These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

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

NASA Astrophysics Data System (ADS)

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

Pugachev, A. O.; Deckner, M.

2012-08-01

2

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

3

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

NASA Technical Reports Server (NTRS)

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

Takahata, Ryoichi; Ueyama, Hirochika; Yotsuya, Tsutom

1992-01-01

4

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 oilfree turbomachinery systems. These bearings are nonlinear 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 to estimate load capacity. This method has been a valuable tool in system development. The current work 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.

Della-Corte, Christopher

2012-01-01

5

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

6

General frost growth mechanism on solid substrates with different stiffness.  

PubMed

Preventing or delaying frost formation on surfaces is of significant importance in many aspects of our daily life. Despite many efforts and improvements recently achieved in the design of new icephobic materials and substrates, not all proposed solutions are universally applicable and frost formation still remains a problem in need of further flexible solutions. In this respect, we propose to take benefit from the tunable viscoelastic properties of soft polymer gel substrates, since they are known to strongly influence the dropwise condensation process of water, and to investigate condensation frosting on them. Using polymer gels with different stiffness and a hard substrate as a reference, we demonstrate their ability to delay frost formation compared to recent results reported in the literature on other solid substrates and in particular on superhydrophobic surfaces. By investigating the frost front propagation we singled out a general behavior of its dynamic evolution consisting of two processes presenting two different time scales. This general growth appears to be independent of experimental conditions as well as substrate stiffness. PMID:24456462

Petit, Julien; Bonaccurso, Elmar

2014-02-01

7

Generalized Coefficients for Hopf Cyclic Cohomology  

NASA Astrophysics Data System (ADS)

A category of coefficients for Hopf cyclic cohomology is defined. It is shown that this category has two proper subcategories of which the smallest one is the known category of stable anti Yetter-Drinfeld modules. The middle subcategory is comprised of those coefficients which satisfy a generalized SAYD condition depending on both the Hopf algebra and the (co)algebra in question. Some examples are introduced to show that these three categories are different. It is shown that all components of Hopf cyclic cohomology work well with the new coefficients we have defined.

Hassanzadeh, Mohammad; Kucerovsky, Dan; Rangipour, Bahram

2014-09-01

8

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

9

Element stiffness matrix and modified coefficients for circular tube with tapered ends  

Microsoft Academic Search

By axially connecting a constant-section circular tube to two tapered circular tubes, a so-called circular tube with tapered ends structural member is obtained. To get the element stiffness matrix of a tube with tapered ends, a transfer matrix method is introduced in this paper. Transfer matrices for the constant-section tube and tapered tubes are derived firstly, and then the element

Yaozhi Luo; Fang Wu; Xian Xu

2006-01-01

10

Generalized formula for the surface stiffness of fluid-saturated porous media containing parallel pore channels  

E-print Network

Institute of Physics. Acoustic wave interaction with a plane interface separat- ing an ambient fluid to the average surface displacement of the fluid p p Ts Un un . 3 Generally, acoustic wave interaction with fluid/fluidGeneralized formula for the surface stiffness of fluid-saturated porous media containing parallel

Nagy, Peter B.

11

Path-Counting Formulas for Generalized Kinship Coefficients and Condensed Identity Coefficients  

PubMed Central

An important computation on pedigree data is the calculation of condensed identity coefficients, which provide a complete description of the degree of relatedness of two individuals. The applications of condensed identity coefficients range from genetic counseling to disease tracking. Condensed identity coefficients can be computed using linear combinations of generalized kinship coefficients for two, three, four individuals, and two pairs of individuals and there are recursive formulas for computing those generalized kinship coefficients (Karigl, 1981). Path-counting formulas have been proposed for the (generalized) kinship coefficients for two (three) individuals but there have been no path-counting formulas for the other generalized kinship coefficients. It has also been shown that the computation of the (generalized) kinship coefficients for two (three) individuals using path-counting formulas is efficient for large pedigrees, together with path encoding schemes tailored for pedigree graphs. In this paper, we propose a framework for deriving path-counting formulas for generalized kinship coefficients. Then, we present the path-counting formulas for all generalized kinship coefficients for which there are recursive formulas and which are sufficient for computing condensed identity coefficients. We also perform experiments to compare the efficiency of our method with the recursive method for computing condensed identity coefficients on large pedigrees. PMID:25165486

Cheng, En; Ozsoyoglu, Z. Meral

2014-01-01

12

Linear equations in general purpose codes for stiff ODEs  

SciTech Connect

It is noted that it is possible to improve significantly the handling of linear problems in a general-purpose code with very little trouble to the user or change to the code. In such situations analytical evaluation of the Jacobian is a lot cheaper than numerical differencing. A slight change in the point at which the Jacobian is evaluated results in a more accurate Jacobian in linear problems. (RWR)

Shampine, L. F.

1980-02-01

13

A compliance\\/stiffness matrix formulation of general Green's function and effective permittivity for piezoelectric multilayers  

Microsoft Academic Search

This paper presents an efficient and stable recursive compliance matrix method for analyzing wave propagation in multilayered piezoelectric media. The effective permittivity and generalized Green's functions for a layered system, a layered system on a substrate, and a layered system between two substrates have been obtained from the elements of the total or surface compliance\\/stiffness matrices, which are calculated recursively,

Lugen Wang; Stanislav I. Rokhlin

2004-01-01

14

Accelerated progression of arterial stiffness in dialysis patients compared with the general population  

PubMed Central

Background/Aims The aim of this study was to compare the progression of aortic stiffness in chronic hemodialysis patients (CHP) with that of general population patients (GPP) over a 36-month period and to evaluate the determinants of this progression. Methods The study group included 80 patients undergoing hemodialysis (aged 59.3 ± 11.8 years; duration of dialysis 5.47 ± 5.16 years). The control group consisted of 60 patients (aged 57.5 ± 10.9 years) with a glomerular filtration rate of > 60 mL/min/1.73 m2. Pulse wave velocity (PWV) was determined from time diversity propagation of the common carotid artery and femoral artery by Doppler ultrasound. Clinical and biochemical parameters were determined in serum using standard laboratory procedures. Results The mean PWV values at baseline and 36 months were 11.18 ± 2.29 and 11.82 ± 2.34 m/sec in the CHP group, and 9.02 ± 1.89 and 9.29 ± 1.93 m/sec in the GPP group, respectively. The average PWV progressions were 63.95 ± 18.373 cm/sec in CHP and 27.28 ± 28.519 cm/sec in GPP. By multiple regression analysis, hemoglobin (standardized coefficient ? [?st] = -0.405, p = 0.004; ?st = -0.364, p = 0.011), albumin (?st = -0.349, p = 0.042; ?st = -0.303, p = 0.034), CRP (?st = 0.458, p = 0.002; ?st = 0.187, p = 0.008), and total cholesterol (?st = 0.236, p = 0.038; ?st = 0.171, p = 0.078) were independently associated with PWV in the CHP and GPP groups, respectively. Conclusions Accelerated arterial stiffness was more pronounced in the CHP group than in the GPP group. The independent determinants of this progression in both groups include traditional risk factors and blood levels of hemoglobin, albumin and CRP. Cholesterol and uremia-related factors are determinants only in CHP. PMID:23864805

Janakievska, Pavlina; Sotiroski, Kosta; Sikole, Aleksandar

2013-01-01

15

Non-monotonic dependence of the friction coefficient on heterogeneous stiffness.  

PubMed

The complexity of the frictional dynamics at the microscopic scale makes difficult to identify all of its controlling parameters. Indeed, experiments on sheared elastic bodies have shown that the static friction coefficient depends on loading conditions, the real area of contact along the interfaces and the confining pressure. Here we show, by means of numerical simulations of a 2D Burridge-Knopoff model with a simple local friction law, that the macroscopic friction coefficient depends non-monotonically on the bulk elasticity of the system. This occurs because elastic constants control the geometrical features of the rupture fronts during the stick-slip dynamics, leading to four different ordering regimes characterized by different orientations of the rupture fronts with respect to the external shear direction. We rationalize these results by means of an energetic balance argument. PMID:25345800

Giacco, F; Ciamarra, M Pica; Saggese, L; de Arcangelis, L; Lippiello, E

2014-01-01

16

Non-monotonic dependence of the friction coefficient on heterogeneous stiffness  

PubMed Central

The complexity of the frictional dynamics at the microscopic scale makes difficult to identify all of its controlling parameters. Indeed, experiments on sheared elastic bodies have shown that the static friction coefficient depends on loading conditions, the real area of contact along the interfaces and the confining pressure. Here we show, by means of numerical simulations of a 2D Burridge-Knopoff model with a simple local friction law, that the macroscopic friction coefficient depends non-monotonically on the bulk elasticity of the system. This occurs because elastic constants control the geometrical features of the rupture fronts during the stick-slip dynamics, leading to four different ordering regimes characterized by different orientations of the rupture fronts with respect to the external shear direction. We rationalize these results by means of an energetic balance argument. PMID:25345800

Giacco, F.; Ciamarra, M. Pica; Saggese, L.; de Arcangelis, L.; Lippiello, E.

2014-01-01

17

A compliance/stiffness matrix formulation of general Green's function and effective permittivity for piezoelectric multilayers.  

PubMed

This paper presents an efficient and stable recursive compliance matrix method for analyzing wave propagation in multilayered piezoelectric media. The effective permittivity and generalized Green's functions for a layered system, a layered system on a substrate, and a layered system between two substrates have been obtained from the elements of the total or surface compliance/stiffness matrices, which are calculated recursively, layer by layer, from the layer compliance/stiffness matrices. The method is very closely related to the transfer matrix method and retains its simplicity and efficiency, but it is numerically stable for high thickness-to-wavelength ratio. Numerical examples for wave propagation in zinc oxide (ZnO)/Diamond/silicon(Si) structures are presented using the compliance matrix formulation for effective permittivity and Green's function. PMID:15139547

Wang, Lugen; Rokhlin, Stanislav I

2004-04-01

18

Warm Inflation with a General Form of the Dissipative Coefficient  

E-print Network

We propose and investigate a general form of the dissipative coefficient $\\Gamma=C_{\\phi}T^{m}/\\phi^{m-1}$ in warm inflation. We focus on discussing the strong dissipative processes $r=\\Gamma/3H\\gg1$ in the thermal state of approximate equilibrium. To this toy model, we give the slow-roll conditions, the amplitude and the index of the power spectrum under the general form of dissipative coefficient. Furthermore, the monomial potential and the hybrid-like potential are analyzed specifically. We conclude that the $m=0,3$ cases are worthy further investigation especially.

Yi Zhang

2009-03-04

19

Calculation of generalized secant integral using binomial coefficients.  

PubMed

A single series expansion relation is derived for the generalized secant (GS) integral in terms of binomial coefficients, exponential integrals and incomplete gamma functions. The convergence of the series is tested by the concrete cases of parameters. The formulas given in this study for the evaluation of GS integral show good rate of convergence and numerical stability. PMID:15082048

Guseinov, I I; Mamedov, B A

2004-05-01

20

Stiffness jump in the generalized XY model on the square lattice  

NASA Astrophysics Data System (ADS)

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.

Hübscher, David M.; Wessel, Stefan

2013-06-01

21

APOE polymorphism is associated with lipid profile, but not with arterial stiffness in the general population  

PubMed Central

Background Cardiovascular diseases (CVD) are the main cause of death and disability in developed countries. In most cases, the progress of CVD is influenced by environmental factors and multifactorial inheritance. The purpose of this study was to investigate the association between APOE genotypes, cardiovascular risk factors, and a non-invasive measure of arterial stiffness in the Brazilian population. Methods A total of 1493 urban Brazilian individuals were randomly selected from the general population of the Vitoria City Metropolitan area. Genetic analysis of the APOE polymorphism was conducted by PCR-RFLP and pulse wave velocity analyzed with a noninvasive automatic device. Results Age, gender, body mass index, triglycerides, creatinine, uric acid, blood glucose, blood pressure phenotypes were no different between ?2, ?3 and ?4 alleles. The ?4 allele was associated with higher total-cholesterol (p < 0.001), LDL-C (p < 0.001), total-cholesterol/HDL-C ratio (p < 0.001), LDL/HDL-C ratio (p < 0.001), lower HDL-C values (p < 0.001) and higher risk to obesity (OR = 1.358, 95% CI = 1.019-1.811) and hyperuricemia (OR = 1.748, 95% CI = 1.170-2.611). Nevertheless, pulse wave velocity (p = 0.66) measures were no different between genotypes. The significant association between APOE genotypes and lipid levels persisted after a 5-year follow-up interval, but no interaction between time and genotype was observed for lipids longitudinal behavior. Conclusion The ?4 allele of the APOE gene is associated with a worse lipid profile in the Brazilian urban population. In our relatively young sample, the observed effect of APOE genotype on lipid levels was not translated into significant effects in arterial wall stiffness. PMID:21059196

2010-01-01

22

Generalized linear mixed models with varying coefficients for longitudinal data.  

PubMed

The routinely assumed parametric functional form in the linear predictor of a generalized linear mixed model for longitudinal data may be too restrictive to represent true underlying covariate effects. We relax this assumption by representing these covariate effects by smooth but otherwise arbitrary functions of time, with random effects used to model the correlation induced by among-subject and within-subject variation. Due to the usually intractable integration involved in evaluating the quasi-likelihood function, the double penalized quasi-likelihood (DPQL) approach of Lin and Zhang (1999, Journal of the Royal Statistical Society, Series B61, 381-400) is used to estimate the varying coefficients and the variance components simultaneously by representing a nonparametric function by a linear combination of fixed effects and random effects. A scaled chi-squared test based on the mixed model representation of the proposed model is developed to test whether an underlying varying coefficient is a polynomial of certain degree. We evaluate the performance of the procedures through simulation studies and illustrate their application with Indonesian children infectious disease data. PMID:15032768

Zhang, Daowen

2004-03-01

23

Generalization of Clustering Coefficients to Signed Correlation Networks  

PubMed Central

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

24

Stiffness effects on the dynamics of the bar-mode instability of Neutron Stars in full General Relativity  

E-print Network

We present results on the effect of the stiffness of the equation of state on the dynamical bar-mode instability in rapidly rotating polytropic models of neutron stars in full General Relativity. We determine the change in the threshold for the emergence of the instability for a range of the adiabatic $\\Gamma$ index from 2.0 to 3.0, including two values chosen to mimic more realistic equations of state at high densities.

Frank Löffler; Roberto De Pietri; Alessandra Feo; Luca Franci; Francesco Maione

2014-11-07

25

Stiff Neck  

MedlinePLUS

... infectious illness that can result in stiff neck, headache , and fever . What to Do If your child has a stiff or sore neck but no ... if symptoms persist Seek Medical Care If Your Child Has a Stiff Neck and: ... headache vomiting eye sensitivity to light a skin rash ...

26

L.R.S. Bianchi type II stiff fluid cosmological model with decaying vacuum energy density ? in general relativity  

NASA Astrophysics Data System (ADS)

Locally rotationally symmetric (L.R.S.) Bianchi type II stiff fluid cosmological model is investigated. To get the deterministic model of the universe, we have assumed a supplementary condition A=Bm between metric potentials A and B, where m is a constant. It is shown that the vacuum energy density ? is positive and proportional to 1t2. The values of deceleration parameter q, matter-energy density ? and dark-energy density ? are found to be in good agreement with the values obtain from 5-years WMAP observations. The predicted value of the jerk parameter is in agreement with the SNLS SNIa and X-ray galaxy cluster distance data but it is not match with the SNIa gold sample data. In general, the model represent accelerating, shearing and non-rotating universe. The physical and geometrical behavior of this model is also discussed.

Amirhashchi, Hassan

2011-03-01

27

Techniques to estimate generalized skew coefficients of annual peak streamflow for natural basins in Texas  

USGS Publications Warehouse

This report presents two techniques to estimate generalized skew coefficients used for log-Pearson Type III peak-streamflow frequency analysis of natural basins in Texas. A natural basin has less than 10 percent impervious cover, and less than 10 percent of its drainage area is controlled by reservoirs. The estimation of generalized skew coefficients is based on annual peak and historical peak streamflow for all U.S. Geological Survey streamflow-gaging stations having at least 20 years of annual peak-streamflow record from natural basins in Texas. Station skew coefficients calculated for each of 255 Texas stations were used to estimate generalized skew coefficients for Texas. One technique to estimate generalized skew coefficients involved the use of regression equations developed for each of eight regions in Texas, and the other involved development of a statewide map of generalized skew coefficients. The weighted mean of the weighted mean standard errors of the regression equations for the eight regions is 0.36 log10 skew units, and the weighted mean standard error of the map is 0.35 log10 skew units. The technique based on the map is preferred for estimating generalized skew coefficients because of its smooth transition from one region of the State to another.

Judd, Linda J.; Asquith, William H.; Slade, Raymond M., Jr.

1996-01-01

28

[Successful treatment of the backward-bending attack due to generalized spasm in stiff-person syndrome with intravenous immune globulin therapy].  

PubMed

We report a 63-year-old man with stiff-person syndrome, who dramatically responded to the treatment with high dose intravenous immunoglobulin (IVIG). He developed stiffness of the right leg and low back five years ago. He was treated with oral diazepam 6 mg/day and showed a marked improvement. He had been maintained on the same dose since then. In 2000, he began to have episodic generalized spasm and painful spasm of his left leg as well as persistent stiffness of his legs and low back. Findings on the physical examination were normal except for a prominent hyperlordosis with co-contracture of the lumbar paraspinal and abdominal muscles. Neurologic examination revealed stiffness in the lower limbs, more marked on the left side, and lower truncal muscles. The left leg had painful spasm, which was provoked by tactile stimuli. There was severe generalized spasm which made him suddenly bend backward. These backward-bending attacks were provoked spontaneously or reflexively by sudden tactile stimuli. He was unable to arise from a chair or stand without assistance. His deep tendon reflexes on both legs were brisk and Babinski sign was negative. He had no diabetes mellitus and thyroid function was normal. Antibodies against glutamic acid decarboxylase(GAD), antinuclear antibody, thyroid peroxidase autoantibody and antithyroglobulin autoantibody in the serum were present. His painful spasm was disappeared and muscle stiffness was moderately improved by treatment with oral diazepam and clonazepam, but backward-bending attacks due to generalized spasms were not controlled. He received IVIG. Three days after the administration of IVIG, these attacks disappeared completely. Subsequently muscle stiffness improved. One week after, he was able to walk without assistance. IVIG may be useful for treatment of generalized spasm, which had no response to treatment with diazepam or clonazepam. PMID:12684995

Wada, Yuko; Suenaga, Toshihiko; Hashimoto, Shuji

2003-02-01

29

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

Microsoft Academic Search

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.

Abdul-Majid Wazwaz; Houria Triki

2011-01-01

30

Evolution equations for eigenvalues and coefficients of polynomials and related generalized dynamics  

E-print Network

In this paper we suggest new classification of polynomials and evolution equations for the roots and the coefficients remaing the polynomials within proper class. In the basis of the developed evolution equations we built new dynamics generalizing the relativistic dynamics.

Robert M. Yamaleev

2008-05-07

31

Generalized soliton solutions to generalized KdV equation with variable coefficients by Exp-function method  

Microsoft Academic Search

In this paper, the generalized KdV equation with variable coefficients is investigated by Exp-function method. The generalized soliton solutions and periodic solutions of this equation are obtained with the help of symbolic computation. It is shown that the Exp-function method provides a straightforward and powerful mathematical tool for solving nonlinear equations.

S.-M. Yu; L.-X. Tian

2008-01-01

32

General Expressions for the Coefficients of Chern Forms Up to the 13th Order in Curvature  

E-print Network

General expressions are given for the coefficients of Chern forms up to the 13th order in curvature in terms of the Riemann-Christoffel curvature tensor and some of its concomitants (e.g., Pontrjagin's characteristic tensors) for n-dimensional differentiable manifolds having a general linear connection.

C. C. Briggs

1999-05-03

33

Some General Expressions for the Coefficient of the 14th Chern Form  

E-print Network

Some general expressions are given for the coefficient of the 14th Chern form in terms of the Riemann-Christoffel curvature tensor and some of its concomitants (e.g., Pontrjagin's characteristic tensors) for n-dimensional differentiable manifolds having a general linear connection.

C. C. Briggs

1999-05-03

34

A generalized fractional sub-equation method for fractional differential equations with variable coefficients  

NASA Astrophysics Data System (ADS)

In this Letter, a generalized fractional sub-equation method is proposed for solving fractional differential equations with variable coefficients. Being concise and straightforward, this method is applied to the space-time fractional Gardner equation with variable coefficients. As a result, many exact solutions are obtained including hyperbolic function solutions, trigonometric function solutions and rational solutions. It is shown that the considered method provides a very effective, convenient and powerful mathematical tool for solving many other fractional differential equations in mathematical physics.

Tang, Bo; He, Yinnian; Wei, Leilei; Zhang, Xindong

2012-08-01

35

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

36

A Reliability Generalization Study of Coefficient Alpha for the Life Orientation Test  

Microsoft Academic Search

Dispositional optimism is a widely studied construct in social science and medicine associated with a variety of important psychological and physiological outcomes. Our purpose in this study was to examine coefficient alpha for a popular optimism measure: The Life Orientation Test (LOT; Scheier & Carver, 1985). We utilized a meta-analytic procedure known as reliability generalization to provide an aggregate estimate

Matt Vassar; Greg Bradley

2010-01-01

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

General model and segregation coefficient measurement for ultrashallow doping by excimer laser annealing  

SciTech Connect

A general model of ultrashallow doping by excimer laser annealing is derived from only one diffusion-segregation equation. In our model, the relative dopant profile after some laser shots reaches a stationary distribution, which only depends on the segregation and liquid-phase diffusion coefficients of the dopant but not on the laser-process parameters. From this result, a one-point method is proposed to experimentally determine the out-of-equilibrium segregation coefficient k. Only the relative dopant concentration at the material surface has to be measured prior to determine the k value. Experimental dopant profiles are compared to simulations generated with experimental k values.

Gillet, Jean-Numa; Degorce, Jean-Yves; Meunier, Michel [Laser Processing Laboratory, Department of Engineering Physics, Ecole Polytechnique de Montreal, C. P. 6079, succ. Centre-ville, Montreal, Quebec H3C 3A7 (Canada)

2005-05-30

39

Stiff railguns  

NASA Astrophysics Data System (ADS)

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

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

1991-01-01

40

Measurement of activity coefficients of mixtures by head-space gas chromatography: general procedure.  

PubMed

Head-space gas chromatography (HS-GC) is an applicable method to perform vapor-liquid equilibrium measurements and determine activity coefficients. However, the reproducibility of the data may be conditioned by the experimental procedure concerning to the automated pressure-balanced system. The study developed in this work shows that a minimum volume of liquid in the vial is necessary to ensure the reliability of the activity coefficients since it may become a parameter that influences the magnitude of the peak areas: the helium introduced during the pressurization step may produce significant variations of the results when too small volume of liquid is selected. The minimum volume required should thus be evaluated prior to obtain experimentally the concentration in the vapor phase and the activity coefficients. In this work, the mixture acetonitrile-toluene is taken as example, requiring a sample volume of more than 5mL (about more than 25% of the vial volume). The vapor-liquid equilibrium and activity coefficients of mixtures at different concentrations (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 molar fraction) and four temperatures (35, 45, 55 and 70°C) have been determined. Relative standard deviations (RSD) lower than 5% have been obtained, indicating the good reproducibility of the method when a sample volume larger than 5mL is used. Finally, a general procedure to measure activity coefficients by means of pressure-balanced head-space gas chromatography is proposed. PMID:23809803

Luis, Patricia; Wouters, Christine; Van der Bruggen, Bart; Sandler, Stanley I

2013-08-01

41

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

42

Variable stiffness torsion springs  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

43

Variable stiffness torsion springs  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

44

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

45

Comparing Regression Coefficients between Nested Linear Models for Clustered Data with Generalized Estimating Equations  

ERIC Educational Resources Information Center

Comparing regression coefficients between models when one model is nested within another is of great practical interest when two explanations of a given phenomenon are specified as linear models. The statistical problem is whether the coefficients associated with a given set of covariates change significantly when other covariates are added into…

Yan, Jun; Aseltine, Robert H., Jr.; Harel, Ofer

2013-01-01

46

Numerical solutions of boundary value problems for variable coefficient generalized KdV equations using Lie symmetries  

E-print Network

The exhaustive group classification of a class of variable coefficient generalized KdV equations is presented, which completes and enhances results existing in the literature. Lie symmetries are used for solving an initial and boundary value problem for certain subclasses of the above class. Namely, the found Lie symmetries are applied in order to reduce the initial and boundary value problem for the generalized KdV equations (which are PDEs) to an initial value problem for nonlinear third-order ODEs. The latter problem is solved numerically using the finite difference method. Numerical solutions are computed and the vast parameter space is studied.

O. O. Vaneeva; N. C. Papanicolaou; M. A. Christou; C. Sophocleous

2013-09-04

47

General dissipative coefficient in warm intermediate inflation in loop quantum cosmology in light of Planck and BICEP2  

E-print Network

In this paper, we study a warm intermediate inflationary model with a general form for the dissipative coefficient $\\Gamma(T,\\phi)=C_\\phi\\,T^{m}/\\phi^{m-1}$ in the context of loop quantum cosmology. We examine this model in the weak and strong dissipative regimes. In general, we discuss in great detail the characteristics of this model in the slow-roll approximation. Also, we assume that the modifications to perturbation equations result exclusively from Hubble rate. In this approach, we use recent astronomical observations from Planck and BICEP2 experiments to restrict the parameters in our model.

Ramón Herrera; Marco Olivares; Nelson Videla

2014-04-10

48

General dissipative coefficient in warm intermediate inflation in loop quantum cosmology in light of Planck and BICEP2  

E-print Network

In this paper, we study a warm intermediate inflationary model with a general form for the dissipative coefficient $\\Gamma(T,\\phi)=C_\\phi\\,T^{m}/\\phi^{m-1}$ in the context of loop quantum cosmology. We examine this model in the weak and strong dissipative regimes. In general, we discuss in great detail the characteristics of this model in the slow-roll approximation. In this approach, we use recent astronomical observations from Planck and BICEP2 experiments to restrict the parameters in our model.

Herrera, Ramón; Videla, Nelson

2014-01-01

49

General dissipative coefficient in warm intermediate inflation in Loop Quantum Cosmology in light of Planck and BICEP2  

NASA Astrophysics Data System (ADS)

In this paper, we study a warm intermediate inflationary model with a general form for the dissipative coefficient ?(T, ?) = C?Tm/?m-1 in the context of Loop Quantum Cosmology (LQC). We examine this model in the weak and strong dissipative regimes. In general, we discuss in great detail the characteristics of this model in the slow-roll approximation. Also, we assume that the modifications to perturbation equations result exclusively from Hubble rate. In this approach, we use recent astronomical observations from Planck and BICEP2 experiments to restrict the parameters in our model.

Herrera, Ramón; Olivares, Marco; Videla, Nelson

2014-09-01

50

Coefficient of performance and its bounds for general refrigerators with nonisothermal processes  

NASA Astrophysics Data System (ADS)

An analysis of the coefficient of performance (COP) and its bounds at maximum \\chi figure of merit for refrigerators is conducted and the heat transfer processes are described using Newton’s law of cooling with a time-dependent heat conductance. The upper bound of the COP, {{\\varepsilon }_{CA}}=\\sqrt{{{\\varepsilon }_{C}}+1}-1, is independent of the time duration completing either process or the heat conductance. The optimal temperature profiles in the heat exchanging processes are analyzed under different dimensionless contact time limits. Provided the dimensionless contact times satisfy certain relations, the endoreversible model is recovered. Furthermore, numerical calculations are conducted to investigate the effect of different heat conductances on temperature profiles under the maximum \\chi criterion. This work can guide design and operation of actual refrigerators.

Long, Rui; Liu, Wei

2014-08-01

51

Reliability Generalization: Exploring Variation of Reliability Coefficients of MMPI Clinical Scales Scores.  

ERIC Educational Resources Information Center

Used reliability generalization to explore the variance of scores on 10 Minnesota Multiphasic Personality Inventory (MMPI) clinical scales drawing on 1,972 articles in the literature on the MMPI. Results highlight the premise that scores, not tests, are reliable or unreliable, and they show that study characteristics do influence scores on the…

Vacha-Haase, Tammi; Kogan, Lori R.; Tani, Crystal R.; Woodall, Renee A.

2001-01-01

52

Exploiting general coefficient representation for the optimal sharing of partial products in MCMs  

Microsoft Academic Search

We propose a new algorithm that maximizes the sharing of partial terms in Multiple Constant Multiplication (MCM) operations under a general number representation for the coecien ts. MCM operations are required by many algo- rithms in digital signal processing and have been the sub- ject of extensive research. By making no assumptions as to the number representation, the algorithm described

Eduardo A. C. Da Costa; Paulo F. Flores; José Monteiro

2006-01-01

53

Warped DGP model in warm intermediate inflation with a general dissipative coefficient in light of BICEP2 and Planck results  

E-print Network

A warm inflationary universe scenario on a warped Dvali-Gabadadze-Porrati brane during intermediate inflation is studied. We consider a general form for the dissipative coefficient $\\Gamma(T,\\phi)\\propto T^{m}/\\phi^{m-1}$, and also study this model in the weak and strong dissipative regimes. We analyze the evolution of the universe in the slow-roll approximation, and find the exact solutions to the equations of motion. In both regimes, we utilize recent data from the BICEP2 experiment and also from the Planck satellite to constrain the parameters in our model in accordance with the theory of cosmological perturbations.

Ramon Herrera; Nelson Videla; Marco Olivares

2014-10-14

54

Warped DGP model in warm intermediate inflation with a general dissipative coefficient in light of BICEP2 and Planck results  

E-print Network

A warm inflationary universe scenario on a warped Dvali-Gabadadze-Porrati brane during intermediate inflation is studied. We consider a general form for the dissipative coefficient $\\Gamma(T,\\phi)\\propto T^{m}/\\phi^{m-1}$, and also study this model in the weak and strong dissipative regimes. We analyze the evolution of the universe in the slow-roll approximation, and find the exact solutions to the equations of motion. In both regimes, we utilize recent data from the BICEP2 experiment and also from the Planck satellite to constrain the parameters in our model in accordance with the theory of cosmological perturbations.

Herrera, Ramon; Olivares, Marco

2014-01-01

55

Warped DGP model in warm intermediate inflation with a general dissipative coefficient in light of BICEP2 and Planck results  

NASA Astrophysics Data System (ADS)

A warm inflationary universe scenario on a warped Dvali-Gabadadze-Porrati brane during intermediate inflation is studied. We consider a general form for the dissipative coefficient ? (T ,? )?Tm/?m -1 , and also study this model in the weak and strong dissipative regimes. We analyze the evolution of the Universe in the slow-roll approximation and find the exact solutions to the equations of motion. In both regimes, we utilize recent data from the BICEP2 experiment and also from the Planck satellite to constrain the parameters in our model in accordance with the theory of cosmological perturbations.

Herrera, Ramón; Videla, Nelson; Olivares, Marco

2014-11-01

56

Stiff Quantum Polymers  

E-print Network

At ultralow temperatures, polymers exhibit quantum behavior, which is calculated here for the moments and of the end-to-end distribution in the large-stiffness regime. The result should be measurable for polymers in wide optical traps.

H. Kleinert

2007-01-02

57

Zero stiffness tensegrity structures  

Microsoft Academic Search

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

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

2007-01-01

58

On Zero Stiffness  

E-print Network

be achieved, for instance, by twisting the wire prior to the coiling of the spring.) The Anglepoise spring mechanism illustrates two zero stiffness interpretations: by generating a constant upward force the weight of the lamp shade is continuously balanced... proven to be powerful in analysing more complex zero-stiffness structures [60]. It is interesting to consider the parallel of this example to a cable-stayed mast, where the tension in the guy-ropes is increased. Intuitively, an increase in pretension...

Schenk, Mark; Guest, Simon D.

2013-11-17

59

Theory versus experiment for the rotordynamic coefficients of annular gas seals. II - Constant-clearance and convergent-tapered geometry  

NASA Technical Reports Server (NTRS)

The leakage and rotordynamic coefficients of constant-clearance and convergent-tapered annular gas seals were measured in an experimental test facility. The results are presented along with the theoretically predicted values. Of particular interest is the prediction that optimally tapered seals have significantly larger direct stiffness than straight seals. The experimental results verify this prediction. Generally the theory does quite well, but fails to predict the large increase in direct stiffness when the fluid is pre-rotated.

Nelson, C. C.; Childs, D. W.; Nicks, C.; Elrod, D.

1985-01-01

60

Measurement of normal contact stiffness of fractal rough surfaces  

E-print Network

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

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

2014-08-26

61

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

62

Stiff quantum polymers  

E-print Network

At ultralow temperatures, polymers exhibit quantum behavior, which is calculated here for the second and fourth moments of the end-to-end distribution in the large-stiffness regime. The result should be measurable for polymers in wide optical traps.

H. Kleinert

2009-10-19

63

Some Possible Features of General Expressions for Lovelock Tensors and for the Coefficients of Lovelock Lagrangians Up to the 15th Order in Curvature (and Beyond)  

E-print Network

This paper presents some possible features of general expressions for Lovelock tensors and for the coefficients of Lovelock Lagrangians up to the 15th order in curvature (and beyond) in terms of the Riemann-Christoffel and Ricci curvature tensors and the Riemann curvature scalar for n-dimensional differentiable manifolds having a general linear connection.

C. C. Briggs

1998-08-18

64

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

65

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

66

An auto-Backlund transformation and exact solutions to a generalized KdV equation with variable coefficients and their applications  

Microsoft Academic Search

By using the homogeneous balance principle, an auto-Backlund transformation (BT) to the generalized KdV equation with variable coefficients is derived. The auto-BT only involves one quadratic homogeneity equation to be solved. Solving the homogeneity equation by use of the ?-expansion method and using the auto-BT, generally speaking, we can obtain an exact solution containing N-solitary wave of the generalized KdV

Mingliang Wang; Yueming Wang; Yubin Zhou

2002-01-01

67

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

68

A new statistical method for transfer coefficient calculations in the framework of the general multiple-compartment model of transport for radionuclides in biological systems  

Microsoft Academic Search

A new and simple statistical procedure (STATFLUX) for the calculation of transfer coefficients of radionuclide transport to animals and plants is proposed. The method is based on the general multiple-compartment model, which uses a system of linear equations involving geometrical volume considerations. By using experimentally available curves of radionuclide concentrations versus time, for each animal compartment (organs), flow parameters were

F. Garcia; J. D. T. Arruda-Neto; M. V. Manso; O. M. Helene; V. R. Vanin; O. Rodriguez; J. Mesa; V. P. Likhachev; J. W. Pereira Filho; A. Deppman; G. Perez; F. Guzman; S. P. de Camargo

1999-01-01

69

Computation of Phase and Group Velocities of Surface Waves in a Spherical Earth Using the Generalized Reflection-Transmission Coefficient Method  

Microsoft Academic Search

We present a new approach to evaluate phase and group velocities of Love and Rayleigh waves in a spherical layered earth using the generalized reflection-transmission coefficient method. The approach is simple and self-efficient to give numerically stable results at all frequency ranges. The method has been previously used for computing phase velocities in a flat layered earth. For spherical earth,

T. Qureshi; S. N. Bhattacharya

2006-01-01

70

[Stiff-man syndrome].  

PubMed

The Stiff-man syndrome is a rare disease, which is characterized by continuous muscular rigidity and painful muscle spasm. Although large dose diazepam, baclofen, clonazepam, or clonidine benefit the symptoms significantly, the pathophysiology had been unknown until recently. In 1988 and 1990, Solimena et al. reported autoantibody against glutamic acid decarboxylase in sera and cerebrospinal fluids. Plasmapheresis was then applied to a patient with this syndrome, and the symptoms and the electromyographic activities decreased dramatically. The syndrome is likely to be an autoimmune disease, but further detailed studies are required as to the cause and pathophysiology and immunological treatment must should be established. PMID:8277586

Shindo, M

1993-11-01

71

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

72

Transfer having a coupling coefficient higher than its active material  

NASA Technical Reports Server (NTRS)

A coupling coefficient is a measure of the effectiveness with which a shape-changing material (or a device employing such a material) converts the energy in an imposed signal to useful mechanical energy. Device coupling coefficients are properties of the device and, although related to the material coupling coefficients, are generally different from them. This invention describes a class of devices wherein the apparent coupling coefficient can, in principle, approach 1.0, corresponding to perfect electromechanical energy conversion. The key feature of this class of devices is the use of destabilizing mechanical pre-loads to counter inherent stiffness. The approach is illustrated for piezoelectric and thermoelectrically actuated devices. The invention provides a way to simultaneously increase both displacement and force, distinguishing it from alternatives such as motion amplification, and allows transducer designers to achieve substantial performance gains for actuator and sensor devices.

Lesieutre, George A. (Inventor); Davis, Christopher L. (Inventor)

2001-01-01

73

Stiffness matrix method with improved efficiency for elastic wave propagation in layered anisotropic media  

Microsoft Academic Search

This paper presents the recursive algorithm of stiffness matrix method with improved efficiency for computing the total and surface stiffness matrices for a general multilayered anisotropic media. Based on the eigensolutions commonly available for analysis of such media, the recursive algorithm deals with eigen-submatrices directly and bypasses all intermediate layer stiffness submatrices. The improved algorithm obviates the need to compute

Eng Leong Tan

2005-01-01

74

Recursive asymptotic stiffness matrix method for analysis of surface acoustic wave devices on layered piezoelectric media  

Microsoft Academic Search

Based on a simple second-order thin layer asymptotic expansion for the transfer matrix, an asymptotic solution for the stiffness matrix for a general anisotropic piezoelectric thin layer is obtained. The total stiffness matrix for thick layers or multilayers is calculated with arbitrary precision by subdividing them into thin sublayers and combining recursively the thin layer stiffness matrices. It is shown

L. Wang; S. I. Rokhlin

2002-01-01

75

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.

76

NOMENCLATURE CD fuselage drag coefficient  

E-print Network

coefficient F vector of overall forces and moments l fuselage half-length Nb number of blades R rotor radius vi induced velocity advance ratio blade azimuth rotor rotational speed Subscripts/superscripts c coaxial helicopter with a stiff main rotor system and a tail-mounted propulsor are investigated using

Alonso, Juan J.

77

Extraordinary stiffness tunability through thermal expansion of nonlinear defect modes  

E-print Network

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

Marc Serra-Garcia; Joseph Lydon; Chiara Daraio

2014-11-19

78

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

79

Stiffness, thermal expansion, and thermal bending formulation of stiffened, fiber-reinforced composite panels  

NASA Technical Reports Server (NTRS)

A method is presented for formulating stiffness terms and thermal coefficients of stiffened, fiber-reinforced composite panels. The method is robust enough to handle panels with general cross sectional shapes, including those which are unsymmetric and/or unbalanced. Nonlinear, temperature and load dependent constitutive material data of each laminate are used to 'build-up' the stiffened panel membrane, bending, and membrane-bending coupling stiffness terms and thermal coefficients. New thermal coefficients are introduced to quantify panel response from through-the-thickness temperature gradients. A technique of implementing this capability with a single plane of shell finite elements using the MSC/NASTRAN analysis program (FEA) is revealed that provides accurate solutions of entire airframes or engines with coarsely meshed models. An example of a composite, hat-stiffened panel is included to demonstrate errors that occur when an unsymmetric panel is symmetrically formulated as traditionally done. The erroneous results and the correct ones produced from this method are compared to analysis from discretely meshed three-dimensional FEA.

Collier, Craig S.

1993-01-01

80

Stiff, Strong, Zero Thermal Expansion Lattices via Material Jeremy Lehman1  

E-print Network

Stiff, Strong, Zero Thermal Expansion Lattices via Material Hierarchy Jeremy Lehman1 and Roderic@engr.wisc.edu adapted from Lehman, J. J. and Lakes, R. S., "Stiff, strong, zero thermal expansion lattices via material of temperatures it becomes desirable to reduce a material's coefficient of thermal expansion. By carefully

Lakes, Roderic

81

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

82

Analytical and experimental evaluation of the leakage and stiffness characteristics of high pressure pocket damper seals  

E-print Network

This thesis presents numerical predictions for the leakage and direct stiffness coefficients of pocket damper seals. Modifications made to earlier flow-prediction models are discussed. Leakage and static pressure measurements on straight...

Gamal Eldin, Ahmed Mohamed

2004-09-30

83

Influence of Ply Waviness on Stiffness and Strength Reduction of Composite Laminates.  

National Technical Information Service (NTIS)

An analytic model is developed to investigate the influence of ply waviness on the stiffness and strength of composite laminates. The model predicts: elastic properties and thermal expansion coefficients of sublaminates containing wavy layers; ply stress ...

T. A. Bogetti, J. W. Gillespie, M. A. Lamontia

1993-01-01

84

Stable recursive algorithm for elastic wave propagation in layered anisotropic media: stiffness matrix method.  

PubMed

An efficient recursive algorithm, the stiffness matrix method, has been developed for wave propagation in multilayered generally anisotropic media. This algorithm has the computational efficiency and simplicity of the standard transfer matrix method and is unconditionally computationally stable for high frequency and layer thickness. In this algorithm, the stiffness (compliance) matrix is calculated for each layer and recursively applied to generate a stiffness (compliance) matrix for a layered system. Next, reflection and transmission coefficients are calculated for layered media bounded by liquid or solid semispaces. The results show that the method is stable for arbitrary number and thickness of layers and the computation time is proportional to the number of layers. It is shown both numerically and analytically that for a thick structure the solution approaches the solution for a semispace. This algorithm is easily adaptable to laminates with periodicity, such as multiangle lay-up composites. The repetition and symmetry of the unit cell are naturally incorporated in the recursive scheme. As an example the angle beam time domain pulse reflections from fluid-loaded multilayered composites have been computed and compared with experiment. Based on this method, characteristic equations for Lamb waves and Floquet waves in periodic media have also been determined. PMID:12243168

Rokhlin, S I; Wang, L

2002-09-01

85

Management of postoperative shoulder stiffness.  

PubMed

Arthroscopic surgery has become the most popular treatment to repair rotator cuff tears. Although the exact prevalence of postoperative stiffness is unknown, many studies report an incidence rate of 4% to 15%. Management of postoperative shoulder stiffness depends on the cause of the stiffness. Nonoperative and operative management modalities are available, but postoperative shoulder stiffness is often resistant to nonsurgical management. When conservative treatment fails, surgical release of the scar tissue and adhesions can be performed both by arthroscopic or open surgery. Arthroscopic capsular release is the preferred technique for capsule contraction and adhesion formation, as it allows precise and selective debridement of the scar tissue and division of the shortened and thickened capsule by partial or extensive capsulectomy. PMID:22089292

Franceschi, Francesco; Papalia, Rocco; Palumbo, Alessio; Vasta, Sebastiano; Maffulli, Nicola; Denaro, Vincenzo

2011-12-01

86

Non-singular Stiff Fluids  

E-print Network

In this talk the possibility of constructing geodesically complete inhomogeneous stiff fluid cosmologies is discussed. A family with infinite parameters is derived. A wide and easy to implement sufficient condition for geodesic completeness is shown.

L. Fernández-Jambrina; L. M. González-Romero

2009-04-08

87

Switchable stiffness scanning microscope probe  

E-print Network

Atomic Force Microscopy (AFM) has rapidly gained widespread utilization as an imaging device and micro/nano-manipulator during recent years. This thesis investigates the new concept of a dual stiffness scanning probe with ...

Mueller-Falcke, Clemens T. (Clemens Tobias)

2005-01-01

88

Passive stiffness of coupled wrist and forearm rotations.  

PubMed

Coordinated movement requires that the neuromuscular system account and compensate for movement dynamics. One particularly complex aspect of movement dynamics is the interaction that occurs between degrees of freedom (DOF), which may be caused by inertia, damping, and/or stiffness. During wrist rotations, the two DOF of the wrist (flexion-extension and radial-ulnar deviation, FE and RUD) are coupled through interaction torques arising from passive joint stiffness. One important unanswered question is whether the DOF of the forearm (pronation-supination, PS) is coupled to the two DOF of the wrist. Answering this question, and understanding the dynamics of wrist and forearm rotations in general, requires knowledge of the stiffness encountered during rotations involving all three DOF (PS, FE, and RUD). Here we present the first-ever measurement of the passive stiffness encountered during simultaneous wrist and forearm rotations. Using a wrist and forearm robot, we measured coupled wrist and forearm stiffness in 10 subjects and present it as a 3-by-3 stiffness matrix. This measurement of passive wrist and forearm stiffness will enable future studies investigating the dynamics of wrist and forearm rotations, exposing the dynamics for which the neuromuscular system must plan and compensate during movements involving the wrist and forearm. PMID:24912766

Drake, Will B; Charles, Steven K

2014-09-01

89

Martial Arts Training Attenuates Arterial Stiffness in Middle Aged Adults  

PubMed Central

Purpose Arterial stiffness increases with age and is related to an increased risk of coronary artery disease. Poor trunk flexibility has been shown to be associated with arterial stiffness in middle-aged subjects. The purpose of our research study was to measure arterial stiffness and flexibility in healthy middle-aged martial artists compared to age and gender matched healthy sedentary controls. Methods Ten martial artists (54.0 ± 2.0 years), who practice Soo Bahk Do (SBD), a Korean martial art, and ten sedentary subjects (54.7 ± 1.8 years) for a total of twenty subjects took part in this cross-sectional study. Arterial stiffness was assessed in all subjects using pulse wave velocity (PWV), a recognized index of arterial stiffness. Flexibility of the trunk and hamstring were also measured. The independent variables were the martial artists and matched sedentary controls. The dependent variables were PWV and flexibility. Results There were significant differences, between the SBD practitioners and sedentary controls, in PWV (P = 0.004), in trunk flexibility (P= 0.002), and in hamstring length (P= 0.003). Conclusion The middle-aged martial artists were more flexible in their trunk and hamstrings and had less arterial stiffness compared to the healthy sedentary controls. The flexibility component of martial art training or flexibility exercises in general may be considered as a possible intervention to reduce the effects of aging on arterial stiffness. PMID:24427479

Douris, Peter C.; Ingenito, Teresa; Piccirillo, Barbara; Herbst, Meredith; Petrizzo, John; Cherian, Vincen; McCutchan, Christopher; Burke, Caitlin; Stamatinos, George; Jung, Min-Kyung

2013-01-01

90

Time simulation of flutter with large stiffness changes  

NASA Technical Reports Server (NTRS)

Time simulation of flutter, involving large local structural changes, is formulated with a state-space model that is based on a relatively small number of generalized coordinates. Free-free vibration modes are first calculated for a nominal finite-element model with relatively large fictitious masses located at the area of structural changes. A low-frequency subset of these modes is then transformed into a set of structural modal coordinates with which the entire simulation is performed. These generalized coordinates and the associated oscillatory aerodynamic force coefficient matrices are used to construct an efficient time-domain, state-space model for basic aeroelastic case. The time simulation can then be performed by simply changing the mass, stiffness and damping coupling terms when structural changes occur. It is shown that the size of the aeroelastic model required for time simulation with large structural changes at a few a priori known locations is similar to that required for direct analysis of a single structural case. The method is applied to the simulation of an aeroelastic wind-tunnel model. The diverging oscillations are followed by the activation of a tip-ballast decoupling mechanism that stabilizes the system but may cause significant transient overshoots.

Karpel, M.; Wieseman, C. D.

1992-01-01

91

Time simulation of flutter with large stiffness changes  

NASA Technical Reports Server (NTRS)

Time simulation of flutter, involving large local structural changes, is formulated with a state-space model that is based on a relatively small number of generalized coordinates. Free-free vibration modes are first calculated for a nominal finite-element model with relatively large fictitious masses located at the area of structural changes. A low-frequency subset of these modes is then transformed into a set of structural modal coordinates with which the entire simulation is performed. These generalized coordinates and the associated oscillatory aerodynamic force coefficient matrices are used to construct an efficient time-domain, state-space model for a basic aeroelastic case. The time simulation can then be performed by simply changing the mass, stiffness, and damping coupling terms when structural changes occur. It is shown that the size of the aeroelastic model required for time simulation with large structural changes at a few apriori known locations is similar to that required for direct analysis of a single structural case. The method is applied to the simulation of an aeroelastic wind-tunnel model. The diverging oscillations are followed by the activation of a tip-ballast decoupling mechanism that stabilizes the system but may cause significant transient overshoots.

Karpel, Mordechay; Wieseman, Carol D.

1992-01-01

92

Stiffness and damping of elastomeric O-ring bearing mounts  

NASA Technical Reports Server (NTRS)

A test rig to measure the dynamic stiffness and damping of elastomer O rings was described. Test results for stiffness and loss coefficient in the frequency range from 50 Hz to 1000 Hz are presented. Results are given for three different materials, for five temperatures, for three amplitudes, for five values of squeeze for three values of stretch for three values of cross-section diameter and for three values of groove width. All test data points were plotted. In addition, trend summary plots were presented which compare the effect of material, temperature, amplitude, squeeze, stretch, cross-section diameter, and groove width. O ring deflections under a static load for different material were presented; and effective static stiffness values were compared with dynamic values.

Smalley, A. J.

1977-01-01

93

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

94

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

95

The interday reliability of ankle, knee, leg, and vertical musculoskeletal stiffness during hopping and overground running.  

PubMed

A number of methods are used to measure lower extremity musculoskeletal stiffness, but there is a paucity of research examining the reliability of these techniques. Therefore, we investigated the reliability of vertical, leg, knee, and ankle stiffness during overground running and hopping in 20 active men. Participants were required to run on a 10 m overground runway at 3.83 m/s (actual; 3.35 ± 0.12 m/s) and to hop in place at 2.2 Hz (actual; 2.37 ± 0.03 Hz), and at a self-selected frequency (actual; 2.05 ± 0.12 Hz) and at 2.2 Hz (actual; 2.39 ± 0.04 Hz). Reliability was determined using the intraclass correlation coefficient, coefficient of variation, mean differences, and Cohen's effect sizes. There was good reliability for vertical stiffness, moderate reliability for leg stiffness, and poor reliability for knee and ankle stiffness during the running task. Similar results were observed during the 2.2 Hz hopping tasks, with good reliability displayed for vertical stiffness and poor reliability for ankle and knee stiffness. In conclusion, our results suggest that vertical stiffness is a reliable measure when running at 3.83 m/s and hopping at 2.2 Hz. PMID:22923423

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

2013-08-01

96

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

SciTech Connect

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 Schroedinger system with higher order effects such as the third-order dispersion, self-steepening and self-frequency shift. Using the Painleve singularity structure analysis, we obtain two cases for this system to admit the Painleve property. Then for case (1) we derive the optical dark solitons via solving the Hirota bilinear equations; and based on the obtained (2N+1)x(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.

Lue Xing; Li Juan; Zhang Haiqiang; Xu Tao; Li Lili [School of Science, Beijing University of Posts and Telecommunications, P.O. Box 49, Beijing 100876 (China); Tian Bo [School of Science, Beijing University of Posts and Telecommunications, P.O. Box 49, 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)

2010-04-15

97

Arterial Stiffness and Cardiovascular Therapy  

PubMed Central

The world population is aging and the number of old people is continuously increasing. Arterial structure and function change with age, progressively leading to arterial stiffening. Arterial stiffness is best characterized by measurement of pulse wave velocity (PWV), which is its surrogate marker. It has been shown that PWV could improve cardiovascular event prediction in models that included standard risk factors. Consequently, it might therefore enable better identification of populations at high-risk of cardiovascular morbidity and mortality. The present review is focused on a survey of different pharmacological therapeutic options for decreasing arterial stiffness. The influence of several groups of drugs is described: antihypertensive drugs (angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers, beta-blockers, diuretics, and nitrates), statins, peroral antidiabetics, advanced glycation end-products (AGE) cross-link breakers, anti-inflammatory drugs, endothelin-A receptor antagonists, and vasopeptidase inhibitors. All of these have shown some effect in decreasing arterial stiffness. Nevertheless, further studies are needed which should address the influence of arterial stiffness diminishment on major adverse cardiovascular and cerebrovascular events (MACCE). PMID:25170513

Janic, Miodrag; Lunder, Mojca; Sabovic, Miso

2014-01-01

98

Scaling stiffness of spin glasses  

Microsoft Academic Search

The concept of a scaling stiffness for frustrated systems is introduced. Physical arguments supported by numerical calculations on a 3d Heisenberg spin glass suggest that its apparent lower critical dimensionality is time dependent, being equal to three on short time scales and bigger than three at sufficiently long times.

J. R. Banavar; M. Cieplak

1983-01-01

99

Bone stiffness predicts strength similarly for human vertebral cancellous bone in compression and for cortical bone in tension  

Microsoft Academic Search

The yield strength and ultimate strength of cortical and cancellous bone tissue are very highly correlated to bone stiffness. For samples of human vertebral cancellous bone in compression and for bovine cortical bone in tension, the coefficient of determination (r2) for regression between ultimate strength and stiffness was 0.89 and 0.92, and between yield strength and stiffness it was 0.94

D. P Fyhrie; D Vashishth

2000-01-01

100

Theory versus experiment for the rotordynamic coefficients of annular gas seals. Part 2: Constant clearance and convergent-tapered geometry  

NASA Technical Reports Server (NTRS)

The leakage and rotordynamic coefficients of constant-clearance and convergent-tapered annular gas seals were measured in an experimental test facility. The results are presented along with the theoretically predicted values. Of particular interest is the prediction that optimally tapered seals have significantly larger direct siffness than straight seals. The experimental results verify this prediction. Generally the theory does quite well, but fails to predict the large increase in direct stiffness when the fluid is pre-rotated.

Nelson, C. C.; Childs, D. W.; Nicks, C.; Elrod, D.

1985-01-01

101

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

102

Conservation Assessment for Groundcedar and Stiff  

E-print Network

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

103

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. PMID:24991809

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

2014-01-01

104

Response of initial field to stiffness perturbation  

E-print Network

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

Chen-Wu Wu

2014-03-18

105

Zero Stiffness Tensegrity Structures M. Schenk a  

E-print Network

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

Guest, Simon

106

Stiffness matrix method with improved efficiency for elastic wave propagation in layered anisotropic media  

NASA Astrophysics Data System (ADS)

This paper presents the recursive algorithm of stiffness matrix method with improved efficiency for computing the total and surface stiffness matrices for a general multilayered anisotropic media. Based on the eigensolutions commonly available for analysis of such media, the recursive algorithm deals with eigen-submatrices directly and bypasses all intermediate layer stiffness submatrices. The improved algorithm obviates the need to compute certain inverse of the original scheme and makes the stiffness matrix recursion more robust. In situation where transfer matrix is numerically stable and easily accessible, an improved recursive algorithm is also given directly in terms of transfer submatrices without involving their explicit inverse.

Tan, Eng Leong

2005-12-01

107

Experimental determination of dynamic force coefficients of a pocket damper seal at higher frequencies  

E-print Network

Experimental results are presented for a two-bladed pocket damper seal (PDS) with eight partition walls on a high-speed test rig. The objective of these experiments is to measure damping coefficients, stiffness coefficients and leakage rates...

Sharma, Ashish

2012-06-07

108

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

109

Constraint-based Equilibrium and Stiffness Control of Variable Stiffness Actuators  

E-print Network

of online teleoperation, to transfer compliant human behaviour to a variable stiffness device. I to 4th order), and assuming a diagonal stiffness matrix, these profiles can be tracked in a similar wayConstraint-based Equilibrium and Stiffness Control of Variable Stiffness Actuators Matthew Howard

Vijayakumar, Sethu

110

Stable recursive algorithm for elastic wave propagation in layered anisotropic media: Stiffness matrix method  

Microsoft Academic Search

An efficient recursive algorithm, the stiffness matrix method, has been developed for wave propagation in multilayered generally anisotropic media. This algorithm has the computational efficiency and simplicity of the standard transfer matrix method and is unconditionally computationally stable for high frequency and layer thickness. In this algorithm, the stiffness (compliance) matrix is calculated for each layer and recursively applied to

S. I. Rokhlin; L. Wang

2002-01-01

111

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

112

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

E-print Network

. Srinivasan, C. E. Patton, andP. de Gasperis Abstract - The spin wave exchange stiffness coefficient has been was a Visiting Professor at Colorado State University. G. Srinivasan andC. E. Patton are with the Department

Patton, Carl

113

Stiffness gradient in the crystalline lens  

Microsoft Academic Search

Background  While the overall stiffness of the lens has been measured in a number of studies, the knowledge about the stiffness distribution\\u000a within the lens is still limited. The purpose of this study was to determine the stiffness gradient in the human crystalline\\u000a lens. A secondary purpose was to determine whether the stiffness gradient depends on age.\\u000a \\u000a \\u000a \\u000a Methods  The local dynamic stiffness

Henk A. Weeber; Gabriele Eckert; Wolfgang Pechhold

2007-01-01

114

Ultrasonic evaluation of interlayer interfacial stiffness of multilayered structures  

NASA Astrophysics Data System (ADS)

A procedure for the ultrasonic evaluation of the interlayer interfacial stiffness of multilayered structures is proposed. As a theoretical background to this proposal, the elastic wave propagation in a multilayered structure, in which the layers are bonded with spring-type interfaces, is analyzed theoretically based on the transfer-matrix method. Using the notion of the Bloch phase which characterizes wave transmission in the corresponding infinite periodic structure, some explicit relations are derived for the reflection coefficient of the multilayered structure. Based on the features clarified theoretically, the interlayer interfacial stiffness of the multilayered structure can be evaluated from the locations of local minima and maxima of the amplitude reflection spectrum. By numerical analysis, the proposed procedure is shown to apply even when the viscous property of the layers is not known precisely, and when a transient waveform of a limited length is used. Using the proposed procedure, the stiffness of interlayer resin-rich regions in a carbon-epoxy cross-ply composite laminate is identified from the experimental reflection spectrum. The identified stiffness is shown to lie within the range as expected from the micrographic observation and a simple estimate for a thin resin layer.

Ishii, Yosuke; Biwa, Shiro

2012-04-01

115

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

116

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

117

Parameter estimation for stiff deterministic dynamical systems via ensemble Kalman filter  

NASA Astrophysics Data System (ADS)

A commonly encountered problem in numerous areas of applications is to estimate the unknown coefficients of a dynamical system from direct or indirect observations at discrete times of some of the components of the state vector. A related problem is to estimate unobserved components of the state. An egregious example of such a problem is provided by metabolic models, in which the numerous model parameters and the concentrations of the metabolites in tissue are to be estimated from concentration data in the blood. A popular method for addressing similar questions in stochastic and turbulent dynamics is the ensemble Kalman filter (EnKF), a particle-based filtering method that generalizes classical Kalman filtering. In this work, we adapt the EnKF algorithm for deterministic systems in which the numerical approximation error is interpreted as a stochastic drift with variance based on classical error estimates of numerical integrators. This approach, which is particularly suitable for stiff systems where the stiffness may depend on the parameters, allows us to effectively exploit the parallel nature of particle methods. Moreover, we demonstrate how spatial prior information about the state vector, which helps the stability of the computed solution, can be incorporated into the filter. The viability of the approach is shown by computed examples, including a metabolic system modeling an ischemic episode in skeletal muscle, with a high number of unknown parameters.

Arnold, Andrea; Calvetti, Daniela; Somersalo, Erkki

2014-10-01

118

Coefficient scaling.  

PubMed

We prove a remarkably simple but powerful recursion relation for the coefficients of iterated polynomials. We also prove that the recursion relation holds for the coefficients of certain functions of the iterated polynomial. Using the recursion relations, we obtain a closed-form expression for the average number of closed-loop self-avoiding walks per site on a family of fractal lattices. We describe numerical results, which exhibit log-periodic oscillations, and find good agreement between these results and the theory developed here, which predicts the existence of the log-periodic oscillations and their amplitudes. Finally, we discuss insights gained into the mathematical origins of critical phenomena. PMID:11969435

Paul, G

1999-05-01

119

Torsional stiffness degradation and aerostatic divergence of suspension bridge decks  

NASA Astrophysics Data System (ADS)

The mechanism of aerostatic torsional divergence (ATD) of long-span suspension bridges is investigated. A theoretical analysis on the basis of a generalized model is presented, showing that the vertical motion of a bridge deck is crucial to the torsional stiffness of the whole suspended system, and that the vertical motion of either cable with a magnitude beyond a certain threshold could result in a sudden degradation of the torsional stiffness of the system. This vertical motion-induced degradation of stiffness is recognized as the main reason for the ATD. Long-span suspension bridges are susceptible to such a type of divergence, especially when they are immersed in turbulent wind fields. The divergences that occur in turbulent wind fields differ significantly from those in smooth wind fields, and the difference is well explained by the generalized model that the loosening of any one cable could result in the vanishing of the part of stiffness provided by the whole cable system. The mechanism revealed in this paper leads to a definition of the critical wind speed of the ATD in a turbulent flow; that is, the one resulting in a vertical motion so large as to loosen either cable to a stressless state. Numerical results from the nonlinear finite-element (FE) analysis of the Xihoumen suspension bridge, in conjunction with observations from wind tunnel tests on an aero-elastic full bridge model, are in support of the viewpoint presented in this study.

Zhang, Z. T.; Ge, Y. J.; Yang, Y. X.

2013-07-01

120

Increased shoe bending stiffness increases sprint performance.  

PubMed

The purposes of this investigation were to determine if increasing the bending stiffness of sprint shoes increases sprinting performance and to determine whether simple anthropometric factors can be used to predict shoe bending stiffness for optimal performance. Thirty-four athletes were tested using four different shoe conditions--a standard condition consisting of their currently used footwear and three conditions where the bending stiffness was increased systematically. The sprinters performed maximal effort 40 m sprints and their sprint times were recorded from 20 to 40 m. On average, increasing the shoe bending stiffness increased sprint performance. The stiffness each athlete required for his or her maximal performance was subject specific but was not related to subject mass, height, shoe size or skill level. It is speculated that individual differences in the force-length and force-velocity relationships of the calf muscles may influence the appropriate shoe stiffness for each athlete to obtain their maximal performance. PMID:15079988

Stefanyshyn, Darren; Fusco, Ciro

2004-01-01

121

Stiffness Simulation Using Non-linear FEA  

SciTech Connect

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

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

2005-08-05

122

Measurement of stiffness during simulated spinal physiotherapy  

Microsoft Academic Search

A new device was designed to simulate a physiotherapist's assessment of spinal stiffness. The device applies an oscillating postero-anterior force over a spinous process and the force-displacement relation is measured. From these data the stiffness of the movement can be computed. The accuracy and repeatability of stiffness values were found to be high when an elastic beam was tested. Test-retest

M. Lee; N. L. Svensson

1990-01-01

123

Increased vascular smooth muscle cell stiffness: a novel mechanism for aortic stiffness in hypertension  

PubMed Central

Increased vascular stiffness is fundamental to hypertension, and its complications, including atherosclerosis, suggest that therapy should also be directed at vascular stiffness, rather than just the regulation of peripheral vascular resistance. It is currently held that the underlying mechanisms of vascular stiffness in hypertension only involve the extracellular matrix and endothelium. We hypothesized that increased large-artery stiffness in hypertension is partly due to intrinsic mechanical properties of vascular smooth muscle cells. After confirming increased arterial pressure and aortic stiffness in spontaneously hypertensive rats, we found increased elastic stiffness of aortic smooth muscle cells of spontaneously hypertensive rats compared with Wistar-Kyoto normotensive controls using both an engineered aortic tissue model and atomic force microscopy nanoindentation. Additionally, we observed different temporal oscillations in the stiffness of vascular smooth muscle cells derived from hypertensive and control rats, suggesting that a dynamic component to cellular elastic stiffness is altered in hypertension. Treatment with inhibitors of vascular smooth muscle cell cytoskeletal proteins reduced vascular smooth muscle cell stiffness from hypertensive and control rats, suggesting their participation in the mechanism. This is the first study demonstrating that stiffness of individual vascular smooth muscle cells mediates vascular stiffness in hypertension, a novel concept, which may elucidate new therapies for hypertension and for vascular stiffness. PMID:23709594

Sehgel, Nancy L.; Zhu, Yi; Sun, Zhe; Trzeciakowski, Jerome P.; Hong, Zhongkui; Hunter, William C.; Vatner, Dorothy E.; Vatner, Stephen F.

2013-01-01

124

Concept for design of variable stiffness damper  

NASA Technical Reports Server (NTRS)

Damping mechanism, containing polymeric-like materials is applicable to a wide range of shock and vibration. The polymeric-like material changes from a relatively stiff material to a relatively soft, rubbery material in the region of their glass transition temperatures. The energy absorption characteristics and stiffness are controllable with temperature.

Lohr, J. J.

1967-01-01

125

Nonparticipatory Stiffness in the Male Perioral Complex  

ERIC Educational Resources Information Center

Purpose: The objective of this study was to extend previous published findings in the authors' laboratory using a new automated technology to quantitatively characterize nonparticipatory perioral stiffness in healthy male adults. Method: Quantitative measures of perioral stiffness were sampled during a nonparticipatory task using a…

Chu, Shin-Ying; Barlow, Steven M.; Lee, Jaehoon

2009-01-01

126

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

127

Stiffness Control of Surgical Continuum Manipulators  

PubMed Central

This paper introduces the first stiffness controller for continuum robots. The control law is based on an accurate approximation of a continuum robot’s coupled kinematic and static force model. To implement a desired tip stiffness, the controller drives the actuators to positions corresponding to a deflected robot configuration that produces the required tip force for the measured tip position. This approach provides several important advantages. First, it enables the use of robot deflection sensing as a means to both sense and control tip forces. Second, it enables stiffness control to be implemented by modification of existing continuum robot position controllers. The proposed controller is demonstrated experimentally in the context of a concentric tube robot. Results show that the stiffness controller achieves the desired stiffness in steady state, provides good dynamic performance, and exhibits stability during contact transitions. PMID:24273466

Mahvash, Mohsen; Dupont, Pierre E.

2013-01-01

128

Stiff Coatings on Compliant Biofibers  

PubMed Central

For lasting holdfast attachment, the mussel Mytilus californianus coats its byssal threads with a protective cuticle 2-5 ?m thick that is 4-6 times stiffer than the underlying collagen fibers. Although cuticle hardness (0.1 GPa) and stiffness (2 GPa) resemble those observed in related mussels, a more effective dispersion of microdamage enables M. californianus byssal threads to sustain strains to almost 120% before cuticle rupture occurs. Underlying factors for the superior damage tolerance of the byssal cuticle were explored in its microarchitecture and in the cuticular protein, mcfp-1. Cuticle microstructure was distinctly granular, with granule diameters (?200 nm) only a quarter of those in M. galloprovincialis cuticle, for example. Compared with homologous proteins in related mussel species, mcfp-1 from M. californianus had a similar mass (?92 kDa) and number of tandemly repeated decapeptides, and contained the same post-translational modifications, namely, trans-4-hydroxyproline, trans-2,3-cis-3,4-dihydroxyproline, and 3,4-dihydroxyphenylalanine (Dopa). The prominence of isoleucine in mcfp-1, however, distinguished it from homologues in other species. The complete protein sequence deduced from cDNAs for two related variants revealed a highly conserved consensus decapeptide PKISYPPTYK that is repeated 64 times and differs slightly from the consensus peptide (AKPSYPPTYK) of both M. galloprovincialis and M. edulis proteins. PMID:19220048

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

2009-01-01

129

Model-Based Estimation of Knee Stiffness  

PubMed Central

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

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

2013-01-01

130

A combined finite element–stiffness equation transfer method for steady state vibration response analysis of structures  

Microsoft Academic Search

An extended finite element transfer matrix method, in combination with stiffness equation transfer, is applied to dynamic response analysis of the structures under periodic excitations. In the present method, the transfer of state vectors from left to right in a combined finite element-transfer matrix (FE-TM) method is changed into the transfer of general stiffness equations of every section from left

Huiyu Xue

2003-01-01

131

A stiffness equation transfer method for transient dynamic response analysis of structures  

Microsoft Academic Search

A stiffness equation transfer method is proposed for transient dynamic response analysis of structures under various excitations. This method is a development and refinement of the combined finite element-transfer matrix (FE-TM) method. In the present method, the transfer of state vectors from left to right in the FE-TM method is changed into the transfer of general stiffness equations of every

Huiyu Xue

2004-01-01

132

Pseudo analytical solution to time periodic stiffness systems  

NASA Astrophysics Data System (ADS)

An analytical form of state transition matrix for a system of equations with time periodic stiffness is derived in order to solve the free response and also allow for the determination of system stability and bifurcation. A pseudo-closed form complete solution for parametrically excited systems subjected to inhomogeneous generalized forcing is developed, based on the Fourier expansion of periodic matrices and the substitution of matrix exponential terms via Lagrange—Sylvester theorem. A Mathieu type of equation with large amplitude is presented to demonstrate the method of formulating state transition matrix and Floquet multipliers. A two-degree-of-freedom system with irregular time periodic stiffness characterized by spiral bevel gear mesh vibration is presented to find forced response in stability and instability. The obtained results are presented and discussed.

Wang, Yan-Zhong; Zhou, Yuan-Zi

2011-04-01

133

Vibrational stiffness of an atomic lattice  

NASA Astrophysics Data System (ADS)

A model is presented to estimate the characteristic vibrational stiffness of an atomic lattice, given the pairwise interaction potential of the constituent atom. Unlike nearest-neighbor approaches (e.g., Slater or Dugdale and MacDonald), the vibrational stiffness is shown to be distinct from the bulk (i.e., volumetric) stiffness. This vibrational stiffness implies a characteristic vibrational frequency of the lattice that varies with the lattice spacing, which is used to infer the Grueneisen function of the lattice. Because non-nearest lattice neighbors are accounted for, the equations are expressed in terms of triple summations of the pairwise potential. However, an analytical fit to these triple summations has been developed. Furthermore, the analytical form calibrates to a range of cold- and shock-compression data, resulting in an analytical frequency-based equation of state (EOS) for crystalline solids.

Segletes, Steven B.

2000-04-01

134

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

135

Semiparametric Estimation of Index Coefficients  

Microsoft Academic Search

This paper gives a solution to the problem of estimating coefficients of index models, through the estimation of the density-weighted average derivative of a general regression function. A normalized version of the density-weighted average derivative can be estimated by certain linear instrumental variables coefficients. The estimators, based on sample analogies of the product moment representation of the average derivative, are

James L. Powell; James H. Stock; Thomas M. Stoker

1989-01-01

136

Arterial stiffness, physical function, and functional limitation: the Whitehall II Study.  

PubMed

Arterial stiffness has been proposed as an indicator of vascular aging. We aimed to examine this concept by analyzing associations of arterial stiffness with age, subjective and objective measures of physical functioning, and self-reported functional limitation. We measured aortic pulse wave velocity by applanation tonometry among 5392 men and women aged 55 to 78 years. Arterial stiffness was strongly associated with age (mean difference [SE] per decade: men, 1.37 m/s [0.06 m/s]; women: 1.39 m/s [0.10 m/s]). This association was robust to individual and combined adjustment for pulse pressure, mean arterial pressure, antihypertensive treatment, and chronic disease. Participants took an 8.00-ft (2.44-m) walking speed test, a spirometry lung function test, and completed health functioning and (instrumental) activities of daily living questionnaires. Associations of stiffness and blood pressure with physical function scores scaled to SD of 10 were compared. One-SD higher stiffness was associated with lower walking speed (coefficient [95% CI]: -0.96 [-1.29 to -0.64] m/s) and physical component summary score (-0.91 [-1.21 to -0.60]) and poorer lung function (-1.23 [-1.53 to -0.92] L) adjusted for age, sex, and ethnic group. Pulse pressure and mean arterial pressure were linked inversely only with lung function. Associations of stiffness with functional limitation were robust to multiple adjustment, including pulse pressure and chronic disease. In conclusion, the concept of vascular aging is reinforced by the observation that arterial stiffness is a robust correlate of physical functioning and functional limitation in early old age. The nature of the link between arterial stiffness and quality of life in older people merits attention. PMID:21444833

Brunner, Eric J; Shipley, Martin J; Witte, Daniel R; Singh-Manoux, Archana; Britton, Annie R; Tabak, Adam G; McEniery, Carmel M; Wilkinson, Ian B; Kivimaki, Mika

2011-05-01

137

Dynamic influences of changing gear tooth stiffness  

SciTech Connect

One of the principal sources of vibratory excitation of gear a system is due to the angular speed fluctuation of meshing gears due to non-linearities and profile errors and tooth and supporting bearings flexibility. The transmission error is also influenced by the varying force at the contact point of the meshing gear teeth. The varying contact force itself is influenced by the varying tooth stiffness due to change of orientation of teeth relative to each other, during the contact phase of each pair. This paper presents a simplified single degree of freedom gear system. It is assumed that one member of the gear pair is rigid and flexibility of the gear tooth is attributed only to one section of the gear system. This enables the equation to be simplified to a single degree of freedom system. The resulting non-linear equation is solved iteratively by employing a method which combines piecewise linearization for the stiffness and resulting contact orientation shift due to shaft and tooth flexibility. The contact shift will be referred as the phase shift in this report. The early finding indicates that there are significant differences between the response of the system incorporating three different tooth stiffness, namely, constant tooth stiffness, rectangular wave tooth stiffness and sinusoidal tooth stiffness. The results also implies that any design specification associated with gears has to include gear tooth influences, especially if the excitation is of a major concern. The rectangular stiffness variation which most accurately describes the tooth stiffness gives a response fluctuation, studied in the frequency domain shows that the effective natural frequencies fluctuates between certain upper and lower limits. Thus the paper suggest that any design study should consider these limits.

Morguel, O.K. [Sakarya Univ. (Turkey). Dept. of Mechanical Engineering; Esat, I. [Brunel Univ., Uxbridge (United Kingdom). Dept. of Mechanical Engineering

1997-07-01

138

Stiff limb syndrome: a case report  

PubMed Central

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

2010-01-01

139

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

140

Measurements of leakage, power loss and rotordynamic force coefficients in a hybrid brush seal  

E-print Network

shoedbrush seal. The HBS predicted effective clearance (~50 ?m) is a small fraction of that in an equivalent one-tooth labyrinth seal. Identified HBS direct stiffness coefficients decrease (~15%) as function of rotor speed for an increasing supply pressure...

Baker, Jose Enrique

2009-05-15

141

Identification of force coefficients in flexible rotor-bearing systems - enhancements and further validations  

E-print Network

Rotor-bearing system characteristics, such as natural frequencies, mode shapes, stiffness and damping coefficients, are essential to diagnose and correct vibration problems during system operation. Of the above characteristics, accurate...

Balantrapu, Achuta Kishore Rama Krishna

2005-11-01

142

Stiff-person syndrome with amphiphysin antibodies  

PubMed Central

Background: Stiff-person syndrome (SPS), formerly Stiff-man syndrome, is a rare autoimmune disease usually exhibiting severe spasms and thoracolumbar stiffness, with very elevated glutamic acid decarboxylase antibodies (GAD Ab). A paraneoplastic variant, less well characterized, is associated with amphiphysin antibodies (amphiphysin Ab). The objective of this study was to identify distinctive clinical features of amphiphysin Ab-associated SPS. Methods: Records associated with 845 sera tested in the Yale SPS project were examined, and 621 patients with clinically suspected SPS were included in the study. Clinical characteristics were assessed with correction for multiple comparisons. Results: In all, 116 patients had GAD antibodies and 11 patients had amphiphysin Ab; some clinical information was available for 112 and 11 of these patients, respectively. Patients with amphiphysin Ab-associated SPS were exclusively female; mean age was 60. All except one had breast cancer; none had diabetes. Compared to patients with GAD Ab-associated SPS, those with amphiphysin Ab were older (p = 0.02) and showed a dramatically different stiffness pattern (p < 0.0000001) with cervical involvement more likely, p ? 0.001. Electromyography showed continuous motor unit activity or was reported positive in eight. Benzodiazepines at high dose (average 50 mg/day diazepam) were partially effective. Four patients were steroid responsive and tumor excision with chemotherapy produced marked clinical improvement in three of five patients. Conclusions: Amphiphysin Ab-associated stiff-person syndrome is strongly associated with cervical region stiffness, female sex, breast cancer, advanced age, EMG abnormalities, and benzodiazepine responsiveness. The condition may respond to steroids and can dramatically improve with cancer treatment. GLOSSARY EAE = experimental autoimmune encephalitis; GAD Ab = glutamic acid decarboxylase antibodies; ICC = immunocytochemistry; PERM = progressive variant with encephalomyelitis, rigidity, and myoclonus; SPS = stiff-person syndrome. PMID:18971449

Murinson, Beth B.; Guarnaccia, Joseph B.

2008-01-01

143

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

144

Voluntary Control of Human Jaw Stiffness Douglas M. Shiller,1  

E-print Network

related to the stiff- ness of the jaw. If the nervous system uses stiffness control as a means to regulateVoluntary Control of Human Jaw Stiffness Douglas M. Shiller,1 Guillaume Houle,1 and David J. Ostry1, Douglas M., Guillaume Houle, and David J. Ostry. Vol- untary control of human jaw stiffness. J

145

Experimental and theoretical rotordynamic coefficients and leakage of straight smooth annular gas seals  

E-print Network

-response function elements obtained during a test. Frequency-response functions for both x and y directions are shown. Rotordynamic coefficients are determined from the frequency-response functions utilizing equation (7). Direct stiffness and direct damping...-response function elements obtained during a test. Frequency-response functions for both x and y directions are shown. Rotordynamic coefficients are determined from the frequency-response functions utilizing equation (7). Direct stiffness and direct damping...

Kerr, Bradley Gray

2005-02-17

146

Design of a variable-stiffness robotic hand using pneumatic soft rubber actuators  

NASA Astrophysics Data System (ADS)

In recent years, Japanese society has been ageing, engendering a labor shortage of young workers. Robots are therefore expected to be useful in performing tasks such as day-to-day support for elderly people. In particular, robots that are intended for use in the field of medical care and welfare are expected to be safe when operating in a human environment because they often come into contact with people. Furthermore, robots must perform various tasks such as regrasping, grasping of soft objects, and tasks using frictional force. Given these demands and circumstances, a tendon-driven robot hand with a stiffness changing finger has been developed. The finger surface stiffness can be altered by adjusting the input pressure depending on the task. Additionally, the coefficient of static friction can be altered by changing the surface stiffness merely by adjusting the input air pressure. This report describes the basic structure, driving mechanism, and basic properties of the proposed robot hand.

Nagase, Jun-ya; Wakimoto, Shuichi; Satoh, Toshiyuki; Saga, Norihiko; Suzumori, Koichi

2011-10-01

147

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

148

[Stiff-person syndrome and related autoantibodies].  

PubMed

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

Tomioka, Ryo; Tanaka, Keiko

2013-04-01

149

Determinants of arterial stiffness in COPD  

PubMed Central

Background Cardiovascular morbidity and mortality is high in patients with chronic obstructive pulmonary disease (COPD) and arterial stiffness is a potentially modifiable risk factor with added predictive value beyond that obtained from traditional risk factors. Arterial stiffness has been the target of pharmacologic and exercise interventions in patients with COPD, but the effects appear limited to those patients with more significant elevations in arterial stiffness. We aimed to identify predictors of increased arterial stiffness in a cohort with moderate to severe COPD. Methods Aortic pulse wave velocity (aPWV) was measured in subjects with moderate to severe COPD enrolled in a multicenter randomized controlled trial. Subjects were categorized into quartiles based on aPWV values and factors affecting high arterial stiffness were assessed. Multivariate models were created to identify independent predictors of high aPWV, and cardiovascular disease (CVD). Results 153 patients were included. Mean age was 63.2 (SD 8.2) years and mean FEV1 was 55.4 (SD 15.2) % predicted. Compared to the quartile with the lowest aPWV, subjects in the highest quartile were older, had higher systolic blood pressure (SBP), were more likely to be current smokers, and had greater burden of thoracic aortic calcification. On multivariate analyses, age (adjusted OR 1.14, 95%CI 1.05 to 1.25, p?=?0.003) and SBP (adjusted OR 1.06, 95% CI 1.02 to 1.09, p?=?0.001) were independent predictors of elevated aPWV. Body mass index, therapy with cholesterol lowering medications and coronary calcification were independent predictors of CVD. Conclusions Elevated arterial stiffness in patients with COPD can be predicted using age, blood pressure and thoracic aortic calcification. This will help identify subjects for enrollment in clinical trials using aPWV for assessing the impact of COPD therapies on CV outcomes. Trial registration Clinicaltrials.gov NCT00857766 PMID:24387157

2014-01-01

150

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. PMID:24734246

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

2014-01-01

151

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.

152

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

NASA Astrophysics Data System (ADS)

Magneto-rheological elastomers (MREs) have attracted notable credits in the development of smart isolators and absorbers due to their controllable stiffness and damping properties. For the purpose of mitigating unwanted structural and/or machinery vibrations, the traditional MRE-based isolators have been generally proven effective because the MR effect can increase the stiffness when the magnetic field is strengthened. This study presents a novel MRE isolator that experienced reduced stiffness when the applied current was increased. This innovative work was accomplished by applying a hybrid magnet (electromagnet and permanent magnets) onto a multilayered MRE structure. To characterise this negative changing stiffness concept, a multilayered MRE isolator with a hybrid magnet was first designed, fabricated and then tested to measure its properties. An obvious reduction of the effective stiffness and natural frequency of the proposed MRE isolator occurred when the current was continuously adjusted. This device could also work as a conventional MRE isolator as its effective stiffness and natural frequency also increased when a negative current was applied. Further testing was carried out on a one-degree-of-freedom system to assess how effectively this device could isolate vibration. In this experiment, two cases were considered; in each case, the vibration of the primary system was obviously attenuated under ON-OFF control logic, thus demonstrating the feasibility of this novel design as an alternative adaptive vibration isolator.

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

2014-10-01

153

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. PMID:22642467

2012-01-01

154

Numerically Generated Tangent Stiffness Matrices for Geometrically Non-Linear Structures  

NASA Astrophysics Data System (ADS)

The aim of this thesis is to develop a general numerical solution method for geometrically non-linear structures. Most common work involves tedious derivations of analytic tangent stiffness matrices. The major objective of the current work is to develop a numerically generated tangent stiffness matrix that allows for a general and easily implementable solution method. The thesis begins with the definition of the tangent stiffness matrix and a discussion of the Newton-Raphson incremental-iterative method typically used to solve geometrically non-linear problems. This is followed by a detailed description of how the tangent stiffness matrix is numerically generated using complex variable differentiation to approximate sensitivities. The thesis proceeds with details of the solution method applied to three different structural elements: 3D truss, membrane, and 3D beam. These discussions include numeric examples for each type of structure, the results of which are compared with the literature and ANSYS solutions. The results from the present work show that solutions obtained using the general numerically generated tangent stiffness matrix are accurate. While computational effort is increased, the method is especially attractive in the context of research involving small finite element models.

Lebofsky, Sonia

155

Adapting a Beam-Based Rotordynamics Model to Accept a General Three-Dimensional Finite-Element Casing Model  

E-print Network

coefficient of ith station about ith y? direction [L4] [ ]K ? System stiffness matrix in Guyan reduction model [ ]cK ? Transformed casing stiffness matrix ; 1: , 1:cicjk i n j= = n ? Stiffness matrix i,j-th entry of casing [FL-1] [ ]cscK... coefficient of ith station about ith y? direction [L4] [ ]K ? System stiffness matrix in Guyan reduction model [ ]cK ? Transformed casing stiffness matrix ; 1: , 1:cicjk i n j= = n ? Stiffness matrix i,j-th entry of casing [FL-1] [ ]cscK...

James, Stephen M.

2011-08-08

156

Elastic Stars in General Relativity: III. Stiff ultrarigid exact solutions  

E-print Network

We present an equation of state for elastic matter which allows for purely longitudinal elastic waves in all propagation directions, not just principal directions. The speed of these waves is equal to the speed of light whereas the transversal type speeds are also very high, comparable to but always strictly less than that of light. Clearly such an equation of state does not give a reasonable matter description for the crust of a neutron star, but it does provide a nice causal toy model for an extremely rigid phase in a neutron star core, should such a phase exist. Another reason for focusing on this particular equation of state is simply that it leads to a very simple recipe for finding stationary rigid motion exact solutions to the Einstein equations. In fact, we show that a very large class of stationary spacetimes with constant Ricci scalar can be interpreted as rigid motion solutions with this matter source. We use the recipe to derive a static spherically symmetric exact solution with constant energy density, regular centre and finite radius, having a nontrivial parameter that can be varied to yield a mass-radius curve from which stability can be read off. It turns out that the solution is stable down to a tenuity R/M slightly less than 3. The result of this static approach to stability is confirmed by a numerical determination of the fundamental radial oscillation mode frequency. We also present another solution with outwards decreasing energy density. Unfortunately, this solution only has a trivial scaling parameter and is found to be unstable.

Max Karlovini; Lars Samuelsson

2004-01-28

157

Vibrational Stiffness of an Atomic Lattice  

NASA Astrophysics Data System (ADS)

A model has been developed to estimate the characteristic vibrational stiffness of an atomic lattice, given the pairwise interaction potential of the constituent atom. Unlike nearest-neighbor approaches (e.g., Slater or Dugdale and MacDonald), the vibrational stiffness is shown to be distinct from the lattice (i.e., volumetric) stiffness. This vibrational stiffness implies a characteristic vibrational frequency of the lattice, which is shown to vary with the lattice spacing. The manner in which the frequency varies with lattice spacing is used to infer the Grueneisen function of the lattice. Because non-nearest lattice neighbors are accounted for, the equations are expressed in terms of triple summations of the pairwise potential. However, an analytical fit to these triple summations has been developed, accurate over a wide range of lattice conditions. Furthermore, the analytical form calibrates to a wide range of cold- and shock-compression data. The result is an analytical frequency-based equation of state for crystalline solids.

Segletes, Steven B.

1999-06-01

158

Elastin in large artery stiffness and hypertension  

PubMed Central

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

Wagenseil, Jessica E.; Mecham, Robert P.

2012-01-01

159

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. We apply perturbative arguments, Flory scaling arguments, a variational replica calculation, and functional renormalization to 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 in detail. 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 equation. We support the proposed relation to directed lines via multifractal analysis, revealing an analogous Anderson transition-like scenario and a matching correlation length exponent. Furthermore, we quantify how the persistence length of the stiff directed line is reduced by disorder.

Boltz, Horst-Holger; Kierfeld, Jan

2013-07-01

160

Nonlinear stiffness characteristics of the annular ligament.  

PubMed

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

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

2014-10-01

161

Non-singular inhomogeneous stiff fluid cosmology  

E-print Network

In this talk we show a stiff fluid solution of the Einstein equations for a cylindrically symmetric spacetime. The main features of this metric are that it is non-separable in comoving coordinates for the congruence of the worldlineS of the fluid and that it yields regular curvature invariants.

L. Fernández-Jambrina

2009-05-29

162

Substrate stiffness regulates cellular uptake of nanoparticles.  

PubMed

Nanoparticle (NP)-bioconjugates hold great promise for more sensitive disease diagnosis and more effective anticancer drug delivery compared with existing approaches. A critical aspect in both applications is cellular internalization of NPs, which is influenced by NP properties and cell surface mechanics. Despite considerable progress in optimization of the NP-bioconjugates for improved targeting, the role of substrate stiffness on cellular uptake has not been investigated. Using polyacrylamide (PA) hydrogels as model substrates with tunable stiffness, we quantified the relationship between substrate stiffness and cellular uptake of fluorescent NPs by bovine aortic endothelial cells (BAECs). We found that a stiffer substrate results in a higher total cellular uptake on a per cell basis, but a lower uptake per unit membrane area. To obtain a mechanistic understanding of the cellular uptake behavior, we developed a thermodynamic model that predicts that membrane spreading area and cell membrane tension are two key factors controlling cellular uptake of NPs, both of which are modulated by substrate stiffness. Our experimental and modeling results not only open up new avenues for engineering NP-based cancer cell targets for more effective in vivo delivery but also contribute an example of how the physical environment dictates cellular behavior and function. PMID:23484640

Huang, Changjin; Butler, Peter J; Tong, Sheng; Muddana, Hari S; Bao, Gang; Zhang, Sulin

2013-04-10

163

Stiff man syndrome in a black girl.  

PubMed Central

A patient suffering from severe and continuous muscular spasms is presented. The condition has been classified as the stiff man syndrome and is the first case recorded of the condition in a young African girl. The electrophysiological, biochemical, histochemical, and ultramicroscopic aspects of this disorder have been studied. The spasm appears to be related to overproduction of brain noradrenaline. Images PMID:501375

Isaacs, H

1979-01-01

164

Impulse response due to jumping on shoes of various stiffness and damping.  

PubMed

The human body is a dynamic system with dynamic behaviour. Linear and nonlinear models of a standing human are investigated. The models simulated the body by 15-lumped masses connected by springs and dampers. A square wave impulse input is applied at the shoes and the lumbar spine response is presented as an example. The results show that the mechanical response is affected by the kind of representation (linear or nonlinear model) and the shoes stiffness and damping coefficients. PMID:12775907

Qassem, W

2003-01-01

165

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

Microsoft Academic Search

We have implemented a force modulation technique for nanoindentation using a three-plate capacitive load-displacement transducer. The stiffness sensitivity of the instrument is ~0.1 N\\/m. We show that the sensitivity of this instrument is sufficient to detect long-range surface forces and to locate the surface of a specimen. The low spring mass (236 mg), spring constant (116 N\\/m) and damping coefficient

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

166

Third Order Elastic Coefficients of Rocks  

Microsoft Academic Search

We present a methodology to determine third order elastic (TOE) coefficients of rock from velocity measurements at different hydrostatic stress level. TOE coefficients help us to obtain a quantitative measure of the variation of velocity with stress. It is one of the most general ways to parameterize the stress sensitivity of rocks. We usually determine the isotropic TOE coefficients from

K. Bandyopadhyay

2006-01-01

167

Upper and lower stiffness bounds for porous anisotropic rocks  

NASA Astrophysics Data System (ADS)

We derive double inequalities providing the bounds for components of the effective stiffness tensor of a two-phase, porous-cracked medium with aligned ellipsoidal inclusions. The bounds are derived on the basis of the Hashin-Shtrikman variational principle, and the conditions for positive semi-definiteness of quadratic forms. Inequalities are presented for isotropic, cubic, hexagonal and orthorhombic overall symmetries. The results obtained for orthorhombic symmetry are valid for the general determination of transport properties (effective permeability, thermal and electrical conductivity). We conclude that inequalities for diagonal components of the effective tensor have the form of bounds, whereas in general these bounds do not exist for off-diagonal components. One important implication of this is that Voigt-Reuss averages do not provide the upper and lower bounds for off-diagonal components of the effective tensor, as is sometimes assumed. We also present numerical results for stiffness bounds obtained by modelling various shales with isotropic, transverse isotropic and orthorhombic overall symmetries.

Bayuk, Irina O.; Gay, Juliana K.; Hooper, John M.; Chesnokov, Evgeni M.

2008-12-01

168

Passive Apaptive Damping for High Stiffness-low Mass Materials Incorporating Negative Stiffness Elements  

E-print Network

starting with the fluid pumping element from the Synthetic Multifunctional Materials program. The low-hydraulic-radius hourglass (LHG) machine modified from Hawkins’ original design provides high stiffness with a high damping ability. The LHG machine pumps...

Cha, Gene

2013-11-07

169

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

Microsoft Academic Search

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

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

2007-01-01

170

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

PubMed Central

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

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

2014-01-01

171

Design and characterization of tunable stiffness flexural bearings  

E-print Network

Compressed flexures have a downwards-tunable stiffness in their compliant directions; their stiffness can theoretically be reduced by up to four orders of magnitude. The compression-stiffiness relation is linear for most ...

Ramirez, Aaron Eduardo

2012-01-01

172

Haptic Stiffness Identification by Veterinarians and Novices: A Comparison  

E-print Network

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

Tan, Hong Z.

173

Lamb Wave Stiffness Characterization of Composites Undergoing Thermal-Mechanical Aging  

NASA Technical Reports Server (NTRS)

The introduction of new, advanced composite materials into aviation systems requires a thorough understanding of the long term effects of combined thermal and mechanical loading upon those materials. Analytical methods investigating the effects of intense thermal heating combined with mechanical loading have been investigated. The damage mechanisms and fatigue lives were dependent on test parameters as well as stress levels. Castelli, et al. identified matrix dominated failure modes for out-of-phase cycling and fiber dominated damage modes for in-phase cycling. In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. To help evaluate the effect of aging, a suitably designed Lamb wave measurement system is being used to obtain bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system works by exciting an antisymmetric Lamb wave and calculating the velocity at each frequency from the known transducer separation and the measured time-of-flight. The same peak in the waveforms received at various distances is used to measure the time difference between the signals. The velocity measurements are accurate and repeatable to within 1% resulting in reconstructed stiffness values repeatable to within 4%. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. A mechanical scanner is used to move the sensors over the surface to map the time-of-flight, velocity, or stiffnesses of the entire specimen. Access to only one side of the material is required and no immersion or couplants are required because the sensors are dry coupled to the surface of the plate. In this study, the elastic stiffnesses D(sub 11), D(sub 22), A(sub 44), and A(sub 55) as well as time-of-flight measurements for composite samples that have undergone combined thermal and mechanical aging for a duration of 10,000 hours are reported.

Seale, Michael D.; Madaras, Eric I.

2004-01-01

174

The passive stiffness of the wrist and forearm  

PubMed Central

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

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

2012-01-01

175

Determinant of leg stiffness during hopping is frequency-dependent  

Microsoft Academic Search

Identifying the major determinant of leg stiffness during hopping would be helpful in the development of more effective training\\u000a methods. Despite the fact that overall leg stiffness depends on a combination of the joint stiffness, it is unclear how the\\u000a major determinants of leg stiffness are influenced by hopping frequency. The purpose of this study was to identify the major

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

176

Assessing Muscle Stiffness from Quiet Stance in Parkinson's Disease  

E-print Network

Assessing Muscle Stiffness from Quiet Stance in Parkinson's Disease Michael Lauk 1;2;4 , MSc Stiffness from Quiet Stance: Applicability to Parkinson's Disease Abstract In previous studies, we developed this measure to patients with Parkinson's disease (PD). We correlated the postural stiffness measure

177

Active stiffness control of a manipulator in cartesian coordinates  

Microsoft Academic Search

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

J. Kenneth Salisbury

1980-01-01

178

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

179

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

180

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

181

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

182

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. PMID:24349136

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

2013-01-01

183

Stiff-Person Syndrome: Case Series  

PubMed Central

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

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

2014-01-01

184

Polyneuropathy and Stiff-man Syndrome  

Microsoft Academic Search

A 49-year-old female patient developed a syndrome of diffuse muscular rigidity associated with the symptoms of a mild polyradiculitis. The muscular rigidity was differentiated from that observed in stiff-man syndrome (spindle myotonia). Proprioceptive reflexes and sensitivity to noise were absent. The increased muscle tonus was found to be due to pathologic spontaneous activity of intact motor units, disappearing only slowly

K. Ricker; H. G. Mertens; G. Paal

1971-01-01

185

Lower Body Stiffness and Muscle Activity Differences Between Female Dancers and Basketball Players During Drop Jumps  

PubMed Central

Background: Anterior cruciate ligament (ACL) injuries often occur during landing, with female athletes at higher injury risk than male athletes. Interestingly, female dancers have lower ACL injury rates than do female athletes in general. Hypothesis: Female dancers will have earlier and greater lower extremity muscle activity and higher sagittal knee joint and leg stiffness than will female basketball players. Study Design: Cross-sectional group comparison. Methods: Fifty-five healthy female athletes (35 dancers, 20 basketball players) performed 5 double-leg drop jumps from a 45-cm box. Surface electromyography (onsets and amplitudes; prelanding and postlanding) was recorded from the lateral gastrocnemius, medial and lateral hamstrings, lateral quadriceps muscles with a 3-dimensional electromagnetic tracking system, and forceplates recording biomechanics (leg spring stiffness and knee joint stiffness). Results: Compared with basketball players, dancers had greater leg spring stiffness (P = 0.047) but similar knee joint stiffness (P = 0.44). Although no significant differences were observed in overall muscle onset times (P = 0.22) or activation amplitudes (prelanding, P = 0.60; postlanding, P = 0.78), small to moderate effect sizes (ESs) suggest trends in dancers toward earlier (ES = 0.53) and higher medial hamstrings activation pre- (ES = 0.55) and post- (ES = 0.41) landing and lower lateral quadriceps (ES = 0.30) and higher gastrocnemius (ES = 0.33) postlanding muscle activation. Conclusions: In dancers, the higher leg spring stiffness and trends toward higher hamstrings prelanding and postlanding, as well as lower quadriceps and higher gastrocnemius activation postlanding with similar knee joint stiffness, indicate lower extremity neuromechanical differences across other joints. Clinical Relevance: Female dancers may have lower extremity neuromechanics that are different from those of basketball players during drop jumps. If dancers use ACL-protective strategies during activity, then their training routines should be further investigated to improve ACL injury prevention programs. PMID:23015996

Ambegaonkar, Jatin P.; Shultz, Sandra J.; Perrin, David H.; Schmitz, Randy J.; Ackerman, Terry A.; Schulz, Mark R.

2011-01-01

186

Factor Scores, Structure Coefficients, and Communality Coefficients  

ERIC Educational Resources Information Center

This paper presents heuristic explanations of factor scores, structure coefficients, and communality coefficients. Common misconceptions regarding these topics are clarified. In addition, (a) the regression (b) Bartlett, (c) Anderson-Rubin, and (d) Thompson methods for calculating factor scores are reviewed. Syntax necessary to execute all four…

Goodwyn, Fara

2012-01-01

187

Role of transverse bulkheads in hull stiffness of large container ships  

Microsoft Academic Search

Ultra large container ships are rather flexible and exposed to significant wave deformations. Therefore, hydroelastic strength analysis is required for these types of ships. Coupling of beam structural model and 3D hydrodynamic model is preferable for the reason of simplicity. In this paper, the contribution of a large number of transverse bulkheads to general hull stiffness is analysed. The prismatic

Ivo Senjanovi?; Stipe Tomaševi?; Smiljko Rudan; Tanja Senjanovi?

2008-01-01

188

Stiff-man syndrome: case report.  

PubMed

Stiff-man syndrome is a rare neurologic disorder characterized by progressive, fluctuating muscle rigidity with painful muscle contractions affecting predominantly the back and proximal extremities. In the ED, the diagnosis can be easily overlooked and misdiagnosed as acute or chronic low back pain and muscle spasm. This syndrome is often associated with diabetes, autoimmune diseases, and cancer. This report describes an illustrative case of a 39-year-old woman who presented to the ED with a two-year history of right leg spasms and low back pain that had become so severe in the preceding two days that she was unable to ambulate. Clues to the patient's proper diagnosis coincide with the diagnostic criteria for stiff-man syndrome: the presence of a slowly progressive stiffness of the axial muscles and proximal limb muscles, making ambulation difficult; hyperlordosis of the lumbar spine; episodic spasms precipitated by jarring or sudden movement; a normal intellectual, sensory, and motor examination when not in spasm; and a marked amelioration of symptoms with the IV administration of diazepam. High-dose oral diazepam is the maintenance drug of choice. PMID:7584754

Kuhn, W F; Light, P J; Kuhn, S C

1995-08-01

189

Damage Detection on Sudden Stiffness Reduction Based on Discrete Wavelet Transform  

PubMed Central

The sudden stiffness reduction in a structure may cause the signal discontinuity in the acceleration responses close to the damage location at the damage time instant. To this end, the damage detection on sudden stiffness reduction of building structures has been actively investigated in this study. The signal discontinuity of the structural acceleration responses of an example building is extracted based on the discrete wavelet transform. It is proved that the variation of the first level detail coefficients of the wavelet transform at damage instant is linearly proportional to the magnitude of the stiffness reduction. A new damage index is proposed and implemented to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. Numerical simulation using a five-story shear building under different types of excitation is carried out to assess the effectiveness and reliability of the proposed damage index for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also investigated. The made observations demonstrate that the proposed damage index can accurately identify the sudden damage events if the noise intensity is limited. PMID:24991647

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

2014-01-01

190

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. PMID:23056368

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

2012-01-01

191

Cell stiffness is a biomarker of the metastatic potential of ovarian cancer cells  

NASA Astrophysics Data System (ADS)

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 that ovarian cancer cells are generally softer and display lower intrinsic variability in cell stiffness than non-malignant ovarian epithelial cells. A detailed study of highly invasive ovarian cancer cells (HEY A8) and their less invasive parental cells (HEY), demonstrates that deformability can serve as an accurate biomarker of metastatic potential. Comparative gene expression profiling indicate that the reduced stiffness of highly metastatic HEY A8 cells is associated with actin cytoskeleton remodeling, microscopic examination of actin fiber structure in these cell lines is consistent with this prediction. Our results indicate that cell stiffness not only distinguishes ovarian cancer cells from non-malignant cells, but may also be a useful biomarker to evaluate the relative metastatic potential of ovarian and perhaps other types of cancer cells.

Xu, Wenwei; Mezencev, Roman; Kim, Byungkyu; Wang, Lijuan; McDonald, John; Sulchek, Todd

2013-03-01

192

Nanocharacterization of the negative stiffness of ferroelectric materials  

NASA Astrophysics Data System (ADS)

Phase changing materials such as ferroelectric materials could exhibit negative stiffness under certain thermomechanical environments. This negative stiffness is embodied by a deflection along the opposite direction of the applied load. So far negative stiffness materials were investigated with the specific morphology of embedded inclusions in stiff matrices then the resulting composite is studied to measure the behavior of each constituent indirectly. In this study, a modified nonisothermal nanoindentation method is developed to measure the negative stiffness of triglycine sulfate single crystal directly. This in-situ method is intended to first demonstrate the feasibility of detecting the negative stiffness via nanoindentation and nanocreep of a ferroelectric material at its Curie point and then to quantify the negative stiffness without the need for embedding the crystal within a stiffer matrix.

Alipour Skandani, A.; Ctvrtlik, R.; Al-Haik, M.

2014-08-01

193

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

PubMed Central

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

Hu, Xiao; Murray, Wendy M.

2011-01-01

194

Stiffness properties of the trunk in people with low back pain.  

PubMed

The purpose of this study was to examine the dynamic properties of the trunk during unstable sitting and to determine differences between healthy and low back pain (LBP) participants. Participants sat on a custom-made chair that was able to swing freely in the sagittal plane. The chair was mounted on a force platform to measure loads acting at the trunk. Each participant was asked to find a balanced position after the chair was tilted backward and released. Movements of the trunk and chair were recorded. Effective moment of inertia, stiffness and damping coefficients were derived using a second order linear model. 10 participants were re-tested to assess reliability. Trunk stiffness was found increased for LBP subjects (p<.05) while no difference was found for damping coefficient. Gender and initial tilt angle did not affect viscoelastic properties of the spine. A second order linear model adequately described the biomechanical response of the trunk. It was shown that the trunk response was mainly elastic for all participants. The increase in trunk stiffness in LBP subjects could be a compensatory strategy to decrease pain and the risk of further injuries, but further investigations are needed to understand the nature of the viscoelastic alterations. PMID:24960212

Freddolini, Marco; Strike, Siobhan; Lee, Raymond Y W

2014-08-01

195

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

PubMed Central

It is widely accepted that age-related changes in lens stiffness are significant for the development of presbyopia. However, precise details on the relative importance of age-related changes in the stiffness of the lens, in comparison with other potential mechanisms for the development of presbyopia, have not yet been established. One contributing factor to this uncertainty is the paucity and variability of experimental data on lens stiffness. The available published data generally indicate that stiffness varies spatially within the lens and that stiffness parameters tend to increase with age. However, considerable differences exist between these published data sets, both qualitatively and quantitatively. The current paper describes new and improved methods, based on the spinning lens approach pioneered by Fisher, R.F. (1971) ‘The elastic constants of the human lens’, Journal of Physiology, 212, 147–180, to make measurements on the stiffness of the human lens. These new procedures have been developed in an attempt to eliminate, or at least substantially reduce, various systematic errors in Fisher’s original experiment. An improved test rig has been constructed and a new modelling procedure for determining lens stiffness parameters from observations made during the test has been devised. The experiment involves mounting a human lens on a vertical rotor so that the lens spins on its optical axis (typically at 1000 rpm). An automatic imaging system is used to capture the outline of the lens, while it is rotating, at pre-determined angular orientations. These images are used to quantify the deformations developed in the lens as a consequence of the centripetal forces induced by the rotation. Lens stiffness is inferred using axisymmetric finite element inverse analysis in which a nearly-incompressible neo-Hookean constitutive model is used to represent the mechanics of the lens. A numerical optimisation procedure is used to determine the stiffness parameters that provide a best fit between the finite element model and the experimental data. Sample results are presented for a human lens of age 33 years. PMID:21040722

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

2011-01-01

196

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

PubMed Central

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

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

2010-01-01

197

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

198

Threshold bracing stiffness of two story frames  

E-print Network

THRESHOLD BRACING STIFFNESS OF TWO STORY FRAMES A Thesis by GHASSAN SUDKI KHADER Submitted to the Graduate College of Texas A/M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE December 1982 Major... and 3. 18 gives Kz = = 2. 412 K/in. (422. 6 N/mm), 2 x 173. 7 and Kz = + 2, 412 = 4. 079 K/in. (714. 6 N/mm) 280. 1 The values in Table 1 are shown graphically in Fig. 12. The variation of Kz with Kz, Kz with Kq and (Kz + Kz) with Kz are shown...

Khader, Ghassan Sudki

2012-06-07

199

Review of 23 patients affected by the stiff man syndrome: clinical subdivision into stiff trunk (man) syndrome, stiff limb syndrome, and progressive encephalomyelitis with rigidity  

Microsoft Academic Search

OBJECTIVETo investigate whether the stiff limb syndrome may be separated from the stiff man syndrome and progressive encephalomyelitis with rigidity on simple clinical grounds, and whether such a distinction has implications for aetiology, treatment, and prognosis.METHODSTwenty three patients referred over a 10 year period with rigidity and spasms in association with continuous motor unit activity, but without evidence of neuromyotonia,

R A Barker; T Revesz; M Thom; C D Marsden; P Brown

1998-01-01

200

The relationship between lower-body stiffness and dynamic performance.  

PubMed

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

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

2014-10-01

201

Influence of ply waviness on the stiffness and strength reduction on composite laminates  

NASA Astrophysics Data System (ADS)

An analytic model based on 2D laminated plate theory is used to conduct parametric studies for AS4 Graphite/PEKK and S2 Glass/PEKK composite laminates with varying degrees of ply waviness. The model is capable of predicting the elastic properties and thermal expansion coefficients of (90/0/90) laminates containing (0) plies; ply stresses for prescribed mechanical and thermal load cases; and strength reduction associated with ply waviness and residual stress. Results reveal that stiffness and strength reduction are significant in the (0) ply direction only. Mechanisms of stiffness reduction are attributed to the out-of-plane rotation of the wavy plies. It is shown that material anisotropy also affects property reduction, with AS4 Graphite/PEKK much more sensitive to ply waviness than S2 Glass/PEKK laminates. Ply waviness induces significant interlaminar shear stress within the (0) layer.

Bogetti, Travis A.; Gillespie, John W., Jr.; Lamontia, Mark A.

1992-10-01

202

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

PubMed Central

Background Independent of other cardiovascular (CV) risk factors, increased arterial stiffness has been established as a predictor of morbidity and mortality. The main aim of this study was to investigate the impact of diabetes on arterial stiffness in a representative sample of an urban Brazilian population plus Amerindians. Methods A total of 1,415 individuals from the general population were randomly selected plus 588 Amerindians from a native community in Brazil. In addition, a sub-sample of 380 individuals from the general population had 5-year follow-up data. Pulse wave velocity (PWV) was measured with a non-invasive automatic device (Complior, Colson; Garges les Gonesses, France) and increased arterial stiffness was defined as PWV???12 m/s. Results In the overall group, diabetic individuals had higher frequencies of increased arterial stiffness and hypertension. They also had higher values of PWV, body mass index, total cholesterol, triglycerides, systolic and diastolic blood pressures compared to non-diabetic individuals (p?stiffness frequency were higher in diabetic individuals in both groups (hypertensive and non-hypertensive) (p?stiffness was observed in the diabetic individuals from the overall group (OR?=?2.27; CI?=?1.47-3.52, p?stiffness compared to non-diabetic individuals. Both diabetic and non-diabetic individuals had higher PWV values after 5 years. There was no significant difference in the 5-year PWV progression in diabetic compared to non-diabetic individuals. Conclusions These results confirm, in a sample of Brazilian population, that the presence of diabetes is associated with increased arterial stiffness and it may contribute in part to increased cardiovascular risk in diabetic patients. PMID:23965633

2013-01-01

203

Index-free heat kernel coefficients  

NASA Astrophysics Data System (ADS)

Using index-free notation, we present the diagonal values 0264-9381/15/8/014/img1 of the first five heat kernel coefficients 0264-9381/15/8/014/img2 associated with a general Laplace-type operator on a compact Riemannian space without boundary. The fifth coefficient 0264-9381/15/8/014/img3 appears here for the first time. For the special case of a flat space, but with a gauge connection, the sixth coefficient is given too. Also provided are the leading terms for any coefficient, both in ascending and descending powers of the Yang-Mills and Riemann curvatures, to the same order as required for the fourth coefficient. These results are obtained by directly solving the relevant recursion relations, working in the Fock-Schwinger gauge and Riemann normal coordinates. Our procedure is thus non-covariant, but we show that for any coefficient the `gauged', respectively `curved', version is found from the corresponding `non-gauged', respectively `flat', coefficient by making some simple covariant substitutions. These substitutions being understood, the coefficients retain their `flat' form and size. In this sense the fifth and sixth coefficient have only 26 and 75 terms, respectively, allowing us to write them down. Using index-free notation also clarifies the general structure of the heat kernel coefficients. In particular, in flat space we find that from the fifth coefficient onward, certain scalars are absent. This may be relevant for the anomalies of quantum field theories in ten or more dimensions.

van de Ven, Anton E. M.

1998-08-01

204

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

205

Explicit stabilized integration of stiff determinisitic or stochastic problems  

NASA Astrophysics Data System (ADS)

Explicit stabilized methods for stiff ordinary differential equations have a long history. Proposed in the early 1960s and developed during 40 years for the integration of stiff ordinary differential equations, these methods have recently been extended to implicit-explicit or partitioned type methods for advection-diffusion-reaction problems, and to efficient explicit solvers for stiff mean-square stable stochastic problems. After a short review on the basic stabilized methods we discuss some recent developments.

Abdulle, Assyr

2012-09-01

206

Human vertebral body apparent and hard tissue stiffness  

Microsoft Academic Search

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

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

1998-01-01

207

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

PubMed Central

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. Acoustoelastic strain gauge 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 ten clinically normal dogs were recorded by two non-independent 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), intraobserver (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

2014-01-01

208

On the relationship between lens stiffness and accommodative amplitude.  

PubMed

The purpose of this study was to investigate the relationship between the stiffness of the material comprising the lens and the loss of accommodative amplitude with age. We used a validated mechanical model to determine the changes in the shape of the lens during accommodation and disaccommodation. The relative contribution of lens stiffness to loss of accommodative amplitude with age was determined by varying lens stiffness in the model. The changes in lens stiffness with age were based on the results of two recently published studies. In the first study we showed that lens stiffness increases exponentially with age, and in the second study we showed that there is a considerable stiffness gradient within the lens that changes with age. The results of both studies were incorporated in the mechanical model. The model showed that it is not the increasing stiffness of the lens with age, but rather the changing stiffness gradient that influences accommodative amplitude. The results show that the changing stiffness gradient in the lens may be responsible for almost the entire loss of accommodation with age. PMID:17720158

Weeber, Henk A; van der Heijde, Rob G L

2007-11-01

209

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

210

Towards ultra-stiff materials: Surface effects on nanoporous materials  

NASA Astrophysics Data System (ADS)

The significant rise in the strength and stiffness of porous materials at nanoscale cannot be described by conventional scaling laws. This letter investigates the effective Young's modulus of such materials by taking into account surface effect in a microcellular architecture designed for an ultralight material whose stiffness is an order of magnitude higher than most porous materials. We find that by considering the surface effects the predicted stiffness using Euler-Bernoulli beam theory compares well to experimental data for spongelike nanoporous gold with random microstructures. Analytical results show that, of the two factors influencing the effective Young's modulus, the residual stress is more important than the surface stiffness.

Lu, Dingjie; Xie, Yi Min; Li, Qing; Huang, Xiaodong; Zhou, Shiwei

2014-09-01

211

Friction Coefficient for Quarks in Supergravity Duals  

E-print Network

We study quarks moving in strongly-coupled plasmas that have supergravity duals. We compute the friction coefficient of strings dual to such quarks for general static supergravity backgrounds near the horizon. Our results also show that a previous conjecture on the bound has to be modified and higher friction coefficients can be achieved.

E. Antonyan

2006-11-22

212

Stiffness of ? subunit of F(1)-ATPase.  

PubMed

F(1)-ATPase is a molecular motor in which the ? subunit rotates inside the ?(3)?(3) ring upon adenosine triphosphate (ATP) hydrolysis. Recent works on single-molecule manipulation of F(1)-ATPase have shown that kinetic parameters such as the on-rate of ATP and the off-rate of adenosine diphosphate (ADP) strongly depend on the rotary angle of the ? subunit (Hirono-Hara et al. 2005; Iko et al. 2009). These findings provide important insight into how individual reaction steps release energy to power F(1) and also have implications regarding ATP synthesis and how reaction steps are reversed upon reverse rotation. An important issue regarding the angular dependence of kinetic parameters is that the angular position of a magnetic bead rotation probe could be larger than the actual position of the ? subunit due to the torsional elasticity of the system. In the present study, we assessed the stiffness of two different portions of F(1) from thermophilic Bacillus PS3: the internal part of the ? subunit embedded in the ?(3)?(3) ring, and the complex of the external part of the ? subunit and the ?(3)?(3) ring (and streptavidin and magnetic bead), by comparing rotational fluctuations before and after crosslinkage between the rotor and stator. The torsional stiffnesses of the internal and remaining parts were determined to be around 223 and 73 pNnm/radian, respectively. Based on these values, it was estimated that the actual angular position of the internal part of the ? subunit is one-fourth of the magnetic bead position upon stalling using an external magnetic field. The estimated elasticity also partially explains the accommodation of the intrinsic step size mismatch between F(o) and F(1)-ATPase. PMID:20549499

Okuno, Daichi; Iino, Ryota; Noji, Hiroyuki

2010-11-01

213

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

PubMed

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

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

2014-03-01

214

Asymmetric vibration in a two-layer vocal fold model with left-right stiffness asymmetry: Experiment and simulation  

PubMed Central

Vibration characteristics of a self-oscillating two-layer vocal fold model with left-right asymmetry in body-layer stiffness were experimentally and numerically investigated. Two regimes of distinct vibratory pattern were identified as a function of left-right stiffness mismatch. In the first regime with extremely large left-right stiffness mismatch, phonation onset resulted from an eigenmode synchronization process that involved only eigenmodes of the soft fold. Vocal fold vibration in this regime was dominated by a large-amplitude vibration of the soft fold, and phonation frequency was determined by the properties of the soft fold alone. The stiff fold was only enslaved to vibrate at a much reduced amplitude. In the second regime with small left-right stiffness mismatch, eigenmodes of both folds actively participated in the eigenmode synchronization process. The two folds vibrated with comparable amplitude, but the stiff fold consistently led the soft fold in phase for all conditions. A qualitatively good agreement was obtained between experiment and simulation, although the simulations generally underestimated phonation threshold pressure and onset frequency. The clinical implications of the results of this study are also discussed. PMID:22978891

Zhang, Zhaoyan; Hieu Luu, Trung

2012-01-01

215

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

216

Idiopathic hypertonicity as a cause of stiffness after surgery for developmental dysplasia of the hip?  

PubMed Central

INTRODUCTION There are various complications reported with surgical treatment of DDH. Most studied complication is avascular necrosis of the femoral head and hip stiffness. The purpose of this report was to describe a case with severe stiffness of the hip due to hypertonicity in periarticular muscles after it was treated for developmental dysplasia of the hip (DDH). PRESENTATION OF CASE Three-year-old patient referred to our institution with bilateral DDH. Two hips were operated separately in one year with anterior open reduction, femoral shortening osteotomy. Third month after last surgery, limited right hip range of motion and limb length discrepency identified. Clinical examination revealed that patient had limited range of motion (ROM) in the right hip and compensated this with pelvis obliquity. Gluteus medius, sartorius and iliofemoral band release performed after examination under general anesthesia. Symptoms were persisted at 3rd week control and examination of the patient in general anesthesia revealed full ROM without increased tension. For the identified hypertonicity, ultrasound guided 100 IU botulinum toxin A injection performed to abductor group and iliopsoas muscles. Fifth month later, no flexor or abductor tension observed, and there was no pelvic obliquity. DISCUSSION Stiffness as a complication is rare and is usually resolved without treatment or simple physical therapy. Usually it is related with immobilization or surgery associated joint contracture, and spontaneous recovery reported. Presented case is diagnosed as hip stiffness due to underlying local hypertonicity. That is resolved with anesthesia and it was treated after using botulinum toxin A injection. CONCLUSION Hypertonicity with hip stiffness after surgical treatment of DDH differ from spontaneous recovering hip range of motion limitation and treatment can only be achieved by reduction of the muscle hypertonicity by neuromuscular junction blockage. PMID:24568944

Akgul, Turgut; Goksan, Suleyman Bora; Eren, Ilker

2014-01-01

217

Study of ultrasound stiffness imaging methods using tissue mimicking phantoms.  

PubMed

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

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

2014-02-01

218

Aortic Compliance and Stiffness Among Severe Longstanding Hypertensive and Non-hypertensive  

PubMed Central

Introduction Abnormal aortic function in hypertension is generally attributed to accelerated breakdown of elastin in the aorta, leading to dilatation of the lumen and stiffening of the wall as elastin is replaced with stiffer collagen. Aortic stiffness is an independent predictor of cardiovascular risk and all-cause and cardiovascular mortality. Vascular stiffening can activate endothelium which in turn may promote atherogenesis. Modulation of arterial stiffness has been shown to be successfully managed via changes in lifestyle and put under control of hypertension pharmacologically with antihypertensive drugs and statins. Methods Hundred and forty four patients have been enrolled in this study. They have been divided in two groups, with hypertension and group of control. Groups were with no age difference. Results Group with hypertension were with reduced aortic strain, distensibility (compliance) and have higher stiffness than control group; GrHTA =9.3 compared to GC=5.4. After successful treatment of hypertension with antihypertensives and statins, for two years, these parameters showed improvement, but still remain out of normal range compared to control group; 7.6 vs. 5.38. Conclusions Hypertensive patients have reduced aortic elasticity and increased stiffness which can be stopped and improved after treatment with antihypertensive and statin. PMID:23572854

Kamberi, Lulzim Selim; Gorani, Daut Rashit; Hoxha, Teuta Faik; Zahiti, Bedri Faik

2013-01-01

219

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

220

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, Brad A.; Howard, Samuel A.

2008-01-01

221

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

222

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

223

Modeling and Control of Stiff Robots for Flexible Manufacturing  

E-print Network

Modeling and Control of Stiff Robots for Flexible Manufacturing #12;#12;Modeling and Control of Stiff Robots for Flexible Manufacturing Isolde Dressler Department of Automatic Control Lund University Lund, September 2012 #12;Department of Automatic Control Lund University Box 118 SE-221 00 LUND Sweden

224

Ultrahigh Torsional Stiffness and Strength of Boron Nitride Jonathan Garel,  

E-print Network

, the stiffest and strongest material discovered so far, in terms of both elastic modulus and tensile strength.1Ultrahigh Torsional Stiffness and Strength of Boron Nitride Nanotubes Jonathan Garel, Itai Leven or CNT bundles markedly decreases their effective stiffness and strength.3,9 CNT-based fibers have still

Hod, Oded

225

Role of Inflammation in the Pathogenesis of Arterial Stiffness  

PubMed Central

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

Park, Sungha

2012-01-01

226

Creatine Supplementation and Its Effect on Musculotendinous Stiffness and Performance  

Microsoft Academic Search

Anecdotal reports suggesting that creatine (Cr) supplemen- tation may cause side effects, such as an increased incidence of muscle strains or tears, require scientific examination. In this study, it was hypothesized that the rapid fluid retention and ''dry matter growth'' evident after Cr supplementation may cause an increase in musculotendinous stiffness. Intui- tively, an increase in musculotendinous stiffness would in-

MARK L. WATSFORD; ARON J. MURPHY; WARWICK L. SPINKS; ANDREW D. WALSHE

2003-01-01

227

Measuring Interfacial Stiffness of Adhesively-Bonded Wood  

E-print Network

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

Nairn, John A.

228

Joint Stiffness Identification of Industrial Serial Robots Claire Dumasa  

E-print Network

Joint Stiffness Identification of Industrial Serial Robots Claire Dumasa , St´ephane Caroa , Mehdi a new methodology for the joint stiffness identification of industrial serial robots and as consequence for the evaluation of both translational and rotational displacements of the robot's end-effector subject

Paris-Sud XI, Université de

229

Anelastic instability in composites with negative stiffness inclusions  

Microsoft Academic Search

Composites with VO2 particulate inclusions as a negative stiffness phase were fabricated through powder metallurgy. The composites are predicted to exhibit enhanced anelastic damping by virtue of the partially constrained negative stiffness of the inclusions in the vicinity of a ferroelastic phase transformation, and are predicted to become unstable for sufficiently high concentration (5?vol%) of inclusions. Composite specimens with 5?vol%

T. Jaglinski; R. S. Lakes

2004-01-01

230

Arterial stiffness and the renin-angiotensin-aldosterone system  

Microsoft Academic Search

Arterial stiffness has recently been recognised as an independent risk factor for cardiovascular morbidity and mortality in hypertension. Many of the complications seen with angiotensin II (Ang II) excess or hyperaldosteronism - an increased event rate, left ventricular hypertrophy, endothelial dysfunction and target organ damage - are also associated with arterial stiffness. It is possible that reduced arterial compliance may

Azra Mahmud; John Feely

2004-01-01

231

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

232

Stiffness Analysis of Machine Tools Using Finite Element Method  

Microsoft Academic Search

Modern machining processes require machine tools to work accurately and dynamically. This leads to the necessity for a method which can analyze the stiffness of machine tools. In this paper, a single module method and a hybrid modeling method for analyzing the stiffness of machine tools are presented. Techniques include building suitable finite element models, determining equivalent loads, simulating the

Yu Lianqing Wang Liping; Wang Liping

2009-01-01

233

The influence of leaflet skin friction and stiffness on the performance of bioprosthetic aortic valves.  

PubMed

Leaflet skin friction and stiffness were found to have a significant influence on the systolic performance of a 19 mm diameter bioprosthetic aortic valve based on fluid-structure interaction simulations at a heart rate of 72 bpm. Four different leaflet skin friction coefficients (0.0, 9.2 × 10(-4), 4.8 × 10(-2) and 4.8 × 10(-1)) were simulated along with three different leaflet elastic moduli (3.0 × 10(6), 3.5 × 10(6), 4.0 × 10(6) N m(-2)). Higher leaflet skin friction was found to increase the magnitude of the systolic transvalvular pressure gradient and the peak velocity through the valve, as well as decrease the valve orifice area. The results for the leaflet opening and closing kinematics also showed that higher leaflet skin friction combined with higher leaflet stiffness produces longer rapid valve opening, closing and ejection times, as well as smaller valve orifice areas. These results are consistent with clinical findings for calcified aortic valves and suggest that valve performance under stenotic conditions is strongly influenced by the combined effect of increasing leaflet stiffness and surface roughness caused by calcification. PMID:24264225

Dellimore, K; Kemp, I; Scheffer, C; Weich, H; Doubell, A

2013-12-01

234

Autoimmune myastenia gravis with thymoma following the spontaneous remission of stiff-man syndrome  

Microsoft Academic Search

A patient who developed generalized autoimmune myasthenia gravis six years after the spontaneous remission of a stiff-man syndrome is described. He also suffered from chronic active hepatitis and had radiological evidence of a thymoma. He did not have diabetes mellitus. Besides anti-nicotinic acetylcholine receptor antibodies, anti-nuclear, anti-DNA, anti-mitochondrial and anti-skeletal muscle antibodies were found in his serum, while islet-cell antibodies

G. Piccolo; G. Martino; A. Moglia; A. Arrigo; V. Cosi

1990-01-01

235

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

236

The Focal Adhesion: A Regulated Component of Aortic Stiffness  

PubMed Central

Increased aortic stiffness is an acknowledged predictor and cause of cardiovascular disease. The sources and mechanisms of vascular stiffness are not well understood, although the extracellular matrix (ECM) has been assumed to be a major component. We tested here the hypothesis that the focal adhesions (FAs) connecting the cortical cytoskeleton of vascular smooth muscle cells (VSMCs) to the matrix in the aortic wall are a component of aortic stiffness and that this component is dynamically regulated. First, we examined a model system in which magnetic tweezers could be used to monitor cellular cortical stiffness, serum-starved A7r5 aortic smooth muscle cells. Lysophosphatidic acid (LPA), an activator of myosin that increases cell contractility, increased cortical stiffness. A small molecule inhibitor of Src-dependent FA recycling, PP2, was found to significantly inhibit LPA-induced increases in cortical stiffness, as well as tension-induced increases in FA size. To directly test the applicability of these results to force and stiffness development at the level of vascular tissue, we monitored mouse aorta ring stiffness with small sinusoidal length oscillations during agonist-induced contraction. The alpha-agonist phenylephrine, which also increases myosin activation and contractility, increased tissue stress and stiffness in a PP2- and FAK inhibitor 14-attenuated manner. Subsequent phosphotyrosine screening and follow-up with phosphosite-specific antibodies confirmed that the effects of PP2 and FAK inhibitor 14 in vascular tissue involve FA proteins, including FAK, CAS, and paxillin. Thus, in the present study we identify, for the first time, the FA of the VSMC, in particular the FAK-Src signaling complex, as a significant subcellular regulator of aortic stiffness and stress. PMID:23626821

Saphirstein, Robert J.; Gao, Yuan Z.; Jensen, Mikkel H.; Gallant, Cynthia M.; Vetterkind, Susanne; Moore, Jeffrey R.; Morgan, Kathleen G.

2013-01-01

237

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

E-print Network

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

Subramaniam, Anandh

238

Limited Dependent Variable Correlated Random Coefficient Panel Data Models  

E-print Network

for the average slopes of a linear CRC model with a general nonparametric correlation between regressors and random coefficients. I construct a sqrt(n) consistent estimator for the average slopes via varying coefficient regression. The identification of binary...

Liang, Zhongwen

2012-10-19

239

Assessment of liver stiffness in patients with HCV and mixed cryoglobulinemia undergoing rituximab treatment  

PubMed Central

Introduction Mixed cryoglobulinemia (MC) is a HCV-related lymphoproliferative disorder generally associated with advanced liver disease. Liver stiffness has been significantly correlated with histopathological stage of fibrosis. Moreover, it was influenced by necroinflammatory activity. Rituximab (RTX) is a chimeric anti-CD20 monoclonal antibody inducing transient B lymphocytes depletion that was shown to be useful and safe in the majority of HCV MC patients, leading also to improvement of cirrhotic syndrome. Aim of this study was to evaluate the modifications of liver stiffness following RTX treatment in HCV-related MC patients. Materials and methods Fourteen consecutive patients (10 F, 4 M; mean age 60.43?±?43) with HCV-related chronic hepatitis (n =?10) or cirrhosis (n =?4) and MC, eligible for RTX treatment, were prospectively enrolled. Intravenous injection of 1 g of RTX was performed at day 0 and at day 15. Assessment of stiffness was carried out by Fibroscan® (Echosens, Paris-France) at baseline, 15 days after the first infusion, and at month 1, 3 and 6 after therapy. Results MC symptoms significantly improved during the study, especially during the first 3 months. Liver stiffness observed 3 months after treatment was significantly reduced when compared with pre-treatment values (p =?0.01). This difference disappeared after 6 months of follow-up. Cytofluorimetric analysis showed a decrease of CD19+ peripheral blood cells, with the nadir at month 3 after therapy and B cell compartment reconstitution after 6 months. Conclusion This study, for the first time showed that RTX-treatment in HCV-related MC induces a reduction of liver stiffness that is strictly associated with the B-cell depletion. PMID:24456582

2014-01-01

240

Lehman, J. and Lakes, R. S., "Stiff lattices with zero thermal expansion", adapted from Journal of Intelligent Material Systems and Structures, 23 (11) 1263-1268 July (2012)  

E-print Network

1 Lehman, J. and Lakes, R. S., "Stiff lattices with zero thermal expansion", adapted from Journal Lattice microstructures are presented with zero coefficient of thermal expansion. These are made-lattices. Introduction Thermal expansion 1 of materials is pertinent in the context of materials that in service may

Lakes, Roderic

241

Stiffness nanotomography of human epithelial cancer cells  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

242

Sources of Variability in Musculo-Articular Stiffness Measurement  

PubMed Central

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

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

2013-01-01

243

Active trunk stiffness increases with co-contraction.  

PubMed

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

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

2006-02-01

244

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

NASA Astrophysics Data System (ADS)

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 rotor bearing system with a spline coupling are found using modal testing for given spline geometry, misalignment, lubrication condition, torque, and rotational speeds. A dual rotor computer algorithm which contains a spline coupling model is developed in order to calculate the analytical modal parameters. Support bearing coefficients are obtained using a pressure dam bearing computer code which employs lubrication theory. Spline coupling coefficients are determined by adjusting the model until the analytical modal parameters match the experimental modal parameters. Both computer simulations and impact testing show that shaft speed and torque are the most important parameters which affect the system natural frequency and logarithmic decrement. However, the modal parameters are not very sensitive to the spine coupling coefficients. Only the second natural frequency shows any sensitivity to the spline angular stiffness. The lateral stiffness coefficient of the spline coupling decreases as rotational speed increases. Lateral and angular damping do not influence the modal parameter until unreasonably large values are considered. This is due to the large value of damping in the pressure dam bearings. Since the modal parameters are insensitive to the spline coefficients, a set of error bounds for the experimental values are chosen to determine the ranges of the loose spline coupling coefficients. The results show that the value of the spline lateral stiffness is between 2.0 x10(exp 7) and 8.0 x 10(exp 8) N/m and the spline angular stiffness is between 2.0 x 10(exp 5) and 8.0 x 10(exp 8) N/m, and the spline angular stiffness is between 2.0 x 10(exp 6) Nm/rad. However, it is impossible to identify the spline damping coefficients because the effect of the support bearing damping coefficients suppress the nonsynchronous whirling motion due to the spline friction even at speeds above the first critical speed.

Park, Sang Kyu

245

A novel energy-efficient rotational variable stiffness actuator.  

PubMed

This paper presents the working principle, the design and realization of a novel rotational variable stiffness actuator, whose stiffness can be varied independently of its output angular position. This actuator is energy-efficient, meaning that the stiffness of the actuator can be varied by keeping constant the internal stored energy of the actuator. The principle of the actuator is an extension of the principle of translational energy-efficient actuator vsaUT. A prototype based on the principle has been designed, in which ball-bearings and linear slide guides have been used in order to reduce losses due to friction. PMID:22256239

Rao, Shodhan; Carloni, Raffaella; Stramigioli, Stefano

2011-01-01

246

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

Microsoft Academic Search

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

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

2002-01-01

247

Canonical Definition of Wigner Coefficients in Un  

Microsoft Academic Search

Two general results applicable to the problem of a canonical definition of the Wigner coefficient in Un are demonstrated: (1) the existence of a canonical imbedding of Un × Un into Un2 and (2) a general factorization lemma for operators defined in the boson calculus. Using these results, a resolution of the multiplicity problem for U3 is demonstrated, in which

L. C. Biedenharn; A. Giovannini; J. D. Louck

1967-01-01

248

Determinants of Arterial Stiffness in Chronic Kidney Disease Stage 3  

PubMed Central

Background Early chronic kidney disease (CKD) is associated with increased cardiovascular (CV) risk but underlying mechanisms remain uncertain. Arterial stiffness (AS) is associated with increased CV risk in advanced CKD, but it is unclear whether AS is relevant to CV disease (CVD) in early CKD. Study Design Cross-sectional. Setting and participants 1717 patients with previous estimated glomerular filtration rate (eGFR) 59–30 mL/min/1.73 m2; mean age 73±9y, were recruited from 32 general practices in primary care. Outcomes Increased arterial stiffness. Measurements Medical history was obtained and participants underwent clinical assessment, urine and serum biochemistry testing. Carotid to femoral pulse wave velocity (PWV) was determined as a measure of AS, using a Vicorder™ device. Results Univariate analysis revealed significant correlations between PWV and risk factors for CVD including age (r?=?0.456; p<0.001), mean arterial pressure (MAP) (r?=?0.228; p<0.001), body mass index (r?=??0.122; p<0.001), log urinary albumin to creatinine ratio (r?=?0.124; p<0.001), Waist to Hip ratio (r?=?0.124, p<0.001), eGFR (r?=??0.074; p?=?0.002), log high sensitivity c-reactive protein (r?=?0.066; p?=?0.006), HDL (r?=??0.062; p?=?0.01) and total cholesterol (r?=??0.057; p?=?0.02). PWV was higher in males (9.6 m/sec vs.10.3 m/sec; p<0.001), diabetics (9.8 m/sec vs. 10.3 m/sec; p<0.001), and those with previous CV events (CVE) (9.8 m/s vs. 10.3 m/sec; p<0.001). Multivariable analysis identified age, MAP and diabetes as strongest independent determinants of higher PWV (adjusted R2?=?0.29). An interactive term indicated that PWV increased to a greater extent with age in males versus females. Albuminuria was a weaker determinant of PWV and eGFR did not enter the model. Limitations Data derived from one study visit, with absence of normal controls. Conclusion In this cohort, age and traditional CV risk factors were the strongest determinants of AS. Albuminuria was a relatively weak determinant of AS and eGFR was not an independent determinant. Long-term follow-up will investigate AS as an independent risk factor for CVE in this cohort. PMID:23383192

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

2013-01-01

249

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

NASA Technical Reports Server (NTRS)

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

Seale, Michael D.; Madaras, Eric I.

2000-01-01

250

Dynamic study of tunable stiffness scanning microscope probe  

E-print Network

This study examines the dynamic characteristics of the in-plane tunable stiffness scanning microscope probe for an atomic force microscope (AFM). The analysis was carried out using finite element analysis (FEA) methods for ...

Vega González, Myraida Angélica

2005-01-01

251

Nondestrutive damage detection by simultaneous identification of stiffness and damping  

E-print Network

The objective of this study is to develop a nondestructive damage evaluation methodology that can identify simultaneously both stiffness and damping changes in a structure. Two approaches are used to meet the stated objectives. First, a method...

Hyung, Sang Su

2009-05-15

252

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

253

Operator-Based Preconditioning of Stiff Hyperbolic Systems  

SciTech Connect

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

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

2009-02-09

254

Contributions of cocontraction and eccentric activity to stiffness regulation.  

PubMed

Individuals commonly adjust joint stiffness in response to changes in environmental and task demands. The objective of the present study was to evaluate the contribution of muscular cocontraction and eccentric activity to this adjustment. In all, 30 healthy volunteers participated in the present study. The authors indirectly manipulated elbow stiffness by modifying (a) the frequency of forearm movements (frequency conditions) and (b) the kinetic properties of the forearm through the addition of external mass (mass conditions). Multilevel regression models identified muscular cocontraction and eccentric activity as predictors of joint stiffness in the frequency conditions but not in the mass conditions. Results indicated that cocontraction is not the sole mechanism for stiffness regulation. Rather, the mechanisms that different participants used varied as a function of the demands of the task. PMID:19366654

Silva, Paula L; Fonseca, Sergio T; Ocarino, Juliana M; Gonçalves, Gabriela P; Mancini, Marisa C

2009-05-01

255

The measurement of plain weft-knitted fabric stiffness  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

256

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

257

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

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

Cornering stiffness estimation based on vehicle lateral dynamics  

Microsoft Academic Search

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

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

2006-01-01

260

Formulation of consistent restoring stiffness in ship hydroelastic analysis  

Microsoft Academic Search

In this article, the role of the restoring stiffness, as one of the basic parameters in ship hydroelastic analysis, is brought\\u000a out. It is formulated using the variational principle and the method of virtual displacements. It is shown that asymmetry\\u000a of the restoring stiffness is a physical reality. Moreover, it is confirmed that modal variation, still disputed in the relevant

Ivo Senjanovi?; Nikola Vladimir; Marko Tomi?

261

A stiffness equation transfer method for natural frequencies of structures  

Microsoft Academic Search

A stiffness equation transfer method is proposed for obtaining vibration frequencies of structures. This method is an extension of the finite element-transfer matrix (FE-TM) method. In the present method, the transfer of state vectors from left to right in the ordinary FE-TM method is changed into the transfer of stiffness equations of every section from left to right. This method

Huiyu Xue

2003-01-01

262

Arterial stiffness: Is it ready for prime time?  

Microsoft Academic Search

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

Stanley S. Franklin

2007-01-01

263

On the determination of the coefficients of the Gaussian general theory of the Earth's magnetism for the year 1885 and about the relationship of the three Earth-magnetic elements  

NASA Technical Reports Server (NTRS)

An attempt is made to judge the value of the Gaussian series for the Earth's magnetism. The computation employed to do this uses the method of the least and greatest coefficients. The number of unknown which had to be calculated from the individual groups was at most only four. All symbols of Gauss were retained.

Fritsche, H.

1983-01-01

264

A vibration technique for the measurement of contact stiffness  

NASA Astrophysics Data System (ADS)

A vibration method for measuring the contact stiffness between two bodies is described. The technique involves the measurement of the dynamic properties of the system comprising the two bodies, which are effectively joined by a spring, whose stiffness is the contact stiffness which is to be determined. Two variants of the method are described, one of which is applicable to the measurement of the contact stiffness between two bodies whose mass is of a similar order of magnitude, and the second which is used when one body is much more massive than the other, and may be modelled as a rigid abutment. The technique has been tested by measuring the contact stiffness between flat surfaces of both steel and aluminium and spherical, steel contact tips of various radii. The results at different loads have been compared with those predicted from Hertzian contact theory, good agreement being obtained. Results are also presented from tests on honeycomb panels with carbon fibre reinforced plastic skins. The method is also applicable to the determination of the stiffness of joints made by welding or mechanical fastening.

Cawley, P.; Clayton, D. L. R.

1987-07-01

265

The accuracy of WinSmash delta-V estimates: the influence of vehicle type, stiffness, and impact mode.  

PubMed

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. PMID:16968630

Niehoff, P; Gabler, H C

2006-01-01

266

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

PubMed

Cerebral palsy (CP), caused by an injury to the developing brain, can lead to alterations in muscle function. Subsequently, increased muscle stiffness and decreased joint range of motion are often seen in patients with CP. We examined mechanical and biochemical properties of the gastrocnemius and soleus muscles, which are involved in equinus muscle contracture. Passive mechanical testing of single muscle fibers from gastrocnemius and soleus muscle of patients with CP undergoing surgery for equinus deformity showed a significant increase in fiber stiffness (p?stiffness difference (p?=?0.28).). When in vivo sarcomere lengths were measured and fiber and bundle stiffness compared at these lengths, both fibers and bundles of patients with CP were predicted to be much stiffer in vivo compared to typically developing (TD) individuals. Interestingly, differences in fiber and bundle stiffness were not explained by typical biochemical measures such as titin molecular weight (a giant protein thought to impact fiber stiffness) or collagen content (a proxy for extracellular matrix amount). We suggest that the passive mechanical properties of fibers and bundles are thus poorly understood. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1667-1674, 2014. PMID:25138654

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

2014-12-01

267

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. PMID:23654401

Yin, Jun; Zhang, Zhaoyan

2013-01-01

268

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. PMID:22691560

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

2012-01-01

269

Effects of Acute Eccentric Contractions on Rat Ankle Joint Stiffness  

PubMed Central

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 examine the relationships of ankle joint stiffness with muscle passive tension. Anesthetized male Wistar rats (n = 23) were firmly secured on a platform in the prone position. A bout of ECs was performed on the gastrocnemius muscle with a combination of electrically induced tetanic contractions via a skin electrode and simultaneous forced dorsiflexion of the ankle joint (velocity, 15°/s; from 0°to 45°). Passive resistive torque (PRT) of the ankle joint was measured to evaluate joint stiffness. Passive tension of the exposed gastrocnemius muscle was also measured when the maximum value of joint stiffness was obtained. The PRT on days 2, 3, and 4 was significantly higher than the pre-treatment value (days 2 and 4; p < 0.001, days 3; p < 0.01). The passive tension on day 4 was significantly higher than that of the sham-operated group. The muscle wet mass was identical in both groups, suggesting the absence of edema. We conclude PRT increases after ECs in rat ankle joint. We also show the possibility that it is associated with muscle passive tension, independent of edema formation. Key pointsWe confirmed that ECs raise joint PRT and are associated with reduction of muscle passive tension.The changes in joint stiffness and muscle passive tension after ECs have been examined independently and the direct relationships have not been examined previously.We experimentally showed that ECs increased both joint PRT and muscle passive tension and these two parameters were significantly correlated. PMID:24149490

Eisuke, Ochi; Naokata, Ishii; Koichi, Nakazato

2007-01-01

270

Independent regulation of tumor cell migration by matrix stiffness and confinement  

E-print Network

Independent regulation of tumor cell migration by matrix stiffness and confinement Amit Pathak of ECM stiffness on cell migration, adhesion, and contractility has been extensively studied in 2D cul of channels of defined wall stiffness and geometry that allows independent variation of ECM stiffness

Kumar, Sanjay

271

Relationship between leg stiffness and lower body injuries in professional Australian football  

Microsoft Academic Search

Leg stiffness is a modifiable mechanical property that may be related to soft tissue injury risk. The purpose of this study was to examine mean leg stiffness and bilateral differences in leg stiffness across an entire professional Australian Football League (AFL) season, and determine whether this parameter was related to the incidence of lower body soft tissue injury. The stiffness

Elizabeth C. Pruyn; Mark L. Watsford; Aron J. Murphy; Matthew J. Pine; Robert W. Spurrs; Matthew L. Cameron; Richard J. Johnston

2011-01-01

272

Relationship between leg stiffness and lower body injuries in professional Australian football  

Microsoft Academic Search

Leg stiffness is a modifiable mechanical property that may be related to soft tissue injury risk. The purpose of this study was to examine mean leg stiffness and bilateral differences in leg stiffness across an entire professional Australian Football League (AFL) season, and determine whether this parameter was related to the incidence of lower body soft tissue injury. The stiffness

Elizabeth C. Pruyn; Mark L. Watsford; Aron J. Murphy; Matthew J. Pine; Robert W. Spurrs; Matthew L. Cameron; Richard J. Johnston

2012-01-01

273

Application of an image-based weighted measure of skeletal bending stiffness to great ape mandibles  

Microsoft Academic Search

Traditional measures of structural stiff- ness in the primate skeleton do not consider the hetero- geneous material stiffness distribution of bone. This as- sumption of homogeneity introduces an unknown degree of error in estimating stiffness in skeletal elements. Measures of weighted stiffness can be developed by in- cluding heterogeneous grayscale variations evident in computed tomographic (CT) images. Since gray scale

Neel B. Bhatavadekar; David J. Daegling; Andrew J. Rapoff

2006-01-01

274

Acute and prolonged reduction in joint stiffness in humans after exhausting stretch-shortening cycle exercise.  

PubMed

The purpose of the present study was to examine the acute and long-term fatigue effects of exhausting stretch-shortening cycle (SSC) exercise on the stiffness of ankle and knee joints. Five subjects were fatigued on a sledge apparatus by 100 maximal rebound jumps followed by continuous submaximal jumping until complete exhaustion. Neuromuscular fatigue effects were examined in submaximal hopping (HOP) and in maximal drop jumps (DJ) from 35 (DJ35) and 55 cm (DJ55) heights on a force plate. Additional force and reflex measurements were made using an ankle ergometer. Jumping tests and ankle ergometer tests were carried out before, immediately after, 2 h (2H), 2 days and 7 days (7D) after the SSC exercise. Kinematics, force and electromyography (EMG) recordings were complemented with inverse dynamics, which was used to calculate joint moments. The quotient of changes in joint moment divided by changes in joint angle was used as a value of joint stiffness (JS). In addition, blood lactate concentrations and serum creatine kinase activities were determined. The exercise induced a clear decrease in knee joint stiffness by [mean (SD)] 29 (13)% (P < 0.05) in HOP, 31 (6)% (P < 0.05) in DJ35 and 34 (14)% (P < 0.05) in DJ55. A similar trend was observed in the ankle joint stiffness with significant post-exercise reductions of 22 (8)% (P < 0.05) in DJ35 and of 27 (19)% (P < 0.05) at 2H in DJ55. The subsequent recovery of JS was slow and in some cases incomplete still at 7D. Generally, all the EMG parameters were fully recovered by 2H, whereas the force recovery was still incomplete at this time. These data indicate that the immediate reduction in JS was probably related to the effects of both central (neural) and peripheral (metabolic) fatigue, whereas the prolonged impairment was probably due to peripheral fatigue (muscle damage). PMID:12436277

Kuitunen, S; Avela, J; Kyröläinen, H; Nicol, C; Komi, P V

2002-11-01

275

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

PubMed

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

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

2014-12-01

276

Control of the stiffness of robotic appendages using dielectric elastomers  

NASA Astrophysics Data System (ADS)

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

Morton, Jeffrey

277

Chronic permanent hypoxemia predisposes to mild elevation of liver stiffness  

PubMed Central

AIM: To evaluate the impact of long term permanent hypoxemia noticed in patients with non operated congenital cyanogenic cyanotic cardiopathy on liver stiffness. METHODS: We included ten adult patients with non operated inoperate cyanotic cardiopathy and ten matched patients for age and gender admitted to the gastroenterology department for proctologic diseases; Clinical and laboratory data were collected [age, gender, body mass index, oxygen saturation, glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), glycemia and cholesterol]. Measurement of hepatic stiffness by transient elastography was carried out in all patients using the Fibroscan device. All patients underwent an echocardiography to eliminate congestive heart failure. RESULTS: Among the patients with cyanotic cardiopathy, median liver stiffness 5.9 ± 1.3 kPa was greater than control group (4.7 ± 0.4 kPa) (P = 0.008). Median levels of GOT, GPT, gamma-glutamyltransferase, glycemia and cholesterol were comparable in cardiopathy and control group. In regression analysis including age, gender, body mass index, oxygen saturation, GOT, GPT, glycemia, cholesterol showed that only oxygen saturation was related to liver stiffness (r = -0.63 P = 0.002). CONCLUSION: Chronic permanent hypoxemia can induce mild increase of liver stiffness, but further studies are needed to explore the histological aspects of liver injury induced by chronic permanent hypoxemia. PMID:25132776

Tahiri, Mohamed; Drighil, Abdenasser; Jalal, Yasmine; Ghellab, Dounia; Hliwa, Wafaa; Fouad, Haddad; Badre, Wafaa; Bellabah, Ahmad; Habbal, Rachida; Alaoui, Rhimou

2014-01-01

278

Influence of Lamination Pressure upon the Stiffness of Laminated Rotor  

NASA Astrophysics Data System (ADS)

In recent years, a laminated rotor made of the insulated silicon steel laminates is increasingly adopted in the electrical machineries. While this laminated rotor offers good electrical performances, it is quite complicated to predict its stiffness as it is influenced by various factors such as material properties and shape of the laminates, characteristics of the insulation layer, lamination pressure and method of fitting. As it is difficult to model or define boundary conditions in the case of lamination pressure or fitting, the stiffness of the laminated rotor cannot simply calculated using conventional analytical method. Therefore, quantitative investigation on the influence of lamination pressure upon the stiffness of laminated rotor is highly required. In this study, natural frequency of the rotor is measured under various conditions of lamination pressure to investigate the influence of lamination pressure upon the stiffness of laminated rotor. It is found from the experiment that the natural frequency is increased with lamination pressure, and saturated near the 20% of the difference between the inner and outer diameters of the laminate. It is also found that the natural frequency can be controlled to 4-14% in the range of 1-10MPa of lamination pressure. The saturated value of the stiffness of laminated rotor is expected to approach to that of shrinkage-fitted cylinder having the same inner and outer diameters under the same assembly condition. It is expected that the results would be helpful to design generators or motors using laminated rotors.

Kim, Yeong-Chun; Kim, Kyung-Woong

279

Nanomechanical measurement of astrocyte stiffness correlated with cytoskeletal maturation.  

PubMed

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

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

2015-01-01

280

Extended graphynes: simple scaling laws for stiffness, strength and fracture  

NASA Astrophysics Data System (ADS)

The mono-atomistic structure and chemical stability of graphene provides a promising platform to design a host of novel graphene-like materials. Using full atomistic first-principles based ReaxFF molecular dynamics, here we perform a systematic comparative study of the stability, structural and mechanical properties of graphynes - a variation of the sp2 carbon motif wherein the characteristic hexagons of graphene are linked by sp1 acetylene (single- and triple-bond) carbyne-like chains. The introduction of acetylene links introduces an effective penalty in terms of stability, elastic modulus (i.e., stiffness), and failure strength, which can be predicted as a function of acetylene repeats, or, equivalently, lattice spacing. We quantify the mechanical properties of experimental accessible graphdiyne, with a modulus on the order of 470 to 580 GPa and a ultimate strength on the order of 36 GPa to 46 GPa (direction dependent). We derive general scaling laws for the cumulative effects of additional acetylene repeats, formulated through a simple discrete spring-network framework, allowing extrapolation of mechanical performance to highly extended graphyne structures. Onset of local tensile buckling results in a transitional regime characterized by a severe reduction of strength (ultimate stress), providing a new basis for scaling extended structures. Simple fracture simulations support the scaling functions, while uncovering a ``two-tier'' failure mode for extended graphynes, wherein structural realignment facilitates stress transfer beyond initial failure. Finally, the specific modulus and strength (normalized by areal density) is found to be near-constant, suggesting applications for light-weight, yet structurally robust molecular components.

Cranford, Steven W.; Brommer, Dieter B.; Buehler, Markus J.

2012-11-01

281

Extended graphynes: simple scaling laws for stiffness, strength and fracture.  

PubMed

The mono-atomistic structure and chemical stability of graphene provides a promising platform to design a host of novel graphene-like materials. Using full atomistic first-principles based ReaxFF molecular dynamics, here we perform a systematic comparative study of the stability, structural and mechanical properties of graphynes - a variation of the sp(2) carbon motif wherein the characteristic hexagons of graphene are linked by sp(1) acetylene (single- and triple-bond) carbyne-like chains. The introduction of acetylene links introduces an effective penalty in terms of stability, elastic modulus (i.e., stiffness), and failure strength, which can be predicted as a function of acetylene repeats, or, equivalently, lattice spacing. We quantify the mechanical properties of experimental accessible graphdiyne, with a modulus on the order of 470 to 580 GPa and a ultimate strength on the order of 36 GPa to 46 GPa (direction dependent). We derive general scaling laws for the cumulative effects of additional acetylene repeats, formulated through a simple discrete spring-network framework, allowing extrapolation of mechanical performance to highly extended graphyne structures. Onset of local tensile buckling results in a transitional regime characterized by a severe reduction of strength (ultimate stress), providing a new basis for scaling extended structures. Simple fracture simulations support the scaling functions, while uncovering a "two-tier" failure mode for extended graphynes, wherein structural realignment facilitates stress transfer beyond initial failure. Finally, the specific modulus and strength (normalized by areal density) is found to be near-constant, suggesting applications for light-weight, yet structurally robust molecular components. PMID:23142928

Cranford, Steven W; Brommer, Dieter B; Buehler, Markus J

2012-12-21

282

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

283

Active pneumatic vibration isolation system using negative stiffness structures for a vehicle seat  

NASA Astrophysics Data System (ADS)

In this paper, an active pneumatic vibration isolation system using negative stiffness structures (NSS) for a vehicle seat in low excitation frequencies is proposed, which is named as an active system with NSS. Here, the negative stiffness structures (NSS) are used to minimize the vibratory attraction of a vehicle seat. Owing to the time-varying and nonlinear behavior of the proposed system, it is not easy to build an accurate dynamic for model-based controller design. Thus, an adaptive intelligent backstepping controller (AIBC) is designed to manage the system operation for high-isolation effectiveness. In addition, an auxiliary control effort is also introduced to eliminate the effect of the unpredictable perturbations. Moreover, a radial basis function neural network (RBFNN) model is utilized to estimate the optimal gain of the auxiliary control effort. Final control input and the adaptive law for updating coefficients of the approximate series can be obtained step by step using a suitable Lyapunov function. Afterward, the isolation performance of the proposed system is assessed experimentally. In addition, the effectiveness of the designed controller for the proposed system is also compared with that of the traditional backstepping controller (BC). The experimental results show that the isolation effectiveness of the proposed system is better than that of the active system without NSS. Furthermore, the undesirable chattering phenomenon in control effort is quite reduced by the estimation mechanism. Finally, some concluding remarks are given at the end of the paper.

Danh, Le Thanh; Ahn, Kyoung Kwan

2014-02-01

284

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. PMID:25050406

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

2014-01-01

285

Evaluation of fatigue life of CRM-reinforced SMA and its relationship to dynamic stiffness.  

PubMed

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. PMID:25050406

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

2014-01-01

286

Ultrasound imaging system for measuring stiffness variation in the fingerpad skin in vivo  

NASA Astrophysics Data System (ADS)

An elasticity imaging system was developed for measuring the stiffness variation at different depths of the human fingerpad skin in vivo. In this system, ultrasonic backscatter microscopy (UBM) with a single high frequency (28MHz) transducer was employed to obtain data on tissue heterogeneity at high axial resolution (~25 mm). The dorsal side of the finger was fixed on a manually controlled vertical stage and an acrylic indentor was applied to the fingerpad. A slit cut vertically through the indentor at the center and a piece of transparency sheet attached to the bottom allowed most of the ultrasound power to pass though while maintaining a flat surface in contact with the skin. With the assumption that the skin can be modeled as a semi-infinite layered structure, only data from a single A-line was obtained for strain analysis. The data at continuous indentation steps were cross-correlated to calculate the displacement at different spots along the depth. The de-correlation at certain regions was resolved by removing the data points with lower correlation coefficients, and curve fitting was applied to overcome the lack of resolution due to sampling. The fingerpads of 10 human subjects were tested in vivo and a gelatin phantom was made and tested for comparison. The results showed that even though some data were degraded due to the hypoechoic nature of the subcutaneous fat, the axial strain profile through the skin thickness (up to 3mm in depth) could be extracted as a measure of the stiffness variation.

Wu, Wan-Chen; Raju, Balasundar I.; Srinivasan, Mandayam A.

2005-04-01

287

Improved compression buckling for rectangular composite plates by stiffness tailoring  

NASA Technical Reports Server (NTRS)

Buckling resistance is often a controlling criterion in the design of structural elements. Design concepts that lead to increased buckling loads (or strains) can directly lower the structural cost and/or weight by a number of means. This study quantifies the improvements that can be achieved in compression buckling loads of rectangular composite plates by using a simple stiffness tailoring concept. The approach is to position the unidirectional lamina through the thickness and over the planform of the plate so that the buckling load is increased with no loss in in-plane stiffness or increase in weight. Finite element analyses have been used to determine the effects of tailoring on the buckling load of plates with various boundary conditions, aspect ratios, thicknesses, and membrane stiffnesses. Increases in buckling loads (or strains) of nearly 200 percent over the uniform plate buckling loads are shown possible with this tailoring concept.

Biggers, Sherrill B.; Srinivasan, Sundar

1991-01-01

288

Intermittent versus constant aerobic exercise: effects on arterial stiffness  

Microsoft Academic Search

Aerobic exercises (of sufficient duration and intensity) decreases arterial stiffness. However, the direct relationship between\\u000a the type of aerobic exercise (i.e. constant versus interval) and the alteration in arterial stiffness has been poorly explored.\\u000a We evaluated the hemodynamic responses of 11 healthy males (22.5 ± 0.7 years, height 177.7 ± 1.1 cm, body mass 70.5 ± 2.4 kg)\\u000a following acute constant (CE) and intermittent cycling exercise (IE). Exercise duration

Nicolas Tordi; Laurent Mourot; Eglantine Colin; Jacques Regnard

2010-01-01

289

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

290

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

291

Estimation of deformation and stiffness of fractures close to tunnels using data from single-hole hydraulic testing and grouting  

SciTech Connect

Sealing of tunnels in fractured rocks is commonly performed by pre- or post-excavation grouting. The grouting boreholes are frequently drilled close to the tunnel wall, an area where rock stresses can be low and fractures can more easily open up during grout pressurization. In this paper we suggest that data from hydraulic testing and grouting can be used to identify grout-induced fracture opening, to estimate fracture stiffness of such fractures, and to evaluate its impact on the grout performance. A conceptual model and a method are presented for estimating fracture stiffness. The method is demonstrated using grouting data from four pre-excavation grouting boreholes at a shallow tunnel (50 m) in Nygard, Sweden, and two post-excavation grouting boreholes at a deep tunnel (450 m) in Aespoe HRL, Sweden. The estimated stiffness of intersecting fractures for the boreholes at the shallow Nygard tunnel are low (2-5 GPa/m) and in agreement with literature data from field experiments at other fractured rock sites. Higher stiffness was obtained for the deeper tunnel boreholes at Aespoe which is reasonable considering that generally higher rock stresses are expected at greater depths. Our method of identifying and evaluating the properties and impact of deforming fractures might be most applicable when grouting takes place in boreholes adjacent to the tunnel wall, where local stresses might be low and where deforming (opening) fractures may take most of the grout.

Fransson, A.; Tsang, C.-F.; Rutqvist, J.; Gustafson, G.

2010-05-01

292

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

293

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

294

Elastomeric substrates with embedded stiff platforms for stretchable electronics  

E-print Network

elastomers,7 2D,8 or 3D10 meandering structures, is required to interconnect electromechanically the stiff|STI|IMT/IBI|LSBI, 1015 Lausanne, Switzerland 2 School of Engineering and Applied Sciences and Kavli Institute for Bionano for stretchable circuits prepared with alternative technologies, such as transfer-printing of inorganic, thinned

Suo, Zhigang

295

Effect of hopping frequency on bilateral differences in leg stiffness.  

PubMed

Understanding the degree of leg stiffness during human movement would provide important information that may be used for injury prevention. In the current study, we investigated bilateral differences in leg stiffness during one-legged hopping. Ten male participants performed one-legged hopping in place, matching metronome beats at 1.5, 2.2, and 3.0 Hz. Based on a spring-mass model, we calculated leg stiffness, which is defined as the ratio of maximal ground reaction force to maximum center of mass displacement at the middle of the stance phase, measured from vertical ground reaction force. In all hopping frequency settings, there was no significant difference in leg stiffness between legs. Although not statistically significant, asymmetry was the greatest at 1.5 Hz, followed by 2.2 and 3.0 Hz for all dependent variables. Furthermore, the number of subjects with an asymmetry greater than the 10% criterion was larger at 1.5 Hz than those at 2.2 and 3.0 Hz. These results will assist in the formulation of treatment-specific training regimes and rehabilitation programs for lower extremity injuries. PMID:23462443

Hobara, Hiroaki; Inoue, Koh; Kanosue, Kazuyuki

2013-02-01

296

Design of a Stiff Steerable Grasper for Sinus Surgery  

E-print Network

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

Webster III, Robert James

297

Polyimide-based intracortical neural implant with improved structural stiffness  

NASA Astrophysics Data System (ADS)

A novel structure for chronically implantable cortical electrodes using polyimide bio-polymer was devised, which provides both flexibility for micro-motion compliance between brain tissues and the skull and at the brain/implant interface and stiffness for better surgical handling. A 5-10 µm thick silicon backbone layer was attached to the tip of the electrode to enhance the structural stiffness. This stiff segment was then followed by a 1 mm flexible segment without a silicon backbone layer. The fabricated implants have tri-shanks with five recording sites (20 µm × 20 µm) and two vias of 40 µm × 40 µm on each shank. In vitro cytotoxicity tests of prototype implants revealed no adverse toxic effects on cells. Bench test impedance values were assessed, resulting in an average impedance value of ~2 MOmega at 1 KHz. For a 5 µm thick silicon backbone electrode, the stiffness of polyimide-based electrodes was increased ten times over that of electrodes without the silicon backbone layer. Furthermore, polyimide-based electrodes with 5 µm and 10 µm thick silicon backbone layer penetrated pia of rat brain without buckling that has been observed in implants without silicon reinforcement.

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

2004-01-01

298

Flexural stiffness of feather shafts: geometry rules over material properties.  

PubMed

Flight feathers of birds interact with the flow field during flight. They bend and twist under aerodynamic loads. Two parameters are mainly responsible for flexibility in feathers: the elastic modulus (Young's modulus, E) of the material (keratin) and the geometry of the rachises, more precisely the second moment of area (I). Two independent methods were employed to determine Young's modulus of feather rachis keratin. Moreover, the second moment of area and the bending stiffness of feather shafts from fifth primaries of barn owls (Tyto alba) and pigeons (Columba livia) were calculated. These species of birds are of comparable body mass but differ in wing size and flight style. Whether their feather material (keratin) underwent an adaptation in stiffness was previously unknown. This study shows that no significant variation in Young's modulus between the two species exists. However, differences in Young's modulus between proximal and distal feather regions were found in both species. Cross-sections of pigeon rachises were particularly well developed and rich in structural elements, exemplified by dorsal ridges and a well-pronounced transversal septum. In contrast, cross-sections of barn owl rachises were less profiled but had a higher second moment of area. Consequently, the calculated bending stiffness (EI) was higher in barn owls as well. The results show that flexural stiffness is predominantly influenced by the geometry of the feathers rather than by local material properties. PMID:22246249

Bachmann, Thomas; Emmerlich, Jens; Baumgartner, Werner; Schneider, Jochen M; Wagner, Hermann

2012-02-01

299

Axial optical trap stiffness influenced by retro-reflected beam  

Microsoft Academic Search

We studied experimentally how the beam retro-reflected from a planar interface (microscope slide) influences the axial stiffness of a single beam trap. Since the incident and retro-reflected beams interfere, weak intensity maxima and minima form a standing wave superposed on the axial single focused beam intensity envelope. Therefore there exists competition between the single beam trap and the weak standing

Petr Jákl; Mojmír Serý; Jan Jezek; Miroslav Liska; Pavel Zemánek

2007-01-01

300

Initial post-buckling of variable-stiffness curved panels  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

301

Design optimization of a twist compliant mechanism with nonlinear stiffness  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

302

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

303

ORIGINAL CONTRIBUTION Investigation of Soft-Tissue Stiffness Alteration in  

E-print Network

effective than one focused on treating established pressure ulcers (10,11). Current documentation for a quantitative assessment and detection technique for pressure ulcers or deep-tissue injury. An ultrasound Words: Spinal cord injuries; Soft-tissue stiffness; Pressure ulcers; Deep-tissue injury; Ultrasound

Makhsous, Mohsen

304

Stiffness Contribution of Various Wood Fibers to Composite Materials  

Microsoft Academic Search

Wood pulp fibers can serve as useful reinforcement of plastics for increased stiffness. To assess the potential of various wood fibers as reinforcement, a method has been developed to determine the contribution of the fibers to the elastic properties of the composite. A micromechanical composite model and classical laminate mechanics are used to relate the elastic properties of the fibers

R. Cristian Neagu; E. Kristofer Gamstedt; Fredrik Berthold

2006-01-01

305

Breast Tissue Stiffness in Compression is Correlated to Histological Diagnosis  

E-print Network

surgery and were tested immediately after removal from the body. We found that there is a significant A. Kern Department of Surgery Hartford Hospital Hartford, CT 06115 University of Connecticut School of Medicine Storrs, CT 06269 Abstract Many researchers have proposed imaging the stiffness distribution

306

Stiffness and strength properties for basic sandwich material core types  

SciTech Connect

Three basic core material types for sandwich structure applications are studied. The three two-dimensional pattern types are: honeycomb, triangular cells, and a new configuration involving star type cells. The specific critical properties of stiffness and strength type are identified and studied, both theoretically and experimentally.

Beomkeun, K; Christensen, R M

1999-08-03

307

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

308

Stiffness Modeling of a Spatial 3-DOF Compliant Parallel Micromanipulator  

E-print Network

Av. Padre Tom´as Pereira S.J., Taipa, Macao SAR, P. R. China Email: ya47401@umac.mo, ymli@umac.mo Abstract-- The stiffness modeling for a compliant parallel manipulator (CPM) is very important since mounted actuators, that is designed to provide three spatial translational DOF for nano scale manipulation

Li, Yangmin

309

Stiff man syndrome: Clinical and laboratory findings in eight patients  

Microsoft Academic Search

The clinical, biochemical, neuroimaging and neurophysiological findings of eight patients with stiff man syndroms (SMS) [four of six being tested with autoantibodies against glutamic acid decarboxylase (GAD)] are presented. In two patients (one GAD-positive, one GAD-negative), transient oculomotor disturbances suggested progressive encephalomyelitis with rigidity and myoclonus (PERM) as differential diagnosis. The catalogue of characteristic clinical symptoms of SMS is extended

H.-M. Meinck; K. Ricker; P.-J. Hülser; E. Schmid; J. Peiffer; M. Solimena

1994-01-01

310

Stiff man syndrome: neurophysiological findings in eight patients  

Microsoft Academic Search

The neurophysiological findings in eight patients with the stiff man syndrome (SMS), including four of six tested with autoantibodies against glutamic acid decarboxylase, are presented. Neurophysiological findings did not make it possible to discriminate between patients with and those without autoimmunity against GABAergic neurons. Investigation of mono-and polysynaptic reflexes revealed abnormal results in a variable number of SMS patients, the

H.-M. Meinck; K. Ricker; P.-J. Hülser; M. Solimena

1995-01-01

311

Electromagnetic Field in Some Anisotropic Stiff Fluid Universes  

E-print Network

The electromagnetic field is studied in a family of exact solutions of the Einstein equations whose material content is a perfect fluid with stiff equation of state (p = $\\epsilon $ ). The field equations are solved exactly for several members of the family.

Pimentel L O

1995-07-25

312

Stiffness of hair bundles in the chick cochlea.  

PubMed

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

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

1992-05-01

313

Verifying Stiffness Parameters Of Filament-Wound Cylinders  

NASA Technical Reports Server (NTRS)

Predicted engineering stiffness parameters of filament-wound composite-material cylinders verified with respect to experimental data, by use of equations developed straightforwardly from applicable formulation of Hooke's law. Equations derived in engineering study of filament-wound rocket-motor cases, also applicable to other cylindrical pressure vessels made of orthotropic materials.

Verderaime, V.; Rheinfurth, M.

1994-01-01

314

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

315

Creatine supplementation and its effect on musculotendinous stiffness and performance.  

PubMed

Anecdotal reports suggesting that creatine (Cr) supplementation may cause side effects, such as an increased incidence of muscle strains or tears, require scientific examination. In this study, it was hypothesized that the rapid fluid retention and "dry matter growth" evident after Cr supplementation may cause an increase in musculotendinous stiffness. Intuitively, an increase in musculotendinous stiffness would increase the chance of injury during exercise. Twenty men were randomly allocated to a control or an experimental group and were examined for musculotendinous stiffness of the triceps surae and for numerous performance indices before and after Cr ingestion. The Cr group achieved a significant increase in body mass (79.7 +/- 10.8 kg vs. 80.9 +/- 10.7 kg), counter movement jump height (40.2 +/- 4.8 cm vs. 42.7 +/- 5.9 cm), and 20-cm drop jump height (32.3 +/- 3.3 cm vs. 35.1 +/- 4.8 cm) after supplementation. No increase was found for musculotendinous stiffness at any assessment load. There were no significant changes in any variables within the control group. These findings have both performance- and injury-related implications. Primarily, anecdotal evidence suggesting that Cr supplementation causes muscular strain injuries is not supported by this study. In addition, the increase in jump performance is indicative of performance enhancement in activities requiring maximal power output. PMID:12580652

Watsford, Mark L; Murphy, Aron J; Spinks, Warwick L; Walshe, Andrew D

2003-02-01

316

Structure, Stiffness and Substates of the Dickerson-Drew Dodecamer  

PubMed Central

The Dickerson–Drew dodecamer (DD) d-[CGCGAATTCGCG]2 is a prototypic B-DNA molecule whose sequence-specific structure and dynamics have been investigated by many experimental and computational studies. Here, we present an analysis of DD properties based on extensive atomistic molecular dynamics (MD) simulations using different ionic conditions and water models. The 0.6–2.4-µs-long MD trajectories are compared to modern crystallographic and NMR data. In the simulations, the duplex ends can adopt an alternative base-pairing, which influences the oligomer structure. A clear relationship between the BI/BII backbone substates and the basepair step conformation has been identified, extending previous findings and exposing an interesting structural polymorphism in the helix. For a given end pairing, distributions of the basepair step coordinates can be decomposed into Gaussian-like components associated with the BI/BII backbone states. The nonlocal stiffness matrices for a rigid-base mechanical model of DD are reported for the first time, suggesting salient stiffness features of the central A-tract. The Riemann distance and Kullback–Leibler divergence are used for stiffness matrix comparison. The basic structural parameters converge very well within 300 ns, convergence of the BI/BII populations and stiffness matrices is less sharp. Our work presents new findings about the DD structural dynamics, mechanical properties, and the coupling between basepair and backbone configurations, including their statistical reliability. The results may also be useful for optimizing future force fields for DNA. PMID:23976886

Drsata, Tomas; Perez, Alberto; Orozco, Modesto; Morozov, Alexandre V.; Sponer, Jirl; Lankas, Filip

2013-01-01

317

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...

318

Calculation of combined diffusion coefficients in SF6-Cu mixtures  

NASA Astrophysics Data System (ADS)

Diffusion coefficients play an important role in the description of the transport of metal vapours in gas mixtures. This paper is devoted to the calculation of four combined diffusion coefficients, namely, the combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient, and combined pressure diffusion coefficient in SF6-Cu mixtures at temperatures up to 30 000 K. These four coefficients describe diffusion due to composition gradients, applied electric fields, temperature gradients, and pressure gradients, respectively. The influence of copper fluoride and sulfide species on the diffusion coefficients is shown to be negligible. The effect of copper proportion and gas pressures on these diffusion coefficients is investigated. It is shown that increasing the proportion of copper generally increases the magnitude of the four diffusion coefficients, except for copper mole fractions of 90% or more. It is further found that increasing the pressure reduces the magnitude of the coefficients, except for the combined temperature diffusion coefficient, and shifts the maximum of all four coefficients towards higher temperatures. The results presented in this paper can be applied to the simulation of high-voltage circuit breaker arcs.

Zhong, Linlin; Wang, Xiaohua; Rong, Mingzhe; Wu, Yi; Murphy, Anthony B.

2014-10-01

319

Hybrid compliance-stiffness matrix method for stable analysis of elastic wave propagation in multilayered anisotropic media.  

PubMed

This paper presents the hybrid compliance-stiffness matrix method for stable analysis of elastic wave propagation in multilayered anisotropic media. The method utilizes the hybrid matrix of each layer in a recursive algorithm to deduce the stack hybrid matrix for a multilayered structure. Like the stiffness matrix method, the hybrid matrix method is able to eliminate the numerical instability of transfer matrix method. By operating with total stresses and displacements, it also preserves the convenience for incorporating imperfect or perfect interfaces. However, unlike the stiffness matrix, the hybrid matrix remains to be well-conditioned and accurate even for zero or small thicknesses. The stability of hybrid matrix method has been demonstrated by the numerical results of reflection and transmission coefficients. These results have been determined efficiently based on the surface hybrid matrix method involving only a subset of hybrid submatrices. In conjunction with the recursive asymptotic method, the hybrid matrix method is self-sufficient without hybrid asymptotic method and may achieve low error level over a wide range of sublayer thickness or the number of recursive operations. PMID:16454263

Tan, Eng Leong

2006-01-01

320

Matrices of Physiologic Stiffness Potently Inactivate Idiopathic Pulmonary Fibrosis Fibroblasts  

PubMed Central

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

Marinkovic, Aleksandar; Liu, Fei

2013-01-01

321

Fractal diffusion coefficient from dynamical zeta functions  

E-print Network

Dynamical zeta functions provide a powerful method to analyze low dimensional dynamical systems when the underlying symbolic dynamics is under control. On the other hand even simple one dimensional maps can show an intricate structure of the grammar rules that may lead to a non smooth dependence of global observable on parameters changes. A paradigmatic example is the fractal diffusion coefficient arising in a simple piecewise linear one dimensional map of the real line. Using the Baladi-Ruelle generalization of the Milnor-Thurnston kneading determinant we provide the exact dynamical zeta function for such a map and compute the diffusion coefficient from its smallest zero.

G. Cristadoro

2005-09-28

322

A stiffness equation transfer method for transient dynamic response analysis of structures  

NASA Astrophysics Data System (ADS)

A stiffness equation transfer method is proposed for transient dynamic response analysis of structures under various excitations. This method is a development and refinement of the combined finite element-transfer matrix (FE-TM) method. In the present method, the transfer of state vectors from left to right in the FE-TM method is changed into the transfer of general stiffness equations of every section from left to right. This method has the advantages of reducing the order of the ordinary transfer equation systems and minimizing the propagation of round-off errors occurring in recursive multiplication of transfer and point matrices. Furthermore, the drawback that the number of degrees of freedom on the left boundary must be the same as that on the right boundary in the ordinary FE-TM method, has now been avoided. The Newmark generalized acceleration formulation for time discretization is employed for a solution of the time problem. At the end, numerical examples are presented to demonstrate the accuracy as well as the potential of the proposed method for transient dynamic response analysis of structures.

Xue, Huiyu

2004-06-01

323

Diffusion coefficients in leaflets of bilayer membranes  

E-print Network

We study diffusion coefficients of liquid domains by explicitly taking into account the two-layered structure called leaflets of the bilayer membrane. In general, the velocity fields associated with each leaflet are different and the layers sliding past each other cause frictional coupling. We obtain analytical results of diffusion coefficients for a circular liquid domain in a leaflet, and quantitatively study their dependence on the inter-leaflet friction. We also show that the diffusion coefficients diverge in the absence of coupling between the bilayer and solvents, even when the inter-leaflet friction is taken into account. In order to corroborate our theory, the effect of the inter-leaflet friction on the correlated diffusion is examined.

Kazuhiko Seki; Saurabh Mogre; Shigeyuki Komura

2014-02-05

324

Helix versus coil polypeptide macromers: gel networks with decoupled stiffness and permeability  

E-print Network

As a platform for investigating the individual effects of substrate stiffness, permeability, and ligand density on cellular behavior, we developed a set of hydrogels with stiffness tuned by polymer backbone rigidity, ...

Oelker, Abigail M.

325

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

326

Parametric excitation of tire-wheel assemblies by a stiffness non-uniformity  

Microsoft Academic Search

A simple model of the effect of a concentrated radial stiffness non-uniformity in a passenger car tire is presented. The model treats the tread band of the tire as a rigid ring supported on a viscoelastic foundation. The distributed radial stiffness is lumped into equivalent horizontal (fore-and-aft) and vertical stiffnesses. The concentrated radial stiffness non-uniformity is modeled by treating the

D. S. Stutts; C. M. Krousgrill; W. Soedel

1995-01-01

327

Estimation of hydrodynamic coefficients for an AUV using nonlinear observers  

Microsoft Academic Search

Hydrodynamic coefficients strongly affect the dynamic performance of an autonomous underwater vehicle. Although these coefficients are generally obtained experimentally such as through the planar-motion-mechanism (PMM) test, the measured values are not completely reliable because of experimental difficulties and errors involved. Another approach by which these coefficients can be obtained is the observer method, in which a model-based estimation algorithm predicts

Joonyoung Kim; Kihun Kim; Hang S. Choi; Woojae Seong; Kyu-Yeul Lee

2002-01-01

328

Kubo Formulae for Second-Order Hydrodynamic Coefficients  

E-print Network

At second order in gradients, conformal relativistic hydrodynamics depends on the viscosity eta and on five additional "second-order" hydrodynamical coefficients tauPi, kappa, lambda1, lambda2, and lambda3. We derive Kubo relations for these coefficients, relating them to equilibrium, fully retarded 3-point correlation functions of the stress tensor. We show that the coefficient lambda3 can be evaluated directly by Euclidean means and does not in general vanish.

Guy D. Moore; Kiyoumars A. Sohrabi

2010-07-29

329

Piezooptic Coefficients and Acoustic Wave Velocities in Sn2P2S6 Crystals  

E-print Network

Piezooptic coefficients of Sn2P2S6 crystals are experimentally determined for l=623.8 nm and T=293 K with the aid of interferometric technique. The components of the elastic stiffness tensor for these crystals are calculated on the basis of studies for the acoustic wave velocities. It is shown that acoustooptic figure of merit can achieve extremely high values for Sn2P2S6 crystals (M2 - 2x10-12s3/kg2).

O. Mys; I. Martynyuk-Lototska; A. Grabar; Yu. Vysochanskii; R. Vlokh

2007-06-28

330

A comparison of experimental and theoretical results for rotordynamic coefficients for labyrinth gas seals  

E-print Network

results of Wachter and Benckert and to the test results presented in this paper. The results presented are for two labyrinth seals, one with teeth on the rotor and one with teeth on the stator. The theory compares poorly with all measured rotordynamic... coefficients iv except the cross-coupled stiffness for a teeth on stator seal. Both seals develop damping which is dependent on the inlet tangential velocity. ACKNOWLEDGENENT This project would not have been possible without the hard work and dedication...

Scharrer, Joseph Kirk

2012-06-07

331

Dynamic testing and stiffness evaluation of a six-storey timber framed building during construction  

Microsoft Academic Search

This paper is concerned with the dynamic testing and stiffness evaluation of a six-storey timber framed building. The principal reason for undertaking the measurements was to quantify the difference between the stiffness of the bare frame, which is used in design, and the stiffness of the complete building. Two types of measurements were taken. Laser measurements, where the building's natural

B. R Ellis; A. J Bougard

2001-01-01

332

EVALUATION OF NON-DESTRUCTIVE METHODS FOR ASSESSING STIFFNESS OF DOUGLAS FIR TREES  

Microsoft Academic Search

Identification and selection of superior trees in forest management and breeding programmes provide a means to improve the properties and value of future wood products. Non-destructive stiffness assessment of standing trees enables selection of individuals for their stiffness, and so the accuracy and cost of four methods for assessing stiffness were evaluated: (1) IML hammer, (2) 5-mm outerwood density cores,

R. LEITH KNOWLES; LARS W. HANSEN; ADELE WEDDING; GEOFFREY DOWNES

333

Independent Stiffness and Force Control of Pneumatic Actuators for Contact Stability during  

E-print Network

Independent Stiffness and Force Control of Pneumatic Actuators for Contact Stability during Robot that controls the stiffness and force of pneumatic actuator independently. This independent control of stiffness, the pneumatic actuators utilized in this work enable two control degrees of freedom. One control degree

334

Scaling of stiffness energy for 3d \\SigmaJ Ising spin glasses Alexander K. Hartmann  

E-print Network

transfer matrix methods [4,6] and Monte Carlo simulations [5]. The stiffness energy shows a finite sizeScaling of stiffness energy for 3d \\SigmaJ Ising spin glasses Alexander K. Hartmann hartmann. A de­ tailed analysis shows that true ground states are obtained. The ground state stiffness (or domain

Hartmann, Alexander K.

335

Dispersion of critical rotational speeds of gearbox: effect of bearings stiffnesses  

E-print Network

affect the characteristics of the meshing stiffness and the dynamic transfer from dynamic meshing force on the natural modes of the overall model (effect of stiffness matrix) but also on excitation source (effectDispersion of critical rotational speeds of gearbox: effect of bearings stiffnesses F. Mayeux, E

Paris-Sud XI, Université de

336

Relationship Between Arterial Stiffness and Athletic Training Programs in Young Adult Men  

Microsoft Academic Search

Background: We examined the relationships of endurance and strength exercise training and the adolescent duration of training to arterial stiffness in young adult men. We hypothesized that young adults participating in endurance sports would have decreased arterial stiffness, whereas those in strength-based sports would have increased arterial stiffness. In addition, we predicted that these trends would be more pronounced with

Takeshi Otsuki; Seiji Maeda; Motoyuki Iemitsu; Yoko Saito; Yuko Tanimura; Ryuichi Ajisaka; Takashi Miyauchi

2007-01-01

337

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. PMID:21359137

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

2011-01-01

338

Vibration in Planetary Gear Systems with Unequal Planet Stiffnesses  

NASA Technical Reports Server (NTRS)

An algorithm suitable for a minicomputer was developed for finding the natural frequencies and mode shapes of a planetary gear system which has unequal stiffnesses between the Sun/planet and planet/ring gear meshes. Mode shapes are represented in the form of graphical computer output that illustrates the lateral and rotational motion of the three coaxial gears and the planet gears. This procedure permits the analysis of gear trains utilizing nonuniform mesh conditions and user specified masses, stiffnesses, and boundary conditions. Numerical integration of the equations of motion for planetary gear systems indicates that this algorithm offers an efficient means of predicting operating speeds which may result in high dynamic tooth loads.

Frater, J. L.; August, R.; Oswald, F. B.

1982-01-01

339

Depinning of stiff directed lines in random media  

NASA Astrophysics Data System (ADS)

Driven elastic manifolds in random media exhibit a depinning transition to a state with nonvanishing velocity at a critical driving force. We study the depinning of stiff directed lines, which are governed by a bending rigidity rather than line tension. Their equation of motion is the (quenched) Herring-Mullins equation, which also describes surface growth governed by surface diffusion. Stiff directed lines are particularly interesting as there is a localization transition in the static problem at a finite temperature and the commonly exploited time ordering of states by means of Middleton's theorems [Phys. Rev. Lett. 68, 670 (1992), 10.1103/PhysRevLett.68.670] is not applicable. We employ analytical arguments and numerical simulations to determine the critical exponents and compare our findings with previous works and functional renormalization group results, which we extend to the different line elasticity. We see evidence for two distinct correlation length exponents.

Boltz, Horst-Holger; Kierfeld, Jan

2014-07-01

340

Depinning of stiff directed lines in random media.  

PubMed

Driven elastic manifolds in random media exhibit a depinning transition to a state with nonvanishing velocity at a critical driving force. We study the depinning of stiff directed lines, which are governed by a bending rigidity rather than line tension. Their equation of motion is the (quenched) Herring-Mullins equation, which also describes surface growth governed by surface diffusion. Stiff directed lines are particularly interesting as there is a localization transition in the static problem at a finite temperature and the commonly exploited time ordering of states by means of Middleton's theorems [Phys. Rev. Lett. 68, 670 (1992)] is not applicable. We employ analytical arguments and numerical simulations to determine the critical exponents and compare our findings with previous works and functional renormalization group results, which we extend to the different line elasticity. We see evidence for two distinct correlation length exponents. PMID:25122245

Boltz, Horst-Holger; Kierfeld, Jan

2014-07-01

341

Stiffness and strength of suture joints in nature  

NASA Astrophysics Data System (ADS)

Suture joints are remarkable mechanical structures found throughout nature composed of compliant interlocking seams connecting stiffer components. This study investigates the underlying mechanisms and the role of geometry governing the unique mechanical behavior of suture joints. Analytical and numerical composite models are formulated for two suture geometries characterized by a single repeating wavelength (e.g., triangular and rectangular). Stiffness, strength, and local stress distributions are predicted to assess variations in deformation and failure mechanisms. A unique homogeneous stress field is observed throughout both the skeletal and interfacial components of the triangular geometry, thus providing advantages in load transmission, weight, stiffness, strength, energy absorption, and fatigue over the rectangular geometry. The results obtained have relevance to biomimetic design and optimization, suture growth and fusion, and evolutionary phenotype diversity.

Li, Yaning; Ortiz, Christine; Boyce, Mary C.

2011-12-01

342

Stiff filamentous virus translocations through solid-state nanopores  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

343

Perturbation Theory for Path Integrals of Stiff Polymers  

E-print Network

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 expansions for all physically interesting quantities in powers of $L/\\xi$, where $L$ is the length and $\\xi$ the persistence length of the polymer. This requires special procedures for regularizing highly divergent Feynman integrals which we have developed in previous work. We show that by adding to the unperturbed action a correction term ${\\cal A}^{\\rm corr}$, we can calculate all Feynman diagrams with Green functions satisfying Neumann boundary conditions. Our expansions yield, order by order, properly normalized end-to-end distribution function in arbitrary dimensions $d$, its even and odd moments, and the two-point correlation function.

H. Kleinert; A. Chervyakov

2005-03-09

344

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

345

Trunk stiffness and dynamics during active extension exertions.  

PubMed

Spinal stability is related to the recruitment and control of active muscle stiffness. Stochastic system identification techniques were used to calculate the effective stiffness and dynamics of the trunk during active trunk extension exertions. Twenty-one healthy adult subjects (10 males, 11 females) wore a harness with a cable attached to a servomotor such that isotonic flexion preloads of 100, 135, and 170 N were applied at the T10 level of the trunk. A pseudorandom stochastic force sequence (bandwidth 0-10 Hz, amplitude +/-30 N) was superimposed on the preload causing small amplitude trunk movements. Nonparametric impulse response functions of trunk dynamics were computed and revealed that the system exhibited underdamped second-order behavior. Second-order trunk dynamics were determined by calculating the best least-squares fit to the IRF. The quality of the model was quantified by comparing estimated and observed displacement variance accounted for (VAF), and quality of the second-order fits was calculated as a percentage and referred to as fit accuracy. Mean VAF and fit accuracy were 87.8 +/- 4.0% and 96.0 +/- 4.3%, respectively, indicating that the model accurately represented active trunk kinematic response. The accuracy of the kinematic representation was not influenced by preload or gender. Mean effective stiffness was 2.78 +/- 0.96 N/mm and increased significantly with preload (p < 0.001), but did not vary with gender (p = 0.425). Mean effective damping was 314 +/- 72 Ns/m and effective trunk mass was 37.0 +/- 9.3 kg. We conclude that stochastic system identification techniques should be used to calculate effective trunk stiffness and dynamics. PMID:16084200

Moorhouse, Kevin M; Granata, Kevin P

2005-10-01

346

Isokinetic Resistance Training Increases Tibial Bending Stiffness in Young Women  

Microsoft Academic Search

Bone mineral content (BMC) and bone mineral density (BMD) are common but imperfect surrogate measures of bone strength. The\\u000a mechanical response tissue analyzer is a device that measures long bone bending stiffness (EI), which strongly predicts bone breaking strength. We hypothesized that isokinetic resistance training of the knee flexor\\u000a and extensor muscles would increase tibial EI, BMC, and BMD in

Larry E. Miller; Sharon M. Nickols-Richardson; David F. Wootten; Warren K. Ramp; Charles R. Steele; John R. Cotton; James P. Carneal; William G. Herbert

2009-01-01

347

Biomechanical imaging of cell stiffness and prestress with subcellular resolution.  

PubMed

Knowledge of cell mechanical properties, such as elastic modulus, is essential to understanding the mechanisms by which cells carry out many integrated functions in health and disease. Cellular stiffness is regulated by the composition, structural organization, and indigenous mechanical stress (or prestress) borne by the cytoskeleton. Current methods for measuring stiffness and cytoskeletal prestress of living cells necessitate either limited spatial resolution but with high speed, or spatial maps of the entire cell at the expense of long imaging times. We have developed a novel technique, called biomechanical imaging, for generating maps of both cellular stiffness and prestress that requires less than 30 s of interrogation time, but which provides subcellular spatial resolution. The technique is based on the ability to measure tractions applied to the cell while simultaneously observing cell deformation, combined with capability to solve an elastic inverse problem to find cell stiffness and prestress distributions. We demonstrated the application of this technique by carrying out detailed mapping of the shear modulus and cytoskeletal prestress distributions of 3T3 fibroblasts, making no assumptions regarding those distributions or the correlation between them. We also showed that on the whole cell level, the average shear modulus is closely associated with the average prestress, which is consistent with the data from the literature. Data collection is a straightforward procedure that lends itself to other biochemical/biomechanical interventions. Biomechanical imaging thus offers a new tool that can be used in studies of cell biomechanics and mechanobiology where fast imaging of cell properties and prestress is desired at subcellular resolution. PMID:24022327

Canovi?, Elizabeth P; Seidl, D Thomas; Polio, Samuel R; Oberai, Assad A; Barbone, Paul E; Stamenovi?, Dimitrije; Smith, Michael L

2014-06-01

348

Arterial Stiffness in Patients with Deep and Lobar Intracerebral Hemorrhage  

PubMed Central

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

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

2014-01-01

349

Lamb wave assessment of stiffness degradation in fatigued composites  

Microsoft Academic Search

A Lamb wave scanning system that measures the elastic properties of a material was used to characterize fatigue damage in composites. The Lamb Wave Imager™ (LWI) uses a pulse\\/receive technique that excites a flexural Lamb mode and measure the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated

Michael D. Seale; Eric I. Madaras

2000-01-01

350

Strength and stiffness reduction factors for infilled frames with openings  

NASA Astrophysics Data System (ADS)

Framed structures are usually infilled with masonry walls. They may cause a significant increase in both stiffness and strength, reducing the deformation demand and increasing the energy dissipation capacity of the system. On the other hand, irregular arrangements of the masonry panels may lead to the concentration of damage in some regions, with negative effects; for example soft story mechanisms and shear failures in short columns. Therefore, the presence of infill walls should not be neglected, especially in regions of moderate and high seismicity. To this aim, simple models are available for solid infills walls, such as the diagonal no-tension strut model, while infilled frames with openings have not been adequately investigated. In this study, the effect of openings on the strength and stiffness of infilled frames is investigated by means of about 150 experimental and numerical tests. The main parameters involved are identified and a simple model to take into account the openings in the infills is developed and compared with other models proposed by different researchers. The model, which is based on the use of strength and stiffness reduction factors, takes into account the opening dimensions and presence of reinforcing elements around the opening. An example of an application of the proposed reduction factors is also presented.

Decanini, Luis D.; Liberatore, Laura; Mollaioli, Fabrizio

2014-09-01

351

Active stiffness modulation of fins using macro fiber composites  

NASA Astrophysics Data System (ADS)

Studies on the role of body flexibility in propulsion suggest that fish have the ability to control or modulate the stiffness of the fin for optimized propulsive performance. Fins with certain stiffness might be efficient for a particular set of operating parameters but may be inefficient for other parameters. Therefore active stiffness modulation of a fin can improve the propulsive performance for a range of operating conditions. This paper discusses the preliminary experimental work on the open loop active deformation control of heaving flexible fins using Macro Fiber Composites (MFCs). The effect of important parameters such as oscillation frequency, flexibility of the fin, applied voltage and the phase difference between applied voltage and heaving on propulsive performance are studied and reported. The results indicate that propulsive performance can be improved by active control of the fins. The mean thrust improved by 30- 38% for the fins used in the experiments. The phase difference of ~90° is found to be optimal for maximized propulsive performance for the parameters considered in the study. Furthermore, there exists an optimal voltage magnitude at which the propulsive performance is a maximum for the range of operating conditions.

Kancharala, Ashok K.; Philen, Michael K.

2013-04-01

352

Glycine Receptor Autoimmune Spectrum With Stiff-Man Syndrome Phenotype  

PubMed Central

Objectives To determine whether glycine receptor ?1 subunit-specific autoantibodies (GlyR?1-IgG) occur in a broader spectrum of brainstem and spinal hyperexcitability disorders than the progressive encephalomyelitis with rigidity and myoclonus phenotype recognized to date, and to ascertain disease specificity. Design Retrospective, case-control study. Settings Mayo Clinic, Rochester, Minnesota, and University of Barcelona, Spain. Patients Eighty-one patients with stiff-man syndrome phenotype, 80 neurologic control subjects, and 20 healthy control subjects. Intervention Glycine receptor ?1–transfected cells to test serum or cerebrospinal fluid from cases and control subjects. Main Outcome Measures Frequency of GlyR?1-IgG positivity among stiff-man syndrome phenotype cases and control subjects. Comparison of GlyR?1-IgG seropositive and seronegative cases. Results Seropositive cases (12% of cases) included 9 with stiff-man syndrome (4 classic; 5 variant; 66% were glutamic acid decarboxylase 65–IgG positive) and 1 with progressive encephalomyelitis with rigidity and myoclonus. Immunotherapy responses were noted more frequently in GlyR?1-IgG–positive cases (6 of 7 improved) than in seronegative cases (7 of 25 improved; P=.02). The single seropositive control patient had steroid-responsive vision loss and optic atrophy with inflammatory cerebrospinal fluid. Conclusions Glycine receptor ?1–IgG aids identification of autoimmune brainstem/spinal cord hyperexcitability disorders and may extend to the glycinergic visual system. PMID:23090334

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

2013-01-01

353

Force distributions and force chains in random stiff fiber networks  

E-print Network

We study the elasticity of random stiff fiber networks. The elastic response of the fibers is characterized by a central force stretching stiffness as well as a bending stiffness that acts transverse to the fiber contour. Previous studies have shown that this model displays an anomalous elastic regime where the stretching mode is fully frozen out and the elastic energy is completely dominated by the bending mode. We demonstrate by simulations and scaling arguments that, in contrast to the bending dominated \\emph{elastic energy}, the equally important \\emph{elastic forces} are to a large extent stretching dominated. By characterizing these forces on microscopic, mesoscopic and macroscopic scales we find two mechanisms of how forces are transmitted in the network. While forces smaller than a threshold $F_c$ are effectively balanced by a homogeneous background medium, forces larger than $F_c$ are found to be heterogeneously distributed throughout the sample, giving rise to highly localized force-chains known from granular media.

Claus Heussinger; Erwin Frey

2007-05-10

354

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

355

Dynamics in the smectic phase of stiff viral rods  

NASA Astrophysics Data System (ADS)

We report on the dynamics in colloidal suspensions of stiff viral rods, called fd-Y21M. This mutant filamentous virus exhibits a persistence length 3.5 times larger than the wild-type fd-wt. Such a virus system can be used as a model system of rodlike particles for studying their self-diffusion. In this paper, the physical features, such as rod contour length and polydispersity have been determined for both viruses. The effect of viral rod flexibility on the location of the nematic-smectic phase transition has been investigated, with a focus on the underlying dynamics studied more specifically in the smectic phase. Direct visualization of the stiff fd-Y21M at the scale of a single particle has shown the mass transport between adjacent smectic layers, as found earlier for the more flexible rods. We could relate this hindered diffusion with the smectic ordering potentials for varying rod concentrations. The self-diffusion within the layers is far more pronounced for the stiff rods as compared to the more flexible fd-wt viral rod.

Pouget, Emilie; Grelet, Eric; Lettinga, M. Paul

2011-10-01

356

Influence of Cohesive Energy and Chain Stiffness on Polymer Glass Formation  

E-print Network

The generalized entropy theory is applied to assess the joint influence of the microscopic cohesive energy and chain stiffness on glass formation in polymer melts using a minimal model containing a single bending energy and a single (monomer averaged) nearest neighbor van der Waals energy. The analysis focuses on the combined impact of the microscopic cohesive energy and chain stiffness on the magnitudes of the isobaric fragility parameter $m_P$ and the glass transition temperature $T_g$. The computations imply that polymers with rigid structures and weak nearest neighbor interactions are the most fragile, while $T_g$ becomes larger when the chains are stiffer and/or nearest neighbor interactions are stronger. Two simple fitting formulas summarize the computations describing the dependence of $m_P$ and $T_g$ on the microscopic cohesive and bending energies. The consideration of the combined influence of the microscopic cohesive and bending energies leads to the identification of some important design concepts, such as iso-fragility and iso-$T_g$ lines, where, for instance, iso-fragility lines are contours with constant $m_P$ but variable $T_g$. Several thermodynamic properties are found to remain invariant along the iso-fragility lines, while no special characteristics are detected along the iso-$T_g$ lines. Our analysis supports the widely held view that fragility provides more fundamental insight for the description of glass formation than $T_g$.

Wen-Sheng Xu; Karl F. Freed

2014-09-24

357

A new method to determine joint range of movement and stiffness in rheumatoid arthritic patients.  

PubMed

Rheumatoid arthritis affects 0.5-1% of the general population. The prediction and prognosis of the disease varies for each individual and its course can detrimentally affect the psychosocial condition of the patient. Clinicians and Therapists aim to quickly diagnose and treat those with this debilitating disease. Detection relies heavily on manual evaluation methods that are dependent on training and can vary between observers. Angle measuring instrument, tape measure and grip strength dynamometer are used to assess the joint range and strength of a patient to determine their hand function. Joint stiffness can be a determining factor when diagnosing the advancement and improvement of Rheumatoid Arthritis (RA). This paper outlines the development of a hand movement measurement tool to accurately quantify patients' flexion, extension, abduction and adduction movement of each finger joint and quantifies the symptom of "early morning stiffness". It also describes the problems that arise when using a data glove to accurately measure Range Of Movement and discusses alternative methods to overcome these issues. PMID:23367390

Connolly, James; Condell, Joan; Curran, Kevin; Gardiner, Philip

2012-01-01

358

Actin-binding proteins sensitively mediate F-actin bundle stiffness  

NASA Astrophysics Data System (ADS)

Bundles of filamentous actin (F-actin) form primary structural components of a broad range of cytoskeletal processes including filopodia, sensory hair cell bristles and microvilli. Actin-binding proteins (ABPs) allow the cell to tailor the dimensions and mechanical properties of the bundles to suit specific biological functions. Therefore, it is important to obtain quantitative knowledge on the effect of ABPs on the mechanical properties of F-actin bundles. Here we measure the bending stiffness of F-actin bundles crosslinked by three ABPs that are ubiquitous in eukaryotes. We observe distinct regimes of bundle bending stiffness that differ by orders of magnitude depending on ABP type, concentration and bundle size. The behaviour observed experimentally is reproduced quantitatively by a molecular-based mechanical model in which ABP shearing competes with F-actin extension/compression. Our results shed new light on the biomechanical function of ABPs and demonstrate how single-molecule properties determine mesoscopic behaviour. The bending mechanics of F-actin fibre bundles are general and have implications for cytoskeletal mechanics and for the rational design of functional materials.

Claessens, Mireille M. A. E.; Bathe, Mark; Frey, Erwin; Bausch, Andreas R.

2006-09-01

359

Coefficient Alpha: A Reliability Coefficient for the 21st Century?  

ERIC Educational Resources Information Center

Coefficient alpha is almost universally applied to assess reliability of scales in psychology. We argue that researchers should consider alternatives to coefficient alpha. Our preference is for structural equation modeling (SEM) estimates of reliability because they are informative and allow for an empirical evaluation of the assumptions…

Yang, Yanyun; Green, Samuel B.

2011-01-01

360

A comparison of experimental results and theoretical predictions for the rotordynamic coefficients of short (L/D = 1/6) labyrinth seals  

E-print Network

-on-stator seal (L/D = 1/8) and published results which included data for both stiffness and damping coefficients with pressure drop as a parameter. Leong and Brown [5] also tested teeth-on-stator and teeth-on-stator with grooves on the rotor seals with L...-on-stator seal (L/D = 1/8) and published results which included data for both stiffness and damping coefficients with pressure drop as a parameter. Leong and Brown [5] also tested teeth-on-stator and teeth-on-stator with grooves on the rotor seals with L...

Pelletti, Joseph Michael

2012-06-07

361

Calculation and measurement of the influence of flow parameters on rotordynamic coefficients in labyrinth seals  

NASA Technical Reports Server (NTRS)

First experimental investigations performed on a new test rig are presented. For a staggered labyrinth seal with fourteen cavities the stiffness coefficient and the leakage flow are measured. The experimental results are compared to calculated results which are obtained by a one-volume bulk-flow theory. A perturbation analysis is made for seven terms. It is found out that the friction factors have great impact on the dynamic coefficients. They are obtained by turbulent flow computation by a finite-volume model with the Reynolds equations used as basic equations.

Kwanka, K.; Ortinger, W.; Steckel, J.

1994-01-01

362

Do thermal diffusion and Dufour coefficients satisfy Onsager's reciprocity relation?  

PubMed

It is commonly admitted that in liquids the thermal diffusion and Dufour coefficients DT and DF satisfy Onsager's reciprocity. From their relation to the cross-coefficients of the phenomenological equations, we are led to the conclusion that this is not the case in general. As illustrative and physically relevant examples, we discuss micellar solutions and colloidal suspensions, where DT arises from chemical reactions or viscous effects but is not related to the Dufour coefficient DF. The situation is less clear for binary molecular mixtures; available experimental and simulation data do not settle the question whether DT and DF are reciprocal coefficients. PMID:25341414

Würger, Alois

2014-10-01

363

Follow-up of ankle stiffness and electromechanical delay in immobilized children: three cases studies.  

PubMed

Clinical manual tests refer to increased ankle stiffness in children immobilized due to hip osteochondritis. The aim of the present study was to investigate musculo-articular stiffness via different techniques in immobilized children to confirm or not and quantify these observations. Ankle stiffness was quantified monthly during the long immobilization period in three diseased children and compared to healthy age-matched children. Sinusoidal perturbations were used to evaluate musculo-articular (MA) stiffness of the ankle plantar-flexors. The stiffness index (SI(MA-EMG)) was the slope of the linear relationship between angular stiffness and plantar-flexion torque normalized with electromyographic activity of the triceps surae (TS). The stiffness of the ankle plantar-flexors was also indirectly evaluated using the TS electromechanical delay (EMD). SI(MA-EMG) was greater for diseased children, and this higher stiffness was confirmed by the higher EMD values found in these immobilized children. Furthermore, both parameters indicated that ankle stiffness continues to increase through immobilization period. This study gives a quantitative evaluation of ankle stiffness changes through the immobilization period imposed to children treated for hip osteochondritis. The use of EMD measurement to indirectly evaluate these stiffness changes is also validated. This study shed for the first time some light into the patterns of muscle modifications following immobilization in children. PMID:20189829

Grosset, Jean-François; Lapole, Thomas; Mora, Isabelle; Verhaeghe, Martine; Doutrellot, Pierre-Louis; Pérot, Chantal

2010-08-01

364

Extracellular matrix stiffness and composition jointly regulate the induction of malignant phenotypes in mammary epithelium  

NASA Astrophysics Data System (ADS)

In vitro models of normal mammary epithelium have correlated increased extracellular matrix (ECM) stiffness with malignant phenotypes. However, the role of increased stiffness in this transformation remains unclear because of difficulties in controlling ECM stiffness, composition and architecture independently. Here we demonstrate that interpenetrating networks of reconstituted basement membrane matrix and alginate can be used to modulate ECM stiffness independently of composition and architecture. We find that, in normal mammary epithelial cells, increasing ECM stiffness alone induces malignant phenotypes but that the effect is completely abrogated when accompanied by an increase in basement-membrane ligands. We also find that the combination of stiffness and composition is sensed through ?4 integrin, Rac1, and the PI3K pathway, and suggest a mechanism in which an increase in ECM stiffness, without an increase in basement membrane ligands, prevents normal ?6?4 integrin clustering into hemidesmosomes.

Chaudhuri, Ovijit; Koshy, Sandeep T.; Branco da Cunha, Cristiana; Shin, Jae-Won; Verbeke, Catia S.; Allison, Kimberly H.; Mooney, David J.

2014-10-01

365

Active muscle stiffness in the human medial gastrocnemius muscle in vivo.  

PubMed

The aims of this study were to 1) directly assess active muscle stiffness according to actual length changes in muscle fibers (fascicles) during short range stretching; and 2) compare actual measured active muscle and tendon stiffness using ultrasonography with the stiffness of active (i.e., muscle) and passive (i.e., tendon) parts in series elastic component of plantar flexors using the alpha method. Twenty-four healthy men volunteered for this study. Active muscle stiffness in the medial gastrocnemius muscle was calculated according to changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions [10, 30, 50, 70, and 90% maximal voluntary contractions (MVC)]. Using the variables measured during this fast stretch experiment, the stiffness of active (i.e., muscle) and passive (i.e., tendon) parts in plantar flexors was assessed using alpha method. Tendon stiffness was determined during isometric plantar flexion by ultrasonography. Active muscle stiffness increased with the exerted torque levels. At 30, 50, 70, and 90% MVC, there were no significant correlations between muscle stiffness using ultrasonography and stiffness of active part (i.e., muscle) by alpha method, although this relationship at 10% MVC was significant (r = 0.552, P = 0.005). In addition, no correlation was noted in tendon stiffness between the two different methods (r = 0.226, P = 0.209). The present study demonstrated that ultrasonography could quantified active muscle stiffness in vivo. Furthermore, active muscle stiffness and tendon stiffness using ultrasonography were not related to active (i.e., muscle) or passive (i.e., tendon) stiffness in series elastic component of plantar flexors by alpha method. PMID:25170073

Kubo, Keitaro

2014-11-01

366

Muscle Stiffness and Spinal Stretch Reflex Sensitivity in the Triceps Surae  

PubMed Central

Context: Greater musculotendinous stiffness may enhance spinal stretch reflex sensitivity by improving mechanical coupling of the muscle spindle and the stretch stimulus. This heightened sensitivity would correspond with a shorter latency and higher-amplitude reflex response, potentially enhancing joint stability. Objective: To compare spinal stretch reflex latency and amplitude across groups that differed in musculotendinous stiffness. Design: Static group comparisons. Setting: Research laboratory. Patients or Other Participants: Forty physically active individuals (20 men, 20 women). Intervention(s): We verified a sex difference in musculotendinous stiffness and compared spinal stretch reflex latency and amplitude in high-stiffness (men) and low-stiffness (women) groups. We also evaluated relationships between musculotendinous stiffness and spinal stretch reflex latency and amplitude, respectively. Main Outcome Measure(s): Triceps surae musculotendinous stiffness and soleus spinal stretch reflex latency and amplitude were assessed at 30% of a maximal voluntary isometric plantar-flexion contraction. Results: The high-stiffness group demonstrated significantly greater stiffness (137.41 ± 26.99 N/cm) than the low-stiffness group did (91.06 ± 20.10 N/cm). However, reflex latency (high stiffness = 50.11 ± 2.07 milliseconds, low stiffness = 48.26 ± 2.40 milliseconds) and amplitude (high stiffness = 0.28% ± 0.12% maximum motor response, low stiffness = 0.31% ± 0.16% maximum motor response) did not differ significantly across stiffness groups. Neither reflex latency (r = .053, P = .746) nor amplitude (r = .073, P = .653) was related significantly to musculotendinous stiffness. Conclusions: A moderate level of pretension (eg, 30%) likely eliminates series elastic slack; thus, a greater change in force per unit-of-length change (ie, heightened stiffness) would have minimal effects on coupling of the muscle spindle and the stretch stimulus and, therefore, on spinal stretch reflex sensitivity. It appears unlikely that differences in musculotendinous stiffness influenced spinal stretch reflex sensitivity when initiated from a moderate level of pretension. Consequently, differences in musculotendinous stiffness did not appear to influence dynamic joint stability with respect to reflexive neuromuscular control. PMID:18335010

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

2008-01-01

367

Planck radiation law and Einstein coefficients reexamined in Kaniadakis ? statistics.  

PubMed

Blackbody radiation is reconsidered using the counterpart of the Bose-Einstein distribution in the ? statistics arising from the Kaniadakis entropy. The generalized Planck radiation law is presented and compared to the usual law, to which it reduces in the limiting case ??0. Effective Einstein's coefficients of emission and absorption are defined in terms of the Kaniadakis parameter ?. It is shown that the Kaniadakis statistics keeps unchanged the first Einstein coefficient A while the second coefficient B admits a generalized form within the present theoretical framework. PMID:25019747

Ourabah, Kamel; Tribeche, Mouloud

2014-06-01

368

Material stiffness effects on neurite alignment to photopolymerized micropatterns.  

PubMed

The ability to direct neurite growth into a close proximity of stimulating elements of a neural prosthesis, such as a retinal or cochlear implant (CI), may enhance device performance and overcome current spatial signal resolution barriers. In this work, spiral ganglion neurons (SGNs), which are the target neurons to be stimulated by CIs, were cultured on photopolymerized micropatterns with varied matrix stiffnesses to determine the effect of rigidity on neurite alignment to physical cues. Micropatterns were generated on methacrylate thin film surfaces in a simple, rapid photopolymerization step by photomasking the prepolymer formulation with parallel line-space gratings. Two methacrylate series, a nonpolar HMA-co-HDDMA series and a polar PEGDMA-co-EGDMA series, with significantly different surface wetting properties were evaluated. Equivalent pattern periodicity was maintained across each methacrylate series based on photomask band spacing, and the feature amplitude was tuned to a depth of 2 ?m amplitude for all compositions using the temporal control afforded by the UV curing methodology. The surface morphology was characterized by scanning electron microscopy and white light interferometry. All micropatterned films adsorb similar amounts of laminin from solution, and no significant difference in SGN survival was observed when the substrate compositions were compared. SGN neurite alignment significantly increases with increasing material modulus for both methacrylate series. Interestingly, SGN neurites respond to material stiffness cues that are orders of magnitude higher (GPa) than what is typically ascribed to neural environments (kPa). The ability to understand neurite response to engineered physical cues and mechanical properties such as matrix stiffness will allow the development of advanced biomaterials that direct de novo neurite growth to address the spatial signal resolution limitations of current neural prosthetics. PMID:25211120

Tuft, Bradley W; Zhang, Lichun; Xu, Linjing; Hangartner, Austin; Leigh, Braden; Hansen, Marlan R; Guymon, C Allan

2014-10-13

369

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

370

A method for measuring exchange stiffness in ferromagnetic films  

SciTech Connect

An exchange stiffness, A{sub ex}, in ferromagnetic films is obtained by fitting the M(H) dependence of two ferromagnetic layers antiferromagnetically coupled across a nonmagnetic spacer layer with a simple micromagnetic model. In epitaxial and textured structures this method allows measuring A{sub ex} between the crystallographic planes perpendicular to the growth direction of ferromagnetic films. Our results show that A{sub ex} between [0001] planes in textured Co grains is 1.54 {+-} 0.12 x 10{sup -11} J/m.

Girt, Erol; Huttema, W.; Montoya, E.; Kardasz, B.; Eyrich, C.; Heinrich, B. [Simon Fraser University, Burnaby, 8888 University Drive, British Columbia V5A 1S6 (Canada); Mryasov, O. N. [University of Alabama, Tuscaloosa, Alabama 35487 (United States); Dobin, A. Yu. [One Bungtown Road, Cold Spring Harbor, New York 11724 (United States); Karis, O. [Uppsala University, P.O. Box 256, SE-751 05 Uppsala (Sweden)

2011-04-01

371

Arterial stiffness in adult patients after Fontan procedure  

PubMed Central

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

2014-01-01

372

On modeling hydraulic fracture in proper variables: stiffness, accuracy, sensitivity  

E-print Network

The problem of hydraulic fracture propagation is considered by using its recently suggested modified formulation in terms of the particle velocity, the opening in the proper degree, appropriate spatial coordinates and $\\varepsilon$-regularization. We show that the formulation may serve for significant increasing the efficiency of numerical tracing the fracture propagation. Its advantages are illustrated by re-visiting the Nordgren problem. It is shown that the modified formulation facilitates (i) possibility to have various stiffness of differential equations resulting after spatial discretization, (ii) obtaining highly accurate and stable numerical results with moderate computational effort, and (iii) sensitivity analysis. The exposition is extensively illustrated by numerical examples.

Mishuris, Gennady; Linkov, Alexander

2012-01-01

373

Validation studies of gyrofluid and gyrokinetic predictions of transport and turbulence stiffness using the DIII-D tokamak  

NASA Astrophysics Data System (ADS)

A series of carefully designed validation experiments conducted on DIII-D to rigorously test gyrofluid and gyrokinetic predictions of transport and turbulence stiffness in both the ion and electron channels have provided an improved assessment of the experimental fidelity of those models over a range of plasma parameters. The first set of experiments conducted was designed to test predictions of H-mode core transport stiffness at fixed pedestal density and temperature. In low triangularity lower single null plasmas, a factor of 3 variation in neutral beam injection (NBI) heating was obtained, with modest changes to pedestal conditions that slowly increased with applied heating. The measurements and trends with increased NBI heating at both low and high injected torque are generally well-reproduced by the quasilinear trapped gyro-Landau fluid (TGLF) transport model at the lowest heating levels, but with decreasing fidelity (particularly in the electron profiles) as the heating power is increased. Complementing these global stiffness studies, a second set of experiments was performed to quantify the relationship between the local electron energy flux Qe and electron temperature gradient by varying the deposition profile of electron cyclotron heating about a specified reference radius in low density, low current L-mode plasmas. Modelling of these experiments using both the TGLF model and the nonlinear gyrokinetic GYRO code yields systematic underpredictions of the measured fluxes and fluctuation levels.

Holland, C.; Kinsey, J. E.; DeBoo, J. C.; Burrell, K. H.; Luce, T. C.; Smith, S. P.; Petty, C. C.; White, A. E.; Rhodes, T. L.; Schmitz, L.; Doyle, E. J.; Hillesheim, J. C.; McKee, G. R.; Yan, Z.; Wang, G.; Zeng, L.; Grierson, B. A.; Marinoni, A.; Mantica, P.; Snyder, P. B.; Waltz, R. E.; Staebler, G. M.; Candy, J.

2013-08-01

374

Breaking the Meyer-Overton rule: predicted effects of varying stiffness and interfacial activity on the intrinsic potency of anesthetics.  

PubMed Central

Exceptions to the Meyer-Overton rule are commonly cited as evidence against indirect, membrane-mediated mechanisms of general anesthesia. However, another interpretation is possible within the context of an indirect mechanism in which solubilization of an anesthetic in the membrane causes a redistribution of lateral pressures in the membrane, which in turn shifts the conformational equilibrium of membrane proteins such as ligand-gated ion channels. It is suggested that compounds of different stiffness and interfacial activity have different intrinsic potencies, i.e., they cause widely different redistributions of the pressure profile (and thus different effects on protein conformational equilibria) per unit concentration of the compound in the membrane. Calculations incorporating the greater stiffness of perfluoromethylenic chains and the large interfacial attraction of hydroxyl groups predict the higher intrinsic potency of short alkanols than alkanes, the cutoffs in potency of alkanes and alkanols and the much shorter cutoffs for their perfluorinated analogues. Both effects, increased stiffness and interfacial activity, are present in unsaturated hydrocarbon solutes, and the intrinsic potencies are predicted to depend on the magnitude of both effects and on the number and locations of multiple bonds within the molecule. Most importantly, the intrinsic potencies of polymeric alkanols with regularly spaced hydroxyl groups are predicted to rise with increasing chain length, without cutoff; such molecules should serve to distinguish unambiguously between indirect mechanisms and direct binding mechanisms of anesthesia. PMID:11325730

Cantor, R S

2001-01-01

375

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

NASA Astrophysics Data System (ADS)

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

Lu, Yiyun; Lu, Bingjuan; Wang, Suyu

2011-09-01

376

Multi-fingered haptic palpation utilizing granular jamming stiffness feedback actuators  

NASA Astrophysics Data System (ADS)

This paper describes a multi-fingered haptic palpation method using stiffness feedback actuators for simulating tissue palpation procedures in traditional and in robot-assisted minimally invasive surgery. Soft tissue stiffness is simulated by changing the stiffness property of the actuator during palpation. For the first time, granular jamming and pneumatic air actuation are combined to realize stiffness modulation. The stiffness feedback actuator is validated by stiffness measurements in indentation tests and through stiffness discrimination based on a user study. According to the indentation test results, the introduction of a pneumatic chamber to granular jamming can amplify the stiffness variation range and reduce hysteresis of the actuator. The advantage of multi-fingered palpation using the proposed actuators is proven by the comparison of the results of the stiffness discrimination performance using two-fingered (sensitivity: 82.2%, specificity: 88.9%, positive predicative value: 80.0%, accuracy: 85.4%, time: 4.84 s) and single-fingered (sensitivity: 76.4%, specificity: 85.7%, positive predicative value: 75.3%, accuracy: 81.8%, time: 7.48 s) stiffness feedback.

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

2014-09-01

377

An incrementally non-linear model for clays with directional stiffness and a small strain emphasis  

NASA Astrophysics Data System (ADS)

In response to construction activities and loads from permanent structures, soil generally is subjected to a variety of loading modes varying both in time and location. It also has been increasingly appreciated that the strains around well-designed foundations, excavations and tunnels are mostly small, with soil responses at this strain level generally being non-linear and anisotropic. To make accurate prediction of the performance of a geo-system, it is highly desirable to understand soil behavior at small strains along multiple loading directions, and accordingly to incorporate these responses in an appropriate constitutive model implemented in a finite element analysis. This dissertation presents a model based on a series of stress probe tests with small strain measurements performed on compressible Chicago glacial clays. The proposed model is formulated in an original constitutive framework, in which the tangent stiffness matrix is constructed in accordance with the mechanical nature of frictional materials and the tangent moduli therein are described explicitly. The stiffness description includes evolution relations with regard to length of stress path, and directionality relations in terms of stress path direction. The former relations provide distinctive definitions for small-strain and large-strain behaviors, and distinguish soil responses in shearing and compression. The latter relations make this model incrementally non-linear and thus capable of modeling inelastic behavior. A new algorithm based on a classical substepping scheme is developed to numerically integrate this model. A consistent tangent matrix is derived for the proposed model with the upgraded substepping scheme. The code is written in FORTRAN and implemented in FEM via UMAT of ABAQUS. The model is exercised in a variety of applications ranging from oedometer, triaxial and biaxial test simulations to a C-class prediction for a well-instrumented excavation. The computed results indicate that this model is successful in reproducing soil responses in both laboratory and field situations.

Tu, Xuxin

378

Changes in arterial stiffness during continued infliximab treatment in patients with inflammatory arthropathies.  

PubMed

Chronic inflammatory arthropathies such as rheumatoid arthritis (RA), ankylosing spondylitis (AS), and psoriatic arthritis (PsA) are associated with an increased risk of cardiovascular disease. TNF-? antagonists may improve vascular function in these patients and thus be beneficial with regard to cardiovascular disease. This study evaluated arterial stiffness and disease activity between two infusions with a TNF-? antagonist (infliximab) in patients with inflammatory arthropathies on long-term infliximab therapy. Augmentation index (AIx), aortic pulse wave velocity (aPWV), and disease activity were measured in 17 patients with RA, AS, or PsA who had been treated with infliximab for at least 12 months. The patients were examined immediately before their infliximab infusion and thereafter every 10th day until their next infusion scheduled at week 4-8. AIx and aPWV did not change during the period between two infliximab infusions. The patients had a temporary improvement in the general disease activity assessed on visual analogue scales by the patients (P = 0.04) and the investigator (P = 0.02) after the infusion. In the group of patients with RA, the Disease Activity Score (DAS28) changed significantly in a similar manner (P = 0.003). C-reactive protein and erythrocyte sedimentation rate remained unchanged. Infliximab infusions did not alter aortic pulse wave velocity or augmentation index in patients with inflammatory arthropathies who were on long-term infliximab therapy. Reductions in the general disease activity and DAS28 were not reflected in alterations of aortic stiffness or augmentation index. PMID:20825487

Angel, Kristin; Provan, Sella Aarrestad; Hammer, Hilde Berner; Mowinckel, Petter; Kvien, Tore Kristian; Atar, Dan

2011-08-01

379

On the Emulation of Stiff Walls and Static Friction with a Magnetically Levitated Input\\/Output Device  

Microsoft Academic Search

This paper addresses issues of mechanical emulation of stiff walls and stick-slip friction with a 6-DOF magnetically levitated joystick. In the case of stiff wall emulation, it is shown that the PD control implementation commonly used severely limits achievable wall damping and stiffness. It is also shown that the perceived surface stiffness can be increased without loss of stability by

S. e. Salcudean; T. d. Vlaar

1996-01-01

380

Variable stiffness material based on rigid low-melting-point-alloy-microstructures embedded in soft poly(dimethylsiloxane) (PDMS)  

E-print Network

Variable stiffness material based on rigid low-melting-point-alloy- microstructures embedded a new type of variable stiffness material based on the combination of a rigid low-melting-point (ms range), and good relative stiffness changes of > 30�, where the absolute stiffness depends

Floreano, Dario

381

Crosslinking and composition influence the surface properties, mechanical stiffness and cell reactivity of collagen-based films  

PubMed Central

This study focuses on determining the effect of varying the composition and crosslinking of collagen-based films on their physical properties and interaction with myoblasts. Films composed of collagen or gelatin and crosslinked with a carbodiimide were assessed for their surface roughness and stiffness. These samples are significant because they allow variation of physical properties as well as offering different recognition motifs for cell binding. Cell reactivity was determined by the ability of myoblastic C2C12 and C2C12-?2+ cell lines (with different integrin expression) to adhere to and spread on the films. Significantly, crosslinking reduced the cell reactivity of all films, irrespective of their initial composition, stiffness or roughness. Crosslinking resulted in a dramatic increase in the stiffness of the collagen film and also tended to reduce the roughness of the films (Rq = 0.417 ± 0.035 ?m, E = 31 ± 4.4 MPa). Gelatin films were generally smoother and more compliant than comparable collagen films (Rq = 7.9 ± 1.5 nm, E = 15 ± 3.1 MPa). The adhesion of ?2-positive cells was enhanced relative to the parental C2C12 cells on collagen compared with gelatin films. These results indicate that the detrimental effect of crosslinking on cell response may be due to the altered physical properties of the films as well as a reduction in the number of available cell binding sites. Hence, although crosslinking can be used to enhance the mechanical stiffness and reduce the roughness of films, it reduces their capacity to support cell activity and could potentially limit the effectiveness of the collagen-based films and scaffolds. PMID:22588074

Grover, Chloe N.; Gwynne, Jessica H.; Pugh, Nicholas; Hamaia, Samir; Farndale, Richard W.; Best, Serena M.; Cameron, Ruth E.

2012-01-01

382

Physical exercise improves arterial stiffness after spinal cord injury.  

PubMed

Objective/background Aortic pulse wave velocity (PWV), the gold-standard assessment of central arterial stiffness, has prognostic value for cardiovascular disease risk in able-bodied individuals. The aim of this study was to compare aortic PWV in athletes and non-athletes with spinal cord injury (SCI). Design Cross-sectional comparison. Methods Aortic PWV was assessed in 20 individuals with motor-complete, chronic SCI (C2-T5; 18 ± 8 years post-injury) using applanation tonometry at the carotid and femoral arterial sites. Ten elite hand-cyclists were matched for sex to 10 non-athletes; age and time since injury were comparable between the groups. Heart rate and discrete brachial blood pressure measurements were collected throughout testing. Outcome measures Aortic PWV, blood pressure, heart rate. Results Aortic PWV was significantly lower in athletes vs. non-athletes (6.9 ± 1.0 vs. 8.7 ± 2.5 m/second, P = 0.044). There were no significant between-group differences in resting supine mean arterial blood pressure (91 ± 19 vs. 81 ± 10 mmHg) and heart rate (60 ± 10 vs. 58 ± 6 b.p.m.). Conclusion Athletes with SCI exhibited improved central arterial stiffness compared to non-athletes, which is in agreement with the previous able-bodied literature. This finding implies that chronic exercise training may improve arterial health and potentially lower cardiovascular disease risk in the SCI population. PMID:24976366

Hubli, Michèle; Currie, Katharine D; West, Christopher R; Gee, Cameron M; Krassioukov, Andrei V

2014-11-01

383

Ritz method for transient response in systems having unsymmetric stiffness  

NASA Technical Reports Server (NTRS)

The DMAP coding was automated to such an extent by using the device of bubble vectors, that it is useable for analyses in its present form. This feasibility study demonstrates that the Ritz Method is so compelling as to warrant coding its modules in FORTRAN and organizing the resulting coding into a new Rigid Format. Even though this Ritz technique was developed for unsymmetric stiffness matrices, it offers advantages to problems with symmetric stiffnesses. If used for the symmetric case the solution would be simplified to one set of modes, because the adjoint would be the same as the primary. Its advantage in either type of symmetry over a classical eigenvalue modal expansion is that information density per Ritz mode is far richer than per eigenvalue mode; thus far fewer modes would be needed for the same accuracy and every mode would actively participate in the response. Considerable economy can be realized in adapting Ritz vectors for modal solutions. This new Ritz capability now makes NASTRAN even more powerful than before.

Butler, Thomas G.

1989-01-01

384

Shear rupture under constant normal stiffness boundary conditions  

NASA Astrophysics Data System (ADS)

A grain based Distinct Element Method and its embedded Grain Based Method are used to simulate the fracturing processes leading to shear rupture zone creation in a calibrated massive (non-jointed) brittle rock specimen deformed in direct shear under constant normal stiffness boundary conditions. Under these boundary conditions, shear rupture zone creation relative to the shear stress versus applied horizontal displacement (load-displacement) curve occurs pre-peak, before the maximum peak shear strength is reached. This is found to be the result of a normal stress feedback process caused by the imposed shear displacement which couples increases in normal stress, due to rupture zone dilation, with shear stress, producing a complex normal-shear stress-path that reaches and then follows the rock's yield (strength) envelope. While the yield envelope is followed, the shear strength increases further and shear stress oscillations (repeated stress drops followed by re-strengthening periods) in the load-displacement curves occur due to fracture creation as the rupture zone geometry smoothens. Once the maximum peak strength is reached (after a series of shear stress oscillations) the largest stress drops occur as the ultimate or residual shear strength is approached. The simulation results provide insight into the fracturing process during rupture zone creation and improve the understanding of the shear stress versus applied horizontal displacement response, as well as the stick-slip behaviour of shear rupture zones that are being created under constant normal stiffness boundary conditions.

Bewick, R. P.; Kaiser, P. K.; Bawden, W. F.

2014-11-01

385

Explicit Integration of Extremely Stiff Reaction Networks: Partial Equilibrium Methods  

SciTech Connect

In two preceding papers [1,2] we have shown that, when reaction networks are well removed from equilibrium, explicit asymptotic and quasi-steady-state approximations can give algebraically stabilized integration schemes that rival standard implicit methods in accuracy and speed for extremely stiff systems. However, we also showed that these explicit methods remain accurate but are no longer competitive in speed as the network approaches equilibrium. In this paper we analyze this failure and show that it is associated with the presence of fast equilibration timescales that neither asymptotic nor quasi-steady-state approximations are able to remove efficiently from the numerical integration. Based on this understanding, we develop a partial equilibrium method to deal effectively with the new partial equilibrium methods, give an integration scheme that plausibly can deal with the stiffest networks, even in the approach to equilibrium, with accuracy and speed competitive with that of implicit methods. Thus we demonstrate that algebraically stabilized explicit methods may offer alternatives to implicit integration of even extremely stiff systems, and that these methods may permit integration of much larger networks than have been feasible previously in a variety of fields.

Guidry, Mike W [ORNL; Billings, J. J. [Oak Ridge National Laboratory (ORNL); Hix, William Raphael [ORNL

2013-01-01

386

Stiffness, compliance, elasticity and force generation of outer hair cells.  

PubMed

Isolated outer hair cells (OHCs) were partially sucked into especially designed cell capillaries allowing an experimental reconstitution of the cells' electroanatomy. The experimental approach separated the apical from the basolateral parts of the cells thus forming an artificial scala media and scala tympani. Resistance between both was 121 +/- 42 M omega. A sequence of negative and positive pressures was applied to the basal cell pole allowing "pulling" or "pushing" of the sensory cell investigated. The resulting length changes together with the known pressures allowed the estimation of an actual longitudinal compliance of 354 +/- 35 m/N. Following "pulling" OHCs tended to resume their initial shape after the force had ceased to be effective indicating elastic distortions. The calculated elasticity modulus of OHCs amounted to 6.1 +/- 3.4 kN/m2. From this data an actual longitudinal whole cell stiffness of OHCs of 3 x 10(-3) N/m was calculated. Ultrasound scanning of immobilized OHCs identified the cuticular plate (CP) and a central core between CP and basal cell pole as structures contributing to the cells' acoustic stiffness. Changes of the potential differences between the artificial scala media and scala tympani resulted in active length changes following the command voltage with a slope of delta 1/(1 x U) = 0.055 V-1. Assuming the validity of Hooke's law, the force generation associated with the active length changes can be calculated since the compliance is known.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1604988

Zenner, H P; Gitter, A H; Rudert, M; Ernst, A

1992-01-01

387

A new hybrid gyroscope with electrostatic negative stiffness tuning.  

PubMed

A variety of gyroscopes have been extensively studied due to their capability of precision detection of rotation rates and extensive applications in navigation, guidance and motion control. In this work, a new Hybrid Gyroscope (HG) which combines the traditional Dynamically Tuned Gyroscope (DTG) with silicon micromachined technology is investigated. The HG not only has the potentiality of achieving the same high precision as the traditional DTG, but also features a small size and low cost. The theoretical mechanism of the HG with a capacitance transducer and an electrostatic torquer is derived and the influence of the installation errors from the capacitance plate and the disc rotor module is investigated. A new tuning mechanism based on negative stiffness rather than the traditional dynamic tuning is proposed. The experimental results prove that the negative stiffness tuning is practicable and a tuning voltage of as high as 63 V is demonstrated. Due to the decreased installation error, the non-linearity of the scale factor is reduced significantly from 11.78% to 0.64%, as well as the asymmetry from 93.3% to 1.56% in the open loop condition. The rebalancing close-loop control is simulated and achieved experimentally, which proves that the fundamental principle of the HG is feasible. PMID:23722826

Yang, Bo; Guan, Yumei; Wang, Shourong; Zou, Qi; Chu, Xian; Xue, Haiyan

2013-01-01

388

Accurate spring constant calibration for very stiff atomic force microscopy cantilevers  

SciTech Connect

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

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

2013-11-15

389

Effect of salicylate on the elasticity, bending stiffness, and strength of SOPC membranes.  

PubMed

Salicylate is a small amphiphilic molecule which has diverse effects on membranes and membrane-mediated processes. We have utilized micropipette aspiration of giant unilamellar vesicles to determine salicylate's effects on lecithin membrane elasticity, bending rigidity, and strength. Salicylate effectively reduces the apparent area compressibility modulus and bending modulus of membranes in a dose-dependent manner at concentrations above 1 mM, but does not greatly alter the actual elastic compressibility modulus at the maximal tested concentration of 10 mM. The effect of salicylate on membrane strength was investigated using dynamic tension spectroscopy, which revealed that salicylate increases the frequency of spontaneous defect formation and lowers the energy barrier for unstable hole formation. The mechanical and dynamic tension experiments are consistent and support a picture in which salicylate disrupts membrane stability by decreasing membrane stiffness and membrane thickness. The tension-dependent partitioning of salicylate was utilized to calculate the molecular volume of salicylate in the membrane. The free energy of transfer for salicylate insertion into the membrane and the corresponding partition coefficient were also estimated, and indicated favorable salicylate-membrane interactions. The mechanical changes induced by salicylate may affect several biological processes, especially those associated with membrane curvature and permeability. PMID:15951377

Zhou, Yong; Raphael, Robert M

2005-09-01

390

Love waves in functionally graded piezoelectric materials by stiffness matrix method.  

PubMed

A numerical matrix method relative to the propagation of ultrasonic guided waves in functionally graded piezoelectric heterostructure is given in order to make a comparative study with the respective performances of analytical methods proposed in literature. The preliminary obtained results show a good agreement, however numerical approach has the advantage of conceptual simplicity and flexibility brought about by the stiffness matrix method. The propagation behaviour of Love waves in a functionally graded piezoelectric material (FGPM) is investigated in this article. It involves a thin FGPM layer bonded perfectly to an elastic substrate. The inhomogeneous FGPM heterostructure has been stratified along the depth direction, hence each state can be considered as homogeneous and the ordinary differential equation method is applied. The obtained solutions are used to study the effect of an exponential gradient applied to physical properties. Such numerical approach allows applying different gradient variation for mechanical and electrical properties. For this case, the obtained results reveal opposite effects. The dispersive curves and phase velocities of the Love wave propagation in the layered piezoelectric film are obtained for electrical open and short cases on the free surface, respectively. The effect of gradient coefficients on coupled electromechanical factor, on the stress fields, the electrical potential and the mechanical displacement are discussed, respectively. Illustration is achieved on the well known heterostructure PZT-5H/SiO(2), the obtained results are especially useful in the design of high-performance acoustic surface devices and accurately prediction of the Love wave propagation behaviour. PMID:21035829

Ben Salah, Issam; Wali, Yassine; Ben Ghozlen, Mohamed Hédi

2011-04-01

391

Acoustic microscopy of functionally graded thermal sprayed coatings using stiffness matrix method and Stroh formalism  

NASA Astrophysics Data System (ADS)

Acoustic microscopy of multilayered media as well as functionally graded coatings on substrate necessitates to model acoustic wave propagation in such materials. In particular, we chose to use Stroh formalism and the recursive stiffness matrix method to obtain the reflection coefficient of acoustic waves on these systems because this allows us to address the numerical instability of the conventional transfer matrix method. In addition, remarkable simplification and computational efficiency are obtained. We proposed a modified formulation of the angular spectrum of the transducer based on the theoretical analysis of a line-focus transducer for broadband acoustic microscopy. A thermally sprayed coating on substrate is treated as a functionally graded material along the depth of the coating and is approximately represented by a number of homogeneous elastic layers with exponentially graded elastic properties. The agreement between our experimental and numerical analyses on such thermal sprayed coatings with different thicknesses confirms the efficiency of the method. We proved the ability of the inversion procedure to independently determine both thickness and gradient of elastic properties. The perspective of this work is the opportunity to non-destructively measure these features in functionally graded materials.

Deng, X. D.; Monnier, T.; Guy, P.; Courbon, J.

2013-06-01

392

Forced Response of Structural Dynamic Systems with Local Time-Dependent Stiffnesses  

NASA Astrophysics Data System (ADS)

This paper deals with a method which is meant to directly approximate the steady state response of linear differential equations with periodic coefficients under external excitations. The interest lies in the use of particular systems with time-independent characteristics (mass, damping) and with periodically time-varying stiffness. A description of the principle of the method is provided. This method has been successfully tested on a single-degree-of-freedom (s.d.o.f) example and compared to the standard Runge-Kutta method. Moreover, the parameters are assumed to be a modification of initial non-parametric systems and allow us the use of the forced reanalysis methods to improve the direct spectral method (DSM). The description of the reanalysis method is made with its implementation within the direct spectral method. Then, a practical application concerning a clamped/free beam with parametric mounts is presented to demonstrate the ability of the proposed method in the analysis of systems which have many d.o.f.s and localized parameters.

DELTOMBE, R.; MORAUX, D.; PLESSIS, G.; LEVEL, P.

2000-11-01

393

Modeling and characterization of stiffness controlled robotic legs using dielectric elastomers  

NASA Astrophysics Data System (ADS)

A new robotic leg design is presented that utilizes dielectric elastomers (3M VHB 4910) to rapidly control stiffness changes for enhanced mobility and agility of a field demonstrated hexapod robot. A set of electromechanical test are utilized to obtain up to 92% reduction in stiffness that is controlled by an electric field. The results are compared to a finite deformation membrane finite element model to understand and improve field driven stiffness changes for real-time robotic applications.

Newton, Jason; Morton, Jeffrey; Clark, Jonathan; Oates, William S.

2012-04-01

394

The differential effects of gender, anthropometry, and prior hormonal state on frontal plane knee joint stiffness  

PubMed Central

Background Gender differences in passive frontal plane knee stiffness may contribute to the increased anterior cruciate ligament injury rate in females. Gender-based stiffness differences have been attributed to anthropometric variations, but little data exist describing this relationship. Furthermore, sex hormone levels appear to influence joint stiffness, but the differential effects of instantaneous and prior hormonal concentrations remain unknown. This study sought to explore the effect of gender, prior hormonal status, and anthropometry on passive frontal plane knee joint stiffness. Methods Twelve males and 31 females participated. Females were grouped by hormonal contraceptive use (non users [n=11], monophasic contraceptive users [n=11], and triphasic contraceptive users [n=9]) and tested at the same point in the menstrual cycle. Subjects’ right knee was passively stretched ±7° in the frontal plane at 3°/s. Stiffness was estimated at three loading levels and normalized by body size to minimize anthropometric biases. A 4 (group) × 3 (load) repeated measures analysis of variance was performed for both raw and normalized stiffness. Linear regression analyses were preformed between stiffness estimates and knee diameter and quadriceps femoris angle. Findings Males displayed significantly greater (P<0.05) frontal plane stiffness than females. When normalized, males displayed significantly greater stiffness in valgus (P<0.05), but not varus (P>0.05) than females. No significant effect (P>0.05) of prior hormonal state was found; however, when normalized, varus stiffness was significantly less for triphasic contraceptive users than the other female groups (P<0.05). Quadriceps femoris angle was negatively correlated and knee diameter was positively correlated to knee stiffness. Interpretation Consistent with earlier in vitro findings, our data may indicate that ligament material properties are gender specific. A deficit in passive knee joint stiffness may place a larger burden on the neuromuscular system to resist frontal plane loading in females. PMID:18479791

Cammarata, Martha L.; Dhaher, Yasin Y.

2012-01-01

395

On advantages of derivation of exact dynamical stiffness matrices from boundary integral equations.  

PubMed

Dynamical stiffness matrices are broadly used for solving problems in wave propagation in elastic structures. For elastic waveguides that support both propagating and evanescent waves, the standard use of transfer matrices to obtain their dynamical stiffness matrix may cause problems in computations. In this letter to the editor, an advanced way to derive dynamical stiffness matrices is proposed and exemplified in the classical Bernoulli-Euler beam theory. PMID:20707421

Søe-Knudsen, Alf

2010-08-01

396

Lower limb joint kinetics and ankle joint stiffness in the sprint start push-off  

Microsoft Academic Search

Sprint push-off technique is fundamental to sprint performance and joint stiffness has been identified as a performance-related variable during dynamic movements. However, joint stiffness for the push-off and its relationship with performance (times and velocities) has not been reported. The aim of this study was to quantify and explain lower limb net joint moments and mechanical powers, and ankle stiffness

Laura Charalambous; Gareth Irwin; Ian N. Bezodis; David Kerwin

2011-01-01

397

Lower limb joint kinetics and ankle joint stiffness in the sprint start push-off  

Microsoft Academic Search

Sprint push-off technique is fundamental to sprint performance and joint stiffness has been identified as a performance-related variable during dynamic movements. However, joint stiffness for the push-off and its relationship with performance (times and velocities) has not been reported. The aim of this study was to quantify and explain lower limb net joint moments and mechanical powers, and ankle stiffness

Laura Charalambous; Gareth Irwin; Ian N. Bezodis; David Kerwin

2012-01-01

398

Exactly Solvable Nonhomogeneous Burgers Equations with Variable Coefficients  

Microsoft Academic Search

We consider a nonhomogeneous Burgers equation with time variable coefficients, and obtain an explicit solution of the general initial value problem in terms of solution to a corresponding linear ODE. Special exact solutions such as generalized shock and multi-shock solitary waves, triangular wave, N-wave and rational type solutions are found and discussed. As exactly solvable models, we study forced Burgers

Sirin A. Buyukasik; Oktay K. Pashaev

2011-01-01

399

Composite sizing and ply orientation for stiffness requirements using a large finite element structural model  

NASA Technical Reports Server (NTRS)

A NASTRAN bulk dataset preprocessor was developed to facilitate the integration of filamentary composite laminate properties into composite structural resizing for stiffness requirements. The NASCOMP system generates delta stiffness and delta mass matrices for input to the flutter derivative program. The flutter baseline analysis, derivative calculations, and stiffness and mass matrix updates are controlled by engineer defined processes under an operating system called CBUS. A multi-layered design variable grid system permits high fidelity resizing without excessive computer cost. The NASCOMP system uses ply layup drawings for basic input. The aeroelastic resizing for stiffness capability was used during an actual design exercise.

Radovcich, N. A.; Gentile, D. P.

1989-01-01

400

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

PubMed Central

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

Kum, Francesca; Karalliedde, Janaka

2010-01-01

401

Relief of morning stiffness: a comparative study of naproxen and ibuprofen.  

PubMed

Morning stiffness in 75 patients with mild to moderate rheumatoid arthritis was treated with 1600 mg ibuprofen 4-times daily or 750 mg naproxen twice daily after a placebo-induced flare of this symptom. With the final daily dose of each drug administered at bedtime, both drugs significantly reduced the duration and severity of morning stiffness compared to baseline values but, on average, duration of morning stiffness tended to be shorter for naproxen patients than for ibuprofen patients. No corresponding between-drug difference was found for severity of morning stiffness. PMID:3886298

Taborn, J; Anderson, S; Goldberg, M; Kantrowitz, F; Menander-Huber, K; Gross, J

1985-01-01

402

Pore pressure evolution in deforming granular material: A general formulation and the infinitely stiff approximation  

E-print Network

of fluidfilled granular media controls many geophysical systems, ranging from shear on geological faults of the granular network leads to pore fluid pressure (PP) changes. If the PP rises enough, the fluidfilled granular media may transition from a stresssupporting grain network to a flowing grainfluid slurry

Einat, Aharonov

403

Pore pressure evolution in deforming granular material: A general formulation and the infinitely stiff approximation  

Microsoft Academic Search

The physics of deformation of fluid-filled granular media controls many geophysical systems, ranging from shear on geological faults to landslides and soil liquefaction. Its great complexity is rooted in the mechanical coupling between two deforming phases: the solid granular network and the fluid-filled pore network. Often deformation of the granular network leads to pore fluid pressure (PP) changes. If the

L. Goren; E. Aharonov; D. Sparks; R. Toussaint

2010-01-01

404

A new correlation coefficient for bivariate time-series data  

NASA Astrophysics Data System (ADS)

The correlation in time series has received considerable attention in the literature. Its use has attained an important role in the social sciences and finance. For example, pair trading in finance is concerned with the correlation between stock prices, returns, etc. In general, Pearson’s correlation coefficient is employed in these areas although it has many underlying assumptions which restrict its use. Here, we introduce a new correlation coefficient which takes into account the lag difference of data points. We investigate the properties of this new correlation coefficient. We demonstrate that it is more appropriate for showing the direction of the covariation of the two variables over time. We also compare the performance of the new correlation coefficient with Pearson’s correlation coefficient and Detrended Cross-Correlation Analysis (DCCA) via simulated examples.

Erdem, Orhan; Ceyhan, Elvan; Varli, Yusuf

2014-11-01

405

Direct Extraction of One-loop Integral Coefficients  

SciTech Connect

We present a general procedure for obtaining the coefficients of the scalar bubble and triangle integral functions of one-loop amplitudes. Coefficients are extracted by considering two-particle and triple unitarity cuts of the corresponding bubble and triangle integral functions. After choosing a specific parameterization of the cut loop momentum we can uniquely identify the coefficients of the desired integral functions simply by examining the behavior of the cut integrand as the unconstrained parameters of the cut loop momentum approach infinity. In this way we can produce compact forms for scalar integral coefficients. Applications of this method are presented for both QCD and electroweak processes, including an alternative form for the recently computed three-mass triangle coefficient in the six-photon amplitude A{sub 6}(1{sup -}, 2{sup +}, 3{sup -}, 4{sup +}, 5{sup -}, 6{sup +}). The direct nature of this extraction procedure allows for a very straightforward automation of the procedure.

Forde, Darren

2007-04-16

406

Genetic parameters of egg quality traits on different pedigree layers with special focus on dynamic stiffness.  

PubMed

Egg quality traits are of utmost importance in layer breeding programs due to their effect on profitability in the egg production industry and on the production of quality chicks. Therefore, the aim of this study was to analyze and estimate genetic parameters of different quality traits: egg weight, breaking strength, dynamic stiffness (Kdyn), egg shape index, eggshell thickness, and albumen height. Eggs were obtained from 4 pure lines of birds. Two different tests were performed: a white breeding program, with eggs from a male and female line of a white egg layer program that were analyzed at 67 to 70 wk of age, and a brown breeding program, with eggs from a male and female line of a brown egg layer program that were analyzed at 32 to 36 wk of age. In general, heritabilities were moderate to high for all traits (h(2) = 0.23 to 0.71). A high genetic correlation was estimated in both tests between breaking strength and Kdyn (rg = +0.40 to +0.61). Shell thickness was also positively correlated with breaking strength (rg = +0.50 to +0.63) and Kdyn (rg = +0.28 to +0.69). These moderate relationships demonstrate that the strength of an egg not only relies on the shell thickness but also on the quality and uniformity of eggshell construction. Dynamic stiffness might be preferred for breeding purposes due to its lower negative genetic correlation with egg weight and its higher heritability (h(2) = 0.35 to 0.70) compared with breaking strength (h(2) = 0.23 to 0.35). Breaking strength and Kdyn were positively correlated with shape index, which confirms that round eggs will show higher shell stability. Therefore, it is necessary to monitor egg shape to maintain an optimal form. PMID:25104763

Blanco, A E; Icken, W; Ould-Ali, D; Cavero, D; Schmutz, M

2014-10-01

407

Asymptotic degeneracy of the transfer matrix spectrum for systems with interfaces: Relation to surface stiffness and step free energy  

SciTech Connect

Two- and three-dimensional Ising-type systems are considered in the finite-cross-section cylindrical geometry. An interface is forced along the cylinder (strip in 2d) by the antiperiodic or /plus minus/ boundary conditions. Detailed predictions are presented for the largest asymptotically degenerate set of the transfer matrix eigenvalues. For rough interfaces, i.e., for O < T < T/sub c/ in 2d, T/sub R/ < T < T/sub c/ in 3d, the eigenvalues are split algebraically, and the spectral gaps are governed by the surface stiffness coefficient. For rigid interfaces, i.e., O < T < T /sub R/ in 3d, the eigenvalues are split exponentially, with the gaps determined by the step free energy.

Privman, V.; Svrakic, N.M.

1989-02-01

408

Conversion coefficients for superheavy elements  

E-print Network

In this paper we report on internal conversion coefficients for Z = 111 to Z = 126 superheavy elements obtained from relativistic Dirac-Fock (DF) calculations. The effect of the atomic vacancy created during the conversion process has been taken into account using the so called "Frozen Orbital" approximation. The selection of this atomic model is supported by our recent comparison of experimental and theoretical conversion coefficients across a wide range of nuclei. The atomic masses, valence shell electron configurations, and theoretical atomic binding energies required for the calculations were adopted from a critical evaluation of the published data. The new conversion coefficient data tables presented here cover all atomic shells, transition energies from 1 keV up to 6000 keV, and multipole orders of 1 to 5. A similar approach was used in our previous calculations [1] for Z = 5 - 110.

T. Kibédi; M. B. Trzhaskovskaya; M. Gupta; A. E. Stuchbery

2011-03-03

409

Conversion coefficients for superheavy elements  

E-print Network

In this paper we report on internal conversion coefficients for Z = 111 to Z = 126 superheavy elements obtained from relativistic Dirac-Fock (DF) calculations. The effect of the atomic vacancy created during the conversion process has been taken into account using the so called "Frozen Orbital" approximation. The selection of this atomic model is supported by our recent comparison of experimental and theoretical conversion coefficients across a wide range of nuclei. The atomic masses, valence shell electron configurations, and theoretical atomic binding energies required for the calculations were adopted from a critical evaluation of the published data. The new conversion coefficient data tables presented here cover all atomic shells, transition energies from 1 keV up to 6000 keV, and multipole orders of 1 to 5. A similar approach was used in our previous calculations [1] for Z = 5 - 110.

Kibédi, T; Gupta, M; Stuchbery, A E

2011-01-01

410

The Transition from Stiff to Compliant Materials in Squid Beaks  

PubMed Central

The beak of the Humboldt squid Dosidicus gigas represents one of the hardest and stiffest wholly organic materials known. As it is deeply embedded within the soft buccal envelope, the manner in which impact forces are transmitted between beak and envelope is a matter of considerable scientific interest. Here, we show that the hydrated beak exhibits a large stiffness gradient, spanning two orders of magnitude from the tip to the base. This gradient is correlated with a chemical gradient involving mixtures of chitin, water, and His-rich proteins that contain 3,4-dihydroxyphenyl-l-alanine (dopa) and undergo extensive stabilization by histidyl-dopa cross-link formation. These findings may serve as a foundation for identifying design principles for attaching mechanically mismatched materials in engineering and biological applications. PMID:18369144

Miserez, Ali; Schneberk, Todd; Sun, Chengjun; Zok, Frank W.; Waite, J. Herbert

2009-01-01

411

Negative stiffness of the FeAl intermetallic nanofilm  

NASA Astrophysics Data System (ADS)

Uniaxial tension of the nanofilm of the FeAl intermetallic alloy has been simulated by the molecular dynamics method. It has been found that the nanofilm is elastically deformed by 37%. There is a region in the stress-strain curve, where the strain increases with a decrease in the tensile stress, which indicates the negative stiffness of the nanofilm in this region. The uniform strain with a decrease in the tensile stress is unstable thermodynamically, which leads to the appearance domains with different elastic strains in the nanofilm. The deformation in the unstable region develops due to the domain-wall motion; as a result, the domains with a higher strain grow at the expense of the domains with a lower strain. A similar deformation mechanism was recently described by Savin with coworkers for the DNA molecule.

Bukreeva, K. A.; Babicheva, R. I.; Dmitriev, S. V.; Zhou, K.; Mulyukov, R. R.

2013-09-01

412

Stiffness Characteristics of Composite Rotor Blades With Elastic Couplings  

NASA Technical Reports Server (NTRS)

Recent studies on rotor aeroelastic response and stability have shown the beneficial effects of incorporating elastic couplings in composite rotor blades. However, none of these studies have clearly identified elastic coupling limits and the effects of elastic couplings on classical beam stiffnesses of representative rotor blades. Knowledge of these limits and effects would greatly enhance future aeroelastic studies involving composite rotor blades. The present study addresses these voids and provides a preliminary design database for investigators who may wish to study the effects of elastic couplings on representative blade designs. The results of the present study should provide a basis for estimating the potential benefits associated with incorporating elastic couplings without the need for first designing a blade cross section and then performing a cross-section analysis to obtain the required beam section properties as is customary in the usual one-dimensional beam-type approach.

Piatak, David J.; Nixon, Mark W.; Kosmatka, John B.

1997-01-01

413

AFM-based indentation stiffness tomography-An asymptotic model  

NASA Astrophysics Data System (ADS)

The so-called indentation stiffness tomography technique for detecting the interior mechanical properties of an elastic sample with an inhomogeneity is analyzed in the framework of the asymptotic modeling approach under the assumption of small size of the inhomogeneity. In particular, it is assumed that the inhomogeneity size and the size of contact area under the indenter are small compared with the distance between them. By the method of matched asymptotic expansions, the first-order asymptotic solution to the corresponding frictionless unilateral contact problem is obtained. The case of an elastic half-space containing a small spherical inhomogeneity has been studied in detail. Based on the grid indentation technique, a procedure for solving the inverse problem of extracting the inhomogeneity parameters is proposed.

Argatov, I. I.

2014-10-01

414

Arterial Stiffness: A Nexus between Cardiac and Renal Disease.  

PubMed

Vascular disease is the leading cause of morbidity and mortality in the Western world, and vascular function is determined by structural and functional properties of the arterial vascular wall. Cardiorenal metabolic syndrome such as obesity, diabetes, hypertension, kidney disease, and aging are conditions that predispose to arterial stiffening, which is a pathological alteration of the vascular wall and ultimately results in target organ damage in heart and kidney. In this review, we provide new insights on the interactions between arterial stiffness, vascular resistance and pulse wave velocity as well as final end-organ damage in heart and kidney. Better understanding of the mechanisms of arterial functional and hemodynamic alteration may help in developing more refined therapeutic strategies aimed to reduce cardiovascular and chronic kidney diseases. PMID:24847335

Jia, Guanghong; Aroor, Annayya R; Sowers, James R

2014-04-01

415

Cell stiffness, contractile stress and the role of extracellular matrix  

SciTech Connect

Here we have assessed the effects of extracellular matrix (ECM) composition and rigidity on mechanical properties of the human airway smooth muscle (ASM) cell. Cell stiffness and contractile stress showed appreciable changes from the most relaxed state to the most contracted state: we refer to the maximal range of these changes as the cell contractile scope. The contractile scope was least when the cell was adherent upon collagen V, followed by collagen IV, laminin, and collagen I, and greatest for fibronectin. Regardless of ECM composition, upon adherence to increasingly rigid substrates, the ASM cell positively regulated expression of antioxidant genes in the glutathione pathway and heme oxygenase, and disruption of a redox-sensitive transcription factor, nuclear erythroid 2 p45-related factor (Nrf2), culminated in greater contractile scope. These findings provide biophysical evidence that ECM differentially modulates muscle contractility and, for the first time, demonstrate a link between muscle contractility and Nrf2-directed responses.

An, Steven S., E-mail: san@jhsph.edu [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States); Kim, Jina [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States)] [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States); Ahn, Kwangmi [Division of Biostatistics, Penn State College of Medicine, Hershey, PA 17033 (United States)] [Division of Biostatistics, Penn State College of Medicine, Hershey, PA 17033 (United States); Trepat, Xavier [CIBER, Enfermedades Respiratorias, 07110 Bunyola (Spain)] [CIBER, Enfermedades Respiratorias, 07110 Bunyola (Spain); Drake, Kenneth J. [Division of Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, MA 02115 (United States)] [Division of Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, MA 02115 (United States); Kumar, Sarvesh; Ling, Guoyu; Purington, Carolyn; Rangasamy, Tirumalai; Kensler, Thomas W.; Mitzner, Wayne [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States)] [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States); Fredberg, Jeffrey J. [Division of Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, MA 02115 (United States)] [Division of Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, MA 02115 (United States); Biswal, Shyam [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States) [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States); Division of Pulmonary and Critical Care Medicine, Johns Hopkins School of Medicine, Baltimore, MD 21205 (United States)

2009-05-15

416

Effect of Bearing Dynamic Stiffness on Gear Vibration  

NASA Technical Reports Server (NTRS)

Noise is a major consideration in the design of high performance geared transmissions, such as for helicopters. Transmission error, that is, the accuracy with which the driven gear follows the driver gear, is a common indicator of noise generation. It is well known that bearing properties have a strong influence on shaft dynamics. However, up to now the contribution of bearings to transmission error has received little attention. In this paper, a torsional-axial-lateral geared rotor analysis is used to determine dynamic transmission error as a function of bearing stiffness and damping. Bearings have a similar effect as found in shaft dynamics; transmission error can be reduced more than 10 decibels by appropriate selection of bearing properties.

Fleming, David P.

2002-01-01

417

Torsional Stiffness Verification of an Adhesively Bonded Joint  

NASA Astrophysics Data System (ADS)

In the present work numerical-experimental analysis for the characterization of a structural adhesive has been performed. The numerical analysis has been carried out through the finite element method by using, for the phases pre / post processing were used commercial programs while for the phase of numerical solution the Abaqus code was used. The experimental analyses were carried out at laboratories of C.R.F. S.C.p.A. by using of a standard quasi static testing machine. Later numerical analysis was performed comparing the torsional stiffness of a vehicle in which the welded connection between the pavilion and the flank has been substituted by bonded one. This comparison has allowed to demonstrate the ability of the bonded joint discussed to provide mechanical performances comparable with those of a welded joint widely used in the automotive industry.

Annicchiarico, A.; Caputo, F.; De Angelis, G.; Frascà, F.; Lamanna, G.

2010-06-01

418

Highly stable explicit technique for stiff reaction-transport PDEs  

SciTech Connect

The numerical simulation of chemically reacting flows is a topic that has attracted a great deal of current research. At the heart of numerical reactive flow simulations are large sets of coupled, nonlinear partial differential equations (PDEs). Due to the stiffness that is usually present, explicit time differencing schemes are not used despite their inherent simplicity and efficiency on parallel and vector machines, since these schemes require prohibitively small numerical stepsizes. Implicit time differencing schemes, although possessing good stability characteristics, introduce a great deal of computational overhead necessary to solve the simultaneous algebraic system at each timestep. This paper proposes an algorithm based on a preconditioned time differencing scheme. The algorithm is explicit and permits a large stable time step. A study of the algorithm's performance on a parallel architecture is presented.

Aro, C. J., LLNL

1996-12-01

419

Hooke's Law and the Stiffness of a Plastic Spoon  

NASA Astrophysics Data System (ADS)

The study of elastic properties of solids is essential to both physics and engineering. Finding simple, easy-to-visualize examples to demonstrate these concepts is often difficult. In a previous article written by one of us (KAPII), a simple method for determining Youngs modulus using marshmallows was given. In this article we will illustrate another method to explore elastic properties of everyday materials. This experiment uses a common plastic spoon exposed to a transverse force in order to determine the stiffness constant, yield point, and rupture point of the plastic spoon. In addition, much like the "Youngs Modulus of a Marshmallow" activity, this experiment visually demonstrates Hooke's law, is fun and easy to perform, and leaves a lasting impression on the students.

Pestka, Kenneth A.; Warren, Cori

2012-11-01

420

Method for determining damping coefficients  

NASA Astrophysics Data System (ADS)

There is disclosed a method for determining damping coefficients, the method including the steps of providing a damper assembly including a bar of known parameters, and a viscous damper, wherein a first end of the bar is disposed in the viscous damper while the second end of the bar is free, applying a known force to the second end of the bar in a direction toward the first end of the bar, measuring the response function of the assembly, comprising the ratio of the bar acceleration to the applied force, determining the eigenvalues of the response function, and from the eigenvalues computing the damping coefficient of the damper assembly.

Austin, Stephen A.; Hull, Andrew J.; Hurdis, David A.; Kasper, Kent D.

1995-05-01

421

Seebeck coefficient of one electron  

NASA Astrophysics Data System (ADS)

The Seebeck coefficient of one electron, driven thermally into a semiconductor single-electron box, is investigated theoretically. With a finite temperature difference ?T between the source and charging island, a single electron can charge the island in equilibrium, directly generating a Seebeck effect. Seebeck coefficients for small and finite ?T are calculated and a thermally driven Coulomb staircase is predicted. Single-electron Seebeck oscillations occur with increasing ?T, as one electron at a time charges the box. A method is proposed for experimental verification of these effects.

Durrani, Zahid A. K.

2014-03-01

422

Effect of Substrate Stiffness on Early Mouse Embryo Development  

PubMed Central

It is becoming increasingly clear that cells are remarkably sensitive to the biophysical cues of their microenvironment and that these cues play a significant role in influencing their behaviors. In this study, we investigated whether the early pre-implantation embryo is sensitive to mechanical cues, i.e. the elasticity of the culture environment. To test this, we have developed a new embryo culture system where the mechanical properties of the embryonic environment can be precisely defined. The contemporary standard environment for embryo culture is the polystyrene petri dish (PD), which has a stiffness (1 GPa) that is six orders of magnitude greater than the uterine epithelium (1 kPa). To approximate more closely the mechanical aspects of the in vivo uterine environment we used polydimethyl-siloxane (PDMS) or fabricated 3D type I collagen gels (1 kPa stiffness, Col-1k group). Mouse embryo development on alternate substrates was compared to that seen on the petri dish; percent development, hatching frequency, and cell number were observed. Our results indicated that embryos are sensitive to the mechanical environment on which they are cultured. Embryos cultured on Col-1k showed a significantly greater frequency of development to 2-cell (68±15% vs. 59±18%), blastocyst (64±9.1% vs. 50±18%) and hatching blastocyst stages (54±25% vs. 21±16%) and an increase in the number of trophectodermal cell (TE,65±13 vs. 49±12 cells) compared to control embryos cultured in PD (mean±S.D.; p<.01). Embryos cultured on Col-1k and PD were transferred to recipient females and observed on embryonic day 12.5. Both groups had the same number of fetuses, however the placentas of the Col-1k fetuses were larger than controls, suggesting a continued effect of the preimplantation environment. In summary, characteristics of the preimplantation microenvironment affect pre- and post-implantation growth. PMID:22860009

Kolahi, Kevin S.; Donjacour, Annemarie; Liu, Xiaowei; Lin, Wingka; Simbulan, Rhodel K.; Bloise, Enrrico; Maltepe, Emin; Rinaudo, Paolo

2012-01-01

423

VAGINAL DEGENERATION FOLLOWING IMPLANTATION OF SYNTHETIC MESH WITH INCREASED STIFFNESS  

PubMed Central

Objective To compare the impact of the prototype prolapse mesh Gynemesh PS to that of two new generation lower stiffness meshes, UltraPro and SmartMesh, on vaginal morphology and structural composition. Design A mechanistic study employing a non-human primate (NHP) model. Setting Magee-Womens Research Institute at the University of Pittsburgh. Population Parous rhesus macaques, with similar age, weight, parity and POP-Q scores. Methods Following IACUC approval, 50 rhesus macaques were implanted with Gynemesh PS (n=12), UltraPro with its blue line perpendicular to the longitudinal axis of vagina (n=10), UltraPro with its blue line parallel to the longitudinal axis of vagina (n=8) and SmartMesh (n=8) via sacrocolpopexy following hysterectomy. Sham operated animals (n=12) served as controls. Main Outcome Measures The mesh-vagina complex (MVC) was removed after 12 weeks and analyzed for histomorphology, in situ cell apoptosis, total collagen, elastin, glycosaminoglycan content and total collagenase activity. Appropriate statistics and correlation analyses were performed accordingly. Results Relative to sham and the two lower stiffness meshes, Gynemesh PS had the greatest negative impact on vaginal histomorphology and composition. Compared to sham, implantation with Gynemesh PS caused substantial thinning of the smooth muscle layer (1557 ± 499?m vs 866 ± 210 ?m, P=0.02), increased apoptosis particularly in the area of the mesh fibers (P=0.01), decreased collagen and elastin content (20% (P=0.03) and 43% (P=0.02), respectively) and increased total collagenase activity (135% (P=0.01)). GAG (glycosaminoglycan), a marker of tissue injury, was the highest with Gynemesh PS compared to sham and other meshes (P=0.01). Conclusion Mesh implantation with the stiffer mesh Gynemesh PS induced a maladaptive remodeling response consistent with vaginal degeneration. PMID:23240802

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

2012-01-01

424

A note on Hansen's coefficients in satellite theory  

NASA Technical Reports Server (NTRS)

General formulas for Hansen's coefficients in satellite theory are derived along with expressions for the eccentricity functions G and H. Recurrence relations for the eccentricity functions and their derivatives are obtained which are valid for all values of the parameter p. It is noted that the recurrence relations obtained by Challe and Laclaverie (1969) as well as by Balmino (1973) do not satisfy certain parity conditions and therefore involve coefficients outside the range of usage.

Giacaglia, G. E. O.

1976-01-01

425

Theory and measurements of labyrinth seal coefficients for rotor stability of turbocompressors  

NASA Technical Reports Server (NTRS)

The prediction of rotordynamic coefficients for gas seals is achieved with the aid of a two-volume bulk flow model based on turbulent rotationally symmetric 3D flow calculations including swirl flow. Comparison of cross-coupling and damping coefficients with measurements confirm this approach. In particular the theoretically predicted phenomenon that labyrinth damping is retained without inlet swirl is confirmed. This is important for the design of high pressure compressors, where labyrinth damping is a major contribution improving rotor stability. Discrepancies are found when comparing theory with measured direct stiffness and the cross-coupling damping coefficients. First measurements of labyrinth seals on a recently installed test rig operated with water are presented. Since forces are larger than on test stands operated with air and since individual chamber forces are obtained phenomena like inlet effects may be studied.

Syssmann, H. R.

1987-01-01

426

Geometrical content of Leslie coefficients  

NASA Astrophysics Data System (ADS)

In this work, we will study how the effective geometry acquired by nematic molecules under thermal vibration contribute to the determination of the Leslie coefficients. To do this, we will divide this work in two sections. In the first section, we present the geometrical fundamentals of the so-called Hess-Baalss (HB) approach [D. Baalss and S. Hess, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.57.86 57, 86 (1986)] where we show that its basic assumptions can be understood as a geometrical interpretation of de Gennes’ passage from the microscopic to the macroscopic order parameter. In the second section, we use an extended version of the HB approach [M. Simões, K. Yamaguti, and A. J. Palangana, Phys. Rev. EPHRVAO1539-375510.1103/PhysRevE.80.061701 80, 061701 (2009)] to obtain the geometrical contribution to each Leslie coefficient. Our results will be compared with experimental data, and we will show that the Miesowicz’s coefficients are connected as long as the ratio ?3/?4 between these Leslie coefficients can be considered small.

Simões, M.; da Silva, J. L. Correia

2011-05-01

427

Coefficient of Meteor Plasma Radiation  

Microsoft Academic Search

We present a historical review of the problem of obtaining the meteor plasma radiation coefficient. Meteor spectrophotometry endures to fail in determining spectral line profiles, because an existing spectrograph has to give a monochrome image of the meteors instead of a spectral line. Therefore, it is rather difficult to take the self-absorption magnitude as affecting the decrease of radiation intensity

V. A. Smirnov

2000-01-01

428

Effective Viscosity Coefficient of Nanosuspensions  

NASA Astrophysics Data System (ADS)

Systematic calculations of the effective viscosity coefficient of nanosuspensions have been performed using the molecular dynamics method. It is established that the viscosity of a nanosuspension depends not only on the volume concentration of the nanoparticles but also on their mass and diameter. Differences from Einstein's relation are found even for nanosuspensions with a low particle concentration.

Rudyak, V. Ya.; Belkin, A. A.; Egorov, V. V.

2008-12-01

429

Conversion coefficients for superheavy elements  

Microsoft Academic Search

In this paper we report on internal conversion coefficients for Z = 111 to Z = 126 superheavy elements obtained from relativistic Dirac-Fock (DF) calculations. The effect of the atomic vacancy created during the conversion process has been taken into account using the so called \\

T. Kibédi; M. B. Trzhaskovskaya; M. Gupta; A. E. Stuchbery

2011-01-01

430

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

431

Experimental determination of the distributed dynamic coefficients for a hydrodynamic fluid film bearing  

NASA Astrophysics Data System (ADS)

Most current rotor bearing analysis utilizes lumped parameter bearing coefficients to model the static and dynamic characteristics of fluid film bearings. By treating the stiffness and damping properties of the fluid film as acting upon the axial centerline of the rotor, these models are limited in their analysis to first order lateral rotor-bearing motion. The development of numerical methods that distribute the dynamic properties of the fluid film around the bearing circumference allow for higher order analysis of the motion between the bearing and rotor. Assessment of the accuracy of the numerical method used to calculate distributed dynamic fluid film bearing coefficients is performed by developing a novel hydrodynamic journal bearing test rig and experimental testing procedure capable of obtaining measured distributed dynamic coefficients over a range of bearing operating conditions. The instrumented bearing test rig is used to measure the dynamic bearing displacement and fluid film pressure responses from application of an externally applied excitation force. Least squares solution to a system of perturbated pressure equations, populated by measured displacement and pressure responses, is used to determine the hydrodynamic stiffness and damping properties for a finite region of the bearing surface. Incremental rotation of pressure sensors embedded in the body of the test bearing allow for measurement of the fluid film circumferential pressure distribution which is used to calculate a set of experimentally determined dynamic bearing coefficients. Distributed bearing coefficients derived from experimental measurements are compared to numerically calculated distributed coefficients as well as to lumped parameter coefficients generated from experimental and numerical methods found in the literature. Overall, the numerically calculated distributed coefficients successfully model both the circumferential distribution and the operating conditions of the experimental distributed bearing coefficient values and show reasonable correlation to results obtained through lumped parameter methods. Excitation frequency independence is validated through experimental testing over multiple frequencies, and damping cross term inequality of the numerically distributed bearing coefficients is validated by lumped coefficient analysis found in the literature. While uncertainty and variation of the test rig dimensional and operating parameters have some effect on the accuracy with which the numerical methods model the experimental results, the most significant source of dissimilarity in numerical and experimental results comes from test rig specific features not captured in the numerical methods, such as bearing surface wear and bearing-shaft misalignment.

Gyurko, John Harrison

432

Collective friction coefficients in the relaxation time approximation F. A. Ivanyuk  

E-print Network

Collective friction coefficients in the relaxation time approximation F. A. Ivanyuk Institute components of the friction coefficient for various single-particle potentials and have found that the nondiagonal component of the friction coefficient depends generally on the diffuseness of the potential

Pomorski, Krzysztof

433

Special functions associated with SU(3) Wigner-Clebsch-Gordan coefficients  

SciTech Connect

The Wigner-Clebsch-Gordan (WCG) coefficients of the unitary groups are a rich source of multivariable special functions. The general algebraic setting of these coefficients is reviewed and several special functions associated with the SU(3) WCG coefficients defined and their properties presented. 29 refs.

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

1990-01-01

434

Implementation of variable joint stiffness through antagonistic actuation using rolamite springs  

Microsoft Academic Search

The addition of variable joint stiffness to an upper limb prosthesis can restore an important function of the natural arm. Design goals for the stiffness and force performance of prosthetic elbow joints are presented. This paper develops configurations of antagonistic actuators, for use in prosthetic arms, with improved energy efficiency, controllability, interaction properties, and size. Implementation of the required quadratic

Chad English; Donald Russell

1999-01-01