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1

Stiffness and viscous coefficient characteristics for ergonomics chair design  

Microsoft Academic Search

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

Ahmad Athif Mohd Faudzi; Koichi Suzumori

2011-01-01

2

Generalized Gaunt coefficients  

Microsoft Academic Search

Solid-harmonic derivatives of solid-harmonic-Gaussian integrals are evaluated. Cross differentiation and the n-j generalized Gaunt coefficients are defined. The generalized Gaunt coefficients ensure that cross differentiation in uncoupled, n-center, solid-harmonic derivatives of rotationally invariant Gaussian matrix elements subtracts zero total angular momentum. This preserves the spherical-tensor properties of quantum-chemical matrix elements. The generalized Gaunt coefficients are (n-1)-dimensional objects because the sum

Brett I. Dunlap

2002-01-01

3

Tilting pad journal bearings - Measured and predicted stiffness coefficients  

SciTech Connect

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

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

1993-07-01

4

Identities for generalized hypergeometric coefficients  

SciTech Connect

Generalizations of hypergeometric functions to arbitrarily many symmetric variables are discussed, along with their associated hypergeometric coefficients, and the setting within which these generalizations arose. Identities generalizing the Euler identity for {sub 2}F{sub 1}, the Saalschuetz identity, and two generalizations of the {sub 4}F{sub 3} Bailey identity, among others, are given. 16 refs.

Biedenharn, L.C.; Louck, J.D.

1991-01-01

5

Dynamic stiffness and damping coefficients of aerodynamic tilting-pad journal bearings  

Microsoft Academic Search

The dynamic gas–film forces of aerodynamic bearing often can be characterized by eight linear stiffness and damping coefficients. How to theoretically predict these coefficients is a very difficult issue for tilting-pad gas bearing design because of its structural complexity. The current study presents a novel and universal theoretical analysis method for calculating the dynamic stiffness and damping coefficients of aerodynamic

Yang Lihua; Li Huiguang; Yu Lie

2007-01-01

6

The construction of free–free flexibility matrices as generalized stiffness inverses  

Microsoft Academic Search

We present generalizations of the classical structural flexibility matrix. Direct or indirect computation of flexibilities as ‘influence coefficients’ has traditionally required pre-removal of rigid body modes by imposing appropriate support conditions. Here the flexibility of an individual element or substructure is directly obtained as a particular generalized inverse of the free–free stiffness matrix. This entity is called a free–free flexibility

C. A. Felippa; K. C. Park; M. R. Justino Filho

1998-01-01

7

Note on Two Generalizations of Coefficient Alpha.  

ERIC Educational Resources Information Center

An important relationship is given for two generalizations of coefficient alpha: (1) Rajaratnam, Cronbach, and Gleser's generalizability formula for stratified-parallel tests, and (2) Raju's coefficient beta. (Author/CTM)

Raju, Nambury S.

1979-01-01

8

Stiffness and Damping Coefficient Estimation of Compliant Surface Gas Bearings for Oil-Free Turbomachinery  

NASA Technical Reports Server (NTRS)

Foil gas bearings are a key technology in many commercial and emerging Oil-Free turbomachinery systems. These bearings are non-linear and have been difficult to analytically model in terms of performance characteristics such as load capacity, power loss, stiffness and damping. Previous investigations led to an empirically derived method, a rule-of-thumb, to estimate load capacity. This method has been a valuable tool in system development. The current paper extends this tool concept to include rules for stiffness and damping coefficient estimation. It is expected that these rules will further accelerate the development and deployment of advanced Oil-Free machines operating on foil gas bearings

DellaCorte, Christopher

2010-01-01

9

The elastic stiffness coefficients of nickel-iron single-crystal alloys at room temperature  

Microsoft Academic Search

The adiabatic elastic stiffness coefficients of four Ni-Fe single-crystal alloys in the composition range from 90 to 50 wt. % of Ni have been determined by the ultrasonic coherent pulse\\/ continuous wave (cw) technique at room temperature at a frequency of 8 MHZ. The alloying composition influences the three independent elastic constants C11, C12, and C44 of the Cubic crystal.

A. Kanrar

1981-01-01

10

Trigonometric series with general monotone coefficients  

NASA Astrophysics Data System (ADS)

We study trigonometric series with general monotone coefficients. Convergence results in the different metrics are obtained. Also, we prove a Hardy-type result on the behavior of the series near the origin.

Tikhonov, S.

2007-02-01

11

Generalized power-law stiffness model for nonlinear dynamics of in-plane cable networks  

NASA Astrophysics Data System (ADS)

Cross-ties are used for mitigating stay-cable vibration, induced by wind and wind-rain on cable-stayed bridges. In-plane cable networks are obtained by connecting the stays by transverse cross-ties. While taut-cable theory has been traditionally employed for simulating the dynamics of cable networks, the use of a nonlinear restoring-force discrete element in each cross-tie has been recently proposed to more realistically replicate the network vibration when snapping or slackening of the restrainer may be anticipated. The solution to the free-vibration dynamics can be determined by "equivalent linearization method". In an exploratory study by the authors a cubic-stiffness spring element, in parallel with a linear one, was used to analyze the restoring-force effect in a cross-tie on the nonlinear dynamics of two simplified systems. This preliminary investigation is generalized in this paper by considering a power-law stiffness model with a generic integer exponent and applied to a prototype network installed on an existing bridge. The study is restricted to the fundamental mode and some of the higher ones. A time-domain lumped-mass algorithm is used for validating the equivalent linearization method. For the prototype network with quadratic-stiffness spring and a positive stiffness coefficient, a stiffening effect is observed, with a ten percent increment in the equivalent frequency for the fundamental mode. Results also show dependency on vibration amplitude. For higher modes the equivalent nonlinear effects can be responsible for an alteration of the linear mode shapes and a transition from a "localized mode" to a "global mode".

Giaccu, Gian Felice; Caracoglia, Luca

2013-04-01

12

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

13

Determination of Nonlinear Stiffness Coefficients for Finite Element Models with Application to the Random Vibration Problem  

NASA Technical Reports Server (NTRS)

In this paper, a method for obtaining nonlinear stiffness coefficients in modal coordinates for geometrically nonlinear finite-element models is developed. The method requires application of a finite-element program with a geometrically non- linear static capability. The MSC/NASTRAN code is employed for this purpose. The equations of motion of a MDOF system are formulated in modal coordinates. A set of linear eigenvectors is used to approximate the solution of the nonlinear problem. The random vibration problem of the MDOF nonlinear system is then considered. The solutions obtained by application of two different versions of a stochastic linearization technique are compared with linear and exact (analytical) solutions in terms of root-mean-square (RMS) displacements and strains for a beam structure.

Muravyov, Alexander A.

1999-01-01

14

Stiffness and Damping Coefficient Estimation of Compliant Surface Gas Bearings for Oil-Free Turbomachinery  

Microsoft Academic Search

Foil gas bearings are a key technology in many commercial and emerging Oil-Free turbomachinery systems. These bearings are non-linear and have been difficult to analytically model in terms of performance characteristics such as load capacity, power loss, stiffness, and damping. Previous investigations led to an empirically derived method, a rule-of-thumb, to estimate load capacity. This method has been a valuable

Christopher DellaCorte

2011-01-01

15

Reply to ``Comment on `Elastic stiffness coefficients of nickel-iron single-crystal alloys at room temperature' ''  

Microsoft Academic Search

Ledbetter’s critical discussion on our work on the elastic stiffness coeffficients of nickel-iron single-crystal alloys at room temperature clearly shows that our conclusion regarding the linear dependence of the shear constants of this alloy crystal on the composition is, in general, not valid throughout the whole range of composition. The linearity is destroyed by the onset of instability of the

A. Kanrar

1985-01-01

16

Group classification of variable coefficient generalized Kawahara equations  

NASA Astrophysics Data System (ADS)

An exhaustive group classification of variable coefficient generalized Kawahara equations is carried out. As a result, we derive new variable coefficient nonlinear models admitting Lie symmetry extensions. All inequivalent Lie reductions of these equations to ordinary differential equations are performed. We also present some examples on the construction of exact and numerical solutions.

Kuriksha, Oksana; Pošta, Severin; Vaneeva, Olena

2014-01-01

17

General Equations Describing Elastic Indentation Depth and Normal Contact Stiffness versus Load.  

PubMed

Continuum mechanics models describing the contact between two adhesive elastic spheres, such as the JKR and DMT models, provide a relationship between the elastic indentation depth and the normal load, but the general intermediate case between these two limiting cases requires a more complex analysis. The Maugis-Dugdale theory gives analytical solutions, but they are difficult to use when comparing to experimental data such as those obtained by scanning force microscopy. In this paper we propose a generalized equation between elastic indentation depth and load that approximates Maugis' solution very closely. If the normal contact stiffness can be described as the force gradient, that is the case of the force modulation microcopy, then a generalized equation between normal contact stiffness and load can be deduced. Both general equations can be easily fit to experimental data, and then interfacial energy and elastic modulus of the contact can be determined if the radius of the indenting sphere is known. Copyright 2000 Academic Press. PMID:11401361

Piétrement, O.; Troyon, M.

2000-06-01

18

Effects of Cross-Sectional Shape, Solidity, and Distribution of Heat-Transfer Coefficient on the Torsional Stiffness of Thin Wings Subjected to Aerodynamic Heating  

NASA Technical Reports Server (NTRS)

A study has been made of the effects of varying the shape, solidity, and heat-transfer coefficient of thin wings with regard to their influence on the torsional-stiffness reduction induced by aerodynamic heating. The variations in airfoil shape include blunting, flattening, and combined blunting and flattening of a solid wing of symmetrical double-wedge cross section. Hollow double-wedge wings of constant skin thickness with and without internal webs also are considered. The effects of heat-transfer coefficients appropriate for laminar and turbulent flow are investigated in addition to a step transition along the chord from a lower to a higher constant value of heat-transfer coefficient. From the results given it is concluded that the flattening of a solid double wedge decreases the reduction in torsional stiffness while slight degrees of blunting increase the loss. The influence of chordwise variations in heat-transfer coefficient due to turbulent and laminar boundary-layer flow on the torsional stiffness of solid wings is negligible. The effect of a step transition in heat-transfer coefficient along the chord of a solid wing can, however, become appreciable. The torsional-stiffness reduction of multiweb and hollow double-wedge wings is substantially less than that calculated for a solid wing subjected to the same heating conditions.

Thomson, Robert G.

1959-01-01

19

Stiffness jump in the generalized XY model on the square lattice.  

PubMed

We study the thermal phase transitions in the generalized classical XY model on the two-dimensional square lattice using single-cluster Monte Carlo simulations. In particular, we examine the (spin-wave) stiffness (helicity modulus) jump at the transition between the low-temperature algebraic phases and the disordered high-temperature regime. Employing a finite-size scaling ansatz from conformal field theory to estimate the termination of the algebraic phases that does not require knowledge of the critical properties, we provide an unbiased estimate of the stiffness jump. Our results are in full accord with the Berzinskii-Kosterlitz-Thouless scenario, i.e., the jump in the helicity modulus does not depend explicitly on the strength of the nematic coupling, but relates directly to the vorticity of the vortex excitations that drive the phase transition. We comment on previous work on related models, where Berzinskii-Kosterlitz-Thouless transition temperatures were based on scaling assumptions contradicted by our findings. PMID:23848632

Hübscher, David M; Wessel, Stefan

2013-06-01

20

Generalization of clustering coefficients to signed correlation networks.  

PubMed

The recent interest in network analysis applications in personality psychology and psychopathology has put forward new methodological challenges. Personality and psychopathology networks are typically based on correlation matrices and therefore include both positive and negative edge signs. However, some applications of network analysis disregard negative edges, such as computing clustering coefficients. In this contribution, we illustrate the importance of the distinction between positive and negative edges in networks based on correlation matrices. The clustering coefficient is generalized to signed correlation networks: three new indices are introduced that take edge signs into account, each derived from an existing and widely used formula. The performances of the new indices are illustrated and compared with the performances of the unsigned indices, both on a signed simulated network and on a signed network based on actual personality psychology data. The results show that the new indices are more resistant to sample variations in correlation networks and therefore have higher convergence compared with the unsigned indices both in simulated networks and with real data. PMID:24586367

Costantini, Giulio; Perugini, Marco

2014-01-01

21

Bianchi VI0 electric type cosmological models in General Relativity with stiff fluid and heat conduction  

NASA Astrophysics Data System (ADS)

The paper consists of some exact tilted solutions for a homogeneous Bianchi type VI0 universe. The material distribution is taken to be a stiff fluid with heat conduction. The physical and kinematical parameters have also been calculated to discuss the models in detail.

Roy, S. R.; Banerjee, S. K.

1996-01-01

22

Generalized approximations of reflection coefficients in orthorhombic media  

NASA Astrophysics Data System (ADS)

Reflection coefficients of qP- (quasi-P) and qS- (quasi-S) incident waves in orthorhombic media can be explicitly expressed by means of impedance matrices. In this paper, we extend previous studies and derive the generalized and linearized equations of reflectivity for all four types of waves in the symmetry-axis plane. These approximations have sufficient accuracy over a wide range of angles, therefore they are suitable for characterizing the seismic amplitude responses of unconventional resources. For example, they can be applied to represent the amplitude variation with offset for shale gas or coalbed methane reservoirs with strong anisotropy and complicated symmetry. Reduced equations are then derived in a transverse isotropic medium with a vertical symmetry axis (VTI) or a horizontal axis (HTI) for the anisotropic amplitude inversion. They retain higher accuracy than the corresponding previously published expressions at a strongly anisotropic interface, because they include the second-order terms of anisotropic parameters contrast. Numerical analyses on the inverse problem using different linearized expressions show the practical value of the new derived expressions in the joint inversion of the qPqP- and qPqS-waves for elastic parameters and anisotropic parameters.

Zhang, Feng; Li, Xiangyang

2013-10-01

23

Effect of porosity on effective diagonal stiffness coefficients (cii) and elastic anisotropy of cortical bone at 1 MHz: a finite-difference time domain study.  

PubMed

Finite-difference time domain (FDTD) numerical simulations coupled to real experimental data were used to investigate the propagation of 1 MHz pure bulk wave propagation through models of cortical bone microstructures. Bone microstructures were reconstructed from three-dimensional high resolution synchrotron radiation microcomputed tomography (SR-muCT) data sets. Because the bone matrix elastic properties were incompletely documented, several assumptions were made. Four built-in bone matrix models characterized by four different anisotropy ratios but the same Poisson's ratios were tested. Combining them with the reconstructed microstructures in the FDTD computations, effective stiffness coefficients were derived from simulated bulk-wave velocity measurements. For all the models, all the effective compression and shear bulk wave velocities were found to decrease when porosity increases. However, the trend was weaker in the axial direction compared to the transverse directions, contributing to the increase of the effective anisotropy. On the other hand, it was shown that the initial Poisson's ratio value may substantially affect the variations of the effective stiffness coefficients. The present study can be used to elaborate sophisticated macroscopic computational bone models incorporating realistic CT-based macroscopic bone structures and effective elastic properties derived from muCT-based FDTD simulations including the cortical porosity effect. PMID:17927440

Baron, Cécile; Talmant, Maryline; Laugier, Pascal

2007-09-01

24

Tape Joint Stiffness.  

National Technical Information Service (NTIS)

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

R. P. Rechard

1986-01-01

25

Comment on ``The elastic stiffness coefficients of nickel-iron single-crystal alloys at room temperature''  

Microsoft Academic Search

We respond to the recent claim that in face-centered-cubic Fe-Ni alloys the two cubic elastic-shear coefficients, Cââ and (Cââ-Cââ)\\/2, vary linearly with composition. Both theory and measurement support a nonlinear variation.

H. M. Ledbetter

1985-01-01

26

A Variable-Coefficient Manakov Model and Its Explicit Solutions through the Generalized Dressing Method  

NASA Astrophysics Data System (ADS)

For waves in inhomogeneous media, variable-coefficient evolution equations can arise. It is known that the Manakov model can derive two models for propagation in uniform optical fibers. If the fiber is nonuniform, one would expect that the coefficients in the model are not constants. We present a variable-coefficient Manakov model and derive its Lax pair using the generalized dressing method. As an application of the generalized dressing method, soliton solutions of the variable-coefficient Manakov model are obtained.

Su, Ting; Dai, Hui-Hui; Geng, Xian-Guo

2013-06-01

27

Abdominal obesity vs general obesity for identifying arterial stiffness, subclinical atherosclerosis and wave reflection in healthy, diabetics and hypertensive  

PubMed Central

Background Our aim was to analyze the relationship between abdominal obesity and general obesity, with subclinical atherosclerosis, arterial stiffness and wave reflection in healthy, diabetics and hypertensive subjects. Methods A cross-sectional descriptive study was made of 305 individuals (diabetics 32.8%, hypertensive subjects 37.0% and healthy individuals 30.2%). Measurements: Body mass index (BMI), waist circumference (WC), body fat percentage (BFP) and waist/height ratio (WHtR). Arterial stiffness was assessed according to pulse wave velocity (PWV), intima-media thickness of the common carotid artery (C-IMT), augmentation index (central and peripheral), ankle-brachial index (ABI), and central and peripheral pulse pressure. Results WC and WHtR showed a positive correlation to PWV and C-IMT in the studied groups. After adjusting for age, gender, high sensitivity c-reactive protein, serum glucose and the presence of diabetes, hypertension, smoking, dyslipidemia, antidiabetic drugs, lipid-lowering drugs, and atherosclerotic plaques, it was seen that for every 0.1 point increase in WHtR, and for every cm increase in WC, the PWV increased 0.041 and 0.029 m/sec, and C-IMT increased 0.001 mm and 0.001 mm, respectively. Conclusions The measures of abdominal obesity (WHtR and WC) correlates better than BMI and BFP with arterial stiffness evaluated by PWV, and with subclinical atherosclerosis evaluated by C-IMT, independently of the presence of diabetes or hypertension. Trial Registration Clinical Trials.gov Identifier: NCT01325064

2012-01-01

28

Sensitivity of overall vehicle stiffness to local joint stiffness  

NASA Technical Reports Server (NTRS)

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

Chon, Choon T.

1987-01-01

29

The Logic and Interpretation of Structure Coefficients in Multivariate General Linear Model Analyses.  

ERIC Educational Resources Information Center

In General Linear Model (GLM) analyses, it is important to interpret structure coefficients, along with standardized weights, when evaluating variable contribution to observed effects. Although often used in canonical correlation analysis, structure coefficients are less frequently used in multiple regression and several other multivariate…

Henson, Robin K.

30

Soliton solutions for a generalized KdV and BBM equations with time-dependent coefficients  

NASA Astrophysics Data System (ADS)

A generalized KdV equation with time-dependent coefficients will be studied. The BBM equation with time-dependent coefficients and linear damping term will also be examined. The wave soliton ansatz will be used to obtain soliton solutions for both equations. The conditions of existence of solitons are presented.

Wazwaz, Abdul-Majid; Triki, Houria

2011-03-01

31

Generalized muscle pseudo-hypertrophy and stiffness associated with the myotilin Ser55Phe mutation: a novel myotilinopathy phenotype?  

PubMed

Myotilinopathies are a group of muscle disorders caused by mutations in the MYOT gene. It was first described in two families suffering from limb girdle muscle dystrophy type 1 (LGMD 1A), and later identified in a subset of dominant or sporadic patients suffering from myofibrillar myopathy, as well as in a family with spheroid body myopathy. Disease phenotypes associated with MYOT mutations are clinically heterogeneous and include pure LGMD forms as well as late-onset distal myopathies. We report here on a 53-year-old male suffering from a unique clinical profile characterized by generalized symmetrical increase in muscle bulk leading to a Herculean appearance. Muscle weakness and stiffness in the lower extremities were the patient's main complaints. Muscle MRI showed extensive fatty infiltration in the thigh and leg muscles and a muscle biopsy showed a myofibrillar myopathy with prominent protein aggregates. Gene sequencing revealed a Ser55Phe missense mutation in the myotilin gene. The mutation was identified in his older brother, who presented a mild hypertrophic appearance and had a myopathic pattern in EMG, despite not presenting any of the complaints of the proband and having normal muscle strength. This finding, and his deceased father and paternal aunt's similar gait disorders, suggest that this is in fact a new autosomal dominant kindred. The present observations further expand the spectrum of clinical manifestations associated with mutations in the myotilin gene. PMID:19027924

Gamez, Josep; Armstrong, Judith; Shatunov, Alexey; Selva-O'Callaghan, Albert; Dominguez-Oronoz, Rosa; Ortega, Arantxa; Goldfarb, Lev; Ferrer, Isidre; Olivé, Montse

2009-02-15

32

Building Generalized Lax Integrable KdV and MKdV Equations with Spatiotemporally Varying Coefficients  

NASA Astrophysics Data System (ADS)

We present a technique based on extended Lax Pairs to derive variable-coefficient generalizations of various Lax-integrable NLPDE hierarchies. As illustrative examples, we consider generalized KdV equations, and three variants of generalized MKdV equations. It is demonstrated that the technique yields Lax- or S-integrable NLPDEs with both time- AND space-dependent coefficients which are thus more general than almost all cases considered earlier via other methods such as the Painlevé Test, Bell Polynomials, and various similarity methods. Some solutions are also presented for the generalized KdV equation derived here by the use of the Painlevé singular manifold method. Current and future work is centered on generalizing other integrable hierarchies of NLPDEs similarly, and deriving various integrability properties such as solutions, Backlund Transformations, and hierarchies of conservation laws for these new integrable systems with variable coefficients.

Russo, M.; Choudhury, S. R.

2014-03-01

33

In-plane, flexural, twisting and thickness-shear coefficients for stiffness and damping of a monolayer filamentary composite, part 1  

NASA Technical Reports Server (NTRS)

Elastic and damping analyses resulting in determinations of the various stiffnesses and associated loss tangents for the complete characterization of the elastic and damping behavior of a monofilament composite layer are presented. For the determination of the various stiffnesses, either an elementary mechanics-of-materials formulation or a more rigorous mixed-boundary-value elasticity formulation is used. The solution for the latter formulation is obtained by means of the boundary-point least-square error technique. Kimball-Lovell type damping is assumed for each of the constituent materials. For determining the loss tangents associated with the various stiffnesses, either the viscoelastic correspondence principle or an energy analysis based on the appropriate elastic stress distribution is used.

Bert, C. W.; Chang, S.

1972-01-01

34

Riccati-type Bäcklund transformations of nonisospectral and generalized variable-coefficient KdV equations  

NASA Astrophysics Data System (ADS)

We extend the method of constructing Bäcklund transformations for integrable equations through Riccati equations to the nonisospectral and the variable-coefficient equations. By taking nonisospectral and generalized variable-coefficient Korteweg—de Vries (KdV) equations as examples, their Bäcklund transformations are obtained under a more generalized constrain condition. In addition, the Lax pairs and infinite numbers of conservation laws of these equations are given. Especially, some classical equations such as the cylindrical KdV equation are just the special cases of the constrain condition.

Yang, Yun-Qing; Wang, Yun-Hu; Li, Xin; Cheng, Xue-Ping

2014-03-01

35

Rogue wave solutions to the generalized nonlinear Schrödinger equation with variable coefficients.  

PubMed

A similarity transformation is utilized to reduce the generalized nonlinear Schrödinger (NLS) equation with variable coefficients to the standard NLS equation with constant coefficients, whose rogue wave solutions are then transformed back into the solutions of the original equation. In this way, Ma breathers, the first- and second-order rogue wave solutions of the generalized equation, are constructed. Properties of a few specific solutions and controllability of their characteristics are discussed. The results obtained may raise the possibility of performing relevant experiments and achieving potential applications. PMID:23848816

Zhong, Wei-Ping; Beli?, Milivoj R; Huang, Tingwen

2013-06-01

36

A generalized correlation coefficient: Application to DTI and multi-fiber DTI  

Microsoft Academic Search

Multi-fiber models have been introduced as an efficient and interpretable way of representing the diffusion signal in areas with crossing fibers. However, no metric has been provided to use multi-fiber features in registration. The normalized correlation coefficient is commonly used in registration of scalar images due to its invariance under linear transformations of the intensities. In this paper, we generalize

Maxime Taquet; Benoit Macq; Simon K. Warfield

2012-01-01

37

Statistical Properties of Generalized Gini Coefficient with Application to Health Inequality Measurement  

ERIC Educational Resources Information Center

In this article, we report statistical properties of two classes of generalized Gini coefficients (G1 and G2). The theoretical results were assessed via Monte Carlo simulations. Further, we used G1 and G2 on life expectancy to measure health inequalities among the provinces of China and the states of the United States. For China, the results…

Lai, Dejian; Huang, Jin; Risser, Jan M.; Kapadia, Asha S.

2008-01-01

38

Soliton-like solutions to the generalized Burgers-Huxley equation with variable coefficients  

NASA Astrophysics Data System (ADS)

In this paper, we consider the generalized Burgers-Huxley equation with arbitrary power of nonlinearity and timedependent coefficients. We analyze the traveling wave problem and explicitly find new soliton-like solutions for this extended equation by using the ansatz of Zhao et al. [X. Zhao, D. Tang, L. Wang, Phys. Lett. A 346 (2005) 288-291]. We also employ the solitary wave ansatz method to derive the exact bright and dark soliton solutions for the considered evolution equation. The physical parameters in the soliton solutions are obtained as function of the time-dependent model coefficients. The conditions of existence of solitons are presented. As a result, rich exact travelling wave solutions, which contain new soliton-like solutions, bell-shaped solitons and kink-shaped solitons for the generalized Burgers-Huxley equation with time-dependent coefficients, are obtained. The methods employed here can also be used to solve a large class of nonlinear evolution equations with variable coefficients.

Triki, Houria; Wazwaz, Abdul-Majid

2013-12-01

39

Stiff magnetofluid cosmological model  

SciTech Connect

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

Bali, R.; Tyagi, A.

1988-05-01

40

No-reference peak signal to noise ratio estimation based on generalized Gaussian modeling of transform coefficient distributions  

NASA Astrophysics Data System (ADS)

We present a no-reference peak signal to noise ratio (PSNR) estimation algorithm based on discrete cosine transform (DCT) coefficient distributions from H.264/MPEG-4 part 10 advanced video codec (H.264/AVC) bitstreams. To estimate the PSNR of a compressed picture without the original picture on the decoder side, it is important to model the distribution of transform coefficients obtained from quantized coefficients accurately. Whereas several conventional algorithms use the Laplacian or Cauchy distribution to model the DCT coefficient distribution, the proposed algorithm uses a generalized Gaussian distribution. Pearson's ?2 (chi-square) test was applied to show that the generalized Gaussian distribution is more appropriate than the other models for modeling the transform coefficients. The ?2 test was also used to find optimum parameters for the generalized Gaussian model. It was found that the generalized Gaussian model improves the accuracy of the DCT coefficient distribution, thus reducing the mean squared error between the real and the estimated PSNR.

Ryu, Ji-Woo; Lee, Seon-Oh; Sim, Dong-Gyu; Han, Jong-Ki

2012-02-01

41

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

42

Integrability study on a generalized (2+1)-dimensional variable-coefficient Gardner model with symbolic computation  

SciTech Connect

Gardner model describes certain nonlinear elastic structures, ion-acoustic waves in plasmas, and shear flows in ocean and atmosphere. In this paper, by virtue of the computerized symbolic computation, the integrability of a generalized (2+1)-dimensional variable-coefficient Gardner model is investigated. Painleve integrability conditions are derived among the coefficient functions, which reduce all the coefficient functions to be proportional only to {gamma}(t), the coefficient of the cubic nonlinear term u{sup 2}u{sub x}. Then, an independent transformation of the variable t transforms the reduced {gamma}(t)-dependent equation into a constant-coefficient integrable one. Painleve test shows that this is the only case when our original generalized (2+1)-dimensional variable-coefficient Gardner model is integrable.

Lue Xing; Zhang Haiqiang; Xu Tao; Li He [School of Science, Beijing University of Posts and Telecommunications, P.O. Box 122, Beijing 100876 (China); Tian Bo [School of Science, Beijing University of Posts and Telecommunications, P.O. Box 122, Beijing 100876 (China); State Key Laboratory of Software Development Environment, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); Key Laboratory of Information Photonics and Optical Communications (BUPT), Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 128, Beijing 100876 (China)

2010-12-15

43

Integrability study on a generalized (2+1)-dimensional variable-coefficient Gardner model with symbolic computation.  

PubMed

Gardner model describes certain nonlinear elastic structures, ion-acoustic waves in plasmas, and shear flows in ocean and atmosphere. In this paper, by virtue of the computerized symbolic computation, the integrability of a generalized (2+1)-dimensional variable-coefficient Gardner model is investigated. Painleve? integrability conditions are derived among the coefficient functions, which reduce all the coefficient functions to be proportional only to ?(t), the coefficient of the cubic nonlinear term u(2)u(x). Then, an independent transformation of the variable t transforms the reduced ?(t)-dependent equation into a constant-coefficient integrable one. Painleve? test shows that this is the only case when our original generalized (2+1)-dimensional variable-coefficient Gardner model is integrable. PMID:21198095

Lü, Xing; Tian, Bo; Zhang, Hai-Qiang; Xu, Tao; Li, He

2010-12-01

44

Stiffness in healing fractures.  

PubMed

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

Richards, J

1987-01-01

45

Aerodynamic Coefficient Prediction of a General Transport Aircraft Using Neural Network  

Microsoft Academic Search

A fast, reliable, and accurate methodology for predicting aerodynamic coefficients of airfoils and transport aircraft was elaborated employing the neural network technique. Basic aerodynamic coefficients are modeled as functions of angle of attack, Mach number, and Reynolds number for a given airfoil or wing-body configuration. In this latter case, the coefficients are also dependent on the wing geometry of the

Ricardo Wallach; Bento S. Mattos; Roberto da Mota Girardi; Marcelo Curvo

46

A computer program for two-particle generalized coefficients of fractional parentage  

NASA Astrophysics Data System (ADS)

We present a FORTRAN90 program GCFP for the calculation of the generalized coefficients of fractional parentage (generalized CFPs or GCFP). The approach is based on the observation that the multi-shell CFPs can be expressed in terms of single-shell CFPs, while the latter can be readily calculated employing a simple enumeration scheme of antisymmetric A-particle states and an efficient method of construction of the idempotent matrix eigenvectors. The program provides fast calculation of GCFPs for a given particle number and produces results possessing numerical uncertainties below the desired tolerance. A single j-shell is defined by four quantum numbers, (e,l,j,t). A supplemental C++ program parGCFP allows calculation to be done in batches and/or in parallel. Program summaryProgram title:GCFP, parGCFP Catalogue identifier: AEBI_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBI_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 17 199 No. of bytes in distributed program, including test data, etc.: 88 658 Distribution format: tar.gz Programming language: FORTRAN 77/90 ( GCFP), C++ ( parGCFP) Computer: Any computer with suitable compilers. The program GCFP requires a FORTRAN 77/90 compiler. The auxiliary program parGCFP requires GNU-C++ compatible compiler, while its parallel version additionally requires MPI-1 standard libraries Operating system: Linux (Ubuntu, Scientific) (all programs), also checked on Windows XP ( GCFP, serial version of parGCFP) RAM: The memory demand depends on the computation and output mode. If this mode is not 4, the program GCFP demands the following amounts of memory on a computer with Linux operating system. It requires around 2 MB of RAM for the A=12 system at E?2. Computation of the A=50 particle system requires around 60 MB of RAM at E=0 and ˜70 MB at E=2 (note, however, that the calculation of this system will take a very long time). If the computation and output mode is set to 4, the memory demands by GCFP are significantly larger. Calculation of GCFPs of A=12 system at E=1 requires 145 MB. The program parGCFP requires additional 2.5 and 4.5 MB of memory for the serial and parallel version, respectively. Classification: 17.18 Nature of problem: The program GCFP generates a list of two-particle coefficients of fractional parentage for several j-shells with isospin. Solution method: The method is based on the observation that multishell coefficients of fractional parentage can be expressed in terms of single-shell CFPs [1]. The latter are calculated using the algorithm [2,3] for a spectral decomposition of an antisymmetrization operator matrix Y. The coefficients of fractional parentage are those eigenvectors of the antisymmetrization operator matrix Y that correspond to unit eigenvalues. A computer code for these coefficients is available [4]. The program GCFP offers computation of two-particle multishell coefficients of fractional parentage. The program parGCFP allows a batch calculation using one input file. Sets of GCFPs are independent and can be calculated in parallel. Restrictions:A<86 when E=0 (due to the memory constraints); small numbers of particles allow significantly higher excitations, though the shell with j?11/2 cannot get full (it is the implementation constraint). Unusual features: Using the program GCFP it is possible to determine allowed particle configurations without the GCFP computation. The GCFPs can be calculated either for all particle configurations at once or for a specified particle configuration. The values of GCFPs can be printed out with a complete specification in either one file or with the parent and daughter configurations printed in separate files. The latter output mode requires additional time and RAM memory. It is possible to restrict the ( J,T) values of the considered particle configurations. (Here J is the total angular momentum and

Deveikis, A.; Juodagalvis, A.

2008-10-01

47

A generalized entering coefficient to characterize foam stability against oil in porous media  

SciTech Connect

This work unifies the two approaches presently accounting for oil-foam interactions: spreading behavior and thin-film stability. We demonstrate the correspondences between stable pseudoemulsion films, negative entering coeffients, and oil-tolerant foams. Frumkin-Deryaguin theory is applied to the problem of oil-foam interactions and reveals that stable pseudoemulsion films are essential to maintain oil-tolerant foams. This hypothesis is critically tested by comparing steady-state foam flow behavior in glass beadpacks that contain residual oil, with newly measured, equilibrium disjoining pressure isotherms for both foam and pseudoemulsion films, along with bulk surface and interfacial tensions. Experimental results together with similar data on a wide variety of systems lead us to conclude that highly repulsive pseudoemulsion film disjoining pressure isotherms (i.e., stable pseudoemulsion films) produce negative generalized entering coefficients and oil-tolerant foams. This in turn provides us with a surfactant design criterion needed to produce oil-tolerant foam in porous media.

Bergeron, V.; Fagan, M.E.; Radke, C.J.

1992-11-01

48

The Exact Solutions of Variable Coefficient Auxiliary High Order Generalized KdV Equation  

Microsoft Academic Search

\\u000a Selecting appropriate trial functions, the nonlinear variable coefficient PDE can be convert transformed to algebraic equations.\\u000a The exact solutions to a class of nonlinear variable coefficient partial differential equations are successfully derived.\\u000a In this paper the second type KdV equation with variable coefficients is studied, and their exact solutions are obtain. The\\u000a method is obviously suitable to solving other nonlinear

Bo Lu; Yuzhen Chen; Qingshan Zhang

49

General method to derive the relationship between two sets of Zernike coefficients corresponding to different aperture sizes  

PubMed Central

Zernike polynomials have been widely used to describe the aberrations in wave-front sensing of the eye. The Zernike coefficients are often computed under different aperture sizes. For the sake of comparison, the same aperture diameter is required. Since no standard aperture size is available for reporting the results, it is important to develop a technique for converting the Zernike coefficients obtained from one aperture size to another size. In this paper, by investigating the properties of Zernike polynomials, we propose a general method for establishing the relationship between two sets of Zernike coefficients computed with different aperture sizes.

Shu, Huazhong; Luo, Limin; Han, Guo-Niu; Coatrieux, Jean-Louis

2006-01-01

50

Stiff-Person Syndrome  

MedlinePLUS

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

51

New solitons for the Hirota equation and generalized higher-order nonlinear Schrödinger equation with variable coefficients  

NASA Astrophysics Data System (ADS)

In this paper, multisoliton solutions of the Hirota equation with variable coefficients are obtained by the Darboux transformation based on the Ablowitz-Kaup-Newell-Segur technology. As an example, we discuss the evolutional behaviour of a two-soliton solution in a soliton control fibre system. The results reveal that one may control the interaction between the pulses by choosing the third-order dispersion parameters d4 and h appropriately. Meanwhile, more generalized forms of bright soliton and dark soliton solutions of generalized higher order nonlinear Schrödinger equations (GHONLSE) with variable coefficients are obtained by the extended tanh-function method. Moreover, new bright and dark combined solitary wave, kink solitary wave and M-shaped solitary wave to GHONLSE with variable coefficients are firstly reported in this paper. Especially, the term proportional to ?1 resulting from the group velocity decides the group velocity and the phase shift of these new solitary waves.

Dai, Chao-Qing; Zhang, Jie-Fang

2006-01-01

52

Offnormal Incidence Reflection-Coefficient Determination for Thick Underwater Acoustic Panels Using a Generalized ONION Method.  

National Technical Information Service (NTIS)

The ONION method is a reflection-coefficient measurement technique designed for use on data acquired from thick underwater acoustic panels in the frequency range 1-10 kHz, but may be used to frequencies as high as 25 kHz. The method extrapolates transient...

J. C. Piquette

1990-01-01

53

GENERAL New Explicit Solutions of (1 + 1)-Dimensional Variable-Coefficient Broer—Kaup System  

NASA Astrophysics Data System (ADS)

By using the compatibility method, many explicit solutions of the (1 + 1)-dimensional variable-coefficient Broer-Kaup system are constructed, which include new solutions expressed by error function, Bessel function, exponential function, and Airy function. Some figures of the solutions are given by the symbolic computation system Maple.

Yan, Zhi-Lian; Zhou, Jian-Ping

2010-12-01

54

GENERAL: Joule-Thomson Coefficient for Strongly Interacting Unitary Fermi Gas  

NASA Astrophysics Data System (ADS)

The Joule-Thomson effect reflects the interaction among constituent particles of macroscopic system. For classical ideal gas, the corresponding Joule-Thomson coefficient is vanishing while it is non-zero for ideal quantum gas due to the quantum degeneracy. In recent years, much attention is paid to the unitary Fermi gas with infinite two-body scattering length. According to universal analysis, the thermodynamical law of unitary Fermi gas is similar to that of non-interacting ideal gas, which can be explored by the virial theorem P = 2E/3V. Based on previous works, we further study the unitary Fermi gas properties. The effective chemical potential is introduced to characterize the nonlinear levels crossing effects in a strongly interacting medium. The changing behavior of the rescaled Joule-Thomson coefficient according to temperature manifests a quite different behavior from that for ideal Fermi gas.

Liao, Kai; Chen, Ji-Sheng; Li, Chao

2010-09-01

55

Exchangeable cluster binary data correlation coefficient estimation with generalized estimating equations  

Microsoft Academic Search

This study used simulated data to evaluate the performance of distinct conditional generalized estimating equations (CGEE) for the analysis of exchangeable correlation for binary data. The CGEE differs from the usual generalized estimating equations (GEE) in that, instead of marginal expectations, the conditional expectations of the responses were used in the estimating equations. The major distinction among the CGEEs compared

Tsung-Shan Tsou

2000-01-01

56

Integrability and optical solitons in a generalized variable-coefficient coupled Hirota-Maxwell-Bloch system in fiber optics  

NASA Astrophysics Data System (ADS)

In this paper, with symbolic computation, a generalized variable-coefficient coupled Hirota-Maxwell-Bloch system is studied, which can describe the ultrashort optical pulse propagation in a variable-coefficient nonlinear, dispersive fiber doped with two-level resonant atoms. Integrable conditions of such system are determined via the Painlevé analysis and the associated Lax pair is explicitly constructed. Furthermore, the analytic one- and two-soliton-like solutions are derived by virtue of the Darboux transformation. Through the graphical analysis of the soliton-like solutions obtained, the propagation features of optical solitons and their interaction behaviors are discussed. Different from the previous results, the two-soliton interaction is found to admit the energy interchanging property.

Xue, Yu-Shan; Tian, Bo; Ai, Wen-Bao; Li, Min; Wang, Pan

2013-06-01

57

A method for assigning species into groups based on generalized Mahalanobis distance between habitat model coefficients  

Microsoft Academic Search

Habitat association models are commonly developed for individual animal species using generalized linear modeling methods\\u000a such as logistic regression. We considered the issue of grouping species based on their habitat use so that management decisions\\u000a can be based on sets of species rather than individual species. This research was motivated by a study of western landbirds\\u000a in northern Idaho forests.

Christopher J. Williams; Patricia J. Heglund

2009-01-01

58

Generalized Skew Coefficients of Annual Peak Flows for Rural, Unregulated Streams in West Virginia  

USGS Publications Warehouse

Generalized skew was determined from analysis of records from 147 streamflow-gaging stations in or near West Virginia. The analysis followed guidelines established by the Interagency Advisory Committee on Water Data described in Bulletin 17B, except that stations having 50 or more years of record were used instead of stations with the less restrictive recommendation of 25 or more years of record. The generalized-skew analysis included contouring, averaging, and regression of station skews. The best method was considered the one with the smallest mean square error (MSE). MSE is defined as the following quantity summed and divided by the number of peaks: the square of the difference of an individual logarithm (base 10) of peak flow less the mean of all individual logarithms of peak flow. Contouring of station skews was the best method for determining generalized skew for West Virginia, with a MSE of about 0.2174. This MSE is an improvement over the MSE of about 0.3025 for the national map presented in Bulletin 17B.

Atkins, John T., Jr.; Wiley, Jeffrey B.; Paybins, Katherine S.

2009-01-01

59

Maximum and anti-maximum principles for the general operator of second order with variable coefficients  

Microsoft Academic Search

This paper is devoted to the study of existence of solutions of the nonlinear second-order differential equation u?(t)+p(t)u?(t)+f(t,u(t))=0 together with different types of linear boundary conditions. To this end we assume the existence of a pair of ordered lower and upper solutions and deduce comparison results for the general linear operator L(p,q)u(t)?u?(t)+p(t)u?(t)+q(t)u(t) together with the condisered boundary conditions.

Irina V. Barteneva; Alberto Cabada; Alexander O. Ignatyev

2003-01-01

60

Effective stiffness of cracked elastic solids  

SciTech Connect

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

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

1992-08-01

61

Stable solitary-waves in a higher order generalized nonlinear Schrödinger equation with space- and time-variable coefficients  

NASA Astrophysics Data System (ADS)

We developed a method that combines a similarity transformation with a mapping that solves a generalized nonautonomous nonlinear Schrödinger (NLS) equation containing cubic, quintic and higher order terms in the conjunction with spatially and temporary varying dispersion, containing higher nonlinearities, and external potential. We have studied various classes of solutions in closed form representing front, bright and dark solitary-like waves. We introduced a transformation that solves the related transformed NLS in the constant coefficients. As an application of this technique, we have analyzed the dynamical behavior of several specific classes of solutions such as moving, breathing, resonant both for periodic and quasi-periodic solitary-like waves. The stability of the obtained solitary-like waves is examined using analytical and numerical methods.

Zakeri, Gholam-Ali; Yomba, Emmanuel

2013-10-01

62

Adiponectin and Arterial Stiffness  

Microsoft Academic Search

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

Azra Mahmud; John Feely

2005-01-01

63

The stiff elbow.  

PubMed

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

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

2009-12-01

64

High air-bearing stiffness slider design  

NASA Astrophysics Data System (ADS)

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

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

2006-08-01

65

Optimized stiffness for linear time-invariant dynamic system according to a new system design  

NASA Astrophysics Data System (ADS)

This paper deals with a linear time-invariant dynamic system such as spring-mass-damper system. General dynamic systems are quite commonly to be redesigned for another purpose of using. For example, if one automobile must be redesigned to have more weights, the existing suspension must be replaced due to that gained weight. Therefore the stiffness and damping coefficient must be recomputed in order to make the automobile become suitable for using as previous. Here the spring-mass-damper system is used as an example to demonstrate the technique through dynamic optimization where the problem is solved in two categories as minimum energy and maximum jerk. Once the state and control variables are provided from the problem of minimum energy and maximum jerk, respectively, these parameter will be substituted in dynamic equations and leave the stiffness and damping coefficient as the unknown parameters to be solved.

Veeraklaew, Tawiwat

2012-11-01

66

Calculation of Rotor's Torsional Vibration Characteristics Based on Equivalent Diameter of Stiffness  

Microsoft Academic Search

In this paper, ANSYS finite element analysis software is used to simulate the twisted state of turbine integral rotor's discs. For various stepped shaft structure, the formula of ¿-stiffness influence coefficient is fit by changing the geometric parameters of the equal-thickness disc, then equivalent diameter of stiffness is obtained. For the cone-shaped disc, the equivalent diameter of stiffness is calculated

Wang-fan Li; Dan-mei Xie; Yong Qian; Xian-bo Zhao; Sun Cai; You-min Hou

2010-01-01

67

Nonlinear stability of oscillatory core-annular flow: A generalized Kuramoto-Sivashinsky equation with time periodic coefficients  

NASA Technical Reports Server (NTRS)

In this paper the nonlinear stability of two-phase core-annular flow in a pipe is examined when the acting pressure gradient is modulated by time harmonic oscillations and viscosity stratification and interfacial tension is present. An exact solution of the Navier-Stokes equations is used as the background state to develop an asymptotic theory valid for thin annular layers, which leads to a novel nonlinear evolution describing the spatio-temporal evolution of the interface. The evolution equation is an extension of the equation found for constant pressure gradients and generalizes the Kuramoto-Sivashinsky equation with dispersive effects found by Papageorgiou, Maldarelli & Rumschitzki, Phys. Fluids A 2(3), 1990, pp. 340-352, to a similar system with time periodic coefficients. The distinct regimes of slow and moderate flow are considered and the corresponding evolution is derived. Certain solutions are described analytically in the neighborhood of the first bifurcation point by use of multiple scales asymptotics. Extensive numerical experiments, using dynamical systems ideas, are carried out in order to evaluate the effect of the oscillatory pressure gradient on the solutions in the presence of a constant pressure gradient.

Coward, Adrian V.; Papageorgiou, Demetrios T.; Smyrlis, Yiorgos S.

1994-01-01

68

Bell-polynomial application and multi-soliton solutions for the generalized variable-coefficient Drinfeld-Sokolov-Satsuma-Hirota system in fluids and plasmas  

NASA Astrophysics Data System (ADS)

With symbolic computation, the generalized variable-coefficient Drinfeld-Sokolov-Satsuma-Hirota (gvcDSSH) system in fluids and plasmas is investigated. Under the constraint conditions on variable coefficients obtained via the Painlevé test, the binary Bell polynomials are applied to the gvcDSSH system for its bilinear forms and multi-soliton solutions. With the different damping, dispersive and dissipative coefficients given, the multi-soliton solutions of the gvcDSSH system are illustrated and discussed. (i) The interactions between/among the solitons are elastic; (ii) the damping coefficient can only affect the amplitude of one field, while it has no effect on the other; (iii) the velocity and characteristic line for each soliton can be affected by the dispersive and dissipative coefficients.

Shen, Yu-Jia; Gao, Yi-Tian; Yu, Xin

2013-09-01

69

Advanced damper with negative structural stiffness elements  

NASA Astrophysics Data System (ADS)

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

Dong, Liang; Lakes, Roderic S.

2012-07-01

70

Development of a contour map showing generalized skew coefficients of annual peak discharges of rural, unregulated streams in New York, excluding Long Island  

USGS Publications Warehouse

Flood-frequency relations that are developed by fitting the logarithms of annual peak discharges to a Pearson Type-III distribution are sensitive to skew coefficients. Estimates of population skew for a site are improved when computed from the weighted average of (1) the sample (station) skew, and (2) an unbiased, generalized skew estimate. A weighting technique based on the number of years of record at each of 226 sites was used to develop a contour map of unbiased, generalized skew coefficients for New York. An attempt was made to group (regionalize) the station skew coefficients into five hydrologically similar areas of New York, but the statewide version proved to be as accurate as the regionalized version and therefore was adopted as the final generalized skew-coefficient map for New York. An error analysis showed the statewide contour map to have lower MSE?s (mean square errors) than those computed from (1) the five regional skewcoefficient contour maps, (2) a previously used (1982) nationwide skew coefficient map, and (3) the weighted mean of skew coefficients for sites within each of five hydrologically uniform, but distinct areas of New York.

Lumia, Richard; Baevsky, Yvonne Halpern

2000-01-01

71

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

72

General method to derive the relationship between two sets of Zernike coefficients corresponding to different aperture sizes  

Microsoft Academic Search

Zernike polynomials have been widely used to describe the aberrations in wavefront sensing of the eye. The Zernike coefficients are often computed under different aperture sizes. For the sake of comparison, the same aperture diameter is required. Since no standard aperture size is available for reporting the results, it is important to develop a technique for converting the Zernike coefficients

Huazhong Shu; Limin Luo; Guoniu Han; Jean-Louis Coatrieux

2006-01-01

73

Interaction of leg stiffness and surface stiffness during human hopping  

Microsoft Academic Search

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

DANIEL P. FERRIS; CLAIRE T. FARLEY

1997-01-01

74

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

75

Multisoliton solutions in terms of double Wronskian determinant for a generalized variable-coefficient nonlinear Schrödinger equation from plasma physics, arterial mechanics, fluid dynamics and optical communications  

Microsoft Academic Search

In this paper, the multisoliton solutions in terms of double Wronskian determinant are presented for a generalized variable-coefficient nonlinear Schrödinger equation, which appears in space and laboratory plasmas, arterial mechanics, fluid dynamics, optical communications and so on. By means of the particularly nice properties of Wronskian determinant, the solutions are testified through direct substitution into the bilinear equations. Furthermore, it

Lue Xing; Hong-Wu Zhu; Zhen-Zhi Yao; Xiang-Hua Meng; Cheng Zhang; Chun-Yi Zhang; Bo Tian

2008-01-01

76

Rigorous Justification of the Localized Approximation to the Beam-Shape Coefficients in Generalized Lorenz-Mie Theory. Part 1; On-Axis Beams  

NASA Technical Reports Server (NTRS)

Generalized Lorenz-Mie theory describes electromagnetic scattering of an arbitrary light beam by a spherical particle. The computationally most expensive feature of the theory is the evaluation of the beam-shape coefficients, which give the decomposition of the incident light beam into partial waves. The so-called localized approximation to these coefficients for a focused Gaussian beam is an analytical function whose use greatly simplifies Gaussian-beam scattering calculations. A mathematical justification and physical interpretation of the localized approximation is presented for on-axis beams.

Lock, James A.; Gouesbet, Gerard

1994-01-01

77

A new theory for multistep discretizations of stiff ordinary differential equations: Stability with large step sizes  

NASA Technical Reports Server (NTRS)

A large set of variable coefficient linear systems of ordinary differential equations which possess two different time scales, a slow one and a fast one is considered. A small parameter epsilon characterizes the stiffness of these systems. A system of o.d.e.s. in this set is approximated by a general class of multistep discretizations which includes both one-leg and linear multistep methods. Sufficient conditions are determined under which each solution of a multistep method is uniformly bounded, with a bound which is independent of the stiffness of the system of o.d.e.s., when the step size resolves the slow time scale, but not the fast one. This property is called stability with large step sizes. The theory presented lets one compare properties of one-leg methods and linear multistep methods when they approximate variable coefficient systems of stiff o.d.e.s. In particular, it is shown that one-leg methods have better stability properties with large step sizes than their linear multistep counter parts. The theory also allows one to relate the concept of D-stability to the usual notions of stability and stability domains and to the propagation of errors for multistep methods which use large step sizes.

Majda, G.

1985-01-01

78

GENERAL: Effect of Spatial Dimension and External Potential on Joule-Thomson Coefficients of Ideal Bose Gases  

Microsoft Academic Search

Based on the form of the n-dimensional generic power-law potential, the state equation and the heat capacity, the analytical expressions of the Joule-Thomson coefficient (JTC) for an ideal Bose gas are derived in n-dimensional potential. The effect of the spatial dimension and the external potential on the JTC are discussed, respectively. These results show that: (i) For the free ideal

Du-Qi Yuan; Can-Jun Wang

2010-01-01

79

Terrace width distributions for vicinal surfaces with steps of alternating stiffness  

NASA Astrophysics Data System (ADS)

For the typical elastic interactions between steps, the generalized Wigner distribution (GWD) has been shown to be in excellent quantitative agreement with terrace width distributions (TWDs) calculated from numerical simulations. Here we show that the TWDs of vicinal surfaces with steps of alternating stiffness (but the same sort of step-step repulsions) are also given by the GWD. In the key parameter, the dimensionless repulsion strength, the step stiffness is generalized to twice the "reduced stiffness" of the two kinds of steps, as befits the inertial nature of stiffness. These results should also be applicable to more general surfaces with steps of different stiffness.

Yancey, Jeremy A.; Richards, Howard L.; Einstein, T. L.

2005-12-01

80

Stiffness Isn't Everything  

Microsoft Academic Search

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

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

1995-01-01

81

Group method solutions of the generalized forms of Burgers, Burgers–KdV and KdV equations with time-dependent variable coefficients  

Microsoft Academic Search

Solutions for the generalized forms of Burgers, Burgers–KdV, and KdV equations with time-dependent variable coefficients and\\u000a with initial and boundary conditions are constructed. The analysis rests mainly on the standard group method. Similarity solutions\\u000a are found which reduce the nonlinear system of partial differential equations to systems of ordinary differential equations\\u000a to obtain some exact solutions and others as numerical

Mina B. Abd-el-Malek; Medhat M. Helal

82

Working Stiff: PBS  

NSDL National Science Digital Library

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

83

Dynamic dorsoventral stiffness assessment of the ovine lumbar spine.  

PubMed

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

Keller, Tony S; Colloca, Christopher J

2007-01-01

84

The generalized correlation for the evaluation of the influence of the Stefan flow on the heat transfer coefficient  

NASA Astrophysics Data System (ADS)

The analytical equations for the steady-state heat-and-mass transfer in the steam evaporation/condensation processes from the steam-gas mixtures on the planar and spherical surfaces are derived. The vapor flow through the motionless dry gas is considered according to the method proposed by Maxwell for the solution of the diffusion problems. The relationships for the calculation of the coefficients taking into account an increase in the mass output and an increase or a decrease in the heat emission (depending on the directions of the heat-and-mass flows) as a result of the influence of the Stefan flow are presented. The derived relationships can be used to calculate the apparatuses in which the steam evaporation or condensation from the steam-gas mixture occurs (the coolers of the vapor from deaerators, the apparatuses for the deep utilization of the heat of the combustion products, the condensation boilers, etc.).

Baskakov, A. P.; Rakov, O. A.

2013-11-01

85

Arterial stiffness in diabetes and the metabolic syndrome: a pathway to cardiovascular disease  

Microsoft Academic Search

Increased arterial stiffness associated with diabetes and the metabolic syndrome may in part explain the increased cardiovascular\\u000a disease risk observed in these conditions. Arterial stiffness can be estimated by quantifying pulse pressure but is better\\u000a described by distensibility and compliance coefficients, pulse wave velocity and wave reflection. The most common non-invasive\\u000a methodologies used to quantify these estimates of arterial stiffness

C. D. A. Stehouwer; R. M. A. Henry; I. Ferreira

2008-01-01

86

The File Drawer Problem in Reliability Generalization: A Strategy to Compute a Fail-Safe N with Reliability Coefficients  

ERIC Educational Resources Information Center

Meta-analytic reliability generalizations (RGs) are limited by the scarcity of reliability reporting in primary articles, and currently, RG investigators lack a method to quantify the impact of such nonreporting. This article introduces a stepwise procedure to address this challenge. First, the authors introduce a formula that allows researchers…

Howell, Ryan T.; Shields, Alan L.

2008-01-01

87

GENERAL: Effect of Spatial Dimension and External Potential on Joule-Thomson Coefficients of Ideal Bose Gases  

NASA Astrophysics Data System (ADS)

Based on the form of the n-dimensional generic power-law potential, the state equation and the heat capacity, the analytical expressions of the Joule-Thomson coefficient (JTC) for an ideal Bose gas are derived in n-dimensional potential. The effect of the spatial dimension and the external potential on the JTC are discussed, respectively. These results show that: (i) For the free ideal Bose gas, when n/s <= 2 (n is the spatial dimension, s is the momentum index in the relation between the energy and the momentum), and T ? TC (TC is the critical temperature), the JTC can obviously improve by means of changing the throttle valve's shape and decreasing the spatial dimension of gases. (ii) For the inhomogeneous external potential, the discriminant ? = [1 - ?[ni = 1(kT/varpii)1/ti?(1/ti + 1)] (k is the Boltzmann Constant, T is the thermodynamic temperature, varpii is the external field's energy), is obtained. The potential makes the JTC increase when ? > 0, on the contrary, it makes the JTC decrease when ? < 0. (iii) In the homogenous strong external potential, the JTC gets the maximum on the condition of kT/varpii < 1.

Yuan, Du-Qi; Wang, Can-Jun

2010-04-01

88

Stiffness of lipid monolayers with phase coexistence.  

PubMed

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

Caruso, Benjamín; Mangiarotti, Agustín; Wilke, Natalia

2013-08-27

89

Infinite-dimensional symmetries of a general class of variable coefficient evolution equations in 2+1 dimensions  

NASA Astrophysics Data System (ADS)

We consider generalized KP-Burgers equations and attempt to identify subclasses admitting Virasoro or Kac-Moody type algebras as their symmetries. We give reductions to ODEs constructed from invariance requirement under these infinite-dimensional Lie symmetry algebras and integrate them in cases where it is possible. We also look at the conditions under which the equation passes the Painlevé test and construct some exact solutions by truncation.

Basarab-Horwath, P.; Güngör, F.; Özemir, C.

2013-11-01

90

NUMERICAL WAVE SCATTERING TAKING ACCOUNT OF ENERGY DISSIPATION AND MEDIA STIFFNESS AS MODELED BY THE TELEGRAPH EQUATION  

Microsoft Academic Search

The telegraph equation is employed to model wave fields taking into account energy dissipation and media stiffness. The time- harmonic scattered waves generated by a line source incident upon cylindrical obstacles of arbitrary cross-section are studied. Solutions are found to depend strongly on the relative values of the frequency, damping, and stiffness coefficients. These coefficients are also found to have

SEBASTIAN ACOSTA; Provo UT; PEDRO ACOSTA

91

Stiffness adaptations in shod running.  

PubMed

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

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

2005-11-01

92

Position-dependent characterization of passive wrist stiffness.  

PubMed

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

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

2014-08-01

93

Painlevé integrability of a generalized fifth-order KdV equation with variable coefficients: Exact solutions and their interactions  

NASA Astrophysics Data System (ADS)

By means of singularity structure analysis, the integrability of a generalized fifth-order KdV equation is investigated. It is proven that this equation passes the Painlevé test for integrability only for three distinct cases. Moreover, the multi-soliton solutions are presented for this equation under three sets of integrable conditions. Finally, by selecting appropriate parameters, we analyze the evolution of two solitons, which is especially interesting as it may describe the overtaking and the head-on collisions of solitary waves of different shapes and different types.

Xu, Gui-Qiong

2013-05-01

94

Quantitative evaluation of stiffness of commercial suture materials.  

PubMed

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

Chu, C C; Kizil, Z

1989-03-01

95

Modulation by Taurine of Human Arterial Stiffness and Wave Reflection  

Microsoft Academic Search

Effects of taurine (1000–2000 mg) on hemodynamic function and the arterial pulse wave were investigated for 102 healthy medical\\u000a and paramedical students. The vascular parameters were generally dependent on aging, with the arterial stiffness parameters,\\u000a such as baPWV, ABI and AI, are considered the indicators of “vascular aging”. Acute administration of taurine decreased BP\\u000a and HR and attenuated the stiffness

Hiroyasu Satoh; Jangmi Kang

96

General model for estimating partition coefficients to organisms and their tissues using the biological compositions and polyparameter linear free energy relationships.  

PubMed

Equilibrium partition coefficients of organic chemicals from water to an organism or its tissues are typically estimated by using the total lipid content in combination with the octanol-water partition coefficient (K(ow)). This estimation method can cause systematic errors if (1) different lipid types have different sorptive capacities, (2) nonlipid components such as proteins have a significant contribution, and/or (3) K(ow) is not a suitable descriptor. As an alternative, this study proposes a more general model that uses detailed organism and tissue compositions (i.e., contents of storage lipid, membrane lipid, albumin, other proteins, and water) and polyparameter linear free energy relationships (PP-LFERs). The values calculated by the established PP-LFER-composition-based model agree well with experimental in vitro partition coefficients and in vivo steady-state concentration ratios from the literature with a root mean squared error of 0.32-0.53 log units, without any additional fitting. This model estimates a high contribution of the protein fraction to the overall tissue sorptive capacity in lean tissues (e.g., muscle), in particular for H-bond donor polar compounds. Direct model comparison revealed that the simple lipid-octanol model still calculates many tissue-water partition coefficients within 1 log unit of those calculated by the PP-LFER-composition-based model. Thus, the lipid-octanol model can be used as an order-of-magnitude approximation, for example, for multimedia fate modeling, but may not be suitable for more accurate predictions. Storage lipid-rich phases (e.g., adipose, milk) are prone to particularly large systematic errors. The new model provides useful implications for validity of lipid-normalization of concentrations in organisms, interpretation of biomonitoring results, and assessment of toxicity. PMID:23672211

Endo, Satoshi; Brown, Trevor N; Goss, Kai-Uwe

2013-06-18

97

Fluid damping and fluid stiffness of tube arrays in crossflow  

SciTech Connect

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

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

1994-06-01

98

Integrability aspects with optical solitons of a generalized variable-coefficient N-coupled higher order nonlinear Schrödinger system from inhomogeneous optical fibers  

NASA Astrophysics Data System (ADS)

For describing the long-distance communication and manufacturing problems of N fields propagation in inhomogeneous optical fibers, we consider a generalized variable-coefficient N-coupled nonlinear Schrödinger system with higher order effects such as the third-order dispersion, self-steepening and self-frequency shift. Using the Painlevé singularity structure analysis, we obtain two cases for this system to admit the Painlevé property. Then for case (1) we derive the optical dark solitons via solving the Hirota bilinear equations; and based on the obtained (2N+1)×(2N+1) Lax pair, we construct the Darboux transformation to obtain the optical bright solitons (including the multisoliton profiles) for case (2). Finally, the features of optical solitons (both dark and bright ones) in inhomogeneous optical fibers are analyzed and graphically discussed.

Lü, Xing; Li, Juan; Zhang, Hai-Qiang; Xu, Tao; Li, Li-Li; Tian, Bo

2010-04-01

99

Monitoring stiffness contrast in elastography  

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

100

Computation of stiffness and stiffness bounds for parallel link manipulators 1 This research was supported by NSF under grant #DDM91-57191. 1  

Microsoft Academic Search

Parallel link spatial mechanisms in general, and Stewart Platforms in particular, are increasingly being studied for possible use in multi-axis machine-tools. An important consideration in the design of such machines is their stiffness. For a given design, stiffness varies with the direction in which it is computed, the posture (or configuration) of the mechanism and the direction of the actuation

Bashar S. El-Khasawneh; Placid M. Ferreira

1999-01-01

101

Lase Ultrasonic Web Stiffness tester  

SciTech Connect

The objective is to provide a sensor that uses non-contact, laser ultrasonics to measure the stiffness of paper during the manufacturing process. This will allow the manufacturer to adjust the production process in real time, increase filler content, modify fiber refining and as result produce a quality product using less energy. The sensor operates by moving back and forth across the paper web, at pre-selected locations firing a laser at the sheet, measuring the out-of-plane velocity of the sheet then using that measurement to calculate sheet stiffness.

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

2009-01-12

102

An adaptive unscented Kalman filter for tracking sudden stiffness changes  

NASA Astrophysics Data System (ADS)

The paper presents an approach to track sudden changes in stiffness of structural systems exposed to earthquake induced base excitations. Such sudden changes in the stiffness could be caused by abrupt damage of one or more structural members. To track such changes through a Kalman filter approach, the stiffness and damping coefficients of structural members to be tracked need to be a part of the state vector of a state space model. However, such state equations become nonlinear even for an otherwise linear system. The use of the unscented transform-based Kalman filter approach has been considered to effectively deal with such nonlinearities in state estimation. But this approach not intended to track sudden changes is unable to achieve this. Herein, an adaptive Kalman filter scheme is proposed for efficient detection as well as tracking of sudden changes in stiffness values. The approach first identifies the instant of a sudden change, followed by appropriate adjustment of the state covariance matrix for efficient tracking of the states. Numerical examples of structural models with several earthquake inputs with different characteristics are used to show that the proposed scheme can effectively track multiple events of sudden stiffness changes in several structural members occurring at different time instances.

Bisht, Saurabh S.; Singh, Mahendra P.

2014-12-01

103

Implicit Extrapolation Methods for Variable Coefficient Problems  

NASA Technical Reports Server (NTRS)

Implicit extrapolation methods for the solution of partial differential equations are based on applying the extrapolation principle indirectly. Multigrid tau-extrapolation is a special case of this idea. In the context of multilevel finite element methods, an algorithm of this type can be used to raise the approximation order, even when the meshes are nonuniform or locally refined. Here previous results are generalized to the variable coefficient case and thus become applicable for nonlinear problems. The implicit extrapolation multigrid algorithm converges to the solution of a higher order finite element system. This is obtained without explicitly constructing higher order stiffness matrices but by applying extrapolation in a natural form within the algorithm. The algorithm requires only a small change of a basic low order multigrid method.

Jung, M.; Ruede, U.

1996-01-01

104

Stiffness and Damping in Postural Control Increase with Age  

PubMed Central

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

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

2011-01-01

105

Wave propagation is long chains of springs with negative stiffness elements  

NASA Astrophysics Data System (ADS)

We investigate dynamic stability, oscillations and wave propagation in a 1D chain of n (n>>1) linear oscillators (masses and springs connected in series) with viscous damping when some of the springs' stiffnesses can assume negative values. We assume that the ends of the chain are fixed. Such chains can model interaction of rotating non-spherical grains or particles in the cases when some of them produce the effect of apparent negative stiffness (this depends upon the shape factor and the magnitude of compression in the vicinity of the grain). It is shown that for such a system to be stable not more than one spring is allowed to have negative stiffness. Furthermore, the value of negative stiffness cannot exceed a certain critical value that depends upon the (positive) stiffness of other springs. At the critical value the system develops an eigenmode with vanishing frequency. In systems with small viscous damping vanishing of an eigenfrequency does not yet lead to instability. Further increase in the value of negative stiffness leads to the appearance of aperiodic eigenmodes with low and high damping. At the critical negative stiffness the low dissipative mode becomes non-dissipative, while for the high dissipative mode the damping coefficient becomes as twice as high as the damping coefficient of the system. We consider systems of larger dimensions with chains that are non-interacting. We determine the concentration of the negative stiffness springs at which the system maintains its dynamic stability.

Dyskin, Arcady; Pasternak, Elena

2014-05-01

106

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

NASA Astrophysics Data System (ADS)

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

Audoin, B.; Reverdy, F.

1999-12-01

107

An automatic multistep method for solving stiff initial value problems  

Microsoft Academic Search

A multistep method with matricial coefficients is developed. It can be used to solve stiff initial value problems of the form y'= Ay + g(x,y). This method bears the nature of the classical Adams-Bashforth-Moulton PC formula and can be shown to be consistent, convergent and A-stable. A careful reformulation of this method legitimatizes the implementation of this algorithm in a

Moody T. Chu

1983-01-01

108

Dynamic Stiffness of Piles in Liquefiable Soils.  

National Technical Information Service (NTIS)

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

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

2002-01-01

109

General expressions for the coupling coefficient, quality and filling factors for a cavity with an insert using energy coupled mode theory  

NASA Astrophysics Data System (ADS)

A cavity (CV) with a dielectric resonator (DR) insert forms an excellent probe for the use in electron paramagnetic resonance (EPR) spectrometers. The probe’s coupling coefficient, ?, the quality factor, Q, and the filling factor, ? are vital in assessing the EPR spectrometer’s performance. Coupled mode theory (CMT) is used to derive general expressions for these parameters. For large permittivity the dominating factor in ? is the ratio of the DR and CV cross sectional areas rather than the dielectric constant. Thus in some cases, resonators with low dielectric constant can couple much stronger with the cavity than do resonators with a high dielectric constant. When the DR and CV frequencies are degenerate, the coupled ? is the average of the two uncoupled ones. In practical EPR probes the coupled ? is approximately half of that of the DR. The Q of the coupled system generally depends on the eigenvectors, uncoupled frequencies (?1, ?2) and the individual quality factors (Q1, Q2). It is calculated for different probe configurations and found to agree with the corresponding HFSS® simulations. Provided there is a large difference between the Q1, Q2 pair and the frequencies of DR and CV are degenerate, Q is approximately equal to double the minimum of Q1 and Q2. In general, the signal enhancement ratio, I/Iempty, is obtained from Q and ?. For low loss DRs it only depends on ?1/?2. However, when the DR has a low Q, the uncoupled Qs are also needed. In EPR spectroscopy it is desirable to excite only a single mode. The separation between the modes, ?, is calculated as a function of ? and Q. It is found to be significantly greater than five times the average bandwidth. Thus for practical probes, it is possible to excite one of the coupled modes without exciting the other. The CMT expressions derived in this article are quite general and are in excellent agreement with the lumped circuit approach and finite numerical simulations. Hence they can also be applied to a loop-gap resonator in a cavity. For the design effective EPR probes, one needs to consider the ?, Q and ? parameters.

Elnaggar, Sameh Y.; Tervo, Richard; Mattar, Saba M.

2014-05-01

110

General expressions for the coupling coefficient, quality and filling factors for a cavity with an insert using energy coupled mode theory.  

PubMed

A cavity (CV) with a dielectric resonator (DR) insert forms an excellent probe for the use in electron paramagnetic resonance (EPR) spectrometers. The probe's coupling coefficient, ?, the quality factor, Q, and the filling factor, ? are vital in assessing the EPR spectrometer's performance. Coupled mode theory (CMT) is used to derive general expressions for these parameters. For large permittivity the dominating factor in ? is the ratio of the DR and CV cross sectional areas rather than the dielectric constant. Thus in some cases, resonators with low dielectric constant can couple much stronger with the cavity than do resonators with a high dielectric constant. When the DR and CV frequencies are degenerate, the coupled ? is the average of the two uncoupled ones. In practical EPR probes the coupled ? is approximately half of that of the DR. The Q of the coupled system generally depends on the eigenvectors, uncoupled frequencies (?1,?2) and the individual quality factors (Q1,Q2). It is calculated for different probe configurations and found to agree with the corresponding HFSS® simulations. Provided there is a large difference between the Q1, Q2 pair and the frequencies of DR and CV are degenerate, Q is approximately equal to double the minimum of Q1 and Q2. In general, the signal enhancement ratio, Iwithinsert/Iempty, is obtained from Q and ?. For low loss DRs it only depends on ?1/?2. However, when the DR has a low Q, the uncoupled Qs are also needed. In EPR spectroscopy it is desirable to excite only a single mode. The separation between the modes, ?, is calculated as a function of ? and Q. It is found to be significantly greater than five times the average bandwidth. Thus for practical probes, it is possible to excite one of the coupled modes without exciting the other. The CMT expressions derived in this article are quite general and are in excellent agreement with the lumped circuit approach and finite numerical simulations. Hence they can also be applied to a loop-gap resonator in a cavity. For the design effective EPR probes, one needs to consider the ?, Q and ? parameters. PMID:24607823

Elnaggar, Sameh Y; Tervo, Richard; Mattar, Saba M

2014-05-01

111

Numerical Simulation of Callus Healing for Optimization of Fracture Fixation Stiffness  

PubMed Central

The stiffness of fracture fixation devices together with musculoskeletal loading defines the mechanical environment within a long bone fracture, and can be quantified by the interfragmentary movement. In vivo results suggested that this can have acceleratory or inhibitory influences, depending on direction and magnitude of motion, indicating that some complications in fracture treatment could be avoided by optimizing the fixation stiffness. However, general statements are difficult to make due to the limited number of experimental findings. The aim of this study was therefore to numerically investigate healing outcomes under various combinations of shear and axial fixation stiffness, and to detect the optimal configuration. A calibrated and established numerical model was used to predict fracture healing for numerous combinations of axial and shear fixation stiffness under physiological, superimposed, axial compressive and translational shear loading in sheep. Characteristic maps of healing outcome versus fixation stiffness (axial and shear) were created. The results suggest that delayed healing of 3 mm transversal fracture gaps will occur for highly flexible or very rigid axial fixation, which was corroborated by in vivo findings. The optimal fixation stiffness for ovine long bone fractures was predicted to be 1000–2500 N/mm in the axial and >300 N/mm in the shear direction. In summary, an optimized, moderate axial stiffness together with certain shear stiffness enhances fracture healing processes. The negative influence of one improper stiffness can be compensated by adjustment of the stiffness in the other direction.

Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim

2014-01-01

112

Numerical simulation of callus healing for optimization of fracture fixation stiffness.  

PubMed

The stiffness of fracture fixation devices together with musculoskeletal loading defines the mechanical environment within a long bone fracture, and can be quantified by the interfragmentary movement. In vivo results suggested that this can have acceleratory or inhibitory influences, depending on direction and magnitude of motion, indicating that some complications in fracture treatment could be avoided by optimizing the fixation stiffness. However, general statements are difficult to make due to the limited number of experimental findings. The aim of this study was therefore to numerically investigate healing outcomes under various combinations of shear and axial fixation stiffness, and to detect the optimal configuration. A calibrated and established numerical model was used to predict fracture healing for numerous combinations of axial and shear fixation stiffness under physiological, superimposed, axial compressive and translational shear loading in sheep. Characteristic maps of healing outcome versus fixation stiffness (axial and shear) were created. The results suggest that delayed healing of 3 mm transversal fracture gaps will occur for highly flexible or very rigid axial fixation, which was corroborated by in vivo findings. The optimal fixation stiffness for ovine long bone fractures was predicted to be 1000-2500 N/mm in the axial and >300 N/mm in the shear direction. In summary, an optimized, moderate axial stiffness together with certain shear stiffness enhances fracture healing processes. The negative influence of one improper stiffness can be compensated by adjustment of the stiffness in the other direction. PMID:24991809

Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim

2014-01-01

113

Arthroscopic capsular release for stiff shoulders  

Microsoft Academic Search

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

Gregory P. Nicholson

2003-01-01

114

Stiffness and Damping in Postural Control Increase With Age  

Microsoft Academic Search

Upright balance is believed to be maintained through active and passive mechanisms, both of which have been shown to be impacted by aging. A compensatory balance response often observed in older adults is increased co-contraction, which is generally assumed to enhance stability by increasing joint stiffness. We investigated the effect of aging on standing balance by fitting body sway data

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

2010-01-01

115

Stiffness in total knee arthroplasty  

Microsoft Academic Search

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

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

2009-01-01

116

Substrate stiffness regulates filopodial activities in lung cancer cells.  

PubMed

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

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

2014-01-01

117

Substrate Stiffness Regulates Filopodial Activities in Lung Cancer Cells  

PubMed Central

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

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

2014-01-01

118

Dynamic stiffness analysis of laminated beams using a first order shear deformation theory  

Microsoft Academic Search

In this paper the exact vibration frequencies of generally laminated beams are found using a new method, including the effect of rotary inertia and shear deformations. The effect of shear in laminated beams is more significant than in homogenous beams, due to the fact that the ratio of extensional stiffness to the transverse shear stiffness is high. The exact dynamic

Haim Abramovich; Oleg Shulepov

1995-01-01

119

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

120

A NASTRAN DMAP alter for determining a local stiffness modification to obtain a specified eigenvalue  

NASA Technical Reports Server (NTRS)

A technique is described which has been programmed as a DMAP Alter to Rigid Format 3, for determining a stiffness matrix modification to obtain a specified eigenvalue for a structure. The stiffness matrix modifications allowable are those that can be described as the product of a single scalar variable and a matrix of constant coefficients input by the user. The program solves for the scalar variable multiplier which will yield a specified eigenvalue for the complete structure (provided it exists), makes the modification to the stiffness matrix, and proceeds in Rigid Format 3 to obtain the eigenvalues and eigenvectors of the modified structure.

Case, W. R., Jr.

1973-01-01

121

Dynamic stiffness and damping of externally pressurized gas lubricated journal bearings  

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

122

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

123

Simple Formulas and Results for Buckling-Resistance and Stiffness Design of Compression-Loaded Laminated-Composite Cylinders  

NASA Technical Reports Server (NTRS)

Simple formulas for the buckling stress of homogeneous, specially orthotropic, laminated-composite cylinders are presented. The formulas are obtained by using nondimensional parameters and equations that facilitate general validation, and are validated against the exact solution for a wide range of cylinder geometries and laminate constructions. Results are presented that establish the ranges of the nondimensional parameters and coefficients used. General results, given in terms of the nondimensional parameters, are presented that encompass a wide range of geometries and laminate constructions. These general results also illustrate a wide spectrum of behavioral trends. Design-oriented results are also presented that provide a simple, clear indication of laminate composition on critical stress, critical strain, and axial stiffness. An example is provided to demonstrate the application of these results to thin-walled column designs.

Nemeth, Michael P.; Mikulas, Martin M., Jr.

2009-01-01

124

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

125

Coefficient Color Constancy  

NASA Astrophysics Data System (ADS)

The goal of color constancy is to take the color responses (for example camera rgb triplets) of surfaces viewed under nn unknown illuminant and map them to illuminant independent descriptors. In existing theories this mapping is either a general linear 3 times 3 matrix or a simple diagonal matrix of scaling coefficients. The general theories have the advantage that the illuminant can be accurately discounted but have the disadvantage that nine parameters must be recovered. Conversely while the coefficient theories have only three unknowns, a diagonal matrix may only partially discount the illuminant. My starting point in this thesis is to generalize the coefficient approach; the goal is to retain its inherent simplicity while at the same time increasing its expressive power. Under the generalized coefficient scheme, I propose that a visual system transforms responses to a new sensor basis before applying the scaling coefficients. I present methods for choosing the best coefficient basis for a variety of statistical models of color responses. These models are rich enough that the generalized coefficient approach suffices for almost all possible sensor sets. To achieve color constancy the correct coefficients must be recovered. Existing algorithms can do so only when strong constraints are satisfied. For example it is often assumed that there is a white reflectance in every scene. In the second part of any thesis, I develop a new coefficient algorithm, which I call color in perspective, based on very weak (and very reasonable) assumptions about the world. I assume only that the range of color responses induced by different reflectances varies with a change in illumination and that illumination itself can vary only within certain bounds. I tested the algorithm on real images taken with a color video camera--extremely good constancy is delivered. Indeed the degree of constancy compares favorably with the best which is theoretically possible. The methods developed in this thesis can be applied to a variety of other areas: including color graphics, color reproduction and color appearance models.

Finlayson, Graham David

1995-01-01

126

Estimation of quasi-stiffness of the human knee in the stance phase of walking.  

PubMed

Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as prostheses and orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75-2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R(2) > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking. PMID:23533662

Shamaei, Kamran; Sawicki, Gregory S; Dollar, Aaron M

2013-01-01

127

3D FEA simulation of segmented reinforcement variable stiffness composites  

NASA Astrophysics Data System (ADS)

Reconfigurable and morphing structures may provide significant improvement in overall platform performance through optimization over broad operating conditions. The realization of this concept requires structures, which can accommodate the large deformations necessary with modest weight and strength penalties. Other studies suggest morphing structures need new materials to realize the benefits that morphing may provide. To help meet this need, we have developed novel composite materials based on specially designed segmented reinforcement and shape memory polymer matrices that provide unique combinations of deformation and stiffness properties. To tailor and optimize the design and fabrication of these materials for particular structural applications, one must understand the envelope of morphing material properties as a function of microstructural architecture and constituent properties. Here we extend our previous simulations of these materials by using 3D models to predict stiffness and deformation properties in variable stiffness segmented composite materials. To understand the effect of various geometry tradeoffs and constituent properties on the elastic stiffness in both the high and low stiffness states, we have performed a trade study using a commercial FEA analysis package. The modulus tensor is constructed and deformation properties are computed from representative volume elements (RVE) in which all (6) basic loading conditions are applied. Our test matrix consisted of four composite RVE geometries modeled using combinations of 5 SMP and 3 reinforcement elastic moduli. Effective composite stiffness and deformation results confirm earlier evidence of the essential performance tradeoffs of reduced stiffness for increasing reversible strain accommodation with especially heavy dependencies on matrix modulus and microstructural architecture. Furthermore, our results show these laminar materials are generally orthotropic and indicate that previous calculations of matrix gap and interlaminar strains based on kinematic approximations are accurate to within 10-20% for many material systems. We compare these models with experimental results for a narrow geometry and material set to show the accuracy of the models as compared to physical materials. Our simulations indicate that improved shape memory polymer materials could enable a composite material that can accommodate ~30% strain with a cold state stiffness of ~30GPa. This would improve the current state of the art 5-10x and significantly reduce the weight and stiffness costs of using a morphing component.

Henry, C. P.; McKnight, G. P.; Enke, A.; Bortolin, R.; Joshi, S.

2008-05-01

128

Numerical Methods for Hyperbolic Conservation Laws with Stiff Relaxation  

NASA Astrophysics Data System (ADS)

We consider the use of a shock capturing finite difference scheme to approximate solutions of hyperbolic systems of conservation laws with stiff, relaxing source terms. We study in particular the problem of obtaining accurate solutions of these systems with a numerical method that uses time and space increments governed solely by the non-stiff part of the equations. We have two main goals in this investigation. The first is to determine when it is possible to obtain first order accurate numerical solutions of these systems without fully resolving the effects of the stiff source terms. The second is to develop a Godunov method for these systems which produces higher order accurate numerical solutions even as the relaxation time tends to zero. We accomplish the first goal in part I of the thesis. We present criteria which insure that a shock capturing finite difference method does not produce spurious solutions as the relaxation time approaches zero. One criterion is that the limits of vanishing relaxation time and vanishing viscosity commute for the viscous regularization of the hyperbolic system. A second criterion is that a certain "subcharacteristic" condition be satisfied by the hyperbolic system. We consider a specific example, the solution of generalized Riemann problems of a model system of equations with a fractional step scheme in which Godunov's method is coupled with the backward Euler method. The analytical and numerical results for this example support our claim that the above criteria are valid. We also generalize our results to determine similar criteria applicable to the numerical solution of stiff detonation problems. In part II we develop a Godunov method which produces higher order accurate numerical solutions even as the relaxation time tends to zero. We assume that the system of equations satisfies the "subcharacteristic" condition mentioned above. We base our development on a higher order Godunov method developed by Colella for hyperbolic conservation laws with non-stiff source terms. Our method differs from the corresponding method for non-stiff systems in its semi-implicit treatment of the stiff source terms and in the manner in which the characteristic form of the system is used. We apply the method to a system of equations similar to the model presented in part I and to a system of equations for gas flow with heat transfer. We present analytical and numerical results which support the claim that the modifications to the non -stiff method are necessary for obtaining second order accuracy as the relaxation time tends to zero. The numerical results also suggest that certain modifications to the Riemann solver used by the Godunov method would help reduce small numerical oscillations that may be produced by the scheme near discontinuities.

Pember, Richard Bissell

1992-01-01

129

Predicting protein diffusion coefficients.  

PubMed Central

Diffusion coefficients for proteins in water are predicted. The numerical method developed is general enough to be applied to a wide range of protein surface shapes, from rodlike to globular. Results are presented for lysozyme and tobacco mosaic virus, and they are compared with actual data and with predictions made by less general methods. Images Fig. 2

Brune, D; Kim, S

1993-01-01

130

Knee stiffness following anterior cruciate ligament reconstruction  

Microsoft Academic Search

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

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

2009-01-01

131

Multi-flexible-body dynamics capturing motion-induced stiffness  

NASA Technical Reports Server (NTRS)

A multi-flexible-body dynamics formulation incorporating a recently developed theory for capturing motion induced stiffness for a arbitrary structure undergoing large rotation and translation accompanied by small vibrations is presented. In essence, the method consists of correcting prematurely linearized dynamical equations for an arbitrary flexible body with generalized active forces due to geometric stiffness corresponding to a system of twelve inertia forces and nine inertia couples distributed over the body. Equations of motion are derived by means of Kane's method. A useful feature of the formulation is its treatment of prescribed motions and interaction forces. Results of simulations of motions of three flexible spacecraft, involving stiffening during spinup motion, dynamic buckling, and a repositioning maneuver, demonstrate the validity and generality of the theory.

Banerjee, Arun K.; Lemak, Mark E.; Dickens, John M.

1989-01-01

132

Stiffness in numerical initial-value problems  

Microsoft Academic Search

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

M. N. Spijker

1996-01-01

133

Bending stiffness of composite plates with delamination  

Microsoft Academic Search

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

J. P. Hou; G. Jeronimidis

2000-01-01

134

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

PubMed

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

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

2014-06-01

135

Improvement of arthroscopic cartilage stiffness probe using amorphous diamond coating.  

PubMed

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

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

2005-04-01

136

Stiff Coatings on Compliant Biofibers  

PubMed Central

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

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

2009-01-01

137

Metabolic syndrome is a significant and independent risk factor for increased arterial stiffness in Japanese subjects  

Microsoft Academic Search

Metabolic syndrome (MetS) has been recognized as a risk factor for cardiovascular disease; however, the impact of MetS on arterial stiffness has not been fully established in the general Japanese population. We analyzed the relationship between MetS and the severity of arterial stiffness using brachial-ankle pulse wave velocity (baPWV) in 2744 male and 358 female subjects aged 38–62 years, adjusted

Hiroki Satoh; Reiko Kishi; Hiroyuki Tsutsui

2009-01-01

138

A stiffness-mediated oncogenic hammer.  

PubMed

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

Ghajar, Cyrus M

2014-05-21

139

Solving Certain Stiff Differential Equations by Transformation.  

National Technical Information Service (NTIS)

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

L. F. Shampine

1977-01-01

140

Programmable variable stiffness 2D surface design  

NASA Astrophysics Data System (ADS)

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

Trabia, Sarah; Hwang, Taeseon; Yim, Woosoon

2014-03-01

141

Bending stiffness of catheters and guide wires.  

PubMed

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

Wünsche, P; Werner, C; Bloss, P

2002-01-01

142

Composite Laminate Stiffnesses and Their Sensitivities.  

National Technical Information Service (NTIS)

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

B. Geier

1992-01-01

143

Macroscopic Stiffness of Breast Tumors Predicts Metastasis  

PubMed Central

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

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

2014-01-01

144

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

145

Stiffness and Confinement Ratios of SMA Wire Jackets for Confining Concrete  

NASA Astrophysics Data System (ADS)

This article discusses the effects of the stiffness and confinement ratios of shape memory alloy (SMA) wire jackets on the behavior of confined concrete. SMA wire jackets are an effective confining material to improve concrete behavior; for example, by increasing peak strength and failure strain. The stiffness and confinement ratios of fiber-reinforced polymer jackets have been extensively discussed and their effects are well known. However, assessment of the stiffness and confinement ratios of SMA wire jackets has not previously been conducted. In this study, we investigate the effects of the stiffness and confinement ratios of steel jackets, and then compare the results with those of SMA wire jackets. In general, the stiffness ratios of SMA wire jackets are relatively smaller than those of steel jackets, and most of them have lower stiffness ratios because the Young's moduli of the SMAs are relatively small. The active confining pressure of the SMA wires does not improve the lower stiffness-ratio effect since the amount of active confining pressure is not sufficiently large.

Richardson, P. L.; Lutjeharms, J. R. E.; Boebel, O.

2014-05-01

146

Longitudinal relaxation of initially straight flexible and stiff polymers  

NASA Astrophysics Data System (ADS)

The present talk considers the relaxation of a single flexible or stiff polymer chain from an initial straight configuration in a viscous solvent. This problem commonly arises when strong flows are turned off in both industrial and biological applications. The problem is also motivated by recent experiments with single biopolymer molecules relaxing after being fully extended by applied forces as well as by the recent development of micro-devices involving stretched tethered biopolymers. Our results are applicable to a wide array of synthetic polymers such as polyacrylamides, Kevlar and polyesters as well as biopolymers such as DNA, actin filaments, microtubules and MTV. In this talk we discuss the mechanism of the polymer relaxation as was revealed through Brownian Dynamics simulations covering a broad range of time scales and chain stiffness. After the short-time free diffusion, the chain's longitudinal reduction at early intermediate times is shown to constitute a universal behavior for any chain stiffness caused by a quasi-steady relaxation of tensions associated with the deforming action of the Brownian forces. Stiff chains are shown to exhibit a late intermediate-time longitudinal reduction associated with a relaxation of tensions affected by the deforming Brownian and the restoring bending forces. The longitudinal and transverse relaxations are shown to obey different laws, i.e. the chain relaxation is anisotropic at all times. In the talk, we show how from the knowledge of the relaxation mechanism, we can predict and explain the polymer properties including the polymer stress and the solution birefringence. In addition, a generalized stress-optic law is derived valid for any time and chain stiffness. All polymer properties which depend on the polymer length are shown to exhibit two intermediate-time behaviors with the early one to constitute a universal behavior for any chain stiffness. This work was supported in part by the Minta Martin Research Fund. The computations were performed on multiprocessor computers provided by the National Center for Supercomputing Applications (NCSA) in Illinois (grant DMR000003), and by an Academic Equipment Grant from Sun Microsystems Inc.

Dimitrakopoulos, Panagiotis; Dissanayake, Inuka

2004-11-01

147

Study of the determination of the coefficients beta and gamma of the generalized metric of Robertson and of the dynamical oblateness of the sun  

NASA Technical Reports Server (NTRS)

Motion of a space probe about a spherical center of attraction is considered, applying the general theory of relativity. Motion of a probe under the influence of the sun's oblateness is also discussed. Estimates of beta, gamma, and J20 using solar probe motion are presented. It is concluded that such measurements are possible if the unknown long-period perturbing acceleration is of the order of 10 to the -11th or -12th power m/sec. sq.

Marchal, C.

1971-01-01

148

Experimental exposure to diesel exhaust increases arterial stiffness in man  

PubMed Central

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

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

2009-01-01

149

Effects of acute eccentric contractions on rat ankle joint stiffness  

Microsoft Academic Search

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

Ochi Eisuke; Ishii Naokata; Nakazato Koichi

2007-01-01

150

Stiffness characteristics of composite hybrid external fixators.  

PubMed

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

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

2002-12-01

151

Peripheral arterial stiffness in primary aldosteronism.  

PubMed

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

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

2012-12-14

152

A unit-cell model of textile composite beams for predicting stiffness properties  

NASA Technical Reports Server (NTRS)

Flexural stiffness properties of a textile composite beam are obtained from a finite-element model of the unit cell. Three linearly independent deformations, namely, pure extension, pure bending and pure shear, are applied to the unit cell. The top and bottom surfaces of the beam are assumed to be traction free. Periodic boundary conditions on the lateral boundaries of the unit cell are enforced by multi-point constraint elements. From the forces acting on the unit cell, the flexural stiffness coefficients of the composite beam are obtained. The difficulties in determining the transverse shear stiffness are discussed, and a modified approach is presented. The methods are first verified by applying them to isotropic and bimaterial beams for which the results are known, and then illustrated for a simple plain-weave textile composite.

Sankar, Bhavani V.; Marrey, Ramesh V.

1993-01-01

153

Quantitative Elastography for Cervical Stiffness Assessment during Pregnancy  

PubMed Central

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

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

2014-01-01

154

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

PubMed Central

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

2012-01-01

155

Real-Time Fracture of Stiff Materials  

Microsoft Academic Search

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

Owen McNally

156

Vibrating Beam With Spatially Periodic Stiffness  

NASA Technical Reports Server (NTRS)

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

Townsend, John S.

1989-01-01

157

Computer program performs stiffness matrix structural analysis  

NASA Technical Reports Server (NTRS)

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

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

1968-01-01

158

Dynamic stiffness of randomly parametered beams  

Microsoft Academic Search

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

C. S. Manohar; Sondipon Adhikari

1998-01-01

159

Graph characterization via Ihara coefficients.  

PubMed

The novel contributions of this paper are twofold. First, we demonstrate how to characterize unweighted graphs in a permutation-invariant manner using the polynomial coefficients from the Ihara zeta function, i.e., the Ihara coefficients. Second, we generalize the definition of the Ihara coefficients to edge-weighted graphs. For an unweighted graph, the Ihara zeta function is the reciprocal of a quasi characteristic polynomial of the adjacency matrix of the associated oriented line graph. Since the Ihara zeta function has poles that give rise to infinities, the most convenient numerically stable representation is to work with the coefficients of the quasi characteristic polynomial. Moreover, the polynomial coefficients are invariant to vertex order permutations and also convey information concerning the cycle structure of the graph. To generalize the representation to edge-weighted graphs, we make use of the reduced Bartholdi zeta function. We prove that the computation of the Ihara coefficients for unweighted graphs is a special case of our proposed method for unit edge weights. We also present a spectral analysis of the Ihara coefficients and indicate their advantages over other graph spectral methods. We apply the proposed graph characterization method to capturing graph-class structure and clustering graphs. Experimental results reveal that the Ihara coefficients are more effective than methods based on Laplacian spectra. PMID:21118772

Ren, Peng; Wilson, Richard C; Hancock, Edwin R

2011-02-01

160

Logistic Regression with Random Coefficients.  

ERIC Educational Resources Information Center

An approximation to the likelihood for the generalized linear models with random coefficients is derived and is the basis for an approximate Fisher scoring algorithm. The method is illustrated on the logistic regression model for one-way classification, but it has an extension to the class of generalized linear models and to more complex data…

Longford, Nicholas T.

161

Theoretical elastic stiffness, structure stability and thermal conductivity of La 2Zr 2O 7 pyrochlore  

Microsoft Academic Search

Elastic stiffness and electronic structure of La2Zr2O7 were calculated by means of the first-principles pseudopotential total energy method. The equation of state (EOS), elastic parameters (including the full set of second-order elastic coefficients, bulk modulus and Young’s modulus) and elastic anisotropy were reported. Furthermore, pressure dependence of crystal structure, electronic structure, and bond strengths were investigated. It is found that,

B. Liu; J. Y. Wang; Y. C. Zhou; T. Liao; F. Z. Li

2007-01-01

162

Stability with large step sizes for multistep discretizations of stiff ordinary differential equations  

NASA Technical Reports Server (NTRS)

One-leg and multistep discretizations of variable-coefficient linear systems of ODEs having both slow and fast time scales are investigated analytically. The stability properties of these discretizations are obtained independent of ODE stiffness and compared. The results of numerical computations are presented in tables, and it is shown that for large step sizes the stability of one-leg methods is better than that of the corresponding linear multistep methods.

Majda, George

1986-01-01

163

Cell shape and substrate rigidity both regulate cell stiffness.  

PubMed

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

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

2011-03-01

164

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

Microsoft Academic Search

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

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

1999-01-01

165

The impact of the type of derotation mechanism on the stiffness of the Ilizarov fixator.  

PubMed

One of the applications of the Ilizarov apparatus is the correction of rotational deformities. There are several types of designs commonly used for derotation. Different types of derotators have different mechanical properties, which affect the stability of the entire Ilizarov apparatus. The aim of this study was to determine the stiffness of the Ilizarov fixator depending on the type of derotation mechanism. We analyse three types of derotators: the type Z, the type H, and the cubicoid derotator. The tests were conducted on physical models in which the fixator analysed was fitted to polyethylene pipe segments. The reference fixator was the Ilizarov apparatus in the configuration adapted for thigh lengthening. The pipe segments intersected at a point corresponding to the osteotomy site of the distal thigh. The fixator was assembled with one proximal arch fixed with two Schanz screws, a proximal ring fixed with two Kirschner wires (K-wires), a middle free ring, and a distal ring fixed with three K-wires. There were three different types of derotation mechanisms installed between the proximal and middle rings. We determined the axial stiffness kA and the transverse stiffnesses of the compared fixators in two planes: frontal kM-L and sagittal kA-P. The results of the research lead to two basic conclusions. Firstly, the use of any of the derotators analysed has no negative impact on the stiffness of the Ilizarov apparatus. Secondly, similar stiffness values of the fixators with different derotation mechanisms suggest their equal applicability and the choice between them can be made based on practical considerations. In the case of axial stiffness, the differences do not exceed 7.5%. The highest value of stiffness kA was obtained for the type H derotator, while the lowest value was obtained for the type Z derotator. There is a greater difference in the case of transverse stiffness in the sagittal plane, which only concerns the fixator with the type Z derotators. The stiffness coefficient kA-P for that fixator is lower by approximately 19% compared to the reference fixator. PMID:22742714

Morasiewicz, Piotr; Filipiak, Jaros?aw; Konietzko, Marcin; Dragan, Szymon

2012-01-01

166

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

PubMed Central

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

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

2014-01-01

167

Dynamic Stiffness Modeling of Composite Plate and Shell Assemblies.  

National Technical Information Service (NTIS)

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

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

2013-01-01

168

Variable Stiffness Spar Wind-Tunnel Model Development and Testing.  

National Technical Information Service (NTIS)

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

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

2004-01-01

169

Quantification of constant stiffness force-shortening model parameters for vehicles tested under United States side impact protocols  

Microsoft Academic Search

This study presents a methodology for deriving all coefficients of the constant stiffness force-shortening model for the sides of vehicles tested under the United States Federal Motor Vehicle Safety Standard 214 dynamic and high-speed lateral New Car Assessment Program tests. The method utilizes the a priori known moving deformable barrier configuration and velocity vector at impact as a constraint for

J. Singh; J. Perry

2005-01-01

170

Recombination coefficients for iron ions  

NASA Technical Reports Server (NTRS)

Radiative recombination coefficients for all Fe ions are calculated by use of the Milne relation of detailed balance. Analytic fits are made to the dielectronic recombination rates computed by Jacobs (1977) and the Burgess general formula (1965). Higher level rates are treated hydrogenically by a quantum defect method based on the energies of the levels. Recombination coefficients for Fe I to Fe 26 are listed.

Woods, D. T.; Shull, J. M.; Sarazin, C. L.

1981-01-01

171

Contact stiffness of randomly rough surfaces  

NASA Astrophysics Data System (ADS)

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

Pohrt, Roman; Popov, Valentin L.

2013-11-01

172

Contact stiffness of randomly rough surfaces  

PubMed Central

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

Pohrt, Roman; Popov, Valentin L.

2013-01-01

173

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

174

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

175

[Stiff person syndrome--case report].  

PubMed

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

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

2014-01-01

176

Electron profile stiffness and critical gradient studies  

SciTech Connect

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

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

2012-08-15

177

Complex stiffness gradient substrates for studying mechanotactic cell migration.  

PubMed

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

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

2012-11-27

178

Numerical study of uncertainty quantification techniques for implicit stiff systems  

Microsoft Academic Search

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

Haiyan Cheng; Adrian Sandu

2007-01-01

179

Estimation of Quasi-Stiffness of the Human Hip in the Stance Phase of Walking  

PubMed Central

This work presents a framework for selection of subject-specific quasi-stiffness of hip orthoses and exoskeletons, and other devices that are intended to emulate the biological performance of this joint during walking. The hip joint exhibits linear moment-angular excursion behavior in both the extension and flexion stages of the resilient loading-unloading phase that consists of terminal stance and initial swing phases. Here, we establish statistical models that can closely estimate the slope of linear fits to the moment-angle graph of the hip in this phase, termed as the quasi-stiffness of the hip. Employing an inverse dynamics analysis, we identify a series of parameters that can capture the nearly linear hip quasi-stiffnesses in the resilient loading phase. We then employ regression analysis on experimental moment-angle data of 216 gait trials across 26 human adults walking over a wide range of gait speeds (0.75–2.63 m/s) to obtain a set of general-form statistical models that estimate the hip quasi-stiffnesses using body weight and height, gait speed, and hip excursion. We show that the general-form models can closely estimate the hip quasi-stiffness in the extension (R2?=?92%) and flexion portions (R2?=?89%) of the resilient loading phase of the gait. We further simplify the general-form models and present a set of stature-based models that can estimate the hip quasi-stiffness for the preferred gait speed using only body weight and height with an average error of 27% for the extension stage and 37% for the flexion stage.

Shamaei, Kamran; Sawicki, Gregory S.; Dollar, Aaron M.

2013-01-01

180

Computer Modeling and Simulation in Support of the Stiff Suspension Active Seismic Isolation for LIGO II  

Microsoft Academic Search

We have developed a very general and versatile approach to model and predict the behavior of complex isolation systems that are being designed for LIGO II. The code is currently being validated against the Stanford prototype, it has already been validated against the GEO 600 code for their triple pendulum, and we will also be validating it with the Stiff

Brian Lantz; Wensheng Hua; Sam Richman

181

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

Microsoft Academic Search

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

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

182

Stiffness and Strength of Two Glass-Fiber Reinforced Cement Laminates  

Microsoft Academic Search

A general description is given of the load-deformation charac teristics in tension, compression and bending of two types of thin cement laminate reinforced with short random glass fibers. Cyclic loading in tension is used to demonstrate that stiffness decreases and residual strain increases as cracking damage accumulates. The dam age depends on the greatest strain previously reached. There is no

H. G. Allen

1971-01-01

183

Arterial stiffness in predialysis patients with uremia  

Microsoft Academic Search

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

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

2004-01-01

184

Stiff-Person Syndrome: Case Series  

PubMed Central

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

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

2014-01-01

185

Dynamic stiffness and crossbridge action in muscle  

Microsoft Academic Search

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

Peter Mason

1978-01-01

186

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

PubMed Central

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

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

2012-01-01

187

Lipedema is associated with increased aortic stiffness.  

PubMed

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

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

2012-06-01

188

Nonaffine rubber elasticity for stiff polymer networks  

NASA Astrophysics Data System (ADS)

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

Heussinger, Claus; Schaefer, Boris; Frey, Erwin

2007-09-01

189

Nonaffine rubber elasticity for stiff polymer networks.  

PubMed

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

Heussinger, Claus; Schaefer, Boris; Frey, Erwin

2007-09-01

190

A Study of the Bounds on Eigenvalues of a Transcendental Dynamic Stiffness Matrix Provided by a Simply Derived Linear Matrix Pencil  

Microsoft Academic Search

The approximate representation of a transcendental dynamic stiffness matrix by a simple matrix pencil is studied herein. For cases in which linearization is performed below the first pole of the dynamic stiffness matrix, interesting and important bounding properties on exact eigenvalues are established. If the linearization is performed above the first pole, it is not possible to make general assertions

C. T. Hopper; A. Simpson; F. W. Williams

1980-01-01

191

Numerical solution of stiff systems of ordinary differential equations with applications to electronic circuits  

NASA Technical Reports Server (NTRS)

Systems of ordinary differential equations in which the magnitudes of the eigenvalues (or time constants) vary greatly are commonly called stiff. Such systems of equations arise in nuclear reactor kinetics, the flow of chemically reacting gas, dynamics, control theory, circuit analysis and other fields. The research reported develops an A-stable numerical integration technique for solving stiff systems of ordinary differential equations. The method, which is called the generalized trapezoidal rule, is a modification of the trapezoidal rule. However, the method is computationally more efficient than the trapezoidal rule when the solution of the almost-discontinuous segments is being calculated.

Rosenbaum, J. S.

1971-01-01

192

Cell Stiffness Is a Biomarker of the Metastatic Potential of Ovarian Cancer Cells  

PubMed Central

The metastatic potential of cells is an important parameter in the design of optimal strategies for the personalized treatment of cancer. Using atomic force microscopy (AFM), we show, consistent with previous studies conducted in other types of epithelial cancer, that ovarian cancer cells are generally softer and display lower intrinsic variability in cell stiffness than non-malignant ovarian epithelial cells. A detailed examination of highly invasive ovarian cancer cells (HEY A8) relative to their less invasive parental cells (HEY), demonstrates that deformability is also an accurate biomarker of metastatic potential. Comparative gene expression analyses indicate that the reduced stiffness of highly metastatic HEY A8 cells is associated with actin cytoskeleton remodeling and microscopic examination of actin fiber structure in these cell lines is consistent with this prediction. Our results indicate that cell stiffness may be a useful biomarker to evaluate the relative metastatic potential of ovarian and perhaps other types of cancer cells.

Kim, Byungkyu; Wang, Lijuan; McDonald, John; Sulchek, Todd

2012-01-01

193

Stiffness change of a graphite epoxy laminate under reverse fatigue loading  

NASA Technical Reports Server (NTRS)

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

Rotem, Assa

1989-01-01

194

Normal stiffness calibration of microfabricated tri-layer conducting polymer actuators  

NASA Astrophysics Data System (ADS)

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

Alici, Gursel; Higgins, Michael J.

2009-06-01

195

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

PubMed Central

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

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

2014-01-01

196

Electron Transport Stiffness and Heat Pulse Propagation on DIII-D  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

197

Damage Detection on Sudden Stiffness Reduction Based on Discrete Wavelet Transform  

PubMed Central

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

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

2014-01-01

198

Preoperative assessment of meningioma stiffness by magnetic resonance elastography  

PubMed Central

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

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

2014-01-01

199

Extreme damping in composite materials with negative-stiffness inclusions  

NASA Astrophysics Data System (ADS)

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

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

2001-03-01

200

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

PubMed Central

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

Hu, Xiao; Murray, Wendy M.

2011-01-01

201

Meta-Analysis of Coefficient Alpha  

ERIC Educational Resources Information Center

The meta-analysis of coefficient alpha across many studies is becoming more common in psychology by a methodology labeled reliability generalization. Existing reliability generalization studies have not used the sampling distribution of coefficient alpha for precision weighting and other common meta-analytic procedures. A framework is provided for…

Rodriguez, Michael C.; Maeda, Yukiko

2006-01-01

202

Determination of loose spline coupling coefficients of rotor bearing systems in turbomachinery  

Microsoft Academic Search

Analytical and experimental studies have been carried out to determine the stiffness and damping coefficients of loose spline couplings used in high speed rotating machinery from which a realistic assessment of rotor stability can be made at the turbomachinery design stage. This is believed to be the first attempt ever to determine these coefficients experimentally. Experimental modal parameters of the

Sang Kyu Park

1991-01-01

203

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

PubMed Central

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

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

2011-01-01

204

Intestinal lymphangiectasia and reversible high liver stiffness.  

PubMed

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

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

2014-08-01

205

Relative stiffness of flat conductor cables  

NASA Technical Reports Server (NTRS)

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

Hankins, J. D.

1976-01-01

206

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

PubMed Central

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

2013-01-01

207

Weyl Coefficients in SU(3)  

Microsoft Academic Search

The Weyl coefficients are by definition the matrix elements of the Weyl operators in SU(3). They are found to be generalized hypergeometric series of the type 4F3, and can be written down in a simple way from the Gel'fand patterns involved.

Klaus J. Lezuo

1967-01-01

208

Vibration transmission through rolling element bearings. I - Bearing stiffness formulation. II - System studies  

NASA Technical Reports Server (NTRS)

How vibratory motion can be transmitted from the rotating shaft to the casing and other connecting structures in rotating mechanical equipment is addressed here by developing a new mathematical model of precision rolling element bearings. A new grating stiffness matrix is proposed in order to demonstrate a coupling between the shaft bending motion and the flexural motion of the casing plate. It is shown that the translational bearing stiffness coefficients currently used in rotor dynamic models are a small subset of the proposed matrix. The theory is validated by examples, and the proposed bearing formulation is then extended to demonstrate its superiority over existing models in vibration transmission analyses. It is shown that the model can easily be incorporated into analytical or numerical models typically used for dynamic analyses.

Lim, T. C.; Singh, R.

1990-01-01

209

Modified face seal for positive film stiffness  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

210

Normal response function method for mass and stiffness matrix updating using complex FRFs  

NASA Astrophysics Data System (ADS)

Quite often a structural dynamic finite element model is required to be updated so as to accurately predict the dynamic characteristics like natural frequencies and the mode shapes. Since in many situations undamped natural frequencies and mode shapes need to be predicted, it has generally been the practice in these situations to seek updating of only mass and stiffness matrix so as to obtain a reliable prediction model. Updating using frequency response functions (FRFs) has been one of the widely used approaches for updating, including updating of mass and stiffness matrices. However, the problem with FRF based methods, for updating mass and stiffness matrices, is that these methods are based on use of complex FRFs. Use of complex FRFs to update mass and stiffness matrices is not theoretically correct as complex FRFs are not only affected by these two matrices but also by the damping matrix. Therefore, in situations where updating of only mass and stiffness matrices using FRFs is required, the use of complex FRFs based updating formulation is not fully justified and would lead to inaccurate updated models. This paper addresses this difficulty and proposes an improved FRF based finite element model updating procedure using the concept of normal FRFs. The proposed method is a modified version of the existing response function method that is based on the complex FRFs. The effectiveness of the proposed method is validated through a numerical study of a simple but representative beam structure. The effect of coordinate incompleteness and robustness of method under presence of noise is investigated. The results of updating obtained by the improved method are compared with the existing response function method. The performance of the two approaches is compared for cases of light, medium and heavily damped structures. It is found that the proposed improved method is effective in updating of mass and stiffness matrices in all the cases of complete and incomplete data and with all levels and types of damping.

Pradhan, S.; Modak, S. V.

2012-10-01

211

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

PubMed

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

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

2012-06-01

212

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

PubMed Central

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

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

2011-01-01

213

A nonlinear negative stiffness metamaterial unit cell and small-on-large multiscale material model  

NASA Astrophysics Data System (ADS)

A persistent challenge in the design of composite materials is the ability to fabricate materials that simultaneously display high stiffness and high loss factors for the creation of structural elements capable of passively suppressing vibro-acoustic energy. Relevant recent research has shown that it is possible to produce composite materials whose macroscopic mechanical stiffness and loss properties surpass those of conventional composites through the addition of trace amounts of materials displaying negative stiffness (NS) induced by phase transformation [R. S. Lakes et al., Nature 410, 565-567 (2001)]. The present work investigates the ability to elicit NS behavior without employing physical phenomena such as inherent nonlinear material behavior (e.g., phase change or plastic deformation) or dynamic effects, but rather the controlled buckling of small-scale structural elements, metamaterials, embedded in a continuous viscoelastic matrix. To illustrate the effect of these buckled elements, a nonlinear hierarchical multiscale material model is derived, which estimates the macroscopic stiffness and loss of a composite material containing pre-strained microscale structured inclusions. The multiscale model consists of two scale transition models, the first being an energy-based nonlinear finite element (FE) method to determine the tangent modulus of the metamaterial unit cell, and the other a classical analytical micromechanical model to determine the effective stiffness and loss tensors of a heterogeneous material for small perturbations from the local strain state of the unit cells. The FE method enables the estimation of an effective nonlinear anisotropic stiffness tensor of a buckled microstructure that produces NS and is sufficiently general to consider geometries different from those given in this work.

Klatt, Timothy; Haberman, Michael R.

2013-07-01

214

Advanced Glycation End-Products and Arterial Stiffness in Hypertension  

Microsoft Academic Search

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

Marie McNulty; Azra Mahmud; John Feely

2007-01-01

215

Bend stiffness of copper and copper alloy foils  

Microsoft Academic Search

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

Yasuo Tomioka; Norio Yuki

2004-01-01

216

Tensile stiffness analysis on ocean dynamic power umbilical  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

217

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

PubMed

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

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

2013-01-01

218

Influence of musculo-tendinous stiffness of the plantar ankle flexor muscles upon maximal power output on a cycle ergometre.  

PubMed

The importance of maximal voluntary torque (T (MVC)), maximal rate of torque development (MRTD) and musculo-tendinous stiffness of the triceps surae for maximal power output on a cycle ergometre (Pmax) was studied in 21 healthy subjects by studying the relationships between maximal cycling power related to body mass (Pmax BM(-1)) with T (MVC), MRTD and different indices of musculo-tendinous stiffness of the ankle flexor. Pmax BM(-1) was calculated from the data of an all-out force-velocity test on a Monark cycle ergometre. T (MVC) and MRTD were measured on a specific ankle ergometre. Musculo-tendinous stiffness was estimated by means of quick releases at 20, 40, 60 and 80% T (MVC) on the same ankle ergometre. Pmax BM(-1) was significantly and positively correlated with MRTD related to body mass but the positive correlation between Pmax BM(-1) and T (MVC) did not reach the significance level (0.05). Pmax BM(-1) was significantly and positively correlated with the estimation of stiffness at 40% T (MVC) (S(0.4)), but not with stiffness at 20, 60 and 80% T (MVC). The results of the present study suggest that maximal power output during cycling is significantly correlated with the level of musculo-tendinous stiffness which corresponds to torque range around peak torque at optimal pedal rate. However, the low coefficient of determination (r2 = 0.203) between Pmax BM(-1) and S (0.4) BM(-1) suggested that Pmax BM(-1) largely depended on other factors than the musculo-tendinous stiffness of the only plantar flexors. PMID:22354446

Driss, Tarak; Lambertz, Daniel; Rouis, Majdi; Vandewalle, Henry

2012-11-01

219

[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

220

Determining cantilever stiffness from thermal noise  

PubMed Central

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

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

2013-01-01

221

Stiff-person syndrome treated with rituximab  

PubMed Central

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

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

2010-01-01

222

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

PubMed

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

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

2014-02-28

223

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

PubMed Central

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

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

2014-01-01

224

Homogenized stiffness matrices for mineralized collagen fibrils and lamellar bone using unit cell finite element models.  

PubMed

Mineralized collagen fibrils have been usually analyzed like a two-phase composite material where crystals are considered as platelets that constitute the reinforcement phase. Different models have been used to describe the elastic behavior of the material. In this work, it is shown that when Halpin-Tsai equations are applied to estimate elastic constants from typical constituent properties, not all crystal dimensions yield a model that satisfy thermodynamic restrictions. We provide the ranges of platelet dimensions that lead to positive definite stiffness matrices. On the other hand, a finite element model of a mineralized collagen fibril unit cell under periodic boundary conditions is analyzed. By applying six canonical load cases, homogenized stiffness matrices are numerically calculated. Results show a monoclinic behavior of the mineralized collagen fibril. In addition, a 5-layer lamellar structure is also considered where crystals rotate in adjacent layers of a lamella. The stiffness matrix of each layer is calculated applying Lekhnitskii transformations, and a new finite element model under periodic boundary conditions is analyzed to calculate the homogenized 3D anisotropic stiffness matrix of a unit cell of lamellar bone. Results are compared with the rule-of-mixtures showing in general good agreement. PMID:23793930

Vercher, Ana; Giner, Eugenio; Arango, Camila; Tarancón, José E; Fuenmayor, F Javier

2014-04-01

225

Apparatus for measurement of coefficient of friction  

NASA Technical Reports Server (NTRS)

An apparatus designed to measure the coefficient of friction in certain controlled atmospheres is described. The coefficient of friction observed during high-load tests was nearly constant, with an average value of 0.56. This value is in general agreement with that found in the literature and also with the initial friction coefficient value of 0.67 measured during self-mated friction of 440C steel in an oxygen environment.

Slifka, A. J.; Siegwarth, J. D.; Sparks, L. L.; Chaudhuri, Dilip K.

1990-01-01

226

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

NASA Astrophysics Data System (ADS)

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

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

227

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

228

Perturbation theory for path integrals of stiff polymers  

Microsoft Academic Search

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

H. Kleinert; A. Chervyakov

2006-01-01

229

Theoretical and experimental determination of capstan drive stiffness  

Microsoft Academic Search

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

Jaime Werkmeister; Alexander Slocum

2007-01-01

230

Boundary stiffness regulates fibroblast behavior in collagen gels.  

PubMed

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

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

2010-03-01

231

Boundary Stiffness Regulates Fibroblast Behavior in Collagen Gels  

PubMed Central

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

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

2010-01-01

232

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

Microsoft Academic Search

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

G. P. Starr

1988-01-01

233

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

234

Stiff child syndrome with mutation of DYT1 gene.  

PubMed

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

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

2005-11-01

235

Axial Stiffness of Retention Pins in Human Dentin  

Microsoft Academic Search

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

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

1979-01-01

236

Stiffness of low rise reinforced concrete shear walls  

Microsoft Academic Search

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

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

1993-01-01

237

Real-time single-cell response to stiffness  

PubMed Central

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

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

2010-01-01

238

Real-time single-cell response to stiffness.  

PubMed

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

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

2010-09-21

239

Assessing appropriate stiffness levels for spudcan foundations on dense sand  

Microsoft Academic Search

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

Mark J. Cassidy; George Vlahos; Mathew Hodder

2010-01-01

240

First-principles calculations of pure elements: Equations of state and elastic stiffness constants  

Microsoft Academic Search

Using the projector-augmented wave method within the generalized gradient approximation, a systematic first-principles calculation for energy vs. volume (E–V) equations of state (EOS’s) and single crystal elastic stiffness constants (cij’s) has been performed for 76 pure elemental solids with face-centered-cubic (fcc), body-centered-cubic (bcc), and hexagonal-close-packed (hcp) crystal structures, wherein the cij’s are determined by an efficient strain–stress method, and the

S. L. Shang; A. Saengdeejing; Z. G. Mei; D. E. Kim; H. Zhang; S. Ganeshan; Y. Wang; Z. K. Liu

2010-01-01

241

Research on the Influence of Spring Stiffness in AN ER Isolator  

NASA Astrophysics Data System (ADS)

In this paper, the problem of Electrorheological(ER) technology's application in the vibration isolation system is empirically studied. Based on the particular characteristics of the Electrorheological Fluids (ERF) tunable damping, a metal-spring ER isolator was designed and its working principle is mainly discussed. By theoretical analysis of its simplified physical model, the dynamic response of an ER isolator is frequency- and amplitude- dependent and sensitive to structural parameters. The controllable parameters here can be the system equivalent spring stiffness K and damping coefficient C of ERF. With experiment, the exertion of ER effect was controlled through the change of K and C. Consequently, the system dynamic stiffness, which is used to describe the dynamic properties of system isolation performance, can be changed obviously. According to the dynamic performance tests, the result confirmed that applying different electric field strength could change the dynamic peculiarity of the metal-spring ER isolator. The configuration design of the ER equipment, such as stiffness ratio of two fluid chambers and the size of the electric field, which are important factors for the tunable range of ER isolator.

Wang, Juan; Zhang, Shaohua

242

Theoretical calculation of bending stiffness of alveolar wall.  

PubMed

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

Jabaraj, D John; Jaafar, Mohamad Suhaimi

2013-12-01

243

Diagnosing Aorta Stiffness by Temporal Analysis of Echocardiographic Images  

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

244

Stiffness coupling application to modal synthesis program, users guide  

NASA Technical Reports Server (NTRS)

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

Kuhar, E. J.

1976-01-01

245

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

Microsoft Academic Search

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

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

2002-01-01

246

A Comparison of Crush Stiffness Characteristics from Partial-Overlap and Full-Overlap Frontal Crash Tests  

Microsoft Academic Search

The CRASH3 computer program models a vehicle structure as a homogeneous body with linear force-deflection characteristics. Crush stiffness coefficients determined from full-overlap crash tests, when used in this computer program, allow for an accurate reconstruction of collisions where the accident damage profiles are full-overlap. In the past, partial-overlap frontal crash tests were not performed. The lack of partial-overlap frontal crash

James A. Neptune

1999-01-01

247

Stiffness characteristics of airfoils under pulse loading  

NASA Astrophysics Data System (ADS)

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

Turner, Kevin Eugene

248

Association of the Fourth Heart Sound with Increased Left Ventricular End-Diastolic Stiffness  

PubMed Central

Background Although the fourth heart sound (S4) is thought to be associated with a stiff left ventricle (LV), this association has never been proven. Recently, single-beat estimation of the end-diastolic pressure volume relationship (EDPVR) has been characterized (P = ?V?), allowing the estimation of EDPVR in larger groups of patients. We hypothesized that the S4 is associated with an upward- and leftward-shifted EDPVR, indicative of elevated end-diastolic stiffness. Methods and Results Ninety study participants underwent acoustic cardiographic analysis, echocardiography, and left heart catheterization. We calculated ? and ? coefficients to define the non-linear slope of the EDPVR using the single-beat method for measuring LV end-diastolic elastance. In the P = ?V? EDPVR estimation, ? was similar (p=0.31) but ? was significantly higher in the S4 group (5.96 vs. 6.51, p=0.002), signifying a steeper, upward- and leftward-shifted EDPVR curve in subjects with an S4. The intensity of the S4 was associated with both ? (r=0.42, p < 0.0001) and E/E’ ÷ stroke volume index, another index of diastolic stiffness (r=0.39, p=0.0008). On multivariable analysis, ? remained associated with the presence (p=0.008) and intensity (p<0.0001) of S4 after controlling for age, sex, and ejection fraction. Conclusions The S4 is most likely generated from an abnormally stiff LV, supporting the concept that the S4 is a pathologic finding in older patients.

Shah, Sanjiv J.; Nakamura, Kenta; Marcus, Gregory M.; Gerber, Ivor L.; McKeown, Barry H.; Jordan, Mark V.; Huddleston, Michele; Foster, Elyse; Michaels, Andrew D.

2008-01-01

249

Determination of bilayer membrane bending stiffness by tether formation from giant, thin-walled vesicles.  

PubMed Central

The curvature elastic modulus (bending stiffness) of stearoyloleoyl phosphatidylcholine (SOPC) bilayer membrane is determined from membrane tether formation experiments. R. E. Waugh and R. M. Hochmuth 1987. Biophys. J. 52:391-400) have shown that the radius of a bilayer cylinder (tether) is inversely related to the force supported along its axis. The coefficient that relates the axial force on the tether to the tether radius is the membrane bending stiffness. Thus, the bending stiffness can be calculated directly from measurements of the tether radius as a function of force. Giant (10-50-microns diam) thin-walled vesicles were aspirated into a micropipette and a tether was pulled out of the surface by gravitational forces on small glass beads that had adhered to the vesicle surface. Because the vesicle keeps constant surface area and volume, formation of the tether requires displacement of material from the projection of the vesicle in the pipette. Tethers can be made to grow longer or shorter or to maintain equilibrium by adjusting the aspiration pressure in the micropipette at constant tether force. The ratio of the change in the length of the tether to the change in the projection length is proportional to the ratio of the pipette radius to the tether radius. Thus, knowing the density and diameter of the glass beads and measuring the displacement of the projection as a function of tether length, independent determinations of the force on the tether and the tether radius were obtained. The bending stiffness for an SOPC bilayer obtained from these data is approximately 2.0 x 10(-12) dyn cm, for tether radii in the range of 20-100 nm. An equilibrium relationship between pressure and tether force is derived which closely matches experimental observation. Images FIGURE 4 p512-b

Bo, L.; Waugh, R. E.

1989-01-01

250

Binomial Coefficient Model  

NSDL National Science Digital Library

The Binomial Coefficient model displays the number of ways k objects can be chosen from among n objects when order is irrelevant.   This number is known as a binomial coefficient and can be used to predict the the flipping of n coins with equal probability of heads and tails. The Binomial Coefficient model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_stp_BinomialCoefficient.jar file will run the program if Java is installed.

Christian, Wolfgang

2010-04-11

251

Identifying Bearing Rotordynamic Coefficients using an Extended Kalman Filter  

NASA Technical Reports Server (NTRS)

An Extended Kalman Filter is developed to estimate the linearized direct and indirect stiffness and damping force coefficients for bearings in rotor-dynamic applications from noisy measurements of the shaft displacement in response to imbalance and impact excitation. The bearing properties are modeled as stochastic random variables using a Gauss-Markov model. Noise terms are introduced into the system model to account for all of the estimation error, including modeling errors and uncertainties and the propagation of measurement errors into the parameter estimates. The system model contains two user-defined parameters that can be tuned to improve the filter s performance; these parameters correspond to the covariance of the system and measurement noise variables. The filter is also strongly influenced by the initial values of the states and the error covariance matrix. The filter is demonstrated using numerically simulated data for a rotor-bearing system with two identical bearings, which reduces the number of unknown linear dynamic coefficients to eight. The filter estimates for the direct damping coefficients and all four stiffness coefficients correlated well with actual values, whereas the estimates for the cross-coupled damping coefficients were the least accurate.

Miller, Bard A.; Howard, Samuel A.

2008-01-01

252

Identifying Bearing Rotodynamic Coefficients Using an Extended Kalman Filter  

NASA Technical Reports Server (NTRS)

An Extended Kalman Filter is developed to estimate the linearized direct and indirect stiffness and damping force coefficients for bearings in rotor dynamic applications from noisy measurements of the shaft displacement in response to imbalance and impact excitation. The bearing properties are modeled as stochastic random variables using a Gauss-Markov model. Noise terms are introduced into the system model to account for all of the estimation error, including modeling errors and uncertainties and the propagation of measurement errors into the parameter estimates. The system model contains two user-defined parameters that can be tuned to improve the filter's performance; these parameters correspond to the covariance of the system and measurement noise variables. The filter is also strongly influenced by the initial values of the states and the error covariance matrix. The filter is demonstrated using numerically simulated data for a rotor bearing system with two identical bearings, which reduces the number of unknown linear dynamic coefficients to eight. The filter estimates for the direct damping coefficients and all four stiffness coefficients correlated well with actual values, whereas the estimates for the cross-coupled damping coefficients were the least accurate.

Miller, Brad A.; Howard, Samuel A.

2008-01-01

253

Stiffness properties for Nucleus standard straight and contour electrode arrays.  

PubMed

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

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

2004-10-01

254

Repeatability of Magnetic Resonance Elastography for Quantification of Hepatic Stiffness  

PubMed Central

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

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

2010-01-01

255

Estimation of quasi-stiffness and propulsive work of the human ankle in the stance phase of walking.  

PubMed

Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as prostheses and orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75-2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R(2) of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking. PMID:23555839

Shamaei, Kamran; Sawicki, Gregory S; Dollar, Aaron M

2013-01-01

256

Rhythmic contraction generates adjustable passive stiffness in rabbit detrusor.  

PubMed

The length-tension (L-T) relationships in airway and vascular smooth muscles have been shown to adapt with length changes over time. Our prior studies have shown that the active and passive L-T relationships in rabbit detrusor smooth muscle (DSM) can adapt and that DSM exhibits adjustable passive stiffness (APS) characterized by a passive L-T curve that is a function of strain and activation history. The present study demonstrates that passive tension due to APS can represent a substantial fraction of total tension over a broad length range. Our previous studies have shown that maximal KCl-induced contractions at short muscle lengths generate APS that is revealed by increased pseudo-steady-state passive tension at longer lengths compared with previous measurements at those lengths. The objective of the present study was to determine the mechanisms involved in APS generation. Increasing the number of KCl-induced contractions or the duration of a contraction increased the amount of APS generated. Furthermore, a fraction of APS was restored in calcium-free solution and was sensitive to the general serine and threonine protein kinase inhibitor staurosporine. Most importantly, rhythmic contraction (RC) generated APS, and because RC occurs spontaneously in human bladder, a physiological role for RC was potentially identified. PMID:20056849

Almasri, Atheer M; Ratz, Paul H; Bhatia, Hersch; Klausner, Adam P; Speich, John E

2010-03-01

257

Antibody biodistribution coefficients  

PubMed Central

Tissue vs. plasma concentration profiles have been generated from a physiologically-based pharmacokinetic model of monoclonal antibody (mAb). Based on the profiles, we hypothesized that a linear relationship between the plasma and tissue concentrations of non-binding mAbs could exist; and that the relationship may be generally constant irrespective of the absolute mAb concentration, time, and animal species being analyzed. The hypothesis was verified for various tissues in mice, rat, monkey, and human using mAb or antibody-drug conjugate tissue distribution data collected from diverse literature. The relationship between the plasma and various tissue concentrations was mathematically characterized using the antibody biodistribution coefficient (ABC). Estimated ABC values suggest that typically the concentration of mAb in lung is 14.9%, heart 10.2%, kidney 13.7%, muscle 3.97%, skin 15.7%, small intestine 5.22%, large intestine 5.03%, spleen 12.8%, liver 12.1%, bone 7.27%, stomach 4.98%, lymph node 8.46%, adipose 4.78%, brain 0.351%, pancreas 6.4%, testes 5.88%, thyroid 67.5% and thymus is 6.62% of the plasma concentration. The validity of using the ABC to predict mAb concentrations in different tissues of mouse, rat, monkey, and human species was evaluated by generating validation data sets, which demonstrated that predicted concentrations were within 2-fold of the observed concentrations. The use of ABC to infer tissue concentrations of mAbs and related molecules provides a valuable tool for investigating preclinical or clinical disposition of these molecules. It can also help eliminate or optimize biodistribution studies, and interpret efficacy or toxicity of the drug in a particular tissue.

Shah, Dhaval K.; Betts, Alison M.

2013-01-01

258

Modulating polymer chemistry to enhance non-viral gene delivery inside hydrogels with tunable matrix stiffness.  

PubMed

Non-viral gene delivery holds great promise for promoting tissue regeneration, and offers a potentially safer alternative than viral vectors. Great progress has been made to develop biodegradable polymeric vectors for non-viral gene delivery in 2D culture, which generally involves isolating and modifying cells in vitro, followed by subsequent transplantation in vivo. Scaffold-mediated gene delivery may eliminate the need for the multiple-step process in vitro, and allows sustained release of nucleic acids in situ. Hydrogels are widely used tissue engineering scaffolds given their tissue-like water content, injectability and tunable biochemical and biophysical properties. However, previous attempts on developing hydrogel-mediated non-viral gene delivery have generally resulted in low levels of transgene expression inside 3D hydrogels, and increasing hydrogel stiffness further decreased such transfection efficiency. Here we report the development of biodegradable polymeric vectors that led to efficient gene delivery inside poly(ethylene glycol) (PEG)-based hydrogels with tunable matrix stiffness. Photocrosslinkable gelatin was maintained constant in the hydrogel network to allow cell adhesion. We identified a lead biodegradable polymeric vector, E6, which resulted in increased polyplex stability, DNA protection and achieved sustained high levels of transgene expression inside 3D PEG-DMA hydrogels for at least 12 days. Furthermore, we demonstrated that E6-based polyplexes allowed efficient gene delivery inside hydrogels with tunable stiffness ranging from 2 to 175 kPa, with the peak transfection efficiency observed in hydrogels with intermediate stiffness (28 kPa). The reported hydrogel-mediated gene delivery platform using biodegradable polyplexes may serve as a local depot for sustained transgene expression in situ to enhance tissue engineering across broad tissue types. PMID:24011715

Keeney, Michael; Onyiah, Sheila; Zhang, Zhe; Tong, Xinming; Han, Li-Hsin; Yang, Fan

2013-12-01

259

Modeling, Modal Properties, and Mesh Stiffness Variation Instabilities of Planetary Gears  

NASA Technical Reports Server (NTRS)

Planetary gear noise and vibration are primary concerns in their applications in helicopters, automobiles, aircraft engines, heavy machinery and marine vehicles. Dynamic analysis is essential to the noise and vibration reduction. This work analytically investigates some critical issues and advances the understanding of planetary gear dynamics. A lumped-parameter model is built for the dynamic analysis of general planetary gears. The unique properties of the natural frequency spectra and vibration modes are rigorously characterized. These special structures apply for general planetary gears with cyclic symmetry and, in practically important case, systems with diametrically opposed planets. The special vibration properties are useful for subsequent research. Taking advantage of the derived modal properties, the natural frequency and vibration mode sensitivities to design parameters are investigated. The key parameters include mesh stiffnesses, support/bearing stiffnesses, component masses, moments of inertia, and operating speed. The eigen-sensitivities are expressed in simple, closed-form formulae associated with modal strain and kinetic energies. As disorders (e.g., mesh stiffness variation. manufacturing and assembling errors) disturb the cyclic symmetry of planetary gears, their effects on the free vibration properties are quantitatively examined. Well-defined veering rules are derived to identify dramatic changes of natural frequencies and vibration modes under parameter variations. The knowledge of free vibration properties, eigen-sensitivities, and veering rules provide important information to effectively tune the natural frequencies and optimize structural design to minimize noise and vibration. Parametric instabilities excited by mesh stiffness variations are analytically studied for multi-mesh gear systems. The discrepancies of previous studies on parametric instability of two-stage gear chains are clarified using perturbation and numerical methods. The operating conditions causing parametric instabilities are expressed in closed-form suitable for design guidance. Using the well-defined modal properties of planetary gears, the effects of mesh parameters on parametric instability are analytically identified. Simple formulae are obtained to suppress particular instabilities by adjusting contact ratios and mesh phasing.

Parker, Robert G.; Lin, Jian; Krantz, Timothy L. (Technical Monitor)

2001-01-01

260

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

PubMed Central

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

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

2011-01-01

261

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

262

Nanoindenter Stiffness Measurements on a MEMS Sound Sensor  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

263

Wing/store flutter with nonlinear pylon stiffness  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

264

Wing/store flutter with nonlinear pylon stiffness  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

265

Stiffness Corrections for the Vibration Frequency of a Stretched Wire  

ERIC Educational Resources Information Center

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

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

1977-01-01

266

Improved Equivalent Linearization Implementations Using Nonlinear Stiffness Evaluation  

NASA Technical Reports Server (NTRS)

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

Rizzi, Stephen A.; Muravyov, Alexander A.

2001-01-01

267

Identification of Contact Dynamics Parameters for Stiff Robotic Payloads  

Microsoft Academic Search

This paper investigates and demonstrates the feasibility of identifying contact dynamics parameters for stiff robotic payloads using a robotic system. The contact dynamics model for stiff payloads is motivated, and theoretical parameter values and bounds are provided. Then, the effect of nonidealities such as surface roughness and plastic deformation on the theoretical values is demonstrated. A row-wise-scaled total least-squares parameter

Diederik Verscheure; Inna Sharf; Herman Bruyninckx; Jan Swevers; Joris De Schutter

2009-01-01

268

Stiffness Detection Strategy for Explicit Runge Kutta Methods  

NASA Astrophysics Data System (ADS)

This paper describes a new practical strategy to detect stiffness based on explicit Runge-Kutta schemes. This strategy implements an operative definition of stiffness based on the computation of two conditioning parameters. Test results, using a modified version of the MATLAB code DOPRI5, indicate that the new strategy is able to detect whether a problem could be solved more efficiently by an implicit method.

Mazzia, F.; Nagy, A. M.

2010-09-01

269

Stiffness between different directions of transpedicular screws and vertebra  

Microsoft Academic Search

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

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

1998-01-01

270

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

271

Changes in human knee ligament stiffness secondary to osteoarthritis.  

PubMed

Stiffness of the medial (MCL) and lateral (LCL) collateral ligaments was compared between a group of 10 patients undergoing total knee arthroplasty for varus degenerative osteoarthritis (OAP), a group of 10 osteoarthritic cadaveric knees (OAC), and a group of 10 non-osteoarthritic cadaveric knees (NOA). A load-elongation curve was obtained for the medial and lateral compartments of each knee using an instrumented Moreland spreader. A strain gage (SG) was attached to the spreader handle and strain was calibrated to load applied against the spread distance. In extension, medial compartment stiffness of the OAP, OAC, and NOA groups was 60.7+/-16, 52.8+/-9.3 and 21.4+/-5.0 N/mm, respectively. Lateral compartment stiffness in extension was 29.2+/-9.2, 33.3+/-10.3 and 19.5+/-5.3 N/mm, for OAP, OAC, and NOA, respectively. Differences in stiffness between the OAP and OAC groups were not statistically significant (p > 0.05). However, the osteoarthritic groups (OAP and OAC) demonstrated a statistically significantly (p < 0.05) increase in ligament stiffness when compared to the NOA group. Following knee arthroplasty, stiffer medial structures in extension may lead to flexion contracture and accelerated polyethylene wear. Adequate bone resection, in conjunction with soft tissue release may alleviate the threefold increase in stiffness observed in the medial compartment secondary to OA without jeopardizing joint stability. PMID:11918298

Fishkin, Zair; Miller, David; Ritter, Christopher; Ziv, Israel

2002-03-01

272

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

273

The SSME HPFTP interstage seals: Analysis and experiments for leakage and reaction-force coefficients  

NASA Technical Reports Server (NTRS)

An improved theory for the prediction of the rotordynamic coefficients of turbulent annular seals was developed. Predictions from the theory are compared to the experimental results and an approach for the direct calculation of empirical turbulent coefficients from test data are introduced. An improved short seal solution is shown to do a better job of calculating effective stiffness and damping coefficients than either the original short seal solution or a finite length solution. However, the original short seal solution does a much better job of predicting equivalent added mass coefficient.

Childs, D. W.

1983-01-01

274

Point shear wave elastography method for assessing liver stiffness  

PubMed Central

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

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

2014-01-01

275

Strength Coefficient of Materials.  

National Technical Information Service (NTIS)

South Dakota's, previously conducted, Flexible Pavement Study indicated a relationship between Strength and Effective Thickness. It was apparent that a simple slope formula used for any two points on the curve produced strength coefficients. The slope of ...

R. A. Crawford

1971-01-01

276

Drag Coefficients of Cones.  

National Technical Information Service (NTIS)

The objective was to provide experimental values for cone drag coefficients in the near free molecule and transitional flow regimes including an examination of the effects of Mach number, wall speed ratio, bluntness, and specific heat ratio. A modulated f...

J. F. Wendt

1972-01-01

277

Coefficients of Effective Length.  

ERIC Educational Resources Information Center

Under certain conditions, a validity Coefficient of Effective Length (CEL) can produce highly misleading results. A modified coefficent is suggested for use when empirical studies indicate that underlying assumptions have been violated. (Author/BW)

Edwards, Roger H.

1981-01-01

278

5E-5 Generated Power Characterization of Piezoelectrics with Electromechanical Coupling Coefficient and Quality Factor  

Microsoft Academic Search

A simple equation for generated power of piezoelectric devices was developed for the case in which deflection is fixed. The generated power equation is expressed in terms of stiffness, resonant frequency, deflection and electromechanical coupling coefficient k2. The generated power equation shows that power is not a function of quality factor Q under this condition. The power output produced by

J. H. Cho; R. F. Richards; D. F. Bahr; C. D. Richards; M. J. Anderson

2006-01-01

279

A Generalized Variable-Coefficient Algebraic Method Exactly Solving (3+1)Dimensional Kadomtsev–Petviashvilli EquationThe project supported by National Natural Science Foundation of China and the Natural Science Foundation of Shandong Province of China under Grant No. 2004ZX16  

Microsoft Academic Search

A generalized variable-coefficient algebraic method is applied to construct several new families of exact solutions of physical interest for (3+1)-dimensional Kadomtsev–Petviashvilli (KP) equation. Among them, the Jacobi elliptic periodic solutions exactly degenerate to the soliton solutions at a certain limit condition. Compared with the existing tanh method, the extended tanh method, the Jacobi elliptic function method, and the algebraic method,

Bai Cheng-Lin; Bai Cheng-Jie; Zhao Hong

2005-01-01

280

VODE. Variable Coefficient ODE Solver  

SciTech Connect

VODE is a package of subroutines for the numerical solution of the initial-value problem for systems of first-order ordinary differential equations. The package can be used for either stiff or nonstiff systems. In the stiff case, the Jacobian matrix is treated as full or banded. An algorithm is included for saving and reusing the Jacobian matrix under certain conditions. If storage is limited, this option may be suppressed.

Brown, P.N.; Hindmarsh, A.C.; Byrne, G.D. [Lawrence Livermore National Lab., CA (United States)

1989-11-01

281

The Accuracy of Winsmash Delta-V Estimates: The Influence of Vehicle Type, Stiffness, and Impact Mode  

PubMed Central

The objective of this paper is to investigate the accuracy of WinSmash delta-V estimates as a function of crash mode, vehicle body type, and vehicle stiffness. The accuracy of WinSmash delta-V estimates was evaluated for 121 NASS/CDS 2000–2003 cases for which direct measurements of delta-V had been retrieved from an Event Data Recorder on the case vehicle. WinSmash was found to underestimate delta-V by 23% on average. WinSmash was found to be most accurate in crashes involving full frontal engagement of the vehicle structure. When using categorical stiffness coefficients, the accuracy of delta-V estimates was found to be a strong function of vehicle type. WinSmash underestimated delta-V for pickup trucks by only 3%, but underestimated delta-V for front-wheel drive cars by 31%. The use of vehicle-specific stiffness coefficients improved the accuracy of the longitudinal delta-V estimate. The single most important factor in improving WinSmash accuracy was the inclusion of restitution. After adjusting for restitution, WinSmash underestimated delta-V in frontal crashes by only 1% on average.

Niehoff, P.; Gabler, H.C.

2006-01-01

282

LSENS, a general chemical kinetics and sensitivity analysis code for gas-phase reactions: User's guide  

NASA Technical Reports Server (NTRS)

A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS, are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include static system, steady, one-dimensional, inviscid flow, shock initiated reaction, and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method, which works efficiently for the extremes of very fast and very slow reaction, is used for solving the 'stiff' differential equation systems that arise in chemical kinetics. For static reactions, sensitivity coefficients of all dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters can be computed. This paper presents descriptions of the code and its usage, and includes several illustrative example problems.

Radhakrishnan, Krishnan; Bittker, David A.

1993-01-01

283

Dynamic stiffness matrix of thin-walled composite I-beam with symmetric and arbitrary laminations  

NASA Astrophysics Data System (ADS)

For the spatially coupled free vibration analysis of thin-walled composite I-beam with symmetric and arbitrary laminations, the exact dynamic stiffness matrix based on the solution of the simultaneous ordinary differential equations is presented. For this, a general theory for the vibration analysis of composite beam with arbitrary lamination including the restrained warping torsion is developed by introducing Vlasov's assumption. Next, the equations of motion and force-displacement relationships are derived from the energy principle and the first order of transformed simultaneous differential equations are constructed by using the displacement state vector consisting of 14 displacement parameters. Then explicit expressions for displacement parameters are derived and the exact dynamic stiffness matrix is determined using force-displacement relationships. In addition, the finite-element (FE) procedure based on Hermitian interpolation polynomials is developed. To verify the validity and the accuracy of this study, the numerical solutions are presented and compared with analytical solutions, the results from available references and the FE analysis using the thin-walled Hermitian beam elements. Particular emphasis is given in showing the phenomenon of vibrational mode change, the effects of increase of the modulus and the bending-twisting coupling stiffness for beams with various boundary conditions.

Kim, Nam-Il; Shin, Dong Ku; Park, Young-Suk

2008-11-01

284

Redox regulation of morphology, cell stiffness, and lectin-induced aggregation of human platelets.  

PubMed

Redox regulation and carbohydrate recognition are potent molecular mechanisms which can contribute to platelet aggregation in response to various stimuli. The purpose of this study is to investigate the relationship between these mechanisms and to examine whether cell surface glycocalyx and cell stiffness of human platelets are sensitive to the redox potential formed by glutathione. To this end, human platelets were treated with different concentrations (0.05 ?M to 6 mM) and ratios of reduced or oxidized glutathione (GSH or GSSG), and platelet morphological, mechanical, and functional properties were determined using conventional light microscopy, atomic force microscopy, and lectin-induced cell aggregation analysis. It was found that lowering the glutathione redox potential changed platelet morphology and increased platelet stiffness as well as modulated nonuniformly platelet aggregation in response to plant lectins with different carbohydrate-binding specificity including wheat germ agglutinin, Sambucus nigra agglutinin, and Canavalia ensiformis agglutinin. Extracellular redox potential and redox buffering capacity of the GSSG/2GSH couple were shown to control the availability of specific lectin-binding glycoligands on the cell surface, while the intracellular glutathione redox state affected the general functional ability of platelets to be aggregated independently of the type of lectins. Our data provide the first experimental evidence that glutathione as a redox molecule can affect the mechanical stiffness of human platelets and induce changes of the cell surface glycocalyx, which may represent a new mechanism of redox regulation of intercellular contacts. PMID:21079947

Shamova, Ekaterina V; Gorudko, Irina V; Drozd, Elizaveta S; Chizhik, Sergey A; Martinovich, Grigory G; Cherenkevich, Sergey N; Timoshenko, Alexander V

2011-02-01

285

The influence of thyroarytenoid and cricothyroid muscle activation on vocal fold stiffness and eigenfrequencies  

PubMed Central

The influence of the thyroarytenoid (TA) and cricothyroid (CT) muscle activation on vocal fold stiffness and eigenfrequencies was investigated in a muscularly controlled continuum model of the vocal folds. Unlike the general understanding that vocal fold fundamental frequency was determined by vocal fold tension, this study showed that vocal fold eigenfrequencies were primarily determined by vocal fold stiffness. This study further showed that, with reference to the resting state of zero strain, vocal fold stiffness in both body and cover layers increased with either vocal fold elongation or shortening. As a result, whether vocal fold eigenfrequencies increased or decreased with CT/TA activation depended on how the CT/TA interaction influenced vocal fold deformation. For conditions of strong CT activation and thus an elongated vocal fold, increasing TA contraction reduced the degree of vocal fold elongation and thus reduced vocal fold eigenfrequencies. For conditions of no CT activation and thus a resting or slightly shortened vocal fold, increasing TA contraction increased the degree of vocal fold shortening and thus increased vocal fold eigenfrequencies. In the transition region of a slightly elongated vocal fold, increasing TA contraction first decreased and then increased vocal fold eigenfrequencies.

Yin, Jun; Zhang, Zhaoyan

2013-01-01

286

Determination of reaeration coefficients for Ohio streams  

USGS Publications Warehouse

The hydrocarbon-gas tracer technique was used to determine reaeration coefficients on 30 reaches of Ohio streams. The studies were done from September 1979 through August 1982 to determine the reaeration coefficients for the individual reaches and to develop general equation that could be used to estimate the coefficients. Multiple linear regression was used to determine relationships among the reaeration coefficients and physical stream characteristics. Four special equation based on the general equation were developed from various combinations of discharge, slope, width, depth, measured velocity, and estimated velocity. The standard errors of estimate for these equations ranged from 37 to 47 percent. The variables that resulted in the lowest standard error of estimate were discharge, slope, width, depth, and measured velocity. The most significant variables were depth and velocity.

Hren, Janet

1984-01-01

287

Psychological Stress and Arterial Stiffness in Korean Americans  

PubMed Central

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

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

2012-01-01

288

Endothelial barrier disruption and recovery is controlled by substrate stiffness  

PubMed Central

Circulating barrier disruptive agonists bind specific cell membrane receptors and trigger signal transduction pathways leading to activation of cell contractility and endothelial cell (EC) permeability. Although all cells in tissues including vascular EC are surrounded by compliant extracellular matrix, the impact of matrix stiffness on agonist-induced signaling, cytoskeletal remodeling and EC barrier regulation is not well understood. This study examined agonist-induced cytoskeletal and signaling changes associated with EC barrier disruption and recovery using pulmonary EC grown on compliant substrates of physiologically relevant (8.6 kPa) stiffness, very low (0.55 kPa) and very high (42 kPa) stiffness. Human pulmonary microvascular and macrovascular EC grown on 0.55 kPa substrate contained a few actin stress fibers, while stress fiber amount increased with increasing matrix stiffness. Thrombin-induced stress fiber formation was maximal in EC grown on 42 kPa substrate, diminished on 8.6 kPa substrate, and was minimal on 0.55 kPa substrate. These effects were linked to a stiffness-dependent increase in thrombin-induced phosphorylation of the Rho kinase target, myosin light chain phosphatase (MYPT1), and regulatory myosin light chains (MLC). Surprisingly, EC barrier recovery and activation of Rac GTPase-dependent barrier protective signaling reached maximal levels in EC grown on 8.6 kPa, but not on 0.55 kPa substrate. In conclusion, these data show a critical role of extracellular matrix stiffness in the regulation of the Rac/Rho signaling balance during onset and resolution of agonist-induced EC permeability. The optimal conditions for the Rho/Rac signaling switch, which provides an effective and reversible EC cytoskeletal and permeability response to agonist, are reached in cells grown on the matrix of physiologically relevant stiffness.

Birukova, Anna A.; Tian, Xinyong; Cokic, Ivan; Beckham, Yvonne; Gardel, Margaret; Birukov, Konstantin G.

2013-01-01

289

Radon diffusion coefficients for residential concretes  

Microsoft Academic Search

Radon gas diffusion through concrete can be a significant mechanism for radon entry into dwellings. Measurements of radon diffusion coefficients in the pores of residential concretes ranged from 2.1 x 10⁻⁸ m² s⁻¹ to 5.2 x 10⁻⁷ m² s⁻¹. The pore diffusion coefficients generally increased with the water-cement ratio of the concrete and decreased with its density. A least-squares regression

Vern C. Rogers; Kirk K. Nielson; Rodger B. Holt; Richard Snoddy

1994-01-01

290

Spatial correlation coefficient images for ultrasonic detection.  

PubMed

In ultrasonics, image formation and detection are generally based on signal amplitude. In this paper, we introduce correlation coefficient images as a signal-amplitude independent approach for image formation. The correlation coefficients are calculated between A-scans digitized at adjacent measurement positions. In these images, defects are revealed as regions of high or low correlation relative to the background correlations associated with noise. Correlation coefficient and C-scan images are shown to demonstrate flat-bottom-hole detection in a stainless steel annular ring and crack detection in an aluminum aircraft structure. PMID:17941390

Cepel, Raina; Ho, K C; Rinker, Brett A; Palmer, Donald D; Lerch, Terrence P; Neal, Steven P

2007-09-01

291

Radon diffusion coefficients for residential concretes  

SciTech Connect

Radon gas diffusion through concrete can be a significant mechanism for radon entry into dwellings. Measurements of radon diffusion coefficients in the pores of residential concretes ranged from 2.1 x 10{sup {minus}8} m{sup 2} s{sup {minus}1} to 5.2 x 10{sup {minus}7} m{sup 2} s{sup {minus}1}. The pore diffusion coefficients generally increased with the water-cement ratio of the concrete and decreased with its density. A least-squares regression of the diffusion coefficients on concrete density gave an r value of -0.73. 16 refs., 2 figs., 3 tabs.

Rogers, V.C.; Nielson, K.K.; Holt, R.B. [Rogers and Associates Engineering Corp., Salt Lake City, UT (United States); Snoddy, R. [Acurex Environmental Corp., Research Triangle Park, NC (United States)

1994-09-01

292

Stiffness of the endplate boundary layer and endplate surface topography are associated with brittleness of human whole vertebral bodies.  

PubMed

Stress magnitude and variability as estimated from large scale finite element (FE) analyses have been associated with compressive strength of human vertebral cancellous cores but these relationships have not been explored for whole vertebral bodies. In this study, the objectives were to investigate the relationship of FE-calculated stress distribution parameters with experimentally determined strength, stiffness, and displacement based ductility measures in human whole vertebral bodies, investigate the effect of endplate loading conditions on vertebral stiffness, strength, and ductility and test the hypothesis that endplate topography affects vertebral ductility and stress distributions. Eighteen vertebral bodies (T6-L3 levels; 4 female and 5 male cadavers, aged 40-98 years) were scanned using a flat-panel CT system and followed with axial compression testing with Wood's metal as filler material to maintain flat boundaries between load plates and specimens. FE models were constructed using reconstructed CT images and filler material was added digitally. Two different FE models with different filler material modulus simulating Wood's metal and intervertebral disc (W-layer and D-layer models) were used. Element material modulus to cancellous bone was based on image gray value. Average, standard deviation, and coefficient of variation of von Mises stress in vertebral bone for W-layer and D-layer models and also the ratios of FE parameters from the two models (W/D) were calculated. Inferior and superior endplate surface topographical distribution parameters were calculated. Experimental stiffness, maximum load and work to fracture had the highest correlation with FE-calculated stiffness while experimental ductility measures had highest correlations with FE-calculated average von Mises stress and W-layer to D-layer stiffness ratio. Endplate topography of the vertebra was also associated with its structural ductility and the distribution parameter that best explained this association was kurtosis of inferior endplate topography. Our results indicate that endplate topography variations may provide insight into the mechanisms responsible for vertebral fractures. PMID:20633709

Nekkanty, Srikant; Yerramshetty, Janardhan; Kim, Do-Gyoon; Zauel, Roger; Johnson, Evan; Cody, Dianna D; Yeni, Yener N

2010-10-01

293

Stiffness of the endplate boundary layer and endplate surface topography are associated with brittleness of human whole vertebral bodies  

PubMed Central

Stress magnitude and variability as estimated from large scale finite element (FE) analyses have been associated with compressive strength of human vertebral cancellous cores but these relationships have not been explored for whole vertebral bodies. In this study, the objectives were to investigate the relationship of FE-calculated stress distribution parameters with experimentally determined strength, stiffness, and displacement based ductility measures in human whole vertebral bodies, investigate the effect of endplate loading conditions on vertebral stiffness, strength, and ductility and test the hypothesis that endplate topography affects vertebral ductility and stress distributions. Eighteen vertebral bodies (T6-L3 levels; 4 female and 5 male cadavers, aged 40-98 years) were scanned using a flat panel CT system and followed with axial compression testing with Wood’s metal as filler material to maintain flat boundaries between load plates and specimens. FE models were constructed using reconstructed CT images and filler material was added digitally. Two different FE models with different filler material modulus simulating Wood’s metal and intervertebral disc (W-layer and D-layer models) were used. Element material modulus to cancellous bone was based on image gray value. Average, standard deviation, and coefficient of variation of von Mises stress in vertebral bone for W-layer and D-layer models and also the ratios of FE parameters from the two models (W/D) were calculated. Inferior and superior endplate surface topographical distribution parameters were calculated. Experimental stiffness, maximum load and work to fracture had the highest correlation with FE-calculated stiffness while experimental ductility measures had highest correlations with FE-calculated average von Mises stress and W-layer to D-layer stiffness ratio. Endplate topography of the vertebra was also associated with its structural ductility and the distribution parameter that best explained this association was kurtosis of inferior endplate topography. Our results indicate that endplate topography variations may provide insight into the mechanisms responsible for vertebral fractures.

Nekkanty, Srikant; Yerramshetty, Janardhan; Kim, Do-Gyoon; Zauel, Roger; Johnson, Evan; Cody, Dianna D.; Yeni, Yener N.

2013-01-01

294

Likelihood-based inference for genetic correlation coefficients  

Microsoft Academic Search

We review Wright's original definitions of the genetic correlation coefficients FST, FIT, and FIS, pointing out ambiguities and the difficulties that these have generated. We also briefly survey some subsequent approaches to defining and estimating the coefficients. We then propose a general framework in which the coefficients are defined, their properties established, and likelihood-based inference implemented. Likelihood methods of inference

David J. Balding

2003-01-01

295

Analysis and design of variable stiffness composite cylinders  

NASA Astrophysics Data System (ADS)

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

Tatting, Brian Frederick

296

Stiffness of soft tissue complex in total knee arthroplasty.  

PubMed

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

Asano, Hiroshi; Muneta, Takeshi; Hoshino, Akiho

2008-01-01

297

A comparison of computation methods for leg stiffness during hopping.  

PubMed

Despite the presence of several different calculations of leg stiffness during hopping, little is known about how the methodologies produce differences in the leg stiffness. The purpose of this study was to directly compare Kleg during hopping as calculated from three previously published computation methods. Ten male subjects hopped in place on two legs, at four frequencies (2.2, 2.6, 3.0, and 3.4 Hz). In this article, leg stiffness was calculated from the natural frequency of oscillation (method A), the ratio of maximal ground reaction force (GRF) to peak center of mass displacement at the middle of the stance phase (method B), and an approximation based on sine-wave GRF modeling (method C). We found that leg stiffness in all methods increased with an increase in hopping frequency, but Kleg values using methods A and B were significantly higher than when using method C at all hopping frequencies. Therefore, care should be taken when comparing leg stiffness obtained by method C with those calculated by other methods. PMID:24676522

Hobara, Hiroaki; Inoue, Koh; Kobayashi, Yoshiyuki; Ogata, Toru

2014-02-01

298

Variable stiffness material and structural concepts for morphing applications  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

299

Stiffness characterisation of microcantilevers based on conducting polymers  

NASA Astrophysics Data System (ADS)

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

Alici, Gursel; Higgins, Michael J.

2008-12-01

300

Optimal semi-active damping of cables with bending stiffness  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

301

The intraclass correlation coefficient: distribution-free definition and test.  

PubMed

A definition of the intraclass correlation coefficient is given on the basis of a general class of random effect model. The conventional intraclass correlation coefficient and the intracluster correlation coefficient for binary data are both particular cases of the generalized coefficient. We derive the score test for the hypothesis of null intraclass correlation in the exponential family. The statistic does not depend on the particular distribution in this family and is related to the pairwise correlation coefficient. The test can be adjusted for explanatory variables. PMID:8068852

Commenges, D; Jacqmin, H

1994-06-01

302

Elastic stiffness and filler size effect of covalently grafted nanosilica polyimide composites: molecular dynamics study.  

PubMed

The filler size-dependent elastic stiffness of nanosilica (?-quartz)-reinforced polyimide(s-BPDA/1,3,4-APB) composites under the same volume fraction and grafting ratio conditions was investigated via molecular dynamics(MD) simulations. To enhance the interfacial load transfer efficiency, we treated the surface oxygen atoms of the silica nanoparticle with additional silicon atoms attached by a propyl group to which the aromatic hydrocarbon in the polyimide is directly grafted. As the radius of the embedded nanoparticle increases, the Young's and shear moduli gradually decrease, showing a prominent filler size effect. At the same time, the moduli of the nanocomposites increase as the grafting ratio increases. The contribution of different nanoparticles to the filler size dependency in elastic stiffness of the nanocomposites can be elucidated by comparing the normalized adhesive interaction energy between the particle and matrix which exhibits prominent filler size dependency. Because of the immobilization of the matrix polymer in the vicinity of the nanoparticles, which was confirmed by the self-diffusion coefficient, the highly grafted interface is found to bring about a greater reinforcing effect than the ungrafted interface. PMID:22931169

Yang, Seunghwa; Choi, Joonmyung; Cho, Maenghyo

2012-09-26

303

Evaluation of Fatigue Life of CRM-Reinforced SMA and Its Relationship to Dynamic Stiffness  

PubMed Central

Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400?kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture.

Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati

2014-01-01

304

Brownian motion of stiff filaments in a crowded environment.  

PubMed

The thermal motion of stiff filaments in a crowded environment is highly constrained and anisotropic; it underlies the behavior of such disparate systems as polymer materials, nanocomposites, and the cell cytoskeleton. Despite decades of theoretical study, the fundamental dynamics of such systems remains a mystery. Using near-infrared video microscopy, we studied the thermal diffusion of individual single-walled carbon nanotubes (SWNTs) confined in porous agarose networks. We found that even a small bending flexibility of SWNTs strongly enhances their motion: The rotational diffusion constant is proportional to the filament-bending compliance and is independent of the network pore size. The interplay between crowding and thermal bending implies that the notion of a filament's stiffness depends on its confinement. Moreover, the mobility of SWNTs and other inclusions can be controlled by tailoring their stiffness. PMID:21205665

Fakhri, Nikta; MacKintosh, Frederick C; Lounis, Brahim; Cognet, Laurent; Pasquali, Matteo

2010-12-24

305

Dynamic instabilities in assemblies of molecular motors with finite stiffness.  

PubMed

We propose a two-state "soft-motor" model for the collective behavior of molecular motors which takes into account both the internal motor stiffness and the periodic interaction with the filament. As in the Prandtl-Tomlinson model of tribology, the important parameter of the model is the pinning parameter, which compares the stiffness of the motors to the stiffness of the potential. The model predicts dynamic instabilities in two disconnected regions of parameter space. These parameter ranges correspond to two existing theories of motor assemblies, the rigid two-state model and the crossbridge model. The model also predicts a discontinuity of the slope of the force-velocity relation at small velocities. PMID:20867339

Guérin, T; Prost, J; Joanny, J-F

2010-06-18

306

Tailoring shear-stiff, mica-like nanoplatelets.  

PubMed

This work introduces a novel facile method to produce shear-stiff, mica-like nanoplatelets by efficient exfoliation. The essence of this procedure is the nonreversible alteration of the interlamellar reactivity of a synthetic fluorohectorite by simple cation exchange. The possibility of switching from highly hydrated to collapsed interlayers permits a highly efficient exfoliation in the swollen state while providing shear-stiffness in the collapsed state. This method restricts cation exchange in the mica-like nanoplatelets to the outer surfaces, which represents a significant advantage for use in nanocomposites as compared to conventional organoclays which contain up to 40%/wt of organocations. It is expected that this new type of rigid, shear-stiff, clay-based nanoplatelets will be superior for reinforcement when used in composite materials like polymer layered silicate nanocomposites or artificial nacre. PMID:20088599

Möller, Michael W; Handge, Ulrich A; Kunz, Daniel A; Lunkenbein, Thomas; Altstädt, Volker; Breu, Josef

2010-02-23

307

Etiology and Surgical Interventions for Stiff Total Knee Replacements  

PubMed Central

Stiffness is the most prevalent early local complication of primary total knee replacement, affecting approximately 6 to 7% of patients undergoing surgery. The definition of stiffness after total knee replacement in terms of restriction of the arc of motion has evolved in the last 2 decades as patients and physicians expect better postoperative functional outcomes. Gentle manipulation under anesthesia within 3 to 4 months of surgery improves the range of motion in most patients. However, approximately 1% of patients, including those in which the window for manipulation has passed, will require further surgical interventions, which may include arthroscopy with lysis of adhesions, open debridement with exchange of the polyethylene insert, or revision of one or more components. This review will focus on describing the etiology of the problem and the results of the different surgical interventions for stiffness after total knee replacement.

Leali, Alejandro; Haas, Steven

2007-01-01

308

Pearson's Correlation Coefficient  

NSDL National Science Digital Library

This tutorial on Pearson's Correlation Coefficient includes the definition, assumptions, and characteristics of r as well as related statistics and hypothesis test procedures. One section instructs users to find correlation in the WINKS software, but those without the software can still use the tutorial. An exercise is given at the end that can be done with any statistical software package.

2009-01-09

309

Point Biserial Correlation Coefficient  

NSDL National Science Digital Library

This page calculates the point biserial correlation coefficient for the case where one variable is dichotomous and the other is non-dichotomous. This page allows the user to input the data directly or copy and paste from a spreadsheet application and provides data summary.

Lowry, Richard, 1940-

2008-06-26

310

Role of mineralocorticoid receptors in arterial stiffness in human aging.  

PubMed

Arterial stiffness, an independent predictor of cardiovascular disease, is increased in aging, but the underlying mechanisms are not completely understood. Mineralocorticoid receptors (MR) may contribute to oxidative stress and arterial stiffness in healthy older adults. To test the hypothesis that short-term MR blockade may reduce oxidative stress and improve arterial stiffness, we conducted a randomized, double blind, crossover study using the selective MR blocker Eplerenone or placebo in 23 older adults (age, 64±1 years; mean±SE) free from overt cardiovascular and other clinical disease (e.g, diabetes, renal and liver disease). In response to MR blockade, brachial and carotid blood pressure decreased (P?0.01). However, MR blockade had no effect on oxidative stress (oxidized LDL, 61.2±6.8 vs. 62.4±7.4 U/L, P=0.9; placebo vs. Eplerenone) and arterial stiffness (aortic pulse wave velocity (PWV), 9.17±1.19 vs. 8.92±1.19 m/s, P=0.5; leg PWV, 13.45±0.45 vs. 12.81±0.47 m/s, P=0.3; arm PWV, 11.43±0.62 vs. 11.73±0.68 m/s, P=0.7; carotid artery compliance, 0.150±0.013 vs. 0.149±0.014 mm(2)/mmHg, P=0.8; distensibility, 23.1±1.8 vs. 23.3±1.7 10(-3)/kPa, P=0.8; ? stiffness index, 3.5±0.3 vs. 3.6±0.3, P=0.6; and augmentation index, 16.0±2.2 vs. 15.6±2.8%, P=0.8). These results provide the first evidence that MR do not appear to contribute to oxidative stress in human aging and that short-term MR blockade does not result in reduced oxidative stress and improved arterial stiffness. PMID:23707930

Hwang, Moon-Hyon; Yoo, Jeung-Ki; Luttrell, Meredith; Kim, Han-Kyul; Meade, Thomas H; English, Mark; Nichols, Wilmer W; Christou, Demetra D

2013-08-01

311

On the geometry of stiff knots  

NASA Astrophysics Data System (ADS)

We analyse the geometry of a thin knotted string with bending rigidity. Two types of geometric properties are investigated. First, following the approach of von der Mosel [H. von der Mosel, Asymptotic Anal. 18, 49 (1998)], we derive upper bounds for the multiplicity of crossings and braids. Then, using a general inequality for the length of 3D curves derived by Chakerian [G.D. Chakerian, Proc. of the American Math. Soc. 15, 886 (1964)], we analyze the size and confinement of a knot

Pierre-Louis, O.

2009-09-01

312

A new technique for cerebral angiography: the variable stiffness guidewire.  

PubMed

Cerebral angiography can be performed with either a small-diameter, thin-walled catheter, or with a larger catheter using the "headhunter" technique. However, neither of these methods is satisfactory for catheterizing tortuous or angular arteries. The author has developed a variable stiffness guidewire (VSGW), which uses a small catheter and enables the neuroradiologist to catheterize tortuous arteries. The VSGW can be changed from flexible to stiff and back again while in the artery. New angiographic techniques based on four simple catheter curves are described. Using these techniques, the author has achieved an overall success rate of 98%. PMID:7352223

Willson, J K

1980-02-01

313

Thermal Testing of Tow-Placed, Variable Stiffness Panels  

NASA Technical Reports Server (NTRS)

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

Wu, K. Chauncey; Guerdal, Zafer

2001-01-01

314

Perception of Stiffness in Laparoscopy - the Fulcrum Effect  

PubMed Central

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

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

2014-01-01

315

Force volume and stiffness tomography investigation on the dynamics of stiff material under bacterial membranes.  

PubMed

The determination of the characteristics of micro-organisms in clinical specimens is essential for the rapid diagnosis and treatment of infections. A thorough investigation of the nanoscale properties of bacteria can prove to be a fundamental tool. Indeed, in the latest years, the importance of high resolution analysis of the properties of microbial cell surfaces has been increasingly recognized. Among the techniques available to observe at high resolution specific properties of microscopic samples, the Atomic Force Microscope (AFM) is the most widely used instrument capable to perform morphological and mechanical characterizations of living biological systems. Indeed, AFM can routinely study single cells in physiological conditions and can determine their mechanical properties with a nanometric resolution. 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 the capabilities and peculiarities of AFM to analyze the mechanical properties of Escherichia coli in order to evidence with a high spatial resolution the mechanical properties of its structure. In particular, we will show that the bacterial membrane is not mechanically uniform, but contains stiffer areas. The force volume investigations presented in this work evidence for the first time the presence and dynamics of such structures. Such information is also coupled with a novel stiffness tomography technique, suggesting the presence of stiffer structures present underneath the membrane layer that could be associated with bacterial nucleoids. PMID:22528189

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

2012-05-01

316

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

PubMed

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

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

2006-01-01

317

Elastic stiffness of single-crystalline FeSe measured by picosecond ultrasonics  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

318

Computational methods for the identification of spatially varying stiffness and damping in beams  

NASA Technical Reports Server (NTRS)

A numerical approximation scheme for the estimation of functional parameters in Euler-Bernoulli models for the transverse vibration of flexible beams with tip bodies is developed. The method permits the identification of spatially varying flexural stiffness and Voigt-Kelvin viscoelastic damping coefficients which appear in the hybrid system of ordinary and partial differential equations and boundary conditions describing the dynamics of such structures. An inverse problem is formulated as a least squares fit to data subject to constraints in the form of a vector system of abstract first order evolution equations. Spline-based finite element approximations are used to finite dimensionalize the problem. Theoretical convergence results are given and numerical studies carried out on both conventional (serial) and vector computers are discussed.

Banks, H. T.; Rosen, I. G.

1986-01-01

319

Asymptotic coefficients for one-interacting-level Voigt profiles  

NASA Astrophysics Data System (ADS)

The asymptotic behavior of general Voigt profiles with general width and shift functions has been determined by Cope and Lovett (1987). The resulting asymptotic coefficients are functions of the perturber/radiator mass ratio; also, the coefficients for the one-interacting-level (OIL) profiles proposed by Ward et al. (1974) were studied. In this paper, the behavior of the OIL asymptotic coefficients for large mass ratio values is determined, thereby providing a complete picture of OIL asymptotics for all mass ratios.

Cope, D.; Lovett, R. J.

1988-02-01

320

Stability of constant coefficient linear singular systems with delay  

Microsoft Academic Search

In this paper, the general class of singular systems with delay and linear constant coefficient singular systems with delay are discussed. First, several definitions of stability are presented for singular systems with delay, and general sufficient stability conditions and instability conditions are obtained. Second, stability and instability are analyzed for linear constant coefficient singular systems with delay.

Yuanqing Li; Weizheng Feng; Yongqing Liu

2000-01-01

321

Second-order bounds for linear recurrences with negative coefficients  

NASA Astrophysics Data System (ADS)

This paper introduces a generalization of Fibonacci and Pell polynomials in order to obtain optimal second-order bounds for general linear recurrences with negative coefficients. An important aspect of the derived bounds is that they are applicable and easily computable. The results imply bounds on all entries in inverses of triangular matrices as well as on coefficients of reciprocals of power series.

Berenhaut, Kenneth S.; Morton, Daniel C.

2006-02-01

322

Actions of selected cardiovascular hormones on arterial stiffness and wave reflections.  

PubMed

The large conduit arteries of the thorax and abdomen are elastic while those in the arms and legs are muscular. Alterations in wall properties of elastic arteries occur over time and are usually permanent in nature; acute changes can, however, occur is response to a change in transmural pressure. Chronic alterations in properties of muscular arteries are minimal but changes (e.g vasoconstriction, vasodilation or tone) do occur in response to smooth muscle cell (SMC) stimulation. In general an increase in arterial stiffness (and wave reflection) increases systolic blood pressure (BP) and is detrimental while a decrease is beneficial. The augmentation in systolic BP increases left ventricular (LV) mass, wasted energy, tension-time index (TTI) and myocardial oxygen demand while the fall in diastolic BP decreases coronary artery perfusion causing a mismatch in ventricular/vascular coupling and an imbalance in the myocardial oxygen supply/demand ratio. Cardiovascular hormones such as renin, angiotensin, aldosterone, parathormone, sympathomimetic amines and endothelin induce vasoconstriction and increase arterial stiffness while insulin, thyroxine, testosterone, atrial natriuretic peptide (ANP), estrogen and nitric oxide (NO) have the opposite effect. The undesirable effects can be reversed with selected blocking agents. Vasodilator drugs have little direct active effect on large elastic arteries and unaugmented BP but can markedly reduce wave reflection amplitude and duration and augmentation index by decreasing stiffness of the muscular arteries and reducing transmission velocity of the reflected wave from the periphery to the heart. This decrease in amplitude and increase in travel time (or delay) of the reflected wave causes a generalized decrease in systolic BP, arterial wall stress, wasted LV energy and TTI. PMID:19149620

Nichols, Wilmer W; Epstein, Benjamin J

2009-01-01

323

The Effects of Massage on Pain, Stiffness, and Fatigue Levels Associated with Ankylosing Spondylitis: A Case Study  

PubMed Central

Objectives: To study the effects of massage on pain, stiffness, and fatigue in a patient recently diagnosed with ankylosing spondylitis (AS). Methods: A 47-year-old woman with AS diagnosed 11 months earlier received 7 massages across a 28-day period. Her pain, stiffness, and fatigue were recorded using visual analogue scales daily during the study period. Spinal mobility was measured at each massage session with finger-to-floor measurements for both forward and lateral flexion. The client also used a daily journal to supply pertinent information on quality of life. Results: Improvement was recorded in all dependent variables, with stiffness intensity showing the greatest improvement, to a final value of 0.75 from an initial value of 5. Duration of stiffness also showed improvement, to a final value of 1.2 from an initial value of 3.5. Improvement was also found in general pain (final value: 1; initial value: 4), fatigue (final value: 1.5; initial value 5), and forward and lateral flexion (forward flexion distance—final: 4 inches; initial: 6 inches; lateral flexion, left distance: final, 16.5 inches; initial, 21 inches; right distance: final, 16.5 inches; initial, 20.5 inches). Conclusions: Massage shows promise as a treatment for symptoms associated with AS. Further study is needed to validate these effects and to determine the feasibility of massage as an adjunct to standard care for AS patients with mild-to-moderate symptoms of AS.

Chunco, Rosemary

2011-01-01

324

Flexural stiffnesses of and dimensional stability in circular quasi-isotropic laminate mirrors  

NASA Astrophysics Data System (ADS)

Composite fiber reinforced plastics are being given favorable consideration for emerging applications in large aperture telescopes, such as the Hubble telescope or communication dishes. Many lightweight mirror fabrication concepts are currently being pursued. Presently, the technology is limited because it has an incomplete understanding of the mechanics associated with quasi-isotropic laminates for diffraction-limited displacement constraints, and lack of understanding for effects of resin buffer layers on composite mirrors for high surface smoothness. In this dissertation document, radial stiffness associated with stacking sequence effects in quasi-isotropic laminates (pi/n, where n=3, 4, and 6) and dimensional stability in the composite laminates are investigated numerically. The numerical results show that directional dependency of flexural stiffness in the laminates, which is strongly associated with stacking sequences, is a significant factor causing unfavorable sinusoidal surface waviness. The maximum radial flexural stiffness variation is found as +/-12.85% in pi/3 laminate while a minimum of +/-5.63% is found in pi/4 laminate. Mechanics of maximum asymmetry by +/-2º misorientation based on ideal pi/n laminate lay-ups are evaluated and the results are compared with ideal lay-up sequence cases. The calculated extensional and flexural stiffness values from the maximum asymmetric cases are within less than 0.05%. As such, the radial flexural stiffness variations in quasi-isotropic laminates are shown to be more problematic than asymmetry caused by common manufacturing variance. The types of surface deformations in quasi-isotropic laminates associated with directional dependency of flexural stiffness are evaluated using finite element analyses. Also, fiber print-through in replicated composite mirrors and the effects of the resin buffer layer present in the mirrors for mitigation of the fiber print-through are investigated and discussed. Numerical results reveal that there will be an unfavorable sinusoidal surface deformation in each ideal p/n laminate and the shapes are strongly associated with principal fiber directions due to stacking sequence effects. The surface deformations in quasi-isotropic laminates are shown to be typical and such surface deformations are inevitable when composite mirrors are fabricated from discrete layers of anisotropic carbon fiber reinforced plastics. Moreover, the use of additional resin layers appears to more adversely influence the composite mirror substrates. The validation of predicted surface deformations and dimensional distortions are achieved by comparing experimental results on a 8-inch-diameter composite mirror sample fabricated at the University of Kansas Dept. of Aerospace Engineering (KUAE) and Bennett Optical Research (BOR). A study of quasi-homogeneous materials such as short fiber products as alternative composite materials is investigated. Furthermore, the relation between resin property effects and corresponding resin thickness effects is evaluated and discussed. The analyses provide information on alternative types of materials that primarily affect optical performance and thus are most important for precision optics. Based on the results, locally varying radial surface deformations in quasi-isotropic laminates fabricated from continuous fiber reinforced plastics distort optical performance. These surface deformations might be eliminated by utilizing short fiber materials and a soft resin system with a very low coefficient of thermal expansion compared to conventional resins.

Kim, Kyung-Pyo

325

Torsion Stiffness of a Protein Pair Determined by Magnetic Particles  

PubMed Central

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

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

2011-01-01

326

Identification of Contact Parameters from Stiff Multipoint Contact Robotic Operations  

Microsoft Academic Search

Computer simulations play an important role in the design and validation of constrained robotic operations. The fidelity of these simulations, however, depends on the specification of contact dynamics parameters, which often need to be determined experimentally. In this paper we investigate the identification of contact parameters from complex stiff multi-point contact scenarios encountered in typical robotic operations using a recently

Diederik Verscheure; Inna Sharf; Herman Bruyninckx; Jan Swevers; Joris De Schutter

2010-01-01

327

Variable stiffness and damping suspension system for train  

NASA Astrophysics Data System (ADS)

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

Sun, Shuaishuai; Deng, Huaxia; Li, Weihua

2014-03-01

328

Simultaneously high stiffness and damping in nanoengineered microtruss composites.  

PubMed

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

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

2014-04-22

329

Study of stiff converging problems in magnetic field calculation  

SciTech Connect

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

Golbazi, M.A.

1985-01-01

330

Variable Stiffness Spar Wind-Tunnel Model Development and Testing  

NASA Technical Reports Server (NTRS)

The concept of exploiting wing flexibility to improve aerodynamic performance was investigated in the wind tunnel by employing multiple control surfaces and by varying wing structural stiffness via a Variable Stiffness Spar (VSS) mechanism. High design loads compromised the VSS effectiveness because the aerodynamic wind-tunnel model was much stiffer than desired in order to meet the strength requirements. Results from tests of the model include stiffness and modal data, model deformation data, aerodynamic loads, static control surface derivatives, and fuselage standoff pressure data. Effects of the VSS on the stiffness and modal characteristics, lift curve slope, and control surface effectiveness are discussed. The VSS had the most effect on the rolling moment generated by the leading-edge outboard flap at subsonic speeds. The effects of the VSS for the other control surfaces and speed regimes were less. The difficulties encountered and the ability of the VSS to alter the aeroelastic characteristics of the wing emphasize the need for the development of improved design and construction methods for static aeroelastic models. The data collected and presented is valuable in terms of understanding static aeroelastic wind-tunnel model development.

Florance, James R.; Heeg, Jennifer; Spain, Charles V.; Ivanco, Thomas G.; Wieseman, Carol D.; Lively, Peter S.

2004-01-01

331

Determination of a Large Tilting Pad Thrust Bearing Angular Stiffness  

Microsoft Academic Search

A finite difference procedure to solve the Reynolds’ and energy equations for the pressure and temperature distribution across the film is described. The film temperature takes viscosity variation and hot oil carryover into consideration. A coupled finite element method using ANSYS determines the important pad deformation. Torques for pad positions 1and 2 are calculated. The angular stiffness pertaining to the

D. V. Srikanth; Kaushal K. Chaturvedi; A. Chenna Kesava Reddy

332

Modeling of laminated rubber bearings using an analytical stiffness matrix  

Microsoft Academic Search

In this paper from Haringx’s theory, which considers lateral displacement and rotation angle in a rubber column as two independent variables, the mechanical behaviors of the column are analyzed. A 4×4 analytical stiffness matrix of the rubber column is obtained from a closed form solution, which is derived in the article. Then rigid body motion relations are used to transfer

Cheng-Hsiung Chang

2002-01-01

333

Acoustic trauma causes reversible stiffness changes in auditory sensory cells  

Microsoft Academic Search

A common cause of hearing impairment is exposure to loud noise. Recent research has demonstrated that the auditory mechanosensory cells are essential for normal hearing sensitivity and frequency selectivity. However, little is known about the effect of noise exposure on the mechanical properties of the auditory sensory cells. Here we report a significant reduction in the stiffness and cell length

E Chan; A Suneson; M Ulfendahl

1998-01-01

334

GEOMETRIC STIFFNESS AND STABILITY OF RIGID BODY MODES  

Microsoft Academic Search

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

H. El-Absy; A. A. Shabana

1997-01-01

335

Can arterial stiffness parameters be measured in the sitting position?  

Microsoft Academic Search

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

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

2011-01-01

336

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

337

Arterial stiffness in chronic kidney disease: causes and consequences  

Microsoft Academic Search

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

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

2010-01-01

338

Independent inverse relationship between serum lycopene concentration and arterial stiffness  

Microsoft Academic Search

ObjectiveEmerging evidence suggests a role of lycopene in the primary prevention of cardiovascular disease. This study aimed to investigate the association of serum lycopene concentration with brachial-ankle pulse wave velocity (baPWV), a marker of arterial stiffness and markers of oxidative stress and inflammation.

Oh Yoen Kim; Hyun Yang Yoe; Hyae Jin Kim; Ju Yeon Park; Ji Young Kim; Sang-Hak Lee; Jin Hee Lee; Kang Pyo Lee; Yangsoo Jang; Jong Ho Lee

2010-01-01

339

Riparian Sediment Delivery Ratio: Stiff Diagrams and Artifical Neural Networks  

EPA Science Inventory

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

340

INTERIOR VIEW WITH STIFF LEG LADLE CRANE OPERATOR, LUKE WALKER, ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

INTERIOR VIEW WITH STIFF LEG LADLE CRANE OPERATOR, LUKE WALKER, POURING OFF SLAG FROM LADLE AS SKIMMER, BRUCE ELLIOTT, RAKES THE SLAG FROM THE MOLTEN METAL. - American Cast Iron Pipe Company, Mixer Building, 1501 Thirty-first Avenue North, Birmingham, Jefferson County, AL

341

A STIFF COLLAR FOR THE TREATMENT OF RHEUMATOID ATLANTOAXIAL SUBLUXATION  

Microsoft Academic Search

SUMMARY Conservative treatment of atlantoaxial subluxation (AAS) has tended to be rather passive, since there has been a lack of effective tools. The stabilizing effect of a stiff collar in the treatment of AAS was evaluated. Fifty successive rheumatoid patients with unstable AAS were interviewed and examined clinically. Lateral view radiographs of the cervical spine were taken in neutral position,

M. KAUPPI; P. ANTTILA

1996-01-01

342

Altered diastolic function and aortic stiffness in Alzheimer's disease  

PubMed Central

Background Alzheimer’s disease (AD) is closely linked to cardiovascular risk factors. Methods Echocardiographic studies were performed, including left ventricular diastolic functions, left and right atrial conduction times, and arterial stiffness parameters, namely stiffness index, pressure-strain elastic modulus, and distensibility, on 29 patients with AD and 24 age-matched individuals with normal cognitive function. Results The peak mitral flow velocity of the early rapid filling wave (E) was lower, and the peak velocity of the late filling wave caused by atrial contraction (A), deceleration time of peak E velocity, and isovolumetric relaxation time were higher in the AD group. The early myocardial peak (Ea) velocity was significantly lower in AD patients, whereas the late diastolic (Aa) velocity and E/Ea ratio were similar between the two groups. In Alzheimer patients, stiffness index and pressure-strain elastic modulus were higher, and distensibility was significantly lower in the AD group compared to the control. Interatrial electromechanical delay was significantly longer in the AD group. Conclusion Our findings suggest that patients with AD are more likely to have diastolic dysfunction, higher atrial conduction times, and increased arterial stiffness compared to the controls of same sex and similar age.

Cal?k, Ali Nazmi; Ozcan, Kaz?m Serhan; Yuksel, Gulbun; Gungor, Bar?ss; Arugarslan, Emre; Varlibas, Figen; Ekmekci, Ahmet; Osmonov, Damirbek; Tatl?su, Mustafa Adem; Karaca, Mehmet; Bolca, Osman; Erdinler, Izzet

2014-01-01

343

Localization transition of stiff directed lines in random media  

NASA Astrophysics Data System (ADS)

We investigate the localization of stiff directed lines with bending energy by a short-range random potential. Using perturbative arguments, Flory arguments, and a replica calculation, we show that a stiff directed line in 1+d dimensions undergoes a localization transition with increasing disorder for d>2/3. We demonstrate that this transition is accessible by numerical transfer matrix calculations in 1+1 dimensions and analyze the properties of the disorder-dominated phase. On the basis of the two-replica problem, we propose a relation between the localization of stiff directed lines in 1+d dimensions and of directed lines under tension in 1+3d dimensions, which is strongly supported by identical free energy distributions. This shows that pair interactions in the replicated Hamiltonian determine the nature of directed line localization transitions with consequences for the critical behavior of the Kardar-Parisi-Zhang (KPZ) equation. Furthermore, we quantify how the persistence length of the stiff directed line is reduced by disorder.

Boltz, Horst-Holger; Kierfeld, Jan

2012-12-01

344

Haptic stiffness identification by veterinarians and novices: A comparison  

Microsoft Academic Search

Palpation is important in both veterinary and medical health professions. It is however difficult to learn, teach and assess. More must be understood about the skills involved in palpation. The present study compares the ability of practicing veterinarians and veterinary students to identify stiffness values. An absolute identification paradigm was used where a force-feedback device rendered virtual surfaces with 5

Neil Forrest; Sarah Baillie; Hong Z. Tan

2009-01-01

345

Stiffness gradients in vascular bundles of the palm Washingtonia robusta  

PubMed Central

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

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

2008-01-01

346

Stiffness gradients in vascular bundles of the palm Washingtonia robusta.  

PubMed

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

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

2008-10-01

347

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

348

Liver Stiffness Measurement by Transient Elastography in Clinical Practice  

Microsoft Academic Search

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

Ioan Sporea; Alexandra Deleanu; Alina Popescu; Marioara Cornianu

349

Sound insulating element featuring high stiffness and low weight  

Microsoft Academic Search

This paper describes a new approach to the problem of combining good sound insulation with high stiffness, low weight and limited thickness. A typical application is shipboard partitions where weight and thickness are essential cost factors and where specified demands on sound insulation are made at an increasing rate. A single leaf wall will as we know under favorable conditions

S. Einarsson; J. Soederquist

1982-01-01

350

Hyperbolic conservation laws with stiff relaxation terms and entropy  

Microsoft Academic Search

We study the limiting behavior of systems of hyperbolic conservation lawswith stiff relaxation terms. Reduced systems, inviscid and viscous local conservationlaws, and weakly nonlinear limits are derived through asymptotic expansions.An entropy condition is introduced for N \\\\Theta N systems that ensuresthe hyperbolicity of the reduced inviscid system. The resulting characteristicspeeds are shown to be interlaced with those of the original

Gui-Qiang Chen; C. David Levermore; Tai-Ping Liu

1994-01-01

351

Usability of photoplethysmography method in estimation of conduit artery stiffness  

NASA Astrophysics Data System (ADS)

Three channel photoplethysmography (PPG) signal waveform studies of leg conduit arteries during a provocative occlusion test were performed. PPG waveform second derivative amplitude ratio and arterial pulse wave velocity values showed significant correlations with ultrasound (US) reference method of local and regional arterial stiffness (AS), showing the ability to use PPG for AS change quantitative assessment.

Grabovskis, A.; Marcinkevics, Z.; Lukstina, Z.; Majauska, M.; Aivars, J.; Lusa, V.; Kalinina, A.

2011-06-01

352

Gauss-Seidel iteration for stiff ODEs from chemical kinetics  

Microsoft Academic Search

A simple Gauss-Seidel technique is proposed which exploits the special form of the chemicalkinetics equations. Classical Aitken extrapolation is applied to accelerate convergence. Thetechnique is meant for implementation in stiff solvers that are used in long range transportair pollution codes using operator splitting. Splitting necessarily gives rise to a great deal ofintegration restarts. Because the Gauss-Seidel iteration works matrix free,

J. G. Verwer

1994-01-01

353

Substrate stiffness affects skeletal myoblast differentiation in vitro  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

354

Method of measurement of optical cable stiffness at low temperatures  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

355

TUNNELING IN LOOSELY CEMENTED SAND LAYER \\/ STIFF CLAY -- LANTAN TUNNEL  

Microsoft Academic Search

The essential factor to successful conduct tunneling in loosely cemented sand layer \\/ stiff clay is to sustain the inherent strength of the surrounding rock after excavation. To achieve this goal, an effective support system must be installed timely so as to confine the convergence of the tunnel as much as possible. A successful case history of tunneling in weak

Chi Tso Chang; Hong Shiang Liu

356

Torsional Directed Walks, Entropic Elasticity, and DNA Twist Stiffness  

Microsoft Academic Search

DNA and other biopolymers differ from classical polymers because of their torsional stiffness. This property changes the statistical character of their conformations under tension from a classical random walk to a problem we call the ``torsional directed walk.'' Motivated by a recent experiment on single lambda-DNA molecules [Strick, T. R., Allemand, J.-F., Bensimon, D., Bensimon, A. & Croquette, V. (1996)

J. David Moroz; Philip Nelson

1997-01-01

357

Statistical Inference for Coefficient Alpha  

Microsoft Academic Search

Rigorous comparison of the reliability coefficients of several tests or measurement procedures requires a sampling theory for the coefficients. This paper sum marizes the important aspects of the sampling theory for Cronbach's (1951) coefficient alpha, a widely used internal consistency coefficient. This theory enables researchers to test a specific numerical hypothesis about the population alpha and to obtain confidence intervals

Leonard S. Feldt; David J. Woodruff; Fathi A. Salih

1987-01-01

358

Matrices of Physiologic Stiffness Potently Inactivate Idiopathic Pulmonary Fibrosis Fibroblasts  

PubMed Central

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

Marinkovic, Aleksandar; Liu, Fei

2013-01-01

359

When Should Epidemiologic Regressions Use Random Coefficients?  

Microsoft Academic Search

SUMMARY. Regression models with random coefficients arise naturally in both frequentist and Bayesian approaches to estimation problems. They are becoming widely available in standard computer packages under the headings of generalized linear mixed models, hierarchical models, and multilevel models. I here argue that such models offer a more scientifically defensible framework for epidemiologic analysis than the fixed-effects models now prevalent

Sander Greenland

2000-01-01

360

The Transport Coefficients  

NASA Astrophysics Data System (ADS)

In this section we wish to give a detailed account of all the transport coefficients related to the vectorial fluxes discussed in the previous chapters. These are the mass flux Ja (=-Jb ), the corresponding charge flux or electrical current Jc , closely related to Ja , and J^'q the heat flux. In every case the magnetic field is chosen as the direction of the z-axis, B=Bhat{k} so that for any vector, its different components respect to B will follow from the decomposition illustrated in Fig. (4.1).

García-Colín, Leopoldo S.; Dagdug, Leonardo

361

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

PubMed Central

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

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

2006-01-01

362

Associations of endothelial dysfunction and arterial stiffness with intradialytic hypotension and hypertension.  

PubMed

Intradialytic hypotension and hypertension are both independently associated with mortality among persons with end-stage renal disease on hemodialysis. Endothelial dysfunction and arterial stiffness are two possible mechanisms underlying these phenomena, but their association with hemodynamic instability during dialysis has not been evaluated. Thirty patients were recruited from chronic dialysis units at San Francisco General Hospital and San Francisco Veterans Affairs Medical Center. Endothelial dysfunction was assessed with flow-mediated dilation of the brachial artery after upper arm occlusion. Arterial stiffness was assessed using carotid-femoral pulse wave velocity measured by tonometry. Intradialytic hypotension and hypertension were defined as the average decrease in systolic blood pressure (SBP) over 1 week, as well as the frequency over 1 month of hypotension or hypertension. Every 5% decrease in flow-mediated dilation was associated with a 7.5 mmHg decrease in SBP after adjustment for phosphorus, body mass index, atherosclerosis, and ultrafiltration (P=0.02). Every 5 m/s increase in pulse wave velocity was associated with an 8 mmHg increase in SBP after adjustment for predialysis SBP and ultrafiltration (P=0.03). Over 1 month, every 5% lower flow-mediated dilation was associated with a 10% higher frequency of hypotension (P=0.09), and every 5 m/s increase in pulse wave velocity was associated with an 15% higher frequency of hypertension (P=0.02). In a cross-sectional analysis of 30 dialysis patients, endothelial dysfunction and arterial stiffness were independently associated with intradialytic hypotension and intradialytic hypertension, respectively. Elucidating these potential mechanisms of hemodynamic instability during dialysis may facilitate development of treatment strategies specific to this pathophysiology. PMID:21658174

Dubin, Ruth; Owens, Christopher; Gasper, Warren; Ganz, Peter; Johansen, Kirsten

2011-07-01

363

Zero finite-temperature charge stiffness within the half-filled 1D Hubbard model  

SciTech Connect

Even though the one-dimensional (1D) Hubbard model is solvable by the Bethe ansatz, at half-filling its finite-temperature T>0 transport properties remain poorly understood. In this paper we combine that solution with symmetry to show that within that prominent T=0 1D insulator the charge stiffness D(T) vanishes for T>0 and finite values of the on-site repulsion U in the thermodynamic limit. This result is exact and clarifies a long-standing open problem. It rules out that at half-filling the model is an ideal conductor in the thermodynamic limit. Whether at finite T and U>0 it is an ideal insulator or a normal resistor remains an open question. That at half-filling the charge stiffness is finite at U=0 and vanishes for U>0 is found to result from a general transition from a conductor to an insulator or resistor occurring at U=U{sub c}=0 for all finite temperatures T>0. (At T=0 such a transition is the quantum metal to Mott–Hubbard-insulator transition.) The interplay of the ?-spin SU(2) symmetry with the hidden U(1) symmetry beyond SO(4) is found to play a central role in the unusual finite-temperature charge transport properties of the 1D half-filled Hubbard model. -- Highlights: •The charge stiffness of the half-filled 1D Hubbard model is evaluated. •Its value is controlled by the model symmetry operator algebras. •We find that there is no charge ballistic transport at finite temperatures T>0. •The hidden U(1) symmetry controls the U=0 phase transition for T>0.

Carmelo, J.M.P., E-mail: carmelo@fisica.uminho.pt [Center and Department of Physics, University of Minho, Campus Gualtar, P-4710-057 Braga (Portugal) [Center and Department of Physics, University of Minho, Campus Gualtar, P-4710-057 Braga (Portugal); Beijing Computational Science Research Center, Beijing 100084 (China); Institut für Theoretische Physik III, Universität Stuttgart, D-70550 Stuttgart (Germany); Gu, Shi-Jian [Beijing Computational Science Research Center, Beijing 100084 (China) [Beijing Computational Science Research Center, Beijing 100084 (China); Department of Physics and ITP, Chinese University of Hong Kong, Hong Kong (China); Sacramento, P.D. [CFIF, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal) [CFIF, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Beijing Computational Science Research Center, Beijing 100084 (China)

2013-12-15

364

Applanation tonometry in mice: a novel noninvasive technique to assess pulse wave velocity and arterial stiffness.  

PubMed

Arterial stiffening is the root cause of a range of cardiovascular complications, including myocardial infarction, left ventricular hypertrophy, stroke, renal failure, dementia, and death, and a hallmark of the aging process. The most important in vivo parameter of arterial stiffness is pulse wave velocity (PWV). Clinically, PWV is determined noninvasively using applanation tonometry. Unlike the clinical value of arterial stiffness and PWV, techniques to determine PWV in mice are scarce. The only way to determine aortic PWV noninvasively in the mouse is by using ultrasound echo Doppler velocimetry. It is a fast, efficient, and accurate technique, but the required tools are expensive and technically complex. Here, we describe the development and validation of a novel technique to assess carotid-femoral PWV noninvasively in mice. This technique is based on applanation tonometry as used clinically. We were able to establish a reproducible reference value in wild-type mice (3.96±0.05 m/s) and to detect altered carotid-femoral PWV values in endothelial nitric oxide synthase knockout mice (4.66±0.05 m/s; P<0.001 compared with control), and in mice sedated with sodium pentobarbital (2.89±0.17 m/s; P<0.001 compared with control). Also, carotid-femoral PWV was pharmacologically modulated and measured in a longitudinal experiment with endothelial nitric oxide synthase knockout mice to demonstrate the applicability of this technique. In general, applanation tonometry can be used to measure carotid-femoral PWV noninvasively in mice. The experimental setup is simple, and the technical requirements are basic, making this technique readily implementable in any mouse model-based research facility interested in arterial stiffness. PMID:24752435

Leloup, Arthur J A; Fransen, Paul; Van Hove, Cor E; Demolder, Marc; De Keulenaer, Gilles W; Schrijvers, Dorien M

2014-07-01

365

STIFFNESS AND DAMPING FORCES IN THE INTERVERTEBRAL JOINTS OF BLUE MARLIN (MAKAIRA NIGRICANS)  

Microsoft Academic Search

Summary The stiffness and damping moments that are transmitted by intervertebral joints during sinusoidal bending were determined in the blue marlin, Makaira nigricans Lac6pede. Using a dynamic bending machine, the angular stiffness (Nmrad\\

JOHN H. LONG

366

On rotation distance between binary coupling trees and applications for 3 nj-coefficients  

Microsoft Academic Search

Generalized recoupling coefficients or 3nj-coefficients for a Lie algebra (with su(2), the Lie algebra for the quantum theory of angular momentum, as generic example) can always be expressed as multiple sums over products of Racah coefficients (i.e. 6j-coefficients). In general there exist many such expressions; we say that such an expression is optimal if the number of Racah coefficients in

V. Fack; S. Lievens; J. Van der Jeugt

1999-01-01

367

A recursive algorithm for evaluating Molodenskii-type truncation error coefficients at altitude  

NASA Astrophysics Data System (ADS)

A recursive method is derived for computing the Molodenskii truncation error coefficients at altitude for the altitude-generalized Stokes integral. Furthermore, the Cook truncation error coefficients at altitude corresponding to the generalized Vening-Meinesz integral are derived in terms of the Molodenskii coefficients. Also, the gravity disturbance truncation error coefficients at altitude are related to the Molodenskii coefficients. By combining these results, it is shown how the truncation error for the complete gravity disturbance vector at altitude may be computed recursively.

Shepperd, Stanley W.

1982-06-01

368

Relationship between markers of body fat and calcaneal bone stiffness differs between preschool and primary school children: results from the IDEFICS baseline survey.  

PubMed

The aim of this study was to investigate the relationship between markers of body fat and bone status assessed as calcaneal bone stiffness in a large sample of European healthy pre- and primary school children. Participants were 7,447 children from the IDEFICS study (spread over eight different European countries), age 6.1 ± 1.8 years (range 2.1-9.9), 50.5 % boys. Anthropometric measurements (weight, height, bioelectrical impedance, waist and hip circumference, and tricipital and subscapular skinfold thickness) as well as quantitative ultrasonographic measurements to determine calcaneal stiffness index (SI) were performed. Partial correlation analysis, linear regression analysis, and ANCOVA were stratified by sex and age group: preschool boys (n = 1,699) and girls (n = 1,599) and primary school boys (n = 2,062) and girls (n = 2,087). In the overall study population, the average calcaneal SI was equal to 80.2 ± 14.0, ranging 42.4-153. The results showed that preschool children with higher body fat had lower calcaneal SI (significant correlation coefficients between -0.05 and -0.20), while primary school children with higher body fat had higher calcaneal SI (significant correlation coefficients between 0.05 and 0.13). After adjusting for fat-free mass, both preschool and primary school children showed an inverse relationship between body fat and calcaneal stiffness. To conclude, body fat is negatively associated with calcaneal bone stiffness in children after adjustment for fat-free mass. Fat-free mass may confound the association in primary school children but not in preschool children. Muscle mass may therefore be an important determinant of bone stiffness. PMID:22907129

Sioen, Isabelle; Mouratidou, Theodora; Herrmann, Diana; De Henauw, Stefaan; Kaufman, Jean-Marc; Molnár, Dénes; Moreno, Luis A; Marild, Staffan; Barba, Gianvincenzo; Siani, Alfonso; Gianfagna, Francesco; Tornaritis, Michael; Veidebaum, Toomas; Ahrens, Wolfgang

2012-10-01

369

Huge Seebeck coefficients in nonaqueous electrolytes  

NASA Astrophysics Data System (ADS)

The Seebeck coefficients of the nonaqueous electrolytes tetrabutylammonium nitrate, tetraoctylphosphonium bromide, and tetradodecylammonium nitrate in 1-octanol, 1-dodecanol, and ethylene-glycol are measured in a temperature range from T = 30 °C to T = 45 °C. The Seebeck coefficient is generally of the order of a few hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here we report huge values of 7 mV/K at 0.1 M concentration for tetrabutylammonium nitrate in 1-dodecanol. These striking results open the question of unexpectedly large kosmotrope or ``structure making'' effects of tetraalkylammonium ions on the structure of alcohols.

Bonetti, M.; Nakamae, S.; Roger, M.; Guenoun, P.

2011-03-01

370

Stabilized multilevel Monte Carlo method for stiff stochastic differential equations  

SciTech Connect

A multilevel Monte Carlo (MLMC) method for mean square stable stochastic differential equations with multiple scales is proposed. For such problems, that we call stiff, the performance of MLMC methods based on classical explicit methods deteriorates because of the time step restriction to resolve the fastest scales that prevents to exploit all the levels of the MLMC approach. We show that by switching to explicit stabilized stochastic methods and balancing the stabilization procedure simultaneously with the hierarchical sampling strategy of MLMC methods, the computational cost for stiff systems is significantly reduced, while keeping the computational algorithm fully explicit and easy to implement. Numerical experiments on linear and nonlinear stochastic differential equations and on a stochastic partial differential equation illustrate the performance of the stabilized MLMC method and corroborate our theoretical findings.

Abdulle, Assyr, E-mail: assyr.abdulle@epfl.ch; Blumenthal, Adrian, E-mail: adrian.blumenthal@epfl.ch

2013-10-15

371

Force, Torque and Stiffness: Interactions in Perceptual Discrimination  

PubMed Central

Three experiments investigated whether force and torque cues interact in haptic discrimination of force, torque and stiffness, and if so, how. The statistical relation between force and torque was manipulated across four experimental conditions: Either one type of cue varied while the other was constant, or both varied so as to be positively correlated, negatively correlated, or uncorrelated. Experiment 1 showed that the subjects’ ability to discriminate force was improved by positively correlated torque but impaired with uncorrelated torque, as compared to the constant torque condition. Corresponding effects were found in Experiment 2 for the influence of force on torque discrimination. These findings indicate that force and torque are integrated in perception, rather than being processed as separate dimensions. A further experiment demonstrated facilitation of stiffness discrimination by correlated force and torque, whether the correlation was positive or negative. The findings suggest new means of augmenting haptic feedback to facilitate perception of the properties of soft objects.

Wu, Bing; Klatzky, Roberta L.; Hollis, Ralph L.

2011-01-01

372

Stiff filamentous virus translocations through solid-state nanopores.  

PubMed

The ionic conductance through a nanometer-sized pore in a membrane changes when a biopolymer slides through it, making nanopores sensitive to single molecules in solution. Their possible use for sequencing has motivated numerous studies on how DNA, a semi-flexible polymer, translocates nanopores. Here we study voltage-driven dynamics of the stiff filamentous virus fd with experiments and simulations to investigate the basic physics of polymer translocations. We find that the electric field distribution aligns an approaching fd with the nanopore, promoting its capture, but it also pulls fd sideways against the membrane after failed translocation attempts until thermal fluctuations reorient the virus for translocation. fd is too stiff to translocate in folded configurations. It therefore translocates linearly, exhibiting a voltage-independent mobility and obeying first-passage-time statistics. Surprisingly, lengthwise Brownian motion only partially accounts for the translocation velocity fluctuations. We also observe a voltage-dependent contribution whose origin is only partially determined. PMID:24932700

McMullen, Angus; de Haan, Hendrick W; Tang, Jay X; Stein, Derek

2014-01-01

373

Contact stiffness of layered materials for ultrasonic atomic force microscopy  

NASA Astrophysics Data System (ADS)

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. The algorithm converges into a couple of iterations and does not suffer from numerical convergence difficulties as does finite element analysis (FEA). In the ultrasonic frequency range, comparisons with Hertzian theory and FEA show the validity of the results in a quasistatic case. Definitions of the minimum detectable layer thickness and the penetration depth of the UAFM are given and evaluated for several thin film-substrate pairs. These results also show the potential of the method for modeling defects and power loss due to radiation in layered materials.

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

2000-05-01

374

Strong, tough and stiff bioinspired ceramics from brittle constituents  

NASA Astrophysics Data System (ADS)

High strength and high toughness are usually mutually exclusive in engineering materials. In ceramics, improving toughness usually relies on the introduction of a metallic or polymeric ductile phase, but this decreases the material’s strength and stiffness as well as its high-temperature stability. Although natural materials that are both strong and tough rely on a combination of mechanisms operating at different length scales, the relevant structures have been extremely difficult to replicate. Here, we report a bioinspired approach based on widespread ceramic processing techniques for the fabrication of bulk ceramics without a ductile phase and with a unique combination of high strength (470 MPa), high toughness (22 MPa m1/2), and high stiffness (290 GPa). Because only mineral constituents are needed, these ceramics retain their mechanical properties at high temperatures (600 °C). Our bioinspired, material-independent approach should find uses in the design and processing of materials for structural, transportation and energy-related applications.

Bouville, Florian; Maire, Eric; Meille, Sylvain; van de Moortèle, Bertrand; Stevenson, Adam J.; Deville, Sylvain

2014-05-01

375

Linear multistep methods applied to stiff initial value problems - A survey  

Microsoft Academic Search

The numerical approximation of solutions of differential equations has been and continues to be one of the principal concerns of numerical analysis. Linear multistep methods and, in particular, backward differentiation formulae (BDFs) are frequently used for the numerical integration of stiff initial value problems. Such stiff problems appear in a variety of applications.While the intuitive meaning of stiffness is clear

Gabriella Kirlinger

2004-01-01

376

Numerical Methods for Stiff Differential Equations - Getting the Power to the People.  

National Technical Information Service (NTIS)

The realization of problems associated with stiff differential equations (DE) is recalled. Stiffness and the so-called BDF methods (early found to be effective on stiff problems) are described. The ways in which these methods have achieved success are dis...

A. C. Hindmarsh

1979-01-01

377

Theoretical and Experimental Determination of the Stiffness Properties of a Capstan Drive  

Microsoft Academic Search

Wire capstan drives are used as rotary transmission elements for their very low (nominally zero) backlash and high stiffness properties. To obtain high stiffness, the cable is typically wrapped around the input and output drum in a figure-eight pattern multiple times. This stiffness can be determined by analyzing the amount of deformation between the cable and the drums and the

Jaime Werkmeister; Alexander Slocum

378

Stiffness and strength of fiber reinforced polymer composite bridge deck systems  

Microsoft Academic Search

This research investigates two principal characteristics that are of primary importance in Fiber Reinforced Polymer (FRP) bridge deck applications: STIFFNESS and STRENGTH. The research was undertaken by investigating the stiffness and strength characteristics of the multi-cellular FRP bridge deck systems consisting of pultruded FRP shapes. A systematic analysis procedure was developed for the stiffness analysis of multi-cellular FRP deck systems.

Aixi Zhou

2002-01-01

379

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

380

Optimal control of antagonistic muscle stiffness during voluntary movements  

Microsoft Academic Search

This paper presents a study on the control of antagonist muscle stiffness during single-joint arm movements by optimal control theory with a minimal effort criterion. A hierarchical model is developed based on the physiology of the neuromuscular control system and the equilibrium point hypothesis. For point-to-point movements, the model provides predictions on (1) movement trajectory, (2) equilibrium trajectory, (3) muscle

Ning Lan; Patrick E. Crago

1994-01-01

381

Ultrastrong, Stiff, and Lightweight Carbon-Nanotube Fibers  

Microsoft Academic Search

From the stone ages to modern history, new materials have often been the enablers of revolutionary technologies.(1) For a wide variety of envisioned applications in space exploration, energy-efficient aircraft, and armor, materials must be signifi- cantly stronger, stiffer, and lighter than what is currently available. Carbon nanotubes (CNTs) have extremely high strength,(2-5) very high stiffness,(6,7) low density, good chemical stability,

Xiefei Zhang; Qingwen Li; Terry G. Holesinger; Paul N. Arendt; Jianyu Huang; P. Douglas Kirven; Timothy G. Clapp; Raymond F. DePaula; Xiazhou Liao; Yonghao Zhao; Lianxi Zheng; Dean E. Peterson; Yuntian Zhu

2007-01-01

382

Surviving stiff-person syndrome: a case report  

Microsoft Academic Search

Stiff-person syndrome (SPS) is a rare condition of progressive muscular rigidity and spasm, frequently accompanied by other\\u000a autoimmune conditions, an association which has been further strengthened by the discovery of anti-GAD antibodies and the\\u000a response of SPS to immunotherapies. Intravenous immunoglobulin (IVIg) is the mainstay therapy. Because of the rarity of the\\u000a GAD antibody associated conditions, most of the information

Sharmilee Gnanapavan; Angela Vincent; Gavin Giovannoni

383

STIFF-INPLANE TILTROTOR AEROMECHANICS INVESTIGATION USING TWO MULTIBODY ANALYSES  

Microsoft Academic Search

This paper presents the development of two multibody dynami cs models to predict the whirl-flutter stability of a stiff-inplane tiltrotor wind-tunnel model and correlates the predic- tions with experimental data. Comprehensive, multibody-b ased dynamics analyses of rotorcraft enable modeling and simulation of the rotor system at a high l evel of detail so that complex mechanics and nonlinear effects associated

Jinwei Shen; Pierangelo Masarati; Beatrice Roget; David J. Piatak; Mark W. Nixon; Jeffrey D. Singleton

384

Anatomical basis of arthroscopic capsulotomy for elbow stiffness  

Microsoft Academic Search

Stiffness is a frequent condition in elbow pathologies, both traumatic and non-traumatic, and usually requires an operative\\u000a treatment including an anterior capsulotomy. Elbow arthroscopy is certainly an alternative to surgery, but the technique of\\u000a arthroscopic capsulotomy remains controversial. Our aim was to study the anterior elbow capsule anatomy to recommend an efficient\\u000a and safe arthroscopic capsulotomy. We dissected ten cadaveric

P. Thoreux; C. Blondeau; S. Durand; A. C. Masquelet

2006-01-01

385

Mesenchymal stem cell durotaxis depends on substrate stiffness gradient strength.  

PubMed

Mesenchymal stem cells (MSCs) respond to the elasticity of their environment, which varies between and within tissues. Stiffness gradients within tissues can result from pathological conditions, but also occur through normal variation, such as in muscle. MSC migration can be directed by shallow stiffness gradients before differentiating. Gradients with fine control over substrate compliance - both in range and rate of change (strength) - are needed to better understand mechanical regulation of MSC migration in normal and diseased states. We describe polyacrylamide stiffness gradient fabrication using three distinct systems, generating stiffness gradients of physiological (1 Pa/?m), pathological (10 Pa/?m), and step change (? 100Pa/?m) strength. All gradients spanned a range of physiologically relevant elastic moduli for soft tissues (1-12 kPa). MSCs migrated to the stiffest region on each gradient. Time-lapse microscopy revealed that migration velocity correlated directly with gradient strength. Directed migration was reduced in the presence of the contractile agonist lysophosphatidic acid (LPA) and cytoskeleton-perturbing drugs nocodazole and cytochalasin. LPA- and nocodazole-treated cells remained spread and protrusive on the substrate, while cytochalasin-treated cells did not. Nocodazole-treated cells spread in a similar manner to untreated cells, but exhibited greatly diminished traction forces. These data suggest that a functional actin cytoskeleton is required for migration whereas microtubules are required for directed migration. The data also imply that, in vivo, MSCs may preferentially accumulate in regions of high elastic modulus and make a greater contribution to tissue repairs in these locations. PMID:23390141

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

2013-04-01

386

Magnetic bearing stiffness control using frequency band filtering  

NASA Technical Reports Server (NTRS)

Active magnetic bearings can be implemented with frequency band-reject filtering that decreases the bearing stiffness and damping at a small bandwidth around a chosen frequency. The control scheme was used for reducing a rotor dynamic force, such as an imbalance force, transmitted to the bearing stator. The scheme creates additional system vibration modes at the same frequency. It also shows that the amount of force reduction is limited by the stability requirement of these modes.

Chen, H. Ming

1989-01-01

387

Smoking increases the cold pressor mediated arterial stiffness  

Microsoft Academic Search

Cigarette smoking is one of the major risk factors to cardiovascular diseases. To assess the changes of vascular stiffness by smoking, smoking (smoking index > 300) and non-smoking groups (n=20 each group, all male) were exposed to a cold pressor test (CPT; ice water hand immersion) and brachial and ankle blood pressure (Bp), ankle-brachial index (ABI), and brachial-ankle pulse wave

Atsushi Nishiyama; Yoshito Kurata; Osamu Niikawa; Hiroshi Mohri; Motoo Tsushima

2003-01-01

388

Mismatch between arterial stiffness increase and left ventricular diastolic dysfunction  

Microsoft Academic Search

Previous studies which included patients with preserved left ventricular (LV) systolic function demonstrated that arterial\\u000a stiffness progressively increased as LV diastolic function decreased. However, it was unknown whether this correlation was\\u000a still present in a heterogeneous study population involving patients with a wide range of LV systolic function. Seventy-five\\u000a patients with depressed LV systolic function were consecutively included and 192

Po-Chao Hsu; Tsung-Hsien Lin; Chee-Siong Lee; Hsiang-Chun Lee; Chun-Yuan Chu; Ho-Ming Su; Wen-Chol Voon; Wen-Ter Lai; Sheng-Hsiung Sheu

2010-01-01

389

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

Microsoft Academic Search

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

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

2010-01-01

390

Canonical Transformation for Stiff Matter Models in Quantum Cosmology  

NASA Astrophysics Data System (ADS)

In the present work we consider Friedmann-Robertson-Walker models in the presence of a stiff matter perfect fluid and a cosmological constant. We write the superhamiltonian of these models using the Schutz's variational formalism. We notice that the resulting superhamiltonians have terms that will lead to factor ordering ambiguities when they are written as quantum operators. In order to remove these ambiguities, we introduce appropriate coordinate transformations and prove that these transformations are canonical using the symplectic method.

Neves, C.; Monerat, G. A.; Corrêa Silva, E. V.; Ferreira Filho, L. G.; Oliveira-Neto, G.

2011-06-01

391

Stiffness measurement of eggshell by acoustic resonance and PLS models  

Microsoft Academic Search

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

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

2011-01-01

392

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

PubMed

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

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

2011-01-01

393

Bone Microarchitecture and Stiffness in Premenopausal Women with Idiopathic Osteoporosis  

PubMed Central

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

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

2009-01-01

394

On a high-potential variable flexural stiffness device  

NASA Astrophysics Data System (ADS)

There are great efforts in developing effective composite structures for lightweight constructions for nearly every field of engineering. This concerns for example aeronautics and spacecrafts, but also automotive industry and energy harvesting applications. Modern concepts of lightweight components try to make use of structures with properties which can be adjusted in a controllable was. However, classic composite materials can only slightly adapt to varying environmental conditions because most materials, like carbon or glass-fiber composites show properties which are time-constant and not changeable. This contribution describes the development, the potential and the limitations of novel smart, self-controlling structures which can change their mechanical properties - e.g. their flexural stiffness - by more then one order of magnitude. These structures use a multi-layer approach with a 10-layer stack of 0.75 mm thick polycarbonate. The set-up is analytically described and its mechanical behavior is predicted by finite element analysis done with ABAQUS. The layers are braided together by an array of shape memory alloy (SMA) wires, which can be activated independently. Depending on the temperature applied by the electrical current flowing through the wires and the corresponding contraction the wires can tightly clamp the layers so that they cannot slide against each other due to friction forces. In this case the multilayer acts as rigid beam with high stiffness. If the friction-induced shear stress is smaller than a certain threshold, then the layers can slide over each other and the multilayer becomes compliant under bending load. The friction forces between the layers and, hence, the stiffness of the beam is controlled by the electrical current through the wires. The more separate parts of SMA wires the structure has the larger is the number of steps of stiffness changes of the flexural beam.

Henke, Markus; Gerlach, Gerald

2013-05-01

395

Integration of chemical stiff ODEs using exponential propagation method  

Microsoft Academic Search

In this paper, we study the numerical long time integration of large stiff systems of differential equations arising from\\u000a chemical reactions by exponential propagation methods. These methods, which typically converge faster, use matrix-vector products\\u000a with the exponential or other related function of the Jacobian that can be effectively approximated by Krylov sabspace methods.\\u000a We equip these methods to an automatic

M. Falati; G. Hojjati

396

Compact, Stiff, Remotely-Actuable Quick-Release Clamp  

NASA Technical Reports Server (NTRS)

The present invention provides a clamp that is compact and lightweight, yet provides high holding strength and stiffness or rigidity. The clamp uses a unique double slant interface design which provides mechanical advantages to resist forces applied to the clamp member as the load increases. The clamp allows for rapid and remote-activated release of the clamp jaws by applying only a small operating force to an over-center lock/release mechanism, such as by pulling a manual tether.

Tsai, Ted W. (Inventor)

2000-01-01

397

Spurious Behavior of Shock-Capturing Methods: Problems Containing Stiff Source Terms and Discontinuities  

NASA Technical Reports Server (NTRS)

The goal of this paper is to relate numerical dissipations that are inherited in high order shock-capturing schemes with the onset of wrong propagation speed of discontinuities. For pointwise evaluation of the source term, previous studies indicated that the phenomenon of wrong propagation speed of discontinuities is connected with the smearing of the discontinuity caused by the discretization of the advection term. The smearing introduces a nonequilibrium state into the calculation. Thus as soon as a nonequilibrium value is introduced in this manner, the source term turns on and immediately restores equilibrium, while at the same time shifting the discontinuity to a cell boundary. The present study is to show that the degree of wrong propagation speed of discontinuities is highly dependent on the accuracy of the numerical method. The manner in which the smearing of discontinuities is contained by the numerical method and the overall amount of numerical dissipation being employed play major roles. Moreover, employing finite time steps and grid spacings that are below the standard Courant-Friedrich-Levy (CFL) limit on shockcapturing methods for compressible Euler and Navier-Stokes equations containing stiff reacting source terms and discontinuities reveals surprising counter-intuitive results. Unlike non-reacting flows, for stiff reactions with discontinuities, employing a time step and grid spacing that are below the CFL limit (based on the homogeneous part or non-reacting part of the governing equations) does not guarantee a correct solution of the chosen governing equations. Instead, depending on the numerical method, time step and grid spacing, the numerical simulation may lead to (a) the correct solution (within the truncation error of the scheme), (b) a divergent solution, (c) a wrong propagation speed of discontinuities solution or (d) other spurious solutions that are solutions of the discretized counterparts but are not solutions of the governing equations. The present investigation for three very different stiff system cases confirms some of the findings of Lafon & Yee (1996) and LeVeque & Yee (1990) for a model scalar PDE. The findings might shed some light on the reported difficulties in numerical combustion and problems with stiff nonlinear (homogeneous) source terms and discontinuities in general.

Yee, Helen M. C.; Kotov, D. V.; Wang, Wei; Shu, Chi-Wang

2013-01-01

398

Optimal design of variable-stiffness fiber-reinforced composites using cellular automata  

NASA Astrophysics Data System (ADS)

The growing number of applications of composite materials in aerospace and naval structures along with advancements in manufacturing technologies demand continuous innovations in the design of composite structures. In the traditional design of composite laminates, fiber orientation angles are constant for each layer and are usually limited to 0, 90, and +/-45 degrees. To fully benefit from the directional properties of composite laminates, such limitations have to be removed. The concept of variable-stiffness laminates allows the stiffness properties to vary spatially over the laminate. Through tailoring of fiber orientations and laminate thickness spatially in an optimal fashion, mechanical properties of a part can be improved. In this thesis, the optimal design of variable-stiffness fiber-reinforced composite laminates is studied using an emerging numerical engineering optimization scheme based on the cellular automata paradigm. A cellular automaton (CA) based design scheme uses local update rule for both field variables (displacements) and design variables (lay-up configuration and laminate density measure) in an iterative fashion to convergence to an optimal design. In the present work, the displacements are updated based on the principle of local equilibrium and the design variables are updated according to the optimality criteria for minimum compliance design. A closed form displacement update rule for constant thickness isotropic continua is derived, while for the general anisotropic continua with variable thickness a numeric update rule is used. Combined lay-up and topology design of variable-stiffness flat laminates is performed under the action of in-plane loads and bending loads. An optimality criteria based formulation is used to obtain local design rules for minimum compliance design subject to a volume constraint. It is shown that the design rule splits into a two step application. In the first step an optimal lay-up configuration is computed and in the second step the density measure is obtained. The spatial lay-up design problem is formulated using both fiber angles and lamination parameters as design variables. A weighted average formulation is used to handle multiple load case designs. Numerical studies investigate the performance of the proposed design methodology. The optimal lay-up configuration is independent of the lattice density with more details emerging as the density is increased. Moreover, combined topology and lay-up designs are free of checkerboard patterns. (Abstract shortened by UMI.)

Setoodeh, Shahriar

399

Mechanochemical model of cell migration on substrates of varying stiffness.  

PubMed

Cells propel themselves along a substrate by organizing structures at the leading edge called lamellipodia that contain the actin network, myosin, integrin, and other proteins. In this article, we describe a quantitative model that couples the response of stretch-sensitive proteins in the lamellipodia to the dynamics of the actin cytoskeleton, therefore allowing the cell to respond to different substrate stiffnesses. Using this model, we predict the various phases of dynamics possible, including continuous protrusion, unstable retractions leading to ruffling, and periodic protrusion-retraction cycles. We explain the necessary conditions for each type of migratory behavior to occur. In particular, we show that, for periodic protrusion-retraction cycles to occur, the stiffness of the substrate must be high, the myosin-dependent maturation rate of nascent to focal adhesions must be high, and the myosin-independent integrin activation rate must be low. In addition, we also predict the dynamics expected at a given substrate stiffness, leading to a quantitative explanation of experimental data that showed that periodic protrusion-retraction cycles disappear when cells are placed on soft substrates. We also suggest experiments with downregulating ? actinin and/or talin and upregulating p130Cas and make predictions on what types of migratory dynamics will be observed. PMID:22304116

Lai, Tanny; Chiam, K-H

2011-12-01

400

Role of Inflammation and Substrate Stiffness in Cancer Cell Transmigration  

NASA Astrophysics Data System (ADS)

Cancer metastasis, the ability for cancer cells to break away from the primary tumor site and spread to other organs of the body, is one of the main contributing factors to the deadliness of the disease. One of the rate-limiting steps in cancer metastasis that is not well understood is the adhesion of tumor cells to the endothelium followed by transmigration. Other factors include substrate stiffness and inflammation. To test these parameters, we designed an in vitro model of transendothelial migration. Our results suggest that cancer cell transmigration is a two-step process in which they first incorporate into the endothelium before migrating through. It was observed that the cumulative fraction of cancer cells that incorporate into the endothelium increases over time. Unlike leukocytes, which can directly transmigrate through the endothelium, cancer cells appear to have a two-step process of transmigration. Our results indicate that inflammation does not act as a signal for cancer cells to localize at specific sites and transmigrate similarly to leukocytes. Cancer cell transmigration also does not vary with substrate stiffness indicating that tissue stiffness may not play a role in cancer's propensity to metastasize to certain tissues.

Hamilla, Susan; Stroka, Kimberly; Aranda-Espinoza, Helim

2013-03-01

401

A Hybrid Stiff Solver for the Rayleigh-Plesset Equation  

NASA Astrophysics Data System (ADS)

We seek to apply efficient computational algorithms to investigate the locations of bubble concentrations in liquid flow. In flows with large velocities, bubbles tend to form in concentrated areas. Moreover, experiments show that bubbles formed at high velocities release large amount of energy once they collapse causing damage to equipment and objects that are in the path of the flow. To gain more insight on the formation of these bubbles, we will first study the dynamics of a single bubble and assume the bubble is a sphere. The dynamics of the bubble in terms of its radius and the driven pressure is modeled by the Rayleigh-Plesset (RP) equation. The RP equation is a second order nonlinear stiff ordinary differential equation (ode) and theoretically, its solution can be obtained numerically using Finite Difference (FD) methods. However, under large pressure variations, the rate of change of the bubble's radius approaches infinity when the bubble is collapsing. Explicit numerical integration methods require time steps of magnitude of (10-12 s) to achieve stable solutions. Iterations under this time scale are highly impractical and require immense CPU time. Therefore, a stiff ode solver is needed to alleviate the computation cost. Therefore, we would like to devise a hybrid algorithm that automatically selects between an explicit method and the stiff ode solver. Once we have a robust implementation, we will use it to process the data and analyze the relations between bubble locations and flow structures.

Alsayegh, Mutaz; Lee, Chung-Min

2011-11-01

402

Mechanochemical model of cell migration on substrates of varying stiffness  

NASA Astrophysics Data System (ADS)

Cells propel themselves along a substrate by organizing structures at the leading edge called lamellipodia that contain the actin network, myosin, integrin, and other proteins. In this article, we describe a quantitative model that couples the response of stretch-sensitive proteins in the lamellipodia to the dynamics of the actin cytoskeleton, therefore allowing the cell to respond to different substrate stiffnesses. Using this model, we predict the various phases of dynamics possible, including continuous protrusion, unstable retractions leading to ruffling, and periodic protrusion-retraction cycles. We explain the necessary conditions for each type of migratory behavior to occur. In particular, we show that, for periodic protrusion-retraction cycles to occur, the stiffness of the substrate must be high, the myosin-dependent maturation rate of nascent to focal adhesions must be high, and the myosin-independent integrin activation rate must be low. In addition, we also predict the dynamics expected at a given substrate stiffness, leading to a quantitative explanation of experimental data that showed that periodic protrusion-retraction cycles disappear when cells are placed on soft substrates. We also suggest experiments with downregulating ? actinin and/or talin and upregulating p130Cas and make predictions on what types of migratory dynamics will be observed.

Lai, Tanny; Chiam, K.-H.

2011-12-01

403

Effects of safflower seed extract on arterial stiffness  

PubMed Central

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

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

2010-01-01

404

Temporal response of arterial stiffness to ultra-marathon.  

PubMed

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

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

2014-07-01

405

Helical growth trajectories in plant roots interacting with stiff barriers  

NASA Astrophysics Data System (ADS)

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

Gerbode, Sharon; Noar, Roslyn; Harrison, Maria

2009-03-01

406

Decrements in stiffness are restored within 10 min.  

PubMed

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

Mizuno, T; Matsumoto, M; Umemura, Y

2013-06-01

407

Integral tau methods for stiff stochastic chemical systems  

NASA Astrophysics Data System (ADS)

Tau leaping methods enable efficient simulation of discrete stochastic chemical systems. Stiff stochastic systems are particularly challenging since implicit methods, which are good for stiffness, result in noninteger states. The occurrence of negative states is also a common problem in tau leaping. In this paper, we introduce the implicit Minkowski-Weyl tau (IMW-?) methods. Two updating schemes of the IMW-? methods are presented: implicit Minkowski-Weyl sequential (IMW-S) and implicit Minkowski-Weyl parallel (IMW-P). The main desirable feature of these methods is that they are designed for stiff stochastic systems with molecular copy numbers ranging from small to large and that they produce integer states without rounding. This is accomplished by the use of a split step where the first part is implicit and computes the mean update while the second part is explicit and generates a random update with the mean computed in the first part. We illustrate the IMW-S and IMW-P methods by some numerical examples, and compare them with existing tau methods. For most cases, the IMW-S and IMW-P methods perform favorably.

Yang, Yushu; Rathinam, Muruhan; Shen, Jinglai

2011-01-01

408

Abnormal Microarchitecture and Stiffness in Postmenopausal Women with Ankle Fractures  

PubMed Central

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

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

2011-01-01

409

Influence of surface interaction and chain stiffness on polymer-induced entropic forces and the dimensions of confined polymers  

NASA Astrophysics Data System (ADS)

The theories of Dolan and Edwards [Proc. R. Soc. London Ser. A 337, 509 (1974)] and Eisenriegler et al. [J. Chem. Phys. 77, 6296 (1982)] for Gaussian chains confined between parallel plates and to a half-space are generalized to chains having arbitrary stiffness. The generalized theory exploits a recently discovered relation between semiflexible polymers and Euclidean-type Dirac fermions in which ``flexible'' and ``stiff'' polymers correspond to the nonrelativistic (massive) and relativistic (massless) limits of the Dirac propagator, respectively. We show that half-space and parallel-plate problems are interrelated and this allows for a simplified and unified treatment of confined semiflexible polymers. The properties of confined semiflexible chains exhibit a complicated dependence on the polymer-surface interaction and chain stiffness. Results for polymer dimensions and entropic Casimir-like forces between plates are consistent with those obtained previously for flexible chains and corresponding results are obtained for semiflexible polymers. The new results for the forces between plates, having a semiflexible polymer in the gap, exhibit qualitative agreement with experimental data on confined chains at nonvanishing concentrations.

Kholodenko, Arkady L.; Bearden, Daniel W.; Douglas, Jack F.

1994-03-01

410

Application of sensitivity coefficients for heat conduction problems  

SciTech Connect

In parameter estimation considerable insight is provided by examining sensitivity coefficients. This paper focuses on the use of sensitivity coefficients in connection with estimating thermal properties in the heat conduction equation. A general methodology for computing sensitivity coefficients can be an important design tool. The use of such a tool is demonstrated in this paper. A control volume, finite element program is used, and briefly described, to implement numerical sensitivity coefficient calculations. In this approach general problems can be studied. Several example problems are presented to demonstrate the insight gained from sensitivity coefficients. The problems are selected from experimental studies to characterize the thermal properties of carbon-carbon composite. Sensitivity coefficients show that in an experiment that is not well designed, additional materials in the experimental configuration can have a larger impact on the temperature than the material of interest. Two-dimensional configurations demonstrate that there can be isolated areas of insensitivity and the difficulty of estimating multiple parameters.

Dowding, K.J.; Blackwell, B.F.; Cochran, R.J.

1998-02-01

411

Recursive calculation of hansen coefficients  

Microsoft Academic Search

Hansen coefficients are used in expansions of the elliptic motion. Three methods for calculating the coefficients are studied: Tisserand's method, the Von Zeipel-Andoyer (VZA) method with explicit representation of the polynomials required to compute the Hansen coefficients, and the VZA method with the values of the polynomials calculated recursively. The VZA method with explicit polynomials is by far the most

Richard L. Branham

1990-01-01

412

Reliability Generalization: "Lapsus Linguae"  

ERIC Educational Resources Information Center

This study examines the proposed Reliability Generalization (RG) method for studying reliability. RG employs the application of meta-analytic techniques similar to those used in validity generalization studies to examine reliability coefficients. This study explains why RG does not provide a proper research method for the study of reliability,…

Smith, Julie M.

2011-01-01

413

Thermomechanical characterization of graphite/polymide composites. [Stiffness; strength; shear properties  

SciTech Connect

The stiffness, strength and shear properties of three polyimide resins (NR-150B2, PMR-15 and CPI-2237) combined with three different moduli graphite fibers (C-6000, F-5A and GY-70) were determined at 20 to 371/sup 0/. Stiffness retention with increasing temperature is affected only by the thermal integrity of the polymide matrix. No loss in modulus occurs up to 316/sup 0/C for the PMR-15 and CPI-2237 based composites (T/sub g/ = 377/sup 0/C) or to 260/sup 0/C for the NR-150B2 based material (T/sub g/ approx. = 349/sup 0/C), with any of the three fibers. Both flexure and shear strengths show fiber dependent behavior with temperature. The higher modulus fiber composites (F-5A, GY-70) undergo little strength change up to 343/sup 0/C. Composite strengths of the lower modulus fibers (C-6000), however, degrade by as much as 50% over the same temperature range. Thermal-oxidative stability of the various graphite fibers, and its effect on interfacial strength degradation, are considered primary causes for the fiber-type dominated strength behavior. In general, strength retention appears directly related to degree of graphitization (modulus) of the fibers. The accumulated mechanical property data, some previously unknown, are correlated with microstructural features such as the fiber-matrix adhesion, porosity and processing defects. 11 figures.

Kunz, S. C.

1980-01-01

414

Liver stiffness: a novel parameter for the diagnosis of liver disease  

PubMed Central

The noninvasive quantitation of liver stiffness (LS) by ultrasound based transient elastography using FibroScan® has revolutionized the diagnosis of liver diseases, namely liver cirrhosis. Alternative techniques such as acoustic radiation impulse frequency imaging or magnetic resonance elastography are currently under investigation. LS is an excellent surrogate marker of advanced fibrosis (F3) and cirrhosis (F4) outscoring all previous noninvasive approaches to detect cirrhosis. LS values below 6 kPa are considered as normal and exclude ongoing liver disease. LS of 8 and 12.5 kPa represent generally accepted cut-off values for F3 and F4 fibrosis. LS highly correlates with portal pressure, and esophageal varices are likely at values >20 kPa. Many other factors may also increase LS such as hepatic infiltration with tumor cells, mast cells (mastocytosis), inflammatory cells (all forms of hepatitis) or amyloidosis. In addition, LS is directly correlated with the venous pressure (eg, during liver congestion) and is increased during mechanic cholestasis. Thus, LS should always be interpreted in the context of clinical, imaging and laboratory findings. Finally, LS has helped to better understand the molecular mechanisms underlying liver fibrosis. The novel pressure-stiffness-fibrosis sequence hypothesis is introduced.

Mueller, Sebastian; Sandrin, Laurent

2010-01-01

415

The Effect of Variable Fiber Aspect Ratio on the Stiffness and Thermal Expansion Coefficients of a Short Fiber Composite  

Microsoft Academic Search

The effect of variable fiber aspect ratio l\\/d on the thermo-mechanical properties of aligned short fiber composites is analytically studied by use of the Eshelby's equivalent inclusion method. Then, the thermo-mechanical properties of the composite predicted for a given density function (l\\/d) are compared with those obtained for the mean value of (l\\/d). Based on this comparison, the validity of

Y. Takao; M. Taya

1987-01-01

416

Stiffness detection and reduction in discrete stochastic simulation of biochemical systems  

NASA Astrophysics Data System (ADS)

Typical multiscale biochemical models contain fast-scale and slow-scale reactions, where ``fast'' reactions fire much more frequently than ``slow'' ones. This feature often causes stiffness in discrete stochastic simulation methods such as Gillespie's algorithm and the Tau-Leaping method leading to inefficient simulation. This paper proposes a new strategy to automatically detect stiffness and identify species that cause stiffness for the Tau-Leaping method, as well as two stiffness reduction methods. Numerical results on a stiff decaying dimerization model and a heat shock protein regulation model demonstrate the efficiency and accuracy of the proposed methods for multiscale biochemical systems.

Pu, Yang; Watson, Layne T.; Cao, Yang

2011-02-01

417

Scaling of Fluid Flow and Seismic Stiffness of Fractures  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

418

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

419

Use of Structure Coefficients in Published Multiple Regression Articles: &bgr; is not Enough  

Microsoft Academic Search

The importance of interpreting structure coefficients throughout the General Linear Model (GLM) is widely accepted. However, regression researchers too infrequently consult regression structure coefficients to augment their interpretations. The authors reviewed articles published in the Journal of Applied Psychology to determine how interpretations might have differed if standardized regression coefficients and structure coefficients (or else bivariate rs of predictors with

Troy Courville; Bruce Thompson

2001-01-01

420

Second-order elliptic equations with variably partially VMO coefficients  

Microsoft Academic Search

The solvability in Wp2(Rd) spaces is proved for second-order elliptic equations with coefficients which are measurable in one direction and VMO in the orthogonal directions in each small ball with the direction depending on the ball. This generalizes to a very large extent the case of equations with continuous or VMO coefficients.

N. V. Krylov

2009-01-01

421

Pseudodifferential Boundary Value Problems with Non-Smooth Coefficients  

Microsoft Academic Search

In this contribution, we establish a calculus of pseudodifferential boundary value problems with Hölder continuous coefficients. It is a generalization of the calculus of pseudodifferential boundary value problems introduced by Boutet de Monvel. We discuss their mapping properties in Bessel potential and certain Besov spaces. Although having non-smooth coefficients and the operator classes being not closed under composition, we will

Helmut Abels

2005-01-01

422

Derivatives of buckling loads and vibration frequencies with respect to stiffness and initial strain parameters  

NASA Technical Reports Server (NTRS)

A uniform variational approach to sensitivity analysis of vibration frequencies and bifurcation loads of nonlinear structures is developed. Two methods of calculating the sensitivities of bifurcation buckling loads and vibration frequencies of nonlinear structures, with respect to stiffness and initial strain parameters, are presented. A direct method requires calculation of derivatives of the prebuckling state with respect to these parameters. An adjoint method bypasses the need for these derivatives by using instead the strain field associated with the second-order postbuckling state. An operator notation is used and the derivation is based on the principle of virtual work. The derivative computations are easily implemented in structural analysis programs. This is demonstrated by examples using a general purpose, finite element program and a shell-of-revolution program.

Haftka, Raphael T.; Cohen, Gerald A.; Mroz, Zenon

1990-01-01

423

The role of body stiffness in wake production for anguilliform swimmers  

NASA Astrophysics Data System (ADS)

We compare wake structures shed by the undulatory motion of physical and computational models of an anguilliform swimmer, the lamprey. The physical model is a robotic lamprey-like swimmer with an actively flexing tail, and with passively flexible tails of different stiffnesses. The computational model is a two-dimensional computational fluid dynamic (CFD) model that captures fluid-structure interaction using the immersed boundary framework. The CFD model included both actively flexing and passively flexible tail regions. Both models produced wakes with two or more same-sign vortices shed each time the tail changed direction (a ``2P'' or higher- order wake). In general, wakes became less coherent as tail flexibility increased. We compare the pressure distribution near the tail tip and the timing of vortex formation in both cases and find good agreement. Differences between self-propelled and tethered cases are detailed. Finally, we examine the effects of material resonance on force production.

Tytell, Eric; Leftwich, Megan; Hsu, Chia-Yu; Cohen, Aves; Fauci, Lisa; Smits, Alexander

2011-11-01

424

Quantifying Local Stiffness Variations in Radiofrequency Ablations with Dynamic Indentation  

PubMed Central

Elastographic imaging can be used to monitor ablation procedures, however confident and clear determination of the ablation boundary is essential to ensure complete treatment of the pathological target. To investigate the potential for ablation boundary representation on elastographic images, local variations in the viscoelastic properties in radiofrequency ablated regions that were formed in vivo in porcine liver tissue were quantified using dynamic indentation. Spatial stiffness maps were then correlated to stained histology, the gold standard for determination of the ablation periphery or boundary. Regions of interest in eleven radiofrequency ablation samples were indented at 18–24 locations each, including the central zone of complete necrosis and more peripheral transition zones including normal tissue. Storage modulus and rate of stiffening were both greatest in the central ablation zone and decreased with radial distance away from the center. The storage modulus and modulus contrast at the ablation outer transition zone boundary were 3.1 ± 1.0 kPa and 1.6 ± 0.4, respectively, and 36.2 ± 9.1 kPa and 18.3 ± 5.5 at the condensation boundary within the ablation zone. Elastographic imaging modalities were then compared to gross pathology in ex vivo bovine liver tissue. Area estimated from strain, shear wave velocity, and gross pathology images were 470 mm2, 560 mm2, and 574 mm2, respectively, and ablation widths were 19.4 mm, 20.7 mm, and 23.0 mm. This study has provided insights into spatial stiffness distributions within radiofrequency ablations and suggests that low stiffness contrast on the ablation periphery leads to the observed underestimation of ablation extent on elastographic images.

DeWall, Ryan J.; Varghese, Tomy; Brace, Christopher L.

2012-01-01

425

Response of large space structures with stiffness control  

NASA Technical Reports Server (NTRS)

For large space structures, such as the 100-meter-diameter wrap-rib deployable antenna and spinning solar sail, whose out-of-plane stiffness is derived from in-plane tension, the out-of-plane motion can be actively controlled by time-varying in-plane tension. An elastic string is used to demonstrate the proposed approach, which results in a nonlinear ordinary differential equation. An approximation method is outlined from which the magnitude of time-varying tension can be determined based on the efficiency factor, the time factor or the optimal factor.

Chen, J.-C.

1984-01-01

426

Surviving stiff-person syndrome: a case report.  

PubMed

Stiff-person syndrome (SPS) is a rare condition of progressive muscular rigidity and spasm, frequently accompanied by other autoimmune conditions, an association which has been further strengthened by the discovery of anti-GAD antibodies and the response of SPS to immunotherapies. Intravenous immunoglobulin (IVIg) is the mainstay therapy. Because of the rarity of the GAD antibody associated conditions, most of the information regarding treatment is case series and individual case reports. Here we describe the 15 year long management of a subject with SPS who has had a favourable outcome. PMID:21442460

Gnanapavan, Sharmilee; Vincent, Angela; Giovannoni, Gavin

2011-10-01

427

Relation of arterial stiffness with gestational age and birth weight  

PubMed Central

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

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

2004-01-01