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1

Vibration Analysis of a Framework Structure by Generalized Transfer Stiffness Coefficient Method  

Microsoft Academic Search

A generalized transfer stiffness coefficient method using graph theory is developed in order to improve the applicability of the transfer stiffness coefficient method. In the new method, an analytical model is expressed by a weighted signal-flow graph, and the graph is contracted according to the series and parallel contraction rules. The computational complexity and the memory requirement for the contraction

Yasuhiro Bonkobara; Takahiro Kondou; Takashi Ayabe; Myung-Soo Choi

2007-01-01

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

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

4

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

Microsoft Academic Search

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

Louis Gold

1950-01-01

5

Stress Tensor and Stiffness Coefficients for EA Potentials in Earthquake Fault Systems  

NASA Astrophysics Data System (ADS)

A general form of an Embedded-Atom (EA) empirical potential with a binary term along with a collective term is considered. The collective term is defined as the sum of distribution functions. The stress tensor and the stiffness coefficients have been derived in closed form. Results are completely compatible with the ones without the EA term. It is shown that although stress and stiffness get their main contribution from nearest neighbours, other neighbours can also contribute significantly once there is a rapid change in the energy distribution - i.e. earthquakes. In order to use a dimensionless equation a “circle of events” outside of which the energy can be neglected has been introduced. One may find it useful both from a mathematical and practical point of view. Mathematically we may ignore spatial scales, when dealing with smaller fault patches. Practically it can be used to apply the theory to a finite fault system without the complication of the boundary conditions, which is an ongoing challenge in earthquake simulations. Relations presented are in three dimensions. Using a 3d fault model gives us the opportunity to consider a system of faults instead of one 2d fault model. This also may solve the fault interaction problem eventually. Because EA potentials are imported from Molecular Dynamics (MD), and in MD simulations the time steps are as small as a femto-second, this may open a window for us to see very small scale phenomenon in earthquake forecasting.

Tavakoli, A.; Tiampo, K. F.

2010-12-01

6

Research on dynamic behaviors in remote pressure-regulating pipeline under the condition of controllable maximum stiffness coefficient  

NASA Astrophysics Data System (ADS)

Aiming at remote pressure-regulating system controlled by pilot overflow valve and based on dynamic-characteristics fundamental equation of distributed-parameter model in hydraulic pipelines, the mathematical model of remote-pressure-regulating hydraulic pipelines is deduced. Discussing the controllability of the remote pressure-regulating system shows that the controllability depends on the controllable maximum stiffness coefficient, which mainly includes the length and the inner radius of remote pressure-regulating pipeline, the spring stiffness coefficient of overflow valve, and the properties of hydraulic oil. And if a remote pressure-regulating system wants to work normally and avoid resonance, the conditions of controllable maximum stiffness coefficient must be derived. The concept, controllable maximum stiffness coefficient, and the mathematical models provide theoretical and practical instruction in study of hydraulic remote pressure-regulating system.

Yang, G. L.; Zhang, L. Q.; Zhang, S. Y.

2012-11-01

7

Generalized Variable-Coefficient KP Equation  

Microsoft Academic Search

The variable-coefficient generalizations of thecelebrated KP equation (GvcKPs) are realistic models forvarious physical and engineering situations. In thisnote, the application of symbolic computation and the truncated Painleve expansion leads toan auto-Backlund transformation and soliton-typedsolutions to a type of the GvcKPs.

Yi-Tian Gao; Bo Tian

1998-01-01

8

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

Microsoft Academic Search

This paper provided an opportunity to quantify the angular stiffness and equivalent viscous damping coefficients of an axial spline coupling used in high-speed turbomachinery. A unique test methodology and data reduction procedures were developed. The bending moments and angular deflections transmitted across an axial spline coupling were measured while a nonrotating shaft was excited by an external shaker. A rotor

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

1994-01-01

9

Generalized QRT mappings with periodic coefficients  

NASA Astrophysics Data System (ADS)

We present an extension of the QRT mapping beyond the familiar symmetric and asymmetric varieties. Starting from our results on discrete Painlevé equations, we show that there exist integrable QRT-like mappings, the coefficients of which are periodic functions. We present several examples of mappings with periodic coefficients of various periods and show that there exist cases where the periods are arbitrarily long. We prove the integrability of all the examples by constructing the corresponding conserved quantities and we show how these systems, just as their QRT siblings, can be explicitly integrated in terms of elliptic functions.

Ramani, A.; Grammaticos, B.; Willox, R.

2011-01-01

10

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.

Janakievska, Pavlina; Sotiroski, Kosta; Sikole, Aleksandar

2013-01-01

11

Factor Scores, Structure Coefficients, and Communality Coefficients: It's All One General Linear Model.  

ERIC Educational Resources Information Center

|This paper explains the meaning and use of three important factor analytic statistics: factor scores, factor structure coefficients, and communality coefficients. For the discussion, 301 observations of junior high school students 11 measured variables from a previous study are analyzed. While factors provide the researcher with general

Marsh, S. Neil

12

The Utility and General Definition of Correlation Coefficients  

Microsoft Academic Search

Previous attempts at defining other correlation measures mostly tried to generalize the inner product definition used in Pearson's correlation coefficient. This does not allow for certain useful correlation's, like the Greatest Deviation, or Gini's. In this work the idea in Gideon and Hollister (1987) of seeing correlation, as the difference between distance from perfect negative and perfect positive correlation will

Rudy A. Gideon

13

Generalized Transport Coefficients of Multicomponent Low-Temperature Plasmas  

Microsoft Academic Search

We present an efficient solution strategy for the calculation of the transport coefficients of a multicomponent nonequilibrium low-temperature plasma based on a generalized heavy-particle transport model. In this regime, the chemical and thermal properties show that the plasma is not in equilibrium. However, the heavy particles themselves are expected to be in a local thermal equilibrium. Hence, we use a

Thomas K. Senega; Ralf Peter Brinkmann

2007-01-01

14

Generalized Heat Kernel Coefficients for a New Asymptotic Expansion  

NASA Astrophysics Data System (ADS)

The method which allows for asymptotic expansion of the one-loop effective action W = lndetA is formulated. The positively defined elliptic operator A = U + M2 depends on the external classical fields taking values in the Lie algebra of the internal symmetry group G. Unlike the standard method of Schwinger - DeWitt, the more general case with the nongenerate mass matrix M = diag(m1, m2, ...) is considered. The first coefficients of the new asymptotic series are calculated and their relationship with the Seeley - DeWitt coefficients is clarified.

Osipov, Alexander A.; Hiller, Brigitte

2003-04-01

15

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

PubMed

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

Hübscher, David M; Wessel, Stefan

2013-06-10

16

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

17

General dissipative coefficient in warm intermediate and logamediate inflation  

NASA Astrophysics Data System (ADS)

We study a general form for the dissipative coefficient ?(T,?)=C?Tm/?m-1 in the context of warm intermediate and logamediate inflationary universe models. We analyze these models in the weak and strong dissipative regimes. In the slow-roll approximation, we describe in great detail the characteristics of these models. In both regimes, we use recent data from the WMAP nine-year data and Planck data to constrain the parameters appearing in our models.

Herrera, Ramón; Olivares, Marco; Videla, Nelson

2013-09-01

18

Stability criterion for self-similar solutions with a scalar field and those with a stiff fluid in general relativity  

NASA Astrophysics Data System (ADS)

A stability criterion is derived in general relativity for self-similar solutions with a scalar field and those with a stiff fluid, which is a perfect fluid with the equation of state P = ?. A wide class of self-similar solutions turns out to be unstable against kink mode perturbation. According to the criterion, the Evans Coleman stiff-fluid solution is unstable and cannot be a critical solution for the spherical collapse of a stiff fluid if we allow sufficiently small discontinuity in the density gradient field in the initial data sets. The self-similar scalar-field solution, which was recently found numerically by Brady et al (2002 Class. Quantum Grav. 19 6359), is also unstable. Both the flat Friedmann universe with a scalar field and that with a stiff fluid suffer from kink instability at the particle horizon scale.

Harada, Tomohiro; Maeda, Hideki

2004-01-01

19

On a Variable-Coefficient Modified KP Equation and a Generalized Variable-Coefficient KP Equation with Computerized Symbolic Computation  

Microsoft Academic Search

The variable-coefficient nonlinear evolution equations, although realistically modeling various mechanical and physical situations, often cause some well-known powerful methods not to work efficiently. In this paper, we extend the power of the generalized hyperbolic-function method, which is based on the computerized symbolic computation, to a variable-coefficient modified Kadomtsov-Petviashvili (KP) equation and a generalized variable-coefficient KP equation. New exact analytic solutions

Yi-Tian Gao; Bo Tian

2001-01-01

20

On a Variable-Coefficient Modified KP Equation and a Generalized Variable-Coefficient KP Equation with Computerized Symbolic Computation  

NASA Astrophysics Data System (ADS)

The variable-coefficient nonlinear evolution equations, although realistically modeling various mechanical and physical situations, often cause some well-known powerful methods not to work efficiently. In this paper, we extend the power of the generalized hyperbolic-function method, which is based on the computerized symbolic computation, to a variable-coefficient modified Kadomtsov-Petviashvili (KP) equation and a generalized variable-coefficient KP equation. New exact analytic solutions thus come out.

Gao, Yi-Tian; Tian, Bo

21

Generalized approximations of reflection coefficients in orthorhombic media  

NASA Astrophysics Data System (ADS)

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

Zhang, Feng; Li, Xiangyang

2013-10-01

22

Timoshenko beam-column with generalized end conditions on elastic foundation: Dynamic-stiffness matrix and load vector  

NASA Astrophysics Data System (ADS)

The dynamic-stiffness matrix and load vector of a Timoshenko beam-column resting on a two-parameter elastic foundation with generalized end conditions are presented. The proposed model includes the frequency effects on the stiffness matrix and load vector as well as the coupling effects of: (1) bending and shear deformations along the member; (2) translational and rotational lumped masses at both ends; (3) translational and rotational masses uniformly distributed along its span; (3) axial load (tension or compression) applied at both ends; and (4) shear forces along the span induced by the applied axial load as the beam deforms according to the “modified shear equation” proposed by Timoshenko. The dynamic analyses of framed structures can be performed by including the effects of the imposed frequency (?>0) on the dynamic-stiffness matrix and load vector while the static and stability analyses can be carried out by making the frequency ?=0. The proposed model and corresponding dynamic-stiffness matrix and load vector represent a general solution capable to solve, just by using a single segment per element, the static, dynamic and stability analyses of any elastic framed structure made of prismatic beam-columns with semi-rigid connections resting on two-parameter elastic foundations. Analytical results indicate that the elastic behavior of framed structures made of beam-columns is frequency dependent and highly sensitive to the coupling effects just mentioned. Three comprehensive examples are presented to show the capacities and validity of the proposed method and the obtained results are compared with the finite element method and other analytical approaches.

Arboleda-Monsalve, Luis G.; Zapata-Medina, David G.; Darío Aristizabal-Ochoa, J.

2008-03-01

23

Considerations for general anesthesia combined with epidural anesthesia in a patient with stiff-person syndrome  

Microsoft Academic Search

We report the successful management of anesthesia in a patient with stiff-person syndrome (SPS) undergoing a thymectomy using\\u000a a volatile anesthetic combined with epidural anesthesia. The anesthetic concern in patients with SPS is the possibility of\\u000a postoperative hypotonia due to the presence of excessive ?-aminobutyric acid (GABA) resulting from an interaction between\\u000a the anesthetic agents and preoperatively taken therapeutic drugs.

Katsumi Yamamoto; Koji Hara; Takafumi Horishita; Takeyoshi Sata

2007-01-01

24

A General Class of Correlation Coefficients for the 2 × 2 Crossover Design  

Microsoft Academic Search

Summary The Pearson correlation coefficient and the Kendall correlation coefficient are two popular statistics for assessing the correlation between two variables in a bivariate sample. We indicate how both of these statistics are special cases of a general class of correlation statistics that is parameterized by g 2 (0, 1). The Pearson correlation coefficient is characterized by g ¼ 1

Vernon M. Chinchilli; Brenda R. Phillips; David T. Mauger

2005-01-01

25

On the general variable-coefficient KP equation with self-consistent sources  

Microsoft Academic Search

A new general variable-coefficient KP equation with self-consistent sources and its Grammian solutions is obtained by using the source generation procedure. Moreover, by applying the Pfaffianization procedure, a new coupled variable-coefficient KP equation is constructed. Its Wronski-type Pfaffian solution and Gramm-type Pfaffian solution are given. At last, a new integrable system of the general variable-coefficient KP equation with self-consistent sources

Ye-Peng Sun; Hon-Wah Tam

2011-01-01

26

On the general variable-coefficient KP equation with self-consistent sources  

NASA Astrophysics Data System (ADS)

A new general variable-coefficient KP equation with self-consistent sources and its Grammian solutions is obtained by using the source generation procedure. Moreover, by applying the Pfaffianization procedure, a new coupled variable-coefficient KP equation is constructed. Its Wronski-type Pfaffian solution and Gramm-type Pfaffian solution are given. At last, a new integrable system of the general variable-coefficient KP equation with self-consistent sources is established.

Sun, Ye-Peng; Tam, Hon-Wah

2011-07-01

27

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

PubMed Central

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

2012-01-01

28

Explicit bi-soliton-like solutions for a generalized KP equation with variable coefficients  

Microsoft Academic Search

A generalized KP equation with variable coefficients, including the KP equation and the cylindrical KP equation as its special cases is investigated using a constructive algorithm and symbolic computation. Explicit bi-soliton-like solutions of the equation are obtained under certain constraints on the coefficient functions. For different coefficient functions, the solutions can model different types of bi-soliton-like waves. Some interesting bi-soliton-like

Zhuosheng Lü; Fuding Xie

2010-01-01

29

Similarity Reductions for a Generalized Variable-Coefficient Kadomtsev-Petviashvili Equation with Symbolic Computation  

Microsoft Academic Search

We use computerized symbolic computation to study the similarity reductions of a generalized Kadomtsev-Petviashvili (KP) equation, with its space- and time-dependent coefficients arising in plasma physics and fluid mechanics. We obtain a couple of reductions involving those coefficient functions, one of which is to the fourth Painlevé equation, while the other is to one of the second Painlevé equation, the

Bo Tian

1999-01-01

30

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

NASA Astrophysics Data System (ADS)

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

Wazwaz, Abdul-Majid; Triki, Houria

2011-03-01

31

EXPERIMENTAL MEASUREMENT OF PRECISION BEARING DYNAMIC STIFFNESS  

Microsoft Academic Search

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

E. R. Marsh; D. S. Yantek

1997-01-01

32

Arterial stiffness  

PubMed Central

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

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

2012-01-01

33

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

34

On the integrability of a generalized variable-coefficient Kadomtsev–Petviashvili equation  

Microsoft Academic Search

By considering the inhomogeneities of media, a generalized variable-coefficient Kadomtsev–Petviashvili (vc-KP) equation is investigated, which can be used to describe many nonlinear phenomena in fluid dynamics and plasma physics. In this paper, we systematically investigate the complete integrability of the generalized vc-KP equation under an integrable constraint condition. With the aid of generalized Bell’s polynomials, its bilinear formalism, bilinear Bäcklund

Shou-Fu Tian; Hong-Qing Zhang

2012-01-01

35

Recursion relations for generalized Fresnel coefficients: Casimir force in a planar cavity  

SciTech Connect

We emphasize and demonstrate that besides using the usual recursion relations involving successive layers, generalized Fresnel coefficients of a multilayer can equivalently be calculated using the recursion relations involving stacks of layers, as introduced some time ago [M. S. Tomas, Phys. Rev. A 51, 2545 (1995)]. Moreover, since the definition of the generalized Fresnel coefficients employed does not imply properties of the stacks, these nonstandard recursion relations can be used to calculate Fresnel coefficients not only for a local but also for a general multilayer consisting of various types (local, nonlocal, inhomogeneous, etc.) of layers. Their utility is illustrated by deriving a few simple algorithms for calculating the reflectivity of a Bragg mirror and extending the formula for the Casimir force in a planar cavity to arbitrary media.

Tomas, Marin-Slobodan [Rudjer Boskovic Institute, Post Office Box 180, HR-10002 Zagreb (Croatia)

2010-04-15

36

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

PubMed

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

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

2013-06-07

37

Exact Solutions for The Generalized Zakharov-Kuznetsov Equation with Variable Coefficients Using The Generalized (G'G)-expansion Method  

NASA Astrophysics Data System (ADS)

In this article, the generalized G'G-expansion method using a generalized wave transformation is applied to find exact traveling wave solutions of the generalized Zakharov-Kuznetsov equation with variable coefficients. As a result, hyperbolic, trigonometric and rational function solutions with parameters are obtained. When these parameters are taken special values, the solitary wave solutions are derived from the hyperbolic function solution. It is shown that the proposed method is direct, effective and can be applied to many other nonlinear evolution equations in mathematical physics.

Zayed, Elsayed M. E.; Abdelaziz, Mahmoud A. M.

2010-09-01

38

A generalized Benford's law for JPEG coefficients and its applications in image forensics  

Microsoft Academic Search

In this paper, a novel statistical model based on Benford's law for the probability distributions of the first digits of the block-DCT and quantized JPEG coefficients is presented. A parametric logarithmic law, i.e., the generalized Benford's law, is formulated. Furthermore, some potential applications of this model in image forensics are discussed in this paper, which include the detection of JPEG

Dongdong Fu; Yun Q. Shi; Wei Su

2007-01-01

39

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

40

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

41

Similarity Reductions for a Generalized Variable-Coefficient Kadomtsev-Petviashvili Equation with Symbolic Computation  

NASA Astrophysics Data System (ADS)

We use computerized symbolic computation to study the similarity reductions of a generalized Kadomtsev-Petviashvili (KP) equation, with its space- and time-dependent coefficients arising in plasma physics and fluid mechanics. We obtain a couple of reductions involving those coefficient functions, one of which is to the fourth Painlevé equation, while the other is to one of the second Painlevé equation, the first Painlevé equation or a Weierstrass elliptic function equation. Our results agree with the Painlevé Conjecture. The cylindrical KP equation is presented as an example, which describes nonlinear cylindrical water waves in shallow water with a weak azimuthal dependence.

Tian, Bo

42

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

NASA Astrophysics Data System (ADS)

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

Triki, Houria; Wazwaz, Abdul-Majid

2013-08-01

43

On the integrability of a generalized variable-coefficient Kadomtsev-Petviashvili equation  

NASA Astrophysics Data System (ADS)

By considering the inhomogeneities of media, a generalized variable-coefficient Kadomtsev-Petviashvili (vc-KP) equation is investigated, which can be used to describe many nonlinear phenomena in fluid dynamics and plasma physics. In this paper, we systematically investigate the complete integrability of the generalized vc-KP equation under an integrable constraint condition. With the aid of generalized Bell’s polynomials, its bilinear formalism, bilinear Bäcklund transformations, Lax pairs and Darboux covariant Lax pairs are succinctly constructed, which can be reduced to the ones of several integrable equations such as KdV, cylindrical KdV, KP, cylindrical KP, generalized cylindrical KP, non-isospectral KP equations, etc. Moreover, the infinite conservation laws of the equation are found by using its Lax equations. All conserved densities and fluxes are given with explicit recursion formulas. Furthermore, an extra auxiliary variable is introduced to obtain the bilinear formalism, based on which, the soliton solutions and Riemann theta function periodic wave solutions are presented. The influence of inhomogeneity coefficients on solitonic structures and interaction properties are discussed for physical interest and possible applications by some graphic analysis. Finally, a limiting procedure is presented to analyze in detail the asymptotic behavior of the periodic waves and the relations between the periodic wave solutions and soliton solutions.

Tian, Shou-Fu; Zhang, Hong-Qing

2012-02-01

44

New Multiple Soliton-like and Periodic Solutions for (2+1)Dimensional Canonical Generalized KP Equation with Variable Coefficients  

Microsoft Academic Search

In this paper, the generalized tanh function method is extended to (2+1)-dimensional canonical generalized KP (CGKP) equation with variable coefficients. Taking advantage of the Riccati equation, many explicit exact solutions, which contain multiple soliton-like and periodic solutions, are obtained for the (2+1)-dimensional CGKP equation with variable coefficients.

Zhang Li-Hua; Liu Xi-Qiang; Bai Cheng-Lin

2006-01-01

45

Solitonic interaction of a variable-coefficient (2 + 1)-dimensional generalized breaking soliton equation  

NASA Astrophysics Data System (ADS)

In fluids, Korteweg-de Vries-type equations are used to describe certain nonlinear phenomena. Studied in this paper is a variable-coefficient (2 + 1)-dimensional generalized breaking soliton equation, which models the interactions of Riemann waves with long waves. By virtue of the Bell-polynomial approach, bilinear forms of such an equation are obtained. N-soliton solutions are constructed in terms of the exponential functions and Wronskian determinant, respectively. Solitonic propagation and interaction are discussed with the following conclusions: (i) the appearance of characteristic lines such as the periodic and parabolic shapes depends on the form of the variable coefficients; and (ii) interactions of two solitons and three solitons are shown to be elastic.

Qin, Yi; Gao, Yi-Tian; Shen, Yu-Jia; Sun, Yu-Hao; Meng, Gao-Qing; Yu, Xin

2013-10-01

46

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

2013-06-14

47

Laminate Stiffnesses and Classical Laminate Theory.  

National Technical Information Service (NTIS)

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

J. W. Gunnink

1985-01-01

48

Moment-equation methods for calculating neoclassical transport coefficients in general toroidal plasmas  

SciTech Connect

A detailed comparison is made between moment-equation methods presented by H. Sugama and S. Nishimura [Phys. Plasmas 9, 4637 (2002)] and by M. Taguchi [Phys. Fluids B 4, 3638 (1992)] for calculating neoclassical transport coefficients in general toroidal plasmas including nonsymmetric systems. It is shown that these methods can be derived from the drift kinetic equation with the same collision model used for correctly taking account of collisional momentum conservation. In both methods, the Laguerre polynomials of the energy variable are employed to expand the guiding-center distribution function and to obtain the moment equations, by which the radial neoclassical transport fluxes and the parallel flows are related to the thermodynamic forces. The methods are given here in the forms applicable for an arbitrary truncation number of the Laguerre-polynomial expansion so that their accuracies can be improved by increasing the truncation number. Differences between results from the two methods appear when the Laguerre-polynomial expansion is truncated up to a finite order because different weight functions are used in them to derive the moment equations. At each order of the truncation, the neoclassical transport coefficients obtained from the Sugama-Nishimura method show the Onsager symmetry and satisfy the ambipolar-diffusion condition intrinsically for symmetric systems. Also, numerical examples are given to show how the transport coefficients converge with the truncation number increased for the two methods.

Sugama, H. [National Institute for Fusion Science, Toki 509-5292 (Japan); Graduate University for Advanced Studies, Toki 509-5292 (Japan); Nishimura, S. [National Institute for Fusion Science, Toki 509-5292 (Japan)

2008-04-15

49

Auto-Bäcklund transformation and exact solutions of the generalized variable-coefficient Kadomtsev Petviashvili equation  

NASA Astrophysics Data System (ADS)

Based on the idea of the homogeneous balance (HB) method, an auto-Bäcklund transformation (BT) to the generalized variable-coefficient Kadomtsev Petviashvili (GvcKP) equation is obtained with symbolic computation. By the use of the auto-BT and the ?-expansion method, we can obtain a soliton-like solution including N-solitary wave of the GvcKP equation. Especially, we get a soliton-like solution including two-solitary wave as an illustrative example in detail. Since the cylindrical KP (cKP) equation, the generalized cKP (GcKP) equation and the spherical KP (SKP) equation are all special cases of the GvcKP equation, we can also obtain the corresponding results of these equations respectively.

Liu, Jian-Guo; Li, Ye-Zhou

2008-11-01

50

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

51

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

52

Prognostic application of arterial stiffness: task forces  

Microsoft Academic Search

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

G. érard M London; Jay N. Cohn

2002-01-01

53

Large deflection analysis of beams with variable stiffness  

Microsoft Academic Search

Summary. In this paper, the Analog Equation Method (AEM), a BEM-based method, is employed to the nonlinear analysis of a Bernoulli-Euler beam with variable stiffness undergoing large deflections, under general boundary conditions which maybe nonlinear. As the cross-sectional properties of the beam vary along its axis, the coefficients of the differential equations governing the equilibrium of the beam are variable.

J. T. Katsikadelis; G. C. Tsiatas

2003-01-01

54

Non-linear dynamic analysis of beams with variable stiffness  

Microsoft Academic Search

In this paper the analog equation method (AEM), a BEM-based method, is employed to the non-linear dynamic analysis of a Bernoulli–Euler beam with variable stiffness undergoing large deflections, under general boundary conditions which maybe non-linear. As the cross-sectional properties of the beam vary along its axis, the coefficients of the differential equations governing the dynamic equilibrium of the beam are

J. T. Katsikadelis; G. C. Tsiatas

2004-01-01

55

Stiff person syndrome.  

PubMed

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

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

2011-10-01

56

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. 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 T is the total isospin of the system.) The

Deveikis, A.; Juodagalvis, A.

2008-10-01

57

GENERAL: Explicit Solutions of (2+1)Dimensional Canonical Generalized KP, KdV, and (2+1)Dimensional Burgers Equations with Variable Coefficients  

Microsoft Academic Search

In this paper, using the generalized (G'\\/G)-expansion method and the auxiliary differential equation method, we discuss the (2+1)-dimensional canonical generalized KP (CGKP), KdV, and (2+1)-dimensional Burgers equations with variable coefficients. Many exact solutions of the equations are obtained in terms of elliptic functions, hyperbolic functions, trigonometric functions, and rational functions.

Lin-Lin Zhang; Xi-Qiang Liu

2009-01-01

58

GENERAL: Explicit Solutions of (2+1)-Dimensional Canonical Generalized KP, KdV, and (2+1)-Dimensional Burgers Equations with Variable Coefficients  

NASA Astrophysics Data System (ADS)

In this paper, using the generalized (G'/G)-expansion method and the auxiliary differential equation method, we discuss the (2+1)-dimensional canonical generalized KP (CGKP), KdV, and (2+1)-dimensional Burgers equations with variable coefficients. Many exact solutions of the equations are obtained in terms of elliptic functions, hyperbolic functions, trigonometric functions, and rational functions.

Zhang, Lin-Lin; Liu, Xi-Qiang

2009-11-01

59

Generalized entering coefficients: A criterion for foam stability against oil in porous media  

SciTech Connect

The unique mobility-control properties of foam in porous media make it an attractive choice as an injection fluid for enhanced oil recovery. Unfortunately, in many cases oil has a major destabilizing effect on foam. Therefore, it is important to understand how oil destabilizes foam and what surfactant properties lead to increased stability against oil. To explain the stability of foam in porous media in the presence of oil, we generalize the ideas of spreading and entering behavior using Frumkin-Deryaguin wetting theory. This formulation overcomes the inherent deficiencies in the classical spreading and entering coefficients used to explain foam stability against oil. We find that oil-tolerant foam can be produced by making the oil surface ``water wet``. To test our theoretical ideas, we measure foam-flow resistance through 45--70 {mu}m glass beadpacks, surface and interfacial tensions, and disjoining pressure isotherms for foam and pseudoemulsion films for a variety of surfactant/oil systems. Most notably, we measure pseudoemulsion-film disjoining pressure isotherms for the first time and directly establish that pseudoemulsion film stability controls the stability of the foam in the systems we tested. Moreover, we demonstrate the correspondence between stable pseudoemulsion films, negative entering behavior, and oil-tolerant foams.

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

1993-09-01

60

New doubly periodic and multiple soliton solutions of the generalized (3 + 1)-dimensional Kadomtsev–Petviashvilli equation with variable coefficients  

Microsoft Academic Search

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

Hong Zhao; Chenglin Bai

2006-01-01

61

PHYSICS OF ELEMENTARY PARTICLES AND FIELDS: Extended Symmetry of Generalized Variable-Coefficient Kadomtsev-Petviashvili Equation  

NASA Astrophysics Data System (ADS)

In this paper, the extended symmetry of generalized variable-coefficient Kadomtsev-Petviashvili (vcKP) equation is investigated by the extended symmetry group method with symbolic computation. Then on the basis of the extended symmetry, we can establish relation among some different kinds of vcKP equations. Thus the exact solutions of these vcKP equations can be constructed via the simple vcKP equations or constant-coefficient KP equations.

Wang, Jia; Li, Biao; Ye, Wang-Chuan

2010-04-01

62

PHYSICS OF ELEMENTARY PARTICLES AND FIELDS: Extended Symmetry of Generalized Variable-Coefficient Kadomtsev-Petviashvili Equation  

Microsoft Academic Search

In this paper, the extended symmetry of generalized variable-coefficient Kadomtsev-Petviashvili (vcKP) equation is investigated by the extended symmetry group method with symbolic computation. Then on the basis of the extended symmetry, we can establish relation among some different kinds of vcKP equations. Thus the exact solutions of these vcKP equations can be constructed via the simple vcKP equations or constant-coefficient

Jia Wang; Biao Li; Wang-Chuan Ye

2010-01-01

63

Determinant of leg stiffness during hopping is frequency-dependent.  

PubMed

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

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

2011-02-12

64

Auto-Bäcklund Transformation and Soliton-Type Solutions of the Generalized Variable-Coefficient Kadomtsev Petviashvili Equation  

Microsoft Academic Search

Using the truncated Painlevé expansion, an auto-Bäcklund transformation and soliton-type solutions of the generalized variable-coefficient Kadomtsev-Petviashvili (GKP) equation are obtained by symbolic computation. Since the cylindrical Korteweg-de Vries (cKdV) equation, the cylindrical KP (cKP) equation and the generalized cKP (GcKP) equation are all special cases of the GKP equation, we can also obtain the corresponding results of these equations.

Jian-Guo Liu; Ye-Zhou Li; Guang-Mei Wei

2006-01-01

65

Auto-Bäcklund Transformation and Soliton-Type Solutions of the Generalized Variable-Coefficient Kadomtsev Petviashvili Equation  

NASA Astrophysics Data System (ADS)

Using the truncated Painlevé expansion, an auto-Bäcklund transformation and soliton-type solutions of the generalized variable-coefficient Kadomtsev-Petviashvili (GKP) equation are obtained by symbolic computation. Since the cylindrical Korteweg-de Vries (cKdV) equation, the cylindrical KP (cKP) equation and the generalized cKP (GcKP) equation are all special cases of the GKP equation, we can also obtain the corresponding results of these equations.

Liu, Jian-Guo; Li, Ye-Zhou; Wei, Guang-Mei

2006-07-01

66

On an Auto-Bäcklund Transformation for (2+1)Dimensional Variable Coefficient Generalized KP Equations and Exact Solutions  

Microsoft Academic Search

By the application of the extended homogeneous balance method, we derive an auto-Bäcklund transformation (BT) for (2+1)-dimensional variable coefficient generalized KP equations. Based on the BT, in which there are two homogeneity equations to be solved, we obtain some exact solutions containing single solitary waves.

Bai Cheng-Jie; Bai Cheng-Lin; Han Ji-Guang; Zhao Hong

2005-01-01

67

Symmetry Groups and New Exact Solutions to (2+1)Dimensional Variable Coefficient Canonical Generalized KP Equation  

Microsoft Academic Search

In this paper, the modified CK's direct method to find symmetry groups of nonlinear partial differential equation is extended to (2+1)-dimensional variable coefficient canonical generalized KP (VCCGKP) equation. As a result, symmetry groups, Lie point symmetry group and Lie symmetry for the VCCGKP equation are obtained. In fact, the Lie point symmetry group coincides with that obtained by the standard

Zhang Li-Hua; Liu Xi-Qiang; Bai Cheng-Lin

2007-01-01

68

Stiff-Person Syndrome  

MedlinePLUS

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

69

Auto-Bäcklund transformation and exact solutions of the generalized variable-coefficient Kadomtsev-Petviashvili equation  

Microsoft Academic Search

Based on the idea of the homogeneous balance (HB) method, an auto-Bäcklund transformation (BT) to the generalized variable-coefficient Kadomtsev–Petviashvili (GvcKP) equation is obtained with symbolic computation. By the use of the auto-BT and the ?-expansion method, we can obtain a soliton-like solution including N-solitary wave of the GvcKP equation. Especially, we get a soliton-like solution including two-solitary wave as an

Jian-Guo Liu; Ye-Zhou Li

2008-01-01

70

General Approach for the Estimation of Octanol\\/Water Partition Coefficient by Reversed-Phase High-Performance Liquid Chromatography  

Microsoft Academic Search

General approach for the relation of reversed-phase high-performance liquid chromatographic retention behaviour to the hydrophobic properties of drugs was developed. Hydrophobicity of compounds was characterized by the logarithm of 1-octanol\\/water partition coefficient (log Po\\/w). Reversed-phase retention times of 26 model compounds (log Po\\/w values of them ranged from ?1.22 to 3.84) were measured using 3 to 5 different mixture of

Klára Valkó

1984-01-01

71

A Generalized Variable-Coefficient Algebraic Method Exactly Solving (3+1)-Dimensional Kadomtsev-Petviashvilli Equation  

NASA Astrophysics Data System (ADS)

A generalized variable-coefficient algebraic method is applied to construct several new families of exact solutions of physical interest for (3+1)-dimensional Kadomtsev-Petviashvilli (KP) equation. Among them, the Jacobi elliptic periodic solutions exactly degenerate to the soliton solutions at a certain limit condition. Compared with the existing tanh method, the extended tanh method, the Jacobi elliptic function method, and the algebraic method, the proposed method gives new and more general solutions. The project supported by National Natural Science Foundation of China and the Natural Science Foundation of Shandong Province of China under Grant No. 2004ZX16

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

2005-11-01

72

Rotordynamic Coefficients of Short Labyrinth Gas Seals—General Dependency on Geometric and Physical Parameters  

Microsoft Academic Search

It is absolutely essential to predict the forces generated in labyrinth seals of turbomachinery as accurately as possible, and it is helpful to clearly specify which options are available in order to improve the dynamic behavior of the seal. With regard to seals operated with compressible fluids, the few general overviews included in the technical literature are mostly based on

K. Kwanka

2007-01-01

73

Stiff person syndrome.  

PubMed

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

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

2013-02-01

74

Solvability of general backward stochastic Volterra integral equation with non-Lipschitz coefficients  

Microsoft Academic Search

In this paper we study the unique solvability of backward stochastic Volterra integral equations (BSVIEs in short), in terms of both the M-solutions introduced in [17] and the adapted solutions in [6], [12] or [14]. A general existence and uniqueness of M-solutions is proved under non-Lipschitz conditions by virtue of a briefer argument than the one in [17], which also

Tianxiao Wang; Yufeng Shi

2010-01-01

75

Arterial Stiffness and Dialysis Calcium Concentration  

PubMed Central

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

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

2011-01-01

76

Discrimination of individuals in a general population at high-risk for alcoholic and non-alcoholic fatty liver disease based on liver stiffness: a cross section study  

PubMed Central

Background Factors associated with liver stiffness (LS) are unknown and normal reference values for LS have not been established. Individuals at high risk for alcoholic (ALD) and non-alcoholic fatty (NAFLD) liver disease need to be non-invasively discriminated during routine health checks. Factors related to LS measured using a FibroScan and normal reference values for LS are presented in this report. Methods We measured LS using a FibroScan in 416 consecutive individuals who presented for routine medical checks. We also investigated the relationship between LS and age, body mass index (BMI), liver function (LF), alcohol consumption, and fatty liver determined by ultrasonography. We identified individuals at high-risk for ALD and NAFLD as having a higher LS value than the normal upper limit detected in 171 healthy controls. Results The LS value for all individuals was 4.7 +/- 1.5 kPa (mean +/- SD) and LS significantly and positively correlated with BMI and LF test results. The LS was significantly higher among individuals with, than without fatty liver. Liver stiffness in the 171 healthy controls was 4.3 +/- 0.81 kPa and the upper limit of LS in the normal controls was 5.9 kPa. We found that 60 (14.3%) of 416 study participants had abnormal LS. The proportion of individuals whose LS values exceeded the normal upper limit was over five-fold higher among those with, than without fatty liver accompanied by abnormal LF test results. Conclusions Liver stiffness could be used to non-invasively monitor the progression of chronic liver diseases and to discriminate individuals at high risk for ALD and NAFLD during routine health assessments.

2011-01-01

77

Materials with negative stiffness  

NASA Astrophysics Data System (ADS)

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

Jaglinski, Tim

78

High stiffness gas journal bearing under the step force  

Microsoft Academic Search

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

K. Czolczynski; L. Brzeski; Z. Kazimierski

1993-01-01

79

Stiff Person Syndrome  

Microsoft Academic Search

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

Martin E. Duddy; Mark R. Baker

2009-01-01

80

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

NASA Astrophysics Data System (ADS)

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

Veeraklaew, Tawiwat

2012-11-01

81

A new method of new exact solutions and solitary wave-like solutions for the generalized variable coefficients Kadomtsev Petviashvili equation  

Microsoft Academic Search

Using the solution of general Korteweg-de Vries (KdV) equation, the solutions of the generalized variable coefficient Kadomtsev-Petviashvili (KP) equation are constructed, and then its new solitary wave-like solution and Jacobi elliptic function solution are obtained.

Jie-Jian Mao; Jian-Rong Yang

2006-01-01

82

Stiff-person syndrome  

Microsoft Academic Search

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

Olavo M. Vasconcelos; Marinos C. Dalakas

2003-01-01

83

Exact self-similar wave solutions for the generalized (3 + 1)-dimensional cubic-quintic nonlinear Schröinger equation with distributed coefficients  

NASA Astrophysics Data System (ADS)

In this paper, a similarity transformation is presented to reduce the generalized (3 + 1)-dimensional cubic-quintic nonlinear Schrödinger equation with distributed coefficients to the related constant-coefficients one. Then a number of spatiotemporal self-similar wave solutions are constructed. Under the specific choice of the dispersion, cubic and quintic nonlinearities, phase modulation and the gain/loss, we investigate the dynamical behaviors of those spatiotemporal self-similar waves in an inhomogeneous optical fiber media.

Liu, Xiao-Bei; Zhang, Xiao-Fei; Li, Biao

2012-03-01

84

Bäcklund transformation, non-local symmetry and exact solutions for (2+1)-dimensional variable coefficient generalized KP equations  

Microsoft Academic Search

With the aid of MATHEMATICA, the idea of improved homogeneous balance method is extended to (2+1)-dimensional variable coefficients KP equation. As a result, Bäcklund transformation and non-local symmetry are found. Then via using the Bäcklund transformation, six families of exact solutions for (2+1)-dimensional variable coefficients KP equation are obtained, which contain new soliton-like solutions.

Zhenya Yan

2000-01-01

85

Reflectional transformation for structural stiffness  

SciTech Connect

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

Vashi, K.M.

1990-01-01

86

Generalized Expressions of Effective Nonlinear Optical Coefficient for Non-collinear Phase Matching in Uniaxial and Cubic Media.  

National Technical Information Service (NTIS)

The conditions of non-collinear phase matched frequency conversion are analyzed and the corresponding expressions of the effective nonlinear optical coefficient (deff) for 13 classes of uniaxial crystals and 3 classes of cubic crystals are derived. The di...

K. Yang S. Tripathy J. Kumar

1997-01-01

87

An Evaluation of Passive Automotive Suspension Systems with Variable Stiffness and Damping Parameters  

Microsoft Academic Search

Passenger discomfort, suspension working space and dynamic tyre loading parameters are calculated for different combinations of spring stiffness and damping coefficient representing the suspension system in a quarter car model subject to realistic random disturbance inputs from roads of widely differing quality. Sprung and unsprung masses and the tyre vertical stiffness and damping coefficient employed derive from a current production

R. S. Sharp; S. A. Hassan

1986-01-01

88

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

89

Pulling a polymer with anisotropic stiffness near a sticky wall  

NASA Astrophysics Data System (ADS)

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

Tabbara, R.; Owczarek, A. L.

2012-11-01

90

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

91

Auto-Baecklund transformation and new exact solutions of the generalized variable-coefficients two-dimensional Korteweg-de Vries model  

SciTech Connect

Describing plasma physics, cluster physics, and geophysical fluid dynamics, a generalized variable-coefficient two-dimensional Korteweg-de Vries (GVCKdV) model is hereby under investigation. In this paper, an extended-variable-coefficient homogeneous balance method with symbolic computation is used to obtain an auto-Baecklund transformation, some rational solutions, and new soliton-type solutions for the GVCKdV model. The solutions of the well-known cylindrical Kadomtsev-Petviashvili equation can be recovered as special cases of the results obtained here.

Li Yezhou; Liu Jianguo [School of Science, Beijing University of Posts and Telecommunications, P.O. Box 91, Beijing 100876 (China)

2007-02-15

92

In-plane stiffness of shear walls with openings  

Microsoft Academic Search

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

M. Qamaruddin

1998-01-01

93

Stiff Heart Syndrome  

PubMed Central

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

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

2011-01-01

94

Stiff heart syndrome.  

PubMed

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

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

2010-09-17

95

Tectorial Membrane Stiffness Gradients  

PubMed Central

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

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

2007-01-01

96

Properties of the grasp stiffness matrix and conservative control strategies  

SciTech Connect

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

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

1999-02-01

97

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

SciTech Connect

In this paper, the multisoliton solutions in terms of double Wronskian determinant are presented for a generalized variable-coefficient nonlinear Schroedinger 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 can be proved that the bilinear Baecklund transformation transforms between (N - 1)- and N-soliton solutions.

Lue Xing [School of Science, P.O. Box 122, Beijing University of Posts and Telecommunications, Beijing 100876 (China)], E-mail: xinglv655@yahoo.com.cn; Zhu Hongwu; Yao Zhenzhi; Meng Xianghua; Zhang Cheng [School of Science, P.O. Box 122, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Zhang Chunyi [Ministry-of-Education Key Laboratory of Fluid Mechanics and National Laboratory for Computational Fluid Dynamics, Beijing University of Aeronautics and Astronautics, Beijing 100083 (China); Meteorology Center of Air Force Command Post, Changchun 130051 (China); Tian Bo [School of Science, P.O. Box 122, Beijing University of Posts and Telecommunications, Beijing 100876 (China); State Key Laboratory of Software Development Environment, Beijing University of Aeronautics and Astronautics, Beijing 100083 (China); Key Laboratory of Optical Communication and Lightwave Technologies, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing 100876 (China)], E-mail: gaoyt@public.bta.net.cn

2008-08-15

98

Terrace width distributions for vicinal surfaces with steps of alternating stiffness  

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

99

New doubly periodic and multiple soliton solutions of the generalized (3+1)-dimensional KP equation with variable coefficients  

Microsoft Academic Search

A new generalized Jacobi elliptic function method is used to construct the exact travelling wave solutions of nonlinear partial differential equations (PDEs) in a unified way. The main idea of this method is to take full advantage of the elliptic equation which has more new solutions. More new doubly periodic and multiple soliton solutions are obtained for the generalized (3+1)-dimensional

Huai-Tang Chen; Hong-Qing Zhang

2003-01-01

100

The influence of artificially increased trunk stiffness on the balance recovery after a trip  

Microsoft Academic Search

Falls occur frequently in the growing population of elderly. Since trunk control is critical for maintaining balance, the higher trunk stiffness in elderly people compared to the general population has been associated with their increased fall-risk. Theoretically, trunk stiffness may be beneficial for balance recovery in walking, i.e. after a trip. A stiff joint may provide a torque that restricts

J. C. E. van der Burg; M. Pijnappels; J. H. van Dieën

2007-01-01

101

Topology design of material layout in structured composites of high stiffness and strength  

Microsoft Academic Search

General continuous topology design formulations based on families of classical Voigt and Reuss mixing assumptions are developed and applied to solve the multiple material layout problem for the design of high stiffness\\/high strength composites. In the novel design framework, computational homogenization is employed to compute stiffness and strength characteristics of individual composite designs. Alternative design formulations for both high stiffness

C. C. Swan; J. S. Arora

1997-01-01

102

Parametric Frequency Domain Identification Using Variable Stiffness and Damping Devices.  

National Technical Information Service (NTIS)

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

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

2003-01-01

103

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

104

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

ERIC Educational Resources Information Center

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

Howell, Ryan T.; Shields, Alan L.

2008-01-01

105

Using Dominance Relationship Coefficients Based on Linkage Disequilibrium and Linkage With a General Complex Pedigree to Increase Mapping Resolution  

Microsoft Academic Search

Dominance (intralocus allelic interactions) plays often an important role in quantitative trait variation. However, few studies about dominance in QTL mapping have been reported in outbred animal or human populations. This is because common dominance effects can be predicted mainly for many full sibs, which do not often occur in outbred or natural populations with a general pedigree. Moreover, incomplete

S. H. Lee

2006-01-01

106

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

Microsoft Academic Search

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

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

2008-01-01

107

Dynamic stiffness removal for direct numerical simulations  

SciTech Connect

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

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

2009-08-15

108

Differential quadrature solution for the free vibration analysis of laminated conical shells with variable stiffness  

Microsoft Academic Search

The free vibration analysis of laminated conical shells with variable stiffness is presented using the method of differential quadrature (DQ). The stiffness coefficients are assumed to be functions of the circumferential coordinate that may be more close to the realistic applications. The first-order shear deformation shell theory is used to account for the effects of transverse shear deformations. In the

Chih-Ping Wu; Chia-Ying Lee

2001-01-01

109

Digital-map grids of mean-annual precipitation for 1961-90, and generalized skew coefficients of annual maximum streamflow for Oklahoma  

USGS Publications Warehouse

This digital report contains two digital-map grids of data that were used to develop peak-flow regression equations in Tortorelli, 1997, 'Techniques for estimating peak-streamflow frequency for unregulated streams and streams regulated by small floodwater retarding structures in Oklahoma,' U.S. Geological Survey Water-Resources Investigations Report 97-4202. One data set is a grid of mean annual precipitation, in inches, based on the period 1961-90, for Oklahoma. The data set was derived from the PRISM (Parameter-elevation Regressions on Independent Slopes Model) mean annual precipitation grid for the United States, developed by Daly, Neilson, and Phillips (1994, 'A statistical-topographic model for mapping climatological precipitation over mountainous terrain:' Journal of Applied Meteorology, v. 33, no. 2, p. 140-158). The second data set is a grid of generalized skew coefficients of logarithms of annual maximum streamflow for Oklahoma streams less than or equal to 2,510 square miles in drainage area. This grid of skew coefficients is taken from figure 11 of Tortorelli and Bergman, 1985, 'Techniques for estimating flood peak discharges for unregulated streams and streams regulated by small floodwater retarding structures in Oklahoma,' U.S. Geological Survey Water-Resources Investigations Report 84-4358. To save disk space, the skew coefficient values have been multiplied by 100 and rounded to integers with two significant digits. The data sets are provided in an ASCII grid format.

Rea, A. H.; Tortorelli, R. L.

1997-01-01

110

Posttraumatic Stiffness in the Hand  

Microsoft Academic Search

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

Matthew D. Putnam

1996-01-01

111

Hormones and arterial stiffness in patients with chronic kidney disease.  

PubMed

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

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

2013-08-02

112

Generalization of the thermal lens model formalism to account for thermodiffusion in a single-beam Z-scan experiment: determination of the Soret coefficient  

NASA Astrophysics Data System (ADS)

A generalization of the thermal lens model formalism is proposed to introduce and characterize the thermodiffusion phenomenon. The theory treats the case in which local heating generates a temperature gradient in a single-phase binary sample (a colloid, for instance) that yields, through thermodiffusion, concentration gradients in an initially homogeneous sample. The treatment generalizes the concept of a thermal lens to a material lens as a result of the coupling of a concentration variation with the optical properties of the medium. This formalism permits the use of the Z-scan technique to determine the Soret coefficient of samples. Applying this theory to the results of a Z-scan experiment with an ionic ferrofluid sample gives values that agree with those obtained from forced Rayleigh scattering measurements of the same material.

Alves, S.; Bourdon, A.; Neto, A. M. Figueiredo

2003-04-01

113

Various local stiffness characterizations of single cells using buckling nanoneedles  

Microsoft Academic Search

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

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

2009-01-01

114

Terrace Width Distributions for Steps of Alternating Stiffness  

NASA Astrophysics Data System (ADS)

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

Yancey, Jeremy; Richards, Howard L.

2003-03-01

115

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

116

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

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

117

Elastic coefficients of animal bone.  

PubMed

The elastic stiffness coefficients of dried bovine phalanx and femur and of fresh bovine phalanx were measured by an ultrasonic technique. An analysis of the crystallographic structure of the principal components of bone and its piezoelectric and pyroelectric behavior showed that bone is a texture that has the same elastic coeffcient matrix as a hexagonal single crystal. The five elastic stiffness coefficients of fresh phalanx are: C(1l), 1.97; C(12), 1.21; C(13), 1.26; C(33), 3.20; and C(44), 0.54 (all in units of 10(11) dynes per square centimeter). Value of axial and transverse Young's and shear moduli, compressibility, and the three Poisson's ratios were calculated. PMID:5787984

Lang, S B

1969-07-18

118

Frequency Effects in Tilting-Pad Journal Bearing Dynamic Coefficients  

Microsoft Academic Search

This paper examines the effects of damped vibrational frequencies on the linear reduced dynamical stiffness and damping coefficients of tilting-pad journal bearings. The frequency ratio (damped frequency\\/running speed) can be used to judge the accuracy of employing synchronously reduced linear coefficients in rotordynamic stability analyses. The use of these coefficients can result in simpler formulations of the system dynamical equations

J. K. Parsell; P. E. Allaire; L. E. Barrett

1983-01-01

119

Efficacy of pregabalin in a case of stiff-person syndrome: Clinical and neurophysiological evidence  

Microsoft Academic Search

Symptomatic treatment of stiff-person syndrome (SPS) might be challenging and a significant improvement of stiffness and rigidity is generally reached with high doses of benzodiazepines or baclofen causing side effects.A 71-year old woman diagnosed with SPS complained of marked stiffness of trunk and lower limb muscles with sudden painful spasms. She was unable to walk and she could not lean

G. Squintani; T. Bovi; L. Ferigo; A. M. Musso; S. Ottaviani; G. Moretto; F. Morgante; M. Tinazzi

120

A position and stiffness control strategy for variable stiffness actuators  

Microsoft Academic Search

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

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

2012-01-01

121

Smart variable stiffness control systems  

NASA Astrophysics Data System (ADS)

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

Nagarajaiah, Satish; Varadarajan, Nadathur

2001-07-01

122

On the geometry of stiff knots  

NASA Astrophysics Data System (ADS)

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

Pierre-Louis, Olivier

2009-03-01

123

Design of variable-stiffness composite panels for maximum buckling load  

Microsoft Academic Search

A generalized reciprocal approximation is presented for design of variable-stiffness laminated composite panels for maximum buckling load. The buckling load is expanded in terms of the inverse of the stiffness tensor. For discretized panels such an approximation has the important property of being separable, which allows the maximization to be carried out at each discrete node separate from the others.

Shahriar Setoodeh; Mostafa M. Abdalla; Samuel T. IJsselmuiden; Zafer Gürdal

2009-01-01

124

Anesthetic management of a patient with stiff person syndrome  

Microsoft Academic Search

We describe the successful anesthetic management of a patient with stiff-person syndrome (SPS) undergoing a right inguinal hernia repair, using a somatic paravertebral block supplemented with conscious sedation. We also present the implications of general anesthesia in patients with SPS. The use of regional anesthetic techniques in patients with SPS has the advantage of avoiding exposure to muscle relaxants. The

Nabil Elkassabany; John E. Tetzlaff; Maged Argalious

2006-01-01

125

Reduced-Stiffness Method in the Theory of Shells  

Microsoft Academic Search

The fundamentals of the reduced-stiffness method, which is used in buckling analysis of reinforced and perfect and imperfect nonreinforced shells, are set out. The method is validated analytically and experimentally. The lower bound determined by this method is very close to the experimental lower bound. Some aspects of the current state and prospects for development and generalization of the method

G. D. Gavrilenko; J. G. A. Croll

2004-01-01

126

The correlation between mineralization degree and bone tissue stiffness in the porcine mandibular condyle.  

PubMed

The aim of this study was to correlate the local tissue mineral density (TMD) with the bone tissue stiffness. It was hypothesized that these variables are positively correlated. Cancellous and cortical bone samples were derived from ten mandibular condyles taken from 5 young and 5 adult female pigs. The bone tissue stiffness was assessed in three directions using nanoindentation. At each of three tested sides 5 indents were made over the width of 5 single bone elements, resulting in a total number of 1500 indents. MicroCT was used to determine the local TMD at the indented sites. The TMD and the bone tissue stiffness were higher in bone from the adult animals than from the young ones, but did not differ between cancellous and cortical bone. In the adult group, both the TMD and the bone tissue stiffness were higher in the center than at the surface of the bone elements. The mean TMD, thus ignoring the local mineral distribution, had a coefficient of determination (R (2)) with the mean bone tissue stiffness of 0.55, p < 0.05, whereas the correlation between local bone tissue stiffness and the concomitant TMD appeared to be weak (R (2) 0.07, p < 0.001). It was concluded that the mineralization degree plays a larger role in bone tissue stiffness in cancellous than in cortical bone. Our data based on bone from the mandibular condyle suggest that the mineralization degree is not a decisive determinant of the local bone tissue stiffness. PMID:23624768

Willems, Nop M B K; Mulder, Lars; den Toonder, Jaap M J; Zentner, Andrej; Langenbach, Geerling E J

2013-04-28

127

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

NASA Astrophysics Data System (ADS)

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

Gunduz, Aydin; Singh, Rajendra

2013-10-01

128

Resonance suppression through variable stiffness and damping mechanisms  

NASA Astrophysics Data System (ADS)

This paper describes the modifications in the dynamic behavior of a building structure when devices with variable stiffness and damping are installed in parallel with a low- damping isolation system. The results of eigen-value analyses of linear-elastic structural models with varying degrees of isolation stiffness and damping direct the subsequent design of a semi-active deice. A hydraulic semi- active actuator is designed to minimize an H2 norm of the closed loop system. Details regarding the energy storage mechanisms of the device are retained in the device model. The energy dissipation mechanisms are idealized to be viscous in nature. The actuator behaves essentially as a visco-elastic Maxwell element with a variable damping coefficient. The response time of the control-valve mechanism in this actuator is studied to reveal the relative benefits of a valve that is fast to open and valve that is fast to close. Device parameters that result in a variable damping and variable damping and variable stiffness properties are given. A model-independent, bang-bang, control rule is employed to illustrate the closed loop control system when variable damping and variable stiffness embodiments are deployed. Rules governing the placement of device with this control rule are given when the device is primarily dissipative.

Gavin, Henri P.; Doke, Nitin S.

1999-05-01

129

Arterial stiffness: a brief review  

PubMed Central

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

SHIRWANY, Najeeb A; ZOU, Ming-hui

2011-01-01

130

STIFF: Converting Scientific FITS Images to TIFF  

NASA Astrophysics Data System (ADS)

STIFF is a program that converts scientific FITS1 images to the more popular TIFF2 format for illustration purposes. Most FITS readers and converters do not do a proper job at converting FITS image data to 8 bits. 8-bit images stored in JPEG, PNG or TIFF files have the intensities implicitely stored in a non-linear way. Most current FITS image viewers and converters provide the user an incorrect translation of the FITS image content by simply rescaling linearly input pixel values. A first consequence is that the people working on astronomical images usually have to apply narrow intensity cuts or square-root or logarithmic intensity transformations to actually see something on their deep-sky images. A less obvious consequence is that colors obtained by combining images processed this way are not consistent across such a large range of surface brightnesses. Though with other software the user is generally afforded a choice of nonlinear transformations to apply in order to make the faint stuff stand out more clearly in the images, with the limited selection of choices provides, colors will not be accurately rendered, and some manual tweaking will be necessary. The purpose of STIFF is to produce beautiful pictures in an automatic and consistent way.

Bertin, Emmanuel

2011-10-01

131

[Stiff man syndrome and variants].  

PubMed

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

Meinck, H-M

2013-04-01

132

Stiff person syndrome: avoiding misdiagnosis  

Microsoft Academic Search

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

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

2007-01-01

133

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

PubMed Central

Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as prostheses and orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75–2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R2 > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.

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

2013-01-01

134

Enhanced Stiffness Modeling, Identification and Characterization for Robot Manipulators  

Microsoft Academic Search

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

Gürsel Alici; Bijan Shirinzadeh

2005-01-01

135

Painlevé analysis, Lax pair, Bäcklund transformation and multi-soliton solutions for a generalized variable-coefficient KdV-mKdV equation in fluids and plasmas  

NASA Astrophysics Data System (ADS)

In this paper, a variable-coefficient non-isospectral Korteweg-de Vries-modified Korteweg-de Vries equation arising in fluids and plasmas is investigated. The integrability of such an equation is studied with Painlevé analysis. Under the integrable condition obtained, the Lax pair is also established through the Ablowitz-Kaup-Newell-Segur procedure. The equation is transformed into its bilinear form by virtue of which the multi-soliton/breather solutions and Bäcklund transformation are derived. Soliton propagation, multi-soliton, soliton-breather and breather-breather interactions are studied: different types of solitary waves can be seen with the change of variable coefficients, the existence of compression or broadening depends on the sign of the non-uniformity coefficient, and during the soliton-breather interaction, the propagating direction of the breather is not influenced by the elevation (positive amplitude) or depression (negative amplitude) soliton.

Meng, Gao-Qing; Gao, Yi-Tian; Yu, Xin; Shen, Yu-Jia; Qin, Yi

2012-05-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

137

Simulation methods with extended stability for stiff biochemical Kinetics  

PubMed Central

Background With increasing computer power, simulating the dynamics of complex systems in chemistry and biology is becoming increasingly routine. The modelling of individual reactions in (bio)chemical systems involves a large number of random events that can be simulated by the stochastic simulation algorithm (SSA). The key quantity is the step size, or waiting time, ?, whose value inversely depends on the size of the propensities of the different channel reactions and which needs to be re-evaluated after every firing event. Such a discrete event simulation may be extremely expensive, in particular for stiff systems where ? can be very short due to the fast kinetics of some of the channel reactions. Several alternative methods have been put forward to increase the integration step size. The so-called ?-leap approach takes a larger step size by allowing all the reactions to fire, from a Poisson or Binomial distribution, within that step. Although the expected value for the different species in the reactive system is maintained with respect to more precise methods, the variance at steady state can suffer from large errors as ? grows. Results In this paper we extend Poisson ?-leap methods to a general class of Runge-Kutta (RK) ?-leap methods. We show that with the proper selection of the coefficients, the variance of the extended ?-leap can be well-behaved, leading to significantly larger step sizes. Conclusions The benefit of adapting the extended method to the use of RK frameworks is clear in terms of speed of calculation, as the number of evaluations of the Poisson distribution is still one set per time step, as in the original ?-leap method. The approach paves the way to explore new multiscale methods to simulate (bio)chemical systems.

2010-01-01

138

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

PubMed

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

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

2013-03-01

139

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

140

Stiff person syndrome presenting with sudden onset of shortness of breath and difficulty moving the right arm: a case report  

Microsoft Academic Search

INTRODUCTION: First described in 1956, stiff person syndrome is characterized by episodes of slowly progressive stiffness and rigidity in both the paraspinal and limb muscles. Although considered a rare disorder, stiff person syndrome is likely to be under-diagnosed due to a general lack of awareness of the disease in the medical community. CASE PRESENTATION: A 27-year-old Hispanic woman presented to

Bradley Goodson; Kate Martin; Thomas Hunt

2010-01-01

141

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

Microsoft Academic Search

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

C. E. English; D. Russell

1999-01-01

142

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

Microsoft Academic Search

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

Z. Gürdal; B. F. Tatting; C. K. Wu

2008-01-01

143

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

Microsoft Academic Search

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

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

2012-01-01

144

Effects of chain stiffness and penetrant size on penetrant diffusion in simple polymers: deduced relations from simulation and PRISM theory  

Microsoft Academic Search

Molecular dynamics simulations in the NVT ensemble were performed for a repulsive system of bead-spring polymer chains with angle constraints. The diffusion coefficients of spherical penetrants were measured for different size penetrants as the angle constraints were varied. The scaling of the diffusion coefficient with penetrant size varies as a function of chain stiffness from liquid-like behavior to polymeric behavior.

Joanne Budzien; John D. McCoy; Dana Rottach; John G. Curro

2004-01-01

145

Dynamic Contact Stiffness of Adhesive Hertzian Contact  

Microsoft Academic Search

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

Jiayong Tian

2011-01-01

146

Anesthetic Implications in Stiff-Person Syndrome  

Microsoft Academic Search

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

Joel O. Johnson; Kirk A. Miller

1995-01-01

147

Study on Torsional Stiffness of Engine Crankshaft  

Microsoft Academic Search

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

Zhao Guangming; Jiang Zhengfeng

2009-01-01

148

Mechanisms, Pathophysiology, and Therapy of Arterial Stiffness  

Microsoft Academic Search

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

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

2010-01-01

149

Increased arterial stiffness in children on haemodialysis  

Microsoft Academic Search

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

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

150

Stiffness Control of Surgical Continuum Manipulators  

Microsoft Academic Search

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

Mohsen Mahvash; Pierre E. Dupont

2011-01-01

151

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

National Technical Information Service (NTIS)

A rigid vertical shaft was operated with known amounts of unbalance at speeds to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. Th...

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

1976-01-01

152

Spontaneous wrinkle branching by gradient stiffness  

NASA Astrophysics Data System (ADS)

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

Ni, Yong; Yang, Dong; He, Linghui

2012-09-01

153

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

PubMed

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

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

2012-11-29

154

Analysis and Design of Variable Stiffness Composite Cylinders.  

National Technical Information Service (NTIS)

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

B. F. Tatting Z. Guerdal

1998-01-01

155

Influence of wavy imperfections in cell walls on elastic stiffness of cellular solids  

Microsoft Academic Search

The stiffness of open and closed cell low density cellular solids, or solid foams, is affected by “imperfections” such as non-uniform cell size (multi-dispersity), non-uniform cell wall thickness, wavy distortions of cell walls, etc. Metal foams generally have lower relative stiffnesses than, for example, expanded PVC based polymer foams, and a comparison of the morphologies suggests that the main difference

Joachim L. Grenestedt

1998-01-01

156

Model-based estimation of knee stiffness.  

PubMed

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

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

2012-07-11

157

Model-Based Estimation of Knee Stiffness  

PubMed Central

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

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

2013-01-01

158

High performance composites with active stiffness control.  

PubMed

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

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

2013-09-13

159

"Contact" of nanoscale stiff films.  

PubMed

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

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

2012-05-31

160

Random Coefficient Models: Theory and Applications  

Microsoft Academic Search

This paper provides an overview of the rationale behind, and the implementation, and uses of, the random coefficient approach to econometric modeling. A simple random coefficient model is presented, and methods for estimating, testing, and validating such a model are described. A more general model is then presented. The general model is shown to include several fixed-coefficient models as special

P. A. V. B. Swamy; George S. Tavlas

1995-01-01

161

Stiffness of contacts between rough surfaces.  

PubMed

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

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

2011-05-20

162

Optimal dynamic stabilisation of a linear system by periodic stiffness excitation  

NASA Astrophysics Data System (ADS)

A theoretical study on the dynamic stabilisation of an unstable mechanical structure is performed. The system is unstable due to negative damping introduced by, for example, a self-excitation of linearised van der Pol type. A minimum model possessing two degrees of freedom with linear spring and damper elements is considered. Based on the effect of a parametric anti-resonance such a system may be stabilised by introducing a time-periodic stiffness variation. Optimum conditions are derived for achieving damping by parametric excitation. All stiffness elements in the system are considered to be available for stiffness variation. Using the averaging method in combination with Fourier series, general conditions for full vibration suppression are derived for arbitrary locations and phase relations of the stiffness variations. Analytical conditions are presented, showing how the maximum gain in stability depends on the amplitude, the phase, the location and the shape function of the periodic stiffness excitation. It is shown that only four characteristic values determine the optimum stiffness variation. These analytical predictions are verified by a numerical stability analysis of an example system. The results can be applied to tune the efficiency of vibration suppression achieved by a periodic variation of one or more stiffness parameters.

Dohnal, Fadi

2009-03-01

163

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

Center for Drug Evaluation (CDER)

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

164

Interphalangeal Joint Stiffness Following Claw Hand Reconstruction  

Microsoft Academic Search

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

G. D. SUNDARARAJ; K. MANI

1984-01-01

165

Stiff skin syndrome--case report.  

PubMed

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

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

166

Stiff man syndrome with invasive thymic carcinoma.  

PubMed

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

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

2013-03-01

167

External mechanical compression reduces regional arterial stiffness  

Microsoft Academic Search

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

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

2007-01-01

168

Bounding the Bogoliubov coefficients  

SciTech Connect

While over the last century or more considerable effort has been put into the problem of finding approximate solutions for wave equations in general, and quantum mechanical problems in particular, it appears that as yet relatively little work seems to have been put into the complementary problem of establishing rigourous bounds on the exact solutions. We have in mind either bounds on parametric amplification and the related quantum phenomenon of particle production (as encoded in the Bogoliubov coefficients), or bounds on transmission and reflection coefficients. Modifying and streamlining an approach developed by one of the present authors [M. Visser, Phys. Rev. A 59 (1999) 427-438, (arXiv:quant-ph/9901030)], we investigate this question by developing a formal but exact solution for the appropriate second-order linear ODE in terms of a time-ordered exponential of 2x2 matrices, then relating the Bogoliubov coefficients to certain invariants of this matrix. By bounding the matrix in an appropriate manner, we can thereby bound the Bogoliubov coefficients.

Boonserm, Petarpa [School of Mathematics, Statistics, and Computer Science, Victoria University of Wellington, P.O. Box 600, Wellington (New Zealand); Visser, Matt [School of Mathematics, Statistics, and Computer Science, Victoria University of Wellington, P.O. Box 600, Wellington (New Zealand)], E-mail: matt.visser@mcs.vuw.ac.nz

2008-11-15

169

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

170

Stiffness transition in anisotropic fiber nets.  

PubMed

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

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

2012-08-23

171

Stiffness transition in anisotropic fiber nets  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

172

The Soret effect in dilute polymer solutions: Influence of chain length, chain stiffness, and solvent quality  

NASA Astrophysics Data System (ADS)

Thermal diffusion in dilute polymer solutions is studied by reverse nonequilibrium molecular dynamics. The polymers are represented by a generic bead-spring model. The influence of the solvent quality on the Soret coefficient is investigated. At constant temperature and monomer fraction, a better solvent quality causes a higher affinity for the polymer to the cold region. This may even go to thermal-diffusion-induced phase separation. The sign of the Soret coefficient changes in a symmetric nonideal binary Lennard-Jones solution when the solvent quality switches from good to poor. The known independence of the thermal diffusion coefficients of the molecular weight is reproduced for three groups of polymers with different chain stiffnesses. The thermal diffusion coefficients reach constant values at chain lengths of around two to three times the persistence length. Moreover, rigid polymers have higher Soret coefficients and thermal diffusion coefficients than more flexible polymers.

Zhang, Meimei; Müller-Plathe, Florian

2006-09-01

173

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

174

Determination of drag coefficients for a buoyant cable antenna  

NASA Astrophysics Data System (ADS)

Samples of buoyant cable antennas of various lengths and surface roughnesses were towed over a range of speeds and depths in different wave conditions. Based on measurements of the forces developed and using computerized prediction techniques, normal and tangential drag coefficients were determined for the submerged segment of the BCA configuration and drag coefficients were determined for the floating length segment. The drag coefficients are presented in both tabular and graphical form. The results indicate that both waves and surface roughness can have a significant effect on the drag coefficients. The results also indicate that the effects of cable stiffness on the accuracy of the cable catenary predictions require further investigation.

Israel, A. M.

1982-03-01

175

Stiff-person syndrome with amphiphysin antibodies  

PubMed Central

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

Murinson, Beth B.; Guarnaccia, Joseph B.

2008-01-01

176

Big bang nucleosynthesis with a stiff fluid  

SciTech Connect

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

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

2010-10-15

177

Influence of joint stiffness on the free vibrations of a marine riser conveying fluid  

Microsoft Academic Search

The marine risers are generally used as the main transport means for economic materials and resources discovered undersea. In general, the marine risers are secured at either an offshore platform or a vessel. Both ends of the riser are to be adjusted to obey with the design criteria but in many cases their rotational stiffness is hardly set free for

S. Kaewunruen; T. McCarthy; J. Leklong; S. Chucheepsakul

2008-01-01

178

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

NASA Astrophysics Data System (ADS)

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

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

1999-08-01

179

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

SciTech Connect

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

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

1999-08-01

180

A parameter optimization method to determine ski stiffness properties from ski deformation data.  

PubMed

The deformation of skis and the contact pressure between skis and snow are crucial factors for carved turns in alpine skiing. The purpose of the current study was to develop and to evaluate an optimization method to determine the bending and torsional stiffness that lead to a given bending and torsional deflection of the ski. Euler-Bernoulli beam theory and classical torsion theory were applied to model the deformation of the ski. Bending and torsional stiffness were approximated as linear combinations of B-splines. To compute the unknown coefficients, a parameter optimization problem was formulated and successfully solved by multiple shooting and least squares data fitting. The proposed optimization method was evaluated based on ski stiffness data and ski deformation data taken from a recently published simulation study. The ski deformation data were used as input data to the optimization method. The optimization method was capable of successfully reproducing the shape of the original bending and torsional stiffness data of the ski with a root mean square error below 1 N m2. In conclusion, the proposed computational method offers the possibility to calculate ski stiffness properties with respect to a given ski deformation. PMID:21451186

Heinrich, Dieter; Mössner, Martin; Kaps, Peter; Nachbauer, Werner

2011-02-01

181

Virion stiffness regulates immature HIV-1 entry  

PubMed Central

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

2013-01-01

182

[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

183

Damping properties of stay cable-passive damper system with effects of cable sag and damper stiffness  

NASA Astrophysics Data System (ADS)

The present paper derivate the asymptotic solution of modal damping of one taut stay cable attached with one passive damper including damper stiffness and viscous damping. The effect of the damper stiffness on the modal damping of the stay cable-passive system was analytical investigated. On the basis of the asymptotic solution of modal damping of one stay cable attached with one passive damper with the effect of cable stiffness and by using the decay factor of damper stiffness and the decay factor of cable sag, maximum modal damping ratio and corresponding optimal damping coefficient, which indicates the relationships of the characteristics of the damper and the cable sag was theoretically analyzed. Numerical analysis of parameters on the effect of dynamic performance of the controlled stay cable was conducted.

Liu, Min; Zhang, Guangqiao

2013-04-01

184

Testing local DNA stiffness by nanoconfinement  

NASA Astrophysics Data System (ADS)

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

Karpusenka, Alena; Riehn, Robert

2008-10-01

185

Condensin Regulates the Stiffness of Vertebrate Centromeres  

PubMed Central

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

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

2009-01-01

186

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

PubMed Central

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

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

2010-01-01

187

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

Microsoft Academic Search

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

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

2007-01-01

188

Precise damping and stiffness extraction in acoustic driven cantilever in liquid  

NASA Astrophysics Data System (ADS)

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

Maali, Abdelhamid; Boisgard, Rodolphe

2013-10-01

189

A methodology for setting grasping force for picking up an object with unknown weight, friction, and stiffness  

Microsoft Academic Search

A methodology for setting the reference value of a grasping force when a multi-finger robotic hand grasps and lifts up an object without knowing its characteristic weight, coefficient of static friction, and stiffness was devised. The grasping force must be set to avoid dropping or deforming the object. To fulfill this requirement, the methodology measures object characteristics by detecting the

Taisuke Sugaiwa; Genki Fujii; Hiroyasu Iwata; Shigeki Sugano

2010-01-01

190

RC beam with variable stiffness and strength  

Microsoft Academic Search

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

Christoph Czaderski; Bernd Hahnebach; Masoud Motavalli

2006-01-01

191

Monitoring the Bending Stiffness of DNA  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

192

Stiff-person syndrome treated with rituximab  

Microsoft Academic Search

Stiff-person syndrome (SPS) is a rare neurological condition consisting of progressive and fluctuating rigidity of the axial muscles combined with painful spasms. The pathophysiology of SPS is not fully understood, but there seems to be an autoimmune component. The use of rituximab, a chimeric monoclonal antibody targeting CD20 protein in the surface of mature B cells, for the treatment of

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

2010-01-01

193

Stability of high stiffness gas journal bearings  

Microsoft Academic Search

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

Krzysztof Czolczynski

1994-01-01

194

Biaxial strain and variable stiffness in aponeuroses  

PubMed Central

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

Azizi, Emanuel; Roberts, Thomas J

2009-01-01

195

Spring stiffness influence on an oscillating propulsor  

Microsoft Academic Search

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

M. M. Murray; L. E. Howle

2003-01-01

196

Leg Stiffness and Expertise in Men Jumping  

Microsoft Academic Search

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

GUILLAUME LAFFAYE; ALAIN DUREY

2005-01-01

197

Pregnancy in stiff-limb syndrome.  

PubMed

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

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

2004-07-01

198

Stiffness discrimination with visual and proprioceptive cues  

Microsoft Academic Search

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

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

2009-01-01

199

Scaling of fluid flow versus fracture stiffness  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

200

Stiffness gradients in radiata pine trees  

Microsoft Academic Search

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

Ping Xu; J. C. F. Walker

2004-01-01

201

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

Microsoft Academic Search

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

Sang Kyu Park

1991-01-01

202

Meta-Analysis of Coefficient Alpha  

ERIC Educational Resources Information Center

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

Rodriguez, Michael C.; Maeda, Yukiko

2006-01-01

203

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

PubMed

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

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

2012-10-30

204

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

205

Increased mean platelet volume is associated with arterial stiffness.  

PubMed

The brachial-ankle pulse wave velocity (baPWV) is a useful index of arterial stiffness. Mean platelet volume (MPV), an indicator of platelet activation, is associated with hypertension, stroke, and coronary artery disease, all of which may be caused by arteriosclerosis. However, little research has been conducted to investigate the relationship between MPV and arterial stiffness. In this cross-sectional study, we investigated the relationship between platelet count, MPV, and baPWV in 2645 apparently healthy Chinese participants (1676 men, 969 women) in a general health examination. Different metabolic parameters were compared across MPV quintiles (Q1: ?8.1 fl, Q2: 8.2-8.5 fl, Q3: 8.6-9.6 fl, Q4: 9.7-10.7 fl, and Q5: ?10.8 fl). Age-adjusted mean values of baPWV gradually increased with MPV quintiles (Q1?=?1124, Q2?=?1134, Q3?=?1199, Q4?=?1207, and Q5?=?1270?cm/s). Univariate analysis showed that age, sex, smoking status, body mass index (BMI), systolic blood pressure (SBP), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), fasting plasma glucose (FPG), total platelet count, and MPV were significantly associated with baPWV. In addition, age, sex, BMI, MPV, SBP, and FPG were significant factors in the multivariate model with baPWV. Notably, MPV was found to be a significant determinant for baPWV (??=?0.198; P?stiffness. PMID:21473674

Wang, Rui-Tao; Li, Ying; Zhu, Xiu-Ying; Zhang, Yi-Na

2011-04-07

206

‘Continuous muscle fibre activity’ in six dogs with episodic myokymia, stiffness and collapse  

Microsoft Academic Search

Continuous muscle fibre activity was observed in a crossbred dog, a Yorkshire terrier, a border collie and three Jack Russell terriers. The clinical signs consisted of episodes of generalised myokymia which developed into muscle stiffness and delayed muscle relaxation and generally led to the dogs collapsing into lateral recumbency. These episodes were preceded by intense facial rubbing in three of

L. Van Ham; S. Bhatti; I. Polis; H. Thoonen; R. Fatzer; K. Braund

2004-01-01

207

C ontinuous muscle fibre activity in six dogs with episodic myokymia, stiffness and collapse  

Microsoft Academic Search

(4) SUMMARY Continuous muscle fibre activity was observed in a crossbred dog, a Yorkshire terrier, a border collie and three Jack Russell terriers. The clinical signs consisted of episodes of generalised myokymia which developed into muscle stiffness and delayed muscle relaxation and generally led to the dogs collapsing into lateral recumbency. These episodes were preceded by intense facial rubbing in

L. Van Ham; S. Bhatti; R. Fatzer; K. Braund; H. Thoonen

208

High-order localized time integration for grid-induced stiffness  

Microsoft Academic Search

We discuss two time integration techniques, aimed at overcoming local grid-induced stiffness in discontinuous Galerkin methods. A local time-stepping approach, utilizing the local properties of the scheme, is shown to work very well. Recently developed additive Runge-Kutta methods are more general and found to be promising when combined with efficient local preconditioning.

C. Chauviere; J. S. Hesthaven; A. Kanevsky; T. Warburton

209

Optimal Design of a Variable Stiffness Joint Using Permanent Magnets  

Microsoft Academic Search

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

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

2007-01-01

210

Representations of multi-joint stiffness for prosthetic limb design  

Microsoft Academic Search

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

Chad E. English; Donald L. Russell

2008-01-01

211

Simulation of conservative properties of stiffness matrices in congruence transformation  

Microsoft Academic Search

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

Shih-Feng Cheng; Imin Kao

1998-01-01

212

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

213

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

214

Optimal chest compression in cardiopulmonary resuscitation depends upon thoracic and back support stiffness.  

PubMed

A biomechanical analysis of the constant peak displacement and constant peak force methods of cardiopulmonary resuscitation (CPR) has revealed that optimal CC performance strongly depends on back support stiffness, CC rate, and the thoracic stiffness of the patient being resuscitated. Clinically the results presented in this study suggest that the stiffness of the back support surfaces found in many hospitals may be sub-optimal and that a backboard or a concrete floor can be used to enhance CC effectiveness. In addition, the choice of optimal CC rate and maximum sternal force applied by clinicians during peak force CPR is ought to be based on a general assessment of the patient's thoracic stiffness, taking into account the patient's age, gender, and physical condition; which is consistent with current clinical practice. In addition, it is important for clinicians to note that very high peak sternal forces, exceeding the limit above which severe chest wall trauma and abdominal injury occurs, may be required for optimal CC during peak force CPR on patients with very stiff chests. In these cases an alternative CPR technique may be more appropriate. PMID:23054380

Dellimore, Kiran H; Scheffer, Cornie

2012-10-09

215

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

216

Effect of Mass Damping and Stiffness Damping in Micromachined Air Coupled Capacitance Transducer  

NASA Astrophysics Data System (ADS)

Performance of MEMS devices relies largely on the interaction between structural actuation membranes and fluids surrounding them. When optimizing these MEMS design it is importent to consider the general characteristics of this fluid-structure interaction. Finite Element approach is used to study the effect of mass damping and stiffness damping arising due to micro fluid layers in Micro-machined Air-coupled Capacitance transducer. Transient dynamics of these systems are completely driven by this fluid-structure interaction. The aim of this paper is to understand the variations in mass and stiffness damping with frequency of operation. Furthermore, the effect of the mass and stiffness damping with geometrical parameters and transient behavior of the system are discussed.

Kumar K. M., Manoj; Goravar, Shivappa; Kommareddy, Vamshi; Fan, Ying; Barshinger, James; Andrew, May; Xuefeng, Wang

2007-03-01

217

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

PubMed Central

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

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

2012-01-01

218

Levetiracetam in stiff-person syndrome  

Microsoft Academic Search

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

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

2008-01-01

219

Ultrastrong and Stiff Layered Polymer Nanocomposites  

Microsoft Academic Search

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

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

2007-01-01

220

METHOD OF HYPERBOLIC SYSTEMS WITH STIFF RELAXATION  

SciTech Connect

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

R. B. LOWRIE; J. E. MOREL

2001-03-01

221

LONG-TERM PLASTIC PIPE STIFFNESS  

Microsoft Academic Search

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

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

222

Estimation of Actual Response Coefficients in the Hildreth-Houck Random Coefficient Model  

Microsoft Academic Search

When the response coefficients in the general linear model are regarded as random variables, the mean of the distribution of these coefficients can be estimated using methods suggested by Hildreth and Houck. This article derives the minimum variance, linear, unbiased estimator for the actual response coefficients which were realized over the sample period. One might suspect that the best estimator

W. E. Griffiths

1972-01-01

223

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

PubMed Central

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

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

2010-01-01

224

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

PubMed Central

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

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

2010-01-01

225

Aortic stiffness and distensibility among hypertensives.  

PubMed

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

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

2009-09-01

226

Chromatic aberration coefficients  

NASA Astrophysics Data System (ADS)

Our work deals with the influence of the wavelength of light on values of wave aberration coefficients. It is proposed a technique for calculation of the dependence of aberration coefficients on the wavelength, their interpretation and the connection to chromatic aberrations. It is also shown the calculation of the Strehl definition using chromatic aberration coefficients and the tolerance limits are given. The proposed method for calculation of chromatic aberration coefficients is shown for the case of the imaging of axial point by the rotationally symmetrical optical system. Relations that enable calculation of chromatic aberration coefficients up to fifth order are carried out. These relations are accurate enough for most optical systems in practice.

Miks, Antonin; Novak, Jiri; Novak, Pavel

2007-05-01

227

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

228

Monitoring stiffness changes in lesions after radiofrequency ablation at different temperatures and durations of ablation.  

PubMed

The variations in the stiffness or stiffness contrast of lesions resulting from radiofrequency (RF) ablation of canine liver tissue at different temperatures and for different ablation durations at a specified temperature are analyzed. Tissue stiffness, in general, increases with temperature; however, an anomaly exists around 80 degrees C, where the stiffness of the lesion is lower than that of the lesion ablated at 70 degrees C. On the other hand, the stiffness increases monotonically with the duration of ablation. Plots illustrating the ratio of mean strains in normal canine liver tissue to mean strains in ablated thermal lesions demonstrate the variation in the stiffness contrast of the thermal lesions. The contrast-to-noise ratio (CNRe) of the lesions, which serves as an indicator of the detectability of the lesions under the different experimental imaging conditions described above, is also presented. The results presented in this paper show that the elastographic depiction of stiffer thermal lesions is better, in terms of the CNRe parameter. An important criterion in the elastographic depiction of RF-ablated regions of tissue is the trade-off between ablation temperature and duration of ablation. Tissue necrosis can occur either by ablating tissue to high temperatures for short durations or to lower temperatures for longer durations. In this paper, we attempt to characterize the elastographic depiction of thermal lesions under these different experimental conditions. This paper provides results that may be utilized by practitioners of RF ablation to decide the ablation temperature and duration, on the basis of the strain images of normal liver tissue and ablated thermal lesions discussed in this paper. PMID:15749565

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

2005-03-01

229

Discontinuous Galerkin for Stiff Hyperbolic Systems  

SciTech Connect

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

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

1999-06-27

230

Kendall's correlation coefficient for vague preferences  

Microsoft Academic Search

The problem of measuring association between preference systems in situations with missing information or noncomparable outputs\\u000a is discussed. New correlation coefficient, which generalizes Kendall’s correlation coefficients used traditionally in statistics,\\u000a is suggested. The construction utilizes IF-sets.

Przemyslaw Grzegorzewski

2009-01-01

231

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

PubMed

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

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

2013-05-13

232

A Stiffness Switch in Human Immunodeficiency Virus  

PubMed Central

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

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

2007-01-01

233

Significance of central aortic stiffness in cardiovascular disease.  

PubMed

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

Arora, Rohit; Khandpur, Ritika

234

A real-time parametric stiffness observer for VSA devices  

Microsoft Academic Search

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

Giorgio Grioli; Antonio Bicchi

2011-01-01

235

Association between arterial stiffness and atherosclerosis: the Rotterdam Study  

Microsoft Academic Search

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

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

2001-01-01

236

Polyimide-based intracortical neural implant with improved structural stiffness  

Microsoft Academic Search

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

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

2004-01-01

237

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

238

Stress determination from hydraulic fracturing tests: the system stiffness approach  

Microsoft Academic Search

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

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

2001-01-01

239

Modelling and prediction of bending stiffness for paper board manufacturing  

Microsoft Academic Search

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

Per-Olof Gutman; Bengt Nilsson

1998-01-01

240

Dynamic Model for Locally Stiff Ring and Straight Chain Polymers  

Microsoft Academic Search

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

Eliot Simon

1970-01-01

241

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.

Zhang, Zhaoyan; Hieu Luu, Trung

2012-01-01

242

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

PubMed Central

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

2011-01-01

243

ESTIMATING COTTON EVAPOTRANSPIRATION CROP COEFFICIENTS WITH A MULTISPECTRAL VEGETATION INDEX  

Technology Transfer Automated Retrieval System (TEKTRAN)

Crop coefficients are a widely used and universally accepted method for estimating the crop evapotranspiration (ETc) component in irrigation scheduling programs. However, uncertainties of generalized basal crop coefficient (Kcb) curves can contribute to ETc estimates that are substantially different...

244

The fully implicit stochastic-{alpha} method for stiff stochastic differential equations  

SciTech Connect

A fully implicit integration method for stochastic differential equations with significant multiplicative noise and stiffness in both the drift and diffusion coefficients has been constructed, analyzed and illustrated with numerical examples in this work. The method has strong order 1.0 consistency and has user-selectable parameters that allow the user to expand the stability region of the method to cover almost the entire drift-diffusion stability plane. The large stability region enables the method to take computationally efficient time steps. A system of chemical Langevin equations simulated with the method illustrates its computational efficiency.

Safique Ahmad, Sk. [Supercomputer Education and Research Centre, Indian Institute of Science, Bangalore 560012 (India)], E-mail: ahmad@math.tu-Berlin.de; Chandra Parida, Nigam [Supercomputer Education and Research Centre, Indian Institute of Science, Bangalore 560012 (India)], E-mail: parida@alumni.iitg.ernet.in; Raha, Soumyendu [Supercomputer Education and Research Centre, Indian Institute of Science, Bangalore 560012 (India)], E-mail: raha@serc.iisc.ernet.in

2009-12-01

245

Stiffness tomography by atomic force microscopy.  

PubMed

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

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

2009-07-22

246

Stiffness Tomography by Atomic Force Microscopy  

PubMed Central

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

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

2009-01-01

247

[Stiff-man syndrome: an immunopathy?].  

PubMed

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

Meinck, H M

1991-12-01

248

Salt-induced aggregation of stiff polyelectrolytes.  

PubMed

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

Fazli, Hossein; Mohammadinejad, Sarah; Golestanian, Ramin

2009-09-30

249

Determining cantilever stiffness from thermal noise.  

PubMed

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

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

2013-03-28

250

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

PubMed Central

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

Wang, Zhijie; Chesler, Naomi C.

2011-01-01

251

Effects of varying machine stiffness and contact area in UltraForm Finishing  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

252

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

SciTech Connect

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

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

2010-02-15

253

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

Microsoft Academic Search

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

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

2005-01-01

254

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

Microsoft Academic Search

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

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

1999-01-01

255

Bone stiffness and failure load are related with clinical parameters in men with chronic obstructive pulmonary disease.  

PubMed

Osteoporosis is frequently seen in patients with chronic obstructive pulmonary disease (COPD). Because research on bone structure and bone strength in COPD patients is limited, the objectives of this pilot study were as follows: (1) to compare bone structure, stiffness, and failure load, measured at the peripheral skeleton, between men with and without COPD after stratification for areal bone mineral density (aBMD); and (2) to relate clinical parameters with bone stiffness and failure load in men with COPD. We included 30 men with COPD (normal aBMD, n?=?18; osteoporosis, n?=?12) and 17 men without COPD (normal aBMD, n?=?9; osteoporosis, n?=?8). We assessed pack-years of smoking, body mass index (BMI), fat free mass index (FFMI), pulmonary function (forced expiratory volume in 1 second [FEV1 ], FEV1 /forced vital capacity [FVC], diffusion capacity for carbon monoxide [DLCO], and transfer coefficient for carbon monoxide [KCO]), and extent of emphysema. Bone structure of the distal radius and tibia was assessed by high-resolution peripheral quantitative computed tomography (HR-pQCT), and bone stiffness and failure load of the distal radius and tibia were estimated from micro finite element analysis (µFEA). After stratification for aBMD and COPD, men with osteoporosis showed abnormal bone structure (p?stiffness (p?stiffness, and failure load compared with men without COPD. In men with COPD, lower FFMI was related with lower bone stiffness, and failure load of the radius and tibia and lower DLCO and KCO were related with lower bone stiffness and failure load of the tibia after normalization with respect to femoral neck aBMD. Thus, this pilot study could not detect differences in bone structure, stiffness, and failure load between men with and without COPD after stratification for aBMD. FFMI and gas transfer capacity of the lung were significantly related with bone stiffness and failure load in men with COPD after normalization with respect to femoral neck aBMD. © 2013 American Society for Bone and Mineral Research. PMID:23553944

Romme, Elisabeth Apm; Rutten, Erica Pa; Geusens, Piet; de Jong, Joost Ja; van Rietbergen, Bert; Smeenk, Frank Wjm; Wouters, Emiel Fm; van den Bergh, Joop Pw

2013-10-01

256

Role of Inflammation in the Pathogenesis of Arterial Stiffness  

PubMed Central

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

Park, Sungha

2012-01-01

257

Dually Stiff Floors for Injury Prevention for the Elderly.  

National Technical Information Service (NTIS)

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

D. A. Streit

1999-01-01

258

Dually Stiff Floors for Injury Prevention for the Elderly.  

National Technical Information Service (NTIS)

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

D. A. Streit

1997-01-01

259

Modeling and design of energy efficient variable stiffness actuators  

Microsoft Academic Search

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

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

2010-01-01

260

Design of a robot joint with variable stiffness  

Microsoft Academic Search

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

Junho Choi; Woosub Lee; Sung-chul Kang

2008-01-01

261

Semiactive vibration isolation system with variable stiffness and damping control  

Microsoft Academic Search

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

Yanqing Liu; Hiroshi Matsuhisa; Hideo Utsuno

2008-01-01

262

Kinetics of stiff-legged gait: induced acceleration analysis  

Microsoft Academic Search

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

Patrick O. Riley; D. Casey Kerrigan

1999-01-01

263

Preliminary investigation of a novel controlled stiffness proximal femoral prosthesis.  

PubMed

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

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

1998-01-01

264

Stiff-Person Syndrome First Manifesting in Pregnancy  

Microsoft Academic Search

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

Denis Cerimagic; Ervina Bilic

2009-01-01

265

Stiff-person syndrome associated with oral isotretinoin treatment  

Microsoft Academic Search

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

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

2002-01-01

266

Optimality principles in variable stiffness control: The VSA hammer  

Microsoft Academic Search

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

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

2011-01-01

267

Contact stiffness of layered materials for ultrasonic atomic force microscopy  

Microsoft Academic Search

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

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

2000-01-01

268

Aggregation Technique for the Transient Analysis of Stiff Markov Systems.  

National Technical Information Service (NTIS)

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

K. S. Trivedi

1985-01-01

269

A methodology for joint stiffness identification of serial robots  

Microsoft Academic Search

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

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

2010-01-01

270

Flexural strength and stiffness of southern pine plywood  

Microsoft Academic Search

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

Evangelos J. Biblis; Yen-Ming Chiu

1970-01-01

271

An evaluation of elastic properties and coefficients of thermal expansion of graphite fibres from macroscopic composite input data  

Microsoft Academic Search

In this work, a methodology has been presented for the evaluation of stiffness properties and temperature-dependent coefficients of thermal expansion of continuous fibres from the macroscopic properties of either unidirectional or woven composites. The methodology was used to determine the stiffness and thermal properties of T650-35 graphite fibres from the macroscopic input data of unidirectional and woven composites based on

P. Rupnowski; M. Gentz; J. K. Sutter

2005-01-01

272

[Anesthetic management of a patient with stiff-person syndrome undergoing thymectomy].  

PubMed

Stiff-person syndrome is an uncommon disease characterized by muscular rigidity and painful spasms in the axial and limb muscles. We report a 58-year-old woman with stiff-person syndrome undergoing thymectomy under general anesthesia. Before surgery, her medications were 25 mg of diazepam, 2 mg of clonazepam, and 15 mg of gabapentin per day. After epidural catheterization for the postoperative analgesia, general anesthesia was induced and maintained with continuous remifentanil infusion and propofol with target controlled infusion. With train-of-four ratio (TOFR) monitoring by stimulating the ulnar nerve, her trachea was intubated after 0.6mg x kg(-1) of rocuronium intravenous administration. Since then, additional rocuronium was not given for 4 hours. After surgery, she was fully awake and TOFR recovered to 100%, but tidal volume was too low to remove the tracheal tube, and mechanical ventilation was continued in ICU. On the next day, the tracheal tube was removed, and she was discharged from ICU. Because anesthetics may delay the recovery of respiratory function in a patient with stiff-person syndrome, careful assessment of respiratory function is needed at the emergence from general anesthesia. PMID:22413445

Tadokoro, Takahiro; Yamashita, Soichiro; Ishigaki, Maiko; Takahashi, Shinji; Tanaka, Makoto

2012-02-01

273

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

274

Arterial Stiffness in Female Patients With Fibromyalgia and Its Relationship to Chronic Emotional and Physical Stress  

PubMed Central

Background and Objectives In patients with fibromyalgia (FM) syndrome, stress and pain may chronically enhance sympathetic activity, altering cardiovascular responses and inducing the arterial wall-stiffening process. We investigated arterial stiffness in FM patients using pulse wave velocity (PWV) and analyzed whether arterial stiffness was affected by the clinical parameters of FM. Subjects and Methods This study included 108 female FM patients (51.5±8.9 years) without any known cardiovascular diseases and 76 healthy female controls (50.1±8.9 years). FM patients underwent a manual tender point survey for tender point counts, and completed the visual analogue scale (VAS) of pain and fibromyalgia impact questionnaire (FIQ), which were composed of a physical and feel score. Brachial-ankle pulse-wave velocity (baPWV) was measured with an automated device. The study participants were subdivided into 2 groups based on the sum of the FIQ score (group A: FIQ ?50, group B: <50). Results Patients with FM had significantly higher baPWV than the controls, and significant increase were noted in baPWV values of group A compared with those of group B. BaPWV showed a significant positive correlation (correlation coefficient=6.83, p=0.022) with severity of disease assessed by FIQ. Conclusion The patients with FM showed significantly increased arterial stiffness, suggesting a pathophysiologic link between FM and endothelial dysfunction. This study provides a basis for clarifying the mechanism by which chronic pain syndrome is associated with an increased risk of vascular stiffness.

Lee, Ji Hyun; Kim, Seong Man; Lee, Hyeon Gook; Kim, Tae Ik

2011-01-01

275

A parameter identification method for the rotordynamic coefficients of a high Reynolds number hydrostatic bearing  

NASA Astrophysics Data System (ADS)

In identifying the rotordynamic coefficients of a high-Reynolds-number hydrostatic bearing, fluid-flow induced forces present a unique problem, in that they provide an unmeasureable and uncontrollable excitation to the bearing. An analysis method is developed that effectively eliminates the effects of fluid-flow induced excitation on the estimation of the bearing rotordynamic coefficients, by using power spectral densities. In addition to the theoretical development, the method is verified experimentally by single-frequency testing, and repeatability tests. Results obtained for a bearing are the twelve rotordynamic coefficients (stiffness, damping, and inertia coefficients) as functions of eccentricity ratio, speed, and supply pressure.

Rouvas, C.; Childs, D. W.

1993-07-01

276

Coefficients of Effective Length.  

ERIC Educational Resources Information Center

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

Edwards, Roger H.

1981-01-01

277

Developing an effective arterial stiffness monitoring system using the spring constant method and photoplethysmography.  

PubMed

This study aimed to develop a fast and effective arterial stiffness monitoring system for diabetic patients using the spring constant method and photoplethysmography (PPG). The experimental group comprised 70 patients (4 type 1 diabetes mellitus patients and 66 type 2 diabetes mellitus patients); 23 participants suffered from atherosclerosis. All were subjected to the measurements of both the carotid-femoral pulse wave velocity (cfPWV) and the spring constants evaluated using the PPG pulse as well as the radial pulse. The control group comprised 70 normal participants (39 men and 31 women) who did not have diabetes mellitus, with an age range of 40-84 years. All control group members were only subjected to the measurement by the spring constant method. For the experimental group, statistical analysis indicated a significantly high correlation between the spring constants computed using PPG and the radial pulse (p < 0.001, correlation coefficient =0.89). The result also showed a significant negative correlation between the cfPWV and the spring constant of PPG (p < 0.001, correlation coefficient = - 0.72); multivariate analysis similarly indicated a close relationship. In addition, we used Student's t test to examine the difference between the experimental and control groups for the spring constant of PPG. A P value less than 0.05 confirmed that the difference between the two groups was statistically significant. In the receiver operating characteristic curve, area under curve (=0.82) indicates a good discrimination, and a spring constant of PPG below 516 (g/s (2)) may imply a risk of arterial stiffness for diabetic patients. These findings imply that the spring constant of PPG could effectively identify normal versus abnormal characteristics of elasticity in normal and diabetic participants. As a result of some excellent characteristics in clinical monitoring, the spring constant computed using PPG shows the effectiveness and feasibility in the monitoring system of arterial stiffness. PMID:22855219

Wei, Ching-Chuan

2012-07-26

278

Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking  

PubMed Central

Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as prostheses and orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75–2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R2 of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.

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

2013-01-01

279

Sources of Variability in Musculo-Articular Stiffness Measurement  

PubMed Central

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

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

2013-01-01

280

Flexural and torsional stiffness in multi-jointed biological beams.  

PubMed

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

Etnier, S A

2001-02-01

281

Polyelectrolyte multilayer films of controlled stiffness modulate myoblast cells differentiation  

PubMed Central

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

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

2008-01-01

282

Evaluation of chain stiffness of partially oxidized polyguluronate.  

PubMed

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

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

283

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

284

[Stiff person syndrome (Moersch-Woltman)].  

PubMed

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

Cerimagi?, Denis; Bili?, Ervina

285

Ionization coefficients in gas mixtures  

NASA Astrophysics Data System (ADS)

We have tested the application of the common E/N (E—electric field, N—gas number density) or Wieland approximation [Van Brunt, R.J., 1987. Common parametrizations of electron transport, collision cross section, and dielectric strength data for binary gas mixtures. J. Appl. Phys. 61 (5), 1773 1787.] and the common mean energy (CME) combination of the data for pure gases to obtain ionization coefficients for mixtures. Test calculations were made for Ar CH4, Ar N2, He Xe and CH4 N2 mixtures. Standard combination procedure gives poor results in general, due to the fact that the electron energy distribution is considerably different in mixtures and in individual gases at the same values of E/N. The CME method may be used for mixtures of gases with ionization coefficients that do not differ by more than two orders of magnitude which is better than any other technique that was proposed [Mari?, D., Radmilovi?-Ra?enovi?, M., Petrovi?, Z.Lj., 2005. On parametrization and mixture laws for electron ionization coefficients. Eur. Phys. J. D 35, 313 321.].

Mari?, D.; Šaši?, O.; Jovanovi?, J.; Radmilovi?-Ra?enovi?, M.; Petrovi?, Z. Lj.

2007-03-01

286

Attenuation coefficients of Rayleigh and Lg waves  

Microsoft Academic Search

Analysis of the frequency dependence of the attenuation coefficient leads to significant changes in interpretation of seismic\\u000a attenuation data. Here, several published surface-wave attenuation studies are revisited from a uniform viewpoint of the temporal\\u000a attenuation coefficient, denoted by ?. Theoretically, ?( f) is expected to be linear in frequency, with a generally non-zero intercept ??=??(0) related to the variations of

Igor B. Morozov

2010-01-01

287

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

288

Radon diffusion coefficients for residential concretes  

SciTech Connect

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

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

1994-09-01

289

Tissue Cells Feel and Respond to the Stiffness of Their Substrate  

NASA Astrophysics Data System (ADS)

Normal tissue cells are generally not viable when suspended in a fluid and are therefore said to be anchorage dependent. Such cells must adhere to a solid, but a solid can be as rigid as glass or softer than a baby's skin. The behavior of some cells on soft materials is characteristic of important phenotypes; for example, cell growth on soft agar gels is used to identify cancer cells. However, an understanding of how tissue cells-including fibroblasts, myocytes, neurons, and other cell types-sense matrix stiffness is just emerging with quantitative studies of cells adhering to gels (or to other cells) with which elasticity can be tuned to approximate that of tissues. Key roles in molecular pathways are played by adhesion complexes and the actin-myosin cytoskeleton, whose contractile forces are transmitted through transcellular structures. The feedback of local matrix stiffness on cell state likely has important implications for development, differentiation, disease, and regeneration.

Discher, Dennis E.; Janmey, Paul; Wang, Yu-li

2005-11-01

290

Influence of the stiffness of testing machines on the adherence of elastomers  

SciTech Connect

It is shown that the introduction of the fracture mechanics concepts, such as the strain energy release rate G, to solve the problem of the adherence of elastomers, the edge of contact being seen as a crack propagating in mode I in the interface, allows one to predict the dependence of the adherence force with stiffness of testing machines. Moreover, it is shown the general equation of the kinetics of adherence proposed in 1978 in Maugis and Barquins, G - w = w(phi)(a/sub T/..nu..), where w is Dupre's work of adhesion and phi a dissipation function characteristic of the material only depending on temperature and crack speed, is confirmed whatever the stiffness of the testing machine and the instantaneous deformation imposed on the system. Experiments realized with a hemispherical glass lens in contact on a polyurethane surface verify theoretical predictions with an accuracy better than 1%.

Barquins, M.

1983-08-01

291

Stiffness and leakage in spiral groove upstream pumping mechanical seals  

NASA Astrophysics Data System (ADS)

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

Salant, Richard F.; Homiller, Stephen J.

1993-01-01

292

Stiffness of grain-bridging elements in a monolithic alumina  

SciTech Connect

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

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

1997-05-01

293

Likelihood-based inference for genetic correlation coefficients  

Microsoft Academic Search

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

David J. Balding

2003-01-01

294

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

Microsoft Academic Search

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

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

2005-01-01

295

Extracting Step Stiffness from Correlation Functions Consistent with the GWD  

NASA Astrophysics Data System (ADS)

The statistics of a pair of neighboring steps can be derived approximately from a two-particle Hamiltonian in which the steps are mapped onto spinless fermions. Under typical circumstances, this mapping results in the two-particle Calogero model, for which the complete set of eigenvalues and eigenfunctions can be obtained. The terrace-width distribution (TWD) resulting from this approximation is the ``generalized Wigner distribution'' (GWD), which has been shown to be in excellent agreement with simulations of the terrace-step-kink (TSK) model and to be a useful approximation for experimental TWDs. Here we discuss the use of the complete eigensolution to obtain information about the correlations of step fluctuations along the direction parallel to the step. Of particular interest is the autocorrelation function for the midpoint between adjacent steps. An improved estimate for step stiffness can be derived from this correlation function. The results are compared with preliminary Monte Carlo simulations of the TSK model and with previous Gruber-Mullins predictions.

Benson, Amber; Richards, Howard

2003-03-01

296

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

2013-09-05

297

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

NASA Astrophysics Data System (ADS)

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

Liu, Xingtian; Huang, Xiuchang; Hua, Hongxing

2013-07-01

298

Determinants of Arterial Stiffness in Chronic Kidney Disease Stage 3  

PubMed Central

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

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

2013-01-01

299

Effective Spring Stiffness for a Planar Periodic Array of Collinear Cracks at an Interface between Two Dissimilar Isotropic Materials.  

PubMed

Explicit analytical expressions are obtained for the longitudinal and transverse effective spring stiffnesses of a planar periodic array of collinear cracks at the interface between two dissimilar isotropic materials; they are shown to be identical in a general case of elastic dissimilarity (the well-known open interface crack model is employed for the solution). Since the interfacial spring stiffness can be experimentally determined from ultrasound reflection and transmission analysis, the proposed expressions can be useful in estimating the percentage of disbond area between two dissimilar materials, which is directly related to the residual strength of the interface. The effects of elastic dissimilarity, crack density and crack interaction on the effective spring stiffness are clearly represented in the solution. It is shown that in general the crack interaction weakly depends on material dissimilarity and, for most practical cases, the crack interaction is nearly the same as that for crack arrays between identical solids. This allows approximate factorization of the effective spring stiffness for an array of cracks between dissimilar materials in terms of an elastic dissimilarity factor and two factors obtained for cracks in a homogeneous material: the effective spring stiffness for non-interacting (independent) cracks and the crack interaction factor. In order to avoid the effect of the crack surface interpenetration zones on the effective spring stiffness, the range of the tensile to transverse load ratios is obtained under the assumption of small-scale contact conditions. Since real cracks are often slightly open (due to prior loading history and plastic deformation), it is demonstrated that for ultrasound applications the results obtained are valid for most practical cases of small interfacial cracks as long as the mid-crack opening normalized by the crack length is at least in the order of 10(-5). PMID:23710104

Lekesiz, Huseyin; Katsube, Noriko; Rokhlin, Stanislav I; Seghi, Robert R

2011-02-01

300

Micropipette Aspiration of Substrate-attached Cells to Estimate Cell Stiffness  

PubMed Central

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

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

2012-01-01

301

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

302

Variable Stiffness Concept For Efficient Aircraft Vertical Tail Design.  

National Technical Information Service (NTIS)

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

J. E. Cooper M. Amprikidis O. Sensburg

2003-01-01

303

Application of NITINOL to High Stiffness Structural Joints.  

National Technical Information Service (NTIS)

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

R. D. Brum J. C. Schutzler

1979-01-01

304

Strength and Stiffness of Reinforced Concrete Columns under Biaxial Bending.  

National Technical Information Service (NTIS)

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

V. Mavichak R. W. Furlong

1976-01-01

305

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

306

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

Treesearch

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

307

Transverse Cracking and Stiffness Reduction in Composite Laminates  

Microsoft Academic Search

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

Ramesh Talreja

1985-01-01

308

Variable Stiffness Actuators for Fast and Safe Motion Control  

Microsoft Academic Search

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

Antonio Bicchi; Giovanni Tonietti; Michele Bavaro; Marco Piccigallo

2003-01-01

309

Spin stiffness of graphene and zigzag graphene nanoribbons  

Microsoft Academic Search

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

Jun-Won Rhim; Kyungsun Moon

2009-01-01

310

Spin stiffness of graphene and zigzag graphene nanoribbons  

Microsoft Academic Search

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

Jun-Won Rhim; Kyungsun Moon

2010-01-01

311

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

312

Stiff-person syndrome first manifesting in pregnancy.  

PubMed

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

Cerimagic, Denis; Bilic, Ervina

2008-11-13

313

PLANETARY GEAR PARAMETRIC INSTABILITY CAUSED BY MESH STIFFNESS VARIATION  

Microsoft Academic Search

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

J. Lin; R. G. PARKER

2002-01-01

314

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

315

Stiffness dependent separation of cells in a microfluidic device.  

PubMed

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

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

2013-10-16

316

Physical activity and arterial stiffness in chronic obstructive pulmonary disease.  

PubMed

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

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

2013-08-07

317

Stiffness Dependent Separation of Cells in a Microfluidic Device  

PubMed Central

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

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

2013-01-01

318

Dynamic isolation systems using tunable nonlinear stiffness beams  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

319

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

Microsoft Academic Search

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

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

2009-01-01

320

Efficacy of pregabalin in a case of stiff-person syndrome: clinical and neurophysiological evidence.  

PubMed

Symptomatic treatment of stiff-person syndrome (SPS) might be challenging and a significant improvement of stiffness and rigidity is generally reached with high doses of benzodiazepines or baclofen causing side effects. A 71-year old woman diagnosed with SPS complained of marked stiffness of trunk and lower limb muscles with sudden painful spasms. She was unable to walk and she could not lean on her right leg. Cortical silent period (CSP) duration evaluated from right abductor pollicis brevis (APB) with transcranial magnetic stimulation was shortened. Polygraphic electromyographic (EMG) evaluation from paraspinal and leg muscles disclosed continuous motor unit activity at rest with interference muscular pattern. Symptomatic treatment with diazepam was withdrawn because of excessive sedation. In order to relieve the intense lumbar pain, she was prescribed pregabalin; since the day after, rigidity and painful spasms dramatically improved and she could walk without assistance. The clinical benefit persisted at 3 months follow-up and was paralleled by almost complete disappearance of EMG activity at rest and prolongation of CSP. The clinical and electrophysiological data in this SPS patient suggest the possible efficacy of pregabalin as symptomatic treatment without any significant side effects, which needs to be replicated in larger case series. PMID:22082988

Squintani, G; Bovi, T; Ferigo, L; Musso, A M; Ottaviani, S; Moretto, G; Morgante, F; Tinazzi, M

2011-11-13

321

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

PubMed

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

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

2010-11-16

322

Explicit integration of extremely stiff reaction networks: quasi-steady-state methods  

NASA Astrophysics Data System (ADS)

A preceding paper by Guidry et al 2013 Comput. Sci. Disc. 6 015001 demonstrated that explicit asymptotic methods generally work much better for extremely stiff reaction networks than has previously been shown in the literature. There we showed that for systems well removed from equilibrium, explicit asymptotic methods can rival standard implicit codes in speed and accuracy for solving extremely stiff differential equations. In this paper, we continue the investigation of systems well removed from equilibrium by examining quasi-steady-state (QSS) methods as an alternative to asymptotic methods. We show that for systems well removed from equilibrium, QSS methods also can compete with, or even exceed, standard implicit methods in speed, even for extremely stiff networks, and in many cases give a somewhat better integration speed than for asymptotic methods. As for asymptotic methods, we will find that QSS methods give correct results, but with a non-competitive integration speed as equilibrium is approached. Thus, we find that both asymptotic and QSS methods must be supplemented with partial equilibrium methods as equilibrium is approached to remain competitive with implicit methods.

Guidry, M. W.; Harris, J. A.

2013-01-01

323

Hole spin relaxation and coefficients in Landau-Lifshitz-Gilbert equation in ferromagnetic (Ga,Mn)As  

NASA Astrophysics Data System (ADS)

We investigate the temperature dependence of the coefficients in the Landau-Lifshitz-Gilbert equation in ferromagnetic GaMnAs by employing the Zener model. We first calculate the hole spin relaxation time based on the microscopic kinetic equation. We find that the hole spin relaxation time is typically several tens of femtoseconds and can present a nonmonotonic temperature dependence due to the variation of the interband spin mixing, influenced by the temperature-related Zeeman splitting. With the hole spin relaxation time, we are able to calculate the coefficients in the Landau-Lifshitz-Gilbert equation, such as the Gilbert damping, nonadiabatic spin torque, spin stiffness, and vertical spin stiffness coefficients. We find that the nonadiabatic spin torque coefficient ? is around 0.1-0.3 at low temperature, which is consistent with the experiment [J.-P. Adam , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.80.193204 80, 193204 (2009)]. As the temperature increases, ? monotonically increases. We show that the Gilbert damping coefficient ? increases with temperature below the Curie temperature, showing good agreement with the experiments [J. Sinova , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.69.085209 69, 085209 (2004); Kh. Khazen , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.78.195210 78, 195210 (2008)]. Moreover, we also calculate the temperature dependences of the spin stiffness and vertical spin stiffness.

Shen, K.; Wu, M. W.

2012-02-01

324

Variable stiffness control of a single-link flexible robotic arm  

Microsoft Academic Search

A case study is presented to demonstrate the use of variable stiffness control to attenuate the excessive oscillations of a single-link robotic arm. This relatively simple control technique actively changes the system’s stiffness to take advantage of strain energy storage capabilities for different stiffnesses. The stiffness changes required for vibration control can be accomplished with minimal effort and without adding

A. Warkentin; S. E. Semercigil

1995-01-01

325

Static analysis of a passive vibration isolator with quasi-zero-stiffness characteristic  

Microsoft Academic Search

The frequency range over which a linear passive vibration isolator is effective, is often limited by the mount stiffness required to support a static load. This can be improved upon by employing nonlinear mounts incorporating negative stiffness elements configured in such a way that the dynamic stiffness is much less than the static stiffness. Such nonlinear mounts are used widely

A. Carrella; M. J. Brennan; T. P. Waters

2007-01-01

326

Topology Design of Compliant Cellular Structures with Contact-Enabled, Graded Stiffness  

Microsoft Academic Search

A topology design method is presented for customizing cellular or lightweight structures with contact-enabled, graded stiffness. Structures with graded structural stiffness exhibit increasing stiffness with the magnitude of applied structural loads. In this work, stiffening is achieved via internal contact within the cellular structure. A continuum-based topology optimization approach is presented for tailoring cellular topologies with customized stiffness profiles that

Gaurav Gupta; Carolyn Conner Seepersad

327

Network community structure and loop coefficient method  

NASA Astrophysics Data System (ADS)

A modular structure, in which groups of tightly connected nodes could be resolved as separate entities, is a property that can be found in many complex networks. In this paper, we propose a algorithm for identifying communities in networks. It is based on a local measure, so-called loop coefficient that is a generalization of the clustering coefficient. Nodes with a large loop coefficient tend to be core inner community nodes, while other vertices are usually peripheral sites at the borders of communities. Our method gives satisfactory results for both artificial and real-world graphs, if they have a relatively pronounced modular structure. This type of algorithm could open a way of interpreting the role of nodes in communities in terms of the local loop coefficient, and could be used as a complement to other methods.

Vragovi?, I.; Louis, E.

2006-07-01

328

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

PubMed Central

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

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

2006-01-01

329

Aortic root dimensions and stiffness in healthy subjects.  

PubMed

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

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

2013-07-17

330

The Transport Coefficients  

NASA Astrophysics Data System (ADS)

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

García-Colín, Leopoldo S.; Dagdug, Leonardo

331

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

2012-11-12

332

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

333

New method for the element stiffness matrix of arbitrary planar bars  

NASA Astrophysics Data System (ADS)

The statical behaviour of a planar bar of an elastic and isotropic material having an arbitrary axis and a cross-section supported elastically by single and/or continuous supports is studied by the stiffness matrix method based on the complementary functions approach. The Timoshenko beam theory is extended for three-dimensional curvilinear bars taking into consideration the effects of axial and shear deformation. By considering the geometrical compatibility conditions together with the constitutive equations and equations of equilibrium, a set of 12 first order differential equations having variable coefficients is obtained for the spatial elements. From expressions developed in such manner for three-dimensional bars, the governing equations for the special case of a planar bar loaded within or perpendicular to its plane are derived, which are next solved by the complementary functions method. The stiffness matrix and the element load vector of a planar bar with an arbitrary axis are obtained taking into consideration both the presence of an elastic support and the effects of axial and shear deformations. The developed model has been coded in Fortran-77, which has been applied to various example problems available in the relevant literature, and the results have been compared.

Haktanir, V.

1994-08-01

334

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

NASA Astrophysics Data System (ADS)

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

Zhou, N.; Liu, K.

2010-04-01

335

Stiffness tomography exploration of living and fixed macrophages.  

PubMed

Stiffness tomography is a new atomic force microscopy imaging technique that allows highlighting structures located underneath the surface of the sample. In this imaging mode, such structures are identified by investigating their mechanical properties. We present here, for the first time, a description of the use of this technique to acquire detailed stiffness maps of fixed and living macrophages. Indeed, the mechanical properties of several macrophages were studied through stiffness tomography imaging, allowing some insight of the structures lying below the cell's surface. Through these investigations, we were able to evidence the presence and properties of stiff column-like features located underneath the cell membrane. To our knowledge, this is the first evidence of the presence, underneath the cell membrane, of such stiff features, which are in dimension and form compatible with phagosomes. Moreover, by exposing the cells to cytochalasin, we were able to study the induced modifications, obtaining an indication of the location and mechanical properties of the actin cytoskeleton. PMID:22528184

Roduit, C; Longo, G; Benmessaoud, I; Volterra, A; Saha, B; Dietler, G; Kasas, S

2012-05-01

336

Position control of seat suspension with minimum stiffness  

NASA Astrophysics Data System (ADS)

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

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

2006-04-01

337

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

338

Opening Dynamic Characteristics of a 32-Ft Ringslot Parachute, Stiffness Index 0.24, and 45.2-Inch Model, Stiffness Index 0.40.  

National Technical Information Service (NTIS)

The stiffness characteristics of full size and model parachutes can be expressed as stiffness indices. A very flexible model was developed with 0.4 stiffness index while a geometrically similar 32-ft ringslot parachute had an index of 0.24. The design det...

H. G. Heinrich T. R. Hektner

1972-01-01

339

Homogenization of Stiff Plates and Two-Dimensional High-Viscosity Stokes Equations  

NASA Astrophysics Data System (ADS)

The paper deals with the homogenization of stiff heterogeneous plates. Assuming that the coefficients are equi-bounded in L 1, we prove that the limit of a sequence of plate equations remains a plate equation which involves a strongly local linear operator acting on the second gradients. This compactness result is based on a div-curl lemma for fourth-order equations. On the other hand, using an intermediate stream function we deduce from the plates case a similar result for high-viscosity Stokes equations in dimension two, so that the nature of the Stokes equation is preserved in the homogenization process. Finally, we show that the L 1-boundedness assumption cannot be relaxed. Indeed, in the case of the Stokes equation the concentration of one very rigid strip on a line induces the appearance of second gradient terms in the limit problem, which violates the compactness result obtained under the L 1-boundedness condition.

Briane, Marc; Casado-Díaz, Juan

2012-09-01

340

Improved compression buckling for rectangular composite plates by stiffness tailoring  

NASA Astrophysics Data System (ADS)

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

341

Sound insulating element featuring high stiffness and low weight  

SciTech Connect

This paper describes a new approach to the problem of combining good sound insulation with high stiffness, low weight and limited thickness. A typical application is shipboard partitions where weight and thickness are essential cost factors and where specified demands on sound insulation are made at an increasing rate. A single leaf wall will as we know under favorable conditions give sound insulation according to the mass law. When a panel is stiffened the coincidence frequency moves to lower frequency and for typical dimensions and material properties it will be found within the interesting frequency region (100 to 3150 Hz). A double leaf wall must have weak connections between the leaves for good sound insulation, which in turn makes the stiffness performance poor. Optimizing stiffness with available space and material will result in a construction with a sandwich cross section.

Einarsson, S.; Soederquist, J.

1982-01-01

342

Dynamic instabilities in assemblies of molecular motors with finite stiffness.  

PubMed

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

Guérin, T; Prost, J; Joanny, J-F

2010-06-16

343

Dynamic Instabilities in Assemblies of Molecular Motors with Finite Stiffness  

NASA Astrophysics Data System (ADS)

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

Guérin, T.; Prost, J.; Joanny, J.-F.

2010-06-01

344

Effect of Surface Stress on the Stiffness of Cantilever Plates  

NASA Astrophysics Data System (ADS)

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

Lachut, Michael J.; Sader, John E.

2007-11-01

345

Generalized Chromodynamic Detection  

Microsoft Academic Search

A Generalized Likelihood Ratio (GLR) detector is formulated for a known spectral contrast signal that may be present with unknown amplitudes in a pair of co-registered hyperspectral image observations. Under multivariate Gaussian hypotheses, the joint likelihood function is a quadratic expression containing the signal coefficients for the two spectral observations. Maximum-likelihood coefficient estimates, obtained by solving a set of linear

Alan Stocker; Pierre Villeneuve

2008-01-01

346

Increased left atrial chamber stiffness in hypertrophic cardiomyopathy.  

PubMed Central

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

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

1993-01-01

347

Generalized quantum entropies  

NASA Astrophysics Data System (ADS)

A deduction of generalized quantum entropies within the Tsallis and Kaniadakis frameworks is derived using a generalization of the ordinary multinomial coefficient. This generalization is based on the respective deformed multiplication and division. We show that the two above entropies are consistent with ones arbitrarily assumed at other contexts.

Santos, A. P.; Silva, R.; Alcaniz, J. S.; Anselmo, D. H. A. L.

2011-08-01

348

Transport coefficients of soft repulsive particle fluids  

NASA Astrophysics Data System (ADS)

Molecular dynamics computer simulation has been used to compute the self-diffusion coefficient, D, and shear viscosity, ?s, of soft-sphere fluids, in which the particles interact through the soft-sphere pair potential, phi(r) = epsilon(?/r)n, where n measures the steepness or stiffness of the potential, epsilon and ? are a characteristic energy and distance, respectively. The simulations were carried out on monodisperse systems for a range of n values from the hard-sphere (n\\to \\infty ) limit down to n = 4 over a range of densities. An ideal glass transition value was estimated from the limit where D and \\eta_{\\mathrm {s}}^{-1}\\to 0 for each value of n. Nucleation of the crystalline phase was found to intervene prior to the formation of the glass itself, as has been found previously for hard spheres (i.e. n\\to \\infty ). With increasing softness the glass transition moves further within the solid part of the phase diagram, as predicted by Cardenas and Tosi (2005 Phys. Lett. A 336 423), although the volume fractions at the glass transition estimated by the current procedure here are systematically lower than the predictions of that study.

Heyes, D. M.; Bra?ka, A. C.

2008-03-01

349

Transport coefficients of soft repulsive particle fluids.  

PubMed

Molecular dynamics computer simulation has been used to compute the self-diffusion coefficient, D, and shear viscosity, ?(s), of soft-sphere fluids, in which the particles interact through the soft-sphere pair potential, ?(r) = ?(?/r)(n), where n measures the steepness or stiffness of the potential, ? and ? are a characteristic energy and distance, respectively. The simulations were carried out on monodisperse systems for a range of n values from the hard-sphere ([Formula: see text]) limit down to n = 4 over a range of densities. An ideal glass transition value was estimated from the limit where D and [Formula: see text] for each value of n. Nucleation of the crystalline phase was found to intervene prior to the formation of the glass itself, as has been found previously for hard spheres (i.e. [Formula: see text]). With increasing softness the glass transition moves further within the solid part of the phase diagram, as predicted by Cardenas and Tosi (2005 Phys. Lett. A 336 423), although the volume fractions at the glass transition estimated by the current procedure here are systematically lower than the predictions of that study. PMID:21694216

Heyes, D M; Bra?ka, A C

2008-02-20

350

Contribution of collagen fibers to the compressive stiffness of cartilaginous tissues.  

PubMed

Cartilaginous tissues such as the intervertebral disk are predominantly loaded under compression. Yet, they contain abundant collagen fibers, which are generally assumed to contribute to tensile loading only. Fiber tension is thought to originate from swelling of the proteoglycan-rich nucleus. However, in aged or degenerate disk, proteoglycans are depleted, whereas collagen content changes little. The question then rises to which extend the collagen may contribute to the compressive stiffness of the tissue. We hypothesized that this contribution is significant at high strain magnitudes and that the effect depends on fiber orientation. In addition, we aimed to determine the compression of the matrix. Bovine inner and outer annulus fibrosus specimens were subjected to incremental confined compression tests up to 60 % strain in radial and circumferential direction. The compressive aggregate modulus was determined per 10 % strain increment. The biochemical composition of the compressed specimens and uncompressed adjacent tissue was determined to compute solid matrix compression. The stiffness of all specimens increased nonlinearly with strain. The collagen-rich outer annulus was significantly stiffer than the inner annulus above 20 % compressive strain. Orientation influenced the modulus in the collagen-rich outer annulus. Finally, it was shown that the solid matrix was significantly compressed above 30 % strain. Therefore, we concluded that collagen fibers significantly contribute to the compressive stiffness of the intervertebral disk at high strains. This is valuable for understanding the compressive behavior of collagen-reinforced tissues in general, and may be particularly relevant for aging or degenerate disks, which become more fibrous and less hydrated. PMID:23443749

Römgens, Anne M; van Donkelaar, Corrinus C; Ito, Keita

2013-02-27

351

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

PubMed

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

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

2012-05-01

352

Analysis and design of passive low-pass filter-type vibration isolators considering stiffness and mass limitations  

Microsoft Academic Search

The aim of this paper is to design stiff and lightweight uniaxial passive vibration isolators that have low stop-band frequency. In order to make fair comparisons, stop-band frequencies of various isolator designs are formulated in a general framework. Two new n-degree-of-freedom (n-dof) isolator designs are introduced. The first design has n-1 anti-resonance frequencies (zeros), which are generated by n-1 single-degree-of-freedom

C. Yilmaz; N. Kikuchi

2006-01-01

353

Arthroscopic Treatment of Posttraumatic Elbow Pain and Stiffness  

Microsoft Academic Search

Nineteen consecutive cases of posttraumatic arthrofi brosis of the elbow secondary to a fracture or fracture- dislocation and treated with arthroscopic debridement and manipulation were retrospectively reviewed. All of the patients had pain and stiffness in their elbows, and all had failed a conservative therapy program. All 19 patients were followed postoperatively for an average of 29 months (range, 12

Laura A. Timmerman; James R. Andrews

1994-01-01

354

A Model for the Variable Stiffness of Undrained Clay  

Microsoft Academic Search

In this paper a theoretical model for the undrained behaviour of clays is presented. The model takes into account the non-linear behaviour of soil at small strains, and also includes effects such as hysteresis and dependence of stiffness on recent stress history. The model uses multiple yield surfaces within the framework of work-hardening plasticity theory. The quality of fit to

G. T. Houlsby

1999-01-01

355

Bidirectional antagonistic variable stiffness actuation: Analysis, design & Implementation  

Microsoft Academic Search

The variable stiffness actuation concept is considered to provide a human-friendly robot technology. This paper examines a joint concept called the bidirectional antagonistic joint which is a extension of antagonistic joints. A new operating mode called the helping mode is introduced, which increases the joint load range. Although the joint can not be pretensioned in the helping mode, it is

Florian Petit; Maxime Chalon; Werner Friedl; Markus Grebenstein; Alin Albu-Schäffer; Gerd Hirzinger

2010-01-01

356

Acetabular cup stiffness and implant orientation change acetabular loading patterns.  

PubMed

Acetabular cup orientation has been shown to influence dislocation, impingement, edge loading, contact stress, and polyethylene wear in total hip arthroplasty. Acetabular implant stiffness has been suggested as a factor in pelvic stress shielding and osseous integration. This study was designed to examine the combined effects of acetabular cup orientation and stiffness and on pelvic osseous loading. Four implant designs of varying stiffness were implanted into a composite hemipelvis in 35° or 50° of abduction. Specimens were dynamically loaded to simulate gait and pelvic strains were quantified with a grid of rosette strain gages and digital image correlation techniques. Changes in the joint reaction force orientation significantly altered mean acetabular bone strain values up to 67%. Increased cup abduction resulted in a 12% increase along the medial acetabular wall and an 18% decrease in strain in inferior lateral regions. Imbalanced loading distributions were observed with the stiffer components, resulting in higher, more variable, and localized surface strains. This study illustrates the effects of cup stiffness, gait, and implant orientation on loading distributions across the implanted pelvis. PMID:22854350

Small, Scott R; Berend, Michael E; Howard, Leah A; Tunç, Didem; Buckley, Christine A; Ritter, Merrill A

2012-07-31

357

Shrinking stature; a new risk factor for arterial stiffness  

Microsoft Academic Search

Pulse pressure (PP) is one of useful markers for arterial stiffness. In addition to reduced Windkessel function, the timing of arterial wave reflection also affects the shape of the arterial waveform and thus is a major determinant of PP. Since a distance to the reflection points is a determinant of the arrival timing, short stature, which increases PP through an

Yasuharu Tabara; Rieko Tachibana-Iimori; Ryuichi Kawamoto; Miyuki Yamamoto; Ikuko Kondo; Tetsuro Miki; Katsuhiko Kohara

2005-01-01

358

Ultra-stiff, low mass, EM gun design  

Microsoft Academic Search

High performance in an electromagnetic (EM) gun implies high velocity with minimal transition from a solid to plasma armature. Factors that affect gun performance include armature integrity, bore straightness and bore stiffness. Experiences firing solid armature at CEM-UT since 1987 have shown that the lack of one or more of these three ingredients will result in less than desirable performance.

M. D. Werst; J. R. Kitzmiller; C. S. Hearn; G. A. Wedeking

2004-01-01

359

Ultra-stiff, low mass, electromagnetic gun design  

Microsoft Academic Search

High performance in an electromagnetic (EM) gun implies high velocity with minimal transition from a solid to plasma armature. Factors that affect gun performance include armature integrity, bore straightness, and bore stiffness. Experiences firing solid armature at the Center for Electromechanics at The University of Texas at Austin since 1987 have shown that the lack of one or more of

M. D. Werst; J. R. Kitzmiller; C. S. Hearn; G. A. Wedeking

2005-01-01

360

Low insulin level is associated with aortic stiffness  

Microsoft Academic Search

Recent studies have demonstrated that hyperinsulinemia is a risk factor for cardiovascular disease. The aim of this study was to evaluate the relationship between serum insulin level and the cardio-ankle vascular index (CAVI), which was developed as a marker of arterial stiffness. We performed a cross-sectional study of 260 consecutive and nondiabetic subjects with clinical suspicion of coronary heart disease.

Hiroshi Okada; Michiaki Fukui; Muhei Tanaka; Satoshi Akabame; Ki-ichiro Tomiyasu; Koji Nakano; Masahiro Yamazaki; Goji Hasegawa; Yohei Oda; Naoto Nakamura

2011-01-01

361

Dual-mode dynamic functional stiffness of articular cartilage  

Microsoft Academic Search

INTRODUCTION: Dynamic stiffness parameters (elastic modulus, loss angle, Poisson's ratio) determine how poroviscoelastic materials or structures (e.g. cartilage) distribute and dissipate loads. Also, these parameters are highly sensitive to structural changes and thus have diagnostic value. Nutrition processes in cartilage occur at slow loading rates which move water in and out of the tissue. In contrast, gait subjects hip, knee

H. Ardura Garcia; A. U. Daniels; D. Wirz

2008-01-01

362

Wave Haptics: Building Stiff Controllers from the Natural Motor Dynamics  

Microsoft Academic Search

Haptics, like the fields of robotics and motion control, relies on high stiffness position control of electric motors. Traditionally DC motors are driven by current amplifiers and encoder-based position feedback creates virtual springs. Unfortunately, sensor quantization, discretization, and amplifier bandwidths impose performance limits, while the amplifiers work hard to cancel the motor's electrical dynamics. We present an alternate approach noting

Nicola Diolaiti; Günter Niemeyer; Neal A. Tanner

2007-01-01

363

Lower limbs power and stiffness after whole-body vibration.  

PubMed

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

Colson, S S; Petit, P-D

2012-11-09

364

Atypical low back pain: stiff-person syndrome  

Microsoft Academic Search

Stiff-person syndrome was diagnosed in a patient with chronic low back pain. The diagnosis of this rare neurological condition rests mainly on the clinical findings of axial and proximal limb rigidity, increased lumbar lordosis often accompanied with pain, and normal neurological findings apart from brisk deep tendon reflexes. Electromyography of the lumbar paraspinal muscles shows motor unit firing at rest

Philippe Gallien; Aurélie Durufle; Sabine Petrilli; Marc Verin; Régine Brissot; Sandrine Robineau

2002-01-01

365

The numerical simulation for stiff systems of ordinary differential equations  

Microsoft Academic Search

In this paper, the variational iteration method is applied to solve systems of ordinary differential equations in both linear and nonlinear cases, focusing interest on stiff problems. Some examples are given to illustrate the accuracy and effectiveness of the method. We compare our results with results obtained by the Adomian decomposition method. This comparison reveals that the variational iteration method

M. T. Darvishi; F. Khani; A. A. Soliman

2007-01-01

366

Effect of adhesive stiffness and thickness on stress distributions in ...  

Treesearch

This paper presents the results of a finite-element analysis of structural finger joints ... of adhesive stiffness and thickness on stress distribution patterns in finger joints. ... We recommend that you also print this page and attach it to the printout of ...

367

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

368

Arterial Stiffness and Osteoporosis in Chronic Obstructive Pulmonary Disease  

Microsoft Academic Search

Rationale: Chronic obstructive pulmonary disease (COPD) is associ- ated with an increased risk of cardiovascular events and osteoporo- sis. Increasedarterialstiffnessis anindependentpredictorofcardio- vascular disease. Objectives: Wetested thehypothesisthat patientswithCOPD would have increased arterial stiffness, which would be associated with osteoporosis and systemic inflammation. Methods: We studied 75 clinically stable patients with a range of severity of airway obstruction and 42 healthy smoker

Ramsey Sabit; Charlotte E. Bolton; Peter H. Edwards; Rebecca J. Pettit; William D. Evans; Carmel M. McEniery; Ian B. Wilkinson; John R. Cockcroft; Dennis J. Shale

2007-01-01

369

On obtaining machine tool stiffness by CAE techniques  

Microsoft Academic Search

In this paper, a single module method and a newly developed hybrid modeling method for analyzing the stiffness of machine tools are introduced in detail. Techniques include building suitable finite element models, determining equivalent loads, simulating the interface between two modules, considering boundary constraints, and interpreting results. By taking a detailed finite element mesh for one of the five modules

David Te-Yen Huang; Jyh-Jon Lee

2001-01-01

370

Stiffness and Strength Properties of Shear Transfer Plate Connections.  

National Technical Information Service (NTIS)

Shear transfer plates (STPs) are light-gauge steel plates with teeth on both sides that are used to transfer load between two layers of lumber. The objective of the study was to evaluate the strength and stiffness characteristics of STP connections throug...

D. Bohnfoff R. Nagel R. Wolfe

1993-01-01

371

Vascular calcification: A stiff challenge for the nephrologist  

Microsoft Academic Search

Vascular calcification: A stiff challenge for the nephrologists—Does preventing bone disease cause arterial disease? There has been an explosion of interest in vascular calcification in the last 5 years. Four key “germinal” findings have fallen onto very fertile soil. First, on the background of an increasing cardiovascular disease burden it has been found that at least cross-sectionally, and in a

DAVID GOLDSMITH; EBERHARD RITZ; ADRIAN COVIC

2004-01-01

372

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

373

Quantitative determination of contact stiffness using atomic force acoustic microscopy  

Microsoft Academic Search

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

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

2000-01-01

374

Reconstruction of Hydroturbine Units with Transition to Stiff Thrust Bearing  

Microsoft Academic Search

Prevailing use of hydraulic thrust bearings in vertical high- and medium-power hydroturbine units for over 30 years has virtually eliminated the experience of mounting, adjusting, and servicing of thrust bearings on a stiff screw support. The author will make an attempt to fill the gap using data obtained in replacement of hydraulic thrust bearing of one of the hydroturbine units

A. I. Popov

2005-01-01

375

Discontinuous Galerkin for Hyperbolic Systems with Stiff Relaxation  

SciTech Connect

A Discontinuous Galerkin method is applied to hyperbolic systems that contain stiff relaxation terms. We demonstrate that when the relaxation time is unresolved, the method is accurate in the sense that it accurately represents the system's Chapman-Enskog approximation. Results are presented for the hyperbolic heat equation and coupled radiation-hydrodynamics.

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

1999-05-24

376

Optimality principles in stiffness control: The VSA kick  

Microsoft Academic Search

The importance of Variable Stiffness Actuators (VSA) in safety and performance of robots has been extensively discussed in the last decade. It has also been shown recently that a VSA brings performance advantages with respect to common actuators. For instance, the solution of the optimal control problem of maximizing the speed of a VSA for impact maximization at a given

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

2012-01-01

377

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

378

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...

379

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

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

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

380

Joint stiffness identification of six-revolute industrial serial robots  

Microsoft Academic Search

Although robots tend to be as competitive as CNC machines for some operations, they are not yet widely used for machining operations. This may be due to the lack of certain technical information that is required for satisfactory machining operation. For instance, it is very difficult to get information about the stiffness of industrial robots from robot manufacturers. As a

Claire Dumas; Stéphane Caro; Sébastien Garnier; Benoît Furet

2011-01-01

381

Evaluation of MESL Membrane-Puncture, Stiffness, Temperature, Solvents.  

National Technical Information Service (NTIS)

Several membrane materials used or considered for MESL(membrane-enveloped soil layer) utilization of poor soils in road contruction have been tested for cold effect on puncture and stiffness. PE(polyethylene) film was also tested for solvent soak effects....

J. M. Sayward

1976-01-01

382

Stiffness and hysteresis properties of some prosthetic feet.  

PubMed

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

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

1990-12-01

383

Studies on the Preparation of Strong/Stiff Polymeric Fibres.  

National Technical Information Service (NTIS)

The thesis presents the results of several studies on the preparation of strong and/or stiff polymeric fibers. The emphasis in the studies lies in high strength fibers prepared from polyethylene and poly(L-lactide). In chapter 1 a brief review is given of...

A. R. Postema

1988-01-01

384

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

385

Predicting Arterial Stiffness From the Digital Volume Pulse Waveform  

Microsoft Academic Search

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

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

2007-01-01

386

Nanoindentation of wood cell walls: Continuous stiffness and hardness measurements  

Microsoft Academic Search

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

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

2007-01-01

387

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

388

Analytical scheme calculations of angular momentum coupling and recoupling coefficients  

NASA Astrophysics Data System (ADS)

We investigate the Scheme programming language opportunities to analytically calculate the Clebsch-Gordan coefficients, Wigner 6j and 9j symbols, and general recoupling coefficients that are used in the quantum theory of angular momentum. The considered coefficients are calculated by a direct evaluation of the sum formulas. The calculation results for large values of quantum angular momenta were compared with analogous calculations with FORTRAN and Java programming languages.

Deveikis, A.; Kuznecovas, A.

2007-03-01

389

Drag Coefficient of Hexadecane Particles  

NASA Astrophysics Data System (ADS)

This paper deals with the drag coefficient of solidified hexadecane particles and their free rising velocity in liquid. The drag coefficient was experimentally investigated in Reynolds number range of about 40-300. The present experimental results are summarized in the following; (1) the drag coefficient of solidified hexadecane particles formed in liquid coolant by direct contact cooling is higher than that of a smooth surface sphere, this high drag coefficient seems to be attributed to the non-smooth surface of the solidified hexadecane particles, (2) experimental correlation for the drag coefficient of the solidified hexadecane particles was proposed, (3 ) the measured rising velocity of the solidified hexadecane particle agrees well with the calculated one, (4) the drag coefficients of hexadecane particles that were made by pouring hexadecane liquid into a solid hollow sphere agreed well with the drag coefficient of smooth surface sphere.

Nakao, Yoshinobu; Hishida, Makoto; Kajimoto, Sadaaki; Tanaka, Gaku

390

Optimum loading mode for axial stiffness testing in limb lengthening.  

PubMed

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

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

2006-03-01

391

Loss coefficient correlation for wet-cooling tower fills  

Microsoft Academic Search

Loss coefficient correlations given in the literature for wet-cooling tower fills are relatively simple and generally do not represent the pressure drop accurately over a wide range of operational conditions. A new form of empirical equation is proposed that correlates fill loss coefficient data more effectively when compared to other forms of empirical equations commonly found in the literature.

Johannes C. Kloppers; Detlev G. Kröger

2003-01-01

392

Coefficients for Tests from a Decision Theoretic Point of View  

Microsoft Academic Search

From a decision theoretic point of view a general coefficient for tests, d, is derived. The coefficient is applied to three kinds of decision situations. First, the situation is considered in which a true score is estimated by a function of the observed score of a subject on a test (point estimation). Using the squared error loss function and Kelley's

Wim J. van der Linden; Gideon J. Mellenbergh

1978-01-01

393

A new descriptive statistic: The parabolic correlation coefficient  

Microsoft Academic Search

This article proposes a new descriptive statistic related to the second order parabola in the same manner in which the familiar correlation coefficient is related to the regression coefficient. The parabolicr describes in standard terms simultaneously the general trend of the regression and the extent and nature of its curvilinearity, and is relatively easy to compute and easy to communicate.

Charles C. Peters

1946-01-01

394

Trace formulas for time delay and the second virial coefficient  

Microsoft Academic Search

A high-temperature expansion for the quantum-mechanical second virial coefficient is derived using newly developed trace formulas for time delay in scattering theory. The known cancellation between the bound state and continuum contributions is explained in this general framework. The method cam be extended to higher virial coefficients.

D. Bollé; H. Smeesters

1977-01-01

395

Calculating potentials of mean force and diffusion coefficients from nonequilibrium processes without Jarzynski's equality.  

PubMed

In general, the direct application of the Jarzynski equality (JE) to reconstruct potentials of mean force (PMFs) from a small number of nonequilibrium unidirectional steered molecular-dynamics (SMD) paths is hindered by the lack of sampling of extremely rare paths with negative dissipative work. Such trajectories that transiently violate the second law of thermodynamics are crucial for the validity of JE. As a solution to this daunting problem, we propose a simple and efficient method, referred to as the FR method, for calculating simultaneously both the PMF U(z) and the corresponding diffusion coefficient D(z) along a reaction coordinate z for a classical many-particle system by employing a small number of fast SMD pullings in both forward (F) and time reverse (R) directions, without invoking JE. By employing Crooks [Phys. Rev. E 61, 2361 (2000)] transient fluctuation theorem (that is more general than JE) and the stiff-spring approximation, we show that (i) the mean dissipative work W(d) in the F and R pullings is the same, (ii) both U(z) and W(d) can be expressed in terms of the easily calculable mean work of the F and R processes, and (iii) D(z) can be expressed in terms of the slope of W(d). To test its viability, the FR method is applied to determine U(z) and D(z) of single-file water molecules in single-walled carbon nanotubes (SWNTs). The obtained U(z) is found to be in very good agreement with the results from other PMF calculation methods, e.g., umbrella sampling. Finally, U(z) and D(z) are used as input in a stochastic model, based on the Fokker-Planck equation, for describing water transport through SWNTs on a mesoscopic time scale that in general is inaccessible to MD simulations. PMID:16483195

Kosztin, Ioan; Barz, Bogdan; Janosi, Lorant

2006-02-14

396

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

National Technical Information Service (NTIS)

Results of an analytical and experimental study to characterize the structural response of two compression-loaded variable stiffness composite panels are presented and discussed. These variable stiffness panels are advanced composite structures, in which ...

K. C. Wu Z. Guerdal J. H. Starnes

2002-01-01

397

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

PubMed Central

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

DUBIN, Ruth; OWENS, Christopher; GASPER, Warren; GANZ, Peter; JOHANSEN, Kirsten

2011-01-01

398

High-arched runners exhibit increased leg stiffness compared to low-arched runners  

Microsoft Academic Search

Leg stiffness between high-arched (HA) and low-arched (LA) runners was compared. It was hypothesized that high-arched runners would exhibit increased leg stiffness, increased sagittal plane support moment, greater vertical loading rates, decreased knee flexion excursion and increased activation of the knee extensor musculature. Twenty high-arched and 20 low-arched subjects were included in this study. Leg stiffness, knee stiffness, vertical loading

Dorsey S Williams; Irene McClay Davis; John P Scholz; Joseph Hamill; Thomas S Buchanan

2004-01-01

399

Generalization of differential quadrature discretization  

NASA Astrophysics Data System (ADS)

The differential quadrature (DQ) is generalized. Various methods for generating the weighting coefficients are developed. The design of a grid model is flexible. Weighting coefficients for general multi-coordinate grid models with arbitrary configurations can also be calculated. The calculation of weighting coefficients is easy. Sample numerical procedures for constructing one-coordinate, two-coordinate and arbitrary finite-coordinate generic differential quadrature models are presented.

Chen, Chang-New

1999-12-01

400

A note on the Painlevé test for nonlinear variable-coefficient PDEs  

Microsoft Academic Search

For a generalized nonlinear PDEs with variable coefficients, it is not Painlevé integrable unless the variable coefficients satisfy certain constraint conditions. In this note a generalized algorithm is proposed for the Painlevé test of nonlinear variable-coefficient PDEs. For the three steps of Painlevé test, i.e. leading order analysis, resonance determination and verification of resonant conditions, the analysis of parametric constraints

Gui-Qiong Xu

2009-01-01

401

Quadrature formulas for Fourier coefficients  

NASA Astrophysics Data System (ADS)

We consider quadrature formulas of high degree of precision for the computation of the Fourier coefficients in expansions of functions with respect to a system of orthogonal polynomials. In particular, we show the uniqueness of a multiple node formula for the Fourier-Tchebycheff coefficients given by Micchelli and Sharma and construct new Gaussian formulas for the Fourier coefficients of a function, based on the values of the function and its derivatives.

Bojanov, Borislav; Petrova, Guergana

2009-09-01

402

Vibration control using an adaptive tuned vibration absorber with a variable curvature stiffness element  

Microsoft Academic Search

An adaptive tuned vibration absorber (ATVA) with a variable stiffness element is capable of retuning itself in response to a time-varying excitation frequency, enabling effective vibration control over a range of frequencies. One way of adjusting the stiffness is by shape change, and this paper presents the design for an ATVA that exploits this principle. The stiffness element is formed

Philip Bonello; Michael J Brennan; Stephen J Elliott

2005-01-01

403

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

Microsoft Academic Search

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

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

1999-01-01

404

Effects of continuous vs. interval exercise training on blood pressure and arterial stiffness in treated hypertension  

Microsoft Academic Search

Exercise is an effective intervention for treating hypertension and arterial stiffness, but little is known about which exercise modality is the most effective in reducing arterial stiffness and blood pressure in hypertensive subjects. Our purpose was to evaluate the effect of continuous vs. interval exercise training on arterial stiffness and blood pressure in hypertensive patients. Sixty-five patients with hypertension were

Guilherme Veiga Guimarães; Emmanuel Gomes Ciolac; Vitor Oliveira Carvalho; Veridiana Moraes D'Avila; Luiz Aparecido Bortolotto; Edimar Alcides Bocchi

2010-01-01

405

Aortic Stiffness Is an Independent Predictor of Primary Coronary Events in Hypertensive Patients A Longitudinal Study  

Microsoft Academic Search

Arterial stiffness may predict coronary heart disease beyond classic risk factors. In a longitudinal study, we assessed the predictive value of arterial stiffness on coronary heart disease in patients with essential hypertension and without known clinical cardiovascular disease. Aortic stiffness was determined from carotid-femoral pulse wave velocity at baseline in 1045 hypertensives. The risk assessment of coronary heart disease was

Pierre Boutouyrie; Anne Isabelle Tropeano; Roland Asmar; Isabelle Gautier; Athanase Benetos; Patrick Lacolley; Stéphane Laurent

406

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

Microsoft Academic Search

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

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

2002-01-01

407

Advantages of a Biomimetic Stiffness Profile in Pitching Flexible Fin Propulsion  

Microsoft Academic Search

The use of oscillating flexible fins in propulsion has been the subject of several studies in recent years, but attention is rarely paid to the specific role of stiffness profile in thrust production. Stiffness profile is defined as the variation in local chordwise bending stiffness (EI) of a fin, from leading to trailing edge. In this study, flexible fins with

Paul Riggs; Adrian Bowyer; Julian Vincent

2010-01-01

408

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

Microsoft Academic Search

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

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

2010-01-01

409

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

Microsoft Academic Search

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

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

1996-01-01

410

Stiffness m-value and the Low Temperature Relaxation Properties of Asphalt Binders  

Microsoft Academic Search

The development of the Strategic Highway Research Program (SHRP) low temperature binder specifications was based on the observation that asphalt mixture creep stiffness at 2 hours correlated well with instances of transverse cracking. Extending the correlation to asphalt binder stiffness and using time-temperature superposition, a maximum stiffness value was imposed on the binders and a limiting temperature at which the

Mihai O. Marasteanu; Arindam Basu

2004-01-01

411

Stiffness and strength of fiber reinforced polymer composite bridge deck systems  

Microsoft Academic Search

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

Aixi Zhou

2002-01-01

412

Management of acute achilles tendinopathy: effect of etoricoxib on pain control and leg stiffness.  

PubMed

Tendinopathies are a major cause of disability in the athletic population; the main purpose of the treatment of these injuries is to reduce pain and improve function promptly. The objective of this randomized, active comparator controlled, blinded study was to evaluate etoricoxib efficacy in pain control and leg stiffness in athletes suffering acute unilateral Achilles tendinopathy. Fifty-six eligible male athletes (mean age 37.5±11.0 y) suffering acute Achilles tendinopathy were randomized to receive either etoricoxib 120 mg oral once daily (n=28) or diclofenac 100 mg oral once daily (n=28). Pain (100-mm visual analogue scale-VAS), analgesic effect (percentage of 100-mm VAS reduction), satisfaction with pain management (PGART), and leg stiffness (LSR) were evaluated after one week of anti-inflammatory treatment. Over the 7-day treatment period, both etoricoxib and diclofenac provided significantly relief of Achilles tendon pain compared to that experienced at baseline (mean VAS 26.7±2.2 and 56.4±1.8, respectively; p<.001). Analgesic effect averaged 53.7±38.1% (etoricoxib= 56.4% and diclofenac 50.6%, p=0.64). Patients referred high level of satisfaction with anti-inflammatory treatment (PGART=2.0±1.3), while leg stiffness showed a significant improvement after one-week therapy (LSR 0.89±0.1 vs. 0.95±0.1; p=0.038). PGART and LSR values within etoricoxib and diclofenac groups were not significant (p=0.46, and p=0.37, respectively). Both drugs were generally well tolerated; patients receiving etoricoxib reported significantly less side effects than those in the diclofenac group (0% and 14,2%, respectively, p=0.037). Etoricoxib is clinically effective in treatment of acute Achilles tendinopathy providing a magnitude of effect comparable to that of diclofenac with fewer side effects. Effective control of tendon pain in the acute phase of such sports-related injuries may be helpful to reduce morbidity and improve capabilities associated with high performance like leg stiffness. PMID:24099813

Maquirriain, Javier; Kokalj, Antonio

2013-09-01

413

Derivation of stiffness matrix in constitutive modeling of magnetorheological elastomer  

NASA Astrophysics Data System (ADS)

Magnetorheological elastomers (MREs) are a class of smart materials whose mechanical properties change instantly by the application of a magnetic field. Based on the specially orthotropic, transversely isotropic stress-strain relationships and effective permeability model, the stiffness matrix of constitutive equations for deformable chain-like MRE is considered. To valid the components of shear modulus in this stiffness matrix, the magnetic-structural simulations with finite element method (FEM) are presented. An acceptable agreement is illustrated between analytical equations and numerical simulations. For the specified magnetic field, sphere particle radius, distance between adjacent particles in chains and volume fractions of ferrous particles, this constitutive equation is effective to engineering application to estimate the elastic behaviour of chain-like MRE in an external magnetic field.

Leng, D.; Sun, L.; Sun, J.; Lin, Y.

2013-02-01

414

Force, Torque and Stiffness: Interactions in Perceptual Discrimination  

PubMed Central

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

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

2011-01-01

415

Stabilized multilevel Monte Carlo method for stiff stochastic differential equations  

NASA Astrophysics Data System (ADS)

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

Abdulle, Assyr; Blumenthal, Adrian

2013-10-01

416

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

417

Effect of surface stress on the stiffness of thin elastic plates and beams  

NASA Astrophysics Data System (ADS)

Nanomechanical doubly-clamped beams and cantilever plates are often used to sense a host of environmental effects, including biomolecular interations, mass measurements, and responses to chemical stimuli. Understanding the effects of surface stress on the stiffness of such nanoscale devices is essential for rigorous analysis of experimental data. Recently, we explored the effects of surface stress on cantilever plates and presented a theoretical framework valid for thin plate structures. Here, we generalize this framework and apply it to cantilever plates and doubly-clamped beams, exploring in detail the relative physical mechanisms causing a stiffness change in each case. Specifically, Poisson's ratio is found to exert a dramatically different effect in cantilevers than in doubly-clamped beams, and here we explain why. The relative change in effective spring constant is also examined, and its connection to the relative frequency shift is discussed. Interestingly, this differs from what is naively expected from elementary mechanics. Finally, a discussion of the practical implications of our theoretical findings is presented, which includes an assessment of available experimental results and potential future measurements on nanoscale devices.

Lachut, Michael J.; Sader, John E.

2012-02-01

418

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

SciTech Connect

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

Kunz, S. C.

1980-01-01

419

Dynamic stiffness matrix of a poroelastic multi-layered site and its Green's functions  

NASA Astrophysics Data System (ADS)

Few studies of wave propagation in layered saturated soils have been reported in the literature. In this paper, a general solution of the equation of wave motion in saturated soils, based on one kind of practical Biot’s equation, was deduced by introducing wave potentials. Then exact dynamic-stiffness matrices for a poroelastic soil layer and halfspace were derived, which extended Wolfs theory for an elastic layered site to the case of poroelasticity, thus resolving a fundamental problem in the field of wave propagation and soil-structure interaction in a poroelastic layered soil site. By using the integral transform method, Green’s functions of horizontal and vertical uniformly distributed loads in a poroelastic layered soil site were given. Finally, the theory was verified by numerical examples and dynamic responses by comparing three different soil sites. This study has the following advantages: all parameters in the dynamic-stiffness matrices have explicitly physical meanings and the thickness of the sub-layers does not affect the precision of the calculation which is very convenient for engineering applications. The present theory can degenerate into Wolfs theory and yields numerical results approaching those for an ideal elastic layered site when porosity tends to zero.

Jianwen, Liang; Hongbing, You

2004-12-01

420

Stiffness in Discrimination of Patients with Vertebral Fractures  

Microsoft Academic Search

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

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

1999-01-01

421

Nanoscale structure and microscale stiffness of DNA nanotubes.  

PubMed

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

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

2013-07-31

422

Investigation of the Arterial Stiffness on Renal Artery Doppler Sonograms  

Microsoft Academic Search

This study aims to identify the effect of stiffness on renal artery Doppler sonograms by using a curve fitting approach. The\\u000a study includes 20 patients with suspected renovascular hypertension. Each patient underwent recordings during renal artery\\u000a examinations before and after administration of Captopril 25 mg (Kapril tablet, MN Pharmaceuticals, Istanbul, Turkey). Doppler\\u000a signals were analyzed with short time Fourier transformation, followed

Mahmut Tokmakçi; Nuri Erdogan

2009-01-01

423

Evaluation of Stiffness Terms for Z -cored Sandwich Panels  

Microsoft Academic Search

This paper presents a model for the stiffness terms of composite sandwich panels with structured cores (referred to as ‘z-core’ panels). Truss-cores, corrugated-cores and double-corrugated cores containing a polymeric foam were considered. The\\u000a model was validated, both through finite element simulation and through comparison with the results of experimental three\\u000a point bend tests on panels. A parametric study was performed

D. Zangani; M. Robinson; A. G. Gibson

2007-01-01

424

Stiff person syndrome: Advances in pathogenesis and therapeutic interventions  

Microsoft Academic Search

Opinion statement  Stiff person syndrome (SPS) varies from mild to severe, but if untreated it can be progressive and disabling. Although progress\\u000a has been made in understanding and treating SPS, the disease remains underdiagnosed, delaying treatment. Antibodies against\\u000a glutamic acid decarboxylase provide an excellent diagnostic marker, but their role in disease pathogenesis is uncertain. Research\\u000a focused on identifying new autoantigens has

Marinos C. Dalakas

2009-01-01

425

The immunological basis for treatment of stiff person syndrome  

Microsoft Academic Search

Antibodies against autoantigens involved in GABAergic neurotransmission are a shared feature of the different subtypes of stiff person syndrome (SPS). The autoantigens can be either presynaptic such as the smaller isoform of glutamic acid decarboxylase (GAD65), postsynaptic such as GABA-A receptor-associated protein and gephyrin, or located at the pre- and postsynaptic side such as amphiphysin. Most of these autoantigens are

Trygve Holmøy; Christian Geis

2011-01-01

426

Surviving stiff-person syndrome: a case report  

Microsoft Academic Search

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

Sharmilee Gnanapavan; Angela Vincent; Gavin Giovannoni

427

[An elderly woman with stiffness of the thumb].  

PubMed

A 81-year-old woman presented with progressive pain, stiffness and swelling of the right thumb. She also complained of dysphagia and Raynaud's phenomenon. Physical examination revealed sclerodactyly and telangiectasia. A plain X-ray showed marked calcifications of the flexor tendon of the right thumb and esophagography demonstrated decreased motility of the lower esophagus. Additionally, anticentromere antibodies were positive. As a result, the patient was diagnosed with calcinosis as a presenting symptom of limited systemic scleroderma. PMID:23171559

Franssen, Laurens E; Franssen, Marcel J A M; Jeurissen, Maurice E C

2012-01-01

428

Noninvasive assessment of arterial stiffness by pulse wave analysis.  

PubMed

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

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

2012-11-01

429

Arterial stiffness and cardiovascular events: The Framingham Heart Study  

PubMed Central

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

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

2010-01-01

430

Ultrastrong, Stiff, and Lightweight Carbon-Nanotube Fibers  

Microsoft Academic Search

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

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

2007-01-01

431

Sensor for Stiffness Measurements Within the Adult Rat Hippocampus  

Microsoft Academic Search

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

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

2008-01-01

432

Sport stretching: Effect on passive muscle stiffness of short hamstrings  

Microsoft Academic Search

Objective: To evaluate the effects of one 10-minute stretch on muscle stiffness in subjects with short hamstrings.Design: Randomized control trial.Setting: Laboratory for human movement sciences in the department of rehabilitation of a university hospital.Subjects: Sixteen students from the Department of Human Movement Sciences participated with informed consent in the experiment. Subjects were limited to men and women without a history

Jan P. K. Halbertsma; Annette I. van Bolhuis; Ludwig N. H. Göeken

1996-01-01

433

Evaluation of aortic stiffness in children with chronic renal failure  

Microsoft Academic Search

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

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

2007-01-01

434

A grey box bending stiffness model for paper board manufacturing  

Microsoft Academic Search

This paper presents a semi-physical grey box model for the bending stiffness of cardboard at the AssiDoman Frovi cardboard plant. The reason for using a semi-physical nonlinear model is that one wants the model to be valid under different production settings, with the intention to use it for both control and simulation. The latter is of great importance, since finding

Jens Pettersson; Per-Olof Gutman; Torsten Bohlin; Bengt Nilsson

1997-01-01

435

Decrements in stiffness are restored within 10 min.  

PubMed

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

Mizuno, T; Matsumoto, M; Umemura, Y

2012-11-09

436

Mechanochemical model of cell migration on substrates of varying stiffness  

NASA Astrophysics Data System (ADS)

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

Lai, Tanny; Chiam, K.-H.

2011-12-01

437

Stiffness measurement of a biomaterial by optical manipulation of microparticle  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

438

Stiffness changes in cultured airway smooth muscle cells.  

PubMed

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

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

2002-09-01

439

Glycine Receptor Autoimmune Spectrum With Stiff-Man Syndrome Phenotype  

PubMed Central

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

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

2013-01-01

440

Explicit integration of extremely stiff reaction networks: asymptotic methods  

NASA Astrophysics Data System (ADS)

We show that, even for extremely stiff systems, explicit integration may compete in both accuracy and speed with implicit methods if algebraic methods are used to stabilize the numerical integration. The required stabilizing algebra depends on whether the system is well removed from equilibrium or is near equilibrium. This paper introduces a quantitative distinction between these two regimes and addresses the former case in depth, presenting explicit asymptotic methods appropriate when the system is extremely stiff but only weakly equilibrated. A second paper (Guidry and Harris 2013 Comput. Sci. Disc. 6 015002) examines quasi-steady-state methods as an alternative to asymptotic methods in systems well away from equilibrium and a third paper (Guidry et al 2013 Comput. Sci. Disc. 6 015003) extends these methods to equilibrium conditions in extremely stiff systems using partial equilibrium methods. All three papers present systematic evidence for timesteps competitive with implicit methods. Because an explicit method can execute a timestep faster than an implicit method, algebraically stabilized explicit algorithms might permit integration of larger networks than have been feasible before in various disciplines.

Guidry, M. W.; Budiardja, R.; Feger, E.; Billings, J. J.; Hix, W. R.; Messer, O. E. B.; Roche, K. J.; McMahon, E.; He, M.

2013-01-01

441

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

442

Torsional directed walks, entropic elasticity, and DNA twist stiffness  

PubMed Central

DNA and other biopolymers differ from classical polymers because of their torsional stiffness. This property changes the statistical character of their conformations under tension from a classical random walk to a problem we call the “torsional directed walk.” Motivated by a recent experiment on single lambda-DNA molecules [Strick, T.?R., Allemand, J.-F., Bensimon, D., Bensimon, A. & Croquette, V. (1996) Science 271, 1835–1837], we formulate the torsional directed walk problem and solve it analytically in the appropriate force regime. Our technique affords a direct physical determination of the microscopic twist stiffness C and twist-stretch coupling D relevant for DNA functionality. The theory quantitatively fits existing experimental data for relative extension as a function of overtwist over a wide range of applied force; fitting to the experimental data yields the numerical values C = 120 nm and D = 50 nm. Future experiments will refine these values. We also predict that the phenomenon of reduction of effective twist stiffness by bend fluctuations should be testable in future single-molecule experiments, and we give its analytic form.

Moroz, J. David; Nelson, Philip

1997-01-01

443

Explicit Integration of Extremely Stiff Reaction Networks: Asymptotic Methods  

SciTech Connect

We show that, even for extremely stiff systems, explicit integration may compete in both accuracy and speed with implicit methods if algebraic methods are used to stabilize the numerical integration. The stabilizing algebra differs for systems well removed from equilibrium and those near equilibrium. This paper introduces a quantitative distinction between these two regimes and addresses the former case in depth, presenting explicit asymptotic methods appropriate when the system is extremely stiff but only weakly equilibrated. A second paper [1] examines quasi-steady-state methods as an alternative to asymptotic methods in systems well away from equilibrium and a third paper [2] extends these methods to equilibrium conditions in extremely stiff systems using partial equilibrium methods. All three papers present systematic evidence for timesteps competitive with implicit methods. Because explicit methods can execute a timestep faster than an implicit method, our results imply that algebraically stabilized explicit algorithms may offer a means to integration of larger networks than have been feasible previously in various disciplines.

Guidry, Mike W [ORNL; Budiardja, R. [University of Tennessee (UTK) and Oak Ridge National Laboratory (ORNL); Feger, E. [University of Tennessee, Knoxville (UTK); Billings, J. J. [Oak Ridge National Laboratory (ORNL); Hix, William Raphael [ORNL; Messer, O.E.B. [University of Tennessee (UTK) and Oak Ridge National Laboratory (ORNL); Roche, K. J. [Pacific Northwest National Laboratory (PNNL); McMahon, E. [University of Tennessee, Knoxville (UTK); He, M. [Shanghai Jiao Tong University, Shanghai

2013-01-01

444

Power Coefficient Anomaly in JOYO.  

National Technical Information Service (NTIS)

Power Coefficient Anomaly appeared in JOYO, which occurred in 75MW Power Ascension Test, Summer 1979. The substance of this anomaly was the non-reproducible power coefficient during the initial power-up from 50MWt to 75MWt and the permanent reactivity los...

M. Ishikawa Y. Yamashita Y. Nara H. Yamamoto

1981-01-01

445

RADIONUCLIDE RISK COEFFICIENT UNCERTAINTY REPORT  

EPA Science Inventory

EPA has published excess cancer risk coefficients for the US population in Federal Guidance Report 13 (FGR 13). FGR 13 gives separate risk coefficients for food ingestion, water ingestion, inhalation, and external exposure for each of over 800 radionuclides. Some information on...

446

Calculate thermal-expansion coefficients  

Microsoft Academic Search

To properly design and use process equipment, an engineer needs a sound knowledge of physical and thermodynamic property data. A lack of such knowledge can lead to design or operating mistakes that can be dangerous, costly or even fatal. One useful type of property data is the thermal-expansion coefficient. This article presents equations and tables to find the thermal-expansion coefficients

Yaws

1995-01-01

447

[Successful treatment with rituximab in a refractory Stiff-person syndrome].  

PubMed

Stiff person syndrome is a rare autoimmune disorder characterized by axial and limb progressive stiffness with surimposed spasms and production of autoantibodies to glutamic acid decarboxylase (GAD). We report a case of a 50-year-old woman who developed a stiff person syndrome resistant to conventional immunosuppressive treatments. Eight months after treatment, indexes of stiffness and spasm frequency improved, while however, the blood and CSF rates of anti-GAD increased. This observation illustrates the complexity of stiff person syndrome immunopathogenesis as well as the relevance of rituximab in this indication. PMID:22340864

Sevy, A; Franques, J; Chiche, L; Pouget, J; Attarian, S

2012-02-14

448

Stiffness detection and reduction in discrete stochastic simulation of biochemical systems  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

449

Bounce scenarios in the Sotiriou-Visser-Weinfurtner generalization of the projectable Horava-Lifshitz gravity  

NASA Astrophysics Data System (ADS)

The occurrence of a bounce in the FRW cosmology requires modifications of general relativity. An example of such a modification is the recently proposed Ho?ava-Lifshitz (HL) theory of gravity, which includes a 'dark radiation' term with a negative coefficient in the analog of the Friedmann equation. A modification of the HL gravity, relaxing the 'detailed-balance' condition, brings additional terms to the equations of motion, corresponding to stiff matter. This paper presents a comparison of the phase structure of the original and modified Ho?ava cosmology. Special attention is paid to the analysis of a wide range of the bouncing solution, appearing in both versions of the Ho?ava theory.

Czuchry, E.

2011-06-01

450

Extended Symmetries and Solutions of (2 + 1)-DIMENSIONAL Nonlinear SCHRÖDINGER Equation with Variable Coefficients  

NASA Astrophysics Data System (ADS)

By generalized symmetry group method, some time-space-dependent finite transformations between two different (2 + 1)-dimensional nonlinear Schrödinger equations (NLSE) are constructed. From these transformations, some (2 + 1)-dimensional variable coefficients NLSE can be reduced to another variable coefficients NLSE or corresponding constant coefficients NLSE. Abundant solutions of some (2 + 1)-dimensional variable coefficients NLSE are obtained from their corresponding constant coefficients NLSE.

Wang, Jia; Li, Biao

451

A simple model for the prediction of the discrete stiffness states of a homogeneous electrostatically tunable multi-layer beam  

NASA Astrophysics Data System (ADS)

The adaptive modification of the mechanical properties of structures has been described as a key to a number of new or enhanced technologies, ranging from prosthetics to aerospace applications. Previous work reported the electrostatic tuning of the bending stiffness of simple sandwich structures by modifying the shear stress transfer parameters at the interface between faces and the compliant core of the sandwich. For this purpose, the choice of a sandwich structure presented considerable experimental advantages, such as the ability to obtain a large increase in stiffness by activating just two interfaces between the faces and the core of the beam. The hypothesis the development of structures with tunable bending stiffness is based on, is that by applying a normal stress at the interface between two layers of a multi-layer structure it is possible to transfer shear stresses from one layer to the other by means of adhesion or friction forces. The normal stresses needed to generate adhesion or friction can be generated by an electrostatic field across a dielectric layer interposed between the layers of a structure. The shear stress in the cross section of the structure (e.g. a beam) subjected to bending forces is transferred in full, if sufficiently large normal stresses and an adequate friction coefficient at the interface are given. Considering beams with a homogeneous cross-section, in which all layers are made of the same material and have the same width, eliminates the need to consider parameters such as the shear modulus of the material and the shear stiffness of the core, thus making the modelling work easier and the results more readily understood. The goal of the present work is to describe a numerical model of a homogeneous multi-layer beam. The model is validated against analytical solutions for the extreme cases of interaction at the interface (no friction and a high level of friction allowing for full shear stress transfer). The obtained model is used to better understand the processes taking place at the interfaces between layers, demonstrate the existence of discrete stiffness states and to find guidance for the selection of suitable dielectric layers for the generation of the electrostatic normal stresses needed for the shear stress transfer at the interface.

Bergamini, A.; Christen, R.; Motavalli, M.

2007-03-01

452

Muscular contributions to dynamic dorsoventral lumbar spine stiffness  

PubMed Central

Spinal musculature plays a major role in spine stability, but its importance to spinal stiffness is poorly understood. We studied the effects of graded trunk muscle stimulation on the in vivo dynamic dorsoventral (DV) lumbar spine stiffness of 15 adolescent Merino sheep. Constant voltage supramaximal electrical stimulation was administered to the L3–L4 interspinous space of the multifidus muscles using four stimulation frequencies (2.5, 5, 10, and 20 Hz). Dynamic stiffness was quantified at rest and during muscle stimulation using a computer-controlled testing apparatus that applied variable frequency (0.46–19.7 Hz) oscillatory DV forces (13-N preload to 48-N peak) to the L3 spinous process of the prone-lying sheep. Five mechanical excitation trials were randomly performed, including four muscle stimulation trials and an unstimulated or resting trial. The secant stiffness (ky = DV force/L3 displacement, kN/m) and loss angle (phase angle, deg) were determined at 44 discrete mechanical excitation frequencies. Results indicated that the dynamic stiffness varied 3.7-fold over the range of mechanical excitation frequencies examined (minimum resting ky = 3.86 ± 0.38 N/mm at 4.0 Hz; maximum ky = 14.1 ± 9.95 N/mm at 19.7 Hz). Twenty hertz muscle stimulation resulted in a sustained supramaximal contraction that significantly (P < 0.05) increased ky up to twofold compared to rest (mechanical excitation at 3.6 Hz). Compared to rest, ky during the 20 Hz muscle stimulation was significantly increased for 34 of 44 mechanical excitation frequencies (mean increase = 55.1%, P < 0.05), but was most marked between 2.55 and 4.91 Hz (mean increase = 87.5%, P < 0.05). For lower frequency, sub-maximal muscle stimulation, there was a graded change in ky, which was significantly increased for 32/44 mechanical excitation frequencies (mean increase = 40.4%, 10 Hz stimulus), 23/44 mechanical excitation frequencies (mean increase = 10.5%, 5 Hz stimulus), and 11/44 mechanical excitation frequencies (mean increase = 4.16%, 2.5 Hz stimulus) when compared to rest. These results indicate that the dynamic mechanical behavior of the ovine spine is modulated by muscle stimulation, and suggests that muscle contraction plays an important role in stabilizing the lumbar spine.

Colloca, Christopher J.; Harrison, Deed E.; Moore, Robert J.; Gunzburg, Robert

2006-01-01

453

Aortic Stiffness, Blood Pressure Progression, and Incident Hypertension  

PubMed Central

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

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

2013-01-01

454

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

PubMed

Carotid-to-radial pulse wave velocity (PWV(cr)) has been proposed to evaluate endothelial function. However, the measurement of PWV(cr) is not without limitations. A new simple approach could have wide application. Stiffness index (SI) is obtained by analysis of the peripheral pulse wave and gives reproducible information about stiffness of large arteries. This study assessed the effects of hyperemia on SI and compared it with PWV(cr) in 14 healthy subjects. Both were measured at rest and during 8 minutes after ischemia. SI temporal course was determined. At 1 minute, SI and PWV(cr) decreased (5.58 ± 0.24 to 5.34 ± 0.23?m/s, P < 0.05; 7.8 ± 1.0 to 7.2 ± 0.9?m/s; P < 0.05, resp.). SI was positively related to PWV(cr) in baseline (r = 0.62 , P < 0.05), at 1 minute (r = 0.79, P < 0.05), and during the whole experimental session (r = 0.52, P < 0.05). Conclusion. Hyperemia significantly decreases SI in healthy subjects. SI was related to PWV(cr) and could be used to facilitate the evaluation of hyperemia-related changes in arterial stiffness. PMID:22919496

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

2012-08-07

455

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

PubMed Central

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

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

2012-01-01

456

Cytoplasmic hydrogen ion diffusion coefficient.  

PubMed Central

The apparent cytoplasmic proton diffusion coefficient was measured using pH electrodes and samples of cytoplasm extracted from the giant neuron of a marine invertebrate. By suddenly changing the pH at one surface of the sample and recording the relaxation of pH within the sample, an apparent diffusion coefficient of 1.4 +/- 0.5 x 10(-6) cm2/s (N = 7) was measured in the acidic or neutral range of pH (6.0-7.2). This value is approximately 5x lower than the diffusion coefficient of the mobile pH buffers (approximately 8 x 10(-6) cm2/s) and approximately 68x lower than the diffusion coefficient of the hydronium ion (93 x 10(-6) cm2/s). A mobile pH buffer (approximately 15% of the buffering power) and an immobile buffer (approximately 85% of the buffering power) could quantitatively account for the results at acidic or neutral pH. At alkaline pH (8.2-8.6), the apparent proton diffusion coefficient increased to 4.1 +/- 0.8 x 10(-6) cm2/s (N = 7). This larger diffusion coefficient at alkaline pH could be explained quantitatively by the enhanced buffering power of the mobile amino acids. Under the conditions of these experiments, it is unlikely that hydroxide movement influences the apparent hydrogen ion diffusion coefficient.

al-Baldawi, N F; Abercrombie, R F

1992-01-01

457

Muscle Stiffness and Spinal Stretch Reflex Sensitivity in the Triceps Surae  

PubMed Central

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

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

2008-01-01

458

Negative coefficient of normal restitution  

NASA Astrophysics Data System (ADS)

This paper shows that negative coefficients of normal restitution occur inevitably when the interaction force between colliding particles is finite. We derive an explicit criterion showing that for any set of material properties there is always a collision geometry leading to negative restitution coefficients. While from a phenomenological point of view, negative coefficients of normal restitution appear rather artificial, this phenomenon is generic and implies an important overlooked limitation of the widely used hard sphere model. The criterion is explicitly applied to two paradigmatic situations: for the linear dashpot model and for viscoelastic particles. In addition, we show that for frictional particles the phenomenon is less pronounced than for smooth spheres.

Müller, Patric; Krengel, Dominik; Pöschel, Thorsten

2012-04-01

459

Seeley-Gilkey Coefficients for Superoperators  

NASA Astrophysics Data System (ADS)

Starting from a expansion of exp[-(A0 + A1)t] in powers of A1, we can obtain Seeley-Gilkey coefficients an(x,y) for when H has dependency on both bosonic and fermionic variables. We consider operators of the form H = p2 + ?L·p + p · ?R + ?(p? - i?) where, in general, ?L ? ?R. To illustrate how these can be used, we compute in closed form the coefficient a1(x,x) and from it the ?-function in a three-dimensional model in which a spinor couples to an Abelian vector field with a topological action. The ?-function turns out not to have the form of the classical action.

McKeon, D. G. C.

460

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

PubMed

This paper reports shear stiffness and viscosity "virtual biopsy" measurements of the three excised noncancerous human prostates using a new tool known as shear wave dispersion ultrasound vibrometry (SDUV) in vitro. Improved methods for prostate guided-bio