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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

Electron temperature measurements of FRX-C/LSM  

SciTech Connect

The electron temperature T/sub e/ has been measured with Thomson scattering field-reversed configurations (FRCs) on the Los Alamos FRX-C/LSM experiment. FRCs formed and trapped in-situ in the theta-pinch source are studied. These experiments mark the first comprehensive FRC T/sub e/ measurements in over five years with data gathered on over 400 discharges. Measurements are performed at a single point in space and time on each discharge. The Thomson scattering diagnostic consist of a Q-switched ruby laser focused from one end to a point 0.2 m from the axial midplane of the theta-pinch coil and at radius of either 0.00 or 0.10 m. Scattered light is collected, dispersed and detected with a 7-channel, triple-grating polychromator configured to detect light wavelengths between 658 and 692 nm. Photomultiplier currents are measured with gated A/D converters, with plasma background signals recorded 100-ns before and 100-ns after the laser pulse. Electron temperatures are measured at either radial position during the time interval, 10 less than or equal to t less than or equal to 70 ..mu..s, between FRC formation and the onset of the n = 2 instability which usually terminates the discharge. A variety of plasma conditions have been produced by adjusting three external parameters: the initial deuterium fill pressure p/sub O/; the reversed bias magnetic field B/sub b/; and the external magnetic field B/sub w/. The fill-pressure scan has been performed at B/sub b/ approx. = 60 mT and B/sub w/ approx. = 0.4 T with p/sub o/ set at either 2, 3, 4 or 5 mtorr. The bias-field scan, 37 less than or equal to B/sub b/ less than or equal to 95 mT, has been performed at p/sub o/ = 3 mtorr and B/sub w/ approx. = 0.4 T. 7 refs., 3 figs., 3 tabs.

Rej, D.J.

1989-01-01

3

Ultrasonographic scoring system score versus liver stiffness measurement in prediction of cirrhosis  

PubMed Central

Background/Aims We compared the cirrhosis-prediction accuracy of an ultrasonographic scoring system (USSS) combining six representative sonographic indices with that of liver stiffness measurement (LSM) by transient elastography, and prospectively investigated the correlation between the USSS score and LSM in predicting cirrhosis. Methods Two hundred and thirty patients with chronic liver diseases (187 men, 43 women; age, 50.4±9.5 y, mean±SD) were enrolled in this prospective study. The USSS produces a combined score for nodularity of the liver surface and edge, parenchyma echogenicity, presence of right-lobe atrophy, spleen size, splenic vein diameter, and abnormality of the hepatic vein waveform. The correlations of the USSS score and LSM with that of a pathological liver biopsy (METAVIR scoring system: F0-F4) were evaluated. Results The mean USSS score and LSM were 7.2 and 38.0 kPa, respectively, in patients with histologically overt cirrhosis (F4, P=0.017) and 4.3 and 22.1 kPa in patients with fibrotic change without overt cirrhosis (F0-F3) (P=0.025). The areas under the receiver operating characteristic (ROC) curves of the USSS score and LSM for F4 patients were 0.849 and 0.729, respectively. On the basis of ROC curves, criteria of USSS ?6: LSM ?17.4 had a sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 89.2%:77.6%, 69.4%:61.4%, 86.5%:83.7%, 74.6%:51.9% and 0.83:0.73, respectively, in predicting F4. Conclusions The results indicate that this USSS has comparable efficacy to LSM in the diagnosis of cirrhosis.

Moon, Kyoung Min; Kim, Gaeun; Choi, Eunhee; Kim, Moon Young; Kim, Hyoun A; Cho, Mee Yon; Shin, Seung Yong; Kim, Jung Min; Park, Hong Jun; Kwon, Sang Ok; Eom, Young Woo

2013-01-01

4

Effects of patient factors on noninvasive liver stiffness measurement using acoustic radiation force impulse elastography in patients with chronic hepatitis C  

PubMed Central

Background Previous research has shown variation in the effects of patient factors, including hepatic necroinflammatory activity, on liver stiffness measurement (LSM). This prospective study attempts to identify explanatory factors for LSM in patients with chronic hepatitis C (CHC) using acoustic radiation force impulse (ARFI) technology. Methods A cohort of 127 Taiwanese patients with CHC underwent ARFI LSM and immediate percutaneous liver biopsy. This study compares the concurrent diagnostic performances of LSM and FibroTest using receiver operating characteristic (ROC) curves. Three multiple linear regression models were used to evaluate the significance of concurrent patient factors in explaining LSM. Results To classify METAVIR fibrosis (F) stages, the areas under ROC curves (AUCs) were ARFI LSM, 0.847 (95% confidence interval (CI), 0.779-0.914) and FibroTest, 0.823 (95% CI, 0.748-0.898), for F1 versus F2-4; ARFI LSM, 0.902 (95% CI, 0.835-0.970) and FibroTest, 0.812 (95% CI, 0.735-0.888), for F1-2 versus F3-4; ARFI LSM, 0.831 (95% CI, 0.723-0.939) and FibroTest, 0.757 (95% CI, 0.648-0.865), for F1-3 versus F4. After adjusting for other demographic and biological covariates, biochemical and histological necroinflammatory factors consistently explained LSM. Factors included serum alanine aminotransferase (ALT)/upper limit of normal (ULN) categories (model R2?=?0.661, adjusted R2?=?0.629), ActiTest A scores (R2?=?0.662, adjusted R2?=?0.636), and METAVIR activity (A) grades (R2?=?0.651, adjusted R2?=?0.620). METAVIR F stages, body mass index, and platelet count were also independently associated with LSM. Necroinflammatory degrees, including ALT/ULN, ActiTest A scores, and METAVIR A grades, explained the false positivity of liver fibrosis staging using ARFI LSM. Conclusions The degree of hepatic necroinflammatory activity independently and significantly exaggerated liver fibrosis evaluation using ARFI LSM. However, comparisons with concurrent FibroTest indicate that ARFI LSM may be a promising alternative, or adjunctive single indicator, for liver fibrosis evaluation in patients with CHC.

2012-01-01

5

Electron temperature measurements of field-reversed configuration plasmas on the FRX-C/LSM experiment  

SciTech Connect

A single-point Thomson scattering diagnostic is used to determine the electron temperature T/sub e/ of field-reversed-configuration (FRC) compact toroids generated in the /theta/-pinch source of the Los Alamos FRX-C/LSM experiment. Measurements are performed close to the axial midplane and near the magnetic and geometric axes. A broad range of plasma conditions is investigated and electron temperatures vary, on average, between 90 and 190 eV. For a given condition, T/sub e/ remains relatively constant during the 60 /mu/s measurement interval between formation and the onset of the n = 2 rotational instability. T/sub e/ increases with plasma diameter and external magnetic field, and decreases slightly with fill pressure. The temperature at the geometric axis is consistently 10--20% lower than that near the field null. The temperature is approximately 35% higher than observed previously on the smaller FRX-C device. The implications of these measurements on plasma confinement properties are discussed. 25 refs., 18 figs., 8 tabs.

Rej, D.J.

1989-09-01

6

Evaluation of liver stiffness measurement by fibroscan as compared to liver biopsy for assessment of hepatic fibrosis in children with chronic hepatitis C.  

PubMed

The study evaluated liver stiffness measurement (LSM) using non-invasive transient elastography (TE) in comparison with liver biopsy for assessment of hepatic fibrosis in children with chronic hepatitis C (CHC). Thirty children (mean age 10.13 +/- 3.4 years) with CHC were subjected to histopathological assessment of liver biopsy specimens using METAVIER score and LSM using TE (FibroScan) as well as appropriate laboratory investigations. The results showed a highly significant stepwise increase of the mean liver stiffness values with increasing histological severity of hepatic fibrosis with the highest level detected in patients with stage F4 "cirrhosis" and significant differences for F3 and F4 vs. other fibrosis stages. There were significant positive correlations between LSM and several parameters of activity and progression of the chronic liver disease including METAVIER fibrosis stages (r=0.774, p=0.0001), necroinflammatory activity grades, AST, ALT, total serum bilirubin, prothrombin time and Child-Pugh grades as well as biochemical serum fibrosis markers (Fibrotest, Actitest, AST-to-platelet ratio index, Forns index and hyaluronic acid). The variables significantly negatively associated with the LSM were platelets count and serum albumin. The highest predictive performance of LSM was detected for stage F4 "cirrhosis", followed by F3 "advanced fibrosis" where accuracy of(96.7%, 85.3%) and AUROC of (1.00, 0.815) were obtained for these fibrosis stages at cutoff values of 9.5 and 12.5 kPa, respectively. The negative predictive values to exclude advanced fibrosis and cirrhosis at these cutoffs were high, whereas positive predictive values were modest. PMID:24640880

Awad, Mohiee El-Deen Abd El-Aziz; Shiha, Gamal Elsayed; Sallam, Fersan Abdallah; Mohamed, Amany; El Tawab, Abd

2013-12-01

7

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

SciTech Connect

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

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

2013-08-08

8

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

NASA Astrophysics Data System (ADS)

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; EDELWEISS Collaboration

2013-08-01

9

The changes of liver stiffness and its associated factors for chronic hepatitis B patients with entecavir therapy.  

PubMed

Liver stiffness measurement (LSM) using transient elastography has been proposed to assess liver fibrosis well in various liver diseases. This study was to determine the changes of LSM and its associated factors for chronic hepatitis B (CHB) patients undergoing Entecavir therapy. Consecutive CHB patients underwent Entecavir therapy with two LSMs were enrolled. Patients with aspartate transaminase (AST) and/or alanine transaminase ?200 IU/L were excluded. The retrospective study enrolled 233 patients including 132 without cirrhosis (group 1) and 101 with cirrhosis (group 2). The mean values of initial liver stiffness were 7.9 and 16.6 kPa for patients in group 1 and group 2, respectively (p<0.001). In addition to the decline of transaminase levels, there was significant reduction of liver stiffness value in a mean interval of 52.8 and 61.9 weeks between the two LSMs for patients in group 1 and 2, respectively (p<0.001). Multivariate analysis showed that higher initial LSM value and presence of hepatitis B e-antigen were associated with a greater decline of LSM value, whereas follow-up AST?40 IU/L with increased LSM value for group 1 patients. For group 2 patients, longer interval between the two LSMs, higher initial LSM value and AST?40 IU/L were associated with a greater decline of LSM value, whereas presence of diabetes mellitus (DM) contributed to increased LSM value. In conclusion, CHB patients improved their LSM values after Entecavir therapy. Higher initial LSM value contributed to greater LSM reduction. However, in cirrhotic patients, DM was associated with an increased LSM value after therapy. PMID:24682088

Kuo, Yuan-Hung; Lu, Sheng-Nan; Chen, Chien-Hung; Chang, Kuo-Chin; Hung, Chao-Hung; Tai, Wei-Chen; Tsai, Ming-Chao; Tseng, Po-Lin; Hu, Tsung-Hui; Wang, Jing-Houng

2014-01-01

10

Nanoindenter Stiffness Measurements on a MEMS Sound Sensor  

NASA Astrophysics Data System (ADS)

We demonstrate a novel technique to extract the various components of the stiffness (or compliance) measured along the surface of a MEMS directional sound sensor. Because the sensor comprises a cantilever beam mounted on torsion springs, the overall stiffness consists of various compliance components added in series. Stiffness measurements made using a nanoindenter are found to agree with an analytical model and a finite element model (FEM) of the sensor. Moreover, by exploiting the differing power-law characteristics of the individual compliance components, we demonstrate extraction of the separate components from a logarithmic plot of the overall stiffness. Finally, we measure the ultimate (failure) strength of the sensor, from which we obtain the maximum acoustic intensity the sensor can tolerate.

Downey, R.; Brewer, L.; Karunasiri, G.

2012-02-01

11

LSM vision gage R&R study  

Microsoft Academic Search

The purpose of this study is to assess whether the laser scanning microscope (LSM) is capable of measuring solder paste height. The LSM projects a scanning laser beam onto the PC board which is deflected around the solder paste deposit. The height of the paste was determined by taking the difference between the highest (top) and lowest (bottom) laser deflection

William S Messina; L. G. Willey

1995-01-01

12

Tilting pad journal bearings - Measured and predicted stiffness coefficients  

SciTech Connect

This paper presents measured and calculated characteristics of a tilting pad journal bearing suitable for high speed machinery. Descriptions are given of the experimental techniques used with this variety of bearing and the theoretical model for predicting performance. Measured values of pad temperature, eccentricity, attitude angle, and the four stiffness coefficients are given for a range of loads and rotational speeds. Data are given for both load on pad and between pad configurations, the two principal loading arrangements. Comparisons are made between the measured and predicted bearing temperatures and stiffness coefficients over a wide range of values. 11 refs.

Parkins, D.W.; Horner, D. (Cranfield Inst. of Technology, Bedford (United Kingdom) Michell Bearings, Newcastle-upon-Tyne (United Kingdom))

1993-07-01

13

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

14

Can arterial stiffness parameters be measured in the sitting position?  

Microsoft Academic Search

Despite the introduction of arterial stiffness measurements in the European recommendation, pulse wave velocity (PWV) and augmentation index (AI) are still not used routinely in clinical practice. It would be of advantage if such measurements were done in the sitting position as is done for blood pressure. The aim of this study was to evaluate whether there is a difference

Jens Nürnberger; Rene Michalski; Tobias R Türk; Anabelle Opazo Saez; Oliver Witzke; Andreas Kribben

2011-01-01

15

Method of measurement of optical cable stiffness at low temperatures  

NASA Astrophysics Data System (ADS)

In this article the new method of determination of optical cable stiffness at low temperatures is offered. The method is allows to simplify process of measurements. Thus presence of technicians at climatic chamber in the course of measurements is not required.

Burdin, Vladimir A.; Alekhin, Ivan N.; Nikulina, Tatiana G.

2014-04-01

16

Liver Stiffness Measurement by Transient Elastography in Clinical Practice  

Microsoft Academic Search

The aim of our study was to evaluate the results of transient elastography assessment of liver stiffness (LS) in various categories of patients. Material and method. We performed transient elastography in 986 patients. We evaluated: the percentage of cases in which valid measurements could be obtained; the values of LS in 40 patients with no history of chronic liver disease

Ioan Sporea; Alexandra Deleanu; Alina Popescu; Marioara Cornianu

17

Stiffness measurement of eggshell by acoustic resonance and PLS models  

Microsoft Academic Search

Non-destructive measurement of eggshell stiffness was carried out by means of acoustic resonance system. It was achieved by analysis of measured frequency response of eggshell excited with a light mechanical. Partial least squares (PLS), synergy interval PLS (si-PLS), genetic algorithm PLS (GA-PLS) and GA-siPLS algorithms were used comparatively to calibrate regression model. The performance of the final model was evaluated

Hao Lin; Jie-wen Zhao; Li Sun; Quan-sheng Chen; Zongbao Sun; Fang Zhou

2011-01-01

18

Liver stiffness 1 year after transplantation predicts clinical outcomes in patients with recurrent hepatitis C.  

PubMed

The value of transient elastography (TE) to assess clinical outcomes in hepatitis C recurrence after liver transplantation (LT) has not been explored so far. We studied 144 hepatitis C-infected and 48 non-hepatitis C virus (HCV)-infected LT recipients and evaluated the prognostic value of TE 1 year after transplantation to predict clinical decompensations and graft and patient survival. In HCV patients, cumulative probabilities of liver decompensation 5 years after LT were 8% for patients with liver stiffness measurement (LSM) <8.7 kilopascals (kPa) versus 47% for patients with LSM ? 8.7 kPa (p<0.001). Five-year graft and patient cumulative survival were 90% and 92% in patients with LSM<8.7 kPa (p<0.001) and 63% and 64% in patients with LSM ? 8.7 kPa, respectively (p<0.001). Patients with low LSM 1 year after LT had excellent outcomes independently from receiving antiviral treatment or achieving sustained virological response (SVR). In contrast, graft survival significantly improved in patients with LSM ? 8.7 kPa who achieved SVR. No association between outcomes and LSM at 12 months was observed in non-HCV patients. In conclusion, LSM 1 year after LT is a valuable tool to predict hepatitis C-related outcomes in recurrent hepatitis C and can be used in clinical practice to identify the best candidates for antiviral therapy. PMID:24410892

Crespo, G; Lens, S; Gambato, M; Carrión, J A; Mariño, Z; Londoño, M-C; Miquel, R; Bosch, J; Navasa, M; Forns, X

2014-02-01

19

Stiffness Measurement of Burkitt's Lymphoma Cells with Atomic Force Microscopy  

Microsoft Academic Search

Cell stiffness is closely related to human health and diseases. Measuring the mechanical property of individual cells may help us to understand the mechanism of diseases at cell level and provide new methods for disease diagnosis and personalized treatment. In this paper, the poly-l-lysine was used to immobilize Burkitt's lymphoma (BL)cells onto the glass substrate for being imaged in fluid

Mi Li; Lianqing Liu; Ning Xi; Yuechao Wang; Zaili Dong; Xiubin Xiao; Weijing Zhang

2010-01-01

20

Stiffness constant measurement in Ni?Fe alloys by neutron inelastic scattering  

NASA Astrophysics Data System (ADS)

Stiffness constant D has been measured in Ni-Fe alloys in a concentration range up to 68% of iron by neutron inelastic scattering, at room temperature and low temperature. Stiffness constant D decreases more strongly in the range of 60-68% iron concentration and a noticeable enhancement of the spin-wave width occurs in that region.

Hennion, M.; Hennion, B.; Castets, A.; Tocchetti, D.

1975-10-01

21

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

22

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

PubMed

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

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

2013-04-12

23

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

PubMed Central

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

Tian, Lian; Chesler, Naomi C.

2012-01-01

24

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

NASA Astrophysics Data System (ADS)

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

Zheng, Yun; Su, Chanmin; Getty, Stephanie

2010-08-01

25

Measures of Arterial Stiffness in Youth With Type 1 and Type 2 Diabetes  

PubMed Central

OBJECTIVE Arterial stiffness occurs early in the atherosclerotic process; however, few data are available concerning risk factors for arterial stiffness in youth with diabetes. We identified factors associated with arterial stiffness in youth with diabetes and assessed the effects of these factors on the relationship between arterial stiffness and diabetes type (type 1 vs. type 2). RESEARCH DESIGN AND METHODS A subset of patients from the SEARCH for Diabetes in Youth study with type 1 (n = 535) and type 2 diabetes (n = 60), aged 10–23 years (52% male; 82% non-Hispanic white; diabetes duration 65 ± 49 months) had arterial stiffness, anthropometrics, blood pressure, fasting lipids, and A1C measured. Arterial stiffness was measured by brachial distensibility (brachD), pulse wave velocity (PWV), and augmentation index adjusted to heart rate of 75 beats/min (AI75). RESULTS Youth with type 2 diabetes had worse brachD (5.2 ± 0.9 vs. 6.1 ± 1.2%/mmHg), PWV (6.4 ± 1.3 vs. 5.3 ± 0.8 m/s), and AI75 (6.4 ± 9.9 vs. 2.2 ± 10.2%) than those with type 1 diabetes (P < 0.01 for each). These differences were largely mediated through increased central adiposity and higher blood pressure in youth with type 2 diabetes. We also found a pattern of association of arterial stiffness measures with waist circumference and blood pressure, independent of diabetes type. CONCLUSIONS Youth with type 2 diabetes have worse arterial stiffness than similar youth with type 1 diabetes. Increased central adiposity and blood pressure are associated with measures of arterial stiffness, independent of diabetes type. Whether these findings indicate that youth with type 2 diabetes will be at higher risk for future complications requires longitudinal studies.

Wadwa, R. Paul; Urbina, Elaine M.; Anderson, Andrea M.; Hamman, Richard F.; Dolan, Lawrence M.; Rodriguez, Beatriz L.; Daniels, Stephen R.; Dabelea, Dana

2010-01-01

26

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

27

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.

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

2011-01-01

28

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.

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

2014-01-01

29

Physical activity is independently associated with multiple measures of arterial stiffness in adolescents and young adults.  

PubMed

Physical activity (PA) is associated with decreased levels of arterial stiffness in adults, but the relationship between PA and multiple measures of arterial stiffness in adolescents and young adults is not clear. The objective of this study was to test the hypothesis that PA is an independent predictor of multiple measures of arterial stiffness in adolescents and young adults. A total of 548 participants were enrolled in a study of the cardiovascular effects of obesity and type 2 diabetes mellitus (T2DM) (lean, 201; obese, 191; T2DM, 156). Anthropometrics, blood pressure, central and peripheral measures of arterial stiffness (pulse wave velocity, brachial distensibility, and augmentation index), blood (lipids and metabolic tests), and accelerometry data were collected. General linear modeling was performed to test for the independent relationship of PA on arterial stiffness. The mean age of the participants was 17.9 years (standard deviation, 3.5 years). After adjusting for other cardiovascular disease risk factors such as age, sex, body size, mean arterial pressure, and the presence of obesity or T2DM, PA was an independent predictor of augmentation index and brachial distensibility (P < .001). A greater effect of PA on pulse wave velocity was found in participants with T2DM (P = .009) compared with participants in the lean or obese groups. Physical activity is significantly and independently associated with multiple measures of arterial stiffness in adolescents and young adults. The role of PA in the prevention of cardiovascular disease target organ damage in youth, independent of energy balance, merits further exploration. PMID:22153839

Edwards, Nicholas M; Daniels, Stephen R; Claytor, Randall P; Khoury, Philip R; Dolan, Lawrence M; Kimball, Thomas R; Urbina, Elaine M

2012-06-01

30

Physical activity is independently associated with multiple measures of arterial stiffness in adolescents and young adults  

PubMed Central

Physical activity (PA) is associated with decreased levels of arterial stiffness in adults, but the relationship between PA and multiple measures of arterial stiffness in adolescents and young adults is not clear. The objective of this study was to test the hypothesis that PA is an independent predictor of multiple measures of arterial stiffness in adolescents and young adults. A total of 548 participants were enrolled in a study of the cardiovascular effects of obesity and type 2 diabetes mellitus (T2DM) (lean, 201; obese, 191; T2DM, 156). Anthropometrics, blood pressure, central and peripheral measures of arterial stiffness (pulse wave velocity, brachial distensibility, and augmentation index), blood (lipids and metabolic tests), and accelerometry data were collected. General linear modeling was performed to test for the independent relationship of PA on arterial stiffness. The mean age of the participants was 17.9 years (standard deviation, 3.5 years). After adjusting for other cardiovascular disease risk factors such as age, sex, body size, mean arterial pressure, and the presence of obesity or T2DM, PA was an independent predictor of augmentation index and brachial distensibility (P < .001). A greater effect of PA on pulse wave velocity was found in participants with T2DM (P = .009) compared with participants in the lean or obese groups. Physical activity is significantly and independently associated with multiple measures of arterial stiffness in adolescents and young adults. The role of PA in the prevention of cardiovascular disease target organ damage in youth, independent of energy balance, merits further exploration.

Edwards, Nicholas M.; Daniels, Stephen R.; Claytor, Randall P.; Khoury, Philip R.; Dolan, Lawrence M.; Kimball, Thomas R.; Urbina, Elaine M.

2011-01-01

31

Prognostic Significance of Home Arterial Stiffness Index Derived From Self-Measurement of Blood Pressure: The Ohasama Study  

Microsoft Academic Search

BackgroundArterial stiffness is a stroke risk factor. The home arterial stiffness index (HASI) can be calculated from self-measured blood pressure using the same formula as the calculation of ambulatory arterial stiffness index (AASI).MethodsIn 2,377 inhabitants (baseline age, 35–96 years) without a history of stroke, home blood pressure was measured once every morning for 26 days (median). HASI was defined as

Masahiro Kikuya; Takayoshi Ohkubo; Michihiro Satoh; Takanao Hashimoto; Takuo Hirose; Hirohito Metoki; Taku Obara; Ryusuke Inoue; Kei Asayama; Haruhisa Hoshi; Kazuhito Totsune; Hiroshi Satoh; Jan A. Staessen; Yutaka Imai

2012-01-01

32

Glycation increases human annulus fibrosus stiffness in both experimental measurements and theoretical predictions  

Microsoft Academic Search

One of the primary age-related changes to collagenous tissues is the increased concentration of advanced glycation endproducts (AGEs). Although AGEs have been shown to increase the mechanical stiffness of many tissues, their influence on the mechanical properties of the annulus fibrosus has not been measured experimentally. In previous theoretical work, we hypothesized that the mechanical influence of AGEs on the

Diane R. Wagner; Karen M. Reiser; Jeffrey C. Lotz

2006-01-01

33

Indentation instrument for the measurement of cartilage stiffness under arthroscopic control  

Microsoft Academic Search

Changes in the biomechanical properties of articular cartilage are one of the first signs of the tissue degeneration. We have developed a small size indentation instrument for the quantification of cartilage stiffness under arthroscopic control. During measurement, the indenter imposes a constant deformation on the cartilage and the maximal indenter force, by which the cartilage resists the deformation, is used

T. Lyyra; J. Jurvelin; P. Pitkänen; U. Väätäinen; I. Kiviranta

1995-01-01

34

Increased osteopontin and liver stiffness measurement by transient elastography in biliary atresia  

PubMed Central

AIM: To analyze plasma osteopontin levels and liver stiffness using transient elastography in postoperative biliary atresia (BA) children compared with healthy controls. METHODS: Thirty children with postoperative BA and 10 normal controls were enrolled. The patients were categorized into two groups according to their jaundice status. Plasma levels of osteopontin were determined using commercially available enzyme-linked immunosorbent assay. Liver stiffness was measured by using transient elastography (Fibroscan). Ten validated Fibroscan measurements were performed in each patient and control with the result expressed in kilopascals (kPa). RESULTS: Plasma osteopontin was significantly elevated in BA children compared with that of healthy controls (47.0 ± 56.4 ng/mL vs 15.1 ± 15.0 ng/mL, P = 0.01). The liver stiffness measurement was markedly elevated in the patients with BA compared with that of controls (26.9 ± 24.6 kPa vs 3.9 ± 0.7 kPa, P = 0.001). Subgroup analysis showed that the BA patients with jaundice had more pronounced plasma osteopontin levels than those without jaundice (87.1 ± 61.6 ng/mL vs 11.9 ± 6.1 ng/mL, P = 0.001). Furthermore, the mean liver stiffness was significantly greater in the jaundiced BA patients compared with non-jaundiced patients (47.7 ± 21.8 kPa vs 8.7 ± 3.0 kPa, P = 0.001). Additionally, plasma osteopontin was positively related to serum total bilirubin (r = 0.64, P < 0.001). There was also a correlation between plasma osteopontin and liver stiffness values (r = 0.60, P < 0.001). CONCLUSION: High plasma osteopontin positively correlated with degree of hepatic fibrosis and could be used as a biochemical parameter reflecting disease severity in postoperative BA children.

Honsawek, Sittisak; Chayanupatkul, Maneerat; Chongsrisawat, Voranush; Vejchapipat, Paisarn; Poovorawan, Yong

2010-01-01

35

Validation of Arteriograph – A New Oscillometric Device to Measure Arterial Stiffness in Patients on Maintenance Hemodialysis  

Microsoft Academic Search

Background: Measuring arterial stiffness (augmentation index (AI), aortic pulse wave velocity (PWV)) in hemodialysis (HD) patients has prognostic significance. To assess its validity, the new oscillometric Arteriograph device (AIA, PWVA) was compared to the validated PulsePen tonometer (AIP, PWVP). Methods: AI and PWV were measured in 98 patients with both devices before HD. Validity was evaluated by Pearson’s correlation, Bland-Altman

János Nemcsik; József Egresits; Taha El Hadj Othmane; Bertalan Csaba Fekete; Erzsébet Fodor; Tamás Szabó; Zoltán Járai; Csaba Jekkel; István Kiss; András Tislér

2009-01-01

36

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

37

Glycation increases human annulus fibrosus stiffness in both experimental measurements and theoretical predictions  

Microsoft Academic Search

One of the primary age-related changes to collagenous tissues is the increased concentration of advanced glycation endproducts (AGEs). Although AGEs have been shown to increase the mechanical stiffness of many tissues,their influence on the mechanical properties of the annulus fibrosus has not been measured experimentally. In previous theoretical work,we hypothesized that the mechanical influence of AGEs on the annulus could

Diane R. Wagnera; Karen M. Reiser; Jeffrey C. Lotz

2005-01-01

38

Estimation of Complex-Valued Stiffness Using Acoustic Waves Measured with Magnetic Resonance  

Microsoft Academic Search

Tissue stiffness can be a useful indicator of diseased tissue. Noninvasive quantitation of the mechanical properties of tissue\\u000a could improve early detection of such pathology. A method for detecting displacement from propagating shear waves using a\\u000a phase-contrast MRI technique has been developed previously. In this chapter the principles behind the measurement technique\\u000a are reviewed, and the mechanical properties that can

Travis Oliphant; Richard Ehman; James Greenleaf

39

Investigation of nanoindentation on Co\\/Mo multilayers by the continuous stiffness measurement technique  

Microsoft Academic Search

The mechanical properties of evaporated Co\\/Mo multilayers with periodicity of 4–16 nm were investigated. The microstructures of the films were analyzed using X-ray diffraction and transmission electron microscopy. Continuous stiffness measurement technique was used in the nanoindentation tests to determine the hardness and elastic modulus of the films. A Hall–Petch-like behavior is observed in the Co\\/Mo multilayers, in which the

G. H. Yang; B. Zhao; Y. Gao; F. Pan

2005-01-01

40

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.

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

2014-01-01

41

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.

2014-01-01

42

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

PubMed Central

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

Wentland, Andrew L.; Grist, Thomas M.

2014-01-01

43

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

PubMed

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

Wentland, Andrew L; Grist, Thomas M; Wieben, Oliver

2014-04-01

44

An Lsm2Lsm7 Complex in Saccharomyces cerevisiae Associates with the Small Nucleolar RNA snR5  

Microsoft Academic Search

Sm-like (Lsm) proteins function in a variety of RNA-processing events. In yeast, the Lsm2-Lsm8 complex binds and stabilizes the spliceosomal U6 snRNA, whereas the Lsm1-Lsm7 complex functions in mRNA decay. Here we report that a third Lsm complex, consisting of Lsm2-Lsm7 proteins, associates with snR5, a box H\\/ACA snoRNA that functions to guide site-specific pseudouridylation of rRNA. Experiments in which

Cesar F. Fernandez; Barbara K. Pannone; Xinguo Chen; Gabriele Fuchs; Sandra L. Wolin

2004-01-01

45

Liver Stiffness by Transient Elastography Predicts Liver-Related Complications and Mortality in Patients with Chronic Liver Disease  

PubMed Central

Background Liver stiffness measurement (LSM) by transient elastography (TE, FibroScan) is a validated method for noninvasively staging liver fibrosis. Most hepatic complications occur in patients with advanced fibrosis. Our objective was to determine the ability of LSM by TE to predict hepatic complications and mortality in a large cohort of patients with chronic liver disease. Methods In consecutive adults who underwent LSM by TE between July 2008 and June 2011, we used Cox regression to determine the independent association between liver stiffness and death or hepatic complications (decompensation, hepatocellular carcinoma, and liver transplantation). The performance of LSM to predict complications was determined using the c-statistic. Results Among 2,052 patients (median age 51 years, 65% with hepatitis B or C), 87 patients (4.2%) died or developed a hepatic complication during a median follow-up period of 15.6 months (interquartile range, 11.0–23.5 months). Patients with complications had higher median liver stiffness than those without complications (13.5 vs. 6.0 kPa; P<0.00005). The 2-year incidence rates of death or hepatic complications were 2.6%, 9%, 19%, and 34% in patients with liver stiffness <10, 10–19.9, 20–39.9, and ?40 kPa, respectively (P<0.00005). After adjustment for potential confounders, liver stiffness by TE was an independent predictor of complications (hazard ratio [HR] 1.05 per kPa; 95% confidence interval [CI] 1.03–1.06). The c-statistic of liver-stiffness for predicting complications was 0.80 (95% CI 0.75–0.85). A liver stiffness below 20 kPa effectively excluded complications (specificity 93%, negative predictive value 97%); however, the positive predictive value of higher results was sub-optimal (20%). Conclusions Liver stiffness by TE accurately predicts the risk of death or hepatic complications in patients with chronic liver disease. TE may facilitate the estimation of prognosis and guide management of these patients.

Pang, Jack X. Q.; Zimmer, Scott; Niu, Sophia; Crotty, Pam; Tracey, Jenna; Pradhan, Faruq; Shaheen, Abdel Aziz M.; Coffin, Carla S.; Heitman, Steven J.; Kaplan, Gilaad G.; Swain, Mark G.; Myers, Robert P.

2014-01-01

46

Simultaneous mechanical stiffness and electrical potential measurements of living vascular endothelial cells using combined atomic force and epifluorescence microscopy  

NASA Astrophysics Data System (ADS)

The degree of mechanical stiffness of vascular endothelial cells determines the endogenous production of the vasodilating gas nitric oxide (NO). However, the underlying mechanisms are not yet understood. Experiments on vascular endothelial cells suggest that the electrical plasma membrane potential is involved in this regulatory process. To test this hypothesis we developed a technique that simultaneously measures the electrical membrane potential and stiffness of vascular endothelial cells (GM7373 cell line derived from bovine aortic endothelium) under continuous perfusion with physiological electrolyte solution. The cellular stiffness was determined by nano-indentation using an atomic force microscope (AFM) while the electrical membrane potential was measured with bis-oxonol, a voltage-reporting fluorescent dye. These two methods were combined using an AFM attached to an epifluorescence microscope. The electrical membrane potential and mechanical stiffness of the same cell were continuously recorded for a time span of 5 min. Fast fluctuations (in the range of seconds) of both the electrical membrane potential and mechanical stiffness could be observed that were not related to each other. In contrast, slow cell depolarizations (in the range of minutes) were paralleled by significant increases in mechanical stiffness. In conclusion, using the combined AFM-fluorescence technique we monitored for the first time simultaneously the electrical plasma membrane potential and mechanical stiffness in a living cell. Vascular endothelial cells exhibit oscillatory non-synchronized waves of electrical potential and mechanical stiffness. The sustained membrane depolarization, however, is paralleled by a concomitant increase of cell stiffness. The described method is applicable for any fluorophore, which opens new perspectives in biomedical research.

Callies, Chiara; Schön, Peter; Liashkovich, Ivan; Stock, Christian; Kusche-Vihrog, Kristina; Fels, Johannes; Sträter, Alexandra S.; Oberleithner, Hans

2009-04-01

47

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.

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

2012-01-01

48

Feasibility and Significance of in vivo Mean Spleen Stiffness Measurement by Magnetic Resonance Elastography for Assessing Portal Hypertension  

PubMed Central

Background Liver stiffness measurement is associated with portal hypertension in patients with chronic liver disease. However, the relationship between spleen stiffness and clinically significant portal hypertension remains unknown. Aims To determine the feasibility of measuring spleen stiffness with magnetic resonance (MR) elastography and to prospectively test this technique in healthy volunteers and patients with liver fibrosis. Methods Following Institutional Review Board approval, spleen stiffness was measured with MR elastography in 12 healthy volunteers (mean age, 37 years; age range, 25-82 years) and 38 patients with various etiologies of chronic liver disease (mean age, 56 years; age range, 36–60 years). Various statistical analyses were performed to assess all measurements. Results MR elastography of the spleen was successfully performed in all volunteers and patients. The mean spleen stiffness was significantly lower in volunteers (mean, 3.6 kPa ± 0.3) than it was in patients with liver fibrosis (mean, 5.6 kPa ± 5.0, range, 2.7–19.2 kPa; p < .001). In addition, a significant correlation between liver and spleen stiffness was observed for the entire cohort (r2=.75, p<0.001). Predictors of spleen stiffness were splenomegaly, spleen volume, and platelet count. In the setting of cirrhosis, the presence of esophageal varices was observed in 100% of patients with mean spleen stiffness values ? 10.5 kPa. Conclusion MR elastography of the spleen is feasible and shows promise as a quantitative method for predicting the presence of esophageal varices in patients with advanced hepatic fibrosis.

Talwalkar, Jayant A.; Yin, Meng; Venkatesh, Sudhakar; Rossman, Phillip J.; Grimm, Roger C.; Manduca, Armando; Romano, Anthony; Kamath, Patrick S.; Ehman, Richard L.

2010-01-01

49

Extrinsic Fabry-Perot interferometer for measuring the stiffness of ciliary bundles on hair cells.  

PubMed

We have developed an extrinsic Fabry-Perot interferometer (EFPI) to measure displacements of microscopic, living organelles in the inner ear. The EFPI is an optical phase-shifted instrument that can be used to measure nanometer displacements. The instrument transmits a coherent light signal to the end of a single glass optical fiber where the measurement is made. As the coherent light reaches the end of the fiber, part of this incident signal is reflected off the internal face of the fiber end (reference reflection) and part is transmitted through the end of the fiber. This transmitted light travels a short distance and is reflected off the surface whose displacement is to be measured (the target). This sensing reflection then reenters the fiber where it interferes with the reference reflection. The resulting interference signal then travels up the same optical fiber to a detector, where it is converted into a voltage that can be read from an oscilloscope. When the target moves, the phase relation between reference and sensing reflections changes, and the detector receives a modulated signal proportional to the target movement. Reflections of as little as 1% at both the sensor tip and target surfaces produce good results with this system. We use the EFPI in conjunction with fine glass whiskers to measure the stiffness (force per unit deflection) of stereociliary bundles on hair cells of the inner ear. The forces generated are in the tenths of picoNewton range and the displacements are tens of nanometers. Here we describe the EFPI and its development as a method for measuring displacements of microscopic organelles in a fluid medium. We also report experiments to validate the accuracy of the EFPI output and preliminary measurements of ciliary bundle stiffness in the posterior semicircular canal. PMID:10097468

Barrett, M D; Peterson, E H; Grant, J W

1999-03-01

50

Intracardiac echocardiography measurement of dynamic myocardial stiffness with shear wave velocimetry.  

PubMed

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 measure quantitatively 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 article 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

2012-07-01

51

Experimental measurements of hydrodynamic stiffness matrices for a centrifugal pump impeller  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

52

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.

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

2012-01-01

53

Shearwave Dispersion Ultrasonic Vibrometry (SDUV) for measuring prostate shear stiffness and viscosity - An in vitro pilot study  

PubMed Central

This paper reports shear stiffness and viscosity “virtual biopsy” measurements of three excised non-cancerous human prostates using shearwave dispersion ultrasound vibrometry (SDUV) in vitro. Improved methods for prostate guided-biopsy are required to effectively guide needle biopsy to the suspected site. In addition, tissue stiffness measurement helps identifying a suspected site to perform biopsy because stiffness has been shown to correlate with pathology. More importantly, early detection of prostate cancer may guide minimally-invasive therapy and eliminate insidious procedures. In this work, “virtual” biopsies were taken in multiple locations in three excised prostates. Then, SDUV shear elasticity and viscosity measurements have been performed at the selected “suspicious” locations within the prostates. SDUV measurements of prostate elasticity and viscosity are generally in agreement with preliminary values reported previously in the literature. It is however important to emphasize that the obtained viscoelastic parameters values are local, and not a mean value for the whole prostate.

Urban, M.W.; Fatemi, M.; Greenleaf, J.F.

2011-01-01

54

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

NASA Astrophysics Data System (ADS)

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

Laurent, Justine; Steinberger, Audrey; Bellon, Ludovic

2013-06-01

55

Feasibility and repeatability for in vivo measurements of stiffness gradients in the canine gastrocnemius tendon using an acoustoelastic strain gauge.  

PubMed

B-mode ultrasound is an established imaging modality for evaluating canine tendon injury. However, full extent of tendon injury often remains difficult to estimate, as small changes in sonographic appearance are associated with large changes in biomechanical strength. The acoustoelastic strain gauge (ASG) is an ultrasound-based tissue evaluation technique that relates the change in echo intensity observed during relaxation or stretching of tendons to the tissue's mechanical properties. This technique deduces stiffness gradient (the rate of change of normalized stiffness as a function of tissue strain) by analyzing the ultrasound dynamic images captured from gradually deforming tissue. ASG has been proven to accurately model strain and stiffness within tendons in vitro. To determine the feasibility and repeatability for in vivo ASG measurements of canine tendon function, stiffness gradients for the gastrocnemius tendons of 10 clinically normal dogs were recorded by two nonindependent observers at three sites (musculotendinous junction, mid tendon, and insertion). Average stiffness gradient indices (0.0132, 0.0141, 0.0136) and dispersion values (0.0053, 0.0054, 0.0057) for each site, respectively, were consistent with published mechanical properties for normal canine tendon. Mean differences of the average stiffness gradient index and dispersion value between observers and between limbs for each site were less than 16%. Using interclass coefficients (ICC), intra-observer (ICC 0.79-0.98) and interobserver (ICC 0.77-0.95) reproducibility was good to excellent. Right and left limb values were symmetric (ICC 0.74-0.92). Findings from this study indicated that ASG is a feasible and repeatable technique for measuring stiffness gradients in canine tendons. PMID:23663072

Ellison, Michelle; Kobayashi, Hirohito; Delaney, Fern; Danielson, Kelson; Vanderby, Ray; Muir, Peter; Forrest, Lisa J

2013-01-01

56

Mechanism of force enhancement during stretching of skeletal muscle fibres investigated by high time-resolved stiffness measurements.  

PubMed

Stretching of active muscles leads to a great enhancement of the force developed without increased ATP consumption. The mechanism of force enhancement is still debated and it is not clear if it is due to increased crossbridge strain or to a stretch-induced increase in crossbridge number. The present study, performed on single fibres from tibialis anterior or interosseus muscles of the frog at 5 °C, was aimed at clarifying this point. A striation follower device was used to measure sarcomere length changes. Force was measured during the application of stretches (0.15-3.9 ms duration, 3-7.8 nm per half-sarcomere amplitude) to activated fibres. Small 4 kHz sinusoidal length oscillations, superimposed on the stretches, were used to calculate fibre stiffness with high time resolution. Stiffness increased during the stretch then subsequently decayed, all in parallel with tension. Likewise, during quick releases, stiffness decreased during the release then subsequently recovered in parallel with tension. Comparison of tension and stiffness both during the tetanus rise and also during stretches which doubled tension, imposed on the tetanus rise, indicated that stretch-induced crossbridge recruitment was only about 11 %, suggesting that force enhancement by stretching is mainly due to an increase of individual crossbridge force, whereas crossbridge recruitment plays only a minor role. The accompanying stiffness changes can be explained by non-linearity of myofilament compliance. PMID:23296372

Nocella, Marta; Bagni, Maria Angela; Cecchi, Giovanni; Colombini, Barbara

2013-02-01

57

Prostate tissue stiffness as measured with a resonance sensor system: a study on silicone and human prostate tissue in vitro.  

PubMed

Prostate cancer is the most common form of cancer in men in Europe and in the USA. Some prostate tumours are stiffer than the surrounding normal tissue, and it could therefore be of interest to measure prostate tissue stiffness. Resonance sensor technology based on piezoelectric resonance detects variations in tissue stiffness due to a change in the resonance frequency. An impression-controlled resonance sensor system was used to detect stiffness in silicone rubber and in human prostate tissue in vitro using two parameters, both combinations of frequency change and force. Variations in silicone rubber stiffness due to the mixing ratio of the two components could be detected (p<0.05) using both parameters. Measurements on prostate tissue showed that there existed a statistically significant (MANOVA test, p<0.001) reproducible difference between tumour tissue (n=13) and normal healthy tissue (n=98) when studying a multivariate parameter set. Both the tumour tissue and normal tissue groups had variations within them, which were assumed to be related to differences in tissue composition. Other sources of error could be uneven surfaces and different levels of dehydration for the prostates. Our results indicated that the resonance sensor could be used to detect stiffness variations in silicone and in human prostate tissue in vitro. This is promising for the development of a future diagnostic tool for prostate cancer. PMID:16937195

Jalkanen, Ville; Andersson, Britt M; Bergh, Anders; Ljungberg, Börje; Lindahl, Olof A

2006-07-01

58

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.

Bastard, Cecile; Bosisio, Matteo R; Chabert, Michele; Kalopissis, Athina D; Mahrouf-Yorgov, Meriem; Gilgenkrantz, Helene; Mueller, Sebastian; Sandrin, Laurent

2011-01-01

59

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

PubMed Central

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

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

2013-01-01

60

Reliability and validity of field-based measures of leg stiffness and reactive strength index in youths  

Microsoft Academic Search

The aim of the study was to assess the reliability of a mobile contact mat in measuring a range of stretch–shortening cycle parameters in young adolescents. Additionally, vertical leg stiffness using contact mat data was validated against a criterion method using force–time data. The reliability study involved 18 youths completing a habituation and three separate test sessions, while 20 youths

Rhodri S. Lloyd; Jon L. Oliver; Michael G. Hughes; Craig A. Williams

2009-01-01

61

Glycation increases human annulus fibrosus stiffness in both experimental measurements and theoretical predictions.  

PubMed

One of the primary age-related changes to collagenous tissues is the increased concentration of advanced glycation endproducts (AGEs). Although AGEs have been shown to increase the mechanical stiffness of many tissues, their influence on the mechanical properties of the annulus fibrosus has not been measured experimentally. In previous theoretical work, we hypothesized that the mechanical influence of AGEs on the annulus could be represented in an additive strain energy function with a separate crosslinking term, but the material coefficients associated with this term were not correlated with AGE concentration. In the current study, we measured the tensile stress-strain response of the human annulus in the axial direction both before and after glycation with methylglyoxal. Using nonlinear regression, the strain energy function was simultaneously applied to these new data and to data from a wide range of experimental protocols reported in the literature to determine values for the material coefficients appearing in the constitutive equation. Nonenzymatic collagen crosslinking induced a statistically significant change in annular material properties. Furthermore, the concentration of AGEs correlated positively with the material coefficients found in the terms of the strain energy function that we associate with collagen crosslinking. These data suggest that AGEs contribute to age-related disc stiffening as well as validate the hypothesis that biochemical constituents can be related mathematically to tissue behavior. In the future, this structurally guided constitutive relationship may provide further insight into the structure-function relationships of the annulus fibrosus. PMID:15878594

Wagner, Diane R; Reiser, Karen M; Lotz, Jeffrey C

2006-01-01

62

Effectof MgATP on stiffness measured at two frequencies in Ca2+-activated muscle fibers.  

PubMed Central

The stiffness of skinned crayfish single muscle fibers was continuously monitored at two frequencies. The length of the fibers was oscillated by the sum of two sine waves (5 Hz and 100 Hz) of small amplitudes. In saline containing saturating amounts of Ca2+, the stiffness ratio (5 Hz:100Hz) was constant as the MgATP (substrate) concentration was raised from 0 to 2 mu M, then it decreased with a further increment in MgATP. The systematic decrease in the stiffness ratio in MgATP above 2 mu M indicates the presence of faster transitions in the cross-bridge cycle. This dependence of the stiffness ratio on MgATP is predictable if we use the two-state model of A. F. Huxley (1957) with a modification, in which MgATP promotes the dissociation of the attached cross-bridges.

Kawai, M; Brandt, P W

1977-01-01

63

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

PubMed

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

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

2012-07-26

64

Measurement of Local Gradients of Thin Film Stiffness using Ultrasonic Force Microscopy  

NASA Astrophysics Data System (ADS)

With the integration of the inlaid copper technology into the manufacturing process for advanced microelectronic products, topics like stress-induced migration and adhesion between Cu interconnects, diffusion barriers and dielectrics have to be understood. Furthermore, porous ultra low-k materials with different mechanical properties compared to the state-of-the art dielectrics will be implemented in the near future. As a consequence, it will be necessary to install the appropriate techniques and tools to measure and monitor mechanical properties with high lateral resolution. One promising method with the capability of mapping thin film stiffness on a nanometer scale is Ultrasonic Force Microscopy (UFM). It will be shown how UFM can be used to detect the delamination of thin films from the substrate. Materials with different mechanical properties can be distinguished based on UFM maps. The effect of topography, surface free energy, and AFM tip shape on the UFM signal as well as the capability of UFM to characterize porous materials will be presented.

Geisler, Holm; Kraatz, Matthias; Zschech, Ehrenfried

2002-03-01

65

In situ measurement of structural mass, stiffness, and damping using a reaction force actuator and a laser Doppler vibrometer  

NASA Astrophysics Data System (ADS)

The problem of structural parameter measurements needs a total solution bridging theory and experiments. In this paper, a practical methodology for in situ measurements of structural mass, stiffness, and damping is presented for built-up structures. As for the experimental uniqueness of the methodology, a reaction force actuator and non-contact optical device are utilized respectively as an input force generator and output displacement measurer, providing a fundamental data set of the proposed numerical algorithm for data-driven structural parameter estimation. The algorithm autonomously estimates the diagonalized mass, symmetric stiffness, optimal non-proportional damping, and suboptimal proportional damping matrices for multi-degrees-of-freedom structures. Structural parameter measurements of two built-up structures followed by a comparison with conventional measurements are used as examples for verification of the accuracy of the proposed methodology.

Kim, Junhee; Kim, Kiyoung; Sohn, Hoon

2013-08-01

66

Microfluidic acoustic trapping force and stiffness measurement using viscous drag effect  

PubMed Central

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

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

2013-01-01

67

Significance of liver stiffness measurement by acoustic radiation force impulse (ARFI) among hepatitis C patients.  

PubMed

The degree of liver fibrosis is strongly associated with the antiviral effect of interferon on chronic hepatitis C patients. In this study, the accuracy of acoustic radiation force impulse (ARFI) in assessing liver fibrosis and the association between liver stiffness using ARFI and antiviral effects were investigated. The 124 patients with chronic hepatitis C enrolled in this study included 94 with HCV genotype 1 and 40 (30%) with moderate fibrosis (METAVIR fibrosis score???F2). Sixty-one patients received pegylated interferon (peg-IFN) plus ribavirin combination therapy and the treatment responses were assessed. The shear wave velocity (Vs value) by ARFI had a strong correlation with the histological fibrosis stage (P?measured by ARFI could not predict the treatment response for patients with HCV genotype 2. It is concluded that the combination of ARFI at cut off of 1.4?m/sec and IL28B may be useful for patients with chronic hepatitis C with genotype 1 treated with peg-IFN/ribavirin combination therapy. PMID:24338811

Yamada, Ryoko; Hiramatsu, Naoki; Oze, Tsugiko; Morishita, Naoki; Harada, Naoki; Miyazaki, Masanori; Yakushijin, Takayuki; Miyagi, Takuya; Yoshida, Yuichi; Tatsumi, Tomohide; Kanto, Tatsuya; Hayashi, Norio; Takehara, Tetsuo

2014-02-01

68

Interaction of leg stiffness and surface stiffness during human hopping  

Microsoft Academic Search

Ferris, Daniel P., and Claire T. Farley. Interaction of leg stiffness and surface stiffness during human hopping. J. Appl. Physiol. 82(1): 15±22, 1997.DWhen mammals run, the overall musculoskeletal system behaves as a single linear ``leg spring.''We used force platform and kinematic measurements to determine whether leg spring stiffness (kleg) is adjusted to accommodate changes in surface stiffness (ksurf) when hu-mans

DANIEL P. FERRIS; CLAIRE T. FARLEY

1997-01-01

69

Nanoindentation and Contact Stiffness Measurement Using Force Modulation with a Capacitive Load-Displacement Transducer.  

National Technical Information Service (NTIS)

We have implemented a force modulation technique for nanoindentation using a three-plate capacitive load-displacement transducer. The stiffness sensitivity of the instrument is approximately 0.1 N/m. We show that the sensitivity of this instrument is suff...

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

1999-01-01

70

Shear wave dispersion ultrasonic vibrometry for measuring prostate shear stiffness and viscosity: an in vitro pilot study.  

PubMed

This paper reports shear stiffness and viscosity "virtual biopsy" measurements of the three excised noncancerous human prostates using a new tool known as shear wave dispersion ultrasound vibrometry (SDUV) in vitro. Improved methods for prostate guided-biopsy are required to effectively guide needle biopsy to the suspected site. In addition, tissue stiffness measurement helps in identifying a suspected site to perform biopsy because stiffness has been shown to correlate with pathologies, such as cancerous tissue. More importantly, early detection of prostate cancer may guide minimally invasive therapy and eliminate insidious procedures. In this paper, "virtual biopsies" were taken in multiple locations in three excised prostates; SDUV shear elasticity and viscosity measurements were performed at the selected "suspicious" locations within the prostates. SDUV measurements of prostate elasticity and viscosity are generally in agreement with preliminary values previously reported in the literature. It is, however, important to emphasize here that the obtained viscoelastic parameters values are local, and not a mean value for the whole prostate. PMID:20595086

Mitri, F G; Urban, M W; Fatemi, M; Greenleaf, J F

2011-02-01

71

In-situ AFM measurement of single fibrin fiber stiffness before and after addition of Factor XIII  

NASA Astrophysics Data System (ADS)

Fibrin fibers are the main structural component of blood clots. Ligation of fibrin by native Factor XIII (FXIII) serves to fine tune the mechanical properties of the clot. Mechanical alteration is important because a clot must be stiff enough to resist forces from blood flow but compliant enough to prevent embolism (fracture). Cone and Plate measurements of fibrin gels, which represent the vast majority of mechanical measurements on fibrin, show that FXIII increases clot stiffness. More recently, measurements on individual fibrin fibers show that they exhibit remarkable extensibility, breaking at strains up to 300%. As of yet, the origin of this extensibility is not fully understood. The different responses of ligated and unligated fibrin fibers can give us clues as to it's mechanism of extension. We use a combined fluorescence/atomic force microscope to stretch individual, isolated, fibrin fibers and then compare force extension curves of the same fiber before and after addition of FXIII. We found up to a 3.5-fold increase in fiber stiffness after addition of FXIII. We also show stiffening of individual fibrin fibers after crosslinking by gluteraldehyde.

Houser, John; O'Brien, E. Timothy; Lord, Susan T.; Superfine, Richard; Falvo, Michael R.

2008-10-01

72

Electrochemical properties of LSM–CBO composite cathode  

Microsoft Academic Search

In order to develop a cathode that can be used in intermediate temperature solid oxide fuel cells (ITSOFC), the composite materials La0.8Sr0.2MnO3–Ce0.7Bi0.3O2 (LSM–CBO) has been prepared and its electrode performances are investigated below 700°C by AC impedance spectroscopy and dc polarization measurements. Results indicate that the oxygen adsorption process is the reaction rate limiting step. The polarization resistance decreases with

Hui Zhao; Lihua Huo; Shan Gao

2004-01-01

73

Performance of liver stiffness measurements by transient elastography in chronic hepatitis  

PubMed Central

AIM: To compare results of liver stiffness measurements by transient elastography (TE) obtained in our patients population with that used in a recently published meta-analysis. METHODS: This was a single center cross-sectional study. Consecutive patients with chronic viral hepatitis scheduled for liver biopsy at the outpatient ward of our Infectious Diseases Department were enrolled. TE was carried out by using FibroScan™ (Echosens, Paris, France). Liver biopsy was performed on the same day as TE, as day case procedure. Fibrosis was staged according to the Metavir scoring system. The diagnostic performance of TE was assessed by using receiver operating characteristic (ROC) curves and the area under the ROC curve analysis. RESULTS: Two hundred and fifty-two patients met the inclusion criteria. Six (2%) patients were excluded due to unreliable TE measurements. Thus, 246 (171 men and 75 women) patients were analyzed. One hundred and ninety-five (79.3%) patients had chronic hepatitis C, 41 (16.7%) had chronic hepatitis B, and 10 (4.0%) were coinfected with human immunodeficiency virus. ROC curve analysis identified optimal cut-off value of TE as high as 6.9 kPa for F ? 2; 7.9 kPa for F ? 3; 9.6 kPa for F = 4 in all patients (n = 246), and as high as 6.9 kPa for F ? 2; 7.3 kPa for F ? 3; 9.3 kPa for F = 4 in patients with hepatitis C (n = 195). Cut-off values of TE obtained by maximizing only the specificity were as high as 6.9 kPa for F ? 2; 9.6 kPa for F ? 3; 12.2 kPa for F = 4 in all patients (n = 246), and as high as 7.0 kPa for F ? 2; 9.3 kPa for F ? 3; 12.3 kPa for F = 4 in patients with hepatitis C (n = 195). CONCLUSION: The cut-off values of TE obtained in this single center study are comparable to that obtained in a recently published meta-analysis that included up to 40 studies.

Ferraioli, Giovanna; Tinelli, Carmine; Dal Bello, Barbara; Zicchetti, Mabel; Lissandrin, Raffaella; Filice, Gaetano; Filice, Carlo; Above, Elisabetta; Barbarini, Giorgio; Brunetti, Enrico; Calderon, Willy; Di Gregorio, Marta; Gulminetti, Roberto; Lanzarini, Paolo; Ludovisi, Serena; Maiocchi, Laura; Malfitano, Antonello; Michelone, Giuseppe; Minoli, Lorenzo; Mondelli, Mario; Novati, Stefano; Patruno, Savino FA; Perretti, Alessandro; Poma, Gianluigi; Sacchi, Paolo; Zanaboni, Domenico; Zaramella, Marco

2013-01-01

74

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

PubMed

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

Munz, Martin; Mills, Tom

2014-04-22

75

The measurement of flexural stiffness of multistranded electrical conductors while under tension  

Microsoft Academic Search

The ACSR Electrical conductor is a complex structure composed of layers of aluminum wires wrapped around one another over a steel-wire core. Three different test arrangements were considered for testing the static flexural stiffness. The cross-load method was easiest to implement and avoided the problems with load-spacing sensitivity of the couple method which used two forcesQ. However, the maximum usable

K. G. McConnell; W. P. Zemke

1980-01-01

76

Plasma Fluctuation Measurements in Ion Stiffness Experiments using Phase Contrast Imaging  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

77

Modeling of precipitation and Cr depletion profiles of Inconel 600 during heat treatments and LSM procedure  

Microsoft Academic Search

A model based on the thermodynamic and kinetic was conducted to simulate the Cr depletion profiles near the grain boundary in Inconel 600 during the heat treatments and laser surface melting (LSM) process using Thermo-Calc and Dictra code. Based on the good agreement of Cr concentration distribution during heat treatments measured by experiments, the microsegregation of Cr induced by cellular

Gang Bao; Kenji Shinozaki; Muneyuki Inkyo; Tomohisa Miyoshi; Motomichi Yamamoto; Yoichi Mahara; Hiroshi Watanabe

2006-01-01

78

Elastic stiffness of single-crystalline FeSe measured by picosecond ultrasonics  

NASA Astrophysics Data System (ADS)

We report investigations on the elasticity of superconducting FeSe using picosecond ultrasonic technique. The tetragonal (001) FeSe thin film, deposited on a processed SrTiO3 substrate by the pulsed laser deposition, exhibits distinct c-axis preferred orientation and single-crystalline features as a result of the x-ray diffraction. The high-quality crystallinity thus enables quantitative examinations of anisotropic stiffness coefficients (C33) of FeSe, correlating to the interatomic interaction in the simplest iron-based superconductor. Our experiment indicates a room-temperature C33 of 40.9 +/- 0.4 GPa and material stiffening of 4.3% at low temperatures, which can be explained by the weakening of anharmonic phonon-phonon interactions.

Wen, Yu-Chieh; Liao, Yang-Chung; Chang, Hsian-Hong; Mok, Boon-How; Lee, Yung-Chi; Huang, Tzu-Wen; Yeh, Kuo-Wei; Luo, Jiu-Yong; Wang, Ming-Jye; Sun, Chi-Kuang; Wu, Maw-Kuen

2011-10-01

79

On linear synchronous motor (LSM) for high speed propulsion  

Microsoft Academic Search

This paper presents the steady state performance characteristics of the LSM fed from a voltage-source frequency converter. A model, similar to the one used for conventional synchronous motor analysis, has been used to study the steady state behaviour of the LSM system. The results of the following investigations are discussed in this paper: Effects of various section lengths of the

P. Sen

1975-01-01

80

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

81

The FRX-C/LSM compression experiment  

SciTech Connect

After two years of preparation, hardware for high-power FRC compression heating studies is now being installed onto FRX-C/LSM. FRCs will be formed and translated out of the theta-pinch source, and into a compressor where the external B-field will be increased from 0.4 to 2 T in 55 ..mu..s. The compressed FRC can then be translated into a third stage for further study. A principal experimental goal is to study FRC confinement at the high energy density, n(T/sub e/ + T/sub i/) less than or equal to 1.0 /times/ 10/sup 22/ keV/m/sup 3/, associated with the large external field. Experiments are scheduled to begin in April. 11 refs., 5 figs.

Rej, D.J.; Siemon, R.E.; Taggart, D.P.

1989-01-01

82

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

83

Friction Test Specimens That Will Be Used to Measure Nonlinear Damping and Stiffness.  

National Technical Information Service (NTIS)

The funds received from the AFOSR were to be used to (1) purchase materials and machine friction test specimens and (2) refurbish a Brown and Sharpe Coordinate Measurement Machine (CMM). The specimens were used in an initially Carnegie Mellon University (...

J. H. Griffin

2004-01-01

84

The effect of regular exercise training during pregnancy on postpartum brachial-ankle pulse wave velocity, a measure of arterial stiffness.  

PubMed

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

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

2012-01-01

85

Stiffness in healing fractures.  

PubMed

Methods are available for direct measurement of stiffness in fracture healing. The methods are generally dissimilar in their technique and in some cases the applied assumptions are contrary to the principles of basic mechanics. External fixation provides the potential for direct measurement of fragment end movement, and techniques associated with this type of treatment have been applied in Belgium on more than 500 patients. These results are generally presented as decreases in flexure of the fixator bar due to constant loading, representative of increases in fracture stiffness. The same procedure is adopted to internal fixation plates and also direct strain gauge application to the healing bone--there are obvious complications due to electrical connections in the latter case. The biomedical changes occurring during healing are illustrated by the work at Cardiff where a biphase characteristic has been identified. The method used has the disadvantage in requiring the removal of the fixator for the application of the stiffness sensor recording deflection and rotation. The advantages of the technique include the more precise modeling of the bending characteristic of the tibia (the results refer to this particular skeletal element). The experimental studies at Oxford show evidence of enhanced osteogenesis when controlled intermittent deformation is applied in a cyclic manner. In a group of some 50 patients treated with induced micromovement, there is evidence that the rate of increasing fracture stiffness would allow removal of the fixator at 15 weeks compared with 24 weeks in the group with rigid fixation. The exact technique of measuring fracture stiffness has to be compared with other noninvasive test methods which include radiological examination, ultrasound, resonant vibration, and modal analysis. Many of these methods are based on linear elastic relationships which are inadequate to describe the anisotropic behavior of bones. The vibration analysis techniques are showing potential as clinical tools, and collaboration within the European community is directed towards a correlation between invasive and noninvasive methods of fracture monitoring. PMID:3319415

Richards, J

1987-01-01

86

Sensorless DTC propulsion control of PM LSM vehicle  

Microsoft Academic Search

This paper presents a sensorless direct torque control (DTC) propulsion method of a 1\\/2-scale controlled-PM linear synchronous motor (LSM) Maglev model vehicle which is not levitated and used as a PM LSM vehicle supported by the wheel. This is the first experiment for DTC to be applied to linear propulsion without position and speed sensors, which is one of the

Kinjiro YOSHIDA; Zheng DAI; M. Sato

2000-01-01

87

Interface chemistry in LSM–YSZ composite SOFC cathodes  

Microsoft Academic Search

(La,Sr)MnO3–3YSZ interface chemistry in air-annealed and operated SOFC cathodes has been studied by high spatial resolution TEM\\/EELS. Major changes in Mn L2,3 and O K ELNES were observed. A mixture of manganese 3+\\/4+ is found in the LSM bulk phase. In contact with LSM, zirconia forms a solid solution with dissolved lanthanum and manganese. Manganese is always divalent in this

M. Backhaus-Ricoult

2006-01-01

88

Stiffness adaptations in shod running.  

PubMed

When mechanical parameters of running are measured, runners have to be accustomed to testing conditions. Nevertheless, habituated runners could still show slight evolutions of their patterns at the beginning of each new running bout. This study investigated runners' stiffness adjustments during shoe and barefoot running and stiffness evolutions of shoes. Twenty-two runners performed two 4-minute bouts at 3.61 m.s-1 shod and barefoot after a 4-min warm-up period. Vertical and leg stiffness decreased during the shoe condition but remained stable in the barefoot condition, p < 0.001. Moreover, an impactor test showed that shoe stiffness increased significantly during the first 4 minutes, p < 0.001. Beyond the 4th minute, shoe properties remained stable. Even if runners were accustomed to the testing condition, as running pattern remained stable during barefoot running, they adjusted their leg and vertical stiffness during shoe running. Moreover, as measurements were taken after a 4-min warm-up period, it could be assumed that shoe properties were stable. Then the stiffness adjustment observed during shoe running might be due to further habituations of the runners to the shod condition. To conclude, it makes sense to run at least 4 minutes before taking measurements in order to avoid runners' stiffness alteration due to shoe property modifications. However, runners could still adapt to the shoe. PMID:16498177

Divert, Carolyn; Baur, Heiner; Mornieux, Guillaume; Mayer, Frank; Belli, Alain

2005-11-01

89

MEASUREMENT OF STIFFNESS CHANGES IN IMMOBILIZED MUSCLE USING MAGNETIC RESONANCE ELASTOGRAPHY  

PubMed Central

Background The isolated evaluation of changes in muscle following immobilization and disuse is a challenge in living subjects. The purpose of this study was to determine whether magnetic resonance elastography is capable of detecting these changes. Methods An animal model was created to produce a mild joint contracture following 42 days of one forelimb immobilization in a maximally flexed position with twice-daily passive exercise. Eight pairs of dog forelimbs were harvested. Magnetic resonance elastography scans were performed on the experimental limb in an extended elbow position with a torque of 0.6 Nm. Scans of the contralateral limb were performed in two conditions, position matching and torque matching. Furthermore, wet weight, cross sectional area, resting muscle length, and range of elbow joint motion were measured. Findings The muscle from the experimental limb showed significant reduction in muscle mass, cross sectional area, slack length, and range of elbow motion. When comparing limbs in position matching condition, the muscle lengths were similar, and the experimental muscle had a significantly higher shear modulus (79.1 (SD 12.0) kPa) than the contralateral muscle (31.9 (SD 24.4) kPa). When comparing limbs in torque matching conditions, the muscle strains were similar, and the experimental muscle had a significantly lower shear modulus than the contralateral muscle (113.0 (SD 24.8) kPa). Interpretation These findings suggest that following immobilization, magnetic resonance elastography has the potential to be used as a clinical tool to guide rehabilitation and as a research tool to study the loss of passive elastic components of muscle.

Muraki, Takayuki; Domire, Zachary J.; McCullough, Matthew B.; Chen, Qingshan; An, Kai-Nan

2011-01-01

90

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.

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

2013-01-01

91

Tectorial Membrane Stiffness Gradients  

PubMed Central

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

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

2007-01-01

92

Stiff-Person Syndrome  

MedlinePLUS

NINDS Stiff-Person Syndrome Information Page Table of Contents (click to jump to sections) What is Stiff-Person Syndrome? Is there ... being done? Clinical Trials Organizations What is Stiff-Person Syndrome? Stiff-person syndrome (SPS) is a rare ...

93

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

94

Assessment of the stiffness tensor of orthotropic materials from phase velocities measured by means of a line source-point receiver laser-ultrasonic method  

NASA Astrophysics Data System (ADS)

The laser ultrasonic technique is used to generate and detect ultrasonic waves in a composite specimen. When the laser beam is focused by means of a cylindrical lens, the line-source generates transient divergent waves that propagate at group velocity. The phase and group velocities of acoustic waves in elastically anisotropic solids are in general not equal. Anisotropy gives rise to folded ray curves in which the acoustic rays are more concentrated in some directions than in others. In particular the energy density can be very high at the cuspidal edges. The propagation in such media gives rise to internal diffraction by which waves are observed which are not explained by ray theory. The measurement of the stiffness tensor of an anisotropic material by means of laser generated ultrasound is a non trivial matter for essentially two reasons. First, the recovering of the coefficients from the group velocities is a double iterative numerical process that requires a high accuracy in the velocity measurement. Second, internal diffraction is not taken into account by such an algorithm and it provides undesired velocity data which induce a shift of the identified stiffness coefficients. In this paper, it is shown that phase velocities can be measured using signals generated by a line source. The measurement of the stiffness coefficients from such velocities avoids the aforementioned difficulties. The process is successfully applied to an actual composite material.

Audoin, B.; Reverdy, F.

1999-12-01

95

LSM-YSZ Cathodes with Reaction-Infiltrated Nanoparticles  

Microsoft Academic Search

To improve the LSM-YSZ cathode performance of intermediate temperature solid oxide fuel cells (SOFCs), Sm0.6Sr0.4CoO3-sigma (SSC) perovskite nanoparticles are incorporated into the cathodes by a reaction-infiltration process. The SSC particles are â20 to 80nm in diameter, and intimately adhere to the pore walls of the preformed LSM-YSZ cathodes. The SSC particles dramatically enhance single-cell performance with a 97 percent H2+3

Chun Lu; Tal Z. Sholklapper; Craig P. Jacobson; Steven J. Visco; Lutgard C. DeJonghe

2006-01-01

96

Catalytic activity and performance of LSM cathode materials in single chamber SOFC  

Microsoft Academic Search

The catalytic activity of symmetrical LSM (La0.8Sr0.2MnO3) cells operated under single chamber solid oxide fuel cell (SC-SOFC) conditions was investigated for methane-to-oxygen ratios Rin between 1 and 2. The oxidation reactions over electrodes sintered at 1100°C (LSM1100) and 1200°C (LSM1200) were studied, and the effect of any combustion was followed through electrochemical impedance spectroscopy (EIS). The activity of the LSM1100

B. Morel; R. Roberge; S. Savoie; T. W. Napporn; M. Meunier

2007-01-01

97

Functions of Lsm proteins in mRNA degradation and splicing  

Microsoft Academic Search

Recent results have identified a family of Lsm (Like Sm) proteins that are related to the Sm protein family. Seven Lsm proteins form a complex, which interacts with the U6 snRNA and functions in splicing. In addition, a different complex of Lsm proteins interacts with cytoplasmic mRNA and promotes its turnover. These diverse functions of Lsm proteins suggest that they

Weihai He; Roy Parker

2000-01-01

98

Hardware Proofs Using LCF-LSM and ELLA.  

National Technical Information Service (NTIS)

A method is described for writing the formal specifications for a digital system, a high level of design which satisfies this requirement and then a gate level realisation, using the languages LCF -LSM and ELLA. Given these formal descriptions, this paper...

W. J. Cullyer C. H. Pygott

1985-01-01

99

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

100

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

101

Tape Joint Stiffness.  

National Technical Information Service (NTIS)

This redport evaluates the stiffness for a standard tape-joint structural connection. This stiffness is frequently necessary when modeling a structure (e.g., a shock model). In general, for a standard cylindrical tape joint, the stiffness is 1.2 times gre...

R. P. Rechard

1986-01-01

102

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

103

Arterial stiffness using radial arterial waveforms measured at the wrist as an indicator of diabetic control in the elderly.  

PubMed

Although current technique of photoplethysmography (PPG) is a popular noninvasive method of waveform contour analysis in assessing arterial stiffness, data obtained are frequently affected by various environmental and physiological factors. We proposed an easily operable air pressure sensing system (APSS) for radial arterial signal capturing. Totally, 108 subjects (young, the aged with or without diabetes) were recruited from July 2009 to May 2010. Arterial waveform signals from the wrist were obtained and analyzed using Hilbert-Huang transformation (HHT). Through ensemble empirical mode decomposition (EEMD), the signals were decomposed into eight intrinsic mode functions (IMF1-8) of which IMF5 was found to be the desired signal with a discernible diastolic peak. The results showed significant differences in reflection index (RI) and stiffness index (SI) from the young subjects and those from the aged participants with or without diabetes. Significant differences in RI and SI were also noted between subjects with well-controlled diabetes and those without. Good reproducibility and correlation were demonstrated. In conclusion, the present study proposed the application of radial arterial signal capturing subsystem and HHT in acquiring more reliable data on RI and SI compared with the conventional PPG method. PMID:20923726

Wu, Hsien-Tsai; Lee, Chun-Ho; Liu, An-Bang; Chung, Wei-Sheng; Tang, Chieh-Ju; Sun, Cheuk-Kwan; Yip, Hon-Kan

2011-02-01

104

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

105

Analysis of the bending behaviour of porcine xenograft leaflets and of natural aortic valve material: bending stiffness, neutral axis and shear measurements.  

PubMed

Flexibility of the materials used in the construction of bioprosthetic heart valves is essential for proper valve operation. We therefore examined the bending behaviour of glutaraldehyde treated porcine aortic valve cusps in comparison with fresh aortic valve tissue. We repeatedly bent a total of 35 strips of fresh and treated tissue to curvatures ranging from 0.2 to 2.2 mm-1. We compared the stiffness of the two materials between circumferential and radial bending, natural and reverse curvatures and constant or variable tensile stress (0.8-40 kPa). Our results showed a weak positive relationship between bending stiffness and applied tensile stress and a strong positive dependance of stiffness on tissue thickness (t). For the fresh tissue, the bending stiffness increased in proportion to t1.14 while for the glutaraldehyde treated tissue it increased with t2.18. Fourteen strips of fresh and treated tissue were also histologically processed, sectioned and examined with polarized light microscopy. Collagen fiber wavelengths and shear deformations were measured utilizing the tissue banding patterns produced by polarized light microscopy. The neutral axis of bending was found to lie very close to the outer surface of the tissue, suggesting that aortic leaflets have a very low compressive elastic modulus. The shear strains measured in fresh tissue were 10 +/- 2.7% vs 3 +/- 4.4% for the treated, indicating a stiffening of the tissue following glutaraldehyde fixation. We conclude that both natural and bioprosthetic valve cusps have a complex flexural behaviour that cannot be modeled using simple bending principles, although the bioprosthetic material more closely approximates the simple beam than does the fresh. The non-linear elastic modulus, high compressibility and shearing between fiber layers are likely responsible for the observed behaviour of the fresh tissue, while the cross-linking and dehydrating effects of glutaraldehyde are believed to be responsible for the alteration in bending properties observed in the treated tissue. Our study suggests that bioprosthetic valve material does not adequately mimic the mechanics of the natural valve tissue, and that the current glutaraldehyde fixation process eliminates many of the beneficial, stress-reducing properties of the aortic leaflet. PMID:2509479

Vesely, I; Boughner, D

1989-01-01

106

Bending stiffness of composite plates with delamination  

Microsoft Academic Search

Cross-ply GFRP circular plates have been impacted repeatedly at increasing input energies. The global bending stiffness of each plate was measured before and after each impact through quasi-static bending tests. The effects of local thickening as well as matrix cracking and delamination on global bending stiffness have been discussed. Approximate analytical solutions for bending of damaged and undamaged plates under

J. P. Hou; G. Jeronimidis

2000-01-01

107

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

NASA Astrophysics Data System (ADS)

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

Qiao, Li; Zheng, Xiaojing

2013-01-01

108

Fast Initial Pole-Position Estimation for Non-Salient PM-LSM Based on Agreement of Two Reference Frames  

Microsoft Academic Search

This paper proposes a new initial pole-position estimation method for non-salient permanent magnet linear synchronous motor (PM-LSM) without any pole sensors, which is based on the agreement of two reference frames in the command and the actual axes. The estimation method consists of the specific force command pattern, the measurement of mechanical mover position, the estimation of the angle error

Kozo Ide; Hyun-Soo Song; M. Takaki; S. Morimoto; S. Ki-Sul

2006-01-01

109

Lsm Proteins Promote Regeneration of Pre-mRNA Splicing Activity  

Microsoft Academic Search

Lsm proteins are ubiquitous, multifunctional proteins that affect the processing of most RNAs in eukaryotic cells [1–11], but their function is unknown. A complex of seven Lsm proteins, Lsm2-8, associates with the U6 small nuclear RNA (snRNA) that is a component of spliceosome complexes in which pre-mRNA splicing occurs. Spliceosomes contain five snRNAs, U1, U2, U4, U5, and U6, that

Loredana Verdone; Silvia Galardi; David Page; Jean D. Beggs

2004-01-01

110

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

Microsoft Academic Search

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

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

2004-01-01

111

Influence of thermodynamic soil and vegetation parameterizations on the simulation of soil temperature states and surface fluxes by the Noah LSm over a Tibetan plateau site  

Microsoft Academic Search

In this paper, we investigate the ability of the Noah Land Surface model (LSm) to simulate temperature states in the soil profile and surface fluxes measured during a 7-day dry period at a micrometeorological station on the Tibetan Plateau. Adjustments in soil and vegetation parameterizations required to ameliorate the Noah simulation on these two aspects are presented, which include: (1)

R. van der Velde; Z. Su; M. Ek; M. Rodell; Y. Ma

2009-01-01

112

Diagnosis of GLDAS LSM based aridity index and dryland identification.  

PubMed

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

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

2013-04-15

113

Bending stiffness of catheters and guide wires.  

PubMed

An important property of catheters and guide wires to assess their pushability behavior is their bending stiffness. To measure bending stiffness, a new bending module with a new clamping device was developed. This module can easily be mounted in commercially available tensile testing equipment, where bending force and deflection due to the bending force can be measured. To achieve high accuracy for the bending stiffness, the bending distance has to be measured with even higher accuracy by using a laser-scan micrometer. Measurement results of angiographic catheters and guide wires were presented and discussed. The bending stiffness shows a significant dependence on the angle of the test specimen's rotation around its length axis. PMID:12451800

Wünsche, P; Werner, C; Bloss, P

2002-01-01

114

Adiponectin and Arterial Stiffness  

Microsoft Academic Search

Background: Adiponectin, an anti-inflammatory adipocytokine, is reduced in hypertension, diabetes, and coronary artery disease (CAD). Arterial stiffness, as aortic pulse wave velocity (PWV) in hypertension and diabetes, and as augmentation index (AIx) in CAD, is independently associated with cardiovascular mortality. We explored the relationship between adiponectin and arterial stiffness in essential hypertension.Methods: Seventy-six untreated patients, 34 women, aged 47 ±

Azra Mahmud; John Feely

2005-01-01

115

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

116

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.

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

2014-01-01

117

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

118

Research on the precision processing method for softness abrasive two-phase flow based on LSM  

Microsoft Academic Search

According to the precision machining problem of the structural surface mould manufacturing process, a method for soft grits two-phase flow precision processing on the level set method (LSM) is proposed. Based on the topological structure transformation of LSM, the mechanics model of liquid-liquid two phase flow in mould structuring surface precision machining was established. And the interface parameters of the

Shiming Ji; Xiaoxing Weng; Dapeng Tan

2010-01-01

119

Theoretical Analysis of Segmented Wolter/LSM X-Ray Telescope Systems.  

National Technical Information Service (NTIS)

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 an...

D. L. Shealy S. H. Chao

1986-01-01

120

Effect of sintering temperature on microstructure and performance of LSM–YSZ composite cathodes  

Microsoft Academic Search

The correlation between sintering temperature, microstructure and performance of composite electrodes comprising lanthanum strontium manganate (LSM) and yttria stabilised zirconia (YSZ) with a current collector of LSM has been studied at 1000°C in air. The microstructure was found to be less dense and to contain smaller grains as the sintering temperature was decreased in the range 1300–1150°C. This increased the

M. J Jørgensen; S Primdahl; C Bagger; M Mogensen

2001-01-01

121

Multiple Functional Interactions Between Components of the Lsm2Lsm8 Complex, U6 snRNA, and the Yeast La Protein  

Microsoft Academic Search

The U6 small nuclear ribonucleoprotein is a critical component of the eukaryotic spliceosome. The first protein that binds the U6 snRNA is the La protein, an abundant phosphoprotein that binds the 39 end of many nascent small RNAs. A complex of seven Sm-like proteins, Lsm2-Lsm8, also binds the 39 end of U6 snRNA. A mutation within the Sm motif of

Barbara K. Pannone; Dennis A. Noe; Sandra L. Wolin

2001-01-01

122

Pulmonary Vascular Input Impedance is a Combined Measure of Pulmonary Vascular Resistance and Stiffness and Predicts Clinical Outcomes Better than PVR Alone in Pediatric Patients with Pulmonary Hypertension  

PubMed Central

Background Pulmonary vascular resistance (PVR) is the current standard for evaluating reactivity in children with pulmonary arterial hypertension (PAH). However, PVR measures only the mean component of right ventricular afterload and neglects pulsatile effects. We recently developed and validated an method to measure pulmonary vascular input impedance, which revealed excellent correlation between the zero-harmonic impedance value and PVR, and suggested a correlation between higher harmonic impedance values and pulmonary vascular stiffness (PVS). Here we show that input impedance can be measured routinely and easily in the catheterization laboratory, that impedance provides PVR and PVS from a single measurement, and that impedance is a better predictor of disease outcomes compared to PVR. Methods Pressure and velocity waveforms within the main PA were measured during right-heart catheterization of patients with normal PA hemodynamics (n=14) and those with PAH undergoing reactivity evaluation (49 subjects; 95 conditions). A correction factor needed to transform velocity into flow was obtained by calibrating against cardiac output. Input impedance was obtained off-line by dividing Fourier-transformed pressure and flow waveforms. Results Exceptional correlation was found between the indexed zero harmonic of impedance and indexed PVR (y=1.095·x+1.381, R2=0.9620). Additionally, the modulus sum of the first two harmonics of impedance was found to best correlate with indexed pulse pressure over stroke volume (PP/SV) (y=13.39·x-0.8058, R2=0.7962). Amongst a subset of PAH patients (n=25), cumulative logistic regression between outcomes to total indexed impedance was better (RL2=0.4012) than between outcomes and indexed PVR (RL2=0.3131). Conclusions Input impedance can be consistently and easily obtained from PW Doppler and a single catheter pressure measurement, provides comprehensive characterization of the main components of RV afterload, and better predicts patient outcomes compared to PVR alone.

Hunter, Kendall S.; Lee, Po-Feng; Lanning, Craig J.; Ivy, D. Dunbar; Kirby, K. Scott; Claussen, Lori R.; Chan, K. Chen; Shandas, Robin

2011-01-01

123

Integrating INS Sensors With GPS Measurements for Continuous Estimation of Vehicle Sideslip, Roll, and Tire Cornering Stiffness  

Microsoft Academic Search

Abstract—This paper details a unique method for estimating key vehicle states—body sideslip angle, tire sideslip angle, and vehicle attitude—using Global Positioning System (GPS) mea- surements in conjunction with other sensors. A method is pre- sented for integrating Inertial Navigation System sensors with GPS measurements to provide higher update rate estimates of the vehicle states. The influence of road side-slope and

David M. Bevly; Jihan Ryu; J. Christian Gerdes

2006-01-01

124

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

125

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.

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

2014-01-01

126

Preoperative assessment of meningioma stiffness by magnetic resonance elastography  

PubMed Central

Object To determine the potential of magnetic resonance elastography (MRE) to preoperatively assess the stiffness of meningiomas. Methods Thirteen subjects with meningiomas underwent a 3D brain MRE exam to measure stiffness in the tumor as well as the surrounding brain tissue. Blinded to the MRE results, the neurosurgeons made a qualitative assessment of tumor stiffness at the time of resection. The ability of MRE to predict the surgical assessment of stiffness was tested with a Spearman rank correlation. Results One case was excluded due to small tumor size. In the remaining 12 cases, both tumor stiffness alone (p=0.023) and the ratio of tumor stiffness to the stiffness in the surrounding brain tissue (p=0.0032) significantly correlated with the surgeons’ qualitative assessment of tumor stiffness. The results of the MRE exam provided a stronger correlation with the surgical assessment of stiffness compared to traditional T1 and T2 weighted imaging (p=0.089), particularly when considering meningiomas of intermediate stiffness. Conclusions In this cohort, MRE was able to predict the tumor consistency at the time of surgery. Tumor stiffness as measured by MRE outperformed conventional MRI since appearance on T1 and T2 images could only accurately predict the softest and hardest meningiomas.

Murphy, Matthew C; Huston, John; Glaser, Kevin J; Manduca, Armando; Meyer, Fredric B; Lanzino, Giuseppe; Morris, Jonathan M; Felmlee, Joel P; Ehman, Richard L

2014-01-01

127

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.

Hu, Xiao; Murray, Wendy M.

2011-01-01

128

FRC (field-reversed configuration) translation studies on FRX-C/LSM  

SciTech Connect

In preparation for upcoming compression-heating experiments, field-reversed configurations (FRCs) have been translated out of the FRX-C/LSM theta-pinch source, and into the 0.4-m-id, 6.7-m-long translation region formerly used on FRX-C/T. Unlike earlier experiments FRCs are generated without magnetic tearing in the larger FRX-C/LSM source (nominal coil id = 0.70 m, length = 2 m); larger, lower-energy-density FRCs are formed: r/sub s/ approx. = 0.17 m, B/sub ext/ approx. = 0.35 T, approx. = 7 /times/ 10/sup 20/m/sup /minus/3/ and T/sub e/ + T/sub i/ approx. = 400 eV. An initial 3-mtorr D/sub 2/ pressure is introduced by either static or puff fill. Asymmetric fields from auxiliary end coils (used for non-tearing formation) provide the accelerating force on the FRC, thereby eliminating the need for a conical theta-pinch coil. An important feature is the abrupt 44% decrease in the flux-conserving wall radius at the transition between the theta-pinch and translation region, similar to that in the compressor. In this paper we review a variety of issues addressed by the recent translation experiments: translation dynamics; translation through a modulated magnetic field; stabilization of the n = 2 rotational instability by weak helical quadrupole fields; and confinement properties. Results from internal magnetic field measurements in translating FRCs may be found in a companion paper. 10 refs., 5 figs.

Rej, D.; Barnes, G.; Baron, M.; Chrien, R.; Crawford, E.; Okada, S.; Siemon, R.; Taggart, D.; Tuszewski, M.; Webster, R.

1989-01-01

129

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

130

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

131

Preparation and evaluation of mechanochemically fabricated LSM\\/ScSZ composite materials for SOFC cathodes  

Microsoft Academic Search

The LSM\\/ScSZ composite powder materials for SOFC cathodes were prepared by the mechanical method using an attrition-type particle composing machine and their electrochemical performance was examined. They are designed in such a way that relatively large LSM particles are coated with fine-grained ScSZ particles prior to the electrode fabrication process such as sintering, thus ensuring the establishment of both the

Akifusa Hagiwara; Natsuro Hobara; Koichi Takizawa; Kazuyoshi Sato; Hiroya Abe; Makio Naito

2006-01-01

132

Sagittal abdominal diameter is a more independent measure compared with waist circumference to predict arterial stiffness in subjects with type 2 diabetes - a prospective observational cohort study  

PubMed Central

Background Anthropometric measurements are useful in clinical practice since they are non-invasive and cheap. Previous studies suggest that sagittal abdominal diameter (SAD) may be a better measure of visceral fat depots. The aim of this study was to prospectively explore and compare how laboratory and anthropometric risk markers predicted subclinical organ damage in 255 patients, with type 2 diabetes, after four years. Methods Baseline investigations were performed in 2006 and were repeated at follow-up in 2010. Carotid intima-media thickness (IMT) was evaluated by ultrasonography and aortic pulse wave velocity (PWV) was measured with applanation tonometry over the carotid and femoral arteries at baseline and at follow-up in a cohort of subjects with type 2 diabetes aged 55–65 years old. Results There were significant correlations between apolipoprotein B (apoB) (r?=?0.144, p?=?0.03), C - reactive protein (CRP) (r?=?0.172, p?=?0.009) at baseline and IMT measured at follow-up. After adjustment for sex, age, treatment with statins and Hba1c, the associations remained statistically significant. HbA1c, total cholesterol or LDL-cholesterol did not correlate to IMT at follow-up. Baseline body mass index (BMI) (r?=?0.130, p?=?0.049), waist circumference (WC) (r?=?0.147, p?=?0.027) and sagittal Abdominal Diameter (SAD) (r?=?0.184, p?=?0.007) correlated to PWV at follow-up. Challenged with sex, SBP and HbA1c, the association between SAD, not WC nor BMI, and PWV remained statistically significant (p?=?0.036). In a stepwise linear regression, entering both SAD and WC, the association between SAD and PWV was stronger than the association between WC and PWV. Conclusions We conclude that apoB and CRP, but not LDL-cholesterol predicted subclinical atherosclerosis. Furthermore, SAD was more independent in predicting arterial stiffness over time, compared with WC, in middle-aged men and women with type 2 diabetes.

2013-01-01

133

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

134

Nuclear LSm8 affects number of cytoplasmic processing bodies via controlling cellular distribution of Like-Sm proteins  

PubMed Central

Processing bodies (P-bodies) are dynamic cytoplasmic structures involved in mRNA degradation, but the mechanism that governs their formation is poorly understood. In this paper, we address a role of Like-Sm (LSm) proteins in formation of P-bodies and provide evidence that depletion of nuclear LSm8 increases the number of P-bodies, while LSm8 overexpression leads to P-body loss. We show that LSm8 knockdown causes relocalization of LSm4 and LSm6 proteins to the cytoplasm and suggest that LSm8 controls nuclear accumulation of all LSm2–7 proteins. We propose a model in which redistribution of LSm2–7 to the cytoplasm creates new binding sites for other P-body components and nucleates new, microscopically visible structures. The model is supported by prolonged residence of two P-body proteins, DDX6 and Ago2, in P-bodies after LSm8 depletion, which indicates stronger interactions between these proteins and P-bodies. Finally, an increased number of P-bodies has negligible effects on microRNA-mediated translation repression and nonsense mediated decay, further supporting the view that the function of proteins localized in P-bodies is independent of visible P-bodies.

Novotny, Ivan; Podolska, Katerina; Blazikova, Michaela; Valasek, Leos Shivaya; Svoboda, Petr; Stanek, David

2012-01-01

135

Advanced Glycation End-Products and Arterial Stiffness in Hypertension  

Microsoft Academic Search

Background: The formation of advanced glycation end-products is associated with arterial stiffness in experimental models and alagebrium (formerly known as ALT-711), an advanced glycation end-product cross-link breaker, has been shown to reduce arterial stiffness in elderly subjects.Methods: We related plasma concentrations of advanced glycation end-products (AGEs), measured using a noncompetitive immunoassay, and markers of aortic stiffness—pulse wave velocity (PWV) and

Marie McNulty; Azra Mahmud; John Feely

2007-01-01

136

Axial Stiffness of Retention Pins in Human Dentin  

Microsoft Academic Search

Axial deflections of pins, anchored in specimens of human dentin by five different procedures, were measured by a specially constructed apparatus to an accuracy of 0.1 ?. Axial stiffness values calculated from these measurements were found to be significantly different for different methods of anchorage. Cemented pins displayed the lowest axial stiffness when compared with friction-locked and self-threading pins.

V. B. Dhuru; K. McLachlan; Z. Kasloff

1979-01-01

137

Stiffness characteristics of composite hybrid external fixators.  

PubMed

New composite hybrid fixators for fracture stabilization using single or multiple rings with monolateral bars and half-pin fixation may provide clinical advantages such as reduced bulk and easier skin access. However, the mechanical properties of these fixators are difficult to estimate from numerous design parameters. Addressing this problem the following research questions were asked: (1) Do composite hybrid fixators have similar stiffness properties to clinically proven triple-ring fixators; (2) How does the fixation mechanism affect the stiffness properties of external fixators, and, (3) Are there interferences between ring number and fixation method? An experimental study was done on simulated metaphyseal tibial fractures and stiffness of 12 fixators was measured for different loading conditions. The results showed that triple-ring fixators provide approximately 20% stiffer properties than double-ring and single-ring fixators. No influence of ring number on the AP bending properties was found and different fixation methods were associated with large differences in fixator stiffness, whereas significant interferences were found between ring number and fixation method. Although the mechanical properties investigated in the current study cannot predict directly the clinical performance of these fixators, the stiffness data provide useful information for making decisions regarding the treatment of fractures using external fixation. PMID:12461383

Windhagen, Henning; Glöckner, Roland; Bail, Hermann; Kolbeck, Stefan; Raschke, Michael

2002-12-01

138

Optimisation of processing and microstructural parameters of LSM cathodes to improve the electrochemical performance of anode-supported SOFCs  

Microsoft Academic Search

To improve the electrochemical performance of LSM-based anode-supported single cells, a systematic approach was taken for optimising processing and materials parameters. Four parameters were investigated in more detail: (1) the LSM\\/YSZ mass ratio of the cathode functional layer, (2) the grain size of LSM powder for the cathode current collector layer, (3) the thickness of the cathode functional layer and

V. A. C. Haanappel; J. Mertens; D. Rutenbeck; C. Tropartz; W. Herzhof; D. Sebold; F. Tietz

2005-01-01

139

Stiffness Isn't Everything  

Microsoft Academic Search

Most robot designers make the mechanical interface between an actuator and its load as stiff as possible(9)(10). This makes sense in traditional position-controlled systems, because high interface stiffness maximizes bandwidth and, for non-collocated control, reduces instability. However, lower interface stiffness has advantages as well, including greater shock tolerance, lower reflected inertia, more accurate and stable force control, less damage during

Gill A. Pratt; Matthew M. Williamson; Peter Dillworth; Jerry E. Pratt; Anne Wright

1995-01-01

140

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

141

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.

142

Repeatability of Magnetic Resonance Elastography for Quantification of Hepatic Stiffness  

PubMed Central

Purpose To determine the sources of variability of MRE hepatic stiffness measurements using healthy volunteers and patients and to calculate the minimum change required for statistical significance. Hepatic stiffness measured with magnetic resonance elastography (MRE) has demonstrated tremendous potential as a non-invasive surrogate of hepatic fibrosis, although the underlying repeatability of MRE for longitudinal tracking of liver disease has not been documented. Materials and Methods MRE stiffness measurements from twenty healthy volunteers and ten patients were obtained twice on the same day, and repeated 2-4 weeks later for volunteers in this IRB-approved study. A linear mixed effects model was used to estimate the component sources of variability in the data. Results The standard deviation of MRE measurements of the same individual on different days is 11.9% (percent of the measured stiffness) using the same reader and 12.0% using different readers. The standard deviation of the difference between two measurements (i.e. longitudinal change in an individual) is 17.4%; the corresponding 95% confidence interval for zero change is (-27.0%, 37.0%). Conclusion MRE is a repeatable method for quantifying liver stiffness. Using the described MRE technique, changes greater than 37.0% of the smaller measured stiffness value represent meaningful changes in longitudinal liver stiffness measurements.

Hines, Catherine D. G.; Bley, Thorsten A.; Lindstrom, Mary J.; Reeder, Scott B.

2010-01-01

143

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

144

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

NASA Technical Reports Server (NTRS)

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

Yoshida, Kinjiro; Hayashi, Kengo; Takami, Hiroshi

1996-01-01

145

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

Microsoft Academic Search

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

K.-Y Wang; D. E Shallcross

2000-01-01

146

Diagnosing Aorta Stiffness by Temporal Analysis of Echocardiographic Images  

NASA Astrophysics Data System (ADS)

In the diagnosis of cardiovascular diseases, information about the intracardiac system function and blood flow can be obtained by echocardiography due to its high spatial resolution capability. However, seldom message is known about the aorta stiffness. This work investigated a method to quantitatively analyze the aorta stiffness. The aorta was modeled as a periodic-force-driven damping oscillator, in which the aorta stiffness was the damping factor. From the analysis of echocardiographic images, the delay time of the maximal aorta distention relative to the R-peak of the electrocardiographic trace was measured to reveal the aorta stiffness. A study based on 10 samples suggested that a delay time greater than 0.17 sec could be a criterion to diagnose that the aorta is quite stiff. This method could also clearly discern some abnormal cardiac performance. A large-scale study with this method should be conducted in the future.

Cheng, Yu-Hsi; Yen, Tsu-Chiang; Lee, Doyal

2005-03-01

147

Boundary stiffness regulates fibroblast behavior in collagen gels.  

PubMed

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

2010-03-01

148

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.

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

2010-01-01

149

Position-dependent characterization of passive wrist stiffness.  

PubMed

Because the dynamics of wrist rotations are dominated by stiffness, understanding wrist rotations requires a thorough characterization of wrist stiffness in multiple degrees of freedom. The only prior measurement of multivariable wrist stiffness was confined to approximately one-seventh of the wrist range of motion (ROM). Here, we present a precise nonlinear characterization of passive wrist joint stiffness over a range three times greater, which covers approximately 70% of the functional ROM of the wrist. We measured the torque-displacement vector field in 24 directions and fit the data using thin-plate spline smoothing optimized with generalized cross validation. To assess anisotropy and nonlinearity, we subsequently derived several different approximations of the stiffness due to this multivariable vector field. The directional variation of stiffness was more pronounced than reported previously. A linear approximation (obtained by multiple linear regression over the entire field) was significantly more anisotropic (eigenvalue ratio of 2.69 ± 0.52 versus 1.58 ± 0.39; ) though less misaligned with the anatomical wrist axes (12.1 ± 4.6° versus 21.2 ± 9.2°; ). We also found that stiffness over this range exhibited considerable nonlinearity-the error associated with a linear approximation was 20-30%. The nonlinear characterization over this greater range confirmed significantly greater stiffness in radial deviation compared to ulnar deviation. This study provides a characterization of passive wrist stiffness better suited to investigations of natural wrist rotations, which cover much of the wrist's ROM. It also provides a baseline for the study of neurological and/or orthopedic disorders that result in abnormal wrist stiffness. PMID:24686225

Pando, Autumn L; Lee, Hyunglae; Drake, Will B; Hogan, Neville; Charles, Steven K

2014-08-01

150

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

Microsoft Academic Search

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

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

2002-01-01

151

UPDATES AND EVALUATION OF THE PX-LSM IN MM5  

EPA Science Inventory

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

152

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

153

Extraction of chromium (VI) from sulphuric acid aqueous solutions by a liquid surfactant membrane (LSM)  

Microsoft Academic Search

Experimental results for the batch extraction of chromium (VI) from sulphuric acid aqueous solutions using a liquid surfactant membrane (LSM) are presented. Effects of various parameters such as time and speed of emulsification, internal phase concentration, extractant concentration, choice and concentration of surfactant, contact time, stirring speed, choice of diluent, and volume ratios of the membrane phase to internal stripping

Mahdi Chiha; Mohamed H. Samar; Oualid Hamdaoui

2006-01-01

154

The performance prediction of controlled-PM LSM in various design schemes by FEM  

Microsoft Academic Search

This paper presents the various design schemes of controlled-permanent magnet (PM) linear synchronous motor (LSM). The motor performance on various design schemes, such as slot shapes, magnetizing patterns of PM and skewing, have been investigated in detail by using FEM and experiment. From this study, it is known that in various design schemes, skewing is most efficient to this system

Ju Lee; Hyung-Woo Lee; Yon-Do Chun; Myoungho Sunwoo; Jung-Pyo Hong

2000-01-01

155

Mass-reduction and propulsion control of PM LSM test vehicle for container transportation  

Microsoft Academic Search

This paper proposes a new concept of mass-reduction and propulsion control for container transportation, which is based on the theory of combined levitation-and-propulsion control. The permanent magnet linear synchronous motor (PM LSM) test vehicle is propelled simultaneously, together with controlling successfully the equivalent vehicle-weight reduced by about 85%

K. Yoshida; H. Takami; X. Kong; A. Sonoda

1999-01-01

156

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

157

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

158

Electron profile stiffness and critical gradient studies  

NASA Astrophysics Data System (ADS)

Electron profile stiffness was studied in DIII-D L-mode discharges by systematically varying the heat flux in a narrow region with electron cyclotron heating and measuring the local change produced in ?Te. Electron stiffness was found to slowly increase with toroidal rotation velocity. A critical inverse temperature gradient scale length 1/LC ~ 3 m-1 was identified at ?=0.6 and found to be independent of rotation. Both the heat pulse diffusivity and the power balance diffusivity, the latter determined by integrating the measured dependence of the heat pulse diffusivity on -?Te, were fit reasonably well by a model containing a critical inverse temperature gradient scale length and varying linearly with 1/LT above the threshold.

DeBoo, J. C.; Petty, C. C.; White, A. E.; Burrell, K. H.; Doyle, E. J.; Hillesheim, J. C.; Holland, C.; McKee, G. R.; Rhodes, T. L.; Schmitz, L.; Smith, S. P.; Wang, G.; Zeng, L.

2012-08-01

159

Electron profile stiffness and critical gradient studies  

SciTech Connect

Electron profile stiffness was studied in DIII-D L-mode discharges by systematically varying the heat flux in a narrow region with electron cyclotron heating and measuring the local change produced in {nabla}T{sub e}. Electron stiffness was found to slowly increase with toroidal rotation velocity. A critical inverse temperature gradient scale length 1/L{sub C} {approx} 3 m{sup -1} was identified at {rho}=0.6 and found to be independent of rotation. Both the heat pulse diffusivity and the power balance diffusivity, the latter determined by integrating the measured dependence of the heat pulse diffusivity on -{nabla}T{sub e}, were fit reasonably well by a model containing a critical inverse temperature gradient scale length and varying linearly with 1/L{sub T} above the threshold.

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

2012-08-15

160

Dynamic stiffness and crossbridge action in muscle  

Microsoft Academic Search

Small sinusoidal vibrations at 300 Hz were applied to frog sartorius muscle to measure the dynamic stiffness (Young's modulus) throughout the course of tetanus. For a peak-to-peak amplitude of 0.4% the dynamic Young's modulus increased from 1.5×105 Nm-2 in the resting state to 2×107 Nm-2 in tetanus. After correction for the external connective tissue, the dynamic Young's modulus of the

Peter Mason

1978-01-01

161

Dynamic dorsoventral stiffness assessment of the ovine lumbar spine.  

PubMed

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

Keller, Tony S; Colloca, Christopher J

2007-01-01

162

Stiffness between different directions of transpedicular screws and vertebra  

Microsoft Academic Search

Objective. This study was undertaken to evaluate the variation in bone density within the vertebral body and to determine the biomechanical stiffness of the screw-bone interface for different superior-inferior transpedicular screw orientations in the vertebral body.Design. The stiffness of three directions of screw placement (upper, middle, and lower) were measured in two modes of loading (flexion and torsion). All screws

Shing-Sheng Wu; W. Thomas Edwards; Hansen A. Yuan

1998-01-01

163

Preparation of yttria-stabilized zirconia (YSZ) films on La 0.85Sr 0.15MnO 3 (LSM) and LSM–YSZ substrates using an electrophoretic deposition (EPD) process  

Microsoft Academic Search

Preparation of high-quality yttria-stabilized zirconia (YSZ) electrolyte films on porous substrates is critical to the fabrication of high-performance solid-state ionic devices such as fuel cells and gas sensors. An electrophoretic deposition (EPD) process is investigated for the preparation of YSZ electrolyte films on both porous La0.85Sr0.15MnO3 (LSM) and porous LSM–YSZ composite substrates. The Pechini process is used for the preparation

Fanglin Chen; Meilin Liu

2001-01-01

164

Monitoring stiffness contrast in elastography  

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

165

Lipedema is associated with increased aortic stiffness.  

PubMed

Lipedema is a disproportional obesity due to unknown pathomechanism. Its major hallmark is frequent hematoma formation related to increased capillary fragility and reduced venoarterial reflex. Beyond microangiopathy, both venous and lymphatic dysfunction have also been documented. However, arterial circulation in lipedema has not been examined, and therefore we explored aortic elastic properties by echocardiography. Fourteen women with and 14 without lipedema were included in the study. Each subject consented to blood pressure measurement, physical examination, and transthoracic echocardiography. Aortic stiffness index (beta), distensibility, and strain were evaluated from aortic diameter and blood pressure data. Mean systolic (30.0 +/- 3.2 vs. 25.5 +/- 3.6, P < 0.05) and diastolic (27.8 +/- 3.3 vs. 22.3 +/- 3.1) aortic diameters (in mm) and aortic stiffness index (9.05 +/- 7.45 vs. 3.76 +/- 1.22, P < 0.05) were significantly higher, while aortic strain (0.082 +/- 0.04 vs. 0.143 +/- 0.038, P < 0.05) and distensibility (2.24 +/- 1.07 vs. 4.38 +/- 1.61, P < 0.05) were significantly lower in lipedematous patients compared to controls. Thus, lipedema is characterized with increased aortic stiffness. PMID:23057152

Szolnoky, G; Nemes, A; Gavallér, H; Forster, T; Kemény, L

2012-06-01

166

Telomerase RNA biogenesis involves sequential binding by Sm and Lsm complexes  

PubMed Central

In most eukaryotes, the progressive loss of chromosome-terminal DNA sequences is counteracted by the enzyme telomerase, a reverse transcriptase that uses part of an RNA subunit as template to synthesize telomeric repeats. Many cancer cells express high telomerase activity and mutations in telomerase subunits are associated with degenerative syndromes including dyskeratosis congenita and aplastic anaemia. The therapeutic value of altering telomerase activity thus provides ample impetus to study the biogenesis and regulation of this enzyme in human cells and model systems. We have previously identified a precursor of the fission yeast telomerase RNA subunit (TER1)1 and have demonstrated that the mature 3? end is generated by the spliceosome in a single cleavage reaction akin to the first step of splicing2. Directly upstream and partially overlapping with the spliceosomal cleavage site is a putative Sm protein binding site. Sm and Like-Sm (LSm) proteins belong to an ancient family of RNA binding proteins represented in all three domains of life3. Members of this family form ring complexes on specific sets of target RNAs and play critical roles in their biogenesis, function and turnover. We now demonstrate that the canonical Sm ring and the Lsm2-8 complex sequentially associate with fission yeast TER1. The Sm ring binds to the TER1 precursor, stimulates spliceosomal cleavage and promotes the hypermethylation of the 5? cap by Tgs1. Sm proteins are then replaced by the Lsm2-8 complex, which promotes the association with the catalytic subunit and protects the mature 3? end of TER1 from exonucleolytic degradation. Our findings define the sequence of events that occur during telomerase biogenesis and characterize roles for Sm and Lsm complexes as well as for the methylase Tgs1.

Tang, Wen; Kannan, Ram; Blanchette, Marco; Baumann, Peter

2012-01-01

167

Characterization of LSM–YSZ composite electrode by ac impedance spectroscopy  

Microsoft Academic Search

The characteristics of La1?xSrxMnO3 perovskite (LSM)–yttria-stabilized zirconia (YSZ) composite electrodes were studied over a range of compositions by ac impedance spectroscopy. The transfer and surface diffusion of oxygen ions were found to be rate-determining steps. The polarization resistance of oxygen ion transfer was found to be independent of the partial pressure of oxygen and proportional to the length of the

Jae-Dong Kim; Goo-Dae Kim; Ji-Woong Moon; Yong-il Park; Weon-Hae Lee; Koichi Kobayashi; Masayuki Nagai; Chang-Eun Kim

2001-01-01

168

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

169

New initial pole-position estimation of surface PM-LSM using reference currents  

Microsoft Academic Search

This paper proposes a new algorithm for the initial pole-position estimation of a surface permanent-magnet linear synchronous motor (PM-LSM), which is carried out under closed-loop control without a pole sensor and is insensitive to the motor parameters. This is based on the principle that the initial pole position (IPP) is calculated by the reverse trigonometric function using the two reference

Tae-Woong Kim; Junichi Watanabe; S. Sonoda; J. Hirai

2005-01-01

170

Effect of LSM-YSZ cathode on thin-electrolyte solid oxide fuel cell performance  

Microsoft Academic Search

The effect of cathode composition, processing and structure on the performance of medium-temperature (600–800 °C) solid oxide fuel cells (SOFCs) is described. The cathodes and physical supports for the SOFCs were two-phase mixtures of (La1 ? xSrx)1 ? yMnO3 (LSM) and Yttria-stabilized Zirconia (YSZ), the electrolytes were < 10 ?m thick YSZ, and the anodes were Ni-YSZ with Y-doped CeO2

Tsepin Tsai; Scott A. Barnett

1997-01-01

171

Analysis of coupled inset dielectric guides under LSE and LSM polarization  

Microsoft Academic Search

The inset dielectric guide (IDG) represents an easy-to-fabricate alternative to the image line that is also less sensitive to loss radiation at discontinuities. Two IDG geometries were analyzed, the so-called deep and shallow IDG structures, operating in the LSE and LSM polarizations, respectively. The propagation constants of single and coupled symmetrical IDGs have been calculated as well as the coupling

Steve R. Pennock; Dragan M. BoSkoviC; Tullio Rozzi

1992-01-01

172

New initial pole position estimation of surface PM-LSM using reference currents  

Microsoft Academic Search

This paper proposes a new algorithm for the initial pole-position estimation of a surface permanent magnet linear synchronous motor (PM-LSM), which is carried out under closed loop control without a pole sensor and is insensitive to the motor parameters. This is based on the principle that the initial pole-position (IPP) is calculated by the reverse trigonometric function using two reference

Tae-Woong Kim; J. Watanabe; S. Sonoda

2001-01-01

173

The valuation of multidimensional American real options using the LSM simulation method  

Microsoft Academic Search

In this paper we show how a multidimensional American real option may be solved using the LSM simulation method originally proposed by Longstaff and Schwartz (2001, The Review of the Financial Studies 14(1): 113-147) for valuing a financial option and how this method can be used in a complex setting. We extend a well-known natural resource real option model, initially

Gonzalo Cortazar; Miguel Gravet; Jorge Urzua

2008-01-01

174

A Comparison of FIFE Observation with GEOS Assimilated Data Including a Heterogeneous LSM  

NASA Technical Reports Server (NTRS)

Several recent studies have shown that much can be learned by comparing grid-point data from a data assimilation system with in-situ observations from field experiments. While the surface heterogeneity is acknowledged in these studies, they lack quantitative representations of the influence of heterogeneity on the near-surface meteorology and surface hydrologic and energy balance. Here, we use the Betts and Ball FIFE site-averaged data. Standard deviations of the site-average will provide an estimate of the FIFE site heterogeneity. Recently, the Mosaic Land-Surface Model (LSM) has been incorporated into the Goddard Earth Observing System (GEOS) Data Assimilation System (DAS). The Mosaic LSM computes the surface energy and hydrologic balance for nine distinct surface types at each grid-point. Each surface type is proportionally weighted to determine the mean grid point properties. Hence, we can compare modeled and observed grid-point variability in addition to the mean properties. Also, assimilated data sets created with and without the LSM are compared. The results indicate the importance of including quantitative estimates of heterogeneity in the analysis of the land surface hydrology and energy balances in assimilation systems.

Bosilovich, M.; Houser, Paul; Molod, Andrea; Nebuda, Sharon

1999-01-01

175

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.

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

2014-01-01

176

Stiffness and Damping in Postural Control Increase with Age  

PubMed Central

Upright balance is believed to be maintained through active and passive mechanisms, both of which have been shown to be impacted by aging. A compensatory balance response often observed in older adults is increased co-contraction, which is generally assumed to enhance stability by increasing joint stiffness. We investigated the effect of aging on standing balance by fitting body sway data to a previously-developed postural control model that includes active and passive stiffness and damping parameters. Ten young (24 ± 3 y) and seven older (75 ± 5 y) adults were exposed during eyes-closed stance to perturbations consisting of lateral pseudorandom floor tilts. A least-squares fit of the measured body sway data to the postural control model found significantly larger active stiffness and damping model parameters in the older adults. These differences remained significant even after normalizing to account for different body sizes between the young and older adult groups. An age effect was also found for the normalized passive stiffness, but not for the normalized passive damping parameter. This concurrent increase in active stiffness and damping was shown to be more stabilizing than an increase in stiffness alone, as assessed by oscillations in the postural control model impulse response.

Cenciarini, Massimo; Loughlin, Patrick J.; Sparto, Patrick J.; Redfern, Mark S.

2011-01-01

177

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.

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

2013-01-01

178

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

NASA Astrophysics Data System (ADS)

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

Lu, Yiyun; Lu, Bingjuan; Wang, Suyu

2011-09-01

179

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.

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

2013-01-01

180

Relative stiffness of flat conductor cables  

NASA Technical Reports Server (NTRS)

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

Hankins, J. D.

1976-01-01

181

Dynamic Stiffness of Piles in Liquefiable Soils.  

National Technical Information Service (NTIS)

This research developed tools and procedures for evaluating the stiffness of pile foundations in liquefiable soils during earthquakes. Previous research on dynamic stiffness performed for the Washington State Department of Transportation resulted in the d...

P. Arduino P. Li S. L. Kramer D. A. Baska

2002-01-01

182

Laminate Stiffnesses and Classical Laminate Theory.  

National Technical Information Service (NTIS)

A method by which the stiffness properties of a combined laminate can be calculated directly from the known stiffnesses of two individually symmetric laminates making up this combined laminate was extended to the general case of stacking an unrestricted n...

J. W. Gunnink

1985-01-01

183

Accurate spring constant calibration for very stiff atomic force microscopy cantilevers  

SciTech Connect

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

Grutzik, Scott J.; Zehnder, Alan T. [Field of Theoretical and Applied Mechanics, Cornell University, Ithaca, New York 14853 (United States)] [Field of Theoretical and Applied Mechanics, Cornell University, Ithaca, New York 14853 (United States); Gates, Richard S.; Gerbig, Yvonne B.; Smith, Douglas T.; Cook, Robert F. [Nanomechanical Properties Group, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)] [Nanomechanical Properties Group, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

2013-11-15

184

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

185

Lsm Proteins Are Required for Normal Processing of Pre-tRNAs and Their Efficient Association with La-Homologous Protein Lhp1p  

Microsoft Academic Search

Depletion of any of the five essential proteins Lsm2p to Lsm5p and Lsm8p leads to strong accumulation of all tested unspliced pre-tRNA species, as well as accumulation of 5 and 3 unprocessed species. Aberrant 3-extended pre-tRNAs were detected, presumably due to stabilization of transcripts that fail to undergo correct transcription termination, and the accumulation of truncated tRNA fragments was also

Joanna Kufel; Christine Allmang; Loredana Verdone; Jean D. Beggs; David Tollervey

2002-01-01

186

Psychological Stress and Arterial Stiffness in Korean Americans  

PubMed Central

Objective Arterial stiffness is identified as a causative factor for hypertension. The purpose of this study was to explore the relationship between psychological stress and arterial stiffness in Korean Americans. Methods A convenience sample of 102 Korean Americans (aged 21–60 years, 60% women) was recruited from North Carolina. Psychological stress was measured by the Perceived Stress Scale, the Social, Attitudinal, Familiar, and Environmental (SAFE) Acculturative Stress Scale, and the Spielberger’s State-Trait Anxiety Inventory. Arterial stiffness was measured by carotid-femoral pulse wave velocity (cfPWV) using the SphygmoCor system (AtCor Medical, Australia). Results This study shows that the emotional stress response, measured by anxiety, significantly predicted arterial stiffness (?= .25, p=.008), independently of such confounding factors as age, mean arterial pressure (MAP), gender, body mass index, smoking, education, and income. Anxiety was neither related to age (r=.12, p=.212) nor MAP (r=.14, p=.151). Additionally, this sample of Korean Americans had higher levels of psychological stress when compared to previous findings from studies of other racial/ethnic groups in the U.S. Conclusion Findings demonstrate that anxiety is a significant and independent determinant of arterial stiffness. Given that anxiety was not related to MAP, these findings suggest that arterial stiffness may be a pathway to explain the connection between anxiety and hypertension risk. Studies that scrutinize the relationship between anxiety and arterial stiffness are an important next step for future research. Further studies are also recommended to explore cultural factors and individual characteristics that may affect anxiety in Korean Americans.

Logan, Jeongok G; Barksdale, Debra J; Carlson, John; Carlson, Barbara W; Rowsey, Pamela J

2012-01-01

187

Arthroscopic capsular release for stiff shoulders  

Microsoft Academic Search

Purpose: The etiology, pathogenesis, time course, and response to treatment of stiff shoulder pathology is still under investigation and debate. This prospective study evaluated arthroscopic capsular release to treat stiff shoulder pathology that was resistant to conservative management. The etiology of the shoulder stiffness was categorized and analyzed for effect on outcomes. Type of Study: Operative technique and prospective evaluation.

Gregory P. Nicholson

2003-01-01

188

Stiffness in total knee arthroplasty  

Microsoft Academic Search

Stiffness is a relatively uncommon complication after total knee arthroplasty. It has been defined as a painful limitation\\u000a in the range of movement (ROM). Its pathogenesis is still unclear even if some risk factors have been identified. Patient-related\\u000a conditions may be difficult to treat. Preoperative ROM is the most important risk factor, but an association with diabetes,\\u000a reflex sympathetic dystrophy,

Alfredo Schiavone Panni; Simone Cerciello; Michele Vasso; Mario Tartarone

2009-01-01

189

Combined Measurement of Carotid Stiffness and Intima-Media Thickness Improves Prediction of Complex Aortic Plaques in Patients With Ischemic Stroke  

Microsoft Academic Search

Background and Purpose—We hypothesized that for the prediction or exclusion of aortic thrombi or plaques 4 mm, the combination of intima-media thickness (IMT) and distensibility (DC) of the common carotid arteries would be superior to the measurement of IMT alone. Methods—We prospectively included 208 stroke patients (mean age, 60 years) undergoing transesophageal echocardio- graphy for screening of aortic plaques. IMT

Andreas Harloff; Christoph Strecker; Matthias Reinhard; Marc Kollum; Michael Handke; Manfred Olschewski; Cornelius Weiller; Andreas Hetzel

2010-01-01

190

Predicting Arterial Stiffness From the Digital Volume Pulse Waveform  

Microsoft Academic Search

Cardiovascular disease (CVD) is currently the biggest single cause of mortality in the developed world, hence, the early detection of its onset is vital for effective prevention therapies. Aortic stiffness as measured by aortic pulse wave velocity (PWV) has been shown to be an independent predictor of CVD, however, the measurement of PWV is complex and time consuming. Recent studies

Stephen R. Alty; Natalia Angarita-Jaimes; Sandrine C. Millasseau; Philip J. Chowienczyk

2007-01-01

191

Quantification of liver stiffness and viscosity with SDUV: In vivo animal study  

Microsoft Academic Search

Measurement of liver elasticity (i.e., stiffness) can be used as a noninvasive alternative to liver biopsy to stage liver fibrosis, a condition afflicting hundreds of millions of patients worldwide. Quantitative measurement of stiffness (in unit of Pascal) is required because liver fibrosis is a diffuse disease where abnormality is not confined to a local region and there is no normal

Shigao Chen; Matthew W. Urban; J. F. Greenleaf; Yi Zheng; Aiping Yao

2008-01-01

192

Optimal semi-active damping of cables with bending stiffness  

NASA Astrophysics Data System (ADS)

The problem of optimal semi-active damping of cables with bending stiffness is investigated with an evolutionary algorithm. The developed damping strategy is validated on a single strand cable with a linear motor attached close to the anchor position. The motor is operated in force feedback mode during free decay of cable vibrations, during which time the decay ratios of the cable modes are measured. It is shown from these experiments that the damping ratios predicted in simulation are close to those measured. The semi-active damping strategy found by the evolutionary algorithm is very similar in character to that for a cable without bending stiffness, being the superposition of an amplitude-dependent friction and negative stiffness element. However, due to the bending stiffness of the cable, the tuning of the above elements as a function of the relevant cable parameters is greatly altered, especially for damper positions close to a fixed end anchor, where the mode shape depends strongly on bending stiffness. It is furthermore demonstrated that a semi-active damper is able to dissipate significantly more energy for a cable with simply supported ends compared to fixed ends due to larger damper strokes and thereby increased energy dissipation in the device.

Boston, C.; Weber, F.; Guzzella, L.

2011-05-01

193

Theoretical and experimental investigation of architected core materials incorporating negative stiffness elements  

NASA Astrophysics Data System (ADS)

Structural assemblies incorporating negative stiffness elements have been shown to provide both tunable damping properties and simultaneous high stiffness and damping over prescribed displacement regions. In this paper we explore the design space for negative stiffness based assemblies using analytical modeling combined with finite element analysis. A simplified spring model demonstrates the effects of element stiffness, geometry, and preloads on the damping and stiffness performance. Simplified analytical models were validated for realistic structural implementations through finite element analysis. A series of complementary experiments was conducted to compare with modeling and determine the effects of each element on the system response. The measured damping performance follows the theoretical predictions obtained by analytical modeling. We applied these concepts to a novel sandwich core structure that exhibited combined stiffness and damping properties 8 times greater than existing foam core technologies.

Chang, Chia-Ming; Keefe, Andrew; Carter, William B.; Henry, Christopher P.; McKnight, Geoff P.

2014-04-01

194

Glenohumeral Joint Laxity and Stiffness in the Functional Throwing Position of High School Baseball Pitchers  

PubMed Central

Context: Repetitive overhead throwing has been theorized to result in chronic adaptations to the capsuloligamentous restraints of the glenohumeral joint. Objective: To compare glenohumeral joint laxity and stiffness between the throwing and nonthrowing shoulders of high school baseball pitchers. Design: Repeated measures. Setting: High school athletic training facilities. Patients or Other Participants: Twenty-two asymptomatic high school baseball pitchers (age = 16.50 ± 0.74 years, height = 178.51 ± 7.66 cm, mass = 75.43 ± 13.24 kg) from a sample of convenience. Main Outcomes Measure(s): We used computerized stress arthrometry to measure glenohumeral joint laxity and stiffness. Anterior glenohumeral joint laxity and stiffness measures were obtained with the shoulder in 90° of abduction and both neutral rotation and 90° of external rotation. Posterior laxity and stiffness measures were obtained with the shoulder in 90° of abduction and neutral rotation. Results: No clinically significant differences were found for glenohumeral laxity or stiffness between sides. However, a statistically significant main effect for position was present for both laxity and stiffness. Anterior glenohumeral joint laxity in the 90° external rotation position was significantly decreased and stiffness was increased in this position compared with the anterior at neutral and posterior at neutral positions. Conclusions: Glenohumeral joint laxity decreases and stiffness increases in the functional throwing position of 90° of abduction and 90° of external rotation. No clinically significant side-to-side differences or directional differences were found in high school baseball pitchers.

Crawford, Scott D; Sauers, Eric L

2006-01-01

195

Stiffness of soft tissue complex in total knee arthroplasty.  

PubMed

The significance of achievement of soft tissue balancing in total knee arthroplasty is well recognized. There are few reports dealing with soft tissue tension in total knee arthroplasty. It is expected that the soft tissue tension will affect post-operative results such as postoperative ROM and stability. The purpose of this study was to evaluate tension properties of soft tissue complex of osteoarthritic knee in total knee arthroplasty. Sixty osteoarthritic knees that underwent primary total knee arthroplasty were investigated with a balancer and torque driver specially developed and adapted for this study. We gradually opened the extension and flexion space and measured the force to open it. We created a force-displacement curve in each case. Inclination of the curve indicated stiffness. We examined the stiffness average of all cases every 10 N. The stiffness was 8.9 and 8.5 N/mm (extension, flexion) in soft tissue tension of 60 N and 26.6 and 21.4 N/mm in 180 N. The stiffness became larger with an increase of soft tissue tension, and the stiffness of extension is significantly larger than that of flexion in each tension except for 60 N. Tension properties of soft tissue complex reveal that soft tissue can be easily extended in low soft tissue tension, and hardly extended in high tension. PMID:17661184

Asano, Hiroshi; Muneta, Takeshi; Hoshino, Akiho

2008-01-01

196

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

197

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.

Kum, Francesca; Karalliedde, Janaka

2010-01-01

198

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

199

Contribution of the musculature to rotatory laxity and torsional stiffness at the knee.  

PubMed

The relationships between the mean rectified EMG from two muscle groups crossing the knee joint and the rotational stiffness and laxity about the longitudinal axis of the lower leg were investigated. The EMG signals from three of the quadricep muscle group and two of the hamstring muscle group were monitored using surface electrodes. Each subject sustained self-induced muscle activity from specific muscle combinations while the foot was twisted internally and externally by the researcher. Joint rotation was measured using an electrogoniometer. Analyses of the data showed increased joint stiffness with increased numbers of active muscles. The stiffness measurements ranged from 0.16 to 2.54 Nm degree-1 depending upon the combination of active muscles. The stiffness measured in different tests were very repeatable with standard deviations ranging from 0.02 to 0.25 Nm degree-1. Increases in joint stiffness of over 400% by activation of these muscles were measured. PMID:3584153

Louie, J K; Mote, C D

1987-01-01

200

Human arm stiffness characteristics during the maintenance of posture  

Microsoft Academic Search

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

T. Flash; F. Mussa-Ivaldi

1990-01-01

201

Knee stiffness following anterior cruciate ligament reconstruction  

Microsoft Academic Search

We reviewed 100 patients retrospectively following primary ACL reconstruction with quadruple hamstring autografts to evaluate the incidence and factors associated with postoperative stiffness. Stiffness was defined as any loss of motion using the contra-lateral leg as a control. The median delay between injury and operation was 15 months.The incidence of stiffness was 12% at 6 months post-reconstruction. Both incomplete attendance at physiotherapy

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

2009-01-01

202

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

PubMed Central

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

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

2014-01-01

203

Assessment of stiffness changes in the ex vivo porcine aortic wall using magnetic resonance elastography  

Microsoft Academic Search

Magnetic resonance elastography (MRE) is a noninvasive phase-contrast technique for estimating the mechanical properties of tissues by imaging propagating mechanical waves within the tissue. In this study, we hypothesize that changes in arterial wall stiffness, experimentally induced by formalin fixation, can be measured using MRE in ex vivo porcine aortas. In agreement with our hypothesis, the significant stiffness increase after

Lei Xu; Jun Chen; Meng Yin; Kevin J. Glaser; Qingshan Chen; David A. Woodrum; Richard L. Ehman

204

Investigation of Soft-Tissue Stiffness Alteration in Denervated Human Tissue Using an Ultrasound Indentation System  

PubMed Central

Background/Objective: Differences in soft-tissue stiffness may provide for a quantitative assessment and detection technique for pressure ulcers or deep-tissue injury. An ultrasound indentation system may provide a relatively convenient, simple, and noninvasive method for quantitative measurement of changes in soft-tissue stiffness in vivo. Methods: The Tissue Ultrasound Palpation System (TUPS) was used to quantitatively measure changes in soft-tissue stiffness at different anatomical locations within and between able-bodied persons and individuals with chronic spinal cord injury (SCI). The stiffness of soft tissue was measured at the ischial tuberosity, greater trochanter, posterior midthigh, and biceps brachii. Additionally, soft-tissue thickness and soft-tissue deformation were also measured. Results: Significant differences in soft-tissue stiffness were observed within the various anatomical locations tested, in both the able-bodied and SCI groups. Differences in soft-tissue stiffness were also observed between the 2 groups. Participants with SCI had significantly softer tissue in their buttock-thigh area. Conclusions: TUPS is a clinically feasible technology that can reliably and effectively detect changes in soft-tissue stiffness. The study has provided a better understanding of the tissue mechanical response to external loading, specifically in the SCI population, suggesting the use of tissue stiffness as a parameter to detect and assess pressure-related soft-tissue injury.

Makhsous, Mohsen; Venkatasubramanian, Ganapriya; Chawla, Aditya; Pathak, Yagna; Priebe, Michael; Rymer, William Z; Lin, Fang

2008-01-01

205

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

PubMed Central

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

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

2013-01-01

206

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

SciTech Connect

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.

1985-05-01

207

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

PubMed

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

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

2013-06-01

208

Shape Sensitivity Analysis for 2D Mixed Mode Fractures Using Extended FEM (XFEM) and Level Set Method (LSM)  

Microsoft Academic Search

This article presents a shape sensitivity analysis method for calculating gradients of crack growth rate and crack growth direction for 2D structural components under mixed-mode loading using extended finite element method (XFEM) and level set method (LSM). XFEM is a computational technique in which special enrichment functions are used to incorporate the discontinuity of structural responses caused by the crack

Mangesh S. Edke; Kuang-Hua Chang

2010-01-01

209

Evaluation of NOAH LSM in predicting soil temperature and moisture at two tropical sites of India  

NASA Astrophysics Data System (ADS)

The soil temperature and moisture are important initial conditions to weather and climate models. Due to the sparsity of observations, surface and subsurface soil temperature and moisture are usually generated using land surface models (LSM). Hence it is important to test the performance of LSMs in predicting these parameters. The NOAH LSM has consistently performed well in studies which compared different land surface models [2, 3] and the performance of the model has been examined over different regions [1, 4]. However, performance of NOAH LSM over India has not been extensively investigated. In the present study, the simulation skill of 1-D NOAH LSM with respect to soil temperature and moisture has been evaluated at two sites in India namely Kharagpur and Ranchi, for a period of two years 2009-2010 in both cases. Model simulated soil temperature and soil moisture over Kharagpur have been validated against observation at three depths, namely 10 cm, 20 cm and 50 cm. For Ranchi, soil temperature has been validated at 10 cm, 20 cm and 40 cm and soil moisture at 15 cm, 30 cm and 45 cm. The parameters have been validated at observation frequency and at daily frequency. Soil moisture is well estimated by the model at all depths and over all time scales at these sites. It is suspected that the model has slower infiltration rate and higher evaporation rate or faster lateral run off than actual values. The model shows a dry bias in the monsoon period and a wet bias in other seasons with maximum over-prediction during spring and winter. The diurnal range of soil temperature is well simulated by the model in all seasons both at Ranchi and Kharagpur. Soil temperature is generally over predicted by the model with a maximum warm bias in spring and minimum in monsoon. Over Ranchi, the model over-prediction decreases with depth at all seasons hinting at possible inaccuracies in representation of land-atmosphere exchange coefficients at least over sites considered in this study. 1. Chen F and Coauthors. 2007. Description and evaluation of the characteristics of the NCAR high-resolution land data assimilation system. J. Appl. Meteor. Climatol. 46: 694-713. 2. Mitchell KE, Lohmann D, Houser PR. 2004. The multi-institution North American land data assimilation system (NLDAS): utilizing multiple GCIP products and partners in a continental distributed hydrological modeling system. J. Geophys. Res. 109: D07S90 3. Schaake J, et al. 2004. An intercomparison of soil moisture fields in the North American land data assimilation system (NLDAS). J. Geophys. Res. 109: D01S90 4. Xia Y. and Coauthors. 2013. Validation of NOAH-simulated soil temperature in the North American land data assimilation system phase 2. J. Appl. Meteor. Climatol. 52: 455-471.

Bhattacharya, Anwesha; Mandal, Manabottam

2014-05-01

210

Stiffness in numerical initial-value problems  

Microsoft Academic Search

This paper reviews various aspects of stiffness in the numerical solution of initial-value problems for systems of ordinary differential equations.In the literature on numerical methods for solving initial value problems the term “stiff” has been used by various authors with quite different meanings, which often causes confusion. This paper attempts to clear up this confusion by reviewing some of these

M. N. Spijker

1996-01-01

211

Torsion Stiffness of a Protein Pair Determined by Magnetic Particles  

PubMed Central

We demonstrate the ability to measure torsion stiffness of a protein complex by applying a controlled torque on a magnetic particle. As a model system we use protein G bound to an IgG antibody. The protein pair is held between a magnetic particle and a polystyrene substrate. The angular orientation of the magnetic particle shows an oscillating behavior upon application of a rotating magnetic field. The amplitude of the oscillation increases with a decreasing surface coverage of antibodies on the substrate and with an increasing magnitude of the applied field. For decreasing antibody coverage, the torsion spring constant converges to a minimum value of 1.5 × 103 pN·nm/rad that corresponds to a torsion modulus of 4.5 × 104 pN·nm2. This torsion stiffness is an upper limit for the molecular bond between the particle and the surface that is tentatively assigned to a single protein G–IgG protein pair. This assignment is supported by interpreting the measured stiffness with a simple mechanical model that predicts a two orders of magnitude larger stiffness for the protein G–IgG complex than values found for micrometer length dsDNA. This we understand from the structural properties of the molecules, i.e., DNA is a long and flexible chain-like molecule, whereas the antibody-antigen couple is orders of magnitude smaller and more globular in shape due to the folding of the molecules.

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

2011-01-01

212

Study of stiff converging problems in magnetic field calculation  

SciTech Connect

This thesis is mainly devoted to the numerical solutions of stiff converging problems in magnetic fields. Stiff problems are the ones whose converging process in iterative methods is extremely slow. The solution of many micromagnetic problems lead to unbounded nonlinear partial differential equations. A standard technique to convert these problems to boundary value problems is to assume that the geometry is periodic and then limit the solution to a bounded region. This can be done by introducing Dirichlet boundary conditions at points of odd symmetry and Neumann boundary conditions at points of even symmetry. These problems are then solved numerically using iterative techniques. It is shown that introducing Neumann boundary condition in any form slows down the convergence of the iterative process. A technique is introduced to give a measure of the degree of stiffness in linear cases. A numerical model for Barkhausen coercivity, which is an elliptic type nonlinear partial differential equation with stiff converging property, is used to calculate the coercivity of a garnet material known as Ca-Ge substituted YIG. This particular garnet, grown by liquid phase epitaxy is used in bubble memory devices and is believed to be the perfect magnetic material. A complete analysis is performed to measure the sensitivity of calculated coercivity to input parameters and the result of this calculation will be compared to experiment.

Golbazi, M.A.

1985-01-01

213

LSm14A is a processing body-associated sensor of viral nucleic acids that initiates cellular antiviral response in the early phase of viral infection  

PubMed Central

Recognition of viral nucleic acids by pattern recognition receptors initiates type I IFN induction and innate antiviral immune response. Here we show that LSm14A, a member of the LSm family involved in RNA processing in the processing bodies, binds to synthetic or viral RNA and DNA and mediates IRF3 activation and IFN-? induction. Knockdown of LSm14A inhibits cytosolic RNA- and DNA-trigger type I IFN production and cellular antiviral response. Moreover, LSm14A is essential for early-phase induction of IFN-? after either RNA or DNA virus infection. We further found that LSm14A-mediated IFN-? induction requires RIG-I–VISA or MITA after RNA or DNA virus infection, respectively, and viral infection causes translocation of LSm14A to peroxisomes, where RIG-I, VISA, and MITA are located. These findings suggest that LSm14A is a sensor for both viral RNA and DNA and plays an important role in initiating IFN-? induction in the early phase of viral infection.

Li, Ying; Chen, Rui; Zhou, Qian; Xu, Zhisheng; Li, Chao; Wang, Shuai; Mao, Aiping; Zhang, Xiaodong; He, Weiwu; Shu, Hong-Bing

2012-01-01

214

Dynamic stiffness and damping of externally pressurized gas lubricated journal bearings  

NASA Technical Reports Server (NTRS)

A rigid vertical shaft was operated with known amounts of unbalance at speeds up to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. The measured stiffness was proportional to the supply pressure, while damping was little affected by supply pressure. Damping dropped rapidly as the fractional frequency whirl threshold was approached. A small eccentricity analysis overpredicted the stiffness by 4 to 55 percent. Predicted damping was close to measured at low speeds but higher at high speeds

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

1976-01-01

215

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

216

Stiff Coatings on Compliant Biofibers  

PubMed Central

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

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

2009-01-01

217

Improvement of arthroscopic cartilage stiffness probe using amorphous diamond coating.  

PubMed

During arthroscopic evaluation of articular cartilage unstable contact and even slipping of the measurement instrument on the tissue surface may degrade the reproducibility of the measurement. The main aim of the present study was to achieve more stable contact by controlling the friction between articular cartilage surface and the arthroscopic cartilage stiffness probe (Artscan 200, Artscan Oy, Helsinki, Finland) using amorphous diamond (AD) coating. In order to obtain surfaces with different average roughnesses (R(a)), polished stainless steel disks were coated with AD by using the filtered pulsed arc-discharge (FPAD) method. Dynamic coefficient of friction (mu) between the articular cartilage (n = 8) and the coated plates along one non-coated plate was then determined. The friction between AD and cartilage could be controlled over a wide range (mu = 0.027-0.728, p < 0.05, Wilcoxon test) by altering the roughness. Possible deterioration of cartilage was investigated by measuring surface roughness after friction tests and comparing it with the roughness of the adjacent, untested samples (n = 8). Importantly, even testing with the roughest AD (R(a) = 1250 nm) did not damage articular surface. On the basis of the friction measurements, a proper AD coating was selected for the stiffness probe. The performance of coated and non-coated probe was compared by measuring bovine osteochondral samples (n = 22) with both instruments. The reproducibility of the stiffness measurements was significantly better with the AD-coated probe (CV% = 4.7) than with the uncoated probe (CV% = 8.2). To conclude, AD coating can be used to safely control dynamic friction with articular surface. Sufficient friction between articular surface and reference plate of the arthroscopic probe improves significantly reproducibility of the stiffness measurements. PMID:15660448

Töyräs, Juha; Korhonen, Rami K; Voutilainen, Tanja; Jurvelin, Jukka S; Lappalainen, Reijo

2005-04-01

218

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

219

High air-bearing stiffness slider design  

NASA Astrophysics Data System (ADS)

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

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

2006-08-01

220

Effective stiffness of cracked elastic solids  

SciTech Connect

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

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

1992-08-01

221

Arterial stiffness, central hemodynamics, and cardiovascular risk in hypertension.  

PubMed

This review summarizes several scientific contributions at the recent Satellite Symposium of the European Society of Hypertension, held in Milan, Italy. Arterial stiffening and its hemodynamic consequences can be easily and reliably measured using a range of noninvasive techniques. However, like blood pressure (BP) measurements, arterial stiffness should be measured carefully under standardized patient conditions. Carotid-femoral pulse wave velocity has been proposed as the gold standard for arterial stiffness measurement and is a well recognized predictor of adverse cardiovascular outcome. Systolic BP and pulse pressure in the ascending aorta may be lower than pressures measured in the upper limb, especially in young individuals. A number of studies suggest closer correlation of end-organ damage with central BP than with peripheral BP, and central BP may provide additional prognostic information regarding cardiovascular risk. Moreover, BP-lowering drugs can have differential effects on central aortic pressures and hemodynamics compared with brachial BP. This may explain the greater beneficial effect provided by newer antihypertensive drugs beyond peripheral BP reduction. Although many methodological problems still hinder the wide clinical application of parameters of arterial stiffness, these will likely contribute to cardiovascular assessment and management in future clinical practice. Each of the abovementioned parameters reflects a different characteristic of the atherosclerotic process, involving functional and/or morphological changes in the vessel wall. Therefore, acquiring simultaneous measurements of different parameters of vascular function and structure could theoretically enhance the power to improve risk stratification. Continuous technological effort is necessary to refine our methods of investigation in order to detect early arterial abnormalities. Arterial stiffness and its consequences represent the great challenge of the twenty-first century for affluent countries, and "de-stiffening" will be the goal of the next decades. PMID:22174583

Palatini, Paolo; Casiglia, Edoardo; G?sowski, Jerzy; G?uszek, Jerzy; Jankowski, Piotr; Narkiewicz, Krzysztof; Saladini, Francesca; Stolarz-Skrzypek, Katarzyna; Tikhonoff, Valérie; Van Bortel, Luc; Wojciechowska, Wiktoria; Kawecka-Jaszcz, Kalina

2011-01-01

222

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.

Marinkovic, Aleksandar; Liu, Fei

2013-01-01

223

Association between serum homocysteine and arterial stiffness in elderly: a community-based study  

PubMed Central

Background Arterial stiffness and homocysteine are both powerful predictors of cardiovascular disease, especially in older populations. Previous studies have investigated the association of homocysteine with arterial stiffness in human subjects, while the relationship between homocysteine and arterial stiffness in the elderly is still indefinite. The current study examined the association of homocysteine with arterial stiffness in Chinese community-based elderly persons. Methods We related serum levels of homocysteine to two measures of arterial stiffness (carotid-femoral pulse wave velocity (PWV) and carotid-radial PWV) in 780 participants (46.3% men, mean age 71.9 years (ranging 65–96 years old)) from two communities of Beijing, China. Arterial stiffness was measured within two days of the time of biomarker measurement. Results In multiple-adjusted models, homocysteine levels were strongly associated with the carotid-femoral PWV (standardized ? = 0.13, P < 0.001), even after adjustment for classical risk factors of cardiovascular disease. The association is also stronger when the carotid-femoral PWV is elevated above normal, whereas no significant association with homocysteine was observed for carotid-radial PWV. Conclusions In Chinese elderly persons, serum homocysteine levels are associated with alterations of aortic stiffness.

Zhang, Song; Bai, Yong-Yi; Luo, Lei-Ming; Xiao, Wen-Kai; Wu, Hong-Mei; Ye, Ping

2014-01-01

224

A stiffness-mediated oncogenic hammer.  

PubMed

A recent study in Nature Medicine identified a tissue stiffness-induced microRNA that mediates oncogenic signaling; its expression stratifies luminal breast cancer survivors to predict accelerated metastatic relapse. PMID:24848253

Ghajar, Cyrus M

2014-05-21

225

Solving Certain Stiff Differential Equations by Transformation.  

National Technical Information Service (NTIS)

Methods for weakening the effects of stiffness when solving a single ordinary differential equation are studied. Particular attention is given to the kind of equation arising in the solution of Sturm--Liouville eigenvalue problems by shooting. A special t...

L. F. Shampine

1977-01-01

226

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

227

Composite Laminate Stiffnesses and Their Sensitivities.  

National Technical Information Service (NTIS)

An analysis of composite laminate stiffnesses and their sensitivities is presented within the framework of the design of structures made of composite materials. One of the columns upon which optimization of structures is built is the mathematical search m...

B. Geier

1992-01-01

228

Active Stiffness and Strength in People With Unilateral Anterior Shoulder Instability: A Bilateral Comparison  

PubMed Central

Context: Active muscle stiffness might protect the unstable shoulder from recurrent dislocation. Objective: To compare strength and active stiffness in participants with unilateral anterior shoulder instability and to examine the relationship between active stiffness and functional ability. Design: Cross-sectional study. Setting: University research laboratory. Patients or Other Participants: Participants included 16 males (age range, 16–40 years; height = 179.4 ± 6.1 cm; mass = 79.1 ± 6.8 kg) with 2 or more episodes of unilateral traumatic anterior shoulder instability. Main Outcome Measure(s): Active stiffness and maximal voluntary strength were measured bilaterally in participants. In addition, quality of life, function, and perceived instability were measured using the Western Ontario Stability Index, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, and Single Alpha Numeric Evaluation, respectively. Results: We found less horizontal adduction strength (t15 = ?4.092, P = .001) and less stiffness at 30% (t14 = ?3.796, P = .002) and 50% (t12 = ?2.341, P = .04) maximal voluntary strength in the unstable than stable shoulder. Active stiffness was not correlated with quality of life, function, or perceived instability (r range, 0.0–0.25; P > .05). Conclusions: The observed reduction in stiffness in the unstable shoulder warrants inclusion of exercises in the rehabilitation program to protect the joint from perturbations that might lead to dislocation. The lack of association between active stiffness and quality of life, function, or perceived instability might indicate that stiffness plays a less direct role in shoulder stability.

Olds, Margie; McNair, Peter; Nordez, Antoine; Cornu, Christophe

2011-01-01

229

Stiff man syndrome with invasive thymic carcinoma.  

PubMed

Stiff man syndrome is a rare disease characterized by painful chronic spasms in the muscle and skeletal system. This syndrome is an autoimmune neurologic disorder which is associated with thymoma. We treated a 32-year-old male patient with a type C thymoma (based on the World Health Organization classification) who had stiff man syndrome. The patient underwent an extended thymectomy which brought about alleviation of his symptoms. PMID:23432176

Aghajanzadeh, Manouchehr; Alavi, Ali; Aghajanzadeh, Gilda; Massahania, Sara

2013-03-01

230

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

231

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

PubMed Central

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

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

2011-01-01

232

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

Microsoft Academic Search

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

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

1999-01-01

233

Advanced damper with negative structural stiffness elements  

NASA Astrophysics Data System (ADS)

Negative stiffness is understood as the occurrence of a force in the same direction as the imposed deformation. Structures and composites with negative stiffness elements enable a large amplification in damping. It is shown in this work, using an experimental approach, that when a flexible flat-ends column is aligned in a post-buckled condition, a negative structural stiffness and large hysteresis (i.e., high damping) can be achieved provided the ends of the column undergo tilting from flat to edge contact. Stable axial dampers with initial modulus equivalent to that of the parent material and with enhanced damping were designed and built using constrained negative stiffness effects entailed by post-buckled press-fit flat-ends columns. Effective damping of approximately 1 and an effective stiffness-damping product of approximately 1.3 GPa were achieved in such stable axial dampers consisting of PMMA columns. This is a considerable improvement for this figure of merit (i.e., the stiffness-damping product), which generally cannot exceed 0.6 GPa for currently used damping layers.

Dong, Liang; Lakes, Roderic S.

2012-07-01

234

Impact of a Land Surface Model (LSM) in a Mesoscale Model on the Prediction of Heavy Precipitation Events  

NASA Astrophysics Data System (ADS)

High-resolution mesoscale models have shown considerable promise in the prediction of mesoscale precipitation events. In particular, the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), developed for use by the U.S. Navy, and applied for real-time prediction by the Interdisciplinary Centre for Mathematical and Computational Modeling (ICM), has shown skill in the prediction of significant mesoscale rainfall events. Although the original version of COAMPS used a slab model to represent the land surface, recent experiments have been conducted with a new version of COAMPS that uses the NOAH land surface model (LSM) and the NASA Land Information System (LIS). The NOAH LSM uses 24 different land-use categories and 15 plant functional types. Each grid cell in COAMPS is comprised of a mosaic of up to 5 different land-use types, and those grid cells with a vegetation land-use type are further broken down into a maximum of 4 different plant functional types. Simulations have been performed using the slab- and NOAH LSM-versions of COAMPS on several significant rain events that occurred over Poland during the spring and summer of 2010. These simulations indicate that the land-surface interactions can alter the generation, maintenance, and decay of these rain systems, although these interactions are often small and subtle. This talk will address the configuration of two versions of COAMPS, a brief description of the rain events under study, and the results and validation of the tests that have been performed; along with suggestions for further work that is required in this area. Within the validation of the runs, a comparison will be given of the structure of the boundary layers that are formed using the slab- and NOAH LSM configurations of COAMPS, and how the differences in the boundary layer structures from these two versions of the model affect the timing, strength, and distribution of these precipitation events.

Hodur, R.; Jakubiak, B.

2012-04-01

235

Oxygen transport through LSM\\/YSZ\\/LaAlO system for use of fuel cell type reactor  

Microsoft Academic Search

Oxygen transport in an LSM\\/YSZ\\/LaAlO solid oxide fuel cell type reactor was studied. The oxygen permeation flux was 8.90×10?8molm?2s?1 at 1173K with an activation energy of 170kJmol?1. By applying an external potential, the oxygen permeation flux increased while the activation energy of oxygen permeation decreased. The oxygen permeation fluxes under methane feed in the anode side are 1–2 orders of

Worapon Kiatkittipong; Tomohiko Tagawa; Shigeo Goto; Suttichai Assabumrungrat; Piyasan Praserthdam

2005-01-01

236

Characterisation of composite SOFC cathodes using electrochemical impedance spectroscopy. Analysis of Pt\\/YSZ and LSM\\/YSZ electrodes  

Microsoft Academic Search

The performance of composite electrodes as a function of the electrode composition is investigated experimentally through electrochemical impedance spectroscopy (EIS). In particular, two different composite cathodes are analysed, i.e. Pt\\/YSZ and LSM\\/YSZ. Typical impedance spectra have been obtained and used to evaluate the overall electrode polarisation resistance Rp. The qualitative features are similar for both cathodes; in particular, in both

A. Barbucci; R. Bozzo; G. Cerisola; P. Costamagna

2002-01-01

237

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

238

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

PubMed Central

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

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

2013-01-01

239

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

PubMed

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

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

2013-07-01

240

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

PubMed Central

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

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

2014-01-01

241

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

242

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)0.95MnO3-? (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

243

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.

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

2014-01-01

244

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

245

Experimental exposure to diesel exhaust increases arterial stiffness in man  

PubMed Central

Introduction Exposure to air pollution is associated with increased cardiovascular morbidity, although the underlying mechanisms are unclear. Vascular dysfunction reduces arterial compliance and increases central arterial pressure and left ventricular after-load. We determined the effect of diesel exhaust exposure on arterial compliance using a validated non-invasive measure of arterial stiffness. Methods In a double-blind randomized fashion, 12 healthy volunteers were exposed to diesel exhaust (approximately 350 ?g/m3) or filtered air for one hour during moderate exercise. Arterial stiffness was measured using applanation tonometry at the radial artery for pulse wave analysis (PWA), as well as at the femoral and carotid arteries for pulse wave velocity (PWV). PWA was performed 10, 20 and 30 min, and carotid-femoral PWV 40 min, post-exposure. Augmentation pressure (AP), augmentation index (AIx) and time to wave reflection (Tr) were calculated. Results Blood pressure, AP and AIx were generally low reflecting compliant arteries. In comparison to filtered air, diesel exhaust exposure induced an increase in AP of 2.5 mmHg (p = 0.02) and in AIx of 7.8% (p = 0.01), along with a 16 ms reduction in Tr (p = 0.03), 10 minutes post-exposure. Conclusion Acute exposure to diesel exhaust is associated with an immediate and transient increase in arterial stiffness. This may, in part, explain the increased risk for cardiovascular disease associated with air pollution exposure. If our findings are confirmed in larger cohorts of susceptible populations, this simple non-invasive method of assessing arterial stiffness may become a useful technique in measuring the impact of real world exposures to combustion derived-air pollution.

Lundback, Magnus; Mills, Nicholas L; Lucking, Andrew; Barath, Stefan; Donaldson, Ken; Newby, David E; Sandstrom, Thomas; Blomberg, Anders

2009-01-01

246

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.

von Dassow, Michelangelo; Davidson, Lance A.

2009-01-01

247

Effects of acute eccentric contractions on rat ankle joint stiffness  

Microsoft Academic Search

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

Ochi Eisuke; Ishii Naokata; Nakazato Koichi

2007-01-01

248

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

PubMed

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

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

2014-06-01

249

Temporal response of arterial stiffness to ultra-marathon.  

PubMed

The purpose of this investigation was to characterize the arterial stiffness of male ultra-marathon runners (n=9) using pulse wave velocity (cfPWV) and radial tonometry over the course of an ultra-marathon and during recovery. Measures were collected at rest, immediately following 45?km/75?km of running, then following 60 and 90?min of recovery. No statistical difference was found between baseline cfPWV and normative values. The cfPWV of ultra-endurance runners decreased at 45?km (3.4±1.6?m/s, p=0.006), followed by an increase (1.6±1.8?m/s, p=0.04) toward baseline levels at the 75?km mark. Radial tonometry measures also indicated small artery stiffness was transiently increased after 75?km. The amount of training time (r=0.82, p=0.007) and the duration of a typical training session (r=0.73, p=0.03) were correlated strongly with persisting decrements in large artery compliance at 60?min of recovery. The finding that arterial stiffness decreased at the 45?km distance and then reverted back toward baseline levels with prolonged running, may indicate a role of exercise duration or accumulated stress for affecting vascular compliance. At present, it is premature to suggest that athletes should alter training or racing practices to protect vascular health. PMID:24408767

Burr, J F; Phillips, A A; Drury, T C; Ivey, A C; Warburton, D E R

2014-07-01

250

Decrements in stiffness are restored within 10 min.  

PubMed

The purpose of this study was to clarify the temporal course of stiffness in the muscle-tendon unit after stretching. In 11 male participants, displacement of the myotendinous junction on the gastrocnemius medialis muscle was measured ultrasonographically during the passive-dorsiflexion test, with the ankle was passively dorsiflexed at 1 °/s to the end of the range of motion. Passive torque, representing resistance to stretch, was also measured using an isokinetic dynamometer. On 4 different days, passive-dorsiflexion tests were performed before and immediately, 5, 10 or 15 min after stretching, which comprised dorsiflexion to end range of motion and holding that position for 1 min, 5 times. As a result, end range of motion and passive torque at end range of motion were significantly increased after stretching (P<0.05) as compared with each previous value. Although stiffness of the muscle-tendon unit was significantly decreased immediately and 5 min after stretching (P<0.05), this change recovered within 10 min. These results suggest that static stretching for 5 min results in significantly increased range of motion over 30 min, but significant decreases in stiffness of the muscle-tendon unit returned to baseline levels within 5-10 min. PMID:23143704

Mizuno, T; Matsumoto, M; Umemura, Y

2013-06-01

251

Abnormal Microarchitecture and Stiffness in Postmenopausal Women with Ankle Fractures  

PubMed Central

Background: Ankle fractures are not typically considered osteoporotic fractures. However, bone quality in patients with low trauma ankle fractures has not been explored. Methods: Women with (n = 17) and without (n = 112) a history of low trauma ankle fracture after menopause had areal bone mineral density measured by dual-energy x-ray absorptiometry, trabecular (Tb) and cortical volumetric bone mineral density, and Tb microarchitecture measured by high-resolution peripheral computed tomography of the radius and tibia. Finite element analysis was performed to estimate bone stiffness. Results: Women with fractures were older (72 ± 2 vs. 68 ± 1 yr; P < 0.02) but similar with respect to race and body mass index. Mean T-scores by dual-energy x-ray absorptiometry of fracture subjects were above the osteoporotic range and did not differ from controls. By high-resolution peripheral computed tomography at the radius, fracture subjects had preferentially lower central trabecular bone density, lower Tb number, and increased separation compared with controls (P < 0.0001–0.04). At the tibia, fracture subjects had lower total and Tb density, lower Tb number, and increased Tb separation and network heterogeneity (P < 0.02). Whole-bone stiffness was 13–17% lower at the radius and tibia in fracture subjects (P < 0.003–0.01). Conclusions: Postmenopausal women with ankle fractures have disrupted microarchitecture and decreased stiffness compared with women with no fracture history, suggesting that low trauma ankle fractures should be considered similarly to other classical osteoporotic fractures.

Stein, Emily M.; Liu, X. Sherry; Nickolas, Thomas L.; Cohen, Adi; Thomas, Valerie; McMahon, Donald J.; Zhang, Chiyuan; Cosman, Felicia; Nieves, Jeri; Greisberg, Justin; Guo, X. Edward

2011-01-01

252

High-Frequency Mode Conversion Technique for Stiff Lesion Detection with Magnetic Resonance Elastography  

PubMed Central

A novel imaging technique is described in which the mode conversion of longitudinal waves is used for the qualitative detection of stiff lesions within soft tissue using Magnetic Resonance Elastography (MRE) methods. Due to the viscoelastic nature of tissue, high-frequency shear waves attenuate rapidly in soft tissues but much less in stiff tissues. By introducing minimally attenuating longitudinal waves at a significantly high frequency into tissue, shear waves produced at interfaces by mode conversion will be detectable in stiff regions, but will be significantly attenuated and thus not detectable in the surrounding soft tissue. This contrast can be used to detect the presence of stiff tissue. The proposed technique is shown to readily depict hard regions (mimicking tumors) present in tissue-simulating phantoms and ex vivo breast tissue. In vivo feasibility is demonstrated on a patient with liver metastases where the tumors are readily distinguished. Preliminary evidence also suggests that quantitative stiffness measurements of stiff regions obtained with this technique are more accurate than those from conventional MRE because of the short shear wavelengths. This rapid, qualitative technique may lend itself to applications in which the localization of stiff, suspicious neoplasms is coupled with more sensitive techniques for thorough characterization.

Mariappan, Yogesh K; Glaser, Kevin J; Manduca, Armando; Romano, Anthony J; Venkatesh, Sudhakar K; Yin, Meng; Ehman, Richard L

2011-01-01

253

Fluid damping and fluid stiffness of tube arrays in crossflow  

SciTech Connect

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

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

1994-06-01

254

Peripheral arterial stiffness in primary aldosteronism.  

PubMed

Aldosterone overproduction increases arterial wall stiffness by accumulation of different types of collagen fibres and growth factors. Our previous studies showed that central (aortic) arterial stiffness is increased in primary aldosteronism (PA) independently of concomitant hypertension and that these changes might be reversible after successful adrenalectomy. There is limited data available on the potential impact of mineralocorticoid overproduction on the deterioration of peripheral arterial stiffness. The current study was thus aimed at investigating the effect of aldosterone overproduction on peripheral arterial stiffness assessed by peripheral (femoral-ankle) pulse wave velocity (PWV) in PA patients compared with essential hypertension (EH) patients. Forty-nine patients with confirmed PA and 49 patients with EH were matched for age, blood pressure, body mass index, lipid profile, and fasting glucose. PWV was obtained using the Sphygmocor applanation tonometer. Both peripheral and central PWV were significantly higher in PA patients compared to EH patients, while clinical blood pressures were similar. Plasma aldosterone level was the main predictor of peripheral PWV in PA. Our data indicate aldosterone overproduction in PA does not preferentially affect central arterial system. Fibroproliferative effect of higher aldosterone levels lead to alteration of central-elastic as well as peripheral-muscular arteries with subsequent increase in its stiffness. PMID:22881232

Rosa, J; Somlóová, Z; Petrák, O; Strauch, B; Indra, T; Senitko, M; Zelinka, T; Holaj, R; Widimský, J

2012-12-14

255

Hyperemia-Related Changes in Arterial Stiffness: Comparison between Pulse Wave Velocity and Stiffness Index in the Vascular Reactivity Assessment  

PubMed Central

Carotid-to-radial pulse wave velocity (PWVcr) has been proposed to evaluate endothelial function. However, the measurement of PWVcr is not without limitations. A new simple approach could have wide application. Stiffness index (SI) is obtained by analysis of the peripheral pulse wave and gives reproducible information about stiffness of large arteries. This study assessed the effects of hyperemia on SI and compared it with PWVcr in 14 healthy subjects. Both were measured at rest and during 8 minutes after ischemia. SI temporal course was determined. At 1 minute, SI and PWVcr decreased (5.58 ± 0.24 to 5.34 ± 0.23?m/s, P < 0.05; 7.8 ± 1.0 to 7.2 ± 0.9?m/s; P < 0.05, resp.). SI was positively related to PWVcr in baseline (r = 0.62 , P < 0.05), at 1 minute (r = 0.79, P < 0.05), and during the whole experimental session (r = 0.52, P < 0.05). Conclusion. Hyperemia significantly decreases SI in healthy subjects. SI was related to PWVcr and could be used to facilitate the evaluation of hyperemia-related changes in arterial stiffness.

Torrado, Juan; Bia, Daniel; Zocalo, Yanina; Farro, Ignacio; Farro, Federico; Armentano, Ricardo L.

2012-01-01

256

Effect of moisture absorption on damping and dynamic stiffness of carbon fiber\\/epoxy composites  

Microsoft Academic Search

In this paper, the damping and dynamic stiffness of UHN125C carbon fiber\\/epoxy composite beam was experimentally measured.\\u000a The effect of fiber orientation angle and stacking sequences on damping, resonance frequency, and dynamic stiffness was discussed\\u000a with a focus on the effect of moisture absorption. Dried specimens were immersed in distilled water for a certain period to\\u000a absorb water for 8,

Behzad Ahmed Zai; M. K. Park; H. S. Choi; Hassan Mehboob; Rashid Ali

2009-01-01

257

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

258

MRI-Guided Biopsy to Correlate Tissue Specimens with MR Elastography Stiffness Readings in Liver Transplants  

PubMed Central

Rationale and Objectives Magnetic resonance elastography (MRE) can non-invasively measure the stiffness of liver tissue and display this information in anatomic maps. Magnetic resonance imaging (MRI)-guidance has not previously been used to biopsy segments of heterogeneous stiffness identified on MRE. Dedicated study of MRE in post-liver transplant patients is also limited. In this study, the ability of real-time MRI to guide biopsies of segments of the liver with different MRE stiffness values in the same post-transplant patient was assessed. Materials and Methods MRE was performed in 9 consecutive post-transplant patients with history of hepatitis C. Segments of highest and lower stiffness on MRE served as targets for subsequent real-time MRI-guided biopsy using T2-weighted imaging. The ability of MRI-guided biopsy to successfully obtain tissue specimens was assessed. The Wilcoxon Signed Rank Test was used to compare mean stiffness differences for highest and lower MRE stiffness segments, with ? = 0.05. Results MRI-guidance allowed successful sampling of liver tissue for all (18/18) biopsies. There was a statistically significant difference in mean MRE stiffness values between highest (4.61 ± 1.99 kPa) and lower stiffness (3.03 ± 1.75 kPa) (P=0.0039) segments biopsied in the 9 post-transplant patients. Conclusion Real-time MRI can guide biopsy in patients after liver transplantation based upon MRE stiffness values. This study supports the use of MRI-guidance to sample tissue based upon functional information.

Perumpail, Ryan B.; Levitsky, Josh; Wang, Yi; Lee, Victoria S.; Karp, Jennifer; Jin, Ning; Yang, Guang-Yu; Bolster, Bradley D.; Shah, Saurabh; Zuehlsdorff, Sven; Nemcek, Albert A.; Larson, Andrew C.; Miller, Frank H.; Omary, Reed A.

2012-01-01

259

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

PubMed

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

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

2014-05-01

260

Muscle passive stiffness increases less after the second bout of eccentric exercise compared to the first bout  

Microsoft Academic Search

Objectives: The purpose of this study was to assess if the protective adaptation after eccentric exercise affects changes in passive stiffness of the biceps brachii muscle. Design: A within-group repeated measures design was used to compare changes in passive muscle stiffness after eccentric exercise between the first and second bouts separated by 2–3 weeks. Method: Maximal isometric torque, passive muscle

Damian Janecki; Ewa Jarocka; Anna Jaskólska; Jaros?aw Marusiak; Artur Jaskólski

2011-01-01

261

Effects of safflower seed extract on arterial stiffness  

PubMed Central

Safflower seed extract (SSE) contains characteristic polyphenols and serotonin derivatives (N-( p-coumaroyl) serotonin and N-feruloylserotonin), which are reported to inhibit oxidation of low-density lipoprotein (LDL), formation of atherosclerotic plaques, and improve arterial stiffness as assessed by pulse wave analysis in animal models. The effects of long-term supplementation with SSE on arterial stiffness in human subjects were evaluated. This doubleblind, placebo-controlled study was conducted in 77 males (35–65 years) and 15 postmenopausal females (55–65 years) with high-normal blood pressure or mild hypertension who were not undergoing treatment. Subjects received SSE (70 mg/day as serotonin derivatives) or placebo for 12 weeks, and pulse wave measurements, ie, second derivative of photoplethysmogram (SDPTG), augmentation index, and brachial-ankle pulse wave velocity (baPWV) were conducted at baseline, and at weeks 4, 8, and 12. Vascular age estimated by SDPTG aging index improved in the SSE-supplemented group when compared with the placebo group at four (P = 0.0368) and 12 weeks (P = 0.0927). The trend of augmentation index reduction (P = 0.072 versus baseline) was observed in the SSE-supplemented group, but reduction of baPWV by SSE supplementation was not observed. The SSE-supplemented group also showed a trend towards a lower malondialdehyde-modified-LDL autoantibody titer at 12 weeks from baseline. These results suggest long-term ingestion of SSE in humans could help to improve arterial stiffness.

Suzuki, Katsuya; Tsubaki, Shigekazu; Fujita, Masami; Koyama, Naoto; Takahashi, Michio; Takazawa, Kenji

2010-01-01

262

Helical growth trajectories in plant roots interacting with stiff barriers  

NASA Astrophysics Data System (ADS)

Plant roots successfully navigate heterogeneous soil environments with varying nutrient and water concentrations, as well as a variety of stiff obstacles. While it is thought that the ability of roots to penetrate into a stiff lower soil layer is important for soil erosion, little is known about how a root actually responds to a rigid interface. We have developed a laser sheet imaging technique for recording the 3D growth dynamics of plant roots interacting with stiff barriers. We find that a root encountering an angled interface does not grow in a straight line along the surface, but instead follows a helical trajectory. These experiments build on the pioneering studies of roots grown on a tilted 2D surface, which reported ``root waving,'' a similar curved pattern thought to be caused by the root's sensitivity to both gravity and the rigid surface on which it is grown. Our measurements extend these results to the more physiologically relevant case of 3D growth, where the spiral trajectory can be altered by tuning the relative strengths of the gravity and touch stimuli, providing some intuition for the physical mechanism driving it.

Gerbode, Sharon; Noar, Roslyn; Harrison, Maria

2009-03-01

263

Bone Microarchitecture and Stiffness in Premenopausal Women with Idiopathic Osteoporosis  

PubMed Central

Context: Idiopathic osteoporosis (IOP) is an uncommon disorder in which low areal bone mineral density (aBMD) and/or fractures occur in otherwise healthy premenopausal women. Objectives: Our objectives were to characterize bone mass, microarchitecture, and trabecular bone stiffness in premenopausal IOP and to determine whether women with low aBMD who have never fractured have abnormal microarchitecture and stiffness. Design, Setting, and Patients: We conducted a prospective cohort study of 27 normal controls and 31 women with IOP defined by low trauma fracture (n = 21) or low BMD (Z score ??2.0; n = 10). Main Outcome Measures: We assessed aBMD by dual-energy x-ray absorptiometry; volumetric BMD and cortical and trabecular microarchitecture of the radius and tibia by high-resolution (82 ?m) peripheral quantitative computed tomography; and trabecular bone stiffness (elastic moduli), estimated by micro-finite element analysis. Results: Fracture subjects did not differ from controls by age or body mass index, which was lower in low-BMD subjects than controls. Fracture subjects also had lower aBMD than controls at all sites (P < 0.05–0.0001). Bone size was similar in controls and fracture subjects but 10.6% smaller in low-BMD subjects (P < 0.05). Every trabecular parameter in both fracture and low-BMD groups was markedly worse than controls (P < 0.01–0.0001). Cortical thickness was significantly lower in both fracture and low-BMD groups at the tibia but not radius. Bone stiffness estimated by micro-finite element analysis was comparably reduced in low-BMD and fracture groups. Conclusion: Premenopausal women with IOP had marked trabecular microarchitectural deterioration at the radius and tibia. Cortical parameters were affected only at the tibia. Although they had not fractured, microarchitectural deterioration was similar in IOP women with low BMD and those with fractures.

Cohen, Adi; Liu, X. Sherry; Stein, Emily M.; McMahon, Donald J.; Rogers, Halley F.; LeMaster, Jeanette; Recker, Robert R.; Lappe, Joan M.; Guo, X. Edward; Shane, Elizabeth

2009-01-01

264

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

265

Assessment of stiffness changes in the ex vivo porcine aortic wall using magnetic resonance elastography  

PubMed Central

Magnetic resonance elastography (MRE) is a noninvasive phase-contrast technique for estimating the mechanical properties of tissues by imaging propagating mechanical waves within the tissue. In this study, we hypothesize that changes in arterial wall stiffness, experimentally induced by formalin fixation, can be measured using MRE in ex vivo porcine aortas. In agreement with our hypothesis, the significant stiffness increase after sample fixation were clearly demonstrated by MRE and confirmed by mechanical testing. The results indicate that MRE can be used to examine the stiffness changes of the aorta. This study has provided evidence of the effectiveness of using MRE to directly assess the stiffness change in aortic wall. The results offer motivation to pursue MRE as a noninvasive method for the evaluation of arterial wall mechanical properties.

Xu, Lei; Chen, Jun; Yin, Meng; Glaser, Kevin J.; Chen, Qingshan; Woodrum, David A.; Ehman, Richard L.

2011-01-01

266

Assessment of stiffness changes in the ex vivo porcine aortic wall using magnetic resonance elastography.  

PubMed

Magnetic resonance elastography (MRE) is a noninvasive phase-contrast technique for estimating the mechanical properties of tissues by imaging propagating mechanical waves within the tissue. In this study, we hypothesize that changes in arterial wall stiffness, experimentally induced by formalin fixation, can be measured using MRE in ex vivo porcine aortas. In agreement with our hypothesis, the significant stiffness increase after sample fixation was clearly demonstrated by MRE and confirmed by mechanical testing. The results indicate that MRE can be used to examine the stiffness changes of the aorta. This study has provided evidence of the effectiveness of using MRE to directly assess the stiffness change in aortic wall. The results offer motivation to pursue MRE as a noninvasive method for the evaluation of arterial wall mechanical properties. PMID:22055848

Xu, Lei; Chen, Jun; Yin, Meng; Glaser, Kevin J; Chen, Qingshan; Woodrum, David A; Ehman, Richard L

2012-01-01

267

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

268

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

269

Association between human cartilage glycoprotein 39 (YKL-40) and arterial stiffness in essential hypertension  

PubMed Central

Background YKL-40, a proposed marker of inflammation and endothelial dysfunction, is associated with atherosclerosis and an increased cardiovascular mortality in the general population. However, the relationship between YKL-40 and arterial stiffness in hypertensive patients has not been adequately assessed. Methods The relationship between serum levels of YKL-40 and arterial stiffness was evaluated in 93 essential hypertensive subjects and 80 normal subjects. Essential hypertensive subjects were divided into two groups based upon urinary albumin-to-creatinine ratio (ACR): nonmicroalbuminuric group, (ACR <30?mg/g, n?=?50) and microalbuminuric group (ACR ?30?mg/g, n?=?43). Large artery wall stiffness was assessed by measuring femoral arterial stiffness and carotid-femoral pulse wave velocity (cf-PWV). Serum levels of YKL-40 were determined by enzyme-linked immunosorbent assay (ELISA). Results The study demonstrated that YKL-40,cf-PWV and femoral arterial stiffness were increased significantly (P<0.05) in the hypertensive group compared with normal controls. These measurements were also increased significantly ( P<0.05) in the microalbuminuric group compared with the nonmicroalbuminuric group. YKL-40 was positively correlated with cf-PWV( r?=?0.44, P?=?0.000) and femoral arterial stiffness ( r?=?0.42, P =0.001). Multiple linear stepwise regression analysis showed that YKL-40 was the impact factor of arterial stiffness ( P<0.05). Conclusion YKL-40 levels are elevated in essential hypertension subjects with an independent association between increasing YKL-40 levels and increasing arterial stiffness. The study suggests it played a positive role of YKL-40 in the progressing vascular complications in patients with essential hypertension.

2012-01-01

270

Real-Time Fracture of Stiff Materials  

Microsoft Academic Search

This paper describes the implementation of system to model the dy- namic fracture of stiff materials in real-time for use in modern game environments. Based around a tetrahedral finite element system, we aim to model the effects of stress tensors over the body of an ob- ject, and to compute the disruptions to the object's surface structure in real time.

Owen McNally

271

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

272

Computer program performs stiffness matrix structural analysis  

NASA Technical Reports Server (NTRS)

Computer program generates the stiffness matrix for a particular type of structure from geometrical data, and performs static and normal mode analyses. It requires the structure to be modeled as a stable framework of uniform, weightless members, and joints at which loads are applied and weights are lumped.

Bamford, R.; Batchelder, R.; Schmele, L.; Wada, B. K.

1968-01-01

273

Dynamic stiffness of randomly parametered beams  

Microsoft Academic Search

A finite element-based methodology is developed for the determination of the dynamic stiffness matrix of Euler-Bernoulli beams with randomly varying flexural and axial rigidity, mass density and foundation elastic modulus. The finite element approximation made employs frequency dependent shape functions and the analysis avoids eigenfunction expansion which, not only eliminates modal truncation errors, but also, restricts the number of random

C. S. Manohar; Sondipon Adhikari

1998-01-01

274

One-chamber solid oxide fuel cell constructed from a YSZ electrolyte with a Ni anode and LSM cathode  

Microsoft Academic Search

An excellent SOFC performance in a mixture of methane and air is achieved by constructing a one-chamber cell from a YSZ solid electrolyte with a 25 wt.% Ce0.8Gd0.2O1.9 (GDC)-added Ni anode and 15 wt.% MnO2-added La0.8Sr0.2MnO3 (LSM) cathode, which are deposited on opposite surfaces (A-type cell) or the same face (B-type cell) of the solid electrolyte. Experiments are carried out

Takashi Hibino; Shuqiang Wang; Shiro Kakimoto; Mitsuru Sano

2000-01-01

275

Functional LSM–ScSZ\\/NiO–ScSZ dual-layer hollow fibres for partial oxidation of methane  

Microsoft Academic Search

In this study, a functional La0.80Sr0.20MnO3?? (LSM)–Scandia-Stabilized-Zirconia (ScSZ)\\/NiO–ScSZ dual-layer hollow fibre has been developed using a single-step co-extrusion and co-sintering process, and has been employed as a dual-layer hollow fibre membrane reactor for partial oxidation of methane. Oxygen permeation rate between 0.49 and 1.82 ml\\/min and methane conversion between 53.55% and 98.78% have been achieved when operating temperature is elevated from

Zhentao Wu; Bo Wang; Kang Li

2011-01-01

276

Stiffness of lipid monolayers with phase coexistence.  

PubMed

The surface dilational modulus--or compressibility modulus--has been previously studied for monolayers composed of pure materials, where a jump in this modulus was related with the onset of percolation as a result of the establishment of a connected structure at the molecular level. In this work, we focused on monolayers composed of two components of low lateral miscibility. Our aim was to investigate the compressibility of mixed monolayers at pressures and compositions in the two-phase region of the phase diagram, in order to analyze the effect of the mechanical properties of each phase on the stiffness of the composite. In nine different systems with distinct molecular dipoles and charges, the stiffness of each phase and the texture at the plane of the monolayer were studied. In this way, we were able to analyze the general compressibility of two-phase lipid monolayers, regardless of the properties of their constituent parts. The results are discussed in the light of the following two hypotheses: first, the stiffness of the composite could be dominated by the stiffness of each phase as a weighted sum according to the percentage of each phase area, regardless of the distribution of the phases in the plane of the monolayer. Alternatively, the stiffness of the composite could be dominated by the mechanical properties of the continuous phase. Our results were better explained by this latter proposal, as in all the analyzed mixtures it was found that the mechanical properties of the percolating phase were the determining factors. The value of the compression modulus was closer to the value of the connected phase than to that of the dispersed phase, indicating that the bidimensional composites displayed mechanical properties that were related to the properties of each phases in a rather complex manner. PMID:23906426

Caruso, Benjamín; Mangiarotti, Agustín; Wilke, Natalia

2013-08-27

277

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

PubMed Central

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

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

2011-01-01

278

Cell shape and substrate rigidity both regulate cell stiffness.  

PubMed

Cells from many different tissues sense the stiffness and spatial patterning of their microenvironment to modulate their shape and cortical stiffness. It is currently unknown how substrate stiffness, cell shape, and cell stiffness modulate or interact with one another. Here, we use microcontact printing and microfabricated arrays of elastomeric posts to independently and simultaneously control cell shape and substrate stiffness. Our experiments show that cell cortical stiffness increases as a function of both substrate stiffness and spread area. For soft substrates, the influence of substrate stiffness on cell cortical stiffness is more prominent than that of cell shape, since increasing adherent area does not lead to cell stiffening. On the other hand, for cells constrained to a small area, cell shape effects are more dominant than substrate stiffness, since increasing substrate stiffness no longer affects cell stiffness. These results suggest that cell size and substrate stiffness can interact in a complex fashion to either enhance or antagonize each other's effect on cell morphology and mechanics. PMID:21354386

Tee, Shang-You; Fu, Jianping; Chen, Christopher S; Janmey, Paul A

2011-03-01

279

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

280

Effect of stem stiffness and bone stiffness on bone remodeling in cemented total hip replacement  

Microsoft Academic Search

The hypothesis in this study is that the stem stiffness-to-bone stiffness ratio influences the incidence and type of bone remodeling and fixation with cemented total hip arthroplasty. Ninety-one patients with 99 hips had cemented stems using 3 different anatomic porous replacement designs. The APR I and APR II titanium stems with proximal porous coating on the proximal one fourth of

Zhinian Wan; Lawrence D. Dorr; Terry Woodsome; Anil Ranawat; Michael Song

1999-01-01

281

Muscle paresis and passive stiffness: Key determinants in limiting function in Hereditary and Sporadic Spastic Paraparesis  

PubMed Central

Background People with Hereditary and Sporadic Spastic Parapresis (SP) walk with a stiff legged gait characterised by a lack of knee flexion. Objective We investigated the relationship between lower limb strength and stiffness and knee flexion during swing phase while walking in 20 people with SP and 18 matched controls. Methods Maximal isometric strength was measured using a dynamometer. Passive stiffness and spasticity was assessed during motor-driven slow (5°/s) and fast (60°/s) stretches at the ankle and knee while the subject was relaxed or preactivating the muscle. Walking was assessed using 3D motion analysis. Results Isometric muscle strength was decreased in people with SP with over a 50% reduction in strength being found in the ankle dorsiflexors. Passive stiffness, assessed during slow stretches, was 35% higher in the plantarflexors in people with SP (P < 0.05). Faster stretches induced large stretch evoked muscle activity and over a 110% increase in stiffness at the ankle and knee in people with SP reflecting the presence of spasticity (P < 0.05). However, stretch reflex size and stiffness was similar between the groups following identical stretches of the pre-activated muscle (P > 0.05). Lower knee flexion during swing phase was associated with reduced knee flexion velocity at the end of stance phase which in turn was associated with reduced plantarflexor strength and increased passive stiffness in the knee extensors. Conclusions The relative importance of muscle paresis and passive stiffness in limiting walking in SP suggests that these impairments should be the target of future therapies.

Marsden, Jon; Ramdharry, Gita; Stevenson, Valerie; Thompson, Alan

2012-01-01

282

Insulin resistance and arterial stiffness in healthy adolescents and young adults  

PubMed Central

Aims/hypothesis Increased arterial stiffness is a risk factor for adverse cardiovascular events in adults with obesity-related insulin resistance (IR) or type 2 diabetes mellitus. Adolescents with type 2 diabetes have stiffer vessels. Whether stiffness is increased in obesity/IR in youth is not known. We sought to determine if IR was a determinant of arterial stiffness in youth, independent of obesity and cardiovascular risk factors. Methods We measured cardiovascular risk factors, IR, adipocytokines and arterial stiffness (brachial artery distensibility [BrachD], pulse wave velocity [PWV]) and wave reflection (augmentation index [AIx]) in 343 adolescents and young adults without type 2 diabetes (15–28 years old, 47% male, 48% non-white). Individuals <85th percentile of BMI were classified as lean (n=232). Obese individuals were grouped by HOMA index as not insulin resistant (n=46) or insulin resistant (n=65) by the 90th percentile for HOMA for lean. Mean differences were evaluated by ANOVA. Multivariate models evaluated whether HOMA was an independent determinant of arterial stiffness. Results Risk factors deteriorated from lean to obese to obese/insulin resistant (all p? 0.017). Higher AIx, lower BrachD and higher PWV indicated increased arterial stiffness in obese and obese/insulin resistant. HOMA was not an independent determinant. Age, sex, BMI and BP were the most consistent determinants, with HDL-cholesterol playing a role for BrachD and leptin for PWV (AIx R2 = 0.34; BrachD R2 = 0.37; PWV R2 = 0.40; all p?0.02). Conclusions/interpretation Although IR is associated with increased arterial stiffness, traditional cardiovascular risk factors, especially obesity and BP, are the major determinants of arterial stiffness in healthy young people.

Urbina, E. M.; Gao, Z.; Khoury, P. R.; Martin, L. J.; Dolan, L. M.

2012-01-01

283

Is the cross-bridge stiffness proportional to tension during muscle fiber activation?  

PubMed

The cross-bridge stiffness can be used to estimate the number of S1 that are bound to actin during contraction, which is a critical parameter for elucidating the fundamental mechanism of the myosin motor. At present, the development of active tension and the increase in muscle stiffness due to S1 binding to actin are thought to be linearly related to the number of cross-bridges formed upon activation. The nonlinearity of total stiffness with respect to active force is thought to arise from the contribution of actin and myosin filament stiffness to total sarcomere elasticity. In this work, we reexamined the relation of total stiffness to tension during activation and during exposure to N-benzyl-p-toluene sulphonamide, an inhibitor of cross-bridge formation. In addition to filament and cross-bridge elasticity, our findings are best accounted for by the inclusion of an extra elasticity in parallel with the cross-bridges, which is formed upon activation but is insensitive to the subsequent level of cross-bridge formation. By analyzing the rupture tension of the muscle (an independent measure of cross-bridge formation) at different levels of activation, we found that this additional elasticity could be explained as the stiffness of a population of no-force-generating cross-bridges. These findings call into question the assumption that active force development can be taken as directly proportional to the cross-bridge number. PMID:20513402

Colombini, Barbara; Nocella, Marta; Bagni, M Angela; Griffiths, Peter J; Cecchi, Giovanni

2010-06-01

284

Modeling effects of sagittal-plane hip joint stiffness on reciprocating gait orthosis-assisted gait.  

PubMed

Upright ambulation is believed to improve quality of life for persons with lower-limb paralysis (LLP). However, ambulatory orthoses for persons with LLP, like reciprocating gait orthoses (RGOs), result in a slow, exhausting gait. Increasing the hip joint stiffness of these devices may improve the efficiency of RGO-assisted gait. The small, diverse population of RGO users makes subject recruitment challenging for clinical investigations. Therefore, we developed a lower-limb paralysis simulator (LLPS) that enabled nondisabled persons to exhibit characteristics of RGO-assisted gait, thereby serving as surrogate models for research. For this study, tests were conducted to determine the effects of increased hip joint stiffness on gait of nondisabled persons walking with the LLPS. A motion capture system, force plates, and spirometer were used to measure the hip flexion, crutch ground reaction forces (GRFs), and oxygen consumption of subjects as they walked with four different hip joint stiffness settings. Increasing the hip joint stiffness decreased hip flexion during ambulation but did not appear to affect the crutch GRFs. Walking speed was observed to initially increase with increases in hip joint stiffness, and then decrease. These findings suggest that increasing hip joint stiffness may increase walking speed for RGO users. PMID:24699979

Johnson, William Brett; Fatone, Stefania; Gard, Steven A

2014-02-01

285

Scaling of Fluid Flow and Seismic Stiffness of Fractures  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

286

Dynamic Stiffness Modeling of Composite Plate and Shell Assemblies.  

National Technical Information Service (NTIS)

This grant sought to develop the dynamic stiffness method for composite shell assemblies. In the first part an exact dynamic stiffness element based on higher order shear deformation theory and extensive use of symbolic algebra is developed for the first ...

F. A. Fazzolari J. R. Banerjee M. Boscolo

2013-01-01

287

Variable Stiffness Spar Wind-Tunnel Model Development and Testing.  

National Technical Information Service (NTIS)

The concept of exploiting wing flexibility to improve aerodynamic performance was investigated in the wind tunnel by employing multiple control surfaces and by varying wing structural stiffness via a Variable Stiffness Spar (VSS) mechanism. High design lo...

J. R. Florance J. Heeg C. V. Spain T. G. Ivanco C. D. Wieseman P. S. Lively

2004-01-01

288

Quantitative Elastography for Cervical Stiffness Assessment during Pregnancy  

PubMed Central

Aim. Feasibility and reliability of tissue Doppler imaging-(TDI-) based elastography for cervical quantitative stiffness assessment during all three trimesters of pregnancy were evaluated. Materials and Methods. Prospective case-control study including seventy-four patients collected between the 12th and 42nd weeks of gestation. The tissue strain (TS) was measured by two independent operators as natural strain. Intra- and interoperator intraclass correlation coefficient (ICC) agreements were evaluated. Results. TS measurement was always feasible and exhibited a high performance in terms of reliability (intraoperator ICC-agreement = 0.93; interoperator ICC agreement = 0.89 and 0.93 for a single measurement and for the average of two measurements, resp.). Cervical TS showed also a significant correlation with gestational age, cervical length, and parity. Conclusions. TS measurement during pregnancy demonstrated high feasibility and reliability. Furthermore, TS significantly correlated with gestational age, cervical length, and parity.

Fruscalzo, A.; Londero, A. P.; Frohlich, C.; Mollmann, U.; Schmitz, R.

2014-01-01

289

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

290

Contact stiffness of randomly rough surfaces  

NASA Astrophysics Data System (ADS)

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.

Pohrt, Roman; Popov, Valentin L.

2013-11-01

291

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.

Pohrt, Roman; Popov, Valentin L.

2013-01-01

292

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

293

[Stiff person syndrome--case report].  

PubMed

Stiff person syndrome (SPS) is the rare disease and cause great inefficient. It is characterized by progressive stiffness muscles of trunk and the limbs on which the cramps of muscles overlap. In the electrophysiological investigation of the patients the involuntary discharge of motor unit potentials find and also simultaneous contraction agonistic and antagonistic muscles. SPS is presented with insulin-dependent diabetes mellitus often or is the symptom of the paraneoplastic syndrome. It is commonly associated with high anti-glutamic acid decarboxylaze (GAD) antibody titters in the serum of the blood of patients. Establishing the diagnosis can cause difficulties. We observed the patient in the last period about the atypical course the disease. The diagnosis was confirmed occurrences of the high titters of antibodies anti-GAD, the discharge of motor unit potential in paraspinal muscles in the rest and good response the treatment with diazepamem. PMID:24645574

Tomczykiewicz, Kazimierz; Pastuszak, Zanna; Staszewski, Jacek; Stepie?, Adam

2014-01-01

294

Complex stiffness gradient substrates for studying mechanotactic cell migration.  

PubMed

Polyacrylamide gels are cast upon a stiff support with controlled topography, resulting in a thin gel layer of variable height. The topographical profiles project a stiffness map onto the gel, resulting in controlled linear and non-linear 2D stiffness gradients. Fibroblasts, which migrate towards stiffer substrates, accumulate in areas with a gel thickness below 15 ?m. PMID:22991224

Kuo, Cheng-Hwa R; Xian, Jian; Brenton, James D; Franze, Kristian; Sivaniah, Easan

2012-11-27

295

Numerical study of uncertainty quantification techniques for implicit stiff systems  

Microsoft Academic Search

Galerkin polynomial chaos and collocation methods have been widely adopted for uncertainty quantification purpose. However, when the stiff system is involved, the computational cost can be prohibitive, since stiff numerical integration requires the solution of a nonlinear system of equations at every time step. Applying the Galerkin polynomial chaos to stiff system will cause a computational cost increase from O(n3)

Haiyan Cheng; Adrian Sandu

2007-01-01

296

Arterial stiffness in predialysis patients with uremia  

Microsoft Academic Search

Arterial stiffness in predialysis patients with uremia.BackgroundHemodialysis patients have advanced arterial wall stiffening as shown by increased aortic pulse wave velocity (PWV), an independent predictor of cardiovascular mortality. We compared aortic PWV of uremic patients before starting hemodialysis treatment with that of patients on maintenance hemodialysis.MethodsThe subjects were 71 patients with end-stage renal disease (ESRD) before starting hemodialysis (predialysis group),

KAYO SHINOHARA; TETSUO SHOJI; YOSHIHIRO TSUJIMOTO; EIJI KIMOTO; HIDEKI TAHARA; HIDENORI KOYAMA; MASANORI EMOTO; EIJI ISHIMURA; TAKAMI MIKI; TSUTOMU TABATA; YOSHIKI NISHIZAWA

2004-01-01

297

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.

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

2014-01-01

298

Nonaffine rubber elasticity for stiff polymer networks  

NASA Astrophysics Data System (ADS)

We present a theory for the elasticity of cross-linked stiff polymer networks. Stiff polymers, unlike their flexible counterparts, are highly anisotropic elastic objects. Similar to mechanical beams, stiff polymers easily deform in bending, while they are much stiffer with respect to tensile forces (“stretching”). Unlike in previous approaches, where network elasticity is derived from the stretching mode, our theory properly accounts for the soft bending response. A self-consistent effective medium approach is used to calculate the macroscopic elastic moduli starting from a microscopic characterization of the deformation field in terms of “floppy modes”—low-energy bending excitations that retain a high degree of nonaffinity. The length scale characterizing the emergent nonaffinity is given by the “fiber length” lf , defined as the scale over which the polymers remain straight. The calculated scaling properties for the shear modulus are in excellent agreement with the results of recent simulations obtained in two-dimensional model networks. Furthermore, our theory can be applied to rationalize bulk rheological data in reconstituted actin networks.

Heussinger, Claus; Schaefer, Boris; Frey, Erwin

2007-09-01

299

Nonaffine rubber elasticity for stiff polymer networks.  

PubMed

We present a theory for the elasticity of cross-linked stiff polymer networks. Stiff polymers, unlike their flexible counterparts, are highly anisotropic elastic objects. Similar to mechanical beams, stiff polymers easily deform in bending, while they are much stiffer with respect to tensile forces ("stretching"). Unlike in previous approaches, where network elasticity is derived from the stretching mode, our theory properly accounts for the soft bending response. A self-consistent effective medium approach is used to calculate the macroscopic elastic moduli starting from a microscopic characterization of the deformation field in terms of "floppy modes"-low-energy bending excitations that retain a high degree of nonaffinity. The length scale characterizing the emergent nonaffinity is given by the "fiber length" lf, defined as the scale over which the polymers remain straight. The calculated scaling properties for the shear modulus are in excellent agreement with the results of recent simulations obtained in two-dimensional model networks. Furthermore, our theory can be applied to rationalize bulk rheological data in reconstituted actin networks. PMID:17930270

Heussinger, Claus; Schaefer, Boris; Frey, Erwin

2007-09-01

300

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.

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

2013-01-01

301

Stress-induced variations in the stiffness of micro- and nanocantilever beams.  

PubMed

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 long-standing 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

2012-06-01

302

Increased epicardial adipose tissue thickness is linked to aortic stiffness in patients with primary hypertension.  

PubMed

Abstract Aims. In patients with hypertension (HT), increased aortic stiffness is related to higher cardiovascular morbidity and mortality. Recent investigations have shown that epicardial adipose tissue (EAT) is a new potential cardiometabolic risk factor. The aim of our study was to examine the relation between echocardiographically measured EAT thickness and aortic stiffness in patients with primary HT. Methods. The study included 144 newly diagnosed and untreated essential hypertensive outpatients. Transthoracic echocardiographic EAT thickness and aortic stiffness measurements were performed for all study participants. Afterwards patients were divided in two groups according to their median EAT thickness values. The patients with EAT thickness of < 7 mm were included in group 1 and patients with EAT thickness of ? 7 mm were included in group 2. Results. Aortic strain and distensibility parameters of group 2 were lower than in group 1. The aortic stiffness index of group 2 was found to be higher than group 1. Multivariate regression analysis revealed that EAT thickness was the only independent variable for all three parameters of aortic stiffness index, aortic strain and aortic distensibility. Conclusion. In patients with newly diagnosed primary HT, increased EAT thickness was significantly linked to impaired aortic elastic properties independently of other conventional adiposity measurements. PMID:24328851

Do?an, Mehmet; Turak, Osman; Akyel, Ahmet; Grboviç, Enis; Mendi, Mehmet Ali; Oksüz, Fatih; Do?an, Aynur; Cimen, Tolga; Bilgin, Murat; Sunman, Hamza; Yeter, Ekrem; Aydo?du, Sinan

2014-08-01

303

Relation of arterial stiffness with gestational age and birth weight  

PubMed Central

Background: The cardiovascular risk of individuals who are born small as a result of prematurity remains controversial. Given the previous findings of stiffer peripheral conduit arteries in growth restricted donor twins in twin–twin transfusion syndrome regardless of gestational age, we hypothesised that among children born preterm, only those with intrauterine growth retardation are predisposed to an increase in cardiovascular risks. Aim: To compare brachioradial arterial stiffness and systemic blood pressure (BP) among children born preterm and small for gestational age (group 1, n = 15), those born preterm but having birth weight appropriate for gestational age (group 2, n = 36), and those born at term with birth weight appropriate for gestational age (group 3, n = 35). Methods: Systemic BP was measured by an automated device (Dinamap), while stiffness of the brachioradial arterial segment was assessed by measuring pulse wave velocity (PWV). The birth weight was adjusted for gestational age and expressed as a z score for analysis. Results: The 86 children were studied at a mean (SD) age of 8.2 (1.7) years. Subjects from group 1, who were born at 32.3 (2.0) weeks' gestation had a significantly lower z score of birth weight (-2.29 (0.63), p<0.001), compared with those from groups 2 and 3. They had a significantly higher mean blood pressure (p<0.001) and their diastolic blood pressure also tended to be higher (p = 0.07). Likewise, their brachioradial PWV, and hence arterial stiffness, was the highest of the three groups (p<0.001). While subjects from group 2 were similarly born preterm, their PWV was not significantly different from that of group 3 subjects (p = 1.00) and likewise their z score of birth weight did not differ (-0.01 (0.71) v -0.04 (1.1), p = 1.00). Brachioradial PWV correlated significantly with systolic (r = 0.31, p = 0.004), diastolic (r = 0.38, p<0.001), and mean (0.47, p<0.001) BP, and with z score of birth weight (r = -0.43, p<0.001). Multiple linear regression identified mean BP and z score of birth weight as significant determinants of PWV. Conclusion: The findings of the present study support the hypothesis that among children born preterm, only those with intrauterine growth retardation are disadvantaged as a result of increase in systemic arterial stiffness and mean blood pressure.

Cheung, Y; Wong, K; Lam, B.; Tsoi, N

2004-01-01

304

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

PubMed Central

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

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

2011-01-01

305

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

306

Simultaneous identification of tire cornering stiffnesses and vehicle center of gravity  

Microsoft Academic Search

INS, GPS measurements are used to simultaneously estimate the location of the center of gravity of a vehicle and the tire cornering stiffnesses. The developed method uses kinematic as well as dynamic equations of a lateral vehicle model to eliminate the bias in the yaw rate and lateral acceleration measurements. An approximation of the moment of inertia is used to

S. Sivaramakrishnan

2008-01-01

307

Extreme damping in composite materials with negative-stiffness inclusions  

NASA Astrophysics Data System (ADS)

When a force deforms an elastic object, practical experience suggests that the resulting displacement will be in the same direction as the force. This property is known as positive stiffness. Less familiar is the concept of negative stiffness, where the deforming force and the resulting displacement are in opposite directions. (Negative stiffness is distinct from negative Poisson's ratio, which refers to the occurrence of lateral expansion upon stretching an object.) Negative stiffness can occur, for example, when the deforming object has stored (or is supplied with) energy. This property is usually unstable, but it has been shown theoretically that inclusions of negative stiffness can be stabilized within a positive-stiffness matrix. Here we describe the experimental realization of this composite approach by embedding negative-stiffness inclusions of ferroelastic vanadium dioxide in a pure tin matrix. The resulting composites exhibit extreme mechanical damping and large anomalies in stiffness, as a consequence of the high local strains that result from the inclusions deforming more than the composite as a whole. Moreover, for certain temperature ranges, the negative-stiffness inclusions are more effective than diamond inclusions for increasing the overall composite stiffness. We expect that such composites could be useful as high damping materials, as stiff structural elements or for actuator-type applications.

Lakes, R. S.; Lee, T.; Bersie, A.; Wang, Y. C.

2001-03-01

308

Normal stiffness calibration of microfabricated tri-layer conducting polymer actuators  

NASA Astrophysics Data System (ADS)

This paper reports on the stiffness characterization of microfabricated tri-layer conducting polymer (PPy) actuators. The rectangular, polypyrrole microactuators, which could operate both in aqueous and non-aqueous media, were fabricated using an excimer laser ablation technique that provided high throughput production and did not require cleanroom facilities. The microactuators were fixed at one end with electrical contacts and the other was end free to act as an electroactive microcantilever beam. An atomic force microscope (AFM) was used to measure the microactuator deflection under a range of normal forces applied by the AFM cantilever. A modified reference spring constant calibration method was employed to determine the stiffness constants of the microactuators. The stiffness of the microactuators in the electroactive (electrically stimulated) and passive state (no stimulation) were evaluated separately and compared. In doing so, the study presents results leading to the stiffness characterization of the first air-operated polymer microactuators and implementation of a simple, reliable and effective method for directly measuring the spring constant of polymer microactuators. This method is an alternative to the use of mechanical modeling methods, which can be difficult to implement for multi-layer (composite) polymer actuators. Importantly, our results highlight several requirements for using the reference spring method to accurately determine stiffness values of any microcantilever generally fabricated from soft, deformable materials.

Alici, Gursel; Higgins, Michael J.

2009-06-01

309

Cocoa intake and arterial stiffness in subjects with cardiovascular risk factors  

PubMed Central

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

2012-01-01

310

An Integrated Indenter-ARFI Imaging System for Tissue Stiffness Quantification  

PubMed Central

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

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

2008-01-01

311

Acoustic Radiation Force Impulse Imaging of Mechanical Stiffness Propagation in Myocardial Tissue  

PubMed Central

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.

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

2012-01-01

312

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.

2014-01-01

313

The decapping activator Lsm1p-7p-Pat1p complex has the intrinsic ability to distinguish between oligoadenylated and polyadenylated RNAs  

PubMed Central

Decapping is a critical step in mRNA decay. In the 5?-to-3? mRNA decay pathway conserved in all eukaryotes, decay is initiated by poly(A) shortening, and oligoadenylated mRNAs (but not polyadenylated mRNAs) are selectively decapped allowing their subsequent degradation by 5? to 3? exonucleolysis. The highly conserved heptameric Lsm1p-7p complex (made up of the seven Sm-like proteins, Lsm1p–Lsm7p) and its interacting partner Pat1p activate decapping by an unknown mechanism and localize with other decapping factors to the P-bodies in the cytoplasm. The Lsm1p-7p–Pat1p complex also protects the 3?-ends of mRNAs in vivo from trimming, presumably by binding to the 3?-ends. In order to determine the intrinsic RNA-binding properties of this complex, we have purified it from yeast and carried out in vitro analyses. Our studies revealed that it directly binds RNA at/near the 3?-end. Importantly, it possesses the intrinsic ability to distinguish between oligoadenylated and polyadenylated RNAs such that the former are bound with much higher affinity than the latter. These results indicate that the intrinsic RNA-binding characteristics of this complex form a critical determinant of its in vivo interactions and functions.

Chowdhury, Ashis; Mukhopadhyay, Jaba; Tharun, Sundaresan

2007-01-01

314

Microstructure control of SOFC cathodes using the self-organizing behavior of LSM\\/ScSZ composite powder material prepared by spray pyrolysis  

Microsoft Academic Search

Composite particles for SOFC cathodes were synthesized by a spray pyrolysis method. The constituent materials for the cathode are provided in the form of a metal ion solution with the addition of an electrolyte sol solution, and sprayed droplets of the solution undergo pyrolysis to form composite LSM\\/ScSZ particles. The resultant particles have been shown to possess a structure on

Akifusa Hagiwara; Natsuro Hobara; Koichi Takizawa; Kazuyoshi Sato; Hiroya Abe; Makio Naito

2007-01-01

315

Evaluation of microscopic techniques (epifluorescence microscopy, CLSM, TPE-LSM) as a basis for the quantitative image analysis of activated sludge  

Microsoft Academic Search

Microscopic techniques ranging from epifluorescence microscopy to confocal laser scanning microscopy (CLSM) and two photon excitation laser scanning microscopy (TPE-LSM) combined with fluorescent stains can help to evaluate complex microbial aggregates such as activated sludge flocs. To determine the application limits of these microscopic techniques, activated sludge samples from three different sources were evaluated after staining with a fluorescent viability

C. Lopez; M. N. Pons; E. Morgenroth

2005-01-01

316

Aortic Stiffness in Lone Atrial Fibrillation: A Novel Risk Factor for Arrhythmia Recurrence  

PubMed Central

Background Recent community-based research has linked aortic stiffness to the development of atrial fibrillation. We posit that aortic stiffness contributes to adverse atrial remodeling leading to the persistence of atrial fibrillation following catheter ablation in lone atrial fibrillation patients, despite the absence of apparent structural heart disease. Here, we aim to evaluate aortic stiffness in lone atrial fibrillation patients and determine its association with arrhythmia recurrence following radio-frequency catheter ablation. Methods We studied 68 consecutive lone atrial fibrillation patients who underwent catheter ablation procedure for atrial fibrillation and 50 healthy age- and sex-matched community controls. We performed radial artery applanation tonometry to obtain central measures of aortic stiffness: pulse pressure, augmentation pressure and augmentation index. Following ablation, arrhythmia recurrence was monitored at months 3, 6, 9, 12 and 6 monthly thereafter. Results Compared to healthy controls, lone atrial fibrillation patients had significantly elevated peripheral pulse pressure, central pulse pressure, augmentation pressure and larger left atrial dimensions (all P<0.05). During a mean follow-up of 2.9±1.4 years, 38 of the 68 lone atrial fibrillation patients had atrial fibrillation recurrence after initial catheter ablation procedure. Neither blood pressure nor aortic stiffness indices differed between patients with and without atrial fibrillation recurrence. However, patients with highest levels (?75th percentile) of peripheral pulse pressure, central pulse pressure and augmentation pressure had higher atrial fibrillation recurrence rates (all P<0.05). Only central aortic stiffness indices were associated with lower survival free from atrial fibrillation using Kaplan-Meier analysis. Conclusion Aortic stiffness is an important risk factor in patients with lone atrial fibrillation and contributes to higher atrial fibrillation recurrence following catheter ablation procedure.

Lau, Dennis H.; Middeldorp, Melissa E.; Brooks, Anthony G.; Ganesan, Anand N.; Roberts-Thomson, Kurt C.; Stiles, Martin K.; Leong, Darryl P.; Abed, Hany S.; Lim, Han S.; Wong, Christopher X.; Willoughby, Scott R.; Young, Glenn D.; Kalman, Jonathan M.; Abhayaratna, Walter P.; Sanders, Prashanthan

2013-01-01

317

Dynamic Postprandial Hepatic Stiffness Augmentation Assessed With MR Elastography in Patients With Chronic Liver Disease  

PubMed Central

Objective MR elastography (MRE) is an MRI-based technique for quantitatively assessing tissue stiffness by studying shear wave propagation through tissue. The goal of this study was to test the hypothesis that hepatic MRE performed before and after a meal will result in a postprandial increase in hepatic stiffness among patients with hepatic fibrosis because of transiently increased portal pressure. Subjects and Methods Twenty healthy volunteers and 25 patients with biopsy-proven hepatic fibrosis were evaluated. Preprandial MRE measurements were performed after overnight fasting. A liquid test meal was administered, and 30 minutes later a postprandial MRE acquisition was performed. Identical imaging parameters and analysis regions of interest were used for pre- and postprandial acquisitions. Results The results in the 20 subjects without liver disease showed a mean stiffness change of 0.16 ± 0.20 kPa (range, ?0.12 to 0.78 kPa) or 8.08% ± 10.33% (range, ?5.36% to 41.7%). The hepatic stiffness obtained in the 25 patients with hepatic fibrosis showed a statistically significant increase in postprandial liver stiffness, with mean augmentation of 0.89 ± 0.96 kPa (range, 0.17–4.15 kPa) or 21.24 ± 14.98% (range, 7.69%–63.3%). Conclusion MRE-assessed hepatic stiffness elevation in patients with chronic liver disease has two major components: a static component reflecting structural change or fibrosis and a dynamic component reflecting portal pressure that can increase after a meal. These findings will provide motivation for further studies to determine the potential value of assessing postprandial hepatic stiffness augmentation for predicting the progression of fibrotic disease and the development of portal hypertension. The technique may also provide new insights into the natural history and pathophysiology of chronic liver disease.

Yin, Meng; Talwalkar, Jayant A.; Glaser, Kevin J.; Venkatesh, Sudhakar K.; Chen, Jun; Manduca, Armando; Ehman, Richard L.

2011-01-01

318

Cardio-ankle vascular index (CAVI) as an indicator of arterial stiffness  

PubMed Central

Arterial stiffness has been identified as an independent predictor of prognostic outcomes for patients with cardiovascular disease. Although measurement of pulse wave velocity has been a widely accepted noninvasive approach to the assessment of arterial stiffness, its accuracy is hampered by changes in blood pressure. Taking the exponential relation between intravascular pressure and arterial diameter into consideration, a stiffness parameter can be obtained by plotting the natural logarithm of systolic–diastolic pressure ratio against the arterial wall extensibility. Cardio-ankle vascular index (CAVI), which is calculated based on the stiffness parameter thus obtained, is theoretically independent of changes in blood pressure. With this distinct advantage, CAVI has been widely applied clinically to assess arterial stiffness in subjects with known cardiovascular diseases including those with diagnosed atherosclerosis, coronary heart disease, and stroke as well as those at risk, including those with hypertension, diabetes, the elderly, and the obese. Because of its enhanced sensitivity, not only has the index been used to discern subtle changes in the disease process, it has also been utilized in studying normal individuals to assess their potential risks of developing cardiovascular diseases. The primary aims of assessing arterial stiffness using CAVI are not only to aid in early detection of arteriosclerosis to allow timely treatment and change in lifestyle, but also to quantitatively evaluate the progression of disease and the effectiveness of treatment. Despite its merit of being unaffected by blood pressure, discretion in data interpretation is suggested because an elevated CAVI represents not just vascular stiffness caused by pathological changes in the arterial wall, but can also be attributed to an increased vascular tone brought about by smooth muscle contraction. Moreover, certain patient populations, such as those with an ankle-brachial index < 0.9, may give falsely low CAVI and are suggested to be excluded from study.

Sun, Cheuk-Kwan

2013-01-01

319

Aortic stiffness and calcification in men in a population-based international study  

PubMed Central

Objectives Aortic stiffness, a hallmark of vascular aging, is an independent risk factor of cardiovascular disease and all-cause mortality. The association of aortic stiffness with aortic calcification in middle-aged general population remains unknown although studies in patients with end-stage renal disease or elderly subjects suggest that aortic calcification is an important determinant of aortic stiffness. The goal of this study was to examine the association of aortic calcification and stiffness in multi-ethnic population-based samples of relatively young men. Methods We examined the association in 906 men aged 40–49 (81 Black Americans, 276 Japanese Americans, 258 White Americans and 291 Koreans). Aortic stiffness was measured as carotid-femoral pulse wave velocity (cfPWV) using an automated waveform analyzer. Aortic calcification from aortic arch to iliac bifurcation was evaluated using electron-beam computed tomography. Results Aortic calcium score was calculated and was categorized into four groups: zero (n=303), 1–100 (n=411), 101–300 (n=110), and 401+ (n=82). Aortic calcification category had a significant positive association with cfPWV after adjusting for age, race, and mean arterial pressure (mean (standard error) of cfPWV (cm/second) from the lowest to highest categories: 836 (10), 850 (9), 877 (17) and 941 (19), p for trend <0.001). The significant positive association remained after further adjusting for other cardiovascular risk factors. The significant positive association was also observed in each race group. Conclusions The results suggest that aortic calcification can be one mechanism for aortic stiffness and that the association of aortic calcification with stiffness starts as early as the 40’s.

Sekikawa, Akira; Shin, Chol; Curb, J. David; Barinas-Mitchell, Emma; Masaki, Kamal; El-Saed, Aiman; Seto, Todd B.; Mackey, Rachel H.; Choo, Jina; Fujiyoshi, Akira; Miura, Katsuyuki; Edmundowicz, Daniel; Kuller, Lewis H.; Ueshima, Hirotsugu; Sutton-Tyrrell, Kim

2012-01-01

320

Intestinal lymphangiectasia and reversible high liver stiffness.  

PubMed

Primary intestinal lymphangiectasia (PIL) is a protein-losing enteropathy characterized by tortuous and dilated lymph channels of the small bowel. The main symptoms are bilateral lower limb edema, serosal effusions, and vitamin D malabsorption resulting in osteoporosis. We report here a case of long-lasting misdiagnosed PIL with a peculiar liver picture, characterized by a very high stiffness value at transient elastography, which decreased with clinical improvement. The complex interplay between lymphatic and hepatic circulatory system is discussed. (Hepatology 2014;60:759-761). PMID:24449480

Milazzo, Laura; Peri, Anna Maria; Lodi, Lucia; Gubertini, Guido; Ridolfo, Anna Lisa; Antinori, Spinello

2014-08-01

321

Acto-myosin based response to stiffness and rigidity sensing  

PubMed Central

Cells sense the rigidity of their environment and respond to it. Most studies have been focused on the role of adhesion complexes in rigidity sensing. In particular, it has been clearly shown that proteins of the adhesion complexes were stretch-sensitive and could thus trigger mechano-chemical signaling in response to applied forces. In order to understand how this local mechano-sensitivity could be coordinated at the cell scale, we have recently carried out single cell traction force measurements on springs of varying stiffness. We found that contractility at the cell scale (force, speed of contraction, mechanical power) was indeed adapted to external stiffness and reflected ATPase activity of non-muscle myosin II and acto-myosin response to load. Here we suggest a scenario of rigidity sensing where local adhesions sensitivity to force could be coordinated by adaptation of the acto-myosin dependent cortical tension at the global cell scale. Such a scenario could explain how spreading and migration are oriented by the rigidity of the cell environment.

Fouchard, Jonathan; Mitrossilis, Demosthene

2011-01-01

322

Symmetrical dimethylation of arginine residues in spliceosomal Sm protein B/B' and the Sm-like protein LSm4, and their interaction with the SMN protein.  

PubMed Central

Arginine residues in RG-rich proteins are frequently dimethylated posttranslationally by protein arginine methyltransferases (PRMTs). The most common methylation pattern is asymmetrical dimethylation, a modification important for protein shuttling and signal transduction. Symmetrically dimethylated arginines (sDMA) have until now been confined to the myelin basic protein MBP and the Sm proteins D1 and D3. We show here by mass spectrometry and protein sequencing that also the human Sm protein B/B' and, for the first time, one of the Sm-like proteins, LSm4, contain sDMA in vivo. The symmetrical dimethylation of B/B', LSm4, D1, and D3 decisively influences their binding to the Tudor domain of the "survival of motor neurons" protein (SMN): inhibition of dimethylation by S-adenosylhomocysteine (SAH) abolished the binding of D1, D3, B/B', and LSm4 to this domain. A synthetic peptide containing nine sDMA-glycine dipeptides, but not asymmetrically modified or nonmodified peptides, specifically inhibited the interaction of D1, D3, B/B', LSm4, and UsnRNPs with SMN-Tudor. Recombinant D1 and a synthetic peptide could be methylated in vitro by both HeLa cytosolic S100 extract and nuclear extract; however, only the cytosolic extract produced symmetrical dimethylarginines. Thus, the Sm-modifying PRMT is cytoplasmic, and symmetrical dimethylation of B/B', D1, and D3 is a prerequisite for the SMN-dependent cytoplasmic core-UsnRNP assembly. Our demonstration of sDMAs in LSm4 suggests additional functions of sDMAs in tri-UsnRNP biogenesis and mRNA decay. Our findings also have interesting implications for the understanding of the aetiology of spinal muscular atrophy (SMA).

Brahms, H; Meheus, L; de Brabandere, V; Fischer, U; Luhrmann, R

2001-01-01

323

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.

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

2006-01-01

324

The influence of a packable resin composite, conventional resin composite and amalgam on molar cuspal stiffness.  

PubMed

Packable resin composites may offer improved properties and clinical performance over conventional resin composites or dental amalgam. This in vitro study examined the cuspal stiffness of molars restored with a packable resin composite, a conventional posterior microfilled resin composite and amalgam. Forty-eight intact caries-free human third molars were distributed into four treatment groups (n=12) so that the mean cross-sectional areas of all groups were equal. Standardized MOD cavity preparations were made and specimens restored using one of four restorative materials: (1) a spherical particle amalgam (Tytin); (2) Tytin amalgam with a dentin adhesive liner (OptiBond Solo); (3) a conventional microfilled posterior resin composite (Heliomolar); (4) a packable posterior resin composite (Prodigy Posterior). Cuspal stiffness was measured using a Bionix 200 biomaterials testing machine (MTS). Specimens were loaded vertically to 300 N at a crosshead speed of 1.0 mm/minute. Stiffness was measured at 10 intervals: (1) prior to cavity preparation (intact); (2) following cavity preparation, but before restoration; (3) seven days after restoration; then (4) 1, 2, 3, 4, 5, 6 and 12 months after restoration. All specimens were stored at 37 degrees C in deionized water throughout the study and thermocycled (5 degrees/55 degrees C; 2000 cycles) monthly for 12 months. Repeated Measures ANOVA revealed significant differences among treatment groups over time (p<0.0001). Cavity preparation reduced cuspal stiffness by more than 60%. At 12 months, the cuspal stiffness of restored teeth was, on average, 58% that of intact specimens. Neither the packable nor the conventional resin composite increased cuspal stiffness over that of amalgam. PMID:12216572

Molinaro, J D; Diefenderfer, K E; Strother, J M

2002-01-01

325

Analysis and experiment of a vibration isolator using a novel magnetic spring with negative stiffness  

NASA Astrophysics Data System (ADS)

The vibration isolator using a novel magnetic spring with negative stiffness (MS-NS) is proposed in this paper. The proposed isolator which combines a positive stiffness spring with the MS-NS in parallel possesses the characteristic of high-static–low-dynamic stiffness. The MS-NS is composed of three cuboidal magnets configured in repulsive interaction. An analytical expression of the stiffness of the MS-NS is derived by using the magnetic charge model, and the approximation to the exact analytical expression is sought. Then, the nonlinearity of the stiffness is analyzed, and it is shown that the MS-NS is approximately linear for small oscillations. In order to validate the correctness and effectiveness of the MS-NS, the vibration transmissibility of the proposed isolator with and without the MS-NS is measured. The experimental results demonstrate that combining a vibration isolator with the MS-NS in parallel can lower the natural frequency of the isolator; and the analytical calculations and experimental results show a good consistency.

Wu, Wenjiang; Chen, Xuedong; Shan, Yuhu

2014-06-01

326

Target renal damage: the microvascular associations of increased aortic stiffness in patients with COPD  

PubMed Central

Background Although renal impairment has been described in COPD, there is opportunity to evaluate further to determine nature and consider optimal management. Increased aortic stiffness, as seen in COPD, leads to reduced buffering of pulsatile flow. We hypothesised that urinary albumin creatinine ratio (UACR) would reflect glomerular damage related to aortic stiffness. Methods Patients with COPD and controls underwent spirometry, blood pressure, arterial stiffness - aortic pulse wave velocity (PWV) and provided a spot urine sample for UACR, with other renal biomarkers measured. Results The UACR was increased in patients (n?=?52): 0.80 mg/mmol compared to controls (n?=?34): 0.46 mg/mmol, p?stiffness. Besides the macrovascular prognostic implications of increased aortic stiffness, the microvascular state in COPD management should be considered.

2013-01-01

327

Bending stiffness, torsional stability, and insertion force of cementless femoral stems.  

PubMed

In cementless total hip arthroplasty, increased femoral stem flexibility and decreased fracture propensity are desirable characteristics. The slotting and tapering of the stem have been introduced to achieve this. These features should not, however, be allowed to interfere with the ability of the distal stem to provide initial mechanical stability, especially under rotation. This study was done to investigate the ability of slotted and tapered stem designs to reduce stiffness and insertion force while still maintaining adequate torsional strength. The torsional strength, maximum insertion force, and insertional work of straight, slotted, and taper stems were measured by inserting each type into rigid polyurethane foam and torque testing to failure. Bending stiffness of each stem design was calculated using numerical methods. When compared to a straight stem, a unislot stem has similar torsional strength, maximum insertional force, and work of insertion. The bending stiffness is decreased by 19% to 82% depending on the bending direction. A trislot design decreased torque strength by 29%, maximal insertion force by 36%, and work by 11%. Bending stiffness was decreased by 74% and was not dependent on bending direction. A 0.5-mm taper decreased torque strength by 11% and insertional work by 14%. No difference was seen in maximum insertional force. We conclude that the design features studied (slots and taper) are effective in decreasing stem stiffness and reducing fracture propensity. PMID:11334454

Incavo, S J; Johnson, C C; Churchill, D L; Beynnon, B D

2001-04-01

328

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.

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

2013-01-01

329

Modified face seal for positive film stiffness  

NASA Technical Reports Server (NTRS)

The film stiffness of a face seal is improved without increasing the sealing and dam area by using an apparatus which includes a primary seal ring in the form of a nose piece. A spring forces a sealing surface on the seal ring into sealing contact with a seat to form a face seal. A circumferential clearance seal is formed in series with this face seal by a lip on the piece. The width of the surface of the lip is substantially the same as the width of the sealing surface on the face seal and the clearance between the surface on the lip and the shaft is substantially the same as the spacing between the face sealing surfaces on the face seal when the shaft is rotating. The circumferential clearance seal restricts the flow of fluid from a main cavity to an intermediate cavity with a resulting pressure drop. The hydrostatic opening face is strongly dependent on the face seal clearance, and the desired axial stiffness is achieved.

Etsion, I.; Lipshitz, A. (inventors)

1981-01-01

330

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

331

Arthroscopic assessment of human cartilage stiffness of the femoral condyles and the patella with a new tactile sensor.  

PubMed

We measured the stiffness of the cartilage of the human femoral condyles via an ultrasonic tactile sensor under arthroscopic control. The stiffness and the degeneration of articular cartilage were assessed in 105 knees in 74 patients (39 men, 35 women, age: 9-72 years) who underwent arthroscopic observation or surgery. Twenty-five knees suffered from traumatic cartilage injury, 14 from osteochondritis dissecans, 13 from osteoarthritis, 11 from meniscal injury and six from ligamentous injury, bipartita patellae (three knees), and symptomatic plica synovialis (two knees). The degeneration of cartilage was classified according to Outerbridge's grading system. The relationships between the stiffness and the grade of cartilage degeneration, and gender were analyzed. The stiffness of grade I (softening) and II (fissuring less than 0.5 inches in length) was significantly lower than that of intact cartilage. In contrast, the stiffness of grade IV (exposed subchondral bone) was significantly higher than that of any other group. The cartilage stiffness of the patella in women was significantly lower than that in men. The tactile sensor was useful for determining the intraoperative stiffness of healthy and diseased human cartilage in all grades. PMID:12135651

Uchio, Y; Ochi, M; Adachi, N; Kawasaki, K; Iwasa, J

2002-07-01

332

Assessments of arterial stiffness and endothelial function using pulse wave analysis.  

PubMed

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

333

Assessment of muscle stiffness using a continuously scanning laser-Doppler vibrometer.  

PubMed

Introduction: A stand-alone and low-cost elastography technique has been developed using a single continuously scanning laser Doppler vibrometer. Methods: This elastography technique is used to measure the propagation velocity of surface vibrations over superficial skeletal muscles to assess muscle stiffness. Results: Systematic variations in propagation velocity depending on the contraction level and joint position of the biceps brachii were demonstrated in 10 subjects. Conclusions: This technique may assist clinicians in characterizing muscle stiffness (or tone) changes due to neuromuscular disorders. Muscle Nerve 50: 133-135, 2014. PMID:24395193

Salman, Muhammad; Sabra, Karim G; Shinohara, Minoru

2014-07-01

334

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.

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

2012-01-01

335

Clinical appraisal of arterial stiffness: the Argonauts in front of the Golden Fleece  

PubMed Central

Interest in evaluating arterial elastic properties has grown in parallel with the widespread availability of non?invasive methods for assessing arterial stiffness. A clinically useful diagnostic index must be pathophysiologically relevant, must be readily measurable, and must indicate the severity of the disease and predict the corresponding risk. Interventional modification of this index must parallel disease regression and benefit prognosis. The current evidence for the clinical value of estimating arterial stiffness (mainly of large, elastic?type arteries, such as the aorta and the carotids) in the contemporary era of cardiovascular medicine is reviewed.

Vlachopoulos, C; Aznaouridis, K; Stefanadis, C

2006-01-01

336

Non-contact Stiffness Sensing by Considering the Change of Fluid Force due to Object Deformation  

NASA Astrophysics Data System (ADS)

Non-contact stiffness sensor is often utilized especially for medical fields due to its advantage of avoiding damage to tissues and keeping sanitary. However, it is hard to measure the force accurately, because the fluid jet based force much depends upon the shape after deformation of object. This paper proposes an innovative approach where the external force is adaptively calibrated based on the deformation of object so that we can evaluate the internal stiffness parameters more accurately than that of conventional approaches. It is shown that the proposed method can improve the accuracy of force application with even 100% at an extreme case.

Tanaka, Nobuyuki; Higashimori, Mitsuru; Kaneko, Makoto

337

Relationship between the mandibular inferior cortex and bone stiffness in elderly Japanese people  

Microsoft Academic Search

Summary  This study assessed the relationship between the mandibular inferior cortex (MIC) and bone stiffness in elderly Japanese subjects.\\u000a Results suggest that MIC classification may be useful for screening patients for the possibility of osteoporosis by measuring\\u000a bone stiffness with ultrasound bone densitometry.\\u000a \\u000a \\u000a \\u000a Introduction  The prevention of fractures is a priority for patients with osteoporosis. Dental panoramic radiographs are frequently taken\\u000a for

B. Kiswanjaya; A. Yoshihara; T. Deguchi; N. Hanada; H. Miyazaki

2010-01-01

338

Stiffness change of a graphite epoxy laminate under reverse fatigue loading  

NASA Technical Reports Server (NTRS)

The stiffness of a flat specimen, made of graphite epoxy (T300/934), was measured during reverse fatigue loading. Laminates of basic layup, unidirectional cross-ply and angle-ply, as well as multidirectional (isotropic) layup, were tested. It was found that all the laminates exhibit rapid stiffness degradation on the last (third) fatigue stage. Except for the 0-deg unidirectional laminate, the last stage starts at about 70 to 80 percent of the fatigue life, regardless of the load level and the final mode of failure (tension or compression). It is shown that, for this material, stiffness degradation is a result of crack accumulation, mainly along the fibers, even for the fiber dominated laminates. This general phenomenon can serve to predict usable safe life of laminates under fatigue loading.

Rotem, Assa

1989-01-01

339

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

340

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.

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

2013-01-01

341

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

PubMed Central

It is widely accepted that age-related changes in lens stiffness are significant for the development of presbyopia. However, precise details on the relative importance of age-related changes in the stiffness of the lens, in comparison with other potential mechanisms for the development of presbyopia, have not yet been established. One contributing factor to this uncertainty is the paucity and variability of experimental data on lens stiffness. The available published data generally indicate that stiffness varies spatially within the lens and that stiffness parameters tend to increase with age. However, considerable differences exist between these published data sets, both qualitatively and quantitatively. The current paper describes new and improved methods, based on the spinning lens approach pioneered by Fisher, R.F. (1971) ‘The elastic constants of the human lens’, Journal of Physiology, 212, 147–180, to make measurements on the stiffness of the human lens. These new procedures have been developed in an attempt to eliminate, or at least substantially reduce, various systematic errors in Fisher’s original experiment. An improved test rig has been constructed and a new modelling procedure for determining lens stiffness parameters from observations made during the test has been devised. The experiment involves mounting a human lens on a vertical rotor so that the lens spins on its optical axis (typically at 1000 rpm). An automatic imaging system is used to capture the outline of the lens, while it is rotating, at pre-determined angular orientations. These images are used to quantify the deformations developed in the lens as a consequence of the centripetal forces induced by the rotation. Lens stiffness is inferred using axisymmetric finite element inverse analysis in which a nearly-incompressible neo-Hookean constitutive model is used to represent the mechanics of the lens. A numerical optimisation procedure is used to determine the stiffness parameters that provide a best fit between the finite element model and the experimental data. Sample results are presented for a human lens of age 33 years.

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

2011-01-01

342

EFFECT OF PASSIVE HEAT STRESS ON ARTERIAL STIFFNESS  

PubMed Central

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

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

2011-01-01

343

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

344

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

345

A mathematical stiffness matrix for characterising mechanical performance of the Orthofix DAF  

Microsoft Academic Search

This study investigates a method for characterising the 3D support to a bone fracture site that is provided by a fracture stabilising device. The method is demonstrated with the Orthofix DAF unilateral external fixator, for which a mathematical stiffness matrix is defined using experimental measurements in six degrees of freedom. Single forces or bending moments are applied to a model

Trevor Noel Gardner; Michiel Weemaes

1999-01-01

346

In Vivo Determination of Hepatic Stiffness Using Steady-State Free Precession Magnetic Resonance Elastography  

Microsoft Academic Search

Objective: The objective of this study was to introduce an magnetic resonance elastography (MRE) protocol based on fractional motion encoding and planar wave acquisition for rapid measurements of in vivo human liver stiffness. Materials and Methods: Vibrations of a remote actuator membrane were fed by a rigid rod to the patient's surface beneath the right costal arch resulting in axial

Dieter Klatt; Patrick Asbach; Jens Rump; Sebastian Papazoglou; Rajan Somasundaram; Jens Modrow; Ingolf Sack

2006-01-01

347

The bursal and articular sides of the supraspinatus tendon have a different compressive stiffness  

Microsoft Academic Search

Objective. To measure the compressive stiffness of the supraspinatus tendon and to determine whether regional difference exists in the bursal and articular side of the tendon.Design. Indentation testing was performed on both the bursal and articular sides of the supraspinatus tendon, focused on the ‘critical area’, where rotator cuff tears often occur.Background. When the supraspinatus tendon wraps around the humeral

Seok-Beom Lee; Tomotaka Nakajima; Zong-Ping Luo; Mark E Zobitz; Yi-Wen Chang; Kai-Nan An

2000-01-01

348

Atomic force microscopy at ambient and liquid conditions with stiff sensors and small amplitudes  

Microsoft Academic Search

We report on atomic force microscopy (AFM) in ambient and liquid environments with the qPlus sensor, a force sensor based on a quartz tuning fork with an all-electrical deflection measurement scheme. Small amplitudes, stiff sensors with bulk diamond tips and high Q values in air and liquid allow to obtain high resolution images. The noise sources in air and liquid

Elisabeth Wutscher; Franz J. Giessibl

2011-01-01

349

Cerebral Microbleeds Are Independently Associated with Arterial Stiffness in Stroke Patients  

Microsoft Academic Search

Background: Cerebral microbleeds (CMB) are now receiving considerable attention for their association with stroke recurrence and white matter lesions (WML). Pulse wave velocity (PWV), which is a measure of arterial stiffness, was found to be one of the predictors of cardiovascular disease and stroke in a large population-based study. The current study set out to investigate the association between CMB

Woo-Keun Seo; Jong-Moon Lee; Moon Ho Park; Kun Woo Park; Dae Hie Lee

2008-01-01

350

Ulnar and tibial bending stiffness as an index of bone strength in synchronized swimmers and gymnasts  

Microsoft Academic Search

The purpose of this study is to compare a mechanical property of bone in world-class female athletes with different loading histories. Bone bending stiffness or EI (E is the modulus of elasticity and I, the moment of inertia) was measured noninvasively with the mechanical response tissue analyzer, that analyzes the response of bone to a vibratory stimulus. We evaluated the

Michael T. C. Liang; Sara B. Arnaud; Charles R. Steele; Patrick Hatch; Alexjandro Moreno

2005-01-01

351

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

352

A high-stiffness axial resonant probe for atomic force microscopy  

Microsoft Academic Search

A high-stiffness, (>500 N\\/m) resonant atomic force microscope probe was constructed to allow force measurements in the presence of large force gradients. The probe employs a piezoresistively detected, electrostatically driven resonant beam sensor oriented perpendicularly to the sample surface. This probe is distinguished from shear force microscopy and noncontact atomic force microscopy in that the design allows for a stationary

Jonah A. Harley; Thomas W. Kenny

2001-01-01

353

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

Microsoft Academic Search

Variability in recombination frequency has been reported in several plant populations. The objectives of the present research were to establish the range in variability in recombination among genotypes in the important corn population Iowa Stiff Stalk Synthetic and to identify individual genotypes which produced increased or decreased recombination frequencies. Approximately 150 individual S0 plants were testcrossed to measure male recombination

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

1993-01-01

354

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

Microsoft Academic Search

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

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

355

Construction Quality Control of Unbound Layers Based on Stiffness Modulus Criteria  

Microsoft Academic Search

NDT methods such as Portable Falling Weight Deflectometer (PFWD) provide measurements based on the engineering properties of materials (stiffness) instead of physical properties like field density and moisture content. However, PFWD testing method is not yet proven to be reliable enough for construction quality control. In this research, a laboratory testing unit box was prepared in which unbound materials were

Kamran Rafiei; Amir Kavussi; Shahaboddin Yasrobi

2012-01-01

356

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

357

Bend stiffness of copper and copper alloy foils  

Microsoft Academic Search

Loop stiffness and permanent deflection in bend testing of tough pitch copper foil and three kinds of copper alloy foils have been evaluated as bend stiffness. The copper alloy foils, in particular precipitation-hardened NK120 and C7025, exhibited high loop stiffness. High Young’s moduli of the alloy foils, which were confirmed by a cantilever resonance method, are considered to increase the

Yasuo Tomioka; Norio Yuki

2004-01-01

358

Scaling of the flow-stiffness relationship in weakly correlated single fractures  

NASA Astrophysics Data System (ADS)

The remote characterization of the hydraulic properties of fractures in rocks is important in many subsurface projects. Fractures create uncertainty in the hydraulic properties of the subsurface in that their topology controls the amount of flow that can occur in addition to that from the matrix. In turn, the fracture topology is also affected by stress which alters the topology as the stress changes directly. This alteration of fracture topology with stress is captured by fracture specific stiffness. The specific stiffness of a single fracture can be remotely probed from the attenuation and velocity of seismic waves. The hydromechanical coupling of single fractures, i.e. the relationship between flow and stiffness, holds the key to finding a method to remotely characterize a fractures hydraulic properties. This thesis is separated into two parts: (1) a description of the hydromechanical coupling of fractures based on numerical models used to generate synthetic fractures, compute the flow through a fracture, and deform fracture topologies to unravel the scaling function that is fundamental to the hydromechanical coupling of single fractures; (2) a Discontinuous Galerkin (DG) method was developed to accurately simulate the scattered seismic waves from realistic fracture topologies. The scaling regimes of fluid flow and specific stiffness in weakly correlated fractures are identified by using techniques from Percolation Theory and initially treating the two processes separately. The fixed points associated with fluid flow were found to display critical scaling while the fixed points for specific stiffness were trivial. The two processes could be indirectly related because the trivial scaling of the mechanical properties allowed the specific stiffness to be used as surrogate to the void area fraction. The dynamic transport exponent was extracted at threshold by deforming fracture geometries within the effective medium regime (near the ``cubic law'' regime) to the critical regime. From this, a scaling function was defined for the hydromechanical coupling. This scaling function provides the link between fluid flow and fracture specific stiffness so that seismic waves may be used to remotely probe the hydraulic properties of fractures. Then, the DG method is shown to be capable of measuring such fracture specific stiffnesses by numerically measuring the velocity of interface waves when propagated across laboratory measured fracture geometries of Austin Chalk.

Petrovitch, Christopher L.

359

Tensile stiffness analysis on ocean dynamic power umbilical  

NASA Astrophysics Data System (ADS)

Tensile stiffness of ocean dynamic power umbilical is an important design parameter for functional implementation and structural safety. A column with radial stiffness which is wound by helical steel wires is constructed to predict the tensile stiffness value of umbilicals in the paper. The relationship between the tension and axial deformation is expressed analytically so the radial contraction of the column is achieved in the relationship by use of a simple finite element method. With an agreement between the theoretical prediction and the tension test results, the method is proved to be simple and efficient for the estimation of tensile stiffness of the ocean dynamic power umbilical.

Tang, Ming-gang; Yan, Jun; Wang, Ye; Yue, Qian-jin

2014-04-01

360

[Stiff-man syndrome: an immunopathy?].  

PubMed

The discovery of autoimmune processes in the stiff-man syndrome (SMS) not only raises questions concerning the syndrome itself, but may also lead to new insights into pathogenetic principles of neurological disorders. Autoantibodies against GAD, the GABA synthesising enzyme, may become a helpful (though not specific) diagnostic tool, and furthermore may serve as a plausible explanation for both the symptoms of the syndrome and the delayed development of type I diabetes mellitus. However, it remains unexplained why autoimmunity against such widespread inhibitory transmitter systems should induce a syndrome which by definition is confined to only a few symptoms, and for which the majority of neurological signs are regarded as exclusion criteria. It is therefore hypothesised that SMS is part of a broad spectrum of encephalomyelopathies with autoimmunity against GABAergic neurones in common, but with a heterotopic manifestation. Progressive encephalomyelitis with rigidity may be an extreme variant within this spectrum. PMID:1795757

Meinck, H M

1991-12-01

361

Determining cantilever stiffness from thermal noise  

PubMed Central

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

Lubbe, Jannis; Temmen, Matthias; Rahe, Philipp; Kuhnle, Angelika

2013-01-01

362

Stiff-person syndrome treated with rituximab  

PubMed Central

Stiff-person syndrome (SPS) is a rare neurological condition consisting of progressive and fluctuating rigidity of the axial muscles combined with painful spasms. The pathophysiology of SPS is not fully understood, but there seems to be an autoimmune component. The use of rituximab, a chimeric monoclonal antibody targeting CD20 protein in the surface of mature B cells, for the treatment of SPS is a recent therapeutical approach showing promising results. The authors present a case report of a 41-year-old female patient diagnosed with SPS who was treated with rituximab in a public hospital in Brasília, Brazil, showing a good and safe response to the treatment so far. Our data go along with some recent articles published in the literature.

Lobo, Marcelo Evangelista; Araujo, Marx Lincoln Barros; Tomaz, Carlos Alberto Bezerra; Allam, Nasser

2010-01-01

363

Circulating Vascular Progenitor Cells and Central Arterial Stiffness in Polycystic Ovary Syndrome  

PubMed Central

Objective Subjects with Polycystic ovarian syndrome (PCOS) are at increased risk of Type 2 diabetes mellitus (T2DM). The mechanism of this enhanced risk is unclear. Circulating vascular progenitor cells (VPC) are immature bone marrow derived cells capable of differentiating into mature endothelial cells. VPC number/function and central arterial stiffness predict cardio-metabolic disease in at-risk populations. Design We studied VPC and arterial stiffness measures in non-obese PCOS subjects as compared to age and body mass index (BMI) matched healthy controls in a cross–sectional study. Methods Fourteen subjects with PCOS and 12 controls of similar age, BMI (all <30 kg/m2) and metabolic profile were studied. VPC number and in vitro function were studied by flow cytometry and tube formation assays respectively. Augmentation index (AIx), a measure of central arterial stiffness, and central (aortic) blood pressures (BP) were measured by applanation tonometry. Results Subjects with PCOS had a reduced number, mean±SEM, of circulating CD34+133+ VPCs (317.5±51.0 vs. 558.3±101.2, p?=?0.03) and impaired in vitro tube formation (completed tube area 1.0±0.06 vs. 1.2±0.05×106 µm2 p?=?0.02). PCOS subjects had significantly higher AIx (18.4±1.9% vs. 4.9±2.0%) and this difference remained significant even after adjustments for age, BMI and smoking (p?=?0.003) in multivariate analyses. Central systolic and pulse pressure were higher in PCOS subjects but these differences were not statistically significant after adjustment for age. Brachial systolic and pulse pressures were similar. VPC number/function and arterial stiffness or BP measures were not correlated. Conclusions Non-obese PCOS is characterized by a reduced VPC number, impaired VPC function and increased central arterial stiffness. These changes in novel vascular risk markers may explain the enhanced risk of T2DM and CVD in PCOS.

Dessapt-Baradez, Cecile; Reza, Maria; Sivakumar, Ghayathri; Hernandez-Fuentes, Maria; Markakis, Kostas; Gnudi, Luigi; Karalliedde, Janaka

2011-01-01

364

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.

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

2007-01-01

365

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

NASA Astrophysics Data System (ADS)

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

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

366

Role of Inflammation in the Pathogenesis of Arterial Stiffness  

PubMed Central

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

Park, Sungha

2012-01-01

367

Perturbation theory for path integrals of stiff polymers  

Microsoft Academic Search

The wormlike chain model of stiff polymers is a nonlinear sigma-model in one spacetime dimension in which the ends are fluctuating freely. This causes important differences with respect to the presently available theory which exists only for periodic and Dirichlet boundary conditions. We modify this theory appropriately and show how to perform a systematic large-stiffness expansion for all physically interesting

H. Kleinert; A. Chervyakov

2006-01-01

368

Stiffness and viscous coefficient characteristics for ergonomics chair design  

Microsoft Academic Search

This report presents a study of stiffness, ks and viscous coefficient, c characteristic on a developed chair apparatus namely Pneumatic Actuated Seating System (PASS). The stiffness and viscous coefficient characteristics represents the spring and damping function respectively. These two characteristics are emulated from spring-damping model to thirty six intelligent pneumatic actuators on PASS. These attributes will facilitate in investigation of

Ahmad Athif Mohd Faudzi; Koichi Suzumori

2011-01-01

369

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

370

Cartesian stiffness control of the JPL\\/Stanford\\/Salisbury hand  

Microsoft Academic Search

To be useful as a dexterous end effector in assembly operations, a multifingered hand must be position-controlled to allow preshaping, and force-controlled to apply and regulate grasp forces. The author describes an implementation of stiffness control on the Salisbury hand, from tendon tension control to coordinated Cartesian object stiffness control. Substantial joint friction effects were observed which were predicted well

G. P. Starr

1988-01-01

371

Kinetics of stiff-legged gait: induced acceleration analysis  

Microsoft Academic Search

Treating spastic paretic stiff-legged gait, defined as reduced knee flexion in swing, holds a high priority in the rehabilitation of patients with upper motor neuron lesions. We propose a method to determine the relative contributions of hip, knee, and ankle inpairments to this disability. We analyzed the gait of ten patients with stiff-legged gait (SLG) due to a single stroke

Patrick O. Riley; D. Casey Kerrigan

1999-01-01

372

Stiff child syndrome with mutation of DYT1 gene.  

PubMed

The authors report a Chinese boy with a DYT1 gene mutation having muscle stiffness, severe painful muscle spasm, myoclonus, and dystonia compatible with stiff child syndrome. Autoantibodies to glutamic acid decarboxylase (anti-GAD) were absent. His asymptomatic mother had a DYT1 mutation. His asymptomatic sister has diabetes mellitus and antibodies to glutamic acid decarboxylase but no DYT1 mutation. PMID:16275837

Wong, Virginia C N; Lam, Ching-Wan; Fung, Cheuk Wing

2005-11-01

373

Stiffness of low rise reinforced concrete shear walls  

Microsoft Academic Search

This paper reviews the history and activities of the ASCE Working Group on the Stiffness of Concrete Shear Wall Structures. This effort was greatly assisted by the US Nuclear Regulatory Commission (NRC) sponsored Seismic Category I Structures Program and their efforts to define a position for the ``reduced concrete stiffness``. The group`s activities and recommendations to account for this effect

R. C. Murray; Q. A. Hossain; A. K. Basak; J. G. Bennett; C. R. Farrar; A. K. Gupta; A. H. Hadjian; P. S. Hashimoto; R. M. Kenneally; R. P. Kennedy; D. A. Nuta; R. F. Jr. Oleck; A. K. Singh; H. T. Tang; N. C. Tsai

1993-01-01

374

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.

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

2010-01-01

375

Real-time single-cell response to stiffness.  

PubMed

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

2010-09-21

376

Assessing appropriate stiffness levels for spudcan foundations on dense sand  

Microsoft Academic Search

Before a jack-up can operate at a given location, a site-specific assessment of its ability to withstand a design storm during operation must be performed. During this assessment, the complex state of stress and strain under a spudcan is usually simplified to a value of foundation stiffness that is integrated as a boundary condition into the structural analysis. Soil stiffness

Mark J. Cassidy; George Vlahos; Mathew Hodder

2010-01-01

377

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.

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

2014-01-01

378

Electron Transport Stiffness and Heat Pulse Propagation on DIII-D  

NASA Astrophysics Data System (ADS)

Experiments on DIII-D have measured the stiffness of electron heat transport using a new method that combines heat pulse (HP) propagation and power balance (PB) analysis. Using a single modulated gyrotron, in addition to 5 cw gyrotrons, the radial profiles of Te oscillations from the fundamental to the 9^th harmonic are fit to determine the diffusion (DHP), convection (VHP) and damping coefficients. The Te gradient is then systematically scanned by varying the electron cyclotron heating profile on a shot-by-shot basis using the cw gyrotrons. Numerically integrating DHP over this scan gives DPB, and the difference between the diffusive heat flux from DPB and the total power-balance heat flux determines VPB. The ratio of DHP to DPB measures the transport stiffness, defined as the fractional increase in diffusive heat flux divided by the fractional increase in the Te gradient. In L-mode plasmas, a sudden increase in electron transport stiffness is seen when the Te scale length exceeds the theoretically predicted threshold value. Similar electron transport stiffness is observed with and without additional NBI.

Petty, C. C.; Deboo, J. C.; Smith, S. P.; Burrell, K. H.; White, A. E.; Hillesheim, J. C.; Holland, C. H.

2012-10-01

379

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

SciTech Connect

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

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

2010-02-15

380

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

PubMed Central

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

2013-01-01

381

Theoretical calculation of bending stiffness of alveolar wall.  

PubMed

The bending stiffness of the alveolar wall is theoretically analyzed in this study through analytical modeling. First, the alveolar wall facet and its characteristics were geometrically simplified and then modeled using known physical laws. Bending stiffness is shown to be dependent on alveolar wall thickness, density, Poisson's ratio and speed of the longitudinal wave. The normal bending stiffness of the alveolar wall was further determined. For the adult human, the normal bending stiffness is calculated to be 71.0-414.7 nNm, while for the adult mouse it is 1.9-30.0 nNm. The results of this study can be used as a reference for future pulmonary emphysema and fibrosis studies, as the bending stiffness of alveolar wall will be lower and higher, respectively; than the theoretically determined normal values. PMID:24121628

Jabaraj, D John; Jaafar, Mohamad Suhaimi

2013-12-01

382

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

383

Development of the probabilistic neural network-cubic least squares mapping (PNN-LSM3) classifier to assess carotid plaque's risk  

Microsoft Academic Search

An efficient classification algorithm based on the cubic least squares mapping (LSM3) and the probabilistic neural network (PNN) classifier is proposed for assessing the carotid plaques risk of causing brain infarcts. Ultrasound images of 24 high-risk and 32 low-risk carotid plaques were manually segmented by an experienced physician using a custom developed software. Three textural features, related to the plaques

Nikolaos Piliouras; Ioannis Kalatzis; P. Theocharakis; Nikos Dimitropoulos; Dionisis Cavouras

2004-01-01

384

Evaluation of MM5 mesoscale model at local scale for air quality applications over the Swedish west coast: Influence of PBL and LSM parameterizations  

Microsoft Academic Search

Summary  The performance of MM5 mesoscale model (Version 3.6.3) using different planetary boundary layer (PBL) and land surface model\\u000a (LSM) parameterizations is evaluated and compared using high temporal and spatial resolution GÖTE2001 campaign data at local\\u000a scale (a few kilometers) over the Greater Göteborg area along the Swedish west coast during 7–20 May 2001. The focus is on\\u000a impact of PBL

J.-F. Miao; D. Chen; K. Wyser; K. Borne; J. Lindgren; M. K. S. Strandevall; S. Thorsson; C. Achberger; E. Almkvist

2008-01-01

385

Land surface model (LSM version 1.0) for ecological, hydrological, and atmospheric studies: Technical description and user`s guide. Technical note  

SciTech Connect

This technical note describes version 1 of the LSM land surface model. In this model, land surface processes are described in terms of biophysical fluxes (latent heat, sensible heat, momentum, reflected solar radiation, emitted longwave radiation) and biochemical fluxes (CO2) that depend on the ecological and hydrologic state of the land. Consequently, ecological and hydrological sub-models are needed to simulate temporal changes in terrestrial biomass and water.

Bonan, G.B.

1996-01-01

386

Assessment of hepatic fibrosis regression by transient elastography in patients with chronic hepatitis B treated with oral antiviral agents.  

PubMed

Transient elastography (TE) has been used as a non-invasive method for liver stiffness measurement (LSM) in patients with chronic liver disease. This study was performed to assess the change of LSM by TE and to assess its clinical usefulness during long-term oral antiviral therapy in patients with chronic hepatitis B (CHB). We retrospectively reviewed 83 CHB patients. The mean interval between two LSM was 411.5 ± 149.5 days. Initial and follow-up LSM was 16.15 ± 12.41 kPa and 11.26 ± 7.36 kPa, respectively (P < 0.001). The degree of regression of liver stiffness was -2.03 ± 0.36% per month. The fibrosis stage classified by LSM value improved in 37 (44.6%) patients during oral antiviral therapy. Of the 30 (36.1%) patients with LSM ? 14.1 kPa (cirrhosis) at 1st LSM, 12 (40%) proved to no longer have cirrhosis (? 1 decrease in fibrosis stage) at 2nd LSM. LSM significantly decreased in both baseline high (> upper limit of normal [ULN] × 2) and low (? ULN × 2) alanine aminotransferase groups during antiviral therapy (P < 0.001; P = 0.001, respectively). Long-term oral antiviral therapy resulted in the improvement of liver stiffness in a substantial portion of patients with CHB. TE may be used a useful clinical tool to assess disease progression in CHB patients. PMID:24753706

Kim, Ja Kyung; Ma, Dae Won; Lee, Kwan Sik; Paik, Yong-Han

2014-04-01

387

Increased stiffness in common carotid artery in hyperthyroid Graves’ disease patients  

Microsoft Academic Search

The present study was undertaken to assess the effect of hyperthyroidism on stiffness in the common carotid artery (CCA) in patients with Graves’ disease (GD) and elucidate the mechanism by which arterial stiffness is increased in hyperthyroidism. The arterial stiffness index beta (stiffness ?) was evaluated in the CCA using an ultrasonic phase-locked echo-tracking system. Stiffness ? was defined as

M. Inaba; Y. Henmi; Y. Kumeda; M. Ueda; M. Nagata; M. Emoto; T. Ishikawa; E. Ishimura; Y. Nishizawa

2002-01-01

388

Kinematic modeling-based left ventricular diastatic (passive) chamber stiffness determination with in-vivo validation.  

PubMed

The slope of the diastatic pressure-volume relationship (D-PVR) defines passive left ventricular (LV) stiffness ?. Although ? is a relative measure, cardiac catheterization, which is an absolute measurement method, is used to obtain the former. Echocardiography, including transmitral flow velocity (Doppler E-wave) analysis, is the preferred quantitative diastolic function (DF) assessment method. However, E-wave analysis can provide only relative, rather than absolute pressure information. We hypothesized that physiologic mechanism-based modeling of E-waves allows derivation of the D-PVR(E-wave) whose slope, ?(E-wave), provides E-wave-derived diastatic, passive chamber stiffness. Our kinematic model of filling and Bernoulli's equation were used to derive expressions for diastatic pressure and volume on a beat-by-beat basis, thereby generating D-PVR(E-wave), and ?(E-wave). For validation, simultaneous (conductance catheter) P-V and echocardiographic E-wave data from 30 subjects (444 total cardiac cycles) having normal LV ejection fraction (LVEF) were analyzed. For each subject (15 beats average) model-predicted ?(E-wave) was compared to experimentally measured ?(CATH) via linear regression yielding as follows: ?(E-wave) = ??(CATH) + b (R(2) = 0.92), where, ? = 0.995 and b = 0.02. We conclude that echocardiographically determined diastatic passive chamber stiffness, ?(E-wave), provides an excellent estimate of simultaneous, gold standard (P-V)-defined diastatic stiffness, ?(CATH). Hence, in chambers at diastasis, passive LV stiffness can be accurately determined by means of suitable analysis of Doppler E-waves (transmitral flow). PMID:22065203

Mossahebi, Sina; Kovács, Sándor J

2012-05-01

389

Stiffness characteristics of airfoils under pulse loading  

NASA Astrophysics Data System (ADS)

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

Turner, Kevin Eugene

390

Effect of Tailored Activity Pacing on Self-Perceived Joint Stiffness in Adults With Knee or Hip Osteoarthritis  

PubMed Central

OBJECTIVE We examined the effects of a tailored activity-pacing intervention on self-perceived joint stiffness in adults with osteoarthritis (OA). METHOD Thirty-two adults with hip or knee OA were randomized to a tailored or general activity-pacing intervention. Participants’ symptoms and physical activity over 5 days were used to tailor activity pacing. The outcome was self-perceived joint stiffness measured at baseline, 4 wk, and 10 wk. A linear mixed regression model was used. RESULTS The tailored group significantly improved in stiffness compared with the general group over time. We found a significantly different linear trend between groups (Time × Group, p = .046) in which the tailored group had decreasing stiffness over the three time points, denoting continued improvement. The general group’s stiffness improved from baseline to 4 wk but returned to baseline levels at 10 wk. CONCLUSION Tailoring activity pacing may be effective in sustaining improvements in self-perceived joint stiffness in adults with OA.

Schepens, Stacey L.; Braun, Marcia E.; Murphy, Susan L.

2014-01-01

391

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

392

Substrate Stiffness affects Sarcomere and Costamere Structure and Electrophysiological Function of Isolated Adult Cardiomyocytes  

PubMed Central

Introduction The mechanical environment is a key regulator of function in cardiomyocytes. We studied the role of substrate stiffness on the organization of sarcomeres and costameres in adult rat cardiomyocytes, and further examined the resulting changes in cell shortening and calcium dynamics. Methods Cardiomyocytes isolated from adult rats were plated on laminin-coated polydimethylsiloxane substrates of defined stiffness (255 kPa, 117 kPa, 27 kPa, and 7 kPa) for 48 h. Levels of ?-actinin and ?1 integrins were determined by immunofluoresence imaging and immunoblotting, both in the absence and presence of the phosphatase inhibitor calyculin A. Quantitative RT-PCR was used to measure message levels of key structural proteins (?-actinin, ?7 integrin, ?1 integrin, vinculin). Sarcomere shortening and calcium dynamics were measured at 2, 24, and 48 hours. Results Overall cardiomyocyte morphology was similar on all substrates. However, well organized sarcomere structures were observed on only the stiffest (255 kPa) and the most compliant (7 kPa) substrates. Levels of ?-actinin in cells were the same on all substrates, while message levels of structural proteins were upregulated on substrates of intermediate stiffness. Inhibition of phosphatase activity blocked the degradation of contractile structures, but altered overall cardiomyocyte morphology. Shortening and calcium dynamics also were dependent on substrate stiffness, however there was no clear causative relationship between the phenomena. Conclusions Extracellular matrix stiffness can affect structural remodeling by adult cardiomyocytes, and the resulting contractile activity. These findings illuminate changes in cardiomyocyte function in cardiac fibrosis, and may suggest cardiac-specific phosphatases as a target for therapeutic intervention

Galie, Peter A.; Khalid, Nashmia; Carnahan, Kelly E.; Westfall, Margaret V.; Stegemann, Jan P.

2012-01-01

393

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

PubMed

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. PMID:23020420

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

2012-09-01

394

Proximal Aortic Stiffness Is Increased in Systemic Lupus Erythematosus Activity in Children and Adolescents  

PubMed Central

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

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

2013-01-01

395

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.

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

2014-01-01

396

Effects of liner stiffness for trans-tibial prosthesis: a finite element contact model.  

PubMed

The socket liner plays a crucial role in redistribution of the interface stresses between the stump and the socket, so that the peak interface stress could be reduced. However, how the peak stress is affected by various liner stiffnesses is still unknown, especially when the phenomenon of the stump slide within the socket is considered. This study employed nonlinear contact finite element analyses to study the biomechanical reaction of the stump sliding with particular attention to the liner stiffness effects of the trans-tibial prosthesis. To validate the finite element outcomes, experimental measurements of the interface stresses and sliding distance were further executed. The results showed that the biomechanical response of the stump sliding are highly nonlinear. With a less stiff liner, the slide distance of the stump would increase with a larger contact area. However, this increase in the contact area would not ensure a reduction in the peak interface stress and this is due to the combined effects of the non-uniform shape of the socket and the various sliding distances generated by the different liner stiffnesses. PMID:14644593

Lin, Chih-Chieh; Chang, Chih-Han; Wu, Chu-Lung; Chung, Kao-Chi; Liao, I-Chen

2004-01-01

397

Truncated dystrophins reduce muscle stiffness in the extensor digitorum longus muscle of mdx mice.  

PubMed

Muscle stiffness is a major clinical feature in Duchenne muscular dystrophy (DMD). DMD is the most common lethal inherited muscle-wasting disease in boys, and it is caused by the lack of the dystrophin protein. We recently showed that the extensor digitorum longus (EDL) muscle of mdx mice (a DMD mouse model) exhibits disease-associated muscle stiffness. Truncated micro- and mini-dystrophins are the leading candidates for DMD gene therapy. Unfortunately, it has never been clear whether these truncated genes can mitigate muscle stiffness. To address this question, we examined the passive properties of the EDL muscle in transgenic mdx mice that expressed a representative mini- or micro-gene (?H2-R15, ?R2-15/?R18-23/?C, or ?R4-23/?C). The passive properties were measured at the ages of 6 and 20 mo and compared with those of age-matched wild-type and mdx mice. Despite significant truncation of the gene, surprisingly, the elastic and viscous properties were completely restored to the wild-type level in every transgenic strain we examined. Our results demonstrated for the first time that truncated dystrophin genes may effectively treat muscle stiffness in DMD. PMID:23221959

Hakim, Chady H; Duan, Dongsheng

2013-02-15

398

Serum Uric Acid Level and Diverse Impacts on Regional Arterial Stiffness and Wave Reflection  

PubMed Central

Background: Both increased arterial stiffness and hyperuricaemia are associated with elevated cardiovascular risks. Little is known about the relations of serum uric acid (UA) level to regional arterial stiffness and wave reflection. The aim of the study was to investigate the gender-specific association of serum UA and indices of arterial function in a community-based investigation in China. Methods: Cross-sectional data from 2374 adults (mean age 58.24 years) who underwent routine laboratory tests, regional pulse wave velocity (PWV) and pulse wave analysis measurements were analyzed in a gender-specific manner. None of the participants had atherosclerotic cardiovascular disease, chronic renal failure, systemic inflammatory disease, gout, or were under treatment which would affect serum UA level. Results: Men had higher serum UA level than women. Subjects with hyperuricaemia had significantly higher carotid-ankle PWV in both genders (P< 0.05), and the carotid-femoral PWV (PWVc-f) was higher in women (P< 0.001) while the augmentation index was marginally lower in men (P = 0.049). Multiple regression analysis showed that serum UA was an independent determinant only for PWVc-f in women (? = 0.104, P = 0.027) when adjusted for atherogenic confounders. No other independent relationship was found between UA level and other surrogates of arterial stiffness. Conclusions: Serum UA levels are associated with alterations in systemic arterial stiffness that differ in men and women. Women might be more susceptible to large vascular damage associated with hyperuricaemia.

Bian, Suyan; Guo, Hongyang; Ye, Ping; Luo, Leiming; Wu, Hongmei; Xiao, Wenkai

2012-01-01

399

Stiffness properties for Nucleus standard straight and contour electrode arrays.  

PubMed

Trauma and damage during insertion of electrode arrays into the human cochlea are strongly related to the stiffness of the array. The stiffness properties of electrode arrays, which were determined by three-point flexural bending and buckling tests, are reported in this paper. To date there has been limited publication on mechanical properties of these electrode arrays. Previous studies mainly focused on characterizing the stiffness of the tip of the Nucleus straight array with little emphasis on characterizing the stiffness of its whole length. In this study, stiffnesses of the Nucleus straight and contour electrode arrays have been determined along their length. Young's modulus of elasticity of the Nucleus straight array has been found to increase from the tip (182 MPa) to the rear end (491 MPa), whereas the stiffness of the contour array is greatest near the tip (480 MPa) and is fairly uniform in the middle and rear sections of the electrode array (380-400 MPa). Buckling experiments have shown that the contour array has much higher critical buckling load (about four times) than the Nucleus straight array. The results from three-point flexural bending and buckling experiments provide significant data for the development of electrode arrays, from which new array designs with improved flexibility can be developed. The results of stiffness properties are also important input for use in finite element models to predict the trajectories during insertion and to help evaluate the effects of different electrode array designs on damage sustained during insertion. PMID:15471696

Kha, H N; Chen, B K; Clark, G M; Jones, R

2004-10-01

400

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

401

Muscle force and stiffness during activation and relaxation. Implications for the actomyosin ATPase  

PubMed Central

Isolated skinned frog skeletal muscle fibers were activated (increasing [Ca2+]) and then relaxed (decreasing [Ca2+]) with solution changes, and muscle force and stiffness were recorded during the steady state. To investigate the actomyosin cycle, the biochemical species were changed (lowering [MgATP] and elevating [H2PO4-]) to populate different states in the actomyosin ATPase cycle. In solutions with 200 microM [MgATP], compared with physiological [MgATP], the slope of the plot of relative steady state muscle force vs. stiffness was decreased. At low [MgATP], cross-bridge dissociation from actin should be reduced, increasing the population of the last cross-bridge state before dissociation. These data imply that the last cross-bridge state before dissociation could be an attached low-force-producing or non-force-producing state. In solutions with 10 mM total Pi, compared to normal levels of MgATP, the maximally activated muscle force was reduced more than muscle stiffness, and the slope of the plot of relative steady state muscle force vs. stiffness was reduced. Assuming that in elevated Pi, Pi release from the cross-bridge is reversed, the state(s) before Pi release would be populated. These data are consistent with the conclusion that the cross-bridges are strongly bound to actin before Pi release. In addition, if Ca2+ activates the ATPase by allowing for the strong attachment of the myosin to actin in an A.M.ADP.Pi state, it could do so before Pi release. The calcium sensitivity of muscle force and stiffness in solutions with 4 mM [MgATP] was bracketed by that measured in solutions with 200 microM [MgATP], where muscle force and stiffness were more sensitive to calcium, and 10 mM total Pi, where muscle force and stiffness were less sensitive to calcium. The changes in calcium sensitivity were explained using a model in which force- producing and rigor cross-bridges can affect Ca2+ binding or promote the attachment of other cross-bridges to alter calcium sensitivity.

1988-01-01

402

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.

2013-01-01

403