONCLUSION: TE significantly decreased with abstinence. Results of TE in alcoholic liver disease cannot be interpreted without taking into account alcohol consumption and liver enzymes. PMID:23382630

Bardou-Jacquet, Edouard; Legros, Ludivine; Soro, Draman; Latournerie, Marianne; Guillygomarc’h, Anne; Le Lan, Caroline; Brissot, Pierre; Guyader, Dominique; Moirand, Romain

2013-01-01

82

SURFACE DISCONTINUITY MODELLING BY LSM THROUGH PATCH ADAPTATION AND USE OF EDGES  

Microsoft Academic Search

This paper handles the aspect of least squares matching (LSM) for DSM generation and focuses mainly on the exploitation of edge information in the least squares approach. The mathematical model of LSM employs an affine transformation to model geometrical distortions between the template and the search images. However, the model, when used for single points that lie close or on

M. Pateraki; E. Baltsavias

83

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

84

Control of New PM LSM Maglev Vehicle Based on Analysis of Pitching Torque and Propulsion Force  

Microsoft Academic Search

The one of the authors Dr. K. Yoshida has been proposed a new controlled-repulsive Maglev vehicle, which can levitate, propel and guide simultaneously from a standstill, independently of the vehicle speeds. A combined levitation-propulsion-guidance control experiment using LSM only in the PM LSM controlled-repulsive Maglev model vehicle has been succeeded. But the pitching motion could not be restrained sufficiently in

Kinjiro Yoshida; Takashi Yoshida; Shinichi Manabe; Tsuyoshi Yorishige

2007-01-01

85

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

86

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

87

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

88

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

89

Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells IV. On the Ohmic loss in anode supported button cells with LSM or LSCF cathodes  

SciTech Connect

Anode-supported solid oxide fuel cells (SOFC) with a variety of YSZ electrolyte thicknesses were fabricated by tape casting and lamination. The preparation of the YSZ electrolyte tapes with various thicknesses was accomplished by using doctor blades with different gaps between the precision machined, polished blade and the casting surface. The green tape was cut into discs, sintered at 1385°C for 2 h, and subsequently creep-flattened at 1350°C for 2 h. Either LSCF with an SDC interlayer or LSM+YSZ composite was used as the cathode material for the fuel cells. The ohmic resistances of these anode-supported fuel cells were characterized by electrochemical impedance spectroscopy at temperatures from 500°C to 750°C. A linear relationship was found between the ohmic resistance of the fuel cell and the YSZ electrolyte thickness at all the measuring temperatures for both LSCF and LSM+YSZ cathode fuel cells. The ionic conductivities of the YSZ electrolyte, derived for the fuel cells with LSM+YSZ or LSCF cathodes, were independent of the cathode material and cell configuration. The ionic conductivities of the YSZ electrolyte was slightly lower than that of the bulk material, possibly due to Ni-doping into the electrolyte. The fuel cell with a SDC interlayer and LSCF cathode showed larger intercept resistance than the fuel cell with LSM+YSZ cathode, which was possibly due to the imperfect contact between the SDC interlayer and the YSZ electrolyte and the migration of Zr into the SDC interlayer to form an insulating solid solution during cell fabrication. Calculations of the contribution of the YSZ electrolyte to the total ohmic resistance showed that YSZ was still a satisfactory electrolyte at temperatures above 650°C. Explorations should be directed to reduce the intercept resistance to achieve significant improvement in cell performance.

Lu, Zigui; Zhou, Xiao Dong; Templeton, Jared W.; Stevenson, Jeffry W.

2010-05-08

90

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

91

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

92

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

93

Stiff-Person Syndrome  

MedlinePLUS

... the NINDS demonstrated the effectiveness of intravenous immunoglobulin (IVIg) treatment in reducing stiffness and lowering sensitivity to noise, ... in people with SPS. What is the prognosis? Treatment with IVIg, anti-anxiety drugs, muscle relaxants, anti-convulsants, and ...

94

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

95

Zero stiffness tensegrity structures  

Microsoft Academic Search

Tension members with a zero rest length allow the construction of tensegrity structures that are in equilibrium along a continuous path of configurations, and thus exhibit mechanism-like properties; equivalently, they have zero stiffness. The zero-stiffness modes are not internal mechanisms, as they involve first-order changes in member length, but are a direct result of the use of the special tension

M. Schenk; S. D. Guest; J. L. Herder

2007-01-01

96

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

97

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

98

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

99

Arterial stiffness: a brief review  

PubMed Central

Physical stiffening of the large arteries is the central paradigm of vascular aging. Indeed, stiffening in the larger central arterial system, such as the aortic tree, significantly contributes to cardiovascular diseases in older individuals and is positively associated with systolic hypertension, coronary artery disease, stroke, heart failure and atrial fibrillation, which are the leading causes of mortality in the developed countries and also in the developing world as estimated in 2010 by World Health Organizations. Thus, better, less invasive and more accurate measures of arterial stiffness have been developed, which prove useful as diagnostic indices, pathophysiological markers and predictive indicators of disease. This article presents a review of the structural determinants of vascular stiffening, its pathophysiologic determinants and its implications for vascular research and medicine. A critical discussion of new techniques for assessing vascular stiffness is also presented. PMID:20802505

Shirwany, Najeeb A; Zou, Ming-hui

2010-01-01

100

Muscle short-range stiffness can be used to estimate the endpoint stiffness of the human arm  

PubMed Central

The mechanical properties of the human arm are regulated to maintain stability across many tasks. The static mechanics of the arm can be characterized by estimates of endpoint stiffness, considered especially relevant for the maintenance of posture. At a fixed posture, endpoint stiffness can be regulated by changes in muscle activation, but which activation-dependent muscle properties contribute to this global measure of limb mechanics remains unclear. We evaluated the role of muscle properties in the regulation of endpoint stiffness by incorporating scalable models of muscle stiffness into a three-dimensional musculoskeletal model of the human arm. Two classes of muscle models were tested: one characterizing short-range stiffness and two estimating stiffness from the slope of the force-length curve. All models were compared with previously collected experimental data describing how endpoint stiffness varies with changes in voluntary force. Importantly, muscle properties were not fit to the experimental data but scaled only by the geometry of individual muscles in the model. We found that force-dependent variations in endpoint stiffness were accurately described by the short-range stiffness of active arm muscles. Over the wide range of evaluated arm postures and voluntary forces, the musculoskeletal model incorporating short-range stiffness accounted for 98 ± 2, 91 ± 4, and 82 ± 12% of the variance in stiffness orientation, shape, and area, respectively, across all simulated subjects. In contrast, estimates based on muscle force-length curves were less accurate in all measures, especially stiffness area. These results suggest that muscle short-range stiffness is a major contributor to endpoint stiffness of the human arm. Furthermore, the developed model provides an important tool for assessing how the nervous system may regulate endpoint stiffness via changes in muscle activation. PMID:21289133

Hu, Xiao; Murray, Wendy M.

2011-01-01

101

LSM14A inhibits porcine reproductive and respiratory syndrome virus (PRRSV) replication by activating IFN-? signaling pathway in Marc-145.  

PubMed

Porcine reproductive and respiratory syndrome virus (PRRSV) is considered as a significant contributor to porcine reproductive and respiratory syndrome, one of the most economically important diseases for the pig industry worldwide. Emerging evidence indicates that pattern recognition receptors play key roles in recognizing pathogen-associated molecular patterns. In the present study, we investigated the effects of a novel pattern recognition receptor LSM14A in regulating PRRSV replication. Results in Marc-145 cells and porcine alveolar macrophages (PAMs) indicated that overexpression of porcine LSM14A effectively inhibited the replication of PRRSV, and knockdown of LSM14A by siRNA enhanced the replication of PRRSV. Mechanistically, LSM14A up-regulated the activities of IFN-? and ISRE promoters, enhanced the production of IFN-?, RIG-I, and ISGs, and inhibited the production of the inflammatory cytokines of TNF-? and IL-6 mRNA. Additionally, the expression pattern of LSM14A during the infection of PRRSV in Tongcheng and Large White pigs was suppressed by the PRRSV challenge. Taken together, our results suggest that LSM14A is an important PRR that inhibits PPRSV replication by inducing IFN-? signaling and restraining inflammatory responses. Furthermore, the down-regulation of LSM14A by PRRSV might represent an important mechanism by which PRRSV invades the host. Our study sheds light on the possibility of developing a new strategy to control this disease. PMID:25408553

Li, Zhenhong; Chen, Rui; Zhao, Jinhua; Qi, Ziyu; Ji, Likai; Zhen, Yueran; Liu, Bang

2015-01-01

102

The use of resonant frequency measurements for the noninvasive assessment of mechanical stiffness of the healing tibia.  

PubMed

A study was performed to assess the usefulness of measuring the resonant frequency of vibration of the tibia as a determinant of its flexural rigidity in fracture healing. The measurement system consisted of an electronic tapper that struck the anteromedial distal surface of the tibia and an accelerometer, held against the proximal surface, that received the response. Custom software displayed the frequency spectrum from which the first mode bending frequency of the tibia could be pinpointed. We have found that resonant frequency was highly correlated to the log of tibial flexural rigidity, with an exponent of 0.582 (r2 = 0.815). In human volunteers, a series of four tests at monthly intervals showed a reproducibility of approximately 3% (95% confidence interval) with no significant variability between right and left legs. In 14 patients with healing tibial fractures, resonant frequency ratio (healing/injured leg) was correlated to time ratio (time of test/time healed) by a second-order polynomial fit (r2 = 0.58). PMID:8433203

Benirschke, S K; Mirels, H; Jones, D; Tencer, A F

1993-01-01

103

Macroscopic Stiffness of Breast Tumors Predicts Metastasis  

PubMed Central

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

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

2014-01-01

104

Sensitivity of overall vehicle stiffness to local joint stiffness  

NASA Technical Reports Server (NTRS)

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

Chon, Choon T.

1987-01-01

105

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

106

Effect of SDC-impregnated LSM cathodes on the performance of anode-supported YSZ films for SOFCs  

Microsoft Academic Search

Sm0.2Ce0.8O1.9 (SDC)-impregnated La0.7Sr0.3MnO3 (LSM) composite cathodes were fabricated on anode-supported yttria-stabilized zirconia (YSZ) thin films. Electrochemical performances of the solid oxide fuel cells (SOFCs) were investigated in the present study. Four single cells, i.e., Cell-1, Cell-2, Cell-3 and Cell-4 were obtained after the fabrication of four different cathodes, i.e., pure LSM and SDC\\/LSM composites in the weight ratios of 25\\/75,

Kongfa Chen; Zhe Lü; Na Ai; Xiangjun Chen; Jinyan Hu; Xiqiang Huang; Wenhui Su

2007-01-01

107

Stiff magnetofluid cosmological model  

SciTech Connect

We investigate the behavior of the magnetic field in a cosmological model filled with a stiff perfect fluid in general relativity. The magnetic field is due to an electric current along the x axis. The behavior of the model when a magnetic field is absent is also discussed.

Bali, R.; Tyagi, A.

1988-05-01

108

Arterial stiffness is increased in asthmatic children.  

PubMed

Altered arterial stiffness is a recognized risk factor of poor cardiovascular health. Chronic inflammation may increase arterial stiffness. We tested whether arterial stiffness is increased children with asthma, a chronic disease characterized by fluctuating airway and systemic inflammation. Arterial stiffness, expressed as carotid-femoral pulse wave velocity (PWVcf), was measured in 37 mild-to-moderate asthmatic children: 11 girls, median (range) age 11.1 years (6-15). PWVcf in asthma was compared to PWVcf in 65 healthy controls matched for age, height, and gender previously studied in Germany and was correlated with airway inflammation and obstruction. PWVcf was higher in asthmatic children compared to controls: PWVcf median (interquartile range) was 4.7 m/s (4.5-4.9) vs. 4.3 m/s (4.1-4.7), p?stiffness is increased in children with mild-to-moderate asthma. The association between impaired lung function and increased arterial stiffness suggests that severity of disease translates into detrimental effects on the cardiovascular system. PMID:25248341

Steinmann, Markus; Abbas, Chiara; Singer, Florian; Casaulta, Carmen; Regamey, Nicolas; Haffner, Dieter; Fischer, Dagmar-Christiane; Simonetti, Giacomo D

2014-09-25

109

3-D FEM field analysis in controlled-PM LSM for Maglev vehicle  

Microsoft Academic Search

The magnetic fields in the controlled-PM LSM for Maglev vehicle, of which the width is not only finite with lateral edges, but also an effective electric-airgap is very large, are accurately analyzed by using 3-D FEM. The lateral airgap-flux due to lateral edges of the machine is made clear and its effects on thrust and lift forces are evaluated quantitatively

Kinjiro Yoshida; Ju Lee; Young Jung Kim

1997-01-01

110

Development of engineering prototype of Life Support Module (LSM)  

NASA Technical Reports Server (NTRS)

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

1984-01-01

111

Assessing muscle stiffness from quiet stance in Parkinson's disease  

Microsoft Academic Search

In previous studies, we developed a postural stiffness mea- sure that is extracted from foot center-of-pressure (COP) trajectories from quietly standing individuals and is based on an analytical mechanical model of posture control. Here we apply this measure to patients with Parkinson's disease (PD). We correlated the postural stiffness measure with different clinical rating scales, obtained from patients. Kendall's rank

Michael Lauk; Carson C. Chow; Lewis A. Lipsitz; Susan L. Mitchell; James J. Collins

1999-01-01

112

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

113

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

114

On Zero Stiffness  

E-print Network

constant amount of material deformation within the zero stiffness mode. A classic example is the Rolamite linear bearing [43]; see Figure 6. A flat blade spring is wrapped around two cylinders; for any displaced configuration of the two rollers... to a change in temperature it will first develop a spherical curvature due to the different thermal expansion coefficients of the two layers, before bifurcating into a cylindrical configuration [28]. As the orientation of the cylindrical axis is ar...

Schenk, Mark; Guest, Simon D.

2013-11-17

115

Human arm stiffness characteristics during the maintenance of posture.  

PubMed

When the hand is displaced from an equilibrium position, the muscles generate elastic forces to restore the original posture. In a previous study, Mussa-Ivaldi et al. (1985) have measured and characterized the field of elastic forces associated with hand posture in the horizontal plane. Hand stiffness which describes the relation between force and displacement vectors in the vicinity of equilibrium position was measured and graphically represented by an ellipse, characterized by its size, shape and orientation. The results indicated that the shape and orientation of the stiffness ellipse are strongly dependent on arm configuration. At any given hand position, however, the values of these parameters were found to remain invariant among subjects and over time. In this study we investigate the underlying causes for the observed spatial pattern of variation of the hand stiffness ellipse. Mathematically analyzing the relation between hand and joint stiffness matrices, we found that in order to produce the observed spatial variations of the stiffness ellipse, the shoulder stiffness must covary in the workspace with the stiffness component provided by the two-joint muscles. This condition was found to be satisfied by the measured joint stiffness components. Using anatomical data and considering the effects that muscle cross-sections and changes in muscle moment arms have on the joint stiffness matrix, we found that these anatomical factors are not sufficient to account for the observed pattern of variation of joint stiffness in the workspace. To examine whether the coupling between shoulder and two-joint stiffnesses results from the coactivation of muscles contributing to these stiffnesses, EMG signals were recorded from shoulder, elbow and two-joint muscles. Our results indicated that, while some muscle coactivation may indeed exist, it can be found for only some of the muscles and in only part of the workspace. PMID:2286234

Flash, T; Mussa-Ivaldi, F

1990-01-01

116

The relationship between lower-body stiffness and dynamic performance.  

PubMed

Greater levels of lower-body stiffness have been associated with improved outcomes for a number of physical performance variables involving rapid stretch-shorten cycles. The aim of this study was to investigate the relationship between several measures of lower-body stiffness and physical performance variables typically evident during team sports in female athletes. Eighteen female athletes were assessed for quasi-static stiffness (myometry) for several isolated muscles in lying and standing positions. The muscles included the medial gastrocnemius (MedGast), lateral gastrocnemius, soleus, and Achilles tendon. Dynamic stiffness during unilateral hopping was also assessed. Participants were separated into relatively stiff and compliant groups for each variable. A number of significant differences in performance were evident between stiff and compliant subjects. When considering the quasi-static stiffness of the MedGast in lying and standing positions, relatively stiff participants recorded significantly superior results during agility, bounding, sprinting, and jumping activities. Stiffness as assessed by hopping did not discriminate between performance ability in any test. Relationships highlighted by MedGast results were supported by further significant differences in eccentric utilisation ratio and drop jump results between stiff and compliant groups for the lateral gastrocnemius and soleus in lying and standing positions. Higher levels of lower-body stiffness appear to be advantageous for females when performing rapid and (or) repeated stretch-shorten cycle movements, including sprinting, bounding, and jumping. Further, the stiffness of the MedGast is of particular importance during the performance of these activities. It is important for practitioners working with athletes in sports that rely upon these activities for success to consider stiffness assessment and modification. PMID:25007238

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

2014-10-01

117

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

118

Self-Gated CINE MRI for Combined Contrast-Enhanced Imaging and Wall-Stiffness Measurements of Murine Aortic Atherosclerotic Lesions  

PubMed Central

Background High-resolution contrast-enhanced imaging of the murine atherosclerotic vessel wall is difficult due to unpredictable flow artifacts, motion of the thin artery wall and problems with flow suppression in the presence of a circulating contrast agent. Methods and Results We applied a 2D-FLASH retrospective-gated CINE MRI method at 9.4T to characterize atherosclerotic plaques and vessel wall distensibility in the aortic arch of aged ApoE?/? mice after injection of a contrast agent. The method enabled detection of contrast enhancement in atherosclerotic plaques in the aortic arch after I.V. injection of micelles and iron oxides resulting in reproducible plaque enhancement. Both contrast agents were taken up in the plaque, which was confirmed by histology. Additionally, the retrospective-gated CINE method provided images of the aortic wall throughout the cardiac cycle, from which the vessel wall distensibility could be calculated. Reduction in plaque size by statin treatment resulted in lower contrast enhancement and reduced wall stiffness. Conclusions The retrospective-gated CINE MRI provides a robust and simple way to detect and quantify contrast enhancement in atherosclerotic plaques in the aortic wall of ApoE?/? mice. From the same scan, plaque-related changes in stiffness of the aortic wall can be determined. In this mouse model, a correlation between vessel wall stiffness and atherosclerotic lesions was found. PMID:23472079

den Adel, Brigit; van der Graaf, Linda M.; Strijkers, Gustav J.; Lamb, Hildo J.; Poelmann, Robert E.; van der Weerd, Louise

2013-01-01

119

Elasticity of stiff biopolymers  

NASA Astrophysics Data System (ADS)

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.

Ghosh, Abhijit; Samuel, Joseph; Sinha, Supurna

2007-12-01

120

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

121

Leg stiffness changes in athletes with Achilles tendinopathy.  

PubMed

Overuse injuries of the Achilles tendon cause impairment in lower leg muscle-tendon function. The purpose of this study was to evaluate leg stiffness in patients suffering unilateral Achilles tendinopathy. 51 athletes with unilateral Achilles tendinopathy underwent leg stiffness testing by modeling the vertical ground reaction force in a contact mat, measuring flight and contact time during hopping. Clinical status was estimated with a pain VAS and a validated questionnaire (VISA-A). The 'leg stiffness ratio' (LSR=stiffness of injured leg/stiffness of healthy leg) was calculated to determine the relative patient affectation and for intra-group comparison. 84 percent of subjects showed lower leg stiffness in the affected side during hopping. Leg stiffness was significantly lower in the limb affected by Achilles tendinopathy than in the healthy side (14.07±3.74 kN/m vs. 15.61±4.01 kN/m, p=0.047); overall LSR was 0.90±0.09. Intra-group comparison did not show significant differences related to patients' age, gender, sport level, and site of tendon injury (midportion or insertional). Leg stiffness was significantly reduced in patients with unilateral Achilles tendinopathy probably related to increasing ankle compliance. Regular leg stiffness assessment would be beneficial for athletes suffering Achilles tendon problems in terms of quantifying performance capabilities and providing objective data for a safer return to sport activity. PMID:22499572

Maquirriain, J

2012-07-01

122

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

123

Frequency-Dependent Fracture Specific Stiffness  

NASA Astrophysics Data System (ADS)

Monitoring the hydraulic properties of fractures remotely through their seismic signatures is an important goal for field hydrology. Empirical studies have shown that the hydraulic properties of a fracture are implicitly related to the fracture specific stiffness through the amount and distribution of contact area and apertures that arise from two rough surfaces in contact. Complicating this simple picture are seismic measurements that indicate frequency-dependent stiffness, i.e., a scale-dependent fracture stiffness where the scale is set by the wavelength. Thus relating the hydraulic properties of fractures to seismic measurements becomes a scale dependent problem. We have performed laboratory experiments to examine the phenomenon of frequency dependent fracture specific stiffness to aid in the assessment of the hydraulic properties of a fracture using seismic techniques. To this end, we have developed a photolithographic technique with which we can construct synthetic fractures of known fracture geometry with feature sizes controlled over several orders of magnitude. The synthetic fracture (and the control non-fractured samples) are made from acrylic cylinders that measure 15.0 cm in diameter by 7.7 cm in height. The diameter of the samples enables us to sample the acoustic properties of the fracture using acoustic lens over regions that range in scale from 10 mm to 60 mm. A confinement cell controls the normal stress on the fracture. Seismic measurements were made with broadband compressional-mode piezoelectric transducers enabling one-order of magnitude in frequency. We found that when the wavelength is smaller than the asperity size, a linear dependence of fracture specific stiffness on frequency occurs. In this geometric ray regime the asymptotic value of the transmission function provides a direct measure of the contact area of the fracture. On the other hand, when the asperity spacing is less than an eighth of a wavelength, the fracture behaves as a displacement discontinuity and exhibits a frequency-independent fracture specific stiffness. For intermediate asperity spacings, mixed behavior (that may include resonant scattering) was observed. By understanding how to interpret fracture specific stiffness as a function of frequency, we seek to develop a better interpretation of the hydraulic properties of fractures based on seismic measurements. Acknowledgments: The Authors acknowledge support of this research by the Geosciences Research Program, Office of Basic Energy Sciences, US Department of Energy. LJPN wishes to acknowledge Purdue University Faculty Scholar

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

2003-12-01

124

Biaxial strain and variable stiffness in aponeuroses.  

PubMed

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

Azizi, Emanuel; Roberts, Thomas J

2009-09-01

125

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

126

Nonlinear stiffness characteristics of the annular ligament.  

PubMed

The annular ligament provides a compliant connection of the stapes to the oval window. To estimate the stiffness characteristics of the annular ligament, human temporal bone measurements were conducted. A force was applied sequentially at several points on the stapes footplate leading to different patterns of displacement with different amounts of translational and rotational components. The spatial displacement of the stapes footplate was measured using a laser vibrometer. The experiments were performed on several stapes with dissected chain and the force was increased stepwise, resulting in load-deflection curves for each force application point. The annular ligament exhibited a progressive stiffening characteristic in combination with an inhomogeneous stiffness distribution. When a centric force, orientated in the lateral direction, was applied to the stapes footplate, the stapes head moved laterally and in the posterior-inferior direction. Based on the load-deflection curves, a mechanical model of the annular ligament was derived. The mathematical representation of the compliance of the annular ligament results in a stiffness matrix with a nonlinear dependence on stapes displacement. This description of the nonlinear stiffness allows simulations of the sound transfer behavior of the middle ear for different preloads. PMID:25324078

Lauxmann, M; Eiber, A; Haag, F; Ihrle, S

2014-10-01

127

Working Stiff: PBS  

NSDL National Science Digital Library

A feature at Public Broadcasting Service's Web Lab, this site offers tales and advice from the front lines of working America. The Workplace Diaries section offers daily updates from the "Work-A-Day World." Diarists include a Northwest customer service rep, a Midwest teacher, an Illinois casino worker, and a Midwest utility worker. The Free Advice section allows users to submit workplace troubles to the site's expert problem-solver. Current Feature Articles include a guide to interoffice romance and a discussion of worker privacy in the workplace. Additional offerings at the site include a worker forum, Stress-O-Meter, and the Working Stiff Action Guide, which contains information on workplace activism.

128

Synthesis and electrochemical properties of LSM and LSF perovskites as anode materials for high temperature steam electrolysis  

Microsoft Academic Search

La0.8Sr0.2MnO3 (LSM) and La0.8Sr0.2FeO3 (LSF) perovskites used as the anode materials for high temperature steam electrolysis (HTSE) were synthesized by sol–gel self-propagating method. These two powders were mixed with yttria-stabilized zirconia (YSZ) powders, respectively to fabricate composite anodes of solid oxide electrolysis cells (SOECs). The LSM–YSZ and LSF–YSZ composite anodes were tested at 1073K SOEC working temperature under electrolysis conditions,

Jiangrong Kong; Yong Zhang; Changsheng Deng; Jingming Xu

2009-01-01

129

Contributions of single and double joint stiffness of human arm during force control  

Microsoft Academic Search

To investigate the motion control mechanism of human arm during force control, shoulder, elbow, and double-joint stiffness were measured by applying a small perturbation, and their contributions to joint torques were estimated. Each joint stiffness greatly altered for the different force direction at hand, and shoulder and elbow single joint stiffness were linearly correlated to each joint torques. By assuming

Hiroaki GOMI; Rieko OSU

1996-01-01

130

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

131

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

132

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

133

Arterial stiffness and cognitive function in the elderly  

PubMed Central

Cognitive decline and dementia are a major cause of disability and mortality among older adults. Cross-sectional evidence from observational studies suggests that greater arterial stiffness is associated with worse cognitive performance. These associations have been observed on measures of global cognition and across multiple domains of cognition. Epidemiologic evidence on the association between arterial stiffness and rate of cognitive decline has been less definitive, and very few studies have investigated the risk of developing dementia. This review summarizes the current research on arterial stiffness and cognition, issues around measurement and the effect that potential intervention might have on the course of cognitive aging. The evidence on pharmacological and non-pharmacological (exercise, nutrition, etc) interventions in older adults with arterial stiffness is promising. Yet there are no studies or trials that directly evaluate how interventions of arterial stiffness reduce or prevent cognitive impairment and risk of developing dementia. More research is needed to elucidate the causal link between arterial stiffness and cognitive decline and dementia, and to identify whether potential interventions to prevent or reduce arterial stiffness may benefit cognitive health of the elderly. PMID:25351110

Hazzouri, Adina Zeki Al; Yaffe, Kristine

2015-01-01

134

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

PubMed Central

Structural and mechanical changes occurring in the myosin filament and myosin head domains during the development of the isometric tetanus have been investigated in intact frog muscle fibres at 4°C and 2.15 ?m sarcomere length, using sarcomere level mechanics and X-ray diffraction at beamline ID2 of the European Synchrotron Radiation Facility (Grenoble, France). The time courses of changes in both the M3 and M6 myosin-based reflections were recorded with 5 ms frames using the gas-filled RAPID detector (MicroGap Technology). Following the end of the latent period (11 ms after the start of stimulation), force increases to the tetanus plateau value (T0) with a half-time of 40 ms, and the spacings of the M3 and M6 reflections (SM3 and SM6) increase by 1.5% from their resting values, with time courses that lead that of force by ?10 and ?20 ms, respectively. These temporal relations are maintained when the increase of force is delayed by ?10 ms by imposing, from 5 ms after the first stimulus, 50 nm (half-sarcomere)?1 shortening at the velocity (V0) that maintains zero force. Shortening at V0 transiently reduces SM3 following the latent period and delays the subsequent increase in SM3, but only delays the SM6 increase without a transient decrease. Shortening at V0 imposed at the tetanus plateau causes an abrupt reduction of the intensity of the M3 reflection (IM3), whereas the intensity of the M6 reflection (IM6) is only slightly reduced. The changes in half-sarcomere stiffness indicate that the isometric force at each time point is proportional to the number of myosin heads bound to actin. The different sensitivities of the intensity and spacing of the M3 and M6 reflections to the mechanical responses support the view that the M3 reflection in active muscle originates mainly from the myosin heads attached to the actin filament and the M6 reflection originates mainly from a fixed structure in the myosin filament signalling myosin filament length changes during the tetanus rise. PMID:16990403

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

2006-01-01

135

LSM–SDC electrodes fabricated with an ion-impregnating process for SOFCs with doped ceria electrolytes  

Microsoft Academic Search

(La0.85Sr0.15)0.9MnO3??(LSM)–Sm0.2Ce0.8O1.9(SDC) composite electrodes were fabricated for intermediate-temperature solid oxide fuel cells with a two-step fabricating process including screen-printing and ion-impregnating. The ion-impregnated LSM–SDC electrodes showed better performance than those fabricated with conventional techniques. At 700°C, the interfacial polarization resistance was only 0.23? cm2 for an ion-impregnated cathode, while it was 0.72? cm2 for a sol-gel derived cathode and 0.75? cm2

Xingyan Xu; Zhiyi Jiang; Xing Fan; Changrong Xia

2006-01-01

136

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

137

Immunohistochemical (cLSM) and ultrastructural analysis of the central nervous system and sense organs in Aeolosoma hemprichi (Annelida, Aeolosomatidae)  

Microsoft Academic Search

The Aeolosomatidae are very small limnetic or terrestrial annelids of apparently simple organisation and uncertain phylogenetic\\u000a position. They have been placed either at the base of the Clitellata, as a highly derived taxon within the Clitellata closely\\u000a related to the Naididae, or as their sister group within the „Polychaeta”. A combined immunohistochemical (cLSM) and ultrastructural\\u000a investigation of the central nervous

R. Hessling; Günter Purschke

2000-01-01

138

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

139

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

140

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

141

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

142

Effect of Meal Ingestion on Liver Stiffness in Patients with Cirrhosis and Portal Hypertension  

PubMed Central

Background and Aims Liver stiffness is increasingly used in the non-invasive evaluation of chronic liver diseases. Liver stiffness correlates with hepatic venous pressure gradient (HVPG) in patients with cirrhosis and holds prognostic value in this population. Hence, accuracy in its measurement is needed. Several factors independent of fibrosis influence liver stiffness, but there is insufficient information on whether meal ingestion modifies liver stiffness in cirrhosis. We investigated the changes in liver stiffness occurring after the ingestion of a liquid standard test meal in this population. Methods In 19 patients with cirrhosis and esophageal varices (9 alcoholic, 9 HCV-related, 1 NASH; Child score 6.9±1.8), liver stiffness (transient elastography), portal blood flow (PBF) and hepatic artery blood flow (HABF) (Doppler-Ultrasound) were measured before and 30 minutes after receiving a standard mixed liquid meal. In 10 the HVPG changes were also measured. Results Post-prandial hyperemia was accompanied by a marked increase in liver stiffness (+27±33%; p<0.0001). Changes in liver stiffness did not correlate with PBF changes, but directly correlated with HABF changes (r?=?0.658; p?=?0.002). After the meal, those patients showing a decrease in HABF (n?=?13) had a less marked increase of liver stiffness as compared to patients in whom HABF increased (n?=?6; +12±21% vs. +62±29%,p<0.0001). As expected, post-prandial hyperemia was associated with an increase in HVPG (n?=?10; +26±13%, p?=?0.003), but changes in liver stiffness did not correlate with HVPG changes. Conclusions Liver stiffness increases markedly after a liquid test meal in patients with cirrhosis, suggesting that its measurement should be performed in standardized fasting conditions. The hepatic artery buffer response appears an important factor modulating postprandial changes of liver stiffness. The post-prandial increase in HVPG cannot be predicted by changes in liver stiffness. PMID:23520531

Berzigotti, Annalisa; De Gottardi, Andrea; Vukotic, Ranka; Siramolpiwat, Sith; Abraldes, Juan G.; García-Pagan, Juan Carlos; Bosch, Jaime

2013-01-01

143

Leg stiffness of sprinters using running-specific prostheses.  

PubMed

Running-specific prostheses (RSF) are designed to replicate the spring-like nature of biological legs (bioL) during running. However, it is not clear how these devices affect whole leg stiffness characteristics or running dynamics over a range of speeds. We used a simple spring-mass model to examine running mechanics across a range of speeds, in unilateral and bilateral transtibial amputees and performance-matched controls. We found significant differences between the affected leg (AL) of unilateral amputees and both ALs of bilateral amputees compared with the bioL of non-amputees for nearly every variable measured. Leg stiffness remained constant or increased with speed in bioL, but decreased with speed in legs with RSPs. The decrease in leg stiffness in legs with RSPs was mainly owing to a combination of lower peak ground reaction forces and increased leg compression with increasing speeds. Leg stiffness is an important parameter affecting contact time and the force exerted on the ground. It is likely that the fixed stiffness of the prosthesis coupled with differences in the limb posture required to run with the prosthesis limits the ability to modulate whole leg stiffness and the ability to apply high vertical ground reaction forces during sprinting. PMID:22337629

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

2012-08-01

144

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

145

Stiffness characterisation of microcantilevers based on conducting polymers  

NASA Astrophysics Data System (ADS)

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

Alici, Gursel; Higgins, Michael J.

2008-12-01

146

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

147

Response of initial field to stiffness perturbation  

E-print Network

Response of initial elastic field to stiffness perturbation and its possible application is investigated. Virtual thermal softening is used to produce the stiffness reduction for demonstration. It is interpreted that the redistribution of the initial strain will be developed by the non-uniform temperature elevation, as which leads to the non-uniform reduction of the material stiffness. Therefore, the initial filed is related to the stiffness perturbation and incremental field in a matrix form after eliminating the thermal expansion effect.

Chen-Wu Wu

2014-03-19

148

Zero Stiffness Tensegrity Structures M. Schenk a  

E-print Network

Zero Stiffness Tensegrity Structures M. Schenk a S.D. Guest b, J.L. Herder a aMechanical, Maritime members with a zero rest length allow the construction of tensegrity struc- tures that are in equilibrium interesting observations regarding zero stiffness tensegrity structures. Key words: zero stiffness, tensegrity

Guest, Simon

149

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

150

Decreased passive stiffness of cardiac myocytes and cardiac tissue from copper-deficient rat hearts.  

PubMed

Passive stiffness characteristics of isolated cardiac myocytes, papillary muscles, and aortic strips from male Holtzman rats fed a copper-deficient diet for approximately 5 wk were compared with those of rats fed a copper-adequate diet to determine whether alterations in these characteristics might accompany the well-documented cardiac hypertrophy and high incidence of ventricular rupture characteristic of copper deficiency. Stiffness of isolated cardiac myocytes was assessed from measurements of cellular dimensional changes to varied osmotic conditions. Stiffness of papillary muscles and aortic strips was determined from resting length-tension analyses and included steady-state characteristics, dynamic viscoelastic stiffness properties, and maximum tensile strength. The primary findings were that copper deficiency resulted in cardiac hypertrophy with increased cardiac myocyte size and fragility, decreased cardiac myocyte stiffness, and decreased papillary muscle passive stiffness, dynamic stiffness, and tensile strength and no alteration in aortic connective tissue passive stiffness or tensile strength. These findings suggest that a reduction of cardiac myocyte stiffness and increased cellular fragility could contribute to the reduced overall cardiac tissue stiffness and the high incidence of ventricular aneurysm observed in copper-deficient rats. PMID:10843880

Heller, L J; Mohrman, D E; Prohaska, J R

2000-06-01

151

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

152

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

153

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

PubMed

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 mm(2) between individual investigator one (IV1) and LSM, and -122 mm(2) 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. PMID:22968138

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

2012-10-01

154

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

155

Effective stiffness of qPlus sensor and quartz tuning fork.  

PubMed

Quartz tuning forks (QTFs) have been extensively employed in scanning probe microscopy. For quantitative measurement of the interaction in nanoscale using QTF as a force sensor, we first measured the effective stiffness of qPlus sensors as well as QTFs and then compared the results with the cantilever beam theory that has been widely used to estimate the stiffness. Comparing with the stiffness and the resonance frequency in our measurement, we found that those calculated based on the beam theory are considerably overestimated. For consistent analysis of experimental and theoretical results, we present the formula to calculate the stiffness of qPlus sensor or QTF, based on the resonance frequency. We also demonstrated that the effective stiffness of QTF is twice that of qPlus sensor, which agrees with the recently suggested model. Our study demonstrates the use of QTF for quantitative measurement of interaction force at the nanoscale in scanning probe microscopy. PMID:24727200

Kim, Jongwoo; Won, Donghyun; Sung, Baekman; An, Sangmin; Jhe, Wonho

2014-06-01

156

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

157

Critical appraisal of the differential effects of antihypertensive agents on arterial stiffness  

PubMed Central

Increased central arterial stiffness, involving accelerated vascular ageing of the aorta, is a powerful and independent risk factor for early mortality and provides prognostic information above and beyond traditional risk factors for cardiovascular disease (CVD). Central arterial stiffness is an important determinant of pulse pressure; therefore, any pathological increase may result in left ventricular hypertrophy and impaired coronary perfusion. Central artery stiffness can be assessed noninvasively by measurement of aortic pulse wave velocity, which is the gold standard for measurement of arterial stiffness. Earlier, it was believed that changes in arterial stiffness, which are primarily influenced by long-term pressure-dependent structural changes, may be slowed but not reversed by pharmacotherapy. Recent studies with drugs that inhibit the renin–angiotensin–aldosterone system, advanced glycation end products crosslink breakers, and endothelin antagonists suggest that blood pressure (BP)-independent reduction and reversal of arterial stiffness are feasible. We review the recent literature on the differential effect of antihypertensive agents either as monotherapy or combination therapy on arterial stiffness. Arterial stiffness is an emerging therapeutic target for CVD risk reduction; however, further clinical trials are required to confirm whether BP-independent changes in arterial stiffness directly translate to a reduction in CVD events. PMID:21949622

Kum, Francesca; Karalliedde, Janaka

2010-01-01

158

Critical appraisal of the differential effects of antihypertensive agents on arterial stiffness.  

PubMed

Increased central arterial stiffness, involving accelerated vascular ageing of the aorta, is a powerful and independent risk factor for early mortality and provides prognostic information above and beyond traditional risk factors for cardiovascular disease (CVD). Central arterial stiffness is an important determinant of pulse pressure; therefore, any pathological increase may result in left ventricular hypertrophy and impaired coronary perfusion. Central artery stiffness can be assessed noninvasively by measurement of aortic pulse wave velocity, which is the gold standard for measurement of arterial stiffness. Earlier, it was believed that changes in arterial stiffness, which are primarily influenced by long-term pressure-dependent structural changes, may be slowed but not reversed by pharmacotherapy. Recent studies with drugs that inhibit the renin-angiotensin-aldosterone system, advanced glycation end products crosslink breakers, and endothelin antagonists suggest that blood pressure (BP)-independent reduction and reversal of arterial stiffness are feasible. We review the recent literature on the differential effect of antihypertensive agents either as monotherapy or combination therapy on arterial stiffness. Arterial stiffness is an emerging therapeutic target for CVD risk reduction; however, further clinical trials are required to confirm whether BP-independent changes in arterial stiffness directly translate to a reduction in CVD events. PMID:21949622

Kum, Francesca; Karalliedde, Janaka

2010-01-01

159

Task Dependency of Grip Stiffness—A Study of Human Grip Force and Grip Stiffness Dependency during Two Different Tasks with Same Grip Forces  

PubMed Central

It is widely known that the pinch-grip forces of the human hand are linearly related to the weight of the grasped object. Less is known about the relationship between grip force and grip stiffness. We set out to determine variations to these dependencies in different tasks with and without visual feedback. In two different settings, subjects were asked to (a) grasp and hold a stiffness-measuring manipulandum with a predefined grip force, differing from experiment to experiment, or (b) grasp and hold this manipulandum of which we varied the weight between trials in a more natural task. Both situations led to grip forces in comparable ranges. As the measured grip stiffness is the result of muscle and tendon properties, and since muscle/tendon stiffness increases more-or-less linearly as a function of muscle force, we found, as might be predicted, a linear relationship between grip force and grip stiffness. However, the measured stiffness ranges and the increase of stiffness with grip force varied significantly between the two tasks. Furthermore, we found a strong correlation between regression slope and mean stiffness for the force task which we ascribe to a force stiffness curve going through the origin. Based on a biomechanical model, we attributed the difference between both tasks to changes in wrist configuration, rather than to changes in cocontraction. In a new set of experiments where we prevent the wrist from moving by fixing it and resting it on a pedestal, we found subjects exhibiting similar stiffness/force characteristics in both tasks. PMID:24324643

Höppner, Hannes; McIntyre, Joseph; van der Smagt, Patrick

2013-01-01

160

High friction from a stiff polymer using microfiber arrays.  

PubMed

High dry friction requires intimate contact between two surfaces and is generally obtained using soft materials with an elastic modulus less than 10 MPa. We demonstrate that high-friction properties similar to rubberlike materials can also be obtained using microfiber arrays constructed from a stiff thermoplastic (polypropylene, 1 GPa). The fiber arrays have a smaller true area of contact than a rubberlike material, but polypropylene's higher interfacial shear strength provides an effective friction coefficient of greater than 5 at normal loads of 8 kPa. At the pressures tested, the fiber arrays showed more than an order of magnitude increase in shear resistance compared to the bulk material. Unlike softer materials, vertical fiber arrays of stiff polymer demonstrate no measurable adhesion on smooth surfaces due to high tensile stiffness. PMID:17026251

Majidi, C; Groff, R E; Maeno, Y; Schubert, B; Baek, S; Bush, B; Maboudian, R; Gravish, N; Wilkinson, M; Autumn, K; Fearing, R S

2006-08-18

161

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

162

Role of cellular tone and microenvironmental conditions on cytoskeleton stiffness assessed by tensegrity model  

Microsoft Academic Search

We have tried to understand the role of cellular tone (or internal tension mediated by actin filaments) and interactions with the microenvironment on cellular stiffness. For this purpose, we compared the apparent elasticity modulus of a 30-element tensegrity structure with cytoskeleton stiffness measured in subconfluent and confluent adherent cells by magnetocytometry, assessing the effect of changing cellular tone by treatment

S. Wendling; E. Planus; V. M. Laurent; L. Barbe; A. Mary; C. Oddou; D. Isabey

2000-01-01

163

Physicochemical compatibility of CGO fluorite, LSM and LSCF perovskite electrode materials with La 2Mo 2O 9 fast oxide-ion conductor  

Microsoft Academic Search

The reactivity of typical electrode materials for solid oxide fuel cells, namely La0.6Sr0.4Co0.2Fe0.8O3?? (LSCF), La0.8Sr0.2MnO3?? (LSM) and Ce0.9Gd0.1O1.95 (CGO), with fast oxide-ion conductor La2Mo2O9 is thoroughly studied using X-ray diffractometry. Modifications in the materials diffraction patterns and occurrence of impurity diffraction peaks are evidenced in LSCF and LSM above 700–800?°C. They are interpreted in terms of cationic migrations from one

Gwenaël Corbel; Samih Mestiri; Philippe Lacorre

2005-01-01

164

Effects of vascularity and differentiation of hepatocellular carcinoma on tumor and liver stiffness: in vivo and in vitro studies.  

PubMed

Tissue stiffness has been found to be a useful predictor of malignancy in various cancers. However, data on the stiffness of hepatocellular carcinomas (HCCs) and their background livers are contradictory. The aim of this study was to investigate the effects of vascularity and histologic differentiation on HCC stiffness. Elastography point quantification (ElastPQ), a new shear wave-based elastography method, was used to measure liver stiffness in vivo in 99 patients with pathology-proven HCC. Lesion vascularity was assessed using contrast-enhanced ultrasound, computed tomography and/or magnetic resonance imaging. The association of HCC vascularity and differentiation with liver stiffness was determined. In addition, in vitro stiffness of 20 of the 99 surgical HCC specimens was mechanically measured and compared with in vivo measurements. We found that in vivo stiffness was significantly higher than in vitro stiffness in both HCCs and their background livers (p < 0.0001). Moreover, significantly higher stiffness was observed in hyper-vascular and poorly differentiated lesions than in hypo-vascular (p = 0.0352) and moderately to well-differentiated lesions (p = 0.0139). These in vivo and in vitro studies reveal that shear wave-based ultrasound elasticity quantification can effectively measure in vivo liver stiffness. PMID:24412176

Ling, Wenwu; Lu, Qiang; Lu, Changli; Quan, Jierong; Ma, Lin; Li, Jiawu; He, Du; Liu, Jianping; Yang, Jiaying; Wen, Tianfu; Wu, Hong; Zhu, Hongguang; Luo, Yan

2014-04-01

165

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

166

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

167

Spontaneous wrinkle branching by gradient stiffness.  

PubMed

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

Ni, Yong; Yang, Dong; He, Linghui

2012-09-01

168

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

169

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

170

Modelling terrestrial biogenic isoprene fluxes and their potential impact on global chemical species using a coupled LSM-CTM model  

NASA Astrophysics Data System (ADS)

In this paper we investigate the important role of the biogenic species isoprene on tropospheric chemistry using a land surface model (LSM) and a three-dimensional (3-D) tropospheric chemistry transport model (CTM). An efficient and conservative coupling scheme is used to couple the LSM to the 3-D CTM. Annual integrations of the coupled model have been performed and the results compared with other estimates. The comparison shows that the annual global isoprene flux from terrestrial vegetation is 530 Tg C yr -1, which is in good agreement with 503 Tg C yr -1 estimated by a high-resolution (0.5°×0.5°) vegetation model of Guenther et al. (1995, Journal of Geophysical Research 100 (D5), 8873-8892). Comparison of the seasonal variations of the surface emission distribution between the coupled model and Guenther et al. (1995) also shows close agreement. The potential impact of isoprene on the levels of tropospheric species is studied by running the same coupled model for the period of June-December but without biogenic isoprene emissions included, and the results are compared with the run which includes biogenic isoprene emissions. Our comparison indicates a significant difference in O 3 and PAN for both hemispheres. The discrepancy between the run with and without isoprene is predominantly governed by the spatial and temporal variations of terrestrial vegetation. The largest difference is seen in the summertime northern hemisphere at locations with extensive terrestrial vegetation (e.g. North America, Europe, east and southeast Asia, South America and equatorial central Africa). For O 3, there is about a 4 ppbv increase over the oceanic areas and about an 8-12 ppbv increase over the mid-latitude land areas. For PAN, a maximum of about one order of magnitude in difference, which increases from 0.01 ppbv (without isoprene emissions) to 0.1-0.3 ppbv (with isoprene emissions), is seen in areas of extensive terrestrial vegetation.

Wang, K.-Y.; Shallcross, D. E.

171

Stiffness matrix formulation for double row angular contact ball bearings: Analytical development and validation  

NASA Astrophysics Data System (ADS)

Though double row angular contact ball bearings are widely used in industrial, automotive, and aircraft applications, the scientific literature on double row bearings is sparse. It is also shown that the stiffness matrices of two single row bearings may not be simply superposed to obtain the stiffness matrix of a double row bearing. To overcome the deficiency in the literature, a new, comprehensive, analytical approach is proposed based on the Hertzian theory for back-to-back, face-to-face, and tandem arrangements. The elements of the five-dimensional stiffness matrix for double row angular contact ball bearings are computed given either the mean bearing displacement or the mean load vector. The diagonal elements of the proposed stiffness matrix are verified with a commercial code for all arrangements under three loading scenarios. Some changes in stiffness coefficients are investigated by varying critical kinematic and geometric parameters to provide more insight. Finally, the calculated natural frequencies of a shaft-bearing experiment are successfully compared with measurements, thus validating the proposed stiffness formulation. For double row angular contact ball bearings, the moment stiffness and cross-coupling stiffness terms are significant, and the contact angle changes under loads. The proposed formulation is also valid for paired (duplex) bearings which behave as an integrated double row unit when the surrounding structural elements are sufficiently rigid.

Gunduz, Aydin; Singh, Rajendra

2013-10-01

172

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

173

Stiffness control of balance in quiet standing.  

PubMed

Our goal was to provide some insights into how the CNS controls and maintains an upright standing posture, which is an integral part of activities of daily living. Although researchers have used simple performance measures of maintenance of this posture quite effectively in clinical decision making, the mechanisms and control principles involved have not been clear. We propose a relatively simple control scheme for regulation of upright posture that provides almost instantaneous corrective response and reduces the operating demands on the CNS. The analytic model is derived and experimentally validated. A stiffness model was developed for quiet standing. The model assumes that muscles act as springs to cause the center-of-pressure (COP) to move in phase with the center-of-mass (COM) as the body sways about some desired position. In the sagittal plane this stiffness control exists at the ankle plantarflexors, in the frontal plane by the hip abductors/adductors. On the basis of observations that the COP-COM error signal continuously oscillates, it is evident that the inverted pendulum model is severely underdamped, approaching the undamped condition. The spectrum of this error signal is seen to match that of a tuned mass, spring, damper system, and a curve fit of this "tuned circuit" yields omega n the undamped natural frequency of the system. The effective stiffness of the system, Ke, is then estimated from Ke = I omega n2, and the damping B is estimated from B = BW X I, where BW is the bandwidth of the tuned response (in rad/s), and I is the moment of inertia of the body about the ankle joint. Ten adult subjects were assessed while standing quietly at three stance widths: 50% hip-to-hip distance, 100 and 150%. Subjects stood for 2 min in each position with eyes open; the 100% stance width was repeated with eyes closed. In all trials and in both planes, the COP oscillated virtually in phase (within 6 ms) with COM, which was predicted by a simple 0th order spring model. Sway amplitude decreased as stance width increased, and Ke increased with stance width. A stiffness model would predict sway to vary as Ke-0.5. The experimental results were close to this prediction: sway was proportional to Ke(-0.55). Reactive control of balance was not evident for several reasons. The visual system does not appear to contribute because no significant difference between eyes open and eyes closed results was found at 100% stance width. Vestibular (otolith) and joint proprioceptive reactive control were discounted because the necessary head accelerations, joint displacements, and velocities were well below reported thresholds. Besides, any reactive control would predict that COP would considerably lag (150-250 ms) behind the COM. Because the average COP was only 4 ms delayed behind the COM, reactive control was not evident; this small delay was accounted for by the damping in the tuned mechanical system. PMID:9744933

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

1998-09-01

174

Optimum loading mode for axial stiffness testing in limb lengthening.  

PubMed

The axial stiffness of the regenerate is an indicator of bone healing after fracture or distraction osteogenesis. The axial stiffness may be assessed clinically by measuring the sharing of load between fixator and limb during loading. The aim of this study was to find out how to perform the stiffness test in order to minimize the influence of confounding factors to the test result. We investigated whether the test score was influenced by two factors: 1) the magnitude of the external load applied to the limb during the test; and 2) the patient's position during the test. The problem was approached by both a clinical study and by theoretical calculations. Thirty-three patients undergoing leg lengthening were tested regularly during the consolidation period. The stiffness test was executed with both high and low load, and in a standing and sitting position. There were significant differences in results between both the tests with high and low load, and between the standing and sitting tests. This indicated that both the magnitude of force and patient position during the test influenced the test result. Accordingly, these factors represent sources of error and must be taken into consideration when performing an axial stiffness test. The result of the theoretical calculations confirmed the result. We recommend performing the test while the patient is sitting, and to apply no more than 20% of the individual's body weight. It is also recommended that the same load be used in every test, when testing a patient several times during the treatment period. PMID:16479567

Aarnes, Gudrun T; Steen, Harald; Kristiansen, Leif Pål; Festø, Ellinor; Ludvigsen, Per

2006-03-01

175

Matrices of Physiologic Stiffness Potently Inactivate Idiopathic Pulmonary Fibrosis Fibroblasts  

PubMed Central

Fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) have been shown to differ from normal lung fibroblasts in functional behaviors that contribute to the pathogenesis of IPF, including the expression of contractile proteins and proliferation, but how such behaviors vary in matrices with stiffness matched to normal and fibrotic lung tissue remains unknown. Here, we tested whether pathologic changes in matrix stiffness control IPF and normal lung tissue–derived fibroblast functions, and compared the relative efficacy of mechanical cues to an antifibrotic lipid mediator, prostaglandin E2 (PGE2). Fibroblasts were grown on collagen I–coated glass or hydrogel substrates of discrete stiffnesses, spanning the range of normal and fibrotic lung tissue. Traction microscopy was used to quantify contractile function. The CyQuant Cell Proliferation Assay (Invitrogen, Carlsbad, CA) was used to assess changes in cell number, and PGE2 concentrations were measured by ELISA. We confirmed differences in proliferation and PGE2 synthesis between IPF and normal tissue–derived fibroblasts on rigid substrates. However, IPF fibroblasts remained highly responsive to changes in matrix stiffness, and both proliferative and contractile differences between IPF and normal fibroblasts were ablated on physiologically soft matrices. We also confirmed the relative resistance of IPF fibroblasts to PGE2, while demonstrating that decreases in matrix stiffness and the inhibition of Rho kinase both potently attenuate contractile function in IPF-derived fibroblasts. We conclude that pathologic changes in the mechanical environment control important IPF fibroblast functions. Understanding how mechanical cues control fibroblast function may offer new opportunities for targeting these cells, even when they are resistant to antifibrotic pharmacological agents or biological mediators. PMID:23258227

Marinkovi?, Aleksandar; Liu, Fei

2013-01-01

176

An acoustic startle alters knee joint stiffness and neuromuscular control.  

PubMed

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

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

2014-09-11

177

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

178

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

PubMed

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

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

2013-10-18

179

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

180

Feasibility of simultaneous temperature and tissue stiffness detection by MRE.  

PubMed

Temperature and tissue stiffness are two indices that can be used to monitor MRI-guided focused ultrasound thermal therapy. It would be beneficial to have both measures available to monitor treatment progression during thermal therapy. MR Elastography (MRE) has already been shown to provide tissue stiffness information; the purpose of this work is to demonstrate how temperature can be derived from the same MRE data acquisition. MRE data were acquired from 1.5% agarose phantoms and ex vivo porcine muscle tissue (from a grocery store) while they were heated slowly. The temperatures were measured using a fluorescent thermometer. The phase average from the MRE acquisition was used to calculate the phase shift induced by the proton resonance frequency shift associated with the temperature change. The results show that the phase shift due to temperature extracted from MRE data correlate well with the temperature change recorded by thermometer, yielding a temperature coefficient of -0.0096 ppm/ degrees C for the agarose phantom, and -0.0103 ppm/ degrees C for the ex vivo porcine tissue. These results indicate that it is possible to simultaneously measure both temperature and tissue shear stiffness using a new method of MRE data reconstruction. PMID:16463357

Le, Yuan; Glaser, Kevin; Rouviere, Olivier; Ehman, Richard; Felmlee, Joel P

2006-03-01

181

Determination of ball bearing dynamic stiffness  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

182

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

183

Natural variation in embryo mechanics: gastrulation in Xenopus laevis is highly robust to variation in tissue stiffness  

PubMed Central

How sensitive is morphogenesis to the mechanical properties of embryos? To estimate an upper bound on the sensitivity of early morphogenetic movements to tissue mechanical properties, we assessed natural variability in the apparent stiffness among gastrula-stage Xenopus laevis embryos. We adapted micro-aspiration methods to make repeated, non-destructive measurements of apparent tissue stiffness in whole embryos. Stiffness varied by close to a factor of 2 among embryos within a single clutch. Variation between clutches was of similar magnitude. On the other hand, the direction of change in stiffness over the course of gastrulation was the same in all embryos and in all clutches. Neither pH nor salinity – two environmental factors we predicted could affect variability in nature – affected tissue stiffness. Our results indicate that gastrulation in X. laevis is robust to at least two-fold variation in tissue stiffness. PMID:19097119

von Dassow, Michelangelo; Davidson, Lance A.

2009-01-01

184

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

185

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

PubMed

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

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

2014-12-01

186

Stiffness transition in anisotropic fiber nets.  

PubMed

We demonstrate the existence of a percolationlike stiffness transition in fiber networks with a bidisperse orientation distribution and with fiber densities clearly above the geometrical and the ordinary stiffness transition. The fibers are oriented parallel and perpendicular to a strain direction and they have a large fiber aspect ratio. The stiffness K of the fiber nets can be described by a scaling relation, K [proportionally] ?(?) g[(? - ?(c))/?(-?)], where ? is the fraction of fibers parallel to strain. g is a scaling function that is roughly described by a power law g(x) [proportionally ] x(?) for stiffness above the transition and by a constant below the transition. The transition point is characterized by qualitative changes in the distribution of the elastic deformation energy of the fibers, the deformation mode of the fibers, the effective Poisson ratio of the nets, the distribution of elastic energy on fibers and cross links, and the ratio of elastic and viscous dissipation energy. This transition opens the possibility of extreme stiffness variations with minimal mesh manipulations in the vicinity of the transition (i.e., a stiffness gate). It is possible that this transition affects the mechanical behavior of the cytoskeleton in cells. PMID:23005800

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

2012-08-01

187

Accelerated initial stiffness schemes for elastoplasticity  

NASA Astrophysics Data System (ADS)

Iterative methods for the solution of non-linear finite element equations are generally based on variants of the Newton-Raphson method. When they are stable, full Newton-Raphson schemes usually converge rapidly but may be expensive for some types of problems (for example, when the tangent stiffness matrix is unsymmetric). Initial stiffness schemes, on the other hand, are extremely robust but may require large numbers of iterations for cases where the plastic zone is extensive. In most geomechanics applications it is generally preferable to use a tangent stiffness scheme, but there are situations in which initial stiffness schemes are very useful. These situations include problems where a nonassociated flow rule is used or where the zone of plastic yielding is highly localized.This paper surveys the performance of several single-parameter techniques for accelerating the convergence of the initial stiffness scheme. Some simple but effective modifications to these procedures are also proposed. In particular, a modified version of Thomas' acceleration scheme is developed which has a good rate of convergence. Previously published results on the performance of various acceleration algorithms for initial stiffness iteration are rare and have been restricted to relatively simple yield criteria and simple problems. In this study, detailed numerical results are presented for the expansion of a thick cylinder, the collapse of a rigid strip footing, and the failure of a vertical cut. These analyses use the Mohr-Coulomb and Tresca yield criteria which are popular in soil mechanics.

Sloan, Scott W.; Sheng, Daichao; Abbo, Andrew J.

2000-05-01

188

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

189

Stiffness nanotomography of human epithelial cancer cells  

NASA Astrophysics Data System (ADS)

The mechanical stiffness of individual cells is important in both cancer initiation and metastasis. We present atomic force microscopy (AFM) based nanoindentation experiments on various human mammary and esophagus cell lines covering the spectrum from normal immortalized cells to highly metastatic ones. The combination of an AFM with a confocal fluorescence lifetime imaging microscope (FLIM) in conjunction with the ability to move the sample and objective independently allow for precise alignment of AFM probe and laser focus with an accuracy down to a few nanometers. This enables us to correlate the mechanical properties with the point of indentation in the FLIM image. We are using force-volume measurements as well as force indentation curves on distinct points on the cells to compare the elastic moduli of the nuclei, nucleoli, and the cytoplasm, and how they vary within and between individual cells and cell lines. Further, a detailed analysis of the force-indentation curves allows study of the cells' mechanical properties at different indentation depths and to generate 3D elasticity maps.

Staunton, Jack R.; Doss, Bryant L.; Gilbert, C. Michael; Kasas, Sandor; Ros, Robert

2012-02-01

190

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 3days 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

2014-11-11

191

Updating Bearing Stiffness and Damping Coefficients of a Rotor System  

NASA Astrophysics Data System (ADS)

Finite element (FE) models of structures have been quite useful in both static and dynamic analyses of structures. However, quite often, these models are not reliable enough since predictions based on them may not be found to have acceptable correlation with experimentally obtained data. This paper attempts updating of bearing radial and tilt stiffness as well as damping parameters of a rotor system by using inverse eigen sensitivity method (IESM). Non-proportional viscous damping model has been used in modelling damping coefficients of bearings. The state space form of equations of motion of the system is used in applying the IESM for model updating. The results show that both stiffness and damping coefficients of bearings can be effectively found out by using the IESM. The method is found to update the eigenvalues quite well even under the presence of measurement noise.

Chouksey, M.; Dutt, J. K.; Modak, S. V.

2013-10-01

192

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

193

Intermittent pneumatic compression effect on eccentric exercise-induced swelling, stiffness, and strength loss  

Microsoft Academic Search

Objective: The purpose was to determine if intermittent pneumatic compression (IPC) affects muscle swelling, stiffness, and strength loss resulting from eccentric exercise-induced injury of the elbow flexors. We hypothesized that the compression would decrease swelling and stiffness. Design: Repeated measures design with a before-after trial comparison within each day. Setting: Conducted at a university Somatic Dysfunction Laboratory. Subjects: Twenty-two college

Gary S. Chleboun; John N. Howell; Heather L. Baker; Tina N. Ballard; Jennifer L. Graham; Holly L. Hallman; Lori E. Perkins; Jonathan H. Schauss; Robert R. Conatser

1995-01-01

194

Nature of passive musculoarticular stiffness increase of ankle in female subjects with fibromyalgia syndrome  

Microsoft Academic Search

The objective of this study was to assess the passive elastic and viscous stiffness components of ankle in young, middle-aged\\u000a and old adult female fibromyalgia subjects and compare the results with age-matched healthy control subjects. The passive\\u000a musculoarticular stiffness of the ankles of 60 fibromyalgia subjects and 52 controls was quantified by measuring the ankle\\u000a resistance to imposed sinusoidal rotary

Frédéric Dierick; Christine Detrembleur; Guilhem Trintignac; Etienne Masquelier

195

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

Microsoft Academic Search

When measured in vivo electromechanical delay (EMD) depends mainly on the elastic properties of the muscle–tendon unit. Recent\\u000a studies have shown changes in stiffness of the triceps surae (TS) following a period of training. To confirm the influence\\u000a of musculo-tendinous stiffness on EMD, this study investigates paired changes in these two parameters after a training period.\\u000a Two types of training

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

2009-01-01

196

Effect of single-leg resistance exercise on regional arterial stiffness  

Microsoft Academic Search

To examine the effects of lower-limb unilateral resistance exercise on central and peripheral arterial stiffness, thirteen participants (7 male and 6 female, mean age = 21.5  0.7 years) performed leg press exercise using their dominant leg. Pulse wave velocity (PWV) was used to measure central (carotid to femoral) and peripheral (femoral to dorsalis pedis of both legs) arterial stiffness before, 5 min post, and 25 min

Kevin S. Heffernan; Lindy Rossow; Sae Young Jae; Halidu G. Shokunbi; Elizabeth M. Gibson; Bo Fernhall

2006-01-01

197

Stiffness-Dependent In Vitro Uptake and Lysosomal Acidification of Colloidal Particles.  

PubMed

The physico-chemical properties of colloidal particles determine their uptake into cells. For a series of microparticles only one parameter, the mechanical stiffness, was varied, whereas other parameters such as size, shape, and charge were kept constant. The uptake was monitored in situ by analyzing individual particle trajectories including the progress of endocytosis, derived from local pH measurements around each particle. Evidence is presented that soft particles with low stiffness are transported faster to lysosomes than stiffer ones. PMID:25483403

Hartmann, Raimo; Weidenbach, Marcel; Neubauer, Martin; Fery, Andreas; Parak, Wolfgang J

2014-12-01

198

Arterial Stiffness in Patients with Deep and Lobar Intracerebral Hemorrhage  

PubMed Central

Background and Purpose Intracerebral hemorrhage (ICH) accounts for approximately 10% of stroke cases. Hypertension may play a role in the pathogenesis of ICH that occurs in the basal ganglia, thalamus, pons, and cerebellum, but not in that of lobar ICH. Hypertension contributes to decreased elasticity of arteries, thereby increasing the likelihood of rupture in response to acute elevation in intravascular pressure. This study aimed to evaluate arterial stiffness (using the arterial stiffness index [ASI]) in patients with deep (putaminal and thalamic) ICH in comparison with patients with lobar ICH. Methods We enrolled 64 patients (mean±SD age: 69.3±10.7 years; 47 men and 17 women) among 73 who referred consecutively to our department for intraparenchymal hemorrhage and underwent brain computed tomography (CT) and cerebral angio-CT. In all the subjects, 24-hour heart rates and blood pressures were monitored. The linear regression slope of diastolic on systolic blood pressure was assumed as a global measure of arterial compliance, and its complement (1 minus the slope), ASI, has been considered as a measure of arterial stiffness. Results In the patients with deep ICH, ASI was significantly higher than in the patients with lobar ICH (0.64±0.19 vs. 0.53±0.17, P=0.04). Conclusions Our results suggest that in deep ICH, arterial stiffening represents a possible pathogenetic factor that modifies arterial wall properties and contributes to vascular rupture in response to intravascular pressure acute elevation. Therapeutic strategies that reduce arterial stiffness may potentially lower the incidence of deep hemorrhagic stroke. PMID:25328877

Guideri, Francesca; Di Donato, Ilaria; Tassi, Rossana; Marotta, Giovanna; Lo Giudice, Giuseppe; D'Andrea, Paolo; Martini, Giuseppe

2014-01-01

199

The Association between Abdominal Visceral Fat and Carotid Stiffness Is Mediated by Circulating Inflammatory Markers in Uncomplicated Type 2 Diabetes  

Microsoft Academic Search

Central obesity, insulin resistance, inflammation, as well as vascularchangesarecommoninpatientswithtype2diabetes. In this study we assessed the relationship among stiffness of the carotid artery, visceral fat, and circulating inflammatory markers in type 2 diabetic subjects. Carotid stiffness, quan- tified as the distensibility coefficient (DC), was measured by ultrasound in asymptomatic, normotensive patients with un- complicated, well-controlled type 2 diabetes and in controls.

Michaela Diamant; Hildo J. Lamb; Marcel A. van de Ree; Edwin L. Endert; Ymte Groeneveld; Michiel L. Bots; Piet J. Kostense; Jasper K. Radder

200

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

PubMed Central

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

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

1993-01-01

201

Deletion analysis of LSm, FDF, and YjeF domains of Candida albicans Edc3 in hyphal growth and oxidative-stress response.  

PubMed

Candida albicans is an opportunistic fungal pathogen whose responses to environmental changes are associated with the virulence attributes. Edc3 is known to be an enhancer of the mRNA decapping reactions and a scaffold protein of cytoplasmic processing bodies (P-bodies). Recent studies of C. albicans Edc3 suggested its critical roles in filamentous growth and stress-induced apoptotic cell death. The edc3/edc3 deletion mutant strain showed increased cell survival and less ROS accumulation upon treatment with hydrogen peroxide. To investigate the diverse involvement of Edc3 in the cellular processes, deletion mutations of LSm, FDF, or YjeF domain of Edc3 were constructed. The edc3-LSm? or edc3-YjeF? mutation showed the filamentation defect, resistance to oxidative stress, and decreased ROS accumulation. In contrast, the edc3-FDF? mutation exhibited a wild-type level of filamentous growth and a mild defect in ROS accumulation. These results suggest that Lsm and YjeF domains of Edc3 are critical in hyphal growth and oxidative stress response. PMID:25626365

Kim, Eung-Chul; Kim, Jinmi

2015-02-01

202

Photoplethysmographic signal waveform index for detection of increased arterial stiffness.  

PubMed

The aim of this research was to assess the validity of the photoplethysmographic (PPG) waveform index PPGAI for the estimation of increased arterial stiffness. For this purpose, PPG signals were recorded from 24 healthy subjects and from 20 type II diabetes patients. The recorded PPG signals were processed with the analysis algorithm developed and the waveform index PPGAI similar to the augmentation index (AIx) was calculated. As a reference, the aortic AIx was assessed and normalized for a heart rate of 75?bpm (AIx@75) by a SphygmoCor device. A strong correlation (r = 0.85) between the PPGAI and the aortic AIx@75 and a positive correlation of both indices with age were found. Age corrections for the indices PPGAI and AIx@75 as regression models from the signals of healthy subjects were constructed. Both indices revealed a significant difference between the groups of diabetes patients and healthy controls. However, the PPGAI provided the best statistical discrimination for the group of subjects with increased arterial stiffness. The waveform index PPGAI based on the inexpensive PPG technology can be considered as a perspective measure of increased arterial stiffness estimation in clinical screenings. PMID:25238409

Pilt, K; Meigas, K; Ferenets, R; Temitski, K; Viigimaa, M

2014-10-01

203

Conformational Analysis of Stiff Chiral Polymers with End-Constraints  

PubMed Central

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

Kim, Jin Seob; Chirikjian, Gregory S.

2010-01-01

204

Joint stiffness of the ankle and the knee in running.  

PubMed

The spring-mass model is a valid fundament to understand global dynamics of fast legged locomotion under gravity. The underlying concept of elasticity, implying leg stiffness as a crucial parameter, is also found on lower motor control levels, i.e. in muscle-reflex and muscle-tendon systems. Therefore, it seems reasonable that global leg stiffness emerges from local elasticity established by appropriate joint torques. A recently published model of an elastically operating, segmented leg predicts that proper adjustment of joint elasticities to the leg geometry and initial conditions of ground contact provides internal leg stability. Another recent study suggests that in turn the leg segmentation and the initial conditions may be a consequence of metabolic and bone stress constraints. In this study, the theoretical predictions were verified experimentally with respect to initial conditions and elastic joint characteristics in human running. Kinematics and kinetics were measured and the joint torques were estimated by inverse dynamics. Stiffnesses and elastic nonlinearities describing the resulting joint characteristics were extracted from parameter fits. Our results clearly support the theoretical predictions: the knee joint is always stiffer and more extended than the ankle joint. Moreover, the knee torque characteristic on the average shows the higher nonlinearity. According to literature, the leg geometry is a consequence of metabolic and material stress limitations. Adapted to this given geometry, the initial joint angle conditions in fast locomotion are a compromise between metabolic and control effort minimisation. Based on this adaptation, an appropriate joint stiffness ratio between ankle and knee passively safeguards the internal leg stability. The identified joint nonlinearities contribute to the linearisation of the leg spring. PMID:12413965

Günther, Michael; Blickhan, Reinhard

2002-11-01

205

A new strategy for stiffness evaluation of sheet metal parts  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

206

A biomechanical model to simulate the effect of a high vertical loading on trunk flexural stiffness.  

PubMed

A human trunk model was developed to simulate the effect of a high vertical loading on trunk flexural stiffness. A force-length relationship is attributed to each muscle of the multi-body model. Trunk stiffness and muscle forces were evaluated experimentally and numerically for various applied loads. Experimental evaluation of trunk stiffness was carried out by measuring changes in reaction force following a sudden horizontal displacement at the T10 level prior to paraspinal reflexes induction. Results showed that the trunk stiffness increases under small applied loads, peaks when the loads were further increased and decreases when higher loads are applied. A sensitivity analysis to muscle force-length relationship is provided to determine the model's limitations. This model pointed out the importance of taking into account the changes in muscle length to evaluate the effect of spinal loads beyond the safe limit that cannot be evaluated experimentally and to predict the trunk instability under vertical load. PMID:23113599

Mehrez, Sadok; Smaoui, Hichem; Ben Salah, Fatma Z

2014-01-01

207

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

208

Vascular Stiffness and Increased Pulse Pressure in the Aging Cardiovascular System  

PubMed Central

Aging leads to a multitude of changes in the cardiovascular system, including systolic hypertension, increased central vascular stiffness, and increased pulse pressure. In this paper we will review the effects of age-associated increased vascular stiffness on systolic blood pressure, pulse pressure, augmentation index, and cardiac workload. Additionally we will describe pulse wave velocity as a method to measure vascular stiffness and review the impact of increased vascular stiffness as an index of vascular health and as a predictor of adverse cardiovascular outcomes. Furthermore, we will discuss the underlying mechanisms and how these may be modified in order to change the outcomes. A thorough understanding of these concepts is of paramount importance and has therapeutic implications for the increasingly elderly population. PMID:21845218

Steppan, Jochen; Barodka, Viachaslau; Berkowitz, Dan E.; Nyhan, Daniel

2011-01-01

209

Effects of isokinetic passive exercise and isometric muscle contraction on passive stiffness.  

PubMed

[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

2013-10-01

210

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

211

Nanoscale Directional Motion towards Regions of Stiffness  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

212

Cosmology with a stiff matter era  

E-print Network

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

Pierre-Henri Chavanis

2014-11-27

213

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

2014-12-01

214

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

215

Arterial stiffness response to exercise in persons with and without Down syndrome.  

PubMed

This study compared arterial stiffness and wave reflection at rest and following maximal exercise between individuals with and without Down syndrome (DS), and the influence of body mass index (BMI), peak oxygen uptake (VO2 peak) on changes in arterial stiffness. Twelve people with DS (26.6 ± 2.6 yr) and 15 healthy controls (26.2 ± 0.6 yr) completed this study. Intima-media thickness (IMT) and stiffness of common carotid artery was examined. Hemodynamic and arterial variables were measured before and 3-min after exercise. Persons with DS had higher BMI and lower VO 2 peak than controls. IMT did not differ between groups. At rest, carotid ? stiffness was significantly higher in persons with DS (P<0.05) but there was no difference in between groups for any of the other arterial stiffness measures. After exercise, persons with DS exhibited attenuated arterial stiffness responses in AIx-75, carotid ? stiffness and Ep in contrast with controls (significant group-by-time interactions). When controlling for BMI and VO 2 peak, the interactions disappeared. In both groups combined, BMI was correlated significantly with carotid Ep and ? at rest. VO 2 peak correlated significantly with AIx-75 and its pre-post change (r=-0.45, P=0.029; r=0.47, P=0.033, respectively). The arterial stiffness responses to maximal exercise in persons with DS were blunted, potentially reflecting diminished vascular reserve. Obesity and particularly VO 2 peak influenced these findings. These results suggest impaired vascular function in people with DS. PMID:23883823

Hu, Min; Yan, Huimin; Ranadive, Sushant M; Agiovlasitis, Stamatis; Fahs, Christopher A; Atiq, Muhammed; Atique, Nazia; Fernhall, Bo

2013-10-01

216

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

217

Elastic stiffness of a skyrmion crystal.  

PubMed

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

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

2014-12-31

218

Preliminary investigation of the mechanisms underlying the effects of manipulation: exploration of a multi-variate model including spinal stiffness, multifidus recruitment, and clinical findings  

PubMed Central

Study Design Prospective case series. Objective Examine spinal stiffness in subjects with low back pain (LBP) receiving spinal manipulative therapy (SMT), evaluate associations between stiffness characteristics and clinical outcome, and explore a multi-variate model of SMT mechanisms as related to effects on stiffness, lumbar multifidus (LM) recruitment and status on a clinical prediction rule (CPR) for SMT outcomes. Summary of Background Data Mechanisms underlying the clinical effects of SMT are poorly understood. Many explanations have been proposed, but few studies have related potential mechanisms to clinical outcomes or considered multiple mechanisms concurrently. Methods Subjects with LBP were treated with 2 SMT sessions over 1 week. CPR status was assessed at baseline. Clinical outcome was based on the Oswestry disability index (ODI). Mechanized indentation measures of spinal stiffness and ultrasonic measures of LM recruitment were taken before and after each SMT, and after 1 week. Global and terminal stiffness were calculated. Multivariate regression was used to evaluate the relationship between stiffness variables and percentage ODI improvement. Zero-order correlations among stiffness variables, LM recruitment changes, CPR status, and clinical outcome were examined. Path analysis was used to evaluate a multi-variate model of SMT effects. Results Forty-eight subjects (54% female) had complete stiffness data. Significant immediate decreases in global and terminal stiffness occurred post-SMT regardless of outcome. ODI improvement was related to greater immediate decrease in global stiffness (p=0.025), and less initial terminal stiffness (p=0.01). Zero-order correlations and path analysis supported a multi-variate model suggesting clinical outcome of SMT is mediated by improvements in LM recruitment and immediate decrease in global stiffness. Initial terminal stiffness and CPR status may relate to outcome though their relationship with LM recruitment. Conclusions The underlying mechanisms explaining the benefits of SMT appear to be multi-factorial. Both spinal stiffness characteristics and LM recruitment changes appear to play a role. PMID:21358568

Fritz, Julie M.; Koppenhaver, Shane L.; Kawchuk, Gregory N.; Teyhen, Deydre S.; Hebert, Jeffrey J.; Childs, John D.

2011-01-01

219

Stiffness Ellipse Control of Tendon Mechanisms with Nonlinear Springs  

NASA Astrophysics Data System (ADS)

Versatile and safe manipulators are required for use in human environments. A tendon mechanism with nonlinear springs that can mechanically adjust joint stiffness is one candidate that can satisfy the requirements of versatility and safety. In this paper, a hybrid stiffness ellipse control for controlling both mechanical and control stiffness at the end of the manipulator is proposed for the tendon mechanisms. This study shows the transformation of the stiffness ellipse at the ends of arms to joint stiffness. The transformation is applied to both mechanical joint stiffness and controller gain of joint angle controller. Simulation results verify the validity of the proposed method.

Okumura, Fumihiro; Komada, Satoshi; Hirai, Junji

220

Stiff aqueous explosive composition containing gilsonite  

Microsoft Academic Search

A stiff or highly viscous explosive composition of high sensitivity to detonation is made up of a mixture of: (1) 40 to 60 Pt. by wt, based on total composition, of ammonium nitrate and 15 to 35 Pt. of sodium nitrate at least partly dissolved in 8 to 15 Pt. of water\\/ (2) it preferably includes 1.5 to 5 Pt.

M. A. Cook; D. T. Bailey

1973-01-01

221

Numerical Methods for Stiff Ordinary Differential  

E-print Network

order differential equation y (x) = f(x, y (x)). Substituting y (x) = z(x), one obtains a first order. The notation of stiffness comes from the consideration of first order systems of ordinary differential equations. There are some connections of such systems to ordinary differential equations of higher order, e

John, Volker

222

Vibrating Beam With Spatially Periodic Stiffness  

NASA Technical Reports Server (NTRS)

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

Townsend, John S.

1989-01-01

223

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

224

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

225

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

PubMed

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

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

2014-12-01

226

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

PubMed Central

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

Hlaing, WayWay M.; Prineas, Ronald J.

2006-01-01

227

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

228

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

PubMed Central

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

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

2013-01-01

229

Effective Elastic Stiffness for Periodic Masonry Structures via Eigenstrain Homogenization  

E-print Network

Effective Elastic Stiffness for Periodic Masonry Structures via Eigenstrain Homogenization Gang eigenstrain method is used to evaluate the effective elastic stiffness of periodic masonry structure. An Eshelby tensor, for a unit cell of the periodic masonry structure, is derived analytically

Li, Shaofan

230

A Variable Stiffness PZT Actuator Having Tunable Resonant Frequencies  

E-print Network

A new approach to a variable stiffness actuator with tunable resonant frequencies is presented in this paper. Variable stiffness actuators have become increasingly important to meet safety requirements and achieve adaptive ...

Secord, Thomas William

231

Wave propagation of myocardial stretch: correlation with myocardial stiffness.  

PubMed

The mechanism of flow propagation during diastole in the left ventricle (LV) has been well described. Little is known about the associated waves propagating along the heart walls. These waves may have a mechanism similar to pulse wave propagation in arteries. The major goal of the study was to evaluate the effect of myocardial stiffness and preload on this wave transmission. Longitudinal late diastolic deformation and wave speed (Vp) of myocardial stretch in the anterior LV wall were measured using sonomicrometry in 16 pigs. Animals with normal and altered myocardial stiffness (acute myocardial infarction) were studied with and without preload alterations. Elastic modulus estimated from Vp (E VP; Moens-Korteweg equation) was compared to incremental elastic modulus obtained from exponential end-diastolic stress-strain relation (E SS). Myocardial distensibility and ?- and ?-coefficients of stress-strain relations were calculated. Vp was higher at reperfusion compared to baseline (2.6 ± 1.3 vs. 1.3 ± 0.4 m/s; p = 0.005) and best correlated with E SS (r2 = 0.80, p < 0.0001), ?-coefficient (r2 = 0.78, p < 0.0001), distensibility (r2 = 0.47, p = 0.005), and wall thickness/diameter ratio (r2 = 0.42, p = 0.009). Elastic moduli (E VP and E SS) were strongly correlated (r2 = 0.83, p < 0.0001). Increasing preload increased Vp and E VP and decreased distensibility. At multivariate analysis, E SS, wall thickness, and end-diastolic and systolic LV pressures were independent predictors of Vp (r2 model = 0.83, p < 0.0001). In conclusion, the main determinants of wave propagation of longitudinal myocardial stretch were myocardial stiffness and LV geometry and pressure. This local wave speed could potentially be measured noninvasively by echocardiography. PMID:25193091

Pislaru, Cristina; Pellikka, Patricia A; Pislaru, Sorin V

2014-11-01

232

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

2014-12-01

233

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

234

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

Microsoft Academic Search

Inthe eggs of the newt, Cynops (Triturus) pyrrhogaster, change in stiffness of the cortex was measured in various regions at the time of the cleavage .Measurements were per- formed by Mitchison andSwarm's cell elastimeter method with a modification, in which two fine pipettes were attached to the surface of one egg at the same time, in order to compare the

TSUYOSHI SAWAI; MITSUKI YONEDA

1974-01-01

235

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

236

Light weight high-stiffness stage platen  

DOEpatents

An improved light weight, stiff stage platen for photolithography is provided. The high stiffness of the stage platen is exemplified by a relatively high first resonant vibrational mode as determined, for instance, by finite element modal analysis. The stage platen can be employed to support a chuck that is designed to secure a mask or wafer. The stage platen includes a frame that has interior walls that define an interior region and that has exterior walls wherein the outer surfaces of at least two adjacent walls are reflective mirror surfaces; and a matrix of ribs within the interior region that is connected to the interior walls wherein the stage platen exhibits a first vibrational mode at a frequency of greater than about 1000 Hz.

Spence, Paul A. (Pleasanton, CA)

2001-01-01

237

Stiff-Person Syndrome: Case Series  

PubMed Central

Stiff-person syndrome (SPS) is a rare disorder, characterized by progressive fluctuating muscular rigidity and spasms. Glutamic acid decarboxylase (GAD) antibody is primarily involved in the pathogenesis of SPS and SPS is strongly associated with other autoimmune disease. Here we report three cases of patients with classical SPS finally confirmed by high serum level of GAD antibodies. All of our patients respond favorably to gamma amino butyric acid-enhancing drugs and immunotherapies. PMID:24926406

Jung, Yu Jin; Jeong, Han G.; Kim, Ryul; Kim, Han-Joon; Jeon, Beom S.

2014-01-01

238

Aortic stiffness, kidney disease, and renal transplantation  

Microsoft Academic Search

In subjects with chronic kidney disease (CKD), treatment of high systolic blood pressure is a key element in preventing disease\\u000a progression and the occurrence of cardiovascular (CV) events. This relationship between the large arterial system and kidney\\u000a function was demonstrated in different renal populations. In subjects with mild to severe renal insufficiency, increased aortic\\u000a stiffness and reduced creatinine clearance are

Sola Aoun Bahous; Jacques Blacher; Michel E. Safar

2009-01-01

239

Aortic Stiffness, Kidney Disease, and Renal Transplantation  

Microsoft Academic Search

\\u000a In individuals with chronic kidney disease (CKD), treatment of elevated systolic blood pressure (SBP) is a key element in\\u000a preventing disease progression and occurrence of cardiovascular events. For a given stroke volume, increased arterial stiffness\\u000a is a key determinant of SBP. Therefore, the relationships between large conduit arteries and kidney function have been extensively\\u000a studied in different CKD populations. In

Sola A. Bahous; Michael Delahousse; Michel E. Safar

240

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

241

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

242

Acoustic radiation force impulse imaging of mechanical stiffness propagation in myocardial tissue.  

PubMed

Acoustic radiation force impulse (ARFI) imaging has been shown to be capable of imaging local myocardial stiffness changes throughout the cardiac cycle. Expanding on these results, the authors present experiments using cardiac ARFI imaging to visualize and quantify the propagation of mechanical stiffness during ventricular systole. In vivo ARFI images of the left ventricular free wall of two exposed canine hearts were acquired. Images were formed while the heart was externally paced by one of two electrodes positioned on the epicardial surface and either side of the imaging plane. Two-line M-mode ARFI images were acquired at a sampling frequency of 120 Hz while the heart was paced from an external stimulating electrode. Two-dimensional ARFI images were also acquired, and an average propagation velocity across the lateral field of view was calculated. Directions and speeds of myocardial stiffness propagation were measured and compared with the propagations derived from the local electrocardiogram (ECG), strain, and tissue velocity measurements estimated during systole. In all ARFI images, the direction of myocardial stiffness propagation was seen to be away from the stimulating electrode and occurred with similar velocity magnitudes in either direction. When compared with the local epicardial ECG, the mechanical stiffness waves were observed to travel in the same direction as the propagating electrical wave and with similar propagation velocities. In a comparison between ARFI, strain, and tissue velocity imaging, the three methods also yielded similar propagation velocities. PMID:22972912

Hsu, Stephen J; Byram, Brett C; Bouchard, Richard R; Dumont, Douglas M; Wolf, Patrick D; Trahey, Gregg E

2012-07-01

243

Increased arterial stiffness in resistant hypertension is associated with inflammatory biomarkers.  

PubMed

Abstract Background. Increased levels of inflammatory biomarkers such as interleukin-6 (IL-6), 10 (IL-10), 1? (IL-1?), tumor necrosis factor-? (TNF-?) high-sensitivity C-reactive protein (hs-CRP) are associated with arterial stiffness in hypertension. Indeed, resistant hypertension (RHTN) leads to unfavorable prognosis attributed to poor blood pressure (BP) control and target organ damage. This study evaluated the potential impact of inflammatory biomarkers on arterial stiffness in RHTN. Methods. In this cross-sectional study, 32 RHTN, 20 mild hypertensive (HTN) and 20 normotensive (NT) patients were subjected to office BP and arterial stiffness measurements assessed by pulse wave velocity (PWV). Inflammatory biomarkers were measured in plasma samples. Results. PWV was increased in RHTN compared with HTN and NT (p < 0.05). TNF-? levels were significantly higher in RHTN and HTN than NT patients. No differences in IL-6 levels were observed. RHTN patients had a higher frequency of subjects with increased levels of IL-10 and IL-1? compared with HTN and NT patients. Finally, IL-1? was independently associated with PWV (p < 0.001; R(2) = 0.5; ? = 0.077). Conclusion. RHTN subjects have higher levels of inflammatory cytokines (TNF-?, IL-1? and IL-10) as well as increased arterial stiffness, and detectable IL-1? levels are associated arterial stiffness. These findings suggest that inflammation plays a possible role in the pathophysiology of RHTN. PMID:25061978

Barbaro, Natália Ruggeri; Fontana, Vanessa; Modolo, Rodrigo; De Faria, Ana Paula; Sabbatini, Andrea Rodrigues; Fonseca, Francisco Helfenstein; Anhê, Gabriel F; Moreno, Heitor

2015-02-01

244

Wave reflections, arterial stiffness, heart rate variability and orthostatic hypotension.  

PubMed

Increased arterial stiffness and wave reflections are independently associated with orthostatic hypotension (OH). This study investigated whether heart rate variability (HRV) is also involved in the modulation of orthostatic blood pressure (BP) change. A total of 429 subjects (65.1±16.4 years, 77.4% men) were enrolled in this study. OH was defined as a ?20?mm?Hg decrease in brachial systolic blood pressure (SBP) or a ?10?mm?Hg diastolic blood pressure (DBP) decrease upon standing. Measurements of carotid-femoral pulse wave velocity (cf-PWV) and the amplitude of the reflected pressure wave from a decomposed carotid pressure wave (Pb) were obtained by carotid tonometry in the supine position. The power spectrum from a 5-min recording of an electrocardiogram at rest was analyzed to provide components in the high frequency (HF) and low frequency (LF) ranges. Subjects with OH (n=59, 13.8%) had significantly higher cf-PWV and Pb and significantly lower LogHF and LogLF than those without OH (n=370). The cf-PWV, Pb, LogHF and LogLF were significantly associated with postural SBP and DBP changes. Furthermore, cf-PWV but not Pb was significantly associated with LogHF and LogLF. Multivariate analysis showed that Pb (odds ratio (OR) per 1 s.d. 1.65, 95% confidence interval (CI) 1.282-2.137; P=0.003) and LogHF (OR 0.628, 95% CI 0.459-0.860, P=0.004), but not cf-PWV (OR 1.279, 95% CI 0.932-1.755, P=0.128), were significant independent determinants of OH. Increased wave reflections may predispose OH independently of arterial stiffness and HRV. In contrast, increased arterial stiffness may cause OH through the modulation of HRV. PMID:25142223

Lu, Dai-Yin; Sung, Shih-Hsien; Yu, Wen-Chung; Cheng, Hao-Min; Chuang, Shao-Yuan; Chen, Chen-Huan

2014-12-01

245

Arterial stiffness in adult patients after Fontan procedure  

PubMed Central

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

2014-01-01

246

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

247

A homogenization sampling procedure for calculating trabecular bone effective stiffness and tissue level stress.  

PubMed

A homogenization sampling procedure is introduced which allows computation of effective trabecular bone stiffness and individual trabecula level stress based on precise models of trabecular bone architecture. Three-dimensional digitized images of 53 trabecular bone specimens with a resolution of 50 microns per voxel were directly converted into three-dimensional finite element meshes by making each voxel an 8-node isoparametric brick element. Owing to the large mesh of 8000 elements, an element-by-element preconditioned conjugate gradient (EBEPCG) program was written to solve the local homogenization finite element equations. Predicted effective stiffness measures correlated well with experimental results (R2 > 0.73). The predicted effective stiffness tended to under estimate the experimental values. Average absolute errors in effective stiffness estimates ranged between 31 and 38% for the sampling procedure compared to a range 49-150% for a regression fit to volume fraction squared. Trabecula level stress ranged between -200 and +300 times that predicted by analyzing trabecular bone as a continuum. Both tensile and compressive tissue stresses were engendered by a continuum compressive stress. Trabecula level strain energy density (SED) ranged between 0 and 100 times the continuum SED value for two trabecular specimens. In conclusion, the homogenization sampling procedure consistently predicted the influence of trabecular bone architecture on effective stiffness. It can also provide trabecular tissue stress and strain estimates for arbitrary global loading of whole bones. Tissue stresses and strains showed large variations compared to corresponding continuum level quantities. PMID:8188724

Hollister, S J; Brennan, J M; Kikuchi, N

1994-04-01

248

Multicomponent supplement containing Chlorella decreases arterial stiffness in healthy young men  

PubMed Central

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

2013-01-01

249

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

250

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

251

Fatigue, Vertical Leg Stiffness, and Stiffness Control Strategies in Males and Females  

PubMed Central

Context: Fatigue appears to influence musculoskeletal injury rates during athletic activities, but whether males and females respond differently to fatigue is unknown. Objective: To determine the influence of fatigue on vertical leg stiffness (K VERT) and muscle activation and joint movement strategies and whether healthy males and females respond similarly to fatigue. Design: Repeated-measures design with all data collected during a single laboratory session. Setting: Laboratory. Patients or Other Participants: Physically active males (n = 11) and females (n = 10). Intervention(s): Subjects performed hopping protocols at 2 frequencies before and after fatigue, which was induced by repeated squatting at submaximal loads. Main Outcome Measure(s): We measured K VERT with a forceplate and peak muscle activity of the quadriceps, hamstrings, gastrocnemius, soleus, and anterior tibialis muscles with surface electromyography. Sagittal-plane kinematics at the knee and ankle were recorded with an electrogoniometer. Results: After fatigue, K VERT was unchanged for all subjects. However, both males and females demonstrated reduced peak hamstrings ( P = .002) and anterior tibialis ( P = .001) activation, coupled with increased gastrocnemius ( P = .005) and soleus ( P = .001) peak activity, as well as increased quadriceps-hamstrings ( P = .005) and gastrocnemius/soleus-anterior tibialis coactivation ratios ( P = .03) after fatigue. Overall, females demonstrated greater quadriceps-hamstrings coactivation ratios than males, regardless of the fatigue condition ( P = .026). Only females showed increased knee flexion at initial contact after fatigue during hopping ( P = .03). Conclusions: Although K VERT was unaffected, the peak muscle activation and joint movement strategies used to modulate K VERT were affected after fatigue. Once fatigued, both males and females used an ankle-dominant strategy, with greater reliance on the ankle musculature and less on the knee musculature. Also, once fatigued, all subjects used an antagonist inhibition strategy by minimizing antagonist coactivation. Overall, females used a more quadriceps-dominant strategy than males, showing greater quadriceps activity and a larger quadriceps-hamstrings coactivation ratio. Changes in muscle activation and coactivation ratios because of fatigue and sex are suggested to alter knee joint stability and increase anterior cruciate ligament injury risk. PMID:17043698

Padua, Darin A; Arnold, Brent L; Perrin, David H; Gansneder, Bruce M; Carcia, Christopher R; Granata, Kevin P

2006-01-01

252

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

253

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

254

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

255

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

256

Stiffness and thermoelastic coefficients for composite laminates  

NASA Technical Reports Server (NTRS)

Simple analytic expressions are presented for the stiffness and thermoelastic coefficients of composite laminates in terms of the material properties of the individual layers. Expressions for the derivatives of the various coefficients with respect to each of the material properties and fiber orientation angles are also included. For typical high-performance composites, numerical values are given showing the effects of the stacking sequence and the fiber orientation angle of quasi-isotropic and angle-ply laminates on the values of the various coefficients and their sensitivity derivatives. The expressions for the thermoelastic coefficients and the sensitivity derivatives are given herein for the first time.

Noor, Ahmed K.; Tenek, Lazarus H.

1992-01-01

257

Optimized movement trajectories and joint stiffness in unperturbed, inertially loaded movements  

Microsoft Academic Search

An attempt is made to integrate theoretically the mechanical, electromyographic, and psychophysical lines of inquiry into the control of movement by investigating the significance of joint stiffness in the reduction of effort. Attention is focused on single-joint, unperturbed movements of specified duration performed from one specified position to another in the presence of an inertial load. A theoretical measure of

Z. Hasan

1986-01-01

258

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

259

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

260

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

PubMed

We demonstrate reliable neural responses to changes in haptic stiffness perception using a functional magnetic resonance imaging (fMRI) compatible particle-jamming haptic interface. Our haptic interface consists of a silicone tactile surface whose stiffness we can control by modulating air-pressure in a sub-surface pouch of coarsely ground particles. The particles jam together as the pressure decreases, which stiffens the surface. During fMRI acquisition, subjects performed a constant probing task, which involved continuous contact between the index fingertip and the interface and rhythmic increases and decreases in fingertip force (1.6 Hz) to probe stiffness. Without notifying subjects, we randomly switched the interface's stiffness (switch time, 300-500 ms) from soft (200 N/m) to hard (1400 N/m). Our experiment design's constant motor activity and cutaneous tactile sensation helped disassociate neural activation for both from stiffness perception, which helped localized it to a narrow region in somatosensory cortex near the supra-marginal gyrus. Testing different models of neural activation, we found that assuming indepedent stiffness-change responses at both soft-hard and hard-soft transitions provides the best explanation for observed fMRI measurements (three subjects; nine four-minute scan runs each). Furthermore, we found that neural activation related to stiffness-change and absolute stiffness can be localized to adjacent but disparate anatomical locations. We also show that classical finger-tapping experiments activate a swath of cortex and are not suitable for localizing stiffness perception. Our results demonstrate that decorrelating motor and sensory neural activation is essential for characterizing somatosensory cortex, and establish particle-jamming haptics as an attractive low-cost method for fMRI experiments. PMID:25570387

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

2014-08-01

261

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:25580550

Pamukoff, Derek N; Blackburn, J Troy

2015-02-01

262

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

263

Contact stiffness of randomly rough surfaces  

PubMed Central

We investigate the contact stiffness of an elastic half-space and a rigid indenter with randomly rough surface having a power spectrum , where q is the wave vector. The range of 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

264

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

265

Substrate stiffness regulates solubility of cellular vimentin  

PubMed Central

The intermediate filament protein vimentin is involved in the regulation of cell behavior, morphology, and mechanical properties. Previous studies using cells cultured on glass or plastic substrates showed that vimentin is largely insoluble. Although substrate stiffness was shown to alter many aspects of cell behavior, changes in vimentin organization were not reported. Our results show for the first time that mesenchymal stem cells (hMSCs), endothelial cells, and fibroblasts cultured on different-stiffness substrates exhibit biphasic changes in vimentin detergent solubility, which increases from nearly 0 to 67% in hMSCs coincident with increases in cell spreading and membrane ruffling. When imaged, the detergent-soluble vimentin appears to consist of small fragments the length of one or several unit-length filaments. Vimentin detergent solubility decreases when these cells are subjected to serum starvation, allowed to form cell–cell contacts, after microtubule disruption, or inhibition of Rac1, Rho-activated kinase, or p21-activated kinase. Inhibiting myosin or actin assembly increases vimentin solubility on rigid substrates. These data suggest that in the mechanical environment in vivo, vimentin is more dynamic than previously reported and its assembly state is sensitive to stimuli that alter cellular tension and morphology. PMID:24173714

Murray, Maria E.; Mendez, Melissa G.; Janmey, Paul A.

2014-01-01

266

Column dampers with negative stiffness: high damping at small amplitude  

NASA Astrophysics Data System (ADS)

High structural damping combined with high initial stiffness is achieved at small amplitude via negative stiffness elements. These elements consist of columns in the vicinity of the post-buckling transition between contact of flat surfaces and edges of the ends for which negative incremental structural stiffness occurs. The column configuration provides a high initial structural stiffness equal to the intrinsic stiffness of the column material. Columns of the polymers polymethyl methacrylate (PMMA) and polycarbonate were used. By tuning the pre-strain, a very high mechanical damping was achieved for small amplitude oscillations. The product of effective stiffness and effective damping as a figure of merit |Eeff|tan?eff of about 1.5 GPa was achieved for polymer column dampers in the linear domain and about 1.62 GPa in the small amplitude nonlinear domain. For most materials this value generally never exceeds 0.6 GPa.

Kalathur, H.; Lakes, R. S.

2013-08-01

267

Cross-bridge attachment and stiffness during isotonic shortening of intact single muscle fibers.  

PubMed Central

Equatorial x-ray diffraction pattern intensities (I10 and I11), fiber stiffness and sarcomere length were measured in single, intact muscle fibers under isometric conditions and during constant velocity (ramp) shortening. At the velocity of unloaded shortening (Vmax) the I10 change accompanying activation was reduced to 50.8% of its isometric value, I11 reduced to 60.7%. If the roughly linear relation between numbers of attached bridges and equatorial signals in the isometric state also applies during shortening, this would predict 51-61% attachment. Stiffness (measured using 4 kHz sinusoidal length oscillations), another putative measure of bridge attachment, was 30% of its isometric value at Vmax. When small step length changes were applied to the preparation (such as used for construction of T1 curves), no equatorial intensity changes could be detected with our present time resolution (5 ms). Therefore, unlike the isometric situation, stiffness and equatorial signals obtained during ramp shortening are not in agreement. This may be a result of a changed crossbridge spatial orientation during shortening, a different average stiffness per attached crossbridge, or a higher proportion of single headed crossbridges during shortening. PMID:8494976

Griffiths, P J; Ashley, C C; Bagni, M A; Maéda, Y; Cecchi, G

1993-01-01

268

Stiff-system problems and solutions at LLNL  

SciTech Connect

Difficult stiff system problems encountered at LLNL are typified by those arising from various atmospheric kinetics models, which include reaction kinetics and transport in up to two space dimensions. Approaches devised for these problems resulted in several general purpose stiff system solvers. These have since evolved into a new systematized collection of solvers, called ODEPACK, based on backward differentiation formulas in the stiff case. A model kinetics-transport problem is used to illustrate the various solvers.

Hindmarsh, A.C.

1982-03-01

269

Arterial Stiffness and Functional Outcome in Acute Ischemic Stroke  

PubMed Central

Objective Arterial stiffness is a common change associated with aging and can be evaluated by measuring pulse wave velocity (PWV) between sites in the arterial tree, with the stiffer artery having the higher PWV. Arterial stiffness is associated with the risk of stroke in the general population and of fatal stroke in hypertensive patients. This study is to clarify whether PWV value predicts functional outcome of acute ischemic stroke. Methods One hundred patients were enrolled with a diagnosis of acute ischemic stroke and categorized into two groups: large-artery atherosclerosis (LAAS) or small vessel disease (SVD) subtype of Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification. Each group was divided into two sub-groups based on the functional outcome of acute ischemic stroke, indicated by modified Rankin Scale (mRS) at discharge. Poor functional outcome group was defined as a mRS ? 3 at discharge. Student's t-test or Mann-Whitney U-test were used to compare maximal brachial-ankle PWV (baPWV) values. Results Twenty-four patients whose state was inadequate to assess baPWV or mRS were excluded. There were 38 patients with good functional outcome (mRS < 3) and 38 patients with poor functional outcome (mRS ? 3). The baPWV values were significantly higher in patients with poor outcome (2,070.05 ± 518.37 cm/s) compared with those with good outcome (1,838.63 ± 436.65) (p = 0.039). In patients with SVD subtype, there was a significant difference of baPWV values between groups (2,163.18 ± 412.71 vs. 1,789.80 ± 421.91, p = 0.022), while there was no significant difference of baPWV among patients with LAAS subtype (2,071.76 ± 618.42 vs. 1,878.00 ± 365.35, p = 0.579). Conclusions Arterial stiffness indicated by baPWV is associated with the functional outcome of acute ischemic stroke. This finding suggests that measurement of baPWV predicts functional outcome in patients with stroke especially those whose TOAST classification was confirmed as SVD subtype. PMID:24765608

Lee, Yeong-Bae; Park, Joo-Hwan; Kim, Eunja; Kang, Chang-Ki

2014-01-01

270

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

271

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

PubMed Central

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

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

2007-01-01

272

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

PubMed Central

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

2011-01-01

273

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

PubMed

The tensegrity hypothesis holds that the cytoskeleton is a structure whose shape is stabilized predominantly by the tensile stresses borne by filamentous structures. Accordingly, cell stiffness must increase in proportion with the level of the tensile stress, which is called the prestress. Here we have tested that prediction in adherent human airway smooth muscle (HASM) cells. Traction microscopy was used to measure the distribution of contractile stresses arising at the interface between each cell and its substrate; this distribution is called the traction field. Because the traction field must be balanced by tensile stresses within the cell body, the prestress could be computed. Cell stiffness (G) was measured by oscillatory magnetic twisting cytometry. As the contractile state of the cell was modulated with graded concentrations of relaxing or contracting agonists (isoproterenol or histamine, respectively), the mean prestress ((t)) ranged from 350 to 1,900 Pa. Over that range, cell stiffness increased linearly with the prestress: G (Pa) = 0.18(t) + 92. While this association does not necessarily preclude other interpretations, it is the hallmark of systems that secure shape stability mainly through the prestress. Regardless of mechanism, these data establish a strong association between stiffness of HASM cells and the level of tensile stress within the cytoskeleton. PMID:11832346

Wang, Ning; Toli?-Nørrelykke, Iva Marija; Chen, Jianxin; Mijailovich, Srboljub M; Butler, James P; Fredberg, Jeffrey J; Stamenovi?, Dimitrije

2002-03-01

274

Cardiovascular health and arterial stiffness: the Maine-Syracuse Longitudinal Study.  

PubMed

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 (PWV) 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 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 PWV and pulse pressure. Those with at least five health metrics at ideal levels had significantly lower PWV (9.8 m s(-1)) than those with two or less ideal health metrics (11.7 m s(-1)) (P < 0.001). This finding remained with the addition of demographic and PWV-related variables (P = 0.004). PMID:24384629

Crichton, G E; Elias, M F; Robbins, M A

2014-07-01

275

Mechanical stiffness as an improved single-cell indicator of osteoblastic human mesenchymal stem cell differentiation  

PubMed Central

Although it has been established that cellular stiffness can change as a stem cell differentiates, the precise relationship between cell mechanics and other phenotypic properties remains unclear. Inherent cell heterogeneity and asynchronous differentiation complicate population analysis; therefore, single-cell analysis was employed to determine how changes in cell stiffness correlate with changes in molecular biomarkers during differentiation. Design of a custom gridded tissue culture dish facilitated single-cell comparisons between cell mechanics and other differentiation biomarkers by enabling sequential measurement of cell mechanics and protein biomarker expression at the single cell level. The Young’s modulus of mesenchymal stem cells was shown not only to decrease during chemically-induced osteoblast differentiation, but also to correlate more closely with the day of differentiation than did the relative expression of the traditional osteoblast differentiation markers, bone sialoprotein and osteocalcin. Therefore, cell stiffness, a measurable property of individual cells, may serve as an improved indicator of single-cell osteoblast differentiation compared to traditional biological markers. Revelation of additional osteoblast differentiation indicators, such as cell stiffness, can improve identification and collection of starting cell populations, with applications to mesenchymal stem cell therapies and stem cell-based tissue engineering. PMID:24296276

Bongiorno, Tom; Kazlow, Jacob; Mezencev, Roman; Griffiths, Sarah; Olivares-Navarrete, Rene; McDonald, John F.; Schwartz, Zvi; Boyan, Barbara D.; McDevitt, Todd C.; Sulchek, Todd

2014-01-01

276

Mechanical stiffness as an improved single-cell indicator of osteoblastic human mesenchymal stem cell differentiation.  

PubMed

Although it has been established that cellular stiffness can change as a stem cell differentiates, the precise relationship between cell mechanics and other phenotypic properties remains unclear. Inherent cell heterogeneity and asynchronous differentiation complicate population analysis; therefore, single-cell analysis was employed to determine how changes in cell stiffness correlate with changes in molecular biomarkers during differentiation. Design of a custom gridded tissue culture dish facilitated single-cell comparisons between cell mechanics and other differentiation biomarkers by enabling sequential measurement of cell mechanics and protein biomarker expression at the single cell level. The Young's modulus of mesenchymal stem cells was shown not only to decrease during chemically-induced osteoblast differentiation, but also to correlate more closely with the day of differentiation than did the relative expression of the traditional osteoblast differentiation markers, bone sialoprotein and osteocalcin. Therefore, cell stiffness, a measurable property of individual cells, may serve as an improved indicator of single-cell osteoblast differentiation compared to traditional biological markers. Revelation of additional osteoblast differentiation indicators, such as cell stiffness, can improve identification and collection of starting cell populations, with applications to mesenchymal stem cell therapies and stem cell-based tissue engineering. PMID:24296276

Bongiorno, Tom; Kazlow, Jacob; Mezencev, Roman; Griffiths, Sarah; Olivares-Navarrete, Rene; McDonald, John F; Schwartz, Zvi; Boyan, Barbara D; McDevitt, Todd C; Sulchek, Todd

2014-06-27

277

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

278

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

279

Real-time single-cell response to stiffness  

PubMed Central

Living cells adapt to the stiffness of their environment. However, cell response to stiffness is mainly thought to be initiated by the deformation of adhesion complexes under applied force. In order to determine whether cell response was triggered by stiffness or force, we have developed a unique method allowing us to tune, in real time, the effective stiffness experienced by a single living cell in a uniaxial traction geometry. In these conditions, the rate of traction force buildup dF/dt was adapted to stiffness in less than 0.1 s. This integrated fast response was unambiguously triggered by stiffness, and not by force. It suggests that early cell response could be mechanical in nature. In fact, local force-dependent signaling through adhesion complexes could be triggered and coordinated by the instantaneous cell-scale adaptation of dF/dt to stiffness. Remarkably, the effective stiffness method presented here can be implemented on any mechanical setup. Thus, beyond single-cell mechanosensing, this method should be useful to determine the role of rigidity in many fundamental phenomena such as morphogenesis and development. PMID:20823257

Mitrossilis, Démosthène; Fouchard, Jonathan; Pereira, David; Postic, François; Richert, Alain; Saint-Jean, Michel; Asnacios, Atef

2010-01-01

280

Theoretical and experimental determination of capstan drive stiffness  

Microsoft Academic Search

Cable or metal band capstan drives are used as rotary transmission elements for their very low (nominally zero) backlash and high stiffness properties. Cable drives, in particular, are found in many types of equipment, and to obtain high stiffness, the cable is typically wrapped around the input and output drum in a figure-eight pattern. This paper develops analytical methods for

Jaime Werkmeister; Alexander Slocum

2007-01-01

281

Ankle Strength and Stiffness Predict Range of Motion During  

E-print Network

Ankle Strength and Stiffness Predict Range of Motion During Walking in Older Adults Erica D Persons, 2001) · Studies focusing on lower extremity vulnerability show weakness in the ankle dorsiflexors and lack of flexibility of ankle plantarflexors increase risk of falling. (Hylton, 2003) · Ankle stiffness

New Hampshire, University of

282

SelfScaling Fast Rotations for Stiff and Equality Constrained  

E-print Network

Self­Scaling Fast Rotations for Stiff and Equality Constrained Linear Least Squares Problems Andrew rotations to the QR decomposition for stiff least squares problems. We show that both fast and standard with extremely large weights when equality constrained least squares problems are solved by the weighting method

Park, Haesun

283

Tunable stiffness of electrorheological elastomers by designing mesostructures  

E-print Network

Tunable stiffness of electrorheological elastomers by designing mesostructures Changyong Cao://apl.aip.org/about/rights_and_permissions #12;Tunable stiffness of electrorheological elastomers by designing mesostructures Changyong Cao1 online 22 July 2013) Electrorheological elastomers have broad and important applications. While existing

Zhao, Xuanhe

284

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

285

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

286

Depression of myocardial force and stiffness without change in crossbridge kinetics: effects of volatile anesthetics reproduced by nifedipine.  

PubMed

The authors examined the effects of nifedipine, a sarcolemmal slow Ca2+ channel blocker, on dynamic stiffness and force of rabbit right ventricular trabeculum and papillary muscle in Ba2+ contracture, in an attempt to reproduce the effects of halothane, enflurane, and isoflurane on a similar preparation as reported by Shibata et al. Once barium contracture force was established, muscle length was perturbed with small amplitude sinusoidal oscillations in the frequency range of 0.1-100 Hz. Nifedipine 1 microM was then added to the superfusate and dynamic stiffness was again measured. Additional barium was used to determine restoration of contracture force to and beyond control levels. Nifedipine produced a significant decrease in contracture force and high-frequency stiffness with no effect on the frequency (fmin) at which stiffness amplitude exhibited a minimum (P less than 0.005). Contracture force and stiffness could be restored by adding additional barium to the nifedipine-treated muscles. These results are similar to those reported by Shibata et al. using volatile anesthetics. Since nifedipine, which acts specifically at the sarcolemmal slow Ca2+ channel, affects contracture force and dynamic stiffness in this preparation in a manner similar to the volatile anesthetics, the authors suggest that the anesthetics studied by Shibata et al. may well exert a significant component of their negative inotropic activity via their action on the sarcolemmal slow Ca2+ channel. PMID:2549819

Chung, O Y; Blanck, T J; Berman, M R

1989-09-01

287

Stiffness coupling application to modal synthesis program, users guide  

NASA Technical Reports Server (NTRS)

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

Kuhar, E. J.

1976-01-01

288

Ultra-low co-seismic stiffness of fault rocks at seismogenic (8-11 km) depth  

NASA Astrophysics Data System (ADS)

During the seismic cycle, elastic stiffness limits the amount of elastic strain energy stored in the wall rocks bordering a fault. Elastic stiffness of fault zone rocks is expected to be highly variable during the seismic cycle due to complicated damage and healing processes. In addition to longer-term alteration which may take place during exhumation, it is impossible to assess how well rock stiffness as measured in the laboratory represents in situ, coseismic rock stiffness at seismogenic depths. Here we estimate the in situ, coseismic rock stiffness of fault rocks from the pseudotachylyte-bearing Gole Larghe Fault Zone of the Adamello Batholith, Italian Southern Alps, using aspect ratio measurements of pseudotachylyte injection veins and numerical Displacement Discontinuity Method simulations. Aspect ratios of over 100 pseudotachylyte injection veins which cut across tonalite, cataclasite, or aplite show that maximum vein aperture is linearly related to vein length. To model vein opening, the fault and the injection vein are assumed to be filled with melt that has a fluid pressure P. Consistent with recent results from modeling of melt lubrication we assume that the magnitude of the fluid pressure P is exactly the same as the fault-normal normal stress such that the fault vein approximately maintains constant thickness during slip (i.e. melt extrusion exactly balances melt production). This model assumes that melt is injected into the sidewall without significant fluid overpressure, taking advantage of pre-existing planes of weakness and transiently reduced fault-parallel normal stress in the wake of the earthquake rupture tip. Numerical simulations of injection vein opening due to fluid pressure of frictional melt indicate that the average in situ coseismic stiffness of the fault rocks ranged from 2-15 GPa, about a factor of two less than typical laboratory measurements of the same rocks, and the stiffness of tonalite and cataclasite are markedly different.

Griffith, W. A.; Mitchell, T. M.; Di Toro, G.; Renner, J.

2011-12-01

289

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

290

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

291

Damage detection on sudden stiffness reduction based on discrete wavelet transform.  

PubMed

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

292

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

293

Temporal delimitation of the healing phases via monitoring of fracture callus stiffness in rats.  

PubMed

The healing process consists of at least three phases: inflammatory, repair, and remodeling phase. Because callus stiffness correlates with the healing phases, it is suitable for evaluating the fracture healing process. Our aim was to develop a method which allows determination of callus stiffness in vivo, the healing time and the duration of the repair phase. The right femurs of 16 Wistar rats were osteotomized and stabilized with either more rigid or more flexible external fixation. Fixator deformation was measured using strain gauges during gait analysis. The strains were recalculated as the callus stiffness over the time course of healing, and the healing phases were identified based on stiffness thresholds. Our hypothesis was that stabilization with more flexible external fixation prolongs the repair phase, therefore resulting in an extended healing time. Confirming our hypothesis, the duration of the repair phase (rigid: approximately 15 days, flexible: approximately 41 days) and the healing time (rigid: approximately 27 days, flexible: approximately 62 days) were significantly longer for more flexible external fixation. Our method allows the quantitative detection of differences in the healing time and duration of the repair phase without multiple time-point sacrifices, which reduces the number of animals in experimental studies. PMID:25183200

Wehner, Tim; Gruchenberg, Katharina; Bindl, Ronny; Recknagel, Stefan; Steiner, Malte; Ignatius, Anita; Claes, Lutz

2014-12-01

294

Modeling and analysis of a negative stiffness magnetic suspension vibration isolator with experimental investigations  

NASA Astrophysics Data System (ADS)

This paper presents a negative stiffness magnetic suspension vibration isolator (NSMSVI) using magnetic spring and rubber ligaments. The positive stiffness is obtained by repulsive magnetic spring while the negative stiffness is gained by rubber ligaments. In order to study the vibration isolation performance of the NSMSVI, an analytical expression of the vertical stretch force of the rubber ligament is constructed. Experiments are carried out, which demonstrates that the analytical expression is effective. Then an analytical expression of the vertical stiffness of the rubber ligament is deduced by the derivative of the stretch force of the rubber ligament with respect to the displacement of the inner magnetic ring. Furthermore, the parametric study of the magnetic spring and rubber ligament are carried out. As a case study, the size dimensions of the magnetic spring and rubber ligament are determined. Finally, an NSMSVI table was built to verify the vibration isolation performance of the NSMSVI. The transmissibility curves of the NSMSVI are subsequently calculated and tested by instruments. The experimental results reveal that there is a good consistency between the measured transmissibility and the calculated ones, which proves that the proposed NSMSVI is effective and can realize low-frequency vibration isolation.

Zhu, Yu; Li, Qiang; Xu, Dengfeng; Hu, Chuxiong; Zhang, Ming

2012-09-01

295

Stiffness matrix of manipulators with passive joints: computational aspects 1 Abstract--The paper focuses on stiffness matrix computation  

E-print Network

of a robotic system. To evaluate stiffness properties, several methods can be applied such as Finite Element that are applicable in the general case and allow obtaining the desired matrix either in analytical or numerical form [1] and other authors. Here, the matrix K aggregates the stiffness coefficients of all elastic

Boyer, Edmond

296

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

297

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

298

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

299

Mechanomyogram amplitude correlates with human gastrocnemius medialis muscle and tendon stiffness both before and after acute passive stretching.  

PubMed

The study aimed to assess the level of correlation between muscle-tendon unit (MTU) stiffness and mechanomyogram (MMG) signal amplitude of the human gastrocnemius medialis muscle, both before and after acute passive stretching. The passive torque (Tpass), electrically evoked peak torque (pT) and myotendinous junction displacement were determined at different angles of dorsiflexion (0, 10 and 20 deg), while maximum voluntary isometric torque (Tmax) was assessed only at 0 deg. Measurements were repeated after a bout of passive stretching. From the MMG signal, the root mean square (RMS) and peak to peak (p-p) were calculated. The MTU, muscle and tendon stiffness were determined by ultrasound and Tpass measurements. Before stretching, correlations between MMG RMS and MTU, muscle and tendon stiffness were found (R(2) = 0.22-0.46). After stretching, Tpass, Tmax, pT and MTU, muscle and tendon stiffness decreased by 25 ± 7, 16 ± 2, 9 ± 2, 22 ± 7, 23 ± 8 and 28 ± 5%, respectively (P < 0.05). During voluntary and electrically evoked contractions, MMG p-p decreased by 9 ± 2 and 5 ± 1%, while MMG RMS increased by 48 ± 7 and 50 ± 8%, respectively (P < 0.05). Correlations between MMG RMS and MTU, muscle and tendon stiffness were still present after stretching (R(2) = 0.44-0.60). In conclusion, correlations between MMG RMS and stiffness exist both before and after stretching, suggesting that a slacker MTU leads to larger muscle fibre oscillations. However, care must be taken in using MMG amplitude as an indirect index to estimate stiffness owing to the relatively small R(2) values of the investigated correlations. PMID:24951499

Longo, Stefano; Cè, Emiliano; Rampichini, Susanna; Devoto, Michela; Limonta, Eloisa; Esposito, Fabio

2014-10-01

300

Association of arterial stiffness with single nucleotide polymorphism rs1333049 and metabolic risk factors  

PubMed Central

Background Increased arterial stiffness is a cardiovascular outcome of metabolic syndrome (MetS). The chromosome 9p21 locus has been identified as a major locus for risk of coronary artery disease (CAD). The single nucleotide polymorphism (SNP), rs1333049 on chromosome 9p21.3 has been strongly associated with CAD and myocardial infarction. Increased arterial stiffness could be the link between the 9p21 polymorphism and increased cardiovascular risk. Since the impact of a genetic polymorphism on arterial stiffness especially in Asian populations has not been well defined, we aimed to investigate the association of arterial stiffness with rs 1333049 variant on chromosome 9p21.3 in Thai subjects with and without MetS risk factors. Methods A total of 208 Thai subjects, aged 35–75 years, 135 with and 73 without MetS, according to IDF and NCEP-ATPIII criteria, were included in this study. Aortic-femoral pulse wave velocity (afPWV), brachial-ankle pulse wave velocity (baPWV) and aortic ankle pulse wave velocity (aaPWV) were measured and used as markers of arterial stiffness. The chromosome 9p21.3 locus, represented by the rs 1333049 variant and blood biochemistry were evaluated. Results Arterial stiffness was elevated in subjects with MetS when compared with nonMetS subjects. PWV, especially afPWV increased progressively with increasing number of MetS risk factors (r = 0.322, P <0.001). We also found that the frequency distribution of the rs1333049 genotypes is significantly associated with the afPWV (P <0.05). In multivariate analyses, there was an association between homozygous C allele and afPWV (Odds ratio (OR), 8.16; 95% confidence interval (CI), 1.91 to 34.90; P = 0.005), while the GC genotype was not related to afPWV (OR, 1.79; 95% CI, 0.84 to 3.77; P = 0.129) when compared with the GG genotype. Conclusions Our findings demonstrate for the first time that arterial stiffness is associated with genetic polymorphism in 9p21 and metabolic risk factors in a Thai population. PMID:23787071

2013-01-01

301

Effect of early exercise engagement on arterial stiffness in patients diagnosed with a transient ischaemic attack.  

PubMed

This study investigated the effects of regular exercise participation on common carotid artery stiffness in patients recently diagnosed with transient ischaemic attack (TIA). A total of 21 male and 4 female participants (mean±s.d.; 66±12 years, 1.72±0.07?m, 85.5±12.4?kg), recruited within 2 weeks of TIA diagnosis, completed a risk stratification assessment (including fasting blood glucose, cholesterol), a health history questionnaire and underwent measures of arterial stiffness (compliance and distensibility). Participants were then randomized to either an exercise (EX; 8-week intervention) or a usual-care control (CON) condition. Identical measures were obtained post intervention. Within-subject, repeated measures analysis of variance, with Condition as the between-subject factor (EX and CON), was used to assess measures of arterial stiffness at the baseline and postintervention assessment. Results revealed a significant interaction whereby an increase in compliance (0.71±0.24 vs 0.83±0.28?mm(2)?kPa(-1), P=0.048, partial ?(2)=0.159) and distensibility (15.98±5.95 vs 19.49±6.60 10(-3)?kPa(-1), P=0.023, partial ?(2)=0.204) was observed for EX but not for CON. The present study has demonstrated that engagement in exercise soon after TIA diagnosis leads to improved large artery health. These improvements in vascular health may reduce the risk of an ensuing or recurring cardio- or cerebrovascular event. PMID:24990421

Woolley, B; Stoner, L; Lark, S; Wong, L; Lanford, J; Faulkner, J

2015-02-01

302

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

303

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

304

Serum Osteoprotegerin is Associated with Arterial Stiffness Assessed According to the Cardio-ankle Vascular Index in Hypertensive Patients.  

PubMed

Aim: Arterial stiffness is recognized to be an independent risk factor for cardiovascular morbidity and mortality. Recent studies have found that osteoprotegerin (OPG) is associated with increased pulse wave velocity and may reflect endothelial dysfunction. The aim of this study was to evaluate the relationship between the serum OPG level and arterial stiffness in hypertensive patients using the cardio-ankle vascular index (CAVI). Methods: Fasting blood samples were obtained from 115 hypertensive patients and 52 healthy participants. The CAVI value was derived using the waveform device (CAVI-VaSera VS-1000). The serum OPG levels were measured using a commercially available enzyme-linked immunosorbent assay. A CAVI value of ?9 defined the high arterial stiffness group. Results: Sixty-five hypertensive patients (56.5%) were included in the high arterial stiffness group. Diabetes (p=0.032), smoking (p=0.044), age (p?0.001), systolic blood pressure (p=0.001), diastolic blood pressure (p=0.024), pulse pressure (p=0.046) and the creatinine (p=0.013) and serum OPG (p?0.001) levels were higher in the high arterial stiffness group than in the low arterial stiffness group, while the glomerular filtration rate (p=0.003) was lower in the high arterial stiffness group than in the low arterial stiffness group among the hypertensive patients. The results of the Spearman's rank correlation coefficient test also indicated a strong positive correlation between the OPG and CAVI values (r=0.484, p?0.001) in the hypertensive patients. In addition, a multivariate logistic regression analysis showed that age (odds ratio: 1.136, 95% confidence interval (CI): 1.053-1.225, p=0.001), diastolic blood pressure (odds ratio: 1.108, 95% CI: 1.035-1.187, p=0.003) and the logarithmically transformed OPG level (log-OPG; odds ratio: 3.740, 95% CI: 1.136-12.318, p=0.030) were independent predictors of arterial stiffness in the hypertensive patients. Conclusions: The serum OPG level is positively associated with arterial stiffness in hypertensive patients. PMID:25318352

Lee, Chung-Jen; Wang, Ji-Hung; Chen, Mei-Ling; Yang, Chiu-Fen; Chen, Yu-Chih; Hsu, Bang-Gee

2014-10-15

305

Clinical measurement of arterial stiffness obtained from noninvasive pressure waveforms  

Microsoft Academic Search

Aortic pulse wave velocity (PWV) and augmentation index are independent predictors of adverse cardiovascular events, including mortality. In hypertension and aging, central elastic arteries become stiffer, diastolic pressure decreases, and central systolic and pulse pressures are augmented due to increased PWV and early return of reflected waves to the heart from the periphery. Valuable information on arterial properties such as

Wilmer W. Nichols

2005-01-01

306

Stiffness of Systemic Arteries in Appropriate and Small-for-Gestational-Age Newborn Infants  

Microsoft Academic Search

OBJECTIVE.The purpose of this work was to study the stiffness of systemic arteries in appropriate and small for gestational age newborn infants. The distance between diametrically opposite points of the arterial lumen was measured with a phase locked loop echo tracking system coupled to a B-mode ultrasonic imager. PATIENTS AND METHODS.A cross-sectional study of 51 appropriate for gestation age infants

Akira Mori; Noa Uchida; Akifumi Inomo; Shun-ichiro Izumi

307

Arterial stiffness and enlargement in mild-to-moderate chronic kidney disease  

Microsoft Academic Search

Chronic kidney disease (CKD) is associated with an increased risk of cardiovascular morbidity and mortality. Arterial stiffness and remodeling have been well documented in patients with end-stage renal disease, but little is known about arterial phenotype in CKD patients with moderate reduction in glomerular filtration rate (GFR). In total, 95 patients (58±15 years, mean±s.d.) with CKD and GFR measured by

M Briet; E Bozec; S Laurent; C Fassot; G M London; C Jacquot; M Froissart; P Houillier; P Boutouyrie

2006-01-01

308

Associations between vascular calcification, arterial stiffness and bone mineral density in chronic kidney disease  

Microsoft Academic Search

Background. Vascular calcification (VC) and arterial stiff- ness are major contributors to cardiovascular (CV) disease inchronickidneydisease(CKD).Bothareindependentpre- dictors of CV mortality and are inversely correlated with bone mineral density (BMD). Few studies have addressed the extent of VC in the pre-dialysis CKD population, with associated measurements of BMD and arterial compliance. Methods. We report cross-sectional data on 48 patients with CKD

Nigel D. Toussaint; Kenneth K. Lau; J. Strauss; Kevan R. Polkinghorne; Peter G. Kerr

2008-01-01

309

Study of ultrasound stiffness imaging methods using tissue mimicking phantoms.  

PubMed

A pilot study was carried out to investigate the performance of ultrasound stiffness imaging methods namely Ultrasound Elastography Imaging (UEI) and Acoustic Radiation Force Impulse (ARFI) Imaging. Specifically their potential for characterizing different classes of solid mass lesions was analyzed using agar based tissue mimicking phantoms. Composite tissue mimicking phantom was prepared with embedded inclusions of varying stiffness from 50 kPa to 450 kPa to represent different stages of cancer. Acoustic properties such as sound speed, attenuation coefficient and acoustic impedance were characterized by pulse echo ultrasound test at 5 MHz frequency and they are ranged from (1564 ± 88 to 1671 ± 124 m/s), (0.6915 ± 0.123 to 0.8268 ± 0.755 db cm(-1)MHz(-1)) and (1.61 × 10(6) ± 0.127 to 1.76 × 10(6) ± 0.045 kg m(-2)s(-1)) respectively. The elastic property Young's Modulus of the prepared samples was measured by conducting quasi static uni axial compression test under a strain rate of 0.5mm/min upto 10 % strain, and the values are from 50 kPa to 450 kPa for a variation of agar concentration from 1.7% to 6.6% by weight. The composite phantoms were imaged by Siemens Acuson S2000 (Siemens, Erlangen, Germany) machine using linear array transducer 9L4 at 8 MHz frequency; strain and displacement images were collected by UEI and ARFI. Shear wave velocity 4.43 ± 0.35 m/s was also measured for high modulus contrast (18 dB) inclusion and X.XX m/s was found for all other inclusions. The images were pre processed and parameters such as Contrast Transfer Efficiency and lateral image profile were computed and reported. The results indicate that both ARFI and UEI represent the abnormalities better than conventional US B mode imaging whereas UEI enhances the underlying modulus contrast into improved strain contrast. The results are corroborated with literature and also with clinical patient images. PMID:24083832

Manickam, Kavitha; Machireddy, Ramasubba Reddy; Seshadri, Suresh

2014-02-01

310

Comparison of liver biopsy and transient elastography based on clinical relevance  

PubMed Central

BACKGROUND: Liver stiffness measurement (LSM) by transient elastography has recently been validated for the evaluation of liver fibrosis in chronic liver diseases. The present study focused on cases in which liver biopsy and LSM were discordant. METHODS: Three hundred eighty-six patients with chronic hepatitis C who underwent a liver biopsy between December 2004 and April 2007 were studied. First, the optimal cut-off value of LSM was selected for the determination of cirrhosis based on the receiver operating characteristic curve. Then, the cases in which liver histology and evaluation by LSM were discordant were selected. Laboratory test results such as serum total bilirubin concentration, prothrombin activity, albumin concentration, platelet count and the aspartate aminotransferase to platelet ratio index, together with the presence of esophageal varices, were analyzed. RESULTS: The optimal cut-off value was chosen to be 15.9 kPa for cirrhosis (fibrosis stage [F] 4) determination to maximize the sum of sensitivity (78.9%) and specificity (81.0%). There were 78 discordant cases: 51 patients showed an LSM of 15.9 kPa or higher and a fibrosis stage of F1 to F3 (high LSM group), and 27 patients had an LSM lower than 15.9 kPa and a fibrosis stage of F4 (low LSM group). Esophageal varices were seen in 11 patients in the high LSM group (n=51) and in no patients in the low LSM group (n=27) (P=0.0012). The aspartate aminotransferase to platelet ratio index was significantly higher in the high LSM group (1.49 versus 0.89, P=0.019). Other parameters did not differ significantly. However, platelet count, prothrombin activity and albumin concentration tended to be lower in the high LSM group. CONCLUSIONS: Patients with a high LSM need proper attention for cirrhosis, even if liver biopsy does not reveal cirrhosis. PMID:18818788

Masuzaki, Ryota; Tateishi, Ryosuke; Yoshida, Haruhiko; Goto, Eriko; Sato, Takahisa; Ohki, Takamasa; Goto, Tadashi; Yoshida, Hideo; Kanai, Fumihiko; Sugioka, Yosuke; Ikeda, Hitoshi; Shiina, Shuichiro; Kawabe, Takao; Omata, Masao

2008-01-01

311

Influence of training background on the relationships between plantarflexor intrinsic stiffness and overall musculoskeletal stiffness during hopping  

Microsoft Academic Search

The aim of this study was to characterize the influence of intrinsic musculotendinous and musculoarticular stiffness of plantarflexor\\u000a muscles on (1) the overall musculoskeletal stiffness and (2) the performance during stretch-shortening cycles-type exercise.\\u000a The influence of plyometric training background on these relationships was also analyzed. Musculotendinous (SIMT), passive (K\\u000a \\u000a P\\u000a ) and active (SIMA) musculoarticular stiffnesses were quantified, using quick-release

Giuseppe Rabita; Antoine Couturier; Daniel Lambertz

2008-01-01

312

On the dynamic stiffness of preloaded vibration isolators in the audible frequency range: modeling and experiments.  

PubMed

The nonlinear, preload-dependent dynamic stiffness of a cylindrical vibration isolator is examined via measurements and modeling within an audible frequency range covering 50 to 1000 Hz at various preloads. The stiffness is found to depend strongly on frequency-resulting in peaks and troughs, and on preload-particularly above 500 Hz. The problems of simultaneously modeling the rubber prestrain dependence and its audible short-term response are removed by adopting a nearly incompressible material model, being elastic in dilatation while displaying viscoelasticity in deviation. The latter exhibits a time strain separable relaxation tensor with a single function embodying its time dependence. This function is based on a continuous fractional order derivative model, the main advantage being the minimum number of parameters required to successfully model the rubber properties over a broad structure-borne sound frequency domain, while embodying a continuous distribution of relaxation time. The weak formulations corresponding to the stiffness problem are solved by an updated Lagrangian nonlinear finite-element procedure. The model and measurement results agree strikingly well with static and dynamic measurements throughout the whole frequency domain for the examined preloads. PMID:12703703

Kari, Leif

2003-04-01

313

[Impact of aortic stiffness on central hemodynamics and cardiovascular system].  

PubMed

Arterial stiffness increases as a result of degenerative processes accelerated by aging and many risk factors, namely arterial hypertension. Basic clinical examination reveals increased pulse pressure as its hemodynamic manifestation. The most serious consequence of increased vascular stiffness, which cannot be revealed by clinical examination, is a change of central hemodynamics leading to increased load of left ventricle, left ventricular hypertrophy, diastolic dysfunction and to overall increase of cardiovascular risk. This review aimed to point at some patophysiological mechanisms taking part in the development of vascular stiffness, vascular remodeling and hemodynamic consequences of these changes. This work also gives an overview of noninvasive examination methods and their characteristics enabling to evaluate the local, regional and systemic arterial stiffness and central pulse wave analysis and their meaning for central hemodynamics and heart workload. PMID:23808736

Bulas, J; Poto?árová, M; Filková, M; Simková, A; Murín, J

2013-06-01

314

HETEROGENEOUS MULTISCALE METHODS FOR STIFF ORDINARY DIFFERENTIAL EQUATIONS  

E-print Network

HETEROGENEOUS MULTISCALE METHODS FOR STIFF ORDINARY DIFFERENTIAL EQUATIONS BJORN ENGQUIST- ical approximation of multiscale problems. It is here developed for ordinary differential equations are presented together with numerical tests. The analysis covers some existing methods and the new algorithms

Soatto, Stefano

315

STIFFNESS MAPPING OF PLANAR COMPLIANT PARALLEL MECHANISMS IN A  

E-print Network

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

Florida, University of

316

Stiffness mapping of compliant parallel mechanisms in a serial arrangement  

E-print Network

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

Florida, University of

317

Effects of bonding stiffness on thermal stresses in sandwich panels  

NASA Astrophysics Data System (ADS)

Sandwich panels made of thin skins and a lightweight core expand and/or bow when subjected to temperature changes. The significance of induced thermal stresses in the panels depends on material properties. The effects of bonding layers on these stresses were not investigated in available works on the structural analysis of sandwich panels. This paper presents elasticity solutions for thermal stresses in sandwich panels with interlayer slip. The effects of finite bonding stiffnesses on the structural behavior of the panels are investigated. The numerical results show that the bonding stiffness, up to a certain level, has a strong effect on panel structural response. The answer to what constitutes perfect bonding is best answered in terms of the ratio of the core stiffness to the bonding stiffness. A heat chamber is designed and used to test sandwich specimens under different temperature changes. The experimental values for normal stresses in the skins are in good agreement with the present theory.

Hussein, R.; Fazio, P.; Ha, K.

1992-10-01

318

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

319

Knee joint stiffness and function following total knee arthroplasty   

E-print Network

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

Lane, Judith

2010-01-01

320

Investigation of strained deformed state of variable stiffness rod.  

PubMed

An equation for bending of a weighable rod with variable transversal stiffness was proposed. On the basis of this analyses the conclusions were drawn about the influence of parameters of construction on values of maximum sag and maximum bending moment. The recommendations for the usage of the simplified model were done. The example of the construction with given parameters for calculation of stiffness and strength according to the represented mathematical models was considered. PMID:25133087

Tsarenko, Sergey; Ulitin, Gennady

2014-01-01

321

Transverse Cracking and Stiffness Reduction in Composite Laminates  

Microsoft Academic Search

A systematic classification of the effects of transverse cracking on the stress-strain response of composite laminates is presented. Stiffness reductions resulting from transverse cracking in glass\\/epoxy and graphite\\/epoxy laminates from crack initiation to crack saturation are predicted using the stiffness-damage relationships developed by the author in a previous work. Good agreement with the experimental results is found. An assessment of

Ramesh Talreja

1985-01-01

322

The initial torsional stiffness of shells with interior webs  

NASA Technical Reports Server (NTRS)

A method of calculating the stresses and torsional stiffness of thin shells with interior webs is summarized. Comparisons between experimental and calculated results are given for 3 duralumin beams, 5 stainless steel beams and 2 duralumin wings. It is concluded that if the theoretical stiffness is multiplied by a correction factor of 0.9, experimental values may be expected to check calculated values within about 10 percent.

Kuhn, Paul

1935-01-01

323

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

324

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

325

Effect of boot shaft stiffness on stability joint energy and muscular co-contraction during walking on uneven surface.  

PubMed

Increased boot shaft stiffness may have a noticeable impact on the range of motion of the ankle joint. Therefore, the ability of the ankle joint to generate power for propulsion might be impaired. This might result in compensatory changes at the knee and hip joint. Besides, adaptability of the subtalar joint to uneven surface might be reduced, which could in turn affect stability. The aim of the study was therefore to investigate the influence of boot shaft stiffness on biomechanical gait parameters. Fifteen healthy young adults walked over coarse gravel wearing two different hiking boots that differed by 50% in passive shaft stiffness. Leg kinematics, kinetics and electromyography were measured. Gait velocity and indicators for stability were not different when walking with the hard and soft boot shaft over the gravel surface. However, the hard boot shaft decreased the ankle range of motion as well as the eccentric energy absorbed at the ankle joint. As a consequence, compensatory changes at the knee joint were observed. Co-contraction was increased, and greater eccentric energy was absorbed. Therefore, the efficiency of gait with hard boots might be decreased and joint loading at the knee might be increased, which might cause early fatigue of knee muscles during walking or hiking. The results of this study suggest that stiffness and blocking of joint motion at the ankle should not be equated with safety. A trade-off between lateral stiffness and free natural motion of the ankle joint complex might be preferable. PMID:20541206

Böhm, Harald; Hösl, Matthias

2010-09-17

326

Absence of cardiotrophin 1 is associated with decreased age-dependent arterial stiffness and increased longevity in mice.  

PubMed

Cardiotrophin 1 (CT-1), an interleukin 6 family member, promotes fibrosis and arterial stiffness. We hypothesized that the absence of CT-1 influences arterial fibrosis and stiffness, senescence, and life span. In senescent 29-month-old mice, vascular function was analyzed by echotracking device. Arterial histomorphology, senescence, metabolic, inflammatory, and oxidative stress parameters were measured by immunohistochemistry, reverse transcription polymerase chain reaction, Western blot, and ELISA. Survival rate of wild-type and CT-1-null mice was studied. Vascular smooth muscle cells were treated with CT-1 (10(-9) mol/L) for 15 days to analyze senescence. The wall stress-incremental elastic modulus curve of old CT-1-null mice was shifted rightward as compared with wild-type mice, indicating decreased arterial stiffness. Media thickness and wall fibrosis were lower in CT-1-null mice. CT-1-null mice showed decreased levels of inflammatory, apoptotic, and senescence pathways, whereas telomere-linked proteins, DNA repair proteins, and antioxidant enzyme activities were increased. CT-1-null mice displayed a 5-month increased median longevity compared with wild-type mice. In vascular smooth muscle cells, chronic CT-1 stimulation upregulated apoptotic and senescence markers and downregulated telomere-linked proteins. The absence of CT-1 is associated with decreased arterial fibrosis, stiffness, and senescence and increased longevity in mice likely through downregulating apoptotic, senescence, and inflammatory pathways. CT-1 may be a major regulator of arterial stiffness with a major impact on the aging process. PMID:23172930

López-Andrés, Natalia; Calvier, Laurent; Labat, Carlos; Fay, Renaud; Díez, Javier; Benetos, Athanase; Zannad, Faiez; Lacolley, Patrick; Rossignol, Patrick

2013-01-01

327

Tension and stiffness of the hard sphere crystal-fluid interface  

E-print Network

A combination of fundamental measure density functional theory and Monte Carlo computer simulation is used to determine the orientation-resolved interfacial tension and stiffness for the equilibrium hard-sphere crystal-fluid interface. Microscopic density functional theory is in quantitative agreement with simulations and predicts a tension of 0.66 kT/\\sigma^2 with a small anisotropy of about 0.025 kT and stiffnesses with e.g. 0.53 kT/\\sigma^2 for the (001) orientation and 1.03 kT/\\sigma^2 for the (111) orientation. Here kT is denoting the thermal energy and \\sigma the hard sphere diameter. We compare our results with existing experimental findings.

Andreas Härtel; Martin Oettel; Roberto E. Rozas; Stefan U. Egelhaaf; Jürgen Horbach; Hartmut Löwen

2012-03-13

328

A model for prediction of bone stiffness using a mechanical approach of composite materials.  

PubMed

A model to predict the bone stiffness is presented in this paper. The objective is to obtain a description of bone stiffness of a representative elementary volume (REV) based on a small set of physical parameters. The main idea is to use measurable information related to the orientation and the density of a basic elementary submicrostructure (ESMS). This ESMS is the first arrangement of the basic components. A simple rule-of-mixtures approach is used to provide the elastic properties for the ESMS. The basic properties are dependent on the volume fraction of the mineralized phase. The orientation and the density of the ESMS is described by a tensor and a scalar, respectively. The model is used to obtain the elastic properties of both the cortical and trabecular bones. Data from femoral bone are used to verify this approach. PMID:17655470

Perreux, Dominique M; Johnson, W Steven

2007-08-01

329

Nucleation and Decay Initiation Are the Stiffness-Sensitive Phases of Focal Adhesion Maturation  

PubMed Central

A cell plated on a two-dimensional substrate forms adhesions with that surface. These adhesions, which consist of aggregates of various proteins, are thought to be important in mechanosensation, the process by which the cell senses and responds to the mechanical properties of the substrate (e.g., stiffness). On the basis of experimental measurements, we model these proteins as idealized molecules that can bind to the substrate in a strain-dependent manner and can undergo a force-dependent state transition. The model forms molecular aggregates that are similar to adhesions. Substrate stiffness affects whether a simulated adhesion is initially formed and how long it grows, but not how that adhesion grows or shrinks. Our own experimental tests support these predictions, suggesting that the mechanosensitivity of adhesions is an emergent property of a simple molecular-mechanical system. PMID:22208190

Walcott, Sam; Kim, Dong-Hwee; Wirtz, Denis; Sun, Sean X.

2011-01-01

330

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

331

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

PubMed Central

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

Wang, Zhijie; Chesler, Naomi C.

2011-01-01

332

An experimental study on the stiffness of size-isolated microbubbles using atomic force microscopy  

NASA Astrophysics Data System (ADS)

In order to fully assess contrast-enhanced acoustic bioeffects in diagnostic and therapeutic ultrasound, the mechanical properties of microbubbles need to be taken into account. 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, phospholipid-coated microbubbles (diameters between 4-6 and 6-8 ?m). The stiffness was found to lie between 4 and 22 mN/m and to decrease exponentially with microbubble size within the diameter range investigated. No cantilever spring constant effect was noted 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 in order to accurately predict their acoustic behavior. The findings provided useful insights to control 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 the oscillating microbubbles.

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

2012-11-01

333

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

334

Role of cellular tone and microenvironmental conditions on cytoskeleton stiffness assessed by tensegrity model  

NASA Astrophysics Data System (ADS)

We have tried to understand the role of cellular tone (or internal tension mediated by actin filaments) and interactions with the microenvironment on cellular stiffness. For this purpose, we compared the apparent elasticity modulus of a 30-element tensegrity structure with cytoskeleton stiffness measured in subconfluent and confluent adherent cells by magnetocytometry, assessing the effect of changing cellular tone by treatment with cytochalasin D. Intracellular and extracellular mechanical interactions were analyzed on the basis of the non-dimensional relationships between the apparent elasticity modulus of the tensegrity structure normalized by Young's modulus of the elastic element versus: (i) element size, (ii) internal tension, and (iii) number of spatially fixed nodes, for small deformation conditions. Theoretical results and rigidity measurements in adherent cells consistently showed that higher cellular tone and stronger interdependencies with cellular environment tend to increase cytoskeleton stiffness. Visualization of the actin lattice before and after depolymerization by cytochalasin D tended to confirm the geometrical and mechanical assumptions supported by analysis of the present model.

Wendling, S.; Planus, E.; Laurent, V. M.; Barbe, L.; Mary, A.; Oddou, C.; Isabey, D.

2000-01-01

335

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.

336

Piezoelectric actuator based on stiffness control and stroke amplification for large lateral actuation  

Microsoft Academic Search

We present a piezoelectric actuator using stiffness control and stroke amplification mechanism in order to make large lateral displacement. In this work, we suggest stiffness control approach that generates lateral displacement by increasing the vertical stiffness and reducing the lateral stiffness using additional structure. In addition, an additional structure of a serpentine spring amplifies the lateral displacement like leverage structure.

Young Ho Seo; Doo-Sun Choi; Joon-Hyung Lee; Taik-Min Lee; Tae-Jin Je; Kyung-Hyun Whang

2005-01-01

337

Fore-and-aft stiffness and damping characteristics of 30 x 11.5-14.5, Type VIII, bias-ply and radial-belted aircraft tires  

NASA Technical Reports Server (NTRS)

Measurements of footprint geometrical properties and fore and aft stiffness and damping characteristics were obtained on 30 x 11.5-14.5 bias-ply and radial-belted aircraft tires. Significant differences in stiffness and damping characteristics were found between the two design types. The results show that footprint aspect ratio effects may interfere with the improved hydroplaning potential associated with the radial-belted tire operating at higher inflation pressures.

Lopez, Mercedes C.; Davis, Pamela A.; Yeaton, Robert B.; Vogler, William A.

1988-01-01

338

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

339

Gender Differences in Leg Stiffness and Stiffness Recruitment Strategy During Two-Legged Hopping  

PubMed Central

The authors compared leg stiffness (KVERT), muscle activation, and joint movement patterns between 11 men and 10 women during hopping. Physically active and healthy men and women performed continuous 2-legged hopping at their preferred rate and at 3.0 Hz. Compared with men, women demonstrated decreased KVERT; however, after the authors normalized for body mass, gender differences in KVERT were eliminated. In comparison with men, women also demonstrated increased quadriceps and soleus activity, as well as greater quadriceps-to-hamstrings coactivation ratios. There were no significant gender differences for joint movement patterns (p > .05). The relationship between the observed gender differences in muscle recruitment and the increased risk of anterior cruciate ligament injury in women requires further study. PMID:15730945

Padua, Darin A.; Arnold, Brent L.; Carcia, Christopher R.; Granata, Kevin P.

2006-01-01

340

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...

341

Collagen crosslinking does not dictate stiffness in a transgenic mouse model of skeletal muscle fibrosis.  

PubMed

Skeletal muscle fibrosis is characterized by increases in tissue stiffness and collagen content. However, a very weak correlation exists between collagen content and stiffness in skeletal muscle. Recently, it has been hypothesized that collagen crosslinking explains tissue stiffness in fibrotic skeletal muscle. Therefore, we addressed this hypothesis by correlating tissue stiffness with lysyl-pyridinoline, hydroxylysyl-pyridinoline, and pentosidine collagen crosslinks. Stepwise regression revealed that, separate or together, collagen crosslinks did not correlate with tissue stiffness. Our result demonstrates that increased tissue stiffness in skeletal muscle fibrosis is not simply explained by increased collagen crosslinks and/or collagen crosslink density. We suggest that collagen organization may affect tissue stiffness. PMID:25529136

Chapman, Mark A; Pichika, Rajeswari; Lieber, Richard L

2015-01-21

342

Substrate Stiffness Regulates Filopodial Activities in Lung Cancer Cells  

PubMed Central

Microenvironment stiffening plays a crucial role in tumorigenesis. While filopodia are generally thought to be one of the cellular mechanosensors for probing environmental stiffness, the effects of environmental stiffness on filopodial activities of cancer cells remain unclear. In this work, we investigated the filopodial activities of human lung adenocarcinoma cells CL1-5 cultured on substrates of tunable stiffness using a novel platform. The platform consists of an optical system called structured illumination nano-profilometry, which allows time-lapsed visualization of filopodial activities without fluorescence labeling. The culturing substrates were composed of polyvinyl chloride mixed with an environmentally friendly plasticizer to yield Young's modulus ranging from 20 to 60 kPa. Cell viability studies showed that the viability of cells cultured on the substrates was similar to those cultured on commonly used elastomers such as polydimethylsiloxane. Time-lapsed live cell images were acquired and the filopodial activities in response to substrates with varying degrees of stiffness were analyzed. Statistical analyses revealed that lung cancer cells cultured on softer substrates appeared to have longer filopodia, higher filopodial densities with respect to the cellular perimeter, and slower filopodial retraction rates. Nonetheless, the temporal analysis of filopodial activities revealed that whether a filopodium decides to extend or retract is purely a stochastic process without dependency on substrate stiffness. The discrepancy of the filopodial activities between lung cancer cells cultured on substrates with different degrees of stiffness vanished when the myosin II activities were inhibited by treating the cells with blebbistatin, which suggests that the filopodial activities are closely modulated by the adhesion strength of the cells. Our data quantitatively relate filopodial activities of lung cancer cells with environmental stiffness and should shed light on the understanding and treatment of cancer progression and metastasis. PMID:24587021

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

2014-01-01

343

Identification of intrinsic and reflexive contributions to low-back stiffness: medium-term reliability and construct validity.  

PubMed

This study aimed at testing the reliability and construct validity of a trunk perturbation protocol (TPP) that estimates the intrinsic and reflexive contributions to low-back stiffness. The TPP consists of a series of pseudorandom position-controlled trunk perturbations in an apparatus measuring forces and displacements at the harness surrounding the thorax. Intrinsic and reflexive contributions to low-back stiffness were estimated using a system identification procedure, leading to 12 parameters. Study 1 methods (reliability): 30 subjects performed five 75-s trials, on each of two separate days (eight weeks apart). Reliability was assessed using the generalizability theory, which allowed computing indexes of dependability (?, analogous to intraclass correlation coefficient) and standard errors of measurement (SEM). Study 2 methods (validity): 20 healthy subjects performed three 75-s trials for each of five experimental conditions assumed to provide different lumbar stiffness; testing the construct validity of the TPP using four conditions with different lumbar belt designs and one control condition without. Study 1 results (reliability): Learning was seen between the first and following trials. Consequently, reliability analyses were performed without the first trial. Simulations showed that averaging the scores of three trials can lead to acceptable reliability results for some TPP parameters. Study 2 results (validity): All lumbar belt designs increased low-back intrinsic stiffness, while only some of them decreased reflex stiffness, which support the construct validity of the TPP. Overall, these findings support the use of the TPP to test the effect of rehabilitation or between-groups differences with regards to trunk stiffness. PMID:25529140

Larivière, Christian; Ludvig, Daniel; Kearney, Robert; Mecheri, Hakim; Caron, Jean-Maxime; Preuss, Richard

2015-01-21

344

Relation of the aortic stiffness with the GRACE risk score in patients with the non ST-segment elevation myocardial infarction  

PubMed Central

Background: Current guidelines recommend clinical risk scoring systems for the patients diagnosed and determinated treatment strategy with in Non-ST-elevation elevation myocardial infarction (NSTEMI). Previous studies demonstrated association between aortic elasticity properties, stiffness and severity CAD. However, the associations between Aortic stiffness, elasticity properties and clinical risk scores have not been investigated. In the present study we have evaluated the relation between the Global Registry of Acute Coronary Events (GRACE) risk score and aortic stiffness in patients with NSTEMI. Method: We prospectively analyzed 87 consecutive patients with NSTEMI. Aortic elastic parameter and stiffness parameter were calculated from the echocardiographically derived thoracic aortic diameters (mm/m2), and the measurement of pulse pressure obtained by cuff sphygmomanometry. We have categorized the patients in to two groups as low ((n = 45) (GRACE risk score ? 140)) and high ((n = 42) (GRACE risk score > 140)) risk group according to GRACE risk score and compare the both groups. Results: Table 1 shows baseline characteristics of patients. Our study showed that Aortic strain was significantly low (3.5 ± 1.4, 7.9 ± 2.3 respectively, p < 0.001) and aortic stiffness index was significantly high (3.9 ± 0.38; 3 ± 0.35, respectively, p < 0.001) in the high risk group values compared to those with low risk group. The aortic stiffness index was the only independent predictor of GRACE risk score (OR: 119.390; 95% CI: 2.925-4872.8; p = 0.011) in multivariate analysis. Conclusion: We found a significant correlation between aortic stiffness, impaired elasticity and GRACE risk score. Aortic stiffness index was the only independent variable of the high GRACE risk score. The inclusion of aortic stiffness into the GRACE risk score could allow improved risk classification of patients with ACS at admission and this may be important in the diagnosis, follow up and treatment of the patients. PMID:25356178

Omer, Gedikli; Gokhan, Aksan; Adem, Uzun; Sabri, Demircan; Korhan, Soylu

2014-01-01

345

Analysis and design of variable stiffness composite cylinders  

NASA Astrophysics Data System (ADS)

An investigation of the possible performance improvements of thin circular cylindrical shells through the use of the variable stiffness concept is presented. The variable stiffness concept implies that the stiffness parameters change spatially throughout the structure. This situation is achieved mainly through the use of curvilinear fibers within a fiber-reinforced composite laminate. The governing static equilibrium equations include sufficient detail to correctly model several types of nonlinearity, including the formation of a nonlinear shell boundary layer as well as the Brazier effect due to nonlinear bending of long cylinders. Four distinct cases of loading and stiffness variation are chosen to investigate. The initial investigation deals cylindrical shells in which all quantities are constant around the circumference of the cylinder. This axisymmetric case includes a stiffness variation exclusively in the axial direction, and the only pertinent loading scenarios include constant loads of axial compression, pressure, and torsion. The results for these cases indicate that little improvement over traditional laminates exists through the use of curvilinear fibers. The second problem involves arbitrary loading of a cylinder with a stiffness variation only in the circumferential direction. The problem takes the form of an analysis of a cross-section for a short cylinder segment. It is found that the most significant improvements in load-carrying capability exist for loads that also vary around the circumference of the shell, namely bending and shear forces. The stiffness variation of the optimal designs contribute to the increased performance in two ways: lowering the stresses in the critical areas through redistribution; and providing a relatively stiff region that alters the buckling behavior of the structure. These results led to an in-depth optimization study involving weight optimization of a fuselage structure subjected to typical design constraints. It is found that standard variable stiffness designs a offer the added advantage of tailorability of distinct regions of the structure that experience drastically different loading conditions. The last two problems work involve the nonlinear phenomenon of long tubes under bending. The dominating influence for long cylinders under bending is the ovalization of the cross-section. Possible improvement of the critical buckling moments for these structures is investigated using either a circumferential or axial stiffness variation. For the circumferential case involving infinite length cylinders, slight improvements can be observed by designing structures that resist the cross-sectional deformation yet do not detract from the buckling resistance at the critical location. The results also indicate that buckling behavior is extremely dependent on cylinder length. For finite length cylinders contain an axial stiffness variation, the only mechanism that exhibits improved response are those that effectively shorten the length of the cylinder. The use of curvilinear fibers was not able to achieve this effect in sufficient degree to resist the deformation, but ring stiffeners produced the desired response. Thus the variable stiffness concept is most effective at improving the bending response of long cylinders through the use of a circumferential stiffness variation. (Abstract shortened by UMI.)

Tatting, Brian Frederick

346

FIDAP capabilities for solving problems with stiff chemistry  

SciTech Connect

In support of the Motorola CRADA, the capabilities of the computational fluid dynamics code FIDAP (Fluid Dynamics International) for simulating problems involving fluid flow, heat transport, and chemical reactions have been assessed and enhanced as needed for semiconductor-processing applications (e.g. chemical vapor deposition). A novel method of treating surface chemical species that uses only pre-existing FIDAP commands is described and illustrated with test problems. A full-Jacobian treatment of the chemical reaction rate expressions during formation of the stiffness matrix has been implemented in FIDAP for both the Arrhenius-parameter and user-subroutine methods of specifying chemical reactions, where the Jacobian terms can be calculated analytically or numerically. This formulation is needed to obtain convergence when reaction rates become large compared to transport rates (stiff chemistry). Several test problems are analyzed, and in all cases this approach yields good convergence behavior, even for extremely stiff fluid-phase and surface reactions. A stiff segregated algorithm has been developed and implemented in FIDAP. Analysis of test problems indicates that this algorithm yields improved convergence behavior compared with the original segregated algorithm. This improved behavior enables segregated techniques to be applied to problems with stiff chemistry, as required for large three-dimensional multi-species problems.

Torczynski, J.R. [Sandia National Labs., Albuquerque, NM (United States). Energetic and Multiphase Processes Dept.; Baer, T.A. [Gram, Inc., Albuquerque, NM (United States)

1996-09-01

347

Control of the stiffness of robotic appendages using dielectric elastomers  

NASA Astrophysics Data System (ADS)

A new robotic leg design is presented that utilizes dielectric elastomers (3M VHB 4910) to rapidly control stiffness changes for enhanced mobility and agility of a field demonstrated hexapod robot. It has been shown that stiffness changes of electro-active membranes made of dielectric elastomers can overcome challenges with other polymer materials that use heat to create modulus and stiffness changes. Applied electric fields eliminate issues with thermal transport rates and thermo-mechanical delaminatation. The dielectric elastomer is characterized uniaxially to understand its hyperelastic and viscoelastic properties. The uniaxial data is fit to a hyperelastic and viscoelastic finite deformation model. The material is then pre-stretched biaxially to stretch ratios ranging from 200%, 300% and 400%. A set of electro-mechanical transverse load experiments are then utilized to obtain up to 92% reduction in stiffness that is controlled by an electric field. The results are compared to a finite deformation membrane finite element model to understand and improve field driven stiffness changes for real-time robotic applications.

Morton, Jeffrey

348

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

PubMed

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

Maquirriain, J; Kokalj, A

2014-03-01

349

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

NASA Technical Reports Server (NTRS)

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

Seale, Michael D.; Madaras, Eric I.

2000-01-01

350

Preliminary study on the effect of stiffness on lamb wave propagation in bovine corneas.  

PubMed

The viscoelastic properties of human cornea could provide valuable information for various clinical applications. Particularly, it will be helpful to achieve a patient-specific biomechanical optimization in LASIK refractive surgery, early detection of corneal ecstatic disease or improved accuracy of intraocular pressure (IOP) measurement. However, there are few techniques that are capable of accurately assessing the corneal elasticity in situ in a nondestructive fashion. In order to develop a quantitative method for assessing both elasticity and viscosity of the cornea, we use ultrasound radiation force to excite Lamb waves in cornea, and a pulse echo transducer to track the tissue vibration. The fresh postmortem bovine eyes were treated via collagen cross-linking to make the cornea stiff. The effect of stiffness was studied by comparing the propagation of Lamb waves in normal and treated corneas. It was found that the waveform of generated Lamb waves changed significantly due to the increase in higher modes in treated corneas. This result indicated that the generated waveform was a complex of multiple harmonics and the varied stiffness will affect the energy distribution over different components. Therefore, it is important for assessing the viscoelastic properties of the cornea to know the components of Lamb wave and calculate the phase velocity appropriately. PMID:24109889

Zhang, Xin-Yu; Yin, Yin; Guo, Yan-Rong; Diao, Xian-Fen; Chen, Xin

2013-01-01

351

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

PubMed Central

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

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

2013-01-01

352

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

SciTech Connect

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

Pratt, Jon R.; Shaw, Gordon A. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Kumanchik, Lee [Department of Mechanical Engineering, University of Florida, Gainesville, Florida 32611 (United States); Burnham, Nancy A. [Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609-2280 (United States)

2010-02-15

353

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

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

354

Longitudinal perspective on the conundrum of central arterial stiffness, blood pressure, and aging.  

PubMed

The age-associated increase in arterial stiffness has long been considered to parallel or to cause the age-associated increase in blood pressure (BP). Yet, the rates at which pulse wave velocity (PWV), a measure of arterial stiffness, and BP trajectories change over time within individuals who differ by age and sex have not been assessed and compared. This study determined the evolution of BP and aortic PWV trajectories during a 9.4-year follow-up in >4000 community-dwelling men and women of 20 to 100 years of age at entry into the SardiNIA Study. Linear mixed effects model analyses revealed that PWV accelerates with time during the observation period, at about the same rate over the entire age range in both men and women. In men, the longitudinal rate at which BP changed over time, however, did not generally parallel that of PWV acceleration: at ages>40 years the rates of change in systolic BP (SBP) and pulse pressure (PP) increase plateaued and then declined so that SBP, itself, also declined at older ages, whereas PP plateaued. In women, SBP, diastolic BP, and mean BP increased at constant rates across all ages, producing an increasing rate of increase in PP. Therefore, increased aortic stiffness is implicated in the age-associated increase in SBP and PP. These findings indicate that PWV is not a surrogate for BP and that arterial properties other than arterial wall stiffness that vary by age and sex also modulate the BP trajectories during aging and lead to the dissociation of PWV, PP, and SBP trajectories in men. PMID:25225210

Scuteri, Angelo; Morrell, Christopher H; Orrù, Marco; Strait, James B; Tarasov, Kirill V; Ferreli, Liana Anna Pina; Loi, Francesco; Pilia, Maria Grazia; Delitala, Alessandro; Spurgeon, Harold; Najjar, Samer S; AlGhatrif, Majd; Lakatta, Edward G

2014-12-01

355

Transforming potential and matrix stiffness co-regulate confinement sensitivity of tumor cell migration  

PubMed Central

It is now well established that tumor cell invasion through tissue is strongly regulated by the microstructural and mechanical properties of the extracellular matrix (ECM). However, it remains unclear how these physical microenvironmental inputs are jointly processed with oncogenic lesions to drive invasion. In this study, we address this open question by combining a microfabricated polyacrylamide channel (?PAC) platform that enables independent control of ECM stiffness and confinement with an isogenically-matched breast tumor progression series in which the oncogenes ErbB2 and 14-3-3? are overexpressed independently or in tandem. We find that increasing channel confinement and overexpressing ErbB2 both promote cell migration to a similar degree when other parameters are kept constant. In contrast, 14-3-3? overexpression slows migration speed, and does so in a fashion that dwarfs effects of ECM confinement and stiffness. We also find that ECM stiffness dramatically enhances cell motility when combined with ErbB2 overexpression, demonstrating that biophysical cues and cell-intrinsic parameters promote cell invasion in an integrative manner. Morphometric analysis of cells inside the ?PAC platform reveals that the rapid cell migration induced by narrow channels and ErbB2 overexpression both are accompanied by increased cell polarization. Disruption of this polarization by pharmacological inhibition of Rac GTPase phenocopies 14-3-3? overexpression by reducing cell polarization and slowing migration. By systematically measuring migration speed as a function of matrix stiffness and confinement, we also quantify for the first time the sensitivity of migration speed to microchannel properties and transforming potential. These results demonstrate that oncogenic lesions and ECM biophysical properties can synergistically interact to drive invasive migration, and that both inputs may act through common molecular mechanisms to enhance migration speed. PMID:23832051

Pathak, Amit

2013-01-01

356

Effect of heat treatment on stiffness and damping of SiC/Ti-15-3  

NASA Technical Reports Server (NTRS)

The effect of heat treatment on material properties of SiC/Ti-15-3 was measured by vibration tests. Heat treatment changes the microstructure, which was found to stiffen the matrix and reduce its damping capacity. Test results indicate how these changes in the matrix affect the corresponding properties of the composite. Measurements show that heat treatment affects damping properties of the composite to a greater extent than stiffness properties. The extent of change in mechanical properties is shown to depend on heat treatment temperature and exposure time.

Grady, Joseph E.; Lerch, Bradley A.

1992-01-01

357

Quantifying molecular stiffness and interaction with lateral force microscopy.  

PubMed

The spatial resolution of atomic force microscopy (AFM) can be drastically increased by terminating the tip with a single carbon monoxide (CO) molecule. However, the CO molecule is not stiff, and lateral forces, such as those around the sides of molecules, distort images. This issue begs a larger question of how AFM can probe structures that are laterally weak. Lateral force microscopy (LFM) can probe lateral stiffnesses that are not accessible to normal-force AFM, resulting in higher spatial resolution. With LFM, we determined the torsional spring constant of a CO-terminated tip molecule to be 0.24 newtons per meter. This value is less than that of a surface molecule and an example of a system whose stiffness is a product not only of bonding partners but also local environment. PMID:24505131

Weymouth, Alfred John; Hofmann, Thomas; Giessibl, Franz J

2014-03-01

358

Comparative study of methods to calibrate the stiffness of a single-beam gradient-force optical tweezers over various laser trapping powers.  

PubMed

Optical tweezers have become an important instrument in force measurements associated with various physical, biological, and biophysical phenomena. Quantitative use of optical tweezers relies on accurate calibration of the stiffness of the optical trap. Using the same optical tweezers platform operating at 1064 nm and beads with two different diameters, we present a comparative study of viscous drag force, equipartition theorem, Boltzmann statistics, and power spectral density (PSD) as methods in calibrating the stiffness of a single beam gradient force optical trap at trapping laser powers in the range of 0.05 to 1.38 W at the focal plane. The equipartition theorem and Boltzmann statistic methods demonstrate a linear stiffness with trapping laser powers up to 355 mW, when used in conjunction with video position sensing means. The PSD of a trapped particle's Brownian motion or measurements of the particle displacement against known viscous drag forces can be reliably used for stiffness calibration of an optical trap over a greater range of trapping laser powers. Viscous drag stiffness calibration method produces results relevant to applications where trapped particle undergoes large displacements, and at a given position sensing resolution, can be used for stiffness calibration at higher trapping laser powers than the PSD method. PMID:25375348

Sarshar, Mohammad; Wong, Winson T; Anvari, Bahman

2014-11-01

359

Comparative study of methods to calibrate the stiffness of a single-beam gradient-force optical tweezers over various laser trapping powers  

NASA Astrophysics Data System (ADS)

Optical tweezers have become an important instrument in force measurements associated with various physical, biological, and biophysical phenomena. Quantitative use of optical tweezers relies on accurate calibration of the stiffness of the optical trap. Using the same optical tweezers platform operating at 1064 nm and beads with two different diameters, we present a comparative study of viscous drag force, equipartition theorem, Boltzmann statistics, and power spectral density (PSD) as methods in calibrating the stiffness of a single beam gradient force optical trap at trapping laser powers in the range of 0.05 to 1.38 W at the focal plane. The equipartition theorem and Boltzmann statistic methods demonstrate a linear stiffness with trapping laser powers up to 355 mW, when used in conjunction with video position sensing means. The PSD of a trapped particle's Brownian motion or measurements of the particle displacement against known viscous drag forces can be reliably used for stiffness calibration of an optical trap over a greater range of trapping laser powers. Viscous drag stiffness calibration method produces results relevant to applications where trapped particle undergoes large displacements, and at a given position sensing resolution, can be used for stiffness calibration at higher trapping laser powers than the PSD method.

Sarshar, Mohammad; Wong, Winson T.; Anvari, Bahman

2014-11-01

360

Aortic-brachial stiffness mismatch and mortality in dialysis population.  

PubMed

We hypothesized that increased aortic stiffness (central elastic artery) combined with a decrease in brachial stiffness (peripheral muscular artery) leads to the reversal of the physiological stiffness gradient (ie, mismatch), promoting end-organ damages through increased forward pressure wave transmission into the microcirculation. We, therefore, examined the effect of aortic-brachial stiffness mismatch on mortality in patients in need of dialysis. In a prospective observational study, aortic-brachial arterial stiffness mismatch (pulse wave velocity ratio) was assessed using carotid-femoral pulse wave velocity divided by carotid-radial pulse wave velocity in 310 adult patients on dialysis. After a median follow-up of 29 months, 146 (47%) deaths occurred. The hazard ratio (HR) for mortality related to PWV ratio in a Cox regression analysis was 1.43 (95% confidence interval [CI], 1.24-1.64; P<0.001 per 1 SD) and was still significant after adjustments for confounding factors, such as age, dialysis vintage, sex, cardiovascular disease, diabetes mellitus, smoking status, and weight (HR, 1.23; 95% CI: 1.02-1.49). The HRs for changes in 1 SD of augmentation index (HR, 1.35; 95% CI, 1.12-1.63), carotid-femoral pulse wave velocity (HR, 1.29; 95% CI, 1.11-1.50), and carotid-radial pulse wave velocity (HR, 0.80; 95% CI, 0.67-0.95) were statistically significant in univariate analysis, but were no longer statistically significant after adjustment for age. In conclusion, aortic-brachial arterial stiffness mismatch was strongly and independently associated with increased mortality in this dialysis population. Further studies are required to confirm these finding in lower-risk groups. PMID:25452473

Fortier, Catherine; Mac-Way, Fabrice; Desmeules, Simon; Marquis, Karine; De Serres, Sacha A; Lebel, Marcel; Boutouyrie, Pierre; Agharazii, Mohsen

2015-02-01

361

The influence of the lubricant film on the stiffness and damping characteristics of a deep groove ball bearing  

NASA Astrophysics Data System (ADS)

This paper experimentally investigates the formation of a lubricant film in a deep groove ball bearing and its effect on the bearing dynamics. A novel test rig is introduced, which allows testing different types and sizes of bearings in real-life conditions. The test rig dynamics are optimised such that the dynamic properties of the bearing are measured in a frequency range below the resonances of the flexible modes. Two properties of the bearing, both its stiffness and damping value in the direction of the static bearing load, are identified. The behaviour of the lubricant film between the rolling elements and raceways is measured based on the electrical resistance through the bearing. For this purpose, the bearing housing is electrically isolated from the surrounding structure. The electrical resistance, stiffness and damping of the test bearing are identified during a speed run-up. The influence of the bearing temperature is analysed as well. During a run-up at constant bearing temperature, the measurement of the electrical resistance describes the formation of the lubricant film. Due to the formation of the lubricant film, the bearing stiffness increases by 3.2% while the damping increases by 24%. During a warm-up of the bearing, the viscosity of the lubricant film decreases strongly. A resulting decrease in electrical resistance, stiffness and damping is measured. Finally, the electrical resistance, stiffness and damping are identified at different speeds, after the bearing has reached a stable temperature at each speed. A combined effect of both rotation and temperature is observed and discussed.

Jacobs, William; Boonen, Rene; Sas, Paul; Moens, David

2014-01-01

362

Micropipette Aspiration of Substrate-attached Cells to Estimate Cell Stiffness  

PubMed Central

Growing number of studies show that biomechanical properties of individual cells play major roles in multiple cellular functions, including cell proliferation, differentiation, migration and cell-cell interactions. The two key parameters of cellular biomechanics are cellular deformability or stiffness and the ability of the cells to contract and generate force. Here we describe a quick and simple method to estimate cell stiffness by measuring the degree of membrane deformation in response to negative pressure applied by a glass micropipette to the cell surface, a technique that is called Micropipette Aspiration or Microaspiration. Microaspiration is performed by pulling a glass capillary to create a micropipette with a very small tip (2-50 ?m diameter depending on the size of a cell or a tissue sample), which is then connected to a pneumatic pressure transducer and brought to a close vicinity of a cell under a microscope. When the tip of the pipette touches a cell, a step of negative pressure is applied to the pipette by the pneumatic pressure transducer generating well-defined pressure on the cell membrane. In response to pressure, the membrane is aspirated into the pipette and progressive membrane deformation or "membrane projection" into the pipette is measured as a function of time. The basic principle of this experimental approach is that the degree of membrane deformation in response to a defined mechanical force is a function of membrane stiffness. The stiffer the membrane is, the slower the rate of membrane deformation and the shorter the steady-state aspiration length.The technique can be performed on isolated cells, both in suspension and substrate-attached, large organelles, and liposomes. Analysis is performed by comparing maximal membrane deformations achieved under a given pressure for different cell populations or experimental conditions. A "stiffness coefficient" is estimated by plotting the aspirated length of membrane deformation as a function of the applied pressure. Furthermore, the data can be further analyzed to estimate the Young's modulus of the cells (E), the most common parameter to characterize stiffness of materials. It is important to note that plasma membranes of eukaryotic cells can be viewed as a bi-component system where membrane lipid bilayer is underlied by the sub-membrane cytoskeleton and that it is the cytoskeleton that constitutes the mechanical scaffold of the membrane and dominates the deformability of the cellular envelope. This approach, therefore, allows probing the biomechanical properties of the sub-membrane cytoskeleton. PMID:23051713

Oh, Myung-Jin; Kuhr, Frank; Byfield, Fitzroy; Levitan, Irena

2012-01-01

363

Arterial Stiffness and Pulse Wave Reflection in Young Adult Heterozygous Sickle Cell Carriers  

PubMed Central

Objective: Pulse wave velocity (PWV) and aortic augmentation index (AI) are indicators of arterial stiffness. Pulse wave reflection and arterial stiffness are related to cardiovascular events and sickle cell disease. However, the effect of these parameters on the heterozygous sickle cell trait (HbAS) is unknown. The aim of this study is to evaluate the arterial stiffness and wave reflection in young adult heterozygous sickle cell carriers. Materials and Methods: We enrolled 40 volunteers (20 HbAS cases, 20 hemoglobin AA [HbAA] cases) aged between 18 and 40 years. AI and PWV values were measured by arteriography. Results: Aortic blood pressure, aortic AI, and brachial AI values were significantly higher in HbAS cases compared to the control group (HbAA) (p=0.033, 0.011, and 0.011, respectively). A statistically significant positive correlation was found between aortic pulse wave velocity and mean arterial pressure, age, aortic AI, brachial AI, weight, and low-density lipoprotein levels (p=0.000, 0.017, 0.000, 0.000, 0.034, and 0.05, respectively) in the whole study population. Aortic AI and age were also significantly correlated (p=0.026). In addition, a positive correlation between aortic PWV and systolic blood pressure and a positive correlation between aortic AI and mean arterial pressure (p=0.027 and 0.009, respectively) were found in HbAS individuals. Our study reveals that mean arterial pressure and heart rate are independent determinants for the aortic AI. Mean arterial pressure and age are independent determinants for aortic PWV. Conclusion: Arterial stiffness measurement is an easy, cheap, and reliable method in the early diagnosis of cardiovascular disease in heterozygous sickle cell carriers. These results may depend on the amount of hemoglobin S in red blood cells. Further studies are required to investigate the blood pressure changes and its effects on arterial stiffness in order to explain the vascular aging mechanism in the HbAS trait population. Conflict of interest:None declared. PMID:24385828

Bayramo?lu, Tünzale; AKKU?, O?uz; Nas, Kamil; Illyes, Miklós; Molnar, Ferenc; Gürkan, Emel; Bash?rov, M. Bayram; Demir, ?erafettin; Akku?, Gamze; Acartürk, Esmeray

2013-01-01

364

Perception of Stiffness in Laparoscopy – the Fulcrum Effect  

PubMed Central

We explored how the perception of stiffness can be distorted in Minimally Invasive Surgery. We combined a mechanical simulator with a haptic device, and implemented linear springs at the tip of the simulated laparoscopic device. To explore the influence of mechanical advantage on perception, we set different values of the ratio between internal and external length of the tool. We found that a nonsymmetrical ratio causes bias in the perceived stiffness when novice tangential probing is compared to radial probing. In contrast, haptic experts did not show similar perceptual bias. PMID:22357009

Nisky, Ilana; Huang, Felix; Milstein, Amit; Pugh, Carla M.; Mussa-ivaldi, Ferdinando A.; Karniel, Amir

2014-01-01

365

Arthroscopic lysis of adhesions for the stiff total knee arthroplasty.  

PubMed

The management of the stiff knee after total knee arthroplasty is controversial. Manipulation under anesthesia and open lysis of adhesions are techniques that can theoretically address the fibrous scar tissue, but their efficacy has been shown to be variable. We describe the technique of arthroscopic lysis of adhesions for the stiff knee after total knee arthroplasty. The advantages of this technique include minimally invasive debridement of scar tissue within defined compartments of the knee and evaluation for the presence and treatment of focal lesions (e.g., loose bodies or impinging synovial or soft tissue). The total arc of motion can be improved with a systematic arthroscopic approach. PMID:25473616

Enad, Jerome G

2014-10-01

366

Thermal Testing of Tow-Placed, Variable Stiffness Panels  

NASA Technical Reports Server (NTRS)

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

Wu, K. Chauncey; Guerdal, Zafer

2001-01-01

367

Factors influencing arterial stiffness in pheochromocytoma and effect of adrenalectomy  

PubMed Central

The aim of the study was to evaluate arterial stiffness and its modulating factors measured by carotid-femoral pulse wave velocity and central augmentation index in patients with pheochromocytoma before and after surgery. Forty-five patients with pheochromocytoma and 45 healthy controls were investigated using an applanation tonometer (SphygmoCor, AtCor Medical). In addition, 27 patients with pheochromocytoma were studied one year after tumor removal. The gender, age, BMI and lipid profiles were comparable among both groups. The main difference in basic characteristic was as expected fasting plasma glucose (P<0.001) and all blood pressure modalities. Pulse wave velocity in pheochromocytoma was significantly higher than in controls (7.2±1.4 vs.5.8±0.5 m.s-1; P<0.001). Between-group difference in pulse wave velocity remained significant even after the adjustment for age, heart rate, fasting plasma glucose and each of brachial (P<0.001) and 24h blood pressure parameters (P<0.01). The difference in augmentation index between groups did not reach the statistical significance (19±14 vs. 16±13 %; NS). In multiple regression analysis, age (P<0.001), mean blood pressure (P=0.002), high sensitive C-reactive protein (P=0.007) and 24h urine norepinephrine (P=0.007) were independently associated with pulse wave velocity in pheochromocytoma. Successful tumor removal led to a significant decrease in pulse wave velocity (7.0±1.2 vs.6.0±1.1 m.s-1; P<0.001). In conclusion, patients with pheochromocytoma have an increase in pulse wave velocity, which is reversed by the successful tumor removal. Age, mean blood pressure, hs-CRP and norepinephrine levels are independent predictors of pulse wave velocity. PMID:20186147

Petrák, Ond?ej; Štrauch, Branislav; Zelinka, Tomáš; Rosa, Jan; Holaj, Robert; Vránková, Alice; Kasalický, Mojmír; Kvasni?ka, Jan; Pacák, Karel; Widimský, Ji?í

2011-01-01

368

Evaluation of blood pressure control using a new arterial stiffness parameter, cardio-ankle vascular index (CAVI).  

PubMed

Arterial stiffness has been known to be a surrogate marker of arteriosclerosis, and also of vascular function. Pulse wave velocity (PWV) had been the most popular index and was known to be a predictor of cardiovascular events. But, it depends on blood pressure at measuring time. To overcome this problem, cardio-ankle vascular index (CAVI) is developed. CAVI is derived from stiffness parameter ? by Hayashi, and the equation of Bramwell-Hill, and is independent from blood pressure at a measuring time. Then, CAVI might reflect the proper change of arterial wall by antihypertensive agents. CAVI shows high value with aging and in many arteriosclerotic diseases and is also high in persons with main coronary risk factors. Furthermore, CAVI is decreased by an administration of ?1 blocker, doxazosin for 2-4 hours, Those results suggested that CAVI reflected the arterial stiffness composed of organic components and of smooth muscle cell contracture. Angiotensin II receptor blocker, olmesartan decreased CAVI much more than that of calcium channel antagonist, amlodipine, even though the rates of decreased blood pressure were almost same. CAVI might differentiate the blood pressure-lowering agents from the point of the effects on proper arterial stiffness. This paper reviewed the principle and rationale of CAVI, and the possibilities of clinical applications, especially in the studies of hypertension. PMID:23807874

Shirai, Kohji; Utino, Junji; Saiki, Atsuhito; Endo, Kei; Ohira, Masahiro; Nagayama, Daiji; Tatsuno, Ichiro; Shimizu, Kazuhiro; Takahashi, Mao; Takahara, Akira

2013-02-01

369

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

PubMed

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

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

2014-06-01

370

Stiffness Study of a Hexapod Telescope Platform  

NASA Astrophysics Data System (ADS)

This paper presents our study on the structure of a hexapod platform used as a coplanar mount for a radio interferometer array. We have surveyed the hexapod platform using the photogrammetry method to measure its upper surface deformation under various pointing positions of the hexapod. We have also measured the strain distribution at the high strain areas of the platform structure. The results provide important information to verify the structural design of the platform, and a direct monitoring on the platform structural integrity. These measurements are compared with the finite-element analysis (FEA) that takes into account the gravity loading and the interaction loading between the platform and the hexapod. This study concludes that the interaction loading between the platform and the hexapod actuators is the dominant factor affecting the platform deformation.

Huang, Yau-De; Raffin, Philippe; Chen, Ming-Tang

2011-06-01

371

Non-invasive technique for assessment of vascular wall stiffness using laser Doppler vibrometry  

NASA Astrophysics Data System (ADS)

It has been shown that in cardiovascular risk management, stiffness of large arteries has a very good predictive value for cardiovascular disease and mortality. This parameter is best known when estimated from the pulse wave velocity (PWV) measured between the common carotid artery (CCA) in the neck and femoral artery in the groin, but may also be determined locally from short-distance measurements on a short vessel segment. In this work, we propose a novel, non-invasive, non-contact laser Doppler vibrometry (LDV) technique for evaluating PWV locally in an elastic vessel. First, the method was evaluated in a phantom setup using LDV and a reference method. Values correlated significantly between methods (R ? 0.973 (p ? 0.01)); and a Bland-Altman analysis indicated that the mean bias was reasonably small (mean bias ? -2.33 ms). Additionally, PWV was measured locally on the skin surface of the CCA in 14 young healthy volunteers. As a preliminary validation, PWV measured on two locations along the same artery was compared. Local PWV was found to be between 3 and 20 m s-1, which is in line with the literature (PWV = 5-13 m s-1). PWV assessed on two different locations on the same artery correlated significantly (R = 0.684 (p < 0.01)). In summary, we conclude that this new non-contact method is a promising technique to measure local vascular stiffness in a fully non-invasive way, providing new opportunities for clinical diagnosing.

Campo, Adriaan; Segers, Patrick; Heuten, Hilde; Goovaerts, Inge; Ennekens, Guy; Vrints, Christiaan; Baets, Roel; Dirckx, Joris

2014-06-01

372

CONTROL OF GULLY EROSION USING STIFF GRASSES  

Technology Transfer Automated Retrieval System (TEKTRAN)

Current practice for riparian gully erosion control involves blocking the gully with a structure comprised of an earthen embankment and a metal or plastic pipe. Measures involving native vegetation are more attractive for habitat recovery and economic reasons. To test the hypothesis that switchgra...

373

Point shear wave elastography method for assessing liver stiffness  

PubMed Central

AIM: To estimate the validity of the point shear-wave elastography method by evaluating its reproducibility and accuracy for assessing liver stiffness. METHODS: This was a single-center, cross-sectional study. Consecutive patients with chronic viral hepatitis scheduled for liver biopsy (LB) (Group 1) and healthy volunteers (Group 2) were studied. In each subject 10 consecutive point shear-wave elastography (PSWE) measurements were performed using the iU22 ultrasound system (Philips Medical Systems, Bothell, WA, United States). Patients in Group 1 underwent PSWE, transient elastography (TE) using FibroScan (Echosens, Paris, France) and ultrasound-assisted LB. For the assessment of PSWE reproducibility two expert raters (rater 1 and rater 2) independently performed the examinations. The performance of PSWE was compared to that of TE using LB as a reference standard. Fibrosis was staged according to the METAVIR scoring system. Receiver operating characteristic curve analyses were performed to calculate the area under the receiver operating characteristic curve (AUC) for F ? 2, F ? 3 and F = 4. The intraobserver and interobserver reproducibility of PSWE were assessed by calculating Lin’s concordance correlation coefficient. RESULTS: To assess the performance of PSWE, 134 consecutive patients in Group 1 were studied. The median values of PSWE and TE (in kilopascals) were 4.7 (IQR = 3.8-5.4) and 5.5 (IQR = 4.7-6.5), respectively, in patients at the F0-F1 stage and 3.5 (IQR = 3.2-4.0) and 4.4 (IQR = 3.5-4.9), respectively, in the healthy volunteers in Group 2 (P < 10-5). In the univariate analysis, the PSWE and TE values showed a high correlation with the fibrosis stage; low correlations with the degree of necroinflammation, aspartate aminotransferase and gamma-glutamyl transferase (GGT); and a moderate negative correlation with the platelet count. A multiple regression analysis confirmed the correlations of both PSWE and TE with fibrosis stage and GGT but not with any other variables. The following AUC values were found: 0.80 (0.71-0.87) for PSWE and 0.82 (0.73-0.89) for TE (P = 0.42); 0.88 (0.80-0.94) for PSWE and 0.95 (0.88-0.98) for TE (P = 0.06); and 0.95 (0.89-0.99) for PSWE and 0.92 (0.85-0.97) for TE (P = 0.30) for F ? 2, F ? 3 and F = 4, respectively. To assess PSWE reproducibility, 116 subjects were studied, including 47 consecutive patients scheduled for LB (Group 1) and 69 consecutive healthy volunteers (Group 2). The intraobserver agreement ranged from 0.83 (95%CI: 0.79-0.88) to 0.96 (95%CI: 0.95-0.97) for rater 1 and from 0.84 (95%CI: 0.79-0.88) to 0.96 (95%CI: 0.95-0.97) for rater 2. The interobserver agreement yielded values from 0.83 (95%CI: 0.78-0.88) to 0.93 (95%CI: 0.91-0.95). CONCLUSION: PSWE is a reproducible method for assessing liver stiffness, and it compares with TE. Compared with patients with nonsignificant fibrosis, healthy volunteers showed significantly lower values. PMID:24782633

Ferraioli, Giovanna; Tinelli, Carmine; Lissandrin, Raffaella; Zicchetti, Mabel; Dal Bello, Barbara; Filice, Gaetano; Filice, Carlo

2014-01-01

374

Cerebellar ataxia impairs modulation of arm stiffness during postural maintenance.  

PubMed

Impedance control enables humans to effectively interact with their environment during postural and movement tasks, adjusting the mechanical behavior of their limbs to account for instability. Previous work has shown that people are able to selectively modulate the end-point stiffness of their arms, adjusting for varying directions of environmental disturbances. Behavioral studies also suggest that separate controllers are used for impedance modulation versus joint torque coordination. Here we tested whether people with cerebellar damage have deficits in impedance control. It is known that these individuals have poor motor coordination, which has typically been attributed to deficits in joint torque control. Subjects performed a static postural maintenance task with two different types of directional force perturbations. On average, patients with cerebellar ataxia modified stiffness differentially for the two perturbation conditions, although significantly less than age-matched control subjects. Thus cerebellar damage may impair the ability to modulate arm impedance. Surprisingly, the patients' intact ability to generally alter their limb stiffness during the postural task (albeit less than age-matched control subjects) improved their movement performance in a subsequent tracing task. The transfer of stiffness control from the static to the movement task may be a strategy that can be used by patients to compensate for their motor deficits. PMID:23843434

Gibo, Tricia L; Bastian, Amy J; Okamura, Allison M

2013-10-01

375

Cerebellar ataxia impairs modulation of arm stiffness during postural maintenance  

PubMed Central

Impedance control enables humans to effectively interact with their environment during postural and movement tasks, adjusting the mechanical behavior of their limbs to account for instability. Previous work has shown that people are able to selectively modulate the end-point stiffness of their arms, adjusting for varying directions of environmental disturbances. Behavioral studies also suggest that separate controllers are used for impedance modulation versus joint torque coordination. Here we tested whether people with cerebellar damage have deficits in impedance control. It is known that these individuals have poor motor coordination, which has typically been attributed to deficits in joint torque control. Subjects performed a static postural maintenance task with two different types of directional force perturbations. On average, patients with cerebellar ataxia modified stiffness differentially for the two perturbation conditions, although significantly less than age-matched control subjects. Thus cerebellar damage may impair the ability to modulate arm impedance. Surprisingly, the patients' intact ability to generally alter their limb stiffness during the postural task (albeit less than age-matched control subjects) improved their movement performance in a subsequent tracing task. The transfer of stiffness control from the static to the movement task may be a strategy that can be used by patients to compensate for their motor deficits. PMID:23843434

Gibo, Tricia L.; Bastian, Amy J.

2013-01-01

376

Initial post-buckling of variable-stiffness curved panels  

NASA Astrophysics Data System (ADS)

Variable-stiffness shells are curved composite structures in which the fibre-reinforcement follow curvilinear paths in space. Having a wider design space than traditional composite shells, they have the potential to improve a wide variety of weight-critical structures. In this paper, a new method for computing the initial post-buckling response of variable-stiffness cylindrical panels is presented, based on the differential quadrature method. Integro-differential governing and boundary equations governing the problem, derived with Koiter's theory (Koiter, 1945), are solved using a mixed generalised differential quadrature (GDQ) and integral quadrature (GIQ) approach. The post-buckling behaviour is determined on the basis of a quadratic expansion of the displacement fields. Orthogonality of the mode-shapes in the expansion series is ensured by a novel use of the Moore-Penrose generalised matrix inverse for solving the GDQ-GIQ equations. The new formulation is validated against benchmark analytical post-buckling results for constant stiffness plates and shells, and compared with non-linear finite-element (FE) analysis for variable-stiffness shells. Stability estimates are found to be in good agreement with incremental FE results in the vicinity of the buckling load, requiring only a fraction of the number of variables used by the current method.

White, S. C.; Raju, G.; Weaver, P. M.

2014-11-01

377

On implicit Taylor series methods for stiff ODEs  

SciTech Connect

Several versions of implicit Taylor series methods (ITSM) are presented and evaluated. Criteria for the approximate solution of ODEs via ITSM are given. Some ideas, motivations, and remarks on the inclusion of the solution of stiff ODEs are outlined. 25 refs., 3 figs.

Kirlinger, G. (Technische Univ., Vienna (Austria). Inst. fuer Angewandte und Numerische Mathematik); Corliss, G.F. (Argonne National Lab., IL (United States))

1991-01-01

378

On implicit Taylor series methods for stiff ODEs  

SciTech Connect

Several versions of implicit Taylor series methods (ITSM) are presented and evaluated. Criteria for the approximate solution of ODEs via ITSM are given. Some ideas, motivations, and remarks on the inclusion of the solution of stiff ODEs are outlined. 25 refs., 3 figs.

Kirlinger, G. [Technische Univ., Vienna (Austria). Inst. fuer Angewandte und Numerische Mathematik; Corliss, G.F. [Argonne National Lab., IL (United States)

1991-12-31

379

INTRODUCTION Stiffness properties of the human motor system depend on  

E-print Network

in motor control mainly for two reasons: increasing stiffness has an impact on movement speed and duration models and adjustable starting length models [2]. In biomechanics the reference muscle model is the Hill of the 11 th International Symposium, Computer Methods in Biomechanics and Biomedical Engineering April 3

Paris-Sud XI, Université de

380

Simultaneously high stiffness and damping in nanoengineered microtruss composites.  

PubMed

Materials combining high stiffness and mechanical energy dissipation are needed in automotive, aviation, construction, and other technologies where structural elements are exposed to dynamic loads. In this paper we demonstrate that a judicious combination of carbon nanotube engineered trusses held in a dissipative polymer can lead to a composite material that simultaneously exhibits both high stiffness and damping. Indeed, the combination of stiffness and damping that is reported is quite high in any single monolithic material. Carbon nanotube (CNT) microstructures grown in a novel 3D truss topology form the backbone of these nanocomposites. The CNT trusses are coated by ceramics and by a nanostructured polymer film assembled using the layer-by-layer technique. The crevices of the trusses are then filled with soft polyurethane. Each constituent of the composite is accurately modeled, and these models are used to guide the manufacturing process, in particular the choice of the backbone topology and the optimization of the mechanical properties of the constituent materials. The resulting composite exhibits much higher stiffness (80 times) and similar damping (specific damping capacity of 0.8) compared to the polymer. Our work is a step forward in implementing the concept of materials by design across multiple length scales. PMID:24620996

Meaud, Julien; Sain, Trisha; Yeom, Bongjun; Park, Sei Jin; Shoultz, Anna Brieland; Hulbert, Gregory; Ma, Zheng-Dong; Kotov, Nicholas A; Hart, A John; Arruda, Ellen M; Waas, Anthony M

2014-04-22

381

The stiffness of prestressed frameworks: a unifying Simon Guest  

E-print Network

is used to understand whether unconventional structures such as tensegrities are `prestress stable derivation of the tangent stiffness matrix for a prestressed pin-jointed structure is given, and is used to compare the diverse formulations that can be found in the literature for finding the structural response

Guest, Simon

382

Arterial stiffness in chronic kidney disease: causes and consequences  

Microsoft Academic Search

Chronic kidney disease is associated with elevated cardiovascular risk, and heart failure and arrhythmias are the biggest causes of cardiovascular death in this population. Increased arterial stiffness is a hallmark of chronic kidney disease and is associated with adverse alterations in cardiac structure and function that may predispose to an increased risk of cardiovascular death. These changes are already apparent

Colin D Chue; Jonathan N Townend; Richard P Steeds; Charles J Ferro

2010-01-01

383

Riparian Sediment Delivery Ratio: Stiff Diagrams and Artifical Neural Networks  

EPA Science Inventory

Various methods are used to estimate sediment transport through riparian buffers and grass jilters with the sediment delivery ratio having been the most widely applied. The U.S. Forest Service developed a sediment delivery ratio using the stiff diagram and a logistic curve to int...

384

Hydrogen-bond reinforced vanadia nanofiber paper of high stiffness.  

PubMed

Low-temperature, solution-based self-assembly of vanadia nanofibers yields a free-standing, ceramic paper with an outstanding combination of high strength, stiffness, and macroscopic flexibility. Its excellent mechanical performance results from a brick-and-mortar like architecture, which combines strong covalent bonding within the single-crystalline nanofibers with an intricate hydrogen bonding network between them. PMID:23468458

Burghard, Zaklina; Leineweber, Andreas; van Aken, Peter A; Dufaux, Thomas; Burghard, Marko; Bill, Joachim

2013-05-01

385

Nondestrutive damage detection by simultaneous identification of stiffness and damping  

E-print Network

is developed on the basis of the conservation of total energy; second, the other method utilizes the acceleration-structural parameters (stiffness and damping) sensitivities. The total energy in a system consists of the sum of the kinetic energy, the potential...

Hyung, Sang Su

2009-05-15

386

Stiffness gradients in vascular bundles of the palm Washingtonia robusta  

PubMed Central

Palms can grow at sites exposed to high winds experiencing large dynamic wind and gust loads. Their stems represent a system of stiff fibrous elements embedded in the soft parenchymatous tissue. The proper design of the interface of the stiffening elements and the parenchyma is crucial for the functioning of the stem. The strategy of the palm to compromise between stiff fibre caps and the soft parenchymatous tissue may serve as a model system for avoiding stress discontinuities in inhomogeneous and anisotropic fibre-reinforced composite materials. We investigated the mechanical, structural and biochemical properties of the fibre caps of the palm Washingtonia robusta at different levels of hierarchy with high spatial resolution. A gradual decrease in stiffness across the fibre cap towards the surrounding parenchymatous tissue was observed. Structural adaptations at the tissue level were found in terms of changes in cell cross sections and cell wall thickness. At the cell wall level, gradients across the fibre cap were found in the degree of orientation of the microfibrils and in the lignin level and composition. The impact of these structural variations in the local material stiffness distribution is discussed. PMID:18595839

Rüggeberg, Markus; Speck, Thomas; Paris, Oskar; Lapierre, Catherine; Pollet, Brigitte; Koch, Gerald; Burgert, Ingo

2008-01-01

387

Substrata Mechanical Stiffness Can Regulate Adhesion of Viable Bacteria  

E-print Network

Substrata Mechanical Stiffness Can Regulate Adhesion of Viable Bacteria Jenny A. Lichter,, M. Todd, 2008 The competing mechanisms that regulate adhesion of bacteria to surfaces and subsequent biofilm and hospital-acquired infections due to bacteria, there is considerable interest in better understanding

Van Vliet, Krystyn J.

388

GEOMETRIC STIFFNESS AND STABILITY OF RIGID BODY MODES  

Microsoft Academic Search

The objective of this study is to examine the effect of geometric stiffness forces on the stability of elastic and rigid body modes. A simple rotating beam model is used to demonstrate the effect of axial forces and dynamic coupling between the modes of displacement on the rigid body motion. The effect of longitudinal deformation due to bending is systematically

H. El-Absy; A. A. Shabana

1997-01-01

389

Variable stiffness and damping suspension system for train  

NASA Astrophysics Data System (ADS)

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

Sun, Shuaishuai; Deng, Huaxia; Li, Weihua

2014-03-01

390

Design optimization of a twist compliant mechanism with nonlinear stiffness  

NASA Astrophysics Data System (ADS)

A contact-aided compliant mechanism called a twist compliant mechanism (TCM) is presented in this paper. This mechanism has nonlinear stiffness when it is twisted in both directions along its axis. The inner core of the mechanism is primarily responsible for its flexibility in one twisting direction. The contact surfaces of the cross-members and compliant sectors are primarily responsible for its high stiffness in the opposite direction. A desired twist angle in a given direction can be achieved by tailoring the stiffness of a TCM. The stiffness of a compliant twist mechanism can be tailored by varying thickness of its cross-members, thickness of the core and thickness of its sectors. A multi-objective optimization problem with three objective functions is proposed in this paper, and used to design an optimal TCM with desired twist angle. The objective functions are to minimize the mass and maximum von-Mises stress observed, while minimizing or maximizing the twist angles under specific loading conditions. The multi-objective optimization problem proposed in this paper is solved for an ornithopter flight research platform as a case study, with the goal of using the TCM to achieve passive twisting of the wing during upstroke, while keeping the wing fully extended and rigid during the downstroke. Prototype TCMs have been fabricated using 3D printing and tested. Testing results are also presented in this paper.

Tummala, Y.; Frecker, M. I.; Wissa, A. A.; Hubbard, J. E., Jr.

2014-10-01

391

Substrate stiffness affects skeletal myoblast differentiation in vitro  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

392

Lower limbs power and stiffness after whole-body vibration.  

PubMed

The interest in whole-body vibration (WBV) for the enhancement of neuromuscular performance has received considerable attention. However, scientific evidence supporting the optimal prescription of WBV settings is lacking. This study investigated the acute effect of WBV combining high frequency/high peak-to-peak displacement (HH) or low frequency/low peak-to-peak displacement (LL) vs. sham intervention (SHAM) on lower limb muscle power and stiffness. A total of 223 volunteers were randomly assigned to either the HH, LL or SHAM group. Countermovement jump (CMJ) height, maximal and average power, maximal and average lower limbs stiffness obtained during a hopping test were recorded before and after the respective intervention. After the intervention, the HH group showed an increase of 4.64% in CMJ height (p<0.001) whereas the values of both the LL and SHAM groups did not change. In addition, maximal and average power of the lower limbs were significantly increased in all groups (p<0.001; 10.89% and 12.82%, respectively) while no effect on lower limbs stiffness was observed. Our data show that high frequency combined with high peak-to-peak displacement is the most optimal WBV setting for CMJ height enhancement. Further investigation should be undertaken to ascertain the effectiveness of WBV on lower limbs stiffness. PMID:23143701

Colson, S S; Petit, P-D

2013-04-01

393

Design of a Stiff Steerable Grasper for Sinus Surgery  

E-print Network

Design of a Stiff Steerable Grasper for Sinus Surgery Andria A. Remirez, Ray A. Lathrop, Paul T Background With the advent of endoscopic sinus surgery in the late 1980's [1], a completely new surgical of the sinuses. Today, functional endoscopic sinus surgery (FESS) is commonly used to improve the sinuses

Webster III, Robert James

394

Adipocyte stiffness increases with accumulation of lipid droplets.  

PubMed

Adipogenesis and increase in fat tissue mass are mechanosensitive processes and hence should be influenced by the mechanical properties of adipocytes. We evaluated subcellular effective stiffnesses of adipocytes using atomic force microscopy (AFM) and interferometric phase microscopy (IPM), and we verified the empirical results using finite element (FE) simulations. In the AFM studies, we found that the mean ratio of stiffnesses of the lipid droplets (LDs) over the nucleus was 0.83 ± 0.14, from which we further evaluated the ratios of LDs over cytoplasm stiffness, as being in the range of 2.5 to 8.3. These stiffness ratios, indicating that LDs are stiffer than cytoplasm, were verified by means of FE modeling, which simulated the AFM experiments, and provided good agreement between empirical and model-predicted structural behavior. In the IPM studies, we found that LDs mechanically distort their intracellular environment, which again indicated that LDs are mechanically stiffer than the surrounding cytoplasm. Combining these empirical and simulation data together, we provide in this study evidence that adipocytes stiffen with differentiation as a result of accumulation of LDs. Our results are relevant to research of adipose-related diseases, particularly overweight and obesity, from a mechanobiology and cellular mechanics perspectives. PMID:24655518

Shoham, Naama; Girshovitz, Pinhas; Katzengold, Rona; Shaked, Natan T; Benayahu, Dafna; Gefen, Amit

2014-03-18

395

Controllable-stiffness components based on magnetorheological elastomers  

Microsoft Academic Search

So-called magnetorheological (MR) elastomers, comprising rubbery polymers loaded with magnetizable particles that are aligned in a magnetic field, possess dynamic stiffness and damping that can subsequently be controlled by applied fields. Tunable automotive bushings and mounts incorporating these materials and an embedded magnetic field source have been constructed. In this article, the response of these components to dynamic mechanical loading

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

2000-01-01

396

A Novel Tactile Force Probe for Tissue Stiffness Classification  

Microsoft Academic Search

In this study, we have proposed a new type of tactile sensor that is capable of detecting the stiffness of soft objects. The sensor consists of a brass cylinder with an axial bore. An iron core can easily move inside the bore. Three peripheral bobbins were machined in the cylinder around which three coils have been wound. One of the

Behafarid Darvish; Siamak Najarian; Elham Shirzad; Roozbeh Khodambashi

2009-01-01

397

Ultrahigh Torsional Stiffness and Strength of Boron Nitride Jonathan Garel,  

E-print Network

Ultrahigh Torsional Stiffness and Strength of Boron Nitride Nanotubes Jonathan Garel, Itai Leven of boron nitride nanotube (BNNT) torsional mechanics. We show that BNNTs exhibit a much stronger mechanical in nanoelectromechanical systems (NEMS), fibers, and nanocomposites. KEYWORDS: Nanotube, boron nitride (BN), atomic force

Hod, Oded

398

Aortic and Carotid Arterial Stiffness and Epigenetic Regulator Gene Expression Changes Precede Blood Pressure Rise in Stroke-Prone Dahl Salt-Sensitive Hypertensive Rats  

PubMed Central

Multiple clinical studies show that arterial stiffness, measured as pulse wave velocity (PWV), precedes hypertension and is an independent predictor of hypertension end organ diseases including stroke, cardiovascular disease and chronic kidney disease. Risk factor studies for arterial stiffness implicate age, hypertension and sodium. However, causal mechanisms linking risk factor to arterial stiffness remain to be elucidated. Here, we studied the causal relationship of arterial stiffness and hypertension in the Na-induced, stroke-prone Dahl salt-sensitive (S) hypertensive rat model, and analyzed putative molecular mechanisms. Stroke-prone and non-stroke-prone male and female rats were studied at 3- and 6-weeks of age for arterial stiffness (PWV, strain), blood pressure, vessel wall histology, and gene expression changes. Studies showed that increased left carotid and aortic arterial stiffness preceded hypertension, pulse pressure widening, and structural wall changes at the 6-week time-point. Instead, differential gene induction was detected implicating molecular-functional changes in extracellular matrix (ECM) structural constituents, modifiers, cell adhesion, and matricellular proteins, as well as in endothelial function, apoptosis balance, and epigenetic regulators. Immunostaining testing histone modifiers Ep300, HDAC3, and PRMT5 levels confirmed carotid artery-upregulation in all three layers: endothelial, smooth muscle and adventitial cells. Our study recapitulates observations in humans that given salt-sensitivity, increased Na-intake induced arterial stiffness before hypertension, increased pulse pressure, and structural vessel wall changes. Differential gene expression changes associated with arterial stiffness suggest a molecular mechanism linking sodium to full-vessel wall response affecting gene-networks involved in vascular ECM structure-function, apoptosis balance, and epigenetic regulation. PMID:25229245

Herrera, Victoria L.; Decano, Julius L.; Giordano, Nicholas; Moran, Ann Marie; Ruiz-Opazo, Nelson

2014-01-01

399

Atomic force microscopy stiffness tomography on living Arabidopsis thaliana cells reveals the mechanical properties of surface and deep cell-wall layers during growth.  

PubMed

Cell-wall mechanical properties play a key role in the growth and the protection of plants. However, little is known about genuine wall mechanical properties and their growth-related dynamics at subcellular resolution and in living cells. Here, we used atomic force microscopy (AFM) stiffness tomography to explore stiffness distribution in the cell wall of suspension-cultured Arabidopsis thaliana as a model of primary, growing cell wall. For the first time that we know of, this new imaging technique was performed on living single cells of a higher plant, permitting monitoring of the stiffness distribution in cell-wall layers as a function of the depth and its evolution during the different growth phases. The mechanical measurements were correlated with changes in the composition of the cell wall, which were revealed by Fourier-transform infrared (FTIR) spectroscopy. In the beginning and end of cell growth, the average stiffness of the cell wall was low and the wall was mechanically homogenous, whereas in the exponential growth phase, the average wall stiffness increased, with increasing heterogeneity. In this phase, the difference between the superficial and deep wall stiffness was highest. FTIR spectra revealed a relative increase in the polysaccharide/lignin content. PMID:22947854

Radoti?, Ksenija; Roduit, Charles; Simonovi?, Jasna; Hornitschek, Patricia; Fankhauser, Christian; Mutavdži?, Dragosav; Steinbach, Gabor; Dietler, Giovanni; Kasas, Sandor

2012-08-01

400

Atomic Force Microscopy Stiffness Tomography on Living Arabidopsis thaliana Cells Reveals the Mechanical Properties of Surface and Deep Cell-Wall Layers during Growth  

PubMed Central

Cell-wall mechanical properties play a key role in the growth and the protection of plants. However, little is known about genuine wall mechanical properties and their growth-related dynamics at subcellular resolution and in living cells. Here, we used atomic force microscopy (AFM) stiffness tomography to explore stiffness distribution in the cell wall of suspension-cultured Arabidopsis thaliana as a model of primary, growing cell wall. For the first time that we know of, this new imaging technique was performed on living single cells of a higher plant, permitting monitoring of the stiffness distribution in cell-wall layers as a function of the depth and its evolution during the different growth phases. The mechanical measurements were correlated with changes in the composition of the cell wall, which were revealed by Fourier-transform infrared (FTIR) spectroscopy. In the beginning and end of cell growth, the average stiffness of the cell wall was low and the wall was mechanically homogenous, whereas in the exponential growth phase, the average wall stiffness increased, with increasing heterogeneity. In this phase, the difference between the superficial and deep wall stiffness was highest. FTIR spectra revealed a relative increase in the polysaccharide/lignin content. PMID:22947854

Radoti?, Ksenija; Roduit, Charles; Simonovi?, Jasna; Hornitschek, Patricia; Fankhauser, Christian; Mutavdži?, Dragosav; Steinbach, Gabor; Dietler, Giovanni; Kasas, Sandor

2012-01-01

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