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1

Measuring graphene's bending stiffness  

NASA Astrophysics Data System (ADS)

Graphene's unusual combination of in-plane strength and out-of-plane flexibility makes it promising for mechanical applications. A key value is the bending stiffness, which microscopic theories and measurements of phonon modes in graphite put at ?0=1.2 eV.^1 However, theories of the effects of thermal fluctuations in 2D membranes predict that the bending stiffness at longer length scales could be orders of magnitude higher.^2,3 This macroscopic value has not been measured. Here we present the first direct measurement of monolayer graphene's bending stiffness, made by mechanically lifting graphene off a surface in a liquid and observing both motion induced by thermal fluctuations and the deflection caused by gravity's effect on added weights. These experiments reveal a value ?eff=12 keV at room temperature --- four orders of magnitude higher than ?0. These results closely match theoretical predictions of the effects of thermally-induced fluctuations which effectively thicken the membrane, dramatically increasing its bending stiffness at macroscopic length scales. [1] A. Fasolino et al., Nat. Mater. (2007) [2] D. R. Nelson and L. Peliti, J Physique (1987) [3] F. L. Braghin and N. Hasselmann, Phys Rev B (2010)

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

2013-03-01

2

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

PubMed

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

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

2012-10-30

3

EXPERIMENTAL MEASUREMENT OF PRECISION BEARING DYNAMIC STIFFNESS  

Microsoft Academic Search

Static stiffness measurement of precision bearing components by influence coefficients is complicated by the task of loading and measuring the baseline test fixture stiffness before including the bearing components. Furthermore, as the displacement of the bearing system is measured for various load conditions, the stiffness of high quality bearings may be difficult to distinguish from the test fixture stiffness. The

E. R. Marsh; D. S. Yantek

1997-01-01

4

Liver stiffness measurement versus liver biopsy to predict survival and decompensations of cirrhosis among HIV/HCV-coinfected patients.  

PubMed

OBJECTIVE:: To compare the prognostic performance of liver biopsy (LB)with that of liver stiffness measurement (LSM) to predict survival and liver decompensations among HIV/HCV-coinfected patients. DESIGN:: Retrospective cohort study. METHODS:: Cohort of 297?HIV/HCV-coinfected patients, who underwent aLB and LSM separated by 12 months or less, followed in ten Spanish tertiary care centers from December 2005 to December 2011 (median follow-up, 5 years; interquartile range, 4.2-5.4 years). LB were staged following the Scheuer's score. LSM was obtained by hepatic transient elastometry. A survival analysis was carried out and the integrated discrimination improvement was computed to compare the ability of the survival models to predict outcomes. The incidence of death from any cause and of development of the first decompensation of cirrhosis were calculated. RESULTS:: Overall mortality rate was 1.63 (95%CI: 1.06-2.49) per 100 person-years. The adjusted hazard ratio [AHR (95%CI)] of baseline fibrosis (per stage of fibrosis) was 1.52 (1.08-2.15, p?=?0.017) and of LSM (per 5?KPa increase) 1.28 (1.12-1.46, p?LSM (per 5?KPa increase) 1.37 (1.21-1.54, p?LSM-based prediction achieves a similar yield than LB-based models to predict overall mortality in HIV/HCV-coinfected patients. Models including LSM couldpredict better liver decompensations than LB. PMID:23736148

Macías, Juan; Camacho, Angela; Von Wichmann, Miguel A; López-Cortés, Luis F; Ortega, Enrique; Tural, Cristina; Ríos, Mjosé; Merino, Dolores; Téllez, Francisco; Márquez, Manuel; Mancebo, María; Pineda, Juan A

2013-06-01

5

Impact of mild to moderate elevations of alanine aminotransferase on liver stiffness measurement in chronic hepatitis B patients during antiviral therapy.  

PubMed

Aim:? The accuracy of liver stiffness measurement (LSM) in the diagnosis of liver fibrosis is affected by elevated serum alanine aminotransferase (ALT) levels. The aim of this study was to assess the impact of mild to moderate elevations of ALT on LSM in patients with chronic hepatitis B (CHB) during antiviral therapy. Methods:? A total of 58 CHB patients with their ALT levels falling into the range of ×2 to ×10 the upper limit of normal (ULN) were recruited. ALT and LSM values were periodically assessed at baseline and 12, 24 and 48?weeks. Results:? The median ALT levels were 153.5 (76-544), 50.5 (11-475), 36.5 (9-265) and 30 (12-239) IU/L at baseline and 12, 24 and 48?weeks, respectively. The corresponding median value of LSM was 8.8 (3.2-47.3), 6.15 (3.2-31.2), 5.9 (3.1-29.1) and 5.5 (2.8-21.5) kpa. However, after the ALT levels were normalized by the treatment, the values of LSM did not vary significantly (6.1 [3.0-17.7] vs 5.25 [2.8-21.5] kpa, P?=?0.381). Pretreatment fibrosis stages of liver biopsies corresponded with LSM after ALT normalization rather than baseline LSM (F0-1, 12/27 vs 23/25, P?LSM values decreased in parallel with the decline in ALT levels in CHB patients with mild to moderate elevation of ALT. LSM became more accurate when applied to document the liver fibrosis or cirrhosis in CHB patients after the elevated ALT level has been treated to normal level. PMID:22978384

Yan, Li-Bo; Zhu, Xia; Bai, Lang; Liang, Ling-Bo; Chen, En-Qiang; Du, Ling-Yao; Wang, Li-Chun; Chen, Li-Yu; Tang, Hong

2012-09-16

6

Nanoindentation of wood cell walls: Continuous stiffness and hardness measurements  

Microsoft Academic Search

The objective of this study was to measure the mechanical properties of individual, native wood fibers using the continuous nanoindentation measurement technique. The indentation depth profile exhibited a small length-scale effect, which was confirmed using the size-effect index derived from the indentation loading curve. The hardness (Hu) or stiffness (Eu) values determined from indentation unloading were also examined for 10

W. T. Y. Tze; S. Wang; T. G. Rials; G. M. Pharr; S. S. Kelley

2007-01-01

7

Engineered rings of mixed yeast Lsm proteins show differential interactions with translation factors and U-rich RNA.  

PubMed

The Lsm proteins organize as heteroheptameric ring assemblies capable of binding RNA substrates and ancillary protein factors. We have constructed simplified Lsm polyproteins that organize as multimeric ring structures as analogues of the functional Lsm complexes. Polyproteins Lsm[2+3], Lsm[4+1], and Lsm[5+6] incorporate natural sequence extensions as linker peptides between the core Lsm domains. In solution, the recombinant products organize as stable ring oligomers (75 A wide, 20 A pores) in discrete tetrameric and octameric forms. Following immobilization, the polyproteins successfully act as affinity pull-down ligands for proteins within yeast lysate, including native Lsm proteins. Interaction partners were consistent with current models of the mixed Lsm ring assembly in vivo but also suggest that dynamic rearrangements of Lsm protein complexes can occur. The Lsm polyprotein ring complexes were seen in gel shift assays to have a preference for U-rich RNA sequences, with tightest binding measured for Lsm[2+3] with U(10). Polyprotein rings containing truncated forms of Lsm1 and Lsm4 were found to associate with translation, initiation, and elongation protein factors in an RNA-dependent manner. Our findings suggest Lsm1 and/or Lsm4 can interact with translationally active mRNA. PMID:20108977

Sobti, Meghna; Cubeddu, Liza; Haynes, Paul A; Mabbutt, Bridget C

2010-03-23

8

Stiffness measurement of a biomaterial by optical manipulation of microparticle  

NASA Astrophysics Data System (ADS)

Since the discovery of the trapping nature of laser beam, optical tweezers have been extensively employed to measure various parameters at micro/nano level. Optical tweezers show exceptional sensitivity to weak forces making it one of the most sensitive force measurement devices. In this work, we present a technique to measure the stiffness of a biomaterial at different points. For this purpose, a microparticle stuck at the bottom of the dish is illuminated by the trapping laser and respective QPD signal as a function of the distance between the focus of the laser and the center of the microparticle is monitored. After this, microparticle is trapped and manipulated towards the target biomaterial and when it touches the cell membrane, QPD signal shows variation. By comparing two different QPD signals and measuring the trap stiffness, a technique is described to measure the stiffness of the biomaterial at a particular point. We believe that this parameter can be used as a tool to identify and classify different biomaterials.

Kim, Jung-Dae; Waleed, Muhammad; Lee, Yong-Gu

2013-02-01

9

SOFC LSM:YSZ cathode degradation induced by moisture: An impedance spectroscopy study  

Microsoft Academic Search

The cause of the degradation effect of moisture during operation of LSM cathode based SOFCs has been investigated by means of a detailed impedance characterization on LSM:YSZ composite cathode based SOFCs. Further the role of YSZ as cathode composite material was studied by measurements on SOFCs with a LSM:CGO composite cathode on a CGO interdiffusion barrier layer. It was found

J. Nielsen; M. Mogensen

2011-01-01

10

Sensor for Stiffness Measurements Within the Adult Rat Hippocampus  

Microsoft Academic Search

This paper presents a sensitive compliance measurement system for determining the stiffness of the adult rat hippocampus. The device has been successfully fabricated which consists of two strain gauges incorporated in the SU-8 based cantilever. The cantilever-sensor has been fully characterized and its strain sensitivity was found to be approximately 2.5. in vitro testing on the brain tissue has successfully

Gloria Y. Yang; Yu-Hsin Wen; Csaba Foldy; William C. Tang; Ivan Soltesz

2008-01-01

11

Right Ventricular Stiffness Measured by a New Method Without Volume Estimation in Coronary Artery Disease  

Microsoft Academic Search

This study was designed to measure the right ventricular (RV) stiffness (?P\\/?V) with a new method without estimating the RV volume itself. RV stiffness has rarely been measured due to the difficulty in estimating the RV volume. Without measuring RV volume itself, stiffness can be determined by measuring its volume change (?V). Tricuspid filling flow volume, which is the diastolic

Yutaka Otsuji; Akira Kisanuki; Kouichi Toyonaga; Shuichi Hamasaki; Shin-ichi Arima; Shoichiro Nakao; Hideki Okino; Hitoshi Toda; Suminori Akiba; Hiromitsu Tanaka

1996-01-01

12

An ultrawideband radar based pulse sensor for arterial stiffness measurement.  

PubMed

A novel pulse sensor based on ultrawideband (UWB) radar to detect the arterial vessel movements on various sites on human body without applying external pressure on the arterial vessel was designed and evaluated for aortic stiffness measurement. The UWB pulse sensor was evaluated for its functional performance and human study was carried out to validate the UWB sensor as a tool for clinical screening of subjects with cardiovascular risks. Good agreement in measurement of pulse wave velocity, an index of arterial distensibility, was achieved between the UWB pulse sensor and the applanation tonometer. PMID:18002297

Tao, Teh-Ho; Hu, Shin-Jen; Peng, Jla-Hung; Kuo, Su-Chen

2007-01-01

13

Variability in ultrasonic measurements of arterial stiffness in the atherosclerosis risk in communities study  

Microsoft Academic Search

Arterial stiffness is emerging as an important risk marker for cardiovascular disease. Ultrasound-based measurements of arterial stiffness are in use by several large epidemiological studies. The reliability of ultrasonic measurements of arterial stiffness was assessed as part of one of these, the Atherosclerosis Risk in communities (ARIC) study. ARIC, a prospective, four-center epidemiological study, used B-mode ultrasound with an electronic

Donna K Arnett; Lloyd E Chambless; Ho Kim; Gregory W Evans; Ward Riley

1999-01-01

14

Crystal structure of Lsm3 octamer from Saccharomyces cerevisiae: implications for Lsm ring organisation and recruitment.  

PubMed

Sm and Sm-like (Lsm) proteins are core components of the ribonucleoprotein complexes essential to key nucleic acid processing events within the eukaryotic cell. They assemble as polyprotein ring scaffolds that have the capacity to bind RNA substrates and other necessary protein factors. The crystal structure of yeast Lsm3 reveals a new organisation of the L/Sm beta-propeller ring, containing eight protein subunits. Little distortion of the characteristic L/Sm fold is required to form the octamer, indicating that the eukaryotic Lsm ring may be more pliable than previously thought. The homomeric Lsm3 octamer is found to successfully recruit Lsm6, Lsm2 and Lsm5 directly from yeast lysate. Our crystal structure shows the C-terminal tail of each Lsm3 subunit to be engaged in connections across rings through specific beta-sheet interactions with elongated loops protruding from neighbouring octamers. While these loops are of distinct length for each Lsm protein and generally comprise low-complexity polar sequences, several Lsm C-termini comprise hydrophobic sequences suitable for beta-sheet interactions. The Lsm3 structure thus provides evidence for protein-protein interactions likely utilised by the highly variable Lsm loops and termini in the recruitment of RNA processing factors to mixed Lsm ring scaffolds. Our coordinates also provide updated homology models for the active Lsm[1-7] and Lsm[2-8] heptameric rings. PMID:18329667

Naidoo, Nishen; Harrop, Stephen J; Sobti, Meghna; Haynes, Paul A; Szymczyna, Blair R; Williamson, James R; Curmi, Paul M G; Mabbutt, Bridget C

2008-01-11

15

Sources of Variability in Musculo-Articular Stiffness Measurement  

PubMed Central

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

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

2013-01-01

16

Lateral stiffness: A new nanomechanical measurement for the determination of shear strengths with friction force microscopy  

SciTech Connect

We present a technique to measure the lateral stiffness of the nanometer-sized contact formed between a friction force microscope tip and a sample surface. Since the lateral stiffness of an elastic contact is proportional to the contact radius, this measurement can be used to study the relationship between friction, load, and contact area. As an example, we measure the lateral stiffness of the contact between a silicon nitride tip and muscovite mica in a humid atmosphere (55{percent} relative humidity) as a function of load. Comparison with friction measurements confirms that friction is proportional to contact area and allows determination of the shear strength. {copyright} {ital 1997 American Institute of Physics.}

Carpick, R.W.; Ogletree, D.F.; Salmeron, M. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

1997-03-01

17

Localized cell stiffness measurement using axial movement of an optically trapped microparticle.  

PubMed

A simple optical tweezers design is proposed to manipulate particles in the axial direction and estimate particle position with nanometer sensitivity. Balb3T3 cell is probed using two different-sized particles, and the localized cell stiffness is evaluated using Hertz model. A series of experiments are performed to obtain the necessary parameters for the cell stiffness computation: particle displacement, trapping stiffness, force exertion, and cell deformation. The computed cell stiffness measurements are 17 and 40 Pa using 4 ?m- and 2 ?m-sized particles, respectively. Results suggest that the proposed optical tweezers scheme can measure the stiffness of a particular cell locale using Hertz model, offering insights about how cells respond to outside mechanical stimulus. PMID:23934015

Dy, Mary-Clare; Kanaya, Shigehiko; Sugiura, Tadao

2013-11-01

18

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

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

19

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

Microsoft Academic Search

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

M. D. Seale; E. I. Madaras

1999-01-01

20

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

21

Association of Arterial Stiffness Indexes, Determined From Digital Volume Pulse Measurement and Cardiovascular Risk Factors in Chronic Kidney Disease  

Microsoft Academic Search

BackgroundProgression of atherosclerosis with increased arterial stiffness is associated with increased cardiovascular morbidity and mortality in patients with chronic kidney disease (CKD). Compliance index (CI) derived from digital volume pulse (DVP), measuring the relationship between volume and pressure changes in fingertip, can evaluate the local arterial stiffness. The purpose of this study was to measure the stiffness of different arteries

Ming-Cheng Wang; An-Bang Wu; Meng-Fu Cheng; Ju-Yi Chen; Chin-Shan Ho; Wei-Chuan Tsai

2011-01-01

22

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

NASA Astrophysics Data System (ADS)

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

Putkis, O.; Croxford, A. J.

2013-04-01

23

Stiffness imaging of the kidney and adjacent abdominal tissues measured simultaneously using magnetic resonance elastography.  

PubMed

To date, non-invasive methods to detect kidney malignancies and mild tumors remain a challenge. The purpose of this study was to establish the proper imaging protocol to determine kidney stiffness and its spatial distribution within the various kidney compartments such as the renal sinus, medulla, and cortex. Here, we have used magnetic resonance elastography (MRE) along with coronal oblique acquisition to simultaneously measure kidney stiffness in comparison with other tissues including the liver, spleen, and psoas. PMID:21724121

Bensamoun, Sabine F; Robert, Ludovic; Leclerc, Gwladys E; Debernard, Laëtitia; Charleux, Fabrice

24

Instrumentation for intraoperative measurement of cervical spine stiffness.  

PubMed

There is scant information on in vivo cervical biomechanics. The majority of limited data available in this area has been obtained using cadaver studies. With this in mind, simple instrumentation for analysing intraoperative cervical motion segment stiffness (load-axial displacement) was developed. The instrumentation consists of a displacement and strain transducer equipped vertebral retractor to be used with Caspar pins during anterior cervical surgery. Paramount to instrument design was incorporation of components complimentary to high electrical and mechanical repeatability, electrical safety, and creation of a sterile barrier. Preliminary studies conducted on a cadaver with this device revealed C3-C4 axial displacements (millimeters) of 1.735, 2.688, and 4.024 using, respectively, loads (newtons) of 44.482, 88,964, and 133.446. These results suggest this technique will be useful in assessing intraoperative spinal stability. PMID:8837055

Frank, E H; Chamberland, D L; Ragel, B T

1996-06-01

25

Aortic wave velocity: a noninvasive method to measure the stiffness of arteries and the clinical results of supplements that appear to improve arterial stiffness.  

PubMed

It has been suggested that arterial stiffness is one of the most important risk factors for the development of a cardiac infarction or stroke. As cardiovascular disease remains the number one killer of individuals before the age of 75, the early detection of cardiovascular disease and its prevention remains paramount in order to sustain a healthy longevity. This article looks at the latest noninvasive technology that can measure arterial stiffness quickly and easily and also highlights a small open trial in which supplements were used to determine their efficacy in helping to reverse/improve arterial stiffness. PMID:23895524

Micans, Philip

2013-02-01

26

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

27

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

NASA Astrophysics Data System (ADS)

In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. The Lamb wave velocity is directly related to the material parameters, so an effective method exists to ascertain the stiffness of composites by measuring the velocity of these waves. In this study, a Lamb wave measurement system was used to measure the bending and out-of-plane stiffness coefficients of thermoset composite laminates undergoing thermal-mechanical loading. A series of 16 ply and 32 ply composite laminates were subjected to thermal-mechanical fatigue (TMF) in load frames equipped with special environmental chambers. The composite system studied was a graphite fiber-reinforced bismaleimide thermoset, IM7/5260. The samples were subjected to both high and low temperature profiles as well as high-strain and low-strain profiles. The bending and out-of-plane stiffnesses for composite samples that have undergone over 6000 cycles of combined thermal and mechanical fatigue are reported. The Lamb wave generated elastic stiffness results have shown decreases of up to 64% at 4706 cycles for samples subjected to TMF at high temperatures and less than a 10% decrease at over 6000 cycles for samples subjected to TMF at low temperatures.

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

1999-08-01

28

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

SciTech Connect

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

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

1999-08-01

29

Optoelectronic tweezers for the measurement of the relative stiffness of erythrocytes  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

30

Measurements of stiff-material compliance on the nanoscale using ultrasonic force microscopy  

NASA Astrophysics Data System (ADS)

Ultrasonic force microscopy (UFM) was introduced to probe nanoscale mechanical properties of stiff materials. This was achieved by vibrating the sample far above the first resonance of the probing atomic force microscope cantilever where the cantilever becomes dynamically rigid. By operating UFM at different set force values, it is possible to directly measure the absolute values of the tip-surface contact stiffness. From this an evaluation of surface elastic properties can be carried out assuming a suitable solid-solid contact model. In this paper we present curves of stiffness as a function of the normal load in the range of 0-300 nN. The dependence of stiffness on the relative humidity has also been investigated. Materials with different elastic constants (such as sapphire lithium fluoride, and silicon) have been successfully differentiated. Continuum mechanics models cannot however explain the dependence of stiffness on the normal force and on the relative humidity. In this high-frequency regime, it is likely that viscous forces might play an important role modifying the tip-surface interaction. Plastic deformation might also occur due to the high strain rates applied when ultrasonically vibrating the sample. Another possible cause of these discrepancies might be the presence of water in between the two bodies in contact organizing in a solidlike way and partially sustaining the load.

Dinelli, F.; Biswas, S. K.; Briggs, G. A. D.; Kolosov, O. V.

2000-05-01

31

Correlation of Ultrasound-Measured Common Carotid Artery Stiffness With Pathological Findings  

Microsoft Academic Search

To quantitatively and noninvasively evaluate com- mon carotid atherosclerosis in a series of patients, we mea- sured the stiffness parameter p, which represents the mechan- ical properties of the vessel. \\/3 was calculated from the relationship between blood pressure and the diameter of the artery as measured by an ultrasonic, phase-locked, echo- tracking system. Increases in the severity grade of

Takashi Wada; Kuniyasu Kodaira; Kentaro Fujishiro; Ken-ichi Maie; Eiji Tsukiyama; Tsutomu Fukumoto; Tomoko Uchida; Sayaka Yamazaki

2010-01-01

32

Simultaneous stiffness and force measurements reveal subtle injury to rabbit soleus muscles  

Microsoft Academic Search

The time course of force generation and the time course of muscle stiffness were measured in rabbit soleus muscles during eccentric contraction to understand the underlying basis for the force loss in these muscles. Muscles were activated for 600 msec every 10 sec for 30 min. Soleus muscles contracting isometrically maintained constant tension throughout the treatment period, while muscles subjected

Robert J. Benz; Richard L. Lieber

1998-01-01

33

Precision and accuracy in film stiffness measurement by Brillouin spectroscopy  

NASA Astrophysics Data System (ADS)

The interest in the measurement of the elastic properties of thin films is witnessed by a number of new techniques being proposed. However, the precision of results is seldom assessed in detail. Brillouin spectroscopy (BS) is an established optical, contactless, non-destructive technique, which provides a full elastic characterization of bulk materials and thin films. In the present work, the whole process of measurement of the elastic moduli by BS is critically analyzed: experimental setup, data recording, calibration, and calculation of the elastic moduli. It is shown that combining BS with ellipsometry a fully optical characterization can be obtained. The key factors affecting uncertainty of the results are identified and discussed. A procedure is proposed to discriminate factors affecting the precision from those affecting the accuracy. By the characterization of a model transparent material, silica in bulk and film form, it is demonstrated that both precision and accuracy of the elastic moduli measured by BS can reach 1% range, qualifying BS as a reference technique.

Beghi, M. G.; di Fonzo, F.; Pietralunga, S.; Ubaldi, C.; Bottani, C. E.

2011-05-01

34

Controlling and measuring substrate stiffness for cell motility studies  

NASA Astrophysics Data System (ADS)

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

Runyan, Lindsay; Hoffmann, Peter; Beningo, Karen

2009-03-01

35

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

36

Requirements for nuclear localization of Lsm2-8p and competition between nuclear and cytoplasmic Lsm complexes  

PubMed Central

Summary Lsm proteins are ubiquitous, multifunctional proteins that are involved in the processing and/or turnover of many RNAs. In eukaryotes, a hetero-heptameric complex of Lsm proteins (Lsm2-8p) affects the processing of small stable RNAs and pre-mRNAs in the nucleus, while a different hetero-heptameric complex of Lsm proteins (Lsm1-7p) promotes mRNA decapping and decay in the cytoplasm. These two complexes have six constituent proteins in common, yet localize to separate cellular compartments and perform apparently disparate functions. Little is known about the biogenesis of the Lsm complexes, or how they are recruited to different cellular compartments. We show that in yeast, the nuclear accumulation of Lsm proteins depends on complex formation and that the Lsm8p subunit plays a crucial role. The nuclear localization of Lsm8p is itself most strongly influenced by Lsm2p and Lsm4p, its presumed neighbors in the Lsm2-8p complex. Furthermore, over-expression and depletion experiments imply that Lsm1p and Lsm8p act competitively with respect to the localization of the two complexes, suggesting a potential mechanism for co-regulation of nuclear and cytoplasmic RNA processing. A shift of Lsm proteins from the nucleus to the cytoplasm under stress conditions indicates that this competition is biologically significant.

Spiller, Michael P.; Reijns, Martin A. M.; Beggs, Jean D.

2008-01-01

37

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

PubMed Central

Introduction The purpose of our study was to examine the relationship between ankle dorsiflexion (DF) range of motion (ROM) and stiffness measured at rest (passively) and plantar loading during gait in individuals with and without diabetes mellitus (DM) and sensory neuropathy. Specifically, we sought to address three questions for this at-risk patient population: (1) Does peak passive DF ROM predict ankle DF ROM used during gait? (2) Does passive ankle stiffness predict ankle stiffness used during gait? (3) Are any of the passive or gait-related ankle measures associated with plantar loading? Methods Ten subjects with DM and 10 age and gender matched non-diabetic control subjects participated in this study. Passive ankle DF ROM and stiffness were measured with the Iowa Ankle ROM device. Kinematic, kinetic and plantar pressure data were collected as subjects walked at 0.89 m/s. Results We found that subjects with DM have reduced passive ankle DF ROM and increased stiffness compared to non-diabetic control subjects, however, subjects with DM demonstrated ankle motion, stiffness and plantar pressures, similar to control subjects, while walking at the identical speed, 0.89 m/s (2 mph). These data indicate that clinical measures of heel cord tightness and stiffness do not represent ankle motion or stiffness utilized during gait. Our findings suggest that subjects with DM utilize strategies such as shortening their stride length and reducing their push-off power to modulate plantar loading.

Rao, Smita; Saltzman, Charles; Yack, H. John

2011-01-01

38

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

PubMed

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

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

2013-03-01

39

Pulmonary vascular stiffness: measurement, modeling, and implications in normal and hypertensive pulmonary circulations.  

PubMed

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

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

2011-07-01

40

Direct measurement of bending stiffness and estimation of Young's modulus of vertically aligned carbon nanofibers  

NASA Astrophysics Data System (ADS)

The bending stiffness of individual, as-grown, vertically aligned carbon nanofibers was measured using a custom-built atomic force microscope placed inside a scanning electron microscope. The internal structure of the nanofiber was best modeled as dual-phase, composed of an inner graphitic core covered with a tapered amorphous carbon shell. It was found that the fibers have a relatively low bending stiffness, with Young's modulus values of about 10 GPa for the inner core and 65 GPa for the outer shell. The low Young's modulus of the inner core is attributed to a non-zero angle between the graphitic sheets and the nanofiber axis. The weak shear modulus between graphitic sheets thereby dominates the mechanical behaviour of the fibers.

Ghavanini, F. A.; Jackman, H.; Lundgren, P.; Svensson, K.; Enoksson, P.

2013-05-01

41

A cross-bridge model for inotropism as revealed by stiffness measurements in cardiac muscle.  

PubMed

Stiffness measurements obtained by means of rapid length changes performed according to Huxley and Simmons (23) showed that the series elasticity of the living frog myocardium obeys Hooke's law and alters in proportion to isometric tension. The same results had previously been reported for glycerol-extracted heart muscle (15, 16). Under conditions of postive inotropism caused by application of noradrenaline, adrenaline or increased extracellular Ca++ concentration, the proportionality between tension and stiffness is maintained (13). As there is strong evidence that the series elasticity of heart muscle resides in the cross-bridges (17, 24) this means that systolic force development and positive inotropism are due to the same process, namely a recruitment of "activated" cross-bridges (an increase in the number of cross-bridges attached to actin at any moment). This rules out the two-component model proposed by Sonnenblick in which a non-linear series elastic element was postulated. PMID:308368

Herzig, J W

42

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

43

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

PubMed

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

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

2012-08-01

44

Measurement of knee stiffness and laxity in patients with documented absence of the anterior cruciate ligament.  

PubMed

Thirty-five patients with documented absence of the anterior cruciate ligament were tested on the University of California, Los Angeles, instrumented clinical knee-testing apparatus and we measured the response curves for the following testing modes: anterior-posterior force versus displacement at full extension and at 20 and 90 degrees of flexion; varus-valgus moment versus angulation at full extension and 20 degrees of flexion; and tibial torque versus rotation at 20 degrees of flexion. Absolute values of stiffness and laxity and right-left differences for these injured knees were compared with identical quantities measured previously for a control population of forty-nine normal subjects with no history of treatment for injury to the knee. For both the uninjured knees and the knees without an anterior cruciate ligament, at 20 and 90 degrees of flexion the anterior-posterior laxity was greatest at approximately 15 degrees of external rotation of the foot. The injured knees demonstrated significantly increased total anterior-posterior laxity and decreased anterior stiffness when compared with the uninjured knees in all tested positions of the foot and knee. The mean increase in paired anterior-posterior laxity for the injured knees in this group of patients at +/- 200 newtons of applied anterior-posterior force was 3.1 millimeters (+39 per cent) at full extension, 5.5 millimeters (+57 per cent) at 20 degrees of flexion, and 2.5 millimeters (+34 per cent) at 90 degrees of flexion. The mean reduction in anterior stiffness for injured knees was also greatest (-54 per cent) at 20 degrees of knee flexion. Only slight reduction in posterior stiffness (-16 per cent) was measured at 20 degrees of flexion, and this probably reflected the presence of associated capsular and meniscal injuries. In the group of anterior cruciate-deficient knees, the patients with an absent medial meniscus showed greater total anterior-posterior laxity in all three positions of knee flexion than did the patients with an intact or torn meniscus. Varus-valgus laxity at full extension increased an average of 1.7 degrees (+36 per cent) for the injured knees, while varus and valgus stiffness decreased 21 per cent and 24 per cent. Absence of the medial meniscus (in a knee with absence of the anterior cruciate ligament) increased varus-valgus laxity at zero and 20 degrees of flexion.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:6693451

Markolf, K L; Kochan, A; Amstutz, H C

1984-02-01

45

Noninvasive assessment of liver fibrosis by measurement of stiffness in patients with nonalcoholic fatty liver disease (NAFLD)  

Microsoft Academic Search

BackgroundLiver fibrosis is the main predictor of the progression of nonalcoholic fatty liver disease. Transient elastography (FibroScan), which measures liver stiffness, is a novel, noninvasive method to assess liver fibrosis.

M. Yoneda; H. Mawatari; K. Fujita; H. Endo; H. Iida; Y. Nozaki; K. Yonemitsu; T. Higurashi; H. Takahashi; N. Kobayashi; H. Kirikoshi; Y. Abe; M. Inamori; K. Kubota; S. Saito; M. Tamano; H. Hiraishi; S. Maeyama; N. Yamaguchi; S. Togo; A. Nakajima

2008-01-01

46

Measurement of muscle fiber stiffness during stretch with two continuous different velocities in skeletal muscle fibers.  

PubMed

Ca2+ activated single glycerinated muscle fibers were stretched by 3% of its slack length Lo with moderate velocities ranging from 0.015 to 0.15Lo, and muscle fiber stiffness during and after stretch was measured by applying sinusoidal vibrations (peak-to-peak amplitude, 0.1% of Lo, 2kHz). During a single stretch, the fiber was first stretched by 1.5% with a velocity, and then it was further stretched by 1.5% with another velocity. It is suggested that, during stretch, a considerable fraction of cross-bridges slow down their cycling rate and increase their force-generating ability. PMID:18003334

Kobayashi, Takakazu; Iwai, Masaaki; Phan, Kien Nguyen

2007-01-01

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

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

Microsoft Academic Search

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

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

1999-01-01

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

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

2013-05-13

51

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

PubMed Central

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

Spoon, Corrie; Grant, Wally

2011-01-01

52

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

PubMed

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

Spoon, Corrie; Grant, Wally

2011-03-01

53

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

2013-01-08

54

Arterial stiffness  

PubMed Central

Measurements of biomechanical properties of arteries have become an important surrogate outcome used in epidemiological and interventional cardiovascular research. Structural and functional differences of vessels in the arterial tree result in a dampening of pulsatility and smoothing of blood flow as it progresses to capillary level. A loss of arterial elastic properties results a range of linked pathophysiological changes within the circulation including increased pulse pressure, left ventricular hypertrophy, subendocardial ischaemia, vessel endothelial dysfunction and cardiac fibrosis. With increased arterial stiffness, the microvasculature of brain and kidneys are exposed to wider pressure fluctuations and may lead to increased risk of stroke and renal failure. Stiffening of the aorta, as measured by the gold-standard technique of aortic Pulse Wave Velocity (aPWV), is independently associated with adverse cardiovascular outcomes across many different patient groups and in the general population. Therefore, use of aPWV has been proposed for early detection of vascular damage and individual cardiovascular risk evaluation and it seems certain that measurement of arterial stiffness will become increasingly important in future clinical care. In this review we will consider some of the pathophysiological processes that result from arterial stiffening, how it is measured and factors that may drive it as well as potential avenues for therapy. In the face of an ageing population where mortality from atheromatous cardiovascular disease is falling, pathology associated with arterial stiffening will assume ever greater importance. Therefore, understanding these concepts for all clinicians involved in care of patients with cardiovascular disease will become vital.

Quinn, Ursula; Tomlinson, Laurie A; Cockcroft, John R

2012-01-01

55

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

56

Dynamically and Statically Measured Small Strain Stiffness of Dense Toyoura Sand  

NASA Astrophysics Data System (ADS)

Small strain stiffness of dense Toyoura sand was investigated by performing triaxial compression tests using large scale apparatus. The specimens were rectangular prismatic with dimensions of 50 cm high and 23.5 cm times 23.5 cm in cross-section. To measure the vertical stress ?1, a load cell is located just above the top cap inside the triaxial cell in order to eliminate the effects of piston friction. The vertical strain ?1 was measured not only externally but also locally with three pairs of vertical local deformation transducers (LDTs). Three tests were conducted using air-dried Toyoura sand (Dmax = 0.35 mm, D50 = 0.23 mm, Uc = 1.80, emax = 0.966, emin = 0.600 and Gs = 2.635) as the test material. The specimens were prepared by employing air pluviation method and keeping dry densities within the range of 1.62 - 1.63 g/cm3. Dynamic and static Young's moduli were evaluated by wave velocity measurement and by conducting small unloading/reloading cycles, respectively.

Maqbool, Sajjad; Sato, Takeshi; Koseki, Junichi

57

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

58

LSM-Based Secure System Monitoring Using Kernel Protection Schemes  

Microsoft Academic Search

Monitoring a process and its file I\\/O behaviors is important for security inspection for a data center server against intrusions, malware infection and information leakage. In the case of the Linux kernel 2.6, a set of hook functions called the Linux Security Module (LSM) has been implemented in order to monitor and control the system calls. By using the LSM

Takamasa Isohara; Keisuke Takemori; Yutaka Miyake; Ning Qu; Adrian Perrig

2010-01-01

59

Evaluation of the Stiffness Coefficients for Beryllium from Ultrasonic Measurements in Polycrystalline and Single Crystal Specimens  

Microsoft Academic Search

The pulsed ultrasonic method has been applied to the determination of the stiffness coefficients for beryllium. The constants c11=30.8×1011 dynes\\/cm2, c33=35.7 were evaluated from compressional wave velocities in single crystals by extrapolating a plot of the effective stiffness coefficient versus 2theta theta being the angle between the hexagonal axis and the direction of wave propagation) to the points theta=pi2 and

Louis Gold

1950-01-01

60

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

2012-06-07

61

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

62

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

PubMed

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

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

2012-07-06

63

Clinical application of liver stiffness measurement using transient elastography in chronic liver disease from longitudinal perspectives  

PubMed Central

Accurate determination of the presence and degree of fibrosis in liver is of great importance, because the prognosis and management strategies for chronic liver disease depend mainly on these factors. To date, liver biopsy (LB) remains the “gold standard” for assessing the severity of liver fibrosis; however, LB is often limited by its invasiveness, sampling error, and intra/inter-observer variability in histological interpretation. Furthermore, repeated LB examinations within a short time interval are indeed ineligible in a real clinical practice. Thus, due to the pressing need for non-invasive surrogates for liver fibrosis, transient elastography (TE), as a novel ultrasound based technology, has allowed a noninvasive measurement of liver stiffness and has gained in popularity over recent years. In the past few years, additional roles for transient TE beyond the initial purpose of a non-invasive surrogate for LB have included the prediction of the most two critical consequences of fibrosis progression: the development of portal hypertension-related complications and hepatocellular carcinoma. This indicates that the role of transient TE is not merely limited to reducing the need for LB, but transient TE can enable the establishment of tailored management strategies by providing more detailed prognostic information. In particular, under the concept in which the clinical course of liver fibrosis is dynamic and bidirectional, especially when appropriate intervention is commenced, transient TE can be used to track the dynamic changes in fibrotic burden during antiviral or antifibrotic treatment. This review discussed extended applications of transient TE in prediction of the development of real clinical endpoints from a longitudinal perspective.

Kim, Beom Kyung; Fung, James; Yuen, Man-Fung; Kim, Seung Up

2013-01-01

64

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

2010-06-28

65

A Non-Invasive, Real-Time Method for Measuring Variable Stiffness  

Microsoft Academic Search

The need for adaptability to the environment, en- ergy conservation, and safety during physical interaction with humans of many advanced robotic applications has prompted the development of a number of Variable Stiffness Actuators (VSA). These have been implemented in a variety of ways, using dif- ferent transduction technologies (electromechanical, pneumatic, hydraulic, but also piezoelectric, active polymeric, etc. ) and arrangements

Giorgio Grioli; Centro Interdipartimentale; E. Piaggio; Antonio Bicchi

66

Measurement of Dynamic Rope System Stiffness in a Sequential Failure for Lead Climbing Falls  

Microsoft Academic Search

Background: Extended rock climbing leader falls resulting from sequential anchor point failures has lead to much speculation regarding rope behavior. It has been postulated that an increase in stiffness (modulus) of the rope was likely responsible for subsequent anchor failures after a top point anchor failure. Understanding and forecasting the system response of a leader fall can help climbers gain

J. Marc Beverly; Stephen W. Attaway

67

A stiffness-based quality measure for compliant grasps and fixtures  

Microsoft Academic Search

This paper presents a systematic approach to quanti- fying the effectiveness of compliant grasps and fixtures of an object. The approach is physically motivated and applies to the grasping of two- and three-dimensional objects by any number of fingers. The approach is based on a characterization of the frame-invariant features of a grasp or fixture stiffness matrix. In particular, we

Qiao Lin; Joel W. Burdick; Elon Rimon

2000-01-01

68

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

69

Electrical degradation of porous and dense LSM\\/YSZ interface  

Microsoft Academic Search

Electrochemical cells formed by the interface between dense and porous lanthanum strontium manganate (LSM) and yttria stabilized zirconia (YSZ) were submitted to annealing temperatures varying from 1373K to 1673K for 200h and studied by Impedance Spectroscopy (IS) in order to investigate how the high annealing temperature can modify the contact between LSM\\/YSZ and to which extension these changes influence the

M. C. Brant; T. Matencio; L. Dessemond; R. Z. Domingues

2006-01-01

70

Evaluation of Performance of Secure OS Using Performance Evaluation Mechanism of LSM-Based LSMPMON  

NASA Astrophysics Data System (ADS)

Security focused OS (Secure OS) is attracting attention as a method for minimizing damage caused by various intrusions. Secure OSes can restrict the damage due to an attack by using Mandatory Access Control (MAC). In some projects, secure OSes for Linux have been developed. In these OSes, different implementation methods have been adopted. However, there is no method for easily evaluating the performance of the secure OS in detail, and the relationship between the implementation method and the performance is not clear. The secure OS in Linux after version 2.6 has often been implemented by Linux Security Modules (LSM). Therefore, we determine the effect of introducing the secure OS on the performance of the OS, and a characteristic by the difference of the implementation method by using the overhead measurement tool, the LSM Performance Monitor (LSMPMON); the LSMPMON can be used to evaluate three different secure OSes.

Yamamoto, Kenji; Yamauchi, Toshihiro

71

Design of an automated device to measure sagittal plane stiffness of an articulated ankle-foot orthosis.  

PubMed

The purpose of this study was to design a new automated stiffness measurement device which could perform a simultaneous measurement of both dorsi- and plantarflexion angles and the corresponding resistive torque around the rotational centre of an articulated ankle-foot orthosis (AAFO). This was achieved by controlling angular velocities and range of motion in the sagittal plane. The device consisted of a hydraulic servo fatigue testing machine, a torque meter, a potentiometer, a rotary plate and an upright supporter to enable an AAFO to be attached to the device via a surrogate shank. The accuracy of the device in reproducing the range of motion and angular velocity was within 4% and 1% respectively in the range of motion of 30° (15° plantarflexion to 15° dorsiflexion) at the angular velocity of 10°/s, while that in the measurement of AAFO torque was within 8% at the 0° position. The device should prove useful to assist an orthotist or a manufacturer to quantify the stiffness of an AAFO and inform its clinical use. PMID:20681928

Kobayashi, Toshiki; Leung, Aaron K L; Akazawa, Yasushi; Naito, Hisashi; Tanaka, Masao; Hutchins, Stephen W

2010-08-04

72

LSM1 over-expression in Saccharomyces cerevisiae depletes U6 snRNA levels  

PubMed Central

Lsm1 is a component of the Lsm1-7 complex involved in cytoplasmic mRNA degradation. Lsm1 is over-expressed in multiple tumor types, including over 80% of pancreatic tumors, and increased levels of Lsm1 protein have been shown to induce carcinogenic effects. Therefore, understanding the perturbations in cell process due to increased Lsm1 protein may help to identify possible therapeutics targeting tumors over-expressing Lsm1. Herein, we show that LSM1 over-expression in the yeast Saccharomyces cerevisiae inhibits growth primarily due to U6 snRNA depletion, thereby altering pre-mRNA splicing. The decrease in U6 snRNA levels causes yeast strains over-expressing Lsm1 to be hypersensitive to loss of other proteins required for production or function of the U6 snRNA, supporting a model wherein excess Lsm1 reduces the availability of the Lsm2-7 proteins, which also assemble with Lsm8 to form a complex that binds and stabilizes the U6 snRNA. Yeast strains over-expressing Lsm1 also display minor alterations in mRNA decay and demonstrate increased susceptibility to mutations inhibiting cytoplasmic deadenylation, a process required for both 5?-to-3? and 3?-to-5? pathways of exonucleolytic decay. These results suggest that inhibition of splicing and/or deadenylation may be effective therapies for Lsm1-over-expressing tumors.

Luhtala, Natalie; Parker, Roy

2009-01-01

73

LSM1 over-expression in Saccharomyces cerevisiae depletes U6 snRNA levels.  

PubMed

Lsm1 is a component of the Lsm1-7 complex involved in cytoplasmic mRNA degradation. Lsm1 is over-expressed in multiple tumor types, including over 80% of pancreatic tumors, and increased levels of Lsm1 protein have been shown to induce carcinogenic effects. Therefore, understanding the perturbations in cell process due to increased Lsm1 protein may help to identify possible therapeutics targeting tumors over-expressing Lsm1. Herein, we show that LSM1 over-expression in the yeast Saccharomyces cerevisiae inhibits growth primarily due to U6 snRNA depletion, thereby altering pre-mRNA splicing. The decrease in U6 snRNA levels causes yeast strains over-expressing Lsm1 to be hypersensitive to loss of other proteins required for production or function of the U6 snRNA, supporting a model wherein excess Lsm1 reduces the availability of the Lsm2-7 proteins, which also assemble with Lsm8 to form a complex that binds and stabilizes the U6 snRNA. Yeast strains over-expressing Lsm1 also display minor alterations in mRNA decay and demonstrate increased susceptibility to mutations inhibiting cytoplasmic deadenylation, a process required for both 5'-to-3' and 3'-to-5' pathways of exonucleolytic decay. These results suggest that inhibition of splicing and/or deadenylation may be effective therapies for Lsm1-over-expressing tumors. PMID:19596813

Luhtala, Natalie; Parker, Roy

2009-07-13

74

A novel photoplethysmography technique to derive normalized arterial stiffness as a blood pressure independent measure in the finger vascular bed.  

PubMed

Stiffening of the small artery may be the earliest sign of arteriosclerosis. However, there is no adequate method for directly assessing small arterial stiffness. In this study, the finger arterial elasticity index (FEI) was defined as the parameter n which denotes the curvilinearity of an exponential model of pressure (P)-volume (V(a)) relationship (V(a) = a - b exp (-nP)). For the original estimation, the FEI was calculated from a compliance index from the finger photoplethysmogram whilst occluding the finger. A simple estimation of the FEI was devised by utilizing normalized pulse volume instead of the compliance index. Both estimations yielded close agreement with the exponential model in healthy young participants (study 1: n = 19). Since the FEI was dependent on finger mean blood pressure, normalized finger arterial stiffness index (FSI) was defined as standardized residual from their relationship: mean and standard deviation (SD) of the FSI were 50 ± 10 (study 2: n = 174). The mean coefficient of variation of the FSI for four measurements was 5.72% (study 3: n = 6). The mean and SD of the FSI in seven arteriosclerotic patients were 100.0 ± 13.5. In conclusion, the FEI and FSI by simple estimation are valid and useful for arteriosclerosis research. PMID:22026968

Tanaka, Gohichi; Yamakoshi, Ken-ichi; Sawada, Yukihiro; Matsumura, Kenta; Maeda, Kimihito; Kato, Yuichi; Horiguchi, Masami; Ohguro, Hiroshi

2011-10-26

75

Stiff railguns  

NASA Astrophysics Data System (ADS)

Stiff guns have been operated with both plasma and solid armatures. A performance gain was seen in the plasma railgun as stiffness was increased. A stiff gun will help to maintain the bore shape and preserve the integrity of the seam between rail and insulator under the extreme asymmetric loads sustained during high-pressure operation. The hydraulically preloaded moly and ceramic gun has been fired six times at pressures as high as 87 ksi, and the bore still holds roughing vacuum up to two hours after the test. The elimination of seam leakage helps control bore erosion associated with plasma reconstitution from the rail and plasma perturbation that might result in loss-initiating instabilities. Reduced rail deflection allows solid and transitioning armatures to track the bore surface. An analysis of the strain energy associated with the deflection of the railgun structure is presented, and this mechanism is found to be a small fraction of the energy associated with armature loss and the rail resistive loss.

Weldon, W. F.; Bacon, J. L.; Weeks, D. A.; Zowarka, R. C., Jr.

1991-01-01

76

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

PubMed

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

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

2010-01-01

77

Prognostic application of arterial stiffness: task forces  

Microsoft Academic Search

Epidemiologic and clinical studies have shown that increased pulse pressure is an independent cardiovascular risk factor in general population. Pulse pressure is determined by combined effects of cardiac factors (stroke volume) and the arterial stiffness. Arterial stiffness can be more directly evaluated by several measurements including the measure of pulse wave velocity (PWV). Aortic PWV, a marker of aortic stiffness,

G. érard M London; Jay N. Cohn

2002-01-01

78

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

Microsoft Academic Search

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

Matthew D. Barrett; Ellengene H. Peterson; J. Wallace Grant

1999-01-01

79

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; Kim, Y.J. [Korea Academy of Industrial Technology, Seoul (Korea, Republic of)

1997-03-01

80

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

PubMed Central

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

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

2012-01-01

81

Prevalence and factors associated with failure of liver stiffness measurement using FibroScan in a prospective study of 2114 examinations.  

PubMed

Liver stiffness measurement using FibroScan is a novel rapid and non-invasive technique that evaluates liver fibrosis. In some cases, however, no elasticity measurement is obtained. The aim of this prospective study was to assess the prevalence and factors associated with failure (no value obtained after 10 measurements) of liver stiffness measurement in patients with chronic liver disease. Two thousand one hundred and fourteen liver stiffness measurements were analyzed. Failure was observed in 96 cases (4.5%). Failure was not associated with operator, gender, or transaminase level. By multivariate analysis, the only factor associated with failure was body mass index greater than 28 (odds ratio, 10.0 degrees; 95% confidence interval, 5.7-17.9, P=0.001). In conclusion, liver stiffness is a good method for the evaluation of liver fibrosis that is feasible in more than 95% of patients. Other non-invasive methods such as biochemical methods or liver biopsy could therefore be used only in patients with failure of FibroScan examination. PMID:16538113

Foucher, Juliette; Castéra, Laurent; Bernard, Pierre-Henri; Adhoute, Xavier; Laharie, David; Bertet, Julien; Couzigou, Patrice; de Lédinghen, Victor

2006-04-01

82

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

83

LSM-YSZ Cathodes with Reaction-Infiltrated Nanoparticles  

SciTech Connect

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

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

2006-01-31

84

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

Microsoft Academic Search

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

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

1995-01-01

85

Wood Joist Floors: Probabilistic Analysis of Joist Stiffness Measured at Retail Lumberyards.  

National Technical Information Service (NTIS)

A systematic sampling of joint lumber was carried out at retail lumber yards over two summers to observe and measure physical and mechanical properties close to point of purchase and use. The study sought to define acceptable performance of the dimension ...

J. F. Sedransk J. F. Senft J. H. Haskell R. L. Ethington W. L. Galligan

1982-01-01

86

Size and stiffness measurements on 9.5 m long LHC dipole coils  

NASA Astrophysics Data System (ADS)

For a 10 m long superconducting dipole prototype magnet for CERN's LHC (Large Hadron Collider) program in total 17 dummy and superconducting coils were manufactured at ELIN company. The paper presents measurements taken during coil manufacturing. The results are compared to results obtained on models. The influence of cable dimensions on the final dimension and the Young's Modulus of the coils is described.

Zerobin, Franz; Painer, Manfred; Eichberger, Siegfried; Pichler, Stefan

1994-07-01

87

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

NASA Astrophysics Data System (ADS)

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

Bullock, James M. R.; Federle, Walter

2011-05-01

88

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

SciTech Connect

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

Brown, Eric [Los Alamos National Laboratory

2012-06-07

89

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

90

Rationale, design and clinical performance of the mechanical response tissue analyser: a non-invasive technology for measurement of long bone bending stiffness.  

PubMed

Prediction of osteoporotic fractures is currently an imperfect science and new tools are desperately needed to identify at-risk patients at an earlier stage in the disease process. The mechanical response tissue analyser (MRTA) is a novel, non-invasive, radiation-free device that measures the bending stiffness of long bones in vivo, an indicator of a bone's ability to resist deformation under a given load and a strong predictor of long bone structural integrity and strength. Bone bending stiffness measured with the MRTA has been consistently shown to be a stronger predictor of post-mortem and ex vivo bone breaking strength compared to bone mineral measured with dual-energy X-ray absorptiometry. Bone bending stiffness measured with MRTA also decreases with advanced age and disease states and increases with chronic physical activity, independent of bone mineral changes. The MRTA measures different parameters than DXA (bone quality vs bone mineral content and density) and may be a more robust tool for identifying those at risk for fracture. Research initiatives focused on improving long-term repeatability and optimizing the signal-to-noise ratio of the measurement are currently underway to further advance the clinical usefulness of this technology. PMID:23360197

Miller, Larry E; Ramp, Warren K; Steele, Charles R; Nickols-Richardson, Sharon M; Herbert, William G

2013-02-01

91

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

92

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

93

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 ... is being done? Clinical Trials Organizations What is Stiff-Person Syndrome? Stiff-person syndrome (SPS) is a rare neurological ...

94

Diagnosis of GLDAS LSM based aridity index and dryland identification.  

PubMed

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

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

2013-03-08

95

Arterial Stiffness Using Radial Arterial Waveforms Measured at the Wrist as an Indicator of Diabetic Control in the Elderly  

Microsoft Academic Search

Although current technique of photoplethysmogra- phy (PPG) is a popular noninvasive method of waveform con- tour analysis in assessing arterial stiffness, data obtained are frequently affected by various environmental and physiological factors. We proposed an easily operable air pressure sensing sys- tem (APSS) for radial arterial signal capturing. Totally, 108 sub- jects (young, the aged with or without diabetes) were

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

2011-01-01

96

Local increase in stiffness of agarose gel layer by patterning with polylysine measured via atomic force microscopy  

Microsoft Academic Search

Films of agarose gel impregnated with polylysine spotted from an aqueous solution have been characterized by atomic force microscopy performed in deionized water. An increase in contact stiffness of the composite substrate on the spotted areas has been observed, for increasing polylysine concentration. For the considered agarose layer thickness of ?0.9 ?m when dry, the polylysine concentration threshold for stiffening is

Marco Salerno; Silvia Dante; Niranjan Patra

2010-01-01

97

Hardness and elastic modulus of Au\\/NiCr\\/Ta multilayers on Al 2O 3 substrate by nanoindentation continuous stiffness measurement technique  

Microsoft Academic Search

Au\\/NiCr\\/Ta soft metallic multilayered films were deposited on hard Al2O3 substrate by magnetron sputtering. The distribution of hardness and elastic modulus was investigated by nanoindentation continuous stiffness measurement technique. The film hardness was constant for all samples at indentation depths 1\\/7?h\\/t?1\\/4, which can be considered as the true hardness. The hardness increased with increasing indentation depths at 1\\/4?h\\/t?1. The hardness

W. Tang; L. Shen; Kewei Xu

2005-01-01

98

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

99

Use of the thick adherend shear test for shear stress-strain measurements of stiff and flexible adhesives  

Microsoft Academic Search

Five commercial structural adhesives were tested using the thick adherend shear test (TAST). These adhesives have mechanical properties ranging from those of high-strength, heat-cured epoxies to ductile, acrylic-based materials. Consideration was given to the adherend selection and dimensions to approach a uniform shear stress-strain in the bonded area, so that the test could be used with both stiff and flexible

F. Kadioglu; L. F. Vaughn; F. J. Guild; R. D. Adams

2002-01-01

100

Single-step direct measurement of amyloid fibrils stiffness by peak force quantitative nanomechanical atomic force microscopy  

NASA Astrophysics Data System (ADS)

We present an original application of a new atomic force microscopy mode called peak force tapping for the investigation of the mechanical properties of ?-lactoglobulin amyloid fibrils. The values of Young's modulus obtained by this technique are in perfect agreement with the indirect evaluation of fibrils stiffness obtained by combining polymer physics and topological statistical analysis on fibrils' structural conformations. This technique shows great promise in the estimation of the elastic properties of nanostructured objects relevant in biology, soft matter, and nanotechnology.

Adamcik, Jozef; Berquand, Alexandre; Mezzenga, Raffaele

2011-05-01

101

Measurements of neutron fluxes in the LSM underground laboratory  

NASA Astrophysics Data System (ADS)

A good particle candidate for Cold Dark Matter (CDM) is the supersymmetric neutralino or more generally a weakly interacting massive particle (WIMP). The expected interaction rate of WIMPs with the detector medium in direct detection experiments is below 0.01 events/kg/day. This makes a good knowledge of the background conditions highly important, especially with ever increasing sensitivity of the detectors. One major component of the background is related to energetic neutrons induced by cosmic muons. However, the flux of low energy and thermal neutrons typically from spontaneous fission and (?, n) reactions in the rock surrounding underground experiments gives also valuable information about the overall environmental activity. Detailed studies carried out in the framework of the EDELWEISS experiment are presented.

Eitel, Klaus; Edelweiss Collaboration

2012-07-01

102

Oscillometric measurement of brachial artery cross-sectional area and its relationship with cardiovascular risk factors and arterial stiffness in a middle-aged male population.  

PubMed

An enlarged arterial diameter is associated with an increased risk for cardiovascular disease. This study examined the relationship of noninvasively measured brachial artery cross-sectional area with cardiovascular risk factors and arterial stiffness in a middle-aged male population. Absolute volumetric changes of the brachial artery were measured with a newly developed oscillometric method during a general health examination in 387 men (mean age: 38±9 years) without known cardiovascular disease. Based on the measurement, the estimated area (eA) of the brachial artery at end-diastole was obtained. Brachial artery volume elastic modulus (VE) and brachial-ankle pulse wave velocity (baPWV) were simultaneously measured as indices of arterial stiffness by the same device. The relationships of eA with cardiovascular risk factors, including age, obesity, hypertension, dyslipidemia, impaired fasting glucose/diabetes mellitus (IFG/DM), hyperuricemia, smoking and their associated continuous variables, as well as VE and baPWV, were examined. Overall, the mean eA was 12.9±2.9?mm(2). The eA was significantly higher in subjects with obesity, hypertension or IFG/DM than in those without each of these risk factors. In a multiple linear regression analysis, body mass index (?=0.31, P<0.001), age (?=0.25, P<0.001), systolic blood pressure (?=0.16, P=0.004) and pulse rate (?=-0.13, P=0.005) were independent determinants of eA. In contrast, neither VE nor baPWV were selected as independent determinants of eA. In conclusion, enlarged brachial artery cross-sectional area was significantly associated with cardiovascular risk factors such as age, body mass index and systolic blood pressure, but it was not associated with increased arterial stiffness. PMID:23784508

Otsuka, Toshiaki; Munakata, Ryo; Kato, Katsuhito; Kodani, Eitaro; Ibuki, Chikao; Kusama, Yoshiki; Seino, Yoshihiko; Kawada, Tomoyuki

2013-06-20

103

Sensitivity evaluation of PBL and LSM parameterization for mesoscale model WRF over the Korean Peninsula  

NASA Astrophysics Data System (ADS)

The numerical model is sensitive to planetary boundary layer (PBL) and land surface model (LSM) at low level wind field. The choice of PBL and LSM parameterizations is important for numerical model to establish wind resource studies. The performance of Weather Reasurch and Forecasting (WRF) model (version 3.1.1) is evaluated using different PBL and LSM parameterizations and validated with wind speed and direction at 10m and 80m above ground level over the Korean Peninsula during 4-6 March 2007, 4-6 August 2008, 19-21 November 2007 and 7-9 January 2009. WRF model has conducted on a nested grid from 27 km down to 1 km horizontal resolution as 4 domains. First of all, a high resolution topography with a 100-m resolution from SRTM and 30-m land-use from LandSat satellite is remapped on WRF model. Statistical verification scores such as bias, RMSE, RMSVE show better results by improvement of bottom boundary condition. This study used some PBL and LSM. PBL consist of YSU, Mellor-Yamada-Janjic (MYJ), Pleim (ACM2) and LSM consist of Noah, Rapid Update Cycle (RUC), Pleim. Although model performance varies according to the weather condition by using different PBL and LSM, experiment with MYJ and RUC represents the best result for lower atmosphere wind speed and the all of the PBL and LSM parameterizations simulated similar on wind directions. The performance of temperature and water vapor at lower level would be presented in the conference.

Seo, Beom-Keun; Byon, Jae-Young; Choi, Young-Jean

2010-05-01

104

Stiff person syndrome.  

PubMed

Recognizing stiff person syndrome is clinically important. It is uncommon, characterized by body stiffness associated with painful muscle spasms, and varies in location and severity. It is subdivided into stiff trunk versus stiff limb presentation, and as a progressive encephalomyelitis. Stiff person-type syndrome also reflects a paraneoplastic picture. Most patients demonstrate exaggerated lumbar lordosis. Roughly 60% of patients have antiglutamic acid decarboxylase antibodies in the blood and the cerebrospinal fluid. The differential diagnosis includes many severe conditions. There are reports of response to muscle relaxants, immunosuppressants, intravenous gamma globulin, plasma exchange, a number of anticonvulsants, and botulinum toxin. PMID:23186907

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

2013-02-01

105

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

2010-10-04

106

Stiffness of the crystal-liquid interface in a hard-sphere colloidal system measured from capillary fluctuations.  

PubMed

Face-centered cubic single crystals of ?=1.55 ?m diameter hard-sphere silica colloidal particles were prepared by sedimentation onto (100) and (110) oriented templates. The crystals had a wide interface with the overlaying liquid that was parallel to the template. The location of the interface was determined by confocal microscopic location of the particles, followed by identification of the crystalline and liquid phases by a bond-orientation order parameter. Fluctuations in the height of the interface about its average position were recorded for several hundred configurations. The interfacial stiffness ? was determined from the slope of the inverse squared Fourier components of the height profile vs the square of the wave number, according to the continuum capillary fluctuation method. The offset of the fit from the origin could quantitatively be accounted for by gravitational damping of the fluctuations. For the (100) interface, ?=(1.3±0.3)k(B)T/?(2); for the (110) interface, ?=(1.0±0.2)k(B)T/?(2). The interfacial stiffness of both interfaces was found to be isotropic in the plane. This is surprising for the (110), where crystallography predicts twofold symmetry. Sedimentation onto a (111) template yielded a randomly stacked hexagonal crystal with isotropic ?=0.66k(B)T/?(2). This value, however, is less reliable than the two others due to imperfections in the crystal. PMID:21230283

Ramsteiner, I B; Weitz, D A; Spaepen, F

2010-10-20

107

Nuclear Pre-mRNA Decapping and 5? Degradation in Yeast Require the Lsm2-8p Complex  

PubMed Central

Previous analyses have identified related cytoplasmic Lsm1-7p and nuclear Lsm2-8p complexes. Here we report that mature heat shock and MET mRNAs that are trapped in the nucleus due to a block in mRNA export were strongly stabilized in strains lacking Lsm6p or the nucleus-specific Lsm8p protein but not by the absence of the cytoplasmic Lsm1p. These nucleus-restricted mRNAs remain polyadenylated until their degradation, indicating that nuclear mRNA degradation does not involve the incremental deadenylation that is a key feature of cytoplasmic turnover. Lsm8p can be UV cross-linked to nuclear poly(A)+ RNA, indicating that an Lsm2-8p complex interacts directly with nucleus-restricted mRNA. Analysis of pre-mRNAs that contain intronic snoRNAs indicates that their 5? degradation is specifically inhibited in strains lacking any of the Lsm2-8p proteins but Lsm1p. Nucleus-restricted mRNAs and pre-mRNA degradation intermediates that accumulate in lsm mutants remain 5? capped. We conclude that the Lsm2-8p complex normally targets nuclear RNA substrates for decapping.

Kufel, Joanna; Bousquet-Antonelli, Cecile; Beggs, Jean D.; Tollervey, David

2004-01-01

108

The Role of Passive Muscle Stiffness in Symptoms of Exercise-Induced Muscle Damage  

Microsoft Academic Search

We examined whether passive stiffness of an eccentrically exercising muscle group affects the subsequent symptoms of muscle damage. Passive hamstring muscle stiffness was measured during an instrumented straight-leg-raise stretch in 20 subjects (11 men and 9 women) who were subsequently classified as “stiff” (N 7), “normal” (N 6), or “compliant” (N 7). Passive stiffness was 78% higher in the stiff

Malachy P. McHugh; Declan A. J. Connolly; Roger G. Eston; Ian J. Kremenic; Stephen J. Nicholas; Gilbert W. Gleim

1999-01-01

109

Increased arterial stiffness in children on haemodialysis  

Microsoft Academic Search

Background. Measures of aortic stiffness—aortic pulse wave velocity (PWV) and augmentation index (AIx)— have been shown to be powerful predictors of survival in adult haemodialysis (HD) patients. Very few data have been reported regarding arterial stiffness in paediatric renal populations. Methods. PWV and aortic AIx were determined from contour analysis of arterial waveforms recorded by applanation tonometry using a SphygmoCor

Adrian Covic; Nicoleta Mardare; Paul Gusbeth-Tatomir; Ovidiu Brumaru; Cristina Gavrilovici; Mihaela Munteanu; Octavian Prisada; David J. A. Goldsmith

110

Stiffness Control of Surgical Continuum Manipulators  

Microsoft Academic Search

This paper introduces the first stiffness controller for continuum robots. The control law is based on an accurate approx- imation of a continuum robot's coupled kinematic and static force model. To implement a desired tip stiffness, the controller drives the actuators to positions corresponding to a deflected robot con- figuration that produces the required tip force for the measured tip

Mohsen Mahvash; Pierre E. Dupont

2011-01-01

111

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

112

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

113

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

114

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

115

FRET measurements of cell-traction forces and nano-scale clustering of adhesion ligands varied by substrate stiffness.  

PubMed

The mechanical properties of cell adhesion substrates regulate cell phenotype, but the mechanism of this relation is currently unclear. It may involve the magnitude of traction force applied by the cell, and/or the ability of the cells to rearrange the cell adhesion molecules presented from the material. In this study, we describe a FRET technique that can be used to evaluate the mechanics of cell-material interactions at the molecular level and simultaneously quantify the cell-based nanoscale rearrangement of the material itself. We found that these events depended on the mechanical rigidity of the adhesion substrate. Furthermore, both the proliferation and differentiation of preosteoblasts (MC3T3-E1) correlated to the magnitude of force that cells generate to cluster the cell adhesion ligands, but not the extent of ligand clustering. Together, these data demonstrate the utility of FRET in analyzing cell-material interactions, and suggest that regulation of phenotype with substrate stiffness is related to alterations in cellular traction forces. PMID:15767572

Kong, Hyun Joon; Polte, Thomas R; Alsberg, Eben; Mooney, David J

2005-03-14

116

Materials with negative stiffness  

NASA Astrophysics Data System (ADS)

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

Jaglinski, Tim

117

Stiff Person Syndrome  

Microsoft Academic Search

Stiff person syndrome (SPS), stiff limb syndrome, jerking SPS and progressive encephalomyelitis with rigidity and myoclonus (PERM) are a family of rare, insidiously progressive diseases of the central nervous system. They all share the core clinical features of appendicular and axial rigidity caused by continuous involuntary motor unit activity, and superimposed stimulus-sensitive spasms. There is good evidence for a primary

Martin E. Duddy; Mark R. Baker

2009-01-01

118

Randomized Comparison of the Therapeutic Effect of Acupuncture, Massage, and Tachibana-Style-Method on Stiff Shoulders by Measuring Muscle Firmness, VAS, Pulse, and Blood Pressure  

PubMed Central

To compare the therapeutic efficacy of acupuncture, massage, and Tachibana-Ryojutsu (one of Japanese traditional body balance therapy techniques (SEITAI)), on stiff shoulders, the subjects' muscle firmness, blood pressure, pulse, VAS, and body temperature were measured before and after the treatment. Forty-seven volunteer subjects gave written informed consent to participate in this study. The subjects were randomly divided into three groups to receive acupuncture, massage, or Tachibana-Ryojutsu. Each therapy lasted for 90 seconds. The acupuncture treatment was applied by a retaining-needle at GB-21, massage was conducted softly on the shoulders, and Tachibana-Ryojutsu treated only the muscles and joints from the legs to buttocks without touching the shoulders or backs. The study indicated that the muscle firmness and VAS of the Tachibana-Ryojutsu group decreased significantly in comparison with the acupuncture and massage groups after treatment.

Tachibana, Kazuhiro; Ueki, Noriyuki; Uchida, Takuji; Koga, Hiroshi

2012-01-01

119

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

SciTech Connect

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

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

2010-05-08

120

Model-based estimation of knee stiffness.  

PubMed

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

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

2012-07-11

121

Model-Based Estimation of Knee Stiffness  

PubMed Central

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

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

2013-01-01

122

Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells: III. Role of volatile boron species on LSM/YSZ and LSCF  

SciTech Connect

Boron oxide is a key component to tailor the softening temperature and viscosity of the sealing glass for solid oxide fuel cells. The primary concern regarding the use of boron containing sealing glasses is the volatility of boron species, which possibly results in cathode degradation. In this paper, we report the role of volatile boron species on the electrochemical performance of LSM/YSZ and LSCF cathodes at various SOFC operation temperatures. The transport rate of boron, ~ 3.24×10-12 g/cm2•sec was measured at 750°C with air saturated with 2.8% moisture. A reduction in power density was observed in cells with LSM/YSZ cathodes after introduction of the boron source to the cathode air stream. Partial recovery of the power density was observed after the boron source was removed. Results from post-test secondary ion mass spectroscopy (SIMS) analysis the partial recovery in power density correlated with partil removal of the deposited boron by the clean air stream. The presence of boron was also observed in LSCF cathodes by SIMS analysis, however the effect of boron on the electrochemical performance of LSCF cathode was negligible. Coverage of triple phase boundaries in LSM/YSZ was postulated as the cause for the observed reduction in electrochemical performance.

Zhou, Xiao Dong; Templeton, Jared W.; Zhu, Zihua; Chou, Y. S.; Maupin, Gary D.; Lu, Zigui; Brow, R. K.; Stevenson, Jeffry W.

2010-09-02

123

Life testing of LSM-YSZ composite electrodes under reversing-current operation.  

PubMed

Durability testing of solid oxide cell electrodes in reversing-current and constant-current operation modes is presented. (La0.8Sr0.2)0.98MnO3-?-Zr0.84Y0.16O2-? (LSM-YSZ) symmetric cells were tested at 800 °C in air with current densities of 0.5 and 1.5 A cm(-2), with current cycle periods of 1 and 12 h. A continuous increase in both ohmic and polarization resistance was observed, via Electrochemical Impedance Spectroscopy (EIS), for cells tested with a reversing current of 1.5 A cm(-2), whereas cells tested at 0.5 A cm(-2) showed no measurable resistance increase. The resistance degradation was explained by delamination in the electrode, observed by post-test Scanning Electron Microscopy (SEM), near the interface with the electrolyte for the 1.5 A cm(-2) cells, but not for those tested at 0.5 A cm(-2). Current cycle period also impacted the degradation observed at 1.5 A cm(-2): both the rate of resistance increase and the extent of post-test delamination decreased on going from constant current mode to a 12 h period to a 1 h period. The results indicate that lower current densities and reversing-current operation are desirable to maximize the lifetime of solid oxide cells. PMID:24019111

Hughes, Gareth A; Yakal-Kremski, Kyle; Barnett, Scott A

2013-09-25

124

Stiff-person syndrome  

Microsoft Academic Search

Opinion statement  Stiff-person syndrome (SPS) is a progressive neurologic disorder characterized by 1) stiffness that is prominent in axial\\u000a muscles, with co-contraction of agonist and antagonist muscles; 2) sudden episodic spasms; and 3) absence of another disease\\u000a that causes similar symptoms. The diagnosis of SPS is based on clinical grounds and requires a high degree of suspicion. The\\u000a diagnosis is, however,

Olavo M. Vasconcelos; Marinos C. Dalakas

2003-01-01

125

Significance of central aortic stiffness in cardiovascular disease.  

PubMed

Cardiovascular health has traditionally been monitored by peripheral measurements of brachial blood pressure. Although these measurements have proven to be of good diagnostic and prognostic value, novel technology now allows us to non-invasively and easily obtain measurements of more central arteries, specifically stiffness of the central aorta. The purpose of this review is to analyze the role of central aortic stiffness in cardiovascular disease and examine the parameters of central aortic stiffness measurement in the clinical setting. PMID:19092645

Arora, Rohit; Khandpur, Ritika

126

Integrating INS sensors with GPS velocity measurements for continuous estimation of vehicle sideslip and tire cornering stiffness  

Microsoft Academic Search

This paper details a unique method for measuring key vehicle states-body sideslip angle, and tire sideslip angle-using GPS velocity information in conjunction with other sensors. A method for integrating inertial navigation system (INS) sensors with GPS measurements to provide higher update rate estimates of the vehicle states is presented. Additionally, it is shown that the tire sideslip estimates can be

David M. Bevly; Robert Sheridan; J. Christian Gerdes

2001-01-01

127

Arterial stiffness: a brief review  

PubMed Central

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

SHIRWANY, Najeeb A; ZOU, Ming-hui

2011-01-01

128

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

129

Reflectional transformation for structural stiffness  

SciTech Connect

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

Vashi, K.M.

1990-01-01

130

Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells II. Role of Ni diffusion on LSM performance  

SciTech Connect

The sintering of a standard (La0.8Sr0.2)0.98MnO3 (LSM-20) solid oxide fuel cell cathode composition (in the temperature range of 1050-1200ºC) on anode-supported cells utilizing a Ni-YSZ anode and thin YSZ electrolyte (<10 ?m thickness) has revealed the need for a protective ceria interlayer to prevent a detrimental interaction between the YSZ and the LSM. The interaction, however, is not the typically assumed formation of insulating La- and/or Sr-zirconate, but rather the result of Ni diffusion from the anode through the YSZ electrolyte and into the LSM resulting in coarsening and increased densification of the LSM microstructure. As an alternative to the use of a protective ceria interlayer, the presence of YSZ in the cathode material was able to suppress coarsening of LSM, thereby significantly improving the electrochemical performance.

Zhou, Xiao Dong; Simner, Steven P.; Templeton, Jared W.; Nie, Zimin; Stevenson, Jeffry W.; Gorman, B. P.

2010-03-26

131

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

132

Stiff reminders, and regenerating for the future: a commentary on "Man as the measure of all things".  

PubMed

Margrit Hugentobler's article, "Man as the Measure of All Things: A Limiting Approach to Urban Regeneration?," took to task the challenges of sustainable development that neither governments nor industry have yet met on the scale that is needed. From a planner's perspective, she gives a philosophical context. In essence, her message is that through thoughtful regeneration, urban environments can become more sustainable and that urban regeneration can meet a variety of human and environmental needs. She proposes a new model, using a multidisciplinary approach to urban regeneration and development. PMID:17434853

Rosskam, Ellen

2007-01-01

133

Modelling and prediction of bending stiffness for paper board manufacturing  

Microsoft Academic Search

A semi-physical auto-regressive moving average model of bending stiffness of the board produced at Assi Domän-Frövifors Bruk AB, as a function of measured control and disturbance variables, was identified. Based on the bending stiffness model, an adaptive on-line bending stiffness index predictor was implemented and found to have an RMS-error within the laboratory measurement accuracy. The predictor has been running

Per-Olof Gutman; Bengt Nilsson

1998-01-01

134

Spin-wave resonances in La0.7Sr0.3MnO3 films: Measurement of spin-wave stiffness and anisotropy field  

NASA Astrophysics Data System (ADS)

We studied magnetic-field-dependent microwave absorption in epitaxial La0.7Sr0.3MnO3 films using an 9.5GHz Bruker electron-spin-resonance spectrometer. By analyzing the angular and temperature dependence of the ferromagnetic and spin-wave resonances we determine spin-wave stiffness and perpendicular anisotropy field. The spin-wave stiffness as found from the spectrum of the standing spin-wave resonances in thin films is in fair agreement with the results of inelastic neutron scattering studies on a single crystal of the same composition [L. Vasiliu-Doloc , J. Appl. Phys. 83, 7343 (1998)].

Golosovsky, M.; Monod, P.; Muduli, P. K.; Budhani, R. C.

2007-11-01

135

Determination of absolute orientation-dependent step energies and stiffnesses from two-dimensional island shape-fluctuation and coarsening measurements  

NASA Astrophysics Data System (ADS)

We report two methods, applicable to both isotropic and anisotropic surfaces, for obtaining absolute step energies ? and step stiffnesses tilde? as a function of orientation \\varphi from scanning tunneling microscopy (STM) observations of two-dimensional (2D) island shapes. In both approaches, we use an analytical formulation of the inverse Wulff construction to obtain relative ?(\\varphi) values within an orientation-independent scale factor ?, the equilibrium island chemical potential per unit area. We determine ? using STM measurements of either temporal fluctuations around the equilibrium island shape or island decay kinetics. In the first method, we derive an expression (exact to second order in the small amplitude of the fluctuations) relating ? to the mean-square amplitude of the fluctuation modes based on (i) an expansion of the free energy functional for the fluctuating island and (ii) the generalized equipartition theorem. In the second method, we obtain ? from a detailed analysis of decay kinetics of equilibrium shaped islands based upon steady-state diffusion equations solved by adaptive finite-element methods along with a generalized form of the Gibbs-Thomson equation describing anisotropic islands. We have used both approaches to obtain absolute values of ?(\\varphi) and tilde?(\\varphi) for 2D islands on TiN(111) and TiN(001) surfaces. For the stable < 110 > steps, we obtain ? = 0.21 0.04 eV/Åwith tilde? = 1.5 0.6 eV/Åon TiN(111) and ? = 0.21 0.05 eV/Åwith tilde? = 0.9 0.2 eV/Åon TiN(001).

Khare, S. V.

2003-03-01

136

Cancer Cell Stiffness: Integrated Roles of Three-Dimensional Matrix Stiffness and Transforming Potential  

PubMed Central

While significant advances have been made toward revealing the molecular mechanisms that influence breast cancer progression, much less is known about the associated cellular mechanical properties. To this end, we use particle-tracking microrheology to investigate the interplay among intracellular mechanics, three-dimensional matrix stiffness, and transforming potential in a mammary epithelial cell (MEC) cancer progression series. We use a well-characterized model system where human-derived MCF10A MECs overexpress either ErbB2, 14-3-3?, or both ErbB2 and 14-3-3?, with empty vector as a control. Our results show that MECs possessing ErbB2 transforming potential stiffen in response to elevated matrix stiffness, whereas non-transformed MECs or those overexpressing only 14-3-3? do no exhibit this response. We further observe that overexpression of ErbB2 alone is associated with the highest degree of intracellular sensitivity to matrix stiffness, and that the effect of transforming potential on intracellular stiffness is matrix-stiffness-dependent. Moreover, our intracellular stiffness measurements parallel cell migration behavior that has been previously reported for these MEC sublines. Given the current knowledge base of breast cancer mechanobiology, these findings suggest that there may be a positive relationship among intracellular stiffness sensitivity, cell motility, and perturbed mechanotransduction in breast cancer.

Baker, Erin L.; Lu, Jing; Yu, Dihua; Bonnecaze, Roger T.; Zaman, Muhammad H.

2010-01-01

137

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

138

A real-time parametric stiffness observer for VSA devices  

Microsoft Academic Search

We consider the problem of estimating non-linear time-varying stiffness of a mechanical system based only on force and position measurements. A recent work presented a non-parametric stiffness observer, which converges to within an Uniformly Ultimately Bounded neighborhood of the real stiffness value. The method provides excellent results for applications where the system is persistently excited. In this paper, we provide

Giorgio Grioli; Antonio Bicchi

2011-01-01

139

Association between arterial stiffness and atherosclerosis: the Rotterdam Study  

Microsoft Academic Search

BACKGROUND AND PURPOSE: Studies of the association between arterial\\u000a stiffness and atherosclerosis are contradictory. We studied stiffness of\\u000a the aorta and the common carotid artery in relation to several indicators\\u000a of atherosclerosis. METHODS: This study was conducted within the Rotterdam\\u000a Study in >3000 elderly subjects aged 60 to 101 years. Aortic stiffness was\\u000a assessed by measuring carotid-femoral pulse wave velocity,

Popele van N. M-L; Diederick E. Grobbee; Michiel L. Bots; Roland Asmar; Jirar Topouchian; Robert S. Reneman; Arnold P. G. Hoeks; Kuip van der D. A; J. C. M. Witteman; A. Hofman

2001-01-01

140

Stiff person syndrome.  

PubMed

Stiff person syndrome (SPS) is a rare disorder, characterised by fluctuating rigidity and stiffness of the axial and proximal lower limb muscles, with superimposed painful spasms and continuous motor unit activity on electromyography. Although rare in general neurology practice, once observed it is unforgettable. The general neurologist may see only one or two cases during his or her career and as such it remains underdiagnosed. Left untreated, SPS symptoms can progress to cause significant disability. Patients have a poor quality of life and an excess rate of comorbidity and mortality. The severity of symptoms and lack of public awareness of the condition create anxiety and uncertainty for people with the disease. This review aims to raise awareness of SPS and to improve the likelihood of its earlier diagnosis and treatment. PMID:21921002

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

2011-10-01

141

Stiff Heart Syndrome  

PubMed Central

Isolated cardiac amyloidosis, or “Stiff Heart Syndrome,” is a rare manifestation of amyloidosis. Some degree of cardiac amyloid deposition is common in elderly patients, as reported in prior post-mortem studies; however, isolated cardiac involvement with predominantly cardiac symptoms and no evidence of systemic disease is a rare presentation. Establishing the correct diagnosis, even with the use of extensive testing including amyloid typing, understanding the clinical significance, and management can be challenging in such cases.

Bhupathi, Satya S.; Chalasani, Sreelatha; Rokey, Roxann

2011-01-01

142

Stiff heart syndrome.  

PubMed

Isolated cardiac amyloidosis, or "Stiff Heart Syndrome," is a rare manifestation of amyloidosis. Some degree of cardiac amyloid deposition is common in elderly patients, as reported in prior post-mortem studies; however, isolated cardiac involvement with predominantly cardiac symptoms and no evidence of systemic disease is a rare presentation. Establishing the correct diagnosis, even with the use of extensive testing including amyloid typing, understanding the clinical significance, and management can be challenging in such cases. PMID:20852084

Bhupathi, Satya S; Chalasani, Sreelatha; Rokey, Roxann

2010-09-17

143

Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells II. Role of Ni diffusion on LSM performance  

Microsoft Academic Search

The sintering of a standard (La0.8Sr0.2)0.98MnO3 (LSM-20) solid oxide fuel cell cathode composition (in the temperature range of 1050-1200ºC) on anode-supported cells utilizing a Ni-YSZ anode and thin YSZ electrolyte (<10 m thickness) has revealed the need for a protective ceria interlayer to prevent a detrimental interaction between the YSZ and the LSM. The interaction, however, is not the typically

Xiao Dong Zhou; Steven P. Simner; Jared W. Templeton; Zimin Nie; Jeffry W. Stevenson; B. P. Gorman

2010-01-01

144

Initial results from FRC (Field-Reversed Configuration) compression experiments on FRX-C\\/LSM  

Microsoft Academic Search

After more than two years of preparation, high-power FRC compression heating studies are now underway on the Los Alamos FRX-C\\/LSM facility. Field-reversed configuration plasmas are formed and translated out of the theta-pinch source, and into a compressor where the external B-field can be increased from 0.4 to 2 T in 55 microseconds. A principal experimental goal is to study FRC

D. J. Rej; G. A. Barnes; M. H. Baron; R. E. Chrien; R. E. Siemon; J. T. Slough; D. P. Taggart; T. Takahashi; M. Tuszewski; B. L. Wright; WA Bellevue

1989-01-01

145

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

146

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

147

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

PubMed Central

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

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

2013-01-01

148

Stiffness discrimination with visual and proprioceptive cues  

Microsoft Academic Search

This study compares the Weber fraction for human perception of stiffness among three conditions: vision, proprioceptive motion feedback, and their combination. To make comparisons between these feedback conditions, a novel haptic device was designed that senses the spring behavior through encoder and force measure- ments, and implements a controller to render linear virtual springs so that the stimuli displayed haptically

Netta Gurari; Katherine J. Kuchenbecker; Allison M. Okamura

2009-01-01

149

Changes in Aortic Stiffness and Augmentation Index After Acute Converting Enzyme or Vasopeptidase Inhibition  

Microsoft Academic Search

Augmentation index (AI), a measure of enhanced wave reflection, has been proposed as a bedside measure of aortic stiffness. However, because AI is potentially sensitive to various factors other than vessel wall stiffness, the utility of AI as a stiffness indicator may be limited. To assess relations between AI and vascular properties, we used arterial tonometry and aortic Doppler flow

Gary F. Mitchell; Yves Lacourciere; J. Malcolm; Mark E. Dunlap; Paul R. Conlin; Joseph L. Izzo

2010-01-01

150

Monitoring the Bending Stiffness of DNA  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

151

Biaxial strain and variable stiffness in aponeuroses  

PubMed Central

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

Azizi, Emanuel; Roberts, Thomas J

2009-01-01

152

Posttraumatic Stiffness in the Hand  

Microsoft Academic Search

Maximalization of motion after healing is a primary goal of treatment when the surgeon is presented with a hand injury. The contribution of muscle\\/tendon, capsule and ligament, and the joint surface to the problem of posttrau- matic stiffness is reviewed. Treatment possibil- ities for posttraumatic stiffness are presented and the importance of remobilization to the outcome of the care delivered

Matthew D. Putnam

1996-01-01

153

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

SciTech Connect

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

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

2009-01-05

154

Sensitivity evaluation of wind fields in surface layer by PBL and LSM parameterizations using WRF over the Korean Peninsula  

NASA Astrophysics Data System (ADS)

Sensitivity experiments of WRF model using different planetary boundary layer (PBL) and land surface model (LSM) parameterizations are evaluated for prediction of wind fields within the surface layer. The experiments were performed with two PBL schemes (YSU, MYJ) in combination with two land surface models (Noah, RUC), and Pleim (ACM2 : PBL) in combination with Pleim (LSM). The WRF model was conducted on a nested grid from 27-km to 1-km horizontal resolution for four domains. We improved bottom boundary conditions such as land-use and topography which are changed from 1km USGS topography and Land-use data to 100 m SRTM and 30m Land-Sat data. The simulations validated wind speed and direction at 10 m and 80 m above ground level at a 1-km spatial resolution over the South Korea during January 2008. Statistical verification results indicate that Pleim and YSU PBL schemes are in good agreement with observed wind at 10 m above ground level, while MYJ scheme produced predictions similar to the observed wind speed at 80 m above ground level. LSM comparisons indicate that the RUC model performs best in predicting 10 m and 80 m wind speed. It is found that MYJ (PBL) _ RUC (LSM) simulations yielded the best results for wind field in the surface layer. More detailed results will be shown. The choice of PBL and LSM parameterization will contribute to more accurate wind predictions for air quality studies and wind power using WRF.

Seo, B.; Byon, J.; Choi, Y.

2010-12-01

155

A Micro-Scale Model for Oxygen Reduction on LSM-YSZ Cathode  

SciTech Connect

In this study, a micro-scale model is developed to simulate the oxygen reduction on LSM-YSZ composite cathode. The model incorporates the effects of cathode microstructural properties on the local transport phenomena and electrochemistry inside the cathode. A detailed reaction mechanism is used in the model which has two parallel routes for oxygen conversion into oxide ions, namely two-phase boundary and three-phase boundary pathways. The model predicts field distributions of local thermodynamic values, over-potential, Faradaic current and other parameters relevant to cathode performance. Electrochemical impedance simulations are performed using the current model to analyze the contribution of various processes to the overall impedance.

Pakalapati, Suryanarayana Raju; Celik, Ismail; Finklea, Harry; Gong, Mingyang; Liu, Xingbo

2011-05-01

156

Distributed Application of the Unified Noah LSM with Hydrologic Flow Routing on an Appalachian Headwater Basin  

NASA Astrophysics Data System (ADS)

Collaboration between scientists at UMBC-GEST and NASA-GSFC, the NCAR Research Applications Laboratory (RAL), and Baron Advanced Meteorological Services (BAMS), has produced a modeling framework for the application of traditional land surface models (LSMs) in a distributed hydrologic system which can be used for diagnosis and prediction of routed stream discharge hydrographs. This collaboration is oriented on near-term system implementation across Romania for flood and flash-flood analyses and forecasting as part of the World Bank-funded Destructive Waters Abatement (DESWAT) program. Meteorological forcing from surface observations, model analyses and numerical forecasts are employed in the NASA-GSFC Land Information System (LIS) to drive the Unified Noah LSM with Noah-Distributed components, stream network delineation and routing schemes original to this work. The Unified Noah LSM is the outgrowth of a joint modeling effort between several research partners including NCAR, the NOAA National Center for Environmental Prediction (NCEP), and the Air Force Weather Agency (AFWA). At NCAR, hydrologically-oriented extensions to the Noah LSM have been developed for LSM applications in a distributed domain in order to address the lateral redistribution of soil moisture by surface and subsurface flow processes. These advancements have been integrated into the NASA-GSFC Land Information System (LIS) and coupled with an original framework for hydraulic channel network definition and specification, linkages with the Noah-Distributed overland and subsurface flow framework, and distributed cell- to-cell (or link-node) hydraulic routing. This poster presents an overview of the system components and their organization, as well as results of the first U.S. case study performed with this system under various configurations. The case study simulated precipitation events over a headwater basin in the southern Appalachian Mountains in October 2005 following the landfall of Tropical Storm Tammy in South Carolina. These events followed on a long dry period in the region, lending to the demonstration of watershed response to strong precipitation forcing under nearly ideal and easily-specified initial conditions. The results presented here will compare simulated versus observed streamflow conditions at various locations in the test watershed using a selection of routing methods.

Garcia, M.; Kumar, S.; Gochis, D.; Yates, D.; McHenry, J.; Burnet, T.; Coats, C.; Condrey, J.

2006-05-01

157

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

158

Vascular Smooth Muscle Cell Stiffness as a Mechanism for Increased Aortic Stiffness with Aging  

PubMed Central

Rationale Increased aortic stiffness, an important feature of many vascular diseases, e.g., aging, hypertension, atherosclerosis and aortic aneurysms, is assumed due to changes in extracellular matrix (ECM). Objective We tested the hypothesis that the mechanisms also involve intrinsic stiffening of vascular smooth muscle cells (VSMCs). Methods and Results Stiffness was measured in vitro both by atomic force microscopy (AFM) and in a reconstituted tissue model, using VSMCs from aorta of young versus old male monkeys (Macaca fascicularis, n=7/group), where aortic stiffness increases by 200 % in vivo. The apparent elastic modulus was increased (P<0.05) in old VSMCs (41.7±0.5 kPa) versus young (12.8±0.3 kPa), but not after disassembly of the actin cytoskeleton with cytochalasin D. Stiffness of the VSMCs in the reconstituted tissue model was also higher (P<0.05) in old (23.3±3.0 kPa) than in young (13.7±2.4 kPa). Conclusions These data support the novel concept, not appreciated previously, that increased vascular stiffness with aging is due not only to changes in ECM, but also to intrinsic changes in VSMCs.

Qiu, Hongyu; Zhu, Yi; Sun, Zhe; Trzeciakowski, Jerome P.; Gansner, Meredith; Depre, Christophe; Resuello, Ranillo R.G.; Natividad, Filipinas F.; Hunter, William C.; Genin, Guy M.; Elson, Elliot L.; Vatner, Dorothy E.; Meininger, Gerald A.; Vatner, Stephen F.

2010-01-01

159

Maps and models of density and stiffness within individual Douglas ...  

Treesearch

... measured wood properties of veneer sheets; and (2) mixed effects models, to test ... tree variables (height, taper, breast-height diameter, and acoustic velocity). ... normally distributed, while stiffness tended to have moderate negative skew.

160

"Contact" of nanoscale stiff films.  

PubMed

We investigated the contact behaviors of a nanoscopic stiff thin film bonded to a compliant substrate and derived an analytical solution for determining the elastic modulus of thin films. Microscopic contact deformations of the gold and polydopamine thin films (<200 nm) coated on polydimethylsiloxane elastomers were measured by indenting a soft tip and analyzed in the framework of the classical plate theory and Johnson-Kendall-Roberts (JKR) contact mechanics. The analysis of this thin film contact mechanics focused on the bending and stretching resistance of thin films and is fundamentally different from conventional indentation measurements where the focus is on the fracture and compression of the films. The analytical solution of the elastic modulus of nanoscopic thin films was validated experimentally using 50 and 100 nm gold thin films coated on polydimethylsiloxane elastomers. The technical application of this analysis was further demonstrated by measuring the elastic modulus of thin films of polydopamine, a recently discovered biomimetic universal coating material. Furthermore, the method presented here is able to quantify the contact behaviors of nanoscopic thin films, effectively providing fundamental design parameters, the elastic modulus, and the work of adhesion, crucial for transferring them effectively into practical applications. PMID:22616836

Yang, Fut K; Zhang, Wei; Han, Yougun; Yoffe, Serge; Cho, Yungchi; Zhao, Boxin

2012-05-31

161

Various local stiffness characterizations of single cells using buckling nanoneedles  

Microsoft Academic Search

We performed in-situ measurements of mechanical properties of individual W303 wild-type yeast cells by using a soft nanoneedle inside an integrated environmental scanning electron microscope (ESEM) - nanomanipulator system. Two different spring constants of soft nanoneedles which can buckle from certain applied compression force were used to measure a general local stiffness, i.e. stiffness property of the whole cell from

Mohd Ridzuan Ahmad; Masahiro Nakajima; S. Kojima; M. Homma; T. Fukuda

2009-01-01

162

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

NASA Astrophysics Data System (ADS)

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

Pugachev, A. O.; Deckner, M.

2012-08-01

163

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

164

Flexural and torsional stiffness in multi-jointed biological beams.  

PubMed

Flexibility, the ability to deform in response to loads, is a common property of biological beams. This paper investigates the mechanical behavior of multi-jointed beams, which are characterized by a linear series of morphologically similar joints. Flexural stiffness and torsional stiffness were measured in two structurally distinct beams, crinoid arms (Echinodermata, Comatulida) and crustacean antennae (Arthropoda, Decapoda). Morphological data from these beams were used to determine the relative contributions of beam diameter and joint density (number of joints per millimeter of beam length) to the flexural and torsional stiffness of these two structures. As predicted by beam theory, beam diameter influenced stiffness in both crinoid arms and crustacean antennae. In crinoid arms, increases in joint density were associated with decreases in stiffness, but joint density had no significant influence on stiffness in crustacean antennae. In both crinoid arms and crustacean antennae, the magnitudes of flexural and torsional stiffness, as well as the ratio of these two variables, were similar to previously reported values for non-jointed biological beams. These results suggest that the structural design of a biological beam is not a limiting factor determining its mechanical properties. PMID:11249208

Etnier, S A

2001-02-01

165

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

2013-03-20

166

A review of models of vertical, leg, and knee stiffness in adults for running, jumping or hopping tasks.  

PubMed

The 'stiffness' concept originates from Hooke's law which states that the force required to deform an object is related to a spring constant and the distance that object is deformed. Research into stiffness in the human body is undergoing unprecedented popularity; possibly because stiffness has been associated with sporting performance and some lower limb injuries. However, some inconsistencies surrounding stiffness measurement exists bringing into question the integrity of some research related to stiffness. The aim of this study was to review literature which describes how vertical, leg and knee stiffness has been measured in adult populations while running, jumping or hopping. A search of the entire MEDLINE, PubMed and SPORTDiscus databases and an iterative reference check was performed. Sixty-seven articles were retrieved; 21 measured vertical stiffness, 51 measured leg stiffness, and 22 measured knee stiffness. Thus, some studies measured several 'types' of stiffness. Vertical stiffness was typically the quotient of ground reaction force and centre of mass displacement. For leg stiffness it was and change in leg length, and for the knee it was the quotient of knee joint moments and change in joint angle. Sample size issues and measurement techniques were identified as limitations to current research. PMID:22845059

Serpell, Benjamin G; Ball, Nick B; Scarvell, Jennie M; Smith, Paul N

2012-07-30

167

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

PubMed Central

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

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

2006-01-01

168

A position and stiffness control strategy for variable stiffness actuators  

Microsoft Academic Search

Variable stiffness actuators (VSAs) have been introduced to improve, at the design level, the safety and the energy efficiency of the new generation of robots that have to interact closely with humans. A wide variety of design solutions have recently been proposed, and a common factor in most of the VSAs is the introduction of a flexible transmission with varying

I. Sardellitti; G. Medrano-Cerda; N. G. Tsagarakis; A. Jafari; D. G. Caldwell

2012-01-01

169

Muscle Stiffness and Spinal Stretch Reflex Sensitivity in the Triceps Surae  

PubMed Central

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

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

2008-01-01

170

Smart variable stiffness control systems  

NASA Astrophysics Data System (ADS)

This paper presents a new and innovative semi-active variable stiffness tuned mass damper (SAIVS-TMD). The system has the distinct advantage of retuning in real time thus making the system robust to changes in building stiffness and damping, whereas the passive tuned mass damper (TMD) can only be tuned to a fixed frequency. The SAIVS-TMD is based on a novel semi-active variable stiffness control (SAIVS) device. SAIVS system requires nominal power for operation as compared to active tuned mass dampers. The SAIVS-TMD is retuned using a new control algorithm based on instantaneous frequency estimation using Hilbert transform and short-time Fourier transform (STFT). An analytical model of a three-story structure with SAIVS-TMD is developed. Numerical simulations are performed using the analytical model. The system is implemented in a 1:10 scale three-story scale model in real time using a digital signal processing system and controller. Shake table test results of the system with the SAIVS-TMD are presented. It is shown that the SAIVS-TMD is very effective in reducing the response and providing retuning capability when the building stiffness changes, whereas the TMD is mistuned and loses its effectiveness. Analytical modeling and comparisons between analytical and experimental results are also presented.

Nagarajaiah, Satish; Varadarajan, Nadathur

2001-07-01

171

Stiffness dependent separation of cells in a microfluidic device.  

PubMed

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

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

2013-10-16

172

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

173

Aortic stiffness and distensibility among hypertensives.  

PubMed

Hypertension is one among many factors that contribute to aortic stiffness, which has repercussions mainly on the heart. To assess aortic stiffness among essential hypertensives of South India and its relationship with gender. An analytical study was designed to assess aortic stiffness among 60 nonobese, nonalcoholic, nonsmoking, and non-caffeine consuming essential hypertensives without any overt illness or infection, and compared with 30 healthy age- and sex-matched nonhypertensives. They were assessed clinically and also by laboratory means. Their left ventricular mass (LV) and left ventricular ejection fraction (LVEF) were measured using Transthoracic echocardiogram. Aortic systolic and diastolic diameters were measured by using M-mode echocardiography during consecutive beats and averaged for each case. Finally, aortic stiffness was calculated. The data were analyzed statistically. Hypertensives were divided into Group I, consisting of patients with hypertension at least for 5 years, who were not adherent to medication, and Group II, consisting of patients with hypertension of duration between 6 months and 1 year. There were 20 males and 10 females in each group. There was no significant difference between the hypertensive groups and a control, normotensive, group with regard to BMI or total cholesterol. The means of LV mass (in grams), systolic BP (in mmHg), diastolic BP (in mmHg), aortic systolic diameter (in mm), aortic diastolic diameter (in mm), aortic distensibility (in mm), and aortic stiffness found in Group I, Group II, and controls were 105.8 +/- 23.8, 101.5 +/- 21, and 84 +/- 9.8; 138 +/- 14.2, 153 +/- 17.1, and 120 +/- 8.3; 90.5 +/- 11.6, 101.7 +/- 17.1, and 76.5 +/- 5; 30.85 +/- 2.6, 28.7 +/- 2.6, and 27.7 +/- 2.4; 28.7 +/- 2.2, 25.8 +/- 2.5, and 24.2 +/- 2.5; 2.14 +/- 0.3, 2.84 +/- 0.5, and 3.5 +/- 0.6; and 1.31 +/- 0.09, 1.14 +/- 0.1, and 1.04 +/- 0.08, respectively. The differences between the hypertensive groups and the control group were significant. Aortic stiffness was greater in hypertensives and it was independent of gender, but increased with duration of hypertension. Hypertension has effects on the aorta (decreased aortic distensibility and increased aortic stiffness) and left ventricle (increased left ventricular mass and left ventricular hypertrophy). These changes can be identified and monitored while the patient is on antihypertensive therapy along with life-style modifications, as these are reversible. Nevertheless, these aspects do not receive due attention in medical education and training on hypertension. PMID:19751418

Meenakshisundaram, R; Kamaraj, K; Murugan, S; Thirumalaikolundusubramanian, P

2009-09-01

174

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

175

Electrical properties and oxygen diffusion in yttria-stabilised zirconia (YSZ)–La 0.8Sr 0.2MnO 3± ? (LSM) composites  

Microsoft Academic Search

Dense YSZ–LSM composites were fabricated for application as an oxygen separation membrane. A density about 95% was achieved for a sintering temperature of 1350 °C; however, an insulating La2Zr2O7 phase was formed during this high-temperature sintering. The percolation threshold was identified at about 30 wt.% (or 28 vol.%) of LSM. Isotopic exchange depth profiling (IEPD)\\/secondary ion mass spectrometry (SIMS) method

Y. Ji; J. A. Kilner; M. F. Carolan

2005-01-01

176

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

177

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

178

Aortic root dimensions and stiffness in healthy subjects.  

PubMed

The aim of the present study was to investigate the full range of aortic root diameters and stiffness in a group of subjects without known cardiovascular risk factors and/or overt cardiovascular disease. Four hundred and twenty-two healthy subjects (mean age 44.35 ± 16.91 years, range 16 to 90, 284 men [67%]) underwent comprehensive transthoracic echocardiography. The leading edge method was used for the end-diastolic aortic root diameters measured at 4 locations (1) the aortic annulus, (2) the sinuses of Valsalva, (3) the sinotubular junction, and (4) the maximum diameter of the proximal ascending aorta. Aortic wall stiffness was assessed using 2-dimensional guided M-mode evaluation of systolic and diastolic aortic diameter, 3 cm above the aortic valve. The absolute aortic root diameters increased with age in both genders. Aortic measurements were significantly greater in men than in women at all levels, whereas body surface area-indexed values were similar in men and women, except for the ascending aorta for which women tended to have greater values. Multivariable regression analysis using age and body size (weight, height, and body surface area) predicted all aortic diameters, whereas blood pressure indexes predicted only the distal part of the aorta. Aortic stiffness increased with age in men and women with no differences between genders; only age predicted aortic stiffness. The increment in aortic diameter with age was lesser when adjusted for aortic stiffness. In conclusion, we define the physiologic range of aortic root diameters and related stiffness in healthy subjects stratified by age and gender. Moreover, aortic stiffness should also be taken into account when the increase of aortic diameter is considered. PMID:23871268

Vriz, Olga; Driussi, Caterina; Bettio, Manola; Ferrara, Francesco; D'Andrea, Antonello; Bossone, Eduardo

2013-07-17

179

Association of Increased Hair Calcium Levels and Enhanced Augmentation Index (AIx): a Marker of Arterial Stiffness  

Microsoft Academic Search

Arterial stiffness is involved in the pathophysiology of cardiovascular disease, and the degree of arterial stiffness is associated\\u000a with the extent of vascular calcification. This study aimed to investigate the association of hair calcium levels with augmentation\\u000a index (AIx), a simple, non-invasive measurement for arterial stiffness. Healthy Koreans (male, n?=?34, female, n?=?70) were enrolled in this study. Anthropometric parameters, lipid

Oh Yoen Kim; Seung Han Baek; Young Jin Lee; Ki Ho Lee

2010-01-01

180

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

181

[Stiff man syndrome and variants].  

PubMed

Stiff man syndrome (SMS) and its variants are rare neurological disorders with unusual, often awkward motor and psychological symptoms. Misdiagnoses are frequent and differentiation from psychogenic movement disorder may be difficult. Clinical suspicion can be substantiated by neurophysiological and immunological testing. Autoimmunity against certain proteins of inhibitory synapses appears to be a key feature that links SMS to other autoimmune encephalopathies and endocrinopathies. According to retrospective analyses a front-loaded long-term methylprednisolone treatment appears to be most effective. PMID:23568166

Meinck, H-M

2013-04-01

182

Stiff person syndrome: avoiding misdiagnosis  

Microsoft Academic Search

Stiff person syndrome (SPS) is a rare neurological disorder characterised by muscular rigidity and superimposed spasms of\\u000a the trunk and limbs that may be precipitated by voluntary movements and unexpected tactile, auditory or emotional stimulation.\\u000a The high prevalence of autoantibodies against glutamic acid decarboxylase (antiGAD) in both serum and cerebrospinal fluid,\\u000a as well as the frequent association of SPS with

E. Andreadou; E. Kattoulas; C. Sfagos; D. Vassilopoulos

2007-01-01

183

Effect of Surface Stress on the Stiffness of Cantilever Plates  

NASA Astrophysics Data System (ADS)

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

Lachut, Michael J.; Sader, John E.

2007-11-01

184

Online Red Blood Cell Stiffness Evaluation System by Utilizing a High Speed Vision and Micro Channel  

NASA Astrophysics Data System (ADS)

This paper challenges online stiffness evaluation of red blood cell (RBC) by using both a micro channel and a high speed vision system. When a RBC passes through a micro channel, the passing time mainly depends upon its stiffness, diamter, and the pressure difference between the input and output ports of the channel. In other words, the stiffness of cell can be evaluated by measuring these three parameters. With the assistance of high speed vision system, we succeded in evaluating the stiffness of RBC with less than 5[msec/cell]. The biggest advantage for utilizing a high speed vision is that we can know exactly what is actually happening in the channel, while it is really hard for other approaches. We also introduced the stiffness evaluation map, by which we can compare the stiffness of RBCs of patients with those of healthy persons.

Hirose, Yuki; Fukui, Wataru; Higashimori, Mitsuru; Tadakuma, Kenjiro; Kaneko, Makoto; Arai, Tatsuo; Sakata, Yasushi; Yamamoto, Kazuhiro; Kawahara, Tomohiro; Yamanishi, Yoko; Arai, Fumihito

185

Nonlinear myofilament regulatory processes affect frequency-dependent muscle fiber stiffness.  

PubMed Central

To investigate the role of nonlinear myofilament regulatory processes in sarcomeric mechanodynamics, a model of myofilament kinetic processes, including thin filament on-off kinetics and crossbridge cycling kinetics with interactions within and between kinetic processes, was built to predict sarcomeric stiffness dynamics. Linear decomposition of this highly nonlinear model resulted in the identification of distinct contributions by kinetics of recruitment and by kinetics of distortion to the complex stiffness of the sarcomere. Further, it was established that nonlinear kinetic processes, such as those associated with cooperative neighbor interactions or length-dependent crossbridge attachment, contributed unique features to the stiffness spectrum through their effect on recruitment. Myofilament model-derived sarcomeric stiffness reproduces experimentally measured sarcomeric stiffness with remarkable fidelity. Consequently, characteristic features of the experimentally determined stiffness spectrum become interpretable in terms of the underlying contractile mechanisms that are responsible for specific dynamic behaviors.

Campbell, K B; Razumova, M V; Kirkpatrick, R D; Slinker, B K

2001-01-01

186

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

SciTech Connect

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

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

1985-01-01

187

Enhanced Stiffness Modeling, Identification and Characterization for Robot Manipulators  

Microsoft Academic Search

This paper presents the enhanced stiffness modeling and analysis of robot manipulators, and a methodology for their stiffness identification and characterization. Assuming that the manipulator links are infinitely stiff, the enhanced stiffness model contains: 1) the passive and active stiffness of the joints and 2) the active stiffness created by the change in the manipulator configuration, and by external force

Gürsel Alici; Bijan Shirinzadeh

2005-01-01

188

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

189

A tunable high-static-low-dynamic stiffness vibration isolator  

NASA Astrophysics Data System (ADS)

In this study, a novel vibration isolator is developed. The developed isolator possesses the characteristics of high-static-low-dynamic stiffness (HSLDS) and can act passively or semi-actively. The HSLDS property of the isolator is obtained by connecting a mechanical spring, in parallel with a magnetic spring that is constructed by a pair of electromagnets and a permanent magnet. The mechanical spring is a structural beam whose stiffness exhibits a hardening behavior. The stiffness of the magnetic spring can be positive or negative, depending on the polarity of the current to the electromagnets. A passive HSLDS isolator is obtained when the electromagnet current is zero. In the stiffness characterization study, the analytical model for each of the springs is established and the tuning parameters are identified. Using the stiffness models, the design optimization issues are investigated. In the experimental study, the effectiveness of the isolator for vibration isolation is tested. The analytical natural frequencies of the isolator are validated experimentally. The relationships between the displacement transmissibility and the exciting frequency are measured both under the passive mode and under the semi-active mode. The on-line tuning capability of the isolator is investigated.

Zhou, N.; Liu, K.

2010-04-01

190

Position control of seat suspension with minimum stiffness  

NASA Astrophysics Data System (ADS)

Quality of vibration isolation of vehicle drivers in the infra-narrow band is the most essential and simultaneously is a hard-hitting goal. Use of the “negative” stiffness’ phenomenon is a unique concept to minimize stiffness of a vibration isolating device and improve the quality so that protected object becomes motionless in inertial space. Though control strategy for the device with minimum stiffness sufficiently differs from the approaches based on attenuation of extraneous resonant responses. An approach for positioning such a device is proposed focusing on motion stability in large. In the approach, a model of the device is structured to generate the control criteria in operating immanently unstable mechanism of “negative” stiffness. A control algorithm effecting variability of the device stiffness in terms of the position and velocity data evaluation is considered. The object protected is motionless under the vibration and motion becomes shock-free under non-vibrational excitation even if there is no external damper. The validity of the approach is assessed by numerical experiment and physical measurement for an actual seat pneumatic suspension restructured via the mechanism and controlled by the program.

Lee, C.-M.; Bogatchenkov, A. H.; Goverdovskiy, V. N.; Shynkarenko, Y. V.; Temnikov, A. I.

2006-04-01

191

A Stiffness Switch in Human Immunodeficiency Virus  

PubMed Central

After budding from the cell, human immunodeficiency virus (HIV) and other retrovirus particles undergo a maturation process that is required for their infectivity. During maturation, HIV particles undergo a significant internal morphological reorganization, changing from a roughly spherically symmetric immature particle with a thick protein shell to a mature particle with a thin protein shell and conical core. However, the physical principles underlying viral particle production, maturation, and entry into cells remain poorly understood. Here, using nanoindentation experiments conducted by an atomic force microscope (AFM), we report the mechanical measurements of HIV particles. We find that immature particles are more than 14-fold stiffer than mature particles and that this large difference is primarily mediated by the HIV envelope cytoplasmic tail domain. Finite element simulation shows that for immature virions the average Young's modulus drops more than eightfold when the cytoplasmic tail domain is deleted (930 vs. 115 MPa). We also find a striking correlation between the softening of viruses during maturation and their ability to enter cells, providing the first evidence, to our knowledge, for a prominent role for virus mechanical properties in the infection process. These results show that HIV regulates its mechanical properties at different stages of its life cycle (i.e., stiff during viral budding versus soft during entry) and that this regulation may be important for efficient infectivity. Our report of this maturation-induced “stiffness switch” in HIV establishes the groundwork for mechanistic studies of how retroviral particles can regulate their mechanical properties to affect biological function.

Kol, Nitzan; Shi, Yu; Tsvitov, Marianna; Barlam, David; Shneck, Roni Z.; Kay, Michael S.; Rousso, Itay

2007-01-01

192

Resistance to Acute Insulin Induced Decreases in Large Artery Stiffness Accompanies the Insulin Resistance Syndrome  

Microsoft Academic Search

Arterial stiffness has recently been recognized as an impor- tant cardiovascular risk marker. Physiological concentra- tions of insulin diminish wave reflection in the aorta in vivo. This decreases central blood pressure augmentation and aug- mentation divided by pulse pressure (the augmentation index (AgI)), a measure of arterial stiffness. In the present study, we examined whether a defect in this action

JUKKA WESTERBACKA; ANNELI SEPPALA; HANNELE YKI-JARVINEN

193

Increased left atrial chamber stiffness in hypertrophic cardiomyopathy.  

PubMed Central

OBJECTIVE--To investigate left atrial chamber stiffness and its influence on left atrial and left ventricular functions in hypertrophic cardiomyopathy. DESIGN--Prospective study. SETTING--Department of internal medicine in a university teaching hospital. PATIENTS--Five control subjects, six patients with essential hypertension, and 11 patients with hypertrophic cardiomyopathy. INTERVENTIONS--Measurement of left atrial pressure by a tip micromanometer and of real-time left atrial volume from left atrial cineangiograms. MAIN OUTCOME MEASURE--Left atrial stiffness constant determined by fitting the ascending limb of the v loop of the left atrial pressure-volume relation to an exponential curve. RESULTS--The mean (SD) left atrial chamber stiffness constant was significantly larger in patients with hypertrophic cardiomyopathy than in controls (0.063 (0.018) v 0.041 (0.006), p < 0.05) and was correlated with left ventricular wall thickness (r = 0.560, p < 0.01). Left atrial reservoir volume (left atrial emptying volume before atrial contraction) was significantly smaller in patients with hypertrophic cardiomyopathy than in the controls (7.3 (2.1) v 12.5 (4.4) ml/m2, p < 0.01) and was inversely correlated with the left atrial chamber stiffness constant (r = -0.598, p < 0.01). The cardiac index was inversely correlated with the left atrial chamber stiffness constant (r = -0.542, p < 0.01). CONCLUSIONS--Left atrial chamber stiffness was increased in patients with hypertrophic cardiomyopathy and this affected the left atrial reservoir function. This may in turn have affected cardiac output.

Sanada, H; Shimizu, M; Sugihara, N; Shimizu, K; Ino, H; Takeda, R

1993-01-01

194

Quantitative determination of contact stiffness using atomic force acoustic microscopy  

Microsoft Academic Search

Atomic force acoustic microscopy is a near-field technique which combines the ability of ultrasonics to image elastic properties with the high lateral resolution of scanning probe microscopes. We present a technique to measure the contact stiffness and the Young's modulus of sample surfaces quantitatively, with a resolution of approximately 20nm, exploiting the contact resonance frequencies of standard cantilevers used in

U. Rabe; S. Amelio; E. Kester; V. Scherer; S. Hirsekorn; W. Arnold

2000-01-01

195

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

196

Stiffness Simulation Using Non-linear FEA  

SciTech Connect

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

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

2005-08-05

197

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

198

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

Microsoft Academic Search

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

C. E. English; D. Russell

1999-01-01

199

Variable stiffness composite panels: Effects of stiffness variation on the in-plane and buckling response  

Microsoft Academic Search

Descriptions of fiber orientation variation for flat rectangular composite laminates that possess variable stiffness properties are introduced. The simplest definition employs a unidirectional variation based on a linear function for the fiber orientation angle of the individual layers. Analyses of variable stiffness panels for in-plane and buckling responses are developed and demonstrated for two distinct cases of stiffness variations. The

Z. Gürdal; B. F. Tatting; C. K. Wu

2008-01-01

200

How design can affect the energy required to regulate the stiffness in variable stiffness actuators  

Microsoft Academic Search

Variable stiffness actuators have been developed based on different design solutions which can be arranged into two groups: antagonistic and series design. In both the cases two actuation units are combined with passive elastic elements to adjust both the stiffness and the equilibrium position of the actuated joint. To regulate the stiffness, mechanical work is required to be done which

Amir Jafari; Nikos G. Tsagarakis; Irene Sardellitti; Darwin G. Caldwell

2012-01-01

201

Novel method to evaluate angular stiffness of prosthetic feet from linear compression tests.  

PubMed

Lower limb amputee gait during stance phase is related to the angular stiffness of the prosthetic foot, which describes the dependence of ankle torque on angular progression of the shank. However, there is little data on angular stiffness of prosthetic feet, and no method to directly measure it has been described. The objective of this study was to derive and evaluate a method to estimate the angular stiffness of prosthetic feet using a simple linear compression test. Linear vertical compression tests were performed on nine configurations of an experimental multicomponent foot (with known component stiffness properties and geometry), which allowed for parametric adjustment of hindfoot and forefoot stiffness properties and geometries. Each configuration was loaded under displacement control at distinct pylon test angles. Angular stiffness was calculated as a function of the pylon angle, normal force, and center of pressure (COP) rate of change with respect to linear displacement. Population root mean square error (RMSE) between the measured and predicted angular stiffness values for each configuration of the multicomponent foot was calculated to be 4.1?N-m/deg, dominated by a bias of the estimated values above the predicted values of 3.8?±?1.6?N-m/deg. The best-fit line to estimated values was approximately parallel to the prediction, with R2?=?0.95. This method should be accessible for a variety of laboratories to estimate angular stiffness of experimental and commercially available prosthetic feet with minimal equipment. PMID:23897236

Adamczyk, Peter G; Roland, Michelle; Hahn, Michael E

2013-10-01

202

Stiffness and hysteresis properties of some prosthetic feet.  

PubMed

A prosthetic foot is an important element of a prosthesis, although it is not always fully recognized that the properties of the foot, along with the prosthetic knee joint and the socket, are in part responsible for the stability and metabolic energy cost during walking. The stiffness and the hysteresis, which are the topics of this paper, are not properly prescribed, but could be adapted to improve the prosthetic walking performance. The shape is strongly related to the cosmetic appearance and so can not be altered to effect these improvements. Because detailed comparable data on foot stiffness and hysteresis, which are necessary to quantify the differences between different types of feet, are absent in literature, these properties were measured by the authors in a laboratory setup for nine different prosthetic feet, bare and with two different shoes. One test cycle consisted of measurements of load deformation curves in 66 positions, representing the range from heel strike to toe-off. The hysteresis is defined by the energy loss as a part of the total deformation energy. Without shoes significant differences in hysteresis between the feet exist, while with sport shoes the differences in hysteresis between the feet vanish for the most part. Applying a leather shoe leads to an increase of hysteresis loss for all tested feet. The stiffness turned out to be non-constant, so mean stiffness is used.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2095529

van Jaarsveld, H W; Grootenboer, H J; de Vries, J; Koopman, H F

1990-12-01

203

Stiffness of hair bundles in the chick cochlea.  

PubMed

The stiffness of hair bundles from isolated chick cochlear hair cells was measured in tissue culture medium. A water jet was used to deflect fiberglass fibers, quartz fibers, and hair bundles of isolated hair cells. A voltage-displacement curve was generated for a water jet ramp stimulus applied to miniature fiberglass and quartz fibers. Fiber displacements were measured using video image subtraction techniques. A force-voltage calibration curve was then derived for the fibers by modelling them as cantilever beams subjected to point forces at the tips. A voltage-displacement curve was then generated for isolated hair cell stereociliary bundles using the same procedure as for the fibers. A corresponding force-displacement curve was derived for isolated hair cells under water jet stimulation by correlating maximum ramp voltage from the hair cell's voltage-displacement curve to a corresponding force applied to a fiber from the fiberglass fiber calibration curve. The stiffness of the hair bundle, which is the slope of the hair cell's force-displacement curve, was then calculated using Hooke's law, assuming the force was distributed along the entire length of the hair bundle. The mean stiffness value was 5.04 +/- 2.68 x 10(-4) N/m for 14 hair cells, and was in close agreement with previously reported stiffness values of several investigators utilizing different animal models and procedures. PMID:1618714

Szymko, Y M; Dimitri, P S; Saunders, J C

1992-05-01

204

Arterial Stiffness and Dialysis Calcium Concentration  

PubMed Central

Arterial stiffness is the major determinant of isolated systolic hypertension and increased pulse pressure. Aortic stiffness is also associated with increased cardiovascular morbidity and mortality in patients with chronic kidney disease, hypertension, and general population. Hemodynamically, arterial stiffness results in earlier aortic pulse wave reflection leading to increased cardiac workload and decreased myocardial perfusion. Although the clinical consequence of aortic stiffness has been clearly established, its pathophysiology in various clinical conditions still remains poorly understood. The aim of the present paper is to review the studies that have looked at the impact of dialysis calcium concentration on arterial stiffness. Overall, the results of small short-term studies suggest that higher dialysis calcium is associated with a transient but significant increase in arterial stiffness. This calcium dependant increase in arterial stiffness is potentially explained by increased vascular smooth muscle tone of the conduit arteries and is not solely explained by changes in mean blood pressure. However, the optimal DCa remains to be determined, and long term studies are required to evaluate its impact on the progression of arterial stiffness.

Mac-Way, Fabrice; Leboeuf, Amelie; Agharazii, Mohsen

2011-01-01

205

Dynamic Contact Stiffness of Adhesive Hertzian Contact  

Microsoft Academic Search

Based on the JKR and DMT models, dynamic contact stiffness of a rigid sphere against an adhesive semiinfinite solid is investigated by the consideration of dynamic contact deformation at the contact interface. The assumption of sufficiently small oscillating force yields a dynamic contact-pressure distribution of constant contact size, and then dynamic contact stiffness. It is found that except for the

Jiayong Tian

2011-01-01

206

Anesthetic Implications in Stiff-Person Syndrome  

Microsoft Academic Search

A 46-yr-old female presented to the operating room for repair of an intrathecal baclofen pump. Her diagnosis of SPS was based on clinical presentation and the presence of an autoantibody against the central nervous system enzyme glutamic acid decarboxylase (GAD). The syndrome began as muscle stiffness in her lower extremities and insidiously progressed to a state of constant stiffness resulting

Joel O. Johnson; Kirk A. Miller

1995-01-01

207

Study on Torsional Stiffness of Engine Crankshaft  

Microsoft Academic Search

Many empirical formulae are used to calculate torsional stiffness of Engine Crank, but discrepancy exists between these calculation results. In this paper, in order to obtain a more precise result, the modified Ker Wilson formula and Carter formula were employed to calculate torsional stiffness of engine crankthrow in the case of different thickness and width of both sides of crankthrows.

Zhao Guangming; Jiang Zhengfeng

2009-01-01

208

Mechanisms, Pathophysiology, and Therapy of Arterial Stiffness  

Microsoft Academic Search

Arterial stiffness is a growing epidemic associated with increased risk of cardiovascular events, dementia, and death. Decreased compliance of the central vasculature alters arterial pressure and flow dynamics and impacts cardiac performance and coronary perfusion. This article reviews the structural, cellular, and genetic contributors to arterial stiffness, including the roles of the scaffolding proteins, extracellular matrix, inflammatory molecules, endothelial cell

Susan J. Zieman; Vojtech Melenovsky; David A. Kass

2010-01-01

209

Spontaneous wrinkle branching by gradient stiffness  

NASA Astrophysics Data System (ADS)

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

Ni, Yong; Yang, Dong; He, Linghui

2012-09-01

210

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

PubMed

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

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

2012-11-29

211

Increased Arterial Stiffness Is Independently Related to Cerebrovascular Disease and Aneurysms of the Abdominal Aorta: The Second Manifestations of Arterial Disease (SMART) Study  

Microsoft Academic Search

Background—Arterial stiffness is a risk factor for stroke and myocardial infarction. We investigated whether carotid arterial stiffness is related to other localizations of manifest arterial disease. Methods—Carotid artery stiffness was measured by ultrasonography as the change in diameter in systole relative to the diastolic diameter in patients enrolled in the Second Manifestations of Arterial Disease (SMART) Study, a cohort study

J. M. Dijk; Y. van der Graaf; D. E. Grobbee; J. D. Banga; M. L. Bots

2004-01-01

212

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

213

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

PubMed

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

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

2011-12-01

214

Analysis and Design of Variable Stiffness Composite Cylinders.  

National Technical Information Service (NTIS)

An investigation of the possible performance improvements of thin circular cylindrical shells through the use of the variable stiffness concept is presented. The variable stiffness concept implies that the stiffness parameters change spatially throughout ...

B. F. Tatting Z. Guerdal

1998-01-01

215

High performance composites with active stiffness control.  

PubMed

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

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

2013-09-13

216

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

217

Evaluating enhanced hydrological representations in Noah LSM over transition zones: An ensemble-based approach to model diagnostics  

NASA Astrophysics Data System (ADS)

This work introduces diagnostic methods for land surface model (LSM) evaluation that enable developers to identify structural shortcomings in model parameterizations by evaluating model 'signatures' (characteristic temporal and spatial patterns of behavior) in feature, cost-function, and parameter spaces. The ensemble-based methods allow researchers to draw conclusions about hypotheses and model realism that are independent of parameter choice. I compare the performance and physical realism of three versions of Noah LSM (a benchmark standard version [STD], a dynamic-vegetation enhanced version [DV], and a groundwater-enabled one [GW]) in simulating high-frequency near-surface states and land-to-atmosphere fluxes in-situ and over a catchment at high-resolution in the U.S. Southern Great Plains, a transition zone between humid and arid climates. Only at more humid sites do the more conceptually realistic, hydrologically enhanced LSMs (DV and GW) ameliorate biases in the estimation of root-zone moisture change and evaporative fraction. Although the improved simulations support the hypothesis that groundwater and vegetation processes shape fluxes in transition zones, further assessment of the timing and partitioning of the energy and water cycles indicates improvements to the movement of water within the soil column are needed. Distributed STD and GW underestimate the contribution of baseflow and simulate too-flashy streamflow. This work challenges common practices and assumptions in LSM development and offers researchers more stringent model evaluation methods. I show that, because of equifinality, ad-hoc evaluation using single parameter sets provides insufficient information for choosing among competing parameterizations, for addressing hypotheses under uncertainty, or for guiding model development. Posterior distributions of physically meaningful parameters differ between models and sites, and relationships between parameters themselves change. 'Plug and play' of modules and partial calibration likely introduce error and should be re-examined. Even though LSMs are 'physically based,' model parameters are effective and scale-, site- and model-dependent. Parameters are not functions of soil or vegetation type alone: they likely depend in part on climate and cannot be assumed to be transferable between sites with similar physical characteristics. By helping bridge the gap between the model identification and model development, this research contributes to the continued improvement of our understanding and modeling of environmental processes.

Rosero Ramirez, Enrique Xavier

218

Stiffness of contacts between rough surfaces.  

PubMed

The effect of self-affine roughness on solid contact is examined with molecular dynamics and continuum calculations. The contact area and normal stiffness rise linearly with the applied load, and the load rises exponentially with decreasing separation between surfaces. Results for a wide range of roughness, system size, and Poisson ratio can be collapsed using Persson's contact theory for continuous elastic media. The compliance due to atomic-scale motion at the interface between solids has little effect on the area and normal stiffness, but can reduce the total transverse stiffness by orders of magnitude. The scaling of this effect with system size is discussed. PMID:21668231

Akarapu, Sreekanth; Sharp, Tristan; Robbins, Mark O

2011-05-20

219

Optimum loading mode for axial stiffness testing in limb lengthening.  

PubMed

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

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

2006-03-01

220

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

PubMed

With respect to cyclic movements such as human gait, running or hopping, leg stiffness is a little variable parameter. The aim of this study was to investigate changes in leg stiffness during the phase of countermovement and take-off when performing a single maximum counter-movement jump. Kistler force plates and a BTS SMART system for comprehensive motion analysis were employed in the study. The study covered a group of 12 athletes from university basketball teams. Leg stiffness was calculated in those parts of countermovement and take-off phases where its level is relatively constant and the relationship F(?l) is similar to linear one. Mean total stiffness (±SD) in both legs in the countermovement phase amounted to 6.5 ± 1.5 kN/m, whereas during the take-off phase this value was 6.9 ± 1 kN/m. No statistically significant differences were found between leg stiffness during the countermovement phase and takeoff phase in the study group at the level of significance set at ? = 0.05. This suggests that the leg stiffness in phase of countermovement and phase of take-off are much similar to each other, despite different function of both phases. Similar to cyclic movements, leg stiffness turned out relatively constant when performing a single vertical jump. There are also reported statistically significant correlations between body mass, body height, length of lower limbs and leg stiffness. The stiffness analysed by the authors should be understood as quasi-stiffness because the measurements of ?F(?l) were made during transient states where inertia and dumping forces are likely to affect the final result. PMID:23952196

Struzik, Artur; Zawadzki, Jerzy

2013-01-01

221

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

222

Association between systemic arterial stiffness and age-related macular degeneration  

Microsoft Academic Search

Background  A number of epidemiological studies suggest that age-related macular degeneration (AMD) and cardiovascular disease share the same risk factors. Systemic arterial stiffness is a clear indicator of cardiovascular disease. We investigated whether there is an association between directly measured systemic arterial stiffness and the presence of AMD.Methods  We used a SphygmoCor 2000 system to noninvasively measure two indicators of the systemic

Eiichi Sato; Gilbert T. Feke; Ephraim Y. Appelbaum; Marcel N. Menke; Clement L. Trempe; J. Wallace McMeel

2006-01-01

223

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

224

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

2013-09-06

225

Stiffness in Discrimination of Patients with Vertebral Fractures  

Microsoft Academic Search

:   We measured the ultrasound parameters of the heels of 49 women with vertebral fractures and 87 age-matched controls using\\u000a an Achilles ultrasound device. Average broadband ultrasound attenuation (BUA), speed of sound (SOS) and Stiffness were significantly\\u000a lower in fracture patients (p<0.0001). We also estimated the ultrasound parameters of patients compared with age-matched non-fracture controls and found\\u000a the mean BUA

M. B. Mikhail; E. Flaster; J. F. Aloia

1999-01-01

226

Evaluation of aortic stiffness in children with chronic renal failure  

Microsoft Academic Search

The measurement of aortic stiffness (As) [aortic strain (S), pressure strain elastic modulus (Ep) and pressure strain normalized\\u000a by diastolic pressure (Ep*)] is suggested as an excellent marker of subclinical arterial sclerosis. We aimed to investigate\\u000a the presence of As and to determine the relationship between As and some risk factors in children with chronic renal failure\\u000a (CRF). Twenty-six pre-dialysis

Ali Rahmi Bakiler; Onder Yavascan; Nilgun Harputluoglu; Orhan Deniz Kara; Nejat Aksu

2007-01-01

227

Public Notification: “Stiff Days” Contains Hidden Drug ...  

Center for Drug Evaluation (CDER)

... FDA laboratory analysis confirmed that “Stiff Days” contains sildenafil, the active ... negative side effects should consult a health care professional as ... More results from www.fda.gov/drugs/resourcesforyou/consumers

228

Interphalangeal Joint Stiffness Following Claw Hand Reconstruction  

Microsoft Academic Search

Conventional immobilisation following surgery for claw hand reconstruction necessitates altogether more than six weeks of post-operative physiotherapy. Two to four weeks of physiotherapy was required for re-education of the transferred tendons and an additional period of physiotherapy was needed to overcome the interphalangeal joint stiffness seen in all hands—even those with no pre-operative I.P. stiffness.Fifty hands with no pre-operative I.P.

G. D. SUNDARARAJ; K. MANI

1984-01-01

229

Stiff skin syndrome--case report.  

PubMed

Stiff skin syndrome is a rare scleroderma-like disorder of unknown etiology characterized by stone-hard indurations of skin, mild hypertrichosis and limited joint mobility. No effective treatment has yet been found. Exercises and rehabilitative therapy are important in maintaining the patient's quality of life. The authors present a case of a two-year-old boy with progressive skin hardening since he was eight-month old and secondary restricted joint mobility, diagnosed as Stiff skin syndrome. PMID:22068804

Amorim, Adriana Gutstein da Fonseca; Aidé, Marcia Kalil; Durães, Sandra Maria Barbosa; Rochael, Mayra Carrijo

230

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

231

External mechanical compression reduces regional arterial stiffness  

Microsoft Academic Search

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

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

2007-01-01

232

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

NASA Astrophysics Data System (ADS)

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

Curà, Francesca; Mura, Andrea

2013-11-01

233

Stiffness transition in anisotropic fiber nets.  

PubMed

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

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

2012-08-23

234

Stiffness transition in anisotropic fiber nets  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

235

Determinant of leg stiffness during hopping is frequency-dependent.  

PubMed

Identifying the major determinant of leg stiffness during hopping would be helpful in the development of more effective training methods. Despite the fact that overall leg stiffness depends on a combination of the joint stiffness, it is unclear how the major determinants of leg stiffness are influenced by hopping frequency. The purpose of this study was to identify the major determinant of leg stiffness over a wide range of hopping frequencies. Fourteen well-trained male athletes performed in a place hopping on two legs, at three frequencies (1.5, 2.2 and 3.0 Hz). We determined leg and joint stiffness of the hip, knee and ankle from kinetic and kinematic data. Multiple linear regression analysis revealed that knee stiffness could explain more of the variance of leg stiffness than could ankle or hip stiffness at 1.5 Hz hopping. Further, only ankle stiffness was significantly correlated with leg stiffness at both 2.2 and 3.0 Hz, and the standardized regression coefficient of ankle stiffness was higher than that of knee and hip stiffness. The results of the present study suggest that the major determinant of leg stiffness during hopping switches from knee stiffness to ankle stiffness when the hopping frequency is increased. PMID:21318314

Hobara, Hiroaki; Inoue, Koh; Omuro, Kohei; Muraoka, Tetsuro; Kanosue, Kazuyuki

2011-02-12

236

Stiffness nanotomography of human epithelial cancer cells  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

237

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

PubMed Central

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

2011-01-01

238

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

2012-11-09

239

The effect of interface stiffness on dentin–composite interfacial fracture resistance  

Microsoft Academic Search

Objectives: The dentin–composite interface should withstand stresses that develop initially during composite polymerization and later during clinical function. The elastic behavior of the dentin–composite interface, which could be represented by an interfacial stiffness parameter, is not completely understood. The purpose of this study was to measure the relative interfacial stiffness of dentin–composite interfaces formed using commercially available dentin bonding agents

L. E Tam; R. M Pilliar

2000-01-01

240

Stiff-person syndrome with amphiphysin antibodies  

PubMed Central

Background: Stiff-person syndrome (SPS), formerly Stiff-man syndrome, is a rare autoimmune disease usually exhibiting severe spasms and thoracolumbar stiffness, with very elevated glutamic acid decarboxylase antibodies (GAD Ab). A paraneoplastic variant, less well characterized, is associated with amphiphysin antibodies (amphiphysin Ab). The objective of this study was to identify distinctive clinical features of amphiphysin Ab-associated SPS. Methods: Records associated with 845 sera tested in the Yale SPS project were examined, and 621 patients with clinically suspected SPS were included in the study. Clinical characteristics were assessed with correction for multiple comparisons. Results: In all, 116 patients had GAD antibodies and 11 patients had amphiphysin Ab; some clinical information was available for 112 and 11 of these patients, respectively. Patients with amphiphysin Ab-associated SPS were exclusively female; mean age was 60. All except one had breast cancer; none had diabetes. Compared to patients with GAD Ab-associated SPS, those with amphiphysin Ab were older (p = 0.02) and showed a dramatically different stiffness pattern (p < 0.0000001) with cervical involvement more likely, p ? 0.001. Electromyography showed continuous motor unit activity or was reported positive in eight. Benzodiazepines at high dose (average 50 mg/day diazepam) were partially effective. Four patients were steroid responsive and tumor excision with chemotherapy produced marked clinical improvement in three of five patients. Conclusions: Amphiphysin Ab-associated stiff-person syndrome is strongly associated with cervical region stiffness, female sex, breast cancer, advanced age, EMG abnormalities, and benzodiazepine responsiveness. The condition may respond to steroids and can dramatically improve with cancer treatment. GLOSSARY EAE = experimental autoimmune encephalitis; GAD Ab = glutamic acid decarboxylase antibodies; ICC = immunocytochemistry; PERM = progressive variant with encephalomyelitis, rigidity, and myoclonus; SPS = stiff-person syndrome.

Murinson, Beth B.; Guarnaccia, Joseph B.

2008-01-01

241

Big bang nucleosynthesis with a stiff fluid  

SciTech Connect

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

Dutta, Sourish; Scherrer, Robert J. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States)

2010-10-15

242

Nanoscale structure and microscale stiffness of DNA nanotubes.  

PubMed

We measure the stiffness of tiled DNA nanotubes (HX-tubes) as a function of their (defined) circumference by analyzing their micrometer-scale thermal deformations using fluorescence microscopy. We derive a model that relates nanoscale features of HX-tube architecture to the measured persistence lengths. Given the known stiffness of double-stranded DNA, we use this model to constrain the average spacing between and effective stiffness of individual DNA duplexes in the tube. A key structural feature of tiled nanotubes that can affect stiffness is their potential to form with discrete amounts of twist of the DNA duplexes about the tube axis (supertwist). We visualize the supertwist of HX-tubes using electron microscopy of gold nanoparticles, attached to specific sites along the nanotube. This method reveals that HX-tubes tend not to form with supertwist unless forced by sequence design, and, even when forced, supertwist is reduced by elastic deformations of the underlying DNA lattice. We compare the hybridization energy gained upon closing a duplex sheet into a tube with the elastic energy paid for deforming the sheet to allow closure. In estimating the elastic energy we account for bending and twisting of the individual duplexes as well as shearing between them. We find the minimum supertwist state has minimum free energy, and global untwisting of forced supertwist is energetically favorable, consistent with our experimental data. Finally, we show that attachment of Cy3 dyes or changing counterions can cause nanotubes to adopt a permanent writhe with micrometer-scale pitch and amplitude. We propose that the coupling of local twist and global counter-twist may be useful in characterizing perturbations of DNA structure. PMID:23879368

Schiffels, Daniel; Liedl, Tim; Fygenson, Deborah K

2013-07-31

243

Arterial stiffness and cardiovascular events: The Framingham Heart Study  

PubMed Central

Background Various measures of arterial stiffness and wave reflection have been proposed as cardiovascular risk markers. Prior studies have not assessed relations of a comprehensive panel of stiffness measures to prognosis in the community. Methods and Results We used proportional hazards models to analyze first-onset major cardiovascular disease (CVD) events (myocardial infarction, unstable angina, heart failure or stroke) in relation to arterial stiffness (pulse wave velocity, PWV), wave reflection (augmentation index, carotid-brachial pressure amplification) and central pulse pressure in 2232 participants (mean age 63 years, 58% women) in the Framingham Heart Study. During median follow-up of 7.8 (range 0.2 to 8.9) years, 151 of 2232 participants (6.8%) had an event. In multivariable models adjusting for age, sex, systolic blood pressure, use of antihypertensive therapy, total and HDL cholesterol concentrations, smoking and presence of diabetes, higher aortic PWV was associated with a 48% increase in CVD risk (95% CI, 1.16 to 1.91 per SD, P=0.002). After adding PWV to a standard risk factor model, integrated discrimination improvement was 0.7% (95% CI, 0.05 to 1.3%, P<0.05). In contrast, augmentation index, central pulse pressure and pulse pressure amplification were not related to CVD outcomes in multivariable models. Conclusions Higher aortic stiffness assessed by PWV is associated with increased risk for a first cardiovascular event. Aortic PWV improves risk prediction when added to standard risk factors and may represent a valuable biomarker of CVD risk in the community.

Mitchell, Gary F.; Hwang, Shih-Jen; Vasan, Ramachandran S.; Larson, Martin G.; Pencina, Michael J.; Hamburg, Naomi M.; Vita, Joseph A.; Levy, Daniel; Benjamin, Emelia J.

2010-01-01

244

Hamstrings Stiffness and Landing Biomechanics Linked to Anterior Cruciate Ligament Loading.  

PubMed

Context : Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks. Objective : To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury. Design : Cross-sectional study. Setting : Research laboratory. Patients or Other Participants : A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg). Intervention(s) : Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests. Main Outcome Measure(s) : Hamstrings stiffness was normalized to body mass (N/m·kg(-1)). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height. Results : Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t22 range = 1.729-2.224, P < .05). Conclusions : Greater hamstrings stiffness was associated with landing biomechanics consistent with less ACL loading and injury risk. Musculotendinous stiffness is a modifiable characteristic; thus exercises that enhance hamstrings stiffness may be important additions to ACL injury-prevention programs. PMID:23768123

Blackburn, J Troy; Norcross, Marc F; Cannon, Lindsey N; Zinder, Steven M

2013-06-14

245

Cartesian stiffness for wrist joints: analysis on the Lie group of 3D rotations and geometric approximation for experimental evaluation  

Microsoft Academic Search

This paper is concerned with the analysis and the numerical evaluation from experimental measurements of the static, Cartesian stiffness of wrist joints, in particular the human wrist. The primary aim is to extend from Euclidean spaces to so(3), the group of rigid body rotations, previous methods for assessing the end-point stiffness of the human arm, typically performed via a robotic

Domenico Campolo

2011-01-01

246

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

Microsoft Academic Search

BACKGROUND: The pendulum test of Wartenberg is a technique commonly used to measure passive knee motion with the aim to assess spasticity. We used this test to evaluate changes of the knee angular displacement, passive stiffness and viscosity in rheumatoid arthritis patients. Stiffness and viscosity represent passive resistances to joint motion associated with the structural properties of the joint tissue

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

2006-01-01

247

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

PubMed

Carotid-to-radial pulse wave velocity (PWV(cr)) has been proposed to evaluate endothelial function. However, the measurement of PWV(cr) 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 PWV(cr) 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 PWV(cr) 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 PWV(cr) 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 PWV(cr) and could be used to facilitate the evaluation of hyperemia-related changes in arterial stiffness. PMID:22919496

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

2012-08-07

248

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

249

The cellular decapping activators LSm1, Pat1, and Dhh1 control the ratio of subgenomic to genomic Flock House virus RNAs.  

PubMed

Positive-strand RNA viruses depend on recruited host factors to control critical replication steps. Previously, it was shown that replication of evolutionarily diverse positive-strand RNA viruses, such as hepatitis C virus and brome mosaic virus, depends on host decapping activators LSm1-7, Pat1, and Dhh1 (J. Diez et al., Proc. Natl. Acad. Sci. U. S. A. 97:3913-3918, 2000; A. Mas et al., J. Virol. 80:246 -251, 2006; N. Scheller et al., Proc. Natl. Acad. Sci. U. S. A. 106:13517-13522, 2009). By using a system that allows the replication of the insect Flock House virus (FHV) in yeast, here we show that LSm1-7, Pat1, and Dhh1 control the ratio of subgenomic RNA3 to genomic RNA1 production, a key feature in the FHV life cycle mediated by a long-distance base pairing within RNA1. Depletion of LSM1, PAT1, or DHH1 dramatically increased RNA3 accumulation during replication. This was not caused by differences between RNA1 and RNA3 steady-state levels in the absence of replication. Importantly, coimmunoprecipitation assays indicated that LSm1-7, Pat1, and Dhh1 interact with the FHV RNA genome and the viral polymerase. By using a strategy that allows dissecting different stages of the replication process, we found that LSm1-7, Pat1, and Dhh1 did not affect the early replication steps of RNA1 recruitment to the replication complex or RNA1 synthesis. Furthermore, their function on RNA3/RNA1 ratios was independent of the membrane compartment, where replication occurs and requires ATPase activity of the Dhh1 helicase. Together, these results support that LSm1-7, Pat1, and Dhh1 control RNA3 synthesis. Their described function in mediating cellular mRNP rearrangements suggests a parallel role in mediating key viral RNP transitions, such as the one required to maintain the balance between the alternative FHV RNA1 conformations that control RNA3 synthesis. PMID:23536653

Giménez-Barcons, Mireia; Alves-Rodrigues, Isabel; Jungfleisch, Jennifer; Van Wynsberghe, Priscilla M; Ahlquist, Paul; Díez, Juana

2013-03-27

250

Virion stiffness regulates immature HIV-1 entry  

PubMed Central

Background Human immunodeficiency virus type 1 (HIV-1) undergoes a protease-mediated maturation process that is required for its infectivity. Little is known about how the physical properties of viral particles change during maturation and how these changes affect the viral lifecycle. Using Atomic Force Microscopy (AFM), we previously discovered that HIV undergoes a “stiffness switch”, a dramatic reduction in particle stiffness during maturation that is mediated by the viral Envelope (Env) protein. Results In this study, we show that transmembrane-anchored Env cytoplasmic tail (CT) domain is sufficient to regulate the particle stiffness of immature HIV-1. Using this construct expressed in trans with viral Env lacking the CT domain, we show that increasing particle stiffness reduces viral entry activity in immature virions. A similar effect was also observed for immature HIV-1 pseudovirions containing Env from vesicular stomatitis virus. Conclusions This linkage between particle stiffness and viral entry activity illustrates a novel level of regulation for viral replication, providing the first evidence for a biological role of virion physical properties and suggesting a new inhibitory strategy.

2013-01-01

251

[Stiff-person syndrome and related autoantibodies].  

PubMed

Central nervous system hyperexcitability disorders, known as stiff-man/person syndrome (SPS), are thought to be related to the regulatory disturbance of inhibitory synaptic transmission of motor neurons in the brainstem and spinal cord. SPS is characterized by stiffness and spasms of the axis and limbs and is divided into two clinical subgroups: classic SPS, which affects the lumbar, trunk, and proximal limb muscles, and SPS-plus syndrome. The latter comprises (1) the stiff-limb subtype, in which symptom is limited to the lower limbs; (2) jerking stiff-man syndrome, characterized by chronically progressive stiffness and myoclonus; and (3) acute-onset and progressive encephalomyelitis with rigidity and myoclonus. Almost 80% of patients with classic SPS harbor autoantibodies against glutamic acid decarboxylase 65 (GAD65). In approximately 30-40% of patients, SPS accompanies type I diabetes, and anti-GAD65 antibodies are detected frequently in type I diabetes. However, the antibody-recognizing epitopes might be different between SPS and diabetes. Other autoantibodies against glycine receptor ?1 (12% of patients with SPS) and GABA(A)-receptor associated protein (70% of patients with SPS) have been reported. In paraneoplastic SPS, anti-amphiphysin antibodies have been shown in patients with breast cancer or small cell lung cancer. One case of mediastinal tumor with anti-gephyrin antibodies has also been reported. However, the roles of these autoantibodies in the pathomechanisms of SPS have not yet been elucidated. PMID:23568987

Tomioka, Ryo; Tanaka, Keiko

2013-04-01

252

Stiffness changes in cultured airway smooth muscle cells.  

PubMed

Airway smooth muscle (ASM) cells in culture stiffen when exposed to contractile agonists. Such cell stiffening may reflect activation of the contractile apparatus as well as polymerization of cytoskeletal biopolymers. Here we have assessed the relative contribution of these mechanisms in cultured ASM cells stimulated with serotonin (5-hydroxytryptamine; 5-HT) in the presence or absence of drugs that inhibit either myosin-based contraction or polymerization of filamentous (F) actin. Magnetic twisting cytometry was used to measure cell stiffness, and associated changes in structural organization of actin cytoskeleton were evaluated by confocal microscopy. We found that 5-HT increased cell stiffness in a dose-dependent fashion and also elicited rapid formation of F-actin as marked by increased intensity of FITC-phalloidin staining in these cells. A calmodulin antagonist (W-7), a myosin light chain kinase inhibitor (ML-7) and a myosin ATPase inhibitor (BDM) each ablated the stiffening response but not the F-actin polymerization induced by 5-HT. Agents that inhibited the formation of F-actin (cytochalasin D, latrunculin A, C3 exoenzyme, and Y-27632) attenuated both baseline stiffness and the extent of cell stiffening in response to 5-HT. Together, these data suggest that agonist-evoked stiffening of cultured ASM cells requires actin polymerization as well as myosin activation and that neither actin polymerization nor myosin activation by itself is sufficient to account for the cell stiffening response. PMID:12176736

An, Steven S; Laudadio, Rachel E; Lai, Jean; Rogers, Rick A; Fredberg, Jeffrey J

2002-09-01

253

Glycine Receptor Autoimmune Spectrum With Stiff-Man Syndrome Phenotype  

PubMed Central

Objectives To determine whether glycine receptor ?1 subunit-specific autoantibodies (GlyR?1-IgG) occur in a broader spectrum of brainstem and spinal hyperexcitability disorders than the progressive encephalomyelitis with rigidity and myoclonus phenotype recognized to date, and to ascertain disease specificity. Design Retrospective, case-control study. Settings Mayo Clinic, Rochester, Minnesota, and University of Barcelona, Spain. Patients Eighty-one patients with stiff-man syndrome phenotype, 80 neurologic control subjects, and 20 healthy control subjects. Intervention Glycine receptor ?1–transfected cells to test serum or cerebrospinal fluid from cases and control subjects. Main Outcome Measures Frequency of GlyR?1-IgG positivity among stiff-man syndrome phenotype cases and control subjects. Comparison of GlyR?1-IgG seropositive and seronegative cases. Results Seropositive cases (12% of cases) included 9 with stiff-man syndrome (4 classic; 5 variant; 66% were glutamic acid decarboxylase 65–IgG positive) and 1 with progressive encephalomyelitis with rigidity and myoclonus. Immunotherapy responses were noted more frequently in GlyR?1-IgG–positive cases (6 of 7 improved) than in seronegative cases (7 of 25 improved; P=.02). The single seropositive control patient had steroid-responsive vision loss and optic atrophy with inflammatory cerebrospinal fluid. Conclusions Glycine receptor ?1–IgG aids identification of autoimmune brainstem/spinal cord hyperexcitability disorders and may extend to the glycinergic visual system.

McKeon, Andrew; Martinez-Hernandez, Eugenia; Lancaster, Eric; Matsumoto, Joseph Y.; Harvey, Robert J.; McEvoy, Kathleen M.; Pittock, Sean J.; Lennon, Vanda A.; Dalmau, Josep

2013-01-01

254

Aortic Stiffness, Blood Pressure Progression, and Incident Hypertension  

PubMed Central

Context Vascular stiffness increases with advancing age and is a major risk factor for age-related morbidity and mortality. Vascular stiffness and blood pressure pulsatility are related; however, temporal relationships between vascular stiffening and blood pressure elevation have not been fully delineated. Objective To examine temporal relationships among vascular stiffness, central hemodynamics, microvascular function, and blood pressure progression. Design, Setting, and Participants Longitudinal community-based cohort study conducted in Framingham, Massachusetts. The present investigation is based on the 2 latest examination cycles (cycle 7: 1998–2001; cycle 8: 2005–2008 [last visit: January 25, 2008]) of the Framingham Offspring study (recruited: 1971–1975). Temporal relationships among blood pressure and 3 measures of vascular stiffness and pressure pulsatility derived from arterial tonometry (carotid-femoral pulse wave velocity [CFPWV], forward wave amplitude [FWA], and augmentation index) were examined over a 7-year period in 1759 participants (mean [SD] age: 60 [9] years; 974 women). Main Outcome Measures The primary outcomes were blood pressure and incident hypertension during examination cycle 8. The secondary outcomes were CFPWV, FWA, and augmentation index during examination cycle 8. Results In a multivariable-adjusted regression model, higher FWA (?, 1.3 [95% CI, 0.5–2.1] mm Hg per 1 SD; P=.002) and higher CFPWV (?, 1.5 [95% CI, 0.5–2.6] mm Hg per 1 SD; P=.006) during examination cycle 7 were jointly associated with systolic blood pressure during examination cycle 8. Similarly, in a model that included systolic and diastolic blood pressure and additional risk factors during examination cycle 7, higher FWA (odds ratio [OR], 1.6 [95% CI, 1.3–2.0] per 1 SD; P < .001), augmentation index (OR, 1.7 [95% CI, 1.4–2.0] per 1 SD; P < .001), and CFPWV (OR, 1.3 [95% CI, 1.0–1.6] per 1 SD; P=.04) were associated with incident hypertension during examination cycle 8 (338 cases [32%] in 1048 participants without hypertension during examination cycle 7). Conversely, blood pressure during examination cycle 7 was not associated with CFPWV during examination cycle 8. Higher resting brachial artery flow (OR, 1.23 [95% CI, 1.04–1.46]) and lower flow-mediated dilation (OR, 0.80 [95% CI, 0.67–0.96]) during examination cycle 7 were associated with incident hypertension (in models that included blood pressure and tonometry measures collected during examination cycle 7). Conclusion In this cohort, higher aortic stiffness, FWA, and augmentation index were associated with higher risk of incident hypertension; however, initial blood pressure was not independently associated with risk of progressive aortic stiffening.

Kaess, Bernhard M.; Rong, Jian; Larson, Martin G.; Hamburg, Naomi M.; Vita, Joseph A.; Levy, Daniel; Benjamin, Emelia J.; Vasan, Ramachandran S.; Mitchell, Gary F.

2013-01-01

255

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

256

Noninvasive assessment of arterial stiffness by pulse wave analysis.  

PubMed

Pulse wave evaluation is an effective method for arteriosclerosis screening. The pulse wave comprises two displacement components, the incident wave ?(i)(t) and the reflected wave ?(r)(t). Because the amplitude of the reflected wave changes markedly with arterial stiffness, analysis of this wave is useful for evaluation of such stiffness. In this paper, a noninvasive method for extracting the reflected component from a pulse wave is proposed. First, the pulse wave ?(i)(t) + ?(r)(t) and blood flow velocity u(i)(t) - u(r)(t) were measured at the common carotid artery. A new approach is used to estimate the displacement wave ?(i)(t) -?(r)(t), in which a transform of the conservation of mass, an elastic tube model, and a Voigt model for a viscoelastic body are applied to blood flow velocity data. Twice the amplitude of the reflected wave [TARW; 2?(r)(t)] was obtained by subtracting the amplitude of the calculated displacement wave from that of the observed pulse wave. This method was applied to subjects aged from their 20s to 60s to evaluate differences in the reflected component. The results indicate moderate correlation between age and TARW (R(2) = 0.65). To evaluate the validity of this method for screening arterial stiffness, we compared TARW with existing diagnostic indices pulse wave velocity (PWV) and cardio-ankle vascular index (CAVI). TARW was moderately correlated with PWV (R(2) = 0.48) and CAVI (R(2) = 0.71). Therefore, this new method has potential for diagnosing arterial stiffness. PMID:23192804

Saito, Masashi; Matsukawa, Mami; Asada, Takaaki; Watanabe, Yoshiaki

2012-11-01

257

Prediction of Liver-Related Events Using Fibroscan in Chronic Hepatitis B Patients Showing Advanced Liver Fibrosis  

Microsoft Academic Search

BackgroundLiver stiffness measurement (LSM) using transient elastography (FibroScan®) can assess liver fibrosis noninvasively. This study investigated whether LSM can predict the development of liver-related events (LREs) in chronic hepatitis B (CHB) patients showing histologically advanced liver fibrosis.MethodsBetween March 2006 and April 2010, 128 CHB patients with who underwent LSM and liver biopsy (LB) before starting nucleot(s)ide analogues and showed histologically

Seung Up Kim; Ji Hoon Lee; Do Young Kim; Sang Hoon Ahn; Kyu Sik Jung; Eun Hee Choi; Young Nyun Park; Kwang-Hyub Han; Chae Yoon Chon; Jun Yong Park

2012-01-01

258

Testing local DNA stiffness by nanoconfinement  

NASA Astrophysics Data System (ADS)

The primary intent of this work is the study of DNA movement inside curved nanochannels. In particular, we considered channels with a cross-section smaller then the DNA persistence length, and channel length far beyond the contour length of the molecule. This allows us approximation of the polymer with the model of an elastic rod (Odijk model). We are testing the local DNA stiffness by bending the molecule in curved channels, and a bending energy landscape is constructed by comparing forces due to bending stiffness to known electrophoretic forces. To estimate the limiting radius of nanochannel curvature permeable for DNA molecules at a given driving force, two sets of nanochips were fabricated. The first set of nanochannels is formed by the sequence of semi-circumferences with descending radius (20 ?m to 50 nm) and tests moderate bending of a set of length scales. A second set of nanochannels is shaped as a zigzag of constant steps, and tests local bending stiffness.

Karpusenka, Alena; Riehn, Robert

2008-10-01

259

Condensin Regulates the Stiffness of Vertebrate Centromeres  

PubMed Central

When chromosomes are aligned and bioriented at metaphase, the elastic stretch of centromeric chromatin opposes pulling forces exerted on sister kinetochores by the mitotic spindle. Here we show that condensin ATPase activity is an important regulator of centromere stiffness and function. Condensin depletion decreases the stiffness of centromeric chromatin by 50% when pulling forces are applied to kinetochores. However, condensin is dispensable for the normal level of compaction (rest length) of centromeres, which probably depends on other factors that control higher-order chromatin folding. Kinetochores also do not require condensin for their structure or motility. Loss of stiffness caused by condensin-depletion produces abnormal uncoordinated sister kinetochore movements, leads to an increase in Mad2(+) kinetochores near the metaphase plate and delays anaphase onset.

Ribeiro, Susana A.; Gatlin, Jesse C.; Dong, Yimin; Joglekar, Ajit; Cameron, Lisa; Hudson, Damien F.; Farr, Christine J.; McEwen, Bruce F.; Salmon, Edward D.

2009-01-01

260

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

PubMed Central

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

Job, Kathleen M.; Dull, Randal O.

2012-01-01

261

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

PubMed

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

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

2013-07-21

262

End-on soft x-ray imaging of Field-Reversed Configurations (FRCs) on the Field-Reversal-C (FRX-C)/ Large Scale Modification (LSM) experiment  

SciTech Connect

Recently, a prototype soft X-ray pinhole camera was fielded on FRX-C/LSM at Los Alamos and TRX at Spectra Technology. The soft X-ray FRC images obtained using this camera stand out in high contrast to their surroundings. It was particularly useful for studying the FRC during and shortly after formation when, at certain operating conditions, flute-like structures at the edge and internal structures of the FRC were observed which other diagnostics could not resolve. Building on this early experience, a new soft X-ray pinhole camera has been installed on FRX-C/LSM, which permits more rapid data acquisition and briefer exposures. It will be used to continue studying FRC formation and to look for internal structure later in time which could be a signature of instability. This paper summarizes the initial operation of this camera. 2 refs., 6 figs.

Taggart, D.P.; Gribble, R.J.; Bailey, A.D III; Sugimoto, Satoshi.

1989-01-01

263

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

PubMed Central

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

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

2011-01-01

264

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

265

Cartesian stiffness for wrist joints: analysis on the Lie group of 3D rotations and geometric approximation for experimental evaluation.  

PubMed

This paper is concerned with the analysis and the numerical evaluation from experimental measurements of the static, Cartesian stiffness of wrist joints, in particular the human wrist. The primary aim is to extend from Euclidean spaces to so(3), the group of rigid body rotations, previous methods for assessing the end-point stiffness of the human arm, typically performed via a robotic manipulandum. As a first step, the geometric definition of Cartesian stiffness from current literature is specialised to the group so(3). Emphasis is placed on the choice of the unique, natural, affine connection on so(3) which guarantees symmetry of the stiffness matrix in presence of conservative fields for any configuration, also out of equilibrium. As the main contribution of this study, a coordinate-independent approximation based on the geometric notion of geodesics is proposed which provides a working equation for evaluating stiffness directly from experimental measurements. Finally, a graphical representation of the stiffness is discussed which extends the ellipse method often used for end-point stiffness visualisation and which is suitable to compare stiffness matrices evaluated at different configurations. PMID:22224937

Campolo, Domenico

2012-01-06

266

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

SciTech Connect

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

Hull, J.R.; Mulcahy, T.M. (Materials and Components Technology Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Salama, K.; Selvamanickam, V. (Texas Center for Superconductivity at University of Houston, Houston, Texas 77004 (United States)); Weinberger, B.R.; Lynds, L. (United Technologies Research Center, East Hartford, Connecticut 06108 (United States))

1992-09-01

267

Achilles tendon stiffness is unchanged one hour after a marathon.  

PubMed

Overuse-induced injuries have been proposed as a predisposing factor for Achilles tendon (AT) ruptures. If tendons can be overloaded, their mechanical properties should change during exercise. Because there data are lacking on the effects of a single bout of long-lasting exercise on AT mechanical properties, the present study measured AT stiffness before and after a marathon. AT stiffness was determined as the slope of the force-elongation curve between 10 and 80% of maximum voluntary force. AT force-elongation characteristics were measured in an ankle dynamometer using simultaneous motion-capture-assisted ultrasonography. Oxygen consumption and ankle kinematics were also measured on a treadmill at the marathon pace. All measurements were performed before and after the marathon. AT stiffness did not change significantly from the pre-race value of 197±62 N mm(-1) (mean ± s.d.) to the post-race value of 206±59 N mm(-1) (N=12, P=0.312). Oxygen consumption increased after the race by 7±10% (P<0.05) and ankle kinematic data revealed that in nine out of 12 subjects, the marathon induced a change in their foot strike technique. The AT of the physically active individuals seems to be able to resist mechanical changes under physiological stress. We therefore suggest that natural loading, like in running, may not overstress the AT or predispose it to injury. In addition, decreased running economy, as well as altered foot strike technique, was probably attributable to muscle fatigue. PMID:23014572

Peltonen, Jussi; Cronin, Neil J; Stenroth, Lauri; Finni, Taija; Avela, Janne

2012-10-15

268

RC beam with variable stiffness and strength  

Microsoft Academic Search

Shape memory alloys (SMA) show a temperature depending stiffness and strength. A reinforced concrete (RC) beam with SMA wires was tested and compared with a conventional RC beam. Furthermore, tensile and pull-out tests with the SMA wires are presented. By using the constrained recovery effect, it was possible to produce a changeable prestress in the RC beam.

Christoph Czaderski; Bernd Hahnebach; Masoud Motavalli

2006-01-01

269

Dynamic stiffness removal for direct numerical simulations  

SciTech Connect

A systematic approach was developed to derive non-stiff reduced mechanisms for direct numerical simulations (DNS) with explicit integration solvers. The stiffness reduction was achieved through on-the-fly elimination of short time-scales induced by two features of fast chemical reactivity, namely quasi-steady-state (QSS) species and partial-equilibrium (PE) reactions. The sparse algebraic equations resulting from QSS and PE approximations were utilized such that the efficiency of the dynamic stiffness reduction is high compared with general methods of time-scale reduction based on Jacobian decomposition. Using the dimension reduction strategies developed in our previous work, a reduced mechanism with 52 species was first derived from a detailed mechanism with 561 species. The reduced mechanism was validated for ignition and extinction applications over the parameter range of equivalence ratio between 0.5 and 1.5, pressure between 10 and 50 atm, and initial temperature between 700 and 1600 K for ignition, and worst-case errors of approximately 30% were observed. The reduced mechanism with dynamic stiffness removal was then applied in homogeneous and 1-D ignition applications, as well as a 2-D direct numerical simulation of ignition with temperature inhomogeneities at constant volume with integration time-steps of 5-10 ns. The integration was numerically stable and good accuracy was achieved. (author)

Lu, Tianfeng; Law, Chung K. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544 (United States); Yoo, Chun Sang; Chen, Jacqueline H. [Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551 (United States)

2009-08-15

270

Stiff-person syndrome treated with rituximab  

Microsoft Academic Search

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

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

2010-01-01

271

Stability of high stiffness gas journal bearings  

Microsoft Academic Search

One of the most important problems in the design of gas bearings is their stability. In this paper, results of investigations of the stability of a new type of gas journal bearing, the so-called 'high stiffness bearing' (HSB), are presented. As linear models of HSB do not allow us to estimate the stability threshold with satisfactory precision, all the numerical

Krzysztof Czolczynski

1994-01-01

272

Spring stiffness influence on an oscillating propulsor  

Microsoft Academic Search

We study the propulsive dynamics of a thin foil pitching about its quarter chord and allowed to passively plunge. Specifically, we focus on the effect of variations in translational spring stiffness on propulsor plunge and on the minimum oscillation frequency required to produce positive thrust. Our numerical simulation utilizes a two-dimensional hydroelasticity model of the propulsor–fluid system in a constant

M. M. Murray; L. E. Howle

2003-01-01

273

Leg Stiffness and Expertise in Men Jumping  

Microsoft Academic Search

LAFFAYE, G., B. G. BARDY, and A. DUREY. Leg Stiffness and Expertise in Men Jumping. Med. Sci. Sports Exerc., Vol. 37, No. 4, pp. 536-543, 2005. Purpose: The aim of the present study is to investigate: a) the leg spring behavior in the one-leg vertical jump, b) the contribution of impulse parameters to this behavior, and c) the effect of

GUILLAUME LAFFAYE; ALAIN DUREY

2005-01-01

274

Pregnancy in stiff-limb syndrome.  

PubMed

To our knowledge, pregnancy in a patient with stiff-limb-syndrome (SLS) has not been reported. We present the case of a woman with SLS who improved during pregnancy, delivered a normal healthy baby by forceps-assisted vaginal delivery, and suffered a mild postpartum "relapse." PMID:15254953

Weatherby, Stuart J M; Woolner, Philippa; Clarke, Carl E

2004-07-01

275

Scaling of fluid flow versus fracture stiffness  

NASA Astrophysics Data System (ADS)

Seismic characterization of fluid flow through fractures requires a fundamental understanding of the relationship between the hydraulic and mechanical properties of fractures. A finite-size scaling analysis was performed on fractures with weakly correlated random aperture distributions to determine the fundamental scaling relationship between fracture stiffness and fracture fluid flow. From computer simulations, the dynamic transport exponent, which provides the power law dependence, was extracted and used to collapse the flow-stiffness relationships from multiple scales into a single scaling function. Fracture specific stiffness was determined to be a surrogate for void area that is traditionally used in percolation studies. The flow-stiffness scaling function displays two exponentially dependent regions above and below the transition into the critical regime. The transition is governed by the stressed flow paths when the flow path geometry deforms from a sheet-like topology to a string-like topology. The resulting hydromechanical scaling function provides a link between fluid flow and the seismic response of a fracture.

Petrovitch, Christopher L.; Nolte, David D.; Pyrak-Nolte, Laura J.

2013-05-01

276

Stiffness gradients in radiata pine trees  

Microsoft Academic Search

A mill study of 62 trees, in which boards were reassembled into their original logs, permitted the construction of wood quality maps. In this instance stiffness profiles were obtained from butt to upper-top logs, based on machine stress grading of all boards and then averaging values from the 62 trees. Traditionally the butt log has been perceived to be the

Ping Xu; J. C. F. Walker

2004-01-01

277

B cell activation is regulated by the stiffness properties of the substrate presenting the antigens.  

PubMed

B lymphocytes are activated upon Ag sensing by BCRs. The substrate presenting the Ag can show different degrees of stiffness. It is not clear whether B cells can respond to changes in substrate stiffness. In this study we use high-resolution, high-speed live cell imaging techniques to capture the molecular events in B cell activation after the recognition of Ags tethered to polyacrylamide gel substrates with variable degrees of stiffness as quantified by Young's modulus (2.6-22.1 kPa). We show that the initiation of B cell activation is extremely sensitive to substrate stiffness. B cells exhibit much stronger activation responses when encountering Ags tethered to substrates with a high degree of stiffness as measured by the accumulation of BCR, phospho-spleen tyrosine kinase, and phosphotyrosine molecules into the B cell immunological synapse. Ags tethered to stiff substrates induce the formation of more prominent BCR and phospho-spleen tyrosine kinase microclusters with significantly enhanced colocalization as compared with Ags tethered to soft substrates. Moreover, the expression of the B cell activation marker CD69 is enhanced in B cells encountering Ags on stiffer substrates. Through time-lapse live cell imaging, we find that the different responses of B cells to substrate stiffness are only demonstrated 5 min after BCR and Ag recognition. Using a series of cytoskeleton inhibitors, we determine that the mechanosensing ability of B cells is dependent on microtubules, and only mildly linked to the actin cytoskeleton. These results suggest the importance of the mechanical properties mediated by substrate stiffness in B cell activation. PMID:23554309

Wan, Zhengpeng; Zhang, Shaosen; Fan, Yilin; Liu, Kai; Du, Feng; Davey, Angel M; Zhang, Huiyuan; Han, Weidong; Xiong, Chunyang; Liu, Wanli

2013-04-03

278

Effects of golf shaft stiffness on strain, clubhead presentation and wrist kinematics.  

PubMed

The aim of this study was to quantify and explain the effect of shaft stiffness on the dynamics of golf drives. Twenty golfers performed swings with two clubs designed to differ only in shaft bending stiffness. Wrist kinematics and clubhead presentation to the ball were determined using optical motion capture systems in conjunction with a radar device for capturing ball speed, launch angle, and spin. Shaft stiffness had a marginally small effect on clubhead and ball speeds, which increased by 0.45% (p < 0.001) and 0.7% (p = 0.008), respectively, for the less stiff club. Two factors directly contributed to these increases: (i) a faster recovery of the lower flex shaft from lag to lead bending just before impact (p < 0.001); and (ii) an increase of 0.4% in angular velocity of the grip of the lower flex club at impact (p = 0.003). Unsurprisingly, decreases in shaft stiffness led to more shaft bending at the transition from backswing to downswing (p < 0.001). Contrary to previous research, lead bending at impact marginally increased for the stiffer shaft (p = 0.003). Overall, and taking effect sizes into account, the changes in shaft stiffness in isolation did not have a meaningful effect on the measured parameters, for the type of shaft investigated. PMID:22900403

Betzler, Nils F; Monk, Stuart A; Wallace, Eric S; Otto, Steve R

2012-06-01

279

Influences of tendon stiffness, joint stiffness, and electromyographic activity on jump performances using single joint  

Microsoft Academic Search

The present study aimed to examine the influences of tendon stiffness, joint stiffness, and electromyographic activity on\\u000a jump performances consisting of a single-joint movement. Twenty-four men performed three kinds of unilateral maximal jump\\u000a using only the ankle joint (squat jump: SJ; countermovement jump: CMJ; drop jump: DJ) on the sledge apparatus. The relative\\u000a differences in the jump height of CMJ

Keitaro Kubo; Masanori Morimoto; Teruaki Komuro; Naoya Tsunoda; Hiroaki Kanehisa; Tetsuo Fukunaga

2007-01-01

280

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

281

Optimal Design of a Variable Stiffness Joint Using Permanent Magnets  

Microsoft Academic Search

Safety and performance are often required for robots interacting with humans. A variable stiffness joint (VSJ) is a useful device to reduce the shock against a human being by decreasing the joint stiffness quickly. In this study, a novel concept of VSJ using permanent magnets is suggested. It can have stronger stiffness compared with previous systems to satisfy payload conditions.

Myung Wook Hyun; Jeonghoon Yoo; Seoung Tack Hwang; Jun Ho Choi; Sungchul Kang; Seung-Jong Kim

2007-01-01

282

Representations of multi-joint stiffness for prosthetic limb design  

Microsoft Academic Search

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

Chad E. English; Donald L. Russell

2008-01-01

283

Simulation of conservative properties of stiffness matrices in congruence transformation  

Microsoft Academic Search

The conservative properties of stiffness matrices via the nonconservative congruence mapping between the joint and Cartesian spaces are investigated with simulation of two fingers manipulating an object. The properties of both constant and configuration dependent stiffness matrices are presented with integration of work when manipulating along a closed path with no self-intersection. A stiffness matrix is conservative if the force

Shih-Feng Cheng; Imin Kao

1998-01-01

284

Quantitative analysis of the relation between soft tissue stiffness palpated from the body surface and tissue hemodynamics in the human forearm  

Microsoft Academic Search

We investigated the quantitative relation between soft tissue stiffness palpated from the body surface and hemodynamics in the human forearm. We examined the relation between pressures and blood flow in both the main artery and vein measured by magnetic resonance imaging (MRI), the cross-sectional area of forearm measured by MRI and soft tissue stiffness. Six male volunteers participated. Two tourniquet

Keisaku Kimura; Yasuharu Watanabe; Masahiro Umeda; Yoshitaka Arima; Tadashi Watsuji; Shoji Shinohara

2007-01-01

285

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

286

The use of treadmill ergometers for extensive calculation of external work and leg stiffness during running  

Microsoft Academic Search

Recently, new treadmill ergometers have been designed to measure the ground reaction forces during numerous successive steps. From ground reaction forces measured in track running, it has been shown to be possible to compute external mechanical work ( W ext) and leg stiffness ( k) of a bouncing spring-mass system. However, to the best of our knowledge, there is still

Patrick Avogadro; Christelle Chaux; Muriel Bourdin; Georges Dalleau; Alain Belli

2004-01-01

287

Levetiracetam in stiff-person syndrome  

Microsoft Academic Search

\\u000a Abstract\\u000a   We studied the effects of oral levetiracetam (LEV) (500 mg twice daily) in three women with stiff-person syndrome in a single-blind,\\u000a placebo-controlled study. The severity of muscle rigidity and of paroxysmal symptoms was assessed by EMG and clinically by\\u000a a rating scale of 0–4 and by the Patients Global Impressions Scale. LEV was well tolerated. On active treatment all

GianPietro Sechi; Marianna Barrocu; Maria G. Piluzza; Giovanni A. Cocco; Giovanni A. Deiana; Gian Franco Sau

2008-01-01

288

Ultrastrong and Stiff Layered Polymer Nanocomposites  

Microsoft Academic Search

Nanoscale building blocks are individually exceptionally strong because they are close to ideal, defect-free materials. It is, however, difficult to retain the ideal properties in macroscale composites. Bottom-up assembly of a clay\\/polymer nanocomposite allowed for the preparation of a homogeneous, optically transparent material with planar orientation of the alumosilicate nanosheets. The stiffness and tensile strength of these multilayer composites are

Paul Podsiadlo; Amit K. Kaushik; Ellen M. Arruda; Anthony M. Waas; Bong Sup Shim; Jiadi Xu; Himabindu Nandivada; Benjamin G. Pumplin; Joerg Lahann; Ayyalusamy Ramamoorthy; Nicholas A. Kotov

2007-01-01

289

METHOD OF HYPERBOLIC SYSTEMS WITH STIFF RELAXATION  

SciTech Connect

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

R. B. LOWRIE; J. E. MOREL

2001-03-01

290

LONG-TERM PLASTIC PIPE STIFFNESS  

Microsoft Academic Search

The parallel-plate loading mechanism (ASTM D2412 standard test method) was used for investigating the long-term pipe stiffness values of HDPE, PVC and ABS pipes. Both conventional and accelerated test procedures were used. The nominal inside diameters of the test pipes were 300 and 400mm. S-type long-term deflection curves were observed for the test plastic pipes on a semi-log scale. Long-term

Chiwan Wayne Hsieh; Chien-Chih Huang; Jau-Bih Wang

291

Adaptive optics in an optical trapping system for enhanced lateral trap stiffness at depth  

NASA Astrophysics Data System (ADS)

In optical trapping systems the trap stiffness, or spring constant, deteriorates dramatically with trap depth due to optical aberrations and system misalignment. This can severely hamper studies that employ optical tweezers to make accurate quantitative measurements. Here, a deformable membrane mirror is used, in conjunction with a random search algorithm, to correct for these aberrations by optimizing on a merit factor that is directly proportional to the trap stiffness. Previous studies have sought to address this issue but none have used a merit factor that is directly proportional to the trap stiffness. We demonstrate that the lateral trap stiffness, measured with and without aberration correction at increasing depths, improves throughout the trapping range of a conventional trap and allows us to extend the maximum depth at which we can trap from 136 to 166 ?m. At a depth of 131 ?m, trap stiffness improved by factors of 4.37 and 3.31 for the x- and y-axes respectively. The aberration correction resulted in deformable membrane mirror shapes where a single shape could be applied throughout a wide range of trap depths, showing significant improvement, and had the added benefit of making the lateral trapping forces more uniform in x and y.

Müllenbroich, M. C.; McAlinden, N.; Wright, A. J.

2013-07-01

292

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

293

An EKF-based approach for estimating leg stiffness during walking.  

PubMed

The spring-like behavior is an inherent condition for human walking and running. Since leg stiffness kleg is a parameter that cannot be directly measured, many techniques has been proposed in order to estimate it, most of them using force data. This paper intends to address this problem using an Extended Kalman Filter (EKF) based on the Spring-Loaded Inverted Pendulum (SLIP) model. The formulation of the filter only uses as measurement information the Center of Mass (CoM) position and velocity, no a priori information about the stiffness value is known. From simulation results, it is shown that the EKF-based approach can generate a reliable stiffness estimation for walking. PMID:24111412

Ochoa-Diaz, Claudia; Menegaz, Henrique M; Bo, Antonio P L; Borges, Geovany A

2013-07-01

294

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

295

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

PubMed

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. PMID:23667317

Sun, Cheuk-Kwan

2013-04-30

296

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

PubMed Central

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

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

2010-01-01

297

On the design of a high-static low-dynamic stiffness isolator using linear mechanical springs and magnets  

NASA Astrophysics Data System (ADS)

The frequency range over which a linear passive vibration isolator is effective is often limited by the mount stiffness required to support a static load. This can be improved upon by incorporating a negative stiffness element in the mount such that the dynamic stiffness is much less than the static stiffness. In this case, it can be referred to as a high-static low-dynamic stiffness (HSLDS) mount. This paper is concerned with a theoretical and experimental study of one such mount. It comprises two vertical mechanical springs between which an isolated mass is mounted. At the outer edge of each spring, there is a permanent magnet. In the experimental work reported here, the isolated mass is also a magnet arranged so that it is attracted by the other magnets. Thus, the combination of magnets acts as a negative stiffness counteracting the positive stiffness provided by the mechanical springs. Although the HSLDS suspension system will inevitably be nonlinear, it is shown that for small oscillations the mount considered here is linear. The measured transmissibility is compared with a comparable linear mass spring damper system to show the advantages offered by the HSLDS mount.

Carrella, A.; Brennan, M. J.; Waters, T. P.; Shin, K.

2008-08-01

298

Clamping stiffness and its influence on load distribution between paired internal spinal fixation devices.  

PubMed

The load distribution between two internal spinal fixation devices depends, besides other factors, on their stiffness. The stiffness ranges were determined experimentally for the clamps of the AO internal fixator with lateral nut and with posterior nut as well as for the clamps of the SOCON fixator. The stiffness of eight devices each differed by a factor of 3.1 for the clamp with lateral nut, by a factor of 1.5 for the clamp with posterior nut, and by a factor of 1.4 for the clamp of the SOCON fixator. For the AO clamp with lateral nut, the influence of the nut-tightening torque on the stiffness was determined. Using instrumented internal spinal fixation devices mounted to plastic vertebrae and simulating a corpectomy, the load distribution between the implants was measured for different tightening torques. It could be shown that, for the AO internal fixator whose clamps have a lateral nut, a nut-tightening torque > 5 Nm has only a negligible influence on load-sharing between the implants. Tooth damage occurs when the teeth of the clamp body and clamping jaw of the clamp with lateral nut do not gear together exactly, which leads to changes in the clamping stiffness and load-sharing between the two implants. PMID:8854279

Rohlmann, A; Calisse, J; Bergmann, G; Radvan, J; Mayer, H M

1996-06-01

299

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

PubMed

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

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

2013-04-22

300

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

301

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

PubMed

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

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

2011-09-01

302

Effect of diamide on force generation and axial stiffness of the cochlear outer hair cell.  

PubMed Central

We found that diamide, which affects spectrin, reduces the axial stiffness of the cochlear outer hair cell, the cylindrically shaped mechanoreceptor cell with a unique voltage-sensitive motility. This effect thus provides a means of examining the relationship between the stiffness and the motility of the cell. For measuring axial stiffness and force production, we used an experimental configuration in which an elastic probe was attached to the cell near the cuticular plate and the other end of the cell was held with a patch pipette in the whole-cell recording mode. Diamide at concentrations of up to 5 mM reduced the axial stiffness in a dose-dependent manner to 165 nN per unit strain from 502 nN for untreated cells. The isometric force elicited by voltage pulses under whole-cell voltage clamp was also reduced to 35 pN/mV from 105 pN/mV for untreated cells. Thus the isometric force was approximately proportional to the axial stiffness. Our observations suggest a series connection between the motor and cytoskeletal elements and can be explained by the area motor model previously proposed for the outer hair cell. Images FIGURE 1 FIGURE 9

Adachi, M; Iwasa, K H

1997-01-01

303

Hinge stiffness is a barrier to RNA folding.  

PubMed

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

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

2008-04-10

304

Torsional stiffness of single superparamagnetic microspheres in an external magnetic field.  

PubMed

We used magnetic tweezers to measure the torsional stiffness of single micrometer-sized superparamagnetic spheres as a function of the applied magnetic field. By investigating the axial fluctuations of DNA-bound microspheres, we found that considerable rotational microsphere fluctuations can occur. Quantitative noise analysis allowed us to determine the rotational stiffness of individual microspheres, which was found to saturate at high magnetic fields. The saturation can be qualitatively explained considering the properties of the magnetic nanoparticles within the microsphere. Consequences for spatial resolution limits in single-molecule magnetic tweezer experiments and usage of DNA mechanics as a sensitive probe in magnetometry are discussed. PMID:19257322

Klaue, Daniel; Seidel, Ralf

2009-01-13

305

Optimizing the optical trapping stiffness of holographically trapped microrods using high-speed video tracking  

NASA Astrophysics Data System (ADS)

Dielectric microrods can be trapped horizontally in pairs of holographically controlled optical traps. External forces acting on these microrods are registered via the rotational and translational displacement of the microrod relative to the traps. In the following paper we demonstrate accurate, real-time tracking of this displacement in two dimensions. The precision of the method is estimated and the translational and rotational stiffness coefficients of the trapped microrod are evaluated by analysing the thermal motion and the Stokes drag. The variation of these stiffness coefficients relative to the displacement of the traps from the ends of the microrods is measured, and optimal trapping conditions are located.

Phillips, D. B.; Carberry, D. M.; Simpson, S. H.; Schäfer, H.; Steinhart, M.; Bowman, R.; Gibson, G. M.; Padgett, M. J.; Hanna, S.; Miles, M. J.

2011-04-01

306

Somatic Stiffness of Cochlear Outer Hair Cells Is Voltage-Dependent  

NASA Astrophysics Data System (ADS)

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

He, David Z. Z.; Dallos, Peter

1999-07-01

307

[Cardiorespiratory fitness and arterial stiffness in sedentary and not sedentary hypertensive workers].  

PubMed

In hypertensive subjects, arterial stiffness and arterial wave early reflection are thought to be the major factor limiting cardiac reserve and exercise capacity. Aortic augmentation index (AIx) is a measure of arterial wave reflection and stiffness, and has been associated with decreased cardiorespiratory fitness. We investigated the role of physical activity at work and its effect on such association. 25 hypertensive middle-aged workers, without history of diabetes, cardiovascular disease, renal failure and inflammatory diseases, were studied. Our study confirms that AIx provides information for the prediction of VO2 peak, being also gained with a non-invasive and practical test. Inside the two groups of sedentary and non sedentary workers, the relation between AIx and VO2 peak is still significant; whereas the non sedentary group showed a worse cardiorespiratory fitness without significantly differences in arterial stiffness. PMID:18409980

D'Alessio, P; Savino, M; Santoro, A; Gabrielli, F A; Pisanello, C; Natali, R; Loperfido, F

308

Discontinuous Galerkin for Stiff Hyperbolic Systems  

SciTech Connect

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

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

1999-06-27

309

Hemoglobin A1c and Arterial and Ventricular Stiffness in Older Adults  

PubMed Central

Objective Arterial and ventricular stiffening are characteristics of diabetes and aging which confer significant morbidity and mortality; advanced glycation endproducts (AGE) are implicated in this stiffening pathophysiology. We examined the association between HbA1c, an AGE, with arterial and ventricular stiffness measures in older individuals without diabetes. Research Design & Methods Baseline HbA1c was measured in 830 participants free of diabetes defined by fasting glucose or medication use in the Cardiovascular Health Study, a population-based cohort study of adults aged ?65 years. We performed cross-sectional analyses using baseline exam data including echocardiography, ankle and brachial blood pressure measurement, and carotid ultrasonography. We examined the adjusted associations between HbA1c and multiple arterial and ventricular stiffness measures by linear regression models and compared these results to the association of fasting glucose (FG) with like measures. Results HbA1c was correlated with fasting and 2-hour postload glucose levels (r?=?0.21; p<0.001 for both) and positively associated with greater body-mass index and black race. In adjusted models, HbA1c was not associated with any measure of arterial or ventricular stiffness, including pulse pressure (PP), carotid intima-media thickness, ankle-brachial index, end-arterial elastance, or left ventricular mass (LVM). FG levels were positively associated with systolic, diastolic and PP and LVM. Conclusions In this sample of older adults without diabetes, HbA1c was not associated with arterial or ventricular stiffness measures, whereas FG levels were. The role of AGE in arterial and ventricular stiffness in older adults may be better assessed using alternate AGE markers.

Zieman, Susan J.; Kamineni, Aruna; Ix, Joachim H.; Barzilay, Joshua; Djousse, Luc; Kizer, Jorge R.; Biggs, Mary L.; de Boer, Ian H.; Chonchol, Michel; Gottdiener, John S.; Selvin, Elizabeth; Newman, Anne B.; Kuller, Lewis H.; Siscovick, David S.; Mukamal, Kenneth J.

2012-01-01

310

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

311

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

312

The Stiffness of Rabbit Skeletal Actomyosin Cross-Bridges Determined with an Optical Tweezers Transducer  

Microsoft Academic Search

Muscle contraction is brought about by the cyclical interaction of myosin with actin coupled to the breakdown of ATP. The current view of the mechanism is that the bound actomyosin complex (or “cross-bridge”) produces force and movement by a change in conformation. This process is known as the “working stroke.” We have measured the stiffness and working stroke of a

Claudia Veigel; Marc L. Bartoo; David C. S. White; John C. Sparrow; Justin E. Molloy

1998-01-01

313

The Design of Externally Pressurized Gas Thrust Bearings for Maximum Stiffness and Stability  

Microsoft Academic Search

Relations governing the common forms of externally pressurized (EP) bearings are reviewed and a simple formula is derived which allows the bearing stiffness to be calculated directly from known parameters. Pneumatic instability is discussed, and the importance of land area for stable operation emphasized. Measurement techniques are described and some experimental data presented to support the theory. It is shown

D. C. Allais

1962-01-01

314

Experimental Dynamic Stiffness and Damping of Externally Pressurized Gas-Lubricated Journal Bearings.  

National Technical Information Service (NTIS)

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. Th...

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

1976-01-01

315

Does aortic stiffness improve the prediction of coronary heart disease in elderly? The Rotterdam Study  

Microsoft Academic Search

It has been demonstrated that aortic stiffness is an independent predictor of cardiovascular disease. We investigated whether this measure is of use in cardiovascular risk stratification in clinical practice for elderly subjects (mean age 71.5 years). Within the framework of the Rotterdam Study, we stratified subjects free of coronary heart disease (CHD) at baseline into categories of low (20%) 10-year

G C Verwoert; S E Elias-Smale; D Rizopoulos; M T Koller; E W Steyerberg; A Hofman; M Kavousi; E J G Sijbrands; A P G Hoeks; R S Reneman; J C M Witteman; JCM Witteman

2012-01-01

316

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

317

Parameter estimation for stiff equations of biosystems using radial basis function networks  

Microsoft Academic Search

Background: The modeling of dynamic systems requires estimating kinetic parameters from experimentally measured time-courses. Conventional global optimization methods used for parameter estimation, e.g. genetic algorithms (GA), consume enormous computational time because they require iterative numerical integrations for differential equations. When the target model is stiff, the computational time for reaching a solution increases further. Results: In an attempt to solve

Yoshiya Matsubara; Shinichi Kikuchi; Masahiro Sugimoto; Masaru Tomita

2006-01-01

318

SCD6 induces ribonucleoprotein granule formation in trypanosomes in a translation-independent manner, regulated by its Lsm and RGG domains  

PubMed Central

Ribonucleoprotein (RNP) granules are cytoplasmic, microscopically visible structures composed of RNA and protein with proposed functions in mRNA decay and storage. Trypanosomes have several types of RNP granules, but lack most of the granule core components identified in yeast and humans. The exception is SCD6/Rap55, which is essential for processing body (P-body) formation. In this study, we analyzed the role of trypanosome SCD6 in RNP granule formation. Upon overexpression, the majority of SCD6 aggregates to multiple granules enriched at the nuclear periphery that recruit both P-body and stress granule proteins, as well as mRNAs. Granule protein composition depends on granule distance to the nucleus. In contrast to findings in yeast and humans, granule formation does not correlate with translational repression and can also take place in the nucleus after nuclear targeting of SCD6. While the SCD6 Lsm domain alone is both necessary and sufficient for granule induction, the RGG motif determines granule type and number: the absence of an intact RGG motif results in the formation of fewer granules that resemble P-bodies. The differences in granule number remain after nuclear targeting, indicating translation-independent functions of the RGG domain. We propose that, in trypanosomes, a local increase in SCD6 concentration may be sufficient to induce granules by recruiting mRNA. Proteins that bind selectively to the RGG and/or Lsm domain of SCD6 could be responsible for regulating granule type and number.

Kruger, Timothy; Hofweber, Mario; Kramer, Susanne

2013-01-01

319

On the geometry of stiff knots  

NASA Astrophysics Data System (ADS)

We report on the geometry and mechanics of knotted strings. We focus on the situation where the string is stiff (it has a large bending rigidity), and thin (its width is much smaller than its length). We find that: (i) the equilibrium energy depends on the type of knot as the square of the bridge number; (ii) braid localization is a general feature of stiff strings entanglements; (iii) there is an upper bound for the multiplicity of the braids and contact points in the ground state. (iv) Finally, a general confinement inequality is used to derive an upper bound on the knot gyration radius. We shall also discuss the asymptotic behavior of the knot when the filament width is small, both in the presence and in the absence of torsion (twist) energy. We conjecture a universal ground state geometry for thin strings with torsion rigidity in the presence of a large twists. Ref: R. Gallotti, O. Pierre-Louis, Phys. Rev. E 75, 031801 (2007).

Pierre-Louis, Olivier

2009-03-01

320

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

321

Pulling a polymer with anisotropic stiffness near a sticky wall  

NASA Astrophysics Data System (ADS)

We solve exactly a two-dimensional partially directed walk model of a semi-flexible polymer that has one end tethered to a sticky wall, while a pulling force away from the adsorbing surface acts on the free end of the walk. This model generalizes a number of previously considered adsorption models by incorporating individual horizontal and vertical stiffness effects, in competition with a variable pulling angle. A solution to the corresponding generating function is found by means of the kernel method. While the phases and related phase transitions are similar in nature to those found previously the analysis of the model in terms of its physical variables highlights various novel structures in the shapes of the phase diagrams and related behaviour of the polymer. We review the results of previously considered sub-cases, augmenting these findings to include analysis with respect to the model’s physical variables—namely, temperature, pulling force, pulling angle away from the surface, stiffness strength and the ratio of vertical to horizontal stiffness potentials, with our subsequent analysis for the general model focusing on the effect that stiffness has on this pulling angle range. In analysing the model with stiffness we also pay special attention to the case where only vertical stiffness is included. The physical analysis of this case reveals behaviour more closely resembling that of an upward pulling force acting on a polymer than it does of a model where horizontal stiffness acts. The stiffness-temperature phase diagram exhibits re-entrance for low temperatures, previously only seen for three-dimensional or co-polymer models. For the most general model we delineate the shift in the physical behaviour as we change the ratio of vertical to horizontal stiffness between the horizontal-only and the vertical-only stiffness regimes. We find that a number of distinct physical characteristics will only be observed for a model where the vertical stiffness dominates the horizontal stiffness.

Tabbara, R.; Owczarek, A. L.

2012-11-01

322

Polyimide-based intracortical neural implant with improved structural stiffness  

Microsoft Academic Search

A novel structure for chronically implantable cortical electrodes using polyimide bio-polymer was devised, which provides both flexibility for micro-motion compliance between brain tissues and the skull and at the brain\\/implant interface and stiffness for better surgical handling. A 5-10 µm thick silicon backbone layer was attached to the tip of the electrode to enhance the structural stiffness. This stiff segment

Kee-Keun Lee; Jiping He; Amarjit Singh; Stephen Massia; Gholamreza Ehteshami; Bruce Kim; Gregory Raupp

2004-01-01

323

Properties of the grasp stiffness matrix and conservative control strategies  

SciTech Connect

In this paper, the authors present fundamental properties of stiffness matrices as applied in analysis of grasping and dexterous manipulation in configuration spaces and linear Euclidean R{sup 3x3} space without rotational components. A conservative-stiffness matrix in such spaces needs to satisfy both symmetric and exact differential criteria. Two types of stiffness matrices are discussed: constant and configuration-dependent matrices are discussed: constant and configuration-dependent matrices. The symmetric part of a constant-stiffness matrix can be derived from a conservative quadratic potential function in the Hermitian form; while the skew-symmetric part is a function of the nonconservative curl vector field of the grasp. A configuration-dependent stiffness matrix needs to be symmetric and must simultaneously satisfy the exact differential condition to be conservative. The theory is most relevant to the Cartesian stiffness control, where the stiffness of the end effector is usually constant, such as that in RCC wrists. Conservative control strategies are proposed for a configuration-dependent stiffness matrix. One of the most important results of this paper is the nonconservative congruence mapping of stiffness between the joint and Cartesian spaces. In general, the congruence transformation (or its inverse transformation), K{sub {theta}} = J{sub {theta}}{sup T}K{sub p}J{sub {theta}}, is a nonconservative mapping over finite paths for a configuration-dependent Jacobian. Thus, to obtain a conservative system with respect to the Cartesian space, one has to either find the corresponding K{sub {theta}} at every configuration due to the constant and symmetric Cartesian stiffness matrix, or determine symmetric yet configuration-varying K{sub {theta}} at every configuration due to the constant and symmetric Cartesian stiffness matrix, or determine the symmetric yet configuration-varying K{sub {theta}} which makes the resulting configuration-dependent K{sub p} conservative. In addition, the stiffness matrix also must be positive definite to maintain stability.

Kao, I.; Ngo, C. [State Univ. of New York, Stony Brook, NY (United States)

1999-02-01

324

Human vertebral body apparent and hard tissue stiffness  

Microsoft Academic Search

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

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

1998-01-01

325

Stress determination from hydraulic fracturing tests: the system stiffness approach  

Microsoft Academic Search

Hydraulic fracturing tests with mud is the most inexpensive method for determining the minor in situ horizontal stress in deep petroleum wells.This paper presents a unified model of pump-in\\/shut-in and pump-in\\/flowback tests. The key element of the model is the system stiffness resulting from the stiffness of the fluid volume pressurised, and the stiffness due to the fracture.It is shown

A. M Raaen; E Skomedal; H Kjørholt; P Markestad; D Økland

2001-01-01

326

Dynamic Model for Locally Stiff Ring and Straight Chain Polymers  

Microsoft Academic Search

The Rouse–Bueche bead–spring model for high polymers is extended to account for stiffness arising from local torsional and bending interactions. A mechanical model including second- and third-nearest-neighbor bead–spring interactions is developed. The effect of local stiffness is introduced into the normal-mode eigenvalue spectrum via second- and third-nearest-neighbor Hooke's law spring constants. A calculation is made of the effect of stiffness

Eliot Simon

1970-01-01

327

Aortic stiffness: an old concept for new insights into the pathophysiology of functional mitral regurgitation.  

PubMed

Functional mitral regurgitation (FMR) is thought to be linked with ventricular afterload. However, the relation between aortic stiffness, which is a main determinant of ventricular afterload, and quantitatively assessed mitral regurgitation is unknown. A total of 175 patients (age 61 ± 13; 85 % male) with left ventricular (LV) systolic dysfunction were studied consecutively. Left ventricular volumes, ejection fraction, and LV outflow tract stroke volume were measured. Aortic pulse wave velocity (PWV), a known marker of aortic stiffness, was determined using Doppler flow recordings as the distance (d) traveled by the pulse wave, measured over the body surface as the distance between the two recording sites, divided by the time (t) taken by the pulse wave to travel from the descending aorta to the abdominal aorta. Mitral effective regurgitant orifice (ERO), regurgitant volume (RV), and fraction (RF) were measured using the proximal isovelocity surface area method. The mean PWV was 6.0 ± 3.5 m/s (range 2.6-25). PWV was significantly associated with ERO (r = 0.35; p < 0.0001), RV (r = 0.36; p < 0.0001) RF (p = 0.41; p < 0.0001). The association of PWV with each variable of mitral regurgitation was independent of LV volume, cardiac output, and systemic vascular resistance. Aortic stiffness is an important determinant of the severity of FMR. Aortic stiffness should be considered an important therapeutic target in patients with LV dysfunction in order to ameliorate both LV systolic and diastolic function and mitral regurgitation. PMID:23064718

Rossi, Andrea; Bonapace, Stefano; Cicoira, Mariantonietta; Conte, Luca; Anselmi, Anna; Vassanelli, Corrado

2012-10-13

328

?2-microglobulin, a novel biomarker of peripheral arterial disease, independently predicts aortic stiffness in these patients.  

PubMed

Arterial stiffness is a prominent feature of vascular ageing and strongly predicts cardiovascular and total mortality. The ?2-microglobulin, (?2M) a newly identified biomarker of peripheral arterial disease (PAD), is related to renal insufficiency, inflammatory and neoplastic diseases, but may also play a role in vascular dysfunction. However, the relationship between arterial stiffness and ?2M has not been previously studied in patients with atherosclerosis. In the present study we examined a possible association between ?2M and arterial stiffness in patients with PAD and in healthy subjects. Plasma ?2M levels and parameters of arterial stiffness such as aortic pulse wave velocity (aPWV) and augmentation index (AIx) were measured in 66 patients with PAD and in 66 apparently healthy subjects. Plasma levels of ?2M, aPWV and AIx were significantly increased in patients with PAD compared with controls (1858.1 ± 472.8 vs 1554.5 ± 277.9 ?g/L, p < 0.001; 9.9 ± 2.2 m/s vs 7.6 ± 1.6 m/s, p < 0.001; 28 ± 8 vs 14 ± 11%, p < 0.001; respectively). There existed significant correlation between aPWV and ?2M for the patient group (R = 0.47; p < 0.001), but not for the controls (R = 0.14; p = 0.26). In multivariate analysis, ?2M remained independently associated with aPWV, fetuin-A, age and glomerular filtration rate in patients (R(2) = 0.5, p < 0.001). We found no relationship between ?2M and AIx in either group. We demonstrated that among patients with PAD elevated plasma ?2M levels were associated with higher aortic stiffness irrespective of cardiovascular disease risk factors. These data suggest that ?2M may influence the pathogenesis of aortic stiffness in atherosclerosis. PMID:21314441

Kals, Jaak; Zagura, Maksim; Serg, Martin; Kampus, Priit; Zilmer, Kersti; Unt, Eve; Lieberg, Jüri; Eha, Jaan; Peetsalu, Ants; Zilmer, Mihkel

2011-02-14

329

Fear of Movement Is Related to Trunk Stiffness in Low Back Pain  

PubMed Central

Background Psychological features have been related to trunk muscle activation patterns in low back pain (LBP). We hypothesised higher pain-related fear would relate to changes in trunk mechanical properties, such as higher trunk stiffness. Objectives To evaluate the relationship between trunk mechanical properties and psychological features in people with recurrent LBP. Methods The relationship between pain-related fear (Tampa Scale for Kinesiophobia, TSK; Photograph Series of Daily Activities, PHODA-SeV; Fear Avoidance Beliefs Questionnaire, FABQ; Pain Catastrophizing Scale, PCS) and trunk mechanical properties (estimated from the response of the trunk to a sudden sagittal plane forwards or backwards perturbation by unpredictable release of a load) was explored in a case-controlled study of 14 LBP participants. Regression analysis (r2) tested the linear relationships between pain-related fear and trunk mechanical properties (trunk stiffness and damping). Mechanical properties were also compared with t-tests between groups based on stratification according to high/low scores based on median values for each psychological measure. Results Fear of movement (TSK) was positively associated with trunk stiffness (but not damping) in response to a forward perturbation (r2?=?0.33, P?=?0.03), but not backward perturbation (r2?=?0.22, P?=?0.09). Other pain-related fear constructs (PHODA-SeV, FABQ, PCS) were not associated with trunk stiffness or damping. Trunk stiffness was greater for individuals with high kinesiophobia (TSK) for forward (P?=?0.03) perturbations, and greater with forward perturbation for those with high fear avoidance scores (FABQ-W, P?=?0.01). Conclusions Fear of movement is positively (but weakly) associated with trunk stiffness. This provides preliminary support an interaction between biological and psychological features of LBP, suggesting this condition may be best understood if these domains are not considered in isolation.

Karayannis, Nicholas V.; Smeets, Rob J. E. M.; van den Hoorn, Wolbert; Hodges, Paul W.

2013-01-01

330

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

Microsoft Academic Search

The aim of this study was to determine whether muscle stiffness measured in vivo was different between males and females.\\u000a Distal displacement of the gastrocnemius medialis myotendinous junction was measured directly using ultrasonography during\\u000a passive dorsiflexion in eight males and eight females (age range 19–28 years). Plantarflexion torque and myotendinous junction\\u000a displacement were measured at 5° intervals, where 0° was with

Christopher I. Morse

331

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

PubMed Central

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

2011-01-01

332

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

333

Arterial stiffness and the development of hypertension. The ARIC study.  

PubMed

Decreased elasticity in large and medium-sized arteries has been postulated to be associated with cardiovascular diseases. We prospectively examined the relation between arterial elasticity and the development of hypertension over 6 years of follow-up in a cohort of 6992 normotensive men and women aged 45 to 64 years at baseline from the biracial, population-based Atherosclerosis Risk in Communities (ARIC) Study. Arterial elasticity was measured from high-resolution B-mode ultrasound examination of the left common carotid artery as adjusted arterial diameter change (in micrometers, simultaneously adjusted for diastolic blood pressure, pulse pressure, pulse pressure squared, diastolic arterial diameter, and height), Peterson's elastic modulus (in kilopascals), Young's elastic modulus (in kilopascals), and beta stiffness index. Incident hypertension (n=551) was defined as systolic blood pressure >/=160 mm Hg, diastolic blood pressure >/=95 mm Hg, or the use of antihypertensive medication at a follow-up examination conducted every 3 years. The age-, ethnicity-, center-, gender-, education-, smoking-, heart rate-, and obesity-adjusted means (SE) of baseline adjusted arterial diameter change, Peterson's elastic modulus, Young's elastic modulus, and beta stiffness index were 397 (5), 148 (2.0), 787 (12.7), and 11.43 (0.16), respectively, in persons who developed hypertension during follow-up, in contrast to 407 (1), 124 (0.6), 681 (3.7), and 10.34 (0.05), respectively, for persons who did not. The similarly adjusted cumulative incident rates of hypertension from the highest to the lowest quartiles of arterial elasticity were 6.7%, 8.0%, 7.3%, and 9.6%, respectively, when measured by adjusted arterial diameter change (P<0.01). One standard deviation decrease in arterial elasticity was associated with 15% greater risk of hypertension, independent of established risk factors for hypertension and the level of baseline blood pressure. These results suggest that lower arterial elasticity is related to the development of hypertension. PMID:10454441

Liao, D; Arnett, D K; Tyroler, H A; Riley, W A; Chambless, L E; Szklo, M; Heiss, G

1999-08-01

334

Stiffness tomography by atomic force microscopy.  

PubMed

The atomic force microscope is a convenient tool to probe living samples at the nanometric scale. Among its numerous capabilities, the instrument can be operated as a nano-indenter to gather information about the mechanical properties of the sample. In this operating mode, the deformation of the cantilever is displayed as a function of the indentation depth of the tip into the sample. Fitting this curve with different theoretical models permits us to estimate the Young's modulus of the sample at the indentation spot. We describe what to our knowledge is a new technique to process these curves to distinguish structures of different stiffness buried into the bulk of the sample. The working principle of this new imaging technique has been verified by finite element models and successfully applied to living cells. PMID:19619482

Roduit, Charles; Sekatski, Serguei; Dietler, Giovanni; Catsicas, Stefan; Lafont, Frank; Kasas, Sandor

2009-07-22

335

Stiffness Tomography by Atomic Force Microscopy  

PubMed Central

Abstract The atomic force microscope is a convenient tool to probe living samples at the nanometric scale. Among its numerous capabilities, the instrument can be operated as a nano-indenter to gather information about the mechanical properties of the sample. In this operating mode, the deformation of the cantilever is displayed as a function of the indentation depth of the tip into the sample. Fitting this curve with different theoretical models permits us to estimate the Young's modulus of the sample at the indentation spot. We describe what to our knowledge is a new technique to process these curves to distinguish structures of different stiffness buried into the bulk of the sample. The working principle of this new imaging technique has been verified by finite element models and successfully applied to living cells.

Roduit, Charles; Sekatski, Serguei; Dietler, Giovanni; Catsicas, Stefan; Lafont, Frank; Kasas, Sandor

2009-01-01

336

[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

337

Salt-induced aggregation of stiff polyelectrolytes.  

PubMed

Molecular dynamics simulation techniques are used to study the process of aggregation of highly charged stiff polyelectrolytes due to the presence of multivalent salt. The dominant kinetic mode of aggregation is found to be the case of one end of one polyelectrolyte meeting others at right angles, and the kinetic pathway to bundle formation is found to be similar to that of flocculation dynamics of colloids as described by Smoluchowski. The aggregation process is found to favor the formation of finite bundles of 10-11 filaments at long times. Comparing the distribution of the cluster sizes with the Smoluchowski formula suggests that the energy barrier for the aggregation process is negligible. Also, the formation of long-lived metastable structures with similarities to the raft-like structures of actin filaments is observed within a range of salt concentration. PMID:21715846

Fazli, Hossein; Mohammadinejad, Sarah; Golestanian, Ramin

2009-09-30

338

Determining cantilever stiffness from thermal noise.  

PubMed

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

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

2013-03-28

339

Effects of Morphology vs. Cell-Cell Interactions on Endothelial Cell Stiffness  

PubMed Central

Biological processes such as atherogenesis, wound healing, cancer cell metastasis, and immune cell transmigration rely on a delicate balance between Cell–Cell and cell–substrate adhesion. Cell mechanics have been shown to depend on substrate factors such as stiffness and ligand presentation, while the effects of Cell–Cell interactions on the mechanical properties of cells has received little attention. Here, we use atomic force microscopy to measure the Young’s modulus of live human umbilical vein endothelial cells (HUVECs). In varying the degree of Cell–Cell contact in HUVECs (single cells, groups, and monolayers), we observe that increased cell stiffness correlates with an increase in cell area. Further, we observe that HUVECs stiffen as they spread onto a glass substrate. When we weaken Cell–Cell junctions (i.e., through a low dose of cytochalasin B or treatment with a VE-cadherin antibody), we observe that cell–substrate adhesion increases, as measured by focal adhesion size and density, and the stiffness of cells within the monolayer approaches that of single cells. Our results suggest that while morphology can roughly be used to predict cell stiffness, Cell–Cell interactions may play a significant role in determining the mechanical properties of individual cells in tissues by careful maintenance of cell tension homeostasis.

Stroka, Kimberly M.; Aranda-Espinoza, Helim

2011-01-01

340

Augmentation index and aortic stiffness in bicuspid aortic valve patients with non-dilated proximal aortas  

PubMed Central

Background We compared aortic stiffness, aortic impedance and pressure from wave reflections in the setting of bicuspid aortic valve (BAV) to the tricuspid aortic valve (TAV) in the absence of proximal aortic dilation. We hypothesized BAV is associated with abnormal arterial stiffness. Methods Ten BAV subjects (47 ± 4 years, 6 male) and 13 TAV subjects (46 ± 4 years, 10 male) without significant aortic valve disease were prospectively recruited. Characteristic impedance (Zc) was derived from echocardiographic images and pulse wave Doppler of the left ventricular outflow tract. Applanation tonometry was performed to obtain pulse wave velocity (PWV) at several sites as measures of arterial stiffness and augmentation index (AIx) as a measure of wave reflection. Results There were no significant differences between BAV and TAV subjects with regard to heart rate or blood pressure. Zc was similar between BAV and TAV subjects (p=0.25) as was carotid-femoral pulse wave velocity (cf-PWV) and carotid-radial PWV (cr-PWV) between BAV and TAV subjects (p=0.99). Carotid AIx was significantly higher in BAV patients compared with TAV patients (14.3 ± 4.18% versus -3.02 ± 3.96%, p=0.007). Conclusions Aortic stiffness and impedance is similar between subjects with BAV and TAV with normal aortic dimensions. The significantly higher carotid AIx in BAV, a proxy of increased pressure from wave reflections, may reflect abnormal vascular function distal to the aorta.

2013-01-01

341

A variable stiffness device selection and design tool for lightly damped structures  

Microsoft Academic Search

Due to the wide variety of types and capabilities of variable stiffness devices, selecting a variable stiffness device for vibration control of a structure can be difficult. A method for selecting and understanding the performance of variable stiffness devices was developed. First, a parameter for roughly comparing variable stiffness devices was identified using the literature. Next, variable stiffness devices in

M. F. Winthrop; W. P. Baker; R. G. Cobb

2005-01-01

342

Relationship between left ventricular diastolic function and arterial stiffness in asymptomatic patients with diabetes mellitus.  

PubMed

Left ventricular (LV) diastolic dysfunction and increased arterial stiffness are common in patients with diabetes mellitus (DM). However, the relation between these two pathophysiological factors remains unclear. The aim of this study was to investigate the relationship between LV diastolic function and arterial stiffness as assessed with applanation tonometry. In 142 asymptomatic patients with DM (mean age 48 years, 75 (53 %) men, 72 (51 %) patients with type 2 DM) LV diastolic function was assessed with echocardiography. Arterial stiffness was evaluated measuring the aortic pulse wave velocity (PWV) whereas wave reflection was assessed measuring central systolic blood pressure (cSBP), central pulse pressure (cPP), and augmentation index (AIx) with applanation tonometry. Mean E/A ratio, E' and E/E' ratio were 1.1 ± 0.3, 8.1 ± 2.3 and 9.2 ± 3.3 cm/s, respectively. Mean PWV, mean cSBP, median cPP and mean AIx were 7.9 ± 2.4 m/s, 122 ± 17 mmHg, 40 [35-51] mmHg and 17.9 ± 12.1 %, respectively. PWV was independently associated with LV diastolic dysfunction grade (? = 0.76, p = 0.03). In contrast, measures of wave reflection, cPP, cSBP and AIx were independently related with E/A ratio, but not with the LV diastolic dysfunction grade. Parameters of arterial stiffness and wave reflection are associated with echocardiographic indices of LV diastolic function in asymptomatic patients with DM. Therapies that prevent progression of arterial stiffness and reduce late-systolic pressure overload may help to reduce the prevalence of LV diastolic dysfunction in this population. PMID:23053856

Roos, Cornelis J; Auger, Dominique; Djaberi, Roxana; de Koning, Eelco J; Rabelink, Ton J; Pereira, Alberto M; Bax, Jeroen J; Delgado, Victoria; Jukema, J Wouter; Scholte, Arthur J

2012-09-28

343

Role of Inflammation in the Pathogenesis of Arterial Stiffness  

PubMed Central

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

Park, Sungha

2012-01-01

344

Dually Stiff Floors for Injury Prevention for the Elderly.  

National Technical Information Service (NTIS)

This proposals builds upon previous work in which a dually stiff floor intended to reduce the incidence of hip fractures in the elderly was successfully designed and developed. The Penn State Safety Floor (PSUSF) is stiff to loads typical of everyday acti...

D. A. Streit

1999-01-01

345

Dually Stiff Floors for Injury Prevention for the Elderly.  

National Technical Information Service (NTIS)

This proposal builds upon previous work in which a dually stiff floor intended to reduce the incidence of hip fractures in the elderly was successfully designed and developed. The Penn State Safety Floor (PSUSF) is stiff to loads typical of everyday activ...

D. A. Streit

1997-01-01

346

Modeling and design of energy efficient variable stiffness actuators  

Microsoft Academic Search

In this paper, we provide a port-based mathematical framework for analyzing and modeling variable stiffness actuators. The framework provides important insights in the energy requirements and, therefore, it is an important tool for the design of energy efficient variable stiffness actuators. Based on new insights gained from this approach, a novel conceptual actuator is presented. Simulations show that the apparent

Ludo C. Visser; Raffaella Carloni; Ramazan Unal; Stefano Stramigioli

2010-01-01

347

Design of a robot joint with variable stiffness  

Microsoft Academic Search

A robot joint with a variable stiffness unit is presented. The variable stiffness unit (VSU) is composed of a motor, two rings that consist of arc-shaped magnets separated by spacers, and a linear guide to change the cross-sectional area of the two rings. Angular displacement between two rings causes the magnets to generate torque, which acts as a nonlinear spring.

Junho Choi; Woosub Lee; Sung-chul Kang

2008-01-01

348

Semiactive vibration isolation system with variable stiffness and damping control  

Microsoft Academic Search

Semi-active systems with variable stiffness and damping have demonstrated excellent performance. However, conventional devices for controlling variable stiffness are complicated and difficult to implement in most applications. To address this issue, a new configuration using two controllable dampers and two constant springs is proposed. This paper presents theoretical and experimental analyses of the proposed system. A Voigt element and a

Yanqing Liu; Hiroshi Matsuhisa; Hideo Utsuno

2008-01-01

349

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

350

Preliminary investigation of a novel controlled stiffness proximal femoral prosthesis.  

PubMed

Previous studies have suggested that a controlled stiffness prosthesis is required to address the conflicting requirements of minimizing stress shielding and micromotion. The design for a controlled stiffness prosthesis is proposed and a preliminary analytical investigation performed to assess its predicted performance before fabrication of a prototype component. The novel prosthesis consisted of a cobalt-chrome core and a flexible composite outer layer. Varying the composite layer thickness allowed the prosthesis stiffness to be controlled. Three variants of the controlled stiffness prosthesis were critically assessed using the finite element method and their predicted performance compared with those of conventional prosthesis designs. The potential for stress shielding was assessed by examining the periosteal strain energy and the potential for migration assessed by examining the endosteal minimum principal cancellous bone stresses. Both the conventional and controlled stiffness implants performed poorly as press-fit prostheses. All the press-fit prostheses generated high cancellous bone stresses, suggesting that excessive migration of these implants would be likely. The controlled stiffness implants performed better than the conventional implants when bonded to the surrounding bone. Although the controlled stiffness implants did not eliminate stress shielding of the calcar, they produced higher strain energies than the conventional designs. The findings of this study are that osseointegrated controlled stiffness implants may perform better than current osseointegrated cementless prostheses and therefore it is worth while progressing to the next stage, of prototyping an implant. PMID:9695635

Simões, J A; Taylor, M; Marques, A T; Jeronimidis, G

1998-01-01

351

Stiff-Person Syndrome First Manifesting in Pregnancy  

Microsoft Academic Search

Stiff-person syndrome (SPS) is a rare neurological disorder characterised by progressive stiffness and painful muscle spasms. We present a case of the autoimmune form of glutamate decarboxylase-positive SPS that initially manifested in pregnancy. The diagnosis was made based on clinical, laboratory and electromyoneurographic criteria. The patient was administered low doses of diazepam and baclofen. Considering the clinical picture of SPS

Denis Cerimagic; Ervina Bilic

2009-01-01

352

Stiff-person syndrome associated with oral isotretinoin treatment  

Microsoft Academic Search

We describe a patient with severe nodulocystic acne who developed disabling muscle stiffness and painful superimposed spasms of the neck, back and upper limbs 10 days after the onset of oral isotretinoin treatment. The muscle hyperactivity condition, which revealed the clinical and electromyographic features of the stiff-person syndrome, gradually resolved 2 weeks after drug withdrawal.

E Chroni; Th Sakkis; S Georgiou; A Monastirli; E Pasmatzi; C Paschalis; D Tsambaos

2002-01-01

353

High stiffness gas journal bearing under the step force  

Microsoft Academic Search

The object of this paper is an analysis of a new type of gas journal bearing, which provides a very high static stiffness coefficient. As the load of bearings is very seldom constant, the response of the high stiffness bearing to the step force and its operation during a transient period are investigated. The pattern of the dynamic response of

K. Czolczynski; L. Brzeski; Z. Kazimierski

1993-01-01

354

Optimality principles in variable stiffness control: The VSA hammer  

Microsoft Academic Search

The control of a robot's mechanical impedance is attracting increasing attention of the robotics community. Recent research in Robotics has recognized the importance of Variable Stiffness Actuators (VSA) in safety and performance of robots. An important step in using VSA for safety has been to understand the optimality principles that regulate the synchronized variation of stiffness and velocity when moving

Manolo Garabini; Andrea Passaglia; Felipe Belo; Paolo Salaris; Antonio Bicchi

2011-01-01

355

Contact stiffness of layered materials for ultrasonic atomic force microscopy  

Microsoft Academic Search

A method to calculate the contact stiffness between a layered material and an ultrasonic atomic force microscope (UAFM) tip is proposed. The radiation impedance method is used to determine the ratio of the applied force to the average displacement within the contact area. This information is used in an iterative algorithm based on Hertzian theory to obtain the contact stiffness.

G. G. Yaralioglu; F. L. Degertekin; K. B. Crozier; C. F. Quate

2000-01-01

356

Aggregation Technique for the Transient Analysis of Stiff Markov Systems.  

National Technical Information Service (NTIS)

An approximation algorithm for systematically converting a stiff Markov chain onto a non-stiff chain defined over a smaller state space is given. The algorithm unifies and extends earlier approaches to the problem in the context of transient analysis. The...

K. S. Trivedi

1985-01-01

357

A methodology for joint stiffness identification of serial robots  

Microsoft Academic Search

This paper presents a new methodology for joint stiffness identification of serial robots. This methodology aims at evaluating all joint stiffness values responsible for both translational and rotational displacements of the robot end-effector subject to an external wrench (force and torque). The links of the robot are supposed to be quite stiffer than the joints and not known as it

Claire Dumas; Stephane Caro; Mehdi Cherif; Sebastien Garnier; Benoit Furet

2010-01-01

358

Flexural strength and stiffness of southern pine plywood  

Microsoft Academic Search

New information is presented that concerns flexural strength and stiffness of southern pine plywood and verification of a method developed by the U. S. Forest Products Laboratory for predicting properties of plywood. This method can predict, with sufficient accuracy, properties of southern pine plywood despite the large natural variability of veneer of this species and other variables. Strength and stiffness

Evangelos J. Biblis; Yen-Ming Chiu

1970-01-01

359

In-plane stiffness of shear walls with openings  

Microsoft Academic Search

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

M. Qamaruddin

1998-01-01

360

Effect of sildenafil on arterial stiffness and wave reflection.  

PubMed

While sildenafil (Viagra) is widely prescribed for erectile dysfunction, its effect on arterial function is not established. The elastic properties of the aorta, as well as the magnitude and timing of wave reflection, are important factors for efficient performance of the cardiovascular system and have been identified as prognosticators of cardiovascular risk. A total of 24 subjects with coronary artery disease, of whom 14 were hypertensives, aged 69 +/- 8 years, were studied in a randomized, placebo-controlled, double-blind, cross-over design. Measurements lasted for 3 h after the sildenafil intake (50 mg, p.o.) or placebo. Aortic elastic properties were evaluated with carotid-femoral pulse wave velocity; wave reflection was evaluated with augmentation index and augmented pressure of the aortic pressure waveform. Pulse wave velocity decreased significantly (by 0.65 m/s, p = 0.005), denoting a decrease in aortic stiffness. Augmentation index and augmented pressure decreased significantly (by 4.47% absolute and by 4.01 mmHg; p < 0.001 and p = 0.001, respectively), denoting a decreased effect of wave reflection from the periphery. Aortic pulse pressure decreased significantly (by 6.74 mmHg, p < 0.05). An active effect of the drug on aortic wall appears to contribute to the decrease in pulse wave velocity, although other mechanisms such as a decrease of blood pressure and autonomic reflexes could also have contributed. The effect of sildenafil lasted throughout the study (3 h), being evident 30 min after drug intake. In conclusion, this study shows, for the first time, that sildenafil has a favorable effect on aortic stiffness and wave reflection in patients with coronary artery disease. This finding may have important implications for cardiovascular performance and exercise capacity during intercourse. PMID:15125484

Vlachopoulos, Charalambos; Hirata, Kozo; O'Rourke, Michael F

2003-11-01

361

Association of Serum Uric Acid With Aortic Stiffness and Pressure in a Chinese Workplace Setting  

Microsoft Academic Search

BackgroundIn the present analysis, we investigated the association of serum uric acid with aortic stiffness and pressure as measured by carotid–femoral pulse wave velocity (cf-PWV) and central systolic blood pressure (SBP), respectively.MethodsOur study was conducted in the framework of cardiovascular health examinations for the employees of a factory and their family members (ages 15–79 years). We performed arterial measurements using

Xin Chen; Yan Li; Chang-Sheng Sheng; Qi-Fang Huang; Yang Zheng; Ji-Guang Wang

2010-01-01

362

Endothelial Function and Arterial Stiffness in Minimally Symptomatic Obstructive Sleep Apnea  

Microsoft Academic Search

OSA, endothelial function was assessed by ultrasonographic mea- surement of flow-mediated dilatation, and by applanation tonom- etry-derived pulse wave analysis (forearm ischemia and salbutamol- induced changes in augmentation index, AIx). Arterial stiffness was assessed by AIx and ambulatory blood pressure (ABP) was measured over 1 week. Measurements and Main Results: In patients with OSA, flow-mediated dilatation was significantly lower than

Malcolm Kohler; Sonya Craig; Debby Nicoll; Paul Leeson; Robert J. O. Davies; John R. Stradling

2008-01-01

363

Precise damping and stiffness extraction in acoustic driven cantilever in liquid  

NASA Astrophysics Data System (ADS)

In this paper, we first explain how to extract accurately the driving force acting on the acoustic driven atomic force microscope cantilever in liquid from the measured resonance curve. We present a model that includes the driving force to extract precisely the damping and the stiffness of the tip sample interaction. The model is validated by an experimental test based on two independent methods to measure the hydrodynamic drag coefficient of a sphere moving perpendicular to flat surface.

Maali, Abdelhamid; Boisgard, Rodolphe

2013-10-01

364

Quantification of shoulder tightness and associated shoulder kinematics and functional deficits in patients with stiff shoulders  

Microsoft Academic Search

Measurement of anterior\\/posterior shoulder tightness, humeral external\\/internal rotation range of motion (ROM), scapular upward rotation\\/tipping ROM, and functional limitations were made in 46 patients with unilateral stiff shoulders (SSs) using a clinical measurement (shoulder tightness), a three-dimensional electromagnetic tracking device (shoulder ROM), and self-reports of function. Patients with SSs in their dominant shoulder demonstrated statistically greater posterior shoulder tightness compared

Jing-lan Yang; Shiau-yee Chen; Chein-wei Chang; Jiu-jenq Lin

2009-01-01

365

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

366

Single-cell response to stiffness exhibits muscle-like behavior  

PubMed Central

Living cells sense the rigidity of their environment and adapt their activity to it. In particular, cells cultured on elastic substrates align their shape and their traction forces along the direction of highest stiffness and preferably migrate towards stiffer regions. Although numerous studies investigated the role of adhesion complexes in rigidity sensing, less is known about the specific contribution of acto-myosin based contractility. Here we used a custom-made single-cell technique to measure the traction force as well as the speed of shortening of isolated myoblasts deflecting microplates of variable stiffness. The rate of force generation increased with increasing stiffness and followed a Hill force–velocity relationship. Hence, cell response to stiffness was similar to muscle adaptation to load, reflecting the force-dependent kinetics of myosin binding to actin. These results reveal an unexpected mechanism of rigidity sensing, whereby the contractile acto-myosin units themselves can act as sensors. This mechanism may translate anisotropy in substrate rigidity into anisotropy in cytoskeletal tension, and could thus coordinate local activity of adhesion complexes and guide cell migration along rigidity gradients.

Mitrossilis, Demosthene; Fouchard, Jonathan; Guiroy, Axel; Desprat, Nicolas; Rodriguez, Nicolas; Fabry, Ben; Asnacios, Atef

2009-01-01

367

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

368

Kettin, a major source of myofibrillar stiffness in Drosophila indirect flight muscle  

PubMed Central

Kettin is a high molecular mass protein of insect muscle that in the sarcomeres binds to actin and ?-actinin. To investigate kettin's functional role, we combined immunolabeling experiments with mechanical and biochemical studies on indirect flight muscle (IFM) myofibrils of Drosophila melanogaster. Micrographs of stretched IFM sarcomeres labeled with kettin antibodies revealed staining of the Z-disc periphery. After extraction of the kettin-associated actin, the A-band edges were also stained. In contrast, the staining pattern of projectin, another IFM–I-band protein, was not altered by actin removal. Force measurements were performed on single IFM myofibrils to establish the passive length-tension relationship and record passive stiffness. Stiffness decreased within seconds during gelsolin incubation and to a similar degree upon kettin digestion with ?-calpain. Immunoblotting demonstrated the presence of kettin isoforms in normal Drosophila IFM myofibrils and in myofibrils from an actin-null mutant. Dotblot analysis revealed binding of COOH-terminal kettin domains to myosin. We conclude that kettin is attached not only to actin but also to the end of the thick filament. Kettin along with projectin may constitute the elastic filament system of insect IFM and determine the muscle's high stiffness necessary for stretch activation. Possibly, the two proteins modulate myofibrillar stiffness by expressing different size isoforms.

Kulke, Michael; Neagoe, Ciprian; Kolmerer, Bernhard; Minajeva, Ave; Hinssen, Horst; Bullard, Belinda; Linke, Wolfgang A.

2001-01-01

369

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

PubMed

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

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

1993-05-01

370

Increased arterial stiffness in children treated with anthracyclines for malignant disease.  

PubMed

Survivors of childhood cancer have a significantly higher late morbidity and mortality from cardiovascular diseases. The aim of this study was to determine whether anthracyclines used in childhood could increase arterial stiffness, a well-known independent predictor of cardiovascular diseases. The study included 53 children and adolescents aged 6-20 years having completed anthracycline treatment for a malignant disease according to various protocols at least a year before. The patients were free from clinical or laboratory signs of the underlying disease or cardiac disease. Control group consisted of 45 age- and sex-matched healthy children. Arterial stiffness was determined by measuring aortic pulse wave velocity (PWVao) using oscillometric method (Arteriograph TensioMed device). PWVao value was significantly increased (6.24 +/- 1.34 m/s vs. 5.42 +/- 0.69 m/s; p < 0.001) in patients having received anthracyclines as compared to control group. Increased arterial stiffness was present irrespective of the following parameters: age, sex, body mass index, systolic and diastolic blood pressure, mean arterial pressure and heart rate. It is possible that the effect of anthracycline on increased cardiovascular morbidity and mortality in long-term childhood cancer survivors is associated not only with cardiotoxicity, but also with increased arterial stiffness. PMID:21755708

Herceg-Cavrak, Vesna; Ahel, Vladimir; Batinica, Maja; Matec, Lana; Kardos, Danijel

2011-06-01

371

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

372

Size scaling and stiffness of avian primary feathers: implications for the flight of Mesozoic birds.  

PubMed

The primary feathers of birds are subject to cyclical forces in flight causing their shafts (rachises) to bend. The amount the feathers deflect during flight is dependent upon the flexural stiffness of the rachises. By quantifying scaling relationships between body mass and feather linear dimensions in a large data set of living birds, we show that both feather length and feather diameter scale much closer to predictions for geometric similarity than they do to elastic similarity. Scaling allometry also indicates that the primary feathers of larger birds are relatively shorter and their rachises relatively narrower, compared to those of smaller birds. Two-point bending tests indicated that larger birds have more flexible feathers than smaller species. Discriminant functional analyses (DFA) showed that body mass, primary feather length and rachis diameter can be used to differentiate between different magnitudes of feather bending stiffness, with primary feather length explaining 63% of variance in rachis stiffness. Adding fossil measurement data to our DFA showed that Archaeopteryx and Confuciusornis do not overlap with extant birds. This strongly suggests that the bending stiffness of their primary feathers was different to extant birds and provides further evidence for distinctive flight styles and likely limited flight ability in Archaeopteryx and Confuciusornis. PMID:22260434

Wang, X; Nudds, R L; Palmer, C; Dyke, G J

2012-01-19

373

Wide cantilever stiffness range cavity optomechanical sensors for atomic force microscopy.  

PubMed

We report on progress in developing compact sensors for atomic force microscopy (AFM), in which the mechanical transducer is integrated with near-field optical readout on a single chip. The motion of a nanoscale, doubly clamped cantilever was transduced by an adjacent high quality factor silicon microdisk cavity. In particular, we show that displacement sensitivity on the order of 1 fm/(Hz)(1/2) can be achieved while the cantilever stiffness is varied over four orders of magnitude (?0.01 N/m to ?290 N/m). The ability to transduce both very soft and very stiff cantilevers extends the domain of applicability of this technique, potentially ranging from interrogation of microbiological samples (soft cantilevers) to imaging with high resolution (stiff cantilevers). Along with mechanical frequencies (> 250 kHz) that are much higher than those used in conventional AFM probes of similar stiffness, these results suggest that our cavity optomechanical sensors may have application in a wide variety of high-bandwidth AFM measurements. PMID:23038376

Liu, Yuxiang; Miao, Houxun; Aksyuk, Vladimir; Srinivasan, Kartik

2012-07-30

374

Acute effects of warm footbath on arterial stiffness in healthy young and older women.  

PubMed

Acute systemic thermal therapy can improve arterial stiffness in both animals and humans. We examined and compared the effects of acute local thermal therapy (footbath) on an indicator of human arterial stiffness, cardio-ankle vascular index (CAVI), in 16 healthy young (29.4 ± 0.4 years) and 16 older (59.8 ± 1.7 years) women. Measurements were made at baseline (BL) and at 0 and 30 min after footbath in footbath trial, and at corresponding time points without footbath in control trial. In the footbath trial, subjects immersed their lower legs and feet in water for 30 min, with water temperature ranging from 41 to 43°C. The results showed that footbath elicited significant reductions in CAVI at 0 min compared to the same trial's baseline in both young and older groups (0.55 ± 0.07, P = 0.01 for young; 0.42 ± 0.15, P = 0.03 for older, respectively) with no changes found in the control trials. The percentage of CAVI change at 0 min was significantly greater in young women (91.9 ± 1.1%) compared to older women (96.5 ± 1.8%, P < 0.05). This study indicated that acute warm footbath results in transient improvement of systemic arterial stiffness in both healthy young and older women. Despite similar intervention, the percentage response of arterial stiffness to footbath was attenuated in older women. PMID:21833487

Hu, Qingfeng; Zhu, Weili; Zhu, Yili; Zheng, Lu; Hughson, Richard L

2011-07-21

375

Reduction in tooth stiffness as a result of endodontic and restorative procedures.  

PubMed

Endodontically treated teeth are thought to be more susceptible to fracture as a result of the loss of tooth vitality and tooth structure. This study was designed to compare the contributions of endodontic and restorative procedures to the loss of strength by using nondestructive occlusal loading on extracted intact, maxillary, second bicuspids. An encapsulated strain gauge was bonded on enamel just above the cementoenamel junction on both the buccal and lingual surfaces, and the teeth were mounted in nylon rings leaving 2 mm of root surface exposed. Under load control, each tooth was loaded at a rate of 37 N per s for 3 s and unloaded at the same rate in a closed loop servo-hydraulic system to measure stiffness. A stress-strain curve was generated from each gauge prior to alteration of the tooth and after each procedure performed on the tooth. Cuspal stiffness, as a measure of tooth strength, was evaluated on one of two series of sequentially performed procedures: 1. (a) unaltered tooth, (b) access preparation, (c) instrumentation, (d) obturation, and (e) MOD cavity preparation; or 2. (a) unaltered tooth, (b) occlusal cavity preparation, (c) two-surface cavity preparation, (d) MOD cavity preparation, (e) access, (f) instrumentation, and (g) obturation. Results on 42 teeth indicate that endodontic procedures have only a small effect on the tooth, reducing the relative stiffness by 5%. This was less than that of an occlusal cavity preparation (20%). The largest losses in stiffness were related to the loss of marginal ridge integrity. MOD cavity preparation resulted in an average of a 63% loss in relative cuspal stiffness.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2639947

Reeh, E S; Messer, H H; Douglas, W H

1989-11-01

376

Aerobic training-induced improvements in arterial stiffness are not sustained in older adults with multiple cardiovascular risk factors  

PubMed Central

There is a well-established relationship between increased arterial stiffness and cardiovascular mortality. We examined whether a long-term aerobic exercise intervention (6 months) would increase arterial compliance in older adults with hypertension complicated by Type 2 diabetes (T2DM) and hyperlipidemia. A total of 52 older adults (mean age 69.3±0.6 years, 30 males and 22 females) with diet/oral hypoglycemic-controlled T2DM, hypertension and hypercholesterolemia were recruited. Subjects were randomly assigned to one of two groups: an aerobic group (6 months vigorous aerobic exercise, AT group) and a non-aerobic group (6 months of no aerobic exercise, NA group). Arterial stiffness was measured as pulse-wave velocity (PWV) using the Complior device. Aerobic training decreased arterial stiffness as measured by both radial (P=0.001, 2-way analysis of variance with repeated measures) and femoral (P=0.002) PWV. This was due to a decrease in arterial stiffness in the AT group after 3 months of training, which was not maintained after 6-month training for either radial (P=0.707) or femoral (P=0.680) PWV. Our findings indicate that in older adults with multiple cardiovascular risk factors, short-term improvements in arterial stiffness became attenuated over the long term.

Madden, K M; Lockhart, C; Cuff, D; Potter, T F; Meneilly, G S

2013-01-01

377

Polyelectrolyte multilayer films of controlled stiffness modulate myoblast cells differentiation  

PubMed Central

Beside chemical properties and topographical features, mechanical properties of gels have been recently demonstrated to play an important role in various cellular processes, including cell attachment, proliferation, and differentiation. In this work, we used multilayer films made of poly(L-lysine)/Hyaluronan (PLL/HA) of controlled stiffness to investigate the effects of mechanical properties of thin films on skeletal muscle cells (C2C12 cells) differentiation. Prior to differentiation, cells need to adhere and proliferate in growth medium. Stiff films (E0 > 320 kPa) promoted formation of focal adhesions and organization of the cytoskeleton as well as an enhanced proliferation, whereas soft films were not favorable for cell anchoring, spreading or proliferation. Then C2C12 cells were switched to a low serum containing medium to induce cell differentiation, which was also greatly dependent on film stiffness. Although myogenin and troponin T expressions were only moderately affected by film stiffness, the morphology of the myotubes exhibited striking stiffness-dependent differences. Soft films allowed differentiation only for few days and the myotubes were very short and thick. Cell clumping followed by aggregates detachment could be observed after ~2 to 4 days. On stiffer films, significantly more elongated and thinner myotubes were observed for up to ~ 2 weeks. Myotube striation was also observed but only for the stiffer films. These results demonstrate that film stiffness modulates deeply adhesion, proliferation and differentiation, each of these processes having its own stiffness requirement.

Ren, Kefeng; Crouzier, Thomas; Roy, Christian; Picart, Catherine

2008-01-01

378

Evaluation of chain stiffness of partially oxidized polyguluronate.  

PubMed

The chain stiffness of macromolecules is considered critical in their design and applications. This study utilizes polyguluronate derived from alginate, a typical polysaccharide widely utilized in many biomedical applications, as a model macromolecule to investigate how the chain stiffness can be tightly regulated by partial oxidation. Alginate has a backbone of inherently rigid alpha-L-guluronate (i.e., polyguluronate) and more flexible beta-D-mannuronate. The chain stiffness of the polyguluronate was specifically studied in this paper, as this component plays a critical role in the formation of alginate hydrogels with divalent cations and is the dominant factor in determining the chain stiffness of alginate. We have utilized size-exclusion chromatography, equipped with refractive index, viscosity, and light-scattering detectors, to determine the intrinsic viscosity and the weight-average molecular weight of each fraction of samples. The chain stiffness of partially oxidized polyguluronate was then evaluated from the exponent of the Mark-Houwink equation and the persistence length. We have found that partial oxidation can be used to tightly regulate the steric hindrance and stiffness of the polyguluronate backbone. This approach to control the chain stiffness of inherently rigid polysaccharides by partial oxidation may find many applications in biomedical utilization of these materials. PMID:12425648

Lee, Kuen Yong; Bouhadir, Kamal H; Mooney, David J

379

Effects of varying machine stiffness and contact area in UltraForm Finishing  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

380

Nanoscale in vivo evaluation of the stiffness of Drosophila melanogaster integument during development.  

PubMed

A quasistatic nanoindentation technique, enhanced by scanning probe microscopy, was used to measure cuticle stiffness of live Drosophila melanogaster during its larval, pupal, and early adult development in vivo. Stiffness was defined as the reduced elastic modulus (E(r)), which is a material property related to the elastic modulus. E(r) was measured at the local contact while indenting the live sample at a constant loading rate using a spherical tip. E(r) was derived from the resultant force-displacement curves. Insect cuticle exhibits viscoelastic behavior. Constant loading rate quasistatic measurements were used so that the effects of viscosity and contact force adhesion introduced systematic measurement effects. E(r) values were as follows: larvae, mean (SE), 0.39 (0.01) MPa; the puparium without evidence of adult structures 15.43 (1.78) MPa; and the adult, measured in the puparium at the completion of metamorphosis, 4.37 (0.31) MPa. Thus, as expected, the puparium and adult cuticle were very much stiffer than larval cuticle. Results also indicated stiffness variation that related to developmental events. This study has shown that this quasistatic nanoindentation-scanning probe microscopy approach is a suitable method for analyzing live biological samples. PMID:12918047

Kohane, M; Daugela, A; Kutomi, H; Charlson, L; Wyrobek, A; Wyrobek, J

2003-09-01

381

[Stiff person syndrome (Moersch-Woltman)].  

PubMed

The prime goal of this paper is to offer an overview of main scientific points in epidemiology, genetics, pathogenesis, clinical course and therapeutic strategies in stiff person syndrome (SPS). This syndrome is characterized by progressive muscle rigidity and painful muscle spasms. Three major forms of SPS are described, according to the pathophysiologic basis, autoimmune, paraneoplastic and idiopathic SPS. In autoimmune form of SPS the antibodies are specific for an enzyme (glutamic acid decarboxylase, GAD). If the paraneoplastic form takes place, the antibodies may be specific for presynaptic (amphyphysin) or the postsynaptic protein (gephyrin). The SPS diagnosis should be based on clinical, laboratory and electromyoneurographic criteria, according to Gordon and Lorish. The therapeutic approaches are focused on symptomatic therapy managing the muscle spasm and on possible immunomodulatory procedures to attenuate an autoimmune reaction. Two cases of SPS are reported in the Republic Croatia since 2005. Although it is a rare medical condition, SPS is of clinical importance, especially because it may be the first sign of an underlying undiagnosed malignant disease or if the anesthesia is necessary in SPS patient. PMID:20540439

Cerimagi?, Denis; Bili?, Ervina

382

Correlates of aortic stiffness in elderly individuals: a subgroup of the cardiovascular health study  

Microsoft Academic Search

Background:Arterial stiffness has been associated with aging, hypertension, and diabetes; however, little data has been published examining risk factors associated with arterial stiffness in elderly individuals.

Rachel H Mackey; Kim Sutton-Tyrrell; Peter V Vaitkevicius; Pamela A Sakkinen; Mary F Lyles; Harold A Spurgeon; Edward G Lakatta; Lewis H Kuller

2002-01-01

383

Stiffness and leakage in spiral groove upstream pumping mechanical seals  

NASA Astrophysics Data System (ADS)

A numerical analysis of the lubricating film in spiral groove upstream pumping mechanical seals, accounting for the occurrence of cavitation, has been performed. Axial stiffness and leakage rate have been determined as functions of the operating conditions and design parameters. Results indicate that properly designed spiral groove upstream pumping seals will perform well in a double seal arrangement, with good stiffness characteristics and negative leakage of the buffer fluid. However, results also suggest that such seals will operate poorly as single seals, due to negative stiffness resulting from excessive cavitation.

Salant, Richard F.; Homiller, Stephen J.

1993-01-01

384

Hormones and arterial stiffness in patients with chronic kidney disease.  

PubMed

Cardiovascular disease constitutes the major cause of mortality in patients with chronic kidney disease. Arterial stiffness is an important contributor to the occurrence and progression of cardiovascular disease. Various risk factors, including altered hormone levels, have been suggested to be associated with arterial stiffness. Based on the background that chronic kidney disease predisposes individuals to a wide range of hormonal changes, we herein review the available data on the association between arterial stiffness and hormones in patients with chronic kidney disease and summarize the data for the general population. PMID:23911970

Gungor, Ozkan; Kircelli, Fatih; Voroneanu, Luminita; Covic, Adrian; Ok, Ercan

2013-08-02

385

Stiffness of grain-bridging elements in a monolithic alumina  

SciTech Connect

The postfracture tensile (PFT) technique isolates the crack wake to characterize the mechanical behavior of the grain-bridging elements as a function of crack-opening displacement. Incorporating the PFT stiffnesses into a Hooke`s law-based model provides insight to the nature of the active bridging mechanism. The conventional model, which presumes to extract prismatic grains from sockets in the mating fracture face, is not consistent with the low wake stiffnesses presented here. In conjunction with fractographic evidence, such low wake stiffnesses suggest the strong influence from other, more compliant, mechanisms such as grain rotation, asperity loading, and ligament bending.

Hay, J.C.; White, K.W. [Univ. of Houston, TX (United States). Dept. of Mechanical Engineering

1997-05-01

386

Ambulatory arterial stiffness index, pulse pressure and pulse wave velocity in children and adolescents.  

PubMed

Arterial stiffness, assessed by carotid-femoral pulse wave velocity (PWV) or indirectly by pulse pressure (PP) or ambulatory arterial stiffness index (AASI), is an independent predictor of cardiovascular disease in adults. However, in children limited evidence is available. This study investigated the usefulness of AASI and PP as indices of arterial stiffness in children and adolescents, by taking PWV as the reference method. Eighty-two children and adolescents (mean age 13.1±2.9 years) had 24-h ambulatory blood pressure (ABP) monitoring, PWV measurement and echocardiography. Compared with normotensives, subjects with hypertension (n=16) had higher 24-h ABP, 24-h PP and PWV, but not AASI. 24-h, PP was strongly correlated with age, weight, height, 24-h systolic ABP, PWV, left ventricular mass (LVM), LVM index, stroke volume and inversely with 24-h heart rate. AASI was also correlated with weight, height, systolic ABP and LVM, yet these associations were weaker than those of PP, and no significant correlations were found with PWV or LVM index. Moreover, closer agreement of PWV was observed with 24-h PP (71%, kappa 0.21) than with 24-h AASI (61%, kappa -0.06) in detecting subjects at the top quartile of the respective distributions. In children and adolescents, 24-h PP compared with AASI appears to be more closely associated with: (i) arterial stiffness assessed by PWV; (ii) target organ damage assessed by LVM index; and (iii) the presence of essential hypertension. These data suggest that the usefulness of AASI as an index of arterial stiffness in the pediatric population is questionable. PMID:20882025

Stergiou, George S; Kollias, Anastasios; Giovas, Periklis P; Papagiannis, John; Roussias, Leonidas G

2010-09-30

387

Dehydroepiandrosterone replacement therapy in older adults improves indices of arterial stiffness  

PubMed Central

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

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

2012-01-01

388

The Change of Intrinsic Stiffness in Gastrocnemius after Intensive Rehabilitation with Botulinum Toxin A Injection in Spastic Diplegic Cerebral Palsy  

PubMed Central

A recent study claimed that botulinum toxin A (BTX-A) injection into the calf muscle of cerebral palsy (CP) children did not change the intrinsic stiffness. Contrary to this recent report, in our case, decreased muscle spasticity, which was measured using a modified Ashworth scale, and increased Gross Motor Function Measure score were demonstrated at 4 weeks after intensive rehabilitation treatment (IRT) with BTX-A injection to the medial gastrocnemius muscle in a child with spastic CP. Additionally, we indentified decreased muscle stiffness which was demonstrated by a decrease in the color-coded scale and shear velocity, and an increase in the strain ratio using dynamic sonoelastography.

Kwon, Dong Rak; Park, Gi Young

2012-01-01

389

On the characteristics of a quasi-zero stiffness isolator using Euler buckled beam as negative stiffness corrector  

NASA Astrophysics Data System (ADS)

The characteristics of a passive nonlinear isolator which is developed by parallelly adding a negative stiffness corrector to a linear spring are studied. The negative stiffness corrector, which is formed by Euler buckled beams can offer negative stiffness to the isolator at the equilibrium position in order to lower the overall dynamic stiffness of the isolator and without sacrificing the support capacity compared to the linear isolator. The static characteristics of the stiffness corrector as well as the nonlinear isolator are presented and the system parameters which can offer zero stiffness at the equilibrium point are derived. The restoring force of the nonlinear isolator after loaded is approximated using the Taylor expansion to pure cubic stiffness. The dynamic equation is established and the frequency response curves (FRCs) are obtained by using the Harmonic Balance Method (HBM) for both force and displacement excitations. The force and displacement transmissibility of the nonlinear isolator are defined and investigated, and the isolation performance is compared with an equivalent linear isolator which can support the same mass with the same static deflection as the nonlinear isolator. The effects of the amplitude of the excitation and damping ratio on the transmissibility performance are considered. The results demonstrate that the proposed zero dynamic stiffness nonlinear isolator can outperform the equivalent linear one for certain frequencies, and the performance is related to the magnitude of the excitation amplitude. Unlike the linear isolator, in the nonlinear isolator for base displacement excitation, unbounded response or transmissibility can occur which is not observed for force excitation case. The performance can also be improved by adjusting the configurations of the beams. Some useful guidelines for choosing system parameters such as the properties of the beams and the stiffness relationship between the beams and the linear spring are given.

Liu, Xingtian; Huang, Xiuchang; Hua, Hongxing

2013-07-01

390

Measurements of trapping efficiency and stiffness in optical tweezers  

Microsoft Academic Search

We report an experimental study concerning the radial forces of an optical tweezers acting on spherical polystyrene particles diluted in water solution. The radius of the trapped beads varied between 0.5 and 7.5 ?m, i.e., in an intermediate range between Rayleigh and geometric optics regime. As a force calibration method we used the viscous drag exerted by a fluid flow.

N. Malagnino; G. Pesce; A. Sasso; E. Arimondo

2002-01-01

391

Antibiotic-induced modifications of the stiffness of bacterial membranes.  

PubMed

In the latest years the importance of high resolution analysis of the microbial cell surface has been increasingly recognized. Indeed, in order to better understand bacterial physiology and achieve rapid diagnostic and treatment techniques, a thorough investigation of the surface modifications induced on bacteria by different environmental conditions or drugs is essential. Several instruments are nowadays available to observe at high resolution specific properties of microscopic samples. Among these, AFM can routinely study single cells in physiological conditions, measuring the mechanical properties of their membrane at a nanometric scale (force volume). Such analyses, coupled with high resolution investigation of their morphological properties, are increasingly used to characterize the state of single cells. In this work we exploit such technique to characterize bacterial systems. We have performed an analysis of the mechanical properties of bacteria (Escherichia coli) exposed to different conditions. Such measurements were performed on living bacteria, by changing in real-time the liquid environment: standard phosphate buffered saline, antibiotic (ampicillin) in PBS and growth medium. In particular we have focused on the determination of the membrane stiffness modifications induced by these solutions, in particular between stationary and replicating phases and what is the effect of the antibiotic on the bacterial structure. PMID:23439239

Longo, Giovanni; Rio, Laura Marques; Trampuz, Andrej; Dietler, Giovanni; Bizzini, Alain; Kasas, Sandor

2013-02-22

392

Short range stiffness elastic limit depends on joint velocity.  

PubMed

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

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

2011-07-28

393

The Effects of Sex, Joint Angle, and the Gastrocnemius Muscle on Passive Ankle Joint Complex Stiffness  

PubMed Central

Objective: To assess the effects of sex, joint angle, and the gastrocnemius muscle on passive ankle joint complex stiffness (JCS). Design and Setting: A repeated-measures design was employed using sex as a between-subjects factor and joint angle and inclusion of the gastrocnemius muscle as within-subject factors. All testing was conducted in a neuromuscular research laboratory. Subjects: Twelve female and 12 male healthy, physically active subjects between the ages of 18 and 30 years volunteered for participation in this study. The dominant leg was used for testing. No subjects had a history of lower extremity musculoskeletal injury or circulatory or neurologic disorders. Measurements: We determined passive ankle JCS by measuring resistance to passive dorsiflexion (5°·s?1) from 23° plantar flexion (PF) to 13° dorsiflexion (DF). Angular position and torque data were collected from a dynamometer under 2 conditions designed to include or reduce the contribution of the gastrocnemius muscle. Separate fourth-order polynomial equations relating angular position and torque were constructed for each trial. Stiffness values (Nm·degree?1) were calculated at 10° PF, neutral (NE), and 10° DF using the slope of the line at each respective position. Results: Significant condition-by-position and sex-by-position interactions and significant main effects for sex, position, and condition were revealed by a 3-way (sex-by-position, condition-by-position) analysis of variance. Post hoc analyses of the condition-by-position interaction revealed significantly higher stiffness values under the knee-straight condition compared with the knee-bent condition at both ankle NE and 10° DF. Within each condition, stiffness values at each position were significantly higher as the ankle moved into DF. Post hoc analysis of the sex-by-position interaction revealed significantly higher stiffness values at 10° DF in the male subjects. Post hoc analysis of the position main effect revealed that as the ankle moved into dorsiflexion, the stiffness at each position became significantly higher than at the previous position. Conclusions: The gastrocnemius contributes significantly to passive ankle JCS, thereby providing a scientific basis for clinicians incorporating stretching regimens into rehabilitation programs. Further research is warranted considering the cause and application of the sex-by-position interaction.

DeMont, Richard G.; Ryu, Keeho; Lephart, Scott M.

2001-01-01

394

Determinants of Arterial Stiffness in Chronic Kidney Disease Stage 3  

PubMed Central

Background Early chronic kidney disease (CKD) is associated with increased cardiovascular (CV) risk but underlying mechanisms remain uncertain. Arterial stiffness (AS) is associated with increased CV risk in advanced CKD, but it is unclear whether AS is relevant to CV disease (CVD) in early CKD. Study Design Cross-sectional. Setting and participants 1717 patients with previous estimated glomerular filtration rate (eGFR) 59–30 mL/min/1.73 m2; mean age 73±9y, were recruited from 32 general practices in primary care. Outcomes Increased arterial stiffness. Measurements Medical history was obtained and participants underwent clinical assessment, urine and serum biochemistry testing. Carotid to femoral pulse wave velocity (PWV) was determined as a measure of AS, using a Vicorder™ device. Results Univariate analysis revealed significant correlations between PWV and risk factors for CVD including age (r?=?0.456; p<0.001), mean arterial pressure (MAP) (r?=?0.228; p<0.001), body mass index (r?=??0.122; p<0.001), log urinary albumin to creatinine ratio (r?=?0.124; p<0.001), Waist to Hip ratio (r?=?0.124, p<0.001), eGFR (r?=??0.074; p?=?0.002), log high sensitivity c-reactive protein (r?=?0.066; p?=?0.006), HDL (r?=??0.062; p?=?0.01) and total cholesterol (r?=??0.057; p?=?0.02). PWV was higher in males (9.6 m/sec vs.10.3 m/sec; p<0.001), diabetics (9.8 m/sec vs. 10.3 m/sec; p<0.001), and those with previous CV events (CVE) (9.8 m/s vs. 10.3 m/sec; p<0.001). Multivariable analysis identified age, MAP and diabetes as strongest independent determinants of higher PWV (adjusted R2?=?0.29). An interactive term indicated that PWV increased to a greater extent with age in males versus females. Albuminuria was a weaker determinant of PWV and eGFR did not enter the model. Limitations Data derived from one study visit, with absence of normal controls. Conclusion In this cohort, age and traditional CV risk factors were the strongest determinants of AS. Albuminuria was a relatively weak determinant of AS and eGFR was not an independent determinant. Long-term follow-up will investigate AS as an independent risk factor for CVE in this cohort.

McIntyre, Natasha J.; Fluck, Richard J.; McIntyre, Christopher W.; Fakis, Apostolos; Taal, Maarten W.

2013-01-01

395

Physiopathogenic Investigations in a Case of Familial Stiff-Skin Syndrome  

Microsoft Academic Search

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

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

1998-01-01

396

Aortic stiffness independently predicts exercise capacity in hypertrophic cardiomyopathy: a multimodality imaging study  

Microsoft Academic Search

BackgroundExercise capacity in patients with hypertrophic cardiomyopathy (HCM) varies despite similar diastolic dysfunction, left ventricular outflow tract (LVOT) obstruction and mitral regurgitation (MR). Pulse wave velocity (PWV), determined by cardiac magnetic resonance (CMR), measures aortic stiffness and is abnormal in patients with HCM in comparison with controls.ObjectiveTo determine potential clinical and imaging predictors of peak oxygen consumption (pVO2) in patients

Bethany A Austin; Zoran B Popovic; Deborah H Kwon; Maran Thamilarasan; Thananya Boonyasirinant; Scott D Flamm; Harry M Lever; Milind Y Desai

2010-01-01

397

Evaluation of Arterial Stiffness in Patients with Branch Retinal Vein Occlusion  

Microsoft Academic Search

Purpose: To assess the arterial stiffness in patients with branch retinal vein occlusion (BRVO). Methods: Brachial-ankle pulse wave velocity (PWV) and ankle-brachial index were measured in 10 patients with BRVO (mean age 67.9 ± 7.5 years) and in 18 age-matched controls (mean age 66.9 ± 6.8 years). The controls were subjects with systemic essential hypertension having no retinal lesions. Results:

Keiko Nakazato; Hideki Watanabe; Keisuke Kawana; Takahiro Hiraoka; Takahiro Kiuchi; Tetsuro Oshika

2005-01-01

398

Spinal stability and role of passive stiffness in dynamic squat and stoop lifts  

Microsoft Academic Search

The spinal stability and passive–active load partitioning under dynamic squat and stoop lifts were investigated as the ligamentous stiffness in flexion was altered. Measured in vivo kinematics of subjects lifting 180 N at either squat or stoop technique was prescribed in a nonlinear transient finite element model of the spine. The Kinematics-driven approach was utilized for temporal estimation of muscle forces,

B. Bazrgari; A. Shirazi-Adl

2007-01-01

399

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

Microsoft Academic Search

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

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

2006-01-01

400

Is passive stiffness in human muscles related to the elasticity of tendon structures?  

Microsoft Academic Search

.   The purpose of this study was to examine in vivo whether passive stiffness in human muscles was related to the elasticity\\u000a of tendon structures and to performance during stretch-shortening cycle exercise. Passive torque of plantar flexor muscles\\u000a was measured during passive stretch from 90° (anatomical position) to 65° of dorsiflexion at a constant velocity of 5°·s–1. The slope of

Keitaro Kubo; Hiroaki Kanehisa; Tetsuo Fukunaga

2001-01-01

401

Variable Stiffness Concept For Efficient Aircraft Vertical Tail Design.  

National Technical Information Service (NTIS)

This report results from a contract tasking University of Manchester as follows: The contractor will investigate using a variable stiffness vertical tail attachment to control aeroelastic performance over a range of dynamic pressures. The contractor will ...

J. E. Cooper M. Amprikidis O. Sensburg

2003-01-01

402

Parametric Frequency Domain Identification Using Variable Stiffness and Damping Devices.  

National Technical Information Service (NTIS)

The process of monitoring structural health and identifying damage severity and location is generally termed structural health monitoring (SHM). The core of this project is to investigate how variable stiffness and damping devices (VSDD) can be most effec...

E. A. Johnson M. I. S. Elmasry

2003-01-01

403

Application of NITINOL to High Stiffness Structural Joints.  

National Technical Information Service (NTIS)

The feasibility of utilizing the unique shape-recovery characteristics of NITINOL to achieve high preloads in structural joints was demonstrated. High performance missile systems require the shell stiffness in the longitudinal bending mode to be above a c...

R. D. Brum J. C. Schutzler

1979-01-01

404

Strength and Stiffness of Reinforced Concrete Columns under Biaxial Bending.  

National Technical Information Service (NTIS)

The strength and stiffness behavior of reinforced concrete columns subjected to biaxial bending and compression was investigated. In order to provide data points on biaxial interaction surfaces, nine rectangular cross section columns and fifteen partial c...

V. Mavichak R. W. Furlong

1976-01-01

405

Operator-Based Preconditioning of Stiff Hyperbolic Systems  

SciTech Connect

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

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

2009-02-09

406

Transverse Cracking and Stiffness Reduction in Composite Laminates  

Microsoft Academic Search

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

Ramesh Talreja

1985-01-01

407

Variable Stiffness Actuators for Fast and Safe Motion Control  

Microsoft Academic Search

In this paper we propose Variable Stiffness actuation [1] as a viable mechanical\\/control co–design approach for guaranteeing control performance for robot arms that are inherently safe to humans in their environment. A new actuator under development in our Lab is then proposed, which incorporate the possibility to vary transmission stiffness during motion execution, thus allowing substantial motion speed-up while maintaining

Antonio Bicchi; Giovanni Tonietti; Michele Bavaro; Marco Piccigallo

2003-01-01

408

Spin stiffness of graphene and zigzag graphene nanoribbons  

Microsoft Academic Search

We theoretically study the spin stiffness of graphene and graphene nanoribbon based on the Hubbard-type Hamiltonian. Using the Hartree-Fock method with the inclusion of the adiabatic spin twist, we have obtained the effective energy functional and investigated the magnetic excitations of the two-dimensional graphene and zigzag graphene nanoribbon (ZGNR). We have analyzed the spin stiffness of the system with varying

Jun-Won Rhim; Kyungsun Moon

2009-01-01

409

Spin stiffness of graphene and zigzag graphene nanoribbons  

Microsoft Academic Search

We theoretically study the spin stiffness of graphene and graphene nanoribbon based on the Hubbard-type Hamiltonian. Using the Hartree-Fock method with the inclusion of the adiabatic spin twist, we have obtained the effective energy functional and investigated the magnetic excitations of the two-dimensional graphene and zigzag graphene nanoribbon (ZGNR). We have analyzed the spin stiffness of the system with varying

Jun-Won Rhim; Kyungsun Moon

2010-01-01

410

Terrace Width Distributions for Steps of Alternating Stiffness  

NASA Astrophysics Data System (ADS)

Some vicinal crystal surfaces are characterized by alternating A-type and B-type steps which have different stiffnesses. Here we show that the same phenomenological approach which gives rise to the ``generalized Wigner distribution" (GWD) when all steps have the same stiffness again gives the GWD if a certain term is small enough. Our Monte Carlo simulations of the TSK model indicate that the GWD does very well here also.

Yancey, Jeremy; Richards, Howard L.

2003-03-01

411

Cornering stiffness estimation based on vehicle lateral dynamics  

Microsoft Academic Search

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

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

2006-01-01

412

Stiff-person syndrome first manifesting in pregnancy.  

PubMed

Stiff-person syndrome (SPS) is a rare neurological disorder characterised by progressive stiffness and painful muscle spasms. We present a case of the autoimmune form of glutamate decarboxylase-positive SPS that initially manifested in pregnancy. The diagnosis was made based on clinical, laboratory and electromyoneurographic criteria. The patient was administered low doses of diazepam and baclofen. Considering the clinical picture of SPS patients, caesarean section is the method of choice for pregnancy termination. PMID:19005261

Cerimagic, Denis; Bilic, Ervina

2008-11-13

413

PLANETARY GEAR PARAMETRIC INSTABILITY CAUSED BY MESH STIFFNESS VARIATION  

Microsoft Academic Search

Parametric instability is investigated for planetary gears where fluctuating stiffness results from the changing contact conditions at the multiple tooth meshes. The time-varying mesh stiffnesses of the sun–planet and ring–planet meshes are modelled as rectangular waveforms with different contact ratios and mesh phasing. The operating conditions leading to parametric instability are analytically identified. Using the well-defined properties of planetary gear

J. Lin; R. G. PARKER

2002-01-01

414

Arterial stiffness: Is it ready for prime time?  

Microsoft Academic Search

Recent interest in arterial stiffness as a possible new biomarker of cardiovascular (CV) disease has emerged. Arterial stiffness\\u000a of the large, elastic conduit arteries is considered a risk marker of vascular aging; it leads to widened pulse pressure (PP)\\u000a and the development of isolated systolic hypertension in the middle-aged and elderly population. However, increased PP is\\u000a not always a good

Stanley S. Franklin

2007-01-01

415

Physical activity and arterial stiffness in chronic obstructive pulmonary disease.  

PubMed

Arterial stiffness is predictive of cardiovascular events and is elevated in chronic obstructive pulmonary disease (COPD). As physical inactivity and exercise intolerance are associated with elevated arterial stiffness in health, we hypothesized that lower physical activity would be related to increased arterial stiffness in COPD; and that active COPD patients would have reduced arterial stiffness compared to sedentary counterparts. Arterial stiffness was evaluated using pulse wave velocity (PWV) in 33 COPD patients (FEV1=65% predicted) and 10 controls. FEV1%pred, peak oxygen consumption (V?O2peak), and physical activity data were obtained. The inactive COPD group had higher PWV than controls (9.6 vs. 8.3ms(-1), p<0.05); while there was no difference in PWV between the active COPD group and controls. Within the COPD patients, V?O2peak (r=-0.44, p=0.01) and physical activity (r=-0.38, p=0.03) were the best predictors of PWV. Physical inactivity and exercise intolerance appear to be related to arterial stiffness in COPD, and may contribute to increased cardiovascular disease risk in COPD. PMID:23933008

Stickland, Michael K; Vogan, Norah; Petersen, Stewart R; Wong, Eric Y L; Bhutani, Mohit

2013-08-07

416

Dynamic isolation systems using tunable nonlinear stiffness beams  

NASA Astrophysics Data System (ADS)

Vibration isolation devices are required to reduce the forcing into the supporting structure or to protect sensitive equipment from base excitation. A suspension system with a low natural frequency is required to improve isolation, but with linear supports the minimum stiffness is bounded by the static stiffness required to support the equipment. However, nonlinear high-static-low-dynamic-stiffness (HSLDS) mounts may be designed, for example by combining elastic springs in particular geometries, to give the required nonlinear force-displacement characteristics. Current approaches to realise the required nonlinear characteristics are often inconvenient. Furthermore, the weight of the supported equipment, the environment, or the structural stiffness may change. This paper investigates the design of HSLDS isolation mounts using beams of tunable geometric nonlinear stiffness. In order to obtain the nonlinear response required, we first study the case of generic beams subject to static loads that are able to tune their nonlinear force-displacement characteristics to ensure that the isolators have very low dynamic stiffness. Tuning is achieved by actuators at the ends of the beams that prescribe the axial displacement and rotation. Secondly, we study a composite beam with an initial thermal pre-stress, resulting in internal stresses that give the required nonlinear response.

Friswell, M. I.; Saavedra Flores, E. I.

2013-09-01

417

Arterial stiffness and the response to carotid sinus massage in older adults  

PubMed Central

Background and aims Carotid sinus hypersensitivity (CSH) is a common cause of fainting and falls in the older adult population and is diagnosed by carotid sinus massage (CSM). Previous work has suggested that age-related stiffening of blood vessels reduces afferent input from the carotid sinus leading to central upregulation of the overall arterial baroreflex response. We examined the differences in arterial stiffness and baroreflex function in older adults at high cardiovascular risk (advanced age, Type 2 diabetes, hypertension and hyperlipidemia) with and without CSH. Methods Forty-three older adults (mean age 71.4±0.7) with Type 2 diabetes, hyperlipidemia and hypertension were recruited. After resting supine for 45 minutes prior to the start of data collection, each subject had arterial stiffness measured by pulse wave velocity (PWV, Complior SD), followed by spontaneous baroreflex measures (Baroreflex sensitivity, BRS) and CSM. Results Of the 43 subjects tested, 10 subjects met the criteria for CSH (8 pure vasodepressor and 2 mixed CSH). CSH subjects had higher measures of arterial stiffness when compared to normal subjects for both radial PWV (11.5±0.6 vs 9.6±0.4 m/s, p=0.043) and femoral PWV (13.4±0.9 vs 11.0±0.5 m/s, p=0.036). The CSH group demonstrated significantly lower BRS as compared to the normal group (BRS, 6.73±0.58 vs 10.41±0.85 ms/mmHg, p=0.038). These results were unchanged when the analysis was repeated with only the VD subjects. Conclusions Older adults with CSH have higher arterial stiffness and reduced arterial baroreflex sensitivity. There was no evidence to support upregulation of the arterial baroreflex in patients with CSH.

Madden, Kenneth M.; Lockhart, Chris; Khan, Karim

2013-01-01

418

Nonlinear decoupled motion-stiffness control and collision detection\\/reaction for the VSA-II variable stiffness device  

Microsoft Academic Search

Variable stiffness actuation (VSA) devices are being used to jointly address the issues of safety and performance in physical human-robot interaction. With reference to the VSA-II prototype, we present a feedback linearization approach that allows the simultaneous decoupling and accurate tracking of motion and stiffness reference profiles. The operative condition that avoids control singularities is characterized. Moreover, a momentum-based collision

Alessandro De Luca; Fabrizio Flacco; Antonio Bicchi; Riccardo Schiavi

2009-01-01

419

Transversal Stiffness and Young's Modulus of Single Fibers from Rat Soleus Muscle Probed by Atomic Force Microscopy  

PubMed Central

Abstract The structural integrity of striated muscle is determined by extra-sarcomere cytoskeleton that includes structures that connect the Z-disks and M-bands of a sarcomere to sarcomeres of neighbor myofibrils or to sarcolemma. Mechanical properties of these structures are not well characterized. The surface structure and transversal stiffness of single fibers from soleus muscle of the rat were studied with atomic force microscopy in liquid. We identified surface regions that correspond to projections of the Z-disks, M-bands, and structures between them. Transversal stiffness of the fibers was measured in each of these three regions. The stiffness was higher in the Z-disk regions, minimal between the Z-disks and the M-bands, and intermediate in the M-band regions. The stiffness increased twofold when relaxed fibers were maximally activated with calcium and threefold when they were transferred to rigor (ATP-free) solution. Transversal stiffness of fibers heavily treated with Triton X-100 was about twice higher than that of the permeabilized ones, however, its regional difference and the dependence on physiological state of the fiber remained the same. The data may be useful for understanding mechanics of muscle fibers when it is subjected to both axial and transversal strain and stress.

Ogneva, Irina V.; Lebedev, Dmitry V.; Shenkman, Boris S.

2010-01-01

420

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

PubMed

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

Böhm, Harald; Hösl, Matthias

2010-06-11

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